Electromagnetic valve driving apparatus

An electromagnetic apparatus for driving a valve such as an intake valve of an internal combustion engine drives the valve to its closing position without generating vibration and noises which are detrimental to durability and reliability of the valve. The valve speed is controlled either mechanically or electrically so that it is reduced to substantially zero when the valve sits on a valve seat. To mechanically control the valve speed, air or magnetic liquid is used as a cushion against the valve movement, or springs having a non-linear spring modulus such as a double-spring or a barrel spring are used to bias the valve movement. To electrically control the valve speed, an electrical signal representing the valve position is used to determine energization timing of the solenoids which drive the valve to an open or closing position. Such electrical signal is generated by an eddy current, resistance or spring load detector.

CROSS-REFERENCE TO RELATED APPLICATIONS
 This application is based upon and claims benefit of priority of Japanese
 Patent Applications No. Hei-9-194885 filed on Jul. 3, 1997, No.
 Hei-9-202502 filed on Jul. 10, 1997, and No. Hei-9-252892, filed on Sep.
 1, 1997, the contents of which are incorporated herein by reference.
 BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The present invention relates to an electromagnetic valve driving
 apparatus, and more particularly to an electromagnetic apparatus for
 directly driving a valve used in an internal combustion engine, such as an
 intake valve, in which noises and vibration occurring when the valve is
 closed or opened are reduced.
 2. Description of the Related Art
 Electromagnetic apparatus for driving a valve used in an internal
 combustion engine have been known hitherto, and an example of this kind of
 apparatus is disclosed in JP-A-7-332044. The apparatus includes an
 armature fixed to a valve stem at its upper portion, a spring biasing the
 armature in a valve closing direction, another spring biasing the armature
 in a valve opening direction and an electromagnetic actuator. The valve is
 held at a neutral position by both springs when the electromagnetic
 actuator is not energized. The electromagnetic actuator includes an
 electromagnet for closing the valve (a closing solenoid) and another
 electromagnet for opening the valve (an opening solenoid), and it opens or
 closes the valve by attracting the armature. An example of relation
 between the valve positions and the valve speed in the conventional
 apparatus is shown in FIG. 18. To bring the valve from an open position to
 a closed position, the valve opening solenoid is deenergized, and thereby
 the valve is moved toward the closed position by the spring biasing the
 valve toward the closed position. Then, the valve closing solenoid is
 energized, and thereby the armature is attached to the valve closing
 solenoid and the valve is brought to the closed position. As shown in the
 graph at the bottom, the valve speed increases just before the closed
 position because magnetic force attracting the armature increases as an
 air gap between the armature and the closing solenoid becomes smaller.
 Then, the valve sits on the valve seat abruptly at the closed position,
 thereby generating vibration and noises. The vibration of the valve is
 detrimental to durability of the valve.
 The valve speed at a vicinity of the closed position cannot be controlled
 in the conventional apparatus, and therefore, the abrupt sitting cannot be
 avoided.
 SUMMARY OF THE INVENTION
 The present invention has been made in view of the above-mentioned problem,
 and an object of the present invention is to provide an electromagnetic
 apparatus for driving the valve such as an intake or exhaust valve used in
 an internal combustion engine, in which vibration and noises generated
 when the valve sits on a valve seat are alleviated or eliminated by
 reducing the sitting speed of the valve. Thereby, durability and
 reliability of the valve are improved.
 A rod for moving the valve between its closed position and open position is
 connected to the valve which is disposed in a valve body. The rod is
 biased toward the closed position by a first spring and toward the open
 position by a second spring. An armature disc made of a magnetic material
 is fixed in the middle portion of the rod. A first solenoid for moving the
 valve to the closed position is disposed above the armature, and a second
 solenoid for moving the valve to the open position is disposed under the
 armature. Two chambers or spaces are formed above and under the armature.
 When both solenoids are not energized, the valve connected to the rod
 maintains an intermediate position between the open and closed positions
 because the biasing forces of both first and second springs are balanced.
 When the first solenoid is energized, the armature is attracted thereto
 and the valve moves to the closed position. When the second solenoid is
 energized, the armature is attracted thereto and the valve moves to the
 open position.
 If the valve hits a valve seat at a high speed when it comes to the closed
 position, harmful vibration and noises are generated. The valve speed at
 the closed position is reduced to substantially zero according to the
 present invention. The valve speed may be controlled mechanically or
 electrically.
 To control the valve speed mechanically, fluid may be filled in both
 chambers above and under the armature and is used as a cushion. Air may be
 used as a cushion fluid, and an one-way check valve is disposed on the
 armature so that the air in the upper chamber is compressed when the valve
 is moving toward the closed position while the air in the lower chamber is
 not compressed when the valve is moving toward the open position.
 Preferably, small orifices are formed on the armature so that the air
 pressure does not accumulate in the upper chamber during repeated
 operation. Alternatively, magnetic fluid comprising lubricant oil and
 small particles of a magnetic material dispersed in the oil may be used as
 a cushion fluid. In this case, small orifices are formed on the armature
 so that the magnetic fluid in both chambers can communicate with each
 other with a certain flow resistance. It is also possible to dispose
 closed spaces containing air therein which functions as an air cushion
 against the valve movement.
 The first and second springs each having a non-linear spring modulus may be
 used so that the spring force becomes higher when the valve approaches the
 closed or open position. Such non-linear modulus spring may be realized by
 using two springs, one having a longer free length and the other having a
 shorter free length disposed in the former spring. Alternatively, a single
 spring having a barrel shape may be used.
 Also, the valve speed can be electrically controlled. A valve position
 detector for generating an electrical signal representing the valve
 position is employed in the apparatus, and energization timing of the
 solenoids is controlled based on the electrical signal. More particularly,
 the first solenoid which is energized to move the valve to the closed
 position is temporarily deenergized to reduce the valve speed when the
 valve comes to a vicinity of the closed position. After the valve speed is
 sufficiently reduced, substantially to zero, the first solenoid is again
 energized to hold the valve on the valve seat. The timing of energization
 or deenergization of the solenoids is determined based on the electrical
 signal from the valve position detector.
 As the valve position detector, an eddy current detector, a resistance
 detector or a spring load detector may be used. An eddy current detector
 of a known type may be additionally assembled with the apparatus, or
 components such as the armature and the solenoids may be utilized as
 elements of the eddy current detector. In this case, the armature may
 function as a target of the eddy current detector, the first solenoid as a
 primary coil, and the second solenoid as a secondary coil. Alternatively,
 a separate coil which functions as the secondary coil of the eddy current
 detector may be disposed on the armature or the first solenoid. In case
 the resistance detector is used as the valve position detector, the
 resistance detector measures a resistance between the armature and the
 valve body which represents the valve position. Further, a spring load
 detector which measures the spring load of the second spring biasing the
 valve toward the opening position may be used.
 According to the present invention, the valve speed is sufficiently
 reduced, and the valve can sit softly on the valve seat without generating
 harmful vibration and noises. In addition, the armature does not hit the
 second solenoid hard when the valve comes to the open position.
 Other objects and features of the present invention will become more
 readily apparent from a better understanding of the preferred embodiments
 described below with reference to the following drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
 Referring to FIGS. 1A and 1B, a first embodiment of the present invention
 will be described. An electromagnetic valve driving apparatus is mounted
 on an engine head H. An intake port H1 is formed in the engine head H as
 shown in FIG. 1A. A valve 1 having a valve 11 and a valve stem 12 is
 installed in the engine head H for opening and closing the intake port H1.
 The valve 11 sits on a valve seat H2 when it closes the intake port H1 and
 leaves the valve seat H2 when it opens the intake port H1. The valve stem
 12 is slidably inserted into a sleeve H3. A spring stopper 13 is fixed to
 the top end of the valve stem 12, and a cavity is formed on the top
 portion of the head H. A lower spring 21 is disposed in the cavity and
 held between the spring stopper 13 and the bottom of the cavity, so that
 the lower spring 21 biases the intake valve 1 in the direction to lift up
 the valve 11 and to close the intake port H1.
 A cylindrical housing 3 having a closed top end and an open bottom end is
 fixedly mounted on the top surface of the engine head H. A cylindrical
 spacer 7 is fixedly disposed in the housing 3. A lower solenoid 51 and an
 upper soleniod 52 are held in the spacer 7 with a space therebetween. A
 lower push rod 41 having an armature disc 6 fixed at its top end is
 slidably held in the lower solenoid 51. The lower push rod 41 abuts with
 the top end of the valve stem 12. An upper push rod 42 having a spring
 stopper 43 fixed at its top end is slidably held in the upper solenoid 52
 and abuts with the top end of the lower push rod 41 at its bottom end.
 Both lower and upper solenoids are electrically connected to a solenoid
 driver 91. An upper spring 22 is disposed between the spring stopper 43
 and the closed top end of the housing 3, so that the upper spring 22
 biases the intake valve 1 in the direction to lower the intake valve 1 and
 to open the intake port H1. The armature 6 is located in the space between
 the lower solenoid 51 and the upper solenoid 52, forming a lower chamber
 71 and an upper chamber 72.
 The biasing force of both springs 21, 22 is set at an equal value, and the
 armature 6 takes a position which is substantially a center of the space
 between solenoids 51 and 52 when neither solenoid is energized. When the
 lower solenoid 51 is energized by the solenoid driver 91, the armature 6
 is attracted to the lower solenoid 51, and thereby the valve 1 is lowered
 and the intake port H1 is opened. When the upper solenoid 52 is energized,
 the armature 6 is attracted to the upper solenoid 52, and thereby the
 valve 1 is lifted and the intake port H1 is closed.
 Since the lower and upper solenoids 51, 52 are contained in the spacer 7,
 the space between solenoids is constant, and an amount of valve movement
 (a valve lift) is defined by the space. The lower and upper spaces 71, 72
 are filled with air. A check valve 8, which permits an one-way air flow
 from the lower chamber 71 to the upper chamber 72 and prevents air flow
 from the upper chamber 72 to the lower chamber 71, is disposed in the
 armature disc 6. A check valve portion "A" in FIG. 1A is shown in FIG. 1B
 in an enlarged scale. The check valve 8 is composed of a passage 61 having
 a tapered seat 62, a ball 81, a spring 82 and a screw 83. The ball 81 is
 pushed down against the tapered seat 62 by the spring 82 which is held in
 the passage 61 by the screw 83. Also, a small orifice 63 is formed at the
 outer periphery of the armature disc 6.
 Now, the operation of the electromagnetic valve driving apparatus described
 above will be explained. Since the armature disc 6 takes a middle position
 and the valve 11 is half open when the apparatus is not operated, the
 valve 11 has to be once brought to the closed position before the engine
 is started. This setting up operation is performed by imposing a voltage,
 which has a frequency equal to a natural frequency determined by mass and
 spring force of a moving unit, alternately on the lower and upper
 solenoids 51, 52. After a certain period of time during which this voltage
 is imposed, the valve 1 starts to vibrate, and the vibration amplitude
 becomes larger. Soon after that, the amplitude becomes a maximum value
 which is determined by the space between the lower and upper solenoids 51,
 52. When the armature disc 6 reaches the position of the upper solenoid
 52, the armature disc 6 is held attracted to the upper solenoid 52,
 bringing the intake valve 1 to the closed position. This completes the
 setting-up operation. After the setting-up operation is completed, the
 engine is started, and the closing and opening of the intake valve 1 are
 controlled according to signals sent to the solenoid driver 91 from
 various sensors.
 The operation of the check valve 8 will be described below. To bring the
 intake valve 1 to the closing position from the open position (where the
 armature disc 6 is attracted to the lower solenoid 51), the lower solenoid
 51 is first deenergized. At this moment, the compressed lower spring 21
 expands and the intake valve 1 starts to move upward. According to this
 upward movement, the valve stem 12 pushes up the lower push rod 41
 carrying the armature disc 6 on its top end. As the armature disc 6 moves
 upward, the volume of the upper chamber 72 is gradually decreased,
 compressing air in the upper chamber 72 because the check valve 8 does not
 permit the air flow from the upper chamber 72 to the lower chamber 71. In
 other words, the air in the upper chamber 72 functions as an air damper to
 decrease the valve speed when the intake valve 1 is about to sit on the
 valve seat H2. The closer the intake valve 1 comes to the valve seat H2,
 the higher the damping force becomes, because the damping force in the
 upper chamber 72 is dependent on the air pressure in the upper chamber 72.
 When the intake valve 1 is about to sit on the valve seat H2, the upper
 solenoid 52 is energized and attracts the armature disc 6 thereon to keep
 the intake valve 1 at the closed position. Because of the damping force,
 the intake valve 1 sits on the valve seat H2 softly without generating
 vibration and noises. In other words, impact force caused by collision of
 the intake valve 1 with the valve seat H2 is greatly reduced by the
 damping force of air in the upper chamber 72.
 To bring the intake valve 1 to the open position from the closed position,
 the upper solenoid 52 is first deenergized. At this moment, the compressed
 upper spring 22 expands, and the armature disc 6 and the intake valve 1
 move downward. The armature disc 6 can move downward smoothly because the
 check valve 8 opens and the air in the lower chamber 71 flows into the
 upper chamber 72 through the check valve 8.
 The small orifice 63 formed on the periphery of the armature disc 6
 functions to relieve the high pressure in the upper chamber 72 which
 otherwise becomes excessively high by repeating the pumping action of the
 armature disc 6. It is preferable to equalize the pressure both in the
 upper and lower chambers 72, 71 while the apparatus is not in operation by
 leading the air in the upper chamber 72 to the lower chamber 71 through
 the small orifice 63. The orifice 63 may be replaced by a small hole
 formed through the armature disc 6.
 Though the present invention is described as being applied to the apparatus
 for driving the intake valve, it is also applicable to an apparatus for
 driving an exhaust valve in the same manner as above.
 Referring to FIG. 2, a modified form of the first embodiment will be
 described. In this modification, magnetic liquid is filled in the lower
 and upper chambers 71, 72 in place of air in the first embodiment. The
 magnetic liquid is composed of liquid as a medium and small particles made
 of a magnetic material dispersed in the liquid. It is preferable to use
 lubricant liquid as the medium liquid to enhance lubrication of sliding
 movement of the armature disc 6. Plural small passages 64 through which
 the magnetic liquid in both chambers communicates are formed on the
 armature disc 6. Preferably, the small passages 64 are uniformly
 distributed on the armature disc 6 to make the magnetic liquid flow
 uniform. Other structures of the apparatus are all the same as those of
 the first embodiment. Therefore, the same parts and components of the
 apparatus are numbered with the same numbers, and detailed explanation is
 not repeated here.
 When the armature disc 6 moves in the space between the lower and upper
 solenoids 51, 52, the magnetic liquid filled in both cambers 71, 72
 functions as a damper in the similar manner as in the first embodiment.
 Therefore, the valve 11 sits softly on the valve seat H2 without
 generating vibration and noises when it is brought to the closing
 position. The cross-sectional area of the small passages 64 is selected in
 relation with the viscosity of the magnetic liquid, so that the magnetic
 liquid gives a proper damping force. Because the magnetic liquid is used
 in this modification in place of air in the first embodiment, magnetic
 flux density increases and magnetic force of the solenoids to attract the
 armature disc 6 becomes larger.
 Referring to FIGS. 3 and 4, a second embodiment of the present invention
 will be described. In this embodiment, the lower spring 21 is composed of
 an outer spring 21a and an inner spring 21b, and the upper spring 22 is
 composed of an outer spring 22a and an inner spring 22b. The lower push
 rod 41 and the upper push rod 42 in the first embodiment are combined into
 a single push rod 4. No air or liquid is filled in the chambers 71 and 72,
 and the check valve 8 is not disposed on the armature disc 6 in the second
 embodiment. Other structures are the same as those of the first
 embodiment.
 The inner spring 21b having a smaller spring modulus and a shorter length
 than the outer spring 21a is inserted in the outer spring 21a. Both outer
 and inner springs 21a, 21b constitute the lower spring 21. Similarly, the
 inner spring 22b having a smaller spring modulus and a shorter length than
 the outer spring 22a is inserted in the outer spring 22a. Both outer and
 inner springs 22a, 22b constitute the upper spring 22. Both outer springs
 21a and 22a have a same spring modulus, and both inner springs 21b and 22b
 have a same spring modulus.
 When both lower and upper solenoids 51, 52 are not energized, the armature
 disc 6 stays in the middle of the space between the solenoids. The
 armature disc 6 is driven downward or upward by energizing either one of
 the solenoids. The solenoids are driven by the solenoid driver 91 to which
 timing signals are fed from a timing controller 92. Signals from various
 sensors including a piston position sensor are fed to the timing
 controller 92. To bring the intake valve 1 to the closing position, the
 upper solenoid 52 is energized to attract the armature disc 6 thereto. At
 this instance, the outer spring 22a of the upper spring 22 is first
 compressed. As the armature disc 6 moves upward and comes closer to the
 upper solenoid 52, the valve speed increases because the solenoid force
 for attracting the armature disc becomes higher. When the armature disc 6
 is about to contact the upper solenoid 52 (the valve 11 is about to sit on
 the valve seat H2), the inner spring 22b of the upper spring 22 contacts
 the upper end of the housing 3 and exerts its spring force on the spring
 stopper 43. In other words, both springs 22a and 22b work together at this
 moment, and accordingly the valve speed is decreased. Therefore, the valve
 11 can sit softly on the valve seat H2 without generating vibration and
 noises. Similarly, when the armature disc 6 is attracted to the lower
 solenoid 51 and the armature disc 6 is about to contact the lower solenoid
 52, the inner spring 21b of the lower spring 21 works cooperatively with
 the outer spring 21a, thereby reducing the speed of the armature disc 6.
 Thus, the noise otherwise caused by hitting the lower solenoid 51 can be
 reduced.
 The spring-load of a double spring arrangement described above is shown in
 FIG. 4 in comparison with that of a single spring arrangement. The
 spring-load on the ordinate versus the valve position on the abscissa is
 shown in the graph of FIG. 4. The line S1 shows the spring-load when the
 lower and upper springs 21, 22 include no inner springs (a single spring
 arrangement), and the line S2 shows the spring-load when both springs
 include respective inner springs 21b, 22b as in the second embodiment. The
 spring-load S1 changes linearly in a whole range of the valve position,
 while the spring-load S2 shows a gradient change at the vicinity of the
 open and closing positions. In the double spring arrangement, when the
 valve 11 is about to come to the closed position, the spring-load of the
 inner spring 22b is added, and accordingly the spring-load gradient
 increases as shown by the line S2. Since the total spring-load at the
 vicinity of the closed position is set to be equal to the magnetic force
 of the upper solenoid 52, the valve speed becomes almost zero at the
 closed position. Therefore, the valve 11 sits softly on the valve seat H2
 without generating vibration and noises. Similarly, when the armature disc
 6 is about to contact the lower solenoid 51 in the valve opening process,
 the additional spring force of the inner spring 21b is added, and
 accordingly the armature disc 6 contacts the lower solenoid 51 softly
 without generating vibration and noises. Though two springs are arranged
 in parallel in the embodiment described above, it is also possible to
 arrange two springs in series, so that a spring having a lower spring
 modulus works first and then a spring having a higher spring modulus
 works.
 FIG. 5 shows a modified form of the second embodiment in which a
 barrel-shaped lower spring 21' and a barrel-shaped upper spring 22' are
 used in place of the double springs 21, 22. The barrel-shaped springs 21',
 22' have a non-linear spring modulus, so that the spring force gradually
 increases as the valve 11 approaches the open or closing position. This
 arrangement also performs the function to slow down the valve speed as the
 valve comes close to the closed position or the open position. The spring
 is not limited to the barrel-shaped spring but it may have variable forms,
 for example, a coil spring having an unequal coil diameter, as long as the
 spring performs the function to decrease the valve speed when the valve
 approaches the open or closed position.
 FIG. 6 shows a third embodiment of the present invention, in which a lower
 closed space 23 and an upper closed space 24 are formed in place of the
 lower spring 21 and the upper spring 22. Air is filled in both closed
 spaces 23 and 24, and is compressed when the volume of the respective
 closed space is decreased according to the movement of the intake valve 1.
 The air contained in the closed spaces 23, 24 functions as a damper to
 slow down the valve speed. Since the smaller the closed space becomes, the
 higher the pressure therein becomes, a higher damping force is given to
 the intake valve 1 at the vicinity of its closed or open position. Thus,
 the valve 11 can sit on the valve seat H2 smoothly and softly.
 Referring to FIGS. 7 to 9, a fourth embodiment of the present invention
 will be described. In this embodiment, an upper housing 9 containing
 therein a valve position detecting sensor 90 is added on the top of the
 housing 3 having a lower portion 31 and an upper portion 32. The valve
 position is detected by the sensor 90, and electrical signals from the
 sensor 90 are fed to the timing controller 92 which in turn controls the
 solenoid driver 91. The valve speed is controlled electrically depending
 on the signals of the valve position detecting sensor 90 in this
 embodiment, as opposed to the valve speed control performed mechanically
 by springs or dampers in the foregoing embodiments. Other structures are
 similar to those of the foregoing embodiments (the same components are
 numbered with the same numbers).
 An additional push rod 42' is sticking out from the top end of the housing
 3, and a metallic disc 44 is fixed to the top end of the push rod 42'. The
 valve position detecting sensor 90 is disposed on the top end of the upper
 housing 9 and faces the metallic disc 44 with a certain air gap. The
 sensor 90 detects eddy current generated in the metallic disc 44 which
 acts as a target plate of the sensor 90.
 Though the sensor 90 detecting eddy current is a known type, the operation
 thereof will be briefly explained, referring to FIGS. 8A to 8C. The sensor
 90 includes a transformer having a primary winding P and a secondary
 winding S. An alternating current source is connected to the primary coil
 P, and voltage Vs of the secondary coil S is used as a signal representing
 the distance between the sensor 90 and the metallic disc 44 as a target T.
 As the target T approaches the sensor 90, eddy current is generated in the
 target T by an alternating magnetic field of the primary coil P (a primary
 field). The eddy current in the target T generates a secondary field the
 direction of which is opposite to the primary field. The secondary field
 weakens the primary field. In other words, a mutual inductance between the
 primary coil P and the secondary coil S is changed. This change is
 detected as a change of the output Vs of the secondary coil S. A
 cross-sectional view of the sensor 90 and the target T is shown in FIG.
 8B. FIG. 8C shows another form of the sensor 90 that detects the distance
 of the target T from the sensor 90 more precisely, in which a pair of
 transformers having respective mutual inductances Mr, M are connected in a
 bridge form. A pair of diodes, resistors R1, R2 and capacitors are
 connected to the secondary coils as shown in FIG. 8C. Voltage e0 is used
 as a signal representing the valve position.
 The output signal from the valve position detecting sensor 90 is fed to the
 timing controller 92 together with signals from other sensors including a
 piston position detecting sensor (not shown in the drawings). The timing
 controller 92 calculates timing for energizing the solenoids 51, 52 based
 on those signals fed thereto and sends the timing signal to the solenoid
 driver 91. The valve speed is controlled by properly setting the timing to
 energize the solenoids 51, 52 in this embodiment. Details of such timing
 will be explained with reference to FIG. 9.
 Graphs in FIG. 9 show energization timing of the lower solenoids 51 and the
 upper solenoid 52, the valve position, and the valve speed, respectively,
 when the intake valve 1 is driven from the open position to the closed
 position. At the open position, the lower solenoid 51 is energized and the
 armature disc 6 is attracted to the lower solenoid 51. To drive the intake
 valve 1 to the closing position, the lower solenoid 51 is deenergized at a
 point (a) in FIG. 9. From this point, the intake valve 1 is pushed up by
 the compressed spring force of the lower spring 21, and the valve speed
 gradually increases. When the intake valve 1 passes the middle point, the
 valve speed starts to decrease because of frictional force given to
 sliding parts such as the stem 12 and the push rods 41, 42. At this point
 (b), the upper solenoid 52 is energized to exert force to attract the
 armature disc 6 thereto. If the upper solenoid 52 is continuously
 energized up to the point where the armature disc 6 contacts the upper
 solenoid 52, the valve speed will become high as shown in FIG. 18 (prior
 art), which generates undesirable vibration when the valve 1 sits on the
 valve seat H2 at the closed position. To avoid the valve speed increase at
 the vicinity of the closed position, the upper solenoid 52 is deenergized
 at point (c) which is detected by the valve position detecting sensor 90.
 The intake valve 1 approaches the closed position by the spring force of
 the lower spring 21, decreasing its speed gradually as shown in the bottom
 graph in FIG. 9. At position (d), just before the closed position, the
 upper solenoid 52 is energized again to attract the armature disc 6 to the
 upper solenoid 52 and to hold it at the closed position. Thus, the valve
 11 can sit softly on the valve seat H2.
 The upper solenoid 52 is energized at a lapse of time t1 after the lower
 solenoid 51 is deenergized. The time period t1 has to be chosen properly,
 not too short and not too long. If it is too short, the magnetic force of
 the upper solenoid 52 is not used effectively because a distance from the
 armature disc 6 to the upper solenoid 52 is too far to attract the
 armature disc 6 to the upper solenoid 52, and accordingly electric power
 is consumed unnecessarily. On the other hand, if the time period t1 is too
 long, too much time is required to bring the intake valve 1 to the closed
 position because the armature disc 6 starts to be attracted to the upper
 solenoid 52 after the valve speed has been slowed down. Therefore, the
 upper solenoid 52 is energized at point (b) where the valve speed reaches
 its maximum in this embodiment. Also, a time period t2 during which the
 upper solenoid 52 is energized has to be properly chosen. If the time
 period t2 is too short, the upper solenoid 52 cannot attract the armature
 disc 6 close enough. If the time period t2 is too long, the armature disc
 6 collides with the upper solenoid 52 with a high speed. Therefore, the
 time period t2 is chosen so that it ends when the armature disc 6 comes to
 a position with a proper distance from the upper solenoid 52. In this
 embodiment, the distance is chosen to be less than 5 .mu.m. A time period
 t3 during which the upper solenoid 52 is deenergized is chosen so that it
 ends when the valve speed becomes substantially zero.
 Referring to FIGS. 10, 11 and 12, a fifth embodiment of the present
 invention will be described. In this embodiment, the valve position
 detecting sensor 90 of the fourth embodiment is replaced by an eddy
 current detector 93, and other structures are same as those of the fourth
 embodiment. The eddy current detector 93 includes an eddy current
 detecting coil 61 disposed on the armature disc 6 which functions as a
 secondary coil of the eddy current detector. The upper solenoid 52
 functions as a primary coil of the eddy current detector, and the armature
 disc 6 as a target disc. The valve position is detected by the eddy
 current detector 93, and energization timing of the upper solenoid is
 controlled based on the valve position detected in the similar manner as
 in the fourth embodiment.
 The eddy current detecting coil 61 of the fifth embodiment is constituted
 by three turns of a wire having a diameter of 0.1 mm. Graphs in FIG. 11
 show energization timing of the upper solenoid 52 which is not controlled
 according to the valve position, a signal from the eddy current detector
 93 and the valve position, respectively. As seen in the middle graph in
 FIG. 11, a peak of the eddy current signal appears when the valve 11 sits
 on the valve seat H2. This means that the valve speed is high at its
 closed position. FIG. 12 shows the same as FIG. 11 when the energization
 of the upper solenoid 52 is controlled according to the valve position
 detected by the eddy current detector 93. That is, the upper solenoid 52
 is deenergized at point (e) before the closed position and energized again
 thereafter in the similar manner as in the fourth embodiment. By
 controlling the energization of the upper solenoid 52 in this manner, the
 peak of the eddy current signal at the closed position at point (f)
 disappears. This means that the valve speed at the closed position is
 sufficiently low. In the actual operation, the timing of deenergizing the
 upper solenoid 52 is determined according to the eddy current signal
 representing the valve position so that the peak of the eddy current
 signal at the closed position disappears. Thus, the valve 11 sits softly
 on the valve seat H2 without generating harmful vibration and noises.
 Since the valve position detector 90 used in the fourth embodiment is
 eliminated and replaced by the eddy current detecting coil 61 disposed on
 the armature disc 6, the whole apparatus can be made more compact in size.
 FIG. 13 shows a first modification of the fifth embodiment, in which the
 eddy current detecting coil 61 is eliminated, instead, the lower solenoid
 51, which is not energized when the the valve is about to close, is
 utilized as a secondary coil for detecting eddy current representing the
 valve position. The enegization control of the upper solenoid 52 is
 performed in the same manner as in the fifth embodiment by the eddy
 current detector 93. In addition, the eddy current detector 93 is also
 connected to the upper solenoid 52 to detect the valve position at the
 vicinity of the open position.
 FIG. 14 shows a second modification of the fifth embodiment, in which a
 band pass filter 94 is additionally connected to the eddy current detector
 93. The band pass filter 94 eliminates noises included in the eddy current
 signal representing the valve position, and then the eddy current signal
 is fed to the timing controller 92. The eddy current peak appearing near
 the closed position is detected more precisely by filtering out the
 noises.
 FIG. 15 shows a third modification of the fifth embodiment, in which the
 eddy current detecting coil 61 disposed on the armature disc 6 is replaced
 by an eddy current detecting coil 53. In this modification, the upper
 solenoid 52 functions as a primary coil and the eddy current detecting
 coil 53 as a secondary coil in detecting the eddy current generated in the
 armature disc 6 as a target disc. Since the upper solenoid 52 is energized
 to close the valve, it is able to function as the primary coil, and the
 valve position can be detected by the eddy current detecting coil 53. The
 modification 3 operates in the same manner as in the fifth embodiment.
 FIG. 16 shows a sixth embodiment of the present invention. In this
 embodiment, a resistance detector 95 is used to detect the valve position
 in place of the eddy current detector 93 used in the fifth embodiment. The
 resistance detector 95 detects an electrical resistance R between the
 armature disc 6 and the engine head H which is a sum of the resistances of
 the armature disc 6, the lower push rod 41, lower solenoid 51 and the
 engine head H. An insulating sheet 45 is inserted between the armature
 disc 6 and the upper push rod 42, and another insulating sheet 45 is
 inserted between the lower push rod 41 and the valve stem 12. As the
 armature disc 6 approaches the upper solenoid 52 for closing the valve,
 the resistance R increases because the rod length between the armature
 disc 6 and the lower solenoid 51 increases, and it becomes the maximum at
 the closed position. Therefore, the valve position can be represented by
 the resistance R. The resistance detector 95 feeds the resistance signal
 to the timing controller 92, and the enegization timing of the solenoids
 is controlled in the same manner as in the foregoing embodiments.
 FIG. 17 shows a seventh embodiment, in which a spring load measuring device
 96 is disposed on the top of the upper spring 22. Since the upper spring
 22 is compressed or expanded according to the opening or closing operation
 of the valve, the valve position can be detected by measuring spring load
 of the upper spring 22. The spring load signal is fed to a spring load
 detector 97 which in turn feeds its output to the timing controller 92.
 The energization timing of the solenoids is controlled in the same manner
 as in the foregoing embodiments.
 Though the electromagnetic valve driving apparatus according to the present
 invention is described as an apparatus for controlling an intake valve of
 an internal combustion engine in all of the foregoing embodiments, it can
 be used as an apparatus for controlling an exhaust valve or other valves
 as well.
 While the present invention has been shown and described with reference to
 the foregoing preferred embodiments, it will be apparent to those skilled
 in the art that changes in form and detail may be made therein without
 departing from the scope of the invention as defined in the appended
 claims.