Motors: expansible chamber type – With motive fluid valve – Relatively movable serial valves
Patent
1995-06-06
1997-12-30
Nguyen, Hoang
Motors: expansible chamber type
With motive fluid valve
Relatively movable serial valves
91448, F15B 1108
Patent
active
057017956
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a hydraulic system with a pressure source, a pressure sink, a work motor, a main valve which is arranged between the pressure source and the pressure sink on the one hand and the work motor on the other hand and is connected to the work motor by way of work connections, a compensating valve, namely, an input compensating valve, between the pressure source and main valve, and an additional valve arrangement between the main valve and the pressure sink, which controls the volume flow from the main valve to the pressure sink.
In the following description, for the sake of simplicity the pressure source is called a pump and the pressure sink is called a tank.
A system of that kind is known from EP 362 409 B1.
In another known system (DE 34 36 246 C2), the compensating valve controls the volume flow of hydraulic fluid through the main valve in dependence on the pressures in the input connection of the main valve, in the tank connection of the main valve and in the work connection of the main valve, which is connected to the single work chamber illustrated here of the work motor. Hydraulic fluid flowing out of the work motor flows through the main valve back to the tank.
In another hydraulic system (WO 90/12165), the compensating valve is controlled by the higher of the two pressures in the work connections. The main valve here additionally assumes the function of directional control. Hydraulic fluid flowing back from the work motor flows through the main valve directly to the tank.
WO 88/05135 describes a control arrangement for hydraulic cylinders that is manually operable. The control arrangement described in this publication corresponds to the main valve of the two above-described systems. This main valve is constructed so that the volume flow through the valve is automatically reduced whenever the work pressure across the valve approaches its maximum. This in an advantage in particular in the connection with cranes operating with the maximum admissible load close to their maximum extension. From this literature reference it is also known, in the case of a negative loading, for example, when lowering a load, to use a combination of inner and outer slide valve so that the volume flow through the tank connection reduces automatically. An especially slow movement can consequently be achieved, which in the operation of cranes is advantageous for safety reasons, particularly when lowering loads. This makes the construction of the main valve very complicated, though.
The invention is based on the problem of providing a hydraulic system combining improved control facilities with a simple construction.
This problem is solved in a system of the kind mentioned in the introduction in that the valve arrangement has a controllable degree of opening.
This measure enables the pressure difference across the main valve to be controlled or regulated not only as hydraulic fluid is flowing to the motor but also as it is returning to the tank. The opportunities for intervention, which can be used for a more rapid regulation or control, are therefore increased. In particular, fluctuations in the hydraulic system can be suppressed. With a negative loading, that is, when the work motor is operating as a pump, the volume flow between the main valve and the tank can additionally be controlled. Because of that, the main valve can be kept fully open, for example as a load is being lowered. It is also no longer necessary for the volume flow to be restricted by the input compensating valve, which results in a minimum pressure demand on the pump. This leads to greater efficiency, since the power loss in the main valve and in the input compensating valve can be sharply reduced. Moreover, reliability is improved through an increased redundancy, since the volume flow from the work motor to the tank can be interrupted both by the main valve and by the additional valve arrangement. Even if one of these two parts should be defective, the other part is still in a position to hold the work motor, or rather the load suspend
REFERENCES:
patent: 4066004 (1978-01-01), Alcalay
patent: 5000001 (1991-03-01), Christensen et al.
patent: 5083430 (1992-01-01), Hirata et al.
patent: 5207059 (1993-05-01), Schexnayder
Danfoss A/S
Nguyen Hoang
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