Electricity: measuring and testing – Electrical speed measuring – Including 'event' sensing means
Patent
1997-05-12
1998-10-20
Strecker, Gerard R.
Electricity: measuring and testing
Electrical speed measuring
Including 'event' sensing means
246122R, 246182R, 324171, 324217, 324243, 364565, G01P 380, G01P 366, B61L 2500, B61K 910
Patent
active
058251774
DESCRIPTION:
BRIEF SUMMARY
This application is a 371 of PCT/SE 95/00783, filed Jun. 26, 1995.
TECHNICAL FIELD
The present invention relates to a device for speed measurement in a rail-mounted vehicle.
BACKGROUND OF THE INVENTION
It has long been desired to be able to measure the speed of a rail-mounted vehicle accurately and with a high reliability over the whole speed range of the vehicle and under all operating conditions. It is desirable to be able to obtain an accurate speed value, by integration, the distance covered by the vehicle and hence the position of the vehicle along the track, such information being required by superordinate traffic control systems. Further, it is desirable to obtain accurate speed value for information to systems for control of vehicle slip during acceleration or deceleration. In addition, it is important to obtain accurate speed measure also at very low speeds.
Also, for reasons of reliability and cost, it is desirable that means for speed measurement and position determination be arranged in their entirety on the vehicle and that they be completely, or to the greatest possible degree, independent of external means, such as stationary signalling or measurement systems arranged at the track or at some other location.
The prior art discloses the use of tachometer generators connected to the wheels of the vehicle. However, slipping of the wheels when driving or braking entails unavoidable measurement errors with such equipment. Further, the measures of speed and distance obtained from a tachometer generator are dependent on the current wheel diameter. This changes with time, both by wear and by the wheels being turned down, which is done at regular intervals. The influence of the diameter change may, to a certain extent, be compensated by recurring calibrations and adjustments of the measurement system, but the need thereof entails an essential drawback. Under all circumstances, a tachometer generator system probably cannot provide a higher accuracy in, for example, distance measurement than about 10 to 30 percent.
The article entitled "Hastighetsmatning med korrelationsmetod", Andermo, Mork, Sjolund, Teknisk Tidskrift 1976, No. 3, pages 18-21, has proposed (FIG. 3 with description) that the speed of a rail-mounted vehicle be measured optically in a contactless manner with the aid of a correlation method. A sensor mounted in a bogie has two light-emitting diodes which illuminate the rail at two different locations at a known distance from each other. The reflected radiation is sensed at both locations with the aid of photodiodes. One of the sensed signals is displaced in time until a maximum correlation is obtained between the two time-variable signals. The time displacement, together with the known distance between the measuring locations, then determines the speed of the vehicle and, by integration, also the distance covered. However, in practice, it has been found that optical systems are sensitive to the heavy fouling of detectors, etc., which is unavoidable during vehicle operation. Further, particles present between the rail and the sensor, such as, for example, raindrops, snow, and brake dust, result in disturbances of the measurement, among other things by heavy damping of the optical signals. Therefore, it has proved to be difficult, or impossible, to obtain a high reliability and high measurement accuracy during operation in vehicle environment using equipment of the above-mentioned type.
In the publication of Jopping, Wennrich: "Radargestutzte Weg- und Geschwindigkeitsmessung auf Schienenfahrzeugen, Signal+Draht, 85 (1993), pages 360-364, a system for speed and road measurement during vehicle operation with the aid of a Doppler radar is described. Such a system has proved to be less sensitive to fouling than an optical system. During vehicle operation in the winter in Nordic or arctic climates, however, the unavoidable presence of snow and ice coating obstructs the radar radiation to such a high extent that the system cannot be used under such conditions. Further, in measurement equipme
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Andemo et al., Hastighetsmatning med korrelationsmetod: Noggrann, beroringsfri, inga rorliga delar Teknisk tidskrift, vol. 3,1976, pp. 18-12.
Joppich et al., Radargestutzte Weg-und Geschwindigkeitsmessung auf Schienenfahrzeugen, Signal+Draht, 85, 1993, pp. 360-364.
Finnestad Askell
Lind Hakan
ABB Daimler-Benz Transportation Signal AB
Strecker Gerard R.
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