METHOD AND DEVICE FOR OPERATING A MOTOR VEHICLE, MOTOR VEHICLE

Abstract

The invention relates to a method for operating a motor vehicle comprising at least one electric machine as a driving device, said method involving the following steps: —verifying whether a current driving situation will allow the motor vehicle to reach a target position at a target speed by letting the motor vehicle coast; —displaying information to the driver of the motor vehicle if the target position can be reached by letting the motor vehicle coast; —measuring the time it takes the driver to react from the moment that the information is displayed to the moment that the driver initiates a coasting process; —actuating the electric machine as a generator in order to generate a deceleration moment if the reaction time exceeds a predefined maximum value.

Claims

1. A method for operating a motor vehicle which has at least one electric machine as a driving device, the method comprising: examining a current driving situation to determine whether a target position can be reached with a target speed by coasting; displaying a message to a driver of the motor vehicle if the target position can be reached by coasting; detecting a reaction time of the driver from the message up to the initiation of a coasting process by the driver; and actuating the electric machine as a generator to generate a deceleration torque if the reaction time exceeds a predefinable limiting value.

2. The method as claimed in claim 1, wherein the deceleration torque is set in such a way that the vehicle is at the target speed at the target position.

3. The method as claimed in claim 1, wherein an accelerator pedal activation by the driver is monitored in order to determine the reaction time.

4. The method as claimed in claim 1, wherein the deceleration torque is regulated as a function of the distance of the motor vehicle from the target position and from the current velocity.

5. The method as claimed in claim 1, wherein the examination is carried out as a function of data of a navigation system of the motor vehicle.

6. The method as claimed in claim 1, wherein the examination is carried out as a function of a surroundings sensor system of the motor vehicle.

7. A device for operating a motor vehicle which has at least one electric machine as a driving device, the device comprising a control unit configured to carry out the method as claimed in claim 1.

8. A motor vehicle having at least one electric machine as a driving device, and further comprising a control unit as claimed in claim 7.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] In the text which follows, the invention will be explained in more detail on the basis of the drawing.

[0013] The FIGURE shows a method for operating a motor vehicle in a flow chart.

DETAILED DESCRIPTION

[0014] FIG. 1 shows a flow chart on the basis of which an advantageous method for operating a motor vehicle needs to be explained in more detail. In a step S1, the method is started when the motor vehicle is actuated. In a subsequent step S2, the current driving situation is examined to determine whether a target position with a target speed can be reached solely by coasting. For this purpose, firstly the data of a navigation system are detected in a step S3, in order to determine possible target positions, in particular a possible following target position on the current section of road. Furthermore, by means of the data of the navigation system it is determined what target speed is to be reached at the target position. The target position can therefore be, for example, an entry to a locality at which a reduced velocity is prescribed by law. Likewise, it can be a stop sign at which the vehicle is to come to a standstill. The evaluation in step S2 is also carried out as a function of the current velocity v, which is determined in a step S4, in particular together with a position of the accelerator pedal or with a position of the brake pedal. It is preferably determined in a step S2, only when the brake pedal is not activated, whether, on the basis of the data which is now known, it is possible to reach the target position of the target speed by coasting of the vehicle starting from a specific starting position and a starting speed, which corresponds at least approximately to the current velocity. If this is case this is communicated to the driver of the motor vehicle in a step S5. For this purpose, there is provision, in particular, that this is communicated to the driver visually, acoustically and/or haptically. There is provision, for example, that the driver is given the message about the possible coasting event by means of a display device. It is also possible to provide that an active accelerator pedal is provided which increases a counter pressure which counteracts the activation force of the driver, in order to indicate the coasting event. When the message is displayed in the step S5, a stopwatch also begins to run, which measures the time t which the driver requires to react to the message in a step S6. The reaction is determined, in particular, as a function of the activation of the accelerator pedal. For this purpose, in a step S7 the activation of the accelerator pedal, in particular the position of the accelerator pedal, is measured. As soon as it is detected that the driver is no longer activating the accelerator pedal, the stopwatch is stopped, and in step S6 the reaction time of the driver is detected. The reaction time which is determined is compared with a predefinable limiting value of preferably between 1 second and 2 seconds. If the reaction time is shorter than the predefinable limiting value, then the motor vehicle is made to coast in a step S8, provided that the driver does not activate the accelerator pedal or the brake pedal again.

[0015] However, if the reaction time exceeds the predefinable limiting value, in a step S9 an electric machine of the motor vehicle, which is provided as a driving machine, is switched to a generator mode. In this context, a deceleration torque, which is calculated as a function of the current velocity, the distance from the target position and the target speed, is predefined to the electric machine. In particular, in this context, data of the navigation system relating to the section of road which has to be traveled along in order to reach the target position is also taken into account. In this context, the deceleration torque is determined in such a way that the motor vehicle reaches the target speed at the target position. If the driver of the motor vehicle therefore does not immediately follow the message and instead initiates the coasting process at a later time, the method becomes active, in particular in the form of a coasting controller, in order to control the coasting speed using the deceleration torque of the electric machine.

[0016] In this context, the deceleration torque is continuously determined in order to reach the desired target speed at the target position. Although the driver has not followed the recommendation or the message immediately, the motor vehicle nevertheless has a velocity corresponding to the target speed at the target position. Since no braking interventions are necessary with a mechanical brake for this deceleration of the motor vehicle, wear-free deceleration of the motor vehicle is ensured. Furthermore, during the generator mode of the electric machines an electric store of the motor vehicle is charged, with the result that the deceleration energy can be stored and can be used to drive the motor vehicle at a later time.

[0017] The motor vehicle preferably has a hybrid drive device which, apart from the electric machine, also has an internal combustion engine and, if appropriate, a further electric machine as driving machines. Furthermore, the motor vehicle also has, preferably as is customary, a conventional, in particular hydraulic braking system for generating a braking torque when the brake pedal is activated.