DE102014212605A1 - Position calibration of a brake actuator - Google Patents

Abstract

A method is provided for calibrating a position (56) of a brake actuator (52) driven via an electric motor (40) to apply a brake (6) in a vehicle (2), comprising: - starting a brake application (6) application a supply current (60, IM) to the electric motor (40), - detecting the supply current (60, IM) after the start (66) of the application process, - determining a force acting on the brake actuator (52) application force (FA) based on the detected Supply current (60, IM); and - calibrating the position (56) of the brake actuator (52) based on a stiffness (f) of the brake (6) and the determined application force (FA).

Description

The invention relates to a method for calibrating a position of an electric motor driven brake actuator for applying a brake in a vehicle, a control device for carrying out the method and the parking brake.

From the DE 10 2008 052 845 A1 For example, a method for determining a position of a brake actuator in a brake of a vehicle is known, based on which a clearance can be set correctly.

It is an object of the present invention to improve the known parking brake.

The object is solved by the features of the independent claims. Preferred developments are the subject of the dependent claims.

According to one aspect of the invention, a method of calibrating a position of an electric motor-driven brake actuator for applying a brake in a vehicle includes the steps of starting a brake application by applying a supply current to the electric motor, detecting the supply current after starting the application, determining a brake application force acting on the brake actuator based on the detected supply current, and calibrating the position of the brake actuator based on a stiffness of the brake and the determined application force.

The specified method is based on the consideration that the correct adjustment of the clearance in a brake, such as an electronic parking brake, is one of the central safety requirements. Since in this case no commercial sensors are available, and the adjustment of the clearance must be carried out with the aid of the measured supply current of the electric motor of the brake, the setting of the clearance is in principle prone to error.

In the context of the method mentioned above, a motor model is used to set the clearance. Here, the position of the brake actuator is based on a detected application point of the controlled via the brake actuator friction element relative to the brake disc relatively updated, so that the application point for an error-free adjustment of the clearance must be known. In other words, the entire application process must always be considered.

Under certain circumstances, however, no complete application procedure could be available. For example, the brake could be clamped out of a partially tensioned state. This means that the friction element already rests against the brake disk at the start of the application process. Then, therefore, no contact point can be detected, and a correct adjustment of the clearance is not possible with the aforementioned method or only with a non-satisfactory result. The same problem arises when, for example, with an electronic parking brake as a brake, for example, an emergency braking dynamic deceleration is performed in the context of which is switched periodically between closing and loosening without the friction element completely loses contact with the brake disc.

Here, the specified method starts with the consideration that a brake does not have an infinitely high rigidity and elastically buckles during each application process. The stiffness of the brake is usually known from characteristics or the like.

On the other hand, based on the supply current supplied to the electric motor, it can be determined how high the application force is, with which the friction element and thus the brake actuator press against the brake disk. Since the stiffness of the brake basically describes the relationship between the application force and the path that the brake actuator must travel to apply the application force, it is also possible to deduce the position of the brake actuator in the case of a known application force.

Therefore, with the specified method, a basis for updating the position of the brake actuator with the above-mentioned engine model can also be found in the partially prestressed state, so that the clearance can also be set correctly when the brake is applied from a partially prestressed state and then again is opened.

In a further development of the specified method, a starting time of the electric motor is waited for before the supply current is detected after starting the application process. In this way it can be avoided that in the determination of the clamping force a starting current is included, but which is not dependent on the clamping force and thus would lead to a false Erebnis.

In another development of the specified method, a profile of the supply current over a predetermined time period is considered for detecting the supply current. In this way, technically conditioned measurement errors that occur during the detection of the supply current due to the principle filter out.

For this purpose, in a preferred embodiment of the specified method for detecting the supply current in the predetermined period of time, the average value can be formed, because in this way measuring errors can be filtered out most effectively.

In yet another further development of the specified method, the supply current is corrected by a movement current, which is responsible for generating the kinetic energy when the brake is applied, for determining the application force. In this way, the basis for updating the position of the brake actuator with the above-mentioned engine model can be determined even more precisely because the kinetic energy and thus the movement current have no influence on the application force and thus falsify the result.

In an additional development of the specified method, a force component originating from the supply current and a force component originating from a hydraulic brake circuit are taken into account for determining the application force, whereby the basis to be updated for updating the position of the brake actuator with the aforementioned engine model is specified further from the hydraulic brake circuit derived power also has an influence on the position of the brake actuator.

• – basierend auf der Steifigkeit der Bremse und der bestimmten Zuspannkraft eine Initialposition des Bremsaktuators bestimmt und basierend auf der Bewegung des Bremsaktuators fortgeschrieben,
• – eine gespeicherte Referenzposition auf der Bewegung des Bremsaktuators fortgeschrieben, und
• – die fortgeschriebene gespeicherte Referenzposition basierend auf der fortgeschriebenen Initialposition korrigiert, wenn eine Gegenüberstellung der fortgeschriebenen gespeicherten Referenzposition und der fortgeschriebenen Initialposition eine vorbestimmte Bedingung erfüllt.

In a further development of the specified method, for calibrating the position of the brake actuator:

• Determines an initial position of the brake actuator based on the stiffness of the brake and the determined application force and updated based on the movement of the brake actuator,
• - Updated a stored reference position on the movement of the brake actuator, and
• - corrects the updated stored reference position based on the updated initial position when a comparison of the updated stored reference position and the updated initial position satisfies a predetermined condition.

The specified further development is based on the consideration that the clearance of the brake can be set reliably with the method mentioned in the majority of cases. Therefore, the method mentioned above, in the context of which the stored reference position is the already mentioned contact point of the friction element to the brake disc, can be used without any problems. The specified method should only be used if the tension is detected as a fault out of a partially tensioned state in order to correct the position of the brake actuator derived from the stored reference position.

For this purpose, the predetermined condition should be considered satisfied if the updated initial position at the end of the application process is greater than the updated stored reference position, because this is the condition for the brake to be clamped out of a partially stressed state.

According to a further aspect of the invention, a control device is designed to carry out one of the aforementioned methods.

In a development of the invention, the specified device has a memory and a processor. The specified method is stored in the form of a computer program in the memory and the processor is provided for carrying out one of the aforementioned methods when the computer program is loaded from the memory into the processor.

According to a further aspect of the invention, a parking brake for blocking a movement of a vehicle with a service brake at a standstill comprises a specified control device.

According to another aspect of the invention, a vehicle includes a specified parking brake.

The invention also relates to a computer program comprising program code means for carrying out all the steps of one of the stated methods when the computer program is executed on a computer or one of the specified control devices.

The invention also relates to a computer program product containing a program code stored on a computer-readable medium and which, when executed on a data processing device, performs one of the specified methods.

The above-described characteristics, features and advantages of this invention, as well as the manner in which they are achieved, will become clearer and more clearly understood in connection with the following description of the exemplary embodiments, which are explained in more detail in conjunction with the drawings, in which:

1 a schematic diagram of a vehicle with a service brake and a parking brake,

2 a perspective view of a parking brake, and

3 show a schematic view of the parking brake.

In the figures, the same technical elements are provided with the same reference numerals and described only once.

It will open 1 Reference is made to a schematic diagram of a vehicle 2 with a service brake 4 and a parking brake 6 shows.

The vehicle 2 has a chassis 8th on, on a road not shown on four wheels 10 can be driven driven by a motor, not shown. At the individual wheels 10 are brake discs in the present embodiment 12 non-rotatably attached, to those still to be described rotatably to the chassis 8th attached brake effectors can attack the wheels 10 block in a manner known per se and the vehicle 2 to slow down while driving or to hold it stationary.

In the present embodiment, the service brake 4 one service brake effector each 14 , such as a brake shoe, on each wheel 10 on. These service brake effectors 14 are from a service brake control unit 16 via hydraulic lines 18 based on a with a brake pedal 20 predefinable service brake request 22 controlled in a known manner.

In contrast, the parking brake 6 at the wheels 10 a particular of the not shown axes of the vehicle 2 one parking brake effect each 24 on, which may for example also be designed as brake shoes. In the present embodiment, the parking brake effectors become 24 from a parking brake control unit 26 via electrical lines 28 either based on one with a parking brake lever 30 predefinable parking brake request 32 in a known manner or alternatively in a further manner, which will be discussed in more detail at a later point.

The structure of the service brake 4 and the parking brake 6 was previously described in the form of a disc brake. The construction of both brakes 4 . 6 is however arbitrary. For example, one of the two brakes 4 . 6 or both brakes 4 . 6 be carried out in a manner known per se as a drum brake, which will not be discussed in more detail for the sake of brevity.

It will open 2 Referred to the parking brake 6 in a perspective view shows. The parking brake 6 is designed as an electromechanical brake and should be a wheel 10 of the vehicle 2 over a brake disc 34 hold tight. This includes the parking brake 6 two friction elements 36 coming from the brake disc 34 seen from axially movable on a caliper 38 are held and by a DC motor 40 executed electric motor via a first transmission 42 , a reset unit 44 and a second gear 46 are driven.

To the DC motor 40 is based on the parking brake request 32 one in 3 shown supply voltage 58 created. By the supply voltage 58 flows through the DC motor 40 a motor current 60 and puts you in the brake 6 an engine torque 48 one. The first transmission 42 transfers the engine torque 48 based on a predetermined gear ratio to the reset unit 44 such that at the reset unit a transmitted torque 50 is applied. The reset unit 44 acts on the transmitted torque 50 in a conventional manner with a restoring moment, the game of the transmission 42 . 46 balances. The second transmission 46 includes a brake actuator 52 with an external thread, into which an internal thread rotates 54 intervenes. With the transmitted and acted upon by the restoring torque 50 becomes the internal thread 54 turned that way the torque 50 in a linear motion 56 implements. The linearly moving brake actuator 52 then can the friction elements 36 to the brake disc 34 press down.

To release the parking brake 6 becomes based on the parking brake request 32 by renewed application of a supply voltage 58 turned in an opposite direction to the friction elements 36 from the brake disc 34 to remove again. It must be ensured that the friction elements 36 with a clearance mentioned predetermined distance from the brake disc 34 remove, so that the brake disc 34 can rotate freely. On the other hand, the clearance must not be set too high.

Therefore, an exact positioning of the friction elements 36 when releasing the parking brake 6 necessary. In order to ensure this, it is proposed in the context of the present embodiment, an in 4 shown current profile 62 of the motor current 60 over time 64 analyze.

For this analysis, the current profile 62 divided into four different phases, the DC motor 40 with a normal application of the parking brake 6 has to go through a clearance. These phases include a start-up phase 66 , an idling phase 68 , a monitoring phase 70 and a pressure phase 72 ,

During the start-up phase 66 is the DC motor 40 in the known start. This is where the current starts 62 of the motor current 60 at a peak current 75 , the only of the not shown ohmic internal resistance of the DC motor 40 is limited. During startup, the rotating DC motor induces 40 in a conventional manner, not shown, against the supply voltage 58 acting counter voltage, so that motor current 60 in the current waveform shown 62 drops. The minimum of this waste is the so-called no-load current 78 However, the motor current, in principle, only approaches asymptotically, which by a dotted course in 3 is clarified.

The start-up phase 66 is defined in the present embodiment for fixed maximum period and may be, for example, 70ms. In this area is the motor current 60 in ordinary DC motors used in parking brakes dropped to a sufficiently low level at which an end to the start can be assumed.

At the start-up phase, the idle phase closes 68 at. In this phase, it is expected that the clearance between the friction elements 36 and the brake disc 34 closes. As long as the clearance is closed, the DC motor has 40 to overcome any significant mechanical resistance and therefore is still idle. In the present embodiment, after the start-up phase 66 basically an idle phase 68 Assuming, whether the DC motor 40 actually idle and close the clearance, or not. This assumed idle lasts over a minimum idle phase 76 which, in the context of the present embodiment, can be defined over a maximum period of, for example, 50 ms. On the background of this minimal idle phase 76 will be discussed later.

Following the minimum idling phase 76 closes in the idle phase 68 a test phase 79 in which it is checked whether the clearance is already closed and the friction elements 36 on the brake disc 34 issue. The point in time at which the clearance is to be closed will be referred to below as the stop time 80 be designated and represents a minimum 81 in the current flow 62 of the motor current 60 dar. Since the minimum 81 and thus the stop time 80 usually not technically definite, can be used as a criterion for the time of the attack 80 be checked if the current 62 is rising. As soon as the increase in current flow 62 and thus the stop time 80 was detected, the idle phase 68 leave within the specified procedure.

The attack time 80 is enormously important for the above setting of the clearance, at this time can the friction elements 36 opposite the brake disc 34 a unique position, ie zero, can be assigned. This position will be referred to below stop position. From this point on, the further course of movement of the friction elements 36 opposite the brake disc 34 modeled and thus the resulting position of the friction elements 36 opposite the brake disc 34 to be appreciated. For this example, the engine speed 48 from the motor current 60 and the motor voltage 58 determined using the known engine resistance and the known engine constant and by integration the absolute position of the friction elements 36 and thus the brake actuator 52 opposite the brake disc 34 be calculated.

Before the stop time 80 is recognized as unique and thus the stop position of the brake actuator 52 opposite the brake disc 34 can be set, which is in the idle phase 68 subsequent monitoring phase 70 the increase of the motor current 60 monitored because at this stage 70 the attack time 80 can not be indicated for metrological reasons. Although the time is up 64 when entering the monitoring phase 70 as a stop time 80 but it can still be corrected during the monitoring phase.

After the monitoring phase 70 is completed and the stop time 80 and thus the stop position of the brake actuator 52 are clearly defined, the friction elements 36 over the brake actuator 52 to the brake disc 34 be pressed until the motor current 60 a certain turn-off current 82 have reached, in which a sufficient pressure force is secured.

Since in the manner described above, starting from the stop time 80 or rather, the stop position of the brake actuator 52 over the motor current 60 and thus the absolute position of the brake actuator via the contact pressure 52 and thus the absolute position of the friction elements 36 opposite the brake disc 34 can be set, the clearance of the friction elements 36 when opening the parking brake 6 be set precisely.

However, it is problematic when the parking brake 6 from a teilzugespannten state is tightened out further. This is for example in 5 shown in the context of which the motor current 60 already in the idle phase 68 rises, because actually no idle of the DC motor 40 is present.

In 5 there is no stop time 80 , so that no stop position can be determined, starting from the absolute position of the friction elements 36 and thus the brake actuator 52 could be determined. Here, the specified method with the proposal, the motor current 60 itself to determine the abovementioned absolute position.

This is the minimum idle phase 76 in the idling phase 68 intended. It has, as already mentioned, a minimum duration of, for example, 50 ms. Within this minimum period, the motor current can be 60 to an average 84 convey. Based on this mean 84 for the motor current 60 can then be closed to the average pressure force with which the friction elements 36 during the minimum idling phase 76 against the brake disc 34 pressed.

Compared to individual current values of the motor current 60 , which are fundamentally very inaccurate due to measurement errors, is the mean value 84 of the motor current 60 very accurate. Therefore, a starting from which can be derived from the mean 84 resulting average contact pressure on the stiffness of the parking brake 6 certain position of the brake actuator 52 as the absolute position of the brake actuator 52 can then be used in the above manner, the absolute position of the brake actuator 52 and thus the friction elements 36 be further developed in the above-mentioned way.

To further increase the accuracy of the result, the motor current should 60 before calculating the pressing force by a movement current for moving the friction elements 36 and the brake actuator 52 be corrected, not for pressing the friction elements 36 contributes to the brake disc.

The parking brake 6 could in principle with the same brake effector and thus with the same friction element 36 operated, such as the service brake 4 , In this case, however, in determining the pressing force and the hydraulic pressure from the hydraulic lines 18 to be taken into account.

Assuming the I _{M is} the mean 84 of the motor current 60 , I _{B is} the aforementioned movement _current , F _{hy is} the service brake force from the hydraulic lines, and I 2F is a constant used to convert the electric currents in the parking brake into resultant forces, then the pressing force F _{A of} the friction elements 36 to the brake disc 34 calculated as follows: F _A = (I _M - I _B ) · I 2 F + F _hyd

If the pressure force F _{A is} known, then the absolute position X _{A of} the brake actuator belonging to the pressing force F _A can be determined 52 Calculate the stiffness curve f via the inverse function f ^-1 as follows: X _A = f ^-1 (F _A )

Of course, the stiffness characteristic must be known in advance.

If the absolute position X _{A is} known, it can be during the monitoring phase 70 then until reaching the breaking current 75 be further developed.

As part of the 6 is the specified procedure outlined in the event that the parking brake 6 is triggered in an almost fully applied state.

In this case, after the forced start-up phase 66 and the enforced minimum idle phase 76 the motor current 60 shut off immediately because of the shutdown current 82 already with completion of the minimum idling phase 76 is exceeded. Then, the absolute position X _A resulting from the above equations is immediately the end position of the brake actuator 52 in the applied state of the parking brake.

QUOTES INCLUDE IN THE DESCRIPTION

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Cited patent literature

• DE 102008052845 A1 [0002]

Claims (10)

Method for calibrating a position ( 56 ) one via an electric motor ( 40 ) driven brake actuator ( 52 ) for applying a brake ( 6 ) in a vehicle ( 2 ), comprising: - starting a brake application procedure ( 6 ) by applying a supply current ( 60 , I _M ) to the electric motor ( 40 ), - detecting the supply current ( 60 , I _M ) after the start ( 66 ) of the application process, - determining one on the brake actuator ( 52 ) acting clamping force (F _A ) based on the detected supply current ( 60 , I _M ), and - calibrating the position ( 56 ) of the brake actuator ( 52 ) based on a stiffness (f) of the brake ( 6 ) and the specific application force (F _A ). Method according to claim 1, wherein prior to detecting the supply current ( 60 , I _M ) after the start of the application process, a start-up time ( 66 ) of the electric motor ( 40 ) is serviced. Method according to claim 1 or 2, wherein for detecting the supply current ( 60 , I _M ) a course ( 62 ) of the supply current ( 60 , I _M ) over a predetermined period of time ( 76 ) is looked at. Method according to claim 3, wherein for detecting the supply current ( 60 , I _M ) in the predetermined period ( 76 ) the mean ( 84 ) is formed. Method according to one of the preceding claims, wherein for determining the application force (F _A ) of the supply current ( 40 , I _M ) is corrected by a movement current (I _B ), generating the kinetic energy when applying the brake ( 6 ) responsible for. Method according to claim 5, wherein for determining the application force (F _A ) a force component originating from the supply current (I _M ) and a hydraulic brake circuit (FIG. 4 ) is considered force component (F _hyd ). Method according to one of the preceding claims, wherein for calibrating the position of the brake actuator ( 52 ): - based on the stiffness (f) of the brake ( 6 ) and the determined application force (F _A ) an initial position ( 84 ) of the brake actuator ( 52 ) and based on the movement of the brake actuator ( 52 ), - a stored reference position ( 80 ) on the movement of the brake actuator ( 52 ), and - the updated stored reference position ( 80 ) based on the updated initial position ( 84 ) is corrected if a comparison of the updated stored reference position ( 80 ) and the updated initial position ( 84 ) satisfies a predetermined condition. The method of claim 7, wherein the predetermined condition is met when the updated initial position ( 84 ) at the end of the application process is greater than the updated stored reference position ( 80 ). Control device ( 26 ) arranged to carry out a method according to any one of the preceding claims. Parking brake ( 6 ) for blocking a movement of a vehicle ( 2 ) at standstill comprising a control device according to claim 9.

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