Autonomous retarder system for a vehicle, and vehicle including same

The invention relates to an autonomous retarder system for a vehicle including a retarder (10) having a central rotor (11) and two stators (12), one on each side of the rotor (11). The rotor (11) is rigidly coupled to an axle (1). A generator (20, 30, 50) is also included, coupled to the retarder (10), for supplying same with electrical energy. In addition, the generator (20, 30, 50) comprises a stator (22) and a rotor (21, 31, 51) coupled to the retarder.

CROSS REFERENCE TO RELATED APPLICATION

This Application is a 371 of PCT/ES2014/070655 filed on Aug. 14, 2014, which is incorporated herein by reference.

TECHNICAL FIELD OF THE INVENTION

The invention belongs to the field of braking systems for vehicles, and specifically for trains. More specifically, it corresponds to electromagnetic braking systems that use the principle of Foucault currents.

BACKGROUND OF THE INVENTION OR STATE OF THE ART

The majority of braking systems are based on mechanical friction to reduce speed. This type of brake presents problems of wear and the need for constant and periodic maintenance. Also, the noise level of these systems decreases passenger comfort.

For this and other reasons, efforts have been made to apply other principles for braking. Specifically, auxiliary brakes that serve as a support to friction-based brakes have been designed. One notable option consists of electrical brakes that are activated based on the induction of Foucault currents (also known as Eddy currents) in the rotor. These are called retarders, and they are made up essentially of a stator equipped with windings and two rotors rigidly coupled to an axle (whose rotation is generally provided by a cardan transmission). When these are excited by means of currents on the induction coils, it creates a magnetic field whose lines of force pass through the rotors, creating induced currents, which in turn generate a moment in the direction opposite the rotation which opposes the movement. As a result, the rotational speed, and with it, the speed of the vehicle, are progressively reduced. The rotor and stator surfaces do not need to be in contact for this effect to be produced. These brakes generate smooth, silent braking, with no wear, and their effectiveness increases the higher the speed. For this reason, retarders are combined with conventional friction brakes to bring the vehicle to a complete stop.

At present, retarders require an electrical energy supply to feed current to the stator windings. The power supplies of known retarder systems are external, provided by batteries. The requirements for these batteries are quite demanding because a large amount of current (approximately 160 A) is required. While these requirements can be fulfilled using the existing technology, these batteries are generally large and costly. On the other hand, if a battery is shared with other devices on the vehicle, the energy stored may be insufficient. Another choice for ensuring the power supply to the retarder is to equip it with its own battery. Regardless of which option is applied, the power supply generally cannot be integrated into the retarder, and the retarder is not compact.

BRIEF DESCRIPTION OF THE INVENTION

The object of the invention is a retarder system for a vehicle that resolves or at least mitigates the problems and limitations observed in the prior art.

Another object of the invention is a vehicle that is equipped with the retarder system.

The retarder system is a compact and energetically autonomous unit. It is equipped with its own integrated generator. This generator shares the axle with the retarder to which it is rigidly affixed, such that it takes advantage of the movement of the axle and/or principal rotor of the retarder to move an additional rotor for the generator and thus produce the necessary current. With this configuration, the generator can be sized with an adequate diameter to supply the necessary energy to the retarder, making it independent from the other elements. The transformation of mechanical energy into electrical energy is done without the need for additional transmission elements, such as chains, pulleys, etc.

The autonomous retarder system for a vehicle in accordance with the invention comprises a retarder with a central rotor and two stators on each side of the rotor, with the rotor in question rigidly coupled to an axle. It also comprises a generator coupled to the retarder to supply it with electrical energy. The generator includes its own stator and rotor that is coupled to the retarder.

Optionally, the generator stator may be located externally and rigidly coupled to the retarder stator by means of the same axle.

Optionally, the generator may be self-excited, use permanent magnets, or have external excitation (which uses soft materials on a fixed core).

Optionally, the permanent-magnet generator is responsible for providing excitation to the external-excitation generator.

Optionally, the permanent-magnet generator and self-excited generator work together so that the permanent-magnet generator supplies electrical energy to the retarder when the axle rotation speed is below an initial threshold and the self-excited magnet generator supplies electrical energy to the retarder when the axle rotation speed is higher than a second threshold.

Optionally, the central rotor may be self-ventilating.

Optionally, the central rotor of the retarder comprises two lateral disks and a plurality of spaced ribs connecting said disks.

Optionally, the system includes a braking regulation module to control the excitation current of the generator according to a control signal.

Optionally, the regulator module includes a rectifier and a voltage stabilizer.

Optionally, the system includes a temperature sensor to measure the temperature of the retarder and report it to the regulator module to reduce the current from the generator when this temperature exceeds a threshold.

DETAILED DESCRIPTION OF THE INVENTION

The figures describe several examples of embodiments but do not limit the invention.

Note that the selected configuration is not the customary configuration with two external rotors and an intermediate stator. The axial arrangement of one rotor and two stators is proposed as an alternative in the embodiments described here. The retarder rotor is positioned centrally, with the stators positioned on either side of it. This configuration mitigates problems of rotor locking caused mainly by exposure to weather. In cold climates, blocks of ice may form on the rotors, which could damage nearby elements if they are thrown off during rotation.

There are other advantages to selecting a central rotor. One is that it provides fixed air gaps. Another is that it can function regardless of the direction of rotation. The direction of rotation is especially important for cooling. With external rotors, when they rotate in one direction, air is forced into the retarder to cool it. Cooling problems may result if the direction of rotation is reversed. On another note, compared with the case of two rotors, the axial forces are neutralized when there is only a single rotor. These forces can cause warping of the retarder rotors.

FIG. 1shows the external appearance of one embodiment of the retarder system. The retarder system is compact despite being equipped with a generator20,30, because the generator is integrated into the assembly. This makes it possible to house all of the components that are protected externally by a series of housings3on each side of the axle1on which it is mounted. This axle1may be an axle with a direct connection to the wheels, or may be a cardan shaft. Generally, the assembly is mounted on the axle1by means of a bushing2.

FIG. 2shows the complete interior of the aforementioned retarder system. For the sake of convenience, the embodiment of the system includes two different electrical generators on each side. Nevertheless, both generators may also be the same. Depending on the application, a single generator may even suffice to provide power to the retarder system. In turn, this single generator may be a permanent-magnet generator30, or a self-excited generator20, depending on the needs. For example, to reduce weight, a permanent-magnet generator would be preferable. On the other hand, if high braking torque is needed, a self-excited generator would be preferred.

The following figures complementFIG. 2, showing the two types of generators separately and in greater detail. The self-excited generator20is illustrated inFIGS. 3, 4, and 5. The permanent-magnet generator30is illustrated inFIGS. 6, 7, and 8.

As shown in the figure, the retarder10is positioned centrally, and the generators20,30are coupled to the outside of the retarder10. The rotating elements: the retarder rotor11and the rotors21(or31) of the generator20(or30) are fixed to a bushing2, forming a monobloc assembly. The rest of the non-rotating elements of the retarder10and the generators20,30are mounted using bearings4.

Preferably, the retarder10rotor11will be a cast steel assembly. The rotor11may be manufactured as two disks13connected by a series of ribs14, which are generally cylindrical. High electrical conductivity is required in the rotor to ensure that the absorbed power is greater for the same electromotive force, thus increasing the induced current. Also, high thermal conductivity facilitates the dissipation of the heat that is generated. Another important factor that promotes heat dissipation is the optimization of the design. To do this, the geometry of the ribs14will preferably be such that it is able to ventilate the inside of the rotor11with air, regardless of the direction of rotation of the rotor11, thus facilitating heat dissipation.

When this assembly is installed on a railroad car axle, it is rigidly affixed to it, generally as a forced joint (pressed) as is done with conventional brakes. In other applications, the retarder10may incorporate its own axle.

The stators of the retarder10and generator20,30will preferably be made of a ferrous alloy. The electromagnets15are fixed inside the retarder10stator12, while the stator22of the generator20,30, with its cores and winding28, is attached to the outside. The stator22is similar for the two types of generators (self-excited20and permanent-magnet30).

An exterior ring with bearings suitable to withstand the weight of the retarder, as well as the axial and radial forces that produce vibration, may be used to mount it on the axle1. To regulate the axial clearance of the bearings4of the stators12, they have been designed with a series of braces5and nuts that set the air gap distances.

Also, a series of supports secure the stators12to a frame or chassis to prevent them from turning with the axis1.

The generator20is self-excited by the winding27of the fixed pole core26, secured to the outside of the retarder10stator12(or stators, if two generators are needed on each side). The remanence on this pole core26must be large enough to make pre-excitation unnecessary (it is made of hard magnetic materials).

The rotor21of the generator20is preferably mounted securely to the bushing2and has an interior configuration with a solid core. The fixed pole core26is included inside, and is frictionless, which is to say that the preliminary air gaps are maintained.

The stator22of the generator20is properly secured to the outside of the stator12(or stators) of the retarder10, on the same side as the fixed pole core26. This stator22is made up of sheets that are insulated from one another, equipped with a series of slits, which are tightly compressed to form a compact core. The stator windings28are installed in the aforementioned slits.

The field magnetizes the disks13of the rotor11, alternating N-S, when they turn, inducing an alternating current on the stator22winding28of the generator20.

The other type of generator shown inFIG. 6toFIG. 8is a permanent-magnet generator30. The source of electrical energy is achieved by means of a rotor31with permanent magnets that are fixed to the bushing2, with the generator30stator22secured to the outside of the retarder10stator12.

Both types of generators20,30are properly sized to supply the necessary power to the retarder10, which is responsible for braking above a certain speed threshold. At slower speeds, the conventional mechanical brake must be applied until the vehicle comes to a complete stop. These two generators20,30may act individually or jointly on the retarder10, functioning independently.

The rotors or inducers21,31of the generators20,30generate the magnetic field necessary for the windings of the stators22of the generators to generate the corresponding alternating current.

The retarder10functions with no wear or friction, and the bearings4are the only parts that are subject to wear. Alloys are preferably used in their manufacture, combining those that are magnetic and non-magnetic, in order to make better use of flows and prevent them from dispersing. Welds should preferably be avoided, bolting the elements and sub-assemblies precisely and securely, based on the thermal fatigue stresses to which they are subjected.

A braking regulator module40will be responsible for controlling the braking force. The braking regulator module40is an electronic control device that converts and controls the current from the power supply for use directly on the windings of the retarder10, based on the parameters programmed according to the required operating conditions.

This regulator module40modifies the power supply of the retarder10linearly, allowing more or less power supply voltage to enter the retarder10in a linear manner, which provides precise control over braking. The braking regulator40generally includes a rectifier and a voltage stabilizer. The generator20,30produces alternating current, transforming the mechanical energy of the rotation produced by the axle1into electrical energy to power the retarder10. Since this is alternating current, it must be rectified for correct functioning and control of the retarder10. The rectifier converts the alternating current into direct current. It also includes a voltage stabilizer to keep it approximately constant, without variations when rpm (revolutions per minute) increase or decrease.

Part of the braking regulator module40is located next to the retarder10, but the control will preferably be located in another place. For example, in railway vehicles, it is generally located inside the train's cab to be manipulated by the operator and to control or monitor the braking force of all of the cars.

The control input that the regulator module40receives is the desired braking signal from the central computer system, which may be manual or automatic. It also receives the actual rotation speed detection signals and the digital input-output signals, to receive information or safety conditions from the vehicle's central system, and also to send these signals to the vehicle's central system.

The regulator module40is preferably programmable for different operating limit curves, for example, direct or inverse signal, or linear or quadratic response. A fully autonomous power supply is achieved by generating current using the integrated generator20,30. The regulator module40controls and sends the excitation current from the generator in the form of a closed servo control loop, to obtain braking current based on the control signal and within the limits of the previously programmed curves.

In addition, for greater safety, a temperature sensor installed on the brake can be used in any of the embodiments described to limit the maximum power levels that are developed.

Finally, another specific embodiment that uses a generator with higher output is described. If the hard materials in a self-excited generator are replaced with soft materials (core56), the generator may no longer be self-excited, but in exchange generates much greater output. This type of generator will be referred to hereinafter as an “external-excitation generator50”.FIG. 9toFIG. 11show a retarder system that is equipped with this generator50as the principal generator, along with a permanent-magnet generator30as an auxiliary. Preferably, the core56(low remanence) has the same composition as the ferrous parts of the stator12.

The self-excitation is due to the fact that hard materials, once magnetized, behave like permanent magnets. Consequently, soft materials are easily demagnetized and their losses are lower, so they may be preferable in applications with higher output (they have lower hysteresis losses than hard materials, so they do not heat up as much and output is higher).

In this case, the excitation to create the magnetic field needed in the generator50must be provided externally to start up. Specifically, this can be done advantageously through a small auxiliary permanent-magnet generator30. This allows the generator50that is acting as the main generator to be optimized as much as possible. In other words, once the rotor51reaches an adequate speed, it is no longer excited by the generator30, which will be deactivated.

This mixed or hybrid configuration is also especially desirable in a situation in which the retarder10has a low number of revolutions. It is then that the braking torque, and consequently the power supply to the retarder, must be the highest. For this reason, soft materials must be used in the fixed pole core as well as in the pole masses. The use of soft materials results in high levels of magnetic saturation, and also eliminates the passive resistance to rotation when there is no excitation, reducing inertia to insignificant levels.

The control of external excitation in a mixed configuration is provided by an electronic system that can be integrated into the regulator module40, which controls the power that is supplied by the auxiliary generator (permanent-magnet generator30) to the induction winding of the retarder generator. This is fixed to the axle and rotates, so the electronic system is responsible for ensuring that the auxiliary generator sends an excitation supply with the highest power when the axle is rotating at lower rpm. And in the opposite case, when the axle is rotating at high rpm, the system will limit the excitation power supply of the induction winding of the retarder generator, because it requires less excitation voltage when it is rotating at high rpm.

Glossary of Numerical References

1Axle.2Bushing.3Housings.4Bearings.5Braces.10Retarder.11Central rotor of the retarder10.12Stator of the retarder10.13Disks.14Ribs.15Electromagnets.20Self-excited generator.21Rotor of the self-excited generator20.22Stator of the generator (either self-excited20, with permanent magnets30, or external excitation50).26Stationary hard core (with high remanence).27Core winding.28Windings (of stators of generators20,30,50).30Permanent-magnet generator.31Rotor of the permanent-magnet generator30.40Regulator module.50External-excitation generator.51Rotor of the external-excitation generator.56Stationary soft core (or low remanence).