Cylinder block for an internal combustion engine

Abstract: A cylinder block (2) for an in-line multi-cylinder engine in which a flywheel (8) is provided at an end of a crankshaft has a bell-shaped bell housing (9,37) integrally formed by enlarging a cylinder outside wall near the flywheel side end. The bell housing (9,37) is formed up to the position of at least a first cylinder (41) located nearest to that end and a second cylinder (42) adjacent to the first cylinder (41). By this, it is possible to provide a cylinder block (2) capable of reducing size and weight of an engine by integrally forming a thermostat housing (12) of a cooling system, while enhancing joining rigidity of a bell housing without increasing the cylinder block weight, or without increasing the number of components. Further, a thermostat chamber (12) is integrally formed in the cylinder block (2) at a wall portion separate from the outer wall of the cylinders (41,42,43,44).

Description: This invention relates to a cylinder block for an in-line multi-cylinder engine having a flywheel at an end of a crankshaft. Cylinder blocks of this type are generally known from the prior art. The flywheel connected to the crankshaft is installed in an end part of a a bell housing which is open toward the flywheel is formed on the cylinder block side, and the bell housing is joined to the contact surface of the flywheel side casing so that the flywheel is connected to and supported with the cylinder block. Such a bell housing can be formed integrally with the cylinder block using metallic molds or the like. In that case, in order to form the bell housing enlarged in a bell shape toward the outside of the cylinder block end part, the outer mold of the cylinder block end part is made in a convex shape complementary to the inside surface of the bell shape. Because of the limit in the depth of the outer mold, the length (in the crankshaft direction) is limited. In recent years, requirement about the engine vibration noise characteristic has increased, and the reduction in the vibration noise caused by the flywheel motion is strongly required. Therefore, it is necessary to increase the rigidity of the flywheel supporting structure connected to the cylinder block by increasing the strength of the flywheel supporting structure. In order to increase the supporting rigidity for the flywheel conventionally, integral reinforcement ribs are formed on the outer side of a bell housing, or a separate stiffener is used to secure and reinforce the flywheel. However, such reinforcement ribs and stiffener cannot achieve the effect of a sufficiently large increase in the rigidity. In order to achieve a large effect with the ribs, their number or thickness must be increased; with the stiffener, its size must be increased. As a result, weight increases. Therefore, the size and weight of the cylinder block cannot be reduced. Further, the cooling water circulation system of the engine is provided with a thermostat for closing the passage to the radiator at a low temperature so that cooling water is directly passed through the cylinder head. The thermostat is housed in a thermostat housing and attached to the cylinder block. Conventionally, the thermostat housing is manufactured as a part separate from the cylinder block, and secured to the vertical wall surface (the surface not enlarged with the bell housing) of the cylinder block using bolts, or formed integrally with the vertical wall surface of the cylinder block. However, when such a thermostat as a separate part is used, the number of components and their costs increase, making mounting work complicated, and causing the possibility of water leakage. Furthermore, in the case the thermostat housing is formed integrally with the vertical wall surface of the cylinder block, the forming is made integral with the top surface of the irregularities inevitably formed on the cylinder block outer wall. As a result, the wall thickness of the integrally formed part increases, and the size and weight of the cylinder block cannot be reduced. The invention addresses the above disadvantages inherent to the prior art. More specifically, it aims at providing a compact, lightweight cylinder block exhibiting a high rigidity around a flywheel arranged at a crankshaft end. To achieve the above object, this invention provides a cylinder block for an in-line multi-cylinder engine having the features of claim 1. In this structure, a space in the bell housing which covers the outside of the first cylinder at the endmost part of the cylinder block is formed using an outer mold having the same depth as that of conventional mold. Open passages, for example, for returning oil from the upper part of the cylinder head to the oil pan located in the lower part of the crank chamber are formed using another mold. This does not increase the wall thickness on the bell housing opening side of the first cylinder. Furthermore, since the open passages are formed in the wall on the deeper side, weight does not increase. As a result, the bell housing may be formed up to the position of the second cylinder without increasing weight, the connecting rigidity of the flywheel is increased, and the size and weight of the cylinder block are reduced. Preferably, the cylinder block comprises a thermostat for opening and closing a cooling passage passing through a radiator, a thermostat housing for housing the thermostat which housing is formed integrally with a cylinder block side wall. According to this structure, the thermostat housing may be integrally formed without increasing the number of components as a result of using separate components, or without increasing weight of the cylinder block because the inside space of the thermostat housing integrally formed to project outward from the cylinder block is enlarged. Further embodiments of the invention are set forth in the subclaims. The invention will be described hereinafter in greater detail by embodiments shown in the accompanying drawings. FIG. 1 is an elevation of a cylinder block as a form of embodying the invention. FIG. 2 is a plan view seen in the direction II of the cylinder block in FIG. 1. FIG. 3 is a plan view seen in the direction III of the cylinder block in FIG. 1. FIG. 4 is an elevation of a cylinder block as another form of embodying the invention. FIG. 5 a detailed view of the thermostat housing area of the embodiment shown in FIG. 4. FIG. 6 is a side view of the embodiment shown in FIG. 4. FIG. 7 is a plan view of the embodiment shown in FIG. 4. FIG. 8 is a side view of another form of embodying the invention. FIG. 9 shows a cross section B-B taken from FIG. 8. FIG. 10 shows a cross section C-C taken from FIG. 8. A first embodiment will now be described with reference to FIGS. 1 to 3. This engine has four cylinders, referred to as the first to the fourth cylinders from front to rear, and a crankshaft 1 shared with the four cylinders and disposed in the front-rear direction. A flywheel is attached to the rear, fourth cylinder side end of the crankshaft 1. As shown in FIG. 1, a cylinder block 2 of this engine is formed by joining together two separate parts; an upper block 2a constituting the cylinder bore 3 and the upper half of a crank chamber 4, and a lower block 2b constituting the lower half of the crank camber 4, along a contact surface (A) by means of bolts (not shown). A cooling water jacket 5 is formed in the cylinder wall around the cylinder bore 3. A hole 6 is for removing sand. An oil return passage 7 for returning oil by letting oil drop from a cam chamber (not shown) in the upper part of a cylinder head (not shown) of each cylinder to an oil pan (not shown) in the lower part of the crank chamber 4 is formed also in the cylinder wall in the up-down direction. The oil return passage 7 is a passage making communication between the cam chamber and the crank chamber, and also serves as a blow-by gas passage. As shown in FIGs. 2 and 3, a flywheel 8 is attached, within a casing 8a, to the rear end side of the crankshaft 1. A bell-shaped (or cone-shaped) bell housing 9 which is open toward the rear end of the cylinder block 2 is formed in the end part of the cylinder block 2 on the flywheel side. The bell housing 9 is formed by casting integrally with and enlarging the cylinder block side walls of the endmost first cylinder 41 nearest to the flywheel 8 and a second or cylinder 42 adjacent to the first cylinder. Around the cylinders 41 to 44 are provided head bolt passage holes 25 for securing together the cylinder head and the cylinder block. The bell housing 9 is of a generally tapered shape in top plan view as shown in Fig. 2. Its outer wall branches off from the cylinder bank, in the vicinity of the second cylinder from the flywheel end side of the cylinder block, preferably between the second and third cylinder from said flywheel end side. The bell housing 9 is either Integral with said casing 8a or said casing 8a is fixed to the open end of the bell housing 9 so as to accommodate the flywheel. In the case the bell housing 9 is formed using casting molds, the enlarged opening side or the rear end side of the first cylinder 41 may form an internal space using an outer mold of a normal depth so that the wall thickness of the bell housing 9 may be reduced. An opening 10 (FIG. 3) for reducing weight is formed on the joining surface (A) on the rear end side. Enlarged oil return passages 11 communicating with the oil return passages 7 formed in the cylinder side walls shown in FIG. 2 are formed in parts of the bell housing 9 wall on the deeper side than the internal space of the bell housing 9 which may be formed with the outer mold on the rear end side, namely in parts of the bell housing 9 wall around the cylinder 41 near the cylinder 42. The enlarged oil return passages 11 are spaces formed with another mold at a position of a depth that cannot be formed with the outer mold located on the opening end side, in parts of the bell housing 9 walls which are formed to enlarge around the cylinder 41 and substantially reduce the wall thickness of the bell housing 9. The crank chamber 4 of the cylinder 42 located second nearest to the open end is, as shown in FIG. 3, enlarged more outward (in the direction at right angles to the crankshaft) than the crank chambers of the cyl inders 41, 43 and 44. This makes it possible to reduce the wall thickness of the bell housing 9 formed outside the cylinder 42 and to form the bell housing 9 up to the position of the cylinder 42 without increasing weight. As described above, part of the bell housing 9 facing the flywheel 8 is formed with the normal outer mold, the enlarged oil return passages 11 are formed in parts of the cylinder 41 wall near the cylinder 42, and the crank chamber 4 of the cylinder 42 is formed in the enlarged size. As a result, the bell housing 9 may be extended along the side wall of the cylinder block 2 up to the position of the cylinder 42 located second nearest to the end without substantially increasing the wall thickness, therefore without increasing weight, and the rigidity for supporting the flywheel 8 may be increased. This also serves to reduce noise caused by engine vibration and rotary vibration of the flywheel. It is further possible to enlarge the crank chamber 4 of the cylinder 43 located third nearest to the end, so that the bell housing 9 may be formed as extended further up to the position of the cylinder 43. FIGs. 4 through 7 show a cylinder block in another form of embodying the invention. FIG. 4 is an elevation. FIG. 5 shows a cross section in the thermostat area. FIG. 6 is a side view. FIG. 7 is a plan view. The engine of this embodiment, like the embodiment shown in FIGs. 1 through 3, an in-line four cylinder engine comprising cylinders 41 to 44, with the cylinder block likewise comprising an upper block 2a and a lower block 2b. A thermostat housing 12 for circulating cooling water is formed integrally with the side wall of the upper block 2a. A thermostat 13 is housed in the thermostat housing 12. To the thermostat housing 12 are connected; a main pipe 14 communicating with a radiator (not shown), a bypass pipe 15 communicating with a cylinder head (not shown), a transfer pipe 17 communicating with a water pump 16 (FIG. 6), and an oil cooler pipe 18 communicating with an oil cooler (not shown), a throttle pipe 19 communicating with a throttle body (not shown), and a heater pipe 20 communicating with a heater (not shown). The thermostat 13 itself is of a publicly known constitution in which a valve member is operated to open and close according to thermal expansion and contraction of wax provided inside. In interlocked motion with the valve member, a valve seat 13a (FIG. 5) is operated to open and close the end 15a of the bypass pipe 15. FIG. 5 shows a state in which the main pipe 14 is closed and the bypass pipe 15 is opened. With such a thermostat, when the cooling water temperature is low, the cooling water is not circulated through the radiator but through the bypass pipe 15 and the cylinder head. When the cooling water temperature reaches a preset value, such as 70 - 80 degrees C, the bypass pipe 15 is closed and the main pipe 14 side is opened to communicate with the radiator. The cooling water flowing back through the thermostat capable of switching water passages by temperature-dependent control and through the pipes 14, 15, 18, 19, and 20 as shown with arrows is led through the transfer pipe 17 to the water pump 16, and distributed to the cylinder head and other parts. A space 21 is formed inside the thermostat housing 12 in which the thermostat 13 is housed, i.e. between the thermostat housing 12 and the cylinders. In other words, the thermostat housing 12 is provided integrally in a wall portion of the cylinder block which is separate from the outer walls of the cylinders. The space 21 is for preventing the wall thickness and weight of the thermostat housing portion from increasing when providing the thermostat housing 12 by integrally forming with the side wall of the cylinder block 2 to project without obstruction on the upper surface of the projecting portion of the cylinder block surface so that respective pipes may be easily disposed. Providing such a space inside makes it possible to form the thermostat housing 12 integrally with the cylinder block without increasing weight while still making oil or water flow sufficiently smooth. Such a thermostat housing 12 may be formed, as shown in FIG. 7, together with the bell housing 9 of the previous embodiment. Here, the engine associated with each of the above embodiment is not limited to that for vehicles such as automobiles but may include outboard motors. In the case of the outboard motor, the crankshaft is disposed vertically (perpendicularly to the water surface), and the flywheel is attached to the lower end part of the crankshaft. FIG. 8 is a side view of still another embodiment of the invention. FIGs. 9 and 10 show cross sections B-B and C-C in FIG. 8, respectively. This embodiment is a cylinder block of deep skirt type. As shown in FIG. 9, the underside surface (A) of the upper block of the cylinder block 2 for joining to a lower block (not shown) extends from the crankshaft center area downward along the circumferential wall to the lower part of the crank chamber 4. In contrast, the embodiment shown in FIG. 1 is a cylinder block of short skirt type and the joining surface (A) is a plane located in the center of the crankshaft 1, with the lower half of the crank chamber 4 being formed with the lower block, a member separate from the upper block 2a. As described above, the basic difference in this embodiment from that shown in FIG. 1 is that the invention is applied to the deep skirt type of cylinder block. A cam chamber (not shown) is formed in the upper part of the cylinder block 2. An oil pan (not shown) is provided in the lower part of the crank chamber 4. Oil return passages 7 for drawing back oil from the cam chamber are formed in the upper side walls of the cylinder block 2; at three positions on the near side, and at four positions on the far side of FIG. 8. Those oil return passages 7 communicate with each other through laterally formed oil return passages 30. Oil return passages 31 communicating with the oil pan (not shown) are formed below the communication passages 30 along the side walls of the cylinder block 2 corresponding to the oil return passages 7 located on the upper side. The outside wall of the cylinder block 2 is provided with reinforcement ribs 35 and bolt holes 36 for attaching auxiliary devices of the engine such as the oil pump, starter motor, and the like. As shown in FIG. 10, this embodiment is a five cylinder engine in which head bolt insertion holes 25 are provided around each cylinder for securing a cylinder head (not shown). A reinforcement wall widcning in a bell shape is formed with part of the outside wall of the cylinder block 2 near the flywheel (not shown) end of the crankshaft 1 to constitute a bell housing 37. The end of the bell housing 37 on the flywheel side is open. When this opening 34 is formed using a casting mold, sand is removed in the opening direction, making manufacture easy, and reducing weight as the entire interior of the opening becomes an open space. The bell housing 37 is formed to cover around the crank chamber, and its inside is formed with an oil return passage 33. The oil return passage 33 is closed on its bottom and its side communicates with an oil return passage 31. In other words, the bottom 37a of the bell housing 37, as shown in FIG. 8, slightly slopes down toward the oil return passage 31 and opens at the oil return passage 31. Oil flows as shown with an arrow (D) in the same drawing from an oil return space 33 along its bottom surface into the oil return passage 31. By the way, the oil return space 33, oil return passages 7 and 31, and the lateral communication passage 30 also serve as gas passages for drawing back blow-by gas by making communication between the cam chamber and the oil pan. In this embodiment, the closed bottom 37a of the bell housing 37 is located below the axial center 1a of the crankshaft 1. This makes it possible to make the crank chamber a closed space and secure an oil returning space, and at the same time, to increase the strength around the area where the flywheel is connected. Forming the closed space below the crankshaft center in this embodiment as described above is made possible because the cylinder block structure of the deep skirt type is employed. The embodiments as described above make it possible to integrally form the bell housing for supporting the flywheel and the thermostat housing for accommodating the thermostat without increasing the number of components and without increasing weight, facilitate assembly work with a simple structure, reduce costs, enhance rigidity, and reduce size and weight of the engine.

Claims: Cylinder block for an in-line multi-cylinder engine having a flywheel (8) at a crankshaft end, said cylinder block comprising an integral bell-shaped housing (9;37) formed by enlarging an outer wall of the cylinder block so as to be opened toward the flywheel end side, wherein the bell housing (9;27) laterally covers at least that cylinder (41) which is nearest to the flywheel end and the cylinder (42) which is the second to the said flywheel end and wherein open passages (10,11) are formed between outer bell housing walls and the outer walls of at least one of said cylinders (41,42) on both sides of said cylinders. Cylinder block according to claim 1, characterized in that said open passages comprise communication passages (11) connecting a cam chamber and a crank chamber (4). Cylinder block according to claim 1 or 2, characterized in that the crank chamber (4) of the cylinder (42) which is the second to the flywheel end extends in lateral direction with respect to the crankshaft and also beyond the crank chambers of further cylinders. Cylinder block according to at least one of claims 1 to 3, characterized in that the outer walls of the bell housing (9) are of a generally tapered section when looking into the direction of a cylinder axis. Cylinder block according to at least one of claims 1 to 4, characterized in that a thermostat (13) for opening and closing a cooling passage (14) through a radiator is provided; and a thermostat housing (12) for accommodating said thermostat (13) is integrally formed with a cylinder block side wall and the bell housing (9). Cylinder block according to claim 5, characterized in that said thermostat housing (12) comprises a chamber accommodating said thermostat (13) and a space (21) separate from said chamber which is arranged between said chamber and the outer wall of the adjacent cylinder. Cylinder block according to at least one of the preceding claims 2-6, characterized in that the cylinder outer walls are formed with at least one oil return communication passage (31) for connecting the cam chamber in an upper part of the cylinder block and an oil pan in a lower part of the crank chamber (4), wherein an oil return space (33) is formed by closing a bottom side of the bell housing (37) around the crank chamber (4) and wherein the said oil return space (33) is fluidedly connected to at least one of said oil return communication passages (31). Cylinder block according to claim 8, characterized in that a bottom wall (37a) of the bell housing (37) slightly slopes down toward said oil return passage (31) and opens at the oil return communication passage (31). Cylinder block according to claim 8 or 9, characterized in that the bottom wall (37a) of the bell housing (37) is formed below the axial center of the crank shaft (1).

Inventors: KORIYAMA MASAO, UEMA HITOSHI, KORIYAMA, MASAO, UEMA, HITOSHI
Applicants: YAMAHA MOTOR CO LTD, YAMAHA HATSUDOKI KABUSHIKI KAISHA
Application year: 1998
Main classification: F02F7
IPC codes: F02F1, F01M1, F02F7, F02B75