Abstract:
The present invention offers a valve driving apparatus provided in an internal combustion engine. The valve driving apparatus drives an exhaust valve by using electromagnetic force. The exhaust valve is movable between an open position and a closed position. The valve driving apparatus includes an armature coupled with the exhaust valve, an electromagnetic coil for generating an electromagnetic force exerted on the exhaust valve, and a control means for controlling the electromagnetic force applied to the armature in the direction of the closed position of the exhaust valve when the exhaust valve is moving to the open position, in the fuel injection cut control, that is, combustion is suspended in the internal combustion engine. The present invention also offers a method for driving the exhaust valve, which comprises the steps of driving the electric current through the electromagnetic coil, biasing the armature and controlling the electromagnetic force applied to the armature.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to a valve driving apparatus provided in an internal combustion engine. Especially, the valve driving apparatus drives an exhaust valve by using an electromagnetic force, and it is appropriate for the exhaust valve to function to be movable between an open and a closed position.  
         BACKGROUND OF THE INVENTION  
         [0002]    A valve driving apparatus which drives an exhaust valve by using electromagnetic force is already known, as disclosed in Japanese Laid-Open Patent Application No. 10-18819 or No. 10-18820. An armature is coupled with an electromagnetic valve (or called exhaust valve) which is provided in this valve driving apparatus. On the upper side of the armature, the first electromagnet and an upper spring are deposited, and on the lower side of the armature, the second electromagnet and a lower spring are deposited. The armature is held at the neutral position in the middle between the first and second electromagnets by the forces of the upper and lower springs. The electromagnetic valve is full closed when the armature touches the first electromagnet, and the electromagnetic valve is full open when the armature touches the second electromagnet. In the above-mentioned valve driving apparatus, the exhaust valve is held at the full closed position by the fact that a predetermined exciting current is supplied to the first electromagnet and the armature is attracted by the first electromagnet. When the supply of the exciting current to the first electromagnet is cut, the armature is pushed by the upper spring and the exhaust valve begins to move in the opening direction. If a predetermined exciting current is supplied to the second electromagnet when the exhaust valve is positioned at a predetermined position, a damping of displacement amplitude by friction of the exhaust valve or remaining pressure of combustion is supplemented and the exhaust valve reaches the full open position by the fact that the electromagnetic force is supplied to the armature in the opening direction.  
           [0003]    If the exhaust valve is moving at a high speed when the exhaust valve arrives at the full open position, that is, the armature touches the second electromagnet, such problems as increasing of activating noise of the exhaust valve or bouncing back of the exhaust valve occur. Therefore, in the aforementioned valve driving apparatus, the speed of the exhaust valve is restrained when the exhaust valve approaches to the full open position, by reducing the exciting current to the second electromagnet when the exhaust valve reaches near the full open position.  
           [0004]    Incidentally, in the internal combustion engine installed on a vehicle, when an accelerator pedal is disengaged during the high speed driving, for example, a fuel injection cut control for stopping a fuel injection to a combustion chamber of the engine is executed. Because combustion does not occur in the process of the fuel injection cut control, the pressure in the combustion chamber of the engine is negative (or called vacuum) when the exhaust valve is at the opening timing, that is, a piston of the engine is near bottom dead center. This negative pressure forces the exhaust valve in the opening direction. Consequently, if the same value of the exciting current is supplied to the second electromagnet in the execution of the fuel injection cut control, the armature touches the second electromagnet at the higher speed. Consumed electric energy increases, because it is necessary to supply the exciting current again to pull the armature back to the second electromagnet in order to prevent the armature from bouncing back. Furthermore, a large noise occurs by the high speed collision between the armature and the second electromagnet.  
         SUMMARY OF THE INVENTION  
         [0005]    It is thus one object of the present invention to solve the aforementioned problems. The present invention provides a valve driving apparatus for driving an exhaust valve, using electromagnetic force, provided in an internal combustion engine. The exhaust valve is movable between an open position and a closed position. The valve driving apparatus has an armature coupled with the exhaust valve, an electromagnetic coil for generating an electromagnetic force exerted on the armature, a valve spring for generating a force exerted on the exhaust valve, and a control means. The control means controls the electromagnetic force applied to the armature in the direction of the closed position of the exhaust valve when the exhaust valve is moving to open, in the case that combustion is suspended because of a fuel injection cut control in the internal combustion engine.  
           [0006]    This control means supplies the electromagnetic force to the armature coupled with the exhaust valve in the direction of the closed position, when the exhaust valve is moving to the open position, in the case that combustion does not occur in the engine. When combustion is suspended in the engine, negative pressure is generated in the combustion chamber of the engine at the timing near the bottom dead center which is the opening timing of the exhaust valve. The force applied to the exhaust valve by the negative pressure is canceled by the electromagnetic force in the direction of the closed position applied to the armature by the control means. Consequently, the armature is prevented from colliding with the electromagnet at high speed. Therefore, the armature does not bounce back from the electromagnet, and the activating noise of the exhaust valve can be restrained. When combustion is suspended in the fuel injection cut control, an engine brake occurs on the basis of the negative pressure of the combustion chamber. Then, the engine brake is obtained securely by the present invention.  
           [0007]    The above-mentioned object is achieved by another embodiment of the present invention. That embodiment is also a valve driving apparatus for driving an exhaust valve, using electromagnetic force, provided in an internal combustion engine. The exhaust valve is movable between an open position and a closed position, in the same way as depicted in the first embodiment. The valve driving apparatus has an armature coupled with the exhaust valve, an electromagnetic coil for generating an electromagnetic force exerted on the armature, a valve spring for generating a force exerted on the exhaust valve, and a valve timing changing means. The valve timing changing means changes an opening timing of the exhaust valve, in the case that combustion is suspended in the internal combustion engine.  
           [0008]    Generally speaking, the combustion chamber pressure is negative near the bottom dead center which is the opening timing of the exhaust valve, when combustion is suspended in the engine. However, since the valve timing changing means in this embodiment changes an opening timing (advanced or delayed) of the exhaust valve, when combustion is suspended in the engine, the pressure in the combustion chamber is restrained low negative (that is, near zero), or becomes positive. Consequently, the armature does not collide with the electromagnet at high speed. Therefore, it prevents the armature from bouncing back from the electromagnet, and the activating noise of the exhaust valve can be restrained. Since extra electromagnetic force to the armature is not necessary, electric power can be saved.  
           [0009]    The above-mentioned object is also achieved by another embodiment of the present invention. That embodiment is also a valve driving apparatus for driving an exhaust valve, using electromagnetic force, provided in an internal combustion engine. The exhaust valve is also movable between an open position and a closed position. The valve driving apparatus has an armature coupled with the exhaust valve, an electromagnetic coil for generating an electromagnetic force exerted on the armature, a valve spring for generating a force exerted on the exhaust valve, and a reducing control means. The reducing control means controls the electromagnetic force applied to the armature in the direction of the open position of the exhaust valve when combustion is suspended in the engine less than when combustion is underway in the engine.  
           [0010]    Since the electromagnetic reducing means controls the electromagnetic force on the armature in the direction of the open position of the exhaust valve when combustion is suspended in the engine less than when combustion is underway in the engine, the electromagnetic force in the direction of the open position of the exhaust valve is reduced. Consequently, the armature does not collide against the electromagnet at high speed. Therefore, the armature does not bounce back from the electromagnet, and the activating noise of the exhaust valve can be restrained. Since extra electromagnetic force to the armature is not necessary, electric power can be saved. Furthermore, since the combustion chamber pressure in the engine is negative, therefore the engine brake can be secured.  
           [0011]    Furthermore, the above-mentioned object is also achieved by another embodiment of the present invention. That embodiment is also a valve driving apparatus for driving an exhaust valve, using electromagnetic force, provided in an internal combustion engine. The exhaust valve is also movable between an open position and a closed position. The valve driving apparatus has an armature coupled with the exhaust valve, an electromagnetic coil for generating an electromagnetic force exerted on the armature, a valve spring for generating a force exerted on the exhaust valve, and a suspending means. The suspending means suspends a moving of the exhaust valve when combustion is suspended in the engine.  
           [0012]    Since the suspending means suspends a moving of the exhaust valve when combustion is suspended in the engine, the armature coupled with the exhaust valve does not collide against a magnet at high speed. Moreover, an exciting current to the electromagnetic coil for attracting the armature can be reduced, therefore saving of an electric power can be attained. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    The above and other objects, features, advantages and technical and industrial significance of this invention will be better understood by reading the following detailed description of a presently preferred embodiment of the invention, when considered in connection with the accompanying drawing, in which:  
         [0014]    [0014]FIG. 1 is a part of a cross-sectional view of an internal combustion engine operated by the valve driving apparatus according to the present invention;  
         [0015]    [0015]FIG. 2 is a magnified cross-sectional view of an exhaust electromagnetic actuator operated by the valve driving apparatus;  
         [0016]    [0016]FIG. 3 is a graph showing characteristics of exciting current to an upper coil and a lower coil, and showing the position of the exhaust electromagnetic valve according to the first embodiment of the present invention;  
         [0017]    [0017]FIG. 4 is a graph showing a combustion chamber pressure and the valve position versus a crank angle of the internal combustion engine;  
         [0018]    [0018]FIG. 5 is a graph showing a characteristic of exciting current to an upper coil, according to the first embodiment;  
         [0019]    [0019]FIG. 6 is a graph showing a characteristic of exciting current to an upper coil, according to a modified embodiment of the first embodiment;  
         [0020]    [0020]FIG. 7 is a graph showing a characteristic of exciting current to an upper coil, according to the other modified embodiment of the first embodiment;  
         [0021]    [0021]FIG. 8 is a graph showing a pressure of a combustion chamber, an exciting current to an upper coil and an exciting current of a lower coil, and showing a position of an electromagnetic valve according to the second embodiment of the present invention;  
         [0022]    [0022]FIG. 9 is a graph showing an exciting current to an upper coil and an exciting current to a lower coil, and showing a position of an electromagnetic valve according to the third embodiment of the present invention; and  
         [0023]    [0023]FIG. 10 is a graph showing an exciting current to an upper coil and an exciting current to a lower coil, and showing a position of an electromagnetic valve according to a modified embodiment of the third embodiment. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0024]    In the following and the accompanying drawings, the present invention will be described in more detail in terms of the embodiments. Initially, the basic structure of a control device concerning this invention is explained. This valve driving apparatus of the present invention is controlled by an ECU  10 , as shown in FIG. 1. An cylinder block  12  is provided in an internal combustion engine (hereinafter called only engine), and a cylinder  14  and a water jacket  16  are deposited in the cylinder block  12 . The engine of this embodiment is multi-cylinder internal combustion engine which includes a plurality of cylinders, however, only one cylinder  14  is illustrated in FIG. 1.  
         [0025]    A piston  18  is inside the cylinder  14 . The piston  18  can slide and move up-and-down as shown in FIG. 1. A cylinder head  20  is fixed to the cylinder block  12  on the upper side. In each cylinder head  20 , an intake port  22  and an exhaust port  24  are respectively shaped.  
         [0026]    A combustion chamber  26  is shaped by the lower surface of the cylinder head  20 , the upper surface of the piston  18 , and the side wall of the cylinder  14 . The above-mentioned intake port  22  and exhaust port  24  respectively connect to the combustion chamber  26 . A valve seat  28  is shaped at the opening edge of the intake port  22  toward the combustion chamber  26 . A valve seat  30  is also shaped at the opening edge of the exhaust port  24  toward the combustion chamber  26 . The tip of an ignition plug  32  extrudes into the combustion chamber  26 .  
         [0027]    Electromagnetic actuators  38 ,  40  included in the valve driving apparatus are deposited in the cylinder head  20 . More specifically, the electromagnetic actuator  38  functions for intake of fuel and air to the combustion chamber  26 , and the actuator  40  functions for exhaust of fuel and air from the combustion chamber  26 . As shown in FIG. 1, the intake electromagnetic actuator  38  has an intake electromagnetic valve  41  and the intake electromagnetic valve  41  has an intake valve body  42 . When the intake valve body  42  touches to and is seated on the valve seat  28 , the intake port  22  is closed to the combustion chamber  26 . When the intake valve body  42  is apart from the valve seat  28 , the intake port  22  connects to the combustion chamber  26 .  
         [0028]    Similarly, as shown in FIG. 1, the exhaust electromagnetic actuator  40  has an exhaust electromagnetic valve  43  and the exhaust electromagnetic valve  43  has an exhaust valve body  44 . When the exhaust valve body  44  touches to and is seated on the valve seat  30 , the exhaust port  24  is closed to the combustion chamber  26 . When the exhaust valve body  44  is apart from the valve seat  30 , the exhaust port  24  connects to the combustion chamber  26 .  
         [0029]    [0029]FIG. 2 shows a magnified view of the exhaust electromagnetic actuator  40 . Referring to FIG. 2, the exhaust electromagnetic actuator  40  has an exhaust electromagnetic valve  43 . A lower part of the exhaust electromagnetic valve  43  is an exhaust valve body  44 , and has a shape like a dish placed upside-down. An upper part of the exhaust electromagnetic valve  43  is a valve stem  62 , and has a shape like a long and slender bar.  
         [0030]    The engine has an intake manifold  46 , as shown in FIG. 1. The intake manifold  46  includes a plurality of pipes connecting a surge tank  48  to each intake port  22 . In each pipe a fuel injection valve  50  is provided. The fuel injection valve  50  injects fuel into the pipe on the basis of command signal from the ECU  10 .  
         [0031]    An intake pipe  52  connects upstream to the surge tank  48 . A throttle valve  54  is deposited in the intake pipe  52 . An air cleaner  56  connects upstream to the intake pipe  52 . Consequently, outside air filtered by the air cleaner  56  flows into the intake pipe  52 . An exhaust manifold  58  connects to each exhaust port  24 .  
         [0032]    A crank angle sensor  60  is provided in the engine. An output signal from the crank angle sensor  60  is supplied to the ECU  10 .The ECU  10  detects a crank angle CA and an engine revolution speed NE according to the output signal of the crank angle sensor  60 .  
         [0033]    In this embodiment of the present invention, the fuel injection from the fuel injection valve  50  is controlled to be cut in the case that an accelerator pedal is disengaged when the revolution speed NE is higher than a predetermined value. When the accelerator pedal is disengaged, that is the throttle valve  54  is closed, a high negative pressure occurs in the surge tank  48 , the intake manifold  46 , and the intake port  22  (hereinafter called the intake system as a whole) downstream from the throttle valve  54 . Incidentally, a high negative pressure means that the difference from the atmospheric pressure is high and it is low as the absolute pressure. When the fuel injection is cut under the condition where an absolute value of negative pressure is high in the intake system, the pressure in the combustion chamber  26  is negative near the bottom dead center of the crank angle CA, because combustion does not occur in the combustion chamber  26 . When the negative pressure occurs in the combustion chamber  26 , an engine brake is generated by a pumping loss of the piston  18  in response to the negative pressure. In these ways, when the fuel injection cut control is executed, a negative pressure is generated in the combustion chamber  26  near the bottom dead center, then the engine brake is generated in response to the absolute value of the negative pressure.  
         [0034]    Next, the structure and acting movement of the electromagnetic actuators  38 ,  40  is explained as follows. Since the electromagnetic actuators  38  and  40  have the same structure, only the electromagnetic actuator  40  is explained as a representative.  
         [0035]    Referring to FIG. 2, the exhaust valve body  44  connects to the exhaust valve stem  62 . The valve stem  62  is supported movable up-and-down in the direction of its axis by a valve guide  64  which is fixed to the cylinder head  20 . An armature shaft  66  is coupled to the valve stem  62  at the upper part. The armature shaft  66  is shaped as a rod and made of non magnetic materials. At the upper end of the valve stem  62 , a lower retainer  68  is fixed to the valve stem  62 . Beneath the lower retainer  68 , a lower spring  70  is deposited. The lower end of the lower spring  70  touches the cylinder head  20 . The lower spring  70  applies an upward pushing force to the armature shaft  66  by way of the lower retainer  68  and the valve stem  62 .  
         [0036]    At the end of the armature shaft  66 , an upper retainer  72  is fixed to the armature shaft  66 . Above the upper retainer  72 , an upper spring  76  is deposited. In the circumference of the upper spring  76 , a cylindrical upper cap  77  is deposited surrounding the upper spring  76 . An adjust bolt  78 , which is coupled to the upper cap  77  by a screw, touches the upper end of the upper spring  76 . The upper spring  76  applies a downward pushing force to the upper retainer  72 , and the armature shaft  66 , as shown in FIG. 2.  
         [0037]    An armature  74  is coupled to the armature shaft  66  in the middle of the armature shaft  66 . The armature  74  is ring-shaped and made of soft magnetic materials. Above the armature  74 , an upper coil  80  and an upper core  82  are provided. Furthermore, under the armature  74 , a lower coil  84  and a lower core  86  are provided. The upper coil  84  and the upper core  86  are made of magnetic materials. The armature shaft  66  is supported in the center part of the upper core  82  and the lower core  86 , being movable up-and-down. The upper coil  80  and the lower coil  84  connect to a drive circuit which is not shown. The drive circuit supplies an exciting current to the upper coil  80  and the lower coil  84  in response to the control signal from the ECU  10 .  
         [0038]    In the outer circumference of the upper core  82  and the lower core  86 , an outer cylinder  88  is provided. The outer cylinder  88  holds the upper core  82  and the lower core  86  a predetermined distance apart. The aforementioned upper cap  77  is fixed to the upper surface of the upper core  82 . The adjust bolt  78  adjusts the armature  74  so that the armature  74  is positioned in the middle between the upper core  82  and the lower core  86 .  
         [0039]    In the exhaust electromagnetic actuator  40 , the exhaust valve  43  seats on the valve seat  30 , when the armature  74  reaches and touches the upper core  82 . This condition is maintained by supplying a predetermined exciting current to the upper coil  80 . Hereinafter, the condition where the exhaust valve  43  seats on the valve seat  30 , is called ‘full closed’, and the position of the exhaust valve  43  is called ‘full closed position’.  
         [0040]    When the exciting current is cut to the upper coil  80  in the condition where the exhaust valve  43  is full closed, the electromagnetic force applied to the armature  74  vanishes. When the electromagnetic force  74  applied to the armature  74  vanishes, the armature  74  moves downward by the spring force of the upper spring  76 . If an appropriate exciting current is supplied to the lower coil  84  when the armature  74  arrives at a predetermined position, the armature  74  is attracted to the lower core  86  by the electromagnetic force of the lower coil  84 , then the exhaust valve  43  moves downward in FIG. 2.  
         [0041]    When the above-mentioned attractive force is applied to the armature  74 , energy loss by sliding resistance and/or remaining pressure of combustion is compensated by the attractive force, and the armature  74  moves downward with the armature shaft  66 , the exhaust valve stem  62 , and the exhaust valve body  44 . The exhaust valve  43  continues to move until the armature  74  touches the lower core  86 . Hereinafter, the condition where the armature  74  touches the lower core  86 , is called ‘full open’, and the position of the exhaust valve  43  is called ‘full open position’. This full open condition is maintained by supplying a predetermined exciting current to the lower coil  84 .  
         [0042]    When the exciting current applied to the lower coil  84  is cut off, in the condition where the exhaust valve  43  is kept at the full open position, the electromagnetic force applied to the armature  74  vanishes. When the electromagnetic force to the armature  74  is extinguished, the armature  74  moves upward in FIG. 2, by the spring force of the lower spring  70 . If an appropriate exciting current is supplied to the upper coil  80  when the armature  74  reaches a predetermined position, the armature  74  is in this case attracted to the upper core  82  by the electromagnetic force of the upper coil  80 . Then, the exhaust valve  43  moves upward in FIG. 2.  
         [0043]    When the above-mentioned attractive force is applied to the armature  74 , energy loss by sliding resistance and/or other is compensated by the attractive force, and the armature  74  moves upward with the exhaust valve  43 . The exhaust valve  43  moves until the armature  74  touches the upper core  82 , that is the full closed position.  
         [0044]    Concerning the exhaust electromagnetic actuator  40  as mentioned above, not only can the exhaust valve  43  be moved toward the full closed position by supplying a predetermined exciting current to the upper coil  80 , but the exhaust valve  43  can also be moved toward the full open position by supplying a predetermined exciting current to the lower coil  84 . Therefore, the exhaust valve  43  can be moved reciprocally between the full open and full closed positions, by supplying the exciting current alternately to the lower and upper coils  84 ,  80 .  
         [0045]    The intake electromagnetic actuator  38  including the intake valve  41  also behaves in the same manner as the aforementioned exhaust electromagnetic actuator  40 . Consequently, according to this embodiment of the present invention, the intake valve  41  and exhaust valve  43  can be driven toward the full open and full closed position at any predetermined timing by supplying the control signal to the drive circuit from the ECU  10  so that the exciting current to the upper coil  80  and the lower coil  84  is alternately applied at the appropriate timing in the electromagnetic actuators  38 ,  40 . (cf. The intake electromagnetic actuator  38  has the same number for the including parts as the actuator  40 , except  41 ,  42 .)  
         [0046]    A rather big activating noise, however, occurs when the armature  74  collides with the lower core  86  or the upper core  82 , in the case that the intake valve  41  and/or the exhaust valve  43  move at a high speed when the armature  74  touches the lower core  86  or the upper core  82 . Furthermore, the armature  74  bounces back from the lower core  86  or the upper core  82 , when the armature  74  collides the lower core  86  or the upper core  82  at the high speed. In this case, the extra exciting current must be supplied in order to attract the armature  74  again to the lower core  86  or the upper core  82 . Consumed energy of the electromagnetic actuators  38 ,  40 , then, increases inevitably. Consequently, it is desirable that the exciting current applied to the lower and upper coils  84 ,  80  is controlled so that the intake and exhaust valves  41 ,  43  move at a slow speed when they reach the full open and full closed positions.  
         [0047]    From the above-mentioned viewpoint, the exciting current supplied to the upper coil  80  in order to drive the valves  41 ,  43  open-closed is shown, responding to elapsed time, in the upper graph of FIG. 3. The exciting current supplied to the lower coil  84  is also shown in the middle graph in FIG. 3. Furthermore, the valve position of the intake valve  41  or exhaust valve  43  corresponding to the exciting currents of the upper and lower coils is shown in the bottom graph of FIG. 3.  
         [0048]    As shown in the top figure of FIG. 3, the exciting current applied to the upper coil  80  is kept constant at the value of I MAX  (called attracting current) during a predetermined interval A, when the valve  41  or  43  moves from the full open position to the full closed position. After the interval A, the attracting current I H  begins to decrease, when the valve  41  or  43  nearly reaches the full closed position, and becomes the value of I H  (called holding current) during a changing interval B. After the changing interval B, the holding current I H  which is lower than the attracting current I MAX  is maintained during a predetermined interval C. When the valve  41  or  43  is indicated to be open, a negative value of the exciting current I R  (called canceling current), which is opposite against the attracting current I MAX  and the holding current I H , is kept in a predetermined interval D. Incidentally, the interval D, in which the canceling current is I R  is supplied, is set so that the remaining electromagnetic field applying the armature  74  can be canceled.  
         [0049]    Similarly, as shown in the middle graph of FIG. 3, the exciting current applied to the lower coil  84  is kept constant value I MAX  (also called attracting current) during a predetermined interval A, when the valve  41  or  43  moves from the full closed position to the full open position. After the interval A, the attracting current I MAX  begins to decrease toward a holding current I H  during a changing interval B. After the changing interval B, the holding current I H  is maintained during a predetermined interval C. When the valve  41  or  43  is indicated to be closed, the canceling current I R  is kept in a predetermined interval D.  
         [0050]    The ECU  10  supplies the above-mentioned current to the upper coil  80  and the lower coil  84  at the synchronizing timing to the crank angle CA, on the basis of the output signal of the crank angle sensor  60 . Consequently, the intake valve  41  and exhaust valve  43  can be driven open or closed at the appropriate timing, synchronizing the operation of the engine.  
         [0051]    As mentioned above, when the accelerator pedal is disengaged at a high revolution speed of the engine, the fuel injection cut control is executed. The negative pressure, then, occurs in the combustion chamber  26  near the bottom dead center of the crank angle CA. The upper graph in FIG. 4 shows pressure in the combustion chamber versus the crank angle CA. The solid line shows the pressure in the case that the fuel injection cut control is not executed, that is in the normal operation, and the dotted line shows the pressure in the case that the fuel injection cut control is executed. In the lower graph in FIG. 4, the solid line shows the position of the exhaust valve  43  when it moves from the full closed position toward the full open position in the normal operation of the engine, and the dotted line shows the position of the exhaust valve  43  in the case that the same value of the exciting current as in the normal driving condition (where the fuel is injected into the combustion chamber  26 ) is applied.  
         [0052]    As shown by the solid line in the upper graph of FIG. 4, the combustion chamber pressure becomes very high by the ignition near the top dead center when the operation of the engine is normal. Even at the bottom dead center, the combustion chamber pressure is maintained positive because the positive pressure remains in the combustion chamber  26 . As shown by the dotted line in the upper graph of FIG. 4, the combustion chamber pressure only changes by expansion and compression in the combustion chamber  26 , the combustion chamber pressure decreases to the negative pressure near the bottom dead center.  
         [0053]    Referring to the lower graph in FIG. 4, the exhaust valve  43  begins to open near the bottom dead center. Corresponding to this, the combustion chamber pressure is positive Pa at the opening timing of the exhaust valve  43 , as shown by the solid line in the upper graph in FIG. 4, in the normal driving condition, therefore the attracting force is not applied to the exhaust valve  43  caused by the combustion chamber pressure. Therefore, the moving speed of the exhaust valve  43  is restrained low when it reaches the full open position, as shown in the lower graph of FIG. 4, and problems of the bouncing back or activating noise of the armature  74  can be avoided.  
         [0054]    On the other hand, during the fuel injection cut control, the combustion chamber pressure is negative Pb when the exhaust valve  43  is the opening timing, as shown by the dotted line in the upper graph of the FIG. 4. Consequently, if the exhaust valve  43  is driven to open at the same timing as the normal operation of the engine when the fuel injection cut control is executed, the force in the direction to open the exhaust valve  43  is applied by the negative pressure of the combustion chamber  26 . Therefore, the force caused by the negative pressure of the combustion chamber  26  becomes surplus, when the same value of the exciting current as in the normal driving condition is applied to the lower coil  84  in the middle graph of FIG. 3.  
         [0055]    Thus, the armature  74  moves and touches the lower core  86  at high speed, when the exhaust valve  43  reaches the full open position and the exhaust valve  43  bounces back from the full open position as shown in the lower graph of FIG. 4. In this case, it is necessary that the excess exciting current is supplied to the lower coil  84  in order to attract again the armature  74  to the lower core  86 , therefore, the consumed energy increases and the noise problem occurs because the armature  74  collides with the lower core  86  at high speed, as mentioned above. Furthermore, when the armature  74  collides with the lower core  86  at high speed, a friction wear of both parts and/or other parts might occur, because impact force is applied to parts of the exhaust electromagnetic actuator  40 .  
         [0056]    In this embodiment, however, the above-mentioned trouble can be avoided, because the electromagnetic force in the closing direction of the closed position is added to the armature  74  when the exhaust valve  43  is opening, during the fuel injection cut control.  
         [0057]    [0057]FIG. 5 shows the magnified view of the wave of the interval D in the top graph of FIG. 3, that is, canceling current I R  which is supplied to the upper coil  80  of the exhaust electromagnetic actuator  40  when the exhaust valve  43  begins to open from the full closed position in the fuel injection cut control. The canceling current I R  in the normal driving condition is shown as the chain line in FIG. 5.  
         [0058]    As shown in FIG. 5, the interval T 1  during which the canceling current I R  is supplied in the fuel injection cut control, is longer than the interval T 0  in the normal driving condition. As mentioned above, the interval D=T 0  in the normal driving condition is set so that the remaining magnetism on the armature  74  can be erased just during the interval T 0 . Since the interval D is set T 1  which is longer than T 0  in this embodiment, the canceling current I R  continues to be supplied to the upper core  82 , even after the remaining magnetism on the armature  74  is erased. The electromagnetic force is furthermore applied between the armature  74  and upper core  82  by this exciting current I R  during the time between (T 1 -T 0 ). Therefore, the opening force of the exhaust valve  43  caused by the negative pressure in the combustion chamber  26  can be canceled. Accordingly, in the fuel injection cut control the armature  74  can be prevented from colliding with the lower core  86  at high speed, and the colliding noise which occurs when the armature  74  runs against the lower core  86  can be restrained. Moreover, the consumed energy of the exhaust electromagnetic actuator  40  can be saved, because it is not necessary that the armature  74  is again attracted to the lower core  86  after the armature  74  bounces back from the lower core  86 .  
         [0059]    Incidentally, the negative pressure in the combustion chamber  26  is certainly obtained in the fuel injection cut control, because the opening timing of the exhaust valve  43  in the fuel injection cut control is the same as one in the normal driving condition, in this embodiment. As mentioned above, the engine brake of the vehicle occurs on the basis of the negative pressure of the combustion chamber  26 , when the fuel injection cut control is executed. Consequently, the aforementioned advantages can be attained while still securing the engine brake in the fuel injection cut control.  
         [0060]    In the fuel injection cut control, the greater the absolute value of the negative pressure in the combustion chamber  26  is, the greater the opening force applied to the exhaust valve  43  is. Furthermore, the higher the revolution speed NE of the engine is, the greater the absolute value of the negative pressure, in the fuel injection cut control. Consequently, by estimating the negative pressure of the combustion chamber  26  on the basis of the revolution speed NE and making the interval D (during D the exciting current I R  is supplied) longer according to the increase of the absolute value of the negative pressure, the collision noise of the armature  74  can be prevented from increasing and the consuming electric power caused by the bouncing of the armature  74  can be restrained. For example, even when the revolution speed NE is high and the absolute value of the negative pressure is large, the above-mentioned merits can be obtained by setting the longer interval D according to the condition of the revolution speed NE and the negative pressure.  
         [0061]    Incidentally, in this embodiment the force to the exhaust valve  43  in the direction of the closed position is applied by elongating the interval D so that the force to the exhaust valve  43  in the direction of the open position responding to the negative pressure is canceled.  
         [0062]    The exciting current shown in the graph FIG. 6 or FIG. 7 can also be adopted. FIG. 6 shows the exciting current which is controlled to decrease gradually. In this case, the electromagnetic attracting force between the armature  74  and the upper core  82  is greater than the force in the case where the exciting current decreases step-wise, because the electromagnetic force between the armature  74  and the upper core  82  gradually reduces. Therefore, the opening force applied to the exhaust valve  43  caused by the negative pressure in the combustion chamber  26  can be canceled by the increase of the closing force applied to the exhaust valve  43 .  
         [0063]    [0063]FIG. 7 shows the wave of the exciting current which is supplied the upper coil  80  by the positive current I p  after being supplied by the negative current I R . In this case, the electromagnetic attracting force is applied between the armature  74  and the upper core  82  by the positive current I p . The closing force applied to the armature  74  increases by the value of the above-mentioned electromagnetic force. Accordingly, the opening force applied to the exhaust valve  43  caused by the negative pressure in the combustion chamber  26  can be canceled.  
         [0064]    In this embodiment, the ECU  10  supplies the canceling current I R  which is shown in FIG. 5, 6 or  7  to the upper coil  80 . This means that a control means for controlling the electromagnetic force applied to the armature is realized.  
         [0065]    Incidentally, in this embodiment the current direction of the canceling current I R  is opposite to the direction of the attracting current I MAX , however, it is not necessarily limited to this case, and the canceling current I R  can also be zero. In this case, in the fuel injection cut control the wave of the exciting current I R= 0 in FIG. 6 or  7  is given, when the armature  74  is taking apart from the upper core  82 .  
         [0066]    Next, the second embodiment is explained. In the second embodiment, the opening valve timing of the exhaust valve  43  in the fuel injection cut control is changed from the condition in the normal driving control, in the same system as shown in FIGS. 1 and 2.  
         [0067]    The upper graph in FIG. 8 shows the pressure in the combustion chamber  26  vs. the crank angle CA of the engine in the fuel injection cut control, in the same manner as the above-mentioned upper graph in FIG. 4. The characteristics is, however, illustrated in the upper graph in FIG. 8 in the hypothesis that the exhaust valve  43  is kept at the full closed position.  
         [0068]    The second and third graphs from the top in FIG. 8 show the exciting current to the upper coil  80  and to the lower coil  84  of the exhaust electromagnetic actuator  40 . In these two graphs the exciting current patterns X and Y are shown respectively by the solid line and the chained line, and the exciting current supplied to the upper and lower coils  80 ,  84  in the normal driving condition is shown by the dotted line.  
         [0069]    In the lower graph of FIG. 8, the solid line shows the position of the exhaust valve  43  given by the exciting current of the pattern X, the chained line shows the position given by the pattern Y, and the dotted line shows the position in the normal driving condition.  
         [0070]    In the fuel injection cut control, as shown in FIG. 8, the opening timing of the exhaust valve  43  is more advanced (the pattern X) or more delayed (the pattern Y) than in the normal driving control. Consequently, the exhaust valve  43  is prevented from opening in the condition where the negative pressure occurs in the combustion chamber  26 . Referring to the upper graph of FIG. 8, in the fuel injection cut control, the combustion chamber pressure is negative near the bottom dead center, and on other hand the pressure is positive in the other range. In this embodiment, the exciting current I R  is supplied to the upper coil  80  to open the exhaust valve  43  (shown in the second graph of FIG. 8) in the condition, where the combustion chamber pressure is positive or is slightly negative such as the armature  74  can not bounce back against the lower core  86 . Accordingly, the exhaust valve can be prevented from being forced to open by the negative pressure of the combustion chamber  26 . Therefore, it can be avoided that the actuating noise of the exhaust electromagnetic valve  40  increases and the armature  74  bounces back from the lower core  86 .  
         [0071]    Incidentally, in this embodiment the aforementioned advantages are obtained by changing the opening timing of the exhaust valve  43 . That is, this does not require the armature  74  to be given the electromagnetic force in order to cancel the force caused by the negative pressure of the combustion chamber  26 . Therefore, the consumed electric power of the exhaust electromagnetic actuator  40  can be restrained.  
         [0072]    In the second embodiment, the ECU  10  supplies the exciting current shown pattern X or Y in FIG. 8 to the upper coil  80  and the lower coil  84  in the fuel injection cut control, thus, a valve timing changing means is realized.  
         [0073]    Next, the third embodiment is explained. In the third embodiment, in the fuel injection cut control, the force to the exhaust valve  43  in the opening direction caused by the negative pressure in the combustion chamber  26  is canceled by means of restraining or nullifying the electromagnetic force in the opening direction to the armature  74 , when the exhaust valve  43  begins to open, in the same system as shown in FIG. 1  and  2 .  
         [0074]    The exciting current supplied to the upper coil  80  of the exhaust electromagnetic actuator  40  is shown in the upper graph in FIG. 9,. The exciting current to the lower coil  84  is shown in the middle graph, and the position of the exhaust valve  43  is shown in the lower graph. The solid line shows the fuel injection cut control, and the dotted line shows the normal driving control.  
         [0075]    With reference to the middle graph of FIG. 9, in the fuel injection cut control, the supplying timing of the attracting current I MAX  to the lower coil  84  in the opening process of the exhaust valve  43  is delayed comparing with the timing in the normal driving control. Furthermore, the attracting current I MAX  is restrained to be lower. In this embodiment, the canceling current I R  is immediately supplied without supplying the holding current I H , and by advancing the beginning timing of supplying the attracting current I MAX  to the upper coil  80 , the exhaust valve  43  is forced to move toward the closed position without being kept at the full open position.  
         [0076]    Since the timing of supplying the attracting current I MAX  to the lower coil  84  is delayed and the value I MAX  is limited to be lower, the kinetic energy of the exhaust valve  43  is decreased. By the decrease of the kinetic energy, the high speed colliding noise between the armature  74  and the lower core  86  can be reduced and it can be avoided that the armature  74  bounces back from the lower core  86 .  
         [0077]    Next, the modified example of the third embodiment is explained. The upper graph of FIG. 10 shows the exciting current supplied to the upper coil  80  of the exhaust electromagnetic actuator  40  when the exhaust valve  43  begins to open in the fuel injection cut control. The middle graph depicts the exciting current supplied to the lower coil  84 , and the lower graph shows the position of the exhaust valve  43 . In these graphs the solid lines indicate the waves in the fuel injection cut control, and the dotted lines indicate the waves in the normal driving control.  
         [0078]    In this case, since the timing of supplying the attracting current I MAX  to the lower coil  84  is delayed and the value of the attracting current I MAX  is restrained to be low in the same manner as in the aforementioned third embodiment, the force applied to the exhaust valve  43  in the opening direction caused by the negative pressure in the combustion chamber  26  is canceled. Furthermore, since the holding exciting current I H  to the lower coil  84  is supplied following the supply of the attracting current I MAX , the exhaust valve  43  can be kept at the full open position.  
         [0079]    In these third and modified embodiments, in the fuel injection cut control, the beginning timing of supplying the attracting current I MAX  to the lower coil  84  is delayed and the attracting current I MAX  is restrained low, and consequently the kinetic energy given to the armature  74  is reduced. The invention, however, is not limited to the above-mentioned embodiments. For example, the method of only delaying the supplying timing of the attracting current I MAX  or the method of only restraining the attracting current I MAX  to be low, can be adopted. Moreover, if the absolute value of the negative pressure of the combustion chamber  26  is large, the method that the exciting current supplied to the lower coil  84  is zero can be available, in this case the exhaust valve  43  is opened by the force caused by the negative pressure of the combustion chamber  26 .  
         [0080]    Incidentally, when the absolute value of the negative pressure in the combustion chamber  26  is large and the armature  74  moves toward the lower core  86  at the high speed, even if the attracting current I MAX  is not supplied to the lower coil  84 , the problems of the colliding noise between the armature  74  and the lower core  86  or the bounce back of the armature  74  can not be avoided completely. From this point of view, the methods explained in the third and modified embodiments are effective when the absolute value of the negative pressure in the combustion chamber  26  is rather low.  
         [0081]    In the above-mentioned third and its modified embodiments, since the exciting current shown in the middle graph of FIG. 9, or in the middle graph of FIG. 10 is supplied to the lower coil  84  in the fuel injection cut control, a reducing control means for controlling the electromagnetic force applied to the armature  74  is realized.  
         [0082]    Next, the fourth embodiment is explained. In this embodiment, the ECU maintains the supply of the holding current I H  to the upper coil  80  of the exhaust electromagnetic actuator  40  in the fuel injection cut control, so that the exhaust valve  43  is kept at the full closed position. Accordingly, the exhaust valve  43  does not move toward the opening side in the fuel injection cut condition. Therefore, the aforementioned problems caused by the collision between the armature  74  and the lower core  86  are avoided. Furthermore, it is not necessary to supply the attracting exciting current I MAX  to the lower coil  84 , because it is enough to supply the holding current I H  to the upper coil  80  of the exhaust electromagnetic actuator  40  in order to hold the exhaust valve  43  at the full closed position. Incidentally, in this case, the engine brake becomes rather low by the fact that the exhaust valve  43  is kept at the full closed position. Consequently, in this embodiment more saving of electric power for the exhaust electromagnetic actuator  40  can be achieved than in the third or its modified embodiment.  
         [0083]    The exhaust valve  43  is kept at the full closed position in the fourth embodiment, however, it is not limited to this method. That is, it is also available that the exhaust valve  43  is kept at the full open position by supplying the holding current I H  to the lower coil  84 . Moreover, it is also available that the exhaust valve  43  is held at the neutral position by supplying the exciting current neither to the upper coil  80  nor the lower coil  84  when the fuel injection cut control is executed. In this case, more electric power saving can be attained.  
         [0084]    A suspending means for suspending a moving of the exhaust valve  43  is realized by the fact that the ECU  10  maintains the supply of the holding current I H  to the upper coil  80  or the lower coil  84  or suspends the supply of the exciting current to both coils  80  and  84 , in the fuel injection cut control.  
         [0085]    Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with the true scope and spirit of the invention being indicated by the following claims.