US2530869A - Engine starter - Google Patents

Description

Nov. 21, 1950 s. GILBERT 2,530,869

ENGINE STARTER Filed Feb. 25, 1949 v INVENTEJIET SAMUEL G/LB 3 BY 1 K A Patented Nov. 21, 1 950 UNITED STATES PATENT OFFICE ENGINE STARTER Samuel Gilbert, Cedar Grove, N. J., assignor to Bendix Aviation Corporation, Teterboro, N. J., a corporation of Delaware Application February 25, 1949, Serial No. 78,380

1 Claim. 1

The present invention relates to starters and more particularly to direct cranking starters for gas high speed engines such as gas turbines for aircraft.

In starters of this type, the starter motor drives the aircraft turbine directly and they are usually provided with a preset torque limiting clutch for protecting the starter mechanism should the engine abnormally resist cranking. This torque limiting clutch, however, does not protect the starter mechanism against shock-loading at the moment the cranking power is applied, and the instantaneous shock-loading, particularly on the starter jaw and the jaw advancing mechanism, may reach values greatly exceeding the preset torque limiting value of the friction clutch. Various means and methods such as the use of additional friction clutches with adjustable friction characteristics have been proposed to reduce the initial shock-loading and yet have sufficient torque transmitting capacity after engagement of the starter jaw with the engine to transmit the torque necessary to crank it. However, it has been found that ordinary friction type slip clutches are not suitable for absorbing the mentioned shock loading in starters operating at very high speeds for use with modern high speed aircraft engines such as gas turbines, because of the tendency of this type of clutch to score or burn up under rapid surface slipping. These problems are becoming acute as the size and starting speed of the aircraft engines are increased, entailing the use of rapidly accelerating high power starter motors such as motors driven by gases released under extremely high pressures.

Accordingly, one object of the present invention is to provide a novel combination in an engine starter whereby a high speed, high power starter motor may be utilized.

Another object of the present invention. is to provide a novel combination in a starter whereby the starter may be made of small size and light weight, yet capable of transmitting large amounts of starting power at rapid acceleration rate and having torque limiting characteristics variable with the speed of the starter.

A further object is to provide a novel combination in an engine starter whereby a standard starter jaw and jaw advancing and driving mechanism may be utilized to crank an engine requiring high speed cranking and high initial turning torque.

The above and other objects and features of the invention will appear more fully hereinafter from a consideration of the following d$ P- tion taken in connection with the accompanying drawing wherein the single figure of the drawing shows a portion of the starter, partly in section and partly in elevation, illustrating one embodiment of the present invention by way of example. The starter motor (not shown) may be an electric motor or a motor driven by steam, compressed air or gases resulting from combustion or other chemical action, and is connected to an output member Ill journaled within a transverse member or wall portion 12 of starter housing M as by ball bearing H5. The driving member I0 is adapted to drive a starter jaw advancing and driving mechanism generally indicated at i6 and including an actuating nut I? through a fluid or hydraulic coupling [8 and a planetary drive 26. The fluid coupling is shown as comprising an inner rotatable driving member or impeller 22 mounted on a stub shaft 24 whose one end is rigidly connected to the motor output member in and Whose other end is journaled closely adjacent and coupled through a fluid to the driven coupling member or runner 26 having a hub portion 28 carrying a pinion 30 and journaled in bearing 32 within flanged end portion 3| of actuating nut H. The other end of the stub shaft 24 is journaled in the hub portion 28. The fluid or hydraulic coupling l8 may be of a type well known in the art and a detailed description thereof is not deemed necessary.

Fluid coupling output pinion 30 is shown as driving a planetary reduction gearing 20 having one or more planet gears 34 meshing with stationary orbit gear 38 and journaled on trunnions 36 shown as integral extensions of end portion 3| of actuating nut 1''. Nut I1 is journaled by a pair of roller bearings M! in housing l4 and adapted to engage externally threaded screw shaft 42 which carries and is splined to starter jaw member 44. A baffle plate 46 secured to mounting flange 41 of starter housing [4 supports a friction split ring 48 surrounding, and in frictional engagement with, jaw 44 in retracted position, and also supports a seal ring 49 adapted to prevent oil or other fluid from entering the starter from the engine to be started. The seal ring may be omitted if roller bearings 40 are replaced by sealed ball bearings.

When the motor is energized, the motor output member will rotate nut ll through the fluid coupling l8 and planetary gearing 20. Rotation of nut I! will force screw shaft to the left as viewed in the drawing because the shaft will be restrained from rotating by the action of the I GfiOn plitring 48 against starter jawmemher 44. When the starter jaw is in full engagement with engine jaw 45 a shoulder 50 on the screw shaft 42 will abut a corresponding shoulder 52 on the nut whereupon further rotation of the nut will rotate the screw shaft and thereby crank the engine. It will be noted that the friction slip ring will have ridden off ramp 54 on the starter jaw 44% when the latter hasengaged engine jaw 45 and will not hinder the free rotation of the screw shaft and starter jaw.

The jaw advancing mechanism per se comprising nut screw shaft 42 and jaw 44-is-well known to those skilled in the art, but heretofore this jaw advancing mechanism has been operated by a barrel surrounding the nut and splined thereto by a disc pack having discs alternately splined to the barrel and thenut and having a preset torque limiting value sufficiently high to insure cranking of the engine. With the use of high speed rapidly accelerating motors the shock and impact loading. on. the starter and engine jaws44 and 45, respectively, screw shaft 42 and nut I? will. reach. instantaneous values greatly exceeding the preset torque limiting value of the disc pack because of. the high static friction thereof. By the use of the fluid coupling in com-' bination with this jaw advancing mechanism, the starter jaw will moveinto engagement with the-engine jaw at a very slow rate compared to the rate which wouldhave resulted had the motor been connected to the jaw advancing mechanism through a preset clutch having a relatively-high torque limiting. value. The torque limiting characteristics of a fluid coupling are extremely favorableunder these conditions because at'low drive speeds, e. g. when the jaw engagement takes place and the initial cranking occurs, the torque limit is relatively low so as to protectthe starter mechanism by slippage should theengine to be started abnormally resist initial cranking;

As the cranking speedincreases the torque limiting: value of the fluid coupling increases up to a predeterminedlimit determined, by the designthereof and the particular fluid employed. Thus; during the cranking operation this novel combination providesinitially maximum protection when the danger of damage is greatest and then gradually brings about the application of increased torque suificient to start an engine under even the most adverse weather conditions. The total absence of shock loading makes it possible to decrease the size of the operating parts of the starter and will eliminate shock failure-of starter. and engine parts which is extremely important for efficient operation of the aircraft.

Although only one embodiment of the invention has been illustrated and described, various changes in the form and relative arrangements of the parts may be made to suit requirements.

What is claimed is:

An engine starter comprising, in combination, astarter motor of a rapidly accelerating high speed type, a jaw advancing mechanism comprising a rotatable internally threaded nut, an externally threaded screw shaft concentrically arranged within-said nut having threads adapted toengage the threads of said nut and having connected thereto a starter jaw, a fluid-coupling including an impeller and a runner, said runner having a hub portion rotatably'supportedby'said nut, said impeller havinga stubshaft one end of which is rigidly' connected to the starter motor and the other end of which is journaled in the hub portion, a planetary reduction gearing drivingly connecting said hub portion to said nut, said screw shaft beingaxially movable upon rotation of said nut to move said starter jaw into engagement with-a mating jaw member of the engine to be started and then to rotate with said nut to crank the engine to be started.

SAMUEL GILBERT.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Ayres Dec. 7, 1937

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