Pumps – Motor driven – Electric or magnetic motor
Reexamination Certificate
1999-11-10
2001-08-14
Thorpe, Timothy S. (Department: 3746)
Pumps
Motor driven
Electric or magnetic motor
C417S555100, C417S549000
Reexamination Certificate
active
06273689
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electromagnetic pump, and more particularly, to an electromagnetic pump suitable for use in a separating oil pump of a two-cycle engine.
2. Background Art
An electromagnetic pump—which applies a pulse current to a solenoid, to thereby reciprocate a plunger and draw oil in and force oil out—has conventionally been employed as a separate oil pump of a two-cycle engine.
FIG. 3
shows an example of such a conventional electromagnetic pump. An illustrated plunger
2
is slidably fitted into a cylinder
1
formed from non-magnetic material, such as aluminum or brass, and is forced rightward by means of restoration force of a compression coil spring
8
.
An inner yoke
3
opposite the plunger
2
is pressingly fitted into an end yoke
4
, and the end yoke
4
is fixed to an outer yoke
5
by means of caulking. A nipple
6
presssingly-fitted into the outer yoke
5
is in close proximity to the plunger
2
. The plunger
2
, the inner yoke
3
, the end yoke
4
, the outer yoke
5
, and the nipple
6
are formed from magnetic material and constitute a magnetic circuit.
A coil
16
, which is wound around a plastic coil bobbin
13
and applies magnetomotive force to the magnetic circuit, is covered with the coil bobbin
13
and a plastic mold
14
. The plastic mold
14
is housed in the space which surrounds the cylinder
1
and which is defined by the end yoke
4
and the outer yoke
5
. The edge of the outer yoke
5
is locked to the end yoke
4
by means of caulking, while the plastic mold
14
remains in pressing contact with the end yoke
4
by means of a cushion member
23
interposed between the outer yoke
5
and the plastic mold
14
. Power is supplied to the coil
16
from an electrode
15
embedded in the plastic mold
14
.
A valve seat
7
is pressed into the inner yoke
3
while being properly positioned. A discharge valve
12
is forced by the compression coil spring
10
so as to close a flow channel of the valve seat
7
. A valve seat
24
is pressingly fitted into the plunger
2
. An inlet valve
11
is forced by a compression coil spring
9
so as to close a flow channel of the valve seat
24
.
An O-ring
19
hermetically seals a space between the inner yoke
3
and the cylinder
1
, and an O-ring
17
hermetically seals a space between the nipple
6
and the cylinder
1
. A spacer
20
interposed between the nipple
6
and the plunger
2
controls the maximum magnetic gap between the plunger
2
and the inner yoke
3
; i.e., a plunger stroke.
In the electromagnetic pump having the foregoing configuration, when an electric current flows through the coil
16
, a magnetic field develops in the magnetic gap between the plunger
2
and the inner yoke
3
, as a result of which the plunger
2
is attracted by the inner yoke
3
against the restoration force of the compression coil spring
8
. When the electric current flowing through the coil
16
is shut off, the plunger
2
is separated from the inner yoke
3
and is brought into pressing contact with the spacer
20
, by means of restoration force of the compression coil spring
8
.
The plunger
2
reciprocates in the manner as mentioned previously. When the plunger
2
is moved rightward the discharge valve
12
is closed and the inlet valve
11
is opened, whereby oil is drawn into a pump chamber (a space between the discharge valve
12
and the inlet valve
11
) from the nipple
6
10
and the center hole of the plunger
2
, by way of a gap between the inlet valve
11
and the valve seat
24
. In contrast, when the plunger
2
is moved leftward, the discharge valve
12
is opened and the inlet valve
11
is closed, whereby oil is forced out to an oil flow channel of the inner yoke
4
from the pump chamber, by way of the space between the discharge valve
12
and the valve seat
7
. An engine control unit controls a pulse current which is to be applied to the coil
16
in response to a signal output from a sensor for detecting the working state of the engine, thus controlling the amount of engine oil to be supplied.
The flow rate of the electromagnetic pump is determined from the number of pulses of the electric current and plunger strokes. The stroke of the plunger
2
corresponds to a difference between the distance between the end face of the spacer
20
and the end face of the inner yoke
3
and the distance between the end face of the plunger
2
and a plane at an opposite end portion of the plunger
2
, which contacts the end face of the spacer
20
. Tolerances of many parts contribute to the distance between the end face of the spacer
20
and the end face of the inner yoke
3
.
More specifically, tolerances stemming from the pressing of the nipple
6
into the outer yoke
5
, fixing of the end yoke
4
to the outer yoke
5
by caulking, and dimensional tolerances of the nipple
6
, the cylinder
1
, the plunger
2
, the spacer
20
, and the inner yoke
5
, contribute to the distance.
In terms of electrical conditions under which the plunger
2
can be actuated, the diameter of the plunger is limited to a value of 6 mm to 7 mm. If the diameter of the plunger is made smaller than this range, the plunger cannot be actuated. Further, in order to diminish power consumption, the stroke of the plunger
2
must be made smaller. In consideration of the amount of oil required to be delivered, the stroke of the plunger
2
assumes a value of 0.5 mm or less for a two-cycle engine. If the tolerance of flow rate is reduced to 10% or less, variations in the stroke of the plunger
2
must be held to ±0.05 mm or less. Thus, in order to reduce the tolerance of stroke of the plunger, the spacer
20
must be prepared in various sizes, and adjustment of stroke requires a lot of time.
Further, since the compression coil spring
9
for constraining the inlet valve
11
is disposed within the pump chamber, the dead volume of the pump chamber becomes large, thereby resulting in a decrease in compression ratio and a drop in air displacement capability. If the air displacement capability of the pump is too small, in the worst case the pump fails to supply oil because of an air-lock phenomenon.
The present invention has been conceived in view of the foregoing problems of the prior art, and an object of the present invention is to provide an electromagnetic pump capable of readily and precisely determining the stroke of a plunger. Another object of the present invention is to provide an electromagnetic pump having large air displacement capability.
SUMMARY OF THE INVENTION
To these ends, the present invention provides an electromagnetic pump, in which a plunger is reciprocated within a cylinder by means of the restoration force of a spring and electromagnetic force acting on a magnetic circuit, comprising an inner yoke and the plunger, so as to reduce a magnetic gap between the inner yoke and the plunger, wherein
the stroke of the plunger is limited by two planes of two members disposed so as to be opposite each other with the cylinder interposed therebetween.
Preferably, one of the two members corresponds to a ring-shaped spacer, and the spacer is brought into pressing contact with the cylinder by means of a wave washer.
Preferably, a fluid inlet channel is formed within the plunger; a spring receiving section which extends to the inside of the inlet channel of the plunger is formed in the inlet valve which opens or closes the inlet channel; and a spring for constraining the inlet valve is locked to the spring receiving section.
Preferably, a protuberance is formed on a plastic mold covering a coil for applying a magnetomotive force to the plunger, and the protuberance is deformed to fix the plastic mold by means of fixing an end yoke to an outer yoke by caulking while the plastic mold is housed within the space defined by the end yoke and an outer yoke, which constitute the magnetic circuit.
REFERENCES:
patent: 3302582 (1967-02-01), Kofink
patent: 4306842 (1981-12-01), Masaka
patent: 4632645 (1986-12-01), Kawakami et al.
patent: 4643653 (1987
Katuya Maita
Kenichi Kubota
Kiyoshi Sato
Norio Takehana
Goodman & Teitelbaum, Esqs.
Mikuniadec Corporation
Solak Timothy P.
Thorpe Timothy S.
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