Automated Parking Brake and Method for Operating an Automated Parking Brake

Abstract

An automated parking brake for a motor vehicle having at least one brake device is configured to adopt at least two states. In a first state, no clamping force is established by the parking brake, and in a second state, a clamping force is established by the parking brake. A transition point defines a transition between the two states. An identification of the transition point is carried out during a releasing process of the parking brake.

Claims

1. A method for operating an automated parking brake for a motor vehicle with at least one brake device, comprising: adopting one of at least two states with the parking brake, in a first state no clamping force is established by the parking brake, and in a second state a clamping force is established by the parking brake, wherein a transition point defines a transition between the first state and the second state; and identifying the transition point during a parking brake releasing process.

2. The method as claimed in claim 1, further comprising: identifying the transition point based on a time profile of a variable representing the clamping force of the parking brake.

3. The method as claimed in claim 1, further comprising: suspending the identification of the transition point during a switch-on phase.

4. The method as claimed in claim 2, further comprising: starting the identification of the transition point if the variable representing the clamping force of the parking brake lies below a defined threshold value.

5. The method as claimed in claim 2, further comprising: during the identification of the transition point, determining whether there is a continuous decline of a profile of values of the variable representing the clamping force of the parking brake; and identifying a continuous decline if a plurality of decreasing chronologically directly successive values are determined.

6. The method as claimed in claim 2, further comprising: identifying the transition point if a change of a profile of values of the variable representing the clamping force of the parking brake is determined.

7. The method as claimed in claim 2, further comprising: identifying the transition point if a decreasing decline of a profile of values of the variable representing the clamping force of the parking brake is determined; and identifying a decreasing decline if a plurality of decreasing difference amounts of chronologically immediately successive values are determined, and/or if a plurality of difference amounts of the chronologically immediately successive values are each smaller than a threshold value associated with the respective difference amounts, wherein in particular the threshold values are equal or there is a reduction of the threshold values according to the chronological ranking of the associated difference amounts.

8. The method as claimed in claim 2, further comprising: evaluating the time profile of the variable representing the clamping force of the parking brake during a force reduction phase for the identification of the transition point.

9. The method as claimed in claim 2, further comprising: during a the determination of the variable representing the clamping force of the parking brake, determining a current value of a parking brake actuator, a voltage of a parking brake actuator, and/or a motor angular rate of a parking brake actuator.

10. The method as claimed in claim 1, wherein the determined transition point is taken into account during the operation of the parking brake as a reference value.

11. The method as claimed in claim 1, wherein: while taking into account the determined transition point the following is carried out: positioning the parking brake, positioning the parking brake directly from the force reduction phase, and/or positioning the parking brake directly from an end point of the parking brake, positioning the parking brake in a free travel phase, and/or positioning the parking brake at a braking starting point, wherein a reduced free travel of the parking brake is set, and wherein the reduced free travel is reduced compared to the usual free travel.

12. The method as claimed in claim 1, wherein a control unit is configured to operate the automated parking brake according to the method.

13. A brake device for a motor vehicle, comprising: an automated parking brake; and a control unit operably connected to the automated parking brake, the control unit configured to cause the parking brake to adopt at least two states, wherein in a first state no clamping force is established by the parking brake, and in a second state a clamping force is established by the parking brake, wherein a transition point defines a transition between the first state and the second state wherein the parking brake comprises an identification unit configured to identify the transition point during a parking brake releasing process.

Description

EMBODIMENTS

[0058] It should be noted that the features mentioned individually in the description can be combined with each other in any technically meaningful manner and reveal further embodiments of the invention. Further features and functionality of the invention arise from the description of exemplary embodiments using the accompanying figures.

[0059] In the figures:

[0060] FIG. 1 shows a schematic sectional view of a brake device with an automated parking brake in a motor on caliper design; and

[0061] FIG. 2 shows a characteristic current and a clamping force profile for a releasing process, and

[0062] FIG. 3 shows an idealized profile of a motor current against time for a decline of the motor current and the proximity relationships of the measurement points, and

[0063] FIG. 4 shows a flow chart of an example of the identification of the transition point, and

[0064] FIG. 5 shows the positioning of the parking brake according to a releasing process and a distance-dependent profile of the electromechanical clamping force.

[0065] FIG. 1 shows a schematic sectional view of a brake device 1 for a vehicle. In this case, the brake device 1 comprises an automated parking brake 13 (also known as an automatic parking brake or automated parking brake, in short APB), which can exert a clamping force to hold the vehicle by means of an actuator 2 (electric motor). The actuator 2 of the illustrated electromechanical parking brake 13 drives a spindle 3 that is supported in an axial direction for this, in particular a threaded spindle 3. On the end of the spindle 3 facing away from the actuator 2, the spindle 3 is provided with a spindle nut 4 that contacts the brake piston 5 when the automated parking brake 13 is in the clamped state. In this way, the parking brake 13 electromechanically transfers a force to the brake linings 8, 8 or the brake disk 7. In this case, the spindle contacts an inner end face of the brake piston 5 (also known as the rear of the base of the brake piston or inner piston floor). The spindle nut 4 is displaced in the axial direction during a rotary motion of the actuator 2 and a resulting rotary motion of the spindle 3. The spindle nut 4 and the brake piston 5 are supported in a brake caliper 6 that overlaps a brake disk 7 in the manner of a claw.

[0066] A respective brake lining 8, 8 is disposed on both sides of the brake disk 7. In the case of a clamping process of the brake 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 in the axial direction towards the brake disk 7 in order to thereby produce a predetermined clamping force between the brake linings 8, 8 and the brake disk 7. Because of the spindle drive and the self-locking connected thereto, a force produced with the parking brake 13 by means of the actuation of the electric motor is also maintained at the end of the actuation.

[0067] The automated parking brake 13 as represented is for example implemented as a motor on caliper system and is combined with the service brake 14. The parking brake 13 could also be considered as being integrated within the system of the service brake 14. Both the automated parking brake 13 and the service brake 14 act on the same brake piston 5 and the same brake caliper 6 in order to establish a braking force on the brake disk 7. However, the service brake 14 comprises a separate actuator 10, for example a foot-operated brake pedal with a brake force booster. The service brake 14 is configured in FIG. 1 as a hydraulic system, wherein the actuator 10 is boosted by the ESP pump or an electromechanical brake force booster (for example a Bosch iBooster) or can be implemented by the same. Further embodiments of the actuator 10 are also conceivable, for example in the form of a so-called IPB (Integrated Power Brake), which in principle constitutes a brake-by-wire system, in which a plunger is used to establish a hydraulic pressure. In the case of service braking, a predetermined clamping force is established hydraulically between the brake linings 8, 8 and the brake disk 7. To establish a braking force by means of the hydraulic service brake 14, a medium 11, in particular an essentially incompressible brake fluid 11, is compressed in a fluid chamber bounded by the brake piston 5 and the brake caliper 6. The brake piston 5 is sealed with respect to the surroundings by means of a piston sealing ring 12.

[0068] The actuation of the brake actuators 2 and 10 is carried out by means of one or a plurality of end stages, i.e. by means of a control unit 9, which for example can be a control unit of a driving dynamics system, such as an ESP (electronic stability program) or another control unit.

[0069] In the case of actuation of the automated parking brake 13, first the free travel or the air gap must be overcome before a braking force can be established. The distance that the spindle nut 4 must overcome during the rotation of the spindle 3 in order to come into contact with the brake piston 5 is referred to as free travel for example. The distance between the brake linings 8, 8 and the brake disk 7 in disk brake systems of motor vehicles is referred to as an air gap. As a rule, said process lasts a relatively long time in relation to the overall actuation, in particular for the automated parking brake 13. At the end of such a preparation phase, the brake linings 8, 8 are in contact with the brake disk 7 and the establishment of force starts in the case of a further actuation. FIG. 1 shows the state with the free travel and air gap already overcome. In this case, the brake linings 8, 8 are in contact with the brake disk 7 and all brakes, i.e. the parking brake 13 and also the service brake 14, can immediately establish a braking force on the corresponding wheel in the event of a subsequent actuation. The descriptions for an air gap also apply in a similar manner to the service brake 14, wherein however, owing to the highly dynamic pressure establishment, overcoming the free travel requires less time than with the parking brake 13.

[0070] The described method can be used for the identification of the transition point of the current signals of the motor-gearbox unit of the automatic parking brake 13 sampled in the control unit 9. FIG. 2 shows an exemplary motor current profile I and a force profile F of the parking brake against time t for an automated parking brake 13 releasing process. The force F shall mean the clamping force applied to the wheel brake, which is achieved by means of the parking brake 13 in the engaged state. Likewise, the current profile I is shown, which is available here on the control unit sampled in a 10ms pattern. The graph D that is shown shows the detection of the transition point from the establishment of clamping force to the free travel by means of a detection signal. If the transition point has been detected, the signal jumps to the value 10.

[0071] The releasing process represented starts from the engaged state of the parking brake 13. In this case, there is a high clamping force F. Because the parking brake 13 is self-locking, no motor current I is necessary for this. In the switch-on phase P1, the actuator 2 is energized in the releasing direction for the first time and the parking brake actuator, i.e. the spindle nut 4 that is driven by the spindle 3 by means of the actuator 1 of the parking brake 13, is activated. Owing to the activation of the actuator 2, a high point-to-point current value I (also known as a switch-on peak) results. Initially, however, the algorithm for identification of the transition point according to the condition 1 is inhibited. If this were not the case, then the algorithm could construe the transition of the switch-on peak in the force reduction phase P2 (at about 3 seconds) as an inflection in the releasing process.

[0072] Subsequently, the clamping force F between the spindle nut 4 and the brake linings 8, 8, or between the brake linings 8, 8 and the brake disk 7, is reduced by the movement of the parking brake 13 in the releasing direction. A reduction also appears in the current value I in the force reduction phase P2, which corresponds to a reduction of the clamping force. During the force reduction phase P2, the current profile I is approximately linear. That means the condition 2 of a continuous decrease is met, but not the condition 3 of reducing reduction. Therefore, no identification of a transition point is carried out, in accordance with the illustrated embodiment.

[0073] In the transition phase P3, the transition from the clamping force reduction phase P2 to the free travel phase P4 is carried out. In this case, the illustrated inflection of the current profile I can be identified very accurately, i.e. identification of the transition point from the establishment of the clamping force to the free travel. In principle, it should be mentioned that there is no unique fixed point for said inflection. The inflection can, as can be seen in FIG. 2, rather be detected in a specific time window. I.e. the inflection can only be detected over a period. The subsequent phase P4 describes the free travel phase, in which the spindle nut 4 establishes the necessary free travel for a brake device 1 that is free of residual braking torque.

[0074] FIG. 3 shows a current profile I against time t, such as arises for example by a reduction of a clamping force F by means of an actuator 2 of the parking brake 13 that is implemented as an electric motor. The current profile I is schematically represented in an idealistic manner.

[0075] Furthermore, in this case the measurement points k-3, k-2, k-1, k are shown. Said data points are now the present digital data points of the motor current signal itself. The measurement of the data points is carried out in each case with an equidistant time interval TA between the measurement points k-3, k-2, k-1, k. The current signals are available sampled in a certain time pattern (here by way of example 10 ms). Moreover, FIG. 3 illustrates the difference d between two adjacent measurement points of the current values I. The current value differences d1, d2, d3 are shown for this. The very accurate identification of the transition point uses an evaluation of the proximity relationships between the measured and digital data points of the motor current in the releasing process that are present in the control unit.

[0076] For example, a change in current value is identified if a continuous decline in the underlying measurement variables, i.e. the current values I, is determined. For example, continuity is identified if a plurality of decreasing measurement variables, for example 4, are determined. FIG. 3 depicts the representation of a decreasing current profile I against time t. Furthermore, it is represented against the Y-axis that the decline in the current values comprises a flattening profile, i.e. there is a decaying motor current signal. This can be seen from the fact that d1 is greater than d2, and in turn d2 is greater than d3. This can be considered as an indication of a decaying decline in the measurement values. This is in turn an indication of a transition from a force reduction phase to free travel.

[0077] FIG. 4 shows a flow chart of an exemplary identification of the transition point between the force reduction phase and the free travel phase. The method starts from a clamped state of the parking brake 13, in which the brake piston takes up the end position thereof (see x.sub.E in FIG. 5). In the first step S1, the releasing process is started. The brake piston is displaced by actuation of the actuator 2 towards a zero-braking torque initial position (see x.sub.A in FIG. 5). The engaged parking brake 13 is released during this, whereby a reduction in the clamping force occurs (see F in FIG. 2). In a further step S2, in this case the current signal I of the actuator 2 is sampled (this may be seen in FIG. 3). This step is implemented until the termination of the method. In a step S3, an analysis is carried out as to whether the current signal I meets a first condition. As a first condition, for example it is set that the current signal I lies below a certain value in order to exclude a switch-on peak from the analysis for example. If the condition 1 is not met (S3=N), furthermore a sampling and analysis of the current values I is carried out. If the condition 1 is met (S3=Y), in a next step S4 an analysis is carried out as to whether the current signal I meets a second condition. As a second condition, it is defined that the current signal I shows a continuous decline, for example that four successively decreasing measurement values were determined. If the second condition is not met (S4=N), the analysis is continued until the method is terminated or the condition is met (S4=Y). Furthermore, after meeting the condition 1 (S3=Y), in a further step S5 an analysis is carried out as to whether the current signal I meets a third condition. As a third condition, it is defined that the current signal I shows a decaying decline, for example that there are three reducing difference amounts (see for example d1, d2, d3 in FIG. 3) between the four successively decreasing measurement values. If the third condition is not met (S5=N), the analysis is continued until the method is terminated or the condition is met (S5=Y). If the second condition (S4=Y) and the third condition (S5=Y) are met (&), the transition point at said point is defined in step S6. Alternatively, it is also conceivable that a sequential check of the conditions takes place, i.e. the condition 3 is only checked if the condition 2 has been met. Likewise, it is conceivable that only one of the two conditions 2 or 3 is checked and the transition point is defined at the point at which the one condition is met in addition to condition 1.

[0078] FIG. 5 shows positioning of the parking brake 13 after or during a releasing process. Furthermore, a distance-dependent profile of the clamping force F is shown that is produced during actuation of the brake actuator 2 of the parking brake 13. Because the parking brake 13 can also be used in order to enable deceleration of the vehicle, the term braking force is used synonymously, which shall describe the braking force applied by the parking brake 13. The braking or clamping force F produced during actuation of the actuator 2 during an engagement process initially lies at the value 0, starting from an initial position x.sub.A, and increases linearly after reaching the transition point x.sub.u. The transition point defines the transition from the free travel phase to the establishment of force, or from the force reduction phase to the free travel phase. At the transition point x.sub.u, the brake piston 5 or the brake lining 8, 8 on the brake piston 5 is in contact with the brake disk 7 for the first time, or for the last time. The transition point x.sub.u of the parking brake can therefore also be referred to as the brake contact point. The initial position X.sub.A of the brake piston 5 of the parking brake 13 characterizes a zero-braking torque initial state, i.e. a disengaged position of the parking brake 13. The distance traversed between the initial position x.sub.A and the transition point x.sub.u is referred to as free travel x.sub.L. With the application of a braking force or clamping force F during a braking process or a clamping process, the brake piston reaches an end position x.sub.E that is located after the transition point x.sub.u and the accurate position of which depends on the level of the braking force or clamping force F applied. The end position x.sub.E thus describes an engaged position of the parking brake 13.

[0079] If the clamped parking brake 13 is released by actuating the actuator 2 so that the brake piston 5 is moved by means of the spindle nut 4 towards the initial position x.sub.A, the clamping force F decreases until reaching the transition point x.sub.u and then remains at the zero level during the further travel (free travel). The transition of the clamping force F from the decrease in force to the zero level at the transition point x.sub.u can be determined using the inflected profile of an electromotive state variable of the actuator 2, in particular using the motor current I, possibly also using the motor speed.

[0080] Using an exemplary embodiment of the method, by means of a positioning process the parking brake 13 can be positioned at a braking starting point x.sub.s that lies between the zero-braking torque initial position x.sub.A and the transition point x.sub.u. The braking starting point x.sub.s is still located within the free travel x.sub.L, but at a short distance from the transition point x.sub.u. If the spindle nut 4 or the brake piston 5 takes up the position at the braking starting point x.sub.s, then the remaining free travel X.sub.R until reaching the transition point x.sub.u and the subsequent establishment of force is traversed in a short time. At the same time, it can be guaranteed that there is a sufficiently large air gap between the brake linings 8, 8 and the brake disk 7 for example to reliably exclude inadvertent, unwanted drag on the brake linings 8, 8 on the brake disk 7 within the occurring temperature range.

[0081] The determination of the braking starting point x.sub.s is thus carried out starting from the transition point x.sub.u with a defined distance thereto in the releasing direction of the parking brake 13. Based on the determined transition point x.sub.u, during a parking brake releasing process the spindle nut 4 of the parking brake 13 is moved by a further positioning distance x.sub.P towards the initial position x.sub.A until the braking starting point x.sub.s is reached. The spindle nut 4 remains in said position until a braking action by means of the parking brake 13 is demanded or the method is terminated. In the event of a demand for a braking force or clamping force F of the parking brake, the spindle nut 4 can be activated directly from the braking starting point x.sub.s. In the event of a termination of the method, the spindle nut 4 can be moved directly from the braking starting point x.sub.s to the end position x.sub.E as necessary (when parking the vehicle) or to the initial position x.sub.A (in the case of normal further operation of the vehicle).