Abstract:
The present invention provides an actuator assembly for operating a cylinder valve of an internal combustion engine. The actuator assembly achieves fast response times by utilizing a solenoid actuator that contains an armature element formed of a powder metal. A valve system that utilizes two of the actuator assemblies in conjunction with a cylinder valve is also provided.

Description:
FIELD OF THE INVENTION 
     The present invention relates to electrohydraulic actuators adapted to operate cylinder valves. More particularly, the present invention relates to an electrohydraulic actuator assembly that couples a high speed solenoid switch with a stem valve, such as a poppet or cylinder valve, to control the flow of hydraulic fluid to a cylinder valve or piston mechanism. 
     BACKGROUND OF THE INVENTION 
     It is well appreciated in the art that significant benefit can be achieved through variation of the lifting and timing of intake and exhaust valves in an internal combustion engine. For example, engine performance can be enhanced by individually controlling the acceleration, velocity and travel time of the valves. 
     Many hydraulic systems for controlling cylinder valves have been proposed. For example, U.S. Pat. No. 5,255,641 to Schecter for a VARIABLE ENGINE VALVE CONTROL SYSTEM describes a system in which the engine valve has a piston attached to its top. Opposite surfaces of the piston are subjected to hydraulic fluid. Selective activation and deactivation of a controlling means, such as a solenoid actuator, causes the hydraulic fluid to act on the appropriate surface of the piston, which causes the valve to move. 
     One problem encountered in the acceptance of hydraulic control systems is the need for a very fast response time. For example, in high speed engines, the response time for engine valve activation in a full stroke typically has to be within 2 milliseconds (ms). Controllers in electrohydraulic systems have thus far not provided the desired response times. For example, solenoid actuators, which are frequently used in electrohydraulic systems, have limitations on their response time, due, at least in part to the presence of eddy currents in the metal armatage element of the valve. The term ‘eddy currents’ refers to the electrical currents that oppose the penetration of flux in the metal which is responsible for developing electromagnetic forces in solenoids. Eddy currents provide a natural inefficiency to electromagnetic systems, such as solenoid valves, because they limit the speed at which a magnetic field can be switched. 
     Powder metals provide materials that are mainly metallic, but have low conductivity which greatly reduces eddy currents. Typically, a powder metal is a compacted form comprising metal particles, such as iron particles, encased in a non-metallic material, such as an epoxy resin. These materials essentially prevent eddy currents because of the low conductivity due to the metal particles not being in contact with each other. As a result, powder metals can be used in electromagnetic systems to overcome the natural inefficiency due to eddy currents. 
     SUMMARY OF THE INVENTION 
     The present invention provides an actuator assembly that utilizes a high speed solenoid in conjunction with a stem valve, such as a poppet valve, to control the flow of hydraulic fluid to an engine intake or exhaust valve. The solenoid has an armature element formed of a powder metal, which essentially prevents eddy currents and allows the solenoid to generate the electromagnetic force to provide the desired response time. As a result, the present invention provides an electohydraulic actuator that allows for effective variable valve lift and timing control. 
     In one embodiment, an actuator assembly according to the present invention comprises a cylinder valve, such as a poppet valve, that is moveable between open and closed positions, a bias spring biased to keep the valve in either the open or closed position, and a solenoid actuator having an armature element formed of a powder metal and adapted to control the movement of the valve between the open and closed positions. 
     The present invention also provides a control assembly for operating a two stage cylinder valve. The control assembly incorporates two actuator assemblies of the present invention, one of which is connected to a high pressure source of fluid and the other of which is connected to a low pressure source of fluid. The solenoid actuators of the actuator assemblies control the position of the respective valves, which ultimately control the type of fluid that flows to the cylinder valve. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional view of an actuator assembly according to a preferred embodiment of the present invention. 
     FIG. 2 is a partial cross-sectional view of a hydraulically activated valve system according to a preferred embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following description of preferred embodiments of the invention provides examples of the present invention. The embodiments discussed herein are merely exemplary in nature, and are not intended to limit the scope of the invention in any manner. Rather, the description of these preferred embodiments serves to enable a person of ordinary skill in the relevant art to make and use the present invention. 
     In one aspect, the present invention provides an actuator assembly for operating a cylinder valve of an internal combustion engine. As illustrated in FIG. 1, the actuator assembly, generally indicated at reference  10 , preferably includes a stem valve  12 , a solenoid actuator  14 , a housing  16  that defines a recess  18 , a plug  20 , and a bias spring  22 . The stem valve  12  is moveable between two positions: an open position and a closed position. In the open position, the stem valve  12  allows flow of fluid through a channel  26  or other passageway. When in the closed position, the stem valve  12  prevents this flow. 
     The stem valve  12  can be any suitable valve type known to those skilled in the art. The stem valve  12  need only be able to regulate the flow of fluid, as described above, and be able to be operably connected to the solenoid actuator  14 , as described below. Examples of suitable valves for use as the stem valve  12  include poppet valves and spool-type valves. 
     The bias spring  22  can be a conventional bias spring employed by those skilled in the art to preferentially position a valve in one of its available positions. As used in the actuator assembly of the present invention, the bias spring can be biased to keep the stem valve  12  in either the open or closed position. 
     The solenoid actuator  14  operates the movement of the stem valve  12  between the open and closed positions. Except as described below, the solenoid actuator  14  is similar to a conventional solenoid actuator in architecture but differs considerably in performance due to the application of powder metal technology. Thus, the solenoid actuator  14  includes a solenoid coil  28 , an armature element  30 , a housing  16  and the plug  20 . The coil  28  is wrapped inside the cylindrical portion of plug  20  in the conventional manner such that the armature element  30  can move into and out of the recess  18  when an electrical current is passed through the coil  28 . The plug  20  is positioned in the recess to stop movement of the armature element  30 . 
     The armature element  30  is adapted to control movement of the stem valve  12  between the open and closed positions. This links the movement of the stem valve  12  to the movement of the armature element  30 , which is controlled by the solenoid coil  28 . As illustrated in FIG. 1, the armature element  30  and stem valve  12  are preferably directly connected with each other, and any suitable means for attaching these elements can be used. Examples of suitable attachment means include adhesive, rivets and other fasteners, and compressive forces. Alternatively, the armature element  30  and stem valve  12  can be integrally formed. Also alternately, the armature element  30  can open a passageway to permit hydraulic fluid to enter and exit the area between armature element  30  and valve  12 , causing valve  12  to move by the difference of pressure between the ends of valve  12 . 
     As indicated above, the actuator assembly  10  of the present invention provides a high speed actuator suitable for use in electrohydraulic valve systems. The assembly achieves very fast actuation speeds by the use of powder metal in one or more components of the assembly. 
     Powder metal, as a composition, is known to those skilled in the art. Typical powder metal composites comprise metal particles, such as iron, encased in a non-metallic material. The powder metal can be formed into various shapes by several processes, such as that disclosed in U.S. Pat. No. 4,030,919 to Lea for A CONTINUOUS METHOD OF AND APPARATUS FOR MAKING BARS FROM POWDERED METAL. 
     The armature element  30  of the actuator assembly  10  is formed of a powder metal. Preferably, other elements of the assembly  10  are also formed of a powder metal. For example, the inventors have discovered that the housing  16  and plug  20  are advantageously formed of powder metal. 
     Any suitable powder metal can be used in forming the parts of the assembly  10 . A preferred powder metal comprises a plurality of iron particles coated with an inorganic material. Also preferable, the inorganic material comprises an inorganic oxide, such as a silicon oxide, which acts as an electrical insulator. Such a powder metal is commercially available from Mii Technologies, LLC, of West Lebanon, N.H. 
     FIG. 2 illustrates a control assembly  150  for operating a cylinder valve  152  of an internal combustion engine. The assembly  150  incorporates two actuator assemblies  110  in accordance with the present invention. Accordingly, similar reference numbers in FIG. 2 refer to similar features and/or components illustrated in FIG.  1 . 
     As illustrated in FIG. 2, the control assembly  150  includes a high pressure source of fluid  154 , low pressure source of fluid  156 , a high pressure actuator assembly  110   a , a low pressure actuator assembly  110   b , a high pressure fluid line  158 , and a low pressure fluid line  160 . 
     The high  110   a  and low  110   b  pressure control assembly each include a stem valve  112   a,    112   b  and a solenoid actuator  114   a ,  114   b . The solenoid actuators  114   a ,  114   b  each include an armature element  130   a ,  130   b.  At least one of the armature elements  130   a ,  130   b  is formed of a powder metal. Preferably, the armature element  130   a  of the solenoid actuator  114   a  of the high pressure control assembly  110   a  is formed of powder metal as described above. Particularly preferable, the armature element  130   b  of the solenoid actuator  114   b  of the low pressure control assembly  110   b  is also formed of a powder metal as described above. 
     The high pressure fluid line  158  communicates with the high pressure source of fluid  154 , the high pressure stem valve  112   a,  and the cylinder valve  152  of the engine by way of a valve  162 . Likewise, the low pressure fluid line  160  communicates with the low pressure source of fluid  156 , the low pressure stem valve  112   b , and the cylinder valve  152  by way of a valve  162 . Thus, the high pressure control assembly  110   a  is adapted to allow high pressure fluid flow to the cylinder valve  152  by way of actuating the armature  130   a  to open the stem valve  112   a,  while the low pressure control assembly  110   b  is adapted to allow low pressure fluid to flow to the cylinder valve  152  by way of actuating the armature  130   b  to open the stem valve  112   b . The control assembly  150  thus opens and closes the cylinder valve  152  by selectively activating and deactivating the actuator assemblies  110   a,    110   b , which controls the type of fluid exposed to the cylinder valve  152 . 
     Bias springs  122   a,    122   b  are biased to place the stem valves  112   a,    112   b  in opposite positions. Preferably, for example, the bias spring  122   a  in the high pressure actuator assembly  110   a  is biased to place stem valve  112   a  in a closed position, while bias spring  122   b  in the low pressure actuator assembly  110   b  is biased to place stem valve  112   b  in an open position. 
     The references cited in this disclosure, except to the extent they contradict any statements or definitions made herein, are incorporated by reference in their entirety. 
     The foregoing disclosure includes the best mode devised by the inventors for practicing the invention. It is apparent, however, that several variations in accordance with the present invention may be conceivable to one of ordinary skill in the relevant art. Inasmuch as the foregoing disclosure is intended to enable such person to practice the instant invention, it should not be construed to be limited thereby, but should be construed to include such aforementioned variations. As such, the present invention should be limited only by the spirit and scope of the following claims.