Abstract:
Using a lateral acceleration measurement to which passengers are subjected in a passenger car of a tilting train, a comparison to an acceptable level of lateral acceleration is made. As a result of this comparison, the control of the tilting system is altered. The tilting system can be shut down automatically, on a car-to-car basis, or manually using the tilting system controller. Passenger comfort will be increased since detection of abnormal operation of the tilting system will be performed rapidly.

Description:
This Appln claims benefit of Prov. No. 60/162,785, filed Nov. 1, 1999. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to monitoring units in tilting systems used in railway vehicles to control longitudinal roll motion mechanisms in order to increase passenger comfort. In particular, knowing the speed, the lateral acceleration and the tilting angle command from the tilting system, the invention enforces the comfortable operation of a train tilting system. 
     BACKGROUND OF THE INVENTION 
     It is becoming necessary to rethink the actual train infrastructure: travel time must be reduced to compete with airlines, existing tracks must be shared with freight trains, and land or budget constraints often prohibit the construction of dedicated high-speed tracks. The only solution is tilt technology. The need for tilting control systems was discussed in the November 1996 issue of  Popular Mechanics  magazine, in an article entitled “American Flyer”, as being a solution to improve passenger comfort during train rides. High-speed tilting trains require finely tuned mechanisms to ensure passenger comfort. 
     A “tilting system” is a combination of electrical, electronic and hydraulic components that control a railway car&#39;s longitudinal roll motion mechanism. It is used in passenger trains in order to increase passenger comfort that is affected by centrifugal acceleration in curves. Centrifugal acceleration is a serious limiting factor to the maximum cruising speed of a passenger train. 
     The maximum speed allowed in curves is limited by three factors: the maximum tilt angle of the car (usually between 5° and 9°), the maximum steady state residual lateral acceleration and the forces applied to the tracks by the non-tilting locomotive, which is almost two times heavier than a passenger car. The dynamic wheel/rail forces are almost identical for both a tilting and a non-tilting car at a given speed. All forces vary with the square of the speed. 
     Railroad curves are generally designed in order to compensate for a portion of the centrifugal acceleration by means of track super-elevation (or cant angle) that will force the car body to tilt along its roll axis. Properly oriented this tilt angle creates a gravitational component vector reducing the centrifugal force felt by the passengers in curves. The maximum super-elevation angle is typically 6°. On conventional tracks, the presence of heavy freight trains is one source of limitation for the maximal super-elevation. There is a maximal force that the inner rail can tolerate when the heaviest vehicle allowed to roll on The said track is immobilized in the curve. 
     Considering this design criteria, one can demonstrate that most passenger railway corridors in North America and Europe presently lack the proper amount of curve super-elevation that would allow the operation of high-speed trains without seriously compromising passenger comfort. Since modifications to conventional tracks are too costly and since speed and passenger comfort are the key to the survival of the passenger train industry, the solution resides in tilting systems. 
     Passenger cars equipped with an active roll motion mechanism, also called a “tilting system” can overcome this cant deficiency problem by giving the proper amount of roll to the car body in order to compensate for the lack of curve super-elevation. Passenger comfort is then improved and high-speed operation becomes possible on most existing railway corridors. 
     Tilting the body of a rail passenger car during curve negotiation offers the possibility of increasing the speed of a trainset in a curve without exceeding the maximum allowed steady state lateral acceleration felt by the passengers. Typically, the lateral acceleration due to centrifugal force should be lower than 1 m/sec 2  (i.e. lower than 0.1 g). This tilting feature reduces the overall traveling time without requiring track modification. Moreover, an effective tilting system greatly improves the passenger ride comfort during curve entry and exit by minimizing the transient accelerations. 
     Usually, the tilting mechanism only cancels 70% of the centrifugal force. A March 1993 article in  Popular Mechanics  magazine entitled “Bullet Train for America” explains the effect of the tilting system on the passenger: “Standing up, a rider notices the floor push gently against the left foot, as the view out the window pitches skyward”. The reason why the centrifugal acceleration is not compensated 100% is because neural signals from the eye would clash with those from the inner ear of the passengers, which senses no change at all and would cause motion sickness. 
     The tilting system is activated by the locomotive engineer before the train undertakes a run. A cab indicator informs the engineer of the tilting system status. When the system is activated, the locomotive engineer can operate the train at higher speeds. If the tilting system is deactivated, the train engineer must return to conventional speed in all curves for passenger comfort purposes. The difference between tilting and conventional speeds in high-speed curves is typically 35 km/h. 
     When passengers travel on such tilting trains, their comfort must be guaranteed at all times. The consequences of a failure to compensate the lateral acceleration correctly are immediate. Miscalculations of the proper compensation or erroneous actuation could result in increased motion sickness felt at the passenger level and, potentially, lost of balance. The generation of a tilt angle command must handle the worst-case scenario and, in addition, means to cancel the tilting command must be provided. 
     Tilting of the car is accomplished by a servo-valve controlling the hydraulic mechanism, which in turn tilts the car. The tilting control system responds to the output of a low-pass filtered inertial sensing system. Within a curve, cant deficiency is stable and passengers experience the cant improved by the tilting system. But delays introduced by the low-pass filtering could lead the passengers to experience a discomfort twice in a curve: at entry and exit. At these locations, the outward acceleration felt by the passengers is compounded by the acceleration of the tilt system, i.e. the outward acceleration due to the curve is added to the outward acceleration due to the roll movement of the compensating tilting. The reaction time and the accuracy of the control system are therefore critical. It is important for the control system to notice malfunctions and react rapidly and adequately. 
     If the tilting system is not closely monitored, various degrees of uncomfortable situations can occur, including passenger loss of balance and beverage spilling. 
     Similar uncomfortable situations would also occur when trains tilt in straight track segments. 
     OBJECTS OF THE INVENTION 
     It is the object of the present invention to provide a method which dynamically adjusts the threshold (or acceptable limit) value for the detection of malfunctions. The decision to generate an alarm signal will automatically arise as a function of the input signal polarities and absolute values. According to a further object of the present invention, passenger comfort will be increased since detection of abnormal operation of the tilting system will be performed rapidly. Finally, one further object of the present invention is to provide a method and system which dynamically adjust the threshold value to measure the performance of the tilting system. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a method that satisfies the need for an early detection of faulty tilting control system behavior due to failures. It allows fast and reliable shutdown capability of a malfunctioning tilting control system. 
     A failure in a part of the tilting system, which can lead to passenger discomfort, can be identified when one of the following is detected: 
     1) There is an inverse tilting command in a curve requiring tilting, i.e. the train tilts on the wrong side; 
     2) There is a tilting command in a straight (tangent) track segment, i.e. the train is going in a straight line but is tilting; and 
     3) The tilting command in a curve is properly oriented, but not sufficient to meet comfort criteria, i.e. the cant angle is too small and the train does not tilt enough. 
     The occurrence of case 1 or 2 denotes an important malfunction of the tilting system, which could greatly affect passenger comfort. Therefore, the detection of these conditions shall be performed according to stringent requirements. 
     On the other hand, since some amount of residual lateral acceleration in a curve is expected for passenger comfort, the occurrence of case 3 could be caused, for example, by a wrong control parameter adjustment, e.g. the ratio of cant deficiency compensation. In this case, the acceptable residual acceleration criterion is different than in cases 1 and 2. An over-speed situation in a curve could also lead to case 3, since there is a limit to the maximum tilting angle achievable. 
     In order to detect a situation where passenger comfort could be affected, an accelerometer can be installed on the passenger car floor level to measure lateral acceleration, which can be compared to a static threshold value. In this case, the threshold would have to be adjusted to a small value in order to obtain a prompt detection for cases 1 and 2. However, the value of this threshold could be too restrictive for normal tilt operation, and would cause false anomalous detection. 
     To generate an alarm when malfunctions or poor performance occur in a train tilting system, according to one broad aspect of the invention, the lateral acceleration to which passengers are subjected in a passenger car is measured. It is compared to an acceptable level of lateral acceleration and this comparison alters the control of the tilting system. This altering can be a trigger for a cab indication, a means for shutting down the tilting system or another alarm output system. This monitoring can be done on a car-by-car basis. 
     According to a preferred feature of the invention, the polarities of the lateral acceleration of a passenger car and the tilting command for that passenger car are compared to determine a polarity check flag. Using this polarity check flag, the absolute value of the tilting command, the train speed and the polarity of the lateral acceleration, a lateral acceleration limit is produced. This lateral acceleration limit can be one of four limit lines, a constant value, a function of speed or chosen via a comparison table. If the lateral acceleration is greater than the lateral acceleration limit for a pre-determined period of time, an alarm is produced. 
     According to another broad aspect of the invention, a system for monitoring malfunctions is composed of means to measure the lateral acceleration, a comparator for comparing the lateral acceleration with a limit for the lateral acceleration and means to alter the control of the tilting system. According to another preferred feature of the invention, a system for monitoring malfunctions is composed of two polarity detectors, an absolute value detector, a comparator for the polarities of the lateral acceleration and the tilting command, a threshold function that generates the limit for the lateral acceleration, another comparator for comparing the lateral acceleration with the limit and a persistency check that outputs an alarm if the tilting system is malfunctioning for a period of time longer than a pre-determined delay. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other features, aspects and advantages of the present invention will become better understood with regard to the following description and accompanying drawings wherein: 
     FIG. 1 shows a passenger train comprising a locomotive and two passenger cars and illustrates the main components of the tilting system and their location n atypical trainset; 
     FIG. 2 is an aerial view of a car showing the convention for signal polarity of the yaw rate and the lateral acceleration and showing a typical curve with the entry spiral and the exit spiral; 
     FIG. 3 is a view from the back of a car showing the convention for signal polarity of the-roll rate; 
     FIG. 4 is the ideal dynamic behavior (roll rate, yaw rate and lateral acceleration) of a body traveling on a railway; 
     FIG. 5 illustrates the actual response of a tilting system lateral acceleration, filtered lateral acceleration and residual lateral acceleration, where a residual lateral acceleration in curve entry and exit is minimized when the tilting system operates normally; 
     FIG. 6 is a block diagram showing the monitoring unit within its environment; 
     FIG. 7 is a schematic of the monintoring unit; and 
     FIG. 8 is an illustration of the limit lines followed by the monitoring unit. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 illustrates the main components of the tilting system and their location on a typical trainset comprising a power car or locomotive  16 , a first passenger car  17 , a second passenger car  18  and so on. Inertial sensors such as roll rate sensor and yaw rate gyroscope and lateral acceleration  22  and a speed sensor  20  are located on the leading truck  21  of the power car to allow advanced detection of the signals required to operate the system. Inertial force sensors  23  can also be located on the leading bogie  24  of the passenger car that is being controlled. The master controller  19  receives signals from sensors  20 ,  22 ,  23 , detects curves and filters the sensor signals. It can compute appropriate tilting angles for all the passenger cars  17 ,  18 , etc. as a function of speed and car position and transmit this information to car controllers  25  via the control network  15 , or simply send the filtered sensor signal to the car controllers  25 . The car controllers  25  perform closed-loop control of the hydraulic actuators  27 , which give the roll motion to the car body. The actuators  27  can also be of other type, such as electric. 
     The system architecture also allows the power car  16  to tilt, if the latter is equipped with appropriate actuating components  27 . On other types of tilting system architectures, all the sensing means can be located in each car in the train to allow for independent control and supervision of the tilting system. 
     Change in direction of a railway vehicle is induced by the railroad curvature. FIG. 2 shows a typical curve. All railroads are constructed as a sequence of straight track segments and curves. Passages through curves always involve three steps: entry spiral  39 , curve  38  and exit spiral  37 . The entry spiral  39  is the transition between straight track segment (infinite radius)  40  and the curve  38  per se, which has a constant radius of curvature. The exit spiral  37  is the transition between the curve  38  and the next straight track segment  36 . 
     Also shown on FIG.  2  and FIG. 3 are the conventions for signal polarity. In FIG. 2 a , the train  41  follows the tracks in a regular direction  46 . In FIG  2   b  and  2   c,  the train  41  undergoes a yaw. Also shown in FIG. 2 is the lateral acceleration convention. In FIG. 3, the train  54  is shown going into the page in a typical direction  55 ; the convention for the roll rate is illustrated. The ideal dynamic behavior of a body traveling on a railway is described in FIG. 4, where the roll rate (FIG. 4 a ), yaw rate (FIG. 4 b ) and lateral acceleration (FIG. 4 c ) are illustrated. These quantities are measurable by inertial sensors and can be used as inputs to a tilting control system. Lateral acceleration is a direct measure of cant deficiency. The effects of entering the entry spiral  61 , the curve  62  and the exit spiral  63  with cant deficiency are shown. 
     The dynamic performance of a tilting system can be measured by is behavior in entry and exit spirals, where lateral acceleration (or cant deficiency) can be rapidly increasing. For sake of simplicity, delays associated with the mechanical components of the actuating system have been neglected, so that the lag  74  is only associated with passenger perception, the centrifugal acceleration is usually not fully compensated (FIG. 5 c ). 
     FIG. 6 presents the monitoring unit, within the context of a tilting system. The latter is typically linked to a set of inertial force sensors  81  installed on the leading bogie of the passenger car  24  or of power car  21 , a speed sensing means  80 , a controller  84  and a closed-loop control means  85 . Both the controller  84  and the closed-loop control means  85  can be located either at the master controller  19  level or at the passenger car controller level  25  via the control network  15 . The controller  84  processes inertial signals S 1  from the inertial force sensors  81  and speed signal S 2  from the speed sensor  80  to generate a tilting angle command S 3 , sent to the closed-loop control  85 . Note that several architectures of tilting systems exist, but this invention only requires the speed signal S 2  and the tilting angle command S 3  to be available on a passenger car basis. The controller  84  could have an indication of the location of the passenger car with respect to the sensors on the locomotive, to be able to calculate the effective delays for each passenger cars. 
     An accelerometer  82  installed on the passenger car floor and sensitive to the transversal axis measures the lateral acceleration S 4  at any time during the travel. It goes without sating that the accelerometer  82  can be adequately installed in other locations in the passenger car. This accelerometer  82  can be of any type. It is located preferably inside the car so that the suspension of the car cancels part of the high frequency component present at the car bogie level. At the same time, it is located close to the center of rotation of the car to permit an accurate reading of the lateral acceleration of the car, even when tilting. The suspension would act as a filter on the lateral acceleration signal. If the suspension has an inherent mechanical delay, this delay should be taken into account when performing the monitoring of the signals. The monitoring unit  83  performs monitoring on speed S 2 , tilting command S 3  and lateral acceleration S 4  and generates an alarm S 5 . The latter can be used by any appropriate element of the tilting system architecture in order to disable the tilting function and re-center the car in case of an inconsistency between speed S 2 , tilting command S 3  and lateral acceleration at the passenger level S 4 . 
     The lateral acceleration signal S 4  is preferably damped prior to the monitoring. The filter  97  produces the signal S 4 ′, a more accurate estimation of the lateral acceleration experienced by passengers. Typically, lateral acceleration should be contained in the range of 0 to 5 Hz. This additional filtering is used if suspension of the passenger car is insufficient to filter the lateral acceleration signal. Well known techniques can be used to damp the lateral acceleration S 4 . This filtering caused by filter  97  help reducing vibrations and thus false signals. Indeed, vibrations would cause the persistency check  95  to be partly disabled when vibrations cause the comparator  94  to change state too often when acceleration oscillates over and under the threshold value S 9 . Also, vibrations could cause fast changes in the threshold function  93  when the acceleration oscillates between positive and negative values. 
     A detailed presentation of the monitoring unit  83  is presented in FIG.  7 . The polarity of lateral acceleration S 4 ′ is determined by polarity detector  90 , which outputs −1 if lateral acceleration S 4 ′ is less than zero or +1 if lateral acceleration S 4 ′ is greater than or equal zero. A similar device, second polarity detector  91 , outputs a signal S 6  that determines the polarity of S 3 . The polarity of the tilting command S 6  and the polarity of the lateral acceleration S 7  are compared in comparator  92 , to produce a polarity check flag S 8  that is positive if both polarities S 6  and S 7  are negative, positive if both polarities S 6  and S 7  are positive, and negative otherwise. If the polarity check flag S 8  is positive, the situation is such that an acceleration residual is in the same direction as the tilting angle command. In parallel, the absolute value of the tilting command S 11  is produced by absolute value determiner  96 . The speed S 2 , the polarity of the lateral acceleration S 7 , the polarity check flag S 8 , and the absolute value of the tilting command S 11  are fed to a limit determination function  93 . 
     FIG. 8 presents how the limit determination function  93  selects the limit value. A limit line (T 1 , T 2 , T 3  or T 4  ) is first selected according to Table 1. Then, a location on the limit line is found with respect to the speed S 2 . Note that Limit Line T 1  and Limit Line T 4  are the only limit lines subjected to give a changing limit value of the lateral acceleration (between b and c and between −c and −b) as a function of speed S 2 . This is to lake account of the fact that some tilting systems do not apply a uniform compensation of cant deficiency over the whole speed range. The actual value of a, b and c are pre-set as a function of the application context: c must be set to accept the lateral acceleration measured at stop in all curves; b is set using measured values to accept expected ride accelerations and reject accelerations caused by faults; a is set using measured values, depends on track quality and is set to avoid false alarms when riding on a straight line or in a zero cant deficiency curve. 
     The values of SP 1  and SP 2  are also pre-set in the same way: SP 1  is the speed over which tilting is performed. SP 2  is a speed used to reach progressively the maximum tilting compensation. These values are usually selected by railway authorities based on track geometry and car limitations. 
     
       
         
               
             
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Limit Line Selection Table 
               
             
          
           
               
                 Tilting 
                   
                   
                   
               
               
                 Command 
                 Lateral Acceleration 
                 Polarity Check Flag 
               
               
                 Amplitude S11 
                 Polarity S7 
                 S8 
                 Limit Line 
               
               
                   
               
               
                 &gt;=1° 
                 +1 
                 +1 
                 T2 
               
               
                 &gt;=1° 
                 +1 
                 −1 
                 T1 
               
               
                 &gt;=1° 
                 −1 
                 −1 
                 T4 
               
               
                 &gt;=1° 
                 −1 
                 +1 
                 T3 
               
               
                  &lt;1° 
                 +1 
                 — 
                 T1 
               
               
                  &lt;1° 
                 −1 
                 — 
                 T4 
               
               
                   
               
             
          
         
       
     
     When tilting command amplitude S 11  is below 1°, the limit line is always T 1  or T 4  (more permissive). The reason for this exception is that when a train goes through a curve with low cant deficiency, it is possible to encounter momentary situations where the polarity check flag  85  will be positive. 
     As will be evident to one skilled in the art, the limit angle of the tilting command amplitude S 11  can be set to another value without changing the essence of the invention. For example, if in a particular system, 2° seems to be more representative of the limit, the angle value can be changed. 
     Such situations include the case where high cant curves are taken at low speed: in this case, the lateral acceleration S 4 ′ can have a relatively large value, because of the gravity component it measures. At low speed, the tilting command is low or zero. If the polarity of the command S 3  is the same as the acceleration S 4 ′, limit line T 2  or T 3  will not be chosen as limit lines. This avoids false alarms. 
     Threshold function  93  produces the lateral acceleration limit S 9 , to which the lateral acceleration S 4 ′ is compared in second comparator  94 , resulting in a comparison signal S 10 , whose value is “below limit” or “above limit”. The persistency check  95 , outputs an alarm S 5  if the comparison signal S 10  has the “above limit” value for more than a preset delay. 
     The following failure cases are covered by this mechanism: 
     1. Tilting on wrong side (inverse tilt): the tilting command S 3  and the lateral acceleration S 4 ′ have the same polarity a or −a is chosen as limit value. 
     2. Tilting on a tangent track segment: similar to case  1 ; tilting command S 3  and lateral acceleration S 4 ′ have the same polarity. 
     3. No or not enough tilting in a curve requiring tilting: the tilting command S 3  is insufficient. In this case the limit value will vary between c and b or −c and −b, depending on the speed value. 
     Note that the acceptable limit for lateral acceleration is more restrictive for cases 1 and 2 than for case 3. This is because a certain amount of residual lateral acceleration is always expected when a tilting train goes through a curve (see FIG.  5 ). On the other hand, the presence of residual lateral acceleration on tangent track is not physically consistent, and therefore this situation is less tolerated. The same reasoning applies to wrong side tilting. 
     In another embodiment of the invention, the limit lines could be replaced by a decision equation. Substituting the values for the tilting command, the lateral acceleration, the speed and their respective polarities in an equation with specific weights would yield a decision for the alarm. 
     In another embodiment of the invention, the limit on the lateral acceleration could be fixed at all times. The analysis of the malfunctions would be less efficient but would have a fixed delay. Another modification would be to monitor a subset of the signals, instead all three signals: lateral acceleration, speed and tilting command. 
     In yet another embodiment of the invention, the lateral acceleration could be obtained from another element of the trainset. 
     In another embodiment of the invention, a feedback loop to the master controller from the monitoring unit could be used. This loop would permit the master controller to know that an alarm has been raised. Using this information, the master controller could try to change some of its parameters to correct the error or enable the shutting down of the system. The master controller could, for example, allow a longer delay for the filtering of the signals of one passenger car or could modify the reference values used to calculate the tilting command to take into account the error associated with a particular sensor.