Solenoid valve

Details Solenoid valve Solenoid valve

1999-05-25

2001-04-24

Walton, George L. (Department: 3753)

Fluid handling

With cleaner, lubrication added to fluid or liquid sealing...

Cleaning or steam sterilizing

C251S129050, C251S129080, C251S129210

Reexamination Certificate

active

06220275

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a solenoid-operated flow control valve which is particularly suitable for use in a hydraulic system wherein a working fluid contaminated by and laden with minute particles of metallic materials is circulated.
2. Description of the Prior Art
Solenoid valves are widely used in various hydraulic systems to electronically control flow of a fluid.
As shown in
FIG. 1A
, a solenoid valve may typically include a movable valve member
1
connected to an armature or plunger
2
. The armature
2
is operated by a solenoid assembly comprised of a solenoid windings
3
, a magnetic pole piece
4
, and a yoke member
5
. The armature is biased downwards by a return coil spring
6
which is supported at its upper end by a spring retainer
7
which may be in the form of an adjusting screw adjustably screwed into the pole piece
4
. An annular spacer
8
made of a non-magnetizable material is fixed to the lower end of the pole piece
4
so as to limit the upward travel of the armature
2
to thereby space the armature at a given distance from the pole piece in the fully open position of the valve.
In the case where the solenoid valve is controlled by an electronic control system, it is customary to operate the solenoid valve on the duty cycle basis by cyclically energizing the solenoid windings with intermittent drive pulses having a frequency which may range, for example, from 200 to 300 cycles per second, the degree of opening of the valve being controlled by varying the width, or duty factor, of respective drive pulses.
Such an intermittent energization of the solenoid coil would result undesirable chattering of the valve. In order to suppress or subdue chattering of the valve that would result from the duty cycle operation of the solenoid, the armature chamber
9
receiving the armature
2
is filled with a fluid to thereby damp the vibratory movement of the armature
2
. To this end, the armature chamber
9
is communicated by an annular passage
10
with the outlet port
11
of the valve to admit the fluid at the outlet to flow into the armature chamber, the passage
10
being formed between the armature and the yoke member
5
. The fluid in the armature chamber is drained by a drain passage
12
which extends axially throughout the spring retainer
7
.
In certain applications of the solenoid valves, a hydraulic fluid is inevitably contaminated by fine particles of ferrous materials resulting from wear of machine parts. For example, in an automatic transmission system of a vehicle, an automatic transmission fluid is circulated through various metallic moving parts such as gear trains and clutch discs so that the fluid will become considerably contaminated by finely divided debris, fragments or particles of ferrous materials resulting from wearing of gears and other metallic parts.
The problem encountered with the solenoid valves as used to control a ferrous contaminant-laden fluid is that ferrous particles born in the hydraulic fluid are magnetically attracted and trapped in the magnetic gaps of the solenoid structure as the fluid is passed through the armature chamber.
More specifically, as shown in
FIG. 1B
wherein parts and members encircled by a circle in
FIG. 1A
are shown in an enlarged scale, ferrous particles are attracted to and deposit on the lower end face of the pole piece
4
as well as on the upper end face of the armature
2
as schematically shown at
12
and
13
. Metallic particles are also magnetically held at the radial gap between the armature and the yoke member as shown at
14
. Furthermore, particles are accumulated between the consecutive turns of the coil spring as shown at
15
.
The ferrous particles magnetically accumulated in this manner at the magnetic gaps of the solenoid will be oriented along the magnetic flux path in an acicular fashion to project from one surface toward the opposite surface of the magnetic gap, thereby giving rise to a situation in which the gap is somewhat bridged or short-circuited by chains of attracted particles. As a result, the magnetic permeability across the gap is inadvertently increased in response to a lapse of time so that the operating property of the solenoid valve, e.g., the current versus fluid pressure characteristics, is undesirably altered during the service life of the solenoid valve.
Accordingly, it is an object of the present invention to provide a solenoid valve which is suitable for use in controlling a fluid which is contaminated by and laden with minute particles of metallic materials.
Another object of the invention is to provide a solenoid valve which is capable of effectively preventing ferrous particles from accumulating at the magnetic gaps of the solenoid assembly.
A still another object of the invention is to provide a solenoid valve which exhibits a constant operating characteristics throughout the service life of the valve.
SUMMARY OF THE INVENTION
This invention provides a solenoid valve having a movable valve member operated by a solenoid actuator having an armature movably received in an armature chamber communicated by an annular passage with an outlet of the valve, a drain passage extending from the chamber to communicate the chamber with the outside of the valve.
The feature of the invention is that the drain passage is arranged to open into the armature chamber at a location radially outwardly offset from the axis of the chamber.
With this arrangement, a flow of fluid flowing from the annular passage into the armature chamber is directly transferred and delivered toward the drain passage without passing the central region of the chamber in which the fluid tends to stay stagnant. As a result, the flow of fluid that has entered into the armature chamber will continue to flow into the drain passage without loosing its velocity to any substantial degree. Accordingly, sludge of ferrous particles magnetically attracted at the magnetic gaps of the solenoid assembly is washed away by the flow of fluid so that the gaps are self-cleaned each time the solenoid valve is actuated.
Another advantage is that the flow of fluid entered into the armature chamber is allowed to leave the armature chamber without being brought into contact with the return coil spring which is arranged at the center of the chamber. This prevents the ferrous particles in the fluid from being attracted and adhering to the coil spring.
Preferably, the drain passage is formed between a magnetic pole piece of the solenoid structure and a spring retainer received in the central bore of the pole piece.
In a preferred embodiment of the invention, the solenoid assembly includes an annular spacer, of a non-magnetizable material, arranged between the armature and the magnetic pole piece. The spacer is mounted to the armature and covers an end face of the armature. With this arrangement, ferrous particles in the fluid is prevented from accessing the end face of the armature.
In an alternative embodiment, the spacer is fixed to the magnetic pole piece and is configured to cover an end face of the pole piece facing the armature in such a manner as to prevent ferrous particles from accessing the end face of the pole piece.
In another embodiment of the invention, the outer surface of the armature exposed in the armature chamber is coated with a coating of a non-magnetizable material, such as a fluorocarbon resin. The resin coating on the armature assists the ferrous particles magnetically held at the radial gap between the armature and the yoke member to be readily released and washed away from the opposite surfaces of the gap.
These features and advantages of the invention, as well as other features and advantages thereof, will become apparent from the following description.


REFERENCES:
patent: 3185177 (1965-05-01), Brandenberg et al.
patent: 3324889 (1967-06-01), Batts
patent: 3550632 (1970-12-01), Noakes
patent: 4639704 (1987-01-01), Shand et al.
patent: 4711265 (1987-12-01), Davis et al.
patent: 4790351 (1988-12-01), Kervagoret
patent: 5358215 (1994-10-01

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