Abstract:
The present invention concerns a method for reducing the drive delay of a rolling stock to reach a destination, the rolling stock being driven by a driver to follow a running profile that defines the speeds and positions of the rolling stock at different timings. The method comprises the steps of: —determining a current timing, —getting a nominal acceleration of the rolling stock, the nominal acceleration being determined by the driver of the rolling stock to follow the running profile at the current timing, —determining the speed error of the rolling stock with the rolling profile, —determining the position error of the rolling stock with the rolling profile, —determining an estimate of the time to reach the destination, —determining a marginal acceleration from the speed error, the position error and the estimated time to reach the destination, —accelerating the rolling stock with the sum of nominal and determined marginal accelerations.

Description:
TECHNICAL FIELD 
     The present invention relates generally to a method and a device for reducing the drive delay of a rolling stock to reach a destination. 
     BACKGROUND ART 
     Between starting stations and stop stations, rolling stocks have to follow a running profile. The running profile indicates the position, the speed and the acceleration of the rolling stock at successive time instants. 
     Running profile are typically designed to setup a transit time between starting and stop station, while keeping the speed of the rolling stock below the speed limits imposed by the track and minimizing the energy consumption of the rolling stock during the transit. 
     The computation of the running profile is typically determined according to assumptions, such as the mass of the rolling stock and of its payload, the slope of the track, the variation law of resistance forces due to air and rail with the speed of the rolling stock, limitations of rolling stock drive to operate at different acceleration notch levels and the availability of electric power at catenary. 
     In the state of art, automatic train control systems typically apply acceleration levels indicated in the running profile or use speed tracking devices in order to catchup speed with that contained in the running profile. 
     Using Drive Advice Systems (DAS), human drivers also use graphical representation of ideal and actual train position to help the driving of the rolling stock according to a running profile. 
     SUMMARY OF INVENTION 
     Technical Problem 
     When using state of art train drive systems in practice, the position and speed of train can differ to that indicated in the running profile. 
     As a typical situation, running profile sometimes indicates an acceleration level which can&#39;t be reached by the train drive, resulting in train getting delayed when reaching the destination. For instance, this could be caused by an excess of payload, the presence of strong wind, of rain on the track, or of voltage drops in the catenary. 
     The present invention aims at reducing the drive delay of a rolling stock to reach a destination. 
     Solution to Problem 
     To that end, the present invention concerns a method for reducing the drive delay of a rolling stock to reach a destination, the rolling stock being driven by a driver to follow a running profile that defines the speeds and positions of the rolling stock at different timings, characterized in that the method comprises the steps of:
         determining a current timing,   getting a nominal acceleration of the rolling stock, the nominal acceleration being determined by the driver of the rolling stock to follow the running profile at the current timing,   determining the speed error of the rolling stock with the rolling profile,   determining the position error of the rolling stock with the rolling profile,   determining an estimate of the time to reach the destination,   determining a marginal acceleration from the speed error, the position error and the estimated time to reach the destination,   accelerating the rolling stock with the sum of nominal and determined marginal accelerations.       

     The present invention concerns also a device for reducing the drive delay of a rolling stock to reach a destination, the rolling stock being driven by a driver to follow a running profile that defines the speeds and positions of the rolling stock at different timings, characterized in that the device comprises:
         means for determining a current timing,   means for getting a nominal acceleration of the rolling stock, the nominal acceleration being determined by the driver of the rolling stock to follow the running profile at the current timing,   means for determining the speed error of the rolling stock with the rolling profile,   means for determining the position error of the rolling stock with the rolling profile,   means for determining an estimate of the time to reach the destination,   means for determining a marginal acceleration from the speed error, the position error and the estimated time to reach the destination,   means for accelerating the rolling stock with the sum of nominal and determined marginal accelerations.       

     Thus, when the nominal acceleration determined by the driver is not effective to drive the rolling stock according to the running profile, the effective acceleration is modified with the marginal acceleration. The speed and position errors can be compensated and be cancelled at time of reaching the destination. At time to reach the destination, the rolling stock is operating according to the running profile, even in presence of perturbations such as drop in catenary voltage, change in payload mass, presence of wind or rain. 
     Furthermore, the assistance to driving brought by the present invention relaxes the driver responsibility to tightly respect the running profile. Driver attention is not distracted from safety issues. 
     According to a particular feature, the destination is the next stop of the rolling stock. 
     Thus, the rolling stock arrives on time at the station. Delays are not propagated in the railway network. 
     According to a particular feature, the destination is the position wherein an automatic stop control system starts to manage the stop of the rolling stock. 
     Thus, automatic stop control system is effective in stopping the rolling stock on time and at precise location along the deck. 
     According to a particular feature, the destination is the position where the rolling stock enters in a speed limited area. 
     Thus, the delay is compensated before the rolling stock enters the speed limited area. 
     The speed of rolling stock does not excess the speed limit after entering the speed limit area. 
     According to a particular feature, the marginal acceleration is determined as minus the sum of speed error times two times a parameter divided by the time to reach the destination and of position error times the square of the parameter divided by the square of time to reach the destination. 
     Thus, the error of position and of speed of the rolling stock is effectively reduced without oscillation, and is fully compensated when reaching the destination. As marginal acceleration is not oscillating, the discomfort to passengers is minimized. 
     According to a particular feature, the parameter is predetermined and is comprised between 3.5 and 5. 
     Thus, the parameter being fixed, it does not need be adapted with respect to time to reach the destination. 
     The parameter being higher than two plus the square root of two, the marginal acceleration also gets to zero when reaching the destination. As a result, additional acceleration power is limited, and discomfort brought to passengers is also reduced. 
     The parameter being lower than 5, the initial marginal acceleration is limited. 
     According to a particular feature, the parameter is equal to 3.7. 
     Thus, the parameter exhibits good properties in terms of marginal acceleration. 
     According to a particular feature, the sum of nominal and marginal accelerations is limited to a maximum acceleration, which is determined as the difference between a speed limit level and the speed of the rolling stock, divided by a time period. 
     Thus, it will take at least the time period for the speed to start exceeding the speed limit. As the time period is typically higher than the refresh time of the proposed algorithm, the rolling stock can never exceed speed limit and the risk of derailment is reduced. 
     According to a particular feature, the sum of nominal and marginal accelerations is limited to a minimum acceleration which is determined as minus the measured of the rolling stock divided by the time period. 
     Thus, it will take at least the time period for the speed to change its sign. As the time period is typically higher than the refresh time of the proposed algorithm, the rolling stock can never change the sign of its speed, and the risk of collision with following train is reduced. 
     According to a particular feature, the method further comprises the steps of:
         checking if the marginal acceleration is enabled by the driver of the rolling stock,   adding the marginal acceleration to the nominal acceleration if the marginal acceleration is enabled by the driver of the rolling stock,   not adding the marginal acceleration to the acceleration of the rolling stock defined by the driver of the rolling stock in order to follow the running profile if the marginal acceleration is not enabled by the driver of the rolling stock.       

     Thus, the driver is assisted for the recovery of delay in presence of perturbations. The driver also keeps full control of the rolling stock, as it can also decide to disable assistance at any time, e.g. for emergency cases. 
     According to still another aspect, the present invention concerns computer programs which can be directly loadable into a programmable device, comprising instructions or portions of code for implementing the steps of the method according to the invention, when said computer programs are executed on a programmable device. 
     Since the features and advantages relating to the computer programs are the same as those set out above related to the method and device according to the invention, they will not be repeated here. 
     The characteristics of the invention will emerge more clearly from a reading of the following description of example embodiments, the said description being produced with reference to the accompanying drawings, among which: 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  represents a rolling stock in a system in which the present invention is implemented; 
         FIG. 2  discloses an algorithm executed by a rolling stock according to the present invention; 
         FIG. 3  represents an example of a running profile for the speed versus the position of a rolling stock; 
         FIG. 4  represents an example nominal and marginal accelerations versus the position of a rolling stock. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
       FIG. 1  represents a rolling stock in a system in which the present invention is implemented. 
     In  FIG. 1 , a rolling stock  120  is shown. The rolling stock  120  comprises a device for reducing the drive delays of the rolling stock  110 . The device for reducing the drive delays of the rolling stock  110  has, for example, an architecture based on components connected together by a communication bus  101  and a processor  100  controlled by the program as disclosed in  FIG. 2 . 
     The communication bus  101  links the processor  100  to a read only memory ROM  102 , a random access memory RAM  103 , nominal acceleration detection module  106 , an acceleration command module  109  and timing, rolling stock position and speed determination means  107 . 
     The nominal acceleration detection module  106  detects acceleration commands of the rolling stock which are set by the driver of the rolling stock in order to follow the running profile at the current timing, 
     The processor  100  determines marginal accelerations from speed errors, position errors and the estimated times to reach the destination. The processor  100  sends acceleration commands to the acceleration command module  109  through the communication bus  101 . 
     The acceleration command module  109  controls at least one traction motor of the rolling stock so that the rolling stock accelerates according to the acceleration commands received from the processor  100 . 
     The memory  103  contains registers intended to receive variables and the instructions of the programs related to the algorithm as disclosed in  FIG. 2  and a running profile. 
     The read only memory  102  contains instructions of the programs related to the algorithm as disclosed in  FIG. 2 , which are transferred, when the device for reducing the drive delays of the rolling stock  110  is powered on, to the random access memory  103 . 
     Any and all steps of the algorithm described hereafter with regard to  FIG. 2  may be implemented in software by execution of a set of instructions or program by a programmable computing machine, such as a PC (Personal Computer), a DSP (Digital Signal Processor) or a microcontroller; or else implemented in hardware by a machine or a dedicated component, such as an FPGA (Field-Programmable Gate Array) or an ASIC (Application-Specific Integrated Circuit). 
     In other words, the device for reducing the drive delays of the rolling stock  110  includes circuitry, or a device including circuitry, causing the device for reducing the drive delays of the rolling stock  110  to perform the steps of the algorithm described hereafter with regard to  FIG. 2 . 
     According to the invention, the device for reducing the drive delay of the rolling stock  110 :
         determines a current timing,   gets a nominal acceleration of the rolling stock, the nominal acceleration being determined by the driver of the rolling stock to follow the running profile at the current timing,   determines the speed error of the rolling stock with the rolling profile,   determines the position error of the rolling stock with the rolling profile,   determines an estimate of the time to reach the destination,   determines a marginal acceleration from the speed error, the position error and the estimated time to reach the destination,   accelerates the rolling stock with the sum of nominal and determined marginal accelerations.       

       FIG. 2  discloses an algorithm executed by a rolling stock according to the present invention. 
     More precisely, the present algorithm is executed by the processor  100  of the device for reducing the drive delays of the rolling stock  110 . 
     At step S 200 , the processor  100  starts the present algorithm. 
     At next step S 201 , the processor  100  obtains the destination position of the rolling stock. 
     The destination position is the next stop position of the rolling stock or may be a predetermined position along the railway line, such as position to enter the range area of a Train Automatic Stop Control (TASC) system, or may be a position to enter a speed limit section of the railway line. 
     TASC is a system activated by the driver of the rolling stock prior to reach the destination and which controls the exact positioning of the rolling along a deck of a station. The destination position is for example stored in the RAM memory  103 . 
     At next step S 202 , the processor  100  gets the running profile of the rolling stock. The running profile indicates timing, positions, speeds the rolling stock should follow if the rolling stock is on time according to a given schedule. The running profile may also indicate the acceleration profile required to keep the schedule. The running profile is for example stored in the RAM memory  103 . 
     At next step S 203 , the processor  100  gets the rolling stock position and speed. The position and the speed are provided by the rolling stock position and speed determination means  107 . 
     At next step S 204 , the processor  100  determines the position error ΔX of the rolling stock for the current time t. The processor  100  subtracts the position X target (t) where the rolling should be located at current time t according to the running profile, from the effective position X(t) of the rolling stock obtained at step S 203 . 
     ΔX=X(t)−X target (t). 
     At next step S 205 , the processor  100  determines the speed error ΔV. The processor  100  subtracts the derivation over the time of the position X target (t) where the rolling should be located at current time t according to the running profile, from the effective speed V(t) of the rolling stock obtained at step S 203 . 
     ΔV=V(t)−dX target (t)/dt(t). 
     At next step S 206 , the processor  100  determines the time to destination ΔT. The processor  100  subtracts the current time t from the time of arrival t a  when the rolling stock should arrive at the destination according to the running profile. 
     At next step S 207 , the processor  100  checks if the time to destination ΔT is equal to null value. 
     If the time to destination ΔT is equal to null value, the processor  100  interrupts the present algorithm. In a variant, the processor moves to step S 201 , where it determines a next destination position. Otherwise, the processor  100  moves to step S 208 . 
     At step S 208  the processor  100  determines, according to the present invention, a marginal acceleration ΔG to be applied. 
     According to the invention, a decay λ=Ω/ΔT is dynamic and is determined from time to reach the station. Ω is a control parameter, typically higher than 2+√2, for example set in a range between 3.5 and 4. For example, Ω is equal to 3.7. 
     The marginal acceleration is determined according to the following formula: 
     
       
         
           
             
               
                 
                   
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     Assuming that at a first given time instant t 0 , the rolling stock experienced an initial position error ΔX 0  and a speed error ΔV 0 , Mathematical analysis shows that, in absence of further perturbation, speed and position errors jointly reduce with time for successive time instants t (t 0 &lt;t&lt;t a ) according to following equations:
 
Δ X ( t )=α 1 ( t   a   −t ) β     1   +α 2 ( t   a   −t ) β     2     [Math.2]
 
Δ V ( t )=−α 1 β 1 ( t   a   −t ) β     1     −1 −α 2 β 2 ( t   a   −t ) β     2     −1   [Math.3]
 
Δ G ( t )=α 1 β 1 (β 1 −1)( t   a   −t ) β     1     −2 +α 2 β 2 (β 2 −1)( t   a   −t ) β     2     −2   [Math.4]
 
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     It has to be noted here that if the control parameter Ω is chosen higher than 2, both speed and position errors get to zero at arrival to destination. If the control parameter Ω is chosen higher than 2+√2, the maximum speed error is kept small, and marginal acceleration also gets to zero at arrival to destination. If the control parameter Ω increases, initial marginal acceleration also increases, and energy consumption of railway degrades. 
     The value of the control parameter Ω may be set to a single value for example between 3.5 and 5, typically 3.7, for which speed and position error always reaches zero at the time of reaching the destination, irrespective of initial speed and position errors while minimizing the marginal acceleration and thus the electric power consumption. 
     At next step S 209 , the processor  100  obtains the nominal acceleration from the nominal acceleration detection module  106  which detects the acceleration set by the driver of the rolling stock  120 . For human-driven rolling stocks, the nominal acceleration is manually set by the human driver e.g. by means of a lever. 
     For automatic train control systems, the nominal acceleration is determined by nominal acceleration detection module  106  from the running profile. As example, the nominal acceleration is the acceleration indicated for the current time t which is stored in RAM  103 . As other example, the nominal acceleration also contains a compensation acceleration resulting from an observed variation of catenary voltage. 
     At next step S 210 , the processor  100  determines the effective acceleration G effective  to be applied. The processor  100  adds the marginal acceleration ΔG to the nominal acceleration G nominal . 
     It has to be noted here that the effective acceleration may be determined taking into account a maximum acceleration, which is determined as the difference between a speed limit level and the speed of the rolling stock, divided by a time period. As example, the time period is one second. 
     It has to be noted here that the effective acceleration is further limited to a minimum acceleration, which is determined as minus the speed of the rolling stock divided by a time period. It has to be noted here that the driver of the rolling stock may deactivate the application of the marginal acceleration ΔG. 
     At next step S 211 , the processor  100  applies the effective acceleration. The processor  100  sends the acceleration command determined at step S 210  to the acceleration command module  109 . 
     At next step S 212 , the processor  100  waits for next time step. Time steps are typically spaced with few hundreds of milliseconds. 
     After that, the processor returns to step S 203 . 
       FIG. 3  represents an example of a running profile for the speed versus the position of a rolling stock. 
     The horizontal axis represents the time in second and the vertical axis represents the speed in kilometers per hour that the rolling stock should have. 
     The speed profile  30   a  of  FIG. 3  shows the speed that the driver of the rolling stock has to apply in order to follow the running profile. 
     In example of  FIG. 3  the rolling stock departs from a first stop station at time t 1  and stops at a second destination stop station at time t 2 . 
     The speed profile  30   b  of  FIG. 3  shows the speed of rolling stock when the acceleration is limited. The limitation of acceleration can be caused by a surplus weight of the rolling stock, or due to voltage drop in the catenary line which supplies the rolling stock. Due to limited acceleration, the train is late to acquire cruise speed, which results in a delay when reaching the destination stop station at time t 2b . 
     The speed profile  30   c  of  FIG. 3  shows the speed of rolling stock when the acceleration is limited and when the train is driven according to the invention. As train has both speed and position errors at the end of acceleration phase, speed evolves according to a marginal acceleration decided by processor  100 . Both speed and position errors are recovered at destination point at time t a , and rolling stock then reaches the destination stop station with no delay. 
       FIG. 4  represents an example nominal and marginal accelerations versus the position of a rolling stock. 
     The horizontal axis represents the time in second and the vertical axis represents the acceleration of the rolling stock in meters per power of two of seconds. 
     The acceleration profile noted  40   a  of  FIG. 4  shows the acceleration that the driver of the rolling stock has to apply in order to follow the running profile. 
     The acceleration profile noted  40   b  of  FIG. 4  shows the acceleration that the driver of the rolling stock effectively applies when the acceleration is limited. 
     The acceleration profile noted  40   c  of  FIG. 4  shows the acceleration that the driver of the rolling stock effectively applies when the acceleration is limited and when the train is driven according to the invention. Acceleration profile  40   c  differs from acceleration profile  40   b  by the marginal acceleration determined according to the present invention. 
     Naturally, many modifications can be made to the embodiments of the invention described above without departing from the scope of the present invention.