Abstract:
An actuator system for actuating a movable structure of a thrust reverser, the system including a first motor, a first actuator driven by the first motor, a second actuator, and a first transmission shaft that is connected to the second actuator and to the first motor so that the second actuator is driven by the first motor, a second motor, a third actuator driven by the second motor, a fourth actuator, and a second transmission shaft that is connected to the fourth actuator and to the second motor so that the fourth actuator is driven by the second motor, and control means for controlling the motors to cause the first actuator, the second actuator, the third actuator, and the fourth actuator to be driven synchronously by the two motors. The invention also relates to a thrust reverser and to a jet engine fitted with such an actuator system.

Description:
[0001]    The invention relates to an actuator system for actuating a movable structure of an aircraft thrust reverser (also known as a “transcowl”). The invention also provides a thrust reverser including such an actuator system. The invention also provides an aircraft jet engine including such an actuator system. 
       TECHNOLOGICAL BACKGROUND OF THE INVENTION 
       [0002]    A thrust reverser of an aircraft turbojet engine serves to improve the braking capacity of the aircraft by redirecting a fraction of the ejection stream from the turbojet engine towards the front of the nacelle associated with the turbojet engine. Various types of thrust reverser are thus known. Under all circumstances, a thrust reverser comprises at least one movable structure that is movable between a neutral position and an active position in which the movable structure serves to deflect the ejection stream towards the front of the nacelle. An actuator system is associated with the movable structure in order to cause the movable structure to move in reversible manner between the neutral position and the active position. 
         [0003]    For this purpose, an actuator system for a movable structure is known that includes an electric motor, four actuators associated with the movable structure, and four flexible transmission shafts, each flexible transmission shaft being connected firstly to a respective one of the actuators and secondly to the motor so that the various actuators can be driven by the motor. Under such circumstances, when the motor is powered, it drives the four actuators that in turn move the movable structure. 
         [0004]    Nevertheless, since the movable structure is usually made of composite material, it presents great flexibility. Under such circumstances, a shift of synchronization between the various actuators leads to significant deformation of the movable structure, and thus potentially to damaging the movable structure. Furthermore, if the movable structure reaches its active position while deformed, it might no longer correctly deflect the ejection stream towards the front of the nacelle, thereby reducing the effectiveness of the thrust reverser. Furthermore, if the movable structure reaches its neutral position while deformed, it may no longer correctly close the thrust reverser completely, thereby leading to an undesirable leak of a fraction of the ejection stream from the turbojet engine towards the front of the nacelle. 
       OBJECT OF THE INVENTION 
       [0005]    An object of the invention is to propose an actuator system for actuating a movable structure of an aircraft thrust reverser that limits the risks of significant deformation of the movable structure during movement of the structure by the actuator system, and also to propose a thrust reverser and a jet engine fitted with such an actuator system. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0006]    In order to achieve this object, the invention provides an actuator system for actuating a movable structure of a thrust reverser of an aircraft, the system comprising:
       a first electric motor;   a first actuator arranged in the proximity of the first electric motor in order to be driven by the first electric motor;   a second actuator and a first flexible transmission shaft that is connected firstly to the second actuator and secondly to the first electric motor so that the second actuator is arranged to be driven by the first electric motor;   a second electric motor;   a third actuator arranged in the proximity of the second electric motor in order to be driven by the second electric motor;   a fourth actuator and a second flexible transmission shaft that is connected firstly to the fourth actuator and secondly to the second electric motor so that the fourth actuator is driven by the second electric motor; and   control means for controlling the electric motors to synchronize drive of the first actuator, of the second actuator, of the third actuator, and of the fourth actuator by means of the two motors.       
 
         [0014]    Because of the presence of two motors and of the control means, it is possible to detect any error of synchronization between the two motors, and to correct the control setpoints generated by the control means for the two motors accordingly. The actuator system of the invention thus makes it possible to avoid the various actuators becoming desynchronized by controlling the two motors, thereby limiting deformation of the movable structure during movement of the movable structure by the actuator system. It is thus possible quickly to detect the beginning of deformation of the movable structure and to adapt accordingly the control applied to the two motors in order to correct the deformation. 
         [0015]    In addition, the particular arrangement of two actuators, each driven by a dedicated motor, makes it possible to have relatively short transmissions of torque between a motor and the actuators associated therewith, thereby further limiting any risk of the actuators becoming desynchronized and thus any risk of the movable structure being deformed. 
         [0016]    The invention also provides an aircraft thrust reverser comprising a movable structure and an actuator system as described above, the system being arranged in such a manner as to move the movable structure between a neutral position and an active position in which the movable structure serves to deflect an ejection stream from a jet engine of the aircraft towards the front of the aircraft. 
         [0017]    Furthermore, the invention provides an aircraft jet engine including a thrust reverser comprising a movable structure and an actuator system as described above, the system being arranged so as to move the movable structure between a neutral position and an active position in which the movable structure serves to deflect an ejection stream from the jet engine towards the front of the aircraft. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0018]    The invention can be better understood in the light of the following description of a particular, non-limiting embodiment of the invention. Reference is made to the accompanying figures, in which: 
           [0019]      FIG. 1  is a diagrammatic perspective view of a movable structure and of an actuator system of the invention associated with said movable structure, the calculation member not be shown; and 
           [0020]      FIG. 2  is a diagrammatic end view of the actuator system shown in  FIG. 1 , the movable structure not being shown. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0021]    With reference to  FIGS. 1 and 2 , the actuator system  1  of the invention in this example is for moving a single movable structure  2  of a turbojet engine thrust reverser (not shown) of an aircraft in translation along a translation axis X between a neutral position and an active position in which the movable structure  2  serves to deflect the ejection stream from the turbojet engine towards the front of the aircraft. 
         [0022]    For this purpose, the actuator system  1  has a first electric motor  11  and a second electric motor  12 . In this example, the two electric motors  11  and  12  are identical and can therefore deliver the same mechanical power. Both motors  11  and  12  are permanent magnet synchronous machines. 
         [0023]    Furthermore, the actuator system  1  has four actuators, all of which in this example are ball jackscrews, and they are referred to below as the first actuator  21 , the second actuator  22 , the third actuator  23 , and the fourth actuator  24 . 
         [0024]    In this example, the first actuator  21  is driven directly by the first motor  11  so that there is no flexible transmission shaft connecting the first actuator  21  to the first motor  11 . The first actuator  21  is integral with the first motor  11 . 
         [0025]    Symmetrically, the third actuator  23  in this example is driven directly by the second motor  12  so that no flexible transmission shaft connects the third actuator  23  to the second motor  12 . The third actuator  23  is integral with the second motor  12 . 
         [0026]    Furthermore, the actuator system  1  has a first flexible transmission shaft  31  that is connected directly both to the second actuator  22  and also to the first motor  11  so that the second actuator  22  can be driven by the first motor  11 . Likewise, the actuator system  1  has a second flexible transmission shaft  32  that is connected directly both to the fourth actuator  24  and also to the second motor  12  so that the fourth actuator  24  can be driven by the second motor  12 . 
         [0027]    Under such circumstances, the particular arrangement of the actuators and of the motors makes it possible to transmit torque directly between the first motor  11  and the first actuator  21  and between the second motor  12  and the third actuator  23 , and also to provide relatively short transmissions between the first motor  11  and the second actuator  22  and between the second motor  12  and the fourth actuator  24 , thereby limiting risks of the actuators losing synchronization and thus limiting risks of the movable structure deforming. 
         [0028]    Advantageously, only two flexible transmission shafts  31  and  32  are thus needed to enable all four actuators  21 ,  22 ,  23 , and  24  to be driven. This limits the number of flexible transmission shafts in the actuator system  1 , which shafts are very flexible and can lead to the actuators to which they are connected losing synchronization. Furthermore, because of their flexibility, the flexible transmission shafts may be subjected to mechanical resonance modes that are sometimes difficult to compensate. 
         [0029]    The four actuators  21 ,  22 ,  23 , and  24  are preferably arranged at regular intervals around one of the edges  3  of the movable structure  2 , an edge being a cross-section at the end of the movable structure  2  normal to the axis X of movement in translation. 
         [0030]    As a result, the movable structure  2  is subjected to thrust around its edge by the four actuators  21 ,  22 ,  23 , and  24  in a manner that is distributed, thereby limiting any risk of said movable structure  2  being deformed. In a preferred embodiment, the two motors  11  and  12 , and thus the first actuator  21  and the third actuator  23 , are arranged on the movable structure  2  at zones of maximum deformation of said movable structure  2 , i.e. at zones that deform the most easily. 
         [0031]    The first motor  11  and the first actuator  21  in this example are positioned at one of the ends of the edge  3 , and the second motor  12  and the third actuator  23  are positioned at the other end of the edge  3 , it being understood that the edge  3  is of section that is open. 
         [0032]    This further limits any risk of the movable structure  2  deforming while it is moving. Specifically, the two motors  11  and  12  are arranged at the ends of the movable structure  2  in such a manner that any error of synchronization between the ends of the movable structure  2 , due to maximum deformation of the movable structure  2 , can be detected and corrected. 
         [0033]    To this end, the actuator system  1  includes control means for controlling the motors  11  and  12  in order to synchronize drive of the first actuator  21 , of the second actuator  22 , of the third actuator  23 , and of the fourth actuator  24  by the two motors  11  and  12 . More precisely, the control means are configured to servo-control the angular positions of the two motors  11  and  12  so as to govern synchronous drive of the various actuators  21 ,  22 ,  23 , and  24 . In particular manner, the control means comprise a first angular position sensor associated with the first motor  11  and a second angular position sensor associated with the second motor  12 . For example, the control means include a first resolver  41  associated with the first motor  11  and a second resolver  42  associated with the second motor  12 . The control means further include a calculation member  43  generating a first angular position setpoint C m1  for the first motor  11  and a second angular position setpoint C m2  for the second motor  12 , as a function of angular position information θ 1  generated by the first resolver  41  and of angular position information θ 2  generated by the second resolver  42 . 
         [0034]    In the event of a synchronization error between the two motors  11  and  12 , the calculation member  43  detects a difference between the angular portions θ 1  and θ 2  as supplied by the two resolvers  41  and  42 , and adapts the setpoints C m1  and C m2  for the two motors  11  and  12  accordingly. 
         [0035]    The actuator system  1  can thus quickly detect a problem of synchronization between the motors  11  and  12  and thus between the actuators  21 ,  22 ,  23 , and  24 , and it can correct the problem effectively, thereby limiting any risk of the movable structure  2  deforming. 
         [0036]    The actuator system  1  preferably includes a third flexible transmission shaft  33  connected firstly to the second actuator  22  and secondly to the fourth actuator  24  so as to provide a driving link between the second actuator  22  and the fourth actuator  24 . Since the actuators  21 ,  22 ,  23 , and  24  are regularly distributed along the edge  3  of the movable structure  2 , the three flexible transmission shafts  31 ,  32 , and  33  in this example are of substantially the same length. 
         [0037]    It should be observed that even without the third flexible transmission shaft  33 , the actuators  21 ,  22 ,  23 , and  24  can be synchronized correctly by the two motors  11  and  12 . The third flexible transmission shaft  33  advantageously serves to further improve the synchronization between the various actuators  21 ,  22 ,  23 , and  24 , thereby limiting any risk of the movable structure  2  deforming. 
         [0038]    In addition, since the second actuator  22  and the fourth actuator  24  are each connected to both motors  11  and  12 , in the event of any one of the flexible transmission shafts  31 ,  32 , and  33  being lost, the second actuator  22  and the fourth actuator  24  can nevertheless be driven by one of the two motors  11  and  12 , thereby ensuring that the movable structure  2  is driven mechanically jointly by the four actuators  21 ,  22 ,  23 , and  24 . Likewise, the presence of the third flexible transmission shaft  33  and of the two motors  11  and  12  makes it possible to ensure that the movable structure  2  is driven mechanically jointly by the four actuators  21 ,  22 ,  23 , and  24 , even in the event of losing one of the motors  11  and  12 . 
         [0039]    Furthermore, in the event of a motor, an actuator, or a flexible transmission shaft seizing, the calculation member  43  is arranged to generate setpoints for generating alternating jolts in the two motors  11  and  12 . As a result of the forces applied in alternation to the two ends of a drive chain constituted by the motors  11 ,  12 , the actuators  21 ,  22 ,  23 , and  24 , and the flexible transmission shafts  31 ,  32 , and  33 , with the motors  11  and  12  being at the ends of said chain, this can make it possible to release the motor, the actuator, or the flexible transmission shaft that was blocked. 
         [0040]    In a particular embodiment, the two motors  11  and  12  are designed so that each of them is capable on its own of driving all four actuators  21 ,  22 ,  23 , and  24 , but at a speed that is lower than the speed at which the four actuators  21 ,  22 ,  23 , and  24  can be driven when both motors  11  and  12  are powered. More particularly, both motors  11  and  12  are designed so that the sum of the powers from the two motors  11  and  12  is equal to the power needed for driving the four actuators  21 ,  22 ,  23 , and  24  during nominal operation. 
         [0041]    Thus, the two motors  11  and  12  remain reasonable in size and weight compared to the situation in which each of them is designed to be capable on its own of driving all four actuators  21 ,  22 ,  23 , and  24  at a speed equal to the speed at which all four actuators  21 ,  22 ,  23 , and  24  can be driven when both motors  11  and  12  are powered. 
         [0042]    Naturally, the present invention is not limited to the embodiment described and variants may be applied thereto without going beyond the ambit of the invention as defined by the claims. 
         [0043]    In particular, although in this example the first actuator is driven directly by the first motor, the first actuator could merely be arranged in the proximity of the first motor. The actuator system would then include a short flexible transmission shaft, and in particular a flexible transmission shaft of length that is much shorter than the length of the flexible transmission shaft connecting the second actuator to the first motor or connecting the fourth actuator to the second motor, which would then be connected firstly to the first actuator and secondly to the first motor, so that the first actuator can be driven by the first motor. Likewise, although in this example the third actuator is driven directly by the second motor, the third actuator could merely be arranged in the proximity of the second motor. The actuator system would then include a short flexible transmission shaft, and in particular a flexible transmission shaft of length much shorter than the length of the flexible transmission shaft connecting the second actuator to the second motor or connecting the fourth actuator to the second motor, which would then be connected firstly to the third actuator and secondly to the second motor, so that the third actuator can be driven by the third motor. Nevertheless, it is preferable for the first motor to drive the first actuator directly and for the second motor to drive the third actuator directly. 
         [0044]    Although in this example the first flexible transmission shaft is connected directly to the first motor, said shaft could be connected directly to the first actuator and to the second actuator so that the second actuator is driven by the first motor via the first actuator. The first flexible transmission shaft would then be connected to the first motor via the first actuator. In addition, although in this example the second flexible transmission shaft is connected directly to the second motor, said shaft could be connected directly to the third actuator and to the fourth actuator so that the fourth actuator is driven by the second motor via the third actuator. The second flexible transmission shaft could then be connected to the second motor via the third actuator. 
         [0045]    The actuator system need not include a third flexible transmission shaft between the second actuator and the fourth actuator. 
         [0046]    Furthermore, the actuator system may include a greater number of actuators and/or of motors than described, providing it has fewer motors than actuators in order to avoid making the actuator system too heavy. 
         [0047]    Although in this example the motors are arranged at the ends of the edge of the movable structure, the motors could be arranged in other zones of the movable structure. Nevertheless, it is preferable for the motors to be arranged at said ends of the edge of the movable structure. 
         [0048]    Furthermore, Although in this example the actuators are distributed regularly around the periphery of the edge of the movable structure, the actuators could be distributed so that the distance between the second and fourth actuators is greater than the distance between the first and second actuators (or between the third and fourth actuators) in order to limit the lengths of the first flexible transmission shaft and of the second flexible transmission shaft. Under such circumstances, the system should preferably include a third flexible transmission shaft between the second actuator and the fourth actuator, of length that is thus longer than the lengths of the other two flexible transmission shafts, in order to enhance synchronization between the various actuators, and in particular between the second actuator and the fourth actuator.