Abstract:
An electric machine ( 10 ) coupled to an internal combustion engine in a motor vehicle is proposed, a control unit ( 11 ) being provided for specifying an optimal efficiency operating state (Bw) or for specifying a dynamically optimal operating state (Bd) for the electric machine ( 10 ). Switchover means are used for switching over the usually specified optimal efficiency operating state to the dynamically optimal operating state (Bd) before operating procedures in the motor vehicle which require a rapid torque setting.

Description:
BACKGROUND INFORMATION  
         [0001]    In today&#39;s motor vehicles, the driving internal combustion engine is usually provided with a starter motor, and in addition, it drives a generator via a belt pulley. In future vehicle concepts, increasingly powerful electrical machines are installed which replace both the present generator and the conventional starter motor. Besides the internal combustion engine, if these electrical machines also contribute to driving the motor vehicle, as a rule, one speaks of hybrid vehicles. Among hybrid vehicles, parallel hybrids are known, for example, in which, in addition to the internal combustion engine, one or more electrical machines are integrated into the power train. Power-splitting hybrid concepts are also known, in which two electrical machines are mounted in such a way that the mechanical power originating from the internal combustion engine contributes both directly and indirectly to the driving power at the wheels, via the two electrical machines.  
           [0002]    Such electrical machines could, in principle, be operated in different types of operation and operating conditions, such as in a dynamically optimal operating state or in an optimal efficiency operating state. The dynamically optimal operating state stands out in that an engine torque build-up can take place very rapidly in response to a corresponding requirement, for instance, having a time factor of 5-10 ms. What is disadvantageous about the dynamically optimal operating state is the poor efficiency, since thereby the flux-forming current component is generally held at its nominal value, that is, independent of a torque requirement. In the optimal efficiency operating state there is a favorable efficiency, but on the other hand one may expect a torque-setting time that is longer by a factor of 10.  
         SUMMARY OF THE INVENTION  
         [0003]    The system according to the present invention has the advantage that, in the normal case, the electrical machine or the electrical machines are driven in optimal efficiency operation at favorable efficiency. Only when a rapid torque setting becomes necessary, because of corresponding processes in the motor vehicle, is there an automatic switchover to the dynamically optimal operating state, so that when needed, a rapid torque setting or a rapid torque build-up is ensured. Since, all in all, these processes occupy only a small fraction of the time, at least one electrical machine works here at good efficiency overall. In this context, the changeover takes place in such a timely fashion that it is concluded by the time the rapid torque setting is actually required.  
           [0004]    Control signals specifying switchover before gearshift processes and/or starting processes of the internal combustion engine and/or acceleration processes of the internal combustion engine are preferably able to be supplied to a switchover control input of the switchover means. This switchover control input may, of course, also be designed, for example, as a bus connection. In this context, a central vehicle control and/or a transmission control device and/or a switching device able to be operated before the starting process or the acceleration process is expediently designed to form the control signals specifying the switchover.  
           [0005]    In an advantageous manner, means for switchover to the dynamically optimal operating state for a specified time or until the close of the respective operating process, which requires a rapid torque setting, is also provided.  
           [0006]    In order to be able to set the operating states in each case, the control unit is designed to specify the flux-forming current and the torque-forming current for the electrical machine.  
           [0007]    For this purpose, the control unit has means for the specification of a pair of values for the flux-forming and the torque-forming current as a function of the respective torque requirement in the functionally optimal operating state, and for the specification of nominal values for the flux-forming current and a torque-forming current being a function of the respective torque requirement in the dynamically optimal operating state.  
           [0008]    In one advantageous embodiment, the electrical machine is connected between the internal combustion engine and an automatic vehicle transmission, a coupling being provided at least between the electrical machine and the internal combustion engine. In this manner, the electrical machine is able to effectively support the switching processes and speed them up.  
           [0009]    The electrical machine, in an advantageous manner, also forms a generator or a motor, depending on the respective requirement or operating state. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    [0010]FIG. 1 shows a schematic representation of the means for controlling the electrical machine.  
         [0011]    [0011]FIG. 2 shows an exemplary embodiment of an electrical machine connected between an internal combustion engine and an automatic transmission.  
         [0012]    [0012]FIG. 3 shows a signal diagram for explaining a switching process of the automatic transmission supported by the electrical machine. 
     
    
     DETAILED DESCRIPTION  
       [0013]    The schematic block diagram as in FIG. 1 is intended to explain the dynamically optimal operating state and the optimal efficiency operating state of an electrical machine  10 . The latter is connected to an electronic control unit  11 , which, in turn, is connected to a current source or sink  12  via a power cable. Furthermore, electronic control unit  11  is connected to a central vehicle control  13 , such as via a CAN bus. Torque-forming current ISQ and flux-forming current ISD are specified for electrical machine  10  by electronic control unit  11 . In this context, magnetizing current Iμ for electrical machine  10  is the flux-forming current ISD delayed by the rotor time constant (ca 100 to 150 ms). The torque equation of an asynchronous motor used, for example, as electric machine  10  is:  
         
       M=K×ISQ×Iμ.  
     
         [0014]    In the dynamically optimal operating state, the flux-forming current ISD, and thus Iμ, is fixed to its nominal value and held constant independently of a torque requirement. Torque changes take place via a change in torque-forming current ISQ. This goes very fast, and time constants are able to be achieved which are smaller than the rotor time constants approximately by a factor of 10.  
         [0015]    In the optimal efficiency operating state, on the other hand, one may expect a longer torque setting time or time constant, which is approximately equivalent to the rotor time constant. In this case, for each torque requirement a value pair ISD and ISQ is specified which results in the best efficiency for the desired torque. This may be done, for example, via a characteristics map or by making calculations using appropriate computational rules. By comparison to the dynamically optimal operating state, the overall efficiency is clearly better, particularly in the partial load operation of the electric machine.  
         [0016]    According to FIG. 1, for example, central vehicle control  13  specifies whether electric machine  10  is to operate in dynamically optimal or the optimal efficiency operation. The appropriate control command may be supplied to a switchover control input of electrical control unit  11  or to a corresponding bus interface.  
         [0017]    Electrical machine  10  may be connected to the internal combustion engine of a motor vehicle directly or or via a coupling, and, in this context, is used both as a starter motor and a current generator. The corresponding switchover from motor operation to generator operation may also be carried out by electronic control unit  11 . The coupling may, for example, be disengaged after the starting process, unless, as in certain cases, electric machine  10  is supposed to contribute to propulsion, such as during acceleration.  
         [0018]    Instead of one single electric machine  10 , several electric machines may, of course, also be connected to the internal combustion engine.  
         [0019]    As a rule, electric machine  10  is operated at optimal efficiency, in order to achieve as low as possible a use of fuel or as high as possible an efficiency. To be sure, there are vehicle conditions in which a rapid torque setting is of great advantage. An example of this is the starting procedure for the internal combustion engine. In this context, electric machine  10  is transferred into the dynamically optimal operating state even before the activation of the starting procedure. This switchover may be made, for example, by operating the ignition key or even by a door switch when the vehicle door is opened. After the starting process has taken place, and successfully so, one then carries out again a switchover to an operating state of optimal efficiency. This may be done either depending on rotational speed or controlled by time.  
         [0020]    A further example, in which the switchover to a dynamically optimal operating state is of advantage is explained below in the light of FIG. 2. According to FIG. 2, an internal combustion engine  14  is connected via a first coupling  15  to electric machine  10 , which is further connected via a second coupling  16  to an automatic or automated standard transmission  17 . Such an arrangement is designated as a parallel hybrid arrangement, second coupling  16  being able to be omitted too, in a simpler execution. Internal combustion engine  14  is controlled by an engine control unit  18 , electric machine  10  is controlled by electrical control unit  11  and standard transmission  17  is controlled by a transmission control device  19 . In this context, central vehicle control  13  coordinates the functions of engine control unit  18 , electronic control unit  11  and transmission control unit  19 . Transmission control unit  19  is additionally used for operating couplings  15 ,  16 .  
         [0021]    During a shifting procedure of standard transmission  17 , electric machine  10  may, or when second coupling  16  is omitted, must contribute to active synchronization by inertia that is great in comparison with the transmission input shaft. In order for the shifting process to proceed as quickly as possible, and so that the interruption of traction is held to as short as possible, electric machine  10  ought to be in dynamically optimal operation even before the shifting procedure. A rapid torque setting during the active synchronization also guarantees a better regulating behavior, particularly even when electric machine  10  or an additional, further electric machine is operated at regulated rotational speed.  
         [0022]    After the driver, in an automated transmission  17 , or the shifting electronics in a fully automatic transmission, initiates shifting, the switchover is brought into dynamically optimal operation by a corresponding signal at the switchover input of electronic control unit  11 . The active synchronization takes place at the same time.  
         [0023]    [0023]FIG. 3 shows the processes during the shifting procedure during an automatically initiated shifting procedure. The shifting command, by which the setpoint value for the currently present gear G S x is replaced by the setpoint value for the next-highest gear G S x+1 (the exemplary embodiment shows a shift-up process), is used at the same time for the switchover from the efficiency optimal operating state Bw into the dynamically optimal operating state Bd. The shifting procedure is initiated only after that. Because of the rapid response behavior of electric machine  10 , the time for the active synchronization may be kept short. Besides, one has to expect a rapid adjustment of setpoint values, which is of advantage in case of a possible synchronization without synchronizer rings in the transmission. After the transmission initial rotational speed n g  has approached or come closer to the rotational speed of the internal combustion engine n b  with the support of electric machine  10 , the actual shifting process takes place, in which the actual value of transmission shifting step Gsubix changes to the actual value of the next-highest transmission step Gsubix+1. After the conclusion of the shifting process, which takes up time t1, there is a reverse switchover of the operating state of the electric machine from the dynamically optimal operating state Bd to efficiency optimal operating state Bw.  
         [0024]    The switchover method of the operating states during shifting processes may also be used correspondingly for Dual-E transmissions.