chap64 pps Automotive technology at University of Cambridge

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Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
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OBJECTIVES:
After studying Chapter 64, the reader should
be able to:

•
•
•

Describe the different types of hybrid electric
vehicles.
Explain how a hybrid vehicle is able to

achieve an improvement in fuel economy
compared to a conventional vehicle design.
Discuss the advantages and disadvantages of
the various hybrid designs.

Continued
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
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OBJECTIVES:
After studying Chapter 64, the reader should
be able to:

•

•

Describe HEV components, including motors,
energy sources, and motor controllers.
Discuss the operation of a typical hybrid
electric vehicle.

Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
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KEY TERMS:
assist hybrid • BAS • BEV • EV
full-hybrid • HEV • HOV lane • hybrid • ICE • idle stop
mode

medium-hybrid • micro-hybrid-drive • mild-hybrid •
motoring mode
parallel-hybrid • power assist mode
series-hybrid • series-parallel-hybrid • strong hybrid
ZEV
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
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HYBRID VEHICLE
A hybrid vehicle, abbreviated HEV, is one that uses uses both an 
internal combustion engine (ICE) and an electric motor to propel 
the vehicle.
Most hybrids use a high­voltage battery pack and a combination 
electric motor and generator to help or assist a gasoline engine. 

The ICE used in a hybrid vehicle can be either gasoline or diesel, 
although only gasoline­powered engines are currently used in hybrid 
vehicles.
An electric motor is used to help propel the vehicle, and in some 
designs, capable of propelling the vehicle alone without having to 
start the internal combustion engine.
Continued
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Background   In the early years of vehicle development, various 
propulsion systems were used, including steam­, gasoline­, and 
electric­motor­powered.
Early electric vehicles (EVs), also called battery electric vehicles 

(BEV) used lead­acid batteries, an electric traction motor, and a 
mechanical controller.
A traction motor is an electric motor used to rotate drive wheels and 
propel the vehicle, which moves as a result of traction between the 
wheel and the road surface.
The controller allowed different voltages to be applied to the 
electric motor, depending on the needs of the driver. 
Continued
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Assume that an early electric vehicle used six 6­volt batteries. If the 
batteries are connected in series, the negative terminal of one battery 
is connected to the positive terminal of the second battery.

Two 6­volt batteries in series result in 12 volts, but the same current 
as one of the batteries. Two 6­volt 500­amp/hour batteries in series, 
then, would output 12 volts and 500­amp/hours. 
Batteries connected in parallel increase the current, but the voltage 
remains the same. Two 6­volt 500­amp/hour batteries in parallel, 
would be six volts and 1,000 amp/hours.
Old electric vehicle mechanical controllers were able to switch all 
six batteries in combinations of series and parallel configurations
to achieve lower voltage for slow speeds and higher voltages for 
higher speeds. 

Continued

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Electric vehicles did not have a long range and needed to have the 
batteries charged regularly.
Electric vehicles were almost more popular than steam power in 
1900, when steam had 40% and electric had 38% of the sales. 
Gasoline­powered cars represented only 22% of the vehicles sold.
NOTE: Due to the oil embargo of 1973 and increased demand for 

alternative energy sources, Congress enacted Public Law 94­413, the 
Electric and Hybrid Vehicle Research, Development, and Demonstration 
Act of 1976, which was designed to promote new technologies.

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In the late 1990s, several manufacturers produced electric vehicles, 
using electronic controllers to meet the demands for zero emission 
vehicles specified California law.
Electric vehicles were produced by Ford, Toyota, Nissan, and 
General Motors.
Legislation was passed in California that included the zero 
emissions vehicle (ZEV) mandate.
As a direct result of the California zero emissions vehicle (ZEV) 
mandate originally calling for 10% ZEV, GM developed the 
Electric Vehicle 1, known as EV1, leased to customers in California 
and Arizona. 

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Figures 64–1 and 64-2 Views of the components of the General Motors electric vehicle (EV-1).
Many of the features of this vehicle, such as regenerative braking and DC-to-DC converters
currently used on hybrid vehicles, were first put into production on this vehicle.
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DRIVING AND OWNING A HYBRID VEHICLE
Driving a hybrid electric vehicle is the same as driving any other 
conventional vehicle. In fact, many drivers and passengers are 
often not aware they are driving or riding in a hybrid electric 
vehicle.

Some unique characteristics that the driver may or may not notice: 
After the internal combustion engine achieves normal operating 
temperature and other conditions are met, the engine will stop 
when the vehicle slows down and stops. This may concern some 
drivers, who, thinking the engine has stalled, try to restart it.

Continued
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The brake pedal may feel different, especially at slow speeds, when 
slowing to a stop. At low speeds the brake system switches from 
regenerative braking to applying brake force to the mechanical 
brakes. A slight surge or pulsation may be felt.

The power steering works even when the engine stops because all 
hybrid electric vehicles use an electric power steering system.
Some hybrid electric vehicles are able to propel the vehicle using 
the electric motor alone, resulting in quiet, almost eerie operation.

Continued
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If a hybrid electric vehicle is being driven aggressively and at a 
high rate of acceleration, there is often a feeling that the vehicle is 
not going to slow down when the accelerator pedal is first 
released. This is caused by two factors:

• The inertia of the rotor of the electric motor attached to the 
crankshaft of the ICE results in the engine continuing to
rotate after the throttle has been closed.

• The slight delay that occurs when the system switches the 
electric motor from powering the vehicle to generating 
(regenerative braking).

While this delay would rarely be experienced, and is not 
dangerous, for a fraction of a second it gives a feeling the 
accelerator pedal did not react to a closed throttle.

Continued

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Fuel economy will be higher compared to a similar­type vehicle.
In city­type driving conditions, engine stop and regenerative 
braking really add to the efficiency of a hybrid electric vehicle.
Range of the hybrid version may be about the same as the 
conventional version of the same vehicle because the hybrid 
version usually has a smaller fuel tank capacity.

Continued
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The hybrid version will cost and weigh more than the 
conventional version.
The increased cost is due to batteries, electric motor(s), and 
controllers used plus additional components needed to allow 
operation of heating and air conditioning systems during idle
stop periods.
While the cost is offset in part by returning improved fuel, it
may take many years of operation before the extra cost is
offset by cost savings from the improved fuel economy. 
Many owners purchase a hybrid electric vehicle for other reasons, 
including a feeling that they are helping the
environment and love of the high technology involved.
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How Fast Does the Motor Generator Turn When
Starting the Engine?
The typical starter motor used on a conventional gasoline or diesel engine
rotates the engine 100 to 300 revolutions per minute (RPM). Because the
typical engine idles at about 600 to 700 RPM, the starter motor is rotating
the engine at a speed slower than it operates. This makes it very
noticeable when starting because the sound is different when cranking
compared to when the engine actually starts and runs.
When the motor-generator of a hybrid-electric vehicle rotates the engine to
start it, the engine is rotated about 1000 RPMs, which is about the same
speed as when it is running.
As a result, engine cranking is just barely heard or felt. The engine is either
running or not running, which is a truly unique sensation to those not
familiar with the operation of hybrid electric vehicles (HEVs).
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CLASSIFICATIONS OF HYBRID-ELECTRIC
VEHICLES
Types of hybrid­electric vehicles include series, parallel, and 
series­parallel designs.
In a series­hybrid design, the 
engine turns a generator, which 
can charge batteries or power
an electric motor that drives the 
transmission.
The internal combustion engine
never powers the vehicle 
directly.
Figure 64–3 A drawing of the power flow in a
typical series-hybrid vehicle.
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
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In a series­hybrid design, sole propulsion is by a battery­powered electric motor.  
Energy for the batteries comes from another on­board energy source, such as an 
internal combustion engine.

Figure 64–4 This diagram shows the components included in a typical series-hybrid design.
The solid-line arrow indicates the transmission of torque to the drive wheels. The dotted-line
arrows indicate the transmission of electrical current.
Continued
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The engine is only operated to keep the batteries charged, thus the 
vehicle could be moving with or without the internal combustion 
engine running.
Series­hybrid vehicles also use regeneration braking to help keep 
the batteries charged. An advantage of a series­hybrid design is
that no transmission, clutch, or torque converter is needed.
A disadvantage of a series­hybrid design is the added weight of the 
internal combustion engine—actually a heavy, on­board battery 
charger—to what is basically an electric vehicle. 
The electric motor and battery capacity have to be large enough to 
power the vehicle under all operating conditions.

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Is a Diesel-Hybrid Electric Vehicle Possible?
Yes, using a diesel engine instead of a gasoline engine in a hybrid electric
vehicle is possible. While the increased efficiency of a diesel engine would
increase fuel economy, the extra cost of the diesel engine is the major
reason this combination is not currently in production.

Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
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In a parallel­hybrid design, multiple propulsion sources can be 
combined, or one energy source alone can drive the vehicle. The 
battery and engine are both connected to the transmission.
Figure 64–5
The power flow in a typical parallel-hybrid vehicle.

The vehicle can be powered
by internal combustion alone, 
by electric motor alone, (full 
hybrids), or a combination.
In most cases, the electric 
motor is used to assist the 
internal combustion engine.
Continued
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Among the advantages of using a parallel­hybrid design is that by 
using an electric motor or motors to assist the internal combustion 
engine, the engine itself can be smaller than normally needed.
NOTE: A parallel­hybrid design could include additional batteries to allow 

for plug­in capability, to extend the distance the vehicle can travel using 
battery power alone.

One disadvantage of a parallel­hybrid design is that complex 
software is needed to seamlessly blend electric and ICE power.
Another concern about the parallel­hybrid design is that it had to 
be engineered to provide proper heating and air­conditioning 
system operation when the ICE stops at idle.
Continued
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Figure 64–6 Diagram showing the components involved in a typical parallel-hybrid vehicle.
The solid-line arrows indicate the transmission of torque to the drive wheels, and the dottedline arrows indicate the flow of electrical current.
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The Toyota and Ford hybrids are classified as series­parallel­ 
hybrids because they operate using electric motor power alone or 
with the assist of the ICE.

NOTE: The internal combustion engine may or may not start when the

driver starts the vehicle depending on the temperature of the engine and
other conditions. This can be confusing to some who are driving a hybrid
electric vehicle for the first time and sense that the engine did not start
when they tried to start the engine.

The internal combustion engine may be operating even though the 
vehicle is stopped if the electronic controller has detected that the 
batteries need to be charged. 

Continued
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Figure 64–7
A series-parallel-hybrid design
allows the vehicle to operate in
electric motor mode only or in
combination with the internal
combustion engine.

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