Linear solenoid actuator for an exhaust gas recirculation valve

A valve assembly is disclosed for metering exhaust gas to the intake manifold of an internal combustion engine. The valve assembly has a base which includes a passage communicating between the intake manifold and the exhaust manifold of the engine. The passage has a valve seat which is operable with a valve member to meter the flow of exhaust gas through the passage to the intake manifold. An actuator assembly is mounted to the base and is operably connected to the valve member to move the valve member into and out of engagement with the valve seat. The actuator assembly includes a solenoid having a magnetic circuit comprising stationary primary and secondary pole pieces and a moveable armature. The primary pole piece includes an inner cylindrical wall operable to define, with the armature, a fixed radial gap for the passage of magnetic flux, and a tapered outer wall operable to increase the mass of the magnetic circuit, through which flux may pass, as the armature moves axially within cylindrical inner primary pole piece includes a n inwardly tapered, conical portion which operates, with an associated conical end of the moveable armature, to increase the axial opening force on the armature by establishing a secondary gap for the passage of magnetic flux as the armature approaches the conical tapered portion of the cylindrical wall. In addition, leakage flux is directed from said conical portion of said armature to said cylindrical inner wall across the entire range of motion of the armature to increase the axial force on said armature during operation of the valve.

TECHNICAL FIELD 
The invention relates to a valve assembly for metering exhaust gas to the 
intake of an internal combustion engine and, particularly, to such a valve 
assembly having an improved linear solenoid actuator. 
BACKGROUND 
Exhaust gas recirculation (EGR) valves are employed in connection with 
internal combustion engines to aid in the lowering of regulated emissions 
and to enhance fuel economy by metering exhaust gas to the intake manifold 
for delivery to the combustion chamber. In the exhaust gas recirculation 
valve assembly set forth in U.S. Pat. 5,020,505 issued Jun. 4, 1991, to 
Grey et al., a base assembly contains a valve member in engagement with a 
valve seat. The base supports an actuator assembly including a linear, 
electromagnetic solenoid actuator which is operable to move the valve 
member relative to the valve seat to regulate the flow of exhaust gas 
therethrough. 
The linear actuator includes primary and secondary pole pieces which 
cooperate to define an axially extending chamber in which is disposed a 
moveable armature. The armature includes a cylindrical member which moves, 
upon energization of the actuator, in the direction of the primary pole 
piece. The primary pole piece includes a substantially cylindrical center 
pole member with inner and outer walls defining a closed and an open end. 
The inner wall is substantially cylindrical and facilitates axial movement 
of the similarly configured armature, relative to the pole. As the 
armature moves in the direction of the closed end, a fixed, radial air gap 
is defined between the outer cylindrical wall of the armature and the 
inner cylindrical wall of the cylindrical center pole. Such a fixed air 
gap provides substantial controllability to the operation of the actuator. 
To provide a linear function to the operation of the actuator, the outer 
cylindrical wall of the cylindrical center pole is tapered outwardly, in 
the direction of the closed end thereof, such that as the armature moves 
in the direction of the closed end of the center pole, generally the 
opening direction of the solenoid operated valve, the mass of the pole 
piece through which the magnetic flux is forced to pass increases, so as 
to control the rate of magnetic saturation necessary to provide the 
desired linear displacement versus current characteristic. 
The configuration results a peak force intermediate of the ends of armature 
travel, which diminishes as the armature continues to move towards its 
maximum axial travel. Such a reduction in opening force as the armature, 
and associated valve, approaches a fully opened position requires an 
increase in current to avoid a reduction in performance due to a loss of 
linear performance of the actuator. 
SUMMARY OF THE INVENTION 
The present invention is directed to an improved exhaust gas recirculation 
(EGR) valve for use with an internal combustion engine. It is an object of 
the present invention to address the reduction in opening force produced 
by the linear actuator as the armature moves the valve towards a fully 
opened position. Force reduction is minimized by providing a novel, 
primary pole piece having a cup shaped body with a substantially 
cylindrical center pole member. The pole member includes an inner wall 
which defines an axially extending chamber configured to receive, for 
axial travel therein, an associated armature. The cylindrical, center pole 
member of the primary pole piece also includes an outer wall having a 
taper which gradually increases the wall thickness in the direction of the 
closed end of the pole piece. As the armature moves in the direction of 
the closed end of the cup shaped pole piece the mass of the pole piece 
through which magnetic flux may pass is increased thereby providing a 
linear function to the operation of the actuator. Adjacent the terminal 
end of the axial chamber of the center pole member, the cylindrical wall 
tapers axially inwardly, defining a semi-conical end. The conical end of 
the axial chamber cooperates with a similarly tapered end on the armature 
to establish a secondary air gap which is operable to provide additional 
opening force on the armature across its range of motion and, more 
importantly, as the armature nears its fully displaced location near the 
closed end of the axially extending chamber of the center pole member. As 
the armature moves within the axial chamber, leakage flux is directed from 
the wall defining the conical end of the taper to the cylindrical wall of 
the center pole member providing an additional force component in the 
axial direction. As the tapered end of the armature approaches the closed 
end of the axial chamber, leakage flux is directed across the secondary 
gap defined by the associated conical surfaces of the axial chamber and 
the armature to rapidly increase the force component in the axial 
direction and thereby compensate for the force reduction experienced in 
prior linear actuators. 
Other objects and features of the invention will become apparent by 
reference to the following description and to the drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring first to FIGS. 1 and 2, an exhaust gas recirculation (EGR) valve, 
designated generally as 10, is shown for operation with an internal 
combustion engine 12. The EGR valve 10 comprises four principal 
subassemblies: the EGR base assembly 14, the valve assembly 16, the 
electromagnetic solenoid actuator assembly 18 and the pintle position 
sensor 20. 
The EGR base assembly 14 includes a housing 22 for attachment to the engine 
12. Located in the bottom 26 of housing 22 are openings 40 and 42 which 
are interconnected by passage 44. Opening 42 receives a valve seat insert 
48 having an opening 50 surrounded by a valve seat 52. Located in the top 
24 of the EGR housing 22 is valve stem opening 54, positioned coaxially 
with the opening 50 in the valve seat insert 48. 
The actuator assembly 18 is carried in a housing 56. The housing 56 
includes an upper cylindrical wall 58, as viewed in the Figures, defining 
an upper, open end 60 and a bottom or base 62. Extending downwardly from 
the bottom 62 of the housing 56 are one or more support members 64 which 
are included as part of the housing extrusion. The bottom of each support 
member 64 includes an opening 70 so that the support member 64 may 
accommodate attachment means such as bolts 72 which, when engaged with a 
corresponding threaded opening 74 in EGR base assembly 14, operate to 
retain the actuator housing 56 in rigid engagement therewith. 
Also extending from the bottom 62 of the actuator housing 56 is a stepped 
extension 76 which comprises bearing housing 78 and valve stem passage 80. 
Both the bearing housing 78 and the valve stem passage 80 are integral 
with the actuator housing 56 and, in addition, occupy a coaxial, adjacent 
relationship to one another. The valve stem passage 80 includes an opening 
90 for the passage of a valve stem 92. 
The actuator housing 56 is assembled to the EGR base assembly 14 by 
alignment of the support members 64 with the threaded openings 74 in the 
housing 22 and insertion of the valve stem passage 80 into the valve stem 
opening 54 in the top 24. The valve stem passage 80 establishes an 
interference fit with the valve stem opening 54 to form a sealing 
interface between the actuator housing 56 and the EGR housing 22. 
Valve assembly 16 comprises a poppet valve having an axially extending 
valve stem 92 with a valve head 94 at a first end. The second, distal end 
96 of the valve stem 92 extends through the opening 50 in valve seat 48, 
and through the valve stem passage 80 and the bearing housing 78 to 
terminate at a location near the upper, open end 60 of the upper 
cylindrical wall 58 of the actuator housing 56. A valve stem bearing 98 is 
received in the bearing housing 78 and has an opening 100 through which 
the valve stem 92 passes. The opening 100 has a diameter which will 
support axial movement of the stem 92 in the bearing while minimizing 
leakage of exhaust gas at the interface thereof. 
Radial clearance is established between the valve stem 92 and the opening 
90 of the valve stem passage 80 and between the bearing 98 and the wall of 
the bearing housing 78, respectively. The bearing 98 is not fixed in 
position but is free to float, to a limited extent, utilizing the 
clearances to allow radial movement of the valve stem 92 occurring as a 
result of such factors as actuator variability or operation-caused wear. 
Lateral movement facilitated by the floating bearing allows the interface 
between the bearing opening 100 and the valve stem 92 to be of an 
extremely close tolerance, virtually eliminating gas leakage into the 
actuator assembly 18. In addition to the sealing interface established 
between the valve stem 92 and the bearing opening 100, a face seal is 
defined between the lower surface of the bearing member 98 and the 
shoulder 84 of the bearing housing. By placing the sealing surface normal 
to the direction of valve stem movement a rigid, or press fit is not 
required between the bearing 98 and the wall of the bearing housing 78 
thereby permitting the utilization of radial clearance to accommodate 
lateral movement of the valve stem and bearing. In order to maintain 
leak-free sealing at the face seal, a biasing force is exerted on the 
bearing 98 by a biasing member such as compression spring 112. 
The actuator assembly 18 includes a linear solenoid 116 which is installed 
in the actuator housing 56 and is connected to the second, distal end 96 
of the valve stem 92. The solenoid 116 is operable to move the valve stem 
92 such that the valve head 94 is moved into and out of engagement with 
the valve seat 52 to initiate and regulate the flow of exhaust gas through 
the passage 44 in the EGR housing 22. As shown in FIGS. 2 and 3, a primary 
pole piece 118 has a cup shaped configuration with a substantially 
cylindrical center pole member 120, a base 122 and a cylindrical outer 
wall 124. The outer wall 124 is dimensioned to permit sliding insertion of 
the pole piece into the open end 60 of the actuator housing 56. The open 
end 128 of the cup-shaped primary pole piece 118 receives the annular 
coil/bobbin assembly 130 in space 132 formed between the upwardly 
projecting center pole member 120 and the outer wall 124. 
Closure of the cup-shaped primary pole piece 118 is by a secondary pole 
piece 134 having a cylindrical center pole member 136 adapted for 
insertion within the axially extending, center opening 138 of the 
coil/bobbin assembly 130. The upper end of the secondary pole piece 134, 
as viewed in the Figures, includes a radially outwardly extending flange 
140 for engagement with the circumference of the open end 128 of the wall 
124 of primary pole piece 118. As thus far described, the magnetic circuit 
of the solenoid actuator 116 comprises primary pole piece 118, which 
establishes an extended magnetic circuit about a substantial portion of 
the coil 130, the secondary pole piece 134, and an armature 146 which is 
fixed to, and movable with, the second end 96 of the valve stem 92. The 
center pole member 120 of the primary pole piece 118 and the 
corresponding, center pole member 136 of the secondary pole piece 134 
cooperate to define a cylindrical passage 152 having an axis which is 
substantially aligned with valve stem axis 93 and having a diameter which 
permits sliding axial movement of the armature 146, and the attached valve 
stem 32, therein. 
Critical to the operation of the armature within the solenoid assembly is 
the maintenance of a circumferential, primary air gap 148 between the 
armature 146 and the center pole members 120,136. Establishment of the air 
gap 148 in the present EGR valve is through the use of a non-magnetic 
sleeve 150 which is positioned in the cylindrical passage 152 of the 
solenoid between the pole pieces and the armature. The sleeve 150 is 
constructed of a thin, non-magnetic material such as stainless steel or a 
temperature resistant polymer and has a series of slotted openings 154 
which extend axially and provide communication between the captive air 
volume 156 above the armature 146 and the space 158 below the armature to 
minimize the effect of pneumatic damping on the movement of the armature. 
In the linear solenoid actuator of the type contemplated herein, a linear 
relationship is desirable between force and current, over the entire range 
of armature, and hence, valve motion. To address the deficiencies inherent 
in prior linear EGR solenoid designs, the outer wall 160 of the 
cylindrical center pole member 120 is tapered outwardly from the actuator 
axis 93 in the direction of the closed end 122 of the primary pole piece 
118 such that, as the armature 146 moves in the direction of the closed 
end 122, the mass of the pole piece through which the magnetic flux passes 
will increase, providing a desired linear displacement versus current 
characteristic. The tapered outer wall 160 of the center pole member 120 
allows the inner wall 162 to remain substantially cylindrical defining the 
fixed, radial air gap 148 between the outer cylindrical wall 164 of the 
armature 146 and the inner cylindrical wall 162 of the cylindrical center 
pole 120. The fixed working air gap 148 provides substantial 
controllability to the operation of the actuator 18 since the force 
characteristics across the gap will not vary due to a changing gap 
dimension. 
Adjacent the terminal end of the axial chamber 152, defined by the 
cylindrical center pole members 120 and 136, the wall 162 tapers axially 
inwardly, towards the center axis 93 of the actuator, to define a 
semi-conical chamber end 166. This conical chamber end 166, along with the 
cylindrical inner wall 162 of the center pole member 120 cooperates with a 
corresponding, similarly tapered end 168 formed on the armature 146 to 
thereby establish a secondary flux path which is operable to provide 
additional opening force on the armature 146, in the axial direction, 
across its full range of motion and, more importantly, as the armature 
nears its fully displaced location near the closed end terminal or bottom 
end of the axial chamber 156. 
Specifically, as the armature 146 moves within the axial chamber 152, 
leakage flux "A", FIG. 5, is directed across the air gap defined by the 
conical armature end 168 and the cylindrical wall 162 of the center pole 
member 120 providing additional opening force in the axial direction. The 
additional opening force provided in this range of armature motion results 
in improved actuator response from a given current input. As the armature 
146 approaches the closed end of the primary pole piece 118, corresponding 
to a fully opened valve position, flux "B", FIG. 6, is directed across the 
secondary gap defined by the associated conical surfaces 166 and 168 of 
the axial chamber 152 and the armature 146. Closure of the gap resulting 
from continued movement of the armature 146 in the valve opening 
direction, rapidly increases the magnetic force. The increase in force 
operates to compensate for the reduction in opening force experienced in 
prior linear actuators at the limits of actuator movement. As such, the 
tapered armature 146 and corresponding tapered wall portion 166 provide an 
additional degree of design freedom which is not available in typical 
solenoid actuators. The added design freedom results in higher axial 
forces acting on the armature in all positions. 
Closing actuator assembly 18 is a pintle position sensor assembly 20. The 
pintle position sensor has a biased follower 165 which contacts the upper 
surface of the armature 146 and moves in concert with the valve shaft 92 
to track its position and, as a result, the position of valve head 94 
relative to seat 52. The position of the valve shaft 92 is translated into 
an electrical signal which is transmitted via the electrical connection 
167 to an appropriate controller (not shown). The pintle position sensor 
20 has a flange 170, extending about the perimeter thereof. The flange 170 
of the sensor 20 is captured, along with an elastomeric seal 174 by the 
upper edge 176 of the open end 60 of the actuator housing 56 which is 
swaged over the flange 170. 
The preferred operation of the EGR valve 10 shall now be described with 
reference to FIGS. 2 and 3. FIG. 2 shows the EGR valve in a closed 
position as might be encountered during a wide-open throttle setting when 
no exhaust gas is required to be recirculated to the engine intake. In the 
closed position, the coil 130 remains in a non-energized state and, as a 
result, no force creating magnetic flux fields are established. The spring 
112 biases the armature 146 and attached valve assembly towards the closed 
position to thereby seat the valve member 94 against the valve seat 52. 
Upon a determination by an associated controller that engine operating 
conditions warrant the introduction of EGR to the intake manifold, a 
current signal is transmitted to the coil 130 via electrical connector 167 
to establish a magnetic field across the radial air gap 148 between the 
outer cylindrical wall 164 of the armature 146 and the inner wall 152 of 
the center pole member 120 of the primary pole piece 118. In addition, as 
shown in FIG. 5, leakage flux "A" is directed across the air gap defined 
by the conical armature end 168 and the cylindrical wall 162 of the center 
pole member 120 providing additional opening force in the opening 
direction. The magnetic fields cause an opening force to be exerted on the 
armature 146 in the direction of the valve stem axis and opposing the bias 
exerted by the spring 112, and the differential pressure across the valve 
member 94, in the closing direction. As the force generated by the 
magnetic fields exceeds the spring bias and differential pressure load, 
the armature 146 and the attached valve assembly 16 moves axially such 
that the valve member is unseated from valve seat 52. As the valve opens, 
exhaust gas flows from the exhaust gas passage 178 through the passage 44 
in the EGR base housing 22 to the intake passage 180. As the armature 
approaches the terminal end of the axial chamber 152, associated with a 
fully open valve position, flux "B", shown in FIG. 6, is directed across 
the secondary gap defined by the associated conical surfaces 168 and 166 
of the axial chamber 152 and the armature 146. Closure of the gap 
resulting from continued movement of the armature 146 in the valve opening 
direction, rapidly increases the magnetic force. 
The foregoing description of the preferred embodiment of the invention has 
been presented for the purpose of illustration and description. It is not 
intended to be exhaustive nor is intended to limit the invention to the 
precise form disclosed. It will be apparent to those skilled in the art 
that the disclosed embodiments may be modified in light of the above 
teachings. The embodiments described are chosen to provide an illustration 
of the principles of the invention and its practical application to 
thereby enable one of ordinary skill in the art to utilize the invention 
in various embodiments and with various modifications as are suited to the 
particular use contemplated. Therefore, the foregoing description is to be 
considered exemplary, rather than limiting, and the true scope of the 
invention is that described in the following claims.