Abstract:
A variable lift electromechanical valve actuator for use with an internal combustion engine. The electromechanical valve includes a first electromagnet, a second electromagnet, and a hydraulic lifting mechanism. The upper electromagnet is fixedly mounted to a housing while the lower electromagnet slides in conjunction with the hydraulic lifting mechanism. Multiple valve lifts are provided for by the movement of the lower electromagnetic electromagnet. Variable valve lift allows for more efficient operation of the engine and reduced power consumption, noise, vibration, and wear concerns.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to electromechanical valve actuators and more particularly to variable lift electromechanical valves for internal combustion engines.  
           [0002]    Engine valves control the flow in and out of the cylinders in internal combustion engines. Engine valves are typically controlled by camshafts that rotate, at a speed proportional to the crankshaft causing the valves to open and close at specified intervals. An example of a typical valve train includes a rotating camshaft having elliptical lobes which contact tappets or lash compensators on the valve. As the elliptical lobe presses against the tappet, the valve is pushed open at determined intervals, and as the elliptical lobes rotate away from the tappet, the valve is closed by a spring. The opening and closing times of the valves are determined by the geometry of the lobes, and the relative angular position with respect to the crankshaft when the engine is assembled. Manufacturers can adjust this timing by altering the shape, size, and angular location of the elliptical lobes. However, the timing as well as the torque curve is typically fixed at the time the engine is assembled. The amount of valve lift is also determined by the lobes on the camshaft and therefore determined when the engine is assembled. The lack of variable valve timing and variable valve lift reduces engine optimization and therefore may reduce engine efficiency.  
           [0003]    Another problem with conventional engines is that they require a throttle body and the associated components. The throttle body restricts air flow into the engine. One problem with using a throttle body is that engine efficiency is reduced due to intake restrictions. When air flows through the throttle body, an air pressure drop occurs across the throttle plate. Therefore, when the intake valve opens under throttled conditions, the piston pulls in air of a lower pressure than the surrounding atmosphere, resulting in engine inefficiencies. Manufacturers have strived to create true throttless engine operation to increase engine efficiency as well as allow for drive-by-wire systems.  
           [0004]    To address problems associated with traditional valves activated by camshafts, some manufacturers have attempted to substitute electromechanical valve actuators (also known as electromagnetic valve actuators) in place of camshafts. Generally, these electromechanical actuators include upper and lower electromagnets that are formed from lamination stacks and coiled wire. The electromechanical valve actuators also include an armature located between the electromagnets. The armature generally forms a plane somewhat perpendicular to the valve stem and includes an armature stem, that passes through both the upper and lower electromagnets, in order to open or close a valve.  
           [0005]    In operation, the electromagnets are selectively energized, creating a magnetic force to draw the armature to the energized electromagnet. The surface of the electromagnet which the armature contacts may be referred to as a pole face. As the armature moves back and forth in pole face to pole face operation, the valve is opened and closed. Electromechanical valve actuators allow for complete control of the timing of every valve. Electromechanical valve actuators may also open more than one valve at the same time. One problem with electromechanical actuated valves is that as the distance between the armature and the magnetized electromagnet decreases, the magnetic force exponentially increases. The increase in magnetic force causes the armature to increase in velocity as it approaches an energized electromagnet. The armature then impacts the electromagnet, causing noise and vibration. Forceful contact between the armature and electromagnet also may cause excessive wear on the components of the electromechanical valve actuator and other engine components.  
           [0006]    Some manufacturers have shaped the power profile supplied to the lamination stack in an effort to soften the impact, but this may increase the time it takes the armature to travel from pole face to pole face. An increase in time to travel from pole face to pole face increases the transition times and may prevent the engine from operating properly because the valve cannot open and close fast enough.  
           [0007]    At idle speeds, electromechanical valves may consume a significant portion of power to overcome the springs in the system, and move the armature from the pole face to pole face. Enough power must be applied to the electromagnet to overcome any exhaust pressure in the cylinder during the opening of an exhaust valve, which creates a large draw on the electrical system of the engine at idle speeds. The springs may be sized to accommodate desired valve transition times as well as provide enough force to open against any exhaust pressure. Another problem with electromechanical valves is that they are not capable of operating throttless in all engine conditions. For many electromechanical valves, varying the valve timing still leaves large regions at mid to high flow regimes where they are not able to operate. These voids in operating conditions many times occur in the most desirable operating regions of the engine. Yet another problem is that electromechanical valves are not as efficient as they can be, because the valve lift or how far the valves open can not be changed. Valve lift is generally set by operating conditions that demand maximum flow, which cause inefficient engine operation in low flow conditions.  
           [0008]    To solve some of the problems associated with electromechanical valves, a few manufacturers have varied the lift of the valves. Varying the lift of the valves may help increase the efficiency of the engine by allowing the lift of the valve to match the operating conditions. Reduced valve lift at idle conditions also helps to reduce noise, vibration, power consumption, and wear concerns.  
           [0009]    A disadvantage some of these systems have is that the valve has only two lift positions, a high and a low position. The inability to adjust the lift throughout the range reduces the optimization of engine operation associated with variable lift and can prevent maximum engine efficiency from being obtained. Another problem with some of these systems is that the spring bias may be offset as the valve lift is changed which may cause the armature plate, when at rest, such as when the valve actuator is unpowered and no magnetic force is applied, to be off center between the lamination stacks. During operation, this bias may cause the armature to be more forcefully attracted to one pole face, causing noise and vibration. This bias may also make it difficult to be attracted to the other electromechanical plate, thereby requiring additional power.  
           [0010]    Another system addresses some of these problems by providing a range of variable lifts. The problem with this variable valve lift system is that it is difficult to accurately determine the lift of the valve. The lash in the system may make it even more difficult. Due to the type of and amount of moving parts, the inaccuracy of the system only increases with use. Yet another problem with this system is the increase in moving parts, including the use of an additional motor may decrease the reliability of the system over time.  
         SUMMARY OF THE INVENTION  
         [0011]    The aforementioned problems are overcome in the present invention where an electromechanical valve includes an actuator that adjusts the lower magnet, varying the valve lift, along with the armature spring seat, varying the bias and spring forces, throughout a range of adjustment. More specifically, the present invention includes a variable lift actuator in conjunction with an electromechanical valve, providing variable valve lift while centering the armature in all lift positions between the two electromagnets and reducing the impact forces of the armature against the electromagnets during pole face to pole face operation.  
           [0012]    A hydraulic actuator is used to vary the lift of the valve, allowing for maximum engine efficiency by allowing a range of flow depending on the engine requirements, in addition to variable valve timing. The present invention allows true throttless operation through its entire engine speed and load ranges. The valve lift can control the air flow, eliminating the need for a throttle body. Variable valve lift and variable timing allow the engine to provide optimum torque at all rpms, unlike some electromechanical valves, which have gaps in the rpm power band where the engine can not function properly without throttling. Another benefit of the hydraulic actuator providing variable valve lift is that a hydraulic pocket also provides a dampening means, which may reduce impact noise and wear concerns. The present invention also allows complete pole face to pole face movement of the armature no matter what lift is being used. Complete pole face to pole face operation also helps accurately determine the amount of valve lift. Variable valve lift also reduces the spring force thereby reducing noise and wear concerns, as well as reduces the power required to hold the armature against either pole face, especially during engine operation with reduced valve lift. Variable valve lift combined with variable valve timing allows for efficient engine operation and minimal energy consumption.  
           [0013]    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  
       [0014]    The present invention will become more fully understood from the detailed description given below, the appended claims, and the accompanying drawings in which:  
         [0015]    [0015]FIG. 1 is a sectional view of an engine valve assembly with the valve shown in the fully closed position with reduced lift;  
         [0016]    [0016]FIG. 2 is a sectional view similar to FIG. 1 but with the valve shown in its middle position with reduced lift;  
         [0017]    [0017]FIG. 3 is a sectional view similar to FIG. 1 but with the valve shown in the open position with reduced lift;  
         [0018]    [0018]FIG. 4 is a sectional view similar to FIG. 1 but with the valve being in the closed position with full lift;  
         [0019]    [0019]FIG. 5 is a sectional view similar to FIG. 3 showing the valve in a open position set in the mode for full lift; and  
         [0020]    [0020]FIG. 6 is a block diagram of the engine valve assembly and control system. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0021]    [0021]FIG. 1 illustrates an electromechanical valve actuator assembly  10  which is mounted on an internal combustion engine to open and close the valves (e.g., intake or exhaust valves).  
         [0022]    The electromechanical valve assembly  10  is generally mounted on the cylinder head  12  of the internal combustion engine. While the cylinder head  12  may be formed in a variety of shapes and configurations, it typically includes a port  14 , a valve seat  16 , and a valve guide  18 . The port  14  may be an intake or an exhaust port depending on the function of the valve.  
         [0023]    The valve  20  includes a valve disc or head  22 , a tapered portion  24 , and a valve stem  26 . An upper spring retainer  32  and a lower spring retainer  34  may also be included. The valve  20  and the cylinder head  12  are formed and assembled as generally well known in the art. The valve guide  18  receives the valve stem  26  and aligns the valve  20  as it moves up and down so that a tight seal is formed between the valve seat  16  and the tapered portion  24  surrounding the valve disc  22 , when the valve  20  is in its closed position, as may be seen in FIGS. 1 and 4.  
         [0024]    The electromechanical valve actuator  10  generally includes a housing  40  defining a cavity containing electromagnets  52  and  54 , an armature stem  60 , an armature  70 , and a hydraulic lift mechanism  80 . The upper and lower electromagnets  52  and  54  move the armature  70  and attached armature stem  60  to drive the engine valve  20  between its open and closed positions.  
         [0025]    The housing  40  may be formed in a variety of sizes and shapes, which may be dictated by space constraints of the internal combustion engine. The housing  40  provides structural rigidity and attaches the electromechanical valve actuator  10  to a cylinder head  12  of an internal combustion engine. Of course, it should be readily apparent to one skilled in the art that a variety of means may be used to provide the structural rigidity or method of attachment.  
         [0026]    In the illustrated embodiment, the upper electromagnet  52  is fixed relative to the housing  40  such as by pins  42  while the lower electromagnet  54  is mounted within the housing  40  so that it is movable relative to the housing  40 . Suitable electromagnets are generally well known in the art and can have a variety of shapes that may be formed from the individual plates of magnetically conductive material to form a lamination stack. The electromagnets  52  and  54  may include a coil of wires  53  wound within the lamination stack. The electromagnets  52  and  54  are connected to a source of electrical current (not shown) which can be selectively turned on and off independently by a controller such as an engine management system  100  (FIG. 6). An energized electromagnet  52  or  54  provides magnetic force to attract the armature  70 . It should readily be recognized that a separate means may be used in place of the housing  40  to hold the upper electromagnet  52  in place.  
         [0027]    The armature  70  is mounted to move with the armature stem  60  and is located between the upper electromagnet  52  and the lower electromagnet  54 . In the illustrated embodiment, the surfaces of the armature  70  facing the electromagnets  52  and  54  are approximately the same size and shape as the surfaces of the electromagnets  52  and  54  facing the armature  70 . Of course, it should be readily obvious to one skilled in the art that the sizes and shapes of the armature  70  and of the electromagnets  50  may vary between applications.  
         [0028]    An armature spring  62  and a valve spring  64  operably engage the valve to urge the valve toward its open or closed positions. The armature spring  62  is mounted above the upper electromagnet  52  within the housing  40  to exert a biasing force urging the valve  20  toward its open position. In the illustrated embodiment, the armature spring  62  is a compression spring and is located between the armature spring retainer  32  and the hydraulic lift mechanism  80 . The armature spring  62  may be any compression spring known in the art for use with traditional valves or electromechanical valves. The size, shape, and location of the armature spring  62  may vary from application to application. A valve spring  64  is mounted, in the illustrated embodiment, between the cylinder head  12  and the valve spring retainer  34 . The valve spring  64  is also a compression spring as shown in the illustrated embodiment. Of course, it should be readily recognized to one skilled in the art that other placements of the springs  62  and  64  are possible and that certain placements may also result in opening and closing of the valves differently than shown in the illustrated embodiment.  
         [0029]    The hydraulic lift mechanism  80  varies the amount of valve lift and, in the illustrated embodiment, includes a hydraulic slide  82  and a hydraulic chamber  84 . The hydraulic slide  82  is formed in the illustrated embodiment in the shape of a sleeve having an upper segment  72 , a lower segment  74 , and a passage  78  to accommodate the upper electromagnet  52  and pins  42 . The lower electromagnet  54  is attached to move with the slide  82  by a variety of means such as a compression fit, adhesive, bonding or pins. The hydraulic chamber  84  is defined in the illustrated embodiment at the upper end of the housing  40  by the housing and the hydraulic slide  82 . As the pressure in the chamber  84  is varied, the slide  82  moves relative to the housing  40 . As the lower electromagnet  54  moves with the slide  82  and the upper electromagnet  52  is fixed to the housing  40 , movement of the slide  82  changes the distance between the electromagnets  52  and  54  and the length of the valve stroke.  
         [0030]    In the illustrated embodiment, hydraulic fluid in the hydraulic chamber  84 , such as engine oil, is pressurized by the oil pressure of the engine or an auxiliary pump. In some embodiments the hydraulic lift mechanism  80  may include hydraulic lines  86 , hydraulic valves  88  and a pump  102 . The hydraulic lines  86  provide a fluid connection between the hydraulic chamber  84  and the pump  102 . Hydraulic valves  88  may be situated between the hydraulic chamber  84  and the pump  102  to control flow through the hydraulic lines  86 . The hydraulic valves  88  control the height of the hydraulic slide  82  in conjunction with the forces from the springs  62  and  64 . The hydraulic valve or valves  88  control the fluid pressure in the hydraulic chamber  84 . In the illustrated embodiment, the hydraulic valve  88  is a spool valve. A spool valve is used because it uses a series of hydraulic channels to maintain a specified position regardless of the forces acting on the slide  82 . The hydraulic valve  88  is controlled by the engine management system  100 . The engine management system  100  can easily control valve lift through existing techniques of determining air flow needed to the engine. Of course, the engine management system may be programmed from lab tests or road tests of what valve lifts are needed under specified engine operating conditions to maximize efficiency. In the illustrated embodiment, the pump  102  is the engine oil pump and engine oil is used as the hydraulic fluid. Of course a separate pump as well as separate hydraulic fluid may be used. A separate means for heating the fluid may also be included (not shown).  
         [0031]    In operation, the valves are opened and closed as is well known in the art for electromechanical valves. While the system is unpowered, the armature  70  is in a neutral position, approximately centered between the upper and lower electromagnets  52  and  54  due to the biasing of the springs  62  and  64 . Upon start up, either the upper or lower electromagnet  52  or  54  is energized, attracting the armature  70 , thereby opening or closing the valve  20 . The power is then switched between the electromagnets  52  and  54  causing the armature  70  to travel pole face to pole face, opening and closing the valve  20 . As with most electromechanical valves, the timing of the opening and closing may also be varied for more efficient engine operation.  
         [0032]    When the valve  20  is commanded to a full open or full closed position, the armature  70  is attracted to an electromagnet pole face. In order to hold the valve  20  closed enough current must be delivered to the electromagnet pole face to produce a magnetic force larger than the spring force which acts in the opposite direction. The illustrated embodiment has the advantage that during reduced lift operation the hydraulic slide moves resulting in a lower spring force that the electromagnet must overcome. In other words, during low lift operation, the spring force opposing the electromagnet force is reduced. This results in less required electromagnet force and therefore less power consumption by the electromagnet when compared to a stationary full lift actuator.  
         [0033]    The amount of valve lift during engine operation may be changed by varying the pressure in the hydraulic chamber  84  and therefore the position of the slide  82 . A low pressure causes the hydraulic slide  82  to be in a reduced lift position, as shown in FIGS.  1 - 3 . Valve spring  64  exerts pressure on the slide  82 , causing the slide to move upward during low pressure conditions such as at low rpms. Of course, other means may be used to exert pressure on the hydraulic slide  82  to move the slide  82  to a reduced lift position such as an additional spring or an oil pocket. The reduced valve lift allows for optimized throttless engine operation through all ranges.  
         [0034]    As the engine revolutions increase, more flow is needed to and from the cylinders for the engine to operate efficiently and at the desired power levels. Engine oil pressure increases as the revolutions increase and pushes the hydraulic slide  82  downward to a desired lift, as shown in FIGS. 4 and 5, at the maximum lift. When the hydraulic slide  82  moves downward so does the lower electromagnet  54 , causing the armature to travel a greater distance between the upper and lower electromagnets  52  and  54 . It should readily be seen that because the hydraulic slide  82  compresses or relaxes spring  62 , the armature  70 , when at rest, is centered between the upper and lower electromagnets  52  and  54 , no matter what lift is being provided.  
         [0035]    To provide more precise control over the valve lift, the hydraulic lifting mechanism  80  may use the hydraulic valves  88  and separate oil pump  102 . A separate hydraulic pump  102  also can be helpful to provide full valve lift in any engine operating conditions. For example, a separate pump  102  is useful at low rpms where lots of torque is needed, such as pulling a heavy trailer, to increase valve lift and allow more flow. The hydraulic valves  88  may reduce valve lift at higher rpm conditions where little power is needed from the engine, for example, during operation at constant speeds such as operation of a vehicle on the highway.  
         [0036]    In operation, the above electromechanical valve also allows for throttless operation. The variability of the valve lift and timing allows the amount of air entering the cylinder to be controlled without a throttle body or throttle plate. This allows the piston to pull in atmospheric pressurized air, thereby increasing engine efficiency.  
         [0037]    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.