Patent Application
20100007224
The present disclosure relates generally to stator assemblies in solenoid actuators and more particularly to a guided solenoid assembly for use in fuel injectors.
People skilled in the art recognize the goal to mass produce a solenoid actuator having smaller initial and final air gaps with improved parallelism between a stator assembly and an armature in a cost efficient manner. Even though it may be possible to produce a solenoid actuator assembly having a very small air gap and where the armature is parallel to the stator assembly, those in the art recognize there are significant costs involved in mass producing such assemblies.
Typical solenoid actuated fuel injectors include an armature connected to a valve member that controls the flow of fuel and/or pressure through the fuel injector. By having the armature connected to the valve member, the movement of the armature within the stator assembly may be compromised. By moving the armature with the valve member coupled thereto, the armature might travel at reduced speeds due to the increased mass, and any attempts to improve parallelism with the stator assembly were also hindered due to the tolerance stack ups that invariably increase during production with more connected parts. Moreover, in the past, some armature assemblies included a hard guide piece that was part of, or drove a fuel injection valve member, and a soft armature piece that served to enhance the magnetic forces acting on the armature. In order to improve parallelism and maintain a predetermined initial and final air gap, manufacturers used various category parts that took into account the inaccuracies that existed in the dimensions of the solenoid actuator assembly despite establishing very tight tolerances during mass production.
When the coil of the solenoid is energized, the armature moves towards the stator assembly, moving the valve member, and thereby controlling the fluid flow and/or pressure in the fuel injector. When the coil ceases to be energized, a mechanical spring or other bias forces the armature away from the stator assembly, causing the valve member to return to its original position and thereby controlling the fluid flow and/or pressure in the fuel injector again. It is known in the art that the time taken for the solenoid actuator, and hence the control valve of a fuel injector, to move from a first position to a second position and back again is a function of the highest possible forces acting on the armature over the shortest possible travel distance. It is desired by those in the art to reduce the time taken for the armature to travel from the initial air gap position to the final air gap position and back to the initial air gap position.
The magnetic forces acting on the armature are functions of the electromagnetic properties of the armature, the initial and final air gap between the armature and the stator assembly and the parallel orientation of the armature with reference to the stator assembly, including others. It is well known in the art that a magnetic field in a solenoid has the greatest force when the armature is parallel to the stator assembly and the air gap between them is as small as possible. Having a larger initial air gap will translate to the armature having a lower initial attraction force and maybe a larger travel distance, hence increasing the time taken to travel from the initial air gap position to the final air gap position. Having a smaller final air gap will allow for a smaller initial air gap and also allow a stronger magnetic force to act on the armature, hence increasing the speed at which the armature travels from the final air gap position to the initial air gap position and back. A lack of parallelism can create side forces leading to imbalance and increased wear at guide interfaces.
There has been an ongoing effort to improve parallelism in prior references, while striving to achieve the smallest final air gap. One prior art reference, U.S. Patent Application Publication No. US2006/0138374 A1 teaches the use of an adjustable spacer coupled between the armature housing and the stator. The spacer is adjusted depending on the tolerance variation of the assembled parts. U.S. Pat. No. 6,550,699 teaches the use of plating a hard film layer on the armature as a spacer. The prior art, although geared towards achieving some of the goals this disclosure aims to achieve, have been met with limited success.
The present disclosure is directed to one or more of the problems set forth above.
In one aspect, a method of assembling a stator assembly of a solenoid actuator is described. The stator assembly comprises a pole piece and a guide sleeve. The method of assembling the stator assembly includes the steps of attaching the guide sleeve into a pole bore defined in the pole piece. The method further includes the steps of forming a guide bore through the guide sleeve after the attaching step, and forming a planar bottom surface on the pole piece after the attaching step. The step of forming the guide bore through the guide sleeve and the step of forming the planar bottom surface on the pole piece includes the step of orienting the axis of the guide bore perpendicularly relative to the planar bottom surface on the pole piece. An alternate step is orienting the planar bottom surface on the pole piece perpendicular or relative to the axis of the guide bore.
In another aspect, a fuel injector assembly comprises a solenoid actuator assembly, which includes a stator assembly and an armature. The stator assembly has a pole piece, a guide sleeve attached to the pole piece and a guide bore defined by an inner surface of the guide sleeve. The guide bore has an axis and the pole piece has a planar bottom surface. The axis of the guide bore is oriented perpendicular relative to the planar bottom surface on the pole piece, or in the alternative, the planar bottom surface on the pole piece is oriented perpendicular relative to the axis of the guide bore. The armature has a guide piece and a flux piece. The armature is slidably movable between a first position where the armature is in contact with a stop surface of the pole piece and out of contact with a valve member, and a second position where the armature is out of contact with the stop surface and in contact with the valve member.
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The stator assembly 121 is an alternative embodiment of the stator assembly 21 in
The guide piece 151 has a top impact surface 149. The top impact surface 149 of the guide piece 151 may be in contact with a spring 156 that biases the armature assembly 140 away from the stator assembly 121. The spring 156 is in contact with the guide piece 151 on one end of the spring 156 and in contact with a spacer 182 on the other end. The spacer 182 is in contact with another spacer 180 and their dimensions together with the dimensions of spacer 81 (not shown in
Conventional wisdom in the art focuses on producing pieces with ever increasing tightened tolerances so that after attachment, the tolerance stack-ups would not amount to substantial variations. This disclosure resolves the problems faced by others in the art by allowing parts to be manufactured under less stringent tolerances, attaching the pieces together and then grinding the guide surfaces on the pieces in a single chucking to achieve a smaller final air gap. Referring now to
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By decoupling the action of solenoid assembly 20 from valve member 61, slight misalignments between an axis of valve member 61 and guide axis 35 can be tolerated with altering performance. In addition, the speed of the valve member 61 moving between seats 64 and 65 are determined primarily by respective pre-loads on springs 56 and 58, which may be set precisely with respective spacers 80, 81 and 82. Seats 64 and 65 may be considered as first and second stops for valve member 61. The decoupled solenoid assembly 20 can now function with greater precision and may allow for a smaller initial and final air gap 69 and 70, respectively. Furthermore, by decoupling the armature assembly 40 and the valve member 61, the armature assembly 40 may function independently of the valve member 61 as long as the armature assembly 40 travels faster than the valve member 61. This also desensitizes the valve member 61 from any axial misalignments that may occur due to construction tolerance variances and any lateral shifting in the armature assembly 40 in order to improve parallelism between the armature assembly 40 and the stator assembly 21.
The present disclosure finds potential application in any solenoid assembly in any machine. Although this particular embodiment of the disclosure is directed towards an electronically controlled valve assembly for use in a common rail fuel injector, the disclosure is not limited to fuel injectors and could find applicability in a much broader array of industries that use solenoid actuators. The present disclosure finds particular application to fuel injectors used in compression ignition engines. Other fuel injector applications include, but are not limited to, cam and/or hydraulically actuated fuel injectors. Electronically controlled valve assemblies may be used to control the flow of fluids and/or pressure through a fuel injector. In the present disclosure, the valve assembly performs repeated cycles of movement at an extremely high rate over many millions of cycles.
The solenoid actuator 20 has two states. An off or de-energized state, which corresponds to the second position of the armature assembly 40 and an on or energized state, which corresponds to the first position of the armature assembly 40. In the off state, the solenoid actuator 20 is switched off and no current is passing through the coil 29 of the solenoid actuator 20. As there is no current passing through the coil 29, there are no magnetic forces produced within the stator assembly 21. The first spring 56 exerts a force on the armature assembly 40 and the valve member 61 biasing them away from the stator assembly 21. The second spring 58 exerts an opposite force on the valve member 61 and the armature assembly 40 towards the stator assembly 21 but the force exerted by the second spring 58 is not great enough to overcome the force exerted by the first spring 56. Therefore, the net resulting force from the two springs 56 and 58 causes the valve member 61 to assume a second stop position in contact with the valve seat 64 that corresponds to either an open or a closed position, which in turn, controls the flow of fluid and/or pressure through the fuel injector 10 depending on the configuration of the valve assembly 60. The armature assembly 40 is positioned away from the planar bottom surface 26 and the distance from the planar surface 50 of the flux piece 45 to the planar bottom surface 26 of the stator assembly 21 along the longitudinal axis 35 of the guide bore 33 is the initial air gap.
As the solenoid actuator 20 is switched to its on state, the armature assembly 40 moves from its second position to its first position. Switching the solenoid actuator 20 on energizes the coil 29. The coil 29 produces a magnetic field around the stator assembly 21 and creates a magnetic force in the surrounding region. The force of the magnetic field is strong enough to pull the armature assembly 40 towards the stator assembly 21. This force is greater than the force of the spring 56 hence causing the armature assembly 40 to move towards the stator assembly 21. In addition, when the armature assembly 40 is pulled towards the stator assembly 21, the armature assembly 40 may be pulled faster than the valve member 61 is pushed upward by the second spring 58. This allows the armature assembly 40 to lose contact with the valve member 61. The valve member 61 moves from the second stop position to a first stop position that corresponds to either an open or a closed position which in turn controls the flow of fluid and/or pressure through the fuel injector 10 depending on the fluid configuration of the valve assembly 60. The guide piece 43 moves up the guide bore 33 of the stator assembly 21 maintaining a guide clearance with the guide sleeve 31. The guide piece 43 stops moving when the stop surface 75 on the guide piece 43 comes in contact with the stop surface 77 on the guide sleeve 31. A top surface 49 on the guide piece 43 remains in contact with the first spring 56. In another exemplary embodiment, the guide piece 151 can stop moving when the top impact surface 149 of the guide piece 151 comes into contact with a bottom impact surface 183 of spacer 180. In one embodiment, the distance between the planar bottom surface 26 of stator assembly 21 and the top surface 50 on the flux piece 45 is at its smallest distance, corresponding to the final air gap 70, and may be equal to the distance between the stop surface 75 on the guide piece 43 and the top surface 50 on the flux piece 45. When the armature assembly 40 is in the first position, the first spring 56 exerts a bias force on the guide piece 43. However, as long as the coil 29 is energized, the magnetic force is exerted on the armature assembly 40 and the armature assembly 40 remains in the first position. Depending on the fluid connections, fuel injection events may be initiated and ended by energizing and de-energizing solenoid actuator 20 in a known manner.
Finally, the solenoid actuator 20 is turned off again and the coil 29 is de-energized. The coil 29 no longer provides a magnetic force therefore allowing the net resulting force of the springs 56 and 58 to force the armature assembly 40 to move from the first position to the second position again. The first spring 56 exerts a force on the top surface 49 on the guide piece 43. The stop surface 75 on the guide piece 43 loses contact with the stop surface 77 on the guide sleeve 31, while the bottom impact surface 48 on the guide piece 43 comes back in contact with the valve member 61 pushing the valve member 61 back to its original position, and thereby allowing the valve member 61 to control the fluid flow and/or pressure through the fuel injector 10 again. The armature assembly 40 finally stops when it reaches the second position, wherein the distance between the flux piece 45 and the planar bottom surface 26 is equal to the initial air gap. In another embodiment, when the solenoid is de-energized, the guide piece 151 is forced away from the stator assembly 121 by the spring 156 making the top impact surface 149 of the guide piece 151 lose contact with the bottom impact surface 183 of the spacer 180.
The armature assembly 40 continues to move from the second position to the first position and back as long as the solenoid actuator 20 is turned on and turned off. This continuous process demonstrates why it may be important for the impact surfaces of the guide piece 43 to be made of a hard, impact resistant material. The repeated pounding of the bottom surface 48 and the stop surface 75 of the guide piece 43 with member 61 and the guide sleeve 31, respectively, cause wear and tear on the surfaces on the guide piece 43 possibly requiring the impact surfaces of guide piece 43 to be made of a material able to withstand these impacts over extended periods of use. It is known to those in the art that the flux piece 45 should be made of a soft material possessing superior magnetic properties in order to move between the first and second position with less force than might otherwise be needed. With the structure shown, the travel distance of valve member 61 will inherently be smaller than the travel distance of armature assembly 40.
This disclosure provides numerous ways to reduce the initial and final air gap of solenoid actuators and improve parallelism between the top surface 50 on the flux piece 45 and the bottom surface 26 on the stator assembly 21. Grinding the stop surface 75 on the guide piece 43, after attaching the flux piece 45 to the guide piece 43 to form the armature assembly 40, may permit smaller geometric variations than in the past. Grinding the surface 75 after the attaching step eliminates the need to develop parts with ever increasingly tightened geometric tolerances because the grinding step after attachment allows parts with larger geometric variations to be ground to the same predetermined dimensions. Furthermore, when the armature assembly 40 is ground (guide surfaces 36, 37 and stop surface 75) in a single chucking, the guide piece 43 and the flux piece 45 are oriented more accurately than if ground in more than a single chucking. This produces an improved, more geometrically aligned stop surface 75 on the guide piece 43 and better parallelism between the top surface 50 on the flux piece 45 and the planar bottom surface 26 of the stator assembly 21. Similar improvements can be achieved by grinding the inner surface 32 of the guide sleeve 31 and the planar bottom surface 26 of the stator assembly 21 as well. If the grinding is performed after attaching the guide sleeve 31 to the pole piece 24, less stringent tolerances may be needed to produce the stator assembly 21 with similar geometric details. Furthermore, grinding after attachment increases the perpendicularity between the guide sleeve 31 and the planar bottom surface 26 of the stator assembly 21, consequently improving parallelism between the top surface 50 of the flux piece 45 and the planar bottom surface 26 of the stator assembly 21.
It should be understood that the above description is intended for illustrative purposes only, and is not intended to limit the scope of the present disclosure in any way. Thus, those skilled in the art will appreciate that other aspects of the disclosure can be obtained from a study of the drawings, the disclosure and the appended claims.
