WO1996026377A1

WO1996026377A1 - Piezo-electrically actuated valve

Info

Publication number: WO1996026377A1
Application number: PCT/US1996/002201
Authority: WO
Inventors: Dale A. Knutson; George R. Steber
Original assignee: Applied Power Inc.
Priority date: 1995-02-21
Filing date: 1996-02-20
Publication date: 1996-08-29
Also published as: WO1996026378A1; AU4869196A; AU4928196A

Abstract

A piezo-electrically actuated hydraulic valve (10) has a nozzle type seat (27), a piezo-electric actuator (20) in a plane orthogonal to the axis of the nozzle (27), an orifice (21A) to a low pressure port (28) downstream of the seat (27), and a control pressure port (30) between the seat (27) and the orifice (21A). The actuator (20) includes a piezo-ceramic layer (50) laminated to an electrode sheet (48), so that the composite is in sheet form and with a surface (51) of the piezo-ceramic layer (50) facing the seat (27). The electrode sheet (48) has opposite edges (20A, 20B) which extend beyond the piezo-ceramic layer (50) and are clamped by the housing (12) of the valve so that the center of the actuator (20) is positioned over the seat (27). When an electric field is applied to the piezo-ceramic layer (50), the actuator (20) bows or dishes so as to displace relative to the nozzle (27) so as to vary the flow area between the seat (27) and the actuator (20). Monomorph (20) or bimorph (120) actuators may be used, and a single nozzle (27) may be provided on only one side of the actuator, or a pair of opposed nozzles (827, 827') may be provided with the actuator between them and normally seated against one. Ends (220A, 220B) of the electrode sheet (248) are bent to increase the deflection of the actuator (220) for a certain input voltage. Subareas (451A, 451B) are provided on the piezo-ceramic layer (450) to produce an electrical feedback signal when the actuator is piezo-electrically deflected.

Description

PIEZO-ELECTRICALLY ACTUATED VALVE

Background of the Invention

Field of the Invention

This invention relates to hydraulic or pneumatic valves, and in particular to such valves having piezo- electric actuators.

Discussion of the Prior Art Solenoid operated pilot valves having a flapper- nozzle type electromagnetically operated actuator are known, for example, from U.S. Patent Nos. 4,774,976 and 5,328,147. The valve disclosed in U.S. Patent No.

4,774,976 has a nozzle type seat which is normally closed by a disk shaped armature or flapper. A pulse width modulated signal or a proportional signal may be applied to a solenoid type electro-magnet positioned on the side of the armature opposite from the nozzle so as to variably open the nozzle. The pressure exterior of the nozzle is typically higher than the pressure interior of the nozzle so that it biases the armature disk against the nozzle and a controlled pressure is produced downstream of the nozzle but upstream of an orifice which bleeds the excess flow to a relatively low tank pressure.

Valves such as those described in U.S. Patent No. 4,774,976 have found wide commercial application and work very well in many applications. However, one limiting factor in the valve has been the requirement of the solenoid type electro-magnet for actuating the valve. The solenoid adds significant cost to the valve, and is relatively large and heavy. In addition, due to the mass of the armature, and the inductance of the coil, the base frequency of a pulse-width-modulated signal that can be used to operate the valve must be kept relatively low, for example 30-40 Hertz. While this is more than adequate for most applications, the resulting controlled pressure signal will display a dither of a corresponding frequency; at low pulse-width-modulated frequencies, the magnitude of the pressure dither is greater and may cause undesirable movements of the device being controlled by the valve. In addition, since the frequency response is dependent upon the pulse-width-modulated base frequency, the valve does not have a particularly fast frequency response and thus the band width of pressures which can be controlled is somewhat limited. Moreover, because of the requirement that the solenoid be opposed from the nozzle, it is not possible to control two nozzles with a single armature. Piezo-electric materials are also well known and have been used in a variety of applications. A material possesses piezo-electric properties if it produces an electric charge when it is subjected to a mechanical stress. When so subjected, a piezo-electric material exhibits what is known as the "generator effect" .

Conversely, when an electric field is applied to a piezo¬ electric material, a mechanical stress is induced in the material which causes it to deflect. This phenomenon is referred to as the "motor effect". Some piezo-electric materials are naturally occurring crystalline materials such as quartz and tourmaline. Artificially produced piezo-electric crystals include rochelle salt, ammonium, dihydrogen phosphate (ADP) and lithium sulphate. Piezo-electric materials also include polarized piezo-electric ceramics. Piezo-electric ceramics include lead zirconate titanate, barium titanate, lead titanate and lead metaniobate.

Various processes are involved in the production of piezo-electric ceramics. Typically, the production process includes mixing the raw materials, heating the powders so as to react the constituents into a compound (known as "calcining") and grinding the calcined powders. Various shapes may then be formed of the powders using a binder to hold the shapes together prior to firing. A number of firing steps may then occur to burn off the binders and provide mechanical strength, and at higher temperatures to chemically bond the material together. Electrodes are then applied to the desired surface or surfaces of the piezo-electric ceramic part. The electrode may take the form of a layer of electrically conductive material such as silver oxide which is chemically deposited on the surface of the piezo-electric ceramic in a coating process, or may be an electrically conductive sheet such as invar, copper, nickel, brass or silver which is laminated to the surface of the piezo- electric ceramic.

The piezo-electric properties are activated in the manufacturing process when the part with the electrodes attached is subjected to a high electric field to align the dipoles within the ceramic material. This is sometimes done while the part is submerged in a heated dielectric bath. Aging of the ceramic then occurs in which the dipoles relax and eventually reach a steady state. Depolarization of the piezo-electric ceramic can result from excessive heat, electrical or mechanical stress or combinations of these conditions.

Piezo-electric ceramics have found usage in many different applications. For example, piezo-electric ceramics are used in sonar and specialized transducers, in fish finders, in ultrasonic applications such as cleaners and other cavitation products, in high sensitivity hydrophones and other receiving devices, in accelerometers, and in electro-acoustic devices.

Piezo-electric ceramics have also been applied to actuate hydraulic valves. In known hydraulic valve actuators, thin sections of piezo-ceramic material have been stacked between multiple electrodes so as to produce a column of alternating layers of piezo material and electrode material. Individual voltages are then applie to the electrodes so that each layer of piezo-ceramic material changes slightly in thickness, but when all the changes in thickness add up due to the mechanical relationship of the piezo ceramic layers to one another, the total deflection of the column is sufficient to modulate the opening and closing of a hydraulic valve. While the force output is high and the displacement can be made sufficient, these types of actuators are bulky and expensive due to the volume of piezo ceramic materia required.

In another application of piezo-ceramic material to actuate a hydraulic valve, sometimes referred to as a "piezo bender", a strip of piezo-ceramic material with a electrode laminated to one side is cantilevered at one end and at the opposite end overlies the seat of the hydraulic valve. The strip can be caused to bend toward or away from the seat, depending upon the magnitude and polarity of the voltage applied across the piezo-ceramic material. A variation on this is laminating two oppositely poled piezo strips to one another, rather tha one piezo strip to a metal electrode. Relatively large displacements (for example .010") can be obtained, but the force output and the stiffness of the strips are ver low.

Thin sheets of piezo-electric ceramics laminated to an electrode sheet are known. When a layer of piezo- electric ceramic is laminated to only one side of the electrode sheet, the composite is known as a monomorph. When the electrode has a layer of piezo-electric ceramic material laminated on both of its sides, the resulting laminate is known as a bimorph. When excited with an electric field, a monomorph or bimorph deflects into a bowed shape if it is relatively long or wide or a cupped shape if it is both long and wide. The amount of deflection of a monomorph or bimorph depends upon the voltage applied, within limits. When the voltage is oscillated, the monomorph or bimorph also oscillates, and can be oscillated at a relatively high frequency, for example 300 Hertz. Perhaps the most common application of monomorphs and bimorphs has been in acoustic devices, in which the monomorph or bimorph has been oscillated to produce a sound, much like the cone of a conventional speaker is oscillated to produce sounds. Such piezo composite actuators have also been applied to valves, for example, as shown in U.S. Patent Nos. 2,928,409, 3,063,422, 3,152,612, 3,524,474, 4,298,181, 4,535,810, 4,610,426, 4,705,059, 5,203,537 and 5,340,081.

Summary of the Invention The invention provides a valve which addresses disadvantages of prior solenoid and piezo-electrically actuated valves. As in the prior art, a valve of the invention has a housing, an inlet port in the housing, an outlet port in the housing, and a nozzle type valve seat having an axis, an interior and an exterior, the interior being in communication with one of the ports and the exterior being in communication with the other of the ports, and with the seat lying in a first plane which is orthogonal to an axis of the seat. A valve actuator is provided adjacent to the seat for varying an opening between the actuator and the seat for flow between the exterior and interior of the seat which includes a layer of piezo-electric material. A single seat may be provided facing a surface of the actuator, or two opposed seats may be provided with the actuator between them and facing opposite surfaces of the actuator.

In one aspect, the actuator is in the shape of a sheet and is mounted in the housing generally parallel to the seat(s) at opposite edges of the actuator so that the housing constrains the edges against movement in the direction of the axis of the seat(s), with the piezo- electric layer of the actuator facing the seat. As such, when the actuator is electrically excited, it bows or cups relative to the seat(s), to vary the opening(s) of the valve. This configuration provides a relatively small and low cost piezo-electric actuator in which the actuation forces and displacements obtainable are adequate to control relatively high pressure differentials and flow rates. In addition, since the actuator has a fast frequency response, the pressure dither can be reduced by using a higher frequency pulse width modulated signal to control the valve, and the controlled pressure bandwidth is increased for any given frequency, as compared to a solenoid operated valve.

If one seat is used in combination with an orifice downstream of the outlet port and opening to a relatively low pressure, simple and accurate pressure control can be achieved at the control port. If two seats are used on opposite sides of the actuator, two different outlet pressures can be provided which are inversely related to one another, for example to provide positive control over a spool position, or the two output pressures may be used independent of one another.

In a preferred aspect, the flexibility of the actuator is increased for a given input level by providing a bent configuration at the ends of an electrode sheet of the actuator which extend beyond the piezo-electric layer of the actuator. Each end has a leg portion which extends generally perpendicularly from the electrode sheet and an edge portion which extends generally perpendicularly from the leg portion, the edge portions being restrained in the housing. Thereby, for a given voltage, the deflection of the actuator is increased.

In addition, the actuator can be made so that the piezo-electric layer has two or more sub-areas which are elecrically isolated from each other on one electrode surface. One sub-area is used for deflecting the actuator, and the other subarea is used for feedback, since deflection of the actuator by the one sub-area causes the other sub-area to produce an electrical signal, as an indication of the deflection of the actuator.

Brief Description of the Drawings Fig. 1 is a cross-sectional view of a piezo- electrically actuated hydraulic valve of the invention assembled in a valve block plumbed for controlling the position of the spool of a hydraulic valve spool, also shown;

Fig. 2 is a bottom plan view of a piezo-electric actuator for the valve of Fig. 1; Fig. 3A is a side plan view of the piezo-electric actuator of Fig.2;

Fig. 3B is a side plan view of a second embodiment of a piezo-electric actuator for a valve of the invention; Fig. 3C is a side plan view of a third embodiment of a piezo-electric actuator for a valve of the invention; Fig. 4 is a bottom plan view of a forth embodiment of a piezo-electric actuator for a valve of the invention; Fig. 5 is a side plan view of the piezo-electric actuator of Fig. 4;

Fig. 6 is a bottom plan view of a fifth embodiment of a piezo-electric actuator of the invention;

Fig. 7 is a bottom plan view of a sixth embodiment of a piezo-electric actuator of the invention;

Fig. 8 is a bottom plan view of a seventh embodiment of a piezo-electric actuator of the invention;

Fig. 9 is a view similar to Fig. 1 of a second embodiment of a hydraulic valve of the invention; and Fig. 10 is a view of a modification to the embodiment of Fig. 9. Detailed Description of the Prefer**»H TiπiV-odiments

Referring to Fig. 1, a piezo-electrically actuated valve 10 of the invention includes a valve housing 12 which is made up of body 14, cap 16 and electrical connector 17. The valve 10 also includes insert 18, which is pressed into the end of body 14 against a filte screen 19, and an orifice plate 21 which is trapped in the insert 18 by insert 23, which is pressed into the insert 18, and includes piezo-electric actuator 20. The body 14 defines an inlet port 26, a relatively low pressure tank port 28 and a control pressure port 30. The inlet port 26 is for receiving a pressurized flow of hydraulic oil from a suitable source such as a pump P, and communicating it through passageways 32 and 34 to th chamber 36 in which the actuator 20 resides.

Ends 20A and 20B of the actuator 20 are clamped between the cap 16 and the body 14. An o-ring 38 seals the cap 16 to the body 14 and the cap 16 is crimped around its perimeter at 40 to secure it to the body 14. Electrical connector 17 is secured to the cap 16 by bolts 41 and is sealed to the cap 16 by o-ring 17A.

Body 14 defines passageway 25 coaxial along axis 11 with nozzle type valve seat 27. Body 14 also defines control port 30 which communicates with passageway 25 downstream of nozzle 27 and upstream of orifice plate 21, in which orifice 21A is formed. The lumen of insert 23, downstream of orifice 21A, leads to tank port 28, which is in communication with a relatively low pressure tank pressure, denoted by tank T. The orifice 21A is sized so as to create a restriction to the flow of fluid through it such that a desired pressure is produced in pressure port 30 when the nozzle 27 is open. Thereby, the pressure created between nozzle 27 and orifice 21A, which is output through port 30, can be controlled either by varying the degree to which the nozzle 27 is opened or the duration that it is opened using a pulse-width modulated signal. A solenoid operated valve which operates on this principal is described in U.S. Patent No. 4,774,976, the disclosure of which is hereby incorporated by reference. However, it should be understood that the invention could be applied to opening and closing a valve seat in any of a variety of valving arrangements, including those described in U.S. Patent No. 5,328,147, which is hereby incorporated by reference, and those described in U.S. Patent Application Serial No. 08/392,016, entitled "Piezo Composite Sheet Actuated Valve" and U.S. Patent Application Serial No. 08/391,887, entitled "Magnetically Assisted Piezo-Electric Valve Actuator", both filed on February 21, 1995 and commonly assigned to Applied Power Inc., the disclosures of which are also hereby incorporated by reference.

As illustrated in Fig. 1, the pressure from port 30 is communicated via passageway 31 in valve block 29 to a chamber 33 at one end of a valve spool 35 which is slidable in bore 38 and has lands 37 and 39. Springs 43 and 45 (the chamber in which spring 45 is located would normally be vented to tank pressure T, although not shown) serve to center the spool 35 with control land 37 blocking main control port 47, the chamber of the bore 38 between lands 37 and 39 being supplied with pressurized fluid from port 49. When chamber 33 is pressurized via passageway 31 by operation of valve 10, spool 35 is shifted (upwardly as viewed in Fig. 1) so as to unblock port 47 and establish communication between ports 49 and 47, through the bore 38, which is controlled by the magnitude of the pressure in chamber 33. It should be understood that spool 35 represents only one configuration of many spool valve types that could be controlled by means of the pressure generated in port 30. The actuator 20 is a piezo-ceramic monomorph, which as illustrated (Figs. 1-3A) includes an electrode sheet 48 which is laminated on one of its sides to a layer 50, which is a sheet of piezo-ceramic material. An electrically conductive coating 51, such as silver oxide is applied to the surface of sheet 50 which is opposite from electrode 48 and a lead wire 52 is soldered so as t establish electrical contact with the conductive coatin electrode 51. A second lead wire 54 is soldered to the surface of electrode 48 which is opposite from piezo- ceramic sheet 50 so as to establish electrical contact with the electrode sheet 48. An electrical potential is applied between the wires 52 and 54 so as to excite the piezo-ceramic sheet 50, which is in the field created between the coated electrode 51 and the sheet electrode 48. Wires 52 and 54 exit the interior of the housing 12 in a fluid tight manner, being sealed by the connector

17, so that they may be connected to an appropriate valv driver circuit, which could be completely or partially housed in the connector 17.

The piezo-ceramic sheet 50 is poled, preferably in the thickness direction, so that when it is excited with an electric field, the actuator 20 bows or cups in the direction indicated by arrow 56 in Fig. 3A. Such monomorphs are available from EDO Corporation, Acoustics Division, of Salt Lake City, Utah. In one embodiment which has been tested with satisfactory results, the electrode sheet 48 was made of invar metal and had dimensions of 2" by 1" by approximately .008" thick. Th piezo-ceramic sheet was EDO Corporation's EC-98 ceramic, which is a lead magnesium niobate composition, and had dimensions of 1.75" by 1" by .020" thick. Since the actuator 20 is assembled in the housing 12 with the piezo-ceramic sheet side facing the nozzle 27, a small area (for example 0.19" diameter) 58 of the coated electrode 51 is removed at the center of the actuator 20 and the nozzle 27 contacts the actuator 20 within this area. At least the electrode coating 51 must be removed in the area 58 or else, since the electrode 51 is positively charged when the actuator 20 is excited, an electrical short would be created between the electrode coating 51 and the nozzle 27. Alternatively, since the electrode sheet 48 is grounded, as is the nozzle 27, the electrode coating 51 and the piezo-ceramic sheet 50 may be removed in the area 58 and the electrode sheet 48 allowed to contact and seal against the nozzle 27.

The actuator 20 is clamped by the housing 12 along only its end edges 20A and 20B, which are the end edges of the electrode sheet 48. The dotted line 64 in Fig. 2 identifies the shape defined by the sidewalls of the chamber 36 relative to the actuator 20 and there it can be seen that a space 66 and 68 exists between the respective side edges 20C and 20D of the actuator 20 and the sidewalls 64 of the chamber 36. The spaces 66 and 68 allow hydraulic fluid entering the chamber 36 from the inlet port 26 to flow around the side edges 20C and 20D of the actuator 20 to the far side (or electrode sheet 48 side) of the actuator 20.

Since the pressure inside of the chamber 36 exterior of the nozzle 27 is the same everywhere within the chamber 36 (when the nozzle 27 is closed, i.e., under no flow conditions) , and is higher than the pressure inside of the nozzle 27, there is a net fluid force on the actuator 20 which biases it toward the nozzle 27. This force can be estimated from the following equation:

F = A-_. (P. - P₂) where F is the force, A._^ is the cross-sectional area of the nozzle 27, P_x is the pressure in the chamber 36 exterior of the nozzle 27 and P₂ is the pressure interior of the nozzle 27.

Although the actuator 20 is quite brittle due to the brittleness of the piezo-ceramic sheet 50, it does have some resilient flexibility contributed by the electrode sheet 48 and its mounting in the housing 12. Thus, although the crimp 40 is formed so that the cap 16 exert a clamping load on the edges 20A and 2OB, the actuator 2 remains able to flex so as to bow or dish when it is electrically excited. The height of the surfaces of the body 14 on which the ends 20A and 20B rest is machined such that the surface of the plane of the nozzle seat 27 in coincident with the plane of area 58 when the actuator 20 is mounte in the body with no electrical signal and no pressure applied. Alternately, a means of adjustment such as screw threads, shims or a friction fit could be provided to axially position the plane of the nozzle seat 27 in the same plane as area 58.

The actuator 20 may be excited by a pulse width modulated electrical signal or by a proportional voltage signal. The voltages required are relatively high. For example, in the actuator described, a voltage of 500 volts is required to produce a center displacement (at axis 11 of nozzle 27) of approximately 0.010 inches. Although the applied voltage is high, the piezo-ceramic actuator draws current only while the actuator is moving. Since the time of motion is usually less than 0.001 seconds, the average current consumption is relatively low compared to an equivalent solenoid. Because actuator 20 has a fast response, a relatively high frequency can be used for the pulse width modulated signal. Using a relatively high frequency for modulating the actuator 20 (relative to the frequency which can be used with a solenoid operated valve) is desirable because it results in smoothing of the resulting pressure signal at the control port 30, i.e., the resulting pressure signal has less "dither" (or fluctuation) at the higher frequencies. Also, for a given pulse width modulated signal frequency, the pressure control band increases with faster valve actuation. While Fig. 3A illustrates an actuator 20 which is a monomorph, meaning that the electrode sheet 48 has only one side laminated to a piezo-ceramic sheet 50, Fig. 3B illustrates an alternate embodiment of an actuator 120 which is a bimorph, in which electrode sheet 148 has each of its sides laminated to a separate piezo-ceramic sheet 150 and 153. The actuator 120 is largely the same as the actuator 20, and the same reference numerals are applied to the actuator 120 as were applied to the actuator 20 for corresponding elements, plus 100.

In the actuator 120, an electrode coating 151 is applied to the outer surface of sheet 150 and an electrode coating 155 is applied to the outer surface of sheet 153. Lead wire 152 is soldered so as to establish electrical contact with coating 151 and lead wire 157 is soldered so as to establish electrical contact with coating 155. Since the bimorph actuator 120 has ceramic sheets on both sides of the electrode sheet, a greater displacement would be possible for a given voltage if electrical potentials were applied to both ceramic sheets with appropriate poling so that they work together to simultaneously cause the actuator to bow in the same direction. Alternatively, with appropriate poling, an electrical potential could be applied to one of the ceramic sheets to cause the actuator to bow in one direction and an electrical potential could be applied to the other ceramic sheet to cause the actuator to bow in the other direction. The nozzle could then be adjusted relative to the actuator to produce an intermediate pressure at port 30 when no electric field is applied so that energizing one of the ceramic sheets would increase the pressure at port 30 and energizing the other sheet would reduce it. It may also be possible to accomplish this with a monomorph by simply reversing the polarity of the electrical field. Fig. 3C illustrates a third alternate embodiment 2 which is essentially the same as the actuator 20, and corresponding reference numerals have been applied, plu 200. The only difference between the actuator 220 and the actuator 20 is that the electrode 248 is extended a bent at its ends so as to define legs 261 and 263 which extend axially (relative to the axis 11 of the nozzle 27 and edges 220A and 220B, which are clamped between the body 14 and cap 16, are provided at the ends of legs 261 and 263 which are opposite from the main portion 265 of the electrode 248. As shown, the edges 220A and 220B extend perpendicularly from the legs 261 and 263 and in plane which is generally parallel to the plane of the main portion 265 and of the piezo-ceramic sheet 250. This configuration provides for additional flexure of th electrode sheet 248 so that greater displacements may be achieved for a given voltage.

Figs. 4 and 5 illustrate another embodiment 420 of monomorph piezo-ceramic actuator for a valve of the invention. Reference numerals have been applied to the embodiment 420 corresponding to the reference numerals o the actuator 20, plus 400. The actuator 420 is the same as the actuator 20 except that the electrode coating has been divided into two sub-areas 451A and 5IB by perimetral zone 453 in which the electrode coating is etched away or masked in the coating process so that in the actuator 420 the coating is absent in this zone. In addition, a third lead wire 449 is soldered so as to provide an electrical connection with the electrode coated sub-area 451B.

As in the actuator 20, a positive voltage is applie to coating sub-area 451A via lead 452 and electrode shee 448 is grounded via lead 454. Coating sub-area 451B, which is provided to act as a generator, does not electrically communicate with coating sub-area 451A.

When a voltage is applied between leads 452 and 454, the actuator 420 deflects, which induces a mechanical stress in the ceramic layer at 451B so that sub-area 451B generates its own potential. Accordingly, lead 449 is provided as an output lead to monitor the voltage of sub- area 451B as an indication of the displacement of the actuator 420 and could be used as a feedback signal.

A piezo-ceramic actuator for a valve of the invention need not be rectangular in shape. To illustrate that, Figs. 6-8 show three embodiments of actuators 520, 620 and 720 having a circular peripheral shape. In the actuators 520, 620 and 720, reference numerals of the various elements have been applied corresponding to the reference numerals of the elements applied in the actuator 20, plus 500, 600, and 700, respectively.

The actuator 520 of Fig. 6, in the form of a thin disc, is most similar to the actuator 420 of Figs. 4 and 5, since the electrode coating on the ceramic layer 550 is divided into motor sub-area 551A and generator sub- area 551B by zones 553 in which the electrode coating is absent. The zones 553 intersect nozzle contact area 558 in which the electrode coating is also absent.

The actuator 620 roughly approximates a rectangular actuator in which a circumferential rim of the electrode sheet 648 extends around the ceramic covered part of the electrode, which bridges the rim. Thus, in the actuator 620, half moon shaped openings 678 and 680 are formed in the electrode sheet 648 and the piezo-ceramic sheet 650 is laminated to the center bridging portion of the electrode 648, which is between the openings 678 and 680. An advantage of the embodiment 620 is that the openings 678 and 680 allow hydraulic fluid or gas to flow freely from one side of the actuator 20 to the other, whereas in the embodiments 520 and 720, if the edges of the electrode sheets 548 and 748 are clamped around all or substantially all of the periphery of the actuator, a separate passage must be provided in the housing to permit oil to flow from one side of the actuator to the other. However, it should be noted that in the embodiments 520, 620 and 720, it is not necessary to clamp them in the housing around their entire periphery, although that is one possible mounting arrangement, but that it is preferred to clamp them at at least two diametrically opposite points on their periphery to restrain those points against axial motion. In the actuator 720, electrode sheet 748 is a disc

(as is the electrode sheet 548) and the piezo-ceramic sheet 750 is an annular sheet, shaped somewhat like a washer. The electrode coating 751 is applied over the exposed surface of the ceramic annulus 751. It is not necessary to mask or etch an area similar to the area 558 in the actuator 720, since the nozzle 27 can make direct contact with the electrode sheet at the center of the disk 748, since the nozzle and the electrode sheet are at the same electrical potential. Fig. 9 illustrates an alternate embodiment of a pilot valve 810 of the invention. In Fig. 9, elements corresponding to the elements illustrated in Fig. 1 are identified by the same reference numeral, plus 800, except respecting the actuator, which is the bimorph actuator 120.

Whereas the valve 10 is operable to shift the spool 35 of a pilot operated hydraulic or gas valve in only one direction, the valve 810 can shift the spool 835 in either direction. This is accomplished essentially by replacing the actuator 20 with a bimorph actuator 120 such as that illustrated in Fig. 3B and replacing the cap 16 with auxiliary body 814' so as to provide nozzles on both sides of the actuator 120. Elements of the auxiliary body 814' corresponding to elements of the body 814 are identified by the same reference numeral, plus a prime (' ) sign. The bodies 814 and 814' define nozzle type seats 827 and 827', one on each side of the actuator 120, and which lead to respective passageways 825 and 825' . The passageways 825 and 825' branch into respective passageways 825A, 825B and 825A' , 825B' . The respective passageways 825A and 825A' lead to control ports 830 and 830' which are connected by connectors 870, 870' to spool control passages 831, 831', respectively, which are formed in valve block 829 and communicate with closed chambers 833 and 833' at the ends of the spool 835.

Screw plugs 892, 892' and locknuts 894, 894' are provided to adjust the forces exerted on the spool 835 by the springs 843 and 845. Bolts 841 and 841' secure the bodies 814 and 814' to the valve block 829 and bolts 872 secure the bodies 814 and 814' to each other.

Passageways 825B and 825B' provide communication with tank port 828 through respective orifices 821 and 821' (which are sealed to the respective bodies 814, 814' and to the valve block 829), passageways 876 and 876', annular passageways 878 and 878' which provide passage around end lands 839 and 837, and passageways 880 and 880' .

Pressure is provided to the chamber 836 by pump P, which supplies port 849. A relief valve RV is desirably provided (also for the pump P of Fig. 1) so as to relieve any excessive pressures which may be developed.

Supply port 849 communicates with chamber 36 through passageway 882, annular passageway 884 which provides passage around control land 841, passageway 886, connector 888 which is sealed between valve block 829 and body 814, and passageway 890. Control land 841 regulates communication between annulus 884 and bore 838 to control the flow to control ports 847 and 851, and end lands regulate communication respectively between port 847 and relief annulus 878, and between port 851 and relief annulus 878' . Passageway 880' is shown in dotted lines in ports 847, 849 and 851 to indicate that it does not intersect them. A cylinder C is shown connected to control ports 847 and 851.

Thus, if sheet 150 of actuator 120 is energized, actuator 120 bows away from nozzle 827 and toward nozzle 827', which increases the pressure at control port 830 and reduces it at port 830' . This has the effect of shifting spool 835, rightwardly to establish communication between ports 849 and 847 and between port 851 and relief port 828. Under these circumstances, the piston of cylinder C is urged rightwardly as viewed in Fig. 9. Conversely, energizing piezo-ceramic sheet 153 bows actuator 120 away from nozzle 827' and toward nozzl 827, which increases the pressure at control port 830' relative to the pressure at control port 830, which shifts spool 835 leftwardly as viewed in Fig. 9, to establish communication between supply port 849 and control port 851 and between control port 847 and relief port 828. Accordingly, the piston of cylinder C moves leftwardly.

It should be noted with respect to Fig. 9 and also with respect to Fig. 1, that the downstream orifices 821A, 821A' and 21A are fixed in size. However, in some applications it may be desirable to make the downstream orifices variable in size, and that this could be accomplished by removing them and routing the flow which would otherwise pass through each of them to an inlet port 26 of a valve 10 (or similar valve) so that each downstream orifice would be variable according to the operation of a piezo-electric actuator 20 of the corresponding valve.

Fig. 10 illustrates a modification to the valve 810, denominated 810', in which a pair of opposed nozzles 827 and 827' are combined with a monomorph actuator 20. In the arrangement illustrated, nozzle 827 is normally closed and nozzle 827' is normally open. However, by exciting layer 50, actuator 20 can be bowed upwardly against the nozzle 827' to close it and open nozzle 827. The effect of this, of course, would be to shift spool 835 rightwardly as viewed in Fig. 9. Deactuating layer 50 or reducing its excitation, shifts the spool 835 leftwardly.

An advantage of the valves in Figs. 9 and 10 is that positive pressures are used on both sides of spool 835 to control its position. This provides more stable control of the spool position may eliminate the need for springs 843 and 845 in some applications.

The invention provides a piezo-electrically actuated hydraulic valve particularly adapted as a pilot valve in which the actuator is smaller, lighter and less expensive than prior solenoid operated or piezo-operated actuators. A valve of the invention has a piezo-electrically operated actuator with a fast frequency response, which may be used to control relatively high pressures over a relatively wider pressure control band and with a lower pressure dither amplitude.

In addition, in a valve of the invention, a single actuator can be arranged to control a pair of nozzle seats. This can be applied in many different ways, for example to provide positive control over the position of a valve spool and/or to control spool position in both directions.

Embodiments of the invention have been described in considerable detail. Modifications and variations of the embodiments described will be apparent to persons skilled in the art. Therefore, the invention should not be limited to the embodiments described, but should be defined by the claims which follow.

Claims

We claim:

1. In a hydraulic valve of the type having a housing, an inlet port in the housing, an outlet port in the housing, and a valve seat having an axis, an interior and an exterior, the interior being in communication with one of the ports and the exterior being in communication with the other of the ports, and with the seat lying in a plane which is orthogonal to an axis of the seat, and a piezo-electric valve actuator for varying a flow area between the exterior and the interior of the seat, wherein the seat is formed on an end surface of a nozzle, the actuator is in the shape of a sheet having opposed planar surfaces, at least one of the surfaces facing and being generally parallel and adjacent to the plane of said seat and the actuator is mounted in the housing at opposite edges of the actuator so that the housing constrains the edges against movement in the direction of the axis of the seat, the one surface of the actuator and the seat defining between them the flow area, and the actuator is a piezo-electric monomorph comprising a layer of piezo- electric material and an electrode sheet laminated to the piezo-electric layer, the improvement wherein: said layer of piezo-electric material is on one side of said actuator and said electrode sheet is on an opposite side, and said one side faces said seat.

2. The improvement of claim 1, wherein said electrode sheet extends beyond said layer of piezo- electric material at ends thereof and defines at each said end a leg portion which extends generally perpendicularly from said electrode sheet and an edge portion which extends generally perpendicularly from said leg portion, said edge portions being restrained in said housing.

3. The improvement of claim 1, wherein said piezo- electric layer has two sub-areas, electrode surfaces of said sub-areas opposite from said electrode sheet are electrically isolated from one another such that applying an electric field to one of said areas to deflect said actuator results in an electrical output from the other sub-area.

4. The improvement of claim 1, wherein said actuator seats against said seat in a contact area which is electrically isolated from an active area of said piezo-electric sheet, wherein said active area is on an exposed side of said piezo-electric sheet which is opposite from said electrode sheet and does not contact said seat.

5. The improvement of claim 1, wherein an electrode layer is on said active area on said exposed side of said piezo-electric sheet, said contact area is on said piezo- electric sheet on said exposed side of said piezo-electric sheet and said electrode layer is absent from said contact area.

6. In a hydraulic valve of the type having a housing, an inlet port in the housing, an outlet port in the housing, and a valve seat having an axis, an interior and an exterior, the interior being in communication with one of the ports and the exterior being in communication with the other of the ports, and with the seat lying in a plane which is orthogonal to an axis of the seat, and a piezo-electric valve actuator for varying a flow area between the exterior and the interior of the seat, wherein said seat is formed on an end surface of a nozzle, said actuator is in the shape of a sheet having opposed planar surfaces, at least one of said surfaces facing and being generally parallel and adjacent to said plane of said seat, and said actuator is mounted in said housing at opposite edges of said actuator so that said housing constrains said edges against movement in the direction of said axis of said seat, said one surface of said actuator and said seat defining between them said flow area, and wherein said actuator includes an electrode sheet laminated to a piezo-electric sheet, said electrode sheet extending beyond said piezo-electric sheet at ends thereof, the improvement wherein: said electrode sheet defines at each said end a leg portion which extends generally perpendicularly from said electrode sheet and an edge portion which extends generally perpendicularly from said leg portion, said edge portions being restrained in said housing.

7. In a hydraulic valve of the type having a housing, an inlet port in the housing, an outlet port in the housing, and a valve seat having an axis, an interior and an exterior, the interior being in communication with one of the ports and the exterior being in communication with the other of the ports, and with the seat lying in a plane which is orthogonal to an axis of the seat, and having a piezo-electric valve actuator for varying a flow area between the exterior and the interior of the seat, wherein said seat is formed on an end surface of a nozzle, said actuator is in the shape of a sheet having opposed planar surfaces, at least one of said surfaces facing and being generally parallel and adjacent to said plane of said seat and wherein said actuator is mounted in said housing at opposite edges of said actuator so that said housing constrains said edges against movement in the direction of said axis of said seat, said one surface of said actuator and said seat defining between them said flow area, said actuator including an electrode sheet laminated to a piezo-electric sheet, the improvement wherein: said piezo-electric sheet has two sub-areas, electrode surfaces of said^'sub-areas opposite from said electrode sheet are electrically isolated from one another such that applying a voltage across one of said sub-areas to deflect said actuator results in an electrical output from the other sub-area.

8. The improvement of claim 7, wherein an electrode layer is absent from a zone of said piezo-electric sheet which divides said piezo-electric sheet into said sub- areas.

9. In a valve of the type having a housing, an inlet port in the housing, a control port in the housing, and a valve seat in a flow passage between said inlet and control ports and having an axis, an interior and an exterior, the interior being in communication with one of the ports and the exterior being in communication with the other of the ports, and with the seat lying in a plane which is orthogonal to an axis of the seat, and a valve actuator for varying a flow area in a flow passage between the exterior and the interior of the seat, said actuator including a sheet of piezo-electric material and said valve including a pair of valve seats, one of said seats being provided on each side of said actuator, so that said actuator may be operated to vary a flow area between said actuator and each seat, the improvement wherein: said actuator normally seats against one of said seats.

10. The improvement of claim 9, wherein said actuator is in the shape of a sheet having opposed planar surfaces, each said surface facing and being generally parallel and adjacent to one of said seats.

11. The improvement of claim 9, wherein said actuator is mounted in said housing at opposite edges of said actuator so that said housing constrains said edges against movement in the direction of said axes of said seats, each said surface of said actuator and said adjacent seat defining between them a flow area.

12. The improvement of claim 9, wherein said actuator is a piezo-electric monomorph comprising a layer of piezo-electric material and an electrode sheet laminated to said piezo-electric layer.

13. The improvement of claim 9, wherein said electrode sheet extends beyond said layer of piezo- electric material and defines said opposite edges which are constrained by said housing.

14. The improvement of claim 9, wherein an orifice is provided in a flow path downstream of each said seat, and a control port is provided in each said flow path between each said seat and the corresponding orifice.

15. The improvement of claim 9, wherein each said orifice is fixed in size.