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Hybrid Synergy Drive
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Hybrid Synergy Drive is a seamless mix of electric motor and petrol engine. Each power source complements the other. Individually petrol engines and electric motors have serious disadvantages, but together they produce a unique "engine" capable of astounding efficiency without sacrificing performance.

How is this efficiency achieved? Well, first you have to remember that standard internal combustion engines are only efficient over a narrow power and torque band. In normal cars the engine has to operate over a wide power and torque band. This is very inefficient. Also when you stop the car, the engine keeps idling. This also wastes fuel.

The Prius allows its' engine to operate at its' most efficient power and torque curve, by adding driving force from the electric motor when more power is needed. Excess power from the engine can also be used to charge the battery. The engine therefore runs at its' most efficient speed and the electric motor compensates for the peeks and dips. When you take your foot off the accelerator pedal, the engine is switched off. The engine may still spin, but fuel is no longer supplied. When you press the accelerator again, the engine switches on instantly. When you put your foot on the brakes the engine shuts off and kinetic energy from the forward motion of the car is converted by the motor (now acting as a generator) to charge the battery. This energy can then be used again later, like when you accelerate hard or go up a hill.

During regenerative braking, kinetic energy from the wheels are used to turn a generator which charges the battery


Operation of Hybrid Synergy Drive

display is for 2003 - 2005 model. 2006+ model is the same, but higher resolution



Press power button


When you press the power button, this display might come on depending on the temperature of the catalytic converter. In this case the catalytic converter is cold and the engine is running to heat it up. The engine spins the generator and the energy is put back into the battery. Catalytic converters only work when they're hot. By preheating the "cat", the Prius reduces emissions even it it means having to burn a little petrol.







Pulling away slowly. Only the motor is driving the wheels. Energy is drawn from the battery. This is EV mode.




Normal Driving




When you pull away initially and at slow speeds, energy is fed from the batteries and the electric motor drives the car. Depending on how hard you accelerate, the engine might come on for extra power. Energy may or may not be drawn from the battery. It depends on how hard you accelerate.

Normal Driving


Cruising. Only the engine is driving the wheels. The motor/generator is charging the battery. The engine is running at its' most efficient RPM range. Excess energy is stored.




Normal Driving



Mild acceleration. The engine is driving the wheels and spinning the generator. Some energy from the generator is sent to the battery and some to the motor to provide extra torque for brisk acceleration.







Hard acceleration or hill climbing. The engine and the motor are driving the wheels. Energy is drawn from the battery as well as the generator. Engine RPM is quite high.







During deceleration energy is fed back into the battery from the generator. If you take your foot off the accelerator, the fuel to the engine will be cut off. The kinetic energy of the car will then be put back into the battery via the generator. This is a type of "magnetic" braking as the car is being slowed down by the resistance of the magnetic field in the generators' coils. If the battery should be come full during "regen" the Prius will switch to engine braking.


You're stopped or gliding.