Abstract:
An electronically controlled variable speed mechanical drive to be used in high power applications where using a direct drive motor is not feasible due to weight and size constraints. The variable speed drive components convert an externally driven fixed displacement pump into a variable displacement pump by electronically setting the pump speed to meet flow demands. A single stage pump and a multi-stage pump are so converted according to the present disclosure.

Description:
REFERENCE TO PROVISIONAL APPLICATION 
       [0001]    The benefit of priority of Provisional Application No. 61/643,981, filed May 8, 2012, is hereby claimed. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates generally to an electronically controlled variable speed drive and pertains particularly to aircraft pumps. The disclosed pump drive can transform a fixed displacement pump into a variable displacement pump so that flow on demand can be achieved. It can be coupled to either a single or a two stage fixed displacement pump and is intended to be used in high horsepower conditions where it is not practical to use a motor driven device. 
         [0003]    Other applications disclosed include decoupling the rotary speed of an alternator or generator from its prime driver so that the alternator or generator can operate at its best efficiency speed no matter the prime driver speed. 
       BACKGROUND OF THE ART 
       [0004]    For aviation platforms, the goal is to design the highest power density system while exceeding the required reliability standards. For aircraft pumps, thermal efficiency is especially important due to the added role of fuel and oil being heat sinks for various subsystems. Aircraft pumps are typically mounted to and driven by the accessory drive gearbox which in turn is driven by the high-pressure gas turbine engine spool. Since the accessory engine gearbox has a constant gear ratio, the aircraft pump input rotary speed is directly related to engine spool speed. 
         [0005]    Pump efficiency is maximized when the fluid displacement of a pump matches the particular demand requirement of the engine and associated subsystems. To accomplish this, various attempts have been made to improve pump efficiency by employing variable displacement pumps coupled with various valving arrangements. 
         [0006]    Today&#39;s variable displacement pumps typically vary the fluid pumped per revolution by varying the stroke of the pumping element, such as a piston in a piston pump or a vane in a vane pump. Another technique that is employed is a multi-stage pump that has the capability to “unload” or switch a stage on and off. 
         [0007]    The fore-mentioned systems do improve pump thermal efficiency but at the expense of increased weight and cost. For instance, an actuation system is required to move a cam so that the stroke of a vane pump can be varied, and in a multi-stage pump, two sets of pumping elements are required as well as special valving to unload a stage. Additionally, when a pumping stage is unloaded the “windage” and “churning” energy losses are still present due to the higher than required pump input speed. 
         [0008]    Embodiments disclosed include a variable speed drive that allows a high horsepower, gearbox driven pump to behave like a motor driven pump without the weight penalty induced by a high horsepower motor. This drive is capable of setting and maintaining the pump rotary speed independent of the external gearbox speed so that the pump can deliver the required flow displacement for any given flight condition. Other advantages include the capability to constantly operate an automotive alternator at its best efficiency speed no matter what the engine speed is. These and other advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein. 
       SUMMARY OF THE INVENTION 
       [0009]    An electronically controlled variable speed drive consists of a compound planetary gear set, a motor, and an electronic controller. The drive is driven by an external drive, and depending on the application, it may contain either one or two output drive shafts. The variable speed drive is capable of continuously varying the gear ratio within a compound planetary gear set by applying an electronically controlled retarding torque to a motor. It is capable of achieving a 1:1 gear ratio to the maximum gear ratio determined by the number of teeth on the gears located within the compound planetary gear set. 
         [0010]    In one aspect, the invention provides a means of electronically setting and controlling the output speed of the drive shaft(s). The speed controller electronics is arranged as a dynamic or regenerative braking system so that a retarding torque can be developed by the motor, whose rotor is attached to the compound planetary gear set output ring gear. If dynamic braking is off then the overall gear ratio is 1:1. If dynamic braking is on, then the output shaft with the sun gear rotates faster than the input drive speed and the output shaft attached to the compound planetary gear set output ring gear and thus the motor rotor rotates slower than the input drive speed. The microprocessor compares the required output speed against the measured output speed and adjusts the retarding torque accordingly. To insure that the sun gear never rotates slower than the input ring gear, a one way bearing helps to support the sun gear carrying output drive shaft. 
         [0011]    In another aspect, the invention provides a means of transforming a fixed displacement pump into a variable displacement pump to provide flow on demand. 
         [0012]    In yet another aspect, the invention provides a means of maintaining the constant speed of an alternator or generator no matter what the input drive speed is. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is an exploded view of a variable speed drive assembly according to one embodiment of the invention; 
           [0014]      FIG. 2  is an exploded view of a variable speed drive assembly according to one embodiment of the invention; 
           [0015]      FIG. 3  is an exploded view of a compound planetary gear set according to one embodiment of the invention; 
           [0016]      FIG. 4  is an exploded view of the installation of the motor rotor and a compound planetary gear set, according to one embodiment of the invention; 
           [0017]      FIG. 5  is an isometric cross-section of a output drive shaft installed in said compound planetary gear set and showing a motor installed onto said compound planetary gear set, according to one embodiment of the invention; 
           [0018]      FIG. 6  schematically depicts the variable speed drive driving a fixed displacement pump, according to one embodiment of the invention; and 
           [0019]      FIG. 7  schematically depicts the variable speed drive driving a two stage fixed displacement pump, according to another embodiment of the invention; 
       
    
    
       [0020]    While the invention will be described in connection with certain preferred embodiments, there is no intent to limit it to those embodiments. On the contrary, the intent is to cover all alternatives, modifications, and equivalents as included within the spirit and scope of the invention as defined by the appended claims. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0021]    An exploded view of the variable speed drive  100  three main sub-assemblies according to one embodiment of the invention is shown in  FIG. 1 . In this embodiment, the variable speed drive  100  includes a compound planetary gear set  102 , a motor  104 , and an electronic control module  106 , all of which may be contained within a common structure. 
         [0022]    An exploded view depicting the variable speed drive  100  according to an embodiment of the invention is also shown in  FIG. 2 . An external drive connects to and drives internal ring gear  110 , which is part of the compound planetary gear set  102  sub-assembly. Motor  104  connects to and is rotated by internal ring gear  122 , which is part of the compound planetary gear set  102  subassembly. Output drive shaft  116 , a part of the compound planetary gear set  102  sub-assembly, rotates at a speed determined by a gear ratio of the gear set  102 . The voltage being produced by motor  104  rotating is electrically flowing through motor  104  windings and the electronic control module  106 , which contains dynamic or regenerative braking circuitry and microprocessor  108 . Microprocessor  108  monitors the speed of output drive shaft  116  against a speed demand input signal. Microprocessor  108  changes the speed of output drive shaft  116  by controlling the torque generating current electrically flowing through motor  104  windings. As motor  104  torque is varied, compound planetary gear set  102  overall gear ratio is also varied. Therefore, the speed ratio between internal ring gear  110  and output drive shaft  116  can be set by microprocessor  108 . 
         [0023]    The compound planetary gear set  102  according to an embodiment of the invention is depicted in more detail in  FIG. 3 . The compound planetary gear set  102  includes an internal ring gear  110 , which rotates on bearings  120  and engages with planetary gears  112  as gear set  102  is rotated by an external drive. Planetary gears  112  rotate the sun gear  114 , which rotates the output drive shaft  116 . Planetary gears  118  are formed integrally with or are rigidly attached to planetary gears  112  and rotate with such planetary gears  112  around sun gear  114 . Planetary gears  118  in turn rotate internal ring gear  122 , which is supported by bearing  124  and rigidly connects to motor  104 . 
         [0024]      FIG. 4  shows the installation of the compound planetary gear set  102  and motor  104  according to an embodiment of the invention. Motor  104  consists of two sub-assemblies, a rotating rotor  126  and a stationary stator  128 . The rotor  126  has a diameter  130  that fits onto and is located by internal ring gear  122  diameter  132 . 
         [0025]      FIG. 5  illustrates a cross section depicting the rotational mechanics of the output drive shaft  116  according to one embodiment of the invention. The output drive shaft  116  along with the integral sun gear  114  are supported by rolling element bearing  134  and a one way bearing (anti-reverse bearing)  148 . The one way bearing  148  transmits torque between the output drive shaft  116  and the internal ring gear  110  in one direction and while allowing free rotation in the opposite direction. This relationship insures that the output drive shaft  116  cannot rotate at a slower speed than the externally driven input internal ring gear  110 . With rotor  126  attached to internal ring gear  122 , when torque is applied by motor  104 , internal ring gear  122  changes rotational speed, which then changes the rotational speed of output drive shaft  116 . Therefore the gear ratio between the internal ring gear  110  and output drive shaft  116  can be varied and set by adjusting the torque on internal ring gear  122  via motor  104 . 
         [0026]      FIG. 6  schematically illustrates how a single stage fixed displacement pump  136  is transformed into a variable displacement pump according to one embodiment of the invention. Pumping element  138  is connected to and rotated by output drive shaft  116 , which is integral to sun gear  114 . With internal ring gear  110  driven by an external drive and rotating at a constant speed, an input signal that could represent required flow, is transmitted to microprocessor  108 , which is located within electronic control module  106 . Microprocessor  108  compares the measured flow signal from sensor  140  against the input signal and directs the voltage being generated by motor  104  through the electronic control module  106  dynamic braking circuit accordingly. If the discharge flow measured by sensor  140  is lower than required, then the current flowing through motor  104  is increased which in turn increases retarding torque. An increase in retarding torque increases the overall gear ratio in the compound planetary gear set  102  and therefore the rotary speed of pumping element  138  is increased. If supply flow is higher than required the rotary speed of pumping element  138  is decreased by decreasing motor  104  retarding toque. 
         [0027]      FIG. 7  schematically illustrates how a multi-stage fixed displacement pump  142  is transformed into a variable displacement pump according to one embodiment of the invention. Pumping element  144  is connected to and rotated by output drive shaft  116 , which is integral to sun gear  114 , and pumping element  146  is connected to and rotated by internal ring gear  122 . When the retarding torque developed by motor  104  is increased by the electronic control module  106 , the rotary speed of pumping element  144  increases and the rotary speed of pumping element  146  decreases. When the retarding torque developed by motor  104  is decreased by the electronic control module  106 , the rotary speed of pumping element  144  decreases and the rotary speed of pumping element  146  increases. If dynamic braking is removed by the electronic control module  106 , the rotary speed of pumping elements  146  and  144  are equal and equal the rotary speed of internal ring gear  110 . 
         [0028]    The maximum achievable gear ratio is determined by the compound planetary gear set  102  internal geometry. 
         [0029]    The overall gear ratio in compound planetary gear set  102  is increased when retarding torque developed by motor  104  is increased. 
         [0030]    The overall gear ratio in compound planetary gear set  102  is decreased when retarding torque developed by motor  104  is decreased. 
         [0031]    When motor  104  retarding, torque is removed, the gear ratio between internal ring gear  110  and output drive shaft  116  is 1:1. 
         [0032]    When motor  104  is rotating, the electronic control module  106  is receiving a voltage from motor  104  and a dynamic or regenerative braking circuit is utilized to control the amount of current available to motor  104 . 
         [0033]    The electronic control module  106  utilizes a closed loop control system to maintain a constant torque and therefore gear ratio. 
         [0034]    Many variations may be made in the invention as shown and in its manner of use without departing from the principles of the invention as described herein and/or as claimed as our invention. Minor variations will not avoid the use of the invention.