Power plants – Pressure fluid source and motor – Having a signal – indicator or inspection means
Patent
1993-12-22
1995-09-26
Lopez, F. Daniel
Power plants
Pressure fluid source and motor
Having a signal, indicator or inspection means
60461, 91 1, 91462, F16D 3102
Patent
active
054525799
DESCRIPTION:
BRIEF SUMMARY
The invention is concerned with a hydraulic system with a pump and at least one load, which load is connected by way of two motor lines for input and output of fluid under pressure to a valve operable by a setting device, wherein each motor line is assigned a load pressure-sensing point, a first comparator establishes which motor line is carrying the higher load pressure, and a control means operates in dependence on the higher load pressure and on an associated change-over valve.
A hydraulic system of that kind is disclosed on page 106, FIG. 1 in the periodical "Ohydraulik und Pneumatik".sup.1 34 (1990). A change-over valve serves as the first comparator, with the aid of which the higher load pressure in each case is rendered effective in the load pressure-sensing line. This serves on the one hand for the triggering of a compensating valve, which holds the pressure drop at the proportional valve constant, and on the other hand for an adjustment of the pump so that the pump pressure lies slightly above the highest load pressure of the system. In this manner the load pressure is used directly as the hydraulic pressure signal.
FIG. 2 of the same citation shows that the load pressure and the pump pressure can be converted by pressure-to-voltage converters into electrical load pressure signals and pump pressure signals respectively, and then be further processed digitally. This means that a compensating valve connected upstream of the proportional valve can be omitted, and a valve regulator with characteristics correction can be used in its place inside the control means; this valve regulator determines the correct position of the proportional valve in dependence on pump pressure, load pressure and setting signal. Besides that, the digital control means is able to adjust the delivery state of the pump, taking into account all the requirements of the load.
In both cases there are problems when a load is being operated externally, that is to say, represents a negative loading for the hydraulic system. In that case, the output-side motor line carries the higher load pressure which may lead to malfunctions both at the proportional valve and in the pump delivery.
The invention is based on the problem of providing a hydraulic system of the kind mentioned in the introduction, in which operation with a negative loading can be recognised in a simple manner and therefore be taken into account in the control.
This problem is solved according to the invention in that a pressure-to-voltage converter is provided, which supplies an electrical load pressure signal corresponding to the higher load pressure to the control means, a directional signal identifying the displacement of the valve from the neutral position is arranged to be generated, and the control means includes a second comparator which establishes whether the input-side motor line identified by the directional signal is carrying the higher pressure and processes the load pressure signal in dependence on the result of the comparison.
By operation of the setting device, the valve is displaced from its neutral position in the desired direction. The direction of movement of the load, and thus the input-side motor line, is established in this manner. This is identified by a directional signal. The first comparator ascertains which motor line is carrying the higher load pressure. The result of its comparison and the directional signal therefore enable the second comparator to determine whether the input-side motor line is carrying the higher pressure. When this is the case, then operation is the normal operation with a positive loading, in which the effective load pressure signal is used in the customary manner. If, on the other hand, the second comparator establishes that the output-side motor line is carrying the higher pressure, the detected load pressure must be taken into account in a different way. For example, the valve is reversed. In the case of pump control, the delivery rate can be increased for the same reason, or, if several loads are connected in parallel
REFERENCES:
patent: 5138838 (1992-08-01), Crosser
patent: 5218820 (1993-06-01), Sepehri et al.
Danfoss A/S
Lopez F. Daniel
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