Procedure for testing the functionality of an actuating unit and actuating unit

Abstract

The present invention relates generally to methods for testing the functionality of an actuating unit, preferably comprising a sliding element or a blocking plunger, wherein the actuating unit can be actuated by means of an electromagnet. The invention further relates to an actuating unit designed accordingly.

Description

[0001] The present invention generally relates to methods for testing the functionality of an actuating unit, preferably comprising a movable sliding element or a movable blocking plunger, wherein the actuating unit is actuated by means of an electromagnet. The invention further relates to a correspondingly designed actuating unit.

[0002] Electrically actuated vehicle brakes, also known as electromechanical vehicle brakes ("EMB"), are increasingly being used as braking systems for motor vehicles. These vehicle brakes offer several advantages over conventional, hydraulically actuated wheel brakes. For example, a complex hydraulic system is no longer required, and an electromechanical wheel brake is also significantly more space-saving.

[0003] Such electromechanical wheel brakes typically have an electric or electronic drive unit that interacts with a mechanism or transmission. A brake unit can then be arranged on the output side, which can comprise a brake part with a friction lining, and which can be pressed onto or against a brake disc or drum by means of a translational movement. This can cause deceleration during operation. An electromechanical wheel brake is described, for example, in the applicant's document DE 10 2017 206 798 A1.

[0004] Electromechanical wheel brakes can be configured as service brakes. The transmission is not self-locking to allow for emergency release of the brake and prevent unwanted braking in the event of a power failure.

[0005] With such wheel brakes, the parking brake function can be realized by locking the transmission. The powerless locking of the parking brake can be achieved, for example, by an electromagnetic actuator, which can move a sliding element or locking plunger into a locking position, thus locking the transmission and implementing a parking brake function.

[0006] The sliding element can, for example, engage a structured surface of a shaft, thereby preventing movement of the structured surface in at least one direction. This can prevent rotation of the shaft, and the associated wheel brake can be held in this locked or applied state. A method for operating such a blocking tappet is known, for example, from DE 10 2021 209 291 A1, owned by the applicant. The described method enables monitoring of the blocking tappet to determine whether it has reached the blocking position during operation.

[0007] Determining whether the sliding element has reached the desired position is done during operation, i.e., when the corresponding button is pressed after a journey has begun. However, in the event of an error or defect, it may not be possible to reach the locking position as desired.

[0008] It is therefore considered advantageous to be able to check whether the parking brake function is working properly and fully before starting a journey.

[0009] It is therefore an object of the present invention to provide a method for testing the functionality of an actuating unit, which, compared to known embodiments, also enables proactive testing of the actuating unit, for example, a parking brake function of an electromechanical motor vehicle brake. It is further an object of the invention to provide such an actuating unit, for example, for a parking brake function of an electromechanical motor vehicle brake, for implementing such a method.

[0010] The inventors have taken on this task.

[0011] This problem is solved surprisingly simply by a method for testing the functionality of an actuating unit, a correspondingly designed actuating unit, and a braking system for a motor vehicle with such an actuating unit according to one of the independent claims. Preferred embodiments and further developments of the invention can be found in the respective subclaims.

[0012] The present invention therefore relates, in a first aspect, to a method for testing the functionality of an actuating unit, wherein the actuating unit - a sliding element, - an electromagnet, and - comprises a spring, wherein - the sliding element can be moved from a first starting position into a second actuating position by switching on a supply voltage to apply a predetermined current to the electromagnet.

[0013] The method according to the invention can comprise the following steps, preferably in the order shown below: - Applying a current to the electromagnet which is at least equal to the holding current, - gradually changing the holding current, - Detecting the current flowing through the electromagnet during and / or after the change of the holding current, - Deriving the inductance from the change in the current flow, and - Comparing the inductance with an inductance characteristic stored in a non-volatile memory.

[0014] The method according to the invention can preferably be carried out when the sliding element is in the actuating position. Therefore, according to a preferred embodiment of the invention, the method can further comprise at least the following step, in particular when the sliding element is still in the starting position at the beginning of the method: - prior movement of the sliding element from the starting position into the actuating position, wherein the electromagnet is subjected to an electric current of a current intensity which corresponds at least to the magnitude of an activation current and the magnitude of the holding current.

[0015] The method according to the invention can thus be used regardless of the current position of the sliding element, whereby the additional aforementioned method step can be applied if the sliding element is in the starting position. To move the sliding element, the supply voltage can be applied, whereby the current strength advantageously includes both the activation current and the holding current components, which will be discussed in more detail below.

[0016] In a further aspect, the invention also relates to methods for operating an actuating unit, wherein a test of the functionality of the actuating unit is carried out before the actuation, wherein preferably a method for testing the functionality of the actuating unit as described above is used.

[0017] In yet another aspect, the invention also relates to an actuating unit comprising - a sliding element, - an electromagnet, and - a spring, whereby - the sliding element can be moved from a first starting position to a second actuating position by switching on a supply voltage of the electromagnet.

[0018] Finally, in yet another aspect, the invention relates to a braking system for a motor vehicle, comprising at least one actuating unit as described above. The actuating unit can, in particular, be a component of an electromechanically actuated wheel brake and can be used, in particular, for a parking brake.

[0019] A motor vehicle in the sense of the invention can refer to a vehicle with axles, wherein at least one of these axles can comprise steerably guided wheels and, in addition, the drive of the wheels of at least one axle can be adjusted wheel-specifically.

[0020] The electromechanically actuated wheel brakes can be designed as electromechanical disc brakes, in which a clamping force or application force can be generated by means of an electric motor, a primary gear, and / or a rotation / translation gear. The application force refers to the force with which the brake pads are pressed against the brake disc. During operation, this then generates a corresponding braking torque at the wheel in question. Depending on the design and control concept, the control can be selected such that either a predefined clamping force or a predefined braking torque is set according to the requested deceleration.

[0021] The electromechanically actuated wheel brakes can also be designed as electromechanical drum brakes, in which the motor / gearbox unit actuates a spreading module which presses the brake pads against the brake drum with a spreading force predetermined on the basis of the requested deceleration and thus generates a corresponding braking torque.

[0022] Depending on the design and control concept, the control can be designed in such a way that a defined spreading force or a defined braking torque is set according to the deceleration request.

[0023] The actuating unit according to the invention can be integrated into a parking brake unit, which can thus be a component of the electromechanically actuated wheel brake. The parking brake unit can be designed to enable the motor vehicle to be immobilized. The parking brake unit with the actuating unit according to the invention can be integrated into either an electromechanical drum brake or an electromechanical disc brake.

[0024] The invention enables a test of the functionality of the actuating unit at a predetermined time. In particular, a test can be performed before the actual operation of the actuating unit to ensure that it will function fully when used later. This is particularly advantageous in connection with a braking system for a motor vehicle, as important and safety-relevant properties of the braking system can be tested before or at the start of a journey. For example, the method according to the invention can be used to check whether the actuating unit is fully available for actuating a parking brake in the motor vehicle before starting a journey.

[0025] According to the invention, the sliding element can be moved from a first position, which can represent a starting position, to a second position, which can represent an actuating position. For this purpose, at least one electromagnet can be provided. By switching on a supply voltage for the electromagnet, the sliding element can be moved, whereby the electromagnet can be supplied with an electric current of a predetermined intensity.

[0026] According to the invention, means can be provided that can hold the sliding element in the starting position. These means can, for example, comprise a spring, preferably a compression spring, which can be relaxed in the starting position and hold the sliding element firmly. The electromagnet can be designed to apply a force component when the supply voltage is applied that exceeds this holding force in the starting position and can thus move the sliding element in the desired direction. In the actuated position, the spring can be tensioned.

[0027] According to a preferred embodiment of the invention, the sliding element can be moved translationally from the starting position to the actuating position. In principle, other forms of movement are also possible, such as pivoting. However, a primarily linear movement appears to be technically easier to implement and may be particularly suitable for the intended use, especially for a parking brake.

[0028] The sliding element can be designed as a blocking plunger or comprise a blocking plunger. A blocking plunger can, for example, be a plunger that is movable in one direction and the opposite direction. Thus, it can, in particular, be a one-dimensional actuation and / or mobility.

[0029] The electromagnet can, in particular, generate a magnetic field to move the sliding element into a specific position. Accordingly, the sliding element can preferably be formed with at least one magnet, for example a permanent magnet or an electromagnet, or from a magnetically active material, so that actuation by an electromagnet is possible.

[0030] In the actuated position, the sliding element can engage a structured surface, for example, formed on a shaft, or a ratchet wheel that is rotationally fixed to the shaft. The structured surface can, in particular, be a surface with suitable structures such as projections, recesses, or notches to achieve the desired effect when the sliding element engages. Movement can be prevented in one direction or in several directions, especially two.

[0031] If the textured surface is formed on a rotating object such as a shaft or comprises a ratchet wheel that is non-rotatably connected to a shaft, rotation of the shaft in one or both directions can be prevented. The actuating position can therefore represent a blocking or locking position in which the shaft can be prevented from rotating.

[0032] The method according to the invention for testing the functionality of the actuating unit can comprise a multi-stage process. The functionality test according to the invention can be carried out at a predetermined time or repeatedly. Since the test can result in movement of the sliding element, it is advantageously carried out at a time when the actuating unit is not in regular use or when regular use is not expected, or generally at a time when actuation cannot be considered obstructive. If the actuating unit is used, for example, for or together with a parking brake, carrying out the test method according to the invention can be disadvantageous if the associated motor vehicle is in motion.

[0033] A favorable time may be, for example, at the beginning of a journey or, in the case of an actuating unit, before the start of the journey if the actuating unit is used in conjunction with a braking system. The test can also be performed repeatedly, for example, at specific intervals when the actuating unit is not in operation. The test according to the invention can also be performed immediately before a planned operation of the actuating unit, thus essentially representing the first step of the actuation. In this way, it can be ensured with a high degree of reliability that the actuating unit is functional when needed.

[0034] Testing the functionality of the actuating unit can comprise several steps, which can preferably be carried out sequentially. In a first step, it can be provided that, starting with a sliding element in the starting position, the electromagnet is supplied with a supply voltage, whereby the current intensity can be composed of an activation current and a holding current. This can overcome the holding force of the spring and move the sliding element from the starting position to the actuated position. Known parameters can be used to control this movement, such as the time for the movement until the sliding element reaches the intended actuated position when the actuating unit is fully functional.

[0035] Once the sliding element has reached the intended actuation position, the current can be reduced in a further step. According to a preferred embodiment of the invention, this can be achieved by reducing the current to the holding current and eliminating the activation current.

[0036] Holding current is therefore a current strength at which the electromagnet can exert a holding force on the sliding element that is at least equal to the holding force of the spring. The holding force exerted by the holding current can also slightly exceed the holding force of the spring. This preferably assumes a fully or normally functioning spring. With a functioning actuating unit, this results in the sliding element being held in the actuated position.

[0037] Activation current, therefore, refers to a current intensity that is added to the holding current to cause the sliding element to move. The current intensity in this step can therefore correspond to the holding current and also to the activation current. The corresponding values ​​for the holding current and the activation current can be stored in the controller.

[0038] The supply voltage applied to the electromagnet typically results in a current flow that can be detected. A current sensor, for example, can be used for this purpose. However, the invention makes highly advantageous use of the finding that the functionality of the actuating unit, and in particular of the spring, can be determined from the change in current flow during different, defined movements or position changes of the sliding element and a comparison with stored characteristic curves. The functionality of an actuating unit can be tested, for example, by monitoring the current flow for a specific pattern and / or for exceeding or falling below certain thresholds or limit values.

[0039] In this way, a drop in current can be detected some time after the supply voltage is switched on. This can be a typical functionality of a specific arrangement, and the controller can be configured to detect such a drop. Typically, the magnetic field is first built up before the drop, with an inductance of the electromagnet counteracting the increase in current. The drop in current typically characterizes the point in time from which the sliding element actually moves. After the drop in current, in particular, an increase in current can be detected. This is typically the second increase since the supply voltage was switched on. Such an increase in current, which occurs after a drop, typically characterizes a point from which the sliding element has reached its end position.In particular, proper reaching of the actuating position can be detected when a transition between a drop in current and a rise in current occurs within a specified time interval after the supply voltage is switched on. This is particularly the rise after the drop in current. If this occurs within a specified time interval, it indicates that the sliding element has been moved into the actuating position as intended and has not, for example, encountered an unexpected obstacle beforehand or jammed and failed to reach the actuating position.

[0040] Proper locking can be detected if the time derivative lies within a specified range. Proper locking means the sliding element correctly reaching the actuating position. This time derivative typically characterizes an inductance of the electromagnet in certain positions of the sliding element, for example an extended sliding element. This inductance is typically greater than the inductance when the electromagnet is retracted, which is why the current rise is slower. The time derivative of the current can be carried out numerically or analytically. In particular, this time derivative can be measured immediately after a detected current rise. It can be determined, for example, by measuring a current change over a specified time.It can also be determined by measuring the time required for a given current change. The time derivative is, in particular, a time derivative.

[0041] The actual test of the functionality of the operating unit can include the steps mentioned above - Changing the holding current, - detecting the current, - Deriving the inductance and / or - Comparing the inductance with an inductance characteristic curve and creating a test cycle in this sequence. This test cycle can be run multiple times to test the functionality of the actuating unit. This allows the holding current to be changed with each run and the effects on the inductance to be analyzed to determine whether the actuating unit is fully functional. Successive test cycles can thus be performed with different holding currents, with the changes in the inductance being checked. This allows potential faults to be detected.

[0042] After each change in the holding current, the current flowing through the electromagnet during and / or after the change in the holding current can be detected or measured. To avoid the need for a sensor, a current and / or voltage waveform can be observed, as described above.

[0043] This can be done at high frequency, for example, with a monitoring frequency of at least 5 kHz and / or at most 15 kHz, or 10 kHz. Other values ​​can also be used. Deviations in the movement sequence can be detected via the current waveform. For this purpose, current gradients can be created, for example, which represent a current increase and characterize the inductance at a known voltage.

[0044] The time derivative or the magnitude of the inductance after a change in the holding current can be compared with a predetermined range or curve, such as an inductance characteristic curve, which can be stored in a non-volatile memory of the controller. In other words, the inductance can be calculated by observing the temporal shift between the current and the voltage. If the derived inductance value deviates from the stored inductance curve, in particular by a predetermined value, it can be concluded that the sliding element is not in the intended position.

[0045] According to a preferred embodiment of the invention, the controller can issue a corresponding error message if the deviations are too large. For example, an error message can be used to warn a driver and prompt them to secure the vehicle in another way and / or to visit a repair shop.

[0046] The control can be integrated into the actuation unit, or, for example, into a higher-level vehicle control system or into a brake control unit.

[0047] According to a preferred embodiment of the invention, changing the holding current can comprise a brief, particularly pulse-wise, interruption of the holding current at the specific current level or at a constant current intensity. If the supply voltage is applied using pulse-width modulation, for example, the supply voltage can be switched off for the duration of a test pulse.

[0048] A further development of the invention can provide that, in a subsequent test cycle, the number of test pulses is increased with the supply voltage interrupted compared to the number of test pulses in the previous test cycle. In this way, it is possible to test, for example, how strong the return force of the spring still is when the time intervals during which the supply voltage is interrupted and, consequently, no holding current is applied to the electromagnet are gradually increased.

[0049] According to a further, likewise preferred embodiment of the invention, changing the holding current can provide for a gradual reduction of the holding current, so that the current level in the subsequent test cycle is lower than in the previous test cycle. By gradually changing the holding current, the holding force by the electromagnet is gradually changed, while the return force by the spring remains unchanged, provided the spring is functioning properly.

[0050] The holding current can be reduced, for example, in small steps, with the holding current – ​​starting from the initial current value – being reduced by a predetermined amount in each subsequent step. This also allows you to test how strong the spring's return force still is. For example, a specific holding current can be specified, at which point the sliding element should be able to be moved back to its original position by the spring.

[0051] The method according to the invention thus makes it possible to prove that the unlocking took place from the locked position or that the locking took place from the unlocked position.

[0052] The invention also enables a check to determine whether the locking mechanism is being held in its respective target position with the specified holding force. Given the safety relevance of the wheel brake, this largely eliminates the risk of unintentional locking due to insufficient holding or restoring forces from the spring. This allows a potential hazard caused by a faulty parking brake to be identified before it occurs.

[0053] The method according to the invention enables monitoring both when the vehicle is stationary and while driving. Monitoring while driving is possible, for example, as long as the current remains low enough that the locking mechanism does not move, thus keeping the sliding element in the unlocked position.

[0054] In summary, this enables position detection or confirmation of the requested positions. The movement of the locking mechanism or sliding element can be monitored by evaluating "peaks" in the current and / or voltage curve induced by the moving armature. The test cycle according to the invention enables continuous, cyclical, or periodic testing, as well as one-time testing. The current level required to maintain the requested end positions can also be determined. Furthermore, the required spring force of the retaining spring can be determined.

[0055] The method according to the invention is characterized, among other things, by the fact that it can be used particularly cost-effectively because no additional sensors are required and the existing hardware can be used. The locking mechanism or the sliding element can be monitored using existing hardware on the basis of electrical signals, so that additional sensors for monitoring are not necessary. The computing time required is very low and the method is comparatively robust. This means that cost-intensive additional measures, for example to achieve the required 0 ppm fault protection on the spring, such as a 100% force test or vibration tests during series production, can be largely dispensed with. The method according to the invention can be used, for example, on coils or magnetic actuators.

[0056] Further details of the invention emerge from the description of the illustrated embodiments and the appended claims.

[0057] The drawings show: Fig. 1 a parking brake unit with an actuating unit, Fig. 2 schematically shows in a sectional view the actuating unit in a starting position, Fig. 3 schematically shows in a sectional view the actuating unit in an actuating position, Fig. 4 examples of different current curves over time at different current intensities, Fig. 5 shows another exemplary current curve over time, and Fig. 6 shows in a graphical representation the inductance found for different parameters of starting current, supply voltage and pulse length.

[0058] In the following detailed description of preferred embodiments, for the sake of clarity, like reference numerals designate substantially similar parts in or on these embodiments. However, to better illustrate the invention, the preferred embodiments illustrated in the figures are not always drawn to scale.

[0059] Fig. 1 shows purely schematically a parking brake unit 1 with an actuating unit 10 according to an embodiment of the invention.

[0060] The parking brake unit 1 has a shaft 30, which can be driven by an electric motor or otherwise. A ratchet wheel 35 is mounted on the shaft 30 in a rotationally fixed manner, with a structured surface 37 formed on the outside. The structured surface 37 faces outward and is connected in a rotationally fixed manner to the shaft 30 via the ratchet wheel 35. The structured surface 37 can, for example, be a serrated surface like a gear or a surface with curved projections and spaces between them.

[0061] If the textured surface is formed on a rotating object, such as a shaft, or comprises a ratchet wheel that is non-rotatably connected to a shaft, rotation of the shaft in one or both directions can be prevented. The actuating position can therefore represent a blocking position in which the shaft can be prevented from rotating.

[0062] Reference numeral 40 shows, purely by way of example, an output pinion that can be rotationally connected to a unit not shown. For example, it can be rotationally connected to a rotation-translation gear (not shown) and thus ensure that an electrically actuated brake, such as a drum brake or a disc brake, can be actuated by means of the shaft 30.

[0063] A sliding element 50 is arranged adjacent to the ratchet wheel 35. This can be actuated by means of an electromagnet 55, ie in the illustration of Fig. 1 is vertically movable. It is thus linearly movable in one dimension and is mounted accordingly, although the mounting is not shown. The actuating unit 10 further comprises a controller 60 configured to carry out the method according to the invention.

[0064] The actuating unit 10 comprises, in addition to the sliding element 50 and the electromagnet 55, a spring 51, which is shown in the Fig. 1 is not shown. The Fig. 2 and Fig. 3 show schematically in a sectional view the actuating unit 10, in which the spring 51 is also visible. Fig. 2 the actuating unit 10 in the initial position in which no locking takes place, and the Fig. 3 the actuating unit 10 in the actuating position, in which the sliding element 50 engages, for example, in a structured surface 37. The structured surface 37 is in the Fig. 2 and Fig. 3 not shown.

[0065] By switching on a supply voltage of the electromagnet 55, the sliding element 50 can be moved from the starting position, as shown in Fig. 2, into the operating position as shown in Fig. 3. The electromagnet 55 is supplied with an electric current of a strength composed of an activation current and a holding current.

[0066] The method according to the invention for testing the functionality of the actuating unit 10 goes through the following steps, preferably in the order shown below: - Applying a current intensity to the electromagnet 55 which corresponds at least to the magnitude of the holding current, - gradually changing the holding current, - detecting the current flowing through the electromagnet 55 during and / or after the change of the holding current, - Deriving the inductance from the change in the current flow, and - Comparing the inductance with an inductance characteristic stored in a non-volatile memory.

[0067] The present invention also includes an actuating unit 10 comprising - a sliding element 50, - an electromagnet 55, and - a spring 51, wherein - the sliding element 50 can be moved from the starting position into the actuating position by switching on a supply voltage of the electromagnet 55.

[0068] The present invention further encompasses a braking system for a motor vehicle, comprising at least one actuating unit 10 as described above. The actuating unit 10 is, in particular, a component of an electromechanically actuated wheel brake. Electromechanically actuated wheel brakes can be designed as electromechanical disc brakes or as electromechanical drum brakes. The actuating unit 10 is integrated into the parking brake unit 1, which is thus a component of the electromechanically actuated wheel brake. The parking brake unit 1 is provided to enable the motor vehicle to be immobilized.

[0069] When the sliding element 50 is in the home position, a preferred embodiment of the invention provides that, prior to the actual test cycle, the sliding element is moved from the home position to the actuating position, wherein the electromagnet 55 is supplied with an electric current of a magnitude that corresponds at least to the magnitude of the activation current and the magnitude of the holding current. This allows the holding force of the spring 51 to be overcome, and the sliding element 50 can be moved from the home position to the actuating position.

[0070] As in the Fig. 2, the spring 51 can hold the sliding element 50 in the initial position, wherein the spring 51 is relaxed. The spring 51 is designed as a compression spring. The electromagnet 55 is designed to apply a force component when the supply voltage is applied, which exceeds this holding force in the initial position and thus moves the sliding element 50 in the desired direction. In the actuated position, the spring 51, as shown in Fig. 3. The movement of the sliding element 50 is translational. The sliding element is, as shown in the Fig. 2 and Fig. 3, designed as a blocking tappet.

[0071] The electromagnet 55 is designed to generate a magnetic field when the supply voltage is applied to it. For this purpose, the sliding element 50 comprises at least one magnet, in particular a permanent magnet or an electromagnet, or a magnetically active material, so that movement by the electromagnet 55 is possible.

[0072] Once the sliding element 50 has reached the intended actuation position, the current is reduced in a further step. The holding current remains, and the current is reduced by the magnitude of the activation current component. The corresponding values ​​for the holding current and the activation current are stored in the controller 60.

[0073] According to a preferred embodiment, the test cycle begins when the sliding element 50 is in the actuating position. The test cycle according to the invention can also be initiated or repeated when the sliding element 50 is in the actuating position, for example, during a prolonged locking operation.

[0074] The test cycle involves changing the holding current step by step. After each change in the holding current, the current flowing through the electromagnet during and / or after the change in the holding current can be recorded or measured. Monitoring is performed at a high frequency of at least 5 kHz. The controller detects deviations in the movement sequence via the current waveform. For this purpose, current gradients can be created, for example, which represent a current increase and characterize the inductance at a known voltage.

[0075] The time derivative or the magnitude of the inductance after a change in the holding current is compared with a predetermined range or curve, in particular an inductance characteristic curve, which is stored in a non-volatile memory of the controller. If the inductance deviates from the stored inductance curve, in particular by a predetermined value, it can be concluded that the sliding element 50 is not in the intended position.

[0076] According to the illustrated embodiment of the invention, the controller outputs a corresponding error message if the deviation of the inductance from the inductance characteristic curve deviates by a value greater than a predetermined limit or a predetermined threshold is exceeded. An error message can, for example, be used to warn a driver and prompt them to secure the vehicle by other means and / or to visit a workshop.

[0077] The control is functionally integrated into the actuation unit, but can also be integrated, for example, into a higher-level vehicle control system or into a brake control unit.

[0078] The test cycle therefore includes at least the following steps - Changing the holding current, - detecting the current, - Deriving the inductance and / or - Compare the inductance with an inductance characteristic curve.

[0079] This test cycle is run multiple times to test the functionality of the actuator. This allows the holding current to be changed during each run and the effects on the inductance to be analyzed to determine whether the actuator is fully functional. Successive test cycles can thus be performed with different holding currents, allowing the changes to be tested on the inductance.

[0080] According to a preferred embodiment of the invention, changing the holding current involves briefly suspending the holding current at the specific current level. If the supply voltage is pulse-width modulated, for example, the supply voltage can be switched off for the duration of a test pulse or in pulses. Such a test pulse can last, for example, less than 10,000 µs, preferably less than 1,000 µs, and particularly preferably less than 700 µs, so that a corresponding test cycle can be completed very quickly.

[0081] A further development of the invention can provide that, in a subsequent test cycle, the number of test pulses is increased with the interruption of the supply voltage compared to the number of test pulses in the previous test cycle. Thus, in a first run of the test cycle, the supply voltage can be switched off for only one test pulse, in the subsequent run for two test pulses, and then for three test pulses, etc. In this way, it is possible to test, for example, how strong the return force of the spring still is when the time intervals in which the supply voltage is interrupted and, consequently, no holding current is applied to the electromagnet 55 are gradually increased.

[0082] According to a further, likewise preferred embodiment of the invention, changing the holding current can provide for a gradual reduction of the holding current, so that the current level or current intensity is lower in the subsequent test cycle than in the previous test cycle. By gradually changing the holding current, the holding force by the electromagnet 55 is gradually changed, in particular reduced, while the return force by the spring 51 remains unchanged, provided the spring 51 functions properly. The overall holding current intensity can be kept very low and, for example, at the beginning of the test cycle, be less than 5,000 mA, preferably less than 3,000 mA, and particularly preferably less than 2,500 mA.The holding current can be reduced in small steps, for example, starting from the initial current value and being reduced by 1%, 2%, or 5% in each subsequent step. This also allows you to test how strong the spring's return force still is. For example, a specific holding current can be specified, at which point the sliding element should be able to be moved back to its original position by the spring.

[0083] Fig. Figure 4 shows examples of different current curves over time at different current intensities.

[0084] Point P1, shown in the example only for the current of 1200 mA, indicates the maximum current at the time the supply voltage is switched off. The various current curves or sets of curves show that for one end position, especially when the supply voltage is switched on, there is a steeper or less steep current increase depending on the position. The steepness is directly related to the inductance. Thus, steep increases indicate smaller inductances and thus the starting position, and less steep increases indicate the larger inductance and the actuating position. In other words, the Fig. Figure 4 shows two groups of lines or sets of curves that clearly differ in their gradient, especially in the rising section. This gradient correlates directly with the inductance.

[0085] Fig. Figure 5 shows another section of an example current curve over time.

[0086] The decaying current is shown when the supply voltage is switched off. At point P5, the current and the resulting magnetic force are so small that the spring begins to move the armature from the actuated position to the starting position. This induces a voltage that again causes the current to rise. However, due to the law of conservation of energy and / or other effects, this does not lead to a reverse movement of the sliding element. At point P6, the other end position is reached and the current decays "normally" again. This current curve can be compared with a stored inductance characteristic curve. If, in this example, point P6 corresponds to the expected curve, it can be assumed that the actuating unit 10 is functioning properly.

[0087] In the case of, for example, a jammed mechanism of the actuating unit 10 in which the sliding element 50 cannot be moved back to its starting position by the spring force, the points P5 and P6 would not be visible, since no corresponding change in the inductance occurs due to the lack of movement of the sliding element 50. In this case, the controller 60 can output a corresponding error message.

[0088] Fig.Finally, Figure 6 shows a graphical representation of the inductance measured for various parameters of current or starting current, supply voltage, and pulse length. Two clusters are visible for each of the two end positions, i.e., the initial position and the actuated position of the sliding element 50. This shows that the inductance differs in the two end positions, and the inductance can be used to determine when the corresponding end position of the sliding element 50 has been reached. List of reference symbols: 1 parking brake unit 10 Actuating unit 30 wave 35 ratchet wheel 37 structured surface 40 output pinions 50 sliding element 51 spring 53 collar 54 housings 55 Electromagnet 60 Control QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2017 206 798 A1

[0003] DE 10 2021 209 291 A1

[0006]

Claims

[1] Method for testing the functionality of an actuating unit (10), wherein the actuating unit (10) - a sliding element (50), - an electromagnet (55), and - comprises a spring (51), wherein - the sliding element (50) is movable from a first starting position into a second actuating position by switching on a supply voltage for applying a predetermined current to the electromagnet (55), comprising at least the following steps: - applying a current intensity to the electromagnet (55) which corresponds at least to the magnitude of a holding current, - gradually changing the holding current, - detecting the current flowing through the electromagnet (55) during and / or after the change in the holding current, - Deriving the inductance from the change in the current flow, and - Comparing the inductance with an inductance characteristic stored in a non-volatile memory. [2] Method for testing according to the preceding claim, characterized by that the method further comprises at least the following step, in particular when the sliding element (50) is in the starting position: - prior movement of the sliding element (50) from the starting position into the actuating position, wherein the electromagnet (55) is subjected to an electric current of a current intensity which corresponds at least to the magnitude of an activation current and the magnitude of the holding current. [3] Method of testing according to one of the preceding claims, characterized by that the method further comprises at least the following step - Outputting an error message if the derived variable for the inductance deviates from the stored inductance curve by a predetermined value, preferably to a controller (60). [4] Method of testing according to one of the preceding claims, characterized by that at least the steps - Changing the holding current, - detecting the current, - Deriving the inductance and / or - Comparing the inductance represents a test cycle, whereby this test cycle is run through several times and preferably the holding current is changed with each run. [5] Method of testing according to one of the preceding claims, characterized by that changing the holding current comprises a brief, in particular pulse-wise, interruption of the holding current at the specific current level, wherein the supply voltage is switched off for the duration of a test pulse. [6] Method for testing according to the preceding claim, characterized by that in a subsequent test cycle the number of test pulses is increased with interruption of the supply voltage compared to the number of test pulses in the previous test cycle. [7] Method of testing according to one of the preceding claims, characterized by that changing the holding current comprises gradually reducing the holding current so that the current level in the subsequent test cycle is lower than in the previous test cycle. [8] Method of testing according to one of the preceding claims, characterized by that the sliding element (50) can be held in the starting position by the spring (51), wherein the spring (51) is relaxed, and / or that the spring (51) is tensioned in the actuating position. [9] Method of testing according to one of the preceding claims, characterized bythat the sliding element (50) is moved translationally from the starting position into the actuating position. [10] Method of testing according to one of the preceding claims, characterized by that the sliding element (50) comprises a blocking plunger. [11] Method for testing according to the preceding claim, characterized by that the sliding element (50) in the actuating position engages in a structured surface (37) on a shaft (30) or in a ratchet wheel (35) which is connected to the shaft (30) in a rotationally fixed manner. [12] Method for operating an actuating unit (10), wherein a test of the functionality of the actuating unit (10) is carried out before the actuation, wherein preferably a method for testing the functionality of an actuating unit (10) according to one of the preceding claims is used, and wherein preferably the functionality of the actuating unit (10) is tested at least once at the beginning of the operation of the actuating unit (10). [13] Method for operating an actuating unit (10) according to the preceding claim, characterized by that the actuating unit (10) comprises a sliding element (50), in particular a blocking tappet, which can engage in an actuating position in a structured surface (37) on a shaft (30) or in a ratchet wheel (35) which is connected to the shaft (30) in a rotationally fixed manner. [14] Actuating unit (10), comprising - a sliding element (50), - an electromagnet (55), and - comprises a spring (51), wherein - the sliding element (50) is movable from a first starting position into a second actuating position by switching on a supply voltage of the electromagnet (55), whereby the electromagnet (55) is supplied with electric current of a predetermined current intensity, designed to carry out a method according to one of the preceding claims. [15] Braking system for a motor vehicle, comprising at least one electromechanically actuated wheel brake and an actuating unit (10) according to the preceding claim, wherein the actuating unit (10) is integrated in particular into a parking brake or a parking brake unit.

Images