US2776571A

US2776571A - Engine starter clutch

Info

Publication number: US2776571A
Application number: US518550A
Authority: US
Inventors: Simone Peter Francis
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1955-06-28
Filing date: 1955-06-28
Publication date: 1957-01-08
Anticipated expiration: 1974-01-08

Description

Jan. 8, 1957 P. F. SIMONE ENGINE STARTER CLUTCH Filed June 28, 1955 INVEN TOR. P572"? E 5/4/04? Unite States Patent C M ENGINE STARTER CLUTCH Peter Francis Simone, Reading, Mass., assignor to General Electric Company, a corporation of New York Application June 28, 1955, Serial No. 518,550

6 Claims. (Cl. 74-7) This invention relates to a starter clutch mechanism for engines and particularly to a synchronizing means for positive engagement of a jaw type clutch before application of a driving torque.

In engine starters, it is desirable to maintain the starter jaw out of mesh with the engine jaw when the engine is running after starting so that there is no sliding contact between the jaws. Any contact between the jaws when the engine is running at high speed will result in wear of the parts and eventual failure of the jaw members.

Accordingly, it is an object of the invention toprovide improved synchronizing means for an engine starter clutch.

Another object of the invention is to provide means for preventing jaw wear in engine starter clutches.

Still another object of the invention is to provide an improved engine starter clutch which may be engaged when the engine is either stationary or rotating.

A further object of the invention is to provide an improved jet engine starter clutch which is automatically disengaged from the engine once it has started.

These and other objects of the invention may be accomplished by the provision of synchronizing means carried by the driven clutch member for contacting the driving clutch member so as to synchronize the engagement of the rotating clutch teeth which synchronizing means are automatically disengaged from the driving clutchmember by a centrifugal force resulting from the rotation of the driven member.

The invention will be better understood from the following description taken inconnection with the accompanying drawing in which Fig. 1 is a longitudinal sectional view of a preferred embodiment of the improved clutch in the disengaged position;

Fig. 2 is a partial sectional view showing the clutch in the engaged position;

Fig. 3 is a view of the synchronizing pawl structure taken along'the line 3-3 of Fig. 1, and j Fig. 4 shows a helical pin and'slot arrangement taken along the lines 44 of Fig. l. i

Referring to Fig. 1, the clutch comprises clutch transmitting members 11 and 12, the former consisting of a rotatable engine dog which is restrained against axial movement, and the latter consisting of a starter dog which is movable axially for engagement with the engine dog 11. Both dogs have conventional type cantilever mounted teeth 13 and 26 on their respective contacting faces, tapered along one edge and straight along their contact edges.

The starter dog 12 has a tubular portion or member 14 which extends away from the engine dog. A helically slotted barrel cam 15 is located concentrically within the tubular member 14. A second tubular member indicated at 16 is connected to an output gear in the gear train (not shown) through which power is transmitted from the starter motor (also not shown). The tubular rotate together.

ice

member 14 is loosely coupled by a spline 17 within the tubular member 16 to permit the starter dog 12 to travel axially to permit clutch engagement. member 15 is connected through an intermediate member 18 to the tubular member 16 so that all three parts A ratchet wheel 19 is attached by four pins 30 to the barrel cam 15 so that it also rotates with the members 15, 16, and 18. The barrel cam 15 is located partly within the tubular member 14 and is provided with a plurality of helical slots 20, two being shown in the drawing. Inwardly extending radial pins 21 equal in number to the slots 20 are secured to the v tubular member 14 and contact the walls of their respective helical slots in the barrel cam member 15.

A compression spring 22 is positioned in an annular space between the tubular'members 14 and intermediate member 18 and reacts against the member 14 to bias the clutch dog 12 out of engagement with the engine dog 11.

Since the intermediate member 18 is restrained against axial movement, the effect of the spring 22 is to exert an axial force on thetubular member 14 which tends to hold starter dog 12 in a disengaged position.

A pair of pawls 25 are pivotably mounted on pins 23 fixed to the engine dog 11 so that they rotate with the engine dog. Each pawl 25 is spring loaded by means of a spring 24 which acts to force the pawl into engagement with theratchet wheel 19 as may be best seen in Fig. 3. The pawl and

spring arrangement

25 and 24 is designed so that centrifugal force acting on the pawls will cause them to move outward against the force of the spring 24 causing them to disengage from the ratchet wheel 19 when the engine dog rotates at a predetermined speed which is at or below the normal running speed of the engine and above the maximum speed during starter operation. Referring to Fig. 3 the position of the pawls under these conditions is illustrated by the broken lines indicating the top pawl in the figure.

When the pawls 25 are in engagement with the ratchet wheel 19 and the clutch members are in a disengaged position, the output torque of the starter motor will be transmitted from the tubular member 16 to the tubular member 14 through the spline 17. This torque will in turn be transmitted through the radially extending pins 21 to the wall surfaces of the helical slots 20 in the barrel cam member 15; The transmission of torque to the helical wall surfaces results in an actual component of force which is proportional to the amount of torque transmitted and the helix angle of the slot. Since the barrel cam member 15 is not free to move axially, a reaction torque will result tending to move the starter dog 12 into engagement with the engine dog 11. If the pawls 25 are not engaged, the amount of torque transmitted to the barrel cam will only be enough to keep the latter rotating at the speed of the starter dog 12. The compression spring 22 is designed to overcome the axial force developed under such conditions so that no axial move ment of the starter dog 12 takes place, unlessthe pawls 22 are engaged with the ratchet wheel 19.

In starting, the engine dog 11 is at rest or rotating at some speed'below the normal running speed of the engine and in the range in which the pawls 25 will be en gaged with the ratchet wheel 19 as shown in Fig. 3. Assuming the engine dog 11 to be at a standstill, when starter dog 12 begins to rotate as when driven by the starter motor, it carries with it the ratchet wheel 19 so that it will rotate in the direction indicated by the arrow in Fig. 3. The engaging action between the ratchet and pawl causes the barrel cam member 15 to be held back as the starter dog 12continues to rotate. This relative rotation between the starter dog 12 and barrel cam member 15 causes a torque to be transmitted through the Fatented Jan. 8, 1957 The barrel cam pins 21 resulting in an axial component of force which causes the starter dog 12 to move against the force of the spring 22 into engaged position with engine dog 11. The axial motion of the starter dog 12 in conjunction with its rotational advancement ahead of the engine dog ll, results in a screw-like action of the starter dog 12 as it comes into engagement with the engine dog 11 By proper design of the parts, this screw-like action of the starter dog 12 is indexed to bring the dog teeth into load carrying Contact in the position of full engagement, the design being such that only a relative motion of one tooth pitch can occur before the clutch members become fully engaged and rotational advancement of starter dog 12 with respect to engine dog 11 stopped. .The amount of relative motion necessary to bring the clutch members into engagement will be the same regardless of the individual absolute velocities of the two clutch dogs 11 and 12.

In the event that the engine dog is rotating at the begining of the engaging cycle, the ratchet Wheel 19 and pawls 25 will undergo a ratchet action until the starter dog reaches the speed equal to that of the engine dog. Thereafter the engagement continues as in a standstill condition above.

The disengagement process occurs automatically when the engine begins to run ahead of the starter or when the starter output torque is discontinued. The action of disengagement is opposite to that of engagement, the action of the pawls and ratchet wheel permitting spring 22 to. withdraw the starter dog 12 into disengaged position, in a screw-like fashion, without the backsides of the teeth on either starter dog 12. or engine dog 11 making contact with each other. 7

The pawls will remain in tooth engaging position so that the ratchet action will take place until the engine speed increases to the predetermined speed at which the centrifugal force forces the pawls 25 outward as indicated by the broken lines in Fig. 3. Thus there is no contact between the synchronizing members so long as the engine rotates at its operating speed.

The compression spring 22 which disengages the starter dog and holds it in that position when the pawls are not engaged with the ratchet wheel 19, must be strong enough to hold the starter dog in the disengaged position under acceleration and deceleration conditions when the clutch unit is airborne.

While a particular embodiment of the invention has been illustrated and described, it will be obvious to those familiar with the art that various changes and modifications may be made without departing from the invention and it is intended to cover in the appended claims all such changes and modifications that come within the true spirit and scope of the invention.

What I claim. as new and desire to secure by Letters Patent of the United States is:

1'. A starting mechanism, in combination with a motor for starting an engine having an engine clutch member with teeth on its engaging face, comprising a first clutch memberadapted to move in rotation and translation and having teeth on a contacting face for engagement with said teeth on said engine clutchmember and having a second clutch member adapted to move in rotation only and mounted interconnectedly and coaxially within said first clutch member, means for causing said first clutch member to move axially upon relative rotation between said first and second clutch elements, biasing means including a spring between said first and second members and biasing said first clutch member away from said engine clutch member, ratchet means including an element carried by said engine clutch member and an element carried by said second member said elements being normally biased into ratcheting engagement by biasing means, and centrifugally operated means carried by said engine clutch member to move said elements out of ratcheting engagement whenever said engine dog rotates at a speed above a predetermined value.

2. Apparatus in accordance with claim 1 wherein said ratchet means comprise a ratchet member carried by said second clutch member and having ratchet teeth thereon, and at least one pawl pivotally mounted on said driven member and biased by biasing means into engagement with said ratchet teeth.

3. Apparatus in accordance with claim 2 wherein said pawl is mounted with its center of gravity between its pivotal axis and the portion of the ratchet which engages said ratchet teeth, whereby said portion is moved radially outward by centrifugal force when the speed of said driven member exceeds a predetermined value.

4. A clutch for releasably coupling a driving and a driven part, comprising a driving member having a first element having a cylindrical sleeve section and a face thereon adapted to engage corresponding teeth on a member adapted to be driven a second element concentrically mounted-within said first member, and means for moving aid dri ng m mber t ga e d d n e said teeth comprising a projection secured to one of said elements ex ending radially therefrom into a helical slot in the other, a ratchet member having ratchet teeth thereon fastened t -said second element so as to be rotatable therewith, and at least one pawl pivotally mounted on said driven mber an b ase by bi sin me nt en a ment with said ratehetteeth,

5, Apparatus in accordance with claim 4 wherein said pawl is mounted with its center of gravity located between the ax is about which it is pivoted and the portion which engages said ratchet teeth whereby said portion moves radially outward by centrifugal force when the speed of said driv n member exceeds a predetermined alu 6. In a starting mechanism, means for transmitting torque comprising a first member having a sleeve-like body and a toothed face adapted to engage a similar toothed face on a clutch dog connected to an engine to be started, a second member having a helical slot and mounted internally concentric with said first member forrotation therewith, interconnecting means for rotating said members together comprising a substantially radial projection carried by said second member which extends into said helical slot, means located between said members for restraining axial movement of said second mem-.

No references cited.