Brake actuator for rail vehicle, computer-implemented method, computer program, non-volatile data carrier and brake system

Abstract

In a rail vehicle (100), a brake actuator (120) receives a braking command (BC) specifying a target force. In response to the brake command (BC), the brake actuator (120) controls an electrically operated brake unit (130) to perform a brake operation. The brake actuator comprises a control unit that generates a brake control signal (BS) based on the brake command (BC). The brake control signal (BS) in turn controls an electric motor (131) in the electrically operated brake unit (130) such that an output shaft of the electric motor (131) reaches a specified angular position (P) in which at least one pressing member (135) is caused to exert a force on a rotating member (136) mechanically connected to an axle (141) of the rail vehicle (100). The control unit also obtains a first sensor signal and a second sensor signal (Pm, FS). The first sensor signal (Pm) reflects a measured position of the output shaft of the motor (131), which measured position constitutes an indication of the specified angular position (P). The second sensor signal (FS) reflects the magnitude of the applied force. The control unit checks the second sensor signal (FS) against a force-to-position mapping describing a linear relationship between the specified angular position (P) and an estimated magnitude of the applied force. Thus, the control unit can verify the relationship between the specified angular position (P) and the estimated value.

Description

TECHNICAL FIELD

[0001] The present invention relates generally to the deceleration of a rail vehicle. In particular, the present invention relates to a brake actuator according to the preamble of claim 1. The present invention also relates to a computer-implemented method performed by a control unit of the brake actuator, a computer program and a non-transitory data carrier storing such a computer program. Furthermore, the present invention relates to a brake system comprising the proposed brake actuator. BACKGROUND

[0002] The brake system of a rail vehicle is used to decelerate the rail vehicle and is also generally used to implement a parking brake function. Typically, the same brakes are used both for parking service and for emergency braking. Of course, for all braking functions, it is of utmost importance that the brake system does not fail or malfunction.

[0003] Today's rail vehicles often use compressed air for regulation, which is referred to as a pneumatically regulated brake. One disadvantage of such pneumatically regulated brakes is that they cannot be regulated quickly. More importantly, air leaks in a pneumatic brake system pose a risk of a severe reduction in braking capacity. Therefore, in addition to safety reasons, various electrically controlled brake systems have started to appear on the market.

[0004] US 2020 / 0198605 shows a microcomputer-controlled electromechanical brake system comprising an electromechanical brake control device and an electromechanical brake unit. The electromechanical brake control device comprises a brake microcomputer control unit, an electromechanical control unit and a backup power module. The brake microcomputer control unit receives brake instruction signals sent by a driver or an automatic driving system, performs target braking force calculation and brake management, and at the same time can communicate with the brake microcomputer control units of other vehicles in the train set.

[0005] While generally, electromechanical brake systems can be controlled substantially faster than pneumatic brake systems, there is still room for improvement in the response time of today's electromechanical brake solutions. For example, it must be ensured that wear of brake pads and / or brake discs does not affect the functionality of the brake system. SUMMARY

[0006] It is therefore an object of the present invention to provide a solution that alleviates the above-mentioned problems and makes the electromechanical brake system of a rail vehicle less sensitive to various forms of wear on the components of the system.

[0007] According to an aspect of the present invention, the object is achieved by a brake actuator for a rail vehicle, the brake actuator being configured to receive a brake command and to control an electrically operated brake unit to perform a braking operation in response to the brake command. The brake actuator comprises a control unit configured to generate a brake control signal based on the brake command. The brake control signal is in turn adapted to control an electric motor in the electrically operated brake unit such that an output shaft of the electric motor reaches a specified angular position, wherein at the specified angular position a force is caused to be exerted by at least one pressing member on a rotating member mechanically connected to an axle of the rail vehicle. The exerted force has a setpoint in the form of a target force specified by the brake command. The control unit is further configured to obtain a first sensor signal reflecting a measured position of the output shaft of the electric motor, which measured position constitutes an indication of the specified angular position.

[0008] The control unit is further configured to obtain a second sensor signal reflecting a magnitude of the exerted force and to check the second sensor signal against a force-to-position map describing a linear relationship between the specified angular position and an estimated magnitude of the exerted force.

[0009] The above brake actuator is advantageous in that, in addition to being able to control the at least one pressing member based on the first sensor signal only, it also detects any deviation between an actual relationship between the specified angular position and the exerted force and an expected relationship. Thus, a consistent braking quality can be guaranteed.

[0010] According to one embodiment of this aspect of the present invention, the control unit is configured to check the second sensor signal against the force-to-position map for at least two angular test positions. If, for the at least two angular test positions, respective magnitudes of the force reflected by the sensor signal are shifted with respect to a set of forces given by the force-to-position map by respective amounts of shift satisfying a similarity criterion with respect to each other, the control unit is further configured to adjust a reference position for the force-to-position map to match the respective at least two test angular positions. Thus, for example, systematic shifts in the force-to-position relationship due to wear of the brake pads and / or brake disc can be compensated in a straightforward manner.

[0011] According to another embodiment of this aspect of the present invention, the control unit is configured to check, while the output shaft of the electric motor causes the exerted force, whether the second sensor signal satisfies a stability criterion during a test period. If the stability criterion is satisfied, the control unit is further configured to obtain, after expiration of the test period, a magnitude of the force reflected by the sensor signal to represent one of the at least two angular test positions. Thereby, the braking function can be calibrated on the fly, i.e. during an ongoing braking operation. This is both efficient and convenient, of course.

[0012] Preferably, the control unit is configured to generate the brake control signal until the first sensor signal reaches a value indicative that the estimated target force has been reached. For example, the electric motor can be a brushless DC motor and the brake control signal can be a drive current to the electric motor, which is generated until the specified angular position and the target force have been reached. Thus, the brake unit can be operated in a very simple way.

[0013] According to yet another embodiment of this aspect of the application, the control unit is configured to wait for the second sensor signal FS to be checked against the force-to-position mapping until after it has been obtained via the first sensor signal that the specified angular position has been reached. That is, this reduces the verification time and thus involves a minimum latency.

[0014] According to another embodiment of this aspect of the application, the force-to-position mapping reflects an expected delay between generating the brake control signal and obtaining the second sensor signal. Thereby, the electric motor can be controlled to a position where the target force is applied even faster. Here, it is assumed that the delay is introduced by the inertia of the electric motor itself and / or at least one component included in a control loop for the electric motor, which is arranged between the control unit and the electric motor.

[0015] The control loop may, for example, contain a drive unit configured to generate a drive current to the electric motor based on the brake control signal. Alternatively or additionally, the control loop can protect a filter unit configured to obtain an unfiltered sensor signal, for example, from the above-mentioned absolute encoder and to generate the second sensor signal as a low-pass filtered version of the unfiltered sensor signal in response to the unfiltered sensor signal. This is beneficial because it can reduce noise and make the design less sensitive to movements such as in the form of rumble and jitter.

[0016] According to another embodiment of this aspect of the application, the control unit is configured to generate an alarm if, for the specified angular position, the second sensor signal reflects that the applied force is outside the hysteresis margin of said linear relationship. That is, this indicates that there is an abnormal situation that should be attended to.

[0017] According to another embodiment of this aspect of the application, the brake actuator is configured to receive a brake command from a brake controller, which in turn is configured to send the brake command to at least one further brake actuator in the rail vehicle. Thus, it is not complicated to incorporate the control unit into the brake system of the rail vehicle.

[0018] According to one embodiment of this aspect of the application, the control unit is configured to obtain, during the control of the electric motor towards the specified angular position, a third sensor signal reflecting the drive current to the electric motor, wherein at the specified angular position the at least one pressing member is caused to exert the target force on the rotating member. If, during the control, the third sensor signal exceeds a current threshold level, the control unit is further configured to generate a current alarm indicating that an excessive drive current is fed to the electric motor. That is, an excessive drive current is indicative of that the electric motor experiences an unexpectedly high mechanical resistance and / or that the electric motor itself exhibits a faulty electrical characteristic.

[0019] Preferably, in order to improve reliability, the brake actuator is configured to low-pass filter the third sensor signal before determining whether the third sensor signal exceeds the current threshold level.

[0020] According to another aspect of the application, the object is achieved by a computer-implemented method for controlling an electrically operated brake unit in a railway vehicle, the method being executed in a processing unit of a control unit in the proposed brake actuator. The method involves receiving a brake command, and controlling the electrically operated brake unit to perform a braking operation in response to the brake command. In particular, the method involves generating a brake control signal based on the brake command. The brake control signal is adapted to control an electric motor in the electrically operated brake unit such that an output shaft of the electric motor reaches a specified angular position, wherein at the specified angular position the at least one pressing member is caused to exert a force on a rotating member mechanically connected to an axle of the railway vehicle. The exerted force has a setpoint in the form of a target force specified by the brake command. The method further involves obtaining a first sensor signal reflecting a measured position of the output shaft of the electric motor, the measured position constituting an indication of the specified angular position; and obtaining a second sensor signal reflecting a magnitude of the exerted force. Furthermore, the method involves checking the second sensor signal against a force-to-position mapping, the force-to-position mapping describing a linear relationship between the specified angular position and an estimated magnitude of the exerted force. The advantages of the method, as well as its preferred embodiments, will be apparent from the above discussion with reference to the proposed brake controller.

[0021] According to yet another aspect of the application, the object is achieved by a computer program loadable into a non-volatile data carrier communicatively connected to a processing unit. The computer program comprises software for executing the above-mentioned method when the program is run on the processing unit.

[0022] According to another aspect of the application, the object is achieved by a non-volatile data carrier containing the above-mentioned computer program.

[0023] According to another aspect of the present invention, the object is achieved by a brake system for a rail vehicle. The brake system comprises an electrically operated brake unit configured to perform a braking operation. The brake system further comprises the brake actuator proposed above, which is arranged to control the electrically operated brake unit. The above-mentioned brake system is advantageous for the same reasons as presented above in relation to the brake actuator.

[0024] According to one embodiment of this aspect of the present invention, the electrically operated brake unit comprises at least one pressing member and a rotating member mechanically connected to an axle of the rail vehicle. The electrically operated brake unit further comprises an electric motor configured to receive a brake control signal generated by the brake actuator. The electric motor in turn comprises an output shaft configured to reach a specified angular position in response to the control signal. The specified angular position causes the at least one pressing member to exert a target force on the rotating member. Thereby, various braking operations can be implemented efficiently and reliably.

[0025] According to another embodiment of this aspect of the present invention, the brake system comprises a Hall sensor and / or an absolute encoder configured to generate a first sensor signal. Thereby, the measured position of the output shaft of the electric motor can be conveniently reflected via the first sensor signal.

[0026] According to another embodiment of this aspect of the present invention, the brake system comprises a drive unit configured to generate a drive current to the electric motor based on the brake control signal. This allows for a direct control of the at least one pressing member of the brake unit.

[0027] According to yet another embodiment of this aspect of the present invention, the brake system comprises a load cell, e.g. arranged in a gear shaft mechanism between the electric motor and the at least one pressing member, configured to generate an unfiltered sensor signal reflecting a magnitude of the force exerted by the at least one pressing member on the rotating member.

[0028] Preferably, the brake system further comprises a filter unit configured to obtain the unfiltered sensor signal from the load cell and to generate a second sensor signal as a low-pass filtered version of the unfiltered sensor signal in response to the unfiltered sensor signal. This reduces noise in the load cell signal and makes the design less sensitive to movements such as in the form of rumble and jitter.

[0029] According to a further embodiment of this aspect of the application, if for a specified angular position the second sensor signal reflects that the applied force is outside the hysteresis margin of said linear relationship, the alarm generated by the control unit is indicative of an error of the load cell, an encoder error, a mechanical failure, an electrical error and / or a wear of at least one pressing member. Thus, based on the alarm, appropriate troubleshooting can be initiated.

[0030] Further advantages, beneficial features and applications of the application will become apparent from the following description and the dependent claims. BRIEF DESCRIPTION OF DRAWINGS

[0031] The application will now be explained in more detail by means of preferred embodiments disclosed by way of example and with reference to the accompanying drawings.

[0032] Figure 1 schematically illustrating a braking system according to an embodiment of the application; Figure 2 showing a graph illustrating how a force-to-position mapping describing a relationship between a specified angular position and a magnitude of force applied by at least one pressing member can be derived; Figure 3 illustrating how a braking unit according to an embodiment of the application can be controlled using a force-to-position mapping of the form Figure 2 ; Figure 4 showing a graph of a linear relationship between a specified angular position and a magnitude of force applied by said at least one pressing member together with a second sensor signal; Figure 5 showing a graph illustrating test periods during which a brake actuator according to an embodiment of the application can be calibrated; Figures 6a to 6b showing a graph illustrating an example of a drive current to an electric motor as a function of time together with a graph showing a magnitude of force applied by said at least one pressing member; Figure 7 showing a block diagram of a brake actuator according to an embodiment of the application; and Figure 8 illustrating a general method according to the application by means of a flow chart; Figure 9 illustrating a method according to an embodiment of the application by means of a flow chart; Figures 10a to 10b showing a graph illustrating a force applied by said at least one pressing member and a speed demand to an electric motor as a function of time, respectively, according to an embodiment of the application; Figure 11It is illustrated how a force-to-position mapping can be used to verify the control of the at least one pressing member during operation of the brake unit according to one embodiment of the present application; and Figure 12 A method for determining whether a target position of a brake operation has been reached according to one embodiment of the present application is illustrated by means of a flow chart. DETAILED DESCRIPTION

[0033] In Figure 1 Fig. 1 we see a schematic illustration of a brake system according to one embodiment of the present application.

[0034] The brake system can comprise at least one brake controller 110 and a plurality of electrically operated brake units 130, each electrically operated brake unit being operated by a respective brake actuator 120. The brake actuator 120 is configured to receive a brake command BC (e.g. from the brake controller 110) and to control the electrically operated brake unit 130 to perform a brake operation in response to the brake command BC. The brake operation typically involves applying a target force specified by the brake command BC. However, of course, according to the present application, the brake operation can also involve releasing the brake or reducing an already applied brake force.

[0035] The brake command BC can in turn be generated based on a brake instruction BI from a train driver and / or automatic functionality comprised in the rail vehicle 100 comprising the brake system. The brake instruction BI can be forwarded to the brake controller 110 via a data bus 105 in the rail vehicle 100.

[0036] According to one embodiment of the present application, the brake controller 110 is configured to send the brake command BCx to at least one additional brake actuator in the rail vehicle 100. That is, typically, in a rail vehicle brake system, each brake controller 110 is arranged to control two or more brake controllers in e.g. one rail vehicle.

[0037] According to the present application, the brake actuator 120 comprises a control unit 700 (see Figure 7 ) configured to generate a brake control signal BS based on the brake command BC. The brake control signal BS is adapted to control an electric motor 131 in the electrically operated brake unit 130 such that an output shaft of the electric motor 131 reaches a specified angular position, wherein at the specified angular position the at least one pressing member 135 of the brake unit 130 is caused to exert a target force on a rotating member 136 of the brake unit 130, e.g. via a gear shaft mechanism. The rotating member 136 is mechanically connected to a wheel axle 141 of the rail vehicle 100. Thus, the brake force exerted by the at least one pressing member 135 on the rotating member 136 affects any rotation of said wheel axle 141.

[0038] According to one embodiment of the application, the electric motor 131 is a brushless DC motor. This type of motor is advantageous in that it enables high torque and high precision in a relatively small size format. For example, a brushless DC motor can operate at approximately 3000 rpm, which guarantees rapid control of the at least one pressing member 135.

[0039] The control unit 700 is further configured to obtain a first sensor signal P m reflecting a measured position of an output shaft of the electric motor 131, e.g. via an absolute encoder 132 producing universally present angle data in a digital format, which measured position is indicative of a specified angular position. Alternatively or additionally, the first sensor signal P m may be produced by a Hall sensor included in the electric motor 131. However, a Hall sensor is typically less sensitive and slightly slower than an absolute encoder. Since there is a fixed mechanical relationship between the specified angular position and the force exerted by the at least one pressing member 135 onto the rotating member 136, the first sensor signal P m also constitutes an indication of the target force. These issues will be discussed in further detail below with reference to Figures 2 to 11 .

[0040] According to one embodiment of the application, the control unit 700 is configured to generate a brake control signal BS until the first sensor signal P m reaches a value indicative of that the estimated target force F T has been reached.

[0041] As Figure 7 illustrated, according to one embodiment of the application, the brake actuator 120 can comprise a drive unit 710 configured to generate a drive current I ctrl based on the brake control signal BS, which drive current I ctrl is adapted to control the electric motor 131 such that its output shaft is rotated in a desired direction, thereby moving the at least one pressing member 135 towards or away from the rotating member 136.

[0042] Figure 2 A graph illustrating how the force F(P) exerted by the at least one pressing member 135 onto the rotating member 136 varies with the angular position P of the rotating shaft of the electric motor 131 is shown. According to the application, Figure 2 the illustrated relationship is used for controlling the electric motor 131.

[0043] For each of a set of angular positions P, a respective force F(P) exerted onto the rotating member 136 is recorded, e.g. by a load cell, and plotted as a function of the angular position P. Figure 2Examples of data points 21, 22, ..., 2(n-1) and 2n for this set of angular positions P are given. It can be seen that the relationship between the angular position P and the corresponding force F(P) is as follows, except for the angular position P. C The surrounding area is almost perfectly linear, and at this angular position, at least one pressing member 135 begins to contact the rotating member 136. Therefore, preferably, the contact angular position P is ignored. C The surrounding force F(P) is measured. Conversely, a linear function based on the measurement of the position of at least one pressing member 135 when it is in close contact with the rotating member 136 is extrapolated to the intersection with the axis P in order to determine the contact angle position P. C From P=0 to P=P C The distance can be represented by the so-called idling distance d. idle That is, after at least one pressing member 135 has been arranged to allow the shaft 141 to rotate freely, when the control braking unit 130 initiates a braking action, the distance covered by the at least one pressing member from its starting position to the rotating member 136.

[0044] The linear force-to-position relationship described above is mapped such that for any given force F(P), there exists a corresponding angular position P. Therefore, to obtain a specific force F(P), it is only necessary to control at least one pressing member 135 to a certain angular position P; that is, no feedback regarding the measurement of force F(P) is required during the control process. This makes the control process extremely fast, which in turn translates into a short braking distance.

[0045] In other words, such as Figure 3 As shown in the diagram, the proposed control principle relies on the target force F specified by the braking command BC. T The specified angular position P of the output shaft of motor 131 set The clear relationship between them makes the target force F T It can be reached from a specified angle position P set The output shaft of the motor 131 reaches [the desired output].

[0046] However, due to wear on at least one pressing member 135 and rotating member 136, the force-to-position mapping must be repeatedly updated / recalibrated during operation of the braking system. Preferably, the force-to-position mapping is reset to zero after the rail vehicle 100 is put into operation following a period of inactivity (e.g., at the start of each shift). This means determining the contact angle position P. C And set the desired idling distance d idle For example, as described above.

[0047] Additionally or alternatively, according to one embodiment of the present application, a calibration rod or similar tool having precisely known physical dimensions can be employed to acquire an explicit reference point for the force-to-position mapping. Preferably, at service occasions, e.g. in relation to brake pad and / or brake disc replacement, a technician can adjust the at least one pressing member 135, e.g. represented by a pair of calipers, relative to the rotating member 136 such that the at least one pressing member 135 and the rotating member 136 achieve a known physical relationship with each other. For example, the calibration rod can be fitted between a first standardized position and a second standardized position inside the pair of calipers to define a known physical relationship that serves as an explicit reference point for the force-to-position mapping. Once the force-to-position mapping has been zeroed using the calibration rod, any adjustment of the at least one pressing member 135 from the original position is preferably recorded such that the control unit 700 can keep track of the precise physical relationship between the at least one pressing member 135 and the rotating member 135 until a subsequent service occasion.

[0048] Furthermore, at repeated occasions during operation, e.g. every nth braking, the control unit 700 is configured to verify that the force-to-position mapping is accurate by obtaining feedback data relating to the actual force applied by the at least one pressing member 135 on the rotating member 136. Thus, according to the present application, the control unit 700 is configured to obtain a first sensor signal P m reflecting a measured position of an output shaft of the electric motor 131, which measured position constitutes an indication of a specified angular position P. The control unit 700 is further configured to obtain a second sensor signal FS reflecting a magnitude of the force applied by the at least one pressing member 135 on the rotating member 136. For example, a load cell 133 located in a gear shaft mechanism between the electric motor 131 and the at least one pressing member 135 can be configured to generate the second sensor signal FS. The control unit 700 is further configured to check the second sensor signal FS against the force-to-position mapping, which force-to-position mapping describes a linear relationship between the specified angular position P and an estimated magnitude of the force applied by the at least one pressing member 135 on the rotating member 136.

[0049] Figure 4 A graph illustrating the linear relationship between the specified angular position P and the magnitude of the force F(P) applied by the at least one pressing member 135 is shown together with the second sensor signal FS. According to one embodiment of the present application, the control unit 700 is configured to check the second sensor signal FS against the linear relationship for at least two angular test positions (at Figure 4The control unit 700 is configured to adjust the reference position P of the force-to- position mapping in response to a comparison of the second sensor signal FS against the force-to-position mapping. If, for at least two angular test positions P1 and P2, respective magnitudes of forces F1'and F2' reflected by the sensor signal FS are displaced with respect to a set of forces F1 and F2 respectively given by the force-to-position mapping by respective amounts of displacement AF satisfying a similarity criterion with respect to each other, the control unit 700 is configured to adjust the reference position P of the force-to-position mapping C , to respectively match the at least two test angular positions P1 and P2. Thus, by simply adjusting the idle distance d idle by an amount of displacement equal to the contact angular position P C , the contact angular position P C may be adjusted in a straightforward manner to compensate for wear on the at least one pressing member 135 and / or the rotating member 136. Of course, minor variations from the force-to-position mapping must be accepted without the need to perform any modifications. This will be discussed below with reference to Fig. 10.

[0050] In order to avoid introducing a delay into the control process, the control unit 700 is preferably configured to wait for the comparison of the second sensor signal FS against the force-to-position mapping until an indication has been obtained via the first sensor signal P m that the specified angular position P has been reached and thus also an indication that the target force F T has been reached.

[0051] Figure 5 A graph illustrating how the second sensor signal FS can vary over time t during braking is shown. According to one embodiment of the present application, the control unit 700 is configured to obtain the second sensor signal FS while the output shaft of the electric motor 131 causes the at least one pressing member 135 to exert a force on the rotating member 136. In particular, the control unit 700 compares whether the second sensor signal FS satisfies a stability criterion during a test period TS, e.g. only varies within a small range of values. If the stability criterion is satisfied, the control unit 700 is further configured to obtain a magnitude of force reflected by the sensor signal FS to represent one of the above-mentioned angular test positions, after the test period TS has expired.

[0052] In Figure 5 , a first test period TS expires at a first point in time t1; at which a first magnitude FS1 of force reflected by the sensor signal FS is measured; and a second test period TS expires at a second point in time t2; at which a second magnitude FS2 of force reflected by the sensor signal FS is measured. Thus, the first and second magnitudes FS1 and FS2 respectively constitute examples of two angular test positions P1 and P2, which can be Online measured, i.e. during operation of the brake actuator 120.

[0053] Reference is now made to Figure 11 Fig. 1, which shows a first graph 1101 illustrating the relationship between the applied force F(P) reflected by the acceptable second sensor signal FS, and a second graph 1102 illustrating the relationship between the applied force F(P) reflected by the second sensor signal FS when the second graph 1102 falls below the lower threshold level L th The control unit 700 is configured to generate an alarm A if the second sensor signal FS reflects an applied force F(P) outside the hysteresis margin H at a point in time t A The second sensor signal FS reflecting the applied force F(P) generating the alarm A.

[0054] As mentioned above, slight variations from the mapping of force to position must be accepted without any modification of the mapping being performed. For example, random errors of the first sensor signal P m (e.g. caused by rounding errors in the absolute encoder 132) will cause fluctuations to occur when the at least one pressing member 135 is pressed against the rotating member 136, the electric motor 131 will temporarily slip and / or stall. Alternatively or additionally, extreme temperature variations and / or poor lubrication of moving parts in the brake unit can cause unpredictable variations of the first sensor signal P m Thus, the control unit 700 is preferably configured to accept variations of a hysteresis margin H around the linear relationship expressed by the mapping of force to position. The hysteresis margin H can be defined as a band between the upper threshold level U th and the lower threshold level L th and accordingly below the linear function describing the variation of the applied force F(P) with the angular position P, as shown in Figure 11 .

[0055] According to one embodiment of the present application, the control unit 700 is configured to generate an alarm A if, for a given angular position P, the second sensor signal FS reflects an applied force F(P) outside the hysteresis margin H.

[0056] Depending on how the hysteresis margin H is broken, the alarm A can be supplemented with additional data, such as data indicating errors of the load cell 133, errors of the absolute encoder, mechanical faults (e.g. faults in the at least one pressing member 135 or the gear shaft mechanism), electrical faults, and wear of the at least one pressing member 135 and / or the rotating member 136.

[0057] Figure 6a Fig. 1 shows a graph illustrating how the drive current I ctrl to the electric motor 131 can vary over time t. The graph also shows how the magnitude of the force FS applied by the at least one pressing member 135 can vary over time in response to the drive current I ctrl Typically, the drive current Ictrl around an increasing average value. Thus, the graph also shows this average value in the form of a low-pass filtered version I ctrl of the drive current I LP .

[0058] In the example shown in Figure 6a , we assume that a brake command BC is received at a time point t0. In response to the command BC, a brake control signal BS is generated as a drive current I ctrl to the electric motor 131, which in turn moves the at least one pressing member 135 towards the rotating member 136. At a time point t C , the at least one pressing member 135 contacts the rotating member 136 and the force FS applied to the rotating member starts to increase. At a time point t M , the force FS reaches a maximum value and even if the drive current I ctrl is further increased, the force tends to level off. For safety reasons, the drive current I ctrl is limited to at least a first threshold current I LIMIT1 , e.g. temporarily. Preferably, to mitigate stress on the electric motor 131, the drive current I ctrl is lowered to a second threshold current I LIMIT2 if, after a test period, the force FS specified by the brake command BC has still not been met.

[0059] Figure 6b shows a graph similar to the graph of Figure 6a . Here, we assume that the brake command BC specifies that the force FS applied by the at least one pressing member 135 should have a setpoint in the form of a target force F T as shown in the figure. The brake command BC is received at a time point t0; and thus, a low-pass filtered version I ctrl of the drive current I LP rises gradually. However, the increase in the drive current I ctrl is larger than expected I EXP , and already at a time point t A , and before the target force F T is reached, a maximum allowed current level I MAX is reached.

[0060] If the electric motor 131 responds to the drive current I ctrl as expected, it is predicted that the target force F E should be reached at a time point t T , which can or can not be earlier than the above-mentioned time point t M . However, by the time the maximum allowed current level I MAXSetting to a suitable value can avoid unnecessary and potentially harmful mechanical and / or electrical stress to the electric motor 131.

[0061] Thus, according to one embodiment of the application, during controlling the electric motor 131 towards the specified angular position P at which the at least one pressing member 135 exerts the target force F T on the rotating member 136, the control unit 700 is configured to obtain a third sensor signal reflecting the driving current I ctrl to the electric motor 131. If the third sensor signal exceeds a current threshold level I MAX , the control unit 700 is configured to generate a current alarm indicating that the excessive driving current I ctrl is fed to the electric motor 131.

[0062] Preferably, in order to improve reliability, the brake actuator 120 is configured to low-pass filter the third sensor signal (i.e. the driving current I ctrl to the electric motor 131) before determining whether the third sensor signal exceeds the current threshold level I MAX .

[0063] Further preferably, the gear mechanism between the output shaft from the electric motor 131 and the at least one pressing member 135 has such inertia that, once the target force F T has been reached, no further driving current I ctrl to the electric motor 131 is needed to maintain the target force F T acting on the rotating member 136. Thus, as soon as the target force F T is reached as intended, the driving current I E can be set to zero at a point in time t ctrl .

[0064] Figure 7 A block diagram illustrating a brake actuator 120 according to one embodiment of the application is shown. Here, the brake actuator 120 comprises a driving unit 710 and a filtering unit 720. The driving unit 610 is configured to generate a driving current I ctrl to the electric motor 131 based on a brake control signal BS. The filtering unit 720 is configured to obtain an unfiltered sensor signal FS r from the absolute encoder 132, for example, and to produce a second sensor signal FS as a low-pass filtered version of the unfiltered sensor signal FS r in response to the unfiltered sensor signal. Low-pass filtering the unfiltered sensor signal FS r is generally advantageous as it makes the design less sensitive to movements such as in the form of rumble and jitter.

[0065] InFigure 7 In the illustrated embodiment, both the drive unit 610 and the filter unit 720 are included in the control loop for the braking unit. Inevitably, each of units 710 and 720 introduces a corresponding delay in the control loop. Therefore, preferably, the aforementioned force-to-position mapping reflects the expected delay between generating the braking control signal BS and obtaining the second sensor signal FS, which depends on the signal path through units 710 and / or 720 (regardless of which unit is included in the control loop). More preferably, the force-to-position mapping reflects the expected delay due to the inertia of the motor 131.

[0066] This is generally advantageous when the control unit 700 is configured to perform the above-described processes by executing a computer program. Thus, the control unit 700 may include a memory unit 705 (i.e., a non-volatile data carrier) storing a computer program 707, which in turn includes software for causing processing circuitry in the form of a processor 703 in the control unit 700 to perform the actions mentioned in this disclosure when the computer program 707 is executed on the processor 703.

[0067] refer to Figure 8 The flowchart in the diagram will now be used to describe a computer-implemented method according to the present invention, which is executed in the processing unit 703 of the control unit 700.

[0068] In the first step 810, it is checked whether a braking command has been received. If so, steps 820 and 830 are followed; otherwise, the process loops back and stops at step 810.

[0069] In step 820, a braking control signal is generated based on a braking command. The braking control signal is adapted to control the motor in the electrically operated braking unit such that the output shaft of the motor reaches a specified angular position, whereby at least one pressing member applies a force to a rotating member mechanically connected to the wheel axle of the rail vehicle. Here, the applied force has a setpoint in the form of a target force specified by the braking command.

[0070] In step 830, a first sensor signal is obtained, which reflects the measured position of the motor's output shaft. The measured position then constitutes an indication of a specified angular position.

[0071] Following steps 820 and 830, the next step is step 840, in which it is checked whether at least one pressing member has reached the target position. If so, the process continues to steps 850 and 860; otherwise, the process loops back and stops at step 840.

[0072] In step 850, the generation of the brake signal is stopped. In parallel, or immediately thereafter, in step 860, a second sensor signal is obtained, which reflects the magnitude of the applied force.

[0073] Thereafter, in step 870, the second sensor signal is checked against a force-to-position mapping that describes a linear relationship between a specified angular position and an estimated magnitude of the applied force, so that it is possible to verify the relationship between the specified angular position and the estimated magnitude.

[0074] Subsequently, the process ends.

[0075] Figure 9 A computer-implemented method according to an embodiment of the application is described, which can be executed in the processing unit 703 of the control unit 700.

[0076] In Figure 9 , the reference signs occurring in Figure 8 also refer to the same steps as described above with reference to Figure 8 . In Figure 8 the embodiment of the application shown, the second sensor signal is obtained in parallel with steps 820 and 830. Thus, when checking in step 840 whether the target position has been reached, it is also possible to check whether Should the target position has been reached, e.g. taking into account the time that has elapsed since the brake command signal was started to be generated in step 820. In particular, if it is found in step 840 that the target position has not yet been reached, step 820 is followed.

[0077] In step 820, it is checked whether the position indicated by the second sensor signal lies within a hysteresis margin, i.e. within an acceptable interval from the target position, e.g. as described above with reference to Figure 11 . If the position indicated by the second sensor signal lies within the hysteresis margin, the process loops back to steps 820, 830 and 820; otherwise, step 930 is followed.

[0078] In step 930, an alarm is generated, which can be supplemented by additional data indicating potential causes of the alarm.

[0079] The above-described embodiment of the application is beneficial in that obtaining the second sensor signal in the control unit 700 in parallel with obtaining the first sensor signal enables the control unit 700 to have generated an alarm already while the brake control signal BS is being generated. Thus, any malfunction in the brake functionality can be communicated to various monitoring systems in the rail vehicle and / or to the train driver already at an early stage of the braking process.

[0080] Reference is made to Figure 12In the flow chart in figure 1 we will now describe a computer implemented method according to an embodiment of the application, which computer implemented method is executed in the processing unit 703 of the control unit 700.

[0081] In a first step 1210 it is checked whether a brake command has been received. If so, steps 1220 and 1230 are followed; otherwise, the process loops back and stays in step 1210.

[0082] Step 1220 generates a brake control signal based on the brake command, which brake control signal is adapted to control an electric motor in the electrically operated brake unit such that an output shaft of the electric motor reaches a specified angular position, in which specified angular position the at least one pressing member exerts a target force on the rotation member mechanically connected to the axle of the rail vehicle, which target force is specified by the brake command.

[0083] In step 1230, which is executed in parallel with step 1220, a first sensor signal is obtained, which first sensor signal reflects a measured position of the output shaft of the electric motor. Since there is a one-to-one relationship between the specified angular position and the target force, the measured position constitutes an indication of the target force.

[0084] After steps 1220 and 1230, step 1240 checks whether the measured position indicates that the target position corresponding to the target force has been reached. If so, step 1250 is followed; otherwise, the process returns to steps 1220 and 1230 in order to continue controlling the at least one pressing member.

[0085] After step 1250, the process ends.

[0086] Reference Figure 8 , Figure 9 and Figure 12Each of the process steps described herein can be controlled by means of a programmed processor. Furthermore, although the embodiments of the invention described above with reference to the accompanying drawings include a processor and processes executed in at least one processor, the invention is therefore extended to computer programs adapted for practicing the invention, particularly computer programs on or in a carrier. The program can be in the form of source code, object code, intermediate source code, and object code (such as in a partially compiled form), or any other form suitable for implementing the processes according to the invention. The program can be part of an operating system or can be a separate application. The carrier can be any entity or device capable of carrying the program. For example, the carrier can include storage media such as flash memory, ROM (read-only memory), such as DVD (digital video / multifunction disc), CD (optical disc), or semiconductor ROM, EPROM (erasable programmable read-only memory), EEPROM (electrically erasable programmable read-only memory), or magnetic recording media such as floppy disks or hard disks. Furthermore, the carrier can be a transmissible carrier, such as an electrical or optical signal that can be transmitted via cable or optical fiber or by radio or other means. When the program is embodied in a signal that can be directly transmitted via cable or other means or devices, the carrier can be constituted by such cables or means. Alternatively, the carrier may be an integrated circuit in which a program is adapted to perform a related process or to be used to perform a related process.

[0087] Figure 10a A general graph illustrating the change of force F applied by at least one pressing member 135 to a rotating member 136 as a function of time t, according to an embodiment of the present invention.

[0088] Figure 10b The corresponding graph is shown, which illustrates the change of the speed demand SD on the motor 131 with time t when at least one pressing member 135 applies force F to the rotating member 136.

[0089] At time t c Previously, at least one pressing member 135 moved toward the rotating member 136 without making any contact with it. Therefore, until t c At least one pressing member 135 is not applying force F, and during this period, the speed demand SD on the motor 131 is relatively high. Once at least one pressing member 135 has contacted the rotating member 136, the force F applied by at least one pressing member 135 increases rapidly, and the speed demand SD gradually decreases until the target force F is reached. T .

[0090] From a study of the accompanying drawings, this disclosure, and the appended claims, those skilled in the art will understand and implement variations of the disclosed embodiments when carrying out the claimed invention.

[0091] The term "comprises" or "comprising" when used in this specification is taken to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components, or groups thereof. The indefinite articles "an" or "a" are not limited to one, but can also mean one or more. In the claims, the word "or" is not to be interpreted as an exclusive or (sometimes referred to as "XOR"), unless otherwise indicated. Rather, such expression is to be interpreted as an inclusive or unless otherwise indicated. The mere fact that certain measures are recited in mutually different dependent clauses does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.

[0092] It should also be noted that features from the various embodiments described herein can be freely combined with each other, unless explicitly stated otherwise.

[0093] The application is not limited to the embodiments described in the drawings, but can vary freely within the scope of the claims.

Claims

1. A brake actuator (120) for a rail vehicle (100), the brake actuator (120) being configured to receive a braking command (BC) and, in response to the braking command, control an electrically operated braking unit (130) to perform a braking operation, characterized in that, The brake actuator (120) includes a control unit (700), the control unit being configured to: A braking control signal (BS) is generated based on the braking command (BC), the braking control signal (BS) being adapted to control the motor (131) in the electrically operated braking unit (130) such that the output shaft of the motor (131) reaches a specified angular position (P), wherein at the specified angular position at which at least one pressing member (135) applies a force to a rotating member (136) mechanically connected to the wheel axle (141) of the rail vehicle (100), the applied force having a target force (F) specified by the braking command (BC). T Setpoint in the form of ); A first sensor signal (P) reflecting the measured position of the output shaft of the motor (131) is obtained. m The measured position constitutes an indication of the specified angular position (P); Obtain a second sensor signal (FS) reflecting the magnitude of the applied force; and The second sensor signal (FS) is checked against a force-to-position mapping, which describes the linear relationship between the specified angular position (P) and an estimated value of the applied force.

2. The brake actuator (120) according to claim 1, wherein the control unit (700) is configured to: For at least two angular test positions (P1, P2), the second sensor signal (FS) is checked against the force-to-position mapping, and if, for the at least two angular test positions, the corresponding magnitude of the force (F1'; F2') reflected by the sensor signal (FS) is shifted relative to a set of forces (F1; F2) given by the force-to-position mapping by a corresponding displacement (ΔF) satisfying a similarity criterion with respect to each other, then Adjusting the reference position (P) used for the force-to-position mapping C ') to match at least two corresponding test angle positions (P1, P2).

3. The brake actuator (120) according to claim 2, wherein when the output shaft of the electric motor (131) generates the applied force, the control unit (700) is configured to: Verify whether the second sensor signal (FS) meets the stability criterion during the test period (TS), and if the stability criterion is met, then... After the test period (TS) expires (t1; t2), the magnitude of the force reflected by the sensor signal (FS) (FS1; FS2) is obtained to indicate one of the at least two angle test positions (P1, P2).

4. The brake actuator (120) according to claim 2 or 3, wherein the control unit (700) is configured to generate the brake control signal (BS) until the first sensor signal (P) m The target force (F) has been achieved as indicated by the estimate. T The value of ).

5. The brake actuator (120) according to claim 4, wherein the control unit (700) is configured to wait for the second sensor signal (FS) to be checked against the force-to-position mapping until the first sensor signal (P) has been detected. m After receiving an indication that the specified angular position (P) has been reached.

6. The brake actuator (120) according to any one of the preceding claims, wherein the force-to-position mapping reflects an expected delay between generating the brake control signal (BS) and obtaining the second sensor signal (FS), said delay being caused by at least one of the following: The electric motor (131), and Includes at least one component (710, 720) in a control loop for the motor (131), the control loop being arranged between the control unit (700) and the motor (131).

7. The brake actuator (120) according to claim 6, wherein the control circuit comprises at least one of the following: Drive unit (710), the drive unit being configured to generate a drive current (Id) to the motor (131) based on the braking control signal (BS). ctrl ),as well as Filtering unit (720), the filtering unit being configured to obtain unfiltered sensor signal (FS) r And in response to the unfiltered sensor signal, a second sensor signal (FS) is generated as the unfiltered sensor signal (FS). r The low-pass filter version of ).

8. The brake actuator (120) according to any one of the preceding claims, wherein the control unit (700) is configured to generate an alarm (A) if, for the specified angular position (P), the second sensor signal (FS) reflects that the applied force (F(P)) is outside the hysteresis margin (H) of the linear relationship.

9. The brake actuator (120) according to claim 8, wherein the control unit (700) is further configured to: The first sensor signal (P) that reflects the measured position of the output shaft of the motor (131) is obtained. m In parallel, the second sensor signal (FS) reflecting the magnitude of the applied force is obtained, and Verify whether the second sensor signal (FS) reflects that the applied force (F(P)) is outside the hysteresis margin (H) when the braking control signal (BS) is generated.

10. The brake actuator (120) according to any one of the preceding claims, wherein the control unit (700) is configured to receive the brake command (BC) from the brake controller (110), the brake controller being configured to send a brake command (BCx) to at least one additional brake actuator in the rail vehicle (100).

11. The brake actuator (120) according to any one of the preceding claims, wherein the control unit (700) is configured to: During the control of the motor (131) toward the specified angular position (P), a drive current (I) reflecting the current going to the motor (131) is obtained. ctrl The third sensor signal, wherein at the specified angular position, causes the at least one pressing member (135) to apply the target force (F) to the rotating member (136). T Furthermore, if the third sensor signal exceeds the current threshold level (I) during the control period MAX ),but Generate an indicator of excessive drive current (I) ctrl The current alarm is fed to the motor (131).

12. The brake actuator (120) according to claim 11, wherein the brake actuator (120) is configured to determine whether the third sensor signal exceeds the current threshold level (I MAX The signal from the third sensor was previously low-pass filtered.

13. A computer-implemented method for controlling an electrically operated braking unit (130) in a rail vehicle (100), the method being executed in a control unit (700) of a brake actuator (120) in the rail vehicle, the method comprising: Receive braking command (BC) and respond to said braking command The electrically operated braking unit (130) is controlled to perform braking operations. The method is characterized by comprising: A braking control signal (BS) is generated based on the braking command (BC), the braking control signal (BS) being adapted to control the motor (131) in the electrically operated braking unit (130) such that the output shaft of the motor (131) reaches a specified angular position (P), wherein at the specified angular position at which at least one pressing member (135) applies a force to a rotating member (136) mechanically connected to the wheel axle (141) of the rail vehicle (100), the applied force having a target force (F) specified by the braking command (BC). T Setpoint in the form of ); A first sensor signal (P) reflecting the measured position of the output shaft of the motor (131) is obtained. m The measured position constitutes an indication of the specified angular position (P); Obtain a second sensor signal (FS) reflecting the magnitude of the applied force; and The second sensor signal (FS) is checked against a force-to-position mapping, which describes the linear relationship between the specified angular position (P) and an estimated value of the applied force.

14. The method of claim 13, further comprising: For at least two angular test positions (P1, P2), the second sensor signal (FS) is checked against the force-to-position mapping, and if, for the at least two angular test positions, the corresponding magnitude of the force (F1'; F2') reflected by the sensor signal (FS) is shifted relative to a set of forces (F1; F2) given by the force-to-position mapping by a corresponding displacement (ΔF) satisfying a similarity criterion with respect to each other, then Adjusting the reference position (P) used for the force-to-position mapping C ') to match at least two corresponding test angle positions (P1, P2).

15. The method of claim 14, wherein when the output shaft of the electric motor (131) causes the applied force, the method comprises: Verify whether the second sensor signal (FS) meets the stability criterion during the test period (TS), and if the stability criterion is met, then... After the test period (TS) expires (t1; t2), the magnitude of the force reflected by the sensor signal (FS) (FS1; FS2) is obtained to indicate one of the at least two angle test positions (P1, P2).

16. The method according to claim 14 or 15, comprising: The braking control signal (BS) is generated until the first sensor signal (P) is received. m The target force (F) has been achieved as indicated by the estimate. T The value of ).

17. The method of claim 16, further comprising: Wait for the force-to-position mapping to be compared with the second sensor signal (FS) until the first sensor signal (P) has been passed. m After receiving an indication that the specified angular position (P) has been reached.

18. The method according to any one of claims 13 to 17, wherein if, for the specified angular position (P), the second sensor signal (FS) reflects that the applied force (F(P)) is outside the hysteresis margin (H) of the linear relationship, the method comprises: Generate an alert (A).

19. The method according to any one of claims 13 to 18, comprising: During the control of the motor (131) toward the specified angular position (P), a drive current (I) reflecting the current going to the motor (131) is obtained. ctrl The third sensor signal, wherein at the specified angular position, causes the at least one pressing member (135) to apply the target force (F) to the rotating member (136). T Furthermore, if the third sensor signal exceeds the current threshold level (I) during the control period MAX ),but Generate an indicator of excessive drive current (I) ctrl The current alarm is fed to the motor (131).

20. The method of claim 19, further comprising: In determining whether the third sensor signal exceeds the current threshold level (I) MAX The signal from the third sensor was previously low-pass filtered.

21. A computer program (707) capable of being loaded into a non-volatile data carrier (705) communicatively connected to a processing circuit (703), the computer program (707) comprising software for performing the method according to any one of claims 13 to 20 when the computer program (707) is run on the processing circuit (703).

22. A non-volatile data carrier (705) comprising the computer program (707) according to claim 21.

23. A braking system for a rail vehicle (100), the braking system comprising an electrically operated braking unit (130) configured to perform braking operations, characterized in that, The braking system includes a brake actuator (120) according to any one of claims 1 to 12, the brake actuator (120) being arranged to control the electrically operated braking unit (130).

24. The braking system according to claim 23, wherein the electrically operated braking unit (130) comprises: At least one pressing member (135). A rotating component (136), mechanically connected to the axle (141) of the rail vehicle (100), and An electric motor (131) configured to receive the braking control signal (BS) generated by the brake actuator (120), the electric motor (131) including an output shaft configured to reach a specified angular position (P) in response to the control signal (BS), and at the specified angular position (P), to cause the at least one pressing member (135) to apply a target force (F) to the rotating member (136). T ).

25. The braking system according to claim 24, wherein the electric motor (131) is a brushless DC motor.

26. The braking system according to claim 24 or 25, comprising: At least one of a Hall sensor and an absolute encoder (132), configured to generate a first sensor signal (P) reflecting the measured position of the output shaft of the motor (131). m ).

27. The braking system according to any one of claims 23 to 26, comprising: Drive unit (610), the drive unit being configured to generate a drive current (I) to the motor (131) based on the braking control signal (BS). ctrl ).

28. The braking system according to any one of claims 23 to 27, comprising: Weighing sensor (133), the weighing sensor being configured to generate an unfiltered sensor signal (FS) r The unfiltered sensor signal reflects the magnitude of the force applied by at least one pressing member (135) to the rotating member (136).

29. The braking system of claim 28, comprising: Filtering unit (720), the filtering unit is configured to: The unfiltered sensor signal (FS) is obtained from the weighing sensor (133). r ), and in response to the unfiltered sensor signal The second sensor signal (FS) is generated as the unfiltered sensor signal (FS). r The low-pass filter version of ).

30. The braking system according to any one of claims 23 to 29, comprising: A brake controller (110) is configured to generate the brake command (BC) in response to a brake command (BI).

31. The braking system according to any one of claims 23 to 30, wherein if, for the specified angular position (P), the second sensor signal (FS) reflects that the applied force (F(P)) is outside the hysteresis margin (H) of the linear relationship, the alarm (A) generated by the control unit (700) indicates at least one of the following: error of the weighing sensor (133), encoder error, mechanical failure, electrical error, and wear of the at least one pressing member (135).

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