Valves and valve actuation – Electrically actuated valve – Including solenoid
Reexamination Certificate
2001-12-07
2004-10-19
Mancene, Gene (Department: 3754)
Valves and valve actuation
Electrically actuated valve
Including solenoid
C335S236000, C335S262000
Reexamination Certificate
active
06805331
ABSTRACT:
TECHNICAL FIELD
The present invention relates to electromagnetically energized actuators, and more particularly to an electromagnetically energized actuator configured for minimization of plunger friction and plunger impact.
BACKGROUND OF THE INVENTION
A conventional pneumatic valve
10
is depicted at
FIGS. 1 through 2
in which an electromagnetically energized actuator used to control flow of fuel vapors from a canister to the engine intake manifold. The conventional pneumatic valve
10
includes a housing
12
, an electromagnet assembly
14
which includes a solenoid
14
a
wound on a spool
14
b
, a brass tube
16
concentrically disposed relative to the spool, a stop
18
fixedly disposed in the tube and composed of a highly permeable material, a plunger
20
reciprocally disposed within the tube and composed of a highly permeable material, a spring
22
of a spring assembly
24
formed at the facing ends
18
f
,
20
f
of the stop and the plunger which biases the plunger away from the stop, and a valve seat
26
located on the plunger at an end thereof distal from the aforementioned facing end. The combination of the plunger, the stop, the spring assembly a first plate
32
and a second plate
34
, as shown at
FIG. 2
, constitutes a conventional electromagnetically energized actuator
38
.
When the solenoid is energized, the plunger is magnetically pulled toward the stop, overcoming the biasing by the spring such that the facing end of the plunger moves toward the facing end of the stop, with the consequence that the valve seat is opened. When the solenoid is de-energized, the spring pushes the plunger away from the stop, thereby again closing the valve seat.
Energization/de-energization of the solenoid
14
a
is current (voltage) source
28
regulated, for example, by a pulse width modulated (PWM) signal generated from a microprocessor
30
, wherein the programming thereof is designed, for example, for enhanced evaporative emission control to meet EPA emissions regulations, and provides precision flow at low PWM duty cycles to maintain the correct air-fuel mixture at low engine speeds. Moreover, the pulse width modulation is used to control the flow through the purge system with typical frequency ranges from 8 to 100 Hz.
In the aforementioned example, the microprocessor is used to generate the PWM signal of the solenoid so as to supply full voltage to the circuit long enough to allow the solenoid to energize. Once the solenoid is energized, the state of the valve changes from OFF to ON allowing full airflow through the valve (for a normally closed valve), and when the pulse ends the valve returns to its normal state (OFF). The duty cycle determines the percentage of time that the valve is energized providing a way to adjust the flow rate required.
As mentioned, the plunger moves toward the stop due to the magnetic force created by the energized solenoid, wherein the magnetic flux flows through the magnetic package, through the first and second plates and through the plunger and through stop. This change of the position of the plunger regulates, via the valve, the flow of air through the system. When the magnetic force disappears, the spring located between the stop and plunger pushes the plunger against the valve seat with enough force to maintain a good seal at the valve, shutting off the flow when no purge is required.
As plunger moves back and forth (reciprocates) while operating, two main problems emerge.
The first problem relates to the tube
16
. Friction between the plunger and the tube occurs as the plunger slidingly reciprocates therealong. The tube is composed of brass which wears over a lifetime of millions of reciprocation cycles. This wear leads to reduced durability and adversely affects the over-all reliability of the pneumatic valve. A conventional redress to this wear problem (and also to prevent tube scratching and oxidation of the plunger) is to TEFLON® coat the plunger using, for example, EMRALON 334. However, this is an extra manufacturing step which does not eliminate the problem. Problems related to the brass tube include wide tolerances, plunger sliding noise, and corrosion. Additionally, as can be seen best at
FIG. 2
, the tube
16
is mounted to opposing first and second plates
32
,
34
with respect to the housing
12
. At the first plate
32
, the tube has a thinned end
36
having a uniformly reduced cross-sectional thickness, which involves yet another added manufacturing step.
The second problem relates to plunger impact. With each reciprocation, the plunger is caused by the co-action of the solenoid and spring to impact at its ends of travel. This impacting results in undesirable noise generation and undesirable wear when the plunger hits the valve seat and the stop. This condition is made worse at low temperatures (ie., below about −10 degrees C.). Related to this problem is the excessive amount of magnetic energy stored in the solenoid. This arises because the secondary air gap G
S
between the first plate
32
and the plunger
20
is constant (basically being about the thickness of the thinned end
36
) even as the plunger reciprocates, the only factor affecting the reluctance is the change in area of the plunger within the first plate
32
, which area change is not significant enough to substantially increase the reluctance at the secondary air gap, wherein the relation for reluctance, A, at the secondary air gap, G
S
, is given by:
=
l/&mgr;A,
where &mgr; is the permeability of the secondary air gap, l is the uniform separation distance between the plunger and the first plate which coincides with the thickness of the tube sidewall at the thinned end
36
, and A is the area of the plunger within the first plate). With the reluctance at the secondary air gap G
S
remaining about the same, and with the reluctance at the primary air gap G
P
between the facing ends of the plunger and the stop, the stored magnetic energy causes the plunger to impact forcefully and also tends to retard the ability of the spring to effect fast valve closure, and also tends to retard the ability of the magnetic field to effect fast valve opening.
Accordingly, what remains needed in the art is an electromagnetically energized actuator which has low friction, low wear, low impact, and low noise attributes.
SUMMARY OF THE INVENTION
The present invention is an improved electromagnetically energized actuator featuring low friction, low wear, low impact and low noise attributes.
The improved electromagnetically energized actuator according to the present invention includes a polymer tube, a stop fixedly disposed in the tube and composed of a highly permeable material, a plunger reciprocally disposed within the tube and composed of a highly permeable material, a spring assembly including a spring which is formed at the facing ends the stop and the plunger which spring serves to bias the plunger away from the stop, a first plate composed of a highly permeable material which is connected to a first end of the tube, and a second plate composed of a highly permeable material which is connected to a second end of the tube.
In an example of an environment of operation, the electromagnetically energized actuator according to the present invention is disposed in a pneumatic valve including a housing, an electromagnet assembly including a solenoid, and a valve seat. The first and second plates are connected to the housing and form part of the electromagnet assembly, and the valve seat is located at an end of the plunger distal from the aforementioned facing end thereof. The plunger is reciprocal between a first position (responsive to biasing by the spring) and a second position responsive to energization of the solenoid (which overcomes the biasing of the spring). The electromagnetically energized actuator according to the present invention may be used in devices other than a pneumatic valve, which is merely presented herein as an exemplification of use.
The tube is composed of a polymer which (relative to a conventional brass tube) allows tighter tolera
Burrola Santos
Pelka Jean-Francois
Rad Mahmood
Delphi Technologies Inc.
Funke Jimmy L.
Keasel Eric
Mancene Gene
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