Abstract:
A decoupler mechanism which provides for disengagement of a series of driving rollers from a toothed driven member by providing roller pockets for retaining the rollers by centrifugal force when the decoupler is activated.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to coupling devices for coupling and decoupling a driving shaft from a prime mover to a driven shaft from which useful work may be extracted. In particular, this invention is directed to a means for decoupling such shafts such that when once decoupled they can not be recoupled until the driving shaft has come to an almost complete stop. 
     Such a coupling is used, for example, in the operation of an auxiliary power unit for modern jet aircraft. In this application the output shaft of the gas turbine of the auxiliary power unit is connected to drive accessories for the aircraft such as the electric power generators. In addition, the APU output shaft is selectively coupled by means of the coupling of this invention, to an air compressor input shaft. The start up procedure for the aircraft would be as follows: The APU is started by means of stored power such as a battery, with the coupling to the air compressor engaged. When the APU is at operating speed the output of the compressor is used to start the main propulsion engines. When these engines are operating, the compressor is decoupled and the APU used for accessory drive and any compressed air required by either aircraft systems is supplied by bleed air from the propulsion engines. Friction clutches are generally rather bulky if the transmitted load is large and, further, in the decoupling and coupling action wear material is deposited in the assembly where it is detrimental to the operation of the device. Further, such clutches are difficult to maintain in balance for rotation at high operational speeds. In the case of toothed or sprag clutches, it is difficult to decouple such devices while under load and such couplings generally have high point loading problems and are complex and costly to manufacture. 
     The present invention overcomes these disadvantages by providing a decoupling mechanism which is readily decoupled while under full load and cannot be recoupled until shafts are at near standstill condition. Further it gives the decoupling ability of a friction clutch in a much smaller precise package that can be rotated and balanced at high speeds without depositing wear material in the mechanism. 
     These functions are accomplished by the use of a simple hydraulic cylinder which when activated rotates a collar having pockets to receive the connecting rollers of the coupler. When these pockets are aligned with the rollers of the coupler, the centrifugal force of the rotating shaft forces the rollers into the pockets and out of engagement with the driven shaft. Since the rollers are maintained out of engagement by centrifugal force, they will not recouple until this force has been removed by stopping rotation of the shaft. 
     SUMMARY OF THE INVENTION 
     The decoupler of the instant invention is comprised of a first toothed member attached to the driven shaft and rotating therewith. There is provided a concentric ring connected to the driven shaft which retains a series of rollers in circumferentially spaced relationship about the shaft and which engage the teeth of the driven ring. The rollers are free to move radially within their slots in the retaining ring but are restrained from axial motion. A third concentric ring surrounds the roller retaining ring and is provided with a series of pockets on its inner surface. There is provided one pocket for each roller of the retaining ring. External of the third ring there is provided an actuating ring in the form of a cup-shaped member which acts as a piston of the hydraulic decoupling mechanism. There is secured in the actuating ring a pin member which engages slots in the roller retaining ring and the third ring containing the roller pockets. These slots are formed at an angle to the rotational axis of the device and are formed at opposite angles with respect to each other. As will be explained in the detailed description below, the application of hydraulic fluid under pressure to the piston member of the actuating ring causes axial movement of the ring. The axial motion of the pin of the actuating ring in the angled slots causes relative rotation between the rotor retaining ring and the third ring. This rotation causes the roller pockets in the third ring to be aligned with the rollers which are in engagement with the toothed member of the driven shaft. When the rollers are aligned with the pockets, centrifugal force of the spinning shaft will force the rollers into the pockets and out of engagement with the toothed member. As long as the third ring is rotating, the rollers will be retained in the pockets by centrifugal force. When the rollers disengage from the tooth member the driven shaft will gradually coast to a stop. 
     U.S. Pat. Nos. 2,002,979; 2,991,861 and 3,380,564 are cited by way of example of pertinent prior art. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a longitudinal sectional view through the decoupler. 
     FIG. 2 is a transverse section taken along line 2--2 of FIG. 1. 
     FIG. 3 is a detail of the slots of the actuating mechanism. 
    
    
     DESCRIPTION OF THE INVENTION 
     Referring now to FIGS. 1 and 2 of the accompanying drawing, there is illustrated one embodiment of the coupling of this invention. 
     The coupling shown generally at 10 connects a driving shaft 12 from a primer mover such as a gas turbine engine and a driven shaft 14 arranged concentrically with the driving shaft. Shaft 12 typically carries gears such as shown at 16 for driving accessory components from the main engine shaft. Driven shaft 14 is connected to an impeller of a compressor shown partially at 18. A frame supporting the shafts is shown generally at 20 and supports the shafts by means of bearings 22 and 24 for the driving and driven shafts respectively. The driven toothed ring of the coupler is shown at 26. This ring is attached to the driven shaft 14 by means of a nut 28 and threads 30. The toothed ring 26 has provisions for accepting rollers 32 in driving engagement with a shoulder on the ring shown generally at 34 in FIG. 2. The driving ring 36 is connected to the driving shaft by means of nut 38 which retains it to a splined end of shaft 12. The driving ring 36 contains a series of slots 40 for retaining the rollers 32. When the rollers 32 are engaged with the ring 36 and the tooth member 26, the shaft will rotate together in a counterclockwise direction. Exterior of the roller retaining ring is a third concentric ring shown at 42 which contains along its inside surface a series of roller pockets 44. When in driving engagement the pockets 44 are aligned between the roller retaining slots 40. External of the third ring is an actuating ring shown generally at 46. This ring is formed generally in a cup-shape as shown in FIG. 1 and is movable axially with respect to the coupling cover 54. This ring 46 is urged in the direction of the cover by means of spring 48. By means of opening 50 and channel 52 a working fluid under pressure from a source not shown may be introduced between operating ring 46 and the cover 54 which encloses the coupling. Retaining ring 46 contains an actuating pin 56 which is attached firmly to the actuating ring. The shank portion 58 of this pin is aligned in slots 60 and 62 which are formed in the roller retaining ring and the third ring respectively. As shown in FIG. 3, these slots are formed at an angle to the rotational axis of the coupler. Further, they are formed at opposite angles to each other with respect to the central axis. The function of these slots will be explained in the operational description below. 
     There are provided between the third ring and the roller retaining ring locating balls 63 retained in grooves 65 and 67 for axially locating and restraining these rings. 
     OPERATION OF THE DEVICE 
     As illustrated in the drawings, the device is coupled together to cause shaft 12 to drive shaft 14 through the coupling device. When the device is to be actuated and the shafts decoupled a working fluid, usually hydraulic oil, is introduced into opening 50 in the cover member 54. This fluid then passes along channel 52 and into chambers 64 on the back side of the actuating member 46. As the pressure of this fluid is increased the actuator 46 translates axially along axis A--A compressing the spring 48. As the actuator translates the pin 56 acts upon the camming slots 60 and 62 to cause the roller retaining member 40 to rotate in one direction and the third ring 42 to rotate in an opposite direction. As these members rotate with respect to each other the pockets 44 in the third ring 42 become aligned with the slots 40 in the roller retaining ring. Since the entire assembly is rotating at a high rotational speed, the rollers 32 will be forced by centrifugal force out of the retaining ring into the roller pockets 44. As these rollers move into the pockets they become disengaged from the toothed member 26 thus disengaging shaft 14 from shaft 12. 
     Since the rollers are held in their respective pockets by centrifugal force, they are prevented from re-engaging the toothed member and recoupling the shafts until the driving shaft 12 has slowed to a nearly stopped position. When the shafts are not rotating the fluid pressure acting upon the actuator 46 may be relieved and the spring 48 will cause the actuator to retract to the position as shown in FIG. 1. When this occurs the roller retaining ring and the third ring will rotate back to their engaged position by the action of the pin from the camming slots and the rollers will again engage respective teeth on the driven member 26. 
     Thus it can be seen that there is provided by this invention a simple and compact decoupling device which will remain decoupled as long as the driving shaft is being rotated. The device provides all the advantages of a clutch type coupler in a smaller space while depositing no wear particles or other detrimental material in the system. 
     While specific embodiments of the invention have been illustrated and described, it is to be understood that these embodiments are provided by way of example only and that the invention is not to be construed as being limited thereto but only by the proper scope of the following claims.