EP0116739A2

EP0116739A2 - Hydraulic valve

Info

Publication number: EP0116739A2
Application number: EP83303677A
Authority: EP
Inventors: Ronald Bernard Walters; Clifford James Balmer
Original assignee: Sperry Corp; Vickers Inc
Current assignee: Vickers Inc
Priority date: 1982-07-02
Filing date: 1983-06-24
Publication date: 1984-08-29
Also published as: EP0116739A3; JPS5923106A; AU1582983A

Abstract

In a pilot-operated hydraulic valve, a non-return valve (7) in the valve inlet (25) is arranged to operate simultaneously as a variable-orifice flow sensor. By combining the non-return and flow-sensing functions in the non-return valve (7) a significant saving in space and weight is achieved.

Description

This invention relates to hydraulic valves and in particular to pilot-operated, flow feedback controlled hydraulic valves.
A pilot-operated, flow feedback controlled hydraulic spool valve is known, for example from British Patent Specification No.1,462,879. The main valve disclosed in Specification No.1,462,879 is a spool valve which controls the amount and direction of fluid flow to a hydraulic actuator. The main valve is operated by means of a pilot valve which regulates the hydraulic pressures in valve chambers at the extreme ends of the main valve spool. The pilot value is controlled by.-an electric force motor whose input signal is derived by summing an electrical demand signal with an electrical feedback signal which is provided by a flow sensor sensing the rate of fluid flow through the valve.
The present invention provides an improvement for pilot-operated, flow feedback controlled hydraulic valves which is of advantage especially, though not exclusively, where more than one valve is operated off a common source of fluid pressure, and particularly so where space and weight limitations are of importance.
According to the present invention there is provided a hydraulic valve comprising a main valve operable to control flow of fluid to a load, a pilot valve operable to control the main valve, and non-return valve means arranged to operate as variable-orifice, flow-sensing means.
Whenever two or more valves are operated off the same pressure supply, it is important that the load conditions on one valve affect the load on other valves connected to the same supply line to the least possible extent. This requirement will frequently arise in mobile equipment in which control of various degrees of freedom of the load has to be provided for. Some examples of such equipment are cranes, earth-moving equipment, and loading apparatus. Frequently, such equipment must allow for the horizontal position of the load to be controlled as well as its height above ground and, perhaps, its orientation and attitude. In order to provide the required degree of independence of operation of the valves controlling the individual degrees of freedom, each valve is supplied from a common pressure supply via a non-return valve. The non-return valve prevents return flow from any given valve back to the supply line, should the pressure in the supply line drop below the current fluid pressure in, and downstream of, that valve. By employing, in accordance with the present invention, a check valve which operates simultaneously as a flow sensing device, a considerable saving in space, weight and complexity of the hydraulic system can be achieved.
When two or more valves controlling different loads or different degrees of freedom of a load are to be operated by the same operator, the various valves are frequently formed into a bank of valves with some common fluid passages such as the supply line and the return lines or lines to tank being provided by fluid passages traversing the bank of, except for minor variations, identical valves, and the present invention enables each of the valves to be provided in a simple manner with its own check valve and flow sensor.
The present invention will now be described in greater detail, by way of example, with reference to the accompanying drawing which shows a partly schematic cross- section through a valve incorporating the present invention.
The drawing shows a sectional view of a hydraulic control valve 1 of the kind normally found in assemblies or banks of two or more valves. The valve, as others (not shown) in the bank, comprises a main stage 2, a main stage actuating attachment 3, a pilot valve 4, and a pair of opposed solenoids 5 controlling the operation of the pilot valve 4. The main stage 2 is a spool valve with a valve spool 21 of conventional design. The valve spool 21 is attached at one end to a back-up manual control lever 6, and at its other end, via a coupling arrangement 31 and a coupling rod 32, to a valve actuating piston 30 which is rigidly coupled to the main valve spool 21. To operate the main valve 2, hydraulic fluid under pressure is supplied from the pilot valve 4 to chambers 33 and 34 on either side of the actuating piston 30. The main spool 21 can thus be shifted along the axis of its valve bore by applying the appropriate control pressures to the chambers 33 and 34. If the valve spool 21 is to be moved to the right(as seen in the drawing), the pressure in the valve chamber 34 must exceed that in the valve chamber 33, and vice-versa if the spool 21 is to be moved to the left. The pilot valve 4 is a conventional spool valve supplied with fluid under pressure through a central port 42 suitably connected, optionally via a pressure reducing valve (not shown), to a pressure supply line 22. The position of the lands of the pilot spool 41, in relation to the adjoining outlet ports 43 and 44, control the respective pressures applied to the chambers 33 and 34. An electrical input signal to the solenoids 5 determines the position of the pilot spool 41 within its valve bore.
Fluid is supplied to the valve under pressure through the fluid supply line 22 and hence, depending on the position of the central lands 28a and 28b in relation to the ports 25a and 25b, to the service ports 29a and 29b which are connected to the load (not shown).
In order to prevent back flow from the valve to the supply line 22, should the pressure in the supply line fall below the pressure in the valve and downstream thereof, a non-return or check valve 7 is provided which is spring biased against a shoulder 23 at one end of a branch passage 24 leading from the supply line 22 to the valve inlet port 25. By shaping the passage 24 downstream (relative to the supply line 22) of the shoulder 23 to form a throat having its narrowest part adjacent the shoulder and widening in a downstream direction, and by choosing the size of the head 73 of the non-return valve 7 to have only a minimal circumferential clearance with the narrowest portion of the throat, the opening of the non-return valve against the spring can be made to be substantially proportional to the amount of fluid flowing from the supply line 22 to the valve 2. By connecting the stem of the non-return valve 7 to a linear displacement detector 8 such as, for example, a commercially available linear variable displacement transducer (LVDT), an electrical signal is derived which is proportional to the displacement of the non-return valve 7; and hence proportional to the flow of fluid under pressure from the supply line 22 to the valve 2. This signal may then be used to generate an error signal to the pilot valve solenoids 5, for example in the manner described in British Patent Specification No.1,462,879.
Considerable saving in weight, space and complexity can be achieved by employing, in accordance with this invention, a combined, non-return valve and flow sensor in place of two separate such devices which have previously been required.

Claims

1. A hydraulic valve comprising a main valve operable to control flow of fluid to a load, and a pilot valve operable to control the main valve, characterised in that the valve further comprises non-return valve means (7) arranged to operate as variable-orifice, flow-sensing means.

2. A valve according to claim 1, characterised in that the non-return valve (7) is located in an inlet (25) to the main valve (2).

3. A hydraulic valve according to claim 1 or 2, characterised in that the main valve is a spool valve (2).

4. A hydraulic valve according to any of the preceding claims, characterised in that the non-return valve (7) comprises a spring-biased member rigidly linked to a sensing element of linear displacement sensing means (8).

5. A hydraulic valve according to any of the preceding claims, characterised in that the non-return valve (7) comprises a valve member (73) movable in a throat (24), with the valve member having a minimal circumferential clearance with the narrowest portion of the throat, whereby flow through the non-return valve.is substantially proportional to the extent of opening of the non-return valve.

6. A hydraulic valve according to claim 5, characterised in that the throat (24) comprises a tapered bore formed in the body of the non-return valve (7).

7. A valve assembly comprising a plurality of valves according to any of preceding claims.