Road Wheelset

Road Wheelset

Wheel speed sensor

special purpose vehicle speed sensors speed sensors driving wheel used in braking systems ABS. Rotational speed sensors for rail vehicles Many of the subsystems in a rail vehicle, a locomotive or multiple unit depend a sign of reliable and precise rotary speed, in some cases as a measure of the speed or change speed. This applies, in particular, traction control, but also to the scroll wheel protection, registration, train control, door control and so on. These tasks are performed by a series of sensors rotational speed can be found in various parts of the vehicle. In the past, the sensors for this purpose often does not function satisfactorily or were not sufficiently reliable and resulted in failure of the vehicle.

This was particularly the case of early analog sensors in large part, but also digital models affected. This was mainly due to extremely harsh conditions found on railway vehicles. The relevant standards specify the criteria detailed tests, but in practical operation conditions often encountered are more extreme (such as shock and vibration and electromagnetic compatibility, especially (CEM)). Rotary engine speed sensors speed sensors for motor vehicles bearing rail Despite occasional use units without most of the sensors, needs a rotation speed sensor of its regulatory system. The most common type is a two-channel sensor that scans a sprocket on the shaft of the motor or gearbox and therefore does not require a proper relationship.

The wheel of destiny can be provided especially for this purpose or may be already present in the transmission system. Modern sensors of this type make use of principle of magnetic field modulation and are suitable for ferromagnetic target wheels with a modulus of between 1 and m = m = 3.5 (SD = 25 and AD = 7). The shape of the teeth is of minor importance; wheels destination or rectangular involute teeth can be scanned. Depending on the diameter and teeth of the wheel, you can get between 60 and 300 pulses per revolution, which is sufficient for the lower performance drives of traction and a half. This type of sensor usually consists of two Hall effect sensors, a rare earth magnet and electronics adequate evaluation. The magnet field is modulated by the teeth of fate happens. This modulation is recorded by Hall sensors, developed by one stage compared to a square wave signal is amplified in a pilot stage. Unfortunately, Hall effect is very variable with temperature. The sensors sensitivity and offset signal therefore depend not only on the air space, but also temperature. This also greatly reduces the permissible maximum air space between the sensor and target wheel.

At room temperature, an air gap of 2 to 3 mm can be tolerated without difficulty for a typical target wheel module m = 2, but the required temperature range of 40C to 120C maximum gap for the registration of effective signal is reduced to 1.3 mm. Smaller wheels target pitch with module m = 1 is often used to obtain a higher resolution or time to make the construction more compact. In this case the maximum difference in air possible only 0.5 to 0.8 mm. For the design engineer, the tube visible that the sensor ends up with is primarily the result of the specific machine design, but is subject to limitations as may be necessary to record the speed rotation. If this means that the air space as possible within the limits is a very small range, then this would also restrict the mechanical tolerances motor housing and the wheels of targets to prevent signal loss during the operation. This means that in practice there may be problems, especially with the wheels launched small module aims m = 1 and combinations of disadvantage to the tolerances and extreme temperatures. From the point of view of the engine manufacturer, and still more the operator, so it's best to find a speed sensor with a wider range of air space. The main sign of a Hall sensor loses amplitude significantly as increased air space. For manufacturers of sensors, meaning they need to provide maximum possible compensation for the physical Hall signal induced to compensate for drift. The conventional way to do this is to measure the temperature sensor and use this information to compensate for the displacement, but this fails for two reasons: firstly because the trend does not vary linearly with temperature, and secondly because even the sign of the drift is the same for all sensors.

For a generation of new sensor that was necessary to find another way: an integrated signal processor now corrects the displacement and the amplitude of Hall sensor signals. This fix is so effective that one can almost double the maximum allowable air space at the speed sensor. In a module m = 1 wheel fate of these new sensors can tolerate a gap of 1.4 mm, which is broader than for conventional speed sensor module m = 2 wheels of fate. At a news module m = 2 target the new speed sensors can tolerate differences of up to 2.2 mm. It has also been possible to markedly improve the quality of the signal. Both the cycle and the displacement phase between the two channels, at least three times more stable to air space fluctuation and temperature change. Moreover, despite the complex electronic also has been possible to increase the average time between failures of speed sensors again by a factor of three to four. So not only provide signals precise, the signal availability is also significantly better. These new sensors, still with the familiar appearance, thus opening new possibilities for Designers set of units of rolling stock. The sensors are a very attractive price and work wear. motor encoders with integral bearing There is a limit in the number of pulses achievable by means of sensors without integral bearing: 300 mm diameter wheel which they usually can not go beyond 300 pulses per revolution. But many locomotives and electric multiple units (EMU) requires a higher number of pulses for the proper functioning of the traction converter, for example, when there are serious restrictions on the regulator of traction at low speeds. These applications really need encoders with built-in bearings, which can tolerate an air separation orders of magnitude smaller because of the work greatly reduced in real sensor as opposed to engine parts. This makes it can choose a much more small scale for measuring up to the module m = 0.22. There are several types of encoder with the property. One used in large quantities in EMU. It can be used to achieve values of less than 100 to more than 130 000 pulses per revolution. In railway applications, however, pulses per revolution as possible is not required. For greater robustness and accuracy of a precision encoder signal can be used. The functional principles of the two encoders are similar: a magneto-resistive sensor scans a multi-channel target wheel with 256 teeth, the generation of sine and cosine signals. Arctangent interpolation is used to generate rectangular pulses 512 each of the 256 signal periods per revolution. Precision encoder also has the breadth and displacement of correction functions located in external unit interpolation. This makes it possible to further improve the signal quality, which has a very positive effect traction on the regulator. Speed sensors in the wheel set bearings speed sensors wheelset bearings speed sensors can be found in almost all wheels of a railway vehicle. They are used mainly for the protection of the slide wheel and usually provided by the manufacturer of the wheel slide protection the system. These sensors require an air gap small enough to be very reliable. A special feature of the rotation speed sensor which used to protect the slide wheel is integrated their supervisory functions. Two-wire sensors with an output current of 7 mA mA/14 are used to detect broken wires. Other designs provide an output voltage of about 7 V as soon as the signal frequency drops below 1 Hz Another method is the detection a 50 MHz signal sensor output when the power is periodically modulated at 50 MHz is also common for two-channel sensors have channels electrically isolated. It is sometimes necessary to remove the top of the wheel protection signal in the traction motor and the output frequency is then often too high for electronics protection wheel slides. For this application there is a speed sensor with an integrated crossover. Now there are products available that meet all the normal rules, with a considerable improvement of technical properties and markedly longer shelf life. Pulse generator wheel bearings An integrated rail vehicle, especially a locomotive, in general, has many subsystems that require a speed signal separately electrically separated. In general, it is not enough places of assembly and not enough space where independent pulse generators could be installed. For many years have been both, generators multichannel pulse that flange bearings or covers of wheelsets. These bearings have an advantage over models that can generate a significantly higher number of pulse. Using a series of speed sensor cables also involve additional bearings, which preferably should be avoided for outdoor equipment because they are very susceptible to damage, for example, flying track ballast. All optical sensor manufacturers engaged in this market primarily uses optical sensors. One to four channels they can be applied, each channel has a photosensor which explores one of a maximum of two tracks of the signal in a slotted disc. Experience shows that the number of channels achievable by this technique is not enough. A series of subsystems, therefore, comply with looped through the electronic signals of protection wheel slide and was forced to accept, for example, the available number of pulses, despite a speed signal separately and may have some advantages. The use of optical sensors has been familiar for many years and is widespread in the industry. Unfortunately it has two fundamental weaknesses that have always made it very difficult ensure that they function reliably for several years, namely - the optical components are extremely sensitive to dirt, and - the light source ages too fast. Even the dirt trails greatly reduce the amount of light passing through the lens and can cause signal dropouts. These encoders are forced to well be closed. Even encoder bearing seals to prevent fat issue is a problem that not even the ingenuity of the designers has been unable to fully resolve. Other problems arise when the pulse generators are used in environments where you pass the dew point: the lens and fog signal is interrupted frequently. The light sources used are light emitting diodes (LED). However, the LEDs are always subject to aging, which in a few years leads to a beam noticeably reduced.

It tries to compensate for this by using special controllers gradually increase current through the LED, but unfortunately this accelerates further the aging process. Magnetic sensor principle used in the exploration of a ferromagnetic magnetic measurement scale does not show these deficiencies. During many years of experience in the use of magnetic encoders have been occasions when a seal has failed and a pulse generator has been found to be completely covered by a thick layer of brake dust and dirt on others, but these pulse generators are still functioning perfectly. Scan before scanning systems were simply too expensive for use, but recently a multichannel pulse generator is provided that is essentially not only higher than the previous pulse generators and strong robustness to dirt, but also establishes a new standard for flexibility. Here, by comparison, are some of its main features: one to eight channels, instead of the last 3:59 to 3:00 different values of pulses per revolution of a single encoder, instead of the previous two 1-400 pulses per revolution 200 instead of the previously achieved output voltage, output current, the signals with a voltage of 7 V idle, instead of only one output voltage as and now there is a new variant with a maximum hysteresis of 90 in conjunction with a signal period. When installed in adverse conditions and exposed to strong vibrations This option suppresses any extraneous pulses while the vehicle is stationary. Together, these innovative pulse generators also offer new features open up entirely new possibilities for system integrators. It is possibly to supply significantly more independent subsystems, electrically isolated output signals. And, of course, installation compatible pulse generators can be configured for all products previously marketed usual. The magnetic measurement principle and optimized the technology increases the reliability taking pulse generators, not only by increasing maintenance intervals, but also significantly reduce maintenance costs. Pulse generators built in accordance with this principle have been successfully tested by several railway companies since the beginning of 2005. Evidence of the specified type in the standard EN 50155 has been successfully completed, so that these pulse generators can now be delivered. pulse generators with integral bearing wheels for trucks inside In serial-serial bogies make particular demands on the designer of the pulse generator because they have no bearing cap in the end, as a basis from which could be the focus of social shaft rotation. In this case the pulse generator must be mounted on a stub shaft attached to the set of wheels and equipped with a torque converter connected to the frame the bogie to prevent it from turning. The In extreme vibration leads to a considerable burden in taking the pulse generator, which, with this method of installation must lead not only the relatively small mass axis pulse generator, but the entire pulse generator. When we consider that reduces bearing life at least third power of the load, we can see that a pulse generator reliable and durable solution to this situation can not be simply an adaptation of the most common pulse generator bogies for the magazine was simply mounting flange and a half or similar construction.

You really need to have a pulse generator with a modified design adapted to the requirements of that place. Previously these pulse generator, were available only serious constraint on the technical value, eg limited to a maximum 140 pulses per revolution or a limited number of channels. A new product has been developed, which provides the complete specification of a pulse generator wheel kit in a capsule that was specially designed for installation inside the bogies magazines. Speed sensors for non-magnetic target wheel or applications produce chips Some carriers face a special problem: The air circulation keeps the engine cool chips is abrasion of the wheels and rails. This builds on the heads of magnetic sensors and can cause damage. This short circuit can occur agnetic loss or complete loss of signal. And there have been cases in which coders were physically damaged by the abrasive effect of particles. There is also an increasing number of engines in which the sensors have to scan white aluminum wheels, for example because the drivers are made of an alloy of aluminum and the manufacturer does not wish to have to reduce by a ring gear separate ferromagnetic. For these applications there is a speed sensor available that manages without a magnet. A series of transmitting and receiving coils are used to generate an alternating electric field with a frequency of 1 MHz and the modulation of coupling between senders and receivers is then evaluated. This sensor is compatible with the installation and the signal from the magnetic sensors, because the most common target wheel modules are interchangeable units, without any another as needed.

In recent years, these sensors have been able to drastically reduce failure rates of many transport companies when installed in critical environments described above. Speed sensors with pulse doubling customers often want a higher number of pulses per revolution can be accomplish in the space available and with the smallest modulus m = 1. A speed sensor compatible industry standard flange has been developed for applications generates two pulses for each tooth wheel. This makes it possible to reach 600 pulses per revolution, with a target wheel module m = 1 and a diameter of 300 mm. These sensors speed are currently being tested in a major systems integrators. References http://www.selectron.ch/downloads/kataloge/normen-EN-50-155/Standard-EN-50155.pdf Links Continental Automotive Systems External SafelyThere - Continental Automotive Systems Vehicle Safety Equipment "Drive Safer America" quick installation Wheel sensor / encoders extraction procedure for rail-road vehicle sensors for road vehicles railway Category: Technology car security | | sensorsHidden speed rail security categories: Articles lacking sources from April 2009 | All you need References

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