GB2298258A

GB2298258A - Worm and wheel reduction gear mechanism

Info

Publication number: GB2298258A
Application number: GB9503586A
Authority: GB
Inventors: James Brian O'hara
Original assignee: Hara J B O
Current assignee: Hara J B O
Priority date: 1995-02-23
Filing date: 1995-02-23
Publication date: 1996-08-28
Also published as: GB9503586D0

Abstract

A reduction gear mechanism comprises a first worm gear (1) , a first worm wheel (2) in meshing engagement with first worm gear (1), a second worm gear (3) coaxial and rotatable with first worm wheel (2), and a second worm wheel (4) in meshing engagement with second worm gear (3). Preferably the worm gears and worm wheels are moulded from synthetic plastics material.

Description

RDUCTTON GEAR MECHANISM.

This invention relates to a reduction gear mechanism.

An educational construction system is known which is used extensively in schools and other educational establishments and which is sold under the Registered Trademark "TACTIC". The system comprises plastics tubes of various lengths and diameters, socketed connectors for connecting the tubes together by a simple twist-and-lock action and, optionally, various wheels, gear wheels, bearings, belts and the like whereby working mechanical models can be constructed. Such models can, if desired, be driven by a suitable electric motor, e.g. a 3 to 24 Volt DC electric motor, through a suitable reduction gear mechanism. The reduction gear mechanism needs to be compact in size and that currently in use comprises a train of toothed gear wheels which, because of the constraint on size, are machined in metal, making the reduction gear mechanism both complex and expensive.

The present invention has as its object to provide a reduction gear mechanism which is of simple construction, comprises comparatively few parts and which, according to a preferred embodiment, comprises parts which can be formed, e.g. moulded, from synthetic plastics material.

The present invention provides a reduction gear mechanism comprising a first driven worm gear, a first toothed worm wheel in meshing engagement with said first worm gear, a second worm gear coaxial and rotatable with said first worm wheel and a second toothed worm wheel in meshing engagement with said second worm gear.

Preferably said first and second worm gears are single helix worm gears, although one or both could comprise two or more helixes if desired.

Said first worm gear may be fast with a driven input shaft, said first worm wheel and said second worm gear may be fast with an intermediate shaft extending at right angles to said input shaft and said second worm wheel may be fast with an output shaft parallel with said input shaft.

Said first and second worm gears and said first and second worm wheels may be contained within a housing and said input, intermediate and output shafts may be journalled in walls of said housing.

The input shaft may extend through a wall of said housing and may be connected or connectable to a suitable prime mover such as an electric motor. Likewise the output shaft may extend through a wall of said housing and may be connectable to a mechanism to be driven. If desired, the intermediate shaft may extend through a wall of said housing and provide an intermediate output shaft providing an intermediate speed reduction.

The arrangement may be such that said first worm wheel is angularly displaced one tooth for each complete rotation of said first worm gear and/or said second worm wheel is angularly displaced one tooth for each complete rotation of said second worm gear.

According to a preferred embodiment of the present invention, said first and second worm wheels each have from twelve to eighteen, preferably fifteen, gear teeth evenly spaced around the periphery thereof.

Said first and second worm gears and said first and second worm wheels are preferably formed, e.g. moulded.

from a suitable synthetic plastics material such as a suitable Nylon or ABS (acrylonitrile-butadiene-styrene) polymer material. To save on mould cost and facilitate manufacture and assembly, said first and second worm gears and said first and second worm wheels may be identical and may be produced from the same mould.

The invention will be more particularly described with reference to the accompanying drawings, in which: Fig. 1 is a plan view of a preferred embodiment of a reduction gear mechanism according to the present invention, and Fig. 2 is a side elevation of the reduction gear mechanism shown in Fig. 1.

Referring to the drawings it will be seen that the reduction gear mechanism illustrated therein comprises a first worm gear 1, a first worm wheel 2 in meshing engagement with first worm gear 1, a second worm gear 3 both coaxial and rotatable with the first worm wheel 2 and a second worm wheel 4 in meshing engagement with the second worm gear 3. If further reduction in speed is required then a third worm gear (not shown) can be provided which is both coaxial and rotatable with the second worm wheel 4 and a third worm wheel (not shown) provided in meshing engagement with the third worm gear, and so on as desired.

The first and second worm gears 1 and 3 and the first and second worm wheels 2 and 4 are contained within a housing H having opposed side walls 5,6, opposed end walls 7,8, and top and bottom walls 9,10.

First worm gear 1 is fast with an input shaft 11 journalled in side walls 5,6. Input shaft 11 is connected to a prime mover in the form of electric motor 12. First worm wheel 2 and second worm gear 3 are fast with an intermediate shaft 13 journalled in end walls 7,8 and extending at right angles to input shaft 11. If desired intermediate shaft 13 can be extended beyond end wall 8 as shown at 13a in Fig. 1 to provide an intermediate output shaft. Second worm wheel 4 is fast with an output shaft 14 journalled in side walls ',,6 and extending parallel to input shaft 11. Output shaft 14 extends outwardly beyond side wall 6 as shown at 14a (Fig. 1) and is connectable to a model mechanism (not shown) to be driven.

First and second worm gears 1,3 are single helix worm gears and, in the illustrated embodiment, have an outside diameter of substantially 12mm., a helix depth of substantially 3mm., a distance between adjacent turns of the helix of substantially 4mm. and a length of substantially 30mm. Worm wheels 2,4, in the illustrated embodiment, each have fifteen teeth evenly spaced around the periphery thereof, an outside diameter of substantially 17mm., a tooth depth of substantially 3mum., a distance between the crowns of adjacent teeth of substantially 3mm. and a tooth length of substantially 5mm. The arrangement is such that the worm wheels 2,4 are angularly displaced one tooth for each complete rotation of respective worm gears 1,3.With the reduction gear mechanism illustrated an input speed of 4500rpm. can be reduced to 20rpm. at output shaft 14a.

Housing H, in the illustrated embodiment, has a length of substantially 50mm., a width of substantially 40mm. and a depth of substantially 45mm.

Worm gears 1,3 and worm wheels 2,4 are formed e.g.

moulded, from a suitable synthetic plastics material such as a suitable Nylon or ABS polymer material.

Advantageously worm gears 1 and 3 are identical as are worm wheels 2 and 4, whereby worm gears 1 and 3 can be produced in a single mould as can worm wheels 2 and 4.

Likewise housing H can be formed, e.g. moulded, from a suitable synthetic plastics material.

From the foregoing description it will be apparent that a reduction gear mechanism is provided which is compact in size, contains a minimum of working parts for the speed reduction obtained and comprises parts which, in the main, can be quickly, easily and economically formed, e.g. moulded, from synthetic plastics material.

Claims

CLAIMS:

1. A reduction gear mechanism comprising a first driven worm gear, a first toothed worm wheel in meshing engagement with said first worm gear, a second worm gear coaxial and rotatable with said first worm wheel and a second toothed worm wheel in meshing engagement with said second worm gear.

2. A reduction gear mechanism according to claim 1 wherein said first and second worm gears are single helix worm gears.

3. A reduction gear mechanism according to claim 1 or 2, wherein said first worm gear is fast with a driven input shaft.

4. A reduction gear mechanism according to claim 3, wherein said first worm wheel and said second worm gear are fast with an intermediate shaft extending at right angles co said input shaft.

5. A reduction gear mechanism according to claim 3 or 4, wherein said second worm wheel is fast with an output shaft parallel with said input shaft.

6. A reduction gear mechanism according to claims 3, 4 and 5, wherein said first and second worm gears and said first and second worm wheels are contained within a housing and wherein said input, intermediate and output shafts are journalled in walls of said housing.

7. A reduction gear mechanism according to any one of the preceding claims, wherein said first worm wheel is angularly displaced one tooth for each complete rotation of said first worm gear.

8. A reduction gear mechanism according to any one of the preceding claims, wherein said second worm wheel is angularly displaced one tooth for each complete rotation of said second worm gear.

9. A reduction gear mechanism according to any one of the preceding claims, wherein said first and second worm wheels each have from twelve to eighteen gear teeth evenly spaced around the periphery thereof.

10. A reduction gear mechanism according to claim 9, wherein said first and second worm wheels each have fifteen gear teeth spaced around the periphery thereof.

11. A reduction gear mechanism according to any one of the preceding claims, wherein said first and second worm gears and/or said first and second worm wheels are formed from suitable synthetic plastics material.

12. A reduction gear mechanism according to claim 11, wherein said first and second worm gears and/or said first and second worm wheels are formed by moulding.

13. A reduction gear mechanism according to claim 12, wherein said first and second worm gears are identical and are produced from the same mould.

14. A reduction gear mechanism according to claim 12 or 13, wherein said first and second worm wheels are identical and are produced from the same mould.

15. A reduction gear mechanism substantially as herein described with reference to the accompanying drawings.