CHASSIS ACTUATOR AND METHOD FOR OPERATING A TRANSMISSION ASSEMBLY OF A CHASSIS ACTUATOR

Abstract

A chassis actuator (1), in particular for a rear axle steering system, includes a rotational-linear transmission (5) which is provided for coupling, on the output side, to a chassis element, wherein a rotatable, input-side element (9) of the transmission (5) is mounted in a housing (13) by means of at least one axial bearing (16, 17). The transmission (5) is self-lockingly set by means of an adjustable preloading device (21), which loads the axial bearing (16, 17) with an axial force.

Claims

1. A chassis actuator, with a rotational-linear transmission which is adapted for coupling, on the output side, to at least one chassis element, wherein a rotatable, input-side element of the rotational-linear transmission is mounted in a housing by means of at least one axial bearing, wherein an adjustable preloading device loads the axial bearing with an axial force, wherein the transmission is self-lockingly set by the axial force.

2. The chassis actuator according to claim 1, wherein the pre-loading device comprises a preloading nut screwed into an internal thread of the housing as a fine readjustment element.

3. The chassis actuator according to claim 2, wherein the pre-loading nut is in contact with a bearing element of the axial bearing.

4. The chassis actuator according to claim 3, wherein the axial bearing is a roller bearing.

5. The chassis actuator according to claim 4, wherein the axial bearing comprises, in addition to rolling elements which perform the axial bearing function, rolling elements for radial bearings, wherein all of the rolling elements are in contact a same bearing element.

6. The chassis actuator according to claim 4, wherein the axial bearing comprises rolling elements which perform both the axial bearing function and a radial bearing function.

7. The chassis actuator according to claim 1, wherein the rotational-linear transmission is a planetary roller gear system.

8. The chassis actuator according to claim 7, wherein a continuously variable transmission is connected upstream of the planetary roller gear systems.

9. A method for operating a two-stage transmission assembly of a chassis actuator, the chassis actuator comprising a continuously variable transmission and a rotational-linear transmission connected downstream of the continuously variable transmission, the method comprising adjusting a pre-load of an input-side element of the rotational-linear transmission using a fine re-adjustment element acting on an axial bearing of the rotational-linear transmission in such a way that the overall efficiency of the transmission assembly is kept below 50%.

10. The method according to claim 9, wherein the efficiency of the entire transmission assembly is set to a value of at least 35% and a maximum of 45% by the axial force acting in the rotational-linear transmission.

11. A method of assembling a chassis actuator, the method comprising: providing a rotational-linear transmission having an input element wherein the input element is supported with respect to a housing by axial bearings; providing a fine-adjustment element between the axial bearings and the housing configured to vary an axial pre-load on the input element; and adjusting the pre-load using the fine-adjustment element to make the chassis actuator self-locking.

12. The method of claim 11 wherein the fine-adjustment mechanism is a preloading nut screwed into an internal thread of the housing.

13. The method of claim 11 further comprising: providing a rotational-rotational transmission upstream of the rotational-linear transmission; and wherein a combined efficiency of the rotational-rotational transmission and the rotational-linear transmission is less than 50% after adjusting the pre-load.

14. The method of claim 13 wherein the combined efficiency is between 35% and 45% after adjusting the pre-load.

15. The method of claim 13 wherein the rotational-rotational transmission is a continuously variable transmission.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In the following, several exemplary embodiments are explained in more detail by means of a drawing. In the figures:

[0017] FIG. 1 shows a schematic overview representation of an electromechanical chassis actuator of a rear axle steering system,

[0018] FIG. 2 shows a sectional view of a detail of a chassis actuator for a rear axle steering system of a motor vehicle,

[0019] FIG. 3 shows an alternative embodiment of a chassis actuator for a rear axle steering system in a similar representation to FIG. 2.

DETAILED DESCRIPTION

[0020] Unless otherwise stated, the following explanations relate to all exemplary embodiments. Parts that correspond to each other or have basically the same effect are marked with the same reference symbols in all figures.

[0021] A chassis actuator, identified as a whole with the reference symbol 1, is provided for use in a rear axle steering system of a two-axle vehicle, namely a passenger car. The chassis actuator 1 thus represents a steering actuator of a rear axle steering system. An electric motor 2 and a transmission assembly 3 actuated by the electric motor 2 are assigned to the chassis actuator 1. A motor controller of the electric motor 2 is labeled with reference symbol 27. The transmission assembly 3 comprises a continuously variable transmission 4, namely a belt drive, as well as a rotational-linear transmission 5 in the form of a planetary roller gear system, which is connected downstream of the continuously variable transmission 4. A belt of the belt drive 4 is labeled with reference symbol 6. A drive belt wheel 7, which is firmly connected to the motor shaft of the electric motor 2, is coupled to an output belt wheel 8 by the belt 6. The output belt wheel 8 is in turn firmly connected to a spindle nut 9, which represents a rotatable, input-side element of the rotational-linear transmission 5. The corresponding threaded spindle, of the rotational-linear transmission 5, labeled with reference symbol 10, represents its output element.

[0022] The threaded spindle 10 is displaceably guided in a housing 13 of the chassis actuator 1 with the aid of linear guides 11, 12. Connection elements 14, 15 are located at the ends of the threaded spindle 10 which enable coupling to the vehicle's wheels to be steered via chassis elements, not shown.

[0023] To mount the spindle nut 9 in the housing 13, two axial bearings 16, 17 are provided. Each axial bearing 16, 17 comprises a housing washer 18 and a shaft washer 19 as bearing washers. Spheres 20 act as rolling elements rolling between the bearing washers 18, 19 and can be guided in a cage, not shown.

[0024] The chassis actuator 1 further comprises a preloading device 21 which loads the housing washer 18 of the axial bearing 17 with an axial force. The efficiency of the rotational-linear transmission 5, which is designed as a planetary roller gear system, is not heavily dependent on this axial force, but is dependent to a significant extent. The axial force is set by means of the preloading device 21 in such a way that the efficiency of the chassis actuator 1 —more precisely: the transmission assembly 3—is at least 35% and a maximum of 45% and thus reliably in the self-locking range, i.e., below 50%. The above-mentioned efficiency of the entire transmission assembly 3 results from the multiplication of the efficiency of the continuously variable transmission 4 by the efficiency of the rotational-linear transmission 5.

[0025] Various possible configurations of the preloading device 21, which are suitable for the arrangement according to FIG. 1, are illustrated in FIGS. 2 and 3, partly in grossly simplified form.

[0026] In the exemplary embodiment according to FIG. 2, two radial bearings 22, 23 can be seen in addition to the axial bearings 16, 17. In the design shown in FIG. 2, the radial bearings 22, 23 comprise spheres 24 as rolling elements. The rolling elements 24 of the radial bearing 22, 23 are not necessarily dimensioned to match the rolling elements 20 of the axial bearings 16, 17. In any case, the row of rolling elements 20, which performs the axial bearing function, rolls on the same housing washer 18 on which the rolling elements 24 performing the radial bearing function also roll.

[0027] The exemplary embodiment according to FIG. 3 differs from the exemplary embodiment according to FIG. 2 in that exactly one row of rolling elements 20 is assigned to a rolling bearing 16, 17, wherein, as can also be seen in FIG. 1, an angular ball bearing is designed as an axial-radial bearing. Since the main loading direction is aligned in the axial direction of the chassis actuator 1, that is to say in the longitudinal direction of the threaded spindle 10, the roller bearings 16, 17 are also referred to as axial bearings in this case.

[0028] In all of the exemplary embodiments, the preloading device 21 comprises a preloading nut 25 which is screwed into the housing 13 and is generally also referred to as a fine readjustment element. Screwing the preloading nut 25 into the housing 13 is accompanied by an increasing preloading and a decreasing efficiency of the rotational-linear transmission 5.

[0029] In FIGS. 2 and 3, the belt 6 and the output belt wheel 8 can also be seen to a limited extent. The output belt wheel 8 is connected to the spindle nut 9 in a rotationally-fixed manner via a sleeve 26 and thus represents a transmission element of the rotational-linear transmission 5.

LIST OF REFERENCE SYMBOLS

[0030] 1 Chassis actuator [0031] 2 Electric motor [0032] 3 Transmission assembly [0033] 4 Continuously variable transmission, belt drive [0034] 5 Rotational-linear transmission, planetary roller gear system [0035] 6 Belt [0036] 7 Drive belt wheel [0037] 8 Output belt wheel [0038] 9 Spindle nut [0039] 10 Threaded spindle [0040] 11 Linear guide [0041] 12 Linear guide [0042] 13 Housing [0043] 14 Connection element [0044] 15 Connection element [0045] 16 Axial bearing [0046] 17 Axial bearing [0047] 18 Housing washer [0048] 19 Shaft washer [0049] 20 Rolling element, sphere [0050] 21 Preloading device [0051] 22 Radial bearing [0052] 23 Radial bearing [0053] 24 Rolling element, sphere [0054] 25 Preloading nut, fine readjustment element [0055] 26 Sleeve [0056] 27 Motor controller