Eddy current brake equipment with torque estimation

#The present invention relates to eddy current equipment for braking a vehicle.

#Equipment of this type conventionally comprises a portion (stator) that is fixed to the chassis of the vehicle and that includes inductor windings, and a moving portion (rotor) including an armature, and coupled to a rotary element of the vehicle, generally its transmission shaft. In certain eddy current braking equipments to which the invention can also be applied, the inductor windings are carried by the rotor and the armature is carried by the stator (see FR-A-2 667 741, for example).

#The term "inductor winding" or more simply "winding" is used herein to cover both an inductor winding proper and a group of such windings that are permanently interconnected in series and/or in parallel. Each winding as defined in this way produces a magnetic field when powered by the vehicle battery.

#FIG. 1 is a circuit diagram of a brake equipment of the invention.

#FIG. 2 is a graph showing one example of how the armature temperature may vary as a function of time in an equipment of the kind shown in FIG. 1.

#FIGS. 3 and 4 are graphs showing one way of determining the coefficients used when computing the torque in an equipment of the kind shown in FIG. 1 .

#The invention is described below, by way of example, with reference to a brake in which the armature rotates. The four inductor windings 3 are included in a stator assembly 1, and the armature 6 is included in a rotor assembly 2.

#Each winding 3 is constituted by a pair of coils, for example, with all eight coils being disposed about the transmission shaft (not shown) from the vehicle gear box, and having their axes parallel to said shaft. The rotor 2 is constituted by a piece of cast steel having a central bore 4 designed for mounting securely to the transmission shaft. The rotor 2 includes one or more disks perpendicular to the transmission shaft and constituting the armature 6 of the rotor. Between the armature 6 and the bore 4, each of the disks conventionally includes a finned structure 7 that provides ventilation while the transmission shaft is rotating. When the equipment is installed on a vehicle, the armature 6 is situated facing the windings 3 of the stator 1. In a typical embodiment, the rotor 2 includes one disk on either side of the stator, such that each rotating armature disk 6 faces a ring of magnetic poles as established by the windings 3 and of polarities that alternate from pole to pole. Rotation of the transmission shaft generates eddy currents in the armature 6 whenever at least one of the windings is electrically powered by the vehicle battery 8. As a result, braking torque is generated that increases with the number of windings that are excited, and simultaneously the armature heats up to an extent that is partially compensated by the ventilation from the fins 7.

#The equipment includes excitation means 9 for selectively powering the windings 3 from the battery 8, which battery typically has a nominal voltage of 24 volts. The excitation means 9 are constituted by four relays 11 each mounted between the positive terminal of the battery and one end of a respective winding 3, the other end of each winding being connected to the negative terminal of the battery 8. The four relays 11 are independently controlled by four signals delivered by control means 12.