Method and device for operating an automated locking brake

Abstract

A method for operating an automated locking brake in a motor vehicle includes setting a defined deceleration of the vehicle with the locking brake during a locking brake process, shutting-off activation of the locking brake when a shut-off condition has been satisfied, and taking into account at least one predicted value of the locking brake process in the shut-off condition.

Claims

1. A method for operating an automated locking brake in a vehicle, comprising: setting a defined deceleration of the vehicle with the automated locking brake during a locking brake process; shutting off activation of the automated locking brake when a shut-off condition has been satisfied; and taking into account at least one predicted value of the locking brake process in the shut-off condition, wherein the predicted value of the locking brake process includes an overtravel time of the locking brake process in the shut-off condition, and further comprising: taking into account a comparison of the overtravel time and the remaining time of the locking brake process in the shut-off condition; and shutting off activation of the automated locking brake when the overtravel time and the remaining time are equal.

2. The method according to claim 1, further comprising: taking into account a remaining time of the locking brake process in the shut-off condition.

3. The method according to claim 2, further comprising: determining the remaining time of the locking brake process based on an acceleration of the vehicle.

4. The method according to claim 2, further comprising: determining the remaining time of the locking brake process based on an actual deceleration of the vehicle and a target deceleration of the vehicle.

5. The method according to claim 2, further comprising: determining the remaining time of the locking brake process based on a progress over time of a deceleration of the vehicle.

6. The method according to claim 1, further comprising: determining a remaining time of the locking brake process based on a change in a deceleration of the vehicle.

7. The method according to claim 1, further comprising: taking into account at least one of a current angular velocity, a current clamping distance, and a current clamping force in determining the overtravel time.

8. A device configured to carry out a method of operating an automated locking brake in a motor vehicle, the device comprising: a processor configured to: set a defined deceleration of the vehicle with the automated locking brake during a locking brake process; shut off activation of the automated locking brake when a shut-off condition has been satisfied; and take into account at least one predicted value of the locking brake process in the shut-off condition, wherein the predicted value of the locking brake process includes an overtravel time of the locking brake process in the shut-off condition; take into account a comparison of the overtravel time and the remaining time of the locking brake process in the shut-off condition; and shut off activation of the automated locking brake when the overtravel time and the remaining time are equal.

9. A computer program stored on a non-transitory computer readable storage medium and configured to be executed by a processor and cause the processor to: set a defined deceleration of the vehicle with the automated locking brake during a locking brake process; shut off activation of the automated locking brake when a shut-off condition has been satisfied; and take into account at least one predicted value of the locking brake process in the shut-off condition, wherein the predicted value of the locking brake process includes an overtravel time of the locking brake process in the shut-off condition; take into account a comparison of the overtravel time and the remaining time of the locking brake process in the shut-off condition; and shut off activation of the automated locking brake when the overtravel time and the remaining time are equal.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The figures show the following:

(2) FIG. 1 a sectional view of a braking mechanism with an automatic locking brake in a “motor on caliper” design; and

(3) FIG. 2 a representation for estimating energy on a model of a linear spring; and

(4) FIG. 3 an exemplary representation of a calculation process for determining the motor actuating signal; and

(5) FIG. 4 a schematic representation of a flow chart containing the relevant process steps.

DETAILED DESCRIPTION

(6) FIG. 1 shows a schematic sectional view of a braking mechanism 1 for a vehicle. The braking mechanism 1 has an automated locking brake 13 (also called an automatic locking brake or automated parking brake; abbreviated APB), which can exert a clamping force by means of an electromechanical actuator 2 (electric motor) in order to stop the vehicle. For this purpose, the electromechanical actuator 2 of the locking brake 13 shown drives a spindle 3, in particular a threaded spindle 3, that is mounted in an axial direction. At its end facing away from the actuator 2, the spindle 3 is provided with a spindle nut 4, which abuts the brake piston 5 when the automated locking brake 13 is in the engaged state. In this way, the locking brake 13 transmits a force to the brake linings 8, 8′ and/or to the brake disk 7. The spindle nut in this instance is located against an inner front face of the brake piston 5 (also called the rear side of the brake piston head or inner piston crown). The spindle nut 4 is displaced in the axial direction when there is 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 mounted in a caliper 6, which engages over a brake disk 7 in a tong-like manner.

(7) A brake lining 8, 8′ is arranged on each of the two sides of the brake disk 7. In the case of an engagement process of the braking mechanism 1 by means of the automated locking 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 to generate a predetermined clamping force between the brake linings 8, 8′ and the brake disk 7. Owing to the spindle drive and the associated self-inhibition, a force generated by the locking brake 13 by means of an activation of the electric motor is also maintained when the activation is ended.

(8) The automated locking brake 13 is configured, for example, as a “motor on caliper” system and is combined with the service brake 14. The locking brake 13 could also be considered to be integrated into the system of the service brake 14. Both the automated locking brake 13 and the service brake 14 access the same brake piston 5 and the same 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, such as a brake pedal with a brake booster. In FIG. 1, the service brake 14 is configured as a hydraulic system, wherein the hydraulic actuator 10 can be supported or implemented by the ESP pump or an electromechanical brake booster (e.g. Bosch iBooster). Further embodiments of the actuator 10 are also conceivable, such as in the form of a so-called IPB (integrated power brake), which in principle represents a brake-by-wire system in which a plunger is used to build up hydraulic pressure. In the case of service braking, a predetermined clamping force between the brake linings 8, 8′ and the brake disk 7 is built up hydraulically. For establishing a braking force by means of the hydraulic service brake 14, a medium 11, in particular a substantially incompressible brake fluid 11, is pressed into a fluid chamber that is delimited by the brake piston 5 and the caliper 6. The brake piston 5 is sealed off from the environment by means of a piston seal ring 12.

(9) The activation of the brake actuators 2 and 10 is carried out by one or more end stages, i.e. by means of a control device 9, which can be, for instance, a control device of a driving dynamics system, such as ESP (electronic stability program) or another control device.

(10) When the automated locking brake 13 is activated, the idle path and/or the air gap must first be overcome before a braking force can be built up. The idle path designates, for example, the distance the spindle nut 4 must overcome through the rotation of the spindle 3 in order to make contact with the brake piston 5. The air gap designates the distance between the brake linings 8, 8′ and the brake disk 7 in brake disk systems of motor vehicles. In particular, overcoming the idle path usually takes a relatively long time in relation to the activation as a whole, in particular in the automated locking brake 13. At the end of a preparation phase such as this, the brake linings 8, 8′ are applied against the brake disk 7, and the build-up of force begins with a further activation. FIG. 1 shows the state in which the idle path and air gap have already been overcome. Here, the brake linings 8, 8′ are applied to the brake disk 7, and all brakes, i.e. the locking brake 13 and the service brake 14, can immediately build up a braking force on the corresponding wheel with a subsequent activation.

(11) FIG. 2 shows a representation for estimating energy on a model of a linear spring. x.sub.1 is the clamping distance at the time of the shut-off. Accordingly, E.sub.feder1 is the energy that has been introduced into the brake caliper to build up force until shut-off. Since the APB system reacts slowly to control actions, dominated by mass inertia, it is not possible to deactivate the APB activation with immediate effect upon reaching the target deceleration. The system continues to function, i.e. clamping force and deceleration are still built up. This is shown by the overtravel distance x.sub.nachlauf. The energy that continues to be introduced during the overtravel is represented in the diagram as E.sub.nachlauf. Therefore, the activation has to be concluded before reaching the target deceleration. This point in time must be calculated. FIG. 2 illustrates the approach on the basis of an approximation via the energies of a linear spring.

(12) FIG. 3 shows an exemplary representation of a calculation process for determining the motor actuating signal. In so doing, it is determined when the APD activation must be ended so that the prescribed deceleration is achieved by a single application. The activation of the locking brake is then ended (actuating signal I for deactivation) when the shut-off condition has been satisfied. That is to say, in this embodiment, when the determined overtravel time t.sub.nachlauf is equal to the determined remaining time t of the locking brake process. Once the condition (1-1) has been satisfied, the motor of the locking brake is deactivated:
t.sub.nachlauf=t.sub.rest  (1-1)

(13) t.sub.nachlauf is the time during which the ARB continues to build up clamping force and thus deceleration after deactivation of the motor as a result of mass inertia. t.sub.rest describes the time that would be required to achieve the target deceleration value at the current wheel deceleration and jerk da/dt. The overtravel time t.sub.nachlauf is determined with the aid of the law of conservation of energy.
E.sub.rot+E.sub.trans−E.sub.verlust=E.sub.brems+E.sub.klemm  (1-2)

(14) In this instance, E.sub.rot describes the rotational energy of the motor gear unit, E.sub.trans the translational energy of the piston and brake lining, E.sub.brems the electrical energy that is dissipated in the H bridge by active braking, E.sub.klemm describes the energy that is required for clamping the brake caliper, i.e. for clamping force build-up, and E.sub.verlust the friction loss energy. For a simplified approach, it was assumed that E.sub.rot>>E.sub.trans and E.sub.klemm>>E.sub.brems, whereby the equation was simplified to
E.sub.rot≅E.sub.klemm  (1-3).

(15) The loss energy E.sub.verlust is hereafter expressed by means of the efficiency η.sub.MoC of the motor gear unit. The calculation of the overtravel time is carried out with the following equations.
E.sub.rot=½.Math.J.Math.ω.sup.2
E.sub.nachlauf=E.sub.rot.Math.η.sub.MoC
E.sub.feder1=½.Math.k.Math.x.sub.1.sup.2
E.sub.feder2=E.sub.feder1+E.sub.nachlauf
x.sub.nachlauf=(2.Math.E.sub.feder2/k).sup.1/2−x.sub.1
t.sub.nachlauf=(x.sub.nachlauf.Math.2π.Math.i.sub.G)/(ω.sup.--.Math.i.sub.s)  (1-4)

(16) In this case, E.sub.feder1 is the energy that has been introduced into the caliper for force build-up until shut-off. E.sub.feder2 is the energy that was introduced into the caliper with the motor at a standstill. x.sub.1 is the clamping distance at the point of shut-off, k is the caliper rigidity, which is assumed to be linear, i.sub.G is the gear transmission ratio, i.sub.s is the incline of the threaded spindle and ω.sup.-- is a mean shut-off angular velocity. The mean shut-off angular velocity ω.sup.-- can be calculated from the angular velocity ω at the shut-off point, for example, by linearizing it in an approximation of the angular velocity at the end point (ω.sub.end=0), and the mean value of the angular velocity over the overtravel path is assumed to be the mean (in this case ω.sup.--=ω/2). Furthermore it is necessary to distinguish between clamping and releasing, since during release the clamping force decreases with the distance traveled; if the shut-off process lasts longer, co.sup.-- is lower.

(17) The remaining time is determined with equation (1-5). Here the acceleration signal is again differentiated to determine the jerk. “Jerk” in a vehicle is understood to mean, for example, the current change in acceleration.
t.sub.rest=(a.sub.soll−a.sub.ist)/(da/dt)  (1-5)

(18) FIG. 3 shows the flow chart for calculating the shut-off point. To determine the remaining time t.sub.rest, the determined values of actual acceleration a.sub.ist, target acceleration a.sub.soll and the derivation of the differentiated acceleration signal da/dt are combined by means of mathematical operations in accordance with the above-mentioned formulas. The overtravel time t.sub.nachlauf is likewise calculated from the determined values F.sub.klemm and the angular velocity ω. The determination is made, in turn, by drawing upon the above-mentioned formulas and transformations while taking into account the other stated values, such as the efficiency of the locking brake η.sub.MoC or the moment of inertia J.

(19) FIG. 4 shows a representation of the method steps of an embodiment of the disclosure. Here, the identification of a driver's desire to brake occurs in a first step S1. In a step S2, an acceleration value corresponding to the driver's desire to brake is identified. The generation of a value a.sub.soll for the locking brake occurs in step S3. In step S4, the difference between the actual acceleration a.sub.ist and the target acceleration a.sub.soll is formed. In step S5, the actual acceleration a.sub.ist is differentiated by the jerk da/dt of the vehicle. From these values, the remaining time t the locking brake process is determined in step S6. In a step S7, the current angular velocity ω of the actuator of the locking brake is determined. Likewise, the currently traveled clamping distance x or x.sub.i—is determined in step S8, and the clamping force F.sub.klemm is determined in step S9. From these values, the overtravel time t.sub.nachlauf is calculated in step S10 in accordance with equations 1-4. In step S11, the condition for ending the activation is defined, as is described in equation 1-1. Within the scope of B1, it is verified whether the condition has been satisfied. If this is the case (Y), then the activation of the locking brake is stopped in step S12. If this is not the case (N), then it is verified within the scope of B2 whether a further condition has been satisfied; in this case, whether the wheels are locked. If this is the case (Y), then countermeasures are introduced in step S14. If this is not the case (N), then it is again verified whether the first condition B1 has been satisfied in the meantime.