Abstract:
Tensioning roller device including a non-rotating part about which there is rotationally mounted a pulley-forming rotating assembly designed to collaborate with a belt or a chain and a rolling bearing positioned between the non-rotating part and the pulley and including a rotating ring, a non-rotating ring and rolling elements, the pulley including a rigid rim including a first part fixed to the rotating ring of the bearing and a second part that can move with respect to the first part under the action of an elastic element, and an expandable sleeve of annular overall shape designed to be in contact with the belt or the chain, the diameter of the expandable sleeve varying according to how hard it is pressed by the second part.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention generally relates to the field of belt or chain tensioning roller devices, particularly automatic tensioning rollers, used in particular to ensure appropriate belt or chain tension, for example in timing belts or belts used to drive auxiliaries or the like. Automatic tensioning rollers such as these can be used in motor vehicle combustion engines and allow the belt tension to be kept always within a predetermined range. 
   2. Description of the Relevant Art 
   Tensioning rollers generally include a support intended to be fixed to an engine block, and a moving part that can move angularly with respect to the support. The moving part is provided with an eccentric and with a rolling bearing on which there is mounted a roller intended to be in contact with the belt. A spring constantly exerts a tensioning force between the support and the moving part, causing the roller to be in contact with the belt under appropriate tension. The moving part is mounted on the support with the possibility of adjustment so that the belt tension can be adapted. Thus, there are automatic tensioning rollers that include an adjustment eccentric used to preposition the roller against the belt, the eccentric then being immobilized with respect to the engine block using a screw, and a working eccentric mounted directly or indirectly about the adjusting eccentric and used to convert the torsional moment of a spring into a radial force on the belt. In operation, the working eccentric can oscillate angularly with respect to the adjustment eccentric or with respect to an intermediate part, thanks to bearing bushes that form a plain bearing. Reference may be made to document EP B 456 142. 
   Document FR 2 624 577 discloses a tensioning roller including a swinging arm pivotably mounted on a pivot pin fixed to the engine block. The arm is angularly actuated by a return spring in a direction that tends to press the roller against a belt. While such devices are satisfactory from the performance standpoint, their very high number of component parts is a disadvantage, and they are generally expensive to manufacture. 
   Document U.S. Pat. No. 6,129,643 describes a variable-diameter pulley including a part in contact with the belt that can off-center itself with respect to a part secured to the shaft. However, this type of pulley is heavy, wears quickly, carries a risk of vibration and noise, and is expensive, as much because of the number of component parts as because of their complexity, which parts need to be fitted together particularly accurately. The part in contact with the belt is in the form of a rigid annulus. 
   Document U.S. Pat. No. 7,033,293 describes an expanding pulley including a plurality of blocks separated from one another and in contact with the belt. The blocks can move radially between two sides of the pulley under the action of a conical element moved by a spring. Once again, the number of component parts is very high. Manufacturing and assembling the blocks are expensive. There is a risk that the conical component will become skewed, causing the pulley to become unbalanced and generating vibrations. Furthermore, the discontinuous contact between the blocks and the belt also causes vibrations and variations in the belt tension, which are likely to result in premature wear. 
   SUMMARY OF THE INVENTION 
   The described embodiments are aimed at an automatic tensioning roller device, of simple and economical design, including a low number of component parts and avoiding the generation of vibration or premature wear. 
   The tensioning roller device includes a non-rotating part about which there is rotationally mounted a pulley-forming rotating assembly designed to collaborate with a belt or a chain and a rolling bearing positioned between the non-rotating part and the pulley and including a rotating ring, a non-rotating ring and rolling elements. The pulley includes a rigid rim including a first part fixed to the rotating ring of the rolling bearing and a second part that can move with respect to the first part under the action of an elastic element, and an expandable sleeve of annular overall shape designed to be in contact with the belt, the diameter of the expandable sleeve varying according to how hard it is pressed by the second part. The first part can be obtained economically by casting or machining a light alloy, alternatively by machining a steel blank. The second part can be formed by pressing a sheet, and this proves particularly economical. The expanding sleeve can be obtained by molding a flexible material, for example a natural and/or synthetic elastomer, possibly containing a filler, for example a filler in fiber or powder form that allows its mechanical properties to be adjusted. 
   In one embodiment, the expanding sleeve can be expanded radially. Thus, the outside diameter of the surface of the pulley in contact with the belt or chain is variable. 
   As a preference, the surfaces of the first and second parts of the rim in contact with the expandable sleeve are annular. This then encourages the expandable sleeve to maintain its annular shape at various stages of expansion of its exterior surface. 
   In one embodiment, the sleeve has frustoconical lateral faces to match the first and second parts of the rim. 
   In one embodiment, the sleeve is symmetric with respect to a radial plane. 
   In one embodiment, the sleeve has an axial bore to match the shape of the first part. 
   In another embodiment, the sleeve has substantially radial lateral faces to match the shape of the first and second parts. 
   In one embodiment, the sleeve has a frustoconical interior face to match the shape of the first part. 
   In one embodiment, the second part is in the form of a cup mounted with the ability to move in axial translation on the first part. The elastic element may exert an axial thrust on the second part. 
   In one embodiment, the elastic element includes a spring positioned between the second part and a bearing surface secured to the first part. The bearing surface may be formed by a plate fixed, for example by bonding or by welding, to one axial end of the first part. The plate may be fixed to the first part after the sleeve, the second part, and the axially elastic element have been fitted. 
   Advantageously, the expandable sleeve is in one piece. The expandable sleeve may be made of a material that is elastically deformable and substantially maintains its volume. 
   In one embodiment, the second part includes a frustoconical portion in contact with the expandable sleeve and an axial portion in contact with the first part. The second part may include a radial portion between the frustoconical portion and the axial portion. 
   In one embodiment, the second part includes a radial portion in contact with the expandable sleeve and an axial portion in contact with the first part. 
   In one embodiment, the spring is a helical spring. 
   In one embodiment, the rolling bearing includes two rows of rolling elements. 
   In one embodiment, the non-rotating ring of the rolling bearing is mounted on an adjustment eccentric. 
   In one embodiment, the first part includes a stepped exterior surface with a small-diameter portion in contact with the second part and a large-diameter portion in contact with the expandable sleeve, a shoulder separating the small-diameter portion from the large-diameter portion. 
   In one embodiment, the first part includes a flange directed outwards from the axial end of the large-diameter portion. 
   Alternatively, the exterior surface of the first part includes a small-diameter portion in contact with the second part, and a frustoconical portion in contact with the expandable sleeve. 
   Alternatively, the exterior surface of the first part includes an axial portion in contact with the second part and with the expandable sleeve. 
   This then yields an automatic tensioning roller device of a reasonable mass, which is compact, is made up of component parts, the shapes of which are relatively simple and economical, both to manufacture and to assemble. Because the sleeve in contact with the belt is of annular shape, the amount of vibration generated is extremely small. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be better understood from reading the detailed description of a number of embodiments taken by way of entirely non-limiting examples and illustrated by the attached drawings in which: 
       FIG. 1  is a view in axial section of a tensioning roller according to a first embodiment; and 
       FIG. 2  is a view in axial section of a tensioning roller according to another embodiment. 
   

   While the invention may be susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. The drawings may not be to scale. It should be understood, however, that the drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed, but to the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present invention as defined by the appended claims. 
   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   As can be seen in  FIG. 1 , the tensioning roller device, referenced  1  in its entirety, includes a stationary part  2  and a rotating part  3  mounted to rotate with respect to the fixed part  2  by means of a rolling bearing  4 . The rotating part  3  is designed to be in contact with a belt or the chain  5  in order to tension the belt or chain  5 . 
   The fixed part  2  includes an adjustment eccentric  6  and a screw  7  positioned in a bore  6   a  of the adjustment eccentric  6 . One end of the screw is engaged in a threaded hole  8  formed in a support  9 , for example an engine block. The adjustment eccentric  6  is in contact via one radial face with the support  9  and via an opposite radial face with the head of the screw  7 . The adjustment eccentric  6  has an exterior surface of revolution which is stepped with a large-diameter portion on the same side as the support  9  and a small-diameter portion on the same side as the head of the screw  7 , the rolling bearing  4  being pushed onto the small-diameter portion. The small-diameter and large-diameter portions are separated by a radial shoulder. The small-diameter portion  6   d  of the exterior surface of the adjustment eccentric  6  has its geometric axis parallel to the geometric axis of the bore  6   a . The small-diameter portion  6   d  is therefore off-centered with respect to the screw  7 . 
   The rolling bearing  4  includes an inner ring  10 , an outer ring  11 , two rows of rolling elements  12  and  13  positioned in parallel planes and held in place by cages  14  and  15  respectively, and two seals  16  and  17 . The inner ring  10  has a bore pushed onto the small-diameter portion  6   d , and two transverse surfaces, one of which is in contact with the shoulder  6   f  of the adjustment eccentric  6 . The inner ring  10  is provided with an exterior surface in which raceways are formed for the rolling elements  12  and  13  and grooves are formed to contact the lips of the sealing members  16  and  17 . The cages  14  and  15  maintain the uniform circumferential spacing of the rolling elements  12  and  13 . The outer rings  10  and  11  are respectively of one piece. The outer ring  11  is equipped with an interior surface in which raceways are formed for the rolling elements  12  and  13  and grooves are formed into which the sealing members  16  and  17  are pushed. The sealing members  16  and  17  provide a static seal against the rotating outer ring  11  and a dynamic seal against the non-rotating inner ring  10 . The outer ring  11  has a cylindrical axial exterior surface. 
   The rotating part  3  of the automatic tensioning roller includes a rim  18  and an expandable sleeve  19 , of annular overall shape and positioned in an annular housing that is open to the outside and formed in the rim  18 . The expandable sleeve  19  has an annular exterior surface  19   a  designed to come into contact with the belt  5 . The expanding sleeve  19  also has a cylindrical bore  19   b  and two slightly frustoconical lateral surfaces  19   c  and  19   d.    
   The rim  18  includes a main part  20  provided with a bore in which the outer ring  11  of the rolling bearing  4  is pushed. The main part  20  includes a flange  20   a  of radial overall shape directed outwards on the same side as the head of the screw  7 , a stepped exterior surface with a large-diameter surface  20   b , a shoulder  20   c  and a small-diameter surface  20   d  at the same end as the support  9 . The face of the flange  20   a  that is adjacent to the large-diameter surface  20   b  is slightly frustoconical to match the shape of the lateral surface  19   c  of the expanding sleeve. The large-diameter surface  20   b  is axial and in contact with the bore  19   b  of the expandable sleeve  19 . 
   The rim  18  includes an axially mobile piece  21  in the form of a sheet metal cup, for example formed by pressing. The moving part  21  includes a frustoconical part  21   a  of matching shape and in contact with the lateral face  19   d  of the expandable sleeve  19 , a radial portion  21   b  extending the frustoconical portion  21   a  inwards and an axial upstand  21   c  extending from the axial portion  21   b  away from the shoulder  20   c  of the main part  20 . The moving part  21  is mounted around the main part  20 , the axial upstand  21   c  surrounding and being in contact with a part of the small-diameter surface  20   d . The moving part  21  is mounted with the freedom to move in terms of translation about the main part  20 . 
   The rim  18  includes a plate  22  fixed to the free end of the main part  20  on the opposite side to the flange  20   a . Attachment may be by bonding, push-fitting and/or welding. The plate  22  may be in the form of a sheet metal roundel while the main part  20  may be produced by machining and/or casting a light alloy or alternatively steel component. 
   The rim  18  also includes an actuator  23  positioned between the moving part  21  and the plate  22 , which is fixed with respect to the main part  20 . The actuator  22  here includes an axially-acting spring  23 , for example in the form of a helical spring made of round-section wire. The actuator  23  exerts an axial force on the plate  22  and on the moving part  21 , tending to push the moving part  21  towards the flange  20   a  of the main part  20 , and therefore tending to reduce the space available for the expandable sleeve  19  by reducing the axial distance between the lateral walls of the expandable sleeve  19 . The actuator  23  is centered by centering lugs  24  formed in the plate  22  by cutting and bending. The actuator  23  is thus kept in an appropriate radial position. 
   The rim  18  may be fitted by placing the expandable sleeve  19  around the large-diameter surface  20   b  then by fitting the moving part  21  followed by the spring  23  and finally the plate  22  permanently fixed to the main part  20 . Since the moving part  21  has a tendency to move towards the flange  20   a  of the main part  20 , the expandable sleeve  19  has a tendency to deform, with a reduction in its axial dimension and an increase in its radial dimension. Since the inside diameter of the expanding sleeve is determined by the large-diameter surface of the main part  20  which is rigid, the increase in the radial dimension of the expandable sleeve  19  is achieved by increasing the diameter of the exterior surface, hence applying additional tension to the belt. 
   The rim  18 , the rolling bearing  4  and the adjustment eccentric  6  may be assembled by push-fitting. Before the screw  7  is fully tightened in the support  9 , the adjustment eccentric  6  can be rotated in such a way that the expandable sleeve  19  comes into contact with the belt, exerting a predetermined force. The eccentric  6  can be adjusted while measuring torque, the torque exerted on the eccentric  6  being maintained until the screw  7  is tightened, thus determining the radial force exerted by the pulley on the belt and therefore the initial tension in the belt  5  in case the belt should become slack, for example through ageing, heating, etc. 
   The outside diameter of the expandable sleeve  19  may then increase slightly under the effect of the thrust exerted by the actuator  23  via the moving part  21 , hence reapplying tension to the belt  5  and compensating for the loss in belt tension. Conversely, if the belt  5  should become excessively tensioned, for example in particularly cold weather, the expandable sleeve  19  will have a tendency to become radially squashed and push the moving part  21  axially, thus countering the effect of the force of the actuator  23 . 
   The embodiment illustrated in  FIG. 2  is similar to the one illustrated in  FIG. 1  except that the moving part  21  has a simplified shape with an axial portion  21   b  extending from the axial upstand  21   c  as far as the free end of the said moving part  21  and in contact with the expandable sleeve  19 . The expandable sleeve  19  has lateral faces  19   c  and  19   d  that is substantially radial and parallel to one another. The interior surface  19   b  of the expandable sleeve  19  is frustoconical, to match the shape of the main part  20  of the rim  18 . The main part  20  has a flange  20   a  with two radial faces, one of them an outer face and the other on the same side of the expanding sleeve  19 , a small-diameter surface  20   d  on the same side as the support  9  and a frustoconical surface  20   e  extending between the flange  20   a  and the small-diameter surface  20   d . The frustoconical surface  20   e  has a large diameter on the same side as the flange  20   a  and a small diameter on the opposite side. The connection between the frustoconical surface  20   e  and the small-diameter surface  20   d  is via a short step of a gradient steeper that the gradient of the frustoconical surface  20   e.    
   The assembly and operation of the automatic tensioning roller is similar to what was described with reference to  FIG. 1 . The mass of the rim  18  is slightly less because of the reduction in the volume of material in the main part  20 . 
   It is also possible to anticipate a main part  20  equipped with a continuous small-diameter axial surface  20   d  connected at one end to the foot of the flange  20   a  and fixed at the other end to the plate  22 , thus increasing the radial thickness of the expandable sleeve  19 , allowing an additional weight saving and simplifying the shape of the main part  20 . 
   Thus, the eccentric allows preadjustment to be performed by rotating the eccentric about the screw and bringing the pulley and belt into contact. The choice of actuator  23 , particularly of the spring, particularly its elasticity and stiffness, and the choice of deformable material for the expandable sleeve, allow the radial deformation of the expandable sleeve  19  to be chosen to suit. In both of the embodiments illustrated hereinabove, the presence of the frustoconical surface in contact with the expandable sleeve allows the axial movement of the moving part to be converted into an expansion of the outside diameter of the expandable sleeve, and allows this to be done in an extremely simple and economical way. 
   Further modifications and alternative embodiments of various aspects of the invention will be apparent to those skilled in the art in view of this description. Accordingly, this description is to be construed as illustrative only and is for the purpose of teaching those skilled in the art the general manner of carrying out the invention. It is to be understood that the forms of the invention shown and described herein are to be taken as examples of embodiments. Elements and materials may be substituted for those illustrated and described herein, parts and processes may be reversed, and certain features of the invention may be utilized independently, all as would be apparent to one skilled in the art after having the benefit of this description of the invention. Changes may be made in the elements described herein without departing from the spirit and scope of the invention as described in the following claims.