strut bearing

Abstract

Strut mount (1) for a motor vehicle, comprising a closing element (2) and a guide ring (3) rotatably mounted relative to the closing element (2), wherein a bearing (4) is arranged between the closing element (2) and the guide ring (3), and a seal (5) arranged on the closing element (2), wherein the seal (5) rests against a guide surface (6) of the guide ring (3), and the guide surface (6) facing the seal (5) has at least in a contact area between the seal (5) and the guide surface (6) an element for minimizing friction (7) with a material different from the base material of the guide ring (3), characterized in that the element for minimizing friction (7) is a band (8) or a film (9) inserted into the guide surface (6).

Description

[0001] The invention relates to a strut mount for a motor vehicle according to the preamble of claim 1.

[0002] Strut mounts are part of the wheel suspension in independent suspension systems of motor vehicles. As a chassis component, the wheel suspension contributes to the vehicle's driving safety, dynamics, and comfort, and enables precise steering response. The wheel suspension is designed to isolate vibrations from the vehicle chassis, thus minimizing road noise. To positively influence vehicle dynamics, the wheel suspension should be as lightweight as possible. Strut mounts are often part of a McPherson strut suspension, where the strut is an assembly comprising a shock absorber, a steering knuckle, a ball joint, and a coil spring tensioned between two spring seats. The strut mount is fitted with an end cap, preferably a cap, which is attached to a strut tower on the chassis.The strut mount also features a guide ring against which the shock absorber spring is supported and through which the spring is guided. The guide ring is rotatably mounted relative to the end element. For this purpose, a bearing, preferably a plain or roller bearing, is provided in the strut mount, which can transmit both axial and radial forces. Thus, when steering, the strut mount allows the spring to rotate relative to the vehicle body, since the entire strut assembly rotates during steering.

[0003] From DE 10 2012 212 522 A1, a strut bearing is known in which a guide ring of the strut bearing is rotatably mounted relative to a cap of the strut bearing, with an axial bearing arranged between the cap and the guide ring. The cap has a seal, the seal bearing in contact with the guide ring. The guide ring has a surface with a glass fiber-free component, the glass fiber-free component forming a contact area for the seal. The glass fiber-free component in the contact area with the sealing lip of the cap prevents the seal from coming into contact with the glass fiber-reinforced plastic of the guide ring.Such contact between the glass fiber reinforced plastic of the guide ring and a seal made of a soft elastomer material can otherwise lead to increased seal wear, meaning that a seal cannot be guaranteed over the service life of the strut. The glass fiber-free component reduces abrasion on the seal, thereby extending its service life.

[0004] A disadvantage of such a solution, however, is that such a guide ring is usually manufactured using a two-component injection molding process, meaning that replacing the fiberglass-free components is not possible and, in case of wear, the entire strut, or at least the guide ring, must be replaced. Furthermore, there is still relatively high friction between the fiberglass-free component and the seal, as well as frictional jumps during the transition from static to sliding friction.

[0005] A strut bearing is also known from JP 2010 - 151 249 A.

[0006] From DE 10 2009 031 211 A1 a rolling bearing arrangement is also known in which a friction-reducing treatment of the counter-running surfaces of sealing lips is proposed.

[0007] According to the invention, a strut mount for a motor vehicle is proposed, comprising an end element and a guide ring rotatably mounted relative to the end element, as well as a bearing, preferably a plain bearing or rolling bearing, arranged between the end element and the guide ring, and a seal arranged on the end element which rests against a guide surface of the guide ring. The guide surface facing the seal has, at least in a contact area between the seal and the guide surface, a friction-minimizing element made of a material different from the base material of the guide ring. This places the seal in contact with a sliding surface, thus reducing the friction between the seal and the guide surface. This results in a substantially constant coefficient of friction, preventing the seal from sticking to the guide surface.This prevents the so-called "stick-slip effect," i.e., a difference in the coefficient of friction between static and kinetic friction and the associated periodic sticking or "rubbing" of the seal in the kinetic friction zone. This results in significantly lower friction and reduced seal wear. This effect is further enhanced by the fact that there is no need to account for the wear-related degradation of the seal, which would otherwise lead to increased contact forces on the seal, at least when new. Thus, an undesirable increase in frictional torque due to higher contact forces on the seal is avoided.

[0008] The features listed in the dependent claims enable advantageous improvements and further developments of the strut bearing specified in the independent claim.

[0009] In a preferred embodiment of the strut mount, the guide ring has a recess for receiving the friction-reducing element. This recess provides a simple and secure space for the friction-reducing element, allowing for both a positive-locking connection, particularly via grooves and / or projections on the guide ring, and a friction-locking connection, especially by screwing the friction-reducing element to the guide ring. Both a (releasable) friction-locking connection and a positive-locking connection enable particularly easy installation of the friction-reducing element.Furthermore, in the event of damage, the friction-reducing element can be easily replaced, eliminating the need to replace the entire guide ring or the complete strut. A positive-locking connection between the friction-reducing element and the guide ring is preferred, as this allows for particularly simple installation – namely, insertion into the recess, which requires no tools.

[0010] It is particularly preferred if the friction-reducing element is positively connected to the recess. The groove(s) and / or projections provided in the recess allow for a simple positive connection between the friction-reducing element and the guide ring.

[0011] According to an advantageous embodiment of the invention, the friction-reducing element is made of polytetrafluoroethylene (PTFE). PTFE components exhibit a particularly low coefficient of friction for a plastic. Furthermore, a PTFE friction-reducing element can be used over a wide temperature range and is therefore suitable for all applications of a motor vehicle strut. PTFE has essentially equal static and kinetic friction, so that even when relative movement between the end element and the guide ring begins, there is no risk of the seal sticking.

[0012] Alternatively, it is advantageous to coat the friction-reducing element with polytetrafluoroethylene (PTFE). This allows the use of simple and cost-effective standard elements, which are then provided with a suitable friction-reducing coating.

[0013] In a first embodiment of the invention, the friction-minimizing element is a strip or film inserted into the guide surface of the guide ring. A strip or film creates a flat guide surface, ensuring uniform contact pressure of the seal against the guide surface. Furthermore, strips or films are easy to manufacture and correspondingly easy to insert into the guide ring.

[0014] In a second embodiment of the invention, the friction-reducing element is an O-ring, in particular an O-ring coated with PTFE or graphite. An O-ring is a cost-effective design element that can simply be placed on the guide ring or inserted into a groove in the guide ring to form a guide surface for the seal. Furthermore, an O-ring can be coated with PTFE or graphite using known, cost-effective methods to minimize friction. It is particularly preferred if the O-ring is inserted into a groove in the guide ring. Due to the elasticity of the O-ring, the friction-reducing element can be installed and removed very easily and cost-effectively, thus enabling a positive-locking connection between the O-ring and the guide ring to be established in a simple manner.The groove width should essentially correspond to the width of the O-ring in order to fix the position of the O-ring and prevent the O-ring from moving within the groove.

[0015] In a further advantageous embodiment, the seal is provided with a sealing lip made of an elastomeric material. A sealing lip allows for line contact between the seal and the guide ring, resulting in a particularly effective seal. Furthermore, due to its narrow width, the sealing lip can glide along the guide surface, i.e., the friction-minimizing element, with very low friction, thus preventing an increase in friction and ensuring a constant frictional torque for the entire bearing assembly.

[0016] Unless otherwise stated in individual cases, the various embodiments of the invention mentioned in this application can be advantageously combined with one another.

[0017] The invention is explained below using exemplary embodiments with reference to the accompanying drawings. These show: Fig. 1 an end section of a strut with a strut bearing according to the invention; Fig. 2 an enlarged detail view of the sealing area between the end element and the guide ring of a strut bearing according to the invention; Fig. 3 an alternative embodiment of the sealing area between the end element and the guide ring of a strut bearing according to the invention.

[0018] Fig. Figure 1 shows a longitudinal section through an embodiment of a strut mount 1 according to the invention for a motor vehicle. The strut mount 1 has an end element 2, in particular a cover, and a guide ring 3, wherein the end element 2 is rotatably mounted relative to the guide ring 3. The guide ring 3 is preferably made of a glass fiber reinforced plastic, for example a polyamide (PA66) with a glass fiber content of 25% to 50%. The end element 2 is attached to a strut tower bearing (not shown) of the motor vehicle body. The guide ring 3 accommodates an end section of a strut spring (not shown). The spring forces of the spring are transmitted via the guide ring 3 into the end element 2 and from there into the strut tower bearing. The guide ring 3 is axially mounted in the direction of a rotation axis 14 of the strut mount 1 via a bearing 4, preferably a rolling bearing, in particular an axial ball bearing.A rolling bearing 4 is arranged between the end element 2 and the guide ring 3, which allows the guide ring 3 to rotate relative to the end element 2. The bearing 4 is preferably designed as a rolling bearing, in particular as an axial ball bearing, and can accommodate both radial and axial forces. For this purpose, a first bearing ring 17 is arranged in the end element 2 and a second bearing ring 18 of the rolling bearing 4 is arranged in the guide ring 3. Rolling elements 16, in particular balls, are arranged between the two bearing rings 17, 18 to enable rotational movement.

[0019] The end element 2 comprises a carrier element 15 and a seal 5. The carrier element 15 preferably consists of a thermoplastic, for example polyamide, into which the sealing element is materially bonded and / or form-fitted by means of an injection molding process. The seal 5 has a sealing lip 13 which rests on a guide surface 6 of the guide ring 3. The seal 5 also has a further sealing lip 20, which is positioned upstream of the sealing lip 13 to prevent the ingress of dirt and dust into the strut bearing 1. A cavity 19 is formed between the sealing lips 13 and 20 and the guide ring 3, in which dirt, dust, and particles can collect or from which such contaminants can be removed without damaging the sealing lip 13 or penetrating further into the strut bearing 1.

[0020] In Fig. Figure 2 shows an enlarged detail view of the sealing area between the end element 2 and the guide ring 3. It can be seen that the seal 5 is integrated into the end element 2 and has a first, inner sealing lip 13 and a second, outer sealing lip 20. A recess 10, preferably in the form of a circumferential groove 12, is formed on the guide surface 6 of the guide ring 3, in which a friction-reducing element 7 is received. The friction-reducing element 7 is preferably positively connected to the guide ring 3 to facilitate easy assembly. The friction-reducing element 7 is made of a material different from the base material of the guide ring 3 and has a significantly reduced coefficient of friction compared to the base material.A significantly reduced coefficient of friction is defined as a coefficient of friction that is reduced by at least 50%, preferably by at least 70%, compared to the base material, if the material of the seal 5, in particular the sealing lip 13, is an elastomer. The sealing lip 13 of the seal 5 bears in a rubbing contact with the friction reduction element 7, while a gap 21 is formed between the outer sealing lip 20 and the guide ring 3 to facilitate the removal of contaminants and the drainage of liquids, especially splash water, from the cavity 19. The friction reduction element 7 is in the form of an O-ring 11. The O-ring 11 is preferably coated with polytetrafluoroethylene (PTFE) or graphite. Both types of coatings are known for O-rings and can significantly reduce friction in the sealing area between the sealing lip 13 of the seal 5 and the guide surface 6.The sealing lip 13 runs along the curvature of the O-ring 11, resulting in a predominantly linear contact surface. The elasticity of a coated O-ring 11 also limits the surface pressure on the sealing lip 13, as the O-ring 11 elastically rebounds to a certain extent if the contact pressure is too high. This provides additional force limitation for the sealing lip 13, preventing premature wear. Such PTFE- or graphite-coated O-rings 11 are readily available at low cost as standard catalog items, allowing the proposed strut mount 1 to be manufactured without significant additional costs compared to a strut mount 1 known from the prior art. Alternatively, a solid polytetrafluoroethylene ring can be inserted into the circumferential groove 12.

[0021] In Fig. Figure 3 shows an alternative embodiment of a strut mount 1 with a friction-reducing element 7. The design is essentially the same as shown in Figure 3. Fig.As described in Figure 2, the recess 10 in the guide surface 6 is designed to accommodate a strip 8 or a film 9 as a friction-reducing element 7. Alternatively, the strip 8 or film 9 can also be applied to a flat surface of the guide surface 6 without a recess 10. Furthermore, it is alternatively provided that a coating with a friction-reducing material, in particular a PTFE coating, is applied to the base material of the guide ring 3 in the contact area with the sealing lip 13 of the seal 5 as a friction-reducing element 7. This also allows for a cost-effective reduction of friction between the guide ring 3 and the seal 5.However, a coating has the disadvantage compared to a tape, a film and especially an elastic O-ring that it is not possible to replace the element to minimize friction 7, and recoating the guide surface 6 requires a complete disassembly of the strut bearing 1. Reference symbol list 1 Strut bearing 2. Final element 3 Guide ring 4 bearings 5 Seal 6 guide surface 7 elements for minimizing friction Volume 8 Slide 9 10 recesses 11 O-ring 12 Nut 13 Sealing lip 14 axis of rotation 15 support element 16 rolling elements 17 first bearing ring 18 second bearing ring 19 Cavity 20 outer sealing lip 21 column

Claims

[1] Strut mount (1) for a motor vehicle, comprising a closing element (2) and a guide ring (3) rotatably mounted relative to the closing element (2), wherein a bearing (4) is arranged between the closing element (2) and the guide ring (3), and a seal (5) arranged on the closing element (2), wherein the seal (5) rests against a guide surface (6) of the guide ring (3), and the guide surface (6) facing the seal (5) has, at least in a contact area between the seal (5) and the guide surface (6), an element for minimizing friction (7) made of a material different from the base material of the guide ring (3), characterized by , that the element for minimizing friction (7) is a band (8) or a film (9) inserted into the guide surface (6). [2] Strut bearing (1) according to the preamble of claim 1, characterized by , that the element for minimizing friction (7) is an O-ring (11). [3] Strut mount (1) according to claim 1 or 2, characterized by , that the guide ring (3) has a recess (10) for receiving the friction reduction element (7). [4] Strut bearing (1) according to any one of the preceding claims, characterized by , that the element for minimizing friction (7) is positively connected to the guide ring (3). [5] Strut bearing (1) according to claims 3 and 4, characterized by , that the element for minimizing friction (7) is positively connected to the recess (10). [6] Strut bearing (1) according to claims 1 to 5, characterized by , that the friction-minimizing element (7) consists of polytetrafluoroethylene (PTFE). [7] Strut bearing (1) according to claims 1 to 5, characterized by , that the element (7) is coated with a polytetrafluoroethylene (PTFE) to minimize friction. [8] Strut bearing (1) according to claim 2, characterized by, that the O-ring (11) is inserted into a groove (12) on the guide ring (3). [9] Strut bearing (1) according to any one of claims 1 to 8, characterized by , that the seal (5) has a sealing lip (13) made of an elastomeric material.

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