Abstract:
An internal combustion engine and method of operating the engine is provided. The engine comprises an engine block defining an engine cylinder, a piston reciprocatingly positioned in the engine cylinder, a head connected with the engine block, the head defining an inlet port and an exhaust port, an intake valve positioned in the inlet port, the intake valve configured to restrict flow through the intake port to the cylinder, an exhaust valve positioned in the exhaust port, the exhaust valve configured to restrict flow through the exhaust port to the cylinder, a cam connected with the intake valve to open the intake valve, and an engine valve actuator connected with the intake valve. The engine valve actuator is configured to hold either or both the intake valve and or exhaust valve open after the cam opens one or both of the valves.

Description:
This application is a continuation of application Ser. No. 10/409,997, filed Apr. 9, 2003, abandoned, which claims priority to Provisional Application No. 60/413,422, filed Sep. 25, 2002; the content of all of the above are hereby incorporated by reference. 

   TECHNICAL FIELD 
   This disclosure relates generally to internal combustion engines and, more particularly, to an apparatus for varying valve timing. 
   BACKGROUND 
   The operation of an internal combustion engine requires, among other things, the timed opening and closing of a plurality of valves. For example, with a typical four-stroke engine, one of ordinary skill in the art will readily recognize such an engine operates through four distinct strokes of a piston reciprocating through a cylinder, with intake and exhaust valves operating in conjunction with the piston. In an intake stroke, the piston moves from top dead center (TDC) where the piston is near a head portion to bottom dead center (BDC) where the piston is at a predetermined distance from the head. An intake valve is opened allowing air or a fuel and air mixture into the cylinder as the piston travels from TDC to BDC. In a subsequent compression stroke, the piston moves from BDC to TDC while both an exhaust valve and intake valve inhibit gas flow from the cylinder, thereby compressing the air and any residual gasses within the cylinder. A combustion or power stroke follows the compression stroke wherein fuel is injected into the compressed air and thereby ignited. Alternatively, an ignition device such as a spark plug may ignite the mixture of fuel and air. The force resulting from the combustion pushes the piston toward BDC while both the intake and exhaust valves are closed. Finally, the piston reverses direction and moves back toward TDC with the exhaust valve open, thereby pushing the combustion gases out of the cylinder. 
   Historically, valves on internal combustion engines have been operated in a regular cyclical fashion through the operation of a cam mechanically connected to the valves. Mechanical operation provides an efficient transfer of energy. However, advanced engine cycles may require at least temporary changes in the regular cyclical operation. 
   As an example, a Miller cycle in an internal combustion engine may be desired to reduce the compression work while maintaining a desired expansion ratio. One method of operating an engine in a Miller cycle closes an intake valve later than provided for by regular cyclical operation of a cam. The exhaust valve may also close later than provided for by the cam to provide internal exhaust gas recirculation (EGR). As known by those skilled in the art, EGR reduces the oxygen available for combustion and reduces formation of an uncertain form of oxides of nitrogen (NOx). 
   In U.S. Pat. No. 6,237,551 issued to Macor et al. on 29 May 2001, a system is described to vary a duration the valve is in an open position. The cam is connected to a rocker arm to cyclically operate a valve. A hydraulic linkage is placed between the rocker arm and the valves. When activated, the hydraulic linkage allows the rocker arm to move the valve according to a profile of the cam. This system, may also be called a “lost motion” system, allows the valve duration to be shortened by decoupling the cam movement from the valve actuation. The decoupling of the valve from cam allows the valve to return to a valve seat or closed position earlier than produce by the cam movement. However, accidental decoupling or loss of hydraulic pressure will let all valves return to their closed position. The engine in turn will not be able to operate. 
   As an alternative an actuating mechanism may instead alter the valve movement by acting against the valve to hold the valve as shown in U.S. Pat. No. 6,321,706 issued to Wing on 27 Nov. 2001. In normal operation, the cam cyclically operates on the valve. However, the regular cyclical operation may be altered to extend duration of valve in its open position through the use of various valve holding devices. In one embodiment, a valve member has a shaft extending through a magneto-rheological fluid placed in a sealed chamber. The shaft includes an enlarged portion positioned within the sealed chamber. The valve closing may be delayed by energizing a magnetic field near the chamber to increase the resistance against the enlarged portion moving through the magneto-rheological fluid and delaying closing of the valve. The valve holding device of Wing requires a specifically designed valve shaft and spring arrangement. 
   The present disclosure is directed to overcoming one or more of the problems or disadvantages associated with the prior art. 
   SUMMARY OF THE INVENTION 
   In one aspect of the present invention an engine valve actuator for varying valve timing includes an actuator cylinder. An electromagnetic coil connects with the actuator cylinder. An actuator piston is reciprocatingly disposed in the actuator cylinder. A biasing means is connected with the actuator piston. An electrorheological fluid is disposed in at least a portion of the actuator cylinder. 
   In another aspect of the present invention an internal combustion engine includes a cam connecting with an intake valve and exhaust valve to cyclically move the valves. An engine valve actuator connects with intake valve. The engine valve actuator includes an actuator cylinder. An actuator piston is reciprocatingly positioned in the actuator cylinder along with an elecrtorheological fluid. An electromagnetic coil is positioned in close proximity with the electrorheological fluid. A biasing means is connected with the actuator piston. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is cross-sectional view of an engine having an engine valve actuator with an embodiment of the present invention; 
       FIG. 2  is a schematic representation an engine valve actuator having an embodiment of the present invention; 
       FIG. 3  is a schematic representation of an engine valve actuator having another embodiment of the present invention; 
       FIG. 4  is a graph plotting valve lift vs. engine crank angle during normal operation; 
       FIG. 5  is a graph plotting valve lift vs. engine crank angle during internal exhaust gas recirculation operation; and 
       FIG. 6  is a graph plotting valve lift vs. engine crank angle during Miller cycle operation. 
   

   DETAILED DESCRIPTION 
   Referring now to the drawings, and with specific reference to  FIG. 1 , an embodiment of an internal combustion engine is generally referred to by reference numeral  20 . While the engine  20  is depicted and will be described in further detail herein with reference to a four stroke, internal combustion diesel engine, it is to be understood that the teachings of the disclosure can be employed in conjunction with any other type of reciprocating engine such as spark ignited engines, two-stroke engines, or rotary engines. 
   The engine  20  may include a plurality of engine cylinders  22  in each of which is reciprocatingly mounted an engine piston  24 . As known in the art, the engine  20  may include any number of cylinders and may be arranged in various manners such as, for example, in-line or “V”. A connecting rod  26  connects with each engine piston  24 , and in turn connects to a crank shaft  27  so as to capitalize on the motion of the engine piston  24  to produce useful work in a machine (not shown) with which the engine  20  is associated. Each engine has an engine block  28  defining the cylinder  24  and a cylinder head  30 . 
   A pair of exhaust ports  38  and intake ports (not shown) may be provided in the cylinder head  30  to allow for fluid communication into and out of the engine cylinder  22 . In normal engine operation, air may be allowed to enter the engine cylinder  22  through the intake ports, while combustion or exhaust gases may be allowed to exit the engine cylinder  22  through the exhaust ports  38 . An exhaust valve  42  may be provided within each gas port. As shown the exhaust ports  38  and exhaust valves  42  will be described in relation to an exhaust system. However, it should be understood that the intake ports and intake valve element act in similar manner as known in the art. 
   Each of the exhaust valves  42  may include a valve head  44  from which a valve stem  46  extends. The valve head  44  includes a sealing surface  48  adapted to seal against a valve seat  50  about a perimeter  52  of the valve ports  38 . A bridge  54  is adapted to contact the valve stems  46  of the valve  42 . A valve spring  56  imparts force between the top of each valve stem  46  and the cylinder head  30 , thereby biasing the stem  46  away from the cylinder head  30  and thus biasing the valve head  44  into seating engagement with the corresponding valve seats  50  or move the exhaust valve  42  into a closed position blocking the exhaust port  38 . 
   Movement of the exhaust valve  42  is controlled not only by the springs  56 , but by a cam assembly  58  as well. As one of ordinary skill in the art will readily recognize, rotation of the cam  60  cyclically causes a push rod  62  to rise, thereby causing a rocker arm  64 , connected thereto, to pivot about a pivot  66 . In so doing, an end  68  of the rocker arm  64  is caused to move downwardly and thereby move the exhaust valve element  42  to an open position unblocking the exhaust port  38 . Under normal engine operation, the cam  60  imparts sufficient force to the valve stem  46  to overcome the biasing force of the spring  56  and thereby push the valve head  44  away from the valve seat  50 , to move the exhaust valve  42  to an open position. Further rotation of the cam  60  allows the spring  56  to push the end  68  of the rocker arm  64  upward and the push rod  62  downward until the cam  60  completes another revolution. Alternatively, the cam  60  may act directly on either the rocker arm  64  or valve element  42  in a conventional manner. 
   In certain modes of engine operation, such as with the compression release braking, Miller cycle operation, and EGR referenced above, it is desirable for the exhaust valves  42  to be held in the open position for longer periods, or at a timing sequence other than that dictated by the cam  60 . In such situations, an engine valve actuator  70  may be used to so hold the exhaust valve  34  in the open position. 
   As shown in  FIG. 2 , the engine valve actuator  70  includes an actuator piston  72  reciprocatingly positioned in an actuator cylinder  74 . The actuator piston has an actuating surface  76  opposite a control surface  78 . An actuating rod  80  may extend from the actuating surface  76  through an opening  82  in the actuating cylinder  74  to engage the actuator arm  68 . In this embodiment, a spring  84  attaches to the control surface  78  as a biasing means to urge the actuating piston to engage with the exhaust valves  42 . Any conventional biasing means may be used such as a pressurized hydraulic or pneumatic cylinder that may be passively or actively controlled. An electromagnetic coil  86  is connected with the actuator cylinder  74 . The electromagnetic coil  86  may be any conventional device capable of generating a magnetic flux or electric current operatively associated with an electrorhelological fluid  88 . As shown, the electromagnetic coil  86  may be integral with actuator cylinder  74 . The electrorehological fluid  88  is contained within the actuator cylinder  74 . The electrorheological fluid  88  includes magnetorheological fluids and other any fluid where viscosity may be controllable in response to controlling an applied magnetic flux or electrical current. The electrorheological fluid  88  may pass from the actuating surface  76  to the control surface  78  via flow control device  90  represented by a plurality of orifices in the present embodiment. An electronic controller  92  is connected with the electromagnetic coils  86 . 
   An alternative engine valve actuator  70 ′ shown in  FIG. 3  includes the actuator piston  72 ′, a control piston  94 , the actuator cylinder  74 ′, and a control cylinder  96  (where the “′” represents a component corresponding to an element of the embodiment shown in  FIG. 2 ). The control piston  94  is reciprocatingly positioned in the control cylinder  96 . The spring  84 ′ or similar biasing means positions the control piston  94  so as to reduce a control volume  98  in the control cylinder  96  for the electrorheological fluid  88 . In this embodiment, the electrorheological fluid  88  is in fluid contact with the control surface  78  of the actuator piston  72 ′. The actuator cylinder  74 ′ and control cylinder  96  may be formed from a single cylinder  100  separated by a partition  102 . The flow control device  90 ′, represented by an orifice in this embodiment, is positioned in the partition  102 . The flow control device  90 ′ allows the electrorhelogoical fluid  88  to fluidly communicate between the control cylinder  96  and the actuator cylinder  74 ′. While this embodiment shows an orifice, any conventional flow control device  90 ′ may be used. The electromagnetic coils  86 ′ in this embodiment are shown as being attached to the single cylinder  100 . 
   INDUSTRIAL APPLICABILITY 
     FIG. 4  shows a typical trace of an exhaust valve  42  when operated using the cam assembly  58 . Each valve opens and closes in a regular, cyclical fashion (i.e. at a predetermined crank angle for each engine cycle.) Alternative engine cycles such as internal EGR and Miller cycle operation require alteration of the regular, cyclical cam operation. In the present invention, the engine valve actuator  70  may be used with existing engine designs without modifying existing components. 
   Taking internal EGR shown in  FIG. 5 , moving the exhaust valve  42  to the closed position may be delayed by sending a signal to the electromagnetic coil  86 . During an exhaust stroke, as the piston  24  moves toward TDC, the cam will cause the exhaust valve  34  to move away from the seat  50 . To prevent the exhaust valve from following the cam motion, a signal is sent by the controller  92  to establish a magnetic flux (not shown) in the electrorhelogical fluid  88  causing the viscosity to increase. Motion of the actuator piston  72  is slowed or stopped by the increased resistance due to the change in viscosity. At such time the exhaust valve  34  is desired to return to its seat  50 , the controller  92  terminates the signal to reduce or eliminate the magnetic flux. The exhaust valve  42  returns to its seat  50 . The flow control device  90  provides dampening to the actuator piston  72 . 
   Continuing with the example of EGR, when the exhaust valve  34  is held in the open position as the engine piston  24  ascends to a TDC position, and remains in the open position after the engine piston  24  reverses and descends. A portion of the exhaust gases vented from neighboring engine cylinders  22  through the exhaust ports  36  are thereby reintroduced to the engine cylinder  22  by the resulting pressure differential. After a predetermined stroke length (e.g., ninety degrees of a seven hundred and twenty degree four stroke cycle), the exhaust valve  42  is in the closed position, while the intake valve remains in the open position to complete the intake stroke as explained above. 
   The teachings of the present disclosure can also be used to provide Miller cycle benefits. As illustrated in  FIG. 6 , the intake valves may be held open during the initial stages of the compression stroke to thereby reduce the compression work of the engine  20  and provide the engine efficiencies of the Miller cycle as well known by those of ordinary skill in the art. The intake valve could be so held by employing the engine actuator  70  after the cam assembly  58  moves the intake valve to the open position during the intake stroke. More specifically, as the intake valve is about to be moved to the closed position by the spring  56  at the conclusion of a normal intake stroke, the electromagnetic coil  86  could be actuated so as to slow movement of the actuator piston and thereby the intake valve toward the seat  50 . 
   Other aspects and features of the present disclosure can be obtained from a study of the drawings, the disclosure, and the appended claims.