Abstract:
An engine mountable gearbox is provided and includes a body formed to define a plurality of connection points at which a main engine generator and one or more accessories are mounted, a first transmission disposed within the body at the connection point of the main engine generator to run the main engine generator at a controlled constant speed at varying speeds of the engine rotation and a second transmission disposed within the body at least at one of the connection points of the one or more accessories to run the one of the one or more of the accessories at a controlled constant speed at varying speeds of the engine rotation.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The subject matter disclosed herein relates to a constant speed transmission embedded in a transmission. 
         [0002]    In a gas turbine engine, the auxiliary gearbox transfers power from a main shaft of the engine to an oil-cooled generator for generating electrical power and to engine accessories such as the fuel control unit, the lube module and cooling fan. In addition, there is also a starter motor connected through the gear train to perform a starting function. 
         [0003]    Currently, the auxiliary gearbox of a gas turbine engine rotates at the speed of the gas turbine engine. However, because the accessories attached to the gearbox must operate over a large range of speeds, the speed of the gas turbine engine is often different from the operating speeds of the accessories. This speed differential between the auxiliary gearbox and the accessories leads to operational inefficiency and a requirement that over capacity be designed into the components. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0004]    According to one aspect of the invention, an engine mountable gearbox is provided and includes a body formed to define a plurality of connection points at which a main engine generator and one or more accessories are mounted, a first transmission disposed within the body at the connection point of the main engine generator to run the main engine generator at a controlled constant speed at varying speeds of the engine rotation and a second transmission disposed within the body at least at one of the connection points of the one or more accessories to run the one of the one or more of the accessories at a controlled constant speed at varying speeds of the engine rotation. 
         [0005]    According to another aspect of the invention, an engine mountable gearbox is provided and includes a body formed to define a plurality of connection points at which a main engine generator and one or more accessories are mounted, a gear train rotatable with engine rotation and disposed within the body to transmit the engine rotation to the main engine generator and the one or more accessories, a first transmission coupled to the gear train at the connection point of the main engine generator to run the main engine generator at a controlled constant speed at varying speeds of the engine rotation and a second transmission coupled to the gear train at least at one of the connection points of the one or more accessories to run the one of the one or more of the accessories at a controlled constant speed at varying speeds of the engine rotation. 
         [0006]    These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0007]    The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
           [0008]      FIG. 1  is a perspective view of a gearbox; 
           [0009]      FIG. 2  is a schematic view of a differential, variable displacement hydraulic units and fixed displacement hydraulic units of the gearbox of  FIG. 1 ; 
           [0010]      FIG. 3  is another schematic view of a differential, variable displacement hydraulic units and fixed displacement hydraulic units of the gearbox of  FIG. 1 ; and 
           [0011]      FIG. 4  is yet another schematic view of a differential, variable displacement hydraulic units and fixed displacement hydraulic units of the gearbox of  FIG. 1 . 
       
    
    
       [0012]    The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0013]    In accordance with aspects of the invention, an auxiliary gearbox, a gearbox or a section of a gearbox having a controlled frequency may eliminate inefficiency and a requirement for over capacity. Such a gearbox utilizes a constant speed transmission that allows for a constant frequency electrical output from a generator. By using this type of transmission embedded in a gearbox, at least a section of the gearbox can be made so that all components attached to this section would run at a controllable constant speed. For example, the current horsepower (HP) capacity of an integrated drive generator (IDG) is about 120 HP and, as such, a fuel pump, an engine pump and motor assembly (PMA), and any other equipment that runs up to 120 HP can be run at a controlled constant speed. This speed could be further controlled for each stage of flight. 
         [0014]    With reference to  FIG. 1 , operation of the IDG is initiated with startup of an aircraft engine. When the aircraft engine starts to rotate, a gear train  11  of the accessory gearbox body  10  is rotated. This leads to rotation of a hydraulic pump  12 , a fuel mixing unit  13 , a main fuel pump  14 , an output gear  15 , a starter/generator  16  and a generator  20 , such as a main engine generator. As shown, the hydraulic pump  12  is coupled to the gearbox body  10  at a first connection point  122 , the fuel mixing unit  13  is coupled to the gearbox body  10  at a second connection point  133 , the main fuel pump  14  is coupled to the gearbox body  10  at a third connection point  144 , the starter/generator  16  is coupled to the gearbox body  10  at a fourth connection point  166  and the output gear  15  and the generator  20  are coupled to the gearbox body  10  at a fifth connection point  155 . The hydraulic pump  12 , the fuel mixing unit  13 , the main fuel pump  14 , the starter/generator  16  and the generator  20  are each representative of equipment that could be run at the controlled constant speed. 
         [0015]    For example, with reference to  FIGS. 2 ,  3  and  4 , the output gear  15 , which normally drives the generator  20 , and the main fuel pump  14  of  FIG. 1  are each configured to be power controlled through first and second transmissions  100 ,  101  that are similar in arrangement and each include a differential, variable displacement hydraulic units and fixed displacement hydraulic units, as described below. Here, while the first and second transmissions  100 ,  101  are being described as relating to the driving of the output gear  15  and the main fuel pump  14 , it is understood that the first and second transmission  100 ,  101  could be adapted to control any or all of the above-mentioned components. 
         [0016]    As shown in  FIGS. 2 ,  3  and  4 , an input shaft  30  is coupled to a main rotor  25  and secondary rotors  26  and  27  of, for example, the output gear  15 , the generator  20  and/or the main fuel pump  14 . The input shaft  30  is further coupled to an accessory gear  29 , which transfers rotation to a governor, a scavenge/inversion pump and a charge pump. Here again, although the main rotor  25  is described as being coupled to the output gear  15 , the generator  20  and/or the main fuel pump  14 , it is understood that the main rotor  25  could be coupled to any of the hydraulic pump  12 , the fuel mixing unit  13 , the starter/generator  16  of  FIG. 1  or any other accessory. 
         [0017]    The input shaft  30  includes an input spline  31  that couples a carrier shaft  32  directly to the gearbox  10  via the main rotor  25 . The carrier shaft  32  always turns in one direction with a speed proportional to engine speed. First and second planet gears  33  and  34  on the carrier shaft  32  engage with each other and rotate independently of the carrier shaft  32  as they orbit around a centerline thereof. A fixed unit ring gear  35  and an output ring gear  36  are added to the carrier shaft  32  with the fixed unit ring gear  35  engaged with the first planet gear  33  and the output ring gear  36  engaged with the second planet gear  34 . With this construction, when the fixed unit ring gear  35  is stationary, rotation of the carrier shaft  32  causes the first planet gear  33  to rotate while orbiting around an inside of the fixed unit ring gear  35  with the second planet gear  34 , which is engaged with the first planet gear  33 , transferring rotation to the output ring gear  36  and causing the output ring gear  36  to rotate at twice the speed of the carrier shaft  32 . 
         [0018]    Because of this 2 to 1 ratio between the output ring gear  36  and the carrier shaft  32 , when the fixed unit ring gear  35  is held stationary and the carrier shaft  32  is turned at a given revolutions per minute (rpm), the output speed will be twice that given rpm. If input speed is less than the given rpm, speed must be added to maintain a constant output speed and, to do this, the fixed unit ring gear  35  is rotated in the opposite direction of the carrier shaft  32  rotation, thereby applying increased rotational speed to the first planet gear  33  engaged with the fixed unit ring gear  35 . Here, as the first planet gear  33  turns faster, the second planet gear  34  also turns faster thereby causing output speed to increase. This is an overdrive condition. When the input speed is above the given rpm, speed must be subtracted and, to do this, the fixed unit ring gear  35  is rotated in the same direction as the carrier shaft  32 , reducing the rotational speed on the first planet gear  33  engaging with the fixed unit ring gear  35 . Because the second planet gear  34  engages with the first planet gear  33 , its speed is also reduced, thereby reducing the speed of the output ring gear  36 . This is an underdrive condition. Therefore, the output speed can be controlled by the rotational direction and speed of the fixed unit ring gear  35 . 
         [0019]    Directional control and speed control of the fixed unit ring gear  35  rotation is accomplished by units  40 . Each of the units  40  includes variable units  50  and fixed units  60 . The fixed units  60  include a cylinder block  61  having pistons  62 . The cylinder block  61  connects to a shaft  63  with a gear  64 , which is engaged with the fixed unit ring gear  35 . The pistons  62  in the cylinder block  61  reciprocate by moving on a fixed wobbler plate  65  which forms an inclined plane. The direction of rotation that the fixed units  60  assume is controlled by the variable units  50 . This is accomplished by positioning a variable wobbler plate  70  on one side or another of a zero angle position. The angle of the variable wobbler plate  70  determines the displacement of the variable units  50 , which controls the rotational speed of the fixed units  60 . 
         [0020]    Each variable unit  50  includes a cylinder block  51  with pistons  52 . The cylinder block  51  is splined to a shaft  53 , which is driven by the carrier shaft  32 . Because the carrier shaft  32  is coupled to the input shaft  30 , the variable units  50  will always rotate in one direction and at a speed proportional to the speed of the engine. The pistons  52  work against the face of the variable wobbler plate  70 . As the position of the variable wobbler plate  70  is moved from its zero angle position, oil is ported from the fixed units  60  to the variable units  50  or vice versa depending on the angle of the variable wobbler plate  70 . 
         [0021]    In the overdrive phase, as shown in  FIG. 2 , when the input speed is below straight-through speed, the variable wobbler plate  70  is moved into an angular position opposite the fixed wobbler plate  65  position which pumps high volume oil from the variable units  50  to the fixed units  60 . The variable wobbler plate  70  position is achieved by the exertion of pressure on the control piston  71 , which moves axially in response, to thereby rotate plate shaft  72 , which is coupled to variable wobbler plate  70 . The fixed units  60  are rotated in a direction opposite that of the variable units  50  and the fixed unit ring gear  35 , being engaged with the fixed units  60 , will rotate in a direction opposite that of the carrier shaft  32 , thereby adding to the output speed. 
         [0022]    In the underdrive phase, as shown in  FIG. 3 , when the input speed is above straight-through speed, the variable wobbler plate  70  is moved into an angular position paralleling the fixed wobbler plate  65  position, which allows high pressure oil to be pumped from the fixed units  60  to the variable units  50 . Here, the fixed unit ring gear  35  is engaged with the fixed units  60  to rotate in the same direction as the carrier  32  shaft and subtract from the output speed. 
         [0023]    In the straight-through drive phase, as shown in  FIG. 4 , when the input speed is sufficient to maintain a desired output speed, the variable wobbler plate  70  is at a zero angle position or is at a slight angle in the amount necessary to compensate for internal leakage. With the variable wobbler plate  70  in this position, the variable unit  50  pistons  52  do not reciprocate. Therefore, the fixed units  60 , which no longer receive or send pressurized oil, stop rotating. Here, the fixed unit ring gear  35 , which is engaged with the fixed units  60 , also stops turning. With the fixed unit ring gear  35  stopped, input rotation is transferred directly through the differential. 
         [0024]    In accordance with aspects of the invention, the differential, the variable displacement hydraulic units and the fixed displacement hydraulic units can be employed with the main rotor  25  of the generator  20 . The same type of differential, variable displacement hydraulic units and fixed displacement hydraulic units can be used with main rotors of one or more of the hydraulic pump  12 , the fuel mixing unit  13 , the main fuel pump  14  and the starter/generator  16 . Thus, any one or more of each of these components may be run at the controlled constant speed at varying speeds of the engine rotation. 
         [0025]    While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.