GB2087659A

GB2087659A - Piezoelectric hydraulic pressure generating system

Info

Publication number: GB2087659A
Application number: GB8128454A
Authority: GB
Original assignee: Carl Schenck AG
Current assignee: Carl Schenck AG
Priority date: 1980-10-03
Filing date: 1981-09-21
Publication date: 1982-05-26
Also published as: JPS6246722B2; JPS5762980A; FR2491559B1; GB2087659B; DE3037380C2; DE3037380A1; FR2491559A1

Abstract

In a hydraulic pressure generating system, sets of piezoelectric elements (5) are mounted in a casing (1) containing a pressure medium. The piezoelectric elements, when energised, change dimensions and cause the pressure medium to be displaced and/or pressure to be generated within the casing. A piston 2 may be made to reciprocate in the casing. The system may be designed as a pump (Fig. 3 not shown) for the pressure medium or to generate pressure and to supply pressure medium in loading devices, particularly in testing machines. <IMAGE>

Description

SPECIFICATION Hydraulic pressure generating system This invention relates to a hydraulic pressure generating system, which may be used as a hydraulic pressure generator or as a system for supplying a medium under pressure, and is particularly useful for loading devices on testing machines.

Hydraulic stations with pumps or pressure reservoirs have hitherto been used exclusively in order to generate pressure and to supply pressure medium in loading devices, particularly in testing machines. Systems such as these necessitate considerable technical resources and require a large amount of space. The requirements are, for example, drive units and pump units, supply lines, control valves, switching and regulating devices etc. In addition, equipment which is driven by pressure media, in particular loading devices which operate with hydraulic servo control- or servo regulating- devices, is limited in its frequency range.

It is an object of the invention to provide a simplified system of generating pressure and supplying pressure medium, particularly in loading devices on testing machines, which can be adapted to operate without the conventional pumping stations and which substantially satisfies the requirements of automatic control technology.

According to the present invention there is provided a hydraulic pressure generating system, wherein a number of sets of piezoelectric elements is mounted in a casing containing or adapted to contain a pressure medium, and wherein means are provided for subjecting the elements to electrical control so that when the casing contains pressure medium and said elements are electrically controlled, the pressure medium is displaced and/or pressure is generated within the casing.

The present system is based on the known property of piezoelectric elements, whereby under electrical control they deform and change dimensions in at least one axial direction or generate forces corresponding to the deformation.

Through series connection (stacking) of individual elements technically useful alterations in length or volume can be achieved by making using of this property.

With the present system, it is possible directly to pressurize or directly to supply a pressure medium to a receiver without the necessity for using a conventional system. With the present system, it is possible for pressure energy to be generated directly where it is required, e.g. in hydraulic loading cylinders, special drive and pump units, supply lines, control valves etc., not being necessary. The control action of the present system is particularly advantageous, because piezoelectric elements can be operated at frequencies which cannot be obtained, for example, with systems having servo-valves. PI-e- set nominal values can be followed with a high degree of accuracy, because piezoelectric elements are particularly sensitive to control.

Various systems in which piezoelectric elements act on a pressure medium have been proposed and serve, for example, to generate a small, non-pulsating flow of pressure medium (DE-OS 27 07 713) or to control injection valves on internal combustion engines. These previously proposed systems are not, however, usable on equipment such as is required, for example, to supply pressure medium to or to generate pressure in hydraulic loading devices for testing machines, and with which, for example, considerable forces must be generated.

In order to enable the invention to be more readily understood, reference will now be made to the accompanying drawings, which illustrate diagrammatically and by way of example some embodiments thereof, and in which:~ Figure 1 is a longitudinal section through a hydraulic loading cylinder with piezoelectric elements, Figure 2 is a longitudinal section through a corrugated tube cylinder with integral piezoelectric elements, Figure 3 is a longitudinal section through a hollow cylinder with piezoelectric elements, designed as a pressure medium supply unit, and Figure 4 is a longitudinal section through a hydraulic loading cylinder with piezoelectric elements in the cylinder walls.

Referring now to Figure 1, there is shown a hydraulic loading cylinder 1 which contains a piston 2 having a piston rod 3 extending outward of the cylinder on one side of the piston. The piston could have a piston rod extending on each side, A test piece, for example, can be connected to the piston rod 3, and can be subjected to a static or dynamic load. A pressure medium can be fed into the cylinder chamber 4 of the loading cylinder by means of connections or pipes (not shown).

Piezoelectric elements 5 are arranged on both sides of the piston 2 within the cylinder chamber 4, the piezoelectric elements consisting of sets of elements which are, in turn, composed of individual elements stacked one on top of the other. Each pile consists, for example, of a number of disc-shaped elements connected in series. The individual piles or sets of elements are, as shown, connected in parallel.

Under electrical control, i.e. on application of a voltage U to the piezoelectric elements, the individual sets of elements can alter their length (as indicated by the dashed line positions). In each case, only the piezoelectric elements 5 on one side of the piston 2 are controlled simultaneously. In this way, they effect a displacement of the pressure medium in the cylinder 1 or pressurize the pressure medium located in the cylinder chamber 4. In this way a force is exerted on the piston 2, which is transmitted via the piston rod 3 as a tractive or compressive force. By alternate control of the piezoelectric elements 5 on the two sides of the piston 2, a back and forth or oscillating movement of the piston 2 and the piston rod 3 can be produced. In this way both static and dynamic forces can be generated in both directions of movement by the piston and piston rod.For dynamic operation it is possible to operate on frequencies in the kilohertz range, i.e.

to produce very quickly oscillating movements (e.g. stimulation in resonance operation).

The effective area of the piezoelectric elements or the volume displacement of pressure medium caused by the piezoelectric elements 5 arranged on each side of the piston 2 is generally chosen to be equal so that the same extent of force or movement can be produced in the two directions of motion (see double arrow) of the piston or piston rod with the cylinder unit shown. The size of the effective areas of the piezoelectric elements 5 can, however, be different and can be adjusted in each case to particular requirements. In operation, the piston 2 can be in a position as shown in Figure 1, or in any mid-position within the cylinder 1. As already mentioned, the pressure medium is fed into the cylinder chambers by means of connections (not shown) and in such a way in each case that the required piston position is reached within the cylinder.

Referring now to Figure 2, there is shown a corrugated tube cylinder 10 in which sets of piezoelectric elements 5, connected in parallel, are arranged in a suitable manner. The free space within the cylinder is filled with a pressure medium, which is introduced into the cylinder by means of connections which are not shown. Under electrical control, the piezoelectric elements increase their length (as shown by the dashed line position) and their volume, whereby pressure medium is displaced. The displacement of pressure medium gives rise to a force acting on a cover plate 1 1 of the corrugated tube cylinder 10 or causes the plate to move in the direction of the arrow.

The return movement of the system into the initial position can take place, for example, by spring tension, whereby for example, the spring tension of the corrugated tube cylinder 10 can also be utilized. The system shown can, for example, be used as an independent forcegenerating component or as a load unit. It is also possible to arrange several units in combination.

The system shown in Figure 3 serves as a pressure medium supply system (pump) or as a pressure generator. Piezoelectric elements 5 are arranged in a casting 20 and substantially fill the interior of the casing, leaving a small free space filled with a pressure medium. The pressure medium can be extracted from a storage container 23 via a supply line 21 and a non-return valve 22, and can be fed to a receiver (PQv) via a further non-return valve 25 and a connection 26.

The individual sets of piezoelectric elements 5 are, as indicated in the drawing, connected in parallel. The sets of elements are controlled in such a way that they intermittently expand and contract. In this embodiment the system therefore acts as a pump, which extracts pressure medium from the storage container 23 and passes it on at the required pressure to the receiver. By interconnecting several pump elements of the type described, larger feed circuits can also be obtained.

Referring now to Figure 4, there is shown a hydraulic loading cylinder 1 with a piston 2 and a piston rod 3 protruding out of the cylinder on each side of the piston. Piezoelectric elements 5 are arranged opposite each other in the cylinder wall 6 of the cylinder 1 on each side of the piston 2. The individual sets of piezoelectric elements 5 can also be distributed in a star-shaped arrangement over the entire circumference of the cylinder wall 6.

Also several rows of star-shaped arrangements can be present in series (seen in axial direction). In addition, piezoelectric elements can also be provided on the front faces of the cylinder in a manner similar to that shown in Figure 1. The internal surface, in particular the cylindrical bore of the cylinder 1 can in this way be largely occupied by such elements or sets of elements. The piezoelectric elements can also be introduced from the outside of the loading cylinder into the cylinder wall 6 and fixed there in a suitable manner. In addition, in contrast to the example embodiment shown, they can be arranged such that under electrical control they do not extend into the cylindrical bore. The system shown in Figure 4 operates essentially like the system shown in Figure 1.

In the embodiments shown in Figures 1, 3 and 4, hydraulic servo control and servo regulating devices with servo-valves can be additionally arranged on the casing or loading cylinders to supply the pressure medium and control it, such devices and valves not being shown. These arrangements can be used, for example, for the static or low-frequency operation of the loading cylinder.

The present system comprising piezoelectric elements can also be provided in the pressure medium chambers of rotary cylinders (vane cylinders) for rotary movement or swinging movement, similar to the embodiments shown in Figures 1 and 4 which have longitudinal cylinders (for longitudinal movement}.

In the embodiments shown, it is possible to use piezoelectric elements which are polarized onedimensionally and/or multidimensionally, i.e. along two or three axes, i.e. which deform under electrical control in two or three axial directions. In the present systems the number of sets of piezoelectric elements is selected so that the required force or movement is generated. With a suitable large number of sets of elements, high power can be transmitted.

Claims

1. A hydraulic pressure generating system, wherein a number of sets of piezoelectric elements is mounted in a casing containing or adapted to contain a pressure medium, and wherein means are provided for subjecting the elements to electrical control so that when the casing contains pressure medium and said elements are electrically controlled, the pressure medium is displaced and/or pressure is generated within the casing.

2. A system as claimed in Claim 1, wherein the casing is in the form of a hydraulic cylinder, in which a piston is arranged so as to be capable of being acted upon by the pressure medium, the piston having at least one piston rod projecting outwards from the casing.

3. A system as claimed in Claim 2, wherein the sets of piezoelectric elements are arranged on both sides of the piston in the cylinder.

4. A system as claimed in Claim 1, wherein the casing is in the form of a corrugated tube cylinder closed on both front faces.

5. A system as claimed in Claim 1, wherein the casing has automatically operable inlet and outlet-valves.

6. A system as claimed in Claim 4 or 5, wherein several casings are interconnected to one unit.

7. A system as claimed in Claim 5 or 6, wherein the system is adapted to operate as a pump.

8. A system as claimed in any one of Claims 1 to 3 or Claim 5, wherein the piezoelectric elements are arranged in the wall(s) of the casing.

9. A system as claimed in Claim 8, wherein the piezoelectric elements are arranged in the form of a star in the wall(s) of the casing.

10. A system as claimed in any one of Claims 1 to 9, wherein the piezoelectric elements are polarized one-dimensionally.

11. A system as claimed in any one of Claims 1 to 10, wherein the piezoelectric elements are polarized multidimensionally.

12. A system as claimed in any one of Claims 1 to 11, wherein means are provided to enable the amplitude and/or frequency of the electrical control and consequently the deformation movement and/or the deformation speed of the piezoelectric elements to be controlled or regulated.

13. A system as claimed in any one of Claims 1 to 3, and 6 to 12, wherein additional hydraulic control- and/or regulating devices with a servovalve are arranged on the casing.

14. A hydraulic pressure generating system substantially as hereinbefore described with reference to any one of Figures 1 to 4 of the accompanying drawings.