Why does the Prius have two electric motors?
The Prius uses two electric motors to separate propulsion from energy generation and engine starting, enabling electric drive at low speeds, smooth transitions between power sources, and regenerative charging for efficiency.
In Toyota’s Hybrid Synergy Drive, two motor/generators—MG1 and MG2—work with a planetary gear set to split power between the gasoline engine, the battery, and the wheels. MG1 primarily handles generating electricity and starting the engine, while MG2 provides the main propulsion and participates in energy recovery.
How the two electric motors work together
Two motors serve distinct roles in the Prius’ hybrid system, and they interact through a power-split device to optimize efficiency across driving conditions.
- MG1 (the generator motor): It starts the gasoline engine, can operate as a generator to charge the high-voltage battery, and helps regulate power flow through the hybrid system.
- MG2 (the traction motor): It provides the primary propulsion by turning the wheels and can run in electric-only mode at low speeds, assist the engine during acceleration, and convert braking energy back into stored electricity during regenerative braking.
The combination enables seamless transitions between electric and gasoline power, reduces the need for a heavy traditional transmission, and lets the engine run at its most efficient RPM under a wide range of conditions.
Benefits of a two-motor design
The dual-motor arrangement offers several practical benefits for efficiency, performance, and longevity of the hybrid system.
- Efficient engine start and shut-off: The electric motors allow the gasoline engine to start and stop smoothly without a heavy clutch or separate starter.
- Electric-drive capability at low speeds: MG2 can propel the car on electric power alone for short distances, reducing fuel use in city driving.
- Regenerative energy recovery: Both motors enable charging of the battery from braking and deceleration, capturing energy that would otherwise be lost.
- Power-split optimization: The planetary gear set combines torque from the engine with MG2 torque and battery power to provide flexible acceleration and efficiency across speeds.
Overall, this architecture helps the Prius maximize fuel efficiency and reduce emissions while delivering a familiar driving feel.
Summary
In brief, the Prius uses two electric motors—the MG1 generator and MG2 traction motor—paired with a power-split planetary gear to manage how the car uses gas and electricity. This arrangement enables electric propulsion at low speeds, efficient engine operation, and energy recovery, all contributing to the Prius’ reputation for efficiency.
