Two auxiliary power sources have been found most practical: electric motor/generators combined with batteries and hydraulic pump/motors combined with hydraulic accumulators. Electric hybrid vehicles have been the first hybrid technology to be mass produced for the commercial passenger car market. A strength of electric hybrids is the high energy density of electric batteries, allowing for large energy storage in relatively compact and lightweight batteries. A substantial shortcoming of electric hybrids is the relatively low power density of both electric motor/generators and batteries at approximately 30-100 W/kgal. This paper presents a hydraulic hybrid vehicle drive train to improve the fuel efficiency of a passenger car. The developed hydro-mechanical drive train enables independent control of the torque at each wheel. The motivation for developing this drive train is a hydraulic hybrid vehicle test bed for the Center for Compact and Efficient Fluid Power at the University of Minnesota. The hydro-mechanical hybrid drive train is modeled and compared to a series hybrid drive train in operation on the EPA Urban Dynamometer Driving Schedule. The hydro-mechanical system demonstrates excellent fuel economy potential, yet requires development work in the area of pump/motors with high efficiency at low displacement fractions. This paper has presented a rudimentary system control strategy that requires significant improvement. Using a formalized optimization of the system controls will create drastic improvements in the system performance. Furthermore, advances in predictive control, such as minimizing the energy stored in the accumulator when expecting a braking event, would be very beneficial to hybrid vehicles. Predictive control could be advanced further by integrating a GPS and communication system into the control computer that would allow the system to predict braking or acceleration events based on upcoming changes in road grade or traffic congestion. The novel innovation presented in this paper that enables independent wheel torque control needs to be exploited for advances in the control of vehicle dynamics. While a good deal of research has previously explored these types of vehicle dynamic controls, they have primarily relied on applying braking systems to certain wheels, which is inherently inefficient. Furthermore, the high torque capability of hydraulics allows a much greater torque differential between wheels, even allowing anti-lock braking without friction brakes. This drive train architecture has the potential to spawn completely new vehicle dynamic control options.
Development of a hydro-mechanical hydraulic hybrid drive train with independent wheel torque control for an urban passenger vehicle
National Conference on Fluid Power, 51 ; 503-514
2008
12 Seiten, 9 Bilder, 3 Tabellen, 11 Quellen
Aufsatz (Konferenz)
Englisch
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