Steering gear shaft for a steering column of a motor vehicle

A steering gear shaft for a steering column of a motor vehicle has at least one crash-deformable section formed as a corrugated tube at least a portion of a longitudinal extent of which that contains at least one of corrugation crests of the corrugated tube, is formed of several layers, with a wall thickness of at least one layer in the at least one of the at least one of the corrugation crests and a respective corrugation trough diminishing over a region of the at least one of the corrugation crests and the respective corrugation trough between a side of the corrugation tube adjacent to which a universal joint is provided, and a side of the corrugation tube remote from the universal joint.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a steering gear shaft for a steering column of a motor vehicle and having at least one crash-deformable section formed as a corrugated tube at least a portion of a longitudinal extent of which that contains at least one of corrugation crests of the corrugation tube, is formed of several layers.

2. Description of the Prior Art

Steering gear shafts of steering columns with deformable sections formed as corrugated tubes are disclosed, e.g., in German Publication DE-196 31 214 A and European Publications EP-0 709 274A1, EP-0 872 401A2, and EP-0 701 070A1. Corrugated tubes, which form the crash-deformable sections, can be arranged in different sections of a steering column. In a steering column, a single corrugated tube can be used or several corrugated tubes can be arranged in different section of the steering column. The corrugated tubes, which function as crash-deformable sections, are compressed axially, on one side, and can be bent sideways under the action of non-axial forces, on the other side.

Different methods of manufacturing of corrugated tubes, which function as crash-deformable sections, are known. Such methods are disclosed, e.g., in European Publication EP-661 117A1, EP-298 832B1, EP-0 782 891 A1, and in German Publication DE-20 27 638A1. A corrugated tube for a steering column, which functions as a crash-deformable section, should meet specific requirements. On one hand, it should be easily deformable in case of a crash to be able to perform its function, with the deformation taking place in a predetermined manner. On the other hand, it should be able to withstand loads acting thereon during a normal operation over its entire service life. Therefore, the corrugated tube should meet very high requirements which should be determined by extensive tests. These test should examine, among others, the stability under the action of torques of predetermined values and under action of static, dynamic, and pulsatory loads. Further, the deformation behavior should be tested. In addition to meeting all of these different requirements, the corrugated tubes have to have as small dimensions as possible for space-saving reasons.

In order to provide for manufacture of corrugated tubes capable of meeting the requirements for crash-deformable section, European Publication EP-0 82 891A1 discloses a method of manufacturing of such corrugated tubes according to which the wall thickness in the region of corrugation trough is increased in comparison with the wall thickness in the region of the corrugation crests. In the region of the corrugation troughs greater loads act on the corrugated tube during transmission of a torque because it is in this region, the wall of the corrugated tube has a smallest distance from the central axis of the corrugated tube.

DE-20 27 638A1 discloses a method of manufacturing of a radially corrugated tube according to which a uniform wall thickness, different wall thickness and/or profile of a corrugated tube can be obtained from shaft to shaft or zonewise. Thereby, a corrugated tube, which functions as a crash-deformable section of a steering gear shaft and having different collapsible zones can be produced.

German Patent DE-32 24 308C2 and Swiss Patent No. 324,476 disclose a corrugated multi-layer metal bellows which is used as a portion of liquid or gas conduits, in particular, for sealingly connecting movable relative to each other, parts. The German and Swiss Patents relate to field remote from and not comparable with steering columns for motor vehicles. They solve different problem and relate to products which have to meet different requirements.

A multi-layer corrugated tube is also disclosed in German Publication DE-25 44 769A1. With the multi-layer, e.g., two-layer corrugated tube, the stability of the tube under the action of a torque acting thereon about its longitudinal axis does not change or changes very little in comparison with conventional, single-layer tube with the same wall thickness, whereas the deformation, in particular, a sideway buckling under the action of non-axial forces takes place when the acting non-axial forces are noticeably smaller. This result in improved crash characteristics in comparison with conventional steering columns during the transmission of high torque. At that, the outer diameter of the corrugated tube can be reduced.

An object of the invention is a steering gear shaft of the type described above and having at least one crash-deformable section formed as a corrugated tube having improved rigidity under the action of a torque acting about the tube longitudinal axis and adequate deformability in case of a crash.

SUMMARY OF THE INVENTION

This and other objects of the present invention, which will become apparent hereinafter, are achieved by providing a steering gear shaft of the type discussed above in which the wall thickness of at least one layer in at least one of the at least one of the corrugation crests and a respective corrugation trough diminishes over a region of the at least one of the corrugation crest and the respective corrugation trough between a side of the corrugation tube adjacent to a universal joint which is provided at one end of the corrugated tube, and a side of the corrugation tube remote from the universal joint.

The present invention improves flexural strength of the corrugation tube in the vicinity of the adjacent universal joint where the greatest bending stresses occur. In case universal joints are provided at both ends of the corrugation tube, the “adjacent universal joint” is a universal joint that is located more closely to the adjacent end of the corrugation tube. E.g., one end of a corrugation tube can be directly connected with the joint yoke of the universal joint, whereas the other end of the corrugation tube can be connected with a connection shaft located between the other end and the corresponding universal joint.

According to an advantageous embodiment of the present invention, at least one of the layers of the corrugation tube can be provided with a plurality of openings in the region of the corrugation crests.

Because the corrugation crests are subjected to less stress during transmission of a torque acting about the tube longitudinal axis as they are being spaced by a greater distance from the longitudinal axis, a crash-deformable section-forming, corrugated tube having improved deformation characteristics with an adequate stability under the torque action is produced. In particular, such a tube is easily bendable under the action of non-linear forces.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1 and 2show schematically two different embodiments of a steering column1. In the embodiment shown inFIG. 1, first portion3of a steering gear shaft, which adjoins a steering wheel2, is connected with a second portion5of the steering gear shaft by a hinged connection4in form of a universal joint. The second portion5is also called an intermediate shaft that eventually includes a shock absorber. The second portion5is further connected with a pitman arm pin7by a hinged connection6.

In the embodiment of a steering column1shown inFIG. 2, a further steering gear shaft portion8is provided between the second portion5of the steering gear shaft and the pitman arm pin7. The further third portion8is connected with the second portion5by a hinged connection26. The hinged connections6and26are also formed as a universal joints. The support for the steering gear shaft and the suspension of the steering column on a chassis, which is adjustable in per se known manner, are not shown in detail inFIGS. 1-2and can be effected in a conventional manner. The inventive steering gear shaft can be also formed differently, i.e., it can have more or less portions3,5, and8.

At least one of the portions3,5, and8of the steering gear shaft is provided with a section9,10deformable in case of a crash. At least one of the deformable sections9,10is formed as a corrugated tube11. In addition to the deformable section9formed as the corrugated tube11, the further section10can be provided with its length being shortened in another way. e.g., the section10can be formed of two telescopic tubes pushed into each other and which, in case of a crash, are axially displaced into each other. The use of tubes telescopically displacing into each other is well known. There can be provided one or more deformable sections9formed each as the corrugated tube11and arranged in one or more of portions3,5, and8of the steering column shaft.

A possible process of forming a corrugation tube for a steering column shaft according to the present invention will be briefly explained with reference toFIGS. 3-9which show consecutive steps of the forming of a corrugation tube. The corrugation tube is formed of two layers over its entire length, with the tube12, which forms an outer layer14, having a closed outer surface. In the embodiment shown in the drawings, the tube12has ends with an increased thickness. In the region between its opposite ends, the tube12has a reduced thickness. InFIG. 3as well inFIGS. 5-7,10, and11, no change of the wall thickness is shown for the sake of clarity. The changes of wall thickness in the intermediate region are shown inFIGS. 13-15. The structure shown inFIGS. 13-15will be described in detail further below. A tube13, which forms an inner layer15, has, in its finished condition, a plurality of openings16. The openings16are arranged, in the finished condition of the tube13, along imaginary circumferential lines17on which in a finished corrugated tube, peaks of the corrugation crests lie, in a spaced relationship to each other. E.g., along each imaginary circumferential line17, there can be provided, e.g., seven, equidistantly circumferential spaced from each other, openings16which, in the embodiment shown in the drawings, have a circular shape. The tube12is slided over the tube13, as shown in FIGS.5. Then, the inner tube13can be expanded by an expanding mandrel so that both layers14,15closely abut each other.

Then, the corrugations are formed, e.g., by a multistage process, as illustrated inFIGS. 6-7. The tubular wall is provided with a corrugation with the use of shaped tools having a respective corrugation and which are pressed against the tubular wall from inside and outside. For forming a required corrugation, several sets of shaped tools having an increased corrugation depth are used. Then, a tube, which has a shape shown inFIG. 6, is axially compressed, with the tube being supported on a mandrel and with cheek plates being inserted in separate corrugation troughs from outside and displaced, as a result of application of a force, axially toward each other. In the finished tube shown inFIG. 7, a plurality of openings16is provided in the region of corrugation crests18in the inner layer (tube13)15. In the embodiment produced as shown inFIGS. 3-7, all of the corrugation crests have a plurality of openings16. Advantageously, the corrugation troughs19are free from openings16(seeFIG. 9) at least up to one/fourth of a height H between the corrugation troughs19and corrugation crests18. The closed outer layer14prevents, e.g., penetration of a corrosive salt water.

Then, the finished corrugated tube can be arranged in the portion3,5and/or8of the steering gear shaft. The corrugated tube11can be connected, at one of its ends, with a joint yoke20, and with a shaft21at its other opposite end, as shown in FIG.10. The corrugated tube11is connected formlockingly with the joint yoke20and the shaft21by knobs22engaging in corresponding recesses in the joint yoke20and the shaft21. The knobs22prevent both layers14,15of the corrugated tube from displacement in a circumferential direction. Instead, of knobs22, other forms of formlocking connections can be used, in particular, a press fit connection can be used or a toothing connection.

In the embodiment shown inFIG. 11, the corrugated tube11is connected with the joint yoke20and the shaft21by welds23and/or welds24. The welds23and/or24also can connect the two layers14,15. The welds23, which can be produced by a laser or ultrasound welding, penetrate both layers14,15and reach the joint yoke20and/or the shaft21. The welds can be used for reliability reasons. The corrugated tube11can be formed as one piece with an adjoining portion of the steering gear shaft.

In the embodiment shown inFIG. 11, only a portion of the corrugation crests18of the inner layer15is provided with openings16, with the crests18, which are provided with openings16, being located in one section of the longitudinal extent of the corrugated tube. The two corrugation crests18which are located on a side of the corrugated tube11adjacent to the universal joints6,20, are free from the openings16. This is because during a normal operation of the steering gear shaft, it is in this region that the largest non-axial forces, which are produced by the universal joint, namely, bending forces prevail.

Basically, it is also possible to provide openings in the corrugation crests18of the outer layer14. Those openings24are shown inFIG. 11with dash lines. Advantageously, the openings24are so offset relative to the openings16of the inner layer15that they are closed by the inner layer15from the interior of the corrugated tube11.

In principle, with corresponding dimensioning of the layers14,15of the corrugated tube11, it is possible to provide openings in the region of the corrugation troughs, with the openings in the corrugation troughs and in the corrugation crests being to dimensioned that the weakness, which is produced by openings provided in the region of corrugation troughs, is smaller than the weakness produced by the openings16,24provided in the region of the corrugation crests.

According to the present invention, the corrugation tube can also be formed without the openings16,24.

As shown inFIGS. 13-15, the tube12, which forms the outer layer14, has region with different wall thicknesses in the region where the corrugations are provided. Thus, the finished corrugation tube has corresponding regions with different wall thicknesses. In the embodiment according toFIG. 13, the region of the tube12, in which the corrugations are formed, has two sections with different wall thicknesses D1and D2that stepwise adjoin each other. The section with a layer wall thickness Dt is provided at a side of the corrugation tube adjacent to the adjacent universal joint6or26. The corrugation crests18and the corrugation troughs, which are formed in the section with the wall thickness D1, have a greater wall thickness than the corrugation crests and the corrugation troughs formed in the section with the wall thickness D2. When a method is used with which during the formation of the corrugations, the wall thickness in the region of the corrugation troughs is greater than in the region of the corrugation crest, these different changes of the wall thickness are superimposed.

In the embodiment ofFIG. 14, the region, in which the corrugations are formed, has three sections with different thicknesses D1, D2, D3, respectively, which stepwise adjoin each other. At that, the wall thickness D2is greater than the wall thickness D3, and the wall thickness D1is greater than the wall thickness D2. The adjacent universal joint6,26is located on a side of the section of the tube12with the thickness D1.

A further embodiment of the outer tube12is shown in FIG.15. InFIG. 15, the points in which the peaks of the corrugations lie, are shown with arrows18. Between these corrugation crests, corrugation troughs are located. In the finished condition of the stearing gear, the tube12has, at its side adjacent to the adjacent universal joint6,26, increased wall thicknesses in the region of the corrugation troughs. The first wall thickness S1is greater than the second wall thickness S2. In the region of the wall between the wall thicknesses S1and S2and in the region of the wall located to the right of the thickness S2, the tube12has a wall thickness S3. In the finished condition of the corrugation tube12, the two corrugation troughs, which are located most closely to the adjacent universal joint6,26, have a greater wall thickness than the remaining corrugation troughs, with the corrugation trough closest to the universal joint having the greatest wall thickness. Also, the wall thicknesses S1, S2of the respective corrugation troughs are greater in comparison with the wall thicknesses in the regions of the adjacent corrugation crests. Advantageously, the wall thicknesses in the regions of the corrugation crests is at least by 20% smaller than in the regions of the adjacent corrugation troughs and, preferably, at least by 10% smaller.

Instead of the outer tube12or in addition thereto, the inner tube13can also have the above-described thickness changes. Thus, in a finished corrugation tube, the wall thickness changes can be observed only in or also in the inner layer.

It is possible to form the two or more layers14,15of the corrugation tube11of different materials. Thus, the outer layer14can function as a heat shield, and an intermediate material, e.g., in form of a metal mesh or a wire grate25(seeFIG. 12) can be provided between the outer layer14and an inner layer15that can be formed from a comparatively low-cost material. To provide for corrosion protection an additional comparatively thin, outer layer can be provided. This layer can be formed of a stainless steel. Generally, all of the layers of a corrugation tube can be formed of a stainless steel.

A multi-layer formation of a corrugated tube can be provided only along a portion of its longitudinal extent, e.g., over the corrugated portion of its longitudinal extent at least a portion of a longitudinal extent of a corrugated tube that has at least one of corrugation crests of the tube, can be formed of several layers. Advantageously, the openings16are provided at least in or only in this region of the corrugation tube. Though a two-layer formation is advantageous, one- or three-layer formation of the corrugation tube is also possible. With a three-layer formation, the thickness of separate layers can lie. e.g., in a region of 0.4 mm.

Also, the height H of the corrugation can be changed so that the distance of the corrugation trough from the longitudinal axis27of the corrugated tube of one or more corrugation troughs, adjacent to the adjacent universal joint26,6is greater than this distance for the troughs located farther away from the universal joints6,26. Thereby, the corrugated tube will be more deflection-resistant in the region adjacent to the adjacent universal joint26,6, where the bending forces are greatest, because the corrugation height H is smaller in this region.

The formation of the steering gear shaft according to the present invention permits to adapt it to loads occurring during its normal operation, on one hand, and to specific predetermined crash requirements on the other hand.