Integrated Motor Assist (IMA)

How the Honda IMA system works


The theory behind IMA is to use regenerative braking to recapture some of the energy lost through deceleration

Honda's IMA system has already received wide acclaim for its economy, practicality and ease of use. It has been re-engineered to be even lighter, more efficient and more intelligent than ever. The IMA uses an electric motor mounted between the internal combustion engine and transmission to act as a starter motor, battery charger, and assist the internal combustion engine with extra power and torque.

The theory behind IMA is to use regenerative braking to recapture some of the energy lost through deceleration, and reuse that energy later on to help accelerate the vehicle. This has two effects: it increases the rate of acceleration, and it reduces the work required of the petrol engine. The acceleration boost is important as it allows the engine to be scaled down to a smaller but more fuel-efficient variant while retaining the power of a traditional engine. This smaller engine is the primary reason cars equipped with IMA get better highway mileage than their more conventional counterparts.

Additionally, vehicles equipped with IMA can shut off their engine when the vehicle stops and use the electric motor to rapidly spin it back up when the driver releases the brake pedal. They also have a conventional starter as a backup, making it the only production petrol/electric hybrid system that can operate with its high voltage electric system disabled, using only its engine like a traditional vehicle.


For a demonstration of IMA operation, try the simulator below.

The Honda IMA Technical Detail:

The engine is the main power source. 

Honda believes that the engine plays an all-important role, even in combined petrol engine and electric motor powerplants.

A variety of combined petrol and electric systems are in use in automobiles today. Honda’s lightweight and simple design features a parallel system in which the motor assists the engine as required.

Since in a parallel system the engine serves as the main power source, Honda has further refined the engine, developing a new i-VTEC engine around the core of its original valve-control technology. In addition to achieving both powerful torque and high fuel economy, the new engine optimises efficiency with such innovations as deactivating all cylinders during deceleration for improved regenerative braking. This results in outstanding environmental performance combined with impressive acceleration.    

Motor-alone and cylinder-Idle modes provide improved fuel efficiency and increased driving pleasure.


The electric motor provides ample power to allow low-speed cruising under motor power alone. Moreover, the i-VTEC engine controls valve operation to permit deactivating of all four cylinders, for improved regenerative braking efficiency during deceleration.    

Vehicle Stationary Startup and acceleration
 Idle Stop  Motor Assist
Low-speed cruising/gentle acceleration High-speed cruising
All 4 cylinders deactivated, the vehicle is powered by the motor alone  Vehicle powered by engine alone
Rapid acceleration Deceleration
Motor assist All 4 cylinders are deactivated and energy is recovered through regenerative braking

Slim and compact, the motor of the Honda IMA System is no larger than the flywheel of a conventional engine.

In a conventional car there is a flywheel between the engine and the transmission, serving to smooth out fluctuations in engine torque for smooth engine operation. The electric motor in the Honda Hybrid System is slim and compact enough to fit into the space usually taken up by the flywheel (the rotor in the electric motor serves as the flywheel.)  This is why the Honda IMA System fits in to existing vehicles as is.

Honda is hard at work on further fuel efficient technology development to make petrol/electric cars easily integrate into our lives.