Oil feeding system of engine

An oil feeding system of an engine equipped with a transmission configured to change a rotational speed of rotation of a crankshaft and to output the rotation, including an oil pump configured to be driven in cooperation with the rotation of the crankshaft, an oil passage through which the oil outflowing from the oil pump flows, in which the oil passage includes a transmission oil passage through which the oil outflowing from the oil pump is guided to the transmission, and an engine body oil passage through which the oil outflowing from the oil pump is guided to portions other than the transmission, and an oil control portion configured to change a ratio between a pressure of the oil flowing through the transmission oil passage and a pressure of the oil flowing through the engine body oil passage.

TECHNICAL FIELD

The present invention generally relates to an oil feeding system of an engine configured to be integral with a transmission. More particularly, the present invention relates to an oil feeding system of an engine that is suitable for use with a motorcycle and is configured to feed oil to a transmission and components other than the transmission.

BACKGROUND ART

Some engines mounted in vehicles such as motorcycles or all terrain vehicles (ATVs) are integral with transmissions. In such engines, an oil pump is driven in synchronization with an engine speed of the engine to suction up oil from an interior of an oil pan mounted at a bottom portion of the engine or from an oil tank externally mounted to the engine, thus delivering the oil to the transmission and engine components.

To be specific, the oil outflows from the oil pump and is delivered, through an oil passage formed in an interior of the engine, to the transmission to lubricate and cool the transmission, and to a crankshaft and a camshaft to lubricate and cool these shafts. In recent years, some engines have been equipped with a hydraulically-powered variable valve timing system configured to change a rotational phase of a camshaft or a hydraulically-powered tensioner lifter. In such engines, the oil is fed to the hydraulically-powered system or component to drive them (see, e.g., Japanese Laid-Open Patent Application Publication No. Hei. 7-127661).

The engine typically runs in a wide speed range from a low engine speed to a high engine speed. In particular, the engine mounted in the motorcycle runs in a very wide speed range. Since the oil pump is driven in synchronization with the engine speed of the engine, oil pressure tends to become high when the engine is running at a high engine speed, and tends to become low when the engine is running at a low engine speed.

A relatively high oil pressure is sometimes required to drive some systems even when the engine is running at a low engine speed. However, it may sometimes be difficult to obtain such a high oil pressure with the engine running at a low engine speed. In order to solve this, a volume of the oil pump may be increased, which undesirably causes a substantial weight increase and a large friction loss in the engine.

SUMMARY OF THE INVENTION

The present invention addresses the above described conditions, and an object of the present invention is to provide an oil feeding system of an engine that is capable of suitably feeding oil to a transmission and portions other than the transmission in a wide engine speed range from a low engine speed to a high engine speed, and of obtaining, in a low engine speed range, an oil pressure required to suitably drive a hydraulically-powered system.

According to the present invention, there is provided an oil feeding system of an engine equipped with a transmission configured to change a rotational speed of rotation of a crankshaft and to output the rotation, comprising an oil pump configured to be driven in cooperation with the rotation of the crankshaft; an oil passage through which oil outflowing from the oil pump flows; wherein the oil passage includes a transmission oil passage through which the oil outflowing from the oil pump is guided to the transmission, and an engine body oil passage through which the oil outflowing from the oil pump is guided to portions other than the transmission; and an oil control portion configured to change a ratio between a pressure of the oil flowing through the transmission oil passage and a pressure of the oil flowing through the engine body oil passage.

With the above mentioned configuration, the ratio of the pressure between the oil delivered to the transmission and the oil delivered to the portions other than the transmission is able to be controlled according to an engine speed of the engine so that the oil is fed in suitable pressures to the transmission and the portions other than the transmission. In general, the pressure of the oil is substantially proportional to a flow rate of the oil. So, the oil control portion may be configured to change a ratio between the flow rate of the oil flowing in the transmission oil passage and the flow rate of the oil flowing in the engine body oil passage. Thus, the ratio of the flow rate between the oil delivered to the transmission and the oil delivered to the portions other than the transmission can be controlled so that the oil is fed in suitable amounts to the transmission and the portions other than the transmission.

The oil passage may further include a distributing passage from which the oil outflowing from the oil pump is distributed to the transmission oil passage and the engine body oil passage which are configured to branch from the distributing passage.

With the above mentioned configuration, in the oil feeding system in which the oil is delivered from the oil pump to the distributing passage, for example, a main gallery, and further through the transmission oil passage and the engine body oil passage that branch from the distributing passage, the oil is able to be fed to the transmission and the portions other than the transmission in suitable pressure and/or amount through the transmission oil passage and the engine body oil passage.

The oil control portion may be provided in the transmission oil passage, and may be configured to restrict a flow rate of the oil flowing in the transmission oil passage to increase the pressure of the oil delivered to the portions other than the transmission, when the pressure of the oil in the transmission oil passage is low.

With the above mentioned configuration, when the engine speed of the engine is high, a sufficient flow rate of the oil can be obtained. Therefore, the oil can be delivered in a sufficient amount to the transmission and a pressure of the oil required to drive the portions other than the transmission can be obtained. On the other hand, when the engine speed is low, the oil control portion reduces the flow rate of the oil in the transmission oil passage, and the pressure of the oil required to drive the portions other than the transmission can be obtained.

The oil control portion may be configured to restrict the flow rate of the oil in the transmission oil passage when the pressure of the oil in the transmission oil passage is a predetermined value or less. With such a configuration, when the engine speed is high and the pressure of the oil is higher than the predetermined value, the oil pressure required to drive the portions other than the transmission can be obtained, and the oil can be fed in a sufficient amount to the transmission through the transmission oil passage. On the other hand, when the engine speed is low and the pressure of the oil is the predetermined value or less, the oil control portion restricts (or reduces) the flow rate of the oil in the transmission oil passage so that the oil is fed in a required amount to the transmission and the oil pressure required to drive the portions other than the transmission can be obtained.

The transmission oil passage may include a first oil passage and a second oil passage which are connected in parallel. The oil control portion may include a valve that is provided in the second oil passage and is configured to restrict a flow rate of the oil in the second oil passage when the pressure of the oil is a predetermined value or less.

With the above mentioned configuration, when the engine is running at a low engine speed and the pressure of the oil is the predetermined value or less, the valve of the oil control portion provided in the second oil passage is closed. Thereby, the flow rate of the oil flowing in the transmission oil passage is restricted, and the oil pressure required to drive the portions other than the transmission can be obtained. On the other hand, when the engine is running at a high speed, and the pressure of the oil is higher than the predetermined value, the valve of the oil control portion is opened to allow the oil to be delivered in sufficient amount to the transmission through the first and second oil passages.

The first oil passage of the transmission oil passage may be partially provided with a restricting portion having a passage with a diameter smaller than a diameter of a region in the vicinity of the restricting portion. With such a configuration, with the engine running at a low engine speed, the flow rate of the oil flowing in the transmission oil passage can be restricted, and the pressure of the oil delivered to the portions other than the transmission can be increased.

The oil pump may include a first oil pump and a second oil pump. The oil outflowing from the first oil pump may be guided to the transmission through the transmission oil passage, and the oil outflowing from the second oil pump may be guided to the portions other than the transmission through the engine body oil passage.

With the above mentioned configuration, in the oil feeding system in which the oil outflowing from the first oil pump is delivered through the transmission oil passage and the oil outflowing from the second oil pump is delivered through the engine body oil passage, the oil can be fed in a sufficient pressure and/or amount to the transmission and the portions other than the transmission through the transmission oil passage and the engine body oil passage.

The oil control portion may include a bypass passage through which the transmission oil passage is connected to the engine body oil passage, and a valve configured to restrict a flow of the oil in the bypass passage. The valve may be configured to increase a flow rate of the oil in the bypass passage flowing from the engine body oil passage to the transmission oil passage, when the pressure of the oil in the engine body oil passage is a predetermined value or more.

With the above mentioned configuration, the first oil pump, which is adapted to suitably feed the oil to the transmission, and the second oil pump, which is adapted to suitably feed the oil to the portions other than the transmission, can be used together. By using the second oil pump, the required oil pressure can be obtained with the engine running at a low engine speed. If the engine equipped with the second oil pump runs at a high engine speed, the pressure of the oil flowing in the engine body oil passage tends to become high up to an undesired level, and the oil tends to be delivered in excess amount. When the pressure of the oil becomes a predetermined value, the valve is opened, causing a surplus of the oil in the engine body oil passage to flow into the transmission oil passage through the bypass passage to be fed to the transmission. Because of the second oil pump, the volume of the first oil pump can be made small.

The oil feeding system may further comprise at least one of a hydraulically-powered variable valve timing system and a hydraulically-powered tensioner lifter, the variable valve timing system being configured to be driven by the pressure of the oil to change a rotational phase of a camshaft, the tensioner lifter being configured to be driven by the pressure of the oil to guide a cam chain installed around the camshaft and a crankshaft. At least one of the hydraulically-powered variable valve timing system and the hydraulically-powered tensioner lifter may be configured to be driven by the pressure of the oil delivered through the engine body oil passage.

With the above mentioned configuration, the hydraulically-powered variable valve timing system and/or the hydraulically-powered tensioner lifter can be suitably operated in a wide engine speed range from a low engine speed to a high engine speed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, an embodiment of an oil feeding system of an engine of the present invention will be described with reference to the accompanying drawings.FIG. 1is a right side view of a motorcycle1in which an engine E according to an embodiment of the present invention is mounted. The motorcycle1is a road sport type motorcycle in which a rider R rides with an upper body leaning forward. Herein, directions are generally referenced from the perspective of the rider R mounting the motorcycle1ofFIG. 1.

Turning now toFIG. 1, the motorcycle1includes a front wheel2and a rear wheel3. The front wheel2is rotatably mounted to a lower region of a front fork5extending substantially vertically. A bar-type steering handle4is attached to an upper region of the front fork5. The front fork5is mounted to a steering shaft (not shown) extending in parallel with the front fork5. The steering shaft is rotatably supported by a head pipe6. When the rider R rotates the steering handle4clockwise or counterclockwise, the front wheel2is turned to a desired direction.

A pair of right and left main frames7(only right main frame7is illustrated inFIG. 1), forming a frame of the vehicle body, extend rearward from the head pipe6. Pivot frames (swing arm brackets)8extend downward from rear regions of the main frames7. A swing arm10is pivotally mounted at a front end portion thereof to a pivot9attached on the pivot frame8. The rear wheel3is rotatably mounted to a rear end portion of the swing arm10.

A fuel tank12is disposed above the main frames7and behind the steering handle4. A straddle-type seat13is disposed behind the fuel tank12. An engine E is mounted between and under the right and left main frames7. The engine E is an inline four-cylinder four-cycle engine, and is a double overhead camshaft (DOHC) engine (seeFIG. 2), including, in an interior of the cylinder head20, a camshaft30configured to drive an intake valve and a camshaft31configured to drive an exhaust valve. An output of the engine E is transmitted, through a chain (not shown), to the rear wheel3, which rotates to generate a driving force to drive the motorcycle1. A cowling19is mounted to cover a front region of the motorcycle1, i.e., front regions of the head pipe6and the main frames7, and side regions of the engine E. Mounting the seat13, the rider R grips a grip4A attached at an end portion of the steering handle4and puts feet on foot rests provided in the vicinity of a rear region of the engine E. Under this condition, the rider is ready to start-up the motorcycle1.

FIG. 2is an enlarged right side view of the engine E ofFIG. 1, showing a structure of an interior of a chain tunnel27provided on a right side of the engine E.FIG. 3is a plan view of the engine E, taken in the direction of arrow III ofFIG. 2, showing a structure of an upper portion of the cylinder head20with a cylinder head cover21removed.

As shown inFIG. 3, the engine E includes four cylinders C1to C4. As shown inFIG. 2, these cylinders C1to C4are inclined forward with a predetermined angle. As shown inFIG. 3, four air-intake ports20A are provided at a rear portion of the cylinder head20so as to respectively correspond to the four cylinders C1to C4. The four air-intake ports20A are configured to open upward and rearward. Four exhaust ports20B are provided at a front portion of the cylinder head20and are configured to open forward.

As shown inFIG. 2, the camshaft30and the camshaft31are mounted at an upper region of the cylinder head20, and a cam holder (not shown) is provided over the camshafts30and31from above. The cylinder head cover21is provided over the cam holder and is fixed to the cylinder head20. In this state, the camshaft30and the camshaft31are rotatably retained between the upper portion of the cylinder head20and a lower portion of the cam holder.

A cylinder block22is coupled to a lower portion of the cylinder head20and is configured to house a piston (not shown). A crankcase23is coupled to a lower portion of the cylinder block22and is configured to accommodate a crankshaft32that is mounted to extend in a width direction of the vehicle body. A chain tunnel outer wall portion27B (its cross-sectional structure is illustrated inFIG. 3) that is recessed rightward is coupled at a periphery thereof to a right wall portion, namely, chain tunnel inner wall portion27A of the cylinder head20, the cylinder head cover21, the cylinder block22, and the crankcase23to cover the chain tunnel inner wall portion27A. An inner space defined by the chain tunnel inner wall portion27A and the chain tunnel outer wall portion27B forms the chain tunnel27configured to accommodate a camshaft drive system28. An oil pan25is mounted to a lower portion of the crankcase23and is configured to store lubricating oil. An oil filter26protrudes from a front portion of the crankcase23and is configured to filter oil suctioned up from the oil pan25.

As shown inFIG. 2, the camshaft drive system28mounted in the interior of the cam chain tunnel27includes an intake cam sprocket40, an exhaust cam sprocket41, and a crank sprocket42. To be specific, as shown inFIG. 3, a right end portion of the camshaft30protrudes from the chain tunnel inner wall portion27A into the interior of the chain tunnel27. The intake cam sprocket40is mounted on the right end portion of the camshaft30. A right end portion of the camshaft31protrudes from the chain tunnel inner wall portion27A into the interior of the chain tunnel27. The exhaust cam sprocket41is mounted on the right end portion of the camshaft31, and is configured to rotate integrally with the camshaft31. As shown inFIG. 2, a right end portion of the crankshaft32protrudes from the chain tunnel inner wall portion27A into the interior of the chain tunnel27. The crank sprocket42is mounted on the right end portion of the crankshaft32and is configured to rotate integrally with the crankshaft32.

A timing chain50is installed around the intake cam sprocket40, the exhaust cam sprocket41, and the crank sprocket42. The intake cam sprocket40and the exhaust cam sprocket41are configured to rotate in cooperation with the rotation of the crank sprocket42. Through the camshaft drive system28including the intake cam sprocket40, the exhaust cam sprocket41, the crank sprocket42, and the timing chain50, the rotation of the crankshaft32is transmitted to the camshaft30and the camshaft31. In the engine E of this embodiment, the crankshaft32rotates clockwise inFIG. 2, and the timing chain50, the intake cam sprocket40, and the exhaust cam sprocket41also rotate clockwise.

As shown inFIG. 2, the engine E is equipped with a hydraulically-powered variable valve timing system60including a hydraulically-powered actuator61and an oil control valve62. The hydraulically-powered actuator61is mounted to a right end portion of the camshaft30and to an outer portion of the intake cam sprocket40(seeFIG. 3). The oil control valve62is mounted to a rear wall portion of the cylinder block22. The oil control valve62may alternatively be mounted to other portions, for example, a wall portion of the cylinder head20. In this case, the oil control valve62may be disposed horizontally laterally of a movable chain tensioner51mentioned later. The oil control valve62may alternatively be mounted to a side wall portion or a front wall portion of the cylinder head20or otherwise may be mounted to the cylinder head cover21.

As shown inFIG. 3, the hydraulically-powered actuator61includes a tubular housing63that has a bottom portion and is configured to rotate integrally with the intake cam sprocket40, and a rotor64that is accommodated in the housing63and is configured to rotate integrally with the camshaft30. The hydraulically-powered actuator61contains, in an interior of the housing63, a plurality of advanced angle (or phase) spaces and retarded angle (or phase) spaces (not shown) that are defined by the housing63and the rotor64. The hydraulically-powered actuator61is coupled to the oil control valve62through an oil passage80, i.e., an eighth oil passage88(seeFIG. 4) as mentioned later. The oil is delivered to the advanced angle spaces and the retarded angle spaces through the oil passage80, i.e., the eighth oil passage88, and a phase difference between the housing63and the rotor64changes according to a flow rate or an oil pressure of the delivered oil.

In the engine E constructed above, the rotation of the crankshaft32is transmitted, through the timing chain50, to the intake cam sprocket40and the exhaust cam sprocket41, which thereby rotate. The camshaft31rotates according to the rotation of the exhaust cam sprocket41in such a manner that the camshaft31rotates once with respect to two rotations of the crankshaft32. The rotation of the intake cam sprocket40is transmitted to the camshaft30through the hydraulically-powered actuator61of the variable valve timing system60. According to the flow rate or oil pressure controlled by the oil control valve62, the camshaft30rotates with a predetermined phase difference (or angle) with respect to the rotation of the crankshaft32. The phase difference between the crankshaft32and the camshaft30changes according to the flow rate or the oil pressure changed by the oil control valve62.

As shown inFIG. 2, the movable chain tensioner51and a fixed chain guide52are mounted in the interior of the chain tunnel27. The movable chain tensioner51is disposed behind the timing chain50to extend substantially vertically. The movable chain tensioner51is mounted in such a manner that a lower end portion thereof is pivoted to a right wall portion of the crankcase23in the vicinity of a region above the crank sprocket42, and an upper end portion thereof is located in the vicinity of a region below the intake cam sprocket40. A hydraulically-powered tensioner lifter55is mounted to a rear wall portion of the cylinder head20and is configured to apply a forward force to an upper portion of the chain tensioner51to enable the timing chain50to be supported from behind and to have a suitable tension.

The fixed chain guide52mounted in the interior of the chain tunnel27extends substantially vertically in front of the timing chain50from a location near and forward of the crank sprocket42to a location near and under the exhaust cam sprocket41. The chain guide52is provided with a groove (not shown) formed at a rear region thereof to extend in a longitudinal direction to allow the timing chain50to be supported from forward. To be specific, a front region of the timing chain50is accommodated in the groove formed at the rear region of the fixed chain guide52so that the timing chain50is movable along the groove.

An output gear43is mounted on a right side portion of the crankshaft32in the interior of the crankcase23and is configured to rotate integrally with the crankshaft32. Through the output gear43, the rotation of the crankshaft32is output. A transmission space24is formed at a rear portion of the crankcase23. A main shaft34and a counter shaft (not shown) are accommodated in the transmission space24to extend in parallel with the crankshaft32. A plurality of gears35A are mounted on the main shaft34and the counter shaft, thereby forming the transmission35. An input gear44is mounted on a right end portion of the main shaft34, and is configured to mesh with the output gear43of the crankshaft32and to rotate integrally with the main shaft34. In this construction, the output of the engine E is transmitted from the crankshaft32to the main shaft34through the output gear43and the input gear44. Further, the transmission35changes a rotational speed of the rotation, and the resulting rotation is output to the rear wheel3(FIG. 1).

The above mentioned engine E includes an oil pump70. The oil pump70is provided with a pump driven gear70A adapted to mesh with a pump drive gear34A mounted on the main shaft34of the transmission35. The oil pump70is driven according to the rotation of the crankshaft32. The engine E is provided with an oil passage80(seeFIG. 4) through which oil71suctioned up by the oil pump70from the oil pan25is delivered to the transmission35and the engine components.

With reference toFIGS. 4 to 7, the oil passage80included in the oil feeding system of the engine E will be described.FIG. 4is a side view showing the structure of the oil passage80in the engine E ofFIG. 2.FIG. 5is a cross-sectional view of the engine E, taken substantially along line V-V ofFIG. 4, showing a vertical section of the crankcase23and its internal structure.FIG. 6is a cross-sectional view of the engine E, taken substantially along line VI-VI ofFIG. 4, showing a horizontal section of an internal structure of the crankcase23.FIG. 7is a schematic view of the oil passage80illustrated inFIGS. 4 to 6.

As shown inFIG. 4, a first oil passage81extends upward from the oil pan25to an inlet of the oil pump70. An oil strainer (not shown) is mounted to a lower end portion of the first oil passage81. A second oil passage82extends forward from an outlet of the oil pump70to an inlet of the oil filter26located at a front portion of the engine E. A third oil passage83extends rearward from an outlet of the oil filter26to a location under the crankshaft32and is coupled at a tip end83A to a main passage (distributing passage)80A with a larger diameter. The oil pump70is driven to suction up the oil from the interior of the oil pan25through the first oil passage81. The oil is delivered to the oil filter26through the second oil passage82. The oil filter26filters the oil, and the resulting oil is delivered to the main passage80A through the third oil passage83.

As shown inFIGS. 5 and 6, the main passage80A extends in a rightward and leftward direction at a lower portion of the crankcase23. As mentioned later, a plurality of oil passages extend from the main passage80A, including a transmission oil passage extending to the transmission35and an engine body oil passage extending to the portions other than the transmission35. Below, the engine body oil passage will be first described and then the transmission oil passage will be described.

As shown inFIG. 5, the crankcase23of the engine E includes an upper crankcase231and a lower crankcase232with respect to an axis of the crankshaft32. The upper crankcase231and the lower crankcase232are coupled to each other. Bulkheads231ato231cand bulkheads232ato232cprotrude from the upper crankcase231and the lower crankcase232, respectively, in such a manner that the bulkheads231ato231ccorrespond to the bulkheads232ato232c,respectively. The crankshaft32is rotatably mounted to the crankcase23in such a manner that crank journals32A are retained from above and below, between the bulkheads231aand232a,between the bulkheads231band232b,and between the bulkheads231cand232c.

As shown inFIG. 5, fourth oil passages84ato84cincluded in the engine body oil passage extend upward from the main passage80A through the interiors of the bulkheads232ato232cof the lower crankcase232. Through the fourth oil passages84ato84cextending upward in the interior of the bulkheads232ato232c,the oil is fed from the main passage80A to contact portions between the crank journals32A and the bulkheads231ato231cand232ato232cto lubricate the contact portions.

The crankshaft32is provided with fifth oil passages85aand85cincluded in the engine body oil passage and connected to the left fourth oil passage84aand the right fourth oil passage84c,respectively. Through the fifth oil passages85aand85c,a part of the oil flowing from the fourth oil passages84aand84cis fed to contact portions between the crankshaft32and connecting rods36to lubricate the contact portions and may be sometimes fed to a balancer shaft (not shown) of the engine E. The left bulkhead231aand the right bulkhead231cof the upper crankcase231are provided with sixth oil passages86aand86cincluded in the engine body oil passage, which are connected to the fourth oil passages84aand84cformed in the left bulkhead232aand the right bulkhead232cof the lower crankcase232, respectively. The sixth oil passages86aand86copen at upper regions of the bulkheads231aand231c.Apart of the oil flowing from the fourth oil passages84aand84cis injected toward back surfaces of pistons (not shown) through the openings of the sixth oil passages86aand86c.Oil passages through which the oil is injected toward the back surfaces of the pistons are not intended to the sixth oil passages86aand86c,but may be provided at the center bulkhead231bas necessary, or otherwise four oil passages may be provided to correspond to the respective of the four pistons.

As shown inFIG. 5, a generator oil passage80aincluded in the engine body oil passage extends from a right end portion of the main passage80A and through an interior of the right wall portion23A of the crankcase23. The generator oil passage80aextends upward in the interior of the right wall portion23A of the crankcase23, within a wall portion of a generator cover29, and to a generator29aaccommodated in an interior of the generator cover29. Through the generator oil passage80a,a part of the oil is fed from the main passage80A to the generator29ato cool the generator29a.

A seventh oil passage87included in the engine body oil passage extends from a left end portion of the main passage80A and through an interior of the left wall portion23B of the crankcase23. As shown inFIG. 4, the seventh oil passage87extends upward in an interior of the left wall portion23B of the crankcase23, through the wall portions of the cylinder block22and the cylinder head20, and to the upper region of the cylinder head20. The oil is fed to the camshaft30and the camshaft31through the seventh oil passage87to lubricate the camshafts30and31.

As shown inFIG. 4, an eighth oil passage88included in the engine body oil passage extends from a region of the seventh oil passage87which corresponds to the cylinder block22. The eighth oil passage88includes two sub-oil passages88aand88b.The sub-oil passage88ais coupled to the advanced angle space (not shown) of the hydraulically-powered actuator61through the oil control valve62. The sub-oil passage88bis coupled to the retarded angle space (not shown) of the hydraulically-powered actuator61through the oil control valve62. The oil is delivered to the oil control valve62through the sub-oil passages88aand88bof the eighth oil passage88. The oil control valve62suitably controls a flow rate and an oil pressure of the oil, and the resulting oil is delivered through the sub-oil passages88aand88b,to the advanced angle space and the retarded angle space to drive the hydraulically-powered actuator61.

A ninth oil passage89included in the engine body oil passage extends from a region of the seventh oil passage87which corresponds to the cylinder head20. The ninth oil passage89is coupled to the hydraulically-powered tensioner lifter55. The oil is fed to the hydraulically-powered tensioner lifter55through the ninth oil passage89to drive the tensioner lifter55.

As shown inFIG. 6, a tenth oil passage90and an eleventh oil passage91included in the transmission oil passage extend rearward from locations of the main passage80A. As shown inFIG. 6, the tenth oil passage90is coupled at an upstream end portion90A to the main passage80A, and then extends rearward to form an intermediate portion90B located under the transmission35. Further, as shown inFIG. 4, the tenth oil passage90extends upward to form a downstream end portion90C located near the main shaft34. As shown inFIG. 6, the eleventh oil passage91is coupled at an upstream end portion91A to the main passage80A, and then extends rearward to form an intermediate portion91B located under the transmission35. Further, the eleventh oil passage91extends upward and rearward to form a downstream end portion91C (seeFIG. 4) located near the countershaft (not shown). The oil is fed to the transmission35including the main shaft34, the countershaft, etc, through the tenth oil passage90and the eleventh oil passage91, to lubricate them (seeFIG. 4).

FIG. 8is an enlarged side view of a structure of a part of the tenth oil passage90, showing an oil control portion90D provided between the upstream end portion90A and the intermediate portion90B. As shown inFIG. 8, the oil control portion90D includes a main oil passage100and a sub-oil passage101arranged in a vertical direction so as to extend in parallel with each other. The main oil passage100and the sub-oil passage101are formed of a pipe member100A and a pipe member101A of a substantially equal length. The sub-oil passage101formed of the pipe member101A has a diameter slightly larger than that of the main oil passage100. A joint102A located on an upstream side and a joint103A located on a downstream side, which have internal passages102and103, respectively, are coupled to both end portions of the pipe members100A and101A. The main oil passage100and the sub-oil passage101are connected to the internal passages102and103. As shown inFIG. 4, the joint103A on the upstream side is connected to the main passage80A (seeFIG. 4) and the joint102A on the downstream side is connected to the downstream end portion90C (seeFIG. 4) of the tenth oil passage90.

A restricting portion100B is provided at an upstream end of the main oil passage100. The restricting portion100B is formed to have an inner diameter smaller than a passage diameter of a region of the main oil passage100which is in the vicinity of the restricting portion100B. This makes it possible to suppress a pressure decrease in the oil71in the interior of the main passage80A when the engine speed of the engine E is low.

A relief valve105is provided between an upstream end of the sub-oil passage101and the joint103A. The relief valve105contains, in an interior of a tubular housing106, a ball107having a diameter smaller than an inner diameter of the housing106, and a coil spring108configured to apply a force to the ball107in an opposite direction to a flow direction of the oil in the housing106. With the ball107in a predetermined position near the upstream end portion90A of the housing106because an oil pressure on an upstream side of the ball107is not higher than a predetermined value, the relief valve105is closed so as not to permit flow of the oil in the sub-oil passage101. On the other hand, with the ball107located to be away in the flow direction of the oil from the predetermined position near the upstream end portion90A of the housing106because the oil pressure on the upstream side of the ball107is higher than the predetermined value, the relief valve105is opened, permitting the oil to flow in the sub-oil passage101. Since the eleventh oil passage91has a structure similar to that of the tenth oil passage90, it will not be further described.

In the engine E constructed above, when the crankshaft32rotates, the oil pump70suctions up the oil71from the oil pan25. The oil pump70causes the oil71to be delivered to the main passage80A through the oil filter26, and further to engine components of the engine E. To be specific, the oil71is delivered from the main passage80A to an upper region of the engine E to lubricate the crankshaft32. In addition, the oil71is fed to the camshafts30and31to lubricate them. In addition, the oil71is delivered to the oil control valve62so as to be controlled to have a suitable oil pressure, and then is fed to the hydraulically-powered actuator61to enable the actuator61to determine a rotational phase of the camshaft30. In addition, the oil71is fed to the hydraulically-powered tensioner lifter55to enable the tensioner lifter55to apply a force to the movable chain tensioner51. Furthermore, the oil71is delivered from the main passage80A to a rear region of the engine E, for example, the transmission35, etc., through the tenth oil passage90and the eleventh oil passage91to lubricate them.

The oil passage80, in particular, the eighth oil passage88and the ninth oil passage89may be formed in the interior of the wall portion of the engine E or otherwise may be a pipe member externally attached to the wall portion of the engine E.

Because the oil pump70is driven in cooperation with the rotation of the crankshaft32, the pressure of the oil71in the interior of the oil passage80is relatively low when the rotational speed of the crankshaft32is low, and increases with an increase in the rotational speed of the crankshaft32. So, when the rotational speed of the crankshaft32is low, the pressure of the oil71in the sub-oil passage101in the oil control portion90D of the tenth oil passage90is low, and the relief valve105provided in the sub-oil passage101is closed. In this state, the oil71is fed to the transmission35only through the main oil passage100. Since the oil71flows only through the main oil passage100in the tenth oil passage90, the pressure of the oil71in the engine body oil passage of the oil passage80is maintained at a predetermined value or more so that the oil71is fed in sufficient pressure or amount to the camshaft30, the camshaft31, the hydraulically-powered actuator61of the variable valve timing system60, and the hydraulically-powered tensioner lifter55, which are positioned in the upper region of the engine E.

The pressure of the oil71increases with an increase in the rotational speed of the crankshaft32. When the pressure of the oil71becomes a predetermined value or more, the relief valve105provided in the sub-oil passage101is opened, in the oil control portion90D of the tenth oil passage90. As a result, the oil71is fed, through the main oil passage100and the sub-oil passage101in the tenth oil passage90, to the transmission35in sufficient pressure and/or amount required for high-speed running of the engine E.

In the above constructed engine E, the relief valve105is opened and closed in the oil control portion90D according to the pressure of the oil71so that the pressure (or flow rate) of the oil71delivered toward the cylinder head20and the pressure (or flow rate) of the oil71delivered toward the transmission35are individually controlled. Therefore, in a whole engine speed range of the engine E, the oil71is fed in sufficient pressure or amount to the transmission35, the crankshaft23, and the camshafts30and31. In addition, with the engine E running at a low engine speed, an oil pressure sufficient to suitably drive the variable valve timing system60and the hydraulically-powered tensioner lifter55is obtained.

Since an operation of a relief valve (not shown) provided in the-sub oil passage of the eleventh oil passage91is similar to that of the relief valve105provided in the sub-oil passage101of the tenth oil passage90, it will not be further described. In this embodiment, the oil control portion90D may include an electromagnetic relief valve, rather than the mechanically-driven relief valve105composed of the ball107and the coil spring108as illustrated in this embodiment.

While in this embodiment, the eighth oil passage88branches from the location of the seventh oil passage87extending from the main passage80A to the camshafts30and31so that the oil71is fed to the variable valve timing system60through the eighth oil passage88, the main passage80A may alternatively be coupled to the variable valve timing system60through an oil passage different from the seventh oil passage87(see two-dotted line inFIG. 7). Furthermore, the oil control portion90D of the tenth oil passage90may be configured to include components instead of the main oil passage100and the sub-oil passage101provided with the relief valve105.

FIG. 9is a view showing another structure of the oil control potion. As shown inFIG. 9, an oil control portion153is mounted between the upstream end portion90A and the intermediate portion90B of the tenth oil passage90ofFIG. 4. As shown inFIG. 9, a pipe member150A having an internal passage150is mounted between the upstream end portion90A and the intermediate portion90B of the tenth oil passage90. An upstream end of the pipe member150A is connected to the main passage80A (FIG. 4) through a joint151, and a downstream end portion of the pipe member150A is connected to a downstream end portion90C (FIG. 4) of the tenth oil passage90through a joint152. The oil control portion153is provided at a position of the internal passage150of the pipe member150A. The oil control portion153is tubular and is constructed to accommodate a ball155and a coil spring156in a housing157. The oil control portion153is forcibly fitted into the internal passage150of the pipe member150A.

The housing157includes a substantially tubular outer housing158configured to accommodate the ball155and a substantially tubular inner housing159that is internally fitted to the outer housing158and is configured to accommodate the spring156. The outer housing158has an inner diameter slightly larger than a diameter of the ball155, and is provided at an upstream end portion thereof with a reduced-diameter portion160protruding radially inward from an inner peripheral surface of the outer housing158. An upstream opening161defined by the reduced-diameter portion160has a diameter slightly smaller than a diameter of the ball155. One or a plurality of cut portions162are formed at the reduced-diameter portion160along the periphery of the upstream opening161. With the ball155positioned within the outer housing158in contact with the reduced-diameter portion160, the interior of the housing157communicates with outside through only the cut portion162.

The inner housing159is internally fitted into the outer housing158through an opening located on a downstream side. The inner housing159has an outer diameter substantially equal to an inner diameter of the outer housing158, and has an inner diameter slightly smaller than a diameter of the ball155. An axial dimension of the inner housing159is smaller than an axial dimension of the outer housing158. A flange portion165is formed at a downstream end of the inner housing159so as to protrude radially outward further than an outer peripheral portion of the inner housing159. With the inner housing159fitted into the outer housing158, the flange portion165is in contact with a downstream end portion of the outer housing158. With the inner housing159fitted into the outer housing158, the ball155is accommodated in a space166formed between the reduced-diameter portion160of the outer housing158and an upstream end portion of the inner housing159. The ball155is movable in the axial direction of the housing157in the space166.

One or a plurality of cut portions167are formed at the upstream end portion of the inner housing159along the periphery of the inner housing159. An opening area of the cut portion167is larger than an opening area of the cut portion162. When the ball155moves in the flow direction of the oil to contact the upstream end portion of the inner housing159, the space166is able to communicate with the interior of the inner housing159though only the cut portion167. The coil spring156is accommodated in the interior of the inner housing159. The coil spring156has a diameter substantially equal to the inner diameter of the inner housing159, and is mounted in such a manner that an axial direction of the coil spring156conforms to an axial direction of the inner housing159. A reduced-diameter portion168is formed at a downstream end portion of the inner housing159so as to protrude radially inward from an inner peripheral surface of the inner housing159. The reduced-diameter portion168defines a downstream opening169through which the interior of the housing157communicates with outside. The coil spring156is mounted in such a manner that a downstream end of the coil spring156is in contact with the reduced-diameter portion168and an upstream end thereof is in contact with the ball155to apply a force to the ball155in an opposite direction to the flow direction of the oil in the housing157.

When a pressure difference between the upstream side and the downstream side of the oil control portion153is small, the oil control portion153is closed with the ball155in contact with an inner side of the reduced-diameter portion160of the outer housing158. As a result, the oil71flows through only the cut portion162formed on the reduced-diameter portion160of the outer housing158. When the pressure of the oil71on the upstream side becomes a predetermined value or more, the ball155moves in the flow direction of the oil against elasticity of the coil spring156and contacts the upstream end portion of the inner housing159, causing the oil control portion153to be opened. As a result, the oil71flows in a large amount through the cut portion167, which is larger than the cut portion162and is formed at the upstream end portion of the inner housing159.

In the tenth oil passage90constructed above, the pressure of the oil71in the interior of the main passage80A is high when the rotational speed of the crankshaft32is high. Under this condition, the oil71is fed in sufficient pressure and/or amount to the crankshaft32, and the camshafts30and31, and an oil pressure sufficient to drive the variable valve timing system60and the hydraulically-powered tensioner lifter55is obtained. In addition, since the pressure of the oil71in the tenth oil passage90is high, the oil control portion153is opened to enable the oil71to be fed in sufficient pressure and/or amount to the transmission35.

On the other hand, when the rotational speed of the crankshaft32is low, the pressure of the oil71in the interior of the tenth oil passage90is low. When the pressure of the oil71becomes a predetermined value or less, the oil control portion153operates to be closed. Under this condition, since the pressure of the oil71in the main passage80A is maintained at a predetermined value or more and the amount of the oil flowing to the transmission oil passage decreases, the oil71can be fed in required amount to the crankshaft32and to the camshafts30and31. In addition, an oil pressure sufficient to drive the variable valve timing system60and the hydraulically-powered tensioner lifter55is obtained. With the oil control portion153closed, the oil71is fed in required amount to the transmission35through the cut portion162.

The oil control portion153illustrated inFIG. 9enables the oil71to be fed in a suitable pressure and/or amount to the transmission35and the portions other than the transmission35. As a matter of course, the structure illustrated inFIG. 9may be applied to the eleventh oil passage91. Also, a system similar to the oil control portion90D ofFIG. 8or the oil control portion153ofFIG. 9may be provided in other oil passages, for example, the seventh oil passage87as well as in the tenth oil passage90and the eleventh oil passage91.

Instead of one oil pump70as mentioned above, a plurality of oil pumps may be mounted to form an oil feeding system. With reference toFIG. 10, the oil feeding system of the engine equipped with two oil pumps will be described.

As shown inFIG. 10, the engine E includes two oil pumps, i.e., a first oil pump111and a second oil pump112, an engine body oil passage120through which the oil71suctioned up by the second oil pump112is delivered to the camshaft30, the hydraulically-powered actuator61, etc., and a transmission oil passage130through which the oil71suctioned up by the first oil pump111is delivered to the transmission130.

To be specific, the engine body oil passage120includes an oil passage121configured to extend upward from the oil pan25to allow the oil71to be drawn to the second oil pump112therethrough, and an oil passage122configured to extend upward from the second oil pump112to the upper region of the cylinder head20. The oil passage122is divided, at the upper region of the cylinder head20, into an oil passage123connected to the camshaft30and an oil passage124connected to the camshaft31. The oil71is fed to the camshaft30and the camshaft31through oil passage123and the oil passage124, respectively. An oil passage125extends from a location of the oil passage122extending upward from the second oil pump112, and is connected to the hydraulically-powered actuator61through the oil control valve (not shown inFIG. 10). The oil71is fed to the hydraulically-powered actuator61through the oil passage125to drive the actuator61.

The transmission oil passage130includes an oil passage131configured to extend upward from the oil pan25to allow the oil71to be drawn to the first oil pump111therethrough, an oil passage132through which the oil71is delivered from the first oil pump111to the oil filter26mounted to the front portion of the crankcase23, and a main passage133configured to extend in a rightward and leftward direction of the engine E to allow the oil71from the oil filter26to be delivered to the transmission35, etc., therethrough.

In this embodiment, the transmission oil passage130further includes an oil passage134configured to extend upward from the main passage133to allow the oil71to be delivered to the crankshaft32therethrough, and an oil passage135configured to extend rearward from the main passage133through an inner bottom portion of the crankcase23to allow the oil71to be fed to the transmission35therethrough. The oil passage135extending toward the transmission35is divided, at a location under the transmission35, into an oil passage136connected to the main shaft34A and an oil passage137connected to a counter shaft34B. The oil71is fed to the main shaft34A and the counter shaft34B through the oil passage136and the oil passage137, respectively.

A bypass passage140, which serves as an oil control portion110, extends from a location near a lower portion of the oil passage122of the engine body oil passage120extending upward from the second oil pump112, and is connected to the main passage133of the transmission oil passage -130. A relief valve141is provided in the bypass passage140. The relief valve141is configured to permit the oil71to flow from the engine body oil passage120to the transmission oil passage130, and to be opened when the pressure of the oil71existing on the engine body oil passage120side becomes a predetermined value or more. The relief valve141may be a known flow rate control valve, and its structure will not be specifically described.

In the engine E constructed above, the second oil pump112serves to deliver the oil71through the engine body oil passage120and the first oil pump111serves to deliver the oil71through the transmission oil passage130. In other words, the second oil pump112enables the camshaft30and the camshaft31to be suitably lubricated, and the hydraulically-powered actuator61to suitably operate, and the first oil pump111enables the crankshaft32and the transmission35to be suitably lubricated.

If the second oil pump112is adapted to enable the hydraulically-powered actuator61to suitably operate when the engine E is running at a low engine speed, the oil71may be fed excessively to the hydraulically-powered actuator61when the engine E is running at a high speed. However, in the engine E of this embodiment, when the amount of the oil71fed to the hydraulically-powered actuator61increases, the pressure of the oil71in the engine body oil passage120increases. When the pressure of the oil71exceeds a predetermined value, then the relief valve141operates to cause the bypass passage140to be opened. Thereby, a surplus of the oil71in the engine body oil passage120is delivered to the main passage133of the transmission oil passage130through the bypass passage140, and is mixed into the oil in the transmission oil passage130. The resulting oil is fed to the transmission35and the crankshaft32. As a result, whether the engine E is running at a high or low engine speed, the oil71is able to be fed to the components of the engine E in a suitable pressure and/or amount.

While in this embodiment, the oil passage134extending to the crankshaft32and the oil filter26are disposed on the transmission oil passage130, the oil passage134and/or the oil filter26may alternatively be disposed on the engine body oil passage120, provided that oil pumps are respectively mounted to an oil passage through which the oil is guided to an engine and an oil passage through which the oil is guided to a transmission and these oil passages are coupled to each other through a bypass passage (oil control passage) in which a relief valve is provided.

The above mentioned oil feeding system may be applied to two-cylinder or three-cylinder engines as well as the above mentioned in-line four-cylinder engine. The engine may be a straight-cylinder engine, a boxer engine or a V-type engine. The engine equipped with the oil feeding system of the present invention may be mounted in vehicles such as all terrain vehicles as well as motorcycles.