Proportional pressure control valve

A proportional pressure control valve includes a valve box (10) having a pump (P), user (A) and reservoir (T) connections. Control piston (18) is guided in a longitudinally displaceably inside the valve box (10) for optionally connecting the pump connection (P) to the user connection (A) and the user connection (A) to the reservoir connection (T). A fluid-carrying connection is established between the pump connection (P) and a pilot chamber (20) of a pilot valve (22). The pilot valve (22) is controlled by a magnet system, especially a proportional magnet system (28). The proportional pressure control valve, for the fluid-carrying connection to the pilot chamber (20), has a bore (27) extending axially inside the wall of the valve box (10) and from a radial bore (9) of the housing (10) forming the pump connection (P).

FIELD OF THE INVENTION

The invention relates to a proportional pressure control valve comprising a valve housing having at least three fluid-conducting connections, particularly in the form of a pump connection, a user connection, and a tank connection. A control piston is guided to be able to move lengthwise within the valve housing for selective connection of the pump connection to the user connection and of the user connection to the tank connection. A fluid-conducting connection is provided between the pump connection and a pilot chamber of a pilot valve. The pilot valve is controllable by a magnet system, in particular a proportional magnet system.

BACKGROUND OF THE INVENTION

For applications in which large volumetric flows are controlled, pilot-controlled pressure control valves are preferably used instead of directly controlled valves. A high volumetric flow means both large opening cross sections of the valves for large strokes and large flow forces which counteract the magnetic force of the magnet system to be actuated as a disturbance variable. To resolve these problems, the magnet system would have to be dimensioned to be correspondingly large for directly controlled valves.

For applications of this type, valves are known in the prior art which have hydraulic piloting, see DE 103 25 178 A1. This known solution is characterized, compared to other proposed solutions which are prior art and which are disclosed by U.S. Pat. No. 6,286,535 B1, in that the valve is able to set a pressure value of 0 bar on the user connection when the magnet system is not actuated. For the valves disclosed in that U.S. patent, this ability is not possible because, according to its construction, the control piston is returned to its end position by a clamped compression spring when the magnet system has not been actuated. Due to this mechanical configuration, these valves still have a pressure level which corresponds to the force of the clamped spring when there is no electrical control signal of the magnet system present.

SUMMARY OF THE INVENTION

An object of the invention is to provide an improved proportional pressure control valve which can be set, according to DE 103 25 178 A1, with the user connection at a residual pressure of 0 bar having a simpler and more compact construction.

According to the invention, this object is basically achieved by a proportional pressure control valve having the fluid-conducting connection to the pilot chamber integrated essentially completely into the valve housing by a bore. The bore extends in the axial direction, is formed in a housing wall and emerges from a radial bore of the valve housing forming the pump connection. In the latter known solution, to form the fluid-conducting connection, the control piston is provided with an inner connecting channel which, before discharging into the pilot chamber, has an orifice to which a flow diffusor is connected downstream and a protective screen is connected upstream. For the control piston this yields not only a comparatively complex construction, but also a considerable installation length, as a result of which in turn a corresponding installation length of the valve housing is dictated. The valve according to the invention is, in contrast, characterized by the desired compact and simplified construction.

In another advantageous configuration, according to the invention the user connection can be formed by the coaxial, end-side opening of the valve housing. This configuration yields the especially advantageous possibility of further reducing the installation length, because, offset in the longitudinal direction of the valve housing, on the valve housing only two connections through which flow takes place radially need be formed by radial bores, specifically the pump connection and the tank connection. The control piston need then has a correspondingly smaller number of peripheral control edges, allowing simplification and a reduction in the required installation length.

Advantageously, the control piston can have, as a movable boundary of the pilot chamber, a closed, planar piston surface which lies in one radial plane.

Advantageously, a valve body of the pilot valve, which body is located stationary in the valve housing, forms a further, stationary boundary of the pilot chamber and the end section of the fluid-conducting connection to the pilot chamber, which section is remote from the pump connection.

In these exemplary embodiments, the end section of the fluid-conducting connection contains a radial channel which extends between an inner coaxial bore of the valve body and an annular gap. Between the peripheral surface of the valve body and the valve housing, the annular gap forms a filtration gap into which the end of the radial bore of the valve housing discharges. This design likewise contributes to a compact structure because the installation of the protective filter for the pilot fluid does not necessitate any additional axial installation length.

Since, as mentioned, a valve system is devised in which it can be ensured that on the user connection a pressure value of 0 bar is set without the magnet system actuated, the invention is especially well suited for use in hydraulically actuated clutches, for whose operational reliability it is essential that when the clutch is released. The clutch packs or disk packs which are engaged are reliably separated from one another. The subject matter of the invention is therefore also the use of the valve according to the invention for hydraulically actuatable clutches.

Other objects, advantages and salient features of the present invention will become apparent from the following detailed description, which, taken in conjunction with the annexed drawings, discloses preferred embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1shows a proportional pressure control valve of the prior art according to DE 103 25 178 A1. The valve, designed as a screw-in cartridge, has a valve housing10which can be screwed into a machine part (not detailed), for example, in the form of a valve block3, via a screw-in section12. For the sealed connection to the valve block3, the valve housing10has gaskets14on the outer peripheral side seated in the corresponding receivers. The valve housing10, viewed in the direction ofFIG. 1, from top to bottom has radial bores5for a tank connection T, radial bores7for a user connection A, and radial bores9for a pump connection P for a hydraulic pump16(cf.FIG. 7). Within the valve housing10, a control piston18is movably guided lengthwise for selective connection of the pump connection P to the user connection A and of the user connection A to the tank connection T.

To establish a fluid-conducting connection between the pump connection P and a pilot chamber20of a pilot valve22, the control piston18is provided with a connecting channel24which is coaxial to the longitudinal axis26. Connecting channel24is offset in its end section at the bottom inFIG. 1leading to a radial bore9of the pump connection P and is connected in its upper end section to the pilot chamber20via an outlet system15. The outlet system15contains an orifice to which, in the fluid flow direction, a protective screen is connected upstream and a diffusor is connected downstream. The diffuser is used preferentially to deflect the directed oil jet flowing out of the orifice so that it does not directly strike the movable closing part40of the pilot valve22.

The pilot valve22has a stationary valve body42in which an inner, coaxial bore11is open, on the one hand, toward the pilot chamber20and, on the other hand, on the opening edge it has a seat13for the movable closing part40of the pilot valve22. Valve22can be actuated via a magnet system28, in particular in the form of a proportional magnet system. If this magnet system is energized, its actuating plunger32is moved downward inFIG. 1, as a result of which the closing part40is pressed against the valve seat13via a spring arrangement17with a closing force dependent on the intensity with which the magnet system28is energized to close the pilot valve22.

If the proportional magnet system28remains deenergized, hydraulic medium (oil) can flow from the user connection A to the tank connection T. In this valve state, the pilot valve22is open, and the control piston18is moved onto its upper stroke stop against the lower side of the valve body42. In this operating position, the oil flows from the pump connection P through the control piston18to the pilot chamber20and from there via the opened pilot valve22to a distributor chamber19from which it drains via channels58to the tank connection T. This volumetric flow can be defined as a pilot oil flow or leakage.

When current is supplied to the magnet system28, the closing part40presses on the valve seat13and, in so doing, interrupts the volumetric flow. The pilot chamber20is thus filled with the hydraulic medium, as a result of which the pressure in this chamber rises. This rising pressure acts on the upper face side of the control piston18and moves it in the direction of the lower stroke stop70against the compressing compression spring64. The pressure in the pilot chamber20then corresponds to the adjusted pressure.

When the closing pressure of the closing part40on the seat13of the valve body42closes the pilot valve22by energizing the magnet system28, the pressure in the pilot chamber22rises to a pressure value at which the control piston18is moved downward in the figure against the main piston spring64until a position is reached in which the user connection A is connected to the pump connection P. When the controlled pressure is reached, the control piston18is moved such that the connection between the pump connection P and the user connection A is throttled. The control piston18is moved into a position in which the two force levels are in equilibrium with one another, and in this way it defines an opening window between the pump connection P and the user connection A. Therefore, a pressure is established on the user connection A, which is in a direct relationship to the electrical control signal of the magnet system28.

FIGS. 2 to 4illustrate a first exemplary embodiment of the proportional pressure control valve according to the invention. Parts which correspond to those of the valve ofFIG. 1are marked with the same reference numbers as inFIG. 1. The plunger of the magnet system28, which plunger is not shown, acts via a pilot spring21on the closing part40of the pilot valve22, which part is formed by a ball. As in the known solution according toFIG. 1, the closing part40interacts with a valve seat13located on the opening edge of an inner coaxial bore11of a stationary valve body42. The bottom of the valve body42which faces away from the valve seat13forms the stationary boundary of the pilot chamber20and the upper stroke stop of the control piston18, whose upper planar piston surface forms the movable boundary of the pilot chamber20. The interior of the coaxial inner bore11of the valve body42is fluid-connected via a damping orifice23to the pilot chamber20. This orifice23forms the end part of the fluid-conducting connection between the pump connection P and pilot chamber20. The main part of the fluid-conducting connection is formed by an axial bore27in the wall of the valve housing10and having its origin on a radial bore9of the pump connection P. From here the axial bore27leads to the outer periphery of the stationary valve body42where the axial bore27undergoes transition into an annular gap29. The gap29forms a filtration gap between the end of the axial bore27and a radial channel31which leads in the valve body42via a control oil orifice33to the inner coaxial bore11, whence the fluid connection via the damping orifice23to the pilot chamber20is completed.

FIG. 2shows an operating state in which the magnet system28is not energized, the pilot valve22conversely is not closed, and thus a fluid pressure does not build up in the pilot chamber20because the fluid which has been supplied via fluid-conducting connection27,29,31,33can drain via the distributor chamber19to the tank side. Accordingly, the control piston18is under the influence of the spring64in the upper end position where it adjoins the stroke stop, i.e., the bottom of the valve body42. Since in the valve according to the invention only the tank connection T and the pump connection P are formed by radial bores5and9respectively, while the user connection A is formed by the coaxial, end-side opening35of the housing10, in the operating position fromFIG. 2the user connection A and the tank connection T are connected to one another. Specifically, the control piston18then has an interior open to the opening35of the valve housing10. Fluid in the interior of control piston18can emerge via passages37in the wall of the piston18to the tank connection T.

FIGS. 3 and 4show operating states depending on the energizing of the magnet system28.FIG. 3shows the operating state in which the closing part40is pressed onto the valve seat13by energizing the magnet system28via the spring21so that in the pilot chamber20a pressure is built up which has moved the control piston18onto its lower stroke stop70. As is apparent, in this piston position the pump connection P and the user connection A are connected to one another. Also apparent fromFIG. 3, is that large opening cross sections between the interior of the control piston18and the radial bores9are formed so that in an application to actuate a clutch cylinder, filling is prompt.

When a fill pressure of the consumer is reached, on the user connection A, for example, of the clutch cylinder, and when there is a force which acts in this way on the piston18, the piston is pushed upwardFIG. 4, until the connection from the pump connection P to the user connection A is throttled or completely blocked. As likewise shown inFIG. 4, the user connection A and the tank connection T can be connected to one another, with a piston position being established in which the piston is in force equilibrium. The illustrated valve construction is characterized by high dynamics and low pressure loss, as a result of which, when used for clutch actuation, rapid filling with oil and rapid evacuation of the clutch are ensured. The invention is therefore also especially well suited for these applications because in the deenergized state of the magnet system28the user connection A is completely relieved.

A second, modified exemplary embodiment of the valve according to the invention is shown inFIGS. 5 and 6. In the example ofFIGS. 2 to 4, the valve is subject to a certain leakage because in almost any operating state a control oil flow drains permanently to the tank. While the control oil orifice33keeps this leakage to a low value, it is still useful to reduce leakage losses. In the exemplary embodiment fromFIGS. 5 and 6, for this purpose the piloting is configured such that, instead of a seat valve with spring-loaded closing part, a directly controlled pressure regulator is integrated into the piloting. The fluid-conducting connection, as in the above described exemplary embodiment, in the starting part is made by the axial bore27extending in the wall of the valve housing10and leading to the inner coaxial bore11in the valve body42via the peripheral annular gap29of the stationary valve body42and via a radial channel31located in it. A valve piston38is guided in inner bore11to be able to move lengthwise and is held nonpositively on the plunger32of the magnet system28via a reset spring39, and, when the magnet system28is energized, can be moved downward inFIGS. 5-6. The valve piston38has a bore41which is open to the pilot chamber20and peripheral control edges43,44which are connected to that bore41so that, depending on the axial position of the valve piston38, the radial channel31and thus the fluid-conducting connection to the pump connection P are connected to the pilot chamber20or are blocked. In the position in which the radial channel31is blocked, the pilot chamber20is opened to the distributor chamber19and thus to the tank via the axial piston bore41and the control edge44. There is no direct connection from the pump connection P to the tank connection T in any operating state. The valve then works without additional losses due to the draining pilot oil. The leakage is therefore reduced to the valve spool leakage, which occurs on the annular gaps of the peripheral surfaces of the two pistons.

The proportional pressure control valve according to the invention is one which is advantageous especially for clutch applications. In these applications, the main demands are for high dynamics and low pressure losses in order to be able to ensure a rapid process of filling with oil and a rapid evacuation of the clutch. These demands are easily accomplished with this valve configuration. Moreover, the valve according to the invention can be completely relieved; i.e., when the electrical control signal on the magnet system28is taken away, the controlled pressure on the user connection A is brought to the pressure value of 0 bar. In conventionally pilot-operated pressure valves, this main stage (control piston) is returned with a clamped compression spring to its end position so that, when there is no electrical control signal on the magnet system, the known valves always have a pressure level that corresponds to the force of the clamped spring, then leading to problems in the decoupling of hydraulically operating clutches.

To illustrate this, the use of the proportional pressure control valve according to the invention is detailed with reference toFIGS. 7 and 8for a hydraulically operating clutch. According to the representation inFIG. 7the proportional pressure control valve is connected between the clutch parts72,74,76and the hydraulic pump16.

Clutches are used, among other things, to connect two shafts, for example the shafts of heavy machinery to transmission shafts. In this hydraulic clutch, a cylinder chamber72is connected to the pressure line or the pressure connection P of the hydraulic pump16by actuating the proportional pressure control valve according to the invention. In so doing, the spring-loaded piston74compresses a clutch disk pack which is not detailed. By switching over the proportional pressure control valve, the cylinder chamber72is then evacuated, and the compression spring arrangement76according toFIG. 7pushes the piston74back into its initial position. In so doing, the remaining hydraulic medium is pushed out in the direction toward the tank T via the user connection A.

FIG. 8shows the progression of a clutch play. First, the clutch must be quickly filled with oil (hydraulic medium). This filling takes place in the time interval t1to t2, with the piston74beginning to compress the clutch disk pack. This process is accompanied by a brief, very high volumetric flow. Afterwards, this state is maintained in the time interval from t2to t3and is slowly “ramped up” in the interval t3to t4by the pressure being slowly raised linearly by the proportional pressure control valve according to the invention. The force from the heavy machinery is then uniformly transmitted to the transmission line. At time t5, by returning the electrical control signal on the magnet system28, the pressure in the clutch is removed so that the compressed disk pack, under additional action of the compression spring arrangement76, can push the piston74back into its original position again. This operation to remove pressure is easily possible since as already shown the pressure value on the connection A has the value 0 in this operating position.