Method for manufacturing a rack for a rack steering system, rack and steering gear with such a rack

Abstract

Method for manufacturing a rack (2) for a rack steering system comprising the following steps: a) Provision of a first rack segment (11) with a toothed structure (16) and with a radially projecting stop ring (13) formed integrally with the first rack segment (11), b) Provision of a second rack segment (12) with a ball screw structure (18) having a ball raceway (17), c) axial positioning of the rack segments (11, 12) relative to each other such that an end face of the first rack segment (11) adjacent to the stop ring (13) faces an associated end face of the second rack segment (12), characterized in that the method further comprises the following step: d) material-bonded connection of the two rack segments (11, 12) to each other in the area of ​​the said end faces by friction welding as a result of relative rotation of the rack segments (11, 12) to each other about a common longitudinal axis (20) and contacting of said end faces.

Description

[0001] The invention relates to a method for producing a rack for a rack-and-pinion steering system according to the preamble of patent claim 1. According to the preamble of claim 4, the invention further relates to a rack for a rack-and-pinion steering system. According to claim 7, the invention further relates to a steering gear with such a rack.

[0002] Rack and pinion steering systems are primarily used in passenger cars and light commercial vehicles. The rack is typically housed in a steering gear housing attached to the vehicle. The rack is axially movable relative to the steering gear housing to adjust the steering angle at the vehicle's wheels. For this purpose, two tie rods leading to the vehicle's wheels are pivotally connected to the ends of the rack. The rack also has a toothed structure that meshes with a steering pinion on a steering shaft to transmit a driver's steering command to the vehicle's wheels. In electromechanical steering systems, an electric motor assists the steering movement.The engine torque is transmitted, for example, via a belt drive to a ball screw nut, which, through the mediation of rolling elements in the form of balls, engages with a ball screw structure formed on the rack and having a ball raceway.

[0003] Such a generic rack is known, for example, from DE 10 2008 028 768 A1. The rack is formed by two rack segments, each having a connecting section at one axial end and axially connected to one another in the region of specially designed connecting sections by forming, such as rolling or rotary swaging. One of the rack segments has the aforementioned toothed structure, whereas the other rack segment has the ball screw structure. Furthermore, a stop ring is provided, which in one embodiment is integrally formed on one of the connecting sections. DE 10 2013 007 072 A1 describes a method for producing a rack of an electric power steering device, wherein a first rod section, a center section, and a second rod section are provided, which are positioned along a common axis and joined to one another at the end faces by friction welding.The two rod pieces each have rack teeth and are produced from a blank by forging.

[0004] Based on this, the object of the invention is to provide an alternative method for producing a rack for a rack-and-pinion steering system, which allows for simple and cost-effective production of said rack. Furthermore, the object of the invention is to create a rack that is simple and cost-effective to manufacture. Furthermore, the object of the invention is to provide a steering gear with such a rack.

[0005] The problem is solved with the features of independent claims 1, 4 and 7.

[0006] The process according to the invention is characterized by the following process steps: a) providing a first rack segment with a toothed structure and with a radially projecting stop ring formed integrally with the first rack segment, b) providing a second rack segment with a ball screw structure having a ball raceway, c) axial positioning of the rack segments relative to one another such that the end face of the first rack segment adjacent to the stop ring faces an associated end face of the second rack segment, and d) material connection of the two rack segments to each other in the area of ​​the said end faces by friction welding as a result of relative rotation of the rack segments to each other about a common longitudinal axis and contacting of the said end faces.

[0007] These measures significantly simplify the production of a rack for a rack-and-pinion steering system, as the number of components is minimized and only two individual parts are joined together to form the rack using a simple and cost-effective joining process. Furthermore, it is possible to easily and cost-effectively join rack segments with different diameters and / or made of different materials, which in turn can result in material, weight, and cost savings.

[0008] The subclaims describe preferred developments or embodiments of the invention.

[0009] Accordingly, with regard to step a), it is preferably provided that the toothing structure including the stop ring of the first rack segment is produced by forging a metal blank of the first rack segment. However, the invention is not limited to this forming method, but also encompasses known machining processes, such as broaching, milling, and / or the like, for forming the toothing structure and / or stop ring. In a further development of the method according to the invention, it is further provided that, with regard to step b), the ball raceway of the ball screw structure is produced by rolling, whirling, and / or grinding a metal blank of the second rack segment.Rolling refers to a forming process based on the generation of compressive stresses by a tool that is imprinted on the workpiece or blank. For example, one or more rollers or balls are used to reshape the surface layer of the blank into the aforementioned ball screw structure. In contrast, the conventional manufacturing processes of whirling and grinding represent machining processes.

[0010] The rack according to the invention for a rack and pinion steering system essentially comprises a) a first rack segment with a toothed structure and with a radially projecting stop ring formed integrally with the first rack segment, and b) a second rack segment with a ball screw structure having a ball raceway, c) wherein the rack segments are positioned relative to one another such that the end face of the first rack segment adjacent to the stop ring faces an associated end face of the second rack segment, and d) wherein the two rack segments are integrally connected in the region of said end faces by friction welding as a result of relative rotation of the rack segments to one another about a common longitudinal axis and contacting of said end faces. The advantages resulting from a rack designed in this way arise from the particularly simple and cost-effective production thereof described above. Preferably, the toothing structure including the stop ring of the first rack segment is produced by forging a metal blank of the first rack segment. However, the invention is not limited to this forming process, but also encompasses known machining processes, such as broaching, milling, and / or the like, for forming the toothing structure and / or the stop ring.It is further preferably provided that the ball track of the ball screw structure is produced by rolling, whirling and / or grinding a metal blank of the second rack segment.

[0011] The invention also relates to a steering gear with a rack of the type described above.

[0012] The invention is explained in more detail below with reference to the exemplary embodiment shown schematically in the drawing. However, it is not limited to this embodiment, but encompasses all embodiments defined by the patent claims. The only Fig. 1 shows a steering gear in a partially sectioned view with a rack according to the invention.

[0013] Fig. 1 shows a steering gear 1 of an electromechanical steering system for a motor vehicle. The steering gear 1 has a rack 2, which is mounted for axial movement in a steering gear housing 3. A pinion 4 of a steering shaft 5 engages the rack 2, via which a steering torque applied by the driver is introduced into the steering gear 1. Furthermore, the rack 2 is operatively connected at its ends to tie rods that lead to the front wheels of the vehicle (not shown in the drawing). An electric motor 6 is arranged in the steering gear housing 3. The drive torque of the electric motor 6, which supports the driver, is applied to the rack 2 as an axial force via a gear stage 7, which includes a ball screw drive 8. In the illustrated embodiment, the axis of rotation of the electric motor 6 runs parallel to the rack 2.

[0014] However, it is also possible to arrange the electric motor 6 coaxially around the rack 2. In principle, the gear stage 7 can also be implemented using gears (not shown in the drawing). However, according to this exemplary embodiment, a belt drive is used between a drive gear coupled to the electric motor 6 and an output gear on a ball screw nut 9 of the ball screw drive 8. The associated belt is designated 10.

[0015] The rack 2 has a first rack segment 11 and a second rack segment 12, which are integrally connected to one another, as discussed in more detail below. The first rack segment 11 has a radially projecting stop ring 13 formed integrally with the second rack segment to limit the axial stroke of the rack 2. For this purpose, counter-stops 14 and 15 are provided in the steering gear housing 3. In addition, the first rack segment 11, viewed in the axial direction, has, next to the stop 13, a toothed structure 16 that engages with the pinion 4 of the steering shaft 5. The toothed structure 16 and the stop ring 13 of the first rack segment 11 are preferably produced by forming, in particular forging, a metal blank (not shown in the drawing).In contrast, the toothing structure 16 and / or the stop ring 13 can also be produced by machining or by a combination of a forming process, such as forging, and a machining process.

[0016] The second rack segment 12 has a section with a ball track 17 of a ball screw structure 18 of the ball screw drive 8. The ball track 17 of the second rack segment 12 is operatively connected to the ball screw nut 9 of the ball screw drive 8 via balls 19. The ball track 17 of the ball screw structure 18 is preferably produced by rolling, whirling, and / or grinding a metal blank of the second rack segment 12 (not shown in the drawing).

[0017] As explained above, the two rack segments 11, 12 are connected to one another in a materially bonded manner. For this purpose, they are first positioned axially relative to one another in such a way that the end face of the first rack segment 11 adjacent to the stop ring 13 faces an associated end face of the second rack element 12. The materially bonded connection of the two rack segments 11, 12 to one another in the region of said end faces is achieved by friction welding as a result of relative rotation of the rack segments 11, 12 to one another about a common longitudinal axis 20 and contacting said end faces by pressing them together in the axial direction. The joint 21 or friction welding point is in Fig. 1 indicated by a dashed line. List of reference symbols 1 steering gear 2 rack 3 steering gear housing 4 pinions 5 Steering shaft 6 Electric motor 7 gear stage 8 ball screw 9 Ball screw nut 10 straps 11 first rack segment 12 second rack segment 13 Stop ring 14 Counter stop 15 Counter stop 16 Gear structure 17 ball track 18 Ball screw structure 19 ball 20 Longitudinal axis 21 joint

Claims

[1] Method for producing a rack (2) for a rack and pinion steering system, comprising the following steps: a) providing a first rack segment (11) with a toothed structure (16) and with a radially projecting stop ring (13) formed integrally with the first rack segment (11), b) providing a second rack segment (12) with a ball screw structure (18) having a ball track (17), c) axial positioning of the rack segments (11, 12) relative to one another such that an end face of the first rack segment (11) adjacent to the stop ring (13) faces an associated end face of the second rack segment (12), characterized by that the procedure further comprises the following step: d) materially bonding the two rack segments (11, 12) to one another in the region of said end faces by friction welding as a result of relative rotation of the rack segments (11, 12) to one another about a common longitudinal axis (20) and contacting of said end faces. [2] Method according to claim 1, characterized by that with regard to step a), the toothing structure (16) including the stop ring (13) of the first rack segment (11) is produced by forging and / or machining a metal blank of the first rack segment (11). [3] Method according to claim 1 or 2, characterized by that with regard to step b), the ball raceway (17) of the ball screw structure (18) is produced by rolling, whirling and / or grinding a metal blank of the second rack segment (12). [4] Rack (2) for a rack and pinion steering system, comprising: a) a first rack segment (11) with a toothed structure (16) and with a radially projecting stop ring (13) formed integrally with the first rack segment (11), and b) a second rack segment (12) with a ball screw structure (18) having a ball track (17), c) wherein the rack segments (11, 12) are positioned relative to one another in such a way that an end face of the first rack segment (11) adjacent to the stop ring (13) faces an associated end face of the second rack segment (12), characterized by , d) that the two rack segments (11, 12) are materially connected in the region of said end faces by friction welding as a result of relative rotation of the rack segments (11, 12) to one another about a common longitudinal axis and contacting of said end faces. [5] Rack (2) according to claim 4, characterized bythat the toothing structure (16) including the stop ring (13) of the first rack segment (11) is produced by forging and / or machining a metal blank of the first rack segment (11). [6] Rack (2) according to claim 4 or 5, characterized by that the ball track (17) of the ball screw structure (18) is produced by rolling, whirling and / or grinding a metal blank of the second rack segment (12). [7] Steering gear (1) with a rack (2) according to one of claims 4 to 6.

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