Abstract:
A valve driving apparatus includes a magnetic flux generating element in which an electromagnetic coil is wound to generate magnetic flux, a magnetic field generating element which has at least two poles to distribute magnetic flux and form at least one magnetic field region, a drive means which includes a magnetic path member, and a magnetized member arranged in accordance with the magnetic field region and having two magnetized faces with mutually different polarity to be connected and moved together with a valve rod united with a valve element. A current supply means supplies driving current to the electromagnetic coil whereby the current has polarities corresponding to either a valve closing direction or a valve opening direction of the valve element. The apparatus reduce impact of valve seating with a simple structure and controls the valve with less power consumption and with precision.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a valve driving apparatus which drives a valve element to control the flow of intake gas or exhaust gas of an internal combustion engine. 
     2. Description of the Related Art 
     An electromagnetic valve drive-apparatus controlling the opening and closing of valves by electromagnetic force is known as an apparatus driving valve bodies such as intake valves or exhaust valves which control the flow of intake gas or exhaust gas of an internal combustion engine. This apparatus does not control the valve opening and closing by a cam which is rotatably driven by a crankshaft, but is capable of controlling the valve opening and closing and its timing regardless of the cam configuration and cam rotational speed. However, by increasing the opening and closing speed of the valve, the valve is liable to collide with a surrounding member when the valve seats and, as a result, problems arise, such as abrasion of the valve and its surrounding member and the generation of impulse sounds. For example, an apparatus disclosed in Japanese Patent Kokai No. 10-141028 is provided with an air damper mechanism in the valve driving apparatus in order to reduce shocks during valve seating, thereby solving these problems. However, this valve driving apparatus has a complex structure, thereby creating a new problem. 
     Also, the valve driving apparatus in which the valves are driven by electromagnetic force needs a power supply to drive the apparatus, and conservation of the power consumption is also required. The apparatus which is disclosed in Japanese Patent Kokai No.8-189315 attempts to conserve power by changing the valve travel distance according to the internal combustion engine driving condition. However, the reduction of the supplied power has caused new problems such as reduced driving force and decreased response characteristics of valve opening and closing. 
     Furthermore, in the apparatus which is disclosed in Japanese Patent No. 2,772,569, the valve driving force has been increased by arranging a plurality of fixed magnetic poles and controlling the current magnitude supplied to the energizing coil. However, this apparatus has caused the structure to become complex and an increase of power consumption. 
     As discussed above, the conventional electromagnetic valve driving apparatus which attempts to reduce the shock of the valve when the valve is seated requires a complex structure and increases power consumption in order to precisely control valve movement. Further, with regard to the conventional valve driving apparatus which applies soft ferromagnetic iron material to the moving element, it is also a problem to align the valve to a predetermined position when power to the valve driving apparatus is not applied. 
     The present invention has been devised in view of the foregoing problems and an object of the invention is to provide an electromagnetic force driven apparatus whereby the structure is simple and the valve seating shock is reduced. Further, valve control is precisely executed with low power consumption, thereby enabling the valve to be placed at a predetermined position when power to the valve driving apparatus is not applied. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     The objects of the present invention is to simplify the structure of a valve driving apparatus and to reduce the shock when the valve is seated. 
     The valve driving apparatus of the present invention is a valve driving apparatus for deriving a valve element controlling intake gas flow or exhaust gas flow of an internal combustion engine. A magnetized path member comprises a magnetic flux generating element in which an electromagnetic coil is wound to generate magnetic flux and a magnetic field generating element comprising at least two pole members to distribute the magnetic flux to form at least one magnetic field. A magnetizing member moves within the magnetic field in cooperation with a valve rod formed integrally with the valve element. The member has two magnetized surfaces with mutually different polarities. A current supply supplies a driving current to the electromagnetic coil corresponding to the poles of either a valve opening direction or a valve closing direction of the valve element. 
    
    
     BRIEF EXPLANATION OF THE DRAWINGS 
     FIG. 1 is a sectional view showing a first embodiment of a valve driving apparatus of the present invention. 
     FIG. 2 is an enlarged exploded view of the valve driving apparatus shown in FIG.  1 . 
     FIG. 3 is a graph showing the relationship between the moving distance of a magnetized member and the driving force applied to the magnetized member. 
     FIG. 4 is a graph showing the relationship between the time to move the magnetized member under optimized control, position of the magnetized member and the acceleration thereof. 
     FIG. 5 is a sectional view of a combustion chamber region wherein in the valve driving apparatus shown in FIG. 1 is applied to the intake valve and the exhaust valve of the driving apparatus. 
     FIG. 6 is a sectional view showing a second embodiment of the valve driving apparatus. 
     FIG. 7 is a sectional view showing a third embodiment of the valve driving apparatus. 
     FIG. 8 is a sectional view showing a fourth embodiment of the valve driving apparatus. 
     FIG. 9 is a sectional view showing a fifth embodiment of the valve driving apparatus. 
     FIG. 10 is an enlarged perspective view of the yoke and the magnetized member of the valve driving apparatus shown in FIG.  9 . 
     FIG. 11 is a perspective view showing a sixth embodiment of the valve driving apparatus. 
     FIG. 12 is a perspective view showing the valve driving apparatus of FIG. 11 wherein the upper frame, lower frame and coil are omitted. 
     FIG. 13 is a perspective view showing the upper frame viewed from below. 
     FIG. 14 is a perspective view showing the yoke held between lower frame portions. 
     FIG. 15 is a perspective view showing the magnetized member and the moving element. 
     FIG. 16 is an enlarged perspective view showing the state in which a roller engages the edge of a protruded portion of the moving element and the lower frame guide groove. 
     FIG. 17 is a sectional view along line X—X, shown in FIG.  11 . 
     FIG. 18 is a sectional view along line Y—Y, shown in FIG.  11 . 
     FIG. 19 is an enlarged perspective view showing the state in which a spheroid engages the edge of the protruded portion of the moving element and the lower frame guide groove. 
     FIG. 20 is an enlarged perspective view showing a fitting portion of the moving element and the valve element. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Embodiments of the present invention will now be described with reference to the drawings. 
     FIG. 1 shows a first embodiment of the valve driving apparatus of the present invention. 
     Valve  11  is integrally formed at one end of a valve rod  12 . The region of the other end portion of the valve rod  12  has a rectangular sectional configuration and through holes  13  and  14  are arranged therein, as shown in FIG.  2 . Two magnetized members  21  and  22  having a thickness the same as the valve rod  12  are inserted into the through holes  13  and  14 , so that upper surfaces and lower surfaces of the magnetizing members are in planer alignment with the upper and the lower surface of the valve rod  12 , respectively. The two magnetized members  21  and  22  are respectively arranged so that the opposing faces have a different magnetic polarity to each other. Magnetized members  21  and  22  are arranged so that the polarity of the two sides of magnetized member  21  have an opposite polarity when compared to the two sides of magnetized member  22 . Along one side of a yoke  31  of the actuator  30 , three poles  34 ,  35  and  36  are in parallel alignment in the lengthwise direction of the valve rod  12 . The valve rod  12  and inserted magnetized members  21  and  22  are arranged in a gap  33  located between a yoke  32  and the magnetic poles  34 ,  35  and  36  which are separate elements. 
     Valve rod  12  is movable in both directions A and B, as shown in the figure. By moving the valve rod  12 , the valve  11  may be moved to an opening position or closing position. Inside the gap  33 , a magnetic field is formed in the regions of poles  34  and  35  and poles  35  and  36 . Magnetized members  21  and  22  are arranged so that each member corresponds to each of the two magnetic field regions. In the central portion, the yoke  31  is formed around a core  37 . Surrounding core  37  is a fixed frame  23  of nonmagnetic material such as resin. At a side wall portion of fixed frame  23 , electromagnetic coil  38  is wound around core  37 . A magnetic gap  39  is arranged between an upper end of core  37  and yoke  31 . The electromagnetic coil  38  is connected to a current source not shown in the figure. The current source supplies a driving current to the electromagnetic coil  38 . The polarity of the driving current corresponds to either the closing direction or the opening direction of the valve element  11 . 
     In the following description, the magnetized member  21  facing the yoke  31  has a magnetic polarity of N, and a magnetic polarity of S on the side facing yoke  32 , for example. The magnetized member  22  facing the yoke  31  has a magnetic polarity of S, and on the side facing yoke  32  has a magnetic polarity of N. 
     When current is not supplied to electromagnetic coil  38 , the magnetic resistance of magnetic gap  39  is greater than the magnetic force of magnetized members  21  and  22 . Therefore, magnetized members  21  and  22  and, therefore, the valve rod  12  are positioned to a predetermined position (referred to as reference position hereinafter). In the reference position, magnetic field paths are circumferentially formed in the following sequence: the N pole of magnetized member  21 , magnetic pole member  34 , yoke  31 , magnetic pole member  36 , the S pole of magnetized member  22 , the N pole of magnetized member  22 , yoke  32 , and the S pole of magnetized member  21 . A second sequence is: the N pole of magnetized member  21 , magnetic pole member  35 , the S pole of magnetized member  22 , the N pole of magnetized member  22 , yoke  32 , and the S pole of magnetized member  21 . 
     However, when current is supplied to electromagnetic coil  38 , magnetic flux is generated inside core  37  and the magnetic flux is distributed inside yoke  31  to create a magnetic pole at each surface of poles  34 ,  35  and  36  and forms a magnetic field in the magnetic field region. The polarities of a magnetic dipole occurring at pole  34  and  36  are the same, whereas the polarity of the magnetic dipole occurring at pole  35  is of opposite polarity. For example, when direct current flowing in a predetermined direction is applied to electromagnetic coil  38 , an S magnetic pole is created at poles  34  and  36 , whereas an N magnetic pole is created at pole  35 . When direct current flowing in the other direction is applied to electromagnetic coil  38 , an N magnetic pole is created at poles  34  and  36 , whereas an S magnetic pole is created at pole  35 . 
     When an S magnetic pole is created at poles  34  and  36  and an N magnetic pole is created at pole  35 , a new magnetic path is circumferentially formed in the following sequence: the N pole of magnetized member  21 , magnetic pole member  34 , yoke  31 , magnetic gap  39 , core  37 , magnetic pole member  35 , the S pole of magnetized member  22 , the N pole of magnetized member  22 , yoke  32 ,and the S pole of magnetized member  21  so as to move the magnetized members  21  and  22  together with valve rod  12  in the direction of arrow A, as shown in FIG.  1 . On the contrary, when an N pole is created at poles  34  and  36  and S pole is created at pole  35 , a new magnetic path is circumferentially formed in the following sequence: the N pole of magnetized member  21 , magnetic pole member  35 , core  37 , magnetic gap  39 , yoke  31 , magnetic pole member  36 , the S pole of magnetized member  22 , the N pole of magnetized member  22 , yoke  32 , and the S pole of magnetized member  21  so as to move the magnetized members  21  and  22  together with valve rod  12  in the direction of arrow B. 
     As mentioned above, when current is not supplied to electromagnetic coil  38 , valve  11  may be positioned to a predetermined position. By changing the direction of the current supplied to electromagnetic coil  38 , valve rod  12  may be moved in either direction A or B so as to position the valve  11  to one of the opened position or the closed position. 
     FIG. 3 shows the relationship between the position of the magnetized members and the driving force applied to the magnetized members when the moving distance of the magnetized member is ±4 millimeters, for example. This graph is obtained by applying a predetermined current (1 ampere to 15 ampere, for example) to the electromagnetic coil of the actuator and detecting the driving force required to stop the magnetized members in a predetermined position e.g., −4 mm to +4 mm. 
     The magnitude of driving force applied to magnetized members decreases as the position of the magnetized members moves in the positive direction. When the valve apparatus is in any one of the predetermined positions, as the magnitude of the current applied to the electromagnetic coil increases, the amount of driving force applied to the valve apparatus increases. The position of the magnetized members, when the driving force is zero, is the reference position of the magnetized members. 
     The graph of FIG. 3 shows the effect of direct current flowing in a predetermined direction applied to the electromagnetic coil. When the direct current flows in the opposite direction, then the driving force is reversed. 
     Driving force in a conventional apparatus as is disclosed in Japanese Patent No. 2,772,569 is in inverse proportion to the second power of the distance of the moving element, whereas the apparatus of the present invention, which is constructed as stated above, is able to provide a stable driving force without relying on the position of the magnetized members which are movable. 
     FIG. 4 shows the relationship between the time required to transfer or move the magnetized members and position of the magnetized member as well as the acceleration of the magnetized members derived from numerical computation. In this graph. the internal combustion engine rotates at high-speed, 6000 rpm for example, and the magnetized members are moved together with the valve member and the valve rod. 
     As shown in the upper portion of the graph of FIG. 4, when driving force is applied to the magnetized members to drive the members, the transformation waveform acceleration is rectangularly shaped. The transformation waveform of displacement of the member is a curved line as shown in the lower portion of the graph of FIG.  4 . Moreover, in this case, when the maximum moving distance of the magnetized members is set to a predetermined value (8 mm for example), the initial position of the magnetized members is −4 mm movement in direction B and the maximum moving distance of the magnetized members is +4 mm movement in the direction A. Then, controlling the velocity of the magnetized members at the initial position and maximum movement position, respectively, to zero velocity may be achieved by altering the acceleration of the magnetized members from −230 G to +230 G as shown in the upper portion of the graph of FIG.  4 . As discussed above, valve  11  is integrally formed in one body by incorporating magnetized members  21 ,  22  and the valve rod  12 , and the position where the magnetized members are located at the initial position corresponds to the valve closing position and the position where the magnetized members are positioned at the position of maximum movement corresponds to the valve opening position. In summary, in order to control the valve so that it does not collide with the valve seat as well as to position the valve at the valve closing and opening positions at a velocity of 0, an acceleration value of ±230 G is applied to the magnetized member (valve element), for example. As a result, the apparatus of the present invention reduces valve impact upon seating by use of a simple structure. 
     FIG. 5 shows a cross section of the region of the combustion chamber of an internal combustion engine, wherein the valve driving apparatus shown in FIG. 1 is applied to control the flow of intake gas and exhaust gas of the internal combustion. Components which correspond to components shown in FIG. 1 are given the same reference numbers. 
     From the suction pipe  51  of internal combustion engine  50 , air having a flow rate controlled by throttle valve  57  is introduced to a combustion chamber intake. From the injector  52  located at the suction pipe  51 , fuel is injected. Intake air and fuel is mixed in suction pipe  51  to form an air-fuel mixture. A crank angle sensor is arranged adjacent to the crank shaft (not shown) so that when the crank angle reaches a predetermined angle, a position signal pulse is transmitted. When the position signal pulse to initiate the intake stroke is transmitted from the crank angle sensor, current is supplied to actuator  30  to move the valve rod  12  inwardly in the direction of combustion chamber  53  together with the magnetized members  21  and  22  and to open the valve  11  to let the air-fuel mixture into the combustion chamber  53 . Subsequently, when the position signal pulse to initiate the compression stroke is transmitted from the crank angle sensor, current in an opposite direction to the current applied at intake is applied to actuator  30  to move the valve rod  12  in the opposite direction to close the valve  11 . When the position signal pulse to initiate the combustion stroke is transmitted, ignition plug  54  is ignited and air-fuel mixture in the combustion chamber  53  is combusted. This combustion increases the volume of air-fuel mixture and moves the piston  55  downward. This piston  55  motion is transmitted to the crank shaft and is converted to rotational motion of the crank shaft. When the position signal pulse to initiate the exhaust stroke is transmitted, current is supplied to actuator  30 ′ and valve rod  12 ′ moves inwardly in combustion chamber  53  together with the magnetized members  21 ′ and  22 ′ and opens the valve  11 ′ to exhaust the combusted air-fuel mixture gas to exhaust pipe  56  as exhaust gas. Subsequently, when the position signal pulse to initiate the intake stroke is transmitted, valve  11 ′ closes and the intake stroke of the next cycle begins. 
     Between the intake pipe  51  and exhaust-pipe  56  of the internal combustion engine  50 , a re-circulation pipe  58  is arranged so as to be connected the intake and exhaust pipes. The re-circulation pipe  58  is provided with an exhaust gas re-circulation system  131  (hereinafter referred as an EGR system) to control the exhaust gas flow. Exhaust gas exhausted from internal combustion engine  50  is supplied to intake pipe  51  by flowing through the re-circulation pipe  58  and has its flow rate controlled by the EGR system  131 . The EGR system  131  comprises the valve driving apparatus shown in FIG. 1, i.e., a valve  11 ″, a valve rod  12 ″, magnetized members  21 ″ and  22 ″, and an actuator  30 ″. Thus, the valve driving apparatus controls the flow of the exhaust-gas supplied to intake pipe  51 . 
     Further, intake pipe  51  of the internal combustion engine  50  has a by-pass pipe  59  which detours around the air supplied upstream of the throttle valve  57  and supplies the air to the downstream side of the throttle valve pipe  51 . The by-pass pipe  59  is equipped with an idle speed control unit  132  (hereinafter referred to as an ISC system) to control the air flow rate supplied to the internal combustion engine  50 . The ISC system comprises a valve driving apparatus shown in FIG. 1, i.e., a valve  11 ′″, a valve rod  12 ′″, magnetized members  21 ′″ and  22 ′″, and an actuator  30 ′″. Thus, the valve driving apparatus controls the air flow rate supplied to the internal combustion engine  50 . 
     Intake gas supplied to internal combustion engine  50  comprises air supplied to intake pipe  51  and air supplied through the ISC system  132  to the downstream side of intake pipe  51  as mentioned above, while exhaust gas exhausted from the internal combustion engine  50  comprises exhaust-gas exhausted from the internal combustion engine  50  and exhaust-gas supplied to the EGR system. 
     The internal combustion engine shown in FIG. 5 is not limited to the valve driving apparatus of the first embodiment shown in FIG.  1 . For example, the second to sixth embodiments of the valve driving apparatus, to be discussed later, may also be applied. 
     FIG. 6 shows a valve driving apparatus of the second embodiment of the present invention. Components which correspond to components shown in FIG. 1 are given the same reference numbers. 
     A hole sensor  41  is arranged in magnetic gap  39  and detects the flux density which passes through the magnetic gap  39 . A voltage signal which corresponds to the detected magnetic flux density is transmitted from hole sensor  41  and the voltage signal is supplied to a position detecting signal processor (not shown). As mentioned above, the position of magnetized members  21  and  22  is determined according to the magnitude of generated flux density in core  37  or flux density which passes through the magnetic gap  39 . Therefore, by detecting the flux density, the position of magnetized members  21  and  22  may be obtained. By providing driving current to electromagnetic coil  38  corresponding to the position of magnetized members  21  and  22 , the valve  11  may be controlled accurately. 
     FIG. 7 shows a valve driving apparatus of the third embodiment of the present invention. Components which correspond to components shown in FIGS. 1 and 6 are numbered in the same manner. 
     Electromagnetic coil  42  is wound at the upper end of core  37  and detects transformation of the magnetic flux generated in core  37  and outputs a voltage signal which corresponds to the detected magnetic flux to be supplied to a velocity detecting signal processor (not shown). Since magnetic flux generated in core  37  changes according to the velocity of the magnetized member, by detecting the transformation of the flux density, the velocity of the magnetized members  21  and  22  may be obtained so as to allow precise control of the valve  11  by supplying driving current corresponding to the velocity of the members  21  and  22  to the electromagnetic coil  38 . 
     FIG. 8 shows the valve driving apparatus of the fourth embodiment of the present invention. Components which correspond to components shown in FIGS. 1,  6  and  7  are given the same reference numbers. 
     Magnetic gap  39  is arranged at yoke  31  in a position offset to the side of pole  34  with respect to the center line C of the core  37 . A magnetic gap  40  is arranged in the lower part of pole  34 . As will be described later, when current is not supplied to electromagnetic coil  38 , valve rod  12  is located below pole  34  so that the magnetic gap  40  is identified as a gap formed between pole  34  and valve rod  12 . To the contrary, when current is supplied to electromagnetic coil  38 , valve rod  12  moves in the direction of arrow A, shown in the figure, together with magnetized members  21  and  22  to place the magnetized member  21  underneath pole  34  so that magnetic gap  40  is identified as a gap formed between pole  34  and magnetized member  21 . Pole element  34  is formed so that the dimension of the gap along the overall length direction of the valve rod is constant. 
     In this valve driving apparatus, when current is not supplied to electromagnetic coil  38 , the magnetic resistance of magnetic gaps  39  and  40  is greater than the magnetic force of magnetized members  21  and  22 . Therefore, magnetized members  21  and  22  are positioned to a predetermined position offset in the direction B, in the figure, together with valve rod  12 , so that a magnetic path is circumferentially formed in the following sequence: the N pole of magnetized member  21 , magnetic pole member  35 , core  37 , yoke  31 , magnetic pole member  36 , the S pole of magnetized member  22 , the N pole of magnetized member  22 , yoke  32 , and S pole of magnetized member  21 . In the case of the valve driving apparatus shown in FIG. 8, this position becomes a reference position and when current is not supplied to electromagnetic coil  38 , valve rod  12  is always set to this reference position. 
     However, when current is supplied to electromagnetic coil  38 , magnetic flux passes through both gaps  39  and  40 . Therefore, magnetized members  21  and  22  move in the direction A, shown in the figure, together with valve rod  12 , so that a magnetic path is circumferentially formed in the following sequence: the N pole of magnetized member  21 , magnetic gap  40 , pole member  34 , yoke  31 , magnetic gap  39 , yoke  31 , core  37 , magnetic pole member  35 , the S pole of magnetized member  22 , the N pole of magnetized member  22 , yoke  32 , and the S pole of magnetized member  21 . A second sequence is: the N pole of magnetized member  21 , magnetic gap  40 , pole member  34 , yoke  31 , magnetic gap  39 , yoke  31 , magnetic pole member  36 , the S pole of magnetized member  22 , the N pole of magnetized member  22 , yoke  32 , and the S pole of magnetized member  21 . 
     Further, when current supplied to electromagnetic coil  38  is increased, magnetized members  21  and  22  move in the direction A in the figure, together with valve rod  12 , so that a magnetic path is circumferentially formed solely in the sequence of the N pole of magnetized member  21 , magnetic gap  40 , pole member  34 , yoke  31 , magnetic gap  39 , yoke  31 , core  37 , magnetic pole member  35 , the S pole of magnetized member  22 , the N pole of magnetized member  22 , yoke  32 , and the S pole of magnetized member  21 . 
     As mentioned above, in the valve driving apparatus shown in FIG. 8, when current is not supplied to electromagnetic coil  38 , valve rod  12  is always set to a predetermined position offset in the direction of arrow B as a reference position. However, where magnetic gap  39  is arranged at yoke  31  in a position offset to the pole  36  side from the central line of the core  37  and the magnetic gap  40  is arranged in the lower part of pole  36 , when current is not supplied to electromagnetic coil  38 , valve rod  12  is always set to a predetermined position offset in the direction of arrow A as reference position. By changing the location of magnetic gaps  39  and  40 , one may select the reference position to be either a position offset in the direction of arrow A (valve open position, for example) or a position offset in the direction of arrow B (valve close position, for example). 
     When varying the gap size of magnetic gaps  39  and  40 , the magnitude of magnetic resistance of magnetic gaps  39  and  40  also varies. Furthermore, the magnitude of magnetic resistance of magnetic gap  40  changes as magnetized members  21  and  22  move with valve rod  12 . Therefore, when magnetic gaps  39  and  40  are changed, even when the magnitude of the current supplied to electromagnetic coil  38  is the same, the formed flux density of the magnetic flux and transformation of the flux density varies. This enables one to establish the required driving force magnitude or driving force transformation rate of the valve rod  12  and magnetized members  21  and  22 . 
     In the aforesaid embodiment, among the plurality of poles positioned in parallel along the lengthwise direction of the valve rod, an example is shown wherein a magnetic gap  40  is arranged at the lower portion of the extreme outer side pole. However, the magnetic gap may be arranged at location of any of the other poles. Also, the magnetic gap dimension (the gap dimension between the valve rod and the pole or gap dimension between the magnetized member and the pole) of the disclosed embodiment is substantially uniform along the lengthwise direction of the valve rod, but the gap may be configured to vary. 
     FIG. 9 shows a valve driving apparatus of the fifth embodiment of the present invention. Components which correspond to components shown in FIGS. 1,  6 ,  7  and  8  are given the same reference numbers. 
     Yoke  71  of actuator  70  is configured to be U shaped and at the inner wall of the leg of the yoke  71 , two poles  72  and  73  are set facing each other. Valve rod  15 , having a rectangular cross section, is arranged at gap  74  of poles  72  and  73  so that it may slide along the lengthwise direction. In like manner as the valve rod  12  shown in FIG. 2, in the through hole (not shown) arranged in valve rod  15 , a magnetic pole is provided such that the N pole of magnetized member  21  faces pole  72  and the S pole of magnetized member  21  faces pole  73 . In the gap  74 , a magnetic field region is formed in the neighborhood of poles  72  and  73  and magnetized member  21  is arranged to correspond with the magnetic field region. Surrounding the trunk of yoke  71 , there is arranged a fixed frame  23  comprising nonmagnetic material such as resin. Along the side wall portion of fixed frame  23 , there is wound electromagnetic coil  38  to surround the trunk of yoke  71 . Electromagnetic coil  38  is connected to current source which is not shown and the current source supplies driving current to the electromagnetic coil  38 , wherein the polarity of the current corresponds to either the valve closing direction or the valve opening direction of valve  11 . Furthermore, yokes  75  and  76 , which are additional magnetic path members, are arranged to sandwich valve rod  15 . The N pole of magnetized member  21  faces yoke  75  and the S pole of magnetized member  21  faces yoke  76 . As shown in FIG. 10, the cross sections of both yokes  75  and  76  are configured to be U-shaped and leg portions of yoke  75  and  76  are arranged so that they are opposed to each other. Also, between the legs of yoke  75  and  76 , magnetic gaps  77  and  78  are arranged. 
     When current is not supplied to electromagnetic coil  38 , magnetized member  21  is positioned at a predetermined position together with valve rod  15  so that a magnetic path is circumferentially formed in the following sequence: the N pole of magnetized member  21 , magnetic pole member  72 , yoke  71 , magnetic pole member  73  and the S pole of magnetized member  21 . 
     When current is supplied to electromagnetic coil  38 , magnetic flux is generated in yoke  71  and a magnetic dipole is generated on the surface of both magnetic pole members  72  and  73 . For example, when direct current in a predetermined direction is supplied to electromagnetic coil  38 , a pole of N polarity is created at magnetic pole member  72  and a pole of S polarity is created at magnetic pole member  73 . When direct current in a direction opposed to the predetermined direction is supplied to electromagnetic coil  38 , the S polarity pole is created at magnetic pole member  72  and the N polarity pole is created at magnetic pole member  73 . 
     In the case where the N pole is created at magnetic pole member  72  and the S pole is created at magnetic pole member  73 , as shown by two dotted line arrows in FIG. 10, new magnetic paths are circumferentially formed in the following sequence: the N pole of magnetized member  21 , yoke  75 , magnetic gap  77 , yoke  76 , the S pole of magnetized member  21 . A second sequence is: the N pole of magnetized member  21 , yoke  75 , magnetic gap  78 , yoke  76  and the S pole of magnetized member  21  so that magnetized member  21  moves in the direction of arrow A, shown in FIGS. 9 and 10, together with the valve rod  15  according to the magnitude of the magnetic flux density generated in yoke  71 . To the contrary, when the S pole is created at magnetic pole member  72  and the N pole is created at magnetic pole member  73 , the two magnetic paths are extinguished so that magnetized member  21  moves to the direction of arrow B together with the valve rod  15  according to the magnitude of the magnetic flux density generated in yoke  71 . 
     FIGS. 11 and 12 show a valve driving apparatus of the sixth embodiment of the present invention. Components which correspond to components shown in FIGS. 1,  6 ,  7 ,  8  and  9  are given the same reference numbers. Also, FIG. 12 shows the valve driving apparatus shown in FIG. 11 in which upper frames  81  and  81 ′, lower frame  88  and coil  38  are omitted. 
     Upper frame  81 , which is a second supporting member, is configured in a U-shape form with top portion  82  and two legs  83 . In the middle of the legs  83  is a bracket member  84  connecting the two legs. Upper frame  81 ′ also has a structure similar to upper frame  81 . 
     The upper frames  81  and  81 ′ have supporting protrusions (not shown) which support yoke  31 . The yoke  31  is provided with supporting holes (not shown) which correspond to the supporting protrusions. By coupling the supporting protrusions and supporting holes the frame is assembled and yoke  31  can be held in a predetermined position between the upper frames  81  and  81 ′. Also, when upper frames  81  and  81 ′ are assembled to the yoke  31 , the winding  38  which is wound around core  37  inside the yoke  31  is placed inside the opening formed by the top portions of upper frames  81  and  81 ′, leg portions  83  and bracket member  84 . 
     As will be discussed later, moving element  91 , which is a supporting body of a magnetized member, is arranged between poles  34  and  36  of yoke  31  and pole  35  of core  37  to provide a gap as shown in FIG.  12 . Furthermore, the moving element  91  is arranged to also form a gap between the yoke  32 , which is an independent magnetic path member. These gaps are retained by rollers  101  and  102 , and  103  and  104  (FIG.  16 ). At an end of moving element  91 , lock member  92  is provided. As mentioned later, lock member  92  has a locking hole  93  and a valve rod supporting groove  94 . At an end of valve rod  12 , there is an enlarged diameter portion  16  which is fit into the locking hole  93 . Valve rod  12  has a valve element  11 . By supplying current to coil  38  to operate the moving element, valve element  11  may be moved in the direction of arrow A (valve opening direction, for example) or in the direction of arrow B (valve closing direction, for example), as shown in the figure. 
     As shown in FIG. 14, to be discussed later, lower frames  88  and  88 ′, which are a first holding member, have supporting protrusions to support yoke  32 , and yoke  32  is arranged with supporting holes (not shown in the figure) in positions corresponding to the supporting protrusions. By coupling supporting protrusions and supporting holes thereby assembling the frame, yoke  32  can be held in a predetermined position between the lower frames  88  and  88 ′. Lower frames  88  and  88 ′ are arranged such that the length in the lengthwise direction is about the same as the distance between the legs  83  or  83 ′ of the upper frames  81  or  81 ′. In the above structure, as shown in FIG. 11, by arranging the lower frame  88  between the two legs  83  of upper frame  81  and the lower frame  88 ′ between the two legs  83 ′ of upper frame  81 ′, yoke  32  may be positioned such that it does not move in either the valve opening direction or the valve closing direction. 
     The upper frames  81  and  81 ′, which are a second holding member, may have support holes (not shown) to fasten the valve driving apparatus to a predetermined location of an internal combustion engine. 
     FIG. 13 shows the upper frame viewed from below. Components which correspond to components shown in FIGS. 11 and 12 are given the same reference numbers. 
     As discussed above, the upper frame  81  has a bracket member  84  which connects the two leg  83 . At the underneath surface of this bracket member  84 , guide grooves  85  and  86  are formed so that the movement of second locking members, that is, rollers  103  and  104  (not shown in the figure) are guided, respectively, as will be discussed later. This guide groove, as a second guide groove, has a rectangular aperture, and its sectional configuration is also rectangular. Since this guide groove is formed underneath the bracket member  84 , when the frame is assembled to form a valve driving apparatus as shown in FIG. 11, the guiding groove faces the moving element  91 . Furthermore, rollers  103  and  104  roll freely in the guide grooves  85  and  86  in their lengthwise direction to form a width dimension of the guide grooves substantially identical to the overall length of the roller. The guide groove is formed so that the dimension of the depth of the guide groove is less than the diameter of the roller. Furthermore, the guide groove is formed such that the overall length of the guide groove corresponds to the moving distance of the moving element. The upper frame  81 ′ is structured in a same manner as the upper frame  81 . 
     FIG. 14 shows yoke  32  supported between lower frames  88  and  88 ′. Components which correspond to components shown in FIGS. 11 and 12 are numbered in the same manner. 
     The lower frame  88 , which is the first supporting member, is supported between two legs  83  of the upper frame  81  such that the dimension of the lower frame  88  in the lengthwise direction is substantially equal to the distance between the two legs  83 . On the top surface of the lower frame  88 , first guide grooves  89  and  90  are formed. The configuration of these guide grooves  89  and  90  is substantially the same as that of guide grooves  85  and  86 . Rollers  101  and  102 , as a first engaging member (not shown) may roll freely in the lengthwise direction of the guide grooves  89  and  90 . The lower frame  88 ′ is structured in the same manner as the lower frame  88  and guide grooves  89 ′ and  90 ′ are formed in its upper surface. 
     FIG. 15 shows the magnetized members and the moving element. Components which correspond to components shown in FIGS. 11 and 12 are given the same reference numbers. 
     The moving element  91  supports the magnetic members, and two magnetized members  21  and  22 , e.g., permanent magnets, are inserted and fixed in the moving element so that the top and bottom surfaces of the magnetized members align with the top and bottom surfaces of the moving element  91 . On the sides of moving element  91 , protrusions  95  and  95 ′ are arranged to protrude in a direction lateral to the length of the moving element  91 . At the underneath surface of protrusions  95 , lower engaging surfaces  96  are provided which respectively engage with rollers  101  and  102  (not shown), whereas at the upper surfaces of protrusion  95 , upper engaging surfaces  98  are provided which respectively engage with rollers  103  and  104  (not shown). Further, underneath the protrusion  95  and at the lateral side of moving element  91 , there is arranged an engaging surface  97  to engage with the circular end of rollers  101  and  102 , and above the protrusion  95  and at the side of moving element  91 , there is arranged an engaging surface  99  to engage with the circular end of rollers  103  and  104 . With regard to protrusion  95 ′, lower engaging surfaces  96 ′ (not shown), upper engaging surfaces  98 ′, engaging surface  97 ′, and engaging surface  99 ′ (not shown) are also arranged in the same manner as with protrusion  95 . 
     FIG. 16 is a perspective view which shows the state of the rollers engaging with the guide grooves and the protrusion of the lower frame. FIG. 17 is a sectional view along line X—X, shown in FIG.  11 . FIG. 18 is a sectional view along line Y—Y, shown in FIG.  11 . Components which correspond to components shown in FIGS. 11,  14  and  15  are given the same reference numbers. 
     Each of the rollers  101  and  102 , which are the first engaging members, and each of the rollers  103  and  104 , which are the second engaging members, are cylindrically configured and have a barrel shape surface and two circular end surfaces. In the following description, a circular end surface faces engaging side face  97  or  99  of the moving element  91  at the inner end surface, and a circular end surface faces in a direction opposed to the engaging side face  97  or  99  at the outer end surface. 
     Referring to FIGS. 16 and 17, the roller  101  is arranged in guide groove  89  of the lower frame  88 , roller  102  is arranged in guide groove  90  of the lower frame  88 , roller  103  is arranged in guide groove  85  of upper frame  81  and roller  104  is arranged in guide groove  86  of upper frame  81 . As discussed above, the guide groove is formed so that the width of the groove is substantially equal to the length of the rollers, and by employing such a configuration, when the rollers rotate in the guide groove, the inner end surface and the outer end surface engages with the guide groove sidewall surfaces, respectively, as shown in FIG. 18, allowing the roller to move only in the lengthwise direction of the guide groove. As shown in FIGS. 16,  17  and  18 , moving element  91  is arranged such that lower engaging surface  96  of the moving element  91  is capable of engaging with the barrel surface of rollers  101  and  102 . Engaging side face  97  of the moving element  91  is capable of engaging with the inner end surfaces of rollers  101  and  102 . Furthermore, moving element  91  is arranged such that upper engaging surface  98  of the moving element  91  is capable of engaging with the barrel surface of rollers  103  and  104 . Engaging side face  99  of the moving element  91  is capable of engaging with the inner end surfaces of rollers  103  and  104 . 
     As shown in FIG. 18, guide groves  85 ′,  86 ′,  89 ′ and  90 ′ are also configured in the same manner. Rollers  101 ′,  102 ′,  103 ′ and  104 ′ are also configured in the same manner as rollers  101  to  104 . Finally, engaging side faces  97 ′ or  99 ′, lower engaging surface  96 ′ and upper engaging surface  98 ′ are configured in the same manner as the above-mentioned counterparts. 
     By employing the above-mentioned configuration, when current is applied to the electromagnetic coil shown in FIG. 11 it forms a circumferential magnetic path in the following sequence: core  37 , yoke  31 , magnetized members  21  and  22 , and yoke  32  to move the moving element  91 . Then as shown in FIG. 18, engaging side face  97  of the moving element  91  engages with the inner end surfaces of rollers  101  and  102 , engaging side face  99  of the moving element  91  engages with the inner end surfaces of rollers  103  and  104 , engaging side face  97 ′ of the moving element  91  engages with the inner end surfaces of rollers  101 ′ and  102 ′ and engaging side face  99 ′ of the moving element  91  engages with the inner end surfaces of rollers  103 ′ and  104 ′ to slide the moving element  91 . 
     By employing the configuration shown in FIGS. 16,  17  and  18 , every roller moves with the guidance of the guide grooves and the moving element  91  slides with the guidance of each of inner end surfaces of rollers. 
     The rollers  101  to  104  and  101 ′ to  104 ′ allow smooth movement of the moving element  91  in the desired direction. As shown in FIG.  17 , these rollers also function to determine the distance between the moving element  91  and upper frames  81  and  81 ′ as well as between the moving element  91  and lower frames  88  and  88 ′. Furthermore, as discussed above, upper frames  81  and  81 ′ support the yoke  21  and the core  37  and lower frames  88  and  88 ′ support the yoke  32  so that rollers  101  to  104  and  101 ′ to  104 ′ determine the gap between magnetized members  21  and  22  and magnetic poles  34 ,  35  and  36  as well as the gap between magnetized members  21  and  22  and the yoke  32 . 
     Magnetic force generated from the magnetic flux of magnetized members  21  and  22  draws the magnetized members  21  and  22  in the direction of yoke  21  and core  37  and also draws yoke  32  in the direction of the magnetized members  21  and  22 . Due to this magnetic force, as shown in FIG. 11 where the lower frame  88  is arranged between two legs  83  of the upper frame  81  and lower frame  88 ′ is arranged between two legs  83 ′ of the upper frame  81 ′, no supporting member is required to hold the yoke  32  towards the yoke  31 (in the upper direction in FIG.  11 ), and yoke  32  and lower frame  88  and  88 ′ may be supported towards the yoke  31 . 
     In the foregoing embodiment, cylindrical rollers  101  to  104  and  101 ′ to  104 ′ were characterized as the first engaging member and the second engaging member. However, as shown in FIG. 19, spheroid elements  111  to  114  may be provided. In this case, by configuring the cross sections of first guide groove  121  and  122  and the second guide groove (not shown) to a V shape, spheroid elements  111  to  114  may be securely engaged to the first guide groove and the second guide groove. 
     FIG. 20 shows a lock member of the moving element and a valve element. 
     Valve head  11  of the valve element  10  is circular when viewed from the front and the valve head  11  is connected to the end of the valve rod  12  to form a uniform member. At the other end of the valve rod  12 , there is an enlarged diameter element  16  having a diameter greater than the valve rod  12 . 
     Referring to lock member  92  fixed at the moving element  91 , a locking hole  93  is formed with a rectangular aperture and a rectangular sectional configuration. In a front portion of the lock member  92 , there is a supporting groove  94  having a U-shaped cross section, viewed from the surface of the lock member  92  towards the locking hole  93 . 
     When inserting the enlarged diameter portion  16  into the locking hole  93  to assemble the valve element  10  to the moving element  91 , the side face of locking hole  93  engages with the barrel surface and circular end surface of the enlarged diameter portion  16  and the support groove engages with the barrel surface of the valve rod  12  to support the valve element  10  to the lock member  92 . By employing such a structure, valve element  10  may be easily and accurately installed to the moving element  91 . Furthermore, when locking hole  93  is designed according to the configuration of the conventional valve element, the conventional valve element may be assembled to the valve driving apparatus disclosed in the sixth embodiment without adding any modification to the valve element. 
     In the foregoing embodiment, the end portion of valve rod  12  is shown as having an enlarged diameter portion  16  of cylinder shape, but the end portion may be formed differently, such as a spherical body. Also, the aperture configuration of the locking hole  93  may be another polygonal shape other than rectangular. 
     As described above, the valve driving apparatus according to the present invention allows to simplification of the configuration of the apparatus, reducing valve seating impact and precisely controlling the valve element.