Abstract:
A steering system and more particularly to a rack-and-pinion assembly, in particular for a rack-and-pinion steering assembly for motor vehicles having an input shaft axis arranged at a distance from the rack axis which is greater than the diameter of a pinion meshing with the rack. Preferably, this pinion is arranged between the rack and an input pinion distant from the latter, on an input shaft of the gear.

Description:
FIELD OF INVENTION 
     The invention relates to a rack-and-pinion gear, in particular for a rack-and-pinion steering of a motor vehicle. 
     BACKGROUND 
     In conventional rack-and-pinion steering assemblies, a rack is coupled to vehicle wheels for use in controlling the direction of the wheels, a pinion arranged on an input shaft meshes directly with the rack. The pinion radius is relatively small, the axes of the rack and of the input shaft are therefore at a slight distance from one another, the order of magnitude of which is predetermined by the radius of the pinion. 
     DE 36 27 088 A1 relates to a rack-and-pinion steering assembly, in which the pinion meshing with the rack is designed as a ring wheel with an external and an internal toothing, the external toothing cooperating with the rack and the internal toothing cooperating with a further pinion arranged on an input shaft. In this case, the input shaft is arranged within a sector of the ring wheel, the said sector being in engagement with the rack via the external toothing. There is therefore only a slight distance between the axes of the rack and input shaft. 
     DE 33 27 979 C1 relates to a rack-and-pinion steering assembly in which a gear with a variable transmission ratio is arranged between a pinion meshing with the rack and a further pinion arranged on the input shaft, the gear is designed in such a way that the axis of the input shaft is positioned at a comparatively slight distance from the axis of the rack. 
     Rack-and-pinion steering assemblies may present installation problems, at least with respect to present-day vehicles having an engine arranged in the region of the front axle thus limiting space for the rack and pinion and for other components. As a result, installation of both the rack and steering column can be difficult. 
     The object of the invention is, therefore, to provide new concepts for rack-and-pinion gears and to improve installation of rack-and-pinion steering assemblies. 
     SUMMARY 
     According to one aspect of the invention, the input-shaft axis and rack axis are separated by a distance which is perpendicular to both axes, the dimension of which is greater than the diameter of the pinion meshing with the rack. 
     According to this aspect of the invention, the invention provides for interposing gear elements between the input shaft and the pinion meshing with the rack such that the distance between the input-shaft axis and rack axis is increased. According to another aspect of the invention, the input-shaft axis is shifted, relative to a conventional position by use of the interposed gear elements, onto the other side of the rack. 
     According to one aspect of the invention, there is provision for an interposing pinion meshing with the rack on one side and meshing on its circumferential region located diametrically opposite the region of engagement of the rack, with an input pinion which is arranged on the input shaft, so that the order of magnitude of the distance between the rack axis and input-shaft axis is predetermined by the radius of the input pinion and by the diameter of the pinion meshing with the rack. 
     This type of construction makes it possible to ensure a particularly efficient design, and it is particularly advantageous that freedom from play can be ensured in the most efficient way, in that the rack is pressed resiliently against the pinion meshing with it and this pinion is mounted so as to be moveable in the pressing direction, so that the pressing forces are transmitted to the radially fixably mounted input pinion of the input shaft. The engagements of the rack and pinion and of the pinion and input pinion are thereby made more efficient and kept free of play in an efficient manner. 
     According to another aspect of the invention, the rack meshes directly with an input pinion having a large diameter relative to conventional rack and pinion assemblies and provides for a more efficient design and input pinion free of play. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 illustrates a sectional diagram of an embodiment of a rack-and-pinion assembly; 
     FIG. 2 illustrates a sectional diagram of an embodiment of a rack-and-pinion assembly along the sectional line II—II in FIG. 1; 
     FIG. 3A illustrates a schematic of a top view of an embodiment of steering components; 
     FIG. 3B illustrates a schematic of a top view of an embodiment of steering components; 
     FIG. 3C illustrates a schematic of a top view of an embodiment of steering components; and 
     FIG. 3D illustrates a schematic of a top view of an embodiment of steering components. 
    
    
     DESCRIPTION OF EMBODIMENTS 
     FIGS. 1 and 2 illustrate an embodiment of a rack-and-pinion assembly. The rack  2  is mounted displaceable in a gear case  1 . The rack  2  meshes with a pinion  3  which has a large diameter compared with a pinion in conventional rack-and-pinion steering assemblies, and in turn meshes, on its side located diametrically opposite the rack  2 , with an input pinion  5  arranged fixedly in terms of rotation on an input shaft  4  or formed on the input shaft  4 . 
     The rack  2  is urged against the pinion  3  by means of a thrust piece  7  loaded by a helical compression spring  6 . The pinion  3  is rotationally mounted, within the gear case  1  in bearings  8  which are displaceable in the gear case  1  in a direction perpendicular to the axes of the rack  2  and input shaft  4 . For this purpose, pockets  9  are arranged in the gear case  1  for receiving the bearings  8  and, as seen in FIG. 2 have an oval shape such that the bearings  8  are moveable in the above-mentioned direction of displacement, but are immovable in the direction perpendicular to the direction of displacement and to the axis of the pinion  3 . 
     The input shaft  4  having the input pinion  5  is mounted in a radially fixed manner. 
     The pressure forces exerted on the rack  2  by the thrust piece  7  are accordingly transferred to the input pinion  5  via the pinion  3 , so that, on the one hand, the toothing engagement between the rack  2  and pinion  3  and, on the other hand, the toothing engagement between the pinion  3  and input pinion  5  are kept free of play. 
     A distance of different size can be obtained between the axes of the rack  2  and of the input shaft  4 , depending on the dimensioning of the diameter of the pinion  3 . 
     It is also possible, in principle, to arrange a plurality of pinions corresponding to the pinion  3  between the input pinion  5  and the rack  2 . 
     FIG. 3A illustrates an embodiment of steering components including a rack-and-pinion steering assembly in which a rack  2  is connected at its ends in an articulated manner to track rods  10 , the ends of which are connected in an articulated manner to steering levers  11  of vehicle wheels  13 . In this case, the outer track-rod joints, that is to say the articulated connections between the track rods  10  and the steering levers  11 , are arranged in front of the wheel center in the forward travel direction F, so that the vehicle wheels  13  are correspondingly steered to the left or to the right when the rack  2  is displaced to the left or to the right. 
     In the embodiment of FIG. 3A the rack  2  meshes directly with an input pinion  5  which in turn, is positively coupled to the steering wheel  14  via a steering column input shaft not illustrated. In order to ensure that rotation of the steering wheel  14  to the right or to the left leads to a steering of the vehicle wheels  13  to the right or to the left, input pinion  5  of this embodiment is arranged behind the rack  2  relative to the travel direction F. The rack  2  of this embodiment is urged directly against the input pinion  5  by a thrust piece loaded by a helical compression spring. 
     FIG. 3B illustrates an embodiment of steering components including a rack-and-pinion assembly in which the input pinion  5  is arranged in front of the rack  2  relative to travel direction F and a pinion  3  is interposed between the input pinion  5  and the rack  2 . The rack  2  of this embodiment is urged against the pinion  3 , and pinion  3  against pinion  5  as shown in FIGS. 1 and 2. 
     Thus, as compared with the conditions in FIG. 3A, a marked shift of the input pinion  5  and, accordingly, of the associated input shaft or the steering column is achieved. 
     FIG. 3C illustrates an embodiment of steering components including a rack-and-pinion assembly including a rack connected at its ends in an articulated manner to track rods  10 . The track rods  10  of this embodiment are connected in an articulated manner to the steering levers  11  behind the wheel center of the vehicle wheels  13 , relative to travel direction F, so that when the rack  2  is displaced to the right or to the left the vehicle wheels  13  are steered to the left or to the right correspondingly. The input pinion  5  meshing directly with the rack  2  is arranged in front of the rack relative to travel direction F, so that a rotation of the steering wheel  14  to the right or to the left results in a steering of the steered vehicle wheels  13  to the right or to the left correspondingly. 
     FIG. 3D illustrates an embodiment of steering components including a rack-and-pinion steering assembly in which pinion  3  is interposed between the input pinion  5  and the rack  2 , the two pinions  3  and  5  being arranged behind the rack  2 , relative to direction F, so that the direction of rotation of the steering wheel  14  is once again translated to steer the vehicle wheels in the direction of the steering wheel. 
     As compared with the conditions in FIG. 3C, a marked shift of the input pinion  5  and consequently also the input shafts is achieved. 
     As a result, by virtue of the invention, the possibilities for arranging the input pinion  5  can be markedly extended. 
     In addition to the embodiments in FIGS. 3A and 3D, in which the track rods  10  adjoin the rack  2  without any transverse offset, there may also be provision for arranging the articulated connections between the rack  2  and track rods  10  on the rack  2  with an offset relative to the rack axis. The number of possibilities for variation is thereby increased even further. 
     Although the invention has been described in detail with reference to certain preferred embodiments and specific examples, variations and modification exist within the scope and spirit of the invention as described and as defined in the following claims.