WO2000047900A1

WO2000047900A1 - Pilot-operated stop valve

Info

Publication number: WO2000047900A1
Application number: PCT/DE2000/000263
Authority: WO
Inventors: Heinz Schulte
Original assignee: Mannesmann Rexroth Ag
Priority date: 1999-02-11
Filing date: 2000-02-01
Publication date: 2000-08-17
Also published as: DE19905704A1

Abstract

The present invention relates to a pilot-operated stop valve (1). A piston valve (30) is arranged in the main piston (20). A pilot-operated piston (32) is inserted into a pilot opening (22) on the front side of the main piston (20). Said pilot-operated piston (32) defines two valve devices which are connected in parallel. One valve device (61b, 61c) becomes active when a weight is slowly lifted at the relevant connection of the stop valve and the other valve device (61a, 61d) becomes active when said weight is slowly lowered. The controllability of the stop valve can thus be improved. An impact plate (46) is provided at the piston valve in order to reduce the disturbing forces when the weight is lowered.

Description

description

Pilot operated check valve

The present invention relates to a pilot operated check valve according to the preamble of patent claim 1.

The use of hydraulics in moving machines has increased in recent years. This is especially true for earth-moving machines, industrial trucks, agricultural tractors and self-propelled harvesting machines. Since hydrostatic travel drives allow speed regulation without shifting, but are not very efficient, hydraulic drives are not primarily geared towards the forward movement. The main area of application of hydraulic drives can be seen in the operation of work organs.

In the case of agricultural vehicles, the working elements can be provided both on the agricultural tractor, which is used for pushing, carrying and driving agricultural and forestry equipment, and on the agricultural and forestry equipment itself. The use of hydraulically controlled working cylinders in the hoist is particularly important. Here, e.g. in the case of plowing, the lifting mechanism on the tractor and in the case of plowing, a lifting mechanism hydraulically fed by the tractor on the harrow. The cylinder is either extended or retracted depending on the operating mode.

In order to shut off the working circuit under pressure and to avoid creeping movements of the working cylinder, an unlockable shut-off valve is connected between the pump and the working cylinder. This check valve can either be hydraulic or electromagnetic. be lockable. The advantage of electromagnetic unlocking is that the unlocking can be carried out optimally over time and that the energy loss is less with frequently changing operating states.

For safety reasons, a predetermined lifting speed must not be exceeded when operating a hoist on the tractor from the rear. This can be implemented, for example, by modifying a pilot-operated check valve in accordance with the previously published patent application DE 197 55 120.3.

1 shows a sectional partial view of such a modified pilot-operated check valve according to the prior art.

A main piston 120 is biased against a valve seat 162 via a spring 150. A control piston 130, which is movable with respect to the valve seat 162 via a magnet armature, is arranged in the main piston 120. A first cone section 142 from the control piston 130 is adjoined in the axial direction of the control piston 130 by an extension 141 which, in this order, towards the front side of the main piston 130 has a cylinder section 144 with a small diameter, a second cone section 143, a cylinder section 145 with a large diameter and one chamfered portion 146. The outer diameter of the first cone section 142 is designed such that it can close a first nozzle 122 provided in the end face of the main piston. A second nozzle 123 is arranged radially in the main piston 130 and establishes a fluid connection with an annular space 126, which can be connected to a pressure chamber of a working cylinder. A pressure chamber 165 is formed on the front side of the main piston 120 and can optionally be connected to a pump or a tank. When the working cylinder, whose pressure chamber is in fluid communication with the annular chamber 126, is slowly lifted, the cylinder section 144 with a small diameter, the second cone section 143 and the cylinder section 145 with a large diameter are located in succession in the first nozzle device 122, which results in a constant control pressure difference.

The flow force at the control piston 130 is, however, load-dependent during slow lowering, so that it cannot be included as a fixed quantity in a control program. Furthermore, due to the very high flow velocity, frictional forces arise which also impair the response behavior of the check valve according to the prior art.

In a pilot operated check valve, which is disclosed in the previously published patent application DE 19 843 911.3, the structure is similar to that of the pilot operated check valve described above, except for the design of the nozzle device. The lowering behavior is improved in the pilot operated check valve from the subsequently published patent application DE 19 843 911.3 in that an axial pilot control opening on the front side of the main piston can be reduced by a closing element in response to the actuation of the control piston and the pressure conditions at the two connections of the check valve. This axial pilot opening is connected in series with the nozzle device, the opening cross-section of which depends on the position of the control piston.

In the case of the two pilot-controlled control valves mentioned above, when the slow lifting begins, the control piston and is controlled exactly at the same time a pump at the first connection. More precisely, a rapid lowering is initiated when a load is present if the pump pressure is too low when the pilot opening is open. If the pilot control opening is opened too late, rapid lifting takes place. Furthermore, controllability is impaired in the lowering mode by interference forces on the first nozzle device.

The object of the present invention is to eliminate the disadvantages of the prior art and to provide a pilot-operated shut-off valve which has improved controllability in the lifting and lowering modes and increased effectiveness in the control.

This object is achieved by a pilot operated check valve according to claim 1.

According to the invention, a pilot operated check valve according to the prior art is developed in such a way that two nozzle devices connected in parallel are arranged in the pilot opening which can be opened by the control piston, the opening cross sections of which are determined by the pressure difference between the rear control chamber and the first connection and the position of the Control piston are changeable. Such an arrangement brings about improved controllability, since the specific conditions in different operating modes, e.g. slow lifting and lowering, can be taken into account by an associated opening of the respective nozzle device. Such a simple design of the pilot operated check valve also results in low flow and energy losses.

An advantageous embodiment can be implemented by using a pilot piston in the pilot opening. In this way one of the parallel Teten nozzle devices between the pilot opening and the outer circumference of the pilot piston and the other of the parallel connected nozzle devices between the control piston and a recess in the pilot piston are implemented to save space.

In a further embodiment, a further nozzle, which is delimited by a section in which the outer diameter of the pilot piston changes, is connected in series with the nozzle on the outer circumference of the pilot piston. This further nozzle is particularly advantageous at the beginning of slow lifting, since in this way, after a previous opening with further axial movement of the control piston, the pilot opening can be closed and thus a higher response speed of the check valve can be realized.

The provision of chamfers on the first and second end portions of the pilot opening and on the portion of the pilot piston where the outer diameter changes prevents sudden changes in parameters of the fluid flow and thus facilitates continuous and effective control.

In the lowering mode, it is advantageous if a further nozzle is provided in a row parallel to the nozzle opening which can be controlled by the control piston. In this way, the pressure drop across the pilot opening can be increased and thus an undesired rapid lowering prevented.

A baffle plate on the control piston opposite the nozzle device, which connects the control chamber and the annular chamber, reduces the flow force component of the disturbing force occurring in the sink mode. This interference is due to the Arrangement of the nozzle device at an acute angle to the longitudinal axis of the control piston can be further reduced.

In order to reduce the stress on the mechanical elements in the check valve, the above-mentioned nozzle device is provided at least in the form of two nozzles.

The control piston is preferably biased in a first area against a first spring, while in a second area the main piston can be opened by compressing another spring. With such an arrangement, when lifting slowly, it is not necessary for a magnetic coil to be energized to move the control piston. The circuit complexity, in particular with regard to the synchronization between the control of the pump and the control of the solenoid coil, and the energy consumption in the pilot-operated check valve according to the invention can therefore be reduced.

Further exemplary embodiments are the subject of the dependent claims.

The invention is described below with reference to the accompanying drawings. Show it:

Fig. 1 is a sectional view of a pilot operated check valve according to the prior art and

Fig. 2 is a sectional view of a pilot operated check valve according to the present invention.

The preferred embodiment of the invention is described in detail below. The structure and function of the check valves correspond from patent applications DE 19 755 120.3 and DE 19 843 911.3, with the exception of the construction of the first and second nozzle devices, essentially that of the preferred exemplary embodiment of the present invention.

The check valve according to the invention is designed as a cartridge-type built-in valve and has a cartridge housing 60 and a pole tube for accommodating the electromagnet, which are detachably connected to one another via threaded sections.

A pressure chamber 65, which is connected to a connection A of the shut-off valve, and an annular pressure chamber or annular space 26, which is connected to a connection B of the shut-off valve, are formed axially one behind the other in the cartridge housing 60. The diameter of the pressure space 65 is equal to the inner diameter of the annular space 26, a shoulder being defined between them. A radial bore star (not shown) is located in the cartridge housing 60 near the shoulder.

The radial bore star establishes a fluid connection between the annular space 26 and an annular space which is located radially outside of the radial bore star and is formed around it. This annular space can be connected to a pressure chamber of a working cylinder. The pressure chamber 65 in the cartridge housing can optionally be connected to a pump or a tank in order to be able to control the extension and retraction of the working cylinder via the shut-off valve.

The section of the cartridge housing 60 in which the

Pressure chamber 65 is formed, can be provided on its outer circumference with a thread in order to screw the cartridge housing 60 into a screw-in section in a receiving bore. This location hole can be in a valve block can be provided for a variety of other valves.

Inside the cartridge housing 60 there is an axially displaceable main piston 20 which has an extension 21 with a conical surface 24. In the closed position shown, the conical surface 24 is in contact with a seat edge 62 which is formed on the radially innermost section of the shoulder in the cartridge housing 60. The main piston 20 is biased by a spring 50 via a spring plate 51 with respect to the cartridge housing 60. The pressure in the pressure chamber 65 acts on a surface with the diameter of the seat edge 62 in the opening direction on the main piston 20. The surface is the partial surface 24a of the conical surface 24.

A conical surface 25 of the main piston, which extends radially outward from the extension 21, delimits the annular space 26 formed in the cartridge housing 60. At the annular surface between the seat edge 62 and the outer circumference of the main piston 20, the pressure in port B acts in the opening direction of the main piston 20th

A pilot control opening 22 is formed centrally in the main piston 20, via which a fluid connection between the pressure chamber 65 and a rear control chamber 35 formed in the main piston 20, which is in fluid connection with the rear of the main piston 20 as described further below, can be established. The pressure in the rear control chamber 35 acts on the cross-sectional area delimited by the outer circumference in the closing direction of the main piston 20.

A first and a second chamfer 22a and 22b are provided on the end sections of the pilot opening 22 lying opposite in the axial direction of the main piston 20. hen. The pilot opening 22 merges via a conical inner surface 29 into an inner bore 27 which defines a part of the rear control chamber 35. Between the conical inner surface 29 and the conical surface 25 on the outer circumference of the main piston 20, two nozzles 23a, 23b extend at an acute angle with respect to the axial direction of the main piston 20. However, a larger number of nozzles can also be provided. In order to ensure a uniform load on the control piston 30, a plurality of nozzles should be arranged at the same angular distance from one another. Two nozzles should preferably be arranged diametrically opposite one another. In the following, this nozzle device is referred to as the fifth nozzle.

The inner bore 27 widens in the axial direction of the main piston 20 to an inner bore 28 with an enlarged diameter. The spring plate 51, by means of which the spring 50 can load the main piston 20 in the direction of the closed position, is supported on the step section between the inner bores 27 and 28.

A pilot piston 32 is inserted into the pilot opening 22 and has a hollow cylindrical central section 32a with a preferably square outer shape, the corner sections of the square being rounded in such a way that they can slide in the pilot opening 22.

The pilot opening 22 can be circular, elliptical or in any other fluidically favorable shape. The purpose of the square outer shape in the pilot piston 32 is both to allow the pilot piston 32 to slide with little friction in the pilot opening 22 and also to allow a fluid flow on the outer circumference of the hollow cylindrical element. to allow section 32a of the pilot piston 32. Depending on the pilot opening 22, however, any other design of the pilot piston 32 is also possible if the two aspects mentioned above are taken into account.

The end section of the pilot piston 32 which faces the control chamber 35 has a radial extension 33 which is annular. The outer circumference of the radial extension 33 is designed in such a way that the pilot piston 32 can be brought into a fluid-tight contact position with the first chamfer 22a of the pilot opening 22. A second nozzle 61b is thus defined by the radial extension 33 and the first chamfer 22a.

The end section of the pilot piston 32 lying opposite the radial extension 33 has a piston section 34 with increased external dimensions. This piston section 34 has an outer shape similar to the cross section of the pilot opening 22 and adjoins the hollow cylinder section 31a via a chamfer 34a. The chamfer 34a is provided at such a distance from the radial extension 33 that when the pilot piston 32 is fully inserted into the pilot opening 22, i.e. if the outer circumference of the radial extension 33 is in contact with the first chamfer 22a of the pilot opening 22, the chamfer 34a together with the second chamfer 22b of the pilot opening 22 defines a gap which decreases with increasing distance of the radial extension 33 from the first chamfer 22a. In this way, a third nozzle 61c is defined.

The pilot piston 32 is penetrated by a recess 31. This recess 31 has a non-adjustable fourth nozzle 61d on the piston section 34 with increased external dimensions. Through this fourth nozzle 61d In the case in which fluid flow through the second and third nozzles 61b, 61c is prevented, a pressure difference between the control chamber 35 and the pressure chamber 65 is constantly maintained when the recess 31 is open. In this way, the static and dynamic part of the interference force can be reduced.

The recess 31 in the pilot piston 32 has, opposite to the piston section 34 with increased outer dimensions, a first nozzle 61a which is defined between a chamfer 31a on the inner periphery of the recess 31 and the outer periphery of a cone section 42 of a control piston 30. Thus, the first nozzle 61a has a much smaller seat diameter than the second nozzle 61b. The cone section 42 is located on an insert element 40 which is provided in a second cylinder section 30b of the control piston, which is preferably made of plastic. The insert element 40 can, as shown in the left half of FIG. 2, be screwed into the cylinder section 30b or, as shown in the right half of FIG. 2, be injected into the cylinder section 30b. The second cylinder section 30b is adjoined in the axial direction of the control piston 30 by a first cylinder section 30a, which is biased with respect to the pole tube in such a direction via a spring (not shown) that is referred to below as a small pole tube spring that the cone portion 42 is pressed toward the chamfer 31a of the recess 31 in the pilot piston 32.

The second cylinder section 30b of the control piston 30 is of such a length that in the contact position in which the cone section 42 is in contact with the chamfer 31a of the pilot piston 32 and the radial extension 33 is in contact with the first chamfer 22a of the pilot valve opening 22 located between the surfaces Before the spring plate 51, which is in contact with the stepped section between the inner bores 27 and 28 in the main piston 20, and the opposite end face of the second cylinder section 30b of the control piston 30, a predetermined distance is provided. Thus, the control piston 30 must first overcome the spring force of the small pole tube spring and then the spring force of the spring 50 when moving axially out of the contact position.

Since the inner bores 27, 28 are provided with play relative to one another with respect to the outer diameter of the cylinder sections 30a, 30b of the control piston 30 or the dimensions of the spring plate 51 and the spring 50, there is an open connection between a control chamber 35 in the inner bore 27 and the Rear of the main piston 20. This is thus acted upon by the pressure in the rear control chamber in its closing direction over its entire area determined by the outer diameter of the conical surface 25, wherein all cavities in which the between the first Nozzle 61a and the fifth nozzle 23a, 23b prevailing control pressure.

A compression of the spring 50 by an axial movement of the second cylinder section 30b from the control piston 30 via the spring plate 51 has the result that the contact position between the conical surface 24 of the control piston 20 and the seat edge 62 of the cartridge housing 60 in the lifting mode only from the pressure difference between the pressure chamber 65 and the rear control room 35 is affected. In the lowering mode, the system position is influenced by the pressure difference between the pressure chamber 26 and the rear control chamber 35. A baffle plate 46 is provided between the section of the insert element 40, which is located in the second cylinder section 30b of the control piston 30, and the cone section 42. A baffle surface 46a of the baffle plate 46 is arranged so that it is opposite the fifth nozzle 23a, 23b, that is to say that the fifth nozzle 23a, 23b radiates onto the baffle plate 46. This baffle surface 46a is preferably elliptical in radial section of the baffle plate 46. The purpose of such a design is that with a fluid flow from the annular space 26 into the control space 35, the baffle surface 46a is moved away from the fifth nozzle 23a, 23b and thus a movement of the cone section 42 away from the pilot opening 22 occurs. In this way, the flow force component of the disturbing force occurring can be reduced.

A precondition for the operation of the pilot-operated check valve is that the spring 50 biasing the main piston 20 limits the path of the control piston 30, as long as a magnet armature attached to the control piston 30 is not moved by energizing a magnet coil surrounding it. The spring 50 acts on the main piston 20 only as long as it is closed. In the normal operation of the main piston, the latter has no contact with the spring 50. In the normal operation of the main piston 20, the spring 50 works exclusively against the magnetic force; hydraulic forces on the main piston cannot cope with them. Before the main piston 20 opens, the control piston 30 must have an axial distance between the spring plate 51 and the stop in the main piston 20 by means of magnetic force. This distance remains during the entire opening stroke due to the hydraulic balance on the main piston 20. The main piston 20 follows the control piston 30 with constant spacing both in the lifting and in the lowering mode. The operation of the pilot-operated check valve according to the invention during slow lifting is examined below. A pump pressure in the pressure chamber 65 acts on the end face 24a of the main piston 20 and on the cross-sectional area of the pilot piston 32. Due to the low spring force of the pole tube spring with which the control piston 30 is biased, the pump pressure causes the pilot piston 32 to move axially to the cylinder section 30b of the control piston 30 rests on the spring plate 51, as a result of which the nozzle cross section of the second nozzle 61b increases on the outer circumference of the radial extension 33. As a result, fluid flows into the control chamber 35 and from there via the fifth nozzle into the annular chamber 26 and thus, for example, to a working cylinder connected to the connection B of the pilot-operated check valve. This working cylinder extends slowly.

The main piston 20 is in the contact position with the seat edge 62, since the sum of the pressure force on the first surface 24a of the extension 21 and the pressure force on the ring surface is not greater than the sum of the pressure in the control chamber 35 on the main piston 20 generated compressive force and the spring force of the spring 50.

When the solenoid is energized, the force of the spring 50 is overcome. The pilot piston 32 is axially displaced in such a manner that the opening of the third nozzle 61c is reduced. As a result, the pressure in the control chamber 35 drops. Even before the third nozzle 61c is completely closed, a balance is finally reached between the pressure forces acting on the main piston 20 in the opening direction and the pressure forces acting in the closing direction. When the control piston 30 moves further, the main piston 20 follows. From this position of the control piston 30, the fluid flow can be increased between the pressure chamber 65 and the annular space 26 when the solenoid is energized and the control piston 30 is moved against the spring force of the spring 50. Such a movement of the control piston 30 then entails a further opening of the main piston 20 and thus a rapid lifting of the working cylinder at port B with a continuously variable speed.

When lifting slowly, the pilot piston acts as a check valve with the spring force of the small pole tube spring. Because of this mechanical device, no current is required to the solenoid for the control piston 30 during slow lifting, which significantly improves controllability and eliminates synchronization problems with the pressure increase in the pressure chamber 65 and the energization of the solenoid.

During rapid lifting, the solenoid coil is energized immediately, as a result of which the main piston 20 can immediately lift off due to the pump pressure on the end face 24a. Even if the pump pressure should be applied to the main piston 20 rather than energizing the solenoid, there is no opening of the main piston 20 since the pilot opening 22 can also be opened without energizing the solenoid.

In the case of slow lowering, after a minimum current supply to the magnetic coil to overcome the force of the pole tube spring and the load-dependent closing force on the second nozzle device 61b, the cylinder section 30b moves up to the spring plate 51. Fluid flow through the fifth nozzle 23a, 23b against the baffle surface 46a of the baffle plate 46 into the control chamber 35 and also a fluid flow from the control chamber 35 via the valve devices 61a and 61d into the pressure chamber 65. The fluid flow now present compensates via the baffle surface 46a the flow force at the cone 42. The baffle plate 46 and the fourth nozzle 61d reduce the static and dynamic components of the interference force in the sink mode.

The limitation for the axial movement of the control piston 30 during slow lowering as well as during slow lifting is the contact position between the second cylinder section 30b and the spring plate 51. When the solenoid provided on the control piston 30 is energized more strongly, the spring 50 is compressed and between the cone section 42 and the Chamfer 31a exposed a larger opening cross-section. Such a reduction in the pressure drop across the pilot opening 22 causes the main piston 20 to lift off the seat edge 62 as soon as the opening force generated by the pressure prevailing in port B is greater than the closing force generated by the pressure prevailing in the control chamber 35.

In the case of rapid lowering, the solenoid coil is energized by the control piston 30 beyond the minimum for the slow lowering, as a result of which the main piston 20 is lifted off immediately.

However, the present invention is not limited to the above exemplary embodiment and can include pilot-operated check valves, in which two nozzle devices connected in parallel are used to separately establish the connection between the pressure chamber and the control chamber in the lifting mode and in the lowering mode. It is particularly advantageous that the opening cross-section of these nozzle devices can be changed as a function of pressure differences at the closing elements, without the need to energize solenoids for piston control. The present invention thus relates to a pilot operated check valve in which a control piston is located in a main piston. A pilot piston, which defines two valve devices connected in parallel, is introduced into a pilot opening on the end face of the main piston. One valve device becomes active when slowly lifting a load at the corresponding connection of the shut-off valve and the other when slowly lowering it. The controllability of the check valve can thus be improved. A baffle plate is provided on the control piston to reduce the interference forces in lowering mode.

Claims

Expectations

1. Pilot-operated check valve (1) with a main piston (20), via which a connection between a first connection (A) and a second connection (B) can be opened and the pressure prevailing at the first connection (A) and the load pressure of a hydraulic one Consumer can be acted upon at the second port (B) in the opening direction and by a control pressure prevailing in a rear control chamber (35) and the force of a first spring (50) in the closing direction, and with a control piston provided in the main piston (20) (30) controllable pilot opening (22), via which the rear control chamber (35) can be hydraulically connected to the first connection (A), a nozzle device (23) formed in the main piston (20), via which the rear control chamber (35) with the second connection (B) can be hydraulically connected, characterized in that in the pilot opening (22) two parallel nozzle devices (61a and 61d, 61b and 61 c) are arranged, the opening cross sections of which can be changed by the pressure difference between the rear control chamber (35) and the first connection (A) and the position of the control piston (30).

2. Pilot-operated shut-off valve according to claim 1, wherein a pilot piston (32) is provided in the pilot opening (22), the first nozzle device of the two nozzle devices connected in parallel has a first nozzle (61a) which is passed through a conical section (42) of the control piston (30 ) and a first end section of a recess (31) is formed in the pilot piston (32), and / or the second nozzle device of the two nozzle devices connected in parallel has a second nozzle (61b) which is formed by a radially outside of a first end section A recess (31) in the pilot piston (32) arranged radial extension (33) and a first end portion of the pilot opening (22) is formed.

3. Pilot operated check valve according to claim 2, wherein the second nozzle device comprises a third nozzle (61c) connected in series with the second nozzle (61b), which passes through a section (34a) of the pilot piston (32) in which the outer diameter of the Pilot piston (32) changes, and a second end portion of the pilot opening (22) opposite the first end portion of the pilot opening (22) is formed.

4. Pilot operated check valve according to claim 3, wherein the first end portion of the pilot opening (22) has a first chamfer (22a) and the second end portion of the pilot opening (22) has a second chamfer (22b) and the portion of the pilot piston (32) in which the diameter of the pilot piston (32) changes, is a third chamfer (34a).

5. Pilot-operated shut-off valve according to claim 4, wherein the first nozzle device has a fourth nozzle (61d) connected in series with the first nozzle (61a), which is provided in the second end section of the recess (31) opposite the first end section.

6. Pilot-operated shut-off valve according to one of the preceding claims, wherein in the rear control chamber (35) adjacent to an end section of the nozzle device (23) formed in the main piston (20), a baffle plate (46) is attached to the control piston (30).

7. Pilot-operated check valve according to claim 6, wherein the central axis of the Du- formed in the main piston (20) seneinrichtung (23) and the longitudinal axis of the control piston (30) to each other at an acute angle.

8. Pilot-operated check valve according to claim 7, wherein the nozzle device formed in the main piston (20)

(23) has at least two radially designed nozzles.

9. Pilot-operated check valve according to one of the preceding claims, wherein the control piston (30) compresses a second spring when moving away from the pilot opening (22) and after reaching the contact position with a spring ring (51) taking the spring ring (51) with it compressed first spring (50), whereby the connection between a first port (A) and a second port (B) can be opened by opening the main piston (20).