Drive system

The term “driveline” denotes an assembly comprising the engine, clutch, gearbox, drive shaft and axle differential. Depending on the exact concept, hybrid vehicles also have other components such as one or more electric motors, a battery and a generator.

Driveline design: how the components interact

On vehicles with a hybrid drive system, an internal combustion engine is combined with an electric drive machine. The internal combustion engine converts thermal energy, and the electric motor converts electric energy, into mechanical force and uses it to drive the vehicle.

This is where the gearbox comes into play, as it provides several gears for driving the vehicle. Due to the various gears in the gearbox, the internal combustion engine remains within a certain speed and consumption range while it is powering the vehicle.

The drive shaft transmits the drive forces to the axle differential. These components (which are also called the “axle drive”) come with a fixed transmission ratio – i.e. one without gears – which optimises how the drive forces are transmitted to the wheels.

Several drive type options are available for vehicles with a hybrid drive:

Series drive

The internal combustion engine drives a generator. The electric motor then uses the electrical energy from the generator to power the vehicle. As such, the power is transmitted in series here: internal combustion engine, generator, electric motor

Parallel drive

Both the internal combustion engine and the electric motor drive the drive wheels. The power from the drive units is added together. The power flows in parallel from the internal combustion engine and/or electric motor.

Split-power drive

A split-power drive combines the series and parallel concepts. With this system, the drive can either be provided solely by the electric motor (serial energy conversion by means of internal combustion engine and generator) or by the electric motor with the internal combustion engine in parallel.

Range extender

The use of a range extender is another option supported by hybrid technology. It is a small internal combustion engine with a generator. If the battery is discharged, it provides the energy for the electric drive power.

It goes without saying that the driveline has to meet very extensive requirements. The driveline must:

• transmit the engine’s power,
• distribute the drive forces to the wheels,
• combine reliability and comfort in one,
• be subject to low levels of wear,
• work quietly and as efficiently as possible.