Method for Holding a Two-Track Motor Vehicle

Abstract

A method for holding a two-track motor vehicle is provided, wherein the motor vehicle has at least one electric drive machine and wherein each of four wheels of the motor vehicle can be held via a service brake. In an initial situation when the motor vehicle is at a standstill, the motor vehicle is held by virtue of a motor torque of the electric drive machine being applied to at least two wheels of the motor vehicle. In a manner dependent on a situation and/or gradient, the motor torque that holds the at least two wheels of the motor vehicle is reduced at one wheel. After the motor torque at the one wheel is reduced, the service brake at the wheel is activated. After the service brake at the one wheel is activated, the motor torque at a further wheel of the vehicle is reduced. After the motor torque at the further wheel of the vehicle is reduced, the service brake at the further wheel is activated.

Claims

1.-10. (canceled)

11. A method for holding a two-track motor vehicle, wherein the motor vehicle comprises at least one electric drive motor, and wherein each of four wheels of the motor vehicle is holdable by a service brake, the method comprising: holding the motor vehicle in an initial situation when the motor vehicle is at a standstill by applying a motor torque of the at least one electric drive motor to at least two wheels of the motor vehicle; reducing the motor torque holding the at least two wheels of the motor vehicle at one wheel or at two wheels; after reducing the motor torque at the one wheel or at the two wheels, activating the service brake at said one wheel or at said two wheels; after activating the service brake at said one wheel or at said two wheels, reducing the motor torque at a further wheel of the vehicle; subsequent to reducing the motor torque at the further wheel of the vehicle, activating the service brake at said further wheel.

12. The method according to claim 11, wherein the motor vehicle comprises two electric drive motors, and wherein: in the initial situation, two of the four wheels of the motor vehicle are held by a respective motor torque of a respective electric drive motor of the motor vehicle.

13. The method according to claim 11, wherein the motor vehicle comprises four electric drive motors, and wherein: in the initial situation, each of the four wheels of the motor vehicle is held by a motor torque of one of the four electric drive motors, respectively.

14. The method according to claim 11, wherein the method is carried out successively on all wheels of the motor vehicle held by an electric motor depending on a situation and/or a gradient and/or a time.

15. The method according to claim 12, wherein the method is carried out successively on all wheels of the motor vehicle held by an electric motor depending on a situation and/or a gradient and/or a time.

16. The method according to claim 13, wherein the method is carried out successively on all wheels of the motor vehicle held by an electric motor depending on a situation and/or a gradient and/or a time.

17. The method according to claim 14, wherein the motor torque at a respective wheel is reduced depending on the situation and/or the gradient and/or time.

18. The method according to claim 17, wherein the reducing of the motor torque at a respective wheel is reduced from a foreseeable and/or achieved dwell time of the motor vehicle in the held position and/or as soon as a limit capability of the electric drive motor is detected.

19. The method according to claim 11, wherein the reducing of the motor torque at a respective wheel is reduced as soon as a limit gradient of a vehicle roadway is detected.

20. The method according to claim 11, wherein the method is carried out as soon as a limit gradient of a vehicle roadway is reached.

21. The method according to claim 11, wherein during the reducing of the motor torque at a particular wheel, the service brake at said particular wheel is deactivated.

22. A motor vehicle, comprising: a two-track vehicle having four wheels; at least one electric drive motor for the two-track vehicle, wherein each of four wheels of the motor vehicle comprises a service brake for holding the respective wheel; and wherein the motor vehicle is configured to: hold the motor vehicle in an initial situation when the motor vehicle is at a standstill by applying a motor torque of the electric drive motor to at least two wheels of the motor vehicle; reduce the motor torque holding the at least two wheels of the motor vehicle at one wheel or at two wheels; after reducing the motor torque at the one wheel or at the two wheels, activate the service brake at said one wheel or at said two wheels; after activating the service brake at the one wheel or at the two wheels, reduce the motor torque at a further wheel of the vehicle; subsequent to reducing the motor torque at the further wheel of the vehicle, activate the service brake at said further wheel.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0043] The single FIGURE is a diagram of torque curves of a motor vehicle having four wheels so as to illustrate the method according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE DRAWING

[0044] The illustrated FIGURE shows a schematic exemplary embodiment of a torque curve (holding or braking torque curve) diagram of a motor vehicle having four wheels (wheel_1; wheel_2; wheel_3, wheel_4) over time. Here, each wheel (wheel_1; wheel_2; wheel_3, wheel_4) comprises a service brake, which can apply a braking torque or service braking torque M.sub.Brake (dashed line) to the respective wheel. Furthermore, a motor torque M.sub.Drive (solid line) of the electric drive motor can be applied to each wheel individually. In particular, an electric drive motor, for example in the form of a wheel hub motor, is provided here for each individual wheel.

[0045] In an initial position, the vehicle is in a holding position, in particular on a hill. The vehicle is held until time t.sub.1 by the application of a motor torque M.sub.Drive of the electric drive motor, which is applied to all four wheels wheel_1, wheel_2; wheel_3, wheel_4 of the vehicle. Additionally, but not limitingly, the vehicle is held in this specific case by the application of the service brake to all four wheels wheel_1, wheel_2; wheel_3, wheel_4. However, it is also contemplated that the vehicle is held stationary solely by the application of a motor torque M.sub.Drive to each wheel. In a vehicle concept with the “one-pedal feeling” described at the outset, the vehicle is held at a standstill by a motor torque M.sub.Drive of the respective wheel-specific electric drive motors applied to each wheel.

[0046] For example, the vehicle may be at a red light and on a road with a gradient.

[0047] The braking process until the vehicle comes to a standstill is preferably also implemented here by the respective electric drive motor (cf. “one-pedal feeling” concept above). As already mentioned, it is also possible for the service brake to be activated at the same time as the vehicle is held by the electric drive motor by applying a service braking torque M.sub.Brake to the wheels.

[0048] If (at time t.sub.1), for example via sensors, navigation data, online data, vehicle data or the like, a low capability or an energetically unreasonable setting of the electric drive motors is detected due to an excessive gradient of the roadway or due to an excessively long dwell time of the vehicle in the holding position that is foreseeable that has or already occurred, it is provided that the service brake ensures and takes over the holding position of the vehicle by applying a corresponding braking torque M.sub.Brake to the relevant wheel.

[0049] In contrast to the prior art, the service brake is then not activated simultaneously and in overlapping fashion with a motor torque M.sub.Drive still applied at each wheel, but is built up sequentially at each wheel in turn, while the motor torque at the respective wheel has already been completely reduced.

[0050] If the service brake is already activated beforehand when the vehicle is held at a standstill, it is fully released before time t.sub.1 at the first wheel, wheel_1, so that there is no service braking torque M.sub.Brake at the time t.sub.1 at the first wheel, wheel_1.

[0051] At the time t.sub.1, the motor torque M.sub.Drive of the first wheel, wheel_1, of the vehicle is then reduced to 0 Nm. Only at the time t.sub.2, when the motor torque M.sub.Drive of the electric drive motor of the first wheel has been completely reduced, is the service brake at this first wheel activated by a building braking torque M.sub.Brake of the service brake. The brake deficit, which occurs between the time of the start of the reduction of the motor torque M.sub.Drive at the first wheel and the complete build-up of the service braking torque M.sub.Brake at the first wheel, can be compensated or bridged by the braking torque M.sub.Brake or M.sub.Drive still present at the other three wheels: wheel_2, wheel_3, wheel_4. Thus, the holding torque M.sub.Brake or M.sub.Drive at the other three wheels, wheel_2, wheel_3, wheel_4, is high enough to keep the vehicle in the holding position. By completely reducing the motor torque M.sub.Drive at the first wheel, wheel_1, during which the service brake of the first wheel, wheel_1 is open or inactive, uncomfortable noise development can be advantageously avoided.

[0052] In a next step, at the time t.sub.3, when the service braking torque M.sub.Brake of the first wheel, wheel_1 has already been fully built up and has completely taken over the holding of the first wheel, the motor torque M.sub.Drive of the electric drive motor of the second wheel, wheel_2, is reduced to 0 Nm at the second wheel, wheel_2. Here, it must again be ensured that the service brake at the second wheel is no longer activated (i.e., open) at the time t.sub.3 of the reduction of the motor torque M.sub.Drive at the second wheel, wheel_2. After complete reduction of the motor torque M.sub.Drive of the electric drive motor of the second wheel, wheel_2, at the time t.sub.4, the service brake at the second wheel, wheel_2, is activated by building up a service braking torque M.sub.Brake of the service brake. The service brake of the second wheel, wheel_2, then takes over the holding of the second wheel.

[0053] Subsequently, as can be seen in the FIGURE, the same method steps are carried out with the other two wheels, wheel_3 and wheel_4. After the service braking torque M.sub.Brake has been fully built up at the second wheel, wheel_2, and while ensuring that the service brake at the third wheel, wheel_3, is deactivated, at the time t.sub.5, the motor braking torque M.sub.Drive of the third wheel, wheel_3, is reduced to 0 Nm. Then, after the motor torque M.sub.Drive at the third wheel, wheel_3, has been completely reduced, at the time t.sub.6, the service brake of the third wheel, wheel_3, is activated.

[0054] After complete activation of the service brake at the third wheel, wheel_3, and while ensuring that the service brake at the fourth wheel, wheel_4, is not activated (i.e., open), the applied motor torque M.sub.Drive at the fourth wheel, wheel_4, is reduced to 0 Nm (time t.sub.7). Only once this torque M.sub.Drive of the fourth wheel, wheel_4, has been completely reduced (start of reduction at the time t.sub.7) is the service brake of the fourth wheel, wheel_4, activated (time t.sub.5).

[0055] While the motor torque M.sub.Drive is being reduced and a service braking torque M.sub.Brake is subsequently being built up at the respective wheel, the holding torques M.sub.Brake or M.sub.Drive acting at the other wheels prevent the vehicle from rolling away when at a standstill.

[0056] The fact that the service brake at the respective wheels is not activated, i.e., is open, during the reduction of the motor torque M.sub.Drive at the respective wheels, means that the described creaking noise is absent.