Automotive Technology: Principles,
Diagnosis, and Service
Seventh Edition
Chapter 131
EV and HEV Transmissions
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Learning Objectives (1 of 2)
131.1 Describe the powertrain configuration.
131.2 Explain the principles involved with vehicle
transmissions/transaxles.
131.3 Describe the function of a hybrid electric vehicle
(HE V) transmission.
131.4 Discuss the transmission in GM parallel hybrid
trucks (P HTs).
131.5 Discuss the GM two-mode hybrid transmission.
131.6 Discuss the Ford/Lincoln 10R80 MHT.
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Learning Objectives (2 of 2)
131.7 Discuss the Toyota/Lexus power-split system.
131.8 Discuss the diagnosis of an HEV transmission.
131.9 Describe the transmissions used in electric vehicles
(E Vs).
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Transmissions and Transaxles (1 of 2)
• Purpose and Function
– All vehicles, regardless of the power source, require
the use of a transmission to achieve reasonable
acceleration and efficiency.
– The transmission is responsible for providing the
following:
▪ Torque applied to the drive wheel to accelerate the
vehicle from a stop.
▪ Power at higher speeds that allows the powertrain
to operate efficiently.
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Transmissions and Transaxles (2 of 2)
• Powertrain Configuration
– In rear-wheel-drive (RW D) applications, it is most
common to use a transmission along with a driveshaft
and differential.
– In a front-wheel-drive (FWD) vehicle, a transaxle
assembly is used with half-shafts to transmit torque to
the drive wheels.
– In a four-wheel-drive (4W D) or all-wheel-drive (AW D)
vehicle, a transfer case or rear electric motor is used to
distribute power to all four wheels.
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Vehicle Configurations
Vehicle FWD/RWD/ Configuration
AWD
Toyota Prius FWD ECVT 2 Motors/1 Planetary
2001–2009
Chevrolet Volt FWD ECVT 2 Motors/1 Planetary/
Clutches
Toyota Prius FWD ECVT 2 motors/2 Planetary
2010–2015
Toyota Prius FWD/ AWD ECVT 2 Motors/2 Planetary/
2016–2021 One-way clutch
General Motors 2 RWD/AWD ECVT 2 Motors/3 Planetary/
Mode Clutches
Honda Accord FWD ECVT 2 Motors/2 Clutches
Hybrid
Nissan Leaf FWD Electric Motor with gear
reduction unit
Chevrolet Bolt FWD Electric Motor with gear
reduction unit
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Figure 131.1
Drivelines
Rear-wheel-drive (RW D) vehicles use transmissions to send
torque to the rear differential and final drive. Front-wheel-
drive (FW D) vehicles use a transaxle, which incorporates the
differential and final drive into the transaxle case.
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Principles Involved (1 of 2)
• Torque Delivery
– Torque is a twisting force.
– Torque is applied to the drive wheels to make the
vehicle accelerate.
– An ICE is most efficient when it is operating near its
torque peak.
– With more transmission ratios, it is easier to match the
vehicle road speed with the most efficient engine R P M.
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Principles Involved (2 of 2)
• Multiple Speed Transmissions/Transaxles
– Years ago, it was common for vehicles with automatic
transmissions to have only 2, 3, or 4 gear ratios.
– Currently, 5-, 6-, 7-, 8- and 10-speed automatic
transmissions are becoming common.
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Figure 131.2
Torque vs. HP
Graph showing engine
torque v s. horsepower
ersus
output for a typical
internal combustion
engine. ICEs produce
maximum torque at a
high RPM, whereas
electric motors produce
maximum torque at low
RPM.
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Principles Involved
• To move vehicle, torque must be applied to drive wheels.
• ICEs produce maximum torque at high RPM.
• Electric motors produce maximum torque at low RPM.
• Keep I CE in most efficient range:
– By increase RPM range where engine produces torque
(“flattening” torque curve).
– By increasing number of gear ratios
– It is easier to match vehicle road speed with most
efficient engine RPM.
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Figure 131.3
Speed & Torque
When output speed decreases in a transmission, output
torque will increase.
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HEV Transmissions (1 of 2)
• Classifications
– A mild hybrid with stop-start system typically contains a
transmission with a single electric motor.
– A full hybrid generally contains a transmission with two
electric motors.
• Electric Auxiliary Pump
– In order to adapt a conventional automatic
transmission to a hybrid powertrain, an electric
auxiliary pump is used.
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Figure 131.4
Hydraulic Circuit
The hydraulic circuit diagram for this GM transmission
includes a mechanical pump and an electric secondary fluid
pump.
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HEV Transmissions (2 of 2)
• Hydraulic Impulse Storage Accumulator
– A hydraulic impulse storage accumulator is used to
provide fluid pressure as the ICE restarts after the idle-
stop mode.
– Eliminates the need for an electric auxiliary pump.
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Figure 131.5
Accumulator
When the solenoid is energized, the accumulator releases
the fluid creating the initial pressure needed at restart.
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GM Parallel Hybrid Truck (1 of 2)
• Description
– The transmission in the 2004–2008 Chevrolet
Silverado/G MC Sierra parallel hybrid truck (P HT) is
based on the 4L60E automatic transmission.
• Operation
– Whenever the engine goes into idle-stop, the electric
fluid pump is turned on to maintain oil pressure.
• Service
– This transmission requires Dexron V I ATF.
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GM Parallel Hybrid Truck (2 of 2)
• Transmission gear selector lever can be placed in 7
positions, as follows:
– P—Park
– R—Reverse
– N—Neutral
– D—Drive
– 3—Manual third
– 2—Manual second
– 1—Manual first
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Figure 131.6
Secondary Fluid Pump
Electric secondary fluid pump from a transmission in a G M
hybrid pickup.
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G M Two-Mode Hybrid Transmission (1 of 3)
• Description
– The two-mode hybrid transmission used in 2009–2013
General Motors hybrid trucks is labeled a 2M L70.
– This unit features two 60-kW motors in the hybrid
drivetrain, a 300-volt battery pack, and a V8 engine.
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Figure 131.7
Two-Mode Trans
The two-mode transmission has orange high-voltage cables
entering the unit to carry electric energy from the high-voltage
battery pack to propel the vehicle and also charge the battery
during deceleration.
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G M Two-Mode Hybrid Transmission (2 of 3)
• Components
– The two-mode unit is effectively an electronically
variable transmission (E VT).
– It includes three simple planetary gear sets with four
multiplate clutches.
– It has four fixed gear ratios with two EV ratios for
smooth, more efficient operation.
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Figure 131.8
Two-Mode Trans
Using two planetary gear
sets, the ICE can be
maintained in the most
efficient speed of about
2000 RPM under most
operating conditions.
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G M Two-Mode Hybrid Transmission (3 of 3)
• First Mode of Operation
– The first mode is for accelerating from standstill to
second gear.
• Second Mode of Operation
– The second mode takes the vehicle from second gear
through to overdrive.
• Two-Mode Service
– Fluid-level check and visual inspection should be all
that is required until the first scheduled fluid change.
– Always use Dexron V I.
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Figure 131.9
GM 2ML70 Service
(a) Disassembly of the 2M L70 transmission requires the use of a special
tool and a lift or engine hoist to remove the motor assembly. (b) The
motor assembly after being removed from the transmission.
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Ford/Lincoln 10R80 MHT
• Ten-Speed Hybrid Transmission 2020 Explorer/Aviator
– Plug-in hybrid.
– Still uses a torque converter.
– Electric motor & disconnect clutch are placed between
engine & converter.
– Electric motor provides low-speed torque and
additional power.
– Six inches longer non-hybrid model
– 10R80 shares 90% of the same components
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Figure 131.10
Ford 10R80 MH T
(a) The driver side of the transmission contains the high-voltage
connections and the shift level assembly. The hybrid portion of the
transmission is forward of the gasket. (b) The passenger side of the
transmission contains the low-voltage connections.
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Figure 131.11
Removing Hybrid
(a) An engine hoist and adapter are used to remove the hybrid portion of
the transmission. (b) The hybrid portion of the transmission resting on two
wooden blocks after being removed from the transmission.
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Figure 131.12
Motor Windings
(a) The motor windings attached to the housing after the rotor has been
removed. (b) The rotor and torque converter assembly after being
separated from the winding.
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Figure 131.13
Resolver
The resolver is the black and gray electrical sensor bolted to
the housing at the bottom of the motor housing.
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Figure 131.14
Three Connectors
The three large flat connectors allow the electric motor to be
connected to the IS C via the high-voltage cables.
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Figure 131.15
Low-Voltage Connector
The low-voltage connector is for transmission control and
monitoring
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Toyota/Lexus Power-Split System
• Toyota/Lexus Power-Split System
– Vehicle stopped
– Light acceleration
– Normal driving
– Full-throttle acceleration and high-speed cruise
– Deceleration and braking
– Reverse
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Figure 131.16
Toyota MG1/MG2
The Toyota Hybrid System uses two electric
motor/generators (MG1 and MG2) and an ICE connected
together by a power-split device, which is a simple planetary
gear set.
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Figure 131.17
Power-Split Device
The power-split device from the Toyota Hybrid System. Note
the vehicle will only move when MG2 (and the ring gear) is
turning.
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Figure 131.18
Planet Carrier
The planetary gearset used in the
Toyota Hybrid System has 2.6
times the number of teeth in its
ring gear as it has in its sun gear.
This means that the ICE
(attached to the planet carrier) will
send 72% of its torque to the ring
gear (drive wheels) and 28% of its
torque to the sun gear (MG1).
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Figure 131.19
Vehicle Stopped
When the vehicle is stopped, the I CE is shut off along with
both motor/generators.
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Light Acceleration
Figure 131.21 Under light acceleration,
Figure 131.20 Under light the engine is stopped (0 RPM), MG2 is
acceleration, power is sent to MG2 to turning forward (+), and MG1 is turning
move the vehicle. backward (−).
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Generator Action
Figure 131.23 Normal driving—ICE is
Figure 131.24 Normal driving—the
now running and some of its torque is
engine is running, MG2 is turning
used to drive MG1. Electricity generated
forward (+), and MG1 is turning
by MG1 is used to power MG2 or
backward (−).
recharge the HV battery.
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Acceleration
Figure 131.25 Full-throttle acceleration and
high-speed cruise—with greater demand for
acceleration, power from M G1 combined Figure 131.26 Full-throttle acceleration and
with power from HV battery to generate high-speed cruise—graph shows MG1
higher output from M G2. It is possible to acting as a motor using power from M G2.
configure M G2 as a generator, send power This increases the speed of the I CE,
to M G1 (acts as a motor). allowing it to produce higher output.
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Decel & Reverse
Figure 131.28 Reverse—M G2
Figure 131.27 Deceleration and alone is used to move the car in
braking—M G2 is configured as a reverse. This is accomplished by
generator and recharges H V reversing the direction of M G2.
battery.
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Figure 131.29
Cooling Water Jackets
(a) Coolant is circulated under the (b) Coolant is circulated in the passages
ring in the bellhousing area to remove near the rear of the transmission to
heat generated by MG1. remove heat generated by M G2.
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Final Drive & Damper Disc
Figure 131.30 The view of the Figure 131.31 The flywheel and
configuration of the final drive clutch assembly serve as the
assembly after the front cover has dampener between the engine and
been removed. transmission.
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Oil Pump & Parking Lock
Figure 131.32 With the cover Figure 131.33 The electronic
removed, the transmission oil actuated park lock mechanism is
pump is visible on the rear of the mounted externally beginning with
transmission. the 2004 model year.
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Hybrid Transmission Diagnosis
• Eight Step Process
– STEP 1 Verify the customer complaint.
– STEP 2 Check fluid level and condition.
– STEP 3 Check DTCs.
– STEP 4 Check for TSBs.
– STEP 5 Check scan tool data
– STEP 6 Perform visual inspections.
– STEP 7 Perform bidirectional control
– STEP 8 Locate and correct root cause
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Electric Vehicle Transmissions (1 of 4)
• Acceleration V S Top Speed
ersu
– Most electric vehicles use single-speed transmission.
– EV manufactures usually design their system
– For optimum low-end acceleration NOT top speeds.
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Electric Vehicle Transmissions (2 of 4)
• Ford Mustang Mach-E
– BorgWarner producing an Integrated Drive Module
(I DM)
– Being used in Ford Mustang Mach-E.
– IDM consists within one compact assembly including:
▪ Electric traction motor
▪ Single-speed gearbox
▪ Thermal-management system (liquid cooling)
▪ Motor and power electronics
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Electric Vehicle Transmissions (3 of 4)
• Chevrolet Bolt
– Chevrolet Bolt drive unit consists of an electric motor.
– Final drive assembly.
– Electric motor is rated at 150 kW.
– Maximum rotation speed of 8810 RPM.
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Electric Vehicle Transmissions (4 of 4)
• Nissan Leaf
– Three-phase A C electric motor that produces produces
40 kilowatts of power.
– LEAF incorporates a reducer that transfers torque from
traction motor to drive wheels.
• Two-Speed Gearing
– Original Tesla Roadster featured two-speed
transmission
– Currently a two-speed unit is used in Porsche Taycan.
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Figure 131.34
Bolt Electric Motor & Final Drive
The electric motor and final drive assembly installed in a
Chevrolet Bolt.
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Figure 131.35
Bolt Drive Unit
A CA TIA drafting of a Chevrolet Bolt electric motor and final
drive assembly.
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Figure 131.36
Dexron HP
Dexron HP synthetic transmission fluid is specified for the
Bolt final drive assembly.
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Figure 131.37
Bolt Coolant Lines
Coolant enters through the hose on the left, travels through
the passageway absorbing heat, and exits to the radiator
through the hose on the right.
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Figure 131.38
Leaf A C Motor
The electric motor assembly and reducer installed in a 2011
Nissan Leaf.
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Figure 131.39
External Connection for Resolver
The external connection for the resolver.
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Figure 131.40
Power Thru Reducer
Power flow through the reducer.
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Frequently Asked Question: What
Happens When You Shift to Neutral?
? Frequently Asked Question
What Happens When You Shift to Neutral? When neutral
is selected, does it just disconnect the power connections?
Or is the motor free to spin? In neutral, there is no power
being supplied to the electric traction motor. The motor is
never disconnected.
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Question 1
• What is the first step when diagnosing a hybrid vehicle
transmission?
a. Check the fluid level
b. Verify the customer concern
c. Check for trouble codes
d. Check for Technical Service Bulletins (TSBs)
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Answer 1
• What is the first step when diagnosing a hybrid vehicle
transmission?
b. Verify the customer concern
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