case study of toyota

8/8/2019 Case Study of Toyota

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2. DIFFERENT TYPES OF HYBRID SYSTEM

2.1. SERIES SYSTEM:

The system supplements electricity generated by the engine (Fig.1.1). It is most

commonly used as a range extenderfor electric vehicles. Since the engine is not

mechanically connected to the drive wheels, this system has an advantage of controlling

the engine independently of the driving conditions. Accordingly the engine is used in its

optimum efficiency and low emission range. This system is particularly suited to engines,

which are hard to mechanically connect to the wheels such as gas turbine engines.

However, include large energy conversion losses because of the necessity of full

electricity conversion of the engine output. Further, a generator large enough to convert

the maximum engine output is required.

2.2. PARALLEL SYSTEM:

With the parallel system, an electric motor that supplements the engine torque is

added to the conventional driveline system of the engine and transmission (Fig.1.2).

Accordingly, operations of the engine are quit similar to those of an engine in normal

vehicle. This system requires no generator, and there is a mechanical connection between

the engine and the drive wheels, providing an advantage of less energy being lost through

conversion to electricity.

On the other hand, this system requires a transmission because no speed

adjustment mechanism is installed, though the motor supplements the torque. When an

automatic transmission is used, a torque converter, oil pump, and other auxiliary

components can reduce the transmission efficiency. Although the engine torque can be

controlled by the motor, the engine speed is determined by gear ratios like a conventional

vehicle. Accordingly the engine operation is linked to the driving conditions.

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2.3. SERIES-PARALLEL COMBINED SYSTEM:

This combined type, having a generator and a motor, features characteristics of

both the series and parallel system, and the following two systems are possible

2.3.1. SWITCHING SYSTEM:

Engagement & disengagement the clutch switches between the series or parallel

systems (Fig.1.3). For driving as by the series system, the clutch is released, separating

the engine and the generator from the driving wheels. For driving with the parallel

system, the clutch is engaged, connecting the engine with the driving wheels.

For example, the city driving requires low loads for driving and low emissions;

the series system is selected with the clutch released. For high speed driving where the

series system would not work efficiently due to higher drive loads and consequently

higher engine output is required, the parallel system is selected with the clutch applied.

2.3.2. SPLIT SYSTEM:

This system acts as the series and parallel systems at all times (Fig.1.4). The engine

output energy is split by the planetary gear into the series path (from the engine to the

generator) and the parallel path (from the engine to the driving wheels). It can control the

engine speed under variable control of the series path by the generator while maintaining

the mechanical connection of the engine and the driving wheels through the parallel path.

2.4 DUEL SYSTEM ADVANTAGES :

Free control of engine while keeping a mechanical connection between the engine

and drive wheels.

Compact design of transaxle integrating two motors requires little modification

for current production vehicle.

Use of generator as motor and its combination with traction motor permits the

engine and driveline to flexibility adapt to driving condition.

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Fig.2.1 Series System

Fig. 2.2 Parallel System

Fig. 2.3 Switching System

Fig. 2.4 Split System

( ___ ) Mechanical Connection, EG: Engine,

(- - - -) Electrical connection, C: Clutch,

G: Generator, PG: Planetary gear,

TM: Transmission, M: Motor, B: Battery.

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3. COMBINATIONS OF MAIN AND AUXILIARY HYBRID DRIVE

TECHNOLOGIES

Fig.3 shows that there are many possible combinations of main and auxiliarydrive, some being more practical than others. The more probable combinations are

marked A with the possible but unlikely ones marked B. If we consider only the probable

combinations it can be seen that there are 11 of these. The number of options is further

increased since those having a heat engine as the main drive can be operated in either the

series or parallel configuration. This adds three further options and makes a total of 14.

Two combinations are discussed here. First with flywheel and then hydraulic accumulator

(Fig.3.1 &Fig. 3.2)

Both flywheel and hydraulic accumulator are capable of supplying, or absorbing

during regeneration, more than 500 W/kg during acceleration or braking and typically of

storing up to 0.5 kWh of energy. Turnaround energy efficiency of these mechanically

storage devices is high about 98% compared to 75-80% for batteries, and as a result the

energy recovered during braking can be as high as 15% of the total energy used.

However problem exists of providing protection from disintegration of the flywheel in an

accident, and this together with the possible requirement for two contra-rotating

flywheels to overcome gyroscopic effects makes the flywheel a potentially expensive

solution. It is perhaps more suited to high rotational speed operation.

The hydraulic accumulator requires a pressure vessel in which a highly

deformable membrane separates high-pressure oil pumped into it by the pump/ hydraulic

motor from a compressible gas. This also requires protection to avoid any risk of failure

in crash conditions. It is, however, potentially a cheaper solution for auxiliary energy

storage in a hybrid of this type than the flywheel and has no vehicle stability problems.

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Fig.3 Combinations of main and auxiliary hybrid drive technologies.

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Fig.3.1 Regeneration and energy storage using a flywheel

Fig. 3.2 Regeneration and energy storage using a hydraulic accumulator

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4. THE TOYOTA PRIUS HYBRID CAR

The five-seater Toyota Prius hybrid operates with more equal sharing of the

power between the gasoline heat engine and the electric motor (Fig.4a & 4b). The battery

in the Prius is charged by regenerative braking, and when necessarily, directly from

gasoline engine power. An interesting thing of this car is that under light load conditions

such as initial acceleration, the Prius is operated solely on electric power from the

temporary battery storage. Depending on how fast you're accelerating and the battery's

state of charge, the Prius's gasoline engine will start when speed reaches between about

21 and 40 kmph. By waiting until this point to start the gasoline engine, this means that

the Prius doesn't operate the gasoline engine under very light power demands, when the

gasoline engine is less efficient. (At zero power demand, such as descending a hill,

braking or sitting at a stop, car can entirely stop operation of the gasoline engine.)

The Prius uses two motor/generators, which split the jobs done by one

motor/generator. The motor/generator "M" is connected to the wheels (via differential

and reduction gear), and is used for:

Providing propulsion to the wheels.

Charging the battery from the wheels during regenerative braking.

The Prius uses a planetary gear as a power-split device that provides a three-wayconnection between the wheels (and motor/generator "M"), the gasoline engine, and

generator/motor "G". Together, this system also forms the Prius's continuously variable

automatic transmission. The generator/motor "G" is used for:

Charging the battery from the gasoline engine.

Starting/stopping the gasoline engine.

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Fig. 4a Power train layout of the Toyota Prius

Fig.4b General layout of the system

4.1 MAIN COMPONENTS OF TOYOTA PRIUS:

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Atkinson cycle engine :

The Priuss 1.5 liter Atkinson cycle engine (Fig.4.1.1) provides an increased

expansion ratio for more efficient energy extraction. Variable intake valve timing reduces

cylinder pressure, to eliminate knocking. Engine speed is limited to 4,500 rpm, allowing

engineers to use smaller, lighter components for improved overall fuel economy.

Nickel-metal hybrid battery :

The sealed nickel-metal hydride (Ni-MH) battery pack (Fig.4.1.2), mounted

behind the rear seats, and provides a total voltage rating of 273.6V. Its temperature is

maintained by a cooling fan that draws air in from vents mounted over the rear parcel

shelf.

Inverter :

The inverter (Fig.4.1.3) converts the battery's DC current to AC for the electric

motor/generators, and vice versa. An intelligent power module provides precise current

and voltage control. A built-in transformer converts some of the hybrid battery's power

into 12V power for vehicle accessory operation.

Hybrid Transaxle (Power split device) :

In the Prius, a "planetary gear" is used as a power split device (Fig.4.1.4),

providing a three-way connection between the wheels (and by extension motor/generator

"M"), the gasoline engine, and generator/motor "G". The easiest way of thinking of the

planetary gear is that the rotation of the wheels is always equal to the sum of the gasoline

engine rotation and the rotation of generator/motor "G".

This means that the gasoline engine may be stationary, with any rotation of the

wheels being directed towards rotation of generator/motor "G". It also means that if the

gasoline engine is turning at a fixed speed, the faster the car is moving, the slower

generator/motor "G" will turn.

In a typical driving situation, the output from the Prius's gasoline engine is split

between the wheels and generator/motor "G". If the batteries are sufficiently charged, all

energy coming from generator/motor "G" will also be routed to the wheels, by using it to

power motor/generator "M". This means that power is taking two separate paths from the

gasoline engine to the wheels, one entirely mechanical, and the other partially electrical.

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Fig.4.1.1 Atkinson cycle engine Fig.4.1.2 Nickel-metal hybrid battery

Fig.4.1.3 Inverter

Fig.4.1.4 Hybrid Transaxle (Power split device)

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Fig. 4.2.1:Energy flow when starting up Fig. 4.2.2:Energy flow when

accelerating

Fig. 4.2.3:Energy flow when cruising Fig. 4.2.4: Energy flow when

regenerative braking

4.3 ENGINE PERFORMANCE :

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Fig.4.3 shows the modeled equivalent fuel economy for the Prius under the

various test cycle. It shows that the Prius achieves the best fuel economy (63 MPG) under

the Japanese 10/15 cycle. Its worst economy is about 35 MPG under the NYCC. Since

the Prius has an electrical CVT and Atkinson cycle engine, its engine peak efficiency,

transmission efficiency, and overall vehicle efficiency are all significantly higher than

that of CVs.

4.3.1 PERFORMANCE FEATURES THAT TOYATA HYBRID SYSTEM GIVES

TO PRIUS:

Double the fuel economy and half the CO2 emissions of a gasoline engine.

CO, HC, and NOx reduced well below Euro4 and California SULEV levels.

Seamless integration of power sources for smooth, powerful acceleration and

response.

Convenience equal or better than that of a CV. Just top it up with gas-no need

to worry about charging the batteries.

Reduced CO2 emissions -The engine shuts off automatically when the car

comes to stop (Fig4.3.1).

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Fig. 4.3 Fuel economy for Toyota Prius under Driving Cycles

Fuel consumption

(L/100 km, EC mode)

CO2

gm/km

Corolla (1.6L) 8 210

1997 Prius 6 140

2000 Prius 5 120

Fig. 4.3.1 CO2 Emissions

Fig.4.4 Cut-way model of engine

4.4 THE TOYOTA HYBRID SYSTEM (THS) ENGINE SPECIFICATIONS:

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Key Data

Project type Special Purpose Vehicle

Engine Size 1.5 litre 16 Valve 4 cylinder

Fuel Consumption 29 km/litre

Transmission ECVT

Power 70bhp at 4500 rpm

Torque 112 N-m at 4200rpm

Bore/Stroke 75.0/84.7 (mm)

Suspension - Front/Rear Independent MacPherson strut with stabilizer bar/ Torsionbeam with stabiliser bar

Steering Rack and Pinion with electro-hydraulic power-assist

Brakes Power-assisted ventilated front discs and rear drums with

ABSLaunch Date 2001

Key Players

Sponsor Toyota

Contractors MacPherson

Key Specifications

Length 4308(mm)

Width 1695(mm)

Height 1463(mm)

Wheelbase 2550(mm)Weight 1255(kgs)

Capacity 44.6 (lit.)

Tires P175/65R14

Electric Motor/Generator/Power Storage:

Motor type: Permanent magnet

Power output: 33 kW/44 hp @ 1,040 - 5,600 rpm

Torque: 350 N-m @ 400 rpm

Battery type: Sealed Nickel-Metal Hydride (Ni-MH)

Output: 273.6 V (228 Nos1.2-V cells)

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5. ADVANTAGES & DISADVANTAGES OF HYBRID VEHICLE

TECHNOLOGY

5.1 ADVANTAGES:

5.1.1REGENERATIVE BRAKING:

It is particularly valuable in the city where one continually slowing down and

speeding up again. Normally, each time you slow down by applying brakes, a lot of

energy is lost. Regenerative braking takes advantage of the fact that an electric motor can

also operate as generator. During regenerative braking, the electric motor operates as a

generator, slowing the vehicle down and turning some of the energy of forward motion

back into electricity that recharges the batteries. This energy that would otherwise be

wasted can now later be used to help propel the car.

5.1.2FUEL ECONOMY:

Improved fuel economy due to following:

Operation of the engine in optimum efficiency range.

Transmission efficiency between the engine and the driving wheels is improved.

Regeneration of deceleration power.

5.1.3 SMALLER ENGINE SIZE:

Smaller engines are more advantageous than bigger engine for the following

reasons:

The big engine is heavier than the small engine so the car uses extra energy every

time it accelerates or drives up the wheel.

The piston and other interior components are heavier, requiring more energy each

time they go up and down in the cylinder.

Bigger engines usually have more cylinders and each cylinder uses fuel every

time the engine fires, even if the car isnt moving.

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5.2 DISADVANTAGES:

The major inhibiting factor in making hybrid vehicles acceptable to the consumer

remains the high cost of a car with two separate propulsion systems. It is difficult to see

how this can be overcome in view of the actual production costs.

6 FUTURE DEVELOPMENT OF HYBRID VEHICLE

TECHNOLOGY

Hybrid electric technology is a leading technology for increasing vehicle fuel

economy, reducing greenhouse gas emission, and reducing criteria pollutant emissions

when equipped to have battery-only range. The mean values of responses by industry

experts to a 1998 survey appear to provide a realistic and technically consistent view of

the future HEVs. Forecast statistics were prepared based on Delphi Study.

The fuel cell is projected to be the most likely power plant for HEVs in 2020;

instead of hydrogen, however, such liquid fuels as gasoline and methanol will likely be

used. Projected HEV fuel economy ranges from 1.7 to 2.6 times the conventional vehicle

fuel economy. Thus, even with the fuel cell as its power plant, the HEV is not likely to

have a fuel economy three times that of conventional vehicle (a PNGV goal). The futures

HEVs are projected to emit significantly less NOx and particulate matter than CVs. Thestudy shows that the cost of a HEV will drop from 66% to 33% more than a $20,000 CV

by 2020. The typical respondent, however, characterized by the median and modal

statistics, expected the cost penalty to drop to 15% (median) or zero (mode) by 2020.

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7. CONCLUSION

From present study it can be concluded safely that Hybrid Electric Vehicle

(HEV) provides better fuel economy and offers advantages of smaller engine size along

with regeneration of deceleration power and less pollution. So fulfilling all the

requirements of a modern car this technology will surely prove itself as a platform for

development of Next-Gen cars.

Only limiting factor is the high cost in making hybrid vehicles acceptable.

However efforts are now being concentrated to reduce the cost.

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case study of toyota

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