AU725451B2

AU725451B2 - Safety brake for column hoists

Info

Publication number: AU725451B2
Application number: AU52746/98A
Authority: AU
Inventors: William K K Lai; John Kerry Wells
Original assignee: ENDUREQUIP Pty Ltd
Current assignee: ENDUREQUIP Pty Ltd
Priority date: 1997-01-28
Filing date: 1998-01-28
Publication date: 2000-10-12
Anticipated expiration: 2018-01-28
Also published as: AU5274698A

Description

P/00/011 Regulation 3.2

AUSTRALIA

Patents Act 1990 a a a. a

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT Invention Title: "SAFETY BRAKE FOR COLUMN HOISTS" The following statement is a full description of this invention, including the best method of performing it known to us: r 2 FIELD OF THE INVENTION This invention relates to a column hoist suitable for lifting vehicles or other loads. The invention is particularly concerned with the provision of a safety system for such hoists.

BACKGROUND TO THE INVENTION Existing column hoists have been developed over a number of years, typically for the elevation of vehicles for maintenance or repair purposes. Column hoists alleviate the requirement for inspection pits which are dangerous, accumulate debris and severely limit useable floor space in a workshop or like premises. They allow greater versatility of use of floor space and are usually supported by rollers or wheels thereby providing portability and ease of storage. Furthermore column hoists may be deployed anywhere in the field provided a suitable level surface 5 is available, thereby offsetting the cost and inconvenience of transporting .e a disabled vehicle to a workshop in order to effect repairs.

S

One known type of column hoist, described in International S Patent Application No. PCT/AU 96/00104, comprises a pair of upright columns from which is cantilevered a lifting carriage. A screw threaded shaft extends downwardly between the columns, which shaft is suspended from a thrust bearing mounted atop the columns. The shaft supports the carriage via recirculating ball bearing assemblies. The ball bearing assemblies effect vertical movement of the lifting carriage up or down when the shaft is rotated in respective directions about its longitudinal axis by drive means. The type of hoist, in which rotation of a screw threaded shaft effects raising or lowering of a lifting carriage, is hereinafter referred to as a screw driven column hoist.

Another variant of screw driven column hoist uses a shaft having a square shaped helical thread thereon (commonly referred to as an "acme" thread) to which is coupled a travelling nut which in turn supports a lifting carriage. The threaded shaft is rotatably mounted 3 adjacent upper and/or lower ends of support columns and is rotated by drive means, typically in the form of a motor and gearbox combination.

Column hoists allow personnel to work underneath a vehicle elevated above the ground and supported on the lifting carriage.

It is therefore highly desirable for safety reasons to ensure there is no possibility of the lifting carriage inadvertently dropping for example if the drive means for rotating the shaft fails. Such a failure, could allow the shaft to rotate freely permitting the associated ball bearing assemblies or travelling nuts to descend in an uncontrolled fashion.

Whilst the column hoist described in International Patent Application No. PCT/AU 96/00104 describes the use of dual bearing assemblies for providing a safety back-up system should one of the bearing assemblies fail, the system does not prevent free rotation of the .:*drive shaft in the event of a failure associated with the shaft mounting or 15 drive means.

OBJECT OF THE INVENTION It is an object of the present invention to provide a safety brake apparatus for a column hoist which ameliorates or overcomes at least some of the problems associated with prior art screw driven column hoists.

It is a secondary object of this invention to provide a screw driven column hoist incorporating a safety brake apparatus which reduces the risks associated with a failure associated with the drive shaft.

Further objects will be evident from the following description.

DISCLOSURE OF THE INVENTION In one form, although it need not be the only or indeed the broadest form, the invention resides in a safety brake apparatus for a column hoist including at least one upright column, an upright threaded 4 shaft rotatably supported adjacent one end thereof adjacent an upper end of the column, drive means coupled to the shaft for selective rotation thereof, a lifting carriage mounted to the column to allow movement of the carriage therealong and at least one load bearing assembly operatively coupled to the shaft for movement therealong whereby selective rotation of the shaft causes selective movement of the carriage along an upright path; wherein said safety brake apparatus comprises: brake rotor means for operative coupling with an opposite end of the shaft adjacent a lower end thereof and rotatable therewith; brake stator means surrounding the brake rotor means; mounting means for restraining the brake stator means against rotation relative to said column; wherein in use said brake rotor means engages with the brake stator means in response to a pre-determined rotational speed of the S15 shaft to restrict the rotational speed of said shaft.

Suitably said brake rotor means is adapted for at least partial rotation relative to said shaft.

S. Preferably the brake rotor means includes two more brake members resiliently retained about the opposite end of said shaft.

20 Suitably, said two or more brake members are resiliently ooooo biassed against radial movement by resilient biassing means.

The resilient biassing means is adapted to retain said two or more brake members in a retracted position below a predetermined value of centripetal force applied to said brake members when said shaft rotates.

Preferably said two or more brake members each include an inner cam surface engageable on a respective one or two or more shaft cam surfaces associated with the lower end of said shaft in use to urge said two or more brake members radially into operative engagement with said brake stator means.

The two or more brake members each may include an inner cam surface configured such that in use said brake members are urged into engagement with said brake stator means when the direction of rotation of said shaft corresponds to descent of said lifting carriage.

If required said brake members may include inwardly facing abutments in use engageable with said shaft to resist radial movement of said brake shoes when the direction of rotation of said shaft corresponds to elevation of said lifting carriage.

The brake stator means suitably comprises a cylindrical surface engageable by said brake rotor means.

Alternatively said brake rotor means may comprise one or more radially extendable members engageable with one or more abutment surfaces associated with said brake stator means.

If required the brake rotor means may comprise one or 15 more radially extendable lugs or pins.

.oo Suitably the one or more abutment surfaces associated with ooo the brake stator may comprise apertures recesses or projections in use ,alignable with said radially extendable lugs or pins.

Suitably said mounting means is adapted to permit in use at least limited lateral movement of said brake stator means relative to said column.

o9 BRIEF DETAILS OF THE DRAWINGS To assist in understanding the invention preferred embodiments will now be described with reference to the following figures in which FIG 1 is a part cross sectioned front view of a hoist incorporating an embodiment of the safety brake apparatus according to the invention; FIG 2 is a left side view of FIG 1; FIG 3 is a cross sectional top plan view of FIG 1 when viewed in the direction AA; 6 FIG 4 is an enlarged part cross sectioned front view of the safety brake apparatus; FIG 5 is an enlarged cross sectional top plan view of the safety brake apparatus of FIG 4 in a disengaged state; FIG 6 is an enlarged cross sectional view of the safety brake apparatus of FIGS 4 and 5 in an engaged state.

DETAILED DESCRIPTION OF THE DRAWINGS Referring to FIGS 1, 2 and 3 there is illustrated a column hoist 10 having a pair of upright spaced columns 11, 12 interconnected at their upper ends by a plate 13. For aesthetic reasons cover plates 13a, 13b are mounted to upper ends of columns 11, 12. The lower ends of columns 11, 12 are connected to a base 14 comprising a pair of parallel extending feet 15, 16 attached to respective ends of a connecting 5 member 17. Further, rollers 18 are rotatably mounted at the free ends of feet 15, 16.

Two pneumatic wheels 19 are rotatably mounted to a wheel mounting 20 which is pivotally attached to a support frame 21 to allow for steering of wheels 19. The support frame 21 is attached adjacent the 20 lower ends of columns 11, 12 and a handle 22 is used to steer hoist o=ooo when it is being transported on rollers 18 and wheels 19.

As shown specifically in FIG 2, wheels 19 are pressurised such that when hoist 10 supports a load, wheels 19 are slightly flattened resulting in two underside plates 22 associated with base 14 contacting a ground surface 23 to stabilize hoist 10 under load.

A lifting carriage 24 is slidably cantilevered on columns 11, 12 to allow vertical movement of carriage 24 along columns 11, 12.

Lifting carriage 24 includes a pair of parallel spaced lifting arms mounted to opposite ends of a transverse member 26. A pair of spaced arms 27 incline upwardly from member 26 between columns 11, 12 to a support strut 26a bridging the upper ends of arms Rotatably mounted to lifting carriage 24 is a first pair of rollers 28 each of which abut a respective first bearing plate pair 29 mounted on opposite surfaces of column 11. Similarly there is a second pair of rollers 30 which abut a respective second bearing plate pair 31 mounted on opposite surfaces of column 12. Each roller of pairs 28, has a respective annular shoulder 28a, 30a which abuts a corresponding edge of plates 29 or 31. Also mounted to lifting carriage 24 are two abutment members 32 which are in sliding contact with a respective one of inwardly facing opposed surfaces 33, 34 of columns 11, 12.

Mounted to the upper end of hoist 10 is a drive means in the form of a gearbox 42 and motor 43 operatively coupled to drive shaft 37. The coupling may be effected by a keyway provided in the shaft 37 which keyway cooperates with an associated key in a manner apparent to a person skilled in the art. The drive shaft 37 is rotatably mounted to 5 a bearing 35 on plate 13 adjacent the drive means. The shaft 37 is suspended in tension from bearing 35 to alleviate problems associated with bowing of the shaft under load.

~To further reduce or alleviate the likelihood of shaft 37 bowing, bearing 35 is self centering and rollers 28, 30 and abutment 20 members 32 restrict lifting carriage 24 from moving laterally with respect ooo.o) o *to the rotational axis of shaft 37. A bearing cover arrangement 39 on the plate 13 covers and protects the bearing 35 mounted on the plate.

self centering coupling 40 between a first recirculating ball bearing assembly 38a and lifting carriage 24 further alleviates or reduces the likelihood of bowing under load. The shaft 37 includes a helically threaded portion which cooperates with the recirculating ball assembly 38a. In use, when power is supplied to motor 43, shaft 37 selectively rotates about its longitudinal axis and causes lifting carriage 24 to be raised or lowered. A second ball bearing assembly 38b is provided as a safety back up arrangement in case first ball bearing assembly 38a should fail.

Mounted at the lower end of the shaft 37 is a safety brake apparatus 45 which restrains the free rotation of the shaft above a predetermined speed. Details of the safety brake apparatus are described in detail with reference to FIGS 4, 5 and 6.

FIGS 4, 5 and 6 show the safety brake apparatus mounted in relation to the column hoist in the foregoing drawings. The shaft 37 includes a tongue portion 37a machined on a lower end thereof, which tongue portion 37a carries brake members in the form of a pair of arcuate brake shoes 46. The brake shoes 46 are retained on shaft 37 by a retaining plate 37b secured to the shaft by grub screws 37c. The brake shoes are retained circumferentially around the tongue portion by resilient biassing means in the form of a pair of springs 47 extending between respective lugs 48 located proximate the opposed ends of each brake shoe 46.

A floating brake drum assembly 50 comprises a base S°portion 51 and a upstanding flange portion 52. The pair of brake shoes 46 are housed within the brake drum assembly 50, which has an internal **circumferential wall 50a for frictional engagement with the shoes. The assembly rests upon the connecting member 17 via a thrust ring 53 20 disposed on a bottom surface of the base portion 51.

ooooo A locating ring 54, which encircles drive shaft 37, is disposed near the top of the brake drum assembly within the upstanding S. flange 52. The locating ring 54 is arranged such that brake shoes 46 are maintained in substantially coaxial relation with the internal circumferential wall of the brake drum assembly. The thrust ring 53 and locating ring 54 are typically constructed of a low friction material such as nylon or the like. The base portion 51 includes a pair of lateral projections 51a defining respective apertures 51b.

The safety brake apparatus 45 further includes a pair of reaction plates 55 which are each anchored to the connecting member 17 by fixing means in the form of bolts 56. Each reaction plate is located 9 over a cooperating lateral projection 51a of the brake drum base portion 51. The reaction plates 55 include respective stop pins 57 which are arranged to extend through the apertures 51b in the base portion 51.

The stop pins 57 are smaller in circumference than the diameter of the apertures 51b such that the brake drum assembly floats laterally with respect to the connecting member 17. According, the drive shaft 37, which carries the brake shoes 46 and slidably engages the locating ring 54, is similarly permitted to float. This arrangement seeks to alleviate any difficulties, such as bowing of the shaft, associated with journalling both ends of the drive shaft 37 in bearings, as discussed above.

With particular reference to FIG 5, the brake shoes 46 each include an internal cam surface having a gradually decreasing radius extending from a first end 46a to a step providing an abutment at a 15 second end 46b. The shaft 37 in the embodiment has been machined .i across two chords of its cross section, thereby forming a tongue portion 37a having a generally rectangular cross section with arcuate cam faces.

The brake shoes 46 are retained in opposing relation on the tongue portion 37a by the springs 47.

20 The tongue portion 37a of the drive shaft is disposed .:.oo between the internal cam surface near the first end of one brake shoe and the step in the second end of an opposing brake shoe, whereby the arcuate cam faces of the tongue portion cooperate with the internal cam •o surfaces of the brake shoes 46.

In normal operation, the tongue portion 37a abuts the respective steps in the brake shoes as the shaft 37 rotates clockwise to effect raising of the lifting carriage 24 and thereby resists radially outward thrust on the brake shoes. Whilst during lowering of the lifting carriage, the shaft 37 rotates counter clockwise and (below a predetermined speed) the springs 47 retain the brake shoes 46 in a retracted position on the tongue portion of the shaft.

In contrast, if the shaft exceeds a predetermined rotational speed (determined in accordance with the rated lifting capacity of the column hoist), such as might occur if the motor 43 or gearbox 42 or more likely the key coupling the gearbox 42 to the shaft 37 failed, the inertial centrifugal force resulting from rotation of the brake shoes 46 would exceed the opposing force supplied by the springs 47. Accordingly the brake shoes would gradually move apart under the influence of the net force and the tongue portion 37a of the shaft is allowed to rotate relative to the shoes 46. In particular, the arcuate cam faces of the tongue portion 37a travel counter clockwise along the internal cam surfaces of the brake shoes, which surfaces are characterised by a gradually decreasing radius.

o. This relative rotation of tongue portion 37a and internal o.o.

~surfaces causes the external frictional surfaces 49 of the brake shoes 46 to contact the internal circumferential wall 50a of the brake drum assembly 50, thereby decelerating the drive shaft 37. It will be appreciated that as the brake shoes contact the brake drum assembly, the stop pins 57 extending through the apertures 51b provided in the lateral protections 51a of the base portion 51, will allow only a small relative rotation between the brake drum assembly 50 and the connecting 999999 member 17. Accordingly the rate of descent of the lifting carriage will be reduced or arrested.

*:Throughout the specification the aim has been to describe the preferred embodiments of the invention without limiting the invention to any one embodiment or specific collection of features.

Claims

1. A safety brake apparatus for a column hoist including at least one upright column, an upright threaded shaft rotatably supported adjacent one end thereof adjacent an upper end of the column, drive means coupled to the shaft for selective rotation thereof, a lifting carriage mounted to the column to allow movement of the carriage therealong and at least one load bearing assembly operatively coupled to the shaft for movement therealong whereby selective rotation of the shaft causes selective movement of the carriage along an upright path; wherein said safety brake apparatus comprises: brake rotor means for operative coupling with an opposite end of the shaft adjacent a lower end thereof and rotatable therewith; brake stator means surrounding the brake rotor means; 15 mounting means for restraining the brake stator means against rotation relative to said column; wherein in use said brake rotor means engages with the brake stator means in response to a pre-determined rotational speed of the ~shaft to restrict the rotational speed of said shaft. 20

2. The safety brake apparatus as claimed in claim 1 wherein ooooo the brake rotor means is adapted for at least partial rotation relative to said shaft.

3. The safety brake apparatus as claimed in either claim 1 or claim 2 wherein the brake rotor means includes two more brake members resiliently retained about the opposite end of said shaft.

4. The safety brake apparatus as claimed in claim 3 wherein said two or more brake members are resiliently biassed against radial movement by resilient biassing means.

The safety brake apparatus as claimed in claim 4 wherein the resilient biassing means is adapted to retain said two or more brake members in a retracted position below a predetermined value of centripetal force applied to said brake members when said shaft rotates.

6. The safety brake apparatus as claimed in any one of claims 3 to 5 wherein said two or more brake members each include an inner cam surface engageable on a respective one or two or more shaft cam surfaces associated with the lower end of said shaft in use to urge said two or more brake members radially into operative engagement with said brake stator means.

7. The safety brake apparatus as claimed in any one of claims 3 to 6 wherein the two or more brake members each may include an inner cam surface configured such that in use said brake members are urged into engagement with said brake stator means when the direction of rotation of said shaft corresponds to descent of said lifting carriage.

8. The safety brake apparatus as claimed in any one of claims i 15 3 to 7 wherein said brake members include inwardly facing abutments in use engageable with said shaft to resist radial movement of said brake shoes when the direction of rotation of said shaft corresponds to S. elevation of said lifting carriage.

9. The safety brake apparatus as claimed in any one of claims 1 to 8 wherein the brake stator means comprises a cylindrical surface engageable by said brake rotor means.

The safety brake apparatus as claimed in any one of claims 1 to 8 wherein said brake rotor means comprises one or more radially extendable members engageable with one or more abutment surfaces associated with said brake stator means.

11. The safety brake apparatus as claimed in any one of claims 1 to 10 wherein the brake rotor means may comprise one or more radially extendable lugs or pins.

12. The safety brake apparatus as claimed in claim 11 wherein said one or more abutment surfaces associated with the brake stator may 14 comprise apertures, recesses or projections in use alignable with said radially extendable lugs or pins.

13. The safety brake apparatus as claimed in any one of claims 1 to 12 wherein said mounting means is adapted to permit in use at least limited lateral movement of said brake stator means relative to said column.

14. A safety brake apparatus substantially as hereinbefore described with reference to the accompanying drawings. Dated this Twenty-eighth day of January 1998 ENDUREQUIP PTY LTD by its Patent Attorneys FISHER ADAMS KELLY *il 0 S Se