Steering gear for a vehicle

Abstract

A steering gear for a vehicle includes a steering pinion and a master rack. A toothing of the master rack includes a constant helix angle and a toothing of the steering pinion includes a changing helix angle.

Claims

1. A steering gear assembly for a vehicle, comprising: a toothed steering rack; and a steering pinion configured to mesh with the toothed steering rack, wherein a transmission ratio of the toothed steering rack and the steering pinion is configured to change with a rotation of a steering wheel of the vehicle, wherein a rack toothing of the toothed steering rack has a constant helix angle, and wherein a pinion toothing of the steering pinion has a helix angle that changes over a circumference of the steering pinion.

2. The steering gear assembly as claimed in claim 1, wherein: the pinion toothing includes at least two helix angle sections having different helix angles; and the helix angle of each of the at least two helix angle sections is constant.

3. The steering gear assembly as claimed in claim 2, wherein the helix angles of the at least two helix angle sections differ by at least 10.

4. The steering gear assembly as claimed in claim 2, wherein the helix angles of the at least two helix angle sections differ by at most 45.

5. The steering gear assembly as claimed in claim 1, wherein: the steering pinion defines an axis of rotation; and the steering pinion is mounted in a gear housing exclusively about the axis of rotation.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further advantages and expedient embodiments emerge from the further claims, from the figure description and from the drawings, in which:

(2) FIG. 1 shows a schematic illustration of a steering system in a vehicle,

(3) FIG. 2 shows a schematic illustration in a plan view of a steering gear with steering pinion and toothed steering rack, wherein the steering pinion has a toothing with different helix angles,

(4) FIG. 3 shows a further exemplary embodiment of a steering gear with steering pinion and toothed steering rack in plan view, wherein steering pinion and toothed steering rack each have a constant helix angle, but the steering pinion is mounted so as to be pivotable,

(5) FIG. 4 shows the steering gear with steering pinion and toothed steering rack as per FIG. 3 with the steering pinion in a pivoted state,

(6) FIG. 5 shows a view of a toothed steering rack whose side on which the toothing is situated is of curved form.

DETAILED DESCRIPTION

(7) In the figures, identical components are denoted by the same reference designations.

(8) The steering system 1 illustrated in FIG. 1 for a vehicle comprises a steering wheel 2, a steering spindle or shaft 3, a steering or gear housing 4, and a steering linkage with a toothed steering rack 5, via which a steering movement is transmitted to the steerable wheels 6 of the vehicle. The gear housing 4 accommodates a steering gear 8 with a steering pinion and the toothed steering rack 5, wherein the steering pinion is connected rotationally conjointly to the steering shaft 3 and meshes with the toothed steering rack 5.

(9) By means of the steering wheel 2, to which the steering shaft 3 is fixedly connected, the driver predefines a steer angle .sub.L which, in the steering gear 8 in the gear housing 4, is transmitted to the toothed steering rack 5 of the steering linkage, whereupon a wheel steer angle .sub.V is set at the steerable wheels 6.

(10) To assist the manual torque imparted by the driver, an electric servo motor 7 is provided, by means of which a servo torque can be fed into the steering gear 8. Instead of an electric servo motor, it is also possible for a hydraulic assistance device to be provided, for example a hydraulic pump, which is driven by an internal combustion engine and which feeds a hydraulic steering system.

(11) FIG. 2 illustrates the steering gear 8 with the toothed steering rack 5 and the steering pinion 9 engaging therein. The toothed steering rack 5 has a toothing with a constant helix angle of greater than 0, such that the tooth flanks of the teeth assume an angle of greater than 0 with respect to an orthogonal to the longitudinal axis 5a of the toothed steering rack 5. The toothing of the toothed steering rack 5 has a constant helix angle .sub.2.

(12) The steering pinion 9 has different helix angle sections 10 and 11, wherein the helix angle is constant within each helix angle section 10, 11, but the helix angles differ between the helix angle sections. The illustration shows the helix angle .sub.1 for the helix angle section 10, wherein the helix angle .sub.1 is defined in relation to the axis of rotation 9a about which the steering pinion 9 can rotate. The helix angle of the toothing in the further helix angle section 11 is significantly smaller than the helix angle .sub.1 of the helix angle sections 10 adjoining said further helix angle section on both sides, and may possibly be 0. The helix angle section 11 is situated in the zero or initial or rest position of the steering system, which is adjoined on both sides by the helix angle sections 10 with the greater helix angle .sub.1.

(13) The transition between the helix angle sections 10, 11 is realized in continuous form and without step changes. Accordingly, between the first helix angle section 10 with the helix angle .sub.1 and the second helix angle section 11 with a different helix angle, there is a transition region in which the helix angle changes even within one tooth.

(14) The helix angles .sub.1 in the helix angle section 10 of the steering pinion 9 and .sub.2 of the toothed steering rack 5 may be equal or may possibly differ from one another.

(15) The toothed steering rack 5 and steering pinion 9 are at an angle with respect to one another, such that the longitudinal axis 5a of the toothed steering rack 5 and the axis of rotation 9a of the steering pinion 9 assume a non-90 angle with respect to one another. The angle lies for example in an angle range between 60 and less than 90.

(16) Owing to the changing helix angle in the toothing of the steering pinion 9, a variable steering transmission ratio as the steering pinion 9 rolls on the toothing of the toothed steering rack 5 is realized with a corresponding variability of pitch and flank angle.

(17) FIGS. 3 and 4 illustrate a further exemplary embodiment of a steering gear 8 with a toothed steering rack 5 and with a steering pinion 9. The toothed steering rack 5 has a helical toothing with variable pitch and flank angle, but a helix angle .sub.2 of greater than 0. The steering pinion 9 has only a single helix angle section 10 with a uniform helix angle .sub.1, which is greater than 0. In order to kinematically exactly correspond to the variable transmission ratio, the steering pinion 9 is mounted in the steering housing or gear housing such that, in addition to its rotation capability about the axis of rotation 9a, it is pivotable about a pivot axis 12. The pivot axis 12 lies in a central plane of the steering pinion 9 and is orthogonal to the axis of rotation 9a. Pivot axes are however also possible which are at a non-90 angle with respect to the axis of rotation.

(18) Furthermore, pivot axes are also possible which lie in a plane which is orthogonally offset and parallel with respect to the central plane.

(19) As can be seen from a comparison of FIGS. 3 and 4, the housing angle at which the steering pinion 9 is positioned relative to the gear housing changes as the steering pinion 9 rolls on the toothed steering rack 5. The pivoting of the steering pinion 9 about the pivot axis 12, and the associated change of the housing angle , takes place with kinematically positive guidance in a manner dependent on the rotational movement of the steering pinion 9 about the axis of rotation 9a. It is hereby ensured that every angle of rotation of the steering pinion 9 about the axis of rotation 9a is assigned exactly one housing angle .

(20) FIG. 5 illustrates a further design variant in which the toothing 13 of the toothed steering rack 5 lies not in a plane but on a curved line 14, whereby it is likewise possible for the transmission ratio to be influenced as the steering pinion rolls on the toothed steering rack. As an alternative to the curved line, the toothing 13 may also be arranged in a plane on the toothed steering rack 5.

LIST OF REFERENCE DESIGNATIONS

(21) 1 Steering system 2 Steering wheel 3 Steering shaft 4 Gear housing 5 Toothed steering rack 5a Longitudinal axis 6 Front wheel 7 Electric servo motor 8 Steering gear 9 Steering pinion 9a Axis of rotation 10 Helix angle section 11 Helix angle section 12 Pivot axis 13 Toothing 14 Curved line