Cylinder block for outboard motor and manufacturing method thereof

Abstract

To provide an outboard-motor cylinder block which can further improve corrosion resistance of an outboard-motor cylinder block and can realize more favorable sealing with a gasket at a joining surface, and a manufacturing method therefor.SOLUTION: After an anodized film 16 is formed on the surface of an aluminum alloy 13 part of an outboard-motor cylinder block body other than cylinder bores 11, sealing treatment is performed on the surface of the anodized film 16, and finishing processing of removing the anodized film 16 on a joining surface 14 to expose the aluminum alloy 13 is performed, and then a chemical conversion coating film 17 is formed on the anodized film 16, which covers the inner peripheral surface of a water jacket 15, and the aluminum alloy 13 on the joining surface 14. Accordingly, an outboard-motor cylinder block in which the aluminum alloy 13 on the inner peripheral surface of the water jacket 15 is covered with the sealed anodized film 16, the sealed anodized film 16 is further covered with the chemical conversion coating film 17, and the aluminum alloy 13 on the joining surface 14 is covered with the chemical conversion coating film 17 can be obtained.SELECTED DRAWING: Figure 13

Description

[Technical Field]

[0001] The present invention relates to a cylinder block for an outboard motor and a method for manufacturing the same. [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 the various components of outboard motors are made up of many different metallic materials, differences in the metallic materials of the components that come into contact with seawater create potential differences, and metallic materials with low natural potentials dissolve in seawater, which can cause corrosion. Aluminum alloys, which are used in components such as cylinder blocks for outboard motors, are particularly susceptible to corrosion compared to other materials.

[0004] To prevent such corrosion from occurring, for example, Patent Document 1 describes a method for preventing such corrosion in a cylinder block body for an outboard motor having a cylinder bore and a water jacket surrounding the cylinder bore. The region of the inner surface of the cylinder bore that encompasses the boundary between the cast iron of the cast-encased cylinder sleeve and the aluminum alloy base material is pressed with an elastic jig, and the cylinder block body is anodized in this state to form an anodized film on the surface of the aluminum alloy.A sealing process is then performed to seal the pores in the anodized film, thereby forming a sealed anodized film on the joining surface to be joined to the cylinder head and on the inner surface of the water jacket. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2023-72944 Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide a cylinder block for an outboard motor, and a manufacturing method thereof, which can further improve corrosion resistance and, since the cylinder block for an outboard motor is joined to a cylinder head via a gasket, can improve the sealing performance with the gasket at the joining surface. [Means for solving the problem]

[0007] In order to achieve the above object, one aspect of the present invention is a cylinder block for an outboard motor, the cylinder block for an outboard motor having a cylinder bore and a water jacket around the cylinder bore at a joining surface where a cylinder head is joined, and a cylindrical cylinder sleeve made of cast iron encased in an aluminum alloy base material on the inner circumferential surface of the cylinder bore, the aluminum alloy being exposed at the joining surface side of the inner circumferential surface of the cylinder bore and forming a boundary between the cast iron and the aluminum alloy, the aluminum alloy being covered on the inner circumferential surface of the water jacket with an anodized coating, pores in the anodized coating being sealed with a sealing product and the sealed anodized coating being further covered with a chemical conversion coating, and the aluminum alloy being covered on the joining surface with the chemical conversion coating.

[0008] In another aspect, the present invention provides a method for manufacturing an outboard motor cylinder block, the method comprising: a cylinder block body for an outboard motor having a cylinder bore and a water jacket formed around the cylinder bore at a joining surface where the outboard motor cylinder block body is joined to a cylinder head; 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 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 comprising 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 forming a chemical conversion coating on the surface of the anodized coating that covers the inner circumferential surface of the cylinder bore on the side of the crankshaft. The method also includes the steps of: pressing an end of the inner circumferential surface of the cylinder bore on the crankshaft side with a second elastic jig; anodizing the end while pressed with the first and second elastic jigs to form an anodized coating on the surface of the aluminum alloy portion of the outboard motor cylinder block body other than the cylinder bore; sealing the surface of the anodized coating by sealing the surface of the anodized coating while pressed with the first and second elastic jigs; removing the first and second elastic jigs and finishing the joining surfaces by removing the anodized coating from the joining surfaces until the aluminum alloy base material is exposed; and forming a chemical conversion coating on the surface of the anodized coating that covers the inner circumferential surface of the water jacket and on the surface of the aluminum alloy exposed at the joining surfaces. [Effects of the Invention]

[0009] According to the present invention, the aluminum alloy base material is covered with a sealed anodized film on the inner surface of the water jacket, and this sealed anodized film is further covered with a chemical conversion film, and the aluminum alloy base material is covered with a chemical conversion film on the joining surface. This improves the sealing performance with the gasket at the joining surface, and further improves the corrosion resistance of the joining surface and the inner surface of the water jacket. [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 perspective view showing a gasket interposed between the cylinder block body for an outboard motor shown in FIG. 1 and a cylinder head. FIG. [Figure 3] 2 is a cross-sectional perspective view showing an outboard motor cylinder block body taken along line AA in FIG. 1. [Figure 4] 2 is a cross-sectional side view showing the cylinder block body for an outboard motor taken along line AA in FIG. 1. [Figure 5] 5 is a partial cross-sectional view of an outboard motor cylinder block body within a dotted line frame B in FIG. 4 for illustrating one embodiment of a manufacturing method of an outboard motor cylinder block according to the present invention. FIG. [Figure 6] 6 is an enlarged cross-sectional view of a portion of the outboard motor cylinder block body within dotted lines C and D in FIG. 5 for illustrating one embodiment of a manufacturing method for an outboard motor cylinder block according to the present invention. FIG. [Figure 7] 6 is an enlarged cross-sectional view of a portion of the outboard motor cylinder block body within dotted lines C and D in FIG. 5 for illustrating one embodiment of a manufacturing method for an outboard motor cylinder block according to the present invention. FIG. [Figure 8] 6 is an enlarged cross-sectional view of a portion of the outboard motor cylinder block body within dotted lines C and D in FIG. 5 for illustrating one embodiment of a manufacturing method for an outboard motor cylinder block according to the present invention. FIG. [Figure 9] 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. [Figure 10] 5 is an enlarged cross-sectional view of a portion of an outboard motor cylinder block body within a dotted line frame E in FIG. 4 for illustrating one embodiment of a manufacturing method of an outboard motor cylinder block according to the present invention. FIG. [Figure 11]5 is an enlarged cross-sectional view of a portion of an outboard motor cylinder block body within a dotted line frame E in FIG. 4 for illustrating one embodiment of a manufacturing method of an outboard motor cylinder block according to the present invention. FIG. [Figure 12] 5 is an enlarged cross-sectional view of a portion of an outboard motor cylinder block body within a dotted line frame E in FIG. 4 for illustrating one embodiment of a manufacturing method of an outboard motor cylinder block according to the present invention. FIG. [Figure 13] 5 is an enlarged cross-sectional view of a portion of an outboard motor cylinder block body within a dotted line frame E in FIG. 4 for illustrating one embodiment of a manufacturing method of an outboard motor cylinder block according to the present invention. FIG. DETAILED DESCRIPTION OF THE INVENTION

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

[0012] The manufacturing method for an outboard motor cylinder block of this embodiment includes a pressing step in which, with an elastic jig, 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; an anodizing treatment step in which, while the ends are pressed, anodizing treatment is performed to form an anodized film on the surface of the aluminum alloy portion of the outboard motor cylinder block body; a sealing treatment step in which, while the areas are pressed, a sealing treatment is performed to seal the anodized film; a finishing step in which, after removing the elastic jig, the anodized film on the joining surface of the outboard motor cylinder block body is removed to expose the base material; and a chemical conversion coating formation step in which a chemical conversion coating is formed on the surface of the anodized film that covers the inner circumferential surface of the water jacket and on the joining surface.

[0013] First, we will explain the cylinder block body, which is the target of anodizing and sealing treatments in this method. As shown in Figures 1 to 4, the cylinder block body 10 has a joint surface 14 where it is joined to a cylinder head (not shown), with multiple cylinder bores 11 and a water jacket 15 formed around these cylinder bores 11. As shown in Figure 2, the cylinder block is joined to the cylinder head via a gasket 40, so the joint surface 14 is required to have good sealing properties with the gasket 40. 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 be one for a single-cylinder engine.

[0014] In particular, as shown in Figure 4, 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 such a cast-insertion method, the entire inner circumferential surface of the cylinder bore 11 is not usually made into the cylinder sleeve 12, and the aluminum alloy base material 13 is exposed on the inner circumferential surface at the end 13A on the cylinder head side and the opposite end 13B on the crankshaft side. In other words, at the end on the cylinder head side and the end on the crankshaft side of the inner circumferential surface of the cylinder bore 11, cast iron Cylinder sleeve 12 and aluminum alloy 4, depending on the cast-in method, the cylinder sleeve 12 may be exposed so as to protrude radially inward from the base material 13, i.e., a step may be formed between the cylinder sleeve 12 and the base material 13.

[0015] The height of the step is, but is not limited to, 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, but is not limited to, 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, but is not limited to, in the range of 2 to 4 mm, for example.

[0016] In the cylinder block body 10 having a step on the inner circumferential surface of the cylinder bore 11 between the cast iron cylinder sleeve 12 and the aluminum alloy base material 13, 12 In this embodiment, in order to perform anodizing without dissolving the cast iron, the pressing step of pressing with 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, as shown in FIG.

[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 that can expand and contract an elastic bag portion by gas pressure, which is commercially available under the name of air picker, 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. 5, so that the two elastic bags can be inflated at the same time. Details of the joint 30 will be described later.

[0021] In this embodiment, first, as shown in Fig. 6, the elastic bags of the first and second elastic jigs 21 and 22 are arranged so that they abut against an end 13A where the base material 13 on the cylinder head side is exposed and an end 13B where the base material 13 on the crankshaft side is exposed, respectively, of the inner peripheral surface of the cylinder bore 11. Preferably, the center position of the elastic bag in the axial direction of the cylinder bore 11 is aligned with the end 13A where the base material 13 on the cylinder head side is exposed. 13 The elastic bag is placed so as to contact the exposed ends 13A and 13B.

[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. 7. 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 8, the maximum radial outer diameter portions 21a, 22a 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 bags 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. 9, 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 22 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 treatment step can employ known methods such as a hydrothermal method, a boiling water method, a nickel acetate method, a low-temperature sealing method, a lithium hydroxide method, etc. As described above, there are various sealing treatments, and although pitting corrosion of the cast iron sleeve occurs due to the application of electrolysis during anodizing treatment, slight surface rust occurs during sealing treatment. Therefore, if the surface rust is acceptable, the sealing treatment step can be performed with the first and second elastic jigs 21, 22 removed.

[0044] As an example of a sealing treatment, a low-temperature sealing treatment will be described. The sealing treatment solution used in the low-temperature sealing treatment contains, for example, chromium and / or zirconium and fluoride ions, and may further contain cobalt, calcium, zinc, etc. In the low-temperature sealing treatment, negatively charged fluoride ions are adsorbed and reacted with the positively charged gel portion of the pores in the anodized film to form a metal hydroxide such as chromium hydroxide. It is believed that aluminum fluoride and the metal hydroxide then co-precipitate through a series of reactions, thereby sealing the pores. The temperature of the sealing treatment solution is preferably in the range of 5 to 70°C, the pH is preferably in the range of 2 to 7, and the treatment time is preferably in the range of 1 to 900 seconds.

[0045] The sealing treatment solution used in this embodiment will be described in detail later, but from the viewpoint of corrosion resistance, it is preferable that it contains chromium or zirconium. As the chromium source, trivalent chromium salts such as chromium nitrate, chromium sulfate, chromium chloride, chromium phosphate, chromium acetate, and chromium hydroxide can be used. As the cobalt source, cobalt nitrate, cobalt sulfate, cobalt chloride, etc. can be used. As the fluoride ion source, hydrogen fluoride, ammonium fluoride, potassium fluoride, sodium fluoride, etc. can be used. As the zirconium source, zirconium oxychloride, zirconium sulfate, zirconium nitrate, zirconium oxide, etc. can be used.

[0046] After the sealing process is completed, the first and second elastic jigs 21, 22 are removed from the cylinder bore 11. Figure 10 shows the cylinder block body 10 with the sealed anodic oxide coating formed in this way. The cast iron of the cylinder sleeve 12 and the aluminum alloy of the base material 13 are exposed on the inner circumferential surface of the cylinder bore 11 of the cylinder block body 10, and a sealed anodic oxide coating 16 is formed on the joining surface 14 of the cylinder block body 10 and the inner circumferential surface of the water jacket 15.

[0047] In this embodiment, the joining surface 14 of the cylinder block body 10 is subjected to a finishing process. As shown in FIG. 11, the anodized film 16 on the joining surface 14 is removed until the aluminum alloy base material 13 is exposed. The finishing process is not particularly limited as long as it can smooth the joining surface 14. For example, a milling machine using a rotating flat milling cutter or a grinding machine using a surface grinding machine can be used. An alkaline cutting fluid is preferably used as the cutting fluid during the finishing process. This helps prevent color unevenness on the joining surface 14 of the cylinder block body 10, as will be described in more detail below.

[0048] Next, a chemical conversion coating process is carried out on the cylinder block body 10 whose joining surface 14 has been finished in this manner. First, the cylinder block body 10 is subjected to a chemical conversion treatment, and a chemical conversion coating 17 is formed on the entire surface of the cylinder block body 10, that is, on the surface of the cast iron of the cylinder sleeve 12 on the inner surface of the cylinder bore 11 of the cylinder block body 10 and the aluminum alloy of the base material 13, on the joining surface 14 where the aluminum alloy of the cylinder block body 10 is exposed, and on the surface of the anodized coating 16 that covers the inner surface of the water jacket 15, as shown in Figure 12.

[0049] While a wide variety of known chemical conversion treatments can be used for the chemical conversion treatment, it is preferable to use a chemical conversion treatment solution containing the same main components as the sealing treatment solution used in the sealing treatment step. For example, when a low-temperature sealing treatment is used in the sealing treatment step, a chemical conversion treatment solution containing chromium or zirconium, as used in the sealing treatment solution, is particularly preferable. As the chromium source, a trivalent chromium salt can be used, as in the sealing treatment solution. Furthermore, as the zirconium source, either organic sources such as zirconium tetraethoxide and zirconium tetraisopropoxide or inorganic sources such as zirconium oxide chloride, zirconium hydroxide, zirconium sulfate, and zirconium carbonate can be used. By using a chemical conversion treatment solution containing the same main components as the sealing treatment solution, the chemical conversion coating 17 and the anodized coating 16 have the same components that are continuous across their surfaces. This allows the chemical conversion coating 17 to form intimately with the anodized coating 16, thereby exhibiting high barrier properties and significantly improving corrosion resistance.

[0050] In the chemical conversion coating forming process, the cylinder block body 10, the entire surface of which is covered with the chemical conversion coating 17, is subjected to a honing process. As shown in FIG. 13, the chemical conversion coating 17 is removed from the inner peripheral surface of the cylinder bore 11, and the cylinder sleeve The surfaces of the cast iron 12 and the aluminum alloy base material 13 are aligned. A conventional method can be used for the honing process, and by inserting a honing tool (not shown) into the cylinder bore 11 and rotating it to grind the inner surface of the cylinder bore 11 with the grinding stone of the honing tool, the inner surface of the cylinder bore 11 can be processed in the same manner as conventional methods, even if the chemical conversion coating 17 has been formed.

[0051] According to the manufacturing method of the cylinder block for an outboard motor of this embodiment, which includes the above-mentioned steps, the cast iron of the cylinder sleeve 12 does not dissolve, and on the inner surface of the water jacket 15, the aluminum alloy base material 13 is covered with an anodized film 16, the pores of the anodized film 16 are sealed with a sealing product, and this sealed anodized film 16 is further covered with a chemical conversion film 17, so that an outboard motor cylinder block can be obtained in which the aluminum alloy base material 13 is covered with the chemical conversion film 17 at the joining surface 14.

[0052] In particular, the inner circumferential surface of the water jacket 15 is close to the combustion chamber, is exposed to high temperatures, and is likely to come into contact with cooling water (seawater). Therefore, corrosion resistance is enhanced by forming a chemical conversion coating on the sealed anodized coating. Furthermore, the joining surface 14 of the cylinder block is also susceptible to corrosion if even a small amount of cooling water (seawater) seeps in between the gasket and the joining surface 14. However, even if a chemical conversion coating 17 is formed on the joining surface 14 after finishing, the smoothness of the joining surface 14 is maintained, providing a good seal with the gasket. Furthermore, since the chemical conversion coating 17 is formed integrally with the inner circumferential surface of the water jacket 15, penetration is prevented, improving corrosion resistance. This type of configuration is particularly advantageous when inexpensive aluminum alloys such as ADC and AC are used, as corrosion resistance can be a concern.

[0053] Before forming the anodized coating, the cylinder block body 10 may be subjected to shot blasting. This shot blasting can remove the Si chill layer that segregates in the aluminum alloy of the base material 13 and causes color unevenness on the exterior surface. This can reduce color unevenness on the surface of the final outboard motor cylinder block.

[0054] The conditions for the shot blasting treatment are not particularly limited as long as they can remove or crush the Si chill layer (segregation) in the aluminum alloy of the base material 13, but it is preferable to use shot particles with an average particle size of 400 to 600 μm. Also, it is preferable to make the surface roughness Ra of the aluminum alloy after the shot blasting treatment 5 μm or more.

[0055] After the shot blasting process and before the anodized film forming process, the cylinder block body 10 may be washed with an alkaline liquid. This allows the silicon and other materials removed by the shot blasting process to be washed away from the cylinder block body 10, and the alkaline liquid can also adjust or suppress color unevenness in the cylinder block body 10. The alkaline liquid is preferably one whose basic component is sodium hydroxide or lithium hydroxide, and for example, commercially available alkaline cleaners or alkaline cutting fluids can be used.

[0056] Furthermore, before the anodized coating is formed, the cylinder block body 10 may be treated with an alkaline liquid instead of shot blasting. This dissolves the aluminum alloy around the silicon chill layer, which causes color unevenness on the exterior surface, and removes the silicon. This also reduces color unevenness on the surface of the final outboard motor cylinder block.

[0057] Furthermore, even if shot blasting is not performed, the sealed anodic oxide coating 16 on the cylinder block body 10 may be treated with an alkaline liquid after the finishing process and before the chemical conversion coating formation process. By adjusting the surface color of the anodic oxide coating 16 with an alkaline liquid in this way, color unevenness on the surface of the final outboard motor cylinder block can be suppressed even if a silicon chill layer segregates in the aluminum alloy base material 13. Of course, this treatment of the anodic oxide coating 16 with an alkaline liquid may be performed in conjunction with the above-mentioned shot blasting process. [Example]

[0058] Tests were conducted to improve the color unevenness of a cylinder block using shot blasting and alkaline liquid. The shot blasting machine used for the shot blasting process was equipped with a projection nozzle and used shot particles with an average particle size of 400 to 600 μm. The shot particles were then sprayed and collided against the cylinder block body made of aluminum alloy ADC12. Before the shot blasting process, the surface roughness Ra of the cylinder block body was about 0.6, but after the shot blasting process, the surface roughness Ra was about 6.0.

[0059] After the shot blasting process, the cylinder block body was degreased and then anodized using a conventional direct current electrolysis method to form an anodized film of 5 to 15 μm. The anodizing process involved immersing the cylinder block in a sulfuric acid bath with a concentration of 200 g / L at a temperature of 20°C and a current density of 1.5 A / dm 2 A voltage was applied for 20 minutes at 40°C. After that, the cylinder block was rinsed with water, subjected to low-temperature sealing treatment (40°C, 4 minutes), rinsed with water, and then rinsed with hot water, after which the bonded surfaces were finished using alkaline cutting fluid. The bonded surfaces were then degreased with alkaline cleaning fluid, and the cylinder block body was then subjected to chemical conversion treatment (50°C, 3 minutes) using a chromate chemical conversion treatment solution (product name: Alsurf). As a result, no color unevenness was observed across the entire surface of the cylinder block, and the color was uniform. [Explanation of symbols]

[0060] 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 16 Anodic oxide film 17 Chemical coating 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 40 gasket

Claims

1. A cylinder block for an outboard motor, the cylinder block having a cylinder bore and a water jacket around the cylinder bore at a joining surface where the cylinder block is joined to a cylinder head, a cylindrical cylinder sleeve made of cast iron cast into an aluminum alloy base material on the inner peripheral surface of the cylinder bore; the aluminum alloy is exposed on the joining surface side of the inner circumferential surface of the cylinder bore, and a boundary between the cast iron and the aluminum alloy is present; the aluminum alloy is covered with an anodized coating on the inner circumferential surface of the water jacket, pores of the anodized coating are sealed with a sealing product, and the sealed anodized coating is further covered with a chemical conversion coating; In the cylinder block for an outboard motor, the aluminum alloy at the joining surfaces is not covered with an anodized coating but is covered with a chemical conversion coating.

2. 2. The cylinder block for an outboard motor according to claim 1, wherein said chemical conversion coating contains a main component of said sealing product.

3. 3. The cylinder block for an outboard motor according to claim 2, wherein the main component of said sealing product is chromium and / or zirconium.

4. 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; removing the first and second elastic jigs, and performing a finish process on the joining surfaces until the anodized film on the joining surfaces is removed and the aluminum alloy base material is exposed; forming a chemical conversion coating on the surface of the anodized coating covering the inner peripheral surface of the cylinder bore and the inner peripheral surface of the water jacket, and on the surface of the aluminum alloy exposed at the joining surface; a step of removing a chemical conversion coating formed on the inner peripheral surface of the cylinder bore and performing processing to align the surface of the cast iron of the cylinder block with the surface of the aluminum alloy base material in the cylinder bore; A method for manufacturing an outboard motor cylinder block, comprising:

5. 5. A method for manufacturing an outboard motor cylinder block according to claim 4, wherein in the pressing step, the first and second elastic jigs are elastic bags fluidly connected to gas supply units, the elastic bags are disposed in the cylinder bores, and gas is supplied from the gas supply units to inflate the elastic bags, thereby pressing the ends of the cylinder head side and crankshaft side where the base material is exposed with the elastic bags.

6. 6. A method for manufacturing an outboard motor cylinder block as set forth in claim 5, wherein the elastic bag body has a maximum radial outer diameter portion formed outwardly of 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 elastic bag body in 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.

7. 5. The method for manufacturing an outboard motor cylinder block according to claim 4, wherein the outboard motor cylinder block body is subjected to shot blasting or alkaline liquid treatment before the step of forming the anodic oxide film.

8. 8. The method for manufacturing an outboard motor cylinder block according to claim 4, wherein after the finishing step and before the chemical conversion coating step, the sealed anodic oxide coating of the outboard motor cylinder block body is treated with an alkaline liquid.

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