GB2040510A

GB2040510A - Servovalve

Info

Publication number: GB2040510A
Application number: GB8001611A
Authority: GB
Original assignee: Honeywell Inc
Current assignee: Honeywell Inc
Priority date: 1979-01-19
Filing date: 1980-01-17
Publication date: 1980-08-28
Also published as: FR2447509A1; DE3001859A1; AU5448780A; GB2040510B; SE8000165L; JPS55100401A

Abstract

A pilot valve 11 operated by a linear force motor 18 controls the actuating pressures 35, 36 applied to a main valve 12. Output pressure 31 or 32 from the pilot valve is transmitted to a channel 13 to oppose the input from the motor. The pilot and main valves are supplied by a common inlet 26 and the output pressure from the main valve acts through channels 72, 75 to oppose its operation by the pilot valve. <IMAGE>

Description

SPECIFICATION Servovalve This invention relates to servovalves and, more particuiarly, to electro-hydraulic servovalves.

According to the invention, there is provided a valve comprising a pilot stage valve having an input for receiving a source of fluid, an output for providing pilot output fluid and an actuator movable by an input force for controlling the flow of fluid between said input and said output; a main stage valve having an input for receiving a supply of fluid, an output for providing main output fluid and an actuator responsive to the pilot output fluid for controlling the flow of fluid between said main stage valve input and output; and wherein the pilot stage valve includes a feed back circuit for directing pilot output fluid back to the pilot actuator whereby to balance the input force thereon.

An embodiment of the invention will now be described by way of example, with reference to the accompanying drawing which is a longitudinal section through a servovalve according to the invention.

Referring to the drawing, the servovalve 10 comprises a pilot stage having pilot spool 11 and a main valve stage having main spool 12. Spool 11 is positioned within channel 1 3 formed through valve body 14 of servovalve 10. For ease of manufacture, channel 1 3 is formed through the entire length of valve body 14. Lands 1 5 and 1 6 of spool 11 are positionable by shaft 1 7 of linear force motor 1 8. Linear force motor 1 8 is mounted by any suitable means (not shown) within end cap 20 and sealing gasket 21 is positioned between valve body 14 and end cap 20. The other end of valve body 14 is sealed by gasket 22 positioned between valve body 14 and end cap 23. End caps 20 and 23 are held to valve body 14 by any suitable means such as bolts (not shown).

Supply port 26 is connected to a source of fluid, such as hydraulic oil, and extends through valve body 14 to define supply pressure chamber 28 of the main stage valve and to define supply chamber 27 of the pilot stage valve. In the centered position of pilot stage valve spool 11, lands 1 5 and 1 6 sealing close output chambers 31 and 32. Output chamber 31 is in communication with feedback chamber 33 and output chamber 32 in communication with feedback chamber 34. Thus, when linear force motor 18 drives lands 1 5 and 1 6 to the left in the drawing, land 1 6 still closes output chamber 32 from supply chamber 27 so that no hydraulic fluid flows to output chamber 32.However, output chamber 31 is opened and hydraulic fluid is supplied from the supply port 26 through supply chamber 27 and into output chamber 31 which is in communication with feedback chamber 33 for balancing the input force applied to spool 11 by linear force motor 1 8.

Also, output chambers 31 and 32 are connected to control chamber 35 and control chamber 36 respectively in the main stage valve.

Thus, when land 1 5 allows fluid to flow from supply chamber 27 to outlet chamber 31, not only is this fluid supplied to feedback chamber 33, but it is also supplied to control chamber 35 for driving main stage valve spool 1 2 to the right.

The channels which connect output chamber 31 to control chamber 35 and feedback chamber 33 also contain a restrictive opening 41 for allowing a portion of the fluid flowing through output chamber 31 to feed return chamber 42.

Similarly, the channels which connect output chamber 32 to feedback chamber 34 and control chamber 36 are also connected through restrictive passage 43 to return chamber 44. Each return chamber 42 and 44 is connected through suitable channels not shown to a return line of the source of hydraulic fluid to which supply port 26 is connected.

Channel 46 connects feedback chamber 33 to output chamber 31 and, for ease of manufacture, is formed through a side valve body 14 and extends therethrough a sufficient amount to connect these two chambers. After the forming is completed, channel 46 is sealed by plug 47.

Similarly, channel 48 which connects control chamber 35 to feedback chamber 33 and output chamber 31 is sealed by plug 49. Plugs 52 and 53 similarly seal channels on the other side of supply chamber 27 which performs functions similar to channels 46 and 48. Likewise, output chambers 31 and 32 are formed by channels 61 and 62 which have corresponding sealing plugs 63 and 64.

Main valve spool 12 has a pair of lands 93 and 94 for closing output chambers 65 and 66 from supply chamber 28 when main valve spool 12 is in its mid-position. Output chamber 65 is connected to output port 67 and output chamber 66 is connected to output port 68.

When the pressure in control chamber 35 increases and main valve spool 12 moves to the right, land 93 allows communication between supply chamber 28 and output chamber 65. At the same time, output chamber 66 remains closed from supply chamber 28. Thus, hydraulic fluid flows from supply port 26 through supply chamber 28, output chamber 65 and output port 67. Output chamber 65 is connected through bore 71 and channel 72 to feedback chamber 73 formed by sleeve 86 for balancing the force applied to spool 1 2 by the pressure within control chamber 35. Similarly, output chamber 66 is connected by bore 74 and channel 75 to feedback chamber 76 formed by sieeve 85 for countering the forces on main valve spool 12 by the pressure within control chamber 36.As can be seen from the drawing, a portion of feedback channel 72 is formed in end cap 20 and a portion of feedback channel 75 is formed in end cap 23.

Lands 81 and 82 of valve spool 1 2 control the return of fluid from respective output chambers 65 and 66 to respective return chambers 42 and 44. Lands 83 and 84 close the return chambers 42 and 44 from respective control chambers 35 and 36. Low frequency response control orifices are used as required in locations 25, 96, 97 and 98.

In operation, when linear force motor drives pilot spool 11 in a direction for land 1 5 to open communication between supply chamber 27 and output chamber 31, the pressure within control chamber 35 increases driving main valve spool 12 to the right. At the same time, the pressure within feedback chamber 33 increases to balance the force applied to pilot valve spool 11 by linear force motor 18. As valve spool 12 moves to the right, land 93 moves permitting fluid to flow from supply chamber 28 to outlet chamber 65. At the same time, land 82 moves permitting fluid to flow from output chamber 66 into return chamber 44 and then back to the supply of fluid. As a result, the pressure at output port 67 increases while the pressure in output port 68 decreases.The increased pressure at outlet port 67 increases the pressure in feedback chamber 73 while the decreasing pressure in output port 68 results in a decreasing pressure in feedback chamber 76 to counterbalance the increased force applied to valve spool 12 by the pressure within control chamber 35.

When the linear force motor applies a force to pilot valve spool 11 to move lands 1 5 and 1 6 such that communication is opened between supply chamber 27 and output chamber 32, the pressure within output chamber 32 increases, which increased pressure is fed back to feedback chamber 34 for countering the force applied to pilot valve spool 11 by linear force motor 18. This increased pressure is also applied to control chamber 36 for applying a force to main valve spool 12 in a direction to the left in the drawing to open communication between supply chamber 28 and output chamber 66 and between return chamber 42 and output chamber 65. Thus, the pressure within output port 68 increases to increase the pressure in feedback chamber 76 while the pressure within output port 67 decreases to decrease the pressure within feedback chamber 73. This differential pressure applies a force to main valve valve spool 12 for counterbalancing the increased force applied to main valve spool 12 by the pressure within chamber 36.

Claims

1. A valve comprising a pilot stage valve having an input for receiving a source of fluid, an output for providing pilot output fluid and an actuator movable by an input force for controlling the flow of fluid between said input and said output; a main stage valve having an input for receiving a supply of fluid, an output for providing main output fluid and an actuator responsive to the pilot output fluid for controlling the flow of fluid between said main stage valve input and output; and wherein the pilot stage valve includes a feedback circuit for directing pilot output fluid back to the pilot actuator whereby to balance the input force therein.

2. The valve of Claim 1, wherein said pilot actuator comprises a pilot spool having pilot land means positionable by said input force between said pilot input and said pilot output, said pilot land means comprising first and second pilot lands, said pilot feedback circuit comprising first and second pilot feedback chambers located at opposite ends of the pilot actuator, said first pilot land being positionable over a first pilot output chamber for controlling the flow of fluid thereto, and said second pilot land being positionable over said second pilot output chamber for controlling the flow of fluid thereto.

3. The valve of Claim 2, wherein said main actuator comprises a main valve spool having first and second main valve lands, and wherein said main output comprises first and second output chambers, said first main valve land being positionable between said main input and said first main output chamber for controlling the flow of fluid therebetween, and said second main valve land being positionable between said main input and said second main output chamber for controlling the flow of fluid therebetween.

4. The valve of Claim 3, wherein said main stage valve further comprises first and second return chambers and said main valve spool further comprises a third land being positionable between said first main output chamber and said first return chamber for controlling the flow of fluid therebetween and a fourth land being positionable between said second main output chamber and said second return chamber for controlling the flow of fluid therebetween.

5. The valve of Claim 4, wherein said main valve spool comprises fifth and sixth lands defining in part first and second main control chambers, said first main control chamber being in communication with said first pilot output chamber and said second main control chamber being in communication with said second pilot output chamber.

6. The valve of any one of the preceding claims, wherein the main stage valve includes a feedback circuit for directing main output fluid back to the main actuator to provide negative feedback thereon.

7. The valve of Claim 6 as appendant to Claim 5, wherein said main stage valve further comprises first and second main feedback chambers at opposite ends of said main spool, said first main feedback chamber being in communication with said second main output chamber and said second main feedback chamber being in communication with said first main output chamber for providing negative feedback to said main valve spool.