The invention provides a multi-cylinder engine wherein, even where it is structured such that a cam chain case is provided on a side portion of the engine, a working fluid supply path can be simplified and the weight and size of a cylinder head reduced. According to the invention, a multi-cylinder engine is provided wherein at least one of a plurality of engine valves of a cylinder head can be cut off from its corresponding combustion chambers such that a first intake valve, a second intake valve, a first exhaust valve, and a second exhaust valve are positioned on the opposite side to a cam chain case.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to JP 2003-085245.

FIELD OF THE INVENTION

This invention relates to a multi-cylinder engine which includes cylinders that can be cut off.

BACKGROUND OF THE INVENTION

A multi-cylinder engine is available wherein a plurality of cylinders are divided into at least two groups and are each formed from cylinders each of which can be cut off (i.e., turned off) by placing a throttle valve thereof into a closed state using a link or a rod such that the number of operating cylinders can be adjusted in response to the engine load. For an example refer to JP 07-150982.

Also another multi-cylinder engine is available wherein a cylinder cut-off mechanism provided for an engine valve is operated hydraulically without a link or a rod to place the engine valve into a closed state. For an example refer to JP 2000-205038 (U.S. Pat. No. 6,318,316).

In the former multi-cylinder engine, the link or rod restricts the degree of freedom of the arrangement of auxiliary apparatuses located around the engine. Similarly, in the latter multi-cylinder engine the port that supplies pressure oil therethrough in a side wall of the engine may restrict the degree of freedom of the auxiliary apparatuses located around the engine.

Moreover, where the latter cylinder cut-off mechanism is applied to a multi-cylinder engine structured such that a cam chain case is disposed transversely across the engine in order to facilitate maintenance and reduce the weight and size of the engine, a working fluid supply port cannot be provided in a side of the engine on which the cam chain case is disposed. Therefore, resulting working fluid supply path is complicated and the cylinder head is obliged to have an increased size and weight.

SUMMARY OF THE INVENTION

The present invention provides a multi-cylinder engine wherein, even where it is structured such that a cam chain case is provided on a side portion of the engine, a working fluid supply path can be simplified thereby reducing the size and the weight of a cylinder head.

According to a first embodiment, a multi-cylinder engine wherein at least one of a plurality of engine valves is provided on a cylinder head is formed as part of a cylinder which can be cut off from a combustion chamber. Wherein the valves corresponding to the combustion chamber are positioned on the opposite side to a cam chain case.

Where the multi-cylinder engine is configured in this manner, it is possible to locate ports for many working fluid supply paths on a side wall of the cylinder head on the opposite side to the cam chain case in which the working fluid supply paths are formed in order to cut off all of the engine valves.

According to the invention, the multi-cylinder engine can be an in-line four cylinder engine. Where the multi-cylinder engine is an in-line four cylinder engine, the length of the engine can be minimized in accordance with the above arrangement. In addition, the cylinders on one end side of the in-line arrangement of the cylinders can be formed as normally operative cylinders while the cylinders on the other end side can be formed as cylinders which can be cut off.

Where the multi-cylinder engine is configured according to the invention, it is possible to set ports for working fluid supply paths to a side wall of the cylinder head of the cylinders which can be cut off.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is described with reference to the drawings.FIG. 1is a side elevational view of a motorcycle1. A vehicle body frame21of the motorcycle1includes a head pipe23, main frames22extending obliquely rearward from the head pipe23, a center frame24extending downward from rear ends of the main frames22, and a seat stay25extending rearward from the main frames22.

A front fork26on which a front wheel WFis supported is supported for steering operation by the head pipe23, and a steering handle bar27is connected to the front fork26. Meanwhile, a rear fork28on which a rear wheel WRis supported is supported for upward and downward rocking motion at a rear portion of one of the main frames22, and a cushion unit29is provided between the center frame24and the rear fork28through a linkage.

An engine E is supported on the main frames22and the center frame24, and power of the engine E is transmitted to the rear wheel WRthrough a speed change gear incorporated in the engine E and a chain power transmission system30. A fuel tank31is carried on the left and right main frames22and the center frame24such that it is positioned above the engine E, and seats32and32′ for a driver and a passenger are attached to the seat stay25. A radiator33is disposed forward of the engine E.

As shown inFIGS. 2 to 4, the engine E is a multi-cylinder engine. For example, the engine can be an in-line four-cylinder 4-cycle DOHC engine wherein at least one intake valve or exhaust valve from among a plurality of intake valves and exhaust valves provided on a cylinder head40is formed as a cylinder which can be cut off using hydraulic pressure for each of combustion chambers43corresponding to cylinder bores37as hereinafter described.

In the following description, the cylinders are individually represented as #1cylinder, #2cylinder, #3cylinder, and #4cylinder in order from a side opposite a cam chain case C. For convenience, the following description is given principally with reference to a sectional view of the #4cylinder. It is to be noted thatFIGS. 2 and 3are sectional views of the #4cylinder and, particularly,FIG. 2is a sectional view taken along line2—2ofFIG. 4andFIG. 3is a sectional view taken along line3—3ofFIG. 4. Further, inFIG. 4, the reference numerals of the corresponding cylinders are denoted in parentheses.

Four cylinder bores37are formed in a cylinder block36of the engine E such that they are arranged in the widthwise direction of the vehicle body frames21. In particular, cylindrical cylinder liners38, which form the cylinder bores37, are securely mounted at positions on the cylinder block36spaced from each other along the widthwise direction of the vehicle body frame21. The cylinder liners38partially project into an upper crankcase39coupled to a lower portion of the cylinder block36.

The cylinder head40is coupled to an upper portion of the cylinder block36. Protrusions41are provided on the coupling face of the cylinder head40to the cylinder block36in an individually corresponding relationship to the cylinder bores37. Pistons42and combustion chambers43including the protrusions41are formed between the tops of the pistons42and the cylinder head40.

A plurality of, for example, a pair of, first and second intake valve ports441and442and a plurality of, for example, a pair of, first and second exhaust valve ports451and452are provided for each of the cylinders in the cylinder head40. The first and second intake valve ports441and442are open to the combustion chamber43, and also the first and second exhaust valve ports451and452are open to the combustion chamber43. The first intake valve port441and the first exhaust valve port451are disposed at substantially symmetrical positions to each other with respect to the center of the combustion chamber43. Also the second intake valve port442and the second exhaust valve port452are disposed at substantially symmetrical positions to each other with respect to the center of the combustion chamber43.

A first intake path461connecting to the first intake valve port441, a second intake path462connecting to the second intake valve port442and an intake port47are provided in the cylinder head40. The intake port47connects commonly to the first and second intake paths461and462and is open to a first side face40aof the cylinder head40. The first side face40aof the cylinder head40to which the intake ports47are open are disposed so as to face the rear side along the running direction of the motorcycle.

A first exhaust path481connecting to the first exhaust valve port451, a second exhaust path482connecting to the second exhaust valve port452and an exhaust port49are provided for each of the combustion chambers43in the cylinder head40. The exhaust port49connects commonly to the first and second exhaust paths481and482and is open to the other or second side face40bof the cylinder head40. The second side face40bof the cylinder head40to which the exhaust ports49are open is disposed so as to face the front side along the running direction of the motorcycle.

An intake apparatus51is connected to each of the intake ports47. The intake apparatus51includes a fuel inject valve50for supplying fuel to each of the intake ports47. It is to be noted that reference character50′ denotes a fuel line, and TH a throttle valve. Further, an exhaust apparatus53is connected to each of the exhaust ports49. The exhaust apparatus53includes an exhaust muffler52disposed on the right side of the rear wheel WRin a state wherein it is directed forward in the running direction of the motorcycle.

Connection/disconnection between the first intake valve port441and the first intake path461and connection/disconnection between the second intake valve port442and the second intake path462are changed over by the first and second intake valves561and562as engine valves. Meanwhile, connection/disconnection between the first exhaust valve port451and the first exhaust path481and connection/disconnection between the second exhaust valve port452and the second exhaust path482are changed over by the first and second exhaust valves571and572as engine valves.

Each of the first and second intake valves561and562includes a valve stem59connected integrally at a base end thereof to a valve body portion58which can close up a corresponding one of the first and second intake valve ports441and442. Meanwhile, each of the first and second exhaust valves571and572includes a valve stem61connected integrally at a base end thereof to a valve body portion60which can close up a corresponding one of the first and second exhaust valve ports451and452.

The valve stems59of the first and second intake valves561and562are fitted for sliding movement in guide tubes62provided in the cylinder head40. Meanwhile, the valve stems61of the first and second exhaust valves571and572are fitted for sliding movement in guide tubes63provided in the cylinder head40.

A retainer64is secured to a portion of the valve stem59of the first intake valve561which projects upward from the guide tube62. The first intake valve561is biased in a direction in which it closes up the first intake valve port441by a valve spring651in the form of a coil spring provided between the retainer64and the cylinder head40. Another retainer64is secured to a portion of the valve stem59of the second intake valve562which projects upward from the guide tube62. The second intake valve562is biased in a direction in which it closes up the second intake valve port442by a valve spring652in the form of a coil spring provided between the retainer64and the cylinder head40.

Similarly, the first exhaust valve571is biased in a direction in which it closes up the first exhaust valve port451by a valve spring671in the form of a coil spring provided between the cylinder head40and a retainer66secured to the valve stem61of the first exhaust valve571. Meanwhile, the second exhaust valve572is biased in a direction in which it closes up the second exhaust valve port452by a valve spring672in the form of a coil spring provided between the cylinder head40and another retainer66secured to the valve stem61of the second exhaust valve572.

The first and second intake valves561and562of the combustion chambers43are driven by an intake side valve system68I. The intake side valve system68I includes a camshaft70, valve lifters711,712of a bottomed cylindrical shape. The camshaft70has provided thereon first intake side valve cams691which individually correspond to the first intake valves561, and second intake side valve cams692which individually correspond to the second intake valves562. The valve lifters711are supported on the cylinder head40such that they slidably move following the first intake side valve cams691. The valve lifters712are supported on the cylinder head40such that they slidably move following the second intake side valve cams692.

The camshaft70has an axial line which intersects perpendicularly with extension lines of axial lines of the valve stems59of the first and second intake valves561and562and is supported for rotation between the cylinder head40and a holder55coupled to the cylinder head40. The valve lifters711are fitted for sliding movement in the cylinder head40in same coaxial directions as the axial lines of the valve stems59of the first intake valves561. The outer faces of the closed ends of the valve lifters711are held in sliding contact with the first intake side valve cams691. Further, the valve lifters712are fitted for sliding movement in the cylinder head40in same coaxial directions as the axial lines of the valve stems59of the second intake valves562. The outer faces of the closed ends of the valve lifters712are held in sliding contact with the second intake side valve cams692.

The tip ends of the valve stems59of the second intake valves562contact with the inner faces of the closed ends of the valve lifters712through shims72such that, during operation of the engine E, the valve stems59are normally operated to open and close the second intake valves562by the second intake side valve cams692.

Meanwhile, a valve cut-off mechanism73I is provided between each of the valve stems59of the first intake valves561and the corresponding valve lifter711. The valve cut-off mechanism73I can change over between an active state and an inactive state in the valve opening direction from the valve lifter711to the first intake valve561. Thus, when the engine E is in a particular operation region, for example, when the engine E is in a low load region such as a low speed operation region, the valve cut-off mechanism73I places the first intake valve561into a cut-off state irrespective of a sliding movement of the valve lifter711.

As shown inFIG. 5which shows part ofFIG. 3in an enlarged scale, the valve cut-off mechanism73I includes a pin holder74, a slide pin76, a return spring77and a stopper pin78. The pin holder74is fitted for sliding movement in the valve lifter711. The slide pin76is fitted for sliding movement in the pin holder74and cooperates with the inner face of the valve lifter711to form a hydraulic pressure chamber75. The return spring77is interposed between the slide pin76and the pin holder74and exerts spring force for biasing the slide pin76in a direction in which the volume of the hydraulic pressure chamber75decreases. The stopper pin78is provided between the pin holder74and the slide pin76and blocks rotation of the slide pin76around its axial line.

As shown inFIGS. 6 and 7, the pin holder74has integrally provided thereon a ring portion74awhich is fitted for sliding movement in the valve lifter711and a bridging portion74bwhich bridges the inner periphery of the ring portion74aalong a diametrical line of the ring portion74a.The inner periphery of the ring portion74aand the opposite side faces of the bridging portion74bare recessed by removing material in order to reduce the weight of the pin holder74. The pin holder74having such a configuration as just described is formed by lost wax casting or forging of iron or aluminum alloy or otherwise from a synthetic resin material. The outer peripheral face of the pin holder74made of metal, that is, the outer peripheral face of the ring portion74a,and the inner peripheral face of the valve lifter711are formed by a cementation process.

An annular groove79is provided on the outer periphery of the ring portion74a,and a bottomed sliding hole80is provided in the bridging portion74bof the pin holder74. The sliding hole80has an axial line along a diametrical line of the ring portion74a,that is, an axial line perpendicular to the axial line of the valve lifter711, and is open at an end thereof to the annular groove79but is closed up at the other end thereof. An insertion hole81is provided at a lower portion of a central portion of the bridging portion74band is open at an inner end thereof to the sliding hole80. An end portion of the valve stem59of the first intake valve561is inserted in the insertion hole81. An extension hole82is provided coaxially with the insertion hole81at an upper portion of a central portion of the bridging portion74bsuch that it can receive an end portion of the valve stem59of the first intake valve561. The extension hole82cooperates with the insertion hole81to sandwich the sliding hole80.

A cylindrical accommodating tubular portion83coaxial with the axial line of the extension hole82is provided integrally with the bridging portion74bof the pin holder74at a location at which it is opposed to the closed end of the valve lifter711. A disk-shaped shim84is partly fitted in the accommodating tubular portion83and closes up an end portion of the extension hole82on the closed end side of the valve lifter711. In addition, a projection85is provided integrally with a central portion of the inner face of the closed end of the valve lifter711and contacts with the shim84. The slide pin76is fitted for sliding movement in the sliding hole80of the pin holder74. It is to be noted that, where the pin holder74is made of a synthetic resin material, only the slidably contacting portion thereof with the slide pin76may be made of a metal material.

The hydraulic pressure chamber75is formed between one end of the slide pin76and the inner face of the valve lifter711in a communicating relationship with the annular groove79. A spring chamber86is formed between the other end of the slide pin76and the closed end of the sliding hole80, and a return spring77is accommodated in the spring chamber86.

As shown inFIG. 8, an accommodating hole87is provided at an intermediate portion in the axial direction of the slide pin76. The accommodating hole87coaxially connects to the insertion hole81and the extension hole82such that it can accommodate an end portion of the valve stem59therein. An end portion of the accommodating hole87on the insertion hole81side is open to a flat contacting face88which is formed on the outer side face of a lower portion of the slide pin76in an opposing relationship to the insertion hole81. Here, the contacting face88is formed comparatively long along the axial direction of the slide pin76, and the accommodating hole87is open to a portion of the contacting face88on the spring chamber86side.

The slide pin76having such a configuration as described above is slidably moved in the axial direction such that the hydraulic force acting upon one end side of the slide pin76by the hydraulic pressure of the hydraulic pressure chamber75and the spring force acting upon the other end side of the slide pin76from the return spring77may balance each other. In an inoperative state wherein the hydraulic pressure of the hydraulic pressure chamber75is low, the valve stem59fitted in the insertion hole81is moved in the upward direction inFIG. 5such that an end portion of the valve stem59is accommodated into the accommodating hole87and the extension hole82. In an operative state wherein the hydraulic pressure of the hydraulic pressure chamber75is high, however, the slide pin76is displaced from the axial line of the insertion hole81and the extension hole82and the valve stem59is moved in the downward direction inFIG. 5such that an end portion of the valve stem59contacts with the contacting face88.

Consequently, when the slide pin76is moved to the position at which the accommodating hole87thereof connects coaxially with the insertion hole81and the extension hole82, the valve lifter711is slidably moved by the pressing force acting thereupon from the first intake side valve cam691, whereupon also the pin holder74and the slide pin76are moved to the first intake valve561side together with the valve lifter711. However, the end portion of the valve stem59is merely accommodated into the accommodating hole87and the extension hole82, but the pressing force in the valve opening direction does not act from the valve lifter711and the pin holder74upon the first intake valve561. Consequently, the first intake valve561remains in an inactive state.

On the other hand, when the slide pin76is moved to the position at which the end portion of the valve stem59contacts with the contacting face88of the slide pin76, since the pressing force in the valve opening direction acts upon the first intake valve561upon movement of the pin holder74and the slide pin76to the first intake valve561side in response to sliding movement of the valve lifter711by the pressing force acting from the first intake side valve cam691, the first intake valve561operates to open and close in response to rotation of the first intake side valve cam691.

Incidentally, if the slide pin76is rotated around the axial line thereof within the pin holder74, then the axial lines of the accommodating hole87and the insertion hole81and extension hole82are displaced from each other and it becomes impossible to allow the end portion of the valve stem59to contact with the contacting face88. Therefore, rotation of the slide pin76around its axial line is blocked by the stopper pin78.

The stopper pin78is mounted in mounting holes89and90provided coaxially in the bridging portion74bof the pin holder74such that a portion thereof on one end side of the sliding hole80is sandwiched between them. The stopper pin78extends through a slit91provided on one end side of the slide pin76such that it is open to the hydraulic pressure chamber75side. In particular, the stopper pin78is mounted on the pin holder74such that it extends through the slide pin76while allowing movement of the slide pin76in the axial direction, and as the stopper pin78contacts with the inner end closed portion of the slit91, also the movement end of the slide pin76to the hydraulic pressure chamber75side is restricted.

A coil spring92is interposed between the pin holder74and the cylinder head40and biases the pin holder74in a direction in which the shim84mounted on the pin holder74contacts with the projection85provided at a central portion of the inner face of the closed end of the valve lifter711. The coil spring92is attached in such a manner as to surround the valve stem59at a position at which an outer periphery thereof is prevented from contacting with the inner face of the valve lifter711. A pair of projections93and94are formed integrally in a projecting manner on the bridging portion74bof the pin holder74. The projections93and94position the end portion of the coil spring92in a direction perpendicular to the axial direction of the valve stem59.

Here, the projections93and94are provided integrally in a projecting manner on the pin holder74with a projecting amount smaller than the wire diameter of the coil spring92and are formed in arcs centered at the axial line of the valve stem59. Further, a stepped portion95is formed on the projection93from between the projections93and94for contacting with an end portion of the stopper pin78on the first intake valve561side to block the stopper pin78from moving toward the first intake valve561side.

The slide pin76has a communication hole96formed therein for communicating the spring chamber86with the accommodating hole87to prevent increase or decrease of the pressure in the spring chamber86by a movement of the slide pin76in the axial direction. Meanwhile, the pin holder74has another communication hole97formed therein for communicating the space between the pin holder74and the valve lifter711with the spring chamber86to prevent the pressure in the space from being varied by a temperature variation.

The cylinder head40has a supporting hole98formed therein for receiving the valve lifter711to support the valve lifter711for sliding movement, and an annular recess99is formed on the inner face of the supporting hole98such that it surrounds the valve lifter711. The valve lifter711has a communication hole100formed therein for communicating the annular recess99with the annular groove79of the pin holder74irrespective of sliding movement of the valve lifter711within the supporting hole98. The valve lifter711further has a release hole101formed therein. The release hole101is provided at a position in the valve lifter711at which, when the valve lifter711moves to its uppermost position as seen inFIG. 5, the release hole101establishes communication of the annular recess99with the inside of the valve lifter711below the pin holder74, but as the valve lifter711moves downward from the uppermost position as seen inFIG. 5, the communication with the valve lifter711is intercepted. Thus, lubricating oil is jetted from the release hole101into the valve lifter711.

Further, working fluid supply paths103A,103B and103C hereinafter described are provided in the cylinder head40and communicate with the annular recesses99provided for the individual combustion chambers43.

The first and second exhaust valves571and572of the combustion chambers43are driven by an exhaust side valve system68E. The exhaust side valve system68E includes a camshaft106, valve lifters1071and1072of a bottomed cylindrical shape. The camshaft106has provided thereon first exhaust side valve cams1051individually corresponding to the first exhaust valves571and second exhaust side valve cams1052individually corresponding to the second exhaust valves572. The valve lifters1071are supported on the cylinder head40such that they can be slidably moved following the first exhaust side valve cams1051. The valve lifters1072are supported on the cylinder head40such that they can be slidably moved following the second exhaust side valve cams1052.

The camshaft106has an axial line perpendicular to the axial line extensions of the valve stems61of the first and second exhaust valves571and572and is supported for rotation between the cylinder head40and the holder55coupled to the cylinder head40similarly to the camshaft70of the intake side valve system68I. The valve lifters1071are fitted for sliding movement in the cylinder head40in same coaxial directions with the axial lines of the valve stems61of the first exhaust valves571and slidably contact at outer faces of the closed ends thereof with the first exhaust side valve cams1051.

Meanwhile, the valve lifters1072are fitted for sliding movement in the cylinder head40in same coaxial directions with the axial lines of the valve stems61of the second exhaust valves572and slidably contact at outer faces of the closed ends thereof with the second exhaust side valve cams1052.

Tip ends of the valve stems61of the second exhaust valves572contact with the inner faces of the closed ends of the valve lifters1072such that, during operation of the engine E, the valve stems61are normally operated to open and close the second exhaust valves572by the second exhaust side valve cams1052. Meanwhile, a valve cut-off mechanism73E is provided between each of the valve stems61of the first exhaust valves571and the corresponding valve lifter1071. The valve cut-off mechanism73E can change over between an active state and an inactive state of the pressing force in the valve opening direction from the valve lifter1071to the first exhaust valve571. Thus, when the engine E is in a particular operation region, for example, when the engine E is in a low load region such as a low speed operation region, the valve cut-off mechanism73E places the pressing force into an inactive state to place the first exhaust valve571into a cut-off state irrespective of a sliding movement of the valve lifter1071. The valve cut-off mechanism73E is configured similarly to the valve cut-off mechanism73I of the intake side valve system68I.

In the #3cylinder, a valve cut-off mechanism73E and another valve cut-off mechanism73I having similar configurations to those of the #4cylinder described above are provided for the second exhaust valve572(corresponding to the second exhaust valve port452) and the second intake valve562(corresponding to the second intake valve port442), respectively, conversely to the arrangement in the #4cylinder. Further, a valve cut-off mechanism73I and a valve cut-off mechanism73E are provided for all of the intake valves and the exhaust valves of the #2cylinder and the #1cylinder.

Accordingly, the #1cylinder and the #2cylinder can perform cylinder cut-off wherein all of the engine valves thereof are cut off while the #3cylinder and the #4cylinder can perform valve cut-off wherein one engine valve is cut off on both of the intake side and the exhaust side (while the cylinders normally operate).

As shown inFIG. 4, the cam chain case C is provided on the side wall of the cylinder head40on the #4cylinder side. A cam chain not shown for driving the camshafts70and106of the intake side and exhaust side valve systems68I and68E is accommodated in the cam chain case C.

Connection ports PA, PB and PC of oil pressure regulating valves113A,113B and113C are formed in a side wall of the cylinder head40on the opposite side to the cam chain case C. The oil pressure regulating valves113A,113B and113C control supply of working fluid to the valve cut-off mechanisms73I and73E of the intake side and exhaust side valve systems68I and68E.

The connection port PA is connected to the working fluid supply path103A which extends along a longitudinal direction of the cylinder head40between a central portion of the cylinder head40in the forward and backward direction and the intake valve ports to the location of the second intake valve port442of the #2cylinder in the cylinder head40and is branched to the second intake valve port442of the #2cylinder and the second exhaust valve port452of the #2cylinder.

The connection port PB is connected to the working fluid supply path103B which extends along the longitudinal direction of the cylinder head40between a central portion of the cylinder head40in the forward and backward direction and the exhaust valve ports to the location of the first exhaust valve port451of the #1cylinder in the cylinder head40and is branched to the first exhaust valve port451of the #1cylinder and the first intake valve port441of the #1cylinder.

The connection port PC is connected to the working fluid supply path103C which extends along the longitudinal direction of the cylinder head40in the second side wall of the cylinder head40to the location of the first exhaust valve port451of the #4cylinder and is branched to the first exhaust valve port451of the #4cylinder, the second exhaust valve port452of the #3cylinder, the first exhaust valve port451of the #2cylinder and the second exhaust valve port452of the #1cylinder. Corresponding to the working fluid supply path103C, a working fluid supply path103C′ is formed along the longitudinal direction of the cylinder head40in the rear wide wall of the cylinder head40and extends to the location of the first intake valve port441of the #4cylinder. The working fluid supply path103C and the working fluid supply path103C′ are connected to each other by a crossing path103X. The working fluid supply path103C′ is branched and connected to the first intake valve port441of the #4cylinder, the second intake valve port442of the #3cylinder, the first intake valve port441of the #2cylinder and the second intake valve port442of the #1cylinder. Note that two valves on #4cylinder and two valves on #3cylinder are in fluid isolation with respect to the working fluid supply paths.

Accordingly, in the #1cylinder and the #2cylinder from among those cylinders which are positioned on the opposite side to the cam chain case C, that is, the #1cylinder, #2cylinder and #3cylinder, all engine valves, that is, the first intake valves561, second intake valve562, first exhaust valves571and second exhaust valves572are formed for cut-off operation.

Thus, each of the oil pressure regulating valves113A,113B and113C applies the working fluid pressure from an in port IN to the connection port PA, PB or PC when the solenoid not shown is operated to ON, but introduces, when the solenoid is operated to OFF, the working fluid pressure to a drain port D such that the working fluid is supplied to the valve cut-off mechanisms73E and73I through the working fluid supply path103A, working fluid supply path103B and working fluid supply path103C (103C′) by the oil pressure regulating valves113A,113B and113C, respectively. It is to be noted that, inFIG. 4, reference character IN denotes an in port, OUT an out port, and D a drain port.

As a result, the engine E of the present embodiment performs, when the engine is idling or in a low load region, cylinder cut-off (cut-off of all valves) in the #1cylinder and the #2cylinder, and performs valve cut-off in the #3cylinder and the #4cylinder as seen in (a) ofFIG. 9. When the engine is in a low or middle load region, the engine E performs cylinder cut-off (cut-off of all valves) in the #1cylinder and performs valve cut-off in the #2cylinder, #3cylinder and #4cylinder as seen in (b) ofFIG. 9. When the engine is in a middle load region, the engine E performs valve cut-off in all of the cylinders from the #1cylinder to the #4cylinder to operate them as seen in (c) ofFIG. 9. When the engine is in a high load region, the engine E can operate all of the engine valves, without performing valve cut-off, in all of the cylinders from the #1cylinder to the #4cylinder as seen in (d) ofFIG. 9.

Accordingly, at least the #4cylinder which is a cylinder on one end side from among the four cylinders disposed in-line serves as a normally operative cylinder (cylinder wherein only some of the engine valves is cut off), and at least the #1cylinder which is a cylinder on the other end side is a cylinder which can be cut off (cylinder wherein all of the engine valves can be cut off).

Here, the timing at which the engine enters into any of the load regions can be determined depending upon the engine speed and the grip opening. Accordingly, while the engine speed changes from the idling or low load region through the low and medium load region and the middle load region to the high load region, valve cut-off and cylinder cut-off can be performed stepwise to achieve smooth acceleration and deceleration. Further, if an electronically controlled throttle is adopted for the throttle valves TH, then since such control that, when cylinder cut-off is to be performed, the throttle valves TH corresponding to the cylinders to be cut off are closed, but when the valve cut-off is to be canceled, the throttle valves TH are successively opened can be performed, upon restoration from the cylinder cut-off, the shock can be minimized thereby to achieve smooth running. It is to be noted that a circle represented by slanting lines indicates an engine valve in a cut-off state.

According to the embodiment described above, all of the first intake valve561, second intake valve562, first exhaust valve571and second exhaust valve572which are engine valves of each of the #1cylinder and the #2cylinder positioned on the opposite side to the cam chain case C are formed such that they can be cut off by the valve cut-off mechanisms73I and73E. Therefore, the connection ports PA, PB and PC of all of the hydraulic circuits for applying a working fluid pressure to the valve cut-off mechanisms73I and73E, that is, all of the working fluid supply path103A, working fluid supply path103B and working fluid supply path103C (working fluid supply path103C′), can be provided in the side wall of the cylinder head40on the opposite side to the cam chain case C. Consequently, the working fluid supply path103A and the working fluid supply path103B which are hydraulic pressure paths from the connection ports PA and PB to the #1cylinder and the #2cylinder can be formed shorter and can be simplified.

Accordingly, the cylinder head can be miniaturized by an amount by which the working fluid supply path103A and the working fluid supply path103B are formed shorter.

In short, where a cylinder wherein all engine valves are cut off is provided on the side on which the cam chain case C is provided, it is necessary to extend the working fluid supply path103A and the working fluid supply path103B corresponding to them up to the cam chain case C side. Consequently, the path length increases as much and the cylinder head40increases in size as much.

As a result, the in-line four-cylinder engine which has a great length in the vehicle widthwise direction from its nature can be miniaturized. Therefore, application to a straight four-cylinder engine wherein the first intake valve561, second intake valve562, first exhaust valve571and second exhaust valve572can be cut off is facilitated.

In particular, while working fluid supply paths are required where it is tried to provide cylinder cutting off and valve cutting off functions to the motorcycle1wherein the cam chain case C is disposed on the outer side in the widthwise direction of the engine E in order to achieve reduction in size and weight of the engine E, the working fluid supply paths can be disposed such that the engine E does not increase in scale as far as possible.

Further, since the #4cylinder which is a cylinder on the one end side from among the four cylinders disposed in-line is formed as a normally operative cylinder while the #1cylinder which is a cylinder on the other end side is formed as a cylinder which can be cut-off, the connection ports PA, PB and PC can be provided in the side wall of the cylinder head40on the side on which the #1cylinder that can be cut off is disposed. Therefore, the working fluid supply path103A and the working fluid supply path103B which are hydraulic pressure paths from the connection ports PA and PB to the #1cylinder and the #2cylinder can be formed shorter and simplified. Consequently, the cylinder head40can be miniaturized by an amount by which they are simplified.

It is to be noted that the present invention is not limited to the embodiment described above but includes also a case wherein, for example, only the #1cylinder can be controlled to a cylinder cut-off state. Further, the valve cut-off mechanisms73I and73E are a mere example, and the present invention is not limited to such a structure as just described only if some cylinder can be hydraulically placed into a cut-off state.

As described above, according to the invention, it is possible to set ports for many working fluid supply paths to a side wall of the cylinder head on the opposite side to the cam chain case in which the working fluid supply paths are formed in order to cut off all of the engine valves. Consequently, there is an effect that the working fluid supply paths from the ports to some of the cylinders wherein all of the engine valves are formed such that they can be cut off from among those cylinders which are positioned on the opposite side to the cam chain case can be formed shorter and can be simplified.

Accordingly, the cylinder head can be miniaturized by an amount by which the working fluid supply paths are simplified.

According to the invention, the in-line four-cylinder engine which has a great length in the vehicle widthwise direction from its nature can be miniaturized. Therefore, there is an effect that application to a straight four-cylinder engine wherein the engine valves can be cut off is facilitated.

According to the invention, it is possible to set ports for working fluid Supply paths to a side wall of the cylinder head on which those cylinders which can be cut off are disposed. Therefore, the working fluid supply paths to the cylinders which can be cut off may be formed shorter and simplified. Accordingly, there is an effect that the cylinder head can be miniaturized by an amount by which the working fluid supply paths are simplified.