Analysis and test on circuit characteristic of multi-stage constant power governing system using double-stator pump

Abstract: Traditional pump-motor constant power governing system can achieve power matching between the load and the prime mover to reduce energy waste under the conditions with the constant power load. In practical application, some conditions demand hydraulic system outputting constant torque but different speeds. For example, agricultural machinery walking in the same road conditions requires different speeds to choose. However, limited by the governing principle (the product of rotational speed and torque will be a fixed value), traditional pump-motor constant power governing system can't meet the above conditions. So it can only use throttle governor, which will inevitably lead to energy waste and efficiency decrease. Therefore, it's necessary to research a new hydraulic system which can meet multi-stage constant power conditions in principle. New double-stator pump (motor) offers the possibility of studying multi-stage constant power governing system. Because internal and external multiple pumps exist in one housing implements and share one rotor, double-stator pump can output a variety of different flows by controlling the working modes of the respective pumps. It is used to replace the old pump in the traditional pump-motor constant power governing system which then becomes a new multi-stage constant power governing system. A comparative analysis of the circuit characteristics was carried out between the multi-stage constant power governing system and the traditional system. Then a test platform was set up to carry out the experiment. The results indicated that the three-stage constant power governing system composed of single-acting double-stator pump could meet constant power condition, which was just as the traditional system. Under the same condition of constant power load, the common quantitative pump hydraulic system's transmission efficiency was only 82%-86%, but both the traditional pump-motor constant power governing system and the three-stage constant power governing system could reach 94%, at least increased by more than 7% compared with the former. Besides, by changing the working mode of double-stator pump, the multi-stage constant power governing system output multi-stage speeds and constant torque. So it could meet multi-stage constant power conditions without throttle governor, which meant more energy was saved. For instance, the multi-stage constant power governing system and the traditional pump-motor constant power governing system both adapted to the condition which needed the power of about 17.5 kW. When the output torque of motor is constant 195 N·m, if the condition's speed requirement dropped from 860 to 540 r/min, the three-stage constant power governing system chose outer pump of double-stator pump working alone to meet the needs of condition. At this time the required power for it was 10.95 kW, which would save 6.67 kW compared to the traditional pump-motor constant power governing system which only used throttle governor to meet the needs of condition. If the condition's speed requirement further dropped to 350 r/min, the three-stage constant power governing system chose inner pump of double-stator pump working alone to meet the needs of condition. And it required 10.95 kW on power, which would save 10.63 kW compared to the traditional pump-motor constant power governing system. The analysis and test not only enrich the application of double-stator pump for the future, but also provide the important reference for the application of constant power governing system in agricultural machinery, engineering machinery, aerospace machinery and other fields to improve their working efficiency.