VALVE

Abstract

The invention relates to a valve, in particular a proportional pressure regulating valve, comprising a valve piston (12) which is longitudinally movable in a valve housing (10) for alternately releasing and connecting a user connection (A) to a pressure supply port (P) or a tank connection (T), which can be actuated by means of an actuating magnet (14) and which produces a dither signal during operation, characterized in that the valve piston (12) reaches a floating position within the valve housing (10) by means of a hydraulic lift limitation for the receipt of the dither signal.

Description

The invention relates to a valve, in particular a proportional pressure control valve, comprising a valve piston which is longitudinally displaceable in a valve housing for alternately releasing and connecting a utility connection or consumer connection A to a pressure supply connection P or a tank connection T, with the valve piston being able to be actuated by means of an actuating magnet, which produces a dither signal during operation.

Valves, such as proportional pressure control valves, are very commonly used in mobile work machines for electrohydraulic pilot control of directional valves. One example of such a valve is disclosed in WO 2010/085991 A2 for example.

For “smaller devices”, directly controlled proportional pressure control valves are usually sufficient. However, in the case of large construction machines, for example earth-moving machines such as diggers, the directional valves of the working hydraulics reach piston diameters at which pilot control with directly controlled proportional pressure control valves is no longer practical. The large slide valves produce during rapid switching a flow of pilot oil which can no longer be tolerated by the small pilot valves.

For such applications, proportional pressure control valves with corresponding surface ratios are therefore used. These valves have a pressure-effective surface which is smaller than the piston diameter. The force produced by the control pressure, which acts against the magnetic system usually in the form of an actuating magnet, is thus significantly reduced. The large piston can however allow the passage of a significantly larger volume flow compared with the directly controlled valve and thus drastically reduce, in a desirable manner, the switching times of the large slide valves.

This principle of surface ratios has the significant advantage over a conventional pilot-controlled proportional pressure control valve that a continuous pilot oil flow is not necessary. The leakage of these valves is extremely low in particular in the flow-free state. This has significant advantages in the case of emergency supply of the proportional valves with a pressure accumulator. However, there is then a fundamental problem when “filling” the directional valve piston to be actuated. In order to be able to achieve the coverage of the directional valve piston as quickly as possible specifically when the function is started, the proportional valve is briefly flowed through with a relatively large volume flow. The proportional valve may be switched up to the stroke stop. If the desired slide position is then achieved, the directional piston must however also be held in the achieved position; and the pilot oil flow must consequently abruptly drop to zero. The proportional valve must therefore then move out of its end position back into a central position, whereby the control edge between the pressure supply connection P or pump connection and the utility connection or working connection A is thus shut.

Irregularities can arise with the solutions of the prior art. In the stroke end position, the valve piston of the valve is at its mechanical stroke stop. Once this stroke stop has been reached, the dither flow which is standard in proportional technology then no longer has the opportunity to transfer the microvibrations of the pilot piston of the actuating magnet, which are standard in other operation, to the valve piston and thus to minimize its friction. The so-called dither voltage or the dither flow is, as a dither signal, superimposed on the analogue actuating signal of the actuating magnet for the actuation of the valve piston of the valve. This signal then causes the valve or its piston to always vibrate slightly, so that no so-called stick-slip effect occurs. As a general rule, it should be possible to set the dither frequency as the frequency of the dither voltage just like the amplitude of the dither voltage or of the dither flow. Incorrectly set dither signal values lead to rapid wear of said valves. If the valve piston is kept at least briefly in its position inside the valve housing due to increased friction caused by the corresponding absence of the required dither signal from the actuating magnet as a result of increased friction, functional impairments are encountered, in particular in the form of jerky movements of the work machine, which represents a safety hazard.

On the basis of this prior art, the problem addressed by the invention is to further improve the known valve solutions while retaining their advantages described above in such a way that no functional impairments of the sort described above can be encountered. This problem is solved by a valve having the features of claim 1 in its entirety.

Because, in accordance with the characterizing portion of claim 1, the valve piston arrives at a floating position inside the valve housing by means of a hydraulic stroke limit for maintenance of the dither signal, the valve piston is thereby prevented from striking the additionally provided mechanical stroke limit, as has been described in the prior art, with the described negative consequences for the dither signal effect. Because the valve according to the invention now has a so-called hydraulic stroke limit, from a hydraulic perspective an additional control edge has been created, which permits a fluidic force build-up on the valve piston, which is greater than the effective magnetic force of the actuating magnet acting upon the valve piston, so that the valve piston can be stopped shortly before it reaches the mechanical stroke limit. In this respect the valve piston then remains floating or in a kind of floating state and the dither signal effect procured via the actuating magnet is fully maintained, so that said friction is still minimized, and functional impairments are ruled out in this regard.

In the shut state of the valve and in normal operation with a balanced directional valve piston of the work machine, the additional new control edge of the proportional valve in the form of the hydraulic stroke limit remains fully shut, so that in this respect no increased leakage occurs there either. The advantages of the above described valve principle of the prior art are thus retained in full in the new valve solution. Overall, the valve according to the invention presents a significantly improved actuation behavior of the directional valve piston and thus also of the corresponding work machine.

The solution according to the invention thus makes it possible to significantly improve the sensitive and at the same time dynamic actuation behavior of hydraulically pilot-controlled directional valve pistons in proportional pressure control valves, which in particular also applies to cold and thus highly viscous hydraulic oil. The system-related advantage of the low leakage volumes in the shut state and with a balanced directional valve piston is likewise retained. There is no equivalent of this solution in the prior art.

Advantageous embodiments of the valve construction according to the invention are the subject of the dependent claims.

The valve solution according to the invention is explained in detail below with reference to an exemplary embodiment according to the drawings in which, in schematic and not to scale depictions,

FIG. 1 shows a known valve solution according to the prior art in a longitudinal section form and

FIGS. 2 and 3 show, in a comparable depiction and in different functional positions, the hydraulic stroke limit according to the invention in a valve according to FIG. 1.

FIG. 1 shows a longitudinal section depiction of a valve in the form of a proportional pressure control valve known from the prior art. The valve has a valve housing 10 with a valve piston 12 which is guided in a longitudinally displaceable manner in the housing 10. This valve piston 12 serves for alternately releasing and connecting a utility connection A to a pressure supply connection P or a tank connection T. The utility connection A is also referred to as a working connection in technical parlance, and for the pressure supply connection P, the term pump connection has also become generally accepted. The tank connection T must not necessarily lead to a supply tank; instead, this description is only intended to indicate that a relatively low pressure is applied at the connection T, for example a tank and/or ambient pressure. The utility connection or working connection A is mounted on the front face of the valve housing 10 and both the pressure supply connection or pump connection P and the tank connection T consist of individual radial bores introduced into the valve housing 10, which are kept at a predeterminable axial spacing from one another. This construction is standard, and it will therefore not be addressed in further detail here.

An actuating magnet which is identified as a whole with the reference numeral 14 serves to actuate the valve piston 12. The actuating magnet 14 has a magnet housing 16, 18 formed in two parts, in which a so-called keeper 20 is guided in a longitudinally displaceable manner inside a pressure sleeve 21. A coil winding 22, which is only schematically depicted, serves to actuate the keeper 20, which coil winding is housed in the magnet housing part 16 and which can be energized from the outside via a connector part 24, wherein the connector part 24 forms, viewed in the viewing direction of FIG. 1, the right final end of the magnet housing part 16. The two magnet housing parts 16, 18 are held together via a cap-like end housing 26 and, in the central region of the magnet housing part 18, a flange plate 28 is placed, which makes it possible to fix the entire valve to a third component which is not depicted in detail, for which purpose the valve housing 10 engages in the manner of a cartridge in a corresponding recess of the third component, and wherein the third component naturally has to have corresponding fluid lines for the purpose of connection to the connections A, P, T in the valve housing 10. For the end-side fixing of the valve housing 10 to the magnet housing part 18, the latter has a projecting sleeve 30, in which a right end region of the valve housing 10 engages and which, correspondingly flanged at its free front-face end, permits the fixing of the valve housing 10 in the magnet housing part 18. In addition, the two magnet housing parts 16, 18 together form a magnetic separation 32 in the form of an air gap in order to obtain a targeted magnetic line conduction into the keeper 20, provided that the coil winding 22 is correspondingly energized during operation of the device or of the valve.

Introduced into the magnet housing part 18 is a longitudinal bore with a guide part 34 arranged in a stationary manner in the magnet housing part 18, which is penetrated along its longitudinal bore by a control piston 36. The one free end of the control piston 36 abuts the rear side 38 of the valve piston 12, and with its other free end it abuts the adjacent opposite front side 40 of the keeper 20. A movement of the keeper 20 can thus be transferred to the valve piston 12; and conversely the valve piston 12 can transfer, in the case of a not energized coil winding 22, its movement direction via the control piston 36 to the keeper 20 for the shifting movement thereof. The keeper 20 is additionally provided with a longitudinal bore 42 in order to allow a pressure compensation in the spaces inside the magnet housing parts 16, 18, which the keeper 20 abuts at the front side, in order to thus prevent obstacles during the travelling operation of the keeper 20.

Said guide part 34 broadens towards its one free end and to this extent forms a contact surface and connection surface with the front face of the valve housing 10 which is on the right side when viewed in the viewing direction of FIG. 1. In addition, the control piston 36 which is guided in the guide part 34 is formed with a reduced diameter in the direction of the rear side 38 of the valve piston 12 compared with the other piston parts of the control piston 36, which are guided in the guide part 34 in the direction of the keeper 20.

As is additionally shown in FIG. 1, the valve piston 12 is drilled hollow and thus permits via its inner side 44 a permanent fluid-conducting connection between the utility connection A and an aperture 46, which radially penetrates the wall of the valve piston 12. Said aperture 46 thus opens with its one free end into the inner side 44 of the valve piston 12 and with its other end it opens into a control space 48. This control space 48 with a variable volume is delimited by the wall parts of the valve housing 10 and of the valve piston 12. In addition, the valve solution has a mechanical stroke limit 50, which consists of a stop 52 between the valve piston 12 and the valve housing 10. In the position of the valve piston 12 depicted in FIG. 1, the mechanical stroke limit 50 is “active”, i.e., the valve piston 12 strikes the valve housing 10 from right to left. In order to form this stop 52, the valve piston 12 is formed correspondingly broadened in a stepped manner at its free, right front side end and the valve housing 10 itself is provided with a stepped taper 54 in this region.

In addition, the flange-like broadening of the valve piston 12 has at least one through hole 56 extending in the axial direction, which establishes a fluid- or media-conducting connection between the first control space 48 and an additional control space 58, which is also referred to hereafter as a so-called third control space. This additional, third control space 58 with variable volume is on the one hand penetrated by the control piston 36 and it is also delimited at the front side by the rear side 38 of the valve piston 12 and by the front face side of the broadened part of the guide 34. In the radial direction, the control space 58 is surrounded by inner wall parts of the valve housing 10 in this region. If, as depicted in FIG. 1, the valve piston 12 assumes its position contacting against the valve housing 10 by means of the mechanical stroke limit 50, a fluid-conducting connection exists between the utility connection A and the pressure supply connection P, wherein the connection to the tank connection T is prevented.

The valve piston 12 also has a transverse channel 60, which can consist of a plurality of radial bores. By means of this transverse channel 60, the inner side 44 of the valve piston 12 is connected in a permanent fluid-conducting manner to an additional second control space 62 between the valve housing 10 and the valve piston 12. This control space 62 is of course guided in a longitudinally displaceable manner in the valve housing 10 together with the valve piston 12 and permits the respective fluid-conducting connection between the individual connections A, P, T or their separation from one another. The axial extension of the second control space 62 is selected such that in a displacement position of the valve piston 12, as is depicted by way of an example in FIG. 2, the valve piston 12 with its wall parts precisely covers the control edges 64, 66 at the connections P or T, which are formed by means of their wall parts of the valve housing 10. In addition, the valve piston 12 has at its one free end a pressure-effective surface 68, upon which the pressure in the utility connection A acts. As is additionally shown in FIG. 1, all mentioned parts are, if necessary, provided with corresponding sealing systems, which is known from the prior art, and this shall not therefore be addressed in further detail here.

The valve solution according to the invention shall now be explained in greater detail below with reference to FIGS. 2 and 3, to the extent that it differs from the known solution according to FIG. 1. The reference numerals introduced up to this point will also be used for the thus changed inventive solution and the differences will be explained only to the extent that they differ significantly from the above described prior art.

In addition to the already presented mechanical stroke limit 50, the solution according to the invention also has a hydraulic stroke limit 70 for the valve piston 12. For this purpose, a groove-like depression 72 is provided on the outer circumference of the valve piston 12, the width of which is selected such that, in the case of a so-called floating state of the valve piston, a fluid-conducting connection is at least temporarily established between the first control space 48 and the tank connection T (cf. FIG. 3), wherein said fluid-conducting connection is delimited by an additional third control edge 74 of the valve housing 10 as part of the hydraulic stroke stop 70, which can be traveled over by the valve piston 12 or its groove-like depression 72. This third control edge 74 is in turn formed by the wall of the respective radial bore for the tank connection T which, lying opposite the second control edge 66, is in turn delimited by its bore wall to the extent that it faces in the direction of the actuating magnet 14.

As is shown in particular in FIG. 2, and as explained above, in a central control position of the valve piston 12 and without an uptake volume in the direction of the utility connection A, the valve piston 12 just closes the pressure supply connection P and the tank connection T with their respective control edges 64 or 66. If, however, the valve is “operating” in the hydraulically controlled stroke limit, the groove-like depression 72 overlaps the valve housing projection 76 in an approximately central manner in this region and in this way then establishes the fluid-conducting connection between the tank connection T and the first control space 48. To support the functioning and operation of the valve piston 12 with its two stroke limits 50, 70, an energy store in the form of a compression spring 78 is arranged in the first control space 48, which compression spring is supported with its one free end on the front side end of the valve housing projection 76 and with its other end on the flange-like broadening of the valve piston 12 in the direction of its rear side 38.

For the sake of improved depiction and the comprehension of the interaction of the two stoke limits 50, 70, a functional process using the valve according to the invention is disclosed below. As already explained, on starting the function, the coverage of the directional valve piston 12 should be achieved as quickly as possible, with the proportional valve then being briefly flowed through with a relatively large volume flow. At the time of this volume flow peak, the proportional valve piston 12 then controls as far as possible to the left side when viewed in the direction of viewing of the figures, with the entire supply at the utility connection A being ensured by means of the pressure supply connection P. In the possible left-hand end control position, the valve piston 12 then strikes, in accordance with the prior art, the mechanical stroke limit 50 in the form of the stop 52, resulting in the described negative consequences for the dither effect in the form of the respective dither signal.

As already disclosed, the valve according to the invention now has an additional control edge 74 however, which forms with the already mentioned additional components such as the aperture 46 and the groove-like depression 72 in the valve piston 12 the so-called hydraulic stroke limit 70. The arrangement in the valve piston 12 is thus selected such that, in any case shortly before the mechanical stroke limit 50 is reached a fluid-conducting connection from the right-hand piston back space to the tank connection T of the valve is established by means of the groove-like depression 72, i.e., the first control space 48 is in a fluid-conducting connection with the tank connection T, with the control occurring by means of the third control edge 74 at the tank connection T. This fluid flow or oil flow between the first control space 48 and the tank connection T builds up a pressure difference at the aperture 46 and, during normal operation, the pressure on both piston front sides 68 and 38 of the valve piston 12 is equal, so that the aperture 46 then acts as damping for the movement of the valve piston 12. Shortly before the mechanical stroke limit 50 is reached, this balance is disturbed however because the left piston side 68 is then subjected to a greater force than the right piston side 38 due to the aperture pressure drop. Because this force is greater than the magnetic force of the actuating magnet 14 in its actuating position, the valve piston 12 halts shortly before the mechanical stroke limit 50 is reached so that it assumes a kind of floating position which results in all of the dither effect of the actuating magnet 14 being maintained.

In the shut state and during normal operation with a balanced directional valve piston 12 of the work machine, the third control edge 74 of the hydraulic stroke limit 70 remains fully shut by means of the valve piston 12 (cf. FIG. 2), so that no leakage can occur in this region either.

The valve solution according to the invention thus makes it possible to significantly improve the sensitive and at the same time dynamic actuation behavior of hydraulically pilot-controlled directional valve pistons 12 by means of the use of the hydraulic stroke limit 70, which is in particular also the case with cold and thus highly viscous oil. The system-related advantage of little leakage in the shut state and with a balanced directional valve piston in its floating state is retained. There is no equivalent of this solution in the prior art.

Claims

1. A valve, in particular a proportional pressure control valve, comprising a valve piston (12) which is longitudinally displaceable in a valve housing (10) for alternately releasing and connecting a utility connection (A) to a pressure supply connection (P) or a tank connection (T), which can be actuated by means of an actuating magnet (14), which produces a dither signal during operation, characterized in that the valve piston (12) arrives at a floating position inside the valve housing (10) by means of a hydraulic stroke limit (70) for maintenance of the dither signal.

2. The valve according to claim 1, characterized in that the hydraulic stroke limit (70) has an aperture (46) in the valve piston (12), which is permanently connected via the inner side (44) of the valve piston (12) to the utility connection (A) and which opens into a control space (48) between the valve piston (12) and the valve housing (10), which is connected in a fluid-conducting manner to the tank connection (T) depending on the displacement position of the valve piston (12), in particular in the floating state thereof

3. The valve according to claim 1, characterized in that an energy store, in particular in the form of a compression spring (78), is housed in the control space (48), which compression spring is supported with its one end on the valve housing (10) and with its other end on the valve piston (12).

4. The valve according to claim 1, characterized in that a groove-like depression (72) is provided on the outer circumference of the valve piston (12), the width of which is selected such that, in the floating state of the valve piston (12), a fluid-conducting connection is at least temporarily established between the control space (48) and the tank connection (T) and in that the fluid-conducting connection is delimited by a control edge (74) of the valve housing (10) as part of the hydraulic stroke stop (70), which can be traveled over by the valve piston (12) or its groove-like depression (72).

5. The valve according to claim 1, characterized in that, in addition to the hydraulic stroke limit (70), an additional mechanical stroke limit (50) is provided, which consists of a stop (52) between the valve piston (12) and the valve housing (10), the reaching of which prevents the fluid-conducting connection between the utility connection (A) and the tank connection (T) and at least partially establishes the fluid-conducting connection to the pressure supply connection (P).

6. The valve according to claim 1, characterized in that, in a central control position of the valve piston (12) and without an uptake volume in the direction of the utility connection (A), the valve piston (12) just closes the pressure supply connection (P) and the tank connection (T) with their respective control edges (64, 66).

7. The valve according to claim 1, characterized in that the valve piston (12) has a transverse channel (60), which permanently connects in a fluid-conducting manner the inner side (44) of the valve piston (12) to an additional, second control space (62) between the valve housing (10) and the valve piston (12) which, guided in a longitudinally displaceable manner in the valve housing (10) together with the valve piston (12), establishes or terminates again the respective fluid-conducting connection between the individual connections (A, P, T).

8. The valve according to claim 1, characterized in that, at the rear side (38) of the valve piston (12) the actuating magnet (14) acts upon a control piston (36), the effective actuating surface of which corresponds to the effective piston surface of the valve piston (12) and in that the rear side (38) of the valve piston (12) is guided in an additional, third control space (58), which is connected in a fluid-conducting manner to the first control space (48), once the valve piston (12) leaves the mechanical stroke limit (50) or the stop (52).

9. The valve according to claim 1, characterized in that the valve piston (12), at its free, front side lying opposite its rear side (38), is exposed by means of a control surface (68) to the pressure at the utility connection (A) and, otherwise interrupted only by the second control space (62), is guided with an essentially constant external diameter in the valve housing (10) until a broadening of the valve piston as part of the stop (52) of the mechanical stroke limit (50) is reached.

10. The valve according to claim 1, characterized in that the valve housing (10) with its connections (A, P, T) is designed as a mounting cartridge for a third component.