When a conventional vehicle applies its brakes, kinetic energy is converted to heat as friction between the brake pads and wheels. This heat is carried away in the airstream and the energy is effectively wasted.
Regenerative braking refers to a process in which a portion of the kinetic energy of the vehicle is stored. Energy normally dissipated in the brakes is directed by a power transmission system to the energy store during deceleration. That energy is held until required again by the vehicle, whereby it is converted back into kinetic energy and used to accelerate the vehicle.
Regenerative braking promises significant gains in town driving since 62,5% of energy is dissipated in the metropolitan area due to frequent braking. If all brake energy could be regenerated with no loss in the regenerative system, fuel consumption would be improved by 33%.
HEV can give a saving of energy if, with suitable control equipment, they convert Kinetic energy to electrical energy for re-use. The drive motor can be made to operate as a generator supplying a resistive load and braking torque to the wheels. In regenerative braking, the electric motor operates as a generator to charge the battery.
Integrated Motor assist:
The Integrated Motor Assist (IMA) system owes much of its remarkable performance to the application of numerous technologies developed over the last four decades. Honda for example have used their knowledge in lean-burn combustion, low emissions, variable valve timing, high efficiency motors, regenerative braking and nickel-metal hybrid battery to their advantage in developing the IMA system for their insight model.
The key part of the IMA system is the intelligent power unit (IPU), which controls the flow of electricity to and from the motor, and controls the storage of the electrical energy in the battery pack. During deceleration and braking, the electric motor acts as a generator, in order to recharge the battery pack. More than 95% of the energy during the braking cycle is recovered for storage in the batteries.
Battery Management system:
The primary goal of the Battery Management System (BMS) is to increase the cell life of the batteries in a HEV. More commonly referred to as the Electronic Control Unit (ECU), it manages the power flow between the generator, battery and the electric motor. By keeping a constant monitor over various driving conditions, the BMS allows the transmission to gain optimal power and fuel consumption from the power train.
In a series configuration HEV the engine never directly powers the vehicle. The concept of the engine is to charge a large battery pack, which in turn will power the electric motor in order to provide power to drive the wheels. One of the disadvantages of the series configuration is that the total system efficiency is reduced due to the conversion of mechanical to electrical power and back to be stored when converted in order to drive the wheels.
The engine in a parallel configuration connects straight to the transmission as does the electric motor. During less intensive power cycles, the parallel hybrid can utilize the engine in charging the battery pack. In this configuration, HEV has the ability to turn off the engine and run purely off the electric motor for short urban driving. Thus, behaving as a fully functional EV, and becoming virtually emissions free during these periods. This cannot be achieved with the series configuration as there is only a direct link from the ICE to the transmission via the electric motor.
There are a few advantages a parallel configured system has over a series configuration. Firstly, unless the battery is low of charge the engine noise is kept to a bare minimum because the engine is only operating when the vehicle is moving. As there is only one conversion between electrical and mechanical energy the system is far more efficient than the series HEV.