4-engine components and systems

Engine components and systems

Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science

1. Combustion engines main principles and definitions

2. Reciprocating combustion engines architecture

3. Reciprocating engines dynamic properties

4. Engine components and systems

5. The engine management system for gasoline and Diesel engines

6. The emission Requirements & Technology

7. Engine vehicle integration

7.1 Engine layout and mounting

7.2 Engine-vehicle cooling system

7.3 Intake system

7.4 Exhaust system


Scuola di Dottorato di Ricerca 2010 - Road vehicle and engine engineering science 2

Crankcase

Cylinder head

Crankshaft

Camshaft

Connecting rod (con-rod)

Engine piston

Engine systems

Engine-vehicle systems

Main engine components and systems

The FIVE “C”



1. The block-crankcase

2. The cylinder head

3. The crankshaft

4. The connecting rod

5. The engine piston

6. The valve train


John Heywood, Internal Combustion Engine Fundamentals / McGraw-Hill

Charles F. Taylor, The internal Combustion Engine in Theory and Practice /The M.I.T. Press

Automotive Handbook – R. Bosch/SAE

Advanced engine technology (Heinz Heisler) – Butterworth/Heinemann



To support the force-transfer mechanism between

the cylinder head and the crankshaft assembly

To bear the crankshaft assembly’s support

bearings

To incorporate the cylinder sleeves

To include separate water jackets and sealed oil

chamber and galleries

To serve as a mounting and support surface for

most of the engine’s auxiliary devices

Blow-by channels

Oil draining

Crankshaft axial thrust bearing

The block-crankcase - Function and components

Bottom view

Side view

Top view



For an increased stiffness, the crankcase is

generally extended to below the crankshaft’s

axis center trough an extension of the block

itself (deep skirt) or through a separate

structure (bedplate) integrating the main

bearing caps


Bedplate

Deep skirt

Single caps

Bottom view Top view



Piston cylinders may be:

Machined from the block casting

with special surface treatment for higher

wear resistance

Separate wet or dry liners, generally

cast iron (aluminum only for niche sport

applications); dry liners are generally

cast-in the cast iron blocks or forced

after a pre-machined cylinder

The cylinder blocks are manufactured by:

grey cast iron, very popular for past

and truck-Diesel engines

aluminum high-pressure die-casting

that is becoming a widely used technique

for passenger car blocks , also of Diesel

engines, because of its weight saving

potential

Machined liner

Separate liner




Cylinder top view

Cylinder bottom view

Cast iron liner top

Cast iron liner bottom

Cast-in iron liners into a light alloy block




Cylinder block construction takes two forms. Closed-deck construction (Figure slide

10) represents long-established practice and resembles a deep box-like enclosure for the

cylinder barrels that also serves as a coolant jacket . Transfer ducts are provided in the

top face or closed deck of the cylinder block, so as to permit the circulation of coolant to

the cylinder head.

With the open-deck construction (Figure slide 9) the cylinder barrels are free-standing

in that they are attached only to the lower deck of the cylinder block, which in past

applications utilized detachable cylinder liners that tended to result in a less rigid

construction. By dispensing with a continuous top face, the open-deck construction

nevertheless reduces the complexity of the cylinder block casting. Where gravity sand

casting is used it facilitates the coring for the mould into which the metal is poured.

However, the increasing preference for using aluminum alloy, rather than grey cast iron,

for the cylinder block and crankcase of modern lighter weight engines, has led to their

manufacture by high-pressure die casting in the interests of economical mass

production. Since this method of casting necessarily involves the use of steel

instead of sand moulds, the need for an open-deck construction to allow

withdrawal of the steel cores becomes mandatory. Also, the liners may be cast

directly into the cylinder block to restore structural rigidity. An open-deck construction

further allows inspection of the coolant jacket for accumulated deposits. To perform this

operation in a closed-deck cylinder block requires the addition of detachable cover

plates.

Cylinder block construction



Aluminum high pressure die-casting open deck block

Open deck




Cast-aluminum closed deck for high

performance application (Pmax>160 bar)

Aluminum bedplate

Cast iron liners casted-in to the

block

The cylinder head bolts oppose the

gas forces to facilitate a force transfer of

maximum linearity and minimal flexural

tendency through transverse support

walls and to the main bearings.

Closed deck




1

2

2

3

4

Block general load path



Cylinder liner temperature profile





Liner deformation due to the

cylinder-head bolt tightening

Horizontal

section

Vertical

section



Pmax+3sP =160+3x160x(2.6/100)=173 bar

4th order less than 5mm with

thin wall liner

It includes compression ratio, VGT actuator,injector and

injection timing dispersion and combustion irregularity


Liner deformation due to the

cylinder-head bolt tightening



Lower block side-bedpalte loads (V6 Diesel engine)




To seal the upper end of the blocks and of

the cylinders

To define the combustion chamber shape

together with the piston top surface

To house the gas exchange valves as well all

the intake and exhaust ducts

To house the spark plugs, injectors and

heating plugs

In most of the designs, to include also the

valve gear, as camshafts, drive gears, etc

The cylinder head - Function and components

Gasoline engine cylinder head

Diesel engine cylinder head



In truck and large industrial engines, individual

cylinder heads are often used on each cylinder for

better sealing force distribution and easier

maintenance and repair.

Separate cylinder head design is required for

improved cooling efficiency of air-cooled engines.

One cylinder head for all cylinders is generally

employed for passenger car engines

The cylinder head of industrial and truck large

water-cooled Diesel engines are made of gray cast

iron or of vermicular castings for more severe

applications (higher combustion pressure)

Aluminum material (AlSi9Mg) is widely used for

the cylinder heads of gasoline and Diesel engines

because of superior heat dissipation and lower

weight (tensile strength 250-300N/mm2, hardness

90-120 HB, elongation 3-5%). The greater heat

conductivity of aluminum alloy is beneficial in

maintaining a more uniform temperature throughout

the cylinder head.


Gasoline engine vertical cross section

Diesel engine vertical

cross section

Diesel engine horizontal

cross section



4 Cyl 16v Diesel engine cyl head

Inlet manifold bottom

part Swirl duct

Inlet manifold bottom

part Straight duct

Intake side view

Exhaust side view




Swirl duct

inlet valve

Straight duct

inlet valve

Exhaust valve

Pre-heating

plug

4 Cyl 16v Diesel engine cylinder head

Bottom view




Blind cam

bearings

machining4 Cyl 16v Diesel engine cyl head – Cam carrier

Bottom view

Top view




Lubrication partial grooves feeded

from the hole on camshaft (the hole

position is in between the couple of

grooves)

No dowels to

center the cap

4 Cyl 16v Diesel engine cyl head – Camshaft bearing cap




Pre-chamber undirect injection engine

INIETTORE

CANDELETTA DI

PRERISCALDO

PRECAMERA

CAMERA DI

COMBUSTIONE

Direct injection engine

ELETTROINIETTORE

CANDELETTA DI

PRERISCALDO

CAMERA DI COMBUSTIONE

Diesel engine cyl head cross section view




Mercedes V6/90° 2.8l Diesel




In the internal combustion a head gasket is necessary

between the engine block and cylinder head. The purpose is to

seal the cylinders to ensure maximum compression and to avoid

leakage of coolant or engine oil into the cylinders

The cylinder head gasket is the most sealing critical

application in any engine and shares the same strength severe

requirements of the other combustion chamber components.

Particularly it must guarantee adequate resistance to high

temperatures and pressures , to gas/water/oil corrosion and to

provide the elasticity necessary for compensating the thermal

expansion generated by the cyclic combustion in to the cylinders

Since mid 90’ years, because of increased cylinder pressure

(over 140bar in the CR Diesel engines) and of environment

reasons, most modern head engines are produced with Multi

Layer Steel gaskets: these typically consist of a number of

steel layers up to four, depending on the working maximum

cylinder pressure. The contact faces are usually coated with a

rubber-like coating such as Viton that adheres to the cylinder

block and cylinder head respectively whilst the thicker center

layer is bare.




Thermal analysis

Temperature distribution

Strengths analysis

Interference force distribution




The crankshaft - Function and components

To convert the reciprocating motion of the

piston, conveyed to it by the connecting rod and the

crank throws or pins, into rotary motion delivering

effective torque at the end of the crankshaft itself

To support the force system characterized by a

highly variable periodicity that generates a complex

stress pattern

To interface the bearing system: main and rod

journals.

To drive the auxiliary devices

To seal the block-crankcase at its ends

To supply engine speed and crank angle position

by proper sensors installed on the crankshaft

To connect the flywheel and the clutch




Engine balance - It is necessary to provide counterweights for the reciprocating

mass of each piston and connecting rod, which are typically cast or forged as part of the

crankshaft but, occasionally, are bolt-on pieces. While counter weights add a considerable

amount of weight to the crankshaft it provides a smoother running engine and allows

higher RPMs to be reached.

The number of crankshaft bearings is primarily determined by the overall load and

by the engine speed. High loads generally require to incorporate a main journal bearing

between each crankshaft throw and at each end

The fatigue strength of crankshafts - It is usually increased by using a radius at the

ends of each main and crankpin bearing. The radius itself reduces the stress in these

critical areas and frequently the radii are rolled to leave some compressive residual

stress in the surface which prevents cracks from forming.

Crankshaft vibration – Flexural vibration is not a critical factor for engine of 3

cylinders or more, while the rotational oscillation of the vibrating system formed by

crankshaft, connecting rods and pistons become increasingly critical with higher number

of cylinders. Vibration dampers are required to reduce the crankshaft torsional vibrations

to acceptable levels and it serves as a pulley for drive belts. The damper is composed of

two elements: a mass and an energy dissipating element: the mass resists the

acceleration of the vibration and the energy dissipating (rubber/clutch/fluid) element

absorbs the vibrations.



Overlap between main journal and crankpin

2cdD

cR=


The proportions of gasoline engine crankshafts are usually such

that the crankpin has a diameter of at least 0.60 of the cylinder

bore dimension and a length of not less than 0.30 of the pin

diameter. Web thickness of the crank-throw is generally in the

region of 0.20 of the cylinder bore dimension. The main bearing

journal is made larger than that of the crankpin with a diameter of

up to 0.75 of the cylinder bore dimension and a length of about

0.50 of the journal diameter.

Adequate crankshaft rigidity to resist both bending and twisting is

a major requirement for smooth operation. With current short-

stroke engines, the proportions of the crankshaft are generally

such that in themselves they contribute to greater rigidity. This

results from the combination of a smaller crank-throw radius and

larger bearing diameters, which permit a beneficial overlap

between the main journals and the crankpins




Since the crankshaft is subjected both to bending and to torsional load

reversals, it must also be designed to resist failure by fatigue. This

condition may be initiated at any point where there is a concentration of

stress or, in other words, a heavy loading confined to a very small area.

In practice, it may occur at any abrupt change of cross-section, or from

the sharp edge of an oil hole or a corner of a keyway. To avoid such

stress raisers and therefore extend the fatigue life of the crankshaft, the

areas in question are provided with carefully controlled small radii. For

example, the corners of each main bearing journal and crankpin may

be subject to what is termed ‘cold rolling’ to a specified fillet radius.

This confers a beneficial compressive stress on the crankshaft

material. The process of cold rolling basically involves rotating the

crankshaft against small hardened steel rollers, which are forced

against the corners of the crankshaft journals with a pressure

sufficient to cause local plastic deformation and therefore

compression of their surface layers. This widely used process

actually dates back to 1938, when J.O. Almen of General Motors in

America suggested its use to restore the durability of a Chevrolet truck

crankshaft following an increase in engine piston stroke

Crankshaft Radii “Cold Rolling”



The disturbing forces applied to the crankshaft are derived from the pulsating gas and inertia torques acting via each

piston, connecting rod and crankthrow combination. If the crankshaft were perfectly rigid, then the only effect of

these pulsating torques would be to cause some irregularity in its speed of rotation, which could be smoothed out by

the action of the flywheel. However the crankshaft cannot in reality be made perfectly rigid, with the result that

the torque pulses are capable of twisting it and therefore of exciting it into a state of torsional vibration.

This vibration is superimposed upon the continuous rotation of the shaft. If the frequency of the disturbing

vibrations should coincide with one of the natural frequencies of crankshaft vibration, then a condition

known as resonance will occur. A danger of resonant vibration is that the energy of the disturbing vibrations may

be greater than that lost by the twisting and untwisting of the crankshaft, so that the amplitude of torsional vibration

builds up to such a degree that the crankshaft can be over-stressed and eventually suffer a fatigue fracture. In

practice, of course, the design of the crankshaft system is contrived such that its natural frequency of vibration is

raised as high as possible: the natural frequency may be raised by making the shaft as short as possible,

increasing its diameter and using a lighter flywheel. A resonant or critical order vibration would therefore only be

expected to occur beyond the normal speed range of the engine, or in other words if the engine is over-revved.

However, it may still be necessary in the interests of both engine smoothness and satisfactory operation of the

timing drive to suppress the less critical orders of torsional vibration, which do occur within the normal speed range.

For this purpose the crankshaft can be fitted with some form of torsional vibration damper.

The most diffused is the rubber dumper in which two masses of different inertia, represented by the crankshaft and

in this case a single small flywheel, were separated by both frictional and elastic means through the medium of

rubber. In long-established practice the rubber damper essentially comprises three concentric parts, these being a

carrier cum hub assembly that is rigidly attached to the nose of the crankshaft, a ring-shaped flywheel or inertia ring

that may be grooved to accept a V-belt, and a layer of rubber which is either bonded to each of these components or

sandwiched between them under precompression, as in later designs.It will be appreciated that there is no other

connection between the carrier and the ring apart from that established by the intervening layer of rubber. The

advantages of the later non-bonded version are that it is less costly to manufacture and allows a wider choice of

rubber specification.

Crankshaft Torsional Damper



Internal Crankshaft Damper

Crankshaft Dampers



Flywheel with torsional vibration damper

Originally developed in the mid-1980s by Toyota for application to

a motor car turbocharged diesel engine, the flywheel with

torsional vibration damper or dual-mass flywheel (DMF) as it

is now often termed, has in more recent years become

increasingly adopted for Diesel engines where manufacturers

seek additional refinement for the transmission system. The

purpose of the dual-mass flywheel is to reduce the extent to

which periodic fluctuations in engine torque are passed on to the

transmission system, which otherwise create vibration, noise and

can lead to wear of components. Typically noticeable with a dual-

mass flywheel installation is therefore a reduction in

transmission gear noise at low engine speeds. In this context

there is a greater opportunity with a modern five-speed and

reverse, all-synchro-mesh, gearbox for light load rattles to occur

between the teeth of the more comprehensive train of constant-

mesh gears. As its name suggests, a dual-mass flywheel

basically comprises a two-piece flywheel with an engine-side

mass and a transmission-side mass. The latter is supported from

the former by an interposed ball-bearing race and its relative

oscillatory movements are cushioned by a series of

circumferentially spaced compression springs, which are retained

in windows shared by the two masses. Frictional resistance to

dampen the oscillatory movements between the two masses is

supplied in a similar manner to that for the centre-plate of a

friction clutch.



At TDC of combustion stroke

Pgas – Fm TDC in the crankshaft direction if Pgas > FmTDC

At TDC of gas exchange stroke

+ Fm TDC in the cylinder head direction

At BDC

- Fm BDC in the crankshaft direction

Crankshaft acting forces combination

Combustion gas forces (Pgas) and mass inertia forces (Fm)

For high combustion load it is convenient to design the crankshaft for the maximum

power operation, where the load oscillates between Pgas – FmTDC (combustion) and

FmTDC (gas exchange).

For high revs engines the engine over-speed operation (1000 revs higher than power

engine speed) might be the most severe condition, being the crankshaft load

oscillating between +FmTDC and -Fm BDC.



Monolithic crankshafts are most common, but some smaller and larger engines use

assembled crankshafts.

Crankshafts can be forged from a steel bar usually through roll forging or cast in ductile

steel. The actual manufacturer trend is favoring the use of forged crankshafts due to their lighter

weight, more compact dimensions and better inherent dampening. With forged crankshafts,

vanadium micro-alloyed steels are mostly used as these steels can be air cooled after reaching

high strengths without additional heat treatment, with exception to the surface hardening of the

bearing surfaces. The low alloy content also makes the material cheaper than high alloy steels.

Carbon steels are also used, but these require additional heat treatment to reach the desired

properties. Iron crankshafts are today mostly found in cheaper production engines where the

loads are lower. Some engines also use cast iron crankshafts for low output versions while

the more expensive high output version use forged steel.

Hardening - Most production crankshafts use induction hardened bearing surfaces since

that method gives good results with low costs. It also allows the crankshaft to be reground

without having to redo the hardening. But high performance crankshafts, billet crankshafts in

particular, tend to use nitridization instead. Nitridization is slower and thereby more costly, and

in addition it puts certain demands on the alloying metals in the steel, in order to be able to create

stable nitrides. The advantage with nitridization is that it can be done at low temperatures, it

produces a very hard surface and the process will leave some compressive residual stress in the

surface which is good for the fatigue properties of the crankshaft. The low temperature during

treatment is advantageous in that it doesn’t have any negative effects on the steel, such as

annealing and nitriding also leaves some compressive residual stresses in the surface.

The crankshaft - Construction



Breakage

starting

High- strength cast iron crankshaft

Flexional fatigue breakage of the first

crankpin (4 cyl Diesel engine) due to no

cold rolled radius



Superficie

di rottura

Perno

di biella

Maschetta

Perno

di biella

Macro ( X 10) picture of no cold rolled

radius: milling operation visible



Perno

di biella

Impronta

dovuta alla

rullatura

Maschetta

Macro ( X 10) picture of a cold rolled radius



Micro (X30) picture of a non cold rolled

crankshaft radius: no profile variation



Micro (X30) picture of a cold rolled

crankshaft radius: profile variation is visible



Basic functions

Transmission of the piston force and piston motion

to the crankshaft

A possible location for holes to supply the piston

with lubricating oil

Basic requirements

Sufficient mechanical strength

Sufficient bearing capacity

Mass as low as possible, because of the crankcase

stress generated by mass forces

Optimum length: short for a reduced engine height,

but not too short because of frictional work caused by

lateral forces and because the 2nd order unbalanced

forces of the 4 cylinder engines

The connecting rod



Design configuration

The small end (eye) of the connecting rod, into which the piston pin is inserted, is

connected to the big end via the connecting rod shank

The connecting rod big end is typically split to be assembled on a single-piece

cranckshaft

Connecting rod stress

The gas forces generate compressive stress on the connecting rod: the maximum

value occurs at ignition TDC

The mass forces generate a tensile stress which are maximum at gas exchange

TDC

This results in alternating stress between ignition TDC and gas exchange TDC:

the gas forces are important at low speed, the mass forces at high speed

The bending stress, caused by mass forces, is usually low and therefore is

neglected

The connecting rod eye and big end are stressed by tension forces and bending

moments

The bearing cap and relative bolts and threads are subjected at high stress,

because located in the power flow, and can be highly deformed weakening the

formation of a stable lubricating film

The connecting rod



Material and Construction

Connecting rod of today fast-running combustion engines are generally forged

in one piece. Once the bolt holes and threads are drilled, the connecting rod cap is

separated from the connecting rod big end

High-carbon steels (C35, C45) are used in standard applications; higher stress

applications require high-alloyed steel (Cr, Mo, Ni, V). For passenger car gasoline

engines malleable cast iron are sometime used while forged sintered connecting

rods are increasingly attractive because of lower weight vs forged

For both cast and forged steel as well sintered connecting rods, the bearing cap

can be separated from the big end through a cracking method, reducing the

manufacturing cost and improving the connection precision

The shaft is most often designed with I-cross section for higher stiffness in the

oscillating direction. To avoid the stress peaks, the transition from the shank to the

con-rod eye and con-rod big end must have large radii

A connecting rod divided at an angle can be necessary to enable disassembly

through the top of the cylinder.

The connecting rod



14.8

1.8

Steel con-rod for Diesel engines

Small

(eye)end

Big end

Shank

The connecting rod



Connecting rod drawing

The connecting rod



The connecting rod

In some designs the big-end bearing parting line is arranged diagonally (45° in the

Figure), because otherwise the width of the housing would be such that the

connecting rod could not be passed through the cylinder for assembly purposes.



The connecting rod

To resist the greater tendency for the cap to be displaced sideways relative to the rod, either a serrated or a stepped

joint is generally preferred for their mating faces. Hence, the securing setscrews in their clearance holes are relieved

of all shear loads. Where the parting line between the rod and cap is arranged at right angles to the axis of the shank,

the cap may be secured by either bolts and nuts, studs and nuts, or setscrews. They are produced from high-tensile

alloy steel with special care being taken in their detail design to avoid stress-raising corners, which would lower their

fatigue resistance. Their clamping load must always be such as to exceed the inertia forces acting on the rod.



Connecting rod guided by the piston (a) and by the crankshaft (b)

a b



The connecting rod



Main piston functions

Transmission of gas force generated by the combustion to the connecting

rod

Kinematic guidance, supporting the normal force applied to the cylinder walls

Together with the piston rings, sealing of the crankcase against combustion

gas and of the combustion chamber against oil

Support of sealing rings (piston rings)

Limit and design of the combustion chamber

Main piston stress due to

Gas and mass forces

Heat flow of the combustion chamber

Frictional forces at the shaft and in the ring grooves

Movements perpendicular to the running direction (“tilt”)

Main design target

Sufficient strength with as little mass as possible

Permissible temperatures through design (heat flow), material and cooling

Correct running clearance for all load levels

Quiet operation with limited tilt

The Piston



Gasoline engine

piston

Diesel engine

piston

Piston rings Piston pins

The Piston



Gasoline and Diesel pistons

The Piston



Piston Rings functions

Sealing the combustion chamber to

the crankcase (compression rings)

Sealing the crankcase to the

combustion chamber (oil control rings)

Regulating the lubricating oil at the

cylinder wall

Heat conduction from the piston to

the cylinder wall

Piston rings must have a split at one

point (ring gap)

The gap clearance of the installed

ring must be small to reduce the

leakage but may never be zero to avoid

seizing

The Piston



Gasoline Pistons

Weights:

Piston 170 g

Piston Pin 60 g

Ring Set 18 g

Circlips 2 g

Assy Weight: 250 g

typical small gasoline engine

The Piston



Material and Construction

The ideal piston material should combine the following characteristics: high thermal

stability (hardness and elasticity), high thermal conductivity, low thermal expansion,

low modulus of elasticity, good running properties /wear and friction) and low density

(low weight)

Most of these requirements are well met by aluminum alloys containing silicon

between 11 and 26%; the only disadvantage is a high coefficient of linear expansion.

The raw mold of the light alloy piston are cast or pressed (forged).

For economical reason the raw piston for combustion engines are mainly produced

via die-casting, while forged piston, more solid and stronger than cast pistons, are

used for high performance applications where mechanical and thermal stress are

much higher

Heat treatment is necessary after casting process to optimize the required physical

properties

Aluminum piston are coated mainly by Fe when combined with aluminum cylinders

Grey cast iron pistons are used for very low speed engines or when thermal stress

are at very high level

The Piston



High Power achieved by high pmi leads

to increased gas force and thermal load

Problem

• fatigue (piston crown, ring groove, pin

boss, skirt)

Solution

• cooling gallery

piston

Advantage

• Temperature reduction in critical areas (-

20°C)

• Permissible loading increased (8%)

• reduced knock sensibility (SPA + 3°)

--> increased power output

• additional reinforcement features

avoidable

Gasoline Pistons for High Power Output Engines

High Power achieved by high engine

speed leads to increased inertia force

Problem

• fatigue (pin boss, skirt fatigue)

Solution

• forged piston

(optimised

material

properties)

Disadvantage

• additional groove reinforcement

required

The Piston



180bar,

58kW/l

160bar, 50kW/l

180bar, 60kW/l

160bar, 50kW/l

200bar, 60kW/l

180bar, 58kW/l

Various Gallery KS Pistons with Basic Engine Data

Combustion peak pressure, specific power output



The Piston



Piston temperature profile

The Piston



The Piston



Mean stress in MPa

High speed DI-piston for Engine 2,0l

85mm dia., version with cooling gallery

Temperature distribution in °C



The Piston



Safety factors, HCF; 9*10*7 cycles



Stress amplitude in MPa



The Piston



Diesel piston failure after 1000hr

durabilty bench testing

The Piston



The Piston

Diesel piston failure after 1000hr

durabilty bench testing



Diesel engine pistons - 1000 hr test bench durability

The Piston



The function of the valve train in a 4-stroke engine is to allow and to control the

exchange of the gases in the internal combustion engine

The valve train includes the intake and exhaust valves, the springs which close them,

the camshaft drive assembly and the various force-transfer devices

The specific tasks of the valve train are to open and close the intake/exhaust valves in

time and to enable a sufficiently large flow cross section

The high acceleration and deceleration required of the valve train parts causes stress

due to mass forces rising with increasing speed

The exhaust valves are subjected to a high thermal stress, due to heat flow from the

combustion chamber and the exhaust gases

vavavahdA =

4

dA va

va

=

Partial lift

Full lift

Flow cross section

The valve train



Valve size

The valve diameter is defined as a compromise among various factors as optimization

of the combustion chamber, flow cross section and thickness of the “bridge” between the

valves or the valves and the spark plug/injector exposed at high thermal stress

according to the experience, for 2 valve gasoline engines:

and for 4 valve gasoline engines:

and for 4 valve DI Diesel engine, where the cylinder head is flat because combustion

chamber is designed inside the piston

The diameter of exhaust valve is generally smaller of about 10% to guarantee a

reasonable valve bridge and for a better cooling

D48.045.0dva

=

D34.032.0dva

=

D33.030.0dva

=

The valve train



4-stroke work cycle

Valve opening and closing timing in respect to TDC / BDC

The valve train



-20

-15

-10

-5

0

5

10

15

20

-80 -60 -40 -20 0 20 40 60 80

Cam Angle[deg]

Lif

t [m

m];

Ve

loc

ity

[m

m / r

ad

]

-100

-80

-60

-40

-20

0

20

40

60

80

100

Ac

ce

lera

tio

n [

mm

/ra

d²]

, J

erk

[m

m/r

ad

³]

Lift Velocity Acceleration

lift

acceleration

velocity

TDC

BDCExhaust valve opening

Intake valve

opening

Overlap

BDCBDC TDC

Exhaust valve Intake valve

overlap

Exhaust valve closing

Intake valve closing

Valve timing diagram showing

valve lift, valve velocity and

valve acceleration



Crankshaft driven camshaft (crank

case location) with push rod operation



Double (twin) overhead

camshaft with direct

tappet actuation

Overhead camshaft with

rocker arm actuation



4 cyl engine V6 engine

2 camshafts

for cylinder head

1 camshaft

for cylinder head



Direct acting camshaft with mechanical valve adjustment



Direct acting camshaft with hydraulic valve adjustment



Cross section of a direct acting camshaft



Rocker arm with insert valve lash adjustment element



Hydraulic Rocker Arm Components

Rocker arm

Hydraulic lash

adjuster

Support plate

Side washers (2x)

Set of needles

Outer ring

ShaftAssembly



Finger follower with roller and pivot element



Roller Finger Follower Valve Trains

Roller finger follower parts

Sheet Metal Body

16MnCr5

Outer Ring

100Cr6

Needles

100Cr6

Axle

100Cr6

Sheet Metal Thickness:

2,5 mm ... 3,5 mm



Roller Finger Follower Valve Trains

HLA composition

high pressure

chamber

reservoir chamber

socket plunger

housing

lower plunger



Variable valve trainsIn the last decades a certain number of unconventional valve trains have been developed to

vary valve timing and lift during operation with the target of controlling the gas exchange

cycle by optimizing the valve activation

Phasing – By camshaft phasing the variation of the intake timing influences on the

cylinder charge and allow a reasonable control of residual gas content, depending on

engine load and speed. The prerequisites for the system are that the engine must have one

intake and one exhaust camshaft and one cannot be driven by the other one. The first

application has been done by Alfa Romeo on the 4 cyl engine for USA spider of 1980 MY.

Transition between cam profiles – The variation of the valve lift is realized by a

transition between two different cams. Today different solution are on the market but the

first one has been the Honda VTEC system, where the second cam is designed to enhance

performance at high engine speed. In more recent application the second cam is designed

to actuate a low lift in order to reduce pumping loss at low load operation

Cylinder deactivation – With multi-cylinder engines fuel consumption can be reduced

under part-load operation through cylinder deactivation. The improvement is achieved

because the pumping losses of the deactivated cylinder s are eliminated and the activated

cylinders are de-throttled. Again technical solutions vary among the Car Makers and some

are substantially the previous one tuned for this target; the first application has been a 4cyl

Mitsubishi engine in middle ‘90 years, but Alfa Romeo in the early ’80s built up a taxi fleet

deactivating partially the cylinders by ignition interruption.



The first cam phase variator

helical/cilindrical toothing

(Alfa Romeo)



Variable cam phaser (Cam phase variator)

Content

• VCT-Concepts

• System function

• Components

• Development tools

• Applications

• Development trend

• Future systems

• Market position



Potential of VCT Concepts

typical benefits for FE & Emissions (related

to FTP 75 cycle)

DIPS

IPS EPS

DEPS

torque /

power

emissions internal EGR

catalyst heating

Fuel

economy

comfort idle

stability

FE ~ - 3%

NOx ~ - 50%

HC ~ - 10%

torque/power + 5%

FE ~ - 5 %

NOx ~ - 70 %

HC ~ - 15 %

torque/power + 10%

FE ~ - 3 %

NOx ~ - 70 %

HC ~ - 15 %

torque/power -

FE ~ - 4-6 %

NOx ~ - 50 %

HC -

torque/power -

( LIVC )



Hydraulic / electronic scheme

cam phasercam positon sensor

triggerwheel

Oil control valve

crank sensor

triggerwheel

connected to oil pump

connected to sump

Engine management system



Cam phase variator-Function (base position)

pump

tanksump

locking pin engaged

example for intake VCT

fully retarded cam position

oil control valve swiched

off



Cam phase variator-Function (shifting)

pump

sump

oil control valve fully

energized

VCT position change

commences

locking pin unlocks

example for intake

VCT



Cam phase variator-Function (controlled position)

pump

sump

oil control valve energized

to mid position (PWM

control)

VCT control position is

frozen

example for intake

VCT

locking pin remains

disengaged



Switchable Tappet Valve Train

Valve/Cylinder De-Activation / Cam Profile Switching

for SOHC and DOHC engines

Outer-Housing

Inner-Housing

Anti Rotation Device

Locking Spring

HLA

Inner Piston

Locking Piston

Lost-Motion-Spring

Electro-hydraulic

solenoid 2/3-Way



Switchable Tappet Valve Train

Valve/Cylinder De-Activation / Cam Profile Switching

for SOHC and DOHC engines



Combined CPV and switchable tappet



Variable valve trains - Flexible valve actuationA flexible valve control allows the possibility to adjust the free flow cross-section to the

engine speed and, overall, provides throttle-free control of load in gasoline engines.

Mechanical valve operation – The first application has been introduced by BMW (see

fig.) with a fully variable control which allows continuous variation of the intake valve lift. An

intermediate element, which is controlled by the eccentric shaft, is inserted between the

camshaft and the finger follower. Moving the intermediate element causes a variation of

valve lift and therefore also the effective opening time. The valve lift and the opening time

determine the quantity of the charge and therefore the engine load level: the timing of the

valve opening is controlled by cam phase variators on intake and exhaust camshafts. This

fully variable mechanical valve control makes load control possible without the throttle use

Hydraulic valve operation – This systems require a dedicated oil circuit and pump to

generate the pressure necessary to actuate the valves with some device: variation of the oil

pressure allows the control of valve lift, being the pressure controlled by electromagnetic

valves. The high complexity, the cost and the losses encored during the pressure

generation limit the use of hydraulic valve control to special applications.

Electromechanical valve operation – Opening the valves against the valve springs

force by using electromagnets requires an excessive amount of current, because the

magnetic field becomes weaker very rapidly with increasing distance. Notwithstanding a lot

of research and experimental activity, this system has not been qualified for vehicle

applications.



BMW Valvetronic – Mechanical variable valve lift



Valvetronic system cylinder head



Variable valve trains - Flexible valve actuation

Fiat Multiair system – It is the last system

introduced on Fire 1.4l engine in 2009. It can be

considered as mechanic-hydraulic valve operation,

using electro-hydraulic elements to manage a

continuously variable intake valve lift. The control piston

and the inlet valve are connected each other through an

oil pressure chamber, the pressure in which is

controlled by a solenoid valve. When the valve is in a

closed position, the inlet valve follows the cam profile.

An early close of the inlet valve can be achieved by

opening the solenoid valve after a particular degree

cam angle. The oil flows out of the high pressure

chamber into the reservoir. The valve is now decoupled

from the cam’s motion and hence is closed by the

return forces of the valve spring. The valve seating

velocities are held within safe limits by a hydraulic

damper. By means of a spring in the reservoir, the oil

flows back into the high pressure chamber after the

completion of the cam stroke. The Multiair system

allows a throttle-free load control and also the

optimization of cylinder filling at full load.

PistonIntake

Valve

Accumulator

Solenoid ValveHigh Pressure

Oil Chamber

Cam

Piston

Hydraulic

Brake &

Lash Adjiuster

Intake

Valve



Crank Angle

0

1

2

3

4

5

6

7

8

9

10

320 360 400 440 480 520 560 600 640 680 720

LIVO

EIVC

Engine Valve Lift

TDC BDC

INTAKE VALVE ACTUATION MODES

F1 F2

SOLENOID VALVESACTIVATION

F1 F2 F1 F2 F1 F2F1F2

INTAKE VALVE LIFT

“FULL LIFT” “EIVC”Early Valve Closing

“LIVO”Late Valve Opening

“MULTI-LIFT”“FULL LIFT” “EIVC”

Early Valve Closing

“LIVO”

Late Valve Opening

“MULTI-LIFT”



High PressureChamber

High ResponseSolenoid Valve

(ON-OFF)

Individual Valve Actuation Assembly

(Piston + Brake + Lash Adjuster)

Pump Piston

Oil Reservoir

Camshaft(Intake + Exhaust)

Low Friction Tappet (RFF)



Fiat 1.4 Multiair - Electric / hydraulic variable valve lift system

4-engine components and systems

Documents