Two simple velocity control systems of a water hydraulic motor are experimentally compared in this study; one with commercial pressure compensated proportional flow control valve and another with parallel-connected low-cost on/off solenoid valves. The aim of the study is to define suitability of these control techniques in a system where good velocity control accuracy is a significant requirement.
In this paper, fuel consumption of a 5.7-ton municipal tractor in a wheel loader application is studied, and methods for improving the fuel efficiency are compared with each other. Experimental data from the baseline machine with load-sensing hydraulics has been gathered during a y-pattern cycle, and the data is inputted to an optimization function having realistic loss models for a hydraulic pump and diesel engine. Dynamic programming is used to analyze different system configurations in order to determine optimal control sequence for each system. Besides optimization of variable engine rotational speed on the baseline system during the working cycle (considering the point of operation), three hybrid supply systems are studied: 1) a hydraulic flywheel, 2) parallel supply pumps and 3) a throttled accumulator. These systems utilize a hydraulic accumulator as an energy source/sink alongside the diesel engine. The optimal sequence for charging and discharging of the accumulator is examined in order to minimize the fuel consumption of the machine. The idea is to use the lowest acceptable, constant engine rotational speed, to cut down the diesel losses. In addition, the study covers an analysis of adjusting the engine rotational speed for each point of operation also when the hybrid systems are considered. The results show that finding advantageous engine rotational speed for each loading condition can decrease the fuel consumption of the baseline machine around 14%, whereas hybridization of the supply system can further improve the result by a couple of percentage units. Hybrid systems also reduce engine’s maximum load by making it more uniform, which allegedly reduces emissions. The possibility of engine downsizing to further improve the fuel efficiency of hybrid systems is not considered, because the maximum engine power is usually determined by the hydrostatic transmission of a municipal tractor. However, the study assumes that actuators are controlled using traditional 4/3 proportional control valves; hence, there are still potential for greater fuel savings. For example, applying independent metering valves on the actuator control can further decrease the system losses.
There is a potential for significant improvement on fuel efficiency of many mobile machines by using hybrid technology as the Diesel engines are often driven at very inefficient operating points in these applications. The load generated by the working hydraulics of a mobile machine is often rapidly changing and contains high peak powers compared to the mean power required. This paper studies three different hydraulic hybrids in a wheel loader application. The study is based on a measured sand-loading Y-cycle. In addition to the hybrid systems, a load sensing proportional valve based reference machine and a modified machine based on independent metering valves are analyzed. All five system alternatives are analyzed systematically to enable a comparison of their fuel efficiency. The study shows that the fuel consumption of the machine can be decreased up to 28 % in such load cycle by using a suitable hydraulic hybrid system.
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