Rack-and-pinion assisted steering system

In a rack-and-pinion assisted steering system with an elastic connection housing, for example made of plastic arranged between the pinion housing (6) and the cylinder housing, the bearing points of the rack (1) and pinion (2) are not fixed in a housing. The alignment of the pinion axis (A) with the pinion housing is effected via the existing contact line (B) between the rack teeth and the pinion teeth. The rack teeth are pressed without play between the pinion teeth by means of an additional pressure member (7) in the lid (5) of the pressure piece (3) thereby aligning the pinion axis (A) with the pinion housing (6). After the rack-and-pinion assisted steering system is mounted in the vehicle, the pressure member (7) is removed and the effect of the spring-mounted pressure piece (3) is reestablished. The aligned pinion axis (A) ensures a good rolling between pinion and rack teeth.

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.

DESCRIPTION OF PREFERRED EMBODIMENT
 As shown schematically in FIG. 2, the present invention is a
 rack-and-pinion assisted steering system 10 including a servo motor 11
 having a cylinder housing 12. System 10 also includes a multi-part
 steering housing 13 having a pinion housing 6 and a highly elastic
 connection housing 14. Connection housing 14 is disposed between pinion
 housing 6 and cylinder housing 12.
 As FIGS. 1 and 2 show, a rack 1 meshes with a pinion 2. The alignment of
 the pinion axis A is effected via the existing contact line B (FIG. 2). A
 pressure piece 3 presses the rack teeth into the pinion teeth by the force
 of a spring 4 and aligns the pinion axis A. The spring 4 is braced in a
 lid 5 in a pinion housing 6. The pinion axis A can still shift slightly,
 however, relative to the rack teeth within the existing pressure piece 3
 play. According to the invention, a pressure member 7 is seated in the lid
 5 and pushes the pressure piece 3 against the rack 1 and the rack against
 the pinion 2. This pressure member screw 7, in contrast to the pressure
 piece 3, defines play-free support of the rack 1 in the pinion 2. In this
 state, the pinion housing 6 is then installed in the vehicle, and after
 that the pressure member 7 is removed again. The pressure piece 3 play
 established beforehand is now again present. A screw can for instance be
 used as the pressure member 7.
 By means of the invention, a similar advantage as in selective installation
 can be attained. In selective installation, the housing bearing points are
 surveyed exactly and consequently paired with selected sets of teeth on
 the pinion and the rack. However, such a selection is not feasible,
 because of the costs and the high numbers of parts involved. When an
 elastic connection housing 14 is used in conjunction with the pressure
 member 7 of the invention, optimal pairing of the components is
 automatically obtained by the alignment of the pinion axis A with the
 teeth of the rack 1.
 Other advantages are obtained in that production errors in the manufacture
 of the pinion and rack teeth can be greater yet without worsening the
 rolling performance. Because of the higher production tolerances, the
 rejection rate drops, and manufacturing processes with a higher machining
 speed can be employed. This leads to a cost reduction for better or equal
 rolling quality of the teeth.
 It is provided that the pressure member fixes the rack, in the state as
 shipped, in the middle position with the pressure piece in the pinion;
 that is, in this position, the vehicle drives straight ahead. This
 shipping state is preferred by many automobile manufacturers, because the
 installation in the vehicle can be simplified thereby.