Method for Operating an Automated Parking Brake

Abstract

A method for operating an automated parking brake in a motor vehicle, having a hydraulic actuator for producing a hydraulic force component and an electromechanical actuator for producing an electromechanical force component, includes superimposing the hydraulic force component and the electromechanical force component to obtain a total clamping force for a parking brake operation, and maintaining the total clamping force by self-locking of the parking brake. The method further comprises during the parking brake operation, setting at least one defined hydraulic pressure level using the hydraulic actuator, and locking-in a defined hydraulic pressure level with a valve when the at least one defined hydraulic pressure level is reached.

Claims

1. A method for operating an automated parking brake in a motor vehicle, having a hydraulic actuator for producing a hydraulic force component and an electromechanical actuator for producing an electromechanical force component, the method comprising: superimposing the hydraulic force component and the electromechanical force component to obtain a total clamping force for a parking brake operation; maintaining the total clamping force by self-locking of the automated parking brake; setting, during the parking brake operation, at least one defined hydraulic pressure level with the hydraulic actuator; and locking-in the at least one defined hydraulic pressure level with a valve when the at least one defined hydraulic pressure level is reached.

2. The method according to claim 1, further comprising: setting a first hydraulic pressure level of the at least one defined hydraulic pressure level when a first condition is met, wherein the first hydraulic pressure level is defined as a pressure for holding the vehicle.

3. The method according to claim 2, further comprising: detecting a parking brake demand; and determining that the first condition is met when the parking brake demand is detected.

4. The method according to claim 1, further comprising: detecting a parking brake demand; and shutting off inlet valves at the front axle when the parking brake demand is detected.

5. The method according to claim 2, further comprising: setting a second hydraulic pressure level of the at least one defined hydraulic pressure level when a second condition is met, wherein the second hydraulic pressure level is defined as a pressure for parking the vehicle.

6. The method according to claim 5, further comprising: determining that the second condition is met when an idle path of the parking brake has been substantially traveled.

7. The method according to claim 5, further comprising: setting the first hydraulic pressure level and the second hydraulic pressure level with actuation of the hydraulic actuator.

8. The method according to claim 1, further comprising: ending actuation of the hydraulic actuator when the at least one defined hydraulic pressure level is reached and the at least one defined hydraulic pressure level is locked-in with the valve.

9. The method according to claim 5, further comprising: taking into account a slope of a roadway in a definition of the at least one defined hydraulic pressure level to enable the vehicle to be held and/or parked on an instantaneous roadway slope.

10. The method according to claim 1, further comprising: opening shut-off valves when the total clamping force is reached.

11. A control unit for operating an automated parking brake for a motor vehicle having a hydraulic actuator configured to produce a hydraulic force component, and an electromechanical actuator configured to produce an electromechanical force component, the control unit comprising: a non-transitory computer readable medium having program instructions configured to cause the control unit to superimpose the hydraulic force component and the electromechanical force component to obtain a total clamping force for a parking brake operation, to maintain the total clamping force by self-locking of the automated parking brake, to set, during the parking brake operation, at least one defined hydraulic pressure level with the hydraulic actuator, and to lock-in the at least one defined hydraulic pressure level with a valve when the at least one defined hydraulic pressure level is reached.

12. A hydraulic brake system for a motor vehicle, comprising: a hydraulic actuator configured to produce a hydraulic force component; an electromechanical actuator configured to produce an electromechanical force component; and a control unit configured to superimpose the hydraulic force component and the electromechanical force component to obtain a total clamping force for a parking brake operation, to maintain the total clamping force by self-locking of the automated parking brake, to set, during the parking brake operation, at least one defined hydraulic pressure level with the hydraulic actuator, and to lock-in the at least one defined hydraulic pressure level with a valve when the at least one defined hydraulic pressure level is reached.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0039] Of the figures:

[0040] FIG. 1 shows a schematic sectional view of a braking device having an automatic parking brake of motor on caliper construction; and

[0041] FIG. 2 shows a hydraulic circuit diagram of a vehicle brake system having a front axle brake circuit and a rear axle brake circuit and having an electronic stability program, which comprises an electric pump unit, and

[0042] FIG. 3 shows an illustration of the method steps in one embodiment of the disclosure, and

[0043] FIG. 4 shows a diagram containing the time-dependent variation in the motor current of the electromechanical actuator and of the hydraulic actuator, in the brake pressure and in the total braking force.

DETAILED DESCRIPTION

[0044] FIG. 1 shows a schematic sectional view of a braking device 1 for a vehicle. Here, the braking device 1 has an automated parking brake 13 (also referred to as an automatic parking brake or automated park brake, referred to as an APB for short), which can exert a clamping force to immobilize the vehicle by means of an electromechanical actuator 2 (electric motor). For this purpose, the electromechanical actuator 2 in the parking brake 13 illustrated drives a spindle 3, in particular a threaded spindle 3, supported in an axial direction. At its end remote from the actuator 2, the spindle 3 is provided with a spindle nut 4, which rests against the brake piston 5 in the applied state of the automated parking brake 13. In this way, the parking brake 13 transmits a force to the brake pads 8, 8 and to the brake disk 7. In this case, the spindle nut rests against an inner end of the brake piston 5 (also referred to as the rear side of the brake piston end or inner piston end). During a rotary motion of the actuator 2 and a resulting rotary motion of the spindle 3, the spindle nut 4 is moved in the axial direction. The spindle nut 4 and the brake piston 5 are supported in a brake caliper 6, which fits over a brake disk 7 in the manner of a pincer.

[0045] Respective brake pads 8, 8 are arranged on each side of the brake disk 7. In the case of a brake application process of the braking device 1 by means of the automated parking brake 13, the electric motor (actuator 2) rotates, whereupon the spindle nut 4 and the brake piston 5 are moved toward the brake disk 7 in the axial direction in order in this way to produce a predetermined clamping force between the brake pads 8, 8 and the brake disk 7. By virtue of the spindle drive and the associated self locking, a force produced in the parking brake 13 by means of an activation of the electric motor can also be maintained when the activation is ended.

[0046] The automated parking brake 13 is designed as a motor on caliper system, for example, as depicted, and is combined with the service brake 14. The parking brake 13 could also be regarded as integrated into the system of the service brake 14. In this arrangement, both the automated parking brake 13 and the service brake 14 act on the same brake piston 5 and on the same brake caliper 6 in order to build up a braking force on the brake disk 7. However, the service brake 14 has a separate hydraulic actuator 10, e.g. a foot brake pedal with a brake booster. In FIG. 1, the service brake 14 is designed as a hydraulic system, wherein the hydraulic actuator 10 is assisted by the ESP pump or by an electromechanical brake booster (e.g. Bosch iBooster) or can be implemented thereby. Other embodiments of the actuator 10 are also conceivable, e.g. in the form of an IPB (Integrated Power Brake), which fundamentally represents a brake-by-wire system, in which a plunger is used to build up hydraulic pressure. During a service braking operation, a predetermined clamping force is built up hydraulically between the brake pads 8, 8 and the brake disk 7. To build up a braking force by means of the hydraulic service brake 14, a medium 11, in particular a substantially incompressible brake fluid 11, is forced into a fluid space delimited by the brake piston 5 and the brake caliper 6. The brake piston 5 is sealed off from the environment by means of a piston sealing ring 12.

[0047] The brake actuators 2 and 10 are activated by means of one or more output stages, i.e. by means of a control unit 9, which can be a control unit of a vehicle dynamics system, such as ESP (electronic stability program), or some other control unit.

[0048] In an activation of the automated parking brake 13, the idle path or release clearance must first of all be traversed before a braking force can be built up. The term idle path is used, for example, to denote the distance which the spindle nut 4 must travel owing to the rotation of the spindle 3 to enter into contact with the brake piston 5. The term release clearance is used to denote the distance between the brake pads 8, 8 and the brake disk 7 in disk brake systems of motor vehicles. This process generally takes a relatively long time in relation to the overall activation, especially in the automated parking brake 13. At the end of a preparatory phase of this kind, the brake pads 8, 8 are applied to the brake disk 7, and the force buildup begins in a further activation. FIG. 1 shows the state of the already traversed idle path and release clearance. In this case, the brake pads 8, 8 are placed against the brake disk 7, and all the brakes, i.e. the parking brake 13 and service brake 14, can immediately build up a braking force at the corresponding wheel in the event of a subsequent activation. The descriptions relating to the release clearance apply similarly also to the service brake 14, although, owing to the high speed of the pressure buildup, the traversing of an idle path represents a smaller time outlay than in the case of the parking brake 13.

[0049] The hydraulic brake system, illustrated in the hydraulic circuit diagram according to FIG. 2, in a brake system 101 has a first brake circuit 102 and a second brake circuit 103 for supplying wheel brake devices 1a and 1c at the front wheels and 1b and 1d at the rear wheels with hydraulic brake fluid. In this sense, there is an X split in the brake system illustrated. As an alternative, a parallel split (II split) of the brake circuits of the brake system is, of course, also possible in a similar way. The two brake circuits 102, 103 are connected to a common brake master cylinder 104, which is supplied with brake fluid by means of a brake fluid reservoir 105. The brake master cylinder 104 is actuated by the driver via the brake pedal 106. The pedal travel performed by the driver is measured by means of a pedal travel sensor 107 in the embodiment illustrated.

[0050] Arranged in each brake circuit 102, 103 is a switchover valve 112, which is situated in the flow path between the brake master cylinder 104 and the respective wheel brake devices 1a, 1b and 1c, 1d, respectively. The switchover valves 112 are open in the deenergized home position thereof. Each switchover valve 112 is assigned a check valve connected in parallel, which allows flow in the direction of the respective wheel brake devices. Between the switchover valves 112 and the respective wheel brake devices 1a, 1b and 1c, 1d, respectively, there are inlet valves 113a of the front wheels and inlet valves 113b of the rear wheels, which are likewise open when deenergized and to which are assigned check valves, which allow flow in the opposite direction, i.e. from the wheel brake devices in the direction of the brake master cylinder.

[0051] Each wheel brake device 1a, 1b and 1c, 1d is assigned an outlet valve 114, which is closed when deenergized. The outlet valves 114 are each connected to the suction side of a pump unit 115, which has a pump 118 and 119, respectively, in each brake circuit 102, 103. The pump unit is assigned an electric drive or pump motor 122, which actuates both pumps 118 and 119 via a shaft 123. In each brake circuit, the pressure side of the pumps 118 and 119 is connected to a line segment between the switchover valve 112 and the two inlet valves 113a, 113b.

[0052] The suction sides of the pumps 118 and 119 are each connected to a main on-off valve 120, which is hydraulically connected to the brake master cylinder 104. During a control intervention into the vehicle dynamics, the main on-off valves 120, which are closed in the deenergized state, can be opened for a rapid brake pressure buildup, ensuring that the pumps 118 and 119 draw in hydraulic fluid directly from the brake master cylinder 104. This brake pressure buildup can be carried out independently of an actuation of the brake system by the driver. The pump unit 115 with the two individual pumps 118 and 119, the electric pump motor 122 and the shaft 123 belongs to a driver assistance system and, in particular, forms an electronic stability program (ESP).

[0053] In each brake circuit 102, 103, there is a hydraulic accumulator 121 between the outlet valves 114 and the suction side of the pumps 118 and 119, said accumulator being used for temporary storage of brake fluid, which is released from the wheel brake devices 1a, 1b and 1c, 1d, respectively, through the outlet valves 114 during an intervention into the vehicle dynamics. Each hydraulic accumulator 121 is assigned a check valve, which opens in the direction of the suction sides of the pumps 118, 119. To measure the pressure, there is a respective pressure sensor 116 in each brake circuit 102, 103 in the region of the wheel brake devices 1a, 1b and 1c, 1d, respectively, in the embodiment illustrated. A further pressure sensor 117 is arranged in brake circuit 102, adjacent to the brake master cylinder 104.

[0054] FIG. 3 shows an illustration of the method steps of one embodiment of the disclosure. Here, a parking brake demand is determined in a first step S1. At time t1, a parking brake demand is recorded. Initially, the inlet valves 113a of the front axle (shutoff valves) are thereupon closed in a step S2. Once the inlet valves 113a of the front axle are fully closed, both the electromechanical actuator of the parking brake and the hydraulic actuator of the service brake are actuated at time t2. A hydraulic pressure buildup takes place in a step S3. By virtue of its high speed, the hydraulic actuator makes available the necessary holding force here just after the beginning of actuation. Whether the pressure level p1 required to hold the vehicle has been reached is interrogated in a condition B1. If this has not yet been reached (N), a further hydraulic pressure buildup takes place. If it has been reached (Y), the switchover valves 112 are closed in a step S4. In a step S5, the activation of the hydraulic actuator is then ended. The hydraulic brake pressure is then held automatically by the closed switchover valves. In an alternative embodiment, closure of one or more other pressure holding valves can also take place in such a way that the hydraulic fluid volume is locked in and/or the built-up pressure in the brake piston is held. At time t3, the hydraulic actuation is ended for the time being.

[0055] At time t2, actuation of the parking brake furthermore starts in a step S11. Driven by the electromechanical actuator, the actuating unit begins to traverse the available idle path. During this process, no hydraulic volume is displaced since the spindle nut moves only within the brake piston. In order to avoid a high load on the onboard electrical system from two simultaneously actuated systems, the electromechanical actuators of the parking brake can also be activated in a somewhat time-delayed manner. A typical value for this is a time offset of approximately 40 ms. While the parking brake traverses the idle path necessary for a brake system which is free from residual braking torque in normal operation, a condition B3 is used to check whether the idle path has been traversed. If this is not the case (N), activation of the electromechanical actuator is continued. Once the parking brake has traversed the idle path at time t4 (condition B3=Y), an electromechanical force buildup takes place in a step S12.

[0056] During this process, there is force superposition of the hydraulic and electromechanical force components. The resulting movement of the brake piston leads to a pressure drop in the hydraulic fluid owing to the volume displacement. This pressure drop is compensated by the hydraulic actuator. The hydraulic force buildup furthermore starts again in step S6 with a pressure increase from p1 to p2. For this purpose, the switchover valves 112 are opened in a step S7. During this process, a parking brake pressure p2 is set. In the process, condition B2 is interrogated to determine whether this pressure p2 has been reached. If this is not the case (N), the hydraulic pressure buildup is continued. If this is the case (Y), the switchover valves 112 are shut off again in a step S9. In a step S9, the hydraulic pressure buildup is then ended. If the hydraulic clamping force component p2 necessary for the overall brake application process has been reached at time t5, the pressure is held by closing the switchover valves 112 again in the rear wheel brakes.

[0057] During the electromechanical force buildup, a condition B4 is used to check whether the required target clamping force has been achieved. If this is not the case (N), the activation of the electromechanical actuator is continued. If this is the case (Y), this leads to ending of the activation. At time t6, the sum of the hydraulic and electromechanical clamping force components is present at the braking piston of the rear wheel brake. This state can be detected inter alia by monitoring the spindle nut travel of the park brake actuators. The power supply to the parking brake is switched off and all the valves (switchover valves, inlet valves, other shutoff valves) of the hydraulic brake system are opened. At time t7, the hydraulic pressure has completely escaped and the park brake actuation process is thus complete. By virtue of the self locking design of the spindle/spindle nut unit of the parking brake, the clamping force is maintained automatically and permanently without the need for additional energy.

[0058] FIG. 4 shows a diagram comprising electric and hydraulic state variables during a brake application process for immobilizing the vehicle at rest. At time t.sub.1, a hydraulic brake pressure p is produced by means of an electrically controllable hydraulic actuator of the hydraulic vehicle brake, e.g. by actuation of the ESP pump. During this process, I.sub.hydr shows the variation of the current of the hydraulic actuator. Initially, this rises abruptly upon activation (startup spike). Until a first pressure level p.sub.1 is reached, the current remains substantially constant at a defined level. At time t.sub.3, the hydraulic brake pressure reaches the first level p.sub.1.

[0059] At time t.sub.2, the energization of the electric brake motor (electromechanical actuator) begins, with the motor current I.sub.mech (i.e. current of the electromechanical actuator), which, after an initial pulse, falls to an idle current and maintains this over the time period between t.sub.3 and t.sub.4. The phase between t.sub.3 and t.sub.4 represents the idling phase of the electric brake motor. As long as the idle path is being traversed, the pressure p is held constant at the pressure level p.sub.1. For this purpose, the hydraulic fluid is locked in by means of valves. Control of the hydraulic actuator is no longer necessary for this time period.

[0060] At time t.sub.4, an electromechanical braking force is produced by means of the electric brake motor, and the motor current I.sub.mech rises in corresponding fashion, starting from the level of the idle current. There is furthermore a renewed actuation of the hydraulic actuator with a current I.sub.hydr in order to set the desired second pressure level p.sub.2. In this case, the hydraulic brake pressure p rises further, starting from the first level p.sub.1, resulting in a total braking force F.sub.ges through superposition of the hydraulic and the electromechanical braking force.

[0061] At time t.sub.5, the hydraulic brake pressure reaches its maximum p.sub.2, which is maintained until time t.sub.6. In the time period between t.sub.5 and t.sub.6, the hydraulic pressure level p.sub.2 reached is once again maintained by locking in the hydraulic fluid by means of valves. As an alternative, it can be held constant and adjusted by control of the hydraulic actuator. This is accomplished with a reduced current I.sub.hydr. In the time period between t.sub.5 and t.sub.6, the electromechanical braking force continues to rise, changing synchronously with the braking current I.sub.mech, until a maximum is reached. The hydraulic pressure is then released or the hydraulic actuator switched off.