GB2153049A

GB2153049A - Proportional air valve and method of providing air flow

Info

Publication number: GB2153049A
Application number: GB08500222A
Authority: GB
Inventors: Logan Harold Mathis
Original assignee: Ross Operating Valve Co
Current assignee: Ross Operating Valve Co
Priority date: 1984-01-20
Filing date: 1985-01-04
Publication date: 1985-08-14
Also published as: DE3501277A1; JPS60159406A; SE8500229D0; IT8519161A0; GB8500222D0; IT1184845B; FR2558611A1; CA1249200A; GB2153049B; SE8500229L

Abstract

A proportional air control valve including a flow control element (43), such as a spool, and a pair of springs (54, 56), at each end, one (54) of which is relatively light in weight and which normally holds a flow control element (43) in its closed position as shown and the other (56) of which has a substantially higher rate and which is effective to resist further movement of the flow control element (43) in its opening direction. When the element has moved a predetermined amount from its closed position. The valve is operated by applying a pulsing actuating force, e.g. by solenoids, to the flow control element (43). <IMAGE>

Description

SPECIFICATION Proportional air valve and method of providing proportional air flow BACKGROUND OF THE INVENTION This invention relates to a proportional air valve and more particularly to a method of achieving proportional air flow.

Although pneumatic and hydraulic controls are interchangeably used in many types of applications, the absence of an effective, and relatively low cost proportional valve for pneumatic systems has limited the application of pneumatics. That is, most pneumatic valves are of the on-off type and, therefore, do not provide a proportional output that permits their utilization in devices such as industrial robots or the like. Although proportionality may be achieved through the use of variable regulators or the like, such devices are very expensive and thus limit the application of pneumatics where proportional control is required.

It is, therefore, a principal object of this invention to provide an improved method for operating a pneumatic valve in a proportional manner.

It is another object of the invention to provide a low cost, proportionally operable pneumatic valve.

SUMMARY OF THE INVENTION A first feature of the invention is adapted to be embodied in a method of achieving proportional control of a pneumatic valve that includes a flow control element that is supported for movement between a closed position, an intermediate position wherein restricted flow is permitted and a fully opened position wherein substantially unrestricted flow is permitted. The method comprises the steps of applying a substantially constant actuating force for moving the flow control element from its closed position toward its opened position. The actuating force is applied sequentially for predetermined time intervals with intervening time intervals wherein no actuating force is applied. A relatively low rate biasing force is exerted on the flow control element for urging the flow control element continuously toward its closed position.In addition, a substantially higher rate biasing force is exerted upon the flow control element for resisting further movement of the flow control element when the flow control element has moved a predetermined amount from its closed position toward its fully opened position.

Another feature of the invention is adapted to be embodied in a proportional, pneumatic flow control valve. Such a valve comprises a housing that defines an inlet port and a supply port. A flow control element is movable from a closed position wherein communication between the ports is substantially precluded and an opened position wherein substantially unrestricted communication between the ports is permitted. First biasing means are provided for constantly urging the flow control element toward its closed position and second biasing means are provided for resisting movement of the flow control element toward its fully opened position when the flow control element moves a predetermined amount from its closed position toward its fully opened position. The second biasing means has a substantially higher rate than the first biasing means.

BRIEF DESCRIPTION OF THE DRAWING The single figure of the drawing is an axial cross-sectional view taken through a spool type pneumatic valve constructed in accordance with an embodiment of the invention and adapted to be operated in accordance with a method of the invention.

DETAILED DESCRIPTION OF THE PRE FERRED EMBODIMENT In the drawing, a proportional pneumatic valve constructed and operated in accordance with an embodiment of the invention is identified generally by the reference numeral 11.

The valve 11 consists of an outer housing, indicated generally by the reference numeral 12, which comprises a main body part 1 3 and end closures 1 4 and 15, that are secured to the main body part 1 3 in any known manner. The main body part 1 3 is provided with a through bore 1 6 that is intersected by a plurality of ports 17, 18, 19, 21 and 22.

The ports 1 7 through 22 terminate in respective annular cavities 23, 24, 25, 26 and 27 that extend around the bore 16.

A sleeve 28 is positioned in the bore 1 6 and is shorter in length than the bore. The sleeve 28 is axially positioned by means of a pair of spacers 29 and 31 and bumpers 32 and 33 that are positioned at the respective ends of the sleeve 28 and which are axially fixed by the end caps 1 4 and 1 5. The sleeve 28 is also provided with a plurality of circumferential grooves 34 in which 0 rings 35 are received so as to provide a seal between the sleeve 28 and the main body 1 3 so that the ports 17, 18, 19, 21 and 22 are isolated from each other.

Although any of a wide variety of porting arrangements may be employed with the valve body and valve sleeve arrangement described, in the illustrated embodiment the port 1 9 comprises an inlet port that is adapted to be communicated with a source of high pressure air (not shown). The ports 18 and 21 are supply ports which may, in a typical application, extend to opposite ends of a double acting pneumatic cylinder (not shown). The ports 1 7 and 22 are exhaust ports and may be opened to the atmosphere either directly or through any suitable exhausting system. The valve sleeve 28 is provided with a plurality of through passages 36, 37, 38, 39 and 41 that permit communication between the annular valve body cavities 23, 24, 25, 26 and 27, respectively, and an internal bore 42 of the sleeve 28.

A flow controlling spool, indicated generally by the reference numeral 43, is slidably supported within the bore 42 of the valve sleeve 28. In the illustrated embodiment and with the porting arrangement described, the valve spool 43 includes a central land 44, and a pair of end lands 45 and 46. A reduced diameter area 47 is provided between the lands 44 and 45 and a similar reduced diameter area is provided between the lands 44 and 46. The lands 45 and 46 are provided with circumferential balancing recesses 49.

In its neutral or closed position, as shown in the figure, the land 44 closes communication of the port 38 with the bore 42 and the reduced diameter sections 47 and 48 permit communication between the respective ports 36, 37 and 39, 41. Thus, the associated pneumatic cylinder has both of its ends opened to exhaust and this cylinder will be held in a fixed position.

In accordance with the invention, a spring arrangement is provided for holding the valve spool 43 in its neutral, closed position and for providing an increasing resistance to movement of the valve spool 43 in either of its directions after a predetermined degree of movement from the closed position. This centering spring arrangement includes a pair of spring retainers 52, each of which is in engagement with a respective end of the valve spool 43. The spring retainers 52 are provided with a bore 53 in which one end of a relatively low rate centering spring 54 is nested. The opposite ends of each of the centering springs 54 are received in respective bores 55 formed in the end closures 14 and 1 5. The springs 54 are preloaded and urge the valve spool 43, as noted, to its closed position.However, the springs 54 are relatively low rate, as has been noted, and any actuating force applied to the valve spool 43 will cause one of the springs retainers 52 to move in an axial direction and compress the associated spring 54.

A second, substantially higher rate spring 56 is positioned at ea,ch end of the valve spool 43. The springs 56 are nested in counterbores 57 of the spring retainers 52 and are adapted to engage the respective end closures 1 4 and 1 5. The springs 56 are slightly shorter in length than the normal distance between the end closures 1 4 and 1 5 and the respective ends of the counterbores 57 of the spring retainers 52 so that when the valve spool 43 is in its neutral or closed position, the springs 56 will be completely unloaded.

A means (not shown) is provided for actuating the valve spool 43 to move it in either direction from its closed position. This means may be an actuator or any known type normally employed with such valves such as a pair of solenoid windings which may be selectively energized so as to draw the spool 43 in one or the other axial direction, depending upon which coil is energized. In accordance with the invention, the proportional control is further achieved by applying successive pulses of force to the spool 43 tending to move it in the desired direction. That is, the associated solenoid windings are energized for brief periods of time with intervening intervals of non-enerization. The proportional control may be achieved by either changing the frequency of the energizations or, alternatively, by increasing the duration of the period of time which the solenoids are energized.

If the solenoid associated with the land 45 is energized, for example, it will exert a force tending to draw the spool 43 to the left.

Initial movement to the left is resisted only by the very light centering spring 54 and the spool 43 will tend to move rapidly in this direction so as to tend to cause the port 38 of the inlet 1 9 to register with the recess 48. At the same time, the communication of the exhaust port 36 with the supply port 37 will.

be increased. Thus, pressurized air will flow from the port 38 to the port 39 and one end of the associated pneumatic cylinder while the other end will be exhausted. When this movement occurs, the exhaust port 41 will be closed by the land 46.

After a predetermined degree of movement, determined by the relative length of the spring 56, the spring retainer 52 will engage the spring 56 at the left hand end of the spool 43 and provide a substantially increased force that resists further opening of the valve spool 43 in this direction. This dual spring arrangement coupled with the proportional actuation of the spool 43 has been found to give a proportional air pressure outlet to the cylinder that will permit proportional actuation in a manner not heretofore possible with such simpls pneumatic valves.

It should be readily apparent that actuation of the spool 43 in the opposite direction so as to expose the supply port 37 to the inlet port 38 and close the exhaust port 36 is done by energizing the solenoid associated with the land 46 in a manner as described in conjunction with actuation in the opposite direction.

It should be readily apparent from the foregoing description that the described valve arrangement and its method of actuation permits highly effective proportional pneumatic control at a relatively low cost. Although the device has been described in conjunction with a spool type valve, the same principle may be applied to poppet valves or any other type of pneumatic valve, for that matter. Also, although the arrangement is disclosed in con junction with two springs for resisting movement, it may also be used with a greater number of springs than two or with springs having non-linear rates.

Although an embodiment of the invention has been illustrated and described and other embodiments described, still further changes and modifications may be made, without departing from the spirit and scope of the invention, as defined by the appended claims.

Claims

1. A method of achieving proportional control of a pneumatic valve comprising a flow control element supported for movement between a closed position, an intermediate position wherein restricted flow is permitted and a fully opened position wherein substantially unrestricted flow is permitted, said method comprising the steps of applying a substantially constant actuating force for moving the flow control element from its closed position toward its opened position, said actuating force being applied sequentially for predetermined time intervals with intervening time intervals when no actuating force is applied, applying a first relatively low rate biasing force on the flow control element for urging the flow control element toward its closed position, and applying a substantially higher rate biasing force upon the flow control for resisting further opening of the flow control element when the flow-control element moves from its closed position a predetermined amount.

2. A method as set forth in Claim 1 wherein the flow control element is movable from its closed position in a first direction as described for controlling flow to a first output and in an opposite second direction for controlling flow to another output than the first output.

3. A method as set forth in Claim 1 wherein the biasing forces are applied to the flow control element by springs having different rates.

4. A proportional pneumatic flow control valve comprising a housing defining an inlet port and a supply port, a flow control element movable from a closed position wherein communication between said ports is substantially precluded and an opened position wherein substantially unrestricted communication between said ports is prgvided, first biasing means for constantly urging said flow control element toward its closed position, and second biasing means for resisting movement of said flow control element toward its fully opened position when said flow control element moves a predetermined amount from its closed position toward its fully open position, said second biasing means having a substantially greater rate than said first biasing means.

5. A proportional pneumatic flow control valve as set forth in Claim 4 wherein the flow control element is movable in a second direction opposite to the movement from its closed position to the opened position and turther including a second supply port adapted to be communicated with the inlet port when the flow control element moves in one of its directions, movement in the other of the diiec- tions controlling the communication between the inlet port and the first mentioned supply port and further including third biasing means for constantly urging said flow control element toward its closed position in the opposite direction and fourth biasing means for resisting movement of the flow control element toward its fully opened position in the opposite direction when the flow control element moves a predetermined amount from its closed position in the opposite direction toward its fully opened position, said fourth biasing having a substantially greater rate than said third biasing means.

6. A proportional pneumatic flow control valve as set forth in Claim 4 wherein the biasing means comprise coil springs.

7. A proportional pneumatic flow control valve as set forth in Claim 6 wherein the flow control element comprises a valve spool slidably supported in a bore.

8. A proportional pneumatic flow control valve as set forth in Claim 7 wherein the valve spool is slidable in the bore in a second direction opposite to the movement from its closed position to the opened position and further including a second supply port adapted to be communicated with the inlet port when said valve spool moves in one of its directions, movement in the other of the directions controlling the communication between the inlet port and the first mentioned supply port and further including third biasing means for constantly urging said valve spool toward its closed position in the opposite direction and fourth biasing means for resisting movement of said valve toward its fully opened position in the opposite direction when said valve spool moves a predetermined amount from its closed position in the opposite direction toward its fully opened position, said fourth biasing having a substantially greater rate than said third biasing means.

9. A proportional pneumatic flow control valve as set forth in Claim 4 further including an exhaust port, said flow control element being effective to provide communication between said exhaust port and said supply port when said flow control element is in a closed position and to close off communication of said supply port with said exhaust port when said flow control element moves from its closed position.

1 0. A proportional pneumatic flow control valve comprising a valve body having an inlet port, a pair of supply ports disposed on opposite sides of said inlet port, and a pair of exhaust ports disposed on opposite sides of said supply ports and outwardly of said inlet port, a bore in said valve body intersecting said ports, a sleeve fixed in said bore and having passages extending therethrough communicating each of said ports independently with a bore of said sleeve, a valve spool slidably supported within said sleeve bore and having a central land and a pair of spaced end lands each connected to said central land by a reduced diameter portion, said valve spool lands and reduced portions being spaced relative to said passages so as to close the communication of said inlet passage with said sleeve bore and communicating respective of the supply and exhaust passages with each other when said valve spool is in a centered position and to communicate said inlet passage with one of said supply passages and the other of said supply passages with its respective exhaust passage when said valve spool is displaced from said central position, first relatively light centering springs operably engaged with opposite ends of said valve spool for urging said valve spool to its centered position and a pair of heavier rate springs each disposed at a respective end of said valve spool and adapted to be operably engaged with said valve spool when said valve spool moves a predetermined amount from its centered position for resisting further movement of said valve spool at a force substantially greater than that of said centering springs.

11. A proportional pneumatic flow control valve substantially as described herein with reference to and as illustrated in the single Figure of the accompanying drawings.