Grade adjusted compensation for slip or slide condition

A system for measuring motion of a locomotive vehicle includes a speed sensor, a decelerometer and an onboard processing unit. The speed sensor is configured to measure wheel speed of the locomotive vehicle. The decelerometer includes a level-sensitive device configured to measure acceleration or deceleration of the locomotive vehicle as a function of a tilt from a level position. The onboard processing unit computes a current grade traversed by the locomotive vehicle prior to detection of a slip or slide condition based on a first measurement signal from the decelerometer. Upon detection of the slip or slide condition, the onboard processing unit obtains a second measurement signal from the decelerometer and filters out the current grade from the second measurement signal. The onboard processing unit determines an actual acceleration or deceleration of the locomotive vehicle during the slip or slide condition from the filtered second measurement signal from the decelerometer.

TECHNICAL FIELD

The present disclosure relates to locomotive control, and in particular, to a technique to accurately measure motion of a locomotive vehicle during a slip or slide condition.

BACKGROUND

A locomotive vehicle in motion may encounter low adhesion conditions such as ice or wet leaves on the rail that cause the wheels to lose traction and lock up, causing a “slide” condition. During this condition, a speed sensor attached to the wheels of the locomotive will be unable to measure either the distance the locomotive is traveling or the speed at which is it moving. A second condition, referred to as “slip”, can be caused, for example, when extremely high torque is applied at low or no speed causing a sharp spike in the speed sensor reading which would falsely indicate a huge change in speed, and consequently, position or location.

In the case of both slip and slide conditions, the onboard processing unit is unable to accurately determine the speed or distance traversed by the locomotive, thus rendering its calculations of braking and alert curves unreliable until such time as the speed and location can be accurately determined.

SUMMARY

Briefly, aspects of the present disclosure relate to a technique to accurately measure motion of a locomotive vehicle during a slip or slide condition by providing grade adjusted compensation.

A first aspect of the disclosure provides a system for measuring motion of a locomotive vehicle. The system comprises a speed sensor configured to measure wheel speed of the locomotive vehicle and a decelerometer including a level-sensitive device configured to measure acceleration or deceleration of the locomotive vehicle as a function of a tilt from a level position. The system further comprises an onboard processing unit. The onboard processing unit is configured to compute a current grade traversed by the locomotive vehicle prior to detection of a slip or slide condition based on a first measurement signal from the decelerometer. The onboard processing unit is configured to detect a slip or slide condition based on a measurement signal from the speed sensor. Upon detection of the slip or slide condition, the onboard processing unit is configured to obtain a second measurement signal from the decelerometer, filter out the current grade from the second measurement signal of the decelerometer, and determine an actual acceleration or deceleration of the locomotive vehicle during the slip or slide condition from the filtered second measurement signal from the decelerometer.

A second aspect of the disclosure provides a method for measuring motion of a locomotive vehicle. The method comprises computing a current grade traversed by the locomotive vehicle prior to detection of a slip or slide condition based on a first measurement signal from the decelerometer. The decelerometer includes a level-sensitive device configured to measure acceleration or deceleration of the locomotive vehicle as a function of a tilt from a level position. The method further comprises detecting a slip or slide condition based on a measurement signal from the speed sensor, the speed sensor configured to measure wheel speed of the locomotive vehicle. Upon detection of the slip or slide condition, the method comprises obtaining a second measurement signal from the decelerometer, filtering out the current grade from the second measurement signal of the decelerometer, and determining an actual acceleration or deceleration of the locomotive vehicle during the slip or slide condition from the filtered second measurement signal from the decelerometer.

A further aspect of the disclosure embodies features of the above-described method in a computer program product.

Additional technical features and benefits may be realized through the techniques of the present disclosure. Embodiments and aspects of the disclosure are described in detail herein and are considered a part of the claimed subject matter. For a better understanding, refer to the detailed description and to the drawings.

DETAILED DESCRIPTION

Various technologies that pertain to systems and methods will now be described with reference to the drawings, where like reference numerals represent like elements throughout. The drawings discussed below, and the various embodiments used to describe the principles of the present disclosure in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the disclosure. Those skilled in the art will understand that the principles of the present disclosure may be implemented in any suitably arranged apparatus. It is to be understood that functionality that is described as being carried out by certain system elements may be performed by multiple elements. Similarly, for instance, an element may be configured to perform functionality that is described as being carried out by multiple elements. The numerous innovative teachings of the present application will be described with reference to exemplary non-limiting embodiments.

Turning now to the drawings,FIG.1illustrates a system100for measurement of motion of a locomotive vehicle102along a railway track104. The system100includes at least one speed sensor106configured for measuring rotational wheel speed of a locomotive wheel108. In one embodiment, the speed sensor106may comprises a shaft encoder or an equivalent device mounted on a wheel axel. The speed sensor106provides a measurement signal116indicative of wheel speed to an onboard processing unit110. The measurement signal116may indicate, for example, the pulses per revolution measured by the shaft encoder. The onboard processing unit110comprises one or more processors configured to execute computer readable instructions. In one embodiment, the processing unit110is embodied as part of a positive train control (PTC) system, an example of which is the product ACSES' manufactured by Siemens Mobility Inc. The onboard processing unit110comprises logic processes that utilize the measurement signal116from the speed sensor106to determine the linear speed, and in dependence thereof, the position or location of the locomotive vehicle102, under normal operation (i.e., in the absence of a slip or a slide condition).

A slide condition refers to the locking up of a locomotive wheel or rotation of a locomotive wheel at a rotational speed less than the rotational speed corresponding to the actual linear vehicle speed. A slide condition typically occurs during vehicle deceleration but may potentially occur during vehicle acceleration. During a slide condition, the locomotive wheels typically lock up under low adhesion, for example, on ice or wet leaves, whereby the speed sensor106reports a much lower apparent speed than the locomotive is actually traveling at. This means the locomotive's actual speed could temporarily go over the allowed speed without penalty or alert, and the location will no longer be highly accurate until the next transponder set is crossed.

A slip condition refers to the rotation of a locomotive wheel at a rotational speed greater than the rotational speed corresponding to the actual linear vehicle speed. During a slip condition, usually at initial acceleration, the locomotive wheels slip, or spin under high torque and low speed conditions, resulting in a very high speed reported by the speed sensor106. This could lead to an improper alert, or even penalty, and the location is also not reliable until the next transponder is read.

The detection of slip and slide conditions are vital for maintaining both accurate speed determination and location details for a locomotive vehicle. Both of these elements serve as important inputs into a PTC system.

As per the disclosed embodiment, the measurement signal116from the speed sensor106is used by the onboard processing unit110to detect a slip or a slide condition. Once a slip or slide condition occurs, the measurement signal116from the speed sensor106can no longer be used to accurately determine vehicle speed and location. Under these conditions, a decelerometer112is used to give an accurate estimate of the actual speed of the locomotive vehicle102, thus leading to an accurate estimate of the location as well.

The decelerometer112includes a level-sensitive device capable of measuring inertial deceleration and acceleration of the locomotive vehicle102as a function of tilt from a level position. The decelerometer112is located onboard locomotive vehicle102, typically (but not necessarily) in a common enclosure114with the onboard processing unit110, and is ordinarily used to measure the braking force used to slow down or stop the locomotive vehicle102. When activated, the decelerometer112produces a measurement signal118that is not only sensitive to the inertial acceleration or deceleration, but also to the grade that the locomotive vehicle102is currently traversing. A level-sensitive onboard decelerometer of the above-mentioned type is typically employed in conjunction with wayside units for signaling purposes, which compensate for distance based on grade. However, for the same reasons, using the input from the above-described decelerometer directly to estimate the vehicle speed and location during a slip or slide condition may potentially lead to inaccuracies.

According to aspects of the present disclosure, the measurement signal118from the decelerometer112is processed to compensate for grade, to improve the accuracy in the estimation of speed and location of the locomotive vehicle102during a slip or slide condition.

FIG.2is a flowchart illustrating a method200in accordance with disclosed embodiments that can be performed by the onboard processing unit110shown inFIG.1or another device.FIG.2is not intended to indicate that the operational blocks of the method200are to be executed in any particular order, or that all of the blocks of the method200are to be included in every case. Additionally, the method200can include any suitable number of additional operations. In some embodiments, one or more operational blocks of the method200may be embodied in a computer program product.

Block202involves obtaining a first measurement signal from the decelerometer112during normal operation of the locomotive vehicle102, i.e., prior to detection of a slip or slide condition.

Block204involves computing a current grade traversed by the locomotive vehicle102based on the first measurement signal from the decelerometer112. The current grade is computed when the locomotive vehicle102is stationary or in motion at a constant speed. Under this condition, since the decelerometer112does not sense any dynamic acceleration or deceleration, the first measurement signal is sensitive solely to the geographical topology or grade of the railway track104. The current grade may be a current running grade (CRG) measured when the locomotive vehicle102is moving at a constant speed or current standing grade (CSG) measured when the locomotive vehicle102is stationary. CSG is typically used for grade compensation when the locomotive vehicle102encounters a slip while moving from stop under very slippery conditions. In one embodiment, the current grade is continuously computed and updated over a rolling time window during normal operation (including when the vehicle is stationary). The CSG or CRG will thus be indicative of the geographical topography value over the last period of time (e.g., the last 5 seconds). As mentioned, the CRG is computed when the locomotive vehicle102is moving at constant speed. If accelerating or decelerating, the most recently computed CRG is retained as the current grade.

In one embodiment, at block204, the processing unit110uses a standard moving average (boxcar) filter to collect CRG measurements over a period of time. A new measurement signal from the decelerometer112may be received, for example, every 100 millisecond logic cycle. While the locomotive vehicle102is in motion at a constant speed, these measurement signals may be saved to the boxcar filter over a defined timespan (e.g., 5 seconds) for a total maximum number (e.g., 50) of saved measurements at any time.

Block206involves obtaining a measurement signal from the speed sensor106. As mentioned, the measurement signal may be indicative, for example, of the number of wheel pulses per revolution measured by the speed sensor106.

At block208, the measurement signal from the speed sensor106is utilized to determine whether a slip or a slide condition has occurred. A slide condition may be detected when a steep decrease in wheel speed is determined from the measurement signal obtained from the speed sensor106. For example, a slide condition may be determined if the wheel deceleration is greater than a defined threshold deceleration. A slip condition may be detected when a steep increase in wheel speed is determined from the measurement signal obtained from the speed sensor106. For example, a slip condition may be determined if the wheel acceleration is greater than a defined threshold acceleration.

If, at block208, a slip or slide condition is not detected (i.e., a normal operation is determined), control moves to block210, in which the speed of the locomotive vehicle102is computed from the speed sensor reading. The preceding operational blocks are repeated.

If, at block208, a slip or slide condition is detected, the PTC is alerted to ignore the pulse readings from the speed sensor106, and control moves to block212. Block212involves obtaining a second measurement signal from the decelerometer112during the slip or slide condition. Under this condition, the second measurement signal from the decelerometer112is sensitive both to the inertial acceleration/deceleration and to the grade traversed by the locomotive vehicle102.

Block214involves filtering out the most recently computed current grade from the second measurement signal obtained from the decelerometer112. For example, in one embodiment, when the processing unit110needs to use the grade adjusted acceleration/deceleration it may take the difference of the current second measurement signal from the decelerometer112and the previously saved CRG moving average from the boxcar filter. The resulting output is the grade adjusted measurement. Thereby, the reading from the decelerometer112is refined to measure only the acceleration or deceleration component of the current reading and not the grade or geographical topography.

Next, at block216, the actual acceleration or deceleration of the locomotive vehicle102during the slip or slide condition is determined from the filtered second measurement signal from the decelerometer112.

Finally, at block218, the speed of the locomotive102during the slip or slide event is determined as a time integral of the computed actual acceleration/deceleration.

In one embodiment, the acceleration/deceleration, and resultantly, the speed of the locomotive vehicle, are computed in pulse-per-revolution from the filtered second measurement signal from the decelerometer112, to generate a data stream that substitutes for the speed sensor reading during the slip or slide event for the logic processes employed by the PTC system.

The embodiments of the present disclosure may be implemented with any combination of hardware and software. In addition, the embodiments of the present disclosure may be included in an article of manufacture (e.g., one or more computer program products) having, for example, a non-transitory computer-readable storage medium. The computer readable storage medium has embodied therein, for instance, computer readable program instructions for providing and facilitating the mechanisms of the embodiments of the present disclosure. The article of manufacture can be included as part of a computer system or sold separately.

The computer readable storage medium can include a tangible device that can retain and store instructions for use by an instruction execution device. The computer readable storage medium may be, for example, but is not limited to, an electronic storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any suitable combination of the foregoing. Computer readable program instructions described herein can be downloaded to respective computing/processing devices from a computer readable storage medium or to an external computer or external storage device via a network, for example, the Internet, a local area network, a wide area network and/or a wireless network.

The system and processes of the figures are not exclusive. Other systems and processes may be derived in accordance with the principles of the disclosure to accomplish the same objectives. Although this disclosure has been described with reference to particular embodiments, it is to be understood that the embodiments and variations shown and described herein are for illustration purposes only. Modifications to the current design may be implemented by those skilled in the art, without departing from the scope of the disclosure.