A cylinder piston device

Abstract: According to an illustrative example of the invention a gas spring is provided with an emergency exit permitting escape of pressurized gas in case of said pressurized gas exceeding a predetermined pressure. The emergency exit is provided by a radial bore (13) through the cylinder (1) or longitudinal grooves (20)(13). The radial bore is covered unter normal conditions by a piston rod seal (6). This piston rod seal (6) is axially displaceable by said pressurized gas at said predetermined pressure such that the radial bore (13) is opened for escape of pressurized gas.

Description: BACKGROUND OF THE INVENTION Cylinder piston devices like gas springs or hydropneumatic springs or hydromechanic springs are frequently used as positioning and gravity compensating elements in many mechanical constructions, for example, in motor vehicles for positioning and weight compensation of boot flaps or engine hoods. Moreover, such cylinder piston devices are used as pressure storing elements. The extension force of such cylinder piston devices is adapted to the respective application by selecting the pressure of a fluid within the respective cylinder piston device. The pressure of this fluid within the cylinder piston device can be increased considerably beyond the respective operational pressure by increase of temperature or by mechanical deformation of the device itself or the mechanical construction incorporating the respective cylinder piston device. STATEMENT OF THE PRIOR ART From the German patent application 24 57 938 it is known to provide breaking points on at least one of the cylinder and the piston rod to act as emergency exit for the respective pressurized fluid. In case of temperature increase by fire or in case of mechanical deformation of the respective vehicle by a crash accident the cylinder or piston rod can break. Thus the pressurized fluid can escape. There is, however, a risk that parts of the cylinder piston device are separated from the remainder of the cylinder piston device at the breaking points. The separated parts may fly away with high velocity and are a risk for sensitive parts of the respective mechanical construction and for persons standing close to the cylinder piston device. Further from the German utility model DE-U-8906615 there is known a cylinder piston device in which a cavity defining the working chambers of the cylinder piston device within the cylinder member is connected to atmosphere via two openings which, under normal operational conditions are closed by a meltable safety valve member. A first one of these openings is disposed in a circumferential wall of the cylinder member and connects a chamber containing a fire extinguishing fluid with atmosphere. A second one of the openings is disposed in a floating wall member separating the afore-mentioned chamber from the cavity within the cylinder member and supported by the pressure of the fire extinguishing fluid. In case the temperature of the atmosphere surrounding the cylinder piston device exceeds a predetermined value, the safety valve members disposed in the respective openings melt and thereby allow a discharge of the fire extinguishing fluid and the pressurized gas or fluid within the cavity of the cylinder member to atmosphere. As the material of the melted safety valve members is expelled under the high pressure within the cylinder piston device to the exterior with a high velocity, there arises the danger that the expelled particles of the melted safety valve members lead to a damage of other members disposed in the surroundings of the cylinder piston device. OBJECT OF THE INVENTION It is a primary object of the present invention to provide a cylinder piston device with an emergency exit for the respective pressurized fluid in which an escape of the pressurized fluid without the risk of constructional members flying away is possible. It is a further object of the present invention to provide a cylinder piston device which is in case of an opening of the emergency exit still operable at least to such an extent that the piston rod is still axially guided by the cylinder. It is a further object of the present invention to provide a cylinder piston device in which the opening of the emergency exit occurs within a relatively narrow range adjacent a predetermined temperature and/or within a narrow range adjacent a predetermined pressure of the fluid. It is a further object of the present invention to provide a cylinder piston device which can be easily and at low costs manufactured in accordance with usual design principals. SUMMARY OF THE INVENTION A cylinder piston device comprises a cylinder member having an axis, a circumferential wall and two ends and defining a cavity within the cylinder member axially between the two ends. A piston rod member is axially guided through at least one of the two ends by piston rod guiding and sealing means. A volume of pressurized fluid is provided within the cavity and acts onto the piston rod member. At least one emergency exit permits escape of fluid from said cavity under emergency conditions. The piston rod member is telescopically movable with respect to the cylinder member against the action of the pressurized fluid, and the emergency exit is located adjacent one of the first and second ends. Under normal operational conditions the emergency exit is closed by a valve unit in sealing engagement with an internal face of the circumferential wall. The valve unit has a first side exposed to the pressurized fluid within the cavity and is axially supported adjacent a second side thereof by a support structure maintaining the valve unit in a closing condition under normal operational conditions against the pressure of the pressurized fluid acting on the first side, such that under normal operational conditions the valve unit interrupts communication between the cavity and atmosphere. The valve unit is transferable by the pressure of said pressurized fluid from the closing condition to an opening condition under which the emergency exit provides a fluid connection between the cavity and atmosphere, in response to occurrence of an emergency condition, said transition being obtained by resilient axial deformation of the support structure or axial collapse of the support structure or plastic axial deformation of the support structure or supporting said valve unit against axial displacement under emergency conditions by said support structure in a support area covering only a part of said first side. The cylinder member and the piston rod member have basic operational shapes. The basic operational shapes of the cylinder member and the piston rod member are substantially unchangeable in case of an opening of the emergency exit. As the shape of the cylinder member and the shape of the piston rod member remain substantially unchanged in case of an opening of the emergency exit there is no risk of parts of the cylinder member and the piston rod member flying away into the sourrounding space. The piston rod member remains telescopically movable with respect to the cylinder member along a major part of an operational stroke of the piston rod member in case of the emergency exit being opened. As a result thereof the constructional parts of the construction incorporating the respective cylinder piston device are still movable with respect to each other when the emergency exit is opened due to increased temperature or due to increased pressure. While the expected function of the cylinder piston device of, for example, weight compensation is not further fulfilled after escape of the pressurized fluid the movement of the respective parts of the mechanical construction by hand is not prevented. This can be of considerable value in case of an accident especially a fire accident. If the piston rod is provided with a piston unit within a cavity and a piston unit is movable along an operational range of movement with respect to the cylinder member, the emergency exit should be located at a location of the cylinder member axially remote from the operational range of movement. In order to prevent flying away of the valve unit the cylinder piston device may comprise catching means preventing separation of the valve unit from the cylinder piston device in case of transition of the valve unit from the closing condition towards the opening condition. These catching means may be provided by the cavity itself when the valve unit is provided within the cavity. Preferably the emergency exit and the valve unit are located at a location outside an operational range of movement of a piston unit connected with the piston rod member inside the cavity. Thus any conflict of the piston unit with the valve unit is avoided. For example, the emergency exit and the valve unit may be located adjacent the guiding and sealing means of the piston rod member. Alternatively, the emergency exit and the valve unit may be located adjacent an end wall of the cylinder member remote from the guiding and sealing means. The valve unit may be a sliding valve unit scalingly movable along a sliding face of the cylinder piston device and the emergency exit may intersect with the sliding face. The support structure can be sensitive to the predetermined value of either the pressure of the fluid and/or the temperature-sensing location of the cylinder piston device. The temperature-sensing location is preferably the location of the support structure itself. The support structure may have a temperature-sensitive support capability decreasing with increasing temperature such that at a predetermined value of temperature, the support capability is insufficient to maintain the valve unit in the closing condition against the action of a corresponding predetermined pressure of the pressurized fluid. The support structure may comprise spring means, and preferably prestressed spring means. The annular valve unit may be part of the piston rod guiding and sealing means. Such the piston rod guiding and sealing means fulfils a second function besides its guiding and sealing function. Thus the total design becomes less expensive and requires a reduced number of components. The support structure may be axially supported adjacent an end thereof remote from the annular valve unit by the cylinder member adjacent the respective end thereof. Preferably the support structure comprises an annular shearing zone. A most convenient form of the support structure comprises two axially overlapping and radially off-set ring portions inter-connected by radial connection means. These radial connection means are separable in response to a predetermined axial force exerted by the pressurized fluid through the annular valve unit onto the annular support structure. Thus the ring portions are telescopically movable with respect to each other in response to separation of the radial connection means. The radial connection means may be an integral destroyable part of said ring portions. The support structure may be made of a material of a rigidity decreasing with increasing temperature. Thus in case of a fire accident the support structure becomes weaker and is finally overcome by the force exerted by the pressurized fluid. The spring means may, for example, comprise a stack of cup springs. The emergency exit may comprise at least one bore extending in radial direction through the circumferential wall at or adjacent the valve unit. Thus the bore may be covered or uncovered according to the axial position of the valve unit. Alternatively, the emergency exit may comprise at least one substantially axially extending groove in the internal face of the circumferential wall adjacent the valve unit. In this case the fluid passage means are opened when the groove extends across the annular valve member. The valve unit may be axially supported against the pressure of the pressurized fluid by a support face of the support structure which supports only a part of the cross-sectional area of the annular valve unit, such that the destruction of the valve unit occurs by shearing. The design principle of a destroyable valve unit may be realized in practice as follows: the valve unit is an annular valve unit located radially between the circumferential wall and the piston rod member. The annular valve unit is axially supported against the pressure of the pressurized fluid by an annular support face. This annular support face supports, however, only one of two radially adjacent ring portions of the annular valve unit. A second one of the ring portions is unsupported. The first and the second ring portions are axially shearable by the pressurized fluid. The shearing stability may be also influenced by the temperature. Also with this embodiment the annular valve may be an annular piston rod sealing member such that the annular valve unit fulfils a double function. The annular valve unit may comprise in such a construction a resilient sealing material reinforced by a reinforcing ring member. This reinforcing ring member may be provided with a weakened zone sensitive to shearing forces. The emergency exit may comprise a fluid collecting chamber within the cylinder member. The fluid collecting chamber may have an exit towards atmosphere. The guiding and sealing means may comprise an annular guiding member having an internal guiding surface. In such a construction the emergency exit may comprise at least one substantially axially extending groove in the guiding surface. The pressurized fluid is preferably a pressurized gas. In this case the cylinder piston device acts as a so-called gas spring. BRIEF DESCRIPTION OF THE DRAWINGS The invention will be explained in greater detail hereinafter with reference to embodiments shown in the accompanying drawings in which Fig. 1 is a longitudinal section through a pneumatic gas spring with a destroyable support bush; Fig. 2 shows a detail of a gas spring in the region of the piston rod seal with a support ring weakenable at increasing temperature; Fig. 3 shows the region of the piston rod seal of a gas spring with a support spring; Fig. 4 shows the region of the piston rod seal of a gas spring, werein the fluid passage is formed by a longitudinal groove; Fig. 5 shows a further embodiment in which the piston rod seal is provided with a destroyable disk and Fig. 6 shows the gas spring according to Figure 5 with the disk being broken. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS When employing such cylinder piston devices in the construction of motor vehicles to simplify operation of the boot flap or the engine hood, pneumatic or hydropneumatic springs ar preferred. For this purpose, the cylinder piston device is articulated on the one hand to the flap or hood and, on the other hand, to a part which is rigid with the chassis. The gas spring according to Figure 1 has a cylinder 1 in the cavity 2 of which there is provided a pressurized fluid preferably a gas filling. A piston rod 4 is provided with a piston 3 and is guided through a piston rod guide 5 and a piston rod seal 6 in the cylinder 1. The cavity 2 is sealed from the exterior. At least a small quantity of liquid lubricant is provided in the cavity 2 for lubricating the piston rod 4. A spacer bush 7 is supported on the one hand by a radially inwards directed annular projection 8 acting as a stop and serves, on the other hand, as an abutment for the piston rod seal 6. Between the piston rod guide 5 and the piston rod seal 6 there is located a destroyable support bush 9 which consists of a radially inner ring portion 10 and a radially outer ring portion 11. These ring portions 10 und 11 are connected by a connecting bridge 12. The connecting bridge 12 is dimensioned such that it breaks from a predetermined axial force acting onto the support bush 9. In this case, the outer ring portion 11 is slid over the inner ring portion 10 so that the piston rod seal 6 can move axially upwardly and, in so doing, passes over and clears bores 13 arranged in the cylinder 1 so that the pressurized fluid in the cavity 2 can escape via these bores 13 into the atmosphere owing to the displacement of the piston rod seal 6. Protection against excess pressure is provided in this way, avoiding an unallowably high rise in pressure in the cavity 2. The connecting bridge 12 of the support bush 9 is designed such that it breaks only when the pressure in the cavity 2 unallowably exceeds a predetermined pressure above the operating pressure, which can occur, for example, during a fire in the vehicle. In the embodiment according to Figure 2, the annular support member arranged between the piston rod guide 5 and the piston rod seal 6 consists of a thermoplastic polymer. The yieldability of this support bush 14 is so great at a predetermined temperature that the piston rod seal 6 clears the bores 13 and the cavity 2 is therefore opened to the atmosphere so that, at an unallowably high temperature of the gas spring, the pressure can be blown out of the cavity 2. Parts which are equivalent to those parts of Figure 1 are designated by the same reference numerals. The embodiment according to Figure 3 exhibits a piston rod seal 6 which is supported against the pressure in the cavity 2 via a pretensioned spring formed by Belleville spring washers 18. These Belleville spring washers 18 are supported on the one hand on a lower end face of the piston rod guide 5 and act onto a contact ring 17 of which the axial movement is limited by a stop 19. The spacer ring 16 rests on the piston rod seal 6 and cooperates with the contact ring 17 so that, in the event of an unallowably high rise in temperature in the cavity 2, the piston rod seal 6 is displaced upwardly against the force of the prestressed Belleville spring washers 18 and the connection between the cavity 2 and the atmosphere via the bores 13 is thus produced. An abutment ring 15 which is supported on the projection 8 of the cylinder 1 is provided for limiting the piston rod seal 6 axially from the cavity 2. The embodiment shown in Figure 4 differs from the one in Figure 1 essentially in that a longitudinal groove 20 located in the cylinder 1 cooperates with the piston rod seal 6. This longitudinal groove 20 bridges over the support bush 9 and the piston rod guide 5 and opens into the atmosphere. As the pressure in the cavity 2 rises above a maximum permitted extreme pressure, the support bush 9 is slid together by breakage of the connecting bridge and the piston rod seal 6 travels over the longitudinal groove 20. The connection between the cavity 2 and the atmosphere via the longitudinal groove 20 is then produced. The longitudinal groove 20 is advantageously formed by cold working so that no splinters or burrs are formed, which could impair operation of the cylinder piston device. A further embodiment of a cylinder piston device shown in Figures 5 and 6 comprises a shearable disk 21 which is embedded into the piston rod seal 6. The upper end face of the piston rod seal 6 rests on an abutment ring 26 which forms a chamber 25 with the internal side of the cylinder 1. This chamber 25 communicates via at least one radially extending channel 24 and an axial groove 23 with the atmosphere. The axial groove can also be replaced be a clearance between the piston rod 4 and the piston rod guide 5, such forming an axial channel which is annular in cross section. The shearable disk 21 has a predetermined breaking point 22 which is designed such that the shearable disk is sheared if a maximum allowable pressure in the cavity 2 is exceeded. The piston rod seal 6 is also divided in such situation and the radially outer part of the piston rod seal resting on the internal wall of the cylinder 1 is pressed with the associated part of the shearable disk 21 into the chamber 25, as shown in Figure 6. The connection between the cavity 2 and the atmosphere is thus produced and the pressurized fluid can escape from the cavity 2 via the radially extending channel 24 and the axial groove 23 into the atmosphere so that the internal pressure of the gas spring is reduced. While specific embodiments of the invention have been shown and described in detail to illustrate the application of the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles as claimed. The reference numerals in the claims are only used for facilitating the understanding and are by no means restrictive.

Claims: A cylinder piston device comprising a cylinder member (1) having an axis (X), a circumferential wall and two ends and defining a cavity (2) within said cylinder member (1) axially between said two ends, a piston rod member (4) axially guided through at least a first one of said two ends by piston rod guiding and sealing means (5,6), a volume of pressurized fluid within said cavity (2) and acting onto said piston rod member (4) and at least one emergency exit (13) permitting escape of fluid from said cavity (2) under emergency conditions, said piston rod member (4) being telescopically movable with respect to said cylinder member (1) against the action of said pressurized fluid, said emergency exit (13) being located adjacent one of said first and second ends, characterized in that said emergency exit (13) is closed under normal operational conditions by a valve unit (6) in sealing engagement with an internal face of said circumferential wall, said valve unit (6) having a first side exposed to said pressurized fluid within said cavity (2) and being axially supported adjacent a second side thereof by a support structure (9) maintaining said valve unit (6) in a closing condition under normal operational conditions against the pressure of said pressurized fluid acting onto said first side such that under normal operational conditions said valve unit (6) interrupts communication between said cavity (2) and atmosphere, said valve unit (6) being transferable by the pressure of said pressurized fluid from said closing condition to an opening condition unter which said emergency exit (13) provides a fluid connection between said cavity (2) and atmosphere, in response to the occurrence of an emergency condition, said transition being obtained by resilient axial deformation of said support structure (18) or axial collapse of said support structure (9) or plastic axial deformation of said support structure (14) or supporting said valve unit (6) against axial displacement under emergency conditions by said support structure (26) in a support area covering only a part of said first side. A cylinder piston device as set forth in claim 1, said piston rod member (4) remaining telescopically movable with respect to said cylinder member (1) along a major part of an operational stroke of said piston rod member (4) in case of said emergency exit (13) being opened. A cylinder piston device as set forth in claim 1 or 2, said piston rod member (4) being provided with a piston unit (3) within said cavity (2), said piston unit (3) being movable along an operational range of movement with respect to said cylinder member (1), said emergency exit (13) being located at a location of said cylinder member (1) axially remote from said operational range of movement. A cylinder piston device as set forth in one of claims 1-3, said cylinder piston device comprising catching means (1) preventing separation of said valve unit (6) from said cylinder piston device in case of transition of said valve unit (6) from said closing condition towards said opening condition. A cylinder piston device as set forth in one of claims 1-4, said emergency exit (13) and said valve unit (6) being located at a location outside an operational range of movement of a piston unit (3) connected with said piston rod member (4) inside said cavity (2). A cylinder piston device as set forth in one of claims 1-5, said valve unit (6) being of annular shape and located adjacent said guiding and sealing means (5,6). A cylinder piston device as set forth in claim 5, said emergency exit and said valve unit being located adjacent an end wall of said cylinder member remote from said guiding and sealing means. A cylinder piston device as set forth in one of claims 1-7, said valve unit (6) being a sliding valve unit (6) sealingly movable along a sliding face of said cylinder member (1), said emergency exit (13) intersecting said sliding face. A cylinder piston device as set forth in one of claims 1-8, said support structure (9) being sensitive to predetermined values of at least one of: pressure of said fluid and temperature at a temperature-sensing location of said cylinder piston device. A cylinder piston device as set forth in claim 9, said support structure (14) having a temperature-sensitive support capability decreasing with increasing temperature such that at a predetermined value of temperature, the support capability is insufficient to maintain said valve unit (6) in said closing condition against the action of a corresponding predetermined pressure of said pressurized fluid. A cylinder piston device as set forth in one of claims 1-10, said support structure (18) comprising spring means (18) and preferably prestressed spring means (18). A cylinder piston device as set forth in one of claims 6-11, said annular valve unit (6) being a component of said piston rod guiding and sealing means (5,6). A cylinder piston device as set forth in one of claims 1-12, said support structure being axially supported adjacent an end thereof remote from said valve unit (6) by said cylinder member (1) adjacent the respective end thereof. A cylinder piston device as set forth in one of claims 1-13, said support structure (9) comprising an annular shearing zone (12). A cylinder piston device as set forth in claim 14, said support structure (9) comprising two axially overlapping and radially off-set ring portions (10,11) interconnected by radial connection means (12), said radial connection means (12) being separable in response to a predetermined axial force exerted by said pressurized fluid through said annular valve unit (6) onto said annular support structure (9), said ring portions (10,11) being telescopically movable with respect to each other in response to separation of said radial connection means (12). A cylinder piston device as set forth in claim 15, said radial connection means (12) being an integral destroyable part of said ring portions (11,10). A cylinder piston device as set forth in one of claims 11-13, said spring means (18) comprising a stack of cup springs of the Belleville type. A cylinder piston device as set forth in one of claims 1-17, said emergency exit (13) comprising at least one bore (13) extending in radial direction through said circumferential wall at or adjacent said valve unit (6). A cylinder piston device as set forth in one of claims 1-17, said emergency exit comprising at least one substantially axially extending groove (20) in said internal face of said circumferential wall adjacent said valve unit (6). A cylinder piston device as set forth in one of claims 1-7, 12 and 13, said valve unit (6) being axially supported against the pressure of said pressurized fluid by a support face of said support structure (26) which supports only a part of the cross-sectional area of said valve unit (6). A cylinder piston device as set forth in claim 20, said valve unit being an annular valve unit (6) located radially between said circumferential wall and said piston rod member (4) and being axially supported against the pressure of said pressurized fluid by an annular support face (26), said annular support face (26) supporting only one of two radially adjacent ring portions of said valve unit (6), a second one of said ring portions being unsupported, said first and said second ring portions being subject to axial shearing forces by said pressurized fluid. A cylinder piston device as set forth in one of claims 1 - 21, said valve unit (6) comprising a resilient sealing material reinforced by a reinforcing ring member (21), said reinforcing ring member (21) optionally being provided with a weakened zone (22) sensitive to shearing forces. A cylinder piston device as set forth in one of claims 1-22, said emergency exit comprising a fluid collecting chamber (25) within said cylinder member (1), said fluid collecting chamber (25) having an exit (23) towards atmosphere. A cylinder piston device as set forth in one of claims 1-23, said guiding and sealing means (5,6) comprising an annular guiding member (5) having an internal guiding surface, said emergency exit comprising at least one substantially axially extending groove (23) in said guiding surface. A cylinder piston device as set forth in one of claims 1-24, said pressurized fluid being a pressurized gas.

Inventors: JOBELIUS KLAUS-DIETER, MORGEN HELMUT, SPURZEM HEINRICH, VOELPEL STEFAN, JOBELIUS, KLAUS-DIETER, MORGEN, HELMUT, SPURZEM, HEINRICH, VOELPEL, STEFAN, Völpel, Stefan
Applicants: STABILUS GMBH
Application year: 1992
Main classification: F16F9
IPC codes: E05F3, F16F9