# Patent

## Title
Vertical engine

## Abstract

In a vertical engine, a bulged portion protrudes upwards, in conformity to a partially cylindrical outer wall of uppermost one of cylinders, on an upper surface of a cylinder block forming a bottom wall of a chain chamber accommodating a chain for driving a camshaft and a balancer shaft through a crankshaft. A pair of oil return bores for returning an oil in the chain chamber to an oil pan are provided in lower portions of the bottom wall on opposite sides of an axis of the bulged portion. The oil which has lubricated the chain in the chain chamber flows so that it is distributed to the opposite sides of the axis, and the oil is returned smoothly from the oil return bores formed in the bottom wall to the oil pan.

## Background
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a vertical engine in which a chain circulated in a generally horizontal plane is wound around sprockets mounted at upper ends of first and second shafts disposed in a generally vertical direction.
2. Description of the Related Art
Japanese Patent Application Laid-open No. 9-41909 discloses a V-type vertical engine for an outboard engine in which a timing chain for transmitting a driving force from a crankshaft to a camshaft is accommodated in a chain chamber provided in upper portions of a cylinder block and a cylinder head of the engine. In this V-type vertical engine, two vertical bores 64b are formed in a bottom wall of the chain chamber.
In the conventional vertical engine, the two vertical bores 64b are provided on cylinder axes in left and right banks, but it is difficult to say that the positions of the vertical bores 64b are suitable for dropping an oil in the chain chamber toward an oil pan.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to ensure that an oil in a chain chamber provided in an upper portion of a vertical engine is smoothly discharged to an oil pan.
To achieve the above object, according to a first feature of the present invention, there is provided a vertical engine comprising: a first shaft disposed in a generally vertical direction; a second shaft disposed in a generally vertical direction and driven by the first shaft; and a chain wound around sprockets mounted at upper ends of the first shaft and the second shaft and circulated in a generally horizontal plane, wherein a bottom wall of a chain chamber accommodating the chain is formed by a bulged portion conformed to a partially cylindrical outer wall of uppermost one of cylinders, and oil return bores for returning an oil in the chain chamber to an oil pan are provided in lower portions of the bottom wall of the chain chamber on opposite sides of an axis of the bulged portion.
With the above-described arrangement, the bottom wall of the chain chamber accommodating the chain wound around the sprockets mounted at the upper ends of the first and second shafts and circulated in the generally horizontal plane, is formed by the bulged portion conformed to the partially cylindrical outer wall of the uppermost cylinder. Therefore, the oil in the chain chamber flows so that it is distributed to the lower bottom portions on the opposite sides of the axis of the bulged portion, and the oil is smoothly returned through the oil return bores formed in the lower bottom portions to the oil pan.
According to a second feature of the present invention, in addition to the arrangement of the first feature, the oil return bores communicate with the oil pan through a crank chamber.
With the above-described arrangement, the oil return bores in the bottom wall of the chain chamber communicate with the oil pan through the crank chamber, and hence not only each of the oil return bores can be shortened and easy to form, but also the oil in the chain chamber can be returned through a minimal distance to the oil pan.
According to a third feature of the present invention, in addition to the arrangement of the first feature, the oil return bores communicate with the oil pan not through a crank chamber.
With the above-described arrangement, the oil return bores communicate with the oil pan without through the crank chamber, and hence the oil can be returned further smoothly to the oil pan without being influenced by a variation in pressure in the crank chamber caused by the rotation of a crankshaft.
According to a fourth feature of the present invention, in addition to any of the first to third features, the vertical engine further comprises an oil jet for injecting the oil to the chain.
With the above-described arrangement, the oil is injected to the chains by the oil jet, and hence the chain can be sufficiently lubricated, leading to an enhancement in durability of the chain.
A crankshaft 13 in an embodiment corresponds to the first shaft of the present invention; a camshaft 73 and a balancer shaft 79 in the embodiment correspond to the second shaft of the present invention; a timing chain 30 and a balancer-driving chain 82 in the embodiment correspond to the chain of the present invention; a cam-driving sprocket 72, a cam follower sprocket 74, a balancer follower sprocket 80 and a balancer-driving sprocket 81 in the embodiment correspond to the sprockets of the present invention; and first, second and third oil jets 101, 103 and 105 correspond to the oil jet of the present invention.
The above and other objects, features and advantages of the invention will become apparent from the following description of the preferred embodiment taken in conjunction with the accompanying drawings.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a side view of the entirety of an outboard engine system according to one embodiment of the present invention.
FIG. 2 is an enlarged sectional view taken along a line 2—2 in FIG. 1.
FIG. 3 is an enlarged sectional view taken along a line 3—3 in FIG. 2.
FIG. 4 is an enlarged view taken in a direction of an arrow 4 in FIG. 2.
FIG. 5 is a view taken in a direction of an arrow 5 in FIG. 4.
FIG. 6 is an enlarged sectional view of essential portions of FIG. 1.
FIG. 7 is an enlarged view (a top view of a mount case) taken along a line 7—7 in FIG. 1.
FIG. 8 is an enlarged view (a bottom view of a pump body) along a line 8—8 in FIG. 1.
FIG. 9 is an enlarged view (a bottom view of an engine subassembly) along a line 9—9 in FIG. 1.
FIG. 10 is an enlarged view taken along a line 10—10 in FIG. 4.
FIG. 11 is an enlarged view taken along a line 11—11 in FIG. 1.
FIG. 12 is an enlarged sectional view taken along a line 12—12 in FIG. 1.
FIG. 13 is an enlarged sectional view taken along a line 13—13 in FIG. 11.
FIG. 14 is an enlarged view taken along a line 14—14 in FIG. 1.
FIG. 15 is an enlarged view taken along a line 15—15 in FIG. 1.
FIG. 16 is an enlarged sectional view taken along a line 16—16 in FIG. 12.
FIG. 17 is an enlarged sectional view taken along a line 17—17 in FIG. 12.
FIG. 18 is an enlarged sectional view taken along a line 18—18 in FIG. 12.
FIG. 19 is an enlarged sectional view taken along a line 19—19 in FIG. 5.
FIG. 20 is an enlarged sectional view taken along a line 20—20 in FIG. 5.
FIG. 21 is an enlarged sectional view taken along a line 21—21 in FIG. 11.
FIG. 22 is a circuit diagram of an engine-cooling system.
FIG. 23 is a circuit diagram of an engine-lubricating system.



DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention will now be described by way of an embodiment shown in the accompanying drawings.
As shown in FIGS. 1 to 3, an outboard engine system O is mounted on a hull so that it can perform a steering motion in a lateral direction about a steering shaft 96 and a tiling motion in a vertical direction about a tilting shaft 97. A water-cooled vertical engine E of an in-line 4-cylinder and 4-stroke type mounted at an upper portion of the outboard engine system O includes a cylinder block 11, a lower block 12 coupled to a front surface of the cylinder block 11, a crankshaft 13 disposed in a generally vertical direction and supported so that five journals 13a, 13a, 13a, 13a, 13a (hereinafter referred to as 13a for simplification) are interposed between the cylinder block 11 and the lower block 12, a crankcase 14 coupled to a front surface of the lower block 12, a cylinder head 15 coupled to a rear surface of the cylinder block 11, and a head cover 16 coupled to a rear surface of the cylinder head 15. Four pistons 18, 18, 18, 18 (hereinafter referred to as 18 for simplification) slidably received in four sleeve-shaped cylinders 17, 17, 17, 17 (hereinafter referred to as 17 for simplification) cast in the cylinder block 11 are connected to four crankpins 13b, 13b, 13b, 13b (hereinafter referred to as 13b for simplification) of the crankshaft 13 through four connecting rods 19, 19, 19, 19 (herein after referred to as 19 for simplification), respectively.
The cylinder block 11, the lower block 12, the crankcase 14 and the cylinder head 15 constitute an engine subassembly 50 of the present invention, and a space defined by the cylinder block 11, the lower block 12 and the crankcase 14 for accommodation of the crankshaft 13 constitutes a crank chamber 42 of the present invention.
Combustion chambers 20 formed in the cylinder head 15 so that they are opposed to top surfaces of the pistons 18, are connected to an intake manifold 22 through intake ports 21 opening into a left side of the cylinder head 15, i.e., toward a port in a travel direction of the boat, and also connected to an exhaust passage 24 in an engine room through exhaust ports 23 opening into a right side of the cylinder head 15. Intake valves 25 adapted to open and close downstream ends of the intake ports 21 and exhaust valves 26 adapted to open and close upstream ends of the exhaust ports 23 are driven to be opened and closed by a valve-operating mechanism 27 of a DOHC type accommodated within the head cover 16. An upstream portion of the intake manifold 22 is connected to a throttle valve 29 fixed to a front surface of the crankcase 14, so that intake air passed through a silencer 28 is supplied to the intake manifold 22. Injectors 58 for injecting a fuel into the intake ports 21 are mounted in an injector base 57 interposed between the cylinder head 15 and the intake manifold 22.
An internal space in the head cover 16 accommodating the valve-operating mechanism 27 is connected to the silencer 28 through a coupling 94 and a breather pipe 95, and a blow-by gas leaked into the internal space in the head cover 16 is returned to an intake system. Reference numeral 67 in FIG. 6 is electric equipment box for accommodation of electric equipment; reference numeral 69 is an AC generator; reference numeral 70 is a starter motor; and reference numeral 99 is a pressure sensor for detecting a hydraulic pressure. The AC generator 69 is driven through a belt by a pulley 68 (see FIG. 13) mounted at an upper end of the crankshaft 13.
A chain cover 31 for accommodation of a timing chain 30 (see FIGS. 12, 13 and 21) for transmitting a driving force from the crankshaft 13 to the valve-operating mechanism 27 is coupled to upper surfaces of the cylinder block 11, the lower block 12, the crankcase 14 and the cylinder head 15 of the vertical engine E. An oil pump body 34 is coupled to lower surfaces of the cylinder block 11, the lower block 12 and the crankcase 14. Further, a mount case 35, an oil case 36, an extension case 37 and a gear case 38 are coupled sequentially to a lower surface of the oil pump body 34.
The oil pump body 34 is adapted to accommodate the oil pump 33 between its lower surface and an upper surface of the mount case 35. A flywheel 32 is disposed between the oil pump body 34 and lower surfaces of the cylinder block 11 and the like opposite from the oil pump body 34, and a flywheel chamber and an oil pump chamber are defined by the oil pump body 34. The oil case 36, the mount case 35 and a periphery of a lower portion of the vertical engine E are covered with an undercover 39 made of a synthetic resin, and an upper portion of the vertical engine E is covered with an engine cover 40 made of a synthetic resin and coupled to an upper surface of the undercover 39.
A drive shaft 41 connected to a lower end of the crankshaft 13 extends downwards into the extension case 37 through the pump body 34, the mount case 35 and the oil case 36, and is connected, through a forward/backward travel switch over mechanism 45 operated by a shifting rod 52, to a front end of a propeller shaft 44 which is provided at its rear end with a propeller 43 and supported longitudinally in the gear case 38. A lower water supply passage 48 extending upwards from a strainer 47 mounted on the gear case 38 is connected to a cooling-water pump 46 mounted on the drive shaft 41.
As shown in FIG. 6, a cooling-water supply bore 36a is formed in a lower surface 36L of the oil case 36, and an upper water supply pipe 49 is connected at its upper end to the cooling-water supply bore 36a. A cooling-water supply passage 36b leading to the cooling-water supply bore 36a is formed in an upper surface 36U of the oil case 36 to surround a portion of a periphery of an exhaust pipe portion 36c integrally formed on the oil case 36. A cooling-water supply passage 35a having the same shape as the cooling-water supply passage 36b and opening into the upper surface 36U of the oil case 36 is formed in a lower surface 35L of the mount case 35 to surround a portion of a periphery of an exhaust passage 35b extending through the mount case 35.
FIG. 7 is a view of the mount case 35 as viewed from above, to a lower surface of which the oil case 36 is coupled. An outer periphery of the exhaust passage 35b is surrounded by cooling-water supply passages 35c and a cooling-water discharge passage 35d. More specifically, the cooling-water supply passages 35c (see FIG. 6) communicating with the cooling-water supply passage 35a formed to open downwards into the lower surface 35L of the mount case 35 are formed so that they open upwards into a portion of an upper surface 35U of the mount case 35 other than a portion where the cylinder block is mounted, and so that they extend along an outer periphery of the cylindrical discharge passage 35b. In the embodiment, the three arcuate cooling-water supply passages 35c are separated from one another by wall portions 35h continuous to an outer wall of the exhaust passage 35b. Further, the single arcuate cooling-water discharge passage 35d is formed outside an area in which the cooling-water supply passages 35c are provided and which is around an outer periphery of the cylindrical discharge passage 35b. The arcuate cooling-water discharge passage 35d is separated from the cooling-water supply passages 35c by wall portions 35i formed on the outer wall.
A cooling-water supply passage 35e is formed into a U-groove shape in the upper surface 35U of the mount case 35 to extend laterally of the outboard engine system O astride a central portion of the cylinder 17 as viewed in a plane and to open upwards into the upper surface 35U (see FIG. 6). The cooling-water supply passage 35a extends upwards to communicate with the cooling-water supply passage 35e. A relief valve 51 is mounted on the upper surface 35U of the mount case 35 and adapted to be opened to release cooling water when the pressure in the cooling-water supply passage 35a increases to a predetermined value or more (see FIGS. 4 and 7). A coupling 116 (see FIG. 7) leading to the cooling-water supply passage 35e is connected to a water-examining port 66 (see FIG. 22) through a hose 117.
The cooling-water discharge passage 35d communicates with an exhaust chamber 63 formed within the oil case 36, the extension case 37 and the gear case 38, through openings 36e (see FIG. 7) formed in the entire area of the lower surface 36L of the oil case 36. A gasket 55 interposed between the lower surface 35L of the mount case 35 and the upper surface 36U of the oil case 36 is provided with punched bores 55a through which the cooling water dropped from the cooling-water discharge passage 35d (see FIG. 7) of the mount case 35 is passed, and punched bores 55b defining a portion of the expansion chamber 63 to exhibit a silencing effect (see FIGS. 6 and 7).
The structure of the exhaust passage 24 within the engine room will be described below with reference to FIGS. 4 to 6 and 10.
An exhaust passage means for the vertical engine E is divided mainly into the exhaust passage 24 section within the engine room, and an exhaust chamber section separated from the engine room. The exhaust passage 24 within the engine room has an exhaust manifold 61 including: single pipe portions 61a which are coupled to a right side of the cylinder head 15, as described hereinafter, and into each of which an exhaust gas from each of the combustion chamber 20 is introduced, and a collection portion 61b in which the pipe portions 61a are collected at their downstream portions; and an exhaust gas guide 62 connected to the exhaust manifold 61 through a coupling portion 62a for guiding the exhaust gas to the outside of the engine room.
As can be seen from FIG. 6, the exhaust gas guide 62 is coupled to the upper surface 35U of the mount case 35 forming a partition wall of the engine room, to communicate with the exhaust passage 35b extending through the mount case 35. The exhaust passage 35b communicates with the exhaust pipe portion 36c integrally formed on the oil case 36 and also communicates with the exhaust chamber 63. In the embodiment, the oil case 36 forms an outer wall of the exhaust chamber 63 and also forms the exhaust pipe portion 36c, but in another construction, the exhaust pipe portion 36c may be a separate passage. The exhaust passage means may be of a construction in which a portion thereof is integrally continuous, but by forming the exhaust passage 24 within the engine room and the passages outside the engine room separately from each other, the assemblability of the various members and the sealability to the exhaust chamber 63 can be ensured.
An upper portion of the exhaust chamber 63 communicates with the outside of the undercover 39 through an exhaust gas discharge pipe 64 provided on the oil case 36, so that the exhaust gas is discharged into the atmosphere through the exhaust gas discharge pipe 64 without being discharged into water during the low-load operation of the vertical engine E.
A flange 62b formed at a lower end of the exhaust gas guide 62 is formed with three bolt bores 62c, three cooling-water inlet ports 62e defined into an arcuate shape to surround an exhaust passage 62d, and a single cooling-water outlet port 62f. When the flange 62b of the exhaust gas guide 62 is bolted to a mounting seat 35f (see FIG. 7) on the upper surface 35U of the mount case 35, the cooling-water inlet ports 62e in the exhaust gas guide 62 is brought into communication with the cooling-water supply passages 35c in the mount case 35, and the cooling-water outlet port 62f is brought into communication with the cooling-water discharge passage 35d in the mount case 35. On the side of the mounting seat 35f closer to the lower surface 35L of the mount case 35, a side of the outer wall forming the cooling-water discharge passage 35d opposite from the exhaust passage 35b lies at a location slightly higher in level than a gasket surface, and the cooling water is discharged from between a lower surface of the outer wall and the gasket surface onto a gasket 55.
The exhaust gas guide 62 is formed with a first exhaust gas guide-cooling water jacket JM1 covering a half of a periphery of an upper surface of the exhaust passage 62d, and a second exhaust gas guide-cooling water jacket JM3 covering a half of a periphery of a lower surface of the exhaust passage 62d. An exhaust manifold-cooling water jacket JM2 is formed to surround a periphery of the exhaust manifold 61, and when a lower end of the exhaust manifold 61 is fitted to an inner periphery of the coupling portion 62a of the exhaust gas guide 62, the exhaust manifold-cooling water jacket JM2 in the exhaust manifold 61 and the first exhaust gas guide-cooling water jacket JM1 in the exhaust gas guide 62 are brought into communication with each other.
As can be seen from FIGS. 4 and 5, two couplings 61d and 61e are provided at an upper portion of the exhaust manifold-cooling water jacket JM2, so that the cooling water in the exhaust manifold-cooling water jacket JM2 is discharged into the exhaust chamber 63 through the couplings 61d and 61e by a pipe line (not shown) or the like.
The structure of a cooling system in the cylinder block 11 will be described below with reference to FIGS. 3 and 7 to 9.
A slit-shaped cooling-water supply passage 34a formed to extend through the pump body 34 communicates with the slit-shaped cooling-water supply passage 35e (see FIG. 7) formed to extend through the mount case 35, and also communicates with a cooling-water supply passage 11c formed in the lower surface of the cylinder block 11 to extend laterally astride laterally widthwise central portions of the cylinders 17 and having the same mating-face shape as the cooling-water supply passage 35e. The cooling-water supply passage 11c in the cylinder block 11 is in the form of a groove with its lower surface opened, and communicates with a lower end of a cylinder block-cooling water jacket JB for the cylinder block 11 through two through-bores 11d and 11e extending through an upper wall of the groove.
The structure of a cooling system in the cylinder head 15 will be described below with reference to FIGS. 3, 6, 9 and 13.
Two short cooling-water supply passages 11g and 11h are branched toward the cylinder head 15 from a sidewall of the slit-shaped cooling-water supply passage 11c formed in the lower surface of the cylinder block 11, and communicate with a cylinder head-cooling water jacket JH for the cylinder head 15 through a gasket 56 between the cylinder block 11 and the cylinder head 15. The cylinder block-cooling water jacket JB surrounding the cylinders 17 in the cylinder block 11 is isolated from the cylinder head-cooling water jacket JH for the cylinder head 15 through the gasket 56 interposed between coupled surfaces of the cylinder block 11 and the cylinder head 15 (see FIGS. 2 and 6).
First and second thermostats 85 and 86 are accommodated within a thermostat-mounting seat 31a provided on the chain cover 31 covering the upper surfaces of the cylinder block 11 and the cylinder head 15, and upper ends JBe and JHe (see FIG. 12) of the cylinder block-cooling water jacket JB and the cylinder head-cooling water jacket JH are connected to the first and second thermostats 85 and 86, respectively. A draining pipe 88 extending from a coupling 87a of a thermostat cover 87 covering the thermostat-mounting seat 31a is connected to the second exhaust gas guide-cooling water jacket JM3 through a coupling 62h (see FIGS. 4 and 5) provided on the exhaust gas guide 62.
The structure of a system for driving camshafts 73, 73 and balancer shafts 78 and 79 by the crankshaft 13 will be described below with reference to FIGS. 11 to 13.
The timing chain 30 comprising a silent chain generating less noise is reeved around a cam-driving sprocket 72 mounted at the upper end of the crankshaft 13 and cam follower sprockets 74, 74 mounted on a pair of camshafts 73, 73 located at a rear portion of the cylinder head 15. A hydraulic chain tensioner 75 is mounted in abutment against a loosened side of the timing chain 30, and a chain guide 76 is mounted in abutment against an opposite side of the timing chain 30. The number of teeth of the cam-driving sprocket 72 is half of the number of teeth of each of the cam follower sprockets 74, 74 and hence, the camshafts 73, 73 are rotated at a number of rotations half of that of the crankshaft.
As shown in detail in FIG. 21, the timing chain 30 comprising the silent chain includes a plurality of plates 30a connected together in an endless fashion by pins 30b, so that teeth formed on the plates 30a are meshed with the cam-driving sprocket 72 and the cam follower sprockets 74, 74. The timing chain 30 is guided along a synthetic resin guide portion 76a made provided on the chain guide 76.
A balancer device 77 is accommodated within the crankcase 14, and a balancer-driving chain 82 comprising a silent chain is reeved around a balancer follower sprocket 80 mounted on one of two balancer shafts 78 and 79 and around a balancer-driving sprocket 81 mounted on the crankshaft 13. A chain tensioner 83 is mounted in abutment against a loosened side of the balancer-driving chain 82, and a chain guide 84 is mounted in abutment against an opposite side of the balancer-driving chain 82. The number of teeth of the balancer-driving sprocket 81 is twice as large as that of balancer follower sprocket 80 and hence, the balancer shafts 78 and 79 are rotated at a number of rotations twice as large as that of the crankshaft 13.
The cam-driving sprocket 72, the cam follower sprockets 74 and the timing chain 30 constitute a first chain mechanism 89, and the balancer-driving sprocket 81, the balancer follower sprocket 80 and the balancer-driving chain 82 constitute a second chain mechanism 90.
The chain cover 31, an upper portion of the crankcase 14 and an upper portion of the head cover 16 define a chain chamber 54 in which the first and second chain mechanisms 89 and 90 are accommodated.
As can be seen from FIGS. 12, 14 and 21, first and second curved ribs 31b and 31c hang from a lower surface of the chain cover 31. A lower surface of the first rib 31b is disposed in proximity to an upper surface of the chain 30 which is moved along the chain guide 76 fixed to the upper surfaces of the cylinder block 11 and the cylinder head 15, and a lower surface of the second rib 31c is disposed in proximity to the upper surface of the chain 30 which is moved along the chain tensioner 75 mounted on the upper surfaces of the cylinder block 11 and the cylinder head 15.
A third circular rib 31e also hangs from the lower surface of the chain cover 31 to surround a portion of a periphery of an opening 31d through which the crankshaft 13 extends, and the first and second ribs 31b and 31c are connected at their ends to opposite ends of the third rib 31e, respectively. Further, a fourth arcuate rib 31f hangs from the lower surface of the chain cover 31 to surround a portion of the periphery of the opening 31d. That is, the substantially entire region of the outer periphery of the opening 31d is surrounded by the third and fourth ribs 31e and 31f. Lower ends of the first, second and third ribs 31b, 31c and 31e terminate in locations higher in level than the upper end of the timing chain 30, but a lower end of the fourth rib 31f extends at substantially the same level as the lower end of the timing chain 30 and to a location higher in level than the lowermost packing face of the chain cover 31.
A detecting portion of an engine rotational speed sensor 59 for detecting a rotational speed of the crankshaft 13 is inserted into a clearance formed between opposed ends of the third and fourth ribs 31e and 31f, and is opposed an outer peripheral surface of a rotational speed-detecting rotor 60 fixed to the crankshaft 13.
As can be seen from FIGS. 14 and 15, first and second arcuate ribs 11n and 11o protrude upwards from the upper surface of the cylinder block 11, and upper ends of the first and second ribs 11n and 11o are opposed to the lower ends of the third and fourth ribs 31e and 31f of the chain cover 31.
As can be seen from FIGS. 11 to 14 and 18, the crankcase 14 covering the balancer device 77 includes a vertical wall 14a disposed to surround substantially a half of the balancer-driving sprocket 81 farther from the crankshaft 13, and an arcuate horizontal wall 14b extending in a horizontal direction from a lower end of the vertical wall 14a so that it is opposed to a lower surface of the balancer-driving sprocket 81. The vertical wall 14a and the horizontal wall 14b are formed integrally with the crankcase 14 by providing a recess 14c (see FIG. 11) protruding inwards at a portion of the crankcase 14.
The head cover 16 covering the valve-operating mechanism 27 includes: vertical walls 16b, 16b each disposed to surround approximately one fourth of an outer periphery of a travel locus of the timing chain 30 on a side of each of the pair of cam follower sprockets 74, 74 farther from the crankshaft 13; and arcuate horizontal walls 16c, 16c extending in a horizontal direction from lower ends of the vertical walls 16b, 16b, so that they are opposed to the lower surfaces of the cam follower sprockets 74, 74. The vertical walls 16b, 16b and the horizontal walls 16c, 16c are formed integrally with the head cover 16 by providing recesses 16d, 16d (see FIG. 11) protruding inwards at a portion of the head cover 16.
The structure of a lubricating system for the vertical engine E will be described below.
As shown in FIGS. 3, 4 and 6 to 9, the oil case 36 is integrally provided with an oil pan 36d, and accommodates a suction pipe 92 including an oil strainer 91. An oil suction passage 33a, an oil discharge passage 33b and an oil relief passage 33c are provided in the oil pump 33. The oil suction passage 33a is connected to a suction pipe 92; the oil discharge passage 33b extends from an outlet which extends to a back of a sheet surface of FIG. 8 and is connected to various portions to be lubricated of the vertical engine E via an oil passage (not shown) in the mount case 35 and an oil supply bore 11m (see FIG. 9) formed in the lower surface of the cylinder block 11; and the oil relief passage 33c is adapted to discharge the oil returned from the oil pump 33 into the oil pan 36d. 
A portion of the oil returned from the valve-operating mechanism 27 provided in the cylinder head 15 and the head cover 16 is returned to the oil pan 36d through a coupling 16a mounted in the head cover 16, an oil hose 93 and an oil return passage 35g (see FIG. 7) extending through the mount case 35, and another portion of the oil returned from the valve-operating mechanism 27 is returned to the oil pan 36d via an oil return passage 15b (see FIGS. 6 and 9) formed in the cylinder head 15, an oil return passage 11j (see FIG. 9) opening into the packing surfaces of the cylinder block 11 and the cylinder head 15, an oil return passage 11k (see FIG. 9) extending through the cylinder block 11, an oil return passage 34b (see FIG. 8) extending through the pump body 34 and the oil return passage 35g (see FIG. 7) extending through the mount case 35. The oil return passage 11j opening into the gasket 56 between the cylinder block 11 and the cylinder head 15 is disposed so that it is interposed between two cooling-water passages 11g and 11h opening into the oil return passage 11j (see FIG. 3).
The oil returned from the crankcase 14 is returned to the oil pan 36d through an oil return passage (not shown) extending through the pump body 34 and the oil return passage 35g (see FIG. 7) extending through the mount case 35.
As can be seen from FIGS. 3 and 15, two oil return bores 11p, 11p are formed in an upper wall of the cylinder block 11 covered with the chain cover 31, so that they are disposed on the left and right sides of a cylinder axis L. A bulged portion 11q of a partially cylindrical shape corresponding to the uppermost cylinder 17 protrudes upwards on the cylinder axis L; other portions of the cylinder block 11 are at locations lower in level than the bulged portion 11q, and the oil return bores 11p, 11p open at such lower locations.
Five oil return bores 11s are formed on the cylinder axes L intermediate between the two oil return bores 11p, 11p to extend axially of the crankshaft 13 through five journal-supporting walls 11r for supporting journals 13a of the crankshaft 13. The uppermost oil return bore 11s communicates with the chain chamber 54, the lowermost oil return bore 11s communicates with the oil pan 36d via the inside of the mount case 35.
As can be seen from FIGS. 12, 13 and 16, a first oil jet 101 is mounted on the upper surface of the cylinder block 11 at a location closer to the crankshaft 13 to lubricate the timing chain 30 meshed with the cam-driving sprocket 72 mounted on the crankshaft 13 and the balancer-driving chain 82 meshed with the balancer-driving sprocket 81 mounted on the crankshaft 13.
The first oil jet 101 includes a jet body 101a fitted in an oil jet support bore 11t formed in the cylinder block 11, a nozzle 101b opening into an upper portion of the jet body 101a, an arm portion 101c extending sideways from the jet body 101a, and a positioning projection 101d formed at a tip end of the arm portion 101c and fitted in a positioning bore 11u in the cylinder block 11. A seal member 102 is mounted around an outer periphery of the jet body 101a fitted in the oil jet support bore 11t. In order to fix the first oil jet 101 to the cylinder block 11, a retaining projection 31g hanging from a ceiling surface of the chain cover 31 is provided to abut against an upper surface of the jet body 101a. 
In this way, the first oil jet 101 is fitted in the oil jet support bore 11t in the cylinder block 11, and the retaining projection 31g of the chain cover 31 is provided to abut against the upper end of the jet body 101a. Therefore, it is possible to fix the first oil jet 101 without need for a special fixing member such as a bolt; a thick boss having a bolt bore is not required to be mounted in a narrow space in the vicinity of the crankshaft 13; and the first oil jet 101 can be disposed easily.
The nozzle 101b of the first oil jet 101 points diagonally upwards through a space below the third rib 31e hanging from the ceiling surface of the chain cover 31, and injects the oil supplied from the oil jet support bore 11t toward the cam-driving sprocket 72 mounted on the crankshaft 13, as shown by an arrow A in FIGS. 12 and 13.
As can be seen from FIGS. 12, 13 and 17, a second oil jet 103 for lubricating the timing chain 30 meshed with the cam follower sprocket 74 mounted on one of the camshafts 73 is mounted on the upper surface of the cylinder head 15. The second oil jet 103 includes a jet body 103a fitted in an oil supply passage 15c formed in the cylinder head 15, a nozzle 103b opening substantially horizontally into an upper portion of the jet body 103a, and an arm portion 103c extending sideways from the jet body 103a. The second oil jet 103 is fixed to the cylinder head 15 by a bolt 104 passed through the arm portion 103c. 
The oil injected substantially horizontally by the second oil jet 103 points to a position in which the timing chain 30 is meshed with the one cam follower sprocket 74 in the vicinity of an upstream end of the chain tension 75, as shown by an arrow B in FIG. 12.
As can be seen from FIGS. 12 and 18, a third oil jet 105 for lubricating the balancer-driving chain 82 meshed with the balancer follower sprocket 80 mounted on the one balancer shaft 79 is mounted within the crankcase 14. The third oil jet 105 opens diagonally upwards into an oil supply passage 14d formed in the crankcase 14, and the oil injected diagonally upwards by the third oil jet 105 points to the balancer-driving chain 82 immediately before being meshed into the balancer follower sprocket 80, as shown by an arrow C in FIG. 12.
As can be seen from FIGS. 3 and 20, two fourth oil jets 118, 118 are mounted in correspondence to upper two 17, 17 of the four cylinders 17, 17, 17, 17 vertically juxtaposed to have the generally horizontal cylinder axes L. The fourth oil jets 118, 118 are mounted for the purpose of cooling the pistons 18, 18, unlike the first, second and third oil jets 101, 103 and 105 mounted mainly for the purpose of lubrication. If the hydraulic pressure in a main gallery 11x extending vertically within the cylinder block 11 exceeds a predetermined value, check valves 119, 119 each receiving a predetermined set load are opened, whereby the fourth oil jets 118, 118 inject the oil in a direction of an arrow D toward rear faces of the piston 18, 18 slidably received in the two cylinders 17, 17.
The structure around an oil filter 106 will be described below with reference to FIGS. 3, 5, 19 and 20.
The oil filter 106 having a cylindrical shape as a whole is mounted on a right side of the cylinder block 11, and screwed into and fixed to a circular oil filter-mounting seat 108a of a base member 108 fixed to the cylinder block 11 by five bolts 107. An inlet-side oil supply passage 108b and an outlet-side oil supply passage 108c are formed within the base member 108. The inlet-side oil supply passage 108b communicates at its lower end with an oil supply passage 11v in the cylinder block 11 through a seal member 109 and has an oil flow-in portion 108d at its upper end, which opens into an outer periphery of the oil filter-mounting seat 108a. The outlet-side oil supply passage 108c communicates at one end thereof with an oil flow-out portion 108e which opens into a central portion of the oil filter-mounting seat 108a, and at the other end with the main gallery 11x through a seal member 110 and via an oil supply passage 11w. 
As shown in FIGS. 5 and 7, a coupling 111 is mounted on the upper surface 35U of the mount case 35 to communicate with a source for supplying the cooling water to the relief valve 51, and a cooling-water supply hose 112 extending from the coupling 111 is connected to a coupling 113 at a lower end of the base member 108. A cooling-water discharge hose 115 extending from a coupling 114 mounted at an upper end of the base member 108 is connected to a coupling 71 mounted at an intermediate portion of the draining pipe 88.
A water jacket 108f connecting the lower coupling 113 and the upper coupling 114 to each other is provided within the base member 108 and disposed to completely surround the inlet-side oil supply passage 108b, and the outlet-side oil supply passage 108c and the periphery of the oil filter-mounting seat 108a of the base member 108.
The operation of the embodiment of the present invention having the above-described arrangement will be described below.
First, the operation concerning the cooling of the vertical engine E will be described with reference mainly to a cooling-water circuit in FIG. 22.
When the drive shaft 41 connected to the crankshaft 13 is rotated by the operation of the vertical engine E, the cooling-water pump 46 mounted on the drive shaft 41 is operated to supply the cooling water drawn up through the strainer 47 to the cooling-water supply port 36a in the lower surface of the oil case 36 through the lower water supply passage 48 and the upper water supply passage 49. The cooling water passed through the cooling-water supply port 36a flows into the cooling-water supply passage 36b in the oil case 36 and the cooling-water supply passage 35a in the mount case 35, and a portion of the cooling water branched therefrom is supplied to the first exhaust gas guide-cooling water jacket JM1 formed in the exhaust gas guide 62 of the exhaust passage 24 within the engine room and the exhaust manifold-cooling water jacket JM2 formed in the exhaust manifold 61. An exhaust gas discharged from the combustion chambers 20 in the cylinder head 15 is discharged to the exhaust chamber 63 via the single pipe portions 61a and the collection portion 61b of the exhaust manifold 61, the exhaust passage 62d in the exhaust gas guide 62, the exhaust passage 35b in the mount case 35 and the exhaust pipe portion 36c in the oil case 36, and the exhaust passage 24 within the engine room heated to a higher temperature by the exhaust gas during this process is cooled by the cooling water flowing through the first exhaust gas guide-cooling water jacket JM1 and the exhaust manifold-cooling water jacket JM2.
The cooling water having a high temperature as a result of flowing upward through the first exhaust gas guide-cooling water jacket JM1 and the exhaust manifold-cooling water jacket JM2 is discharged from the couplings 61d and 61e mounted at the upper end of the exhaust manifold 61 through the pipe line (not shown) to the exhaust chamber 63.
A portion of the cooling water of a lower temperature supplied to the cooling-water supply passages 36b and 35a connected to the cooling-water supply port 36a flows through the two through-bores 11d and 11e opening into the cooling-water supply passage 11c in the lower end of the cylinder block 11 into the lower end of the cylinder block-cooling water jacket JB. The portion of the cooling water of the lower temperature supplied to the cooling-water supply passages 36b and 35a also flows from the cooling-water supply passage 11c in the lower end of the cylinder block 11 via the two cooling-water supply passages 11g and 11h into the lower end of the cylinder head-cooling water jacket JH.
During the warming operation of the vertical engine E, the first thermostat 85 connected to the upper end of the cylinder block-cooling water jacket JB and the second thermostat 86 connected to the upper end of the cylinder head-cooling water jacket JH are in closed states, and the cooling water in the cylinder block-cooling water jacket JB and the cylinder head-cooling water jacket JH resides therein without flowing and hence, the warming of the vertical engine E is promoted. During this process, the cooling-water pump 46 is continued to be rotated, but is brought into a substantially racing state by the leakage of the cooling water from a motor impeller made of a rubber.
When the temperature of the cooling water is raised after completion of the warming operation of the vertical engine E, the first and second thermostats 85 and 86 are opened, whereby the cooling water in the cylinder block-cooling water jacket JH and the cooling water in the cylinder head-cooling water jacket JH flow from the common coupling 87a of the thermostat cover 87 via the draining pipe 88 and the coupling 62h of the exhaust gas guide 62 into the second exhaust gas guide-cooling water jacket JM3. The cooling water which has cooled the exhaust gas guide 62 while flowing through the second exhaust gas guide-cooling water jacket JM3 is passed upward to flow through the mount case 35 and the oil case 36, and discharged into the exhaust chamber 63. When the rotational speed of the vertical engine E is increased to cause the internal pressure in the cooling-water supply passages 36b and 35a to become equal to or higher than a predetermined value, the relief valve 51 is opened, thereby permitting the surplus cooling water to be discharged into the exhaust chamber 63.
The cooling water diverted from an upstream side of the relief valve 51 into the cooling-water supply hose 112 flows into the lower end of the water jacket 108f in the base member 108 of the oil filter 106, and while flowing upwards through the water jacket 108f, the cooling water cools the oil flowing through the inlet-side oil supply passage 108b and the outlet-side oil supply passage 108c formed in the base member 108, and flows through the oil filter-mounting seat 108a for the oil filter 106 to cool the oil within the oil filter 106. The cooling water after the heat exchange with the oil is discharged from the upper end of the water jacket 108f through the cooling-water discharge hose 115 into an intermediate portion of the draining pipe 88.
Then operation concerning the lubrication of the vertical engine E will be described below with reference mainly to an oil circuit in FIG. 23.
The oil in the oil pan 36d is drawn into the oil pump 33 through the oil strainer 91 and the oil suction passage 33a (see FIG. 8), and the oil discharged by the oil pump 33 is supplied from the oil discharge passage 33b (see FIG. 8) through the oil passage in the mount case 35 into the oil supply bore 11m (see FIG. 9) formed in the lower surface of the cylinder block 11. At this time, the surplus oil discharged by the oil pump 33 is passed through the relief valve 51 and returned to the suction side of the oil pump 33. The relived oil may be returned to the oil pan 36d. 
The oil supplied to the oil supply passage 11v (see FIG. 3) in the cylinder block 11 is supplied therefrom via the inlet-side oil supply passage 108b in the base member 108 to the oil filter 106 (see FIGS. 19 and 20), and the oil after being filtered is supplied from the outlet-side oil supply passage 108c in the base member 108 via the oil supply passage 11w in the cylinder block 11 to the main gallery 11x vertically formed in the cylinder block 11. The oil diverted from the main gallery 11x lubricates the journals 13a and the crankpins 13b of the crankshaft 13 and also lubricates the two balancer shafts 78 and 79.
As described above, the base member 108 separate from the cylinder block 11 is formed with the inlet-side oil supply passage 108b for supplying the oil to the oil filter 106 and the outlet-side oil supply passage 108c for discharging the oil from the oil filter 106. Therefore, it is unnecessary to increase the thickness of the wall of the cylinder block 11 or to form a bulged portion surrounding the oil passages in order to form the outlet-side oil supply passage 108c and the inlet-side oil supply passage 108b. This can contribute to a reduction in weight of the cylinder block 11. Moreover, because the inlet-side oil supply passage 108b and the outlet-side oil supply passage 108c are formed in the base member 108, their layouts can be established freely without being restricted to the shape of the cylinder block 11 to contribute an increase in degree of freedom for the design.
In addition, because the water jacket 108f facing the inlet-side oil supply passage 108b, the outlet-side oil supply passage 108c and the oil filter-mounting seat 108a are formed in the base member 108 supporting the oil filter 106, the degree of freedom for the layout of the water jacket 108f can be increased as compared with a case where the water jacket is formed in the cylinder block 11. Moreover, the lower-temperature cooling water which is not heated and which has just exited from the cooling-water pump 46 is supplied to the water jacket 108f and hence, the oil can be cooled effectively by the cooling water flowing through the water jacket 108f. As a result, it is possible to enhance the lubricating effect and the cooling effect for portions to be lubricated such as sliding portions of the cylinders 17 and the pistons 18, the crankshaft 13, the camshafts 73, 73, the balancer shafts 78 and 79, the timing chain 30 and the balancer-driving chain 82.
The first oil jet 101 (see FIGS. 13 and 16) is connected to the oil jet support bore 11t diverted from the oil supply passage extending from the main gallery 11x to the uppermost journal 13a; the second oil jet 103 (see FIG. 17) is connected to the oil supply passage 15c diverted from the main gallery 11x, and the third oil jet 105 (see FIG. 18) is connected to the oil supply passage 14d diverted from the main gallery 11x. 
The nozzle 101b of the first oil jet 101 injects the oil to the cam-driving sprocket 72 mounted at the upper end of the crankshaft 13 to lubricate the timing chain 30 reeved around the cam-driving sprocket 72. The balancer-driving sprocket 81 is mounted on the crankshaft 13 so that it is located immediately below the cam-driving sprocket 72, and the oil dropped from the cam-driving sprocket 72 is sprinkled on the balancer-driving sprocket 81 to lubricate the balancer-driving chain 82 reeved around the balancer-driving sprocket 81.
In this way, the cam-driving sprocket 72 and the balancer-driving sprocket 81 are disposed at vertical two stages, and the oil can be injected toward the cam-driving sprocket 72 disposed at the upper stage, whereby the oil colliding with the cam-driving sprocket 72 and dropping therefrom can be brought into contact with the balancer-driving sprocket 81, thereby effectively lubricating both the cam-driving sprocket 72 and the balancer-driving sprocket 81. At this time, the oil dropping from the cam-driving sprocket 72 can be brought further effectively into contact with the balancer-driving sprocket 81, leading to an enhancement in lubricating effect, because the diameter of the balancer-driving sprocket 81 disposed at the lower stage is set to be larger than that of the cam-driving sprocket 72 disposed at the upper stage.
The periphery of the cam-driving sprocket 72 to which the oil is injected from the first oil jet 101 is surrounded by the third and fourth arcuate ribs 31e and 31f hanging from the ceiling surface of the chain cover 31. Therefore, it is possible to prevent the injected oil from being scattered wastefully, thereby further enhancing the effect of lubricating the cam-driving sprocket 72 and the balancer-driving sprocket 81.
The oil injected from the nozzle 103b of the second oil jet 103 points to the position in which the timing chain 30 is meshed into the one cam follower sprocket 74, and moreover, this position is largely spaced apart from a position in which the first oil jet 101 is mounted. Therefore, the entire region of the timing chain 30 can be lubricated equally by cooperation between the first and second oil jets 101 and 103.
The first and second ribs 31b and 31c hanging from the ceiling surface of the chain case 31 are disposed in proximity to the upper surface of the timing chain 30. Therefore, the oil flowing down from the ceiling surface along the first and second ribs 31b and 31c is positively supplied to sliding portions between the pins 30b and the bores in the plurality of plates 30a of the timing chain 30 and sliding portions between the timing chain 30 and the chain guide 76 to lubricate them. Particularly, in the timing chain 30 comprising the silent chain, the plates 30a and the sprocket are meshed directly with each other, and a driving force for the chain acts directly on the sliding portions of the bores in the plates 30a and the pins 30b. However, the wear of the sliding portions can be alleviated by supplying a sufficient amount of the oil to them through the first and second ribs 31b and 31c to provide the lubricating effect, as described above.
The two recesses 16d, 16d of the head cover 16 are provided with the horizontal walls 16c, 16c opposed to the lower surface of the timing chain 30, and hence the dropped oil can be accumulated temporarily on the horizontal walls 16c, 16c to lubricate the timing chain 30 traveling through the horizontal walls 16c, 16c. Moreover, the oil can be guided in an entraining direction along an arcuate travel locus of the timing chain 30 by cooperation with the vertical walls 16b, 16b opposed to the outer peripheral surface of the timing chain 30. Therefore, it is possible to ensure the contact of the oil with the timing chain 30 over a long time and a long distance.
Further, the oil scattered diametrically outwards from the cam follower sprockets 74, 74 by a centrifugal force can be caught on the vertical walls 16b, 16b, and the oil flowing down along the vertical walls 16b, 16b can be retained on the horizontal walls 16c, 16c. Therefore, the oil can be brought effectively into contact with the timing chain 30 circulating at a predetermined distance along the vertical walls 16b, 16b and the horizontal walls 16c, 16c, thereby enhancing the lubricating effect. Moreover, because the vertical walls 16b, 16b and the horizontal walls 16c, 16c are integrally formed by providing the recesses 16d, 16d on a portion of the head cover 16, there is no possibility that the number of parts is increased.
The oil injected from the third oil jet 105 points to the position in which the balancer-driving chain 82 is meshed into the balancer follower sprocket 80 and moreover, this position is largely spaced apart from a position in which the first oil jet 101 is mounted. Therefore, the entire region of the balancer-driving chain 82 can be lubricated equally by cooperation between the first and third oil jets 101 and 105.
Because the recess 14c of the crankcase 14 is provided with the horizontal wall 14b opposed to the lower surface of the balancer-driving chain 82, the dropped oil can be accumulated temporarily on the horizontal wall 14b to lubricate the balancer-driving chain 82 passed through the horizontal wall 14b. Moreover, the oil can be guided in an entraining direction along an arcuate travel locus of the balancer-driving chain 82 by cooperation with the vertical wall 14a opposed to the outer peripheral surface of the balancer-driving chain 82. Therefore, it is possible to ensure the contact of the oil with the balancer-driving chain 82 over a long time and a long distance.
Further, the oil scattered radially outwards from the balancer follower sprocket 80 by a centrifugal force can be caught on the vertical wall 14a, and the oil flowing down along the vertical wall 14a can be retained on the horizontal walls 14b. Therefore, the oil can be brought effectively into contact with the balancer-driving chain 82 circulating at a predetermined distance along the vertical wall 14a and the horizontal wall 14b, thereby enhancing the lubricating effect. Moreover, because the vertical wall 14a and the horizontal wall 14b are integrally formed by providing the recess 14c on a portion of the crankcase 14, there is no possibility that the number of parts is increased.
In the embodiment, the vertical walls 16b, 16b and the horizontal walls 16c, 16c of the head cover 16 are formed integrally and continuously, but they may be formed by members separate from the head cover 16 and fixed to the head cover 16 at any locations. This is advantageous to absorb an error upon the assembling, if there is a slight clearance between each of the vertical walls 16b, 16b and each of the horizontal walls 16c, 16c. 
Likewise, in the embodiment, the vertical wall 14a and the horizontal wall 11b of the crankcase 14 are formed integrally and continuously, but they may be formed by members separate from the crankcase 14 and fixed to the crankcase 14 at any locations. This is advantageous to absorb an error upon the assembling, if there is a slight clearance between the vertical wall 14a and the horizontal wall 11b. 
In general, if the timing chain 30 and the balancer-driving chain 82 are disposed at the upper ends of the crankshaft 13, the camshafts 73, 73 and the balancer shaft 79, it is impossible to expect an effect of sufficient lubrication of the timing chain 30 and the balancer-driving chain 82 by only the oil leaked from bearings of these shafts 13, 73, 73 and 79 and for this reason, a reduction in durability of these chains 30 and 82 is feared. Therefore, as in the present embodiment, the oil is injected from the first, second and third oil jets 101, 103 and 105 to the timing chain 30 and the balancer-driving chain 82; the oil scattered to the ceiling surface of the chain case 31 is guided to the timing chain 30 and the balancer-driving chain 82 by the first, second, third and fourth ribs 31b, 31c, 31e and 31f; and further, the oil is retained on the vertical walls 14a, 16b, 16b and the horizontal walls 14b, 16c, 16c formed on the crankcase 14 and the head cover 16, respectively, whereby an effect of sufficient lubrication of the timing chain 30 and the balancer-driving chain 82 can be ensured.
The first and second oil jets 101 and 103 are disposed at the opposite ends of the timing chain 30, and the first and third oil jets 101 and 105 are disposed at the opposite ends of the balancer-driving chain 82. Therefore, the oil can be injected equally to the entire regions of the timing chain 30 and the balancer-driving chain 82 to enhance the lubricating effect.
By the provision of the first and second oil jets 101 and 103 inside the travel locus of the timing chain 30, it is easy to dispose the first and second oil jets 101 and 103 within the narrow chain chamber 54. In addition, by the provision of the third oil jet 105 outside the travel locus of the balancer-driving chain 82, the third oil jet 105 can be disposed without hindrance, even when a space cannot be ensured inside such travel locus.
Further, even when the oil cannot be injected horizontally due to the presence of an obstacle, because the directions of injection of the oil from the first and third oil jets 101 and 103 are inclined with respect to the rotational planes of the timing chain 30 and the balancer-driving chain 82, the disposition of the first and third oil jets 101 and 105 cannot be impeded.
If a breather pipe is connected to the chain chamber 54, there is a possibility that the oil injected from each of the first, second and third oil jets 101, 103 and 105 into the chain chamber 54 may clog the breather pipe. In the present embodiment, however, the breather pipe 95 (see FIG. 2) is connected to the inside of the head cover 16 isolated from the chain chamber 54, whereby the breather pipe 95 can be prevented from being clogged with the oil.
The oil which has lubricated the first and second chain mechanisms 80 and 90, namely, the cam-driving sprocket 72, the cam follower sprockets 74, 74, the timing chain 30, the balancer-driving sprocket 81, the balancer follower sprocket 80 and the balancer-driving sprocket 82 in the above described manner is dropped through the oil return bores 11p, 11p and 11s (see FIGS. 3 and 15) formed in the upper surface of the cylinder block 11, and the oil is passed sequentially through the four oil return bores 11s (see FIG. 3) formed in the upper second and more journal support walls 11r of the cylinder block 11 to be returned to the oil pan 36d. 
As can be seen from FIG. 15, the bulged portion 11q of the uppermost cylinder 17 protrudes on the upper surface of the cylinder block 11, and the left and right oil return bores 11p, 11p are formed at lowermost locations displaced from the bulged portion 11q toward the crankshaft 13. Therefore, the oil on such bulged portion 11q flows so that it is distributed to the opposite sides of the axis of the bulged portion 11q; and the oil is caught smoothly in the oil return bores 11p, 11p; and returned to the oil pan 36d. 
The upper most oil return bore 11s disposed in the upper surface of the cylinder block 11 between the left and right oil return bores 11p, 11p is not necessarily required. In the present embodiment, the uppermost oil return bore 11s is secondarily formed in processing the four oil return bores 11s formed in the upper second and more journal support walls 11r. 
In the process in which the oil injected into the chain chamber 54 is returned through the oil return bores 11p, 11p and 11s provided in the journal support walls 11r of the cylinder block 11 to the underlying oil pan 36d, the oil passed through the oil return bores 11s collides against the connecting rods 19, whereby it is scattered and brought into contact with the connecting rods 19, the pistons 18, the cylinders 17 and the like, to thereby contribute to the cooling the pistons 18 heated to a higher temperature by a heat from the combustion chamber 20. At the same time, the oil scattered by the centrifugal force after lubricating the journals 13a and the crankpins 13b of the crankshaft 13 is also brought into contact with the connecting rods 19, the pistons 18, the cylinders 17 and the like, to thereby contribute to the cooling of the pistons 18 by cooperation with the oil returned from the chain chamber 54.
The amount of the oil cooling the pistons 18 is larger at a location closer to the lower portion of the cylinder block 11 and hence, there is a tendency that the cooling of the upper piston(s) 18 is insufficient, and the cooling of the lower piston(s) 18 is excessive. In the present embodiment, however, the oil injected from the fourth oil jets 118, 118 mounted at upper two 17, 17 of the four cylinders 17 is brought into contact with the rear faces of the upper two pistons 18, 18 to exhibit a cooling effect, whereby the four pistons 18 can be cooled equally to prevent the occurrence of the insufficient cooling and excessive cooling. Moreover, the amount of the oil required for the cooling can be minimized to a necessary amount.
When the rear faces of the pistons 18, 18 are cooled by the oil injected from the fourth oil jets 118, 118, the temperature of the oil is liable to increase by the heat taken away from the pistons 18, 18. In the present embodiment, however, the rising of the temperature of the oil can be suppressed reliably, because the cooling effect of the oil in the oil filter 106 is extremely high.
Although the embodiment of the present invention has been described in detail, it will be understood that the present invention is not limited to the above-described embodiment, and various modifications in design may be made without departing from the spirit and scope of the invention defined in the claims.
For example, the vertical engine E used in the outboard engine system O has been illustrated in the embodiment, but the present invention is applicable to any vertical engine E not for the outboard engine system O.
The oil return bores 11p, 11p formed in the bottom wall of the chain chamber 54 communicate with the oil pan 36d through the crank chamber 42 in the embodiment, but they may communicate with the oil pan 36d not through the crank chamber 42, as in the case of the third feature of the present invention. With such arrangement, the oil in the chain chamber 54 can be returned further smoothly to the oil pan 36d without being influenced by a variation in pressure in the crank chamber 42 caused by the rotation of the crankshaft 13.

## Claims

1. A vertical engine comprising:
a first shaft disposed in a generally vertical direction;
a second shaft disposed in a generally vertical direction and driven by the first shaft; and
a chain wound around sprockets mounted at upper ends of the first shaft and the second shaft and circulated in a generally horizontal plane,
wherein a bottom wall of a chain chamber accommodating the chain is formed by a bulged portion conformed to a partially cylindrical outer wall of an uppermost one of cylinders, and oil return bores for returning an oil in the chain chamber to an oil pan are provided in lower portions of the bottom wall of the chain chamber on opposite sides of an axis of the bulged portion.

2. A vertical engine according to claim 1, wherein the oil return bores communicate with the oil pan through a crank chamber.

3. A vertical engine according to claim 1, wherein the oil return bores communicate with the oil pan not through a crank chamber.

4. A vertical engine according to any of claims 1 to 3, further comprising an oil jet for injecting the oil to the chain.