This video provides a detailed mechanical demonstration of the Toyota Hybrid System's power-split transmission, often called an e-CVT. Professor John Kelly systematically introduces the core components: the engine's crankshaft, two motor-generators (MG1 and MG2), and the central planetary gear set that connects them. The video clarifies the specific connections: the crankshaft drives the planet carrier, MG1 is connected to the sun gear, and MG2 is linked to the ring gear, which ultimately drives the wheels. Through a hands-on demonstration, the video explains how varying the rotational speed of MG1 relative to the engine creates a continuously variable transmission effect, enabling underdrive, direct drive, and overdrive ratios. It also covers the system's various operational modes, including engine-starting via MG1, pure electric vehicle (EV) operation using MG2, regenerative braking, and the distinction between series hybrid (engine-generator-motor) and parallel hybrid (engine and motor combined power) modes.
How a Toyota Hybrid Power-Split Transmission Works
0:00:17 The Three Power Sources: The system integrates three key components: the internal combustion engine (represented by its crankshaft), Motor Generator 1 (MG1), and Motor Generator 2 (MG2).
0:01:12 The Planetary Gear Set: The heart of the transmission is a planetary gear set that links the three power sources. The engine crankshaft connects to the planet carrier, MG1 connects to the sun gear, and MG2 connects to the ring gear.
0:03:40 Driving the Wheels: Motor Generator 2 (MG2) is directly responsible for propelling the vehicle by sending power through gears or chains to the differential and front tires.
0:04:03 Starting the Engine: To start the internal combustion engine, MG1 spins the sun gear, which turns the planet carrier and crankshaft at a 3.6:1 gear reduction. Once the engine is running, it overdrives MG1, turning it into a generator to charge the high-voltage battery.
0:05:14 Electronic Continuously Variable Transmission (e-CVT): The system achieves different drive ratios by electronically controlling the speed of MG1 relative to the engine's crankshaft.
Direct Drive (1:1 Ratio): At certain highway speeds, the engine, MG1, and MG2 all rotate at the same speed.
Underdrive: For acceleration, MG1's speed is manipulated to create gear reduction, delivering more torque to the wheels.
Overdrive: At higher speeds, MG1 is spun slower than the crankshaft. It can even be stopped or spun backward to achieve higher overdrive ratios, allowing the wheels (MG2) to spin much faster than the engine.
0:08:16 EV and Reverse Modes: In full electric mode, the engine is off and MG2 powers the vehicle alone. There is no reverse gear; the vehicle reverses by simply spinning MG2 backward.
Series Hybrid: The engine turns MG1, which acts as a generator to produce electricity that powers MG2 to move the car. There is no direct mechanical link from the engine to the wheels.
Parallel Hybrid: Power from both the engine (mechanically, through the planetary gear set) and MG2 are combined to propel the vehicle.
0:10:36 Regenerative Braking: During deceleration, MG2 functions as a generator, converting the vehicle's momentum back into electricity to recharge the battery.