GB2392403A

GB2392403A - Spindle locking device for an electric power tool

Info

Publication number: GB2392403A
Application number: GB0220141A
Authority: GB
Inventors: Man Cheong Tse
Original assignee: Johnson Electric SA
Current assignee: Johnson Electric SA
Priority date: 2002-08-30
Filing date: 2002-08-30
Publication date: 2004-03-03
Also published as: GB0220141D0

Abstract

A spindle locking device has a spindle 16, lock ring 24, driver 26 and gearbox output carrier 30. The carrier 30 engages the driver 26 through C-shaped projections 38 which allows limited relative rotational movement and locking rollers 28 automatically prevent rotation of the spindle 16 by an externally applied torque. In addition the carrier 30 is an output means from the planetary type gearbox housed within the electric powertool.

Description

i Spindle Locking Device Of An Electric Power Tool This invention relates

to electric power tools and in particular, to a spindle locking device for us in such tools.

Electric power tools, such as drills and electric screwdrivers are commonplace. In use, such tools experience an external force which tries to rotate their output spindle.

In a drill, this may be when tightening or loosening a keyless chuck and in a screwdriver, it may be when tightening or loosening the collet holding the driver bits, 10 for example. In these examples, it is not desirable for the spindle to rotate. A similar situation occurs when trying to use the electric screwdriver manually as may occur when there is no power supply or the battery is flat.

In such situations, it is desirable for the spindle not to rotate with respect to the 15 housing. This has been achieved in the past by manually operated locks and more recently by automatically operated locking mechanisms as shown for example, in GB 1 179105.

While these automatic locking mechanisms work well, they tend to be suitable only 20 for low torque applications by their design. However, modern electric screwdrivers, especially drill/driver devices can be used manually to generate significant torque, due in part to their shape including long handles, sufficient torque to do serious damage to the locking mechanism.

25 Thus there exists a need for a robust spindle locking device which can withstand the high torque applied externally to the spindle.

Accordingly, in one aspect thereof, the present invention provides a spindle locking device for use with a portable power tool having a spindle and a housing, the device 30 comprising: a driver adapted to be fixed to one end of the spindle for rotation therewith; a lock ring, adapted to be fixed with respect to the housing; a carrier arranged to be driven by the motor; and a plurality of rollers 35 wherein the lock ring is coaxial with the driver and the carrier and is radially spaced from the driver; the carrier has a plurality of axially extending carrier projections equidistantly spaced about the axis of the carrier, each carrier projection having an axial channel

open along a radially inner side so as to form inwardly facing C-shaped cross sections, the driver has a central opening for receiving the end of the spindle and has a plurality of radially extending large driver projections interposed between a corresponding 5 plurality of radially extending small driver projections, the large driver projections being disposed within the channels of the carrier projections and having a circumferential extent less than the circumferential extent of the opening in the carrier projection so as to couple the driver and carrier together but allowing limited relative rotation there between and the small driver projections being located in between 10 adjacent carrier projections, the small driver projections having a radially outer surface which faces a radially inner surface of the lock ring and shaped so that the distance D between the small driver projections and the lock ring is greatest DmaX at about the circumferential center of each small driver projection and least Dmjn near the circumferential edges of each small driver projection; 15 the rollers are disposed axially in respective roller voids defined by the lock ring, the small driver projections and the carrier projections and have a diameter Dr which is less than DmaX and greater than Dmin,; and whereby rotation of the driver by the carrier causes the carrier projections to move towards the trailing edge of the small driver projections, preventing the rollers 20 from being pinched between the edges of the small driver projections and the lock ring and rotation of the carrier by the driver causes the carrier projections to move away from the trailing edges of the small driver projections allowing the roller to be pinched between the small drive projections and the lock ring preventing further rotation of the driver.

Preferred and/or optional features are set forth in the dependent claims.

One preferred embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is an elevational view of a drill/driver incorporating a spindle locking device according to the present invention; Figure 2 is an exploded isometric view of the spindle locking device of the drill/driver 35 of Figure 1; and Figure 3 is an end view of the spindle locking device, assembled.

Figure 1 shows a drill/driver type power tool 10. The tool 10 has a housing 12 including a handle 14. Extending from the housing is a spindle 16 supporting a chuck 18. The housing 12 accommodates an electric motor connected by a trigger switch 20 to a battery in the handle. The motor drives the spindle 16 through a gearbox and a 5 torque mechanism and a spindle locking device.

Figure 2 illustrates the spindle locking device 22. The device 22 includes the spindle 16, a lock ring 24, a driver 26, three rollers 28 and a carrier 30.

10 The spindle 16 has a threaded end 32 for connection of the chuck 18. The other end 34 mates with a hole in the driver 26 for fixed rotation therewith. The lock ring 24 is fixed to the housing 12 so as to be stationary. The lock ring 24 locates radially about the driver 26.

15 The carrier 30 is the output of the gearbox. Here the gearbox is of the planetary type and the carrier 30 is a disc with three pins or spigots 36 projecting axially away from the locking device 22. These spigots 36 are mounts for three planetary gears (not shown) of the gearbox which drive the carrier 30. On the opposite side of the carrier 30 are three axial projections 38. These projections are equidistantly spaced on a 20 common pitch circle. Each projection 38 has a substantially arcuate shape to match the contour of the inner surface of the lock ring 24. The circumferential ends 40 of each projection 38 are enlarged radially inwardly to form an axially extending channel 42 open on the radially inner side giving the projection 38 an inwardly facing C-

shaped cross-section.

The driver 26 is an annular ring fixed to the drive end 34 of the spindle 16. The driver 26 has three large radial projections 44 and three small projections 46 equally spaced about its radially outer surface. The circumferential extent of the large projections 44 is less than the circumferential extent ofthe recess 42 in the carrier projections 38.

When assembled, as shown in Figure 3, the carrier projections 38 fit neatly inside the lock ring 24. The large projections 44 on the driver locate within the channel 42 of the carrier projections 38, and the small projections 46 fit in the gap 48 between adjacent carrier projections 38. The top or radially outer surfaces of the small projections 46 35 are substantially flat or at least do not form part of a common circle so that the radial distance between the top of the small projections 46 and the inner surface of the lock ring 24 is not uniform and is greatest (dc) at the center of the projections 46 when viewed axially and least (as) at the circumferential edges thereof.

The rollers 28 are placed in the spaces 48 defined by the carrier projections 38, the lock ring 24 and the small projections 46 and have a diameter (dr) sized to fit between the center of the small projections 46 and the lock ring 24 but not between the 5 circumferential edge of the small projections 46 and the lock ring 24, i.e. the diameter dr is between ds and do [ds<dr<dc].

In operation, when the carrier 30 turns, it pushes the driver 26 through the connection between the carrier projections 38 and the large projections 44. At the same time, due 10 to the difference in the circumferential extend of the large projections 44 and the recess in the carrier projections, the carrier projections also push the rollers 28 to keep them away from the trailing edge of the small projections 46.

When the spindle 16 tries to drive the driver 26, the driver 26 rotates slightly to 15 engage the carrier 30 through the large projections 44 and the carrier projections 38 but as the carrier projections have moved away from the trailing edge of the small projections 46, the rollers 28 roll towards the trailing edge and become wedged between the edge of the small projections 46 and the lock ring 24 preventing further rotation of the driver 24 and hence, automatically lock the spindle 16.

The use of C-shaped carrier projections gives the locking device inherent strength against shearing off of the carrier projections against the driver under severe torque operating conditions, resulting in a very robust and reliable connection between the spindle and the output of the gearbox. The arrangement is robust over designs with 25 pairs of stops as the C-shaped projections act as a pair of stops with the stops reinforced and strengthened against shearing off by the "back" of the "C" which functions as a support tying the two stops together and providing a greater area integral with the carrier. This greater area allows the projections to withstand substantially greater shear force than the pair of stops design. This allows the 30 coupling to transmit greater torque to the spindle as is required by the greater power produced by the motor driving the device to satisfy the needs of the operator.

The embodiment described above is given by way of example only and various modifications will be apparent to persons skilled in the art without departing from the 35 scope of the invention as defined in the appended claims.

Claims

s Claims

1. A spindle locking device for use with a portable power tool having a spindle and a housing, the device comprising: 5 a driver adapted to be fixed to one end of the spindle for rotation therewith; a lock ring, adapted to be fixed with respect to the housing; a carrier arranged to be driven by the motor; and a plurality of rollers wherein the lock ring is coaxial with the driver and the carrier and is radially 10 spaced from the driver; the carrier has a plurality of axially extending carrier projections equidistantly spaced about the axis of the carrier, each carrier projection having an axial channel open along a radially inner side so as to form inwardly facing C-shaped cross sections, 15 the driver has a central opening for receiving the end of the spindle and has a plurality of radially extending large driver projections interposed between a corresponding plurality of radially extending small driver projections, the large driver projections being disposed within the channels of the carrier projections and having a circumferential extent less than the circumferential extent of the opening in the carrier 20 projection so as to couple the driver and carrier together but allowing limited relative rotation therebetween and the small driver projections being located in between adjacent carrier projections, the small driver projections having a radially outer surface which faces a radially inner surface of the lock ring and shaped so that the distance D between the small driver projections and the lock ring is greatest Dmax at 25 about the circumferential center of each small driver projection and least Dmjn near the circumferential edges of each small driver projection; the rollers are disposed axially in respective roller voids defined by the lock ring, the small driver projections and the carrier projections and have a diameter Dr which is less than DmaX and greater than Don,; and 30 whereby rotation of the driver by the carrier causes the carrier projections to move towards the trailing edge of the small driver projections, preventing the rollers from being pinched between the edges of the small driver projections and the lock ring and rotation of the carrier by the driver causes the carrier projections to move away from the trailing edges of the small driver projections allowing the roller to be 35 pinched between the small drive projections and the lock ring preventing further rotation of the driver.

2. A device according to claim 1, wherein the small driver projections have a planar radially outer surface.

3. A device according to claim I or 2, wherein the circumferential extent of the S small driver projections is about the same as the diameter of the rollers.

4. A device according to claim 1, 2 or 3, wherein the carrier is a part of a speed reduction mechanism of the tool.

10 S. A device according to claim 4, wherein the speed reduction mechanism is a planetary gear type gearbox; and the carrier is an output element of the gearbox and has at least three axially extending spigots for mounting of planet gears.

6. A device according to any one of the preceding claims, wherein the carrier 15 projections are arcuate having a radially outer surface conforming to the inner surface of the lock ring with enlarges circumferential ends forming the inner recess therebetween.

7. A spindle locking device for use with a portable power tool substantially as 20 hereinbefore described with reference to the accompanying drawings.