The invention relates to a safety valve according to the preamble of claim 1.

The invention also relates to a pneumatic actuator and a vehicle.

Safety valves are generally known. A safety valve ensures a safe operation of a pneumatic system, in particular by enabling a release airflow in the pneumatic system when a pressure threshold is exceeded. Safety valves generally com prises a valve piston for enabling and blocking such release airflow depending on a pressure in the pneumatic system.

Safety valves have to be reliable, as their function is critical to the safety of the pneumatic system and of a superordinate system such as a vehicle. In particu lar, a safety valve must reliably switch when a certain, predetermined airflow rate and/or pressure is reached. Another important aspect is the manufactura bility, in particular an economical manufacturing, of the safety valve.

Safety valves can still be improved, in particular with respect to a reliable func tion and/or their manufacturability. It is therefore desirable to address at least one of the above problems.

This is where the invention comes in, with the object to specifically improve safety valves with respect to a reliable function and an improved manufactura bility.

In accordance with the invention the object is solved in a first aspect by a safety valve as proposed according to claim 1. A safety valve is proposed for a pneumatic conduit, in particular a pneumatic actuator, the safety valve comprising: a valve body, arranged in the pneumatic conduit, in particular at the ac tuator piston, the valve body comprising a pressure port pneumatically connect ed to a pressure side of the pneumatic conduit and a release port pneumatically connected to a release side of the pneumatic conduit, a valve piston, arranged in the valve body and axially movable along a valve axis relative to the valve body between a release-side end position on an axial side facing the release port and a pressure-side end position on another axial side facing the pressure port, and a valve piston spring, adapted to push the valve piston into the pressure- side end position.

In accordance with the invention, it is proposed that the safety valve comprises a bypass conduit, which extends through the valve body or the valve piston and is adapted to permit a release airflow to flow between the pressure port and the release port.

It shall be understood that the bypass conduit is additional to a possible annular gap between a circumferential surface of the valve piston and an inner surface of the valve body. In particular, the bypass conduit is a channel for the airflow to bypass the valve piston, in particular with a defined, unobstructed cross section.

The invention is based on the finding that conventional safety valves, which have a valve body and a valve piston and only permit an airflow through an an nular gap between the valve body and the valve piston, have disadvantages. In particular, the cross-section of the annular gap defining the airflow rate depends on the shape and form tolerances of two parts manufactured independently, namely the valve piston and the valve body. Even when these parts are manu factured with high precision and resulting small tolerances, it is hard to achieve a reliable, constant airflow. This is mainly due to the varying cross-section de pending on the position of the valve piston relative to the valve body. The invention includes the finding that a bypass conduit extending through the valve body of the valve piston, provides a better means for the airflow to flow through the safety valve, in particular when the valve piston is in between its two end positions. By providing a defined, unobstructed cross-section, the safe ty valve according to the concept of the invention enables a predictable airflow from the pressure port to the release port, providing a reliable behavior of the safety valve.

Further developments of the invention can be found in the dependent claims and show particularly advantageous possibilities to realize above described concept in light of the object of the invention and regarding further advantages.

Preferably, the pneumatic conduit is part of a pneumatic actuator. The pneumat ic conduit can preferably be arranged in or at an actuator piston of the pneumat ic actuator, pneumatically connecting a pressure side and a release side of the pneumatic actuator. In other preferred developments, the pneumatic conduit is arranged in another part of a pneumatic system, in particular of a pneumatic actuator. A safety valve according to the concept of the invention can be applied in any pneumatic conduit where the achieved flow characteristic of an air flow is needed between a pressure side and a release side.

Developments, in which the pneumatic conduit is part of a pneumatic actuator, include the finding that by enabling the release airflow, an unintended activation of the pneumatic actuator, in particular of a pneumatic clutch, through a leakage airflow is advantageously prevented by the safety valve. By means of a valve piston, that is axially movable along a valve axis relative to the valve body, a simple yet reliable design is achieved for the function of a safety valve.

A safety valve according to the concept of the invention is preferably adapted to enable a release airflow from the pressure port to the release port when the pressure at the pressure side is below or equal to a leakage pressure, in partic ular a maximum leakage pressure. A safety valve according to the concept of the invention is further preferably adapted to inhibit the release airflow when the pressure is above said leakage pressure, in particular above the maximum leakage pressure. By enabling the release airflow, an unintended activation of the pneumatic actuator, in particular of a pneumatic clutch, through a leakage airflow is advantageously prevented.

It is preferably suggested that the bypass conduit has a circumferentially closed cross section, preferably is a cylindrical channel, and extends in an axial or in a substantially axial direction. A cylindrical channel such as a drill hole or bore can be manufactured precisely with a relatively small effort. With a defined closed cross-section, in particular a defined diameter of the cross section, a flow rate of the release airflow can be predefined. "Circumferentially closed cross- section" means that the cross-section is entirely surrounded by material the ob ject that the conduit extends through. The conduit in that case can accordingly be considered a tunnel. Preferably, the bypass conduit is in the valve piston.

It is accordingly advantageous that the bypass conduit has a circumferentially open cross section, preferably is a groove on a circumferential surface of the valve piston or on an inner surface of the valve body. "Circumferentially open cross-section" means that the cross-section is only partly surrounded by the material of the object that the conduit extends through. The conduit in that case is an open channel protruding on the surface. In developments of the invention with an open cross-section, a defined airflow is nevertheless achieved by the interaction of the bypass conduit with a second safety valve component, in par ticular with the valve piston, closing the cross-section of the bypass conduit.

The bypass conduit with an open cross-section is arranged axially along the valve axis such that the bypass conduit is not functional, in particular not in con tact with the valve piston, when the valve piston is in one of its two end posi tions. When the valve piston is in between its two and positions, the release airflow can flow through the passage which is formed by the bypass conduit and the valve piston. Preferably, the groove has a rectangular cross-section. A rec tangular cross-section is easy to manufacture, for example by milling. Prefera bly, the bypass conduit is in the valve body. A preferred development suggests that the safety valve comprises a pressure-side gasket, which is adapted to inhibit the release airflow between the pressure port and the release port in an annular gap when the valve piston is in the pressure-side end position, wherein the annular gap is between a circumferential surface of the valve piston and an inner surface of the valve body.

In accordance with a further development, it is proposed that the pressure-side gasket is arranged on, in particular molded onto, the pressure-side end face of the valve piston, or the pressure-side gasket is arranged on, in particular molded onto, a pressure-side stop of the valve body.

In accordance with a further development, it is proposed that the pressure-side gasket is arranged in the annular gap, in particular extends radially in a plane perpendicular to the valve axis. A development where the pressure-side gasket is arranged in the annular gap is particularly advantageous when the bypass conduit has a circumferentially open cross-section, because the function of the bypass conduit can be effected in dependence of the axial position of the valve piston. When the pressure-side gasket is outside of the axial range of the by pass conduit, in particular when the valve piston is in one of its two end posi tions, the bypass conduit is not functional and consequently, the release airflow cannot pass.

A preferred development suggests that the pressure-side gasket is arranged on, in particular molded onto, the circumferential surface of the valve piston. Prefer ably, the pressure-side gasket has a rotationally symmetric shape. In another preferred embodiment, the pressure-side gasket is glued to the valve piston or to the valve body lid, in particular to the washer, by means of an adhesive.

In accordance with a further development, a release-side gasket is proposed, which is adapted to inhibit the release airflow between the pressure port and the release port when the valve piston is in the release-side end position. Preferably, the release-side gasket is arranged between a release-side end face of the valve piston and a release-side stop of the valve body, in particular extends axially in the direction of the valve axis. Through such axial arrange ment of the release-side gasket, a blocking of the release airflow in the release- side end position of the valve piston is advantageously achieved.

A preferred development suggests that the release-side gasket is arranged on, in particular molded onto, the release-side end face, or the release-side gasket is arranged on, in particular molded onto, the release-side stop.

The pressure-side gasket and/or the release-side gasket and/or the lid gasket is preferably made of rubber, in particular silicone.

In accordance with a further development, it is proposed that the valve body comprises a valve body lid, which in particular comprises the pressure-side stop and/or the pressure port.

In accordance with a further development, it is proposed that the valve body lid is releasably connected to the valve body, in particular comprises a lid thread adapted to be engaged to a corresponding body thread of the valve body. With such detachable connection between the valve body lid and the valve body, the valve body can be reopened in a nondestructive manner, for example for repair purposes.

In other preferable developments, it is proposed that the valve body lid is re leasably connected to the valve body by means of a snap-fit connection. In par ticular, the valve body lid can comprise a snap hook, adapted to engage with the valve body, in particular with a lid recess.

A preferred development suggests that the valve body lid is mounted to the valve body in a positively locking manner, in particular axially locked in a lid recess by a body rim, wherein the body rim is preferably created by a bordering process after inserting the valve body lid into the lid recess. Such development, in particular with a body rim manufactured by bordering, a safety valve can be manufactured under relatively small effort in terms of machining steps.

In a second aspect of the invention, a pneumatic actuator, in particular pneu matic clutch actuator or pneumatic transmission actuator, is proposed, compris ing a pneumatic conduit with a pressure side and a release side, and a safety valve according to the first aspect of the invention. Preferably, the pneumatic actuator comprises an actuator piston. Preferably, the pneumatic conduit is ar ranged in the actuator piston, wherein consequently the safety valve is arranged in the actuator piston. In other developments of the pneumatic actuator, the pneumatic conduit and/or the safety valve is arranged elsewhere, for example in a housing of the pneumatic actuator or in an electro pneumatic valve module, and connected to the pressure side and/or to the release side by means of a pneumatic conduit or the like pneumatic connection. In a preferred development of the pneumatic actuator, the pneumatic conduit and/or the safety valve is con nected to a pressure conduit at a pressure side, preferably at the pressure port of the safety valve. In a preferred development of the pneumatic actuator, the pneumatic conduit and/or the safety valve is connected to a release conduit at a release side, preferably at the release port of the safety valve.

In a third aspect of the invention, a vehicle, in particular a commercial vehicle, is proposed, comprising a pneumatic actuator according to the second aspect of the invention, in particular a pneumatic clutch actuator, and/or a safety valve according to the first aspect of the invention.

It shall be understood that the safety valve according to the first aspect of the invention, the pneumatic actuator according to the second aspect of the inven tion and the vehicle according to the third aspect of the invention comprise iden tical or similar developments, in particular as described in the dependent claims. Therefore, a development of one aspect of the invention is also applicable to another aspect of the invention.

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. The embodiments of the invention are described in the following on the basis of the drawings in com parison with the state of the art, which is also partly illustrated. The latter is not necessarily intended to represent the embodiments to scale. Drawings are, where useful for explanation, shown in schematized and/or slightly distorted form. With regard to additions to the lessons immediately recognizable from the drawings, reference is made to the relevant state of the art. It should be borne in mind that numerous modifications and changes can be made to the form and detail of an embodiment without deviating from the general idea of the inven tion. The features of the invention disclosed in the description, in the drawings and in the claims may be essential for the further development of the invention, either individually or in any combination.

In addition, all combinations of at least two of the features disclosed in the de scription, drawings and/or claims fall within the scope of the invention. The gen eral idea of the invention is not limited to the exact form or detail of the preferred embodiment shown and described below or to an object which would be limited in comparison to the object claimed in the claims. For specified design ranges, values within the specified limits are also disclosed as limit values and thus arbi trarily applicable and claimable.

Further advantages, features and details of the invention result from the follow ing description of the preferred embodiments as well as from the drawings, which show in:

Fig. 1 a first preferred embodiment of a safety valve according to the concept of the invention,

Fig. 2A, Fig. 2B a second preferred embodiment of a safety valve according to the concept of the invention, Fig. 3 a third preferred embodiment of a safety valve according to the concept of the invention,

Fig. 4 a pneumatic actuator in the form of a pneumatic clutch actuator,

Fig. 5 an excerpt of another pneumatic actuator with a safety valve, wherein the pneumatic actuator is in the form of a pneumatic transmission actuator,

Fig. 6 a vehicle comprising a pneumatic actuator with a safety valve ac cording to the concept of the invention.

Fig. 1 shows a safety valve 100 according to the first preferred embodiment of the invention. The safety valve 100 comprises a valve body 120 and a valve piston 140, which are both in principle rotationally symmetrical with respect to a valve axis VA. The safety valve 100 comprises on a pressure side 840 a pres sure port 122, which is pneumatically connectable to a pressure source for re ceiving a pressure P. The safety valve 100 is insertable into a pneumatic con duit 798, in particular of a pneumatic actuator 800, which is not shown here. For example, the pneumatic conduit 798 can be located in an actuator piston 820 as shown in Fig. 4 or in an electro pneumatic valve module 890 as shown in Fig. 5. In accordance with an exemplary embodiment, the pressure source could, in particular be a pressure chamber 846 of a pneumatic actuator 800, such as a pneumatic clutch actuator 802. In another exemplary embodiment, the pressure source could be an inlet that bridges one or more solenoid valves and a com pressed air reservoir. By providing a pressure P to the pressure side 840 of ac tuator piston 820 in a controllable manner, the pneumatic actuator 800 can be selectively actuated.

The safety valve 100 comprises on a release side 860 a release port 124, which is pneumatically connectable to a release line, in particular to an environment with ambient pressure PE. In the embodiment shown, the release port compris es a first release port 124.1 and a second release port 124.2.

The valve piston 140 is held within the valve body 120 in an axially movable manner, adapted to move along the valve axis VA between two axial end posi- tions, namely a first, release-side end position SP1 defined by a release-side stop 129, and a second, pressure-side end position SP2 defined by a pressure- side stop 128.

Between a circumferential surface 145 of the valve piston 140 and an inner sur face 126 of the valve body 120, there is an annular gap 146 for providing a cer tain clearance between the valve body 120 and the valve piston 140 to allow for a relative axial movement between the two.

The safety valve 100 further comprises a valve piston spring 160, which is ar ranged inside the valve body 120 and is adapted to push the valve piston 140 into the pressure-side end position SP2.

A pressure P at the pressure port 122 results in a pressure force FP acting on a pressure-side end face 142 of the valve piston 140.

The valve piston spring 160 is configured such that the valve piston 140 lifts from the pressure-side end position SP2 when the pressure P at the pressure port 122 exceeds a minimum leakage pressure PLMIN.

The valve piston spring 160 is further configured such that the valve piston 140 reaches the release-side end position SP1 when the pressure P at the pressure port 122 reaches a maximum leakage pressure PLMAX.

The valve piston spring 160 has a spring constant 162, which is adapted to fulfill the valve piston spring's 160 characteristics with respect to the minimum leak age pressure PLMIN and the maximum leakage pressure PLMAX.

According to the concept of the invention, the valve piston 140 comprises a by pass conduit 150, which is adapted to permit a release airflow AF from the pressure port 122 to the release port 124. The bypass conduit 150 has a cir cumferentially closed cross-section 152, meaning that the cross-section of the bypass conduit 150 is completely covered by material, here completely covered by the valve piston 140. The circumferentially closed cross-section 152 in this embodiment has a circular shape, resulting in a cylindrical channel 153, extend ing through the center of the valve piston 140 along the valve axis VA from the pressure-side end face 142 to the release-side end face 144.

On a release-side end face 144 of the valve piston 140, which is arranged op posite of the pressure-side end face 142, the valve piston 140 comprises at least one release-side gasket 134, adapted to sealingly close the release port

124 or ports 124.1 and 124.2 when the valve piston 140 is in the release-side end position SP1.

On a pressure-side end face 142 of the valve piston 140, the valve piston 140 comprises a pressure-side gasket 130, which is adapted to sealingly close the pressure port 122, in particular pneumatically separate the pressure port 124 from the annular gap 146, when the valve piston 140 is in the pressure-side end position SP2. In the embodiment shown, the pressure-side gasket 130 is a seal ing ring molded onto the pressure-side end face 142.

The safety valve 100 further comprises a valve body lid 125, which is releasably attached to the valve body 120 by means of a threaded connection. The valve body 120 has on the pressure side 840 a lid recess 135, adapted to hold the valve body lid 125. The lid recess 135 comprises on its inner circumferential surface a body thread 132, which is adapted to engage with a corresponding lid thread 131 of the valve body lid 125. The inner end face of the valve body lid

125 facing the valve piston 140 serves as the pressure-side stop 128.

The safety valve 100 further comprises a lid gasket 170, which is adapted to sealingly connect the valve body lid 125 to the valve body 120 when both are mounted together.

The safety valve 100 functions as follows: when a pressure P in a pneumatic actuator 800, in particular in a pneumatic clutch actuator 802, is below a mini mum leakage pressure PLMIN, an airflow AF can pass from the pressure port 122 through the bypass conduit 150 to the release port 124. When the pressure P reaches or exceeds the minimum leakage pressure PLMIN, the pressure force FP is high enough to compress the valve piston spring 160 and lift the valve piston 140 from its pressure-side end position SP2. In such condition, the air flow AF is still able to pass from the pressure port 122 via the bypass conduit 150 to the release port 124.

Once the rising pressure P reaches or exceeds the maximum leakage pressure PLMAX, the valve piston 140 reaches the release-side end position SP1 and the airflow between the pressure port 122 and the release port 124 is blocked by the release-side gasket 134, 134.1, 134.2, sealing off the release port 124, or ports 124.1, 124.2. In this case, the pressure P at the pressure port 122 and in the pneumatic actuator 800 can further increase, preferably for actuating a pneumatic system 880 such as a pneumatic clutch 882.

The valve body comprises a fixation thread 906 for positively locking the safety valve 100 in the pneumatic conduit 798 at an interface 900 between the valve body 120 and the pneumatic conduit 798.

Fig. 2A and Fig. 2B show a second preferred embodiment of a safety valve 100' according to the concept of the invention. The safety valve 100' is shown in a schematic cross-sectional side view in Fig. 2A.

Compared to the first embodiment of the safety valve 100, the second embodi ment of the safety valve 100' comprises a bypass conduit 150 with a circumfer entially open cross-section 154. The term "circumferentially open cross-section" means that the cross-section of the bypass conduit 150 is not completely cov ered by material, as the bypass conduit 150 extends along a surface, resulting in a channel open on at least one side, such as a groove. In the embodiment shown, the bypass conduit 150 is in the form of a groove 155 extending parallel to the valve axis VA along an inner circumferential surface 126 of the valve body 120. The groove 155 extends from a release-side conduit end 155.1 to a pressure-side conduit end 155.2. The axial dimension and arrangement of the groove 155 is such that the further pressure-side gasket 130' exceeds the pressure-side conduit end 155.2 when the valve piston 140 travels to the pressure-side end position SP2, and also such that the further pressure-side gasket 130' exceeds the release-side con duit end 155.1 when the valve piston 140 travels to the release-side end posi tion SP1. Consequently, no airflow, in particular no release airflow AF, between the pressure port 122 and the release port 124 is possible when the valve pis ton is either in the release-side end position SP1 or in the pressure-side end position SP2.

By blocking the release airflow AF also in the pressure-side end position SP2 (in addition to the release-side end position SP1 compared to the first embodi ment), the second embodiment advantageously inhibits any airflow AF, also in an opposite direction from the release port 124 to the pressure port 122, for ex ample when the pressure P at the pressure port 122 is below the ambient pres sure PE. In this case, the valve piston 140 is in the pressure-side end position SP2, sealing the pressure port 122 and preventing any airflow through the pres sure port 122 into the pneumatic actuator 800.

In other words, the bypass conduit 150 in the form of the groove 155 is only functional (i.e. only permits an airflow) when the valve piston 140 is in between its two end positions SP1 , SP2.

As a further difference to the first embodiment, the safety valve 100' comprises - instead of a pressure-side gasket 130 - a further pressure-side gasket 130' which is arranged on an outer circumferential surface 145 of the valve piston 140.

Due to the form of the bypass conduit 150 with the open cross-section 154 and the further pressure-side gasket 130' moving relative to the bypass conduit 150, no further gasket, in particular no release-side gasket 134, is needed. Fig. 3 shows an excerpt of a third preferred embodiment of a safety valve 100", comprising an alternative pressure-side gasket 130" for sealingly blocking an airflow AF through the annular passage 146. The alternative pressure-side gas ket 130" can in particular be used as an alternative in the first embodiment shown in Fig. 1. The alternative pressure-side gasket 130" is attached to a fur ther valve body lid 125', which in the present embodiment is formed as a wash er 127. The washer 127 is mounted to the valve body 120 in a positively locking manner, here axially locked in a lid recess 135 by means of a body rim 133. Preferably, the body rim 133 is created by a bordering process or the like form ing process, after the valve body lid 125 is inserted into the lid recess 135.

In the present embodiment, the alternative pressure-side gasket 130” is molded onto the washer 127. The alternative pressure-side gasket 130" is preferably made of rubber. The alternative pressure-side gasket 130" is overmolded over the washer 127, or as shown here, onto the washer 127.

Fig. 4 shows a pneumatic actuator 800 in the form of a pneumatic clutch actua tor 802. A safety valve 100 according to the concept of the invention, in particu lar all of the shown embodiments of a safety valve 100, 100', 100” can be ap plied in the shown pneumatic actuator 800. The pneumatic clutch actuator 802 comprises an actuator piston 820, which is axially movable within an actuator body 830. The actuator piston 820 has a pressure side 840 facing a pressure chamber 846 of the pneumatic actuator 800. When a pressure P is applied on the pressure side 840 of the actuator piston 820, an actuation force FA results, acting on the actuator piston 820. Consequently, an actuation is effected by moving the actuator piston 820. The actuator piston 820 has a release side 860 on the opposite side of the pressure side 840. A safety valve 100 according to the concept of the invention is arranged in the actuator piston 820, with its pres sure port 122 facing the pressure side 840 and its release port 124 facing the release side 860.

A safety valve 100 according to the concept of the invention, in particular all of the shown embodiments of a safety valve 100, 100', 100", can be applied in other pneumatic actuators 800, in particular can be arranged in a place other than an actuator piston 820, for example in a receptacle in a housing of the pneumatic actuator 800. In such cases, the safety valve can be pneumatically connected to the pressure side 840 and/or the release side 860 by means of pneumatic passages or conduits, such as a pressure conduit 848 and/or a re lease conduit 868 as shown in Fig. 5.

The previous figures illustrate use of safety valve 100, 100' or 100” within pneumatic clutch actuator 802 only for the sake of exemplary illustration. It is noted however, that safety valve 100, 100' or 100” can be used in another pneumatic conduit 798, for instance, as part of a pneumatic transmission actua tor 804 (shown in Fig. 5) or gearbox actuator (not shown in any of the figures) where it forms part of an interface between a closed space within said pneumat ic transmission or gearbox actuator and atmosphere, in order to relieve pres sure from the closed space when a predetermined pressure is achieved. In case of using safety valve 100, 100' or 100” as part of the pneumatic transmis sion actuator, safety valve 100, 100' or 100” need not be provided as part of an actuator piston (not shown in any of the figures) of the transmission actuator.

For instance, safety valve 100 can be part of various inlets and/or outlets within the transmission actuator that interacts with the external atmosphere.

Fig. 4 illustrates use of safety valve 100 within pneumatic clutch actuator 802 only for the sake of exemplary illustration. It is noted, however, that safety valve 100 can be used, for instance, as part of a pneumatic transmission or gearbox actuator where it forms part of an interface between a closed space within said pneumatic transmission or gearbox actuator and atmosphere, in order to relieve pressure from the closed space when a predetermined pressure is achieved. In case of using safety valve 100 as part of the pneumatic transmission actuator, safety valve 100 need not be provided as part of an actuator piston of the transmission actuator. For instance, safety valve 100 can be part of various in lets and/or outlets within the transmission actuator that interacts with the exter nal atmosphere. Fig. 5 shows an excerpt of another example of an electropneumatic actuator 800 with a safety valve 100, wherein the electropneumatic actuator 800 is in the form of a pneumatic transmission or gearbox actuator 804 used in association with a vehicle gearbox (not shown in Fig. 5), in a pneumatic diagram. In the shown embodiment, the safety valve 100 is not arranged in an actuator piston 820, but in an electro pneumatic valve module 890 as a part of the electro pneumatic actuator 800. The safety valve 100 (explained in various embodi ments) is arranged in a pneumatic conduit 798 in the electro pneumatic valve module 890 (extending from a pressure side 840). The pneumatic conduit 798, and consequently also the safety valve 100, is pneumatically connected to the pressure side 840 by means of a pressure conduit 848. Preferably, the pressure conduit 848 is pneumatically connected to the pressure side 840 of an actuator piston 820, for example of a pneumatic clutch actuator 802 arranged outside of the electro pneumatic valve module 890, as shown here. The pneumatic conduit 798, and consequently also the safety valve 100, is pneumatically connected to a release side 860 by means of a release conduit 868. An exemplary general working principle of pneumatic actuator 800 is discussed herewith.

In accordance with the present example as shown in Fig. 5, the electropneu matic valve module 890 is controlled by an Electronic Control Unit 890.5, which is configured to at least transmit electronic control signals to individual valves 890.2 and 890.3. Inlet solenoid valves are labeled in Fig. 5 as 890.2 whereas exhaust solenoid valves labeled as 890.3. Both inlet and exhaust solenoid valves 890.2 and 890.3 receive control signals to open/close from ECU 890.5 depending on whether pneumatic clutch actuator 802 needs to be activated or deactivated.

A pneumatic inlet 890.1 receives pressurized pneumatic air and passes through firstly, inlets of inlet solenoid valves 890.2, which are shown in a closed state in Fig. 5. The outlets of inlet solenoid valves 890.2 lead to both pressure side 840 as well as to inlets of exhaust solenoid valves 890.3. In the illustrated example, exhaust solenoid valves 890.2 are also shown in a closed state. If exhaust so lenoid valves 890.3 are in open state, the pressurized air present in the line in- cheated as pressure side 840 and/or in the outlets of inlet solenoid valves 890.2 are connected to release side or exhaust 860 via exhaust lines 890.4.

In accordance with the present example, in order to maintain pressure at pres sure side 840 (connection line to actuator 802), safety valve 100 is provided at pressure conduit 848. When the residual or remaining pressure in conduit 848 is above a certain threshold, safety valve 100 opens and a connection is estab lished between conduits 848 and 868 and/or release port 124 of safety valve 100. Thereafter said residual or remaining pressure is exhausted at release side 860. In the present example, there are two inlet solenoid valves 890.2 and two exhaust solenoid valves 890.3 are shown for the sake of illustration. However, a simplified construction with one inlet and one exhaust solenoid along with safety valve 100 can also be envisaged by the skilled person.

Fig. 6 schematically shows a vehicle 1000 in the form of a commercial vehicle 1010, comprising a pneumatic actuator 800 in the form of a pneumatic clutch actuator 802 with a safety valve 100 according to the concept of the invention. The P pneumatic clutch actuator 802 comprises an actuator piston 820 for ac tuating a pneumatic system 880 such as a pneumatic clutch 882. The pneumat ic clutch actuator 802 is pneumatically connected to a pressurized air supply unit 560.

List of reference signs (part of the description)

100, 100’, 100” safety valve 120 valve body 122 pressure port

124 release port

124.1 first release port

124.2 second release port

125 valve body lid

126 inner surface of the valve body

127 washer

128 pressure-side stop

129 release-side stop

130 pressure-side gasket

131 lid thread

132 body thread

133 body rim

134 release-side gasket

134.1 first release-side gasket

134.2 second release-side gasket

135 lid recess

140 valve piston

142 pressure-side end face

144 release-side end face

145 circumferential surface of the valve piston

146 annular gap 150 bypass conduit

152 circumferentially closed cross-section

153 cylindrical channel

154 circumferentially open cross-section

155 groove

155.1 release-side conduit end

155.2 pressure-side conduit end 160 valve piston spring 162 spring constant

170 lid gasket

560 pressurized air supply unit

798 pneumatic conduit

800 pneumatic actuator

802 pneumatic clutch actuator

804 pneumatic transmission actuator

820 actuator piston

830 actuator body

840 pressure side

846 pressure chamber

848 pressure conduit

860 release side

868 release conduit

880 pneumatic system

882 pneumatic clutch

890 electro pneumatic valve module

890.1 pneumatic inlet

890.2 inlet solenoid valves

890.3 outlet solenoid valves

890.4 exhaust or outlet lines from outlet solenoid valves 890.3

890.5 Electronic Control Unit (ECU)

900 interface

906 fixation thread 1000 vehicle 1010 commercial vehicle

AF release airflow FA actuation force FP pressure force P pressure PE ambient pressure PLMAX maximum leakage pressure

PLMIN minimum leakage pressure

VA valve axis