Patent Publication Number: US-2009217893-A1

Title: Four-stroke cycle internal combusion engine

Description:
This application claims priority under 35 U.S.C. §119 to Japanese Patent Application No. 2008-037235 filed on Feb. 19, 2008, the entire disclosure of which is incorporated herein by reference in its entirety. 
     BACKGROUND 
     1. Field of the Invention 
     The preferred embodiments of the present invention relate, inter alia, to a four-stroke cycle internal combustion engine equipped with a plurality of intake valves and exhaust valves, and more particularly, to switching control of an amount of lift and the opening/closing timing of each of the valves. 
     2. Description of the Related Art 
     The following description sets forth the inventor&#39;s knowledge of related art and problems therein and should not be construed as an admission of knowledge in the prior art. 
     Some of four-stroke cycle internal combustion engines are provided with a valve system configured to switch an amount of lift of each intake valve between a large amount and a small amount depending on a high speed range or a low speed range (see, e.g., Japanese Unexamined Laid-open Patent Publication No. 2002-303109). 
     In the conventional internal combustion engine described above, the amounts of lift of two intake valves per cylinder are switched depending on the high speed range or the low speed range, but the amounts of lift of both intake valves are always switched to amounts equal to each other. 
     However, there is a need for a technique to enable switching of the amount of lift in an increased number or range of steps according to, e.g., a desired use, an operating range, and so on of the internal combustion engine. 
     The description herein of needs for certain techniques or disadvantages of background technologies is in no way intended to limit the present invention. For example, certain features of the preferred embodiments of the invention may be capable of overcoming certain disadvantages and/or providing certain advantages, such as, e.g., disadvantages and/or advantages discussed herein, while retaining some or all of the features, embodiments, methods, and apparatus disclosed therein. 
     SUMMARY 
     The preferred embodiments of the present invention have been developed in view of the above-mentioned and/or other problems in the related art. The preferred embodiments of the present invention can significantly improve upon existing methods and/or apparatuses. 
     The preferred embodiments of the present invention was made in view of the above-described conventional circumstances, and has an object to provide a four-stroke cycle internal combustion engine in which an amount of lift is switchable in more multiple steps according to an operating range. 
     The preferred embodiments of the present invention provide a four-stroke cycle internal combustion engine including an intake valve, an exhaust valve, and a valve driving device open/close-driving the intake valve and the exhaust valve, wherein: at least one of the intake valve and the exhaust valve is provided in plurality; and the valve driving device includes a variable valve system performing multi-step switching control of at least one of an opening/closing timing and an amount of lift of the valve provided in plurality, independently on a per valve basis. 
     In a preferable embodiment of the present invention, the variable valve system includes: a cam nose which is provided in plurality per one valve; and a transmission switching mechanism transmitting only a driving force of one of the cam noses to the valve. 
     In another preferable embodiment of the present invention, the transmission switching mechanism is of a hydraulic type and includes a hydraulic cylinder mechanism, a hydraulic pressure supply path through which a hydraulic pressure is supplied to the hydraulic cylinder mechanism, and a hydraulic pressure control valve controlling the supply and discharge of the hydraulic pressure through the hydraulic pressure supply path. 
     The preferred embodiments of the present invention include a variable valve system which performs the multi-step switching control of at least one of the opening/closing timing and the amount of lift of the valve provided in plurality, independently on a per valve basis. The above-described embodiment of the present invention includes the cam nose provided in plurality per one valve and the transmission switching mechanism transmitting only the driving force of one of the cam noses to the valve. In the above-described another embodiment of the present invention, the transmission switching mechanism is of the hydraulic type and includes the hydraulic cylinder mechanism, the hydraulic pressure supply path through which the hydraulic pressure is supplied to the hydraulic cylinder mechanism, and the hydraulic pressure control valve controlling the supply and the discharge of the hydraulic pressure through the hydraulic pressure supply path. Therefore, as contrast to a conventional valve system which switches amounts of lift of all of a plurality of valves to the same amount, it is possible to achieve the switching control in more multiple steps, which can realize the control appropriate for a larger number of operating ranges. 
     In still another preferable embodiment of the present invention, a first intake valve and a second intake valve are provided; and the variable valve system includes: a first cam nose and a second cam nose provided for the first intake valve; a third cam nose and a fourth cam nose provided for the second intake valve; a first transmission switching mechanism of a hydraulic cylinder type transmitting a driving force of one of the first cam nose and the second cam nose to the first intake valve; and a second transmission switching mechanism of a hydraulic cylinder type transmitting a driving force of one of the third cam nose and the fourth cam nose to the second intake valve. 
     The above-described still another embodiment of the present invention includes the first and second cam noses for the first intake valve and the third and fourth cam noses for the second intake valve, and the driving forces of the first and second cam noses are selectively transmitted to the first intake valve, and the driving forces of the third and fourth cam noses are selectively transmitted to the second intake valve. This enables two-step switching of the amount of lift or the like of each of the first intake valve and the second intake valve, resulting in four-step switching as a whole, which can realize the control appropriate for a larger number of operating ranges. 
     In still another preferable embodiment of the present invention, the first transmission switching mechanism and the second transmission switching mechanism include: a first and a second rocker arm and a third and a fourth rocker arm rockably driven by the first and second cam noses and the third and fourth cam noses; a first and a second cylinder portion formed in a cam carrier pivotally supporting a portion, of an intake camshaft, between the first and second cam noses and the third and fourth cam noses; a first and a second piston slidably disposed in the first and second cylinder portions; and a first and a second lock pin reciprocatably driven by the first and second pistons to be engaged with or disengaged from the first or second rocker arm and the third or fourth rocker arm. 
     In the above-described still another embodiment of the present invention, the first and second cylinder portions are formed in the cam carrier pivotally supporting the intake camshaft, the first and second pistons are disposed in the first and second cylinder portions, the first and second lock pins are reciprocated by the first and second pistons to be engaged with or disengaged from the first or second rocker arm and the third or fourth rocker arm. Therefore, it is possible to realize the four-step switching. 
     In still another preferable embodiment of the present invention, a cam profile of the first cam nose is set so that the first intake valve has a valve operating angle of 250° or more and is closed at a timing of 90° or larger after a bottom dead center, and a cam profile of the third cam nose is set so that an amount of lift of the second intake valve becomes 2 mm or less; and in a low speed/low load operating range, the variable valve system open/close-drives the first intake valve by the first cam nose and open/close-drives the second intake valve by the third cam nose. 
     In still another preferable embodiment of the present invention, the intake valve is provided in plurality; and at least one of the plural intake valves has a valve operating angle of 250° or more and is closed at a timing of 90° or larger after a bottom dead center, and an amount of lift of at least one of the remaining intake valves is 2 mm or less. 
     In the above-described still another embodiment of the present invention, in the low speed/low load operating range, the first intake valve has a valve operating angle of 250° or more and is closed at the timing of 90° or larger after the bottom dead center, and the amount of lift of the second intake valve is set to 2 mm or less. Therefore, the closing timing of the first intake valve is, what is called, late closing, and the second intake valve is closed substantially completely. This can greatly reduce a pumping loss in an intake stroke to improve fuel efficiency. Further, since an air intake via the second intake valve is set to substantially zero and an intake air can be sucked only via the first intake valve, it is possible to generate a swirl (horizontal swirl) in the cylinder, leading to good stirrability of an air-fuel mixture and as a result the stabilization of a combustion state, which enables lean burn. Therefore, also from this point of view, it is possible to improve fuel efficiency. 
     Further, in a high speed/high load operating range, the first cam for the first intake valve and the third cam for the second intake valve drive the first intake valve and the second intake valve so that the both valves have the operating angle of 250° or more and are closed at a timing of 90° or larger after the bottom dead center. This can improve charge efficiency to improve the peak power. 
     The above and/or other aspects, features and/or advantages of various embodiments will be further appreciated in view of the following description in conjunction with the accompanying figures. Various embodiments can include and/or exclude different aspects, features and/or advantages where applicable. In addition, various embodiments can combine one or more aspect or feature of other embodiments where applicable. The descriptions of aspects, features and/or advantages of particular embodiments should not be construed as limiting other embodiments or the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The preferred embodiments of the present invention are shown by way of example, and not limitation, in the accompanying figures, in which: 
         FIG. 1  is a front cross-sectional view of a four-stroke cycle internal combustion engine according to one embodiment of the present invention (cross-sectional view taken along the line I-I in  FIG. 4 ; 
         FIG. 2  is a side cross-sectional view of the internal combustion engine (cross-sectional view taken along the line II-II in  FIGS. 1 and 4 ); 
         FIG. 3  is a front cross-sectional view of the internal combustion engine (cross-sectional view taken along the line III-III in  FIG. 4 ); 
         FIG. 4  is a plane cross-sectional view of a port portion of the internal combustion engine (cross-sectional view taken along the line IV-IV in  FIG. 1 ); 
         FIG. 5  is an exploded perspective view of a valve driving device of the internal combustion engine; 
         FIG. 6  is a perspective view of the valve driving device of the internal combustion engine; 
         FIGS. 7(   a ) to  7 ( d ) are explanatory views showing the operations of the valve driving device of the internal combustion engine; 
         FIG. 8  is an engine speed-load characteristic chart, in which operating ranges of the valve driving device of the internal combustion engine are shown; and 
         FIG. 9  is a chart showing the operating ranges and the valve timings of the valve driving device of the internal combustion engine. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the following paragraphs, some preferred embodiments of the invention will be described by way of example and not limitation. It should be understood based on this disclosure that various other modifications can be made by those in the art based on these illustrated embodiments. 
     Hereinafter, an embodiment of the present invention will be described based on the appended drawings. 
       FIGS. 1 to 9  are views used to describe an illustrative four-stroke cycle internal combustion engine according to one embodiment of the present invention. In this embodiment, the following description will be given, taking a four-stroke cycle internal combustion engine for automobile as an example. 
     In the drawings, “1” denotes a water-cooled four-cycle inline four-cylinder internal combustion engine, and the internal combustion engine  1  has roughly the following structure and is mounted on a vehicle with its crankshaft extending in a vehicle back and forth direction. On an upper joint surface  2   a  of a cylinder block  2 , a cylinder head  3  is mounted to be joined by head bolts (not shown), and on an upper joint surface  3   a  of the cylinder head  3 , a head cover  4  is detachably mounted. 
     In the cylinder block  2 , four cylinder bores  2   b  are arranged in parallel in the crankshaft direction, and a piston  5  slidably disposed in each of the cylinder bores  2   b  is coupled to a crankshaft (not shown) by a connecting rod (not shown). 
     In a lower joint surface  3   b  of the cylinder head  3 , a combustion recessed portion  3   c  forming a combustion chamber is formed. In the combustion recessed portion  3   c , front and rear exhaust valve openings  3   d  and  3   d ′ and front and rear intake valve openings  3   e  and  3   e ′ which are disposed on front and rear sides in terms of the vehicle front and rear direction are opened. The exhaust valve openings  3   d  and  3   d ′ are led out toward one vehicle-widthwise side of the cylinder head  3  from branch exhaust ports  3   f ′ and  3   f ′ branching off from a confluent exhaust port  3   f . The intake valve openings  3   e  and  3   e ′ are led out toward the other vehicle-widthwise side of the cylinder head  3  from branch intake ports  3   g  and  3   g ′ branching off from a confluent intake port  3   g.    
     In a lower portion between the branch intake ports  3   g ′ and  3   g ′, a fuel injector  27  is disposed, and the fuel injector  27  injects a fuel directly to an upper portion of the cylinder bore  2   b.    
     The exhaust valve openings  3   d  and  3   d ′ are opened/closed by valve heads  6   a  of front and rear exhaust valves  6  and  6 ′ respectively, and the intake valve openings  3   e  and  3   e ′ are opened/closed by valve heads  7   a  of front and rear intake valves (first and second intake valves)  7  and  7 ′ respectively. Valve stems  6   b  of the exhaust valves  6  and  6 ′ and valve stems  7   b  of the intake valves  7  and  7 ′ extend upward so that an angle there-between become a predetermined angle. The exhaust valves  6  and  6 ′ and the intake valves  7  and  7 ′ are open/close-driven by a valve driving device  8  disposed in the head cover  4 . 
     This valve driving device  8  has an exhaust valve driving device  9  driving the exhaust valves  6  and  6 ′ and an intake valve driving device  10  driving the intake valves  7  and  7 ′. Further, in the valve driving device  8  of this embodiment, there are provided, though not shown, an exhaust-side valve timing varying mechanism variably controlling the opening/closing timings of the exhaust valves  6  and  6 ′ and an intake-side valve timing varying mechanism variably controlling the opening/closing timings of the intake valves  7  and  7 ′. 
     An exhaust camshaft  1  of the exhaust valve driving device  9  is rotatably supported by an exhaust carrier portion  14   a  and an exhaust cap  14   b  of a cam carrier  18 . Further, an intake camshaft  13  of the intake valve driving device  10  is rotatably supported by an intake carrier portion  15   a  and an intake cap  15   b  of the cam carrier  18 . The cam carrier  18 , in which the exhaust carrier portion  14   a  and the intake carrier portion  15   b  are integrally coupled, is detachably fixed to the upper joint surface  3   a  of the cylinder head  3  with bolts  14   c ,  14   c ,  15   c , and  15   c.    
     The exhaust valve driving device  9  has the exhaust camshaft  1 , and exhaust rocker arms  12  and  12  rockably disposed between exhaust cam noses  11   a  and  11   a  and the exhaust valves  6  and  6 ′, the exhaust cam noses  11   a  and  11   a  having the same cam profile and being formed in portions, of the exhaust camshaft  1 , facing the two exhaust valves  6  and  6 ′. 
     Each of the exhaust rocker arms  12  is supported by a rocker shaft  12   a  fixedly supported by a coupling portion  18   b  of the cam carrier  18 , so as to be capable of rocking up and down. Not only the exhaust carrier portion  14   a  and the intake carrier portion  15   a  but the coupling portion  18   b  of the cam carrier  18  is detachably mounted to the upper joint surface  3   a  of the cylinder head  3  by bolts  18   a  and  18   a.    
     Accompanying the rotation of the exhaust camshaft  1 , the exhaust cam noses  11   a  open/close-drive the exhaust valves  6  and  6 ′ via the exhaust rocker arms  12 . 
     In the intake camshaft  13  of the intake valve driving device  10 , two cam noses per one front-side intake valve  7  and two cam noses per one rear-side intake valve  7 ′, that is, four first to fourth intake cam noses  13   a ,  13   b ,  13   c , and  13   d  per one cylinder are formed. The first intake cam nose  13   a  and the fourth intake cam nose  13   d  produce a large amount of lift and have the same cam profile (hereinafter referred to as “front and rear high cams  13   a  and  13   d ”). The second intake cam nose  13   b  produces a small amount of lift (hereinafter referred to as “low cam  13   b ”), and the third intake cam nose  13   c  produces the smallest amount of lift, for example, 0.3 mm (hereinafter referred to as “lowest cam  13   c ”). 
     In more detail, the cam profile of the high cams  13   a  and  13   d  is set so that the intake valves  7  and  7 ′ have an operating angle of 250° or more in terms of crank angle, concretely, about 270°, and have a large maximum amount of lift, concretely, 10.0 mm, as shown in  FIGS. 9(   a ) and  9 ( c ). Further, a cam profile of the low cam  13   b  is set so that the front-side intake valve  7  has an operating angle of about 232° and has a small maximum amount of lift, concretely, 6.5 mm, as shown in  FIG. 9(   b ). Furthermore, a cam profile of the lowest cam  13   c  is set so that the rear-side intake valve  7 ′ has a maximum amount of lift of 2 mm or less, concretely, 0.3 mm. 
     The cam profile of the cam noses  11   a  and  11   a  for the exhaust valves  6  and  6 ′ is set so that the operating angles and amounts of lift of the exhaust valves  6  and  6 ′ become constant, concretely, 232° and 8.5 mm, for instance. 
     The intake camshaft  13  is rotatably supported by the intake carrier portion  15   a  and the cam cap  15   b  which are disposed at a portion between the low cam  13   b  and the lowest cam  13   c . The intake carrier portion  15   a  and the cam cap  15   b  are provided independently for each cylinder, and are detachably fixed to the upper joint surface  3   a  of the cylinder head  3  by the bolts  15   c  and  15   c.    
     A high cam rocker arm (first rocker arm)  16   a  and a low cam rocker arm (second rocker arm)  16   b  are disposed between the front-side high cam  13   a  and the front-side intake valve  7  and between the front-side low cam  13   b  and the front-side intake valve  7 . Further, between the lowest cam  13   c  and the rear-side intake valve  7 ′ and between the high cam  13   d  and the rear-side intake valve  7 ′, a lowest cam rocker arm (third rocker arm)  16   c  and a high cam rocker arm (fourth rocker arm)  16   d  are disposed. The rocker arms  16   a  and  16   b  and the rocker arms  16   c  and  16   d  are rockably supported by rocker shafts  17   a  and  17   a . The rocker shafts  17   a  and  17   a  are fixedly supported by the cam carrier  18 . In  FIG. 5 , the reference numeral “21” denotes biasing springs which rotatably bias the high cam rocker arms  16   a  and  16   d  so that the high cam rocker arms  16   a  and  16   d  are constantly in slidable contact with the high cams  13   a  and  13   d , and the reference numeral “22” denotes spacers for restricting an axial direction position of the rocker arms. 
     Here, the high cam rocker arm  16   a  and the low cam rocker arm  16   b  are independently rockable, and a boundary surface b where the both rocker arms  16   a  and  16   b  are in slidable contact with each other coincides with the center line between the high cam  13   a  and the low cam  13   b , and thus, with an axis a of the front-side intake valve  7 . Similarly, a boundary surface b between the lowest cam rocker arm  16   c  and the high cam rocker arm  16   d  coincides with an axis a′ of the rear-side intake valve  7 ′. 
     In a base end portion  16   e  of each of the rocker arms  16   a  to  16   d , a rocker hole  16   f  through which the rocker shaft  17   a  is inserted is formed. Further, on tip portions of the high cam rocker arms  16   a  and  16   d , cam surfaces  16   g  coming into slidable contact with the high cams  13   a  and  13   d  are formed. 
     In tip portions of the low cam rocker arm  16   b  and the lowest cam rocker arm  16   c , lock holes  16   h  are formed, and on upper portions of outer peripheral surfaces of the tip portions, cam surfaces  16   i  coming into slidable contact with the low cam  13   b  and the lowest cam  13   c  are formed. Furthermore, pressing surfaces  16   j  pressing the intake valves  7  and  7 ′ are formed in lower portions of the outer peripheral surfaces of the tip portions. On these pressing surfaces  16   j , projecting portions  16   j ′ projecting toward the high cam rocker arms  16   a  and  16   d  across the axes a and a′ of the intake valves  7  and  7 ′ are formed. The projecting portions  16   j ′ are located under the high cam rocker arms  16   a  and  16   d.    
     In the lock holes  16   h  and  16   h  of the low cam rocker arm  16   b  and the lowest cam rocker arm  16   c , a first and a second lock pins  19  and  19 ′ are reciprocatably disposed/inserted. Further, between the lock pins  19  and  19 ′ and the low cam rocker arm  16   b  and the lowest cam locker arm  16   c , biasing springs  20  biasing the lock pins  19  and  19 ′ toward the opposite side of the high cam rocker arms  16   a  and  16   d , that is, backward are disposed. 
     In the intake cam carrier portion  15   a , a sleeve for the intake valve  7  (first cylinder portion)  15   d  and a sleeve for the intake valve  7 ′ (second cylinder portion)  15   e  are separately pres-fit. In the sleeves  15   d  and  15   e , first and second pistons  23  and  23 ′ are reciprocatably inserted respectively. 
     A first oil chamber c surrounded by the sleeve  15   d  and the piston  23  is connected to a hydraulic pump (not shown) by a first hydraulic pressure path  24 , and in the middle of the first hydraulic pressure path  24 , a first hydraulic pressure control valve  25  is disposed. Similarly, a second oil chamber c′ surrounded by the sleeve  15   e  and the piston  23 ′ is connected to the hydraulic pump by a second hydraulic pressure path  24 ′, and in the middle of the second hydraulic pressure channel  24 ′, a second hydraulic pressure control valve  25 ′ is disposed. 
     A first variable valve system  26  for front-side intake valve which open/close-drives the front-side intake valve  7  by one of the high cam  13   a  and the low cam  13   b  and a second variable valve system  26 ′ for rear-side intake valve which open/close-drives the rear-side intake valve  7 ′ by one of the lowest cam  13   c  and the high cam  13   d  are structured as described above. 
     When the hydraulic pressure is supplied to the first oil chamber c, the first piston  23  moves the first lock pin  19  forward, the first lock pin  19  enters an area under the high cam rocker arm  16   a , and the high cam  13   a  open/close-drives the front-side intake valve  7  with a large amount of lift via the high cam rocker arm  16   a  and the pressing surface  16   j  of the low cam rocker arm  16   b  (see  FIG. 2 ,  FIGS. 7(   b ) and  7 ( d )). At this time, the driving force of the high cam  13   a  is transmitted to the intake valve  7  efficiently owing to the projecting portion  16   j ′ formed on the pressing surface  16   j.    
     On the other hand, when the hydraulic pressure to the first oil chamber c is released, the first lock pin  19  is moved back toward a cylinder axis E by a spring force of the biasing spring  20 , so that the first lock pin  19  and the high cam rocker arm  16   a  are disengaged from each other. Consequently, the high cam rocker arm  16   a  rotates idle, and the low cam  13   b  open/close-drives the intake valve  7  with a small amount of lift via the pressing surface  16   j  of the low cam rocker arm  16   b  (see  FIGS. 7(   a ) and  7 ( c )). 
     Further, when the hydraulic pressure is supplied to the second oil chamber c′, the second piston  23 ′ moves the second lock pin  19 ′ forward, the second lock pin  19 ′ enters an area under the high cam rocker arm  16   d , and the high cam  13   d  open/close-drives the rear-side intake valve  7 ′ with a large amount of lift via the high cam rocker arm  16   d  and the pressing surface  16   j  of the lowest cam rocker arm  16   c  (see  FIGS. 7(   c ) and  7 ( d )). At this time, the driving force of the high cam  13   d  is transmitted to the intake valve  7 ′ efficiently, owing to the projecting portion  16   j ′ formed on the pressing surface  16   j.    
     On the other hand, when the hydraulic pressure to the second oil chamber c′ is released, the second lock pin  19 ′ is moved back toward the cylinder axis E by the spring force of the biasing spring  20 , so that the second lock pin  19 ′ and the high cam rocker arm  16   d  are disengaged from each other. Consequently, the high cam rocker arm  16   d  rotates idle, and the lowest cam  13   c  open/close-drives the intake valve  7 ′ with the lowest amount of lift via the pressing surface  16   j  of the lowest cam rocker arm  16   c  (see  FIGS. 7(   a ) and  7 ( b )). 
       FIG. 8  is a chart showing a relation between operating ranges of the internal combustion engine of this embodiment and amounts of lift of the front and rear intake valves  7  and  7 ′. The operating range of the internal combustion engine  1  of this embodiment is divided into four ranges A, B, C, and D shown in  FIG. 8 , and the supply and discharge of the hydraulic pressure are controlled so as to produce amounts of lift corresponding to the respective operating ranges. 
     Here, the operating range A represents a low/mid speed/low load operating range, the operating range B represents a mid speed/mid-load operating range, the operating range C represents a mid speed/high load operating range, and the operating range D represents a high speed/high load operating range. It should be noted that such division into these operating ranges is not strictly defined one, but is conceptual one which has a considerable allowance, and this division is not to limit the technical scope of the present invention. 
     In the operating range A, the hydraulic pressure is supplied to the first oil chamber c and the hydraulic pressure of the second oil chamber c′ is released as shown in  FIG. 7(   b ). As a result, the front-side intake valve  7  comes into a high lift state (in this embodiment, for example, 10 mm. The same applies to the description below), and the rear-side intake valve  7 ′ comes into a lowest lift state (0.3 mm). Further, the operating angle of the intake valve  7  becomes 270° (see  FIG. 9(   a )) and the operating angle of the intake valve  7 ′ becomes substantially zero. 
     In the operating range B, the hydraulic pressures of the first oil chamber c and the second oil chamber c′ are both released as shown in  FIG. 7(   a ). As a result, the front-side intake valve  7  comes into a low lift state (6.5 mm), and the rear-side intake valve  7 ′ comes into a lowest lift state (0.3 mm). Further, the operating angle of the intake valve  7  becomes 232° (see  FIG. 9(   b )) and the operating angle of the intake valve  7 ′ becomes substantially zero. 
     In the operating range C, the hydraulic pressure of the first oil chamber c is released and the hydraulic pressure is supplied to the second oil chamber c′ as shown in  FIG. 7(   c ). As a result, the front-side intake valve  7  comes into a low lift state, and the rear-side intake valve  7 ′ comes into a high lift state. Further, the operating angle of the intake valve  7  becomes 232° (see  FIG. 9(   b )) and the operating angle of the intake valve  7 ′ becomes 270° (see  FIG. 9(   c )). 
     In the operating range D, the hydraulic pressure is supplied both to the first oil chamber c and the second oil chamber c′ as shown in  FIG. 7(   d ). As a result, the front-side intake valve  7  and the rear-side intake valve  7 ′ both come into a high lift state, and the operating angles of the both become 270°. 
     As described above, in the internal combustion engine  1  of this embodiment, the first and second valve systems  26  and  26 ′ are provided for the two-step switching of the amounts of lift of the two intake valves  7  and  7 ′ per cylinder, which enables four-step switching control of the amount of lift of each cylinder. Therefore, it is possible to divide the operating range into the four ranges and to set an amount of lift to a value appropriate for each of the operating ranges. This can realize improvement in fuel efficiency and exhaust gas properties in wide operating ranges and can ensure high output power. 
     For example, in the operating range A, the front-side intake valve  7  comes into the high lift state, has an operating angle of 270°, and is closed at a timing of 110° after the bottom dead center, while the rear-side intake valve  7 ′ comes into the lowest lift state and has an operating angle of substantially zero. Therefore, the late closing of the intake valve is realized, which can reduce a pumping loss to improve fuel efficiency. Further, since the intake air flows in only from the first intake valve  7  side, a swirl (horizontal swirl) can be generated in the cylinder, leading to better diffusion of an air-fuel mixture, improvement in combustibility, and as a result, stabilization of lean burn. Therefore, it is possible to improve fuel efficiency and exhaust gas properties. 
     Further, in the operating range B, the front-side intake valve  7  comes into the low lift state, and has an operating angle of 232°, while the rear-side intake valve  7 ′ comes into the lowest lift state and has an operating angle of substantially zero. This can stabilize combustibility owing to the generation of a swirl, resulting in improved fuel efficiency owing to lean burn. 
     Further, in the operating range C, the front-side intake valve  7  comes into the low lift state and has an operating angle of 232°, while the rear-side intake valve  7 ′ comes into the high lift state and has an operating angle of 270°. This can ensure the generation of a swirl while increasing an air intake, contributing to improvement in the maximum torque. 
     Further, in the operating range D, the front-side intake valve  7  and the rear-side intake valve  7 ′ both come into the high lift state and have an operating angle of 270°. This can enhance charge efficiency to improve the peak power. 
     Incidentally, in the description of the above illustrative embodiments, the number of the intake valves shown is two, but the present invention is also applicable to a case where the number of the intake valves is three or more. Further, an applicable range of the present invention is not limited to the intake valve but the present invention is also applicable to an exhaust valve (e.g., which can be, e.g., similarly provided as a plurality of valves) and further applicable to both the intake valve and the exhaust valve. Moreover, while the present application describes some illustrative mechanisms for open/close driving and amount of lift driving of valves, it is contemplated that in various embodiments any device to enable such open/close driving and/or amount of lift driving can be employed. 
     Further, in the description of the above embodiment, the operating range is divided into the four ranges, but the present invention is also applicable to a case where the operating range is divided into a larger number of operating ranges. 
     Broad Scope of the Invention 
     The present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The embodiments described herein are therefore to be considered in all respects as illustrative and not as restrictive; the scope of the invention being indicated by the appended claims rather than by the foregoing description, and the claims should be construed as encompassing the very broadest range of equivalency. 
     While the present invention may be embodied in many different forms, a number of illustrative embodiments are described herein with the understanding that the present disclosure is to be considered as providing examples of the principles of the invention and such examples are not intended to limit the invention to preferred embodiments described herein and/or illustrated herein. While illustrative embodiments of the invention have been described herein, the present invention is not limited to the various preferred embodiments described herein, but includes any and all embodiments having equivalent air filter elements, modifications, omissions, combinations (e.g., of aspects across various embodiments), adaptations and/or alterations as would be appreciated by those in the art based on the present disclosure. The limitations in the claims are to be interpreted broadly based on the language employed in the claims and not limited to examples described in the present specification or during the prosecution of the application, which examples are to be construed as non-exclusive. For example, in the present disclosure, the term “preferably” is non-exclusive and means “preferably, but not limited to.” In this disclosure and during the prosecution of this application, means-plus-function or step-plus-function limitations will only be employed where for a specific claim limitation all of the following conditions are present in that limitation: a) “means for” or “step for” is expressly recited; b) a corresponding function is expressly recited; and c) structure, material or acts that support that structure are not recited. In this disclosure and during the prosecution of this application, the terminology “present invention” or “invention” is meant as an non-specific, general reference and may be used as a reference to one or more aspect within the present disclosure. The language present invention or invention should not be improperly interpreted as an identification of criticality, should not be improperly interpreted as applying across all aspects or embodiments (i.e., it should be understood that the present invention has a number of aspects and embodiments), and should not be improperly interpreted as limiting the scope of the application or claims. In this disclosure and during the prosecution of this application, the terminology “embodiment” can be used to describe any aspect, feature, process or step, any combination thereof, and/or any portion thereof, etc. In some examples, various embodiments may include overlapping features. In this disclosure and during the prosecution of this case, the following abbreviated terminology may be employed: “e.g.” which means “for example.”