US2557958A

US2557958A - Hoist drive and brake mechanism

Info

Publication number: US2557958A
Application number: US18983A
Authority: US
Inventors: Harold C Fitzsimmons
Original assignee: Sharples Corp
Current assignee: Sharples Corp
Priority date: 1948-04-05
Filing date: 1948-04-05
Publication date: 1951-06-26
Anticipated expiration: 1968-06-26

Description

June 26, 1951 H. c. FITZSIMMONS 2,557,958

. noxs'r DRIVE AND BRAKE MECHANISM Filed April 5, 1948 2 Sheets-Sheet 1 F fg.

INVENTOR. Harold C. Fitzsimmons BY a ays June 26, 1951' H. c. FITZSIMMONS 2,557,958

' HOIST DRIVE AND BRAKE MECHANISM Filed April 5, 1948 2 Sheets-Sheet 2 F/gZ INVENTOR. C. Fifzsimrhons Attorneys Patented June 26, 1951 HOIST DRIVE AND BRAKE MECHANISM Harold C. Fitzsimmons, West Chester, Pa, assignor to The Sharplcs Corporation, a corporation of Delaware Application April 5, 1948, Serial No. 18,983

1 Claim.

This invention relates to improvements in gear driving mechanisms and more particularly to an improved form of a reversible gear driving mechanism having automatically operable braking means to prevent reverse driving of the mechanism.

Hand-cranked crane hoist mechanisms are frequently used to lift the bowl and related parts of the larger types of centrifugal separating machines. Such crane mechanisms are usually attached to the frame of the centrifugal machine as an integral part in a manner to permit the movement of the crane boom over the machine so that the lifting cable and hook may be lowered to engage and lift the bowl or other heavy parts of the machine.

It has been common in such cranes to wind the lifting cable onto a drum, to mount on the drum a worm wheel and to engage this worm wheel with a worm rotated by a hand-crank. Worms and worm wheels were so chosen as to provide a so-called self-locking or non-reversible system so that the gears could be readily turned by the hand-crank, but loads on the crane would not cause rotation.

Such gear systems had a high ratio and provided for only slow raising and lowering of the load. When attempts were made to increase the speed by lowering the gear ratio, the gear system became reversible or non-self-locking, so that loads on the cable lowered spontaneously with accelerating speed with damage to the load unless the crank handle was held at all times by the crane operator. If the operating handle of such a system should be lost from the grasp of the operator, it is obvious that the operator would be risking his limbs in trying to stop the rotating crank handle.

With such cranes having high lifting speeds and reversible gear mechanisms, various types of ratchet mechanisms requiring manual operation by the crane operator were used. The principal difficulty with all of these were that the crane operator had to exercise considerable dexterity in manipulating the ratchet along with the operation of the hand-crank while lowering heavy loads, as it was necessary to hold the ratchet out while lowering and to reset it before letting go of the crank handle.

Such low ratio worm gear systems could be made non-reversible only by the use of excessively large diameter worms with low angles of the threads.

It is a principal object of this invention to provide an improved gear drive mechanism of the reversible drive type having automatically operable braking means to prevent the reverse driving of the mechanism while not interfering with any desired rotation.

It is another object of this invention to provide a reversible drive gear hoist mechanism suit- I able for use in connecting the operating handle of a hand-cranked crane mechanism to the crane lifting cable drum in a manner to afford a high lifting rate of speed and having automatically operable means to brake the rotation of the lifting cable drum in the direction to cause lowering of the cable without interfering with the desirable high rate of rotational speedfor the cable drum in the direction to lift the cable and crane load.

Still another object of the invention is to provide a hand-cranked gear drive mechanism connected to produce rotation of the hoist cable drum of a crane in a manner which will enable a high rate of lifting speed under heavy load conditions and which will further provide an automatic brake of the mechanism upon reverse rotational drive, the automatic braking means being further effective in proportion to the weight of the load to produce an increased braking force with increased loads.

The invention in one of its principal aspects provides for a rotatable drive shaft having a hand-crank on one end. On the other end of the drive shaft is keyed a worm mounted in operative association with a worm gear connected to the lifting cable winding drum or sheave. The worm and worm gear are of a low ratio design to provide a relatively high lifting rate of speed for the crane mechanism and therefore are essentially reversible in drive characteristics. A thrust bearing assembly of the ball bearing anti-friction type is associated with the drive shaft and worm in such manner as to absorb the end thrust of the worm under rotation. The provision of the anti-friction bearing assembly facilitates the ratation of the gear mechanism in response to rotation of the hand-crank, in a direction to achieve a lifting motion by the crane, but is also effective in either direction of rotation, since the thrust from the worm is always in the same direction regardless of the direction of rotations. In order to prevent spontaneous rotation of the mechanism in reverse direction in response to a heavy load being lowered by the crane mechanism, this form of the invention provides for an automatically operable one-way clutch mechanism to be operated in response to the reverse direction of rotation during the lowerin motion of the crane to apply a brake upon the rotation of the driving shaft carrying the worm. Such automatically operable brake mechanism may be so designed as to be responsive to the amount of loading on the crane mechanism producing the reverse lowering direction of rotation, so that the braking effect increases with and is a function of the load, thus providing adequate braking effect to prevent spontaneous rotation irrespective of load.

Further objects and advantages of the invention will be apparent with reference to the following specification and drawings, in which Figure 1 is an elevational view of a crane mechanism associated as an integral unit with a centrifugal machine shown in part;

Figure 2 is a longitudinal section through the axis of the drive shaft of a worm gear type of crane hoist mechanism embodying the features of the invention;

Figure 3 is a plan view of the ratchet collar as used in the automatically operable one-way clutch associated with the drive and braking;

arrows on the line 6-5 of Figure 5.

Referring to Figure l of the drawings, in which a crane mechanism unitarily associated with a centrifugal machine is shown for the purpose of illustration, the crane boom I6 is rotatably mounted upon the support H which is bolted at 42 and I3 to suitable flanges on the body of a centrifugal separating machine M. A locking .mechanism having an operating hand wheel i6 -may be provided to lock the position of the crane ID in any desired rotational position such as the position in which the crane hook ['6 is over the centrifugal machine l4, or the position in which the hook I6 is away from the centrifugal ma-- chine M. The lock mechanism and operating handwheel l do not form a part of this invention and may be of any form suitable for the purpose.

Enclosed within the crane boom 16 and rotatably mounted at 2B is a cable winding drum or sheave 2| carrying therewith the worm gear 22.. The lifting cable 23 is wound around the cable drum 2i and passes over the pulley 24 to be connected at its remote end to the crane lifting hook l6. A drive shaft 25 is journaled within suit-- able bearings (not shown in detail) within the crane boom housing and mounts a worm 25 in operative association with the worm gear 22. An operating handle 21 is also provided on one end of the driving shaft 25 (as shown) to enable marual rotation of the operating shaft 25 and worm 26 to cause a raising or lowering of the crane cable 23 by winding or unwinding such cable upon the drum 2|.

, 1n the hand-cranked crane mechanism as described for use in connection with the lifting of the bowl of a centrifugal separating machine, it is desirable to have a low gear ratio such as to provide a high lifting rate of speed in order to be able to lift and change separator bowls as quickly as possible. When designing a worm hoisting gear mechanism for use in hand-cranked crane assemblies, and of a physical size small enough to be mounted within the crane boom while still obtaining the desired gear ratio, it is necessary to provide a relatively high pitch for the worm. The provision of a high pitched worm and worm gear assembly results in a mechanism which is essentially reversible in its drive characteristics so that the load on the end of the crane cable would tend to produce a reverse driving through the worm gear mechanism of the drive shaft and handle once the load had started spontaneously to lower. This invention provides for an improved worm gear driving arrangement of such type in which the reverse driving of the gear assembly by the load at excessive rotational speeds is substantially prevented by the automatic operation of the combined one-way clutch and brake assembly to be described in the following paragraphs.

The details of one form of combined one-way clutch and brake mechanism in association with a worm gear driving mechanism are shown in Figures 2 through 6 of the drawings. Referring to such figures of the drawings, the worm 26 is pinned to the drive shaft 25 by the pin 30. A ratchet collar 3! is co-axially mounted on One end of the worm 26 (as shown), and is also connected for rotation with the shaft 25 and worm 25 by the pin 36 which passes through the

pin bores

32 and 33, as shown inFigure 3 of the drawings. Also as shown in Figure 3 of the drawings, the ratchet collar3l is provided with a plurality of

ratchet indentations

34, 35 and 36 .having the tapering bottom surfaces approaching the end surface of the collar as at 31, 38 and 39, 'respectively. Such ratchet indentations are conventional in having steep

end side walls

40, 4| and 42, respectively, opposite to the tapering port-ions 31-55, respectively.

Again, referring to Figure 2 of the drawings, it will be seen that a ratchet pawl collar 45 is coaxially mounted around the main driving shaft 25 freely rotatable in a manner to be normally not connected for rotation with the shaft 25, as shown. The main driving shaft 25 may be journaled in non-rotatable member 46 fastened by

bolts

41 and 48 to the crane boom housing l6 partially shown in Figure 2. The ratchet pawl collar 45 is provided with an end wall surface 49 in frictional engagement with the end wall surface 56 of a non-rotatable member 46 fastened to the crane housing iii, as previously described. The anti-friction ball hearing assembly 5! is interposed between the thrust end of the worm 25 and the internal wall surface 52 of the ratchet pawl collar 45 which, as previously mentioned, is freely rotatable upon the shaft 25. It will be seen that the anti-friction ball bearing assembly 5! functions as an anti-friction thrust bearing, and that the pawl collar es and member 46 at their

respective surfaces

49 and 50 cooperate to form what may be termed a friction thrust bearing or brake.

Referring to Figures 2, 5 and 6 of the drawings, it will be seen that the ratchet pawl collar 45 is provided with a plurality of

pawl receiving pockets

55, 56 and 51 within which the ratchet pawls, such as the one shown at 58; are journaled against the compression of pawl springs such as shown at 59. It will be noted that each of the ratchet pawls such as 53 are urged by their respective compression springs such as 59 into engagement with the ratchet indentations 34- 36 of the ratchet collar 3|. Such an assembly of ratchet and ratchet pawl collars is representative of one form of automatically operable oneway clutch which may be used in the drive system of this invention.

A clockwise rotation of the shaft 25 by manual operation of the handle 23' or otherwise to produce a lifting motion of the cable drum 24 will also cause clockwise rotation of the worm 26 and the ratchet collar 6!. The ratchet indentations 34-36 are shaped to permit a ratchet release action by each of the spring-pressed pawls and cause the ratchet collar 3! to rotate without rotating the ratchet pawl collar 95 during clockwise rotation of the ratchet collar. Thus, the end thrust from the worm 25 for clockwise rotation of the shaft 25 is absorbed by the antifriction ball bearing assembly 5i between the thrust end of the rotating worm 26 and the nonrotated pawl collar 45 freely rotatable on the shaft 25 but held against rotation by the worm end thrust forcing the

frictional surfaces

49 and 59 together. In such manner the lifting force is applied to the cable drum 2! in a relatively frictionless mode affording easy operation during clockwise rotation of the drive shaft 25.

Upon reverse or counter-clockwise direction of rotation of the shaft 25, in response to a reverse rotation of the handle 27 assisted by (but preferably not caused by) the gear mechanism from the worm gear 22 through the worm 26 due to heavy loading on the crane and the high pitch of the worm, each of the ratchet pawls will engage one of the respective steep

end wall surfaces

49, 4| or 42 of the ratchet indentations S t-66 to cause a rotation of the ratchet pawl collar 45 with the ratchet collar SI and the worm 26 pinned to shaft 25. The counter-clockwise rotation of the ratchet pawl collar 45 is resisted by the frictional contact between its end wall surface 49 and the end wall surface 50 of the non-rotatable journal member 66 as produced by the end thrust of the worm 26. Thus the frictional brake surfaces 49 and 59 are preferably of such size and arrangement as to be effective to provide a sufficient frictional brake against any spontaneous rotation of the shaft 25 as a result of a load on the crane.

It will be noted that the thrust of the worm gear 26 through the ball bearing assembly 5| against the pawl collar 65 will increase the frictional contact between the

surfaces

49 and 59 as a function of the increase of such thrust or loading of the crane. Thus, the braking effect against counter-clockwise rotation of the driving shaft 25 in the worm gear mechanism of this invention is automatically obtained in response to such counter-clockwise rotation and is variable in effect to increase the braking force with increases in the amount of loading on the gear mechanism causing the reverse rotation. Such braking effect is obtained through the medium of the automatically operable one-way clutch or ratchet mechanism in association with an antifriction bearing assembly in such relation that clockwise rotation of the shaft 25 is enabled under relatively frictionless conditions, the braking surfaces being rendered ineffective during such clockwise rotation.

The braking effort may be varied by changing the character of the

surfaces

49 and 50, and also by varying the radius from the axis of the shaft 25 at which the

surfaces

49 and 50 contact with respect to the radii of the teeth on the worm 26. By such variation the braking force can be adjusted so as to be preferably at least slightly greater than the rotational force due to a load on the crane, thus preventing spontaneous rotation from such a load. -With such adjustment only a resultant or differential force need then be applied to the handle 2? to lower the load on the crane.

It should be pointed out that the gear driving mechanism and automatic brake arrangements of this invention are not to be limited to a specific adaptation in crane mechanisms, either in association with or without centrifugal separating machines, since the reversible gear drive having automatic braking means may find useful application in various other machines and devices.

Modifications will be obvious to those skilled in the art and I do not therefore wish to be limited except by the scope of the claim.

What is claimed is:

Crane hoist mechanism, comprising a rotatable shaft, a worm secured to said shaft, a worm gear operatively associated with said worm, said worm and said Worm gear having enmeshed teeth of a sufficiently high pitch to cause said Worm and Worm gear to be essentially reversible in drive characteristics, means for connecting a liftinglowering load to said worm gear to cause a unidirectional torque thereon, a ratchet collar coaxially and fixedly mounted on said shaft at the thrust end of said worm and rotatable therewith, a second ratchet collar coaxially mounted on said shaft next, to said first-mentioned collar with said first-mentioned collar nearest said worm gear, said second-mentioned collar being rotatable relative to said shaft, an antifriction thrust bearing operatively positioned between said first-mentioned and second-mentioned collars, ratchet-means associated with said collars and adapted to automatically engage said collars when said worm is rotated in a lowering direction and to disengage said collars when said Worm is rotated in a lifting direction, a bearing for said shaft having said collars and said worm on the same side thereof, a brake face on said bearing adjacent said second-mentioned collar, a juxtaposed brake face on said second-mentioned collar, said bearing brake face and said collar brake face being held in frictional contact by the thrust on said worm due to said unidirectional torque on said worm gear, and means for rotating said shaft.

HAROLD C. FITZSIMMONS.

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

UNITED STATES PATENTS Number Name Date 1,257,576 Boehock Feb. 26, 1918 1,287,966 Gormley Dec. 17, 1918 1,756,459 Gormley Apr. 29, 1930 1,892,940 Erdahl Jan. 3, 1933 2,408,179 Schuetz Sept. 24, 1946 FOREIGN PATENTS Number Country Date 113,136 Germany Apr. 15, 1899 2,684 Great. Britain A. D. 1906 195,331 Great Britain Mar. 29, 1923