The present invention generally relates to a multiple-cylinder four-cycle engine mounted in a vehicle such as a motorcycle. More particularly, the present invention relates to a crankcase and a method of casting the crankcase.
Typically, a crankcase and a cylinder block forming a multiple-cylinder four-cycle engine equipped in a vehicle such as a motorcycle are manufactured by casting. In case of the motorcycle, the engine is mounted to a frame member disposed between a front wheel and a rear wheel. The engine and a transmission are mounted in a limited space below a fuel tank mounted to an upper region of the frame member to drive the rear wheel. So, a cylinder of the engine is positioned on the front wheel side and the transmission is positioned on the rear wheel side. The engine is typically manufactured in such a way that the cylinder block, a transmission case and a crankcase are integrally cast by die casting.
In the multiple-cylinder four-cycle engine, since crank chambers of respective cylinders are separated by separating walls, air in each crank chamber is compressed by a piston moving downward, causing a pumping loss. In addition, a mixture of air and oil, namely, an oil mist, existing in the respective crank chambers, is scattered by a crank web or the like rotating at a high speed in the crank chambers to cause a large friction resistance. In some engines, crank chambers of adjacent cylinders are connected to each other through a connecting hole in order to reduce the pumping loss or the friction resistance.
Prior art that was configured to address these concerns is disclosed by Japanese Laid-Open Patent Application Publication No. Hei. 11-182325. According to this application, connecting holes connecting crank chambers of cylinders are formed to extend over piston sliding surfaces inside cylinders and crankcase parts, and a center of each connecting hole is located on the sliding surface side of the piston.
A similar prior art concept is disclosed in Japanese Laid-Open Patent Application Publication No. 2005-69170 which was previously filed by the applicant. In this application, connecting holes are formed to penetrate separating walls defining cylinder bores and crank chambers of adjacent cylinders.
A multiple-cylinder four-cycle engine for motorcycles in some cases has a cylinder block having a closed deck structure in which an upper region of a water jacket formed in a cylinder block is closed, in order to increase a degree of roundness of an inner diameter of the cylinder at an upper region of the cylinder block. However, since it may be difficult to manufacture via die casting, a cylinder block having a closed deck structure is generally manufactured via sand casting using a sand mold.
As shown in
In casting, flash may be left at an end portion E of the parting plane 75. The flash must be removed to smooth-finish the inner wall surface, or the like, of the crank chamber 56. However, in the prior art discussed above the parting plane 75 is positioned in close proximity to a joint portion at which the upper crankcase 52 is joined to the cylinder block 53, (i.e. in a narrow space) and cut portion 78 is located closer to the cylinder side H than parting plane 75. For these reasons, an operator may have to take painstaking efforts to carefully remove the flash by hand. In order to smooth-finish corner regions of the cut portions 78 and surfaces of the separating walls 57, the operator must remove the flash not only in the vicinity of the parting plane 75 but in the vicinity of the cut portions 78 existing in the narrow spaces.
In addition, it will be appreciated that it may be desirable to increase the output of high-power engines such as the above described engine for motorcycles, and that it may also be desirable to increase the output of multiple-cylinder four-cycle engines for motorcycles.
The present invention addresses the above described conditions, and an object of the present invention is to provide a crankcase which enables a higher output power of an engine, and a casting method thereof, which enables easy finishing after casting, as well as a multi-cylinder four-cycle engine comprising the crankcase.
According to one aspect of the present invention, there is provided a crankcase for a multiple-cylinder four-cycle engine, comprising an upper crankcase and a lower crankcase which are joined to each other at a joint surface, the upper crankcase having a cylinder block at an opposite side of the joint surface and an upper transmission case at a rear portion thereof, the lower crankcase having a lower transmission case at a rear portion thereof; a separating wall which is integrally cast with the upper crankcase and the lower crankcase to extend from the joint surface toward the opposite side of the joint surface and is configured to define crank chambers corresponding to adjacent cylinders; and a crank journal bearing hole which is formed on the separating wall such that an axis of the bearing hole passes through the joint surface of the upper crankcase and the lower crankcase and is configured to support a crankshaft; wherein at least the separating wall formed in the upper crankcase has a thickness that increases from the joint surface of the crankcase to a region near a deepest portion of the crank journal bearing hole and decreases from the region near the deepest portion of the crank journal bearing hole toward the opposite side of the joint surface of the crankcase.
In such a construction, since each of the separating walls defining the crank chambers corresponding to adjacent cylinders within the crankcase has a thickness that decreases from the region near the deepest portion of the crank journal bearing hole toward the opposite side of the joint surface of the crankcase, an internal volume of the crankcase can be increased and thus a pressure fluctuation occurring in the interior of the crank chamber can be reduced. As a result, the output power of the engine can be increased. In addition, since a sufficient distance is provided between a crank web of a crankshaft accommodated in the crank chamber and the separating wall, friction resistance of the crank web can be reduced, and a power loss can be decreased.
The upper crankcase may have a cylinder block which is formed integrally therewith and is located on an opposite side of the joint surface.
The crankcase may further comprise a cut portion which is formed in a portion of the separating wall whose thickness decreases from the region near the deepest portion of the crank journal bearing hole toward the opposite side of the joint surface and is configured to allow the crank chambers corresponding to adjacent cylinders to fluidically communicate with each other, and a corner portion of the cut portion formed on a surface of the separating wall may be formed by a curved surface. The cut portion enables smooth air flow between the crank chambers. Thereby, a pressure fluctuation in the interior of each crank chamber can be reduced. Also, by forming the corner portion of the cut portion by a large curved surface, an operation to remove the flash at the corner portion may be omitted, and the stress generated at the corner portion can be decreased.
According to another aspect of the present invention, there is provided a multiple-cylinder four-cycle engine comprising a crankcase, the crankcase including: an upper crankcase and a lower crankcase which are joined to each other at a joint surface, the upper crankcase having a cylinder block at an opposite side of the joint surface and an upper transmission case at a rear portion thereof, the lower crankcase having a lower transmission case at a rear portion thereof; a separating wall which is integrally cast with the upper crankcase and the lower crankcase to extend from the joint surface toward the opposite side of the joint surface and is configured to define crank chambers corresponding to adjacent cylinders; and a crank journal bearing hole which is formed on the separating wall such that an axis of the bearing hole passes through the joint surface of the upper crankcase and the lower crankcase and is configured to support a crankshaft; wherein at least the separating wall formed in the upper crankcase has a thickness that increases from the joint surface of the crankcase to a region near a deepest portion of the crank journal bearing hole and decreases from the region near the deepest portion of the crank journal bearing hole toward the opposite side of the joint surface of the crankcase.
Thereby, the multiple-cylinder four-cycle engine is able to reduce pressure fluctuation occurring inside the crank chamber and reduce friction resistance associated with rotation of the crank web, thereby increasing the output power with a small power loss.
According to another aspect of the present invention, there is further provided a method of casting a crankcase for a multiple-cylinder four-cycle engine, including an upper crankcase and a lower crankcase which are joined to each other at a joint surface, the upper crankcase having a cylinder block at an opposite side of the joint surface and an upper transmission case at a rear portion thereof, the lower crankcase having a lower transmission case at a rear portion thereof, a separating wall which is integrally cast with the upper crankcase and the lower crankcase to extend from the joint surface toward the opposite side of the joint surface and is configured to define crank chambers corresponding to adjacent cylinders; and a crank journal bearing hole which is formed on the separating wall such that an axis of the bearing hole passes through the joint surface of the upper crankcase and the lower crankcase and is configured to support a crankshaft; the method comprising: providing a joint surface side core and a joint surface opposite side core, the joint surface side core having a draft for increasing a thickness of the separating wall from the joint surface of the crankcase to a region near a deepest portion of the crank journal bearing hole, the joint surface opposite side core being provided in contact with the joint surface side core to form a contact surface and having a draft for decreasing a thickness of the separating wall from the region near the deepest portion of the crank journal bearing hole toward the opposite side of the joint surface of the crankcase; feeding liquid metal into a casting mold in a state where a parting plane between the joint surface side core and the joint surface opposite side core is located in close proximity to the deepest portion of the crank journal bearing hole; and forming the separating wall to have the thickness that increases from the joint surface of the crankcase to the region near the deepest portion of the crank journal bearing hole and decreases from the region near the deepest portion of the crank journal bearing hole toward the opposite side of the joint surface of the crankcase.
In the above method, since the crankcase is cast in such a manner that the each of the separating walls defining the crank chambers corresponding to the cylinders within the crankcase has a thickness that decreases from the region near the deepest portion of the crank journal bearing hole toward the opposite side of the joint surface of the crankcase, the internal volume of the crankcase is increased so as to reduce the pressure fluctuation occurring in the interior of the crank chamber, and the output power of the engine can be increased. In addition, since a sufficient distance can be provided between a crank web of a crankshaft accommodated in the crank chamber and the separating wall, friction resistance associated with rotation of the crank web can be reduced, and a power loss can be decreased. Furthermore, in this casting method, the flash left at the parting plane between the joint surface side core and the joint surface opposite side core can be positioned near the deepest portion of the crank journal bearing hole. As a result, the flash at the parting plane can be removed easily after the casting.
The method may further comprise forming a cut portion which is formed by the joint surface opposite side core in a portion of the separating wall with a thickness that decreases from the region near the deepest portion of the crank journal bearing hole toward the opposite side of the joint surface of the crankcase and is configured to allow the crank chambers corresponding to adjacent cylinders to fluidically communicate with each other. A corner portion of the cut portion formed on a surface of the separating wall may be formed by a curved surface. In this construction, the large cut portion is formed on the separating wall to extend from the region near the deepest portion of the crank journal bearing hole to the opposite side of the joint surface so that the air smoothly communicates between the cylinders of the crank chambers, and thus pressure fluctuation caused by up-down movement of a piston in a cylinder of the engine can be reduced. Since the corner portion of the cut portion is formed by the large curved surface by the joint surface opposite side core, an operation to remove the flash at the corner portion may be omitted, and the stress generated at the corner portion can be decreased.
The above and further objects and features of the invention will more fully be apparent from the following detailed description with accompanying drawings.
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
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The pouring gate die 14 and the upper die 20 are arranged forward and rearward, respectively. A pouring gate 15 is defined by a rear end surface of the pouring gate die 14 and a front end surface of the upper die 20. Liquid metal is fed into the pouring gate 15 from above, i.e., from the crankshaft side C. The pouring gate 15 extends in the lateral direction, i.e., in the direction perpendicular to the sheet of
The lower die 11 is provided with a cylinder bore die 16 to form the cylinder bore in the cylinder block 3. A water jacket shell core 22 is provided between the cylinder bore die 16 and the lower die 11 and between the cylinder bore die 16 and the front die 12 to form a water jacket in the cylinder block 3. The lower die 11, the front die 12, the cylinder bore die 16, and the water jacket shell core 22 form a cylinder block forming part of the casting mold 10.
A cylinder side core (core on the opposite side of the joint surface 5) 1B forming a part of the inner wall surface 6a of the crank chamber 6 of the upper crankcase 2 is provided at an upper portion of the cylinder bore die 16. A crankshaft side core (joint surface side core) 19 is provided at an upper position of the cylinder side core 18 so as to form the inner wall surface 6a of the crank chamber 6 with the cylinder side core 18. The crankshaft side core 19 and the cylinder side core 18 form a crank chamber forming the core of the casting mold 10. The crank chamber forming core, the lower die 11, the front die 12, and the side die form a crank chamber, which in turn forms a part of the casting mold 10.
During casting, the crankshaft side core 19 is located under and connected to a lower end surface of a front portion of the upper die 20, and a transmission case portion core 21 forming an inner wall surface of the upper transmission case 4 is located under and connected to a lower end surface of a rear portion of the upper die 20. The upper die 20 is positioned in a vertical direction and in the lateral direction by the rear die 13 and the side die. The transmission case portion core 21, the crankshaft side core 19, and the cylinder side core 18 are formed of shell molds. In
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In accordance with the crankcase 1 constructed above, the separating wall 7 of the upper crankcase 2 of
By positioning the parting plane 25 between the cylinder side core 18 and the crankshaft side core 19 in close proximity to the deepest portion 27, the cut portions 28 and 29 formed by the cylinder side core 18, are positioned distant from the parting plane 25, and corner regions 28a and 29a of the cut portions 28 and 29 are formed by the large curved surfaces. Therefore, stress generated near the cut portions 28 and 29 can be reduced. By reducing the stress generated near the cut portions 28 and 29 in this manner, the whole thickness of the separating wall 7 can be reduced.
Since the thickness of the separating wall 7 is made smaller on the joint surface 5 side and on the opposite side of the joint surface 5 and the thickness of the whole separating wall 7 can be reduced by reducing the stress at the cut portions 28 and 29, a space defined by the separating walls 7 is increased, and hence an internal volume of each of the crank chambers 6 separated by the separating walls 7 is increased. Thereby, a pressure fluctuation occurring inside the crankcase 1 can be reduced. In addition, a sufficient distance can be provided between the crank web rotating in each of the crank chambers 6 between the crank journal bearing holes 26 and the separating wall 7. This makes it possible to reduce friction resistance of the crank web. As a result, the output of the engine can be increased.
Since the parting plane 25 between the cylinder side core 18 and the crankshaft side core 19 is located in close proximity to the deepest portion 27 of the crank journal bearing hole 26 which is comparatively near the joint surface 5, an operator can easily remove the flash left at the end portion E of the parting plane 25. By positioning the parting plane 25 between the cylinder side core 18 and the crankshaft side core 19 on the crankshaft side C rather than the cylinder side H in the crank chamber 6, the operator can easily remove the flash left at the parting plane 24 from the crankshaft side C (from the joint surface 5 side).
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Next, as shown in
Furthermore, after the liquid metal poured into the casting mold 10 is filled into the crank chamber forming part and the upper transmission case forming part, it is fed from the pouring gate 15 until the liquid metal of a specified volume has been filled into the risers 23 provided in the upper die 20. It should be noted that the risers 23 are located above the separating walls 7 in the crank chamber forming part, and the liquid metal is fed into the risers 23 from below. Thereafter, under the state where the crank chamber forming part and the upper transmission case forming part are subjected to the gravitational force from the liquid metal in the pouring gate 15 and from the liquid metal in the risers 23, the liquid metal equal in amount to solidification shrinkage is fed from the porting gate 15 and the riders 23 into the crank chamber forming part and the upper transmission case forming part, thus forming the upper crankcase 2 including the cylinder block 3 and the upper crankcase 2 as a unitary component.
During casting, the cylinder bore die 16 may be cooled to a specified temperature to inhibit generation of porosities and other imperfections. For example, in a case where aluminum alloy is cast, the cylinder bore die 16 may start to be cooled when its temperature becomes approximately 470° C. to 500° C. Furthermore, the front die 12 may be air-cooled to inhibit temperature of the front die 12 from rising from a specified temperature. For example, in the case where aluminum alloy is cast, the specified temperature is 350° C. to 400° C. Moreover, residual heat may be kept in the crankshaft side core 19 to enable smooth flow of the liquid metal. The residual heat of the crankshaft side core 19 is set to approximately 60° C. to 100° C. in the case where aluminum alloy is cast. These temperature conditions may be suitably set depending on casting conditions.
As described above, in the method of casting the upper crankcase 2, as shown in
As should be appreciated from the above, in accordance with the casting mold 10, by utilizing the advantage of the pouring of the inclined casting and the advantage of the falling of the gravity casting, the liquid metal is filled into the cylinder block forming part and the forming part of the upper transmission case 4. In addition, since the liquid metal is fed from the pouring gate 15 and from the risers 23 in amount to equal to solidification shrinkage, high quality can be achieved for the upper crankcase 2, which includes the cylinder block 3 and the upper transmission case 4.
In accordance with the engine 35 (
Whereas in the above described embodiment, an upper crank case 2 of an in-line four-cylinder engine is illustrated, the present invention may be applicable to upper crankcases and lower crankcases of other multi-cylinder engines.
Furthermore, whereas efficiency of casting is improved by utilizing the advantage of the pouring of the inclined casting and the advantage of falling of the gravity casting, in some embodiments only the gravity casting may be employed depending upon the number of cylinders and casting conditions.
As this invention may be embodied in several forms without departing from the spirit of essential characteristics thereof, the present embodiments are therefore illustrative and not restrictive, since the scope of the invention is defined by the appended claims rather than by the description preceding them, and all changes that fall within metes and bounds of the claims, or equivalence of such metes and bounds thereof are therefore intended to be embraced by the claims.
Number | Date | Country | Kind |
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2006-251035 | Sep 2006 | JP | national |
Number | Date | Country |
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11-182325 | Jul 1999 | JP |
2005-069170 | Mar 2005 | JP |
Number | Date | Country | |
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20080066573 A1 | Mar 2008 | US |