POWER-ASSISTED STEERING SYSTEM FOR A MOTOR VEHICLE

Abstract

An electromechanical power steering system for a vehicle may include a worm that can be driven rotationally about a drive axis by an electric motor, that interacts with a worm gear that is coupled to a steering shaft, and that is mounted such that it can be rotated about the drive axis in a bearing that is held in a holder. The holder may be movable relative to the worm gear. To make a decreased development of noise possible, the holder has a core element that is made from a core material and is connected to at least one contact element. The contact element may be made from a soft material that can be deformed elastically more easily and is softer relative to the core material.

Claims

1.-11. (canceled)

12. An electromechanical power steering system for a vehicle, comprising: a holder that includes a core element that is made from a core material and is connected to a contact element, wherein the contact element is comprised of a soft material that is more easily elastically deformed and that is softer than the core material; and a worm that is rotatably drivable about a drive axis by an electric motor, that interacts with a worm gear that is coupled to a steering shaft, and that is mounted such that the worm is rotatable about the drive axis in a bearing that is held in the holder, with the holder being movable relative to the worm gear.

13. The electromechanical power steering system of claim 12 wherein the core material is a thermoplastic polymer and the soft material is a thermoplastic elastomer.

14. The electromechanical power steering system of claim 12 wherein the holder is a two-component injection molded part, wherein the core element and the contact element are connected via two-component plastic injection molding.

15. The electromechanical power steering system of claim 12 wherein the bearing includes a bearing ring that is attached in the holder in a bearing seat and makes contact with the contact element that is disposed in the bearing seat.

16. The electromechanical power steering system of claim 15 wherein the bearing seat includes a supporting element that is integral with the core element.

17. The electromechanical power steering system of claim 12 wherein the contact element is a damping body that projects to an outside from the holder.

18. The electromechanical power steering system of claim 17 wherein the damping body is attached in an outwardly open recess of the core element.

19. The electromechanical power steering system of claim 18 wherein the damping body projects out of the outwardly open recess to the outside in a convexly curved manner.

20. The electromechanical power steering system of claim 18 wherein the outwardly open recess passes through into a bearing seat of the bearing, wherein the contact element of the bearing seat and a damping element are connected in one piece to one another through the outwardly open recess.

21. The electromechanical power steering system of claim 12 wherein the holder is configured as a pivoting lever that is pivotable relative to the worm gear about a pivot axis that is spaced apparat from the drive axis.

22. The electromechanical power steering system of claim 12 wherein the holder is biased by a spring element in a direction of the worm gear.

Description

DESCRIPTION OF THE DRAWINGS

[0028] Advantageous embodiments of the invention will be described in greater detail in the following text on the basis of the drawings, in which, in detail:

[0029] FIG. 1 shows a motor vehicle steering system in a diagrammatic perspective view,

[0030] FIG. 2 shows a gear mechanism (steering assistance gear mechanism) of a motor vehicle steering system according to FIG. 1 in a diagrammatic perspective view,

[0031] FIG. 3 shows the mechanism elements of a gear mechanism according to FIG. 2 in a diagrammatic perspective view without a mechanism housing (housing),

[0032] FIG. 3a shows a holder according to the invention of a gear mechanism according to FIG. 2 or 3 in an axial view in the direction of the drive axis,

[0033] FIG. 3b shows a diagrammatic illustration of the mounting of the holder according to FIG. 3a in a first embodiment,

[0034] FIG. 3c shows a diagrammatic illustration of the mounting of the holder according to FIG. 3a in a second embodiment,

[0035] FIG. 4 shows a pivoting lever according to the invention of the holder according to FIG. 3 or 3a in a perspective view with a partial section through the holder,

[0036] FIG. 5 shows the pivoting lever according to FIG. 4 in a further perspective view,

[0037] FIG. 6 shows a core element of the pivoting lever according to FIG. 4 or 5 in a further perspective view,

[0038] FIG. 7 shows an enlarged detail view of a section through the pivoting lever according to FIG. 4 or 5 along the drive axis,

[0039] FIG. 8 shows an exploded partial illustration of the gear mechanism according to FIG. 3,

[0040] FIG. 9 shows the pivoting lever according to FIG. 4 or 5 in an axial view in the direction of the drive axis,

[0041] FIG. 10 shows the pivoting lever according to FIG. 9 in an axial view in an opposite direction of the drive axis, and

[0042] FIG. 10a shows a sectional illustration of the pivoting lever according to FIG. 9 in an opposite direction of the drive axis.

EMBODIMENTS OF THE INVENTION

[0043] In the various figures, identical parts are always provided with the same designations, and will therefore as a rule also be named or mentioned in each case only once.

[0044] FIG. 1 diagrammatically shows a motor vehicle steering system 100 which is configured as an electromechanical power steering system, it being possible for a driver to introduce a steering torque (steering moment) as a steering command into a steering shaft 1 via a steering wheel 102. The steering torque is transmitted via the steering shaft 1 to a steering pinion 104 which meshes with a rack 106 which then for its part transmits the predefined steering angle to the steerable wheels 110 of the motor vehicle via a displacement of the track rods 108.

[0045] An electric power assistance means can be provided in the form of a power assistance means 112 which is coupled on the input side to the steering shaft 1, a power assistance means 114 which is coupled to the pinion 104, and/or a power assistance means 116 which is coupled to the 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 rack 106, as a result of which the driver is assisted in the steering work. The three different power assistance means 112, 114 and 116 which are shown in FIG. 1 show possible positions for their arrangement.

[0046] Only a single one of the positions which are shown is usually occupied by a power assistance means 112, 114 or 116. The auxiliary torque or the auxiliary force which is to be applied by means of the respective power assistance means 112, 114 or 116 in order to assist the driver is defined with consideration of a steering torque which is introduced by the driver and is determined by a torque sensor 118. As an alternative to 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 which is applied by the driver via the steering wheel 102.

[0047] On the input side, the steering shaft 1 has an input shaft 10 which is connected to the steering wheel 102 and, on the output side, has an output shaft 12 which is connected to the rack 106 via the steering pinion 104. The input shaft 10 and the output shaft 12 are coupled to one another in a torsionally flexible manner via a torsion bar 119 (cannot be seen in FIG. 1). In this way, a torque which is input into the input shaft 10 by a driver via the steering wheel 102 always leads to a relative rotation of the input shaft 10 with regard to the output shaft 12 when the output shaft 12 does not rotate exactly synchronously with respect to the input shaft 10. Said relative rotation between the input shaft 10 and the output shaft 12 can be measured via a rotary angle sensor, and a corresponding input torque relative to the output shaft 12 can be determined accordingly on account of the known torsional rigidity of the torsion bar. In this way, the torque sensor 118 is configured by way of the determination of the relative rotation between the input shaft 10 and the output shaft 12. A torque sensor 118 of this type is known in principle and can be, for example, an electromagnetic sensor arrangement, or can be realized by way of a different measurement of the relative rotation.

[0048] Accordingly, a steering torque which is applied by the driver via the steering wheel 102 to the steering shaft 1 or the input shaft 10 will bring about the input of an auxiliary torque by way of one of the power assistance means 112, 114, 116 only when the output shaft 12 is rotated relative to the input shaft 10 counter to the rotational resistance of the torsion bar.

[0049] As an alternative, the torque sensor 118 can also be arranged at the position 118′, the division of the steering shaft 1 into input shaft 10 and output shaft 12 and the torsionally flexible coupling via the torsion bar then being present accordingly at a different position, in order for it to be possible for a relative rotation and therefore correspondingly an input torque and/or an auxiliary torque to be introduced to be determined from the relative rotation of the output shaft 12 which is coupled to the input shaft 10 via the torsion bar.

[0050] Furthermore, the steering shaft 1 according to FIG. 1 comprises at least one Cardan joint 120, by means of which the course of the steering shaft 1 in the motor vehicle can be adapted to the spatial conditions.

[0051] In the example which is shown, the power assistance means 112 or 114 comprises a gear mechanism 2 which forms a steering assistance mechanism. The gear mechanism 2 is shown in FIG. 2 in a perspective view, and in FIG. 3 in a diagrammatic view, in the case of which the mechanism housing 21 is omitted for improved clarity and exposes a view into the interior of the gear mechanism 2.

[0052] The gear mechanism has a mechanism housing 21, also called a housing 21 for short in the following text. A worm gear 22 which is connected fixedly to the steering shaft 1 for conjoint rotation is mounted in the housing 21 such that it can be rotated about the longitudinal axis L. A worm 23 is in tooth engagement with the worm gear 22 in order to form a worm gear mechanism, and can be driven rotationally about the drive axis A which is identical to the worm axis by an electric motor 24 which is flange-connected to the housing 21. As can be seen in FIG. 3, the drive axis A lies substantially perpendicularly with respect to the longitudinal axis L.

[0053] At its end which is close to the motor (on the right in FIG. 3), the worm 23 is connected to the motor shaft via a clutch, in particular a claw clutch, of the motor 24, and is mounted in a bearing 25 such that it can be rotated about the drive axis A. At its end which is remote from the motor (on the left in FIG. 3), the worm 23 is mounted in a bearing 26. The bearing 26 is received in a holder which is configured as a pivoting lever 3 and makes a compensation movement of the bearing 26 and therefore the worm 23 toward the worm gear 22 and away from the worm gear 22 possible, as is indicated in FIG. 3 by way of the double arrow. To this end, the pivoting lever 3, which is shown in FIG. 3a on an enlarged scale in an axial view from the side which is remote from the motor in the direction of the drive axis A, is mounted in the housing 21 such that it can be pivoted about a pivot axis S which runs at a spacing from and substantially parallel to the drive axis A. For mounting about the pivot axis S, the pivoting lever 3 is mounted rotatably by way of a bearing bore 31 on an axle pin 27 which is held by the housing 21 and serves as a bearing journal. This is shown diagrammatically in FIG. 3b. As an alternative, the axle pin 27 can be fixed firmly in the bearing bore 31 and can be mounted rotatably in the housing 21, as shown diagrammatically in FIG. 3c.

[0054] A spring element 28 which is configured as a leg spring is arranged on the axle pin 27 and is supported with one leg on the housing 21 and with the other leg from the outside against the pivoting lever 3, with the result that the latter is pressed elastically against the worm gear 22 in the pivoting direction about the pivot axis S by way of the spring force.

[0055] The pivoting lever 3 is shown individually in different perspectives in FIGS. 4 and 5.

[0056] The bearing 26 is preferably configured as an anti-friction bearing, and has an outer bearing ring 260 which is attached such that it cannot be rotated in a bearing seat 32 in the pivoting lever 3. The bearing seat 32 is formed by way of a bearing seat opening which passes through coaxially with respect to the drive axis A.

[0057] The pivoting lever 3 has a core element 4 which is configured as a plastic injection molded part made from a thermoplastic polymer (TP) which forms the core material and has a relatively high strength and inherent stability, such as, for example, PA 66-GF50. The bearing seat 32 has a contact element 5 which runs around over its inner wall and is formed by way of a soft material which is connected to the core element 4 using the two-component injection molding method and is preferably a thermoplastic elastomer which has a lower Shore hardness than the core material of the core element 4 and can be deformed in a rubber-elastic manner, for example TPU.

[0058] The core element 4 which is shown individually without the contact element 5 in FIG. 6 has supporting elements 41 which project radially inward into the bearing seat 32 and are arranged offset in a manner which is distributed over the circumference. The supporting elements 41 are surrounded at least partially by the soft material of the contact element 4, and project radially beyond it, with the result that, in the assembled state according to FIG. 3a, the bearing ring 260 is connected exclusively or at least predominantly to the soft material of the contact element 4. Furthermore, the soft material also extends in the direction of the bearing bore 31, and can therefore at least partially take up the region between the bearing seat 32 and the bearing bore 31, as shown in FIG. 4 in the partial sectional view.

[0059] The bearing bore 31 is configured in the core element 4. The bearing bore 31 can comprise the soft material at least partially, for example in the engagement region of the axle pin 27.

[0060] A stop damper 51 is arranged in an opening 42 which is open radially toward the outside in the core element 4 as viewed from the drive axis A, which stop damper 51, as a further contact element, is likewise configured from the abovementioned soft material and is likewise connected to the core element 4 using the two-component injection molding method. As shown in FIG. 10a which shows a section through the pivoting lever 3 transversely with respect to the drive axis A, the soft component flows through the cutouts in the region of the opening 42 and extends further in one piece along the inner circumferential face of the bearing seat 32 and as far as into the interior of the pivoting bearing.

[0061] The stop damper 51 protrudes to the outside from the pivoting lever 3 in a spherical cap-shaped curved manner, as can be seen clearly in that longitudinal section in the direction of the drive axis A which is shown in FIG. 7.

[0062] Furthermore, it can be gathered from FIG. 7 that the opening 42 in the core element 4 passes through from the outside as far as into the bearing seat 32, that is to say opens radially into the inner wall of the bearing seat opening. Here, the stop body 51 is connected through the opening 42 in one piece to the contact element 5 on the inner wall of the bearing seat 32. In other words, the stop body 51 is formed by way of a radially projecting, single-piece shaped-out formation of the contact element 5.

[0063] A prestressing element 6 can be arranged between the stop body 51 and the housing 21. Said prestressing element 6 can be of spring-elastic or rubber-elastic configuration, and can exert a prestressing force which is directed counter to the worm gear 22 on the pivoting lever 3 via the stop damper 51.

[0064] FIGS. 9 and 10 show axial views of the pivoting lever 3. On the end side which faces the observer in FIG. 9 and faces away from the observer in FIG. 10, the core element 4 has positioning elements 43 which project from the outside radially into the bearing seat 32 and against which the bearing 26 bears axially in the assembled state.

LIST OF DESIGNATIONS

[0065] 1 Steering shaft [0066] 10 Input shaft [0067] 12 Output shaft [0068] 100 Motor vehicle steering system [0069] 102 Steering wheel [0070] 103 Steering gear [0071] 104 Steering pinion [0072] 106 Rack [0073] 108 Track rod [0074] 110 Wheel [0075] 112 Power assistance means [0076] 114 Power assistance means [0077] 116 Power assistance means [0078] 118 Torque sensor [0079] 118′ Torque sensor [0080] 119 Torsion bar [0081] 120 Joint [0082] 2 Gear mechanism [0083] 21 Housing [0084] 22 Worm gear [0085] 23 Worm [0086] 24 Motor [0087] 25 Bearing [0088] 26 Bearing [0089] 260 Bearing ring [0090] 27 Axle pin [0091] 28 Spring element [0092] 3 Pivoting lever [0093] 31 Bearing bore [0094] 32 Bearing seat [0095] 4 Core element [0096] 41 Supporting elements [0097] 42 Opening [0098] 43 Positioning elements [0099] 5 Contact element [0100] 51 Stop damper [0101] 6 Prestressing element [0102] A Drive axis [0103] L Longitudinal axis [0104] S Pivot axis