Tool driving or impacting – Impacting devices – With anvil arranged to transmit torsional impact to tool
Reexamination Certificate
2000-06-15
2002-01-01
Smith, Scott A. (Department: 3721)
Tool driving or impacting
Impacting devices
With anvil arranged to transmit torsional impact to tool
C173S093000, C173S177000
Reexamination Certificate
active
06334494
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a control unit for a hydraulic impact wrench. More particularly, the present invention relates to a control unit for a hydraulic impact wench where a pulsed torque is controlled with high precision. Even more particularly, the present invention relates to a control unit that permits particularly simple construction.
Referring to
FIG. 4
, a conventional control unit for an impact wrench includes a cylinder casing
51
containing a main shaft
52
. Cylinder casing
51
is rotatively driven by an air motor (not shown). The distal end of main shaft
52
is adapted to be engage members to be torqued. An oil cylinder
53
, is formed inside cylinder casing
51
. The sectional contour of oil cylinder
53
consists of a pair of two circular arcs whose centers are displaced to slightly eccentric positions from the rotational center of main shaft
52
. The two circular arcs are aligned with each other to form a generally elliptical configuration. Sealed portions
53
a
,
53
b
,
53
c
, and
53
d
are defined at substantially quadrisected positions on the inner circumferential surface of the oil cylinder
53
. Sealed portions
53
a
,
53
b
,
53
c
, and
53
d
extend along the axial direction of the oil cylinder. Oil cylinder
53
is filled with hydraulic operating fluid (not shown). A proximal end portion of main shaft
52
is disposed in the oil cylinder
53
perpendicular to the plane of the drawing sheet of FIG.
4
.
A blade groove
54
, is defined by the site corresponding to the disposition of the proximal end portion of the main shaft
52
and the oil cylinder
53
. A pair of blades
55
,
55
are placed slidably in the blade groove
54
.
Referring to
FIG. 5
, a spring
56
energizes blades
55
,
55
outwardly in the diametrical direction thereof to move the distal end portions of blades
55
,
55
into slidable contact with the inner circumferential wall of the oil cylinder
53
. Seal portions
52
a
and
52
b
in the main shaft
52
are formed at positions perpendicular to the respective blades
55
,
55
.
Referring now also to
FIG. 4
, when cylinder casing
51
is rotatively driven by an air motor a relative rotating position, defined between the main shaft
52
and the oil cylinder
53
, changes. When respective seal portions
52
a
,
52
b
of the main shaft, and the distal ends of respective blades
55
,
55
, are in contact with the respective seal portions
53
a
,
53
b
,
53
c
, and
53
d
, a position shown in
FIG. 5
is reached. When the position shown in
FIG. 5
is reached, hydraulic operating fluid, contained on either side of the respective blades
55
,
55
, defines a high pressure chamber H. Low pressure chamber L, not containing hydraulic operating fluid, is defined opposite the high pressure chamber H with respect to blades
55
,
55
. The low pressure chamber L has a lower pressure than the high pressure chamber H. Containment of the hydraulic operating fluid produces a pulse of high pressure that rotatively acts upon a main shaft
52
to apply a pulsed torque condition to a member to be torqued. The same condition for the containment of hydraulic operating fluid, as described above, appears where the cylinder casing
51
rotates 180 degrees from the position shown in FIG.
5
.
A bypass mechanism is arranged so that one torque pulse is produced per rotation of the cylinder casing
51
. The communication path mechanism communicates pressure from high pressure chamber H to low pressure chamber L only under conditions where respective seal portions
53
b
,
53
d
,
52
a
, and
52
b
are in contact with each other.
After the high pressure chamber H and the low pressure chamber L are defined in the oil cylinder
53
, a portion of the high pressure hydraulic operating fluid contained in the high pressure chamber H must be bypassed to the lower pressure chamber L to release cylinder casing
51
for further rotation. A bypass passage
57
is defined in the cylinder casing
51
for this purpose. A valve shaft insertion hole
58
, is bored on the cylinder casing
51
facing the bypass passage
57
. An adjustable valve shaft
59
is inserted into the insertion hole
58
.
A communication path
60
on the valve shaft
59
allows hydraulic operating fluid to penetrate the bypass passage
57
. The communication path
60
functions as a variable aperture where the flow passage area of communication path
60
changes through axial adjustment of valve shaft
59
. The peak pressure pulse in high pressure chamber H is controlled by the adjustment of the flow passage area. Thus the pulsed torque is controlled by varying the flow passage area of the communication path
60
. When the flow passage area is reduced, high peak pressure is produced and a high pulsed torque is obtained for the hydraulic pulse generation mechanism.
A mechanism for stopping automatically the operation of the hydraulic pulse generation mechanism when a predetermined pulsed torque is obtained includes a relief valve
61
mounted on a shaft end portion on the distal side of the valve shaft
59
. Relief valve
61
includes a ball
62
which is pressed by a spring
63
into contact with a shaft end surface of valve shaft
59
. Hydraulic operating fluid in communication path
60
, acts upon ball
62
through a pressure leading path
64
, defined in a shaft center portion of valve shaft
59
, so that pressure opposes the force of spring
63
.
A secondary side of relief valve
61
communicates with a cylinder chamber
65
on a top cover. A piston
66
is contained inside cylinder chamber
65
. An automatic shut off mechanism (not shown) is operated by a movement of a piston
66
upon a rod
67
.
As a result, during operation when a predetermined peak pressure is produced in the high pressure chamber H and hydraulic operating fluid in communication path
60
exceeds a predetermined pressure, relief valve
61
is opened against the force of spring
63
. Thus, the hydraulic operating fluid is released to flow into the cylinder chamber
65
to push a piston
66
and operate the automatic shut off mechanism through rod
67
. This ends the operation.
Pulsed torque in the hydraulic pulse mechanism is generated when valve shaft
59
is transferred axially to adjust the flow path area of communication passage
60
. At the same time valve shaft
59
adjusts the spring force of spring
63
in relief valve
61
.
When the pulsed torque is increased, valve shaft
59
is translated to the right side of
FIG. 5
thus increasing the opening of the aperture in communication path
60
. This increases the peak pressure of hydraulic operating fluid produced in high pressure chamber H. Simultaneously, spring
63
of relief valve
61
is compressed to set the relief pressure to a high value.
The pulsed torque is influenced by two related values, the peak pressure of a hydraulic operating fluid in high pressure chamber H, and the spring force in relief valve
61
. When the peak pressure and the spring force repeat with the same characteristics as that of the original response to transfer of valve shaft
59
an operator achieves a similar torque. In a conventional hydraulic impact wrench, the peak pressure and the spring force are correlative but do not vary with quite the same characteristics. In hydraulic impact wrench operations where the spring force is more that the increase in peak pressure, relief valve
61
may not operate and thereby cause inconvenience to operators. In hydraulic impact wrench operations where a sufficient peak pressure is obtained, relief valve
61
, may open before a predetermined peak pressure is obtained if a sufficient spring force is not achieved. This results in less than the desired torque for the operator.
Conventional pulse generation mechanisms are particularly disadvantaged by very high dimensional accuracy requirements and close attention to manufacturing and assembly details to achieve the desired precision torque control and reduce persistent failures to operate. Manufacturing and assembly details, for conventional pulse general mechanisms,
Fuji Air Tools Co., Ltd.
Morrison Law Firm
Smith Scott A.
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