Cha DESIGN OF A N FOR THE CALIB Giorgio Diana 1 , Ferruccio Ma 1 Dipartimento di Meccanica, *Corresponding ABSTRACT Instrumented wheelsets have been International Standards (EN 14363 [ new vehicle. As far as running safety and the derailment coefficient (Y/Q contact forces is mandatory when the In order to use wheelsets as a me Usually instrumented wheelsets are wheel web (or both). During the ca wheelset and the corresponding stra correlation between the output of procedure appears crucial in order to Rolling test-rig are often used to pe wheel-rail contact interface are usu equilibrium of the system, thus reduc the accuracy of the device, a new ful Department of Politecnico di Milan wheelsets, depending on the vehicle is mounted on the test-rig. This al instrumented wheelset that are of fu the contact forces and on reaction f re-distribution of reaction forces and Instrumented rail elements are posit rail element is equipped with 7 load each direction (vertical, lateral and l secondary suspensions by means of directly to the rail elements. 1. INTRODUCTION Test rigs for the calibration of instrum in Figure 1) or non-rolling (see Figure allenge E: Bringing the territories closer together a NEW FULL SCALE TEST BRATION OF INSTRUME WHEELSETS o Resta 1 , Francesco Braghin 1 *, Egidio Di Gialleonar arco Bocciolone 1 , Pietro Crosio 1 , Politecnico di Milano, Via La Masa 1, 20156 Milan g author, email: [email protected]n used for years to assess running safety of ra [1]) prescribe a complete testing procedure for th y is concerned, the sum of the guiding forces in str Q) in curve must be measured. Therefore, measu e so-called “normal method” must be applied. easuring device, a preliminary calibration procedu based on strain gauge bridges placed either on the alibration phase forces of known magnitude are ain values are measured. In this way it is possible strain gauge bridges and the applied forces. o assess the accuracy of the measuring system. erform the calibration of the wheelset [2]. In this ually not directly measured but are determined b ucing significantly the accuracy of the system. In o ull scale test-rig has been designed at the Mechani no. A bogie assembly made up of a bogie fra e architecture, or a single wheelset in case of a no llows to correctly reproduce the real working co undamental importance: in fact, measured strains forces; hence, an error on the boundary condition thus a measuring error. tioned under each wheel of the wheelset under ca cells in order to measure wheel rail contact force longitudinal). Vertical forces are applied to the bo f a load beam, whereas lateral and longitudinal for mented wheelsets are of two kinds: rolling (such as e 2). at higher speeds T-RIG ENTED rdo 1 , no, Italy ailway vehicles. he approval of a raight track (ΣY) uring wheel-rail ure is required. e axle or on the applied to the e to establish a The calibration way, forces at by imposing the order to improve ical Engineering ame and 2/3/4 on-bogie vehicle onditions of the depend both of ns determines a alibration. Each e components in ogie through the rces are applied s the one shown
Transcript
Challenge E: Bringing the territories closer together at higher speeds
DESIGN OF A NEW FULL SCALE TEST-RIGFOR THE CALIBRATION OF INSTRUMENTED
WHEELSETSGiorgio Diana1, Ferruccio Resta1, Francesco Braghin1*, Egidio Di Gialleonardo1,
Marco Bocciolone1, Pietro Crosio1
1Dipartimento di Meccanica, Politecnico di Milano, Via La Masa 1, 20156 Milano, Italy
ABSTRACTInstrumented wheelsets have been used for years to assess running safety of railway vehicles.International Standards (EN 14363 [1]) prescribe a complete testing procedure for the approval of anew vehicle. As far as running safety is concerned, the sum of the guiding forces in straight track (ΣY)and the derailment coefficient (Y/Q) in curve must be measured. Therefore, measuring wheel-railcontact forces is mandatory when the so-called “normal method” must be applied.In order to use wheelsets as a measuring device, a preliminary calibration procedure is required.Usually instrumented wheelsets are based on strain gauge bridges placed either on the axle or on thewheel web (or both). During the calibration phase forces of known magnitude are applied to thewheelset and the corresponding strain values are measured. In this way it is possible to establish acorrelation between the output of strain gauge bridges and the applied forces. The calibrationprocedure appears crucial in order to assess the accuracy of the measuring system.Rolling test-rig are often used to perform the calibration of the wheelset [2]. In this way, forces atwheel-rail contact interface are usually not directly measured but are determined by imposing theequilibrium of the system, thus reducing significantly the accuracy of the system. In order to improvethe accuracy of the device, a new full scale test-rig has been designed at the Mechanical EngineeringDepartment of Politecnico di Milano. A bogie assembly made up of a bogie frame and 2/3/4wheelsets, depending on the vehicle architecture, or a single wheelset in case of a non-bogie vehicleis mounted on the test-rig. This allows to correctly reproduce the real working conditions of theinstrumented wheelset that are of fundamental importance: in fact, measured strains depend both ofthe contact forces and on reaction forces; hence, an error on the boundary conditions determines are-distribution of reaction forces and thus a measuring error.Instrumented rail elements are positioned under each wheel of the wheelset under calibration. Eachrail element is equipped with 7 load cells in order to measure wheel rail contact force components ineach direction (vertical, lateral and longitudinal). Vertical forces are applied to the bogie through thesecondary suspensions by means of a load beam, whereas lateral and longitudinal forces are applieddirectly to the rail elements.
1. INTRODUCTIONTest rigs for the calibration of instrumented wheelsets are of two kinds: rolling (such as the one shownin Figure 1) or non-rolling (see Figure 2).
Challenge E: Bringing the territories closer together at higher speeds
DESIGN OF A NEW FULL SCALE TEST-RIGFOR THE CALIBRATION OF INSTRUMENTED
WHEELSETSGiorgio Diana1, Ferruccio Resta1, Francesco Braghin1*, Egidio Di Gialleonardo1,
Marco Bocciolone1, Pietro Crosio1
1Dipartimento di Meccanica, Politecnico di Milano, Via La Masa 1, 20156 Milano, Italy
ABSTRACTInstrumented wheelsets have been used for years to assess running safety of railway vehicles.International Standards (EN 14363 [1]) prescribe a complete testing procedure for the approval of anew vehicle. As far as running safety is concerned, the sum of the guiding forces in straight track (ΣY)and the derailment coefficient (Y/Q) in curve must be measured. Therefore, measuring wheel-railcontact forces is mandatory when the so-called “normal method” must be applied.In order to use wheelsets as a measuring device, a preliminary calibration procedure is required.Usually instrumented wheelsets are based on strain gauge bridges placed either on the axle or on thewheel web (or both). During the calibration phase forces of known magnitude are applied to thewheelset and the corresponding strain values are measured. In this way it is possible to establish acorrelation between the output of strain gauge bridges and the applied forces. The calibrationprocedure appears crucial in order to assess the accuracy of the measuring system.Rolling test-rig are often used to perform the calibration of the wheelset [2]. In this way, forces atwheel-rail contact interface are usually not directly measured but are determined by imposing theequilibrium of the system, thus reducing significantly the accuracy of the system. In order to improvethe accuracy of the device, a new full scale test-rig has been designed at the Mechanical EngineeringDepartment of Politecnico di Milano. A bogie assembly made up of a bogie frame and 2/3/4wheelsets, depending on the vehicle architecture, or a single wheelset in case of a non-bogie vehicleis mounted on the test-rig. This allows to correctly reproduce the real working conditions of theinstrumented wheelset that are of fundamental importance: in fact, measured strains depend both ofthe contact forces and on reaction forces; hence, an error on the boundary conditions determines are-distribution of reaction forces and thus a measuring error.Instrumented rail elements are positioned under each wheel of the wheelset under calibration. Eachrail element is equipped with 7 load cells in order to measure wheel rail contact force components ineach direction (vertical, lateral and longitudinal). Vertical forces are applied to the bogie through thesecondary suspensions by means of a load beam, whereas lateral and longitudinal forces are applieddirectly to the rail elements.
1. INTRODUCTIONTest rigs for the calibration of instrumented wheelsets are of two kinds: rolling (such as the one shownin Figure 1) or non-rolling (see Figure 2).
Challenge E: Bringing the territories closer together at higher speeds
DESIGN OF A NEW FULL SCALE TEST-RIGFOR THE CALIBRATION OF INSTRUMENTED
WHEELSETSGiorgio Diana1, Ferruccio Resta1, Francesco Braghin1*, Egidio Di Gialleonardo1,
Marco Bocciolone1, Pietro Crosio1
1Dipartimento di Meccanica, Politecnico di Milano, Via La Masa 1, 20156 Milano, Italy
ABSTRACTInstrumented wheelsets have been used for years to assess running safety of railway vehicles.International Standards (EN 14363 [1]) prescribe a complete testing procedure for the approval of anew vehicle. As far as running safety is concerned, the sum of the guiding forces in straight track (ΣY)and the derailment coefficient (Y/Q) in curve must be measured. Therefore, measuring wheel-railcontact forces is mandatory when the so-called “normal method” must be applied.In order to use wheelsets as a measuring device, a preliminary calibration procedure is required.Usually instrumented wheelsets are based on strain gauge bridges placed either on the axle or on thewheel web (or both). During the calibration phase forces of known magnitude are applied to thewheelset and the corresponding strain values are measured. In this way it is possible to establish acorrelation between the output of strain gauge bridges and the applied forces. The calibrationprocedure appears crucial in order to assess the accuracy of the measuring system.Rolling test-rig are often used to perform the calibration of the wheelset [2]. In this way, forces atwheel-rail contact interface are usually not directly measured but are determined by imposing theequilibrium of the system, thus reducing significantly the accuracy of the system. In order to improvethe accuracy of the device, a new full scale test-rig has been designed at the Mechanical EngineeringDepartment of Politecnico di Milano. A bogie assembly made up of a bogie frame and 2/3/4wheelsets, depending on the vehicle architecture, or a single wheelset in case of a non-bogie vehicleis mounted on the test-rig. This allows to correctly reproduce the real working conditions of theinstrumented wheelset that are of fundamental importance: in fact, measured strains depend both ofthe contact forces and on reaction forces; hence, an error on the boundary conditions determines are-distribution of reaction forces and thus a measuring error.Instrumented rail elements are positioned under each wheel of the wheelset under calibration. Eachrail element is equipped with 7 load cells in order to measure wheel rail contact force components ineach direction (vertical, lateral and longitudinal). Vertical forces are applied to the bogie through thesecondary suspensions by means of a load beam, whereas lateral and longitudinal forces are applieddirectly to the rail elements.
1. INTRODUCTIONTest rigs for the calibration of instrumented wheelsets are of two kinds: rolling (such as the one shownin Figure 1) or non-rolling (see Figure 2).
Challenge E: Bringing the territories closer together at higher speeds
Figure 1. Example of rolling test rig(courtesy of Lucchini RS)
Figure 2. Example of non-rolling test rig (courtesy ofDB and HBM)
Rolling test rigs are mainly made up a of two rail discs on which the wheelset to be calibrated is set. Inorder to apply known loads on the wheelset, hydraulic/electric load actuators equipped with load cellsare used [3]. Typically, two vertical actuators (to simulate the load transfer), one lateral actuator (toreproduce the overall lateral force that is applied to the wheelset through the bogie) and twolongitudinal actuators (to impose the desired angle of attack) are used. Moreover, to take into accountthe relative wheel-rail position, displacement transducers (e.g. laser sensors) at contact level areused. The advantage of such test rigs is that the wheelset can be tested in working conditions that aresimilar to those encountered during line tests. Instead, the typical main drawback is due to the factthat no direct measure of wheel-rail contact forces is achievable [2]: wheel-rail contact forces areusually determined either through dynamic equilibria of the whole wheelset, knowing the forcesapplied by the actuators and the wheelset position, and/or through indirect measures, e.g. thedeformation of rail discs near the contact area. Moreover, the lateral forces on the two wheels, as wellas the wheel-rail relative lateral position, cannot be adjusted independently but are a function of theimposed angle of attack of the wheelset and of the applied overall lateral force. Finally, due to theadopted suspension system of the wheelset on the roller rig (usually primary suspensions), thebandwidth of the measuring wheelset that can be explored though the test rig is limited to few Hz andthe curvature of the rails modifies (even though slightly) the contacting conditions, thus the contactstress distribution and the contact forces.Non-rolling test rigs, instead, have a much simpler structure: the wheelset to be calibrated is placedon two dynamometric balances having a minimum of three measuring directions (up to a maximum ofsix measuring directions, i.e. three forces and three moments, [4],[5]) and a shape that approximatesreal rails. Wheel-rail contact forces are therefore directly measured thus greatly improving theaccuracy of the calibration procedure. The drawback, instead, is that the wheelset is not rolling. Thus,if the output of the measuring set-up of the wheelset is a function of the wheelset angular position,calibration tests have to be repeated for different angular positions. Moreover, in order to calibrate thewheelset under realistic working conditions, it is useful to carry out numerical simulations of therunning behaviour of the wheelset. However, being the "equivalent rails" non moving with respect tothe wheelset, it is possible to apply external forces either to the wheelset through the journal bearingor directly to the rails. Thus, the bandwidth of the wheelset that can be assessed during the calibrationtests is not determined by the suspension system of the wheelset to the test rig but by the bandwidthof the actuators (that is typically higher). Moreover, if lateral and longitudinal actuators are applied toeach dynamometric balance, independent lateral and longitudinal contact forces can be applied toeach wheel (obviously, appropriate bounding conditions on the wheelset are required) up to theirfriction limit. It is also very easy to test the influence of different gauges (as well as different wheel-railrelative lateral positions) and no rail curvature effect is present.Looking at the pros and cons, non-rolling test rigs seem more suitable for calibrating instrumentedwheelsets except for the fact that the calibration procedure is longer and more complicated since ithas to be repeated for different wheelset's angular positions and numerical codes (with their intrinsicapproximations) for assessing realistic working conditions are usually required.
Challenge E: Bringing the territories closer together at higher speeds
Figure 1. Example of rolling test rig(courtesy of Lucchini RS)
Figure 2. Example of non-rolling test rig (courtesy ofDB and HBM)
Rolling test rigs are mainly made up a of two rail discs on which the wheelset to be calibrated is set. Inorder to apply known loads on the wheelset, hydraulic/electric load actuators equipped with load cellsare used [3]. Typically, two vertical actuators (to simulate the load transfer), one lateral actuator (toreproduce the overall lateral force that is applied to the wheelset through the bogie) and twolongitudinal actuators (to impose the desired angle of attack) are used. Moreover, to take into accountthe relative wheel-rail position, displacement transducers (e.g. laser sensors) at contact level areused. The advantage of such test rigs is that the wheelset can be tested in working conditions that aresimilar to those encountered during line tests. Instead, the typical main drawback is due to the factthat no direct measure of wheel-rail contact forces is achievable [2]: wheel-rail contact forces areusually determined either through dynamic equilibria of the whole wheelset, knowing the forcesapplied by the actuators and the wheelset position, and/or through indirect measures, e.g. thedeformation of rail discs near the contact area. Moreover, the lateral forces on the two wheels, as wellas the wheel-rail relative lateral position, cannot be adjusted independently but are a function of theimposed angle of attack of the wheelset and of the applied overall lateral force. Finally, due to theadopted suspension system of the wheelset on the roller rig (usually primary suspensions), thebandwidth of the measuring wheelset that can be explored though the test rig is limited to few Hz andthe curvature of the rails modifies (even though slightly) the contacting conditions, thus the contactstress distribution and the contact forces.Non-rolling test rigs, instead, have a much simpler structure: the wheelset to be calibrated is placedon two dynamometric balances having a minimum of three measuring directions (up to a maximum ofsix measuring directions, i.e. three forces and three moments, [4],[5]) and a shape that approximatesreal rails. Wheel-rail contact forces are therefore directly measured thus greatly improving theaccuracy of the calibration procedure. The drawback, instead, is that the wheelset is not rolling. Thus,if the output of the measuring set-up of the wheelset is a function of the wheelset angular position,calibration tests have to be repeated for different angular positions. Moreover, in order to calibrate thewheelset under realistic working conditions, it is useful to carry out numerical simulations of therunning behaviour of the wheelset. However, being the "equivalent rails" non moving with respect tothe wheelset, it is possible to apply external forces either to the wheelset through the journal bearingor directly to the rails. Thus, the bandwidth of the wheelset that can be assessed during the calibrationtests is not determined by the suspension system of the wheelset to the test rig but by the bandwidthof the actuators (that is typically higher). Moreover, if lateral and longitudinal actuators are applied toeach dynamometric balance, independent lateral and longitudinal contact forces can be applied toeach wheel (obviously, appropriate bounding conditions on the wheelset are required) up to theirfriction limit. It is also very easy to test the influence of different gauges (as well as different wheel-railrelative lateral positions) and no rail curvature effect is present.Looking at the pros and cons, non-rolling test rigs seem more suitable for calibrating instrumentedwheelsets except for the fact that the calibration procedure is longer and more complicated since ithas to be repeated for different wheelset's angular positions and numerical codes (with their intrinsicapproximations) for assessing realistic working conditions are usually required.
Challenge E: Bringing the territories closer together at higher speeds
Figure 1. Example of rolling test rig(courtesy of Lucchini RS)
Figure 2. Example of non-rolling test rig (courtesy ofDB and HBM)
Rolling test rigs are mainly made up a of two rail discs on which the wheelset to be calibrated is set. Inorder to apply known loads on the wheelset, hydraulic/electric load actuators equipped with load cellsare used [3]. Typically, two vertical actuators (to simulate the load transfer), one lateral actuator (toreproduce the overall lateral force that is applied to the wheelset through the bogie) and twolongitudinal actuators (to impose the desired angle of attack) are used. Moreover, to take into accountthe relative wheel-rail position, displacement transducers (e.g. laser sensors) at contact level areused. The advantage of such test rigs is that the wheelset can be tested in working conditions that aresimilar to those encountered during line tests. Instead, the typical main drawback is due to the factthat no direct measure of wheel-rail contact forces is achievable [2]: wheel-rail contact forces areusually determined either through dynamic equilibria of the whole wheelset, knowing the forcesapplied by the actuators and the wheelset position, and/or through indirect measures, e.g. thedeformation of rail discs near the contact area. Moreover, the lateral forces on the two wheels, as wellas the wheel-rail relative lateral position, cannot be adjusted independently but are a function of theimposed angle of attack of the wheelset and of the applied overall lateral force. Finally, due to theadopted suspension system of the wheelset on the roller rig (usually primary suspensions), thebandwidth of the measuring wheelset that can be explored though the test rig is limited to few Hz andthe curvature of the rails modifies (even though slightly) the contacting conditions, thus the contactstress distribution and the contact forces.Non-rolling test rigs, instead, have a much simpler structure: the wheelset to be calibrated is placedon two dynamometric balances having a minimum of three measuring directions (up to a maximum ofsix measuring directions, i.e. three forces and three moments, [4],[5]) and a shape that approximatesreal rails. Wheel-rail contact forces are therefore directly measured thus greatly improving theaccuracy of the calibration procedure. The drawback, instead, is that the wheelset is not rolling. Thus,if the output of the measuring set-up of the wheelset is a function of the wheelset angular position,calibration tests have to be repeated for different angular positions. Moreover, in order to calibrate thewheelset under realistic working conditions, it is useful to carry out numerical simulations of therunning behaviour of the wheelset. However, being the "equivalent rails" non moving with respect tothe wheelset, it is possible to apply external forces either to the wheelset through the journal bearingor directly to the rails. Thus, the bandwidth of the wheelset that can be assessed during the calibrationtests is not determined by the suspension system of the wheelset to the test rig but by the bandwidthof the actuators (that is typically higher). Moreover, if lateral and longitudinal actuators are applied toeach dynamometric balance, independent lateral and longitudinal contact forces can be applied toeach wheel (obviously, appropriate bounding conditions on the wheelset are required) up to theirfriction limit. It is also very easy to test the influence of different gauges (as well as different wheel-railrelative lateral positions) and no rail curvature effect is present.Looking at the pros and cons, non-rolling test rigs seem more suitable for calibrating instrumentedwheelsets except for the fact that the calibration procedure is longer and more complicated since ithas to be repeated for different wheelset's angular positions and numerical codes (with their intrinsicapproximations) for assessing realistic working conditions are usually required.
Challenge E: Bringing the territories closer together at higher speeds
Before introducing the proposed full scale test rig for the calibration of instrumented wheelsets, it isimportant to briefly describe how a measuring wheelset works: by correlating measured (usingtraditional resistive or innovative optical/piezoelectric strain gauges) strains on the axle and/or wheelwebs to the forces at wheel-rail contact during the calibration phase, it is possible to determine acorrelation matrix [2] that, during the line tests, allows to pass from the measured strains to wheel-railcontact forces. However strains are a function of both contact forces and reaction forces at axle box.It is therefore of great importance to reproduce on the wheelset's calibration test rig the real contactconditions (rail profile) and boundary conditions (axlebox connecting elements).
2. SPECIFICATIONS AND DESIGN OF THE TEST BENCHAccording to the considerations done in the previous paragraph, it was decided to design a non-rollingtest-rig for the calibration of instrumented wheelsets since it allows to directly measure contact forces.Moreover, in order to be able to exactly reproduce both the contact and boundary conditions, and thusobtain an instrumented wheelset that is able to measure contact forces with high accuracy, it wasdecided to design a test-rig that allows to accommodate a complete bogie. In this case, in fact, theinstrumented wheelset has boundary conditions that are exactly those it will be experience duringinline tests. Note that, in order to reduce the complexity (and cost) of the test-rig, only oneinstrumented wheelset can be calibrated at a time. If the bogie is equipped with more than oneinstrumented wheelset, the calibration procedure has to be repeated for each instrumented wheelset.This will be explained better later on.In Europe different kind of bogies are adopted on vehicles designed for passenger or goodtransportation. Bogie characteristics in terms of dimensions and architecture vary based on loadrequirements and type of transportation.The main parameters to be taken into account are:
number of axles: bogie wheelbase; rail gauge: wheel diameter; maximum values of wheel rail contact forces.
With regard to the architecture of the bogie it is possible to find in service bogieless vehicles up tofour-axle bogies, when heavy weight vehicles are involved. Bogie wheelbase is strictly related to thearchitecture, usually the larger the number of wheelsets the smaller the wheelbase.The rail gauge used is unified for interoperability purposes to 1435 mm, but different values are foundall over the railways, for example the gauge of the “Circumvesuviana” (a narrow gauge railway nearNaples) is set to 950 mm, whereas values up to 1668 mm are adopted in Spanish and Portugueserailways. Even the diameter of the wheels changes in order to satisfy the requirements, the range ofvariation is from 360 mm for low-flatcar wagons up to 1200 mm for high-speed trains or locomotives.The maximum axle load can vary between 17 tonnes (for passenger vehicles) and 22.5 tonnes (forloaded freight wagons). Usually vertical loads are limited to those values in order to prevent trackdamages. In order to define the maximum lateral load applied to the wheel it has to be taken intoaccount that the maximum Nadal coefficient Y/Q (lateral load over vertical load on the wheel), withoutobtaining derailment, depends on track geometry and on wheel and rail actual profiles and can reachvalues up to 1.8 [3]. As far as the longitudinal load is concerned the maximum achievable load isapproximately equal to vertical load acting at wheel-rail contact.The project specifications of the test-rig are defined based on the range of variation of the parameterspreviously described, in order to guarantee the maximum flexibility of use.The structure of the test-rig is essentially composed by two parts, the base and the portal.The base (shown in green in Figure 3) is constrained to the ground and the rails (grey) are installedon the upper part, having the possibility of varying the rail gauge. Each rail is equipped with thestandard UIC60 profile and is mounted with a 1/20 cant, it is divided into two parts, the first one isused only to support the bogie whereas the second part has a measuring function; in fact this part isconnected by means of a shaped plate (orange) to the load cells in order to obtain a direct measure ofwheel-rail contact forces. Each plate is also connected to both lateral and longitudinal actuators(black) in order to apply directly forces to the rail in these directions.
Challenge E: Bringing the territories closer together at higher speeds
Figure 3. Solid model of the test rig for the calibration of instrumented wheelsets
The base is also composed by two lateral beams (green), placed parallel to the rails, where the portalis fixed. On the surface of the beams several holes are arranged in order to fix the portal in suitablelongitudinal positions with respect to the test-rig. Since the portal acts as ground for the verticalactuators, its longitudinal position is chosen for keeping aligned the vertical actuators with respect tothe vertical secondary suspensions.The portal is made up of two lateral columns (blue) connected to the base and a transversal beam(blue) linking the columns which can be fixed in different positions. the vertical actuators (black) areinstalled on the transversal beam through spherical joints and their vertical position depends on thecan be modified acting on the transversal beam. Additionally their lateral position can be set in orderto match the lateral distance of the vertical secondary suspensions. In order to avoid large bogiedisplacements, bumpstops in lateral and longitudinal directions are used.With regard to the actuators, hydraulic ones were chosen due to their capability to generate hugeforces (greater than electric drives for equal volume) and apply small displacements around the sameworking position without the development of backlashes in the transmission. To obtain a pass-bandas high as possible, it has been decided to place the hydraulic actuators, where possible (i.e. forlongitudinal and lateral motions), at wheel-rail interface and equip them with high performance servo-valves. In the vertical direction, instead, it was decided to place the actuators on top of the bogie so toapply the forces through the secondary suspension. This decision was taken in order to keep theheight of the test rig as small as possible for safety reasons. Thus, although high performance servo-valves were chosen also for the vertical actuators, the pass-band in vertical direction is limited by thepass-band of primary and secondary suspensions (where available).To be able to calibrate almost any kind of instrumented wheelset, it was decided to adopt verticalactuators that could generate a load up to 250kN each. However, due to the flexible configuration ofthe test rig, even more powerful and, eventually, more than two vertical actuators should be able to fitinto the test rig. For what concerns the longitudinal and lateral actuators, although only two actuatorsfor each dynamometric balance would be sufficient (one in longitudinal and one in lateral direction), itwas decided to use three actuators (due to the available space two placed longitudinally and oneplaced laterally) in order to be able to generate any in-plane motion and thus to also assess theinfluence of the contact point position on the calibration matrix. To achieve the required flexibilitytarget, also for both longitudinal and lateral actuators it was decided to adopt actuators able togenerate a force of 50kN. As for the vertical actuators, if higher forces are required, both longitudinaland lateral actuators should easily be replaced by more powerful ones.
Challenge E: Bringing the territories closer together at higher speeds
Figure 3. Solid model of the test rig for the calibration of instrumented wheelsets
The base is also composed by two lateral beams (green), placed parallel to the rails, where the portalis fixed. On the surface of the beams several holes are arranged in order to fix the portal in suitablelongitudinal positions with respect to the test-rig. Since the portal acts as ground for the verticalactuators, its longitudinal position is chosen for keeping aligned the vertical actuators with respect tothe vertical secondary suspensions.The portal is made up of two lateral columns (blue) connected to the base and a transversal beam(blue) linking the columns which can be fixed in different positions. the vertical actuators (black) areinstalled on the transversal beam through spherical joints and their vertical position depends on thecan be modified acting on the transversal beam. Additionally their lateral position can be set in orderto match the lateral distance of the vertical secondary suspensions. In order to avoid large bogiedisplacements, bumpstops in lateral and longitudinal directions are used.With regard to the actuators, hydraulic ones were chosen due to their capability to generate hugeforces (greater than electric drives for equal volume) and apply small displacements around the sameworking position without the development of backlashes in the transmission. To obtain a pass-bandas high as possible, it has been decided to place the hydraulic actuators, where possible (i.e. forlongitudinal and lateral motions), at wheel-rail interface and equip them with high performance servo-valves. In the vertical direction, instead, it was decided to place the actuators on top of the bogie so toapply the forces through the secondary suspension. This decision was taken in order to keep theheight of the test rig as small as possible for safety reasons. Thus, although high performance servo-valves were chosen also for the vertical actuators, the pass-band in vertical direction is limited by thepass-band of primary and secondary suspensions (where available).To be able to calibrate almost any kind of instrumented wheelset, it was decided to adopt verticalactuators that could generate a load up to 250kN each. However, due to the flexible configuration ofthe test rig, even more powerful and, eventually, more than two vertical actuators should be able to fitinto the test rig. For what concerns the longitudinal and lateral actuators, although only two actuatorsfor each dynamometric balance would be sufficient (one in longitudinal and one in lateral direction), itwas decided to use three actuators (due to the available space two placed longitudinally and oneplaced laterally) in order to be able to generate any in-plane motion and thus to also assess theinfluence of the contact point position on the calibration matrix. To achieve the required flexibilitytarget, also for both longitudinal and lateral actuators it was decided to adopt actuators able togenerate a force of 50kN. As for the vertical actuators, if higher forces are required, both longitudinaland lateral actuators should easily be replaced by more powerful ones.
Challenge E: Bringing the territories closer together at higher speeds
Figure 3. Solid model of the test rig for the calibration of instrumented wheelsets
The base is also composed by two lateral beams (green), placed parallel to the rails, where the portalis fixed. On the surface of the beams several holes are arranged in order to fix the portal in suitablelongitudinal positions with respect to the test-rig. Since the portal acts as ground for the verticalactuators, its longitudinal position is chosen for keeping aligned the vertical actuators with respect tothe vertical secondary suspensions.The portal is made up of two lateral columns (blue) connected to the base and a transversal beam(blue) linking the columns which can be fixed in different positions. the vertical actuators (black) areinstalled on the transversal beam through spherical joints and their vertical position depends on thecan be modified acting on the transversal beam. Additionally their lateral position can be set in orderto match the lateral distance of the vertical secondary suspensions. In order to avoid large bogiedisplacements, bumpstops in lateral and longitudinal directions are used.With regard to the actuators, hydraulic ones were chosen due to their capability to generate hugeforces (greater than electric drives for equal volume) and apply small displacements around the sameworking position without the development of backlashes in the transmission. To obtain a pass-bandas high as possible, it has been decided to place the hydraulic actuators, where possible (i.e. forlongitudinal and lateral motions), at wheel-rail interface and equip them with high performance servo-valves. In the vertical direction, instead, it was decided to place the actuators on top of the bogie so toapply the forces through the secondary suspension. This decision was taken in order to keep theheight of the test rig as small as possible for safety reasons. Thus, although high performance servo-valves were chosen also for the vertical actuators, the pass-band in vertical direction is limited by thepass-band of primary and secondary suspensions (where available).To be able to calibrate almost any kind of instrumented wheelset, it was decided to adopt verticalactuators that could generate a load up to 250kN each. However, due to the flexible configuration ofthe test rig, even more powerful and, eventually, more than two vertical actuators should be able to fitinto the test rig. For what concerns the longitudinal and lateral actuators, although only two actuatorsfor each dynamometric balance would be sufficient (one in longitudinal and one in lateral direction), itwas decided to use three actuators (due to the available space two placed longitudinally and oneplaced laterally) in order to be able to generate any in-plane motion and thus to also assess theinfluence of the contact point position on the calibration matrix. To achieve the required flexibilitytarget, also for both longitudinal and lateral actuators it was decided to adopt actuators able togenerate a force of 50kN. As for the vertical actuators, if higher forces are required, both longitudinaland lateral actuators should easily be replaced by more powerful ones.
Challenge E: Bringing the territories closer together at higher speeds
As already pointed out, the advantage of non-rolling test-rigs with respect to rolling ones is that wheel-rail contact forces can be directly measured. Therefore, in the test-rig under each wheel of theinstrumented wheelset, a seven component dynamometric balance is positioned having a piece of railplaced on top of it. Besides the three load cells on top of the in-plane hydraulic (longitudinal andlateral) actuators, four load cells should be placed on top of four rods with spherical joints at theextremities that connect the balance to the base of the test-rig. This configuration of thedynamometric balance allows to measure not only the three contact force components (longitudinal,lateral and vertical) but also the resultant torques (pitch, roll and spin torques) that can be profitablyused to determine the wheel-rail contact point position as will be explained later on. Load cells shouldbe chosen to measure forces up to the highest possible value, i.e.
the maximum load applied by the actuators (for the longitudinal and lateral ones) times,eventually, a safety factor, and
one fourth of the sum of maximum load applied by the two vertical actuators plus the weightof the bogie divided by the number of wheels plus the weight of the wheelset divided by twotimes, eventually, a safety factor.
Obviously, due to the fact that also the static force component is of interest, strain gauge load cellsshould be used.The engineering solutions adopted in the design of the test-rig guarantee the flexibility of userequested by the specifications, in fact:
the rail gauge can range from 600 mm to 1700 mm; bogies with different architecture and wheelbase can be mounted into the test-rig; wheelsets with different wheel radii up to 1200 mm can be tested; the maximum total vertical force which can be applied to the bogie through the secondary
suspensions is set to 500 kN; the maximum lateral force applicable to each plate is set to 50 kN; the maximum longitudinal force is set equal to two times the lateral one.
3. REALIZATION OF THE TEST BENCH AND SENSORLAYOUTAs described in the previous paragraph, the specifications and requirements of the test rig impose tohave quite a bulky structure that is mainly made by a basement that contains the dynamometricbalances with the longitudinal and lateral actuators and on top of which the complete bogie with theinstrumented wheelset(s) to be calibrated is placed. To be able to apply the vertical loads throughhydraulic actuators on the bogie's secondary suspensions, a portal is used. Figure 3 shows a pictureof the developed test rig.Before producing the test rig, stresses and deformations in the test rig structure were investigatedthrough a finite element model in order to verify that no failures nor excessive deformations wouldoccur. Fe350 steel was considered for the structure. Figures 4 and 5 show von Mises stresses(maximum value equal to 55MPa) and the vertical displacement component (maximum value equalto 3mm) respectively when both vertical actuators are applying a force of 250kN. Both values areconsidered acceptable.As previously described, to obtain a high pass-band, high performance servo-valves were used.Figure 6 shows the transfer function of the servo-valves, produced by MOOG, adopted for thelongitudinal and lateral actuators. It can be seen that the pass-band reaches almost 130Hz with aphase lag of about 60°. Note that the phase lag between the input (reference signal) and the output(generated force/displacement) of the actuators is of no importance. The phase lag that should beconsidered is the one being the applied displacement and the measured contact force. However, dueto the fact that the load cells are placed on top of the actuators and that the actuators are rigidlycoupled with the rail piece below the wheel, this phase lag is always equal to zero in the frequencyrange of interest.
Challenge E: Bringing the territories closer together at higher speeds
Figure 4. Von Mises stresses in the test rigstructure due to the application of 250kN
through the vertical actuators
Figure 5. Vertical displacement component in thetest rig structure due to the application of 250kN
through the vertical actuators
Figure 6. Transfer function of the servo-valvesadopted for the longitudinal and lateral hydraulic
actuators (courtesy of MOOG)
Figure 7. Transfer function of the servo-valvesadopted for the vertical hydraulic actuators
(courtesy of MTS)
For what concerns the vertical actuators an MTS servo-valve (model 252.25), having pass-bandreported in Figure 7, is adopted. Note that the servo-valve has a pass-band of more than 30Hz.However, as already pointed out, the effective pass-band in vertical direction is much more limiteddue to the filtering effect of primary and secondary suspensions (where available).Each actuator is equipped with a load cell for force feedback. These load cells are dimensioned onthe maximum force the actuator is able to generate: vertical actuators are equipped with MTS loadcells having full scale equal to 250kN while longitudinal and lateral actuators are equipped with HBMload cells having full scale equal to 50kN. Finally, the (four) vertical rods of the dynamometricbalances are equipped with HBM load cells having full scale equal to 100kN.Figure 8 shows two pictures of the dynamometric balance adopted. The four instrumented rods belowthe balance are clearly visible as well as the lateral actuator (with its load cell on top) and one of thetwo longitudinal actuators (with its load cell on top). Both rods and actuators are connected to the railpiece and to the ground through spherical joints. Thus, the absolute position of the rail piece is fullydefined by knowing the lengths of the rods and of the longitudinal and lateral actuators.
Challenge E: Bringing the territories closer together at higher speeds
Figure 4. Von Mises stresses in the test rigstructure due to the application of 250kN
through the vertical actuators
Figure 5. Vertical displacement component in thetest rig structure due to the application of 250kN
through the vertical actuators
Figure 6. Transfer function of the servo-valvesadopted for the longitudinal and lateral hydraulic
actuators (courtesy of MOOG)
Figure 7. Transfer function of the servo-valvesadopted for the vertical hydraulic actuators
(courtesy of MTS)
For what concerns the vertical actuators an MTS servo-valve (model 252.25), having pass-bandreported in Figure 7, is adopted. Note that the servo-valve has a pass-band of more than 30Hz.However, as already pointed out, the effective pass-band in vertical direction is much more limiteddue to the filtering effect of primary and secondary suspensions (where available).Each actuator is equipped with a load cell for force feedback. These load cells are dimensioned onthe maximum force the actuator is able to generate: vertical actuators are equipped with MTS loadcells having full scale equal to 250kN while longitudinal and lateral actuators are equipped with HBMload cells having full scale equal to 50kN. Finally, the (four) vertical rods of the dynamometricbalances are equipped with HBM load cells having full scale equal to 100kN.Figure 8 shows two pictures of the dynamometric balance adopted. The four instrumented rods belowthe balance are clearly visible as well as the lateral actuator (with its load cell on top) and one of thetwo longitudinal actuators (with its load cell on top). Both rods and actuators are connected to the railpiece and to the ground through spherical joints. Thus, the absolute position of the rail piece is fullydefined by knowing the lengths of the rods and of the longitudinal and lateral actuators.
Challenge E: Bringing the territories closer together at higher speeds
Figure 4. Von Mises stresses in the test rigstructure due to the application of 250kN
through the vertical actuators
Figure 5. Vertical displacement component in thetest rig structure due to the application of 250kN
through the vertical actuators
Figure 6. Transfer function of the servo-valvesadopted for the longitudinal and lateral hydraulic
actuators (courtesy of MOOG)
Figure 7. Transfer function of the servo-valvesadopted for the vertical hydraulic actuators
(courtesy of MTS)
For what concerns the vertical actuators an MTS servo-valve (model 252.25), having pass-bandreported in Figure 7, is adopted. Note that the servo-valve has a pass-band of more than 30Hz.However, as already pointed out, the effective pass-band in vertical direction is much more limiteddue to the filtering effect of primary and secondary suspensions (where available).Each actuator is equipped with a load cell for force feedback. These load cells are dimensioned onthe maximum force the actuator is able to generate: vertical actuators are equipped with MTS loadcells having full scale equal to 250kN while longitudinal and lateral actuators are equipped with HBMload cells having full scale equal to 50kN. Finally, the (four) vertical rods of the dynamometricbalances are equipped with HBM load cells having full scale equal to 100kN.Figure 8 shows two pictures of the dynamometric balance adopted. The four instrumented rods belowthe balance are clearly visible as well as the lateral actuator (with its load cell on top) and one of thetwo longitudinal actuators (with its load cell on top). Both rods and actuators are connected to the railpiece and to the ground through spherical joints. Thus, the absolute position of the rail piece is fullydefined by knowing the lengths of the rods and of the longitudinal and lateral actuators.
Challenge E: Bringing the territories closer together at higher speeds
Figure 8. Picture of one of the two actuated dynamometric balances used to directly measure wheel-rail contact forces.
Through simple equilibria and assuming negligible friction in the spherical joints that suspend the railpiece, it is possible to determine both wheel-rail contact force components as well as the position ofthe geometric wheel-rail contact point. Figure 9 shows a scheme of the dynamometric balance withthe considered reference system. Fx1 and Fx2, Fy and Fz1, Fz2, Fz3 and Fz4 are the measuredlongitudinal, lateral and vertical forces respectively while X, Y and Q are the longitudinal, lateral andvertical wheel-rail contact force components. a1 is the lateral distance between the longitudinalactuators while a2 and a3 are the longitudinal and lateral distance between the vertical actuators.Finally, xc, yc and zc are the wheel-rail contact point coordinates with respect to the adopted referencesystem.
Fz4Fx1
x
z
QX
Y
yc
zc
xc
Fx2
a1/2 a1/2
Fz2Fz2
Fy
a2/2 a2/2
a3/2
a3/2
Figure 9. Scheme of the dynamometric balance with the considered reference system.Thus, through static equilibrium equations along x, y and z directions, the longitudinal, lateral andvertical wheel-rail contact force components can be determined:
2
1xi
iX F
(1)
yY F (2)
Challenge E: Bringing the territories closer together at higher speeds
Figure 8. Picture of one of the two actuated dynamometric balances used to directly measure wheel-rail contact forces.
Through simple equilibria and assuming negligible friction in the spherical joints that suspend the railpiece, it is possible to determine both wheel-rail contact force components as well as the position ofthe geometric wheel-rail contact point. Figure 9 shows a scheme of the dynamometric balance withthe considered reference system. Fx1 and Fx2, Fy and Fz1, Fz2, Fz3 and Fz4 are the measuredlongitudinal, lateral and vertical forces respectively while X, Y and Q are the longitudinal, lateral andvertical wheel-rail contact force components. a1 is the lateral distance between the longitudinalactuators while a2 and a3 are the longitudinal and lateral distance between the vertical actuators.Finally, xc, yc and zc are the wheel-rail contact point coordinates with respect to the adopted referencesystem.
Fz4Fx1
x
z
QX
Y
yc
zc
xc
Fx2
a1/2 a1/2
Fz2Fz2
Fy
a2/2 a2/2
a3/2
a3/2
Figure 9. Scheme of the dynamometric balance with the considered reference system.Thus, through static equilibrium equations along x, y and z directions, the longitudinal, lateral andvertical wheel-rail contact force components can be determined:
2
1xi
iX F
(1)
yY F (2)
Challenge E: Bringing the territories closer together at higher speeds
Figure 8. Picture of one of the two actuated dynamometric balances used to directly measure wheel-rail contact forces.
Through simple equilibria and assuming negligible friction in the spherical joints that suspend the railpiece, it is possible to determine both wheel-rail contact force components as well as the position ofthe geometric wheel-rail contact point. Figure 9 shows a scheme of the dynamometric balance withthe considered reference system. Fx1 and Fx2, Fy and Fz1, Fz2, Fz3 and Fz4 are the measuredlongitudinal, lateral and vertical forces respectively while X, Y and Q are the longitudinal, lateral andvertical wheel-rail contact force components. a1 is the lateral distance between the longitudinalactuators while a2 and a3 are the longitudinal and lateral distance between the vertical actuators.Finally, xc, yc and zc are the wheel-rail contact point coordinates with respect to the adopted referencesystem.
Fz4Fx1
x
z
QX
Y
yc
zc
xc
Fx2
a1/2 a1/2
Fz2Fz2
Fy
a2/2 a2/2
a3/2
a3/2
Figure 9. Scheme of the dynamometric balance with the considered reference system.Thus, through static equilibrium equations along x, y and z directions, the longitudinal, lateral andvertical wheel-rail contact force components can be determined:
2
1xi
iX F
(1)
yY F (2)
Challenge E: Bringing the territories closer together at higher speeds
4
1zi
iQ F
(3)
For the determination of the longitudinal, lateral and vertical wheel-rail geometric contact pointposition, the static equilibrium equations around x, y and z axis are used:
11 2 0
2c c x xa
Yx Xy F F (4)
21 2 3 4 0
2c c z z z za
Qy Yz F F F F (5)
31 2 3 4 0
2c c z z z za
Qx Xz F F F F (6)
thus requiring the solution of the following matrix equation:
11 2
21 2 3 4
31 2 3 4
200
20
2
x x
c
c z z z z
c
z z z z
aF F
Y X xa
Q Y y F F F FQ X z a
F F F F
(7)
The accuracy of the described methodology to determine the wheel-rail geometric contact pointposition relies on the accurate measurement of the distances a1, a2 and a3 as well as on theassumption that the measured forces are purely along the corresponding axis. In case of inclinedrods/actuators, in fact, the measured forces are no longer parallel to the axis of the consideredreference system (that is fixed to the plate of dynamometric balance supporting the rail piece).Therefore it is necessary to define their inclination with respect to the considered reference axis or,equivalently, the rotation of the shaped plate, to this aim two inclinometers are placed on top of it,whereas the third rotation is determined using the actual displacements of the longitudinal actuators.The above equations become a little more complicated but still wheel-rail contact force componentsand geometric contact point position can be accurately determined.Note that each dynamometric balance outputs 16 analogue channels:
- 7 forces measured by the seven load cells;- 3 displacements measured by the position sensors integrated into the actuators;- 2 rotations provided by the inclinometers adopted to determine the rotation of the
rods/actuators.With regard to the accuracy of the measure of wheel-rail contact forces by means of thedynamometric balance it is possible to give an estimate of the uncertainty associated with themeasure. Assuming that each load cell belongs to the same ISO class, having a maximumuncertainty U approximately equal to 0.025% of the full scale and taking into account equations (1),(2) and (3) the standard deviations of the measured wheel-rail contact forces are:
0.018X kN (8) 0.013y kN (9) 0.050Z kN (10)
4. CALIBRATION EXAMPLEThe test-rig previously described has been used for the calibration of the wheelset of a bogie used formetro service. In the following the calibration procedure used to determine the calibration matrix of theinstrumented wheelset will be presented together with the results of the calibration process.In order to use the wheelset as a measuring device it is necessary during the calibration phase tocorrelate the measured strains to the wheel-rail contact forces which generates them. Using the test-rig it is possible to apply vertical, lateral and longitudinal forces to the wheels by means of thehydraulic actuators and to measure simultaneously the strains on the axle and on the wheels and alsothe effective value of the wheel-rail contact force by means of the seven component dynamometricbalance.The calibration process is articulated essentially into four phases. The first phase consists of thedefinition and the execution of a test schedule, by which it is possible to determine the calibrationmatrix which relates the inputs (wheel-rail contact forces) of the system (measuring wheelset) to its
Challenge E: Bringing the territories closer together at higher speeds
outputs (strains). The second phase consists of the evaluation of the uncertainty associated with theestimation of wheel-rail contact force components, by means of the direct comparison between thereference values measured by the seven component dynamometric balance and the ones obtainedby the measuring wheelset, by means of the calibration matrix. The third phase allow to identify,thanks to the redundancy of the system, some backup calibration matrices to be used in case of amalfunctioning of some strain gauge bridges during in-line tests.The fourth phase, finally, allows to verify on the test-rig the dynamic properties of the measuringwheelset. In particular, a time history, representative of curve negotiation, is imposed to the actuatorsin order the verify that the calibration matrix allows to reproduce correctly the loads at wheel-railcontact.At the basis of the calibration procedure there is the definition of the test schedule, which has toexplore, as far as possible, different load combinations the wheelset can be subjected to. To this aimnumerical simulations on a vehicle model, to which the bogie belongs, can be performed in order toidentify some load levels for each wheel-rail contact force component. A DoE (Design of Experiments)is then set-up generating a test schedule composed by different load combinations. Additionally inorder to investigate and quantify the effect of the axial and circumferential position of the contactpoint, the schedule is repeated for three different lateral positions of the wheelset with respect to therail (flange contact on the left wheel, tread contact on both the wheels and flange contact on the rightwheel) and four different angular positions of the wheelset. In each test signals measured by thestrain gauge bridges are acquired and sampled with a frequency of 200 Hz. In order to reduce theeffect of noise a mean over 10 s of time history is calculated. In this way it is possible to obtain for thei-th test the six component of wheel-rail contact forces, which can be collected in a column vector Fi:
, , , , , ,T
i r i l i r i l i r i l iF Q Q Y Y X X (11)indicating again with Q the vertical component of the contact force, with Y the lateral one and with Xthe longitudinal one; subscripts r and l are referred to the right and left wheel. Analogously it ispossible to collect the mean values of the signals measured by the strain gauge bridges in a columnvector i, whose dimensions depend on the number of strain gauge bridges installed on the wheelset.In the case in analysis 14 strain gauge bridges are installed on the axle and 2 strain gauge bridges onthe wheels. For each test the following relation holds:
i iF A (12)
[A] being the calibration matrix of the wheelset to be estimated.Collecting in a matrix [F] the contact forces of each i-th test Fi performed and analogously in a matrix[] the measurements of the strain gauge bridges i it is possible to write:
*F A (13)where [A*] represents the estimation of the calibration matrix [A], [F] is a matrix of dimension n x 6and [] is a matrix n x number of strain gauge bridges, n being the total number of tests. Manipulatingin a suitable way Equation (13) it is possible to define explicitly matrix [A*]:
1* T TA F
(14)Recalling the definition of the Moore–Penrose pseudoinverse of a rectangular matrix:
1T T
(15)it is possible to define the estimation of the calibration matrix [A*] as the product of the matrix F bythe pseudoinverse []+ of the matrix []. Matrix [A*] defined in such a way is the best fit of thecalibration matrix [A] in the least-squares sense. Once matrix [A*] is defined it is possible to calculate,for each test performed, the values of the contact forces and compare them with the ones measuredby means of the seven component dynamometric balances. In particular it is possible to define theestimation error the measured value of each component of the contact force as the differencebetween the reference force value obtained by direct measure and the one obtained by means of theinstrumented wheelset:
ref estF F (16)A measure of the uncertainty associated with the estimation of the contact forces can be expressedby the standard deviation of the estimation error , taking into account that the standard deviations ofthe wheel-rail contact forces measured by means of the dynamometric balance are very small, asshown by Equations (8), (9) and (10), and, therefore, from an engineering point of view, practicallynegligible.In Figures 10, 11 and 12, the comparison between the reference and the measured force values arereported for each contact force component. The x axis represent the reference values, whereas the
Challenge E: Bringing the territories closer together at higher speeds
values measured by means of the instrumented wheelset are on the y axis. Therefore, each point onthe diagram represent a calibration test, additionally the band Fref± is shown by mean of red dashedlines.
Figure 10. Comparison between the reference and measured values of the vertical component of thecontact force.
Figure 11. Comparison between the reference and measured values of the lateral component of thecontact force.
Figure 12. Comparison between the reference and measured values of the longitudinal component ofthe contact force.
-10 0 10 20 30 40 50 60-10
0
10
20
30
40
50
60
Reference force [kN]
Mea
sure
d fo
rce
[kN
]
Right wheel: vertical contact force component - = 2.944%
-10 0 10 20 30 40 50 60-10
0
10
20
30
40
50
60
Reference force [kN]
Mea
sure
d fo
rce
[kN
]
Left wheel: vertical contact force component - = 4.443%
-5 0 5 10 15 20 25-5
0
5
10
15
20
25
Reference force [kN]
Mea
sure
d fo
rce
[kN
]
Right wheel: lateral contact force component - = 2.021%
-25 -20 -15 -10 -5 0 5-25
-20
-15
-10
-5
0
5
Reference force [kN]
Mea
sure
d fo
rce
[kN
]
Left wheel: lateral contact force component - = 1.778%
-15 -10 -5 0 5 10 15-15
-10
-5
0
5
10
15
Reference force [kN]
Mea
sure
d fo
rce
[kN
]
Right wheel: longitudinal contact force component - = 1.615%
-15 -10 -5 0 5 10 15-15
-10
-5
0
5
10
15
Reference force [kN]
Mea
sure
d fo
rce
[kN
]
Left wheel: longitudinal contact force component - = 1.329%
Challenge E: Bringing the territories closer together at higher speeds
Table 1 report the values of the standard deviation of the estimation error , both in absolute termsand percent terms with respect to the maximum value assumed by the corresponding component ofthe contact force.
Table 1: Standard deviation of the estimation error .
It is observed that the percent standard deviation error is never larger than 5%, whereas in absoluteterms it is always smaller than 3 kN.
5. CONCLUSIONSIn the paper the design and the realization of a test-rig for the calibration of instrumented wheelsetshas been described. The flexibility of the test-rig allows to accommodate a bogie assembly made upof a bogie frame and 2/3/4 wheelsets, depending on the vehicle architecture, or a single wheelset incase of a non-bogie vehicle. This solution allows to correctly reproduce the boundary conditions onthe wheelsets, since they are exactly those it will be experience during inline tests, thus resulting in asystem that is able to measure contact forces with high accuracy. Additionally using a non-rolling testrig it is possible to have a direct measure of wheel-rail contact forces by means of two dynamometricbalances, thus greatly improving the accuracy of the calibration procedure. The drawback, instead, isthat the wheelset is not rolling, therefore the calibration procedure must be repeated for differentangular positions in order to ensure that a unique calibration matrix can be used. It is also described aprocedure allowing to define the position of the contact point between the wheel and the rail using asinputs the forces measured by means of the dynamometric balances and their geometricaldimensions. Additionally a calibration example is reported. The wheelset under calibration belongs toa bogie used for metro service. The calibration procedure is described and adopted in order to obtainthe calibration matrix of the wheelset, it is also shown that the direct measure of wheel-rail contactforces allows to obtain an estimate of the accuracy of the system. In particular the standard deviationof the estimation error is used in order to quantify the accuracy of the device, showing that inpercentage terms, its value is never larger than 5%.
REFERENCES[1] EN 14363:2005 ”Railway applications. Testing for the acceptance of running characteristics ofrailway vehicles. Testing of running behaviour and stationary tests”, 2005.[2] Braghin F., Bruni S., Cervello S., Cigada A., Resta F., "A new method for the measure of wheel-railcontact forces", 6. International Conference on Contact Mechanics and Wear of Rail/Wheel Systems(CM2003), Gothenburgh, Sweden June 10-13, 2003, 313-319.[3] Braghin F., Bruni S., Diana G., “Experimental and numerical investigation on the derailment of arailway wheelset with solid axle”, Vehicle System Dynamics 44 (4), 2006, 305–325.[4] M. Ostermeyer, H. Berg, H.H. Zuck, “Der heutige Entwicklungsstand der MeßmethodeRadsatzwellenverfahren zur Bestimmung der Kräfte zwischen Rad und Schiene”, ZEV GlasersAnnalen, 102(2), 1978, 53-61.[5] H. Berg, G. Gossling, H. Zuck, “Radsatzwelle und Radscheibe - die richtige Kombination zurMessung der Krafte Zwischen Rad und Schiene”, ZEV Glasers Annalen, 120 (2), 1996, 40-47.
