Method for controlling an electric machine for driving a motor vehicle, and motor vehicle

Abstract

A method for controlling an electric machine for driving a motor vehicle. A flux density of at least one magnetic field generated in the electric machine is increased when an announcement signal is present that announces an upcoming acceleration command by the driver, and when a confirmation signal is present that confirms the announced acceleration command, the electric machine is controlled in such a way that the speed and/or torque thereof increases.

Claims

1. A method for controlling an electric machine for driving a motor vehicle, comprising: increasing a flux density of at least one magnetic field generated in the electric machine when an announcement signal that announces an upcoming acceleration command by the driver is present, and when a confirmation signal that confirms the announced acceleration command is present, the electric machine is controlled in such a way that the rotational speed and/or the torque thereof increases, wherein an announcement signal is used that is generated when an operating element that does not correspond to a driving actuation device is actuated, and/or wherein an announcement signal is used that is generated by evaluation of information describing the surroundings of the motor vehicle in the direction of travel.

2. The method according to claim 1, wherein the electric machine has a stator with a plurality of stator windings for generating a stator field as a magnetic field, wherein the stator windings are supplied with current to increase the flux density of the stator field.

3. The method according to claim 1, wherein the electric machine has a rotor with at least one exciter winding for the generation of an exciter field as a magnetic field, wherein the at least one exciter winding is supplied with current to increase the flux density of the exciter field.

4. The method according to claim 1, wherein a confirmation signal is used that is generated when a driving actuation device of the motor vehicle is actuated.

5. The method according to claim 1, wherein an additional announcement signal is used that is generated when a braking actuation device is released and/or by evaluation of sensor data of a proximity sensor measuring an approach of the driver to a driving actuation device.

6. The method according to claim 1, wherein, when the motor vehicle is at a standstill, an additional announcement signal is used that is generated when a driving actuation device is actuated together with a braking actuation device, wherein, in the presence of said additional announcement signal, a confirmation signal is used that is generated when the braking actuation device is released.

7. The method according to claim 1, wherein the information about the surroundings describes a cancellation or an increase of a speed limit and/or a passing of a crest of a curve traveled by the motor vehicle and/or a light signal of a set of traffic signals that gives permission to drive or provides notice of the giving or termination of permission to drive.

8. The method according to claim 1, wherein, after the presence of the announcement signal, if a predetermined time span has elapsed and a confirmation signal is absent, the flux density is reduced.

9. A motor vehicle, comprising an electric machine for driving the motor vehicle and a control device, wherein the electric machine can be controlled by the control device in accordance with a method according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further details and advantages of the invention ensue from the exemplary embodiments described below as well as on the basis of the drawings. Shown herein are:

(2) FIG. 1 a schematic sketch of a motor vehicle according to the invention; and

(3) FIG. 2 a flow chart of a method according to the invention for controlling an electric machine for driving the motor vehicle shown in FIG. 1.

DETAILED DESCRIPTION

(4) FIG. 1 shows a schematic sketch of a motor vehicle 1, comprising an electric machine 2 for driving the motor vehicle 1, a plurality of wheels 3, to which the torque of the electric machine 2 is transmitted, a control device 4 that controls the electric machine 2, and a databus 5, to which the control device 4 has access.

(5) The motor vehicle 1 has, in addition, a driving actuation device 6 in the form of an accelerator pedal with a proximity sensor 7, which measures an approach of a foot of a driver to the driving actuation device 6 and generates sensor data that describe said approach. Additionally provided is a first braking actuation device 8 in the form of a brake pedal, which acts on an operating brake unit of the motor vehicle 1, as well as a second braking actuation device 9 in the form of a hand lever, which acts on a parking brake of the motor vehicle 1. Via the operating element 10, which is designed as a touch-controlled element or as a possible input at a human-machine interface, the driver can activate a sport mode of the motor vehicle 1, in which, among other things, also a harder or harsher chassis adjustment is specified. Furthermore, the motor vehicle 1 has a driving dynamics regulation device 11, which implements the function of an electronic stability program (ESP) and comprises a large number of sensors for the determination of driving parameters, such as the yaw rate or a steering lock angle. Moreover, a navigation device 12 is provided, which provides topographical data on the surroundings of the motor vehicle 1. Arranged at the front end of the motor vehicle are, furthermore, a camera 13 and another environmental sensor 14 in the form of, for example, a radar sensor, an ultrasound sensor, or a laser sensor, which detects the surroundings of the motor vehicle in the direction of travel. By way of example, a traffic signal 15 as well as a set of traffic lights 16 are shown, which can be situated in the surroundings of the motor vehicle 1. Via a communication device 17 of the motor vehicle, the motor vehicle 1 receives, in addition, information about the operating state of the set of traffic lights 16 via motor vehicle-to-infrastructure communication. The aforementioned components each have a communication link to the bus system 5 and supply to it data signals for the control device 4.

(6) The electric machine 2 is designed as an asynchronous machine and comprises a stator 18 with a plurality of stator windings 19 as well as rotor 20 in the form of a squirrel cage rotor. The stator windings 20 generate a magnetic field in the form of a stator field, the flux density of which can be varied depending on a control by the control device 4. The control device 4 has, in addition, a memory unit 21 and a timer 22 and controls the electric machine 2 as described below.

(7) FIG. 2 is a flow chart of a method for controlling the electric machine 2 for driving the motor vehicle 1.

(8) In a step S1, the electric machine 2 is found in a first operating state, in which the stator windings 19 are supplied with current at only very low power, because the motor vehicle 1 is at a standstill or is driving in coasting operation. The method is then aimed at initiating the acceleration operation as rapidly as possible when there is an acceleration command of the driver, that is, without or with only very short latency times, which are required for the building up of the stator field generated by the stator windings 19.

(9) For this purpose, in a step S2, it is continuously checked whether an announcement signal announcing an acceleration command of the driver is present. For this purpose, the data signals are recorded and evaluated on the bus system 5, wherein, in the memory unit 21, certain characteristics of the data signals that are to be evaluated as announcement signals are on file. The announcement signals used are defined here in such a way that, when they are present, it can be concluded that an imminent acceleration command of the driver is present.

(10) On the one hand, it can be assumed that the driver wants to accelerate when he releases one of the braking actuation devices 8, 9 and actuates the operating element 8 in order to shift to the sport mode or when the proximity sensor 7 generates sensor data that indicate an approach of the foot of the driver to the driving actuation device 6. Moreover, the control device 4 also evaluates certain information about the surroundings, which is generated by the driving dynamics regulation device 11, the camera 13, the additional environmental sensor 14, or the communication device 17, as control signals.

(11) In this way, the detection of a cancellation or an increase of a speed limit by the traffic light 15 is evaluated as an announcement signal, because, in this case, it can be anticipated that the driver wants to accelerate the motor vehicle 1. In analogy to this, when permission to drive is given or when notice of the giving or termination of permission to drive is provided by a traffic light of the set of traffic lights 16, such an imminent acceleration command is assumed. This situation exists, for example, when the traffic light (depending on the sequence of lights dictated by traffic law regulations) changes from red to green, from red to yellow, from red to red-yellow, from yellow to green, or from red-yellow to green. It is likewise provided that, when a termination of permission to drive is detected, that is, when there is a change from green to yellow or from green to green-yellow, an announcement signal is evaluated, because, in this case, the driver wishes to accelerate in the near term in order to still legally pass the set of traffic lights 16 before permission to drive is cancelled. When the set of traffic lights 16 is appropriately equipped, the respective signal state can also be transmitted and correspondingly evaluated via the communication device 17 by way of motor vehicle-to infrastructure-communication.

(12) It is further provided that, in the case of information about the surroundings that describes passing the crest of a curve traveled by the motor vehicle 1, an announcement signal is generated. For this purpose, the steering angle and the yaw rate of the motor vehicle 1, which are recorded by the driving dynamics device 11, and topographical data on the curve course of the navigation device 17 are evaluated.

(13) Another announcement signal is generated, in addition, when the motor vehicle is at a standstill and, at the same time, the driving actuation device 7 and the first braking actuation device 8 are actuated. Such an actuation of the accelerator pedal and the brake pedal corresponds to a launch control function of classical motor vehicles with an internal combustion engine, for which the internal combustion engine is brought to a high speed when the starting clutch is disengaged in order to generate a starting acceleration that is as high as possible.

(14) If none of the aforementioned announcement signals are present, then step S2 is repeated cyclically. In contrast, once an announcement signal is present, the method is continued in a step S3 and the electric machine 2 is switched to a second operating state. In this case, the electric machine 2 is controlled to increase the flux density of the stator field of the stator 18, wherein the stator windings 19 are supplied with current at a high power. Therefore, through pre-magnetization, a strong rotating field is built up within the stator 18 in order to make possible a rapid acceleration of the motor vehicle 1 when there is an upcoming acceleration command of the driver. This can also be regarded as a feed-forward control of the electric machine 2. The frequency of the rotating field is chosen here in such a way that it is synchronous with the rotational speed of the rotor 20 and thus no torque is generated by the electric machine 2. Moreover, in the step S3, the timer 22 is started.

(15) In a step S4, said timer checks whether a predetermined time span on file in the memory unit 21 has elapsed. If this is not the case, the method is continued with a subsequent step S5 by checking for the presence of a confirmation signal confirming the announced acceleration command. An actuation of the driving actuation device 7 is on file in the memory unit 21 as a confirmation signal. However, an exception applies for the case when the announcement signal was the simultaneous actuation of the driving actuation device 6 and the first braking actuation device 8. In the latter case, the release of the first braking actuation device 8 is detected as a confirmation signal, since this corresponds to the accelerated startup during launch control with a classical internal combustion engine. If no confirmation signal is present, then there is a jump back to S4 for further carrying out the method.

(16) Otherwise, when there is a confirmation command, a step S6 is carried out by controlling the electric machine 2 so as to increase its rotational speed and its torque. This means that the stator windings 19 are supplied with current only in such a way that a slippage is given in regard to the rotational frequency of the rotor 20 and thus the torque with the increased rotational speed is conveyed to the wheels 3. Consequently, the acceleration occurs directly when the acceleration command of the driver is detected, either through the actuation of the driving actuation device 6 or through the release of the first braking actuation device 8. For the control of a conventional electric machine that uses only the actuation of an accelerator pedal for control, it would be necessary at this point in time first to build up a magnetic field in order to then be able to accomplish an increase in the rotational speed or in the torque and consequently an acceleration. By way of the method, the required latency time for this purpose is avoided and a faster commencement of the acceleration is made possible.

(17) If the timer reaches the predetermined time span in step S4 and a confirmation signal has not ensued within said time, the method is continued in a step S7. In said step, the flux density of the stator field is decreased by controlling the electric machine 2 to reduce the supply of current to the stator windings 19. In anticipation of the acceleration command, there thus does not follow any actual corresponding action of the driver, so that, in order to avoiding any further energy expenditure for the preparatory maintenance of the stator field, a switch is made back to the first operating state. The method is then continued in step S2 with the checking for the presence of a new announcement signal.

(18) However, the method described above is not limited to asynchronous machines, so that basically any type of machine can be used. The increase or the building up of the magnetic field can occur, for example, directly in the rotor 20 and also, through induction effects, in the stator 18. In another exemplary embodiment of a motor vehicle 1, the electric machine 2 is a permanently excited synchronous machine, wherein, here, too, in the step S3, the flux density of the stator field is increased in order to achieve a certain reduction in the latency times for such electric machines 2.

(19) In another exemplary embodiment of a motor vehicle 1, the electric machine 2 is designed as a separately excited synchronous machine, wherein the rotor 20 has an exciter winding for generation of an exciter field. In the step S3, when said electric machine 2 is controlled, additionally a flux density of the exciter field is also increased by supplying current to exciter windings of the rotor 20. This also makes possible a significant reduction in latency times when the motor vehicle 1 is accelerated.