METHOD FOR PRODUCING UNITS WITH AXIALLY MOVABLE COMPONENTS

Abstract

A method for producing an axially movable connection between two tubular components with a plastic as a sliding material therebetween may involve providing the components to be joined where either at least one of the two components has a plastic coating or a plastic sleeve is provided between the components, joining the components to form a unit via a pressing force in an axial direction, clamping the unit in a device in which the components can be clamped and subjected to a displacement force in the axial direction, pressing a sonotrode against an outer of the two components, injecting an ultrasound signal into the sonotrode at a frequency close to the resonance frequency of one of the components, and moving the tubular components back and forth in the axial direction until the displacement force or the displacement velocity reaches a target, and ending the ultrasound signal.

Claims

1-8. (canceled)

9. A method for producing an axially movable connection between two tubular components, between which two tubular components a plastic is disposed as a sliding material, the method comprising: providing the two tubular components to be joined, wherein either at least one of the two tubular components has a plastic coating on a surface facing the other tubular component, or a plastic sleeve is disposed between the two tubular components; joining the two tubular components to form a unit by a pressing force in an axial direction; clamping the unit in a device in which the two tubular components are clampable and subjectable to a displacement force in the axial direction; pressing a sonotrode from one side against an outer of the two tubular components and bracing the outer of the two tubular components against a counter-holder; injecting an ultrasound signal into the sonotrode at a frequency close to a resonance frequency of one of the two tubular components and moving the two tubular components back and forth in the axial direction until a displacement force or a displacement velocity reaches a target value; and ending the ultrasound signal and removing the unit from the device.

10. The method of claim 9 wherein the frequency lies in a range of 20 to 35 kHz.

11. The method of claim 9 comprising varying the frequency of the ultrasound signal while the ultrasound signal is injected into the sonotrode.

12. The method of claim 9 comprising determining the resonance frequency in a simulation prior to providing the two tubular components.

13. The method of claim 9 wherein the two tubular components comprise an inner casing tube and an outer casing tube of an axially telescopic motor vehicle steering system.

14. The method of claim 9 wherein the sonotrode is a first sonotrode, the method comprising pressing the first sonotrode and a second sonotrode against the outer of the two tubular components.

15. The method of claim 14 comprising injecting the first and second sonotrodes with ultrasound signals of different frequencies.

16. The method of claim 9 wherein the frequency is within 15% of the resonance frequency.

17. The method of claim 9 wherein the frequency is within 10% of the resonance frequency.

18. A motor vehicle steering system having a telescopic casing tube unit that is produced by the method of claim 9.

Description

[0027] Exemplary embodiments of the invention shall be described below with the aid of the drawing. There are shown:

[0028] FIG. 1: a schematically represented motor vehicle steering system;

[0029] FIG. 2: a casing tube unit;

[0030] FIGS. 3-4: the casing tube in perspective representation;

[0031] FIG. 5: the casing tube of FIGS. 2-4 in a cross section;

[0032] FIG. 6: the casing tube of FIGS. 2-5 during the calibrating of the plastic sleeve;

[0033] FIG. 7: the casing tube of FIGS. 2-5 during the calibrating of the plastic sleeve; and

[0034] FIG. 8: the casing tube of FIG. 7 during the calibrating of the plastic sleeve in a longitudinal section.

[0035] FIG. 1 shows in a schematic representation a motor vehicle steering system 1 having a steering wheel 2, which is rotationally fixed to an upper steering shaft 3. The upper steering shaft 3 is mounted in a bracket 4 in a height adjustable and axially movable manner. By a Cardan joint 5, the upper steering shaft 3 can swivel, but it is rotationally fixed to a lower steering shaft 6. The lower steering shaft 6, finally, is connected by a second Cardan joint 7 to a pinion 8, which engages with a rack segment 9 of a rack 10.

[0036] A rotary movement of the steering wheel 2 thus results in a displacement of the rack 10 and in known manner to a swiveling of steered wheels 11 of the motor vehicle, thereby producing a steering movement and a changing of the direction of travel.

[0037] FIGS. 2 to 5 show an example of a telescoping casing tube unit 60. The telescoping casing tube unit 60 comprises the upper steering shaft 3, which has been described above in FIG. 1. The upper steering shaft 3 is mounted rotatably about its longitudinal axis 73 in an inner casing tube 61 and an outer casing tube 62. For the axial displacement of the steering column, the inner casing tube 61 is adapted to be displaceable with respect to the outer casing tube 62 in the axial direction, corresponding to the longitudinal direction of the longitudinal axis 73. Between the inner casing tube 61 and the outer casing tube 62 there is provided a sliding sleeve 63, which is shown separately in FIG. 3. The sliding sleeve 63 sits between the inner casing tube 61 and the outer casing tube 62, as can be seen in FIGS. 4 and 5. The inner casing tube 61 and the outer casing tube 62 are not shafts in the technical sense, especially since they have a round circular cross section in the example depicted and cannot transmit any torques. Even so, it is advantageous for the seating of the two casing tube parts in the region of the sliding sleeve 63 to be free of play, yet smooth in movement. For this purpose, the method according to the invention is used for calibrating the sliding sleeve 63 between the inner casing tube 61 and the outer casing tube 62. This is illustrated in FIGS. 5 and 6. The sonotrode 35 is placed on the outside of the outer casing tube 62, which is braced against the oppositely placed anvil 36. The sonotrode 35 is then actuated by a control unit 66 with electrical voltage of a given frequency or frequency variation, corresponding to a resonance frequency of the outer casing tube 62. The vibrational energy, in turn, results in a heating of the sliding sleeve 63.

[0038] FIG. 6 illustrates how the inner casing tube 61 is clamped between clamping jaws 40 during the process, while the outer casing tube 62 is clamped between clamping jaws 41. While the sliding sleeve 63 is being heated, the inner casing tube 61 is moved back and forth in the direction of the double arrow 42. The displacement force F required for this is detected with a force sensor 65. The displacement force F decreases with the number of reciprocating movements in the direction of the double arrow 42. As soon as a given threshold value is reached or undershot, the calibrating of the sliding sleeve 63 is terminated. The process control occurs by a control and evaluation unit 68. The casing tube unit 60 so prepared is then removed from the clamping jaws 40 and 41, the anvil 36 and the sonotrode 35 are removed, and the casing tube can be installed in a bracket 4 according to FIG. 1.

[0039] FIGS. 7 and 8 illustrate an alternative process control. Alternatively or in combination with the use of a force sensor 65, a speed sensor 67 may be provided, which can also be designed as a displacement sensor, the speed being determined in a control and evaluation device 68. FIG. 8 illustrates the calibrating process in a longitudinal section. The sonotrode 35 and the anvil 36 are each placed on the surface of the outer casing tube 62. The inner casing tube 61 is inserted in the plastic sleeve 63 and the outer casing tube 62. The two casing tubes are now grasped by clamping jaws 40 and 41. The clamping jaw 41 is held stationary, while the clamping jaw 40 can be subjected to movement by a piston 69 of a pneumatic cylinder. A control and evaluation unit 68 undertakes the process control. The sonotrode 35 is actuated by a control unit 66 in order to transmit an ultrasound vibration to the outer casing tube 62. In this way, the outer casing tube 62 is placed in a mechanical vibration. Since the outer casing tube 62 itself vibrates relatively freely, the vibrational energy is transmitted in large measure to the plastic sleeve 63, which is thereby deformed with high frequency. The plastic sleeve 63 becomes heated in this process. At the same time, the inner casing tube 61 is moved back and forth in the axial direction by a relative movement in the direction of the double arrow 42 by means of the clamping jaws 40 and 41. For this, the pressures p1 and p2 are alternately increased and decreased, so that the piston 69 is moved back and forth. The piston 69 is accordingly coupled mechanically to the clamping jaw 40. The heated plastic sleeve 63 becomes adapted to the two mutually facing surfaces of the inner casing tube 61 and of the outer casing tube 62. The adapting process can be monitored by detecting the speed with which the clamping jaw 40 is moved by means of a distance sensor or a speed sensor 67. Preferably, the heating of the plastic sleeve 30 by means of ultrasound and the movement in the direction of the double arrow 42 is continued until such time as the maximum value of the displacement velocity exceeds a given minimum target value. The adapting process is then finished.

[0040] After switching off the excitation of the sonotrode 35, the plastic sleeve 63 cools down quickly, since the two casing tube pieces 61 and 62 themselves were essentially not heated by the ultrasound excitation and hence they are cold compared to the plastic sleeve 63. This promotes the dimensional stability of the plastic sleeve 63 so calibrated. What is more, the outer casing tube 62 and the inner casing tube part 61 undergo practically no thermal changes in their dimensions during this process. This improves the achievable precision of the calibrating process of the plastic sleeve 63.

[0041] The heating and cooling times of the described process are short, on account of the slight mass of the plastic sleeve 63 to be heated, so that a short cycle time can be achieved. Furthermore, it is enough to heat the plastic sleeve only at the surface, to the point that it can be easily molded. The sequence of the above-described processes thus provides the following partly optional process steps as an exemplary embodiment: [0042] providing the two tubular components to be joined, wherein [0043] either at least one of the two tubular components has a plastic coating on the surface facing toward the other shaft component, [0044] or a plastic sleeve is provided for butting between the tubular components, [0045] joining the tubular components, optionally with the plastic sleeve in between, [0046] wherein the tubular components and optionally the plastic sleeve are configured such that the joining can occur only by overcoming a pressing force, since the sliding fit is designed with an oversize, [0047] clamping the unit in a device in which the two tubular components can be clamped and subjected to a displacement force in the axial direction. The device is preferably outfitted such that a displacement force can be measured. [0048] pressing a sonotrode from one side against the respectively outer shaft component and bracing the inner component against a counter-holder (anvil), [0049] injecting an ultrasound signal into the sonotrode and moving the tubular components back and forth in the axial direction until the displacement force reaches a desired target value. Alternatively, the method can be executed such that the tubular components are moved relative to each other with a constant force and the displacement velocity is measured. The process is then ended when a particular displacement velocity is achieved. [0050] After the end of the process, the shaft is removed from the device as a finished component and is installed elsewhere.