GB2143165A - Ratchet mechanism - Google Patents

Abstract

A ratchet mechanism suitable for use in a hand tool such as a wrench comprises a cylindrical ratchet wheel 6 having part-cylindrical recesses therein which are engaged by a complementary shaped pawl 3. The pawl is urged into engagement with the wheel by a spring 11 and prevents rotation in one direction by jamming against a hardened insert 10. <IMAGE>

Description

SPECIFICATION Ratchet mechanism This invention relates to a ratchet mechanism and particularly to a ratchet mechanism suitable for use in a hand tool such as a wrench.

Ratchet wrenches are commonly provided with a reversible ratchet mechanism wherein two pawls are selectively engaged with the teeth of a ratchet wheel. The teeth are of generally sharp V-shaped profile and the pawl has a corresponding angular profile.

A major problem with such ratchets is that the sharp toothed profile of the ratchet wheel leads to high stress concentration in the angles between the teeth and the wheel is likely to fail radially from these angles.

In order to raise thestrength of ratchet wheeis it has therefore been previously necessary that they be made out of extremely tough steel. A compromise has always been necessary between the hardness required so that the wheel can engage the pawl without plastic deformation, and the tensile strength required to avoid failure under load as described above. The cost incurred by the use of these materials and the precision required in manufacture has led to most ratchet wrenches being very expensive.

The present invention overcomes these disadvantages by providing a ratchet mechanism which is sufficiently strong to stand substantial loads but which can be very economically manufactured.

According to the present invention there is provided a ratchet mechanism comprising a generally cylindrical ratchet wheel having an outer cylindrical surface which is provided with a plurality of spaced part-cylindrical recesses; the axes of the recesses extending parallel to the axis of the ratchet wheel, a pawl having a cross section complementary to thecross section of therecesses, spring means which urges the pawl into engagement with the ratchet wheel, and bearing means comprising at least one surface against which the pawl is urged by rotation of the ratchet wheel in one sense so as to prevent further rotation in that sense.

A brief description of a ratchet mechanism according to the invention will now be described with reference to the accompanying drawings in which; Figure 1 is a part cut-away side elevation of a ratchet mechanism in a wrench; Figure 2 is a cross-section on the line AA shown in Figure 1, and Figure 3 is a cross-section on the line BB shown in Figure 1.

In the embodiment shown in Figures 1-3 a ratchet mechanism comprises a ratchetbody 1 which is supported in one end of a wrench handle 2 and which is engaged by a spring biassed cylindrical pawl 3. The body 1 has a square section bore therethrougn which engages complementary sectioned tools as is well known in the art.

The body 1 is generally cylindrical but has three distinct radii along its length defining end sections 4, enlarged intermediate sections 5, and a further enlarged central wheel section 6.

The wheel section 6 is profiled by spaced part-cylindrical recesses 7 extending across its axial width. The radius of therecesses is substantially identical to that of the cylindrical pawl 3 and the bottoms of the recesses are substantially tangential to the surface of the intermediate sections 5. The handle of the wrench is formed from four strips of steel which can be stamped out from a sheet. The strips are rivited or otherwised fixed together at intervals along their length. This construction of the handle provides for an economical manufacture of the wrench arid for its simple assembly. A unitary cast handle may be provided, however, and a separate bearing insert, as described below, may then be dispensed with; the bearing surface against which the pawl is urged then being provided by a surface on the handle itself.

Circular holes are provided in the strips 8 to accommodate the body 1. In the case of the two outer strips the radius of the holes is substantially equal to that of the intermediate sections 5 and the transverse edges of the holes thus provide bearing surfaces for the intermediate sections.

The two inner strips are provided with circular holes having radii very slightly larger than the radius of the wheel section 6. The circular holes in the inner strips are also enlarged to form a opening 9 which houses the cylindrical pawl 3. An insert 10 of hardened steel is also housed in the opening and provides a bearing surface for the pawl which is also made of hardened steel. The insert 10 has a dog-leg shape such that the pawl when engaged in a recess 7 of the wheel section will be pushed into contact with both portions of the insert.

The pawl is urged to a position where it will be engaged by the wheel section by a coil spring 11. This spring may be provided with a cap (not shown) to avoid snagging.

When the body is rotated in one sense (anti-clockwise as shown) the pawl will be pushed away from engagement with the wheel section against the action of spring 11.

If the body is rotated in the opposite sense the pawl will become nested in a recess 7 and will be jammed up against the two portions of the dog-leg insert 1 0. To reverse the action of the ratchet it is only necessary to remove the tool engaged in the bore and turn the wrench over.

The smoothly continuous profile of the recesses 7 avoids stress concentrations found in prior ratchet mechanism and allows for much more economical methods of manufacture.

For example, in one preferred form of the invention the ratchet body is made by a sintering process. The body 1 is located in the handle by means of washers 1 2 and cir clips 13.

Numerous variations of the construction details of the ratchet and wrench handle described are possible. For example the handle may be of unitary construction and the ratchet wheel may extend for a greater part of the axial dimension of the body such as right across the intermediate portions. The insert 10 need not be of dog-leg construction and/or the pawl may be arranged to bear on one face only of the insert.

Whilst the pawl is preferably of cylindrical construction it may alternatively be provided by a spherical ball.

The ratchet mecanism may also be used in applications other than in wrenches.

Claims (9)

1. A ratchet mecanism comprising a generally cylindrical ratchet wheel having an outer cylindrical surface which is provided with a plurality of spaced part-cylindrical recesses; the axes of the recesses extending parallel to the axis of the ratchet wheel, a pawl having a cross section complentary to the cross section of the recesses, spring means which urges the pawl into engagement with the ratchet wheel, and bearing means comprising at least one surface against which the pawl is urged by rotation of the ratchet wheel in one sense so as to prevent further rotation in that sense.

2. A ratchet mechanism as claimed in Claim 1, wherein the pawl is formed as a cylinder.

3. A ratchet mechanism as claimed in Claim 1, wherein the ratchet wheel is formed as a radial extension on a generally cylindrical body having a square section bore therethrough.

4. A ratchet mechanism as claimed in Claim 3, where in the said body has three distinct radii along its length defining end sections, enlarged intermediate sections, and a further enlarged central section forming the ratchet wheel.

5. A ratchet mechanism as claimed in any preceding claim wherein the ratchet wheel is formed by a sintering process.

6. A wrench comprising a handle housing a ratchet mechanism, as claimed in any preceding claim, at one end thereof.

7. A wrench as claimed in Claim 6, comprising a handle formed out of a plurality of strips stamped out from sheet material wherein the bearing means comprises a hardened bearing insert supported by the handle.

8. A ratchet mechanism substantially as described with reference to the accompanying drawings.

9. A wrench substantially as described with reference to the accompanying drawings.