Motor vehicles – Steering gear – With fluid power assist
Reexamination Certificate
1999-05-19
2001-02-27
Johnson, Brian L. (Department: 3618)
Motor vehicles
Steering gear
With fluid power assist
C074S422000
Reexamination Certificate
active
06193008
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a rack-and-pinion assisted steering system, in particular for motor vehicles, having a multiple-part steering housing, which has a pinion housing and a cylinder housing, with a highly elastic connection housing disposed between the two housing parts. A pinion rotates in the pinion housing. A rack axially displaceably guided in the multiple-part steering housing is held in engagement with the pinion in the pinion housing by a spring-loaded pressure piece. The rack is connected via a piston rod to a piston, which divides two pressure chambers of a servo motor from one another in the cylinder housing. The connection housing is embodied such that no position-determining forces are transmitted from the pinion housing to the cylinder housing.
BACKGROUND OF THE INVENTION
The invention takes as its point of departure German Patent Disclosure DE 195 45 439, which was not published prior to the filing date of the present application, and which describes a rack-and-pinion assisted steering system in which overdetermination of the bearing of the rack in the steering housing is avoided without complicated tightening of the tolerances in the manufacture of the steering housing and the rack. The production is simplified by providing that the connection housing between the pinion housing and the cylinder housing is of an elastic material. By means of the elastic connection housing, which itself does not transmit any forces or moments, an overdetermination of the bearing of the rack in the steering housing can be avoided. The location of the pinion housing relative to the cylinder housing is defined by the rack.
In rack-and-pinion assisted steering systems with a relatively rigid connection between the pinion housing and the cylinder housing, production errors between the pinion axis and the rack axis worsens the rolling performance. On the one hand, the teeth of the pinion and rack determine the axes and on the other, the bearing points of the rack and the pinion determine two further axes. So that these axes will match, the components in question must be machined very precisely. The dimensional tolerances and the shape and position tolerances are correspondingly narrow, which means high production costs. In the design in DE 195 45 439, the bearing points of the rack and the pinion are not rigidly fixed in a housing. The alignment of the pinion axis A is effected via the existing contact line B of the teeth. The rack teeth are pressed by the pressure piece into the pinion teeth, thereby aligning the pinion axis. Because of the existing pressure piece play, however, the pinion axis can still shift slightly relative to the rack teeth. This again leads to poor rolling performance of the teeth.
BRIEF SUMMARY OF THE INVENTION
The object of the invention, in rack-and-pinion assisted steering systems with an elastic connection housing, is to avoid the source of error that is still present because of the pressure piece play, so that optimal rolling performance of the teeth is obtained.
This object is attained by the rack-and-pinion assisted steering system as discussed here after. This is accomplished in that an additional pressure member acts on the springloaded pressure piece and, in the state of the rack-and-pinion assisted steering system in which it is not yet installed on the vehicle, presses the rack without play into the pinion and after installation of the steering in the vehicle is removed. As a result, the pinion axis can be aligned with the pinion housing via the existing teeth. The pressure member thus eliminates the pressure piece play by pressing the pressure piece against the rack and the rack against the pinion. This cancels the action of the pressure piece. In this way, the alignment of the pinion axis with the line of contact of the rack teeth and the pinion teeth is assured without play between these components.
An expedient embodiment is where the pressure member is supported in a lid of the pressure piece and is embodied as a screw. In this way, an economical way of achieving an additional pressure member acting on the rack is achieved.
In accordance with the expediant embodiment, the pressure member secures the rack in the middle position, so that the vehicle is in position for driving straight ahead. This position is preferred by automobile manufacturers for installing the steering system.
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Johnson Brian L.
Larson & Taylor PLC
Yeagley Daniel
ZF Friedrichshafen AG
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