Method for operating a drive with an internal combustion engine and an eletric machine

#The invention relates to a method for operating a drive with an internal combustion engine and an electric machine according to the preamble of patent claim 1; such a method is known, for example, from DE 197 52 661 A1.

#DE 197 52 661 A1 describes an on-board power system for a motor vehicle with a combined drive by means of an electric machine and an internal combustion engine which act on the same drive train. On the one hand, the electric machine supports, for example, the starting process of the internal combustion engine as a motor and, on the other hand, outputs charge power to a vehicle operating battery, and possibly to an additional short-term starting capacitor, as a generator. In order to be able to operate with the highest possible efficiency and thus with the lowest possible loading of the energy stores or energy supply means in the generator operating mode, the electric losses both in the converter and in the asynchronous machine which is provided for the starter-generator are advantageously kept low by virtue of the fact that, in a field-oriented control, the internal torque of the asynchronous machine of the start-generator is set according to the principle of controlling or regulating the rotor flow with optimum loss by correspondingly adapting the magnetizing current as a function of an active current which is determined in accordance with the respectively required drive torque.

#The object of the present invention is to use simple means to be able to reduce further the environmental stress of a combined drive with mixed electric motor/internal combustion engine, in particular of a motor vehicle with a corresponding hybrid drive.

#The FIGURE shows, on the basis of the vehicle on-board power system known from DE 197 52 661 A1, a drive for a motor vehicle hybrid drive with an internal combustion engine VB and an electric machine in the form of an asynchronous machine as a starter-generator SG with field-oriented control.

#The vehicle on-board power system illustrated in the FIGURE can basically be divided into a first vehicle on-board power system component U1 with a voltage level of, for example, 12 volts corresponding to the voltage of the battery B, a second vehicle on-board power system component U2 for supplying high-power loads with a voltage level of, for example, 180 volts, and a third vehicle on-board power system component U3 with a voltage level of for example 400 volts for charging a starting capacity K for starting an internal combustion engine VB using a starter-generator SG which can be fed via a converter U; the third vehicle on-board power system component U3 is also used in the generator operating mode of the starter-generator SG to adapt its output voltage of approximately 180 volts, set by means of the converter U, to the voltage level of the second vehicle on-board power system component U2. A control component is used for power-optimum operation of the asynchronous machine, which is provided as a starter-generator SG, preferably with a squirrel-cage rotor.

#In the course of the preparation of the starting of the internal combustion engine VB by means of the starter-generator SG, which then operates as an asynchronous motor, for example after the ignition key is activated, a starter

#capacitor K in the third on-board power system component U3 is charged to a voltage of approximately 400 volts via the connection VI using step-up controller (DC/DC converter) HSST. Switches S1 and S2 in the connection V2 or V3, respectively, are opened during this charging phase of the starting capacitor K. The connection V1 is blocked in the opposite direction to the battery B by means of a diode D1 in the connection V1.