GB2146397A - Automatic brake mechanism - Google Patents

Abstract

The mechanism, primarily utilized in a mobile hoist, includes a boss 32 welded to a centrifugal lever(s) 12 mounted for pivotal movement on a rotating member, specifically hoist cable drum 10; an adjustable carrier 19 has rollers 20 set to contact boss 32 and is connected to a lever 21, which itself is connected to an oscillating lever 24 fitted at both ends with respective springs 26 and swivel links 27 operable on a brake lever 30 to apply a brake e.g. a band brake. When speed of rotating member 10 exceeds a predetermined maximum the centrifugal force acting on lever(s) 12 will move lever(s) 12 outwards to cause the boss 32 to run eccentric as in Figure 3 - this will move carrier 19 to move lever 21 to cause brake application. The lever 21 is moved up and down by up and down movement of carrier 19 and side to side carrier movement if required. Positioning rods 28 have nuts 29 adjustable to control length of time brake is applied per revolution. <IMAGE>

Description

SPECIFICATION Automatic brake This invention relates to an Automatic Brake mechanism intended primarily but not necessarily exclusively for application to the cable winding drums of hoists such as are employed on building sites.

In mobile hoists, such for example of the kind described in prior patent specification No. 905928 it is the practice to effect the lifting and lowering of a load platform through the medium of a hoist rope or cable which is wound on to and off a drum, the latter being driven from a suitable prime mover through the intermediary of a clutch. Commonly the operation of such hoists is controlled by a manually operable control lever which is moveable between one limiting position wherein the clutch is disengaged and a brake is effectively applied to the drum and a secondary limiting position wherein the brake is released and the clutch is engaged. At an intermediate position between the aforesaid limiting positions of the control lever there is a neutral position wherein the brake is released and the clutch is not engaged.With non-skilled labour often employed on building sites it can happen that when the load platform is in an elevated position and the operator moves the lever to release the brake and to allow lowering of the said platform, he will move said lever into the neutral position so that the platform will be free to descend under the action of gravity. If the operator is not sufficiently skilled in the use of hoists to control the speed of the descending platform by means of the brake the load platform could rush down at high speed which could be the cause of accident and damage.

Some makes of hoists employ two sets of gearing, one set runs from the engine to the drum via a clutch and is used for lifting the platform, the other set runs from the drum to the engine via a "Sprag" clutch and is used when the platform is being lowered. A centrifugal brake is also fitted to the engine crankshaft to prevent overspeed of the engine when the hoist is being used for lowering materials. This arrangement often called a 'Drive up and drive down winch unit' is a relatively expensive unit.

It is the chief object of the present invention to evolve a mechanism which will automatically apply the brake on the hoist winding drum in a manner which limits the descending speed of the load platform.

In accordance with the invention it is proposed to provide the following: A hollow boss projecting from a lever for mounting on a rotating member to be actuated when said member exceeds a predetermined speed, such mechanism comprising of a single or compound lever arrangement mounted on the rotating member for pivotal movement about a fixed point on the centre line of the axis of rotation of such member, the position of the fixed point on the rotating member is such that when the lever welded to the hollow boss or a lever of a compound arrangement is held against a fixed stop on the rotating member the outside of the hollow boss will run true and concentric with the rotating member.

A restraining element effective to maintaining said lever or levers in an inoperative position against the fixed stop during such times as said member is rotating at or below the predetermined maximum speed. The arrangement being such that when the speed of the rotating member exceeds the predetermined maximum the centrifugal force acting on the lever or levers will overcome the power of the restraining element and cause the lever or levers to move outwards this in turn will cause the hollow boss to run eccentric in relation to the axis of the rotating member, the amount of eccentricity will vary according to the speed of the rotating member and will be limited by a stop on the said member.

An adjustable carrier fitted with four rollers which run on the outside of the hollow boss, the carrier is connected for pivotal movement to a horizontal lever which in turn is pivotally connected to a post welded to the framework of the winch unit. The carrier is moved up and down and from side to side when the rotating member is revolved with the hollow boss in an eccentric position. The horizontal lever only moves in an up and down direction.

The opposite end of the horizontal lever connection to the post is connected by means of a short pivotable bar to the end of an oscillating lever mounted on another post welded to the framework of the winch unit.

When the end of the horizontal lever moves down it pulls the connected end of the oscillating lever down, the other end moves up. When the end of the horizontal lever moves up it pushes the connected end of the oscillating lever up, the other end moves down.

Two tension springs are provided fitted with swivel links and threaded rods and nuts for positional adjustment. One end of each spring is attached to each end of the oscillating lever, the other ends via the swivel links and positioning rods are connected to an L shaped lever.

One end of the L shaped lever is pivotably connected to a rigid member of the winch unit frame-work, the other end rests on or is hingedly connected to the brake. When the oscillating lever is moved up and down by the horizontal lever the brake is applied and released in an on and off manner via the springs. The length of time between the brake being applied and released can be adjusted by means of the positioning rods and nuts.

The arrangement described and shown in the drawings uses only the up and down movement for applying the brake. The brake is applied and released twice during each revolution of the rotating member. If required the mechanism could be arranged to use the side to side movement of the carrier as well as the up and down movement, in this case the brake would be applied and released four times during each revolution of the rotating member.

The arrangement described and shown on the drawings is for a rotating member and a band brake, the mechanism could be arranged for a rotating member coupled to any type of brake.

When the above mechanism is mounted on a smail rotating member or drum compound levers are used to obtain the necessary centrifugal force to overcome the power of the restraining element.

For a better understanding of the invention reference will now be made to the accompanying drawings wherein: Figure 1 shows a perspective drawing of an automatic brake mechanism in the inoperative position.

Figure 2 A diagrammatic drawing of the layout of a manual operated brake.

Figure 3 A diagrammatic drawing of the automatic brake in the operative position.

Figure 4 a diagrammatic drawing of the adjustable carrier.

Referring now to the drawings.

10 denotes an end plate or disc of a winch drum. It will be assumed that the drum is incorporated in a hoist and that when it is rotating in the direction of arrow A the cable will be unwound from the drum thereby to effect lowering of the hoist platform.

The hollow Boss 32 which has an internal diameter of a size that will go over any thrust bearing mounted on the drum shaft plus room to move from the inoperative position (Figure 1) to the maximum operative position (Figure 3) without rubbing on the shaft 18 or bearing is welded to the centrifugal lever 12. The said lever with the hollow boss attached is mounted for pivotable movement about a fixed point 38 on the centre line of the axis of rotation of the drum. The position of the fixed point 38 on the drum is such that when the centrifugal lever 12 is held against the fixed stop 14 which is welded to the end plate 10 of the drum the outside of the hollow boss will run true and concentric with the revolving drum.

One end of the restraining spring 15 is attached to the centrifugal lever by means of a hook 13 which is welded to the said lever, the other end is secured to the end plate 10 of the drum by means of a bolt screwed into any one of the tapped holes 17. The pull of the spring 15 which holds the centrifugal lever against the stop 14 can be increased or decreased by means of the tapped holes.

The power of the pull of the spring 15 which holds the centrifugal lever 12 against the stop 14 predetermines the speed at which the descending load platform operates the automatic brake (via the speed of the revolving drum). The arrangement being such that when the speed of the revolving drum exceeds the predetermined maximum the centrifugal force acting on the lever 12 or levers will overcome the restraining pull of the spring 15 and cause the lever 12 or levers to move outwards, this in turn will cause the hollow boss 32 to run eccentric in relation to the axis of the revolving drum, the maximum amount of eccentricity will be limited by the stop 11 which is welded at a fixed point to the end plate 10 of the drum, see Figure 3.

Figure 4 shows the details of the adjustable carrier 19. The carrier is made in two sections to facilitate the fitting to the hollow boss 32. Means of adjustment are provided by way of the two tapped holes 41 and the two clearance holes 42 to enable the 4 rollers 20 to be set in close contact with the hollow boss 32.

The carrier 19 is connected for pivotal movement to the horizontal lever 21 this in turn is connected for pivotable movement to the fixed post 22. When the speed of the revolving drum exceeds the maximum pre-set speed the centrifugal force acting on the lever 12 will move the hollow boss 32 into the eccentric or operating position see Figure 3, this will cause the carrier 19 which runs by means of the 4 rollers on the hollow boss to move up and down and from side to side. The up and down movement will in turn cause the horizontal lever 21 to move up and down.

The short pivotable bar 23 is connected from the end of the horizontal lever 21 to the end of the oscillating lever 24. The oscillating lever is mounted for pivotable movement on the fixed post 39 which is welded to the winch unit base frame. The up and down movement of the horizontal lever 21 is transferred to the oscillating lever 24 by the bar 23.

The two tension springs 26 fitted with the swivel links 27 and the threaded positioning rods and nuts 28 are pivotably connected by the spring end to the ends of the oscillating lever 24 they are then connected by means of the positioning rods and nuts to the mounting Plate 29 which is welded to the L shaped brake lever 30.

The L shaped brake lever 30 is pivotably connected on the long side to a rigid member of the winch unit frame or to a rigid upright post welded to the base frame, the short side which carries the mounting plate 29 has a short return lip which rests on a lug welded to the brake band 31. The springs 26 are set in relation to the L shaped brake lever 30 and the oscillating lever 24 by means of the positioning rods and nuts 28.

The setting is as follows:- It is assumed that the mechanism has been correctly assembled as shown in Figures 1 and 3 and that the centrifugal lever 12 is held against the fixed stop 14 by means of the restraining spring 15 so that the hollow boss 32 runs concentric with the drum when turned by hand also that the carrier 19 has been adjusted so that the 4 rollers 20 run without any play on the outside of the hollow boss 32.

The brake lever welded to the brake weight 37 Figure 2 is raised and temporary held or fixed in the neutral position so that neither the clutch or brake is engaged, the drum is now free to be turned by hand.

The nuts of the positioning rods 28 on the underside of the mounting plate 29 are slacked off by screwing downwards, the top nuts are then screwed up or down until the tension springs and swivel links hang in a straight line from the L shaped lever 30 to the oscillating lever 24 see Figures 1 and 3. The drum should be just free to turn by hand after this adjustment has been made. The nuts on the underside of the mounting plate are then screwed up to lock the positioning rods in the adjusted position.

The above setting gives the maximum length of time the brake is applied per revolution of the drum when the hollow boss 32 is running eccentric in relation to the axis of the drum see Figure 3.

The length of time the brake is applied per revolution of the drum and the pressure at which the tensions springs 26 apply the brake can be decreased by lowering the positions of the positioning rods.

The swivel links 27 and the tension springs 26 will fold as shown in Figure 3 to accommodate this adjustment. This folding arrangement will also accommodate the upward movements of the oscillating lever 24.

Claims (12)

1. A automatic brake mechanism comprising, a boss welded to a centrifugally operated lever mounted for pivotable movement on a rotating member, adjustable restraining means for holding the centrifugal lever at low speeds against a fixed stop, a adjustable carrier fitted with rollers being adapted to fit over the boss, means of connecting the carrier to a pivotable lever mounted on a rigid member of the winch unit framework, means of connecting the pivotable lever to a oscillating lever, a oscillating lever fitted at both ends with springs, swivel links and adjustable rods adapted for connection to a pivotable brake operating lever.

2. A automatic brake mechanism as claimed in claim 1 wherein the position of the fixed bolt securing the pivotable centrifugal lever to a rotating member is such that when the said lever is held against a fixed stop on the rotating member the boss welded to the said lever runs true and concentric with the axis of the rotating member.

3. A automatic brake mechanism as claimed in claim 1 - 2 wherein when the revolving speed of the rotating member causes the centrifugal force acting on the centrifugally operated lever to overcome the preset pull of the restraining means, the said lever with the said boss moves outwards causing the said boss to run eccentric with the axis of the rotating member.

4. A automatic brake mechanism as claimed in claim 1 wherein the adjustable carrier is fitted with rollers which run on the boss welded to the centrifugally operated lever.

5. A automatic brake mechanism as claimed in claim 1 - 4 wherein a pivotable lever connected to the adjustable carrier which runs on the boss welded to the centrifugally operated lever is stationary when the said boss is revolving concentric with the axis of the rotating member, the pivotable lever moves up and down when the said boss is revolving eccentric with the axis of the revolving member.

6. A automatic brake mechanism as claimed in claim 1 - 5 wherein the pivotable lever which moves up and down is connected by means of a pivotable bar to one end of a oscillating lever mounted for oscillating movement on a post welded to the winch unit framework.

7. A automatic brake mechanism as claimed in claim 1 - 6 wherein both ends of the oscillating lever are connected to a pivotable brake operating lever by means of tension springs, swivel links and adjustable threaded rods and nuts.

8. A automatic brake mechanism as claimed in claim 1 - 7 wherein the pull on the pivotable brake operating lever can be increased or decreased by means of stronger or weaker tension springs.

9. A automatic brake mechanism as claimed in claim 1 - 7 wherein the swivel links fold in operation to accommodate the upward movement of the ends of the oscillating lever.

10. Aautomatic brake mechanism as claimed in claim 1 - 7 wherein the position of the pivotable brake operating lever in relation to the oscillating lever can be adjusted by means of the adjustable threaded rods and nuts.

11. A automatic brake mechanism as claimed in claim 1 - 10 wherein a brake is applied in an on and off manner to a rotating member when the boss welded to the centrifugally operated lever is revolving in a eccentric position.

12. A automatic brake mechanism substantially as described herein with reference to Figures 1 - 4 of the accompanying drawings.