Abstract:
Engine speed and/or vehicle velocity limitation apparatus of engine-driven motor vehicles, wherein a controller defines, as a function of the difference between an actual speed value or actual velocity value as controlled variable, on the one hand, and a speed limit value or velocity limit value or a speed limit function or velocity limit function, on the other hand, a torque setpoint for the engine of the motor vehicle as the manipulated variable. As a result, the combustion processes occur at the stoichiometric ratio even during the limiting operation, and the elimination of torque surges results in a considerable increase in drivability for the driver.

Description:
FIELD OF THE INVENTION 
     The present invention relates to an apparatus for speed limitation of engines and/or for velocity limitation of engine-driven motor vehicles, having a controller that regulates the engine speed to an applied maximum permissible speed or regulates it to a speed that corresponds to an applied maximum permissible velocity. 
     RELATED TECHNOLOGY 
     In current production vehicles, speed limitation is accomplished by fuel blanking, i.e. if the predefined maximum permissible speed limit is exceeded, individual cylinders are shut down. The disadvantages of the this type of speed limitation system are that it is impossible to output a defined actual torque to external control units. Since combustion can no longer occur at the stoichiometric ratio when speed limitation has been instituted, emissions values deteriorate. In addition, the shutdown and initiation of injection occurring with such speed limitation systems cause severe torque surges, which result in a severe impairment of drivability. 
     German Patent No. 39 37 846 A1 describes an apparatus for speed limitation of engines having a controller for which, as a function of the difference between an actual speed value as controlled variable and a speed limit value, a torque setpoint (load torque) is defined as the manipulated variable. Also, German Patent No. 43 27 654 A1 and German Patent No. 44 34 022 A1, describe apparatuses for velocity limitation of engine-driven motor vehicles having a controller that correspondingly, as a function of the difference between an actual velocity value as controlled variable and a velocity limit value, defines a torque setpoint for the engine of the motor vehicle as the manipulated variable. These known apparatuses do achieve better drivability as compared to a cylinder shutdown system, but on the one hand disadvantages in terms of emissions values must be accepted, and on the other hand the resulting drivability has still not proven to be adequate. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to create an apparatus for speed limitation and/or velocity limitation that operates more smoothly and with better emissions values than conventional apparatuses, and can be utilized regardless of the type of engine used. 
     The present invention provides an apparatus for speed limitation of engines, having a controller ( 13 ) that, as a function of the difference (n diff ) between an actual speed value (n ist ) as controlled variable and a speed limit value or a speed limit function (n maxeff ), defines a torque setpoint (m vorg ) for the engine as the manipulated variable. The controller ( 13 ) is equipped with means ( 10 - 12 ) for defining the torque setpoint (m vorg ) as a function of the gradient (n grad ) of the controlled variable (n ist ). Means ( 11 ) for constituting a reduction torque (m red ) as a function of the gradient (n grad ) of the controlled variable (n ist ) and of the actual torque value (m ist ) are provided. A subtraction stage ( 12 ), in order to constitute an anticipated torque (m vorh ) from the difference between the reduction torque (m red ) and the actual torque value (m ist ), is in working engagement with the controller ( 13 ) to define the torque setpoint (m vorg ) as a function of the anticipated torque (m vorh ). 
     The present invention also provides an apparatus for velocity limitation of engine-driven motor vehicles, having a controller ( 13 ) that, as a function of the difference between an actual velocity value as controlled variable and a velocity limit value or a velocity limit function, defines a torque setpoint (m vorg ) for the engine of the motor vehicle as the manipulated variable. The controller ( 13 ) is equipped with means ( 10 - 12 ) for defining the torque setpoint (m vorg ) for the engine of the motor vehicle as the manipulated variable. Means ( 11 ) for constituting a reduction torque (m red ) as a function of the gradient (n grad ) of the controlled variable (n ist ) and of the actual torque value (m ist ) are provided. A subtraction stage ( 12 ), in order to constitute an anticipated torque (m vorh ) from the difference between the reduction torque (m red ) and the actual torque value (m ist ), is in working engagement with the controller ( 13 ) to define the torque setpoint (m vorg ) as a function of the anticipated torque (m vorh ). 
     With the torque-based speed limitation system and velocity limitation system according to the present invention, the controller is advantageously equipped with means for defining the torque setpoint as a function of the gradient of the controlled variable. In this context, means for constituting a reduction torque as a function of the gradient of the controlled variable and of the actual torque value, in particular by way of a characteristics diagram, are preferably also provided. A subtraction stage then serves to constitute an anticipated torque from the difference between the reduction torque and the acrual torque value. This is in working engagement with the controller in order to define the torque setpoint as a function of this anticipated torque. Influencing the torque setpoint by way of the gradient of the controlled variable, i.e. the actual torque value and/or actual velocity value, especially by way of the anticipated torque constituted according to the present invention, contributes substantially to the increase in drivability, and allows limitation to occur smoothly. The combustion processes occur at a stoichiometric ratio (lambda=1), so that good emissions values are maintained even while speed is being limited. Torque surges are prevented, which results in a considerable improvement in drivability for the driver of a motor vehicle. 
     Advantageously, a limit function stage is provided in order to constitute the speed limit function if the actual speed value exceeds a maximum continuous speed. This limit function stage preferably possesses a timing element for defining a maximum speed that exceeds the maximum continuous speed for a definable time period; a ramp generator is then provided in order to return the maximum speed to the maximum continuous speed after the definable time period. Allowing the maximum continuous speed to be exceeded briefly in this fashion also prevents torque surges, since it is thereby possible, by avoiding such torque surges, to return smoothly to the maximum continuous speed. This limit function stage thus prevents unpleasant surges even if the maximum continuous speed is exceeded as a result of a sharp rise in torque. 
     A subtraction stage is advantageously provided in order to constitute the difference between the speed limit function or the speed limit value and the actual speed value; this difference can then be conveyed to an input of the controller. 
     In order to avoid unnecessary control operations and to relieve stress on the controller, it is advantageous to provide a logic stage to constitute an anticipated value as a function of the gradient of the controlled variable and of the limit value or the limit function; a first comparison stage activates the controller if the controlled variable exceeds this anticipated variable and/or deactivates it if it falls below. This means that the greater the (positive) gradient of the speed or the velocity, the earlier the controller is activated. Because of this correlation with the gradient, the controller is optimally initiated or activated when such is necessary in order to prevent predefined limit values from being exceeded. 
     The logic stage can also, advantageously, have at least one second comparison stage that deactivates the controller if the controlled variable falls below a fixed value which is below the anticipated value. This ensures reliable shutdown of the controller if the difference between the controlled variable and the limit value has become sufficiently great. 
     A controller configured substantially as a PI controller is principally suitable for the speed limitation system or velocity limitation system. In this context, the torque setpoint constituted as the manipulated variable is provided in particular in order to intervene on devices for controlling the system regulating the delivery of air and/or fuel to the engine; acting on the air delivery system has proven to be particularly favorable. With an intervention of this kind, the combustion operations take place substantially at a stoichiometric ratio (lambda=1). 
     An exemplary embodiment of the present invention is depicted in the drawings and explained in more detail in the description below. In the drawings: 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a block diagram of an apparatus for speed limitation of engines, as an embodiment of the present invention. 
     FIG. 2 shows a more detailed depiction of the limit function stage depicted in FIG.  1 . 
     FIG. 3 shows a signal diagram to explain the manner of operation of the limit function stage. 
     FIG. 4 shows a more detailed depiction of the logic stage depicted in FIG.  1 . 
    
    
     DETAILED DESCRIPTION 
     In the embodiment depicted in FIG. 1, the actual speed value n ist  of an internal combustion engine of a motor vehicle, sensed by way of an ordinary speed sensor, is conveyed to a gradient stage  10  in order to constitute a speed gradient n grad . By way of a characteristics diagram  11 , a reduction torque m red  is then constituted as a function of that speed gradient n grad  and an actual torque value m ist  of the internal combustion engine. The actual torque value m ist  is usually determined by calculation, for example from the air mass flow and the engine speed, or from the delivered fuel quantity and the engine speed. The greater the speed gradient n grad , the greater the reduction torque m red  becomes. Therefore, the more quickly the actual torque value n ist  approaches the limit value, the greater the reduction in the torque must be in order to prevent this speed threshold from being exceeded. 
     In a subsequent subtraction stage  12 , this reduction torque m red  is then subtracted from the actual torque value m ist , yielding an anticipated torque m vorh  that is delivered to a PI controller  13 . This anticipated torque m vorh  therefore influences controller  13  in such a way that the manipulated variable which is output, i.e. the torque setpoint m vorg , depends not only on the system deviation but additionally on the speed gradient n grad . This means that not only the system deviation but also this anticipated torque m vorh  acts on the torque setpoint m vorg  in such a way that it becomes smaller, the greater the speed gradient n grad . 
     A limit function stage  14  serves to ascertain the current limit speed n maxeff  for soft speed limitation. This limit speed n maxeff  is constituted as a function of the maximum continuous speed n dauer , the maximum speed n max , and the actual speed value n ist , as will be explained in further detail with reference to FIGS. 2 and 3. n dauer  and n max  are fixed quantities that are determined individually for each type of internal combustion engine. 
     A downstream subtraction stage  15  constitutes the differential value n diff  between the actual speed value n ist  and the limit speed n maxeff  constituted in limit function stage  14 . This value is conveyed as the controlled variable to controller  13  which, by correspondingly reducing the torque setpoint m vorg , brings this differential value n diff  back toward zero. This means that in the event the maximum continuous speed n dauer  is exceeded, the speed is smoothly brought back to this value of the continuous speed n dauer . This is explained below with reference to FIGS. 2 and 3. 
     Limit function stage  14  is activated only if the actual speed value n ist  exceeds the maximum continuous speed n dauer . This initialization is performed by way of a comparison stage  16 . In a downstream function generator  18 , to which the maximum speed n max  is supplied as a value, the limit function depicted in FIG. 3 is then constituted. After initialization at time t 0 , first the value of the maximum speed n max  for a definable time period t 1  is defined. Then this value is ramped, by way of a ramp generator, back to the value of the maximum continuous speed n dauer . By way of this function for the limit speed n maxeff , the actual speed n ist  is thus, if the maximum speed n dauer  is exceeded, brought in smooth and controlled fashion, by way of a ramp, to this value of the maximum continuous speed n dauer , which is accomplished by controller  13 . Once the continuous speed n dauer  has been reached, the limit speed n maxeff  remains at that value, and cannot return briefly to the value of the maximum speed n max  until its value has fallen below a defined reset value, and controller  13  is no longer feeding through. Only then can another cycle be run through using comparison stage  16 . 
     A logic stage  18  serves to activate (output signal  1 ) and deactivate (output signal  0 ) controller  13  as a function of the speed gradient n grad , the limit speed n maxeff , and the actual speed value n ist . This logic stage  18  is depicted in more detail in FIG.  4  and will be explained below with reference to FIG.  4 . 
     A speed anticipation threshold n vorg  is determined that is dependent on speed gradient. This is constituted in a function stage  19  on the basis of the speed gradient n grad  and the limit speed n maxeff . A subsequent comparison stage  20  checks whether the actual speed value n ist  has reached or exceeded this speed anticipation threshold n vorh . If so, an activation of controller  13  takes place by way of an anticipation bit, via an AND stage  21 . The result of this is that the greater the speed threshold, the earlier controller  13  is activated (i.e. at lower actual speed values). 
     If the actual speed falls below an applicable shutdown threshold n grenz  that lies below the anticipation threshold n vorh , controller  13  is deactivated. This shutdown threshold n grenz  is constituted, as a difference between the limit speed n maxeff  and a fixed value n K , in a subtraction stage  22 . Of course this shutdown threshold n grenz  could also be defined directly as a fixed value. A downstream comparison stage  23  then checks whether the actual speed value n ist  is equal to or greater than this shutdown threshold n grenz . If so, AND stage  21  becomes conductive for signals of comparison stage  20 . Otherwise AND stage  21  is inhibited, and controller  13  is thus shut down or deactivated. 
     This deactivation or direct shutdown of controller  13  can be accomplished without further secondary conditions, but further conditions can also be met for deactivation; for example, deactivation can be completed only if the controller torque is maintaining no further feedthrough. In the case of a shutdown with multiple secondary conditions, several such lines with comparison stages can be present so as to effect stepwise deactivation and activation of controller  13 . 
     Controller  13 , presented in FIG. 1 as a PI controller, can in principle also exhibit a different controller characteristic, e.g. P, I, PID, or the like. Individual controller sections can also be activated or deactivated as a function of controller parameters. 
     The exemplary embodiment described with reference to FIGS. 1 through 4 concerns an apparatus for speed limitation of engines. An apparatus for velocity limitation of engine-driven motor vehicles can also, however, be correspondingly implemented, in which case speed variables are to be replaced respectively by velocity variables. What is essential in this context is that in the case of velocity limitation as well, controller  13  defines a torque setpoint for the engine of the motor vehicle as the manipulated variable. A combined apparatus for speed limitation and velocity limitation can also be correspondingly implemented, in which case precedence is to be given, in the event of conflicting parameters, to the smaller defined torque m vorg . 
     The torque setpoint m vorg  constituted by the controller as the manipulated variable acts, for example, on an actuating apparatus for the throttle valve of an internal combustion engine, i.e. acts on the air delivery system of the internal combustion engine, which represents a preferred solution. As an alternative to this, it would also be possible to act on the fuel delivery system, which may represent the most sensible solution in the case of a diesel engine. A combined intervention is also possible. 
     The present invention is not limited, however, to the speed limitation of internal combustion engines or to the velocity limitation of combustion-powered motor vehicle, but can also be applied to other types of engines, for example electric motors. In the case of an electric motor, the torque setpoint n vorg  acts as manipulated variable, for example via an electronic control system, on the current and/or voltage being supplied to the electric motor.