Drive axles and wheels of rail vehicles are subjected to immense stress. Railway experts refer to sliding as soon as an axle of the vehicle becomes blocked and this causes the wheels is turning slower than speed of vehicle. This effect extends the braking distance of a vehicle and results in wheel flat spots. This flats lead to an unpleasant, rumbling noise which reduces the comfort of passengers, a noise nuisance to people living adjacent to railway lines and finally unnecessary maintainance costs.
Furthermore, damaged wheels impair the quality of the rails in the long term. In order to prevent this, an electronic device is required: wheel slide protection. In automobiles, this function is known as ABS (anti-lock braking system).
The new CPU 731-TG and CDT 731-TG modules are combined into an electronic wheel slide protection system in accordance with UIC 541-05*.
Electronic speed sensors register the rotation speed of the wheelsets.
The wheel slide protection valves are activated for venting the brake pressure based on the deceleration and slip speed calculated in the CPU.
The wheel slide protection control unit compares the wheel deceleration with the switching thresholds preprogrammed in the CPU. Depending on the switching thresholds, the wheel slide protection valves are activated accordingly to block the compressed air supply to the brake cylinder or to reduce the brake cylinder pressure. Evaluating the deceleration only cannot reliably prevent the wheelsets from blocking. As a result, the slip speed is also calculated. In order to calculate the wheel slip, the speed of the vehicle must be determined or, if the vehicle speed is not measured directly, then it must be estimated with sufficient accuracy. 
Safe condition of a train during normal operation is considered as ”rail vehicle stationary“.
On the other hand a wheel slide protection system in “axle blocked” condition is performing the technical function of “release brake“. Therefore safety-critical intervention is performed inside the brake system. As a result, the Selectron wheel slide protection units MAS 73x-TG are designed according to safety-relevant standards such as EN 61508, EN 50126 and EN 50128. Selectron pursues the policy of a “wheel slide protection island”, i.e. it only implements truly safety-relevant functions with certified modules where it is used.
This has the following advantages:
- Existing train control and management systems can easily be expanded with a
wheel slide protection system.
- The complexity of vehicle acceptance is significantly reduced
- It is an inexpensive solution because only the level of safety actually required by the
application is implemented
- Clearly defined system limits regarding safety perspectives of the wheel slide
protection controller
The CDT 731-TG counter module can measure the speed of max. 4 axles. This means up to 4 pulse encoders can be connected. The system is configured for vehicles up to 200 km/h. The counter module controls max. 2 wheel slide protection valves per modul according to SIL 2 with functions for parameter settings of the activation and lock times.
Do you have further questions, any remarks or statements? Please do not hesitate to reply.
* UIC homologation in preparation