CA1093426A

CA1093426A - Servo valve

Info

Publication number: CA1093426A
Application number: CA307,244A
Authority: CA
Inventors: Kishor J. Patel
Original assignee: Dynex Rivett Inc
Current assignee: Dynex Rivett Inc
Priority date: 1977-07-13
Filing date: 1978-07-12
Publication date: 1981-01-13
Also published as: JPS61116205U; EP0000445A1; DE2862092D1; EP0000445B1; JPS5420275A

Abstract

Abstract of Disclosure A servo valve having a pilot control balance network in which a variable orifice is established between the main control spool and the actuator member of a force motor wherein movement of said member causes the main spool to assume a new corresponding position that re-establishes the balance in said network.

Description

~ 10934Z6 Background of the Invention There are many hydraulic applications in which a signal from a remote source such as an electric force motor is used to cause hydraulic response in a hydraulic control valve. Other workers in the prior art have utilized control pressure networks for establishing a movement in the main spool of the hydraulic valve in response to a movement in a remote control motor. For instance, the United States patent to W.C. Moog, Jr. 2,625,136, issued January 13, 1953, discloses a pilot stage circuitry in which a half-bridge pilot circuit with a stationary nozzle is disclosed. In the Moog patent, the torque motor is a force generating device whereas in the instant invention, a displacement-type force motor is used. In Moog, the control pressure Pc is fed back to the armature via a nozzle bore and reacts with the torque motor and reaction spring to achieve a constant P regardless of the pilot pressure Ps magnitude. In the instant invention, the control pressures vary with pilot supply pressure since Pc is used as a feedback parameter.
United States Patent 3,410,308, issued to W.C. Moog, Jr. on November 12, 1968, United States Patent 3,430,656, issued March 4, 1969 to J. W. Hawk, and United States Patent 2,934,765, issued April 26, 1960 to T. H. Carson, are also of interest.

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Another patent of interest is that to E. C. Jupa, issued March 7, 1961, United States Patent No. 2,973,746, which shows a bridge network.
In Jupa, the adjustable nozzle is stationary and not attached to the main spool as in the instant invention. Thus, Jupa does not incorporate a moving nozzle with a one-to-one position feedback. Jupa also has two variable orifices. The flapper nozzle, of course, is adjustable and his needle valve, on the end of the spool, is also adjustable.
According to the invention, a flow control servo valve has a valve housing having a bore therethrough and a valve spool reciprocally received in said bore, said housing having first and second work ports, a tank port, and a pressure port communicating with said bore at spaced intervals along its length and said valve spool having lands and grooves to selectively route fluid between the ports. This servo valve includes first and second chambers at either end of said valve spool, a source of pilot pressure;
first and second conduit means communicating said source of pilot pressure to said first and second chambers respectively; first and second equal orifices respectively in said conduit means; a passageway extending the length of said valve spool and leading to said first and second chambers; a third orifice equal to said first and second orifices between said passageway and said first chamber; a control stem extending into said second chamber -~
and having a planar surface in said chamber, said planar surface being sub- -Jected to the reduced pilot pressure in said second chamber; said passageway having a reduced circumference defining an opening juxtaposed opposite said planar surface defining a fourth orifice that is adjustable through the movement of said surface toward and away from said opening; a source of supply pressure isolated from said source of pilot pressure, said source of supply pressure being in fluid communication with said pressure port; and first and second spool centering springs housed respectively in said first and second chambers.
A principal objective of this invention is to provide a servo control valve wherein a signal causes a mechanical movement which varies one orifice of a bridging network, which is carried by the main hydraulic spool,

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10~34Z6 which causcs a moVement in the spool until balance is restored and accurate and continuous feedback is present for spool positioning.
Another important objective of this invention is to provide a flow control servo valve which is simple in its construction, rugged in its performance and accurate in its functioning.
A still further objective of this invention is to provide a pilot stage for a hydraulic control valve which comprises three fixed orifices and a single adjustable orifice~ In the preferred embodiment, the adjustable orifice cooperates with an electromagnetic motor displacement to establish a variable orifice area that will control main spool location.
In the preferred embodiment there is a force motor to proportionally vary pilot fluid pressure to thereby move the spool in proportion to the current or voltage used to adjust the space between the motor piston and a nozzle formed on the main spool.
Other features ant advantages will become re apparent to those skilled in the art by reference to the following detailed description when viewet in light of the accompanying drawings.
In the drawings, FIGURE I is a side view of a se wo valve according to this invention;
2Q FIGURE 2 is an elongated cross-sectional view, partially schematic, of the principal elements of the servo valve shown in Figure 1;
PIGURe 3 is an enlarged section of the variable nozzle portion of Pigure 2; and PIGURE 4 is a schematic of the control pressure network of the apparatus o Pigure 1.
Referring now to the drawings wherein like numerals indicate like parts, the numeral 10 indicates a valve housing having a bore 12 therethrough.
Reciprocally received within the bore 12 is a spool 14 equipped with four land areas 16, 18, 20, and 22. Between land areas 16 and 18 is a groove area 24, and between land areas 20 and 22 is a groove area 26. Land areas 18 and 20 are machined with close tolerances for reasons which will become apparent hereinafter.

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The valve housing 10 is machined with four internal grooves 28, 30, 32 and 34 located opposite the axial extremities of the land areas 18 and 20 when the spool 14 is in the position shown in Figure 2. Groove areas 24 and 26 communicate with a tank 36 (shown only in Figure 4) by way of a passageway 38 and a return port 40. Internal grooves 28 and 30 -communicate with a load 42 by way of passageway 44, and internal grooves 32 and 34 communicate with the load 42 by way of a passageway 46. Passageways 44 and 46 are closed and opened by the movements of land areas 18 and 20, respectively; in the location of the spool 14 shown in Figure 2, both passageways are closed. `:- -In the middle of spool 14, between land areas 18 and 20, is a pressure groove 48 which communicates with a port 50 shown in Figure 1. The port S0 is connected to the output of a pump 52, so that pressure from the pump 52 is communicated to the pressure groove 48 and can then be communicated to either passageway 44 or passageway 46, depending on the position of spool 14. Of course, in the position shown in Figure 2, pressure from the pressure groove 48 is communicated to neither passageway. However, as the spool 14 moves ~o the left as viewed in Figure 2, pressurized fluid will flow to the load 42 through internal groove 30 and passageway 44 and return to tank 36 via passageway 46 and internal groove 34. Conversely, as the spool 14 moves to the right as viewed in Figure 2, pressurized fluid will flow to the load 42 through internal groove 32 and passageway 46 and return to tank 36 via passageway 44 and internal groove 28.

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- 1~934Z6 At the left end of bore 12 as viewed in Figure 2 is a chamber 54 closed by an end gland 56 retained in position on the valve housing 10 by clips 58 and bolts 60~ End gland 56 receives a piston 62, a screw 64, a jam nut 66, and a centering spxing 68. At the right end of bore 12 is a chamber 70 which receives a second centering spring 72 and which is closed by apparatus described hereinafter. The piston 62, the screw 64, the jam nut 66 and the two centering springs 68 and 72 collectively serve as a mechanical "null"
adjustment for the spool 14. That is, by adjusting screw 64 it is possible to initially locate land areas 18 and 20 on the spool 14 so that the internal grooves 28 and 30 align with land 18 and grooves 32 and 34 align with land 20 of spool 14.
Chambers 54 and 70 are subjected to intermediate control pressures by means of orifices 7~)(Al) and 76 (A2), which communicate with the chambers 54 and 70 via the conduits 78 and 80, respectively. The orifices 74 and 76 are of fixed dimensions and are equal to each other. An isolated pilot port 82, which serves as a source of isolated pilot pressure, communicates with the orifices 74 and 76 via an internal filter 84 which protects those orifices from fluid contamination.
As is well known in the art, isolated pilot pressures can be obtained either by use of an independent pump ~i.e., a pump separate from the drive pump 52) or by leading fluid pumped by the drive pump through a branch conduit which contains a pressure reducing valve. The pressure reducing valve has a constant pressure output regardless of input ~so long as the input exceeds the desired output), thereby ensuring that variations in the control pressure do not affect the pressure communicated to the branch conduit. Since both techniques are well known in the art, neither is illustrated.
Throughout the length of spool 14 is a conduit 86. The conduit 86 communicates at its right end with the groove area 26 via a hole 88 in the spool 14 and at its left end with the chamber 54 via a third fixed orifice 90 (A3) which is equal to orifice 74 (Al) and 76 (A2).

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~ 10934Z6 Attached to the right end of valve housing 10 as seen in Figure 2 by means of a mounting cap 92 is a orce motor 94 having a force motor stem 96 terminating in a planar end 98 which extends toward the right end of the spool 14. As best seen in Figure 3, the end of the spool 14 which faces the force motor 94 carries a pressed-in nozzle 100 having a planar annular surface 102 disposed opposite and parallel to the planar end 98 of the force motor stem ~6. The area between the planar end 98 of the force motor stem 96 and the planar annular surface 102 on the nozzle 100 constitutes a fourth orifice 104 (A4), which, as explained hereinafter, is of variable area. As is well known in the art, the force motor 94 preferably includes a built~in bias spring to overcome any force built up on the force motor stem 96 due to the pressure at the nozzle 100 ope~ling. ~~
Mounting cap 92 is retained in position on the valve housing 10 by clips 106 and bolts 108. At the left end of unting cap 92 is a flat washer 110 which abuts the centering spring 72 and which limits the travel of the spool 14 in the right-hand direction. The force motor 94 is mounted ~ -in the mounting cap 92 by threads 112 and retained for locking purposes by locl~ing ring 114. This arrangement allows external adjustment of the force motor stem 96, which in turn permits external manual adjustment of the variable oriice 104 (A4).
Initially, after the screw 64 has been adjusted to align the spool 14 in the valve housing 10 as shown in Figure 2, the force motor 94 is adjusted so that the variable orifice 104 (A4) equals the fixed orifices 74 (Al), 76 tA2), and 90 tA3) in effective area. At that point, the pressures ~A
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, 1 .: : ' ~ 10~93426 in each of the cham~ers 54 and 70 is exactly hal the pilot supply pressure applied to pilot port 82 Since the pressures in the chambers 54 and 70 are equal to each other? the spool 14 is held stationary, which is called the "null" of the valve.
When current or voltage applied to the force tor 94 causes the force motor stem 96 to move to the left toward spool 14, orifice 104 (A4) is reduced in area. As a result, the pressure in chamber 70 increases, and the spool 14 moves to the left, causing pressurized fluid to actuate the load 42 through internal groove 30 and passageway 44. Correspondingly, when current or voltage applied to the face motor 94 causes the force motor stem 96 to ve to the right away from spool 14, orifice 104 (A4) is increased in area.
As a result, the pressure in the chamber 70 decreases, and the spool 14 moves to the right, causing pressurized fluid to actuate the load 42 through internal groove 32 and passageway 46. In each case, of course, the spool 14 will move only that amount necessary to re-establish the force balance. When the orces are again in balance, the spool 14 is held in the newly attained position. If the input to the force motor 94 is later varied, the spool 14 will quickly move to a new position re-establishing the force balance. In particular, if the input to the force motor 94 later ceases, the spool 14 will return to the "null" of the valve. Similarly, lack of controlling pressures in the chambers 54 and 70 caused, for instance, by failure of the pump 52 (if the isolated pilot pressure is derived from the pump 52) will cause the spool 14 to return to its "null" position.
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The foregoing control pressure bridge is displayed j schematically in Figure 4. As shown therein, the subject in-~' vention provides a pilot pressure bridge arrangement in which ,~ there are four orifices, only one of which is variable. An ., :
S Is automatic feedback is thus developed which provides accurate, continuous control.
il In a general manner, while there has been disclosed an effective and efficient embodiment of the invention, it j, should be well understood that the invention is not limited to such an embodiment as there might be changes made in the arrangement, disposition, and form of the parts wlthout departing ~ from the principle of the present invention as comprehended s within the scope of the accompanying claims.
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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A flow control servo valve comprising:
(a) a valve housing having a bore therethrough;
(b) a valve spool reciprocally received in said bore and having a passageway extending the length thereof leading to first and second chambers, said spool equipped with four land areas which form first and second grooves and a third central groove;
(c) a source of pilot pressure;
(d) first and second conduit means containing first and second equal orifices communicating said source of pilot pressure to said first and second chambers, respectively, (e) a third orifice equal to said first and second orifices between said passageway and said first chamber;
(f) a control stem extending into said second chamber and having a planar surface in said chamber, said planar surface being subjected to the reduced pilot pressure in said second chamber;
(g) said passageway having a reduced circumference defining an opening juxtaposed opposite said planar surface to define a fourth orifice that is adjustable through the movement of said surface toward and away from said opening;
(h) a source of supply pressure isolated from said source of pilot pressure;
(i) a third conduit means communicating said source of supply pressure to said third central groove;
(j) fourth and fifth conduit means for respectively and selectively communicating said first and second grooves to tank;
(k) sixth and seventh conduit means for respectively and selectively communicating said first and second grooves to a load;
(l) said land areas and said grooves on said spool, and said fourth, fifth, sixth, and seventh conduit means being sized and positioned so that:

(i) when said spool is in its null position pressure from said source of supply pressure is not communicated past said third central groove;
(ii) when said spool is in a first work position, pressure from said source of supply pressure is communicated from said third central groove, through said sixth conduit means to a load, back through said seventh conduit means to one of said first and second grooves and through said fourth conduit means to tank; and (iii) when said spool is in a second work position, pressure from said source of supply pressure is communicated from said third central groove, through said seventh conduit means to a load, back through said sixth conduit means to the other one of said first and second grooves, and through said fifth conduit means to tank; and (m) first and second spool centering springs housed respectively in said first and second chambers.

2. The servo valve of claim 1 wherein the position of said control stem is obtained electrically.

3. The servo valve of claim 2 wherein lack of current will cause said valve spool to return to the "null" position,

4. The servo valve of claim 1 wherein loss of pilot pressure will cause said valve spool to return to the "null" position.

5. The servo valve of claim 1 and further comprising means for external mechanical "null" adjustments.

6. In a flow control servo valve of the type having a valve housing having a bore therethrough and a valve spool reciprocally received in said bore, said housing having first and second work ports, a tank port, and a pressure port communicating with said bore at spaced intervals along its length and said valve spool having lands and grooves to selectively route fluid between said ports, the improvement comprising:
(a) first and second chambers at either end of said valve spool;
(b) a source of pilot pressure;
(c) first and second conduit means communicating said source of pilot pressure to said first and second chambers respectively;
(d) first and second equal orifices respectively in said conduit means;
(e) a passageway extending the length of said valve spool and leading to said first and second chambers;
(f) a third orifice equal to said first and second orifices between said passageway and said first chamber;
(g) a control stem extending into said second chamber and having a planar surface in said chamber, said planar surface being subjected to the reduced pilot pressure in said second chamber;
(h) said passageway having a reduced circumference defining an opening juxtaposed opposite said planar surface defining a fourth orifice that is adjustable through the movement of said surface toward and away from said opening;
(i) a source of supply pressure isolated from said source of pilot pressure, said source of supply pressure being in fluid communication with said pressure port; and (j) first and second spool centering springs housed respectively in said first and second chambers.