Hydraulic hybrid drive

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The hydraulic hybrid drive ( English hydraulic hybrid vehicle , HHV) is analogous to the hybrid electric vehicle , an alternate drive system for vehicles.

Principle of the hydraulic hybrid

The vehicle has a classic combustion engine that provides torque or drive power. In addition, at least one hydraulic motor is integrated in the drive train, which draws its energy from a pressure storage device (accumulator). The pressure accumulator is filled with a compressed gas and hydraulic oil. When the gas expands, the oil is displaced and flows through the hydraulic motor into a collecting container (low pressure accumulator). When the vehicle is braked, part of the kinetic energy can be recovered by using a pump integrated in the drive train to pump the oil from the low-pressure tank back into the pressure accumulator. The gas bubble is compressed again in the pressure accumulator. Usually a hydrostatic piston machine is used as the motor. The same hydrostatic unit can be operated as a pump to recover the energy.

Benefits of the hydraulic hybrid drive

Compared to a conventional vehicle with only one internal combustion engine, consumption and emissions can be reduced. This is achieved on the one hand by recovering the kinetic energy and on the other hand by avoiding unfavorable operating conditions for the internal combustion engine. The energy recovery also reduces brake wear.

Types of hydraulic hybrid drive

As with the electric hybrid, a distinction can be made between serial, parallel or power-split hybrid.

Advantages and disadvantages compared to electric hybrid vehicles

There is currently no known series vehicle manufacturer that is considering using a hydraulic hybrid drive. Hydraulic systems and hydrostats in particular have problems with noise.

But if a sufficiently powerful hydraulic system is already on board, a hydraulic hybrid or travel drive can also make sense. As a result, the first near-series vehicles from different manufacturers were garbage trucks. Driving over long distances without an internal combustion engine is hardly possible with the hydraulic hybrid, but load peaks in the garbage disposal as well as when starting the vehicle can be intercepted and braking torques can be recuperated.

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