Cylinder piston device

Abstract: A cylinder piston device comprises a cylinder (1) and a piston rod (2). The piston rod (2) is guided through one end of the cylinder inwards and outwards of the cylinder (1). A damping body (8,108,208) is provided for damping the axial movement of the piston rod (2) with respect to the cylinder (1). This damping body (8,108,208) is deflectable in response to change of direction of the axial movement. A deflection of the damping body (8,108,208) results in change of the frictional resistance.

Description: This invention relates to a cylinder piston device in which the movement of the piston rod with respect to the cylinder is frictionally damped. Such cylinder piston devices are used e. g. as gas springs provided for facilitating the lifting movement of a trunk lid in a motor-vehicle. They may be used, however, also as frictional dampers e. g. in washing machines. Moreover, they may be constructed as combined dampers which have both a frictional and a fluidic damping. From German laid open publication DE-A- 2 834 649 a cylinder-piston device is known which comprises a plurality of elastic annular discs which are fixed with respect to the the piston rod of the cylinder-piston device. The elastic annular discs ensure the development of a frictional force upon movement of the piston rod with respect to the cylinder by slidingly engaging a friction surface of the cylinder. In order to ensure different frictional forces depending on the direction of movement of the piston rod with respect to the cylinder, the annular discs are supported by a piston member in the entire radial and circumferential extension on one of the axial end faces and by a support disc on the other one of the end faces. The support disc provides a non-circular support face with portions radially extending to a radially outer edge of the annular discs and portions radially extending to an intermediate radial position of the annular discs. Upon movement of the piston rod with respect to the cylinder in a-one-way axial direction (outward direction), the annular discs arc in full face contact with the piston member and provide a high damping force. On axial movement of the piston rod with respect to the cylinder in an other-way axial direction (inward direction) portions of the annular discs allocated to the portions of the support disc extending to the intermediate radial position are deflected with the result that the damping force is reduced. This embodiment has several disadvantages: The elastic annular discs are subject to a complicated shape of deformation and to an uneven frictional wear. Thus, they have a reduced lifetime. Moreover, the selection of the amount of difference between the damping forces allocated to opposite axial directions is relatively poor due to deflectability of the annular discs being restricted to certain portions of the circumference. Moreover, the shape of the support disc is relatively complicated and difficult to be obtained. From German Utility Model 85 02 121 a gas spring is known in which the piston rod is introduced through an end portion of a cylinder. Adjacent this end portion of the cylinder, an annular friction element is provided which may be compressed in axial direction. By the compression of the annular friction element this element is brought in frictional contact with the cylindrical surface of the piston rod so that a frictional action is exerted onto the piston rod, when the piston rod is moved in axial direction with respect to the cylinder. From US Patent 4,881,723 a gas spring is known in which a piston accommodated within the cavity of a cylinder is provided with an annular friction member frictionally engaging the internal cylindrical face of the cylinder. From German Publication 36 27 816, corresponding to US Patent 4,792,127, a gas spring is known in which an annular friction member is fixed to a piston rod, and a mechanical spring provided radially inwards of the annular friction member radially urges the friction member towards the internal cylindrical face of the cylinder. Further frictionally damped cylinder piston devices are known from French Publication 2 164 158, French Patent 1 488 878, German Publication 29 42 716, German Patent 26 22 879 and German Publication 24 21 007. It is a primary object of the invention to provide a frictionally damped cylinder piston device in which the damping action can be adapted to varying need for damping action for different directions of movement. It is a further object of the present invention to provide a frictionally damped cylinder piston device which can be assembled in a most simple and economic way from most simple and easily available components. A cylinder piston device comprises a cylinder member having an axis and two ends and further comprises a piston rod member axially movable with respect to the cylinder member through at least one of said two ends. Frictional damping means are provided for damping the axial movement of the piston rod member with respect to the cylinder member. The frictional damping means comprises at least one elastic damping body. This at least one elastic damping body has a first portion and a second portion. The first portion is axially fixed with respect to one of the cylinder member and the piston rod member. The second portion has a friction-face-engagement face frictionally engageable with a substantially axially extending friction face of the other one of the cylinder member and the piston rod member. The elastic damping body is prestressed against the friction face for exerting a damping force onto the piston rod member when being axially moved with respect to the cylinder member. The fixation of the first portion with respect to said one of the cylinder member and the piston rod member is effected by support elements axially adjacent to oppositely axially directed end faces of the elastic damping body and substantially fixed in axial direction with respect to said one of the cylinder member and the piston rod member. A primary one of the support elements provides a primary support face extending in a radial direction toward the other one of the cylinder member and the piston rod member to a circumferential edge line nearer to said other one of the cylinder member and the piston rod member. A secondary one of the support elements provides a secondary support face extending in a radial direction towards said other one of the cylinder member and the piston rod member to a further circumferential edge line more remote from said other one of the cylinder member and the piston rod member. The second portion of the elastic damping body is deflectable between a rest position closer to the primary support element and a deflected position less close to the primary support element. The second portion is transformed flexibly moved from said deflected position toward the rest position in response to a one-way axial movement of the piston rod member with respect to the cylinder member and is flexibly moved from said rest position toward the deflected position in response to an other-way axial movement of the piston rod member with respect to the cylinder member. The respective deflection is due to frictional engagement of the friction-face-engagement face and the axially extending friction face. The axial deflection of said elastic damping body provides a larger damping force during said one-way axial movement and a smaller damping force during the other-way axial movement. Such a device is known from DE-A-2 834 649. According to the invention defined by claim 1 the further circumferential edge line is substantially circular about the axis. By the variation of the frictional force in response to the direction of axial movement the behaviour of the cylinder piston device can be adapted to various appliances in which the cylinder piston device is included. E. g., it is frequently necessary that in the damper of a washing machine, the damping action is dependent on the direction of axial movement. Particularly in gas springs used for lifting trunk lids or motor bonnets, different friction forces may be required for the lifting movement and the lowering movement. The elastic damping body may be made of various materials, such as synthetic plastic materials, natural and synthetic elastomeric materials. Preferably, the elastic damping bodies have an annular shape about the axis. The damping bodies may be made by usual manufacturing methods known in the art for shaping plastic and elastic materials. E. g., the elastic damping body may be produced by injection moulding. The support elements may have annular support faces substantially orthogonal with respect to the axis. The second portion of the elastic damping body may have a friction face-engagement face engageable with the friction face, which friction face-engagement face is convex towards the friction face when viewed in a plane of section containing the axis. By selecting the radius of curvature of the friction face-engagement face, the degree of variation of the damping force in response to change of axial direction may be influenced. The second portion of said annular elastic damping body may be provided with slots opening towards the friction face. Such slots may be used for providing an additional fluidic damping effect, when the piston rod is moved with respect to the cylinder member. This is particularly true, if the damping body is axially fixed on the piston rod as a piston member or as a part of a piston member. The annular elastic damping body may have an annular recess about the axis in at least one end face thereof orthogonal with respect to the axis. This annular recess is preferably provided in the second portion. By such an annular recess the deflecting behaviour of the damping body may be varied. If a high degree of deflection is desired, the annular elastic damping body may be provided with axial opposite annular recesses in both end faces thereof. The first portion of the elastic body may be fixed with respect to the cylinder member, and the second portion of said elastic body may thus be engageable with a friction face of the piston rod member. The elastic damping body may be located within the cylinder member adjacent one end of the cylinder member through which the piston rod member is guided. If a guiding and sealing unit is provided at this end, the elastic damping body may be located adjacent this guiding and sealing unit. In an alternative embodiment, the elastic damping body is fixed with the first portion thereof with respect to the piston rod member, and the second portion of the elastic damping body is engageable with an internal friction face of the cylinder member. In particular, the elastic damping body may be fixed to an inner end portion of the piston rod member within the cylinder member. The elastic damping body may be a part of a piston unit provided at the inner end of the piston rod member. As mentioned above, besides the frictional damping, there may be provided a fluidic damping. Such fluidic damping can be achieved in that a throttled passage extends between two working chambers provided on both sides of a piston unit. The throttled passage may be located within the damping body or within another component of a piston unit. It is also possible that the flow resistance of the throttled passage is responsive to the direction of relative movement of the piston rod member on the one hand, and the cylinder member on the other hand. At least two elastic damping bodies may be provided which are deflectable in opposite axial directions for obtaining a desired damping behaviour in opposite directions of axial movement. E.g., the piston unit may comprise two annular elastic damping bodies and a support disc therebetween. The principles of the present invention may e. g. be applied to a gas spring in which the cylinder member contains a pressurized gas. Such gas springs are used e. g. for assisting the opening movement of a trunk lid or motor bonnet in a motor-vehicle. The expelling force of the piston rod member is defined by the pressure of the pressurized gas and the cross-sectional area of the piston rod. This expelling force is adapted to the weight of the respective part, i. e. the trunk lid or motor bonnet. The expelling force may exceed the weight of the respective part such that the respective part is moved upwards by the expelling force until respective abutments come into engagement. In this case, no intermediate positions of the respective part can be maintained. It is possible, however, due to the action of the frictional damping means of the present invention to maintain the respective part in an intermediate position. It is only necessary to select the frictional damping means such that the resulting friction force exceeds the difference between the expelling force of the gas spring or gas springs on the one hand and the effective weight of the respective part on the other hand. Such, the assistance of the gas spring for facilitating the opening movement further exists and, nevertheless, the respective part, i. e. trunk lid or motor bonnet, can be located in desired intermediate positions. An analogous situation occurs, when the gas spring per se is selected such that it cannot lift the respective part without the help of the operator. In such case, the respective part, i. e. trunk lid or motor bonnet, would sink downwards, after the operator has removed his hands from the respective part. If, however, according to the present invention, frictional damping means are provided, these frictional damping means may again be selected so that the friction force exceeds the difference between the weight of the respective part and the expelling force of the gas spring or gas springs. In this case again, the lifting assistance of the gas spring is maintained and nevertheless, the respective part can be located in any desired lifted position. The overall frictional damping force for opposite directions of movement may be equalized by a combination of at least two elastic damping bodies. The principle of this invention can also be applied to hydraulic dampers such that besides the velocity dependent fluidic damping action, a frictional damping action exists. The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed hereto and forming a part of the disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which there are illustrated and desscribed preferred embodiments of the invention. The invention will be explained in greater detail hereinafter with reference to an embodiment shown in the accompanying drawings in which Fig. 1 shows a partial section of a gas spring; Fig. 2 shows a longitudinal section of an elastic damping body to be used in a gas spring according to Fig. 1; Fig. 3 shows an end view of the elastic damping body of Fig. 2; Fig. 4 shows a modification of the gas spring of Fig. 3; Fig. 5 shows a detail at the location Z of Fig. 4; Fig. 6 shows an alternative embodiment of a gas spring and Fig. 7 shows an end view of an elastic damping body as used in Fig. 6. In Fig. 1, the cylinder of a gas spring is designated by 1, and the piston rod member is designated by 2. The piston rod member 2 is guided through a sealing member 5 and a guiding member 4 at one end of the cylinder. The piston rod member 2 is provided with a connection eye 3 for fastening the gas spring to a construction such as the body work or a movable part of a motor-vehicle. An annular elastic damping body 8 is clamped between a support plate 7 and a support sleeve 9. The support plate 7 is supported by a spacer ring 6, and the support sleeve 9 is axially fixed by a bead 10. The annular elastic damping body is shown in more detail in Figs. 2 and 3. The elastic damping body 8 comprises a radially outer portion 8a which is to be clamped between the support plate 7 and the support sleeve 9. Further, the elastic damping body 8 comprises a radially inner portion 8b. This radially inner portion is provided with radially inwards open slots 8c. The radial inward portion 8b is in contact with the circumferential face 2a of the piston rod member 2. On axial inward movement of the piston rod member 2, the elastic damping body 8 takes the position as shown in Fig. 1. The friction force is relatively small. When the piston rod member 2 moves in axial outward direction, the elastic damping body approaches the support plate 7. Thus, the radial compression of the elastic damping body is increased, and the friction force is also increased. The deflection properties of the elastic damping body can be controlled by the number and cross-section of the slots 8c. The elastic damping body 8 is made of a plastic or elastomeric material, e. g. a foamed polyurethane material. The elastic damping body may be wetted with a lubricant agent for controlling the friction properties. It is to be noted that Figs. 2 and 3 show a most simple elastic damping body having a constant profile along its axis and end faces orthogonal to said axis. This elastic damping body may be easily manufactured in mass production, e. g. by extrusion. The gas spring of Fig. 1 is most adapted for assisting the lifting movement of a trunk lid or motor bonnet: on outward movement of the piston rod member 2 corresponding to lifting movement of the respective vehicle part, there exists a hight friction force. This friction force is larger than the difference between the expelling force of the piston rod member and the effective weight of the vehicle part. Such, the vehicle part comes to a standstill in any position, when the operator stops a manual lifting effect. On inward movement, corresponding to lowering movement of the vehicle part, only a small frictional resistance must be overcome. In the embodiment of Fig. 4, analogous parts are designated by the same reference numbers as in the embodiments of Figs. 1 to 3 increased by 100. The elastic damping body 108 has a modified shape. This damping body 108 is provided with annular recesses 108 d and 108e in the end faces 108f and 108g. The radially outer circumferential surface 108h is convex. The curve defining the convex face 108h is responsible for the variation of frictional damping force in response to change of direction of movement. In the embodiment as shown in Fig. 5, the friction force is at a maximum on outward movement of the piston rod member as shown in Fig. 4, when the elastic damping body 108 is fully supported by the support plate 107. When the piston rod member 102 is moved inwards as shown in Fig. 4, a reduced damping force exists. In Fig. 6 and 7, a third embodiment is shown, in which two damping bodies 208 are fixed to the inner end of the piston rod 202 on both sides of a common support plate 211. The elastic damping bodies 208 have the shape as shown in Fig. 7, similar to the shape as shown in Figs. 2 and 3. Alternatively, the elastic damping bodies 208 could also have a shape as shown in Fig. 5 with the convex circumferential face engaging the internal surface of the cylinder 201. In this embodiment, the right-hand damping body 208 provides a larger frictional force on inward movement and a smaller frictional force on outward movement of the piston rod member 202. On the other hand, the left-hand damping body 208 provides a smaller frictional force on inward movement and a larger frictional force on outward movement. By making the damping bodies 208 identic, one can achieve that the resulting frictional force resisting inward and outward movement of the piston rod member 202 is equal. It is, however, also possible that different damping bodies 208 are used on both sides of the support plate 211 such that the frictional resistance to the movement of the piston rod 202 is different in response to change of direction of movement. Both damping bodies 208 have a first or radially inner portion 208a, a second or radially outer portion 208b and slots 208c. The respective radially outer portion is in frictional engagement with an internal face 201a of the cylinder 201. In Fig. 6 one can see that the two elastic damping bodies 208 are located between a shoulder of the piston rod 202 and an annular ring 220 which both provide respective support elements by a rivet head 221. The reference numerals in the claims are only used for facilitiating the understanding and are by no means restrictive.

Claims: A cylinder piston device comprising a cylinder member (1;101;201) having an axis and two ends and further comprising a piston rod member (2;102;202) axially movable with respect to said cylinder member (1;101;201) through at least one of said two ends, frictional damping means (8;108;208) being provided for damping the axial movement of said piston rod member (2;102;202) with respect to said cylinder member (1;101;201), said frictional damping means (8;108;208) comprising at least one elastic damping body (8;108;208), said at least one elastic damping body (8;108;208) having a first portion (8a;108a;208a) and a second portion (8b;108b;208b), said first portion (8a;108a;208a) being axially fixed with respect to one (1;101;202) of said cylinder member (1;101;201) and said piston rod member (2;102;202), said second portion (8b;108b;208b) having a friction- face-engagement face frictionally engageable with a substantially axially extending friction face (2a;102a;201a) of the other one (2;102;201) of said cylinder member (1;101;201) and said piston rod member (2;102;202), said elastic damping body (8;108;208) being prestressed against said friction face (2a;102a;201a) for exerting a damping force onto said piston rod member (2;102;202) when being axially moved with respect to said cylinder member (1;101;201), said fixation of said first portion (8a;108a;208a) with respect to said one (1;101;202) of said cylinder member (1;101;201) and said piston rod member (2;102;202) being effected by support elements (7,9;107,109;211,202,220) axially adjacent to oppositely axially directed end faces (108f,108g) of said elastic damping body (8;108;208) and substantially fixed in axial direction with respect to said one (1;101;202) of said cylinder member (1;101;201) and said piston rod member (2;102;202), a primary one (7;107;211) of said support elements (7,9;107,109;211,202,220) providing a primary support face extending in a radial direction toward the other one (2;102;201) of said cylinder member (1;101;201) and said piston rod member (2;102;202) to a circumferential edge line nearer to said other one (2;102;201) of said cylinder member (1;101;201) and said piston rod member (2;102;202), a secondary one (9;109;202,220) of said support elements (7,9;107,109;211,202,220) providing a secondary support face extending in a radial direction towards said other one (2;102;201) of said cylinder member (1;101;201) and said piston rod member (2;102;202) to a further circumferential edge line more remote from said other one (2;102;201) of said cylinder member (1;101;201) and said piston rod member (2;102;202), said second portion (8b;108b;208b) of said elastic damping body (8;108;208) being deflectable between a rest position closer to said primary support element (7;107;211) and a deflected position less close to said primary support element (7;107;211), said second portion (8b;108b;208b) being flexibly moved from said deflected position toward said rest position in response to a one-way axial movement of said piston rod member (2;102;202) with respect to said cylinder member (1;101;201) and being flexibly moved from said rest position toward said deflected position in response to an other-way axial movement of said piston rod member (2;102;202) with respect to said cylinder member (1;101;201), the respective deflection being due to frictional engagement of said friction- face-engagement face and said axially extending friction face (2a;102a;201a), said axial deflection of said elastic damping body (8;108;208) providing a larger damping force during said one-way axial movement and a smaller damping force during said other-way axial movement, characterized in that said further circumferential edge line is substantially circular about said axis. A cylinder piston device as set forth in claim 1, said elastic damping body (8) having an annular shape about said axis. A cylinder piston device as set forth in claim 1 or 2, said support elements (7,9) having annular support faces substantially orthogonal with respect to said axis. A cylinder piston device as set forth in one of claims 1 to 3, said second portion (108b) of said elastic damping body (108) having a friction face-engagement face (108h) convex towards said friction face (102a) when viewed in a plane of section containing said axis. A cylinder piston device as set forth in one of claims 1 to 4, said second portion (8b) of said elastic damping body (8) being provided with substantially radially extending slots (8c) opening towards said friction face (2a). A cylinder piston device as set forth in one of claims 1 to 5, said annular elastic damping body (108) having an annular recess (108d,108e) about said axis in at least one end face (108f,108g) thereof orthogonal with respect to said axis, said annular recess (108d,108e) being provided in said second portion (108b). A cylinder piston device as set forth in claim 6, said annular elastic damping body (108) being provided with axial opposite annular recesses (108d,108e) in both end faces (108f,108g) thereof. A cylinder piston device as set forth in one of claims 1-7, said elastic damping body (8) being fixed with respect to said cylinder member (1) and being located within said cylinder member (1) adjacent one end of said cylinder member (1) through which said piston rod member (2) is guided. A cylinder piston device as set forth in claim 8, said elastic damping body (8) being located adjacent a guiding and sealing unit (4,5) of said cylinder member (1) through which said piston rod member (2) is guided. A cylinder piston device as set forth in one of claims 1-7, said elastic damping body (208) being fixed to an inner end portion of said piston rod member (202) within said cylinder member (201). A cylinder piston device as set forth in claim 10, said elastic damping body (208) being part of a piston unit (211,208) provided at the inner end of said piston rod member (202). A cylinder piston device as set forth in one of claims 1 to 11, comprising a combination of at least two elastic damping bodies (208) deflectable in opposite axial directions. A cylinder piston device as set forth in claim 12, said piston unit (211,208) comprising two annular elastic damping bodies (208) and a support disc (211) therebetween, respective second portions (208b) of said two annular elastic damping bodies (208) being deflectable in axial opposite directions. A cylinder piston device as set forth in one of claims 1 to 13, said cylinder piston device being a gas spring comprising at least one chamber containing a pressurized gas. A cylinder piston device as set forth in one of claims 1 to 13, said cylinder piston device being an oscillation damper. A cylinder piston device as set forth in one of claims 1 to 15, said elastic damping body (8) being made of a plastic material and particularly of an elastomeric material.

Inventors: MINTGEN ROLF, MINTGEN, ROLF
Applicants: STABILUS GMBH
Application year: 1991
Main classification: F16F7
IPC codes: F16F11, F16F9, F16F7