GB2265189A - Hydraulic control device - Google Patents

Abstract

A device (10) for controlling a hydraulic device (18), has a circulation valve (40) disposed between the pump channel and the tank channel, said valve (40) both in the circulation mode position (80) of directional valve (24) and in the return mode position (82) of valve (24) relieving pressure via a relief line (38), which leads via directional valve (24) to reservoir (36), and in the forward function being kept closed by a piston (50) acted upon by the pump pressure. Piston (50) is opened in the two above modes by means of throttle (60) which causes a pressure drop across the piston when fluid is flowing therethrough. <IMAGE>

Description

Hydraulic control device The invention relates to a hydraulic control device which may be used for a single-action cylinder. A hydraulic device is generally known which has a fixed displacement pump, which delivers continuously and at a fixed delivery rate; a directional valve; a tank; a pump channel, which connects the pump to the directional valve; a consumer channel, for connecting the directional valve to a device to be controlled; and a tank channel, which connects the directional valve to the tank.

The aim of the invention is to provide a hydraulic control device which to a large extent operates in a low-loss manner and is therefore particularly suitable for applications which involve long idle periods and only short operating times.

Accordingly, the invention provides a hydraulic control device having a fixed displacement pump, which delivers continuously and at a fixed delivery rate; a directional valve; a tank; a pump channel, which connects the pump to the directional valve; a consumer channel, for connecting the directional valve to a device to be controlled; and a tank channel, which connects the directional valve to the tank; wherein the pump channel is connected to the tank by a circulation line which incorporates a circulation valve; the circulation valve has a circulation piston which, by its movement, causes the circulation line to be open or closed; the circulation piston is loaded at an opening side in the direction of opening by the pump pressure and at an opposite closing side in the direction of closing by a spring and lies with said closing side in a control chamber; the control chamber is connected via a loading channel to the pump channel and via a relief channel to the tank; the relief channel leads via the directional valve to the tank; the relief channel is connected to the tank by the directional valve in a blocking position, in which the valve blocks the pump channel, and in a return position;; the relief channel is blocked by the valve in a forward position, in which the valve connects the pump channel to the consumer channel.

Owing to the fact that during the idling phase (circulation phase), i.e. while the pump is operating but the cylinder is at rest, a channel parallel to the circulation valve is held open by special control edges of the three-position directional valve and connects the pump channel to the tank channel, the circulation valve is relieved in that said relief channel takes over some of the pressure oil, which would otherwise flow exclusively through the valve, and carries it off in a low-loss manner to the tank. The feed pump also may be relieved as a result of the reduction in the delivery pressure by the relief channel.

On the other hand, the oil pressure needed to extend the telescopic cylinder in the forward throughflow position of the three-position directional valve is available owing to the fact that the special control edges of the relief channel keep the circulation valve closed. However, by providing the channel with a bypass which leads to the tank channel and is normally kept closed by the pressure relief valve, in the event of malfunctions, e.g. overload, pressure oil may be racked off into the tank channel and the device protected from pressure-induced damage.

By means of a further bypass which incorporates the circulation valve, the oil pressure load on the inlet of the valve may be conveyed to the spring-loaded side of the valve piston to counteract the pressure acting on the inlet of the valve so that the circulation valve remains closed during the supply of pressure oil to the cylinders. Said effect may be enhanced by a suitably dimensioned end face of the closure piston and by throttling resistors. Said valve may advantageously be used to actuate a tiltable loading area or the like of a lorry.

In a preferred embodiment of the invention, the directional valve is provided with a housing, in which a bore slidingly receives a valve piston. Said piston is provided with special control edges, which lie adjacent to the bore and, depending on the position of the piston inside the bore, either connect channels opening out into the bore with one another in specific patterns or interrupt the connections. Here it is particularly important for the control edges to be so designed that the bypass bypassing the circulation valve is closed before a connection has been established between the pump channel and the consumer channel. On the other hand, said control edges are so tuned to one another that a direct connection arises between the consumer channel and the tank channel while bypassing the circulation valve and the channel leading from the pump channel to the tank channel.

The circulation valve is preferably spring-loaded at one side and connected at said side to a direct-acting pressure relief valve, and a control line provided with a throttle resistor may lead from the pump channel to the spring side of the circulation valve. When the pressure level set at the pressure relief valve is exceeded, the function of the circulation valve then changes to that of a pressure relief valve.

An embodiment of the invention is illustrated in the drawings and is described in detail hereinafter.

The drawings show: Fig.1 the schematic diagram of the device according to the invention; Fig.2 a broken longitudinal section of a three position directional valve suitable for use in a control device according to the invention.

The schematic diagram of Fig.l shows the hydraulic control device 10. Said device is used to lift the loading area 12 of a lorry. To said end, the loading area 12 is fastened by a joint 14 in a hinged manner to the body 16 of the vehicle, which is otherwise not shown. A piston/cylinder unit 18 is used for lifting. Its cylinder 18 is connected by a joint 20 to the body 16. The piston or the piston rod is fastened by a joint 22 to the loading area. The piston here is of a telescopic construction, with a plurality of pistons being nested telescopically one inside the other.

The cylinder is connected by consumer channel V to a directional valve 24. Said valve is a 3/3-way valve which has three connections and three positions. The control piston, which is diagrammatically illustrated in Fig.2, is displaceable by an actuating and drive device 26 into its various positions, with continuous adjustment being possible.

The drive device 26 represented here is a pressure-mediumoperated piston/cylinder unit, whose piston is clamped between springs 28 and 30 and via corresponding control lines at either end may be acted upon by a controllable pressure and moved in opposing directions. The adjusting movement is transmitted via a piston rod 32 to the piston. The directional valve 24 is connected on the one hand via a pump channel P to a pump 34 and on the other hand via a tank channel T to a tank 36. A further connection of the directional valve 24 is connected to a relief line 38 which is described below.

The pump channel P is connected to the tank 36 via a circulation line which incorporates a circulation valve 40.

The circulation line comprises a channel 2, which connects the input 44 of the circulation valve 40 to the pump channel P, and a further channel t6 which connects the output 48 of the circulation valve 40 to the tank 36. The circulation valve 40 has a circulation piston 50, which projects into a valve chamber and is movable counter to the force of a relatively weak spring 52. The face of the piston 50 remote from the spring 52 is acted upon via the channel 56 of the circulation line 58 by pump pressure and pressed by the spring 52 with the front against a seat at the input 44. As a result of the front lifting from the seat, the two channels of the circulation line are connected to one another. The area of the piston 50 loaded by the spring 52 lies in a control chamber 54.Said control chamber 54 is connected via the relief line 38 already mentioned to the tank connection of the directional valve 24. A throttle 56 is provided at the output of the control chamber 54. The control chamber 54 is further connected via a control channel 58 to the pump channel P. In the illustrated example, the control channel 58 branches off from the channel 42 of the circulation line and is connected to the relief line 38 emanating from the control chamber 54.

Said connection - viewed from the control chamber 54 - lies downstream of the throttle 56. In addition, a throttle 60 is disposed in the loading line 58.

A pressure relief valve 62 is further provided, by means of which the control chamber 54 may be connected to the tank 36.

To said end, the relief line 38 is connected via pressure relief lines 64 and 66 to the tank 36.

In the illustrated example, the pressure relief valve 62 or the pressure relief line 64 is connected to the relief line 38 at a point which - viewed from the control chamber 54 - lies downstream of the throttle 56 and also downstream of the junction with the loading line 58.

The construction of the directional valve 24 is evident particularly from Fig.2. The control piston 70 of the valve is designed so that it may control the pump channel P, the consumer channel V, the tank channel T and the relief line 38.

To said end, the control piston 70 is provided with three annular collars 72, 74 and 76. Said collars are disposed relative to one another in such a way that the annular collar 74, in the middle - known as the blocking - position of the control piston, blocks the consumer channel V. As a result, the pump channel P which lies to the one side of the consumer channel V and the tank channel T which lies to the other side of the consumer channel V are also blocked. The annular collar 76 is used for pressure equalization, with the chamber of the valve disposed at its rear being connected for pressure relief purposes to the tank 36, but has no further function.

The annular collar 72 dispbsed on the other side of the annular collar 74 controls the relief line 38 with its face remote from the annular collar 74. To said end, the valve chamber, towards which said face is directed, is connected to the relief line 38 on the one hand and to the tank channel T on the other hand. When the control piston 70 is then displaced out of its blocking position to the left, its previously mentioned face, which here acts as a control edge, progressively closes the junction of the relief channel 38.

At the same time, the consumer channel V is cleared by the annular collar 74 and so is connected to the pump channel P.

The connection between consumer channel V and tank channel T still remains blocked by the annular collar 74. In the present application, said position is described as the forward position.

When, on the other hand, the control piston 70 is displaced out of the blocking position to the right - i.e. towards the pump channel P, the connection between pump channel P and consumer channel V still remains blocked by annular collar 74.

However, the annular collar 74 progressively clears the opening of the consumer channel V, thereby establishing a connection to the tank channel T. During said-movement, the relief channel 58 continues to stay open so that it is still connected to the tank channel T and ensures unpressurized circulation.

Re: the mode of operation A. Lifting of the loading area 18: The control piston 70 is moved into the forward position by being displaced - according to Fig.2 - to the left.

Said forward position is designated 78 in the schematic diagram of Fig.l. As a result, the pump 34 is connected via pump channel P and consumer channel V to the cylinder/piston unit 18. The relief channel 38 is previously blocked so that the valve 40 switches from its circulation function to a pressure relief function. Via loading line 58, the pump pressure acts also upon the rear of the circulation valve 40 in control chamber 54.

As a result, the circulation piston 50 at the spring side is acted upon both by the pump pressure and by the spring 52. The opposite face is acted upon only by the pump pressure. The force balance at the circulation piston is therefore such that said piston is pressed - in the schematic diagram of Fig.l - to the left against its seat and closes the channel 42 of the circulation line. This allows the establishment of a load-dependent pump pressure in the pump channel P and in the consumer channel V as well as in the cylinder 18.

To avoid overloading, a pressure relief valve 62 is provided, by means of which the pump channel P is connected to the tank 36 via the loading line 58 and via the pressure relief lines 64 and 66 in the event of an excessively high pressure. Said case arises, for example, when the loading area 12 is fully raised and the piston or the loading area moves against a stop which prevents any further swivelling movement. In such a case, the valve 64 opens. As a result of the pressure drop consequently arising at the throttle 56, the valve 10 also opens so that said valve then also functions as a pressure relief valve and carries away the oil delivered by the pump to the tank 36.

At said moment it is advantageous to change the position of the directional valve 24, because carrying away the pressure oil via the pressure relief valve a0, which is set at a high pressure, entails an energy loss of 100%.

The valve 24 is therefore moved into the blocking position 80 for as long as the loading area 18 is to remain raised. In the blocking position 80 all the channels, i.e. pump channel P, consumer channel V and tank channel T, are closed off from one another. Only the relief channel 38 is connected to the tank channel T.

The effect thereby achieved is that the pressure in the control chamber 54 is reduced. Acting upon the piston 50 there is therefore only the spring 52 and, at the other side, the pump pressure. Since pump channel P of the directional valve 24 is blocked, a high enough pump pressure builds up to overcome the spring force and the piston 50 moves - in Fig.1 - to the right. As a result, the channel 42 of the circulation line is connected to the channel 46. The oil delivered by the pump 34 may flow off via the circulation line in a low-loss manner into the tank 36. In the process, a pressure is established which - multiplied by the loaded piston area - is in equilibrium with the spring force 52. The force of the spring 52 should be designed as low as possible because the energy loss of the pump 34 is proportional to the spring force.

B. Return Dosition: To lower the loading area 12, the consumer channel V is connected to the tank side. As a result, the loading area returns under its own weight into the horizontal position indicated by dashes. To relieve the pressure in the consumer channel V said channel is connected, in the return position of the directional valve 24, to the tank 36. The return position is designated 82 in Fig.1. As already stated above, the piston 70 of the directional valve 24 is so designed that, in the return position 82, the relief line 38 too remains connected to the tank 36, while the pump channel is blocked. This allows low-loss circulation of the oil delivered by the pump 34.

The load situation at the circulation valve 40 therefore corresponds to the load situation in the blocking position 78 of the directional valve 24. As regards the function of the circulation valve 40 in the return position, reference may therefore be made to the functional description relating to the blocking position 78.

LIST OF REFERENCE NUMERALS 10 control device 12 loading area 14 hinge 16 body 18 cylinder 20 hinge 22 hinge 24 directional valve 26 actuating device 28 spring 30 spring 32 piston rod 34 pump 36 tank 38 relief line 40 circulation valve 42 branch 44 input 46 branch 48 output 50 circulation piston 52 spring 54 control chamber 56 throttle 58 loading line 60 throttle 62 pressure relief valve 64 pressure relief line 66 pressure relief line 68 control line 70 piston 72 annular collar 74 annular collar 76 annular collar 78 forward 80 blocking position P pump channel T tank channel V consumer channel

Claims (5)

1. CLAIMS 1. Hydraulic control device having a fixed displacement pump, which delivers continuously and at a fixed delivery rate; a directional valve; a tank; a pump channel, which connects the pump to the directional valve; a consumer channel, for connecting the directional valve to a device to be controlled; and a tank channel, which connects the directional valve to the tank; wherein the pump channel is connected to the tank by a circulation line which incorporates a circulation valve; the circulation valve has a circulation piston which, by its movement, causes the circulation line to be open or closed; the circulation piston is loaded at an opening side in the direction of opening by the pump pressure and at an opposite closing side in the direction of closing by a spring and lies with said closing side in a control chamber; the control chamber is connected via a loading channel to the pump channel and via a relief channel b the tank; the relief channel leads via the directional valve to the tank; ; the relief channel is connected to the tank by the directional valve in a blocking position, in which the valve blocks the pump channel, and in a return position; the relief channel is blocked by the valve in a forward position, in which the valve connects the pump channel to the consumer channel.
2. 2. Hydraulic control device according to claim 1, wherein the control chamber is connected via a pressure relief valve to the tank.
3. 3. Hydraulic control device according to claim 1 or 2, wherein the control chamber is connected to the relief channel via a throttle.
4. 4. Hydraulic control device according to one of the preceding claims, wherein the control chamber is connected to the loading channel via a throttle.
5. 5. Hydraulic control device as described herein with reference to the accompanying drawings.