METHOD AND DEVICE FOR DETERMINING THE TENSION FORCE OF A BRAKE DEVICE OF A MOTOR VEHICLE

Description

[0001] The invention relates to a method for determining a clamping force of a braking device of a motor vehicle, wherein the motor vehicle has at least one rotatably mounted wheel and a braking system with at least one braking device and at least one electric motor, wherein the braking device has a braking element connected to the wheel in a rotationally fixed manner and at least one braking body that can be pressed against the braking element, wherein the electric motor has a motor winding and a rotatably mounted rotor, wherein the rotor is coupled to the braking body by a gear device such that a clamping force can be generated by rotation of the rotor, by which the braking body is pressed against the braking element, wherein the rotor is rotatable by applying an electric motor current to the motor winding, wherein a rotation angle of the rotor and / or a displacement path of a displaceably mounted element of the gear device are determined,and wherein the level of the generated clamping force is determined as a function of the angle of rotation and / or the displacement path.

[0002] The invention also relates to a method for operating a motor vehicle.

[0003] Furthermore, the invention relates to a device for determining a clamping force, with an evaluation device. State of the art

[0004] A motor vehicle usually has a plurality of rotatably mounted wheels. In order to reduce the driving speed of the motor vehicle, the motor vehicle generally has a braking system with at least one braking device. The braking device is assigned to one of the wheels of the motor vehicle and is designed to generate a friction braking torque by means of which a current rotational speed of the wheel is reduced. For this purpose, the braking device has a braking element, such as a brake disc, which is connected to the wheel in a rotationally fixed manner and at least one braking body that can be pressed against the braking element. If the braking body is pressed against the braking element, the friction braking torque is generated. The braking system preferably has a plurality of braking devices, wherein each of the braking devices is assigned to a different one of the wheels.

[0005] Brake systems are increasingly also featuring an electric motor, particularly with a multi-phase motor winding, and a rotatably mounted rotor to actuate the braking device. The rotor is coupled to the brake body by a gear mechanism such that rotation of the rotor generates a clamping force that presses the brake body against the braking element. The rotation of the rotor is thus converted by the gear mechanism into a displacement of the brake body. The magnitude of the clamping force generated corresponds to the magnitude of the friction braking torque. The higher the clamping force, the higher the friction braking torque. The rotor can be rotated by applying an electric motor current to the motor winding.

[0006] Methods for determining the magnitude of the generated clamping force are known from the prior art. Knowing the clamping force enables advantageous control of the electric motor. In this case, it is known to determine the angle of rotation of the rotor and / or the displacement of a displaceably mounted element of the gear mechanism. The angle of rotation and the displacement correspond to the magnitude of the clamping force. The greater the angle of rotation or the displacement, the greater the generated clamping force. Accordingly, the magnitude of the clamping force is then determined as a function of the angle of rotation and / or the displacement.

[0007] Patent KR 101 338 433 B1 discloses a method for determining the clamping force of a braking device, in which the clamping force is determined as a function of the rotation angle of a rotor of an electric motor and as a function of the motor current of the electric motor. Such a method is also described in published patent applications EP 3 156 294 A1 and US 2017 / 321773 A1. Disclosure of the invention

[0008] The method according to the invention with the features of claim 1 has the advantage that the accuracy with which the level of the generated clamping force is determined is increased. According to the invention, the level of the motor current is determined, and the level of the clamping force is determined as a function of the level of the motor current. In gear systems subject to slip, the sole consideration of the angle of rotation and / or the displacement path leads to inaccuracies in determining the level of the generated clamping force as the absolute angle of rotation or displacement path increases. These inaccuracies are at least partially compensated for by the additional consideration of the level of the motor current. The level of the motor current also corresponds to the level of the generated clamping force, at least at certain operating points of the electric motor. For example, the clamping force increases with an increase in the motor current.Preferably, the motor current is detected or measured. This also includes determining the motor current. A sensor device is then provided that is designed to detect the magnitude of the motor current. Alternatively, a parameter corresponding to the magnitude of the motor current, for example, an electrical motor voltage of the motor winding, is preferably detected or measured. The magnitude of the motor current is then determined depending on the detected parameter.

[0009] According to a preferred embodiment, the magnitude of the clamping force is determined based on a first characteristic curve that describes the clamping force as a function of the angle of rotation or the displacement path. The generated clamping force can be precisely determined using the first characteristic curve. Using the first characteristic curve, a corresponding clamping force can be assigned to a plurality of angles of rotation or displacement paths.

[0010] Preferably, the first characteristic curve is changed depending on the determined motor current level. This allows for simple evaluation of the motor current level. For example, the gradient of the first characteristic curve is changed depending on the determined motor current level.

[0011] According to the invention, a corrected angle of rotation is determined as a function of the level of the motor current on the one hand and the determined angle of rotation on the other, wherein the level of the clamping force is determined as a function of the corrected angle of rotation, and / or a corrected displacement path is determined as a function of the level of the motor current on the one hand and the determined displacement path on the other, wherein the level of the clamping force is determined as a function of the corrected displacement path. The originally determined angle of rotation or the originally determined displacement path is therefore corrected as a function of the determined level of the motor current. For example, a correction factor is determined as a function of the level of the motor current, and the determined angle of rotation or the determined displacement path is multiplied by the correction factor for correction.Accordingly, the corrected angle of rotation or the corrected displacement distance are then used to determine the clamping force level. For example, the clamping force level is determined as a function of the corrected angle of rotation or the corrected displacement distance using the first characteristic curve.

[0012] According to a preferred embodiment, a current-based clamping force is determined depending on the level of the motor current and a second characteristic curve that describes a clamping force ratio of the braking device depending on the level of the motor current, wherein the first characteristic curve is changed depending on the current-based clamping force, and / or wherein the corrected angle of rotation and / or the corrected displacement path are determined depending on the current-based clamping force. By using the second characteristic curve, the determined level of the motor current is precisely taken into account when determining the clamping force. By means of the second characteristic curve, a corresponding clamping force ratio can be assigned to a plurality of motor current values. The current-based clamping force can then be calculated, for example, using the equation F Spann , I = K F , I I Mot × I Mot where F Spann,I is the current-based clamping force, KF,I is the clamping force ratio and I Mot is the determined motor current.

[0013] According to the invention, it is monitored whether a correction situation exists, wherein the corrected angle of rotation and / or the corrected displacement path are only determined when the correction situation exists. Preferably, the characteristic curve is only changed as a function of the motor current level when the correction situation exists. A correction situation is understood to be a situation in which it can be assumed that taking the motor current level into account will achieve a desired increase in accuracy when determining the level of the generated clamping force. If the correction situation does not exist, the determined motor current level is preferably not taken into account when determining the level of the generated clamping force.

[0014] According to a preferred embodiment, it is provided that a rotational speed threshold is specified, wherein if the rotational speed of the rotor falls below the rotational speed threshold, it is determined that the correction situation exists, and / or that a displacement speed threshold is specified, wherein if the displacement speed of the element falls below the displacement speed threshold, it is determined that the correction situation exists. It is assumed that the correction situation exists when the braking device or the electric motor is in a static state, i.e. when the state of the braking device and the electric motor no longer changes or changes only slightly. This can be reliably determined based on the rotational speed or the displacement speed.

[0015] Preferably, a current change threshold is specified, and if the motor current change falls below the current change threshold, it is determined that the correction situation exists. As mentioned above, the correction situation exists when the electric motor is in a static state. Accordingly, the existence of the correction situation can also be reliably determined depending on the motor current change.

[0016] The invention also relates to a method for operating a motor vehicle, wherein the motor vehicle has at least one rotatably mounted wheel and a braking system with at least one braking device and at least one electric motor, wherein the braking device has a braking element connected to the wheel in a rotationally fixed manner and at least one braking body that can be pressed against the braking element, wherein the electric motor has a motor winding and a rotatably mounted rotor, wherein the rotor is coupled to the braking body by a gear device in such a way that a clamping force can be generated by rotation of the rotor, by which the braking body is pressed against the braking element, wherein the rotor is rotatable by applying an electric motor current to the motor winding, wherein a level of the generated clamping force is determined, and wherein the motor winding is applied with the motor current in such a way,that the generated clamping force corresponds to a predetermined target clamping force. The method for operating the motor vehicle is characterized by the features of claim 8 in that the magnitude of the clamping force is determined by the method according to the invention for determining the clamping force. This also results in the aforementioned advantages. Further preferred features and combinations of features emerge from the above description and from the claims.

[0017] The device according to the invention for determining a clamping force of a braking device of a motor vehicle, wherein the motor vehicle has at least one rotatably mounted wheel and a braking system with at least one braking device and at least one electric motor, wherein the braking device has a braking element connected to the wheel in a rotationally fixed manner and at least one braking body that can be pressed against the braking element, wherein the electric motor has a motor winding and a rotatably mounted rotor, wherein the rotor is coupled to the braking body by a gear device such that a clamping force can be generated by rotating the rotor, by means of which the braking body is pressed against the braking element, and wherein the rotor is rotatable by applying an electric motor current to the motor winding, is characterized by the features of claim 9 by an evaluation device that is specially designed toWhen used as intended, the method according to the invention for determining the clamping force can be carried out. This also results in the aforementioned advantages. Further preferred features and combinations of features emerge from the above description and from the claims.

[0018] According to a preferred embodiment, the transmission device is coupled immediately or directly to the brake body. In this respect, the displaceably mounted element or another displaceably mounted element of the transmission device lies axially directly against the brake body, at least when the brake device is actuated, relative to a displacement axis along which the brake body is displaceable. A hydraulic connection between the transmission device and the brake body is dispensed with. For example, the transmission device has a planetary roller gear, with the displaceably mounted element then being a planetary roller thread spindle. Typically, a different braking device is assigned to each of the wheels of the motor vehicle. Preferably, each of the braking devices is then assigned a different electric motor and a different transmission device.The evaluation device is then designed to determine the clamping forces generated by the various electric motors using the method according to the invention.

[0019] According to a further preferred embodiment, the transmission device is coupled to a master brake cylinder of the brake system in such a way that when the motor winding is energized with motor current, a hydraulic piston displaceably mounted in the master brake cylinder is actuated. The master brake cylinder is fluidly connected to the brake body in such a way that the brake body is pressed against the brake element when the hydraulic piston is actuated. In this respect, the transmission device according to this embodiment is indirectly coupled to the brake body.

[0020] The invention is explained in more detail below with reference to the drawings. Figure 1 shows a motor vehicle in a simplified representation, Figure 2 shows another motor vehicle in a simplified representation, Figure 3 shows a first characteristic curve, Figure 4 shows a second characteristic curve and Figure 5 shows a method for determining a clamping force.

[0021] Figure 1 shows a simplified representation of a motor vehicle 1. The motor vehicle 1 has a front wheel axle 2 and a rear wheel axle 3. The front wheel axle 2 has a rotatably mounted first wheel 4 and a rotatably mounted second wheel 5. The rear axle 3 has a rotatably mounted third wheel 6 and a rotatably mounted fourth wheel 7.

[0022] The motor vehicle 1 also has a braking system 8. The braking system 8 has a number of braking devices 9, 10, 11 and 12 corresponding to the number of wheels. The braking devices 9, 10, 11 and 12 are arranged in Figure 1shown only schematically. Each of the wheels 4, 5, 6 and 7 is assigned a different one of the braking devices 9, 10, 11 or 12. The braking devices 9, 10, 11 and 12 are designed to generate a friction braking torque in order to reduce the rotational speed of the wheel to which they are assigned. For example, a first braking device 9 of the braking devices is designed to reduce the current rotational speed of the first wheel 4. For this purpose, the first braking device 9 has a braking element that is connected in a rotationally fixed manner to the first wheel 4 and at least one braking body that can be pressed against the braking element. The braking devices 10, 11 and 12 correspond in terms of their design to the first braking device 9. In this respect, the braking devices 10, 11 and 12 also each have a braking element and at least one braking body that can be pressed against the braking element.

[0023] The brake system 8 also has an electric motor 13. The electric motor 13 is also Figure 1 shown only schematically. The electric motor 13 has a rotatably mounted rotor and a motor winding. The rotor is rotatable by applying an electric motor current I Mot to the motor winding.

[0024] The rotor is coupled to a gear mechanism 14. The gear mechanism 14 has at least one displaceably mounted element and is designed to convert a rotation of the rotor into a displacement of the displaceably mounted element. For example, the gear mechanism 14 has a spindle gear with a rotatably mounted spindle nut and a displaceably mounted spindle.

[0025] The brake system 8 also has a master brake cylinder 15. In this case, the master brake cylinder 15 is designed as a tandem master brake cylinder 15, so that two hydraulic pistons are displaceably mounted in the master brake cylinder 15. The rotor is coupled to the master brake cylinder 15 by the transmission device 14 such that the hydraulic pistons can be displaced by rotation of the rotor.

[0026] The braking system 8 also has a hydraulic block 16. The master brake cylinder 15 is fluidly connected to the hydraulic block 16 via two input lines 17 and 18. The hydraulic block 16 is in turn fluidly connected to the wheel brake cylinders of the braking devices 9, 10, 11, and 12 via four output lines 19, 20, 21, and 22. If the hydraulic pistons are displaced in an actuating direction, a clamping force F clamp acting on the brake bodies is generated by a hydraulic fluid present in the lines 17, 18, 19, 20, 21, and 22, which force presses the brake bodies against the respective braking elements.

[0027] Because the rotor is coupled to the hydraulic pistons by the gear mechanism 14, the clamping force can be generated by the rotation of the rotor. The magnitude of the generated clamping force corresponds to a rotation angle ϕ of the rotor and a displacement path of the displaceably mounted element. The greater the rotation angle ϕ, the greater the generated clamping force F clamp . Furthermore, the magnitude of the generated clamping force F clamp corresponds to the magnitude of the friction braking torque. The higher the clamping force F clamp , the higher the friction braking torque.

[0028] The motor vehicle 1 also has a device 23. The device 23 has a rotation angle sensor 24, which is assigned to the rotor and is designed to detect the rotation angle ϕ of the rotor. The device 23 also has a current sensor 25, which is assigned to the motor winding and is designed to detect the level of the electrical motor current I Mot flowing through the motor winding. In addition, the device 23 has an evaluation device 26. The evaluation device 26 is communicatively connected to the rotation angle sensor 24 and the current sensor 25, so that the detected rotation angle ϕ and the level of the motor current I Mot are provided to the evaluation device 26. The evaluation device 26 is designed to determine the level of the generated clamping force F Spann as a function of the rotation angle ϕ of the rotor, on the one hand, and the level of the motor current I Mot, on the other.

[0029] The evaluation device 26 is also designed to determine control signals for switches of the power electronics of the electric motor 13 and to control the switches depending on the control signals. In this respect, the evaluation device 26 is designed as a control unit 26. If a friction braking torque is to be generated by the braking devices 9, 10, 11 and 12, the evaluation device 26 controls the power electronics of the electric motor 13 in a controlled manner such that the generated clamping force F Spann corresponds to a predetermined target clamping force. The motor winding is therefore supplied with the electrical motor current I Mot in such a way that the generated clamping force F Spann corresponds to the predetermined target clamping force. For example, the target clamping force is specified by a driver of the motor vehicle 1 actuating a brake pedal.

[0030] Figure 2 shows a further embodiment of the motor vehicle 1. The Figure 2The motor vehicle 1 shown differs from the one shown in Figure 1 motor vehicle 1 shown with regard to the design of the braking system 8. The Figure 2 The motor vehicle shown has the braking devices 9, 10, 11 and 12.

[0031] The brake system 8 of the Figure 2 The motor vehicle 1 shown has a number of electric motors 13 corresponding to the number of braking devices 9, 10, 11, and 12. Furthermore, the braking system 8 has a number of transmission devices 14 corresponding to the number of braking devices 9, 10, 11, and 12. Each braking device 9, 10, 11, and 12 is assigned a different one of the electric motors 13 and a different one of the transmission devices 14.

[0032] The rotors of the electric motors 13 are also coupled to the brake bodies of the brake devices 9, 10, 11, and 12 by the gear units 14 in such a way that by applying a motor current I Mot to the motor windings of the electric motors 13, a clamping force F Spann can be generated, which presses the brake bodies of the brake devices 9, 10, 11, and 12 against the respective brake elements. The gear units 14 are each coupled directly to the brake bodies, i.e., without the interposition of a master brake cylinder.

[0033] The device 23A of the Figure 2 The motor vehicle 1 shown has a number of rotation angle sensors 24 corresponding to the number of electric motors 13, wherein each of the electric motors 13 is assigned a different one of the rotation angle sensors 24.

[0034] The device 23A also has a number of current sensors 25 corresponding to the number of electric motors 13, wherein each of the electric motors 13 is assigned a different one of the current sensors 25.

[0035] The angle of rotation sensors 24 and the current sensors 25 are connected to the evaluation device 26A via communication technology, so that the angle of rotation ϕ detected by the angle of rotation sensors 24 and the motor currents I Mot detected by the current sensors 25 are provided to the evaluation device 26A.

[0036] The evaluation device 26A of the Figure 2 The motor vehicle 1 shown is designed to determine the level of the clamping forces F Spann generated by the electric motors 13 as a function of the angle of rotation ϕ of the respective rotor on the one hand and the level of the respective motor current I Mot on the other hand.

[0037] In addition, the control unit 26A is designed to determine control signals for switches of the power electronics of the electric motors 13 and to control the switches depending on the control signals. The evaluation unit 26A is designed to control the electric motors 13 independently of one another. The evaluation unit 26A controls the power electronics such that the clamping forces F clamp generated by the electric motors 13 each correspond to the specified target clamping force, as described above with reference to the evaluation unit 26.

[0038] Figure 3 shows a first characteristic curve L1. The first characteristic curve L1 describes the level of the generated clamping force F clamp as a function of the rotation angle ϕ of the rotor. As can be seen from Figure 3 As can be seen, the clamping force F clamp increases with an increase in the angle of rotation ϕ.

[0039] Figure 4shows a second characteristic curve L2. The second characteristic curve L2 describes the level of a clamping force ratio KF,I of the braking devices as a function of the motor current I Mot . As can be seen from Figure 4 As can be seen, the clamping force ratio KF,I decreases with an increase in the motor current I Mot .

[0040] As previously mentioned, the evaluation device 26 controls the electric motor 13 such that the generated clamping force F clamp corresponds to the specified target clamping force. Accordingly, the evaluation device 26A controls the electric motors 13 such that the generated clamping force F clamp corresponds to the specified target clamping force.

[0041] In the following, with reference to Figure 5 An advantageous method for determining the level of the generated clamping force F Spann is explained. Figure 5 The process is illustrated by a flow chart. The process is illustrated by the evaluation device 26 of the Figure 1However, the evaluation device 26A of the vehicle 1 shown in Figure 2 illustrated motor vehicle 1 is designed to carry out the method and to determine by means of the method the clamping force F clamp generated by the electric motors 13.

[0042] In a first step S1, the rotation angle sensor 24 detects the current rotation angle ϕ of the rotor. Furthermore, the rotation angle sensor 24 provides the detected rotation angle ϕ to the evaluation device 26.

[0043] In a second step S2, the current sensor 25 detects the magnitude of the motor current I Mot . Furthermore, the current sensor 25 provides the detected magnitude of the motor current I Mot to the evaluation device 26.

[0044] At least steps S1 and S2 are carried out continuously so that a profile of the angle of rotation ϕ and a profile of the motor current I Mot are provided to the evaluation device 26.

[0045] In a third step S3, the evaluation device 26 determines, as a function of the magnitude of the motor current I Mot using the second characteristic curve L2, a clamping force ratio KF,I corresponding to the magnitude of the motor current I Mot. Depending on the determined clamping force ratio KF,I, the evaluation device 26 then determines in step S3 using the equation F Bucket , I = KF,I ( Against ) × Against a current-based clamping force F Spann,I .

[0046] In a fourth step S4, the evaluation device 26 checks whether a correction situation exists. A correction situation is assumed when the braking devices 9, 10, 11 and 12 and the electric motor 13 are in a static state. For this purpose, the evaluation device 26 specifies a rotational speed threshold and a current change threshold. In addition, the evaluation device 26 determines a rotational speed of the rotor as a function of the course of the rotational angle ϕ and a motor current change in the motor current I Mot as a function of the course of the motor current I Mot . The evaluation device 26 then determines that the correction situation exists when the determined rotational speed of the rotor falls below the rotational speed threshold and the determined motor current change falls below the current change threshold.

[0047] If the evaluation device 26 determines in step S4 that the correction situation does not exist, the program proceeds to a fifth step S5. In the fifth step S5, the evaluation device 26 then determines the magnitude of the generated clamping force F clamp as a function of the rotation angle ϕ detected in step S1 using the first characteristic curve L1. The magnitude of the motor current I Mot is not taken into account.

[0048] However, if the evaluation device 26 determines in step S4 that the correction situation exists, reference is made to a sixth step S6. In the sixth step S6, the evaluation device 26 then determines a current-based rotation angle ϕ I of the rotor using the first characteristic curve L1 as a function of the current-based clamping force F Spann,I determined in the third step S3.

[0049] In a seventh step S7, the evaluation device 26 compares the current-based angle of rotation ϕ I determined in step S6 with the angle of rotation ϕ detected in step S1. If the detected angle of rotation ϕ deviates from the current-based angle of rotation ϕ I, the evaluation device 26 corrects the detected angle of rotation ϕ. The evaluation device 26 thus determines a corrected angle of rotation ϕ korr . For example, a rotation angle that is less than the detected angle of rotation ϕ is determined as the corrected angle of rotation ϕ korr if the current-based angle of rotation ϕ I is less than the detected angle of rotation ϕ.

[0050] In an eighth step S8, the evaluation device 26 then determines the generated clamping force F clamp as a function of the corrected angle of rotation ϕ korr by means of the first characteristic curve L1.

[0051] Preferably, the evaluation device 26 changes the first characteristic curve L1 depending on the corrected angle of rotation ϕ korr . The evaluation device 26 thus determines a corrected first characteristic curve. If step S5 is performed again, the evaluation device 26 then determines the generated clamping force F clamp as a function of the detected angle of rotation ϕ using the corrected first characteristic curve.

[0052] As previously mentioned, the rotation angle ϕ of the rotor corresponds to the displacement path of the displaceably mounted element of the transmission device 14. According to a further embodiment of the method, the displacement path of the element is detected and used as the basis for determining the generated clamping force F clamp instead of the detected rotation angle ϕ. For example, a first characteristic curve L1 is then used, which describes the generated clamping force F clamp as a function of the displacement path of the element.

Claims

1. Method for determining a clamping force of a brake device of a motor vehicle, wherein the motor vehicle (1) has at least one rotatably mounted wheel (4) and a brake system (8) having at least one brake device (9) and at least one electric motor (13), wherein the brake device (9) has a brake element co-rotationally connected to the wheel (4), and at least one brake body which is able to be pressed against the brake element, wherein the electric motor (13) has a motor winding and a rotatably mounted rotor, wherein the rotor is coupled by a gear device (14) to the brake body in such a manner that, by rotating the rotor, a clamping force (FSpann) by which the brake body is pressed against the brake element is able to be generated, whereby the rotor is rotatable by impinging the motor winding with an electric motor current (IMot), wherein a rotation angle (φ) of the rotor and / or a displacement travel of a displaceably mounted element of the gear device (14) are / is determined, wherein a size of the generated clamping force (FSpann) is determined as a function of the rotation angle (φ) and / or the displacement travel, wherein a size of the motor current (IMot) is determined, and wherein the size of the clamping force (FSpann) is determined as a function of the size of the motor current (IMot), characterized in that it is monitored whether there is a correction situation in which the brake device (9) and / or the electric motor (13) are / is in a static state, in that only if the correction situation is present, a corrected rotation angle (ϕkorr) is determined as a function of the size of the motor current (IMot) on the one hand and the determined rotation angle (φ) on the other hand, and the size of the clamping force (FSpann) is determined as a function of the corrected rotation angle (φkorr), and / or in that only when the correction situation is present, a corrected displacement travel is determined as a function of the size of motor current (IMot) on the one hand and the determined displacement travel on the other hand, and the clamping force (FSpann) is determined as a function of the corrected displacement travel.

2. Method according to Claim 1, characterized in that the size of the clamping force (FSpann) is determined as a function of a first characteristic curve (L1) which describes the clamping force (FSpann) as a function of the rotation angle (φ) or the displacement travel.

3. Method according to Claim 2, characterized in that the first characteristic curve (L1) is varied as a function of the size of the motor current (IMot).

4. Method according to one of Claims 2 and 3, characterized in that, as a function of the size of the motor current (IMot) and a second characteristic curve (L2) which describes the clamping force ratio (KF,I) of the brake device (9) as a function of the size of the motor current (IMot), a current-based clamping force (FSpann,I) is determined, wherein the first characteristic curve (L1) is varied as a function of the current-based clamping force (FSpann,I), and / or wherein the corrected rotation angle (φcorrect) and / or the corrected displacement travel are / is determined as a function of the current-based clamping force (FSpann,I).

5. Method according to one of Claims 2 to 4, characterized in that the first characteristic curve (L1) is varied only when the correction situation as a function of the size of the motor current (IMot) is present.

6. Method according to one of the preceding claims, characterized in that a rotating speed threshold is specified, wherein in the presence of a rotating speed of the rotor that falls below the rotating speed threshold, it is determined that the correction situation is present, and / or in that a displacement speed threshold is specified, wherein in the presence of a displacement speed of the element that falls below the displacement speed threshold, it is determined that the correction situation is present.

7. Method according to one of the preceding claims, characterized in that a current variation threshold is specified, wherein in the presence of a motor current variation that falls below the current variation threshold it is determined that the correction situation is present.

8. Method for operating a motor vehicle, wherein the motor vehicle (1) has at least one rotatably mounted wheel (4) and a brake system (8) having at least one brake device (9) and at least one electric motor (13), wherein the brake device (9) has a brake element co-rotationally connected to the wheel (4), and at least one brake body which is able to be pressed against the brake element, wherein the electric motor (13) has a motor winding and a rotatably mounted rotor, wherein the rotor is coupled by a gear device (14) to the brake body in such a manner that, by rotating the rotor, a clamping force (FSpann) by which the brake body is pressed against the brake element is able to be generated, whereby the rotor is rotatable by impinging the motor winding with an electric motor current (IMot), wherein a size of the generated clamping force (FSpann) is determined, and whereby the motor winding is impinged with the motor current (I Mot) in such a manner that the generated clamping force (FSpann) corresponds to a predefined target clamping force, characterized in that the size of the clamping force (FSpann) is determined by a method according to one of Claims 1 to 7.

9. Device for determining a clamping force of a brake device of a motor vehicle, wherein the motor vehicle (1) has at least one rotatably mounted wheel (4) and a brake system (8) having at least one brake device (9) and at least one electric motor (13), wherein the brake device (9) has a brake element co-rotationally connected to the wheel (4), and at least one brake body which is able to be pressed against the brake element, wherein the electric motor (13) has a motor winding and a rotatably mounted rotor, wherein the rotor is coupled by a gear device (14) to the brake body in such a manner that, by rotating the rotor, a clamping force (FSpann) by which the brake body is pressed against the brake element is able to be generated, and wherein the rotor is rotatable by impinging the motor winding with an electric motor current (IMot), characterized by an evaluation apparatus (26, 26A) which in its intended use is specially equipped to carry out the method according to one of Claims 1 to 7.