Abstract:
An electromechanical valve actuator with an armature stem guidance system that ensures that the armature stem stays aligned with the valve stem during operation. The stem guidance system may also allow for adjustment of the lash gap during assembly.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to electromechanical valve actuators and more particularly to electromechanical valve actuators that are easy to assemble and include armature stem self-aligning features to ensure that the armature stem stays centered above the valve stem during operation. 
     As engine technology advances and manufacturers strive to increase engine power, improve fuel economy, decrease emissions, and provide more control over engines, manufacturers are developing electromechanical valve actuators (also known as electromagnetic valve actuators or EMVA) to replace camshafts for opening and closing engine valves. Electromechanical valve actuators allow selective opening and closing of the valves in response to various engine conditions. 
     Electromechanical valve actuators generally include two electromagnets formed from a lamination stack and an embedded power coil. A spring loaded lever armature located between the electromagnets is movable between the electromagnets as the power coils are selectively energized to create a magnetic force to attract the armature to the energized electromagnet. The surface of the electromagnets to which the armature is attracted when the power coil of an electromagnet is energized is generally referred to as a pole face. The armature is operationally coupled to the valve so that as the armature moves between pole faces in pole-face-to-pole-face operation, the valve is opened and closed. 
     Electromechanical valve actuators have typically been made as linear electromechanical valve actuators (not shown). Linear electromechanical valve actuators generally draw a substantial amount of power from the alternator and require significant space over the cylinder. In view of the drawbacks associated with linear electromechanical valve actuators, many manufacturers have recently been turning to lever electromechanical valve actuators, which due to their mechanical properties have substantial power savings and are more space efficient. One problem with lever electromechanical valve actuators is that, unlike linear electromechanical valve actuators, due to the mechanical properties of the pivoting lever armature plate, the armature stem also pivots. Pivoting of the armature stem may cause problems during operation, such as, keeping the armature stem, specifically end of the armature stem, aligned with the valve stem. Any misalignment of the armature stem with the valve stem may cause an operational fault, inefficient operation, or excessive wear. Therefore, there is a need for a lever electromechanical valve actuator with self-aligning features to ensure that the armature end of the armature stem stays aligned with the valve stem. 
     SUMMARY OF THE INVENTION 
     The present invention relates to electromechanical valve actuators and, more particularly to an electromechanical valve actuator with an armature stem guidance system that ensures that the armature stem stays aligned with the valve stem during operation. The stem guidance system may also allow for adjustment of the lash gap during assembly. 
     In a first embodiment, the present invention is directed to an electromechanical valve actuator having an armature stem, a valve stem, and a lash cap between the armature stem and the valve stem, and wherein the lash cap has first surface defining a cavity for receiving the armature stem. The armature stem includes an armature end having a center point that is approximately aligned with the valve stem axis, when the armature stem is received in the cavity. The lash cap has a thickness, the thickness of the lash cap being selected to compensate for tolerance variations in the electromechanical valve actuator, which includes tolerance variations in the actuator portion and the head portion. 
     In a second embodiment, the present invention is directed to an electromechanical valve actuator comprising a spring assembly having an armature spring retainer and a valve spring retainer, an armature stem coupled to the armature spring retainer, a valve stem coupled to the valve spring retainer and wherein the valve spring retainer defines a cavity for receiving the armature stem, and a lash cap located within the cavity and between the armature stem and the valve stem. The valve spring retainer may further include a lock assembly defining the cavity. The valve spring retainer may also form the cavity such that the valve spring retainer includes an inside diameter and the armature stem includes an armature stem diameter, the armature stem diameter being smaller than the valve spring retainer inside diameter, however, in this sub-embodiment, the lock assembly has an inside diameter that is less than the armature stem diameter. 
     In a third embodiment, the present invention is directed to an electromechanical valve actuator comprising a spring assembly including an armature spring retainer, an armature spring, a valve spring and a valve spring retainer; an armature stem coupled to the armature spring retainer; a valve stem coupled to the valve spring retainer; and a lash cap located between the armature stem and the valve stem and having a thickness and wherein one of the valve spring retainer and the lash cap defines a cavity for receiving the armature stem, the electromechanical valve actuator assembled by the process of: determining tolerance variations of the electromechanical valve actuator; selecting the lash cap having a thickness; and inserting the lash cap between the armature stem and the valve stem. 
     Further scope of applicability of the present invention will become apparent from the following detailed description, claims, and drawings. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will become more fully understood from the detailed description given here below, the appended claims, and the accompanying drawings in which: 
         FIG. 1  is a sectional view of the electromechanical valve actuator; 
         FIG. 2  is a perspective exploded view of a portion of the electromechanical valve actuator; 
         FIG. 3  is an enlarged sectional view of the spring assembly and a lash cap with a first thickness; 
         FIG. 4  is an enlarged sectional view of the spring assembly and a lash cap with a second thickness; 
         FIG. 5  is an enlarged sectional view of a first alternative embodiment of the spring assembly and lash cap; and 
         FIG. 6  is an enlarged sectional view of a second alternative embodiment of the spring assembly and lash cap. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A lever electromechanical valve actuator  10 , mounted on an internal combustion engine  12  to open and close a valve  20  to a valve port  14  (e.g., the intake or exhaust valves), is illustrated in  FIG. 1 . The electromechanical valve actuator  10  generally includes an armature assembly  30  having an armature plate  32  and an armature stem  90 ; an electromagnet assembly  70  having electromagnets  72 ,  76 ; a spring assembly  50 ; and a guidance mechanism  60 . The armature plate  32  is alternatively attracted to the electromagnets  72 ,  76  thereby applying a bi-directional force to the spring assembly  50  through the armature stem  90  to open and close the valve  20 . 
     The valve  20  is similar to traditional valves and generally includes a valve head  22  with a valve stem  24  extending therefrom and having a valve stem diameter  19 . The valve  20  has an open and a closed position wherein in the closed position, the valve head  22  seals a valve port  14  to a corresponding cylinder. The valve stem  24  moves along a valve stem axis  26  as the valve  20  is opened and closed. 
     The spring assembly  50  includes springs  52  and  56  to bias the armature plate  32  into an intermediate position (not shown) while the electromagnets  72 ,  76  are not energized. The spring assembly  50  further includes a valve spring retainer  54  coupled to the valve stem  24  and an armature spring retainer  58  coupled to the armature stem  90  ( FIG. 1 ). The spring retainers  54 ,  58  operationally couple the springs  52 ,  56  to the valve stem  24  and armature stem  90 . The spring retainers  54  and  58  generally include a retainer cavity  57  having an inner diameter  55 . The spring retainers  54  and  58  also further include a lock assembly  100  to couple the retainers  54  and  58  to the valve stem  24  or armature stem  90 . The lock assembly  100  generally includes two keepers  102  as is well known in the art ( FIG. 2 ). 
     The electromagnet assembly  70  controls the movement of the armature assembly  30  and thereby the movement of the valve  20 . The electromagnets  72 ,  76  each include cores  80  which may be formed from laminated plates (not shown) to improve the magnetic efficiency of the electromagnets  72 ,  76 . A coil  82  is situated within each core  80  and is selectively energized to attract the armature plate  32  to the electromagnets  72 ,  76 . The electromagnets  72 ,  76  are generally secured to a housing  16  and a base plate  18  may be located between the housing  16  and internal combustion engine  12  to provide support to the armature spring  56 . 
     As discussed above, the armature assembly  30  includes the armature plate  32  and the armature stem  90 . The armature stem  90  includes an armature end  92  having an outside diameter  91  and a centerpoint  93 , which is generally the center of the outside diameter  91  at the armature end  92 . The armature stem  90  also includes a tip  94  opposing the armature end  92 . The armature plate  32  pivots about an armature pivot axis  44 , to open and close the valve  20 . The armature stem  90  is coupled to armature plate  32  opposite the armature pivot axis  44  in a manner that transmits force from the armature plate  32  to the armature stem  90 . The present invention is shown in  FIG. 1  with the armature stem  90  receiving forces from the armature plate  32  in both the opening and closing directions during operation, due to the configuration of the spring assembly  50 . However, it should be readily apparent to one skilled in the art that the present invention may also be applied to an electromechanical valve actuator wherein force is transmitted to the armature stem  90  only in the opening directions due to the use of a torsion bar, other mechanism, or through rearrangement of the springs  52 ,  56  (not shown) to apply force to the armature plate  32  in the closed direction independent of the armature stem  90 . 
     The present invention also includes a guidance mechanism  60 . The guidance mechanism is generally a cavity sized to receive and retain the armature stem  90  so that the centerpoint  93  of the armature end  92  is approximately aligned or in operation with the valve stem axis  26  and substantially prevented from moving axially relative to said valve stem  24 . In other words, the cavity concentrically restrains the movement of the armature stem  90  relative to the valve stem  24  while still allowing movement of the armature stem  90  relative to the valve stem  24  along the valve stem axis  26 . By keeping the centerpoint  93  approximately aligned with the valve stem axis  26  the electromechanical valve actuator  10  may operate more efficiently in that forces applied by the armature plate  32  to the armature stem  90  are predominantly transferred along the valve stem axis  26 . By keeping the armature stem  90  approximately aligned with the valve stem  24 , the amount of force required to open the valve  20  is less than an electromechanical valve actuator  10  where the force applied to the valve  20  is not approximately aligned with the valve stem axis  26 . Not only is the force reduced, but the wear on the valve stem bushing  28  and valve stem  24  is reduced by maintaining the concentric alignment. Another advantage of the guidance mechanism  60  keeping the armature stem  90 , particularly the centerpoint  93 , concentrically aligned with the valve stem  24  is that the guidance mechanism  60  may also ensure that the armature stem  90  does not become misaligned with the valve stem  24  due to the pivoting nature of the armature plate  32  thereby causing an operational fault. 
     In the illustrated embodiment, the guidance mechanism  60  is formed using a lash cap  61  having a first surface  62  defining a cavity  64  ( FIGS. 1 and 2 ). The lash cap  61  further includes a second surface  68  that engages the valve stem and has an outer diameter  69 . The cavity  64  has an inner diameter  65  for receiving the armature stem  90 . More specifically, the inner diameter  65  of the cavity  64  is larger than the armature end outer diameter  91 . For ease of assembly, the lash cap  61  further includes rounded edges  66  where the cavity  64  meets the first surface  62 . The lash cap  61  also has a thickness  63  between the bottom of the cavity  67  and the second surface  68 . The thickness  63  is selected to adjust for tolerance differences so that the electromechanical valve actuator  10  has the proper lash gap  86  to allow for thermal expansion differences. Lash caps  61  with different thicknesses  63  are illustrated in  FIGS. 3 and 4 . 
     In a first alternative embodiment illustrated in  FIG. 5 , the guidance mechanism  60  may also be formed using a cavity  104  defined by the locking mechanism  100 . The locking mechanism  100  may be configured to extend beyond the valve stem  24  to create a cavity  104  into which the armature stem  90  is received. A lash cap  61 ′ having two flat surfaces may be inserted between the armature stem  90  and the valve stem  24  to adjust for tolerance differences and thereby to provide the proper lash gap. 
     In a second alternative embodiment illustrated in  FIG. 6 , the armature stem  90  may be configured to have an armature end outer diameter  91  that is larger than the valve stem&#39;s diameter. With a larger armature stem diameter  91 , as shown in  FIG. 6 , the valve spring retainer  54  may receive the armature stem  90  within the retainer cavity  57 . The outside diameter  91  of the armature stem  90  is enlarged to fit within the retainer cavity  57  with minimal movement axially relative to the valve stem axis  26  by the centerpoint  93 . A lash cap  61 ′ having two flat surfaces may be inserted between the armature stem  90  and the valve stem  24  to adjust for tolerance differences to provide the proper lash gap. 
     The electromechanical valve actuator  10  is generally assembled onto an engine  12  as is well known in the art with the addition of assembling the guidance mechanism  60  onto the electromechanical valve actuator  10 . The electromechanical valve actuator  10  generally includes an actuator portion  11  and a head portion  15 . An exemplary method of assembling the actuator portion  11  and the head portion  15  is described below, however it should be readily apparent to one skilled in the art that changes in the steps, added steps, or any other changes in the assembly process may be made without departing from the spirit of the invention. The actuator assembly is generally assembled by forming the valve electromagnets  72  and armature electromagnet  76  and respectively assembling these electromagnets  72 ,  76  into the housing  16 . The armature assembly  30  is then installed with the armature stem  90  passing through the valve electromagnet  72 . The armature spring  66  and armature spring retainer  58  are then installed and coupled to the armature stem  90  with the locking assembly  100 . The head portion  15  is also generally assembled by installing the valve  20  into the internal combustion engine  12 , specifically the cylinder head of an internal combustion engine. If necessary, a valve spring guide  59  ( FIG. 1 ) can also be installed with the valve spring  52  being installed thereupon. The valve spring retainer  54  is then coupled to the valve stem  20  with the locking assembly  100 . With the actuator portion  11  and head portion  15  being assembled, the guidance mechanism  60  is assembled onto either the head portion  15  or actuator portion  11  before the two portions  11 ,  15  are assembled together to form the electromechanical valve actuator  10 . It should be readily recognized to one skilled in the art that the actuator portion  11  and head portion  15  may be assembled at different places at different times and also that a third assembly location may provide the assembly of the guidance mechanism  60  and the actuator portion  11  onto the head portion  15  to create the electromechanical valve actuator  10 . 
     Before the guidance mechanism  60  is installed, the proper thickness  63  of the lash cap  61 ,  61 ′ must first be determined. The thickness  63  of the lash cap  61  or  61 ′ between the armature stem  90  and valve stem  24  adjusts for tolerance differences, specifically the tolerance difference between the base plane  17  of the base plate  18  through the armature end  92  of the armature stem  90  and the tolerance difference between the mounting plane  13  of the internal combustion engine  12  and the valve end  29  of the valve stem  24 . Of course, the tolerance differences can be measured from any other reference point, but using the mounting plane  13  and base plane  17  as a reference point allows easy measuring of the tolerance differences because when the base plate  18  is mounted on the internal combustion engine  12 , the mounting plane  13  and base plane  17  basically form the same planes. Therefore, calculations of the proper thickness  63  may easily be determined. For example, where the desired lash gap for a particular engine is known, to determine the thickness of the washer, the difference is calculated between the distance between the mounting plane  13  and armature end  92  and the difference between the mounting plane  13  and the valve stem end  29 . The lash gap is then subtracted from this calculated difference, which provides the desired thickness. For example, if the distance between the mounting plane  13  and the armature end  92  is 4.97 and the distance between the base plane  17  and valve stem end  29  is 4.56 and the desired lash gap is 0.18, then 4.56 is subtracted from 4.97 and then the lash gap of 0.18 is subtracted therefrom to give a desired thickness of 0.23. Once the desired thickness is determined, a lash cap  61  or  61 ′ is selected having the closest thickness  63  and inserted into the retainer cavity  57  of the valve spring retainer  54  or the cavity  104  formed by the locking assembly  100 . The actuator portion  11  is then installed on the cylinder head of the internal combustion engine  12  to form the electromechanical valve actuator  10 . The bolts  8  on the electromechanical valve actuator  10  are then tightened. 
     The foregoing discussion discloses and describes an exemplary embodiment of the present invention. One skilled in the art will readily recognize from such discussion, and from the accompanying drawings and claims that various changes, modifications and variations can be made therein without departing from the true spirit and fair scope of the invention as defined by the following claims.