METHOD FOR PRODUCING A STEERING SHAFT PART AND STEERING SHAFT FOR A MOTOR VEHICLE

Abstract

A method may be utilized to produce a steering spindle part configured as a hollow shaft and having a connecting portion at its end. At least a part of the connecting portion includes increased wall thickness relative to a portion of the steering spindle part adjoining the connecting portion. The method may involve providing a circular, hollow cylindrical tube with an inner surface that is smooth in a circumferential direction, providing a circular, hollow cylindrical sleeve with an outer surface that is smooth in a circumferential direction, inserting the sleeve into an end portion of the tube, and jointly deforming the end portion of the tube and the sleeve such that a flow of material occurs. This flow may form positively locking elements on the tube and the sleeve that engage into one another in the circumferential direction and generate positive locking in the circumferential direction.

Claims

1-9. (canceled).

10. A method for producing a steering spindle part that forms a portion of a steering spindle for a motor vehicle, wherein the steering spindle part is configured as a hollow shaft with a connecting portion at least at one end of the hollow shaft, wherein at least a portion of a length of the connecting portion has an increased wall thickness relative to a portion of the steering spindle part that adjoins the connecting portion, the method comprising: providing a hollow cylindrical tube with an inner surface that is smooth in a circumferential direction and that comprises a circular cross section; providing a hollow cylindrical sleeve that includes an outer surface that is smooth in a circumferential direction and that comprises a circular cross section; inserting the hollow cylindrical sleeve into an end portion of the hollow cylindrical tube; and jointly deforming the end portion of the hollow cylindrical tube and the hollow cylindrical sleeve, wherein a flow of material of the hollow cylindrical tube and the hollow cylindrical sleeve occurs, the flow forming positively locking elements on the hollow cylindrical tube and the hollow cylindrical sleeve, which positively locking elements engage into one another in the circumferential direction to generate positive locking that acts in the circumferential direction.

11. The method of claim 10 wherein the joint deformation comprises deforming the circular cross sections of the hollow cylindrical tube and the hollow cylindrical sleeve into a non-circular shape.

12. The method of claim 10 wherein the joint deformation comprises reducing outer and inner diameters of the hollow cylindrical tube and the hollow cylindrical sleeve at least over a portion of a common length extant of the hollow cylindrical tube and the hollow cylindrical sleeve.

13. The method of claim 10 wherein the joint deformation is performed by way of cold working.

14. The method of claim 10 wherein the joint deformation comprises: introducing a mandrel with a non-circular cross section into the hollow cylindrical sleeve; and exerting an external deformation pressure on the hollow cylindrical tube to mold the hollow cylindrical tube and the hollow cylindrical sleeve jointly on the mandrel.

15. The method of claim 14 wherein a deformation tool exerts the external deformation pressure on the hollow cylindrical tube.

16. The method of claim 10 comprising forming a coupling portion into an inner wall of the hollow cylindrical sleeve after the joint deformation of the end portion of the hollow cylindrical tube and the hollow cylindrical sleeve.

17. The method of claim 10 wherein the joint deformation comprises forming a conical portion that narrows in a direction of an adjacent end of the hollow cylindrical tube of the steering column part, and a hollow cylindrical portion that is disposed further in the direction of the adjacent end relative to the conical portion.

18. A steering spindle comprising a steering spindle part that forms a portion of a steering spindle for a motor vehicle and that is configured as a hollow shaft, the steering spindle part comprising: a connecting portion disposed at an end of the hollow shaft, wherein at least a part of a length of the connecting portion comprises an increased wall thickness relative to a portion of the steering spindle part that adjoins the connecting portion; and a sleeve disposed in the connecting portion within the hollow shaft, wherein the sleeve lies against and is connected to an inner wall of the hollow shaft; wherein the hollow shaft and the sleeve comprise, at least over a portion of the length of the connecting portion, jointly deformed positive-locking elements that engage into one another in a circumferential direction and generate positive locking that acts in the circumferential direction.

Description

DESCRIPTION OF THE DRAWINGS

[0007] Advantageous embodiments of the invention will be discussed in more detail below on the basis of the drawings, in which, in detail:
FIG. 1 shows a motor vehicle steering system,
FIG. 2 shows a steering spindle part according to the invention in a perspective illustration,
FIG. 3 shows a tube and a sleeve prior to the insertion in a perspective illustration,
FIG. 4 shows a tube and a sleeve after the insertion in a perspective illustration,
FIG. 5 shows a longitudinal section through the arrangement shown in FIG. 3,
FIG. 6 shows a longitudinal section through the arrangement shown in FIG. 4,
FIG. 7 shows a detail illustration of FIG. 6,
FIG. 8 shows a longitudinal section through a steering spindle part in a deforming device prior to the deformation,
FIG. 9 shows a longitudinal section through a steering spindle part in a deforming device after the deformation,
FIG. 10 shows a detailed view of the fully deformed steering spindle part as per FIG. 9,
FIG. 11 shows the deformed steering spindle part as per FIG. 9 in an exploded illustration,
FIG. 12 shows a deforming mandrel in a perspective illustration,
FIG. 13 shows a second embodiment of a steering spindle part according to the invention.

EMBODIMENTS OF THE INVENTION

[0008] In the various figures, identical parts are always denoted by the same reference designations, and will therefore generally also be named or mentioned only once in each case.
FIG. 1 schematically illustrates a motor vehicle steering system 100, wherein a driver can input a corresponding steering torque (steering moment) as a steering command into a steering shaft 1 using a steering wheel 102. The steering moment is transmitted by the steering shaft 1 to a steering pinion 104, which meshes with a toothed rack 106, which then in turn transmits the predefined steering angle to the steerable wheels 110 of the motor vehicle by means of a displacement of the track rods 108.
An electrical power assistance means may be provided in the form of a power assistance means 112 coupled at the input side to the steering shaft 1, of a power assistance means 114 coupled to the pinion 104, and/or of a power assistance means 116 coupled to the toothed rack 106. The respective power assistance means 112, 114 or 116 couples an auxiliary torque into the steering shaft 1 and/or the steering pinion 104 and/or an auxiliary force into the toothed rack 106, whereby the driver is assisted in performing steering work. The three different power assistance means 112, 114 and 116 illustrated in FIG. 1 show possible positions for the arrangement thereof.
Normally, only a single one of the positions shown is occupied by a power assistance means 112, 114 or 116. The auxiliary torque or the auxiliary force which is to be imparted by the respective power assistance means 112, 114 or 116 for the purpose of assisting the driver is determined to take into consideration a steering moment input by the driver and detected by a torque sensor 118. Alternatively or in combination with the introduction of the auxiliary torque, an additional steering angle can be introduced into the steering system by the power assistance means 112, 114, 116, which additional steering angle is added to the steering angle imparted by the driver using the steering wheel 102.
The steering shaft 1 comprises, at the input side, an input shaft 10 connected to the steering wheel 102 and, at the output side, an output shaft 12 connected to the toothed rack 106 via the steering pinion 104. The input shaft 10 and the output shaft 12 are coupled to one another in a rotationally elastic manner by means of a torsion bar which is not shown in FIG. 1. Thus, a torque input into the steering shaft 10 by the driver using the steering wheel 102 leads to a relative rotation of the input shaft 10 with respect to the output shaft 12 whenever the output shaft 12 does not rotate exactly synchronously with respect to the input shaft 10. This relative rotation between input shaft 10 and output shaft 12 can be measured by means of a rotational angle sensor and, correspondingly, on the basis of the known torsional stiffness of the torsion bar, a corresponding input torque relative to the output shaft 12 can be determined. In this way, through the determination of the relative rotation between input shaft 10 and output shaft 12, the torque sensor 118 is formed. A torque sensor 118 of said type is known in principle and may for example be realized by means of an electromagnetic sensor arrangement, as described further below, or by either means of measurement of the relative rotation.
Correspondingly, a steering moment imparted to the steering shaft 1 or to the input shaft 10 by the driver using the steering wheel 102 will give rise to the introduction of an auxiliary torque by one of the power assistance means 112, 114, 116 only if the output shaft 12 is rotated relative to the input shaft 10 counter to the torsional resistance of the torsion bar.
The torque sensor 118 may also alternatively be arranged at the position 118, wherein then, the division of the steering shaft 1 into input shaft 10 and output shaft 12 and the rotationally elastic coupling by means of the torsion bar are correspondingly present at a different position in order, from the relative rotation of the output shaft 12 coupled to the input shaft 10 via the torsion bar, to be able to determine a relative rotation and thus correspondingly an input torque and/or an auxiliary torque to be introduced.
The steering shaft 1 as per FIG. 1 furthermore comprises at least one cardanic joint 120, by means of which the profile of the steering shaft 1 in the motor vehicle can be adapted to the spatial conditions.
The input shaft 10 of the steering shaft 1, to which the steering wheel 102 is attached in the illustrated example, is designed according to the invention as a variable-length steering shaft 10. The outer part of the steering shaft 10 of telescopic construction is formed by a steering spindle part 3.
FIG. 2 shows the steering spindle part 3 which, in the motor vehicle steering system 100 as per FIG. 1, forms that part of the input shaft 10 to which, at the rear end in relation to the direction of travel, the steering wheel 102 is attached. The steering wheel 102, which is not illustrated in FIG. 2, is attached to a connecting portion 31, which is formed at that end region of the steering spindle part 3 which faces toward the viewer in FIG. 2. The connecting portion 31 may be equipped on the outside with an external toothing 311, and on the inside with an internal thread 312, which in this case is merely schematically illustrated in order to give an improved overview. Onto the external toothing 311, which is formed for example as a spline toothing, a steering wheel 102 can be mounted in positively locking fashion by way of a corresponding internal toothing, and fixed by virtue of a screw being screwed into the internal thread 312.
In the connecting portion 31, the wall thickness is D.
The connecting portion 31 is adjoined in a longitudinal directionforward in relation to the direction of travelby a conically widening portion 32, which in turn is adjoined by a tube portion 33. The tube portion 33 transitions into a steering moment transmission portion 34, which is equipped with a contour that deviates from a circular arc. A further steering spindle part (not illustrated here) is inserted axially, that is to say telescopically in the longitudinal direction, into said steering moment transmission portion in order to form a torque-transmitting connection which is telescopic for the purposes of adjusting the position of the steering wheel 102. The steering torque transmission portion 34 may be formed in particular with a arcuate toothing formed over the circumference or a cloverleaf profile, which corresponds to the cross section of the telescopic steering spindle part in order to form a connection which is positively locking with respect to rotation and fixed in terms of torque.
As illustrated in FIGS. 3 and 5, as a starting product for producing a steering spindle part 3, a hollow cylindrical tube 4 is provided, which comprises a uniform wall thickness d over its entire longitudinal extent, and a likewise hollow cylindrical sleeve 5. The tube 4 comprises an inner surface 41 which is smooth in the circumferential direction and which is in the shape of a cylindrical shell and comprises a cross section in the shape of a circular line, and which comprises no structures protruding radially from the inner surface or recessed into said inner surface. The sleeve 5 comprises an outer surface 51 which is smooth in the circumferential direction and which is likewise in the shape of a cylindrical shell with a cross section in the shape of a circular line, and which likewise comprises no radial projections or depressions.
The wall thickness d of the tube 4 is selected to be only as large as is necessary for the stability of the steering spindle part 3, in particular for the transmission of the occurring torques.
The outer diameter of the sleeve 5 and the inner diameter of the tube 4 are selected such that the sleeve 5 can be inserted in a frictionally locking manner in a longitudinal direction into an end portion 42 of the tube 4, that is to say can be axially pressed in, as indicated by the arrow in FIGS. 3 and 5.
After the insertion, the state illustrated in FIGS. 4 and 6 is attained, in which the sleeve 5 terminates flush with the end of the tube 4.
FIG. 7 illustrates an enlarged longitudinal section showing how the sleeve 5 is seated in frictionally locking fashion in the end portion 42 of the tube.
In the next step, a mandrel 6 is introduced into the tube 4 and the sleeve 5, as illustrated in longitudinal section in FIG. 8. The mandrel 6 is formed in three parts and comprises a deforming mandrel 61, a first supporting mandrel 62 and a second supporting mandrel 63. The deforming mandrel 61 is, in the longitudinal direction, positioned in the end portion 42 in the opening of the sleeve 5 and lies with its outer machining surface against the sleeve 5 from the inside. The first supporting mandrel 62 is positioned in the adjoining portion of the tube 4 and, there, lies against the inner surface 41 of the tube 4. The second supporting mandrel 63 comprises a bore in which a pin of the deforming mandrel 61 is received and supports said pin radially. Furthermore, the second supporting mandrel 63 comprises a conical outer surface portion 631, which projects at least partially into the end portion 42. The deforming mandrel 61 and the second supporting mandrel 63 do not lie axially against one another in the longitudinal direction, that is to say the deforming mandrel 61 and the second supporting mandrel 63 are not moved into a block state.
The deforming mandrel 61 is illustrated in an enlarged perspective view in FIG. 12. In this figure, it can be seen that said deforming mandrel comprises a cylindrical molding surface 611 which comprises outwardly protruding molding projections 612 which are formed as ribs which run in a longitudinal direction and which comprise a rounded cross section. In the example shown, four of these molding projections 612 are arranged so as to be distributed uniformly over the circumference.
For the deformation, the mandrel 6 with the tube 4 and the sleeve 5 is arranged in a deforming device with a hammering tool 7. It is preferable for multiple hammering tools 7 to be arranged in the deforming device so as to be distributed uniformly over the circumference. To illustrate the principle, in each case only one hammer head 7 is shown in the simplified illustration of FIGS. 8 and 9.
As can be seen in FIG. 8, the tube 5 initially comprises a continuously uniform diameter R over its entire length, even in the end region 42. During the deformation, by means of the hammering tool 7, impacts are exerted in a radial direction on the end region 42 of the tube 4, as indicated by the double arrow in FIG. 9. Between individual hammer impacts, the mandrel 6 together with tube 4 and sleeve 5 is rotated continuously, as indicated by the curved arrow. In this way, by means of the hammer surface 71 of the hammering tool 7, the entire outer circumference is deformed in a sequence of hammer impacts.
Upon the impacting of the hammer surface 71, the tube 4 is, in the end region 42, deformed radially inward against the sleeve 5. The sleeve 5 is itself plastically deformed by the deforming pressure and, in the process, is reduced in diameter. In the final state as illustrated in FIG. 9, on the tube 4, the end portion 42 has been deformed into the connecting portion 31, the diameter r of which is smaller than the diameter R of the tube 4. During the deformation, the sleeve 5 comes into continuous contact with the molding surface 611 of the deforming mandrel 61. Here, the molding projections 612 are plastically molded from the inside into the inner side of the sleeve 5 so as to form indentations 52, as can be seen in FIG. 11, which shows the individual parts after the deformation as per FIG. 9 in the exploded state.
Owing to the indentations 52, projections 53 which protrude from the outer surface 51 of the sleeve 5 are plastically pushed out, which projections form positive-locking elements according to the invention on the sleeve 5. During the deformation, said projections 53 press radially from the inside into the inner surface 41 of the tube 4, whereby depressions 43 are formed in, which form positive-locking elements according to the invention in the tube 4. As can be seen in the enlarged sectional illustration of FIG. 10, the projections 53 of the sleeve 5 engage in positively locking fashion into the depressions 43 of the tube 4.
It is alternatively or additionally possible, as in the embodiment as per FIG. 13, for polygon surfaces 44 arranged so as to be distributed over the circumference to be formed during the deformation. In this way, during the joint deformation according to the invention, the sleeve 5 and the tube 4 are, in the connecting portion 31, formed as polygonal elements which engage into one another in positively locking fashion, for example as hexagons. Said polygonal elements may be of conical form, like the polygonal surfaces 44 in FIG. 13.
All of the examples shown have in common the fact that, according to the invention, the positive-locking elements, for example the projections 53 and the depressions 43, or else the polygon surfaces 44, are not formed in in advance in a separate machining step as in the prior art, but rather are produced during the joint deformation of tube 4 and sleeve 5. This permits more economical manufacture, and an improved connection of sleeve 5 and tube 4.

LIST OF REFERENCE DESIGNATIONS

[0009] 1 Steering shaft [0010] 10 Input shaft [0011] 12 Output shaft [0012] 100 Motor vehicle steering system [0013] 102 Steering wheel [0014] 103 Steering gear [0015] 104 Steering pinion [0016] 106 Toothed rack [0017] 108 Track rod [0018] 110 Steerable wheel [0019] 112 Power assistance means [0020] 114 Power assistance means [0021] 116 Power assistance means [0022] 118 Torque sensor [0023] 118 Torque sensor [0024] 120 Joint [0025] 3 Steering spindle part [0026] 31 Connecting portion [0027] 311 External toothing [0028] 312 Internal thread [0029] 32 Conical portion [0030] 33 Tubular portion [0031] 34 Steering moment transmission portion [0032] 4 Tube [0033] 41 Inner surface [0034] 42 End portion [0035] 43 Depressions [0036] 44 Polygon surfaces [0037] 5 Sleeve [0038] 51 Outer surface [0039] 52 Indentation [0040] 53 Projection [0041] 6 Mandrel [0042] 61 Deforming mandrel [0043] 611 Molding surface [0044] 612 Molding projections [0045] 62 First supporting mandrel [0046] 63 Second supporting mandrel [0047] 7 Hammering tool [0048] 71 Hammer surface