The invention relates generally to electromagnetic devices, and more particularly to an improved linear actuator for use, for example, in a valve assembly.
Automobiles equipped with automatic transmissions have become ubiquitous. A conventional automatic transmission includes a planetary gearset, a set of bands used to engage parts of the gearset, a set of wet-plate clutches to engage other parts of the gears, a hydraulic system for controlling the clutches and bands, and a transmission fluid pump. Numerous solenoid valves or actuators are used to control the flow of transmission fluid through the automatic transmission. More specifically, pressure control valves are used to modulate the fluid pressure provided to individual clutches within the transmission. Conventional design practice provides for the use of a spool type of valve assembly or a poppet type of valve assembly for these applications. Due to the robustness as to contamination, a poppet type of valve assembly may be preferred.
Known magnetic designs generally include a solenoid assembly having a spool supported between a primary plate and a secondary plate, a plunger disposed in a central bore of the spool, and a coil wound on the spool. When energized, the magnetic flux circulates in a flux path through the plunger, to the primary plate, through a frame to the secondary plate and back through the plunger.
As further background, the poppet type of valve assembly referred to above may be configured as a variable bleed solenoid (VBS) valve assembly. A VBS valve assembly is a current-controlled, electro-hydraulic actuator that provides an outlet pressure that corresponds to the input electrical current level applied to the valve assembly. A relatively constant supply pressure may be applied to the valve assembly through a supply port, which internally leads to a control port. The pressure level present on the control port (output) can be controlled by allowing the control port to bleed to a reservoir (“exhaust”) through a variable orifice formed in the valve body. With this basic structure, a VBS valve assembly can regulate fluid line pressure on the control port from a maximum value to a minimum value, as seen by reference to published U.S. patent application, publication number US 2004/0045611 A1 entitled “LOW LEAK PRESSURE CONTROL ACTUATOR” to Avila.
Along its axial length the plunger of a valve assembly, such as illustrated in Avila, has a “straight” or uniform diameter, which presents a predetermined level of magnetic reluctance for an air gap between the plunger and the secondary plate. This in turn produces a corresponding predetermined magnetic force acting on the plunger.
An important aspect of performance, however, involves providing a design that is relatively small in size and weight, on the one hand, yet provides, on the other hand, an internal magnetic configuration that results in increased levels of magnetic force acting on the moving part—the plunger—for example to overcome an inlet or supply fluid pressure acting on a check ball or the like.
There is therefore a need for a linear actuator design that improves upon and overcomes one or more of the problems as set forth above.
An object of the present invention is to solve one or more of the problems as set forth in the Background. One advantage of the present invention is that provides a linear actuator that is reduced in size while having the same performance levels (e.g., about the same level of magnetic force acting on the moving part, such as the plunger) compared to conventional approaches. The present invention provides a linear actuator design that includes an improved plunger configuration—one that reduces the magnetic reluctance in the air gap in the radial space between the plunger and the secondary plate. This magnetic circuit design provides a reduced size, for the same force, due to increased efficiency. Another aspect of the invention involves a double step geometry at the plunger/primary plate magnetic interface that in-effect increases the magnetic force acting on the plunger, as compared to similar designs for the same amp turns A-T through the energizing coil.
A linear actuator in accordance with the present invention includes a frame, a plunger reciprocably movable within the frame, and a solenoid assembly. The solenoid assembly is configured to move the plunger between at least first and second axially offset positions.
In a constructed embodiment, there are a plurality of intermediate axial positions based on the level of current through the coil.
The solenoid assembly includes a spool supported between a primary plate and a secondary plate. The spool includes an electromagnetic coil wound thereon for receiving electrical current and producing magnetic flux. The magnetic flux flows in a flux path extending through the secondary plate, the plunger, the primary plate, the frame and back through the secondary plate.
The plunger extends along a main axis and has a first axial end proximate or near the primary plate and an opposing second axial end proximate or near the secondary plate. The first axial end is generally cylindrical in shape and has a first diameter. This first diameter, in a constructed embodiment, extends at least the majority of the length of the plunger toward the second end. The second axial end is also generally cylindrical and has a second diameter that is larger than the first diameter. Enlarging the diameter of the second axial end increases the area in the air gap there, which decreases the magnetic reluctance, thus increasing the magnetic force acting on the plunger. The increase in the air gap area also reduces the variation of the force as a function of travel (during operation).
In another embodiment of the invention, the primary plate is generally annular and includes a first axial side facing the plunger. The primary plate includes a circular trough formed in the first axial side, which is defined by a first step and a second step disposed radially outwardly of the first step. The plunger includes an annular hub that is in registry with the circular trough. In this further embodiment, the flux path that extends from the plunger to and through the primary plate includes (i) a first subpath from the radially outermost part of annular hub through the first step and (ii) a second subpath from the radially innermost part of the annular hub through the second step. The double step configuration increases the amount of force acting on the plunger.
In another aspect of the present invention, a valve assembly is provided which employs one or more of the features set forth above for the linear actuator, and which may be used, for exemplary purposes only, as an automatic transmission pressure control valve assembly, an oil control valve assembly such as for a cam phaser or a fuel vapor control valve assembly such as a carbon canister purge valve assembly.
The present invention will now be described by way of example, with reference to the accompanying drawings:
Referring now to the drawings wherein like reference numerals are used to identify identical components in the various views,
Housing 22 further includes a generally cylindrical, centrally disposed bore 30 formed therein which extends along the longitudinal axis “A.” Bore 30 may include a relatively enlarged diameter first portion near distal end 26 that narrows as the bore 30 progresses toward the proximal end 24 of housing 22 to a second, reduced diameter portion.
End cap 40 is configured to close the enlarged opening (bore 30) of housing 22. End cap 40 includes an axially extending supply port 44 to be described in greater detail below.
It should be understood that
With continued attention to
Hydraulic portion 14 further includes a poppet or pin 56 slidably disposed within the central bore 34 of insert 32. Pin 56 includes a proximal end 58, a distal end 60 with a frusto-conical surface or seat 62 formed on an outer portion thereof. The surface 62 is configured in size and shape to engage a corresponding pin seat 64 when control valve assembly 10 is fully energized, as described in greater detail below. Pin seat 64 circumscribes variable orifice 66.
When control valve assembly 10 is fully deenergized, the pin 56 assumes the position shown in
Pin 56 may assume a variety of intermediate positions between a fully open position for orifice 66, and a fully closed or sealed off position for orifice 66. The precise position of pin 56 (and thus the degree of fluid communication between the control port 46 and the exhaust port 48) corresponds to the level of current applied to the coil portion of the linear actuator 12, in a more or less substantially linear relationship (hence “linear actuator”).
With continued reference to
Plunger 72 is reciprocably moveable within the frame 16 and has at least a first axial position when valve assembly 10 is completely deenergized and a second axial position when control valve assembly 10 is completely energized.
The solenoid assembly 70 is configured to move the plunger 72 from the first axial position referred to above, through a plurality of intermediate positions, to the second axial position referred to above. Movement of the plunger 72 is operative to alter the hydraulic portion 14, as described above.
The solenoid assembly 70 is generally configured to produce magnetic flux that flows in a flux path 92 extending through the secondary plate 80, the plunger 72, the primary plate 78, the frame 16 and back through the secondary plate 80. Accordingly, these components are preferably formed of ferromagnetic materials.
Plunger 72 extends along main axis “A” and has a first axial end 94 proximate the primary plate 78, a second axial end 96 proximate the secondary plate 80, and a central bore 98. Plunger 72 is generally cylindrical along its length. The first axial end 94 is generally cylindrical and includes a first annular hub 100 having a first outside diameter 102OD and a first inside diameter 102ID. The second axial end 96 of plunger 72 includes a second annular hub 104 having a second outside diameter designated 106OD and a second inside diameter 106ID. The configuration of plunger 72 is such that the second annular hub 104 defines a circular shaped land 108. As shown, the second outside diameter 106OD is larger than the first outside diameter 102OD. As will be described in greater detail below, the increased diameter 106OD forming a generally T-shaped component in radial cross-section (shown in
Spool 74 is disposed within frame 16 and is configured to retain electromagnetic coil 76 and includes a main body 110 configured and arranged so as to define an enlarged central bore 112. Spool 74 is arranged to include a winding bay 114 defined between axially opposing flanges 116. Spool 74 further includes a pair of lips 118 configured to fit into corresponding flanges on the primary and secondary plates 78, 80.
Electromagnetic coil 76 is shown as surrounding spool 74, particularly wound in the winding bay 114 thereof, in a generally toroidal shape. Coil 76 may be selectively, magnetically coupled to the plunger 72 when the coil is energized and deenergized, as described below by providing electrical current through the coil, as known in the art.
Primary plate 78 is generally annular in shape and includes a main body portion 120, a first axial side 122 facing plunger 72, a second, opposing axial side 124, a central bore 126, and a circular trough 128 formed in the first axial side 122. Trough 128 is defined by a first step 130 and a second step 132 that is disposed radially outwardly of the first step 130. The circular trough 128 and the central bore 126 together define a radially, inwardly disposed central hub 134. Primary plate 78 further includes a flange 136 configured to engage lip 118 of spool 74.
As shown, the hub 100 formed on the end of plunger 72 is in registry with the circular trough 128 of the primary plate. In the deenergized condition (as shown in
Secondary plate 80 is generally annular in shape and includes a main body portion 138, and an enlarged central bore 140 having a predetermined, inside diameter that is greater than the outside diameter 106OD of the enlarged portion of plunger 72. The difference in diameter between the outside diameter of plunger 72 and the inside diameter of the secondary plate defines an air gap 144. As alluded to above, the air gap has an increased area, due to the increased outside diameter 106OD, of the plunger 72 at its proximal end, relative to the diameter at the opposing end, 102OD The increased area provides for an increased force on plunger 72. Secondary plate 80 further includes a first flange configured to engage lip 118 of spool 74, and a second flange configured to engage a corresponding annular flange on bushing 82.
Bushing 82 is provided to guide the second axial end of plunger 72 as plunger 72 reciprocates in frame 16. Bushing 82 includes a main body portion and an enlarged central bore 152 configured in size to be slightly larger than the outside diameter of plunger 72.
Collar 84 provides an axial end closure function for the linear actuator 12 and includes a main base 154, which is disk-shaped. In base 154 there is a centrally-disposed, axially projecting hub, through which extends a threaded bore 156. Collar 84 further includes an annular flange 158, which extends in the opposite direction of the central hub of collar 84.
Screw 86 is configured to fill or close threaded bore 156, and also provides a mechanism for adjusting the force provided by spring 88 due to an amount of axial compression between screw 86 and plunger 72. Screw 86 includes outside threads configured to be in mesh with the corresponding threads 156 of collar 84. Screw 86 further includes a reduced diameter portion 162 that projects axially inwardly and is configured to have a diameter that is less than the inside diameter of compression spring 88. Projection 162 provides a suitable centering mechanism for spring 88. Screw 86 further includes a land 164.
Spring 88, as referred to above, provides an adjustable amount of force in an axial direction to plunger 72. The amount of force provided by bias spring 88 is selected to be less than the force needed to dislodge check ball 42, yet maintain main rod 90 in engagement with pin 56. The force on check ball 42 is a function of both the nominal inlet fluid pressure and the surface area of check ball 42 against which the supply fluid bears. Spring 88 is disposed between the land 108 of plunger 72 and the land 164 on screw 86.
Main rod 90 is secured to plunger 72 for movement therewith. Main rod 90 is configured, in general terms, to translate the movement of plunger 72 to pin 56 to adjust or alter the degree of opening of variable orifice 66. Main rod 90 includes a first main portion having a diameter that is less than that of central bore 98 of plunger 72, and at least one, and as shown in
As shown in the illustrated embodiment, plunger 72 is disposed, on one end, through the central bore of the secondary plate 80. The plunger 72 is supported, on its first axial end 94, by virtue of rod 90 being in sliding engagement with the through bore of the primary plate 78. The plunger 72 is supported on its second axial side 96, by virtue of the bushing 82. Accordingly, the plunger 72 is slidably disposed within the linear actuator 12 for axial reciprocation.
In general operation, and now referring to
Features of the present invention involve improved performance and a reduced size package. To this end, referring again to
Another feature of the present invention relates to the double step configuration at the plunger-to-primary plate interface.
Referring now to
In one embodiment, for plunger 72, the outside diameter 102OD at the hub 100, which represents the main diameter of plunger 72, is 4.5 mm while the maximum diameter of the plunger, at hub 104, has an outside diameter 106OD of 6.6 mm. The basic diameter of the magnetic package (i.e., the outside diameter of frame 16) is 20 mm while the length of the magnetic package (i.e., linear actuator 12) is 29 mm. In this embodiment, a force of 0.84 N may be developed at 136 A-T through coil 76. Accordingly, a plunger ratio (i.e., ratio of 106OD to 102OD) may be between 1.4 and 1.5, more preferably between 1.46 and 1.47 and may be about 1.467 in one embodiment. An actuator ratio, defined between the diameter and length of the linear actuator 12, may be between about 1.4 and 1.5.