DE102021214102A1 - Method of operating an electrically operated brake and brake assembly - Google Patents

Abstract

The invention relates to a method for operating an electrically actuated brake, with a setpoint value for an operating parameter of the brake being received and the operating parameter being controlled based on the setpoint value, and with a comparison value also being calculated for the operating parameter, with the presence of a predefined deviation between an error message is output based on a measured value of the operating parameter and the comparison value. The invention further relates to an associated brake assembly.

Description

The invention relates to a method for operating an electrically operated brake and an associated brake assembly.

Brakes are typically used in motor vehicles in order to decelerate them in a targeted manner. Today's braking systems are often actuated hydraulically or pneumatically. However, future brakes will increasingly have electrical actuation.

Electrically actuated brakes should always work in a defined and clearly controllable manner.

It is therefore an object of the invention to provide a method for operating an electrically actuated brake, which is designed alternatively or better than known designs. It is a further object of the invention to provide an associated brake assembly. According to the invention, this is achieved by a method and a brake arrangement according to the respective main claims. Preferred configurations can be found, for example, in the respective dependent claims. The content of the claims is made part of the content of the description by express reference.

• - Empfangen eines Sollwerts für einen Betriebsparameter der Bremse,
• - Regeln des Betriebsparameters auf den Sollwert,
• - Berechnen eines Vergleichswerts für den Betriebsparameter basierend zumindest auf dem Sollwert,
• - Messen eines Messwerts des Betriebsparameters,
• - Vergleichen des Messwerts mit dem Vergleichswert, und
• - Ausgeben einer Fehlermeldung, wenn das Vergleichen mindestens eine vordefinierte Abweichung zwischen Messwert und Vergleichswert anzeigt.

The invention relates to a method for operating an electrically actuated brake, the method having the following steps:

• - Receiving a target value for an operating parameter of the brake,
• - adjusting the operating parameter to the setpoint,
• - Calculating a comparison value for the operating parameter based at least on the target value,
• - measuring a reading of the operating parameter,
• - comparing the measured value with the comparison value, and
• - Outputting an error message if the comparison shows at least one predefined deviation between the measured value and the comparison value.

Such a method makes it possible to continuously monitor a brake. In this case, the setpoint typically represents a value of the operating parameter which is to be set and which is determined, for example, by a vehicle dynamics control system, a driver assistance function or based on a brake pedal actuation by the driver detected by sensors. A regulation can be understood in particular as a typical regulation, for example using a proportional-integral controller or a proportional-integral-derivative controller. In this case, the operating parameter represents in particular the variable actually present in the brake. The comparison value represents a value which the operating parameter should at least approximately currently assume. It can differ from the target value in particular because it takes a certain amount of time to regulate a target value and the target value has typically not yet been reached during the regulation time. For example, the comparison value can be a value between a previous actual value and the new target value. In this way, the brake can also be monitored during a control process to a new setpoint. However, monitoring can also be used accordingly with a constant setpoint.

The measured value can be measured using a sensor, for example. If at least one predefined deviation between the measured value and the comparison value is displayed, it can be assumed that the brake or the control of the brake is not working properly and an error message can be output accordingly. This can be used, for example, within a control of the brake, it can be passed on to other components of a motor vehicle, and/or it can lead to a warning to the driver and, for example, prompt him to visit a workshop.

The comparison value can be calculated from the setpoint, for example using a dynamic approximation model for the actuator control. In other words, such a dynamic approximation model can, for example, predict which actual value should be assumed at least approximately at a certain point in time during control, so that, for example, it can then be checked during comparison whether the brake behaves as predicted by the dynamic approximation model became. Deviations can indicate a malfunction.

The dynamic approximation model can be a dynamic model with low-pass behavior, for example. In this way, in particular, the typically system-inherent inertia of a regulation can be taken into account. In particular, it can be a second-order low-pass filter. In particular, a dynamic approximation model can have the property that a limitation of the minimum and maximum rate of change of the comparison value in the model is possible. Such limitations can, for example, also be changed externally, ie in particular in the form of input signals. This allows the model to be adapted to current operating situations.

According to one embodiment, to calculate the comparison value, a variable previously used in the calculation is limited in such a way that it is at least as large as a lower threshold value. According to one embodiment, to calculate the comparison value, a variable previously used in the calculation is limited in such a way that it is at most as large as an upper threshold value. It can thereby be ensured that certain limits, for example physical limits, are taken into account when calculating the comparison value and unrealistic comparison values are prevented.

The lower threshold value and/or the upper threshold value can be determined based on parameters of the brake. This allows a current operating situation to be taken into account.

In particular, the variable previously used in the calculation, which is subject in particular to the restriction already described with regard to the lower and/or upper threshold value, can be an angular velocity of an actuator. Limiting such an angular velocity has proven to be sensible, since any unrealistic calculated values for the angular velocity are automatically corrected in this way before a further calculation.

The predefined deviation can be displayed in particular when the measured value is outside a tolerance band around the comparison value. In particular, the tolerance band can be defined in such a way that typical, tolerable deviations lie within the tolerance band and a deviation outside the tolerance band indicates an error.

An upper distance between an upper end of the tolerance band and the comparison value and/or a lower distance between a lower end of the tolerance band and the comparison value can be calculated, in particular, based on the comparison value. This allows the tolerance band to be tracked, in particular to the effect that the tolerance band can also be adapted as a function of the value of the comparison value and/or its rate of change. For example, the tolerance band can be expanded in the case of high comparison values compared to small comparison values.

The upper distance and/or the lower distance can in particular be calculated based on a derivation of the comparison value. In particular, the upper distance and/or the lower distance can thus be increased in the event of a rapid change in the comparison value. In particular, the faster the comparison value changes, the higher the upper distance and/or the lower distance can be calculated. In particular, it can be a time derivation.

According to one embodiment, the predefined deviation is displayed only if the deviation persists for a predetermined period of time. In particular, this can prevent an error message from being triggered if there is only a short-term deviation. Only if the deviation persists for a predetermined period of time is a reaction typically required and accordingly only then is the error message triggered.

According to one embodiment, the error message is only output if the predefined deviation has been displayed at least as often as a predefined threshold value indicates. This can prevent a single deviation from leading to an error message, thereby avoiding undesirably frequent error messages that may no longer be taken seriously.

In particular, the embodiments described can be combined with the predetermined time period and the predefined threshold value. It can therefore always first be checked whether a deviation persists for at least a predetermined period of time. If so, a counter is incremented by one. If the counter is greater than or equal to the predefined threshold, the error message is issued. In combination, this has proven to be an advantageous method for reliably displaying error messages when an error situation actually occurs, but at the same time avoiding false warnings.

The operating parameter can be a clamping force. This is typically the force with which brake shoes and/or brake pads are pressed against a brake disk.

The operating parameter can be a spreading force. This is typically the force with which brake pads are pressed against a brake drum.

The operating parameter can be an angular position of an actuator. This can be measured, for example, by an angle sensor.

The operating parameter can be an actuator position of an actuator, for example. The actuator position can be measured by a displacement sensor, for example. This can, for example, be a path by which a spindle of the actuator is displaced.

The operating parameter can be a braking force or a braking torque, for example. These can be braking variables that lead to an actual deceleration in a motor vehicle.

In particular, a manipulated variable can be output to an electric actuator during regulation. In particular, this manipulated variable can result in the electrical actuator behaving in a defined manner. The manipulated variable can, for example, also be used again as an input for further regulation.

The brake can be a disc brake or a drum brake, for example. However, other brakes can also be used.

The invention further relates to a brake arrangement with an electric actuator and a control device, which is configured to carry out a method described herein. With regard to the method, all of the versions and variants described herein can be used. The brake arrangement can in particular also have a brake on which the electric actuator acts.

The invention further relates to a non-transitory computer-readable storage medium on which program code is stored, during the execution of which a processor executes a method described herein. With regard to the method, all of the versions and variants described herein can be used.

• 1: eine Bremsenanordnung,
• 2: einen Zusammenhang zwischen Aktuatorposition und Zuspannkraft,
• 3: eine Spannkraftregelung,
• 4: eine Positionsregelung,
• 5: einen Regelkreis,
• 6: einen funktionalen Zusammenhang,
• 7: ein Ablaufdiagramm,
• 8: ein Ablaufdiagramm,
• 9: ein Ablaufdiagramm, und
• 10: mathematische Zusammenhänge.

The person skilled in the art will derive further features and advantages from the exemplary embodiment described below with reference to the attached drawing. show:

• 1 : a brake assembly,
• 2 : a relationship between actuator position and clamping force,
• 3 : a clamping force control,
• 4 : a position control,
• 5 : a control circuit,
• 6 : a functional connection,
• 7 : a flowchart,
• 8th : a flowchart,
• 9 : a flowchart, and
• 10 : mathematical relationships.

1 shows purely schematically a brake assembly 10 according to an embodiment of the invention.

The brake assembly 10 has an electrically operated brake 15 and a control device 60 .

The electrically actuated brake 15 has an actuator 20 which is designed as an electric motor. The actuator 20 acts on brake shoes 40 via a shaft 30. When actuated, these can act on a brake disk 50, so that a rotation of the brake disk 50 is braked.

A clamping force sensor 45 is assigned to the brake shoes 40 . This measures a currently actually applied clamping force.

The control device 60 is connected both to the actuator 20 and to the clamping force sensor 45 . It can thus control and actuate the actuator 20 . It can also receive the respective measured value measured by the clamping force sensor 45 . In this way, it can regulate the application force, for which purpose a setpoint value for the application force is typically received from a device (not shown), such as a vehicle dynamics control function. In this way, it is also possible to directly implement a braking force request sensed by a manually operated brake pedal.

The control device 60 is furthermore configured to carry out a method according to the invention in accordance with at least one exemplary embodiment. This is discussed in more detail below.

If there is a requirement to apply a defined application force or a defined braking torque, the actuator 20 together with the associated components is moved from an idle position/standby position (see 2 ) moves forward, ie in the direction of application, and sets the required application force. If there is no request or if an existing brake application request is reset (set value = 0), the actuator 20 is transferred or maintained in an unactuated state in which a defined distance from the brake pad to the brake disc (release clearance, release clearance position X _LS ) is maintained by the actuator 20 is set and maintained so that there is no residual braking torque.

Instead of an electromechanical disc brake, an electromechanically actuated drum brake can also be considered, in which the motor/gear unit typically actuates an expanding module that presses the brake pads onto a brake drum with a specified expanding force and thus generates a corresponding braking torque.

Without limiting the generality, the following considerations and the method according to the invention are presented using a disc brake as an example. They can also be easily transferred to an electric drum brake.

As already mentioned above, the main task of the force control of the electromechanical brake 15 is that when there is a force request, the actuator 20 is controlled in such a way that it is moved out of the clearance position or its standby position, overcomes the clearance and sets the requested clamping force for the required braking effect takes place, and this should be done within a defined time and with a defined accuracy. This is usually done using a force controller for clamping force, spreading force or braking torque, depending on which control variable is to be set.

3 shows the basic arrangement, using the example of a clamping force control for a disc brake. Based on a target value F _Sp,Request and a measured application force Fs _p , a manipulated controller variable is calculated, which is used to control a motor that acts on a clamping module via a transmission module.

If there is no force request, then the force is reduced and the movement started and, if necessary, the clearance is adjusted. Since a certain distance from the lining to the disc or drum is set here, this is usually done with a position controller.

4 shows a possible arrangement, using the example of an actuator position control, in which case the setpoint for setting the clearance results from φ _Akt,Request = -(X _LS / v). The parameter v indicates the overall ratio of the gear and clamping module. φ _Act denotes a measured motor angle.

As long as the force and position control of the electromechanical brake meets the tasks and requirements presented in the previous section, it will work correctly. As soon as it no longer meets these requirements, this can be recognized and a warning issued or an appropriate error mode set. This error mode can be, for example, switching off partial functions or the entire function of the electromechanical brake 15 . A possible error reaction can also be an adaptation of the control strategy and parameterization of the higher-level normal braking function and/or driving dynamics control function.

In particular, a monitor function for monitoring the static and dynamic follow-up behavior of the clamping force and actuator position control is described here. The goal is to determine correct operation and to identify faulty operation of the electromechanical brake as early and reliably as possible due to significantly large deviations from an expected behavior to the behavior that is actually present and measured.

In order to provide the monitor function for monitoring the static and dynamic follow-up behavior of the clamping force and actuator position control, the actuator dynamics of the electromechanical brake are mapped according to the invention by a corresponding dynamic approximation model that adequately reflects the static and dynamic behavior of the superimposed control circuit of the electromechanical brake (force or position). accurately describes. The approximation model describes the input/output behavior of the control loop under consideration, e.g. in the form of a differential equation.

The deviation of the measured controlled variable from the value expected on the basis of the approximation model can be compared with a tolerance range for verification, which results from the safety goals and the definition of which deviations are classified as faulty.

A dynamic model with low-pass behavior is proposed here as an approximation model for the position control loop of the actuator control, as is described in 5 is shown. The arrangement specified here basically represents a second-order low-pass behavior, with the minimum and maximum angular velocity being limited. The limiting values n _Akt,Min and n _Akt,Max represent the limiting values or threshold values that are defined in the controlled electromechanical brake 15 as engine speed limiting values. These can be defined as limiting values of a regulation or based on the available engine dynamics. In the 5 The arrangement shown describes the input/output behavior for the monitor function with sufficient accuracy.

If the position control is activated in the actuator control, then the position monitor is also activated. This uses the approximation model to calculate an actual position to be expected at the respective point in time based on the target specification and forms the difference between the position set by the actuator control and the expected position: $$\Delta \mathrm{\phi }={\mathrm{\phi }}_{\text{act}\text{,Exp}}-{\mathrm{\phi }}_{\text{act}}.$$

This difference is then compared with a tolerance range for error-free operation. If this tolerance band is left, then this indicates faulty behavior of the actuator control. So that leaving the tolerance band only for a short time leads to an undesired error reaction, this error reaction is only activated if the difference is permanently outside the currently valid tolerance band for a predefined period of time. When determining the maximum permissible difference, a constant value is not assumed here, but a value ε _Akt dependent on the angular velocity ω _Akt of the model signal is determined. this is in 6 shown as an example. This takes into account that, in the case of rapid changes in the actuator position, larger differences between the measured and expected position are permissible without leading to an error response.

In principle, the tolerance ε _Akt determined in this way can be determined symmetrically for Δφ, ie −ε _Akt ≦Δφ≦ε _Akt . In a further embodiment, a different tolerance threshold is defined for negative values of Δφ than for positive values of Δφ. In this case, the following then applies: -ε _Akt,neg ≤ Δφ ≤ ε _Akt,pos .

The overall arrangement of the monitor function according to the invention for monitoring the static and dynamic subsequent behavior of the actuator position control shows 7 . The function block monitoring for maximum values shown here checks whether the maximum permissible time for leaving the tolerance band has been exceeded. If this is the case, the status of the monitoring function Status _Mon,φ is set to error.

the inside 7 The specified block "position-controlled electromechanical brake" corresponds to the real process to be monitored and is in the basic structure in 4 shown. The block "model position control loop" can be implemented by an arrangement that is shown in the example in 5 is shown.

In a further embodiment, an error counter can be provided for leaving the negative and positive tolerance threshold, so that the error detection also supplies the information about which tolerance threshold led to the error detection.

A monitoring function for a force controller is described below.

If there is a force requirement (e.g. clamping force, spreading force or braking torque) for the electromechanical brake 15, the actuator 20 is controlled in such a way that it is moved out of the clearance position (standby position), the clearance is overcome and the requested clamping force for the required braking effect is applied takes place, whereby this should take place within a defined time and with a defined accuracy. This is usually done using a force controller for clamping force, spreading force or braking torque (depending on which controlled variable is to be set). The defined times and accuracies are determined on the one hand with regard to performance. Thresholds or tolerance bands, which are defined on the basis of performance, can therefore be used in connection with the monitor function to determine performance losses of the electromechanical brake 15 at an early stage and to report them to higher-level systems. On the other hand, these times and accuracies and the tolerance bands derived from them can be defined according to safety criteria, so that safe operation of the entire brake system cannot be guaranteed if these tolerance bands are violated.

If there is a force request and the actuator is activated to set the requested force, the monitor function for the input/output behavior of the force-controlled electromechanical brake 15 is also activated.

An arrangement is used as an approximation model for the force-controlled electromechanical brake 8th suggested. In this case, force requirements are converted into actuator position requirements. The force expected based on the model is calculated using a model for the position control loop (see 5 ) and a model for the relationship between actuator position and clamping force. If there is no force request or if the force request is less than a predefined activation threshold for the force control, then the signal φ _{Akt_1_LS} = -(X _LS / v) is set, so that the setpoint for the model of the position control loop φ _Akt-1,Req is the clearance position results. Otherwise φ _{Akt_1_LS} = 0 and the target value φ _{Akt_1,Req} corresponds to the actuator position that is necessary to set the requested clamping force. Output size according to the arrangement 8th is a value for the expected clamping force and a value for the gradient of the expected force to be determined therefrom. In principle, another one can than the arrangement shown in Figure 7 as an approximation model for describing the static and dynamic behavior of the force-controlled electromechanical brake. The limitation values given here for the engine speed are also the same as in the explanations for 5 was described.

The resulting overall arrangement of the monitor function according to the invention for monitoring the static and dynamic behavior of the force-controlled electromechanical brake when force control is activated shows 9 and corresponds in essential points to the arrangement as in 7 has already been described, except that here a force is the quantity to be observed.

The tolerance band to be determined here advantageously depends both on the force gradient and on the magnitude of the clamping force value to be expected. The higher the force, the larger the tolerance band that can be selected.

10 shows a corresponding arrangement in the form of a block diagram as an example for one of the two module outputs (ε _{F_SP,Pos} and ε _{F_Sp,Neg} ).

In particular, the monitor function for monitoring the static and dynamic follow-up behavior of the clamping force control ( 9 ) and actuator position control ( 7 ) of an electromechanical brake. Depending on the force required, typically only one monitor function is active at a time. The monitor function, which is not active, changes to a passive state with corresponding status information, in which the error counters go into their initialization state or are reset, and the checking of the behavior for compliance with the tolerance bands is deactivated. The simulation of the actuator dynamics ( 5 and 8th ) can always remain active.

By providing the monitor function described for monitoring the static and dynamic subsequent behavior of the clamping force and actuator position control in the form of a dynamic approximation model, the actuator dynamics in the nominal state can be described very well and with sufficient accuracy. The aim is to determine correct operation. Significant deviations in the measured behavior from this nominal state, which indicate incorrect behavior, can thus be detected early and reliably and forwarded to a higher-level system as status information so that appropriate measures can be taken.

Mentioned steps of the method according to the invention can be carried out in the order given. However, they can also be executed in a different order, as far as this is technically reasonable. The method described herein can be carried out in one of its implementations, for example with a specific combination of steps, in such a way that no further steps are carried out. In principle, however, further steps can also be carried out, including those which are not mentioned.

It should be noted that in the claims and in the description features can be described in combination, for example to facilitate understanding, although they can also be used separately. The person skilled in the art recognizes that such features can also be combined independently of one another with other features or combinations of features.

Back-references in dependent claims can identify preferred combinations of the respective features, but do not exclude other combinations of features.

Reference List

10

brake arrangement

15

brake

20

actuator

30

Wave

40

brake shoes

50

brake disc

60

control device

n

thresholds

FSp

clamping force

φact

motor angle

Mact

engine torque

ωAct

angular velocity

ε

Value for defining a tolerance band

Claims (20)

Method for operating an electrically actuated brake (15), the method having the following steps: - receiving a target value for an operating parameter of the brake (15), - adjusting the operating parameter to the target value, - calculating a comparison value for the operation parameters based at least on the setpoint, - measuring a measured value of the operating parameter, - comparing the measured value with the comparison value, and - outputting an error message if the comparison indicates at least one predefined deviation between the measured value and the comparison value. procedure after claim 1 , - where the comparison value is calculated from the target value by means of a dynamic approximation model for the actuator control. procedure after claim 2 , - where the dynamic approximation model is a dynamic model with low-pass behavior. Method according to one of the preceding claims, - wherein for the calculation of the comparison value a variable previously used in the calculation is limited in such a way that it is at least as large as a lower threshold value (n _AktMin ), and/or - wherein for the calculation of the comparison value an in The size previously used in the calculation is limited in such a way that it is at most as large as an upper threshold value (n _AktMax ). procedure after claim 4 - The lower threshold value (n _AktMin ) and/or the upper threshold value (n _AktMax ) being determined on the basis of parameters of the brake (15). Procedure according to one of Claims 4 or 5 , - wherein the variable previously used in the calculation is an angular velocity (ω _Akt ) of an actuator (20). Method according to one of the preceding claims, - whereby the predefined deviation is displayed if the measured value is outside a tolerance band around the comparison value. procedure after claim 7 , - An upper distance between an upper end of the tolerance band and the comparison value and/or a lower distance between a lower end of the tolerance band and the comparison value being calculated on the basis of the comparison value. procedure after claim 8 , - wherein the upper distance and/or the lower distance are calculated based on a derivation of the comparison value. Procedure according to one of Claims 8 or 9 , - where the upper distance and/or the lower distance are calculated higher, the faster the comparison value changes. Method according to one of the preceding claims, - the predefined deviation being displayed only if the deviation persists for a predetermined period of time. Method according to one of the preceding claims, - whereby the error message is only issued if the predefined deviation has been displayed at least as often as a predefined threshold value indicates. Method according to one of the preceding claims, - where the operating parameter is a clamping force (Fsp). Method according to one of the preceding claims, - wherein the operating parameter is a spreading force. Method according to one of the preceding claims, - wherein the operating parameter is an angular position (φ _Akt ) of an actuator (20). Method according to one of the preceding claims, - wherein the operating parameter is an actuator position (X _Akt ) of an actuator (20). Method according to one of the preceding claims, - wherein the operating parameter is a braking force or a braking torque. Method according to one of the preceding claims, - A manipulated variable being output to an electric actuator (20) during regulation. Method according to one of the preceding claims, - wherein the brake (15) is a disc brake or a drum brake. A brake assembly (10) comprising: - an electric actuator (20), and - a control device (60) which is configured to carry out a method according to any one of the preceding claims.

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