The invention relates to an axle generator for a brake system for a railway vehicle incorporating wheel slide protection.

Railway vehicle braking systems are typically air brakes. Such systems incorporating wheel slide control and wheel spin control have established themselves in recent years in the passenger train market. Both wheel slide and wheel spin stem from low wheel to rail adhesion. Wheel slide typically occurs when braking a railway car and is a major cause of wheel damage, which in turn can lead to track damage.

A typical wheel slide control system comprises a sensor on each axle of the vehicle, which measure the speed of rotation of the axle. The sensors are individually wired back to a central vehicle brake control unit. In use, the outputs of the sensors are then fed to the brake control unit, which compares the values with those of adjacent axles and if the difference exceeds a pre-determined limit, releases and re-applies the brake pressure until the axle speed falls within acceptable limits. This system has proven itself in practice and leads to improved braking performance and reduces the probability of damage to wheels and track. The problem of damage to wheels is particularly severe on freight trains, which as a consequence tend to travel more slowly than would otherwise be possible.

Freight vehicles generally have large brake cylinders. This leads to a number of problems, in particular in relation to the relatively large volumes of air that need to be released during wheel slide operation requiring the use of high flow valves.

Most freight wagons do not have an autonomous electrical power supply, which effectively has prevented the widespread adoption of wheel slide protection in freight trains. Consequently, freight trains tend to travel much more slowly than passenger trains to avoid track damage, in particular that caused by wheel flats caused by wheel slide events.

US5488287 (Keschwari) discloses a method of producing electrical energy from the rotary motion of an axle by coupling a generator to the axle. The arrangement has a rotor coupled to the axle with permanent magnets distributed over the circumference and a stator provided with induction coils and an electronic unit for evaluating function. Before being supplied to a rectifier, the direct three phase output of the stator is taken up in parallel and is supplied to an arrangement of optical couplers, which are arranged in such a way that the optical couplers are always arranged between two phases with one of the couplers handling the upper half-wave and one the lower half-wave. Before being supplied to the electronic control unit the signal is supplied through an Rc section, Schmitt trigger and monostable multi-vibrator to ensure that spurious signals are kept away from the ECU. The disclosed arrangement provides six pulse width signals appropriately offset with respect to time and are finally combined in a logical unit and co-ordinated and evaluated with respect to time.

The proposed solution enables an evaluation of the rate of rotation after a sixth of a revolution of a wheel, which is of particular relevance when used in a wheel slide protection system.

This arrangement has proved to be not particularly efficient and requires careful alignment of the parts on the axle end. The solution in this document is difficult to implement, can only be used with an axle box and requires making the axle itself into a generator, which may be unreliable.

The present invention seeks to provide an axle end generator which can be used for both power generation and for speed sensing for use in a railway braking system that is more reliable and lower cost than the existing known solutions.

According to the invention there is provided an axle generator assembly for a brake system for a railway vehicle comprising a motor adapted to be driven from an axle end of a freight wagon, wherein the motor is a two phase motor, such that both phases can be rectified to generate power for the brake system and the assembly further comprising frequency detection circuitry to detect the frequency of the phases, wherein the frequency of at least one of said phases is used to generate a speed signal.

Preferably, both phases are used to determine direction of the railway vehicle. Preferably, the motor comprises a stepper motor, in particularly having at least 6 steps, more preferably a greater number of steps. Preferably, the frequency response of the frequency detection circuitry is filtered to limit the expected frequency resulting from the speed of the axle.

The invention advantageously uses a two phase stepper motor in which both phases are used for generation but one or both phases are used for frequency detection. As the two phases are out of phase with one another, it is also possible to determine direction with the solution of the invention.

In the solution according to the invention, there is no internal source of spurious signals so the protection is primarily for induced signals from external influences. These are primarily EMI or EMC and can be significantly limited by the impedance of the rectification section. The solution according to the invention advantageously dispenses with the opto-isolators of the prior art solution thereby enabling a significant simplification of the circuitry as no galvanic isolation is required. The filtering arrangement further enables the pulse rejection circuitry to be dispensed with. The use of the stepper motor enables the speed of rotation to be evaluated much more quickly than in the prior art.

Exemplary embodiments will now be described in greater detail with reference to the drawings in which:

Fig. 1 shows a first coupling arrangement

Fig. 2 shows schematically an electrical block diagram

Figure 1 shows a first coupling arrangement suitable for a generic axlebox having exterior bearings comprising an axle coupling hub 1 adapted to be fixed to the axle hub having an axial opening adapted to receive a generally cylindrical coupling element 2. The coupling hub 1 comprises a first part a rigidly connected to the axle end and a second part rotatably connected to the part a. The coupling element 2 is provided with a generally rectangular opening at its end remote from the axle, which rectangular opening is slightly recessed from the surface of the end. The rectangular opening is adapted to receive a peg, which peg is rigidly and rotatably connected with the generator 8. The generator 8 comprises a two phase stepper motor. The peg is adapted to engage the drive shaft in the generator 8 so as to produce electricity when in motion.

In use, either or both of the two phases can be rectified to power the brake system and the frequency of one or both phases can be used by the braking ECU to determine the speed of the vehicle. As the phases are offset from one another, the two phases can also be used to determine the direction of the vehicle.

Fig. 2 shows schematically an electrical block diagram with four axle end generators, 30, 31, 32 and 33. Each of the axle end generators has two pairs of outputs which represent the two phases and each is representative of a possible different configuration depending on system requirements. In general only one axle end generator is required per axle. The axle-end generator comprises a 200 step stepper motor providing 50 pulses per revolution. In principle this enables an instantaneous speed determination at 1/50 of a revolution, which is significantly faster than the prior art solutions.

With axle end generator 30 both outputs are rectified to generate power for the brake system and the direction is taken by analysing the respective phases by the braking ECU (not shown). The frequency is taken from only one of the outputs to provide an indication of vehicle speed, which again can be determined by the ECU. The frequency conversion uses a differential amplifier with a limited bandwidth, the output of which is then Schmitt triggered to provide a square wave form for further processing. The direction can then be extracted by taking this square wave form of both phases and putting these into a D-type flip flop.

With axle end generator 31 , again both outputs are rectified to generate power for the brake system and the frequency is taken from both of the outputs to provide an indication of the axle speed. With axle end generators 32 and 33, only one of the outputs is rectified to generate power and the frequency is also taken from only one of the outputs to provide an indication of the axle speed.

The frequency response of the frequency detection circuit is limited to the expected frequency relating to the maximum axle speed