GB2042135A

GB2042135A - Hydraulic control valves

Info

Publication number: GB2042135A
Application number: GB8003608A
Authority: GB
Original assignee: Claas KGaA mbH
Current assignee: Claas KGaA mbH
Priority date: 1979-02-05
Filing date: 1980-02-04
Publication date: 1980-09-17
Also published as: GB2042135B; FR2448059A1; FR2448059B1; DE2904293A1; DE2904293C2

Abstract

A hydraulic control valve for controlling a load (6) in the form of a hydraulic piston-cylinder unit comprises a control spool (2) and an associated magnetically-operable pilot control valve (24). The spool (2) is held solely by the circulation pressure against the force of a spring (3) in a free neutral position which permits a flow of oil, when the pilot control valve (24) is not actuated. When the pilot control valve (24) is actuated, the spool (2) is put by the pressure of a pump (19) into a hydraulic equilibrium condition and is moved only by the force of the spring (3) into a position for stopping the free flow of oil and passing the pump pressure to the load (6). <IMAGE>

Description

SPECIFICATION Hydraulic control valves This invention relates to hydraulic control valves for controlling loads, such as for example hydraulic piston-cylinder units in agricultural harvesters.

Magnetic actuated hydraulic control valves are known, wherein magnets act directly on a control spool. In this arrangement, the magnet must apply high forces and must provide for a long travel movement. This causes the magnets to be expensive and to require a large amount of space. Also known are pilot-controlled magnetic valves in which there is a permanent pressure which initiates the control operation. In valves of this kind, the pressure medium producer (pump) must operate against a pressure restriction, in which case the work is converted into heat, or it is necessary to provide a pressure medium storage device to store the amount of oil which is required for the switching operation.

According to the present invention there is provided a hydraulic control valve comprising at least one control spool, a magnetically operable pilot control valve associated with the control spool or a respective said pilot valve associated with each of the control spools, a pump conduit, and at least one return, wherein in a neutral position, in use, there is always a low circulation pressure in the valve, wherein the control spool or at least one control spool is, in use, held solely by the circulation pressure against the force of a spring in a free neutral position which permits a flow of hydraulic medium, when the associated pilot control valve is not actuated, and wherein, when the pilot control valve is actuated, the control spool is, in use, put by the pump pressure into a hydraulic equilibrium condition and is moved only by the force of the spring into a position for stopping the free flow of hydraulic medium and passing the pressure of a pump to a load to be controlled by the hydraulic control valve.

In valves embodying the invention and described hereinbelow, the pressure flow resistance in the neutral position is at a minimum. Also, the valves can be produced at low cost and require a small amount of space.

The invention will now be further described, by way of illustrative and non-limiting example, with reference to the accompanying drawings, in which: Figure 1 is a cross-sectional and displaced view of a hydraulic control valve embodying the invention for a single-acting load; and Figure 2 is a corresponding view of a hydraulic control valve embodying the invention for a doubleacting load.

Referring to Figure 1, a valve housing 1 contains a control spool 2 which is continuously urged by a compression spring 3 in the direction of a seat or closure edge 22. Circulation pressure of oil acts against the spring 3 and shifts the spool 2 as far as a pilot control valve 24. A check valve 4 and a check (lowering)m valve 5 which are in the form of seat valves ensure that the oil in a load 6 including a cylinder and a piston which is continuously subjected to a loading a force P cannot pass to a tank 20 or to the system onward feed 21. A check valve 7 in a pilot control block 8 pressure-tighly closes a passage 25.A check valve 13 is pressed against its seat by the circulation pressure and at the same time prvent the spool 2 from being influenced by actuation of valves connected downstream of the illustrated valve, with a simultaneous rise in the pressure in the system onward feed 21. when solenoids 9 and 10 are energised, they actuate push rods 11 and 12 which in turn close valves 15 or 17. While the valves 15 or 17 are closed, the valves 13 or 7 are opened by way of valve push rods 14 or 16. In the illustrated neutral position, the valve 13 is closed by the circulation pressure which presses on the valve 15 by the way of the valve push rod 14 so that there is a direct communication with the tank 20 from the chamber in which the spring 3 is disposed.The difference in pressure of some bars between circulation pressure and no pressure at the tank is in fact sufficient further to bias the suitably dimensioned compression spring 3 until the spool 2 comes into a position of abutment against the spring force, and the oil supplied by a pressure medium producer or pump 19 can flow to the system onward feed 21 without a rise in pressure. The check valve 7 is closed by way of the passage 25 by the pressure in the cylinder of the load 6, and, by way of the valve push rod 16, presses on the check valve 17 so that there is no pressure in a passage 16", because that passage 16" is connected directly to the tank 20 by a passage 28.

Any desired number of valves can be actuated by the system onward feed 21, such valves being connected by pipe conduits to the illustrated valve or being connected thereto by being screwed together to form a block.

The mode of operation of the valve shown in Figure 1 will now be described. When the solenoid 9 is energised in known manner by a switch (not shown), the push rod 11 presses the check valve 15 against its seat, while at the same time the check valve 13 is lifted from its seat by the valve push rod 14. This enables the circulation pressure from a pump port 30 to act on the spool 2 by way of a passage 29. This means that, from the point of view of pressure, the spool 2 is in an equilibrium condition. However, the spring force of the spring 3 remains as a free force, pressing the spool 2 on to the seat 22, so that the communication of the pump 19 with the feed 21 is broken. At the same time, due to the movement of the spool 2, an annular passage or transverse bore 31 in the spool is under an annular passage 32 in the housing 1.The oil conveyed by the pump 19 now flows through a passage or blind bore 36 in the spool 2 into the two annular passages 31 and 32 and through à passage 33, and opens the check valve 4 and from there flows through a conduit 34 to the load 6. Due to the different areas involved (the spool surface area is large and the sealing surface area is small), the spool 2 is held firmly pressed against the seat 22. When energisation of the solenoid 9 is stopped, the valve 13 closes and the valve push rod 14 opens the valve 15 so that the spool 2 is pressed towards the pilot control valve 24, overcoming the spring force of the spring 3. This therefore results in the free flow from the pump 19 to the onward feed 21 being restored.If the solenoid 10 is energised for the purpose of lowering the cylinder, the push rod 12 urges the check valve 17 on to its seat and at the same time, by way of the valve push rod 16, opens the check valve 7 so that a piston 18 is subjected to the effect of pressure oil from the cylinder of the load 6, by way of the passage 25 and a passage 35, so that a push rod 23 opens the check valve 5 and the oil in the load can flow back to the tank 20 by way of the conduit 34, the passage 35, a passage 36 and a conduit 27.When the energisation of the solenoid 10 is terminated, the valve 7 closes due to the pressure which then builds up in the passage 25 and opens the valve 17 by way of the valve push rod 16 so that the passage or chamber 16" below the piston 18 has a dircect communication with the tank 20 by way of the passage 28 and 36 and the conduit 27, the valve 5 is then pressed on to its seat by the oil pressure, and the return flow from the load is interrupted.

Figure 2 shows another hydraulic control valve which is generally similar to that shown in Figure 1, but is for use with double-acting rather than singleacting loads. In Figure 2, oil conveyed by a pressure medium producer or pump 20' flows by way of a passage 33' into a chamber 35' and from there passes through a communicating passage 34' into a chamber 36' and then to the system onward feed 21' to which further valves may be connected. This arrangement compriss a first control spool 3' and another, like control spool (not referenced).The two spools are urged by the circulation pressure against the force of springs 4' and 5' in the direction of associated respective pilot control valves 8' and 9' because at the same time check valves 11' and 13' which are directly connected to the chamber 35' by control passages 37' and 38' are closed by the circulation pressure, in which case check valves 10' and 12' are opened bivalve push rods 14' and 15' and thus, behind the spools, communicatuion is made with a passage 59', and a direct communication is made with a tank, by way of control passages 39' and 41', and 40' and 42', respectively.

A passage 46' connects an annular chamber 48' to a cylinder port 43' and a passage 45' connects an annular chamber 47' to a cylinder port 44'. When a solenoid 17' is energised, a push rod 19' urges the check valve 12' against its seat, the valve push rod 15' pressing the check valve 13' open. This causes the communication with the tank behind the spool 3' to be interrupted, and makes a direct communication with the pressure medium producer 20' so that, from the point of view of hydraulic pressure, there is a condition of pressure equilibrium at the spool.There remains as a free force however the force of the spring 5' which moves the spool 3' so that a tapered portion thereof moves towards a seat 7', in which case case the pressure rises due to the throttle action and, due to the different surface areas involved, the spool 3' is pressed firmly with its tapered portion against the seat 7', and is thus pressure-tightly closed. When this occurs, an annular passage or transverse bore 51' of the spool 3' has moved to a position under the passage 44'; in addition, by way of a turned groove or recess 56' in the spool, a communication is formed between the annular passage 48' and an annular passage 50' and thus an end 23' of the load cylinder is communicated with the tank byway of the passage 46' and a passage 49'. The oil conveyed by the pressure medium producer 20' necessarily flows through a passage or blind bore 54' in the spool 3' by way of the annular passage 51' to the cylinder port 44' and into the load cylinder chamber.

If the piston or piston rod is to be moved in the other direction, a solenoid 16' is energised to move a push rod 18'. The control operation is then suitably effected in a similar manner to that described above.

Claims

1. A hydraulic control valve comprising at least one control spool, a magnetically operable pilot control valve associated with the control spool or a respective said pilot valve associated with each of the control spools, a pump conduit, and at least one return, wherein in a neutral position, in use, there is always a low circulation pressure in the valve, wherein the control spool or at least one control spool is, in use, held solely by the circulation pressure against the force of a spring in a free neutral position which permits a flow of hydraulic medium, when the associated pilot control valve is not actuated, and wherein, when the pilot control valve is actuated, the control spool is, in use, put by the pump pressure into a hydraulic equilibrium condition and is moved only by the force of the spring into a position for stopping the free flow of hydraulic medium and passing the pressure of a pump to a load to be controlled by the hydraulic control valve.

2. A hydraulic control valve according to claim 1, wherein the control spool or at least one of the control spools has a blind bore which is connected to the pump conduit in every position, and a transverse bore which is connected to the blind bore, and wherein, after the pilot control valve has been actuated and the control spool has been displaced by the spring, the transverse bore is connected, in use, to the load by an annular passage provided in a housing of the control valve.

3. A hydraulic control valve according to claim 1 or claim 2, wherein the or each pilot control valve comprises a valve push rod having a check valve at each end thereof.

4. A hydraulic control valve according to claim 1, claim 2 or claim 3, wherein the or each pilot control valve is closable, in use, by the hydraulic medium pressure and can be opened by way of a solenoid.

5. A hydraulic control valve according to any one of claims 1 to 4, for a single-acting load, wherein a piston is associated with the control spool for pressure actuation, the piston, after actuation of the pilot control valve, providing in use for a return flow of hydraulic medium from the load.

6. A hydraulic control valve according to claim 5, wherein the piston has a push rod for actuating a lowering valve.

7. A hydraulic control valve according to any one of claims 1 to 4, for a double-acting load, comprising two said control spools, the spools being actuable alternately.

8. A hydraulic control valve according to claim 7, wherein, for each control spool, a housing of the control valve has an annular passage and an annular conduit which, after displacement of a control spool, provide in use for the free dips'charge flow of hydraulic medium from a non-actuated side of the load, by way of suitable bores.

9. A hydraulic control valve substantially as herein described with reference to Figure 1 or Figure 2 of the accompanying drawings.

10. The combination of a load and a hydraulic control valve according to any one of the preceding claims operative to control the load, the load being a hydraulic piston-cylinder unit.

11. Acombination according to claim 10, wherein the piston-cylinder unit is installed on an agricultural harvester.