Abstract:
The yoke device comprises a rotary pad ( 10 ), the inner periphery ( 11 ) of which is eccentric with respect to the outer periphery ( 12 ) and is applied against the back of the rack, which is thus pushed towards the teeth of the steering pinion. The rotary pad ( 10 ) is rotationally biased and positioned by a backlash compensation mechanism ( 17 ) with spring means. This mechanism comprises a rotating movable stop ( 21 ), including gearings ( 24, 25 ) having staggered teeth that engage with the notches ( 26, 27 ) of a push member ( 19 ). The staggered gear teeth comprise, on one sector, a pilot gearing ( 24 ) having planar teeth ( 28 ) provided with a protrusion ( 29 ) and, in another sector, at least one gearing ( 25 ) having planar teeth ( 30 ) with no protrusion.

Description:
TECHNICAL FIELD 
     The present invention relates to, in general, the steering systems with racks of motor vehicles. More particularly, this invention is concerned with the “yoke” device of such a steering system, the function of which is to maintain the rack in mesh contact with a steering pinion, itself linked to a steering column, by compensating the defects of the gearings and wear thereof. Even more particularly, the invention relates to an “eccentric” type yoke device, which is a rotary pad device provided with an automatic compensation mechanism of the clearance between the steering pinion and the rack. 
     BACKGROUND 
     In a steering system with rack, the steering pinion is linked in rotation with the steering column, maneuverable using the driving wheel of the vehicle, and this pinion engages with the rack slidably mounted in a steering casing of elongated shape. The two ends of the rack, external to the casing, are coupled to steering rods respectively associated with the right and left steering wheels of the vehicle. Thus, the rotation of the wheel in one direction or the other is transmitted by the steering column to the steering pinion, and is converted into a corresponding translation of the rack which, by means of the steering rods, itself causes the coordinated orientation of the two steering wheels of the vehicle, for a “sharp turning” to the right or left. 
     In such a steering system, the yoke device elastically acts on the back of the rack, in the region of the steering pinion, to strongly press the gearing of this rack against said pinion, thus preventing any risk of loss of contact of the gearings. The yoke device is usually exhibited as a “yoke line”, with a mobile part forming a friction pad, guided in translation and biased by elastic means towards the back of the rack. 
     It is also known the “eccentric” yoke devices, which replace the traditional concept of “linear” yoke by a rotating concept. In such a yoke device, it is provided a rotary pad of annular or arched shape which has an outer circular periphery and an inner periphery also circular but off centered with respect to the outer periphery thereof. The rotary pad is rotatably mounted in the steering casing, around a rotation axis parallel with the longitudinal axis of the rack. The inner off centered periphery of this pad presses against the back of the rack. The rotary pad is biased in rotation or positioned angularly in such a manner that its inner periphery, applied against the back of the rack, pushes back the latter towards the teeth of the pinion in such a manner as to keep the gearings engaged. 
     Particularly, French patent FR 2 951 797 or its international equivalent WO 2011/048328, on behalf of the applicant, describes a yoke device with eccentric, such as reminded above, in which a clearance compensation mechanism comprises a thrust member pressed on a radial arm of the rotary pad as a result of a compression spring inserted between the thrust member and a stationary support of the pad, or an integral element of said support. A mobile stop, rotatably mounted relatively to the support or to said element, comprises at least one gearing with stepped teeth which cooperates with at least one notch of the thrust member or vice versa. The mobile stop is linked by means of a torsion spring to the support or to the element integral with the support. Thus, the notch or notches successively cooperate with the stepped teeth of the or each gearing of the mobile stop, in such a manner as to “catch up” with the mechanical clearance in particular caused by wear. 
     Even more particularly, in the embodiment described by the aforementioned documents, the mobile stop is provided, at its end nearest the rotary pad, with at least two gearings with stepped teeth, disposed in as many toothed sectors, such as two diametrically opposed gearings each occupying a sector of 180°, these gearings cooperating with as many notches formed on the thrust member. The gearings of the mobile stop, by the number of two at minimum, are in theory identical, in particular to teeth all with globally triangular profile, and thus all simultaneously playing the same role. 
     However in practice, in the case where the mobile stop thus comprises several gearings, it may occur that due to the manufacturing defects certain toothed sectors block the rotation of the mobile stop when close to the maximum allowed clearance value, while another gearing already sees its following tooth engage on the corresponding notch of the thrust member. This may cause abnormal and premature wear of the parts of the clearance compensation mechanism and erratic operating of this mechanism, in which the contacts no longer take place on the required areas. 
     BRIEF SUMMARY 
     The purpose of the present invention is to prevent these drawbacks, and hence aims to provide a yoke device with eccentric of which the clearance compensation mechanism is perfected, at the gearings, in such a manner as to ensure the good operation and longevity of this mechanism and consequently of the yoke device assembly. 
     To this end, the invention provides a yoke device with eccentric for steering a motor vehicle, the yoke device comprising a rotary pad which has an outer periphery and an inner periphery off centered with respect to the outer periphery, the rotary pad being rotatably mounted in a steering casing around a rotation axis parallel with the longitudinal axis of the rack, the outer periphery of this pad bearing against a cradle of arched shape belonging to a support mounted in the steering casing, whereas its off centered inner periphery is applied against the back of the rack, in such a manner as to push back the latter towards the teeth of a steering pinion, said pad being biased and/or positioned in rotation by a clearance compensation mechanism with spring means, acting on a radial arm of the rotary pad, the clearance compensation mechanism comprising:
         a thrust member mounted moveable in translation on the support but immobilized in rotation with respect to this support and pressed against the radial arm of the rotary pad as a result of a spring inserted between this thrust member and the support or an element integral with the support.   a mobile stop rotatably mounted relatively to said support or said element,   at least two gearings with stepped teeth disposed on as many sectors at an end of the mobile stop and cooperating with notches formed on the thrust member, or vice versa,   and a torsion spring linking the mobile stop to the support or to the element integral with the support,       

     in such a manner that the notches may successively cooperate with the stepped teeth of the gearings, 
     this yoke device being substantially characterized by the fact that the gearings with stepped teeth comprise on a sector a gearing called pilot gearing, with teeth of globally planar shape but each provided with a relief, and at least one gearing located on another sector, with teeth of globally planar shape, without relief. 
     Thus, the invention provides, on at least two sectors of the mobile stop, respective stepped gearings of different appearance, namely a pilot gearing with planar teeth, but also provided with reliefs and at least another gearing with simply planar teeth, without relief nor any other feature. 
     In an embodiment of the invention, the teeth of the pilot gearing exhibit, for example on their external edge, a relief of globally triangular profile. 
     The teeth of the pilot gearing, thus fashioned, ensure the minimum clearance value J1 and the maximum clearance value J2, such as defined in aforementioned French patent FR 2 951 797. On the sector or sectors, the teeth of planar configuration bear against the corresponding notches, at the same time as the teeth of the pilot gearing, to absorb the forces in an appropriately distributed manner around the central axis of the clearance compensation mechanism. Thus, only the teeth of the pilot sector, with their reliefs, block or allow the displacement of the mobile stop, caused by the torsion spring, the gearings of the other sector or other sectors having solely as role to absorb the forces, thus preventing any contradictory action of the gearings, with abnormal notch passages. 
     The notches, which cooperate with these gearings, remain identical for all sectors, and are each compatible with both the teeth of the pilot gearing and with the teeth of the other gearing or gearings. These notches may be simple notches, or double notches each cooperating with two successive teeth of a stepped gearing, thus increasing the mechanical resistance without decreasing the number of increments (?) for displacing the mobile stop. 
     It is worth noting that, while notably improving the operation of the clearance compensation mechanism, the solution provided by the present invention remains simple and cost effective. Particularly, the advantage of this solution is to require the devising of a single set of teeth, on a sector, whereas the geometry of the other gearings, on the other sectors, becomes simplified. As a result, the manufacture of the components of the clearance compensation mechanism and the operations of devising the equipment required for this production, become simplified. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Anyway, the invention will be better understood using the following description, with reference to the accompanying schematic drawing representing, by way of example, an embodiment of this yoke with eccentric with clearance compensation for steering a motor vehicle. 
         FIG. 1  is an external view of a power-assisted steering equipped with the yoke device with eccentric object of the present invention; 
         FIG. 2  is a sectional view according to line II-II of  FIG. 1 , ranging from the yoke device with eccentric; 
         FIG. 3  is a perspective exploded view of this yoke device; 
         FIG. 4  represents, in exploded perspective, the clearance compensation mechanism of the yoke device, with its diverse components; 
         FIG. 5  is a perspective view of the pilot gearing formed on the mobile stop; 
         FIG. 6  is a side view of this pilot gearing; 
         FIG. 7  is a side view of the other gearing formed on the mobile stop; 
         FIG. 8  is a perspective view of the thrust member with its notches; 
         FIG. 9  is a sectional view of the thrust member, showing a double notch of this member; 
         FIG. 10  is a block diagram of the clearance compensation mechanism. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a power assisted steering of motor vehicle, with (in the case of this example) an assistances acting at the steering pinion. This steering comprises a steering casing  2 , which extends along a longitudinal axis. In the steering casing  2  is slidably mounted a rack  3 , of which the ends external to the casing  2  are coupled to steering rods (here not represented). An assisted power motor  4  is coupled, by means of a gear reducer, to a steering pinion  5  which is engaged with the gearing  6  of the rack  3  (see also  FIG. 2 ). The steering pinion  5  is linked to the inlet shaft  7 , to which is coupled the steering column (not represented), maneuvered using the driving wheel of the vehicle. 
     A yoke device, designated in its assembly by the frame of reference  8 , is provided in the vicinity of the steering pinion  5 , to squeeze the gearing  6  of the rack  3  against the steering pinion  5 , the yoke device  8  being represented in detail on  FIG. 2  and after. 
     The yoke device  8  is placed on the side of the back  9  of the rack  3 , in other words opposite the gearing  6  of this rack  3  and also opposite the steering pinion  5 , this yoke device  8  being housed in a corresponding part of the steering casing  2 . 
     The yoke device  8 , of “eccentric” type, comprises a rotary pad  10 , which is a rounded profile part and, more particularly, an arched part which has a “corner” shape. The rotary pad  10  exhibits an inner periphery  11  of profile in a circular arc which is off centered with respect to its outer periphery  12 , also of profile in a circular arc. The off centered inner periphery  11  of the rotary pad  10  forms a bearing surface applied against the back  9  of the rack  3 , in such a manner as to push back the gearing  6  of this rack  3  against the teeth of the steering pinion  5 . 
     The rotary pad  10  is mounted and guided on a supporting part  13 , itself mounted in the concerned region of the steering casing  2 , the configuration of the supporting part  13  being visible on  FIG. 3 . This supporting part  13  comprises a cradle  14  of arched shape, on which slidably bears the outer periphery  12  of the rotary pad  10 . At one end, the supporting part  13  exhibits a protrusion  15  of oblong shape meshed into a corresponding recess  16  of the steering casing  2  (see also  FIG. 2 ). 
     The rotary pad  10  is put in rotation with respect to the supporting part  13  by applying a thrust, exerted by a clearance compensation mechanism  17  on a radial arm  18  comprised by the rotary pad  10 . The clearance compensation mechanism  17 , visible on  FIG. 4  and after, mainly comprises a thrust member  19 , a compression spring  20 , a mobile stop  21 , a torsion spring  22  and a bearing element  23 . 
     The thrust member  19 , of general cylindrical shape, is guided in translation and immobilized in rotation on the supporting part  13 . This thrust member  19  is applied against the radial arm  18  of the rotary pad  10  under the force of the compression spring  20 , which is inserted between the thrust member  19  and the bearing element  23 , itself integral with the supporting part  13 . 
     The mobile stop  21  is a general cylindrical shaped part, cored-out in its center, which is rotatably mounted relatively to the bearing element  23 . The torsion spring  22 , housed in the central recess of the mobile stop  21 , connects this mobile stop  21  to the bearing element  23 , by biasing said mobile stop  21  in rotation in a predefined direction. 
     The mobile stop  21  is provided, at its end farthest from the bearing element  23  hence the nearest to the rotary pad  10 , with two gearings  24  and  25  with stepped teeth, distributed on its circumference along two opposite sectors 180° each. The two gearings  24  and  25  of the mobile stop  21  respectively cooperate with two diametrically opposite notches  26  and  27 , formed at one end of the thrust member  19 . As a result of the torsion spring  22 , the two notches  26  and  27  successively cooperate with the stepped teeth of the two gearings  24  and  25 , as the wear increases. 
     According to the invention, the two gearings  24  and  25  with stepped teeth of the mobile stop  21  have different configurations, as illustrated by  FIGS. 5 to 7 . 
     The gearing  24 , called pilot gearing, has stepped teeth  28  of globally planar shape, completed for each tooth  28  by a relief  29  of globally triangular profile, formed on the external edge of this gearing  24 —see  FIGS. 5 and 6 . 
     The other gearing  25  has stepped teeth  30  of globally planar shape, similar to the teeth  28  of the pilot gearing  24  but without any relief—see  FIG. 7 . 
     As  FIG. 8  and especially  9  show, the two notches  26  and  27  of the thrust member  19  are advantageously double notches, that is to say, notches which each exhibits two axially offset areas in such a manner as to be able to cooperate with two successive teeth  28  or  30  of the pilot gearing  24  or of the other gearing  25 . The two notches  26  and  27  are here identical, contrarily to the two gearings  24  and  25 . 
     In standard operation, as is schematically illustrated on  FIG. 10 , the clearance compensation mechanism  17  is in a configuration such that each notch  26  or  27  of the thrust member  19  is in contact against a wall of a tooth  28  or  30  of the gearing  24  or  25  of the mobile stop  21 . The thrust F of the compression spring  20  is exerted on the thrust member  19 , which transmits it itself to the radial arm  18  of the rotary pad  10 , in such a manner that the rack  3  be maintained in contact with the steering pinion  5 . This state of operation is maintained for any clearance value J ranging between a minimum clearance value J1 and a maximum clearance value J2. 
     The stepped teeth  28  of the pilot gearing  24 , and particularly the reliefs  29  of these teeth  28 , have a shape and dimensions which ensure the minimum clearance value J1 and the maximum clearance value J2. Thus, the distance (measured axially) between the summit of a relief  29  and the planar surface of the corresponding tooth  28  corresponds to the minimum clearance value J1. The distance (measured axially) between the planar surface of a tooth  28  and the summit of the relief  29  of the following tooth  28  corresponds to the maximum clearance value J2. 
     In operation, only the pilot gearing  24  controls, by the reliefs  29  of the teeth  28  thereof, the passage of the notches  26  and  27  on the following teeth, hence the displacement of the mobile stop  21 , when the clearance J exceeds the maximum clearance value J2. The teeth  30  of planar shape of the other gearing  25  press at the same time as the teeth  28  of the pilot gearing  24 , in order to distribute and absorb the load, without intervening in the control of the displacement of the mobile stop  21 . 
     As it is known per se, the invention is not limited to the sole embodiment of this yoke with eccentric with clearance compensation which has been described above, by way of example; it encompasses, on the other hand, all the alternative embodiments and application alternatives pertaining to the same principle. Thus, one would not depart in particular, from the scope of the invention:
         by modifying the shapes of detail, particularly those of the reliefs of the teeth of the pilot gearing;   by multiplying the number of stepped gearings other than the pilot gearing, all the gearings being distributed on the circumference of the mobile stop according to corresponding sectors;   by inverting the roles of the thrust member and of the mobile stop, that is to say by forming the stepped gearings on the thrust member and the notches on the mobile stop;   by intending the same yoke with eccentric for all types of steering systems: manual steering, power assisted steering, hydraulic assisted steering, with assistance able to act on diverse points of the steering system.