Method for investigating closed-loop hydraulic transmission with accumulator maintenance of overpressure in the suction line of a pump

The aim of the study is to verify the operability, reliability and functionality of a closed-loop hydrostatic transmission, which enhances the durability of the hydraulic drive by isolating the working fluid from atmospheric air and maintaining excess pressure at the pump inlet. The selected research object is a closed-loop hydrostatic transmission configuration, where drain leakage return is carried out by an ejector pump, while a hydropneumatic accumulator serves as a closed hydraulic reservoir that maintains excess pressure. Theoretical relationships for the designed components of the hydraulic system were derived using mathematical modelling by equations of normal dimensionless hydraulic numbers and a Microsoft Excel package. Design methods of continuity and modification were applied to construct the test bench. Based on existing research, the influence of various contaminants on the system failure characteristics was determined, and the positive effect of the purity of the working fluid on the durability and reliability of the hydraulic drive was highlighted. An overview of existing open, combined open-closed and closed hydrostatic transmissions revealed their disadvantages in terms of ensuring fluid purity. A proposed hydraulic schematic formed the basis for designing and manufacturing a test stand for investigating the closed-loop hydrostatic transmission. Criteria for selecting the pneumatic-hydraulic accumulator were defined, and a methodology for calculating parameters was substantiated. A versatile design of the ejector pump, operating under various flow pressure conditions, was developed, including replaceable components for the flow section (nozzles, mixing chambers, throats and confusers). The test program and methodology involve four test algorithms: stand preparation, tests without drain leakage, tests with maximum allowable drain leakage, and tests with intermediate drain leakage volumes, resulting in a total of one hundred sixty experiments. This study allows the feasibility of applying the presented closed-loop hydrostatic transmission in various types of machinery to be assessed.