Brakes – Operators – Electric
Patent
1997-04-22
1999-01-26
Oberleitner, Robert J.
Brakes
Operators
Electric
188164, 105 77, B60L 700
Patent
active
058628916
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND AND SUMMARY OF THE INVENTION
The invention relates generally to an electromagnetic or permanent-magnetic rail brake, and more particularly to a linear eddy current brake for rail vehicles.
In modern wheel/rail engineering, there is demand for brake technologies which have a brake force that is as much as possible independent of the coefficient of adhesion between the wheel and the rail. Linear eddy current brakes naturally meet this requirement in an ideal fashion because, as non-contact service brakes, they are absolutely independent of the coefficient of adhesion.
A short introduction into the technology of the eddy current brakes for rail vehicles--whose function is based on the law of induction--is found, for example, in the book by Saumweber, et al. "AET--Archiv fur Eisenbahntechnik (Archive for Railway Technology)"--Hestra Publishers, Volume 43, Chapter 2.5.2. Eddy current brakes consist of an iron yoke with several pole cores. Electric coils magnetically excite the brake such that magnetic north and south poles are generated in an alternating manner. When the excited eddy current brake is moved along the rail--that is, during a braking--, electromagnetic fields and eddy currents are generated as a result of the changes of the time rate of flow. The secondary magnetic field caused by the eddy currents is opposed to the magnetic field of the brake. The resulting horizontal force component which acts opposite to the travelling direction is the brake force.
Despite the important advantage of this brake of having no contact with respect to rail, the practical use of eddy current brakes in large part is delayed by the fact that the compatibility of the brake with the existing operating equipment of various railroad operators can still be optimized.
A problem of the above-mentioned type, which results in serious difficulties during the practical application, is the interfering influence of the eddy current brakes on electromagnetic axle counters and/or similar sensing devices.
This problem is described in detail in European Patent Document EP 0 309 651. A large portion of the currently existing track sections of the varied railroad operators have rails which are provided with axle counting sensors laterally below the rail surface. Generally, electromagnetic sensors are used for the axle counting. That is, a transmitter sends out an electromagnetic alternating field (of a frequency of 5 to typically 43 kHz) and, when a metal wheel travels over a sensor arranged on the opposite side of the rail, the sensor registers changes of the electric field, which are caused by the metal wheel, with respect to the amplitude and the direction as counting pulses. A train passing through the sensor arrangements triggers a counting pulse in the sensors by each axle or wheel passing there through. If, during a pass through locally mutually separate axle counters, different counting results are registered, the track section is blocked for the following train.
Since, during a braking, eddy current brakes are lowered from a high position into a low position just above the rail, they may also trigger counting pulses in the axle counting sensors during the braking. However, they trigger counting pulses only in their low position (thus, during the braking) but not in their high position. Eddy current brakes may therefore falsify the result of an axle count and stop a train for no reason.
For solving this problem, European Patent Document EP 0 309 651 A2 suggests that guiding plates made of a ferromagnetic material be mounted on the outside in the area of the lower longitudinal edges of each coil of the brake magnet. These guiding plates each extend along the lower corner edges of the exciter coil. Although the suggested solution eases the problem, faulty signals cannot be excluded to an extent required for a controlled train operation.
From Austrian Patent Document 317 290, corresponding to U.S. Pat. No. 3,805,927, an electromagnetic rail brake is known in which a rod made of a ferromagnetic material extends along the
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Grundlagen der Schienenfahrzeug Bremse, Eckart Saumweber, Eduard Gerum, Peter J. Berndt.
Grautstuck Heinrich
Kroger Uwe
Wirth Wolfgang
Bartz C. T.
Knorr-Bremse Systeme Fur Scheinenfahrzeuge GmbH
Oberleitner Robert J.
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