Abstract:
Double shock-absorbing steering wheel, in particular for automobile vehicles, comprising a primary inertia mass connected to an engine shaft ( 12 ), a secondary inertia mass ( 14 ) connected by clutch E to a gearbox BV, and a torsion damper ( 18 ) rotatably connecting the two inertia masses ( 10, 14 ), this torsion damper including an epicycloidal gear train whose outer crown wheel ( 22 ) engages with a spring ( 28 ) for absorption of vibrations and rotation acyclisms, said spring being mounted around the crown wheel ( 22 ) in a fixed frame ( 26 ).

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS AND CLAIM TO PRIORITY 
       [0001]    This application is a divisional of application Ser. No. 12/601,334 filed on Mar. 30, 2010 which is a national stage application of International Application No. PCT/FR2008/000707 filed on May 22, 2008, which claims priority to French Patent Application No. 07/55200 filed on May 22, 2007, of which the disclosures are incorporated herein by reference and to which priority is claimed. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention. 
         [0003]    The invention concerns a double-flywheel damper, in particular for automobile vehicles, including two inertia masses mobile in rotation about the same axis and connected by a torsion damper including spring means and an epicyclic gear train. 
         [0004]    2. Description of the Related Art. 
         [0005]    A double-flywheel damper of this type is known already, in particular from the document FR-A-2714131, which describes a double-flywheel damper in which the torsion damper includes an epicyclic gear train. In one embodiment described in the above prior art document, the sun gear is driven in rotation by a first inertia mass fastened to the crankshaft of an internal combustion engine, the outer crown wheel is fastened to the second inertia mass, and coil springs are mounted in a chamber delimited by the first inertia mass between that first inertia mass and the planet gear carrier, between the first inertia mass and the outer crown wheel or between the outer crown wheel and the planet gear carrier. 
         [0006]    One advantage of using an epicyclic gear train in the torsion damper of a double-flywheel damper is the transmission of torque between the two inertia masses with a transmission ratio determined by the epicyclic gear train. However, the embodiments described in the document FR-A-2714131 have the drawback that the springs of the torsion damper, which are driven in rotation with the inertia masses and are situated at the external periphery of those inertia masses, are very sensitive to centrifugal forces and have a hysteresis that increases when the rotation speed increases, with risks of blocking and jerky operation. 
       SUMMARY OF THE INVENTION 
       [0007]    One object of the present invention is to avoid these drawbacks of the prior art. 
         [0008]    To this end it proposes a double-flywheel damper of the aforementioned type, including two inertia masses rotatable about the same axis and connected by a torsion damper including spring means and an epicyclic gear train consisting of three elements consisting of a sun gear, an outer crown wheel and a planet gear carrier the planet gears of which mesh with the sun gear and the outer crown wheel, characterized in that the spring means are disposed in a fixed chassis and associated with one of the three elements of the epicyclic gear train. 
         [0009]    An essential advantage of the double shock-absorbing steering wheel of the invention is that the spring means of the torsion damper are not driven in rotation with the inertia masses and are therefore not subjected to centrifugal forces in operation. 
         [0010]    In this double shock-absorbing steering wheel, the spring means bear on the one hand on the element of the epicyclic gear train and on the other hand on the fixed chassis, the rotation of that element relative to the fixed chassis being limited by the spring means. 
         [0011]    In a preferred embodiment of the invention, the spring means comprise a coil spring that is mounted in the fixed chassis around said element and that at rest extends approximately 360° around the rotation axis of the inertia masses. In this case, the angular range of movement of said element can reach 120° to either side of a rest position, the authorized angular range of movement between the two inertia masses being a function of the transmission ratio of the epicyclic gear train, for example 80° to either side of a rest position if the transmission ratio of the epicyclic gear train is 1.5, which represents a performance very much better than that of current double-flywheel dampers. 
         [0012]    In another embodiment of the invention, the spring means of the torsion damper comprise a plurality of springs mounted end-to-end in the fixed chassis over an angle of approximately 360°. 
         [0013]    The spring or springs of the torsion damper can be curved in their free state to facilitate mounting them in the fixed chassis. 
         [0014]    According to another feature of the invention, this double-flywheel damper includes a pre-damper between the primary inertia mass and the element of the epicyclic gear train that is connected to the primary inertia mass. 
         [0015]    This feature absorbs and damps vibrations and acyclic rotation when idling and at very low loads. 
         [0016]    The double-flywheel damper of the invention can be mounted in the conventional way in an automobile vehicle between the internal combustion engine and a gearbox. It can also be wholly or partially included in the internal combustion engine, which has the advantage that the gears of the epicyclic gear train are lubricated by the engine lubricating oil. 
         [0017]    Another advantage of the double-flywheel damper of the invention is that it eliminates the problem of passing through the resonant frequency on starting and stopping the engine by immobilizing the secondary inertia mass relative to the primary inertia mass, which can be done very simply by immobilizing the element of the epicyclic gear train on the fixed chassis. 
         [0018]    Alternatively, it is possible to free the element of the epicyclic gear train completely relative to the fixed chassis so as in this way to separate totally the secondary inertia mass from the primary inertia mass and pass without difficulty through the resonant frequency on starting and stopping the engine. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    The invention will be better understood and other features, details and advantages of the invention will become more clearly apparent on reading the following description given with reference to the appended drawings in which: 
           [0020]      FIG. 1  is a simplified diagrammatic view of a double-flywheel damper of the invention; 
           [0021]      FIG. 2  is a front view of the torsion damper of this double-flywheel damper in a rest position; 
           [0022]      FIGS. 3 and 4  are views similar to  FIG. 2  representing the torsion damper in two different operating positions; 
           [0023]      FIGS. 5 to 9  represent variants of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0024]    The double-flywheel damper represented diagrammatically in  FIG. 1  includes a primary inertia mass  10  (in the form of a primary flywheel) fixed to the end of a drive shaft  12 , such as the crankshaft of an internal combustion engine M, and a secondary inertia mass  14  (in the form of a secondary flywheel) fixed to a driven shaft  15  and coaxial with the primary inertia mass  10 . The secondary inertia mass  14  is, for example, connected by a clutch E to an input shaft of a gearbox BV. The two inertia masses (or flywheels)  10 ,  14  are connected together in rotation by a pre-damper  16  and by a torsion damper  18 . 
         [0025]    According to the invention, the torsion damper  18  includes an epicyclic gear train consisting of a sun wheel  20 , an outer crown wheel  22  and a planet gear carrier  24  the planet gears  25  of which mesh with external teeth on the sun wheel  20  and internal teeth on the outer crown wheel  22 . 
         [0026]    In the embodiment of  FIG. 1 , the pre-damper  16 , which is of a standard type, is mounted between the primary inertia mass  10  and the planet gear carrier  24 . The driven shaft  15  of the sun wheel  20  is fastened to the secondary inertia mass  14 , which can be centered and guided in rotation on the primary inertia mass  10  in the standard manner. The outer crown wheel  22  is guided in rotation in a fixed chassis  26  which surrounds the epicyclic gear train. 
         [0027]    In this example, the torsion damper  18  also includes a coil spring  28  around the outer crown wheel of the epicyclic gear train that extends approximately 360° around the rotation axis of the double-flywheel damper, this spring  28  being housed and guided in an annular chamber of the fixed chassis  26 , for example. 
         [0028]    The ends of the spring  28  bear on the one hand on a radial lug  30  of the fixed chassis  26  and on the other hand on a radial lug  32  of the outer crown wheel  22 , the radial lug  30  of the chassis  26  extending inward whereas the radial lug  32  of the outer crown wheel  22  extends outward. 
         [0029]    In a known manner, the radial lug  32  of the outer crown wheel  22  can extend in a diametral plane of the end turns of the spring  28 , whereas in this case the chassis  26  has two radial lugs  30  on respective opposite sides of the diametral lug  32  of the outer crown wheel  22 , as is often the case in torsion dampers using circumferential springs. 
         [0030]    The spring  28  of the torsion damper can be curved in the free state to facilitate fitting it around the outer crown wheel  22 . Alternatively, it can be straight in the free state and bent into a curve in order to fit it around the outer crown wheel  22 . 
         [0031]    In another variant, the spring  28  can be replaced by two or more springs mounted end-to-end, these springs being curved or straight in the free state. 
         [0032]    The double-flywheel damper that has just been described operates in the following manner: 
         [0033]    When idling and at low loads, vibrations and acyclic rotation are absorbed and damped by the pre-damper  16 , whereas the spring  28  of the torsion damper  18  remains in the state represented in  FIG. 2 , where it extends approximately 360° around the outer crown wheel  22 , its two ends bearing on the radial lug  30  of the fixed chassis and on the radial lug  32  of the outer crown wheel  22 . 
         [0034]    When the torque transmitted by the double-flywheel damper increases, vibration and acyclic rotation transmitted by the drive shaft  12  to the primary inertia mass  10  are absorbed by the spring  28 , which is compressed either in the forward direction as represented in  FIG. 3  or in the opposite direction as represented in  FIG. 4 , the vibrations and acyclic rotations being damped by friction means mounted in the standard manner in the torsion damper  18  between the two inertia masses, these friction means being well known to the person skilled in the art and not being represented in the drawings for reasons of clarity. 
         [0035]    In  FIGS. 3 and 4 , the spring  28  is in a maximally compressed state, its turns being contiguous or substantially contiguous. 
         [0036]    In this state, the rotation of the outer crown wheel  22  relative to the fixed chassis  26  is approximately 120°, for example. The corresponding rotation of the secondary inertia mass relative to the primary inertia mass is determined by the transmission ratio of the epicyclic gear train. If this ratio is 1.5, for example (which means that the rotation speed of the secondary inertia mass  14  is 1.5 times the rotation speed of the primary inertia mass  10 ), the maximum possible angular range of movement of the secondary inertia mass  14  relative to the primary inertia mass  10  is 80° to either side of a median position if the angular range of movement of the outer crown wheel  22  relative to the fixed chassis is 120° to either side of a median position. The resulting vibration damping performance is very much better than that of a standard double-flywheel damper. 
         [0037]    Passage through the resonant frequency, which is a problem encountered in all double-flywheel dampers when stopping and starting the engine of the vehicle, can be solved very simply in the double-flywheel damper of the invention, either by preventing rotation of the outer crown wheel  22  or by releasing the outer crown wheel, the secondary inertia mass being then either prevented from rotating relative to the primary inertia mass or free to rotate relative to that primary inertia mass on passing through the resonant frequency. 
         [0038]    The outer crown wheel  22  can be immobilized by immobilizing its radial lug  32  or by application of a brake shoe to the outer crown wheel. Releasing it so that it can rotate is simply achieved by retracting the radial lug  30  of the fixed chassis on passing through the resonant frequency. 
         [0039]    When the double-flywheel damper of the invention is mounted in the standard way in an automobile vehicle between the engine and the gearbox, the epicyclic gear train of the torsion damper must be accommodated in a sealed chamber containing a lubricating liquid. 
         [0040]    If the double-flywheel damper of the invention is included fully or at least partially in the internal combustion engine of the vehicle, the sealed chamber is no longer necessary and the components of the epicyclic gear train are lubricated directly by the engine oil. 
         [0041]    An electro-rheological or magneto-rheological fluid can also be used as an energy dissipating element in the double-flywheel damper of the invention, these fluids consisting of suspensions of solid particles the mechanical properties of which can be adjusted by an external electric or magnetic field. 
         [0042]    In the  FIG. 5  variant, the primary inertia mass  10  is constrained to rotate with the outer crown wheel  22  and the planet gear carrier  24  is retained by the spring means  28  housed in a chamber of a fixed element  26 . 
         [0043]    This embodiment differs from that of  FIG. 1  in that the connections of the primary mass  10  and the chassis to the planet gear carrier and to the outer crown wheel are reversed, the secondary inertia mass  14  remaining connected to the sun wheel  20 . 
         [0044]      FIG. 6  shows the  FIG. 5  embodiment to which has been added a second stage of planet gears  25 ′. The planet gears  25  of the first stage mesh with the outer crown wheel  22  and the planet gears  25 ′ mesh with the sun wheel  20 , the planet gears  25  and  25 ′ being mounted on the same support  24 . 
         [0045]    These two stages of planet gears offer greater freedom in the choice of the transmission ratio of the epicyclic gear train for a small overall size in the radial direction. The input and output rotation directions of the epicyclic gear train are reversed. 
         [0046]      FIG. 7  shows the device from  FIG. 6  with a modification of the contacts of the outer crown wheel  22  and the planet gears  25  from the outside to the inside of the planet gears. This arrangement has the advantage that the input and output rotation directions of the epicyclic gear train are the same. 
         [0047]    The device represented in  FIG. 8  is that from  FIG. 1  with the addition of a second stage of planet gears  25 ′ as in  FIG. 6 . The input and output rotation directions of the gear train are identical. There is a wider choice of transmission ratios of the gear train for a small overall size in the radial direction. 
         [0048]    The  FIG. 9  variant features the arrangement of the epicyclic gear train of the type used in a gearbox differential, that includes two coaxial sun wheels  20  and  22 , and a planet gear carrier  24  having planet gears  25  meshing with both of the sun wheels  20  and  22 . Specifically, as illustrated in  FIG. 9 , the planet gears  25  are in the form of 45° bevel gears of the type used in a gearbox differential. The transmission ratio of the gear train is equal to 1, the input and output rotation directions are reversed, and the overall size is minimal 
         [0049]    In all the embodiments represented in the drawings, the inertia masses are interchangeable, i.e. the primary inertia mass  10  can be connected to the sun wheel  20  and the secondary inertia mass  14  can be connected to the outer crown wheel  22  or to the planet gear carrier  24 .