Abstract
A method for determining defects of an automated parking brake for a motor vehicle with at least one brake device includes detecting damage to the parking brake on the basis of a time profile of a variable representing an output torque of a parking brake actuator. The parking brake includes the parking brake actuator configured to be activated. The detection of the damage includes analyzing the time profile of the variable representing the output torque of the parking brake actuator during a first phase of an activation process of the parking brake for the identification. The activation process of the parking brake has at least two phases. A first phase of the activation process includes a no build up or reduction of a clamping force between at least one brake lining and a brake disk. A second phase includes a build up or reduction of the clamping force.
Claims
1. A method for determining defects of an automated parking brake for a motor vehicle with at least one brake device, comprising: operating, with a control unit, an actuator to rotate a spindle that engages a spindle nut to move a brake lining toward a brake disk or away from the brake disk while the brake lining is not in contact with the brake disk; measuring, with the control unit, a profile of a current that is supplied to the actuator over a predetermined time period during the operating of the actuator; and identifying, with the control unit, that at least one of the spindle and the spindle nut is damaged in response to the profile of the current including a positive change in current amplitude followed by a negative change in the current amplitude during the predetermined time period.
2. The method of claim 1 further comprising: measuring, with the control unit, a profile of a voltage that is supplied to the actuator over the predetermined time period during the operating of the actuator; and identifying, with the control unit, that at least one of the spindle and the spindle nut in the automated parking brake is damaged in response to the profile of the current including the positive change in current amplitude followed by the negative change in the current amplitude during the predetermined time period and the profile of the voltage including an increase in voltage level that does not exceed a predetermined voltage limit during the predetermined time period.
3. A method for determining defects of an automated parking brake for a motor vehicle with at least one brake device, comprising: operating, with a control unit, an actuator to rotate a spindle that engages a spindle nut to move a brake lining toward a brake disk or away from the brake disk while the brake lining is not in contact with the brake disk; measuring, with the control unit, a profile of a rotational rate of the actuator over a predetermined time period during the operating of the actuator; and identifying, with the control unit, that at least one of the spindle and the spindle nut is damaged in response to the profile of the rotational rate including a reduction in the rotational rate of the actuator followed by an increase in the rotational rate of the actuator during the predetermined time period.
4. An automated parking brake for a motor vehicle, comprising: an actuator configured to rotate a spindle that engages a spindle nut to move a brake lining toward a brake disk or away from the brake disk; and a control unit operatively connected to the actuator, the control unit being configured to: operate the actuator to move the brake lining toward the brake disk or away from the brake disk while the brake lining is not in contact with the brake disk; measure a profile of a current that is supplied to the actuator over a predetermined time period during the operating of the actuator; and identify that at least one of the spindle and the spindle nut is damaged in response to the profile of the current including a positive change in current amplitude followed by a negative change in the current amplitude during the predetermined time period.
5. The automated parking brake of claim 4, the control unit being further configured to: measure a profile of a voltage that is supplied to the actuator over the predetermined time period during the operating of the actuator; and identify that at least one of the spindle and the spindle nut in the automated parking brake is damaged in response to the profile of the current including the positive change in current amplitude followed by the negative change in the current amplitude during the predetermined time period and the profile of the voltage including an increase in voltage level that does not exceed a predetermined voltage limit during the predetermined time period.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) In the figures:
(2) FIG. 1 shows a schematic sectional view of a brake device with a service brake and an automated parking brake in a motor on caliper design; and
(3) FIG. 2a-c shows a representation of the displacement of the spindle stop and of the spindle nut stop in the profile of a revolution; and
(4) FIG. 3a, 3b shows an idealized profile of a motor current against time for a rise or a decline of the motor torque as well as the adjacency relationships of the measurement points; and
(5) FIG. 4 shows a general profile of the motor current for a rise of the motor torque against time as well as measurement points with rising current value; and
(6) FIG. 5 shows a flow chart of a damage check of a parking brake;
(7) FIG. 6 shows a profile of the motor current as well as identified negative and positive current changes for a parking brake without damage; and
(8) FIG. 7 shows a profile of the motor current as well as identified negative and positive current changes for a parking brake with damage.
DETAILED DESCRIPTION
(9) FIG. 1 shows a schematic sectional view of a brake device 1 for a vehicle. The brake device 1 comprises in this case an automated (automatic) parking brake, which can exert a clamping force for holding the vehicle stationary by means of an actuator 2 (brake motor), which in the present case is in the form of a d.c. motor. The actuator 2 of the parking brake drives a spindle 3 that is supported in an axial direction, in particular a threaded spindle 3, for this purpose. On the end thereof that is remote from the actuator 2, the spindle 3 is provided with a spindle nut 4 that is in contact with a brake piston 5 in the applied state of the automated parking brake. The parking brake electromechanically transfers a force to brake linings 8, 8 and a brake disk (7) in this way. The spindle nut is in contact with an inner end face of the brake piston 5 during this. The spindle nut 4 and the brake piston 5 are supported in a brake caliper 6 that engages around the brake disk 7 as jaws. As illustrated, the automated parking brake is for example in the form of a motor on caliper system and is combined with the service brake or integrated within a service brake. The service brake comprises a separate actuator 10 for performing the regular service braking. The service brake in FIG. 1 is designed as a hydraulic system, wherein the actuator 10 is represented for example by a brake booster or an ESP pump. For building up a braking force by means of the hydraulic service brake, a medium 11 is compressed in a fluid chamber that is bounded by the brake piston 5 and the brake caliper 6. The brake piston 5 is sealed relative to the surroundings by means of a piston sealing ring 12.
(10) The illustrated spindle nut 4 comprises a mechanical rotary end stop represented by a spindle nut stop 14. A spindle stop 13 is also formed on the spindle 3 as a counterpiece. Such an end stop is required so that the spindle nut 4 is not axially braced on the spindle 3 in the end position. Said axial bracing could result in the drive torque not being sufficient in the reverse direction (i.e. in the direction of engaging the parking brake) and hence in the spindle nut remaining locked in the end position thereof.
(11) The activation of the brake actuators 2 and 10 is carried out by means of an end stage, i.e. by means of a control unit 9 that can be for example a control unit of a vehicle dynamics system, such as an ESP (electronic stability program) or any other control unit. FIG. 1 shows the state in which the free travel and air gap have already been overcome.
(12) FIGS. 2a, 2b and 2c show a representation of the displacement of the spindle stop 13 and of the spindle nut stop 14 in the profile of a revolution of the spindle 3. Possible damage to the end stop 13, 14 is illustrated using said representations. FIG. 2a shows the spindle nut 4 and the spindle 3 in the end stop, in which the spindle stop 13 and the spindle nut stop 14 are in contact with each other. FIG. 2b shows the position of the two stops 13 and 14 following an incomplete revolution. FIG. 2c shows the position of the two stops 13, 14 following an almost complete revolution. Owing to the illustrated deformation of the stops 13, 14, the position of the stops 13, 14 illustrated in FIG. 2c results in contact between the stops, which is associated with a rise in the drive torque. The end stops 13, 14 are designed for a defined number of contacts. If said number is exceeded, a defect can occur. Damage can already be identified in advance. The damage is local binding of the threaded spindle. Said damage is caused by a plastic deformation of the spindle 3 and/or the spindle nut 4. During this a type of whisker (plastic deformation) forms on the radial stop 13 of the spindle 3 and/or on the radial stop 14 of the spindle nut 4. After about one rotation of the spindle, measured from the end stop starting point, the two stops 13, 14 are traversed. Owing to the deformation of the stops 13, 14, there is mechanical contact and a temporary rise of the drive torque of the electric motor 2 of the parking brake. This results in a brief increase in current, which can be measured by means of the current measurement system of the parking brake electronics. The increase in current is exhibited by a rise in the current with a fall following shortly thereafter. Such a characteristic shape of the current curve must be robustly detected in order to be able to make a valid statement about possible damage to the parking brake.
(13) FIG. 3a shows a current profile I against time t, such as arises for example as a result of an increase in the drive torque of the electric motor 2 of the parking brake (also known as the motor torque M.sub.Mot). The current profile I as well as the motor torque M.sub.Mot are represented in a schematically idealized manner. Furthermore, the measurement points k3, k2, k1, k are also shown. The measurement of the data points is carried out in each case with an equidistant time interval T.sub.A between the measurement points. Moreover, FIG. 3a illustrates the difference d of the current values I that exists between two adjacent measurement points. For this purpose, the current value differences d1, d2, d3 are shown. For example, a change current value change can be detected if a steady rise of the underlying measurement variables, i.e. the current values, is determined, wherein a steadiness is detected if a plurality of, for example 4, rising measurement variables can be determined in a directly successive time sequence. FIG. 3a illustrates the representation of a rising current profile I against time, wherein of course said profile can and will also be used in an analogous way for a declining current profile I. FIG. 3b shows in an analogous way a current profile I against time t, such as for example arises as a result of a reduction of the drive torque of the electric motor 2 of the parking brake.
(14) The representation depicted in FIG. 4 shows the identification of the increase in the motor torque based on rising current values, and should contribute in particular to a suitable understanding of the components of the disclosure.
(15) FIG. 4 shows an exemplary profile of the motor current I for a rise of the motor torque M.sub.Mot against time as well as measurement points with rising current values. The profile of the motor current shows first a switch-on peak, which is caused for example by the initial or further switch-on of the electric motor of the automated parking brake. The representation in FIG. 4 shows by way of example a so-called reclamping, i.e. a further clamping process for an already activated parking brake. The motor torque M.sub.Mot therefore already markedly lies in the positive region on activation of the parking brake actuator. Owing to the re-activation of the parking brake actuator, in this case a motor torque M.sub.Mot is built up immediately. This can be seen in the illustrated profile of the motor torque M.sub.Mot. In parallel with this, an increase of the motor current I also takes place. For the identification of an increase of the motor torque, the condition of four successively occurring rising current values can be used for example. Said measurement points are sketched in FIG. 4. A sampling time of 5 milliseconds was selected for this.
(16) The method according to the disclosure can of course be carried out with any activation of the parking brake. A clamping process of an automated parking brake is represented in FIG. 5 as well as FIG. 6 and FIG. 7 by way of example.
(17) FIG. 5 shows an exemplary flow chart of a damage check of the parking brake in order to detect damage to the parking brake. Within the scope of the method, it is in particular necessary that a positive current change is detected followed by a negative current change. The method starts with the start of the clamping process in a step S1. In a step S2, the current profile is determined continuously, for example by a measurement or an estimation of the current values. The determined current values are temporarily stored in a memory. A current change is identified based on the determined current values. A positive current change is determined in a step S31 or a negative current change is determined in a step S32. For the determination of current changes, for example the method illustrated in FIG. 3, the conditions thereof can be used, both for a positive current change and also analogously for a negative current change. The current changes are also temporarily stored in a memory. In a further step S4, it is determined whether a negative current change follows a positive current change. Then in a step S51 the time t between the change from the positive current change to the negative current change is analyzed. Here it is provided as a condition that the time t between the positive and the negative current changes is to lie within a defined time period t.sub.D, i.e. the time between the positive and negative current changes is to be less than a defined maximum time t.sub.D. In a further step S52, the voltage change U.sub.D is analyzed. Here it is provided as a condition that the voltage change U.sub.D for a positive current change lies within a defined interval U, i.e. the increase in the voltage for the current change is less than a defined value U. If the conditions of the steps S51 and S52 in the illustrated exemplary embodiment are represented by means of an AND combination, there is an explicit reference to the fact that the method can also advantageously provide an OR combination. In summary, the exemplary procedure can be described as follows: it is concluded that there is damage if the motor current first increases (positive change), then the motor current decreases again (negative change) and the time between the positive and negative current change lies within a defined time period t.sub.D and the voltage U.sub.D for a current increase does not increase by more than a defined voltage limit U for a voltage change. Typical values for t.sub.D here are 0.01 seconds to 0.1 seconds. Typical values for are 0.1 Volts to 2 Volts.
(18) FIG. 6 shows a profile of the motor current I as well as identified negative and positive current changes for a parking brake without damage. The description of the regular good case (normal situation) should serve to clarify the operation of the method. The simulation illustrated in FIG. 6 shows the measurement data of the motor current I and the detection points in time of the algorithm for current changes. Furthermore, negative current changes (by means of round markers) and positive current changes (by means of square markers) are shown by way of example. The algorithm is used on all of the measured current measurement points. Two case examples are illustrated. Case example A: during motor run-up, two successive negative current changes are detected. This is the case because the current curve comprises a slightly positive profile owing to further loads being switched on. The criterion for detecting damage is not met because a negative change follows a negative change. Case example B: here a positive current change follows a negative change. The condition (negative current change to positive current change) for the detection of damage is not met. Moreover, between the two detection points there is a time period of greater than t.sub.D (with the assumption of t.sub.D between 0.01 and 0.1 seconds).
(19) FIG. 7 shows a profile of the motor current I as well as identified negative and positive current changes for a parking brake without damage. The description of the error case (detection situation) should further clarify the operation of the proposed method. The representation shows a damaged actuator that is carrying out a clamping process. The defect is not yet great enough to significantly adversely affect the operation of the parking brake. However, such a defect is magnified by operation of the parking brake. This can result in the parking brake failing. Case example A: here no detection of damage takes place (see remarks for case example A FIG. 6). Case example B: here no detection of damage takes place (see remarks for case example B FIG. 6). Case example C: here a detection of damage does take place. The damage is detected because all criteria that are necessary for detection are fulfilled. This enables a timely repair of the system to be carried out for example. Case example D: here no detection of damage takes place (see remarks for case example B FIG. 6).
