The present invention relates to a worm gear for a worm gear system of a motor vehicle steering device having the features of the preamble of claim 1, to a worm gear system for a motor vehicle steering device, as well as to a method for producing a worm gear for a worm gear system of a motor vehicle steering device having the features of the preamble of claim 12.
Gear systems which transmit an auxiliary torque from an electric motor to a steering shaft are inter alia required in the use of electro-mechanical power-assisted steering devices. The electric motor usually drives a worm which engages with a worm gear which is disposed in a rotationally fixed manner on the steering shaft or on a pinion.
The worm gear comprises an insert which is connectable in a rotationally fixed manner to the steering shaft or to the pinion, wherein said insert is enhanced with a plastics material. Said plastics material configures the so-called gear rim.
A gear wheel having an insert part which has a radial elevation is known from the first and unexamined publication EP 1 780 445 A1, wherein said insert part is enhanced with a gear rim configured by overmolding. A disadvantage of this solution lies in the radial disposal of the elevation, on account of which unfavorable flow conditions are created in the plastics material when injecting and a non-homogenous plastics-material structure is configured.
It is an object of the present invention to specify a worm gear for a worm gear system of a motor vehicle steering device, said worm gear by way of ideally simple means having a plastics-material structure with improved homogeneity.
This object is achieved by a worm gear for a worm gear system of a motor vehicle steering device having the features of claim 1, and by a method for producing a worm gear for a worm gear system of a motor vehicle steering device having the features of claim 12.
Advantageous refinements of the invention are specified in the dependent claims.
Accordingly, a worm gear for a worm gear system of a motor vehicle steering device is provided, comprising a hub, a support element, and a gear rim, wherein the gear rim has a multiplicity of teeth which extend radially outward in terms of a worm gear longitudinal axis, and wherein the support element is a support ring which by means of an injection-molding method is injected between the gear rim and the hub and which connects in a form-fitting manner the hub and the gear rim.
The gear rim preferably has reinforcement ribs which, on both end sides, from the teeth extend radially in the direction of the worm gear longitudinal axis or the gear rim center.
The insert part forming the hub is preferably made from steel.
The gear rim is preferably configured as a single-component plastics material part and thus so as to be integral. An application of teeth to a support part by means of injection-molding is thus unnecessary. The gear rim can thus be produced in a particularly economical manner.
The insert part preferably has a gear rim which engages in a corresponding recess in an internal side of the gear rim. The insert part and the gear rim can thus be connected to one another in a simple manner in a first production step.
It is advantageous for the gear rim to have injection bores which between the worm gear longitudinal axis and the reinforcement ribs are provided for injecting a plastics material for configuring the support ring. The gear rim and/or the support ring are/is preferably composed of artificial resin or a thermoplastic material, in particular of polyamide, polyoxymethylene, saturated polyester, polyether, and/or ether ketone, or comprises reinforcement fibers or a fiber-reinforced plastics material.
The injection bores are preferably disposed at uniform spacings along the gear rim circumference. Preferably, at lest four injection bores, furthermore preferably more than six injection bores, are provided along the gear rim circumference. Twelve injection bores are particularly preferably provided along the gear rim circumference. It is furthermore conceivable and possible for injection bores to be provided in a plurality of, for example two, rows along the gear rim circumference so as to connect in a materially integral and form-fitting manner the insert part to the gear rim.
The injection-molding method is carried out such that the support ring does not project beyond the end sides of the teeth of the gear rim. The support ring is preferably configured so as to be planar on the external sides and does not have any protrusions or recesses.
In one preferred embodiment, the support ring in terms of a worm gear vertical axis has inward pointing ribs which in the radial direction are configured so as to be conical. It is advantageous herein for the ribs of the support ring to have a rib thickness and rib spacings which in size are smaller than or equal to the basic wall thickness of the support ring.
The support ring preferably has undercuts which in the production permit jamming between the support ring and the gear rim.
Furthermore provided is a worm gear system for a motor vehicle steering device having a worm gear as described above, wherein the worm gear engages with a worm.
Moreover provided is a method for producing a worm gear for a worm gear system of a motor vehicle steering device. The worm gear system herein comprises a hub, a support element, and a gear rim, wherein the gear rim has a multiplicity of teeth which extend radially outward in terms of a worm gear longitudinal axis. The method comprises the following steps:
It is preferable herein for the gear rim to have injection bores into which the plastics material for configuring the support ring is injected specifically in such a manner that the plastics material is uniformly distributed on both lateral faces between the insert part and the gear rim. As has been described above, the injection bores are positioned at uniform spacings along the gear rim circumference.
The support ring in the cured state preferably does not project beyond the end sides of the teeth of the gear rim. It is advantageous herein for the support ring to be configured planar on the external sides and not to have any protrusions or recesses.
The gear rim is preferably configured in such a manner that the support ring in the cured state has inward pointing ribs which in the radial direction are configured so as to be conical.
The gear rim is furthermore preferably configured in such a manner that the ribs of the support ring in the cured state have a rib thickness and rib spacings which in size are smaller than or equal to the basic wall thickness of the support ring.
The gear rim is preferably configured in such a manner that the support ring in the cured state has undercuts which in the production permit jamming between the support ring and the gear rim.
A preferred embodiment of the invention will be explained in more detail hereunder by means of the drawings. Components of the same type or equivalent function are identified by the same reference signs in the figures. In the drawings:
An electro-mechanical motor vehicle steering device 1 having a steering wheel 2 which is coupled in a rotationally fixed manner to an upper steering shaft 3 and to a lower steering shaft 4 is schematically illustrated in
The worm gear 12 having a hub 15, a support ring 16, and a gear rim 17 is illustrated along the worm gear longitudinal axis S in
As is shown in
The assembled state of the insert part 150 having the gear rim 17 is illustrated in
The configured support ring 16 is illustrated in the longitudinal section in
The support ring 16 formed by injection-molding enables a form-fit and at least in part a materially integral connection between the gear rim 17 and the support ring 16. Said support ring 16 is a highly rigid load-bearing structure which can be economically produced.
Number | Date | Country | Kind |
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10 2017 131 173.4 | Dec 2017 | DE | national |
Filing Document | Filing Date | Country | Kind |
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PCT/EP2018/085637 | 12/18/2018 | WO | 00 |