Method for adjusting the air clearance of a hydraulic vehicle brake

Abstract

Method for operating a hydraulic vehicle brake which is equipped with a brake force support device (8) and has a parking brake function with a locking actuator, characterized in that in the event of a partial or complete failure of the brake force support device (8) the distance between brake pads (15, 16) of the vehicle brake (1) and a brake disc (18) is reduced by actuating the locking actuator.

Description

[0001] The invention relates to a method for operating a hydraulic vehicle brake according to claim 1, as well as a control unit according to claim 9 and a vehicle brake in a vehicle with such a control unit according to claim 10. State of the art

[0002] Hydraulic braking systems are well-known in which the braking force applied by the driver to the brake pedal is converted into hydraulic brake pressure via a hydraulic brake cylinder and a brake force assist device. This pressure is then used to apply pressure to the brake pads against a brake disc. If the brake force assist device fails, for example, a hydraulic pump, only the brake force amplification provided by the brake cylinder is available. In this case, a hydraulic dead volume must first be pumped to achieve a significant braking effect before the braking force is built up.

[0003] Furthermore, parking brakes in vehicles are known which have an electric brake motor, the actuation of which presses a brake piston, which carries a brake pad, against the brake disc. Such a parking brake is described, for example, in DE 103 61 042 B3. A hydraulic brake system which adjusts a brake pad to set a clearance on a wheel brake is known from WO 2010 / 017998 A1. Disclosure of the invention

[0004] The invention is based on the objective of improving the braking behavior of a hydraulic vehicle brake in the event of a failure of the brake force support device using simple measures.

[0005] This problem is solved according to the invention by the features of claim 1. The dependent claims specify advantageous further developments.

[0006] The method according to the invention relates to the operation of a hydraulic vehicle brake in a motor vehicle, wherein the vehicle brake comprises the braking system for braking the vehicle wheels by actuating the brake pedal. The vehicle brake has a brake force assist device, for example, a hydraulic pump for generating increased hydraulic pressure in a hydraulic accumulator to assist the brake force generation. The vehicle brake also has a parking brake function, in which a braking or parking force is generated via a parking actuator when the vehicle is stationary, thus securing it.

[0007] If a partial or complete failure of the brake force assist system is detected, the parking actuator is actuated in the inventive method to reduce the distance between the brake pads of the vehicle brake and the brake disc in at least one wheel brake unit. The parking actuator acts on the same wheel brake unit as the hydraulic vehicle brake. During a regular braking operation to slow the vehicle, the hydraulic brake pressure acts axially against the brake disc on a brake piston in the wheel brake unit, which carries a brake pad. The parking actuator, which implements the parking brake, also acts on the brake piston to lock the vehicle in a stationary position, thus pressing the brake pad against the brake disc.

[0008] In the event of a partial or complete failure of the brake force assist system, the parking brake actuator is automatically activated to reduce the gap between the brake pad and brake disc. This creates a link between the parking brake function and the regular braking function for decelerating the vehicle, with the aim of reducing the clearance in the wheel brake assembly between the brake pad and brake disc. Activation of the parking brake actuator reduces this clearance only, enabling faster and more efficient braking during subsequent regular braking maneuvers, whether initiated by the driver pressing the brake pedal or automatically by a driver assistance system.Due to the reduced air clearance, the hydraulic dead volume, which normally has to be pumped during regular braking until the brake pads contact the brake disc, is correspondingly reduced. By reducing or eliminating this hydraulic dead volume, the driver's braking request is implemented more directly when the brake pedal is pressed, due to the reduced hydraulic volume required in the braking system. This also has the advantage of allowing the use of a smaller master cylinder with smaller hydraulically effective surfaces.

[0009] The locking actuator can be activated to reduce the air play while driving.

[0010] The locking actuator is, for example, an electric brake motor of an electric parking brake. The brake motor acts on the brake piston and moves it towards the brake disc.

[0011] The reduction of the gap between the brake pads and the brake disc can be so significant that the brake pads are in contact with the brake disc. However, to prevent the brake pads from rubbing against the brake disc even when the driver is not requesting the brakes, it may be advisable, after contact has been reached, to actuate the locking actuator in the opposite direction to move the brake pads away from the brake disc by a reduced amount. This reversing movement is smaller than the immediately preceding movement towards the brake disc to ensure that the overall gap between the brake pad and brake disc is reduced.

[0012] The reduced clearance is advantageously maintained for the duration of the partial or complete failure of the brake force assist system. As soon as the partial or complete failure is detected, the locking actuator is automatically engaged to reduce the clearance. The reduced clearance between the brake pad and brake disc is maintained.

[0013] The method according to the invention is carried out in the event of a complete failure and also in the event of a partial failure of the brake force assist device, insofar as the reduction in brake force assist exceeds a minimum level. If the reduction in assist is below a threshold value, it may, however, be advantageous to forego the actuation of the locking actuator according to the invention for reducing the free play.

[0014] Adjusting the brake piston and thus reducing the brake clearance by actuating the locking actuator is, according to a further advantageous embodiment, force-controlled or displacement-controlled. In this case, the distance traveled by an actuator of the locking actuator is determined by a sensor, or the distance traveled is calculated from a measured value, whereby the actuator is adjusted by a defined amount. In a force-controlled adjustment movement, the force with which the brake pad contacts the brake disc is advantageously determined by a sensor. In an embodiment of the locking actuator as an electric brake motor, the force is determined, for example, by measuring the current drawn in the brake motor, which increases sharply as the brake pad contacts the brake disc.Once such an increase in braking force has been detected, it may be advisable, as described above, to move the locking actuator slightly in the opposite direction to prevent the brake pad from contacting the brake disc and the resulting friction, as long as there is no driver request to brake.

[0015] The inventive method for operating the vehicle brake takes place in a control unit, which can be part of the vehicle brake or the parking brake.

[0016] Further advantages and practical designs can be found in the additional requirements, the figure description, and the drawings. These show: Fig. 1. Schematic representation of a hydraulic vehicle brake in a motor vehicle, Fig. 2 a section through a wheel brake unit of the vehicle brake, which is also used as a parking brake and has an electric brake motor, Fig. 3 a flowchart showing the procedure steps for operating the vehicle brake in the event of a failure of the brake force support device.

[0017] In the figures, identical components are labelled with the same reference symbols.

[0018] In Fig. Figure 1 shows a hydraulic vehicle brake 1, which has a brake circuit 2 (shown only schematically) through which a wheel brake unit 3 is actuated to decelerate the vehicle. The brake circuit 2 is hydraulically connected to a master brake cylinder 6, which is connected to a brake fluid reservoir 7. The master brake cylinder 6 is actuated by the driver via the brake pedal 4, the pedal travel of which is determined by a pedal travel sensor 5. The master brake cylinder 6 is connected to a hydraulic brake force assist device 8, which includes a hydraulic pump and a hydraulic accumulator. The master brake cylinder 6 is also connected to a reservoir 9. The braking force or brake pressure generated by the driver and amplified in the master brake cylinder 6 is transmitted via the brake circuit 2 to the wheel brake unit 3 assigned to a vehicle wheel.

[0019] How Fig. As can be seen from Figure 2, the wheel brake unit 3 comprises a brake caliper 10 with a caliper 17, which engages a brake disc 18. A brake pad 15 is arranged on a brake piston 14, which is pressed axially against an end face of the brake disc 18. The brake piston 14 is actuated by the hydraulic fluid of the brake circuit. On the opposite side of the brake disc 18 is another brake pad 16, which is held stationary on the caliper 17.

[0020] To implement a parking brake function, by which the vehicle is secured when stationary (parking brake), the wheel brake unit 3 is equipped with an electric brake motor 11, which rotates a spindle 12 on which a spindle component 13 designed as a spindle nut is rotatably mounted.

[0021] When the spindle 12 rotates, the spindle component 13 is axially adjusted. This component moves within the brake piston 14, which carries the brake pad 15. The brake motor 11 is driven to generate a clamping force that secures the vehicle. This force is applied to the brake disc 18 via the brake piston 14 and the brake pads 15 and 16, achieving a minimum required braking force. The clamping force generated by the brake motor 11 can be determined, for example, by monitoring the current flow of the brake motor. As soon as the current draw increases, the brake pads 15 and 16 contact the brake disc 18 and exert a clamping force.

[0022] In Fig.Figure 3 shows a flowchart with procedure steps for operating the vehicle brakes in the event of a brake force assist failure. In the first procedure step 20, it is checked at regular intervals whether the brake force assist has partially or completely failed. As long as this is not the case, i.e., the brake force assist is functioning correctly, the vehicle brakes are in their normal operating mode and can generate the required braking force without restrictions. In this case, following the "No" branch ("N"), the process returns to the beginning of procedure step 10, and the check in step 20 is repeated at regular intervals.

[0023] If, however, the query in step 20 indicates a failure of the brake force assist system, the process continues to the next step 21, following the "Y" branch, according to which the electric brake motor assigned to the parking brake function is actuated. This reduces the clearance, i.e., the distance between the brake pads and the brake disc in the wheel brake unit.

[0024] In the following process step 22, it is checked whether the brake pads are already in contact with the brake disc. This can be determined, for example, by monitoring the current curve of the electric brake motor. If the current curve rises significantly, this indicates that the brake pads are in contact with the brake disc. If no increase in motor current or clamping force is detected in the check according to step 22, the process returns to process step 21 following the "no" branch, and the clamping process continues via the electric braking process. If, on the other hand, the check in step 22 shows a significant increase in motor current or clamping force, the process proceeds to the next step 23.

[0025] In step 23, the electric brake motor is activated in the opposite direction, causing the brake pads to move away from the brake disc and preventing frictional contact between the pads and the disc. However, this retraction only occurs until the brake pads are positioned with only a small axial gap to the disc.

[0026] The brake pads remain in this position, immediately adjacent to the brake disc, where the clearance is reduced to a minimum. When the vehicle brakes are applied, the hydraulic brake pressure acts on the brake piston and pushes it towards the brake disc to generate the desired braking force. Because the clearance is reduced to a minimum, the driver only needs to deliver a correspondingly reduced volume of hydraulic fluid when pressing the brake pedal.

Claims

[1] Method for operating a hydraulic vehicle brake which is equipped with a brake force assist device (8) and has a parking brake function with a parking actuator, characterized by , that in the event of a partial or complete failure of the brake force support device (8) by actuating the locking actuator the distance between brake pads (15, 16) of the vehicle brake (1) and a brake disc (18) is reduced. [2] Method according to claim 1, characterized by , that when the distance is reduced the brake pads (15, 16) are adjusted until they make contact with the brake disc (18). [3] Method according to claim 2, characterized by , that after contact with the brake disc (18) is reached by actuating the locking actuator in the opposite direction, the brake pads (15, 16) are moved away from the brake disc (18) by a reduced amount. [4] Method according to any one of claims 1 to 3, characterized by, that the reduction of the distance between the brake pads (15, 16) and the brake disc (18) is controlled by actuating the locking actuator. [5] Method according to any one of claims 1 to 3, characterized by , that the reduction of the distance between the brake pads (15, 16) and the brake disc (18) is force-controlled by actuating the locking actuator. [6] Method according to any one of claims 1 to 5, characterized by , that the reduced distance between the brake pads (15, 16) and the brake disc (18) is maintained for the duration of the partial or complete failure of the brake force support device (8). [7] Method according to any one of claims 1 to 6, characterized by , that the locking actuator is designed as an electric brake motor (11). [8] Method according to claim 7, characterized by, that the current flow of the electric brake motor (11) indicates contact between the brake pads (15, 16) and the brake disc (18). [9] Control device for carrying out the method according to any one of claims 1 to 8. [10] Vehicle brake in a vehicle with a control unit according to claim 9.

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