Method for actuating an electromechanical parking brake

Abstract

The invention relates to a method for operating an electrical output stage (1) comprising four electrical power transistors (4a, 4b, 4c, 4d) for an electromechanical parking brake. According to the method, the output stage (1) is operated when there is a locking request (FBA) from a control / adjustment mechanism in a locking process (V) of the parking brake. According to the invention, the locking process is continued by means of an electronic circuit arrangement (6) different from the control / adjustment mechanism (5) when the control / adjustment mechanism (5) fails.

Description

TECHNICAL FIELD

[0001] The invention relates to a method for actuating an electric output stage for an electromechanical parking brake. The invention also relates to such an electric output stage for an electromechanical parking brake and to a controller. The invention also relates to an electromechanical parking brake with such an electric output stage. BACKGROUND

[0002] In modern motor vehicles, electromechanical parking brakes are used in order to prevent a parked vehicle from rolling away, in particular after being parked on a road with a sloping surface. For this purpose, the electromechanical parking brake can be adjusted into a locking position in which it locks at least one wheel of the motor vehicle.

[0003] The brake force required for this is generated by means of an electric motor, usually embodied as a DC motor, and a transmission directly on the brake caliper of the parking brake. Here, the DC motor only needs to be energized in order to adjust a mechanical actuator which can be used to adjust the brake caliper.

[0004] In order to energize the DC motor, an electric output stage comprising controllable power transistors is usually used in conventional electromechanical parking brakes. A so-called H-bridge with four power transistors is usually used here, wherein the power transistors are used as (semiconductor) switches by means of which the energization of the DC motor can be controlled. Here, the four power transistors are arranged in the H-bridge in such a way that when two specific power transistors which are opposite each other at a right angle in the H-bridge are activated, i.e. switched from the off state to the on state, the DC motor is energized in such a way that its rotating output shaft moves the actuator with the brake caliper into a locking position in which the relevant wheel of the motor vehicle is locked by the actuator connected to the brake caliper.

[0005] The control of the switching of the power transistors is carried out here by means of a microcontroller, referred to below as a "control / regulation unit", which is electrically connected to the electrical control inputs of the power transistors and can also be used to execute a software code.

[0006] The control of the power transistors of the H-bridge by means of the microcontroller thus implemented has proved to be disadvantageous: in the event of a functional fault in the microcontroller, in particular when the microcontroller fails completely, the locking process cannot even be started or at least cannot be successfully completed. In both cases, the parking brake cannot be locked as intended. SUMMARY

[0007] It is therefore an object of the invention to propose an improved method for locking an electric parking brake by means of which the above-mentioned disadvantages are eliminated.

[0008] This object is achieved by the subject matter of the independent claims. Advantageous embodiments are the subject matter of the dependent claims.

[0009] The basic idea of the present application is therefore that, in order to control the adjustment process of the electric parking brake, in addition to the microcontroller mentioned at the outset, an electronic circuit arrangement is provided which, in the event of a functional disturbance in the microcontroller, including a complete failure, ensures that the adjustment process of the parking brake is still carried out or, if a functional disturbance occurs in an already started adjustment process, is successfully completed or ended.

[0010] In this way, the operating safety is improved both when locking and when unlocking the electric parking brake in a motor vehicle. In particular, it is prevented that, as a result of a fault condition in the microcontroller, the locking process cannot be carried out or at least cannot be successfully completed again, so that the parking brake is not locked as desired. When using the method according to the application, the risk of the motor vehicle rolling away, in particular when it is already parked on a road with a slope, is therefore reduced.

[0011] Correspondingly, the risk of the parking brake not being able to be released or at least not being able to be released completely and thus of the parked vehicle not being able to be driven away is reduced in the unlocking process.

[0012] In the method according to the application for operating an electric output stage with at least four electric power transistors for an electromechanical parking brake, the output stage is operated by a control / adjustment mechanism, which comprises the above-mentioned "microcontroller" or is such a "microcontroller", in the presence of an adjustment request and in this way an adjustment process of the parking brake is carried out. According to the application, in the event of a failure of the control / adjustment mechanism, the adjustment process, i.e. the operation of the output stage with power transistors, is continued by means of an electronic circuit arrangement which is different from the control / adjustment mechanism. The term "failure" of the control / adjustment mechanism currently means any functional disturbance in the control / adjustment mechanism by means of which the electric output stage can no longer be operated in such a way that the adjustment process is carried out or successfully completed.

[0013] The electronic circuit arrangement can comprise at least two, preferably a plurality of electronic components. As such electronic components, integrated switching circuits (IC) are considered. The integrated switching circuits here preferably have a signal output which, in particular preferably, controls an electric transistor via an ohmic resistor, which is electrically connected to the control input of one of the four power transistors. The activation and deactivation of this power transistor can thus be controlled by means of the integrated switching circuit of the electronic circuit arrangement.

[0014] The four power transistors are preferably arranged in an electric H-bridge, which in turn is designed for operating a DC motor of the parking brake.

[0015] In a preferred embodiment, the regulating process is a locking process for locking the unlocked, i.e. released, parking brake. In this embodiment, the regulating request is a locking request for locking the parking brake. The operating safety of the parking brake when locking can thus be improved by means of the method.

[0016] Alternatively, the regulating process can also be an unlocking process for unlocking, i.e. releasing, the locked parking brake. In this way, the operating safety of the parking brake when unlocking can also be improved by means of the method.

[0017] The first power transistor of the four power transistors of the H-bridge is suitably activated by means of the control / regulating mechanism before the locking process is started when a locking request is present. In this way, the direct current motor is prepared for energization.

[0018] Particularly preferably, a further second power transistor is activated by the control / regulating mechanism after the first power transistor has been activated when the control / regulating mechanism is functioning properly. By activating the second power transistor, the current path from the power supply via the direct current motor to the electrical ground is closed inside the H-bridge and the direct current motor is thus energized and driven in this way. By activating the second power transistor in addition to the first power transistor, the actual locking process is started.

[0019] Alternatively, if the failure of the control / regulating mechanism occurs in time after the activation of the first power transistor but before the activation of the second power transistor and thus before the actual locking process is started, the second power transistor is activated by the electronic circuit arrangement, starting the locking process.

[0020] Preferably, when the control / regulating mechanism fails during the locking process, the activation state of at least the second power transistor is maintained by means of the electronic circuit arrangement until the locking process is completed. In this way, premature interruption of the locking process and the resulting situation of the parking brake being unlocked can be prevented.

[0021] According to an advantageous refinement of the application, at least the second power transistor is deactivated by means of the electronic circuit arrangement as soon as the parking brake is classified as locked when the control / regulating mechanism fails. The locking process is thus ensured to end properly, in particular in time. Overloading of the electrical output stage, the direct current motor and the actuator cooperating with the direct current motor is thus avoided.

[0022] According to a further advantageous refinement, the parking brake is classified as locked as soon as the current flowing through the DC motor during the locking process exceeds a predetermined threshold value. In an alternative variant, the parking brake is automatically classified as locked as soon as a predetermined period of time has elapsed since the start of the locking process. An "or" combination of the two variants, i.e. both conditions are interrogated and the parking brake is classified as locked as soon as one of the two conditions is met, is also conceivable. Both variants can be implemented technically simply, either individually or in combination.

[0023] The application also relates to an electrical output stage for actuating an electromechanical parking brake. The output stage comprises an electrical H-bridge in which four activatable power transistors for controlling a locking process of the parking brake are arranged. The output stage further comprises a control / adjustment mechanism by means of which each of the four power transistors can be selectively activated or deactivated. The output stage further comprises electronic circuit means, different from the control / adjustment mechanism, by means of which at least one of the four power transistors can be activated or deactivated independently of the control / adjustment mechanism.

[0024] Preferably, the control / adjustment mechanism and the electronic circuit means are designed and coordinated with one another such that the above-described method according to the application is carried out. The above-described advantages of the method according to the application thus also apply to the electrical output stage according to the application.

[0025] According to a preferred embodiment, the control / adjustment mechanism for activation and deactivation is electrically connected to the respective control input of the four power transistors. In this embodiment, the electronic circuit means for activation and deactivation are electrically connected to the control input of at least the second power transistor.

[0026] The application also relates to a controller for an electromechanical parking brake. The controller comprises an output stage according to the application, so that the above-described advantages of the output stage also apply to the controller. In addition to comprising the output stage, the controller further comprises a communication interface by means of which at least the control / adjustment mechanism of the electrical output stage, preferably also the electronic circuit means of the output stage, can be connected to a field bus of a motor vehicle, in particular a LIN bus or a CAN bus, for data transmission. The method according to the application can thus be carried out, monitored and controlled by means of the field bus.

[0027] Finally, the invention relates to an electromechanical parking brake for a motor vehicle. The parking brake comprises an adjustable actuator and a DC motor for adjusting the actuator. The parking brake further comprises an electric output stage according to the invention. According to the invention, the control / adjustment mechanism and the electronic circuit arrangement of the output stage are designed for carrying out the above-mentioned method according to the invention. The above-mentioned advantages of the method according to the invention or of the electric output stage according to the invention thus also transfer to the electromechanical parking brake according to the invention.

[0028] Further important features and advantages of the invention result from the dependent claims, the figures and the associated figure description by means of the figures.

[0029] It is self-evident that the features mentioned above and still to be explained below can be used not only in the combinations indicated, but also in other combinations or alone, without leaving the scope of the invention.

[0030] Preferred embodiments of the invention are shown in the figures and will be explained in more detail in the following description, in which identical reference signs denote identical or similar or functionally identical components. BRIEF DESCRIPTION OF DRAWINGS

[0031] Preferred embodiments of the invention are shown in the figures and will be explained in more detail in the following description, in which identical reference signs denote identical or similar or functionally identical components.

[0032] wherein respectively schematically shown is:

[0033] Figure 1 a circuit diagram for an example of an electric output stage according to the invention;

[0034] Figure 2 a flow chart for illustrating a method according to the invention. DETAILED DESCRIPTION

[0035] Figure 1 The construction of an electric output stage 1 according to the invention is shown exemplarily in a circuit diagram, which is used to operate an electric parking brake for a motor vehicle, which is not shown in Figure 1 . Figure 2 A diagram is shown in a schematic view, which illustrates the flow of a method according to the invention.

[0036] The electric output stage 1 comprises an H-bridge 2, in which a first, second, third and fourth power transistor 4a, 4b, 4c, 4d for controlling the locking process of the parking brake are arranged and for this purpose are electrically connected in a known manner with a DC motor 3. The power transistors 4a-4d can each be constituted by a field effect transistor (FET).

[0037] Furthermore, the electrical output stage 1 comprises a control / adjustment mechanism 5, also known to the person skilled in the art under the name "microcontroller" 7, by means of which each of the four power transistors 4a, 4b, 4c, 4d can be activated or deactivated selectively. For this purpose, the control / adjustment mechanism 5 is electrically connected to the respective control inputs 8a, 8b, 8c, 8d of the four power transistors 4a, 4b, 4c, 4d.

[0038] The four power transistors 4a, 4b, 4c, 4d are here electrically connected to one another and to the DC motor 3 in such a way that, when the first and second power transistors 4a, 4b are activated, the mechanical actuator (not shown) of the parking brake, which is driven by the DC motor 3, is moved into the locked position as a result of the DC motor 3 being energized. When the first and second power transistors 4a, 4b are activated, current flows from the voltage source 9, which is electrically connected to the H-bridge 2, via the first power transistor 4a, the DC motor 3 and the second power transistor 4b to the electrical ground 10. This current path is indicated by the arrow with reference numeral 11a in Figure 1 .

[0039] Instead of the locking process V explained above, the adjustment process of the method according to the application can also be an unlocking process for unlocking the parking brake.

[0040] Correspondingly, when the third and fourth power transistors 4c, 4b are activated and the DC motor 3 is energized in the opposite current direction as a result, the mechanical actuator is adjusted from the locked position to the unlocked position. In the unlocking process, the current path from the voltage source 9 via the third power transistor 4c, the DC motor 3 and the fourth power transistor 4d to the electrical ground 10 is indicated by the arrow with reference numeral 1 lb.

[0041] The electrical output stage 1 comprises, in addition to the control / adjustment mechanism 5, an electronic circuit arrangement 6 by means of which the second power transistor 4b and also the fourth power transistor 4d can be activated and deactivated again independently of the control / adjustment mechanism 5. An activated power transistor 4a-4d is in the on state, which corresponds to a closed electrical switch. A deactivated power transistor 4a-4d is in the off state, which corresponds to an open electrical switch.

[0042] As shown in Figure 1 , the electronic circuit arrangement 6 can comprise a plurality of electronic elements 15. In Figure 1In the example of Fig. 2, for these electronic components 15, a switch circuit (IC) 12 is shown, which is only roughly schematically shown, the signal output 16 of which controls a transistor 14 via an ohmic resistor 13, which in turn is electrically connected to the control input 8b of the second power transistor 8b. The activation and deactivation of the second power transistor 6b can thus be controlled by means of the integrated switch circuit 12 of the electronic circuit arrangement 6.

[0043] The above-described structure of the electrical output stage 1 makes it possible to carry out the method according to the application when the electrical output stage 1 is installed in a motor vehicle as part of an electromechanical parking brake. The method according to the application is explained below by means of Figure 2 the flowchart of Fig. 1 and relates to a locking process for locking a parking brake.

[0044] According to Figure 2 the flowchart of Fig. 1, in order to react to a locking request FBA, which can be generated either automatically by a controller of the motor vehicle or manually by a driver of the motor vehicle, a first measure M1 is first carried out, in which it is checked whether the current driving speed v of the motor vehicle does not exceed a maximum permissible driving speed v max . Instead of the maximum permissible driving speed v max , as a standard, it is also possible to require and furthermore check that the motor vehicle is completely stopped, i.e. the maximum driving speed v max is 0 km / h. Only when this standard is met, the method continues with a measure M2 and the actual locking process V is started. Otherwise, the check of the current driving speed v is repeated or the method according to the application is interrupted.

[0045] Before the actual locking process V is started, all four power transistors 4a to 4d are in an off state, which corresponds to an open electrical switch. In this state, the DC motor 3 is not energized.

[0046] In order to prepare the locking process V, according to the measure M2, the first power transistor 4a of the H-bridge 2 is activated, i.e. switched from the off state to the on state, by means of the control / adjustment mechanism 5 by a corresponding actuation. However, this is not yet sufficient to energize the DC motor 3, because for this purpose it is also necessary to activate, i.e. switch to the on state, the second power transistor 4b. Only then can an electrical current flow from the voltage source 9 along the first current path 11a via the first power transistor 4a, the DC motor 3 and the second power transistor 4b to the electrical ground 10.

[0047] Thus, in the normal operation of the control / regulation mechanism 5, after the first power transistor 4a has been activated by the control / regulation mechanism 5 in accordance with the measure M3, the second power transistor 4b is also activated by switching into the conducting state, so that the direct current motor 3 is energized and, in turn, the locking process V is started. During the locking process V, which is started by means of the measure M3, an output shaft (not shown) of the direct current motor 3, which cooperates with a mechanical actuator of the parking brake, is rotated, so that the actuator, which is in turn connected to a brake caliper (not shown), is adjusted towards the locking position of the parking brake.

[0048] If the control / regulation mechanism 5 fails due to a fault during the locking process V, the electronic circuit arrangement 6 takes over instead and, in particular, takes over the control of the second power transistor 4b until the locking process V has been successfully completed. The term "failure" of the control / regulation mechanism 5 in the present case means any disturbance of the function in the control / regulation mechanism 5 by means of which the power transistors 4a to 4d, in particular the second power transistor 4b, cannot be manipulated anymore, i.e. cannot be switched between the off state and the conducting state, respectively. If this failure of the control / regulation mechanism 5 occurs after the activation of the first power transistor 4a, but before the actual locking process has started, the second power transistor 4b is activated by the electronic circuit arrangement 6. Since both the first and the second power transistor 4a, 4b are thus in the conducting state, the direct current motor 3 is energized via the first current path 11a, as is necessary for adjusting the actuator of the parking brake into the locking position.

[0049] If the control / regulation mechanism 5 fails during the locking process V, i.e. after the first and the second power transistor 4a, 4b have been activated, the activated state of the first and the second power transistor 4a, 4b is maintained by means of the electronic circuit arrangement 6 until the locking process V is completed.

[0050] In the example case, upon failure of the control / regulation mechanism 5, the second power transistor 4b is deactivated again by means of the electronic circuit arrangement 6 in accordance with the measure M4, and thus the locking process V is completed as soon as the parking brake is classified as locked.

[0051] In the example scenario, the parking brake is classified as locked as soon as the current I for driving the direct current motor 3 has exceeded a predetermined threshold value I0. This occurs as soon as the actuator of the parking brake has reached the locking position, so that the parking brake is locked.

[0052] As an alternative, the parking brake can also be classified as locked as soon as a time period t, which elapses from the start of the locking process V, has exceeded a predetermined threshold value t0.

[0053] In order to ascertain the current I for driving the DC motor 3, a current sensor (not shown) can be provided in the output stage 1 or on the DC motor 3 or at another suitable location, by means of which the current I flowing through the DC motor 3 can be determined and evaluated both by the control / regulating mechanism 5 and by the electronic circuit arrangement 6.

Claims

1. Method for operating an electrical output stage (1) comprising four electrical power transistors (4a, 4b, 4c, 4d) for an electromechanical parking brake, - according to which method, when there is an adjustment request from a control / adjustment mechanism (5) during an adjustment process of the parking brake, the output stage (1) is operated; - according to which method, when the control / adjustment mechanism (5) fails, the adjustment process is continued by means of electronic circuit means (6) different from the control / adjustment mechanism (5), wherein - the adjustment process is a locking process (V) for locking the parking brake; - the adjustment request is a locking request (FBA) for locking the parking brake, wherein, when there is the locking request (FBA), a first power transistor (4a) of the four power transistors (4a, 4b, 4c, 4d) is activated by means of the control / adjustment mechanism (5) before the start of the locking process (V), wherein, - when the control / adjustment mechanism (5) is functioning correctly, after the first power transistor (4a) has been activated, a further second power transistor (4b) of the four power transistors (4a, 4b, 4c, 4d) is activated by the control / adjustment mechanism (5), starting the locking process (V); or, - when the control / adjustment mechanism (5) fails after the activation of the first power transistor (4a) but before the start of the locking process (V), the further second power transistor (4b) is activated by the electronic circuit means (6), starting the locking process (V).

2. Method according to claim 1, characterized in that: when the control / adjustment mechanism (5) fails during the locking process (V), the activation state of the first and second power transistors (4a, 4b) is maintained by means of the electronic circuit means (6) until the locking process (V) is completed.

3. Method according to claim 1 or 2, characterized in that: when the control / adjustment mechanism (5) fails, as soon as the parking brake is classified as locked, the second power transistor (4b) is deactivated again at least by means of the electronic circuit means (6).

4. Method according to claim 3, characterized in that: - as soon as the current (I) flowing through a DC motor (3) has exceeded a predetermined threshold value (10); or / and, - as soon as a period of time (t) elapsed since the start of the locking process (V) has exceeded a predetermined threshold value (to), the parking brake is classified as locked.

5. Electrical output stage (1) for operating an electromechanical parking brake, with: - an H-bridge (2) in which four power transistors (4a, 4b, 4c, 4d) activatable for operating a locking process (V) of the parking brake are arranged; - a control / adjustment mechanism (5) by means of which each of the four power transistors (4a, 4b, 4c, 4d) can be selectively activated or deactivated. - an electronic circuit arrangement (6) different from the control / adjustment mechanism (5), by means of which at least one power transistor (4b) can be activated and deactivated again, in addition to and independently of the control / adjustment mechanism (5), wherein - the control / adjustment mechanism (5) and the electronic circuit arrangement (6) are designed to implement the method according to any one of claims 1 to 4.

6. Output stage according to claim 5, characterized in that - for activation and deactivation, the control / adjustment mechanism (5) is electrically connected to the respective control input (8a, 8b, 8c, 8d) of all four power transistors (4a, 4b, 4c, 4d); - for activation and deactivation, the electronic circuit arrangement (6) is electrically connected at least to the control input (8b) of the second power transistor (4b).

7. Controller for an electromechanical parking brake, with - an electrical output stage (1) according to claim 5 or 6; - a communication interface, by means of which the control / adjustment mechanism (5) of the electrical output stage (1) can be connected to a field bus of a motor vehicle for data transmission.

8. The controller for an electromechanical park brake as defined in claim 7, wherein, The field bus is configured as a LIN bus or a CAN bus.

9. Electromechanical parking brake for a motor vehicle, with - an adjustable actuator; - a DC motor (3) for adjusting the actuator; - an electrical output stage (1) according to claim 5 or 6; - wherein, - the control / adjustment mechanism (5) and the electronic circuit arrangement (6) are designed to implement the method according to any one of claims 1 to 4.

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