Method for determining the motor constants of an electric motor of an electromechanical parking brake, control method for the operation of a drive of an electromechanical parking brake and electromechanical parking brake

Abstract

A method (86) for determining the motor speed constant of an electric motor (44) of an electromechanical parking brake (12) is presented, as is a control method (68) for operating a drive (42) of an electromechanical parking brake (12), and an electromechanical parking brake (12) with an electronic controller (64) and a drive (42). The electromechanical parking brake (12) is integrated into a hydraulic service brake (14). A spindle nut (34) of the electromechanical parking brake (12) is arranged to be displaceable at least partially within a hydraulically actuated actuating piston (24) of a braking device (10) such that the spindle nut (34) can be moved against the actuating piston (24).Before determining the motor speed constant, if the required idle distance between the spindle nut (34) and the actuating piston (24) is not present, the hydraulically actuated actuating piston (24) of the brake device (10) is pressurized with a hydraulic fluid corresponding to an idle distance pressure, and at least the idle distance is set. Subsequently, the electric motor (44) is energized, and a test run is performed within the idle distance.

Description

[0001] The present invention relates to a method for determining the motor constants of an electric motor of an electromechanical parking brake, a control method for the operation of a drive of an electromechanical parking brake and an electromechanical parking brake with a controller and a drive.

[0002] Electromechanical parking brakes are widely used today, for example, as a complementary component of a braking system (vehicle brake) to a hydraulic service brake. Electromechanical parking brakes serve as braking devices that can permanently ensure frictional engagement between brake pads and a brake disc, even when the hydraulic circuit pressure is not present, for example, when the vehicle is shut down or parked.

[0003] In some embodiments, the electromechanical parking brake can have a spindle arrangement with a nut / spindle combination. The electromechanical parking brake can then be integrated into a hydraulic service brake. A spindle nut of the electromechanical parking brake can then be arranged displaceably, at least partially, within a hydraulically actuated brake piston (hollow piston) of the service brake of the braking device (vehicle brake) such that the spindle nut can be moved relative to the brake piston. For example, rotation of the spindle can result in a translation of the spindle nut along a displacement axis, effectively ensuring a travel path for the spindle nut of the parking brake. The rotation of the spindle can be effected, in particular, by an electric motor.As a result, after reaching a contact point, the spindle nut can act on (engage with) a brake piston of the braking system, which includes the electromechanical parking brake and the hydraulic service brake. This allows the brake piston to be moved toward the brake disc of the braking system, causing a brake pad coupled to the brake piston to be brought into frictional engagement with the brake disc at the contact point.

[0004] In some embodiments, the spindle nut can be positioned close to the piston crown of the brake piston, e.g., when a small clearance is required (small gaps / gap dimensions). Then, if the spindle nut is not optimally aligned, for example, it can always be in contact with the brake piston, which can cause residual drag torque. For example, in some designs, the brake pads can also be permanently pressed against the spindle nut due to strong spring elements.

[0005] In these situations, it may be the case that a minimum travel distance cannot be guaranteed for executing a reference run using the electric motor at idle speed in order to adjust the parking brake using a control procedure or to determine control parameters of the drive underlying the parking brake. In other words, the gap between the spindle nut and the brake piston may be so small that a sufficient travel distance cannot be guaranteed for the electric motor or spindle nut at idle speed, along which only negligible friction torques occur. Rather, residual drag torques may make it impossible to assume that the electric motor is idle without torque. Executing a control procedure would then lead to an incorrect determination of the motor speed constant k. Eand consequently lead to an incorrect determination of other drive parameters, such as the total resistance R ges of the drive.

[0006] For this reason, the invention is based on the object of eliminating or at least mitigating the relevant disadvantages of the prior art. In particular, there is a need to be able to provide an electromechanical parking brake in such a way that the permissible conditions for implementing a control method in the form of a (substantially) frictionless minimum travel distance can be guaranteed.

[0007] This problem is solved by the subject matter of the independent patent claim. Advantageous embodiments are specified in the dependent patent claims and the following description, each of which, individually or in (sub)combination, may represent aspects of the invention. Individual aspects are presented with reference to devices, others with reference to methods. However, the features and advantages are to be transferred in a corresponding manner.

[0008] According to one aspect, a method is provided for determining the motor constant of an electric motor of an electromechanical parking brake. The electromechanical parking brake is integrated into a hydraulic service brake (also called a vehicle brake). A spindle nut of the electromechanical parking brake is arranged at least partially within a hydraulically actuated brake piston (also called an actuating piston) of the braking device such that the spindle nut can be moved against the brake piston (actuating piston). Before determining the motor speed constant k EIf the required idle distance between the spindle nut and the brake piston is not present, the hydraulically actuated brake piston of the brake device is pressurized with hydraulic fluid corresponding to the idle distance pressure, and at least the idle distance is set. The electric motor is then energized, and a test run is performed within the idle distance.

[0009] This means that the hydraulic service brake of the braking device can be used to ensure the conditions for executing the previously outlined control procedure based on an idle distance guaranteed by hydraulic pressure for the spindle nut. Thus, a sufficient gap can be created between the hydraulically actuated brake piston (also called the actuating piston) and the spindle nut to ensure the minimum travel distance required to evaluate the electric motor at idle with regard to its speed and the induced countervoltage. During idle, the spindle nut moves in accordance with the measurement travel caused by the electric motor at idle.This ensures sufficient idle distances for the spindle nut, even when the brake pistons are loaded by sufficiently strong springs, allowing a control process to determine the parking brake drive parameters to be carried out. This consequently increases the precision of the electromechanical parking brake control.

[0010] In this case, the idle distance can be understood as the minimum distance (minimum gap) between the spindle nut and the brake piston required to allow the electric motor to be moved a sufficient distance during idle operation, for example, to determine the induced countervoltage and the speed of the electric motor during idle operation. During idle operation, the electric motor is moved toward the brake application state during the execution of the control process.

[0011] The idle distance pressure is to be understood here as the pressure that is sufficient to ensure the idle distance between the spindle nut and the hydraulically actuated brake piston.

[0012] Preferably, the idle distance pressure is adjustable during operation. This ensures that a sufficient idle distance can be maintained even in the event of changing operating parameters of the braking device, and in particular of the electromechanical parking brake. This increases the variability of the braking device, making the method and the control method outlined more robust against influences on the braking device, such as aging effects or brake pad wear.

[0013] Optionally, the idle distance is greater than a predefined or adjustable threshold during operation. This further increases the variability of the method, as the idle distance can be varied according to the desired characteristics. For example, for certain operating scenarios of the braking system, it may be desired that the idle distance be greater than required for other operating scenarios.

[0014] In some embodiments, the idle distance pressure is set based on the threshold. Since the idle distance pressure influences the idle distance achieved as a result of applying the idle distance pressure, the idle distance pressure can be selected as needed by varying the threshold value provided for the idle distance. This ensures that an idle distance greater than the specified threshold is always achieved.

[0015] Preferably, an operating pressure already exerted on the brake piston by means of the hydraulic fluid prior to execution of the method is maintained during the method, taking into account the idle distance pressure. Since the braking device comprises both the hydraulic service brake and the electromechanical parking brake, it can naturally happen that the hydraulic service brake is already actuated before the idle distance for implementing the control method outlined is to be ensured. The actuation of the hydraulic service brake is accompanied by an operating pressure acting on the brake piston, exerted by the hydraulic fluid. In this case, the already exerted operating pressure serves as the base value, which is additionally increased by the idle distance pressure so that the idle distance for the spindle nut relative to the brake piston can be ensured.Thus, the present method makes it possible to maintain the desired functionality of the hydraulic service brake while ensuring the idle distance so that the control procedure outlined can be implemented. This increases the functionality of the method and the control procedure outlined.

[0016] Optionally, after reaching the threshold, the electric motor is ramped up to a minimum idle speed, and a counter voltage induced by the idle motor is measured. Additionally, the speed of the idle motor can be recorded, for example, using an asynchronous counter. This allows the motor speed constant k to be determined. E Based on the engine speed constant k E then, as explained below, the total resistance R gesof the drive system that includes the electric motor. Advantageously, the total resistance of the electric motor of the electromechanical parking brake can be determined without the need for a speed sensor.

[0017] In some embodiments, the electric motor is de-energized (no longer energized) after the electric motor has been ramped up to the minimum idle speed and the induced counter voltage has been measured. The electric motor then continues to rotate due to its inertia. This allows the measurement pause for the electric motor's idle running to be extended. For example, the determination of the motor speed constant k E and thus also the total resistance R ges possible with higher precision.

[0018] The electric motor can in particular be a permanently excited DC motor.

[0019] According to a further aspect, a braking device for a vehicle is also provided, which has a hydraulically actuated service brake, an electromechanical parking brake and an electronic control, and in which the electronic control is configured to carry out the method as explained above.

[0020] When controlling electromechanical parking brakes, manufacturing tolerances or wear on the brake pads can cause the air gap, i.e. the totality of all air gaps (generally: gap dimensions) between various components of the hydraulic service brake, to change during vehicle brake operation. For example, the gap between the friction side of the brake pad and the brake disc can increase over time due to brake pad wear. This means that frictional engagement is only guaranteed after a greater travel of the electromechanical parking brake when the parking brake is used. This reduces comfort for the user, as the larger gap not only increases the response time of the parking brake, but also allows the friction torque to vary.

[0021] To compensate for such effects, methods for operating the drive system that provides the parking brake are being considered, which aim to compensate for such effects as much as possible. For example, it is known to determine a combined signal from a current signal and a voltage signal of the electric motor underlying the parking brake. The signal oscillations are then evaluated to determine a rotation angle signal of the electric motor. This allows the speed of the electric motor to be determined, which allows the parking brake drive to be controlled.

[0022] However, these approaches assume predetermined total resistances of the respective drive, which includes the electric motor of the electromechanical parking brake. Since the total resistance also influences the actual motor speed of the electric motor, manufacturing tolerances or aging processes can result in the assumed total resistance of the respective drive no longer corresponding to the actual total resistance of the drive. This limits the precision of the control of the drive, which includes the electromechanical parking brake. This leads to the electromechanical parking brake not having consistent desired braking parameters, such as travel or response time.

[0023] The invention is therefore also based on the further object of eliminating or at least mitigating the disadvantages of the prior art. In particular, it is intended to create a way to control an electromechanical parking brake more precisely than before, thus increasing user comfort.

[0024] The problem is solved by the techniques explained below. Advantageous embodiments are specified in the dependent patent claims and the following description, each of which, individually or in (sub)combination, may represent aspects of the invention. Individual aspects are presented with reference to devices, others with reference to methods. However, the features and advantages are to be transferred in a corresponding manner.

[0025] According to one aspect, a control method for operating a drive of an electromechanical parking brake is provided. The drive has an electric motor and is coupled to a voltage source. The control method comprises at least the following steps: A motor speed and a first voltage value of an induced counter voltage are recorded when the electric motor is idling (generator operation of the electric motor).

[0026] An idle engine speed constant is determined by an electronic control based on the engine speed and the first voltage value of the induced counter voltage.

[0027] A total resistance of the drive is determined by means of the electronic control based on a second voltage value of a supply voltage provided by the voltage source and a current value of the phase current occurring in the drive during idle operation.

[0028] This makes it possible to determine the total resistance of the drive without having to assume it is fixed. Advantageously, only a few recorded drive parameters are required for this purpose. The total resistance determined in this way then makes it possible to increase the precision of drive control compared to previous approaches, since the total resistance can be assumed to be constant over relatively long periods of time. In particular, the present control method does not require any assumption of the value of the total resistance of the drive, but ensures that the total resistance can be determined from the intrinsic parameters of the drive when the drive's electric motor is operating at idle. This makes it possible to compensate for deviations that are caused, for example, by manufacturing tolerances. In addition, the contact force of the electromechanical parking brake can be adjusted more precisely than before.Residual drag torques can also be avoided. Furthermore, controlling the electromechanical parking brake drive eliminates the need for repeated evaluation of the signal oscillations of combined current and voltage signals. This reduces the effort required to operate the drive compared to previous approaches, as the present control method requires less computing power and less memory than conventional approaches.

[0029] In this case, idling of the electric motor can be understood as operation of the electric motor at an idle speed at which the electric motor does not exert any significant mechanical torque on another component (generator operation of the electric motor). This means that the rotor of the electric motor is not in mechanical engagement with another component to such an extent that it would cause a non-negligible mechanical torque. However, (negligible) friction torques can occur during generator operation, for example, due to the translation of a component coupled to the electric motor, such as a spindle nut.

[0030] Preferably, at least one component coupled to the electric motor or a component of the electric motor itself can move toward the applied state of the electromechanical parking brake when idling. However, the movement of the corresponding component does not cause any significant mechanical torques, except for negligible friction torques (this does not mean the friction torque that occurs when the brake pad engages a brake disc).

[0031] The applied state of the electromechanical parking brake is understood to mean the engagement of at least one brake pad with a brake disc. However, during the neutral position, this frictional engagement (and thus the applied state) does not yet occur. Overall, the electromechanical parking brake (also called the parking brake) is thus moved toward the applied state during the neutral position mentioned here.

[0032] As soon as the electric motor is moving, a countervoltage is induced in the electric motor, depending on the electric motor's speed. This generally results in the actual voltage acting in the electric motor not matching the electrical voltage absorbed by the electric motor. Rather, the absorbed electrical voltage is effectively reduced by the induced countervoltage. The absorbed electrical voltage is provided by a supply circuit of the drive, which includes the electric motor. For example, the supply circuit can include the voltage source and be coupled to the electric motor.

[0033] In the present case, the electronic control can be understood as a control device which has at least one data processing device.

[0034] The electronic control system may comprise sensors or at least be coupled to them in order to be able to record parameters when controlling the electric motor, for example voltage values ​​or phase current values.

[0035] In this case, the total resistance of the drive can be understood as the sum of a series resistor and an effective electrical armature resistance of the supply circuit of the electric motor itself. The series resistor includes, in particular, resistances of cables, filter devices, and components of the drive's supply circuit, which is required to supply the electric motor with the appropriate voltages so that effective phase currents are established in the electric motor.

[0036] In some embodiments, for the determination of the total resistance, it is assumed that the motor speed constant k Eof the electric motor in generator mode of the electromechanical parking brake and the motor torque constant k M (in motor operation of the electric motor), i.e.: k E = k M This advantageously simplifies the determination of the total resistance of the drive.

[0037] The preferred engine speed is ω RC at idle using an asynchronous counter (also called ripple counter) during a measurement pause. During the measurement pause, the course of the induced counter voltage U ind for a period of time. The recorded signal curve of the induced counter voltage U ind is then evaluated by the electronic control system with regard to the local maxima or minima, which are determined by the relative positions of the rotor poles to the stator poles (e.g., overlap vs. no overlap). Knowing the measurement pause time, the motor speed ω RCcan be determined without the need for a speed sensor. This makes the drive design very compact and less complex. Since no mechanical torque is exerted by the electric motor during idle (or only a negligible one), the motor speed constant k E can then be advantageously determined very efficiently as: kE=UindωRC.

[0038] In some embodiments, the asynchronous counter can be implemented as part of the electronic control system. Generally, the asynchronous counter can also be separate from the electronic control system and transmit the corresponding count values ​​to the electronic control system.

[0039] Assuming that the engine speed constant k E (in generator mode of the electric motor) with the motor torque constant k M (in motor operation of the electric motor), then the total resistance R gesof the drive taking into account the voltage value of the voltage source U ECU be determined: Rtotal=RV+RA=UECU−UindIA.

[0040] With R V is a series resistor that is created by the electronic supply circuit for controlling the electric motor. In contrast, R A the intrinsic armature resistance of the supply circuit with respect to the electric motor, which can be caused, for example, by the line resistance of the electric motor's windings. In this case, it is assumed that the phase current I occurring in the electric motor A is constant over time (diA(t)dt=0), This is due to the fact that the electric motor is idling and does not produce any mechanical torque to be considered. Here, i A the time-varying magnitude of the phase current occurring in the electric motor.

[0041] Optionally, the measurement pause is between 50 ms and 30 seconds, preferably between 100 ms and 25 seconds, and more preferably between 200 ms and 20 seconds. This demonstrates that only a very short measurement pause is required to apply the present control method. For example, a vehicle standstill can be used to provide the measurement pause for the control method and enable the corresponding determination of the engine speed and the induced countervoltage.

[0042] Preferably, at least the determined total resistance R ges of the drive and the determined motor speed constant k Ein the application state of the electric motor in the electronic control system to determine the motor speed ω of the electric motor in the application state. As a good approximation, the fact that the total resistance of the drive is constant over time can be used to determine the speed in the application state of the electromechanical parking brake (at least beyond predetermined periods). In particular, it can be used that the total resistance of the drive is constant during the implementation of the application state of the electromechanical parking brake from idle. This assumption is based on the fact that the temperature of the motor and the supply circuit of the electric motor changes only negligibly during the implementation of the application state and during the measurement pause for determining the motor speed in idle. In addition, it is used that the motor speed constant k E in generator mode of the electric motor and the motor torque constant kM during motor operation. As a result, the speed of the electric motor can be determined efficiently and precisely even without a speed sensor. This enables a compact and precise control method for controlling the electric motor.

[0043] Optionally, when determining the motor speed ω of the electric motor in the application state, at least the second voltage value of the supply voltage U provided by the voltage source is also taken into account. ECU and the current value of the phase current i that occurs in the drive when the electric motor is engaged A This means that only a few simple and precise parameters need to be detected to determine the speed. The speed of the electric motor can then be efficiently determined using: ω=UECU−iA⋅RgeskM.

[0044] This allows the motor speed of the electromechanical parking brake's electric motor to be determined very efficiently, even for the electromechanical parking brake's application state. This is possible even though the phase current i occurring in the electric motor A and of course the provided supply voltage U ECU are temporally variable. To measure these variables, the electronic control system is equipped with or linked to appropriate sensors. This ensures a robust yet compact control process for the drive of the electromechanical parking brake. The advantage is that the computational effort required to execute the control process is reduced compared to conventional approaches. Furthermore, it is not necessary to continuously use an asynchronous counter to evaluate signals.

[0045] Due to the ability to determine the electric motor's speed, the relative position of the rotor relative to the stator can also be determined, since the angle of rotation of the rotor relative to the stator is determined by the motor speed as a function of a reference position. This improves the precision of electric motor control compared to previous approaches.

[0046] In some embodiments, the electronic control also determines a motor torque M of the electric motor at least based on the determined motor torque constant k M certainly: M=kM⋅PRtot

[0047] Here, P denotes the electrical power of the electric motor, which can be determined from the recorded parameters, for example based on the phase current i that occurs in the electric motor. A , the provided supply voltage U ECUand the counter voltage U induced as a function of the speed ω ind . In the application state, the motor torque generated by the electric motor is equivalent to the applied application force F Zuspann , which presses the friction linings onto the brake disc. This allows for even more precise parking brake control.

[0048] Based on the determination of the motor torque M, the support point (also called the "touch disc" point or "set point") can also be determined. This is the point along the travel path of the electromechanical parking brake at which at least one component of the parking brake, for example a spindle nut, engages the brake disc, generating a friction torque that can no longer be neglected. In other words, at the support point, all gaps within the braking device are reduced to zero. The brake device's clearance is then bridged. Any further movement of the parking brake starting from the support point accordingly causes a brake pad to be pressed against the brake disc, thus changing or generating a braking force.Typically, the spindle nut acts on a brake piston that is coupled to a brake pad and engages the brake disc at the support point. The support point is determined by the fact that the characteristic of the phase current curve in the electric motor changes significantly as a result of the engagement with the brake disc, generating frictional torques that can no longer be neglected. This means that the phase current has different gradients on either side of the support point depending on the travel distance. This also causes a significant change in the motor torque M of the electric motor as soon as the support point is reached. Knowing the position of the support point along the travel distance of the electromechanical parking brake, in particular of its spindle nut, enables the electromechanical parking brake to be controlled more precisely than before.For example, it can then be ensured that the brake device's clearance does not exceed a predetermined threshold. In particular, the desired gap dimensions between the spindle nut of the electromechanical parking brake and the base of the brake piston of a hydraulic service brake can be set and maintained within the control system. This allows the response time and travel of the electromechanical parking brake to be influenced.

[0049] In addition, the present control also allows the maximum current of the phase current i A,Max of the drive and / or the maximum motor torque M Max It can be taken into account that the maximum phase current i A,Max knowing the total resistance R assumed to be constant ges of the drive depending on the provided supply voltage U ECUThis only needs to be taken into account according to the formula above in order to determine the maximum engine torque M Max to determine the maximum achievable clamping force F Zuspann,Max As a result, the electromechanical parking brake can be controlled even more precisely than before.

[0050] Optionally, the control procedure can be repeated to obtain at least updated values ​​of the total resistance R ges of the drive. For example, aging processes can lead to the total resistance R ges of the drive. By repeatedly executing the control procedure outlined above, updated values ​​of the total resistance R gesbe determined so that the control process for operating the electromechanical parking brake can be carried out again, at least for a certain period of time, in the manner outlined here, in particular in a compact, precise and efficient manner.

[0051] According to a further aspect, an electromechanical parking brake with an electronic control and a drive is also provided. The drive has an electric motor. The drive can be coupled to a voltage source providing a supply voltage. The electronic control is configured to execute the control method as previously explained.

[0052] The advantages achieved by the control method explained above are also achieved by the parking brake shown here.

[0053] Preferably, the electronic control comprises at least one data processing device.

[0054] According to an additional aspect, a vehicle with an electromechanical parking brake as previously explained or a braking device as previously described is also provided. A vehicle can be understood, in particular, as a land vehicle, namely, among other things, an off-road or road vehicle, such as a passenger car, a bus, a truck, or another commercial vehicle. Vehicles can be manned or unmanned. Vehicles can be at least partially electrically powered.

[0055] The invention, as well as further advantageous embodiments and developments thereof, are described and explained in more detail below with reference to the example shown in the drawing. The features shown in the description and the drawing can be used individually or in any combination according to the invention. They show: - Fig. 1 is a schematic representation of a braking device for a vehicle with an electromechanical parking brake according to an embodiment of the invention, - Fig. 2 a schematic representation of an equivalent circuit diagram of the drive of the electromechanical parking brake according to an embodiment of the invention, - Fig. 3 a schematic representation of a control method for the operation of a drive of an electromechanical parking brake according to an embodiment of the invention, and - Fig. 4 a schematic representation of a method for determining the motor speed constant of an electric motor of an electromechanical parking brake according to an embodiment of the invention.

[0056] All features disclosed below with respect to the embodiments and / or the accompanying figures may be combined alone or in any sub-combination with features of the aspects of the present disclosure, including features of preferred embodiments, provided that the resulting combination of features is meaningful to a person skilled in the art.

[0057] Fig. 1 shows a schematic representation of a braking device 10 for a vehicle (also called vehicle brake) with an electromechanical parking brake 12 according to an embodiment of the invention.

[0058] From a mechanical perspective, the braking device 10 is designed as a generally known floating caliper brake, with only selected components of the braking device 10 being illustrated. In addition to the electromechanical parking brake 12, the braking device also includes a hydraulically actuated service brake 14, which at least partially encloses the electromechanical parking brake 12, as will be explained below.

[0059] The braking device 10 has a brake housing 16 in the form of a known brake caliper and a brake disc 18 which is non-rotatably coupled to a vehicle wheel (not shown). Brake pads 20, 20A, 20B (also called friction pads) are located opposite the brake disc 18 on both sides and can be brought into contact with the brake disc 18 to achieve a braking force. For this purpose, a service brake 14 of the braking device 10 comprises a displaceable actuating piston 24 (also called a brake piston) received in a bore 22 in the brake housing 16. This is designed as a hollow piston and has a hydraulic chamber 26 inside it. By introducing and discharging hydraulic fluid into the hydraulic chamber 26, a hydraulic pressure in the hydraulic chamber 26 can be varied and the actuating piston 24 can be moved along a displacement axis V in a generally known manner. A movement along the displacement axis V in Fig. 1 to the left corresponds to a movement in an application direction Z of the brake device 10. Overall, the brake pads 20 can thus be brought into contact with the brake disc 18 to achieve a braking force and can be released from it again when the hydraulic pressure is reduced in order to ensure the function of the service brake 14.

[0060] To achieve the desired return movement of the actuating piston 24 to its starting position after the hydraulic pressure is released, the braking device 10 further comprises a schematically indicated seal 28. This seal is received in a groove 30 extending from the bore 22 and bears against an outer wall of the actuating piston 24. The seal 28 provides, in a generally known manner, a so-called "rollback" function, which assists in pushing the actuating piston 24 back to its starting position when the hydraulic pressure is released.

[0061] The electromechanical parking brake 12 is also accommodated within the hydraulic chamber 26 and can also move along the displacement axis V. From a mechanical perspective, the parking brake 12 is again designed according to known solutions and includes an actuator unit 32, which is configured as a nut / spindle arrangement. More precisely, the actuator unit 32 includes a spindle nut 34, which can be moved translationally along the displacement axis V by rotating a spindle 36. The spindle nut 34 can also be brought into contact with a piston crown 38, which is configured as an inner end wall region of the actuating piston 24, opposite the spindle nut 34 and delimiting the hydraulic chamber 26.

[0062] The actuator unit 32 is further connected to the brake housing 16 via a coupling region 40, wherein a schematically illustrated electric motor drive 42 is flanged to the coupling region 40 from the outside of the brake housing 16. The drive 42 comprises at least one electric motor 44. By means of the electric motor 44, the drive 42 drives the spindle 36 in rotation to ensure the desired displacement movement of the spindle nut 34 along the axis V.

[0063] When the service brake 14 and the electromechanical parking brake 12 are not actuated, gaps S exist within the braking device between various components that must be bridged to achieve braking force. These gaps include (from left to right): a gap S between the brake housing 16 and the left brake pad 20A, a gap S between this left brake pad 20A and the brake disc 18, a gap S between the right brake pad 20B and the brake disc 18, and a gap S between the actuating piston 24 and the right brake pad 20B. To generate braking forces, the electromechanical parking brake 12 must also overcome a gap S between the spindle nut 34 and the piston crown 38 of the actuating piston 24.

[0064] The gaps S between the brake pads 20 and the brake disc 18 are generally referred to as "air gap" or "brake air gap," which is why these gaps S are additionally provided with the reference symbol L. The air gap L should assume a predetermined minimum value in order to avoid residual grinding torques in the sense of an unwanted contact of the brake pads 20 with the brake disc 18 when the braking device 10 is not actuated.

[0065] The gap S between the spindle nut 34 and the piston crown 38 of the actuating piston 24 is a safety distance, which is why this gap S is additionally provided with the reference symbol X. The safety distance X should generally assume a predetermined minimum value for reasons of system safety in order to be able to guarantee proper function of the service brake 14 if the electromechanical parking brake 12 is not actuated. The gap S between the spindle nut 34 and the piston crown 38 of the actuating piston 24 is additionally designated as idle distance D. The idle distance D denotes a Fig. 3 outlined control method required travel of the spindle nut 34 along the displacement axis V in the direction of the application state. As explained further below, in certain operating situations of the brake device 10 or in certain embodiments thereof, it may happen that the idle distance D is not present per se. For this eventuality, the method from Fig. 4, by means of which the required idle distance D can be generated, so that the control procedure from Fig. 3 is made possible.

[0066] During a normal driver-controlled service braking application, hydraulic pressure is built up in the hydraulic chamber 26, and the actuating piston 24 is moved along the application direction Z into a braking force-generating actuation position. In doing so, it comes into contact with the right-hand brake pad 20B, brings it into contact with the brake disc 18, and applies the braking device 10 in a known manner according to a floating caliper design. In this process, all gap dimensions S, including the air gap L, are bridged, with the exception of the safety distance X between the spindle nut 34 and the piston crown 38 of the actuating piston 24. To reduce the braking force, the actuating piston 24 moves counter to the application direction Z as a result of a reduction in the hydraulic pressure and with "rollback" support from the seal 28, whereupon the previously bridged gap dimensions S, L are reset.

[0067] The electromechanical parking brake 12 can generally be activated in the presence or absence of hydraulic pressure (i.e., independently of the service brake 14) to move the actuating piston 24 into its actuating position and / or mechanically lock it therein. For this purpose, the spindle nut 34 is moved along the axis V in the manner described above and is supported (at least when moving in the application direction Z) on the piston crown 38.

[0068] For the regulatory procedure pursuant to Fig. In the embodiment shown in Fig. 3, it is provided that activation of the parking brake 12 takes place without prior generation of a hydraulic pressure, that is to say that the braking device 10 is generally kept free of a hydraulic pressure.

[0069] In contrast, the Fig. 4, an operating situation in which the idle distance D between the spindle nut 34 and the piston crown 38 of the actuating piston 24 is not present, but must first be brought about. This can occur, for example, if the brake pads 20 and consequently also the actuating piston 24 are permanently pressed against the spindle nut 34 due to the use of strong return elements (spring elements) (e.g. in so-called "zero drag calipers") or at least the gap S between the spindle nut 34 and the piston crown 38 is smaller than the idle distance D. In addition, this situation can also occur if, due to the return elements used, a hydraulic pressure generated by the service brake 14 is insufficient to ensure the idle distance D. In this case, the Fig. 4 can be used to achieve the idle distance D.

[0070] Fig. 2 shows a schematic representation of an equivalent circuit diagram 46 of the drive 42 of the electromechanical parking brake 12 according to an embodiment of the invention.

[0071] The actual supply circuit 48 of the drive 42 for supplying the electric motor 44 is shown here in the form of an equivalent circuit 46, which has an armature circuit 50. The electric motor 44 is supplied with electrical signals, in particular phase voltages, via corresponding supply lines 52 of the armature circuit 50. Due to the relative positions of the magnetic poles of the electric motor 44 as a function of the motor speed ω, time-varying phase currents i(t) arise within the electric motor based on the phase voltages.

[0072] In order to provide the phase voltages, the supply circuit 48 has at least one voltage source 54 or is coupled thereto. In the present case, a supply voltage U ECU provided for drive 42.

[0073] According to this embodiment, the supply circuit 48 also has an input section 56 with a series resistor 58 R V which can, for example, perform filter functions to suppress or at least attenuate signal interference. The precise design of the input section 56 is not important for the invention. In any case, an (effective) series resistor 58 R V of the supply circuit 48 of the drive 42. A corresponding current I A and (via terminals A1, A2) a corresponding voltage U A away.

[0074] The armature circuit 50 includes further components, here for example in the form of an inductance 60 L A and an armature resistance of 62 R A. In this equivalent circuit diagram 46, the armature resistance (also called drive resistance) includes the intrinsic line resistances of the electric motor 44 itself. The exact design of the armature circuit 50 can differ from the embodiment shown here, but is not essential for the invention. Ultimately, time-varying phase voltages are provided via the supply lines 52 for the electric motor 44, by means of which time-varying phase currents i(t) are driven in the electric motor 44 and are established in the electric motor 44. As a result of the phase currents i(t), the electric motor provides a motor torque M, by means of which a component coupled to the electric motor 44 of the drive 42 can be moved, for example the spindle 36. As a result of the rotation of the spindle 36, the spindle nut 34 can be moved along the displacement axis V.

[0075] In this case, the electric motor 44 is designed as a permanently excited DC motor. The operating characteristics of the electric motor 44 are determined by its total resistance R ges and its operating constants, i.e. the speed constant k E in generator mode of the electric motor and the torque constant k M during motor operation. For the control procedure explained below, it is assumed that the total resistance R ges is constant over time and that the engine speed constant k E in generator mode of the electric motor and the motor torque constant k M during motor operation. The total resistance R ges of the drive 42 consists of the sum of the series resistance R V 58 and the armature resistance R A 62 of the supply circuit 48 together: R ges = R V + R A .

[0076] As a result of the rotation of the rotor of the electric motor 44, a counter voltage U ind induced. This effectively reduces the voltage amplitudes acting in the electric motor 44 due to the absorbed phase voltages.

[0077] The braking device 10 has at least one electronic control 64 which is coupled to the supply circuit 48 of the drive 42 and is configured to control the operation of the electric motor 44, for example based on the supply voltage U provided by the voltage source 54 ECU For this purpose, the electronic control unit can, for example, output corresponding pulse-width modulated control signals. In any case, the electronic control unit 64 is configured to measure the voltage values ​​of the supply voltage U by means of sensors. ECU , the induced counter voltage U ind (in generator operation with no supply voltage U ECU) and the phase currents i(t) occurring in the electric motor 44. The sensors can be internal or external to the electronic control system.

[0078] In addition, the electronic control according to this embodiment also comprises an asynchronous counter 66, which is configured to detect local minima and / or maxima of signals, for example the induced counter voltage U ind to detect, for example, when the electric motor 44 is idling, in which the torque M produced by the electric motor 44 is essentially zero.

[0079] Fig. Figure 3 shows a schematic representation of a control method 68 for operating a drive 42 with an electromechanical parking brake 12 according to one embodiment of the invention. Optional steps are shown in dashed lines.

[0080] The control method 68 initially comprises step 70, in which a motor speed ω and a first voltage value of the counter voltage U induced by the motor rotation are determined. ind when the electric motor 44 is idling. For this purpose, the electronic control 64, which has corresponding sensors or is coupled thereto, can be used in particular. When the electric motor 44 is idling, no torque M or only a negligible torque M is output by the electric motor 44.

[0081] In order to detect the motor speed ω, the electronic control 64 can, for example, use an asynchronous counter 66 according to the optional step 76 as an embodiment of step 70. Using the asynchronous counter 66, the local minima and / or maxima of the detected induced counter voltage U ind be evaluated during a given period of time, whereby the engine speed ω RC can be determined.

[0082] Optionally, step 70 can be configured such that the electromechanical parking brake 12 moves toward the applied state using the electric motor 44 during the determination according to step 70. This means, for example, that the spindle nut 34 can be moved along the displacement axis V in the direction of the brake disc 18 by the rotation of the spindle 36, but without the spindle nut 34 coming into contact with the piston crown 38 of the actuating piston 24 (brake piston). Since the spindle nut 34 can be moved along the displacement axis V essentially without resistance, except for negligible friction torques, only a negligible torque M is applied by the electric motor 44.

[0083] This also makes it clear that the spindle nut 34 travels an idle distance D along the displacement axis V during step 70 when the electric motor 44 is idling. The size of the idle distance D is due to a measurement pause as an optional embodiment of step 70, for which the induced counter voltage U ind is evaluated. According to the present embodiment, the measurement pause has a duration between 200 msec and 20 sec.

[0084] The control method 68 comprises the subsequent step 72 in which an engine speed constant k E when the electric motor 44 is idling in generator mode by means of the electronic control 64 based on the engine speed ω RC and the first voltage value of the induced counter voltage U ind This can be done using the formula explained above: kE=UindωRC.

[0085] In the further course of the control procedure 68 it is assumed that the engine speed constant k E when the electric motor 44 is idling with the motor torque constant k M of the electric motor 44 during motor operation.

[0086] In the following step 74, the total resistance R ges of the drive 42 by means of the electronic control 64 based on a second voltage value of a supply voltage U provided by the voltage source 54 ECU and a current value of the phase current I occurring in the drive 42 during idle operation A certainly: Rtotal=RV+RA=UECU−UindIA.

[0087] Here, it is exploited that for the electric motor 44 which is in idle mode, it can be assumed that the resulting phase current I Ais constant over time. As a result, the operating parameters of the electric motor 44 are generally known, enabling precise control of the electric motor 44 even during motor operation.

[0088] Accordingly, the control method 68 can be further developed by the optional step 78, in which at least the determined total resistance R ges of the drive 42 and the determined motor speed constant k E in the application state of the electric motor 44 in the electronic control 64 to determine the motor speed ω of the electric motor 44 in the application state: ω=UECU−iA⋅RgeskM.

[0089] Here, in particular, it is exploited that the determined engine speed constant k E in generator mode of the electric motor 44 with the motor torque constant k M in motor operation of the electric motor 44.

[0090] The step 78 can be further developed in particular by the optional step 80, in that when determining the motor speed ω in motor operation of the electric motor 44, at least the second voltage value of the supply voltage U provided by the voltage source 54 is additionally used. ECU and the current value of the phase current i occurring in the application state of the electric motor 44 in the drive 42 A (t) must be taken into account. Thus, the motor speed ω can be determined for all operating states of the electric motor 44 and thus of the spindle nut 34 along the displacement axis V. In particular, the motor speed ω can also be used to determine the angular position of the electric motor 44 and thus the position of the spindle nut 34 along the displacement axis V.

[0091] The control method 68 can also be further developed by the optional step 82, in which a motor torque M of the electric motor 44 is determined at least based on the determined motor torque constant k M is determined by means of the electronic control 64: M=kM⋅PRtot

[0092] This makes it possible, in particular, to determine the support point of the braking device 10 along the displacement axis V. Thus, the point along the displacement axis V at which the displacement of the spindle nut 34 causes the brake pads 20 to engage with the brake disc 18 can be determined. In general, the position of the support point along the displacement axis V can vary over time, for example, as the brake pads 20 wear. Based on the position determination of the support point, the desired travel distances and response times of the electromechanical parking brake 12 can be set, for example, by the electronic control 64.

[0093] The control method 68 can also be further developed by the optional step 84, in which the determined total resistance R ges of the drive 42 and the second voltage value of the supply voltage U provided by the voltage source 54 ECUin the electronic control 64 to achieve a maximum current i A,Max (t) of the phase current of the drive 42 and / or a maximum motor torque M Max of the electric motor 44. The maximum motor torque M Max of the electric motor 44 corresponds in particular to a maximum clamping force F Zuspann,Max , with which the brake pads 20 can be pressed onto the brake disc 18. Knowing the maximum current i A,Max (t) of the phase current and / or the maximum motor torque M Max The electric motor 44 can further increase the precision of the control of the electromechanical parking brake 12. This can increase comfort for the user.

[0094] In principle, the control procedure 68 does not depend on being carried out repeatedly, since the total resistance R gesof the drive 42 can be assumed to be constant over relatively long periods of time. However, in order to counteract aging effects, such as variations in temperature dependence, the control method 68 can also be carried out repeatedly, in which case only updated values ​​of the motor speed constant k E in generator mode of the electric motor 44 and the total resistance R ges of the drive 42 must be determined, whereby the other sizes result accordingly.

[0095] Fig. 4 shows a schematic representation of a method 86 for determining the engine speed constant k E of an electric motor 44 in generator mode of an electromechanical parking brake 12 according to an embodiment of the invention. The method 86 can optionally be implemented with individual or multiple steps or with the entire control method 68 from Fig.3, which will then follow procedure 86.

[0096] As already explained, in certain operating situations of the electromechanical parking brake 12, it may happen that the idle distance D between the spindle nut 34 and the piston crown 38 of the actuating piston 24 is not available prior to the control process 68. In this case, the spindle nut 34 of the electromechanical parking brake 12 cannot be sufficiently moved along the displacement axis V in accordance with an idle run of the electric motor 44, so that a reliable determination of the motor speed constant k E of an electric motor 44 in generator mode. The method 86 presented here provides a remedy for this case.

[0097] In step 88 of the method 86, the hydraulic service brake 14 of the braking device 10 is used by determining the engine speed constant k Eaccording to the control method 68, when a required idle distance D between the spindle nut 34 and the actuating piston 24 is not present, the hydraulically actuated actuating piston 24 of the brake device 10 is filled with a hydraulic fluid corresponding to an idle distance pressure P D and at least the idle distance D between the spindle nut 34 and the piston crown 38 of the actuating piston 24 is adjusted. This means that the spindle nut 34 is effectively moved away from the piston crown 38 of the actuating piston 24 by increasing the pressure in the hydraulic chamber 26. For example, the actuating piston 24 can be moved further along the displacement axis V in the direction of the brake disc 18, thereby increasing the gap between the spindle nut 34 and the piston crown 38.

[0098] Optionally, step 88 can be further developed in various ways. For example, the idle distance pressure P D be adjustable during operation according to the optional step 92. This increases the variability of the method 86, for example, when an adjustment of the idle distance pressure P D is necessary due to changed operating parameters of the braking device 10.

[0099] Optionally, step 88 can also be further developed by step 94, in which the idle distance D is greater than a predetermined or during operation adjustable threshold value S1. For example, the threshold value S1 can be determined by the engine speed ω RC in generator mode of the electric motor 44 for a specific period of time, which corresponds to a corresponding idle distance D. If the period of time is varied, this may also require an adaptation of the idle distance D.

[0100] Furthermore, step 88 can also be developed according to a combination of steps 92 and 94, in which the idle distance pressure P D is set based on the threshold value S1. Logically, a variation of the desired idle distance D can lead to a changed idle distance pressure P D is required so that the gap between the spindle nut 34 and the piston crown 38 is greater than the threshold value S1.

[0101] The method 86 also includes step 90, in which the electric motor 44 is energized and then a measurement run is carried out within the idle distance D. This makes it possible, in particular, to carry out the previously explained control method 68. For this purpose, the electric motor 44 is first set in rotation and then operated in idle mode (generator mode), whereby the detection of the engine speed ω RCin generator mode of the electric motor 44 and the detection of the counter voltage U induced by the motor rotation ind This creates a method 86 that makes it possible to ensure corresponding idle distances D between the spindle nut 34 and the piston crown 38 of the actuating piston 24, even though these are not actually present due to the operating situation of the braking device 10, for example because strong return elements are integrated into the braking device 10.

[0102] In addition, step 88 of method 86 can also be further developed by the optional step 96, in which an operating pressure P already exerted on the actuating piston 24 by means of the hydraulic fluid before the execution of method 86 Betrieb taking into account the idle distance pressure P Dis maintained during method 86. This enables the braking device 10 to continue to be used in accordance with the functionality of the service brake 14 even during the execution of method 86. This avoids the need to release the service brake 14 in order to execute method 86. The functionality of the braking device 10 is thereby increased.

[0103] In addition, the method 86 can be further developed by the optional step 98, in which the electric motor 44 is reduced to a minimum idle speed ω Min ramped up and then an induced counter voltage U ind measured when the electric motor 44 is idling. The minimum idle speed ω Min It can be exploited that the speed determination by means of the asynchronous counter 66 within the control process 68 can be carried out with increased precision, since averaging can be ensured.

[0104] In addition, the method 86 may include the optional step 100 in which the electric motor 44 is started up to the minimum idle speed ω Min and measuring the induced counter voltage U ind is de-energized and the electric motor 44 continues to rotate, for example due to its inertia. This essentially corresponds to the state of the electric motor 44 during step 70 of the control method 68. The electric motor 44 is then operated in a generator mode in which a rotation of the rotor of the electric motor 44 produces an induced counter voltage U ind causes.

[0105] In particular, procedure 86 can therefore create the conditions for regulatory procedure 68.

[0106] Certain embodiments disclosed herein, in particular the respective module(s), use circuitry (e.g., one or more circuits) to implement standards, protocols, methods, or technologies disclosed herein, operatively couple two or more components, generate information, process information, analyze information, generate signals, encode / decode signals, convert signals, transmit and / or receive signals, control other devices, etc. Circuitry of any type may be used.

[0107] In one embodiment, a circuit (circuit) includes, among other things, one or more computing devices such as a processor (e.g., a microprocessor), a central processing unit (CPU), a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), a system on a chip (SoC), or the like, or any combination thereof, and may include discrete digital or analog circuit elements or electronics, or combinations thereof. In one embodiment, the circuit includes hardware circuit implementations (e.g., implementations in analog circuits, implementations in digital circuits, and the like, and combinations thereof).

[0108] In one embodiment, circuitry includes combinations of circuitry and computer program products with software or firmware instructions stored on one or more computer-readable memories that cooperate to cause a device to execute one or more of the protocols, methods, or technologies described herein. In one embodiment, the circuitry includes circuitry, such as microprocessors or portions of microprocessors, that require software, firmware, and the like to operate. In one embodiment, the circuitry includes one or more processors or portions thereof and the associated software, firmware, hardware, and the like.

[0109] In the present application, reference may be made to quantities and numbers. Unless expressly stated, such quantities and numbers are not to be considered limiting, but rather as examples of the possible quantities or numbers in the context of the present application. In this context, the term "plurality" may also be used in the present application to refer to a quantity or number. In this context, the term "plurality" means any number greater than one, e.g., two, three, four, five, etc. The terms "about," "approximately," "near," etc., mean plus or minus 5% of the stated value.

[0110] Although the disclosure has been illustrated and described with respect to one or more implementations, those skilled in the art will recognize equivalent changes and modifications upon reading and understanding this description and the accompanying drawings. Although a particular feature of the disclosure has been disclosed with respect to only one of several embodiments, that feature may be combined with one or more other features of the other embodiments as may be desired and advantageous for a given or particular application.

Claims

[1] Method (86) for determining the motor speed constant of an electric motor (44) of an electromechanical parking brake (12) which is integrated into a hydraulic service brake (14), wherein a spindle nut (34) of the electromechanical parking brake (12) is arranged at least partially within a hydraulically actuated actuating piston (24) of a brake device (10) such that the spindle nut (34) can be moved against the actuating piston (24), characterized bythat, before determining the engine speed constant, if a required idle distance between the spindle nut (34) and the actuating piston (24) is not present, the hydraulically actuated actuating piston (24) of the braking device (10) is pressurized with a hydraulic fluid corresponding to an idle distance pressure and at least the idle distance is set, and that subsequently the electric motor (44) is energized and a measuring run is carried out within the idle distance. [2] Method (86) according to claim 1, characterized by that the idle distance pressure can be adjusted during operation. [3] Method (86) according to claim 1 or 2, characterized by that the idle distance is greater than a predetermined or during operation adjustable threshold. [4] Method (86) according to claim 3, characterized by that the idle distance pressure is set based on the threshold value. [5] Method (86) according to one of the preceding claims, characterized by that an operating pressure already exerted on the actuating piston (24) by means of the hydraulic fluid before the execution of the method (86) is maintained during the method (86), taking into account the idle distance pressure. [6] Method (86) according to one of claims 3 to 5, as far as related to claim 3, characterized by that the electric motor (44) is accelerated to a minimum idle speed after reaching the threshold value and an induced counter voltage is measured when the electric motor (44) is idle. [7] Method (86) according to claim 6, characterized by that the electric motor (44) is de-energized after the electric motor (44) has been run up to the minimum idle speed and the induced counter voltage has been measured, and the electric motor (44) continues to rotate.

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