WO1994013961A1

WO1994013961A1 - Arrangement for controlling a pressure fluid operated apparatus

Info

Publication number: WO1994013961A1
Application number: PCT/FI1992/000346
Authority: WO
Inventors: Pentti Rita
Original assignee: Pentti Rita
Priority date: 1992-12-17
Filing date: 1992-12-17
Publication date: 1994-06-23

Abstract

The object of the present invention is a device for controlling a pressure fluid operated actuator, comprising a pilot actuator (1) and a valve assembly (7). The valve assembly comprises two valve means (7a, 7b) which are acted upon by displacing the control members (2, 5) of said pilot actuator (1). Each one of said two valve means comprises four valves. The first valve (8a, 8b) is disposed between the actuator (22) and the pressure fluid tank (T) for controlling the exit flow of pressure fluid. The second valve (10a, 10b) is disposed between the pressure fluid source (P) and the actuator (22) for controlling the pressure fluid supply flow. The third valve (9a, 9b) is disposed inside the stem (27a, 27b) of the first valve (10a, 10b) for governing this valve. The fourth valve (11a, 11b) is disposed in conjunction with the second valve (10a, 10b) for controlling this valve in accordance with the state of the first valve (8a, 8b).

Description

ARRANGEMENT FOR CONTROLLING A PRESSURE FLUID OPERATED APPARATUS.

The present invention concerns a device for controlling a pressure fluid operated actuator, as specified in the preamble to Claim 1.

In prior art is known a hydraulic cylinder control arrangement in which with the aid of slide valves and utilization of an on/off control means pres- surized oil is directed to one side or the other of the hydraulic cylinder's piston and the piston and its rod are moved through the desired distance.

The drawback encumbering the arrangement men¬ tioned is that the piston of the cylinder cannot be moved rapidly, flexibly and accurately. Moreover, the piston is not stationary in positions between the ex¬ tremes: it tends to move under influence of pressure, whereby corrective control measures become necessary in order to maintain the piston's position. A further drawback of this arrangement is that the starting/- stopping accelerations are not under control. Another problem is stability of the cylinder: the piston has a tendency to get into oscillation.

The same problems frequently embarrass rota- ting hydraulic apparatus as well, such as hydraulic motors, for instance.

In prior art a control means for a rotating hydraulic motor is known through USI> 4,362,018. The control means comprises a number of valves, of which the first valve pair is disposed between the pressure fluid source and the hydraulic motor for controlling the pressure fluid supply flow and a second pair of valves, between the hydraulic motor and the pressure fluid tank, for controlling the pressure fluid exit flow. The operation of these valves is controlled in pairs with the aid of a toggle switch and two control valves. The drawback in the control device just de¬ scribed is that with the toggle switch two control valves are simultaneously controlled which affect the positions of the first and second valve pairs. Thus the control device easily falls out of stable state and begins to oscillate. A further drawback is slow and inaccurate control of the hydraulic motor owing to potential instability.

The object of the invention is to eliminate the problems mentioned. Specifically, the object of the invention is to provide an improved device serving rapid, accurate and flexible control of a pressure fluid operated actuator.

The device of the invention is characterized by that which is stated in Claim 1.

The device of the invention for controlling a pressure fluid operated actuator comprises a pilot actuator and a valve assembly, said valve assembly comprising two valve means which are influenced by moving the control members of the pilot actuator. The two valve assemblies each comprise a number of cooper¬ ating valves, the first of these valves comprising a chamber; a stem, linearly movable in said chamber; a seat and a first aperture, said seat and aperture being located on a first end of the chamber and the aperture being controlled by moving said stem relative to said seat, and the pressure fluid tank and the chamber com¬ municating with each other through said aperture; and a second aperture through which the actuator communicates with the chamber, and pressure fluid exit flow through the first aperture, from the actuator to the pressure fluid tank, being controllable by moving said stem; and the second valve comprises a chamber; a stem, linearly movable in said chamber; a seat and a first aperture, said seat and aperture being located at a first end of the chamber and the aperture being controlled by moving said stem relative to said seat, and the pressure fluid tank and the chamber communicating with each other through said aperture; and a second aperture through which the actuator communicates with the chamber, and the pressure fluid supply flow through the first aper- ture, from the pressure fluid tank to the actuator, being controllable by moving said stem.

As taught by the invention, the two valve as¬ semblies furthermore comprise a third valve each, dis¬ posed in conjunction with the respective first valve, advantageously in a passage in its stem, to said valve belonging a closing member, disposed in said passage, a spring member, a seat and an aperture, these being advantageously disposed in said passage and the closing member resting against said seat and closing the aper- ture, urged by said spring member, and said closing member can be acted on in opposition to the spring member by means of the pilot actuator's control members so that through said passage a flow path can be opened from the pressure fluid tank to the rear chamber space of the first valve, which further communicates by a passage with the pressure fluid source; and a fourth valve, which is a three-way valve communicating by a first passage with the rear chamber space of the second valve, by a second passage with the pressure fluid source and by a third passage with the pressure fluid tank; and to the fourth valve is connected an actuator for connecting the first passage either to the second or third passage for controlling the second valve in accordance with the state of the first valve. In an embodiment of the device, the first and third valves of both valve assemblies are disposed in conjunction with a first intermediate space or equiv¬ alent, said intermediate space communicating with the pressure fluid tank; and the second valves are disposed in conjunction with a second intermediate space or equivalent, this intermediate space communicating with a pump or equivalent pressure source. In an embodiment of the device, to the fourth valve belongs a chamber with two seats and correspond¬ ing apertures and with a closing member for closing these apertures, to said chamber being connected a first passage, a second passage through the first aperture and a third passage through the second aper¬ ture, and said closing member being urged, with the aid of a first stem provided with a spring member, against the second seat in order to close the second aperture, and said closing member being urged in the opposite direction towards the first seat for closing the first aperture, with the aid of a second stem, this second stem being connected to said actuator.

In an embodiment of the device, the actuator connected to the fourth valve is a differential pres¬ sure governor, by the aid of which the differential pressure between the pressure fluid source and the rear chamber space of the first valve is sensed, the fourth valve being controlled on its basis. In an embodiment of the device, the differen¬ tial pressure governor comprises a chamber in which a piston is disposed, the first side of this piston con¬ necting by a passage with the pressure fluid source and the second side, by a passage with the rear chamber space of the first valve, and the piston connecting with a stem or an equivalent member for controlling the closing member of the fourth valve.

The invention affords the advantage that with its aid simple, accurate and reliable control of a pressure fluid operated actuator can be implemented.

The invention further offers the advantage that in it can be implemented a pressure fluid oper¬ ated, , advantageously hydraulic, control arrangement featuring a closed pressure fluid circulating system. This closed system is hermetically enclosed and compact of its design.

The invention further offers the advantage that said pressure fluid system is also a so-called rigid arrangement, in the actuator prevailing at all times, in principle, pressurized state on the supply as on the exit side, e.g. on both sides of the piston of a hydraulic cylinder or of a hydraulic motor.

The invention offers the advantage that in the valve arrangement unnecessary clearance plays have been successfully eliminated, and this results in highly accurate control of the actuator's output, if required. The invention offers the advantage that the valve arrangement is simply and accurately controlla¬ ble. It is a further advantage that the valve arrange¬ ment has been implemented in a way such that it will not easily go into a state of unstable oscillation. This feature affords the possibility that the speeds of the actuator in moving the piston, or other equivalent motion member, can be rather high.

The invention further offers the advantage that the actuator can be directly controlled, electri- cally or mechanically, through the pilot actuator. The position of the actuator output can be electrically measured and fed back to the pilot actuator so as to achieve accurate position control. The movement of the actuator may also be fed back by means of a motion transducer to the pilot actuator, whereby the position of the actuator output will be accurately known at all times when its initial position is known. In such case no separate measuring instruments are needed in con¬ junction with the actuator for piston or shaft position determination.

The invention further offers the advantage that the device for controlling a pressure fluid oper¬ ated actuator can be applied with ease to serve pres¬ sure fluid operated actuators of a different pressure class, such as hydraulic cylinders, hydraulic swivel¬ ling apparatus or hydraulic motors.

It is also an advantage of the invention that the control pressure circuit constitutes a side circuit relative to the operating fluid circuit proper, whereby the control pressures are comparatively low, easy to manage and comparatively independent of the operating pressure.

In the following the invention is described in detail, referring to the drawings attached, in which Fig. 1 presents, in longitudinal cross section, a de¬ vice according to the invention for controlling a pressure fluid operated actuator; and

Fig. 2 shows schematically the fourth valve of the valve arrangement.

The device of the invention for controlling a pressure fluid operated actuator 22 comprises a pilot actuator 1 and a valve assembly 7, as shown in Fig. 1.

The pilot actuator 1 comprises the actuator proper, 2 , such as a mechanical or electrical switching means, preferably with adjustable travel, and control members provided in conjunction therewith, to wit, a control shaft 3 and a lever means 5. The actuator 2 is connected to the control shaft 3, which can be moved with its aid, axially in opposed directions B, C. The control shaft 3 is carried by one or several bearings, such as a sleeve bearing 4, on the body 12. The passage of the first end of the control shaft 3 through the aperture 13 to the outside of the body 12 is furnished with a packing 14. To this shaft end is, in turn, con¬ nected the actuator 2, which has been disposed e.g. in a suitable protective enclosure 15. The lever means 5 of the control members is attached to the control shaft 3 in such manner that it moves together with the shaft when the shaft is being linearly moved by means of the actuator 2. The lever means 5 projects from the shaft 3, advantageously in a plane perpendicular thereto. On the free end of the lever means 5 projections 17a, 17b and pins 18a, 18b have been provided. The projections 17a,17b are ad- vantageously formed of the opposite ends of an in¬ tegral, straight rod. This rod is substantially paral¬ lel to the axis A-A of the control shaft 3 in the present case. The valve assembly 7 comprises two valve means

7a and 7b, disposed in conjunction with each other, to constitute a cooperating entity. Both valve means 7a,7b are advantageously identical. Each valve means has a common inlet passage 19 for pressure fluid, this inlet passage being connected to a pump P or another equiva¬ lent pressure fluid source. Similarly, the valve means have a joint exit passage 20 for pressure fluid, con¬ nected to a tank T for removing the pressure fluid from the valve assembly 7. The tank T is connected to the intake side of the pump P by a passage. Pressure fluid is once again pumped into the valve assembly by the aid of the pump P when the device is switched on. Further¬ more, there is from both valve means a connecting pas¬ sage 2la,2lb to the pressure fluid operated actuator 22.

The two valve means 7a,7b of the valve as¬ sembly 7 are acted upon by moving with the aid of the actuator 2 the control members of the pilot actuator, i.e., the control shaft 3 and the lever means 5. This is accomplished in that the first valve means 7a is acted upon by moving the control members 3,5 in a first direction B and the second valve means 7b is acted upon by moving the control members 3,5 in the second, or opposite, direction C. In the embodiment of Fig. 1, both valve means

7a,7b comprise four valves each. The first valve 8a,8b is disposed between the actuator 22 and the tank T for controlling the pressure fluid exit flow. The second valve 10a,10b is disposed between the pump or equival- ent pressure fluid source and the actuator 22, for con¬ trolling the pressure fluid supply flow. The third valve 9a,9b is disposed in parallel with the first valve 10a,10b in order to control this valve. The fourth valve 11a,lib is disposed in conjunction with the second valve 10a,10b to control this valve in ac¬ cordance with the state of the first valve 8a,8b, ad- vantageously the pressure prevailing across the stem. The valve means 7a,7b of the valve assembly 7 are disposed in conjunction with each other to consti¬ tute a cooperating entity. The first 8a,8b and third 9a,9b valves are disposed in communication with the first intermediate space 23. This intermediate space 23 is connected by an exit passage 20 with the pressure fluid tank T. The second valves 10a,10b are disposed in communication with the second intermediate space 24. This intermediate space 24 is connected by the supply passage 19 with the pump or equivalent pressure fluid source P. The first 8a,8b, second 10a,10b and third 9a,9b valves are disposed within a first body 12. The fourth valves 11a,lib are disposed in second bodies 5la,5lb, which are advantageously connected to the first body 12.

The first valve 8a,8b comprises a mantle 25a,25b enclosing an advantageously cylindrical cham¬ ber 26a,26b; a stem 27a,27b, which is axially dis- placeable in the chamber's longitudinal direction; a seat 28a,28b; a first aperture 29a,29b, said seat and aperture being located on the first end of the chamber, and the first intermediate space 23 and the chamber 26a,26b communicating with each other through said aperture; and a second, advantageously annular aperture 30a,30b, provided in the mantle 25a,25b and opening into the chamber 26a,26b. On the second end of the chamber of the first valve 8a,8b is located a rear chamber space 31a,31b. In this space, furthermore, a spring member 32a,32b has been provided between the stem 27a,27b and the bottom of the chamber.

The second apertures 30a,30b of the first valves 8a,8b are connected with respective passages 21a and 21b and further through these, to the pressure fluid operated actuator 22. The flow path between the first aperture 29a,29b and the second annular aperture 30a,30b and the pressure fluid exit flow from the ac- tuator 22 to the tank T can be controlled by appropri¬ ately displacing each stem 27a,27b.

The second valve 10a,10b comprises elements corresponding to those of the first valve 8a,8b, and advantageously they are identical. Thus, the second valve 10a,10b comprises a mantle 33a,33b enclosing an advantageously cylindrical chamber 34a,34b; a stem 35a,35b, which is axially displaceable in the chamber's longitudinal direction; a seat 36a,36b; a first apertu¬ re 37a,37b, said seat and aperture being located on the first end of the chamber, and the second intermediate space 24 and the chamber 34a,34b communicating with each other through said aperture; and a second, advan¬ tageously annular aperture 38a,38b, provided in the mantle 33a,33b and opening into the chamber 34a,34b. On the second end of the chamber of the second valve 10a,10b is located a rear chamber space 39a,39b. In this space, furthermore, a spring member 40a,40b has been provided between the stem 35a,35b and the bottom of the chamber. The second apertures 38a and 38b of the second valves 10a,10b are connected with respective passages 21a and 21b, which connect both valve means 7a,7b with the actuator 22. The flow path between the first aperture 37a,37b and the second aperture 38a,38b and the pressure fluid supply flow from the pump, or from the equivalent pressure fluid source, P to the ac¬ tuator 22 can be controlled by appropriately displacing each stem 35a,35b.

The third valve 9a,9b is disposed in con¬ junction with the respective first valve 8a,8b, ad- vantageously in a passage 41a,41b in the stem 27a,27b thereof. The third valve 9a,9a comprises a closing member 42a,42b, disposed in the passage; a spring mem- ber 43a,43b, likewise disposed in the passage, between the closing member and the stem of the third valve; a seat 44a,44b and an aperture 45a,45b, both located in the passage 4la,4lb. The closing member 42a,42b rests against the seat 44a,44b and closes the aperture 45a,45b, urged by the spring member 43a,43b. The closing member 42a,42b can be acted upon, against the spring load of the spring member 43a,43b, by means of the control members of the pilot actuator 1, i.e., by means of the control shaft 3 and the pins 18a,18b of the lever means 5, so that a flow path can be opened through the passage 41a,41b from the pressure fluid tank T to the rear chamber space 31a,31b of the first valve 8a,8b. This rear chamber space communicates fur- ther by passages 63a,63b; 65a,65b and 64a,64b with the pressure fluid source P. A throttling element 66 is disposed in the passage 65.

It is thus understood that the third valve 9a,9b has been arranged in the stem 27a,27b of the first valve, whereby it moves along with said stem. Therefore, the position of the third valve 9a,9b and its distance from the projections 17a,17b and pins 18a,18b of the control menbers 2 also exerts a con¬ trolling effect on the first valve 8a,8b and, further, on the flow path of the exiting pressure fluid. With the aid of this arrangement, the first valve 8a,8b and the third valve 9a,9b can be disposed in conjunction with each other so that the exit flow from the actuator 22 is under control and that in the actuator on the exit passage side prevails a suitable pressure lower than the operating pressure.

The fourth valve 11a,lib is a three-way valve. It connects by a first passage 47a,47b with the rear chamber space 39b,39a of the second valve 10b,10a, by a second passage 48a,48b with the pressure fluid source P, and by a third passage 49a,49b with the pressure fluid tank T. To the fourth valve 11a,lib is connected an actuator 50a,50b for connecting the first passage 47a,47b either to the second 48a,48b or third passage 49a,49b, for controlling the second valve 10b,10a in accordance with the functional state of the first valve 8a,8b.

The fourth valve 11a,lib comprises a body 51a,51b within which is disposed a chamber 52a,52b. The valve carries on opposite ends, on the central axis D- D, two seats: a first 53a,53b and a second seat 55a,55b, and corresponding apertures: a first 54a,54b and a second aperture 56a,56b. In the chamber 52a,52b is disposed a closing member 57a,57b for alternatingly closing the apertures. To the chamber 52a,52b is di¬ rectly connected the first passage 47a,47b. The second passage 48a,48b is connected with the chamber 52a,52b through the first aperture 54a,54b and the third pas¬ sage 49a,49b, through the second aperture 56a,56b. The valve further comprises a first stem 59a,59b, located on the central axis D-D of the valve, in the vicinity of the first aperture 54a,54b. The stem 59a,59b is in¬ directly braced against the body 51, over a spring member 58a,58b. The valve comprises a second stem 60a,60b, located on the central axis D-D of the valve, in the vicinity of the second aperture 56a,56b. The closing member 57a,57b can be pressed by means of the first stem 59a,59b, provided with spring member 56a,56b, against the second seat 55a,55b for closing the second aperture 56a,56b and opening the first aperture 54a,54b, and similarly the closing member 57a,57b can be pressed with the aid of the second stem 60a,60b in the opposite direction, towards the first seat 53a,53b, for closing the first aperture 54a,54b and opening the second aperture 56a,56b.

The second stem 60a,60b is connected to the actuator 50a,50b, advantageously a differential pres¬ sure governor. This actuator is used to sense the dif¬ ferential pressure between the pressure fluid source P and the rear chamber space 31a,31b of the first valve 8a,8b, on the basis of which the fourth valve 11a,lb is controlled.

The differential pressure governor serving as actuator 50a,50b comprises a chamber 6la,6lb, in which a piston 62a,62b is disposed. To the first side of the piston is connected a passage 63a,63b from the pressure fluid source P and to the second side, a passage 64a,64b from the rear chamber space 3la,3lb of the first valve 8a,8b. To the piston 62a,62b is connected a stem 60a,60b for controlling the closing member 57a,57b of the fourth valve 11a,lib.

The first and second valve means 7a;7b are connected crosswise so that the rear chamber space 31a of the first valve 8a of the first valve means 7a is connected by the passage 64a to the actuator 50a in conjunction with the fourth valve 11a and the fourth valve 11a, through the passage 47a to the rear chamber space 39b of the second valve 10b of the second valve means 7b. In similar way, the rear chamber space 31b of the first valve 8b of valve means 7b is connected by the passage 64b to the actuator 50b in conjunction with the fourth valve lib and the fourth valve lib, through the passage 47b to the rear chamber space 39a of the second valve 10a of the first valve means 7a.

In both valve means 7a;7b the cross section areas of the stems 27a;27b and 35a;35b of the first 8a;8b and second 10a;10b valves on the first end of the stem, i.e., on the side of the aperture 29a;29b, res- pectively 37a;37b, are smaller than those of the other stem end on the side of the rear chamber 31a;31b and 39a;39b, respectively. Owing to this disposition the first as well as second valve will always go into the closed position when the pressures are equal on both sides of the stem. Therefore, said valves will in the main rule always operate with the aid of the pressures acting across them. The purpose with the spring members 32a;32b and 40a;40b, respectively, placed in the rear chamber spaces 31a;31b and 39a;39b, respectively, of the valves is in the first place to make sure that these valves will always close if the pressures are lost for one reason or another, thus preventing pressu¬ re fluid exit from the actuator 22. The output tap of the actuator 22 will thus remain locked.

In the valve assembly 7, the first valves 8a,8b of both valve means 7a,7b are advantageously so arranged that the longitudinal axes of these chambers 26a,26b and the motion axes of the stems 27a,27b coin¬ cide with the same straight line and that the projec¬ tions 17a,17b and pins 18a,18b of the lever means 5 of the pilot actuator 1 lie between the stems 27a,27b and, at the same time, between the second valves 9a,9b, specifically between their closing members 42a,42b and passages 4la,4lb, in the second intermediate space 24.

In both valve means 7a,7b, the second valves 10a,10b are advantageously arranged in the same way as the first valves 8a,8b, so that the longitudinal axes of the chambers 35a,35b are aligned with each other.

Between the first valves 8a,8b and second valves 10a,10b of the valve means 7a,7b an intermediate body 46 has been provided in the embodiment of the drawing. The passages 21a,21b leading from the valve means 7a,7b to the actuator 22 connect with bores in the intermediate body 46 and further, therethrough, respectively with the aperture 30a of the first valve 8a and the aperture 38a of the second valve 10a of the first valve means 7a, and similarly, with the aperture 30b of the first valve 8b and the aperture 38b of the second valve 10b of the second valve means 7b.

In the following, the operation of the device of the invention is described, and reference is made to the accompanying drawings. The pressure fluid source is, for instance, a pressure fluid pump P. When the pump is not running, the first 8a,8b, second 10a,10b and third valves 9a,9b are in closed position and, similarly, the closing member 57a,57b of the fourth valve has closed the second aperture 56a,56b. As soon as the pump P is started, the rear chamber space 31a,31b of the first valve 8a,8b is pressurized through the passage 63a,63b, the chamber 61a,61b of the diffe¬ rential pressure governor and the passages 65a,65b; 64a,78b, and similarly the rear chamber space 39a,39b of the second valve 10a,10b is pressurized through the fourth valve 11a,lib, the passage 48a,48b, the aperture 54a,54b, the chamber 52a,52b and the passage 47a,47b. The first 8a,8b and second 10a,10b valves are now clo¬ sed by action of the pressurized fluid (and secured by the spring members 32a,32b and 40a,40b). When the control shaft 3 is acted upon with the aid of the actuator 2 and moved from its initial position in the direction B through an apppropriate travel, the pin 18a of the projection 17a belonging to the control members 1 presses on the closing member 42a and opens the third valve 9a so that the passage 41a between the first intermediate space 23 and the rear chamber space 31a of the first valve 8a opens. The pressure in the rear chamber space 31a goes down rerla- tive to the pressure of the pressure fluid source P, whereby this differential pressure acts across the piston 62a of the fourth valve serving as differential pressure governor, and the piston 62a as well as the stem 60a thereto connected are displaced. The stem 60a urges the closing member 57a of the fourth valve 11a against the spring member 58a onto the first seat 53a and the aperture 54a, closing this aperture. The rear chamber space 39b of the second valve 10b is thus con¬ nected with the pressure fluid tank T through the pas¬ sage 47a, chamber 52a and passage 49a. The pressure in the rear chamber space 39b goes down. Across the stem 35b of the second valve 10b is now acting the differ¬ ential pressure between the pressure fluid source P, from the intermediate space 24, and the pressure fluid tank T, through the fourth valve 11a. A flow path opens from the pressure fluid source P through the second intermediate space 24, through aperture 37b further to the passage 38b, to passage 21a and to the actuator 22. Hereby the pressure of the pump P begins to act on the actuator 22.

Simultaneously, pressure fluid discharges through the second passage 21b out from the actuator 22. This is directed from the passage 21b through the aperture 30a to the first valve 8a of the first valve means 7a. The pressure of the outgoing fluid acts on the stem 27a of the first valve, pressing it towards the rear chamber space 31a, whereby the first aperture 29a opens and the fluid can discharge into the first intermediate space 23, and further through the exit passage 20 to the tank T. It depends on the pressure of the exiting fluid how far the stem 27a of the first valve 8a opens and opens the first aperture 29a. It is thus understood that the fluid exits from the actuator 22 in controlled manner.

When one desires to stop the actuator 22, the actuator 2 is used to act upon the control shaft 3 and this shaft is moved back into initial position; the projection 17a and pin 18a belonging to the control members 1 cease to act on the closing member 42a of the third valve 9a, and the passage 41a between the first intermediate space 23 and the rear chamber space 31a of the first valve 8a is closed. The pressure in the rear chamber space 31a increases owing to the effect of fluid arriving through the passages 64a, 65a, 63a. Owing to the restriction 66 in the passage 65, however, the pressure increases in a controlled manner. When the pressure in the rear chamber space 31a has reached the same order of magnitude as the pressure of the pressure fluid source P, the piston 62a of the actuator 50 can¬ not with the aid of the stem 60a keep the first apertu- re 54a of the fourth valve 11a closed: the spring-bia¬ sed stem 59a urges the closing member against the se¬ cond seat 55a and closes the second aperture 56a in its turn. The pressure fluid can discharge through the passage 48a, the first aperture 54a, the chamber 52a and the passage 47a into the rear chamber space 39b of the second valve 10b. The pressure in the rear chamber space 39b increases up to the pressure of the pressure fluid source. Now the pressure P of the pressure fluid source acts on both sides across the stem 35b of the second valve 10b, but the larger cross section area of the stem on the side towards the rear chamber causes the valve 10b to close. The flow path from the pressure fluid source P through the sewcond intermediate space 24, through the aperture 37b further to the passage 38b, passage 21a and to the actuator 22 is closed down. The pressure of the pump P thus ceases to act on the actuator 22.

The discharge of exiting fluid through the first valve 8a is also controlled with the aid of the third valve 9a. When the stem 27a of the first valve means 8a moves in the chamber 26a toward the rear chamber space 31a, the third valve means 9a is dis¬ placed along with the stem 27a. The lever means 5 of the pilot actuator, and in particular the pin 18a, keeps the third valve 9a open through a given, permis¬ sible travel of the stem 27a. If this displacement is surpassed, the effect of the pin 18a on the closing member 42a of the third valve 9a ceases and this valve closes. The pressure in the rear chamber space 31a of the first valve increases owing to the pressue fluid entering there through the passage 64 and tends to move the stem 27a toward the seat 28a, and to close the aperture 29a. The closing member 42a of the third valve 9a comes once more into reach of the lever means 5 and the pin 18a.

The pressure increase in the rear chamber space 31a of the first valve 8a also acts on the ac¬ tuator 50 of the fourth valve 11a and, therethrough, on the fourth valve 11a, as was observed in the foregoing in a similar situation in connection with discontinuing control of the pilot actuator 1. In this way, in all conditions, the supply and exit flows of pressure fluids through the passages 2la,2lb to the actuator are controlled.

When it is desired to change the direction of action of the output of the actuator 22, such as the direction in which a cylinder piston moves, relative to that described above, the control shaft 3 is acted upon with the actuator 2 by shifting the shaft in the direc¬ tion opposite to the above, that is in direction C. This produces action, with the control shaft 3 of the pilot actuator 1 and with the devices 17b,18b asso¬ ciated with the lever means 5, on the third valve 9b of the second valve means 7b in similar manner as was described above with relation to the first valve means 7a. The operation of the second valve means 7b is fully analogous with that of the valve means 7a discussed in the foregoing. The only difference is that the pressure fluid flows passing through the passages 21a,21b have different direction and therefore the operating direc- tion of the actuator 22 is reversed.

It should be noted that the displacements of the control shaft 3 in the direction of its axis A-A are rather minor, e.g. 5 mm or even less. It is there¬ fore possible, with the pilot actuator 1 and with the action members 2,5 thereto attached, to exert very fast action on the first or second valve means 7a,7b of the valve assembly 7 and on the respective third valves 9a,9b.

The actuator 2 of the pilot actuator 1 can be controlled from a control unit, comprising a micro¬ processor, for instance. The amount of displacement of the actuator 22, such as length of movement or degrees of rotation or number of turns, can be pre-set in the control unit, and the implementation thereof can be monitored by means of an appropriate feedback arrange¬ ment. The invention is not exclusively limited to concern the embodiment examples presented in the fore¬ going: numerous modifications are feasible within the scope of the inventive idea defined by the claims.

Claims

1. A device for controlling a pressure fluid operated actuator, comprising a pilot actuator and a valve assembly, said valve assembly comprising two valve means (7a,7b) which are acted upon by displacing the control members (2,5) of said pilot actuator (1), each one of said two valve means comprising a number of valves in cooperation with each other and of which - the first valve (8a,8b) comprises a chamber (26a,26b); a stem (27a,27b) which is linearly movable in said chamber; a seat (28a,28b) and a first aperture (29a,29b), said seat and aperture being located at a first end of said chamber, and the aperture (29a,29b) being controlled by moving said stem relative to said seat, and the pressure fluid tank (P) and said chamber communicating with each other through said aperture; and a second aperture (30a,30b), through which the actuator (22) is connected with said chamber (26a,26b), and the exit flow of pressure fluid from the actuator (22) to the pressure fluid tank (P), passing through the first aperture, being controllable by moving said stem; and the second valve (10a,10b) comprises a chamber (34a,34b); a stem (35a,35b), which is linearly movable in the chamber; a seat (36a,36b) and a first aperture (37a,37b), said seat and aperture being located at a first end of said chamber, and the aperture being con¬ trolled by moving said stem relative to said seat, and the pressure fluid source (P) and said chamber commu¬ nicating with each other through said aperture; and a second aperture (38a,38b), through which the actuator (22) is connected with said chamber (34a,34b), and the pressure fluid supply flow from the pressure fluid source (P) to the actuator (22), passing through the first aperture, being controllable by moving said stem, c h a r a c t e r i z e d in that each one of the two valve means (7a,7b) additionally comprises

- a third valve (9a,9b), disposed in conjunction with the respective first valve (8a,8b), advantageously within a passage (41a,41b) provided in the stem (27a,27b) thereof, said valve (9a,9b) comprising a closing member (42a,42b), disposed in said passage, a spring member (43a,43b), a seat (44a,44b) and an aper¬ ture (45a,45b), these being advantageously located in said passage (41a,41b), and the closing member (42a,42b) resting against said seat (44a,44b) and closing the aperture (45a,45b), urged by the spring member (43a,43b), said closing member being affectable against the spring loading of the spring member by means of the control members (2,5) of the pilot actua- tor (1) so that through the passage (4la,4lb) a flow path can be opened from the pressure fluid tank (T) to the rear chamber space (31a,31b) of the first valve (8a,8b), this rear chamber space being further con¬ nected by a passage with the pressure fluid source (P); and

- a fourth valve (11a,lib), which is a three-way valve, connected by a first passage (47a,47b) to the rear chamber space (39a,39b) of the second valve (10a,10b), by a second passage (48a,48b) to the pressure fluid source (P) and by a third passage (49a,49b) to the pressure fluid tank (T); and to the fourth valve (11a,lib) is connected an actuator (50a,50b) for con¬ necting the first passage (47a,47b) either to the se¬ cond (48a,48b) or to the third passage (49a,49b) for governing the second valve (10a,10b) in accordance with the state of the first (8a,8b) valve.

2. Device according to claim 1, c h a r a c¬ t e r i z e d in that the first (8a,8b) and third valves (9a,9b) of each valve means are disposed in conjunction with a first intermediate space (23) which communicates with the pressure fluid tank (T); and the second valves (10a,10b) are disposed in conjunction with a second intermediate space (24) which communica¬ tes with the pump or equivalent pressure fluid source

⁽P⁾.

3. Device according to claim 1 or 2, c h a r a c t e r i z e d in that the fourth valve (11a,lib) comprises a chamber (52a,52b) having two seats (53a,53b;55a,55b) and corresponding apertures (54a,54b;56a,56b) and a closing member (57a,57b) for closing said apertures, to said chamber (52a,52b) being connected a first passage (47a,47b), a second passage (48a,48b) through the first aperture (54a,54b) and a third passage (49a,49b) through the second aperture (56a,56b), and said closing member (57a,57b) being pressed by the aid of a first stem (59), provided with a spring member (58), against the second seat (55) for closing the second aperture (56), and said closing member (57a,57b) being pressed by the aid of a second stem (60a,60b) in the opposite direction toward the first seat (53a,53b) for closing the first aperture (54a,54b), said second stem (60a,60b) being connected to said actuator (50a,50b).

4. Device according to claim 1, 2 or 3, c h a r a c t e r i z e d in that the actuator (50a,50b) connected to the fourth valve (11a;lib) is a differential pressure governor, by the aid of which the differential pressure between the pressure fluid source (P) and the rear chamber space (31a,31b) of the first valve (8a,8b) is sensed, the fourth valve being cont¬ rolled on the basis of this differential pressure.

5. Device according to claim 4, c h a r ¬ a c t e r i z e d in that the differential pressure governor serving as actuator (50a,50b) comprises a chamber (61a,61b) in which a piston (62a,62b) is dis¬ posed, on the first side thereof being connected a passage (63a,63b) from the pressure fluid source (P) and to the second side, a passage (64a,64b) from the rear chamber space (31a,31b) of the first valve (8a,8b), to said piston (62a,62b) being connected a stem (60a,60b) or another equivalent member for gover¬ ning the closing member (57a,57b) of the> fourth valve.