Method for monitoring electric brakes and brake mechanism

Abstract

The present invention relates to a method for monitoring an electric brake (15), wherein the basic friction and mechanical efficiency of the brake are determined and, based thereon, the expected residual torque is determined. If the residual torque is at least greater than a threshold value, an error message is output. Additionally, the present invention relates to a related brake mechanism (10).

Description

Technology Field

[0001] The present invention relates to a method for monitoring an electric brake and a related brake mechanism. Background Technology

[0002] Brakes are generally used to decelerate a vehicle in a intended manner. Modern braking systems are often hydraulically or pneumatically operated. However, in the future, electric operation will be increasingly incorporated into brakes.

[0003] A general requirement for automotive brakes is that they must be designed to release upon non-operation, ensuring that no further braking action is taken. This also applies, for example, in cases of power failure where the brakes can no longer be actively released. If the brakes are not released in such situations, the vehicle's response becomes uncontrollable. The problem to be solved

[0004] Accordingly, the object of the present invention is to provide a method for monitoring an electrically operated brake, through which safety can be enhanced, for example, in relation to the release behavior of the brake. Additionally, the object of the present invention is to provide a brake mechanism for implementing such a method. According to the present invention, these objects are achieved by the method and brake mechanism as claimed in each independent claim. Advantageous improvements are, for example, in each dependent claim. The description of the claims is incorporated into the description by explicit reference. means of solving the problem

[0005] The present invention relates to a method for monitoring an electrically operated brake. This method is,

[0006] - Step to check the basic friction of the brake;

[0007] - Step to verify the mechanical efficiency of the brake;

[0008] - A step of determining the expected residual application force based on basic friction and mechanical efficiency; and

[0009] - Step of sending an error message when the residual power is at least as high as the threshold value

[0010] Includes

[0011] In the method just described, the expected residual applied force can be calculated, representing, for example, the residual applied force that can be expected in the event of non-operation due to loss of power. Thus, the brake is generally in a state where it is initially at least partially applied, which is also desirable in principle. For example, if operation is interrupted and the brake cannot be actively switched to a released state because electrical energy can no longer be used to operate the brake, the expected residual applied force is calculated by the above method. In particular, it should be noted that in the latter case, energy can no longer be used to actively release the brake. If the expected residual applied force is calculated to be higher than a threshold value, an error message may be sent, and accordingly, if necessary, additional measures can be taken to ensure the safe operation of the vehicle even in such operating conditions. For example, the error message leads to a warning provided to the driver, and accordingly, the driver may reduce speed or, for example, visit a repair shop.

[0012] Basic friction can be understood, in particular, as the friction that must be overcome to change the operating state of the brake. Mechanical efficiency can be understood, in particular, as the ratio between the force acting on the brake and the force applied by the motor or actuator. The brake may, in particular, be a drum brake or a disc brake, but may also be another type of brake. In particular, the brake may be provided to brake a vehicle, such as, for example, a passenger car or a truck. The expected residual applied force is generally a quantity that is not measured directly but is instead determined based on other verified data—that is, is, generally calculated. Error messages may be used internally, for example, by the brake control unit, or may be transmitted to other components within the vehicle.

[0013] The verification step may be performed occasionally or always, particularly during or after the release of the brake following a service brake request. In particular, part of the method may also be performed during the accumulation of force. This procedure enables continuous monitoring of the brake, so that it is always possible to know whether sufficient release is also guaranteed when a situation arises where the brake must be released.

[0014] In particular, the threshold value can be set so that a force below the threshold value does not lead to vehicle instability. Therefore, this force is an allowable residual applied force. The threshold value may be greater than 0, but may also be 0, which effectively means that an expected residual applied force is not allowed.

[0015] The verification step can be performed occasionally or always, particularly in a separate test cycle. Additionally, this allows the braking force request to be verified independently, for example, to control the brake while it is not being used for braking.

[0016] Such determinations can be performed, in particular, by a deterministic function. For example, a function that specifies the expected residual applied force from a combination of basic friction and mechanical efficiency can be stored accordingly. Such a function may be determined, for example, for a specific brake or a specific brake type.

[0017] This decision may be made by a simulation model according to one embodiment. This simulation model may, for example, simulate specific parameters of a brake and output an expected residual applied force based on input variables. The decision may also be made through a relationship determined by an upstream simulation study.

[0018] The determination of the residual applied force can be performed, in particular, by simulating the operating time, for example, the operating time of an electromechanical brake controller. The determination can also be performed using parameters and dependencies identified from the simulation.

[0019] The determination may be made by an experimentally measured relationship according to one embodiment. Thus, such a relationship may be used for the operating time after it has been experimentally determined for a single brake or a single brake type. In particular, such a relationship may be a previously experimentally measured relationship between residual applied force, mechanical efficiency, and basic friction. Thus, other parameters, such as the parameters described herein, for example, may be considered.

[0020] The residual applied force can be determined, in particular, as the force remaining when the brake is passively released. For example, such passive release may occur in the case of power loss. In such cases, the brake can no longer be actively released. Active release should be understood as, in particular, the active return of the brake shoe or other device, to which the actuator generally operates in the opposite direction compared to the direction required for operation. However, in the case of passive release, the brake no longer operates in the intended manner; it is released only by a mechanically acting force in some way.

[0021] In particular, the brake application force can also be measured. The decision can also be made based on the brake application force. By doing so, the decision can be further improved. The brake application force can be measured, for example, by a force sensor.

[0022] Threshold values ​​may be applied, in particular, depending on the vehicle type and / or driving conditions. Thus, for example, a somewhat higher residual applied force may be allowed for larger and heavier vehicles than for smaller vehicles. Additionally, threshold values ​​may vary depending on driving conditions, for example, speed or load condition, and accordingly, higher threshold values ​​may be allowed in non-critical driving situations if necessary.

[0023] According to one embodiment, the determination is performed only when the brake force applied, measured as a setpoint value or applied, is greater than a threshold value or greater than a lower additional threshold value. As a result, the execution of the method can be largely omitted if only a brake force that is not important in itself is applied in any way. Since a brake force higher than the threshold value is not applied during release, the threshold value of the brake force should not be expected during release. Since the lower additional threshold value may be lower than the threshold value, a specific safety buffer may be provided between the lower additional threshold value and the threshold value.

[0024] According to one embodiment, the determination is performed only when the applied brake force, measured as a setpoint value or applied, is lower than a larger additional threshold value. As a result, if the brake force is somehow too high so that the related release of the brake due to the mechanically acting force can be expected, or if the vehicle is already braked very strongly, for example, stopped in some way, the execution of the method may be largely omitted.

[0025] For example, computing power can be saved by omitting the execution of a method or by omitting a decision.

[0026] The measured brake application force can be measured, in particular, by a force sensor. The brake application force applied as a setpoint value can, in particular, be a brake application force derived as a braking force request from the detected position of the brake pedal, or a brake application force generated by vehicle movement dynamic control or other driving assistance functions capable of generating a braking force request. In particular, the threshold value can be as high as, at most, the brake application level of the released brake that is permissible from the perspective of vehicle movement dynamics. This allows an error message to be reliably transmitted when the expected residual application force is greater than the brake application level permissible from the perspective of vehicle movement dynamics. In this way, an unstable state from the perspective of vehicle movement dynamics can be reliably prevented.

[0027] Basic friction can be determined, in particular, when the brake is in the released state. Here, the friction that must be overcome to operate the brake can be identified.

[0028] The brakes can be disc brakes or drum brakes, in particular. This corresponds to the general design of brakes for passenger cars, trucks, or other vehicles. However, other designs are also possible.

[0029] The base friction can be identified, for example, in a position control test cycle, within the polar position of the brake based on the actuator torque determined in the process. For example, the actuator torque may be used as the base friction, or a predefined relationship between the actuator torque and the base friction may be used. In such cases, sliding adjustment is also possible, for example, as described in other parts of this specification.

[0030] For example, when a brake is applied, mechanical efficiency can be determined based on the brake application force and the compensated actuator torque. The compensated actuator torque may be, for example, the actuator torque minus the acceleration torque. This procedure has proven advantageous for determining mechanical efficiency because it can take into account the effect of the relevant compensated actuator torque on the brake.

[0031] In addition, the present invention relates to a brake mechanism having an electrically actuated brake; and a control device configured to perform a method as described herein. With respect to the method, all embodiments and variations described herein may be referenced.

[0032] Furthermore, the present invention relates to a non-volatile computer-readable storage medium in which program code is stored, wherein, during execution, a processor executes a method as described herein. With respect to the method, all embodiments and variations described herein may be referenced.

[0033] Those skilled in the art will understand other features and advantages through the exemplary embodiments described below with reference to the attached drawings. Brief explanation of the drawing

[0034] Figure 1 illustrates a brake mechanism. Figure 2 illustrates a flowchart. Figure 3 illustrates a diagram for verifying basic friction. Specific details for implementing the invention

[0035] FIG. 1 simply schematically illustrates a brake mechanism (10) according to an exemplary embodiment of the present invention.

[0036] The brake mechanism (10) has an electric brake (15) and a control device (60).

[0037] The electric brake (15) has an actuator (20) designed as an electric motor. The actuator (20) acts on a brake shoe (40) through a shaft (30). When actuated, this brake shoe can act on a brake disc (50), and accordingly, the rotation of the brake disc (50) can be braked.

[0038] An applied force sensor (45) is coupled to the brake shoe (40). This applied force sensor measures the brake applied force that is currently actually applied.

[0039] The control device (60) is connected to both the actuator (20) and the applied force sensor (45). Thus, the control device can activate and operate the actuator (20). The control device can also receive each measurement value measured by the applied force sensor (45). Thus, the control device can control the brake applied force, and for this purpose, the setpoint value for the brake applied force is generally received from a device not shown, such as a vehicle movement dynamic control function, for example. In addition, in this way, a braking force request detected from a manually operated brake pedal can be implemented immediately.

[0040] The control device (60) is also configured to execute the method according to the present invention according to at least one exemplary embodiment. This will be described in more detail below.

[0041] As can be seen, in an electromechanical brake such as the brake (15) shown in FIG. 1, the electromechanical drive train, i.e., the actuator (20), shaft (30), and possibly a rotary-translational motion mechanism (not shown), generally has less than 100% mechanical efficiency and therefore does not guarantee passive “self” release of the brake (15) by design. In addition, mechanical basic friction, which varies depending on the rotational direction of the actuator (20), also has an effect. These two parameters, in particular, depend on the load applied to the components during operation and the lubrication condition of the mechanism / drive components, etc.

[0042] Self-release of the electromechanical brake in a passive state may be a safety concern, as, for example, if power loss occurs when the brake is applied, incomplete release of the brake can lead to vehicle instability. Here, the electromechanical brake, without active assistance by an electric motor within a specific time, has a first brake application level (F) set based on a request. Sp,A A lower (as small as possible) brake application level (F) from ) (at least acceptable from the perspective of vehicle motion dynamics) Sp,B < F Sp,Limit It must be moved to ). Therefore, this description also applies to the case of a braking torque actuator, except that braking torque is considered instead of the applied force level.

[0043] For example, it is proposed to determine characteristic values ​​for diagnosing the expected residual applied force or evaluating the passive self-release function of the brake (15) by determining parameters important to the characteristics of the passive self-release. These parameters are generally at least mechanical efficiency and / or mechanical basic friction, which vary depending on the direction of rotation.

[0044] These parameters are primarily determined during normal operation of the electromechanical brake (15). Here, there is an advantage that no special test or test excitation is required when the brake (15) is in an operating state, and instead, the signal and signal profile measured during normal operation can be used.

[0045] When determining characteristic values ​​for diagnosing residual applied force, in addition to the aforementioned parameters, the initial level (F Sp,A ) can also be considered. The electromechanical actuator applies force level (F Sp,A In the case of ,1), given mechanical efficiency of η = η1 and given basic mechanical friction (M C0+- = M C0. Passive self-release of a device having 1) residual applied force (F Sp,B It causes this residual applied force (F Sp,B ,1)is F Sp,B,Limit If it is smaller, this can be considered acceptable, at least from the perspective of vehicle motion dynamics. A decrease in mechanical efficiency (η < η1) or an increase in basic mechanical friction (M C0+- > M C0. 1) also leads to an increase in the expected residual applied force. Applicable relational equations can be determined, for example, theoretically or in the form of simulation studies.

[0046] Accordingly, in the context of the present invention, the efficiency (η) and basic friction torque (M) confirmed at a given brake application force and during normal operation of the actuator (20) C0+- It is proposed to determine or estimate the possible residual applied force based on the parameters of ).

[0047] Verified parameters and (generally brake application force (F) SpBased on the current applied state (characterized by ), a set residual applied force (F) that occurs when the electromechanical brake fails at this applied force level or after passive self-release Sp,B,Est ) can now be estimated. For this purpose, the necessary relationship F Sp,B,Est = f (F Sp , M C0+- , η) is determined according to each electromechanical brake type and can be obtained, for example, through theoretical or simulation considerations. Depending on the vehicle, the limit value (F), which may vary depending on driving conditions and / or the position of the wheel brake, is a limit value (F). Sp,B,Limit A comparison with ) now provides a corresponding state regarding whether the self-release function is still guaranteed, or whether the brake (15) under consideration failure and the residual applied force expected to be set will lead to a stability critical state in terms of vehicle movement dynamics. In the latter case, appropriate measures, such as warning the driver or preemptive deactivation of the affected brake (15), can be taken in a timely manner.

[0048] An exemplary procedure is illustrated in FIG. 2. Here, the basic friction (M C0+- The parameter of ) is the angular velocity (ω) of the actuator (20). Act ), torque (M) of actuator (20) Act It is determined based on ) and the activation signal ("Enable"). In addition, the parameter of efficiency (η) is determined based on the same input variable and also the brake application force (F Sp It is determined based on ). Subsequently, basic friction (M C0+- ), efficiency (η) and brake application force (F Sp Using ) residual applied force (F Sp,B,Est ) estimates. Subsequently, this is the threshold value (F Sp,B,Limit It is compared with ), and from this, the state of the residual applied force is determined, and this state is Status_F Sp,BIt is designated as such. If this is positive, in other words, the expected residual power (F Sp,B,Est ) is the threshold value (F Sp,B,Limit If it is lower than ), nothing is done anymore. However, if it is higher, an error message is generated to recognize the potentially critical state and respond to it.

[0049] An alternative embodiment of FIG. 2 is such that the currently set applied force exceeds the limit force or threshold value, i.e., F Sp > F Sp,B,Limit and / or, less than the second higher limiting force, i.e., F Sp < F Sp,C Provides that the calculations provided in block "Estimation of Residual Force" are performed only when . For example, F Sp,C The value for is, in the case of an applied force greater than this value, the applied force (F Sp The deformation energy of the caliper and pad (deformed) stored by ) can be selected so that it is always sufficient for the passive self-release of the electromechanical brake.

[0050] Using the described monitoring function, it is possible to check whether the stability threshold function of the self-release of the brake (15) is still guaranteed even in a passive state.

[0051] In this case, the performance of a special test excitation when the brake (15) is in the applied state can be omitted, and the observation of the signal profile during the test excitation can be omitted. Instead, the monitoring function determines parameters (efficiency (η) and basic friction torque (M)) that are determined from the actuator signal and essentially characterize the wear state of the actuator. C0+- It uses knowledge regarding )). Since decisions can be made during and after each braking operation, the estimation related to the function of passive self-release is much more up-to-date than the case of how a special test is executed when the brake is applied.

[0052] Basic friction (M C0+- ) or basic friction value (M C0+ And each M C0- The determination of the friction parameter of ) is explained below. Indicated by M C0+- Here, if both rotation directions are possible, M respectively C0+ and M C0- It can be understood as a placeholder for.

[0053] These markings are, M C0+ represents the component existing with respect to the positive rotation direction, and M C0- It is used to specify a certain component for the negative rotation direction. The positive rotation direction corresponds to applying the brake; the negative rotation direction corresponds to releasing it.

[0054] If there is no request for the electromechanical brake (15) to set a defined force that generates a braking effect, or if the existing force request is reset (set value = 0), the actuator (20) moves to or remains in a non-operating state. In this state, a defined distance (polarity, polarity position (X)) between the brake pad and the brake disc is maintained so that residual braking torque is not generated. LS )) is set and determined by the actuator position maintained by the actuator. As long as the EMB performs movement within the pole, when the motor acceleration (dω / dt) ends, the specified motor torque corresponds to a nearly constant friction torque, especially at slow speeds. The motor torque is the brake application force (F) only when transitioning to non-positive movement. Sp Load torque (M) induced by ) Sp, Load It increases depending on ).

[0055] Accordingly, according to one possible embodiment, after the brake (15) is released, a position control test cycle is performed within a polar position at a slow (especially constant) speed, and a value for static friction (M C0+, M C0- ) is the basic friction coefficient (M C0+ and M C0- It is proposed that the motor torque be determined by evaluation for the purpose of determining the ( ). This test cycle may be executed only when necessary after each release process or at the latest after a time (T) has elapsed. If there is another force request during the test cycle, the cycle is interrupted and the requested force is set.

[0056] To perform a test move, a polar position (X) is set for a move position-controlled by a negative slow motor speed. LS It is performed from ). The value for motor torque recorded in the process is the basic friction (M C0- It is determined by ). Therefore, ω Act The average value of the motor torque recorded at < 0 provides an estimate of the parameters of the underlying friction in the negative direction of movement. For example, during position-controlled movement backward X Target = -2 * X LS If the target value is reached, conversely, the starting point (polar position (X LS Slow motor speed (ω) at )) Act Movement controlled by position with > 0) is performed. Subsequently, basic friction (M C0+ The desired parameter for ) is the motor torque (M) determined during this partial movement Act The average value of )(ω Act It is obtained by > 0). In one embodiment, this determination may also be performed only within a predefined band, which is defined by a specific distance from the start and end positions of the test movement. This is illustrated more specifically in FIG. 3. Here, the actuator position (X Sp The bands following ) are indicated in both directions by narrow horizontal rectangles, specifically by positive actuator torque (positive angular velocity) and negative actuator torque (negative angular velocity).

[0057] MC0+ and M C0- Regarding this, the value determined in this manner is not immediately adopted at 100%, but instead may be provided to be adjusted by a weighting factor. Therefore, whenever it is recalculated, this value may be multiplied by a weighting factor, and the previous value (multiplied by the value obtained by subtracting the weighting factor from 1) may be added to it.

[0058] The determination of the friction parameter efficiency (μ or η) is explained below.

[0059] To determine efficiency, the starting point used is a simplified model of the actuator dynamics of an electromechanical brake in the form of the following differential equation:

[0060] M Act = J Ges * d(ω Act ) / dt + i (-1) *F Sp (X Sp ) * (1+μ * sign (ω Act )) + M C0+- * sign ω Act )

[0061] For further simplification, the positive direction of movement (ω Act > 0 -> F Gradient Only when > 0) is considered, the following simplified mathematical formula is obtained for such cases:

[0062] M Act - J Ges * d (ω Act ) / dt = i (-1) *F Sp * (1+μ) + M C0+

[0063] Torque compensated by the influence of acceleration torque

[0064] M Act,Comp = M Act - J Ges * d (ω Act ) / dt

[0065] If is defined, positive direction of movement (ω Act > 0 -> F Gradient For > 0), it is maintained as follows:

[0066] M Act,Comp = i (-1) *F Sp * (1+μ) + M C0+

[0067] To determine the parameter (μ) representing the influence of mechanical efficiency, the signal brake application force (F Sp ) and motor torque or compensated motor torque (M Act,Comp It is suggested that ) be recorded during the movement of the actuator (20)'s power accumulation.

[0068] A defined force sample point can be defined.

[0069] During the force accumulation phase, the first exceeded force sample point value (F Sp,i If ) is clearly identified, the compensated motor torque (M) associated with these force values Act, Comp,Measure, i ) can be stored.

[0070] If a specified minimum force and a sufficient number of sample points are recorded, the current parameter (μ) can be determined, for example, by minimizing the quadratic quality criterion:

[0071] Σ (M Act,comp,i - (i (-1) *F Sp,i * (1+μ) + M C0+ ))² -> minimum

[0072] Value for basic friction (M C0+ Since ) is known or predetermined (see Fig. 3), the decision equation:

[0073] μ Est = (Σ M Act,comp,i - Σ M C0+ - Σ i (-1) *F Sp,i ) / (Σ i(-1)*F Sp,i )

[0074] This is obtained for the desired parameter. Here, in addition, to increase robustness, the parameter determined accordingly is adjusted by a weighting factor (ß1):

[0075] μ Mod,New = ß1* μ Est + (1 - ß1) * μ Mod,Old

[0076] Next, the following is obtained regarding mechanical efficiency:

[0077] η Est,New = (1 + μ Est,New ) -1

[0078] In order to determine the dynamic reserve in the direction of force accumulation, the friction parameter (M) identified in the context of the present invention C0+- and η or μ) are parameters of an electromechanical brake that indicate the state of the mechanism (especially the state of wear).

[0079] The steps of the method according to the present invention described may be executed in a specific order. However, if technically feasible, such steps may be executed in a different order. For example, in one embodiment having a specific set of steps, the method according to the present invention may be executed in such a manner that additional steps are not executed. However, in principle, additional steps, even unmentioned steps, may be executed.

[0080] It should be noted that although features may be used individually, they may be described in combination, for example, in the claims and detailed description, for the sake of understanding. Those skilled in the art will understand that such features may also be individually combined with other features or combinations of features.

[0081] References to dependency in dependent terms may characterize a desirable combination of each feature, but do not exclude combinations of other features. Explanation of the symbols

[0082] 10 Brake mechanism 15 brakes 20 actuators 30 shafts 40 brake shoes 50 brake disc 60 control unit η efficiency F Sp,B,Limit threshold value F Sp Brake application force M C0+- Basic friction torque F Sp,B,Est Expected remaining authorization Status_F Sp,B situation M Act Motor Torque ω Act Angular velocity

Claims

Claim 1 As a method for monitoring an electric brake (15), - the basic friction (M) of the brake (15) C0+- A step of verifying ) - A step of verifying the mechanical efficiency (η) of the brake (15), which is the ratio between the force acting on the brake disc (50) of the brake (15) from the brake shoe (40) of the brake (15) and the force applied by the motor or actuator of the brake (15); - The basic friction (M C0+- Expected residual applied force (F) remaining between the brake shoe (40) and the brake disc (50) when the brake shoe (40) cannot be actively switched to a released state based on the above mechanical efficiency (η). Sp,B,Est A step of determining ); and- the residual applied force (F Sp,B,Est ) is at least the threshold value (F Sp,B,Limit A method including the step of sending an error message when the value is as high as ). Claim 2 In paragraph 1, the verification step is performed occasionally or always during or after the release of the brake (15) in response to a service brake request. Claim 3 In paragraph 1, the verification step is performed occasionally or always in a separate test cycle, a method. Claim 4 In paragraph 1, - the above determination is performed by a deterministic function, a method. Claim 5 In paragraph 1, the above decision is performed by a simulation model. Claim 6 In paragraph 1, the above determination is performed by a method based on an experimentally measured relationship. Claim 7 In paragraph 1, - the above residual applied force (F Sp,B,Est ) is a method determined as the remaining force when the brake (15) is passively released. Claim 8 In paragraph 1, - brake application force (F Sp ) is also measured, and- the above decision is also the brake application force (F Sp A method performed based on ). Claim 9 In paragraph 1, - the above threshold value (F Sp,B,Limit ) is a method that is applied depending on the vehicle type and / or driving conditions. Claim 10 In paragraph 1, - the above determination is a brake applied force (F) measured or applied as a setpoint value. Sp ) is the above threshold value (F Sp,B,Limit A method performed only when greater than ) or greater than an additional lower threshold value. Claim 11 In paragraph 1, - the above determination is a brake applied force (F) measured or applied as a setpoint value. Sp A method performed only when ) is lower than a larger additional threshold value. Claim 12 In paragraph 1, - the above threshold value (F Sp,B,Limit ) is, to the maximum, a method as high as the brake application level of the released brake (15) that is permissible in terms of vehicle movement dynamics. Claim 13 In paragraph 1, - the above basic friction (M C0+- ) is a method determined when the above brake (15) is in a released state. Claim 14 In claim 1, the method wherein the brake (15) is a disc brake (15) or a drum brake (15). Claim 15 A brake mechanism (10) comprising: an electric brake (15); and a control device (60) configured to perform the method claimed in any one of claims 1 to 14.

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