GB2395452A

GB2395452A - Portable hand-held drill with overload clutch

Info

Publication number: GB2395452A
Application number: GB0226945A
Authority: GB
Inventors: Colin Cochrane; Scott Keenlyside
Original assignee: Black and Decker Inc
Current assignee: Black and Decker Inc
Priority date: 2002-11-19
Filing date: 2002-11-19
Publication date: 2004-05-26
Also published as: GB0226945D0

Abstract

A portable hand-held electric drill comprises a motor (10, fig 1) for rotatably driving a tool holder (8, fig 1) via at least one torque overload clutch. The torque overload clutch comprises two metal components rotatably mounted about the same axis of rotation adjacent to each other, each component having a friction engaging surface which faces towards the friction engaging surface of the other component. Biassing means bias the friction engaging surfaces towards each other. A clutch plate is located between the two surfaces so that the friction engaging surfaces are frictionally engaged with the clutch plate so that rotation of one component part is transferred to the second component part via the clutch plate. Preferably the clutch plate comprises a non-metallic moulded washer, and may comprise brass chippings.

Description

Torque clutch for a drill.

The present invention relates to a drill and in particular, to a torque overload clutch for use in a drill.

A typical design of drill comprises an electric motor which rotatingly drives a tool holder, such as a chuck, via a series of gears. In order to protect the motor, the drill drives the tool holder via a torque overload clutch. When an excessive torque is applied to the motor via the gear chain due to the rotation of the tool holder either being hindered or stopped usually caused by the tool located within the tool holder encountering an object which prevents it from rotating, the clutch slips thereby preventing excessive torque on the motor. Without the torque clutch, the motor would be damaged.

Typical designs of torque overload clutch comprise two metal gears which are mounted on a spindle adjacent to each other so that they have a common axis of rotation. The two gears are biased together by means of a spring so that the two metal gears are frictionally engaged with each other. One of the metal gears is rigidly attached to the spindle so that rotation of the spindle by the motor results in rotation of the first gear. The second gear is able to freely rotate about the spindle. When the spindle is rotated, the first gear rotates with it, causing the second gear to rotate due to the frictional engagement caused by the biasing means. The second gear would then drives the tool holder. However, when an excessive torque is applied, for example, by the tool holder being prevented from rotation, the frictional engagement between the two gears is insufficient to transfer the torque from one gear to the other gear and therefore the first gear slips in relation to the second gear allowing of the motor to continue rotating even though the tool holder has been stopped thus preventing excessive torque on the motor.

However, such designs of torque overload clutch suffer from the problem that manufacturing such a clutch with a consistent predetermined separation torque is difficult. Furthermore, with metal to metal contact in the clutches, small defects would sometimes tear small groves into the surface of either the faces of the two gears. These tears would cause the surfaces to bind together and effectively weld the clutch solid.

Accordingly, there is provided a portable hand-held electric drill comprising: a motor for rotatingly driving a tool holder via at least one torque overload clutch; the torque overload clutch comprising: two metal components rotatably mounted about the same axis of rotation adjacent to each other, each component having a friction engaging surface which faces towards the friction engaging surface of the other component; biasing means to bias the friction engaging surfaces towards each other; characterized in that a clutch plate substantially formed from a none metallic material is located between the two surfaces so that the friction engaging surfaces are frictionally engaged with the clutch plate so that rotation of one component part is transferred to the second component part via the clutch plate.

The two metal components can be gears mounted on a spindle, one gear being able to freely rotate about the spindle, the second gear being prevented from freely rotating

about the spindle, the two gears being biased towards each other. If so, the clutch plate can be in the form of washer sandwiched between the gears.

Ideally, the clutch plate is made from fibrous material moulded in resin. The resin washer, after some actuation, beds into the surface of the metal plate so that their profiles match. It has a stable coefficient of friction (which metal does not), which allows the assembly to clutch at a predictable torque value. It has very low wear and is resilient to high temperatures and pressures.

Preferably, the clutch plate comprises brass chippings. The chippings of brass aid the heat dissipation properties of the clutch plate.

An embodiment of the present invention will now be described with reference to the accompanying drawings of which: Figure 1 shows a design drawing of a drill with the rear section in cross-section vertically; Figure 2 shows a design drawing of a vertical cross-section of the front section of the drill; Figure 3 shows a design drawing of a vertical cross section of the clutch mechanism; Figure 4 shows a design drawing of a vertical cross section of the clutch mechanism in close-up; Figure 5 shows a design drawing of the spindle of the clutch mechanism; Figure 6 shows a drawing of the spindle of the clutch mechanism; Figure 7 shows a design drawings of the first gear; Figure 8 shows a perspective view of the first gear; Figure 9 shows a drawing of a top view of the moulded frictional washer.

Referring to figures I and 2, the drill comprises a rear housing 2 and a forward housing 4 in which are located the internal mechanisms of the drill. Mounted on the front of the drill on an output drive spindle 6 is a tool holder 8. The output drive spindle 6 rotatingly drives the tool holder 8. A tool such as a drill bit can be inserted in the tool holder 8 in order to drill a hole in well known manner.

Located within the rear housing 2 of the.drill is an electric motor 10 which is used to rotatingly drives the tool holder 8. The electric motor 2 is powered by a mains electricity supply via an electric cable 12. The electric cable 12 connects to the motor 10 via a switch 14. The electric switch 14 is operated by depression of a button 16 by the operator in well known manner. The electric motor comprises a drive spindle 18 which rotatingly drives the tool holder 8 via a series of gears and a torque overload clutch.

The motor drive spindle 18 has a plurality of teeth formed around the end of the motor drive spindle 18 which mesh with a first gear 20. The first gear is shown in more detail in figures 7 and 8 and is described in more detail below.

The first gear 20 is connected to a gear spindle 22 via a torque overload clutch in accordance with the present invention. The gear spindle is shown in more detail in figures 5 and 6. The design of the torque overload clutch is shown in figures 3 and 4 in more detail. Both the gear spindle 22 and the torque overload clutch are described in more detail below.

The gear spindle 22 rotatingly drives a second gear 24 which is mounted on the output shaft 26. The output shaft 26 comprises a plurality of the elongate grooves 28 which run lengthwise along the shaft parallel to the longitudinal axis of the output shaft. The second gear 24 comprises a plurality of axial ridges which correspond to the elongate grooves 28 and which locate within the grooves. The second gear 24 is prevented from rotating about the shaft due to the axial ridges being located within the elongate grooves 28. However, the second gear is able to slide along the output shaft 26 as the axial ridges can slide within the elongate grooves 28. The position of the second gear 24 is controlled by a pin 30 which is able to move the second gear along the output shaft 26. A knob 32 is used by the operator to move the pin 30 in order to move the second gear 24 along the output shaft 26.

The purpose of being able to slide to the second gear along the output shaft 26 is to adjust the speed at which the output shaft 26 rotates in relation to the motor drive spindle 18. The second gear 24 is able to mesh with the gear spindle 22 in two different positions. Referring to figure 6, the gear spindle 22 comprises two sets of teeth 34, 36 formed around the spindle at different locations along the length of the spindle. The outer diameter of one set of teeth 34 is larger than the other set of teeth 36. Similarly, the second gear 24 comprises two sets of teeth 38, 40 formed around the second gear 24 into different axial positions. The outer diameter of one set of teeth 38 formed around the second gear 24 is greater than the outer diameter of the second sets of teeth 40 formed around the second gear 24. When the second gear is located in a rear position as shown in figure 2, the smaller diameter set of teeth 40 on the second gear 24 mesh with the larger diameter set of teeth 34 on the spindle. This reduces the rate of rotation of the output shaft 26 by a predetermined amount. When the second gear 24 is moved to a forward position by the operator rotating the knob 32 to move the second gear 24 via the pin 30, the larger diameter set of teeth 38 on the second gear 24 mesh with the smaller diameter set of teeth 36 on the gear spindle 22.

This reduces the rate of rotation of the output shaft 26 by a smaller predetermined amount. A hammer mechanism 42 comprising two ratchet plates 44, 46 is located at the rear of the output shaft 26. The hammer mechanism, can be activated or deactivated depending on the mode of use of the drill via the operator. The design of the hammer mechanism is well known and shall not be described in any further detail.

The torque overload clutch will now be described in more detail with reference to figures 3 and 4.

Referring to figure 3, the gear spindle 22 has two sets of teeth 34, 36 in trouble is formed on the gear spindle 22. Adjacent with the larger diameter set of gear teeth 36 is a shoulder 48 which has a larger diameter than the section 50 of gear spindle 22 adjacent the shoulder 38 on the opposite side of the shoulder 48 to that of the larger diameter set of gear teeth 36. Mounted on the section 50 of the gear spindle 22 are a plurality of spring washers 52 which abut against the shoulder 48. The diameter of the hole 54 formed through the washers 52 is smaller than that of the shoulder 48 so that the washers 52 are unable to slide past the shoulder 48. Mounted on the section 50 adjacent to the spring washers 52 is the first gear 20. The first gear 20 is able to freely rotate around the section 50 of the gear spindle 22 and to freely slide axially along the section 50 of the gear spindle 22.

The first gear 20 will now be described in more detail with reference to Figure 8 and Figures 7. The first gear 20 comprises teeth 60 formed around the periphery of the gear and which mesh with the teeth formed on the end of the motor spindle 18 as described previously. The first gear 20 has a large circular recess 62 formed symmetrically about the longitudinal axis of the first gear 20 in one side of the gear 20 as best seen in figures 7 to form a cup shape. The base 64 on the recess 62 is flat. An a circular aperture 66 formed symmetrically about the longitudinal axis of the first gear 20 is formed in the base of the recess 62 and has a similar dimensional to the section 50 of the spindle gear 22.

When the first gear 20 is mounted on the section 50 of the gear spindle 22, the circular recess 62 faces away from the spring washers 52. A moulded washer 68 is mounted on the section 50 of the gear spindle 22 and is located within the circular recess of the first gear 20 so that one side of the moulded washer 68 is located against the base 64 the first gear 22. An anchor washer 70 is press fitted onto the spindle adjacent the moulded washer 68. The anchor washer is prevented from both rotating about the gear spindle 22 and from axially sliding along the gear spindle 22. When the torque overload clutches is assembled, the anchor washer 70 is pushed onto the spindle to the extent that it presses the moulded washer 68 against the base 64 of the first gear 20 which intern sandwiches the spring washers 52 between the shoulder 48 and the side of the first gear 20. This causes the spring washers 52 to be compressed and thereby exert a biasing force against the first gear 20 towards the anchor washer which is press fitted onto the gear spindle 22. The frictional contact is made between the base 64 of the first gear 20 and the moulded washer 68 which intern has a frictional engagement between the moulded washer 68 and the anchor washer 70.

When the motor rotates, the drive spindle rotates the first gear 20 via the teeth 60. As mentioned previously, the first gear is able to freely rotate about the section 50 of the gear spindle 22. Due to the biasing force of the spring washers 52 sandwiched between the shoulder 48 and the first gear 20, the first gear 20 frictionally engages and causes the moulded washer 68 to rotate which intern, is frictionally engaged with the anchor washer 70 and thus to causes it to rotate. As the anchor washer 70 is press fitted onto the spindle in such a manner that it is unable to rotate around the spindle, when the anchor washer 70 rotates, it causes the gear spindle 22 to rotate. The gear spindle rotating drives the tool holder by a one of the two sets of teeth 34, 36 as described previously.

The moulded washer 70 is rigidly moulded from a fibrous material comprising synthetic fibres with a resin bonded agent having chippings of brass moulded into the moulded washer 70. The chippings of brass aids the heat dissipation properties of the moulded washer 70.

The moulded washer, after some use, will bed into the surface of the gear so that their profiles match. It has a stable coefficient of friction which allows the assembly to clutch at a predictable torque value. It has very low wear and is resilient to high temperatures and pressures.

Claims

1 A portable hand-held electric drill comprising: a motor for rotatingly driving a tool holder via at least one torque overload clutch; the torque overload clutch comprising: two metal components rotatably mounted about the same axis of rotation adjacent to each other, each component having a friction engaging surface which faces towards the friction engaging surface of the other component; biasing means to bias the friction engaging surfaces towards each other; characterized in that a clutch plate substantially formed from a none metallic material is located between the two surfaces so that the friction engaging surfaces are frictionally engaged with the clutch plate so that rotation of one component part is transferred to the second component part via the clutch plate.

2 A portable hand-held electric drill as claimed in claim 1 wherein the two metal components are gears mounted on a spindle, one gear being able to freely rotate about the spindle, the second gear being prevented from freely rotating about the spindle, the two gears being biased towards each other.

3 A portable hand-held electric drill as claimed in claim 2 wherein the clutch plate is in the form of washer.

4 A portable hand-held electric drill as claimed in any one of the previous claims wherein the clutch plate is made from fibrous material moulded in resin.

5 A portable hand-held drill as claimed previously wherein the clutch plate comprises brass chippings.