Abstract:
The invention relates to an electric damper ( 10 ) for damping the relative motion between a first and a second mass, comprising a generator ( 26 ) that can be driven by the mass motion. The invention is characterized in that, in addition to the field generating means ( 18 ) present in the generator ( 26 ), an additional field winding ( 24 ) is provided for producing a secondary magnetic field, the additional field winding ( 24 ) being arranged in such a way that the primary and secondary magnetic fields have oppositely oriented field lines.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is the U.S. National Stage of International Application No. PCT/EP2013/000914, filed Mar. 27, 2013, which designated the United States and has been published as International Publication No. WO 2013/149710 and which claims the priority of German Patent Application, Serial No. 10 2012 007 120.5, filed Apr. 5, 2012, pursuant to 35 U.S.C. 119(a)-(d). 
     BACKGROUND OF THE INVENTION 
     The invention relates to an electric damper for damping the relative motion between a first and a second mass. 
     The underlying operating principle of an electric damper for damping the relative motion between a first and a second mass by using a generator is known from DE 101 15 858 A1. A generator is known to include a stator and a rotor rotatable relative to the stator, and corresponding magnetic field generating means, wherein a current is induced upon rotation of the rotor relative to the stator due to the rotational motion in the magnetic field, i.e. energy is generated. This means that, on the one hand, damping takes place as a result of the energy to be generated for performing the rotational motion in the magnetic field; on the other hand, the energy in form of the generator-side generated current which can be fed into the onboard electrical system can be utilized. It is also known from DE 101 15 858 A1 to provide a gearbox between two damper elements, which converts a linear motion into a rotational motion. Since the current induced by the rotational motion is proportional to the velocity, a proportional curve shape of the damping force characteristic results for the damper according to DE 101 15 858 A1. 
     SUMMARY OF THE INVENTION 
     It is the object of the invention to improve an electric damper for damping the relative motion between a first and a second mass such that the damping force characteristic has a degressive curve shape for high damper velocities. 
     According to an aspect of the present invention, the electric damper for damping the relative motion between a first and a second mass includes in a conventional manner a generator, which can be driven by the mass motion. 
     In addition to primary field generating means necessary for the induction in the generator, an additional field winding is provided for generating a secondary magnetic field, wherein the additional field winding is arranged and energized so that the primary and secondary magnetic field have field lines oriented in opposite directions. 
     By providing the additional field winding and the corresponding arrangement thereof according to the present invention, the field strength of the primary magnetic field can be influenced, meaning that the current induced during the rotational motion and hence the curve shape of the damping characteristics can be influenced. The damping characteristics of the damper according to the invention can thus be adjusted in a particularly advantageous manner, i.e. the characteristic curve can also have a degressive curve shape. 
     Preferably, the electrical conductor for conducting the induced current and the additional field winding are connected to one another in such a way that a portion of the induced current is supplied to the other field winding only when the induced current exceeds a predetermined threshold value. In this way, the additional field winding is energized from a predeterminable value on, which in turn causes the magnetic field to weaken and thus a degressive characteristic curve. 
     Preferably, the field generating means are formed as a field winding for separate excitation or as permanent magnetic elements for self-excitation. 
     According to a particularly advantageous embodiment of the invention, the generator is integrated in a gearbox. With this approach, the relative motion between the stator and the rotor of the generator can advantageously be influenced or adjusted. 
     The gearbox may be constructed in different ways, for example, formed as a strain wave gear or as a planetary gear or as a cycloidal gear. 
     Further advantages, features and possible applications of the present invention will become apparent from the following description taken in conjunction with the exemplary embodiments illustrated in the drawings. 
     The invention is described in more detail below with reference to the exemplary embodiments shown in the drawing. 
     In the description, in the claims and in the drawings, the terms used in the list of the reference characters and associated reference numerals listed below will be used. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawing shows in: 
         FIG. 1  a lever element of a motor vehicle suspension with an electric damper according to the present invention integrated in a bore of the lever element; 
         FIG. 2  a plan view of the damper according to the present invention of  FIG. 1 ; 
         FIG. 3  an exploded view of the electric damper according to the present invention of  FIG. 2 ; 
         FIG. 4  a circuit arrangement for the additional field winding; 
         FIG. 5  a schematic diagram of a possible installation of the damper according to the present invention in the area of a motor vehicle axle, and 
         FIG. 6  a schematic diagram of another embodiment of the damper according to the present invention. 
     
    
    
       FIG. 1  shows a lever element  100  of a motor vehicle suspension of a motor vehicle. The lever element  100  has a bore  110  in which a damper designated generally by the reference numeral  10  is integrated. 
     As shown in  FIG. 2 , the damper  10  is constructed in the form of a planetary gear and includes a first gear element  12  formed as a ring gear and second gear element  14  formed as a sun gear. The first gear element  12  formed as a ring gear is hereby fixedly mounted along its outer circumference in the bore  110  of the lever element  100 . The ring gear formed as a first gear element  12  has on the inner periphery an internal gearing which is not shown here for sake of clarity. The second gear element  14  arranged in the center and formed as a sun gear is in meshing engagement with the first gear element  12  having the internal gearing via three planet gears  16  by way of the outside gearing disposed on the sun gear and the planetary gears, is not shown here for sake of clarity. 
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     A rotational motion of the first gear element constructed as a ring gear  12  initiated by a pivoting motion of the lever element  100  thus causes in a known manner a geared rotational motion in the opposite direction of the direction of rotation of the second gear  14  element formed as a sun gear. 
     As further shown in  FIG. 2 , the damper  10  also includes several field generating means  18  for generating a primary magnetic field which are arranged in the ring gear, i.e. in the first gear element  12 . In addition, the second gear element  14  formed as a sun gear has an extension in the form of an armature  22  with armature coils  20 . In other words, a generator is integrated the planetary gear wherein the first gear element  12  formed as ring gear operates as a stator and the second gear element  14  formed as a sun gear operates as rotor, so that a current is induced in the armature windings  20  in a known manner when the armature  22  rotates in the primary magnetic field. 
     The damping effect is causes by the rotation of the rotor, i.e. the second gear element  14 , in the primary magnetic field, whereby the energy extracted from system is not lost, but is recovered to a considerable degree through induction of the current. 
     As shown in  FIG. 3 , an additional field winding  24  is provided, which can be used to generate a secondary magnetic field. The additional field winding  24  is connected in series with the field-generating means  18  provided on the first gear element  12  that generate the primary magnetic field. The arrangement of the additional field winding  24  and the direction of the current flow through the additional field winding  24  are selected such that the field lines of the secondary magnetic field are oriented in a direction opposite to the field lines of the primary magnetic field. 
     The electrical connection of the additional field winding is shown schematically in  FIG. 4 . In the schematic diagram of  FIG. 4 , the reference numeral  18  designates the field generating means for generating the primary magnetic field, the reference numeral  24  designates the additional field winding for generating the secondary magnetic field, and reference numeral  26  designates the generator. 
     A current is induced in the generator  26  through interaction with the primary magnetic field, with the current being discharged via the electrical connection to the two terminals  28 . These terminals can be connected, for example, to the onboard electrical system. 
     The additional field winding  24  is energized only when the required switching voltage is reached at the transistor  30 . When this switching voltage has been reached, the transistor  30  becomes conducting and energizes the additional field winding  24 , which in turn causes buildup of the secondary magnetic field. Due to the previously discussed arrangement and selected direction of current flow through the additional field winding  24 , the field lines of the secondary magnetic field are oriented opposite to the field lines of the primary magnetic field. In other words, the effective excitation field is weakened, thereby producing a degressive curve shape of the damping force. 
     A possible installation situation is shown in  FIG. 5 . As part of a motor vehicle, a wheel  120  together with a wheel carrier  130  is shown, wherein a push rod  140 , which is for example connected to the lever element  100 , is arranged on the wheel carrier  130 . The lever element  100  is supported for rotation about the rotation axis D, wherein the damper  10  according to the invention is disposed in this rotation axis. 
     It would also be conceivable to integrate the damper  10  directly in the rotary suspension of one or both of the transverse control arms  150 . In either case, the stator, i.e. the first gear element  12 , is always connected to the drive, i.e. is the driving element, whereas the rotor, i.e. second gear element  14 , is always the driven element. When the wheel  120  is now compressed or rebounds, the lever element  100  is moved so that it rotates about the axis of rotation D, via which the damper  10  according to the invention is operated in the aforedescribed manner. 
     In the damper  10  illustrated in  FIG. 6 , the lever element  100  is connected directly to the rotor  14  of the generator. That means that a pivoting motion of the lever element  100  causes a direct rotation of the rotor  14 . 
     The rotor  14  includes windings  20 . Furthermore, field generating means  18  for generating a primary magnetic field are arranged outside the rotor  14 . In the present example, the primary field generating means  18  are constructed as permanent magnets. A current is then induced in the windings  20  in a known manner through rotation of the rotor. 
     As further shown in  FIG. 6 , in addition to the primary field generating means  18  for generating the exciting magnetic field necessary for the induction, an additional field winding  24  is provided for generating a secondary magnetic field. The arrangement of the additional field winding  24  and the direction of current flow through the additional field winding  24  are selected such that the primary and the secondary magnetic field have field lines oriented in opposite directions. 
     As a result, the effective excitation field is weakened, i.e. a degressive damping force curve can be intentionally adjusted by controlling the current flow through the additional field winding  24 .