WO2009004475A2

WO2009004475A2 - Engine lubrication apparatus

Info

Publication number: WO2009004475A2
Application number: PCT/IB2008/001764
Authority: WO
Inventors: Teru Ogawa
Original assignee: Toyota Jidosha Kabushiki Kaisha
Priority date: 2007-07-05
Filing date: 2008-07-04
Publication date: 2009-01-08
Also published as: WO2009004475A3; JP2009013887A

Abstract

An engine lubrication apparatus has an oil sump provided at a lower side of an engine, a scavenge pump for sending oil in the oil sump to an oil tank, and a feed pump for supplying the oil in the oil tank to the engine. The engine lubrication apparatus has: a crankcase with side portions extending in parallel with the axis of a crankshaft on both sides and each constituted of inner and outer sidewalls arranged to create a space open at the lower side between the sidewalls; a first oil-pan member attached to lower portions of the inner sidewalls of the crankcase and forming the oil sump; and a second oil-pan member attached to lower portions of the outer sidewalls and forming the oil tank together with the spaces, the second oil-pan member being spaced apart from the first-oil-pan member an covering the first oil-pan member from below.

Description

ENGINE LUBRICATION APPARATUS

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0001] The invention relates to an engine lubrication apparatus and in particular to a dry-sump type engine lubrication apparatus.

2. Description of the Related Art

[0002] In general, engine lubrication apparatuses are provided in the wet-sump type and the dry-sump type.

[0003] A typical wet-sump type engine lubrication apparatus has an oil pan provided below the engine unit and having a capacity large enough to store the entire lubricant distributed to respective portions of the engine to be lubricated, and the oil in this oil pan is pumped up by an oil pump and then sent to the respective portions of the engine for lubrication. Because of such a simple structure, wet-sump type engine lubrication apparatuses are widely used in various vehicles in market However, wet-sump type engine lubrication apparatuses have the following drawbacks: the depth of the oil pan is required to be large enough to store a sufficient amount of lubricant; the drive power of the engine is used to agitate the oil in the oil pan using the crankshaft (i.e., drive power loss); and a pumping failure of the oil pump tends to occur when the oil in the oil pan moves during the acceleration or deceleration of the vehicle or during the turning of the vehicle.

[0004] In view of these drawbacks, dry-sump type engine lubrication apparatuses have been developed especially for racing engines, and the like. In dry-sump type engine lubrication apparatuses, an oil tank is provided outside of the engine unit, and the oil in an oil sump (dry sump) provided at the bottom of the engine unit is pumped up by a scavenge pump and then stored in the oil tank, and the oil in the oil tank is then distributed via an oil-feed pump to respective portions to be lubricated.

[0005] In such dry-sump type engine lubrication apparatuses, however, because the oil tank is separately provided from the engine unit, a large space is needed around the engine unit, and further, because the pipe between the oil sump and the oil tank and the pipe between the oil tank and the engine unit are both long, these pipes increase the head loss of the oil, reducing the hydraulic pressure response when said pressure is increased by the oil pump. To solve these problems, Japanese Patent Application Publication No. 06-248927 (JP-A-06-248927) describes the following engine lubrication apparatus.

[0006] According to the engine lubrication apparatus described in this publication, the oil used in the engine is stored in an oil tank integrated with the engine unit and the oil is distributed to respective portions of the engine via a main oil pump. The oil tank is integrally formed on one side of an oil pan and an oil storage chamber is integrally formed on the other side of the oil pan, and the oil in the oil pan is delivered to the oil tank by the scavenge pump, and the oil in the oil tank is delivered by the main oil pump to the respective portions of the engine through corresponding oil passages, the oil storage chamber, and corresponding oil-distribution pipes.

[0007] Meanwhile, Japanese Patent Application Publication No. 04-246216 (JP-A-04-246216) describes an internal combustion engine lubrication apparatus that has an oil pan covering the lower side of the crankcase of the engine and having a pump mounting space formed by a concave portion at one corner of the oil pan and that also has an oil tank portion formed below the oil pan adjacent the pump mounting space and partitioned from the crankcase by a partition on the upper side.

[0008] According to the engine lubrication apparatus described in JP-A-06-248927, however, although a sufficient space is created around the engine as a result of the integration of the engine unit and the oil tank, because the oil tank is integrally formed on one side of the oil pan and the oil storage chamber is integrally formed on the other side of the oil pan and the oil passage extending between the oil tank and the oil storage chamber is integrally formed at the bottom of the oil pan, there are some problems regarding the capability of securing a sufficient amount of oil, the manufacturability, and the serviceability, and therefore it is difficult to put the engine lubrication apparatus described in JP-A-06-248927 in practical use.

[0009] Meanwhile, the main purpose of using dry-sump type lubrication systems is to reduce the drive power loss caused by the resistance against the oil agitation by the crankshaft. In the case of a dry-sump type lubrication system having a scavenge pump, the drive power of the engine is used to drive the scavenge pump, and therefore the drive power loss is large as compared to wet-sump type lubrication systems. However, because the oil-agitating resistance at the crankshaft is relatively low in a low engine speed range, when the engine is running at a low speed, the aforementioned advantage of the dry-sump type lubrication systems is not adequate, simply resulting in a decrease in the fuel economy of the engine due to the power loss for driving the scavenge pump.

SUMMARY OF THE INVENTION

[0010] The invention provides an engine lubrication apparatus that is highly manufacturable and serviceable and is capable of minimizing the reduction of the fuel economy of the engine.

[0011] The first aspect of the invention relates to an engine lubrication apparatus having an oil sump provided at a lower side of an engine, a scavenge pump for sending oil in the oil sump to an oil tank, and a feed pump for supplying the oil in the oil tank to the engine. This engine lubrication apparatus has: a crankcase having side portions extending in parallel with the axis of a crankshaft of the engine on both sides, wherein each side portions is constituted of an inner sidewall and an outer sidewall that are arranged such that a space is formed between the inner sidewall and the outer sidewall and such that the space is open at the lower side; a first oil-pan member attached to lower portions of the inner sidewalls of the crankcase and forming the oil sump; and a second oil-pan member attached to lower portions of the outer sidewalls of the crankcase and forming the oil tank together with the spaces, the second oil-pan member being spaced apart from the first-oil-pan member and arranged to cover the first oil-pan member from below. [0012] According to the engine lubrication apparatus described above, the side portions of the crankcase that extend in parallel with the axis of the crankshaft of the engine on both sides and each side portion is constituted of the inner sidewall and the outer sidewall arranged such that a space is formed between the inner sidewall and the outer sidewall and such that the space is open at the lower side, and the oil sump is formed by the first oil-pan member attached to the lower portions of the inner sidewalls of the crankcase, and the oil tank is formed by the second oil-pan member attached to the lower portions of the outer sidewalls of the crankcase. The second oil-pan member is spaced apart from the first-oil-pan member and arranged to cover the first oil-pan member from below. Thus, the oil tank includes, as its internal spaces, the space between the first oil-pan member and the second oil-pan member, the space between the inner sidewall and the outer sidewall of one of the sides portions of the crankcase, and the space between the inner sidewall and the outer sidewall of the other of the side portions of the crankcase. Having such a structure, the engine lubrication apparatus is compact in size but has an oil storage large enough to store a sufficient amount of oil. Further, because the first oil-pan member forming the oil sump and the second oil-pan member forming the oil tank can be detached from each other, the engine lubrication apparatus is highly manufacturable and serviceable.

[0013] The above-described engine lubrication apparatus may be such that: a portion of the lower edge of the inner sidewall of one of the side portions of the crankcase and a portion of the lower edge of the inner sidewall of the other of the side portions of the crankcase are connected to each other via a bottom wall; the rest of the lower edge of the inner sidewall of one of the side portions of the crankcase and the rest of the lower edge of the inner sidewall of the other of the side portions of the crankcase together define an opening; and the first oil-pan member is attached to the opening.

[0014] According to this structure, the rigidity of the crankcase is relatively high due to the lower edges of the inner walls being partially connected to each other via the bottom wall, and this suppresses vibrations of the engine unit.

[0015] Further, the above-described engine lubrication apparatus may be such that: a partition wall is provided between the first oil-pan member and the second oil-pan member to form an oil passage; an outlet of the scavenge pump is located near an upstream end of the oil passage; and an opening of an oil strainer of the feed pump is located near a downstream end of the oil passage.

[001(Q According to this structure, even if bubbles, and the like, are formed in the oil as the oil is discharged from the scavenge pump, the bubbles are removed from the oil as the oil flows all the way from the upstream end to the downstream end of the oil passage. Thus, this structure effectively reduces the possibility of oil containing bubbles being sucked into the oil strainer of the feed pump at the downstream end of the oil passage.

[0017] In the above-described engine lubrication apparatus, the oil passage may be generally spiral.

[0018] In this case, the oil passage can be made long within a limited space, and this prolongs the time the oil stagnates in the oil passage, facilitating the removal of bubbles from the oil.

[0019] Further, the above-described engine lubrication apparatus may be such that an oil-return path to the oil tank is composed of a first oil-return passage through which oil is delivered by the scavenge pump and a second oil-return passage through which oil supplied to the engine is directly returned to the oil tank.

[0020] According to this structure, the drive power used for driving the scavenge pump is reduced as compared to the case where the entire oil supplied to the engine is returned to the oil tank using the scavenge pump, and therefore the fuel economy improves.

[0021] Further, the above-described engine lubrication apparatus may be such that the second oil-return passage is constituted of at least one of an oil-return passage which is formed in a chain cover of the engine so as to communicate with at least one of the spaces and through which oil is delivered from a cylinder head of the engine and an oil-return passage which is formed in a cylinder block of the engine and through which oil is delivered from the cylinder head.

[0022] According to this structure, through either of the oil-return passage in the chain cover and the oil return-passage in the cylinder head, the oil is directly returned to the oil tank due to gravity, and therefore the drive power for driving the scavenge pump can be effectively saved. Thus, the above-described structure improves the fuel economy of the engine by saving the drive power for driving the scavenge pump in a low engine speed range where the oil agitation resistance is relatively low while securing the general effects of dry-sump type lubrication systems that are exerted in a high engine speed range where the loss of the engine drive power due to the oil agitation resistance is relatively large.

[0023] In the above-described engine lubrication apparatus, the pumping capacity of the scavenge pump may be smaller than the pumping capacity of the feed pump.

[0024] This structure further reduces the engine drive power required to drive the scavenge pump, thus reducing the production cost.

BRIEF DESCRIPTION OF THE DRAWINGS [0025] The foregoing and further features and advantages of the invention will become apparent from the following description of example embodiments with reference to the accompanying drawings, wherein like numerals are used to represent like elements and wherein:

FIG 1 is a longitudinal cross-sectional view schematically showing the structure of an engine lubrication apparatus according to an example embodiment of the invention; FIG 2 is a lateral cross-sectional view schematically showing the structure of the engine lubrication apparatus of the example embodiment of the invention;

FIG 3 A is a perspective view of a second oil pan member forming the lower portion of an oil tank before it is attached to a craαkcase and a chain cover; FIG 3B is a transparent view of the oil tank as seen from below; and FIG 4 is a block diagram illustrating the oil circulation system of the engine lubrication apparatus of the example embodiment of the invention.

DETAILED DESCRIPTION OFTHE EMBODIMENTS [0026] Hereinafter, example embodiments of the invention will be described in detail with reference to the drawings.

[0027] Referring to FIQ 1, an engine unit 100 is constituted of a cylinder block 110, a crankcase 120 attached to the bottom of the cylinder block 110, a cylinder head 130 mounted on the cylinder block 110, and a head cover 140 mounted on the cylinder head 130. The crankcase 120 has a front wall 121 and a rear wall 122 extending perpendicular to the axis of the crankshaft (See FIG 1) and inner sidewalls 123 and outer sidewalls 124 extending in parallel to the axis of the crankshaft. A space 125 is formed between the inner sidewall 123 and the outer sidewall 124 on each side. The bottom side of the space 125 is open (See FIG 2).

[0028] Referring to HG 2, flanges 123f are formed at the lower edges of the inner sidewalls 123 on both sides. A first oil pan member 150, which will be described in detail later, is attached to the flanges 123f. On the other hand, flanges 124f are formed at the lower edges of the outer sidewalls 124 on both sides. An oil tank, which will be described in detail later, is attached to the flanges 124f. In this example embodiment of the invention, in the rear side of the crankcase 120, the lower edges of the inner sidewalls 123 on both sides of the crankcase 120 are integrated with the rear wall 122 via the bottom wall 127 shown in FIG 1, forming an oil storage space and providing a high rigidity. The portion of the bottom side of the crankcase 120 other than the bottom wall 127 is occupied by an opening 129 surrounded by the flanges 123f to which the first oil pan member 150 is attached.

[0029] The first oil pan member 150 has a generally flat bottom face and is shallow. A flange 15Of of the first oil pan member 150 is attached to the bottom face of the flange 123f by bolts, which are not shown in the drawings, thus forming a main oil sump 155. As such, the interior of the crankcase 120 for accommodating various rotational elements including the crankshaft 112 and a pair of balance shafts 114 is defined by the first oil pan member 150, the front wall 121, the rear wall 122, the inner sidewalls 123, and the bottom wall 127.

[0030] Referring to FIG 1, pistons 116 are disposed in the respective bores of the cylinder block HO such that they can reciprocate therein. The reciprocation of each piston 116 is converted into rotational motion of the crankshaft 112 via a connecting rod 118. Combustion chambers are formed in the cylinder head 130. Intake ports and exhaust ports communicate with the respective combustion chambers. The intake ports are connected to an intake manifold, which is not shown in the drawings, while the exhaust ports are connected to an exhaust manifold, which is not shown in the drawings. The intake ports and the exhaust ports are opened and closed as the corresponding intake and exhaust valves operate. The intake valves and the exhaust valves are driven by an intake camshaft and an exhaust camshaft, which are not shown in the drawings. As will be described in detail later, the engine unit 100 incorporates a variable intake valve timing mechanism WT-i that variably controls the operation timing of the intake valves. Oil control valves OCV for controlling the hydraulic oil supplied to the variable intake valve timing mechanism are disposed in the cylinder head 130 and in the head cover 140. Referring to FIG 2, oil return passages 119 through which part of the hydraulic oil supplied to the cylinder head 130 is returned to an oil tank 165, which will be described in detail later, are formed in the cylinder block UO. A sprocket 117 provided at the front end of the crankshaft 112 and sprockets provided on the intake and exhaust camshafts, which are not shown in the drawings, are connected to each other via a riming chain wound around said sprockets. A chain cover 111 is attached to the cylinder block UO so as to cover the sprockets and the timing chain.

[0031] A second oil pan member 160 is attached, via a flange 16Of of the second oil pan member 160, to the bottom face of the flanges 124f of the outer sidewalk 124 of the crankcase 120 and to the bottom face of a flange HIf of the chain cover 111 using bolts, or the like, which are not shown in the drawings. Referring to FIG 1 and FIG 2, the depth of the second oil pan member 160 is larger than that of the first oil pan member ISO. The second oil pan member 160 is spaced at a predetermined distance apart from the first oil pan member 150 such that it covers the first oil pan member 150 from below. Thus, the space 125 of the crankcase 120 and the oil tank 165 are together formed. The oil tank 165 includes, as its internal spaces, the space between the generally flat bottom wall of the second oil pan member 160 and the bottom face of the first oil pan member ISO, the space between the front wall 121 of the crankcase 120 and the chain cover 111, the space 125 between the inner sidewall 123 and the outer sidewall 124 on one side, and the space 125 between the inner sidewall 123 and the outer sidewall 124 on the other side. The oil tank 165 is substantially symmetrical about the center plane of the engine unit 100 extending along the axis of the crankshaft 112. The capacity of the oil tank 165 is set such that an oil level OL representing the oil level in the oil tank 165 when the engine is not operating is higher than the bottom face of the flange 123f to which the first oil pan member 150 is attached.

[0032] In the crankcase 120, a scavenge pump 170 is provided which is driven by one of the two balance shafts 114 to send the oil in the main oil sump 155 to the oil tank 165, and a feed pump 180 is provided which is driven by the other of the two balance shafts 114 to send the oil in the oil tank 165 to the engine unit 100.

[0033] A driven gear 113 provided on one of the two balance shafts 114 is driven by a drive gear 115 press-fit on a counter weight of the crankshaft 112. The two balance shafts 114 rotate in synchronization in opposite directions via driven gears meshed with each other, which are not shown in the drawings.

[0034] The suction port of the scavenge pump 170 is connected via a suction pipe 172 to an oil strainer 171 having an oil inlet located near the upper face of the first oil pan member 150 defining the main oil sump 155. On the other hand, the discharge port of the scavenge pump 170 is connected to a discharge pipe 174. The outlet of the discharge pipe 174, that is, a discharge outlet 176 of the scavenge pump 170 is located in the oil tank 165.

[0035] The suction port of the feed pump 180 is connected via a suction pipe 182 to an oil strainer 181 having an oil inlet located near the second oil pan member 160 defining the oil tank 165. The discharge port of the feed pump 180 is connected to a discharge pipe communicating via an oil filter, which is not shown in the drawings, with a passage formed in the crankcase 120 or in the cylinder block 110 for distributing lubricant or hydraulic oil. A partition wall 190 defining an oil passage 200, which will be described in detail later, is provided upright on the bottom side of the oil tank 165, that is, on the second oil pan member 160.

[0036] In the following, the positional relation among the oil passage 200 defined by the partition wall 190, the discharge outlet 176 of the scavenge pump 170, and the oil inlet of the oil strainer 181 of the feed pump 180 will be described with reference to FIG 3A and FIG 3B. FIG 3A is a perspective view of the second oil pan member 160 forming the lower portion of the oil tank 165 before it is attached to the crankcase 120 and the chain cover 111, and FIG 3B is a transparent view of the oil tank 165 as seen from below.

[0037] In this example embodiment of the invention, the oil tank 165 has a generally rectangular outline as viewed from above. The four corners of the rectangular oil tank 165 are curved inward, and a concave portion 166 for mounting the oil filter 195 is formed at one corner. The partition wall 190 is constituted of first to fourth partition wall 190A to 190D connected in series substantially at a right angle. One end of the partition wall 190A is slightly spaced from the inner face of the wall of the concave portion 166, and an inlet 204 of a center chamber 202 in which the oil strainer 181 of the feed pump 180 is disposed is formed between the end of the partition wall 190D and said end of the partition wall 190A. The top faces of the first to fourth partition walls 190A to 190D are in contact with the bottom face of the first oil pan member 150 when the second oil pan member 160 is attached to the crankcase 120. Thus, a generally spiral oil passage 200 is formed, and through this oil passage 200, the oil mainly flows toward the center chamber 202 as indicated by the black arrows in FIG 3 A and FIG 3B.

[0038] The discharge outlet 176 of the scavenge pump 170 is located upstream of the oil passage 200, and oil is discharged from the discharge outlet 176 in the direction indicated by the white arrow in FIG 3B coinciding with the main flow direction of the oil passage 200 indicated by the black arrows.

[0039] Next, the effects obtained with the above-described structure of the example embodiment will be described. When the engine unit 100 is running, the oil in the oil tank 165 is pumped up by the feed pump 180 via the oil strainer 181 and then supplied via the oil filter 195 to oil distribution passages formed in the crankcase 120 and the cylinder block 110. The oil is then supplied to given portions to be lubricated or to given potions to be hydraulically driven, after which the oil is collected at the main oil sump 155 in the crankcase 120. Subsequently, the oil in the main oil sump 155 is pumped up by the scavenge pump 170 together with blow-by gas, etc., via the oil strainer 171 and then discharged from the discharge outlet 176 located in the upstream side of the oil passage 200 defined by the partition wall 190 provided upright on the bottom side of the oil tank 165.

[0040] Discharged from the discharge outlet 176, the oil then flows in the oil passage 200 along the main flow direction indicated by the black arrows and enters the center chamber 202 through the inlet 204. Then, the oil is pumped up by the feed pump 180 via the oil strainer 181 that is the oil inlet located in the center chamber 202 at the downstream end of the oil passage 200, whereby the oil is distributed again to the engine unit 100 via the feed pump 180.

[0041] Even if bubbles are contained in the oil discharged from the scavenge pump 170, the bubbles are effectively removed as the oil flows all the way from the discharge outlet 176 of the scavenge pump 170 at the upstream side of the oil passage 200 to the oil strainer 181 of the feed pump 180 at the downstream end of the oil passage 200. The removed bubbles gather at the portion of the space 125 higher than the oil level OL of the oil tank 165 and return to the crankcase 120 via communication holes. Thus, even if the oil discharged from the scavenge pump 170 contains bubbles, the oil is not directly pumped up by the feed pump 180, but the oil is made to flow through a relatively long path of the oil passage 200 by taking a long time, whereby the bubbles are removed from the oil. As such, the bubble-containing oil is not supplied from the feed pump 180. Note that a gas-liquid separator 400 may be provided at the discharge outlet 176 of the scavenge pump 170 to remove bubbles from the oil discharged from the discharge outlet 176.

[0042] Next, the oil circulation system adopted in this example embodiment of the invention will be described with reference to FIG 4. First, oil is pumped up from the oil tank 165 by the feed pump 180 via the oil strainer 181, and the oil is then sent at a high pressure to a main oil hole 210 formed at the cylinder block 110 via the oil filter 195. Then, as the first oil-distribution passage from the main oil hole 210, the oil is sent from the main oil hole 210 to the cylinder head 130 via a distribution passage formed in the cylinder block 110, after which the oil is sent from the cylinder head 130 to camshaft journals 220 of the intake and exhaust camshafts, to oil control valves OCV 230 of the variable intake valve timing mechanism VVT-i, and to a chain tensioner 240. The oil is also sent from the main oil hole 210 to an oil injector 250. This oil is injected to the timing chain 117 from the oil injector 250.

[0043] As the second oil-distribution passage from the main oil hole 210, the oil is sent from the main oil hole 210 to a crankshaft journal 260 of the crankshaft 112 in the cylinder block 110, and then the oil is sent from the crankshaft journal 260 to a crank pin via which the crankshaft 112 and the connecting rod 118 are connected to each other, and on the other hand, the oil is sent from the crankshaft journal 260 to an oil injector 280, and the oil is injected from the oil injector 280 to the bottom faces of the respective pistons 116. After lubricating the respective portions, the oil distributed through the second oil-distribution passage falls due to gravity to the bottom wall 127 and the main oil sump 155 at the lower side of the crankcase 120 and returns to the main oil sump 155 formed by the first oil pan member 150.

[0044] On the other hand, the oil distributed via the feed pump 180 is returned to the oil tank 165 via the following two oil-return passages. As the first oil-return passage, the oil returned into the main oil sump 155 as described above is pumped up by the scavenge pump 170 and sent to the oil tank 165. As the second oil-return passage, the oil supplied to the cylinder block 110 and to the cylinder head 130 of the engine unit 100 is directly returned to the oil tank 165. The second oil-return passage will be described below in more detail. One side of the second oil-return passage is formed by an oil-return passage 300 formed in the chain cover 111 as a passage for the oil supplied to the chain tensioner 240 and the timing chain 117, and the other side of the second oil-return passage is formed by the oil-return passages 119 formed in the cylinder block 110 as passages through which the oil falls due to gravity from the cylinder head 130 and communication passages 128 formed at the upper side of the crankcase 120 and communicating with the respective oil-return passages 119 on one side and with the space 125 on the other side.

[004S] The flow resistance at the first oil-distribution passage through which the oil is distributed from the main oil hole 210 to the cylinder head 130 and to the oil injector 250, the flow resistance at the second oil-distribution passage in the cylinder block 110, and the discharge capacities of the feed pump 180 and the scavenge pump 170 are set such that the ratio between the oil flow rate at the first oil-return passage and the oil flow rate at the second oil-return passage becomes approximately 7 : 3. More specifically, because the oil supplied to the first oil-distribution passage falls due to gravity into the oil tank 165 via the second oil-return passage and the oil supplied to the second oil-distribution passage falls due to gravity onto the bottom wall 127 of the crankcase 120 and to the main oil sump 155 and is finally returned to the main oil sump 155 via the scavenge pump 170 as described above, the pumping capacity of the scavenge pump 170 is set to about 70 % of the pumping capacity of the feed pump 180, in other words, the ratio of the pumping capacity of the scavenge pump 170 to the pumping capacity of the feed pump 180 is set to about 0.7. As such, the amount of power required for driving the scavenge pump 170 is small as compared to when the oil distributed to the engine is fully returned to the oil tank 165 via the scavenge pump 170 as in dry-sump type engine-lubrication systems in the related art, and therefore the fuel economy of the engine unit 100 improves.

[0046] In the foregoing example embodiment of the invention, the second oil-return passage is formed by the oil-return passage 300 formed in the chain cover 111, through which the oil is returned from the cylinder head, and/or the communication passages 128 extending to the space 125 of the crankcase 120 and communicating with the respective oil-return passages 119 formed in the cylinder block 110, through which the oil is returned from the cylinder head. Therefore, the oil can be directly returned to the oil tank 165 without using the scavenge pump 170, thus effectively saving the drive power for driving the scavenge pump 170. Thus, the above-described structure improves the fuel economy of the engine by saving the drive power for driving the scavenge pump 170 in a low engine speed range where the oil agitation resistance is relatively low while securing the general effects of wet-sump type lubrication systems that are exerted in a high engine speed range where the loss of the engine drive power due to the oil agitation resistance is relatively large.

[0047] Further, the above-described structure of the example embodiment allows the pumping capacity of the scavenge pump 170 to be smaller than that of the feed pump 180, and it is desirable in terms of the production cost.

Claims

1. An engine lubrication apparatus having an oil sump provided at a lower side of an engine, a scavenge pump for sending oil in the oil sump to an oil tank, and a feed pump for supplying the oil in the oil tank to the engine, the engine lubrication apparatus being characterized by comprising: a crankcase having side portions extending in parallel with the axis of a crankshaft of the engine on both sides, wherein each side portions is constituted of an inner sidewall and an outer sidewall that are arranged such that a space is formed between the inner sidewall and the outer sidewall and such that the space is open at a lower side; a first oil-pan member attached to lower portions of the inner sidewalls of the crankcase and forming the oil sump; and a second oil-pan member attached to lower portions of the outer sidewalls of the crankcase and forming the oil tank together with the spaces, the second oil-pan member being spaced apart from the first-oil-pan member and arranged to cover the first oil-pan member from below.

2. The engine lubrication apparatus according to claim 1, wherein: a portion of the lower edge of the inner sidewall provided at one of the side portions of the crankcase and a portion of the lower edge of the inner sidewall provided at the other of the side portions of the crankcase are connected to each other via a bottom wall; the rest of the lower edge of the inner sidewall provided at one of the side portions of the crankcase and the rest of the lower edge of the inner sidewall provided at the other of the side portions of the crankcase together define an opening; and the first oil-pan member is attached to the opening.

3. The engine lubrication apparatus according to claim 1 or 2, wherein: a partition wall is provided between the first oil-pan member and the second oil-pan member; an oil passage is constituted of the first oil-pan member, the second oil-pan member and the partition wall; an outlet of the scavenge pump is located near an upstream end of the oil passage; and an opening of an oil strainer of the feed pump is located near a downstream end of the oil passage.

4. The engine lubrication apparatus according to claim 3, wherein the oil passage is generally spiral.

5. The engine lubrication apparatus according to any one of claims 1 to 4, wherein the oil tank is provided with a first oil-return passage through which oil is returned by the scavenge pump and a second oil-return passage through which oil supplied to the engine is directly returned to the oil tank.

6. The engine lubrication apparatus according to claim S, wherein the second oil-return passage is constituted of at least one of an oil-return passage which is formed in a chain cover of the engine so as to communicate with at least one of the spaces and through which oil is delivered from a cylinder head of the engine and an oil-return passage which is formed in a cylinder block of the engine and through which oil is delivered from the cylinder head.

7. The engine lubrication apparatus according to any one of claims 1 to 5, wherein the pumping capacity of the scavenge pump is smaller than the pumping capacity of the feed pump.

8. The engine lubrication apparatus according to claim 3, wherein the partition wall is constituted of a first partition member, a second partition member, a third partition member, and a fourth partition member that are connected in series substantially at a right angle.

9. The engine lubrication apparatus according to claim 8, wherein: the second oil-pan member is generally rectangular as viewed from above and the four comers of the second oil-pan member are curved inward; the first partition member, the second partition member, the third partition member, and the fourth partition member extend in parallel with the four sides of the second oil-pan member, respectively; one end of the first partition member is located near an inner face of a wall at one of the four curved comers; the other end of the first partition member is connected to one end of the second partition member; the other end of the second partition member is connected to one end of the third partition member; the other end of the third partition member is connected to one end of the fourth partition member, and the other end of the fourth partition member is spaced from the curved comer near which the one end of the first partition member is located.

10. The engine lubrication apparatus according to any one of claims 1 to 9, wherein the oil tank communicates with the space.