The hybrid hydraulic vehicle (HHV) is a new technology that uses hydraulic power in conjunction with the conventional vehicle internal combustion engine (ICE) in order to improve fuel economy for road vehicles propulsion. In addition to propulsion, a portion of the hydraulic power can be used to drive hydraulic accessories, through a power take-off point. A power take-off method with HHV decreases the cost of implementation on the vehicle as the main power source is readily available. The transferred power, with the appropriate interface using controlled hydraulic circuit, drives the accessories system.
This research preliminary analysis investigates three proposed systems: hydraulic intensifier, hydraulic transformer, and pump/motor configuration or hydrostatic system. The research studies the systems efficiencies and the impact of these systems on the main hydraulic circuit. The impact is measured by the system ability to isolate the hydraulic accessories fluid from the main circuit fluid in order to maintain the main circuit performance. The hydraulic intensifier and the hydraulic transformer do not isolate the main source fluid from the load fluid effectively. The estimated efficiency is around 55% for the hydraulic intensifier while it is around 90% for the hydraulic transformer. Accordingly, both of them are not suitable for the application.
A hydrostatic transmission or the pump/motor configuration provides complete isolation as the load fluid is separated from the source fluid. In addition efficiency expected to be in range of 80% to 90%. Consequently, the hydrostatic transmission system design is used in this application.
A comprehensive analysis is performed on the hydrostatic transmission. The analysis starts by defining two pressure working ranges from hydraulic tools manufacturer's datasheets; the low pressure at 2,000 psi and the high pressure at 10,000 psi. After selection of loading pressure, the design of the driving pumps, and hydraulic motor with the control valve is performed. The analysis includes controller design to the system in order to maintain the load demand.
The hydrostatic transmission system design is modeled and then simulated using MATLAB/SIMULINK. The model simulation incorporates several loading cases in order to define the time required to drive the hydraulic accessories efficiently. The model result reports the maximum operating time and the input power consumption rate for each load case. The input power consumption rates and the assumed efficiencies are verified by comparing to the manufacturer's datasheet values and to the model output efficiencies. Conclusions and recommendations are provided at the end of this research.