METHOD FOR PRODUCING A VARIABLE-LENGTH STEERING SHAFT AND INJECTION MOLDING DEVICE FOR CARRYING OUT THE METHOD

Abstract

A method may be used to produce a variable-length steering shaft. The method may involve positioning a shaft core within a mold cavity of an injection molding tool coaxially with respect to a mold surface that delimits a toothing region, injecting molten plastic into the mold cavity between the shaft core and the mold surface of the mold cavity with an injection nozzle, removing a toothed shaft from the injection molding tool after the plastic has solidified, providing a hollow shaft and axially inserting the toothing region into an internal toothing, and for the positioning of the shaft core arranging positioning elements at least partially in a region of the mold surface of the toothing. The positioning elements, by way of positioning surfaces, may lie against the shaft core radially from an outside in a region of the toothing and hold the shaft core coaxially in the mold cavity.

Claims

1.-14. (canceled)

15. A method for producing a variable-length steering shaft that includes a hollow shaft with an internal toothing in which a toothed shaft that engages in positively locking fashion is disposed so as to be telescopic in an axial direction, wherein the toothed shaft comprises a toothing region with teeth disposed on an outer circumference and extending in the axial direction, wherein in the toothing region a shaft core is overmolded in an injection molding process with a sliding coating comprised of thermoplastic material, the method comprising: positioning the shaft core within a mold cavity of an injection molding tool coaxially with respect to a mold surface that delimits the toothing region; injecting molten plastic into the mold cavity between the shaft core and the mold surface of the mold cavity with an injection nozzle; removing the toothed shaft from the injection molding tool after the molten plastic has solidified; providing the hollow shaft and axially inserting the toothing region into the internal toothing; and for the positioning of the shaft core, arranging positioning elements at least partially in a region of the mold surface of the toothing, wherein by way of positioning surfaces the positioning elements lie against the shaft core radially from an outside in the toothing region and hold the shaft core coaxially in the mold cavity.

16. The method of claim 15 wherein the shaft core comprises radially outwardly projecting core teeth that are disposed at least in a region of the teeth of the toothing region.

17. The method of claim 16 wherein at least one of the positioning elements comprises at least one of the positioning surfaces, which in a circumferential direction engages in a positively locking fashion between flanks of the radially outwardly projecting core teeth that are adjacent in the circumferential direction.

18. The method of claim 15 comprising uniformly distributing at least three of the positioning elements over a circumference.

19. The method of claim 15 comprising positioning a plurality of the positioning elements to be parallel to a radial plane of the mold cavity.

20. The method of claim 15 comprising configuring the positioning elements as positioning pins that project radially inwardly into the mold cavity and such that the positioning elements are narrower than a length of the toothing region in an axial direction.

21. The method of claim 20 comprising: positioning a first group of the positioning elements parallel to a first radial plane of the mold cavity; and positioning a second group of the positioning elements parallel to a second radial plane axially spaced apart from the first radial plane.

22. The method of claim 15 comprising positioning at least one of the positioning elements to be axially spaced apart from the toothing region.

23. An injection molding device for performing the method of claim 15, the injection molding device comprising: the injection molding tool with the mold cavity that extends along a longitudinal axis and includes the toothing region with the mold surface that, over a section of the longitudinal axis, delimits a coaxial toothing; and the positioning elements for coaxially positioning the shaft core, wherein the positioning elements are disposed in the mold cavity, wherein at least one of the positioning elements is disposed within the toothing region.

24. The injection molding device of claim 23 wherein at least one of the positioning elements is disposed on a slide that is movable radially relative to the longitudinal axis of the mold cavity.

25. A toothed shaft for installation into a hollow shaft with an internal toothing in which the toothed shaft can be received and to which the toothed shaft can be coupled in a positively locking fashion so as to be telescopic in a direction of a longitudinal axis, wherein the toothed shaft comprises a toothing region with teeth disposed on an outer circumference and extending in an axial direction, wherein in the toothing region a shaft core is overmolded by way of an injection molding process with a sliding coating comprised of thermoplastic material, wherein the sliding coating comprises at least three impressions.

26. The toothed shaft of claim 25 wherein the sliding coating comprises six impressions, wherein three of the impressions are disposed in a first radial plane and three of the impressions are disposed in a second radial plane, wherein the first radial plane comprises a spacing in the direction of the longitudinal axis.

27. The toothed shaft of claim 25 wherein the at least three impressions comprise an aperture through the sliding coating to a surface of the shaft core.

28. The toothed shaft of claim 27 wherein the aperture is formed in a region of a tooth flank of an adjacent core tooth of the shaft core.

Description

DESCRIPTION OF THE DRAWINGS

[0045] Advantageous embodiments of the invention will be discussed in more detail below on the basis of the drawings, in which, in detail:

[0046] FIG. 1 shows a motor vehicle steering system,

[0047] FIG. 2 shows a steering shaft according to the invention in a perspective view,

[0048] FIG. 3 shows a steering shaft according to the invention as per FIG. 2 in an illustration in which they have been axially pulled apart,

[0049] FIG. 3a shows a hollow shaft as per FIG. 3 in a perspective view,

[0050] FIG. 4 shows a toothed shaft of a steering shaft as per FIG. 2 with positioning elements, prior to the overmolding with plastic,

[0051] FIG. 5 shows a toothed shaft of a steering shaft as per FIG. 2 with positioning elements, after the overmolding with plastic,

[0052] FIG. 6 shows a cross section through an injection molding tool according to the invention with a toothed shaft clamped therein, after the injection of the plastic,

[0053] FIG. 6a shows a detailed view of a cross section through an injection molding tool according to the invention similar to FIG. 6 with a toothed shaft clamped therein, prior to the injection of the plastic,

[0054] FIG. 7 shows an enlarged cross-sectional view of the toothed shaft as per FIG. 6 clamped in the injection molding tool,

[0055] FIG. 8 shows a longitudinal section along the longitudinal axis through an injection molding tool according to the invention,

[0056] FIG. 9 shows a longitudinal section along the longitudinal axis as in FIG. 8 through an injection molding tool according to the invention in a second embodiment,

[0057] FIG. 10 shows a toothed shaft of a steering shaft with positioning elements, after the overmolding with plastic, in an alternative embodiment,

[0058] FIG. 11 shows a toothed shaft of a steering shaft as per FIG. 5 without positioning elements, after the overmolding with plastic,

[0059] FIG. 12 shows an enlarged detail view of the cross section as per FIG. 7 with a retracted positioning element.

EMBODIMENTS OF THE INVENTION

[0060] In the various figures, identical parts are in all cases denoted by the same reference designations, and will therefore each also generally be mentioned only once.

[0061] FIG. 1 schematically illustrates a motor vehicle steering system 100, wherein a driver can use a steering wheel 102 to input a corresponding steering torque (steering moment) as a steering command into a steering shaft 1. The steering moment is transmitted via the steering shaft 1 to a steering pinion 104, which meshes with a toothed rack 106, which then in turn, by means of a displacement of the track rods 108, transmits the predefined steering angle to the steerable wheels 110 of the motor vehicle.

[0062] An electric 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 couples an auxiliary force into the toothed rack 106, whereby the driver is assisted in performing steering work. The three different assistance means 112, 114 and 116 illustrated in FIG. 1 show possible positions for the arrangement thereof.

[0063] Normally, only a single one of the illustrated positions is occupied with a power assistance means 112, 114 or 116. The auxiliary torque or the auxiliary force that is to be imported in order to assist the driver by means of the respective power assistance means 112, 114 or 116 is determined taking into consideration a steering moment input by the driver and ascertained by a torque sensor 118. Alternatively or in combination with the introduction of the auxiliary torque, the power assistance means 112, 114, 116 may introduce an additional steering angle into the steering system, which is added to the steering angle imparted by the driver by means of the steering wheel 102.

[0064] The steering shaft 1 comprises, at the input side, an input shaft 10 connected to the steering wheel 102 and, at the output side, and 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 (not shown in FIG. 1). Thus, a torque input into the steering shaft 10 by a driver using the steering wheel 102 always leads to a relative rotation of the input shaft 10 with respect to the output shaft 12, if the output shaft 12 does not rotate exactly synchronously with respect to the input shaft 10. Said 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, the torque sensor 118 is formed by means of the determination of the relative rotation between input shaft 10 and output shaft 12. 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 will be described further below, or by means of some other measurement of the relative rotation.

[0065] Correspondingly, a steering moment that is imparted by the driver to the steering shaft 1 or to the input shaft 10 using the steering wheel 102 will effect an introduction of an auxiliary torque by one of the power steering 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.

[0066] The torque sensor 118 may also alternatively be arranged at the position 118, wherein then, the division of the steering shaft 1 into the 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 to be able, from the relative rotation of the output shaft 12 coupled to the input shaft 10 via the torsion bar, to determine a relative rotation and thus correspondingly an input torque and/or an auxiliary torque to be introduced.

[0067] 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 steering intermediate shaft of the steering shaft 1, which in the example illustrated is arranged between two cardanic joints 120 and connects the output shaft 12 to the pinion 104 of the steering gear 103, is designed according to the invention as a variable-length steering shaft 2.

[0068] FIG. 2 and FIG. 3 show the steering shaft 2 in the assembled state (FIG. 2) and in a state in which they have been pulled apart in the axial direction (FIG. 3).

[0069] The steering shaft 2 comprises a hollow shaft 21 and a toothed shaft 22. The toothed shaft 22 comprises a toothing region 23 with a multiplicity of teeth 24 arranged on the outer circumference, which teeth extend in the direction of the longitudinal axis L, that is to say axially over the length V of the toothing region 23.

[0070] It can be seen from FIG. 3a that the hollow shaft 21 comprises a receiving opening 26 which is open toward the toothed shaft 22 and which comprises an internal toothing 211 in which the toothing region 23 can be received in positively locking fashion. To produce a connection fixed in terms of torque, the toothed shaft 22 is, proceeding from the situation illustrated in FIG. 3, inserted in an axial direction, as indicated by the arrow, in the direction of the longitudinal axis L into the receiving opening 26 of the hollow shaft 21, such that the assembled state illustrated in FIG. 2 is realized. In this assembled state, the toothed shaft 22 and the hollow shaft 21 can move relative to one another along the longitudinal axis L for the purposes of compensating spacing differences, as indicated by the double arrow.

[0071] It can be seen from FIG. 3 that the toothed shaft 22 comprises a cylindrical shank 25 outside the toothing region 23, wherein, in the example illustrated, the length V of the toothing region 23 corresponds to only a part of the total length of the toothed shaft 22.

[0072] FIG. 4 shows a toothed shaft 22 in the partially fabricated state prior to the overmolding. Said toothed shaft is formed by a shaft core 3 which are composed preferably of metal, preferably steel. In the toothing region 23 of the finished toothed shaft 22 as per FIG. 5, the shaft core 3 comprises core teeth 31 which are arranged in the region of the teeth 24 of the finished toothing region 23, such that said core teeth constitute the main body is composed of steel, which main bodies are overmolded with plastic to form the finished teeth 24. The length of the core teeth 31 in the direction of the longitudinal axis L corresponds substantially to the length V of the fully overmolded teeth 24, specifically minus the wall thickness of a possible end-side, that is to say axial, overmolding of the core teeth 31.

[0073] It can be seen from FIGS. 4 and 5 that the longitudinal axis L of the toothed shaft 22 and of the shaft core 3 is identical.

[0074] FIG. 6 shows a cross section perpendicular to the longitudinal axis L through an injection mold 4 for carrying out the method according to the invention. In particular, it can be seen in this illustration how the shaft core 3 is clamped in a centered manner, that is to say concentrically with respect to the longitudinal axis L, between positioning elements 42a, 42b and 42c. The arrangement of the positioning elements 42a, 42b and 42c is also schematically shown in FIG. 4 and FIG. 5, wherein the rest of the injection mold 4 has been omitted for the sake of better clarity.

[0075] The positioning elements 42a, 42b and 42c are of pin-like form, with, in the illustrated example, a rectangular or square cross section, the dimension of which in the direction of the longitudinal axis L amounts to only a fraction of the length V of the toothing region 23. It is likewise conceivable and possible for the positioning elements to comprise a circular cylindrical cross section. In the example shown, the three positioning elements 42a, 42b and 42c are arranged so as to be distributed uniformly over the circumference and are, with their free ends 43, directed radially inward toward the longitudinal axis L, such that the shaft core 3 is clamped coaxially in centered fashion relative to the longitudinal axis L in a mold cavity 41 between the free ends 43. In the injection mold 4, the shaft core 3 is surrounded in the toothing region 23 by the mold surface 411 that delimits the teeth 24, that is to say said mold surface 411 forms the negative impression of the toothing region 23. The mold surface 411 is likewise oriented coaxially with respect to the longitudinal axis L. The mold surface 411 and the mold cavity 41 can be seen particularly clearly in FIG. 6a, which illustrates a detail view of the cross section of the injection molding tool illustrated in FIG. 6 with a toothed shaft clamped therein, prior to the injection of the plastic.

[0076] An enlarged cross-sectional view of the toothed shaft clamped in the injection molding tool as per FIG. 6 is illustrated in detail in FIG. 7. The positioning elements 42a, 42b and 42c comprise positioning surfaces 43 in the region of their free ends 43. The positioning surfaces 44 are arranged such that they come into contact with the tooth flanks, facing toward one another in the circumferential direction, of adjacent core teeth 31a and 31b. In this way, the positioning elements 42a, 42b and 42c can, by way of the positioning surfaces 44, engage in each case in positively locking fashion between adjacent core teeth 31a and 31b from the outside. In this way, the shaft core 3 is, by means of the positioning elements 42a, 42b and 42c, clamped so as to be accurately angularly oriented with respect to a rotation about the longitudinal axis L within the mold cavity 41 and in a centered manner.

[0077] The positioning elements 42a, 42b and 42c are arranged in a first radial plane, specifically in the cross-sectional plane shown in FIG. 6. As can be seen from FIG. 4 and FIG. 5, second positioning elements 45a, 45b and 45c, which are in principle of identical design, are arranged in a second radial plane which comprises a spacing P (see FIG. 4) to the first radial plane in the direction of the longitudinal axis L. For the example shown, it is the case that P is smaller than V, such that all of the positioning elements 45a, 45b, 45c, 42a, 42b and 42c are arranged within the toothing region 23. In this way, the shaft core 3 is, at the intersection points of the first and of the second radial plane, centered exactly on the longitudinal axis L, and is, at the spacing P, oriented correspondingly exactly concentrically in the mold cavity 41.

[0078] To be able to clamp the shaft core 3 within the mold cavity 41, the positioning elements 42a, 42b and 42c are in each case attached to a slide 46 which is of segmented form and which is movable radially relative to the longitudinal axis L, as indicated in FIG. 6 by the double arrows. It is preferable for in each case two positioning elements 42a and 45a, 42b and 45b and also 42c and 45c arranged in the same circumferential position to be fastened in each case to one slide 46.

[0079] Arranged between the slides 46 in a circumferential direction are slides 47, which are likewise of segmented form and which, for the purposes of demolding, can be moved apart from one another, radially with respect to the longitudinal axis L, together with the slides 46, without colliding.

[0080] If the slides 46 and 47 are moved radially apart from one another, a shaft core 3 can be introduced into the injection mold 4. Subsequently, the slides 46 and 47 are moved together in a radially inward direction, wherein the shaft core 3 is, as described above, clamped in a centered and angularly oriented manner in the mold cavity 41 between the positioning surfaces 44 of the positioning elements 45a, 45b, 45c, 42a, 42b and 42c. At the same time, as a result of the slides 46 and 47 being moved together, the injection mold 4 is closed, wherein the mold surface 411 is closed in a circumferential direction.

[0081] When the injection mold 4 is closed, molten plastic is injected into the mold cavity 41 between the mold surface 411 and the outer circumference of the shaft core 3 in the toothing region 23. This mold cavity 41, which can be clearly seen in FIG. 6a, defines the dimensions and thus the wall thickness of the plastics overmolding that is still to be introduced, and which forms the sliding coating. The plastics overmolding thus equates to the sliding coating.

[0082] The injection of the molten plastic into the injection mold 4 may be performed via axial injection nozzles, arranged at the end side on the mold cavity 41, at the gate points 48, as is schematically illustrated in FIG. 8. The gate points 48 are situated in an end wall 49 of the injection mold 4, which end wall is situated opposite the free end of the core shaft 3. For the purposes of demolding, said end wall 49 can be moved away from the core shaft 3 in an axial direction.

[0083] Alternatively, the gate points 48 may be arranged radially, as shown in FIG. 9.

[0084] After the cooling and solidification of the plastics overmolding 5, the slides 46 and 47 are, for the purposes of demolding, moved radially apart from one another in stellate fashion, such that the fully overmolded toothed shaft 22 can be removed from the injection mold 4. This is demonstrated in FIG. 5 by way of example on the basis of the positioning element 42c that has been moved away in a radially outward direction. In said figure, it can likewise be seen that the positioning element 42c has, by means of the positioning surfaces 44 lying against the shaft core 3 during the overmolding process, left behind an impression 51 in the plastics overmolding 5 within the toothing region 23. Contrary to the widespread opinion in the prior art, this is not critical for the functioning of the variable-length steering shaft 2, such that the advantages of the method according to the invention can be utilized with regard to more economic manufacture and a more exact plastics overmolding 5 without limitations.

[0085] FIG. 10 illustrates a toothed shaft 22 of a steering shaft 1 with positioning elements (42a, 42b, 42c, 45d, 45f, 45g), after the overmolding with plastic, in an alternative embodiment. The toothed shaft 22 comprises a core-toothed shaft 251 outside the toothing region 23. The positioning elements 42a, 42b and 42c are arranged in a first radial plane. The second positioning elements 45a, 45b and 45c, which are in principle of identical design, are arranged in a second radial plane which comprises a spacing P to the first radial plane in the direction of the longitudinal axis L. For the exemplary embodiment shown, it is the case that P is greater than V, such that only the positioning elements 42a, 42b and 42c are arranged within the toothing region 23. The positioning elements 45d, 45e and 45f are arranged outside the toothing region 23. The shaft core 3 comprises the core teeth 31, which extend over the entire shank 251, beyond the toothing region 23 in the direction of the longitudinal axis L. The shaft core 3 is preferably formed as a drawn profile or extruded profile. An advantage of this embodiment is that the first and second radial plane are at a great distance from one another, such that an oblique positioning of the clamped toothed shaft 22 is minimized, because a radial offset of the positioning elements in one radial plane in relation to the ideal state has little influence on the oblique positioning, because the supporting length is relatively large.

[0086] FIG. 11 illustrates the toothed shaft 22 as per FIG. 4 without positioning elements, after the overmolding with plastic. The positioning elements 42a, 42b and 42c and 45a, 45b and 45c have, by means of the positioning surfaces 44 lying against the shaft core 3 during the overmolding process, left behind the impressions 51 in the plastics overmolding 5 within the toothing region 23. The impressions 51 have formed as a result of the injected plastic flowing around the positioning elements 42a, 42b, 42c, 45a, 45b and 45c, and the positioning elements 42a, 42b, 42c, 45a, 45b and 45c having been removed only after the solidification of the liquid plastic. The impressions 51 are depressions in the plastics overmolding 5, which comprise an aperture 51 through the plastics overmolding 5 to the surface of the core shaft 3. The aperture is formed in the region of the tooth flanks 311a, 311b of the adjacent core teeth 31a, 31b. As a result of the contact between the respective positioning surface 44 of the positioning element 42a, 42b, 42c, 45a, 45b, 45c and the respective tooth flank 311a, 311b of the adjacent core tooth 31a, 31b during the overmolding, said contact surface is not coated with the plastic. At this point, at which no overmolding can form owing to the contact between the positioning surface 44 and the tooth flank 311a, 311b, the aperture 511 is formed in the sliding coating 5.

[0087] The aperture 511 can be seen particularly clearly in FIG. 12. FIG. 12 shows an enlarged detail view of the cross section as per FIG. 7 with a retracted positioning element 42b. The impression 51 constitutes a negative impression in the sliding coating 5 of the free end 43 of the positioning element 42b. The impression 51 is a depression in the sliding coating 5, which depression comprises an aperture 511 in the region of the tooth flanks 311a, 311b, because no sliding coating 5 is formed in this region. In other words, the outer surface of the core shaft 3 is not coated in the region of the contact between the positioning element and the tooth flanks 311a, 311b. At this point, the aperture 511 is formed such that the surface of the core shaft 3 is visible through the aperture 511 in the impression 51.

LIST OF REFERENCE DESIGNATIONS

[0088] 1 Steering shaft [0089] 10 Input shaft [0090] 12 Output shaft [0091] 100 Motor vehicle steering system [0092] 102 Steering wheel [0093] 103 Steering gear [0094] 104 Steering pinion [0095] 106 Toothed rack [0096] 108 Track rod [0097] 110 Steerable wheel [0098] 112 Power assistance means [0099] 114 Power assistance means [0100] 116 Power assistance means [0101] 118 Torque sensor [0102] 118 Torque sensor [0103] 120 Joint [0104] 2 Variable-length steering shaft [0105] 21 Hollow shaft [0106] 22 Toothed shaft [0107] 23 Toothing region [0108] 24 Tooth [0109] 25, 251 Shank [0110] 26 Receiving opening [0111] 3 Shaft core [0112] 31 Core tooth [0113] 31a,b Adjacent core tooth [0114] 311 Tooth flank [0115] 4 Injection mold [0116] 41 Mold cavity [0117] 411 Mold surface [0118] 42a,b,c Positioning element [0119] 43 Free end [0120] 44 Positioning surface [0121] 45a,b,c Positioning element [0122] 45d,e,f Positioning element [0123] 46, 47 Slide [0124] 48 Gate point [0125] 49 End wall [0126] 491 End wall [0127] 5 Plastics overmolding [0128] 51 Impression [0129] 511 Aperture [0130] L Longitudinal axis [0131] V Length of toothing region [0132] R Radius