Motors: expansible chamber type – With motive fluid valve – Relatively movable serial valves
Patent
1995-02-16
1997-06-24
Nguyen, Hoang
Motors: expansible chamber type
With motive fluid valve
Relatively movable serial valves
91448, 91461, F15B 1108, F15B 1304
Patent
active
056408927
DESCRIPTION:
BRIEF SUMMARY
FIELD AND BACKGROUND OF THE INVENTION
The present invention relates to a hydraulic control device having a directional valve by which the direction of movement and the speed of a hydraulic consumer, especially a mobile working device, can be modified. Such a hydraulic control device is known from actual use on excavators.
Mobile working machines such as, in particular, wheel excavators or wheel loaders frequently operate without support. Under these circumstances the entire vehicle can be incited to oscillation upon rapid actuation of a working function, these oscillations then being propagated via the cab to the driver. If the oscillating circuit is closed over the operating element of the pre-control device, the operating movement is unstable and can no longer be controlled. A sudden transition to large control signals namely brings about large forces of acceleration so that strong oscillations can be excited. Furthermore, the control slide of the directional valve is then in a steeply ascending region of the characteristic curve of the directional valve and thus in the region of high amplification, so that the tendency to oscillate is further promoted.
In order to dampen the oscillations it is known to install valve arrangement developed as throttle non-return valves in the control lines to the control slide of the directional valve. Good damping action would be obtained if the damping cross section were selected very small. In that way, however, the course of the movement is delayed. A delaying of the start of the movement is annoying for the part of the operator and leads to the danger of overcontrol. A delay in the end of the movement results in an "overrunning" of the working device, which makes precise work difficult and furthermore represents a safety risk. For these reasons, only slight damping is used in the known control devices, which, however, does not reduce the susceptibility to oscillation of the entire system to the extent desired.
SUMMARY OF THE INVENTION
The object of the invention is so to develop such a hydraulic control device so that the tendency of the entire system to oscillate can be further reduced without unacceptable delays in the course of the movement of a working device.
According to the present invention a hydraulic control device is provided, wherein the damping of the movement of the control slide of the directional valve can be controlled as a function of the control pressure in a second control chamber. With a hydraulic control device in accordance with the invention, the two requirements, which at first sight might appear to be contradictory, for a good damping of oscillations and a delay-free start and end of the operation can be satisfied simultaneously. The movement of the control slide is then essentially only damped when the pre-control device is in the region of high control pressures and thus of a steep rise of the stroke/volume flow characteristic curve of the directional valve. Upon the start and the end of the movement, there is also passed over, in each case, a region of the characteristic curve in which the control pressure and the rise of the characteristic curve are slight and which is generally referred as the fine-control region. In this region, the damping is greatly reduced or entirely done away with in the manner that the damping of the movement of the control slide (9) is disconnected below a given control pressure and connected above said control pressure. The start of the movement and the end of the movement of an operation are therefore not delayed.
As already stated, the characteristic curve of known directional valves have a slowly rising region and a steeply rising region, the transition between the two region being located at about one third of the maximum control pressure. According to a feature of the invention, it is now advantageously provided that the movement of the control slide can be damped as from a control pressure which is about one third of the maximum control pressure. As long as the control pressure is below one third of t
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Kauss Wolfgang
Stellwagen Armin
Farber Martin A.
Mannesmann Rexroth GmbH
Nguyen Hoang
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