US3734240A

US3734240A - Safety lock for portable lift mechanism

Info

Publication number: US3734240A
Application number: US00243775A
Authority: US
Inventors: A Tang
Original assignee: Crown Controls Ltd
Current assignee: Crown Controls Ltd
Priority date: 1972-04-13
Filing date: 1972-04-13
Publication date: 1973-05-22
Anticipated expiration: 1990-05-22

Abstract

A portable lift truck has a vertically movable load receiving carriage which is driven up and down by a power drive mechanism, such as a hydraulic cylinder and chains connecting a cylinder to the lift carriage. In the event of a malfunction of the lift mechanism, such as due to chain breakage or a major hydraulic failure, the lift mechanism is prevented from free falling beyond a predetermined speed. Equally spaced stop lugs on the mast are engaged by an arm on a rotatable stop member which is spring loaded to dump rotation of the stop member when the arm engages the stop lugs. If the relative speed between the stop lugs and the rotatable member substantially exceeds the maximum rate of movement obtainable from the drive mechanism, the spring damping will not react fast enough to prevent an interference lug on the rotatable stop member from jamming into the path of one of the stop lugs, thus locking the lift mechanism against further movement before it achieves any excessive speed.

Description

United States Patent [1 1 Tang [ 1 May 22,1973

[54] SAFETY LOCK FOR PORTABLE LIFT MECHANISM [75] Inventor: Alexander Reuben Tang, Mervue,

Galway, Ireland [73] Assignee: Crown Controls Limited, New

Bremen,Ohio

[22] Filed: Apr. 13, 1972 21 Appl. No.: 243,775

[52] US. Cl ..187/89, 187/9 [51] Int. Cl. ..B66b 5/16 [58] Field of Search ..187/9, 38, 89

[56] References Cited UNITED STATES PATENTS 764,038 7/1904 Carpenter ..l87/89 3,084,766 4/1963 Donaldson ..187/89 3,276,747 10/1966 Zimmerman ..l87/38 Primary ExaminerHarvey C. Homsby Attorney-Lawrence B. Biebel et al.

57 ABSTRACT A portable lift truck has a vertically movable load receiving carriage which is driven up and down by a power drive mechanism, such as a hydraulic cylinder and chains connecting a cylinder to the lift carriage. In the event of a malfunction of the lift mechanism, such as due to chain breakage or a major hydraulic failure, the lift mechanism is prevented from free falling beyond a predetermined speed. Equally spaced stop lugs on the mast are engaged by an arm on a rotatable stop member which is spring loaded to dump rotation of the stop member when the arm engages the stop lugs. If the relative speed between the stop lugs and the rotatable member substantially exceeds the maxirnum rate of movement obtainable from the drive mechanism, the spring damping will not react fast enough to prevent an interference lug on the rotatable stop member from jamming into the path of one of the stop lugs, thus locking the lift mechanism against further movement before it achieves any excessive speed.

3 Claims, 4 Drawing Figures Patented May 22, 1973 SAFETY LOCK FOR PORTABLE LIFT MECHANISM BACKGROUND OF THE INVENTION This invention relates to the lift mechanism of portable lift trucks, particularly the kind having a vertically movable power operated lift carriage having forks or the like for lifting and transporting heavy loads. In the particular embodiment shown, the type of truck illustrated is one in which the operator rides on the vertically movable carriage, however the invention is not limited to that type of truck.

The usual lift mechanism for the carriage, and in some cases for the moving part of a multi-piece telescopic mast, comprises one or more hydraulic cylinders connected through a chain and sprocket mechanism to the lift carriage. In the event of a massive hydraulic failure, such as a burst hose, or in the event of breaking of one or more of the chains, if the carriage has a substantial load and is in its raised position, it can accelerate rapidly and dangerously, dropping or damaging the load and possibly injuring the operator or other persons in the vicinity. This is especially true if the operator is riding on the carriage in the case of the so-called stock picker truck. There is a need for some automatically operable safety mechanis which is simple, sure in its operation, and capable of functioning automatically without attention or careful regular maintenance.

SUMMARY OF THE INVENTION In accordance with the invention the carriage of a lift truck has a rotatable spring loaded stop member mounted on a supporting shaft which is carried on the carriage, and an arm extends from the stop member into a path along one of the parts of the mast. Regularly spaced stop lugs extend from this mast part, thus the arm is in position to strike each of the stop lugs during motion of the carriage on the mast.

An interfering lug is also provided on the rotatable member, at an angular position such that normally it is withdrawn from the path of the stop lugs. The rotatable motion of the stop member is damped by a spring device which raises the arm into position behind a stop lug which the arm has engaged, and around which the arm is moving as the carriage rises or lowers at a normal rate. If the motion of the carriage and/or the lift mechanism substantially exceeds the maximum rate obtainable from the drive mechanism, the operation of the spring system is such that the unusual acceleration motion of the rotatable stop member will cause the interference lug to swing between the stop lugs and engage the next one before the stop member can rotate back out of the way. This locks the lift mechanism against further movement. During normal operation of the lift mechanism, the interfering lug is returned out of the path of the stop lugs and does not engage them, but the interference occurs automatically if the rate of relative movement between the appropriate lift mechanism parts substantially exceeds the normal rate achieved with the drive mechanism.

The primary object of the invention, therefore, is to provide a novel, simple, and reliable safety device for the lift mechanism of portable lift trucks and the like, as hereinafter described.

Other objects and advantages of the invention will be apparent from the following description, the accompanying drawings and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side view illustrating a typical portable lift truck to which the present invention is applied;

FIG. 2 is a fragmentary view with parts shown in section, illustrating the novel safety stop mechanism on the carriage of a stock picker type of lift truck, having a telescopic mast arrangement;

FIG. 3 is a view on the same scale, taken from the right of FIG. 2, with parts broken away to illustrate the safety stop mechanism; and

FIG. 4 is a fragmentary view similar to FIG. 2, but on a slightly large scale, showing the manner in which the rotatable stop member acts to prevent further relative movement of the lift mechanism.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring first to FIG. 1, which illustrates a portable lift truck of the so-called stock picker type, the body of the truck is shown at 10, and includes, for example, suitable storage space for electric storage batteries which provide motive power for a drive motor that in turn is connected to the rear steering and traction wheel 12. Details of such a drive are well known. Forwardly of the body there are outriggers 14 carrying front support wheels 50, and a mast structure 18 extends vertically from the front edge of the body, generally centrally of the truck. In a typical embodiment, the mast (see FIG. 2) includes stationary channel members 20, vertically movable channel members 22 which are guided by rollers 23 to run vertically along the stationary channels 20. The carriage 25 is mounted through further rollers 26 to run vertically within the movable channels 22. The load carrying forks 28 project from the carriage, generally above the outriggers 14 and provide support for loads to be lifted and moved.

In the particular embodiment shown, the 'operator stands on a platform 30 which is supported as part of the carriage adjacent to the mast, and suitable controls (not shown) are provided for operation of the truck from this position.

The drive mechanism for the lift is typically a hydraulic cylinder located between the mast channels, and powered through an electrically driven hydraulic pump which derives its power from the storage batteries. Details of these parts are not shown since they are conventional. The hydraulic cylinder is connected through chains or the like 32 to the carriage 25, and through suitable threading arrangements of the chain over sprockets, to the telescopic movable mast channels 22 (when these are used). Thus, extension and retraction of the hydraulic cylinder produces raising and lowering movement of the carriage 25.

The rate of operation of this lifting device is normally controlled by the rate of movement of the hydraulic cylinder, but in the event of some breakage in the drive mechanism connections, such as breaking of one of the chains, the carriage could free fall rapidly, particularly if there is a substantial load on the forks. To prevent this, an automatically operating safety device is provided by the invention.

This device consists of side brackets 35 fastened to the carriage, and having a sturdy pivot pin 36 mounted between them. On this pin, preferably carried on a sleeve bushing 37, is a rotatable stop member 40 having an arm 42 which extends into a path along one of the channels 22. On this channel there are regularly spaced outwardly extending stop lugs 45 which project along the path of the arm 42. Angularly spaced from the arm 42, also extending from the member 40, is an-interfering lug 48 which is normally out of the path of the stop lugs 45. A U-shaped guide rod 50 extends around the rotatable stop member 40, being suitable bolted to the bracket, and an ear member 52, fastened to the member 40, slides on the rod 50. Coil springs 54 and 55 surround the rod and engage opposite sides of the ear 52, tending to damp the rotating motion of the member 40 introduced by the arm 42 striking one of the stop lugs 45.

As the carriage lowers relative to the channels 22, the arm 42 will engage one of the lugs 45, and the member 40 will rotate generally clockwise, with the stop lug passing between the arm 42 and the interfering lug 48. The spring mechanism returns the swinging or rotating member 40 as soon as the arm 42 clears the stop lug, thus causing the interfering lug 38 to move away from the path of the stop lugs, and the arm strikes the next lug, etc. This continues so long as the relative movement between the parts does not exceed that rate normally achieved by the lift drive mechanism.

However, if the carriage should accelerate due to a lift mechanism failure, the spring rate of the return spring device is such that it will not function rapidly enough to withdraw the interfering lug in a timely way, and it will engage the next stop lug 45, the position of the parts being as shown in FIG. 4. The member 40 is held in this position due to the fact that stop ears 55, which project as integral extensions of the member 40, engage a stop surface 57 on the brackets. These stops prevent further clockwise motion of the member 40 and the interfering lug remains in engagement with the stop lug 45, immediately halting the motion of the carriage.

It will be readily apparent to those skilled in the art that this safety mechanism is of a simple and relatively inexpensive construction, and that it functions automatically if the carriage achieves a speed in excess of its normal lowering speed. Obviously, the arrangement of the parts could be reversed or otherwise modified and the stop lugs could be provided on the stationary mast channels 20 when the telescopic mast members 22 are not used.

I claim:

1. In a lift truck having a lift mechanism including a mast with a vertically movable power operated carriage for lifting and lowering loads, and a drive mechanism connected to raise and lower the carriage, an improved safety apparatus comprising a series of stop lugs spaced equally by a predetermined amount and a spring loaded stop member with an arm arranged to move into engagement with said stop lugs, said stop lugs and said stop member being mounted on relatively movable parts of the lift mechanism such that said arm engages and releases from said stop lugs in succession during raising and lowering of the mechanism, said stop member also having an interfering lug normally out of the path of said stop lugs, and a spring device retarding the motion of said stop member in response to engagement of said arm and said stop lugs whereby the interfering lug will clear said stop lugs only if the relative movement between said arm and said stop lugs does not substantially exceed the maximum rate of movement attainable from said drive mechanism.

2. Safety apparatus for a lift truck, as defined in claim 1, wherein said stop member is rotatably mounted and said arm swings into and out of the path of said stop lugs.

3. Safety apparatus as defined in claim 1 wherein said interfering lug is arranged to jam against a stop lug in response to excessive carriage speed, and a stop device operates to hold the interfering lug in the jammed position.