Patent Application
20090269127
The invention concerns a lever mounting arrangement of a pivotable lever that is configured as a cast part and mounted through a hub for pivoting on a stationary axle or shaft. A sliding bearing is inserted into an annular gap defined in radial direction by a reception bore of the hub and a peripheral surface of the axle.
A lever mounting arrangement of the pre-cited type is known, for instance, from the document DE 195 23 647 A1. This document shows a pivoting lever tensioning device in which a lever designated as a tensioning lever and configured as a toggle lever out of a casting material is rotatable about a stationary axle. In the operational state, a tension roller-arranged for rotation on a first end of the lever is supported by force-locking on a traction element of a traction drive. Force loading is effected through a tension spring element that is articulated on a further end of the lever and force-loads the lever in anti-clockwise direction. For forming the lever mounting arrangement, the hub comprises a reception bore made by mechanical processing. The lever is mounted for rotation on the axle through two axially spaced sliding bearing bushings inserted into the reception bore. To each front end of the lever hub is associated a washer that is positionally fixed on the axle and serves to guide the lever in axial direction. For sealing an annular gap defined by the installation space of the sliding bearing, sealing rings are provided at both front ends. These elastically deformable sealing rings are inserted into a front-end reception of the hub and are sealed relative to the hub and to the peripheral surface of the axle as also relative to the washer. A drawback of this prior art lever mounting arrangement is the high cost of processing and assembly due to the large number of components.
It is an object of the invention to provide a lever mounting arrangement optimized with regard to the number of components and costs.
This and other objects and advantages of the invention will become obvious from the following detailed description.
The invention achieves its objects by the fact that a sliding bearing in form of a bushing of a plastic material is injected into the unprocessed reception bore of the hub of the cast lever. Through this measure, advantageously, there is no need to chuck the cast lever for a cost-intensive machine-finishing of the reception bore in form of a fitting bore as in the prior art for receiving the sliding bearing prior to insertion of sealing rings into the reception bore. Disadvantageously, tolerances cumulate due to the finishing treatment of the reception bore and the wall thickness of the sliding bearing and directly determine the sliding bearing lash relative to the bearing pin or axle. Through the invention, advantageously, the desired closely toleranced mounting lash between the sliding bearing and the bushing or the axle can be attained by the injection of the plastic material into the injection molding die. The number of components of the inventive lever mounting arrangement that includes an injected plastic bushing forming the sliding bearing is reduced compared to known solutions, and this has a direct advantageous effect on the tolerance chain. Moreover, the invention reduces the number of work steps and components, so that, together with a closely toleranced sliding bearing lash, an optimal lever mounting arrangement is realized. For obtaining an improved durability of the lever mounting arrangement, the invention advantageously proposes to provide the plastic bushing that forms the sliding bearing with friction-reducing and/or wear-reducing elements. The injected plastic bushing configured as a multi-function component can further comprise at least one seal that is integrally connected to the plastic bushing.
The outer contour or peripheral surface of the inventive injected plastic bushing that constitutes the sliding bearing enables the production-inherent inclined forming surfaces or contours of the reception bore of the hub made by casting to be compensated or leveled without pre-treatment. Thus, advantageously, no tolerance requirements or other special requirements need to be made of the surface structure in the region of the reception bore of the cast lever made particularly as an aluminum die-casting. In this connection, the shape of the forming contour plays no role because the inventive plastic bushing levels, for example, even a conical or a convex forming contour.
Keeping in mind the intended multi-functionality of the inventive sliding bearing, this bearing may further comprise, at least on one front end, an integrally formed right-angled rim that assumes the function of a thrust bearing. A sliding bearing of the invention with such a configuration can be used, for instance, in a lever mounting arrangement in which the lever hub is loaded by an axial force, i.e. requires a thrust bearing.
Moreover, the sliding bearing of the invention can comprise, at least on one side, a flexible seal integrally connected to the sliding bearing. If need be and depending on installation conditions, it may be appropriate to provide a flexible seal on both ends of the sliding bearing. For achieving an improved sealing effect, the seal preferably comprises an inclined sealing lip extending radially outward. In the installed state, this sealing lip is supported by force-locking on a contact surface. Another suitable seal can be made in the form of a sealing element or seal comprising two radially outward directed sealing lips forming a V-shaped cross-sectional profile. Through this spread arrangement of the sealing lips, each of these sealing lips can be supported by force-locking in a sealing gap between the lever hub and, for example, a washer disposed on the stationary axle. In a further configuration, the seal comprises two sealing lips offset radially to each other, so that, for example, an inner sealing lip is supported on the lever and an outer sealing lip is supported on a component adjoining the lever.
The invention further proposes as a measure for obtaining a friction-optimized sliding bearing, an enrichment of the plastic material of the sliding bearing with a lubricant, particularly PTFE. Appropriately, for example, the lubricant is inserted in the form of lamellae into the plastic material, so that independently of the state of wear of the sliding bearing, an adequate quantity of lubricant is present in the contact zone between the stationary axle and the sliding bearing.
A particularly suitable plastic as base material for the sliding bearing is preferably a polymer compound that, interspersed with a suitable lubricant, forms the sliding bearing. It is further possible to make the sliding bearing of the invention as a one-component plastic part or a two-component plastic part. An appropriate measure for realizing an improved shape stability or general rigidity of the sliding bearing is to provide the sliding bearing with an armoring in the form of a hard plastic element.
The lever configured as a casting is preferably made of aluminum. A particularly suitable and preferred cost-optimized fabrication method even for large piece numbers is die-casting.
The lever mounting arrangement of the invention is particularly intended for a tensioning system of traction drive in which a pivotable lever loaded through force-locking by a spring means is supported in the installed state by force-locking through a tension roller on a traction element.
The invention further concerns a fabrication method for the lever mounting arrangement of the invention comprising the following fabrication steps. In a first step, the lever configured as a casting comprising an unprocessed forming contour is positioned in the lever hub in an injection molding tool. In a next step, the sliding bearing is formed by injection of a plastic material into the lever hub, so that a peripheral surface of the sliding bearing levels the forming contour of the hub, and the sliding bearing is thus fitted by positive engagement. By virtue of this method, advantageously, no special requirements are made of the surface structure or tolerances in the region of the forming contour of the lever made as a die-cast part. At the same time, the method clearly reduces the costs of assembly because both a mechanical finishing of a reception bore and the pressing-in of the sliding bearing as also the insertion of seals are omitted. The injected plastic sliding bearing of the invention is suitable for many uses. Moreover, by providing sufficiently large contact surfaces between the sliding bearing and the associated axle or shaft, the surface contact pressure and the concomitant load rating of the sliding bearing can be reduced, so that plastic as a base material for the sliding bearing is adequate enough for achieving a long durability of the inventive lever mounting arrangement.
Further advantages and details of the invention will now be described with reference to examples of embodiment and the appended figures showing schematic representations.
The bearing 20b shown in
The sliding bearing 20c of
The hub 11 shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2008 021 037.4 | Apr 2008 | DE | national |
