Abstract:
The invention relates to a method for manufacturing a pulley device for a tension roller or a roller of a transmission element providing a pulley, at least two rolling-element bearings and a sleeve, the rolling-element bearings being assembled adjacently on the sleeve before the pulley is formed by injecting material onto the rolling-element bearings.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to French patent application no. 1557575 filed on Aug. 6, 2015, the contents of which are fully incorporated herein by reference. 
       FIELD OF THE INVENTION 
       [0002]    The present invention relates to a method for manufacturing a pulley device for a tension roller or roller designed to cooperate with a transmission element, for example a cam belt or chain of an internal-combustion engine of a motor vehicle. The invention also relates to an engine fitted with such a pulley device. 
       BACKGROUND OF THE INVENTION 
       [0003]    Such a roller is usually used to permanently keep the tension of a transmission element, such as a belt or chain, within a given range, or to locally modify the path of the belt or chain. These are referred to respectively as tension rollers or rollers. 
       BRIEF SUMMARY OF THE INVENTION 
       [0004]    In a roller, a pulley is mounted in rotation on a screw or a shaft by means of a bearing, the roller then being attached directly or indirectly to an engine block or to an element of a tension roller device, for example an articulated arm or a crank. 
         [0005]    The bearing is a mechanical device designed to provide a pivot link between the pulley and the screw or the shaft. For this purpose, the bearing may be a rolling-element bearing. 
         [0006]    It is known to provide a roller with a rolling-element bearing fitted with an inner ring, an outer ring surmounted by the pulley and a row of rolling elements, such as balls, seated radially between the races formed on each of the rings. 
         [0007]    To bear greater loads, the rolling-element bearing may be fitted with at least two rows of rolling elements. According to an alternative, the roller may be fitted with at least two rolling-element bearings in a single row of rolling elements. 
         [0008]    However, the use of a plurality of axially adjacent rolling-element bearings requires the use of a pulley mounted by interference on the outer rings of the rolling-element bearings, as described for example in WO 01/033108 A1. Indeed, manufacturing defects and tolerances inherent in the elements of each rolling-element bearing mean that there are axial and radial alignment faults even between two rolling-element bearings deemed to be identical. A pulley press fitted onto the outer rings of axially adjacent rolling-element bearings helps to eliminate alignment faults between the outer rings. 
         [0009]    A rigid plastic or metal pulley can then be used for this purpose, the inner rings of the rolling-element bearings being mounted in an inner cylindrical surface of a central bore of the pulley. 
         [0010]    However, such a constraint makes it impossible to manufacture a pulley by injecting material onto the outer rings of the rolling-element bearings. Indeed, in this case, the alignment faults cannot be eliminated by the pulley since the material forming the pulley is merely deposited and fits the rings. A pulley made of material that is less rigid, less solid and less expensive cannot be used. The process of overmoulding, which is known to the person skilled in the art and cheap, is also not appropriate. 
         [0011]    The purpose of the present invention is to propose a new method for manufacturing a pulley device that is particularly simple and cheap to implement. 
         [0012]    For this purpose, the invention relates to a method for manufacturing a pulley device for a tension roller or roller of a transmission element. 
         [0013]    According to the invention, the device provides a pulley, at least two rolling-element bearings and a sleeve, and the method provides the following successive steps:
       (a) At least two rolling-element bearings each having a single row of rolling elements are assembled in advance, the rolling-element bearings each comprising an inner ring having a bore, an outer ring having an outer cylindrical surface, and a single row of rolling elements seated radially between the inner rings and the outer rings, in which the rings may be in relative rotation about a central axis,   (b) A sleeve is positioned coaxially with the rolling-element bearings,   (c) The at least two rolling-element bearings, each having a single row of rolling elements, are assembled successively on an outer cylindrical surface of the sleeve, the inner rings of the rolling-element bearings bearing axially and successively against one another, the sleeve being common to all of the inner rings of the rolling-element bearings, and such that the outer cylindrical surface of the sleeve interferes with the bores of the inner rings of the axially adjacent rolling-element bearings; and   (d) A plastic pulley is formed by injecting material onto the outer cylindrical surfaces of the outer rings of the rolling-element bearings.       
 
         [0018]    According to the invention, the inner rings of the adjacent rolling-element bearings are all positioned and adjusted in relation to the outer cylindrical surface of the sleeve. The relative axial and radial alignment faults between the rings are compensated by the cylindricity of the outer surface of the sleeve. Such cylindricity is relatively easy to manufacture for the person skilled in the art. 
         [0019]    Subsequently, a pulley is formed by injecting material onto the outer rings of the adjacent rolling-element bearings that have all been adjusted in relation to one another in the previous step. The injection process deposits material that fits the outer surfaces and any interstices between the outer rings of the rolling-element bearings, the interstices having been limited during the preceding positioning and adjustment step. 
         [0020]    Consequently, the invention enables a plurality of single-row rolling-element bearings to be used in place of a multiple-row rolling-element bearing while retaining the technical advantages for the equivalent number of rows of rolling elements. Furthermore, a multiple-row rolling-element bearing is more expensive and requires greater precision to manufacture than several single-row rolling-element bearings, for the equivalent number of rows of rolling elements. 
         [0021]    The invention also relates to a pulley device for a tension roller or roller obtained using such a manufacturing method. 
         [0022]    According to advantageous but optional aspects of the invention, a pulley device obtained using such a manufacturing method may include one or more of the following features in any technically admissible combination:
       The rolling elements of the rolling-element bearing are balls.   The rolling elements of the rolling-element bearing are held substantially regularly spaced out around the circumference by a cage.   The pulley is made of a material that can be injected, cast or moulded, for example plastic.   The pulley is made of polyamide PA66 with 30% glass fibre.   The pulley includes an outer axial portion designed to cooperate with a transmission element, an inner axial portion surmounting the outer rings of the rolling-element bearings, and a radial annular intermediate portion linking the axial portions.   The pulley has stiffening ribs arranged between the inner and outer axial portions and connected to the intermediate portion.   The inner axial portion of the pulley has two shoulders oriented radially towards the inside of the pulley device, the shoulders being positioned axially on either side of the assembly formed by the rolling-element bearings of the pulley device such that the adjacent outer rings of the rolling-element bearings are held axially by the shoulders.   The inner axial portion of the pulley is extended at one axial extremity by attachment means designed to cooperate with a cover.   The attachment means for a cover consist of an annular axial portion having a relief designed to be seated in a related cavity in the cover.   The relief is annular.   The sleeve is made of steel.   The sleeve is made of D10 sintered steel with binder.   The sleeve has a tubular portion including the outer cylindrical surface on which the rolling-element bearings are assembled, the tubular portion being extended at one axial extremity by an annular radial flange of greater diameter.   The external diameter of the flange of the sleeve is no greater than 90% of the internal diameter of the pulley such as to leave a free radial space between the flange and the pulley to enable a mould to be closed over the outer rings of the rolling-element bearings during the overmoulding process of the pulley.   The sleeve has a bore designed to hold a screw or a shaft.   The sleeve is provided with attachment means designed to be rigidly connected to a supporting element.       
 
         [0039]    The invention also relates to an internal-combustion engine including at least one roller or tension roller device for a torque transmission element according to one of the embodiments mentioned above. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0040]    The invention and other advantages of the invention are explained in greater detail in the following description of a single embodiment of a pulley device according to the principle of same, provided purely by way of example and with reference to the attached drawings representing an axial half section of such a pulley device. 
           [0041]      FIG. 1  is a cross-sectional view of a pulley device for a tension roller or roller of a transmission element according to an exemplary embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0042]    A pulley device for a tension roller or roller of a transmission element, indicated as a whole using reference sign  1 , includes a pulley  2 , two rolling-element bearings  6  and  10 , and a sleeve  14 . 
         [0043]    The pulley  2  includes an inner axial portion  3 , an outer axial portion  5  and a radial annular intermediate portion  4  linking the inner and outer portions  3 ,  5 . The pulley  2  as a whole, and specifically the portions  3 ,  4 ,  5  forming the pulley, are annular about a central axis X 1 . Stiffening ribs  4   a  are provided between the inner and outer axial portions  3 ,  5  and are connected to the intermediate portion  4 . 
         [0044]    The outer axial portion  5  of the pulley  2  provides an outer cylindrical surface  5   a  designed to cooperate with a transmission element  17  shown using a dotted line, for example a belt or a chain. 
         [0045]    The inner axial portion  3  of the pulley  2  has an axial extremity  3   d  extended axially by attachment means  3   e  designed to cooperate with a cover  18 , shown using a dotted line. The axial extremity is annular and the attachment means provide an annular relief  3   e  designed to be seated in a related groove in a cover. Alternatively, the attachment means may involve gluing, or any other appropriate means. 
         [0046]    The inner axial portion  3  of the pulley  2  has a bore  3   a  in which the two rolling-element bearings  6 ,  10  are seated. 
         [0047]    The rolling-element bearing  6  includes an outer ring  7  having two radial front edges  7   a ,  7   b , an outer cylindrical surface  7   c  and a bore  7   d , and an inner ring  8  having two radial front edges  8   a ,  8   b , an outer cylindrical surface  8   c  and a bore  8   d.    
         [0048]    The rolling-element bearing  6  has a single row of rolling elements  9 , in this case balls, arranged between the toroidal races formed in the bore  7   d  of the outer ring  7  and in the outer cylindrical surface  8   c  of the inner ring  8 . 
         [0049]    The rings  7 ,  8  of the rolling-element bearing  6  may be in relative rotation about the central axis X 1 . 
         [0050]    Similarly, the rolling-element bearing  10  includes an outer ring  11  having two radial front edges  11   a ,  11   b , an outer cylindrical surface  11   c  and a bore  11   d , and an inner ring  12  having two radial front edges  12   a ,  12   b , an outer cylindrical surface  12   c  and a bore  12   d.    
         [0051]    The rolling-element bearing  10  has a single row of rolling elements  13 , in this case balls, arranged between the toroidal races formed in the bore  11   d  of the outer ring  11  and in the outer cylindrical surface  12   c  of the inner ring  12 . 
         [0052]    The rings  11 ,  12  of the rolling-element bearing  10  may be in relative rotation about the central axis X 1 . 
         [0053]    In the example embodiment illustrated, the outer rings  7 ,  11  and inner rings  8 ,  12  are solid, i.e. the rings are shaped by machining tubes, bars, forged blanks and/or rolled blanks with stock removal (turning, grinding). 
         [0054]    The rolling elements  9 ,  13  may be seated in a cage (not shown) that maintains the circumferential spacing of the rolling elements. 
         [0055]    The rolling-element bearings  6 ,  10  may each have one or two annular sealing means (not shown) on each side of the single row of rolling elements. 
         [0056]    According to the invention, the rolling-element bearings  6 ,  10  with a single row of rolling elements  9 ,  13  respectively are axially adjacent. 
         [0057]    The outer rings  7 ,  11  and inner rings  8 ,  12  of the two rolling-element bearings  6 ,  10  are respectively axially adjacent, such that the radial front edges  7   b ,  11   a  of the outer rings  7 ,  11  and the radial front edges  8   b ,  12   a  of the inner rings  8 ,  12  abut axially. Both of the rolling-element bearings  6 ,  10  are seated radially inside the pulley  2 . 
         [0058]    More specifically, the outer cylindrical surfaces  7   c ,  11   c  of the outer rings  7 ,  11  of the rolling-element bearings  6 ,  10  respectively are in contact with the bore  3   a  of the inner axial portion  3  of the pulley  2 . 
         [0059]    The inner axial portion  3  of the pulley  2  has two shoulders  3   b ,  3   c  oriented radially towards the inside of the pulley device  1 , the shoulders  3   b ,  3   c  being positioned axially on both sides of the assembly formed by the rolling-element bearings  6 ,  10  of the pulley device  1 . The shoulder  3   b  bears axially against the radial front edge llb of the outer ring  11  of the rolling-element bearing  10  and the shoulder  3   c  bears axially against the radial front edge  7   a  of the outer ring  7  of the rolling-element bearing  6 . Consequently, the axially adjacent outer rings  7 ,  11  of the rolling-element bearings  6 ,  10  are held axially by the shoulders  3   b ,  3   c  of the pulley  2 . 
         [0060]    The axially adjacent inner rings  8 ,  12  of the rolling-element bearings  6 ,  10  have adjacent bores  8   d ,  12   d  in which a sleeve  14  is seated. 
         [0061]    The sleeve  14 , having the central axis X 1 , has a cylindrical axial portion  15  providing an outer cylindrical surface  15   a  onto which the bores  8   d ,  12   d  of the inner rings  8 ,  12  of the rolling-element bearings  6 ,  10  respectively are fitted. 
         [0062]    The cylindrical axial portion  15  is extended at one of the axial extremities of same by a radial annular flange  16  of greater diameter. On one side, the flange covers the free radial space between the bore  11   d  of the outer ring  11  and the outer cylindrical surface  12   c  of the inner ring  12  to prevent the ingress of contaminants from outside the device  1 . 
         [0063]    The flange  16  also forms an axial stop surface against which the radial front edge  12   b  of the inner ring  12  of the rolling-element bearing  10  bears. 
         [0064]    Since the inner ring  8  of the other rolling-element bearing  6  of the device  1  also bears against the inner ring  12  of the rolling-element bearing  10 , the flange  16  can be used as a reference for adjusting the axial position of the abutting adjacent inner rings. 
         [0065]    Furthermore, the flange  16  may bear axially against a supporting element (not shown) outside the pulley device  1  to enable the assembly and attachment of the device  1  on the supporting element. The supporting element may for example be an engine block, and articulated arm or a crank of the related automatic tension roller. For this purpose, the sleeve  14  as a whole is provided with a through hole  15   b  into which a screw intended to rigidly connect the pulley device  1  to the supporting element can be inserted. 
         [0066]    According to the invention, the device  1  is assembled according to the following successive steps: 
         [0067]    The two rolling-element bearings  6  and  10 , each having a single row of rolling elements, are assembled in advance, the rolling-element bearings  6 ,  10  each comprising an inner ring  8 ,  12  having a bore  8   d ,  12   d  respectively, an outer ring  7 ,  11  having an outer cylindrical surface  7   c ,  11   c  respectively, and a single row of rolling elements  9 ,  13  seated radially between the inner rings  8 ,  12  and outer rings  7 ,  11  respectively, in which the rings  7 ,  8  and  11 ,  12  may be in relative rotation about a central axis X 1 . 
         [0068]    The sleeve  14  is positioned coaxially with the rolling-element bearings  6 ,  10 . 
         [0069]    The two rolling-element bearings  6 ,  10 , each having a single row of rolling elements, are assembled successively on the outer cylindrical surface  15   a  of the cylindrical axial portion  15  of the sleeve  14 , the axial portion  15  being common to all of the inner rings  8 ,  12  of the rolling-element bearings  6 ,  10  respectively. The outer cylindrical surface  15   a  of the axial portion  15  interferes with the bores  8   d ,  12   d  of the inner rings  8 ,  12  of the axially adjacent rolling-element bearings  6 ,  10 . 
         [0070]    More specifically, the position of the inner rings  8 ,  12  is adjusted on the cylindrical portion  15  to abut axially. Furthermore, the inner ring  12  of the rolling-element bearing  10  also bears axially against the flange  16  extending radially from the axial portion  15  of the sleeve in order to form a positioning reference and a stop for the inner rings  8 ,  12 . Consequently, the outer rings  7 ,  11  move closer to one another until same bear axially against one another. 
         [0071]    The plastic pulley  2  is then overmoulded onto the assembly formed by the outer rings  7 ,  11  of the rolling-element bearings  6 ,  10 . 
         [0072]    The pulley may advantageously be made of plastic, for example polyamide PA66 reinforced with 30% glass fibre. 
         [0073]    According to an alternative (not shown), the device  1  may include more than two axially adjacent rolling-element bearings. 
         [0074]    Preferably, the external diameter of the flange  16  of the sleeve  14  is no greater than 90% of the internal diameter of the pulley  2 , and specifically of the shoulder  3   b , such as to leave a free radial space between the flange  16  and the pulley  2  to enable a mould to be closed over the outer rings  7 ,  11  of the rolling-element bearings  6 ,  10  during the overmoulding process of the pulley  2 . 
         [0075]    The invention described above uses ball bearings. Other rolling elements, such as rollers or needles, can also be used. 
         [0076]    The technical features of the embodiments and variants provided for above may be combined.