Valve device for a pneumatically actuated friction clutch

Abstract

Valve device (2) for a pneumatically operable friction clutch, which friction clutch is arranged in a vehicle between a drive motor and a shift transmission and can be engaged by spring force, the valve device having at least one inlet valve (16, 18) configured as a two-way two-position solenoid seat valve, which is connected on the input side to a reserve line for the pilot pressure and on the output side to the working chamber of an adjusting cylinder of the friction clutch, an outlet valve configured as a two-way two-position solenoid seat valve, which is connected on the input side to the working chamber of the adjusting cylinder and on the output side to an exhaust outlet, and a pressure holding valve (20, 28) arranged upstream or downstream of the inlet valve and configured as a check valve that closes in the return flow direction. The pressure holding valve is a valve springless check valve and comprises a housing ring (22, 30) with a holding cage (36), a closing body (24, 32) and a valve seat (26, 34), wherein the closing body can be held form-fittingly and force-fittingly in the holding cage (36) of the housing ring (22, 30) in the pressureless state and in the case of a positive pressure gradient coming from the direction of the escape hole of the assigned inlet valve (16, 18), and can be lifted out of the holding cage (36) and pressed against the valve seat (26, 34) in the case of a negative pressure gradient in the direction of the escape hole of the assigned inlet valve.

Description

Field of the Invention

[0001] The invention relates to a valve device for a pneumatically actuable friction clutch which is arranged in a vehicle between a drive motor and a shift transmission and can be engaged by spring force. The valve device has at least one inlet valve configured as a two-way two-position solenoid seat valve which is connected on the input side to a reserve line for a pilot pressure and on the output side to a working chamber of an adjusting cylinder of the friction clutch, an outlet valve configured as a two-way two-position solenoid seat valve which is connected on the input side to the working chamber of the adjusting cylinder and on the output side to an exhaust outlet, and a pressure holding valve which is arranged upstream or downstream of the inlet valve and is configured as a check valve which closes in the return flow direction. Background Art

[0002] In the case of a pneumatically separable and engagable friction clutch, by opening the inlet valve, air is supplied from the reserve line to the assigned adjusting cylinder, whereby the friction clutch is separated against the closing or restoring force of the pressure spring. The adjusting cylinder is exhausted by opening the outlet valve, whereby the friction clutch is engaged again under the action of the closing or pressure spring. If the supply pressure present in the reserve line decreases, for example, due to a defect in the compressed air supply line, a line rupture, or a greater draw-off of compressed air by another consumer, then the pressure holding valve has the function of maintaining the working pressure in the adjusting cylinder at least for a certain period of time when the adjusting cylinder is supplied with air and the inlet valve is closed. Based on the structural design as a seat valve provided herein, the inlet valve is not able to maintain the working pressure enclosed in the adjusting cylinder in the closed state because the switching element configured as a membrane or piston is pushed out of the valve seat in the case of a negative pressure gradient, i.e., a higher pressure in the working chamber of the adjusting cylinder than in the reserve line.

[0003] DE 10 2011 075 168 A1 describes a method for identifying a leak in an adjusting device of a pneumatically actuable friction clutch. A circuit diagram of a valve device with a pneumatically actuable friction clutch is described therein, in which a check valve that closes in the return flow direction is arranged upstream of an inlet valve for an adjusting cylinder of the friction clutch. In the case of a drop in the supply pressure in the reserve line due to a fault, the check valve prevents the exhaust of the adjusting cylinder and thus the accidental engagement of the friction clutch.

[0004] In view of the accidental engagement of the friction clutch, the starting situation is particularly critical, in which the drive motor is running, the friction clutch is disengaged, and the starting gear is engaged, because the engagement of the friction clutch caused by a sudden exhaust of the adjusting cylinder causes the vehicle to start suddenly. However, if the air pressure present in the working chamber of the adjusting cylinder is kept as constant as possible by the pressure holding valve for at least a certain period of time (which is sufficient to disengage the starting gear and / or stop the drive motor), then this uncontrolled starting of the vehicle can be prevented.

[0005] So far, the pressure holding valve has been configured as a conventional check valve, in which a substantially spherical closing body is pressed against the valve seat in the closing direction by a valve spring. Such a check valve consists of precision components and is therefore relatively complex and expensive to manufacture. During each air supply of the regulating cylinder or during each disengagement of the friction clutch, starting from the effective positive pneumatic gradient, the closing body is extruded from the valve seat against the closing direction against the restoring force of the valve spring and thus the check valve is opened. When the regulating cylinder exhausts air through the outlet valve, the closing body presses against the valve seat again under the action of the valve spring, where the closing body impacts the valve seat. Since the friction clutch disengages and engages millions of times during the service life of the vehicle, the pressure holding valve implemented as a conventional check valve is subject to high wear and can therefore lose its function at some point. In addition, checks are to be carried out such that a pressure drop caused by a fault in the reserve line (for which the pressure holding valve is actually installed) occurs relatively rarely and less than ten times during the service life of the vehicle. Summary of the Invention

[0006] Therefore, the object of the present invention is to provide a valve device for a pneumatically actuable friction clutch of the type mentioned at the beginning, which has a pressure holding valve arranged upstream or downstream of the inlet valve, the pressure holding valve being simply constructed, can be manufactured inexpensively and can operate with little wear.

[0007] This object is solved by a valve device having the features of claim 1. Advantageous designs and improvements are defined in the dependent claims.

[0008] Therefore, the present invention relates to a valve device for a pneumatically actuable friction clutch, which is arranged in a vehicle between a drive motor and a gearshift transmission and can be engaged by a spring force, the valve device having at least one inlet valve configured as a two-way two-position solenoid seat valve, which is connected on the input side to a reserve line conducting a pilot pressure and on the output side to the working chamber of the regulating cylinder of the friction clutch, an outlet valve configured as a two-way two-position solenoid seat valve, which is connected on the input side to the working chamber of the regulating cylinder and on the output side to an exhaust outlet, and a pressure holding valve arranged upstream or downstream of the inlet valve and configured as a check valve that closes in the return flow direction.

[0009] To solve the mentioned task, in such a valve device, it is provided that the pressure holding valve is configured as a non-valve spring check valve and has a housing ring with a holding cage, a closing body, and a valve seat. Herein, the closing body of the pressure holding valve can be held form-locked and force-locked in the holding cage of the housing ring in a pressureless state and in the case of a positive pressure gradient coming from the direction of the escape hole of the assigned inlet valve, and can be lifted from the holding cage in the case of a negative pressure gradient in the direction of the escape hole of the assigned inlet valve, and can be pressed against the valve seat.

[0010] By configuring the pressure holding valve as a non-valve spring check valve, wherein the closing body is held form-locked and force-locked in the holding cage of the housing ring in a pressureless state and in the case of a positive pressure gradient, and is lifted from the holding cage in the case of a negative pressure gradient and pressed against the valve seat, the pressure holding valve according to the invention, especially with a soft closing body, is as wear-free as possible. The closing body is only extruded from the holding cage of the housing ring in the relatively rarely occurring fault cases (in which the supply pressure in the reserve line suddenly drops when the regulating cylinder is supplied with air and thus the friction clutch is disengaged), and the pressure holding valve closes. Thereby, the air pressure enclosed in the working chamber of the regulating cylinder is maintained there for at least a long time until the drive motor stops. In contrast, during the normal operation of the friction clutch and the assigned compressed air circuit, the closing body is held in the holding cage of the housing ring, and differently from a conventional check valve, the closing body does not move during the engagement and disengagement of the friction clutch. Therefore, the pressure holding valve according to the invention can also be inexpensively manufactured with low manufacturing costs by simple shaping and the use of inexpensive materials. Furthermore, it should be determined that, compared with a conventional check valve, the proposed valve arrangement is very compact in terms of structural space.

[0011] In a preferred refinement of the valve device, it is provided that the holding cage of the housing ring consists of holding projections constructed on the radially inner side of the housing ring and distributed circumferentially, and these holding projections each have an arcuate inner surface, which together form the spherical segment-shaped holding geometry of the holding cage. Thereby, there is a sufficiently large clearance on the circumferential side between the holding projections for compressed air to flow through in the open state of the respective pressure holding valve.

[0012] In order to avoid complex mechanical finishing of the retaining cage or retaining projection and the valve seat, the closing body advantageously has a spring-elastic surface. Due to this elastic surface, the closing body not only matches the contour of the retaining cage or retaining projection in the open state of the pressure-retaining valve, but also matches the contour of the valve seat in the closed state of the pressure-retaining valve. This geometric adjustment of the closing body is relatively small and reversible, thereby ensuring that the closing body alternately not only does not get stuck in the retaining cage, but also rests sealingly on the valve seat of the inlet valve. In addition, mechanical wear on the retaining cage or its retaining projection and the valve seat is prevented by the elastic surface of the closing body.

[0013] In order to achieve a spring-elastic surface of the closing body, the closing body can be made completely of a spring-elastic material. Alternatively, however, the closing body can also have a core made of a hard material, which is coated with the spring-elastic material. However, the closing body can also have a central cavity, which is surrounded by the spring-elastic material in a spherical shell-like manner. As a result, the closing body has a particularly low weight. The spring-elastic material of the closing body is preferably rubber or silicone rubber.

[0014] Since the closing force of the closing body on the inlet valve depends on the flow resistance and the mass of the closing body, the flow resistance of the closing body is as great as possible and its mass is as low as possible.

[0015] In a preferred embodiment of the valve arrangement according to the invention, it is provided that the pressure holding valve is arranged downstream of the inlet valve and close to the outlet opening of the inlet valve, and that the edge of the outlet opening of the inlet valve serves and / or is designed as a valve seat for the pressure holding valve. As a result, a valve seat on the valve side, i.e., a component of the housing ring, for example, is eliminated in a cost-effective and space-saving manner. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The present invention will be described in more detail below with reference to the embodiments shown in the accompanying drawings.

[0017] Figure 1 A control module of a valve device according to the invention of a pneumatically actuatable friction clutch is shown in a partially perspective sectional view, the valve device having two inlet valves and two pressure holding valves;

[0018] Figure 2 A perspective cross-sectional or side view is shown according to Figure 1 The housing ring and closing body of the pressure retaining valve; and

[0019] Figure 3 The time curves of the supply pressure and the clutch pressure are shown graphically. DETAILED DESCRIPTION

[0020] Pneumatically operated friction clutch Figure 1The valve device 2 shown has two inlet valves 16, 18 and two pressure holding valves 20, 28, which are arranged in a two-part housing 6, 8 of the control module 4. The inlet valves 16, 18 are designed as 2 / 2-way electromagnetic seat valves and are each arranged in one of the two connecting channels 10, 12, which are arranged in parallel between an input channel (not visible here) to which a supply line for the pilot pressure is connected and an output channel 14 (to which a control cylinder (not shown here) of a friction clutch is connected. The pressure holding valves 20, 28 are designed as non-return valves that close in the return direction without valve springs and are each arranged downstream of one of the inlet valves 16, 18 in the respective connecting channel 10, 12.

[0021] Figure 1 The first inlet valve 16 and the associated first pressure-holding valve 20 are shown in the installed state, and the second inlet valve 18 and the associated second pressure-holding valve 28 are shown in the non-installed state above the housing 8. The inlet valves 16, 18 can be designed in the same structure or have different opening cross sections. The pressure-holding valves 20, 28 are designed in the same structure and each include a housing ring 22, 30 with a retaining cage 36, a closing body 24, 32 and a valve seat 26, 34.

[0022] exist Figure 2 2 shows an enlarged example of the housing ring 30 and the closing body 32 of the second pressure holding valve 28. The closing body 32 of the pressure holding valve 28 is spherical in design and the retaining cage 36 of the housing ring 30 is formed by retaining projections 38a, 38b, 38c which are arranged distributed on the circumference on the radial inside of the housing ring 30 and have arc-shaped inner surfaces 40a, 40b, 40c which form the spherical segment-shaped retaining geometry of the retaining cage 36. Between the retaining projections 38a, 38b, 38c, there are recesses 42 which are sufficiently large on the circumference for the compressed air to flow through in the open state of the pressure holding valve 28.

[0023] The closing body 32 has a spring-elastic surface 44. For this purpose, the closing body 32 can be made completely of a spring-elastic material, such as rubber or silicone rubber, or have a core made of a hard material which is coated with a spring-elastic material. In the installed state, the pressure holding valves 20, 28 are each arranged near the outlet opening of the associated inlet valve 16, 18 and use the edge of the associated outlet opening as a valve seat 26, 34.

[0024] To disengage the friction clutch, the inlet valves 16, 18 are energized and thus opened. Thereby, air is supplied from the reserve line to the working chamber of the regulating cylinder of the friction clutch, whereby the friction clutch disengages against the restoring force of the closing or pressing spring. To engage the friction clutch, the inlet valves 16, 18 are de-energized and thus closed again, and an outlet valve, which is not shown here and is configured as a two-position two-way solenoid seat valve, is energized and thus opened. Thereby, the working chamber of the regulating cylinder of the friction clutch is vented into the exhaust line leading to the exhaust outlet, whereby the friction clutch is engaged again under the action of the closing or pressing spring, which is known to a person skilled in the art.

[0025] In the state without pressure and with a positive pressure gradient, i.e., when the pressure in the reserve line is higher than the pressure in the working chamber of the regulating cylinder, the closing bodies 24, 32 of the respective pressure holding valves 20, 28 are form-locked and force-locked in the holding cage 36 of the housing rings 22, 30. In the case of a negative pressure gradient, i.e., when the pressure in the reserve line is lower than the pressure in the working chamber of the regulating cylinder (which occurs when the supply pressure in the reserve line decreases due to a fault), the closing bodies 24, 32 are pressed out of the holding cage 36 and are pressed towards their respective valve seats 26, 34. Thereby, the connecting channels 10, 12 are blocked, and in the case where the friction clutch is disengaged and the inlet valves 16, 18 are closed, the exhaust of the regulating cylinder and thus the accidental engagement of the friction clutch are prevented.

[0026] In Figure 3 the diagram shown, according to the supply pressure p V present in the reserve line and the clutch pressure p K acting in the working chamber of the regulating cylinder of the friction clutch, the curves over time t (in seconds s) show the action of the pressure holding valves 20, 28. Until the time point t = 10 s, the supply pressure p V increased three times from 0 Pa to approximately 3×10 5 Pa and then decreased again to 0 Pa. In the case where the inlet valves 16, 18 are open and in the absence of the pressure holding valves 20, 28 or when they are not functioning, the clutch pressure p K follows the supply pressure p V with a delay of approximately 0.5 s when the regulating cylinder is supplied with air, and follows the supply pressure p V almost without delay when the regulating cylinder is vented.

[0027] Starting from the time point t = 10 s, the supply pressure p V rises again from 0 Pa to approximately 3×10 5Pa. Starting from this time point, the pressure holding valves 20, 28 are present and operative. Now, the inlet valves 16, 18 are opened at time point t = 11.5 s, so that the working chamber of the adjusting cylinder is supplied with air and the friction clutch is disengaged. At the supply pressure p V which drops to 0 Pa due to a fault at time point t = 14 s, the pressure holding valves 20, 28 automatically close, so that the clutch pressure p K drops by a pressure difference Δp of approximately 0.2×10 5 Pa, but then remains as constant as possible within a time period Δt of approximately 10 s. During the starting process in which the drive motor is running and the starting gear is engaged, this time period is far sufficient to disengage the starting gear and / or stop the drive motor. In such a starting situation, the action of the pressure holding valves 20, 28 can thus reliably prevent an uncontrolled sudden start of the assigned vehicle.

[0028] Figure 3 It is also shown that the pressure holding valves 20, 28 without valve springs advantageously completely ignore a certain relatively small drop in the clutch pressure p K before the pressure holding valve performs its function as a check valve. In the given example, this pressure difference Δp is approximately 0.2×10 5 Pa at time point t = 14 s and at an output pressure of 3×10 5 Pa. This pressure drop has not yet caused the friction clutch to close.

[0029] Through the spring-elastic surface 44, in the open state of the pressure holding valves 20, 28, the closing bodies 24, 32 are form-fittingly applied against the inner surfaces 40a, 40b, 40c of the holding projections 38a, 38b, 38c of the housing rings 22, 30, and in the closed state of the pressure holding valves 20, 28 are applied against the edges acting as valve seats 26, 34 of the escape holes of the inlet valves 16, 18. Thus, the housing rings 22, 30 and the holding projections 38a, 38b, 38c of the pressure holding valves 20, 28 can be designed relatively simply and manufactured inexpensively. In addition, mechanical finishing of the inlet valves 16, 18 in the region of the hole edges 26, 34 of the escape holes is not required. Since the pressure holding valves 20, 28 close only in the case of a very small pressure drop of the supply pressure p V during the supply of the adjusting cylinder of the friction clutch, this type of construction of the pressure holding valves 20, 28 is as wear-free as possible compared to conventional check valves and is thus very reliable in function.

[0030] List of reference numerals

[0031] 2 Valve device

[0032] 4 Control module

[0033] 6 The first part of the housing

[0034] 8 The second part of the housing

[0035] 10 The first connection channel

[0036] 12 The second connection channel

[0037] 14 The output channel

[0038] 16 The first inlet valve, two - way two - position solenoid seat valve

[0039] 18 The second inlet valve, two - way two - position solenoid seat valve

[0040] 20 The first pressure - holding valve, check valve

[0041] 22 The first housing ring

[0042] 24 The first closing body, ball

[0043] 26 The first valve seat, hole edge

[0044] 28 The second pressure - holding valve, check valve

[0045] 30 The second housing ring

[0046] 32 The second closing body, ball

[0047] 34 The second valve seat, hole edge

[0048] 36 The holding cage

[0049] 38a The first holding projection

[0050] 38b The second holding projection

[0051] 38c The third holding projection

[0052] 40a The first inner surface

[0053] 40b The second inner surface

[0054] 40c The third inner surface

[0055] 42 The space between the holding projections

[0056] 44 The surface of the closing body

[0057] p Pressure

[0058] p K Clutch pressure

[0059] p V Supply pressure

[0060] t time, time point

[0061] Δp differential pressure

[0062] Δt time period

Claims

1. A valve device (2) for a pneumatically actuable friction clutch, which friction clutch is arranged in a vehicle between a drive motor and a shift transmission and can be engaged by spring force, the valve device having: an inlet valve (16, 18) configured as a two-way two-position solenoid seat valve, which is connected on the input side to a reservoir line for guiding pressure and on the output side to a working chamber of an adjusting cylinder of the friction clutch; an outlet valve configured as a two-way two-position solenoid seat valve, which is connected on the input side to the working chamber of the adjusting cylinder and on the output side to an exhaust outlet; and a pressure holding valve (20, 28) arranged upstream or downstream of the inlet valve (16, 18) and configured as a check valve that closes in the return flow direction, characterized in that, the pressure holding valve (20, 28) is configured as a check valve without a valve spring and has a housing ring (22, 30) with a retaining cage (36), a closing body (24, 32) and a valve seat (26, 34), wherein the closing body (24, 32) of the pressure holding valve (20, 28) can be held form-fittingly and force-fittingly in the retaining cage (36) of the housing ring (22, 30) in a pressureless state and in the case of a positive pressure gradient coming from the direction of the escape hole of the assigned inlet valve (16, 18), i.e., when the pressure in the reservoir line is higher than the pressure in the working chamber of the adjusting cylinder, and can be lifted from the retaining cage (36) and pressed against the valve seat (26, 34) in the case of a negative pressure gradient in the direction of the escape hole of the assigned inlet valve (16, 18), i.e., when the pressure in the reservoir line is lower than the pressure in the working chamber of the adjusting cylinder, wherein the pressure holding valve (20, 28) is arranged downstream of the inlet valve (16, 18) and is arranged close to the escape hole of the inlet valve (16, 18), and the edge of the escape hole of the inlet valve (16, 18) serves as and / or is configured as the valve seat (26, 34) of the pressure holding valve (20, 28).

2. The valve device according to claim 1, characterized in that, the retaining cage (36) of the housing ring (22, 30) is formed by retaining projections (38a, 38b, 38c) arranged circumferentially on the radially inner side of the housing ring (22, 30), and the retaining projections (38a, 38b, 38c) each have an arcuate inner surface (40a, 40b, 40c), and the inner surfaces together form a spherical segment-shaped retaining geometry of the retaining cage (36).

3. The valve device according to claim 1 or 2, characterized in that, the closing body (24, 32) of the pressure holding valve (20, 28) is configured spherically and has a spring-elastic surface (44).

4. The valve device according to claim 3, characterized in that, the closing body (24, 32) is made entirely of a spring-elastic material.

5. The valve device according to claim 3, characterized in that, the closing body (24, 32) has a core made of a hard material, and the core is coated with a spring-elastic material.

6. The valve device according to claim 3, characterized in that, the closing body (24, 32) has a central cavity, and the cavity is surrounded by a spherical shell of spring-elastic material.

7. The valve device according to claim 3, characterized in that, the spring-elastic material of the closing body (24, 32) is rubber.

8. The valve device according to claim 3, characterized in that, the spring-elastic material of the closing body (24, 32) is silicone rubber.

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