METHOD OF OPERATING A MOTOR VEHICLE

Abstract

A method for operating a motor vehicle having two wheels, each of which is associated with a parking brake. The parking brakes are controlled as a function of a friction between the respective wheel and the ground.

Claims

1. A method for operating a motor vehicle having two wheels, each of which is associated with a parking brake, in which the parking brakes are actuated as a function of friction between the respective wheel and the ground.

2. The method according to claim 1, wherein a clamping force of that parking brake is increased which is associated with that wheel at which the higher friction prevails.

3. The method according to claim 2, wherein the clamping force is increased only if the two frictions differ by more than 20%.

4. The method according to claim 1, wherein the respective friction is determined at least partially during a rotation of the associated wheel.

5. The method according to claim 4, wherein the respective friction is determined on the basis of a braking of the associated wheel.

6. The method according to claim 1, wherein the respective friction is determined at least partially on the basis of a steering angle of the associated wheel.

7. The method according to claim 1, wherein the frictions are determined at least partly on the basis of an environmental parameter.

8. The method according to claim 7, wherein the environmental parameter is received by radio means.

9. The method according to claim 7, wherein the environmental parameter is determined by a camera.

10. A motor vehicle having two wheels, each of which is associated with a parking brake, and which is operated in accordance with a method according to claim 1.

11. The method according to claim 2, wherein the respective friction is determined at least partially during a rotation of the associated wheel.

12. The method according to claim 3, wherein the respective friction is determined at least partially during a rotation of the associated wheel.

13. The method according to claim 2, wherein the respective friction is determined at least partially on the basis of a steering angle of the associated wheel.

14. The method according to claim 3, wherein the respective friction is determined at least partially on the basis of a steering angle of the associated wheel.

15. The method according to claim 4, wherein the respective friction is determined at least partially on the basis of a steering angle of the associated wheel.

16. The method according to claim 5, wherein the respective friction is determined at least partially on the basis of a steering angle of the associated wheel.

17. The method according to claim 2, wherein the frictions are determined at least partly on the basis of an environmental parameter.

18. The method according to claim 3, wherein the frictions are determined at least partly on the basis of an environmental parameter.

19. The method according to claim 4, wherein the frictions are determined at least partly on the basis of an environmental parameter.

20. The method according to claim 5, wherein the frictions are determined at least partly on the basis of an environmental parameter.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0036] In the following, an exemplary embodiment of the invention is explained in more detail by means of a drawing. In particular:

[0037] FIG. 1 shows a motor vehicle with two parking brakes, and

[0038] FIG. 2 shows a method for operating the motor vehicle.

[0039] Corresponding parts are marked with the same reference signs in all figures.

DETAILED DESCRIPTION

[0040] FIG. 1 shows in a schematic simplified view a motor vehicle 2 in the form of a passenger car. The motor vehicle 2 has a total of four wheels 4, of which only two are shown here. The wheels 4 are attached to a body 6 of the motor vehicle 2 by means of a chassis not shown in greater detail. The wheels 4, each comprising a tire and a rim, rest on a ground 8 and thus serve to establish contact between the motor vehicle 2 and the ground 8.

[0041] The motor vehicle 2 comprises a drive 10 which is operatively connected to at least one of the wheels 4. In this embodiment, the drive 10 comprises only one or more electric motors, so that the motor vehicle 2 is designed as an electric vehicle. In addition, the motor vehicle 2 comprises a steering system 12, by means of which a steering angle of at least one of the wheels 4 with respect to the body 6 can be changed, so that a direction of travel of the motor vehicle 2 is changed. Also, the motor vehicle 2 comprises a braking system 14, which comprises four disc brakes not shown in more detail. By means of the braking system 14, it is possible to brake a rotation of the wheels 4 and thus to bring the motor vehicle 2 to a standstill.

[0042] Furthermore, the motor vehicle 2 has a total of two parking brakes 16, which are separate from the braking system 14. The two parking brakes 16 are identical in construction to each other but are associated with different ones of the wheels 4. Each of the parking brakes 16 has a first component 18 in the form of a brake disc, which is non-rotatably connected to the associated wheel 4. Thus, when the respective wheel 4 rotates, the respective first component 18 also rotates. In addition, each parking brake 16 has a second component 20 which comprises a plurality of brake pads not shown in greater detail. When the respective parking brake 16 is actuated, the second component 20 is pressed against the first component 18 so that a frictional connection is created between them. In other words, the brake pads are brought against the brake disc, thus preventing rotation of the brake disc. The parking brakes 16 have an electric motor, not shown in more detail, by means of which the brake pads are driven at least indirectly, so that the parking brakes 16 are electric parking brakes. The design of the parking brakes 16 is such that they essentially enable the motor vehicle 2 to be held in a fixed position. Braking of the motor vehicle 2 during movement, on the other hand, should not or cannot be performed by means of the parking brakes 16, and the braking system 14 is used for this purpose.

[0043] The motor vehicle 2 comprises a plurality of cameras 22, only one of which is shown. By means of the cameras 22, the environment of the motor vehicle 2 is optically detected, in particular also the ground 8. The cameras 22 are thereby associated with a lane departure warning system, by means of which lane markings are detected when the motor vehicle 2 is moving and the position of the motor vehicle 2 with respect to the lane markings is determined.

[0044] In addition, the motor vehicle 2 has a radio system 24 that complies with a mobile radio standard. By means of the radio system 24, it is possible to establish a radio connection to a server, which is not shown in more detail, and to exchange data therewith. The motor vehicle 2 also has an output device 26 which is arranged in an interior of the motor vehicle 2 which is surrounded by the body 6. The output device 26 is a display screen.

[0045] Also, the motor vehicle 2 comprises a control device 28 comprising a computer 30 in the form of a programmable microprocessor. Further, the control unit 28 comprises a memory unit in the form of a memory 32 on which a computer program product 34 is stored. The computer program product 34 includes a plurality of instructions which, when executed by the computer 30, cause the computer to perform a method 36 for operating a motor vehicle 2 as shown in FIG. 2. In other words, the control unit 28 is provided and arranged to perform the method 36, and the motor vehicle 2 is operated in accordance with the method 36.

[0046] The method 36 is started when a speed of the motor vehicle 2 falls below 5 km/h. In this case, a first operation step 38 is performed. In this, the braking system 14 is read out and, based on this, a value of a friction between each of the wheels 4, each of which is associated with one of the parking brakes 16, and the ground 8 is at least preliminarily determined. Also, a braking action is changed by means of the braking system 14, so that one of the wheels 4 is braked at least temporarily more strongly than the other wheel, wherein the total braking force applied remains constant or the same. This is performed alternately for the two wheels 4, and based on the different reactions of the wheels 4, the friction between the respective wheel 4 and the ground 8 is further adjusted. In other words, the friction between each of the wheels 4 and the ground 8 is determined based on the deceleration of the associated wheel 4 while it is still rotating, namely while the motor vehicle 2 is moving.

[0047] In addition, the drive 10 is briefly actuated so that the wheels 4 which are operatively connected thereto are accelerated, wherein an acceleration of the motor vehicle 2 itself is prevented by means of a suitable control of the braking system 14. Also on the basis of the resulting rotation of the wheels 4, the friction between the respective wheel 4 and the ground 8 is determined.

[0048] When the motor vehicle 2 is at a complete standstill, a second step 40 is performed. In this step, the ground 8 is optically detected by means of the cameras 22. In the example shown, an ice plate 42 is thus detected on which one of the wheels 4, with which one of the parking brakes 16 is associated, is standing. The ice plate 42 is here an environmental parameter 44, which is thus detected in the second step 40. If there were sand or gravel on the ground 8, for example, this would be used as the respective environmental parameter 44. In particular, these environmental parameters 44 only concern one of the wheels 4.

[0049] In addition, further environmental parameters 44 are retrieved from a server by means of the radio system 24, which are thus received by means of radio. These environmental parameters 44 concern an air humidity as well as a temperature. Thus, in this embodiment, these environmental parameters 44 apply to all wheels 4. Based on the environmental parameters 44, the already determined frictions are further adjusted, so that the frictions are also determined at least partially based on the environmental parameters 44. Due to the ice plate 42, one of them is reduced, wherein due to an incipient or impending rain, which was detected by means of the radio system 24, this tends towards 0 (zero).

[0050] Also, in order to determine the friction, a steering angle of the wheels 4 is taken into account. For this purpose, the setting of the wheels 4 is retrieved, which was caused by means of the steering system 12. Depending on the steering angle of the wheels 4, the respective camber results in a different contact surface on the ground 8, so that the friction is at least partially determined by the steering angle of the respective wheel 4.

[0051] In a subsequent third step 46, it is checked whether the determined friction between the wheels 4 and the ground 8 differs by more than 20%. It is also checked whether the friction between all wheels 4 and the ground 8 falls below a certain fixed limit value. If this is the case or will change in the near future due to environmental conditions 44 detected by means of the radio system 24, a warning is issued via the output device 26. Thus, it is possible for a driver of the motor vehicle 2 to park it at another location where higher friction is present.

[0052] If this is not done, and the driver, for example, leaves the motor vehicle 2 and locks it from the outside, a fourth step 48 is carried out. In this step, the two parking brakes 16 are actuated and thus controlled. In this case, the clamping force of that parking brake 16 is increased which is associated with that wheel 4 at which the higher friction is present. For this purpose, 25 A is selected for a cut-off current, up to which the electric motor by means of which the brake pads are actuated is operated, whereas the clamping force is not changed for the remaining parking brake 16 and 20 A continues to be used as cut-off current. By means of the wheel 4 with which the associated parking brake 16 is actuated with the increased clamping force, an increased holding force of the motor vehicle 2 is exerted on the ground 8, so that the holding force reduced due to the reduced friction between the other wheel 4, with which the remaining parking brake 16 is associated, and the ground 8 is at least partially compensated. Thus, even in adverse conditions, holding of the motor vehicle 2 on the ground 8 is possible.

[0053] If the determined frictions are greater than a predetermined limit value and do not differ by more than 20%, the control of the parking brakes 16 is always identical, regardless of the friction actually present. In this case, the cut-off current is always 20 A. Thus, excessive wear of the parking brakes 16 is reduced, while in unfavorable situations a safe holding of the motor vehicle 2 in the desired position is nevertheless ensured.

[0054] The invention is not limited to the exemplary embodiment described above. Rather, other variants of the invention may also be derived therefrom by the person skilled in the art without departing from the subject matter of the invention. In particular, all the individual features described in connection with the exemplary embodiment can also be combined with one another in other ways without departing from the object of the invention.

LIST OF REFERENCE NUMERALS

[0055] 2 motor vehicle [0056] 4 wheel [0057] 6 body [0058] 8 ground [0059] 10 drive [0060] 12 steering system [0061] 14 braking system [0062] 16 parking brake [0063] 18 first component [0064] 20 second component [0065] 22 camera [0066] 24 radio system [0067] 26 output device [0068] 28 control unit [0069] 30 computer [0070] 32 memory [0071] 34 computer program product [0072] 36 method [0073] 38 first operation step [0074] 40 second operation step [0075] 42 ice plate [0076] 44 environmental parameters [0077] 46 third operation step [0078] 48 fourth operation step