VALVE, AND THE USE THEREOF FOR A CLUTCH

Abstract

A valve, in particular proportional pressure regulating valve, having a valve piston (12) which is guided in longitudinally movable fashion in a valve housing (10) and which can be actuated by means of an operation device (14), wherein the valve housing (10) has multiple fluid ports (P, A, T) and wherein, in one movement position of the valve piston (12), a fluid-conducting connection is produced between a pressure supply port (P) and a working port (A), and in another movement position, a further fluid-conducting connection is produced between the working port (A) and a tank port (T), is distinguished by the fact that the respective pressure difference that arises between the working port (A) and the tank port (T) as flow passes through the further fluid-conducting connection acts, by way of an actuation device (30), on the valve piston (12) such that the latter passes from a stop position (32), proceeding from which the further fluid-conducting connection is substantially shut off, into a fully open opening position, in which, in relation to the stop position (32), an enlarged opening cross section from working port (A) to tank port (T) is realized.

Description

The invention relates to a valve, in particular to a proportional pressure regulating valve, having a valve piston guided longitudinally displaceably in a valve housing and controllable by means of an actuator device, wherein the valve housing has several fluid ports and wherein, in a movement position of the valve piston, a fluid-carrying connection is establishable between a pressure supply port and a utility port and, in another driving position, another fluid-carrying connection between the utility port and a tank port is establishable. The invention further relates to the use of such a valve in clutches.

Such valves in the form of so-called proportional pressure regulating valves are widely used for mobile working devices for the electro-hydraulic control of clutches.

These clutches must be filled regularly with an operating fluid in the form of oil when activated initially until their friction surfaces reach the point of contact in order to be able to act as a clutch. To this end, spring forces must be overcome in the clutch. The pressures created by spring forces are often very low (less than 2 bar), and a further increase in the clutch pressure then results in normal forces on the clutch linings, which can ultimately transmit the torque through frictional forces.

These low spring forces result in problems when switching off the clutches because, in order to move the respective clutch disc away from the assignable contact surface, only the pressure caused by these spring forces is available to produce the oil flow through the proportional pressure regulating valves.

There is therefore a requirement for these valves that the pressure loss in the flow from the working port to the tank port should be extremely small because that is the only way to ensure fast and safe switching off of the clutch.

In the current prior art, the largest possible flow cross-section is opened in directly controlled proportional pressure regulating valves through the use of magnets with large working strokes. At the same time, this requires as much magnetic force as possible in order not to let the ratio between magnetic force and flow force become too unfavorable. Large and expensive actuator devices in the form of actuating magnets are therefore required.

If one were now to overcome these disadvantages by using smaller, and thus more economical actuating magnets with the same force, which is within the average skill of a person skilled in the art in the field of valve and clutch technology, it would necessarily decrease the length of the linear force-stroke range. If one does not intend to reduce the full opening cross-section for the fast emptying of the fluid medium from the clutch, one must not shorten the actual valve stroke of the valve piston, but this in turn inevitably results in the spring forces holding the actuating magnet in its non-linear force range when the valve is switched on, requiring a large magnet current for “breaking away the magnet” from the end position.

At the moment, however, where the magnetic force becomes greater than the spring force, one moves on the strongly ascending branch of the characteristic force-stroke line and the balance between magnetic force and spring force would be lost in favor of the magnetic force. On the PI characteristic line of the valve this would be noticeable from a start-up jump with the result that, upon releasing the clutch, the vehicle starts with a jump, which is particularly unacceptable for safety reasons for mobile working devices.

Starting from this prior art, the object of the invention is to further improve the known valve solutions while retaining their advantages so that, at least for use in a clutch, the start-up jumps described above are avoided, while the valve should be economical in its implementation and functionally reliable in operation.

This object is achieved by a valve having the features of claim 1 in its entirety.

Due to the fact that, according to the characterizing portion of claim 1, the respective differential pressure that arises during the flow through the further fluid-carrying connection between the utility port and the tank port acts on the valve piston by means of a control device in such a way that it acts against a stop position, from which the further fluid-carrying connection is noticeably inhibited, to arrive at a fully open port position, in which, compared to the stop position, an enlarged opening cross-section from utility port to tank port is achieved, an opportunity is created to increase the valve piston stroke without having to accept the start-up jump of the PI characteristic line. Thus, the valve of the invention can produce a very large opening cross-section upon release of the clutch and thus ensure a rapid separation of the coupling.

The valve according to the invention need not be limited to applications in clutches, but rather can be generally used where, for space and/or cost reasons, only small actuator devices in the form of actuating magnets can be used while simultaneously increasing the free travel path of the valve piston beyond the possible operating range of the actuating magnet in order to thus arrive at very large opening cross-sections, which, apart from improved fluid removal, also serve to supply larger fluid amounts to hydraulic systems.

It is preferably provided that the control device carries the respective differential pressure, by means of a control duct preferably arranged in the valve housing, to a piston ring surface of the otherwise pressure-equalized valve piston, which, starting from the stop position, reaches the fully open port position under the influence of this differential pressure. The mentioned pressure regulation is carried out with the help of the pressure effect on this piston ring surface, preferably designed as an annular surface. Furthermore, it is provided that the stop position is formed by a disc-shaped stop element, which is pressurized by an energy accumulator, preferably by a compression spring, wherein the stop element is supported in its stop position on fixed parts of the valve housing or the actuating magnet.

As set forth above and as is common for other comparable valve constructions, the spring force of said energy accumulator is not passed directly to the valve piston forming the regulating piston. It is true that, in the valve solution according to the invention, a stop element, preferably formed as a disc, is incorporated, as usual, between the valve piston and the compression spring, wherein the stop element normally moves synchronously with the valve piston while transferring the spring force in order to move the valve piston to its initial position when the actuating magnet is not energized; however, the valve piston can continue to move and thus enable a larger opening cross-section by reaching its fully open port position opening beyond said stop position under control of the differential pressure. The pertinent further movement takes place without the support of the spring force, only under the influence of the differential pressure, which inevitably arises during the flow through the valve from the utility port to the tank port.

As set forth above, the clutch is thus relieved with fluid connection to the tank port by switching off the actuating magnet. The mentioned spring force hereby presses the valve piston into a position which permits the flow from the utility port, i.e. the clutch load, to the tank port and the disc-shaped stop element abuts the pole core of the actuating magnet. As a result of the differential pressure acting on the annular surface of the valve piston, the piston is now moved in the direction of the actuating magnet, but without the spring force, and as soon as the clutch is completely emptied, the differential pressure, and hence the force acting on the valve piston, is eliminated.

The valve piston is now in a so-called indifferent state and, when switching on the electric actuating magnet again, a minimum magnetic force is now sufficient to move the piston back to the point of contact with the stop disc. A low actuation force of the magnet in the nonlinear region is thus sufficient to be able to move the piston out of this indifferent region. As soon as the contact point with the return spring has been reached, the electrical magnet or actuating magnet is in its linear region and the mentioned PI characteristic line can be run through cleanly without a start-up jump, ensuring a smooth engagement. The invention thus provides the use of an inexpensive actuating magnet with a low linear stroke range, yet achieving high magnetic force without limiting the valve stroke, which is so important for the low-loss flow.

The valve solution according to the invention is explained in greater detail below based on an exemplary embodiment according to the drawing.

It is shown in a basic representation, not to scale, in the figures:

FIG. 1 shows the complete valve, formed as a proportional pressure regulating valve, by way of a longitudinal section;

FIG. 2 shows an enlarged figure section of FIG. 1, showing the valve in a relief position, with a partially opened fluid connection from the utility port A to the tank port T without overtravel;

FIG. 3 is a longitudinal section representation corresponding to FIG. 1, wherein the valve is shown in the overtravel position with an enlarged opening cross-section from utility port A to tank port T; and

FIG. 4 an enlarged figure section of FIG. 3, corresponding to FIG. 2, but with a control duct, closed by a plug, drawn in on the opposite side.

The valve shown in the figures is formed as a proportional pressure regulating valve. The valve includes a valve piston 12, longitudinally displaceably guided in a valve housing 10. The valve or control piston 12 is controllable by means of an actuator device 14 in the form of a so-called actuating magnet for assuming its individual movement positions. The actuating magnet 14 is designed according to the prior art and includes a coil winding 20, energizable by means of a plug 18, for moving a magnet armature 16. The actuating magnet 14 is designed as a so-called push magnet, i.e., when current flows through the coil winding 20, the magnet armature 16 moves downward in viewing direction on FIG. 1, and, with the one free end of the valve piston 12, exerts a force on the same via its actuating plunger 22, which abuts with its free front end, thus triggering a movement of the valve piston 12.

The actuating magnet 14 is designed to be pressure-tight and its pole core 24 opens into a flange plate 26 at its end, by means of which the complete valve can be affixed to a valve or control block, not shown. In front of the corresponding port on such a complete valve or control block, the valve housing, on its outer circumference, is designed as a plugged part in cartridge design and, on its outer circumference, equipped with sealing rings for the connection to the corresponding fluid connection points in the valve or control block.

In particular, for this purpose, the valve housing 10 includes a pressure supply port P and a utility port A in radial direction and a tank port T at the free front end of the valve housing 10, viewed in axial direction. Via the pressure supply port P, a hydraulic fluid of a predeterminable amount and a predeterminable pressure, for example provided by a hydraulic pump (not shown), can be supplied, for example, to its other ports A, T. For the herein particularly preferred mentioned use of the valve in clutches, the utility port A is connected to a pertinent clutch device (not shown). If a tank port T is concerned here, this can also concern a common return line, which need not necessarily open into a storage tank, but which at least needs to have a lower pressure, for example, of the magnitude of the tank or ambient pressure, which is generally lower than the pressure at the pressure supply port P or at the utility port A.

The design of a valve as described above is known. In contrast, the solution according to the invention distinguishes itself, inter alia, by the fact that the respective differential pressure created when flowing through the fluid-carrying connection between the utility port A and the tank port T, acts on the valve piston 12 in such a way that it acts against a stop position 32 by means of a control device 30 to reach, in accordance with the representation of FIG. 1, a fully open port position in which an enlarged opening cross-section from utility port A to tank port T (see FIG. 3) is reached, compared to the stop position 32 (see FIG. 1).

For this purpose, the control device 30 includes a control duct 34, extending in the axial direction in the valve housing 10, which guides the respective differential pressure to a piston ring surface 36 of the otherwise pressure-equalized valve piston 12, which, starting from the stop position 32, can move to the fully open port position (see FIG. 3) under the influence of this differential pressure.

The mentioned pressure-effective piston ring surface 36 results from the difference in diameter d₁−d₂ (see FIG. 2) of the valve piston 12 in its upper stepped recess region. The control duct 34 opens into a diametrally expanded fluid chamber 38 of the valve housing 10, in which, in every movement position of the valve piston 12, its one piston ring surface 36 is guided, which, as previously mentioned, results from a stepped transition of different piston diameters d₁/d₂ of the valve piston 12, which tapers in this way in the direction of the tank port T.

Viewed in the direction on FIGS. 1 and 2, the control duct 34, at its upper free end, opens in axial direction from the valve housing 10 out of its free end face where it is sealed by a closure plug 40. At the lower end at a transverse guide, the control duct 34 opens into the connection point A′ at which the respective pressure between utility port A and tank port T is permanently present via the valve or control block, not shown. The pressure A′ here corresponds to the pressure A. If the control duct 34 is closed at its upper end by the closure plug 40, it at least leaves a connection between the control duct 34 and the fluid chamber 38. In order to be able to seal the fluid chamber 38 against the actuating magnet 14 as well as against the pressure supply port P, the valve piston, on its outer circumference, has duct-like fluid seals of conventional design as well as a pressure centering groove 42.

The previously mentioned stop position 32 is essentially formed by means of a disc-shaped stop element 46, pressurized by an energy accumulator in the form of a compression spring 44, wherein the stop element 46 is supported for this purpose on the fixed parts of the actuating magnet 14 in the form of the pole core 24. To receive the compression spring 44, the pole core 24 has a cylindrical chamber-like recess 48, which tapers down in diameter towards the free end of the actuating plunger 22 in order to form a stop shoulder 50, against which the disc 46 can abut the front end.

As shown in the figures, the valve piston 12 with its tapered diameter end 52 penetrates a cylindrical central recess of the disc-shaped stop element 46 and, in the region of its free end 52, has a diameter widening in the manner of a catch 54 which, as shown in FIGS. 1 and 2, overlaps the disc 46 from above while abutting the same. By operating the actuator device 14, the stop element 46 is moved against the action of the energy accumulator in the form of the compression spring 44 out of the stop position 32 to a maximum possible effective position in which the fluid-carrying connection between the supply port P and the utility port A is established and the connection between utility port A and tank port T is completely blocked (not shown). In this valve position, the clutch, which is connected to the utility port A, can then be supplied with a fluid of predeterminable pressure in a predeterminable amount from the pressure supply port P, and, as described above, the clutch plates can then be gradually brought into contact, while overcoming clutch spring forces, for the purpose of transmitting torque through friction.

In order to establish complete pressure equalization both within the actuating magnet 14 and for the valve piston 12, both the valve piston 12 and the rod-shaped actuating element 22 in the form of the actuating plunger are provided with a continuous pressure-equalizing duct 56 that, at its one free end, opens in the direction of the tank port T and, at its other free end, comes into abutment with parts of the movable magnet armature 16. As further shown in the individual figures, the pressure equalization duct 56 opens via a transverse bore 58 into the cylindrical recess 48, which forms the spring chamber for the compression spring 44 inside the pole core 24. The compression spring 44, with its upper free end when viewed in the direction on figures, is in direct contact with the disc-shaped stop element 46 and, with its other lower end, is in contact with a termination disc 60, which is affixed pressure-tight between one free end of the valve housing 10 and the adjacent front end of the pole core 24.

When assuming the stop position 32, the valve piston 12 has a further reduction in diameter 62 with an axial length such that at least the supply port P can be open and the utility port A can be blocked by the valve piston 12, wherein, when moving the valve piston 12 under the influence of the actuator device 14 in the direction of the tank port T, i.e. downward in viewing direction on the figures, the connection between supply port P and utility port A is increasingly established and the connection of the supply port A to tank port T is blocked.

To disengage the clutch, not shown, it must be relieved with fluid connection to the tank port T, to which end the actuating magnet 14 must be turned off first. The spring force of the compression spring 44 here pushes the valve piston 12 into a position which allows the flow from utility port A to tank port T, wherein the disc 46 moves against the pole core 24, assuming the stop position 32. The respective valve-relief position of utility port A to tank port T without overtravel is shown in FIGS. 1 and 2.

However, starting from this stop position 32, the valve piston 12 can now continue to move upwards, according to the representations according to FIGS. 3 and 4, wherein the catch 54 is removed from the upper face of the disc 46, thereby allowing for a larger opening cross-section between the utility port A and the tank port T. FIGS. 3 and 4 show the valve in the respective overtravel position. This overtravel of the valve piston 12 takes place without the support of the spring force of the compression spring 44 by taking advantage of the differential pressure at the connection point A of the control duct 34 that inevitably arises during the flow through the valve from utility port A to the tank port T. This differential pressure at the connection point A acts on the annular surface 36 of the piston 12 and, without the spring force, moves it further upward in the viewing direction in FIGS. 3 and 4.

When the clutch is completely emptied of fluid by the clutch springs again bringing the individual clutch discs to a distance from each other, the differential pressure, and hence the force effect on the valve piston 12, is eliminated. The valve piston 12 is thus in an indifferent state and, when switching on the actuating magnet 14 again, a minimal force is now sufficient to return the valve piston 12 to the point of contact with the disc 46, whereby the catch 54 again abuts the disc 46. If this point of contact is reached with the compression spring 44, as shown in FIGS. 1 and 2, the actuating magnet or electromagnet 14 is in its linear region, so that the so-called PI characteristic line can be run through cleanly without a start-up jump. As shown in particular in FIG. 4, the fluid chamber 38 is conically tapered towards the top, so that a conical transition region 64 is formed between fluid chamber 38, significantly enlarged in diameter, with respect to the diameter d₁ of the valve piston 12 within its valve housing 10.

Overall, the valve construction according to the invention thus achieves the use of an inexpensive actuating magnet with a low linear stroke range, thus achieving high magnetic force without limiting the full valve stroke, which is so important for the low-loss flow.

Claims

1. A valve, in particular a proportional pressure regulating valve, having a valve piston (12) longitudinally displaceably guided in a valve housing (10) and controllable by means of an actuator device (14), said valve housing (10) having a plurality of fluid ports (P, A, T) and wherein, in a movement position of the valve piston (12), a fluid-carrying connection between a pressure supply port (P) and a utility port (A) is established and, in another movement position, another fluid-carrying connection between the utility port (A) and a tank port (T) is established, characterized in that the respective differential pressure, created when flowing through the further fluid-carrying connection between the utility port (A) and the tank port (T), acts on the valve piston (12) by means of a control device (30) in such a way, that the valve piston (12) acts against a stop position (32), from which the further fluid-carrying connection is noticeably inhibited, to arrive at a fully open port position in which, compared to the stop position (32), an enlarged opening cross-section from utility port (A) to tank port (T) is achieved.

2. The valve according to claim 1, characterized in that the control device (30) carries the respective differential pressure, by means of a control duct (34) preferably arranged in the valve housing (10), to a piston ring surface (36) of the otherwise pressure-equalized valve piston (12), which, starting from the stop position (32), reaches the fully open port position (FIG. 3) under the influence of this differential pressure.

3. The valve according to claim 1, characterized in that the stop position (32) is formed by a stop element (46) pressurized by means of an energy accumulator, preferably by a compression spring (44), wherein the stop element (46) is supported on fixed parts of the valve housing (10) or actuator device (14).

4. The valve according to claim 1, characterized in that the stop element is formed of a disc (46) with a central recess, that the disc (46) in the stop position (32) on its front end is supported on the pole core (24) of the actuating magnet (14) and that the compression spring (44), with its one free end, is supported on the disc (46) and, with its other free end, is supported on a termination disc (60) affixed between the valve housing (10) and the pole core (24).

5. The valve according to claim 1, characterized in that the valve piston (12) with its one free end (52) penetrates the stop element (46) and in the region of this free end (52) has a catch (54), which, upon actuating the actuator device (14), moves the stop element (46) against the action of the energy accumulator (44) from the stop position (32) to a maximum possible effective position, in which the fluid-carrying connection between the supply port (P) and the utility port (A) is established and the connection from utility port (A) to tank port (T) is blocked.

6. The valve according to claim 1, characterized in that the actuator device (14) is formed of a push-action actuating magnet and that both the valve piston (12) and the rod-shaped actuating element (22) of the actuating magnet (14) have a continuous pressure-equalizing duct (56), which opens on one side thereof into the tank port (T), regardless of the movement position of the valve piston (12).

7. The valve according to claim 1, characterized in that the control duct (34) opens into a diametrically expanded fluid chamber (38) of the valve housing (10), in which, in every movement position of the valve piston (12), its one piston ring surface (36) is guided, which results from a stepped transition of different piston diameters (d1/d2) of the valve piston (12), which tapers in this way in the direction of the tank port (T).

8. The valve according to claim 1, characterized in that the control duct (34), at its one end-side outlet from the valve housing (10), is closed by a closure plug (40) in this region, which keeps the inlet of the control duct (34) into the fluid chamber (38) free, and that the other end of the control duct opens into a connection point (A′), which picks up the differential pressure between the utility port (A) and the tank port (T).

9. The valve according to claim 1, characterized in that when assuming the stop position (32), the valve piston (12) has a further reduction in diameter (62) with an axial length such that the supply port (P) is opened and the utility port (A) is blocked by the valve piston (12), wherein, when moving the valve piston (12) under the influence of the actuator device (14) in the direction of the tank port (T), the fluid-carrying connection between the supply port (P) and utility port (A) is increasingly established.

10. An application of a valve according to an embodiment according to claim 1 in a clutch, comprising at least two clutch discs which, in the coupled state, establish a frictional connection with each other against the action of a clutch energy accumulator under the actuating pressure at the utility port (A) of the actuated valve and, in the uncoupled state, under the influence of the clutch energy accumulator, pushes operating fluid from the utility port (A) to the tank port (T) with the valve not being actuated, having a first opening cross-section until reaching the stop position (32) and having a comparatively larger opening cross-section with further movement of the valve piston (12) away from the stop position (32) in the direction of the armature (16) of the actuator device (14).

11. The application according to claim 10, characterized in that, after complete decoupling, the valve piston (12) is in an indifferent state so that, when actuating the clutch by switching on the actuator device (14) again, a minimum magnetic force is sufficient to move the valve piston (12) into its stop position to make contact with the stop element (14, 40).