Manufacturing method of cylinder block for outboard engine

Abstract

To provide a manufacturing method of a cylinder block for an outboard engine which can achieve excellent sealability for an inner peripheral surface of a cylinder bore to perform anodic oxidation treatment and sealing treatment without melting cast iron of a cylinder sleeve even when a step exists in a border between the cylinder sleeve and a base material on the inner peripheral surface of the cylinder bore.SOLUTION: When ends 13A, 13B, at which a base material at a cylinder head side and a crank shaft side is exposed, of an inner peripheral surface of a cylinder bore 11 are pressed with elastic bag bodies of first and second elastic jigs 21, 22, the elastic bag bodies are expanded so that maximum outer diameter parts of the elastic bag bodies in a radial direction of the cylinder bore 11 are formed at the outer side relative to cylinder head side and crank shaft side ends of the cylinder bore 11 and maximum outer diameters in the radial direction of the cylinder bore of the elastic bag bodies become larger than inner peripheral diameters of the ends 13A, 13B, at which the base material is exposed, of the inner peripheral surface of the cylinder bore. Then, anodic oxidation treatment and sealing treatment are performed in a state that the ends 13A, 13B are pressed in the above-described manner.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a cylinder block for an outboard motor. [Background technology]

[0002] In industrial internal combustion engines, cooling water is circulated to maintain performance and control the temperature of the engine. The cooling water typically used in automobiles contains water with additives such as ethylene glycol, and if the amount of water decreases, it must be replenished. On the other hand, engines such as outboard motors use seawater (salt water), which is readily available in the operating environment, as cooling water.

[0003] However, because outboard motor components are made of many different metallic materials, potential differences arise between the metallic materials of the components in contact with seawater. Metallic materials with low natural potentials dissolve in seawater, potentially causing corrosion. Aluminum alloys, particularly those used in outboard motor cylinder blocks, are more susceptible to corrosion than other materials. Therefore, anodizing treatment and subsequent sealing treatment are known for aluminum alloys. Outboard motor cylinder blocks have a cylindrical cast-iron cylinder sleeve cast into the aluminum alloy base material on the inner periphery of the cylinder bore. Immersing the entire cylinder block in an anodizing solution for this type of cylinder block can dissolve the cast iron of the cylinder sleeve, resulting in pitting corrosion.

[0004] In order to perform anodizing and subsequent sealing without dissolving the cast iron of the cylinder sleeve, Patent Document 1 discloses a method for manufacturing an outboard motor cylinder block that includes a step of pressing, with an elastic jig, an area encompassing the boundary between the cast iron of the cylinder sleeve and the aluminum alloy base material of the cylinder block body. Patent Document 1 also describes a method in which the elastic jig is an elastic bag equipped with a gas supply unit that is placed in the cylinder bore and gas is supplied from the gas supply unit to inflate the elastic bag, thereby pressing the area encompassing the boundary with the elastic bag. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2024-1587 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in an outboard motor cylinder block in which the cylinder sleeve is exposed at the cylinder head end and crankshaft end of the inner circumferential surface of the cylinder bore so as to protrude radially inward of the cylinder bore and there is a step at the boundary between the cast iron and the aluminum alloy, it was found that there is room for improvement in the sealing performance with the inner circumferential surface of the cylinder bore using the elastic jig disclosed in Patent Document 1.

[0007] In view of the above problems, an object of the present invention is to provide a method for manufacturing a cylinder block for an outboard motor that exhibits excellent sealing properties with respect to the inner peripheral surface of the cylinder bore, even if a step exists at the boundary between the cast iron and the aluminum alloy on the inner peripheral surface of the cylinder bore, and that allows anodizing and subsequent sealing to be performed without dissolving the cast iron of the cylinder sleeve. [Means for solving the problem]

[0008] In order to achieve the above object, a method of manufacturing an outboard motor cylinder block according to the present invention includes a cylinder block body for an outboard motor, the cylinder block body having a cylinder bore and a water jacket formed around the cylinder bore at a joining surface where the cylinder block body is joined to a cylinder head, a cylindrical cylinder sleeve made of cast iron cast-in-place in an aluminum alloy base material on the inner circumferential surface of the cylinder bore, the cylinder sleeve being exposed so as to protrude radially inward from the base material, and the base material being exposed at an end of the inner circumferential surface of the cylinder bore on the cylinder head side and at an opposite end on the crankshaft side, the method includes the steps of pressing the end of the inner circumferential surface of the cylinder bore where the base material is exposed on the cylinder head side with a first elastic jig and pressing the end of the inner circumferential surface of the cylinder bore where the base material is exposed on the crankshaft side with a second elastic jig, and performing an anodizing treatment while the cylinder block body is pressed with the first and second elastic jigs, The method includes the steps of: forming an anodized film on the surface of an aluminum alloy portion of the outboard motor cylinder block body other than the cylinder bore; and sealing the surface of the anodized film by performing a pore sealing treatment while pressing with the first and second elastic jigs, wherein in the pressing step, the first and second elastic jigs are elastic bags fluidly connected to gas supply units, and the elastic bag is placed in the cylinder bore and inflated by supplying gas from the gas supply unit, thereby pressing the ends of the elastic bag where the base material is exposed on the cylinder head side and the crankshaft side with the elastic bag; and further, the elastic bag is inflated so that the maximum outer diameter portion of the elastic bag in the radial direction of the cylinder bore is formed outside the ends of the inner circumferential surface of the cylinder bore on the cylinder head side and the crankshaft side, and the maximum outer diameter of the elastic bag in the radial direction of the cylinder bore is larger than the inner circumferential diameter of the ends of the inner circumferential surface of the cylinder bore on the cylinder head side and the crankshaft side where the base material is exposed. [Effects of the Invention]

[0009] Thus, according to the present invention, when the first and second elastic jigs press against the ends of the inner surface of the cylinder bore where the base material on the cylinder head side and crankshaft side is exposed, the elastic bag is inflated so that the maximum radial outer diameter of the elastic bag body is formed outside the ends of the cylinder bore on the cylinder head side and crankshaft side, and the maximum radial outer diameter of the elastic bag body is larger than the inner diameter of the ends of the inner surface of the cylinder bore where the base material on the cylinder head side and crankshaft side is exposed.This provides excellent sealing to the inner surface of the cylinder bore, and allows anodizing and subsequent sealing to be performed without dissolving the cast iron of the cylinder sleeve. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a perspective view of the cylinder head side of an example of an outboard motor cylinder block body that is the subject of an anodizing treatment and a sealing treatment in a manufacturing method of an outboard motor cylinder block according to the present invention. FIG. [Figure 2] 2 is a cross-sectional perspective view showing an outboard motor cylinder block body taken along line AA in FIG. 1. [Figure 3] 2 is a cross-sectional side view showing the cylinder block body for an outboard motor taken along line AA in FIG. 1. [Figure 4] 4 is a partial cross-sectional view of an outboard motor cylinder block body within a dotted line frame B in FIG. 3 for illustrating one embodiment of a manufacturing method of an outboard motor cylinder block according to the present invention. FIG. [Figure 5] 5 is an enlarged cross-sectional view of a portion of the outboard motor cylinder block body within dotted lines C and D in FIG. 4 for illustrating one embodiment of a manufacturing method for an outboard motor cylinder block according to the present invention. FIG. [Figure 6] 5 is an enlarged cross-sectional view of a portion of the outboard motor cylinder block body within dotted lines C and D in FIG. 4 for illustrating one embodiment of a manufacturing method for an outboard motor cylinder block according to the present invention. FIG. [Figure 7]5 is an enlarged cross-sectional view of a portion of the outboard motor cylinder block body within dotted lines C and D in FIG. 4 for illustrating one embodiment of a manufacturing method for an outboard motor cylinder block according to the present invention. FIG. [Figure 8] 1 is a cross-sectional view showing an example of a joint used in an elastic jig in a method for manufacturing an outboard motor cylinder block according to an embodiment of the present invention. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0011] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a method for manufacturing an outboard motor cylinder block according to the present invention will now be described with reference to the accompanying drawings.

[0012] The method for manufacturing an outboard motor cylinder block of this embodiment includes a pressing step in which ends of the inner circumferential surface of the cylinder bore of the outboard motor cylinder block body where the base material is exposed on the cylinder head side and the crankshaft side are pressed with an elastic jig; an anodizing step in which the ends are anodized while being pressed to form an anodized coating on the surface of the aluminum alloy portion of the outboard motor cylinder block body; and a sealing step in which the areas are sealed while being pressed to seal the anodized coating.

[0013] First, we will explain the cylinder block body, which is the target of the anodizing and sealing treatments in this method. As shown in Figures 1 to 3, the cylinder block body 10 has a plurality of cylinder bores 11 and a water jacket 15 formed around these cylinder bores 11 at a joining surface 14 where it is joined to a cylinder head (not shown). Note that these figures show the cylinder block body 10 with three cylinder bores 11 aligned horizontally, but in an actual outboard motor (not shown), the cylinder block body 10 is mounted with the cylinder bores 11 aligned vertically. The number of cylinder bores 11 may also be one for a single-cylinder engine.

[0014] In particular, as shown in Figure 3, a cylindrical cylinder sleeve 12 made of cast iron is cast-inserted into the aluminum alloy base material 13 on the inner circumferential surface of each cylinder bore 11. In this type of cast-insertion method, the entire inner circumferential surface of the cylinder bore 11 is not usually covered by the cylinder sleeve 12, and the aluminum alloy base material 13 is exposed on the inner circumferential surface at a cylinder head end 13A and an opposite crankshaft end 13B. In other words, there is a boundary between the aluminum alloy of the cylinder sleeve 12 and the cast iron base material 13 at the cylinder head end and the crankshaft end of the inner circumferential surface of the cylinder bore 11. Furthermore, depending on the cast-insertion method, as shown in Figure 3, the cylinder sleeve 12 may be exposed and protrude radially inward from the base material 13 of the cylinder bore 11, resulting in a step between the cylinder sleeve 12 and the base material 13.

[0015] The height of the step is not limited to, but is in the range of 0.5 to 2 mm, for example. The axial length of end 13A of cylinder bore 11, where base material 13 on the cylinder head side of the inner circumferential surface of cylinder bore 11 is exposed, is not limited to, but is in the range of 3 to 5 mm, for example. The axial length of end 13B of cylinder bore 11, where base material 13 on the crankshaft side of the inner circumferential surface of cylinder bore 11 is exposed, is not limited to, but is in the range of 2 to 4 mm, for example.

[0016] In a cylinder block body 10 having a step between the cast iron cylinder sleeve 12 and the aluminum alloy base material 13 on the inner surface of such a cylinder bore 11, an anodizing process is performed without dissolving the cast iron of the cylinder sleeve 20. In this embodiment, as shown in Figure 4, the pressing process using an elastic jig involves pressing an end 13A of the inner surface of the cylinder bore 11 where the base material 13 on the cylinder head side is exposed with a first elastic jig 21, and pressing an end 13B of the inner surface of the cylinder bore 11 where the base material 13 on the crankshaft side is exposed with a second elastic jig 22.

[0017] The first elastic jig 21 and the second elastic jig 22 are expandable and contractible elastic bags equipped with a gas supply section 23. By placing these elastic bags in the cylinder bore 11 and supplying gas from the gas supply section 23 to expand the first and second elastic jigs 21 and 22, respectively, it is possible to press against the ends 13A and 13B of the inner surface of the cylinder bore 11 where the base material 13 on the cylinder head side and crankshaft side is exposed.

[0018] The material of the elastic bag bodies of the first and second elastic jigs 21 and 22 may be any material that has enough elasticity to apply uniform pressure to the entire inner circumferential surface of the cylinder bore 11, such as rubber or a thermoplastic elastomer. Examples of rubber include silicone rubber, nitrile butadiene rubber (NBR), styrene rubber (SBR), butyl rubber (IIR), fluororubber (FKM), ethylene propylene diene rubber (EPDM), and chloroprene rubber. Examples of thermoplastic elastomers include polyester (TPC), polyurethane (TPU), and polyvinyl chloride (TPVC). In particular, since the elastic jigs will come into contact with the treatment solution in the subsequent anodizing process, a material with excellent chemical resistance is preferred, and it is more preferable to use silicone rubber, for example.

[0019] The dimensions of the elastic bags of the first and second elastic jigs 21, 22 may be such that the maximum outer diameter when expanded in the radial direction of the cylinder bore 11 is larger than the inner diameter of the ends 13A, 13B where the base material 13 is exposed on the inner circumferential surface of the cylinder bore 11, and the minimum outer diameter when contracted makes the elastic bag detachable from the inner circumferential surface of the cylinder bore 11. Furthermore, the length of the elastic bag in the axial direction of the cylinder bore 11 is preferably longer than the lengths of the ends 13A, 13B where the base material 13 is exposed on the cylinder head side and the crankshaft side of the inner circumferential surface of the cylinder bore 11.

[0020] As such an elastic bag, for example, a jig commercially available under the name of air picker, which has an elastic bag portion that can be expanded and contracted by gas pressure, can be used. Furthermore, the first elastic jig 21 and the second elastic jig 22 may be connected by a joint 30 equipped with a gas supply unit, as shown in Fig. 4, which allows the two elastic bags to be inflated at the same time. Details of the joint 30 will be described later.

[0021] 5, the elastic bags of the first and second elastic jigs 21, 22 are arranged so that they abut against end 13A where the base material 13 on the cylinder head side is exposed and end 13B where the base material 13 on the crankshaft side is exposed, respectively, of the inner circumferential surface of the cylinder bore 11. Preferably, the elastic bags are arranged so that the center position of the elastic bag in the axial direction of the cylinder bore 11 abuts against end 13A, 13B where the base material 12 is exposed.

[0022] Next, gas is supplied to each of the elastic bags of the first and second elastic jigs 21, 22, and the elastic bags begin to expand as shown in Fig. 6. This causes the elastic bags to come into face-to-face contact with the ends 13A, 13B of the inner circumferential surface of the cylinder bore 11 where the base material 13 is exposed.

[0023] Then, gas is further supplied to each of the elastic bags of the first and second elastic jigs 21, 22, and the elastic bags are inflated until, as shown in Figure 7, the maximum radial outer diameter portions 21a, 22a of each of the elastic bags of the first and second elastic jigs 21, 22 are formed outside the cylinder head side end 11A and the crankshaft side end 11B of the cylinder bore 11, and the maximum radial outer diameter of the elastic bag of the cylinder bore becomes larger than the inner diameter of the ends 13A, 13B of the inner surface of the cylinder bore 11 where the base material 13 on the cylinder head side and the crankshaft side is exposed.

[0024] Supplying gas to this state increases the pressing force of the elastic bags of the first and second elastic jigs 21, 22 while providing sufficient surface contact areas with the ends 13A, 13B of the base material 13 exposed on the cylinder head side and crankshaft side of the inner circumferential surface of the cylinder bore 11, thereby improving sealing of the aluminum alloy base material 13. This prevents the treatment solution from seeping past the ends 13A, 13B of the exposed aluminum alloy and into the cast iron cylinder sleeve 12 during the subsequent anodizing process. Furthermore, because the first elastic jig 21 and the second elastic jig 22 are connected by a joint 30, the cylinder bore 11 is sandwiched between the expanded elastic bag of the first elastic jig 21 and the expanded elastic bag of the second elastic jig 22. This prevents the first and second elastic jigs 21, 22 from shifting axially in the subsequent anodizing process.

[0025] The joint 30 preferably has a configuration that allows for adjustable expansion and contraction in the axial direction of the cylinder bore, as shown in Fig. 8, for example. This adjustable expansion and contraction joint 30 includes a first support portion 31 that supports the elastic bag of the first elastic jig 21 so that it can be expanded and contracted, a second support portion 32 that supports the elastic bag of the second elastic jig 22 so that it can be expanded and contracted, and a joint portion 33 that connects the first support portion 31 and the second support portion 32 so that it can be expanded and contracted. The first support portion 31, the second support portion 32, and the joint portion 33 each have a gas passage 24 therein for flowing gas from the gas supply portion 23 to the first support portion 31, the joint portion 33, and the second support portion 32 in this order. Furthermore, the first and second support portions 31 and 32 each have a gas passage 25 therein for flowing gas from the gas passage 24 to the elastic bag.

[0026] The first support part 31 has a cylindrical housing part 31a for housing the cylindrical tip part 33a of the coupling part 33. The second support part 32 has a cylindrical tip part 32a with a male thread formed therein and a cylindrical base part 32b with a larger outer diameter than the tip part 32a. The coupling part 33 has a cylindrical first housing part 33b with a female thread formed therein for housing the tip part 32a of the second support part 32, and a cylindrical second housing part 33c for housing the base part 32b of the second support part 32. The inner diameters of the first and second housing parts 33b, 33c of the coupling part 33 correspond to the outer diameters of the tip part 32a and the base part 32b of the support part 32. By rotating the screw, the second support part 32 can slide in the axial direction of the cylinder bore 11 relative to the coupling part 33. The space between the accommodating portion 31a of the first support portion 31 and the tip end portion 33a of the joint portion 33 is sealed with an O-ring 34, and the space between the base end portion 32b of the second support portion 32 and the accommodating portion 33c of the joint portion 33 is sealed with an O-ring 35.

[0027] A position sensor 36 is provided in the second housing portion 33c of the joint portion 33 along the axial direction of the cylinder bore 11. This position sensor 36 detects the base end portion 32b of the second support portion 32, thereby measuring the amount of sliding movement of the second support portion 32 relative to the joint portion 33. A display device 37 is provided on the outer circumferential surface of the joint portion 33, displaying the amount of sliding movement measured by the position sensor 36.

[0028] The adjustable expansion joint 30 configured as described above allows the distance between the first elastic jig 21 and the second elastic jig 22 to be adjusted as desired. To ensure good sealing performance for both the first elastic jig 21 and the second elastic jig 22, the positions of both the first elastic jig 21 and the second elastic jig 21 must be finely adjusted relative to the inner circumferential surface of the cylinder bore 11, and it is desirable to be able to adjust them in increments of approximately 1 mm. The amount of sliding movement of the second support portion 32 is displayed on the display device 37 by rotating the screw, making it easy to fine-tune the distance between the first elastic jig 21 and the second elastic jig 22. Furthermore, the elastic jig can be quickly attached to models with different bore strokes, eliminating the need to prepare and store elastic jigs for each model.

[0029] 5 to 7 show a case where the end 13B of the crankshaft-side exposed base material 13 is shorter in the axial direction of the cylinder bore 11 than the end 13A of the cylinder bore 11 where the cylinder head-side exposed base material 13 is. In this case, due to the presence of a step with the cylinder sleeve 12, the area where the end 13B of the exposed base material 13 and the elastic bag make surface contact may be insufficient. In such a case, as shown in FIGS. 5 to 7, the corners of the inner circumferential surface of the cylinder sleeve 12 near the end 13B of the crankshaft-side exposed base material 13 are chamfered. This allows the chamfered surface 12a of the cylinder sleeve 12 to make surface contact with the elastic bag, thereby widening the area where the elastic bag makes surface contact beyond the boundary between the cylinder sleeve 12 and the base material 13 and significantly improving sealing performance. Furthermore, the chamfering process also removes burrs from the corners of the inner circumferential surface of the cylinder sleeve 12, preventing damage to the elastic bag by burrs.

[0030] 5 to 7, the chamfered surface 12a of the cylinder sleeve 12 is chamfered so as to be directly adjacent to the end 13B where the base material 13 is exposed, but this is not limited to this, and the side surface of the cylinder sleeve 12 may remain between the chamfered surface 12a of the cylinder sleeve 12 and the end 13B where the base material 13 is exposed. Also, although the case where the inner peripheral corner of the cylinder sleeve 12 on the crankshaft side is chamfered has been described, the chamfering is not limited to the crankshaft side, and the inner peripheral corner of the cylinder sleeve 12 on the cylinder head side may also be chamfered as necessary.

[0031] Furthermore, the chamfering is not limited to the corners of the inner circumferential surface of the cylinder sleeve 12. The corners of the inner circumferential surface of the cylinder bore 11, at the ends 13A and 13B on the cylinder head side and the crankshaft side where the base material 13 is exposed, may also be chamfered. This increases the surface contact area between the ends 13A and 13B where the base material 13 is exposed and the elastic bag. Of course, both the corners of the inner circumferential surface of the cylinder sleeve 12 and the corners of the inner circumferential surface of the ends 13A and 13B where the base material 13 is exposed may also be chamfered. In this case, the chamfered surfaces of the cylinder sleeve 12 and the chamfered surfaces of the ends 13A and 13B where the base material 13 is exposed may be aligned flush with each other. This increases the surface contact area between the elastic bag and the boundary between the cylinder sleeve 12 and the base material 13.

[0032] A masking agent may be applied to the inner peripheral surface of the cylinder bore 11 before pressing with the first and second elastic jigs 21 and 22. As the masking agent, a commercially available masking agent for metal surface treatment may be used.

[0033] Then, with the first and second elastic jigs 21, 22 positioned inside the cylinder bore 11, the cylinder block body 10 is immersed in a treatment solution for electrolysis, which is an anodizing process for forming a porous anodized film on the surface of the cylinder block body 10. The electrolysis dissolves the aluminum alloy that is the base material of the cylinder block body 10, and the dissolved aluminum combines with oxygen in the treatment solution to form an anodized aluminum film on the surface of the aluminum alloy portion of the cylinder block body 10.

[0034] The treatment liquid for the anodizing treatment may be an acidic bath such as sulfuric acid, oxalic acid, phosphoric acid, or chromic acid, or a basic bath such as sodium hydroxide, sodium phosphate, or sodium fluoride. The electrolytic treatment is performed by applying a voltage between the cylinder block body 10 as the anode and an electrode plate (not shown) made of titanium, carbon, or the like as the cathode.

[0035] The thickness of the anodized film formed in the anodizing treatment step is not particularly limited, but is preferably 1 to 60 μm, and more preferably 3 to 20 μm, for example.

[0036] In anodizing, when the aluminum in the base material of the cylinder block body 10 is oxidized to form a film, the aluminum changes to aluminum oxide, causing a volume expansion. That is, about half of the anodized film formed is a permeation film that penetrates deep into the surface of the aluminum alloy base material, and about the remaining half is a growth film that grows from the surface of the base material toward the elastic jig.

[0037] On the other hand, because the inner circumferential surface of the cylinder bore 11 is covered by the first and second elastic jigs 21, 22, it does not come into contact with the treatment liquid and can prevent dissolution of the cast iron of the cylinder sleeve 12. Furthermore, even if the treatment liquid seeps into the gap between the first and second elastic jigs 21, 22 and the ends 13A, 13B where the base material 13 is exposed and an electrolytic reaction occurs with the aluminum alloy that is the base material 13, the anodized film grows on the elastic jigs side as described above, eliminating even the slightest gap with the elastic jigs and further suppressing the seepage of the treatment liquid.

[0038] To further explain the anodizing treatment process, direct current electrolysis and alternating current / direct current superimposed electrolysis can be used as the electrolysis method. The anodized film formed by either electrolysis method is an anodizing reaction that includes a permeation film and a growth film, as described above, but the properties of the resulting anodized film differ.

[0039] Anodized films formed by DC electrolysis have cells that grow linearly while eroding perpendicularly to the base material surface. When there are many impurities or additives (such as silicon) in the aluminum alloy, cells do not grow around the impurities or additives near the surface, and depressions appear on the surface where the impurities or additives are precipitated, resulting in an anodized film with high surface roughness. In addition, an anodized film with large variations in film thickness is formed.

[0040] Anodized films formed by AC / DC superimposed electrolysis have a structure in which cells form a series of nearly continuous spheres or ellipses with a height less than twice the cell diameter, and these cells gather together to form a cluster of grapes. Therefore, anodized films formed by AC / DC superimposed electrolysis have a low ratio of the volume of the pores contained within the cells to the cell wall. In contrast, anodized films formed by DC electrolysis have a high ratio of the volume of the pores contained within the cells to the cell wall, because the cells are formed in a continuous cylindrical shape.

[0041] Furthermore, an anodic oxide film formed by AC / DC superimposed electrolysis avoids and incorporates impurities or additives that inhibit cell growth during cell growth, preventing cell growth from being inhibited by the impurities or additives. This allows the anodic oxide film to have a substantially uniform film thickness on the surface of the base material. Because the cell growth direction of an anodic oxide film formed by AC / DC superimposed electrolysis is minutely bent in random directions relative to the surface of the base material, resistance to water penetration is provided at the points where the direction changes, preventing water from reaching the base material. This provides higher corrosion resistance than an anodic oxide film formed by DC electrolysis.

[0042] Next, the cylinder block body 10 with the anodized coating formed on its surface is immersed in a sealing solution while the first and second elastic jigs 21, 22 are still in place, or the sealing solution is applied to perform the sealing process. This seals the pores in the porous anodized coating, improving the corrosion resistance of the anodized coating. Before performing the sealing process, it is preferable to perform a pretreatment such as washing with water to prevent any adhering anodized coating solution from mixing with the sealing solution and to remove any remaining coating solution in the pores of the anodized coating.

[0043] The sealing process can employ known methods, such as hydrothermal, boiling water, nickel acetate, and lithium hydroxide. The lithium hydroxide method, which exhibits self-repairing properties, will be described as an example. An aqueous solution containing lithium ions is used as the sealing solution. Examples of lithium ions or chemicals that serve as lithium ion sources include lithium hydroxide, lithium sulfate, lithium chloride, lithium silicate, lithium nitrate, lithium carbonate, lithium phosphate, and lithium hydroxide. Among these, lithium hydroxide, lithium carbonate, and lithium silicate are preferred because their aqueous solutions are basic. However, lithium silicate is highly toxic and poorly soluble in water, making it impractical. Therefore, lithium hydroxide and lithium carbonate are more suitable. As mentioned above, various sealing processes are available. While pitting corrosion of the cast iron sleeve occurs during anodizing due to the application of electrolysis, mild surface rust occurs during sealing. If this surface rust is acceptable, the sealing process can be performed with the first and second elastic jigs 21 and 22 removed.

[0044] In the lithium hydroxide method, the surface and pores of the anodized film are dissolved slightly by the sealing solution, and then the dissolved film components react with the sealing solution components to precipitate a sealing product. This sealing product blocks the interior of the pores in the film, and the surface layer of the film transforms into a dense sealing product layer, completely sealing the pores in the film. Therefore, a sealing product of lithium, aluminum, and oxygen is present on the surface and inside the pores of the anodized film. After the sealing process is completed, the first and second elastic jigs 21 and 22 are removed from the cylinder bore 11.

[0045] By performing the pressing, anodizing, and sealing processes in this manner, it is possible to manufacture an outboard motor cylinder block having a sealed anodized coating on the aluminum alloy portion of the cylinder block without dissolving the cast iron of the cylinder sleeve 12. In particular, the joint surface 14 of the cylinder block and the inner surface of the water jacket 15 are close to the combustion chamber, are exposed to high temperatures, and are likely to come into contact with cooling water (seawater), making them prone to corrosion. Therefore, forming a sealed anodized coating can prevent corrosion in the outboard motor cylinder block. When using inexpensive aluminum alloys such as ADC and AC, corrosion resistance can be a concern, so forming a sealed anodized coating is particularly advantageous. [Example]

[0046] A cast-in insert cylinder sleeve was prepared, and a cylinder block was fabricated using aluminum alloy ADC12. The cast-in insert cylinder sleeve protruded 1 mm radially inward from the aluminum alloy base material on the inner circumferential surface of the cylinder bore. The boundary between the cast iron and the aluminum alloy was confirmed to be formed 4.7 mm from the end of the inner circumferential surface of the cylinder bore on the cylinder head side and 2.8 mm from the end of the inner circumferential surface of the cylinder bore on the crankshaft side. The step between the cast iron and the aluminum alloy on the crankshaft side of the inner circumferential surface of the cylinder bore of this cylinder block was then chamfered.

[0047] Two air pickers were inserted into the cylinder bore at the cylinder head end and the crankshaft end as elastic jigs, and the air pickers were inflated until the maximum radial outer diameter of the air pickers in the cylinder bore was larger than the inner diameter of the exposed aluminum alloy portion on the inner circumferential surface of the cylinder bore. The cylinder block in this state was then anodized. The anodization was performed using direct current electrolysis, where the cylinder block was immersed in a sulfuric acid bath with a temperature of 20°C and a concentration of 200 g / L, and a current density of 1.5 A / dm 2A voltage was applied for 20 minutes at this temperature. The air pressure of the air picker was reduced and the air picker was removed from the cylinder bore, and the inner surface of the cylinder bore on the crankshaft side of this cylinder block was observed.

[0048] As a result, a 5-15 μm thick anodic oxide film was formed on the parts other than the cylinder bore. Furthermore, there was no evidence that the anodizing treatment liquid had come into contact with the cast iron cylinder sleeve, either on the cylinder head side or the crankshaft side, and no dissolution or pitting of the cast iron was confirmed. [Explanation of symbols]

[0049] 10 Cylinder block body 11 Cylinder bore 12 Cylinder sleeve (cast iron) 12a Chamfered surface 13 Base material (aluminum alloy) 14 Cylinder head interface 15 Water Jacket 21 First elastic jig 22 Second elastic jig 23 Gas supply section 24, 25 Gas passage 30 Joints 31 First support part 32 Second support 33 Joint 36 Position Sensor 37 Display device

Claims

1. A method of manufacturing an outboard motor cylinder block, comprising: An outboard motor cylinder block body has a cylinder bore and a water jacket formed around the cylinder bore at a joining surface where the cylinder head is joined, a cylindrical cylinder sleeve made of cast iron is cast-inserted into an aluminum alloy base material on the inner circumferential surface of the cylinder bore, the cylinder sleeve is exposed so as to protrude radially inward from the base material of the cylinder bore, and the base material is exposed at an end of the inner circumferential surface of the cylinder bore on the cylinder head side and at an opposite end on the crankshaft side, pressing an end portion of the inner circumferential surface of the cylinder bore where the base material on the cylinder head side is exposed with a first elastic jig, and pressing an end portion of the inner circumferential surface of the cylinder bore where the base material on the crankshaft side is exposed with a second elastic jig; performing anodizing treatment while being pressed by the first and second elastic jigs to form an anodized film on the surface of the aluminum alloy portion of the cylinder block body for outboard motors other than the cylinder bores; a step of performing a sealing treatment while being pressed by the first and second elastic jigs to seal the surface of the anodized coating; Including, In the pressing step, the first and second elastic jigs are elastic bags fluidly connected to gas supply units, and the elastic bags are disposed in the cylinder bores. Gas is supplied from the gas supply units to inflate the elastic bags, thereby pressing the ends of the cylinder head side and the crankshaft side where the base material is exposed with the elastic bags; and a cylinder block for an outboard motor, the elastic bag body having a maximum radial outer diameter portion of the cylinder bore formed outside the cylinder head side end and the crankshaft side end of the inner circumferential surface of the cylinder bore, and the elastic bag body is inflated so that the maximum radial outer diameter of the cylinder bore is larger than the inner circumferential diameter of the ends of the inner circumferential surface of the cylinder bore where the base material on the cylinder head side and the crankshaft side is exposed.

2. 2. The method for manufacturing an outboard motor cylinder block according to claim 1, wherein, before the pressing step, a chamfering process is performed on a corner of the inner peripheral surface of the cylinder sleeve that is located on the shorter axial length of the cylinder bore between an end of the inner peripheral surface of the cylinder bore where the base material is exposed on the cylinder head side and an end of the inner peripheral surface of the cylinder bore where the aluminum alloy is exposed on the crankshaft side.

3. 3. The method for manufacturing an outboard motor cylinder block according to claim 1, wherein the first elastic jig and the second elastic jig are connected via a joint that is adjustable in extension and contraction in the axial direction of the cylinder bore.

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