Hydraulic Hybrid Technology Review – Perspectives and Benefits of its Implementation on Public Transportation Vehicles

Abstract

IC engines amount to 25% in global energy consumption, which is mostly due to their massive share in road transport of approximately 99%. The motivation for development of fuel efficient vehicle propulsion systems arises from strong dependence of the transportation sector on fossil fuels and the need for a rapid response to the global warming challenge. Hybridization has, globally, proven its capabilities in enhancing the powertrain efficiency and is the only technology offering significant breakthroughs in near and mid-term. While there are a number of approaches, Hydraulic Hybrid Technology (HHT) has been lately utilized as an alternative power source for vehicles. HHT gives unique advantages for easy and cost-effective implementation in current production vehicles as well as an aftermarket solution. It seems to be the replacement for expensive, bulky and environmentally hazardous battery technology. Hydraulic energy conversion and storage provide exceptional power density and efficiency making them ideally suited for regenerative powertrain design. It is particularly efficient in city traffic conditions, characterized by frequent stops, coasting and long idling periods. Additionally, emissions are reduced, particularly at idling and low speeds, compared to conventionally powered vehicles. While HHT is still in the prototype and simulation stage, this paper reviews current state-of-the-art.