Power plants – Pressure fluid source and motor – Having a signal – indicator or inspection means
Patent
1994-01-03
1996-02-27
Lopez, F. Daniel
Power plants
Pressure fluid source and motor
Having a signal, indicator or inspection means
60452, F16D 3302
Patent
active
054938619
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a hydraulic system with a pump and at least one load supplied by the pump.
A hydraulic system of that kind is known from DE-PS 25 14 624. There, the control valves are in the form of proportional valves, upstream of each of which there is connected a compensating valve which keeps the pressure drop at the proportional valve constant. The pump has a fixed delivery volume. The bleed valve returns an amount of fluid under pressure to the tank that is sufficiently large for the pump pressure to lie above the maximum load pressure by a predetermined pressure difference, which is preset by a spring acting on the slider of the bleed valve.
Instead of the pump with a fixed delivery rate and bleed valve, it is furthermore known (DE-OS 37 02 000) to provide a pump with a variable delivery rate which is adjusted with the help of a pump control device. This control device includes an electronic control apparatus which is supplied with position signals from the sliders of the compensation valves.
In a hydraulic system with a pump control device it is furthermore known (DE-OS 37 16 200) to use an electronic control apparatus supplied by setting devices with setting signals which, after electronic processing, are relayed as corrected setting signals to the proportional valves. If a further load is connected up with the help of a setting device, the control apparatus also ensures that the pump is correspondingly adjusted. In addition, if a desired value is specified, as a result of which the pump has to deliver more than the maximum delivery rate, the power demand of the load is moderated.
The invention is based on the problem of improving the operation of hydraulic systems. The basic concept of the invention consists in using the bleed valve in new functional relationships.
According to the invention, a pump control device is present, that is, a variable pump is provided. Such pressure control devices are, however, comparatively slow-acting. Sudden load pressure peaks, for example, when a load is suddenly switched off, have an effect throughout the entire hydraulic system. This disadvantage is prevented with the help of the bleed valve which in normal operation has no influence at all because it is closed as a consequence of the choice of its pressure difference in relation to the pressure difference of the pump control device, and only opens when the said pressure peaks occur. The slider of the bleed valve responds quickly so that the pressure peaks are not able to have an effect in the hydraulic system. This measure also does not require a large outlay, because in a conventional hydraulic system with a variable pump and a standard construction of the control valves, in particular of the proportional valves, only the bleed valve needs to be added.
The invention also is concerned with the problem of the slow response of the pump control device. Because the setting signals from the setting device appear before the control valves are actuated, the pump delivery rate is pre-adjusted in good time. This may, however, still be inaccurate. It therefore has superimposed on it a control based on the pressure difference signal which leads very quickly, namely, when the bleed valve has just closed, to the desired pump delivery rate.
According to one form of the invention which is suitable both for variable pumps and for fixed pumps, results in the hydraulic system being prevented in a simple manner from being overloaded. The pressure difference between the pump pressure and the maximum load pressure dependent on the bleed valve is in fact a measure of the loading on the system. If the pressure difference is compared with difference limits that are stored in the control apparatus, the loading limit zone is identified so that an overload protection is afforded by throttling the control valves.
The overload protection can be further improved by using other features of the invention, because the intensity of the throttling is matched from the start to the particular difference limits exceeded.
On account of the
REFERENCES:
patent: 4738102 (1988-04-01), Kropp
patent: 4870819 (1989-10-01), Walzer
patent: 4967554 (1990-11-01), Kauss
patent: 4967557 (1990-11-01), Izumi et al.
patent: 5056312 (1991-10-01), Hirata et al.
Danfoss A/S
Lopez F. Daniel
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