WO2012017101A1

WO2012017101A1 - Method for controlling wheel-slippage in electric traction vehicles

Info

Publication number: WO2012017101A1
Application number: PCT/ES2011/000118
Authority: WO
Inventors: Adur Alberdi Ugrte; Txomin Nieva Fatela; Ibon Eciolaza Echeverria
Original assignee: Trainelec, S.L.
Priority date: 2010-08-02
Filing date: 2011-04-14
Publication date: 2012-02-09
Also published as: CN103052552A; ES2374232A1; ES2374232B1; CN103052552B

Abstract

The invention relates to a method for controlling wheel-slippage in electric traction vehicles, which acts on the traction torque of an electric engine that transmits a rotary movement to a drive shaft linked to the vehicle wheels, such that when wheel-slippage is detected, the traction torque of the electric engine is acted on in two consecutive stages: a) exponential reduction in the traction torque during a predetermined reduction time (t_red); and b) linear recovery of the traction torque until the required traction torque (T_ref) is reached or a new slip is detected.

Description

METHOD OF CONTROL OF VEHICLE WHEEL SKATING

ELECTRICAL TRACTION

Technical sector

The present invention relates to the methods and procedures used in electric traction vehicles to avoid, or reduce, the skating or sliding that occurs between the wheels of the vehicles and the raceway through which they travel.

State of the art

The electric traction control systems of railway vehicles ensure that the electric traction motors under their control provide a traction torque, or a braking torque, equal to a reference torque value demanded by the driver of the railway vehicle, or by the control system itself. Thus, when a certain reference torque is demanded, the control system increases the revolutions of electric traction motors to transmit respective turning movements to drive axles to which the wheels of the railway vehicle are associated.

When the traction torque transmitted by the electric motor to the driving axle of the vehicle is greater than the sturdy torque, that is, when the required reference torque exceeds the friction between the wheel and the rail, a skating or sliding phenomenon occurs , of the wheel on the raceway through which it circulates. This phenomenon usually occurs in low grip conditions, when the lane is dirty, wet, or in poor condition, and mainly in the commissioning of the rail vehicle under acceleration conditions to reach the desired traffic speed.

By sliding, the relative speed between the wheel and the rails should be understood, that is, the difference between the linear speed of the wheel and the speed of the vehicle. The wheel tends to suffer a skating when it is split, or tends to block when braking, this produces vibrations that decrease the comfort of the users of the railway vehicle and produces degradations of the material that constitutes the wheels, being able to produce defects that cause a malfunction of the wheels, or even their destruction, such as planes, cracks, coke, exfoliations, etc.

The maximum tensile stress that can be transmitted, that is, the maximum torque that the electric traction motor can transmit to the drive axle depends on the adhesion between the wheel and the rail. The tensile stress to be transmitted can be improved by increasing the adhesion, a conventional solution to increase the adhesion consists of throwing sand on the rail, thus, in the driver's cabin there is a light that warns at the time of skating or sliding , so that at that moment the driver drops sand on the rail to increase adhesion.

Another solution to improve adhesion and optimize traction effort is to associate each electric traction motor that has the rail vehicle to a greater number of axles drives, so that the tensile stress that must be transmitted to each drive axle is reduced. By having a greater number of axles the total weight of the vehicle is increased, which improves the grip between wheel and rail, however, this increase in weight implies a higher energy consumption by electric traction motors, in addition to result in a complex and expensive assembly.

A conventional solution to act on the skating, or sliding, of the wheels of a railway vehicle is that the driver of the vehicle manually reduce the speed of the vehicle, however, this reduction is not fast or precise enough to maximize the tensile stress that is transmitted to the drive axles.

To solve this problem, electric traction control systems that act electronically on the traction torque are known, maximizing the use of the tensile stress transmitted to each driving axle of the rail vehicle. These control systems are based on a reduction, according to a linear expression, of the traction torque transmitted by the electric motor at the time a skating or sliding is detected. This linear reduction of the torque is not optimal, since it can produce vibrations, which reduces the stability of the vehicle, the airship of the vehicle and the comfort of the users.

It is therefore necessary to provide a method to control the skating of railway vehicles, which acts immediately on the wheel slip gradually attenuating it, reducing vibrations and increasing user comfort.

Object of the invention

In accordance with the present invention, a method of controlling the skating of the wheels of electric traction vehicles is proposed, mainly railway traction vehicles, such as trains, trams or meters, which is based on acting on the traction torque of the electric motor controlling its revolutions, so that when a wheel slip on the rail is detected, the traction torque is acted upon by a reduction according to an exponential expression.

Thus, when a sliding, or skating, of the wheel is detected on the running track through which it circulates, the electric motor's driving torque is electronically acted upon according to two consecutive phases:

A. Exponential reduction of traction torque during a predefined reduction time.

B. Linear recovery of traction torque until the required traction torque is reached or a new slip is detected.

The method object of the invention allows a maximum tensile or braking effort to be applied with respect to the conditions of adherence of the road through which the vehicle is traveling.

It also minimizes wheel slippage acting immediately on them, which reduces the value of slip peaks and avoid prolonged slippage over time. Thus, excessive planes and wear on the material that constitutes the wheels are avoided.

On the other hand, vibrations are minimized at the box level of the vehicle, that is, the cars where users travel. The reduction of the traction torque exponentially prevents the torque variations from being too strong, reducing the stress of the mechanical system and improving comfort at the box level. In the same way, greater stability of control of the vehicle in different operating conditions is achieved, such as road defects, winding curves, etc.

A method of very advantageous characteristics is thus obtained, acquiring its own life and preferential character for the application function to which it is intended in relation to the control of the skating of the wheels of a railway vehicle on the raceways through which it circulates.

Description of the figures

Figure 1 shows a graph that relates the evolution of the traction torque of an electric traction motor of a railway vehicle over time.

Detailed description of the invention

Rail vehicles usually have rolling structures, called bogies, on which rest the cars in which the users of the vehicle travel. A bogie consists of a platform where some axes are arranged, which have at their ends the corresponding wheels to travel on some traffic lanes, in the case of a tractor bogie, these axes are driving axes which are associated with an electric traction motor that transmits a traction torque to said drive axles. It may also be the case that each bogie wheel has an independent electric drive motor.

According to this provision, when a tensile torque is demanded from electric motors exceeding the maximum tensile stress that can be transmitted, that is, when the demanded tensile torque (T_ref) exceeds the grip between the wheel and the rail, it is produced a skating or sliding of the wheel. To avoid this fact, the invention proposes a method of controlling the roller skating of electric traction vehicles based on a real-time control of the traction torque transmitted to the drive axles, or if applicable to the drive wheels.

The method is based on acting on the traction torque of the electric motor by controlling its revolutions, so that when a wheel slip on the rail is detected, the traction torque is acted on according to two consecutive phases:

A. Exponential reduction of the traction torque of the electric motor.

B. Linear recovery of the traction torque of the electric motor. With the exponential reduction of the traction torque of the electric motor, the vibrations can be reduced and the stability and airship of the vehicle is improved, thus achieving greater comfort for rail vehicle users than in conventional solutions in which it is carried out a linear reduction of traction torque.

The method object of the invention is composed entirely in the following three stages:

A first stage where a series of rail vehicle variables are assigned and monitored in real time. A second stage where it is detected if there has been a skating, or sliding, of the wheel on the rail, by comparing the variables monitored in the previous stage with preset values. And a third stage that occurs if a skating or sliding is detected in the previous stage, and in which the traction torque is acted upon by a reduction thereof.

Each of these stages is defined in detail below.

Stage 1. Assignment of variables:

A reference torque value (T_ref) is assigned for the traction motor, corresponding to the torque demanded by the driver of the railway vehicle.

The following rail vehicle variables are monitored continuously and in real time. • Acceleration and angular speed of the drive shaft of the electric traction motor.

• Acceleration and tangential or linear speed of the wheel.

• Acceleration and linear speed of the train.

These variables are calculated using conventional techniques, so they are not described in detail in the Patent. The acquisition of these variables can be carried out by means of speed sensors (tachometers) located on the wheels and in the vehicle, or incremental or absolute encoders coupled to traction motors that count a series of pulses to obtain the speed in the driving axis of the engine.

Stage 2. Slip detection:

The variables of the railway vehicle monitored in the previous stage are compared in real time with a series of preset values for the detection of a sliding, or skating, of the wheel on the rail. The detection of a slip, or skating, occurs if any of the following conditions are met:

• If the angular acceleration of the driving axle that drives the wheels is greater than a linear acceleration threshold value.

• If the difference between the linear speed of the wheel and the linear speed of the vehicle is greater than a linear speed threshold value. Since accelerations and decelerations are variable depending on the modes of operation that the rail vehicle can adopt, the linear acceleration threshold can take different values. Thus, the linear acceleration threshold value can be between 2 m / s ² and 6 m / s ² .

In the event of a blockage due to a braking of the rail vehicle, the linear acceleration threshold value is between -2 m / s ² and -6 m / s ² .

Similarly, the linear speed threshold may be variable with the vehicle speed to obtain optimum operation at different vehicle speeds. Thus, the linear velocity threshold value can be between 0.5 m / s and 2 m / s. Stage 3. Action on the pair:

This stage of the method occurs when a slip is detected in the previous stage. If no slippage is detected, the railway vehicle is maintained in a normal state where the required traction torque (T ref) is maintained.

When the slip, or skating, is detected, the electric motor drive torque is activated according to two consecutive phases:

A. Exponential reduction of traction torque during a predefined reduction time (t_red) according to the following expression: T end = T ini - J, eq where T_fin is the value of the tensile torque in the exponential reduction, J _eq is the equivalent inertia that relates the tensile torque expressed in rotation of the electric motor with the linear acceleration of the wheel, a _max is the angular acceleration of the drive shaft and T_ini is the initial value of the traction torque. The initial value of the traction torque (T_ini) is calculated according to the expression:

T ini = T ref C where T_ref is the required torque to the electric traction motor, and C is a constant in the range [0.85 - 0.95].

Thus, the initial value of the traction torque (T_ini) is between 5% and 15% lower than the required traction torque (T_ref).

The reduction time (t_red) is a predefined value that is calculated in a parameterization test of the route through which the railway vehicle circulates. The reduction time (t_red) takes values in the time interval between 0.05 seconds and 0.5 seconds. B. Linear recovery of traction torque until reaching the required traction torque (T_ref) or the detection of a new slip.

Once after the reduction time (t_red) has elapsed, the torque of the traction, this linear recovery of the traction torque is performed along a straight line whose slope is between 100 Nm / s and 500 Nm / s.

This linear recovery is maintained until the demanded traction torque (T_ref) is reached, or until a new slip detection occurs, in which case the reduction of the traction torque according to step 3 of the method again occurs.

Steps 1 and 2 of the method, variable assignment and slip detection are carried out continuously and in real time during the entire time the vehicle is in operation, while stage 3 of acting on the traction torque is only Performs when a slip is detected.

Figure 1 shows a graph of the evolution of the traction torque, where the detection of a slip occurs at a point designated as (D), observing how an exponential reduction occurs during a reduction time (t_red) from an initial value of the traction torque (T_ini) until a final value of traction torque (T_fin) is reached, from this exponential reduction a linear recovery of the traction torque occurs until reaching the required traction torque (T_ref).

The method object of the invention is applicable to limit the skating, or sliding, of the wheels of a railway vehicle on the traffic lane, both in traction conditions and in braking conditions in which wheel locks occur.

Claims

1. - Method of controlling the roller skating of electric traction vehicles, which acts on the traction torque of an electric motor that transmits a turning movement to a driving axle to which the wheels of the vehicle are associated, characterized in that when Wheel skating is detected and the electric motor is driven on two consecutive phases:

A. Exponential reduction of traction torque during a predefined reduction time (t_red).

B. Linear recovery of traction torque to reach a required traction torque (T_ref) or the detection of a new slip.

2. - Control method of wheel skating of electric traction vehicles, according to the first claim, characterized in that the exponential reduction of the traction torque during the predefined reduction time (t_red) is calculated according to:

T end = T ini - Jeq where T_fin is the value of the tensile torque in the exponential reduction, Jeq is the equivalent inertia that relates the tensile torque expressed in rotation of the electric motor with the linear acceleration of the wheel, a _max is the angular acceleration of the drive shaft and T_ini the initial value of the traction torque.

3.- Wheel skating control method of electric traction vehicles, according to the first and second claims, characterized in that the initial value of the T_ini traction torque is calculated according to:

T_ini = T_ref. C where T_ref is the required torque to the traction motor, and C is a constant in the range [0.85 - 0.95].

4. - Control method of wheel skating of electric traction vehicles, according to the first claim, characterized in that the detection of wheel skating occurs if any of the following conditions are met:

• If the angular acceleration of the driving axle that drives the wheels is greater than a linear acceleration threshold value. The linear acceleration threshold value is between 2 m / s ² and 6 m / s ² .

• If the difference between the linear speed of the wheel and the linear speed of the train is greater than a linear speed threshold value. The linear speed threshold value is between 0.5 m / s and 2 m / s.

5. - Method of controlling the roller skating of electric traction vehicles, according to the first claim, characterized in that the reduction time t_red takes values in the time interval between 0.05 s and 0.5 s.

6. - Wheel skating control method of electric traction vehicles, according to the first claim, characterized in that the linear recovery of the traction torque occurs according to a straight slope between 100 Nm / s and 500 Nm / s.