Metal working – Method of mechanical manufacture – Impeller making
Reexamination Certificate
1999-09-20
2001-01-30
Rosenbaum, Igida (Department: 3726)
Metal working
Method of mechanical manufacture
Impeller making
C029S888025
Reexamination Certificate
active
06178633
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a vane for use in various displacement-type actuators and a method for producing the vane.
The operation of a vane actuator exemplified by a hydraulic vane pump is first explained referring to FIG.
8
. In this vane pump which may be used as a hydraulic motor as it is, a rotor
11
is fixed to a shaft
22
and rotatable in a closed space defined by a cam ring
13
and a pair of side blocks (not-shown) fluid-tightly fixed to both side ends of the cam ring
13
. A member such as the cam ring
13
which is brought into contact with the rotor
11
may sometimes be called “contact member” herein.
Each vane
1
is substantially in a flat rectangular parallelepiped shape, both wide side surfaces thereof being slidably guided in a radial groove
12
of the rotor
11
, and both narrow side surfaces thereof being slidably guided along inner surfaces of the side blocks. The rotor
11
rotates together with the vanes
1
in the direction shown by the arrow
20
. During the rotation of the rotor
11
, a top surface
1
a
of each vane
1
is always pressed into contact with a cam surface
14
of the cam ring
13
by a centrifugal force, a spring force, an outward force exerted by a pressurized hydraulic fluid entering into a space between the vane
1
and the radial groove
12
of the rotor
11
.
Each pump room
15
defined by the rotor
11
, the adjacent vanes
1
, the cam surface
14
of the cam ring
13
and the side blocks has a volume variable depending on the rotation of the rotor
11
, with the maximum volume at upper left and lower right positions and the minimum volume at lower left and upper right positions in FIG.
8
. Accordingly, the hydraulic fluid is sucked into the pump room
15
through intake ports
16
,
16
provided in the side block and discharged from the pump room
15
through discharge ports
17
,
17
provided in the side block.
The top surface
1
a
of the vane
1
which is in slidable contact with the cam surface
14
is arcuately or roundly projecting, such that good sealing is always kept between the vane
1
and the cam surface
14
regardless of a relative angle of the vane
1
to the cam surface
14
. Therefore, it has conventionally been considered that the arcuately projecting or round top surface
1
a
of the vane
1
should have high precision in dimension, straightness and surface roughness.
To achieve high precision in dimension and surface roughness, the top surface
1
a
of the vane
1
has conventionally been ground by a creep feed grinding wheel
9
as shown in
FIG. 9
, which has a grinding groove
9
a
formed on a circumferential surface by a dressing tool. The grinding wheel
9
is moved back and forth while rotating along the top surface
1
a
of the vane
1
in the direction perpendicular to the plane of the paper presenting FIG.
9
. Though this grinding method can provide the round top surface
1
a
of the vane
1
with high precision in straightness and surface smoothness, it is a time-consuming process poor in efficiency, making the total production cost of the vanes high.
In view of these facts, methods of producing vanes without creep feed grinding have been proposed.
Japanese Patent Laid-Open No. 58-206896 discloses a method for producing a vane comprising the steps of subjecting a flat bar having a round surface at a top end to a normalization treatment; cutting the flat bar to a predetermined length to provide a vane; hardening the vane by a heat treatment; grinding surfaces of the vane to predetermined dimensions except for the round top surface to provide a vane having a predetermined cross section; assembling the resultant vanes into a vane pump such that the round top surface of each vane is pressed onto a cam surface of a cam ring; and carrying out a running-in operation of the vane pump to wear away a decarburized layer formed on the round top surface of each vane in the normalization step, such that the top surface of the vane is provided with a shape adapted to the cam surface of the cam ring. However, this method is not usable because it generates a large amount of wear dust which causes various troubles.
Japanese Patent Laid-Open No. 2-308993 discloses a method for producing a vane by plastic working such as drawing or extruding. As shown in FIGS.
11
(
a
),
11
(
b
), both side surfaces
30
c
,
30
c
′ of a flat bar
30
are rolled by a pair of rolls
21
,
22
having circumferential grooves
23
,
24
. Each of the circumferential grooves
23
,
24
has a flat bottom surface
23
a
,
24
a
, a pair of rounded corners
23
b
,
23
c
,
24
b
,
24
c
to impart to the flat bar
30
flat side surfaces
30
c
,
30
c
′, a rounded top surface
30
a
and a chamfered bottom end surface
30
b
. Because of rolling in the thickness direction, however, high precision in shape, straightness and surface smoothness cannot be achieved in the top surface
30
a
of the flat bar
30
. As a result, the resultant vane fails to provide sufficient sealing without finish-grinding of a top surface.
Like the above two methods, vanes have been produced from flat bars which are cut to predetermined length by band saws, grinders, presses (shearing), etc., at a proper production stage. These cutting methods, however, are insufficient in cutting precision in length, surface roughness, scars, straightness, rectangularity, etc. In the case of shearing, the cross-sectional shape of the resultant vane may inevitably be distorted at cut ends, making it necessary to shear-cut the flat bar with a proper margin which is then removed by finish-grinding. Thus, the cutting method and the subsequent finish-grinding are also important factors determining the production cost of the vanes.
To improve the overall efficiency of an actuator, it is important to decrease friction between the vane and the cam ring while suppressing leaks. For this purpose, the vanes and the cam ring should have sufficiently precise dimension with minimum surface roughness. Since an inner surface of the cam ring is usually ground by a small-diameter grinding wheel supported by a projected shaft, the precise grinding of the inner surface of the cam ring cannot be carried out efficiently. The cam ring receives larger grinding pressure in an inner portion than in both opening (edge) portions from the grinding wheel, leading to larger grinding in both edge portions of the cam ring. As a result, a slight taper is inevitably formed in a ground inner surface of the cam ring within a range of about 0.5 mm from each opening of the cam ring.
The vane is usually barrel-finished, leaving a droop in a round top surface of the vane within a range of about 0.1 mm or more from the end thereof. Accordingly, when these vanes are assembled with the cam ring, leaking of a hydraulic fluid inevitably takes place because of the gap between the droops of the vanes at both ends of their round top surfaces and the tapered opening ends of the cam ring in its inner surface.
OBJECT AND SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a vane adapted to be in a slidable contact with a contact member which may have drooping to some extent, without suffering from the leaking of a hydraulic fluid.
Another object of the present invention is to provide a method for producing such a vane at a low cost.
In view of the fact that drooping or tapering is unavoidable in the contact member such as a cam ring, the inventor has come to the conclusion that the top surface of a vane should be in an arcuate or round projection shape with small upward bulging at both ends to compensate for the drooping of the contact member, and has investigated how a vane can be provided with such bulging on a round top surface thereof. As a result, it has been found that when a vane is cut from a long flat bar by a shearing cutter in the thickness direction D
2
in
FIG. 6
, the vane is subjected to pressure in the thickness direction D
2
to cause bulging in a vertical direction D
3
at both vertical ends of the sheared surface, and that the bulged
Hitachi Metals Ltd.
Rosenbaum Igida
Sughrue Mion Zinn Macpeak & Seas, PLLC
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