Abstract:
The invention relates to a push device ( 8 ) which includes a rotary pad ( 10 ) in which the inner periphery ( 11 ) is off-centre relative to the outer periphery ( 12 ) and applied to the rear ( 9 ) of the rack ( 3 ) which is thereby pushed towards the teeth of the steering pinion ( 5 ). A clearance compensation mechanism ( 17 ) includes a thrust member ( 19 ) pressed against a radial arm ( 18 ) of the pad ( 10 ) by a compression spring ( 20 ) inserted between said member and an element ( 23 ) secured to the support ( 13 ) of the pad ( 10 ). A mobile stop ( 21 ) rotatably mounted relative to the element ( 23 ) comprises toothings having staggered gear teeth cooperating with notches of the thrust member ( 19 ). The stop ( 21 ) is connected to the element ( 23 ) by means of a torsion spring ( 22 ). The notches successively cooperate with the staggered teeth.

Description:
TECHNICAL FIELD 
       [0001]    The present invention generally relates to rack-and-pinion steering for motor vehicles. More particularly, this invention relates to the so-called “push line” device, or more simply a “pusher” for such steering, the function of which is to keep the rack meshing with the steering pinion while offsetting the toothing defects, this device also serving to facilitate the mounting of the pinion in the casing of the rack-and-pinion steering system. Also more particularly, the invention relates to a so-called “off-center” pusher, which is provided with a system for automatically compensating for the clearance between the pinion and the rack. 
       BRIEF SUMMARY OF RELATED ART 
       [0002]    In a motor vehicle rack-and-pinion steering system, a steering pinion is rotatably connected to a steering column, maneuvered using the steering wheel of the vehicle, often with the help of a hydraulic or electric assistance system. The steering pinion is engaged with a rack, slidingly mounted in the longitudinal direction in a steering gear-box. The two ends of the rack, outside the box, are respectively coupled to two tie rods, which in turn are respectively associated with the left and right steering wheels of the vehicle. In this way, the rotation of the wheel in one direction or the other, transmitted by the steering column to the pinion, is converted into a corresponding translational movement of the rack which, via the rods, causes the orientation of the steering wheels for steering right or steering left. 
         [0003]    In such a steering system, the rack-and-pinion mechanism, connected to the front wheels of the vehicle via rods, is subject to the transfer of loads, shocks and vibrations, depending on the road traveled by the vehicle. Due to the angle formed by the rods with the rack, a load may then be produced on the rack, which risks moving it away from the pinion. For that reason, the rack is usually continuously pressed against the pinion by a so-called “pusher” device, acting elastically on the back of the rack in the region of the pinion to strongly press the toothing of that rack against the pinion. Owing to such a pusher, the meshing defects of the rack with the pinion are offset, and said pusher also ensures the guiding of the rack, while controlling the sliding force of that rack in the steering gear-box. 
         [0004]    In its most common embodiment, the pusher device comprises the pusher strictly speaking, which is a rigid piece translationally mounted in a direction substantially perpendicular to the longitudinal axis of the rack, and which is stressed toward the back of the rack by elastic means, so as to press on the back of the rack by an end portion with a suitable shape, in particular a concave profile, generally made up of a friction pad making it possible to have a low coefficient of friction between said pad and the rack. The elastic means can be made up of a spiral spring alone or a metal or elastomer elastic washer, or by associating such elastic elements. These elastic means bear on an adjusting screw, which makes it possible to adjust the withdrawal of the pusher and thus embodies the end-of-travel stop of the pusher. 
         [0005]    As previously indicated, such a device makes it possible to obtain permanent contact between the pinion and the rack, while offsetting the flaws in the toothings of these components. The elastic means, due to their action between the adjusting screw and the pusher, also make it possible to offset the wear during operation of the pinion, the rack and the friction pad, but in that case the withdrawal, i.e. the gap between the pusher and its stop formed by the adjusting screw, is increased by a value equal to the cumulative wear of these three components. 
         [0006]    The main drawbacks of such a pusher, and the effect of increasing the withdrawal that is not offset, are a probability of the appearance of noise in case of rolling of the vehicle on a deteriorated roadway, and an increase in the bending momentum in the contact zone of the gear teeth of the pinion and the rack, in particular in case of operation at a full load. Another drawback of this pusher device is that it requires an expensive adjustment on an assembly line. 
         [0007]    Pusher devices are also known with a different design, called “off-center” pushers, as for example described in patents U.S. Pat. No. 6,247,375 B1, FR 2219868, EP 0770538 A2 and US 2008/0190229 A1. In such a device, a rotary pad comprises an off-center part that pushes the rack toward the pinion, the rotary pad being mounted rotating in a casing, around an axis parallel to the longitudinal axis of the rack. The inner periphery of this pad is off-centered relative to the outer periphery thereof, such that, when it rotates in the casing, its off-centered part forms a step that is pressed against the back of the rack and pushes the latter toward the gear teeth of the pinion, so as to keep them engaged. 
         [0008]    In one particular embodiment of an off-center pusher, described in French patent application 08.06207, filed on Nov. 6, 2008 in the Applicant&#39;s name, published on May 7, 2010 under number FR 2938034, the rotary pad is mounted rotating on a support housing, which in turn is slidingly mounted in the steering gear-box, in a direction parallel to the plane of the toothing of the rack and orthogonal to the longitudinal axis of that rack. An elastic element such as a compression spring is positioned between the wall of the sliding housing and the rotary pad, to stress that pad in rotation in a predefined direction. Another elastic element such as an O-ring is positioned between the sliding housing and a stationary part, such as the steering gear-box. The pad comprises a radial arm, on which the force of the compression spring is exerted. The pad has a bowed “corner” shape that allows the device to be particularly compact. 
         [0009]    However, the current off-center pusher devices generally do not have a robust and irreversible system, allowing, however, slight operating clearance, to absorb the clearance of the gear teeth. 
       BRIEF SUMMARY 
       [0010]    The present invention therefore aims to provide an improved embodiment of an off-center pusher, which in particular has an automatic clearance compensating function, with controlled withdrawal. 
         [0011]    To that end, the invention relates to an off-center push device for the rack-and-pinion steering of a motor vehicle, the push device comprising a bowed pad whereof the inner periphery is off-centered relative to the outer periphery, the pad being rotated in one direction by spring means and being provided to be pressed by its off-centered inner periphery against the rear of the rack to push the latter back toward the gear teeth of the steering pinion, the pad being rotatably mounted on a support and the spring means, arranged at the support, preferably acting in a plane parallel to the toothing of the rack on a radial arm secured to the pad, said off-center push device being characterized in that it comprises a clearance compensation mechanism including a thrust member translationally mounted on the support, but immobilized in rotation relative to said support, and pressed against the radial arm of the pad by a compression spring inserted between said thrust member and the support or an element secured to the support, whereas a movable stop is rotatably mounted, coaxially to the compression spring, relative to the support or the element secured to the support, the movable stop being provided, at the end thereof closest to the pad, with at least one toothing with staggered gear teeth cooperating with at least one notch formed on the thrust member, or vice versa, the movable stop being connected via a torsion spring to the support or to the element secured to the support, so that the notch(es) can successively cooperate with the staggered gear teeth of the or each toothing. 
         [0012]    Advantageously, the movable stop is provided with at least two toothings with staggered gear teeth, arranged on as many sectors, for example two diametrically opposite toothings each occupying a sector of 180°, and the thrust member comprises the same number of notches cooperating with those toothings, so as to stabilize the mechanism. 
         [0013]    The thrust member can comprise two diametrically opposite longitudinal grooves, which cooperate with two corresponding ribs provided on opposite surfaces of the support, to ensure translational guiding and rotational immobilization of this thrust member. 
         [0014]    The off-center pusher is thus provided with a clearance compensation mechanism, which operates by “thresholds” going from one tooth to the other of the staggered gear teeth of the movable stop, which makes it possible to reduce the operating clearance. The components of this mechanism also ensure the basic operation of the off-center pusher: the thrust member is the part that transmits the thrust exerted by the compression spring to the pad, the compression spring in turn bearing against said thrust member, to generate the force that keeps the rack in contact with the pinion. 
         [0015]    In normal operation, between two clearance adjustments, the mechanism is in a configuration where the notches of the thrust member are in contact against the gear teeth of the movable stop, the contact being maintained by the torsion spring. When, after wear, and under the action of the compression spring, the clearance exceeds a certain value with the result that there is no longer any contact between the notches of the thrust member and the gear teeth of the toothings of the movable stop, the torsion spring rotates said movable stop until a new contact is created, made between the notches of the thrust member and the gear teeth along the toothings of the movable stop. The clearance is thus reduced to a smaller value, and so forth. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    The invention will be better understood upon reading the following description, in reference to the appended diagrammatic drawing showing, as an example, one embodiment of this off-center push device. 
           [0017]      FIG. 1  is an outside view of a power-assisted steering system, equipped with the off-center push device according to the present invention; 
           [0018]      FIG. 2  is a cross-sectional view along II-II of  FIG. 1 , i.e. along a plane perpendicular to the longitudinal axis of the rack and passing through the off-center push device; 
           [0019]      FIG. 3  is an exploded perspective view of this push device; 
           [0020]      FIG. 4  shows, in exploded perspective view, the clearance compensation mechanism of the push device, with its various components; 
           [0021]      FIG. 5  is a perspective view, on a larger scale, of the movable stop of the clearance compensation mechanism; 
           [0022]      FIG. 6  is another perspective view of the movable stop, showing the end thereof opposite the toothings; 
           [0023]      FIG. 7  is a perspective view of the bearing member of the clearance compensation mechanism; 
           [0024]      FIG. 8  is a perspective view of the thrust member of said mechanism; 
           [0025]      FIGS. 9 and 10  are diagrams illustrating the operation of the clearance compensation mechanism; 
           [0026]      FIG. 11  is a diagram similar to the preceding figures, showing an alternative relative to the toothings of the movable stop. 
       
    
    
     DETAILED DESCRIPTION 
       [0027]      FIG. 1  shows a power-assisted steering system for a motor vehicle, with an assistance system acting at the steering pinion. The steering system comprises a steering gear-box  2 , which extends along a longitudinal axis A. Slidingly mounted in the steering gear-box  2  is a rack  3 , the ends of which leave the ends of the casing  2  and are coupled to tie rods (not shown here). A power assistance motor  4  is coupled, via a speed reduction gear, to a steering pinion  5  that is engaged with the toothing  6  of the rack  3  (see also  FIG. 2 ). Reference  7  indicates the input shaft, which is connected to the steering pinion  5  and to which the steering column (not shown) is coupled, maneuvered using the steering wheel of the vehicle. 
         [0028]    A push device, designated overall by reference  8 , is provided near the steering pinion  5 , to press the toothing  6  of the rack  3  against the pinion  5 , the push device  8  being shown in detail in  FIGS. 2  and following. 
         [0029]    The push device  8  is placed on the rear side  9  of the rack  3 , in other words opposite the toothing  6  of that rack  3  and also opposite the pinion  5 , this push device  8  being housed in a corresponding part of the steering gear-box  2 . 
         [0030]    The push device  8 , of the “off-center” type, comprises a pad  10  as main component, which is a part with a rounded profile, and, more particularly, an arched part with a “corner” shape. The pad  10  has an inner periphery  11  in an arc of circle that is off-centered relative to its outer periphery  12 , which is also in an arc of circle. The inner periphery  11 , thus off-centered, of the pad  10  forms a step pressed against the rear  9  of the rack  3 . 
         [0031]    The pad  10  is mounted and guided on a support  13 , which in turn is mounted in the considered part of the steering gear-box  2 , the configuration of the support  13  being clearly visible in  FIG. 3 . This support  13  comprises a cradle  14  with a bowed shape, on which the outer periphery  12  of the pad  10  bears slidingly. At one end, the support  13  has an oblong protuberance  15 , engaged in a corresponding recess  16  of the concerned casing portion. 
         [0032]    The pad  10  is shown as a monolithic piece, but it can also be made in two or more parts from separate materials, adapted for sliding contact with the rack  3  on the one hand and with the support  13  on the other hand. Various methods of guiding the pad  10  on the cradle  14  of the support  13  can be considered, to produce the rotational connection between the pad  10  and the support  13 . 
         [0033]    The pad  10  is set in rotation relative to the support  13  by applying thrust, exerted by a clearance compensation mechanism  17  on a radial arm  18  comprised by the pad  10 . The details of the clearance compensation mechanism  17  are shown in  FIG. 2 , as well as  FIGS. 4  and following. 
         [0034]    The clearance compensation mechanism  17  is made up of five main elements, i.e.: a thrust member  19 , a compression spring  20 , a movable stop  21 , a torsion spring  22 , and a bearing member  23 , all arranged coaxially. 
         [0035]    The bearing member  23 , shown only in  FIG. 7 , is connected to the support  13  in the part thereof opposite the protuberance  15 , so that there is no relative movement between the bearing member  23  and the support  13  during operation. 
         [0036]    The movable stop  21 , generally cylindrical and hollow in the center thereof (see  FIG. 5 ), is mounted rotating relative to the bearing member  23 , in which it fits. At its end spaced away from the bearing member  23 , the movable stop  21  has two staggered toothings  24 , which respectively extend over two  180 ° sectors. Each toothing  24  comprises a series of gear teeth  25 . 
         [0037]    At its end opposite the toothings  24  (see  FIG. 6 ), the movable stop  21  has a housing  26  provided to receive one end of the torsion spring  22 . The other end of the torsion spring  22  is received in a fastening zone  27  provided on the bearing member  23  (see  FIG. 7 ). 
         [0038]    The thrust member  19 , shown only in  FIG. 8 , is generally cylindrical. It comprises two diametrically opposite longitudinal grooves  28 , which cooperate with ribs  29  provided on opposite surfaces of the support  13  (see also  FIG. 2 ), to guide the translation of said thrust member  19  while immobilizing it in rotation. In the mounted position, the thrust member  19  is pressed against the radial arm  18  of the pad  10 . The thrust member  19  also comprises two diametrically opposite notches  30 , which are provided each to cooperate with one of the gear teeth  25  of the toothings  24  of the movable stop  21 . 
         [0039]    In the mounted position of the clearance compensation mechanism  17 , in the illustrated example, the compression spring  20  is situated outside the movable stop  21 . One end of the compression spring  20  bears on the bearing member  23 , while the other end thereof bears against the thrust member  21 . The torsion spring  22  is housed in the central recess of the movable stop  21 ; this torsion spring  22  is hooked by one end to said movable stop  21 , in the housing  26 , while the other end thereof is fastened to the bearing member  23 , in the fastening zone  27 . 
         [0040]    During normal operation, as illustrated in  FIG. 9 , the clearance compensation mechanism  17  is in a configuration for which each notch  30  of the thrust member  19  is in contact against a wall of a gear tooth  25  of a toothing  24  of the movable stop  18 , the contact being maintained by the torsion spring  22 , which acts in the direction of arrow F 1 . The thrust from the compression spring  20 , acting in the axial direction of the arrow F 2 , is exerted on the thrust member  19 , which transmits it to the pad  10 , so that the rack  3  is kept in contact with the steering pinion  5 . This operating state is maintained for any clearance J comprised between a minimum clearance value J 1  and a maximum clearance value J 2 . 
         [0041]    When the clearance J exceeds the maximum clearance value J 2 , due to wear that has become relatively significant, the contact between the notches  30  of the thrust member  19  and the gear teeth  25  of the movable stop  21  no longer exists (see  FIG. 10 ). At that time, the torsion spring  22  rotates the movable stop  21 , until a new contact occurs between each notch  30  of the thrust member  19  and the following gear teeth  25  of the toothings  24  of the movable stop  21 . The clearance J has thus been reduced to the minimum clearance value J 1 , the clearance compensation mechanism  17  being brought back into the configuration of  FIG. 9 , but with contact on the following, “higher” gear tooth  25  of each staggered toothing  24 . 
         [0042]    As also shown in  FIGS. 9 and 10 , the gear teeth  25  of at least one staggered toothing  24  advantageously have a globally triangular profile. Owing to such a configuration, during the rotation of the movable stop  21 , a slight withdrawal of the pad  10  is authorized in the idle position, which makes it possible to obtain clearance between the rack  3  and the steering pinion  5 , to absorb the toothing defects of those elements. 
         [0043]      FIG. 11  shows an alternative form of the gear teeth  25  of the staggered toothings  24 . Keeping a triangular appearance, the gear teeth  25  here comprise asperities and/or notches  31 , which are provided for embedding of the notches  30 , so as to stabilize the movable stop  21  in the idle position. 
         [0044]    Lastly, in a manner not shown, the support  13  can be mounted in the corresponding casing portion with the interposition of one or more seals capable of absorbing noises and vibrations. 
         [0045]    It would not be beyond the scope of the invention, as defined in the appended claims, to:
       Modify the details of the toothings of the movable stop;   Use any equivalent arrangements, in particular in the clearance compensation mechanism where the position of the parts can be inverted, for example with a torsion spring having a larger diameter placed outside the movable stop, and a compression spring having a smaller diameter placed inside the movable stop, or with other staggered toothings formed on the thrust member and notches provided on the movable stop;   Use this type of push device for all types of steering systems: manual steering, power-assisted steering, hydraulically-assisted steering.