Abstract:
The invention relates to a method of powering at least one brushless DC electric motor having a plurality of phases for powering, the method including the steps of associating a static contactor with the motor for taking input voltage pulses and delivering polyphase voltage pulses to the motor in a manner that is servo-controlled to the angular position of the rotor of the motor, and for generating from a DC voltage source voltage pulses of frequency that is fixed and at a duty ratio that is controllable, thereby forming the input voltage pulses to the static contactor.

Description:
The invention relates to a method of controlling a brushless direct current (DC) motor. 
     TECHNOLOGICAL BACKGROUND OF THE INVENTION 
     Such motors are generally controlled by means of a static converter that is connected to a DC voltage source and that delivers voltages for each of the phases of the motor, e.g. by means of power transistors that are controlled to switch on and off in a manner that is servo-controlled to the angular position of the rotor of the motor. For this purpose, the motor is generally fitted with means for measuring its angular position, which means deliver a signal that is representative of said position, the signal being used by the static converter to switch the power transistors on and off so as to perform the automatic synchronous switching function that is performed by the commutator in a motor with brushes. 
     It is also appropriate to adapt the voltage that is delivered to the level of power or torque that is required. For this purpose, the static converter is generally controlled to vary the voltage delivered to the motor as a function of the mechanical power or the torque that it is supposed to deliver. Thus, in response to a power or torque setpoint, the static converter sends a variable voltage to the motor so as to enable the motor to develop the requested power or torque. For this purpose, various voltage-varying methods are known, such as for example pulse width modulation (PWM). 
     Control arrangements are also known that include a static contactor associated with an angle position sensor for controlling power transistors, the static contactor then not performing the voltage-varying function of static converters, but only the synchronizing function. The voltage is varied by means of an upstream DC/DC converter that delivers a variable DC voltage to the static contactor. 
     OBJECT OF THE INVENTION 
     An object of the invention is to provide another way of powering a brushless DC motor. 
     SUMMARY OF THE INVENTION 
     To this end, the invention provides a method of powering at least one brushless DC electric motor having a plurality of phases for powering, the method comprising the steps of:
         associating a static contactor with the motor for the purpose of taking an input voltage and delivering to the motor a polyphase voltage in a manner that is servo-controlled to the angular position of the rotor of the motor; and   using a DC voltage source to generate voltage pulses of frequency that is fixed and of duty ratio that is controllable so as to form the input voltage to the static contactor.       

     The arrangements of the invention present numerous advantages:
         the static contactor associated with the motor is very simple, since it serves only to perform the sequencing of the phase voltages, and not to vary them. It may be arranged as close as possible to the motor, and may even be incorporated directly therein, with a rotor angle position sensor being integrated therein and delivering a signal that is used directly by the static contactor. The static contactor can be thought of as replacing the commutator and the brushes of a motor having brushes;   the input voltage generator may also be very simple, since it delivers a single-phase voltage at a frequency that is fixed. Only the duty ratio of the pulses is variable, and that is technologically very simple to implement; and   the static contactor and the voltage pulse generator may be physically remote from each other, and may be connected together by means suitable for transmitting voltage pulses at fixed frequency. In particular, the voltage pulses may be transmitted via a transformer, thereby achieving electrical isolation.       

    
    
     
       DESCRIPTION OF THE FIGURES 
       The invention can be better understood in the light of the following description of a particular embodiment of the invention given with reference to the accompanying figures, in which: 
         FIG. 1  is a diagrammatic view of a device enabling the method of the invention to be implemented; 
         FIG. 2  is a diagrammatic view of a device analogous to that of  FIG. 1  for powering a plurality of motors; and 
         FIG. 3  is a section view of the bottom portion of an aircraft undercarriage with electromechanical brakes implementing the method of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to  FIG. 1 , the method is used for powering an electric motor  1  of the brushless DC type. According to the invention, the motor  1  is associated with a static contactor  10  having controllable switches that interrupt an input voltage  12  in order to deliver it to phases of the motor  1  as a function of information  13  concerning the angular position of the motor, as delivered by an angular position sensor  14 . The sole function of the static contactor  10  is to interrupt the input voltage in order to generate voltage for the phases. The controllable switches may be thyristors, for example. 
     Still according to the invention, the input voltage  12  is a pulsed voltage U pulse , that is generated by a voltage pulse generator  20  from a DC source voltage. The voltage pulse generator  20  is preferably a chopper having controlled switches that convert the DC voltage source into a pulsed single-phase voltage at a fixed frequency (in the diagram of the figure there can be seen the equivalent period Δt that is of constant duration), but of duty ratio that is controllable in order to produce voltage pulses of controllable mean value, e.g. as a function of a force setpoint delivered to the pulse generator  20 . 
     Where appropriate, it is possible to provide a filter stage at the input to the static contactor  10  for the purpose of smoothing the input voltage before applying it to the controlled switches of the static contactor. 
     The static contactor  10  and the sensor  14  are preferably located in the immediate proximity of the motor, or indeed incorporated therein. The assembly arranged in this way and shown symbolically in the figure by a dashed-line rectangle, has only two input wires for supplying it with the input voltage pulses. 
     The voltage pulses may be transmitted from the voltage pulse generator  22  to the static contactor  10  by means of cables  15 , as shown. They could also be transmitted, as shown in  FIG. 2 , by means of a single-phase transformer  30  providing electrical isolation between these two elements. Given the frequency of the input voltage  12  (typically of the order of 100 kilohertz (kHz)), the transformer may be very compact. 
     As shown in  FIG. 2 , the voltage pulses are easily transmitted by means of the transformer to a plurality of assemblies each comprising a motor plus a static contactor plus an angle position sensor. 
     The invention is particularly adapted for application to electromechanical aircraft brakes. Indeed, as suggested in document U.S. Pat. No. 3,977,631, it is advantageous to provide a brake on an undercarriage in which the ring, i.e. the part that supports the actuators, and the associated torsion tube are mounted on the corresponding axle with the possibility of rotating. By controlling the braking actuators in such a manner as to compress the stack of disks and thereby constrain the ring to rotate with the wheel, this arrangement enables rotation of the wheel to be controlled by causing the ring to rotate by using a motor member. 
     In the above-mentioned document, the actuators are hydraulic actuators. Powering them while the ring is rotating therefore requires a hydraulic circuit to be provided that has a rotary coupling compatible with rotation of the ring. 
     As shown in  FIG. 3 , that teaching may be applied to an undercarriage  100  having wheels  101  with brakes  102  that are fitted with electromechanical braking actuators  110  that are carried by the ring  104 . Here the ring  104  is mounted to rotate on the axle  105  that receives the wheel  101 . Each of the actuators  110  is fitted with a brushless DC motor that is associated, in accordance with the invention, with a static contactor and with an angle position sensor, these two elements being arranged directly in the actuator. The motor is used for selectively moving a pusher  16  of the actuator facing a stack of friction disks  116  in order to press the disks together in selective manner, by means of a transformation member transforming the rotary movement of the motor into linear movement of the pusher. The assembly forms an integrated actuator that can be removed as a unit from the ring  104 . 
     The ring  104  is secured to a torsion tube  106  that rotates with the ring  104 . The friction disks  116  comprise disks that are constrained in rotation with the wheel  101  alternating with disks that are constrained in rotation with the torsion tube  106 . 
     In a particular arrangement of the invention, the ring  104  carries the secondary  120  of a transformer having its primary  121  fastened to the undercarriage facing the secondary. The primary  121  is connected by means of a cable  122  extending along the undercarriage to a voltage pulse generator that is mounted in the fuselage of the aircraft, in this example. The transformer transmits these voltage pulses to the integrated actuators  110 . As before, these voltage pulses are interrupted and sequenced by the static contactors of the actuators in order to power the phases of the associated motors as a function of the angular positions of the rotors of the motors. 
     Because of this contactless connection, the integrated actuators  110  can be powered while the ring is rotating, without any need for rotary contacts. 
     In order to control rotation of the ring  104  in selective manner, a motor  130  for driving the ring  104  in rotation is arranged on the bottom portion of the undercarriage and co-operates in this example with the ring by means of a bevel gear connection. 
     These arrangements make several modes of operation possible:
         a first mode of operation during which the ring  104  is prevented from rotating, the integrated actuators  110  then being powered by the transformer having its primary  121  and its secondary  120  stationary relative to each other, thereby serving to press the brake disks together and thus slow down rotation of the wheel. This is the conventional braking mode;   a second mode of operation in which the ring  104  is driven in rotation by the motor  130 . In order to drive the wheel in rotation, it is then appropriate to power the integrated actuators  110  via the transformer, with its secondary  120  then rotating in register with the primary  121 . This is independent taxiing mode, enabling the aircraft to move without using its engines; and   a third mode of operation in which the ring  104  is driven in rotation by the motor  130 , without the integrated actuators  110  being powered. This is a mode of operation for verifying proper operation of the motor member.       

     The invention is not limited to the above description, but on the contrary covers any variant coming within the ambit defined by the claims.