1. Transmissions for Hybrid Vehicles
2009 Chevy Tahoe
Image courtesy of General Motors Corp.

2. Manual transmissions and Hybrids
The only hybrid vehicle sold in the US with a manual transmission was the 2000 Honda insight
Manual transmissions do not work well with hybrids as they must remain in gear as the vehicle is slowing down
To gain full advantage from regenerative braking the Insight driver needed to keep the clutch applied while slowing down so that the engine could be driven by the driveline while the IMA motor generated electricity
This is contrary to the way that most drivers of manual transmission cars drive their vehicles – they apply the clutch and coast to a stop

3. Light and Mild Hybrids
The electric motor/generator is connected to the engine crankshaft on a light or mild hybrid.
This allows a conventional automatic transmission to be used.
During regenerative braking driveline torque must be passed through the transmission, turning the crankshaft and allowing the motor / generator to generate electricity.
During regenerative braking roller clutches that normally allow the transmission to freewheel must be locked out.
The torque converter clutch must remain applied for the driveline torque to be transferred to the crankshaft.

4. Light and Mild Hybrids
Motor/Generator
Torque Converter
Clutch
Overrunning
Clutch
In order for the motor/generator to receive torque from the driveline during regenerative braking the torque converter clutch and overrunning clutches must remained locked.
To reduce engine drag and maximize regenerative braking some systems deactivate cylinders during braking.

5. Conventional Automatic transmissions
A vehicle that has a start/stop function needs to be able to keep the transmission in gear and ready to accelerate the moment the gas pedal is depressed
Electrically driven pump
The electrically driven hydraulic pump on this transaxle keeps hydraulic pressure applied to the clutches inside the transmission during engine stop mode
Image courtesy of General Motors Corp.

6. CVT Transmissions
Continuously Variable Transmissions are ideal for mild hybrid applications.
CVT transmissions use metal belts and pulleys to transmit power through an infinite number of gear ratios.
A CVT transmission allows the engine RPM to stay at a constant speed as the vehicle accelerates and decelerates.
Image courtesy of
General Motors Corp.
Saturn CVT Transaxle
Image courtesy of General Motors Corp.

7. Image courtesy of General Motors Corp.
Mild Hybrid CVT
Output pulley
Hydraulic piston
Mild hybrids often use a mechanical CVT type transmission to optimize fuel economy
Gear reduction is accomplished by a multi-link steel belt running between two pulleys
The depth of the V-groove in the pulleys can be altered by changing the hydraulic pressure applied to one side of the pulley
The only gears used inside the transaxle drive reverse gear or are used to transfer torque from the output pulley to the differential
Hydraulic piston
Input pulley
Image courtesy of General Motors Corp.

8. lowest overdrive ratio
Acceleration RPM / MPH
4000
Conventional
Transmission
3500
3000
2500
CVT
Transmission
2000
Point where CVT
transmission reaches
lowest overdrive ratio
1500
1000
500 10 20 30 40 50 60 70 80 90
100

9. CVT Transmission
Belt
Input Pulley
Output Pulley
A CVT transmission uses a metal belt running between two adjustable pulleys to achieve an infinite number of gear ratios.

10. CVT Pulleys Two cones combine to make a single pulley.
The distance between the cones can be adjusted by a hydraulic cylinder.
As the distance between the cones decreases the belt must ride further away from the center – effectively increasing the diameter of the pulley.
Fixed Cone
Moving Cone

11. CVT Pulleys
Input Pulley
To maintain belt tension the output pulley must mirror the change in the input pulley.
When the spacing between the cones of the input pulley becomes smaller the spacing between the cones of the output pulley must become larger by the same amount.
Output Pulley

12. Gear Ratios
When the input pulley is at minimum diameter and the output pulley is at maximum diameter the transmission is at maximum reduction. Typically 2.5:1
Max
Reduction
When the input pulley is at maximum diameter and the output pulley is at minimum diameter the transmission is at maximum Overdrive. Typically 0.4:1
Max
Overdrive

13. CVT Drive Belt
The belt is made up of hundreds of ‘T’ shaped links that a held together by two highly flexible steel bands.
Unlike a rubber ‘V’ belt the metal belt transfers power by pushing through the belt – not by pulling.

14. CVT Drive Belt and Pulleys
Output
Pulley
Drive
Belt
Input
Pulley
Forward/Reverse
Clutch

15. CVT Pulley Actuator
A hydraulic piston applies pressure to the moving cone.
The piston is held inside the bore by spring tension.
As the hydraulic pressure increases, the moving cone is forced into the fixed cone.
Hydraulic
Pressure
Feed

16. CVT Transmissions
A CVT transmission changes ratios by adjusting the spacing between two cones that form the ‘V’ pulley.
Moving the two cones together effectively increases the diameter that the belt contacts.
Moving the cones apart effectively decreases the pulley diameter.

17. CVT Transmissions Reverse Planetary Belt Flywheel Input Pulley Drum
Output Pulley
Drum
Starting Clutch
Valve Body
Differential

18. Starting Clutch Honda hybrids do not use a torque converter.
Flywheel
And Damper
Honda hybrids do not use a torque converter.
A multi-disc hydraulic clutch is used to couple and decouple the transmission form the final drive.
Starting Clutch
To get the car rolling from a dead stop the TCM applies a PWM duty cycle that lightly applies the clutch. Once the vehicle begins to move at a speed that will allow the engine to engage the driveline without stalling the clutch is fully engaged.
Starting
Clutch
Solenoid
TCM

19. Honda CVT Starting Clutch Belt Output Pulley Drum Flywheel
Input Pulley
Drum
Damper
Pressure
Regulator
Solenoid

20. Reverse Gear Planetary gearset Idler Gearset
Ring Gear
Reverse can be accomplished by two methods:
Planetary
Carrier
Sun Gear
Driving Gear
Planetary gearset
Idler Gear
Idler
Gearset
Driven Gear

21. Electronic CVT

22. Electronic CVT
Motor/Generator #1
Motor/Generator #2
The Electronic CVT transmission uses two electric motor/generators and a planetary gearset as a torque combining device

23. Two types of E-CVT Toyota Single Mode system used by:
Toyota/Lexus
Ford
Nissan
Dual Mode hybrid system used by:
General Motors
BMW
Mercedes Benz
Chrysler

24. Toyota developed the single mode E-CVT for the original Prius.
Toyota now licenses it’s hybrid system technology to Ford and Nissan
2006 Ford
Escape Hybrid
Single Mode E-CVT

25. Torque Combining Device
The single mode hybrid CVT uses a planetary gearset to combine torque from an ICE engine and two electric motor/generators.

26. Planetary Gearsets
The individual elements of the planetary gearset can be input, output or held.
How the elements are driving, driven or held determines what gear ratio and direction of rotation is produced.
Ring Gear
Planetary
Carrier
Sun Gear

27. Single Mode Transmission
Ring gear
Connected to the final drive
Also connected to MG2
Rotates whenever the vehicle is in motion
Ring Gear
Planetary carrier
Connected to the engine crankshaft
Rotates whenever the engine is running
Is effectively held whenever the engine is not running
Planetary
Carrier
Sun gear
Connected to MG1
The sun gear and MG1 determine the gear ratio and vehicle speed
Sun Gear

28. Single Mode Drive System
Planetary
Gearset
MG2
MG1
Oil
Pump
Damper
Transfer
Chain
Final
Drive

29. Prius Transaxle
Transfer
Chain
MG2
Damper
Planetary
Gearset
MG1

31. Freewheeling Backwards
Operating Modes
ICE
MG1
MG2
Reverse
Off
Freewheeling Forward
Motor
Mode
0 -25 MPH
OFF
Freewheeling Backwards
25 MPH Engine Start
Starts
Holding
25 – 65 MPH
Cruise
Running
Generator
Full Throttle Acceleration
Deceleration

32. Toyota Single Mode Transaxle
Drive
Chain
Damper
MG2
Oil
Pump
Coolant
In/Out
MG1
Planetary
Gearset

33. Transmission & Inverter Cooling System
Reservoir and
Pressure Cap
Electric
Water
Pump
Dedicated Radiator
for Inverter
and Motor / Generator

34. Transmission Cooling System
2006
Highlander
Hybrid
Drain for Inverter
/ Transaxle coolant
Drain for Transmission Fluid
Note how the transaxle has 2 drain plugs.

35. Controls
Park switch activates the park servo motor that engages the parking pawl in the transmission.
There is no transmission control cable. All transmission controls are done electronically.
Range Selector knob electronically signals Hybrid Control Module for operating range.
The ‘B’ range is used for engine braking on prolonged downhill driving.

36. Single Mode inefficiency at highway speeds
The single mode system is less efficient at highway speeds than a conventional transmission.
At highway speeds MG2 generates electricity and MG1 uses that electricity to produce power.
In this process about 20% of the overall energy produced by MG2 is lost to heat in the motors and inverter.
Inverter
MG1
MG2

37. Dual Mode System
The dual mode transmission combines the low speed efficiency of the single mode system with the high speed efficiency of a conventional mechanical planetary system.

38. Dual Mode System
The dual mode system was a joint development project by engineers from:
General Motors
BMW
Mercedes Benz
Chrysler
The first vehicle to use this system is the 2008 Chevy Tahoe & 2008 GMC Yukon.
The basic system was developed in 1997 for GMC city busses – over 1000 of these are on the road.

39. Dual Mode Transmission
3 Planetary Gearsets
4 Multiple disc clutches
Image courtesy of General Motors Corp.

40. Dual Mode Transmission
Damper
The Dual Mode transmission has a damper unit and does not use a torque converter.
The damper drives an oil pump for high speed operation.
An electrically driven oil pump is used for low speed operation.
Mechanical
Oil Pump
Electric
Oil Pump

41. Dual Mode Transmission components
MG2
MG1
Output
Planetary
Gearset
Input
Planetary
Gearset
Damper
Two 60 KW [80 HP] electric motor / generators provide power for low speed electrical operation.

42. Three Planetary Gearsets
The two electric motors are connected to elements of the front and center planetary gearsets

43. Four Hydraulic Clutches
Multiple
Disc
Clutches
Image courtesy of General Motors Corp.

44. Dual Mode Components Input Planetary Reaction Planetary Output
MG1
MG2
Damper
Driving
Clutch A
Holding
Clutch B
Driving
Clutch C
Holding
Clutch D

45. Input Split Mode
Clutch D
Applied
Input split mode functions just like the single mode of the Toyota System
The two electric motors provide torque for low speed operation and the power of the ICE engine can be combined with the two motors to provide maximum torque for acceleration.
Hydraulic clutch ‘D’ [ 2nd gear] is needed to connect the two front planetaries to the output shaft.

46. Input Split Mode
In Input-Split mode the vehicle can operate under electric power or a combination of electric power and ICE power.
Under electric operation MG1 acts as a generator and MG2 acts as a motor.
Input-split mode uses 1st and 2nd gear fixed gear ranges.
The Input-Split mode usually functions at speeds between 0 and 30 MPH.

47. Compound Split Mode
Compound-Split mode provides 4 fixed gear ratios using multiple disc clutches and planetary gearsets.
Power from the engine is delivered directly to the four multiple disc clutches and two rear planetary gearsets.

48. Compound Split Mode First Gear Second Gear Third Gear Fourth Gear A B
Clutch ‘A’
Clutch ‘B’
Clutch ‘C’
Clutch ‘D’
First Gear On
Off
Second Gear
Third Gear
Fourth Gear

49. Compound Split Mode
Compound-Split mode provides greater efficiency than Input-split mode at highway speeds.
When running in the Compound-Split mode the electric motors can kick-in whenever additional torque is required.
Compound-Split mode usually begins at about 30 MPH.
When the vehicle is running in compound split mode the electric motors can be turned off.

50. Dual Mode System
Inverter
12 volt
Battery
300 volt
Ni-MH Battery
pack
Dual Mode
Transmission
The Duel Mode electrical system is essentially the same as the single mode system.
Since the Dual Mode system is more efficient a simple transmission cooler is sufficient for removal of excess heat from the electric motors.
Image courtesy of General Motors Corp.

51. Additional Fuel Saving Technology
The Dual Mode system also uses:
Adaptive Fuel Management
2 or 4 Cylinders are turned of during cruise
Active pulsation dampening is used to reduce vibration
Late Intake valve closing
Atkinson cycle

52. Dual Mode System for Front Wheel Drive
Just before the GM bankruptcy GM introduced a front wheel drive version of the Dual Mode system using a 3.6 liter V6
The transaxle for the Vue was adopted for use in the Chevy Volt plug in hybrid
Image courtesy of General Motors Corp.

53. Dual Mode System for Front Wheel Drive
The FWD Dual Mode transaxle is designed for small SUVs and full size cars powered by V6 engines.
The FWD Dual Mode transaxle is designed for small SUVs and full size cars powered by V6 engines.
Image courtesy of General Motors Corp.

54. GM 2009 Hybrid FWD Powertrain
3.6 liter V-6 ICE engine with direct injection
This powertrain was used brifely in the 2009 on the:
Chevy Malibu Hybrid
Saturn Aura Hybrid
330 Volt Ni-MH
battery array
Dual Mode Transaxle
12 Volt auxiliary battery
Image courtesy of General Motors Corp.

55. End of Presentation