Pawl And Ratchet Clutch

Abstract

A pawl and ratchet clutch for use between a starter and a gas turbine engine in which the pawls of the clutch are held in engagement with ratchet teeth by both resilient and centrifugal force, during the engine starting operation. After self-sustaining engine speed is attained, the pawls are disengaged and held in such condition, also by centrifugal force, during engine operation. When engine operation is discontinued and its speed is reduced sufficiently, the pawls will be resiliently urged toward the ratchet teeth and a light ratcheting will occur. If the starter is energized during engine coastdown, the pawls may be moved into engagement with the ratchet teeth by centrifugally responsive actuating means in addition to the resilient force.

Description

SUMMARY

This invention relates to clutch mechanisms by which a driving means, such as a starter, may be automatically connected with a driven means, such as an engine, to effect an engine starting operation and then automatically disconnected when engine operation becomes self-sustaining. More specifically, the invention relates to a pawl and ratchet clutch having novel means for effecting and maintaining the engagement between the pawls and ratchet during the engine starting operation and the disengagement of the pawls from the ratchet after self-sustaining operation has been effected, the clutch also being so constructed that after the disengagement of the pawls and ratchet the former will be held in such condition by centrifugal force as long as a predetermined engine speed is maintained. If necessary, an engine starting engagement of the pawls with the ratchet can be effected during rotation of the engine by causing the starter speed to match the engine speed. No engagement or ratcheting will take place as long as the engine speed exceeds the predetermined rate. By this arrangement the mechanism is given a high load capacity and long life.

An object of this invention is to provide a clutch mechanism of the pawl and ratchet type which has centrifugally responsive means for maintaining pawl and ratchet engagement during the high-speed range of the starter and centrifugally actuated means for effecting and maintaining the separation of pawl and ratchet after self-sustaining engine speed is reached, certain parts being responsive to the operation of the starter motor and other parts being responsive to engine operation.

Another object of the invention is to provide a clutch mechanism for use between a starter and an engine wherein a ratchet is secured for rotation with a starter motor and cooperative pawl elements are mounted on the engine shaft or a part carried thereby, the pawl elements being bell crank shaped with weighted arms which serve as the pawls and other arms acting as levers, the pawl elements being pivotally mounted in such a location and manner that actuator means supported for rotation with the ratchet will, during a predetermined speed range of the starter motor, respond to centrifugal force by engaging the lever arms and urging the pawl elements toward the ratchet, this action being maintained as long as the rate of rotation of the engine does not exceed that of the starter. When engine speed starts to exceed that of the starter in the high-speed range, the weighted pawls then respond to their own centrifugal force and are disengaged and spaced from the ratchet. Such spacing is maintained as long as engine speed exceeds starter speed.

Other objects and advantages will be made apparent by the following description of the embodiment of the invention selected for illustration in the accompanying drawings.

THE DRAWINGS

FIG. 1 is an axial sectional view taken through a clutch formed in accordance with the present invention and showing the same in operative relation with engine and starter motor parts;

FIG. 2 is a vertical transverse sectional view taken on the plane indicated by the line II--II of FIG. 1;

FIG. 3 is a similar view of a portion of the clutch showing a pawl element in its disengaged position; and

FIG. 4 is a view similar to FIG. 2 taken through the clutch mechanism on the plane indicated by the line IV--IV of FIG. 1 and showing actuator elements responding to centrifugal force to urge pawl elements toward the ratchet.

DESCRIPTION

The clutch mechanism shown in the drawings includes a part 10 in the form of a hollow body with a shaft portion 11 splined or otherwise shaped to fit the end of the engine shaft 12 to transmit rotary motion thereto. The clutch includes a ratchet 13, this element being generally cylindrical and suitably secured, as at 14, to a part 15 forming the output shaft of a starter motor. The part 15 has a disk 16 with a flange 17 receiving the outer race of a bearing 18 suitably supported in the starter housing 20. The bearing rotatably supports the starter output shaft 15 and ratchet 13.

In the form of the invention shown, the ratchet is hollow to receive centrifugally responsive actuating means 21 for an overspeed switch 22 mounted in connection with the housing 20. The ratchet 13 is shaped to receive a plurality of arcuate actuator elements 23 which are guided for radial movement by an end wall of the ratchet and a retaining washer 24, fixed as at 25, to the ratchet. The ratchet is also provided on its periphery with a plurality of ratchet teeth 26, these elements being slightly undercut, as at 27, for a purpose to be hereinafter set forth. The body 10 is formed with spaced inwardly extending flanged portions 28, between which pawl elements 30 are supported for pivotal movement on pins 31. These pins are disposed outwardly of the ratchet and extend parallel to the axis of rotation of the ratchet. The pawl elements are relatively elbow or bell crank shaped, each having a pair of arms 32 and 33. The arms 32 are weighted and shaped at their outer ends for engagement with the ratchet teeth 26, the outer ends also being shaped to be received in the undercut portions 27 for retention when rotary motion is being transmitted by the ratchet to the body 10 through the pawls. The arms 33 serve as lever elements during certain phases of operation of the clutch. These elements are offset relative to the pawl portions 32, as shown in FIG. 1, to overlie the arcuate actuator elements 23. Actuators 23 are segmental in construction and shaped to be grouped around the reduced end of the ratchet. They are yieldably held in this position by a garter spring 34 which is disposed in a recess formed in the outer portions and adjacent one side of the actuator elements.

At the opposite side, the actuator elements are provided with a shoulder 35 for engagement with a second shoulder 36 formed on the ratchet to limit the outward movement of the actuator elements under centrifugal force. Since the arms 33 overlie the actuator elements 23, outward movement of the latter will cause their engagement with the arms and tend to rock the pawl members about their pivots, moving the pawl ends into firmer engagement with the rachet teeth. As shown in FIGS. 2 and 3, the arms 32 have a small projection 37 provided thereon to engage the inner surface of the body 10 and limit outward movement of such arms under centrifugal force. This movement is opposed by relatively flat leaf springs 38 which are secured at one end to the inner surface of the body, the opposite end engaging the pawls 32 to yieldably urge the same toward the rachet for engagement therewith in the lower speed range of the starter.

As shown in FIG. 4, the actuator members 23 are secured for rotation with the ratchet by suitable means, such as guide pins 40, secured to the ratchet and disposed in recesses in the arcuate actuator elements. These pins insure the rotation of the actuator elements, yet permit outward movement thereof to the positions shown in FIG. 4 in response to centrifugal force. Such outward movement is yieldably opposed by the garter spring 34.

In an engine starting operation, rotary movement is transmitted to the ratchet by the starter motor through the shaft 15. Since the pawls 32 will be in engagement with the teeth on the ratchet due to the force exerted by springs 38, rotary movement will in turn be transmitted to the body 10 and shaft 12 to effect the rotation of the engine. As the starter and engine rotary speeds increase, centrifugal forces will be developed in the pawls 32 and the actuators 23. Outward movement of these elements is opposed by the forces of springs 38 and 34 and the engagement of the pawl ends in undercut 27 of the ratchet teeth until the engine speed starts to exceed the starter speed. One of the objectives is to make spring 34 of such strength that outward movement of the actuators 23 in response to centrifugal force will be prevented until the lower limit of a predetermined starter speed range is reached. During this speed range, which may be designated as the high-speed range of the starter, a combination or overlapping of forces exerted by the springs 38 and the centrifugal force of the actuators 23 will tend to urge the pawls into engagement with the ratchet teeth. After the speed of engine rotation required to effect self-sustaining operation is reached, the starter is shut off and its speed will being to decay while the engine's speed increases. At this time the centrifugal force on the pawls will swing them away from the ratchet. As this action starts, the pawls 32 may ratchet lightly over the ratchet teeth, but due to the increasing speed of rotation of the engine the centrifugal force of the pawls 32 will cause them to swing outwardly in opposition to the force of the springs 38 and centrifugal force of segments 23 until such outward movement is limited by the engagement of projections 37 with the inner surface of the body 10. The decline in starter speed reduces the centrifugal force of the segments 23 and spring 34 moves them to their completely retracted position spaced from lever arms 33, as shown in FIG. 3, and complete disengagement of engine and starter exists. The starter coasts to rest.

It will be noted that during the high-speed range of an engine start, the centrifugal force on the actuator elements 23 combines with the force of springs 38 to retain the pawls in engagement with the ratchet teeth, as shown by dotted lines in FIG. 4, until the engine reaches a self-sustaining operating speed and the starter is shut down. It is this combination of forces which provides for running starts, for if the starter motor is energized during the rotation of the engine, the centrifugal force of the actuators will tend to cause the pawls 32 to move toward the ratchet. It should be obvious, however, that if the engine speed is sufficient, the centrifugal force developed by the pawls may be strong enough to oppose outward movement of the actuators. When the engine speed decays to equal the starter speed, however, the force of the actuators coupled with springs 38 will be sufficient to reengage the pawls with the ratchet and driving force may then be applied by the starter to the engine. During normal operation, the actuators will remain inoperative during normal rundown and the flat springs 38 will reengage the pawls at a low speed, causing the pawls to ratchet only for a relatively short time.

With the clutch construction shown and described, long life will be obtained since the overrunning side of the clutch is on the engine, and moving parts on the starter which might wear during the engine overrun are eliminated. This construction provides positive load transmission and safe running engagements between the starter and the engine. It also permits the clutch to operate dry, i.e., without lubrication, and eliminates the requirement of seal means between the clutch and the engine. The use of light springs to move the pawls toward the ratchet permits the pawls to move outwardly in response to engine rotation and prevents high-speed ratcheting, thereby eliminating wear.

Claims

What we claim is:

1. A pawl and ratchet clutch mechanism between driving and driven elements, comprising:

a. ratchet means secured for rotation with the driving element;

b. pawl means mounted on the driven element for movement to engage said ratchet means and transmit rotary movement of the driving to the driven element, said pawl means having portions responsive to centrifugal force resulting from rotation of the driven element to tend to move said pawl means out of engagement with said ratchet means; and

c. actuator means secured for rotation with the driving element and constructed to be responsive to centrifugal force resulting from rotation of the driving element to tend to move said pawl means into engagement with said ratchet means.

2. The pawl and ratchet clutch mechanism of claim 1 in which the ratchet and pawl means are shaped to retain said pawl means in engagement with the ratchet means until the rate of rotation of the driven means starts to exceed that of the driving means.

3. The pawl and ratchet clutch mechanism of claim 1 in which resilient means are provided to urge said pawl means into engagement with said ratchet means.

4. The pawl and ratchet clutch mechanism of claim 1 in which resilient means are provided to engage said actuator means and yieldably resist movement thereof by centrifugal force.

5. The pawl and ratchet clutch mechanism of claim 1 in which the actuator means comprises a plurality of arcuate elements supported adjacent said ratchet means.

6. The pawl and ratchet clutch mechanism of claim 1 in which said pawl means are substantially bell crank shaped with one arm serving as the pawl portion and the other serving as a lever portion engaged by said actuator means.

7. The pawl and ratchet clutch mechanism of claim 6 in which a substantially hollow body is provided and said pawl means are pivotally mounted within the body so that the arms serving as the pawl portions move toward the ratchet means when the arms serving as lever portions are moved by said actuator means.

8. The pawl and ratchet clutch mechanism of claim 5 in which a garter spring is provided to engage said arcuate elements and yieldably resist movement thereof in response to centrifugal force.

9. The pawl and ratchet clutch mechanism of claim 5 in which the pawl means are substantially bell crank shaped with the arms offset to dispose the arms serving as the pawl portions over the ratchet teeth and the other arms over the actuator means.

10. The pawl and ratchet clutch mechanism of claim 7 in which the arms serving as the pawl portions are shaped to engage an inner surface of said body to limit the extent of movement of said pawl means in response to centrifugal force.

11. The pawl and ratchet clutch mechanism of claim 3 in which the resilient means is composed of substantially flat leaf springs, each secured at one end to the body of said driven means and engaged at the other end with a pawl.

12. The pawl and ratchet clutch mechanism of claim 5 in which means are provided to engage and guide the arcuate elements in their movement in response to centrifugal force.

13. The pawl and ratchet clutch mechanism of claim 5 in which the arcuate elements are each provided with a groove and a grater spring is disposed in such grooves to hold said elements in assembled relationship and yieldably resist movement thereof in response to centrifugal force.

14. The pawl and ratchet clutch mechanism of claim 7 in which the ratchet means has a cylindrical portion, the actuator means is composed of arcuate elements disposed around the cylindrical portion, the substantially hollow body extends around the ratchet means, the pawl means are substantially bell crank shaped with one arm serving as a pawl and the other as a lever, the juncture of the arms being pivotally secured in said body at points disposed radially outwardly of the ratchet and actuator means so that the pawl and lever means radially register with the ratchet and actuator means respectively, flat leaf spring means being secured to the body and engaging the pawl means to resiliently urge them toward the ratchet means, a garter spring surrounding said arcuate elements and yieldably resisting movement thereof in response to centrifugal action, rotation of the driven element at a rate in excess of that of the driving element serving to cause the disengagement of the pawl means from said ratchet means, rotation of the driving element at a predetermined rate serving to cause radial movement of said arcuate actuator elements in response to centrifugal force and engagement with lever arms on said pawl means to urge the pawl arms toward engagement with said ratchet teeth.