GB2400635A

GB2400635A - Tapered spline slip clutch

Info

Publication number: GB2400635A
Application number: GB0309055A
Authority: GB
Inventors: Manfred Droste
Original assignee: Black and Decker Inc
Current assignee: Black and Decker Inc
Priority date: 2003-04-17
Filing date: 2003-04-17
Publication date: 2004-10-20
Also published as: GB0309055D0

Abstract

A hammer comprising a spindle (4,Fig 2A) capable of being rotatingly driven by a motor via a drive chain, the drive chain comprising an overload spindle clutch which is capable of slipping when a torque which is greater than a predetermined amount is applied to it wherein the clutch comprises a sliding hub (2, Fig 2A) which is slidably mounted on the spindle (4, Fig 2A) having at least one spline 16 formed along its inner surface which engages with at least one corresponding trough 12 formed along the length of the spindle (4, Fig 2A) characterised in that the trough 12 and the splines 16 are correspondingly tapered along their length. The end of the spline 16 adjacent an O-ring, which prevents the sliding hub (2, Fig 2A) from travelling rearwardly more than a predetermined position due to a biasing force of a spring, has been tapered at an angle relative to the longitudinal axis (14, Fig 2A) of the sliding hub (2, Fig 2A).

Description

ROTARY HAMMER

Present invention relates to rotary hammers and in particular, to rotary hammers incorporating an overload clutch arrangement.

Rotary hammers normally have a housing and a hollow cylindrical spindle mounted in the housing. The spindle allows insertion of the shank of the tool or bit, for example a drill bit or a chisel bit, into the front end thereof so that is retained in the front end of the spindle with a degree of axial movement. The spindle may be a single cylindrical part or may be made of two or more coaxial cylindrical parts, which together form the hammer spindle. For example, a front part of the spindle may be formed as a separate tool holder body for retaining the tool or bit.

Such hammers are provided with an impact mechanism which converts the rotational drive from an electric motor to a reciprocating drive for driving a piston, which may be a hollow piston, to reciprocate within the spindle. The piston reciprocatingly drives a ram by means of a closed air cushion located between the piston and the ram. The impact from the ram is transmitted to the tool or bit of the hammer, optionally via a beatpiece.

Rotary hammers can be employed in combination impact and drilling mode, and also in some cases in a drilling mode only, in which the spindle, borrow forward most part of the spindle, and hence the bit inserted therein will be caused to rotate. In combination impact and drilling mode, the bit will be caused to rotate at the same time as the bit receives a repeated impact. A rotary drive mechanism transmits the rotary drive from the electric motor to the spindle to cause the spindle, or a forward most part thereof, to rotate.

Rotary hammers are known to have overload clutches in the drive train which transmit rotary drive from the motor to the spindle, or the forward most part of the spindle. Such overload clutches are designed to transmit rotary drive when the transmitted drive torque is below a predetermined threshold and to slip when the transmitted drive torque exceeds threshold. During rotary hammering or drilling, and working on materials of none uniform hardness, for example aggregate or steel reinforced concrete, the bit becomes stuck, which causes the torque transmitted via the rotary drive train to increase and causes the hammer housing inturn to rotate against grip of the user. The torque can increase rapidly and in some cases the user can lose control of the hammer. The use of an overload clutch, can reduce the risk of this occurring, by ensuring that the clutch slips and rotary drive to the bit is interrupted at a torque threshold below that where a user is likely to lose control the hammer. Accordingly, the clutch must slip reliably at a predetermined torque throughout the lifetime of the hammer, even after sustained use of the hammer.

Relevant prior art is DE2522446, DE3828309, DE4216808 and EP0552328.

It is an object of the present invention to provide a clutch with improved performance.

Accordingly there is provided a hammer comprising a spindle capable of being rotatingly driven by a motor via a drive chain, the drive chain comprising an overload spindle clutch which is capable of slipping when a torque which is greater than a predetermined amount is applied to it wherein the clutch comprises a sliding hub which is slidably mounted on the spindle having at least one spline formed along its inner surface which engages with at least one corresponding trough formed along the length of the spindle characterized in that the trough and the splines are correspondingly tapered along their length.

Preferably, the end of the spline adjacent a stop mechanism, which prevents the sliding hub from travailing rearward a Iy more than a predetermined position due to a biasing force, has been tapered at an angle relative to the longitudinal axis of the sliding hub. This can enable a rubber O-ring to be mounted adjacent the end of the spline to prevent the sliding hub from travailing rearwardly more than a predetermined position due to a biasing force.

An embodiment of the invention will now be described with reference to the following six drawings of which: Figures 1A to 1 F show the existing design of sliding hub located around the spindle; Figures 2A to 2F show the new design of sliding hub located around the spindle; Figure 3A to 3F show a design drawing of the old design of sliding hub; Figure 4A to 41 show a design drawing of the new design of sliding hub; Figure 5A to 5D shows a design drawing of the old design of spindle; and Figure 6A to BE shows a design drawing of the new design of spindle.

Referring to figures 1A to 1F, which show an old design of parts of the spindle clutch, a sliding hub 2 is mounted on a spindle 4 of the hammer. A helical spring 6 is wrapped around the sliding hub 2 and biases the sliding hub rearwardly. A circlip 8 prevents the sliding hub 2 from travailing further rearwardly due to the biasing force of the spring 6.

Teeth 10 are formed around one end of the sliding hub 2. Formed in the spindle 4 are two elongate troughs 12 which will run in a direction parallel to the longitudinal axis 14 of the spindle 4. These troughs 12 can be best seen in Figure 5 which is a design drawing of the old design of spindle 4. The troughs have a uniform cross-section along the length of the troughs, the sides of the troughs running parallel to each other.

Formed on the inner surface of the sliding hub are two splines 16 which correspond to the elongate troughs 12 in the spindle 4. When the sliding hub 2 is mounted on the spindle 4, the splines 16 locate within the elongate troughs 12. The sliding hub 2 is able to slide along the length of the spindle 4 with the splines 16 sliding within the troughs 12. Though the splines 16 allow the sliding movement of the sliding hub, they prevent the sliding hub s from rotating around the spindle 4. This enables a rotation force to be transferred from the sliding hub to the spindle due to the splines located within the elongate troughs.

The cross-section of the splines 16 is uniform along their length, the sides of the splines 16 being roughly parallel along the length of the splines. The end 20 of the splines 16 adjacent the circlip 8 is perpendicular 18 to the longitudinal axis 14 of the sliding hub 2 and spindle 4 as best seen in Figure 3.

Some problems have been experienced with the sliding hub 2 sliding back. Therefore, a design change has been made to the spindle 4 and sliding hub 2 to introduce some friction into the system to slow down the sliding movement of the sliding hub 2.

Referring to figures 2a to 2f, the shape of the elongate troughs 12 have been altered so that they taper as can be seen in figure 6. This results in the trough narrowing as it travels away from the circlip. Similarly, the splines 16 formed on the sliding hub 4 have also been tapered as can be seen in figure 4. This results in the side of the splines 16 having to travel against the wall of the tapered elongate troughs 12 against the rotational movement of the spindle 4 thus increasing the resistance between the two. Furthermore, the end 20 of the splines 16 adjacent the circlip has been tapered at an angle 26 relative to the longitudinal axis of the sliding hub as best seen in figure 4. This enables a rubber O-ring to be used to stop the sliding hub is opposed to a metal circlip 8.

Claims

Claims 1 A hammer comprising a spindle capable of being rotatingly driven

by a motor via a drive chain, the drive chain comprising an overload spindle clutch which is capable of slipping when a torque which is greater than a predetermined amount is applied to it wherein the clutch comprises a sliding hub which is slidably mounted on the spindle having at least one spline formed along its inner surface which engages with a corresponding trough formed along the length of the spindle characterized in that the trough and the spline are correspondingly tapered along their length.
2 A hammer as claimed in claim 1 wherein the end of the spline adjacent a stop mechanism, which prevents the sliding hub from travailing rearwardly more than a predetermined position due to a biasing force, has been tapered at an angle relative to the longitudinal axis of the sliding hub.
3 A hammer as claimed in any of the previous claims wherein a rubber Oring is mounted adjacent the end of the spline to prevent the sliding hub from travailing rearwardly more than a predetermined position due to a biasing force.