Parallel Hybrid Electric Vehicle

In parallel hybrid electric vehicle, the electric motor and the internal combustion engine (ICE) are installed so that they can both individually or together power the vehicle.  

The drive train for a parallel hybrid is more complex than that of a series hybrid as both the electric motor and the APU must be mechanically linked to the driveshaft. Since parallel hybrids only works with APU’s that produce a mechanical output, fuel cells cannot be used for this option. In the parallel hybrid configuration, an APU capable of producing motive force is mechanically linked to the drive train. This approach eliminates the generator of the series approach. Then the APU is on, the controller divides energy between the drive train (propulsion) and the batteries (energy storage). The amount of energy divided between the two is determined by the speed and driving pattern. When the vehicle is under acceleration, more power is allocated to the drive train than to the batteries. During periods of idle or low speeds, more power goes to the batteries than the drive train.

In parallel hybrid electric vehicle, in addition to the battery drive, transmission is required to allow the engine to drive the wheels. Moreover there must be a means of coupling the engine, motor and transmission. Further, the batteries in parallel hybrids can be recharged through regenerative braking. Since, parallel drive trains typically use small battery packs, much of the recharging can be done by regenerative breaking.  The main advantage of this configuration is the ability to turn the engine off during idling.

Since motor speed is linked to the engine, the vehicle cannot operate in electric mode other than for extremely low speed. When the APU is off, the parallel hybrid runs like an electric vehicle. The batteries provide electricity to the electric motor which drives the vehicle. The batteries also provide additional power to the drive train when the APU is not producing enough power.

Most designs combine a large electrical generator and a motor into one unit, often located between the combustion engine and the transmission, replacing both the conventional starter motor and the alternator. Accessories such as power steering and air conditioning are powered by electric motors instead of being attached to the combustion engine. This arrangement is good for hiway driving in comparison of city driving. Examples of parallel hybrid electric vehicles are Honda’s Insight, Civic, Accord and Saturn VUE Aura Greenline a, Chevrolet Malibu hybrids etc. The schematic diagram of Parallel Hybrid Vehicle is given in Fig. (a), (b).