US3720077A - Hoist having yielding means for load limiting - Google Patents

Abstract

A HAND OPERATED HOIST HAS A HAND WHEEL THAT IS FORMED IN PARTS OPERATIVELY CONNECTED THROUGH SPRING PRESSED ROLLER DETENTS ENGAGING DETENT RECESSES OF ASYMMETRICAL SHAPE FOR APPLYING LOAD LIFTING TORQUE TO THE HOIST. THE RECESSES HAVE LONG INCLINED SURFACES ON WHICH THE DETENTS WILL RIDE AFTER AN OVERLOAD AMOUNT OF LIFTING TORQUE CAUSES THE DETENTS TO LEAVE SEATED POSITION IN THE RECESSES. THEREBY THE DETENTS WILL YIELD GRADUALLY WHILE IN EFFECT RELEASING THE LOAD LIGTING EFFORT THAT AN OPERATOR APPLIES TO THE HAND WHEEL, BUT OFFERING RESISTANCE TO THE OPERATOR''S EFFORT SO AS TO REDUCE THE HAZARD THAT WOULD BE INCIDENTAL TO A SUDDEN RELEASE. THE ASYMMETRICAL SHAPE OF EACH RECESS INCLUDES A STEEP SURFACE THAT WILL HOLD A DETENT IN THE RECESS SO AS TO PERMIT AN APPLICATION OF THE AMOUNT OF FORCE NECESSARY TO RELEASE A LOAD BRAKE WHEN A LOAD IS TO BE LOWERED.

Description

March 13, 1973 H. YQJACKSON ETAL 3,720,077

HOIST HAVING YIELDING MEANS FOR LOAD LIMITING Filed April 12, 1971 2 sheets -sheet 1 lNVENTO/PS J. RAMOS/(A H. X JACKSON 6. C. WALKER A TTORNEYS March 13, 1973 H. Y. JACKSON ET AL 3,720,077

HOIST HAVING YIELDING MEANS FOR LOAD LIMITING Filed April 12, 1971 2 Sheet-Sheet 2 fJg.5

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J-IPAMOSKA H X JACKSON C. C. WALKER ATTORNEYS United States Patent 3,720,077 HOIST HAVING YIELDING MEANS FOR LOAD LIMITING Harry Y. Jackson, Cherry Hill, N..I., Charles C. Walker,

Forrest City, Ark., and John Ramoska, Philadelphia, Pa., assignors to Eaton Yale 8; Towne Inc., Cleveland,

ABSTRACT OF THE DISCLOSURE A hand operated hoist has a hand wheel that is formed in parts operatively connected through spring pressed roller detents engaging detent recesses of asymmetrical shape for applying load lifting torque to the hoist. The recesses have long inclined surfaces on which the detents will ride after an overload amount of lifting torque causes the detents to leave seated position in the recesses. Thereby the detents will yield gradually while in effect releasing the load lifting effort that an operator applies to the hand wheel, but offering resistance to the operators effort so as to reduce the hazard that would be incidental to a sudden release. The asymmetrical shape of each recess includes a steep surface that will hold a detent in the recess so as to permit an application of the amount of force necessary to release a load brake when a load is to be lowered.

This invention relates to hoists, and more particularly to a novel hoist that will limit its operation to the amount of load that it can safely lift.

Those persons who are skilled in the art will appreciate that overloading of a hoist is a dangerous matter, causing early failure of the hoist and sometimes inflicting grave injury upon persons nearby. The manufacturers of hoists do indicate the load capacity of each hoist. Unfortunately, however, the manufacturer has no effective control over the loading of a hoist after it leaves his hands. Many users of hoists persist in overloading, due to impatience or other carelessness, and perhaps a desire to avoid the cost of a hoist having the necessary capacity. More and more instances of severe overloading have appeared, causing failures that are a matter of increasing concern.

The prior art does contain hoists designed with load limiting features but those hoists have not been fully satisfactory in present day operation, particularly where the hoist is hand operated. In some cases the hoists have been so designed that a driving member, such as a hand wheel, will lock the hoist so that it cannot operate when subjected to a force that would be necessary to lift an overload. Those hoists may limit the load quite effectively, but it has been found that there are objections because a person operating the hoist, not recognizing that it is locked, may use some expedient that is dangerous in an attempt to force operation. Also, hoists have been designed in which there are yielding means that enable a driving member to yield or slip when the load is excessive, but the yielding means often are not reliable or require a rather costly construction, and in some cases there may be sudden yielding that oifers a considerable hazard when the driving member is a manually operated member. The yielding means of the prior art may cause further trouble where the hoist is equipped with a load brake, because the driving member then may be unable to overcome a tendency of the brake to bind when a load is to be lowered.

We now have conceived by our invention a novel load limiting hoist that will operate extremely well and that we believe will solve the problem that is caused by hoist users who tend to overload the hoists. In the hoist of our invention, we apply the hoist operating force through yielding detent means that will continue to accept a substantial part of the force after yielding due to an overload. Thereby the detent means will offer a continuing resistance to the operating force that is applied to the hoist, while in effect releasing the hoist relatively to the load. The detent means nevertheless will accept all of the force that may be necessary to effect release of a load brake.

An important feature of our invention resides in detent recesses having an asymmetrical shape that yielding detents will engage to control movements between operating parts of the hoist. More particularly, the asymmetrical shape of each detent recess will comprise an inclined surface that will cause a detent to yield in a gradual manner upon the application of an overload lifting force, and a relatively steep surface that will enable a following detent to move more quickly to a seated position in the recess. As a further feature of our invention, the relatively steep surface of the recess will extend at an angle positively holding a detent against movement when accepting force in a load lowering direction.

We have thus outlined rather broadly the more important features of our invention in order that the detailed description thereof that follows may be better understood, and in order that our contribution to the art may be better appreciated. There are, of course, additional features of our invention that will be described hereinafter and which will form the subject of the claims appended hereto. Those skilled in the art will appreciate that the conception on which our disclosure is based may readily be utilized as a basis for the designing of other structures for carrying out the several purposes of our invention. It is important, therefore, that the claims be regarded as including such equivalent constructions as do not depart from the spirit and scope of our invention, in order to prevent the appropriation of our invention by those skilled in the art.

In the drawings:

FIG. 1 shows a longitudinal section of a portion of a load limiting hoist utilizing our invention, taken substantially on the line 1-1 in FIG. 2;

FIG. 2 shows a section on the line 2-2 in FIG. 1; and

FIG. 3 shows a somewhat different position of parts that are shown in FIG. 2.

For the purpose of describing our invention, we have chosen to show in FIG. 1 a construction much like that found in the hand operated hoist which is shown on the patent to Schroeder, No. 2,690,240, including a drive shaft 10 that accepts torque due to a load on the hoist, a hand wheel 11 that forms a drive wheel of the hoist, and a load brake generally indicated by the numeral 12, through which hand wheel 11 acts to rotate drive shaft 10 in load lifting direction, and to control rotation of the shaft in load lowering direction.

In utilizing the novel concept of our invention, We form the hand wheel 11 so as to include a hub portion 13 and an outer driving portion 14 that may rotate on the hub portion 13. As shown in FIG. 1, the hub portion 13 coacts with the load brake 12, and the driving portion 14 is shaped to accept a hand operated chain (not shown). The periphery of the hub portion 13 has a surface 15 in which is a series of openings 16 that contain detents 17 in the form of rollers, best seen in FIG. 2, and springs 18 that press the detents in outward direction. Hub portion 13 has a flange 19 that extends somewhat beyond its peripheral surface 15, and there is an opposed retaining plate 20 assembled by rivets 21 to hub portion 13 and holding detents 17 and their springs in assembled position in the openings 16.

The driving portion 14 of hand wheel 11 comprises a 3 circular part 22 that engages in position between the flange 19 and retaining plate 20 so that the driving portion is held assembled for rotation on the hub portion 13. As shown, the circular part 22 is assembled through screws 23 on driving portion 14, but that part 22 may very well be formed integrally with the driving portion.

Referring to FIG. 2, the part 22 of the driving wheel portion 14 has a series of detent recesses 24 that will coact with the roller detents 17, and we particularly form each of those recesses 24 in an asymmetrical shape. Thus, the bottom of each recess 24 forms a detent seating surface that, as an example, we may consider to extend in the area indicated by the bracket 25 shown in FIG. 2, and there is an inclined surface 26 and a relatively steep surface 27 extending in opposed directions from the seating surface 25. 'In the form that we prefer, each seating surface 25 conforms to the surface curvature of a roller detent 17 so that the detents will seat in surface contact with the surface 25. Also, the depth of each recess 24 is such that its recess will accept approximately onehalf the circumference of a roller detent 17. The inclined surface 26 extends a considerable distance from the seating surface 25, and the relatively steep surface 27 is shaped to fit against a side of the detent, all as may be seen in FIG. 2.

In the form shown, there are twelve of the roller detents 17 equally spaced around the periphery of the wheel hub portion 13. Generally, those detents will engage alternate recesses 24, though a complete series of the recesses is not essential and in some positions the detents may instead engage lands 24a that are shown in FIGS. 2 and 3. A particular quantity of the roller detents 17 and recesses 24 is not actually important to an understanding of our invention.

To proceed with a description of the asymmetrical detent recesses 24, it is necessary to indicate that the load lifting rotation of hand wheel 11 will be in a clockwise direction as viewed in FIG. 2. That is to say that the driving portion 14 of hand wheel 11 when rotating to lift a load will apply torque in a clockwise direction through recesses 24 and roller detents 17 to the hub portion 13 of the wheel. The inclined surface 26 of each detent recess 24 is particularly arranged to lie on that side of the recess which will tend to move toward a detent in the recess when the load lifting torque is applied.

So long as the detents 17 accept the lifting torque, their spring pressure naturally will hold them in position against the seating surfaces 25, causing the wheel hub portion 13 to rotate integrally with the driving portion 14. When more than a predetermined amount of torque is applied, as when attempting to lift an overload, the detents 24 will start to yield while leaving the seating surfaces 25, and the driving portion 14 of the wheel will start to rotate on hub portion 13.

It is important to realize that each roller detent 17 will continue to engage a recess 24 while driving portion 14 rotates farther. The detent then will yield gradually while riding on the relatively long inclined surface 26 of the recess. By its gradual yielding, each detent 17 will act for a considerable time to oppose the rotation that is taking place between the driving and hub portions of hand wheel 11.

Unless the hoist operator immediately ceases his effort to lift the load, the driving portion 14 of the wheel will continue to rotate while detents 17 engage successive recesses 24, as will be understood. When moving into a successive recess 24, each spring pressed detent 17 merely need pass the relatively steep surface 27 of the recess 24, thereby moving rather quickly to position seated in the recess. That movement of detents 17 will offer relatively little assistance to the rotation that is taking place between the driving and hub portions of the wheel, and the resisting effect that is due to the inclined surfaces 26 actually will prevail when the rotation continues. Thereby the detents 17, while releasing the driving portion 14 due to an overload, nevertheless will offer a substantial amount of resistance to the effort being applied by the hoist operator.

The steep surfaces 27 of the detent recesses 24 extend at an angle that will hold detents 17 in the recesses when accepting torque in the load lowering direction, or counterclockwise as viewed in FIG. 2. The value of that will be appreciated when it is remembered that hoist load brakes sometimes will bind so that an unusual amount of torque must be applied when a load is to be lowered. To explain, consider the load brake 12 that is shown in FIG. 1, in which hand wheel 11 must be rotated sufficiently in load lowering direction on screw threads 28 to relieve the pressure that acts between friction surfaces indicated at 29. In load brakes where pressure must be relieved in that way, the friction surfaces may bind to an extent that does not easily permit release rotation of the hand wheel. In the present invention, the steep surfaces 27 of the asymmetrical detent recesses 24, FIG. 2, will accept the amount of torque that may be necessary to overcome any binding of friction surfaces such as surfaces 29, so as to permit release of the load brake. Thus, while achieving extremely effective load limiting operation, the concept of our invention nevertheless will enable a hoist to lower a load as is necessary.

Those skilled in the art will understand that a desired overload point, at which torque release should take place, may be achieved by a particular pressure of roller detents 17, as by choosing detent springs 18 that have an appropriate strength. It is conceivable that the inclined recess surfaces 26 may be formed at an inclination differing from that shown in FIG. 2, but it is merely important that surfaces 26 extend for a considerable distance through which a detent will ride after leaving the seating surfaces of the recesses. We have found that an inclination of 30 to a wheel tangent is very satisfactory.

While we have merely described detents 17 that are rollers, it is to be understood that the detents may take the form of spherical balls, should that be desired. It is conceivable also that the detents may be plungers having end portions that will engage the asymmetrical recesses 24, and therefore we do not wish to limit our invention by rollers.

We believe that it will now be understood that we have conceived a novel hoist construction that will very effectively limit the operation of a hoist to the amount of load that the hoist can safely lift. Through our concept, it will be possible not only to achieve an effective load limit, but also to eliminate to a great extent the hazard that may be due to the operation of the load limiting means of the prior art. Moreover, our load limiting concept will in no way reduce the ability of a hoist to lower a load. Therefore, we believe that the very considerable value of our invention will be fully appreciated by persons who are skilled in the art.

We now claim:

1. In a hoist of the class having a drive shaft that accepts torque due to a load on the hoist, and a drive wheel acting when rotated to rotate the drive shaft in a load lifting direction and to control rotation of the drive shaft in a load lowering direction, the load limiting means that comprise a hub portion of said drive wheel operatively connected to said drive shaft, a driving portion that is mounted for rotation on said hub portion, a series of asymmetrical detent recesses formed on one of said portions of the drive wheel, a series of detents normally spring pressed into a stationary seated position engaging between the other of said wheel portions and said asymmetrical recesses so as to form a driving connection between the driving and hub portions of the wheel, said detents simultaneously yielding and moving into successive recesses to enable said driving portion to rotate on said hub portion of the wheel only when subjected to more than a predetermined amount of torque in the load lifting direction, the asymmetrical shape of each recess comprising an inclined surface on which a spring pressed detent will ride so as to offer resistance to the rotation of the driving portion of the wheel while the detent moves toward a successive recess, a seat surface conforming to the surface curvature of each of said detents within which said detents are seated to drive said drive shaft in a load lifting direction, and a relatively steep surface over which a spring pressed detent will move from said seat surface into the next recess without allowing rotation of the drive shaft.

2. The construction set forth in claim 1 in which said inclined surface of each asymmetrical recess extends from said seating surface a considerable distance so that a spring pressed detent when moving from said seating surface will yield gradually while riding on the inclined surface.

3. The construction set forth in claim 2, in which the relatively steep surface of each asymmetrical recess is shaped to fit against a side surface of a detent while the detent is in position against the bottom seating surface of the recess.

4. The construction set forth in claim 3 in which the References Cited UNITED STATES PATENTS 924,749 6/ 1909 Drapier 64-29 2,311,230 2/1943 Hill 64-29 3,599,781 8/ 1971 Hoadley 64-29 CHARLES J. MYHRE, Primary Examiner R. HEALD, Assistant Examiner US. Cl. X.R. 6428; l9256 R

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