Abstract:
An engine valve operating system of an electromagnetic type is arranged to locate a movable member between two electromagnets through a distance block and to connect the two electromagnets through side walls. By alternately energizing the electromagnets, the movable member is reciprocated against spring forces of two springs. An engine valve is interlocked with the movable member and operates according to the reciprocal movement of the movable member. The side wall and/or distance block is made of soft magnetic material and forms a magnetic circuit penetrating a side surface of the movable plate. This new magnetic circuit increases the attracting force of the electromagnet when a clearance between the movable member and the electromagnet is greater than a predetermined clearance. This arrangement decreases energy consumption for the initializing operation of the valve operating system from a neutral position between the electromagnets.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to an engine valve operating system for an internal combustion engine, and more particularly to an engine valve operating system which operates engine valves of an internal combustion engine by means of an electromagnetic force generated by alternately energizing two electromagnets.  
           [0002]    Various electromagnetic valve operating systems for operating engine valves have been proposed. Generally such electromagnetic valve operating systems require larger electric energy in an initializing operation for starting the valve operation as compared with the electric energy required during a valve operating period. A Japanese Patent Provisional Publication No. 58-213913 discloses an initialization method which largely improves the energy consumption necessary for executing the initializing operation of the engine valve.  
         SUMMARY OF THE INVENTION  
         [0003]    However, this initialization method is required to further certainly execute the initializing operation even if the electromagnet type valve operating system employing this method is put in any condition.  
           [0004]    It is therefore an object of the present invention to provide an engine valve operating system which is arranged to increase the attracting force of electromagnets and decrease the energy consumption during the initializing operation.  
           [0005]    An engine valve operating system according to the present invention is for an internal combustion engine and comprises a movable member, first and second electromagnets, first and second springs, and a magnetic-circuit member. The movable member interlocks with an engine valve of the engine. The first electromagnet moves the movable member in a valve opening direction when the first electromagnet is energized. The second electromagnet moves the movable member in a valve closing direction when the second electromagnet is energized. The first spring is installed to the engine valve and applies a force directing in the valve opening direction to the movable member. The second spring is installed to said movable member and applies a force directing in the valve closing direction to the movable member. The magnetic-circuit member is connected to the first electromagnet and the second electromagnet. The magnetic-circuit member is made of soft magnetic material. The magnetic-circuit member and one of the first and second electromagnets forms a magnetic circuit when a clearance between the movable member and the one of the first and second electromagnets is within a predetermined range. The magnetic circuit passes magnetic flux from the movable member to the magnetic-circuit member. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]    [0006]FIG. 1A is a cross sectional view of an engine valve operating system according to a first embodiment of the present invention, and  
         [0007]    [0007]FIG. 1B is another cross sectional view of the engine valve operating system of FIG. 1A.  
         [0008]    [0008]FIG. 2 is a cross sectional view taken in the direction of the arrows substantially along the line II-II of FIG. 1A.  
         [0009]    [0009]FIG. 3 is a cross sectional view taken in the direction of the arrows substantially along the line III-III of FIG. 1A.  
         [0010]    [0010]FIG. 4 is a graph showing a relationship of an attracting force of an electromagnet and a spring force with respect to air gap between a movable plate and an electromagnet.  
         [0011]    [0011]FIG. 5 is an enlarged cross sectional view for explaining a magnetic circuit generated by the electromagnet, the movable plate, and side walls.  
         [0012]    [0012]FIG. 6 is a graph showing an advantage of the first embodiment according to the present invention.  
         [0013]    [0013]FIG. 7A is a cross sectional view of an engine valve operating system according to a second embodiment of the present invention, and  
         [0014]    [0014]FIG. 7B is another cross sectional view of the engine valve operating system of FIG. 7A.  
         [0015]    [0015]FIG. 8A is a cross sectional view showing a magnetic circuit generated when the movable plate is located near the electromagnet in the second embodiment, and  
         [0016]    [0016]FIG. 8B is another cross sectional view showing a magnetic circuit according to the present invention when the movable plate is apart from the electromagnet.  
         [0017]    [0017]FIG. 9 is an enlarged cross section view showing a distance block employed in a third embodiment according to the present invention.  
         [0018]    [0018]FIG. 10 is an enlarged cross section view showing a relationship between the distance block and the movable plate employed in a fourth embodiment according to the present invention.  
         [0019]    [0019]FIG. 11 is an exploded perspective view showing the electromagnet, an end block and the distance block which are employed in a fifth embodiment according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0020]    Referring to FIGS. 1A to  6 , there is shown a first embodiment of an engine valve operating system for an internal combustion engine in accordance with the present invention.  
         [0021]    As shown in FIGS. 1A and 1B, a valve  2  for intake valve or exhaust valve is installed to an intake or exhaust port  1   a  of a cylinder head  1  of the engine. Valve  2  is slidably installed to cylinder head  1  through a guide  5  embedded in cylinder head  1 . A retainer  3  for receiving an end of a valve spring  4  is provided at an upper portion of valve  2 . Valve spring  4  is provided between retainer  3  and cylinder head  1  while being biased in a compressed condition. Valve spring  4  biases valve  2  toward a direction for closing the port  1   a.    
         [0022]    A bottom piece  6  functioning as a base of a valve drive mechanism is installed to cylinder head  2  so that a lower half portion of bottom piece  6  is embedded in cylinder head  2 . An electromagnet  7  for opening valve  2  during an energized condition is installed on the bottom piece  6 .  
         [0023]    Electromagnet  7  is produced by winding an electromagnetic coil  7   a  to grooves of a core having a E-shaped cross section and by fixedly installing end blocks  9  and  10  to both ends of electromagnetic coil  7   a . A shaft  16  penetrates a center portion of electromagnet  7  and is slidable with respect to electromagnet  7 . A movable plate  15  is fixed to an upper end of shaft  16  and is made of soft magnetic material such as iron. A lower end portion of shaft  16  is in contact with a tope end  2   a  of a stem of valve  2  as shown in FIG. 1A so that movable plate  15  can interlock with valve  2 .  
         [0024]    An electromagnet  8  for closing valve  2  during an energized condition is installed opposite to electromagnet  7  through movable plate  15 . The structure of electromagnet  8  for closing valve  2  is constituted by an electromagnetic coil  8   a  and end blocks  11  and  12 . The structure is basically the same as that of electromagnet  7  for opening valve  2  except that electromagnet  8  for opening valve  2  is inversely arranged with respect to a horizontal plane perpendicular to an axis of shaft  16  as compared with electromagnet  7  for closing valve  2 . Electromagnets  7  and  8  are fixed to have a predetermined clearance therebetween by providing distance blocks  13  and  14  therebetween while movably locating movable plate  15  in the predetermined clearance.  
         [0025]    An upper spring shaft  17  penetrates a center portion of electromagnet  8  and is slidable with respect to electromagnet  8 . An upper surface of movable plate  15  is connected to a lower end of upper spring shaft  17 , and an upper-spring retainer  18  is fixedly installed to an upper end portion of upper spring shaft  17 . A top piece  20  of a body part of the valve operating system receives an end of an upper spring  19  through a spring receiver  21 . Upper spring  19  for opening valve  2  is disposed between upper-spring retainer  18  and spring receiver  21  while being put in a compressed condition.  
         [0026]    When both electromagnets  7  and  8  are put in deenergized condition, movable plate  15  is kept at a neutral position between both electromagnets  7  and  8  due to valve spring  4  and upper spring  19 . Further, when electromagnet  7  for opening valve  2  is energized, electromagnet  7  attracts movable plate  15  in the valve opening direction against the spring force of valve spring  4  to open valve  2 . When electromagnet  8  for closing valve  2  is energized, electromagnet  8  attracts movable plate  15  in the valve closing direction against the spring force of upper spring  19  to close valve  2 .  
         [0027]    Bolts  24  penetrate top piece  20 , eng block  12  fixed to electromagnet  8 , distance plate  14 , end block  10  fixed to electromagnet  7  and bottom piece  6 , and fixedly connect these elements to cylinder head  1 .  
         [0028]    Side walls  22  and  23  are made of soft magnetic material such as iron, and are installed to side surfaces of the E-shaped cores of the respective electromagnets  7  and  8  while ensuring a predetermined clearance with respect to the side surfaces of movable plate  15 , as is clearly shown in FIG. 1B.  
         [0029]    Movable plate  15  and electromagnets  7  and  8  are formed into a rectangular shape, respectively, as viewed from an upper side and as shown in FIGS. 2 and 3. The longitudinal direction of the rectangular of these elements  15 ,  7  and  8  is the same as a perpendicular direction perpendicular to an axial direction of a crankshaft of the engine. Therefore, distance blocks  13  and  14  are oppositely disposed to face to both short sides of movable plate  15  as shown in FIGS. 1A and 2, and therefore, distance blocks  13  and  14  are disposed along the perpendicular direction with respect to the crankshaft when the valve system is installed to the engine.  
         [0030]    Next, there will be discussed the manner of operation of the engine valve operating system according to the present invention.  
         [0031]    [0031]FIG. 4 shows characteristics of electromagnet  7 ,  8  of a plate type and the spring employed in this embodiment. More specifically, FIG. 4 shows a relationship between an attracting force of electromagnet  7 ,  8  to movable plate  15  and an air gap between electromagnet  7 ,  8  and movable plate  15  and a relationship between a spring force of the spring and the air gap under a condition that a predetermined electric current I 0  is applied to electromagnet  7 ,  8 . Curve a of FIG. 4 shows the attracting force of electromagnet  7 ,  8  with respect to the air gap, and curve b of FIG. 4 shows the spring force of the spring with respect to the air gap.  
         [0032]    As is clearly shown in FIG. 4, electromagnet  7 ,  8  generates a large attracting force when the air gap, which is a distance between movable plate  14  and the surface of electromagnet  7  or  8 , is very small. Further, when the air gap is relatively large, the attracting force radically decreases. Therefore, the attracting force of the electromagnet  7 ,  8  under current I 0  is balanced with the spring having a composite spring constant k which is a resultant constant of upper spring  19  and valve spring  4 , at two balancing points P and Q. The balancing pointy P is an unstable balancing point, and therefore if the position of movable plate  15  shifts any quantity from the point P, the composite force of the attracting force and the spring force acts to increase the shifted quantity with respect to the point P. In contrast to this, the balancing point Q is a stable balancing point, and therefore even if the position of movable plate  15  shifts from the point Q by a predetermined quantity, the composite force acts to return the movable plate  15  to the point Q.  
         [0033]    Accordingly, the attracting force of electromagnet  7 ,  8  becomes greater than the spring force when one of electromagnets  7  and  8  is switched off during normal operation and when movable plate  15  is moved by simple harmonic motion to a position which is nearer than the point P with respect to the other of electromagnets  7  and  8 . Therefore, the valve operating system (valve actuator) can attract the movable plate  15  under this condition.  
         [0034]    On the other hand, when the initialization of the actuator is started, movable plate  15  first stays at the neutral position S. Under this condition, even if an electric current I 0  is applied to one of electromagnets  7  and  8 , movable plate  15  merely moves to at most the point Q. Since the point Q is the stable balancing point, even if movable plate  15  is further moved near the electromagnet, movable plate  15  is returned to the point Q by the spring force larger than the attracting force of the electromagnet.  
         [0035]    In order to achieve the initialization of the valve operating system, it is necessary that movable plate  15  is put in the attracted condition where movable plate  15  is attracted to electromagnet  7  or  8 . That is, it is necessary to apply an electric current I 1  larger than the electric current I 0  to the electromagnetic coil. Although the current I 0  is sufficiently large to execute the normal valve opening and closing operation, the initialization requires the current I 1  larger than the current I 0 . Therefore, it is necessary to provide a power source and a drive circuit for supplying such electric current I 1 , if the valve operating system is constructed conventionally without side walls  22  and  23  of soft magnetic material.  
         [0036]    As mentioned above, the engine valve operating system for operating valve  2  in accordance with the present invention comprises side walls  22  and  23 . Accordingly, the engine valve operating system having side walls  22  and  23  ensures the following advantages.  
         [0037]    The attracting force characteristic of the electromagnet  7  shown by the curve a in FIG. 4 is ensured by the magnetic circuit shown by A in FIG. 5.  
         [0038]    By installing side walls  22  and  23  of soft magnetic material at side surfaces of the plate type electromagnet  7  having an E-shaped cross-section, a new magnetic circuit of magnetic flux is generated as shown by arrows B in FIG. 5 when a distance between electromagnet  7 ,  8  and movable plate  15  is greater than a first predetermined distance. The magnetic circuit shown by the arrow B circulates in the order of the inner magnetic pole of electromagnet  7 , air gap, a lower surface of movable plate  15 , a side surface of the movable plate  15 , side wall  22  or  23  and the outer side of electromagnet  7 .  
         [0039]    The reason for generating the new magnetic circuit B is that when the distance between movable plate  15  and electromagnet  7  is relatively large, the magnetic resistance of the magnetic circuit B becomes smaller than that of the magnetic circuit A. On the other hand, when movable plate  15  sufficiently approaches electromagnet  7 , the magnetic resistance of the magnetic circuit A becomes smaller than a second predetermined distance. Therefore, when the air gap between movable plate  15  and electromagnet is zero or sufficiently small, the magnetic circuit A generates the attracting force as same as the attracting force a of the normal plate type electromagnet.  
         [0040]    Due to the function of the magnetic flux B, the attracting force of electromagnet performs the attracting force shown by curve e in FIG. 6 so as to become larger than the attracting force of a normal plate type without side walls  22  and  23 , in the relatively large gap region. More specifically, the function of the first embodiment according to the present invention is explained as follows:  
         [0041]    First, it is considered as to a case that no side wall  22 ,  23  is provided to the actuator. When no side wall  22 ,  23  is provided, only the magnetic circuit A shown in FIG. 5 is generated under that condition that there is no leakage of magnetic flux and the dispersion of the magnetic flux is equivalent in the magnetic-circuit cross section and the saturation of magnetic field of material is neglected. When the air gap is g, the magnetomotive force NI and the magnetic field Hg in the air gap have a relationship represented by the following equation (1).  
           NI≅ 2 H   g   ·g   (1)  
         [0042]    The equation (1) shows that almost of magnetomotive force NI of electromagnet coil  7   a  generates the magnetic field at the air gap.  
         [0043]    By utilizing the equation (1), the attracting force F 1  applied to movable plate  15  is represented by the following equation (2):  
         [0044]    [0044] F   1 =2 KB   g   2   S   a =2μ 0   2   KH   g   2   S   a   
                     F   1     =                2        KB   g   2          S   a                   =                2        μ   0   2          KH   g   2          S   a                   ≅                  1   4              μ   0          (   NI   )       2            S   a       g   2                       (   2   )                               
 
         [0045]    In this equation (2), μ 0  is the permeability in vacuum space, K is a proportion constant (K=1/(2μ 0 ), Bg is a magnetic flux density at the air gap, and Sa is an inner magnetic pole area of electromagnet  7 . Similarly, an outer magnetic pole area of electromagnet  7  is Sa.  
         [0046]    On the other hand, in case that there are provided side walls  22  and  23 , the magnetic circuit B is formed as shown in FIG. 5. Therefore, when a clearance between movable plate  15  and side walls  22  and  23  is d, the magnetomotive force NI and the magnetic field Hg in air gap have a relationship shown by the following equation (1)′ 
           NI≅ 2 H   g   ·g+H   d   ·d   (1)′ 
         [0047]    In this equation (1)′, Hd is a magnetic field at a clearance.  
         [0048]    By utilizing the equation (1)′, the attracting force F 2  in case of providing side walls  22  and  23  is represented by the following equation (2)′:  
           F   2   =KB   g   2   S   a =μ 0   2   KH   g   2   S   a    
         [0049]    [0049]                     F   1     =                  KB   g   2          S   a                   =                2        μ   0   2          KH   g   2          S   a                     ≅                  1   4              μ   0          (     NI   -       H   d        d       )       2            S   a       g   2           ,                 (   2   )                                 
         [0050]    By comparing the equation (2) and the equation (2)′, it becomes clear that the attracting force in the case of providing side walls  22  and  23  gradually approaches twice the attracting force in the case of no side wall  22  and  23  as the clearance d between the movable plate  15  and side wall  22 ,  23  sufficiently decreases.  
         [0051]    The initializing operation for attracting movable plate  15  from the neutral position S requires the large attracting force under the condition that the air gap is large. Therefore, by providing side walls  22  and  23  in contact with electromagnet  7 ,  8 , the initializing operation can be executed by the electric current I 2  smaller than the electric current I 1  required when the actuator having no side wall starts the initializing operation. Accordingly, this arrangement is capable of decreasing the energy consumption of electromagnets  7  and  8 , of decreasing the size of electromagnets  7  and  8  by decreasing the diameter of wire employed in electromagnetic coil, and of employing small and inexpensive drive circuits by decreasing the current capacity of electromagnet drive circuit or electric wires.  
         [0052]    Referring to FIGS. 7A to  8 , there is shown a second embodiment of the engine valve operating system according to the present invention.  
         [0053]    As shown FIGS. 7A and 7B, the engine valve operating system of the second embodiment is different from the first embodiment in that end blocks  9  and  10  for fixing electromagnet  7 , end blocks  11  and  12  for electromagnet  8 , and distance blocks  13  and  14  for forming a space between electromagnets  7  and  8  are made of soft magnetic material such as iron, instead of employing side walls  22  and  23 . That is, the second embodiment does not employ side walls  22  and  23 . The other construction of the engine valve operating system of the second embodiment is the same as that of the first embodiment. The shapes of movable plate  15 , electromagnets  7  and  8  and distance blocks  13  and  14  are basically the same as those shown in FIGS. 2 and 3.  
         [0054]    In this second embodiment, when movable plate  15  sufficiently approaches electromagnet  7 ,  8 , the attracting force applied to movable plate  15  becomes the same as that formed by the magnetic circuit A in the first embodiment.  
         [0055]    On the other hand, when movable plate  15  is relatively apart from electromagnet  7 ,  8 , a magnetic circuit is generated as shown by arrows C in FIG. 8B. The magnetic circuit shown by the arrow C circulates in the order of the inner magnetic pole of electromagnet  7 , the air gap, a lower surface of movable plate  15 , a side surface of the movable plate  15 , distance block  13  ( 14 ), end block  9  ( 10 ,  11 ,  12 ) and the outer side of electromagnet  7 . The magnetic circuit C is formed around a center axis of movable plate  15  so as to direct from electromagnet  7  to movable plate  15  through inside and direct from movable plate  15  to electromagnet  7  through outside, as shown in FIG. 8B.  
         [0056]    This arrangement of the second embodiment similarly ensures the advantages gained by the first embodiment. Since the second embodiment is arranged by employing conventional structural parts so as to form the magnetic circuit without providing side walls  22  and  23 , it becomes possible to ensure the above mentioned advantages without newly employing parts and increasing the size of the system.  
         [0057]    With reference to FIG. 9, a third embodiment of the engine valve operating system according to the present invention will be discussed hereinafter.  
         [0058]    The third embodiment is arranged such that end blocks  9 ,  10 ,  11  and  12 , and distance blocks  13  and  14  are made of soft magnetic material, which is basically the same as the second embodiment. Further, the third embodiment is particularly arranged such that a projecting portion  13   a ,  14   a  is formed on a surface of distance block  13 ,  14  faced to movable plate  15  as shown in FIG. 9.  
         [0059]    By providing projecting portions  13   a  and  14   a  at surfaces of distance blocks  13  and  14  directed to movable plate  15 , the magnetic flux of the magnetic circuit C is concentrated to projecting portions  13   a  and  14   a . This arrangement improves the attracting force of electromagnet  7 ,  8  under the large air-gap condition and can decrease the electric energy consumption.  
         [0060]    With reference to FIG. 10, a fourth embodiment of the engine valve operating system according to the present invention will be discussed hereinafter.  
         [0061]    The fourth embodiment is basically the same as the third embodiment shown in FIG. 9. The fourth embodiment is particularly arranged such that projecting portions  13   a  and  14  are located at a center of a vertical dimension C of distance block  13 ,  14  as shown in FIG. 10. This arrangement enables the attracting forces of respective electromagnets  7  and  8  to be equalized with respect to movable plate  15  when the magnetomotive force is applied thereto. Accordingly, even if the initializing operation is executed to move valve  2  into closed direction or into open direction, the initializing operation is smoothly executed regardless the moved direction of valve  2 .  
         [0062]    Further, a vertical dimension (width) T of projecting portion  13   a  ( 14   a ) is determined so as to be greater than a difference between the vertical dimension (thickness) X of distance plate  13  ( 14 ) and the vertical dimension (thickness) t of movable plate  15  as represented by the following equation (3).  
           T&gt;X−t   (3)  
         [0063]    By this arrangement, movable plate  15  is always overlapped with projecting portion  13   a ,  14   a  partially. Accordingly, even if movable plate  15  slightly rotates around shaft  16  during when movable plate  15  is moved to operate valve  2 , movable plate  15  is never scratched with projecting portions  13   a  and  14   a . Movable plate  15  smoothly reciprocates in the space between electromagnets  7  and  8 .  
         [0064]    With reference to FIG. 11, a fifth embodiment of the engine valve operating system according to the present invention will be discussed hereinafter.  
         [0065]    The fifth embodiment is arranged such that end blocks  9 ,  10 ,  11  and  12 , and distance blocks  13  and  14  are partially made of soft magnetic material. More specifically, as shown in FIG. 11, only the parts  9   c  and  13   c  of end block  9  and distance block  13  are made of soft magnetic material such as iron. The width of the parts  9   c  and  13   c  corresponds to the width L of inner magnetic pole of electromagnet  7 . The other parts  9   b  and  13   b  of end block  9  and distance block  13  are made of non-magnetic material.  
         [0066]    In a conventional system, distance block  13  and end block  9  have not been designed so as to circulate the magnetic flux. Rather, they have been generally made of non-magnetic material such as aluminum alloy, nonmagnetic stainless steel so as not to relate the magnetic circuit. Particularly, in order to decrease the mass weight at the top of engine head, they have generally been made of aluminum alloy.  
         [0067]    In order to suppress the weight of engine head including the valve operating system, end blocks  9 ,  10 ,  11  and  12  and distance blocks  12  and  14  are partially made of soft magnetic material. By partially employing soft magnetic material at the part having the width L as same as the width of inner magnetic pole of electromagnet  7 ,  8 , and by employing non-magnetic material such as aluminum alloy at the other part, the increase of the head weight is suppressed. In these embodiments according to the present invention, the soft magnetic material applicable to the system according to the present invention includes iron (soft iron), Permalloy, iron-nickel alloy and silicon steel.  
         [0068]    The entire contents of Japanese Patent Application No. 2000-116966 filed on Apr. 18, 2000 in Japan are incorporated herein by reference.  
         [0069]    Although the invention has been described above by reference to certain embodiments of the invention, the invention is not limited to the embodiments described above. Modifications and variations of the embodiment described above will occur to those skilled in the art, in light of the above teaching. The scope of the invention is defined with reference to the following claims.