Spindle drive for an adjustment element of a motor vehicle

Abstract

Spindle drive for an adjusting element (1) of a motor vehicle with a drive motor (2) with a downstream spindle-spindle nut drive (3) for generating a drive force along a geometric spindle axis (4), wherein two connections (5, 6) are provided for transmitting the drive force, wherein an inner housing (7) connected to one connection (5) and an outer housing (8) connected to the other connection (6) are provided, and wherein, during motorized adjustment, the inner housing (7) runs telescopically in the outer housing (8), characterized in that at least the inner housing (7) is designed in at least two parts and is accordingly provided via a first axial housing section (9) by a first housing part (10) made of a first material and via a second axial housing section (11) by a second housing part (12) made of a second material, wherein the first material is different from the second material.and that the arrangement is such that the first axial housing section (9) is always outside the force flow for the driving force.

Description

The present invention relates to a spindle drive for an adjusting element of a motor vehicle according to the preamble of claim 1. The term "adjusting element" is to be understood broadly in this context. It includes, for example, a tailgate, trunk lid, hood, side door, cargo door, sunroof, or similar component of a motor vehicle. In the following, the focus is on the application of the motorized adjustment of a motor vehicle's tailgate. This is not to be understood as a limitation. In the context of motorized operation of tailgates or similar devices, the use of spindle drives is becoming increasingly important. The known spindle drive (DE 10 2008 062 391 A1), from which the invention is based, is equipped with a drive motor and a downstream spindle-spindle nut drive for generating a drive force along a geometric spindle axis, the drive force being transmitted via two end connections. The spindle drive has an inner housing for the drive motor and an outer housing, which telescopically slide into one another during motorized adjustment. At least part of the inner housing or the outer housing is made of a plastic material to ensure weight reduction and the simple implementation of detent connections. A similar spindle drive is also known from DE 10 2008 061 118 A1. Another known spindle drive (DE 20 2005 000 559 U1) also demonstrates the use of plastic materials for the spindle drive housing. The use of plastic materials necessitates, for example, the manufacture of the inner or outer housing from plastic half-shells. The use of plastic materials for the inner and outer housings of spindle drives, as described above, offers advantages not only in terms of weight and design, but also in terms of the resulting costs. However, there is room for improvement regarding the structural design of the spindle drive, whose mechanical properties, particularly its resulting rigidity, should not be inferior to those of a spindle drive with a metal housing. The invention is based on the problem of designing and further developing the known spindle drive in such a way as to improve its mechanical properties. The above problem is solved in a spindle drive according to the preamble of claim 1 by the features of the characterizing part of claim 1. The essential consideration is to design the inner housing in at least two parts. This two-part design results in a first axial housing section made of one material and a second axial housing section made of a second material. As proposed, the arrangement is now such that the first axial housing section is always outside the force flow for the drive force. This allows for a particularly cost-effective design of the first axial section, for example, using a plastic material. The proposed solution, namely manufacturing the inner housing in axial housing sections from different materials, allows for a design of the spindle drive housing adapted to the actual force conditions. The targeted use of appropriate materials enables the mechanical properties to be improved at minimal cost. The preferred embodiment according to claim 2 takes into account the fact that the main force flow runs through the second axial housing section of the two-part housing, so that the second material is optionally harder, tougher and / or less elastic than the first material. In practical tests, the particularly preferred embodiment according to claim 3, in which the first material is a plastic material and the second material is a metal material, has proven particularly successful. In the further preferred embodiment according to claim 4, the second housing part accommodates the drive motor, which is particularly advantageous when the second housing part is made of a metal material. This allows the spindle drive to be optimally designed, especially with regard to electromagnetic compatibility. A particularly advantageous variant for connecting the two housing parts of the two-part housing is the subject of claims 8 and 9. Here, the two housing parts are connected to each other exclusively by an axial force-fit (claim 8), which, in a particularly preferred embodiment, is provided by an existing spring arrangement (claim 9). This ensures that the two-part design of the housing in question does not result in any additional costs due to the connection. The preferred embodiments according to claims 11 and 12 relate to equipping at least one of the housing parts of the two-part housing with a sealing arrangement comprising at least one seal inside one of the two housing parts. If the housing part in question is designed as a plastic part, at least part of the sealing arrangement can be easily produced using a two-component plastic injection molding process. The invention will now be explained in more detail with reference to a drawing that illustrates only one embodiment. In the drawing, Fig. 1 shows a schematic side view of the rear of a motor vehicle with a proposed spindle drive, Fig. 2 shows the spindle drive according to Fig. 1 in an external view (left) and a sectional view (right), each from the side, and Fig. 3 shows the inner housing of the spindle drive according to Fig. 1 in an exploded view. The spindle drive shown in the drawing serves for the motorized adjustment of an adjustment element 1 of a motor vehicle, designed as a tailgate. Other applications of the proposed spindle drive are conceivable, as will be explained in detail below. The spindle drive is conventionally equipped with a drive motor 2 and a downstream spindle-spindle nut gearbox 3 to generate a drive force along a geometric spindle axis 4. Here, and preferably, an intermediate gearbox 2a is located between the drive motor 2 and the spindle-spindle nut gearbox 3, which serves to reduce the speed. The spindle drive has two connections 5, 6 for transmitting the drive force. Connections 5, 6 preferably provide ball-and-socket couplings. Fig. 2 shows that an inner housing 7 connected to one terminal 5 and an outer housing 8 connected to the other terminal 6 are provided, wherein during motorized adjustment the inner housing 7 runs telescopically in the outer housing 8. It is essential that at least one of the two housings 7, 8, in particular the inner housing 7, is designed in at least two parts. This is best seen by looking at Figures 2 and 3 together. The wall of the inner housing 7 is provided by a first housing part 10 made of a first material via a first axial housing section 9 and by a second housing part 12 made of a second material via a second axial housing section 11. Figure 3 shows the two housing parts 10, 12, which are accordingly made of different materials, in an exploded view. As proposed, the arrangement is now such that the first axial housing section 9 is always outside the force flow for the driving force. This means that the first housing part 10 of the inner housing 7 can, for example, have a covering or sealing function. This will become clear from the preceding explanations regarding the generation of the driving force. The following primarily concerns the design of the inner housing 7, preferably the two housing parts 10, 12 of the inner housing 7. However, all designs relating to the inner housing 7 apply accordingly to the outer housing 8. The drive motor 2 and the intermediate gearbox 2a are housed in the second housing part 12, which is connected to the first housing part 10 in a manner to be explained later. The spindle 13 of the spindle-spindle nut assembly 3 extends from the intermediate gearbox 2a and meshes with a spindle nut 14. The spindle nut 14 is connected to the upper connection 6 of the spindle drive via a tube 15, referred to here as the guide tube 15. The upper connection 6 is, in turn, connected to the outer housing 8, as mentioned above. In the motorized adjustment, the force flow for the drive force passes via the connection 5, the second housing part 12 of the inner housing 7, there the second axial housing section 11, the drive motor 2 and the intermediate gear 2a, the spindle 13, the spindle nut, the guide tube 15 and the upper connection 6. It is interesting to note that no force flow passes via the first housing part 10, in particular the first axial housing section 9, of the inner housing 7. Accordingly, the first housing part 10 can be designed to be weaker than the second housing part 12. Preferably, the second material is harder than the first material and / or has a higher toughness than the first material and / or is less elastic than the first material. In summary, the proposed solution allows for a design of the inner housing 7 and outer housing 8 tailored to the actual force conditions. In a particularly preferred embodiment, the first material from which the first axial housing section 9 is made is a plastic material, and the second material from which the second axial housing section 11 is made is a metal material, in particular a steel material. When the second axial housing section 11 is made of a metal material, good electromagnetic compatibility is advantageous, provided that, as shown in the drawing, the drive motor 2 is arranged in the second axial housing section 11, i.e., in the second housing part 12. Fig. 2 shows that the lower connection 5 for transmitting the drive force is arranged on the second housing part 12. The connection 5 essentially forms a cover for the inner housing 7. This cover can be crimped, glued, screwed, or similarly attached to the inner housing 7. The drawing shows that, preferably, the inner housing 7 is designed as an inner tube and the outer housing 8 as an outer tube, with the inner tube 7 running telescopically within the outer tube 8 during motorized adjustment. Various cross-sectional shapes are conceivable for the inner tube 7 and the outer tube 8. Preferably, the inner tube 7 and the outer tube 8 have a substantially circular cross-section. Fig. 2 shows that the first axial housing section 9 extends over more than half the total axial length of the two-part inner housing 7. This clearly demonstrates that, with the proposed solution, a large portion of the inner housing 7 is made of plastic, while the smaller, but force-transmitting, part is made of a metal material. The illustrated design of the inner tube 7 is particularly advantageous with regard to its basic mechanical structure. This applies especially to the mechanical connection of the two housing parts 10, 12. A comparison of Figs. 2 and 3 shows that the first housing part 10 and the second housing part 12 of the two-part inner housing 7 are axially inserted into one another, thereby forming an axial overlap area 16. Here, and preferably, the second housing part 12 is inserted into the first housing part 10. A particularly interesting aspect of the connection between the two housing parts 10 and 12 of the inner housing 7 is the fact that they are connected exclusively by an axial force-fit. The term "connected" here is to be understood in a narrow sense, meaning that the two housing parts 10 and 12 cannot be separated by external forces. This means that if the axial force-fit were to fail, the two housing parts 10 and 12 could be separated. For this axial force-fit, the two housing parts 10 and 12 are equipped with corresponding coupling surfaces 10a and 12a. The generation of the axial force required for connecting the two housing parts 10, 12 is solved in a remarkably simple manner in the illustrated and thus preferred embodiment. As proposed, a spring arrangement 17 is provided which axially preloads the inner housing 7 against the outer housing 8. This axial preload is preferably applied such that the two connections 5, 6 are forced apart. The spring arrangement 17 is shown by way of example in Fig. 2 and is found in a number of known spindle drives. Such a spring arrangement 17 is regularly used to assist the drive motor 2 during motorized adjustment against the weight of the tailgate 1 or the like. It is essential that the axial force required for the connection between the two housing parts 10, 12 of the two-part inner housing 7 is due to the spring assembly 17. In the illustrated and thus preferred embodiment, the spring assembly 17 has a helical compression spring 18 in which the spindle 13 of the spindle-spindle nut drive 3 runs. The helical compression spring 18 presses via the coupling surface 10a on the first housing part 10 onto the coupling surface 12a on the second housing part 12 on the one hand, and onto the upper connection 6 or the outer housing 8 on the other. A corresponding force is exerted on the spindle nut 14 via the guide tube 15, so that the spindle nut 14 is driven upwards in Fig. 2. The helical compression spring 18 is designed such that a considerable preload force acts even when the spindle drive is fully extended. As explained above, this preload force causes the two coupling surfaces 10a, 12a to be pressed together, thus creating a positive connection between the two housing parts 10, 12. Several advantageous configurations are conceivable for the design of the coupling surfaces 10a, 12a. Here, and preferably, the coupling surface 10a of the first housing part 10 of the inner housing 7 is an inwardly projecting annular surface. The annular surface 10a forms an annular collar that is arranged circumferentially on the inner wall of the first housing part 10 with respect to the geometric spindle axis 4. The inner housing 7 is preferably equipped with a sealing arrangement 19 comprising a series of seals 19a-d. Seals 19a-d serve to seal the first housing part 10 against the second housing part 12, while seal 19e serves to seal the inner housing 7 against the outer housing 8. Seals 19a-c bear against the outer wall 20 of the second housing part 12, while seal 19c additionally bears against the cone 21 formed by the second housing part 12. Accordingly, seal 19c is arranged at an axial end of the first housing part 10 of the inner housing 7. Fig. 3 shows that the seals 19a-c are essentially ring-shaped. An axially offset arrangement has proven particularly advantageous. The seal 19d runs essentially axially, which is not only advantageous from a sealing perspective but also helps to dampen vibrations. The manufacture of the seals 19a-d which are located inside the inner housing 7, here inside the first housing part 10 of the inner housing 7, is the subject of a further teaching which has independent significance. In the proposed method, at least one opening 22 is created in the inner housing 7 or housing part 10 to produce the at least one soft elastic seal 19a-d inside the inner housing 7 or housing part 10. Subsequently, an injection mold (not shown) is positioned inside the inner housing 7 or housing part 10, forming a cavity with the inner wall of the inner housing 7 or housing part 10 that corresponds to the at least one opening 22. Finally, the soft elastic seal is injected through the at least one opening 22 using a plastic injection molding process. The proposed method allows the sealing assembly 19 to be manufactured using simple injection molds, in this case the internal injection mold. Furthermore, it is possible to subsequently injection mold an outer seal 19e that covers the openings 22. With regard to the proposed method, the specific design of the sealing arrangement 19 shown in Fig. 3 offers a particular advantage, namely the possibility of injection molding all three annular seals 19a-c with a single axial injection point. This is possible because all three annular seals 19a-c are connected by the axially extending seal 19d. Thus, all internal seals 19a-d can be advantageously produced in a single injection molding operation. The proposed spindle drive is applicable to all possible adjustment elements 1 of a motor vehicle. Examples include the tailgate, trunk lid, engine hood, side door, cargo hatch, sunroof, or similar components of a motor vehicle, as described above.

Claims

Spindle drive for an adjusting element (1) of a motor vehicle with a drive motor (2) with a downstream spindle-spindle nut drive (3) for generating a drive force along a geometric spindle axis (4), wherein two connections (5, 6) are provided for transmitting the drive force, wherein an inner housing (7) connected to one connection (5) and an outer housing (8) connected to the other connection (6) are provided, and wherein, during motorized adjustment, the inner housing (7) runs telescopically in the outer housing (8), characterized in that at least the inner housing (7) is designed in at least two parts and is accordingly provided via a first axial housing section (9) by a first housing part (10) made of a first material and via a second axial housing section (11) by a second housing part (12) made of a second material, wherein the first material is different from the second material.and that the arrangement is such that the first axial housing section (9) is always outside the force flow for the driving force. Spindle drive according to claim 1, characterized in that the second material is harder than the first material, and / or that the second material is less compliant than the first material, and / or that the second material has a higher toughness than the first material. Spindle drive according to claim 1 or 2, characterized in that the first material is a plastic material and the second material is a metal material, in particular a steel material. Spindle drive according to one of the preceding claims, characterized in that the second housing part (12) accommodates the drive motor (2) and optionally an intermediate gearbox (2a) connected downstream of the drive motor (2), and / or that one of the two connections (5, 6) for directing the drive force is arranged on the second housing part (12). Spindle drive according to one of the preceding claims, characterized in that the inner housing (7) is designed as an inner tube and the outer housing (8) as an outer tube and that during motorized adjustment the inner tube (7) runs telescopically in the outer tube (8), preferably that the inner tube (7) and the outer tube (8) have a substantially circular cross-section. Spindle drive according to one of the preceding claims, characterized in that the first axial housing section (9) extends over at least half the axial length of the two-part housing (7). Spindle drive according to one of the preceding claims, characterized in that the first housing part (10) and the second housing part (12) of the two-part housing (7) are axially inserted into one another and thereby form an axial overlap area (16). Spindle drive according to one of the preceding claims, characterized in that the two housing parts (10, 12) of the two-part housing (7) are connected to each other exclusively by an axial force connection, preferably that the two housing parts (10, 12) have corresponding coupling surfaces (10a, 12a) for this purpose. Spindle drive according to claim 8, characterized in that a spring arrangement (17) is provided which preloads the inner housing (7) against the outer housing (8) in the axial direction and that the axial force transmission required for the connection between the two housing parts (10, 12) of the two-part housing (7) is due to the spring arrangement (17), preferably that the spring arrangement (17) has a helical compression spring (18) in which the spindle (13) of the spindle-spindle nut drive (3) runs. Spindle drive according to claim 8, characterized in that the coupling surface (10a) of one of the housing parts (10, 12) of the two-part housing (7) is designed as an inwardly projecting annular surface. Spindle drive according to one of the preceding claims, characterized in that a sealing arrangement (19) is provided which has at least one, in particular, a soft elastic seal (19a - d) inside one of the housing parts (10, 12) of the two-part housing (7). Spindle drive according to claim 11, characterized in that the sealing arrangement (19) serves to seal the two housing parts (10, 12) of the two-part housing (7) and has a particularly soft elastic seal (19a - d) inside and / or at an axial end of one of the housing parts (10, 12). Spindle drive according to one of the preceding claims, characterized in that the adjusting element (1) is a tailgate, a rear cover, a hood, a side door, a cargo hatch, a pop-up roof or the like of a motor vehicle.

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