Method for reducing the clamping force exerted by a parking brake

Abstract

Method for reducing the clamping force exerted by a parking brake (1), which can be generated at least partially by an electromechanical braking device with an electric brake motor (3) and, if necessary, additionally by a hydraulic braking device, wherein the brake motor (3) adjusts a brake piston (6) which can be acted upon by the hydraulic pressure of the hydraulic braking device, characterized in that in the event that the brake motor (3) cannot be released to reduce the clamping force, a signal for actuating the hydraulic braking device is generated, wherein the case that the brake motor (3) cannot be released to reduce the clamping force is preventively determined on the basis of a state or operating variable of the parking brake (1) if the parking brake (1) was actuated with maximum braking force in a previous application process.

Description

[0001] The invention relates to a method for reducing the clamping force exerted by a parking brake. State of the art

[0002] DE 103 61 042 B3 discloses a parking brake used to immobilize a vehicle when stationary. The clamping force for immobilizing the vehicle is generated electromechanically by an electric brake motor of the parking brake axially applying pressure to a brake piston, which carries a brake pad, toward a brake disc. When the locking process is terminated, the position of the brake motor's rotor is held and the clamping force is conserved. To move the vehicle again, the clamping force must be released, for which the brake motor is adjusted in the opposite direction.

[0003] DE 10 2007 041 162 A1 discloses a braking system with an electromechanical parking brake and a hydraulic vehicle brake. To release the parking brake, a predetermined hydraulic pressure is applied, after which the parking brake is reversed to release the braking force. Disclosure of the invention

[0004] The invention is based on the object of ensuring with simple measures that an electromechanical parking brake can be released under different operating conditions.

[0005] This object is achieved according to the invention with the features of the independent claims. The subclaims specify expedient developments.

[0006] The method according to the invention relates to an electromechanical parking brake in a vehicle with an electric brake motor, via which a clamping force can be generated that immobilizes the vehicle. Upon actuation of the brake motor, the rotational movement of the rotor of the brake motor is translated into an axial actuating movement of an actuator, via which a brake piston, which carries a brake pad, is pressed axially against a brake disc. The parking brake is additionally equipped with a hydraulic braking device, via which a hydraulic clamping force can be generated as needed.The hydraulic braking device, which is in particular the vehicle's regular hydraulic vehicle brake, generates hydraulic pressure that acts on the brake piston, so that the total clamping force is composed of a component generated by the electric brake motor and a component from the hydraulic braking device.

[0007] In extreme situations in which the parking brake can no longer be released purely electromechanically after a clamping force has been generated, the invention generates a signal to actuate the hydraulic braking device. This occurs both in cases of actual locking of the brake motor and in cases of imminent locking. The signal generated in these cases can be used to trigger the hydraulic braking device either automatically, for example by controlling an ESP (Electronic Stability Program) hydraulic system. It is also possible to generate a signal that is displayed to the driver visually, acoustically, or haptically, prompting them to actuate the hydraulic vehicle brake.By increasing the hydraulic pressure, a lockup of the electromechanical parking brake can be released, allowing the parking brake to be adjusted toward the open position as desired and the clamping force to be reduced. If the driver does not respond to the request to apply the hydraulic vehicle brake, the signal can be repeated or continued if necessary. The same applies if the automatic generation of hydraulic pressure or manual application by the driver is not sufficient to release the lockup.

[0008] Locking can generally be detected preventively. The preventive detection of an impending lock is determined primarily based on the state or operating variables of the parking brake that are to be examined. Various variables can be examined, with an extreme or lock situation being identified or imminent if one of the examined variables is already outside a permissible value range.

[0009] The hydraulic pressure of the hydraulic brake device acting on the brake piston from a previous parking brake application can be examined as a state or operating variable of the parking brake that is analyzed to detect an impending locking. If it turns out that the hydraulic brake pressure exceeds a limit, locking is imminent, so that after the parking brake has been applied and before the desired release, measures to remove the locking are taken. The hydraulic pressure from the previous parking brake application is either generated by the driver by pressing the brake pedal (pre-pressure) or automatically generated by an actuator, for example, via the ESP hydraulics.

[0010] Another criterion for determining an extreme or locking situation is the level of clamping force from a previous parking brake application. If the parking brake was applied by operating the electric brake motor with maximum braking force or a braking force exceeding a limit, an extreme or potential locking situation can also be assumed.

[0011] According to another criterion, an extreme or locking situation exists or is imminent if the temperature in the parking brake exceeds a certain limit. An actual or imminent locking situation can also be assumed if a re-tensioning process has been performed after the parking brake has been applied, or if the electrical voltage in the vehicle electrical system, which is available for actuating the brake motor, falls below a certain limit.

[0012] As an additional measure, in the event that the brake motor cannot be released to reduce the clamping force, a signal can be generated to start the drive motor. This signal is displayed to the driver in an appropriate manner, prompting them to start the drive motor. If necessary, the drive motor can also be started automatically.

[0013] An actual blocking situation can be detected by examining the motor variables of the electric brake motor. If a release process is initiated by controlling the brake motor and the motor current exceeds a limit, it can be assumed that the motor is blocked, after which the release process is aborted. The same applies if the motor speed falls below a limit; in this case, too, the electric brake motor is blocked, which leads to the abort of the release process or the control of the brake motor, whereupon one of the measures mentioned above is taken to remove the blocking.

[0014] The method according to the invention runs in a control unit in the vehicle, which can be part of the parking brake system.

[0015] Further advantages and practical embodiments can be found in the further claims, the description of the figures, and the drawings. They show: Fig. 1 a section through an electromechanical parking brake for a vehicle, in which the clamping force is generated by an electric brake motor, Fig. 2 a flow chart with process steps for reducing the clamping force exerted by the parking brake when the brake motor is blocked.

[0016] In Fig. 1 shows an electromechanical parking brake 1 for immobilizing a vehicle when stationary. The parking brake 1 comprises a brake caliper 2 with a caliper 9 that engages over a brake disc 10. As an actuator, the parking brake 1 has an electric motor as the brake motor 3, which drives a spindle 4 in rotation, on which a spindle component 5 designed as a spindle nut is rotatably mounted. When the spindle 4 rotates, the spindle component 5 is adjusted axially. The spindle component 5 moves within a brake piston 6, which supports a brake pad 7 that is pressed against the brake disc 10 by the brake piston 6. On the opposite side of the brake disc 10 is another brake pad 8, which is held stationary on the caliper 9.

[0017] Within the brake piston 6, the spindle component 5 can move axially forward toward the brake disc 10 upon rotation of the spindle 4, or axially backward until it reaches a stop 11 upon an opposite rotation of the spindle 4. To generate a clamping force, the spindle component 5 acts on the inner end face of the brake piston 6, whereby the brake piston 6, which is mounted axially displaceably in the parking brake 1, is pressed with the brake pad 7 against the facing end face of the brake disc 10.

[0018] If necessary, the parking brake can be assisted by a hydraulic vehicle brake, so that the clamping force is composed of an electric motor component and a hydraulic component. With hydraulic assistance, the rear side of the brake piston 6 facing the brake motor is pressurized with hydraulic fluid.

[0019] Fig.Figure 2 shows a flow chart with the individual process steps for implementing the method for reducing the clamping force exerted by a parking brake in the event of an actual or imminent locking of the electric brake motor. In the first process step 20, the driver is requested to release the applied parking brake. In the next process step 21, a query is made as to whether an extreme situation exists in the parking brake that would lead to the electric brake motor locking. This query is a preventative detection of an extreme situation in which various state or operating variables of the parking brake are checked for exceeding a permissible value range. If just one of these state or operating variables exceeds or falls below the permissible value range, it must be assumed that an extreme situation with an imminent or actual locking of the brake motor exists.

[0020] In step 21, the system queries whether the driver actuated the hydraulic brake system with a pre-pressure exceeding a limit value during the previous parking brake application process. A further query in step 21 checks whether the parking brake was applied with maximum braking force during the previous application process. Furthermore, the system queries whether the temperature in the parking brake exceeds a limit value. Further queries check whether a re-tensioning process was performed after the parking brake was applied and whether the electrical voltage in the vehicle electrical system, which is available for actuating the brake motor, falls below a limit value.

[0021] If one or more of the queries apply and thus the checked state, operating, or characteristic variable exceeds or falls below a permissible value range, the brake motor is actually or imminently blocked. In this case, the yes branch ("Y") is followed by the next process step 22, in which measures are taken to prevent or eliminate the brake motor from blocking. If, on the other hand, the query in process step 21 shows that none of the checked variables is outside the permissible value range, the no branch ("N") is followed by the no branch ("N") and the process step 26, in which the parking brake is released by actuating the electric brake motor to reduce the clamping force.

[0022] In method step 22, which is carried out when the brake motor is about to lock or is actually locking, a check is made to determine whether the vehicle engine - usually an internal combustion engine - is switched on. If this is not the case, the process continues after the "No" branch to step 23, in which the driver is requested to start the engine and apply the regular vehicle brake by pressing the brake pedal. The process then continues to step 24, in which a check is made to determine whether the brake pedal is being operated by the driver. Even if the "Yes" branch is made in method step 22 (engine switched on), the process continues to step 24. If the query in method step 24 shows that the brake pedal is not being operated by the driver, the process continues after the "No" branch to step 25, and the driver is requested to apply the vehicle brake.The system then returns to process step 24 and checks again whether the brake pedal is being pressed down by the driver.

[0023] If the query in method step 24 shows that the driver is depressing the brake pedal, the process proceeds to step 26 following the yes branch, according to which the parking brake is released by controlling the electric brake motor to reduce the clamping force. The process then continues to step 27, in which it is checked whether the electric brake motor is blocked, which can be detected based on the motor current curve or the motor speed of the brake motor. The brake motor may block despite the previous measures, in particular the actuation of the brake pedal. By generating a hydraulic pre-pressure via the brake pedal, blocking is to be prevented or released; however, if the query in method step 27 determines that blocking exists despite the measure, the process proceeds to step 29 following the yes branch.Otherwise, there is no blocking and, following the No branch, the process proceeds to step 28, according to which the parking brake is released in the desired manner until the clamping force is completely reduced.

[0024] To detect a blockage of the electric brake motor in step 27, a query is made as to whether the motor current exceeds a limit value. Additionally or alternatively, a query can be made as to whether the motor speed falls below a limit value. If one of the conditions is met, the brake motor is blocked, and the process continues following the "yes" branch to step 29, in which an additional query is made as to whether the brake motor blockage has been detected for the first time. If this is the case, the process returns to step 22 following the "yes" branch, and the check or request to start the vehicle engine or depress the brake pedal is repeated.If, however, the query in step 29 shows that the brake motor has been locked more than once, the process continues to step 30 following the "No" branch; in this case, releasing the lock is not possible, and the parking brake cannot be activated.

Claims

[1] Method for reducing the clamping force exerted by a parking brake (1), which can be generated at least partially by an electromechanical braking device with an electric brake motor (3) and, if necessary, additionally by a hydraulic braking device, wherein the brake motor (3) adjusts a brake piston (6) which can be acted upon by the hydraulic pressure of the hydraulic braking device, characterized by in that, in the event that the brake motor (3) cannot be released to reduce the clamping force, a signal for actuating the hydraulic brake device is generated, wherein the case that the brake motor (3) cannot be released to reduce the clamping force is preventively determined on the basis of a state or operating variable of the parking brake (1) if the parking brake (1) was actuated with maximum braking force in a previous application process. [2] Method for reducing the clamping force exerted by a parking brake (1), which can be generated at least partially by an electromechanical braking device with an electric brake motor (3) and, if necessary, additionally by a hydraulic braking device, wherein the brake motor (3) adjusts a brake piston (6) which can be acted upon by the hydraulic pressure of the hydraulic braking device, characterized by in that, in the event that the brake motor (3) cannot be released to reduce the clamping force, a signal for actuating the hydraulic brake device is generated, wherein the case that the brake motor (3) cannot be released to reduce the clamping force is preventively determined on the basis of a state or operating variable of the parking brake (1) when the temperature in the parking brake (1) exceeds a limit value. [3] Method for reducing the clamping force exerted by a parking brake (1), which can be generated at least partially by an electromechanical braking device with an electric brake motor (3) and, if necessary, additionally by a hydraulic braking device, wherein the brake motor (3) adjusts a brake piston (6) which can be acted upon by the hydraulic pressure of the hydraulic braking device, characterized by in that, in the event that the brake motor (3) cannot be released to reduce the clamping force, a signal for actuating the hydraulic brake device is generated, wherein the case that the brake motor (3) cannot be released to reduce the clamping force is preventively determined on the basis of a state or operating variable of the parking brake (1) if a re-tensioning process has been carried out after the parking brake (1) has been applied. [4] Method for reducing the clamping force exerted by a parking brake (1), which can be generated at least partially by an electromechanical braking device with an electric brake motor (3) and, if necessary, additionally by a hydraulic braking device, wherein the brake motor (3) adjusts a brake piston (6) which can be acted upon by the hydraulic pressure of the hydraulic braking device, characterized by that in the event that the brake motor (3) cannot be released to reduce the clamping force, a signal for actuating the hydraulic brake device is generated, wherein the case that the brake motor (3) cannot be released to reduce the clamping force is preventively determined on the basis of a state or operating variable of the parking brake (1) when the electrical voltage in the vehicle electrical system falls below a limit value. [5] Method for reducing the clamping force exerted by a parking brake (1), which can be generated at least partially by an electromechanical braking device with an electric brake motor (3) and, if necessary, additionally by a hydraulic braking device, wherein the brake motor (3) adjusts a brake piston (6) which can be acted upon by the hydraulic pressure of the hydraulic braking device, characterized by that in the event that the brake motor (3) cannot be released to reduce the clamping force, a signal for actuating the hydraulic brake device is generated, wherein the case that the brake motor (3) cannot be released to reduce the clamping force occurs when the brake motor (3) blocks after being activated to reduce the clamping force. [6] Method according to claim 5, characterized by that blocking is detected when the motor current exceeds a limit. [7] Method according to claim 5 or 6, characterized bythat blocking is detected when the engine speed falls below a limit. [8] Method for reducing the clamping force exerted by a parking brake (1), which can be generated at least partially by an electromechanical braking device with an electric brake motor (3) and, if necessary, additionally by a hydraulic braking device, wherein the brake motor (3) adjusts a brake piston (6) which can be acted upon by the hydraulic pressure of the hydraulic braking device, characterized by that in the event that the brake motor (3) cannot be released to reduce the clamping force, a signal is generated to actuate the hydraulic braking device and the drive motor of the vehicle is started or a request is made to start the drive motor. [9] Method according to one of claims 1 to 8, characterized by that the hydraulic braking device is activated via the signal. [10] Method according to one of claims 1 to 9, characterized by that the signal prompts the hydraulic braking device to be activated. [11] Control or regulating device for carrying out the method according to one of claims 1 to 10. [12] Parking brake in a vehicle with a control device according to claim 11.

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