Abstract:
The invention relates to a flexible flywheel ( 2 ), in particular for a motor vehicle, comprising at least two stacked flexible discs ( 9, 10, 11 ). The inner peripheries ( 12 ) of the flexible discs are secured to a drive shaft, and the outer peripheries ( 30 ) of are secured to an inertia mass ( 31 ). Each flexible disc ( 9, 10, 11 ) includes at least two parallel flat parts ( 15, 16, 17 ), which are offset axially (D 1 , D 2 ) and connected to one another by a curved part ( 18, 19 ). The curved parts ( 18, 19 ) of the discs ( 9, 10, 11 ) are substantially nested one inside the other, characterized in that, in at least one region adjacent to a curved part, the discs ( 9, 10, 11 ) are spaced one from the other so as to form a space ( 23, 27, 29 ) which facilitates the axial deformation of the discs ( 9, 10, 11 ).

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS AND CLAIM TO PRIORITY 
     This application relates to International Application No. PCT/FR2009/052464 filed Dec. 9, 2009 and French patent application Ser. No. 09/50077 filed Jan. 8, 2009, of which the disclosures are incorporated herein by reference and to which priority is claimed. 
     FIELD OF THE INVENTION 
     The present invention relates to flexible flywheel, such as, for example, a primary flexible flywheel for a double damping flywheel, in particular in a torque transmission system for a motor vehicle. 
     BACKGROUND OF THE INVENTION 
     A double damping flywheel comprises two coaxial inertia flywheels, i.e. a primary flywheel which is fitted fixed at the end of the crankshaft, and a secondary flywheel which forms a reaction plate of the clutch. The secondary flywheel is centred and guided in rotation on the primary flywheel by means of a bearing. 
     A torsion damper with springs and friction means is fitted between the two flywheels, in order to transmit rotational torque from one flywheel to the other, whilst absorbing and damping the vibrations and impacts. 
     The ends of the springs are supported on stops which are integral with the flywheels, and are arranged such that any rotation or oscillation of one flywheel relative to the other gives rise to compression of the springs of the damper in one direction or the other, and is countered by this compression. 
     The axial frequency of the primary flywheel itself must be low, for example lower than 50 Hz, so that it does not begin to resonate when the engine is running at low speed. For this purpose it is known to use a flexible primary flywheel comprising at least two stacked flexible discs, the inner peripheries of which are designed to be secured to a drive shaft, and the outer peripheries of which are designed to be secured to an inertia mass, each flexible disc comprising two flat parallel parts which are offset axially and are connected to one another by a curved part. The flexible discs have identical profiles, and are superimposed on one another and nested in one another. A structure of this type is known in particular from document EP 0 984 184. 
     The axial vibrations of the flexible flywheel generate deformation of the aforementioned discs. Since the curved parts of the discs are nested in one another without play, the discs cannot be displaced radially relative to one another, which gives rise to buttressing of the discs at the level of their curved part, and thus to stiffening of the assembly. This tends to reduce the efficiency of the flexible flywheel. 
     SUMMARY OF THE INVENTION 
     The object of the invention is in particular to provide a simple, efficient and economical solution to this problem. 
     For this purpose, the invention proposes a flexible flywheel, in particular for a motor vehicle, comprising at least two stacked flexible discs, the inner peripheries of which are designed to be secured to a drive shaft, and the outer peripheries of which are designed to be secured to an inertia mass, each flexible disc comprising at least two parallel flat parts, which are offset axially and connected to one another by a curved part, the curved parts of the discs being substantially nested one inside the other or inside one another, characterised in that, in at least one region adjacent to a curved part, the discs are spaced from one another so as to form a space which facilitates the axial deformation of the discs. 
     By this means, the occurrence of the phenomenon of buttressing or stiffening of the discs under the effect of the axial vibrations is avoided. 
     According to one embodiment of the invention, the curved parts of the discs are offset radially and axially from one disc to the other. 
     According to a characteristic of the invention, the axial distance between the curved parts of the discs is between 0.5 and 5 mm at rest, in other words when the flexible discs are not being subjected to stress by the axial vibrations, and are therefore not deformed. 
     Advantageously, the radial distance between the curved parts of the discs is between 0.5 and 5 mm (at rest). 
     According to one embodiment of the invention, the axial distances between the flat parts of the discs are zero or substantially zero. 
     As a variant, the flat parts of the discs are spaced axially in at least one region which is adjacent to a curved part, for example by a distance of less than 1 mm. 
     According to a preferred embodiment of the invention, the flexible flywheel comprises three stacked flexible discs. 
     In general, the flexible discs are made of steel plate, and have a thickness of between 0.5 and 12 mm. They can in that case be manufactured by stamping. 
     Advantageously, each curved part comprises two annular connection shoulders which respectively connect each of the flat parts to a curved annular part, the curvature of which has a point of inflection. 
     According to one possible embodiment of the invention, the radius of curvature of each connection shoulder is between 5 and 40 mm. 
     As a variant, each curved part comprises two annular connection shoulders which connect each of the flat parts respectively to a frusto-conical part. 
     Preferably, each flexible disc comprises three successive parallel flat parts, which are offset axially from one another relative to the others, the flat parts being connected in pairs by curved parts. 
     Each disc then comprises a radially inner curved part and a radially outer curved part which are opposite one another, such that each radially outer fiat part extends on a plane which is disposed axially between the planes of the two other corresponding flat parts. 
     The flexible flywheel according to the invention can be an inertia flywheel which is fitted at the end of a crankshaft, and forms the reaction plate of a clutch, or it can be a primary flywheel of a double damping flywheel. 
     The invention also proposes a double damping flywheel, in particular for a motor vehicle, characterised in that it comprises a primary flywheel formed by a flexible flywheel of the above-described type. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be better understood, and other details, characteristics and advantages of it will become apparent, from reading the following description provided by way of non-limiting example with reference to the attached drawings, in which: 
         FIG. 1  is an exploded perspective view of a double damping flywheel according to the invention; 
         FIG. 2  is a view in axial cross-section of the double damping flywheel in  FIG. 1 ; 
         FIG. 3  is a detailed view of the discs; 
         FIG. 4  is a detailed view of the curved parts of the discs; 
         FIG. 5  is a view corresponding to  FIG. 4 , representing a variant embodiment of the invention; and 
         FIG. 6  is a front view, in partial cross-section of the double damping flywheel in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 1 ,  2  and  6  represent a double damping flywheel  1  according to the invention, which is designed to couple an engine, for example an engine of the diesel type, to a gear box of a motor vehicle. 
     This double damping flywheel comprises a primary flywheel  2 , which is designed to be secured to the end of a crankshaft of the engine by screws or bolts. 
     The primary flywheel  2  comprises a central appendage  3  with an axis A, with a generally tubular form, comprising a first part  4  which has a cylindrical outer surface  5  around which there is fitted a bearing  6 , which part is extended by a second part  7  with a larger diameter which forms a collar, and the front end of which has a flange  8  which extends radially towards the exterior. 
     The primary flywheel  2  additionally comprises at least two discs made of steel plate, and preferably three discs  9 ,  10 ,  11  which are stacked on one another, and are fitted around the second part  7  of the central appendage  3 . The mean thickness of the discs is between 0.5 and 1.2 mm. 
     An inner peripheral part  12  of each of the discs  9  to  11  is clamped between the flange  8  and a washer  13 , which is fitted around the second part  7 , to the rear of the flange  8 , the assembly being secured by rivets  14 . 
     Each disc  9  to  11  is of the curved type, and comprises an inner peripheral part  15 , a median part  16 , and an outer peripheral part  17 , which are flat and parallel, and extend transversely relative to the axis A. 
     The inner peripheral part  15  is connected to the median part  16  by a first curved part  18 , the median peripheral part  16  being connected to the outer peripheral part  17  by a second curved part  19 . 
     The first curved parts  18  of the discs  9  to  11  are oriented in the same direction, and are substantially parallel to one another, the discs being nested in one another. 
     The second curved parts  19  of the discs  9  to  11  are oriented in the opposite direction to that of the first curved parts  18 , such that each outer peripheral part  17  extends on a plane which is disposed axially between the planes of the inner  15  and median  16  flat parts. 
     More particularly, the median flat parts  16  are disposed to the front of the inner flat parts  15 , and the outer flat parts  17  are disposed to the rear of the median flat parts  16 . 
     This arrangement limits the axial dimension of the double damping flywheel  1 . 
     The axial distance D 1  between the median part  16  of a disc and its inner peripheral part  15  is between 2 and 10 mm, and these distances D 1  are substantially identical for the three discs  9  to  11 . 
     The axial distance D 2  between the outer peripheral part  17  of a disc and its median part  16  is between 0.5 and 5 mm, and these distances D 2  are substantially identical for the three discs  9  to  11 . 
     As can be seen better in  FIG. 4 , each first curved part  18  comprises a radially inner annular connection shoulder  20  and a radially outer annular connection shoulder  21 , which connect respectively the inner peripheral part  15  and the median part  16  to an arched annular part  22 , the curvature of which has a point of inflection  1 . 
     Each shoulder  20 ,  21  has a radius of curvature r of between 5 and 40 mm, and preferably between 10 and 20 mm. 
     It will be appreciated that the arched annular part  22  could be replaced by a frusto-conical part. 
     The first curved parts  18  of two adjacent discs are offset axially by a distance d 1  corresponding substantially to the thickness of a disc in the case of  FIG. 4 , since the flat parts  15 ,  16  of the discs  9  to  11  are in contact on one another. The first curved parts  18  are also offset radially by a distance d 2  of between 0.5 and 5 mm. 
     Thus, an annular space  23  is formed between two adjacent discs, this space being delimited by a portion of flat part  15  of a disc, for example the median disc  10 , by the radially inner wall, with a concave form, of the inner shoulder  20  of the disc  10 , by the radially inner wall of the arched annular region  22  of the disc  10 , by the radially inner wall, with a convex form, of the outer shoulder  21  of the disc  10 , by a portion of flat part  16  of the disc  11 , which is situated directly to the front of the first disc  10 , by the radially outer wall, with a concave form, of the outer shoulder  21  of the disc  11 , by the radially outer wall of the arched annular region  22  of the disc  11 , and by the radially inner wall, with a convex form, of the inner shoulder  20  of the disc  11 . 
     The second curved parts  19  have a structure similar to that of the first curved parts  18 , and define in the same manner an annular space  24  between two adjacent discs. It should be remembered however that the second curved parts  19  are oriented in the direction opposite that of the first curved parts  18 . 
     According to a variant embodiment of the invention, represented in  FIG. 5 , it is the flat parts of the discs adjacent to the curved parts which are offset axially relative to one another, at rest, in order to prevent buttressing of the discs during functioning. In  FIG. 5 , each first curved part  18  comprises a radially inner annular connection shoulder  20  and a radially outer annular connection shoulder  21 , which connect respectively the inner peripheral part and the median part to a frusto-conical part  25 . 
     The median  10  and front  11  discs each have a first set-back  26  towards the front, at the level of the flat inner parts  15 , such as to delimit spaces  27  between the discs  9  and  10  and between the discs  10  and  11 . 
     Each disc  10  and  11  additionally has a second set-back  28  towards the front, at the level of the flat median parts  16 , such as to delimit spaces  29  between the discs  9  and  10  and between the discs  10  and  11 . 
     The set-backs  26  and  28  are adjacent to the first curved parts  18 . 
     The spacing e between the discs is preferably less than 1 mm. 
     In each of the above-described variants, the spaces  27 ,  29  formed between the discs  9  to  11  have dimensions such as to permit the free deformation of the discs  9  to  11  when they are subjected to axial displacements, such as to avoid the occurrence of the phenomenon of buttressing or stiffening of the discs which occurred in the prior art. For this purpose it is necessary to assure that, for maximum deformation of the discs  9  to  11 , spacing exists between the discs, even if this is only slight. 
     The outer peripheral parts  30  of the discs  9  to  11  are secured to a first inertia mass  31  made of cast iron or steel, with a generally annular form, which surrounds the sheet metal discs  9  to  11 . 
     More particularly, the first inertia mass  31  has a hollow annular region  32  in which the outer edges of the discs  9  to  11  are secured by rivets  33 . The first inertia mass  31  additionally supports a toothed starter ring  34  on its outer periphery. 
     The double damping flywheel  1  also comprises a secondary flywheel  35 , comprising a second inertia mass  46 , which acts as a reaction plate of a clutch mechanism. 
     In a conventional manner, the rear radial surface of the second inertia mass  46  forms a support surface for a friction disc (not represented), which is connected in rotation with an intake shaft of the gear box, and is thrust by a pressure plate which is integral in rotation with the secondary flywheel, when the clutch is in the engaged position. 
     The secondary flywheel  35  is centred and guided in rotation on the central appendage of the primary flywheel  2 , by means of the bearing  6 . 
     The primary  2  and secondary  35  flywheels are coupled by a torsion damper  36 , which is designed to absorb and damp the vibrations and acyclisms generated by the motor vehicle engine. 
     The torsion damper comprises two guide washers  37 ,  38  which are rendered integral in rotation with the primary flywheel  2  by means of rivets or screws, and delimit between one another receptacles in which there are fitted arched springs  39  which are distributed circumferentially around the axis A. 
     The torsion damper  36  also comprises two guide washers  40 ,  41  which are rendered integral in rotation with the secondary flywheel  35  by means of rivets or screws, and delimit between one another receptacles  42  in which there are fitted straight springs  43  which are distributed circumferentially around the axis A. 
     On its radially outer periphery, the guide washer  37  comprises a flange  44  which extends axially as thr as the guide washer  38 . This flange  44  can retain a viscous lubricant, such as grease or oil, around the arched springs  39 , thus in particular preventing this lubricant from escaping under the effect of a centrifugal force. In addition, this flange  44  can also retain the arched springs  39  when they are subjected to centrifugal force, at a high engine speed. 
     The damping means additionally comprise friction means which are fitted between the two inertia masses  31 ,  46 , and make it possible to damp the vibrations and acyclisms absorbed by the springs  39 ,  43 , by braking the oscillations relating to the two inertia masses  31 ,  46 . 
     Finally, the double damping flywheel  1  can also comprise torque limitation means  45  which are integrated in the secondary flywheel  35 .