Patent Publication Number: US-7913655-B2

Title: Electromagnetically-driven valve

Description:
INCORPORATION BY REFERENCE 
     The disclosure of Japanese Patent Application No. 2007-151528 filed on Jun. 7, 2007 including the specification, drawings and abstract is incorporated herein by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates generally to an electromagnetically-driven valve, and more specifically to an electromagnetically-driven valve that collectively opens and closes multiple valves provided in an internal combustion engine. 
     2. Description of the Related Art 
     For example, the specification of U.S. Pat. No. 6,467,441 describes art related to an existing electromagnetically-driven valve, more specifically, an electromagnetic actuator that actuates a valve of an internal combustion engine using electromagnetic force and elastic force of a spring in combination. The electromagnetic actuator described in the specification of U.S. Pat. No. 6,467,441 includes a valve that has a stem, and a pivot arm. The pivot arm has a first end portion that is pivotally supported by a support frame, and a second end portion that contacts a tip of the stem. Electromagnets each include a core and a coil wound around the core, and are arranged above and below the pivot arm. 
     The electromagnetic actuator further includes a torsion bar that is fitted to the first end portion of the pivot arm and that applies force to the valve to open the valve, and a spiral spring that is arranged around the outer periphery of the stem and that applies force to the valve to close the valve. The pivot arm is alternately attracted to the cores of the electromagnets arranged above and below the pivot arm on the basis of the elastic force of the torsion bar and the elastic force of the spiral spring. 
     Electromagnetically-driven valves that are structured in a fashion similar to that described above are described in Japanese Patent Application Publication No. 2007-23889 (JP-A-2007-23889), Japanese Patent Application Publication No. 2007-32436 (JP-A-2007-32436), the specification of German Patent Laid-Open Publication No. 10025491, the specification of U.S. Pat. No. 7,088,209, the specification of U.S. Pat. No. 6,571,823, and the specification of U.S. Pat. No. 6,481,396. 
     A structure in which two valves of an engine are collectively driven using the electromagnetically-driven valve described in each of the above documents may be employed. However, when the engine is operating at low speed or low load, a sufficient amount of air may be introduced into the engine or a sufficient amount of exhaust gas may be discharged from the engine by driving only one valve. If two valves are kept driving in such a case, the electromagnetically-driven valve may consume unnecessarily large amount of electric power. 
     SUMMARY OF THE INVENTION 
     The invention provides an electromagnetically-driven valve that consumes less amount of electric power. 
     An aspect of the invention relates to an electromagnetically-driven valve, that includes: a first valve and a second valve that are provided in an internal combustion engine, and that are arranged side by side; a connection member which connects the first valve with the second valve, wherein driving force that is generated by electromagnetic force is transferred to the connection member; and a changing mechanism that is fitted to the connection member. The changing mechanism changes the valve drive state between the first state, in which the first valve and the second valve are both driven, and the second state, in which the first valve is driven and the second valve is stopped. 
     In the thus structured electromagnetically-driven valve, the drive state of the first valve and the second valve is changed between the first state and the second state based on the operating state of the internal combustion engine. Thus, it is possible to stop the second valve when a proper operation of the internal combustion engine is ensured by driving only the first valve. As a result, the amount of electric power that is consumed by the electromagnetically-driven valve is reduced. 
     In the first aspect of the invention, the connection member may include a first connection portion that is connected to the first valve and a second connection portion that is connected to the second valve. In addition, the changing mechanism may include an actuator that actuates the connection member. When the changing mechanism changes the valve drive state from the first state to the second state, the actuator may cause the connection member to pivot about the first connection portion to thereby disconnect the second valve from the second connection portion. In the thus structured electromagnetically-driven valve, it is possible to change the valve drive state of the first valve and the second valve between the first state and the second state by actuating the connection member using the actuator. 
     In the first aspect of the invention, the connection member may include a support portion that movably supports the second valve. In addition, the changing mechanism may include a fixing member that fixes the second valve to the support portion, and an actuator that actuates the fixing member. When the changing mechanism changes the valve drive state from the first state to the second state, the actuator may actuate the fixing member to cancel fixation of the second valve to the support portion by the fixing member to thereby allow the support portion to move relative to the second valve. In the thus structured electromagnetically-driven valve, it is possible to change the valve drive state of the first valve and the second valve between the first state and the second state by actuating the fixing member using the actuator. 
     In the first aspect of the invention, the connection member may include a support portion that movably supports the second valve. In addition, the changing mechanism may include a hydraulic mechanism that applies hydraulic pressure to the second valve to fix the second valve to the support portion. When the changing mechanism changes the valve drive state from the first state to the second state, fixation of the second valve to the support portion by the hydraulic mechanism may be cancelled to thereby allow the support portion to move relative to the second valve. In the thus structured electromagnetically-driven valve, it is possible to change the valve drive state of the first valve and the second valve between the first state and the second state by applying the hydraulic pressure to the second valve using the hydraulic mechanism or stopping the application of the hydraulic pressure to the second valve. 
     In the first aspect of the invention, the hydraulic mechanism may include a hydraulic pressure control unit that controls a degree of hydraulic pressure that is applied to the second valve. In the thus structured electromagnetically-driven valve, it is possible to adjust the relative position between the second valve and the connection member by controlling the degree of hydraulic pressure. Thus, it is possible to adjust the distance traveled by the second valve, that is, the valve lift amount. 
     As described above, the invention provides the electromagnetically-driven valve that consumes less amount of electric power. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and further features and advantages of the invention will become apparent from the following description of example embodiments with reference to the accompanying drawings, wherein the same or corresponding portions will be denoted by the same reference numerals and wherein: 
         FIG. 1  is a plane view showing a gasoline engine that is provided with electromagnetically-driven valves according to a first embodiment of the invention; 
         FIG. 2  is a cross-sectional view showing the electromagnetically-driven valve according to the first embodiment of the invention; 
         FIG. 3  is a cross-sectional view showing the electromagnetically-driven valve, taken along the line III-III in  FIG. 2 ; 
         FIG. 4  is a cross-sectional view showing an operating state of a valve plate in  FIG. 3 ; 
         FIG. 5  is a cross-sectional view showing an electromagnetically-driven valve according to a second embodiment of the invention; 
         FIGS. 6A and 6B  are cross-sectional views showing drive states of the electromagnetically-driven valve in  FIG. 5 ; 
         FIG. 7  is a cross-sectional view showing an electromagnetically-driven valve according to a third embodiment of the invention; 
         FIGS. 8A and 8B  are cross-sectional views showing drive states of the electromagnetically-driven valve in  FIG. 7 ; and 
         FIG. 9  is a cross-sectional view showing a modification of the electromagnetically-driven valve in  FIG. 7 . 
     
    
    
     DETAILED DESCRIPTION OF THE EXAMPLE EMBODIMENTS 
     Hereafter, embodiments of the invention will be described with reference to the accompanying drawings. Note that, the same or corresponding portions will be denoted by the same reference numerals in the drawings. 
     First Embodiment of the Invention 
       FIG. 1  is a plane view showing a gasoline engine provided with electromagnetically-driven valves according to a first embodiment of the invention. As shown in  FIG. 1 , electromagnetically-driven valves  10  are provided in a gasoline engine  60  that is an internal combustion engine. The gasoline engine  60  includes a plurality of cylinders  200 . The cylinders  200  are aligned in one direction with predetermined intervals. The gasoline engine  60  is an in-line multi-cylinder engine. 
     The type of an internal combustion engine in which the electromagnetically-driven valve  10  is provided is not particularly limited. For example, the electromagnetically-driven valve  10  may be provided in a diesel engine. The internal combustion engine may be a single-cylinder engine. The layout of the cylinders  200  is not particularly limited. The electromagnetically-driven valve  10  may be provided in, for example, a V engine, a horizontally opposed engine, or a W engine. 
     Each cylinder of the gasoline engine  60  is provided with intake valves  14   p  and  14   q  and exhaust valves  15   p  and  15   q . At each cylinder, the intake valve  14   p  and the intake valve  14   q  are arranged side by side, and the exhaust valve  15   p  and the exhaust valve  15   q  are arranged side by side. The electromagnetically-driven valve  10  collectively opens or closes the intake valve  14   p  and the intake valve  14   q  of each cylinder of the gasoline engine  60 . Similarly, the electromagnetically-driven valve  10  collectively opens or closes the exhaust valve  15   p  and the exhaust valve  15   q  of each cylinder of the gasoline engine  60 . 
     The electromagnetically-driven valve  10  may be structured so as to collectively open or close three or more intake valves or exhaust valves. 
       FIG. 2  is a cross-sectional view showing the electromagnetically-driven valve according to the first embodiment of the invention. Hereafter, the electromagnetically-driven valve  10  that collectively opens or closes the intake valve  14   p  and the intake valve  14   q  will be described. Note that, the electromagnetically-driven valve  10  that collectively opens or closes the exhaust valve  15   p  and the exhaust valve  15   q  have the same structure. 
     As shown in  FIGS. 1 and 2 , each electromagnetically-driven valve  10  is a pivot-type electromagnetically-driven valve that is driven by combination of electromagnetic force and elastic force. The electromagnetically-driven valve  10  includes the intake valves  14   p  and  14   q , a disk  21  that pivots about a central axis  25 , which is a virtual axis, and electromagnets  51   m  and  51   n  that apply electromagnetic force to the disk  21 . 
     The intake valve  14   p  and the intake valve  14   q  include a stem  11   p  and a stem  11   q , respectively. The stem  11   p  and the stem  11   q  extend in parallel to each other. The intake valve  14   p  and the intake valve  14   q  reciprocate in the direction in which the stems  11   p  and  11   q  extend (direction shown by arrows  101 ) in accordance with the pivot motion of the disk  21 . 
     The intake valves  14   p  and  14   q  are provided in a cylinder head  18 . Intake ports  16  are formed within the cylinder head  18 . Valve seats  19  are provided at positions at which the intake ports  16  are communicated with a combustion chamber  17 . The intake valve  14   p  and the intake valve  14   q  include bell portions  12  that are fitted to the tips of the stem  11   p  and the stem  11   q . In accordance with the reciprocation of the intake valves  14   p  and  14   q , the bell portions  12  contact the valve seats  19  or move away from the valve seats  19 , whereby the intake ports  16  close or open. 
     The electromagnetically-driven valve  10  includes a valve plate  31  and an intermediate stem  32 . The valve plate  31  extends from the intake valve  14   p  toward the intake valve  14   q . The valve plate  31  connects the intake valve  14   p  and the intake valve  14   q  with each other. The valve plate  31  transfers the driving force generated by the electromagnetic force to the intake valves  14   p  and  14   q . The intermediate stem  32  connects the disk  21  and the valve plate  31  to each other. The driving force generated by the electromagnetic force is transferred from the disk  21  to the valve plate  31  through the intermediate stem  32 . 
     The electromagnetically-driven valve  10  includes guide members  41  that guide the stems  11   p  and  11   q  so that the stems  11   p  and  11   q  slide in their axial direction. The electromagnetically-driven valve  10  includes a guide member  42  that guides the intermediate stem  32  so that the intermediate stem  32  slides in its axial direction. The guide members  41  and the guide member  42  are made of metal, for example, stainless, so that these guide members endure high-speed slide over the stems. 
     Lower springs  43 , which serve as first spring members, are supported on the peripheries of the stems  11   p  and  11   q  by lower retainers  44  having a brimmed shape. The lower springs  43  are formed of coil springs. The lower springs  43  apply elastic forces for moving the stems  11   p  and  11   q  upward to the intake valves  14   p  and  14   q.    
     A support base  48  is fixed onto the top face of the cylinder head  18 . The support base  48  supports the electromagnets  51   m  and  51   n . The electromagnet  51   m  is arranged above the disk  21 , and the electromagnet  51   n  is arranged below the disk  21 . 
     The electromagnet  51   m  and the electromagnet  51   n  are the same in shape. The shape of the electromagnet  51   n  will be described below. The electromagnet  51   n  includes a coil  53  and a core  52 . The coil  53  is wound around the core  52 . 
     The core  52  is made of magnetic material. In the first embodiment of the invention, the core  52  is formed of multiple electromagnetic steel plates that are stacked on top of each other. The core  52  may be made of magnetic material other than electromagnetic steel plates, for example, a green compact made of magnetic power. The coil  53  of the electromagnet  51   m  and the coil  53  of the electromagnet  5  in may be made of a continuous single coil wire, or made of separate coil wires. 
     The support base  48  supports the disk  21 . The disk  21  is made of magnetic material. The disk  21  is formed of a bulk material to maintain a sufficient level of strength. The disk  21  includes a support portion  23  and a connection portion  22 . The central axis  25  is defined in the support portion  23 . The disk  21  extends from the support portion  23  toward the connection portion  22  in the direction that intersects with the stems  11   p  and  11   q.    
     A through-hole  24  is formed in the support portion  23 . A torsion bar  30 , which serves as a second spring member, is press-fitted into the through-hole  24 . The torsion bar  30  extends in the axial direction of the central axis  25 . The support portion  23  is pivotally supported by the support base  48  via the torsion bar  30 . When a tip  32   c  of the intermediate stem  32  contacts the connection portion  22 , the intermediate stem  32  and the disk  21  are connected to each other. 
     The torsion bar  30  applies elastic force for causing the disk  21  to pivot counterclockwise about the central axis  25  to the disk  21 . That is, the torsion bar  30  applies elastic force for moving the stems  11   p  and  l  q downward to the intake valves  14   p  and  14   q  via the valve plate  31 . When the electromagnetic force is not applied to the disk  21 , the disk  21  is kept at the middle portion between the valve-open position and the valve-closed position due to the elastic forces of the lower spring  43  and the torsion bar  30 . 
     When an electric current is supplied to the coil  53  of the electromagnet  51   m , a magnetic flux flow is formed so as to pass through the core  52  of the electromagnet  51   m  and the disk  21 . Thus, the electromagnet  51   m  generates electromagnetic force that attracts the disk  21  to the electromagnet  51   m . When an electric current is supplied to the coil  53  of the electromagnet  5  in, a magnetic flux flow is formed so as to pass through the core  52  of the electromagnet  51   n  and the disk  21 . Thus, the electromagnet  5  in generates electromagnetic force that attracts the disk  21  to the electromagnet  51   n.    
     The disk  21  is attracted alternately to the electromagnet  51   m  and the electromagnet  51   n  by the electromagnetic force generated by the electromagnet  51   m  and the elastic force of the lower spring  43 , and the electromagnetic force generated by the electromagnet  51   n  and the elastic force of the torsion bar  30 . As a result, the disk  21  pivots about the central axis  25 . When the disk  21  is attracted to the electromagnet  51   m , the stems  11   p  and  11   q  move upward, and the intake valves  14   p  and  14   q  are brought to the valve-closed positions. When the disk  21  is attracted to the electromagnet  51   n , the steps  11   p  and  11   q  move downward, and the intake valves  14   p  and  14   q  are brought to the valve-open positions. 
       FIG. 3  is a cross-sectional view of the electromagnetically-driven valve, taken along the line III-III in  FIG. 2 .  FIG. 4  is a cross-sectional view showing an operating state of the valve plate in  FIG. 3 . 
     As shown in  FIGS. 2 to 4 , the valve plate  31  includes a connection portion  34 , which serves as a first connection portion, and a connection portion  35 , which serves as a second connection portion. The intake valve  14   p  and the intake valve  14   q  are connected to the connection portion  34  and the connection portion  35 , respectively. A hole  36  and a hole  37  are formed in the connection portion  34  and the connection portion  35 , respectively. The stem  11   p  of the intake valve  14   p  and the stem  11   q  of the intake valve  14   c  are fitted into the hole  36  and the hole  37 , respectively. 
     A cutout portion  37   g  is formed in the connection portion  35 . The cutout portion  37   g  is formed in such a manner that the periphery of the hole  37  is partially open. The width of the cutout portion  37   g  is larger than the diameter of the stem  11   q . The entire periphery of the hole  36  is closed. 
     The electromagnetically-driven valve  10  includes hydraulic cylinders  61  and  62  which serve as actuators. The hydraulic cylinder  61  and the hydraulic cylinder  62  are provided with an arm  61   g  and an arm  62   g , respectively. The hydraulic cylinder  61  and the hydraulic cylinder  62  are arranged on the respective sides of the valve plate  31 . The arm  61   g  and the arm  62   g  contact the valve plate  31 , at the positions between the connection portion  34  and the connection portion  35 . 
     The hydraulic cylinders  61  and  62  change the valve drive state between a two-valve drive state in which the intake valve  14   p  and the intake valve  14   q  are both driven, and a one-valve drive state in which the intake valve  14   p  is driven and the intake valve  14   q  is stopped. 
     More specifically, when hydraulic pressure is supplied to the hydraulic cylinder  61 , the arm  61   g  pushes the valve plate  31 . At this time, the valve plate  31  pivots about the connection portion  34 , whereby the stem  11   q  moves out of the hole  37  through the cutout portion  37 . Thus, the connection portion  35  and the intake valve  14   q  are disconnected from each other. The intake valve  14   q  that is free from the pivot motion of the disk  21  is kept at the valve-closed position due to the elastic force of the coil spring  43 . As a result, the electromagnetically-driven valve  10  is placed in the one-valve drive state in which only the intake valve  14   p  is driven. 
     When hydraulic pressure is supplied to the hydraulic cylinder  62 , the arm  62   g  pushes the valve plate  31 . At this time, the valve plate  31  pivots in the direction opposite to the direction described above. As a result, the stem  11   q  is fitted into the hole  37  through the cutout portion  37   g . Thus, the connection portion  35  and the intake valve  14   q  are connected to each other. As a result, the electromagnetically-driven valve  10  is placed in the two-valve drive state in which the intake valve  14   p  and the intake valve  14   q  are both driven. 
     Note that, devices other than the hydraulic cylinders may be used as the actuators that drive the valve plate  31 . For example, air cylinders or an electric motor may be used as the actuator. 
     The electromagnetically-driven valve  10  according to the first embodiment of the invention is provided in the gasoline engine  60  which is an internal combustion engine. The electromagnetically-driven valve  10  includes: the intake valve  14   p  and the intake valve  14   q  that are arranged side by side, and that serve as a first valve and a second valve, respectively; the valve plate  31  that connects the intake valve  14   p  and the intake valve  14   q  to each other, and that serves as a connection member to which the driving force generated by the electromagnetic force is transferred; and the hydraulic cylinders  61  and  62 , which serve as changing mechanism, fitted to the valve plate  31 . The hydraulic cylinders  61  and  62  change the valve drive state between the first state in which the intake valve  14   p  and the intake valve  14   q  are both driven and the second state in which the intake valve  14   p  is driven and the intake valve  14   q  is stopped. 
     With the thus structured electromagnetically-driven valve  10  according to the first embodiment of the invention, a sufficient amount of air is taken in the cylinder by opening one of the intake valve  14   p  and the intake valve  14   q , for example, when the gasoline engine  60  is operating at low speed or low load. According to the first embodiment of the invention, in such a case, the valve drive state is changed from the two-valve drive state to the one-valve drive state in which only the intake valve  14   p  is driven. Thus, it is possible to minimize the electromagnetic force that is required to drive the valve, thereby reducing the electric power consumed by the electromagnetically-driven valve  10 . In addition, it is possible to make the relative displacement between the valve plate  31  and the intermediate stem  32  substantially equal to zero when the valve is driven, because the changing mechanism is fitted to the valve plate  31 . 
     Second Embodiment of the Invention 
       FIG. 5  is a cross-sectional view showing an electromagnetically-driven valve according to a second embodiment of the invention.  FIGS. 6A and 6B  are cross-sectional views showing drive states of the electromagnetically-driven valve in  FIG. 5 . The electromagnetically-driven valve according to the second embodiment of the invention has mostly the same structure as that of the electromagnetically-driven valve  10  according to the first embodiment of the invention. The structure common between the first and second embodiments will not be described below. 
     As shown in  FIG. 5  and  FIGS. 6A and 6B , the valve plate  31  includes a support portion  65 . The support portion  65  movably supports the intake valve  14   q . The support portion  65  supports the intake valve  14   q  in such a manner that the intake valve  14   q  is allowed to reciprocate. A hole  66  is formed in the support portion  65 . The hole  66  is a through-hole. The stem  11   q  of the intake valve  14   q  is fitted into the hole  66 . The stem  11   q  is fitted into the hole  66  so as to be slidable in the axial direction. 
     The electromagnetically-driven valve according to the second embodiment of the invention includes a pin  68 , which serves as a fixing member, and a hydraulic cylinder  69 , which serves as an actuator that actuates the pin  68 . For example, the engine oil within the cylinder head  18  is supplied to the hydraulic cylinder  69 . 
       FIG. 6A  describes the state in which the valve plate  31  is kept at the valve-open position in the two-valve drive state. As shown in  FIG. 6A , when the hydraulic pressure is supplied to the hydraulic cylinder  69 , the pin  68  is fitted into the valve plate  31  and the intake valve  14   q . Thus, the intake valve  14   q  is fixed to the support portion  65 . At this time, the electromagnetically-driven valve is placed in the two-valve drive state in which the intake valve  14   p  and the intake valve  14   q  are both driven. 
       FIG. 6B  shows the state in which the valve plate  31  is kept at the valve-open position in the one-valve drive state. As shown in  FIG. 6B , when the supply of hydraulic pressure to the hydraulic cylinder  69  is stopped, the pin  68  moves to the position at which the pin  68  retracts from the valve plate  31  and the intake valve  14   q . Thus, the fixation of the intake valve  14   q  to the support portion  65  by the pin  68  is cancelled. The intake valve  14   q  is then free from the pivot motion of the disk  21  and stops at the valve-closed position due to the elastic force of the lower spring  43 . The valve plate  31  reciprocates while causing the support portion  65  to slide over the stem  11   q . As a result, the electromagnetically-driven valve is placed in the one-valve drive state in which only the intake valve  14   p  is driven. 
     Note that, devices other than the hydraulic cylinders may be used as the actuators that drive the pin  68 . For example, air cylinders or an electric motor may be used as the actuator. The fixing member that fixes the intake valve  14   q  to the support portion  65  is not limited to a pin-shaped member. For example, a friction plate that uses friction engagement to fix the intake valve  14   q  to the support portion  65  may be used as the fixing member. 
     With the thus structured electromagnetically-driven valve according the second embodiment of the invention, it is possible to produce mostly the same effects as those in the first embodiment of the invention. 
     Third Embodiment of the Invention 
       FIG. 7  is a cross-sectional view showing an electromagnetically-driven valve according to a third embodiment of the invention.  FIGS. 8A and 8B  are cross-sectional views showing drive states of the electromagnetically-driven valve in  FIG. 7 . The electromagnetically-driven valve according to the third embodiment of the invention has mostly the same structure as that of the electromagnetically-driven valve  10  according to the first embodiment of the invention. The structure common between the first and third embodiments will not be described below. 
     As shown in  FIG. 7 , according to the third embodiment of the invention, the valve plate  31  includes the support portion  65 . The support portion  65  has mostly the same structure as that of the support portion  65  according to the second embodiment of the invention. The electromagnetically-driven valve according to the third embodiment of the invention includes a hydraulic mechanism  70 . The hydraulic mechanism  70  applies hydraulic pressure to the intake valve  14   q  to fix the intake valve  14   q  to the support portion  65 . Namely, the hydraulic pressure that is applied to the intake valve  14   q  by the hydraulic mechanism  70  has a function similar to that of the pin  68  according to the second embodiment of the invention. 
     The hydraulic mechanism  70  includes a hydraulic chamber  71 . The oil for applying hydraulic pressure to the intake valve  14   q  is supplied to the hydraulic chamber  71 . The support portion  65  is fitted into the hydraulic chamber  71  in such a manner that the support portion  65  slides in the direction in which the valve plate  31  reciprocates. An O-ring  72 , which serves as a seal member, is arranged between the stem  11   q  and the support portion  65 . Similarly, an O-ring  73 , which serves as a seal member, is arranged between the support portion  65  and the inner wall of the hydraulic chamber  71 . With this structure, leakage of oil from the hydraulic chamber  71  is prevented. 
       FIG. 8A  shows the state in which the valve plate  31  is kept at the valve-open position in the two-valve drive state. As shown in  FIG. 8A , when the hydraulic pressure is applied to the intake valve  14   q  by the hydraulic mechanism  70 , the position of the intake valve  14   q  with respect to the support portion  65  is fixed. The valve plate  31  reciprocates the intake valves  14   p  and  14   q  while sliding over the inner wall of the hydraulic chamber  71 . At this time, the electromagnetically-driven valve is placed in the two-valve drive state in which the intake valve  14   p  and the intake valve  14   q  are both driven. 
       FIG. 8B  shows the state in which the valve plate  31  is kept at the valve-open position in the one-valve drive state. As shown in  FIG. 8B , when the supply of hydraulic pressure to the hydraulic mechanism  70  is stopped, the intake valve  14   q  is kept at the valve-closed position due to the elastic force of the coil spring  43 . The valve plate  31  reciprocates the intake valve  14   p  while sliding over the inner wall of the hydraulic chamber  71  and the stem  11   q  of the intake valve  14   q . At this time, the electromagnetically-driven valve is placed in the one-valve drive state in which only the intake valve  14   p  is driven. 
     With the thus structured electromagnetically-driven valve according to the third embodiment of the invention, it is possible to produce mostly the same effects as those in the first embodiment of the invention. 
       FIG. 9  is a cross-sectional view showing a modification of the electromagnetically-driven valve in  FIG. 7 .  FIG. 9  shows the state in which the valve plate  31  is kept at the valve-open position in the two-valve drive state. 
     As shown in  FIG. 9 , in this modification, the hydraulic mechanism  70  includes a hydraulic pressure control unit  76 . The hydraulic pressure control unit  76  controls the degree of hydraulic pressure that is applied to the intake valve  14   q  by the hydraulic mechanism  70 . With this structure, the position at which the intake valve  14   q  is fixed to the support portion  65  may be adjusted, thereby making it possible to change the lift amount of the intake valve  14   q . For example, as shown in  FIG. 9 , the lift amount of the intake valve  14   q  is reduced by setting the degree of hydraulic pressure that is applied to the intake valve  14   q  to a smaller value. 
     The hydraulic mechanism  70  that includes the hydraulic pressure control unit  76  may be provided to each of the intake valves  14   p  and  14   q . In this case, it is possible to change the lift amount of the intake valve  14   p  and the lift amount of the intake valve  14   q , thereby increasing the flexibility of change in the lift amounts. 
     The structure of an electromagnetically-driven valve to which the invention is applied is not limited to the structures described above. For example, a structure in which an upper disk and a lower disk are arranged above and below an electromagnet, respectively, and an intermediate stem is connected to these disks may be employed. An electromagnetically-driven valve to which the invention is applied is not limited to a pivot type. The invention may be applied to, for example, a translational type electromagnetically-driven valve that drives a valve using a liner motion achieved by electromagnetic force. 
     Thus, the embodiments of the invention that have been disclosed in the specification are to be considered in all respects as illustrative and not restrictive. The technical scope of the invention is defined by claims, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.