Method for calibrating an acquisition chain of a brake device or a brake system of at least one vehicle, in particular of at least one rail vehicle

Abstract

A method for calibrating an acquisition chain (100) of a braking device or braking system (102) of at least one vehicle, in particular at least one railway vehicle, is described, the method comprising the steps of: a) measuring a predetermined reference value (116) of a physical quantity by means of a calibration means (114) having an accuracy higher than a predetermined threshold value; b) measuring the predetermined reference value of the physical quantity by the acquisition chain (100); c) determining a measurement error of the acquisition chain by comparing the predetermined reference value measured by the calibration means (114) with the predetermined reference value measured by the acquisition chain; and d) based on the comparison between the predetermined reference value measured by the calibration means and the predetermined reference value measured by the acquisition chain, the measurement error of the acquisition chain is minimized or zeroed by modifying the at least one coefficient of the transfer function of the control means of the acquisition chain.

Description

[Technical field]

[0001] The present invention generally lies in the field of calibration systems for vehicles, in particular rail vehicles, and in particular relates to a method for calibrating the acquisition chain of a brake device or a brake system of at least one vehicle, in particular at least one rail vehicle. [Background technology]

[0002] The prior art is explained below with particular reference to the field of rail vehicles, although what is explained may also be applied, where possible, to other fields of vehicles.

[0003] Over the last 50 years, braking systems on rail vehicles and elsewhere have changed from pneumatic to electro-pneumatic (and the same goes for hydraulic and mechanical) systems. As a result of this change, there is an increasing need to rely on control measurements that allow monitoring the forces exerted by these braking systems.

[0004] The change from purely pneumatics to electro-pneumatics brought many advantages, including improved accuracy and reduced weight and volume. In addition to this change in the type of system, the car manufacturers' requirements for precision in terms of stopping distance are also changing, and with that the requirements for precision in the pressure in the brake cylinder of the braking system are also changing. The pressure precision in the brake cylinder was previously + / - 250 mbar. Now the precision in the brake cylinder is + / - 100 mbar in the cylinder.

[0005] Braking accuracy, and therefore stopping distance accuracy, was previously ensured by manually calibrating the various pneumatic components of the braking system, which could include, for example, the VCAV (vacuum-load valve, from the French "vide-charge auto-variable"), the LPV (load proportional valve) or the distributor.

[0006] The calibration method was performed by measuring the brake cylinder pressure for a given load pressure and verifying that the brake cylinder pressure satisfied a given transfer function, taking into account positive or negative deadband intervals (+ / -) when this pressure was lower or higher than a provided value, and the mechanical object being calibrated was physically calibrated and this calibration was recorded in the appropriate maintenance file.

[0007] Throughout the life cycle of a braking system, mechanical subassemblies / mechanical components are exposed to wear, vibrations, and temperature fluctuations, which result in internal microscopic / macroscopic changes. These changes affect the performance of the subassembly or mechanical component. These changes can increase or decrease the pressure in the brake's cylinder. Such changes in the pressure in the brake cylinder may not guarantee the safe stopping distance that the braking system normally provides. Taking this drawback into account, the calibration explained above was performed.

[0008] For example, with regard to the electronic components of an electro-pneumatic braking system, electronic sensors have an initial accuracy offset from the manufacturer that can deviate from the actual value depending on time, usage, temperature fluctuations, and the magnitude of the change in the measurement. The characteristics of the electrical circuitry that reads the sensor's output also change due to similar factors. All these factors reduce the accuracy of the acquisition chain and therefore the accuracy of the emergency and service braking functions.

[0009] Unfortunately, because electro-pneumatic systems are not comprised of purely mechanical components and subassemblies, calibration methods used for pneumatic systems may not be applicable to electro-pneumatic systems.

[0010] For example, WO 2017 / 194512 describes a method and a braking system that can perform automatic calibration based on cylinder fill and discharge times rather than absolute pressure values, but does not address the problem of maintaining braking accuracy of electro-pneumatic braking systems.

[0011] In another example, WO 2019 / 048261 describes a braking system incorporating an observer and model that estimates cylinder pressure based on the outlet pressure of a pressure regulating device, again leaving the problem of maintaining braking accuracy of an electro-pneumatic braking system unsolved. Therefore, new calibration techniques are needed. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] International Publication No. 2017 / 194512 [Patent Document 2] International Publication No. 2019 / 048261 Summary of the Invention [Problem to be solved by the invention]

[0013] It is therefore an object of the present invention to provide a calibration method suitable for use in an electro-pneumatic device or system, which is also suitable for solving the problem of maintaining braking accuracy in an electro-pneumatic braking system. [Means for solving the problem]

[0014] The above mentioned and other objects and advantages are achieved according to one aspect of the invention by a method for calibrating an acquisition chain of a braking device or a braking system of at least one vehicle, in particular at least one railway vehicle, having the features defined in claim 1. Preferred embodiments of the invention are defined in the dependent claims, the content of which is to be understood as an integral part of this description. [Brief description of the drawings]

[0015] The functional and structural characteristics of some preferred embodiments of the method according to the invention for calibrating an acquisition chain of a braking device or of a braking system of at least one vehicle, in particular at least one rail vehicle, will now be described with reference to the attached drawings, in which: [Figure 1] FIG. 1 is a diagram showing an example of an acquisition chain. [Diagram 2] FIG. 2 is a diagram showing an example of a brake system including the acquisition chain. [Diagram 3] FIG. 3 shows an example of a setup suitable for carrying out the method according to the invention for calibrating an acquisition chain of a braking equipment or a braking system of at least one vehicle, in particular at least one rail vehicle. [Figure 4] FIG. 4 is a diagram showing an example of an electro-pneumatic brake device / system. [Diagram 5] FIG. 5 is a control block diagram showing the electro-pneumatic brake device / system of FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Before describing the embodiments of the present invention in detail, it should be made clear that the present invention is not limited in its application to the design details and configuration of components set forth in the following description or illustrated in the drawings. The present invention can envision other embodiments and can actually be implemented or constructed in different ways. It is also to be understood that the phraseology and terminology are for descriptive purposes and should not be construed as limiting. The use of "include" and "comprise" and variations thereof should be understood to encompass the elements described below and their equivalents, as well as additional elements and their equivalents.

[0017] Referring first to FIG. 1, an acquisition chain 100 includes the following: - sensor means 104 configured to measure the value of a physical quantity 106 and to provide an analog signal 108 whose value is a function of the value of said physical quantity; - analog / digital conversion means 110 configured to convert said analog signal into a digital signal; control means 112 adapted to determine the value of said physical quantity from said digital signal according to a transfer function 113 comprising at least one coefficient;

[0018] For example, the control means may be or include at least one of a processor, a controller, an FPGA, a microcontroller, a microprocessor, and the like.

[0019] Obviously, the sensor means may have its own transfer function. The sensor means may provide an analog signal based on the value of said physical quantity and its own transfer function. The analog / digital conversion means may also have its own transfer function. The analog / digital conversion means may convert an analog signal into a digital signal according to its own transfer function.

[0020] The acquisition chain 100 may be defined as all elements that allow the interpretation of a physical quantity determined by a measurement. In other words, the acquisition chain may comprise sensors, electrical interfaces (analog / digital conversion means) and software code (executed by the control means). Each element may have its own transfer function. For example, the transfer function of the sensor means converts the value of the physical quantity into an analog electrical signal, the transfer function of the electrical interface converts the analog electrical signal into a digital signal and the software code SW converts the digital signal into the value of the interpreted physical quantity.

[0021] In a first embodiment, the calibration method according to the present invention includes the following steps. a) measuring a predetermined reference value 116 of said physical quantity by means of calibration means 114 having an accuracy higher than a predetermined threshold value, b) measuring said predetermined reference value of said physical quantity by said acquisition chain, c) determining the measurement error of the acquisition chain by comparing the predetermined reference value measured by the calibration means with the predetermined reference value measured by the acquisition chain; d) based on the comparison between the predetermined reference value measured by the calibration means and the predetermined reference value measured by the acquisition chain, the measurement error of the acquisition chain is minimized or reduced to zero by modifying at least one coefficient of the transfer function of the control means of the acquisition chain.

[0022] For example, if a comparison of the values ​​measured by the calibration means and the values ​​measured by the acquisition chain results in a difference within an acceptable deviation range, the calibration may be continued. Alternatively, if a comparison of the values ​​measured by the calibration means and the values ​​measured by the acquisition chain results in a difference outside the acceptable deviation range, the calibration method may not be performed and the acquisition chain and its associated units may be disabled. This acceptable deviation range may typically be based on the maximum annual error increase of the sensor means and the maximum annual deviation of the analogue / digital conversion means.

[0023] For example, but not limited to, the comparison may include a subtraction operation between the value measured by the calibration means and the value measured by the acquisition chain, or vice versa.

[0024] An example of a calibration means is shown by way of example in the configuration of Fig. 3. The calibration means is for example a calibration system or a calibration device. The calibration means may include therein a replica of the acquisition chain to be calibrated. The reconstructed acquisition chain therein may ensure that the calibration means has an accuracy higher than a predefined threshold.

[0025] For example, the physical quantity may be a pressure. This pressure may be, for example, the pressure in a brake cylinder of an electro-pneumatic braking system arranged to perform emergency braking and / or service braking. In this case, the sensor means may be a pressure sensor. Analogous for other physical quantities. For example, if the physical quantity is a temperature, the sensor means may be a temperature sensor. If the physical quantity is a force, the sensor means may be a force sensor. If the physical quantity is a torque, the sensor means may be a torque sensor etc.

[0026] Steps a) to d) may preferably be repeated for each acquisition chain of at least one vehicle, in particular at least one rail vehicle, configured to measure physical quantities related to emergency braking. For example, if there are two vehicles, for example two rail vehicles, each with two brake cylinders arranged to perform emergency braking, steps a) to d) may be repeated four times for each of said brake cylinders.

[0027] Steps a) to d) may preferably be repeated for each acquisition chain of said at least one vehicle, in particular at least one railway vehicle, configured to measure a physical quantity related to service braking. For example, if there are two vehicles, e.g. two railway vehicles, each with two brake cylinders arranged to perform service braking, steps a) to d) may be repeated four times for each of said brake cylinders.

[0028] The step of measuring predetermined reference values ​​of the physical quantities using an acquisition chain may comprise the following steps. - measuring said predetermined reference value of said physical quantity by means of a pressure sensor, or - measuring said predetermined reference value of said physical quantity by means of a force sensor, or - measuring the predetermined reference value of the physical quantity using a torque sensor, or - measuring said predetermined reference value of said physical quantity by means of a speed sensor;

[0029] In other words, the sensor means of the acquisition chain may be or include at least a pressure sensor, a force sensor, a torque sensor or a velocity sensor.

[0030] Steps a) to d) may preferably be performed during a manufacturing phase of said acquisition chain before it is put into service, for example the calibration method according to the invention can be used during an initial construction phase of the braking system of a vehicle, in particular at least one rail vehicle comprising an acquisition chain, before it is put into service.

[0031] Steps a) to d) may preferably be performed during a calibration phase of the acquisition chain of the braking system after the braking system has been put into service. For example, the calibration method according to the invention can be used after a vehicle, in particular at least one rail vehicle, has been put into service, when a readjustment of the acquisition chain needs to be performed as a result of deviations from actual values.

[0032] The calibration method may preferably also include the following steps: - repeating said steps a) to d) for at least two of said environmental test conditions in order to modify at least one coefficient of said transfer function of the control means of the acquisition chain for a range of values ​​of said environmental test conditions. The environmental test conditions are preferably two different temperature conditions.

[0033] The predetermined reference value of the physical quantity is preferably a value between a maximum value and a minimum value that can be measured by the sensor means.

[0034] Step d) may preferably comprise the step of modifying at least one coefficient of said transfer function of a control means of the acquisition chain according to interpretation parameters configured to enable interpretation of said digital signal.

[0035] The number of points used for the calibration depends on the transfer function of the control means of the acquisition chain being calibrated and how the accuracy drifts during its life cycle.

[0036] The offset can be corrected by one-point calibration. For a linear transfer function, offset and gain deviations can be corrected by a two-point calibration. For nonlinear functions, the nonlinear deviations can be corrected by multi-point calibration. Possible uses of the present invention are described below. EXAMPLES

[0037] Example 1 - Use of interpretation parameters The following examples are based on an "acquisition chain" with a linear transfer function. Here, two points with coordinates (X,Y) are sufficient to explain the examples.

[0038] To calculate the interpreted physical quantities, the software of the control means of the acquisition chain to be tested has access to interpretation parameters to enable it to interpret the digital signals. These parameters may be present in an EEPROM or flash memory to ensure that the coefficients are available after a shutdown.

[0039] The values ​​selected as default values ​​for the interpretation parameters may be based on the sensor means data sheet. The following table shows the interpretation parameters for a particular acquisition chain.

[0040] [Table 1]

[0041] The software of the control means may use the default interpretation parameters of the acquisition chain 1 to calculate the coefficients a and b of the linear equation (transfer function of the control means).

number

[0042] X min (X 最小値 ) and X max (X 最大値 ) unknown value X nFor , the coefficients a and b can be used to calculate the value of the interpreted physical quantity.

number

[0043] The two different reference values ​​do not necessarily have to be the minimum and maximum values ​​of the measurement capability of the sensor means, and in some circumstances these values ​​may not be reachable due to surrounding devices or systems. In any case, in the case of a linear function, two different values ​​with a difference of at least 10% between the highest and lowest points may allow to correct the deviation. The value of the physical quantity interpreted by the calibration means may then be substituted for the interpretation parameter, permanently erasing the previous value in the EEPROM or flash memory. This action corrects the value of the physical quantity interpreted by the acquisition chain under test, bringing its digital signal and the value of the physical quantity to coincide with the accuracy of the calibration means.

[0044] [Table 2]

[0045] This technique utilizes the capabilities of the calibration means to access interpretation parameters within the acquisition chains and calibrate the different acquisition chains. The updated formula is shown below:

number

[0046] Suppliers of sensor means will typically specify an accuracy range for a particular temperature range where extreme temperatures will cause the accuracy of the sensor means to decrease. To counteract this effect, different interpretation parameters may be used depending on the temperature.

[0047] This operating temperature range may be divided into, for example, three temperature ranges depending on the effective temperature, and a particular set of interpretation parameters may be selected.

[0048] Instead of using the interpretation parameters ((X1,Y1'),(X2,Y2')), the coefficients (a',b') of the transfer function of the control means can be used to calibrate and store updated information of the acquisition chain.

[0049] Example 2 - Calibration applied to a braking system of a railway vehicle FIG. 4 shows an example of an electro-pneumatic braking device / system that performs the service braking function.

[0050] The electro-pneumatic braking device / system may include: -Air Suspension (AS) Pressure: This represents the load on the rail vehicle. -Cylinder pressure (Cyl): represents the force applied to the axle. - Acquisition chain 1 (AC1): Transfer function, interpreted pressure value from pressure. - Acquisition chain 2 (AC2): Transfer function, interpreted pressure value from pressure. -Actuator (A): Controls the pressure inside the cylinder. -SW load pressure to cylinder intended pressure (SW_L2T): pressure to pressure transfer function. - Controller (C): gives commands to the actuator in a closed loop that minimizes the error between the intended pressure in the cylinder and the feedback of the pressure in the cylinder.

[0051] FIG. 5 is a control block diagram showing the braking device / system shown in FIG. Each control block has its own transfer function. For the purposes of this invention, only the grey blocks are of interest.

[0052] AC1 represents the transfer function of acquisition chain 1. Its input is the air suspension pressure, P_AS, and its output is the interpreted air suspension pressure, IP_AS.

[0053] SW_L2T is a transfer function, i.e. load on cylinder versus intended pressure, and is design dependent, as it depends on the type of vehicle suspension, type of braking system, etc. Its input is the interpreted air suspension pressure, IP_AS, and its output is the target pressure for the cylinder, P_target. The error due to AC1 is modulated according to the transfer function SW_L2T.

[0054] AC2 represents the transfer function of acquisition chain 2. Its input is the pressure in the cylinder, P_Cyl, and its output is the interpreted pressure in the cylinder, IP_Cyl. The AC2 output error is then "subtracted" from the SW_L2T error to create an output Δ that represents the difference between P_Target (intended pressure) and IP_Cyl (interpreted cylinder pressure).

[0055] The input of controller C may use a deadband around the difference Δ. The deadband is shifted by the error resulting from the subtraction. The controller may send commands to an actuator to control the pressure in the cylinder, P_Cyl.

[0056] The following table shows example sensor means and control means data used to calculate the service brake pressure error. The full scale of the sensor is 10 bar.

[0057] [Table 3]

[0058] These design data can be used to characterize the error propagation in the control block diagram shown in FIG.

[0059] The table below shows the error propagation along the system as we finish production. The resulting maximum error in a cylinder is + / - 123.92mbar.

[0060] [Table 4]

[0061] The table below shows the error propagation along the system after one year of use. The resulting maximum error in a cylinder is + / - 166.16mbar.

[0062] [Table 5]

[0063] In none of the tables shown above did a single braking device / system with components having the characteristics defined in Table 3 meet the accuracy requirement of + / - 100mbar in the cylinder.

[0064] By means of the calibration method according to the invention, the acquisition chain of the relevant devices can be calibrated before being put into use. This calibration improves the accuracy of the acquisition chain.

[0065] With the accuracy of the sensor means calibrated by the calibration tool equal to + / - 0.05 [FS], a table of resulting braking parameters is obtained.

[0066] [Table 6]

[0067] As shown in the table above, the error of the resulting acquisition chain will be equal to the accuracy of the calibrated acquisition chain. The effects on error propagation are as follows:

[0068] [Table 7]

[0069] As can be seen in the table above, the maximum error in P_Cyl is + / -57.04mbar, which is below the target of + / -100mbar.

[0070] [Table 8]

[0071] In the table above, the error on P_Cyl is + / -99.28mbar, which is quite close to the target of + / -100mbar, so annual calibration is required to ensure the accuracy of the brake cylinder.

[0072] Thus, an advantage achieved is to provide a calibration method suitable for use in an electro-pneumatic device or system.

[0073] A further advantage thus achieved is the provision of a calibration method suitable for solving the problem of maintaining braking accuracy in an electro-pneumatic braking system.

[0074] As mentioned above, the present invention is suitable for application to at least one rail vehicle traveling on a railroad track. For example, the vehicle referred to herein may be a locomotive or a passenger car, and the course / route may include the track on which the wheels of the locomotive roll. Also, the embodiments described herein are not limited to vehicles on a railroad. For example, the vehicle may be a passenger car, a truck (e.g., a highway semi-trailer truck, a mining truck, a timber truck, etc.), a motorcycle, etc., and the route may be a paved or unpaved road.

[0075] Various aspects and embodiments of the method for calibrating an acquisition chain of a braking device or a braking system of at least one vehicle, in particular at least one rail vehicle, according to the present invention have been described. It is to be understood that each embodiment can be combined with any other embodiment. Moreover, the invention is not limited to the described embodiments, but may vary within the scope defined by the appended claims.

Claims

1. A method for calibrating an acquisition chain (100) of a braking device or braking system (102) of at least one vehicle, comprising: The acquisition chain comprises: - a sensor means (104) configured to measure the value of a physical quantity (106) and to provide an analog signal (108), the value of which is a function of the value of said physical quantity; Analog / digital conversion means (110) configured to convert said analog signal into a digital signal; - control means (112) adapted to determine the value of said physical quantity from said digital signal according to a transfer function (113) comprising at least one coefficient; Equipped with The calibration method is a) measuring a predetermined reference value (116) of said physical quantity by means of calibration means (114) having an accuracy higher than a predetermined threshold value; b) measuring said predetermined reference value of said physical quantity by said acquisition chain (100); c) determining the measurement error of the acquisition chain by comparing the predetermined reference value measured by the calibration means (114) with the predetermined reference value measured by the acquisition chain; d) based on the comparison of the predetermined reference value measured by the calibration means with the predetermined reference value measured by the acquisition chain, the measurement error of the acquisition chain is minimized or zero by modifying the at least one coefficient of the transfer function of the control means of the acquisition chain; A calibration method comprising:

2. 2. The calibration method according to claim 1, wherein steps a) to d) are repeated for each acquisition chain (100, 100', ...) of the at least one vehicle configured to measure physical quantities related to emergency braking.

3. 3. Calibration method according to claim 1 or 2, wherein steps a) to d) are repeated for each acquisition chain (100, 100', ...) of the at least one vehicle configured to measure physical quantities related to service braking.

4. The step of measuring the predetermined reference value of the physical quantity by means of the acquisition chain (100) further comprises: - measuring the predetermined reference value of the physical quantity by means of a pressure sensor; or - measuring the predetermined reference value of the physical quantity by means of a force sensor, or Measuring the predetermined reference value of the physical quantity by a torque sensor; or measuring the predetermined reference value of the physical quantity by a speed sensor; The calibration method according to claim 1 , further comprising:

5. Calibration method according to any of the preceding claims, wherein steps a) to d) are performed during a manufacturing phase of the acquisition chain before it is put into service.

6. Calibration method according to any of the preceding claims, wherein steps a) to d) are performed during a calibration phase of the acquisition chain after start-up.

7. The calibration method further comprises: repeating steps a) to d) for at least two environmental test conditions in order to modify the at least one coefficient of the transfer function of the control means of the acquisition chain for a range of values ​​of the at least two environmental test conditions; The calibration method according to claim 1 , further comprising:

8. The method of claim 7 , wherein the at least two environmental test conditions are two different temperature conditions.

9. 9. A calibration method according to claim 1, wherein the predetermined reference value of the physical quantity is an average value between a maximum value and a minimum value that can be measured by the sensor means.

10. The step d) further comprises: - modifying said at least one coefficient of said transfer function of said control means of said acquisition chain according to interpretation parameters according to which said digital signal is adapted to be interpreted, The calibration method according to claim 1 , comprising:

Images