Abstract:
A valve stopping mechanism wherein when hydraulic fluid pressure is low a cylinder operating state is set and a response of a switch from a cylinder stop state to the cylinder operating state is high. An intake valve and an exhaust valve, a first intake valve spring and a first exhaust valve spring are provided for energizing the valves in the direction of closing the valves, valve drive cams, valve stopping mechanisms, on the basis of a stop hydraulic fluid pressure and energization of plunger springs, for selectively generating valve operating and valve stop states. The valve stopping mechanism generates the operating state when the energizing force of the plunger spring is larger than the press force of the stop hydraulic fluid pressure and generates the stop state when the press force of the stop hydraulic fluid pressure is larger than the energizing force of the plunger spring.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims priority under 35 USC 119 to Japanese Patent Application No. 2007-047560 filed on Feb. 27, 2007 the entire contents of which are hereby incorporated by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to an engine having a valve stopping mechanism capable of stopping operation of intake/exhaust valves for opening/closing a communication part between an engine cylinder chamber and an intake or exhaust path. 
         [0004]    2. Description of Background Art 
         [0005]    An engine is known having a valve stopping mechanism for stopping the operation of a part or all of intake/exhaust valves in a state where a valve drive cam rotates in accordance with an operating state of the engine. 
         [0006]    As such a valve stopping mechanism, there is a configuration disclosed in JP-A No. H10-184327 wherein the valve stopping mechanism includes a lifter  11   a  which is reciprocated in a valve opening/closing direction by a valve drive cam  7 , a lifter spring  24  for energizing the lifter  11   a  so that the lifter  11   a  abuts on the valve drive cam  7 , and a plunger  23  sliding in a cylinder hole  21   a  formed extending at the right angle with the opening/closing direction in the lifter. In the plunger  23 , a through hole  23   b  in which a valve shaft  5   a  of an exhaust valve  5  can be inserted and a power transmission face  23   g  on which the tip of the valve shaft  5   a  abuts are formed. 
         [0007]    In the valve stopping mechanism, when the lifter  11   a  is reciprocated by the valve drive cam  7  in a state where the plunger  23  energized by the plunger spring  25  is moved to a stop position, the valve shaft  5   a  is inserted in a through hole  23   a,  and the exhaust valve  5  is held closed irrespective of the reciprocating movement of the lifter  11   a,  thereby obtaining a cylinder stop state. On the other hand, when the plunger  23  receives hydraulic fluid pressure on the side opposite to the plunger spring  25 , the plunger  23  moves to the operating position against energization of the plunger spring  25 . In this state, when the lifter  11   a  is reciprocated by the valve drive cam  7 , the valve shaft  5   a  abuts on the power transmission face  23   g  and is reciprocated together with the lifter  11   a,  and the exhaust valve  5  is opened/closed, thereby obtaining a cylinder operating state. 
         [0008]    In such a related valve stopping mechanism, the plunger  23  moves to the stop position by being energized by the plunger spring  25  and moves to the operating position by receiving hydraulic fluid from the opposite side. With this configuration, on start of an engine or the like, it takes time for the hydraulic fluid to become larger than the energizing force of the plunger spring. During the time, the valve is not opened/closed, and the cylinder stop state is obtained. Consequently, there is a problem such that it is difficult to obtain a sufficiently large engine output. To be concrete, for example, in the case of driving a hydraulic pump by an engine and generating the hydraulic fluid from a discharge of the hydraulic pump, when the engine is operated at very low speed on start of the engine or the like, it takes time for the hydraulic fluid to become large. During the time, the cylinder stop state is obtained. There is a problem such that it is difficult to increase an engine output. 
         [0009]    To improve the steering feel for the driver, it is also requested to promptly switch from a valve stop state to a valve operating state by hydraulic control in response to a request for increasing an engine output of the driver, that is, to promptly switch from a cylinder stop state (state where the valve stops and the cylinder does not operate) to a cylinder operating state (state where the valve is opened/closed and the cylinder operates). 
       SUMMARY AND OBJECTS OF THE INVENTION 
       [0010]    According to an embodiment of the present invention, an engine having a valve stopping mechanism capable of setting a cylinder operating state by opening/closing a valve in accordance with rotation of a crankshaft when hydraulic fluid is low at the time of start of an engine or the like is provided wherein an excellent response of switch from a cylinder stop state to the cylinder operating state is realized. 
         [0011]    According to an embodiment of the present invention, an engine includes an intake valve  20  and an exhaust valve  30  provided for a cylinder head of the engine. A valve energizing member, for example, a first intake valve spring  24   a  and a first exhaust valve spring  34   a  are provided for energizing the valve in the direction of closing the valve. A valve drive cam is rotated in correspondence with rotation of a crankshaft of the engine. A valve stopping mechanism is provided between the valve drive cam and the valve and, on the basis of a stop hydraulic fluid pressure supplied from the outside and an operation energizing member, for example, plunger springs  47  and  57 , for generating an energizing force against the stop hydraulic fluid pressure, selectively generating an operating state of opening/closing the valve in response to an operation of the valve drive cam and a stop state of holding the valve in a valve closing position irrespective of the operation of the valve drive cam. A stop hydraulic fluid pressure supply controller is provided for controlling supply of the stop hydraulic fluid pressure. The valve stopping mechanism generates the operating state when the energizing force of the operation energizing member is larger than the press force of the stop hydraulic fluid pressure, and generates the stop state when the press force of the stop hydraulic fluid pressure is larger than the energizing force of the operation energizing member The stop hydraulic fluid pressure supply controller includes a switching member, for example, a spool valve  85 , which can be moved between a hydraulic fluid supply position in which a pressure source path is connected to a pressure source for supplying the stop hydraulic fluid pressure and a stop pressure supply path for supplying the stop hydraulic fluid pressure to the valve stopping mechanism are communicated with each other. A hydraulic fluid discharging position for closing the pressure source path and making the stop pressure supply path communicate with the drain side is provided together with a switching energizing member, for example, a spool spring  86 , for energizing the switching member to move to the hydraulic fluid supply position side. A switching pressure supply control mechanism, for example, a solenoid mechanism  90 , applies a pressure force to move the switching member to the hydraulic fluid discharge position side. 
         [0012]    In the engine having such a configuration, preferably, the switching pressure supply control mechanism is constructed by a solenoid valve and, when a solenoid is energized, applies the pressure force to move the switching member to the hydraulic fluid discharge position side. 
         [0013]    In the engine, preferably the valve stopping mechanism includes a holder, for example, plunger holders  41  and  51 , reciprocated in the direction of opening/closing the valve by the valve drive cam. A stop selecting member, for example, stop selecting plungers  45  and  55 , is provided in the holder that is capable of moving between an operating position to open/close the valve in accordance with a reciprocating operation of the holder and a stop position to hold the valve in a valve close position irrespective of the reciprocating operation of the holder. The operation energizing member energizes the stop selecting member to the operation position side, and the stop selecting member which receives the stop hydraulic fluid pressure is pressed to the stop position side against the energizing force of the energizing member. 
         [0014]    In this case, preferably, the valve includes a valve body for opening/closing the communication part and a valve stem connected to the valve body and extending toward the valve stopping mechanism. The tip of the valve stem passes through the holder and faces the stop selecting member. In the stop selecting member, a stem abutment face and a stem receiving part are formed. When the stop selecting member is in the operating position, the stem abutment face abuts on the tip of the valve stem and moves the valve in the open/close direction together with the holder. When the stop selecting member is in the stop position, the tip of the valve stem is fit in the stem receiving part, and the stem receiving part moves the holder but maintains the valve closed. The stem abutment face and the stem receiving part are formed adjacent to each other in the direction of moving the stop selecting member, and the stop hydraulic fluid pressure is received on the side opposite to the stem abutment face in the direction of moving the stop selecting member while sandwiching the stem receiving part. 
         [0015]    Further, preferably, in the stop selecting member, an energizing member housing part for housing the operation energizing member is formed on the same side as the side on which the stem abutment face is formed in the movement direction of the stop selecting member, and a stem communication hole via which the energizing member housing part and the stem housing part communicate with each other is provided in a position overlapping the stem abutment face in the movement direction. 
         [0016]    In the engine having the configuration, the holder may be pressed via a rocker arm which swings by being pressed by the valve drive cam, and reciprocate in the direction of opening/closing the valve. The holder may be disposed in a bottomed cylindrical valve lifter, thereby constructing the valve stopping mechanism, and the valve lifter may be pressed by the valve drive cam so as to reciprocate in the direction of opening/closing the valve together with the holder. 
         [0017]    With the engine of the present invention, the valve stopping mechanism is constructed to generate the operating state when the energizing force of the operation energizing member is larger than the press force of the stop hydraulic fluid pressure, and generates the stop state when the press force of the stop hydraulic fluid pressure is larger than the energizing force of the operation energizing member. When the engine is operated at very low speed at the time of start of the engine or the like and the stop hydraulic fluid pressure is low, a valve operating state is generated, and a cylinder operating state is obtained. Consequently, a large engine output can be obtained with reliability as a cylinder operating state upon the start of the engine. 
         [0018]    In the stop hydraulic fluid pressure supply controller, the switching member is moved to the hydraulic fluid supply position side by the energizing force of the switching energizing member, and the pressure force is applied from the switching pressure supply control mechanism to move the hydraulic fluid discharge position side. Consequently, at the time of switching the cylinder stop state to the cylinder operating state, the pressure force is applied from the switching pressure supply control mechanism and a control of moving the switching member to the hydraulic fluid discharge position is performed. Since the control of forcedly moving the switching member by using the pressure force is performed, a control of promptly moving the switching member to the hydraulic fluid discharge position can be performed, and the response of a switch from the cylinder stop state to the cylinder operating state can be improved. Consequently, in the case such that the driver performs an operation of opening the throttle in the cylinder operating state, the state is promptly switched to the cylinder operating state, and the response to a request for increasing an engine output can be improved. 
         [0019]    In the engine, preferably, the switching pressure supply control mechanism is constructed by a solenoid valve and, when a solenoid is energized, a control of applying the pressure force so as to move the switching member to the hydraulic fluid discharge position side is performed. With this configuration, the cylinder operating state and the cylinder stop state can be easily switched by the control of passing current to the solenoid. 
         [0020]    In the engine, preferably, the valve stopping mechanism includes a holder reciprocated by the valve drive cam and a stop selecting member capable of moving between an operating position to open/close the valve in accordance with the reciprocating operation of the holder and a stop position to hold the valve in a valve close position irrespective of the reciprocating operation of the holder. The operation energizing member energizes the stop selecting member to the operation position side, and the stop selecting member which receives the stop hydraulic fluid pressure is pressed to the stop position side against the energizing force of the energizing member. With such a configuration, the operation control of setting the valve stopping mechanism in the stop position or the operating position on the basis of the balance between the energizing member and the stop hydraulic fluid pressure can be performed easily and reliably. 
         [0021]    In this case, in the stop selecting member, a stem abutment face and a stem receiving part are formed. When the stop selecting member is in the operating position, the stem abutment face abuts on the tip of the valve stem and moves the valve in the open/close direction together with the holder. When the stop selecting member is in the stop position, the tip of the valve stem is fit in the stem receiving part, and the stem receiving part moves the holder but maintains the valve closed. The stem abutment face and the stem receiving part are formed adjacent to each other, and the stop hydraulic fluid pressure is received on the side opposite to the stem abutment face. With this configuration, in the stop selecting member, the stem abutment face for receiving the press force from the valve stem and the portion for receiving the stop hydraulic fluid pressure are apart from each other via the stem receiving part. Consequently, the influence of the press force acting from the valve stem to the stem abutment face, exerted on the part of receiving the stop hydraulic fluid pressure is suppressed. Therefore, deformation of the portion for receiving the stop hydraulic fluid pressure is small, the sealing performance of the portion is maintained excellent, and durability can be improved. 
         [0022]    Further, in the stop selecting member, when the energizing member housing part is formed on the same side as the side on which the stem abutment face is formed, and a stem communication hole is provided in a position overlapping the stem abutment face, the stem communication hole becomes longer, the weight of the stop selecting member can be reduced by that amount, and response at the time of moving the stop selecting member improves. Thus, the weight of the whole valve stop mechanism is reduced. 
         [0023]    The configuration can be applied to the valve opening/closing mechanism of the rocker arm driving type in which the holder is reciprocated via a rocker arm. The configuration can be also applied to a valve opening/closing mechanism of a cam direct driving type in which a holder is disposed in a valve lifter and the valve lifter is pressed by a valve drive cam and is reciprocated. 
         [0024]    Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]    The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein: 
           [0026]      FIG. 1  is a cross section showing the structure of a peripheral portion of a cylinder head in an engine to which the present invention is applied; 
           [0027]      FIG. 2  is a cross section showing the structure of a peripheral portion of an exhaust valve stopping mechanism in the engine; 
           [0028]      FIG. 3  is a cross section showing the structure of a peripheral portion of the exhaust valve stopping mechanism in the engine; 
           [0029]      FIG. 4  is an exploded perspective view of members constructing the exhaust valve stopping mechanism; 
           [0030]      FIG. 5  is a cross section showing the structure of a peripheral portion of the exhaust valve stopping mechanism in the engine; 
           [0031]      FIG. 6  is a cross section showing the structure of a peripheral portion of the exhaust valve stopping mechanism in the engine; 
           [0032]      FIG. 7  is a cross section showing the configuration of a stop hydraulic fluid pressure supplying device; 
           [0033]      FIG. 8  is a cross section showing the configuration of the stop hydraulic fluid pressure supplying device; 
           [0034]      FIG. 9  is a cross section showing the structure of a peripheral portion of an intake valve stopping mechanism in the engine; and 
           [0035]      FIG. 10  is a cross section showing the structure of a peripheral portion of the intake valve stopping mechanism in the engine. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0036]    Preferred embodiments of the present invention will be described hereinbelow with reference to the drawings.  FIG. 1  shows a structure of a portion of a cylinder head in a four-stroke engine E to which the present invention is applied. The engine E is a multi-cylinder engine, and a cross section of only one of the cylinders is shown. A piston  2  is slidably disposed in a cylinder hole  1   a  of a cylinder block  1  as a component of the cylinder. The piston  2  is coupled to an engine crankshaft via a connecting rod to rotate the engine crankshaft in accordance with reciprocation of the piston  2 . Since the configuration is not directly related to the present invention and is a known one, it will not be described. 
         [0037]    A cylinder head  10  is coupled to the top face of the cylinder block  1 . In a state where the cylinder head  10  is attached, a combustion chamber  3  is formed in a portion surrounded by the cylinder hole  1   a  and facing the top face of the piston  2 . An intake path  11  and an exhaust path  12  that communicate with the combustion chamber  3  are formed in the cylinder head  10 . In the communication part among the intake path  11 , the exhaust path  12 , and the combustion chamber  3 , an intake valve  20  and an exhaust valve  30  for opening/closing an intake port  11   a  and an exhaust port  12   a  forming the communication part are provided. 
         [0038]    The intake valve  20  has a valve body  21  openably closing the intake port  11   a  and a rod-shaped valve stem  22  connected integrally with the valve body  21  and extending therefrom. The valve stem  22  is slidably guided by a cylindrical stem guide  23  attached to the cylinder head  10 , and the intake valve  20  is slidable in the extension direction of the valve stem  22 . The tip of the valve stem  22  is energized in the valve closing direction (upward direction in the diagram) by a first intake valve spring (valve energizing member)  24   a  via a retainer  25 . In a free state, the valve body  21  closes the intake port  11   a.    
         [0039]    Similarly, the exhaust valve  30  has a valve body  31  openably closing the exhaust port  12   a  and a rod-shaped valve stem  32  connected integrally with the valve body  31  and extending therefrom. The valve stem  32  is slidably guided by a cylindrical stem guide  33  attached to the cylinder head  10 , and the exhaust valve  30  is movable in the extension direction of the valve stem  32 . The tip of the valve stem  32  is energized in the valve closing direction (upward direction in the diagram) by a first exhaust valve spring (valve energizing member)  34   a  via a retainer  35 . In a free state, the valve body  31  closes the exhaust port  12   a.    
         [0040]    In the cylinder head  10 , a guide hole  13 , extending coaxially from the attachment part of the stem guide  23  for the intake valve  20  to the upper side (outside), is formed so as to penetrate to the top face side. An intake valve stopping mechanism  40  is disposed slidable in the axial direction in the guide hole  13 . On the top face side of the cylinder head  10 , a camshaft  6  is disposed so as to extend in the crankshaft direction (direction perpendicular to the drawing face), and an intake valve drive cam  8  provided for the camshaft  6  faces the top end of the intake valve stopping mechanism  40  (refer to  FIGS. 9 and 10 ). The intake valve stopping mechanism  40  is energized to the camshaft direction (toward the upper side in the drawing) by a second intake valve spring  24   b  disposed in the guide hole  13 , and the upper end face of the intake valve stopping mechanism  40  is in contact with cam faces  8   a  and  8   b  of the intake valve drive cam  8 . 
         [0041]    Similarly, a guide hole  14  extending coaxially from the attachment part of the stem guide  33  for the exhaust valve  30  to the upper side (outside) is formed so as to penetrate to the top face side. An exhaust valve stopping mechanism  50  is disposed slidable in the axial direction in the guide hole  14 . On the top face side of the cylinder head  10 , a rocker arm mechanism  70  having a rocker arm  72  slidably supported by a supporting shaft  71  so as to extend in the crankshaft direction (direction perpendicular to the drawing face) is provided. A cam follower  73  is rotatably attached to one end (right end)  72   a  of the rocker arm  72 , and the cam follower  73  abuts on cam faces  7   a  and  7   b  of an exhaust valve drive cam  7  provided for the camshaft  6 . A press member  74  is attached to the other end  72   b  of the rocker arm  72 , and the lower end of the press member  74  faces the upper end of the exhaust valve stopping mechanism  50 . The press member  74  is screwed in the other end  72   b  of the rocker arm  72 . By adjusting the screw amount, the amount of downward projection can be adjusted. Consequently, a groove  74   a  to which a driver or the like is inserted is formed in the upper end of the press member  74 . 
         [0042]    The exhaust valve stopping mechanism  50  is energized toward the rocker arm side (toward the upper side in the drawing) by a second exhaust valve spring  34   b  disposed in the guide hole  14 , and the upper end face of the exhaust valve stopping mechanism  50  is in contact with the press member  74  to press the press member  74  upward, and the rocker arm  72  is energized so as to swing clockwise in the diagram, thereby making the cam follower  73  abut on the cam faces  7   a  and  7   b  of the exhaust valve drive cam  7 . 
         [0043]    A cylinder head cover  5  is coupled to the top face of the cylinder head  10  so as to cover the cam shaft  6 , the rocker ram mechanism  70 , and the like. Although not shown, a spark plug facing the combustion chamber  3  is attached to the cylinder head  10 , and an intake pipe connected to the intake path  11  and an exhaust pipe connected to the exhaust path  12  are attached to the cylinder head  10 . To the intake pipe, an air cleaner, a throttle valve, a fuel injection valve, and the like are attached, with the air-fuel mixture of fuel and air being supplied to the combustion chamber  3  in accordance with the operation of the engine E. Combustion gas generated in the combustion chamber  3  is exhausted from the exhaust passage  12  to the outside via the exhaust pipe. 
         [0044]    In the engine having the above configuration, first, the configuration of opening/closing the exhaust valve  30  via the exhaust valve stopping mechanism  50  by the rocker arm mechanism  70  will be described in detail hereinbelow with reference to  FIGS. 2 to 8 . 
         [0045]    The exhaust valve stopping mechanism  50  has, as shown in  FIG. 4 , a plunger holder  51  whose outer shape is formed cylindrically and slidably fit in the guide hole  14 , a stop selecting plunger  55  is slidably fit in a plunger hole  52   a  that is formed so as to penetrate the plunger holder  51  in the direction orthogonal to the sliding direction of the plunger holder  51 . A plunger spring  57  is provided for energizing the stop selecting plunger  55  to one side in the sliding direction (to the right side in the drawing). In the plunger holder  51 , a holder-side stem receiving hole  52   b  penetrating the plunger holder  51  in the vertical direction in the center of the outer cylindrical shape is formed. A disc-shaped abutment plate  54  covering the holder-side stem receiving hole  52   b  is fixed at the upper end. The size of the holder-side stem receiving hole  52   b  is set larger than the diameter of the end of the valve stem  32  of the exhaust valve  30  so that, as will be described later, the tip of the valve stem  32  can project into the holder-side stem receiving hole  52   b.    
         [0046]    One end of the plunger hole  52   a  formed in the plunger holder  51  is open and the other end is closed. The plunger spring  57  is attached into the plunger hole  52   a  so as to abut on the close wall. After that, the stop selecting plunger  55  is slidably fit in the plunger hole  52   a.  In the stop selecting plunger  55 , a slit  55   c  extending in the radial direction is formed on one end side in the axial direction (the right end side in the diagram). A spring receiving recess  55 d for receiving the plunger spring  57  is formed on the other end side (the left end side in the diagram). Further, a plunger-side stem receiving hole  55   a  extending orthogonally and passing the center of the axis is formed in the center portion in the axial direction. The size of the plunger-side stem receiving hole  55   a  is set larger than the diameter of the end of the valve stem  32  of the exhaust valve  30  so that, as will be described later, the tip of the valve stem  32  can project into the plunger-side stem receiving hole  55   a.  The lower end opening of the plunger-side stem receiving hole  55   a  is cut in a plane, thereby forming a step abutment face  55   b.    
         [0047]    In the plunger holder  51 , further, a pin hole  52   c  is formed that is positioned near the open end of the plunger hole  52   a,  crossing the center of the plunger hole  52   a,  and penetrating in the vertical direction. A stopper pin  53  is fit in the pin hole  52   c.  The stopper pin  53  is fit in the slit  55   c  in the stop selecting plunger  55  fit in the plunger hole  52   a.  The stop selecting plunger  55  is pressed to the right side in the diagram by the plunger spring  57 , and the bottom of the slit  55   c  abuts on the stopper pin  53  and is held in the position shown in  FIG. 2 . In the position, rotation of the stop selecting plunger  55  is regulated by the stopper pin  53 , the stem abutment face  55   b  is positioned on the under face side, and the plunger-side stem receiving hole  55   a  is positioned deviated from the holder-side stem receiving hole  52   b  in the axial direction. The upper end of the valve stem  32  of the exhaust valve  30  closely faces the step abutment face  55   b.  The position of the stop selecting plunger  55  at this time will be called an operating position. 
         [0048]    On the other hand, a ring-shaped hydraulic fluid receiving groove  51   c  is formed in an intermediate portion on the cylindrical peripheral face of the plunger holder  51 . A cylindrical upper guide wall  51   a  and a cylindrical lower guide wall  51   b  are formed with the hydraulic fluid receiving groove  51   c  therebetween. When the plunger holder  51  is fit in the guide hole  14 , the upper and lower guide walls  51   a  and  51   b  arc guided so as to be slidably fit in the guide hole  14 , and the plunger holder  51  can smoothly slide in the guide hole  14 . The plunger hole  52   a  is open to the inside of the hydraulic fluid receiving groove  51   c.    
         [0049]    In the cylinder head  10 , an exhaust valve hydraulic fluid supply path  16  is formed, which supplies exhaust valve stop hydraulic fluid supplied from a stop hydraulic fluid pressure supplying device  80  which will be described later into the hydraulic fluid receiving groove  51   c  in the plunger holder  51 . A front-end fluid passage  16   a  of the exhaust valve hydraulic fluid supply path  16  is open to the inside of the guide hole  14  and is communicated with the hydraulic fluid receiving groove  51   c  in this portion. The plunger holder  51  is pressed by the rocker arm mechanism  70  and slides vertically in the guide hole  14 . When the plunger holder  51  moves upward as shown in  FIG. 2 , and also when the plunger holder  51  moves downward as shown in  FIG. 3 , the hydraulic fluid receiving groove  51   c  at least partially communicates with the front-end fluid passage path  16   a.  The exhaust valve stop hydraulic fluid supplied via the exhaust valve hydraulic fluid supply path  16  is supplied into the hydraulic fluid receiving groove  51   c.  In such a manner, the stop hydraulic fluid supplied into the hydraulic fluid receiving groove  51   c  acts on the right end of the stop selecting plunger  55  to press the stop selecting plunger  55  to the left side. 
         [0050]    Next, a stop hydraulic fluid pressure supplying device  80  for the exhaust valve performs control so as to supply an exhaust valve stop hydraulic fluid pressure to the exhaust valve hydraulic fluid supply path  16 . The stop hydraulic fluid pressure supplying device  80  will be described with reference to  FIGS. 7 and 8 . The stop hydraulic fluid pressure supplying device  80  has a valve body  81 , a spool valve  85  disposed slidably in a spool hole  81   a  formed in the valve body  81 , a plug  87  closing the spool hole  81   a  in which the spool valve  85  is disposed at the left end, a spool spring  86  for energizing the spool valve  85  to the right direction, and a solenoid mechanism  90  attached at the right end of the valve body  81 . 
         [0051]    In the stop hydraulic fluid pressure supplying device  80 , an inlet port  82   a  connected to a stop hydraulic pressure supply source P for supplying the stop hydraulic fluid whose pressure is adjusted to not-shown predetermined hydraulic pressure, an outlet port  82   b  is connected to the exhaust valve hydraulic fluid supply path  16 , and a drain port  82   c  is connected to the drain side are connected to a spool hole  81   a  as shown in the diagram. By performing a control of laterally sliding the spool valve  85  in the spool hole  81   a,  a hydraulic fluid supply stop state (state shown in  FIG. 7 ) and a hydraulic fluid supply state (state shown in  FIG. 8 ) are generated. In the hydraulic fluid supply stop state, communication via the spool hole  81   a  between the inlet port  82   a  and the outlet port  82   b  is interrupted, and the outlet port  82   b  and the drain port  82   c  are communicated with each other via the spool hole  81   a.  In the hydraulic fluid supply state, the inlet port  82   a  and the outlet port  82   b  are communicated with each other via the spool hole  81   a,  and the communication via the spool hole  81   a  between the outlet port  82   b  and the drain port  82   c  is interrupted. 
         [0052]    In the valve body  81 , a first bypass  83   a  and a second bypass  83   b  are formed. The first bypass  83   a  is communicated with the inlet port  82   a  and the outlet port  82   b  via small holes  82   d  and  82   e  and is provided with, at its end, an open/close port member  84  having an open/close hole  84   a  which is opened/closed by a poppet  91  of the solenoid mechanism  90 . The second bypass  83   b  makes the right-side space of the open/close port member  84  and the right end of the spool hole  81   a  communicate with each other. 
         [0053]    The solenoid mechanism  90  has a solenoid  92  energized by power supplied via a cable (not shown) connected to a connector  93 , the poppet  91  pulled to the right by reception of the excitation force of the solenoid  92 , and a poppet spring  94  for energizing the poppet  91  to the left. At the left end of the poppet  91 , an open/close projection  91   a  which projects into the open/close hole  84   a  from the right side and closes the open/close hole  84   a  is formed on the left end of the poppet  91 . In a non-energizing state of the solenoid  92 , the poppet  91  is moved to the left by being energized by the poppet spring  94 , and the open/close projection  91   a  enters the open/close hole  84   a  to close the open/close hole  84   a.  On the other hand, when the solenoid  92  is energized, the poppet  91  is moved to the right against the force of the poppet spring  94 , and the open/close projection  91   a  is apart from the open/close hole  84   a.    
         [0054]      FIG. 7  shows an energization state of the solenoid  92 . In the energized state, a force of pulling the poppet  91  by the solenoid  92  acts. The poppet  91  is moved to the right against the force of the poppet spring  94 , and the open/close projection  91  a of the poppet  91  is apart from the open/close hole  84   a  in the open/close port member  84  to open the open/close hole  84   a.  Consequently, the hydraulic fluid supplied from the stop hydraulic fluid supply source P to the inlet port  82   a  passes from the small hole  82   d  through the first bypass  83   a  and the open/close hole  84   a  and is supplied to the second bypass  83   b.  Further, the hydraulic fluid flows into a spool fluid chamber  81   b  surrounded by a plug  87  and the right end face of the spool valve  85  in the spool hole  81   a.    
         [0055]    As a result, the stop hydraulic fluid pressure of the hydraulic fluid in the spool fluid chamber  81   b  moves the spool valve  85  to the left against the force of the spool spring  86  and is positioned in the position in  FIG. 7 . By a spool groove  85   c  and a land  85   d  formed as shown in the diagram in the spool valve  85 , communication between the inlet port  82   a  and the outlet port  82   b  via the spool hole  81   a  is interrupted, the outlet port  82   b  and the drain port  82   c  are communicated with each other via the spool hole  81   a,  and the hydraulic fluid in the hydraulic fluid supply path  16  is exhausted to the drain side. In such a manner, the hydraulic fluid supply stop state is generated in which the hydraulic pressure for moving the stop selecting plunger  55  against the force to the stop selecting plunger  55  of the plunger spring  57  is not applied to the stop selecting plunger  55 . The hydraulic fluid supplied from the inlet port  82   a  into the first bypass  83   a  flows in the outlet port  82   b  via the small hole  82   e.  However, the inflow amount is small and all of the hydraulic fluid is exhausted to the drain side. Thus, the fluid pressure in the hydraulic fluid supply path  16  decreases. 
         [0056]    Since the spool valve  85  is forcedly moved to the left by using the stop hydraulic fluid pressure of the hydraulic fluid supplied into the spool fluid chamber  81   b,  by properly setting the degree of the stop hydraulic fluid pressure, the spool valve  85  can be moved to the left at an arbitrary speed. In the embodiment, by rapidly moving the spool valve  85  to the left and promptly discharging the hydraulic fluid in the hydraulic fluid supply path  16  connected to the outlet port  82   b  to the drain side, the fluid pressure acting on the stop selecting plunger  55  is rapidly decreased. It quickens the movement of the stop selecting plunger  55  by the force of the plunger spring  57  at the time of shift from the stop state of the exhaust valve  30  to the operation state, and the response is increased. 
         [0057]    On the other hand, the non-energization state of the solenoid  92  is shown in  FIG. 8 . Since the force of pulling the poppet  91  to the right by the solenoid  92  does not act, the poppet  91  is moved to the left by the force of the poppet spring  94 , and the open/close projection  91   a  of the poppet  91  enters the open/close hole  84   a  in the open/close port member  84  to close the open/close hole  84   a.  Consequently, the hydraulic fluid supplied from the stop fluid pressure supply source P to the inlet port  82   a  and supplied to the first bypass  83   a  does not flow in the second bypass  83   b.  The hydraulic fluid in the spool fluid chamber  81   b  is drained via the small holes  85   a  and  85   b  formed in the spool valve  85 . 
         [0058]    As a result, the spool valve  85  is moved to the right by the force of the spool spring  86  to the position of  FIG. 8 . By the spool groove  85   c  and the land  85   d  formed as shown in the diagram in the spool valve  85 , the inlet port  82   a  and the outlet port  82   b  are communicated with each other via the spool hole  81   a,  and the communication between the outlet port  82   b  and the drain port  82   c  is interrupted. Consequently, the hydraulic fluid supplied to the inlet port  82   a  is supplied to the exhaust valve hydraulic fluid  16 , the stop selecting plunger  55  is moved against the force of the plunger spring  57 , and the hydraulic fluid supply state is generated. 
         [0059]    Next, the intake valve stopping mechanism  40  will be described with reference to  FIGS. 9 and 10 . The operation principle of the mechanism  40  is similar to that of the exhaust valve stopping mechanism  50 . 
         [0060]    The intake valve stopping mechanism  40  has a bottomed cylindrical valve lifter  48  slidably fit in the guide hole  13 . A plunger holder  41  is fit in an insertion hole  48   a  formed in the valve lifter  48 . The plunger holder  41  has a configuration almost the same as that of the plunger holder  51  of the exhaust valve stopping mechanism  50 . In the plunger holder  41 , a plunger hole  42   a  extending in the direction orthogonal to the sliding direction of the valve lifter  48  is formed so as to penetrate. A stop selecting plunger  45  is slidably fit in the plunger hole  42   a  and is energized to one side in the sliding direction (to the left in the diagram) by a plunger spring  47 . In the plunger holder  41 , a holder-side stem receiving hole  42   b  passing the center of the outer cylindrical shape and penetrating in the vertical direction is formed, and the upper end abuts on the bottom face of the valve lifter  48 . The holder-side stem receiving hole  42   b  is set larger than the diameter of the tip of the valve stem  22  of the intake valve  20 . As will be described later, the size of the tip of the valve stem  22  is set so that it can project to the inside of the holder-side stem receiving hole  42   b  and be received. 
         [0061]    In the stop selecting plunger  45 , a slit  45   c  extending in the radial direction is formed on one end side in the axial direction (the left end side in the diagram). On the other end side (the right end side in the diagram), a plunger-side stem receiving hole  45   a,  receiving the plunger spring  47  and extending orthogonally and passing the center of the axis, is formed in the center portion in the axial direction. The size of the plunger-side stem receiving hole  45   a  is set larger than the diameter of the end of the valve stem  22  of the intake valve  20  so that, as will be described later, the tip of the valve stem  22  can project into the plunger-side stem receiving hole  45   a.  The lower end opening of the plunger-side stem receiving hole  45   a  is cut in a plane, thereby forming a step abutment face  45   b.    
         [0062]    In the plunger holder  41 , further, a pin hole  42   c  positioned near the open end of the plunger hole  42   a,  crossing the center of the plunger hole  42   a,  and penetrating in the vertical direction is formed. A stopper pin  43  is fit in the pin hole  42   c.  The stopper pin  43  is fit in the slit  45   c  in the stop selecting plunger  45  fit in the plunger hole  42   a.  The stop selecting plunger  45  is pressed to the left side in the diagram by the plunger spring  47 , and the bottom of the slit  45   c  abuts on the stopper pin  43  and is held in the position shown in  FIG. 13 . In the position, rotation of the stop selecting plunger  45  is regulated by the stopper pin  43 , the stem abutment face  45   b  is positioned on the under face side, and the plunger-side stem receiving hole  45   a  is positioned deviated from the holder-side stem receiving hole  42   b  in the axial direction. The upper end of the valve stem  22  of the intake valve  20  closely faces the step abutment face  45   b.  The position of the stop selecting plunger  45  at this time will be called an operating position. 
         [0063]    On the other hand, a ring-shaped hydraulic fluid receiving groove  41   c  is formed in an intermediate portion on the cylindrical peripheral face of the plunger holder  41 . In the state where the plunger holder  41  is fit in the insertion hole  48   a  in the valve lifter  48 , the hydraulic fluid receiving groove  41   c  faces a communication hole  48   b  formed in the outer periphery of the valve lifter  48 . In the cylinder head  10 , an intake valve hydraulic fluid supply path  17  for supplying passage hydraulic fluid supplied from the stop hydraulic fluid pressure supplying device  80  is formed. A front-end fluid passage  17   a  of the intake valve hydraulic fluid supply path  17  is connected to a hydraulic fluid receiving groove  17   b  formed in a ring shape in the guide hole  13  and, in this part, communicated with the communication hole  48   b  in the valve lifter  48 . 
         [0064]    A top face  48   c  of the valve lifter  48  is pressed by the intake valve drive cam  8  provided for the camshaft  6  and vertically slides and moves in the guide hole  13   e  together with the plunger holder  41 . During the vertical movement, the communication hole  48   b  is at least partly communicated with the hydraulic fluid receiving groove  17   b.  The intake valve stop hydraulic fluid supplied via the hydraulic fluid supply path  17  is supplied from the communication hole  48   b  into the hydraulic fluid receiving groove  41   c.  The intake valve stop hydraulic fluid supplied into the hydraulic fluid receiving groove  41   c  enters the plunger holder  42   a,  and the hydraulic fluid acts on the left end of the stop selecting plunger  45  to press it to the right direction. 
         [0065]    The operation of the valve when the engine E constructed as described above operates will be described hereinbelow. First, the operation in a state where the intake valve stop hydraulic fluid is not supplied to the exhaust valve hydraulic fluid supply path  16  and the intake valve hydraulic fluid supply path  17  will be described. As described above, when the hydraulic fluid is not supplied to the exhaust valve hydraulic fluid supply path  16 , in the exhaust valve stopping mechanism  50 , a press force overcoming the force of the plunger spring  57  based on the hydraulic fluid pressure is not generated at the end on the side where the slit  55   c  in the stop selecting plunger  55  fit in the plunger hole  52   a  is provided. As shown in  FIGS. 2 and 3 , the stop selecting plunger  55  is moved to the right by the force of the plunger spring  57  and is positioned in the operating position. In the state where the stop selecting plunger  55  is in the operating position as described above, the plunger-side stem receiving hole  55   a  formed in the stop selecting plunger  55  is positioned deviated from the holder-side stem receiving hole  52   b,  and the tip of the valve stem  32  of the exhaust valve  30  enters the holder-side stem receiving hole  52   b,  and closely faces the stem abutment face  55   b  of the stop selecting plunger  55 . 
         [0066]    When the engine E is operated in this state, the camshaft  6  is rotated in correspondence with the rotation of the crankshaft, and the rocker arm  72  is made swing by the exhaust valve drive cam  7  provided for the camshaft  6 . More specifically, in a state where the cylindrical cam face  7   a  of the exhaust valve drive cam  7  abuts on the cam follower  73 , the rocker arm  72  is in the position shown in  FIGS. 1 and 2 . In a state where the projection cam face  7   b  abuts on the cam follower  73 , the cam follower  73  is pushed upward and the rocker arm  72  swings counterclockwise to the position shown in  FIG. 3 . That is, in the state shown in  FIGS. 1 and 2 , the press member  74  attached to the left end  72   b  of the rocker arm  72  is in an upward movement position. In the state shown in  FIG. 3 , the press member  74  is in a downward movement position. 
         [0067]    At this time, the exhaust valve stopping mechanism  50  is pushed upward by the second exhaust valve spring  34   b  and the abutment plate  54  abuts on the lower end face of the press member  74 . Consequently, the exhaust valve stopping mechanism  50  vertically slides in the guide hole  14  together with the vertical movement of the press member  74 . On the other hand, when the press member  74  is in the upward movement position shown in  FIGS. 1 and 2 , the tip of the valve stem  32  of the exhaust valve  30  enters the holder-side stem receiving hole  52   b  and closely faces the stem abutment face  55   b  of the stop selecting plunger  55 . In this state, the exhaust valve  30  lifted by the first exhaust valve spring  34   a  closes the exhaust port  12   a  by the valve body  31 . In other words, the attachment position to the rocker arm  72  of the press member  74  is adjusted so that the valve body  31  closes the exhaust port  12   a  and the upper end of the valve stem  32  closely faces the stem abutment face  55   b.    
         [0068]    When the press member  74  is moved downward from the upper movement position shown in  FIG. 2 , together with the press member  74 , the exhaust valve stopping member  50  slides downward in the guide hole  14  as shown in  FIG. 3 . Concurrently, the upper end of the valve stem  32  abuts on the stem abutment face  55   b  to press the exhaust valve  30  downward, and the valve body  31  is apart from the exhaust port  12   a  to open the exhaust port  12   a.  After that, the engine E is operated, the camshaft  6  is rotated, and the rocker arm  72  is made swing by the exhaust valve drive cam  7 . According to the swing, the exhaust valve  30  is opened/closed. 
         [0069]    When the exhaust valve  30  is opened/closed as described above, the stem abutment face  55   b  receives the press force from the valve stem  32  (press force reaction of the exhaust valve drive cam  7 ). The part for receiving the exhaust valve stop hydraulic fluid pressure (the right end in the diagram of the stop selecting plunger  55 ) is apart from the stem abutment face  55   b  while sandwiching the plunger-side stem receiving hole  55   a.  Consequently, the influence of the press force (for example, elastic deformation) acting on the stem abutment face  55   b  on the part for receiving the stop hydraulic fluid pressure is suppressed. Deformation of the right end of the stop selecting plunger  55  is very small, so that sealing performance of the portion is excellently maintained, and durability improves. This point is similarly applied to the stop selecting plunger  45  of the intake valve stopping mechanism  40 . 
         [0070]    Further, by forming a communication hole  55 e connecting the stem receiving hole  55   a  and the spring receiving recess  55   d  in an overlap portion in the sliding direction with the stem abutment face  55   b  in the stop selecting plunger  55 , the weight of the stop selecting plunger  55  is reduced. It improves sliding response of the stop selecting plunger  55 . Further, the weight of the whole exhaust valve stopping mechanism  50  is reduced, and operation response of the exhaust valve  30  also improves. This point is also similarly applied to the intake valve stopping mechanism  40  and the stop selecting plunger  45 . 
         [0071]    The intake valve stopping mechanism  40  also performs similar operations. More specifically, since the fluid pressure does not act on the left end of the stop selecting plunger  45 , the stop selecting plunger  45  is moved to the left by the force of the plunger spring  47  and positioned in the operating position shown in  FIG. 13 . In this state, the plunger-side stem receiving hole  45   a  formed in the stop selecting plunger  45  is positioned to be deviated from the holder-side stem receiving hole  42   b,  the tip of the valve stem  22  of the intake valve  20  enters the holder-side stem receiving hole  42   b,  and closely faces the stem abutment face  45   b  of the stop selecting plunger  45 . 
         [0072]    When the engine E is operated in this state and the camshaft  6  is rotated in correspondence with rotation of the crankshaft, the intake valve stopping mechanism  40  is lifted by the second intake valve spring  24   b  and the top face  48   c  of the valve lifter  48  abuts on the intake valve drive cam  8 , so that the valve lifter  48  is pressed downward by the intake valve drive cam  8 , and the intake valve mechanism  40  is moved in the vertical direction. That is, when the cylindrical cam face  8   a  of the intake valve drive cam  8  abuts on the top face  48   c  of the valve lifter  48 , the intake valve stopping mechanism  40  is moved upward. When the projected cam face  8   b  abuts on the top face  48   b,  the intake valve stopping mechanism  40  is moved downward. 
         [0073]    On the other hand, when the intake valve stopping mechanism  40  is in the upper movement position shown in  FIG. 9 , the tip of the valve stem  22  of the intake valve  20  lifted by the first intake valve spring  24   a  enters the holder-side stem receiving hole  42   b  and closely faces the stem abutment face  45   b  of the stop selecting plunger  45 . In this state, the valve body  21  of the intake valve  20  closes the intake port  11   a.    
         [0074]    When the intake valve stopping mechanism  40  is moved downward from the upper movement position shown in  FIG. 9  according to the rotation of the intake valve drive cam  8 , the upper end of the valve stem  22  abuts on the stem abutment face  45   b,  the intake valve  20  is pressed downward, and the valve body  21  is apart from the intake port  11   a  and opens the intake port  11   a.  After that, the engine E is operated to rotate the camshaft  6 . By the intake valve drive cam  8 , the intake valve stopping mechanism  40  is moved in the vertical direction. According to the vertical movement, the intake valve  20  is opened/closed. 
         [0075]    As described above, in a state where the intake valve stopping hydraulic fluid is not supplied to the exhaust valve hydraulic fluid supply path  16  and the intake valve hydraulic fluid supply path  17 , the engine E is operated. In correspondence with rotation of the crankshaft, the cam shaft  6  is rotated. By the exhaust valve drive cam  7  provided for the cam shaft  6 , the rocker arm  72  is allowed to swing to open/close the exhaust valve  30 . By the intake valve drive cam  8 , the intake valve  20  is opened/closed. In the cylinder, normal operation is performed. 
         [0076]    Next, the case where the exhaust valve hydraulic fluid is supplied from the stop hydraulic fluid pressure supplying device  80  to the exhaust valve hydraulic fluid supply path  16  and the intake valve stop hydraulic fluid is supplied from the stop hydraulic fluid pressure supplying device  80  to the intake valve hydraulic fluid supply path  17  will be described. A control is performed to simultaneously stop the intake valve  20  and the exhaust valve  30  by supplying the stop hydraulic fluid simultaneously from the stop hydraulic fluid pressure supplying device  80  to the exhaust valve hydraulic fluid supply path  16  and the intake valve hydraulic fluid supply path  17 . 
         [0077]    Amen the exhaust valve stop hydraulic fluid is supplied to the exhaust valve hydraulic fluid supply path  16 , in the exhaust valve stopping mechanism  50 , the stop selecting plunger  55  fit in the plunger hole  52   a  receives the press force generated by the hydraulic fluid pressure, is moved to the left against the force of the plunger spring  57  and is positioned in the stop position, as shown in  FIGS. 5 and 6 . In a state where the stop selecting plunger  55  is in the stop position, the plunger-side stem receiving hole  55   a  formed in the stop selecting plunger  55  matches the holder-side stem receiving hole  52   b  in the vertical direction. The tip of the valve stem  32  of the exhaust valve  30  enters the holder-side stem receiving hole  52   b  and can also enter the plunger-side stem receiving hole  55   a.    
         [0078]    When the engine E is operated in this state, the camshaft  6  is rotated in correspondence with rotation of the crankshaft, and the rocker arm  72  is swung by the exhaust valve drive cam  7 , as described above, the exhaust valve stopping mechanism  50  is pressed by the press member  74  and slides vertically in the guide hole  14 . However, when the exhaust valve stopping mechanism  50  is moved in the vertical direction and moved from the position shown in  FIG. 5  downward as shown in  FIG. 6 , the tip of the valve stem  32  of the exhaust valve  30  enters the holder-side stem receiving hole  52   b  and also the plunger-side stem receiving hole  55   a.  Consequently, the exhaust valve  30  is held while being lifted by the first exhaust valve spring  34   a.    
         [0079]    As a result, even when the camshaft  6  is rotated, the rocker arm  72  is swung by the exhaust valve drive cam  7 , and the exhaust valve stopping mechanism  50  slides vertically in the guide hole  14 , the exhaust valve  30  is held while closing the exhaust port  12   a  with the valve body  31 . That is, the exhaust valve  30  is stopped in a closed state. 
         [0080]    The intake valve stopping mechanism  40  also performs similar operations. More specifically, when the stop hydraulic fluid pressure acts on the left end of the stop selecting plunger  45 , the stop selecting plunger  45  receives the hydraulic pressure, is moved to the right against the force of the plunger spring  47 , and is positioned in the stop position shown in  FIG. 10 . In this state, the plunger-side stem receiving hole  45   a  formed in the stop selecting plunger  45  matches the holder-side stem receiving hole  42   b.  The tip of the valve stem  22  of the intake valve  20  enters the holder-side stem receiving hole  42   b  and can also enter the plunger-side stem receiving hole  45   a  in the stop selecting plunger  45 . 
         [0081]    When the engine E is operated in this state and the camshaft  6  is rotated in correspondence with rotation of the crankshaft, the valve lifter  48  is pressed downward by the intake valve drive cam  8 . Even when the intake valve mechanism  40  is moved vertically, the tip of the valve stem  22  of the intake valve  20  enters the holder-side stem receiving hole  42   b  and also the plunger-side stem receiving hole  45   a.  Consequently, the intake valve  20  is held while being lifted by the first intake valve spring  24   a.  As a result, even when the camshaft  6  is rotated and the intake valve stopping mechanism  40  is moved so as to slide in the vertical direction in the guide hole  13  by the intake valve drive cam  8 , the intake valve  20  is held while closing the intake port  11   a  with the valve body  21 . That is, the intake valve  20  is held stopped in the closed state. 
         [0082]    As understood from the above description, in the engine E described in the embodiment, at the time of operating the engine in a state where the stop hydraulic fluid is not supplied from the stop hydraulic fluid pressure supplying device  80  and the like to the exhaust valve hydraulic fluid supply path  16  and the intake valve hydraulic fluid supply path  17  (or in a state where the internal fluid pressure is low), when the camshaft  6  is rotated according to rotation of the crankshaft, normal operations of opening/closing the intake and exhaust valves  20  and  30  are performed. On the other hand, when the stop hydraulic fluid pressure is supplied from the stop hydraulic fluid pressure supplying device  80  or the like to the exhaust valve hydraulic fluid supply path  16  and the intake valve hydraulic fluid supply path  17 , regardless of the rotational drive of the camshaft, the intake and exhaust valves  20  and  30  are always held closed, and the cylinder having the intake and exhaust valves is in a stop state. 
         [0083]    Consequently, when the stop hydraulic fluid pressure is low at the start of the engine or the like, the normal operations of opening/closing the intake and exhaust valves  20  and  30  are performed. Also in a very-low-speed operating state at start of the engine or the like, a predetermined large output can be obtained. Thus, an engine having an excellent starting performance is obtained. 
         [0084]    At the time of switching a cylinder stop state where the stop hydraulic fluid is supplied from the stop hydraulic fluid supplying device  80  or the like to the exhaust valve hydraulic fluid supply path  16  and the intake valve hydraulic fluid supply path  17  and the intake and exhaust valves  20  and  30  are always held closed to a cylinder operation state where the intake and exhaust valves  20  and  30  are operated by making the exhaust valve hydraulic fluid supply path  16  and the intake valve hydraulic fluid supply path  17  communicate with the drain side in the stop hydraulic fluid pressure supplying device  80  to decrease the hydraulic fluid pressure, as described above, the solenoid  92  is energized in the stop hydraulic fluid pressure supplying device  80  to move the poppet  91  to the right, the fluid pressure is applied to the right end face of the spool valve  85 , the spool valve  85  is rapidly moved to the left, and the hydraulic fluid in the valve hydraulic fluid supply path  16  and the intake valve hydraulic fluid supply path  17  is forcedly and promptly discharged to the drain side. Consequently, response of a switch from the cylinder stop state to the cylinder operation state is high. When the driver performs an operation of opening the throttle in the cylinder stop operation state, the state is promptly shifted to the cylinder operation state by movement of the stop selecting plunger  55  by the energizing force of the plunger spring  57 . Thus, response to a request for increasing an output of the engine improves. 
         [0085]    The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.