Machine element or mechanism – Gearing – Directly cooperating gears
Reexamination Certificate
1999-05-25
2001-08-14
Marmor, Charles A (Department: 3681)
Machine element or mechanism
Gearing
Directly cooperating gears
C074S400000, C074S500000
Reexamination Certificate
active
06272942
ABSTRACT:
FIELD AND BACKGROUND OF THE INVENTION
The invention relates to a worm gear unit having at least one worm shaft displaceable in the axial direction.
As already described in DE 198 11 977.1 (date of application: Mar. 19, 1998), worm gear units are classed as standard gear units and are used in a multiplicity of applications at the most widely varying transmission ratios. Depending on the application, worm gear units with or without self-locking may be selected.
In some applications, for example when a worm gear unit is used as a step-down gear unit in electric steering aids, it is necessary to keep the play of the worm gear unit slight in order to transmit a drive force directly and without play to the output. High-precision manufacture of the worm and the worm gear of the worm gear unit or even the use of certain tooth-flank forms could be considered as possible measures for reducing the play. However, this has the disadvantage that this is complicated and thus very cost-intensive precisely during the mass production of worm gear units, in particular for the use of electric steering aids in vehicles.
SUMMARY OF THE INVENTION
The object of the invention therefore is to provide a worm gear unit in which the play between a worm gear and a worm can be set simply and quickly, in particular within the context of mass production, in which case no great demands with regard to precise design techniques are to be imposed on the components of the gear unit.
Means which act on a worm shaft of the worm gear unit are provided by the invention, in which case this worm shaft, in order to set the play, can be secured once in the axial direction by the means (the rotation of the worm shaft still being ensured at the same time), the means being irreversibly secured after the play has been set. As a result, after assembly of the worm gear unit, which has, for example, a conventionl spur or helical tooth system, quick setting of the play is possible by the worm shaft being moved in the axial direction with such a force as to eliminate the play from the worm gear unit. After the play has been set, the means are irreversibly secured, so that, on the one hand, the means can no longer come loose during operation, in which case play would occur again. On the other hand, the irreversible securing of the means can be realized very simply from the point of view of production, so that complicated measures such as, for example, setting the play by means of a screw which is locked with a lock nut after the play has been set may be dispensed with. The measures available here for permanently securing the means are, for example, the adhesive bonding, brazing, welding or the like of the means to a corresponding mating part. In particular, such measures with which the permanent securing is effected by means of friction grip are especially advantageous, since a form grip is out of the question here on account of the setting of the play. To permanently secure the means, it is also possible for the means to be squeezed, pressed, “crushed” or the like together with a corresponding mating part, as a result of which form grip is obtained. Combinations of said possible measures are also conceivable.
In a development of the invention, the worm gear unit is arranged in a housing in a manner known per se, provision now being made according to the invention for the means to be supported on the housing (mating part). This results in a compact type of construction, in which case a receptacle for the means may already be provided during the manufacture of the housing. This also results in the advantage that, after installation of the worm gear unit in the housing, the latter can be fixed in position on a production unit, the play can be set and then the means can be permanently secured in the course of this production step, so that this also results in quick production.
In a development of the invention, the means have at least one pin, which can be permanently secured in particular to the housing after the play has been set. The use of a pin has the advantage that on the one hand, this pin may be made of a conventional bar or tube material, in which case, on the other hand, the receptacle for this at least one pin in the housing may be designed simply as a bore. Since the pin is to be permanently secured in the housing preferably by means of friction grip, it is not necessary either for any great precision-related demands to be imposed on the design of the pin and/or of the receptacle in the housing.
In a development of the invention, provision is made for the means to act directly on the worm shaft. This simple design is especially suitable if the worm shaft is not subjected to any excessively high axial forces, which would lead to wear in the abutment region between the means and the one end of the worm shaft. In addition, such a design may be used if the worm shaft has force (for example spring force) applied to it in the axial direction away from the means, so that, although certain friction would be produced in the abutment region between the one end of the worm shaft and the means, this friction would not lead to high wear.
In a development of the invention, the means act in the axial direction on at least one bearing of the worm shaft. This ensures that, compared with the direct action of the means on the worm shaft, not only is the worm shaft itself carried in a bearing, but also the play can be set via such a bearing, so that no friction can appear between the means for the permanent securing after the setting of the play and the relevant end of the worm shaft and thus wear is avoided.
In a development of the invention, the means, in particular the at least one pin, are arranged in the axial direction with the worm shaft, an axial bearing being located between one end of the worm shaft and one end of the means (the pin). In this arrangement, the worm shaft, the axial bearing and the means (pin) are arranged in alignment one behind the other in the longitudinal axis of the worm shaft, so that there is optimum action of force of the pin on the worm shaft in order to set the play, the forces for setting the play acting on the worm shaft via the axial bearing, so that wear and friction are avoided. In addition, such an arrangement, with the geometry resulting therefrom, also has the advantage that such a worm gear unit, at least in the one region of the end of the worm shaft, is of elongated and flat construction, so that this geometric design, depending on the available construction space, may be of advantage.
In a development of the invention, the means, in particular the at least one pin, are arranged in the axial direction and/or in an axis parallel to the longitudinal axis of the worm shaft, the means acting on a radial bearing of the worm shaft via a pressure ring. In such a design, the radial bearing is utilized not only for the mounting of the worm shaft but also for setting the play of the latter in the axial direction. A pressure ring is provided for the uniform distribution of force, and this pressure ring, on the one hand, can have force applied to it by the means of (the pin) and, on the other hand, acts on an outer ring of a radial bearing, designed as a ball bearing, in order to transmit the forces of the means to the worm shaft via the periphery of the radial bearing. Thus there is the advantage that the force application, which is concentrated to a certain extent, is transmitted to a force area arranged concentrically to the worm shaft and is conveyed to the worm shaft, the quick setting also being ensured on account of the use of only one pin. As an alternative, it is conceivable to use two or more pins over the outer periphery of the radial bearing, and these pins may be used to set the play. This would have the advantage that the pressure ring could be dispensed with, although the advantages of quick setting, a compact type of construction and lighter weight compared with the version having only one pin do turn out to be so optimal.
In a development of the invention, the pressure ring is designed to b
Farber Martin A.
Mannesmann VDO AG
Marmor Charles A
Pang Roger
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