Abstract:
The invention describes a starter wherein the second front bearing is inserted axially between the armature windings and the speed reducer. This configuration helps solve the problem that the operating forces of known starter armature shafts are too great for the armature shaft guide ring to withstand long term intensive stresses. The structure includes a supporting section of the armature shaft received in the front bearing, the supporting section being of an outside diameter greater than or equal to the other sections of the armature shaft; the front bearing forms a sealed baffle between the armature windings and the planetary gear speed reducer; the electric motor is housed in a cylindrical frame, coaxial with the armature shaft, the front bearing being centered directly with respect to the frame by radial support against the internal cylindrical face of the front peripheral edge of the frame.

Description:
FIELD OF THE INVENTION 
     The invention relates to a motor vehicle starter. 
     The invention relates more particularly to a motor vehicle starter comprising:
         an electric motor comprising a rear armature shaft which carries armature windings and which is rotationally guided by a first rear bearing and by a second front bearing;   a coaxial front output shaft which carries a starter drive assembly and which is rotationally driven by the armature shaft;   an epicyclic gear train speed reducer which is inserted axially between the rear armature shaft and the front output shaft for the coupling thereof.       

     BACKGROUND OF THE INVENTION 
     Internal combustion engined motor vehicles are conventionally fitted with a starter comprising a drive gear which engages with a ring gear of the engine, for rotationally driving the engine when it is being started. 
     A starter is generally designed to be used just once for each journey by the vehicle, at the time of starting of the engine. 
     However, more and more vehicles are fitted with so-called heat engine stop and restart systems, hereinafter designated “heat engine stop-restart system”, otherwise known by the name “stop and start”. 
     By means of these systems, it is possible to stop the heat engine during the vehicle stoppage phases and to restart it on the occurrence of a stimulus such as the driver&#39;s first request or another criterion intended to make fuel savings. 
     Therefore, in the course of one single journey, the engine is likely to be stopped several times, at each red traffic light or in traffic jams, for example. The starter of a vehicle fitted with a stop-restart system is thus likely to be stressed much more than a starter of a conventional vehicle. 
     Because of this intensive use, certain parts of the starter are likely to be worn prematurely, thus shortening the starter&#39;s life. This is particularly the case with one of the bearings of the starter&#39;s armature shaft. 
     The starter is in fact fitted with an electric motor comprising an armature carried by an armature shaft. An output shaft, coaxial with the armature shaft, is rotationally driven by the latter via an epicyclic gear train speed reducer. 
     In a known way, an intermediate axial section of the armature shaft carries a planetary gear of the epicyclic gear train speed reducer which transmits rotary movement from the armature shaft to the output shaft. The epicyclic gear train speed reducer comprises an assembly of planetary gears which are carried by the output shaft. 
     An axial bore is formed in a rear axial end of the speed reducer output shaft. It opens on to the rear radial face of the rear free end of the output shaft and is blind at its other front end. 
     By means of this configuration, the front free end section of the motor armature shaft can be guided rotationally in the speed reducer output shaft axial bore with the insertion of a plain guide ring or a needle roller guide ring. 
     However, the armature shaft guiding front end section is of a smaller diameter than the other sections of the armature shaft, particularly to make possible the fitting of elements such as the planetary gear on to the armature shaft but also because the diameter of the bore in the output shaft is limited by the dimensions of the output shaft. The front end guiding section is of a diameter of 10 mm for example. 
     SUMMARY OF THE INVENTION 
     The weight and the moment of inertia of the armature shaft are too great with respect to the diameter of the armature shaft guiding section for the guide ring to be able to withstand intensive stresses for a life of the order of ten years. 
     To solve this problem in particular, the invention proposes a starter of the type described above, characterised in that the second front bearing is inserted axially between the armature windings and the speed reducer. 
     According to other features of the invention:
         a supporting section of the armature shaft is received in the front bearing, the supporting section being of an outside diameter greater than or equal to the other sections of the armature shaft;   the armature shaft comprises a shouldering face which is intended to come into abutment axially forwards against the second front bearing to limit the displacement of the armature shaft axially forwards;   the shouldering face is carried by a collar which runs radially outwards from the armature shaft;   the front bearing forms a sealed baffle between the armature windings and the speed reducer;   the speed reducer comprises planetary gears which are carried by the output shaft and which are fitted rotationally between two front and rear radial flanges, the flanges being kept apart axially by at least one spacer in order to prevent the nipping of the planetary gears when the rear flange is supported axially against the bearing;   the spacer is formed by a rotary shaft of a planetary gear;   the electric motor is housed in a cylindrical frame, coaxial with the armature shaft, the front bearing being centred directly with respect to the frame by radial support against the internal cylindrical face of the front peripheral edge of the frame;   the starter comprises a front case to which are fastened the electric motor and a contactor which is intended for controlling the axial sliding of the starter drive assembly, the front bearing being inserted axially between the case and the frame;   the front bearing comprises means of angular indexing of the frame with respect to the case;   the front bearing is angularly indexed with respect to the case by means of at least one recess which is carried by either the front bearing or by the case and which is intended for receiving a lug carried by the other element;   the starter comprises an inductor which is formed by a plurality of magnetised bars of axial orientation which are arranged evenly around the armature windings, the front bearing comprising notches, each of which is intended for receiving the front end of a magnetised bar for angularly indexing the front bearing with respect to the frame. However, in accordance with other embodiments of the invention, the inductor can be of any type whatsoever, with a plurality of magnets and/or coils which can be arranged in various different ways.   the magnetised bars are separated circumferentially by axial spacers, the axial sliding forwards of the spacers being limited by a rear end radial face of the front bearing. Moreover, it is also possible to limit the axial sliding forwards of certain parts of the inductor, the magnets and shunts for example.       

     Other features and benefits will appear with the reading of the detailed description which will follow, for the understanding of which reference will be made to the attached drawings, among which: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a starter according to the invention, illustrated in partial axial section; 
         FIG. 2  is a perspective view which shows the front bearing of the armature shaft which is made according to the teaching of the invention; 
         FIG. 3  is an axial section view according to the section plane  3 - 3  in  FIG. 2 ; 
         FIG. 4  is an axial section exploded view which shows the armature shaft, on to which a sleeve provided with a collar and a planetary gear are mounted; 
         FIG. 5  is an axial section, larger-scale detail view which shows a planetary gear of the epicyclic gear train speed reducer in  FIG. 1 ; and 
         FIG. 6  is an exploded perspective view of the starter. 
     
    
    
     DETAILED DESCRIPTION 
     In the further description, an axial orientation directed from rear to front and indicated by the arrow “A” in the illustrations will be adopted on a non-limiting basis. 
     In the further description, elements having similar, analogous or identical functions will be indicated by one single reference number. 
       FIG. 1  shows a motor vehicle starter  10  which comprises a front case  12 , to which a contactor  14  and an electric motor  16  are fastened. 
     The electric motor  16  rotationally drives a rear armature shaft  18  which itself rotationally drives a front output shaft  20 . The front output shaft  20  is coaxial with the armature shaft  18  of the electric motor  16 . 
     The electric motor  16  is housed in a substantially cylindrical tubular frame  21  of circular section which is coaxial with the armature shaft  18  and which is rigidly fastened to the case  12 . 
     The motor  16  is a DC series electric motor with inductors  106 . Its purpose is to convert the electrical energy which is supplied to it to mechanical energy to turn the armature shaft  18 . 
     The electric motor  16  comprises the armature shaft  18 , an intermediate section of which carries the armature windings  22  of the motor  16  and a rear axial section  24  of which carries an annular track commutator  26 . 
     A closing rear cap  28  is fastened axially to the rear end circular edge of the frame  21 . 
     A rear free end  30  of the armature shaft  18  is rotationally guided in a first rear bearing  32  formed by a housing in the closing cap  28 . This rear housing  32  is secured to the closing cap  28 . 
     A guide bush  34 , such as a drawn cup needle roller bearing or a slip ring, is fitted to the inside diameter of the rear housing  32 . By means of this fitting, the friction of the rear free end section  30  of the armature shaft  18  in the rear housing  32  can be minimised. 
     An axial stop means (not shown), such as a washer, is inserted between the rear end radial face  36  of the armature shaft  18  and the base  38  of the housing  32  in the closing cap  28 . 
     The front part of the armature shaft  18  is stepped. A front free end section  40  is defined towards the rear by a planetary gear  42  of an epicyclic gear train speed reducer  44  which transmits the rotary movement of the armature shaft  18  to the output shaft  20 . 
     The epicyclic gear train speed reducer  44  is inserted axially between the rear armature shaft  18  and the front output shaft  20 . 
     The reducer  44  comprises an assembly of planetary gears  46 , numbering three here, the rotary shafts  48  of which are carried by a first front flange  50  of radial orientation which is secured in translational movement and rotationally to the reducer output shaft  20  and which is fastened to the latter, by crimpage for example. The planetary gears  46  are thus carried by the output shaft  20 , which forms a planetary gear holder. 
     The planetary gears  46  are axially immobilised with respect to translational movement by a second rear flange  52 , force fitted to the shafts  48  of the planetary gears  46 . 
     Thus, the planetary gears  46  are fitted so as to rotate between the front radial flange  50  and rear radial flange  52 . 
     According to a variant (not shown) of the invention, the holding with respect to translational movement of the planetary gears  46  is effected by planetary gear shafts  48  screwed into the front flange  50  and each comprising a head. 
     The reducer  44  also comprises a peripheral, internally toothed crown  54  which is fastened, in the assembly shown, by potting in a front radial plate  56  fastened in the case  12  of the starter  10 . 
     An axial bore  58  is made in a rear axial end  60  of the reducer output shaft  20 . It opens on to the rear radial face  60  of the rear free end  62  of the output shaft  20  and it is blind at its other front end. 
     The free front end section  40  of the armature shaft  18  is received in the bore  58  with an axial clearance with respect to the base of the bore  58  and also with a radial clearance. The front free end section  40  is of a diameter smaller than that of the section which carries the planetary gear  42 . 
     By means of this configuration, an axial clearance can be reserved between the front free end section  40  of the armature shaft  18  of the motor  16  and the reducer output shaft  20 . 
     According to a variant (not shown) of the invention, the output shaft does not comprise any bore and the armature shaft is shortened so as not to rub against the output shaft. 
     A front starter drive assembly  64  slides axially on a splined front section of the reducer output shaft  20 , which thus constitutes the starter drive assembly shaft, between a front position of engagement with a starter ring gear (not shown) and a rear stop position, as illustrated in  FIG. 1 . In the stop position, it is supported axially towards the rear on a shouldering front surface  66  of the reducer output shaft  20 . 
     The contactor  14  is intended for controlling the axial sliding of the starter drive assembly  64  between its front axial position and rear axial position. 
     According to the teaching of the invention, the armature shaft  18  is guided rotationally by a second front bearing  68  which is inserted axially between the armature windings  22  and the epicyclic gear train speed reducer  44 . 
     As shown in greater detail in  FIGS. 2 and 3 , the second front bearing  68  is formed by a disc which is oriented in a radial plane and which comprises in its centre an axial sleeve  70  with a central hole  72  through which the armature shaft  18  passes. The sleeve  70  is projecting, with respect to the disc  68 , forwards and backwards. 
     The central sleeve  70  and the disc  68  are rigidly connected. Here, they are made in one piece of material. The disc  68  is made of steel or aluminium for example or alternatively a plastic. 
     A supporting section  74  of the armature shaft  18  is thus received so as to rotate in the central hole  72  with the insertion of a plain guide ring or a needle roller guide ring, as illustrated in  FIG. 1 . 
     The supporting section  74  of the armature shaft  18  is of a greater diameter than the rear intermediate section which carries the armature windings  22  and than the front section which carries the planetary gear  42  of the reducer  44 . In the example shown in the illustrations, the supporting section  74  is of an outside diameter greater than or equal to that of the other sections of the armature shaft  18 . 
     Thus, the armature windings  22  are in axial abutment forwards against a shouldering rear radial face  78  of the supporting section  74 . 
     The armature shaft  18  comprises a collar  82  which is oriented radially from the armature shaft  18  radially outwards in the extension of the shouldering rear face  78 . The front face  84  of the collar  82  forms a shouldering face which is intended to come into abutment axially forwards against the rear end edge  86  of the sleeve  70  to lock the armature shaft  18  axially forwards. 
     As shown in  FIG. 4 , the collar  82  is made here in one piece with a sleeve  88 . The collar  82  is oriented radially outwards from a rear edge  90  of the sleeve  88 . The sleeve  88  is force fitted on to the armature shaft  18  to form the external cylindrical face of the supporting section  74  of the armature shaft  18 . 
     In a variant (not shown) of the invention, the armature shaft does not comprise a collar and the axial locking of the armature shaft forwards is carried out by an axial stop, such as a ball, which is inserted between the base of the bore in the rear axial end of the reducer output shaft and a free front end radial face of the armature shaft. According to further embodiments, the armature shaft can be made in one or two parts. 
     As shown in  FIGS. 2 and 3 , the disc  68  comprises, on its rear face, an extra thickness  92  which is oriented axially backwards and which has a cylindrical face with a circular external outline  94 , hereinafter called external outline  94 , which is concentric with the free external circular edge  96  of the disc  68 . 
     Similarly, an annular skirt  98  is oriented axially forwards from the front face of the disc  68 . 
     Thus, the disc  68  comprises an annular peripheral tongue  102  which is oriented radially outwards from the external outlines  94 ,  100  of the extra thickness  92  and of the skirt  98 , up to the free external edge  96  of the disc  68 . 
     The extra thickness  92  is more particularly intended for being fitted into the front end of the frame  21  so as to centre the front bearing  68  directly with respect to the frame  21  by radial support against the internal face of the front peripheral edge of the frame  21 . For this purpose, the inside diameter of the front peripheral edge of the frame  21  is substantially equal to the diameter of the external outline  94  of the extra thickness  92 . 
     Similarly, the skirt  98  is intended for being fitted into a rear end of the front case  12  so as to ensure the co-axial state of the armature shaft  18  and output shaft  20 . For this purpose, the inside diameter of the rear end of the case  12  is substantially equal to the diameter of the external outline  100  of the skirt  98 . 
     Thus, as illustrated in  FIG. 1 , the annular tongue  102  is inserted axially and pressed between the front end peripheral edge of the frame  21  and the rear end peripheral edge of the case  12 . Thus, the disc  68  is fixed axially with respect to the rigid assembly formed by the case  12  and the frame  21  after they have been assembled. 
     The case  12  is, for example, fastened to the frame  21  with axial ties (not shown) and bolts with which the case  12  can be axially pressed against the frame  21 . 
     The disc  68  thus forms a dust-tight baffle which prevents the passing of dust from the armature windings  22  to the reducer  44  and vice versa. By means of the disc  68 , it is also possible to prevent splashes of lubricant, necessary for the correct operation of the epicyclic gear train speed reducer  44 , on to the armature windings  22 . 
     The rear extra thickness  92  of the disc  68  comprises notches  104  in its external outline  94 , which are four in number here and which are evenly distributed around its periphery. 
     More particularly, the frame  21  carries on its internal cylindrical face an inductor  106  which is formed by a plurality of magnetised bars  106  (or exciting coils in other embodiments) of axial orientation which are evenly arranged around the armature windings  22 . The magnetised bars  106  are four in number here. The magnetised bars  106  are separated circumferentially by spacers (not shown) in the form of an axial clip with a transverse profile in the shape of a “U” open radially inwards. The inductor  106  is fixed with respect to the frame  21 . 
     By means of the free rear face  110  of the extra thickness  92 , it is also possible to block the forward axial displacements of the spacer clips of the inductor  106  or of the magnets, according to the arrangement of the inductor. 
     Moreover, during operation of the starter  10 , the rear flange  52  for fastening the planetary gears  46  of the reducer  44  is capable of resting axially against the front edge  112  of the sleeve  70  of the disc  68 . 
     As shown in  FIG. 5 , to prevent the planetary gears  46  from being pressed between the two flanges  50 ,  52  and thus being braked in their own rotation, the rotary shaft  48  of each planetary gear  46  is extended forwards and backwards respectively by a front pin  114  and a rear pin  116  respectively, these being of a diameter smaller than that of the rotary shaft  48 . Each pin  114  and  116  extends into the flanges  50 ,  52  and is intended for being force fitted or received by screwing or crimpage in an associated hole in the front flange  50  and rear flange  52  for the fastening of the rotary shaft  48  to the flanges  50 ,  52 . 
     Thus, the rotary shaft  48  forms an axial spacer to prevent the axial nipping of the planetary gears  46  between the two flanges  50 ,  52  when the front bearing  68  is supported axially against the rear flange  52 . The flanges  50 ,  52  are thus kept axially apart sufficiently to allow the free rotation of the planetary gears  46 . In other words, as shown in  FIG. 5 , the rotary shaft (or spacer)  48  provides an axial clearance between the planetary gears  46  and at least one of the radial flanges  50 ,  52 . 
     According to the method of fastening, the rear pin of each rotary shaft  48  of the planetary gears  46  can run in projections axially backwards from the rear face of the rear flange  52 . To allow them to pass without increasing the axial overall dimension of the starter  10 , the front face of the disc  68  has an annular depression  118  forming a track so that the projecting ends of the rear pins  116  of the rotary shafts  48  can pass. 
     The disc  68  also comprises means of angular indexing of the frame  21  with respect to the case  12 . 
     For this purpose, the disc  68  comprises two opposite recesses  120  which are formed in its free external edge  96 . Each recess bites into the rear extra thickness  92 . 
     As shown in  FIG. 1 , each recess  120  is intended for receiving an associated lug  122  which runs axially backwards from the case  12 . The lugs  122  are here carried by the external crown  54  of the reducer  44 . The crown  54  is in fact fastened rigidly in the case  12 . Angular indexing is thus made possible. 
     According to a variant of the invention not shown, the disc comprises a lug which runs axially forwards from a front edge, for example from the annular tongue and which is intended for being received in a recess of the case. The case can then comprise a plurality of recesses so that the frame can be indexed as desired in one of several angular positions around its shaft. 
     By means of the fitting of the lugs  122  into the recesses  120 , it is also possible to strengthen the rotational immobilisation of the disc  68  with respect to the rigid assembly formed by the frame  21  and case  12  after assembly. 
     As shown in  FIGS. 4 and 6 , the assembly of the starter  10  is carried out by successive assembly of its components and particularly by the placing of the reducer output shaft  20  and of the epicyclic gear train speed reducer  44  in the case  12  and then of the disc  68  forming the front bearing  68 , after which the armature shaft  18  is introduced axially forwards into the central hole  72  of the sleeve  70  of the disc  68 . 
     For this purpose, the inside diameter of the central hole  72  is larger than the outside diameter of the planetary gear  42  so that it can be passed through for engagement with the planetary gears  46 . 
     To prevent friction between rotationally movable elements and fixed elements, it is necessary to provide axial operation clearances at the time of design of the starter  10 , particularly between the front face  84  of the collar  82  on the armature shaft  18  and the rear end edge  86  of the sleeve  70  of the disc  68 . 
     By means of the disc  68 , forming the front bearing  68 , it is possible to perform several functions due to its arrangement, inserted between the armature windings  22  and the reducer  44 . 
     Thus, with the disc  68 , it is possible to centre the armature shaft  18  with respect to the frame  21  by means of support being provided directly on the internal cylindrical face of the frame  21  due to the external outline  94  of the extra thickness  92 . 
     In addition, by means of the diameter of the supporting section  74  which is greater than that of the other sections of the armature shaft  18 , it is possible to increase the strength of the starter  10 , avoiding premature wear of the front bearing  68  or of the plain rotational guide ring or a needle roller guide ring with respect to other elements of the starter  10 . In fact, with the large diameter, it is possible to obtain a larger cylindrical bearing surface between the armature shaft  18  and the front bearing  68 , by means of which the stresses can be distributed and wear can thus be slowed down. 
     Moreover, the rear end edge  86  of the sleeve  70  of the disc  68  advantageously forms an axial stop for the axial locking forwards of the armature shaft  18 . Thus, by means of the disc  68 , it is possible to perform a radial centring function and axial stop function at the same time. 
     When the collar  82  on the armature shaft  18  is supported axially forwards against the sleeve  70  of the disc  68 , the axial stress is transmitted to the peripheral edge of the case  12  via the annular tongue  102 . 
     In addition, the disc  68 , arranged thus, forms a sealed baffle between the armature windings  22  and epicyclic gear train speed reducer  44 , with which the integrity of each of these two elements can be preserved. 
     With the disc  68  thus provided with notches  104 , angular indexing can be carried out so as to simplify assembly of the starter  10 . 
     Moreover, with the portion of extra thickness  92  arranged circumferentially between two notches  104 , it is possible to ensure the axial locking of the spacer clips of the inductor  106  of the electric motor  16 . 
     Finally, the form of the rotary shafts  48  of the planetary gears  46  forms a spacer with which it is possible to keep the two flanges  50 ,  52  sufficiently apart so that the planetary gears  46  can rotate freely in any circumstances.