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The consumption of fossil fuels is one of the largest problems facing humankind. One of the heaviest users of our non-renewable resources is the automotive industry, in particular, the heavy road transport sector. Tightening worldwide legislation aims to place restrictions on the heavy transport industry to reduce its use of fossil fuels and reduce the levels of pollution being released to the atmosphere. Although several different alternatives to the conventional Internal Combustion Engine (ICE) have been investigated, none have as yet become a competitive source of energy. Alternative research into development of hybrid-drive vehicles was specifically concerned with electric hybrids especially for passenger vehicles. Currently there is a resurgence of interest in the Hydraulic-type Hybrid Vehicle (HHV) in application to commercial and to a lesser degree to large passenger vehicles. This paper gives an overview of hydraulic hybrid technology.

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The objective of the research project, the subject of this paper, is to develop ahybrid diesel-hydraulic drive for large commercial vehicles e.g. urban freight delivery, buses or garbage trucks. The system incorporates a Regenerative Drive Shaft (RDS) which consists of a variable pump/motor coaxial with the drive shaft.Hydraulic energy is supplied to the wheels of the vehicle in parallel with energy supplied by the truck drive system.The objective is to store/supply energy to assist truck braking/acceleration.The unit works as a pump during braking of the truck and thus performs two functions-it stores energy in the accumulator and at the same time provides hydrostatic braking. When the truck accelerates the pump operates as a motor assisting the truck engine. The major advantages of the proposed RDS system over other systems is the application of microprocessor control to optimise power utilisation and elimination of losses during transfer of energy between the truck drive system and the hydraulic pump/motor. This technology offers additional advantages of lower noise, increased reliability, lower maintenance costs and a substantially reduced environment impact. The paper presents and discusses the development of the system, modelling approaches and the results of preliminary performance tests on 10 ton vehicle.