engine power train

7/29/2019 Engine Power Train

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Basic Engine Edition

(Common to all work ranks)

Basics of an Engine1. Chapter 1 Basics of an Engine2. Chapter 5 Cooling System3. Chapter 8 Lubrication System4. Chapter 9 Electronic System of an Engine5. Chapter 11 Other Units

Performance of an Engine6. Chapter 1 Performance of an Engine7. Chapter 4 Diesel Engine8. Chapter 5 LPG Engine

Structure of Textbook


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Chapter 1 Basics of an Engine

1. Internal Combustion Engine: An Overview

As an example of automobiles having engines utilizing thermal energy, the steam engine (external

combustion engine) was used previously. However, from the viewpoint of performance, safety, ease of

handling, etc., it has been gradually replaced by internal combustion engines using petroleum as fuel;

and at present, the internal combustion engine forms the mainstream of engines driving automobiles.

The internal combustion engine basically utilizes thermal energy as a driving power and converts it to

mechanical energy, and it is considered that the engine made by Gottlieb Daimler in 1885 was the first

gasoline engine for use in automobiles.

Since then, the gasoline engine has greatly improved aiming to realize small-sizing and high

performance. Especially, from the technological viewpoint, recent innovations in the exhaust emission

control system and energy saving technology have established great milestones in the development

history of gasoline engines through fundamental renovation of engine itself as well as introduction of

newer ideas and mechanisms.

There are different types of gasoline engines include reciprocal type (reciprocal engine) and rotary

type (rotary engine, gas turbine engine, etc.); however, in this document, the reciprocal engine will be

mainly described.

2. Types of engines used in automobiles

The engines used in automobiles can be categorized into the following types depending on the fuel

utilized.

1) Gasoline engine

Using gasoline as fuel, this type is widely employed in passenger vehicles and small trucks because of

its compact, high-revolution, high-power, and light-weight nature.

2) Diesel engine

Using diesel oil (light oil) as fuel, this type is mostly employed in buses and big trucks that require

economic efficiency because this type consumes less fuel and diesel oil and is less expensive than

gasoline. Although small diesel engines are utilized in a few passenger vehicles, they fall short in high-

revolution, power, weight, and noise, etc. when compared to gasoline engines.

3) Gas engine

Using LP gas or natural gas as fuel, this type is widely used in taxis because it works with high fuel

efficiency even though the output power is lower than gasoline engines.


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3Features required for an engine

(1) Output powerIts needless to say that high

power is better. Even if power isnot completely used, remainingpower becomes a margin.

(2) DriveabilityAn engine that operates

smoothly over the whole rangeof engine speed and is easy-to-drive is enjoyable for drivers.

(3) DurabilityEven if the other features of an

engine are excellent, it isuseless if it breaks down easily.

(4) MaintainabilityIt is not good if there is no room

to insert hands into the engineroom for adjusting or fixing it. Anengine that requires frequentadjustment is also bad.

(5) Light weightA compact and light weight

engine is required for gooddriving performance and gasmileage.

(6) DesignFor the present and future

engines, high level performanceas well as visual appeal isrequired.

(7) CalmnessIt is needless to say that noiseand vibration of an engineshould be low.

(8) CostEven if an engine is excellent, itposes a problem if it is tooexpensive.

(9) Economic efficiencyEconomic efficiency ofmaintenance, including gas andmileage is an important factorfor engines used in vehicles.

In addition, it also requires an appropriate balance of these conditions.

* VG-type engine

VG-type engine is an excellent V-type, 6-cylinder engine developed by Nissan to obtain high-performance and calmness features applicable for small-to-mid range passenger vehicles whileimproving gas mileage and being small-sized and light-weight in order to meet the demands oftodays resource/energy saving age.

Too narrow!


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4. Operation principle of a gasoline engine

1) Reciprocal engine

Gasoline engines intake gasoline-air-mixed gas that is

compressed and exploded by electric spark inside a

cylinder, and the pressure generated by this rapid fuel

combustion is transferred to the piston to make the

crank-shaft rotate.

* Reciprocal engine converts reciprocal motion of the

piston caused by explosive combustion of fuel-air-mixed

gas to rotational motion of crank-shaft to generate the

driving power.

(1) 4-cycle engine

A case when the piston is at the highest position inside

the cylinder is called top dead center and a case when

the piston is at the lowest position inside the cylinder is

called bottom dead center. The distance covered by

the piston while moving between the top dead center

and the bottom dead center positions is called stroke.

When the piston is at the top dead center, the remaining

room in the cylinder is called combustion chamber.

In order to operate the engine continuously, it is

necessary to repeat a series of actions in a fixed order.

That is, this type of engine intakes mixed-air into the

cylinder, compresses it, explodes the compressed gas,

and finally, discharges the combusted gas outside the

cylinder. In this way, a series of actions comprising

intake, compression, combustion, and exhaustion are

repeated. This process is called cycle.

A 4-cycle engine is an engine in which 1 cycle is

completed by 4 strokes of the pistons motion, or by 2rotations of the crankshafts motion.

Piston

Con rod

Crankshaft

Rotation of engine

Combustion roomTop dead center

Stroke

Bottom dead center

Top dead center and bottom dead center

Intake

Compression

Combustion

Exhaustion

1 cycle of engine


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(2) Operation of a 4-cycle engine

(i) Intake process

As shown in Fig-1, when an intake valve is opened, the piston goes

down and negative pressure is generated inside the cylinder due to

which fuel-air-mixed gas is sucked into the cylinder. In order toincrease the intake efficiency of the mixed-gas, the intake valve is

opened before the piston reaches to the top dead center and closed

after the piston passes the bottom dead center. In this process, the

piston moves 1 stroke, and the crankshaft completes 1/2 rotation.

(ii) Compression process

As shown in Fig-2, in this process, exhaust valve remains closed.

When the intake valve is closed and the piston goes upward, the

mixed-gas is compressed inside the cylinder and the pressure

increases. The fuel produced by the mixed-gas is completelyvaporized by the increased temperature due to high pressure. By the

end of this process, the piston has moved 2 strokes and the

crankshaft has completed 1 rotation.

(iii) Explosion (combustion) process

As shown in Fig-3, in this process, mixed-gas combustion is induced

by ignition by the spark plug, and the combusted and inflated gas

due to the rapidly increased temperature and pressure presses the

piston downward to rotate the crankshaft. By the end of this process,

the piston has moved 3 strokes, and the crankshaft has completes1.5 rotations. Power is actually generated only in this process.

(iv) Exhaustion process

As shown in Fig-4, in this process, the exhaust valve is opened.

When the piston goes upward, combusted gas is exhausted from the

cylinder by the piston. When the ascent of piston is almost stopped,

next intake of mixed-gas begins. Here, in order to speed-up the

exhaustion of combusted gas, the exhaust valve is opened before

the piston reaches to the bottom dead center and closed just after

the piston passes the top dead center. By the end of this process,the piston has moved 4 strokes, and the crankshaft has completed 2

rotations. During all other processes other than combustion process,

the piston moves up and down due to the inertial force of the

flywheel.

Intake valve

Fig-1 Operation of a 4-cycleengine (Intake)

Mixed air

Piston

Cylinder

Exhaust valve

Fig-2 Operation of a 4-cycleengine (compression)

Spark plug

Fig-3 Operation of 4-cycleengine (Combustion)

Connecting rod

Crankshaft

Fig-4 Operation of a 4-cycleengine (exhaustion)

Exhaust valve

Exhaust gas


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(3) Valve timing of a 4-cycle engine

Valve timing means the open/close timing of the valve for

each piston stroke.

Intake valve opens before mixed-gas absorption, or before

the piston reaches the top dead center and closes after theinlet process, or some time after the piston passes the

bottom dead center. This is to enable absorption of as

much gas as possible into the cylinder by utilizing the

inertia of inhalation.

Exhaustion valve is opened before the exhaustion process,

or before the piston reaches the bottom dead center to

rapidly exhaust the combusted gas, and it is closed just

after the exhaustion process is finished and the inlet

process begins, or just after the piston passes the top dead center.

(4) 2-cycle engine

A 2-cycle engine completes 1 cycle with 2 strokes of piston movement or 1 rotation of crankshaft.

Since the number of times of combustion is more, engine structure is simpler, and it is smaller and

lighter, as well as can possibly generate a higher power compared to a 4-cycle engine with a similar

cylinder capacity. A 2-cycle engine is used in light motor vehicles and motorcycles as a compact

engine.

(5) Operation of a 2-cycle engine(i) Scavenging and inhaling process

Scavenging (inhaling) port and exhaust port are closed, and the piston goes upward. At this time, the

pressure within the crank chamber decreases, and when this negative pressure overcomes the

reactive force of the lead valve, the intake valve opens and mixed-gas flows into the crank chamber.

On the other hand, mixed-gas within the cylinder is in the compression process.

(ii) Compression process

Compressed mixed-gas is ignited by the spark plug slightly before the piston reaches the top dead

center, and high-pressure gas generated by the combustion presses down the piston. On the other

hand, as the piston goes down, the gas within the crank chamber is compressed. (The lead valve isclosed by this pressure and prevents the backward flow of the gas.)

Inlet valve openedTop dead center

Exhaust valve closed

Exhaust valve openedBottom deadcenter

Inlet valveclosed

Relation between valve timing andstroke in a 4-cycle engine

Scavenginghole

(1) Scavenging

Exhaust hole

Lead valve

Crankcase

(2) Compression

Spark plug

(3) Combustion (4) Exhaustion

Operation of a 2-cycle engine


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(iii) Explosion process

The piston goes down and the exhaustion port is opened to discharge the combustion gas.

(iv) Exhaustion process

When the piston goes down further and the scavenging (inhaling) port is opened, mixed-gas from thecrank chamber flows into the cylinder from this port and fills the cylinder chamber while scavenging the

residual combustion gas to the exhaust port.

This gas exchanging cycle is completed when the piston passes the bottom dead center, goes

upward, closes the exhaustion port again, and returns to the start point.

5. Specifications and units of an engine

In this chapter, of the specifications of an engine listed in the catalog, air volume displacement,

compression ratio, output power, torque, and gas mileage are described.

1) Air volume displacement

As shown in the diagram, air volume displacement is

defined as the volume of gas that is discharged while the

piston moves from the top dead center to the bottom dead

center.

A value obtained by multiplying the number of cylinders to

this volume is called total piston displacement and is

denoted by cc.

Total piston displacement is expressed by following

formula:

Where, V (cc) is the air volume displacement, D (cm) is inner diameter, L (cm) is the stroke, and N is

the number of cylinders.

[Example] In a situation when D is 73.6 mm, L is 88 mm, and N is 4, total piston displacement is given

as:

Total piston displacement (cc) =

Total piston displacement =

Top dead center

Bottom deadcenter

Air volume displacement


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2) Compression ratio

As shown in this diagram, compression is the ratio of

the volume present above the piston when it is at the

bottom dead center to the volume present above the

piston when it is at the top dead center.The volume present above the piston when it is at the

top dead center is called combustion chamber

volume. The volume present above the piston when it

is at the bottom dead center corresponds to the sum

of air volume displacement and combustion chamber

volume.

Compression ratio is given by the following

expression:

V + N

Compression ratio (P) =v

Where, P is Compression ratio, V (cc) is air volume displacement, and v (cc) is combustion chamber

volume.

[Example] In a case when V is 374 cc and v is 45 cc, the total piston displacement is given as:

374 + 45

P = 9.3

45

When mixed-gas is combusted, its pressure varies depending on the degree of compression. In order

to obtain enough rotation power, the compression ratio should be set rather higher so as to obtain

higher combustion gas pressure.

By making the combustion gas pressure high, it becomes possible to increase the output power in the

case with the same amount of mixed-gas; that is, to make thermal efficiency higher.

3) Torque and horse power

Torque is a force required to rotate something; that

is, a rotational power. In the case of bolt tightening

with a spanner, the longer the length of the spanner,

the smaller is the tightening force. Torque is given

as the product of the length of spanner and applied

force.

(1) Torque (rotational power)

Torque (T) = Force x Length = F (kg) x r (m)

It is expressed in the units of kg-m. Output power is

defined as the product of the amount of work and

speed. That is, the output power is the amount of

work done per unit time and is expressed in

Top dead center

Bottom deadcenter

Compression ratio

Torque (rotational power)

F(force)

1 Horsepower (PS)

1 s

Torque and Horsepower

1 m


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horsepower in the case of engines. One horsepower corresponds to the amount of power that can

move something by 1 m/s with a force of 75 kg.


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(1) Air-fuel ratio

Ratio of air to fuel required for combustion is called air-fuel ratio, which is denoted by a weight ratio

and not by volume ratio as shown in the following

expression.

Inhaled air (g)

Air-fuel ratio =

Inhaled fuel (g)

Air is mainly composed of oxygen and nitrogen, each of

which exists in the following ratio of weight and volume.

Weight ratio(%)

Volume ratio(%)

Oxygen (O2) 23.2 20.9Nitrogen (N2) 76.8 79.1

Theoretically, to make 1 g of gasoline to combust

perfectly, 14.7 g of air is required. Air-fuel ratio at this

condition is called theoretical air-fuel ratio. An actual

engine generally uses various air-fuel ratios

corresponding to the driving conditions.

For example, an economical air-fuel ratio is used at

normal driving conditions, while a power air-fuel ratio is

used at driving conditions requiring power.

However, in recent engines, theoretical air-fuel ratio is

mostly utilized from comprehensive viewpoint, includingusage of 3-way catalyst, exhaust emission regulation, or

gas mileage, etc.

When air and fuel are mixed perfectly, mixed-gas can be

perfectly combusted at an air-fuel ratio of 14.7. However,

since it is not possible to realize perfect and uniform

mixing of air and fuel in actual engines, quasi-perfect

combustion is realized by increasing the amount of air by

10% more than the theoretical air-fuel ratio. This ratio

(approximately 16) is called economical air-fuel ratio.

Power air-fuel ratio is an air-fuel ratio at which(approximately 12.5) maximum power can be obtained

by increasing the amount of fuel by 20% more than the

theoretical air-fuel ratio.

Incidentally, possible air-fuel ratio of combustible gasoline is generally in range of 810.

Air14.7 g

Perfectcombustion

Fuel

Theoretical air-fuel ratio

Economicalair-fuel ratio

Power air-fuelratio

Economical air-fuel ratio andPower air-fuel ratio

Air-fuel ratio and Torque

Strong

Torque(kg-m)

TorqueTorque

Specific fuelconsumption

Power air-fuel ratio

Theoretical air-fuel ratio

Economicalair-fuel

Specific fuelconsumption

(g/PS-h)High (dense) Air-fuel ratio Low (thin)


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(2) Ignitability and inflammability

When fuel is heated in air atmosphere, it is naturally ignited

and combusted at some temperature without the need of

an external flame or electric spark. This nature of fuel is

called ignitability, and the temperature at which it getsignited naturally is called ignition temperature or firing

point.

As shown in the diagram, when light-oil and gasoline are

dropped on a heated iron plate, light-oil combusts

instantaneously, whereas gasoline does not combust that

faster. This is because of the difference in ignition

temperature between light-oil and gasoline, which is 350C

and 550C, respectively.

Diesel engine was developed by focusing attention to this fact that ignition temperature of light-oil is

low. While heating fuel in air, vapor is heavily generated, and by an additional flame or electric sparkthis vapor gets ignited and begins to combust. This nature is called inflammability and the

temperature at which ignition takes place is called inflammation point.

Inflammation points of gasoline and light-oil are lower than -40C and higher than 50C, respectively.

Therefore, gasoline is easily ignited at normal room temperature.

2) Combustion of a gasoline engine

(1) Normal combustion

When mixed-gas inhaled and compressed inside a

cylinder is ignited by an electric spark, initiallycombustion starts at the ignited position and when this

flash point grows to some extent, combustion will rapidly

expand to the whole chamber and the pressure will

reach maximum level. The time delay from the point of

ignition to actual inflammation is called ignition lag.

The adjacent figure shows a relation between the

rotation angle of crankshaft and pressure inside a

cylinder in a gasoline engine.

When mixed-gas is ignited at point-A, flame is generated

at point-B, and it expands rapidly within the cylinder.Pressure and temperature are rapidly increased and

reach maximum levels at point-C, and then, combustion

finishes at point-D.

(Time lag between the points A and B is called ignition

lag)

If we look virtually inside the cylinder, we will see that the

flame surface expands radially starting from the spark

plug as shown in this Figure. The speed with which the

flame expands is called combustion speed. This speed

is generally 1525 m/sec.

Gasoline Light-oil

Heated iron plate

Ignitability and inflammability

High

Pressurewithin acylinder When not ignited

Crankshaft angleCompression top dead center

Firing pressure within a cylinder

Spark plug

Piston

Firing pressure within a cylinder

Diesel engine


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(2) Abnormal combustion

(i) Knocking

In a gasoline engine, when we quickly accelerate the

speed or charge excess load on the engine to go up steepslope, we may sometimes hear a sound such as the one

that is generated when a cylinder is knocked with a

hammer. This phenomenon is called knocking.

Knocking occurs due to the following reason. When mixed-

gas is compressed and ignited naturally by the high

temperature and high pressure of the combusted gas

before the flame plane is fully expanded within the

combustion chamber after ignition, the pressure wave

generated knocks the cylinder wall or piston head and

produces a metallic sound.When the knocking occurs heavily, since pressure and

temperature increase rapidly, piston head, head gasket, or

valve may get damaged.

The common methods for avoiding knocking are as

follows:

To lower compression ratio

To use high-octane fuel*

To delay ignition timing

In addition, knocking may occur due to other causes such as inadequacies of air-fuel ratio, inhaled air

temperature, cooling water temperature, and amount of exhaust gas recirculation (EGR), etc.

* Octane rating is a value showing an anti-knocking capability of gasoline. The higher this value, the

lesser is the knocking.

(ii) Pre-ignition

Mixed-gas may unexpectedly get ignited by hot areas

inside the combustion chamber such as top edge of

spark plug or exhaust valve before it is ignited by the

spark plug. This phenomenon is called pre-ignition.Although it resembles the knocking phenomenon in that

mixed air is ignited naturally by increased temperature

pre-ignition differs in that mixed-gas is ignited

spontaneously before the ignition produced by a spark

plug.

In case an engine enters into the pre-ignition state when

ignition was stopped by turning off the key switch, the

engine may not stop and continue to rotate. This status is called run on.

Combustion speed at knocking state1,000 m/sec

Loss ofenergy Kin Kin Low gas

mileage

KnockingInhaling temperatureIgnition timing

Air-fuel ratioCooling waterEGR

Knocking

Enginedoesnt stop!Why?

Broon Brroon

Run on


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(iii) Backfiring

A phenomenon when mixed-gas in an inlet pipe is ignited

and combusted by flames blown back from the cylinder is

called backfiring.

This is an abnormal combustion phenomenon that isgenerated in such a way that mixed-gas in an inlet pipe is

ignited and combusted by the combusted gas blown back

from a cylinder at the time when the inlet- and exhaust-

valve open incorrectly or when combustion continues for

a longer time since the mixed-gas is thin.

(iv) Afterburning

When the mixed-gas is too thin or too little, it may not beignited within the cylinder but may be combusted within

the exhaust pipe. This phenomenon is called

afterburning.

In adverse cases of afterburning, a loud sound may be

generated, and when it occurs within a muffler, the

muffler may get damaged.

Backfiring (within inlet pipe)

High speedcombustiongas

Afterburning(withinexhaust pipe)

Backfiring and Afterburning


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2. Cylinder and Cylinder Block

A cylinder comprises a combustion chamber, cylinder

head, and piston, in which the piston moves

reciprocally.

Inside the cylinder is a part in which the piston moves

reciprocally to generate power, to which the most

complex force is applied, compared to any other parts

of the engine. This structure is most heavily affected by

pressure and temperature generated due to combusted

gas.

A structure consisting of cylinder, cooling water conduit,

oil conduit, and crankshaft bearing is called cylinder

block.

1) Cylinder

(1) Categorization by linerThere are 2 types of cylinders, one is of the liner type in

which a liner (cylinder) is pressed into the cylinder

block, and another is a monocoque type in which the

cylinder block is directly molded.

(i) Liner type

Liner type is used in diesel engine and Al-alloy cylinder

block, etc. that require wear proof capability of

cylinders. There is a wet-liner type in which the outer

surface of the liner contacts with water, and a dry-linertype in which the outer surface does not contact with

water.

(MAC-type engine is used in the dry-liner type, and FD-

type engine is used in the wet-liner type)

(ii) Monocoque type

Most gasoline engines and some diesel engines use

the monocoque-type cylinder that is manufactured by

processing a single steel cylinder block itself.

(CA, RB, VG engine, etc.)

VG cylinder block

Monocoque type Liner type

Cylinder


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(2) Categorization on the basis of cylinder arrangement

On the basis of the typical arrangement of cylinders, they are classified as series type, V type, and

horizontally opposed type, and each type has its own advantages and disadvantages.

Types of cylinder arrangement

(i) Series type

This is the most common type of engines in which cylinders are arranged in line. The width of the

engine is rather narrow, and the total length becomes longer depending on the number of cylinders.

(e.g., CA and RB type engine)

(ii) V type

Since cylinders are arranged in V shape, V-type engines are compact as compared to the series-type

engines even if a number of cylinders are accommodated.

(e.g., VG and VH type engine)

(iii) Horizontally opposed type

In this type of engines, cylinders are arranged horizontally, opposing to each other, and centering

around the crankshaft. Height of an engine can be lowered, but it is wider. It is a feature of this type of

engine that generates less vibration than the other types.

2) Cylinder block

Name and role of each part of a cylinder block are shown in this diagram.

Series type V-type Horizontally opposed type

Cylinder headtightening hole

Oil galleryCylinder bore

Water pumpmounting position

Crankshaft bearing part

Cooling water path(water jacket)

Reinforcing rib

Cylinder block


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Water jacket

Cooling water path for lowering the heat generated by an engine.

Oil gallery

Lubrication oil path for replenishing oil that is soaked up by an oil pump.

Crankshaft bearing partHolds the crankshaft using bearing.

Besides the abovementioned elements, an engine is composed of other elements such as oil-pan-

mounting part, oil-level-gauge-mounting part, distributor-mounting part, fuel-pump-mounting part,

water-pump-mounting part, oil-filter-mounting part, etc. (In some engines, these elements are mounted

as separate parts other than the cylinder block.)

3) Category of cylinder blocks

Cylinder block can be categorized into deep-skirt type and half-skirt type depending on the position of

the blocks bottom.

(1) Deep-skirt type

Since the strength in the longitudinal direction of such

cylinder block is higher, this type is used in many

engines.

(GA, RB type engine, etc.)

(2) Half-skirt type

This type has an advantage that it is light in weight.

(CA, VG type engine, etc.)

Deep-skirt type Half-skirt type

Types of cylinder block


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3. Cylinder head

The cylinder head is mounted on the upper surface of

a cylinder block. The combustion chamber consists of

the cylinder head, cylinder, and piston head. The

cylinder head has mounting holes for mounting a

water jacket, which cools the combustion chamber

and its periphery, and has inlet and exhaust ports,

intake and exhaust manifolds, and lubrication oil path.

The structure of a cylinder head differs greatly

depending on the shape of a combustion chamber,

position of camshaft, and valve mechanism. The material of cylinder head castings are either of cast

iron or aluminum. However, aluminum casting is mostly utilized because of its light-weight feature and

good thermal conductivity.

1) Structure of cylinder head

(1) Intake port (path for

inhaled gas)

This is a path for inhaled

mixed-gas between the

intake manifold and

combustion chamber. Itsshape is designed such that

the gas-flow resistance is as

small as possible.

(2) Exhaust port (path for

exhaust gas)

This is a path between the

combustion chamber and

exhaust manifold through

which combusted gas flowsout.

(3) Valve seat

In order to maintain hermetic condition of the combustion

chamber together with the valve, which operates within

high-temperature and high-pressure environment, the

valve seat is made from sintered cast iron or heat

resistant steel. This is a seating face for a ring-shaped

valve, and is pressed into the cylinder head from the

combustion chamber side.

Cylinder head

Rocker shaft

Rocker arm

Valve lifterguide

Intake valve

Hydraulic valve lifter

Intake port

Camshaft

Exhaust valve

Exhaust port

Structure of a cylinder head

Valve seat


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(4) Valve guide

Valve guide, in which valve stem slides up and down,

is made from sintered iron alloy and pressed into the

cylinder head. Since the valve receives a great lateral

pressure, it supports this lateral pressure with lengthcorresponding to 6 10 times of the valve stems

diameter.

2) Shape of a combustion chamber

Combustion chamber requires a shape that makes it possible

to effectively combust mixed-gas. Therefore, in order to

completely convert inhaled mixed-gas (fuel is mostly in

particle state) to gaseous state, the shape of combustion

chamber is designed such that it can generate a swirling

current during inlet and compression processes.

Since swirling current within the combustion chamber makes

combustion of mixed-gas faster and generates higher

combustion pressure, it is helpful in generating powereffectively in a short time.

(1) Bath-tab type combustion chamber

Bath-tab type chamber is simple in shape, easy to manufacture, and can possibly allow longer

movements (length of up/down) of valve. However, since the bend of inlet/exhaust port is large, the

efficiency of inhaling and exhaustion becomes relatively low. Therefore, it is not expectable to obtain

higher output power.

(e.g., TB engine)

Valve collet

Valve spring

(inner)

Valve guide

Valve seat

Valve stem

Valve springretainer

Valve spring

(outer)Oil seal

Waterjacket

Valve guide

Combustion chamber

(i) Bath-tab type (ii) Wedge type (iii) Hemisphere type (iv) Bent-roof type

Shape of combustion chamber


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5. Piston

In order to execute inlet, compression, explosion, and

exhaustion in good condition, it is necessary to seal the

piston and cylinder closely at all times for any operation. In

addition, materials with low thermal expansion coefficient,

structure, and strength that can tolerate high pressure and

temperature conditions are required for making the piston.

Furthermore, since the piston executes high-speed reciprocal

motion, light weight and ideal shape are required to reduce

the inertial force.

1) Structure of a piston

Basic structure of a piston is shown in this diagram.

(1) Ring groove

Ring groove is a part in which the piston ring is inserted.

The most common type is the 3-groove type.

(2) Oil discharging hole

Oil discharging hole opens into the oil ring insertion groove.

Oil swept down by the piston ring is dropped down to the

oil pan through this hole.

(3) Skirt

Lower part from the center of a piston pin is called skirt.

Light-weight,strength,and lowthermalexpansionrequired.

Going tobe burned

out!

Piston

Ring land Piston head

Ring groove

Rib

Oildischarginghole

Skirt

Pin boss

Structure of a piston


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The material mostly used for making piston is aluminum

alloy. Since thermal expansion is higher, various shapes

and structures of pistons have been devised.

For example, as shown in Fig-1, since the piston head is

heated and it expands greatly, it is designed such that it issmaller than the skirt part.

Since the pin boss part has thick walls and thermal

expansion of this part is greater than the other parts, as

shown in Fig-2, diameter in the pin boss direction is

generally less than that of the perpendicular direction

(ellipsoid piston).

2) Types of piston

Piston can be categorized on the basis of the structure of each part. However, there are no clear and

simple categorizations. Instead, all the categorizations are combined.

(1) Categorization by shape of skirt

Short

Long

Shape of piston (1)

Pin boss

Short

Long

Shape of a piston (2)

Solid-skirt-type piston Split-skirt-type pistonSlipper-skirt-type piston

Shape of skirt-type piston


21/111

On the basis of the shape of the skirt, there are 3 types of pistons as shown in Table 2-1. At present,

slipper-skirt type is mostly utilized.

Table 2-1 Categorization on the basis of shape of skirt

(2) Categorization on the basis of shape of oil discharging hole

Depending on the shape of oil discharging hole, ability to transfer heat from piston head to lower part

(skirt part) differs. On the basis of the shape of oil discharging hole, there are 2 types of piston asshown in Table 2-2.

Type FeatureSlit-type piston Shape of the oil discharging

hole is slit-like. Abnormalchange in the shape bythermal expansion of piston issuppressed by appropriatelycontrolling the thermalconduction to the lower part.

Thermal-flow-typepiston

Shape of the oil discharginghole is circular. Thermalconduction to the lower part is

good. In case of engineswhere the piston headtemperature becomes veryhigh, this type of piston isutilized to lower the pistonhead temperature.

Table 2-2 Categorization on the basis of the shape of oil discharging hole

3) Auto-thermic piston

This is a piston made from a different alloy of

steel which can suppress the thermal

expansion of a piston. On the basis of thedifference of thermal expansion coefficients

between steel and aluminum, this is devised so

as to make the shape of piston to become

perfect circle in a thermally expanded state.

Type FeatureSolid-skirt type piston Pressure tightness is prioritized rather than thermal expansion.

No slits in the skirt part. This type is utilized in severe operatingconditions.

Split-skirt type piston There is a slit between the ring groove and skirt part to absorbthermal expansion or lateral pressure.

Slipper-skirt type piston Skirt in the pin direction is cut off. Since this is light-weight andhas small frictional resistance, this is utilized in most passengervehicles.

Slit-typepiston

Thermal-flow-type piston

Oil discharginghole

Shape of oil discharging hole in a piston

a-a cross section

Auto-thermicpiston


22/111

Recently, a piston known as auto-thermatech piston is also used. Although this is similar to auto-

thermic piston in structure, oil ring groove is not slit-like, but is of the drill-hole type. This type has

excellent performance, i.e., thermal resistance and noiseless.

(4) Offset pistonPiston pin position is slightly shifted from the center.

Since this is effective to suppress generation of tapping

sound of piston, this type is widely utilized.

3) Clearance between piston and cylinder

It is necessary to keep a specified clearance (in gasoline

engine, 0.030.06 mm) between the piston and cylinder.

If this clearance is too small, burn out occurs caused by

thermal expansion. While, if clearance is too large,

problems such as insufficient compression, bad heat

radiation, increase of lubrication oil consumption, or

generation of tapping sound on piston may occur.

To avoid these troubles, a piston with appropriate outer

diameter has to be combined with the inner diameter ofcylinders finished inner surface.

4) Material of piston

Since the material required for making a piston must

have small thermal expansion coefficient and high

thermal conductivity, and must be easy-to-process,

aluminum alloy is generally utilized. Aluminum alloy that

comprises aluminum, copper, silicon, nickel, etc. has

good thermal conductivity and is light weight.

Offset

Piston pincenter line

Piston center line

Offset pin

Cylinder

Piston clearance0.030.06 mm

Gap between a piston and cylinder


23/111

6. Piston ring

Piston is designed to have a slight clearance against

the inner surface of the cylinder considering the thermal

expansion that occurs during operation. It is a piston

ring that closes this clearance, inhibits compressed

mixed-gas and combusted gas leak out from

combustion chamber to lower part of cylinder block, and

smoothen the inner surface of the cylinder by

maintaining an appropriate thickness of oil film.

Piston ring having the former role is called

compression ring, and that having the latter role is

called oil ring.

Piston ring also has an important function to transfer

heat generated within the piston to the cylinder wall;

that is, a heat radiation function to cool the piston.

Since the piston ring must always closely contact the

inner surface of the cylinder, it is designed so as to

generate a force (tensile force) that pushes itself to the

inner surface of the cylinder.

Hence, the piston ring must have the following features.

should not be easily worn out

should not abrade cylinder wall

should be able to transfer heat properly to the cylinder wall to suppress thermal expansion of the

piston

should have a small thermal expansion coefficient

should fit rapidly with the cylinder wall and have good hermetic ability

should not generate change of tensile force during longer operation times

should not get damaged by the substances

generated during combustion

should not cause oil shortage even at start-

up time when oil is not supplied

Topring

Secondring

Compressionring

Oil ring

Piston rings role

Piston ring


24/111

1) Shape of a piston ring

(1) Compression ring

Compression ring can be categorized as follows depending on the difference in cross sectional shape. Plain type: This is the most basic type. Hermetic ability and thermal conductivity are good.

Taper-face type: Since the outer surface is tapered, this type contacts with the cylinder wall in line,

and easily fits with the surface. Hermetic ability and thermal conductivity are good. Top ring is

mostly plated with chrome.

Inner-bevel type, undercut type, and taper-undercut type: These types change shape so that the

lower edge contacts with the cylinder wall working similarly like the taper-face type.

Keystone type: Upper and lower surfaces are tapered. This type is good for preventing sticky

phenomenon (ring does not work because of hardened carbon and the performance of ring

becomes low).

Barrel-face type: Since a part of the curved surface contacts with the cylinder in line, this type offersstable hermetic ability against deformation.

(2) Oil ring

There are various types such as:

Stand-alone type: This type of oil ring has an in-built

lubrication oil feeding hole.

Expander type: This type is equipped with an

expander behind the ring to enhance the contact

force against the cylinder wall.

Combined-ring type: This type has a high oilscraping performance, and is commonly used in

recent years. Aided by a wave-like spring, the

tensile force of the side rail for conditioning by the

lubrication oil is kept optimal, and it is possible to

make the area of the oil feeding hole to be large. As

a result, oil-up phenomenon (scraping oil is insufficient and oil goes up to the combustion chamber)

may not occur.

Plain type Taper-face type Inner-bevel type Undercut type

Taper-undercut type One-side-keystone type Both-side-keys tone type Barrel-face type

Compression ring

Cutter type Spacer

Bevel-cutter type

Stand-alone typeoil ring

Side rail

Combined ring

Types of oil ring


25/111

2) Parts of a piston ring

Names of each part of a piton ring are shown in this figure.

Since a piston ring is designed such that it contacts closely

the cylinder wall with an appropriate tensile force, the outerdiameter of the piston in free state becomes larger than the

diameter of the cylinder.

It has a cutout of appropriate length to absorb thermal

expansion.

3) Material of piston ring

Since a piston ring should have features such as wear resistivity, heat resistivity, impact resistivity, and

oil retention capacity, special cast iron is generally utilized for making a piston ring. For combined ring,

spring steel, etc. are utilized.For improving wear resistivity, chrome may be plated on the surface that is in contact with the cylinder

wall.

7. Connecting rod

Connecting rod is a part that connects the piston to the crankshaft, and has a role to transform the

reciprocal motion of the piston to a rotational motion of crankshaft.

Since it receives strong compression and tension during engine operation, enough strength is

required. In addition, since it contains a heavily moving part like piston, it has to be light-weight. In

order to meet these requirements, forged irons such as carbon steel and chrome-molybdenum steel

are utilized for making connecting rods.

1) Structure and name of each part of

the connecting rod

As shown in this figure, connecting rod

consists of small end part that connects

the piston through the piston pin, large

end part that connects the pin part of

crankshaft and can be divided into 2

parts (upper/lower parts), and a rod that

connects large end part and small end

part.

Thickness (T)

Slip surface

Nominal diameterCutout

Width (B)

Upper/Lowersurface

Name of each part of a piston ring

PistonSmall end part

Piston pin

Rod Bearing

Reamer bolt

Large end part

Connectingrod cap

Nut

Components of a connecting rod


26/111

2) How to connect the piston and connecting rod

There are 3 types of connections between the piston and

connecting rod.

Fix type (Lock type)

Piston pin is fixed to the piston with a screw.

Semi-floating type

Piston pin is fixed to the connecting rod. Although

there is a type such that the piston pin is fixed with

bolt, at present, a press fit type by press-fitting is

mostly utilized.

Full-floating type

Movement in the axial direction is inhibited by snap-ring, etc., and movement in rotation

direction is free from both of piston and connecting rod.

8. Crankshaft

Crankshaft receives the pressure that the

piston received via the connecting rod and

converts the reciprocal motion of piston to

rotational motion.

Crankshaft has a complex shape as shown in

this diagram.

In order to operate each cylinder in good order

depending on the number of cylinders, etc.,

such complex shape is required. In addition, it

changes depending on the bearing that holds

the crankshaft and number of journal part.

After the pressure from the piston passes to the crankshaft, the crankshaft generates bend or twist

during rotation and tends to generate vibration of engine caused by an unbalance of each moving part.

Vibration is suppressed as much as possible by optimizing combustion order of each cylinder, or by

devising bearing and balance weight.

ScrewFixed type

Bolt

Semi-floatingtype(Bolt type)

Snap-ringFull-floating type

Method for connecting the piston andconnecting rod

ArmCrank pin

Crank journal Balance weight

Shape of a crankshaft (in case of 4-cylinder engine)


27/111

1) Crankshaft of each engine

(1) Serial 4-cylinder engine

In 4-cycle engine, crankshaft rotates twice

during each cycle (intake, compression,combustion, and exhaustion). While

crankshaft rotates twice (720),

combustion occurs 1 time in each cylinder

of 4-cylinder engine. That is, while the

crankshaft rotates 180, combustion

occurs 1 time in a 4- cylinder engine.

As shown in Fig-A, cylinders are called 1st,

2nd, 3rd, and 4th starting from the front

cylinder. The order of ignition is either 1-3-

4-2 (in case of Nissan vehicles) or 1-2-4-3.In either case, pistons of 1st and 4th

cylinders and 2nd and 3rd cylinders move in

pairs.

As shown in Fig-B, there are 2 types of

methods for supporting crankshaft; 5-

bearing type and 3-bearing type. At

present, 5-bearing type that is strong

against the bend generated by high-speed

revolution is mostly utilized.

(2) Series 6-cylinder engine

In the case of 6-cylinder engine,

combustion occurs 6 times while the

crankshaft rotates 2 times. Since

combustion is executed at each 120,

crank pins are arranged with an interval of

120. As a result, 6-cylinder engine

generates less vibration and operates

more smoothly than 4-cylinder engine.

Although it is possible to select variousorders of ignition, order of 1-5-3-6-2-4 (in

case of Nissan vehicle) and 1-4-2-6-3-5

are mostly utilized.

Front

Center ofcrankshaft

Fig-A. Example of serial cylinder engine

Piston

Bearing

Balanceweight

5-bearing support3-bearing support

Fig-B. Method for supporting crankshaft of serial 4-cylinder engine

Example of serial 6-cylinder engine (Nissan vehicle)


28/111

(3) V6 cylinder engine

Like serial 6-cylinder engine, in V6 cylinder engine,

combustion is executed 6 times while crankshaft rotates 2

times.Since the total length of V6 cylinder engine is short, 4

bearing support in which 2 crank pins are equipped

between the bearings is utilized. The 1-2-3-4-5-6 order of

ignition is used in the case of Nissans VG series engine.

(4) V8 cylinder engine

In V8 cylinder engine, since 2 connecting rods are connected to 1 crank pin, 5 bearings are used.

Because combustion is executed 8 times during 1 cycle in this engine, vibration is very weak and

noise is low.

The order of ignition of 1-8-4-3-6-5-7-2 and 1-8-7-3-6-5-4-2 are used in Nissans Y44-type engine and

VH45-type engine, respectively.

2) Oil path in crankshaft

In crankshaft, an oil path is provided from the journal part to

each crank pin. Lubrication oil sent from the oil pump passes

through the oil gallery in the cylinder block and goes into oil

pass and lubricates each bearing.

Example of V6 cylinder

Cross section A-A

Oil path in crankshaft


29/111

3) Material of crankshaft

Because crankshaft receives strong impact or torsion generated by explosion, material with excellent

rigidity must be selected.

There are 2 types of material; the one is cast type and another is forged type. Although cast type iseasier to manufacture than the forged type, the former is inferior in strength and rigidity. So, in general,

forged product of carbon steel or alloy steel is utilized.

9. Bearing

Since crank journal and crank pin, which are major rotational parts in an engine, rotate while always

receiving strong fluctuating load, bearing is used in shaft bush so as to smoothen the rotation of crank

pin and journal as well as to protect the shaft bush from wear.

1) Type and shape of bearing

Bearings for automobile engine such as plain bearings, are

mostly utilized in the upper/lower parts divided system. Plain

bearing is the one manufactured such that, as shown in this

diagram, metal material is deposited or sintered (flour of metal

is combined and hardened at temperature below melting point)

on the surface of circular steel plate (back metal).

Central groove is the oil path for supplying lubrication oil to the

bearing and a hole in the center is an oil feeding hole.

On the back side of a bearing, fixing nail is set so that the

bearing does not rotate along with the crankshaft.

(1) Name of bearing

Bearing may be called by the following names depending on the part for which it is used.

(i) Crank journal part

Main bearing or parent metal

(ii) Crank pin part

Connecting rod bearing or child metal (there is also a bearing that has no oil path)

Cast product: A product manufactured by a method in which the metal isheated, melted, and casted into mold to form a desired shape.

Forged product: A product manufactured by a method in which the metal isheated and beaten out to form a desired shape using a press machine. Bybeating out metal, the tissue structure of metal is changed and its strength isenhanced.

Reference

Fixing nail

Oilfeeding

Oil groove

Back metal

Metal layer

Plain bearing


30/111

(2) Thrust bearing

The thrust bearing that receives axial direction force of

crankshaft and defines axial direction allowance (end play) is

used for the main bearing. Such main ring (flange metal) is

used at single location such as the center part of the crankshaft.There is also a type wherein the thrust bearing is independent.

(3) Characteristics necessary for bearing

Bearing requires the following characteristics:

should have good affinity with sliding surface

should be possible to bury tiny extraneous substances within

the lubrication oil under the surface of the bearing

should be hard to generate burn out

should not cause oil shortage even at start-up time when oil is not supplied

should have appropriate strength and hardness and not get damagedshould not get affected by lubrication oil in which the substances generated by combustion, etc. are

mixed.

should have good thermal conductivity and small thermal expansion coefficient

should have good lubricity and strong resistance against wear.

2) Material of bearing

The material of bearing can be of white metal of tin/lead

series and kelmet metal of copper/lead series. Although whitemetal has good affinity with sliding surface and ability to burry

extraneous substance, it has lower load bearing ability and is

not suitable for todays high revolution engines.

While, kelmet metal has high load bearing ability, but it has

low affinity with sliding surface.

So, a material called three layer metal that was made by

combining good features of these materials is widely utilized

as material for making bearings.

Flange

Thrust bearing

Copper/Lead 3-layer metal

1. Steel back2. Copper-lead alloy layer generatedby combustion

3. Nickel plated layer4. White metal plated layer

(iii) Thickness: about 8m

Structure of bearing

(iv) Thickness: about2m


31/111

(3) Double overhead camshaft type (DOHC type)

This is a type in which the inlet valve and

exhaust valve have a respective camshaft,

and have no locker arm. Since camshaft

pushes the valve directly, the structure ofvalve system is simple.

As a result, it is possible to let valve

open/close in accordance with the cam

profile (good followability) even even when

an engine rotates at higher r.p.m. Hence, this

type suits most to high-revolution engines. In

some engines, because it is possible to

secure the amount of valve lifting, locker arm

is utilized.

Since this type has 2 camshafts, it is easilypossible to equip it with 2 inlet and exhaust

valves per cylinder; that is, to equip with total

4 valves per cylinder. As a result, opening

area for intake/exhaustion becomes large

and inhalation efficiency can be improved.

DOHC type is utilized in high output power engine. (e.g., CA-series, RB-series, VG-series)

2. Camshaft

Cam of the camshaft operates to let the inlet/exhaust

valves open and close with the most appropriate

timing driven by pistons moving up and down so as to

enable complete functioning of an engine. Even if the air

volume displacement of an engine, shape of

combustion chamber, shape and size of inlet/exhaust

port, etc. have been determined, performance and

nature of an engine are still subject to changes

depending on the determination of the shape and

relative position with reference to the camshaft and

cam.

Therefore, it can be said that cam of camshaft is a key part of the valve open/close mechanism and

has a decisive impact on the performance of an engine.

Intakecamshaft

Intake valve

Exhaustcamshaft

Hydraulic valvelifter

Exhaust valve

DOHC type

Cam is thekey ofvalvemechanism

Camshaft


32/111

1) Valve timing

The time required to make the inlet/exhaust valve

to open/close is denoted by before top dead

center, after top dead center, before bottomdead center, and after bottom dead center, for

rotational angle against the position of piston.

This open/close timing is called Valve timing,

and the one that illustrates this timing

relationship, as shown in this diagram, (in the

case of 4-cycle engine) is called timing diagram.

In the following paragraphs, the open/close of

valve is described.

(1) Open/Close of intake valve

Since the intake of mixed-gas delays slightly from the open timing of intake valve, the intake valve is

opened at A (1020) before the top dead center so as to enable inhaling of mixed-gas as much as

possible using momentum (inertia) of the mixed-gas that is moving inside . Even after the piston

passes over the bottom dead center and begins to ascend, mixed-gas flows in by inertia, so the intake

valve is closed at B (4060) after the bottom dead center after the complete intake of the mixed-gas.

(2) Open/Close of exhaust valve

In order to remove combusted gas perfectly from the cylinder, exhaust valve is opened at C (around50) before the bottom dead center when the internal pressure of the piston is still high, sacrificing a

part of the explosion pressure. Exhaust valve is closed when the piston ascends and next cycles

inhalation starts, and the combusted gas is completely exhausted; that is, at point D (10 20) after

the top dead center.

(3) Overlapping of valve (overlapping of opening time of intake/exhaust valves)

While the intake and exhaust valve are both opened around the top dead center of exhaustion and

when the exhaustion process was almost completed and inhalation started, that phenomenon is called

overlapping of valve.

This setting is done so that the intake and exhaustion can be fully executed even when the engineoperates at high-revolution. The timing is determined appropriately depending on purpose of the

engine.

When overlapping is too small, intake/exhaustion is not enough in high-revolution range and output

power is decreased. On the other hand, when overlapping is too large, combusted gas leaks back to

the mixed-gas side, or exhausted gas goes back to intake port side, which creates a problem.

Recently, a system is available, in which while compensating intake/exhaustion performance in high-

revolution range by using turbo charger, etc., it is possible to enhance power (torque) in low to middle

speed range by setting the overlapping of valve to be small or zero.

Intake

Compressio

n

Combustion

Intake valveopen

Top dead center

Exhaust valve open

Exhaust valve closed

Bottom dead center

Intake valveclosed

Valve timing diagram


33/111

2) Structure of a camshaft

(1) Shape of cam

Profile of cam is designed so as to open the valve at exact

timing with large lift and close the valve softly.Profile of cam that is generally utilized is shown in this

diagram.

A is called base circle. In this area, valve is closed.

H is the overall height of cam and h corresponds to the lift

height of cam.

corresponds to the range in which the valve is opens.

During this range, ab act to open the valve and bc act

to close the valve. Since the range a b and b c are

equal in generally used cams, 1/2 of is called operation angle. In addition, a cam in which the

operation angle of the intake valve is 60and that of exhaust valve is 62

is called 6062 cam.

Features that affect the performance of an engine are an opening height (lift) and opening time

(operation angle) of the valve.

For example, if the operation angle was set to large values,

overlapping becomes large, intake/exhaust efficiency in

high-revolution range is improved, and output power

becomes large. However, inversely, revolution becomes

unstable and performance decreases in low-speed

revolution range. On the other hand, if the operation angle

was set to small values, adverse results may be obtained

to enhance the performance in low speed range.The actual profile of cam is designed such that collision

between cam and valve lifter and its related parts as well

as valve and valve seat may occur always at low speed by providing a low speed buffer part to rise

and closing phases of lift. Therefore, adjustment of valve clearance must be executed avoiding this

buffer part.

(2) Name of each part of a camshaft

Names of each part of the camshaft are

shown in this diagram. There are some

camshafts to which driving gear or drivingcam for driving oil pump, fuel pump, or

distributor are equipped, or to which oil

feeding hole as a path to feed lubrication oil

is created.

(Operation

angle)

(Valve opening range)

(Cam lift)

(Total

Rotationaldirection(Base

circle)

Shape of cam

(Low-speed type)

SmallLarge

(High-speed type)

Operation angle and feature

Journal Cam

Oil pump drivegear

Fuel pump drivegear

Distributor drivegear

Names of each part of camshaft


34/111

2) Hydraulic calve lifter

Hydraulic valve lifter is used to keep the valve clearance

to 0 by the action of oil pressure. This is used in some

engines. By using this hydraulic valve lifter, noise can be

reduced because of 0 valve clearance.

(1) Structure and operation of a hydraulic valve lifter

In case of OHC engine, hydraulic valve lifter is used inbetween camshaft and locker arm or locker arm and

valve supported by valve lifter guide. In valve lifter guide,

there is an oil path for feeding lubrication oil to hydraulic

valve lifter.

[Operation principle]

(a) Before starting of cam-lift ((a) in diagram)

Plunger is pushed up by return spring and valve

clearance becomes 0. At this time, high-pressure

chamber is filled with oil.

(b) During cam-lift ((b) in diagram)

Load from the valve locker acts on the

plunger, and oil pressure in the high-

pressure chamber is increased. As a result,

oil slightly leaks from the gap between the

plunger and body. Due to this the plunger

descends.

(c) When cam-lift just finished ((c) indiagram)

Since there is a slight leak, as described in

(b), valve reaches to valve seat just before

cam-lift becomes 0. Next, the plunger ascends by an amount just corresponding to the leak by the

action of return spring and returns to the original position. At this time, the relief spring is pushed to

open check ball and oil is refilled. By repeating (a)(c), the valve clearance is always kept to 0.

Hydraulicvalve lifter

Camshaft

Exhaustvalve

Locker shaft

Locker arm

Lifter guide

Intake valve

Mounting position of a hydraulic valve li fter

Body

Plunger

Check ball

Relief spring

High-pressurechamber

Return spring

Structure of hydraulic valve lifter

Returnspring

Checkball

Reliefspring

Leak

Operation of hydraulic valve lifter


35/111

4. Valve and valve spring

As shown in this diagram, valve is

assembled on the cylinder head using a

valve spring, valve spring retainer, and

valve collet, and it moves up and down to

close/open the inlet and exhaust valves.

1) Valve

(1) Names of each part of a valve

Names of each part of a valve are shown in the above diagram. Valve consists mainly of valve stem

and valve, and a surface that closely contacts with the valve seat of the cylinder head is called valveface.

As shown in above-right diagram, the angles of valve face are 30, 45, or 60 in both the intake and

exhaust valves.

Valve

Cross sectional view of valve mechanism

Valve spring(inner)Valve collet

Valve springretainer

Valvespring(outer)

WaterjacketWater

jacket

Valvespring

retainer

Separate collet

Valve stem end

Valve stem

Seat widthValve face

Valve head

Seat angle

Names of each part of a valve

Valve seat

Angle of valve face

Note: Intake valve seat is processed with multiple stepshaving a different angle to lower the intakeresistance

Valve guide

Valve sheet


36/111

(2) Material of valve

Since the valve receives repetitive impact of being exposed to high-temperature gas, following

properties of the material for making valves are required.

Should be bearable against high-temperature and have good heat conductivity

Should not get eroded by high-temperature gas Should be strong against impact even at high-temperature

Should be abrasion-resistant

Accordingly, it is required that the valve should be a forged product of special steel with high heat

resistance. The exhaust valve is often manufactured by attaching a special alloy (Stellite) on the valve

face part. In addition, there is a case in which heat radiation ability of the valve is improved by making

molten sodium to flow within the cavity that has been bored inside the valve stem.

2) Valve spring

Valve spring operates to close or open the valve definitely according to the movement of cam with its

spring force. In the case of single spring, it may often generate undesirable vibration during intensivemovement of cam while the engine is running at high-revolution and does not follow the movement of

cam (this phenomenon is called surging).

To avoid this surging phenomenon, double-spring type in which reversely-wound spring is inserted into

the spring is also utilized.

Double springSingle spring

Valve spring


37/111

3) Aerodynamic port

By narrowing a part of the intake port, since it is possible

to secure an appropriate fluid speed of the inhaled

mixed-gas even if the piston speed is slowed down,inhalation efficiency in low-to-middle speed range can be

improved.

4) Method for heating intake manifold

In order to aid the vaporization of mixed-air that passes through the intake manifold, the riser part ofthe intake manifold is heated externally. There are 2 types of methods for heating; one is to utilize

exhaust gas and another is to utilize cooling water (hot water) of engine.

(1) Exhaust gas heating method

This is a method for heating mixed-gas by guiding

exhaust gas to pass under the riser part, as shown in the

diagram on the right. When the engine starts, since the

temperature of the riser part goes up in a short time, it is

desirable that the engine is not hot. However, as the

engine is heated, the degree of heating may becomevery high and the output power may be decreased.

Hence, such a structure that is possible to stop heating

by the action of bimetal when the temperature reaches a

specified value by providing heat control valve to

exhaust manifold is used.

This method can be adopted only in such type of engines in which intake/exhaust system is located in

the same side as the cylinder head (turn flow system).

(2) Hot water heating method

Since this method executes heating by guiding thecooling water (hot water) into a jacket under the riser

part, the absolute value of the temperature is not high

and the rising speed of temperature is slower than that

in the exhaust gas heating method. Temperature does

not go up beyond the boiling point of water in any

operating conditions and complex structure is not

required. Hence, even though this method is not

effective when the engine is not hot, i.e., just after the

engine has started up, this is widely utilized. In

addition, this method has an advantage that it can be adopted independent of the type ofintake/exhaust system.

Wide

Fluidspeed islow

Narrow

Inhaled air

Air intake system (AD port)

Carburetor

Exhaust gas

Heat control valve

Exhaust manifold

Exhaust gas heating system

Carburetor

Riser

Engine cooling water

Intake manifold

Hot water heating system


38/111

* Riser: Heating device


39/111

5. Exhaust manifold

Exhaust manifold has a role that

combines the exhaust gas discharged

from each cylinder and guides it

smoothly to the exhaust tube so that

there is no resistance to the flow of

exhaust gas. In this case, a shape that

does not obstruct the flow of exhaust

gas by interacting with the discharged

gas is required. If the exhaust gas does

not flow smoothly, combusted gas

remains inside the cylinder, and makes

the intake of mixed-gas insufficient in

the next inhaling process, which results

in the decrease of power. Length and

shape of the collected exhaust manifold also affects the output performance of an engine.

The material of exhaust manifold is mostly cast iron; however, stainless sheet metal is also utilized in

such engines that place great importance on performance; for example, a racing vehicle.

Typical examples of exhaust manifold are shown in the above diagram.

6. Exhaust tube and muffler

When high temperature and pressure of combusted gas

exhausted from a cylinder is emitted directly to air, it expands

rapidly to generate explosive roaring sound. A device for

muffling the sound by making the exhausted gas to expand

and cool gradually inside a chamber is called muffler.

A pipe that guides the combusted gas from the exhaust

manifold to the muffler and further from the muffler to behind

the vehicle for discharging the cooled exhaust gas to air is

called exhaust tube.

Basic type

Dual type

Collected

Examples of exhaust manifold

Detonatingsound

Muffler

Mufflers role


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Chapter 5 Cooling system

1. Overview

Since the combustion of mixed-gas within the

combustion chamber is executed at temperatures as

greater than 2,000C during engine operation, the

temperature of each part of the engine rises. If nothing

is done about it, the temperature of the cylinder wall,

piston, and valve, etc., will become very high, and it

would become impossible to operate the engine any

further. Therefore, it is necessary to always cool each

part of the engine to maintain them at an appropriate

temperature. This is what the cooling system does.

There are 2 types of cooling systems for automobile

engines, one is the air cooling type and another is the

water cooling type. Except for motorcycles and some

light-vehicles, water cooling system is generally

utilized.

Oil will beburned!Engine may bedeformed bythermalexpansion!

Air-cooling

Water-cooling

Cooling system

Coolingfan

Fan belt

Radiator

Coolingwater

emits heathere.

Water pumpThermostat

To heater

Water jacket

Cooling waterremoves heat fromengine.

Structure of water-cooling system


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1) Structure of water-cooling system

Water-cooled engine cools down the heat generated by an engine and emits the heat of the cooling

water from the radiator to air.

For circulating cooling water, a forced circulation system that uses a water pump, which forcibly

circulates cooling water, is used. Heat dissipation from the radiator is executed by forcibly inhaling

external air by a cooling fan or by using natural air during motion.

In the above diagram, when the engine is in a low temperature state, in order to facilitate warming up

of an engine, cooling water path to the radiator is closed by a thermostat to circulate cooling waterwithin the engine only. When the engine gets warmed, the thermostat opens the cooling water path to

the radiator. Next, the cooling water enters into the radiator through the top inlet and goes inside the

radiator while being cooled down by the wind blown by a cooling fan or by natural wind, following

which it goes out from the bottom outlet to be returned to the engine again for recirculation to each

part of the engine.

In addition, some part of the cooling water is circulated to the intake manifold and carburetor in order

to heat and boost vaporization of inhaled mixed-gas, or to facilitate automatic choking mechanism of

the carburetor, as well as it is circulated to the heater core in order to heat the interior of a vehicle.

Thermostat

From radiator

To radiator

Block

Water pump

From heater

Return pipe

Throttle chamberFrom head

Blow-by control valve

VGseries

Air drain cock

Collector

AAC valve

Surge tank

Water outlet

Radiator

Thermostat

Water pump

Cylinder block (lef t) Cylinder block (right)

Cylinder head (left) Cylinder head (right)

(Valve opens at 76.5 )Throttle chamber

AAC valve(air cut valve)

Throttle chamber

Reserve tank

Heater


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4. Water pump

This is a pump that is used to circulate cooling water

uniformly to complex water jacket of each cylinder. Water

pump rotates at a speed of 0.81.5 times that of engine

revolution driven by V-belt from the crank pulley.

As shown in this diagram, when the impeller is rotatedby the V-belt, cooling water is inhaled from the radiator

by the impeller and sent from the outlet port to the water

jacket of the cylinder block.

Fan

Bearing

Pulley

Packing

Pump cover

Impeller

Pump shaft

Seal unit

Pump body

Impeller (convolution type)

To waterjacket ofcylinder

From lower tank of radiator

Water pump

Circulation in a water pump


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5. Fan belt

To drive water pump, cooling fan, or alternator, a V-belt is generally utilized.

The V-belt is named such because the cross-section of the belt is formed in a V-shape in order to

increase the power transmission efficiency. There are various types of V-belts. The most appropriate

V-belt for a required application is selected.

Poly V-belt has a cross-sectional shape such that multiple V-shapes are connected. Since poly V-belt

has a wide contact area with the pulley, it operates with less slip. Moreover, since poly V-belt is thinner

and more flexible than conventional V-belts, it generates less heat.

Cog-type belt has a cog-like inner surface. Since cog-type belt has good flexibility, it is highly durable.

Recently, low-maintenance-type belt that does not require frequent adjustment is mostly used.

Low-maintenance belt is a belt that includes a thermally contractible cord that, when slipping occurs,

contacts by heat generated provides restoration of its tensile strength.

Note: Poly means many and cog means gear.

6. Thermostat

Thermostat is a device that is mounted to the outlet or

inlet port of cooling water to automatically maintain

constant temperature of cooling water. The optimum

temperature of cooling water to extract maximum

performance of an engine is in the range of 80C and

90C, and it is not desirable that the temperature is very

high or very low.

Thus, it is required to maintain appropriate temperature

by stopping the circulation of cooling water to the

radiator when the temperature of the cooling water is low

so that the engine heats up as soon as possible; i.e., by

circulating cooling water only when its temperature is

high.

Thermostat plays a role keeping maintaining constant

Canvas

Rubber

Rubber Canvas

Canvas

Rubber

Cord Cord

(Cross-section) (Cross-section)

Low edge belt Poly V-belt

(Outlook)

Cog type belt

Rubber Rubber

Structure of belt

Case

Pellet

Spindle

Jiglu valve

Spring

Wax-pellet-type thermostat


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cooling water temperature by changing the amount of water circulating through the radiator.


46/111

There are 2 types of thermostats that are categorized by the difference of expanding/contracting part

depending on temperature; one is wax-pellet type and another is bellows type. Since cooling system

mostly utilizes the pressurization method, bellows type in which the valve opening force is weak is not

utilized.

1) Operation of a thermostat

For controlling the circulation of cool water through the radiator, there are 2 methods; one is by

mounting a thermostat to the outlet port of cooling water and another is by mounting a thermostat to

the inlet port of cooling water. Recently, there also is a system that utilizes bottom bypass type

thermostat that controls not only cooling water that circulates through engine but also cooling water

flowing inside the engine at the same time.

In general, thermostat is mounted to the outlet port of cooling water of an engine. However, in the case

of bottom bypass system, there are 2 methods; one is a type in which thermostat is mounted to theinlet port and another is a type in which thermostat is mounted to the outlet port.

(1) Thermostat without bypass valve

Here, an example in which a thermostat is

mounted to the outlet port of cooling water

of an engine is described.

The diagram on the right shows an

operating state of wax-pellet type

thermostat. Inside the pellet (vessel), solid

wax, rubber, and bar-piston areassembled, and a part of the piston is

fixed to the external case. A valve controls

the amount of fluid present outside the

pellet, and when the thermostat is not

working, it closes the water path by

springs force. When the temperature

of cooling water rises, the wax melts

and its volume expands. Bar-piston is

pushed by the force generated by this

expansion, but since one end of thebar-piston is fixed to case, the pellet

is moved down prevailing against the

spring force to open the valve. When

cooling water that was cooled by

passing through the radiator is

returned to the thermostat, the valve

closes again.

Case Spindle

Wax Syntheticrubber

Pellet

Low temperature, closed state High temperature, opened

Thermostat

Waterpump

Water jacket

Engine

(Low temperature state)

Radiator

(High temperature state)

Flow of cooling water

Structure and operation of thermostat


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In this way, the thermostat maintains the temperature of cooling water by controlling the amount of

fluid while repeating the open and close actions. This diagram (previous page) shows how cooling

water circulates. When the temperature of cooling water is lowsince thermostat is closedcooling

water is not sent to the radiator but it circulates within the engine. When the temperature rises, the

thermostat is opened and cool water begins to circulate even through the radiator.

(2) Bottom-bypass type thermostat

Here, an example in which a

thermostat is mounted on the

inlet port of cooling water of the

engine is described.

The diagram on the right shows

an operating state of a bottom-

bypass type thermostat.

This type has a structure with anadditional bypass valve that

controls the circulation of cooling

water that is mounted to the

bottom of a conventional

thermostat.

When the temperature of cooling

water is low, radiator side valve

is closed while bypass valve is

opened and cooling water

circulates through the radiator. When the temperature of cooling water is high, radiator side valve isopend to permit cooling water to

circulate through the radiator. In this

case, since the bypass valve is closed,

circulation of cooling water through the

engine is limited.

In thermostats other than bottom-

bypass type, even when it is fully

opened, circulation of cooling water

through the engine is executed in

parallel; however, in the case of bottom-bypass type, since circulation of cooling

water through the engine is stopped and whole cooling water is circulated the radiator instead, thereby

improving cooling performance. In addition, since this type of a thermostat has a function to control

water circulation through the engine, it is possible to widen the circulation path within the engine, and

as a result, fluid resistance becomes less when the temperature of cooling water is low compared to

that in the conventional thermostats. Thus, load on the water pump reduces and the output loss of

engine can be decreased.

To water

pump

From radiator

Valve

Bypassvalve

From cylinder headLow temperature state

High temperature state

Structure and operation of bottom-bypass type thermostat

Water jacket

Waterpump

Engine

Thermostat (Low temperature state)

Radiator

(High temperature state)

Flow of cooling water


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2) Jiglu valve

When we drain cooling water for the purpose of changing,

it is required to introduce air into the cooling water path

within the engine. In addition, when we refill cooling water,it is required to remove the residual air from the water path.

Jiglu valve is used for securing the air path. When an

engine is not running, the valve is opened by its own

weight, whereas when the engine is running, the valve is

closed by the water pressure generated by the water

pump.

In modern engines, air-drain plug is provided. The position

where the radiator is mounted is lower than the engine body for lowering air resistance and styling. As

a result, since it is not easy to drain air

that is remaining in the top of engine,air-drain plug is provided.

3) Cooling fluid

Water is mostly used as a cooling fluid for automobile that have water-cooling engine. Water is

considered to be optimum cooling fluid because its specific heat and evaporative latent heat are both

greater than other liquids. However, there are many kinds of water, such as water containing lot of iron

and impurities, water containing salt, water containing sulfur trioxide or hydrogen sulfide that is found

in thermal region, etc. Since these substances may lead to the deposition of water stain, corrosion of

metal, hardening of rubber hose, etc., when an engine is used for a long time, the use of such water

should be avoided. Especially, since modern engines use many light alloy metals that are easily

affected by such impurities, it is strongly recommended to use softened water as cooling fluid.

One of the weak points of water is that it freezes at 0C. If water freezes inside the engine, it may

cause destruction of the engine due to expansion. Since vehicles may be used at low temperature

environment (under -20C), cooling fluid that has a freezing temperature corresponding to such a low

temperature conditions is required.

Air path

When engine is notrunning (open)

Water pressure

When engine is running(close)

Operation of Jiglu valve

Headdrop

Radiator

Air-drain plug

Thermostat

Position relationship between radiator and engine


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Chapter 6 Lubrication system

1. Overview

There are many sliding parts in engine. When 2 metals move while relatively contacting with each

other, heat or scratch may be generated at the contacting surface, and may finally result in a burn-out.

The lubrication system protects metals from burn-out by creating an oil layer on the sliding surface

between the metals.

1) Role of lubrication oil

Lubrication oil has many roles such as to decrease wear on sliding surface (smoothing action), to

maintain hermetic ability of moving parts (sealing action), to absorb and disperse impact (buffering

action), to prevent rusting (anti-rusting action), to clean up extraneous substances (cleaning action),

etc.

2) Circulation of lubrication oil

(1) Positions requiring lubrication

Positions requiring lubrication are:

(i) Surface of piston and cylinder wall

(ii) Piston pin part of connecting rod

(iii) Journal and crank-pin parts of crankshaft

(iv) Valve opening/closing mechanism (camshaftvalve stem)

(v) Timing chain mechanism

Locker shaft

Hydraulicvalve lifter

Valvelocker

Valve lifter guide

Camshaft

Main gallery

Oil filter

Oil pump

Crankshaft

Pressure regulator

Oil strainer


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2. Oil pan and oil level gauge

(1) Oil pan

Oil pan is a tank for storing lubrication oil. It is generally

made by press molding of a thin sheet of steel or aluminum

with good heat radiation performance.

Inside the oil pan, a screen board for preventing fluctuation

of oil is provided, and a drain plug for draining oil is

provided at the bottom of the oil pan.

Usually, the capacity of oil pan is in the range of 35 liters.

(2) Oil level gauge

Oil level gauge is a bar-like gauge used for checking the

amount of oil in the oil pan that is mounted to the side plain

of a cylinder block.

To this gauge, the positions indicating the upper and lower

limits of the optimum amount of oil are marked, and the

difference between these marks corresponds to about 1

liter.

Screen board

Drain hole

Oil pan

Oil levelgauge

Oil pan

Oil level gauge


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3. Oil pump

There are several types in oil pumps. In general, gear type and trochoid type are mostly utilized.

1) Gear-type oil pump

(1) External tooth gear pump

In external tooth gear pump, 2 gears with the same diameter are combined inside a housing. One of

the 2 gears (drive gear) is driven by the driving gear of the camshaft or crankshaft thereby driving a

driven gear. Oil is transferred by utilizing the cavity between the teeth and inner surface of pump

housing. Lubrication oil is inhaled and carried along the outer circumference of the gear and sent to

the oil path. Although the structure of the external tooth gear is simple, it has no sliding parts and has

excellent durability; it has a disadvantage that its size is large. (e.g., SD series, ED series, FD series

engine)

(2) Internal tooth gear pump

engine power train

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