VALVE SYSTEM OF A PNEUMATICALLY ACTUATED FRICTION COUPLING

Description

[0001] The invention relates to a valve device of a pneumatically actuated friction clutch, which is arranged in a vehicle between a drive motor and a manual transmission and can be engaged by means of spring force, with at least one inlet valve designed as a 2 / 2-way solenoid seat valve, which is connected on the inlet side to a pressurised supply line and on the outlet side to a working chamber of an actuating cylinder of the friction clutch, an outlet valve designed as a 2 / 2-way solenoid seat valve, which is connected on the inlet side to the working chamber of the actuating cylinder and on the outlet side to a vent outlet, and a pressure holding valve arranged upstream or downstream of the inlet valve and designed as a check valve closing in the return flow direction.

[0002] In a pneumatically disengageable and engageable friction clutch, the opening of an inlet valve vents the associated actuating cylinder from the supply line, thereby disengaging the friction clutch against the restoring force of a closing or pressure spring. Opening an outlet valve vents the actuating cylinder, thereby re-engaging the friction clutch under the action of a closing or pressure spring. With the actuating cylinder pressurized and the inlet valve closed, the function of a pressure-maintaining valve is to maintain the working pressure in the actuating cylinder, at least for a certain period of time, when the supply pressure in the supply line drops, for example, due to a defect in the compressed air supply system, a line break, or a large amount of compressed air being drawn by another consumer.Due to the design as a seat valve provided here, the inlet valve is not able to maintain the working pressure enclosed in the actuating cylinder when closed, because the switching element designed as a diaphragm or piston is pushed away from the valve seat in the event of a negative pressure gradient, i.e. higher pressure in the working chamber of the actuating cylinder than in the supply line.

[0003] EP 3374675A1 discloses a check valve comprising a valve body comprising: a first portion; a second portion; and an opening through which the first and second portions are in fluid communication with each other; and a seat at the opening.

[0004] DE102010038506A1 discloses a valve arrangement, in particular for slip-controlled motor vehicle braking systems.

[0005] JPS59180128A discloses a valve assembly having the features of the preamble of claim 1.

[0006] EP0255982 A2 discloses an adjustable ball check valve for use in pipelines.

[0007] GB606229A discloses valve balls for check valves and of the type having a hard spherical core coated with a layer of hard rubber or other elastic material.

[0008] US2648311A relates generally to a valve mechanism and, more particularly, to a power-operated and manually-operated three-way valve mechanism suitable for use as a control device in a mechanism for controlling the operation of the friction clutch of a motor vehicle.

[0009] DE 10 2011 075 168 A1, which describes a method for detecting a leak in the actuating device of a pneumatically actuated friction clutch, describes a circuit diagram with a valve device of a pneumatically actuated friction clutch. A check valve closing in the reverse flow direction is connected upstream of an inlet valve for the actuating cylinder of the friction clutch. The check valve is intended to prevent venting of the actuating cylinder and thus unintentional engagement of the friction clutch in the event of a malfunction-related drop in supply pressure in the supply line.

[0010] With regard to unintentional engagement of the friction clutch, a particularly critical starting situation is one in which the drive motor is running, the friction clutch is disengaged, and a starting gear is engaged, since the engagement of the friction clutch caused by a sudden venting of the actuating cylinder would then lead to an abrupt start of the vehicle. However, if the air pressure in the working chamber of the actuating cylinder is kept largely constant by the pressure-maintaining valve, at least for a certain period of time sufficient to disengage the starting gear and / or shut off the drive motor, such an uncontrolled start of the vehicle can be prevented.

[0011] Until now, the pressure retention valve has been designed as a conventional check valve in which a usually spherical closing body is pressed against a valve seat in the closing direction by a valve spring. Such a check valve consists of precision parts and is therefore relatively complex and expensive to manufacture. Each time the actuating cylinder is pressurised or each time the friction clutch is disengaged, the closing body is pushed away from the valve seat by an effective positive pneumatic pressure gradient against the restoring force of the valve spring, counter to the closing direction, thus opening the check valve. When the actuating cylinder is vented via the outlet valve, the closing body is pressed back against the valve seat under the action of the valve spring, where it strikes the valve seat.Since the friction clutch disengages and engages millions of times over the life of a vehicle, a pressure relief valve designed as a conventional check valve is subject to significant wear and tear and can therefore eventually lose its function. Furthermore, studies have shown that a malfunction-related pressure drop in the supply line, for which the pressure relief valve is actually intended, occurs relatively rarely, occurring less than ten times over the life of a vehicle.

[0012] The present invention is therefore based on the object of providing a valve device of a pneumatically actuated friction clutch of the type mentioned at the outset with a pressure holding valve arranged upstream or downstream of the inlet valve, which is of simple construction, can be manufactured cost-effectively and can be operated with low wear.

[0013] This object is achieved by a valve device having the features of claim 1. Advantageous embodiments and further developments are defined in the dependent claims.

[0014] Accordingly, the invention is based on a valve device for a pneumatically actuated friction clutch, which is arranged in a vehicle between a drive motor and a manual transmission and can be engaged by means of spring force, wherein the valve device has at least one inlet valve designed as a 2 / 2-way solenoid seat valve, which can be connected on the inlet side to a pressurized supply line and on the outlet side to a working chamber of an actuating cylinder of the friction clutch, an outlet valve designed as a 2 / 2-way solenoid seat valve, which can be connected on the inlet side to the working chamber of the actuating cylinder and on the outlet side to a vent outlet, and a pressure holding valve arranged upstream or downstream of the inlet valve and designed as a check valve closing in the return flow direction.

[0015] To achieve the stated object, this valve device is provided with the pressure holding valve being designed as a valve spring-less check valve and having a housing ring with a holding cage, a closing body and a valve seat, wherein the closing body of the pressure holding valve can be held in the holding cage of the housing ring in a form-fitting and force-fitting manner in the pressure-free state and with a positive pressure gradient from the direction of the outlet bore of the associated inlet valve and can be lifted out of the holding cage and pressed against the valve seat in the direction of the outlet bore of the associated inlet valve with a negative pressure gradient.

[0016] By designing the pressure-maintaining valve as a valve-spring-less check valve, in which the closing body is held positively and non-positively in the retaining cage of the housing ring when depressurized and at a positive pressure gradient, and is lifted out of the retaining cage and pressed against the valve seat when a negative pressure gradient is present, the pressure-maintaining valve according to the invention is largely wear-free, particularly with a soft closing body. Only in the relatively rare event of a malfunction in which the supply pressure in the supply line suddenly drops when the actuating cylinder is ventilated and the friction clutch is thus disengaged, is the closing body pushed out of the retaining cage of the housing ring and the pressure-maintaining valve closed. This maintains the air pressure trapped in the working chamber of the actuating cylinder at least until the drive motor is switched off.In contrast, during normal operation of the friction clutch and the corresponding compressed air circuit, the closing body remains in the retaining cage of the housing ring and, unlike a conventional check valve, is not moved when the friction clutch is disengaged and engaged. Therefore, the pressure-retaining valve according to the invention can be manufactured cost-effectively with low manufacturing effort thanks to its simple design and the use of inexpensive materials. Furthermore, it should be noted that the proposed valve arrangement is very compact in terms of installation space compared to a conventional check valve.

[0017] In a preferred development of the valve device, the retaining cage of the housing ring consists of retaining webs formed radially inside the housing ring and distributed circumferentially. These retaining webs each have a circular segment-shaped inner surface, which together form a spherical segment-shaped retaining geometry of the retaining cage. Thus, there are sufficiently large recesses on the circumference between the retaining webs for the flow of compressed air when the respective pressure-retaining valve is open.

[0018] To avoid complex mechanical fine machining of the retaining cage or the retaining webs and the valve seat, the closing body advantageously has a spring-elastic surface. This elastic surface allows the closing body to adapt to the contour of the retaining cage or the retaining webs both when the pressure retaining valve is open and to the contour of the valve seat when the pressure retaining valve is closed. This geometric adaptation of the closing body is comparatively small and reversible, ensuring that the closing body alternately does not jam in the retaining cage and also seals against the valve seat of the inlet valve. In addition, the elastic surface of the closing body prevents mechanical wear on the retaining cage or its retaining webs and on the valve seat.

[0019] To achieve the spring-elastic surface of the locking body, it can be made entirely of a spring-elastic material. Alternatively, the locking body can also have a core made of a hard material coated with a spring-elastic material. The locking body can also have a central cavity, which is surrounded by the spring-elastic material in the shape of a spherical shell. This makes the locking body particularly lightweight. The spring-elastic material of the locking body is preferably rubber or silicone rubber.

[0020] 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 large as possible and its mass as small as possible.

[0021] According to the valve arrangement according to the invention, the pressure-maintaining valve is arranged downstream of the inlet valve and close to the outlet bore of the inlet valve, and the edge of the outlet bore of the inlet valve serves and / or is designed as the valve seat of the pressure-maintaining valve. This eliminates the need for a valve-side valve seat, i.e., a valve seat designed as a component, for example, of the housing ring, in a cost-effective and space-saving manner.

[0022] The invention will be explained in more detail below with reference to an embodiment shown in the accompanying drawing. Fig. 1 a control module of a valve device according to the invention of a pneumatically actuated friction clutch with two inlet valves and two pressure-maintaining valves in a partial perspective sectional view, Fig. 2 a housing ring and a closing body of a pressure retaining valve according to Fig. 1 in a perspective sectional view or side view, and Fig. 3 Time courses of a supply pressure and a clutch pressure in a diagram.

[0023] The Fig. 1 The illustrated valve device 2 of a pneumatically actuated friction clutch has two inlet valves 16, 18 and two pressure-maintaining valves 20, 28, which are arranged in a two-part housing 6, 8 of a control module 4. The inlet valves 16, 18 are designed as 2 / 2-way solenoid seat valves and are each arranged in one of two connecting channels 10, 12, which are arranged in parallel between an inlet channel (not visible here), to which a pressurized supply line is connected, and an outlet channel 14, to which an actuating cylinder (not shown here) of the friction clutch is connected. The pressure-maintaining valves 20, 28 are designed as valve-springless check valves that close in the return flow direction and are each arranged downstream of one of the inlet valves 16, 18 in the respective connecting channel 10, 12.

[0024] In the Fig. 1 The first inlet valve 16 and the associated first pressure-maintaining valve 20 are shown in the installed state, and the second inlet valve 18 and the associated second pressure-maintaining valve 28 are shown in the non-installed state above the housing 8. The inlet valves 16, 18 can be of identical construction or have different opening cross-sections. The pressure-maintaining valves 20, 28 are of identical construction and each comprise a housing ring 22, 30 with a retaining cage 36, a closing body 24, 32, and a valve seat 26, 34.

[0025] In the Fig. 2 The housing ring 30 and the closing body 32 of the second pressure-maintaining valve 28 are shown enlarged as an example. The closing body 32 of the pressure-maintaining valve 28 is spherical, and the holding cage 36 of the housing ring 30 consists of holding webs 38a, 38b, 38c arranged radially inwardly on the housing ring 30 and distributed circumferentially, with circular-segment-shaped inner surfaces 40a, 40b, 40c, which form a spherical-segment-shaped holding geometry of the holding cage 36. Between the holding webs 38a, 38b, 38c, there are sufficiently large recesses 42 on the circumference for the flow of compressed air when the pressure-maintaining valve 28 is open.

[0026] The closing body 32 has a resilient surface 44. For this purpose, the closing body 32 can be made entirely of a resilient material, such as rubber or silicone rubber, or it can have a core made of a hard material coated with a resilient material. When installed, the pressure-maintaining valves 20, 28 are each arranged close to the outlet bore of the associated inlet valve 16, 18 and use the edge of the respective outlet bore as the valve seat 26, 34.

[0027] To disengage the friction clutch, the inlet valves 16, 18 are energized and thereby opened. This vents the working chamber of the friction clutch actuating cylinder from the supply line, disengaging the friction clutch against the restoring force of a closing or pressure spring. To engage the friction clutch, the inlet valves 16, 18 are deactivated and thereby closed again, and outlet valves (not shown here) designed as 2 / 2-way solenoid seat valves are energized and thereby opened. This vents the working chamber of the friction clutch actuating cylinder into a vent line leading to a vent outlet, whereby the friction clutch is re-engaged under the action of the closing or pressure spring, which is known per se to those skilled in the art.

[0028] In the depressurized state and with a positive pressure gradient, i.e., when the pressure in the supply line is higher than in the working chamber of the actuating cylinder, the closing body 24, 32 of the respective pressure-maintaining valve 20, 28 is held positively and non-positively in the holding cage 36 of the housing ring 22, 30. In the case of a negative pressure gradient, i.e., when the pressure in the supply line is lower than in the working chamber of the actuating cylinder, which occurs in the event of a malfunction-related drop in the supply pressure in the supply line, the closing body 24, 32 is pushed out of the holding cage 36 and pressed against the respective valve seat 26, 34. This blocks the connecting channels 10, 12 and, when the friction clutch is disengaged and the inlet valves 16, 18 are closed, prevents venting of the actuating cylinder and thus unintentional engagement of the friction clutch.

[0029] In the Fig. 3 The diagram shown illustrates the effect of the pressure holding valves 20, 28 using the curves of the supply pressure p V present in the supply line and the clutch pressure p K effective in the working chamber of the actuating cylinder of the friction clutch over time t in seconds s. Up to the time t = 10 s, the supply pressure p V is increased three times from 0 Pa to approximately 3 × 10 5< Pa and then reduced again to 0 Pa. When the inlet valves 16, 18 are open and the pressure holding valves 20, 28 are not present or effective, the clutch pressure p K follows the supply pressure p V with a delay of approximately 0.5 s when the actuating cylinder is vented and almost immediately when the actuating cylinder is vented.

[0030] From time t = 10 s, from which the supply pressure p V rises again from 0 Pa to approximately 3 × 10 5< Pa, the pressure holding valves 20, 28 are present and effective. Now the inlet valves 16, 18 are opened at time t = 11.5 s, so that the working chamber of the actuating cylinder is ventilated and the friction clutch is disengaged. After the supply pressure p V drops to 0 Pa at time t = 14 s due to a fault, the pressure holding valves 20, 28 close automatically, so that the clutch pressure p K drops by a pressure difference Δp of approximately 0.2 × 10 5< Pa due to the switching time, but is then kept largely constant over a period Δt of approximately 10 seconds. When starting off with the engine running and the starting gear engaged, this period is more than sufficient to disengage the starting gear and / or switch off the engine.In such a starting situation, the effect of the pressure holding valves 20, 28 can thus reliably prevent an uncontrolled, sudden start of the vehicle in question.

[0031] Fig. 3 It also shows that the valve-springless pressure-maintaining valve 20, 28 advantageously ignores a certain, comparatively small drop in the clutch pressure pk before it assumes its function as a check valve. In the example presented, this pressure difference Δp is approximately 0.2 × 10 5 < Pa at time t = 14 s with an output pressure of 3 × 10 5 < Pa. Such a pressure drop does not yet lead to the friction clutch being closed.

[0032] Due to the spring-elastic surface 44, the closing bodies 24, 32 nestle in a form-fitting manner against the inner surfaces 40a, 40b, 40c of the retaining webs 38a, 38b, 38c of the housing rings 22, 30 when the pressure-retaining valves 20, 28 are open, and against the edges of the outlet bores of the inlet valves 16, 18, which act as valve seats 26, 34, when the pressure-retaining valves 20, 28 are closed. Therefore, the housing rings 22, 30 and retaining webs 38a, 38b, 38c of the pressure-retaining valves 20, 28 can be designed relatively simply and manufactured cost-effectively. Furthermore, this eliminates the need for any fine mechanical machining of the inlet valves 16, 18 in the area of ​​the bore edges 26, 34 of the outlet bores.Since the pressure holding valves 20, 28 are only closed in the event of a very rare pressure drop in the supply pressure p V while the actuating cylinder of the friction clutch is ventilated, this type of pressure holding valves 20, 28 is largely wear-free compared to conventional check valves and is therefore very reliable. Reference symbol

[0033] 2Valve assembly 4Control module 6First housing part 8Second housing part 10First connecting channel 12Second connecting channel 14Outlet channel 16First inlet valve, 2 / 2-way solenoid seat valve 18Second inlet valve, 2 / 2-way solenoid seat valve 20First pressure-retaining valve, check valve 22First housing ring 24First closing body, ball 26First valve seat, bore edge 28Second pressure-retaining valve, check valve 30Second housing ring 32Second closing body, ball 34Second valve seat, bore edge 36Retaining cage 38aFirst retaining web 38bSecond retaining web 38cThird retaining web 40aFirst inner surface 40bSecond inner surface 40cThird inner surface 42Recesses between retaining webs 44Surface of the closing body pPressure p K Coupling pressure p V Supply pressure tTime, point in time ΔpPressure difference ΔtPeriod

Claims

1. Valve device (2) for a pneumatically actuated friction clutch, which is arranged in a vehicle between a drive motor and a gearbox and can be engaged by means of spring force, the valve device comprising at least one inlet valve (16, 18) which is designed as a 2 / 2-way solenoid seat valve and can be connected on the inlet side to a pressurized supply line and on the outlet side to a working chamber of an actuating cylinder of the friction clutch, an outlet valve which is designed as a 2 / 2-way solenoid seat valve and can be connected on the inlet side to the working chamber of the actuating cylinder and on the outlet side to a vent outlet, and a pressure-maintaining valve (20, 28) arranged upstream or downstream of the inlet valve (16, 18) and designed as a check valve closing in the reverse flow direction, characterized in that the pressure-maintaining valve (20, 28) is designed as a valve springless check valve and comprises a housing ring (22, 30) having a retaining cage (36), a closing body (24, 32) and a valve seat (26, 34), the closing body (24, 32) of the pressure-maintaining valve (20, 28) being able to be held by interlocking and frictional engagement in the retaining cage (36) of the housing ring (22, 30) in the depressurized state and with a positive pressure gradient from the direction of the outlet bore of the associated inlet valve (16, 18) and being able to be lifted out of the retaining cage (36) in the direction of the outlet bore of the associated inlet valve (16, 18) with a negative pressure gradient and be pressed against the valve seat (26, 34), and in that the pressure-maintaining valve (20, 28) is arranged downstream of the inlet valve (16, 18) and is arranged close to the outlet bore of the inlet valve (16, 18), and in that the edge of the outlet bore of the inlet valve (16, 18) serves and / or is designed as a valve seat (26, 34) of the pressure-maintaining valve (20, 28).

2. Valve device according to claim 1, characterized in that the retaining cage (36) of the housing ring (22, 30) consists of retaining ribs (38a, 38b, 38c) formed radially inside the housing ring (22, 30) and arranged distributed around the circumference, and in that the retaining ribs (38a, 38b, 38c) each have a circular segment-shaped inner surface (40a, 40b, 40c), which together form a spherical segment-shaped retaining geometry of the retaining cage (36).

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

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

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

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

7. Valve device according to claims 3 to 6, characterized in that the spring-elastic material of the closing body (24, 32) is rubber.

8. Valve device according to claims 3 to 6, characterized in that the spring-elastic material of the closing body (24, 32) is silicone rubber.