Title of Invention

IMPROVED POSITIVE LOCKING SYSTEM OF IDLER GEAR SHAFT

Abstract

This invention relates to improved locking arrangement of idler gear shaft of a piston engine and overcomes the deficiencies in positive locking of an idler gear shaft of a piston engine. The main utility of this invention is to substantially prevent the axial movement and spinning of the idler shaft of piston engines to obviate the oil starvation of the engine and resultant seizure of engine during aircraft flight.

Full Text

IMPROVED POSITIVE LOCKING SYSTEM OF IDLER GEAR SHAFT The invention is related to a system for positive locking of idler gear shaft in piston engine propellers. Light aircraft powered by piston engines with propellers are used for the purposes of training, short haul, joyride, etc. depending on the purpose for which the aircraft is used, the propellers fitted on the engines can either be of fixed pitch or variable pitch type, i.e., the angle of the propeller blades can be varied depending on the requirement of power. This variation of the pitch angle (propeller blade angle) is dependent on the speed of the engine. This function is performed by a governor mechanism (Constant Speed Unit). The governor is driven by engine gear train. Generally the engine gear train mechanism for driving the governor consists of a beveled gear fitted on an idler gear shaft and in some cases governor is driven directly by engine gear mechanism. The shaft on which the idler gear rotates is to be kept firmly tact in its position to act as a bearing for the bevel gear. If the idler shaft is not held in its intended position firmly, it can cause damage to the engine components. Engine crankcase is normally filled with oil that is pressurized by oil pump for lubrication of the moving components of the engine. The oil pressure acting on the idler gear shaft exerts axial force in the bore of the idler gear shaft and the bevel gear rotation there by inducing a rotary thrust on the idler gear shaft. The isolated or combined axial and radial forces exert pressure on the shaft to move axially and/or radially. Such repeated applications of pressure during operations can cause dislodgement of the idler gear shaft from its housing and simultaneously result in the wear of the associated components and at times draining of crank case oil and subsequent damages to the engine. It is therefore imperative to have a locking system to prevent the undesirable axial and/or radial movements of idler gear shaft. Various locking systems are used in the aviation industry to overcome the problem described above and those trained in the art are familiar with the usual approaches taken to overcome the problem. Some of the commonly used locking systems for protection against looseness resulting from vibration and corrosion of assembled components are discussed in the Civil Aircraft AinA^orthiness Information and Procedures Part 2, Engineering Practices and Process, Leaflet 2-5 Locking and Retaining devices [Civil Aviation Authonty U.K. 1990]. They are also covered by Military Standard MS 20995 [US Air Force 1995]. The problem of idler gear shaft locking gets further compounded due to the constraint of space, accessibility and maintainability especially in aircrafts. To arrest the axial and/or radial movement of a shaft held in the bores of a casing, following locking mechanisms are either used singly or in combination based on the specific requirements, availability of space, visibility, accessibility and maintainability:- - Split pins used in conjunction with drilled bolts and slotted or castellated nuts. - Locking washers like spring, cup, shake proof and tab washers. The related washer for the present case is spring washer. These washers are used to provide good bolt tension per unit of applied torque for tight assemblies, hardened bearing surfaces to create uniform torque control, uniform load distribution through controlled radii and protection against looseness resulting from vibration and corrosion. - Locking plates placed over hexagonal nuts or bolts heads for protection against looseness of nuts or bolts that are tightened down and secured by a screw to an adjacent part of a structure. - Lock nuts tightened against plain nuts or components into which male threaded items are fitted for protection against looseness resulting from vibration and corrosion. - Circlip and Locking rings used for locking screwed parts together or for locating components within bores or housings. - Twisted wire locking to prevent against looseness of bolts from screwed components resulting from vibration. - Self-locking components such as nuts or bolts in which inset nylon patch or stud applying friction between male and female components providing locking among screwed components. - Grub screw with peening used for locking two components. - Locking by adhesives such as shellac, araldite or similar material outside of the nut face or protruding screw thread or the component or the screw head after tightening to prevent the movement between the parts. - Taper pins and parallel pins used on tubular and solid sections to secure control levers to torque shafts. The idler gear shaft locking mechanism has conventionally been a grub screw or parallel pin especially in piston engine crankcase where pressurized oil lubricating system is used. Grub screw locking mechanism has not been very effective as the resultant force exerted on the idler gear shaft in the piston engine crankcase often leads to dislodging the grub screw from its casing. The parallel pin locking system is also not found useful as the resultant force exerted on the idler gear shaft in the piston engine crankcase may shear the parallel pin. There is a long standing need to resolve issues related such locking systems especially for positive locking of idler gear shafts in piston engine propellers. US Patent 5,735,557 of Lucas Industries describes a lock for thrust reversal system of a gas turbine engine. The locking member is held in the locking position by a pin that engages within an opening formed in the locking member. The pin is biased by a spring and is movable by a hydraulic piston against the action of spring to withdraw the pin from the opening. The locking system is also provided with a sensor for indicating the position of the piston and locking member. The locking system mentioned cannot be used for positive locking of idler gear shaft which is a purely mechanical lock. us Patent 6,322,306, discloses an anti rotation clip which is adopted to be attached to a fastener or a connector assembly to ensure tightened threaded connection of the assembly. This invention relates to non-airborne application where locking is effected only to prevent the rotation of hexagonal nut and is not useful for airborne application because of visibility to operation and degree of vibrations and environmental conditions. US Patent no. 5,765,957 relates to lockable turnbuckle assembly describing a locking mechanism that can be used in a limited space of turnbuckle application. The locking is effected using a single handle and does not need tools. The lock pin is used to fix the jam nut in appropriate position. This invention has a specific application in turnbuckles but cannot be used to resolve issues in idler gear shafts described above. Summary of the invention The present invention relates to improved positive locking arrangement of idler gear shaft of a piston engine and overcomes the deficiencies as mentioned above in positive locking of an idler gear shaft of a piston engine. The main utility of this invention is to substantially prevent the axial movement and spinning of the idler shaft of piston engines to obviate the oil starvation of the engine and resultant seizure of engine during aircraft flight. A further utility is also to prevent premature withdrawal of engines from service due to excessive play on the idler shaft. The main object of present invention is to provide a positive locking arrangement in the governor idler shaft of an engine, which obviates the drawbacks of earlier invention as detailed above. Another objective of the present invention is to standardize this method of locking on different types of engines where grub screw mechanism is in vogue. Accordingly an improved positive locking of idler gear shaft comprises a screw, supported by bush, spring guide, spacer, spring, spring washer and shim all assembled to form the locking system. In an embodiment of present invention, this system of locking can be adopted to positive locking of governor idler shaft of Textron Lycoming Engine IO-54-K1B5 fitted on Islander aircraft. Description of tlie invention The invention is illustrated with a drawing showing the assembly of the various components. Figure 1 (a) shows the cross section of locking system with various components. - Collared bush (Part 2) made out of high strength steel material with external threads to suit the threads in the crankcase and internal threads to receive the mating screw threads. - Screw (Part 3) of hardness between 35 to 60 RC made out of high strength steel, normally of round head and screw driver slot, with a hole in the head to facilitate wire locking, threads conforming to internal threads of Part 2 and extended shank portion with a lower diameter and rounded end. - Spring washer (Part 4) made out of steel the specification of which matches the usage with the other mating parts. Figure -1(a) shows the introduction of steel collared bush(Pt.No. 2) to accommodate the locking screw with a pip (Pt. No. 3) along with a spring washer (Pt.No. 4). Plan view shows the locking of screw with steel locking wire to the crankcase body. Figure- 1 (b) shows an exploded view of the locking system with the crankcase body being the forward end (part 1). The shim (part 5) is introduced between the idler gear shaft and spring guide to gain advantage of wear resistance and is made out of high strength steel. The spacer (Pt. 6) is introduced to guide the spring and is made out of suitable metal alloy of brass and copper. The spring (Pt. 7) is made out of music wire of suitable diameter to enable restriction of axial movement of the shaft with defined no. of coils to exert predetermined pressure on the idler shaft to hold in its intended position. The spring (Pt. 8) made out of stainless steel conditionally heat-treated to the established requirements to guide the spring. Fig. 1(b) also shows the system for arresting the axial play by providing spring guide (Pt. No. 8), spring (Pt. No. 7), spacer (Pt. No. 6) and shim (Pt. No. 5) along with existing parts plug and gasket. The mechanism of locking is innovative in its nature wherein, the collar bush and a screw with spring washer is used for locking the idler gear shaft and to ensure a positive locking additional mechanism by introducing the spring, spring guide, spacer and shim to arrest axial as well as radial movements of the idler shaft. This also ensures positive locking in limited space and available access. Engines with invented method of locking were examined on the engine test bed and the performance of the engines was monitored. No engine failure due to idler shaft back out was observed. No engine failures were reported even on extended flight trials thereby solving the problem of the engine damage due to idler gear back out and avoiding the loss of aircraft and life due to engine cut problems attributable to the idler shaft back out. 1 We claim: 1. An improved positive locking system of idler gear shaft of piston engine which substantially prevents the axial movement and spinning of the idler gear shaft in piston engines, characterised in that said system comprising of a first assembly of bush, screw with wire locking facility and spring washer perpendicular to the idler shaft in conjunction with a second assembly of shim, spacer, spring and spring guide, axial to the idler shaft, with the first assembly of the said system preventing axial and radial movement of the idler shaft and the second assembly of the said system preventing the axial movement of the idler shaft. 2. An improved positive locking system of idler gear shaft as claimed in Claim 1 wherein the bush is a collared bush. 3. An improved positive locking system of idler gear shaft as claimed in Claim 1 and 2 wherein the collared bush is of high strength steel material threaded externally to accommodate in the casing and threaded internally to receive the screw. 4. An improved positive locking system of idler gear shaft as claimed in Claim 1 wherein the screw is of high strength steel of hardness in the range of about 35-60 RC ,with round head ,screwdriver slot and with a hole drilled in the head to facilitate wire locking. 5. An improved positive locking system of idler gear shaft as claimed in Claim 1 and 4 wherein the screw is provided with extended shank portion with a lower diameter and spherical end. 6. An improved positive locking system of idler gear shaft as claimed in Claim 1 wherein the spring washer is positioned between the bush and the screw and is of a material matching with the other mating parts 7. An improved positive locking system of idler gear shaft as claimed in Claim 1 wherein the shim is of high strength steel positioned axially between idler gear shaft and spacer. 8. An improved positive locking system of idler gear shaft as claimed in Claim 1 wherein the spacer is of a suitable phosphor bronze alloy and positioned axially between shim and spring with higher diameter towards shim and lower diameter towards spring to act as spring guide. 9. An improved positive locking system of idler gear shaft as claimed in Claim 1 wherein the spring is constructed of music wire of suitable diameter and defined no. of coils and positioned axially between spacer and spring guide. 10. An improved positive locking system of idler gear shaft as claimed in Claim 1 wherein the spring guide is constructed of conditionally heat treated stainless steel positioned with lower diameter towards spring. 11. An improved positive locking system as claimed in claim 1 wherein the locking system is a sequential assembly of collared bush, spring washer and sctew in conjunction with shim, spacer, spring and spring guide.

Documents:

0005-mas-2002 form-2.pdf

0005-mas-2002 drawings.pdf

0005-mas-2002 form-13.pdf

0005-mas-2002 form-19.pdf

0005-mas-2002 form-3.pdf

0005-mas-2002 others.pdf

0005-mas-2002 power of attorney.pdf

0005-mas-2002 claims.pdf

0005-mas-2002 description(complete).pdf

0005-mas-2002 form-1.pdf

0005-mas-2002 abstract.pdf

0005-mas-2002 correspondence others.pdf

0005-mas-2002 correspondence po.pdf