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Mathematical Models of Engines and Hydraulic Pumps The hydrostatic energy storage transmission system's power source refers to a system consisting of an engine, a hydraulic pump, and a hydraulic accumulator. Among them, hydraulic accumulators are used as energy storage components, which mainly affect the power source's working mode, cycle efficiency and energy recovery. This article focuses only on the efficiency of engines, hydraulic pumps, and accumulator systems. It can be seen that the relationship between the engine load and the system pressure and the displacement of the hydraulic pump is Te=pDp2PGm where Te is the engine torque, pp is the outlet pressure of the pump, Dp is the displacement of the pump, and Gm is the mechanical efficiency of the pump.
The efficiency model of the power source system regards the efficiency of the integrated system consisting of the engine, the hydraulic pump and the accumulator as the evaluation index of the best economic matching. The efficiency of the engine and hydraulic pump system refers to the ratio of the actual output hydraulic power of the system to the heat value of the engine input fuel combustion, Gs is the system efficiency, Ge is the engine efficiency, Gpt is the hydraulic pump efficiency, qp is the pump flow, and Te is the engine Output torque; ne is the engine output speed; be is the engine fuel consumption rate; hu is the fuel low calorific value.
Using the surface fitting method, the model parameters A and s are determined to determine the mathematical model of engine universal characteristics, ie, the function relationship of be=f(Te, ne), and the fuel consumption rate is calculated. The efficiency of the power source system with different rotational speeds and displacement ratios can thus yield a set of efficiency curves. The speed and displacement ratio obtained through optimization can meet the best match between the engine and the pump system and the high efficiency of the system.
The Matching Operating Characteristics of the Engine and the Hydraulic Pump System The main factors affecting the fuel consumption of the engine are the operating speed and the load rate, which are determined by the load characteristics of the engine. It can be seen that when the engine speed is 15001900 rmin-1, the fuel consumption rate is the lowest; when the pressure is 12.532.5 MPa and the rotation speed is 12002000 rmin-1, the efficiency of the hydraulic pump is above 90%. By comparison, the engine's economical working area is narrower than the high-efficiency area of ​​the hydraulic pump. This shows that when the engine is working in the economical working area, it can ensure that the hydraulic pump is working in a high-efficiency area. The most ideal working speed range of the system is 15001900rmin-1, and the best speed is 1700rmin-1, but this depends on the allowable speed of the hydraulic pump, which is the allowable speed corresponding to different displacement of the A4VSO series variable displacement pump. According to the results, for the A4VSO series displacement 71,125,180mLr-1 hydraulic pump speed is 22002700,18002200,18002100rmin-1; Therefore, under the engine characteristics conditions, if choose A4VSO series variable pump, the maximum displacement is not Should be more than 180mLr-1, in order to meet the system can be matched in the high efficiency zone, in the 12002000rmin-1 speed range, the system can also obtain a more economical match. The best match is obtained with less than full displacement, because in this case, the variable displacement pump can be operated at high speed so that the engine can work in the lowest fuel consumption area. It is known from the literature that when the suction port is under atmospheric pressure and the displacement of the hydraulic pump is reduced from full displacement to 70% displacement, the pump speed can be increased by about 25%. It is known that the system pressure ps is 1530 MPa in the economic zone. The power matching is satisfied within the engine so that the engine can reach or approach the full load rate under different loads. This shows that setting the working pressure of the system to 50% 90% of the maximum pressure of the system can not only meet the requirements for high-efficiency work, but also increase the safety and service life of the system components, and at the same time provide sufficient energy recovery. space.
Conclusion Using the test data and characteristic curves of the engine and the hydraulic pump, the mathematical model of the power source system, the system evaluation index and the efficiency map were established. The speed and power matching characteristics of the system are analyzed to obtain the system matching efficiency. The working speed of the power source system composed of engine and hydraulic pump is 15002000rmin-1, the working pressure of the system is 1530MPa, and the displacement pump displacement ratio should be varied between 0.61.0. Under these three conditions, the power source system can be To achieve the best economic matching efficiency in the economic zone. The use of a variable displacement pump in a power source system is more reasonable than a quantitative pump.
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