Thursday, 10 March 2016

IMA Hybrid System

Caution!! The Honda IMA system uses high-voltage circuits (158 V). For this reason, prior to working on the IMA system, turn off the main switch to cut off the electric circuit. Moreover, the operator must respect the security measures corresponding to work with cables and high voltage components.

The Honda Civic IMA (Integrated Motor Assisted) uses a hybrid system which operates in parallel with the heat engine. The heat engine is normally driven, while the electric motor assists the heat engine. The electric motor acts as a generator during deceleration and braking.

The heat engine is equipped with the i-VTEC system, and a valve pause system that reduces engine pumping loss and increases the generation of electric energy during deceleration. 

The IMA motor is mounted directly to the engine crankshaft. It works as a motor assist unit to the engine in order to reduce fuel consumption and increase the engine output (this allows a 30% torque increase and a 46% combined output). The IMA motor also acts as a generator during deceleration and as a starter motor. It is a synchronous motor formed by a 3-phase stator and a rotor of natural magnets. A commutation sensor detects the rotor position and its rpm speed at all times.

The vehicle uses a nickel-metal hydride battery (NiMH). Its function is to assist the hybrid system with the required voltage. The battery consists of eleven modules and each module contains twelve cells of 1.2 volts, providing a total nominal voltage of 158.4 V and 5.5 Ah.

IMA System Modes of Operation
Heat Engine Start-up
Under normal conditions, the IMA motor of the hybrid system is the one that starts the heat engine. The electric energy is provided by the high-voltage battery of the hybrid system. If the high-voltage battery is discharged or its temperature is excessive, the engine is started up as in conventional vehicles.

When the vehicle accelerates, the IMA motor provides extra torque and the motor performance is improved (provided that the battery charge is sufficient). This allows for greater fuel economy.

Constant speed is less than 50 km/h
At certain times, if a constant speed is kept and the high-voltage battery allows it, the heat engine electronics stops injecting petrol. The i-VTEC system keeps the valves closed and the vehicle is propelled only by the IMA motor. The only conditions to be met are that a speed of less than 50 km/h with the motor speed of less than 1,300 rpm should be maintained.

During deceleration, the IMA motor operates as a generator, generating electricity to be stored in the high-voltage battery.

At rest
When idling, if the battery charge is above a certain threshold, the heat engine shuts off completely, increasing fuel economy (Start-Stop system). During that time, the high-voltage battery keeps supplying power to the A/C compressor and the 12 V electrical system. The heat engine is started by the IMA motor after releasing the brake pedal.

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