Piezoelectrically actuated quick-action hydraulic valve

Abstract

A hydraulic valve (3) includes an actuation device (1, 1 a, 1 b) for a control piston (2). The valve (3) is simple, robust, and insensitive to dirt. The is an actuation device (1, 1 a, 1 b) has a flexurally rigid metal plate (5), with an outer region fixed to the housing (4) in a stationary manner. A piezoelectric actuator (6) can bend a central region of the metal plate (5); and a pressure chamber (7) is filled with a pressurized liquid during operation. The pressure chamber (7) is delimited by the housing (4), the metal plate (5), and the control piston (2). The metal plate (5) seals the pressure chamber (7), and the pressure chamber (7) acts on the control piston (2). A surface area AP of the metal plate (5) over the pressure chamber (7) is larger than the cross-sectional area A.sub.K of the control piston (2).

Claims

1. A hydraulic valve comprising: a control piston; an actuating device for displacing the control piston; the hydraulic valve comprises: a housing; the control piston has a cross-sectional area A.sub.K, and the control piston is configured to be displaced in the housing in an axial direction of the control piston, and the control piston is configured such that a throughflow of a pressurized liquid may be set by the displacement of the control piston; and the actuating device includes: a flexurally rigid metal plate, having an outer peripheral region of the metal plate fixed to the housing in a stationary manner, a central region of the metal plate being thicker than the outer peripheral region of the metal plate; a curved surface located between the central region of the metal plate and the outer peripheral region of the metal plate; a piezoelectric actuator operable into contact with the metal plate to bend a central region of the metal plate; and a pressure chamber configured to be filled with the pressurized liquid during operation of the valve; wherein the pressure chamber is delimited by the housing, the metal plate and the control piston; wherein the metal plate is configured to seal off the pressure chamber and the pressure chamber acts on the control piston; wherein an area A.sub.P of the metal plate over the pressure chamber is greater than a cross-sectional area A.sub.K of the control piston; and wherein the piston has an end face opposite the metal plate, the end face having a convex crowned formation to prevent sticking of the control piston to the metal plate.

2. The hydraulic valve as claimed in claim 1, wherein an area A.sub.P of the metal plate over the pressure chamber is at least four times greater than a cross-sectional area A.sub.K of the control piston where the piston is at the metal plate.

3. The hydraulic valve as claimed in claim 1, further comprising the piezoelectric actuator has a travel measurement system configured for measuring an expansion of the piezoelectric actuator in the axial direction of the control piston.

4. The hydraulic valve as claimed in claim 1, further comprising the metal plate consists of steel.

5. The hydraulic valve as claimed in claim 1, further comprising the metal plate is round.

6. The hydraulic valve as claimed in claim 1, further comprising a fluid-tight seal between the peripheral region of the metal plate and the housing.

7. The hydraulic valve as claimed in claim 1, further comprising the pressure chamber is configured to be supplied with the pressurized liquid under pressure by a line having an orifice.

8. The hydraulic valve as claimed in claim 1, further comprising the control piston consists of steel.

9. The hydraulic valve as claimed in claim 1, further comprising the housing comprises a valve block and a cover, and the cover is detachably connected to the valve block and the piezoelectric actuator is supported against the cover.

10. The hydraulic valve as claimed in claim 9, further comprising the valve block has a travel measurement system located and configured for measuring a position of the control piston.

11. The hydraulic valve as claimed in claim 10, further comprising an amplifier amplifying a control signal (S) and electrically energizes the piezoelectric actuator by the amplified control signal (S*).

12. The hydraulic valve as claimed in claim 11, further comprising a regulator configured to calculate a manipulated variable signal u in dependence on a difference between a target position and an actual position of the control piston, and the amplifier is configured to electrically energize at least one of the piezoelectric actuator by the amplified manipulated variable signal.

13. The hydraulic valve as claimed in claim 1, further comprising two of the actuating devices; and the control piston having two ends, each being actuated by a respective one of the actuating devices.

14. The hydraulic valve as claimed in claim 1, further comprising: ports in the housing defining a pathway in the housing for pressurized liquid to pass the piston and out of or into the ports which are served by the valve; at least two of the ports are selectable by the piston; one or the other of the at least two of the selectable ports is selectively served by the pathway at one time, and the at least two selectable ports being placed in the housing such that axial displacement of the piston in the housing connects a selected one of the at least two selectable ports into the pathway; and a third one of the ports being in the pathway to complete passage of liquid past the piston and the pathway.

15. The hydraulic valve as claimed in claim 1, further comprising a cylinder in the housing through which the piston is displaced; the at least two selectable ports and the third port each communicating into the cylinder at respective locations; the piston having a recess therein which is part of the pathway, the recess is of a smaller diameter than a diameter of the piston adjacent the recess, the recess being of an axial length such that during displacement of the piston, the recess communicates with one of the two selectable ports and not with the other selectable port; and the third port also communicating with the recess during the displacement of the piston while the recess is communicating with the one or the other of the two selectable ports.

16. The hydraulic valve as claimed in claim 1, further comprising the recess in the piston having a first diameter which is less than a second diameter of the cylinder through which the piston is displaced.

17. A hydraulic valve comprising: a control piston; an actuating device for displacing the control piston; the hydraulic valve comprises: a housing; the control piston has a cross-sectional area A.sub.K, and the control piston is configured to be displaced in the housing in an axial direction of the control piston, and the control piston is configured such that a throughflow of a pressurized liquid may be set by the displacement of the control piston; and the actuating device includes: a flexurally rigid metal plate, having an outer peripheral region of the metal plate fixed to the housing in a stationary manner; a piezoelectric actuator operable into contact with the metal plate to bend a central region of the metal plate; and a pressure chamber configured to be filled with the pressurized liquid during operation of the valve; wherein the pressure chamber is delimited by the housing, the metal plate and the control piston; wherein the metal plate is configured to seal off the pressure chamber and the pressure chamber acts on the control piston; wherein an area A.sub.P of the metal plate over the pressure chamber is greater than a cross-sectional area A.sub.K of the control piston; wherein the piston has an end face opposite the metal plate, the end face having a convex crowned formation to prevent sticking of the control piston to the metal plate, and wherein the piston is comprised of a ferromagnetic metal, wherein the piston is actuated purely hydraulically, and further comprising a holding magnet located at a central region of the metal plate opposite the end face of the piston to hold the piston in an end position.

18. A hydraulic valve comprising: a control piston; an actuating device for displacing the control piston; the hydraulic valve comprises: a housing; the control piston has a cross-sectional area AK, and the control piston is configured to be displaced in the housing in an axial direction of the control piston, and the control piston is configured such that a throughflow of a pressurized liquid may be set by the displacement of the control piston; and the actuating device includes: a flexurally rigid metal plate, having an outer peripheral region of the metal plate fixed to the housing in a stationary manner, a central region of the metal plate being thicker than the outer peripheral region of the metal plate; a peripheral wall located between the central region of the metal plate and the peripheral region of the metal plate, the peripheral wall being adjacent a flat surface that spans across the central region of the metal plate; a piezoelectric actuator operable into contact with the metal plate to bend a central region of the metal plate; and a recessed pressure chamber configured to be filled with the pressurized liquid during operation of the valve, and having a bottom, flat surface opposite the flat surface of the central region of the metal plate, the recessed pressure chamber being sized and shaped to receive the central region of the metal plate therein; wherein the pressure chamber is delimited by the housing, the metal plate and the control piston; wherein the metal plate is configured to seal off the pressure chamber and the pressure chamber acts on the control piston; wherein an area AP of the metal plate over the pressure chamber is greater than a cross-sectional area AK of the control piston; and wherein the piston has an end face opposite the metal plate, the end face having a convex crowned formation to prevent sticking of the control piston to the metal plate.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further advantages and features of the present invention will emerge from the description below of non-restrictive exemplary embodiments, wherein, in the following figures:

(2) FIG. 1 shows a longitudinal section through a hydraulic valve with an actuating device and a spring,

(3) FIG. 2 shows a quarter-section through a first alternative of the hydraulic valve, with an actuating device having a holding magnet,

(4) FIG. 2A and FIG. 2B are each illustrations showing the functioning of the actuating device of the hydraulic valve,

(5) FIG. 3 shows a longitudinal section through a hydraulic valve with two actuating elements and illustrates the hydraulic valve in an inactive condition,

(6) FIG. 3A and FIG. 3B each show a longitudinal section through a hydraulic valve with two actuating devices, and each illustrates connection of the valve to a respective port,

(7) FIG. 3C shows a fragment of the valve including the piston of the valve of FIG. 3,

(8) FIG. 4 is a schematic illustration showing the coils of a travel measurement device for the control piston of a hydraulic valve,

(9) FIG. 5 is an illustration showing the actuation of a piezoelectric actuator,

(10) FIG. 6 is an illustration showing the regulation of the axial expansion of a piezoelectric actuator,

(11) FIG. 7 is an illustration showing the regulation of the position of a control piston of a hydraulic valve with two actuating devices,

(12) FIG. 8 shows a half-section through a hydraulic valve with two variants of an actuating device.

DESCRIPTION OF THE EMBODIMENTS

(13) FIG. 1 shows a 3/2-way hydraulic valve 3 (the digit before the forward slash standing for the number of ports and the digit after the forward slash standing for the number of positions of the hydraulic valve) with an actuating device 1, which is arranged on the left side in the figure. The hydraulic valve 3 operates as a switching valve and has a control piston 2 which is guided displaceably in a bore or cylinder in the valve block 4a of the housing 4. Depending on the position of the control piston 2, the pressure port p of the valve 3 is connected either to the consumer port A or to the consumer port B. The control piston 2 is acted on by the actuating device 1, on the one hand, and a spring 14, on the other hand.

(14) The actuating device 1 has a circular, flexurally rigid metal plate 5 composed of spring steel, which is braced between the valve block 4a and the cover 4b of the housing 4. Both parts of the housing 4 are detachably connected to one another by way of screw connections 15, and so the piezoelectric actuator 6 (piezo for short), the metal plate 5 or even the entire actuating device 1 can be easily replaced.

(15) A piezo 6 configured in the form of a piezo stack 6a is arranged on the left side of the metal plate 5. As a result, the central region of the metal plate 5 can be bent by the piezo. Since the metal plate 5 is thinner in the outer region than in the central region, the necessary force for bending the metal plate is kept low.

(16) A pressure chamber 7 is situated on the right side of the metal plate 5. The electrical energization of the piezoelectric actuator 6 results in the piezo expanding in the axial direction x and bending the central region of the metal plate 5. See FIG. 2B. The actual amount of bending of the metal plate is typically small, but enough to increase pressure p in the pressure chamber to move the piston due to the pressure increase. The illustration of the bending of the plate in FIG. 2B is exaggerated to explain the disclosed bending. Since the pressure chamber 7 is filled with a pressurized liquid (hydraulic oil in this case), the pressure p in the pressure chamber 7 increases as a result of the bending of the metal plate 5, which describes a bending curve. The left side of the pressure chamber 7 is sealed off in a fluid-tight manner by the metal plate 5 and a seal 9 which is situated between the metal plate 5 and the valve block 4a. The other sides of the pressure chamber 7 are sealed off in a pressure-tight manner by the valve block 4a of the housing 4. The increased pressure in the chamber 7 due to the bending of the plate increases the pressure in chamber 7 sufficiently so that the end face of the piston is urged to the right in FIG. 2B and in FIG. 3B by the pressure in the chamber 7 at the left in those Figures. Since the pressure chamber 7 acts on the end face of the control piston 2, the control piston 2 is pushed away in the direction of the spring 14 by the force F=p.Math.A.sub.K, where A.sub.K is the cross-sectional area of the control piston. As a result of the displacement of the control piston 2, the pressure port p of the hydraulic valve 3 is connected to the port B. After the electrical energization of the piezoelectric actuator 6 is ended, the control piston 2 is displaced by the compression spring 14 to the left again, with the result that the port p is connected to the port A of the hydraulic valve again.

(17) According to the illustration in FIG. 1, the ratio between the area A.sub.P of the metal plate 5 over the pressure chamber 7 to the cross-sectional area A.sub.K of the control piston 2 is approximately 225. The actuating device 1 according to the invention thus allows a change in length of the piezoelectric actuator 6 of, for example, 60 μm to displace the control piston 2 by approximately 10 mm in a simple manner. It is a major advantage that the “travel amplification” functions purely hydraulically and the actuating device 1 has no moved parts apart from the metal plate 5 and the actuator 6. Thus, the hydraulic valve 3 with the actuating device 1 is very simple, reliable and also has low sensitivity to dirt. The movement of a control piston 2 in relation to a spring 14 is known to a person skilled in the art from numerous valve types, and so a detailed explanation of the right side of the hydraulic valve 3 in FIG. 1 may be omitted. In comparison with the prior art, the moved masses are extremely small, and so a switching time of <2 ms can be achieved without any problems.

(18) FIGS. 2A and 2B illustrate a quarter-section through a hydraulic valve 3 with another actuating device 1. The embodiment in FIGS. 2, 2A and 2B have, in addition to the actuating device 1 in FIG. 1, a control piston 2 with a crowned formation 10 of the end face. The crowned end formation is seen in FIGS. 2, 3 and 4. Consequently, the so-called “sticking” of the control piston 2 to the metal plate 5 is prevented. Moreover, the central region of the metal plate 5 has a permanent-magnetic holding magnet 8 which is able to hold in an end position the ferromagnetic control piston 2 composed of steel. The radius r.sub.K of the cylindrical control piston 2 and the radius r.sub.P of the circular metal plate 5 over the pressure chamber 7, where A.sub.K=r.sub.K.sup.2.Math.π and A.sub.P=r.sub.P.sup.2.Math.π hold, are furthermore illustrated. The metal plate 5 has a rounding r between the thicker and thinner parts, which increases the operational stability of the metal plate 5.

(19) In FIGS. 2a and 2b, the functioning of the hydraulic valve according to the invention with the actuating device 1 is illustrated in a simplified manner. In FIG. 2a, the piezo 6 is in the rest state, the metal plate 5 is not bent and also the control piston 2 is in an initial position. In FIG. 2b,] in contrast, the piezo 6 has extended in the axial direction x and has caused the metal plate 5 to bend. The bending of the metal plate causes the pressure p in the pressure chamber 7′ to increase, such that the control piston 2 is displaced to the right as a result of the pushing-away. After a short time, the pressure chambers 7 and 7′ are of equal size, with the result that the control piston 2 is situated further to the right in FIG. 2b than in FIG. 2a.

(20) FIGS. 3A and 3B show a schematic longitudinal section through a non-continuous 3/2-way hydraulic valve 3 with two actuating devices 1a, 1b.

(21) FIGS. 3A, 3B and 3C illustrate a centrally located recess 21 in the piston 2, so located and of an axial width that axial shifting of the piston connects the port p with one or the other of ports A and B. (Other Figures suggest the presence of the recess by two axial lines).

(22) In FIG. 3, the valve and the actuating devices 1a and 1b are in a neutral or inoperative position in which the port p is blocked by the housing section above it and there is no connection of port p to either of ports A or B.

(23) The two actuating devices 1a and 1b are symmetrical, essentially mirror images in their functional aspects disclosed herein. Operation of the valve for connecting port p to one or the other of ports A or B is illustrated in FIGS. 3A and 3B.

(24) The left side activating device 1a has a bent plate 5, as in FIGS. 2B and 3B, which increases pressure in the pressure chamber 7 at the left side device. That pressure moves the piston 2 to the right to create a pathway between ports p and B. In FIG. 3A, the right side activating device 1b has a bent plate 5 which increases pressure in that pressure chamber 7 at the right side device. That pressure moves the piston to the left to create a pathway between ports p and A. The structural design of each of the actuating devices 1a, 1b is very similar to the design in FIGS. 2 and 3, but the control piston 2 is acted on by the two actuating devices 1a and 1b and is held in the respective end positions by the two holding magnets 8. In this way, an extremely quick switching valve is created. In particular during the quick-switching operation of the hydraulic valve 3, to ensure complete filling of both of the pressure chambers 7 at all times, the pressure chambers 7 are connected via a line to a control-pressure port p.sub.S which compensates for any leakage from the pressure chamber 7 via a narrow orifice or throttle 18. Alternatively, as illustrated by dashed lines, it is also possible for branch lines to lead from the pressure port p to the pressure chambers 7.

(25) The following describes an example of use of the valve as shown in FIGS. 3A and 3B. It is non-limiting. The pressure port p is pressurized, e.g. by means of a hydraulic pump. Also, the areas connected to the pressure port p are pressurized. In FIG. 3A, the pressure from the pressure port p is transmitted via the recess 21 in the piston 2, to the consumer port A, and in FIG. 3B, to the consumer port B. The consumer ports A or B may e.g., be the lines to and from a hydraulic motor. For example, if the consumer port A of the hydraulic motor is pressurized, the motor rotates in a first direction. If the consumer port B of the hydraulic motor is pressurized, the motor rotates in a second reverse direction.

(26) There is a cylindrical passage, cylinder or bore 22 in the housing for guiding the piston for axial displacement between its end positions at the pressure chambers.

(27) FIG. 3C illustrates recess 21 in the piston located between the two adjacent cylindrical regions of the piston. The example illustrated shows the recess 21 as annular, having a diameter D1 which is smaller than diameter D2 of the adjacent cylindrical regions. This defines the passage through the recess and past the piston in the cylinder. The recess is of such axial direction length that the recess in the piston enables connection with a then selected one of ports A and B, while the piston surfaces beyond both sides of the recess blocks connection with the other of ports B or A and port p. The recess is at the axial center of the piston consistent with the left-right symmetry. Any pathway across the cylinder or bore 22 and to port p and one of ports A and B may perform like the recess does.

(28) FIG. 4 schematically shows the coils of a travel measurement system 11 for determining the actual position s.sub.Ist of the control piston 2. The control piston 2 is magnetic (for example composed of steel with a ferritic structure), but also has at least one non-magnetic part 20. The two coils 19a, 19b which form a differential inductor. This makes it possible for the position s.sub.Ist of the control piston 2 to be determined by evaluation electronics, not illustrated, for inductive travel transducers (see for example FIG. 7). Evaluation electronics for inductive travel transducers are known to a person skilled in the art (see for example http://www.lvdt.de).

(29) FIG. 5 schematically shows a control system 12 for a piezoelectric actuator 6, in the form of a piezo stack 6a, of an actuating device 1. The control signal S, simply pulses in this case, is amplified according to the signal form by the amplifier 16, and the amplified control signal S* is supplied as a voltage signal to the piezo stack 6a. The piezo stack 6a expands in the axial direction x in a manner dependent on the control signal S and bends a metal plate 5 (not illustrated here) of the actuating device 1, which leads to displacement of a control piston 2.

(30) FIG. 6 schematically shows regulation for a piezo actuator 6, which is in the form of a piezo stack 6a, of an actuating device 1. The target signal s.sub.Soll again in the form of pulses for the expansion of the piezo actuator 6 here is supplied to a regulator 13, which calculates a manipulated variable u in dependence on the difference between the actual expansion s.sub.Ist of the piezo actuator 6 and the target signal s.sub.Soll. The manipulated variable u is amplified by the amplifier 16, and the amplified signal u* is supplied as a voltage signal to the piezo stack 6a. FIG. 6 thus shows simple position regulation for the expansion of the piezo actuator 6.

(31) FIG. 7 schematically shows position regulation for the position of a control piston 2 in a hydraulic valve 3 with two actuating devices 1a, 1b. The position s.sub.Ist of the control piston 2 is determined via the two coils of the travel measurement device 11 (see FIG. 4 for design). The actual position s.sub.Ist of the control piston and the target position s.sub.Soll thereof are supplied to a regulator 13, which calculates two manipulated variables u.sub.1, u.sub.2 in dependence on the difference between s.sub.Soll and s.sub.Ist. The manipulated variables are amplified by the amplifier 16, and the amplified signals u.sub.1*, u.sub.2* are supplied as voltage signals to the piezo stacks 6a of the two actuating devices 1a, 1b. FIG. 7 thus indicates simple regulation for the position of the control piston 2 of a hydraulic valve 3 by means of two actuating devices 1a, 1b.

(32) FIG. 8 shows a half-section through two variants of an actuating device 1, which are respectively indicated above and below the horizontal axis of symmetry. In order to reduce the necessary force for the piezoelectric actuator 6 to bend the metal plate 5, the metal plate 5 is mounted in an articulated manner in both variants and the actuator is of “wet” design. The bottom variant of the actuating device 1 is not designed according to the invention since the metal plate 5 is not fixed to the housing 4a, 4b in a stationary manner.

(33) In the above variant, the metal plate 5 bears on in each case one elevation in the valve block 4a and in the cover 4b and is sealed off via two elastic seals 9. Moreover, the pressure chamber 7 and the chamber in which the piezoelectric actuator 6 or the piezo stack 6a is situated are connected via multiple lines with orifices or throttles 18 to a control-pressure port p.sub.S. The static pressure on the left and the right of the metal plate 5 is thereby equalized, with the result that the metal plate 5 is relieved of load. The bending of the metal plate 5 by the piezoelectric actuator 6 or the piezo stack 6a in turn leads to an increase in pressure in the respective pressure chamber 7, which displaces the control piston 2. In the bottom variant, the metal plate bears on a stiff seal 9, this likewise corresponding to an articulated mounting of the metal plate 5.

(34) Even though the invention has been illustrated and described in more detail by way of the preferred exemplary embodiments, the invention is not restricted by the examples disclosed, and other variations may be derived therefrom by a person skilled in the art without departing from the scope of protection of the invention.

LIST OF REFERENCE SIGNS

(35) 1, 1a, 1b Actuating device 2 Control piston 3 Hydraulic valve 4 Housing 4a Valve block 4b Cover 5 Metal plate 6 Piezoelectric actuator 6a Piezo stack 7, 7′ Pressure chamber 8 Holding magnet 9 Seal 10 Crowned formation 11 Travel measurement system 12 Control system 13 Regulator 14 Spring 15 Screw connection 16 Amplifier 18 Orifice 19a, 19b Coil 20 Non-magnetic part of the control piston 21 Piston recess 22 Cylinder/bore for piston A Consumer port A of the hydraulic valve B Consumer port B of the hydraulic valve p Pressure port p of the hydraulic valve p.sub.S Control-pressure port of the hydraulic valve r Radius r.sub.K Radius of the control piston r.sub.P Radius of the metal plate over the pressure chamber S Control signal S* Amplified control signal s.sub.Ist Actual position s.sub.Soll Target position u, u.sub.1, u.sub.2 Manipulated variable u*, u.sub.1*, u.sub.2* Amplified manipulated variable signal x Axial direction