GB2153958A

GB2153958A - Gearwheel

Info

Publication number: GB2153958A
Application number: GB08403432A
Authority: GB
Inventors: Ian Peter Collins
Original assignee: PA Consulting Services Ltd
Current assignee: PA Consulting Services Ltd
Priority date: 1984-02-09
Filing date: 1984-02-09
Publication date: 1985-08-29
Also published as: GB2153958B; GB8403432D0

Abstract

A gearwheel has teeth each of which is shaped to prevent the gearwheel abutting crown to crown when brought into engagement with another similar gearwheel. Each tooth has a crown with a central ridge (26) positioned between sloping sides (28) which facilitate engagement of the gearwheels. <IMAGE>

Description

SPECIFICATION Gearwheel Field of the Invention This invention relates to gearwheels and to mechanisms including gearwheels.

Background to the Invention It is sometimes necessary to bring two rotatable gearwheels into engagement by moving their axes of rotation towards one another to bring the teeth of the two grearwheels into mesh. If one or other gearwheel is rotating when the gearwheels are brought together, the teeth of the two gearwheels will normally mesh satisfactorily, but if neither gearwheel is rotating it is possible for the teeth to abut crown-to-crown and in consequence to fail to mesh. The invention aims to provide a gearwheel having a crown shaped to avoid this problem, and to provide a mechanism incorporating such gearwheels.

Summary of the Invention According to one aspect a gearwheel has teeth each of which has a crown shaped so as to have a central ridge positioned between sloping sides which extend from the ridge to the corresonding face of the tooth.

According to another aspect the invention provides a mechanism comprising two rotatable gearwheels which are capable of being taken into and out of engagement by relative movement of the axes of rotation of the gearwheels, wherein each gearwheel has teeth each of the which has a crown shaped so as to have a central ridge positioned between sloping sides which extend from the ridge to the corresponding face of the tooth, the sloping sides of the crowns facilitating interengagement of the gearwheels when the latter are brought into crown to crown engagement in a non-rotating condition.

Hence, in the invention the sides of each tooth crown are shaped so that when they come into contact the interaction of one side upon the other effects sufficient rotation of one or other (or both) gearwheels that the teeth mesh smoothly with one another, without there being any risk of the crowns abutting and preventing interengagement of the gearwheels.

Preferably the sides are planar, the minium angle of inclination (to a notional planar crown) being a function of the coefficient of friction of the material (or materials) of the gearwheels. To a first approximation, the tangent of the angle of inclination of each side is equal to the coefficient of friction of the two gearwheels. For plastics materials, the angle is preferably between 20 and 30 , and for acetal 25 has been found to be suitable.

The invention is applicable to single spur gearwheels in which case the rotational axes will be parallel and the direction of relative movement of the axes will be perpendicular to the axes, or to more complicated gear wheels which transmit rotational movement between non-parallel rotational axes.

The invention will now be further described by way of example with reference to the accompanying drawings in which: Figure 1 shows two conventional gearwheels, and Figure 2 shows the shape of a tooth of a gearwheel according to the invention.

Summary of the Invention Referring to Fig. 1, two conventional gearwheels 10 and 1 2 have respective parallel axes of rotation 14 and 1 6. The gearwheels 10 and 12 are part of a mechanism in which rotational movement is transmitted from the gearwheel 10 to the gearwheel 1 2 by bringing the two gearwheels into mesh, this being done by moving the axes of rotation 14 and 1 6 towards one another.

The two gearwheels 10 and 1 2 are brought into mesh with the gearwheels 10 and 1 2 in a non-rotating condition. In this condition it is possible for teeth on the two gearwheels 10 and 1 2 to abut in crown-to-crown relationship, for example for the crown 1 8 to abut the crown 20. If this happens the teeth are not brought into mesh.

By recourse to the invention the gearwheels such as 10 and 1 2 are provided with teeth having the profile shown in Fig. 2. Each tooth has opposed, curved faces 22, 24 which converge towards the tooth crown. The crown has a central ridge 26 positioned between sloping sides 28 which extend from the ridge 26 to the corresponding face 22 or 24. Each side 28 of the crown is planar and is inclined at an angle of about 65 to the central axis 30 of the tooth.

1. A gearwheel having teeth each of which has a crown shaped so as to have a central ridge positioned between sloping sides which extend from the ridge to the corresponding face of the tooth.

2. A gearwheel according to claim 1, wherein the sides are planar, the minimum angle of inclination (to a notional planar crown) being a function of the coefficient of friction of the material (or materials) of the gearwheels.

3. A gearwheel according to claim 2, wherein the angle is between 20 and 30 .

4. A gearwheel according to claim 3, wherein the gearwheel is of acetal and said angle is 25%.

5. A mechanism comprising two rotatable gearwheels which are capable of being taken into and out of engagement by relative movement of the axes of rotation of the gearwheels, wherein each gearwheel has teeth

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Gearwheel Field of the Invention This invention relates to gearwheels and to mechanisms including gearwheels. Background to the Invention It is sometimes necessary to bring two rotatable gearwheels into engagement by moving their axes of rotation towards one another to bring the teeth of the two grearwheels into mesh. If one or other gearwheel is rotating when the gearwheels are brought together, the teeth of the two gearwheels will normally mesh satisfactorily, but if neither gearwheel is rotating it is possible for the teeth to abut crown-to-crown and in consequence to fail to mesh. The invention aims to provide a gearwheel having a crown shaped to avoid this problem, and to provide a mechanism incorporating such gearwheels. Summary of the Invention According to one aspect a gearwheel has teeth each of which has a crown shaped so as to have a central ridge positioned between sloping sides which extend from the ridge to the corresonding face of the tooth. According to another aspect the invention provides a mechanism comprising two rotatable gearwheels which are capable of being taken into and out of engagement by relative movement of the axes of rotation of the gearwheels, wherein each gearwheel has teeth each of the which has a crown shaped so as to have a central ridge positioned between sloping sides which extend from the ridge to the corresponding face of the tooth, the sloping sides of the crowns facilitating interengagement of the gearwheels when the latter are brought into crown to crown engagement in a non-rotating condition. Hence, in the invention the sides of each tooth crown are shaped so that when they come into contact the interaction of one side upon the other effects sufficient rotation of one or other (or both) gearwheels that the teeth mesh smoothly with one another, without there being any risk of the crowns abutting and preventing interengagement of the gearwheels. Preferably the sides are planar, the minium angle of inclination (to a notional planar crown) being a function of the coefficient of friction of the material (or materials) of the gearwheels. To a first approximation, the tangent of the angle of inclination of each side is equal to the coefficient of friction of the two gearwheels. For plastics materials, the angle is preferably between 20 and 30 , and for acetal 25 has been found to be suitable. The invention is applicable to single spur gearwheels in which case the rotational axes will be parallel and the direction of relative movement of the axes will be perpendicular to the axes, or to more complicated gear wheels which transmit rotational movement between non-parallel rotational axes. The invention will now be further described by way of example with reference to the accompanying drawings in which: Figure 1 shows two conventional gearwheels, and Figure 2 shows the shape of a tooth of a gearwheel according to the invention. Summary of the Invention Referring to Fig. 1, two conventional gearwheels 10 and 1 2 have respective parallel axes of rotation 14 and 1 6. The gearwheels 10 and 12 are part of a mechanism in which rotational movement is transmitted from the gearwheel 10 to the gearwheel 1 2 by bringing the two gearwheels into mesh, this being done by moving the axes of rotation 14 and 1 6 towards one another. The two gearwheels 10 and 1 2 are brought into mesh with the gearwheels 10 and 1 2 in a non-rotating condition. In this condition it is possible for teeth on the two gearwheels 10 and 1 2 to abut in crown-to-crown relationship, for example for the crown 1 8 to abut the crown 20. If this happens the teeth are not brought into mesh. By recourse to the invention the gearwheels such as 10 and 1 2 are provided with teeth having the profile shown in Fig. 2. Each tooth has opposed, curved faces 22, 24 which converge towards the tooth crown. The crown has a central ridge 26 positioned between sloping sides 28 which extend from the ridge 26 to the corresponding face 22 or 24. Each side 28 of the crown is planar and is inclined at an angle of about 65 to the central axis 30 of the tooth. CLAIMS

3. A gearwheel according to claim 2, wherein the angle is between 20 and 30 .

5. A mechanism comprising two rotatable gearwheels which are capable of being taken into and out of engagement by relative movement of the axes of rotation of the gearwheels, wherein each gearwheel has teeth each of which has a crown shaped so as to have a central ridge positioned between sloping sides which extend from the ridge to the corresponding face of the tooth, the sloping sides of the crowns facilitating interengagement of the gearwheels when the latter are brought into crown to crown engagement in a non-rotating condition.

6. A mechanism according to claim 5, wherein each gearwheel is in accordance with any of claims 2 to 4.

7. A gearwheel constructed and arranged substantially as herein particularly described with reference to the accompanying drawings.

CLAIMS Amendments to the claims have been filed, and have the following effect: New or textually amended claims have been filed as follows:-

1. A gearwheel having teeth each of which has a crown shaped so as to have a central ridge positioned at the junction between planar sloping sides which extend from the ridge to the corresponding face of the tooth.

2. A gearwheel according to claim 1, wherein the sides have an angle of inclination (to a notional planar crown) which is a function of the coefficient of friction of the material (or materials) of the gearwheels.

3. A gearwheel according to claim 2, wherein the angle is between 20 and 30 .

4. A gearwheel according to claim 3, wherein the gearwheel is of acetal and said angle is 25 .

5. A mechanism comprising two rotatable gearwheels which are capable of being taken into and out of engagement by relative movement of the axes of rotation of the gearwheels, wherein each gearwheel has teeth each of which has a crown shaped so as to have a central ridge positoned at the junction between sloping sides which extend from the ridge to the corresponding face of the tooth, the sloping sides-of the crowns facilitating interengagement of the gearwheels when the latter are brought into crown to crown engagement in a non-rotating condition.