Steering pinion for a steering system and method for the production thereof

Steering pinions and methods for producing the same are described. The steering pinion has a toothed section for meshing with a gear rack and a connection section for connecting to a steering shaft. The toothed section includes a toothed part and the connection section includes a connection part. The toothed part and the connection part are pressed together in a rotationally fixed manner.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a national stage of International Application No. PCT/EP2012/063841, filed Jul. 13, 2012, which claims priority from German Patent Application No. 10 2011 079 274.0 filed on Jul. 15, 2011 in the German Patent and Trademark Office, the disclosure of which is incorporated herein by reference in its entirety.

BACKGROUND

1. Technical Field

The present invention relates to a steering pinion for a steering system of a motor vehicle and a method for the production of such a steering pinion.

2. Related Art

Steering pinions as coupling connections between the steering shaft and the gear rack of a motor vehicle are known in the prior art. These steering pinions are provided in order to transmit to a gear rack the torque applied to the steering shaft by the driver via the steering wheel. The gear rack in turn acts via the track rods to swivel the corresponding wheels of the vehicle. Such a steering pinion accordingly comprises a toothed section, which meshes with the teeth of the gear rack, and a connection section, which connects the steering pinion to the steering shaft. The toothed section typically has helical toothing, which is meshed with corresponding toothing in the gear rack.

In the prior art, steering pinions are formed in one piece, and are typically manufactured from a material which has high strength, in order to achieve reliable functioning and a long service life in the toothed section.

In this context, GB 953,793 is cited as an example which shows such a steering pinion. The steering pinion which it discloses is formed as a single part and, in accordance with its use, is formed from a high-strength material.

DE 10 2009 029 407 A1 discloses a method for manufacturing a steering pinion by initial machining of a semi-finished product, then a subsequent rolling operation. The steering pinion is formed as a single part.

From U.S. Pat. No. 3,688,374, a method of producing a one-piece steering pinion by cold forming is known.

Furthermore, from DE 102 60 426 B3, a one-piece steering pinion is known, which is produced by cold or hot working.

Typically, the diameter of the toothed section is greater than the diameter of the shaft and the connection section. When a conventional steering pinion is produced, high processing costs are accordingly incurred, since the connection section must be formed to the lower diameter either by turning or by laborious reshaping.

From US 2007/0068726 A1, a steering apparatus with electrical steering support is known, wherein a steering pinion is provided which has a pinion-side shaft and a torque-side shaft which are linked together by means of a linking pin.

SUMMARY

The present disclosure describes a steering pinion which can be produced using a reduced amount of material and with reduced production costs, and provides a method for producing such a steering pinion.

The steering pinion, which can be used as a coupling connection between the steering shaft and gear rack of a motor vehicle, comprises a toothed section for meshing with a gear rack, and a connection section for connecting to a steering shaft. According to the present disclosure, a toothed part having the toothed section and a connection part having the connection section are provided, wherein the toothed part and the connection part are pressed together in a rotationally fixed manner.

By forming the steering pinion from two components, namely the toothed part having the toothed section and the connection part having the connection section, both the toothed part and the connection part can be formed in accordance with the demands placed respectively upon each. Thus, the steering pinion can be produced using a reduced amount of material.

In particular, the toothed part may be manufactured using a solid piece of high-grade material, so that the toothed part, and in particular the toothing itself, can withstand the operational loads. The connection part, on the other hand, can be formed from a less high-grade material, and be hollow.

Furthermore, the division of the steering pinion into a toothed part and a connection part enables its production to be simplified, since the connection part can be supplied already with the desired thickness and/or with the desired diameter, with the result that appropriate turning of the shaft or laborious reshaping of the connection section of the connection part is unnecessary.

Because the parts are pressed together in a rotationally fixed manner, it is further possible to dispense with separate method steps for producing the rotationally fixed connection. For example the insertion of a pin, a bolt or another connection means can be dispensed with, so that production can be simplified. Furthermore, the pressing together creates a fully play-free connection, at least with respect to rotation, which enables precise functioning of the steering and a long service life to be achieved. Accordingly, in one embodiment, the connection is made by pressing together without additional connecting components or additional securing components.

In order to further simplify production while still achieving a rotationally fixed connection which satisfies the demands placed upon a steering pinion, the connection part and the toothed part advantageously overlap. In particular, a fixing section of the toothed part overlaps with a fixing area of the connection part. The steering pinion can accordingly be produced by pushing the toothed part into the connection part, and subsequently pressing them together.

The connection between the toothed part and the connection part is, in one embodiment, formed to be durable and not disassemblable. The term “not disassemblable” is to be understood here as meaning that the design of the connection is such that no disassembly of the toothed part and the connection part is provided. In particular, disassembly and subsequent reassembly is not provided. It can thus even be conceivable and possible that the toothed part and the connection part cannot be disassembled in a manner that would allow them to be subsequently reassembled. In this case, disassembly of the connection between the connection part and the toothed part cannot therefore be carried out without destroying the parts.

In order further to improve the resistance to rotation between the toothed part and the connection part, the fixing section can have at least one material elevation, for example, in the form of a knurl and/or a nub and/or a roller-burnished region.

In an embodiment, in the fixing section and/or the fixing area, material elevations and/or material depressions are provided, such as nubs, knurls, roller-burnished regions and/or grooves, to increase the available torque transmission. By the use of such connecting means, positive locking for the connection can be provided, in addition to non-positive locking.

In a further advantageous embodiment, in order to increase the available torque transmission, the fixing section and/or the fixing area are formed conically.

In order to reduce the material costs and the weight of the steering pinion, the toothed part and the connection part can, in an embodiment, use different materials, and thereby be efficiently adapted to their different tasks.

Less weight combined with reliable functioning results when the toothed part is manufactured from a solid piece and the connection part is formed from a tube. In this case the toothed part can be manufactured in a cold forming process. Cost-effective provision of the connection part is also achieved due to the widespread and inexpensive availability of tubes with standard dimensions.

Simple production and reliable functioning result if the connection part and the toothed part are connected to each other either non-positively, or both positively and non-positively. An even simpler production can be achieved by the fixing of the connection part to the toothed part by a pressing operation only. In an embodiment, the fixing section is at least in part conical, in order to facilitate assembly.

The toothed part, in an embodiment, has a depression, for example, a groove and/or a recess around all or part of its circumference, into which material of the connection part is introduced, such as by knurling and/or roller burnishing and/or pressing-on and/or rolling, in order to form a positive connection as a protection against separation.

In an exemplary embodiment, the depression can have at least one serration or knurl, in order to enable the creation of a connection between the connection part and the toothed part that is as rotationally fixed as possible.

The toothed part, in an embodiment, has a bearing seat to accommodate a rolling bearing, which can serve as a radial bearing and/or an axial bearing for the steering pinion.

In another embodiment, the rolling bearing is held compressively between the connection part and the toothed part, and in this manner retained positively and under pre-tension between the connection part and the toothed part. In this case, the rolling bearing is particularly retained positively in the radial direction and under pre-tension in the axial direction.

In yet another embodiment, the connection part and the toothed part are pressed together in a rotationally fixed manner and the rolling bearing is simultaneously clamped, or pre-tension is applied such that it is retained fixedly with its inner ring on the steering pinion. In other words, pressing the connection part and the toothed part together in a rotationally fixed manner can at the same time achieve secure fixing of the rolling bearing.

The term “pressed together in a rotationally fixed manner” is understood here to mean that the connection part and the toothed part are connected by the pressing and the non-positive locking resulting therefrom, and in one embodiment, the press fit that is formed, in such a manner that the torques applied via the connection part can be transmitted to the toothed part via the connection that is formed by pressing. A certain amount of positive locking can additionally be provided, in particular by pressing above a knurled or roller-burnished section, or by means of an additional possible rolling of material into a serrated section.

A method for the production of a steering pinion with a toothed section for meshing with a gear rack and a connection section for connecting to a steering shaft comprises the steps of providing a toothed section having the toothed part and providing a connection section having the connection part. The toothed part and the connection part are subsequently connected together in a rotationally fixed manner, and the parts are pressed together in order to produce the rotationally fixed connection.

In this manner a reliable production method is provided, by means of which a steering pinion can be produced with efficient use of material.

A rolling bearing can be accommodated, prior to the connection of the toothed part with the connection part, on a bearing seat of the toothed part. In one embodiment, the rolling bearing is pressed between the toothed part and the connection part with the application of pre-tension to the rolling bearing.

In order to provide protection against the connection being pulled apart, at least one depression, such as in the form of a groove and/or a recess, can be formed in the toothed part, and material of the connection part can be introduced into the depression, in particular by roller burnishing or by framing a bead. In this case, the circumferential edges of the depression in the form of a circumferential groove can, in one embodiment, have a serration, into which the pressed-on connection part is introduced as it is roller-burnished or rolled into shape, thus providing an additional positive connection.

In an exemplary embodiment, the method for the production of a steering pinion with a toothed section for meshing with a gear rack of a motor vehicle steering system and with a connection section for connecting the steering pinion to a steering shaft comprises at least the following steps: providing a toothed part having the toothed section and a fixing section; providing a connection part having the connection section and a fixing area, wherein a receptacle in the form of an opening for receiving the fixing section of the toothed part is formed in the fixing area; forming a material elevation, such as in the form of a roller-burnished region and/or a knurl, on the fixing section, such that the material is elevated beyond the original external diameter of the fixing section and its inscribed diameter is greater than the internal diameter of the opening of the connection part; and pressing the fixing area together with the fixing section to form a non-positive connection.

In an exemplary embodiment, the receptacle in the form of the opening is perfectly cylindrical, and the diameter of the opening is enlarged by less than 0.2 mm during the pressing. The term “perfectly cylindrical” is to be understood in the present disclosure to mean a shape which deviates from an exact cylindrical shape only by normal manufacturing tolerances.

In one embodiment, prior to the connection of the toothed part with the connection part, a rolling bearing can be accommodated on a bearing seat of the toothed part. In this manner, a particularly efficient production of the steering pinion can take place.

DETAILED DESCRIPTION

Examples of embodiments are described below with the aid of the figures. In the figures, elements which are identical or similar, or have identical effects, are designated with identical reference signs, and repeated description of these elements is in part dispensed with in the description below, in order to avoid redundancy.

FIG. 1shows schematically the structure of a typical steering system of a motor vehicle. Accordingly, a steering wheel2is provided, by means of which the driver carries out the steering movements, which must then be transmitted to the wheels6in order to bring about a change in the direction of the motor vehicle.

The steering movements of the steering wheel2are transmitted via a steering shaft3to a steering pinion1, which has a toothed area which meshes with a gear rack4. The rotation of the steering pinion1causes the gear rack4to move translationally along its axis. The gear rack4is connected to track rods5, which in turn transmit the translational movement of the gear rack4into a steering movement of the schematically-shown wheels6.

The steering forces can be increased and/or assisted by a power steering system7or8. In the example embodiment of a typical steering system that is shown, the schematically-indicated power steering systems7,8are disposed between the steering wheel2and the steering pinion1. A power steering system7,8can thereby either provide pure power assistance, or alternatively—or in combination with this function—it can also increase the steering angle when this is demanded by the applicable control system of the motor vehicle.

The steering shaft3is usually formed from multiple parts, and extends from the steering wheel2to the steering pinion1, with the installation path of the steering shaft adapted by means of universal joints9to the installation conditions of the particular motor vehicle.

The steering pinion1must, depending on the configuration and design of the applicable steering system, for example, transmit large torques of up to 250 Nm. For this reason, in the prior art each steering pinion is formed as a single part, manufactured by metal cutting processes from a solid piece, and usually additionally hardened, in order to ensure that it is capable of the demands placed upon it to transmit the high torques with the required precision in steering the motor vehicle, as well as having a high degree of stability and an adequate service life.

The steering pinion1is accordingly provided as a coupling connection between the steering shaft3and the gear rack4. In order to be able to fulfill this function, it has a toothed section for meshing with the gear rack4and a connection section10for connecting to the steering shaft3.

FIG. 2shows a steering pinion1according to the present disclosure. The steering pinion1has a connection part12and a toothed part11, with the toothed part11and the connection part12formed as two separate components which are connected together in at least a rotationally fixed manner in order to form the steering pinion1. The toothed part11has the toothed section18for meshing with the gear rack4, and the connection part12has the connection section10for connection to the steering shaft3.

In an embodiment, the connection section10of the connection part12is, as seen inFIGS. 2 and 12, tapered relative to the remainder of the shaft of the connection part12, and has a ribbing in order to ensure that the connection to the steering shaft3is rotationally fixed. Besides the ribbing that is shown, other measures affecting the geometry can also be used to achieve an adequately rotationally fixed connection—capable of being assembled and disassembled—between the connection part12and a steering shaft3. In an exemplary embodiment, the ribbing is in the form of a spline, or a polygon. This spline, or plurality of surfaces and flat sections formed as a polygon, may be produced in a reforming process by pressing or hammering. Production by means of a high internal pressure method is conceivable and possible. To assemble the connection part12with the steering shaft3, a screwed bolt—not shown here in the Figures—is normally provided. The connection part12further has a fixing area13, in which a receptacle in the form of a cylindrical opening26is disposed. At the end of the connection part12that faces away from the connection section10, an end face is formed which surrounds the opening26and serves as a shoulder20in the steering pinion1.

The toothed part11has, in the area of the toothed section18, helical toothing which is intended to mesh with the gear rack4of the steering system. Rotation of the steering pinion1, and in particular of the toothed part11, accordingly brings about translational movement of the gear rack4. Although helical toothing is depicted in the example embodiment that is shown, it is also possible to use any other toothing that enables the transmission of force from the toothed part11to the gear rack4.

The connection part12and the toothed part11are connected to each other in a rotationally fixed manner by being pressed together such that a press fit is formed. The connection part12and the toothed part11overlap in a fixing area13of the connection part12and a fixing section25of the toothed part11, as can be seen inFIGS. 5 and 6 and/or 7 and 8.

In an embodiment, this connection between the toothed part11and the connection part12is formed to be durable and not disassemblable. The term “not disassemblable” is to be understood in the present disclosure to mean not that disassembly is completely impossible, but that the design is such that disassembly and subsequent reassembly of the disassembled parts is not intended.

The formation of a rotationally fixed press fit is aided by the provision of material elevations, such as nubs, a knurl or a roller-burnished region in the fixing section25of the toothed part11. The fixing area13and/or the fixing section25can also be formed slightly conically over at least part of its length, in order to simplify the formation of a press fit when pressing the two components together, and so facilitate assembly.

In order to provide—alongside the formation of a rotationally fixed connection—protection from axial displacement, or against the pulling apart of the toothed part11relative to the connection part12, protection against pulling apart in the region14, for example, in the form of a circumferential beading, is provided, by means of which the connection part12is fixed to the toothed part11in the direction of pulling apart or in the direction of the axis of the steering pinion1. The precise formation of the protection against pulling apart region14will be described in the context of the descriptions of the example embodiments inFIGS. 5 and 6 and/or 7 and 8.

Protection against pulling apart of the connection part12and the toothed part11can additionally be achieved by the press fit, such that, in a particular embodiment, the pressing of the connection part12onto the toothed part11is sufficient in itself to protect against disassembly.

To support the steering pinion in the housing of the steering gear, a bearing is provided. In one embodiment, at least one rolling bearing16is used. This rolling bearing16can be formed in a simple manner integrally with the steering pinion1of the present disclosure. To achieve this the rolling bearing16is, in an embodiment, disposed between the connection part12and the toothed part11. The rolling bearing16is positioned by means of a first shoulder19disposed on the toothed part11and by means of a second shoulder20formed by the end face of the connection part12which faces the toothed part11. The rolling bearing16is retained between the toothed part11and the connection part12by the pressing together of the toothed part11with the connection part12. In an exemplary embodiment, a pre-tension is applied in this manner by the two above-mentioned parts to the rolling bearing16, with the result that the rolling bearing16is retained non-positively between the connection part12and the toothed part11.

In addition to the rolling bearing16, which serves as a radial bearing, a further bearing21can be provided, which serves as an axial bearing. This bearing21can be formed as a sliding bearing or as a rolling bearing.

The bearing21can also be a radial bearing, in addition to an axial bearing. It is conceivable and possible to provide the axial bearing in the rolling bearing16and dispense with the bearing21.

In the embodiment shown inFIG. 3, a further example of a steering pinion1with a toothed part11and a connection part12is shown, in which the connection part12is formed from a tube. In this case, the connection section10is produced by a flattening and tapering of the tube, so that a connection of the steering shaft3to the connection section10can be made by means of a receptacle in the steering shaft3, which cooperates with the connection section10.

In order, in addition to the rotationally fixed connection, to achieve fixing and security in an axial direction, protection against pulling apart region14is also provided, such as in the form of non-circumferential depressions.

FIG. 4shows a toothed part11formed from a solid piece, which has, in addition to the actual toothed section18, a bearing seat15, which is provided to accommodate a rolling bearing16, such as shown inFIGS. 2 and 3. In an exemplary embodiment, the axial extension of the bearing seat15is smaller than the axial extension of the rolling bearing16. In other words, the rolling bearing16is wider than the bearing seat15. In this manner, it is possible to achieve the adjustment to a predetermined value of the pre-tension which is applied to the rolling bearing16by the shoulder19of the toothed part11and the shoulder20of the connection part12—independently of the tolerances in the widths. Accordingly, the connection part12and the toothed part11do not abut each other in a manner that would prohibit the application of the pre-tension to the rolling bearing16.

The fixing section25of the toothed part11is also shown, onto which the complementary fixing area13of the connection part12is pushed or pressed in a subsequent operation. The fixing section25here shows a depression17, into which material of the connection part12can flow, in order to produce here a positive connection in the axial direction of the steering pinion1between the connection part12and the toothed part11. By this means, additional pre-tension can also be applied to the rolling bearing16, in order to retain the rolling bearing16in the desired position.

The fixing section25further shows a flattened cross-sectional geometry, which is suitable for forming an alternative rotationally fixed connection.

In order to be able to fix the rolling bearing16during the production of the steering pinion1in a precise manner and for its entire service life, the inner race of the rolling bearing16is fixed under pre-tension on the bearing seat15between a shoulder19disposed on the toothed part11and the shoulder20, which is formed by the end of the connection part12, which faces the rolling bearing16. The pre-tension is, in one embodiment, applied during the pressing of the toothed part11together with the connection part12, and maintained by the resulting press fit.

The formation of a rotationally fixed press fit of the tube-shaped connection part12on the fixing section25of the toothed part11can, in one embodiment, be achieved by providing material elevations on the fixing section25of the toothed part11, which provide an additional non-positive and, in one embodiment, also positive connection between the connection part12and the toothed part11. The material elevations are for example in the form of nubs, but may be in the form of a knurl22, such as shown inFIG. 10, or in the form of a roller-burnished region23, such as shown inFIG. 11.

The embodiment shown inFIGS. 5 and 6shows an additional embodiment of a steering pinion1. In this embodiment, a circumferential beading is provided in the connection part12, which forms the protection against pulling apart region14. The protection against pulling apart region14in the form of the beading is disposed in the connection part12in a position corresponding to a depression or groove17below it in the toothed part11. Accordingly, the beading, which serves as the protection against pulling apart region14, is formed around the entire circumference of the connection part12, and in this manner provides reliable protection against pulling apart. By means of a beading operation, material from the connection part12, which is formed as a tube, is rolled into the depression17, which is in the form of a circumferential groove, so that material flows into the groove.

The flowing of material into the groove17also applies further pre-tension to the rolling bearing16, which as a result can be retained fixedly in its position.

A beading operation of this kind can form the circumferential beading around the depression17in a simple manner, using a roller24, indicated schematically, which is set in rotation. The material of the connection part12accordingly flows into the depression17of the toothed part11. By means of such rolling, the strength of the connection between the connection part12and the toothed part11can also be increased over the entire area of the fixing section25and the fixing area13. The stresses acting in the axial direction provide a corresponding material flow, which also forces material into the depressions between the material elevations. In addition, pre-tension is applied to the rolling bearing16to fix the rolling bearing16between the shoulder19of the toothed part11and the shoulder20of the connection part12.

Particularly inFIG. 6, it is clear to see that not only is the rolling bearing16retained on the toothed part11by being pushed onto or accommodated on the bearing seat15, but also in particular that a corresponding pre-tension is applied by the pressed-on connection part12, which provides a positive-locking fit and a corresponding pre-tension by directly abutting the rolling bearing in the area of the bearing seat, with the result that the rolling bearing is also fixed in place when the connection part12is pressed onto the toothed part11.

FIGS. 7 and 8show an additional embodiment, in which the protection against pulling apart region14of the connection part12has again been carried out by means of simple pressing of material from the connection part12into a corresponding depression in the toothed part11.

InFIG. 8it can also be seen that not only is the tube-shaped connection part12pressed onto the fixing section25of the toothed part11in order to achieve a rotationally fixed connection, but also, in the area of the protection against pulling apart region14, material from the connection part12is introduced into a depression17in the form of a recess. The material of the connection part12is simply pressed into the depression17in this manner to produce a positive-locking fit as protection against pulling apart.

InFIG. 8it can again be seen clearly that the rolling bearing16is positively retained in the steering pinion1by the connection part12. For this purpose, in the toothed part11, a shoulder19, which the rolling bearing16abuts, is formed in the end of the bearing seat15facing away from the fixing section25. Accordingly the rolling bearing16is held compressively, and thereby securely retained, between the shoulder19and the shoulder20, which is formed by the end of the connection part12. A pre-tension is, in one embodiment, applied to the rolling bearing16in the axial direction, with the result that it is retained securely.

Because the toothed part11is formed from a solid piece and the connection part12is formed as a conventional tube, the steering pinion can be produced cost-effectively, and the use of high-grade material in the pinion can be reduced.

FIG. 9shows an additional measure to further increase the resistance to rotation of the connection part12relative to the toothed part11. In particular, the edges of the depression17in the form of the circumferential groove in the toothed part11are serrated or knurled. When material of the connection part12is introduced into, or flows into, the depression17, the resistance to rotation is at the same time increased further by means of the serrated edge.

The toothed part11is, in one embodiment, produced by means of a cold forming process, and the connection part12is formed from a tube. As a result, an advantageous selection of material can be carried out, in that the toothed part11can be formed in accordance with the requirements placed upon it in terms of strength in the toothed area, as a part cut from a solid piece of material and possibly hardened, while in contrast the connection part12can be formed using a less expensive and/or lighter material, and be formed as a tube, which can also achieve a saving of material.

In order to produce the steering pinion1, a toothed part11and a connection part12are first provided. The connection part12is then connected in a rotationally fixed manner to the toothed part11. This rotationally fixed connection is achieved by pressing.

In certain embodiments the protection against pulling apart region14is additionally produced, in that the connection part12undergoes a beading operation in the location of a corresponding depression17in the toothed part11, and material of the connection part12accordingly flows into the depression17.

In a further advantageous embodiment, prior to the pressing of the connection part12onto the toothed part11, the rolling bearing16is in addition pushed or pressed onto the bearing seat15of the toothed part11, and only then is the connection part12pressed onto the fixing section25of the toothed part11. In this manner a pre-tension is again applied to the rolling bearing16in the axial direction, in order to fix it securely.

InFIG. 10a toothed part11is illustrated in which the fixing section25is provided with a knurl22. InFIG. 11a toothed part11is illustrated in which the fixing section25is provided with a roller-burnished region23. The external diameter of the greatest material elevation of the roller-burnished region23or the knurl22is greater than the internal diameter of the opening26of the connection part12in the fixing area13. When the connection part12is pushed onto the fixing section25, the tips of the material elevations of the roller-burnished region or knurl are flattened and dig themselves into the inner surface of the opening of the fixing area13of the connection part12. A non-positive connection is thereby achieved, and/or a press fit is formed, which enables the fixed connection. In an embodiment, the widening of the connection part12in the fixing area13remains below 0.2 mm, in order to achieve a durable connection. The connection can thereby be formed in such a durable manner that no additional protection against pulling apart region14, with a corresponding depression17, is necessary.

To the extent practicable, all individual features described in the individual example embodiments can be combined with each other and/or exchanged, without departing from the field of the invention.