Adjustable valve train for an internal combustion engine, and engine and motorcycle incorporating same

A valve train for an internal combustion engine includes a camshaft, a valve-operating cam for operating an engine valve, and a link mechanism for swinging the valve-operating cam. The valve train also includes a holder member operable to turn around the camshaft, and a drive mechanism operable to turn the holder member for varying positions of the link mechanism. The drive mechanism includes a ball screw provided perpendicularly to the camshaft, a slider threadably engaged with the ball screw, an arm member swingably attached to the slider, and a connecting bolt having one end secured to an arm-connecting portion of the arm member, and the other end secured to the holder member. In such movable valve train for an internal combustion engine, the holder member and the drive mechanism are connected to each other with a small and lightweight configuration, requiring a minimal number of parts.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present invention claims priority under 35 USC 119 based on Japanese patent application No. 2009-295155, filed on Dec. 25, 2009. The entire subject matter of this priority document, including specification claims and drawings thereof, is incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a movable valve train for an internal combustion engine, and to an engine and a motorcycle incorporating the same. More particularly, the present invention relates to a valve train having a link mechanism for swinging a valve-operating cam, and a drive mechanism operable to turn a holder member for varying positions of the link mechanism, and to an engine and a motorcycle including the same.

2. Description of the Background Art

There is known a movable valve train for an internal combustion engine. The movable valve train includes a drive cam rotated integrally with a camshaft supported by a cylinder head, and a valve-operating cam swingably supported by the camshaft to operate, i.e., to open and close engine valves. In addition, the movable valve train includes a link mechanism supported swingably around the camshaft for transmitting a valve driving force of the drive cam to the valve-operating cam for swing, a holder member connected to the link mechanism and turnable around the camshaft, and a drive mechanism for turning the holder member for varying positions of the support member of the link mechanism. The valve train configured as above can vary operating characteristics of the engine valve depending on the swing position of the swung link mechanism.

An example of such known movable valve train for an internal combustion engine is disclosed in the Japanese Patent Laid-open No. 2008-208800.

Incidentally, the movable valve train as described above is desired to connect the holder member connected to the link mechanism with the drive mechanism by a simple configuration and by using small number of parts.

In view of the above situations, the present invention has been made. Accordingly, one of the objects of the present invention is to provide a movable valve train for an internal combustion engine that can connect a holder member connected to a link mechanism with a drive mechanism by means of a small-sized lightweight configuration having a small number of parts.

SUMMARY OF THE INVENTION

In order to achieve the above objects, the present invention provides a variable valve train for an internal combustion engine. The variable valve train includes a camshaft rotatably supported by a cylinder head and rotated in synchronization with rotation of a crankshaft of the engine; a drive cam rotated integrally with the camshaft; a valve-operating cam swingably supported by the camshaft and opening/closing an engine valve; a link mechanism supported swingably around the camshaft to transmit valve drive force of the drive cam to the valve-operating cam for swinging the valve-operating cam; a holder member on which a support member of the link mechanism is provided and which can turn around the camshaft; and a drive mechanism turning the holder member to vary a position of the support member of the link mechanism. The operating characteristics of the opening and closing engine valve being capable of being varied depending on the swung position of the swung link mechanism.

The drive mechanism includes a ball screw provided perpendicularly to the camshaft, a slider threadably engaged with the ball screw, an arm member swingably attached to the slider, and a connecting member having one end secured to a swing portion-end of the arm member and the other end secured to the holder member.

With this configuration, the arm member is swingably attached to the slider and the swing portion-end of the arm member and the holder member are secured to each other through the connecting member. Therefore, the slider and the holder member can be connected to each other with a simple configuration. Thus, the holder member and the drive mechanism can be connected to each other by a small-sized and lightweight configuration having a small number of parts.

In the above configuration, the connecting member may be configured to have a first thread portion fastened to the holder member side and a second thread portion fastened to a connecting portion of the arm member.

In this case, the connecting member has the first and second thread portions, and is separately fastened on the holder member side and on the arm member side. Therefore, the connecting member can reliably be secured. This can reduce the assembly error between the holder member and the arm member.

The first thread portion may be configured to have a thread diameter smaller than that of the second thread portion.

In this case, the second thread portion, on the holder member side, requiring greater fastening force is increased in diameter and the first thread portion requiring smaller fastening force is reduced in diameter. This makes the fastening force appropriate, so that the assembly error can be reduced.

Further, a nut fastening the first thread portion may be configured to have the other end thereof extended to the connecting portion of the arm member, and to fasten the arm member to the connecting member in cooperation with a nut fastening the second thread portion.

In this case, the nut fastening the first thread portion is extended to the connecting portion of the arm member. In addition, the nut fastened to the second thread portion and the extended portion of the nut of the first thread portion can cooperatively fasten the arm member to the connecting member. Therefore, it is not necessary to use a spacer receiving the nut fastening the second thread portion. Thus, the number of component parts can be reduced.

An attachment portion for the slider and the arm member may be configured as a vertical groove. That is, the slider includes an attachment portion having a vertical groove formed therein. The arm member is assembled with the slider via said vertical groove.

In this case, the slider and the arm member are attached to each other using the vertical groove; therefore, the assembly of the arm member can be facilitated.

EFFECTS OF THE INVENTION

In the variable valve train of the internal combustion engine according to the present invention, the arm member is swingably attached to the slider and the swing portion-end of the arm member and the holder member are secured by means of the connecting member. Therefore, the slider and the holder member can be connected to each other with a simple configuration. Thus, the holder member and the drive mechanism can be connected to each other with a small-sized and lightweight configuration having a small number of parts.

The connecting member has the first and second thread portions and is separately fastened on the holder member side and on the arm member side. The connecting member can reliably be secured. This can reduce the assembly error between the holder member and the arm member.

The second thread portion, on the holder member side, requiring fastening force is increased in diameter and the first thread portion requiring smaller fastening force is reduced in diameter. This makes the fastening force appropriate, so that the assembly error can be reduced.

The nut fastened to the second thread portion and the extended portion of the nut of the first thread portion can cooperatively fasten the arm member to the connecting member. Therefore, it is not necessary to use a spacer receiving the nut fastening the second thread portion. Thus, the number of component parts can be reduced.

The slider and the arm member are attached to each other using the vertical groove; therefore, the assembly of the arm member can be facilitated.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

An embodiment of the present invention will now be described, with reference to the drawings. Throughout this description, relative terms like “upper”, “lower”, “above”, “below”, “front”, “back”, and the like are used in reference to a vantage point of an operator of the vehicle, seated on the driver's seat and facing forward. It should be understood that these terms are used for purposes of illustration, and are not intended to limit the invention.

Illustrative embodiments of the present invention will hereinafter be described with reference to the drawings. It may be noted that orientations such as the front, back or rear, left and right, and upside and downside in the explanation are described based on an operative orientation of a vehicle body.

FIG. 1is a lateral view of a motorcycle employing a valve train of an internal combustion engine according to an embodiment of the present invention. The motorcycle10includes a body frame11; a pair of left and right front forks13turnably supported by a head pipe12attached to a front end of the body frame11; a steering handlebar15attached to a top bridge14supporting an upper end of the front forks13; and a front wheel16rotatably supported by the front fork13. The motorcycle10further includes an engine17as an internal combustion engine supported by the body frame11; exhaust mufflers19A and19B connected via exhaust pipes18A and18B, respectively, to the engine17; a rear swing arm21supported swingably up and down by a pivot20at a rear lower portion of the body frame11; and a rear wheel22rotatably supported by a rear end of the rear swing arm21. A rear cushion23is disposed between the rear swing arm21and the body frame11.

The body frame11includes a main frame25extending rearward downward from the head pipe12; a pair of left and right pivot plates (also called center frames) connected to a rear portion of the main frame25; and a down tube27extending downward from the head pipe12, then bending and extending, and connected to the pivot plate26. A fuel tank28is supported by the main frame25so as to straddle it. A rear portion of the main frame25extends to above the rear wheel22and supports a rear fender29. A seat30is supported between above the rear fender29and the fuel tank28. As shown inFIG. 1, the motorcycle includes a radiator31supported by the down tube27, a front fender32, a side cover33, a headlight34, a taillight35, and an occupant step36.

The engine17is supported in a space surrounded by the main frame25, the pivot plate26and the down tube27. The engine17is a fore-aft V-type 2-cylinder water-cooled 4-cycle engine whose cylinders are banked forwardly and rearwardly in a V-shaped manner. The engine17is supported by the body frame11via a plurality of engine brackets37(only partially illustrated inFIG. 1) so that a crankshaft105may be oriented in a left-right horizontal direction relative to the vehicle body. Power of the engine17is transmitted to the rear wheel22via a drive shaft (not shown) disposed on the left side of the rear wheel22.

The engine17is such that a V-angle (also called a bank angle) formed between a front bank110A and a rear bank110B both constituting corresponding cylinders is smaller (e.g.52degrees) than 90 degrees. The respective valve trains of the banks110A,110B are each configured as a 4-valve double over head camshaft (DOHC) type.

An air cleaner41and a throttle body42constituting an engine air intake system is disposed in a V-shaped space defined between the front bank110A and the rear bank110B. The throttle body42supplies air purified by the air cleaner41to the front bank110A and the rear bank110B. The exhaust pipes18A and18B, which constitute an engine exhaust system, are connected to the banks110A and110B, respectively. The exhaust pipes18A and18B pass on the right side of the vehicle body and connect with exhaust mufflers19A and19B, respectively, at their rear ends. Exhaust gas is discharged through the exhaust pipes18A,18B and corresponding exhaust mufflers19A,19B.

FIG. 2is a lateral view of an internal configuration of the engine17.FIG. 3is an enlarged view of an internal configuration of the front bank110A ofFIG. 2.

Referring toFIG. 2, the front bank110A and rear bank110B of the engine17have the same configuration.FIG. 2illustrates the vicinity of the piston in the front bank110A and the vicinity of a cam chain in the rear bank110B. InFIG. 2, reference symbol121denotes an intermediate shaft (a rear balancer shaft),123denotes a main shaft and125denotes a counter shaft. These shafts121,123,125including the crankshaft105are offset from one another in the back and forth, and up and down directions of the vehicle body so as to be arranged parallel to one another. A gear transmission mechanism configured to transmit the rotation of the crankshaft105to the intermediate shaft121, the main shaft123and the counter shaft125in this order is disposed in a crankcase110C supporting these shafts.

As illustrated inFIG. 2, a front cylinder block131A and a rear cylinder block131B are disposed on the upper surface of the crankcase110C of the engine17so as to form a predetermined V-angle in the back and front of the vehicle body. A front cylinder head132A and a rear cylinder head132B are joined to the upper surfaces of the cylinder blocks131A and131B, respectively. Further, head covers133A and133B (cylinder head covers) are mounted to the upper surfaces of the cylinder heads132A and132B, respectively. In this way, the front bank110A and the rear bank110B are configured.

The cylinder blocks131A,131B are each formed with a cylinder bore135, into which a piston136is slidably inserted. The piston136is connected to the crankshaft105via a connecting rod137.

The cylinder heads132A,132B are each formed in a lower surface with a combustion recessed portion141constituting a top surface of a combustion chamber formed above the piston136. An ignition plug142is disposed such that its distal end faces the combustion recessed portion141. In addition, the ignition plug142is provided generally concentrically with a cylinder axis C.

The engine17is a direct injection engine which directly injects fuel into the combustion chamber from an injector143provided on the combustion recessed portion141. The injector143is disposed to be inserted from a V-bank inner lateral surface of each of the cylinder heads132A,132B so that its distal end faces the associated combustion recessed portion141. The injector143is mounted so as to have an angle relative to the cylinder axis C.

A fuel pump144is disposed above the cylinder head133A. Fuel is supplied from the fuel pump144via the fuel pipe144A to the injectors143.

The cylinder heads132A,132B are each formed with intake ports145communicating with the corresponding combustion recessed portion141at a pair of opening portions145A and with exhaust ports146communicating with the combustion recessed ports141at a pair of opening portions146A. The intake port145is disposed between the cylinder axis C and the injector143.

As illustrated inFIGS. 2 and 3, the intake port145includes a lower intake port145B provided integrally with each of the cylinder heads132A,132B, and an upper intake port145C provided separately from each of the cylinder heads132A,132B. The upper intake port145C is attached to the lower intake port145B so as to have an angle varied in a direction coming closer to each of the head covers133A,133B.

The intake ports145merge into an intake chamber43, which is joined to the throttle body42. The throttle body42employs throttle-by-wire (TBW) which varies the sectional area of the throttle valve by driving of an actuator. An exhaust port146of the cylinder head132A is joined to the exhaust pipe18A (FIG. 1). An exhaust port146of the cylinder head132B is joined to the exhaust pipe18B (FIG. 1).

A pair of intake valves147(engine valves) for opening and closing the opening portions145A of the intake ports145and a pair of exhaust valves148(engine valves) for opening and closing the opening portions146A of the intake ports146are arranged on each of the cylinder heads132A,132B. The intake valves147and the exhaust valves148are biased by corresponding valve springs149,149in a direction of closing the corresponding ports.

The valve bodies147,148are driven by a valve train50(a movable valve train) that can vary valve operating characteristics such as opening/closing timing, a lift amount, etc. of the engine valve. The valve train50includes intake side and exhaust side camshafts151and152rotatably supported by the cylinder heads132A and132B, respectively. The camshafts151and152are rotated in conjunction with the rotation of the crankshaft105. The camshafts151,152are rotated in a counterclockwise rotating direction inFIGS. 2 and 4.

The camshaft151is formed integrally with an intake cam153(a drive cam). The intake cam153includes a base circular portion153A forming a circular cam surface and a cam lobe portion153B forming a cam surface projecting from the base circular portion153A toward the external circumferential side. The camshaft152is formed integrally with an exhaust cam154(a drive cam). The exhaust cam154includes a base circular portion154A forming a circular cam surface and a cam lobe portion154B projecting from the base circular portion154A toward the external circumferential side to form a lobe-like cam surface.

As illustrated inFIG. 2, the intermediate shaft158is rotatably supported on one end side in the width direction of each of the cylinder heads132A,132B and intermediate sprockets159,160are secured to the intermediate shaft158. A driven sprocket161is secured to one end side of the camshaft151. A driven sprocket162is secured to one end side of the camshaft152. A drive sprocket163is secured to both end sides of the crankshaft105. A first cam chain164is wound between the sprockets159,163and a second cam chain165is wound between the sprockets160to162. The sprockets159to163and the cam chains164,165are housed in a cam chain chamber166formed on one end side of each of the banks110A,110B.

A reduction ratio from the drive sprocket163to the driven sprockets161,162is set to 2. If the crankshaft105is rotated, the drive sprocket163is rotated integrally therewith to rotate the driven sprockets161,162via the cam chains164,165at a rotation speed half that of the crankshaft105. In this way, the intake valves147and the exhaust valves148open and close the intake ports145and the exhaust ports146, respectively, in accordance with the cam profiles of the camshafts151,152rotated integrally with the driven sprockets161,162.

A generator (not shown) is provided at a left end portion of the crankshaft105. A drive gear (also referred as the crank side drive gear)175is secured to the right end of the crankshaft105and inside (on the left side of the vehicle body) the right drive sprocket163mentioned above. The crank side drive gear175meshes with a driven gear (also referred as the intermediate side driven gear)177provided on the intermediate shaft121. In addition, the crank side drive gear175transmits the rotation of the crankshaft105to the intermediate shaft121at a constant-speed to rotate it at the same speed as and reversely to that of the crankshaft105.

The intermediate shaft121is rotatably supported rearward of and below the crankshaft105and forward of and below the main shaft123.

An oil pump drive sprocket181, the intermediate side driven gear177and a drive gear (also referred as the intermediate side drive gear) smaller in diameter than the driven gear177are mounted in this order to the right end portion of the intermediate shaft121.

The oil pump drive sprocket181is adapted to transmit the rotational force of the intermediate shaft121via a transmission chain187to a driven sprocket186to drive a oil pump184. The driven sprocket186is secured to a drive shaft185of the oil pump184disposed rearward of the intermediate shaft121and below the main shaft123.

The intermediate side drive gear182meshes with a driven gear (also referred as the main side driven gear)191provided relatively rotatably on the main shaft123to reduce the rotation speed of the intermediate shaft121and transmit it to the main shaft123via a clutch mechanism (not shown). In other words, the reduction ratio from the crankshaft105to the main shaft123, i.e., a primary reduction ratio of the engine17is set based on the reduction ratio between the intermediate side drive gear182and the main side driven gear191.

The main shaft123is rotatably supported rearwardly of and above the crankshaft105and the counter shaft125is rotatably supported generally rearward of the main shaft123. Speed-change gear groups not shown are arranged to straddle the main shaft123and the counter shaft125to constitute a transmission device.

A drive shaft (not shown) extending in the back and forth direction of the vehicle body is coupled to a left end portion of the counter shaft125. Thus, the rotation of the counter shaft125is transmitted to the drive shaft.

FIG. 4is a partially broken-out lateral view of the valve train50andFIG. 5is a longitudinal cross-sectional view of the valve train50of the front bank110A as viewed from the rear side.

As illustrated inFIG. 3, the valve trains50are provided on the intake side and on the exhaust side symmetrically to the cylinder axis C and independently of each other. Since the respective valve trains50of the front bank110A and the rear bank110B have generally the same configuration, the valve train50on the intake side of the front bank110A is described in the present embodiment.

Referring toFIGS. 4 and 5, the valve train50includes the camshaft151(the camshaft152on the exhaust side); the intake cam153(the intake cam154on the exhaust side) rotated integrally with the camshaft151; and a rocker arm51opening and closing the intake valves147(the exhaust valves148on the exhaust side). The valve train50further includes a valve-operating cam52relatively rotatably supported by the camshaft151and opening and closing the intake valves147via the rocker arm51; a holder member53swingable around the camshaft151; a link mechanism56swingably supported by the holder member53to transmit the valve driving force of the intake cam153to the valve-operating cam52for swing; and a drive mechanism60(see FIG.6) turning the holder member53. The link mechanism56includes a sub-rocker arm54connected to the holder member53and a connecting link55swingably connecting the sub-rocker arm54with the valve-operating cam52.

The rocker arm51is formed wide so that one rocker arm51opens and closes the pair of intake valves147. The rocker arm51is swingably supported at one end by a rocker arm pivot51A secured to the cylinder head132A. Screw-type adjustment portions51B are provided at the other end of the rocker arm51so as to come into abutment against the upper ends of the intake valves147. A roller51C is rotatably supported by the central portion of the rocker arm51so as to come into contact with the valve-operating cam52.

Referring toFIG. 5, the camshaft151has on one end side a sprocket securing portion151A to which the driven sprocket161(FIG. 2) is secured. In addition, in order from the sprocket securing portion151A, a positioning portion151B, the intake cam153, a valve-operating cam supporting portion151C and a collar fitting portion151D are provided on the camshaft151. The positioning portion151B is formed circular in cross-section to project from the outer circumference of the camshaft151.

The valve-operating cam supporting portion151C swingably supports the valve-operating cam52. The collar fitting portion151D is formed to have a diameter smaller than that of the valve-operating cam supporting portion151C. A camshaft collar155functioning as a bearing of the camshaft151is fitted to the collar fitting portion151D. The camshaft collar155is pressed against the valve-operating cam52by a securing bolt156fastened to the other end side of the camshaft151.

The camshaft151is rotatably supported at both ends by camshaft supporting portions201,202. Specifically, the camshaft support portions201,202are configured such that caps201B and202B each having a support portion semicircular in cross-section are secured to head side support portions201A and202A, respectively, semi-circular in cross-section, formed on the upper portion of the cylinder head132A.

The camshaft support portion201provided on the side of the positioning portion151B is formed with a groove201C formed to conform to the shape of the positioning portion151B. The position of the positioning portion151B is restricted by the groove201C to axially position the camshaft151.

Holder support portions201D and202D supporting the holder member53are provided on the surfaces of the camshaft support portions201and202, respectively, on the side of the intake cam153.

The valve-operating cam52is pivotally supported by the valve-operating cam support portion151C provided at the intermediate portion of the camshaft151. As illustrated inFIG. 4, the valve-operating cam52is formed with a base circular portion52A adapted to maintain the intake valves147in a closed state and with a cam lobe portion52B adapted to press down the intake valve147to open it. The cam lobe portion52B is formed with a through-hole52C. A valve-operating cam return spring57(seeFIG. 5) is attached at one end57A to the through-hole52C. The valve-operating cam returning spring57is adapted to bias the valve-operating cam52in a direction where the cam lobe portion52B is moved away from the roller51C of the rocker arm51, i.e., in a direction of closing the intake valves147.

As illustrated inFIG. 5, the valve-operating cam return spring57is a torsion coil spring and has a coil portion57B wound around the camshaft151and attached to the holder member53at the other end. The coil portion57B is formed axially lengthwise to go over a groove portion69. The other end57C is wound toward the one end57A so as to overlap the coil portion57B. While ensuring the number of windings of the valve-operating cam return spring57, this can dispose the valve-operating cam return spring57in an axially compact manner.

The holder member53includes first and second plates53A,53B holding the intake cam153and the valve-operating cam52and spaced at a predetermined interval from each other in the axial direction of the camshaft151; and a sub-rocker arm holder59connecting together the first and second plates53A,53B in the axial direction of the camshaft151. The first plate53A is disposed at one end side of the camshaft151to which the driven sprocket161is secured. The second plate53B is disposed at the other end side of the camshaft151.

The sub-rocker arm holder59is configured to include shaft portions59A and59C parallel to the camshaft151and a joining portion45integrally joining the shaft portion59A and the shaft portion59C together. The joining portion45is formed with a cylindrical receiving portion74, in which a sub-rocker arm return spring58(also referred as a return spring) biasing the sub-rocker arm54toward the intake cam153is received.

The shaft portion59A is formed at an end close to the first plate53A with a sub-rocker arm support portion59B (the support member) connected to one end of the sub-rocker arm54. The sub-rocker arm portion59B is a shaft formed smaller in diameter than the shaft portion59A.

The first and second plates53A,53B and the sub-rocker arm holder59are secured to each other by means of a pair of bolts53D and a pair of bolts53E. The pair of bolts53D fastens the first plate53A and the sub-rocker arm holder59together from the external surface side of the first plate53A. The pair of bolts53E fastens the second plate53B and the sub-rocker arm holder59together from the external surface side of the second plate53B. An internal thread portion79to be threadably engaged with the bolt53D is formed on the shaft portion59A. An internal thread portion79to be threadably engaged with the bolt53E is formed on the shaft portion59C.

The second plate53B is formed with a bolt hole53C connected to the drive mechanism60.

The first and second plates53A and53B have shaft holes157A and158A, respectively, adapted to receive the camshaft151passed therethrough as shown inFIG. 5. The respective circumferential edge portions of the shaft holes157A and158A serve as circular projecting portions157B and158B projecting toward the holder support portions201D and202D of the camshaft support portions201and202, respectively. The holder member53is supported by the projecting portions157B and158B fitted respectively to the holder support portions201D and202D, so as to be swingable around the camshaft151. In addition, the circular projecting portions157B,158B are coaxially assembled to the camshaft151.

A clearance S is axially defined between an end of the cap201B and the bolt53D, and also between the cap202B and the bolt53E. The clearance S is set at such a size that when the cap201B is assembled to the head side support portion201A from upside, it is prevented from coming into contact with the bolt53D, and that when the cap202B is assembled to the head side support portion202A from upside, it is prevented from coming into contact with the bolt53E. In this way, since during assembly work the bolts53D,53E do not lie in the way, assembly performance is satisfactory.

The sub-rocker arm54, along with the intake cam153and the valve-operating cam52, is disposed between the first and second plates53A,53B. In addition, the sub-rocker arm54is supported at one end by the sub-rocker arm support portion59B of the sub-rocker arm holder59so as to be swingable around the sub-rocker arm support portion59B. A roller54A is rotatably supported by the central portion of the sub-rocker arm54so as to come into contact with the intake cam153and press the base circular portion153A and the cam lobe portion153B.

One end of the connecting link55is connected to the other end portion of the sub-rocker arm54via a pin55A swingably supporting the connecting link55. In addition, the other end of the connecting link55is connected to the valve-operating cam52via a pin55B swingably supporting the valve-operating cam52.

The sub-rocker arm54is biased by the return spring58. Thus, the roller54A of the sub-rocker arm54is constantly pressed against the intake cam153.

The sub-rocker arm54includes a holder connecting portion54B joined to the sub-rocker arm support portion59B and extending perpendicularly to the camshaft151; an eccentric portion54C curved downward from the holder connecting portion54B along the outer diameter of the camshaft151; and a link portion54D connected to the valve-operating cam52via the connecting link55.

The eccentric portion54C is eccentric in the axial direction of the camshaft151from the side of the first plate53A toward the second plate53B so as to avoid the intake cam153. In addition, the eccentric portion54C is formed on a lateral surface with a plate-like stepped portion76protruding in the axial direction of the camshaft151. The stepped portion76is provided to curve along the lower edge portion of the sub-rocker arm54. The lower end of the return spring58is received by the stepped portion76via a spring washer77(FIG. 4). The upper end of the return spring58is received by a circlip78engaging with a receiving portion74.

The link portion54D is provided to merge with the end of the eccentric portion54C and is joined to the valve-operating cam52via the connecting link55. As described above, since the eccentric portion54C is eccentric, the sub-rocker arm54connects together the intake cam153and the valve-operating cam52located at respective positions different from each other in the axial direction of the camshaft151.

A description is next given of the operation of the valve train50.

Referring toFIG. 4, in the valve train50configured as described above, when the camshaft151is rotated counterclockwise in the figure, the intake cam153rotated integrally with the camshaft151allows the cam lobe portion153B to lift the sub-rocker arm54via the roller54A and swing around the shaft portion59A. Along with this, the valve-operating cam52is rotated clockwise inFIG. 4around the camshaft151via the connecting link55. The rotation of the valve-operating cam52allows the cam lobe portion52B to press the rocker arm51via the roller51C and press down the intake valves147via the roller51C, opening the intake valves147.

In the state where the camshaft151is further rotated to bring the base circular portion153A of the intake cam153into abutment against the roller54A, the sub-rocker arm54is pressed down by the return spring58. At the same time, the valve-operating cam52is rotated counterclockwise, inFIG. 4, by the valve-operating cam return spring57to bring the base circular portion52A into abutment against the roller51C. In this way, the intake valves147are pressed up and closed by the valve spring149(FIG. 2).

As illustrated inFIG. 4, the valve train50is such that the drive mechanism connecting member63is connected to the holder member53. The drive mechanism connecting member63is connected to the drive mechanism60(FIG. 6) and the holder member53is swung in an arrow-A direction and in an arrow-B direction by driving the drive mechanism60.

If the holder member53is swung in the arrow-A direction, the sub-rocker arm support portion59B, along with the holder member53, is positionally varied so that the link mechanism56is swung around the axial center of the camshaft151clockwise, the roller54A is swung clockwise, and the valve-operating cam52is swung clockwise. On the other hand, if the holder member53is shifted in the arrow-B direction, the link mechanism56, along with the holder member53, is swung around the axial center of the camshaft151counterclockwise, the roller54A is swung counterclockwise, and the valve-operating cam52is swung counterclockwise.

In this manner, the valve train50is configured so that the position of the roller54A and the initial position of the swing of the valve-operating cam52are varied to make it possible to control valve operating characteristics of the intake valve147and of the exhaust valve148, i.e., opening/closing timing, opening/closing periods and an lift amount of the intake valve147and of the exhaust valve148.

The initial position of swing of the valve-operating cam52here means a swing position of the valve-operating cam52in the state where the roller54A is in abutment against the base circular portion153A of the intake cam153and the sub-rocker arm54is not lifted by the cam lobe portion153B.

For example, if the intake side holder member53is further swung in the arrow-A direction (clockwise inFIG. 4), the roller54A and the valve-operating cam52are rotated clockwise and the cam lobe portion52B comes close to the roller51C. In this state, if the camshaft151is rotated, the lift start timing of the roller54A by the cam lobe portion153B is advanced and period where the cam lobe portion52B depresses the roller51C and a depressing amount are increased. This advances the opening timing of the intake valve147and increases the opening period and lift amount of the intake valve147.

FIG. 6is a longitudinal cross-sectional view of the drive mechanism60as viewed from the lateral side.FIG. 7is a longitudinal cross-sectional view of the drive mechanism60as viewed from the front side.FIG. 8is a transverse cross-sectional view of the engine17as viewed from above. Further,FIG. 8illustrates the front and rear banks110A,110B as viewed from above the engine17along the cylinder axis C (FIG. 2).

Referring toFIG. 6, the drive mechanism60is connected to the holder members53via the corresponding drive mechanism connecting members63. The drive mechanism60includes a rod-like ball screw61disposed to straddle the camshafts151,152; two respective sliders62installed on the intake side and the exhaust side so as to be axially movable on the ball screw61; an electric actuator70adapted to turn the ball screw61(FIG. 8); and the drive mechanism connecting members63. The drive mechanism connecting member63is installed between the slider62and the holder member53.

A gear64is secured to one end portion of the ball screw61on the side of the camshaft152. The electric actuator70is connected to the gear64via a gear ring train. The electric actuator70is controlled by an electronic control unit (ECU) of the vehicle. The ECU drives the electric actuator70to swing the holder members53via the ball screw61and the drive mechanism connecting members63. Thus, the opening/closing operating characteristics of each of the intake valve147and the exhaust valve148are controlled according to the operating conditions of the engine17.

The electric actuator70includes an electric motor71; a drive shaft72of the electric motor71; and an intermediate shaft73adapted to receive the drive force of the electric motor71supplied from the drive shaft72. The electric motor71is disposed on a vehicle-widthwise external side surface on the upper portion of the cylinder head132A in such a manner that the drive shaft72is substantially parallel to the ball screw61.

The drive shaft72is formed with a drive gear72A. A first intermediate gear73A meshing with the drive gear72A and a second intermediate gear73B meshing with the gear64provided on the ball screw61are secured to the intermediate shaft73.

The ball screw61is disposed perpendicularly to the camshafts151,152and on the side opposite the other end side of the camshafts151,152, i.e., opposite the side where driven sprockets161,162are secured. As described above, the ball screw61does not extend in the vertical direction of the engine17but is disposed to lie and straddle the camshafts151,152. Therefore, the height of the engine17can be suppressed to a low level.

The ball screw61is rotatably supported at both ends by ball screw support portions203. As illustrated inFIG. 5, the ball screw support portion203is configured such that a cap203B having a support portion semicircular in cross-section is secured to a camshaft side support portion203A formed on the upper portion of the camshaft support portion202.

As illustrated inFIG. 6, the ball screw61is formed on the outer circumferential surface with a helical screw thread61A and a helical thread groove61C on the intake side and with a helical screw thread61B and a helical thread groove61D on the exhaust side. The thread61A and thread groove61C, and the thread61B and thread groove61D are set reversely to each other in a screw winding direction between the intake side and the exhaust side. The ball screw61is turned to shift the sliders62in a direction reverse to each other, which swing the intake side and exhaust side holder members53.

The slider62is formed like a block and has a through-hole62A adapted to receive the ball screw61passed therethrough. The through-hole62A is formed on an inner circumferential surface with a helical nut-thread62B corresponding to the thread61A,61B and with a helical nut thread groove62C corresponding to the shaft thread groove61C,61D. A plurality of rollable balls65is disposed between the nut thread grooves62C and the corresponding shaft thread grooves61C,61D. The rotation of the ball screw61allows the sliders62to travel on the ball screw61via the balls65in the axial direction.

The slider62is formed on both lateral surfaces with grooves66(vertical grooves) extending vertically and perpendicularly to the ball screw61. An upper end of the groove66is formed as an opening portion66A communicating with an upper surface of the slider62. A lower end of the groove66is formed as a wall portion66B not communicating with a lower surface of the slider62.

A sensor80for detecting a turning amount of the ball screw61is provided at the other end of the ball screw61on the intake side. The ECU calculates a swing amount of the holder member53on the basis of the turning amount of the ball screw61detected by the sensor80.

The sensor80is secured to a side wall portion of the head cover133A (133B) located on the inside of the V-bank. Since the sensor80is disposed on the inside of the V-bank as described above, it is possible to reduce the length of the engine17in the anteroposterior direction of the vehicle body and to surround the sensor80by the front bank110A and the rear bank110B (FIG. 2).

The sensor80includes a turning shaft81provided at the other end portion of the ball screw61; a fixed shaft82composed of a hexagonal screw disposed below and substantially parallel to the turning shaft81and secured to the lower portion of the ball screw support portion203; a driven gear84rotatably supported by the fixed shaft82; and a sensor body85connected to the driven gear84to detect a turning amount of the driven gear84. A drive gear83is formed on the outer circumferential surface of the turning shaft81and meshes with the driven gear84.

The ball screw61is turned to transmit the turning of the turning shaft81turning integrally with the ball screw61to the driven gear84via the drive gear83. The turning number of the drive gear83is reduced by the driven gear84. The sensor body85detects the turning amount of the driven gear84. The turning amount of the ball screw61is determined based on the turning amount of the driven gear84.

As illustrated inFIGS. 6 and 7, the drive mechanism connecting member63includes an arm member86connected to the slider62; a connecting bolt87(connecting member) connecting the arm member86with the second plate53B of the holder member53; and a connecting nut88provided between the arm member86and the second plate53B. Also, the slider62and the arm member86are such that identical component parts are arranged on the intake side and the exhaust side symmetrically to the axially intermediate portion of the ball screw61. AlthoughFIG. 7illustrates the periphery of the drive mechanism connecting member63on the exhaust side, the drive mechanism connecting member63on the intake side is configured similarly to that on the exhaust side.

FIG. 9is a plan view of the arm member86.

As illustrated inFIGS. 6,8and9, the arm member86includes a pair of arms89extending to hold the slider62from both the lateral surfaces thereof; and an arm-connecting portion90(swing portion end) formed at the widthwise intermediate portion of the pair of arms89and at the proximal end portions of the arms89.

The arms89are provided to face each other. The arms89are each formed at a distal end with a pin support hole89A passing through the arm89widthwise. The pin hole support hole89A is adapted to receive an arm connecting pin91inserted therethrough, the arm connecting pin91connecting the arm89with the slider62.

The arm connecting pin91includes a pin portion91A fitted to the pin support hole89A; and a disk-like flange portion91B formed to have a diameter greater than that of the pin support hole89A. The pin portion91A is formed at an end with a clip groove portion91C going round the outer circumferential surface of the pin portion91A. The arm connecting pin91is inserted through the pin support hole89A from the inside of the pair of arms89.

In addition, a ring-like clip92is engaged with the clip groove portion91C located outside the arm89. Thus, the arm connecting pin89is provided integrally with the arm member86. The flange portion91B is located inside the arm89. A washer93is provided between the flange portion91B and the arm89.

The arm member86is connected to the slider62by the flange portions91B fitted to the pair of corresponding grooves66on the side surface of the slider62. Specifically, the flange portion91B is provided in the groove66in a vertically slidable and turnable manner. While being supported in the grooves66, the arm member86is swingable around the flange portions91B. In other words, when the arm member86is swung, it swings around the flange portions91B with the arm-connecting portion90being the end of the swing.

As illustrated inFIG. 6, the arm member86is formed in a general L-shape as viewed from the side. In addition, the arm-connecting portion90is formed to project perpendicularly to the arm89from the end opposite the pin support hole89A. As illustrated inFIG. 7, the arm-connecting portion90is formed with an arm connecting hole90A (the connecting portion) parallel to the pin support hole89A. The arm member86is connected to a second plate53B via a connecting bolt87inserted through the arm connecting hole90A.

FIG. 10is a lateral view of the connecting bolt87.

Referring toFIGS. 7 and 10, the connecting bolt87includes a shaft portion87A formed with a thread portion; and a bolt head portion87B formed at an end of the shaft portion87A. The shaft portion87A is a stepped shaft and has a holder side shaft portion94formed close to the bolt head portion87B; and an arm side shaft portion95formed to have a diameter smaller than that of the holder side shaft portion94and to terminate at the distal end of the connecting bolt87.

The holder side shaft portion94is formed with a first thread portion94A and the arm side shaft portion95is formed at a distal end portion with a second thread portion95A having a diameter smaller than that of the first thread portion94A. The holder side shaft portion94has, on the proximal end side, a smooth portion94B not formed with the first thread portion94A. The arm side shaft portion95has a smooth portion95B not formed with the second thread portion95A, in an interval between the second thread portion95A and the first thread portion94A. Because of requiring greater fastening force, the first thread portion94A secured to the holder member53is formed to have a diameter greater than that of the second thread portion95A.

The connecting bolt87is inserted through the bolt hole53C of the second plate53B from the side of the sub-rocker arm holder59, i.e., from the inside surface of the second plate53B and extends toward the arm member86in general parallel to the camshaft151. The end of the second thread portion95A goes over the ball screw61and reaches the vicinity of the external side surface of the slider62.

As illustrated inFIG. 7, the connecting bolt87is secured to the second plate53B by means of the connecting nut88fastened to the shaft portion87A from the external side surface side of the second plate53B. The connecting nut88includes a nut side thread portion88A and a seat portion88B. The nut side thread portion88A is formed like an axially extending cylinder and threadably engaged with the first thread portion94A.

The seat portion88B extends from the nut side thread portion88A to the vicinity of the second thread portion95A and of the arm connection hole90A in the assembled state. A runout portion88C is formed in the inner circumferential surface of the seat portion88B so as to have a diameter greater than that of the smooth portion95B.

A nut96is fastened to the second thread portion95A of the connecting bolt87. The arm member86is fastened and secured to the connecting bolt87in the state where the arm-connecting portion90is held between the nut96and the seat portion88B of the connecting nut88. In other words, the connecting nut88allows the arm member86to be fastened to the connecting bolt87in cooperation with the nut96.

A flat washer97is provided between the nut96and the arm-connecting portion90and between the arm-connecting portion90and the seat portion88B.

The second plate53B and the arm member86are secured to each other via the connecting bolt87, the connecting nut88, the nut96and the like. The arm member86is secured to the second plate53B while maintaining a predetermined position and angle relative thereto. If the slider62is shifted on the ball screw61by the drive mechanism60, the arm member86is swung around the arm connecting pin91to swing the holder member53while the arm connecting pin91is vertically slid in the groove66.

As described above, the arm member86is secured to the second plate53B and the arm connecting pin91fitted to the groove66of the slider62is made to serve as the center of the swing of the arm member86. Therefore, it is not necessary to provide a swingable link and the like on the second plate53B. Thus, the second plate53B and the slider62can be connected to each other with a small-sized and lightweight configuration having a small number of parts.

The nut96is fastened to the second thread portion95A at one end of the connecting bolt87so that the arm member86is secured to the connecting bolt87. The nut side tread portion88A is fastened to the first thread portion94A at the other end of the connecting bolt87so that the connecting bolt87is secured to the second plate53B. The connecting bolt87is independently fastened to the side of the second plate53B and to the side of the arm member86. In this way, the arm member86can reliably be secured to the second plate53B. Thus, an assembly error between the holder member53and the arm member86can be reduced. Friction occurring when the drive mechanism60swings the holder member53can be reduced and the distortion of the overall valve train50including the drive mechanism60can be reduced, thereby achieving desirable valve operating characteristics.

A description is here given of an assembly procedure for the drive mechanism connecting member63.

As illustrated inFIG. 7, first, the connecting bolt87is inserted through the bolt hole53C of the second plate53B and the connecting nut88is fastened to the first thread portion94A, whereby the connecting bolt87is secured to the second plate53B. Next, the arm connecting pins91of the arm member86are fitted to the corresponding grooves66from the corresponding opening portions66A of the slider62to thereby connect the arm member86to the slider62.

Thereafter, the arm side shaft portion95of the connecting bolt87is inserted through the arm connecting hole90A of the arm-connecting portion90and the nut96is fastened to the second thread portion95A, whereby the arm member86is secured to the connecting bolt87. In this way, the drive mechanism60and the holder member53are connected to each other via the drive mechanism connecting member63.

In the present illustrative embodiment, when the arm member86is assembled to the slider62, the arm connecting pins91of the arm member86can be fitted to the corresponding grooves66from the corresponding opening portions66A of the slider62. Thus, the arm member86can easily be assembled to the slider62. In the state where the arm connecting pins91are fitted to corresponding the grooves66, the arm member86is secured to the second plate53B by means of the connecting bolt87and the like, the arm connecting pin91will not disengage from the opening portion66A.

Further, when the nut96is fastened to the second thread portion95A to secure the arm member86to the connecting bolt87, in the state where the angle of the holder member53is made appropriate the attachment angle of the arm member86with respect to the second plate53B and the position of the slider62are finely adjusted and fixed. This can accommodate the dimension accuracy and assembly error of the parts among the drive mechanism60, the drive mechanism connecting member63and the holder member53. Thus, it is possible to prevent the valve train50from being assembled in a distorted state.

A description is next given of a method of assembling the camshaft151of the valve train50and its peripheral parts.

The valve train50is assembled by installing a camshaft structure200configured by assembling the parts, on the camshaft support portions201,202(FIG. 5) of the cylinder head132A. The camshaft structure200is assembled using an assembling jig250(seeFIG. 11).

FIG. 11is a partial broken-out cross-sectional view illustrating the camshaft structure200set on the assembling jig250.FIG. 12is a lateral cross-sectional view illustrating the assembling jig250and the camshaft structure200.

The assembling jig250is configured to include a base plate251, and camshaft holders252,253provided on the base plate251. The camshaft holders252,253are provided at both ends of the base plate251to support the corresponding ends of the camshaft151. Specifically, the camshaft holders252,253are provided to have respective shapes and a positional relationship corresponding to the camshaft support portions201,202of the cylinder head132A.

In addition, the camshaft holder252,253are configured to be able to support the camshaft151in a state equivalent to the camshaft support portions201,202. In short, the assembling jig250is such that the support portions equivalent to the camshaft support portions201,202are configured on the base plate251.

The camshaft holder252is formed with a shaft support portion252A rotatably supporting the camshaft151and with a holder support portions252B supporting an annular projecting portion158B of the second plate53B. The camshaft holder253is formed with a shaft support portion253A rotatably supporting the camshaft151and with a holder support portion253B supporting an annular projecting portion157B of the first plate53A. The camshaft holders252,253are each provided so as to be divided into upper and lower portions. Specifically, the camshaft holder252is configured by combining a lower half portion254A forming the lower portion with an upper half portion254B forming the upper portion.

Similarly, the camshaft holder253is configured by combining a lower half portion255A forming the lower portion with an upper half portion255B forming the upper portion. The shaft support portion252A and the holder support portion252B are each formed circularly by integrally assembling together the lower half portion254A and the upper half portion254B. Similarly, the shaft support portion253A and the holder support portion253B are each formed circularly by integrally assembling together the lower half portion255A and the upper half portion255B.

The shaft support portions252A,253A and the holder support portions252B,253B are machined with a high-degree of accuracy so that a portion supporting the camshaft151and a portion supporting each of the annular projecting portions157B,158B are coaxial with each other.

The lower half portions254A,255A are secured to the base plate251from the bottom surface side thereof by means of bolts256. The upper half portions254B,255B are secured to the respective lower half portions254A,255A from the corresponding upper surfaces thereof by means of a plurality of bolts257.

A description is next given of an assembly procedure of the camshaft structure200.

The camshaft151is integrally formed at one end with a sprocket securing portion151A having a large diameter. The first and second plates53A,53B and the valve-operating cam52cannot be inserted through the camshaft151from one end side. Therefore, the component parts of the camshaft structure200such as the first and second plates53A,53B, the valve-operating cam52and the like are inserted through from the front side which is the side of the collar fitting portion151D on the other end side toward the back side where the sprocket securing portion151A is located.

First, an integral assembly composed of the first plate53A, the sub-rocker arm holder59, the sub-rocker arm54, the connecting link55and the valve-operating cam52is passed through the camshaft151and the valve-operating cam52is assembled to the valve-operating cam support portion151C. In this state, the bolts53D are temporarily fastened, so that the sub-rocker arm holder59is not secured to the first plate53A completely.

Next, the camshaft color155is fitted to the color fitting portion151D and the securing bolt156is fastened with a washer156A interposed therebetween and secured to the camshaft collar155. Thereafter, the return spring57is passed through the camshaft collar155. One end57A of the return spring57is inserted into the through-hole52C and the other end57C is hooked on the sub-rocker arm holder59. Then, the second plate53B is passed through the camshaft151and is temporarily fastened to the sub-rocker arm holder59by means of the bolts53E.

The procedure, as described above, brings the camshaft structure200into a temporarily assembled state. In this state, the first plate53A and the second plate53B are not secured to the sub-rocker arm holder59completely and also the positions of the first and second plates53A,53B relative to the camshaft151are not fixed.

Next, the camshaft structure200in the temporarily assembled state is set on the assembling jig250. Specifically, the camshaft structure200is disposed in such a manner that both the ends of the camshaft151are supported by the shaft support portions252A,253A and the annular projecting portions157B,158B are supported by the holder support portions252B,253B, respectively. The upper half portions254B,255B are secured by the bolts257, whereby the setting of the camshaft structure200is completed.

As described above, the shaft support portions252A,253A and the holder support portions252B,253B are machined with a high-degree of accuracy so as to be coaxial with each other. Therefore, the camshaft structure200set on the assembling jig250is in the state where the coaxial degree between the camshaft151and the annular projecting portions157B,158B, i.e., where the axial centers of both generally coincide with each other. In this state, the bolts53D and the bolts53E are completely fastened, whereby the camshaft structure200can be assembled in the state where the coaxial degree between the camshaft151and the annular projecting portions157B,158B is high.

As described above, the high coaxial degree can be obtained only by setting the camshaft structure by use of the assembling jig250; therefore, the assembly performance of the valve train50can be improved.

The coaxial degree between the first plate53A and the second plate53B and between the first and second plates53A,53B and the camshaft151can be improved. Therefore, friction occurring when the drive mechanism60can swing the holder member53can be reduced and the distortion of the entire valve train50including the drive mechanism60can be reduced to achieve desired valve operating characteristics. Further, friction on the periphery of the drive mechanism60can be reduced; therefore, the load of the electric actuator70can be reduced and fuel consumption can be improved.

If the assembling jig250is not used, the camshaft structure200in the temporarily assembled state may be set on the camshaft support portions201,202of the cylinder head132A and in this set state, the bolts53D and the bolts53E may completely be fastened.

As described above, according to the embodiment of the present invention, the arm member86is swingably attached to the grooves66of the slider62via the arm connecting pins91and the arm-connecting portion90of the arm member86and the holder member53are secured to each other by means of the connecting bolt87. Therefore, the slider62and the holder member53can be connected to each other with a small-sized and lightweight configuration. Thus, the holder member53and the drive mechanism60can be connected to each other with a configuration simplified and having a small number of parts.

The connecting bolt87has the first thread portion94A and the second thread portion95A. The connecting nut88and the first thread portion94A are fastened to each other on the side of the holder member53. The nut97and the second thread portion95A are fastened to each other on the side of the arm member86. The connecting bolt87is fastened separately on the side of the holder member53and on the side of the arm member86. Therefore, the holder member53and the arm member86can reliably be secured to each other. Thus, the assembling error between the holder member53and the arm member86can be reduced.

The second thread portion95A, on the side of the holder member53, requiring greater fastening force is made to have a greater diameter. In addition, the first thread portion94A requiring only smaller fastening force is made to have a diameter smaller than that of the second thread portion95A. Accordingly, it is possible to make the fastening force appropriate, thereby reducing an assembling error.

Further, the connecting nut88fastening the first thread portion94A is extended to the vicinity of the arm connecting hole90A of the arm member86. The nut96fastened to the second thread portion95A and the seat portion88B resulting from the extension of the connection nut88cooperatively fastens the arm member86to the connecting bolt87. Therefore, it is not necessary to use a spacer or the like receiving the nut96fastening the second thread portion95A, thereby reducing the number of component parts.

Further, the arm connecting pin91of the arm member86can be attached to the vertically extending grooves66of the slider62from the corresponding opening portions66A of the grooves66. Therefore, the arm member86can easily be assembled to the slider62.

Incidentally, the embodiment described above represents one aspect embodying the present invention. The present invention is not limited to the embodiment described above.

In the illustrative embodiment described above, the connecting bolt87is described as being inserted through the bolt hole53C from the inside surface of the second plate53B. However, the present invention is not limited to this. For example, a connecting bolt is disposed in a direction reverse to that of the connecting bolt87. This connecting bolt is inserted through the arm connecting hole90A from the side of the arm89and secured to the arm89with a connecting bolt. The distal end of the connecting bolt may be fastened to the bolt hole53C of the second plate53B with a nut. The other detail configurations can arbitrarily be modified.

In other words, although the present invention has been described herein with respect to a number of specific illustrative embodiments, the foregoing description is intended to illustrate, rather than to limit the invention. Those skilled in the art will realize that many modifications of the illustrative embodiment could be made which would be operable. All such modifications, which are within the scope of the claims, are intended to be within the scope and spirit of the present invention.