Electric Vehicle Power Transmission Characteristics
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Jun 24, 2024
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About This Presentation
Electric Vehicles
Slide Content
20EEP53 –Electric Vehicle
Electric Vehicles –
Power Train Transmission Characteristics
E. Ramkumar
Assistant Professor (Sr.Gr)
Department of EEE
Electric Vehicles –
Power Train Transmission Characteristics
E. Ramkumar
Assistant Professor (Sr.Gr)
Department of EEE
Tractive Effort
•Thetorqueandrotatingspeedofthepowerplant
outputshaftaretransmittedtothedrivewheels
throughtheclutchortorqueconverter,gearbox,
finaldrive,differential,anddriveshaft.
!!=#"
$#=%$%&'!#%
$#
ig–Inputgearraio
io–Outputgearratio
Tp–Torqueoutput
!!–Wheelradius
20EEP53 -EV Department of EEE2
i i
—
—
30i i
V
FIGURE 1.9
Tractive effort and torque on a driven wheel
The friction in the gear teeth and the friction in the bearings create
losses in mechanical gear transmission. The following are
representative values of the mechanical efficiency of various
components:
Clutch: 99%
Each pair of gears: 95–97%
Bearing and joint: 98–99%
The total mechanical efficiency of the transmission between the engine
out- put shaft and drive wheels or sprocket is the product of the
efficiencies of all the components in the driveline. As a first
approximation, the following average values of the overall mechanical
efficiency of a manual gear-shift transmission may be used:
Direct gear: 90%
Other gear: 85%
Transmission with a very high reduction ratio: 75–80%
The rotating speed (rpm) of the driven wheel can be expressed as
N
p
Nw = — , (1.30)
g 0
where Np is the output rotating speed (rpm). The translational speed of the
wheel center (vehicle speed) can be expressed as
V =
π N
w
r
d
(m/s). (1.31)
30
Substituting (2.30) into (2.31) yields
V =
π N
p
r
d
(m/s). (2.32)
g 0
1.5 Vehicle Power Plant and Transmission Characteristics
There are two limiting factors to the maximum tractive effort of a vehicle. One
is the maximum tractive effort that the tire – ground contact can support (equa-
tion [1.21] or [1.23]) and the other is the tractive effort that the power plant
N
w
T
w
r
d
F
t
Engine
•Thetorqueandrotatingspeedofthepowerplant
outputshaftaretransmittedtothedrivewheels
throughtheclutchortorqueconverter,gearbox,
finaldrive,differential,anddriveshaft.
!!=#"
$#=%$%&'!#%
$#
ig–Inputgearraio
io–Outputgearratio
Tp–Torqueoutput
!!–Wheelradius
20EEP53 -EV Department of EEE2
i i
—
—
30i i
V
FIGURE 1.9
Tractive effort and torque on a driven wheel
The friction in the gear teeth and the friction in the bearings create
losses in mechanical gear transmission. The following are
representative values of the mechanical efficiency of various
components:
Clutch: 99%
Each pair of gears: 95–97%
Bearing and joint: 98–99%
The total mechanical efficiency of the transmission between the engine
out- put shaft and drive wheels or sprocket is the product of the
efficiencies of all the components in the driveline. As a first
approximation, the following average values of the overall mechanical
efficiency of a manual gear-shift transmission may be used:
Direct gear: 90%
Other gear: 85%
Transmission with a very high reduction ratio: 75–80%
The rotating speed (rpm) of the driven wheel can be expressed as
N
p
Nw = — , (1.30)
g 0
where Np is the output rotating speed (rpm). The translational speed of the
wheel center (vehicle speed) can be expressed as
V =
π N
w
r
d
(m/s). (1.31)
30
Substituting (2.30) into (2.31) yields
V =
π N
p
r
d
(m/s). (2.32)
g 0
1.5 Vehicle Power Plant and Transmission Characteristics
There are two limiting factors to the maximum tractive effort of a vehicle. One
is the maximum tractive effort that the tire – ground contact can support (equa-
tion [1.21] or [1.23]) and the other is the tractive effort that the power plant
N
w
T
w
r
d
F
t
Engine
Efficiency
•MechanicalEfficiency.
•Clutch:99%
•Gearpairs:95%
•BearingandJoints:98%
20EEP53 -EV Department of EEE3
•MechanicalEfficiency.
•Clutch:99%
•Gearpairs:95%
•BearingandJoints:98%
20EEP53 -EV Department of EEE3
Speed
•Therotatingspeed(rpm)ofthedrivenwheel,
!!=!"
###$
•The translational speed of the wheel centre (vehicle speed) can be
expressed as
$=!"!#"
$%m/s
!=!""##
$%&$&%m/s
20EEP53 -EV Department of EEE4
•Therotatingspeed(rpm)ofthedrivenwheel,
!!=!"
###$
•The translational speed of the wheel centre (vehicle speed) can be
expressed as
$=!"!#"
$%m/s
!=!""##
$%&$&%m/s
20EEP53 -EV Department of EEE4
Ideal Characteristics of Power Train
•Idealperformancecharacteristicofapowerplantistheconstantpoweroutputoverthefullspeedrange.
•Atlowspeeds,thetorqueis
constrainedtobeconstant
•Itprovidesthevehiclewithahightractiveeffortatlowspeeds,wheredemandsforacceleration,orgradeclimbingcapabilityarehigh.
20EEP53 -EV Department of EEE5
torque with given driveline gear ratios can provide (equation [1.29]). The
smaller of these two factors will determine the performance potential of the
vehicle. For on-road vehicles, the performance is usually limited by the second
factor. In order to predict the overall performance of a vehicle, its power plant
and transmission characteristics must be taken into consideration.
Power Plant Characteristics
For vehicular applications, the ideal performance characteristic of a power
plant is the constant power output over the full speed range. Consequently,
the torque varies with speed hyperbolically as shown in Figure 1.10. At low
speeds, the torque is constrained to be constant so as not to be over the max-
ima limited by the adhesion between the tire–ground contact area. This con-
stant power characteristic will provide the vehicle with a high tractive effort
at low speeds, where demands for acceleration, drawbar pull, or grade
climbing capability are high.
Since the internal combustion engine and electric motor are the most com-
monly used power plants for automotive vehicles to date, it is appropriate to
review the basic features of the characteristics that are essential to predicat-
ing vehicle performance and driveline design. Representative characteristics
of a gasoline engine in full throttle and an electric motor at full load are
shown in Figure 1.11 and Figure 1.12, respectively. The internal combustion
engine usually has torque–speed characteristics far from the ideal perform-
ance characteristic required by traction. It starts operating smoothly at idle
speed. Good combustion quality and maximum engine torque are reached at
an intermediate engine speed. As the speed increases further, the mean effec-
tive pressure decreases because of the growing losses in the air-induction
manifold and a decline in engine torque. Power output, however, increases
to its maximum at a certain high speed. Beyond this point, the engine torque
decreases more rapidly with increasing speed. This results in the decline of
engine power output. In vehicular applications, the maximum permissible
Speed
Figure 1.10
Ideal performance characteristics
for a vehicle traction power plant
Power
Torque
•Idealperformancecharacteristicofapowerplantistheconstantpoweroutputoverthefullspeedrange.
•Atlowspeeds,thetorqueis
constrainedtobeconstant
•Itprovidesthevehiclewithahightractiveeffortatlowspeeds,wheredemandsforacceleration,orgradeclimbingcapabilityarehigh.
20EEP53 -EV Department of EEE5
torque with given driveline gear ratios can provide (equation [1.29]). The
smaller of these two factors will determine the performance potential of the
vehicle. For on-road vehicles, the performance is usually limited by the second
factor. In order to predict the overall performance of a vehicle, its power plant
and transmission characteristics must be taken into consideration.
Power Plant Characteristics
For vehicular applications, the ideal performance characteristic of a power
plant is the constant power output over the full speed range. Consequently,
the torque varies with speed hyperbolically as shown in Figure 1.10. At low
speeds, the torque is constrained to be constant so as not to be over the max-
ima limited by the adhesion between the tire–ground contact area. This con-
stant power characteristic will provide the vehicle with a high tractive effort
at low speeds, where demands for acceleration, drawbar pull, or grade
climbing capability are high.
Since the internal combustion engine and electric motor are the most com-
monly used power plants for automotive vehicles to date, it is appropriate to
review the basic features of the characteristics that are essential to predicat-
ing vehicle performance and driveline design. Representative characteristics
of a gasoline engine in full throttle and an electric motor at full load are
shown in Figure 1.11 and Figure 1.12, respectively. The internal combustion
engine usually has torque–speed characteristics far from the ideal perform-
ance characteristic required by traction. It starts operating smoothly at idle
speed. Good combustion quality and maximum engine torque are reached at
an intermediate engine speed. As the speed increases further, the mean effec-
tive pressure decreases because of the growing losses in the air-induction
manifold and a decline in engine torque. Power output, however, increases
to its maximum at a certain high speed. Beyond this point, the engine torque
decreases more rapidly with increasing speed. This results in the decline of
engine power output. In vehicular applications, the maximum permissible
Speed
Figure 1.10
Ideal performance characteristics
for a vehicle traction power plant
Power
Torque
Characteristics of ICE
•ICengineusuallyhastorque–
speedcharacteristicsfarfromthe
idealperformancecharacteristic
requiredbytraction.
•Operatessmoothlyatidlespeed.
•Goodcombustionqualityand
maximumenginetorqueare
reachedatanintermediate
enginespeed.
20EEP53 -EV Department of EEE6
Torque
Power
Specific fuel
consumption
Power
Torque
Base
speed
100 300
80 240
60 180
40
20
0
1000 2000 3000 4000 5000
Speed (rpm)
310
290
270
Figure 1.11
Typical performance characteristics of gasoline engines
80
70
60
50
40
30
20
10
0
0 1000
400
350
300
250
200
150
100
50
2000 3000 4000 5000
Motor (rpm)
Figure 1.12
Typical performance characteristics of electric motors for traction
speed of the engine is usually set just a little above the speed of the maxi-
mum power output. The internal combustion engine has a relatively flat
torque–speed profile (compared with an ideal one), as shown in Figure 1.11.
Consequently, a multi-gear transmission is usually employed to modify it, as
shown in Figure 1.13.
Electric motors, however, usually have a speed–torque characteristic that is
much closer to the ideal, as shown in Figure 1.12. Generally, the electric motor
starts from zero speed. As it increases to its base speed, the voltage increases
to its rated value while the flux remains constant. Beyond the base speed, the
Motor
power (kW)
Power
(kW)
Specific fuel
consumption
(g/kWh)
Torque
(Nm)
Motor
torque (Nm)
•ICengineusuallyhastorque–
speedcharacteristicsfarfromthe
idealperformancecharacteristic
requiredbytraction.
•Operatessmoothlyatidlespeed.
•Goodcombustionqualityand
maximumenginetorqueare
reachedatanintermediate
enginespeed.
20EEP53 -EV Department of EEE6
Torque
Power
Specific fuel
consumption
Power
Torque
Base
speed
100 300
80 240
60 180
40
20
0
1000 2000 3000 4000 5000
Speed (rpm)
310
290
270
Figure 1.11
Typical performance characteristics of gasoline engines
80
70
60
50
40
30
20
10
0
0 1000
400
350
300
250
200
150
100
50
2000 3000 4000 5000
Motor (rpm)
Figure 1.12
Typical performance characteristics of electric motors for traction
speed of the engine is usually set just a little above the speed of the maxi-
mum power output. The internal combustion engine has a relatively flat
torque–speed profile (compared with an ideal one), as shown in Figure 1.11.
Consequently, a multi-gear transmission is usually employed to modify it, as
shown in Figure 1.13.
Electric motors, however, usually have a speed–torque characteristic that is
much closer to the ideal, as shown in Figure 1.12. Generally, the electric motor
starts from zero speed. As it increases to its base speed, the voltage increases
to its rated value while the flux remains constant. Beyond the base speed, the
Motor
power (kW)
Power
(kW)
Specific fuel
consumption
(g/kWh)
Torque
(Nm)
Motor
torque (Nm)
Characteristics of ICE
•Asthespeedincreasesfurther,the
meaneffectivepressuredecreases
becauseofthegrowinglossesinthe
air-inductionmanifoldanda
declineinenginetorque.
•Poweroutput,increasestoits
maximumathighspeed.
•Athighspeed,enginetorque
decreasesmorerapidlyresultingin
declineofenginepoweroutput.
20EEP53 -EV Department of EEE7
Torque
Power
Specific fuel
consumption
Power
Torque
Base
speed
100 300
80 240
60 180
40
20
0
1000 2000 3000 4000 5000
Speed (rpm)
310
290
270
Figure 1.11
Typical performance characteristics of gasoline engines
80
70
60
50
40
30
20
10
0
0 1000
400
350
300
250
200
150
100
50
2000 3000 4000 5000
Motor (rpm)
Figure 1.12
Typical performance characteristics of electric motors for traction
speed of the engine is usually set just a little above the speed of the maxi-
mum power output. The internal combustion engine has a relatively flat
torque–speed profile (compared with an ideal one), as shown in Figure 1.11.
Consequently, a multi-gear transmission is usually employed to modify it, as
shown in Figure 1.13.
Electric motors, however, usually have a speed–torque characteristic that is
much closer to the ideal, as shown in Figure 1.12. Generally, the electric motor
starts from zero speed. As it increases to its base speed, the voltage increases
to its rated value while the flux remains constant. Beyond the base speed, the
Motor
power (kW)
Power
(kW)
Specific fuel
consumption
(g/kWh)
Torque
(Nm)
Motor
torque (Nm)
•Asthespeedincreasesfurther,the
meaneffectivepressuredecreases
becauseofthegrowinglossesinthe
air-inductionmanifoldanda
declineinenginetorque.
•Poweroutput,increasestoits
maximumathighspeed.
•Athighspeed,enginetorque
decreasesmorerapidlyresultingin
declineofenginepoweroutput.
20EEP53 -EV Department of EEE7
Torque
Power
Specific fuel
consumption
Power
Torque
Base
speed
100 300
80 240
60 180
40
20
0
1000 2000 3000 4000 5000
Speed (rpm)
310
290
270
Figure 1.11
Typical performance characteristics of gasoline engines
80
70
60
50
40
30
20
10
0
0 1000
400
350
300
250
200
150
100
50
2000 3000 4000 5000
Motor (rpm)
Figure 1.12
Typical performance characteristics of electric motors for traction
speed of the engine is usually set just a little above the speed of the maxi-
mum power output. The internal combustion engine has a relatively flat
torque–speed profile (compared with an ideal one), as shown in Figure 1.11.
Consequently, a multi-gear transmission is usually employed to modify it, as
shown in Figure 1.13.
Electric motors, however, usually have a speed–torque characteristic that is
much closer to the ideal, as shown in Figure 1.12. Generally, the electric motor
starts from zero speed. As it increases to its base speed, the voltage increases
to its rated value while the flux remains constant. Beyond the base speed, the
Motor
power (kW)
Power
(kW)
Specific fuel
consumption
(g/kWh)
Torque
(Nm)
Motor
torque (Nm)
Characteristics of ICE
•Theinternalcombustion
enginehasarelativelyflat
torque–speedprofile
20EEP53 -EV Department of EEE8
Torque
Power
Specific fuel
consumption
Power
Torque
Base
speed
100 300
80 240
60 180
40
20
0
1000 2000 3000 4000 5000
Speed (rpm)
310
290
270
Figure 1.11
Typical performance characteristics of gasoline engines
80
70
60
50
40
30
20
10
0
0 1000
400
350
300
250
200
150
100
50
2000 3000 4000 5000
Motor (rpm)
Figure 1.12
Typical performance characteristics of electric motors for traction
speed of the engine is usually set just a little above the speed of the maxi-
mum power output. The internal combustion engine has a relatively flat
torque–speed profile (compared with an ideal one), as shown in Figure 1.11.
Consequently, a multi-gear transmission is usually employed to modify it, as
shown in Figure 1.13.
Electric motors, however, usually have a speed–torque characteristic that is
much closer to the ideal, as shown in Figure 1.12. Generally, the electric motor
starts from zero speed. As it increases to its base speed, the voltage increases
to its rated value while the flux remains constant. Beyond the base speed, the
Motor
power (kW)
Power
(kW)
Specific fuel
consumption
(g/kWh)
Torque
(Nm)
Motor
torque (Nm)
•Theinternalcombustion
enginehasarelativelyflat
torque–speedprofile
20EEP53 -EV Department of EEE8
Torque
Power
Specific fuel
consumption
Power
Torque
Base
speed
100 300
80 240
60 180
40
20
0
1000 2000 3000 4000 5000
Speed (rpm)
310
290
270
Figure 1.11
Typical performance characteristics of gasoline engines
80
70
60
50
40
30
20
10
0
0 1000
400
350
300
250
200
150
100
50
2000 3000 4000 5000
Motor (rpm)
Figure 1.12
Typical performance characteristics of electric motors for traction
speed of the engine is usually set just a little above the speed of the maxi-
mum power output. The internal combustion engine has a relatively flat
torque–speed profile (compared with an ideal one), as shown in Figure 1.11.
Consequently, a multi-gear transmission is usually employed to modify it, as
shown in Figure 1.13.
Electric motors, however, usually have a speed–torque characteristic that is
much closer to the ideal, as shown in Figure 1.12. Generally, the electric motor
starts from zero speed. As it increases to its base speed, the voltage increases
to its rated value while the flux remains constant. Beyond the base speed, the
Motor
power (kW)
Power
(kW)
Specific fuel
consumption
(g/kWh)
Torque
(Nm)
Motor
torque (Nm)
Characteristics of ICE –Multi gear
•Amulti-geartransmissionis
usuallyemployedtomodify
this.
20EEP53 -EV Department of EEE9
5
4
3
2
1
0
0 20 40 60 80 100 120 140 160 180 200
Vehicle speed (km/h)
Figure 1.13
Tractive effort of internal combustion engine and a multigear transmission vehicle
vs. vehicle speed
7
6
5
4
3
2
1
0
0 50 100 150
Speed (km/h)
200
Figure 1.14
Tractive effort of a single-gear
electric vehicle vs. vehicle speed
voltage remains constant and the flux is weakened. This results in constant
output power while the torque declines hyperbolically with speed. Since the
speed–torque profile of an electric motor is close to the ideal, a single-gear or
double-gear transmission is usually employed, as shown in Figure 2.14.
Transmission Characteristics
The transmission requirements of a vehicle depend on the characteristics of
the power plant and the performance requirements of the vehicle. As men-
tioned previously, a well-controlled electric machine such as the power plant
of an electric vehicle will not need a multigear transmission. However, an
internal combustion engine must have a multigear or continuously varying
transmission to multiply its torque at low speed. The term transmission here
includes all those systems employed for transmitting engine power to the
drive wheels. For automobile applications, there are usually two basic types
of transmission: manual gear transmission and hydrodynamic transmission.
1st gear
2nd gear
3rd gear
4th gear
Tractive
effort on wheel (kN)
Tractive
effort on wheel (kN)
•Amulti-geartransmissionis
usuallyemployedtomodify
this.
20EEP53 -EV Department of EEE9
5
4
3
2
1
0
0 20 40 60 80 100 120 140 160 180 200
Vehicle speed (km/h)
Figure 1.13
Tractive effort of internal combustion engine and a multigear transmission vehicle
vs. vehicle speed
7
6
5
4
3
2
1
0
0 50 100 150
Speed (km/h)
200
Figure 1.14
Tractive effort of a single-gear
electric vehicle vs. vehicle speed
voltage remains constant and the flux is weakened. This results in constant
output power while the torque declines hyperbolically with speed. Since the
speed–torque profile of an electric motor is close to the ideal, a single-gear or
double-gear transmission is usually employed, as shown in Figure 2.14.
Transmission Characteristics
The transmission requirements of a vehicle depend on the characteristics of
the power plant and the performance requirements of the vehicle. As men-
tioned previously, a well-controlled electric machine such as the power plant
of an electric vehicle will not need a multigear transmission. However, an
internal combustion engine must have a multigear or continuously varying
transmission to multiply its torque at low speed. The term transmission here
includes all those systems employed for transmitting engine power to the
drive wheels. For automobile applications, there are usually two basic types
of transmission: manual gear transmission and hydrodynamic transmission.
1st gear
2nd gear
3rd gear
4th gear
Tractive
effort on wheel (kN)
Tractive
effort on wheel (kN)
Characteristics of Electric Motor
•Electricmotors,usuallyhaveaspeed–torquecharacteristicsthatismuchclosertotheidealcharacteristics.
•Electricmotorstartsfromzerospeed.
•Asspeedincreasestobasespeed,the
voltageincreasestoitsratedvalue
whilethefluxremainsconstant.
•Beyondthebasespeed,thevoltageremainsconstantandthefluxisweakenedresultinginconstantoutputpowerwhilethetorquedeclineshyperbolicallywithspeed.
20EEP53 -EV Department of EEE10
Torque
Power
Specific fuel
consumption
Power
Torque
Base
speed
100 300
80 240
60 180
40
20
0
1000 2000 3000 4000 5000
Speed (rpm)
310
290
270
Figure 1.11
Typical performance characteristics of gasoline engines
80
70
60
50
40
30
20
10
0
0 1000
400
350
300
250
200
150
100
50
2000 3000 4000 5000
Motor (rpm)
Figure 1.12
Typical performance characteristics of electric motors for traction
speed of the engine is usually set just a little above the speed of the maxi-
mum power output. The internal combustion engine has a relatively flat
torque–speed profile (compared with an ideal one), as shown in Figure 1.11.
Consequently, a multi-gear transmission is usually employed to modify it, as
shown in Figure 1.13.
Electric motors, however, usually have a speed–torque characteristic that is
much closer to the ideal, as shown in Figure 1.12. Generally, the electric motor
starts from zero speed. As it increases to its base speed, the voltage increases
to its rated value while the flux remains constant. Beyond the base speed, the
Motor
power (kW)
Power
(kW)
Specific fuel
consumption
(g/kWh)
Torque
(Nm)
Motor
torque (Nm)
•Electricmotors,usuallyhaveaspeed–torquecharacteristicsthatismuchclosertotheidealcharacteristics.
•Electricmotorstartsfromzerospeed.
•Asspeedincreasestobasespeed,the
voltageincreasestoitsratedvalue
whilethefluxremainsconstant.
•Beyondthebasespeed,thevoltageremainsconstantandthefluxisweakenedresultinginconstantoutputpowerwhilethetorquedeclineshyperbolicallywithspeed.
20EEP53 -EV Department of EEE10
Torque
Power
Specific fuel
consumption
Power
Torque
Base
speed
100 300
80 240
60 180
40
20
0
1000 2000 3000 4000 5000
Speed (rpm)
310
290
270
Figure 1.11
Typical performance characteristics of gasoline engines
80
70
60
50
40
30
20
10
0
0 1000
400
350
300
250
200
150
100
50
2000 3000 4000 5000
Motor (rpm)
Figure 1.12
Typical performance characteristics of electric motors for traction
speed of the engine is usually set just a little above the speed of the maxi-
mum power output. The internal combustion engine has a relatively flat
torque–speed profile (compared with an ideal one), as shown in Figure 1.11.
Consequently, a multi-gear transmission is usually employed to modify it, as
shown in Figure 1.13.
Electric motors, however, usually have a speed–torque characteristic that is
much closer to the ideal, as shown in Figure 1.12. Generally, the electric motor
starts from zero speed. As it increases to its base speed, the voltage increases
to its rated value while the flux remains constant. Beyond the base speed, the
Motor
power (kW)
Power
(kW)
Specific fuel
consumption
(g/kWh)
Torque
(Nm)
Motor
torque (Nm)
Transmission Characteristics
•Thetransmissionrequirementsofavehicledependonthecharacteristicsofthepowerplantandtheperformancerequirementsofthevehicle.
•Awell-controlledelectricmachinesuchasthepowerplantofanelectricvehiclewillnotneedamulti-geartransmission.
•However,anICenginemusthaveamulti-gearorcontinuouslyvaryingtransmissiontomultiplyitstorqueatlowspeed.
20EEP53 -EV Department of EEE11
•Thetransmissionrequirementsofavehicledependonthecharacteristicsofthepowerplantandtheperformancerequirementsofthevehicle.
•Awell-controlledelectricmachinesuchasthepowerplantofanelectricvehiclewillnotneedamulti-geartransmission.
•However,anICenginemusthaveamulti-gearorcontinuouslyvaryingtransmissiontomultiplyitstorqueatlowspeed.
20EEP53 -EV Department of EEE11
Transmission Characteristics
•Transmission-allsystemsemployedfortransmitting
enginepowertothedrivewheels.
•Inautomobileapplications,thereareusuallytwo
basictypesoftransmission:
•Manualgeartransmission
•Hydrodynamictransmission.
20EEP53 -EV Department of EEE12
•Transmission-allsystemsemployedfortransmitting
enginepowertothedrivewheels.
•Inautomobileapplications,thereareusuallytwo
basictypesoftransmission:
•Manualgeartransmission
•Hydrodynamictransmission.
20EEP53 -EV Department of EEE12
Manual transmission
•Manualgeartransmissionconsistsofaclutch,gearbox,finaldrive,anddriveshaft
•Thefinaldrivehasaconstantgear
reductionratiooradifferentialgear
ratio.
•Thegearboxprovidesanumberof
gearreductionratiosrangingfrom
threetofiveforpassengercarsand
moreforheavycommercial
vehicles
20EEP53 -EV Department of EEE13
Engine
•Manualgeartransmissionconsistsofaclutch,gearbox,finaldrive,anddriveshaft
•Thefinaldrivehasaconstantgear
reductionratiooradifferentialgear
ratio.
•Thegearboxprovidesanumberof
gearreductionratiosrangingfrom
threetofiveforpassengercarsand
moreforheavycommercial
vehicles
20EEP53 -EV Department of EEE13
Engine
Manual transmission
•Maximumspeedrequirementofthe
vehicledeterminesthegearratioofthe
highestgear
•Maximumtractiveeffortrequirement
ofthevehicledeterminesthegear
ratiooflowestgear.
•Ratiosbetweenthemshouldbespaced
insuchawaythattheywillprovide
thetractiveeffort–speed
characteristicsasclosetotheidealas
possible
20EEP53 -EV Department of EEE14
Manual Gear Transmission
Manual gear transmission consists of a clutch, gearbox, final drive, and drive
shaft as shown in Figure 1.8. The final drive has a constant gear reduction
ratio or a differential gear ratio. The common practice of requiring direct
drive (nonreducing) in the gearbox to be in the highest gear determines this
ratio. The gearbox provides a number of gear reduction ratios ranging from
three to five for passenger cars and more for heavy commercial vehicles that
are powered with gasoline or diesel engines.
The maximum speed requirement of the vehicle determines the gear ratio
of the highest gear (i.e., the smallest ratio). On the other hand, the gear ratio
of the lowest gear (i.e., the maximum ratio) is determined by the require-
ment of the maximum tractive effort or the gradeability. Ratios between them
should be spaced in such a way that they will provide the tractive effort–
speed characteristics as close to the ideal as possible, as shown in Figure 1.15.
In the first iteration, gear ratios between the highest and the low- est gear may
be selected in such a way that the engine can operate in the same speed range
for all the gears. This approach would benefit the fuel economy and
performance of the vehicle. For instance, in normal driving, the proper gear
can be selected according to vehicle speed to operate the engine in its
optimum speed range for fuel-saving purposes. In fast acceler- ation, the
engine can be operated in its speed range with high power output. This
approach is depicted in Figure 1.16.
For a four-speed gearbox, the following relationship can be established
(see Figure 1.16):
i
g1
—
i
g2
i
g2
= —
i
g3
i
g3
= —
i
g4
= K
g (1.33)
where i
g1, i
g2, i
g3, and i
g4 are the gear ratios for the first, second, third, and
fourth gear, respectively. In a more general case, if the ratio of the highest
Speed
FIGURE 1.15
Tractive effort characteristics of a gasoline
engine-powered vehicle
Ideal tractive effort
1st gear
2nd gear
3rd Gear
4th gear
Tractive effort
Gear box ratio,
!!1
!!2=!!2
!!3=!!3
!!4=#$
•Maximumspeedrequirementofthe
vehicledeterminesthegearratioofthe
highestgear
•Maximumtractiveeffortrequirement
ofthevehicledeterminesthegear
ratiooflowestgear.
•Ratiosbetweenthemshouldbespaced
insuchawaythattheywillprovide
thetractiveeffort–speed
characteristicsasclosetotheidealas
possible
20EEP53 -EV Department of EEE14
Manual Gear Transmission
Manual gear transmission consists of a clutch, gearbox, final drive, and drive
shaft as shown in Figure 1.8. The final drive has a constant gear reduction
ratio or a differential gear ratio. The common practice of requiring direct
drive (nonreducing) in the gearbox to be in the highest gear determines this
ratio. The gearbox provides a number of gear reduction ratios ranging from
three to five for passenger cars and more for heavy commercial vehicles that
are powered with gasoline or diesel engines.
The maximum speed requirement of the vehicle determines the gear ratio
of the highest gear (i.e., the smallest ratio). On the other hand, the gear ratio
of the lowest gear (i.e., the maximum ratio) is determined by the require-
ment of the maximum tractive effort or the gradeability. Ratios between them
should be spaced in such a way that they will provide the tractive effort–
speed characteristics as close to the ideal as possible, as shown in Figure 1.15.
In the first iteration, gear ratios between the highest and the low- est gear may
be selected in such a way that the engine can operate in the same speed range
for all the gears. This approach would benefit the fuel economy and
performance of the vehicle. For instance, in normal driving, the proper gear
can be selected according to vehicle speed to operate the engine in its
optimum speed range for fuel-saving purposes. In fast acceler- ation, the
engine can be operated in its speed range with high power output. This
approach is depicted in Figure 1.16.
For a four-speed gearbox, the following relationship can be established
(see Figure 1.16):
i
g1
—
i
g2
i
g2
= —
i
g3
i
g3
= —
i
g4
= K
g (1.33)
where i
g1, i
g2, i
g3, and i
g4 are the gear ratios for the first, second, third, and
fourth gear, respectively. In a more general case, if the ratio of the highest
Speed
FIGURE 1.15
Tractive effort characteristics of a gasoline
engine-powered vehicle
Ideal tractive effort
1st gear
2nd gear
3rd Gear
4th gear
Tractive effort
Gear box ratio,
!!1
!!2=!!2
!!3=!!3
!!4=#$
Manual transmission
##1
##2>##2
##3>##3
##4
Gearrationcanbeobtainedby,
!#)−1="#!#$
20EEP53 -EV Department of EEE15
g
g
Engine operating
speed range
V
4
V
3
V
2
V
1
n
e1
Engine speed
n
e 2
gear, i
gn (smaller gear ratio), and the ratio of the lowest gear, i
g1 (largest gear
ratio), have been determined and the number of the gear n
g is known, the
factor K
g can be determined as
K =(
i
g1
)
(ng—1)
, (1.35)
g
—
i
gn
and each gear ratio can be obtained by
i
gn—1 = K
g
i
gn
i
gn—2 = K
2
i
gn (1.36)
⁝
i
g2 = K
ng—1
i
gn
.
For passenger cars, to suit changing traffic conditions, the step between the
ratios of the upper two gears is often a little closer than that based on (1.36).
That is,
i
g1
—
i
g2
i
g2
> —
i
g3
> —
i
g3
.
i
g4
(1.37)
This, in turn, affects the selection of the ratios of the lower gears. For com-
mercial vehicles, however, the gear ratios in the gearbox are often arranged
based on (1.37).
Figure 1.17 shows the tractive effort of a gasoline engine vehicle with four-
gear transmission and that of an electric vehicle with single-gear transmission.
It is clear that electric machines with favorable torque–speed characteristics
can satisfy tractive effort with simple single-gear transmission.
FIGURE 1.16
Demonstration of vehicle speed range and engine speed range for each gear
Vehicle
speed
1st
2nd
3rd
4th Gear
##1
##2>##2
##3>##3
##4
Gearrationcanbeobtainedby,
!#)−1="#!#$
20EEP53 -EV Department of EEE15
g
g
Engine operating
speed range
V
4
V
3
V
2
V
1
n
e1
Engine speed
n
e 2
gear, i
gn (smaller gear ratio), and the ratio of the lowest gear, i
g1 (largest gear
ratio), have been determined and the number of the gear n
g is known, the
factor K
g can be determined as
K =(
i
g1
)
(ng—1)
, (1.35)
g
—
i
gn
and each gear ratio can be obtained by
i
gn—1 = K
g
i
gn
i
gn—2 = K
2
i
gn (1.36)
⁝
i
g2 = K
ng—1
i
gn
.
For passenger cars, to suit changing traffic conditions, the step between the
ratios of the upper two gears is often a little closer than that based on (1.36).
That is,
i
g1
—
i
g2
i
g2
> —
i
g3
> —
i
g3
.
i
g4
(1.37)
This, in turn, affects the selection of the ratios of the lower gears. For com-
mercial vehicles, however, the gear ratios in the gearbox are often arranged
based on (1.37).
Figure 1.17 shows the tractive effort of a gasoline engine vehicle with four-
gear transmission and that of an electric vehicle with single-gear transmission.
It is clear that electric machines with favorable torque–speed characteristics
can satisfy tractive effort with simple single-gear transmission.
FIGURE 1.16
Demonstration of vehicle speed range and engine speed range for each gear
Vehicle
speed
1st
2nd
3rd
4th Gear
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