NL2020072B1

NL2020072B1 - System for assessment of traction between a rail and a wheel and method for assessment of the same

Info

Publication number: NL2020072B1
Application number: NL2020072A
Authority: NL
Inventors: Medendorp Harm; Berrier Tim
Original assignee: Laser Tribology B V
Priority date: 2017-12-12
Filing date: 2017-12-12
Publication date: 2019-06-19
Also published as: WO2019117716A1

Abstract

Measurement system for assessment of available traction between a rail and a wheel on the rail, wherein the system is designed for assessment of at least a normal force of the wheel on the rail, a friction force between the wheel and the rail and a difference between the rotational speed of the wheel and a linear speed of the wheel relative to the rail, and a processing unit for processing data acquired by the system for calculating available traction.

Description

Title: System for assessment of traction between a rail and a wheel and method for assessment of the same

The invention relates to methods and systems for assessment of traction between a rail and a wheel driven thereon.

Such systems are known in the art and are commonly referred to as tribometer. A known tribometer is a hand operated tribometer. This is a relatively simple device which can be hand held and can measure traction with a very low accuracy and depends very much on the operator. A more elaborate system for assessment of rail traction is a rail vehicle specifically designed for the purpose and is known as a Tribo Train, designed by Network Rail. This train again is relatively inaccurate in traction assessment.

An aim of the present disclosure is to provide for system for assessment of traction between a wheel and a rail. An aim of the present disclosure is to provide for a method for assessment of traction between a rail and a wheel driven thereon. An aim of the present disclosure is to provide for a system and method for aiding in control of train management. An aim of the disclosure is to provide for a system and method for adjusting engine management and/or brake management of a train based at least on traction assessment.

At least one of these aims is at least in part achieved with a method and/or system according to the disclosure.

In an aspect a system according to the disclosure can be characterized in that the system is designed for assessment of at least a normal force of the wheel on the rail, a friction force between the wheel and the rail and a difference between the rotational speed of the wheel and a linear speed of the wheel relative to the rail. A processing unit can be provided for processing data acquired by the system for calculating available traction. For obtaining the required data related to normal force, friction force, rotational speed and linear speed sensor systems can be provided, which can be individual sensor systems for the forces and the speeds or combined sensors, for example a single sensor system for both rotational and linear speed and a single sensor system for both normal force and friction force.

In an aspect the forces can be measured using stress and/or strain measurement in the wheel and/or an axes to which the wheel is connected.

In an aspect speeds of the wheel relative to the rail can be measured using a laser system, such as a Doppler based laser system. Such system is especially advantageous for measurement of accurate linear speed.

In an aspect the sensors for at least sensor systems for assessment of rotational speed and/or linear speed can be designed for measurement of or at least assessment of at least one of and preferably both of the rotational speed and the linear speed at a contact area between the wheel and the rail.

In an aspect a method according to the disclosure can comprise assessment of traction between a rail and a wheel on the rail, wherein at least a normal force of the wheel on the rail, a friction force between the wheel and the rail and a difference between the rotational speed of the wheel and a linear speed of the wheel relative to the rail are assessed. The data acquired by the system is used in calculating available traction.

In an aspect a method according to the disclosure can comprise assessing rotational speed of the wheel and linear speed of the wheel using a laser Doppler based system, especially a laser Doppler anemometry based system, preferably for assessment of both rotational speed and linear speed.

In an aspect a method according to the disclosure can comprise assessment of traction or available traction between a wheel of a train and a rail on which said wheel is driven, for example by assessing momentary slip between said wheel and said rail, and providing the outcome of said assessment to an engine management and/or braking management of said train and/or providing said outcome to a train track management system for managing multiple trains on a track system.

In further elucidation of the present invention embodiments of the present disclosure, such as embodiments of methods and systems shall be described hereafter, with reference to the drawings. Herein shows:

Fig. IA and B schematically show a wheel mounted on an axle, in perspective view (fig. IA) and in side view (fig IB) showing different forces and speeds;

Fig. 2 shows in perspective side view schematically a wheel on an axle, provided with sensors;

Fig. 3 shows schematically a wheel on a rail, in side view, with sensors provided for measurement of at least one speed component;

Fig. 4 shows schematically part of a tribometer according to the disclosure, for off track measurements;

Fig. 5 shows schematically a Stribeck type curve;

Fig. 6 shows schematically a traction curve for a train;

Fig. 7 shows schematically a feedback display for traction; and

Fig. 8 shows schematically a mapping of historical data obtained with a system and/or method according to the disclosure;

Fig. 9 shows schematically a system according to the disclosure comprising a processing unit connected to a management system.

In this description embodiments of the invention will be described with reference to the drawings by way of example only. These embodiments should by no means be understood as limiting the scope of the disclosure. At least all combinations of elements and features of the embodiments shown are also considered to have been disclosed herein. In this description the same or similar elements and features will be referred to by the same or similar reference signs.

In this description expressions of orientation such as top, bottom, vertical etcetera are used for convenience only and refer to the orientation of a train in a normal, horizontal position as seen in the accompanying drawings. Such expressions are not to be regarded as limiting the orientation of elements of the system in use.

In this description a train has to be understood as a vehicle or a series of coupled vehicles, driven on a track comprising at least one rail. A train wheel has to be understood as a wheel of such train, preferably a driven wheel. Such wheel can be a wheel mounted to, especially fixed to an end of a wheel axle. Such wheel can be fixed to the axle such that it cannot rotate relative to the axle. In such embodiment a force aiming to rotate the wheel relative to the axle would result in torque in at least the axle. In embodiments the wheel and rail will be made of metal.

In a system 100 according to the disclosure, for assessment of available traction between a rail 2 and a wheel 1 on the rail 2, the system can be designed for assessment of at least a normal force Q of the wheel 1 on the rail 2, a friction force X between the wheel 1 and the rail 2 and a difference between the rotational speed VI of the wheel 1 and a linear speed V2 of the wheel 1 relative to the rail 2. A processing unit 101 can be provided for processing data acquired by the system 100 for calculating available traction T.

In embodiments a first sensor system 9 for assessment of the normal force Q and the friction force X. In embodiments a second sensor system 12 can be provided for measuring the rotational speed Vi and the linear speed Va. The second sensor system 12 can be provided for assessment of slip S of the wheel 1 relative to the rail 2. In embodiments the processing unit 101 can be designed for receiving and processing data received from the sensor systems 9, 12, and calculating available traction T for the wheel 1 on the rail 2. A processing unit 101 has to be understood at least as a single unit or a series of cooperating units, for electronically processing data received from one or more sensor systems. The processing unit 101 can be designed for determining a Stribeck curve for the wheel 1.

In embodiments the processing unit 101 can be coupled to a management system 102, for example an engine management system 103 and/or a brake management system 104, for at least aiding in operation of an engine of the train and/or brakes of the train. Additionally and/or alternatively the data received and processed could be used in a train operating process, such as for example for planning, time table systems, track use, train assembling and the like.

In this disclosure contact between a wheel and a rail has to be understood as including but not limited to direct contact, that is for example metal on metal contact, or indirect contact, for example through a lubricant and/or friction lowering or increasing substance and/or dirt on the rail and/or the wheel.

In a system and method according to the present disclosure one or more sensors are used for measuring at least a rotational speed Vi of a wheel 1 and linear speed V2 of the wheel 1 relative to a rail 2.

In this description rotational speed Vi has to be understood as the speed, for example in meter/second (m/s), of a contact surface portion 3 of the wheel 1. A contact surface portion 3 may be defined as a portion of the wheel which will make contact with the rail 2, at a contact area CA between the wheel 1 and the rail 2, at the relevant surface area 4 of the rail 2. The contact surface portion 3 will extend circumferentially around the wheel, and may have a width perpendicularly to the rail surface 4, substantially parallel to a longitudinal axis Y - Y of the axle. The contact area CA may be substantially a point contact, a line contact or a small surface contact. The rotational speed can be measured directly by a relevant sensor system, or can be calculated based on other parameters measured, such as for example a rotating speed of the wheel or the axle, for example in degree or radial per second, and the diameter of the wheel measured at the contact surface portion 3.

In this description linear speed V2 has to be understood as a speed, for example in m/s, of the wheel 1 measured parallel to a longitudinal direction LD of the rail 2, measured at or near the contact area CA, Again, the linear speed V2 can be measured directly or indirectly, or can be calculated based on other parameters. Preferably a linear speed V2 is measured directly by using a sensor system mounted on a train to which the wheel is attached, sensing displacement of at least one sensor along the rail in said longitudinal direction LD.

From the above it can follow that a difference in Vi and V2 is an indication of slip of the wheel 1 over the rail 2 in the contact area CA. This slip S can be calculated as S=(2* | V1-V21 )/(Vi+V2)).

Slip S is the relative motion between a train wheel 1 and the rail surface 3 it is moving on. This slip S can be generated either by the wheels rotational speed being greater or less than the free-rolling speed. This is usually described as percent slip. In embodiments a difference in rotational speed between a free rotating axle and a braked/driven axle of a train can be used to detect slip with the use of tachometers. In alternative embodiments slip S can be determined based on the difference in speed of the train in the longitudinal direction LD of the rail measured using satellite based positioning, such as GPS, with rotating speed of the train-wheel, for example measured using a tachometer. A more accurate measurement can be obtained with an absolute measurement, especially by the use of a laser based sensor system, such as Laser Surface Velocimeters.

In this disclosure a normal force Q will be understood at least as a substantially vertical force, for example in Newton (N), substantially perpendicular to the longitudinal axis Y - Y of the axle 5 and substantially perpendicular to the contact area CA. In this disclosure a friction force X, for example measured in N, will be understood at least as a force due to friction between the wheel 1 and the rail 2 in or at the contact area CA, substantially parallel to the surface area 4 of the rail 2 at the contact area CA. The friction force will depend at least on the Coefficient of Friction between the wheel and the rail and/or any layer provided between the two in the contact area CA, and the normal force Q.

Fig. 1A and B schematically show a wheel 1 mounted on an axle 5, in perspective view (fig. 1A) and in side view (fig IB) showing different forces Q, X and speeds Vi and V2. In fig. 1A and B only one wheel 1 is shown, at one end 5A of the axle 5. In embodiments another wheel may be mounted to the opposite end of the axle 5 (not shown) which may or may not be the same as the wheel as shown. In embodiments the wheel 1 can be a driven wheel 1, for example driven by an engine 6 of a train 7 to which the axle 5 is mounted, or by a different engine or motor, for example a motor dedicated to the measuring system 100 comprising the wheel 1 and relevant sensors 10, 15, 16 as will be discussed further hereafter.

Fig. 2 shows in perspective side view schematically a wheel on an axle, provided with sensors 10 of a first sensor system 9, for measuring the normal force Q and frictional force X. In this embodiment a plurality of first sensors 10 is fitted to the wheel, for example in or on a surface of the wheel 1, especially a side surface 11 thereof. The relevant side surface 11 can for example be a surface 11 facing the axle 5. The first sensors 10 can be designed for measuring stress and/or strain in the wheel. The sensors 10 can for example comprise or be formed by strain gauges 10A or the like, which can be spaced regularly, for example over the surface 11 of the wheel 1. The first sensors such as strain gauges 10 can be coupled to a control unit 13, for example provided in a closed housing 14, shielded from the environment.

The control unit 13 can comprise a transmitter for wireless transmitting data obtained from the first sensors 10, as raw data and/or as data processed by the control unit, to the processing unit 101.

Processing data obtained from strain gauges 10A as shown in fig. 2 or similar sensors 10 in order to calculate at least a normal force Q and a friction force X is well known in the art and is for example disclosed in WO2006/128878, herein incorporated by reference for such arrangement and calculations. WO2006/1298878 discloses a mathematical process for calculating, among others, a vertical or normal force Fi and a horizontal or friction force F2 from data obtained from sensors as arranged in general as disclosed in fig. 2 of the present disclosure, especially from first sensors 10 as described, especially strain gauges 10A. In the present system for example such calculations can be used for defining the normal force Q and the friction force X, represented in WO2006/128878 as forces FI and F2. To this end the first sensors 10, 10A and the control unit 13 can be designed according to WO2006/128878.

Fig. 3 shows schematically a wheel 1 on a rail 2, in side view, with sensors 15, 16 of a second sensor system 12, provided for measurement of at least one speed component, especially rotational speed Vi and linear speed V2. As described before the second sensor system 12, especially the sensors 15, 16, which can be referred to as second and third sensor 15, 16 respectively, are preferably designed for direct measurement of the speeds Vi and V2. The second and third sensors 15, 16 can for example be designed as laser based sensors 15, 16. For example laser surface velocimeters.

In fig. 3 by way of example the second and third sensor 15, 16 are designed as laser based velocimeters, using Doppler effect measurement as known in the art, which can also be referred to as Laser Doppler Anemometry (LDA).

Laser Doppler anemometry (LDA), is the technique of using a Doppler shift in a laser beam 17 of a laser 18 to measure velocity of a linear motion of opaque and or reflecting surfaces. The measurement with LDA can be absolute, linear with velocity and requires no pre-calibration.

In a simple and generally used form, LDA crosses two beams of collimated, monochromatic, and coherent laser light on a surface being measured. The two beams are preferably obtained by splitting a single beam 17 of a laser 18, ensuring coherence between the two beams. Lasers 18 with wavelengths in the visible spectrum are commonly allowing a beam path of the beam 17 or beams to be observed. A transmitting optics 16A, 17A focuses the beams 17 to intersect at a focal point, where they interfere and generate a set of straight fringes. As irregularities on the surface 3, 4 of which the relative speed Vi, V2 is to be measured move along the fringes, they reflect laser light from the beams 17 that is then collected by a receiving optics 15B, 16B of the relevant sensor 15, 16 and focused on a photodetector thereof.

The reflected light fluctuates in intensity, the frequency of which is equivalent to the Doppler shift between the incident and scattered light, and is thus proportional to the component of the surface velocity Vi, 2 which lies in the plane of two laser beams 17.

In fig. 3 the second sensor 15 for measurement of the rotational speed Vi is positioned next to the wheel 1, to the front of the wheel 1 or to the rear of the wheel 1, seen in a direction of movement F of the train moving “forward”, in fig. 3 indicated as a direction F to the right of the drawing. The optics 15A, 15B are directed to the surface area 3 of the wheel 1, for example at a level Li crossing a centre C of the wheel 1. The laser beams 17 from the sensor 15 are thus directed directly onto the relevant surface area 3 of the wheel and thus the speed of said surface relative to the sensor 15 can be measured, as the rotational speed Vi of the wheel 1.

In fig. 3 the third sensor 16 for measurement of the linear speed V2 is positioned such that the optics 16A, 16B are directed such that the laser beams 17 are directed towards close by and preferably at the contact area CA between the wheel 1 and the rail 2. With this arrangement the relative speed of the rail 2 relative to the sensor 16 can be measured accurately.

The placement of the LDA sensors 15, 16 in regards to the surfaces 3, 4 can be determined by the dimensions of the wheel and can therefore be dependent on the wheel geometry. It is preferred to measure the linear speed, representative for the velocity of the train, close to the contact area CA of the wheel 1 to avoid inaccuracies which may result from creep forces. Relatively close should in this description preferably be understood as less than about the radius R of the wheel 1, measured near the contact surface portion 3, more preferably less than about three quarters of said radius R, such as for example between halve and one eight or less of said radius R.

When mounted on a train 7 the sensors 15, 16 will move relative to the rail 2 which will be in a fixed position. However, a similar system can be used in a test system, in which for example a wheel 1 can be in a fixed position, mounted on an axle 5, whereas a rail 2 can be moved relative to the wheel 1. Such system is schematically shown in fig. 4, in which schematically part of a tribometer 105 according to the disclosure is shown, for off track measurements.

The second and third sensors 15, 16 are connected to the processing unit 101 too, in order to transmit the relative data obtained with the LDA for processing.

Fig. 5 schematically shows a Stribeck type curve which can be established by the processing unit 101. With at least the sensors 10, 15 and 16 as described a basic Stribeck curve can be determined. This allows to determine in what type of lubrication regime a train is operating and what the optimal tractive effort is or can be. It is known that what the maximal tractive capacity a train is, is determined primarily, and especially as far as the present disclosure is concerned, by the regime in which a train is operating, which can be distinguished as boundary lubrication BL, mixed lubrication ML or elasto-hydrodynamic lubrication EHL. Graphs can be calculated in a known manner for isothermal and for thermal circumstances. By knowing these parameters for a train, the traction effort can be optimized, especially maximized, for example in low friction environments. Additionally or alternatively the system can be used to reduce wear and tear of the wheel-rail interface (Rolling Contact Fatigue), especially in high friction environments and/or it can be used to reduce the waste of energy, for example in medium-to-low friction environments, and/or to reduce the onset of rolling contact fatigue.

Fig. 6 schematically shows a traction curve for a train. Along the vertical axis the Coefficient of friction (COF) is shown, whereas along the horizontal axis the slip S, especially percent slip S% is shown. The coefficient of friction (COF) can be defined as the usable force for traction divided by the force of the weight on the wheel, i.e. the normal force Q. The usable traction can hence be defined as the COF times the normal force Q.

In a system and method according to the disclosure a feedback system 107 can be used in which data obtained by and/or processed by the processing unit 101 can be used for feedback to for example a train operator, for example for engine management and/or brake management, for control of the speed of the train, for example based on available traction and a traction curve as shown.

In a feedback system 107 towards for example an operator of a train, such as a driver of a rail operator, an optimal traction curve as shown can be determined for a given efficiency, capacity, maintenance and safety of the rail network. Each country historically has its own optimal range for a traction coefficient of a rail system. A range between μ 0.15 and μ 0.35 is most common in use. A feedback system 107 can for example comprise a simple sound indicator and/or a visual indicator for the train driver when he approaches the for example 90% of a predetermined maximum COF and for example an another sound and/or visual signal at reaching the maximum COF (Δ). This can also or alternatively be used automated by directly inputting the signal(s) into an engine and/or braking management system of a train. An auditive and/or visual feedback system 107 can be provided in the cabin of a driver, as for example as shown in figure 7. In such visual feedback system 107 as for example shown in fig. 7 different areas can be indicated, for example for a traction too low, a traction good and a traction too high. This provides the driver or engine management system and/or braking system with information on the bases of which the train speed can be adjusted and/or traction can be improved, for example by applying friction increasing means to the wheel-rail interface or contact area CA, such as sand or gel, and/or cleaning the surface 4 of the rail 2 and/or the surface portion 3 of the wheel 1.

In a system and method according to the disclosure a train driver and/or rail-operator can be given a heatmap of historical data, as for example shown in fig. 8, which may at least in part be obtained with a system 100 according to the disclosure, to plan out a current driving strategy and/or an optimal daily routing for the rail operator. These heatmaps can average out, for example to have a day by day or a week-byweek planning for the rail-planners and can be used to further minimize the maintenance and maximize the efficiency, capacity, safety of the rail networks. The heatmap can for example be used for planning train schedules, optimizing train travel times, energy consumption and/or use of traction increasing means, such as for example gel, sand or rail cleaning equipment.

Fig. 9 shows schematically in a block diagram a system according to the disclosure comprising a processing unit 101 connected to a management system 106, for example a train operation management system, an engine management system and/or a brake management system. The first and second sensor systems 9, 12 can be coupled to the processing-unit 101, for example through a control unit as discussed, for example by wire or wireless. Alternatively or additionally such management system may comprise friction increasing means, such as a well known sand box for providing fiiction increasing sand or gel onto the rail surface for increasing traction, or similar means.

The invention is by no means limited to the embodiments as specifically disclosed herein. Many variations thereof are possible within methods or systems of the disclosure, within the scope as defined by the claims. For example different sensors can be used as first, second and/or third sensors. For example a torque sensor can be used in stead of or next to strain gauges as first sensors. For assessment of the rotational speed alternatively or additionally the number of rotations of the wheel can be measured in a given time frame, on the bases of which the rotational speed can be calculated using the radius of the wheel at the desired contact surface area 3 of the wheel, for linear speed alternatively or additionally other sensors or sensor systems can be used, such as for example tachometers or GPS based systems. In the embodiments shown sensors are shown of one wheel on an axle. However, also multiple wheels can be provided with some or all of such sensors, for example wheels on opposite ends of an axle. Communication between sensors and a control unit and/or a processing unit and/or a management system can be obtained differently, for example by wire based systems, wireless based systems or combinations thereof, wherein at least two of the control unit, the processing unit and the management system can be integrated. In embodiments the or each wheel can be provided on a dedicated measurement train or wagon for integration in a train. Alternatively the or each wheel can be the wheel of a further standard train, such as a passenger train or a freight train. In embodiments a train according to the disclosure could be a different type of rail bound vehicle, such as a crane, a monorail vehicle or a transport cart. In embodiments the wheel can be a free rotating or free floating” wheel, for example a rollercoaster cart, for which traction and especially negative traction may be relevant. With a system and method according to the present disclosure available traction can be assessed, for a wheel on a rail, both for acceleration and for deceleration of the wheel, for example for braking.

These and many such variations are considered falling within the scope of the claims.

Claims

Measurement system for determining available traction between a rail and a wheel on the rail, the system being arranged for determining at least a normal force of the wheel on the rail, a frictional force between the wheel and the rail and a difference between the rotational speed of the wheel and a linear speed of the wheel relative to the rail, and a processing unit for processing data obtained by the system for calculating available traction.

Measuring system according to claim 1, wherein the system has a first sensor system for determining the normal force and the frictional force.

Measuring system according to claim 2, wherein the first sensor system comprises at least a strain sensor and / or a tension sensor, for determining elongation and / or tension in the wheel and / or in an axle to which the wheel is attached.

Measuring system according to claim 1 or 2, wherein the first sensor system comprises a control unit, preferably mounted on an axle of the wheel, the control unit comprising a transmitter for transmitting data from the first sensor system to the processing unit, preferably wirelessly.

Measuring system according to any one of the preceding claims, wherein a second sensor system is provided for determining slip between the wheel and the rail, and a transmitter for transmitting data obtained by the second sensor system to the processing unit.

Measuring system according to claim 5, wherein the second sensor system comprises at least one sensor for determining the rotational speed of the wheel relative to the rail, preferably a rotational speed determined at the contact surface between the wheel and the rail, and / or a sensor for linear speed of the wheel relative to the rail.

Measuring system according to claim 5 or 6, wherein at least one of the wheel rotation speed sensor and the wheel linear speed sensor is a laser-based, in particular a laser Doppler-based, system. especially includes a laser Doppler anemometry based system, preferably for both rotational and linear velocity.

Measuring system according to any one of the preceding claims 5-7, wherein the sensor for measuring the rotational speed of the wheel comprises a sensor system based on a laser surface speedometer, and / or the sensor for measuring the linear speed of the wheel a laser surface speedometer based system includes.

Measuring system according to any one of claims 5-8, wherein the sensors are arranged to measure or at least determine at least one of and preferably both the rotational speed and the linear speed at the contact surface between the wheel and the rail.

Measuring system according to any one of the preceding claims, wherein the processing unit is arranged for determining a Stribeck curve on the basis of at least data received from the sensors of the system.

Measuring system according to any one of the preceding claims, wherein the processing unit is arranged to determine a traction curve, preferably an optimal traction curve for a train equipped with the wheel, based on at least the data received from the sensor systems of the system, in particular based on a Stribeck curve provided by the processing unit, and a predetermined friction factor p, wherein a feedback system is connected to the processing unit for providing feedback to an operator of the train when a friction coefficient threshold is reached, preferably different feedback signals for different predetermined threshold values.

Measuring system according to any one of the preceding claims, wherein the processing unit is connected to a train engine management system and / or a train braking system for at least partially controlling the engine and / or the brakes of the train.

Measuring system according to any of the preceding claims, wherein the processing unit is arranged for planning a train control process on the basis of at least data from a database of data obtained by the sensor systems of the measuring system.

14. Method for determining traction between a rail and a wheel on a rail, wherein at least a wheel's normal force on the rail, a frictional force between the wheel and the rail and a difference between the rotational speed of the wheel and the linear speed of the wheel relative to the rail is determined and the data obtained by the system is used to calculate available traction.

The method of claim 14, wherein at least one of the normal force and the frictional force are determined based on a measurement of elongation and / or tension in the wheel and / or an axle to which the wheel is attached.

A method according to claim 14 or 15, wherein wheel rotational speed and linear wheel speed are determined using a laser Doppler based system, in particular a laser Doppler anemometry based system, preferably for determining both the rotational speed as the linear speed.

The method of any one of claims 14-16, wherein wheel rotation speed is determined using a laser surface speedometer based sensor system, and / or linear wheel speed is determined using a laser surface speedometer based sensor system.