Fluid handling – With cleaner – lubrication added to fluid or liquid sealing... – Cleaning or steam sterilizing
Reexamination Certificate
2002-03-01
2003-12-09
Michalsky, Gerald A. (Department: 3753)
Fluid handling
With cleaner, lubrication added to fluid or liquid sealing...
Cleaning or steam sterilizing
C137S546000, C137S625650, C251S129150
Reexamination Certificate
active
06659121
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a proportional solenoid for driving a spool of a hydraulic control valve and also pertains to a hydraulic control valve using the solenoid.
BACKGROUND ART
Prior Art
FIG. 1
is a sectional view showing a structural example of a conventional solenoid of the type described above. The solenoid is a proportional solenoid that generates electromagnetic force proportional to the electric current supplied to an excitation coil. The solenoid
100
has a cylindrical casing
101
. An axially movable plunger
102
is placed in the casing
101
, together with an excitation coil
104
wound around a bobbin
103
. The excitation coil
104
is disposed to surround the outer periphery of the plunger
102
. The sides of the casing
101
are covered with covers
105
and
106
.
A push pin
107
projects through the center of the cover
106
to transmit force generated from the plunger
102
and the displacement thereof to the outside of the solenoid
100
. The cover
106
has a disk-shaped cover portion
106
a
made of a magnetic material and a cylindrical portion
106
b
projecting from the cover portion
106
a
in such a manner as to surround a part of the outer periphery of the plunger
102
. The cylindrical portion
106
b
has a tapered portion at the distal end thereof. The tapered portion is engaged with a tapered portion of a non-magnetic cylindrical member
108
. A magnetic cylindrical member
109
is engaged with an end of the non-magnetic cylindrical member
108
on the side thereof remote from the cover
106
. The cylindrical portion
106
b
of the cover
106
, together with the non-magnetic cylindrical member
108
and the magnetic cylindrical member
109
, surrounds the plunger
102
.
The tapered portion of the cylindrical portion
106
b
and the tapered portion of the non-magnetic cylindrical member
108
allow a part of the axial magnetic flux produced from the excitation coil
104
to escape to the outer peripheral side, whereby the axial attraction force acting on the plunger
102
is kept constant independently of the position of the plunger. The cover
106
is provided with a through-hole
111
communicating with a compartment
110
accommodating the plunger
102
. The through-hole
111
is a hole for allowing fluid to come in and out of the compartment
110
therethrough in an amount corresponding to a change in the volume of fluid in the compartment
110
due to displacement of the plunger
102
.
In
FIG. 1
, if the plunger
102
moves rightward from the solid-line position by dx to the broken-line position, an amount of fluid corresponding to A
PL
dx flows in the space at the left-hand side of the plunger
102
from the right-hand space. Meanwhile, an amount of fluid corresponding to (A
PL
−A
PIN
)dx is discharged from the right-hand space. An amount of fluid corresponding to the volume difference A
PIN
dx is sucked into the solenoid
100
through the through-hole
111
from the outside of the solenoid
100
. Here, A
PL
denotes the sectional area of the plunger, and A
PIN
denotes the sectional area of the push pin
107
.
In the above-described conventional solenoid
100
, the through-hole
111
formed in the cover
106
is at a position below the top of the cylindrical compartment
110
accommodating the plunger
102
. Therefore, an air reservoir
112
is undesirably formed in the compartment
110
. That is, in
FIG. 1
, the distance Dh from the axis of the plunger
102
to the uppermost part of the through-hole
111
is smaller than the distance Di from the axis of the plunger
102
to the uppermost part of the compartment
110
. Consequently, the conventional solenoid
100
has a structure in which air stays in the upper part of the compartment
110
without being exhausted therefrom (i.e. the air reservoir
112
is formed).
In a case where the air reservoir
112
is not present, when the plunger
102
moves rightward in the figure, for example, the fluid at the right-hand side of the plunger
102
flows leftward, and at this time, a moderate damping action is applied to the plunger
102
by the viscosity of the fluid flowing from the right to the left. However, if there is air in the compartment
110
, because the viscosity of the air is extremely smaller than that of a liquid used as a working fluid, the damping action applied to the plunger
102
is reduced, and hence vibrations occur unfavorably.
If the air reservoir
112
is present in the solenoid
100
as used in a hydraulic control valve having a damping orifice (described later), a change in the volume of the solenoid-side space due to the displacement of the spool is undesirably absorbed by the compressibility of the air. Consequently, the damping effect cannot be obtained, and hence the spool vibrates unfavorably. Accordingly, the operation of the hydraulic control valve cannot be stabilized.
Further, when water is used as a working fluid, if there is air in the compartment
110
, the air oxidizes the plunger
102
and the surrounding members. This causes friction to increase and degrades performance unfavorably.
DISCLOSURE OF THE INVENTION
Problem to be Solved by the Invention
The present invention was made in view of the above-described circumstances. An object of the present invention is to provide a solenoid wherein air cannot be collected in the space inside the solenoid, and hence the plunger or the spool operates stably without vibrating, and there is no possibility of an increase in friction or performance degradation which would otherwise be caused by oxidation of the plunger and the surrounding members, and also provide a hydraulic control valve using the solenoid.
Means for Solving the Problem
To solve the above-described problem, a first feature of the present invention resides in a solenoid having a cylindrical excitation coil and a plunger movable in the excitation coil and adapted to generate electromagnetic force to move the plunger when an electric current is supplied to the excitation coil. A cover for closing a side of a plunger compartment accommodating the plunger is provided with upper and lower through-holes extending through the cover from the outside of the solenoid to the plunger compartment. The uppermost part of the upper through-hole is above or level with the uppermost part of the plunger compartment. The lowermost part of the lower through-hole is below or level with the lowermost part of the plunger compartment.
A second feature of the present invention resides in a hydraulic control valve including a hydraulic control valve body having a spool sliding in a sleeve, and a solenoid having a plunger and an excitation coil for generating magnetic force to move the plunger. The solenoid is attached to the hydraulic control valve body to apply moving force to the spool by the movement of the plunger. A cover for a side of the solenoid at which the solenoid is attached to the hydraulic control valve body is provided with upper and lower through-holes communicating with a plunger compartment accommodating the plunger. The uppermost part of the upper through-hole is above or level with the uppermost part of the plunger compartment. The lowermost part of the lower through-hole is below or level with the lowermost part of the plunger compartment. The hydraulic control valve body has upper and lower vertical holes. The upper vertical hole is provided at a position above the upper through-hole provided in the cover of the solenoid in communication with the upper through-hole. The lower vertical hole is provided at a position below the lower through-hole provided in the cover of the solenoid in communication with the lower through-hole. The upper vertical hole is in communication with a tank port.
As stated above, the cover of the solenoid is provided with upper and lower through-holes extending through the cover to the plunger compartment. The uppermost part of the upper through-hole is above or level with the uppermost part of the plunger compartment. The lowermost part of the lower through-hole is below or level with the lowermost pa
Takahashi Tamami
Yamashina Chishiro
Ebara Corporation
Michalsky Gerald A.
Wenderoth , Lind & Ponack, L.L.P.
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