Tools – Wrench – screwdriver – or driver therefor – Machine
Reexamination Certificate
2002-06-05
2004-09-14
Wilson, Lee D (Department: 3723)
Tools
Wrench, screwdriver, or driver therefor
Machine
C081S057130
Reexamination Certificate
active
06789448
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a power ratchet wrench and more particularly to an improvement in a power ratchet wrench for mounting and dismounting threaded items such as bolts, nuts and screws in, for instance, assembling, disassembling and maintaining automobiles and various other devices and structures.
2. Prior Art
Prior art power ratchet wrenches are disclosed in, for instance, Japanese Patent Application Laid-Open Nos. S63-28571, S63-256373, H6-35115 (S61-260982), H10-217140, and 2001-30179.
In these power ratchet wrenches, two sides of a yoke are received by opposing faces of a distal end bifurcated portion of a housing, and a spindle having a workpiece engagement portion, a small diameter portion, and a large diameter portion is inserted inside the yoke. The rotary motion of a motor provided on a proximal side of the housing is transmitted through a motion converter that converts a rotary motion into a reciprocal swing motion, thereby reciprocally rotating the yoke by way of using a center line of the spindle as a center of its rotational-motion, so that a ratchet pawl of a ratchet mechanism installed in a space inside the large diameter portion of the spindle is alternately engaged with and disengaged from an internal teeth formed around an inner peripheral surface of a hole of the yoke, thus causing the spindle to rotate in steps and causing a workpiece, such as a bolt, nut, screw, and the like, to turn with a workpiece engagement portion provided at one end of the spindle.
In above power ratchet wrenches, the internal teeth of the yoke are supported in the large diameter portion of the spindle. This structure will be described in detail with reference to FIG.
5
.
Two sides of a yoke
1
are received by the opposing faces of the retaining elements
2
b
′ and
2
b
″ of the distal end bifurcated portion of a housing
2
; and the yoke
1
, using the center line of the spindle
3
inserted in the yoke
1
as its rotational center, reciprocally rotates by a motor
4
provided inside the proximal side of the housing
2
through a speed-reduction assembly
5
, a power transmission shaft
6
, and a motion converter
7
that converts a rotary motion into a reciprocal swing motion. As a result, the ratchet pawl
8
a
of a ratchet mechanism
8
installed inside the large diameter portion
3
c
of the spindle
3
is alternately engaged with and disengaged from an internal teeth
1
a
of the yoke
1
, thus causing the spindle
3
to rotate in steps and to turn the workpiece, such as a bolt, nuts and screws, with the workpiece engagement portion
3
a
provided at the distal end of the spindle
3
.
The power ratchet wrench disclosed in Japanese Patent Application Publication (Kokoku) H6-35115 has a hammer structure that provides hammer rotation in place of the speed-reduction assembly
5
.
As generally known, the ratchet mechanism
8
comprises a ratchet pawl
8
a
, a pin shaft
8
b
on which the middle portion of the ratchet pawl
8
a
pivots, a knob shaft
8
c
fitted in a hole made in the end face on the large diameter portion
3
c
of the spindle
3
, a spring
8
d
housed in a side hole of the knob shaft
8
c
, and a pin
8
e
that is biased by the spring
8
d
so as to be pressed into a recess on the back of the ratchet pawl
8
a.
This mechanism is designed so that the location where the push pin
8
e
presses can be varied by twisting the knob shaft
8
c
to either the right or the left. When the knob shaft
8
c
is twisted to the right, the right-hand portion of the ratchet pawl
8
a
is alternately engaged with and disengaged from the internal teeth
1
a
of the yoke
1
, so that the spindle
3
is rotated in steps to the right. When the knob shaft
8
c
is twisted to the left, the left-hand portion of the ratchet pawl
8
a
is alternately engaged with and disengaged from the internal teeth
1
a
of the yoke
1
, so that the spindle
3
is rotated in steps to the left.
Two sides of the yoke
1
is supported by the opposing faces of the retaining elements
2
b
′ and
2
b
″ of the distal end bifurcated portion of the housing
2
, a guide
9
is fitted in a circular hole formed in the retaining element
2
b
″ of the distal end bifurcated portion, and a hole snap ring
10
is attached so that the small diameter portion
3
b
of the spindle
3
is supported by the guide
9
. Springs
11
and balls
12
are housed in two or three holes provided so as to be equidistantly spaced in a circle at the step end face of the small diameter portion
3
b
and large diameter portion
3
c
of the spindle
3
, and the balls
12
are pushed into the guide
9
, thus creating a braking force that brakes the free rotation of the spindle
3
. Also, the large diameter portion
3
c
of the spindle
3
is supported while being pressed by a guide
13
that serves as a spring seat, thereby causing the spindle
3
to function as a support shaft for the yoke
1
.
The motion converter
7
for converting rotary motion into reciprocal swing motion comprises an eccentric shaft
7
a
integrally provided at the distal end of the power transmission shaft
6
, a ball
7
b
into which the eccentric shaft
7
a
is fitted, and a recess
7
c
formed in a jutting portion of the proximal side of the yoke
1
and in which the ball
7
b
is engaged.
The above-described power ratchet wrench, however, has drawbacks.
(1) When a bolt is being fastened tightly, or when a tightly fastened bolt is being loosened, the yoke
1
hits the retaining elements
2
b
′ and
2
b
″ of the distal end bifurcated portion of the housing
2
while rotating. The inventors discovered the following as a result of investigating this mechanism.
The inside periphery of the internal teeth
1
a
of the yoke
1
is supported by the large diameter portion
3
c
of the spindle
3
, and thus, the internal teeth
1
a
of the yoke
1
are inherently worn out quickly. Furthermore, right from the outset there is a large clearance between the large diameter portion
3
c
of the spindle
3
and the diameter of the internal teeth
1
a
of the yoke
1
, and this clearance grows even larger if the internal teeth
1
a
of the yoke
1
wears out quickly.
There is also a clearance between the yoke
1
and the retaining elements
2
b
′ and
2
b
″ of the distal end bifurcated portion of the housing
2
.
Therefore, when the ball
7
b
engages the recess
7
c
of the yoke
1
and undergoes planetary rotation that causes the yoke
1
to pivot, the rotational center of the yoke
1
will be greatly shifted with respect to the spindle
3
, and the rotational center will also be tilted as the yoke
1
rotate. It is even possible that the yoke
1
tilts around a line perpendicular to both the rotational center of the spindle
3
and the centerline of the ratchet.
The run-out of the yoke
1
when a bolt was being tightened was examined by photography with a high-speed video camera. The examination shows that every time the ball
7
b
undergoes one planetary rotation, the yoke
1
tilts around a line perpendicular to both the rotational center of the spindle
3
and the center line of the ratchet, then returns, tilts again, returns, and this is repeated.
The yoke
1
hits the retaining elements
2
b
′ and
2
b
″ of the distal end bifurcated portion of the housing
2
while rotating. The reason found for this is that the cycle in which the yoke
1
tilts around a line perpendicular to both the rotational center of the spindle
3
and the center line of the ratchet, returns, tilts, and then returns is repeated over and over at high speed, and the yoke
1
repeatedly exerts a wedge action that spreads open the gap between the retaining elements
2
b
′ and
2
b
″ of the distal end bifurcated portion.
(2) The function whereby the yoke
1
rotates the spindle
3
in steps becomes unreliable, and it shortens the useful life of the product. The inventors discovered the following as a result of investigation of this shortened product service life.
Ver
Ono Akira
Yumoto Akio
Koda & Androlia
Saitama Seiko Kabushiki Kaisha
Wilson Lee D
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