METHOD FOR BRAKING A VEHICLE HAVING TWO ELECTRIC DRIVE MOTORS, A COMPUTING UNIT, AND A COMPUTER PROGRAM

Abstract

The invention relates to a method for braking a vehicle (10) having a first (14) and a second (16) electric drive motor, wherein, in a first braking phase, a first target value for a braking torque is specified to the first electric drive motor (14), and a second target value for a braking torque is specified to the second electric drive motor (16), wherein a current speed of the vehicle (10) is sensed as the actual speed, wherein, when the actual speed reaches a first threshold value (v.sub.0) for a vehicle speed, the first target value for a braking torque is increased in a redistribution phase and the second target value for a braking torque is simultaneously reduced, wherein, when the actual speed reaches a second threshold value (v.sub.1) for a vehicle speed, the specification of the first target value for a braking torque is ended and a speed target value trajectory (202) is specified in a second braking phase, wherein the speed target trajectory proceeds from the second threshold value (v.sub.1) for the vehicle speed to a speed of zero.

Claims

1. A method of braking a vehicle (10) having a first (14) and a second (16) electric drive motor, wherein, in a first braking phase, a first target value for a braking torque is specified for the first electric drive motor (14), and a second target value for a braking torque is specified for the second electric drive motor (16), wherein a current speed of the vehicle (10) is sensed as the actual speed, wherein, when the actual speed reaches a first threshold value (v.sub.0) for a vehicle speed, the first target value for a braking torque is increased in a redistribution phase and the second target value for a braking torque is simultaneously reduced, wherein, when the actual speed reaches a second threshold value (v.sub.1) for a vehicle speed, the specification of the first target value for a braking torque is ended and a speed target trajectory (202) is specified in a second braking phase, wherein the speed target trajectory proceeds from the second threshold value (v.sub.1) for the vehicle speed to a speed of zero.

2. The method according to claim 1, wherein the first target value for a braking torque is increased during the redistribution phase to a sum of the first target value and the second target value at the start of the redistribution phase and the second target value for a braking torque is reduced to zero.

3. The method of claim 2, wherein the first threshold value (v.sub.0) for a vehicle speed is determined from an amount of time (tRamp) needed to increase the first target value for a braking torque to a sum of the first target value and the second target value at the start of the redistribution phase and reduce the second target value for a braking torque to zero.

4. A The method according to claim 1, wherein the first threshold value (v.sub.0) for a vehicle speed is determined from a current deceleration of the vehicle (10).

5. The method of claim 1, wherein the first threshold value (v.sub.0) for a vehicle speed is determined from the second threshold value (v.sub.1) for a vehicle speed.

6. The method of claim 3, wherein the first threshold value (v.sub.0) for a vehicle speed is determined as the sum of the second threshold value (v.sub.1) for a vehicle speed and a product of the current deceleration (a) of the vehicle (10) and the time period (tRamp), that is needed to increase the first target value for a braking torque to a sum of the first target value and the second target value at the start of the redistribution phase, and reduce the second braking torque target value to zero.

7. A computing unit (12) configured to perform all method steps of a method according to claim 1.

8. (canceled)

9. A non-transitory computer-readable containing instructions that when executed by a computer cause the computer to control braking of a vehicle (10) having a first (14) and a second (16) electric drive motor, by in a first braking phase, specifying a first target value for a braking torque for the first electric drive motor (14), and specifying a second target value for a braking torque for the second electric drive motor (16), sensing a current speed of the vehicle (10) as the actual speed, when the actual speed reaches a first threshold value (v.sub.0) for a vehicle speed, increasing the first target value for a braking torque in a redistribution phase and simultaneously reducing the second target value for a braking torque, wherein, when the actual speed reaches a second threshold value (v.sub.1) for a vehicle speed, the specification of the first target value for a braking torque is ended and a speed target trajectory (202) is specified in a second braking phase, wherein the speed target trajectory proceeds from the second threshold value (v.sub.1) for the vehicle speed to a speed of zero.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] FIG. 1 shows a schematic diagram of a vehicle configured to perform an exemplary embodiment of the method according to the invention;

[0023] FIG. 2 shows a progression of a speed in an exemplary stopping operation according to a configuration of the invention.

DETAILED DESCRIPTION

[0024] FIG. 1 shows a schematic diagram of a vehicle 10 configured to perform an exemplary embodiment of the method according to the invention. The vehicle 10 comprises a controller 12, which may in particular be the control unit of a power electronics. The vehicle 10 further comprises a first electric drive motor 14 configured to drive at least one wheel 11 of the vehicle 10, for example a rear wheel or the rear axle. A sensor device 15 is disposed on the first electric drive motor 14 such that the sensor device 15 senses and/or transmits an angular position and/or a speed of the first electric drive motor 14 to the controller 12.

[0025] The vehicle 10 further comprises a second electric drive motor 16 configured to drive at least one (other) wheel of the vehicle 10, such as a front wheel or the front axle. A sensor device 17 is disposed on the second electric drive motor 16 such that the sensor device 17 senses and transmits an angular position and/or a speed of the second electric drive motor 16 to the controller 12.

[0026] The controller 12 is in communication with the first electric drive motor 14 and the second electric drive motor 16 via a signal line so that the electric drive motors 14 and 16, respectively, can be regulated and/or controlled by the controller 12.

[0027] For example, if a driver wants to bring the vehicle to a standstill, he or she will typically apply a brake. In the context of one embodiment, it is contemplated that the braking operation may be performed initially using the first drive motor 14 and second drive motor 16, and finally only utilizing the first drive motor 14, as will be described below by way of example, with reference to the figures, contiguously and comprehensively.

[0028] FIG. 2 shows an exemplary stopping operation in the form of a graph in which a vehicle speed v is plotted in relation to time t. Deceleration is carried out in a first braking phase up to time t.sub.0 using the first drive motor 14 and the second drive motor 16, for example by actuating the first drive motor 14 and the second drive motor 16 with a target value for a constant, in particular the same, braking torque. Thus, in this first braking phase, a first target value for a braking torque is provided to the first electric drive motor 14 and a second target value for a braking torque is provided to the second electric drive motor 16.

[0029] At the time t.sub.0, the speed v.sub.0 is reached as the first threshold value for a vehicle speed, which represents the trigger event for transitioning to a redistribution phase.

[0030] In the redistribution phase, the first target value for a braking torque is increased while the second target value for a braking torque is reduced. In particular, in the redistribution phase, the first target value for a braking torque is increased to a sum of the first target value and the second target value at the start of the redistribution phase, and the second target value for a braking torque is reduced to zero, and the sum of the first and second target value remains constant. The braking operation is thus continued unchanged for the driver, wherein the braking torque is concentrated on the first drive motor. For example, braking may be carried out with a constant deceleration, for example a.

[0031] At time t.sub.1 the speed v.sub.1 is reached as the second threshold value for a vehicle speed, which represents the triggering event for the transition to the second braking phase. At this time, a speed target trajectory (in particular, as v(t)) is determined and then the first drive motor 14 is decelerated to a standstill in accordance with this speed target trajectory. The second drive motor 16 is operated in an idle state.

[0032] In particular, the speed target trajectory may result in a decrease in the deceleration from the current value a to the value zero at a speed of zero. The decrease in the deceleration can be linear, i.e. a jerk is constant.

[0033] A method for calculating the redistribution phase or the first threshold value v.sub.0 for a vehicle speed is described below.

[0034] The starting point can be the current deceleration, which is specified by the current braking torque and thus remains unchanged during the redistribution phase according to the above embodiment, meaning it still prevails at the end of the redistribution phase. For this current deceleration or the braking torque associated therewith, an amount of time tRamp is known to be required to increase the first target value for a braking torque to a sum of the first target value and the second target value at the start of the redistribution phase and to reduce the second target value for a braking torque to zero, i.e., a time period for the redistribution. For example, it can be determined in advance in test bench measurements and stored in a characteristic diagram or the like.

[0035] From this time period tRamp and the current deceleration a, the speed decrease during the redistribution can be determined as: tRamp*a, and the forecasted speed at the end of the redistribution can be determined as if it were started at the present time with v, as: vabs (tRamp*a).

[0036] The second threshold value v.sub.1 for the vehicle speed results, for example, from the request to decelerate from the speed vabs (tRamp*a) and the deceleration a with constant jerk to brake to a deceleration of zero and speed of zero. The jerk defines how hard or soft stopping feels for the driver. Thus, it is possible to thereby calculate the entry point of the speed control sequence. A suitable jerk value can, for example, still be selected with respect to comfort or safety aspects.

[0037] The first threshold value v.sub.0 for the vehicle speed then results from this as: v.sub.0=v.sub.1+abs (tRamp*a).