Method for manufacturing a cylinder block, and a jig.

Abstract

To enhance the durability of a thermal spray coating.SOLUTION: A manufacturing method of a cylinder block has a jig attachment step for accommodating a jig in a water jacket and making a salient part of the jig oppose an external peripheral face of a bore wall. The manufacturing method of the cylinder block has a heating step for expanding the bore wall by heating the cylinder block, and protrusively deforming an internal peripheral face of the bore wall. The manufacturing method of the cylinder block has a thermal spray step for forming a coating by thermally spraying a metal material to the internal peripheral face in a state that the internal peripheral face is protrusively deformed. The manufacturing method of the cylinder block also has a jig removal step for contracting the bore wall by cooling the cylinder block, and withdrawing the jig from the water jacket.SELECTED DRAWING: Figure 14

Description

Technical Field

[0001] The present invention relates to a manufacturing technique for a cylinder block.

Background Art

[0002] In order to achieve performance improvement and miniaturization and weight reduction of an engine, an aluminum alloy cylinder block without a cast iron cylinder liner has been developed. On the inner wall surface of a cylinder bore formed in this cylinder block, a film made of an iron-based material, that is, a thin metal layer, is formed. When forming the film on the inner wall surface of the cylinder bore, a spraying technique in which an iron-based material is melted and sprayed is used (see Patent Documents 1 and 2).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, since the piston reciprocates in the cylinder bore, an impact load is input from the piston to the inner wall surface of the cylinder bore. Therefore, it is required to improve the durability of the sprayed film formed on the inner wall surface.

[0005] An object of the present invention is to improve the durability of the sprayed film.

Means for Solving the Problems

[0006] A method for manufacturing a cylinder block according to one embodiment is a method for manufacturing a cylinder block having a bore wall that separates a cylinder bore and a water jacket, comprising: a jig mounting step of housing a jig in the water jacket and positioning the projection of the jig facing the outer circumferential surface of the bore wall; a heating step of heating the cylinder block to expand the bore wall and pressing the projection and the outer circumferential surface against each other to deform the inner circumferential surface of the bore wall into a convex shape; a thermal spraying step of thermal spraying a metal material onto the inner circumferential surface while the inner circumferential surface is deformed into a convex shape to form a coating; and a jig removal step of cooling the cylinder block to shrink the bore wall and removing the jig from the water jacket.

[0007] A jig according to one embodiment is a jig housed in a water jacket when manufacturing a cylinder block, and comprises an annular body, a first projection consisting of a plurality of first protrusions protruding from the inner circumference of the body, and a second projection consisting of a plurality of second protrusions protruding from the inner circumference and facing the first projection. [Effects of the Invention]

[0008] According to one aspect of the present invention, the durability of the thermal spray coating can be improved. [Brief explanation of the drawing]

[0009] [Figure 1] This figure shows an example of a vehicle equipped with a powertrain. [Figure 2] This is a cross-sectional view showing an example of the internal structure of an engine along the line II-II in Figure 1. [Figure 3A] This figure shows an example of a cylinder block viewed from the deck side. [Figure 3B] This figure shows a cross-section of the cylinder block along the line III-III in Figure 3A. [Figure 4A] This figure shows an example of a cylinder block viewed from the deck side. [Figure 4B] This figure shows a cross-section of the cylinder block along the line IV-IV in Figure 4A. [Figure 5] It is a diagram showing an example of a piston. [Figure 6] It is a diagram showing the occurrence situation of piston slap. [Figure 7] It is a diagram showing the execution procedure of the manufacturing method of the cylinder block according to the first embodiment. [Figure 8A] It is a diagram showing the jig according to the first embodiment. [Figure 8B] It is a cross-sectional view showing the jig along the line VIII-VIII of FIG. 8A. [Figure 9A] It is a diagram showing the bore wall and its vicinity. [Figure 9B] It is a cross-sectional view showing the bore wall and its vicinity along the line IX-IX of FIG. 9A. [Figure 10A] It is a diagram showing the bore wall and its vicinity in the jig attachment process. [Figure 10B] It is a cross-sectional view showing the bore wall and its vicinity along the line X-X of FIG. 10A. [Figure 11] It is a diagram showing an example of a virtual plane in the cylinder block. [Figure 12] It is a diagram showing the bore wall and its vicinity in the heating process. [Figure 13] It is a diagram showing the bore wall and its vicinity in the spraying process. [Figure 14] It is a cross-sectional view showing the bore wall and its vicinity along the line XIV-XIV of FIG. 13. [Figure 15] It is a cross-sectional view showing the bore wall along the line XIV-XIV of FIG. 9B. [Figure 16A] It is a diagram showing the jig according to the second embodiment. [Figure 16B] It is a cross-sectional view showing the jig along the line XVI-XVI of FIG. 16A. [Figure 17A] It is a cross-sectional view showing the jig according to the third embodiment. [Figure 17B] It is a cross-sectional view showing the jig according to the fourth embodiment. [Figure 17C] It is a cross-sectional view showing the jig according to the fifth embodiment. [Figure 17D]This is a cross-sectional view showing a jig according to the sixth embodiment. [Figure 18A] This is a diagram showing a jig according to the seventh embodiment. [Figure 18B] Figure 18A is a cross-sectional view showing the jig along the line XVIII-XVIII. [Figure 19] This figure shows a heating process in which the jig according to the eighth embodiment is used. [Figure 20] Figure 19 is a cross-sectional view showing the cylinder block and fixture along the line XX-XX. [Modes for carrying out the invention]

[0010] <First Embodiment> The method for manufacturing a cylinder block according to the first embodiment and the jig will be described in detail below with reference to the drawings. In the following description, identical or substantially identical components and elements will be denoted by the same reference numerals, and repeated descriptions will be omitted.

[0011] <Vehicle Structure> Figure 1 shows an example of a vehicle 11 equipped with a powertrain 10. As shown in Figure 1, the vehicle 11 has a powertrain 10 consisting of an engine 12 and a transmission 13. The output shaft 14 of the powertrain 10 is connected to the wheels 17 via a propeller shaft 15 and a differential mechanism 16. The powertrain 10 shown is a rear-wheel drive powertrain, but is not limited to this, and may also be a front-wheel drive or all-wheel drive powertrain. Also, as will be described later, the engine 12 shown is a four-cylinder horizontally opposed engine, but is not limited to this, and may be an inline engine, a V-type engine or a single-cylinder engine, for example.

[0012] <Engine Structure> Figure 2 is a cross-sectional view showing an example of the internal structure of engine 12 along the line II-II in Figure 1. As shown in Figure 2, engine 12 has a cylinder block 20 that constitutes one cylinder bank and a cylinder block 21 that constitutes the other cylinder bank. Engine 12 also has a crankshaft 22 that is rotatably supported by the pair of cylinder blocks 20 and 21. Each cylinder block 20 and 21 is fitted with a cylinder head 24 equipped with a valve train 23 and the like. Each cylinder head 24 has an intake port 26 that communicates with the combustion chamber 25 and an exhaust port 27 that communicates with the combustion chamber 25. Each cylinder head 24 also has an intake valve 28 that opens and closes the intake port 26 and an exhaust valve 29 that opens and closes the exhaust port 27. Each cylinder head 24 also has a spark plug (not shown) that ignites the air-fuel mixture in the combustion chamber 25 and an injector (not shown) that injects fuel into the intake air.

[0013] Each cylinder block 20, 21 has a support wall 31 on which a semicircular journal bore (crank journal bore) 30 is formed. Bearing metal (not shown) is assembled to the journal bore 30, and the support wall 31 supports the crank journal 32 of the crankshaft 22 via the bearing metal. Each cylinder block 20, 21 also has a cylinder bore 34 that houses a piston 33. The small end 37 of a connecting rod 36 is connected to the piston 33 housed in the cylinder bore 34 via a piston pin 35. The large end 39 of the connecting rod 36 is connected to the crank pin 38 of the crankshaft 22. In this way, the crankshaft 22 and the piston 33 are connected to each other via the connecting rod 36. The material of the cylinder blocks 20, 21 is an aluminum alloy.

[0014] <Cylinder block structure> Figure 3A shows an example of the cylinder block 20 viewed from the deck surface 40 side. Figure 3B shows a cross-section of the cylinder block 20 along line III-III in Figure 3A. Figure 4A shows an example of the cylinder block 21 viewed from the deck surface 41 side. Figure 4B shows a cross-section of the cylinder block 21 along line IV-IV in Figure 4A. Furthermore, Figure 5 shows an example of the piston 33.

[0015] As shown in Figures 3A and 3B, the cylinder block 20 has two sleeve-shaped bore walls B1 and B3, and an outer wall 42 surrounding these bore walls B1 and B3. The cylinder bore 34 is partitioned radially inside the bore walls B1 and B3, and the water jacket 43 is partitioned radially outside the bore walls B1 and B3. In other words, the cylinder block 20 has bore walls B1 and B3 that separate the cylinder bore 34 and the water jacket 43. The water jacket 43, which is partitioned between the bore walls B1 and B3 and the outer wall 42, is exposed on the deck surface 40 of the cylinder block 20. Thus, the illustrated cylinder block 20 has a so-called open deck structure. The bore walls B1 and B3 are also called aluminum sleeves or aluminum hoops.

[0016] Similarly, as shown in Figures 4A and 4B, the cylinder block 21 has two sleeve-shaped bore walls B2 and B4, and an outer wall 44 surrounding these bore walls B2 and B4. The cylinder bore 34 is partitioned radially inside the bore walls B2 and B4, and the water jacket 43 is partitioned radially outside the bore walls B2 and B4. In other words, the cylinder block 21 has bore walls B2 and B4 that separate the cylinder bore 34 and the water jacket 43. The water jacket 43, which is partitioned between the bore walls B2 and B4 and the outer wall 44, is exposed to the deck surface 41 of the cylinder block 21. Thus, the illustrated cylinder block 21 has a so-called open deck structure. The bore walls B2 and B4 are also called aluminum sleeves or aluminum hoops.

[0017] As shown in the enlarged portions of Figures 3B and 4B, a coating 46 made of iron-based material such as carbon steel or special steel is formed on the inner circumferential surfaces 45 of the bore walls B1 to B4, that is, the inner circumferential surfaces 45 of the cylinder bore 34. In other words, a thin metallic layer, a coating 46 made of iron-based material, is formed on the bore walls B1 to B4, which are made of aluminum alloy. As will be described later, when forming the coating 46 on the inner circumferential surfaces 45 of the bore walls B1 to B4, a thermal spraying technique is used, in which iron-based material is melted and sprayed onto the inner circumferential surfaces 45. By forming a coating 46 of iron-based material (hereinafter referred to as thermal spray coating 46) on the bore walls B1 to B4 in this way, the cast iron cylinder liner can be omitted from the cylinder blocks 20 and 21. In other words, the thermal spray coating 46 can function as a cylinder liner, thereby improving the performance and reducing the size and weight of the engine 12.

[0018] Incidentally, the piston 33, which reciprocates within the cylinder bore 34, may collide with the thrust-side bore wall B1 to B4 due to so-called piston slap. Here, as shown in Figures 3B and 4B, there is a pair of parts α1 on the thrust-side inner circumferential surface 45 that are separated by a virtual plane PL2, and these are the parts to which impact loads are input from the piston 33. The virtual plane PL2 is a plane that includes the center line C1 of the cylinder bore 34 and is perpendicular to the virtual plane PL1, which will be described later. The pair of parts α1 on the inner circumferential surface 45 are considered to be the parts to which the edge α2 of the piston skirt 49 makes contact, as shown in Figure 5. Thus, since impact loads are input from the piston 33 to parts α1 on the inner circumferential surface 45, it is necessary to increase the durability of the thermal spray coating 46 located at parts α1.

[0019] The thrust side, as will be described later, is the side on which the piston 33 is biased by the side thrust generated during the expansion stroke. In other words, the thrust side is the side opposite to the direction of rotation of the crankshaft 22. That is, the thrust side is the side opposite to the direction of movement of the crankpin 38 near the top dead center of the piston 33. As shown in Figure 2, for one cylinder block 20, the lower side in the vertical direction is the thrust side, and for the other cylinder block 21, the upper side in the vertical direction is the thrust side. That is, the bore walls B1 and B3 of the cylinder block 20 have a thrust-side bore wall portion 47a that constitutes the lower part of the block and a non-thrust-side bore wall portion 47b that constitutes the upper part of the block. On the other hand, the bore walls B2 and B4 of the cylinder block 21 have a thrust-side bore wall portion 48a that constitutes the upper part of the block and a non-thrust-side bore wall portion 48b that constitutes the lower part of the block.

[0020] <Piston slap> This section explains piston slap, which is the oscillating motion of piston 33. Figure 6 shows the conditions under which piston slap occurs. Figure 6 shows the conditions towards the end of the compression stroke. <btdc>This is shown as the situation near top dead center when transitioning from the compression stroke to the expansion stroke. <tdc>This is shown. Also, Figure 6 shows the initial situation during the expansion process. <atdc1>This is shown as the situation in the middle of the expansion process. <atdc2>These are shown as follows: BTDC stands for "Before Top Dead Center," TDC stands for "Top Dead Center," and ATDC stands for "After Top Dead Center."

[0021] In the following explanation, the two pistons 33 incorporated into the cylinder block 20 will be referred to as piston P1. On the other hand, the two pistons 33 incorporated into the cylinder block 21 will be referred to as piston P2. Also, the arrow R1 shown in Figure 6 indicates the direction of rotation of the crankshaft 22. Note that the inclination of pistons P1 and P2 is exaggerated in Figure 6 to facilitate understanding of piston operation.

[0022] Figure 6 <btdc>As shown in Figure 6, towards the end of the compression stroke, a side thrust S1a acts on the piston P1, corresponding to the inclination angle of the connecting rod 36. As a result, the piston P1, moving towards top dead center, is pressed against the upper bore wall 47b. Next, in Figure 6 <tdc>As shown, near the top dead center of the piston P1, the inclination angle of the connecting rod 36 becomes almost zero, so the side thrust acting on the piston P1 becomes extremely small.

[0023] Figure 6 <atdc1>As shown, in the initial stages of the expansion stroke, a side thrust S1b acts on the piston P1, corresponding to the inclination angle of the connecting rod 36. At this time, as indicated by the symbol X1a, the piston skirt is in contact with the lower bore wall 47a, while as indicated by the symbol X1b, the piston head remains against the upper bore wall 47b. In other words, a large frictional force is generated on the piston rings due to the combustion pressure during the expansion stroke, causing the piston head to remain against the upper bore wall 47b.

[0024] Figure 6 <atdc2>As shown, in the middle of the expansion stroke, the side thrust S1c acting on the piston P1 increases. Also, in the middle of the expansion stroke, the frictional force of the piston rings gradually decreases due to the decrease in combustion pressure. As a result, a counterclockwise moment M1 acts on the piston P1, and as indicated by the symbol X1c, the piston P1 collides with the lower (thrust side) bore wall 47a. Similarly, in the middle of the expansion stroke, a counterclockwise moment M2 acts on the piston P2 housed in the cylinder block 21. Then, as indicated by the symbol X2c, the piston P2 collides with the upper (thrust side) bore wall 48a.

[0025] Furthermore, due to the aforementioned piston slap, piston P1 rotates around piston pin 35. As a result, piston P1 collides not only with the lower (thrust side) bore wall 47a but also with the upper (anti-thrust side) bore wall 47b. In other words, although the impact load is smaller than the impact load applied from piston P1 to bore wall 47a, it is considered that a collision load is also applied from piston P1 to bore wall 47b. Similarly, due to the aforementioned piston slap, piston P2 rotates around piston pin 35. As a result, piston P2 collides not only with the upper (thrust side) bore wall 48a but also with the lower (anti-thrust side) bore wall 48b. In other words, although the impact load is smaller than the impact load applied from piston P2 to bore wall 48a, it is considered that a collision load is also applied from piston P2 to bore wall 48b.

[0026] <Manufacturing method for cylinder blocks> As mentioned above, impact loads are applied from the piston 33 to the bore walls B1 to B4, so it is necessary to increase the durability of the thermal spray coating 46. Therefore, by using the cylinder block manufacturing method described later, the durability of the thermal spray coating 46 formed on the bore walls B1 to B4 of the cylinder blocks 20 and 21 is increased. In the illustrated example, the thermal spray coating 46 is formed on the bore wall B3, but it goes without saying that the thermal spray coating 46 can also be formed on the bore walls B1, B2, and B4 using the same procedure.

[0027] Figure 7 is a diagram showing the execution procedure for the manufacturing method of a cylinder block according to the first embodiment. Note that Figure 7 shows a part of the cylinder block manufacturing process, including the manufacturing method of a cylinder block according to the first embodiment. Figure 8A is a diagram showing the jig 50 according to the first embodiment. Figure 8B is a cross-sectional view showing the jig 50 along the line VIII-VIII in Figure 8A. Figure 9A is a diagram showing the bore wall B3 and its vicinity. Figure 9B is a cross-sectional view showing the bore wall B3 and its vicinity along the line IX-IX in Figure 9A.

[0028] Figure 10A shows the bore wall B3 and its vicinity during the jig mounting process. Figure 10B is a cross-sectional view showing the bore wall B3 and its vicinity along line XX in Figure 10A. Figure 11 shows an example of a virtual plane PL1 in the cylinder block 20. Figure 12 shows the bore wall B3 and its vicinity during the heating process. Figure 13 shows the bore wall B3 and its vicinity during the thermal spraying process. Figure 14 is a cross-sectional view showing the bore wall B3 and its vicinity along line XIV-XIV in Figure 13.

[0029] As shown in Figure 7, the cylinder block manufacturing process includes a surface treatment step S100 in which the inner circumferential surfaces 45 of the bore walls B1 to B4 are roughened. In the surface treatment step S100, the inner circumferential surfaces 45 of the bore walls B1 to B4 are subjected to cutting, blasting, or other processes. This gives the inner circumferential surfaces 45 of the bore walls B1 to B4 an appropriate roughness, thereby improving the adhesion of the thermal spray coating 46 to the inner circumferential surfaces 45.

[0030] As shown in Figure 7, once the surface preparation process S100 is completed, the process proceeds to the jig mounting process S110, where the jig 50 is attached to the water jackets 43 of the cylinder blocks 20 and 21. Here, as shown in Figures 8A and 8B, the jig 50 has an annular body 51. The jig 50 also has a first projection (projection) 54 consisting of a plurality of first protrusions 53 protruding from the inner circumference 52 of the body 51, and a second projection (projection) 56 consisting of a plurality of second protrusions 55 protruding from the inner circumference 52 of the body 51. The first projection 54 and the second projection 56 are arranged opposite each other. In other words, the first projection 54 and the second projection 56 are arranged axially symmetrically with respect to the center line C3 of the jig 50 as the axis of symmetry. The material of the jig 50 is steel such as carbon steel or special steel, which has a lower coefficient of thermal expansion than aluminum alloy. In other words, the linear expansion coefficient of jig 50 is smaller than that of the bore walls B1 to B4. The linear expansion coefficient, which is the ratio of length expansion due to temperature rise, is also called the linear expansion rate.

[0031] As shown in Figures 10A and 10B, in the jig installation process S110, the jig 50 is housed in the water jacket 43 from the deck surface 40 side. That is, the main body 51 of the jig 50 is positioned to surround the bore wall B3, and the protrusions 54 and 56 of the jig 50 face the outer circumferential surface 60 of the bore wall B3. In the jig installation process S110, the jig 50 may be inserted into the water jacket 43 using equipment such as a robot arm, or it may be inserted into the water jacket 43 by an operator manually.

[0032] As shown in Figures 10A and 11, a virtual plane PL1 is defined as a plane that includes the center line C1 of the cylinder bore 34 and coincides with or is parallel to the center line C2 of the journal bore 30 of the cylinder block 20. In this case, the outer circumferential surface 60 of the bore wall B3 is composed of a first outer circumferential surface 61 located on the thrust side of the virtual plane PL1 and a second outer circumferential surface 62 located on the anti-thrust side of the virtual plane PL1. Then, as shown in Figure 10A, in the jig mounting process S110, the first projection 54 of the jig 50 faces the first outer circumferential surface 61 of the bore wall B3, and the second projection 56 of the jig 50 faces the second outer circumferential surface 62 of the bore wall B3. In other words, the pair of first projections 53 of the first projection 54 are positioned on either side of the virtual plane PL2 which is perpendicular to the virtual plane PL1. Similarly, the pair of second projections 55 of the second projection 56 are positioned on either side of the virtual plane PL2 which is perpendicular to the virtual plane PL1. In the illustrated example, the virtual plane PL1 coincides with the center line C2 of the journal bore 30, but this is not the only case. If the cylinder block 20 is an offset cylinder, the virtual plane PL1 will be parallel to the center line C2 of the journal bore 30.

[0033] As shown in Figure 8A, the length from the center line C3 of the jig 50 to the tip of the first projection 53 is defined as "L1", and the length from the center line C3 of the jig 50 to the tip of the second projection 55 is defined as "L2". Also, as shown in Figure 9A, the length from the center line C1 of the bore wall B3 to the outer surface 60 is defined as "L3". At this time, the lengths L1, L2, and L3 are approximately the same under a predetermined ambient temperature environment (for example, 20°C). Since the lengths L1, L2, and L3 are approximately the same, in the jig mounting process S110, the projections 53 and 55 of the jig 50 are in contact with the outer surface 60 of the bore wall B3. In the jig mounting process S110, it is desirable for the projections 53 and 55 of the jig 50 to be in contact with the outer surface 60, but a gap may be present between the projections 53 and 55 and the outer surface 60.

[0034] As shown in Figure 7, once the jig mounting process S110 is completed, the process proceeds to the heating process S120, where the cylinder blocks 20 and 21 are placed in a heating furnace (not shown). In the heating process S120, the cylinder blocks 20 and 21 and the jig 50 are heated to a predetermined temperature (e.g., 190°C). Here, as mentioned above, since the coefficient of linear expansion of the jig 50 is smaller than that of the bore walls B1 to B4, the bore walls B1 to B4 expand radially outward while being constrained by the jig 50. In other words, as shown in Figure 12, each projection 53 and 55 of the jig 50 is pressed against the outer circumferential surface 60 of the bore wall B3, and the inner circumferential surface 45 of the bore wall B3 is deformed into a convex shape. Note that the heating process S120 is sometimes called the preheating process.

[0035] As shown in Figure 7, once the heating process S120 is completed, the process proceeds to the thermal spraying process S130, where a thermal spray coating 46 is formed on the inner circumferential surfaces 45 of the bore walls B1 to B4. As shown in Figures 13 and 14, in the thermal spraying process S130, the thermal spray gun 70 is inserted into the cylinder bore 34 and rotated while molten iron-based material (metal material) is sprayed from the thermal spray gun 70 onto the inner circumferential surfaces 45. As mentioned above, since the inner circumferential surface 45 of the bore wall B3 is convex, the thermal spray coating 46 is also layered in a convex shape along the inner circumferential surface 45. Special steels such as chromium-molybdenum steel can be used as the iron-based material sprayed from the thermal spray gun 70. Furthermore, as the thermal spraying method for the iron-based material using the thermal spray gun 70, an arc spraying method that uses an arc and compressed air to spray the iron-based material may be adopted, or a plasma spraying method that uses plasma to spray the iron-based material may be adopted.

[0036] As shown in Figure 7, once the thermal spraying process S130 is completed, the process proceeds to the cooling process S140 and then to the fixture removal process S150, where the fixture 50 is removed from the water jacket 43 of the cylinder blocks 20 and 21. In other words, the cooling process S140 shrinks the bore walls B1 to B4, releasing the fixture 50 from its restraint, and then the fixture removal process S150 removes the fixture 50 from the water jacket 43. In the fixture removal process S150, the fixture 50 may be removed from the water jacket 43 using equipment such as a robotic arm, or it may be removed manually by an operator. In the cooling process S140, the cylinder blocks 20 and 21 are cooled, for example, by natural air cooling.

[0037] Figure 15 is a cross-sectional view showing the bore wall B3 along the line XIV-XIV in Figure 9B. Figure 15 shows the bore wall B3 with a thermal spray coating 46 formed on it. As indicated by arrow β1 in the enlarged portion of Figure 15, compressive stress can be applied to the thermal spray coating 46 formed on the inner circumferential surface 45. In other words, after forming the thermal spray coating 46 on the convexly bulging inner circumferential surface 45, the bulge of the inner circumferential surface 45 is eliminated by the cooling of the bore wall B3, so the thermal spray coating 46 can be compressed in conjunction with the elimination of the bulge of the inner circumferential surface 45. Moreover, the portion of the inner circumferential surface 45 that is pushed out by the jig 50 is the portion that overlaps with portion α1 shown in Figures 3B and 4B. In other words, compressive stress can be applied to the thermal spray coating 46 covering portion α1, so the thermal spray coating 46 that receives the impact load of the piston 33 can be appropriately strengthened.

[0038] In the example shown in Figure 15, compressive stress is applied to the thermal spray coating 46, but this is not the only option. For example, the tensile stress of the thermal spray coating 46 may be relaxed, or the internal stress of the thermal spray coating 46 may be eliminated. Even in these cases, the tensile stress of the thermal spray coating 46 can be reduced, and the durability of the thermal spray coating 46 can be increased. In other words, the residual strain on the tensile side of the thermal spray coating 46 can be reduced, and the durability of the thermal spray coating 46 can be increased. After the jig removal process S150 is completed, a honing process to adjust the surface roughness of the thermal spray coating 46, a cleaning process to clean the cylinder blocks 20 and 21, and an inspection process to inspect the cylinder blocks 20 and 21 for scratches, etc. are performed. After these processes, the cylinder blocks 20 and 21 with the thermal spray coating 46 on the bore walls B1 to B4 are completed.

[0039] <Second Embodiment> The jig 80 according to the second embodiment will be described in detail below with reference to the drawings. In the following description, components and elements that are the same or substantially the same as those in the previously described embodiment will be denoted by the same reference numerals, and repeated descriptions will be omitted. Figure 16A is a diagram showing the jig 80 according to the second embodiment. Figure 16B is a cross-sectional view showing the jig 80 along the line XVI-XVI in Figure 16A.

[0040] In the example shown in Figures 8A and 8B, the main body 51 of the jig 50 is provided with first and second projections 54 and 56 facing each other, but it is not limited to this. As shown in Figures 16A and 16B, the jig 80 has an annular main body 81 and a projection 84 consisting of a pair of projections 83 that protrude from the inner circumference 82 of the main body 81. When such a jig 80 is used, in the jig mounting process S110 described above, the projection 84 is made to face either the first outer peripheral surface 61 or the second outer peripheral surface 62. This makes it possible to increase the durability of the thermal spray coating 46 formed on the thrust side or the anti-thrust side.

[0041] As mentioned above, due to the piston slap, which is the oscillating motion of the piston 33, the piston 33 mainly collides with the thrust-side bore walls 47a and 48a. Therefore, when using a jig 80 equipped with one projection 84, it is desirable to increase the durability of the thermal spray coating 46 located on the thrust side by positioning the projection 84 opposite the first outer peripheral surface 61 on the thrust side. However, depending on the piston structure, the input point of the impact load may change, so it is also possible to increase the durability of the thermal spray coating 46 located on the anti-thrust side by positioning the projection 84 opposite the second outer peripheral surface 62 on the anti-thrust side.

[0042] <Embodiments 3-6> The jigs 90, 100, 110, and 120 according to the third to sixth embodiments will be described in detail below with reference to the drawings. In the following description, components and elements that are the same or substantially the same as those in the previously described embodiments will be denoted by the same reference numerals, and repeated descriptions will be omitted. Figure 17A is a cross-sectional view showing the jig 90 according to the third embodiment. Figure 17B is a cross-sectional view showing the jig 100 according to the fourth embodiment. Figure 17C is a cross-sectional view showing the jig 110 according to the fifth embodiment. Figure 17D is a cross-sectional view showing the jig 120 according to the sixth embodiment. Figures 17A to 17D show cross-sections similar to those shown in Figure 8B.

[0043] In the examples shown in Figures 8A and 8B, the main body 51 of the jig 50 is provided with a projection 54 (56) consisting of a pair of protrusions 53 (55), but the number and shape of the protrusions are not limited to the examples shown. As shown in Figure 17A, the main body 91 of the jig 90 may be provided with a projection 93 consisting of multiple point-shaped protrusions 92. As shown in Figure 17B, the main body 101 of the jig 100 may be provided with a projection 103 consisting of a single linear protrusion 102. Also, as shown in Figure 17C, the main body 111 of the jig 110 may be provided with a projection 113 consisting of a single point-shaped protrusion 112. Furthermore, as shown in Figure 17D, the main body 121 of the jig 120 may be provided with a projection 123 consisting of a single linear protrusion 122 extending in the circumferential direction.

[0044] <Seventh Embodiment> The jig 130 according to the seventh embodiment will be described in detail below with reference to the drawings. In the following description, components and elements that are the same or substantially the same as those in the previously described embodiments will be denoted by the same reference numerals, and repeated descriptions will be omitted. Figure 18A is a diagram showing the jig 130 according to the seventh embodiment. Figure 18B is a cross-sectional view showing the jig 130 along the line XVIII-XVIII in Figure 18A.

[0045] In the example shown in Figure 8A, one jig 50 is attached to one bore wall B3, but this is not limited to this, and one jig 130 may be attached to multiple bore walls B1, B3. As shown in Figures 18A and 18B, the jig 130 has a roughly C-shaped first body 131 and a roughly C-shaped second body 141 connected to the first body 131. The jig 130 also has a projection 134 consisting of a pair of protrusions 133 protruding from the inner circumference 132 of the first body 131, and a projection 136 consisting of a pair of protrusions 135 protruding from the inner circumference 132 of the first body 131. Furthermore, the jig 130 has a projection 144 consisting of a pair of protrusions 143 protruding from the inner circumference 142 of the second body 141, and a projection 146 consisting of a pair of protrusions 145 protruding from the inner circumference 142 of the second body 141.

[0046] In this way, by providing roughly C-shaped bodies 131 and 141 to the jig 130, one jig 130 can be attached to two bore walls B1 and B3. Furthermore, by using the jig 130 shown in Figures 18A and 18B, the cylinder block manufacturing process described above can be performed even in a cylinder structure where adjacent bore walls are connected to each other. In the illustrated example, one jig 130 is attached to two bore walls B1 and B3, but this is not limited to this, and one jig may be attached to three or more bore walls.

[0047] <Eighth Embodiment> The jig 150 according to the eighth embodiment will be described in detail below with reference to the drawings. In the following description, components and elements that are the same or substantially the same as those in the previously described embodiments will be denoted by the same reference numerals, and repeated descriptions will be omitted. Figure 19 is a diagram showing a heating process S120 in which the jig 150 according to the eighth embodiment is used. Figure 20 is a cross-sectional view showing the cylinder block and jig 150 along the line XX-XX in Figure 19.

[0048] In the example shown in Figure 3A, a cylinder block 20 with a so-called open deck structure is used, but it is not limited to this, and a cylinder block 160 with a so-called closed deck structure may also be used. As shown in Figures 19 and 20, two fixtures 150 are attached to each bore wall B1, B3. Each fixture 150 has a projection 152 consisting of a pair of protrusions 151. In the fixture attachment process S110 described above, the fixture 150 is housed through the opening 161 of the thrust-side water jacket 43, and the projection 152 of the fixture 150 faces the outer circumferential surface 60 of the bore walls B1, B3. Also, the fixture 150 is housed through the opening 162 of the non-thrust-side water jacket 43, and the projection 152 of the fixture 150 faces the outer circumferential surface 60 of the bore walls B1, B3.

[0049] As the material for each jig 150, a material with a larger coefficient of thermal expansion than the material of the bore walls B1 and B3 is used. For example, if the bore walls B1 and B3 are formed from an aluminum alloy, the jig 150 can be formed from a magnesium alloy. By making the coefficient of thermal expansion of each jig 150 larger than that of the bore walls B1 and B3, the jig 150 can be expanded in the heating process S120 described above, causing the inner circumferential surface 45 of the bore walls B1 and B3 to deform into a convex shape. As a result, the tensile stress of the thermal spray coating 46 can be reduced as described above, and thus the durability of the thermal spray coating 46 can be increased.

[0050] The present invention is not limited to the embodiments described above, and it goes without saying that various modifications are possible without departing from the spirit of the invention. The illustrated engine 12 is an engine mounted on a vehicle 11, but it is not limited to this, and the cylinder block manufacturing method and jig according to the present invention may be applied to engines used as a power source for other devices, etc. Furthermore, the illustrated engine 12 is a gasoline engine that uses gasoline as fuel, but it is not limited to this, and the cylinder block manufacturing method and jig according to the present invention may be applied to engines that use diesel fuel, hydrogen, etc. as fuel.

[0051] In the above description, as shown in Figures 3B and 4B, a portion α1 to which an impact load is applied from the piston 33 is exemplified, and the durability of the thermal spray coating 46 covering this portion α1 is enhanced, but the invention is not limited to this. In other words, depending on the piston structure, the portion to which the impact load is applied may change, so the portion to which the durability of the thermal spray coating 46 is enhanced may be appropriately changed by changing the position of the protrusions 54 and 56. Also, in the above description, aluminum alloy is exemplified as the material for the cylinder blocks 20, 21, and 160, but the invention is not limited to this material. Also, in the above description, steel is exemplified as the material for the jig 50, and magnesium alloy is exemplified as the material for the jig 150, but the invention is not limited to these materials. Also, in the above description, steel is exemplified as the iron-based material for the coating 46, but the invention is not limited to this material. [Explanation of Symbols]

[0052] 20,21 Cylinder block 30 Journal Bore (Crank Journal Bore) 34 Cylinder bore 43 Water Jacket 45 Inner surface 46 Coating 50 jigs 51 Main unit 52 Inner circumference 53 1st protrusion 54 1st protrusion (protrusion) 55 2nd protrusion 56 2nd protrusion (protrusion) 60 Outer surface 61 1st outer peripheral surface 62 Second outer peripheral surface 80 jigs 84 Protrusion 90 jigs 93 Protrusion 100 jigs 103 Protrusion 110 Jig 113 Protrusion 120 jigs 123 Protrusion 130 Jig 134,136,144,146 Protrusion 150 jigs 152 Protrusion 160 Cylinder Block B1-B4 Bore Wall C1 center line C2 center line PL1 Virtual Plane < / tdc> < / btdc> < / tdc> < / btdc>

Claims

1. A method for manufacturing a cylinder block having a bore wall that separates the cylinder bore and the water jacket, A jig mounting step involves housing the jig in the water jacket and positioning the projection of the jig facing the outer circumferential surface of the bore wall, A heating step in which the cylinder block is heated to expand the bore wall, and the projection and the outer surface are pressed against each other to deform the inner surface of the bore wall into a convex shape, A thermal spraying step in which a metal material is thermal sprayed onto the inner circumferential surface while the inner circumferential surface is deformed into a convex shape, A jig removal step involves cooling the cylinder block to shrink the bore wall and removing the jig from the water jacket, A method for manufacturing a cylinder block, comprising:

2. In the method for manufacturing a cylinder block according to claim 1, The jig comprises a main body surrounding the bore wall and a projection extending from the main body. The coefficient of thermal expansion of the jig is smaller than the coefficient of thermal expansion of the bore wall. A method for manufacturing a cylinder block.

3. In the method for manufacturing a cylinder block according to claim 1, If a virtual plane is defined as a plane that includes the center line of the cylinder bore and coincides with or is parallel to the center line of the crank journal bore of the cylinder block, The outer circumferential surface consists of a first outer circumferential surface located on the thrust side of the virtual plane and a second outer circumferential surface located on the antithrust side of the virtual plane. In the jig mounting step, the projection is positioned to face at least one of the first outer peripheral surface and the second outer peripheral surface. A method for manufacturing a cylinder block.

4. In the method for manufacturing a cylinder block according to claim 3, The jig has a first projection and a second projection facing the first projection as its projection. In the jig mounting step, the first projection is positioned facing the first outer surface, and the second projection is positioned facing the second outer surface. A method for manufacturing a cylinder block.

5. A jig that is housed in a water jacket when manufacturing a cylinder block, The ring-shaped body, The first projection consists of a plurality of first protrusions that protrude from the inner circumference of the main body, It consists of a plurality of second protrusions projecting from the inner circumference, and the second protrusions are opposite to the first protrusion, A jig having

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