Hydraulically adjustable shock absorber for a motor vehicle

Abstract

A hydraulically adjustable shock absorber for a motor vehicle comprises a telescopic shock absorber with a shock absorber housing and a shock absorber rod that moves in a damped manner relative to and immerses in the shock absorber housing, a hydraulic actuator surrounding the shock absorber housing with an actuator housing (6') fixed to the shock absorber housing and a piston unit (7') movable relative to the actuator housing, and a coil spring acting between a first spring support associated with the piston unit (7') and a second spring support associated with the shock absorber rod. The piston unit (7') comprises an annular piston (19') which moves into an annular space (15') formed between a cylindrical inner wall (11') and a cylindrical outer wall (13') of the actuator housing (6') and is sealed against the inner wall (11') and the outer wall (13') of the actuator housing (6').A double-acting sealing ring (40) is arranged on the end face of the ring piston (19'), which provides a dynamic seal against the inner wall (11') of the actuator housing (6') on a first sealing surface (34) and a dynamic seal against the outer wall (13') of the actuator housing (6') on a second sealing surface (41).

Description

[0001] The present invention relates to a hydraulically adjustable spring strut for a motor vehicle, comprising - a telescopic shock absorber with a shock absorber housing and a shock absorber rod which is movable relative to the housing and plunges into the housing, - a hydraulic actuator surrounding the shock absorber housing with an actuator housing fixed to the shock absorber housing and a piston unit movable relative to the actuator housing, - a helical spring acting between a first spring support, which is assigned to the piston unit, and a second spring support, which is assigned to the shock absorber rod, wherein the piston unit comprises an annular piston, which extends into an annular space formed between a cylindrical inner wall and a cylindrical outer wall of the actuator housing and is sealed from the inner wall and the outer wall of the actuator housing. In particular, the present invention relates to a hydraulically adjustable spring strut of the type specified above, in which furthermore - a double-acting sealing ring is arranged on the end face of the annular piston, which provides a dynamic seal against the inner wall of the actuator housing on a first sealing surface and a dynamic seal against the outer wall of the actuator housing on a second sealing surface, and - the inner wall of the actuator housing has a cylindrical guide surface which runs coaxially to the first sealing surface cooperating with the sealing ring and is axially offset relative thereto, wherein an inner guide ring arranged on the piston unit is slidably guided on the guide surface.

[0002] Hydraulically adjustable automotive suspension struts—also known as spring-damper units—are well known. The implemented hydraulic adjustability allows the body to be conveniently lowered, for example, to reduce drag and thus fuel consumption, or raised, particularly to negotiate uneven terrain and / or ramps without the body bottoming out. Fig. 1 shows a known hydraulically adjustable strut whose actuator is in Fig. 2 is shown enlarged. For structural details of this strut, please refer to the explanations contained in the figure description.

[0003] DE 10 2013 222 249 A1 discloses a hydraulically adjustable motor vehicle suspension strut of the generic type. The annular piston is guided on the cylindrical inner wall of the actuator housing. For this purpose, the inner wall of the actuator housing is designed as a "guide tube" that protrudes or extends axially relative to the outer wall of the actuator housing. Two axially spaced annular guide elements are arranged on the annular piston: a first adjacent to the double-acting sealing ring arranged on the end face of the annular piston, and a second near the opposite end of the annular piston associated with the first spring support.

[0004] Another hydraulically adjustable spring strut can be found in DE 10 2007 044 538 A1. Unlike in DE 10 2013 222 249 A1, the annular piston is guided along the outer wall of the actuator housing. For this purpose, a groove-shaped receptacle for a guide band guiding the annular piston is provided on the end section of the outer wall of the actuator housing, which protrudes axially beyond the inner wall of the actuator housing. Another guide band, also inserted into a groove-shaped receptacle, is arranged on the annular piston adjacent to the double-acting sealing ring arranged on its end face.

[0005] The present invention has for its object to provide a hydraulically adjustable spring strut which is improved in terms of practical usability compared to this prior art.

[0006] This object is achieved according to the present invention, as stated in claim 1, in that in a generic hydraulically adjustable spring strut, the guide surface of the inner wall of the actuator housing is constricted relative to its first sealing surface, i.e., has a smaller diameter than the latter. In this case, according to a particularly preferred embodiment of the invention, a scraper ring is arranged on the piston unit adjacent to the inner guide ring, which also bears against the guide surface of the inner wall of the actuator housing. The guidance of the piston unit in the said manner, i.e., at a considerable distance from the end face of the annular piston equipped with the double-acting sealing ring, contributes to a Fig. 1 and Fig. 2 improved support of transverse forces. In addition, damage to the first sealing surface by elements serving to guide the piston unit (particularly in the form of a guide ring) is excluded. By constricting the guide surface relative to the sealing surface, an improved, namely purely axial, force flow can be achieved from the first spring support through the annular piston to its end face equipped with the double-acting sealing ring; this is because the respective guide ring (or the other guide element interacting with the guide surface) and the optionally provided wiper ring can be accommodated in a radially inwardly directed annular projection of the piston unit, i.e. in a respective annular groove provided there. The web located radially outside the said annular groove can (or the webs located radially outside the said annular grooves can) thus be aligned with the opposite end face of the annular piston.these at least overlap.

[0007] By implementing the present invention, several advantages of considerable practical relevance can be achieved in a surprisingly simple manner. Thus, the suspension strut according to the invention is suitable for use in significantly heavier vehicles or vehicles with significantly higher axle loads (e.g., electric vehicles) than is possible with the state of the art according to the Fig. 1 and Fig. 2 applies. In this respect, it is important to note that with the known spring strut (cf. Fig. 1) Due to the radial offset of the remaining annular lands of the annular piston in the area of ​​the two grooves that accommodate the sealing rings that seal against the outer wall and the inner wall of the actuator housing, an axial load on the annular piston leads to its deformation in the sense of a local expansion in the area of ​​the seal that seals against the inner wall of the actuator housing. This creates the risk that the annular piston will jam against the outer wall of the actuator housing under strong axial load, which impairs functional reliability. A weakening of the annular piston, as results in the known spring strut from the existence of the two aforementioned grooves, can also be avoided with the spring strut according to the invention; because it does not require such grooves. This leads to a significant increase in its load-bearing capacity.These advantageous results can even be achieved without increased structural effort; in fact, the structural effort for the spring strut according to the invention can be even lower than that of the prior art according to the . Fig. 1 and Fig. 2.

[0008] According to a preferred development of the present invention, an outer guide ring is arranged on the piston unit adjacent to the sealing ring, which outer guide ring is slidably guided on the sealing surface of the outer wall of the actuator housing. The spatial proximity of the outer guide ring to the sealing ring facilitates the greatest possible distance (see above) between the outer guide ring and an inner guide ring provided in the region of the opposite end of the piston unit. In this sense, the axial distance between the inner guide ring and the outer guide ring particularly preferably corresponds to at least the radius of the first sealing surface.

[0009] Yet another preferred development of the present invention is characterized in that a protective cap is connected to the piston unit, which is movable relative to the actuator housing and is stepped in terms of its diameter such that a wide first region surrounds the outer wall of the actuator housing and a narrow second region surrounds the inner wall of the actuator housing. Such a protective cap is significantly less complex, both in terms of its manufacture and assembly, than a bellows, as required for known generic spring struts, and is also more durable.

[0010] In the following, the present invention is explained in more detail with reference to a preferred embodiment illustrated in the drawing and its comparison with the prior art. Fig. 1 a generic spring strut according to the state of the art, Fig. 2 the actuator of the known spring strut according to Fig. 1 in detailed view and Fig. 3 the actuator of a spring strut according to the invention.

[0011] The Fig. The known hydraulically adjustable spring strut for a motor vehicle, shown in Figure 1 of the drawing, comprises as essential components a telescopic shock absorber 1, a coil spring 2, and a hydraulic actuator 3. The telescopic shock absorber 1 has a shock absorber housing 4 and a shock absorber rod 5 that is movable relative to the shock absorber housing and extends into the shock absorber housing. The hydraulic actuator 3 surrounds the shock absorber housing 4 and has an actuator housing 6 fixed to the shock absorber housing 4 and a piston unit 7 that is movable relative to the actuator housing. The coil spring 2 acts between a first spring support 8, which is assigned to the piston unit 7 of the hydraulic actuator 3, and a second spring support 9, which—by means of the plate 10—is assigned to the shock absorber rod 5.

[0012] As far as the hydraulic actuator 3 is concerned, (cf. Fig. 2) whose actuator housing 6 comprises a first housing part 12 forming a cylindrical inner wall 11 and a second housing part 14 firmly connected to the first housing part and forming a cylindrical outer wall 13. The cylindrical inner wall 11 and the cylindrical outer wall 13 of the actuator housing 6 define an annular space 15, which forms an annular cylinder 17 that can be acted upon via the hydraulic connection 16. A further connection 18 communicating with the annular cylinder 17 is provided for venting the annular cylinder 17.

[0013] The piston unit 7 comprises an annular piston 19, which extends into the annular cylinder 17. Adjacent to its end face 20, a circumferential groove 21 is provided on the outer circumference of the annular piston 19, into which a sealing ring 22 (which seals the annular piston 19 against the outer wall 13 of the actuator housing 6) and a guide ring 23 (“backup ring”) (which guides the annular piston 19 on the outer wall 13 of the actuator housing 6) are received. Furthermore, at the end of the annular piston 19 opposite its end face 20, a further circumferential groove 24 is provided on its inner circumference, in which a sealing ring 25 (which seals the annular piston 19 against the inner wall 11 of the actuator housing 6) and a guide ring 26 (“backup ring”) (which guides the annular piston 19 on the inner wall 11 of the actuator housing 6) are received.

[0014] The piston unit 7 further comprises an end region 28 connected to the annular piston 19 via a cylinder section 27. This serves to connect the piston unit 7 to a support ring 29, on which the spring support 8 assigned to the piston unit 7 is formed. Three measures are provided to prevent the penetration of protective material into the annular cylinder 17. For example, the support ring 19 carries a wiper sleeve 30, which bears against a cylindrical extension 31 of the inner wall 11 of the actuator housing 6. Furthermore, a further wiper ring 32 is fixed to the end region of the inner wall 11 of the actuator housing 6, which - depending on the position of the piston unit 7 - bears against the inner circumference of the support ring 29 or against the inner circumference of the cylinder section 27 of the piston unit 7.And a bellows 33 acts between the piston unit 7 and the actuator housing 6, which is connected on the one hand to the end region of the piston unit 7 and on the other hand to the outer wall 13 of the actuator housing 6.

[0015] A preferred embodiment of a spring strut according to the invention is obtained in that the spring strut according to Fig. 1 of the Fig. 2 in detail illustrated actuator 3 by that actuator 3' according Fig. 3 is replaced.

[0016] The latter is characterized, in deviation from the known spring strut according to Fig. 1 actuator 3 used, is characterized by the following special features: Instead of merging into a thin-walled extension, the inner wall 11' of the actuator housing 6' continues - with a substantially unchanged wall thickness - beyond the area that interacts with the annular piston 19' and defines a first cylindrical sealing surface 34, beyond a step 35 in a constricted area 36. This likewise cylindrical area 36 of the inner wall 11' of the actuator housing 6', which is coaxial with the area that interacts with the annular piston 19', has, axially offset from the first sealing surface 34, a guide surface 37 on which an inner guide ring 38 arranged on the piston unit 7' is slidably guided. Adjacent to the inner guide ring 38, a scraper ring 39 is arranged on the piston unit 7' and bears against the guide surface 37 of the inner wall 11' of the actuator housing 6'.

[0017] The sealing of the annular piston 19' in the annular cylinder 17' is achieved by means of a single double-acting sealing ring 40 arranged on the end face of the annular piston 19'. This creates a dynamic seal against the inner wall 11' of the actuator housing 6' on the first sealing surface 34 and a dynamic seal against the outer wall 13' of the actuator housing 6' on a second cylindrical sealing surface 41 formed on the outer wall 13' of the actuator housing 6'. By means of a pressure groove 42 running on the end face of the sealing ring 40, a pressure-dependent contact force (and thus pressure-dependent sealing effect) of the two sealing lips resting on the inner wall 11' and the outer wall 13' of the actuator housing 6' is achieved, i.e. the dynamic sealing of the annular piston 19' against the annular cylinder 17'.

[0018] Adjacent to the sealing ring 40, an outer guide ring 43 is arranged on the piston unit 7', which is slidably guided on the second sealing surface 41 formed on the outer wall 13' of the actuator housing 6'. To ensure favorable guidance properties, the axial distance between the inner guide ring 38 and the outer guide ring 43, measured as the center-to-center distance, corresponds to approximately 1.2 times the radius of the first sealing surface 34.

[0019] By reinforcing the piston unit 7' where the inner guide ring 38 and the adjacent scraper ring 39 mentioned above are each accommodated in an associated groove 44 or 45, radially inwards compared to the adjacent cylinder section 27' by a greater wall thickness, it is achieved that the forces introduced into the piston unit 7' by the helical spring are guided to a significant extent exclusively axially, ie without any deflection with a radial component, up to the sealing ring 40 closing the hydraulic working chamber 46.

[0020] Connected to the piston unit 7' is a protective cap 47 that can be displaced relative to the actuator housing 6'. Its diameter is stepped such that a wide first region 48 abuts the outer wall 13' of the actuator housing 6', and a narrow second region 49 abuts the guide surface 37 of the inner wall 11' of the actuator housing 6', which surrounds the inner wall 11' of the actuator housing 6', which projects axially relative to the outer wall 13'.

Claims

[1] Hydraulically adjustable spring strut for a motor vehicle, comprising - a telescopic shock absorber (1) with a shock absorber housing (4) and a shock absorber rod (5) which is movable relative to the latter and which plunges into the latter, - a hydraulic actuator (3) surrounding the shock absorber housing (4) with an actuator housing (6') fixed to the shock absorber housing (4) and a piston unit (7') movable relative to the latter, - a helical spring (2) acting between a first spring support (8) associated with the piston unit (7') and a second spring support (9) associated with the shock absorber rod (5), wherein - the piston unit (7') comprises an annular piston (19') which is immersed in an annular space (15') formed between a cylindrical inner wall (11') and a cylindrical outer wall (13') of the actuator housing (6') and is sealed off from the inner wall (11') and the outer wall (13') of the actuator housing (6'), - a double-acting sealing ring (40) is arranged on the end face of the annular piston (19'), which sealing ring provides a dynamic seal against the inner wall (11') of the actuator housing (6') on a first sealing surface (34) and a dynamic seal against the outer wall (13') of the actuator housing (6') on a second sealing surface (41), and - the inner wall (11') of the actuator housing (6') has a cylindrical guide surface (37) which runs coaxially with the first sealing surface (34) cooperating with the sealing ring (40) and is axially offset relative thereto, wherein an inner guide ring (38) arranged on the piston unit (7') is slidably guided on the guide surface (37), characterized by that the guide surface (37) of the inner wall (11') of the actuator housing (6') is constricted relative to its first sealing surface (34). [2] Suspension strut according to claim 1, characterized by that a scraper ring (39) is arranged on the piston unit (7') adjacent to the inner guide ring (38) and rests against the guide surface (37) of the inner wall (11') of the actuator housing (6'). [3] Suspension strut according to claim 1 or claim 2, characterized bythat an outer guide ring (43) is arranged on the piston unit (7') adjacent to the sealing ring (40), which is slidably guided on the second sealing surface (41) of the actuator housing (6'). [4] Suspension strut according to claim 3, characterized by that the axial distance between the inner guide ring (38) and the outer guide ring (43) corresponds at least to the radius of the first sealing surface (34). [5] Suspension strut according to one of claims 1 to 4, characterized by that a protective cap (47) which is displaceable relative to the actuator housing (6') is connected to the piston unit (7'), which protective cap is stepped with regard to its diameter in such a way that a wide first region (48) surrounds the outer wall (13') of the actuator housing (6') and a narrow second region (49) surrounds the inner wall (11') of the actuator housing (6') which projects axially relative to the outer wall (13').

Images