Method for manufacturing a rack for a steering system in a motor vehicle

Abstract

Method for manufacturing a rack for a steering system of a vehicle, wherein the rack has at least one toothed section (6), comprising the following steps: providing a blank made of round steel; manufacturing a preform (3) of the toothed section (2) from the blank by a stamping process, wherein a stamping surface (2) of a stamping tool (1) has several segments, whereby, compared to the central section (9) of the toothing, the material provided is different at the end sections (10); manufacturing the toothing by wobbling.

Description

[0001] The present invention relates to a method and a device for producing a rack for a steering system of a motor vehicle. State of the art

[0002] Rack and pinion steering systems for motor vehicles typically feature a steering housing in which a rack is mounted for longitudinal displacement. A pinion rotatably mounted in the steering housing engages the rack's teeth. When the steering shaft, which is non-rotatably connected to the pinion, rotates, this causes the rack to shift laterally. This, in turn, leads to a pivoting of the vehicle's steered wheels via tie rods and steering knuckles.

[0003] The rack is generally made from round steel. The teeth are created either by forming or machining. Racks with variable teeth are either hot-formed or cold-formed in series production.

[0004] In orbital extrusion, an oscillating movement of the upper tooth tool leads to the gradual deformation of the material.

[0005] DE 197 26 697 A1 discloses a method for producing a rack in which the rack is formed from the blank by wobble forging.

[0006] German Patent Application No. 198 39 428 A1 discloses a method for producing a blank for such a rack. The starting material, which has a circular cross-section, is placed in a stamping device containing three molding tools that are movable relative to one another. After stamping, the blank has a shape that deviates from a circular cylinder in the area of ​​the toothing. The blank is then provided with two symmetrically arranged inclined flattened portions.

[0007] Such racks are highly stressed components. Therefore, it is important that the rack cross-section remains constant across the entire length of the gearing and that all teeth are formed across the entire width.

[0008] During the forming process, however, material from the forming blank flows into other areas of the rack. This results in a reduction in the active tooth width at the last teeth before the transition to the shaft area. The cross-section thus tapers, reducing the strength of the rack. Furthermore, acoustic abnormalities arise.

[0009] The invention is therefore based on the object of avoiding the aforementioned disadvantages and designing the forming process in such a way that all teeth of the gearing are formed uniformly. Furthermore, the material should be distributed in such a way that the teeth can be made wider in the end regions.

[0010] This object is achieved by the method disclosed in claim 1 and by the embossing device characterized in claim 5 for carrying out the method.

[0011] The invention is based on the fact that during the production of the blank, more material volume is available for orbital forming in the highly stressed end areas of the gearing. According to the invention, the stamping tools for producing the blank are optimized for this purpose.

[0012] The stamping surface of a stamping tool is first segmented. Various parameters can then be adjusted for each segment. This results in variable stamping angles and degrees of deformation on the stamped part, which thus receives an optimized preform for the subsequent tumbling process. The parameters for each segment can be determined in a computer simulation.

[0013] The invention increases the overall strength of the rack in the critical end areas of the gearing. Since material is specifically allocated for wider gearing, a blank with a reduced initial diameter can be used. The material is allocated – viewed in cross-section – primarily to the side of the preform (x-axis). This allows for better meeting customer requirements and also reduces weight.

[0014] Advantageous further training is specified in the dependent claims.

[0015] The segments of the stamping surface on the stamping tool can be of different sizes and have different stamping angles. These parameters are determined in a computer simulation to ensure that the material is available at every position according to requirements for the subsequent tumbling process.

[0016] For example, when stamping the preform, more material can be made available laterally (x-axis) in the end areas of the toothing compared to the middle area.

[0017] Since the segment parameters are calculated three-dimensionally, a different height (z-axis) can be created in the center of the preform compared to the end areas of the preform during embossing (viewed in longitudinal section). This also aims to provide the material in the preform exactly where it is needed for the subsequent tumbling process.

[0018] An embodiment of the invention is explained with reference to the following figures. Fig. 1A the stamping tool for the preform according to the state of the art Fig. 1B a preformed stamped part according to the state of the art Fig. 2A the inventive embossing tool for the preform Fig. 2B a preformed stamped part according to the invention Fig. 3A a rack manufactured using the method according to the invention Fig. 3B a cross section of the rack Fig. 4 Toothing of the rack, which was manufactured using the method according to the invention

[0019] In the Fig. Figure 1A shows a stamping tool 1 for producing a preform according to the prior art. The active stamping surface 2 is designed to be constant. With this stamping tool 1, the Fig. 1B, a preform 3 is produced, which is characterized by constant forming angles. The material distribution between the central region 9 and the end regions 10 is uniform.

[0020] The Fig. Figure 2A shows the embossing tool 1 according to the invention for producing the preform. The embossing surface 2 is now divided into several segments, with variable embossing angles defined for each segment in order to optimize the preform accordingly. A preform 3 produced with this embossing tool 1 according to the invention is then in the Fig. 2B is shown in a top view. The form angles are variable. It can be seen that the end regions 10 are wider than the central region 9, so that more material is available in these regions during the subsequent toothing production. This allows the teeth to be made wider in the end regions.

[0021] In the Fig. 3A shows a finished rack 4. Such racks 4 can have a shaft area 5 and a toothing area 6. Since material for a wide toothing is specifically provided by the segmented stamping tool during the pre-stamping process, it is possible to work with a smaller starting diameter than before. This is shown in the cross-sectional view of Fig. 3B. The enveloping circle 7 of the finished rack is larger than the initial diameter 8.

[0022] In the Fig. Figure 4 shows a partial top view of the toothed section 6 of a finished rack 4. The wider teeth in the end regions 10 of the toothing are clearly visible. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 197 26 697 A1

[0005]

Claims

[1] Method for producing a rack for a steering system of a vehicle, wherein the rack has at least one toothed area (6), comprising the following steps: Providing a blank made of round steel; Producing a preform (3) of the toothing region (2) from the blank by a stamping process, wherein a stamping surface (2) of a stamping tool (1) has a plurality of segments, whereby the material provided at the end regions (10) is different compared to the central region (9) of the toothing; Creating the gear teeth by wobbling. [2] Method according to claim 1, characterized by that the segments of the embossing surface (2) on the embossing tool (1) are of different sizes and have different embossing angles. [3] Method according to one of claims 1 or 2, characterized bythat when stamping the preform (3) more material is made available in the end areas (10) of the toothing compared to the middle area (9). [4] Method according to one of claims 1 to 3, characterized by that when embossing the preform (3) a different height is produced in the middle area (9) compared to the end areas (10) of the preform. [5] Embossing tool for producing a preform for a rack for a steering system of a vehicle with an embossing surface (2), characterized by that the embossing surface (2) has several segments, wherein the segments have different sizes and embossing angles in order to specifically provide material for a subsequent forming process.

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