GB2105013A

GB2105013A - Hydraulic control valve

Info

Publication number: GB2105013A
Application number: GB08225032A
Authority: GB
Inventors: Stephen Owen; John Richard Archer
Original assignee: Prutec Ltd
Current assignee: Prutec Ltd
Priority date: 1981-09-02
Filing date: 1982-09-02
Publication date: 1983-03-16

Abstract

The invention is concerned with a hydraulic control valve of sandwich format and in particular with a control block to be incorporated in such a valve to provide pressure compensation enabling the speed of an actuator to be controlled independently of the load on the actuator. The control block incorporates a shuttle valve 18 to sense the higher of the pressures in the service lines A and B and controls a variable throttle 20 connected in the hydraulic circuit of the actuator 12, the throttling cross section increasing as the pressure across the actuator 12 increases. In an alternative embodiment, the lower of the two pressures may be sensed and used to control a variable throttle of which the throttling cross section increases with decreasing pressure. <IMAGE>

Description

SPECIFICATION Hydraulic control valve The present invention relates to pressure compensation in hydraulic control valves having a sandwich format.

It is often desired to provide a hydraulic control valve with additional features such as for limiting the pressure in the supply or return line or for limiting the pressure difference between two service lines connected to a load. In order to avoid the need to construct a particular valve for each application, valves having a so-called sandwich format have been proposed in the past. This construction relies on a modular approach. Each valve consists of a stack of control blocks or modules sandwiched between a manifold block at one end and a solenoid operated spool valve at the other end. The manifold block includes conduits connected to a supply line, a return line and to two service lines connected to a load to be controlled, the two service lines being generally referred to as the A line and the B line.The solenoid operated spool valve serves when energised to establish connection between the various lines and is connected to the conduits in the manifold block through bores which extend through all of the control blocks. Each control block contains elements such as valves, throttles etc to achieve a particular control feature, such as pressure regulation.

Because of this modular construction, it is possible to bolt together any desired combination of solenoid valves and control blocks to produce the desired combination of features in any given application.

Speed control of a hydraulic actuator is normally achieved by proportional or servo valves. Many simple designs of proportional valves and also servo valves have an important deficiency in that they are not pressure compensated and therefore the actuator speed is load dependent.

Pressure compensation of simple proportional or servo valves may be achieved by using a pressure transducer to monitor the pressure difference across the two service lines of the valves and by using a feedback signal to control the current applied to the solenoid to adjust the valve spool position so as to give the required flow rate. This solution however is expensive to implement because of the number of components that are involved and because of the need for electrical circuitry which requires an electrical power supply.

The present invention seeks to provide a control block which may be incorporated in a valve of sandwich format to enable the speed of a hydraulic actuator controlled by the valve to be regulated independently of the load on the actuator.

In accordance with the present invention, there is provided a control block for use in a hydraulic control valve of sandwich format which comprises a variable throttle which, in use, is connected in series in the hydraulic circuit leading to the hydraulic load, and means for sensing the higher or lower of the pressures prevailing in the service lines which, in use, are connected across the load, the variable throttle being connected to the sensing means to be controlled in dependence upon the sensed pressure, in such a manner as to render the flow rate of hydraulic fluid through the valve independent of the pressure across the load.

The invention will now be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a valve constructed using a sandwich block in accordance with a first embodiment of the invention, and Figure 2 is a similar view to Fig. 1 of a valve employing a second embodiment of sandwich block.

In Fig. 1, there is shown a solenoid valve 10 having two solenoid 1 0a and lOb arranged one at each end. The valve serves to control the supply of hydraulic fluid to a hydraulic actuator 1 2 from a pressure supply 14 and back to a tank or reservoir 16. The valve 10 is designed as a proportional valve, that is to say the amount of fluid flowing through the valve is proportional to the current applied to the actuating solenoid. Because of the provision of two solenoids, the valve is bi-directional and allows the speed of the actuator 1 2 to be controlled in both directions of movement.

In order to regulate the rate at which fluid is supplied to the actuator 1 2 in a manner independent of the load on the actuator and hence the pressure across it, a shuttle valve 1 8 is connected to the service lines A and B and serves to connect the higher of the two pressures in the these two service lines to a line 22 which leads to a variable throttle generally designated 20. The shuttle valve 1 8 comprises a ball 24 slidable in a bore having valve seats at its opposite ends. The higher of the two pressures prevailing in the service lines A and B moves the ball 24 to the opposite valve seat so as to establish communication between the line 22 and the service line carrying the higher pressure while isolating the line having the lower pressure.

The higher pressure is applied to a control chamber 26 at the upper end of a spool 28 forming part of the variable throttle 20. The spool 28 has a land 30 which partially closes a port 32 to define the variable restriction orifice.

In operation, the pressure supply 14, in the form of a hydraulic pump, produces a pressure regulated by means of a valve 34 which connects the high pressure to the reservoir 1 6 when a threshold pressure is exceeded. The supply pressure is fed by way of a line 36 and through the restriction orifice of the variable throttle 20 to 'he port 32 leading in turn to the pressure input port P of the solenoid valve 10. Depending on which of the two solenoid 10a and lOb is actuated, the higher pressure is applied either to the service line A or to the service line B and after passing through the hydraulic actuator 1 2 in one direction or the other the flow returns through the other of the two service lines A and B and back through the port T of the solenoid valve 10 to the reservoir 16.

As the load on the hydraulic actuator 1 2 increases then so will the pressure difference across the service lines A and B. The higher of these two pressures, as previously explained, is applied through the shuttle valve 1 8 to the line 22 and as the pressure rises, the shuttle 28 moves downwards, as viewed, to open the restriction orifice and reduce the resistance to flow from the variable throttle 20.The throttling effects of the variable throttle 20 and the hydraulic actuator 1 2 are connected in series with one other and it can therefore be seen that by appropriately dimensioning the spring acting on the spool 28 and the restriction orifice it is possible to ensure that the total resistance to flow in the hydraulic circuit is constant and independent of the load on the hydraulic actuator 1 2. Since the pressure from the supply 1 4 is also regulated by the valve 34, a constant rate of flow is ensured determined by the extent of the opening of the solenoid valve 10 and independent of the hydraulic load on the actuator 1 2.

In the embodiment shown in Fig. 2, the operation is analogous with the exception that the shuttle valve 1 8 is replaced by shuttle 18' operative to connect the pressure chamber at the upper end, as viewed, of the variable throttle device 20' to the lower of the two pressures in the service lines A and B. The shuttle valve 18' comprises a spool with pressure chambers at opposite ends connected to the respective service lines A and B. Movement of the spool is operative to shut off the port connected to the higher pressure and establish connection between the line 22' and the lower pressure. The land 30 is also replaced by a land 30' in the throttle valve 20' which is now arranged to open the throttling aperture between the port 32' and the land 30' as the pressure in the control chamber decreases.Because of the general resemblance to the first embodiment it is believed that Fig. 2 requires no further explanation.

in the mechanical construction of the valve, the solenoid valve 10 is constructed as a block which is mounted at the top of a stack terminated at its lower end by a manifold block. The stack has in both the embodiments described two control blocks. The first control block incorporates the pressure regulating valve 34 while the second control block incor porates the shuttle valve and the variable throttle. At the lower end of the stack, the manifold block has four lines leading one to the pressure supply 14, one to the reservoir 16 6 and two to the hydraulic actuator. Each of the control blocks has four through bores in communication with the respective lines in the manifold block and the connections between the elements of the blocks and the respective bores are achieved in the manner illustrated in the hydraulic circuits of Figs. 1 and 2.

It will be appreciated that such control blocks are manufactured in accordance with industry standards such that the location of the various bores in the control blocks is predetermined and it is possible to sandwich further control blocks, as desired to achieve further regulation functions.

Claims

1. A control block for use in a hydraulic control valve of sandwich format which com prises a variable throttle which, in use, is connected in series in the hydraulic circuit leading to the hydraulic load, and means for sensing the higher or lower of the pressures prevailing in the service lines which, in use, are connected across the load, the variable throttle being connected to the sensing means to be controlled in dependence upon the sensed pressure, in such a manner as to render the flow rate of hydraulic fluid through the valve independent of the pressure across the load.

2. A control block as claimed in Claim 1, wherein the means for sensing the pressure prevailing in the service lines comprises a ball shuttle valve operative to sense the higher of the pressures prevailing in the service lines.

3. A control block as claimed in Claim 2, in which the variable thottle comprises a spool and a variable restriction orifice defined be tween a land on the spool and a port, the spool being acted upon by the higher of the sensed pressures in a sense to increase the size of the restriction orifice as the sensed pressure increases.

4. A control block as claimed in Claim 1, in which the means for sensing the pressure in the service lines comprises a shuttle valve operative to connect the lower of the two pressure prevailing across the hydraulic load to a control line leading to the variable throt tle.

5. A control block as claimed in Claim 4, wherein the variable throttle comprises a spool and a restriction orifice defined between a port and a land on the spool, the spool being arranged to move in response to a decrease in the sensed pressure in a direction to increase the size of the restriction orifice.

6. A hydraulic control valve of sandwich format incorporating a control block as claimed in any preceding claim.

7. A control block for a hydraulic circuit constructed substantially as herein and before described, with reference to, and as illustrated in Fig. 1 or Fig. 2 of the accompanying drawings.