Methods and devices for releasing an electric actuator in a reliable manner using a quasi-elastic release end stop

Abstract

Methods and corresponding control devices for releasing an electric actuator in a reliable manner, such as an electric parking brake in particular, in a motor vehicle brake system. The aim of the invention is to provide an improved function and architecture which helps prevent the disadvantages of open-loop control systems when using a rationalized sensor system, thereby obviating closed-loop control systems. This is achieved by a release method and a corresponding electronic control unit which obtains an especially modulated change in the power requirement during the release process upon impacting the quasi-elastic release end stop of the electric actuating unit such that the change is fed back, the change being detected in order to be used as information for a power interruption or a termination of the power supply to the electric actuating unit.

Claims

1. A method for releasing an electric parking brake of a brake system of a motor vehicle, said motor vehicle having an electronic control unit which is configured to control a plurality of electric actuator units, wherein the electronic control unit is embodied with a respective channel for each of the plurality of electric actuator units, and wherein an activation request is generated electrically by an operator control element or automatically and is executed by the plurality of electric actuator units, and wherein a release request is generated electrically by the operator control element or automatically and is executed by the plurality of electric actuator units, the method comprising: a) moving, by at least one of the plurality of electronic actuator units, an actuator element in the direction of a release end stop in the release process by energizing the at least one of the plurality of electronic actuator units, b) observing, by the electronic control unit, a power demand of the at least one of the plurality of electric actuator units, c) wherein the release end stop has a defined elasticity, with the result that d) the approach, formation of contact and impacting between the actuator element and the release end stop feeds back a particularly modulated change in the power demand of the at least one of the plurality of electric actuator units, which is observed by the electronic control unit, e) calculating with the electronic control unit a switch-off current using a predefined relationship and based on one or more physical parameters, f) selecting with the electronic control unit a defined switch-off current limiting value based on the calculated switch-off current, wherein the electronic control unit selects the switch-off current limiting value from a plurality of stored values, and g) automatically interrupting, by the electronic control unit, the energization of the at least one of the plurality of electric actuator units after detection of the approach, formation of contact and impacting against the release end stop, wherein the interruption of the energization is performed by the electronic control unit if an observed power demand reaches or exceeds the selected switch-off current limiting value.

2. The method for releasing an electric parking brake of a brake system of a motor vehicle as claimed in claim 1, wherein the electronic control unit automatically ends a release process or an interruption or a termination of the energization of the at least one of the plurality of electric actuator units if a new activation request is received in the electronic control unit.

3. The method for releasing an electric parking brake of a brake system of a motor vehicle as claimed in claim 1, wherein the electronic control unit determines a minimum brake application force based on sensor information in a first method step, and wherein in a second subsequent step the electronic control unit calculates the switch-off current as a function of the determined minimum brake application force using the predefined relationship, and wherein the one or more physical parameters relate to the determined minimum brake application force, to a measured open-circuit power demand, to a measured on-board power system voltage, to the measured ambient temperature, to a measured wheel rotation behavior and/or to a hydraulic admission pressure fed into the service brake system.

4. The method for releasing an electric parking brake of a brake system of a motor vehicle as claimed in claim 1, wherein a) the electronic control unit energizes the at least one of the plurality of electric actuator units while measuring the power demand and observes the power demand in the process, b) the electronic control unit continuously or periodically compares the measured power demand with a selected switch-off current limiting value, and c) the electronic control unit interrupts or terminates the energization of the at least one of the plurality of electric actuator units if the observed power demand is higher than or equal to the switch-off current limiting value.

5. An electronic control unit comprising hardware with at least one microprocessor configured to execute the method as claimed in claim 1.

6. A method for releasing an electric parking brake of a brake system of a motor vehicle, said motor vehicle having an electronic control unit which is configured to control a plurality of electric actuator units for adjusting respective actuator elements, wherein the electronic control unit is embodied with a respective channel for each of the plurality of electric actuator units, and wherein an activation request is generated electrically by an operator control element or automatically and is executed by the plurality of electric actuator units, and wherein a release request is generated electrically by the operator control element or automatically and is executed by the plurality of electric actuator units, the method comprising: a) releasing, by the electronic control unit, the actuator element of at least one of the plurality of electric actuator units with clocked energization in the release direction moves in the direction of the release end stop, b) observing, by the electronic control unit, a power demand of the at least one of the plurality of electric actuator units, c) the approaching, formation of contact or impacting between the actuator element and the release end stop feeds back a particularly modulated power demand of the at least one of the plurality of electric actuator units, d) calculating with the electronic control unit a switch-off current using a predefined relationship and based on one or more physical parameters, e) selecting with the electronic control unit a defined switch-off current limiting value based on the calculated switch-off current, wherein the electronic control unit selects the switch-off current limiting value from a plurality of stored values, and f) automatically terminating, by the electronic control unit, the energization of the at least one of the plurality of electric actuator units after detection of the approaching, formation of contact and impacting against the release end stop, wherein the termination of the energization is performed by the electronic control unit if an observed power demand reaches or exceeds the selected switch-off current limiting value.

7. The method for releasing an electric parking brake of a brake system of a motor vehicle as claimed in claim 6, wherein the electronic control unit automatically ends a release process or an interruption or a termination of the energization of the at least one of the plurality of electric actuator units if a new activation request is received in the electronic control unit.

8. The method for releasing an electric parking brake of a brake system of a motor vehicle as claimed in claim 6, wherein the electronic control unit determines a minimum brake application force based on sensor information in a first method step, and wherein in a second subsequent step the electronic control unit calculates the switch-off current as a function of the determined minimum brake application force using the predefined relationship, and wherein the one or more physical parameters relate to the determined minimum brake application force, to a measured open-circuit power demand, to a measured on-board power system voltage, to the measured ambient temperature, to a measured wheel rotation behavior and/or to a hydraulic admission pressure fed into the service brake system.

9. The method for releasing an electric parking brake of a brake system of a motor vehicle as claimed in claim 6, wherein a) the electronic control unit energizes the at least one of the plurality of electric actuator units while measuring the power demand and observes the power demand in the process, b) the electronic control unit continuously or periodically compares the measured power demand with a selected switch-off current limiting value, and c) the electronic control unit interrupts or terminates the energization of the at least one of the plurality of electric actuator units if the observed power demand is higher than or equal to the switch-off current limiting value.

10. An electronic control unit comprising hardware with at least one microprocessor configured to execute the method as claimed in claim 6.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Details of aspects of the invention are described below with reference to preferred exemplary embodiments and in conjunction with the appended drawing.

(2) In the drawing, in each case schematically:

(3) FIG. 1 shows relationships that are modelled in an idealized manner between the force (F) over an actuation travel s and an actuator (spindle), which is mounted in a rotationally fixed and axially displaceable fashion, of an electric actuator unit,

(4) FIG. 2 shows a stage sequence I-V of the observed power demand I of the electric actuator unit over the time t, modelled in an idealized fashion, in combination with FIG. 1 in order to illustrate the method for feeding back the release end stop (release position, without application of the brake, end stop),

(5) FIG. 3 shows an embodiment of a system constructed with a single channel,

(6) FIG. 4 shows an embodiment of a system constructed with four channels.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(7) In the characteristic curve profiles which are each modelled in an idealized fashion, an electromechanical brake application process is indicated using a double arrow, while an electromechanical release process in the opposite direction is symbolized by a single arrow. In this context, an actuator (activation cable, spindle) of an electric actuator unit 3 is therefore in the released state when free of force in each case in the characteristic curve sections indicated by dashed lines (red) or with crosses (green). A particular elasticity is effective in the release end stop exclusively in the characteristic curve region marked with crosses (green). The effectiveness of elasticity is a function of the actuation travel s which is carried out. The elasticity acts as an end stop which is elastically integrated into the force flux of the bearing forces, with the result that a change in the characteristic curve of the current/time profile, which can be detected without a sensor, occurs and is processed and evaluated by the electronic control unit by observation of the current profile. This is brought about in particular by virtue of the fact that an elastic element increasingly acts on the actuator at the start of the phase IV and in the phase V. Another characteristic curve range, respectively marked by circles in FIGS. 1 and 2, relates, in contrast, to the actuation range of the electric actuator unit which is loaded by tractive force. A release process is therefore basically divided into the following process phases, in each case starting from the activation state b and considered in the release direction:

(8) Phase I: Motor startup in the release direction (start of energization)

(9) Phase II: Depletion of force in the release direction

(10) Phase III: Open-circuit operation in the release direction

(11) Phase IV: Engagement on the elastic element

(12) Phase V: End of action (end of energization)

(13) Of course, a brake application process occurs in precisely opposite fashion.

(14) FIG. 1 shows a (traction) force profile F over the actuation travel s of the actuator unit. In this context, a characteristic curve branch f(s) in principle shows a force-related relationship between the actuator and the activation cable, that is to say the branch of the application of the tractive force between the actuator and the activation cable. This characteristic curve branch is marked by dashed lines (red) in the travel interval of the idle travel (free of tractive force) and by circles (blue) in the travel interval which is loaded by tractive force. Conversely, a characteristic curve branch h(s), which lies on the other side of the 0 point and is also marked with crosses (green), shows a force effect of the elastic element with respect to the actuator. This force effect occurs only in an interval between the trasversing of the 0 point and the location where the rear end stop is reached. This force effect of the elastic element is directed counter to the release movement of the actuator.

(15) As is apparent in detail from FIG. 1, when the brake is applied with the phase III, the electric actuator unit overcomes an idle travel s0 in a manner essentially free of force (F0) in accordance with the characteristic curve part indicated by dashed lines (red). When the travel mark scp is reached, actuation force (tractive force) is built up in the phase II. The electronic control unit serves to perform closed-loop control, and, in particular, to switch the energization on and off. The electrical power profile is observed by the electronic control unit both during the application and during the release of the electric actuator unit, and is subsequently analyzed to determine to what extent a significant change has occurred in the power demand. This serves to detect whether, on one hand, the required brake application force has been reached or, on the other hand, the release state has been reached by abutment against the release end stop when a corresponding switch-off current limiting value iA occurs, before the actuator unit energization is ended.

(16) The electronic control unit contains a microprocessor with a memory and assumes, according to an EDP-assisted and software-based cyclically executed control routine using a physical system model which is stored on a software basis, that the drum brake system is always safety transferred to the release position if the brake calipers have reached their release position which is free of brake application force. This is achieved when the brake calipers just still rest on a support device under the effect of the prestressed spring elements, that is to say free of tractive force but still in defined fashion. The electronic control unit therefore detects, in accordance with the specified model, the phase V after the phase III, that is to say the open-circuit level which is free of tractive force, is overcome, and also the phase IV has been terminated. Accordingly, it is monitored and correspondingly detected whether the power demand of the actuator unit rises in response to the end of the phase IV in a marked and reproducibly secured fashion. In other words, use is made of the particular feature that when the electric actuator unit moves into its “rear” securely released end position—that is to say the release position on the other side of the 0 point—through elastic deformation of the elastic element, a linearly or progressively rising significant change in the profile of the current/time characteristic curve is observed. This fact is automatically monitored and detected by the electronic control unit through monitoring of the characteristic curve. After it has been detected that the switch-off current limiting value iA has been reached or exceeded, the power supply of the electric actuator unit is automatically switched off by the electronic control unit without inertia effects in the drivetrain of the electric actuator unit still being able to generate any adverse effects on comfort (running on). After the switching of the energization, the drivetrain of the electric actuator unit comes to rest instantaneously, owing to self-locking, in the release position which has been reached.

(17) FIG. 3 shows a schematic view, on the basis of a first embodiment in an exemplary manner, of a brake system 1 which is constructed with a single-channel, for two wheel brake systems 2, 2′ comprising an electronic control unit 3 which has one or more microprocessors 12, 13 and is electrically connected to at least one operator control element 10, and serves to supply electricity to an electric actuator unit 4 in accordance with demand. The electronic control unit 3 includes one or more microprocessors 12, 13 which are fed with information acquired by sensor, such as, in particular, with wheel rotation information or by a sensor 11 for measuring and observing the power demand of the electric actuator unit 4. Each wheel brake system 2, 2′ includes brake linings 5, mounted fixedly in terms of rotation, with friction faces 7. A rotor 6 is rotatably mounted on a axle or hub 9 of the motor vehicle (not illustrated) and has friction faces 8. Friction faces 7 of the brake linings 5 are assigned to one or more friction faces 8. The electric actuator unit 4 and the brake linings 5 are basically effectively connected mechanically by means of an activation cable 14, but can also be directly driven, in order to permit a tension-compression adjustment. On the basis of the described parallel connection of the two electric actuator units 4, 4′ in the two wheel brake systems 2, 2′, braking requests are implemented essentially identically in accordance with demand by generating the correspondingly requested braking effect using the two wheel brake systems 2, 2′. In this simplified configuration, the summed power demand of the two electric actuator units 4, 4′ is primarily fed back to the electronic control unit 3.

(18) Because of a basic correspondence in the components, details are given below exclusively about the systematic differences in the embodiment according to FIG. 4, wherein for the purpose of simplification the component description in FIG. 3 is referred to. Accordingly, FIG. 4 shows a four-channel design. In this context, the electric actuator unit 4, 4′, 4″, 4′″ of each wheel brake system 2, 2′, 2″, 2′″ is connected individually to the electronic control unit 3, and receives an individual supply for the purpose of wheel-specific open-loop or closed-loop control. The wheel-specific separation of all the open-loop and/or closed-loop control processes, including the feeding back while observing the power demand, switch-off current limiting value specification etc. takes place in this context. Refinements or simplifications which can permit speeding up of the process or a lower expenditure on computing in the electronic control unit 3 are conceivable for the separation, insofar as such adaptation is requested. For example, it is possible to divide the individual wheel brake systems 2, 2′, 2″, 2′″ electrically into brake circuits which can be adapted in any desired way, that is to say in a systematically paired fashion, and wherein the wheel brake systems 2, 2′, 2″, 2′″ of a brake circuit can basically be treated and processed in the same way according to the principle of “select low”, or even on a wheel-specific basis. As a result, the respectively most critical wheel brake system can respectively be allocated a dominant guiding role, also in the control of the other wheel brake systems which are also connected into the same brake circuit. Accordingly, improved safety is achieved, and unstable vehicle (braking) states can be avoided. Even though FIG. 4 expressly shows a four-channel design, any other desired numbers of channels can be correspondingly formed (a 2-channel, 3-channel or x-channel design).

LIST OF REFERENCE NUMBERS

(19) 1 Brake system 2, 2′, 2″, 2′″ Wheel brake system 3 Electronic control unit 4, 4′, 4″, 4′″ Electric actuator unit/units 5 Brake lining 6 Rotor (brake drum or brake disk) 7 Friction face 8 Friction face 9 Axle, wheel hub 10 Operator control element 11 Sensor 12 Microprocessor 13 Microprocessor 14, 14′, 14″, 14′″ Activation cable