Abstract:
A filtering device is provided for filtering vibrations transmitted by a rotating engine component ( 11 ) adapted to drive in rotation an output shaft ( 19 ), which device comprises a drive shaft damper ( 20 ) tuned at a frequency substantially locked within a range of frequencies to be damped: electromagnetic modulating systems ( 23 ) are designed to adapt the frequency of the damper ( 20 ) to the frequency of the vibrations transmitted by the rotary component ( 11 ). Moreover, a transmission is provided for motor vehicle comprising a drive shaft ( 11 ), linked to a rotary component formed by the motor vehicle engine crankshaft, an output shaft ( 19 ) linked to the drive shaft releasable via a clutch, a gearbox ( 50 ), the output shaft ( 19 ) being the input shaft of the gearbox ( 50 ), a filtering device being provided for filtering vibrations emitted, hence transmitted, by the rotary component.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a device for filtering out rotational vibrations, for filtering out vibrations transmitted by a rotary power component adapted to drive an output shaft in rotation; the said rotary power component is for example the crankshaft of a motor vehicle heat engine. 
   2. Description of the Prior Art 
   Devices are known for filtering out rotational vibrations, that consist of a mass which is elastically coupled on the shaft: such devices, known as passive dampers, work very well in filtering out vibrations tuned to a single frequency which is clearly determined, but for neighbouring frequencies, the vibrations are, by contrast, amplified. 
   So-called active drive shaft dampers have been proposed, as for example in the document FR-A-2 658 888, the construction of which is similar to that of an electric motor; it is so controlled that the torque which it supplies works in opposition to the vibration to be filtered out, over a given range of rotation: the electrical power consumption of such devices is not insignificant. 
   An object of the invention is to overcome these drawbacks. 
   SUMMARY OF THE INVENTION 
   According to the invention, a filtering device for filtering out vibrations transmitted by a rotating power component adapted to drive in rotation an output shaft, which device comprises a drive shaft damper tuned to a frequency which is substantially inside the range of frequencies to be damped out, is characterised by the fact that modulating means of the electromagnetic type are provided for the purpose of matching the frequency of the damper to the frequency of the vibrations transmitted by the rotating component. 
   Preferably, the damper comprises a rotor consisting of a mass which is mounted elastically on the output shaft and associated with a stator, the modulating means comprising electromagnetic means carried by the rotor and the stator. 
   Preferably, the electromagnetic means comprise magnets defining a succession of poles carried by the rotor and coils carried by the stator and defining a succession of poles disposed in line with the magnets. 
   Advantageously, the coils are disposed axially in line with the magnets. 
   In another version, the coils are disposed radially in line with the magnets. 
   Preferably, the rotor is in the form of a disc or is frusto-conical or cylindrical. 
   Advantageously, the magnets are held in position radially by a counter-centrifugal radial retaining hoop. 
   Preferably, the filtering device includes a vibration sensor adapted to measure the amplitude of the vibration to be damped out. 
   Advantageously, means are provided for supplying current to the coils of the electromagnetic means, the said supply being responsive to the result of the measurement of amplitude performed by the vibration sensor, whereby to create in the damper a torque equal and opposite to that created by the said amplitude. 
   Advantageously, the device comprises a main vibration damper disposed on the output shaft upstream of the damper. 
   The present invention also provides a transmission for a motor vehicle of the type comprising a drive shaft, coupled to a rotary component consisting of the crankshaft of the engine of the motor vehicle, an output shaft coupled to the drive shaft releasably through a clutch, a gearbox, the said output shaft being the input shaft of the gearbox, a filtering device being provided for filtering out vibrations emitted, and therefore transmitted, by the rotary component, the filtering device being as described above. 
   Advantageously, the clutch comprises a reaction plate, which is coupled directly or otherwise to the rotary component, a pressure plate which is coupled in rotation to the reaction plate but displaceable axially with respect thereto, the two plate, namely the reaction plate and pressure plate, being adapted to clamp between them, under the action of axially acting resilient means, friction liners carried by a friction disc at its outer periphery, the said friction disc having a hub which is mounted in rotation on the output shaft. 
   Preferably, the friction disc comprises a torsion damper which constitutes the main damper. 
   In another version, the reaction plate constitutes the secondary part of a two-part flywheel, the other part of which, namely the primary part, is coupled to the rotary component, the two parts being coupled elastically for rotation together. 
   Preferably, control of disengagement of the clutch is carried out electrically, the gearbox is a so-called automated gearbox, gear changes being controlled by a computer which takes into account, in particular, information delivered by a sensor as to the speed of the input shaft of the gearbox, and by a sensor as to the speed of the output shaft of the gearbox, firstly after the clutch is disengaged, and secondly after the damper has been tuned to the speed of the input shaft of the gearbox, having regard to the new gear ratio to be engaged; a mechanical gearbox with assisted control can of course also be used: the engine ensures assistance to the synchronising operation, governed by a detector of the gear ratio engaged. 
   In a modified application of the invention, the damper is used as an electric motor and controlled in such a way as to supply an additional driving torque on the output shaft, besides that which is supplied by the engine of the vehicle. 
   In another modified version, the damper is used as an energy recuperator during braking; the clutch is disengaged during the energy recuperation phase; the gear ratios are changed down. 

   
     BRIEF DESCRPTION OF THE DRAWINGS 
     In order that the invention shall be more clearly understood, some embodiments, which are shown in the attached drawings, will now be described by way of purely illustrative and non-limiting example. 
     In these drawings: 
       FIG. 1  is a diagram illustrating the application of the invention to a transmission for a motor vehicle; 
       FIG. 2  is a partial view in cross section showing another version; 
       FIG. 3  is a plan view showing part of the spring of the drive shaft damper in  FIG. 2 ; 
       FIG. 4  is a scrap view in cross section showing another version of the damper spring; 
       FIG. 5  is a view in cross section of a further version of the damper; 
       FIG. 6  is a partial view, in cross section, showing another version of the damper shown in  FIG. 5 ; 
       FIG. 7  is a partial view in transverse cross section showing the arrangement of the windings in the damper of  FIG. 6 ; 
       FIG. 8  is a scrap side view showing another arrangement of the windings; 
       FIG. 9  is a diagram of the same kind as that in  FIG. 1 , showing a further application of the invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   With reference to  FIG. 1 , this shows the application of the invention to a transmission for a motor vehicle comprising, starting from an engine  10  of the vehicle, a drive shaft or crankshaft  11 , the engine being coupled to a flywheel or reaction plate  12 , and a clutch mechanism consisting of a cover plate  13  which supports a pressure plate  14  and axially acting resilient means, in this example a diaphragm  15 . 
   Axially disposed between the reaction plate  12  and pressure plate  14 , a friction disc  16  carries at its outer periphery friction liners which are adapted to be gripped axially between the said plates  12  and  14 , and a central hub  17  which is connected elastically, through circumferentially acting springs  18 , to the peripheral portion carrying the said liners. 
   The hub  17  of the friction disc  16  is mounted in rotation on a so-called output shaft  19 . 
   Since these clutches are well known, they will not be described any more here. 
   A drive shaft damper  20  is mounted on the output shaft  19 . 
   The damper  20  consists of a mass  21  or rotor, which is mounted for rotation about the output shaft  19 , with which it is coupled elastically through an interposed spring  22 . 
   In accordance with the invention, modulating means (or device) are provided for matching the frequency of the damper  20  to the frequency of vibrations transmitted through the drive shaft  11  via the damper disc  16 , and not filtered by the latter. 
   These modulating means are of the electromagnetic type, and in this example they consist of magnets  27  located at the periphery of the rotor  21 , with which inductive windings, carried by a stator, which is indicated diagrammatically at  23  in  FIG. 1 , are arranged to cooperate electromagnetically. 
   The damper  20  is tuned to a frequency which is within the range of frequencies to be damped out; by passing through the inductive windings  23  a current which is a function of the amplitude measured, for example by a vibration sensor not shown, that is to say the amplitude of the vibration to be damped out, an oscillating torque is set up which is opposed to the vibration. 
   A computer  24  receives the measurement in real time of the vibration that remains to be damped out, so as to set the current which is to pass through the windings  23 , operation being therefore, with advantage, of the closed loop type. 
   Thanks to the invention, the electric power consumed by the filtering device is only of the order of a hundred watts. 
   In the diagram of  FIG. 1 , the windings  23  are disposed radially in line with the magnets of the rotor  21 . 
   In a modified version in  FIG. 2 , they are disposed axially in line with the magnets. 
   More precisely, with reference to  FIG. 2 , this shows a drive shaft damper  120  consisting of a rotor  121  and a stator  126 . 
   The stator  126  carries the windings  123 ; a ring  128  with an L-shaped cross section is carried by the stator  126  and provides centring for the coils and fastening of the stator  126 . 
   The rotor  121  comprises a disc  129  which is provided with a hub  130  mounted for free rotation on the output shaft  119  through, here, an interposed plain bearing  131 ; the disc  129  carries, on its surface that faces towards the windings  123 , magnets  127 ; an annular hoop  132 , which is for example made of steel, or glass fibres, or some other material, secures the fastening of the magnets  127  against centrifugal force. 
   A spring  122  couples the rotor  121  and output shaft  119  together elastically in rotation. 
   This spring  122 , which is best seen in  FIG. 3 , is in the form of a disc which is cut out in such a way that it has an annular outer rim  133  and an inner annular rim  134 , which are joined together by arms  135  that are generally radial in this example. 
   The annular inner rim  134  has at its inner periphery teeth  136  which are adapted to cooperate with grooves  137 ,  FIG. 2 , of the shaft  119  so as to couple the spring  122  and output shaft  119  together in rotation. 
   The annular outer rim  133  has apertures  138  which are adapted to cooperate with axial bosses  139 ,  FIG. 2 , which are formed in the disc  129  for coupling the rotor  121  and spring  122  together in rotation. 
   In the present case, the damper  120  is associated with a clutch in which the liners of the friction disc  116  are coupled rigidly with the hub  117 , while the reaction plate  112 B, associated with the pressure plate  114 , constitutes the secondary part of a two-part flywheel  112 , the primary part  112 A of which is coupled directly to the rotating member  111 , the primary part  112 A and secondary part  112 B both being coupled elastically to each other in rotation, in this example through interposed springs  118  extending generally radially. 
   In  FIG. 4 , the damper  120  is similar to that in  FIG. 2 , but here the spring  122  consists of a plurality of helical springs  150  which bear on the radial edges, on one side, of windows which are formed in a radial disc  151  which is coupled in rotation with the shaft  119 , and on the other side, of windows formed in counter-plates  152  disposed on either side of the plate  151  and mounted in rotation on the shaft  119  and coupled in rotation to the yoke  129  which carries the magnets  127 . 
   As has been seen in particular with respect to  FIG. 2 , the rotor  121  of the damper  120  is mounted on the shaft  119  by means of its hub  130 , the spring  122  being disposed kinematically between the rotor  121  and shaft  119 . 
   The drive shaft damper  220  shown in  FIG. 5  is mounted on the end of the primary shaft  219  of the gearbox, the secondary shaft of which can be seen at  120 . In this example it is the spring  222  that supports the rotor  221  of the damper; for this purpose it has an annular inner rim  234  in the form of a hub, which is secured axially on the end of the shaft  219  by a nut  241  screwed on to the shaft  219 , with a washer  242  interposed; the outer ends of the arms  235  of the spring  222  are in mesh with axial returns of the disc  229 , in the form of a yoke carrying the magnets  227 , in line with which the windings  223  carried by the armature  226  of the stator are placed, which armature  226  is itself carried by the base portion of a cover plate  243 ; preferably, the armature  226  is made in laminated form, by winding a metallic band around the axis of the shaft  219 , or in the form of a plurality of sintered iron elements, whereby to minimise losses due to Foucault currents. 
     FIG. 6  shows a variant of the drive shaft damper  220  which is located at the end of the primary shaft  219  of the gearbox. In this case, the axial order of the stator  226  and rotor  221  has been reversed, the rotor  221  being disposed on the outside; the rotor  221  is mounted in rotation on the shaft  219  and carries, directed outwards, a skirt  244  which extends parallel to the axis of the shaft  219  and which is formed with circumferential slots  245 , and the springs  222  engage on one side against one of the edges of these slots; on the other side, the springs  222  which extend circumferentially bear on transverse returns  246  of a solid ring  247  which is mounted in rotation on the shaft  219 . 
   In this example, the windings  223  are in the form of coils which are not interleaved but, as can be seen in  FIG. 7 , are disposed in two superimposed rows. 
   In another version they are interleaved, with the edge of one coil lying on the edge of the next as shown in  FIG. 8 : in this configuration, the coils are slightly inclined with respect to a transverse plane at right angles to the axis of the shaft  219 . 
   Thanks to the drive shaft damper according to the invention, it is also possible to synchronise the shafts concerned during gear changes, especially where the gear changes may be carried out by means of electrically controlled actuators, as is the case in so-called automated gearboxes. 
   In the diagram of  FIG. 1 , such a gearbox  50  can be seen disposed between the input shaft  19  and output shaft  51  for driving the drive train  52  of a motor vehicle. 
   Thus, when the shaft  19  is released following the declutching operation, the velocity of this shaft is rapidly reset according to the gear ratio to be engaged; such an arrangement has the advantage that it gives the drive shaft damper the function of a centralised synchroniser, and conventional synchronisers arranged in each gear ratio are omitted; in addition, synchronisation time is reduced, as is cost. 
   Operation is precise, and is facilitated by the presence of speed sensors  53 ,  54  upstream and downstream of the gearbox  50 ; by providing for an electrically controlled declutching actuator  55 , the computer  24 , which incorporates the electronic power control, generates all the functions described above, also having regard to certain parameters  65  of the engine, such as torque, speed, etc. 
   As to the damping function of the drive shaft damper, its closed loop operation described above may be replaced by operation in accordance with a vibration map, as a function of various parameters predetermining the values of torque to be given to the damper. 
   It will also be understood that the damper may be used as an energy recuperator, or even as an alternator and synchronous motor; with reference to  FIG. 9 , this shows an embodiment in which the damper  20  is mounted on the primary shaft  19  of the gearbox, downstream of a clutch  58 ; this primary shaft  19  in this example carries two pinions  60 ,  62  associated with two pinions  61 ,  63  respectively which are carried by the secondary or output shaft  51 ; a controlled dog-clutch  64  ensures that the said secondary shaft  51  will be driven either by the pinion  61  or by the pinion  63 . 
   Thanks to a fastening device  56 , the battery  57  of the vehicle may be charged for example during a braking operation; by action on the brake pedal  59 , after the accelerator has been released, the clutch  58  is disengaged and the damper  20  operates as a generator which discharges into the battery  57 ; in order that the speed of rotation of the generator is sufficiently high, the gears are changed down by controlling the clutch  64 .