Abstract:
An apparatus is described for the adjustment of horizontal stabilizers for aircraft in relation to the aircraft axis with mechanical power transmission from two drives to the horizontal stabilizer. The apparatus may include two differential transmissions coupled via a connection shaft that drive the horizontal stabilizer via a mechanical transmission, such as a respective spindle and a spindle nut.

Description:
This application claims priority to German Patent Application Serial No. DE 10 2004 047 008.1 filed Sep. 28, 2004, which is hereby incorporated by reference in its entirety for all purposes. 
   FIELD 
   The present disclosure relates to an apparatus for the adjustment of horizontal stabilizers for aircraft. 
   BACKGROUND AND SUMMARY 
   Horizontal stabilizers for current transport aircraft are adjustable in their setting to the axis of the aircraft. An additional torque about the pitch axis of the aircraft can be generated by this change of the blade angle of the horizontal stabilizer in order to establish trimming conditions or to support the effect of the elevators during maneuvers. 
   In aircraft construction, systems critical for safety, which also include the horizontal stabilizer adjustment system THSA (=trimmable horizontal stabilizer actuator), have to be secured against simple mechanical failures. For this reason, all load-bearing components of a THSA are designed such that at least two independent mechanical load paths arise from the force introduction points from the horizontal stabilizer up to the connection to the aircraft structure (fail-safe principle). 
   The fail-safe architecture of a conventional stabilizer system such as is used in transport aircraft today is represented by way of example with reference to  FIG. 1 . The mechanical power in this system is guided by two drives or motors  1   a  and  1   b  via a speed summing differential transmission  2  to a spindle  3  whose spindle nut  4  moves in a translatory manner and thus imposes a pivot movement on the rotatably supported horizontal stabilizer  5 . 
   The motors  1   a  and  1   b  are fed by two mutually independent energy systems  6   a  and  6   b  and are controlled by a control and monitoring electronic system (motor control electronics MCE)  7   a  and  7   b . Each drive  1   a  and  1   b  is provided with a brake (power off brake, POB)  8   a  and  8   b  whose braking effect is generated by a biased spring. The spring is relaxed at the command of the respective MCE unit  7   a  and  7   b  via an actuating mechanism which draws its power from the energy system of the associated drive  1   a  and  1   b . If the energy system  6   a  and  6   b  or the electronics  7   a  and  7   b  are not available anymore due to a failure, the POB  8   a  and  8   b  is set automatically. This procedure is also called the power-off principle. The differential transmission  2  has the required two independent load paths and is designed such that half a sum of the speeds of both motors  1   a  and  1   b  is always transmitted to the output shaft  9 . If a motor  1   a  or  1   b  is stopped due to an occurring failure and if the corresponding transmission input is blocked with the associated POB  8   a  or  8   b , the remaining intact drive  1   a  or  1   b  continues to drive the output shaft  9  at a reduced speed. The power is transmitted to the spindle  3  via a further transmission  10 . 
   Two independent load paths are integrated in the spindle structure, of which one primary load path formed by the actual function spindle  3  bears the complete load in the failure-free operating case, whereas a secondary load path has no load in the failure-free operating case. This secondary load path  11  is realized as a tension rod  11  in the interior of the hollow spindle  3 . If the spindle  3  breaks, it is held together by the tension rod  11  so that the force transmission is maintained over the held-together spindle  3  and the spindle nut  4  likewise made in duplicate mechanically and the horizontal stabilizer  5  is fixed with respect to the structure. Both the spindle head  12  of the primary load path and the secondary load path  11  inside the spindle  3  are gimbal-mounted at the aircraft structure. The secondary load path  11  is, for example, gimbal-mounted via a ball and socket joint  13 . A so-called “no-back”  14  protects the adjustment system and so the stabilizer against an uncontrolled escape from a secure holding position under the effect of aerodynamic forces at the stabilizer in the case of a simple mechanical failure (e.g. breakage of a drive shaft between the drives  1   a  and  1   b  and the differential transmission differential gear  2 ). The no-back  14  in this case acts as an autonomous mechanical emergency brake. 
   Apparatus of this type for the adjustment of the horizontal stabilizers for aircraft in accordance with the present prior art are made in duplicate mechanically in all mechanical load-bearing groups—from the transmission  2  and  10  to the spindle head  12 , the spindle  3  with secondary load path  11  and motor  4 —for reasons of safety. This makes a very complex fail-safe construction necessary which is not testable, or is only testable with limitations, for freedom of failure of both load paths (avoidance of so-called “sleeping failures”). Neither the no-back POB  14  nor the integrated, secondary load path  11  permit an automated test routine in the installed state. With the no-back  14 , it is not possible to apply the external loads required for the testing of the function. In modern adjustment systems, a sensor system will be implemented which, following a failure of the primary load path, however, only indicates a load on the tension rod in operation. The previously described complex construction and the automatable testability of the system on the ground, which is only possible in a very restricted manner or even not completely at all, are the major serious disadvantages of the apparatus for the adjustment of the horizontal stabilizers for aircraft of the prior art. 
   It is one object of the present disclosure to further develop a generic apparatus for the adjustment of horizontal stabilizers for aircraft in relation to the axis of the aircraft with a mechanical power transmission between the aircraft horizontal stabilizer and the aircraft structure such that fail-safe system is mechanically ensured and that it is permitted to test all load-bearing elements of the structure in an automated manner on the ground. In one embodiment it is desired to be able to perform automated testing without any special tools, load simulation or similar. 
   This and other objects may be solved in accordance with an apparatus for the adjustment of horizontal stabilizers for aircraft in relation to the aircraft axis with a mechanical power transmission of two drives to the horizontal stabilizer is provided in which two differential transmissions coupled via a connection shaft drive the horizontal stabilizer via a mechanical transmission, such as one spindle and one spindle nut each. Accordingly, instead of a secondary load path integrated in the spindle—such as has been customary up to the present day in accordance with the aforesaid discussion of the prior art—a structure is formed with two mechanically separate primary load paths. These two separate primary load paths may respectively include: differential transmissions, transmission output shafts, transmissions, spindles and spindle nuts up to the plate on the horizontal stabilizer, each made simply in a mechanical construction manner. 
   In one example, the two differential transmissions can also effect an automatic load and speed synchronization of the spindles with different speeds of the drives. 
   Also, the apparatus each only have simply load-bearing components. 
   A speed sensor for the determination of the speed of the connection shaft and a shaft brake for the braking of the connection shaft may be particularly advantageously present, which allow cases of breakage in a mechanical component of the power-carrying load paths to be recognized and to reliably fix the system in the case of failure. 
   It is furthermore advantageous for shaft brakes and sensors to be arranged in each case on the drive shafts arranged between the drives and the differential transmissions and for additional sensors to be present for the speed recognition of the transmission output shafts. Mechanical failures and the function capability of all brakes can be determined using automatable test routines via MCEs likewise advantageously present for the evaluation of the sensor signals. An integrity test of the total system is thus possible on the ground. 
   The drives and brakes can advantageously be based on hydraulic power supply, electric power supply or a combination thereof. 

   
     BRIEF DESCRIPTION OF THE FIGURES 
     Further features, details and advantages of the present disclosure will be explained with reference to an embodiment shown in the drawing. There are shown: 
       FIG. 1 : a schematic representation of a trimmable horizontal stabilizer actuator (THSA) in accordance with the prior art; 
       FIG. 2 : a schematic representation of the apparatus in accordance with the present disclosure in accordance with a first embodiment; 
       FIG. 3 : a schematic representation of the power flux in the apparatus in accordance with  FIG. 2 ; and 
       FIG. 4 : a representation in accordance with the embodiment of  FIG. 2  in which the sensor system of the apparatus is drawn. 
   

   DETAILED DESCRIPTION 
   In the embodiment variant in accordance with  FIG. 2 , those parts which were already contained in the device in accordance with the prior art of  FIG. 1  are designated with the same reference numerals. 
   In the embodiment variant in accordance with  FIG. 2 , two separate load paths having differential transmissions  2   a  and  2   b , transmission output shafts  9   a  and  9   b , transmissions  10   a  and  10   b , spindles  3   a  and  3   b  and spindle nuts  4   a  and  4   b  up to the plate at the horizontal stabilizer  5  are provided, each made simply in a mechanical construction manner. The mechanical power is provided by two drives or motors  1   a  and  1   b  which are fed by two mutually independent energy systems  6   a  and  6   b  and are controlled by motor control electronics (MCE)  7   a  and  7   b.    
   A major feature is presented by the two differential transmissions  2   a  and  2   b  which are coupled via a connection shaft  15  and, in failure-free normal operation, transmit the mechanical power of the motors  1   a  and  1   b  to the respectively associated spindles  3   a  and  2   b . The connection shaft  15  is provided with a so-called power-off brake (POB)  16  which can be opened by either of the two MCEs  7   a  and  7   b . On the failure of both energy systems  6   a  and  6   b  or of both MCEs  7   a  and  7   b , the POB  16  is actuated via a biased spring (not shown in any more detail here). 
   The drive shafts  17   a  and  17   b  each extend from the motors  1   a  and  1   b  to the differential transmissions  2   a  and  2   b . Both drive shafts  17   a  and  17   b  are provided with so-called power-off brakes  8   a  and  8   b  which are supplied via the energy system  6   a  and  7   b  and are switched via the electronics  7   a  and  7   b  of the associated motor  1   a  and  1   b . The mechanical power is transmitted from the respective transmission output shaft  9   a  and  9   b  to the spindles  3   a  and  3   b  via a respective further transmission stage  10   a  and  10   b.    
   The respective power fluxes in the system in accordance with the present disclosure are shown in  FIG. 3 . The differential transmissions  2   a  and  2   b  shown schematically in the figure act in a speed summing manner. Half the sum of the speeds of the motor shaft ω in  and of the connection shaft ω cs  is thereby always applied to the transmission output shaft  9   a  or  9   b  according the principle since it leads to the spindle  3   a  or  3   b  . Likewise according to the principle, the motor shaft  17   a  or  17   b  and the connection shaft  15  have to guide torques T in =T cs  of equal amount which are supported at the transmission output shaft  9   a  or  9   b . Twice the torque T out  of the motor and connection shaft  15  is thus applied to the transmission output shaft  9   a  or  9   b  without taking the efficiencies into account. Since both spindles  3   a  and  3   b  are connected to the rigid horizontal aircraft stabilizer  5 , the speeds of both transmission output shafts ω out,1 =ω out,2  must also be identical. Different speeds of the motors  1   a  and  1   b  are therefore distributed via the connection shaft  15  such that identical speeds apply at both transmission output shafts  9   a  and  9   b . In failure-free normal operation, the system of the two spindles  3   a  and  3   b  therefore synchronizes itself kinematically. If the two engine speeds are identical, the connection shaft  15  is stationary. If they are different, the faster motor  1   a  or  1   b  drives a speed difference via its associated differential transmission  2   a  or  2   b  and the connection shaft  15  into the second differential transmission  2   b  or  2   a.    
   The resulting power fluxes are shown in  FIG. 3 . With identical input speeds ω in,1  and ω in,2 , the connection shaft  15  is stationary ω cs =0) so that the power flux is guided without branching from the motor shaft  17   a  or  17   b  to the output shaft  9   a  or  9   b . If, however, the input speed ω in,2  is larger than ω in,1 , some of the power of the motor  1   b  is transmitted via the connection shaft  15  and the differential transmission  2   a  to the transmission output shaft  9   a  due to the speed summing properties resulting from the principle of the differential transmissions  2   a  or  2   b  as well as the output speeds ω out,1 =ω out,2  coupled via the aircraft horizontal stabilizer  5  and thus identical. Since, as already mentioned, the connection shaft  15  and the two motor shafts  17   a  or  17   b  have equal torques due to the principle which are supported at the transmission output shafts  9   a  or  9   b , both spindles  3   a  and  3   b  always carry the same load. The power fluxes in the two spindles  3   a  and  3   b  are thus identical in each operation condition. 
   Both motors  1   a  and  1   b  are operated with speed regulation in a superimposed position control circuit. Angle and speed sensors are provided both for the control of the motors  1   a  and  1   b , for the positioning of the aircraft horizontal stabilizer  5  and for the monitoring of cases of breaking or jamming of the total adjustment system. The position of the aircraft horizontal stabilizer is controlled and monitored via angle sensors  18   a  and  18   b  at the two spindles  3   a  and  3   b . This signal serves as feedback of the control parameter for the motors  1   a  and  1   b  in the position control circuit. The speed control of the motors  1   a  and  1   b  needs the signals of the speed at the motor shafts  19   a  and  19   b  and at the connection shaft  20 . The system can be operated in a controlled manner and can be completely monitored for cases of breaking and jamming with these signals. 
   If a break occurs at any position in the powertrain, no power can be transmitted at this position. Since all torques mutually support one another at the differential transmission  2   a  and  2   b , the shaft speed ω cs  will increase abruptly. This jump in speed is recognized by each of the integrated MCEs ( 7   a ,  7   b ) which thereupon stop the system. The motors  1   a  and  1   b  are switched off when stopped and the POBs  8   a  and  8   b  brake the motor shafts  17   a  and  17   b  and the POB  16  brakes the connection shaft  15 . 
   Jamming cases are recognized at any position of the load-bearing components, for example the differential transmissions  2   a  and  2   b , the transmissions  10   a  and  10   b , the spindles  3   a  and  3   b  and the spindle nuts  4   a  and  4   b  at predetermined control rates of the active drive both in normal two-motor operation and in one-motor operation, also with reference to signal patterns of position sensors in conjunction with speed sensors  18   a ,  18   b ,  19   a ,  19   b  and  20 . 
   The arrangement of brakes and sensors in accordance with the present disclosure shown in  FIG. 4  permits a complete check of all mechanical components for mechanical failures such as breaking or jamming in an automatic test and of the brakes themselves for functional capability under operating loads. This checking capability by means of specific automated test routines is possible on the ground. 
   Test routines can, for example, be defined as follows: 
   The motor shaft  17   a  can be checked for breakage as follows: The motor  1   a  is switched on; the brake  8   a  is set. The speed sensor  19   a  must assume the value 0 with an intact motor shaft  17   a.    
   A case of breakage in the total powertrain of the motor shaft  17   a ,  17   b  is generally checked over the differential transmission  2   a ,  2   b , over the transmission output shaft  9   a ,  9   b , over the transmissions  10   a ,  10   b  and the spindles  3   a ,  3   b  toward the aircraft horizontal stabilizer  5  in that the respective speed sensor signal on the driving motor side is zero with an intact system for the case that the motors  1   a  or  1   b  are driven on braking by means of the POBs  8   a  and  8   b  and of the POB  16  on the connection shaft  15 . 
   For the case that a jamming case is found at any position in a powertrain of the differential transmission  2   a  or  2   b , the transmission  10   a ,  10   b  and the spindles  3   a ,  3   b  or the spindle nuts  4   a  and  4   b , the speed sensor signal of the driving motor  1   b  or  1   a  must be not equal to  0  in the case that a motor brake  8   a  or  8   b  engages and the motor  1   b  or  1   a  opposite it is driving.