Hydraulic unit with increased torque

Details Hydraulic unit with increased torque Hydraulic unit with increased torque

2002-01-11

2004-03-23

Rada, Rinaldi I. (Department: 3721)

Tool driving or impacting

Impacting devices

With anvil arranged to transmit torsional impact to tool

C173S093000, C173S093500, C173S104000, C173S105000

Reexamination Certificate

active

06708778

ABSTRACT:

RELATED APPLICATION
This application claims the benefit and priority of Japanese Patent Application No. 2001-005478, filed Jan. 12, 2001, and Japanese Patent Application No. 2001-111685, filed Apr. 10, 2001, the contents of which are incorporated herein by reference.
FIELD OF THE INVENTION
The present invention relates to hydraulic units for use in electric power tools such as torque wrenches for generating pulsating instantaneous torque by means of hydraulic pressure.
BACKGROUND OF THE INVENTION
FIG. 6
shows a conventional hydraulic unit
50
. The hydraulic unit includes a cylindrical case
51
which integrally accommodates a liner
52
coupled to the output shaft of a tool motor for receiving torque therefrom. The hydraulic unit
50
further includes front and rear caps (not shown) as closing elements that plug the axial front and rear ends of the case
51
, thus forming a fluid chamber
53
therein. The front and rear caps also rotatably support a spindle
54
within the fluid chamber
53
. Furthermore, inserted radially in the spindle
54
is a pair of blades
55
that are biased generally outwardly in mutually opposing directions by a coil spring
62
so that the blades can be retracted into the spindle when inward pressure exceeding the biasing force of the coil spring is applied to the top surfaces of the blades
55
. The spindle
54
additionally includes a pair of ribs
56
which protrudes therefrom at diametrically opposite positions and which are 90 degrees phase-shifted from the blades
55
. Formed at the axial front and rear ends of the liner
52
are two generally oblong guide holes
57
along which the top surfaces of the blades
55
slide. Two axially extending first sealing bodies
58
are disposed between the guide holes
57
, with each sealing body
58
provided with a first sealing surface
59
which is flush with and conforms to the interior surface of the guide hole
57
. Additionally, two axially extending second sealing bodies
60
are disposed between the guide holes
57
, with each sealing body
60
provided with a second sealing surface
61
which also conforms to the interior surface of the guide hole
57
. The first sealing bodies
58
are 90 degrees phase-shifted from the second sealing bodies
60
. As shown in
FIG. 6A
, in the operation of the electric power tool, as the liner
52
rotates in the direction indicated in the arrow, the blades
55
rotate relative to the case
51
along the interior surfaces of the guide holes
57
. When the blades
55
reach the first sealing surfaces
59
and the ribs
56
reach the second sealing surfaces
61
, the fluid chamber
53
are divided into four partitions, creating alternate high and low pressure chambers. This differential pressure in the fluid chamber causes generation of impact torque (generation of a hydraulic impulse) to the spindle
54
. One example of such an hydraulic unit is disclosed in Japanese Published Examined Utility Model Application No. 6-27341.
In the foregoing hydraulic unit
50
, upon generation of a hydraulic impulse, the liner
52
continues its rotation, thus removing the blades
55
and the ribs
56
from the first and second sealing surfaces
59
and
61
, respectively. As the seal within the fluid chamber
53
is opened at this moment, no hydraulic impulse is generated, such that the liner
52
alone rotates (FIG.
6
B). As the liner
52
continues its rotation, the blades
55
slide along the interior surfaces of the guide holes
57
, approaching the second sealing surfaces
61
. As this gradually pushes the blades
55
into the spindle
54
, the basing force of the coil spring
62
against the blades
55
increases (
FIG. 6C
) until it peaks when the blades reaches the second sealing surfaces
61
(FIG.
6
D). Accordingly, the blades' pressure on the interior surfaces of the guide holes
57
acts as rotational resistance to the spindle
54
, thus impeding its rotation. In addition, as illustrated, the cross section of the guide holes
57
is a combination of three circles such that the guide holes
57
have low axial ridges on both sides of each second sealing surface
61
, where the intermediate circle intersects the two side circles. Thus, as shown in
FIG. 6D
, when the blades
55
ride over the intersection points P, additional resistance to rotation of the blades
55
is created.
FIG. 8
is a graph showing a pattern of torque production in the conventional hydraulic unit
50
. Peaks “a” indicate intended torque produced by hydraulic impulses, whereas lower torque peaks “b” are produced between these hydraulic impulses by the above-described rotational resistance. Such useless low torque disadvantageously decreases the intended torque produced by hydraulic impulses.
FIG. 7
shows another conventional hydraulic unit
50
′ similar to the foregoing conventional hydraulic unit
30
.
FIGS. 7A-L
are similar to
FIGS. 6A-D
, but they show the movement of the blades
55
′ with respect to the case
51
′ in a more detailed sequence, with each figure depicting unit's parts or elements in the position 10 degrees further rotated from the position in the immediately preceding figure. Additionally, identical or similar reference numerals or characters denote identical or similar parts or elements of those in FIG.
6
throughout the several views. Therefore, description of such elements is omitted.
As shown in
FIGS. 7A-C
, when the blades
55
′ and the ribs
56
′ reach the first and second sealing bodies
58
′ and
60
′, respectively, with the counterclockwise rotation of the case
51
′ and the liner
52
′, the fluid chamber
53
′ is divided into four partitions or sub-chambers, thus producing impact torque (hydraulic impulse), as in the foregoing unit
30
. Referring to
FIGS. 7D-L
, following the production of impact torque, as the liner
52
′ continues to rotate, the blades
55
′ are gradually retracted into the spindle
54
′ against the biasing force of the coil spring and eventually slide across the second sealing bodies
60
′ over the ridges on the inner surfaces of the guide holes
57
′. Compared to
FIG. 6
,
FIGS. 7D-L
illustrate in greater detail the increased resistance to the rotation of the spindle
54
′ due to the cross section of the guide holes
57
′ being a combination of three circles.
Moreover, as the cross section of the guide holes has a complex shape due to the combination of three intersecting circles, the interior surfaces of the guide holes
57
′ requires high-precision polishing, thus increasing the number of manufacturing steps and resulting in higher cost.
In the foregoing hydraulic unit
60
′, the cross section of the guide holes
57
′ of the liner
52
′ is a combination of three circles, and the first and second sealing bodies
58
′ are required, thus making the entire structure of the liner complex.
SUMMARY OF THE INVENTION
In view of the above-identified problems, the present invention provides a hydraulic unit wherein the rotational resistance to the spindle can be effectively reduced except upon generation of hydraulic impulses, thus augmenting the torque produced by such hydraulic impulses.
The present invention also provides a hydraulic unit which has a simplified construction and thus a greater cost advantage over conventional hydraulic units.
In accordance with one embodiment of the present invention a hydraulic unit is provided including a generally cylindrical case containing working fluid, with the case including an interior surface, front and rear closing elements at two axial ends thereof, and at least one first blade-sealing surface and at least one second rib-sealing surface. The hydraulic unit further includes a spindle which is inserted into the case and includes front and rear ends rotatably supported by the front and rear closing elements, respectively, with the spindle further including at regular intervals at least one blade and at least one rib for circumferentially partitioning an interio

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