Parking brake actuation method for an electric motor vehicle parking brake system

Abstract

An electric-motor-operated parking brake system carries out metered actuation without a force and travel sensor. A control unit initiates a primary tensioning process with observation of the current, and wherein secondary or tertiary tensioning processes with increased brake application force are executed exclusively automatically by the control unit if monitoring of the stationary state during an energization interval detects an undesired vehicle movement.

Claims

1. A parking brake actuation method for an electric-motor-operated motor vehicle parking brake system comprising: transmitting movement via a transmission element, a spreading device and a traction cable from each of a plurality of electromechanical wheel brake actuators to each of a plurality of brake shoes which are each associated with a duo-servo type drum brake; observing and regulating the power demand of each of the plurality of wheel brake actuators on a wheel-specific base with a central electronic control unit for performing one of open-loop and closed-loop control of the traction cable tension; terminating the energization of the respective wheel brake actuator with said control unit after detection of a defined preset cable tension and transferring said wheel brake actuator into a currentless self-locking state; executing a primary tensioning process of the respective wheel brake actuator in the cable tensioning process with continued observation of the power demand with said control unit, terminating the primary tensioning process at a first percentage of a preset minimum cable pull tension; checking of the stationary state of the motor vehicle with the control unit using one of measured and determined vehicle sensor data when energization of the wheel brake actuator has been terminated, wherein said checking is over a chronologically limited time period; evaluating with the control unit the result of the checking of the stationary state on the basis of stored criteria; triggering automatically a secondary tensioning process with renewed actuator energization and observation of the current subsequent to a faulty or inadequate result from the checking of the stationary state, and wherein energizing in the secondary tensioning process correlates with a second percentage of a preset minimum cable pull tension, wherein said second percentage is greater than said first percentage.

2. The parking brake actuation method as claimed in claim 1, wherein the first percentage is 60% of the minimum cable pull tension and the second percentage is at least 90% of the minimum cable pull tension.

3. The parking brake actuation method as claimed in claim 1, further comprising executing secondary checking of the stationary state of the motor vehicle with the control unit over a chronologically limited time period when the energization of the wheel brake actuator has terminated after the secondary tensioning process.

4. The parking brake actuation method as claimed in claim 3, further comprising triggering automatically a tertiary tensioning process with renewed actuator energization and observation of the current after a faulty or inadequate result from the secondary checking of the stationary state.

5. The parking brake actuation method as claimed in claim 4, wherein the energization in the tertiary tensioning process correlates with at least 120% of the minimum cable pull tension.

6. The parking brake actuation method as claimed in claim 4, wherein the chronologically limited time period is at least approximately one second, and wherein after a fault-free result of the checking of the stationary state the control unit regularly causes on of the secondary tensioning process and the tertiary tensioning process to be executed.

7. The parking brake actuation method as claimed in claim 1, wherein the control unit has at least one vehicle sensor set point data set stored as a fixed evaluation criterion in a separately protected program module, and wherein the vehicle sensor set point data set correlates with at least one secure vehicle parking profile of the generic motor vehicle.

8. The parking brake actuation method as claimed in claim 7, wherein the program module automatically compares one of measured and acquired vehicle sensor data of the motor vehicle with the at least one stored vehicle sensor set point data set for checking of the stationary state.

9. The parking brake actuation method as claimed in claim 7, wherein the at least one stored vehicle sensor set point data set includes at least one inclination angle information item and a wheel rotation information item which is correlated therewith.

10. The parking brake actuation method as claimed in claim 1, wherein the chronologically limited time period for checking of the stationary state is at least approximately 70 ms during a computing process time of the control unit of approximately 7 ms.

11. The parking brake actuation method as claimed in claim 1, wherein the stored minimum cable pull tension is provided such that the stored minimum cable pull tension can be varied as a function of one of a measured and determined vehicle inclination angle.

12. The parking brake actuation method as claimed in claim 1, wherein at least two differently stored minimum cable pull tensions for the drum brakes of a common vehicle axle are provided such that the at least two differently stored minimum cable pull tensions can be varied as a function of their positioning.

13. The parking brake actuation method as claimed in claim 12, wherein said variation as a function of positioning is one of a self-boosting effect, a rotational position, and a function of the at least two differently stored minimum cable pull tensions with a respective slope of the vehicle.

14. The parking brake actuation method as claimed in claim 13, wherein the respective slope is one of uphill, downhill, pointing downhill and pointing uphill.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be explained in more detail with reference to the drawing in which an embodiment of the invention is illustrated. In the drawing, in each case schematically:

(2) FIG. 1 shows, by way of example, a sensorless wheel brake actuator system from the prior art and has a short traction cable, which wheel brake actuator system is suitable to be actuated with a parking brake actuation method; and

(3) FIG. 2 shows a qualitative sketch of the synchronous profiles for representing the actuator current demand I, braking torque M, cable tensioning force Fs and vehicle rolling distance s, in each case plotted against the time t, during the actuation method according to the invention.

DETAILED DESCRIPTION

(4) At least one initial tensioning process or primary tensioning process is provided by the traction cable. Then, in principle a further, secondary tensioning process or another additional tertiary tensioning process can be carried out on the traction cable.

(5) An exemplary tensioning process of an electric parking brake takes place as follows. A first primary/initial tensioning process ends at a level of approximately 80 percent of the necessary tractive force.

(6) An undesired movement of the vehicle is monitored and evaluated in a sensitive fashion during and after the primary tensioning process. If an unsuitable movement of the vehicle is sensed within the scope of the monitoring of the stationary state, which movement for example does not correspond to a customary, previously known, stored movement profile of a vehicle with an actuated duo-servo brake at a defined inclination angle, a second, secondary tensioning process is triggered at the electric actuator. A defined, increased tractive force, which is suitably assigned to the detected inclination angle or the state of the vehicle, is applied to the traction cable. For example, the tension in the secondary tensioning process corresponds to 90% of a predefined minimum tension.

(7) If, for example, a vehicle movement is detected after a primary tensioning process, it is often not unambiguously clear whether the brake shoes are still adhering to the brake drum or not, and whether a reduction in the holding torque is to be expected. The reaction time of a customary electric actuator is, however, usually at least approximately 70 ms. Depending on the rigidity of the overall system, the tractive force on the traction cable can, to some extent, be increased considerably above the actually required amount in 70 ms. Therefore, it is necessary to ensure in each case that there is a sufficient interval in terms of time and force between the primary tensioning process, secondary tensioning process and tertiary tensioning process.

(8) If no undesired vehicle movement and no actuation of the service brake is registered within a defined time period of, for example, approximately one second after a primary tensioning process has been carried out, the energization is terminated, that is to say that there is currentless self-locking. However, it is also possible for a secondary tensioning process to be triggered at the actuator for providing additional protection, which secondary tensioning process applies a yet further increased tractive tension to the traction cable.

(9) The the brake application force can be metered appropriately for demand during the parking operation. As a result of the demand-appropriate actuation, an actuator does not have to be actuated continuously and usually unnecessarily with an overload, or even does not have to be configured in an overdimensioned fashion. In other words, the first time an actuator can be configured to have smaller dimensions or less powerful dimensions. As result, the risk of damage owing to overloading or material fatigue is appropriately decreased.

(10) It is possible to reduce the number of individual brake application processes in that a plurality of brake application forces/tensions which are assigned to the inclination angles or the vehicle payload are preset. This decreases the loading of the hardware components involved and reduces a reaction time up to the perceptible holding effect.

(11) The parking brake system permits use of standardized components of a conventional mechanical duo-servo brake to be used. It is possible to dispense with additional components such as, in particular, elastic elements in the sense of a brake application force reservoir as in the case of spring-loaded brakes of utility vehicles.

(12) The foregoing preferred embodiments have been shown and described for the purposes of illustrating the structural and functional principles of the present invention, as well as illustrating the methods of employing the preferred embodiments and are subject to change without departing from such principles. Therefore, this invention includes all modifications encompassed within the scope of the following claims.