Abstract:
In a method for operating a drive device of a hybrid vehicle, in particular a hybrid motor vehicle, having at least one internal combustion engine and at least one electric machine, the torques of the internal combustion engine and the electric machine are added. A torque/torque component which, with respect to a request, is not deliverable by the internal combustion engine because of the system-related inertia of the internal combustion engine, is compensated at least partially by a torque/torque component delivered by the electric machine.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method for operating a drive device of a hybrid vehicle, in particular a hybrid motor vehicle, having at least one internal combustion engine and at least one electric machine, the torques of the internal combustion engine and electric machine being added together. 
     2. Description of Related Art 
     Methods of the kind mentioned at the outset are known. To reduce fuel consumption and emissions, the goal is an optimal distribution of the driving torque requested by the driver between the internal combustion engine and the electric machine. The driving torque is divided so that the internal combustion engine is operated in the range of favorable efficiencies and it is possible to charge an electric accumulator belonging to the electric machine. At low driving speeds, however, the internal combustion engine should be turned off and the requested torque should be applied only by the electric machine. In addition, the braking energy in braking of the vehicle may be utilized by recuperation for charging the electric accumulator. Modern gasoline engines having intake manifold injection usually have an electronic throttle valve for regulating the air flow. The accelerator pedal is then decoupled mechanically from the throttle valve. The ultimate setting speed of the throttle valve control element and dynamic charge effects in the intake manifold do not allow a highly dynamic setting of a predefined air flow and of the internal combustion engine torque thereby generated. Electric machines, however, have a much more dynamic response. If the driver requests an increased driving torque, and the internal combustion engine thereby enters ranges of favorable efficiency, the electric machine is usually controlled so that it operates more as a generator. The machines may be triggered in such a way that the negative torque having a higher absolute value coming from the electric machine, which is operated as a generator, is compensated by an increased torque of the internal combustion engine. Due to the fact that, in comparison with the internal combustion engine, the electric machine has a highly dynamic response, the actual driving torque of the vehicle initially declines before approaching the torque requested by the driver. This has a negative effect on drivability and comfort. This undershooting may under some circumstances also excite unwanted vibrations in the drivetrain. To avoid this undershooting, it would be possible to additionally apply the difference between the setpoint torque and the actual torque of the internal combustion engine to the electric machine, to thereby compensate for the delayed torque buildup by the internal combustion engine. In a dynamic style of driving, i.e., with frequent changes in driving torque requirements, the electric machine would be under a highly dynamic load. This would be associated with a highly dynamic electric power demand of the energy accumulator connected to the electric machine, resulting in a high energy conversion in the energy accumulator and shortening its lifetime. In addition, frequent cyclic charging and discharging operations result in high conversion losses, having a deleterious effect on overall efficiency. 
     In addition, a method for operating the drive device of a hybrid vehicle is known from published German patent document DE 102 01 264. In the case of a negative driving torque demand, the drive unit and a brake system of the hybrid vehicle are triggered in a consumption-optimized manner. The goal in this method is to optimally utilize the available energy of the hybrid vehicle. By recovering braking energy through recuperation in particular, this energy may be fed into the vehicle electrical system, thereby decreasing the fuel consumption of the internal combustion engine. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention has the advantage that a delayed change in torque produced by the inertia in the torque triggering of the internal combustion engine, e.g., due to the intake manifold dynamics or due to a “turbohole,” is at least partially compensated by a torque of the electric machine. The driver is thus able to obtain the expected reproducible driving torque. Furthermore, undershooting in the acceleration procedure is also preventable in this way. 
     According to a refinement of the present invention, it is advantageous if, depending on the requirement, an allowed range for an actual driving torque and/or its gradient is predefined as a function of at least one parameter. In other words, when the driver requests a driving torque, an upper limit and a lower limit for the driving torque and/or its gradient are predefined as a function of this request; the actual driving torque that actually occurs and/or its gradient must not exceed this upper limit or drop below this lower limit, these limits being predefined as a function of at least one parameter that changes during the operation of the hybrid vehicle. 
     In a refinement of the present invention, the allowed actual torque range is predefined in such a way that vibration excitations of a drivetrain in the hybrid vehicle are prevented. This should prevent the driving torque from dropping at first when acceleration is requested by the driver due to the highly dynamic response of the electric machine, thereby resulting in so-called undershooting, which may unwantedly excite vibrations in the drivetrain. The allowed actual driving torque range is therefore predefined in such a way that a change in driving torque is possible only in the requested “direction” selected by the driver. 
     It is further advantageous if the performance of the electric machine is predefined within limits. This reduces conversion losses occurring during operation of the electric machine and the components belonging to it, in particular an electric accumulator. 
     At least one range limit of the allowed actual torque range is advantageously influenced as a function of the power of the electric machine, which is predefined within limits so as not to exceed the aforementioned conversion losses. 
     It is also advantageous if the electric machine supplies an additional torque contribution when the actual driving torque departs from the allowed range, so that the actual driving torque returns to the allowed range. 
     According to a further refinement of the present invention, the parameter determining the allowed range for the actual driving torque is a function, for example, of the cruise control and/or of the adaptive cruise control. Furthermore, the allowed actual driving torque range may also depend on the velocity and/or rotational speed. The driver may thus expect a reproducible driving torque at different velocities and/or rotational speeds. Furthermore, it is also conceivable for a signal of an ESP-ASR-ABS system to be used as a parameter for the allowed actual torque range or to allow a more or less dynamic response, depending on the driver. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         FIG. 1  shows a simulation model for the torque distribution illustrating the present invention in a parallel hybrid drivetrain. 
         FIG. 2  shows a simulation model of an exemplary embodiment of the present invention with a limitation of the allowed range by absolute limits. 
         FIG. 3  shows the response of the absolute limits and the actual total torque on a sudden change in the total setpoint torque. 
         FIG. 4  shows the response of the actual torque of the electric machine to a sudden change in the unlimited setpoint torque of the electric machine. 
         FIG. 5  shows a simulation model of an exemplary embodiment of the present invention with a limitation of the allowed range by limits for the gradient of the actual total torque. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a simulation model for the torque distribution, illustrating the present invention in a parallel hybrid drivetrain, an element  1 , a sensor here for detecting the driver&#39;s input, for example, sending a signal, in particular a setpoint driving torque, over a connection  2  to a control unit  3  of the drive device of a hybrid vehicle, from which a connection  4  leads to an internal combustion engine  5 , the response of which in the case of a change in torque is characterized by a diagram, and a connection  6  leads to an electric machine  7 , the response of which in the case of a change in torque is also characterized by a diagram, connections  8 ,  9  leading from internal combustion engine  5  and electric machine  7  to an adder  10 , in which the torques of internal combustion engine  5  and electric machine  7  are added up and which has a connection  11  to an element  12 , which likewise characterizes the response of the overall drivetrain by a diagram. If the driver requests a certain driving torque via the position of an operating element, in particular an accelerator pedal, this is detected by the sensors in element  1  and forwarded to control unit  3 , which distributes the requested torque to internal combustion engine  5  and electric machine  7 , so that when the internal combustion engine enters a range of favorable efficiencies, the electric machine is controlled to operate more as a generator. The characteristic diagram of the internal combustion engine has two torque curves plotted against time, the one curve describing setpoint torque  13  of the internal combustion engine and having a sudden change toward a higher torque and the other curve describing actual torque  14  of the internal combustion engine. Due to the inertia in torque triggering of internal combustion engine  5 , actual torque  14  of the internal combustion engine responds with a time lag and only asymptotically approaches setpoint torque  13  of the internal combustion engine. 
     The highly dynamic response characteristic of electric machine  7  depicted in the characteristic diagram of electric machine  7  produces a rapid asymptotic approach of actual torque  15  of the electric machine to a sudden change in setpoint torque  16  of the electric machine. 
     The total of the actual torques of internal combustion engine  5  and electric machine  7  produces the response of the overall drivetrain represented in element  12 . The total of setpoint torque  13  of the internal combustion engine and setpoint torque  16  of the electric machine corresponds to setpoint torque  18  requested by the driver. With an increase in setpoint torque  18  requested by the driver, internal combustion engine  5  enters a range of more favorable efficiencies, and electric machine  7  goes into generator operation to a greater extent, thereby increasing the charging capacity for an electric accumulator connected thereto. To compensate for the higher load of electric machine  7 , setpoint torque  13  of the internal combustion engine changes suddenly to a higher level. Due to the highly dynamic response characteristic of electric machine  7 , the so-called undershooting of actual driving torque  17  occurs, i.e., the actual driving torque declines at first, and only then asymptotically approaches setpoint driving torque  18 . 
       FIG. 2  shows an exemplary embodiment of the present invention using the example of a parallel hybrid, in which the allowed actual driving torque range is limited by absolute limits (trqLimHi and trqLimLo), which result from setpoint torque  18  via PT1 response. A calculation procedure that is processed cyclically in the sense of a sampling system at individual sampling increments is shown. A few values calculated in a previous sampling step and then stored are used to calculate valid values for the instantaneous sampling step. Element  1  from  FIG. 1  is shown; it sends a setpoint driving torque  18  (trqDes) requested by the driver in the upper area of  FIG. 2  over a connection  19  to a node  20 , from which a connection  21  leads to an input  22  of an operator  23 , which performs a greater than/equal to comparison of two values and forwards the result as output quantity true or false. Over a second input  24  of operator  23 , the latter receives as the second value an upper limit value  26  (trqLimHi) calculated in the previous sampling step as the second value for the allowed range of actual driving torque  17  over a connection  25 . A connection  28  goes from an output  27  of operator  23  to an input  29  of IF circuit  30 , which has an output  31  to which is allocated a time constant  32  (TPT1Hi), which is determined from a value  34  (TPT1_Fast) via a connection  33 , and to an output  35 , to which is in turn allocated time constant  32  (TPT1Hi), which is determined from a value  38  (TPT1_Slow) via a connection  37 . Depending on whether the value coming from operator  23  is true or false and/or whether setpoint driving torque  18  is greater than/equal to or less than upper limit  26 , a different value is allocated to time constant  32  (TPT1Hi) by IF circuit  30 . 
     Another connection  39  leads from node  20  to an input  40  of a subtractor  41 , having a second input  42 , to which is allocated, via a connection  43 , upper limit value  26  (trqLimHi) as a subtrahend calculated in the previous sampling step. From an output  45  of subtractor  41 , a connection  46  leads to an input  47  of a divider  48 , to which is allocated at another input  49 , via a connection  50 , a time constant  32  (TPT1Hi) calculated previously as a divisor. From an output  52  of divider  48 , an output quantity is sent via a connection  53  to an element  54 , from which a connection  55  leads to an input  56  of a multiplier  57 , to which is allocated another quantity  60  (dT) at its input  58  via a connection  59 . The value of additional quantity  60  (dT) corresponds to the sampling time (sampling period, time between two sampling steps). 
     A connection  62  leads from an output  61  to an input  63  of an adder  64 , to which is allocated upper limit  26  (trqLimHi) calculated in the previous sampling step (and then stored) at another input  65  via a connection  66  and which outputs upper limit value  26  (trqLimHi) calculated for the present sampling step at an output  68  via connection  69 . The calculation procedure described corresponds to implementation of a time-delay element of the first order as a sampling system; when considered continuously, the following applies to upper limit value  26  (trqLimHi):
 
 TPT 1 Hi·d ( trqLimHi )/ dt+trgLimHi=trqDes.  
 
     Time constant TPT1Hi is selected differently by the IF circuit with positive and negative gradients of trqLimHi, where it holds that:
 
 TPT 1 Hi=TPT 1_Fast if  trqDes≧trqLimHi  
 
 TPT 1 Hi=TPT 1_Slow if  trqDes&lt;trqLimHi.  
 
     With TPT1_Slow&gt;TPT1_Fast, a rapid rise and a slow decline in the upper limit (trqLimHi) are achieved. The lower limit behaves conversely with a rapid decline and a slow rise. Parameterization as a function of the operating state of the drivetrain is advantageous here. 
     The middle part of  FIG. 2  shows a calculation procedure for ascertaining a lower limit  78  (trqLimLo). The calculation procedure equals that of upper limit  26  (trqLimHi), where the elements shown that have the same function are provided with the same reference numerals. 
     The calculation formulas differ in that values  38  (TPT1_Slow) and  34  (TPT1_Fast) of time constant  86  (TPT1Lo) are selected in the opposite way, as mentioned above:
 
 TPT 1 Lo=TPT 1_Slow if  trqDes≧trqLimLo,  
 
 TPT 1 Lo=TPT 1_Fast if  trqDes&lt;trqLimLo,  
 
the part for determining time constant  86  being connected to a node  72 , which has a connection  71  to node  20 , and another connection  91  to a node  92 , from which a connection  93  leads for calculation of lower limit  78  (trqLimLo).
 
     Another connection  125  leads from node  92  to control unit  3 , which is known from  FIG. 1 , and from which a connection  126  leads to internal combustion engine  5 . This connection  126  transmits actual torque  14  of the internal combustion engine via a connection  127  to a node  128 , from which a connection  129  leads to an input  130  of an adder  131 , and a connection  132  leads to an input  133  of a subtractor  134 , and a connection  135  leads to an input  136  of a subtractor  137 , the value for upper limit  26  (trqLimHi) calculated for the present sampling step in the upper area being introduced as the minuend via a connection  139  through another input  138  of subtractor  134 , and the value calculated for lower limit  78  (trqLimLo) for the present sampling step in the middle area of  FIG. 2  being also introduced as the minuend at an input  141  of subtractor  137  via a connection  142 . 
     A connection  145  leads from an output  144  of subtractor  134  to an input  146  of element  147 , which compares two values and forwards the smaller value. A connection  149  leads from an output  148  of subtractor  137  to an input  150  of element  151 , which compares two values and forwards the larger value to an input  154  of element  147  via a connection  153 . Furthermore, the setpoint torque of electric machine  7  is supplied via a connection  155  from control unit  3  to an input  156  of element  151 . Thus, by subtraction of the actual torque of the internal combustion engine from limits  26  and  78 , this yields limits for setpoint torque  16  of electric machine  7 . 
     In addition, a connection  157  leads to electric machine  7 , from which another connection  158  leads to an input  159  of adder  131 , in which the torques of the drive units are added to form actual driving torque  162  available at output  160 . 
       FIG. 3  shows a diagram of the response of the limits ascertained from  FIG. 2  for the allowed range of actual driving torque  162  to a sudden change in setpoint driving torque  18 , the torque being plotted as a function of time (abscissa) on the coordinate. Four curves are plotted in the diagram, one curve representing setpoint driving torque  18  running parallel to the abscissa at a constant level initially, then rising to a higher value almost perpendicular/parallel to the ordinate at a point in time  164  and then again running parallel to the abscissa at a constant value. Another curve  165  represents upper limit  26  and initially runs parallel to setpoint driving torque  18 , then rises steeply after point in time  164 , next asymptotically approaching setpoint driving torque  18 . A third curve  166  representing lower limit  78  for the allowed range of actual driving torque  162  initially runs at the same level as setpoint driving torque  18  and curve  165 , then rises steeply after point in time  164 , but remains definitely below curve  165  and approaches setpoint driving torque  18  much more slowly. Fourth curve  167  representing actual driving torque  162  rises steeply after point in time  164 , but then initially remains below curve  166 , but intersects it thereafter and remains between curves  165  and  166 , likewise asymptotically approaching setpoint driving torque  18 . Thus if setpoint driving torque  18  changes, e.g., when the driver operates the accelerator pedal, initially the upper limit (curve  165 ) and lower limit (curve  166 ) of the allowed actual driving torque range are calculated according to the exemplary embodiment from  FIG. 2 . Actual driving torque  162  initially follows the lower limit (curve  166 ), resulting in a slight, noncritical deviation from the lower limit (curve  166 ) due to the PT1 response in the torque regulation of electric machine  7 . Since actual driving torque  162  is between upper limit  26  and lower limit  78 , i.e., within the allowed range, there is no additional intervention in the torque of electric machine  7 , so the electric power defined by control unit  3  from  FIG. 2  is maintained, which has a positive effect on the energy accumulator. 
     The intervention in the torque of electric machine  7  is represented in a diagram in  FIG. 4 . A setpoint torque  168  defined by control unit  3  from  FIG. 2  and an actual torque  169  of the electric machine are plotted against time. First setpoint torque and actual torque  168 ,  169  run at a constant level  170 . At a point in time  171 , the setpoint torque changes suddenly to a lower level  172 . Actual torque  169  of the electric machine initially increases steeply to a higher level  173  and then drops steeply, to then asymptotically approach setpoint torque  168 . With an increase in setpoint driving torque  18 , setpoint torque  168  of the electric machine defined by control unit  3  from  FIG. 2  drops to a low level, so that the electric machine operates more as a generator. However, in order not to depart from the allowed actual driving torque range, according to the exemplary embodiment in  FIG. 2  the control unit intervenes in the torque of the electric machine so that the delayed torque buildup of the internal combustion engine is compensated. 
       FIG. 5  shows another exemplary embodiment of the present invention, in which the allowed actual driving torque range is defined by a maximum limit and a minimum limit (trqLimGradMax and trqLimGradMin) for the gradient (first derivative) of the characteristic of an actual driving torque  211  (trq). A PT1 response is again assumed.  FIG. 5  shows element  1 , representing the setpoint driving torque (trqDes) (known from  FIG. 1 ) connected to a node  175  via a connection  174 . A connection  176  leads from node  175  to an input  177  of a subtractor  178 , in which actual driving torque (trq) is subtracted from setpoint driving torque (trqDes). A connection  180  leads from an output  179  of subtractor  178  to an input  181  of an element  182  in which allowed changes trqMaxDelta and trqMinDelta for actual driving torque  211  between two sampling steps have been calculated from the limits for the allowed gradient (first derivative) of actual driving torque  211  by multiplication by quantity dT characterizing the sampling time (sampling period, time between two calculation cycles). Limits trqLimGradMax and trqLimGradMin for the allowed gradient (first derivative) of actual driving torque  211  are ascertained in the sense of a PT1 response from the difference between setpoint driving torque (trqDes) and actual driving torque (trq) applied to output  179  of subtractor  178 . Allowed changes trqMaxDelta and trqMinDelta are each sent via two outputs  183  and  184  of element  182  over one connection  185  and  186  each to two inputs  187  and  188  of an element  189 . For example, for an increasing actual driving torque  211  (trq) it holds that:
 
 trqLimGrad Min≦ d ( trq )/ dt≦trqLimGrad Max
 
where:
 
 trqLimGrad Max=( trqDes−trq )/( TPT 1_Fast)
 
 trqLimGrad Min=( trqDes−trq )/( TPT 1_Slow)
 
     From node  175 , another connection  190  leads to control unit  3  known from  FIG. 1 , from which a connection  191  leads to internal combustion engine  5  known from  FIG. 1  and another connection  192  leads to another input  193  of element  189 . A connection  194  leads from internal combustion engine  5  to a node  195 , from which a connection  196  leads to another input  197  of element  189 , and another connection  198  leads to an input  199  of an adder  200 . In element  189 , the change in setpoint torque  16  of electric machine  7  is limited between two samplings, taking into account an actual torque change in internal combustion engine  5  between two samplings via trqMaxDelta and trqMinDelta from element  182 . 
     From an output  201  of element  189 , the limited setpoint torque of electric machine  7  is sent over a connection  202  to electric machine  7 , from which another connection  203  carries the actual torque of electric machine  7  to another input  204  of adder  200 , in which the torques of electric machine  7  and internal combustion engine  5  are added. From an output  205  of adder  200 , a connection  206  leads to a node  207 , from which a connection  208  carries actual driving torque  211  as the subtrahend to another input  209  of subtractor  178  and is situated as the output quantity via a connection  210  at node  207 . 
     Again in this exemplary embodiment, the ratio of the actual torque predefined by control unit  3  to the setpoint torque of the electric machine is as depicted in  FIG. 4 , in that the actual torque initially increases due to the limitation and only then approaches the setpoint torque. Likewise, actual driving torque  211  of the entire drivetrain behaves like actual driving torque  167  depicted in  FIG. 3 . Here again, undershooting is prevented by an additional torque from electric machine  7 . This gradient-based method is suitable in particular in conjunction with a guide shaping for load knock damping. With a corresponding guide shaping, the gradient of actual driving torque  211  is limited in the range of the zero crossing (e.g., in transition from push to pull operation).