Abstract:
The invention relates to a method ( 30 ) for the active damping control for an electric vehicle or hybrid vehicle having an electric motor drive element ( 4 ), comprising the steps of receiving a current target torque value (tq ElmDes ) of the electric motor drive element ( 4 ), determining a current rotational angle value (φ ElmAct ) of the electric motor drive element ( 4 ), and determining a current damping torque value (tq Dmp ), characterized in that the current damping torque value (tq Dmp ) is determined using a reduced drive train model (rTSM).

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to drive technology in vehicles. In particular, the present invention relates to the damping of a vibration behavior of an electric motor drive element. The present invention also especially relates to a method for active damping control for an electric vehicle or hybrid vehicle having an electric motor drive element and a controller and a vehicle. 
     Electric motors are being ever more often used as at least one drive component in motor vehicles. However, one property of a vehicle drive train having an electric motor as the drive motor is its ability to vibrate. It can therefore be possible that the revolution rate of an electric motor can oscillate significantly, especially during dynamic load changes, despite an essentially smooth profile of a propulsive torque of the electric motor. 
     The illustrations of  FIGS. 1 a, b    show the torque tq Elm  at the point in time t=1 s as an essentially step increase from 0 Nm to e.g. 50 Nm, whereas, however, the revolution rate of the electric motor n Elm  in revolutions/minute has a known oscillation characteristic in the range of times between t=1 s and t=1.5 s up to t=2 s. From t=2 s the applied torque tq Elm  gives an essentially linear rise of the revolution rate n Elm . 
     In this connection, such behavior occurs regularly independently of a special implementation of a drive train, whereby it can be shown as irrelevant whether the drive train is a so-called electric axle, a combination of an electric motor with a differential transmission, a conventional drive train or a wheel hub drive. 
     Such occurring oscillations also mean, besides a loss of comfort, a significantly increased mechanical load on the drive train. 
     SUMMARY OF THE INVENTION 
     One aspect of the present invention can thus be seen in the preferred damping of the oscillation behavior of an electric motor of a vehicle. Accordingly, a method for active damping control for an electric vehicle or hybrid vehicle with an electric motor drive element, a controller for a vehicle arranged to perform the method according to the invention and a vehicle comprising a controller according to the invention are shown. 
     The oscillation characteristic or the tendency to oscillate can be reduced or completely prevented by the use of a so-called observer element, which estimates the oscillation characteristic of a downstream vehicle drive train from a calculated or specified torque and a measured revolution rate of an electric motor element and superimposes an oscillation compensation torque on the specified target torque. 
     Furthermore, the method according to the invention is described with reference to a so-called reduced drive train model (rDTM), essentially a two-mass oscillator, which simulates the dynamics of the drive train with adequate accuracy. 
     It is significant here that the electric motor drive element has a first angular speed or revolution rate ω 1  of its rotor and the vehicle or its mass has a second angular speed/revolution rate ω 2 . The second revolution rate can be represented e.g. by the slip-free rotation of the drive wheels, but where the mass of the drive wheels has been compensated such that it essentially relates to an equivalent vehicle mass, thus representing as it were the entire vehicle mass combined or located in the drive wheels. 
     In cases where ω 1  equals ω 2  this means that, at least currently, there is no oscillation behavior in the reduced drive train model. An oscillation behavior ω Osc  of the vehicle drive train is represented as follows:
 
ω Osc =ω 1 −ω 2  
 
     In cases where ω Osc  is not equal to 0, the reduced drive train model exhibits an oscillation behavior. A compensation torque or damping torque tq Dmp  can subsequently be determined from the oscillation characteristic ω Osc  in a further step. 
     The damping torque value tq Dmp  can initially be determined from the oscillation characteristic ω Osc  according to tq Dmp =k Dmp *ω Osc  using a constant factor or multiplier k Dmp . 
     For a calculation of the damping torque value tq Dmp , referred to below as the compensation torque or compensation moment, that is as ideal as possible this must be adapted under the influence of the usual constant factor k Dmp  for effective use in hybrid vehicles and/or electric vehicles. Because of the oscillation behavior of a drive train being dependent on different factors, a non-constant form of the factor k Dmp  is to be preferred to achieve preferred damping of a drive train. 
     For example, the natural damping of a drive train can vary depending on the speed of the vehicle, e.g. the natural damping of the drive train can increase with increasing speed of the vehicle, while on the other hand the dynamics of the torque regulation of an electric machine can decrease. A preferred reduction of oscillation behavior can thus be achieved by designing the scaling factor k Dmp  to be dependent on the speed of the vehicle, the wheel revolution rate or the revolution rate of the rotor of the electric motor drive element or the estimated revolution rate ω 2 . 
     In addition, the compensation torque tq Dmp  cannot be implemented in its maximum possible bandwidth. The magnitude of the compensation torque tq Dmp  can be limited to a value tq Dmpmax  here, because on the one hand it is not necessary to compensate a tendency to oscillate of a drive train with a maximum possible torque of an electric motor drive element and on the other hand an unnecessarily high torque can load mechanical components such as e.g. axle shafts or transmission elements to an unnecessary extent. 
     Furthermore, in certain driving situations erroneous or corrupted sensor information can result in stimulation of oscillation of the vehicle drive train. In other words, e.g. inaccurate or incorrectly determined sensor information can lead to an effective worsening of the situation. Such erroneous drive train stimulation through inaccurate or erroneous sensor information, especially in a very low speed range of the vehicle, can be avoided by means of an activation threshold. In other words a compensation torque is only effectively applied to the drive train if the compensation torque tq Dmp  has exceeded a known activation threshold tq Dmpmin . Below said activation threshold a compensation torque tq Dmp =0 is achieved. 
     A compensation torque tq Dmp  is thus only applied on exceeding an activation point tq Dmpmin  and is further limited to a maximum value tq Dmpmax . The compensation torque tq Dmp  can also be adapted to the speed of the vehicle by representing the scaling factor k Dmp  as a function of the speed of the vehicle (k Dmp =f(v)), a function of the wheel revolution rate (k Dmp =f(n Rad )) or rotor revolution rate (k Dmp =f(ω 1 )) of the electric machine or the estimated revolution rate (k Dmp =f(ω 2 )) of the equivalent vehicle mass. 
     If in the context of the present description a reduced drive train model (rDTM) is mentioned, then in the following this especially means the reduced drive train model according to  FIG. 3 . 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention are illustrated in the figures and explained in detail in the following description. 
       In the figures 
         FIGS. 1 a, b    show an exemplary oscillation characteristic of a drive train; 
         FIG. 2  shows a model of a vehicle drive train according to the present invention; 
         FIG. 3  shows an exemplary embodiment of a reduced drive train model rDTM according to the present invention; and 
         FIG. 4  shows an exemplary process diagram of the method for active damping control according to the present invention 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 2  shows a model of a vehicle drive train according to the present invention. 
     The modeled vehicle drive train  2  for a hybrid electric vehicle or an electric vehicle comprises an electric motor drive element  4 , which is coupled to a gearbox  6  using a drive shaft  8 . Starting from the gearbox  6 , two drive wheels  12  are connected to the electric motor  4  via axle shafts  10  by way of example. A rotation of the electric motor  4  is thus transferred via the drive shaft  8 , gearbox  6  and axle shafts  10  into a rotation of the drive wheels  12 . 
     Because of the transfer of the rotary motion from the electric motor drive element  4  to the drive wheels  12  using a plurality of intermediate elements, especially by means of their predominant elasticities and dampings, electric motor  4  can vibrate when driving the drive wheels  12 . 
       FIG. 3  shows an exemplary embodiment of a reduced drive train model rDTM according to the present invention, especially an equivalent circuit diagram or a reduced model using a reduced drive train model rDTM of  FIG. 2 . 
     In the reduced model of  FIG. 3  the rotation of the electric motor drive element  4  or its rotor rotation is transferred to the rotation of the vehicle  14 , especially its drive wheels  12 . An equivalent moment of inertia J 2 , which especially takes into account an equivalent vehicle mass, which ultimately transfers the vehicle mass to a rotation of the drive wheels  12 , is used as the moment of inertia of the electric motor  4  J 1 , as the moment of inertia of the vehicle including all running resistances. Thus the drive or forward movement of the vehicle  14  can be converted into a rotation of the drive wheels  12 , taking into account a corresponding equivalent vehicle mass. 
     The connection of the electric motor drive element  4  to the drive wheels  12  or the vehicle  14  takes place in  FIG. 3  using an equivalent elasticity of the drive train, therefore a mathematical model of the physical behavior of the drive train, especially the following elements: drive shaft  8 , gearbox  6  and axle shafts  10  of the vehicle drive train  2  according to  FIG. 2 . 
     The mathematical model of the drive train consists here of a mutually parallel spring element  16  and a damping element  18 . The spring element  16  here has an equivalent stiffness c and the damping element  18  has an equivalent damping coefficient d. 
     The electric motor drive element  4  uses a system stimulation u, e.g. the torque of the electric motor drive element  4 . The moment of inertia of the vehicle J 2  is affected by the load torque tq Last  of the vehicle, e.g. friction. The angular acceleration ω 1  of the rotor of the electric motor drive element  4  and ω 2  the angular acceleration of the vehicle mass, converted to a rotary motion using the equivalent vehicle mass, can be represented respectively by the two following equations: 
     
       
         
           
             
               
                 
                   
                     
                       
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     where 
     J 1 : moment of inertia of the electric motor drive element; 
     J 2 : moment of inertia of the vehicle; 
     c: equivalent stiffness of the vehicle drive train according to rDTM; 
     d: equivalent damping coefficient of the vehicle drive train according to rDTM; 
     u: system stimulation/torque of the electric motor drive element; 
     tq Last : load torque of the vehicle; 
     {acute over (ω)} 1 : angular acceleration of the rotor of the electric motor drive element; 
     {acute over (ω)} 2 : angular acceleration of the equivalent vehicle mass; 
     ω 1 : angular speed/revolution rate of the rotor of the electric motor drive element 
     ω 2 : angular speed/revolution rate of the equivalent vehicle mass; 
     φ 1 : current angle of rotation of the rotor of the electric motor drive element; and 
     φ 2 : current angle of rotation of the rotor of the equivalent vehicle mass. 
     ω 1  corresponds here to the angular speed or revolution rate of the rotor of the electric motor drive element  4  and ω 2  to the angular speed/revolution rate of the equivalent vehicle mass of the vehicle  14 . 
     φ1 or φ2 respectively form the angle of rotation of the rotor of the electric motor drive element  4  or the equivalent vehicle mass, related to the drive wheels  12 . 
     The oscillation characteristic ω Osc  represents the difference of ω 1  and ω 2 . 
     Continuing to refer to  FIG. 4 , an exemplary process diagram of the method for active damping control according to the present invention is illustrated. 
     Method  30  for active damping control for an electric vehicle or hybrid vehicle with an electric motor drive element uses a current target torque value tq ElmDes , which e.g. is specified by a driver of a vehicle using a gas pedal  20 . A current damping torque value tq Dmp  can be determined using the reduced drive train model rDTM according to  FIG. 3  and taking account of the equivalent stiffness c of the vehicle drive train, the equivalent damping coefficient d of the vehicle drive train and the current angle of rotation of the machine φ ElmAct . The current angle of rotation φ ElmAct  of the electric motor drive element  4  may be determined e.g. by a measurement on the electric motor drive element. φ ElmAct  corresponds here to φ 1  of equations 1 and 2. 
     The target torque tq ElmDes  corresponds here to u(t). In particular, the damping torque tq Dmp  can be determined from ω Osc , thus as ω 1 −ω 2 . Furthermore, tq Dmp  especially represents ω Osc  multiplied by the factor element k Dmp . 
     Factor element k Dmp  can initially be a constant factor as previously mentioned, but should especially be dynamically adapted to the speed of the vehicle v, a wheel revolution rate n Rad  or a rotor revolution rate of the electric motor drive element  4  or else to the estimated revolution rate ω 2  of the equivalent vehicle mass or should be dependent thereon. 
     The damping moment of inertia tq Dmp  can then be limited in its maximum value tq Dmpmax  using a saturation block  22  and can have an activation threshold tq Dmpmin . A corresponding implementation of a curve profile between tq DmpEin  and tq DmpAus  of the saturation block is shown in  FIG. 4 . 
     After the saturation block  22  the calculation of the delivered torque of the electric motor tq ElmAct  takes place as tq ElmAct =tq ElmDes −tq DmpAus . 
     The resulting torque of the electric motor drive element  4  is in turn coupled into the reduced drive train model of  FIG. 3 . A corresponding calculation can now be continued in its next iteration. 
     At the same time the reduced drive train model provides the estimated angle of rotation φ ElmEst , which signal can be used instead of φ ElmAct  as the signal for current regulation of the electric motor drive element  4 . Because of the use of the angle of rotation φ 2  compared to φ 1  or ω 2  compared to ω 1 , a directly compensated control of the electric motor drive element  4  takes place. The signal quality of the angle of rotation used for the regulation can generally be significantly improved by this compared to the angle of rotation φ ElmAct  directly determined from a sensor. 
     In particular, with the method of the present invention a speed of the vehicle v is not determined or used for calculation of a compensation torque, but rather a current revolution rate of the rotor of an electric motor drive element is used. As a result, speed-dependent parameterization of a drive control may be performed. Alternatively, an estimated revolution rate ω 2  of the electric motor drive element  4  or of a drive wheel  12  can also be used. 
     In addition it is determined that the method according to the invention does not intervene in the revolution rate control, but rather in the torque control. Thus success according to the invention can also be achieved when driving off from a stationary vehicle state. The oscillation characteristic is thus uniquely determined by a revolution rate signal or a bearing angle signal of an electric motor drive element  4  and especially not from a difference measurement between a target revolution rate and an actual revolution rate. The current control of an electric motor drive element  4  remains unaffected by this and does not have to be adapted. The only task of the current control is the adjustment of the torque tq ElmAct .