Tool driving or impacting – Automatic control of power operated means – Drive means responsive to torque or speed condition
Reexamination Certificate
1997-02-06
2001-10-23
Harrison, Jessica J. (Department: 3713)
Tool driving or impacting
Automatic control of power operated means
Drive means responsive to torque or speed condition
C173S216000, C192S056620
Reexamination Certificate
active
06305481
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a clutch mechanism provided in a power-driven tool, such as a power-driven screwdriver and a power-driven hammer drill. More particularly, the present invention relates to a clutch mechanism for use in a power-driven tool that can adjust torque transmitted to the attached bit.
2. Description of the Prior Art
FIG. 6
shows a power-driven screwdriver
40
as disclosed in Japan Published Examined Patent Application No. S57-1393. In this screwdriver, the torque or a motor
41
is transmitted from a motor shaft
42
to a spindle
47
while being decelerated by a deceleration mechanism which includes planetary gears
45
engaged with internal gears
43
and
44
and a carrier
46
supporting the planetary gears
45
. The torque eventually rotates a tool bit held by a chuck
48
. The internal gear
44
is rotatably mounted in the deceleration mechanism and has on its front end a clutch face
44
a.
Balls
50
inserted in through-holes are formed in a gear case
49
which supports the spindle
47
. The balls
50
are pressed against the clutch face
44
a
by a leaf spring
51
. Provided in front of (toward the chuck
48
) the leaf spring
51
is a clutch handle
52
with pressure protrusions
53
formed thereon. The clutch handle
52
is axially movable between a front position and a rear position where the pressure protrusions
53
are in abutment with the leaf spring
51
.
When the clutch handle
52
is moved to the rear position, the pressure protrusions
53
presses the balls
50
against the clutch face
44
a
via the leaf springs
51
. Even if a large load is applied to the spindle
47
, the balls
50
cannot ride over the clutch face
44
a,
thus keeping the clutch engaged. In this so-called drill mode, the internal gear
44
continues to be prevented from rotating, so that the rotation of the motor
51
continues to be transmitted to the spindle
41
even if an excessive load develops.
When the clutch handle
52
is moved forward, the pressure protrusions
53
are detached from the leaf spring
51
, allowing it to deform in the axial direction. The spring force of the leaf spring
51
sets the torque at which the internal gear
44
starts to rotate (this torque is referred to as “rotation-start torque” hereinafter). If a large load exceeding the rotation-start torque of the internal gear
44
is applied to the spindle
47
, the balls
50
ride over the clutch face
44
a.
This causes the internal gear
44
to rotate idly. In this so-called screwdriver mode, the clutch is disengaged to prevent the rotation of the motor
51
from being transmitted to the spindle
41
if an excessive load develops.
Japan Published Unexamined Utility Model Application No. H6-39364 discloses another power-driven tool with a torque adjustment device. The tool comprises a compression spring for biasing a plate backward against balls (corresponding to the balls
50
in the foregoing example). The tool also includes a spring holder for adjusting the compression of the spring. When the spring is fully compressed, the tool is placed in the drill mode, in which the balls do not ride over the clutch face. When the spring is not fully compressed, the tool is placed in the screwdriver mode with the rotation-start torque corresponding to the spring compression set for the internal gear. If a load exceeding this rotation-start torque is applied to the internal gear, the balls ride over the clutch face, thereby causing the internal gear to rotate idly.
In either of the aforementioned clutch mechanisms, however, if the tool is mistakenly used as a screwdriver when the drill mode is selected, the spindle is locked as the screw is tightened since the clutch cannot be disengaged, causing an abrupt impact to be transmitted from the tool bit to the tool mechanism, sometimes damaging the gear case, the planetary gears, and other parts of the tool. Moreover, jolts are transmitted to the operator's hand.
SUMMARY OF THE INVENTION
In view of the above-identified problems, an object of the present invention is to provide in a power-driven tool a clutch mechanism that can lessen an impact transmitted to the tool mechanism when large torque is applied in the drill mode.
It is another object of the present invention to provide a power-driven tool that can avoid damage to the tool mechanism otherwise caused by such impacts.
It is still another object of the present invention to provide a power-driven tool with pleasant handling during operation.
The above and other related objects are realized by providing a clutch mechanism for use in a power-driven tool, comprising: a freely rotatable gear of a deceleration mechanism interposed between a motor and a spindle, a clutch assembly provided on the freely rotatable gear, a plate member abutting on the clutch assembly, a biasing means for biasing the clutch assembly via the plate member, and an adjustment means for adjusting the biasing force of the biasing means and for applying force to the plate member to prevent the plate member from moving, whereby torque at which the freely rotatable gear starts to rotate can be set by adjusting, with the adjustment means, the biasing force of the biasing means applied to the clutch assembly, the plate member being elastic so as to allow the freely rotatable gear to rotate when a load greater than a predetermined level is applied to the spindle even if the plate member is prevented from moving by the adjustment means.
Preferably, the part of the plate member to which the force that prevents the plate member from moving is applied is not axially aligned with the part of the plate member which abuts on the clutch assembly.
In carrying out the invention in one preferred mode, the plate member is a washer provided with a means for preventing the rotation thereof.
In this mechanism, the clutch assembly preferably comprises a clutch cam with a plurality of protrusions formed on an end surface thereof, a flange formed on the freely rotatable gear, the flange having a plurality of through-holes formed therein, and a plurality of balls retained in the through-holes of the flange, the balls being pressed against the end surface of the clutch cam by the biasing means.
Preferably, the freely rotatable gear is an internal gear and the biasing means is a compression spring.
In a preferred mode of the present invention, the adjustment means comprises a gear case which supports the spindle, the gear case being provided with an externally threaded portion, and a spring holder provided with an internally threaded portion engaging the externally threaded portion.
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Oda Zenichi
Tozawa Katsumi
Yamazaki Takashi
Foley Hoag & Eliot LLP
Harrison Jessica J.
Makita Corporation
Paradiso John
LandOfFree
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