Method and device for operating a braking device, braking device

Abstract

The invention relates to a method for operating a braking device, in particular a parking brake device, of a vehicle, which has at least one wheel brake device (1) with an electric motor actuator (7), wherein the actuator (7) has an electric motor (8) and an actuator element (10) movable by the electric motor, wherein the actuator element (10) is movable to actuate the wheel brake device (1) into a clamping position and to release the wheel brake device (1) into a release position, and wherein a movement path of the actuator element (10) is monitored at least when releasing the wheel brake device (1), characterized in that the electric motor (8) is switched from a control operation to a freewheeling operation during a release process and a freewheeling voltage (UEMK) then generated by the electric motor (8) is detected.and that, depending on the detected free-running voltage (UEMK), a minimum movement duration of the actuator element (10) to reach the release position is calculated and compared with a movement duration of the actuator element (10) measured until the end of the release process to verify the plausibility of the movement path.

Description

[0001] The invention relates to a method for operating a braking device, in particular a parking brake device, of a vehicle, which has at least one wheel brake device with an electric motor actuator, wherein the actuator has an electric motor and an actuator element movable by the electric motor, wherein the actuator element is movable to actuate the wheel brake device into a clamping position and to release the wheel brake device into a release position, and wherein a movement path of the actuator element is monitored at least when releasing the wheel brake device.

[0002] Furthermore, the invention relates to a device for operating such a braking device, as well as a braking device. State of the art

[0003] Methods, devices, and braking systems of the type mentioned above are known from the prior art. In a parking brake, a wheel of a vehicle is blocked or released by means of an electromechanical actuator via a wheel braking system. For this purpose, an actuator element is moved into an engagement position, in which brake pads of the wheel braking system are typically pressed against a brake disc that is rotationally fixed to a wheel of the vehicle, or into a release position, in which the actuator element is moved back far enough to allow the brake disc to move freely between the brake pads. For reasons of cost and installation space, current actuators for such parking brake systems are used without a speed sensor. Therefore, the displacement for the correct positioning of the actuator element can only be estimated using the supply voltage and the motor current.Estimating the distance is necessary to set the correct brake clearance, i.e., the distance between the brake pads and the brake disc, when releasing the brakes. The correct brake clearance is crucial for safe driving; an improperly set clearance can lead to premature wear and should therefore be avoided. Disclosure of the invention

[0004] The method according to the invention, with the features of claim 1, has the advantage that the position estimation function is validated based on a required release time or movement duration. A position estimation or the attainment of the release position is validated or achieved using the simplest means. According to the invention, it is provided that the electric motor is switched from a control mode to a freewheeling mode during a release process, and a freewheeling voltage then generated by the electric motor is detected. Depending on the detected freewheeling voltage, a minimum movement duration of the actuator element to reach the release position is calculated and compared with a movement duration measured until the end of the release process to validate the movement path.Whether the actuator element has reached the release position is therefore not detected by speed or displacement sensors, but rather verified by time measurements. The speed or freewheeling speed of the electric motor can be determined based on its freewheeling voltage. Knowing the relevant gear characteristics of the electric motor, such as its gear ratio, the current speed of the actuator element can be determined. Based on this current speed, the necessary time for the actuator element to move to achieve a minimum release position is then calculated. This minimum movement time is then compared with the actual duration of the release process. The latter is measured from the moment the actuator is activated to release the brake.This allows for the simple detection of whether or not the actuator element has reached its release position. The measured movement duration preferably begins with the actuator being activated, i.e., with the start of the release process, and ends with reaching the clamped position or with the completion of the release process. The measured movement duration also includes the time during the transition from controlled operation to freewheeling operation. This is advantageously taken into account when comparing the measured movement duration with the calculated movement duration, particularly when switching back to controlled operation after the freewheeling voltage has been detected.According to an alternative embodiment of the invention, it is preferably provided that the measured movement duration begins with the return to control mode and ends upon reaching the clamped position. Preferably, the calculated minimum movement duration is also determined from the return to control mode until reaching the clamped position, allowing for a simple and direct comparison of the actual movement duration and the minimum movement duration. In particular, it is assumed that the switch to freewheeling mode for determining the freewheeling voltage is only brief. During freewheeling, the electric motor continues to rotate, ultimately inducing the freewheeling voltage and further moving the actuator element. Therefore, the brief switch to freewheeling mode, i.e., the freewheeling duration, is negligible for both the measured and calculated movement durations.

[0005] According to an advantageous embodiment of the invention, the electric motor is switched back to control mode after the minimum operating time has been calculated. This means that the electric motor only switches briefly from control mode to freewheeling mode. In freewheeling mode, a power output stage that drives the electric motor is put into a high-impedance state, so that no current flows through the electric motor and the output stage. The freewheeling voltage can be measured shortly after the freewheeling mode is activated. Preferably, the freewheeling voltage is measured only after a decay time of, for example, 10 ms. As soon as the voltage has been measured, the system can switch back to control mode. Therefore, preferably, the electric motor is switched back to control mode immediately after the freewheeling voltage has been measured.The calculation of the minimum movement duration can then also be carried out or terminated during the restarted control operation.

[0006] According to an advantageous embodiment of the invention, it is further provided that the electric motor is activated again to release the wheel brake device if the measured movement duration falls below the minimum movement duration. In particular, it is provided that the electric motor is activated until the measured movement duration has at least reached the minimum movement duration. This ensures that the actuator element is reliably moved into the release position.

[0007] Furthermore, it is preferably alternatively or additionally provided that an error message is issued if the measured movement duration falls below the minimum movement duration. The error message alerts, for example, a driver of the vehicle equipped with the braking system, in particular a motor vehicle, that the clearance of one of the wheel brake systems of their vehicle is not correctly adjusted and should possibly be checked in a workshop.

[0008] According to an advantageous embodiment of the invention, the minimum operating time is calculated as a function of an estimated or assumed motor constant. For this purpose, the value of the motor constant is taken, for example, from a datasheet of the electric motor. Preferably, the value of the motor constant is adjusted during operation of the electric motor. Optionally, a method for calculating the motor constant can be provided, by means of which the motor constant can be estimated during operation. "Estimation" refers in particular to parameter determination based on measurement data, and "assumption" refers to a parameterization of software (non-adaptive).

[0009] Furthermore, it is preferably provided that the electric motor for releasing the wheel brake device – as already mentioned – is controlled depending on a target release travel. By verifying the plausibility of the electric motor's control by comparing the calculated and actual movement duration, it can be easily determined whether the actual release travel of the actuator element has reached the target release travel.

[0010] The device according to the invention, with the features of claim 7, is characterized by a control unit that carries out the method according to the invention. In particular, the control unit has a voltage measuring device that is connected to the electric motor in order to detect the freewheeling voltage of the electric motor. This results in the advantages already mentioned above.

[0011] The braking device according to the invention, with the features of claim 8, is characterized by the device according to the invention. This results in the advantages already mentioned. Further advantages and features become apparent from the foregoing and from the claims.

[0012] The invention will now be explained in more detail with reference to the drawing. The drawing shows:

[0013] Fig. 1 a wheel brake device in a simplified sectional view,

[0014] Fig. 2. A flowchart illustrating the chain of actions of the wheel braking system.

[0015] Fig. 3 a device for controlling the wheel brake system in a simplified representation, and

[0016] Fig. 4 an advantageous method for operating the wheel brake device.

[0017] Fig. Figure 1 shows a simplified sectional view of a wheel brake device. 1a braking system of a motor vehicle not shown in detail here. The wheel braking system 1 It is designed as a disc brake and has a brake caliper for this purpose. 2 on the brake pads 3 carries, between which a brake disc is non-rotatably connected to a wheel of the motor vehicle 4 It can be clamped. For this purpose, the brake caliper 2 an actuator 5 assigned to a brake piston 6 features a hydraulically actuated mechanism to adjust the brake disc 4 if necessary between the brake pads 3 to clamp down.

[0018] The wheel brake system 1 It is also equipped with a parking brake function. The wheel brake system features this function. 1 also an electric motor actuator 7 up. This is powered by an electric motor. 8 , an actuator gearbox 9 and an actuator element 10formed. An output shaft of the electric motor is connected to the actuator gearbox. 9 connected. This is driven by a drive spindle. 11 formed, which is rotationally fixed to the output shaft and has an external thread that engages with an internal thread along the drive spindle 11 movable actuator element 10 interacts. By controlling the electric motor. 8 This will thus be the drive spindle 11 set in a rotational movement to move the actuator element 10 to relocate. The actuator element is involved. 10 can be moved from a release position to a clamping position, in which the actuator element 10 the brake piston 6 against the brake disc 4 pushes and thereby the brake caliper 2 The actuator element is used for this purpose. 10 coaxial to the brake piston 6 and inside the brake piston 6arranged. In this respect, the wheel brake system corresponds 1 a conventional combined wheel brake / parking brake device.

[0019] To release the parking brake, the electric motor 8 controlled to activate the actuator element 10 to move from the clamping position to the release position, so that there is a ventilation gap between the brake pads. 3 and brake disc 4 The correct ventilation clearance is set. To ensure that the correct clearance is set, the following procedure is provided, which is carried out by a control unit assigned to the brake device or brake system. This procedure determines the travel path of the actuator element. 10 The duration of the movement is estimated or validated based on the required movement time. This involves determining the actual movement time, i.e., the time during which the actuator element... 10The relocation is compared with a minimum movement duration for plausibility purposes.

[0020] Controlling the actuator 7 is in Fig. 2 summarized in a flowchart. Depending on an operating voltage U provided by a power output stage S (t) the electric motor 8 operated. This results in an angular velocity ω(t) of the output shaft of the electric motor. 8 . With a resulting angular velocity ω G (t) the drive spindle 11 driven, preferably via a reduction gear, in particular rotationally fixed to the rotor or the output shaft of the electric motor 8 is connected. Through the threaded teeth of the drive spindle. 11 with the actuator element 10 This results in a conversion of the rotational movement into a translational movement of the actuator element. 10, which moves at a speed v Bk (t) moves.

[0021] To control the electric motor 8 is a power electronics 12 planned. Fig. Figure 3 shows a simplified representation of the electric motor. 8 and the power electronics 12 The electric motor is present. 8 as a two-phase electric motor 8 trained, which of course also includes three-phase training or multi-phase training of the electric motor 8 and the power output stage 12 is possible. The power output stage 12 a bridge circuit 13 to operate the phases of the electric motor 8 on. This involves the power electronics. 12 connected to an electrical storage device or other energy source, so that it has a supply voltage U Battis available. By actuating switching elements, in particular semiconductor switching elements, of the bridge circuit 13 will the electric motor 8 controlled to drive the spindle 11 to drive in one direction or the other, in order to drive the actuator element 10 to move it into the engaged or disengaged position. When disengaging the wheel brake device 1 or when relocating the actuator element 10 In the released position, the required motor current is significantly lower than when tightening. When adjusting the clearance, the motor current is almost constantly in an idle current range and thus at the lower limit of the measuring range. Since the tolerance is unfavorable at the lower limit of the measuring range for determining the position of the actuator element based on the measured current, 11 The following procedure is used to determine this.

[0022] First, a so-called freewheel control of the electric motor is required. 8 necessary. For this, the power output stage is required. 12 of the electric motor 8 put into a high-resistance state, so that no current flows through the electric motor 8 and the power output stage 12 flows, as in Fig. 3 shown. Does the electric motor rotate? 8 If it continues in this state, it is in generator mode, since it has a freewheeling voltage U EMK induced at voltage measurement points, as in Fig. 3 shown, can be measured. The generator's freewheeling voltage is proportional to the motor speed and follows the following law: U EMK (t) = K M ·ω(t) (1)

[0023] K M This represents the motor constant of the electric motor. 8 and ω for the angular velocity of the output shaft of the electric motor 8If the electric motor 8 When in generator mode, the following equation also applies: U Mot (t) = U EMK (t) (2)

[0024] From equation (1) the angular velocity ω of the motor armature or the drive spindle can be determined by rearranging. 11 as follows:

[0025] Due to the angular velocity ω of the motor armature or the drive spindle 11 can be done with knowledge of the gear ratio i G on the movement path of the actuator element 10 will be closed. The following applies:

[0026] Where v Bk for the movement speed of the actuator element 10 , S Sp for the pitch of the thread of the drive spindle 11 and i G for the gear ratio of the gearbox 9is. To engage the parking brake or the wheel brake system. 1 To open or release in a functional manner, a minimum travel distance of the actuator element is required. 10 , by which the actuator element 10 The movement from the clamped position to the released position is necessary. This target path s App is predetermined or known in the control logic of the braking system. Using the speed of movement and the required release distance, a time duration T can be calculated as follows: App The amount of clearance required for the disassembly process to ensure the desired ventilation clearance will be calculated.

[0027] By substituting equation (3) into equation (4) and then into equation (5), the required solution time, which is therefore a minimum movement time for the actuator element, can be determined. 10To achieve the release position with the desired air gap, the following calculations are made for the current situation, which depends, for example, on a voltage level, an operating temperature, or the like:

[0028] Since the current motor constant K M If the value is unknown, but a robust procedure is to be implemented, a datasheet value K is used. M_Data of the electric motor 8 used, which therefore represents an estimated value. Due to the operation and aging of the actuator. 7 The motor constant can change over time. In particular, the motor constant can decrease over time due to wear. A smaller motor constant, in turn, leads to a faster release process, since the electric motor 8It becomes weaker, but also faster. This can be taken into account in the process, for example, by regularly adjusting the motor constant, e.g., depending on the number of operating cycles. All other parameters are known or fixed by design. The electric motor 8 generated voltage U EMK In freewheeling mode, measurements can be taken shortly after switching to freewheeling control. Preferably, however, the measurement is only started after a decay time of 5 to 15 ms, particularly 10 ms. Due to an inductive term in the motor differential equation, a large voltage U is generated by the very rapid drop in the no-load current. ind induced, which leads to the outflow of charge carriers towards a lower potential, for example via a freewheeling diode: U ind (t) = L di(t) dt (7)

[0029] L represents the inductance of the windings of the motor armature of the electric motor. 8 The decay time preferably corresponds to five times the time constant of the inductance L: T = L R (8)

[0030] Where R is the resistance of the freewheel circuit including the electric motor. 8 is. Due to the assumption made regarding the motor constant K M_Data and the measured generator voltage U EMK Equation (6) provides an estimate of the minimum movement time required for a successful solution. Estimated values ​​are subsequently marked with “^”.

[0031] For a successful unwinding process or for a safely adjusted ventilation clearance, the following equation must be fulfilled: T App ≥ T^ App (10)

[0032] This plausibility check of the release process of the wheel brake device 1 is now completely independent of a measured current signal and therefore offers a high and advantageous level of safety.

[0033] Fig. Figure 4 summarizes the previously described procedure in a flowchart using an application example. In the first step, S1, the unwinding process is started and the electric motor 8 corresponding to moving the actuator element 10 controlled from the clamping position to the release position.

[0034] In step S2, it is determined whether the electric motor is in idling or quasi-idling mode. 8was achieved. If this is the case (j), the electric motor is switched from the control mode to the freewheeling mode in a subsequent step S3. In the freewheeling mode, the freewheeling voltage UEMK induced by the electric motor continuing to rotate due to its inertia is measured and the minimum release time T^ App as previously described. If necessary, the electric motor is then 8 switched back to control mode.

[0035] In a subsequent step S4, it is monitored whether the desired target movement path of the actuator element is achieved. 10 was set. Only when this is the case (j) is the movement time T required to reach the goal solution path determined in a subsequent step S5. AppThe system calculates the required movement time. For example, a counter starts running when the release process begins and is read in step S5 after the target release path has been reached. This measures the actual movement time required. In a subsequent step S6, the measured release time is compared with the estimated minimum movement time. If the actual movement time matches the minimum movement time (j), the release process is considered successful, and a corresponding signal / indication is output in step S7. If the actual movement time falls below the minimum movement time (n), a faulty release process is detected, and a warning message is issued in step S8, for example, to the driver of the vehicle.

[0036] The present procedure is therefore used to monitor the release of the parking brake function of the wheel brake system. 1This is preferably done using the no-load friction torque of the electric motor actuator. 7 The minimum movement duration is taken into account, as this reduces the motor speed, particularly during freewheeling. This can be achieved using a factor λ, which depends on the gradient of the generator voltage.

[0037] If the gradient is (much) smaller than in the nominal case, a reduced idling friction moment must be assumed and the minimum movement time can be shorter.

[0038] Alternatively or additionally, it is advantageously provided that the method is also functionally suitable for controlling the wheel brake device. 1 is carried out. It is planned that the target-position-controlled control duration of the electric motor will be determined. 8 will be extended if the measured

[0039] Movement duration T App is shorter than the estimated minimum movement duration T^App . In this procedure, it is unnecessary to take into account the reduction of the idle torque, as this would only lead to a longer loosening process.

[0040] The described procedure can, in principle, be used with all braking systems or vehicles with braking systems featuring an electromechanical parking brake.

Claims

[1] Method for operating a braking device, in particular a parking brake device, of a vehicle, which includes at least one wheel brake device ( 1 ) with an electromechanical actuator ( 7 ) exhibits, wherein the actuator ( 7 ) an electric motor ( 8 ) and an actuator element movable by the electric motor ( 10 ) has, wherein the actuator element ( 10 ) to operate the wheel brake device ( 1 ) into a clamping position and to release the wheel brake device ( 1 ) is movable into a release position, and wherein a movement path of the actuator element ( 10 ) at least when releasing the wheel brake device ( 1 ) is monitored, characterized by that the electric motor ( 8 ) during a release process, switching from a control operation to a freewheeling operation and then driven by the electric motor ( 8 ) generated freewheeling voltage (U EMK) is recorded, and that depending on the recorded free-running voltage (U) EMK ) a minimum movement duration of the actuator element ( 10 ) calculated to reach the release position and with a movement duration of the actuator element measured until the end of the release process ( 10 ) to verify the plausibility of the movement path. [2] Method according to claim 1, characterized by that the electric motor ( 8 ) after the minimum movement duration has been calculated, the system switches back to control mode. [3] Method according to any one of the preceding claims, characterized by that the electric motor ( 8 ) to release the wheel brake device ( 1 ) is activated again if the measured movement duration falls below the minimum movement duration. [4] Method according to any one of the preceding claims, characterized bythat an error message is issued if the measured movement duration falls below the minimum movement duration. [5] Method according to any one of the preceding claims, characterized by that the minimum movement duration depends on an assumed motor constant (K) M ) is calculated. [6] Method according to any one of the preceding claims, characterized by that the electric motor ( 8 ) to release the wheel brake device ( 1 ) depending on a target solution path of the actuator element ( 10 ) is controlled. [7] Device for operating a braking device, in particular a parking brake device of a vehicle, wherein the braking device includes at least one wheel brake device ( 1 ) with an electromechanical actuator ( 7 ) exhibits, wherein the actuator ( 7 ) an electric motor ( 8 ) and one powered by the electric motor ( 8 ) movable actuator element ( 10) characterized by a control unit which, when used as intended, performs the procedure according to one or more of the preceding claims. [8] Braking device, in particular parking brake device of a vehicle, in particular motor vehicle, with at least one wheel brake device ( 1 ) with an electromechanical actuator ( 7 ), where the actuator ( 7 ) an electric motor ( 8 ) and one powered by the electric motor ( 8 ) movable actuator element ( 10 ) has a mechanism for actuating the wheel brake device ( 1 ) into a clamping position and to release the wheel brake device ( 1 ) is movable into a release position, characterized by a device according to claim 7.