Toyota Hybrid Transmission Operation - 15 Years on YouTube!

Main ideas and lessons conveyed

The video explains how a Toyota hybrid transaxle with a power-split (planetary) transmission uses the interaction between:

• Engine crankshaft
• Motor-Generator 1 (MG1)
• Motor-Generator 2 (MG2)
• Planetary gear set (planet carrier, sun gear, ring gear)
• Torque-damping clutch / flywheel to mechanically manage crankshaft oscillations

By changing the relative rotational speeds of MG1 vs. the engine, the system continuously creates:

• Underdrive ratios (for acceleration)
• Direct drive (1:1) (typical highway speeds)
• Overdrive ratios (higher speeds)

The hybrid system can operate in multiple “hybrid modes,” including:

• Electric-only mode (Prius / Plug-in Prius cases)
• Series hybrid mode
• Parallel hybrid mode

During deceleration, MG2 switches to generator mode to convert kinetic energy into electrical energy and charge the high-voltage battery.

The demonstrator emphasizes that the concept remains consistent across generations of the transaxle, even if motor placement changes (motors may be offset rather than positioned identically).

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Key components described (conceptual “parts list”)

• Engine crankshaft

  • Connects to pistons/connecting rods to convert reciprocating motion into rotation.

• Flywheel

  • Includes a torque-damping clutch.

• Torque-damping clutch + damping springs

  • Damp oscillations of the crankshaft during compression and power strokes.

• Planetary gear set (three elements)

  • Planet carrier
    • Rotates with the internal combustion engine (via a shaft that engages the clutch area).
  • Sun gear
    • Rotates inside the planet carrier and is mechanically connected to MG1.
  • Ring gear
    • Surrounds the outside of the planet carrier and is connected to MG2.

• MG1 (Motor-Generator 1)

  • Used to:
    • Start the engine (motoring)
    • Then act as a generator to charge the battery once the engine is running.

• MG2 (Motor-Generator 2)

  • Used to:
    • Drive the wheels (propulsion)
    • Become a generator during deceleration to recharge the battery.

• Drive path to wheels

  • Uses gear drive or chain drive depending on model year, routing power from MG2 through the differential to the front tires.

• No reverse gear

  • The system provides reverse by spinning MG2 backward.

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Methodology / operational logic (modes and ratio behavior)

A) Starting and engine running behavior

• Engine start

  • Rotate MG1 forward.
  • It takes 3.6 revolutions of MG1 to produce 1 revolution of the engine crankshaft.
  • This is effectively a 3.6:1 gear reduction for starting.

• Once the engine starts

  • The engine crankshaft overdrives MG1 by 3.6×.
  • MG1 then transitions to generator mode to charge the high-voltage battery.

B) How drive ratios are created (electronic CVT behavior)

The combined rotational relationships among:

• Engine crankshaft
• MG1
• Through the planetary gear set (sun/planet/ring interactions)

determine the torque split and therefore the effective gearing between engine and MG2.

The video demonstrates three ratio regimes using relative speeds:

1) Direct drive (1:1)

• Condition: Rotate MG1 and the engine crankshaft at the same speed.
• Result: MG2 spins at the same speed as the engine crankshaft (and MG1).
• Usage: Intended for highway speeds.

2) Underdrive (acceleration / “low gear”)

• Condition: Engine is running, but MG1 is rotated faster than the crankshaft.
• Result: A gear reduction occurs; MG2 still rotates to enable stronger torque multiplication for acceleration.
• Analogy: Like a low gear on a bicycle.

3) Overdrive (higher speed)

• Condition: MG1 spins slower than the crankshaft.
  • Around roughly 55–65 mph (varies by vehicle), MG1 can reach complete stop.
• Result: MG2 spins faster than the crankshaft, providing higher effective vehicle speed capability.
• Further overdrive: Spin MG1 backward to get an even higher overdrive (“double overdrive”).
  • This is likened to an electronic continuously variable transmission (eCVT) effect.

C) Electric vehicle (EV) mode (Prius / Plug-in Prius)

• Condition: Engine off (crankshaft not rotating).
• Drive: Vehicle propulsion uses only MG2 powered from the high-voltage battery.
• Propulsion direction logic:
  • Forward: forward rotation of MG2 moves the vehicle forward.
  • Reverse: rotate MG2 backward (no dedicated reverse gear).

D) Series hybrid mode (Toyota terminology; “series hybrid” concept)

• Definition: An internal combustion engine runs to turn a generator, which powers an electric motor with no direct mechanical connection between engine and motor.
• Operation:
  • If the engine is running:
    • Engine turns MG1 as a generator
    • Power goes through an inverter to MG2
    • MG2 propels the vehicle.

E) Parallel hybrid mode (Toyota terminology; “parallel hybrid” concept)

• Definition via behavior: MG2 can assist the engine so both contribute to propulsion.
• Operation:
  • At higher speeds (highway/freeway):
    • MG2 can help the crankshaft rotate
    • Vehicle receives power from:
      • Engine crankshaft
      • MG2
  • The video frames this as “power split” because both sources feed into the system through the planetary gear set and drive path.

F) Deceleration / regenerative charging

• Condition: When the vehicle slows down (deceleration).
• Action: MG2 becomes a generator.
• Effect: It becomes harder to rotate and sends current back to the high-voltage battery to charge it.

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What is claimed historically in the video

• Toyota hybrid system operation is described as being around since the original Prius in December 1997.
• The speaker mentions updating/redoing an older (15-year-old) explanation video to improve accuracy and show how crankshaft alignment relates to motor assistance.

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Speakers / sources featured

• Professor John Kelly (host/speaker)
• Weber Auto YouTube channel (channel/source where the explanation originates)