Patent Application
20100193714
The present invention relates to a hydraulic actuator, in particularly though not exclusively an electro-hydraulic actuator, and to a control valve therefor.
Electro-hydraulic actuators are finding increased application, due to better reliability that electromagnetic devices.
U.S. Pat. No. 6,519,939 discloses one such electro-hydraulic actuator, having a complex manifold, described in its abstract in the following terms:
A hydraulic system manifold having a body, a counterbalancer in the body and a flow controller in the body is disclosed. The body has first and second pump ports, first and second cylinder ports, first and second compensator ports and first and second supply conduits in communication with the first and second pump ports, the counterbalancer and the flow controller. The counterbalancer is in communication with the first and second supply conduits and the cylinder ports, to communicate hydraulic fluid between the first and second supply conduits and the first and second cylinder ports while counterbalancing hydraulic fluid pressure in the first and second supply conduits. The flow controller is in communication with the first and second supply conduits and the compensator ports, to control the flow of hydraulic fluid between the compensator ports and the first and second supply conduits to supply and store hydraulic fluid in a volumetric compensator in communication with the compensator ports.
The object of the present invention is to provide an improved electro-hydraulic actuator and control valve therefor.
According to the invention, there is provided a control valve for a double-acting hydraulic actuating device to be actuated by a reversible, flow-and-return source of hydraulic pressure, the control valve comprising:
The shuttle valve being spring biased, the biasing holds the shuttle away from the other non-return valve until the one non-return valve has opened and allowed pressure to be applied to the piston and cylinder unit and to rise. The raised pressure acts on the shuttle to overcome its centring spring and move to open other non-return valve. Thus the flow non-return valve opens first. When the source is controlled to stop the flow, the pressure acting on the shuttle drops and allows the spring to centralise the shuttle, closing the return side before the flow side is closed. This results in the residual pressure acting on the shuttle at closure being maintained in the return side.
Since the non-return valves are spring biased to their closed position, they require appreciable pressure/force to open and they close with appreciable pressure retained in the actuating device.
The equilibrium of forces on the shuttle as it touches the closure member of the non-return valve, preferably a ball, is:
1. Acting on the flow side, the flow pressure times the shuttle piston area and
2. Acting on the return side, the source return pressure times the shuttle area, plus the effective ball area times actuating device return pressure, plus the centring spring force, namely its rate times the shuttle valve displacement, plus the ball spring force.
When the flow side force (1) (less any seal friction on the shuttle) exceeds the return side force (2), the shuttle will open the return ball valve. This may cause an increase in the source return pressure, resulting in an increase in the return side force and consequent urging of the shuttle away from the ball and a reduction of flow and a reduction in the return side pressure. An equilibrium results.
To further facilitate the equilibrium, in case of friction and/or disturbing factors such as load biasing of the actuating device in the direction in which its piston is being moved, the shuttle spring is preferably relatively strong in comparison with the non-return valve springs. In practice this can be achieved by making the shuttle spring with a higher spring constant than the non-return valve springs.
Preferably, the closure-member movers extend on the central axis of the bore and the non-return valves are also provided on the central axis, with their seats facing away from the shuttle.
Preferably, the non-return valves are ball valves, with springs arranged remote from the shuttle and urging their balls towards the shuttle.
Preferably, the shuttle springs are coil springs arranged to act co-axially of the shuttle, between the shuttle and parts of the non-return valves fitting respective ends of the bore.
Normally, the a control valve will be incorporated in an actuator built as unit including the double-acting hydraulic actuating device and the reversible flow-and-return source of hydraulic pressure. However, the source of hydraulic pressure can be remote.
Where the double-acting hydraulic actuating device, normally a piston and cylinder unit has a difference between the effective areas of its extend and return sides, due to the cross-sectional area of its piston rod (referred to below as the “piston rod effect”), accumulator means will be provided for accommodating the difference in hydraulic liquid displaced. Whilst the accumulator could be a diaphragm unit, in the preferred embodiment, the accumulator comprises an accumulation cylinder with a spring biased piston. Conveniently connection is provided to the accumulator via a common point of a back-to-back pair of non-return valves, respectively connected to the ports in the bore of the control valve on either side of the shuttle.
The back-to-back non-return valves are conveniently a pair of ball valves with a shuttle rod between them of such length that whichever of them is closed by flow pressure, the other is opened by shuttle rod.
Preferably oppositely directed non-return valves are provided between the flow and return lines from the source to the shuttle valve to provide by-pass flow routes in event of bottoming of the actuating device.
In the preferred embodiment, an over-ride control is included and has a pair of back-to-back, non-return valves arranged between the inlets of the two ends of the actuating device and means for mechanically opening these non-return valves to allow movement of the double-acting hydraulic actuating device independently of the reversible, flow-and-return source of hydraulic pressure.
Preferably, the means for mechanically opening these non-return valves comprises a central doubling acting cam and a pair of rods arranged to be acted on by the cam and act on and open the valves.
Further there is preferably provided a pair of front-to-front non-return valves parallel to the manual movement valves, to allow for thermal expansion of the hydraulic liquid and/or shock loading of the actuating device.
Whilst the source of hydraulic pressure can be a remotely pumped source, in the preferred embodiment, it is a locally, electrically driven gear pump.
To help understanding of the invention, a specific embodiment thereof will now be described by way of example and with reference to the accompanying drawings, in which:
Referring to the drawings, an actuating device 1 has a cylinder 2 with a piston 3 connected to a rod 4. The rod's exit from the cylinder is sealed at 5, whereby the actuating device is double acting, with an extend side 6 of the piston and a retract side 7. The cylinder is provided with ports 8,9 at opposite ends for flow/return lines 10,11 to provide flow of hydraulic liquid to whichever side of the piston is to be pressurised for its movement and to provide return of hydraulic liquid from the other side. Due to the presence of the piston rod on the retract side, a lesser volume of liquid is displaced through the port 9 and line 11 than through port 8 and line 10 per unit of actuating device movement.
A filter 12 is provided in line 11, with a pair of non-return valves 14, arranged so that flow passes through the filter in one direction only.
The lines 10,11 pass to opposite ends of a shuttle valve 20. It has a body 21 with a bore 22 accommodating a double acting piston 23 having short rods 24,25 extending on either side. Each rod carries a centring spring 26,27 acting against its face of the shuttle piston and an end fitting 28,29 of the body. The springs are relatively stiff (in comparison with springs 33 mentioned below) and are held in constant opposed compression to centralise the shuttle. The fittings seal the bore, except that each has a central drilling 30 which can freely accommodate the rod on its side of the piston and allow hydraulic liquid flow at the same time. Outwards of the drilling, each fitting has a tapered bore 31 for receiving a non-return valve ball 32 normally held against the bore 31 by a spring 33 retained in the fitting by an end union 34 for its one of the lines 10,11. The bore has two ports 35,36 respectively close to the end fittings 28,29.
Branched from the lines 10, 11 are further lines 40,41 leading to a manual release unit 42. This has a pair of back-to-back, non-return valves 44,45, arranged similarly to the valves 31,32,33,34 at opposite ends of a body 46, having a centrally mounted elliptical cam 47 and rods 48,49 extending to valve balls 50. Turning of the eccentric by means of an external lever 51 urges the rods against the balls 50 of the valves 44,45, moving them off their seats and allowing flow of hydraulic fluid through the unit in response to manual movement of the piston rod 4. This flow will necessitate the need for exhaustion of an excess of liquid or influx of additional liquid due to the effect of the piston rod 4. This flow is via a line 52 connected into the central flow passage 53 of the manual release unit 42 and remotely connected to an accumulator 54, comprising a cylinder 55 with a spring biased piston 56.
A thermal expansion valve arrangement 43 comprises a pair of front-to-front arranged non-return valve 57,58 between the lines 40,41, with a central line 59 tee-ed into the line 52 to the accumulator. A high pressure—in comparison with normal operating pressures—is required to open the valves 57,58.
The body 21 of the shuttle valve has two ports 61,62, opening into the bore 22 adjacent the end fittings 28,29, to which ports are connected flow and return lines 63,64 from a reversible gear pump 65, selectively driven in either direction by an electric motor 66. Between the lines 63,64 are a pair of back-to-back non-return valves 67,68, arranged at opposite ends of a body 69 having a rod 70 in a central bore 71 of a length to keep one or other of the balls 72,73 of the valves off their seats. The central bore is connected to the accumulator via line 75 to provide for the piston rod effect in normal use. Also connected between the lines 63,64 are two spring biased non-return valves 76,77, one directed to one line and the other to the other. These provide bypass routes for pumped liquid in the event of the actuating device bottoming or otherwise being unable to move.
In normal operation, the pump is driven in the direction required for the desired movement of the actuator, as a whole. The springs in the bypass valves 76,77 are of a strength for the valves to be normally closed. Flow of hydraulic liquid is to one end of the shuttle valve. The pressure of the liquid lifts the valve in the respective end fitting 28,29. Pressure is applied to the actuating device and via its piston to the liquid in the respective line back to the other of the fittings. Until the valve in this fitting is opened no movement can occur. The pressure acts on the shuttle, moving it towards this valve, which it opens via its rod 24,25, the effective area of the balls 33 seating in their tapers 31 being less than that of the shuttle piston. Movement can then occur with the return of liquid back to the pump and piston rod effect flow to or from the accumulator via the line 75.
In the event of the actuator being loaded so that movement is resisted, the flow pressure from the pump increases to overcome the load. If the load is in the opposite direction, the piston will be urged to over-run the pump. However, this will result in a reduction in the pressure, which is causing the shuttle to open the return non-return valve. The latter then closes sufficiently to create a pressure drop across itself, which supports the actuator against run away. The pressure in the flow lines settles at a level to allow controlled movement. Provision of relatively strong centring springs 26,27—in comparison with the valve springs 33—ensures that the flow pressure and the centring spring forces predominate in determining the position of the shuttle and degree of opening of the return valve for controlled movement.
Whilst not immediately apparent from the drawings, the above described actuator, including the double-acting piston and cylinder unit, the pump and motor, the accumulator and the valves in a block are incorporated in a single integrated unit, controlled merely by application or not of voltage of polarity for its desired movement.
It should be noted that envisaged uses of the actuator are in the first instance in airliners, in particular for actuating seats and doors and in light aircraft for actuating landing gear. However, it is anticipated that the invention will find other uses.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0704106.4 | Mar 2007 | GB | national |
| 0704397.9 | Mar 2007 | GB | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/GB08/00744 | 3/5/2008 | WO | 00 | 3/8/2010 |
