Patent Publication Number: US-6334413-B1

Title: Electromagnetic actuating system

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an electromagnetic actuating system, and particularly to an electromagnetic actuating system which actuates a valve member by cooperation of an electromagnetic force generated by an electromagnet and a resilient force generated by a spring. 
     2. Description of the Related Art 
     Conventionally, a solenoid valve is known as disclosed in Japanese Laid-Open Patent Application No. 7-335437. The solenoid valve has a valve member which is movably guided in an axial direction. An armature is connected to the valve member, and a pair of electromagnets are provided on respective sides of the armature. The armature is pressed toward a neutral position between the electromagnets by a pair of springs. When an exciting current is supplied to one of the electromagnets, an electromagnetic force is exerted on the armature in a direction toward that electromagnet. Thus, according to the above-mentioned solenoid valve, it is possible to actuate the valve member to be closed and opened by alternately supplying exciting currents to the electromagnets. In such a solenoid valve, it is desired to actuate the valve member with a high response while reducing power consumption of the solenoid valve. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an electromagnetic actuating system which can actuate a valve member with a high response while reducing power consumption of the system. 
     The above-mentioned object of the present invention can be achieved by an electromagnetic actuating system, comprising: a valve member; an armature which moves with the valve member; an electromagnet which attracts the armature in a direction of movement of the valve member by being supplied with a current; a spring which presses the armature away from the electromagnet; a permanent magnet which can exert a magnetic attracting force between the armature and the electromagnet; and a current controller which supplies a release current to the electromagnet so that magnetic flux is generated in a direction opposite to a direction of magnetic flux generated by the permanent magnet when the armature is released from the electromagnet. When the valve member functions as an intake valve or an exhaust valve of an internal combustion engine, the current controller may control an amount of the release current in accordance with an operating state of the internal combustion engine. 
     In the invention, the permanent magnet can exert a magnetic attracting force between the armature and the electromagnet. Thus, a current which is required to be supplied to the electromagnet to attract the armature can be reduced. On the other hand, the magnetic attracting force generated by the permanent magnet acts on the armature against movement thereof when the armature is released from the electromagnet. The current controller supplies the release current to the electromagnet so that magnetic flux is generated in a direction opposite to a direction of magnetic flux generated by the permanent magnet when the armature is released from the electromagnet. Thus, the magnetic attracting force against the movement of the armature can be reduced. Consequently, it is possible to improve a response of movement of the valve member. That is, it is possible to shorten a time which is required for the valve member to move from one of a fully closed position and a fully opened position to the other (hereinafter referred to as a valve transition time). 
     In the invention, the valve transition time becomes smaller for a larger amount of the release current since the magnetic attracting force generated by the permanent magnet is reduced to a greater extent. On the other hand, as the amount of the release current becomes larger, the power consumption becomes greater. Thus, the amount of the release current which achieves an optimum valve transition time is not identical to the amount of the release current which minimizes the power consumption of the system. In the invention, the current controller controls the amount of the release current in accordance with the operating state of the internal combustion engine. Thus, according to the invention, it is possible to achieve a valve transition time which is required in accordance with the operating state of the internal combustion engine while reducing the power consumption of the electromagnetic actuating system. When the valve member functions as the exhaust valve of the internal combustion engine, the electromagnet may attract the armature in a valve opening direction. 
     In this invention, the exhaust valve is opened in a situation where a relatively high combustion pressure remains in a combustion chamber of the internal combustion engine. Thus, a large electromagnetic force must be exerted on the armature in a valve opening direction so as to actuate the exhaust valve against the high pressure in the combustion chamber. According to the invention, since the permanent magnet can exert a magnetic attracting force between the armature and the electromagnet which attracts the armature in the valve opening direction, it is possible to reduce power consumption of the system when the valve member is actuated to be opened. 
     When the valve member functions as the intake valve of the internal combustion engine, the electromagnet may attract the armature in a valve closing direction. In this invention, a time for which the intake valve is held in a fully closed position is relatively long. Thus, electric power required to hold the intake valve in the fully closed position occupies a relatively large part of the total power consumption of the electromagnetic actuating system. According to the invention, since the permanent magnet can exert a magnetic attracting force between the armature and the electromagnet which attracts the armature in the valve closing direction, it is possible to reduce power consumption of the system when the valve member is held in the fully closed position. 
     Other objects and further features of the present invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagram showing an electromagnetic actuating system of a first embodiment of the present invention; 
     FIG. 2A is a time chart showing a displacement of a valve member when the valve member moves from a fully closed position to a fully opened position; 
     FIG. 2B is a time chart showing a release current supplied to an upper coil; 
     FIG. 2C is a time chart showing a magnetic force exerted by an upper magnet on an armature; 
     FIG. 2D is a time chart showing an electromagnetic force exerted on the armature by the release current supplied to the upper coil; 
     FIG. 3 is a diagram showing a valve transition time and power consumption of the system against an amount of the release current; 
     FIG. 4 is a diagram showing an electromagnetic actuating system of a second embodiment of the present invention; 
     FIG. 5A is a time chart showing a displacement of the valve member when the valve member moves from the fully closed position to the fully opened position; 
     FIG. 5B is a time chart showing the release current and an attracting current supplied to the upper coil and a lower coil, respectively; 
     FIG. 6 is a diagram showing power consumption of the electromagnetic actuating system of the present embodiment and a comparison structure with a distribution to the upper coil and the lower coil; and 
     FIG. 7 is a diagram showing an electromagnetic actuating system of a third embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 is a diagram showing an electromagnetic actuating system  100  according to a first embodiment of the present invention. As shown in FIG. 1, the electromagnetic actuating system  100  has a valve member  12 . In the present embodiment, the valve member  12  functions as an intake valve or an exhaust valve of an internal combustion engine (hereinafter simply referred to as an engine). The valve member  12  is disposed in a cylinder head  16  so that the valve member  12  is exposed in a combustion chamber  14  of the engine. The cylinder head  16  is provided with a valve seat  18  which is associated with the valve member  12 . 
     The valve member  12  has a valve shaft  20  which extends upwardly in FIG.  1 . The valve shaft  20  is guided by a valve guide  22  so that the valve shaft  20  can move in an axial direction. The valve guide  22  is supported in the cylinder head  16 . A lower retainer  26  is fixed to an upper end part of the valve shaft  20 . A lower spring  28  is disposed between the lower retainer  26  and a spring supporting surface  16   a  formed in the cylinder head  16 . The lower spring  28  generates a resilient force which presses the valve member  12  via the lower retainer  26  in an upward direction, that is, in a valve closing direction. 
     An armature shaft  30  is disposed coaxially with the valve shaft  20 . The armature shaft  30  is made of a non-magnetic material. A lower end face of the armature shaft  30  is in contact with an upper end face of the valve shaft  20 . An upper retainer  32  is fixed to an upper end part of the armature shaft  30 . A lower end of an upper spring  34  abuts on a top surface of the upper retainer  32 . An upper end of the upper spring  34  abuts on an upper cap  36  which is fixed to the cylinder head  16 . The upper spring  34  pushes the armature shaft  30  via the upper retainer  32  in a downward direction. Thus, the upper spring  34  pushes the valve member  12  in a downward direction, that is, in a valve opening direction. 
     An armature  38  is fixed to an outer circumferential surface of the armature shaft  30  at a substantially center position in an axial direction thereof. The armature  38  is an annular member which is made of a soft magnetic material. 
     An upper core  40  is disposed above the armature  38 , and a lower core  42  is disposed below the armature  38 . Each of the upper core  40  and the lower core  42  is a substantially cylindrical member made of a magnetic material. The upper core  40  and the lower core  42  are provided with through holes  40   a  and  42   a , respectively, which go though the center parts thereof. An upper bush  44  is disposed in an upper end part of the through hole  40   a , and a lower bush  46  is disposed in a lower end part of the through hole  42   a . The armature shaft  30  extends through the through holes  40   a ,  42   a , and is guided by the upper bush  44  and the lower bush  46  so that the armature shaft  30  can move in the axial direction. 
     Annular recesses  40   b  and  42   b  are formed on faces of the upper core  40  and the lower core  42 , respectively, facing the armature  38 . An upper coil  48  and a lower coil  50  are contained in the annular recesses  40   b  and  42   b , respectively. 
     The upper coil  48  and the lower coil  50  are electrically connected to an actuating circuit  52 . The actuating circuit  52  supplies predetermined instruction currents to the upper coil  48  and the lower coil  50  in accordance with a control signal supplied from an electronic control unit (hereinafter referred to as an ECU)  54 . 
     A revolution sensor  55  is connected to the ECU  54 . The revolution sensor  55  outputs a signal to the ECU  54  in accordance with a revolution speed of the engine (hereinafter referred to as an engine speed NE). The ECU  54  detects the engine speed NE based on the output signal of the revolution sensor  55 . 
     The upper core  40  is provided with an annular slit  40   c  which extends from an upper face of the upper core  40  to an upper face of the annular recess  40   b . Similarly, the lower core  42  is provided with an annular slit  42   c  which extends from a lower face of the lower core  42  to a bottom face of the annular recess  42   b . An upper magnet  56  and a lower magnet  58  are supported in the annular slits  40   c  and  42   c , respectively. Each of the upper magnet  56  and the lower magnet  58  is a permanent magnet having an annular shape. The upper magnet  56  and the lower magnet  58  are radially magnetized so that, for the upper magnet  56 , an inner side is an S pole and an outer side is an N pole, and, for the lower magnet  58 , an inner side is an N pole and an outer side is an S pole, for example. According to such directions of magnetization, magnetic flux generated by the upper magnet  56  and magnetic flux generated by the lower magnet  58  go through the armature  38  in opposite directions to each other so that concentration of the flux is relaxed in the armature  38 . Thus, a loss of electric power due to eddy currents can be reduced. 
     Next, a description will be given of an operation of the electromagnetic actuating system  100 . 
     When the armature  38  is in contact with the upper core  40 , the magnetic flux generated by the upper magnet  56  goes through the upper core  40  and the armature  38 . In such a situation, a magnetic attracting force is exerted between the armature  38  and the upper core  40 . The upper magnet  56  is so constructed that the above-mentioned magnetic attracting force is strong enough to maintain the armature  38  in contact with the upper core  40  against a resilient force of the upper spring  34 . Thus, a state in which the armature  38  is in contact with the upper core  40  can be maintained without energizing the upper coil  48 . In this state, the valve member  12  is seated on the valve seat  18 . Hereinafter, a position of the armature  38  or the valve member  12  in a state where the armature  38  is in contact with the upper core  40  is referred to as a fully closed position of the armature  38  or the valve member  12 . 
     When the upper coil  48  is supplied with an instruction current which generates magnetic flux in a direction opposite to a direction of the magnetic flux generated by the upper magnet  56  in a state where the armature  38  is held in the fully closed position, the magnetic attracting force exerted between the armature  38  and the upper core  40  becomes smaller than the resilient force of the upper spring  34 . Thus, the armature  38  starts moving in a downward direction in FIG. 1 by being pressed by the upper spring  34 . 
     When the armature  38  has reached a predetermined position, the lower coil  50  is supplied with an instruction current which generates magnetic flux in the same direction as magnetic flux generated by the lower magnet  58 . In this case, an attracting force which attracts the armature  38  toward the lower core  42 , that is, an attracting force which actuates the valve member  12  in a downward direction in FIG. 1, is generated. 
     When this attracting force is exerted on the armature  38 , the armature  38  downwardly moves with the valve member  12  against a resilient force of the lower spring  28 . In this case, since the magnet flux generated by the lower coil  50  and the magnet flux generated by the lower magnet  58  have the same direction as mentioned above, the attracting force which attracts the armature  38  toward the lower core  42  is increased by an extent corresponding to a magnitude of the magnetic flux generated by the lower magnet  58  when the armature  38  comes close to the lower core  42 . The valve member  12  continues to move until the armature  38  comes into contact with the lower core  42 . Hereinafter, a position of the armature  38  or the valve member  12  in a state where the armature  38  is in contact with the lower core  42  is referred to as a fully opened position of the armature  38  or the valve member  12 . 
     When the armature  38  has reached the fully opened position, the lower coil  50  is de-energized. In this case, the attracting force generated by the lower coil  50  vanishes and only the magnetic attracting force generated by the lower magnet  58  is exerted between the armature  38  and the lower core  42 . The lower magnet  58  is so constructed that this magnetic attracting force is strong enough to maintain the armature  38  in contact with the lower core  42  against the resilient force of the lower spring  28 . Thus, the valve member  12  and the armature  38  are maintained in the fully opened position after the lower coil  50  has been de-energized. 
     When the lower coil  50  is supplied with an instruction current which generates magnetic flux in a direction opposite to a direction of the magnetic flux generated by the lower magnet  56  in a state where the armature  38  is held in the fully opened position, the attracting force exerted between the armature  38  and the lower core  42  becomes smaller than the resilient force of the lower spring  28 . Thus, the armature  38  starts moving in an upward direction in FIG. 1 by being pressed by the lower spring  28 . 
     When the armature  38  has reached a predetermined position, the upper coil  48  is supplied with an instruction current which generates magnetic flux in the same direction as the magnetic flux generated by the upper magnet  56 . In this case, an attracting force which attracts the armature  38  toward the upper core  40 , that is, an attracting force which actuates the valve member  12  in an upward direction in FIG. 1, is generated. 
     When the above attracting force is exerted on the armature  38 , the armature  38  upwardly moves with the valve member  12  against the resilient force of the upper spring  34 . In this case, since the magnet flux generated by the upper coil  48  and the magnet flux generated by the upper magnet  56  have the same direction as mentioned above, the attracting force which attracts the armature  38  toward the upper core  40  is increased by an extent corresponding to a magnitude of the magnetic flux generated by the upper magnet  56  when the armature  38  comes close to the upper core  40 . The valve member  12  continues to move until the armature  38  comes into contact with the upper core  40 , that is, until the valve member  12  and the armature  38  reach the fully closed position. The valve member  12  and the armature  38  can be maintained in the fully closed position after the upper coil  48  is de-energized, as mentioned above. 
     Hereinafter, the instruction current which is supplied to the upper coil  48  or the lower coil  50  for releasing the armature  38  from the fully closed position or the fully opened position (that is, the instruction current which generates the magnetic flux in a direction which is opposite to the direction of the magnetic flux generated by the upper magnet  56  or the lower magnet  58 ) is referred to as a release current. Additionally, the current which is supplied to the upper coil  48  or the lower coil  50  for attracting the armature  38  toward the fully closed position or the fully opened position (that is, the instruction current which generates the magnetic flux in the same direction as the magnetic flux generated by the upper magnet  56  or the lower magnet  58 ) is referred to as an attracting current. 
     As described above, according to the electromagnetic actuating system  100 , it is possible to actuate the valve member  12  between the fully closed position and the fully opened position by supplying the attracting current and the release current to the upper coil  48  and the lower coil  50  at proper timings. 
     It should be noted that the electromagnetic actuating system  100  is constructed so that a tappet clearance is formed between the armature shaft  30  and the valve shaft  20  in a state where the valve member  12  and the armature  38  are held in the fully closed position, that is, in a state where the valve member  12  is seated on the valve seat  18  and the armature  38  is in contact with the upper core  40 . According to this structure, the tappet clearance can absorb a change in a relative position of the valve shaft  20  and the armature shaft  30  due to a difference in a thermal expansion between the cylinder head  16  and the valve shaft  20  or wear of the valve seat  18  and the valve member  12 . 
     As mentioned above, the armature  38  can be maintained in the fully closed position or the fully opened position by the magnetic attracting force generated by the upper magnet  56  or the lower magnet  58  without a necessity of energizing the upper coil  48  or lower coil  50  in the present embodiment. Additionally, since the magnetic attracting force generated by the upper magnet  56  or the lower magnet  58  is exerted on the armature  38  when the armature  38  is actuated toward the fully closed position or the fully opened position, it is possible to reduce the attracting currents required to be supplied to the upper coil  48  and the lower coil  50 . Thus, according to the present embodiment, it is possible to effectively reduce power consumption of the electromagnetic actuating system  100 . 
     However, when the valve member  12  starts moving from the fully closed position or the fully opened position, the magnetic attracting force generated by the upper magnet  56  or the lower magnet  58  acts against movement of the armature  38 . Thus, if the upper magnet  56  and the lower magnet  58  are simply provided, a time which is required for the valve member  12  to move between the fully closed position and the fully opened position (hereinafter referred to as a valve transit time) could be increased, resulting in a low response of the movement of the valve member. 
     In the present embodiment, the attracting forces generated by the upper magnet  56  and the lower magnet  58  can be quickly cancelled by supplying the release currents to the upper coil  48  and the lower coil  50 , respectively, when the valve member  12  starts moving from the fully closed position and the fully opened position, respectively, as mentioned above. Thus, according to the present embodiment, it is possible to prevent an attracting force from being exerted on the armature  38  against the movement thereof so that the valve member  12  can start moving from the fully closed position and the fully opened position with a high response. 
     FIGS. 2A to  2 D are time charts showing a displacement of the valve member  12 , a release current supplied to the upper coil  48 , a magnetic attracting force exerted on the armature  38  by the upper magnet  56 , and an electromagnetic force exerted on the armature  38  by the upper coil  48  being supplied with the release current, respectively, when the valve member  12  moves from the fully closed position to the fully opened position. 
     As shown in FIG. 2A, the valve member  12  starts moving at a time t1, and, as shown in FIG. 2C, the magnetic attracting force generated by the upper magnet  56  continues to be exerted between the armature  38  and the upper core  40  after the armature  38  has been released from the upper core  40 . In the preset embodiment, the release current continues to be supplied to the upper core  48  until a time t2 at which the valve member  12  is spaced away from the upper core  40  such that the magnetic attracting force exerted by the upper magnet  56  between the armature  38  and the upper core  40  becomes sufficiently small. Thus, as can be seen from FIGS. 2C and 2D, the magnetic attracting force generated by the upper magnet  56  is substantially cancelled by the electromagnetic force generated by the upper coil  48 . As a result, the valve member  12  can move from the fully closed position toward the fully opened position with a high response. Similarly, the valve member  12  can move from the fully opened position toward the fully closed position with a high response by the release current being supplied to the lower coil  50  after the armature  38  is released from the lower core  42 . 
     As mentioned above, the attracting force can be prevented from being exerted on the armature  38  against the movement thereof when the armature  38  starts moving from the fully closed position or the fully opened position. Thus, according to the present embodiment, it is possible to actuate the valve member  12  with a high response, that is, to shorten the valve transit time. Additionally, since kinetic energy of the armature  38  can be prevented from being lost by the magnetic attracting force generated by the upper magnet  56  or the lower magnet  58 , it is unnecessary to increase the attracting current supplied to the opposite lower coil  50  or the upper coil  48  to compensate for the energy loss of the armature  38 . Thus, power consumption of the electromagnetic actuating system  100  can be reduced. 
     When an amount of the release current changes, the valve transit time of the valve member  12  and power consumption of the electromagnetic actuating system  100  also change. FIG. 3 is a diagram showing the valve transit time of the valve member  12  and the power consumption of the electromagnetic actuating system  100  against a change in the amount of the release current by a solid line and a dotted line, respectively. It should be noted that the amount of the release current is a value obtained by integrating the release current. Thus, when at least one of a time during which the release current is supplied and a magnitude of the release current is changed, the amount of the release current is changed. 
     As the amount of the release current becomes larger, the magnetic attracting current exerted on the armature  38  by the upper magnet  56  or the lower magnet  58  is cancelled to a larger extent. Thus, as shown in FIG. 3, the valve transit time decreases as the amount of the release current increases. 
     Additionally, when the amount of the release current to the upper coil  48  increases, power consumption of the system corresponding to the release current to the upper coil  48  increases. In this case, since the magnetic attracting force exerted by the upper magnet  56  on the armature  38  is cancelled to a larger extent as mentioned above, the attracting current to be supplied to the lower coil  50  decreases. Thus, power consumption of the system corresponding to the attracting current to the lower coil  50  decreases. Similarly, when the amount of the release current to the lower coil  50  increases, power consumption of the system corresponding to the release current to the lower coil  50  increases and power consumption of the system corresponding to the attracting current to the upper coil  48  decreases. In this way, the power consumption corresponding to the release current and the power consumption corresponding to the attracting current change in opposite directions when the amount of the release current changes. Thus, the total power consumption of the electromagnetic actuating system  100  exhibits a minimum value when the amount of the release current is equal to a certain value M as indicated by the dotted line in FIG.  3 . 
     As mentioned above, the valve transit time of the valve member  12  and the power consumption of the electromagnetic actuating system  100  change in accordance with a change in the amount of the release current. Thus, when the engine is operating with a high revolution speed exceeding a predetermined value, it is possible to actuate the valve member  12  with a high response by increasing the amount of the release current so that the valve transit time becomes small. On the other hand, when the engine is operating with a low revolution speed below the predetermined value, the valve member  12  need not be actuated with a high response. In this case, it is possible to reduce the power consumption of the electromagnetic actuating system  100  by setting the amount of the release current to be the above-mentioned value M. 
     As mentioned above, according to the present embodiment, it is possible to improve the response of the movement of the valve member  12  by supplying the release current to the upper coil  48  or the lower coil  50  when the valve member  12  is moved from the fully closed position or the fully opened position. In this case, the response of the valve member  12  can be further improved by continuing to supply the release current after the valve member  12  has started moving from the fully closed position or the fully opened position. 
     Additionally, the power consumption of the electromagnetic actuating system  100  can be changed in accordance with the amount of the release current. Thus, according to the present embodiment, it is possible to achieve a high response of the movement of the valve member  12  when the engine is operating with a high engine speed NE and to reduce the power consumption of the electromagnetic actuating system  100  when the engine is operating with a low engine speed NE, by changing the amount of the release current based on the engine speed NE. 
     Next, a description will be given of a second embodiment of the present invention. FIG. 4 is a diagram showing an electromagnetic actuating system  200  of the present embodiment. In FIG. 4, parts which have the same functions as the parts shown in FIG. 1 are given the same reference numerals, and descriptions thereof will be omitted. 
     As shown in FIG. 4, the electromagnetic actuating system  200  of the present embodiment is achieved by omitting the upper magnet  56  in the electromagnetic actuating system  100  of the first embodiment. In the present embodiment, the valve member  12  functions as an exhaust valve of the engine. 
     Generally, the exhaust valve is opened in a situation where a high combustion pressure remains in the combustion chamber  14 . Thus, the amount of the attracting current to be supplied to the lower coil  50  is relatively large since a sufficiently large electromagnet force must be exerted on the armature in the valve opening direction against the high pressure in the combustion chamber  14  when the valve member  12  is actuated to be opened. For this reason, in the electromagnetic actuating system  200  of the present embodiment in which the valve element  12  functions as the exhaust valve, power consumption of the lower coil  50  occupies a relatively large part of the total power consumption. 
     In the present embodiment, since only the lower magnet  58  is provided with the upper magnet  56  being omitted, a magnetic attracting force can be prevented from being exerted on the armature  38  against the movement thereof when the valve member  12  is actuated to be opened. Thus, since kinetic energy of the valve member  12  and the armature  38  is not lost by the magnetic attracting force, it is unnecessary to increase the attracting current to the lower coil  50  to compensate for the energy loss. Additionally, similar to a case of the electromagnetic actuating system  100  of the first embodiment, since the lower magnet  58  is provided to the lower core  42 , the attracting current to be supplied to the lower coil  50  can be reduced by the magnetic attracting force exerted by the lower magnet  58  between the armature  38  and the lower core  42 . Thus, according to the present embodiment, the power consumption of the electromagnetic actuating system  200  can be effectively reduced since the power consumption of the lower coil  50  which occupies a large part of the total power consumption of the system is reduced. 
     Additionally, since the upper magnet  56  is omitted, it is possible to reduce the amount of the release current to be supplied to the upper coil  48  when the valve member  12  is actuated from the fully closed position. Thus, the power consumption of the electromagnetic actuating system  200  can be further saved. 
     FIG. 5A is a time chart showing displacement of the valve member  12  which functions as the exhaust valve when the valve member  12  moves from the fully closed position to the fully opened position, and FIG. 5B is a time chart instruction currents supplied to the upper coils  48  and the lower coil  50  to achieve the displacement shown in FIG.  5 A. In FIGS. 5A and 5B, solid lines indicate a case of the electromagnetic actuating system  200  of the present embodiment, and dotted lines indicate a case of a structure in which permanent magnets are provided to both the upper core  40  and the lower core  42  (that is, a structure of the electromagnetic actuating system  100  of the first embodiment; hereinafter referred to as a comparison structure). 
     As shown in FIGS.5A and 5B, according to the electromagnetic actuating system  200 , since no magnetic attracting force is exerted by a permanent magnet between the armature  38  and the upper core  40 , the valve element  12  moves in the valve opening direction with a high response, and additionally, the release current to be supplied to the upper coil  48  is reduced, as compared to a case of the comparison structure. Additionally, since the valve member  12  moves in the valve opening direction with a high response as mentioned above, the attracting current to be supplied to the lower coil  50  so as to actuate the valve member  12  to the fully closed position is reduced as compared to the case of the comparison structure. 
     FIG. 6 is a diagram showing power consumption of the electromagnetic actuating system  200  and power consumption of the comparison structure with distributions to the upper coil  48  and the lower coil  50 . As shown in FIG. 6, the power consumption of the electromagnetic actuating system  200  is reduced as compared to the comparison structure due to a decrease in the power consumption of the lower coil  50 . Since the upper coil  48  must be energized to hold the valve member  12  in the fully closed position in the electromagnetic actuating system  200  while the valve member  12  can be held in the fully closed position without energizing the upper coil  48  in the comparison structure, the power consumption of the upper coil  48  of the electromagnetic actuating system  200  is slightly increased as compared to a case of the comparison structure. However, since the power consumption of the lower coil  50  which is sufficiently larger than the power consumption of the upper coil  48  is reduced, it is possible to effectively save the total power consumption of the electromagnetic actuating system  200 . 
     Additionally, according to the electromagnetic actuating system  200  of the present embodiment, amounts of heat generated by the upper coil  48  and the lower coil  50  are balanced since the power consumption of the lower coil  50  is reduced. Thus, it is possible to alleviate a cooling performance which is required of a cooling system of the electromagnetic actuating system  200 . In this case, since maximum electric power which can be supplied to the coils is increased for a certain cooling performance of the cooling system, it is possible to operate the electromagnetic actuating system  200  in a situation where the engine operates with a higher load and a higher revolution speed. 
     Further, as mentioned with reference to the first embodiment, when the upper magnet  56  and the lower magnet  58  are provided to the upper core  40  and the lower core  42 , respectively, the upper magnet  56  and the lower magnet  58  must be magnetized in opposite directions to each other so that the magnetic fluxes generated by these magnets go through the armature  38  in opposite directions to each other. In this case, two kinds of permanent magnets are required. On the contrary, in the present embodiment, since only the lower magnet  58  is provided, only one kind of a permanent magnet is required in the electromagnetic actuating system  200 . Thus, according to the present embodiment, it is possible to reduce a cost of the electromagnetic actuating system  200 . 
     Next, a description will be given of a third embodiment of the present invention. FIG. 7 is a diagram showing an electromagnetic actuating system  300  of the present embodiment. In FIG. 7, parts which have the same functions as the parts shown in FIG. 1 are given the same reference numerals, and descriptions thereof will be omitted. 
     As shown in FIG. 7, the electromagnetic actuating system  300  of the present embodiment is achieved by omitting the lower magnet  58  in the electromagnetic actuating system  100  of the first embodiment. In the present embodiment, the valve member  12  functions as an intake valve of the engine. 
     Generally, a time for which the intake valve is held in the fully closed position is longer than a time for which the intake valve is opened. Additionally, since the tappet clearance is provided between the valve shaft  20  and the armature shaft  30  in a state where the armature  38  and the valve member  12  are held in the fully closed position, as mentioned in the first embodiment above, the resilient force of the lower spring  28  does not contribute to a force for holding the armature  38  in the fully closed position. Thus, an attracting force to be exerted on the armature  38  to hold the valve member  12  in the fully closed position is relatively large. On the other hand, when the intake valve is opened, a high combustion pressure does not remain in the combustion chamber  14 , contrary to a case of the exhaust valve. For these reasons, in the electromagnetic actuating system  300  in which the valve member  12  functions as the intake valve, electric power which is required to hold the valve member  12  in the fully closed position occupies a relatively large part of the total power consumption. 
     According to the present embodiment, since the upper magnet  56  is provided to the upper core  40 , the amount of a current required to hold the armature  38  in the fully closed position is reduced, and, thus, the power consumption of the upper coil  48  is suppressed. In particular, when a specific volume of air of the engine is small, a control is generally performed for holding some of the intake valves in the fully closed position. According to the electromagnetic actuating system  300 , the above-mentioned control can be achieved without energizing the upper coil  48  since the upper magnet  56  is provided. On the other hand, since a permanent magnet is not provided to the lower core  42 , no magnetic attracting force is exerted by a permanent magnet between the armature  38  and the lower core  42  when the valve member  12  is actuated to be opened. Thus, power consumption of the lower coil  50  increases as compared to a case where the lower magnet  58  is provided to the lower core  42 . 
     As mentioned above, in the electromagnetic actuating system  300  of the present embodiment, the power consumption of the upper coil  48  which occupies a relatively large part of the total power consumption of the system is reduced and the power consumption of the lower coil  50  which occupies a relatively small part of the total power consumption is increased. Thus, the amount of heat generated by the upper coil  48  and the amount of heat generated by the lower coil  50  are balanced. Consequently, according to the present embodiment, similar to the case of the electromagnetic actuating system  200  of the second embodiment, it is possible to alleviate the cooling performance of the cooling system of the electromagnetic actuating system  300  and to operate the electromagnetic actuating system  300  in a situation where the engine operates with a higher load and a higher revolution speed. 
     Additionally, since a permanent magnet is not provided to the lower core  42 , no magnetic attracting force is exerted between the armature  38  and the lower core  42  when the valve member  12  is moved from the fully opened position toward the fully closed position. Thus, according to the electromagnetic actuating system  300 , it is possible to actuate the valve member  12  from the fully opened position with a high response. 
     Further, since only the upper magnet  56  is provided as a permanent magnet, only one kind of a permanent magnet is required in the electromagnetic actuating system  300 , and thus, a cost of the system can be reduced, as in the case of the second embodiment. 
     The present invention is not limited to these embodiments, but variations and modifications may be made without departing from the scope of the present invention. 
     The present application is based on Japanese priority application No. 10-347405 filed on Dec. 7, 1998, the entire contents of which are hereby incorporated for reference.