| 摘要 |
The first hydraulic pump (10) controls the non-return valve (40) upstream pressure. Pressure upstream of the non-return valve (NRV, 40) tends to close the plug (71) in the pressure limiting valve (70). Preferred features: The control chamber (72) of the pressure limiting valve is connected to a preset pilot valve (77) and via a nozzle (75) with a line (45) upstream of the NRV. Pressure upstream of the NRV is measured by an electronic sensor (44). The first hydraulic pump controller (11, 12, 16, 20) includes a proportional valve (20) controlled as a function of the actual pressure measured by the sensor, and a desired pressure value. Output flowrate is varied by the inclination or eccentricity of the first pump, which is measured by an electronic sensor (15). Its control system (11, 12, 16, 20) includes a proportional valve (20), adjusted in accordance with desired pressure value. The flow of hydraulic fluid from the second pump (50) into the supply line (43) is all or nothing, varying only with pump speed fluctuations. Between the pressure connection (25) of the second pump and the supply line (43) there is a second NRV (60). The second hydraulic pump is a constant delivery pump; its output returns to a tank via a circulation valve. The second pump is alternatively an adjustable delivery pump with control system (11, 12, 16, 51, 52). The control valve (52) includes a piston regulator responding to differential pressure. It tends to reduce flowrate, from the output pressure (25) of the second pump. It tends to increase flowrate, under spring (54) action and from pressure in a control chamber (55) connecting via a nozzle from the pressure connection (25) of the second pump, which is released via a valve (57) to the tank (17).
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