US3028461A - Overspeed protection devices - Google Patents

Description

April 3, 1962 K. M.' PEARCE OVERSPEED PROTECTION DEVICES 2 Sheets-Sheet 1 Filed Dec. 26, 1957 NTOR PL MLW ATTORNEY S April 3, 1962 K. M. PEARCE 3,023,461

OVERSPEED PROTECTION DEVICES Filed Dec. 26, 1957 2 SheetsSheet 2 25 26 Q Z 1 /J K[////./

N'IVENTOR ATTORNEYS United States Patent 3,028,461 OVERSPEED PROTECTION DEVICES Kenneth Maxwell Pearce, Timperley, Altrincham, England, assignor to Metropolitan-Vickers Electrical Company Limited, London, England, a British company Filed Dec. 26, 1957, Ser. No. 705,244 Claims priority, application Great Britain Jan. 11, 1957 17 Claims. (Cl. 200--80) This invention relates to overspeed protection devices for use with mine hoists or the like.

Known forms of such devices employ relatively heavy spring-loaded fiyweight governors which are arranged to position a switch tripping arm according to the hoist winding or banking speeds. If these speeds become excessive the arm trips the switch thereby causing an electro-magnetic brake to arrest the hoist. By reason of their relatively large movable mass, and the presence of large frictional forces, these governors fail to respond instantaneously to rapid increases in hoist speeds, with the result that operation of the switch to apply the hoist brake may be seriously delayed causing the mine cage to overwind in certain circumstances.

The present invention therefore has for an object to provide an improved hoist overspeed protection device whereby the risk of overwinding is considerably reduced.

In accordance with the present invention, an overspeed protection device, for use with mine hoists or the like, comprises means for subjecting a shaft to a torque that is dependent on the hoist speed over a predetermined range of speeds, means coupling the shaft to a movable member such as a shaft and effective to convert said torque into a force that acts on the movable member in a direction of movement thereof, snap means effective in its unoperated condition to exert on the movable member a restraining force equal and opposite to said force transmitted to said movable member through said coupling means, and a switch responsive to the operation of said snap means, whereby upon the hoist speed reaching a predetermined value, the restraining force will be overcome by the force transmitted by said coupling means to bring about substantially instantaneous operation of the snap means and said switch.

Means may be provided for adjusting the hoist speed at which the snap means is to operate, said means being adjustable both during operation of the device and during idle periods thereof.

In carrying the invention into effect, the torque referred to may be exerted on the first said shaft by securing at least one pair of weights to the shaft at radially opposite positions and causing the shaft to be revolved in a plane containing its central axis at a speed proportional to the hoist speed so that the centrifugal forces acting on said weights produce a torque on the shaft. The first said shaft may be revolved by providing a driving connection between the hoist winding drum and a cage or frame supporting the shaft with or without the intervention of gearing, the first said shaft being revolved in a plane substantially at right angles to the axis of the movable member which is coupled in any suitable manner to the cage or frame so as to be rotated with it.

In one contemplated form of the device the said shaft is coupled to the movable member by a system of earns, the shaft having secured to it a generally elliptical cam which bears against a pivoted cam carried by a second shaft supported by the cage or frame and having the same general configuration and which in turn engages a concave cam surface provided at one end of the movable member. In response to rotation of the cage or frame imparted by way of the driving connection previously referred to, the first said shaft, together with the system of cams, is caused to revolve in a plane normal to the axis of rotation of the movable member. Due to the torque exerted on the first said shaft the cams co-operate to move the movable member axially but any such movement is prevented until the force exerted on the member overcomes the restraining force imposed by the snap means and operation of the snap means takes place.

The snap means conveniently comprises co-operating magnetic elements which lock with respect to one another to provide the requisite restraining force and may, if desired, be embodied in the switch of the device.

The revolving parts of the device are preferably balanced dynamically to reduce mechanical vibrations and bearing friction to a minimum, and, for this purpose, counter weights or the like may be provided.

Reference will now be made by way of example to the accompanying drawings in which:

FIG. 1 shows a perspective view of one embodiment of the invention;

FIG. 2 is an enlarged cross-sectional view of the switch incorporating the snap means of FIG. 1;

FIG. 3 is a diagrammatic representation of part of the device of FIG. 1; and

FIG. 4 shows an alternative system of cams for the device of FIG. 1.

Referring to FIG. 1, there is shown a dynamically balanced mine hoist overspeed protection device comprising three parallel shafts 1, 2 and 3, each of which is rotatably supported at its ends in substantially frictionless bearings 36 carried by a cage or frame 37.

Secured to shaft 1 is a pair of lightweight toothed wheels 4 and 4 that mesh respectively with a pair of similar wheels 5 and 5' carried by shaft 2 Which in the present example passes through a transverse slot 6 in a movable member preferably formed by a vertically disposed shaft 7, each of the toothed wheels being provided with a pair of similar diametrically opposed weights 8. For the sake of illustration the axial spacing between the Wheels 4 and 4', and between wheels 5 and 5 has been somewhat exaggerated. Also secured to the shaft 1 inter mediate the wheels 4 and 4' is a generally elliptical cam 9 the under-surface of which makes line contact with a similarly shaped cam 10 secured to the shaft 3. The cam 10 engages a concave cam surface 11 presented by an enlarged head portion of the shaft 7. In order to secure a balance of the shafts 1 and 3 about their axes, discs, indicated at 12 and 13 may be secured to said shafts and have cut-away portions 14 and 15, the configurations of which correspond approximately to the cams "9 and 10 respectively. Here again the axial spacing between the cams 9 and 10 and their balancing discs 12 and 13 has been exaggerated.

The cage or frame 37 is rotatably supported by bearings 38 and 39 mounted in support arms 40 and 41 respectively of main frame 42 and engaged by stub shafts 43 and 44 forming parts of the cage or frame 37. A driving connection is made to the shaft 44 which is hollow from the hoist winding drum (not shown) through a gear wheel 45 carried by shaft 44.

The shaft 7 extends into the shaft 44 and is coupled to a contact operating push-rod 16 of a magnetically restrained switch 17 providing snap means through a ball or other thrust bearing 18 slidable within the shaft 44, the bearing 18 enabling the shaft 7 to rotate independently of the push-rod 16. The switch housing has secured to its base a depending rod 19 bifurcated at its lower end for the accommodation of a circular cam follower 20 that engages a rotary cam 21. The push-rod 16 and the rod 19 are slidably supported by bearings 46 and 47 carried by support arms 48 and 49 of main frame 42.

Reference will now be made to FIG. 2 which shows an enlarged cross-sectional view of the combined switch and snap means in the form of a snap-action switch indicated at 17 in FIG. 1. It comprises a pot magnet element 22 secured at the lower end of the push-rod 16 which passes through the top 23 of the switch housing comprised by an annular element of magnetic material. The annular pole of the magnet element 22, in the unoperated condition of the snap-action switch as illustrated in the figure, lies closely adjacent the annulus 23. Also secured to the push-rod 16 but electrically insulated from it is a radial contact bridging arm 24 which bridges fixed contacts 25 and 26 supported by insulating bushes mounted in apertures extending through the annulus 23. It will readily be observed that the force of magnetic attraction between the poles of the pot magnet element 22 and the annulus 23 will lock the magnetic elements with respect to one another and thus oppose any downward force applied tothe push-rod 16. The contacts 25 and 26 are connected over leads 27 and 28 to a hoist winding drum brake control circuit (not shown), which may be of conventional type.

Reverting to FIG. 1, when the hoist Winding drum (not shown) is set in rotation rotational movement will be imparted to the cage or frame 37 through the driving connection as aforesaid through a gear wheel 45. At the same time, the shafts 1, 2 and 3 and cams 9 and 10 wil revolve, about the central axis of the shaft 7 which will also rotate such as due to the passage of shaft 2 through slot 6 in the example taken. The centrifugal forces set up by the Weights 8 as they revolve will exert torques on shafts 1 and 2 which tend to rotate them in the clockwise and counter-clockwise directions respectively, as viewed from the right in FIG. 1, and these torques will be substantially proportional to the hoist winding drum speed in any given angular position of cam 21 as will hereinafter be apparent.

By reason of the fact that apart from bearing friction, shaft 2 is itself unrestrained for movement about its axis except for that restraint exercised by shaft 1 through the toothed wheels 4 and 4' the whole of the torque developed in shaft 2 will be transmitted to the shaft 1. It will be clear therefore that the weighted wheels and 5 not only serve to provide a balance for the weighted wheels 4 and 4' but also serve to double the torque on the shaft 1. The cam 9 bears down on the cam 10, which in turn exerts a downward force on the shaft 7 at its line of contact with cam surface 11. This force is opposed by the magnetic restraining force applied from the magnetic snap-means of switch 17 through the thrust bearing 18. It will readily be appreciated that if the hoist winding speed increases the cage or frame 37 will likewise speed up and the magnitude of the torque on shaft 1 increases accordingly. However, when the cage is rotating at a speed corresponding to the maximum hoist winding speed consistent with safety, as predetermined by the angular position of the cam 21, the downward force exerted on shaft 7 by the cam will exceed the upward restraining force to bring about the operation of snap-action switch 17. The winding drum brake control circuit will be disconnected at contacts and 26 and consequently the brake (not shown) will be applied to the winding drum to arrest it. The angular position of the cam 21 may be varied at will both during operation of the device such as by driving the cam 21 from the hoist winder and during idle periods thereof and the cam is suitably contoured to enable the hoist speed at which the snapaction switch 17 is to operate to be finely adjusted.

The system of cams and other constituent parts of the present example will now be further described with reference to FIG. 3 of the drawings. The various parts of the device illustrated bear the same designations as in FIG. 1. It will readily be observed that the angular displacement A of the line joining the centres of weights 8 may be adjusted by rotating the cam 21. However, for the device to be etfective, it is essential that the displacement A be less than 90 degrees at all times, otherwise, the device will be rendered completely inoperative due to the absence of torque when the lines of action of the centrifugal forces acting through the weights 8 pass through the central axis of shaft 1 (i.e. when A equals degrees).

The generally elliptical cams 9 and 10 and the concave cam surface 11 co-operates to produce a variable mechanical advantage according to their relative points of contact. The dotted lines 29 and 30 represent the loci of the points of contact between the cams 9 and 10 and the cam 10 and cam surface 11 respectively. When the displacement A is varied by means of the cam 21 the points of contact between cams 9 and 10 and lit) and 11 will move respectively along loci 29 and 30 and thus vary the mechanical advantage of the system. The effect of this is to extend the range of hoist winding speeds over which the switch 17 may be operated (thus rendering the device suitable for use over a considerable range of hoist speeds) by reason of the fact that the downward force transmitted to the shaft 7 when the cage or frame 37 is rotating is determined not only by the displacement A but also by the mechanical advantage of the cam systern, both of which are simultaneously adjusted by rotation of the cam 21.

An alternative system of cams for the device of FIG. 1 is shown in FIG. 4. It comprises a cam 31 formed in two generally elliptical parts, one of which is engaged by a generally elliptical cam 32 carried by shaft 1 and the other of which contacts a cam surface 33 provided by an enlarged head part of shaft 7. The loci of the points of contact between the cam surfaces are indicated by the dotted lines 34 and 35. It will be noted that the cam 31, which corresponds to cam 10 of FIGS. 1 and 3, is loosely carried by the shaft 2, thus enabling the shaft 3 (FIGS. 1 and 3) and its hearings to be dispensed with.

It should be understood that other embodiments of the invention are envisaged in which the cams have different configurations from those shown in the drawings. Moreover, notched cams or suitable gears which mesh may be employed.

The invention thus provides an overspeed protection device, which, by reason of the :fact that the parts effective to produce operation of the snap action switch are stationary with respect to one another (i.e. in the operating direction of said switch) and in continuous contact with the switch and that balanced centrifugal forces exist at the shaft bearings, responds substantially instantaneously to rapid changes in hoist speeds thereby providing efficient protection against overwinding.

What I claim is:

1. An overspeed protection device for use with mine hoists or the like, comprising a shaft means for revolving said shaft about an axis perpendicular to the central axis of said shaft and means for subjecting said shaft as it revolves to a torque dependent on the hoist speed over a predetermined range of speeds, a movable member and means coupling said shaft to said movable member and effective to convert said torque into a force that acts on said movable member in a direction of movement thereof, sna-p means effective in its unoperated condition to exert on said movable member a restraining force equal and opposite to said force transmitted to said movable memher through said coupling means, and a switch responsive to the operation of said snap means, whereby upon the hoist speed reaching a predetermined value, said restraining force will be overcome by the force transmitted by said coupling means to bring about substantially instantaneous operation of said snap means and said switch.

2. An overspeed protection device, for use with mine hoists or the like, comprising a shaft and means for revolving said shaft in a plane containing its central axis at a speed proportional to the hoist speed, at least one pair of weights secured to said shaft at diametrically opposite positions for subjecting said shaft as it revolves to a torque dependent on the hoist speed over a predetermined range of speeds, a movable member and means coupling said shaft to said movable member and efiective to convert said torque into a force that acts on said movable member in a direction of movement thereof, snap means effective in its unoperated condition to exert on said movable member a restraining force equal and 0pposite to said force transmitted to said movable member through said coupling means, and a switch responsive to the operation of said snap means, whereby upon the hoist speed reaching a predetermined value, said restraining force will be overcome by the force transmitted by said coupling means to bring about substantially instantaneous operation of said snap means and said switch.

3. An overspeed protection device, for use with mine hoists or the like, as claimed in claim 2, in which the means for revolving the shaft comprises a rotatable cage carrying bearings which support said shaft, and a driving connection between the hoist winding drum and said cage.

4. An overspeed protection device, for use with mine hoists or the like, comprising a shaft and means for revolving said shaft in a plane containing its central axis including a rotatable cage carrying bearings supporting said shaft, a pair of spaced wheels carried by said shaft and each having a pair of weights secured thereto at diametrically opposite positions for subjecting said shaft as it revolves to a torque dependent on the hoist speed over a predetermined range of speeds, a movable member and means coupling said shaft to said movable member and effective to convert said torque into a force that acts on said movable member in a direction of movement thereof, snap means effective in its unoperated condition to exert on said movable member a restraining force equal and opposite to said force transmitted to said movable member through said coupling means, and a switch responsive to the operation of said snap means, whereby upon the hoist speed reaching a predetermined value said restraining force will be overcome by the force transmitted by said coupling means to bring about substantially instantaneous operation of said snap means and said switch.

5. An overspeed protection device, for use with mine hoists or the like, as claimed in claim 4, comprising a second shaft supported parallel to the first said shaft by bearings carried by the cage, a pair of spaced wheels each having a pair of weights secured thereto at diametrically opposite positions and in driving engagement respectively with the wheels of the first said shaft.

6. An overspeed protection device, for use with mine hoists or the like, as claimed in claim 1, comprising a system of cams coupling the shaft to the movable member, said cams being relatively adjustable and providing a mechanical advantage that varies according to the position of the movable member relative to the shaft.

7. An overspeed protection device, for use with mine hoists or the like, comprising a first shaft and means for subjecting said shaft to a torque dependent on the hoist speed over a predetermined range of speeds, and an axially movable second shaft coupled to said first shaft through a system of cams comprising a first generally elliptical cam secured to said first shaft, a second generally elliptical pivoted cam against which said first cam bears and a concave cam surface provided at one end of said second shaft and engaged by said second cam, said system of cams being effective to convert said torque into a force which acts on said second shaft in its direction of movement, snap means effective in its unoperated condition to exert on said second shaft an axial restraining force equal and opposite to said force transmitted to said second shaft through said system of cams, and a switch responsive to the operation of said sn-ap means, whereby upon the hoist speed reaching a predetermined value, said axial restraining force will be overcome by the force transmitted by said system of cams to bring about substantially instantaneous operation of said snap means and said switch. e

8. An overspeed protection device, for use with mine hoists or the like, comprising a first shaft and means for subjecting said first shaft to a torque dependent on the hoist speed over a predetermined range of speeds, and an axially movable second shaft coupled to said first shaft through a system of cams comprising a first generally elliptical cam secured to said first shaft, a second pivoted cam having two generally elliptical parts inclined to each other, one of said parts being engageable by said first cam, and a concave cam surface provided at one end of said second shaft and engageable by the other part of said second cam, said system of cams being effective to convert said torque into a force which acts on said second shaft in its direction of movement, snap means effective in its unoperated condition to exert on said second shaft an axial restraining force equal and opposite to said force transmitted through said system of cams, and a switch responsive to the operation of said snap means, whereby upon the hoist speed reaching a predetermined value said axial restraining force will be overcome by the force transmitted by said system of cams to bring about substantially instantaneous operation of said snap means and said switch.

9. An overspeed protection device, for use with mine hoists or the like, as claimed in claim 1, in which the snap means comprises co-operating magnetic elements which are magnetically looked together in abutting relationship to provide the restraining force on the movable member.

10. An overspeed protection device, for use with mine hoists or the like, as claimed in claim 1, in which the snap means and the switch are combined in a snap-action electric switch.

11. An overspeed protection device, for use with mine hoists or the like, comprising a first shaft and means for revolving said shaft in a plane containing its central axis at a speed proportional to the hoist speed, means secured to said shaft for subjecting it as it revolves to a torque dependent on the hoist speed over a predetermined range of speeds, an axially movable second shaft and a system of cams coupling said first and second shaft and effective to convert said torque into a force that acts on said second shaft in its direction of movement, snap means comprising co-operating magnetic elements which look with respect to one another to provide an axial restraining force on said second shaft which is equal and opposite to said force transmitted to said second shaft through the system of cams, and a switch responsive to the operation of said snap means, whereby upon the hoist speed reaching a predetermined value, said restraining force will be overcome by the force transmitted by said system of cams to bring about substantially instantaneous operation of said snap means and said switch.

12. An overspeed protection device, for use with mine hoists or the like, as claimed in claim 11, in which the snap means and the switch are combined to form a snapaction electric switch.

13. An overspeed protection device, for use with mine hoists or the like, comprising a first shaft and means for revolving said shaft in a plane containing its central axis at a speed proportional to the hoist speed, means secured to said first shaft for subjecting it as it revolves to a torque dependent on the hoist speed over a predetermined range of speeds, an axially movable second shaft and a system of cams coupling said first and second shafts and effective to convert said torque into a force that acts on said second shaft in its direction of movement, snap means effective to exert on said second shaft an axial restraining force equal and opposite to the force applied to said second shaft through said system of cams, a switch responsive to the operation of said snap means and means for varying the force transmitted by said system of cams for a given hoist speed, whereby upon the hoist speed reaching a value predetermined by adjustment of said varying means said axial restraining force will be overcome by the force transmitted through said system of cams to bring about substantially instantaneous operation of said snap means and said switch.

14. An overspeed protection device, for use with mine hoists or the like, as claimed in claim 13, in which the means for varying the force transmitted by the system of cams comprises a cam follower coupled to the second shaft and co-operable with a suitably contoured rotary cam to provide axial movement of said second shaft.

15. An overspeed protection device, for use with mine hoists or the like, comprising a first shaft and means for revolving said shaft in a plane containing its central axis, a pair of spaced wheels carried by said first shaft each having a pair of weights secured thereto at diametrically opposite positions for subjecting said first shaft as it revolves to a torque dependent on the hoist speed over a predetermined range of speeds, at second shaft supported parallel to said first shaft and arranged to revolve with it, said second shaft having secured to it a pair of spaced wheels in driving engagement respectively with the wheels of said first shaft and each having a pair of weights secured thereto at diametrically opposite positions, an axially movable third shaft and a system of cams coupling said third shaft to said first shaft and effective to convert said torque into a force that acts on said third shaft in its direction of movement, said system of cams comprising a first generally elliptical cam secured to said first shaft, a second generally elliptical cam engaged by said first cam and secured to a fourth shaft supported parallel to the first shaft and adapted to be revolved with it, and a concave cam surface engaged by said second cam and provided at one end of said third shaft, snap means comprising co-operating magnetic elements which lock with respect to each other to provide an axial restraining force on said third shaft equal and opposite to said force applied to said third shaft through said system of cams and a switch 5 combined with said snap means, and a cam follower coupled to said third shaft and co-operable with a suitably contoured rotary cam to provide axial movement of said third shaft whereby to vary the force transmissible to said third shaft from said system of cams for a given hoist speed, whereby upon the hoist speed reaching a value as predetermined by the angular position of said rotary cam said axial restraining force will be overcome by the force transmitted through the system of cams to bring about substantially instantaneous operation of said combined snap means and switch.

16. An overspeed protection device, for use with mine hoists or the like, as claimed in claim 15, in which the first, second and fourth shafts are supported in bearings carried by a rotatable cage, and in which the third shaft is coupled up to said cage so as to be rotated with it about its axis.

17. An overspeed protection device, for use with mine hoists or the like, as claimed in claim 15, comprising dynamic balancing discs having cut-away portions corresponding approximately to the first and second cams and secured to the first and fourth shafts respectively.

References Cited in the file of this patent UNITED STATES PATENTS 2,099,849 Holmes Nov. 23, 1937 2,558,223 Reger June 26, 1951 2,643,871 Warrick June 30, 1953 2,738,968 Fleischel Mar. 20, 1956 2,766,347 Gaylord et a1. Oct. 9, 1956 2,821,590 Maerker Jan. 28, 1958 FOREIGN PATENTS 509,423 Great Britain July 14, 1939

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