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Hybrid Drive Trains | Hybrid Vehicles

Hybrid Drive Trains

Hybrid vehicles

The term “hybrid drive” denotes such vehicles’ drives with more than one drive source. Hybrid drives can incorporate several similar or dissimilar types of energy stores and/or power converters.

The goal of the hybrid drive developments is to combine different drive components, such that the advantages of each are utilized under varying operating conditions in such a manner that the overall advantages outweigh the higher technical and cost outlay associated with hybrid drives.


Hybrid drive trains.

Hybrid drive trains are broadly classified into series and parallel depending on the configuration of the power source.



In a series drive train, only the electric power is coupled to the wheels. The second power source converts fuel energy into electric power. This electric power is then passed in a series fashion through the electric drive and motor to the wheels. Typically, an IC engine is coupled to an alternator to provide fuel-based electric power. The engine and alternator combination is often referred to as an auxiliary power unit.

The HYBRID SERIES engines have the following characteristics:

The engine and the energy storage devices are closely coupled. more efficient, satisfying light load power demands.


In parallel hybrid drive trains, two power sources operate in parallel to propel the vehicle. Power from the electric motor and internal combustion engine is combined via the vehicle transmission to satisfy the road power demand.

Parallel hybrid engines have the following characteristics:

Drive train losses between the engine and the engine and the road are minimal. generally more efficient and satisfying in high power demand.

Parallel hybrids have speed coupling between the road and the engine. Series hybrids do not have speed-coupling. Both series and parallel hybrids can be operated with the engine to road power decoupling. Both parallel and series hybrids can be implemented with large engines and small energy storage, or vice versa.

Series and parallel combined systems.

This combined system called the dual system, has a generator and a motor, features characteristics of both the series and parallel systems, and the following systems are possible.


Switching system

This implies the application and release of the clutch switch between the series and parallel systems. For driving by the series system, the clutch is released, separating the engine and the generator from the driving wheels. For driving with the parallel system, the clutch is engaged, connecting the engine and the driving wheels.

Since city driving requires low loads for driving and low emissions, the series system is selected with the clutch released. For high-speed driving where the series system would not work efficiently due to higher drive loads and consequently higher engine output is required, the parallel system is selected with the clutch applied.

Split system

This system acts as a series and parallel systems at all times. The engine’s output energy is split by the planetary gear into the series path and the parallel path. It can control the engine speed under variable control of the series path by the generator while maintaining the mechanical connection between the engine and the driving wheels through the parallel path.

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