Abstract:
A method for operating a motor vehicle having a hybrid drive, including a combustion engine having an engine management and at least one electro machine having a control unit, which is at least intermittently operated in an rpm-regulated manner and which is able to be in operative connection with a drive shaft of the combustion engine. For the closed-loop speed control of the electro machine, its torque is influenced by its rotational speed or a signal derived therefrom.

Description:
FIELD OF THE INVENTION 
     The present invention is based on a method for operating a hybrid drive, and on a motor vehicle having a hybrid drive. 
     BACKGROUND INFORMATION 
     Motor vehicles having a hybrid drive are discussed in the German patent document DE 10241018 A1, for example. Referred to as hybrid drives are drives in which at least one electro machine is provided in addition to a conventional internal combustion engine; depending on the design of a parallel hybrid drive, this electro machine can be coupled or is fixedly coupled to a drive shaft in the drive train of the motor vehicle and can operate both as generator or as motor. In generator operation, the electro machine is driven by the internal combustion engine and is thus able to generate electric current to supply electric loads of the motor vehicle. In motor operation, current is supplied from the vehicle battery in order to convert this current into driving energy for the motor vehicle or into starter energy for the internal combustion engine. Apart from the vehicle battery as energy store, a flywheel or some other store for kinetic energy may be provided as well, by which kinetic energy released during braking, for example, is storable and can be released via the electro machine to the loads in the vehicle electrical system of the motor vehicle or later to its drive train. 
     An electric driving operation requires a closed-loop speed control of the electro machine, especially in a number of cases. For an automatic transmission having an open mechanical lockup clutch, and for the oil-pressure supply of a conventional automatic transmission, an input speed of &gt;0 is required, and in electrical driving operation, even for a stationary vehicle, a rotational speed of the electro machine of &gt;0 is therefore required. With an automatic transmission and an open mechanical lockup clutch, the drive-away behavior of a conventional motor vehicle in a torque-controlled operation of the electro machine is representable only inadequately. The driver is expecting a crawl torque when disengaging the brake. In the case of an open mechanical lockup clutch, this requires an electro machine speed of &gt;0, even if the vehicle is at a standstill. To ensure a behavior that corresponds to the standing-start behavior of the combustion engine out of idle speed control of the internal combustion engine, the electro machine must be operated in an rpm-controlled manner. In the case of a hybrid vehicle having manual gear-shifting, the drive-away behavior during electric operation should not differ from the behavior with a running internal combustion engine. The driver is used to a drive-away behavior against an rpm-controlled power unit, using the starting clutch. A drive-away in a torque-controlled operation of the electro machine, starting from a rotational speed of 0, i.e., with a starting clutch that is not depressed and with the gear engaged, is unfamiliar to the driver and should be avoided. 
     The hybrid operation likewise requires a closed-loop speed control of the electro machine. For future diagnostic and monitoring functions, the electro machine drags the internal combustion engine to a specifiable rotational speed, for example in a drag torque adaptation in no-load running, the internal combustion engine being operated using deceleration fuel cutoff. If corresponding functions are implemented during no-load running, then the electro machine must take over the idle speed control of the internal combustion engine. Depending on the operating state of the vehicle, it will be necessary to operate the internal combustion engine and the electro machine jointly or separately in an rpm-regulated manner; if a torque is requested, for example by the actuation of the driving pedal, a steady transition into the torque-controlled operation must take place. 
     SUMMARY OF THE INVENTION 
     A method is provided for operating a motor vehicle having a hybrid drive, including an internal combustion engine, which has an engine control and at least one electro machine having a control unit, the electro machine being at least intermittently operated in an rpm-regulated manner and able to be in operative connection with a drive shaft of the internal combustion engine. To regulate the rotational speed of the electro machine, its torque is influenced by its rotational speed or a signal derived therefrom. If a torque is requested, for instance by the driver through the actuation of the driving pedal, a continuous transition from the rpm-regulated to the torque-controlled range takes place. In an advantageous manner, the exemplary embodiments and/or exemplary methods of the present invention is able to be used in cases of electric driving and hybrid driving. In electric driving, an interrupting clutch is open, the internal combustion engine is decoupled, and the electro machine is driving the drive shaft. The rotational speed of the electro machine (oil-pressure supply for a conventional automatic transmission, etc.) is regulated. During hybrid driving, the internal combustion engine and the electro machine are active, and the interrupting clutch is closed. The joint rotational speed of internal combustion engine and electro machine is regulated by the electro machine. 
     In one advantageous method step, the closed-loop speed control is divided into a fast component, e.g., a proportional component, and a slow component, e.g., an integral-action component, the proportional component being calculated in the control unit of the electro machine, and the integral-action component being calculated in a control unit in which a torque path is calculated, and/or in which torque requests, e.g., from the driving pedal or the vehicle speed controller, are read in and/or calculated. Most of the signals required for the transition from rpm-regulated to torque-controlled operation are available there. The calculation of the integral-action component may be implemented in the engine control unit. Since the proportional component is calculated in the control unit of the electro machine, a limitation of the effect of the controller by signal propagation delays between different control units is able to be reduced. High control performance or high dynamics of the control is achievable. 
     In an advantageous manner, the proportional component is able to respond to deviations between an actual speed and a setpoint speed in a highly dynamic manner, while the integral-action component controls a transition from rpm-regulated operation to a torque-controlled operation of the electro machine. In addition, the integral-action component may be used to compensate for inaccuracies in the closed-loop control system. 
     In one advantageous method step, the proportional component is limited to a maximum value and a minimum value, the minimum value resulting from the negative value of the integral-action component. 
     The integral-action component and a requested setpoint torque are advantageously added to the limited proportional component. 
     In an advantageous manner, if a torque is requested, the integral-action component is frozen, and the setpoint torque is increased in accordance with the requested torque. When the setpoint torque is increased, the rotational speed of the electro machine rises. 
     With a rising setpoint torque, a falling, negative proportional component is able to compensate the frozen integral-action component as the deviation of the rotational speed from a rotational speed setpoint value increases. An overcompensation of the integral-action component is avoided due to the limitation of the proportional component to the negative value of the integral-action component. 
     As soon as the rotational speed exceeds a rotational-speed threshold above the setpoint value of the rotational speed, a torque-controlled operation automatically results in an advantageous manner. 
     A motor vehicle having a hybrid drive is provided, which includes an internal combustion engine having an engine control unit and at least one electro machine, which is at least intermittently rpm-controlled and which is able to be in operative connection with a drive shaft of the internal combustion engine; a controller having a fast component, e.g., a proportional component, and a slow component, e.g., an integral-action component, is provided for the closed-loop speed control, the fast component and the slow component being accommodated in different control units. Because of the hardware distribution, high control performance is able to be achieved. 
     In one advantageous development, the integral-action component is integrated in the control unit, which may be in the engine control, in which a torque path is calculated and/or in which torque requests are read in and/or calculated. Most of the information necessary for a torque-controlled operation is available in the control unit in which the integral-action component is calculated. 
     In one advantageous development, the proportional component is integrated in the control unit of the electro machine. This hardware partitioning (which may be used) results in a small interface width between the control units, and in high control performance or high dynamics of the control. 
     Additional specific embodiments, aspects and advantages of the exemplary embodiments and/or exemplary methods of the present invention also derive, independently of their combination in the claims and without limiting the universality, from an exemplary embodiment of the present invention presented below with reference to the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1   a  shows a schematic of an exemplary motor vehicle having a hybrid drive. 
         FIG. 1   b  shows one example with a decoupled combustion engine during electric driving. 
         FIG. 2  shows a graphic representation of a signal-flow diagram for speed-controller coordination of a hybrid drive. 
     
    
    
     DETAILED DESCRIPTION 
     The hybrid drive of an exemplary motor vehicle, shown in  FIG. 1   a  by way of example, as usual includes a combustion engine  10 , whose crankshaft  12  is able to be coupled to driven shaft  20  of an electro machine  22  of the motor vehicle via two gear wheels  14 ,  16  and a clutch  18  acting as interrupting clutch, in particular. By way of example,  FIG. 1   b  shows a hybrid drive for electric driving using combustion engine  10  decoupled from electro machine  22 , i.e., with an open clutch  18 . The output for the remaining drive train (starting clutch  66 , gearing  68 , drive wheels) takes place at driven shaft  20  of electro machine  22 . 
     Electro machine  22  has a control unit  24  and is connected via this control unit  24  to a battery  26  of the motor vehicle, which supplies direct current to a multitude of loads  28 ,  30 ,  32  etc. in a vehicle electrical system  34 . Loads  28 ,  30 ,  32  may encompass all power units of the motor vehicle that are operated by current, such as the rear-window defroster, the radio, the glow plug, and the individual lights of the lighting system. Furthermore, control unit  24  is connected to, for example, an angular-position sensor  36  for determining the rotational speed of crankshaft  12 . In addition, control unit  24  is connected to a sensor (not shown further), which records the angle of rotation of driven shaft  20  of electro machine  22 . 
     Electro machine  22  is used, for example, as starter generator for combustion engine  10 . Upon each start of the motor vehicle, it is first brought to a specified rotational speed by a current supply from battery  26 , whereupon clutch  18  is closed and combustion engine  10  is started by electro machine  22  in a torque-controlled or rpm-regulated manner. As soon as combustion engine  10  has reached a specified idling speed, control unit  24  infers the starting end on the basis of the signals from angular-position sensor  36 . Afterwards, combustion engine  10  is able to be operated with the aid of electro machine  22  and control unit  24 , in an rpm-regulated manner, for example, electro machine  22  ensuring that the specified idling speed is maintained. 
     Control unit  24  of electro machine  22  is equipped with a computer  38 , to which a central on-board computer  40  of the motor vehicle transmits the on-position of individual loads  28 ,  30 ,  32  of vehicle electrical system  34 . In addition, computer  38  is connected to a battery controller  44 , which determines the instantaneous terminal voltage and the instantaneous charge state of battery  26  and, if necessary, ensures recharging of battery  26 , for example when the charge state drops below 70%. 
     Combustion engine  10 , designed as diesel engine, for example, has an engine management  48 , which is in connection with control unit  24  of electro machine  22 , as can be gathered from the signal-flow diagram from  FIG. 2  for the transition from rpm-regulated operation of electro machine  22  to torque-controlled operation. Identical elements are provided with the same reference symbols. In engine management device  48 , the torque path is calculated, and a datum MW, which indicates a desired torque, such as from the driving pedal or the vehicle speed controller, is read in and/or calculated. 
     Engine speed n ist  of electro machine  22  is regulated with the aid of a proportional-integral controller, whose slow integral-action component M I  is calculated in an integral-action controller  50  in engine management device  48  of combustion engine  10 , and whose fast proportional component M p  is calculated in a proportional controller  52  of control unit  24  of electro machine  22 . The proportional-integral controller is thus partitioned in its hardware and distributed to different control devices. 
     Integral-action controller  50  receives a torque request MW and, as input, a setpoint value n soll  of the rotational speed, and outputs an integral-action component M I . 
     Proportional controller  52  likewise receives setpoint speed n soll  as input, as well as a controller coefficient K p , and outputs proportional component M p . Proportional component M p  responds very dynamically to deviations of an instantaneous speed n ist  from a setpoint speed n soll . Proportional component M p  is limited to a maximum value M pmax  and a minimum value M pmin  using a limiter  54 , minimum value M pmin  resulting from the negative value of integral-action component M I , which is picked off at the output of integral-action controller  50  and provided with an inverted operational sign in element  56 . Integral-action component M I  and requested setpoint torque M soll  are added to limited output value M pG  of proportional controller  52 . 
     In the absence of a torque request, i.e., without actuation of the driving pedal or the vehicle speed controller, setpoint torque M soll  is negative. With an active closed-loop speed control of electro machine  22 , a positive integral-action component M I  comes about, which compensates negative M soll . 
     If a torque is requested in that, for example, the driver actuates the driving pedal, proportional component M I  at the output of integral-action controller  50  is frozen. Setpoint torque M soll  increases in accordance with the requested torque, for instance given further actuation of the driving pedal. 
     Due to increased setpoint torque M soll , speed n ist  of electro machine  22  rises. A falling, negative proportional component M p  is the result, which compensates frozen integral-action component M I  as the deviation between rotational speed n ist  and rotational speed setpoint value n soll  increases. Since proportional component M p  is limited to the negative value of integral-action component M I , an overcompensation is avoided. If rotational speed n ist  lies above rotational speed setpoint value n soll  by a specific difference, then the closed-loop speed control is completely detached, automatically resulting in a torque-controlled operation in which M EIM -M soll  applies. Integral-action component M I  therefore controls a transition from rpm-regulated operation to a torque-controlled operation of electro machine  22 . Variable M EIM  is forwarded to electro machine  22 , from whose output rotational speed n ist  is returned to integral-action controller  50  and proportional controller  52 . 
     Controller coefficient K p  of proportional controller  52 , rotational speed setpoint value n soll , and the parameters of the proportional limitation in limiter  54  are generated in engine management  48  of combustion engine  10  and thus may be influenced and coordinated by the vehicle control.