EP1175967A2

EP1175967A2 - Torque screwdriver

Info

Publication number: EP1175967A2
Application number: EP01306028A
Authority: EP
Inventors: Terrence Clifford Bullen
Original assignee: MHH ENGINEERING CO Ltd
Current assignee: MHH ENGINEERING CO Ltd
Priority date: 2000-07-17
Filing date: 2001-07-12
Publication date: 2002-01-30
Also published as: GB0017439D0; EP1175967A3

Abstract

The present invention relates to torque screwdrivers. The screwdriver comprises a handle and fastener engaging component, and uses a ratchet and pawl mechanism as a torque coupling between them.

Description

This invention relates to improvements relating to torque screwdrivers.

Torque screwdrivers are well known in the art. Such screwdrivers generally have a shaft, a handle at one end of the shaft, and a fastener-engaging bit possibly being substituted by a plug or a socket (or other coupling) for the temporary attachment of a detachable fastener-engaging bit of a selected size and/or shape. The fastener to be operated by the screwdriver may be a screw, a bolt, a nut or some other form of fastener, such fasteners having the common characteristic that they are all operated by rotation (either for tightening or loosening), the requisite torque being delivered to the fastener through the shaft of the screwdriver.

The coupling mechanism between the handle and the shaft is generally a ball-and-clutch mechanism, which is complex to form and fit, and therefore has a relatively high level of manufacturing cost.

According to one aspect of the present invention, there is provided a torque screwdriver comprising a handle, a fastener coupling, and an intermediate shaft assembly, wherein the screwdriver includes a torque coupling for rotationally coupling the handle to the fastener coupling, the torque coupling being provided by a ratchet and pawl mechanism.

When moulded, ratchet and pawl mechanisms are considerably easier to make and/or apply to the shaft assembly of a screwdriver, thereby making such screwdrivers considerably easier and cheaper to make.

The parts of the ratchet and pawl mechanism may be of any suitable size, shape or design. Generally, the "ratchet" is provided by a ratchet wheel having a plurality of teeth, notches, etc., and the pawl is a moveable catch engaging with the wheel. The present invention includes any arrangement of the ratchet and pawl able to provide the torque coupling.

In general, the pawl is such as to be biased to engage one or more positions on the ratchet. Generally, the biasing is provided by a spring, which could be any suitable form of spring including coil springs, leaf springs, etc. More preferably, the biasing force acting on the ratchet and/or pawl is adjustable so as to provide the ability to more accurately calibrate the level of torque provided by the screwdriver.

The parts of the ratchet and pawl mechanism could be formed separately or integrally with the other features of the screwdriver.

In one embodiment of the present invention, the ratchet is formed by and/or with the handle. Preferably, the ratchet is formed by grooving or notching an internal part of the handle.

In another embodiment of the present invention, the pawl is wholly or substantially within the shaft of the shaft assembly, and is rotatable therewith.

Preferably, the formable parts of the present invention are wholly or substantially formable by moulding, such as injection moulding, and/or machining. This significantly reduces the time and effort required to form the screwdriver.

According to a second aspect of the present invention, there is provided a method of rotatably coupling a handle and a fastening coupling of a torque screwdriver, wherein the torque coupling is provided by a ratchet and pawl mechanism.

An embodiment of the present invention will now be described by way of example only and with reference to the accompanying diagrammatic drawings in which:

Fig. 1 is a cross-sectional longitudinal view of a torque screwdriver according to one embodiment of the present invention; and

Fig. 2 is an enlarged cross-sectional view along line AA in Fig. 1.

Referring to the drawings, Fig. 1 shows a torque screwdriver 10 having a handle 12 and a fastener coupling 14. The fastener coupling 14 has a hexagon shank, and includes at one end a drive bit 16 designed to engage a suitable fastener-engaging bit.

Between the handle 12 and the fastener coupling 14, there is a shaft assembly. One part of the assembly is a shaft 18. At the end of the shaft 18 distal from the fastener coupling 14 is a steel ball 20 for end thrust. Within and around the shaft 18 is a ratchet and pawl mechanism described in greater detail with respect to Fig. 2.

Fig. 2 shows, in an enlarged cross-sectional view of the handle 12, a series of longitudinal triangular notches 22 on the inner circumference thereof. Within the shaft 18, there is located a pawl 24. One end of the pawl 24 is biased by one end of a flat leaf spring 26, which spring 26 is conjoined with the shaft 18 as further discussed below. The other end of the pawl 24 is a notched head section 28 having a top projected shape designed to complement the notches 22 in the handle 12. The pawl 24 is designed to be moveable 'up and down' within the shaft 18.

As mentioned above, the leaf spring 26 is conjoined with the shaft 18. Around the shaft 18 and the spring 26 is a longitudinally sliding collar 30 having a set screw 32, such as a grub screw, therethrough to lock the position of the collar 30 on the shaft 18 where desired.

The screwdriver 10 also includes a retaining cover 34.

In manufacturing the torque screwdriver of the present invention, the simplicity of the various parts and their ease of manufacture can be seen from the above and the accompanying drawings. The shaft 18 and handle 12 can easily be machine-formed, or formed by injection moulding. The fastener coupling 14 is a well-known and available part in the art. Once the shaft 18 has been formed, it is a simple operation to attach the flat leaf spring 26 thereto, locate the collar 30 therearound, and add the pawl 24. Because a torque screwdriver must be able to provide a predetermined degree of torque, the position of the collar 30 along the shaft 18 can be adjusted to increase or decrease the 'free' length of the leaf spring 26, and thereby to increase or decrease the force required to deflect the 'free end' of the spring 26. The force required to deflect the spring is directly related to the torsional resistance provided by the screwdriver. Once the calibration of the torque effect has been achieved, use of the set screw 32 locks the collar 30 in place around the shaft 18.

The shaft assembly can now be immediately located in the handle 12, and the retaining cover 34 added. Preferably, the retaining cover 34 provides securement, possibly irreversibly, of the shaft 18 and related parts within the handle 12. The retaining cover 34 may have a 'snap fit' for ease of assembly and fitting.

In use, rotation of the handle 12 by a user in an anti-clockwise fashion, as shown by an arrow in Fig. 2, provides rotational coupling of the fastener coupling 14 against any suitable fastener (not shown) under the level of the pre-determined torque setting. However, once the pre-determined torque is reached, the head section 28 of the pawl 24 will travel down the angled faces of the notches 22 in the handle 12 and thereby slip into the next notch 22 when the resistance of the flat spring 26 is overcome.

The vertical radial faces of the head section 28 of the pawl 24 and the notches 22 also provide a solid reverse torque transmission, without the ability of the pawl 24 slipping. This thus enables tightened fasteners to be unscrewed by the screwdriver 10.

The number of notches 22 in the handle 12 may be any suitable number depending upon the size, shape and design of the screwdriver. In one embodiment of the present invention, there are provided an odd number of notches 22 in the handle 12.

The present invention provides a torque screwdriver of relatively simple construction and assembly, thereby reducing the cost of manufacture. Calibration of the torque of the screwdriver is provided by an internal moveable collar.

Claims

A torque screwdriver comprising a handle, a fastener coupling, and an intermediate shaft assembly, wherein the screwdriver includes a torque coupling for rotationally coupling the handle to the fastener coupling, the torque coupling being provided by a ratchet and pawl mechanism.
A torque screwdriver according to Claim 1 in which the ratchet is provided by a ratchet wheel having a plurality of teeth.
A torque screwdriver according to Claims 1 or 2 in which the pawl is a moveable catch engaging with the ratchet.
A torque screwdriver according to any preceding claim in which the pawl is biased to engage at least one position on the ratchet.
A torque screwdriver according to any preceding claim in which the pawl is biased by a spring.
A torque screwdriver according to Claim 5 in which the spring is a leaf spring.
A torque screwdriver according to any of Claims 4 to 6 in which the biasing force acting on the pawl is adjustable to more accurately calibrate the level of torque provided by the screwdriver.
A torque screwdriver according to Claim 7 when dependent on Claim 6, in which the biasing force is adjustable by way of a collar moveable within the handle to adjust the free spring length of the leaf spring.
A torque screwdriver according to any preceding claim in which the ratchet is formed by notches provided on the interior surface of the handle.
A torque screwdriver according to any preceding claim in which the pawl is substantially within the shaft of the shaft assembly and is rotatable therewith.
A torque screwdriver according to any preceding claim in which the formable parts are formed by injection moulding.
A torque screwdriver according to any of Claims 1 to 10 in which the formable parts are formed by machining.
A method of rotatably coupling a handle and a fastener coupling of a torque screwdriver, wherein the coupling is provided by a ratchet and pawl mechanism.