JP4850672B2 - Cylinder block - Google Patents

Description

  The present invention relates to a cylinder block in which a cylinder liner is cast in an air-cooled engine.

  As is well known, a vehicle engine, a general-purpose engine, and the like are usually configured by a cylinder block made of a cast product of cast iron or aluminum alloy. The cylinder block is manufactured separately from the cylinder block, and a cylinder liner on which the piston slides is cast.

  Various proposals have been made for this cylinder liner. For example, Japanese Patent Laying-Open No. 2005-188398 (Patent Document 1) discloses a cylinder liner structure in which the end on the cylinder head side is chamfered into a tapered shape. This technique suppresses the generation of cracks in the vicinity of the joint end portion between the cast-in part of the cylinder block and the cylinder liner with the protrusion, and prevents deterioration in sealing performance due to damage to the cylinder gasket.

By the way, in the air-cooled OHV engine or SV engine, a push rod chamber that houses a push rod that drives an intake / exhaust valve via a rocker arm is disposed on the side of the cylinder. In such an engine, it is difficult to design a cooling fin for radiating the cylinder on the side surface of the cylinder in which the push rod chamber is formed, so that the heat between the cylinder liner and the push rod chamber becomes high. A malfunction occurs. Conventionally, various proposals have been made to solve the problem. For example, Japanese Utility Model Laid-Open No. 5-32753 (Patent Document 2) discloses a cylinder block structure in which a cooling air passage space is formed between a cylinder liner and a push rod chamber.
JP 2005-188398 A Japanese Utility Model Publication No. 5-32753

  However, if the surrounding wall thickness is reduced in order to sufficiently secure the cooling air passage between the cylinder liner and the push rod chamber, it is not possible to ensure the hot water flow property when casting the cylinder block. For this reason, a certain distance must be provided between the cylinder liner and the push rod chamber, and there is a limit to downsizing the cylinder block.

  In addition, if the cooling air passage is made smaller in order to reduce the size of the cylinder block, the cooling air flow rate is insufficient and the cooling of the cylinder becomes insufficient. There was a problem to do.

  The present invention has been made in view of the above circumstances, and provides a cylinder block that does not impair the hot water flow and the cooling efficiency of the engine when casting the cylinder block when the engine is downsized. Objective.

In order to achieve the above object, a cylinder block according to the present invention includes a cylinder liner in which four planar portions formed in an axial direction on an outer peripheral surface are arranged at equal intervals in the circumferential direction , and a side of the cylinder liner. The cylinder is provided with a push rod chamber that accommodates a push rod that drives the valve operating mechanism, and a cooling air passage that is formed between the cylinder liner and the push rod chamber and that cools the cylinder liner. One of the planar portions of the liner is disposed to face the push rod chamber.

  According to the cylinder block of the present invention, the location where the flat portion of the cylinder liner is formed avoids the location where the cooling air passage is formed, so that the cooling air passage is sufficiently secured while the cooling air passage is sufficiently secured. The hot water flow around the passage can be improved. Therefore, the distance between the center axis of the cylinder liner and the push rod chamber can be shortened, and a cylinder block that does not reduce the cooling efficiency of the engine while reducing the size of the engine can be realized.

  Embodiments of an air-cooled OHV engine to which the present invention is applied will be described below with reference to the drawings. FIG. 1 is a cross-sectional view schematically illustrating an engine configuration according to an embodiment of the present invention. 2 is a cross-sectional view of the cylinder block cut along the line II-II in FIG. 3, FIG. 3 is a cross-sectional view of the cylinder block cut along the line III-III in FIG. 2, and FIG. FIG. 5 is a cross-sectional view of the cylinder liner cut along line IV, and FIG. 5 is a cross-sectional view of the cylinder liner cut along line V-V in FIG.

  The engine 100 is an air-cooled OHV single-cylinder four-cycle general-purpose engine used for various applications such as a generator, a work machine, and a snowmobile.

  As shown in FIG. 1, the engine 100 includes a cylinder block 1 in which a crankcase 3 is integrally formed on the lower side of a cylinder 2, and a cylinder head 21 is attached to the upper side of the cylinder 2. A cylinder head cover 25 is attached to the upper side of the cylinder head 21.

  The crankcase 3 rotatably supports a crankshaft (not shown) therein. A lubricating oil 35 is stored in the lower part of the crankcase 3.

  A cylinder liner 4 extending in the vertical direction is cast in the cylinder 2. A piston 31 is slidably fitted in the cylinder liner 4.

  A combustion chamber 22 is formed by the bottom wall surface of the cylinder head 21 and the top of the piston 31. A spark plug 24 and a pair of intake and exhaust valves 23 are disposed on the bottom wall surface of the cylinder head 21 so as to be exposed to the combustion chamber 22.

  A small end portion of a connecting rod 32 is rotatably connected to the piston 31. Further, a crank pin 33 is inserted into the large end portion of the connecting rod 32 and is rotatably connected to the crankshaft. As a result, the crankshaft rotates as the piston 31 slides in the cylinder liner 4.

  A scraper 34 protrudes downward from the large end of the connecting rod 32. The scraper 34 swings as the crankshaft rotates. As a result, the lubricating oil 35 stored in the lower part of the crankcase 3 is scraped up, scattered in a mist form in the crankcase 3, and supplied to the lubrication required portion of the engine 100.

  The valve cam 36 pivotally supported in the crankcase 3 is interlocked with the crankshaft by a transmission mechanism (not shown) and abuts against the tappet 37 via the cam surface. A push rod chamber 7 extending in the vertical direction is formed inside one side of the cylinder 2, and a push rod 38 that contacts the upper end of the tappet 37 is inserted into the push rod chamber 7. When the valve cam 36 rotates in conjunction with the crankshaft, the push rod 38 moves up and down via the tappet 37. Further, the vertical movement of the push rod 38 is transmitted to a rocker arm 39 disposed in the cylinder head 21 to open / close the intake / exhaust valve 23 at a predetermined timing.

  A cooling fan (not shown) is fixed to the extended portion of the crankshaft extending to the outside of the crankcase 3. Then, the cooling air taken in from the outside by the cooling fan is supplied to the cylinder block 1 and the cylinder head 21. Further, by extending a plurality of cooling fins 5 projecting in a direction substantially orthogonal to the cylinder 2 on the outer circumferential surface of the cylinder 2, the cooling area by the cooling air is expanded, and the cylinder The cooling efficiency of 2 is improved. Since the cylinder of the OHV engine has a structure in which the push rod chamber 7 is formed in the vicinity of the side of the cylinder 2, the cooling fin 5 is provided on the surface of the outer peripheral surface of the cylinder 2 facing the push rod chamber 7 by design. Can not be provided.

  Therefore, in order to cool the portion of the cylinder 2 where no cooling fin is provided, a direction substantially perpendicular to the vertical direction of the cylinder 2 is provided between the push rod chamber 7 and the cylinder liner 4 as shown in FIGS. The cooling air passage 6 is formed in the through hole. Then, the cooling air supplied to the cylinder block 1 by the cooling fan passes through the cooling air passage 6 and cools the cylinder 2 effectively.

  Examples of the present invention in the engine having the above configuration will be described below.

  As shown in FIGS. 4 and 5, the cylinder liner 4 includes a substantially cylindrical heat-resistant portion 8 made of cast iron and the like, and a body that is integrally formed below the heat-resistant portion 8 and is thinner than the heat-resistant portion 8. Part 9. The heat resistant portion 8 is formed with a predetermined thickness in order to ensure high temperature resistance and high pressure resistance against combustion in the combustion chamber 22.

  A plurality of flat portions 10 extending in the axial direction of the cylinder 2 are formed at equal intervals in the circumferential direction of the cylinder liner 4 on the outer peripheral surface of the cylinder liner main body portion 9. In the present embodiment, the plane portion 10 is equally distributed at four locations at intervals of approximately 90 degrees in the circumferential direction of the main body portion 9, and is formed at a predetermined distance from the central axis of the cylinder liner 4. . Therefore, the thickness of the cylinder liner 4 is the smallest at the place where the flat portion 10 is formed.

  The inner peripheral surface of the cylinder liner 4 of this embodiment is formed by honing a cylindrical body formed by centrifugal casting, and the flat surface portion 10 is formed by cutting. For this reason, the dimensional accuracy from the center axis | shaft of the cylinder liner 4 in the plane part 10 to an outer peripheral surface is high.

  As shown in FIG. 2, when casting the cylinder liner 4 into the cylinder 2, any one of the plurality of flat portions 10 is positioned to face the push rod chamber 7. Here, the planar portion 10 of the cylinder liner 4 is equally arranged on the outer peripheral surface of the cylinder liner 4 every 90 degrees. Therefore, the operator can accurately position the flat portion 10 of the cylinder liner 4 with respect to the casting mold only by rotating the cylinder liner 4 in any direction of 90 degrees at the maximum.

  In the cylinder block 1 having the above-described configuration, the flattened portion 10 of the cylinder liner 4 that is the thinnest and the push rod chamber 7 face each other, and the cooling air passage 6 is interposed between the cylinder liner 4 and the push rod chamber 7. It is possible to take a sufficient distance for the formation of. Therefore, when casting the cylinder block 1 provided with the cooling air passage 6, the hot water flow around the cooling air passage 6 can be sufficiently ensured.

  Further, the distance between the center axis of the cylinder liner 4 and the push rod chamber 7 is shortened by the amount of cutting of the plane portion 10 of the cylinder liner while maintaining the opening area of the cooling air passage 6 and the surrounding wall thickness in the conventional engine. be able to. That is, the engine can be downsized without impairing the cooling efficiency of the cylinder and the hot water flow of the cylinder block.

  When the outer dimensions of the engine 100 are the same as the conventional one, the bore diameter of the cylinder 2 can be increased while maintaining the opening area of the cooling air passage 6 and the surrounding wall thickness, and the engine output can be increased. Can do. Therefore, it is possible to create a new engine having a large displacement easily and inexpensively without creating a new engine casting mold.

  Further, the distance between the central axis of the cylinder liner 4 and the flat portion 10 is less varied than the other regions of the cylinder liner 4. Therefore, the thickness around the cooling air passage 6 of the cylinder block 1 after casting can be stably made equal to or greater than a predetermined value without variation. For this reason, the rate of occurrence of defective casting at the location is lowered, and the yield at the time of manufacturing the cylinder block 1 is increased.

  Since the planar portion 10 of the cylinder liner 4 is equally distributed every 90 degrees on the outer peripheral surface of the cylinder liner 4, the cylinder liner 4 expands isotropically around the central axis when the engine 100 is in operation. Therefore, even when the flat portion 10 is formed on the outer peripheral surface of the cylinder liner 4, the roundness of the cylinder liner 4 is not deteriorated, and the reliability of the engine 100 can be maintained. Further, the operator can accurately position the flat portion 10 of the cylinder liner 4 with respect to the casting mold only by rotating the cylinder liner 4 in any direction of 90 degrees at the maximum. Therefore, when the cylinder liner 4 is set in the casting mold, it is not particularly necessary to hold the cylinder liner 4 again, and the working efficiency is increased, so that the working time when casting the cylinder block 1 can be shortened.

  In addition, the plane part of a cylinder liner may be equally formed by 180 degree | times, and may be formed in two places.

  The casting method of the cylinder block may be a gravity casting method or a pressure / high pressure casting method.

  In the present embodiment, the present invention is applied to an OHV type air-cooled engine, but may also be applied to an air-cooled SV type in which a push rod chamber in which a valve operating mechanism is accommodated is formed.

  The present invention is not limited to the above-described embodiment, and can be appropriately changed without departing from the spirit or concept of the invention that can be read from the claims and the entire specification. The support structure is also included in the technical scope of the present invention.

1 is a cross-sectional view schematically illustrating an engine of an embodiment. Sectional drawing of the cylinder block which concerns on embodiment of this invention and cut | disconnected along the II-II line | wire of FIG. Sectional drawing of the cylinder block cut | disconnected along the III-III line of FIG. Sectional drawing of the cylinder liner cut | disconnected along the IV-IV line of FIG. Sectional drawing of the cylinder liner cut | disconnected along the VV line of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Cylinder block, 2 Cylinder, 3 Crankcase, 4 Cylinder liner, 5 Cooling fin, 6 Cooling air passage, 7 Push rod chamber, 8 Heat-resistant part, 9 Main part, 10 Plane part

Claims (3)

A cylinder liner in which four plane portions formed to extend in the axial direction on the outer peripheral surface are arranged at equal intervals in the circumferential direction ;
A push rod chamber formed on the side of the cylinder liner and containing a push rod for driving a valve operating mechanism ;
A cooling air passage formed between the cylinder liner and the push rod chamber for cooling the cylinder liner ;
A cylinder block, wherein one of the planar portions of the cylinder liner is disposed so as to face the push rod chamber. The cylinder liner has a cylindrical heat-resistant part, and a main body part integrally formed below the heat-resistant part and thinner than the heat-resistant part,
The cylinder block according to claim 1 , wherein the planar portion is formed on an outer peripheral surface of the main body portion . The cylinder block according to claim 1 or 2, wherein the cooling air passage is formed so as to penetrate in a direction orthogonal to a vertical direction of the cylinder.

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