EP0012743A1

EP0012743A1 - Piezoelectric control valve

Info

Publication number: EP0012743A1
Application number: EP79930028A
Authority: EP
Inventors: Kail Lester Linebrink; Lawrence Sidney Smith
Original assignee: United Technologies Corp
Current assignee: Raytheon Technologies Corp
Priority date: 1978-12-18
Filing date: 1979-11-20
Publication date: 1980-06-25
Also published as: JPS5582802A; CA1115172A; IL58598A0

Abstract

A piezoelectric fluid control valve comprises a jet pipe (14) whose position in one axis is controlled by a piezoelectric actuator (22) mechanically connected to the jet pipe (14). The fluid output from the jet pipe nozzle (16) is normally positioned between a pair of control ports (28, 30) whereby fluid divides evenly between the ports. Energization of the piezoelectric actuator (22) by applying a voltage thereto moves the jet pipe (14) thereby increasing the pressure at one port and decreasing the pressure at the other port.

Description

This invention relates to a control valve, and specifically to a valve in which fluid flowing through a jet pipe is continuously varied between two control ports by energization of a pair of piezoceramic actuator sheets mechanically connected to the jet pipe. The difference in pressure between the two control ports may be used to regulate the position of a servo actuator.
Advances in gas turbine technology have resulted in demands for more and more control functions to such an extent that full authority electronic controls have been developed. An advanced variable cycle engine may require as many as twelve actuation loops for engine geometry and main and augmenter fuel flow control. Advances in microprocessor and other electronic technology resulting in more functional capability at lower electrical power are offset by increased power requirements as more servo functions are added. Increased electrical power requirements are particularly detrimental to engine mounted electronic controls that must regulate power supplied for servo control since this results in an additional heat load for the electronic package.
The present invention provides a low power electron- hydraulic control valve suitable for operation in engines and which may be operated using contaminated fuel or other fluids. The control valve uses piezoelectric elements for actuation of the valve element, such elements requiring lower electrical power and being of lower cost than alternate electromagnetic actuators such as torque motors, stepper motors, or solenoids. A piezoelectric actuator operated in the bending mode also reduces supply voltage requirements. The combination of a piezoelectric element with a jet pipe valve provides a contamination resistant electrohydraulic interface for an electronic servo controller, and when used as a fuel valve is insensitive to magnetic particles suspended in the working fluid.
While piezoelectric and piezoceramic elements energized by an electric signal have been used in the past to vary the direction of fluid flow in a pneumatic device as as shown in Russian Patent 387154, and to switch bistable and multistable fluid devices as shown in U. S. Patents 3,266,511, 3,457,933, and 3,771,561, the present invention differs in that it utilizes the bending mode of a piezoceramic device to continuously vary the radial position of a jet pipe valve and thereby continuously vary the relative pressures between two output ports. The pressure difference between the two output ports is then used to control a servo actuator which in turn positions a controlled device. The control is provided in response to a voltage applied to the piezoceramic device,
It is therefore an object of this invention to provide a simple, inexpensive and low power-consuming electrohydraulic control valve.
Another object of this invention is a piezoelectric control valve in which the principal element is a piezoceramic actuator which is connected to and controls the. movement of a jet pipe control valve,
A further object of this invention is a low power piezoelectric control valve suitable for operation with contaminated fuel.
Another object of this invention is a control valve which is adapted to respond to a control signal and produce a continuously variable pressure difference between two output ports, the pressure difference being used to control a servo actuator.
In accordance with a preferred embodiment of the invention, there is provided a jet pipe adapted to pass fluid therethrough, the fluid being fuel or other hydraulic oil under pressure. A nozzle is located at the end of the jet pipe. Directly in line with the end of the nozzle are two adjacent fluid receiving ports adapted to receive the fluid output from the jet pipe. At its null position, the output from the jet pipe is divided evenly between the two ports, and the pressure difference between the two ports is zero. A piezoceramic actuator is mechanically connected to the jet pipe and adapted to move the jet pipe, in response to an electric voltage applied to the piezoceramic actuator, in a direction such that the jet pipe fluid output will increase the pressure at one port and decrease the pressure at the other port. An actuator or servo connected to the ports is responsive to the pressure difference therebetween and will move a load in accordance therewith. The electric voltage applied to move the piezoceramic actuator is either a positive or negative voltage, and causes movement of the jet pipe in one of two directions in a plane containing the two ports. The voltage is normally produced in response to a demand signal indicative of a desired change in the load as part of a control system.

Figure 1 is a schematic drawing showing the features of the present invention.
Figure 2 is a plot showing the pressure versus voltage characteristics of the control valve.
Figure 3 is a cross-sectional view of a control valve constructed in accordance with the present invention.
Figure 4 is a partial top view of the jet pipe and piezoceramic actuator of Fig. 3.

Fig, 1 is a schematic representation showing the main features of the present invention, and is meant to be representative of the oprational features, a preferred implementation and the best mode of construction thereof being shown with respect to Figs, 3 and 4. Referring to Fig. 1, a source of pressurized fluid such as the fuel in a turbine engine is fed from a source, not shown, to an inlet 12 from which it passes into a flexible metal pipe 14 having a jet nozzle 16 at the end thereof. Typically the pipe 14 is steel with a diameter of 0.090 inches, while the nozzle has a diameter of 0.008 inches, the nozzle being designed to efficiently convert the fluid pressure into fluid velocity, as is well known in the art. The inlet end of the pipe 14 is inserted in a housing 18, typically of steel or any other suitable stiff material. The nozzle end of the pipe 14 has an extended flange 20 to which is attached, via a rabbet in the flange 20, a piezoceramic actuator element 22 composed of two layers of piezoelectric material, 24a and 24b, bonded together. The actuator element 22 is preferably bonded to the rabbet in flange 20, and securely attached at its other end to the housing 18 such as by clamps, not shown.
The piezoelectric elements 24a and 24b are commonly- available piezoelectric crystals such as lead zirconate titanate, preferred for use in turbine engine controls because of its temperature characteristics, but other similar crystals may be used. When an electric field is placed across the crystal it changes its length. Technically, application of an electric field causes the crystal to expand or contract in certain directions. The directions in which compression or tension develop polarization parallel to the strain are called the piezoelectric axes of the crystal. The magnitude of the piezoelectric polarization is proportional to the strain and the corresponding stress. The direction is reversed when the strain changes from compression to tension,
The electric field is applied to the piezoelectric crystals 24a and 24b from a variable voltage source 26, the magnitude of the voltage being a function of the composition and size of the particular crystals. In general, the two piezoelectric crystals 24a and 24b are arranged so that when one layer expands the other contracts causing both layers to bend in the same manner that a temperature change causes a bimetal thermostat to deflect. The piezoelectric crystals 24a and 24b can be operated in parallel or series connection, parallel being preferred in that it provides twice the output deflection for the same voltage as the series connection, although the series connection has the advantage of eliminating an electrical lead wire between the two crystals, The variable voltage source is shown as a block 26, but in practice it will normally be a voltage produced by a preceding stage in a control system such as an electronic fuel control, the voltage being positive or negative and of a magnitude to produce the desired direction and magnitude of bending of the piezoceramic actuator 22 and, as will be described, the desired change in pressure required to vary a load, Alternatively, a controllable push-pull amplifier may be used as the variable voltage source, The electrical connection between the crystals are not shown but will be apparent to those skilled in the art,
Deflection of the piezoceramic actuator 22 in response to an applied voltage will cause deflection of flange 20 and pipe 14 in a vertical direction as shown in Fig. 1, The pressurized fluid exiting from nozzle 16 is directed toward two outlet or control ports, 28 and 30, contained in-housing 18, and fed through passages in the housing wall to respective outlets 32 and 34. In its undeflected position, the pipe 14 and nozzle 16 are positioned relative to ports 28 and 30 such that fluid exiting from nozzle 16 is divided equally between ports 28 and 30 whereby the pressures P_B and P_A at outlets 32 and 34 are equal. Moving the pipe and nozzle in a vertical direction by application of a voltage from source 26 to piezoceramic actuator 22 will increase the pressure at the port in the direction of nozzle movement, and decrease the pressure at the other port. The actuator or servo, not shown, connected to outlets 32 and 34 will respond to the pressure differential and ultimately cause movement of a load, not shown.
A fluid return port 36 and outlet 38 provide a path for any fluid not fed to the control ports to be removed from the housing, this fluid typically being returned to the fluid source.
Figure 2 is a plot of the pressure characteristics of the control ports 28 and 30 relative to the applied voltage. The direction of deflection of the nozzle will depend on the orientation of the crystals and the polarity of the voltage, so that Fig. 2 is meant only to be representative in this regard. However, Fig. 2 shows that deflection of the piezoelectric actuator 22 and jet pipe 14 are proportional to the applied voltage and produce the pressure versus voltage characteristics shown by line 40. Full deflection in one direction will cause the curve to flatten and produce a maximum pressure differential as shown by the formulae PA P_B/P_S-P₀
The jet pipe flow forces are axial and do not place a load on the piezoelectric actuator 22, thus resulting in the lowest possible power requirements. The piezoelectric actuator 22 is a capacitor element, preferably in the range of .02 to .20 u∫ depending on actuator size, and results in actuator power requirements of less than 0.010 watts with a 28 volt dc supply.
Figs. 3 and 4 show a preferred construction of the control valve, The fluid supply _Ps comprises line 42 external of housing 44 and the pipe 46 connected to line 42 contains a metallic flexible coupling 48 to avoid splitting of the pipe due to the flexing thereof. A nozzle 50, having attached thereto horizontally extending flange portions 52 on either side thereof and shown best in the top view of Fig. 4, is positioned over the end of pipe 46. The piezoceramic elements 54a and 54b, not shown in Fig. 3, are bonded to the flange portions 52 on both sides of pipe 46, and are fixedly secured at their opposite ends to a clamp 56 attached to housing 44 such as by screws 58. Each of the two piezoceramic elements 54a and 54b are preferably two layers of piezoelectric material bonded together as shown in Fig. 1, with an electric voltage applied to each of the two elements 54 to produce movement of the elements 54 and nozzle 50 bonded thereto. The voltage source and electrical connections are not shown in Figs. 3 and 4. Mechanical stops 60 (Fig. 3) which may be adjustable screw-type inserts in housing 44 prevent deflection of nozzle 50 beyond preadjusted limits. A fluid return line 62 is also connected to housing 44. Control ports 62 and 64 providing respectively pressures P_A and P_B feed a servo, not shown, which uses the pressure differential to vary a load in response to the voltage applied to the elements 54 and described with respect to Fig. 2.
When used as a control valve in a fuel control for turbine engines, the valve of the present invention provides a contamination-resistant electrohydraulic interface for an electronic servo controller, requires lower electrical power and is of lower cost than alternate actuators, reduces supply voltage requirements, and is insensitive to magnetic particles suspended in the fluid which is typically jet fuel.
While the invention has been described with respect to a preferred embodiment thereof and in the best mode presently contemplated, it is apparent that alternate configurations or changes in the precise details may be made without departing from the scope of the invention as hereinafter claimed,

Claims

1. An electrohydraulic control valve comprising:

a housing,

a jet pipe having a nozzle at one end thereof with the other end connected to an inlet port in said housing, the nozzle end of said jet pipe being adapted for movement within said housing,

means for supplying a pressurized fluid to said jet pipe through said inlet port, said fluid exiting from said jet pipe through said nozzle,

first and second control ports situated side by side immediately opposite said nozzle whereby the fluid exiting from said jet pipe nozzle passes into said control ports and produces a pressure therein,

first and second passage means conducting the fluid from said respective control ports,

a piezoceramic element secured at one end to said housing and at its opposite end to said jet pipe,

and means for supplying a voltage to said piezoceramic element,

said piezoceramic element being deflected in response to said voltage and moving said jet pipe in a direction to produce a reduction in the fluid flow from said nozzle into one of said control ports and an increase in the fluid flow from said nozzle to the other of said control ports thereby creating a relative pressure change between said ports, the direction and amount of movement of said jet pipe and the pressure difference between said ports being directly proportional to the polarity and magnitude of said voltage.

2. An electrohydraulic control valve as in claim 1 in which each of said control ports is of the same size and wherein said jet pipe in its undeflected position is located relative to said control ports whereby the fluid exiting from said jet pipe nozzle is directed equally to said control ports whereby the pressure in said control ports is equal.

3. An electrohydraulic control valve as in claim 1 in which said piezoceramic element comprises two layers of piezoelectric crystal material bonded together.

4. An electrohydraulic control valve as in claim 3 in which said two layers of piezoelectric crystal material are connected electrically in series,

5. An electrohydraulic control valve as in claim 3 in which said two layers of piezoelectric crystal material are connected electrically in parallel,

6. An electrohydraulic control valve as in claim 1 in which said jet pipe includes a flexible coupling.

7. An electrohydraulic control valve as in claim 1 and further including a fluid return port in said housing.

8. An electrohydraulic control valve as in claim 1 and including first and second mechanical stop means located in said housing on opposite sides of said jet pipe for preventing deflection of said jet pipe beyond preselected limits,

9. An electrohydraulic control valve as in claim 1 in which said jet pipe nozzle includes first and second flange means extending therefrom in diametrically opposite directions, and in which said piezoceramic element comprises first and second piezoelectric crystal means secured respectively to said first and second flange means.

10. An electrohydraulic control valve as in claim 9 in which each of said piezoelectric crystal means comprises two layers of piezoelectric crystal material bonded together,

11, An electrohydraulic control valve as in claim 1 in which said piezoelectric element comprises two layers of lead zirconate titanate bonded together.