EP0000445A1

EP0000445A1 - Servo valve

Info

Publication number: EP0000445A1
Application number: EP78300136A
Authority: EP
Inventors: Kishor J. Patel
Original assignee: Dynex Rivett Inc
Current assignee: Dynex Rivett Inc
Priority date: 1977-07-13
Filing date: 1978-07-10
Publication date: 1979-01-24
Also published as: EP0000445B1; DE2862092D1; JPS5420275A; JPS61116205U; CA1093426A

Abstract

A servo valve having a pilot control balance network in which a variable orifice (104) is established between the main control spool (14) an the actuator member (96) of a force motor (94) wherein movement of said member causes the main spool to assume a new corresponding position that re-establishes the balance in said network.

Description

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 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 P, is fed back to the armature via a nozzle bore and reacts with the torque motor and reaction spring to achieve a constant P_c regardless of the pilot pressure P magnitude. In the present invention., the control pressures vary with pilot supply pressure since P_c 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.
Another patent of interest-is that to E. C. Jupa, issued March 7, 1961, 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 present invention there is provided a flow control servo valve comprising a valve housing having an axial bore therethrough, a valve control spool axially movable within the bore so as to take up a balanced position with the housing and having an axial passageway therein extending from end to end of the spool to communicate with first and second end chambers one disposed at each end of the spool, a source of pilot pressure connected through first and second equal orifices respectively to the first and second end chambers, a third orifice equal to the first and second orifices and extending between the axial bore and the first end chamber, a fourth orifice of variable size between the axial bore and the second end chamber, and a force motor with an axially movable actuator member so arranged that axial movement of the actuator member varies the size of the variable orifice which in turn causes the control spool to move axial to assume a new position to reestablish the balance.
This invention therefore provides a servo control valve wherein an electrical signal may be used to cause a mechanical movement which varies one orifice of a bridging network, which is carried by the main hydraulic spool, which causes a movement in the spool until balance is restored and accurate and continuous feedback is present for spool positioning.
The invention also provides a pilot stage for a hydraulic control valve which comprises three fixed orifices and a single adjustable orifice, the latter of which may cooperate with an electromagnetic motor displacement to establish a variable orifice area that will control main spool location. The force motor proportionally varies pilot fluid pressure to thereby move the spool in proportion to the current or voltage used to adjust the space between a piston of the motor and a-nozzle formed on the main spool.
These and other objects of the invention will become more apparent to those skilled in the art by reference to the following detailed description given by way of example when viewed in light of the accompanying drawings.

Brief Description of the Drawings

FIGURE 1 is a side view of a servo valve according to this invention;
FIGURE 2 is an elongated cross-sectional view, partially schematic, of the principal elements of the servo valve shown in Figure 1;
FIGURE 3 is an enlarged section of the variable nozzle portion of Figure 2; and
FIGURE 4 is a-schematic of the control pressure network of the apparatus of Figure 1.

Detailed Description of the Presently Preferred Embodiment

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.
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 can port 40. Internal grooves 28 and 30/communicate with a load 42 by way of passageway 44, and ihternal grooves 32 and 34 can 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 50 is connected to the output of a pump 52, so that pressure from the pump 52 is communicated to the pressure groove4§ and can then be communciated 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 groove48 is communicated to neither passageway. However, as the spool 14 moves to 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 2R.
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 spring 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 witn land 2u of spool 14.
Chambers 54 and 70 are subjected to intermediate control pressures by means of orifices 74 (A₁) 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 communicates with the orifices 74 and 76 via an internal filter 84 which protects those orifices from fluid contamination.
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 (A,) and orifice 76 (A₂).
Attached to the right end of valve housing 10, as seen in Figure 2 by means of a mounting cap 92 is a force 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 96. 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 ap on the force motor stem 96 due to the pressure at the nozzle 100 opening.
Mounting cap 92 is retained in position on the valve housing 10 by clips 106 and bolts 108. At the left end of mounting cap 94 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 locking ring 114. This arrangement allows external adjustment of the force motor stem 96, which in turn permits external manual adjustment of the variable orifice 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 (A,), 76(A₂), and 90 (A3) in effective area. At that point, the pressures in each of the chambers 54 and 70 is exactly half 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 motor 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 move 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 3? and passageway 46. In each case, of course, the spool 14 will move only that amount necessary to re-establish the face balance. When the faces 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-establishinq 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 chamber 54 and 70 caused, for instance, by failure of the pump 52 will cause the spool 14 to return to its "null" position.
The foregoing control pressure bridge is displayed schematically in Figure ₄. As shown therein, the subject invention provides a pilot pressure bridge arrangement in which there are four orifices, only one of which is variable. An automatic feedback is thus developed which provides accurate, continuous control.
In a general manner, while there has been disclosed an effective and efficient embodiment of the invention, it 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 without departing from the principle of the present invention as comprehended within the scope of the accompanying claims.

Claims

1. A flow control servo valve comprising a valve housing having an axial bore therethrough, a valve control spool axially movable within the bore so as to take up a balanced position within the housing and having an;axial passageway therein extending from end to end of the spool to communicate with first and second end chambers one disposed at each end of the spool, a source of pilot pressure connected through first and second equal orifices respectively to the first and second end chambers, a third orifice equal to the first and second orifices and extending between the axial bore and the first end chamber, a fourth orifice of variable size between the axial bore and the second end chamber, and a force motor with an axially movable actuator member so arranged that axial movement of the actuator member varies the size of the variable orifice which in turn causes the control spool to move axial to assume a new position to reestablish the balance.

₂. 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 therof leading to first and second chambers;

(c) a source of pilot pressure;

(d) first and second conduit means containing first and second equal orifices communicating said source to said first and second chambers, respectively;

(e) a third orifice equal to said first and second orifices between said bore and said first chamber;

(f) a control piston extending into said second chamber and having a planar surface in said chamber; and

(g) said bore 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.

3. The servo valve of Claim 1 or 2 wherein first and second spool centering springs are housed respectively in said first and second chambers.

The servo valve of Claim 1or 2 or 3, wherein said housing is formed with a pressure port, and first and second work ports and land portions of said spool are located to alternately connect said pressure port to one of said work ports.

5. The servo valve of any of the preceding Claims wherein the position of said control piston is obtained electrically.

6. The servo valve of Claim -5 wherein lack of current will cause said valve spool to return to the "null" position.

7. The servo valve of Claim 1 or 2 wherein loss of pilot pressure will cause said valve spool to return to the "null" position.

8. The servo valve of Claim 1 or 2 and further comprising means for external mechanical "null" adjustments.

9. 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 to said first and second chambers respectively;

(d) first and second equal orifices respectively in said conduit means;

(e) a third orifice equal to said first and second orifices betwen said bore and said first chamber;

(f) a control piston extending into said second chamber and having a planar surface in said chamber, and

(g) said bore 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.

.0. A flow control sero valve substantially as hereinbefore lescribed with reference to the accompanying drawings.