Engine and method of assembling an engine

Abstract

The present application aims to provide an engine capable of inserting a piston into a cylinder bore from a crankcase side and improving the assembly workability of the piston. To solve the above problem, the present application provides an engine comprising: a cylinder block having a cylinder bore in which a piston is accommodated; and a crankcase integrated with the cylinder block and having a crank bearing; and the crank bearing is arranged to overlap an extension line of the cylinder bore; the crankcase has a piston sliding space in which the crank bearing is cut from the cylinder bore side, whereby the piston can be accommodated in a state in which a central axis of the piston and a central axis of the cylinder bore are aligned.

Description

Technical Field

[0001] This invention relates to an engine and a method for assembling the engine. Background Technology

[0002] A multi-cylinder opposed engine is known in which a piston is inserted from the cylinder head side into a cylinder bore of a cylinder block that is separate from the cylinder head, and then the cylinder head is installed on the cylinder block (for example, see Patent Document 1).

[0003] Furthermore, an engine that integrates the cylinder head and cylinder block is also known (for example, see Patent Document 2).

[0004] [Previous Technical Documents]

[0005] (Patent Documents)

[0006] Patent Document 1: Japanese Patent Publication No. 52-46567

[0007] Patent Document 2: Japanese Patent Application Publication No. 7-317594 Summary of the Invention

[0008] [The problem the invention aims to solve]

[0009] In the case of an engine in which the cylinder head and cylinder block are integrated, when the piston is inserted into the cylinder bore of the cylinder head, the cylinder block must be operated from the crankcase side, which is located on the opposite side of the cylinder head.

[0010] However, in the crankcase, the crankshaft journals that rotatably support the crankshaft are configured to overlap the extension line of the cylinder bore. Therefore, when inserting the piston from the crankcase side into the cylinder bore, the crankshaft bearing becomes an obstacle, resulting in poor piston assembly workability.

[0011] The purpose of this invention is to provide an engine and an engine assembly method, wherein the engine allows the piston to be inserted from the crankcase side into the cylinder bore, and the piston assembly workability is improved.

[0012] [Technical means to solve the problem]

[0013] (1) The engine of the present invention (e.g., engine 1 described later) comprises: a cylinder block (e.g., cylinder block 22 described later) having a cylinder bore (e.g., cylinder bore 221 described later) for internally accommodating a piston (e.g., piston 3 described later); and a crankcase (e.g., crankcase 23 described later) integrated with the aforementioned cylinder block and having a crank bearing (e.g., crank bearing 232 described later); and the aforementioned crank bearing is configured to overlap the extension line of the aforementioned cylinder bore; the aforementioned crankcase has a piston sliding space (e.g., piston sliding space 233 described later), the piston sliding space cutting off the aforementioned crank bearing from the aforementioned cylinder bore side, thereby enabling the aforementioned piston to be accommodated in a state where the central axis of the aforementioned piston (e.g., central axis J2 described later) is aligned with the central axis of the aforementioned cylinder bore (e.g., central axis J1 described later).

[0014] (2) Optionally, in the engine described in (1) above, a circumferential groove (e.g., circumferential groove 223 described later) is provided at the end periphery of the piston sliding space side in the aforementioned cylinder bore. When the piston is inserted into the aforementioned cylinder bore, the circumferential groove can engage with a cylindrical clamp (e.g., cylindrical clamp 33 described later) mounted on the outer periphery of the aforementioned piston.

[0015] (3) Optionally, in the engine described in (1) or (2) above, the engine may be a multi-cylinder opposed engine, wherein the aforementioned crankcases of the engine block half (e.g., engine block half 2, 2A described later) which integrates the aforementioned cylinder block and the aforementioned crankcase are connected to each other, and the aforementioned pistons are arranged opposite to each other.

[0016] (4) Optionally, in any one of the engines described in (1) to (3) above, a cylinder head (e.g., cylinder head 21 described later) is provided on the opposite side of the crankcase relative to the cylinder block, and the cylinder head is integrated with the cylinder block.

[0017] (5) The present invention provides an assembly method for an engine (e.g., engine 1 described later), the engine comprising: a cylinder block (e.g., cylinder block 22 described later) having a cylinder bore (e.g., cylinder bore 221 described later) for internally accommodating a piston (e.g., piston 3 described later); and a crankcase (e.g., crankcase 23 described later), integrated with the aforementioned cylinder block, and having a crank bearing (e.g., crank bearing 232 described later); and the aforementioned crank bearing being configured to overlap the extension line of the aforementioned cylinder bore; the aforementioned crankcase having a piston sliding space (e.g., piston sliding space 233 described later), the piston sliding space cutting off the aforementioned crank bearing from the aforementioned cylinder bore side, thereby enabling the central axis of the aforementioned piston (e.g., central axis J2 described later) and the central axis of the aforementioned cylinder bore (e.g., central axis described later) to be aligned. In the J1) aligned state, the aforementioned piston is received, and the end of the aforementioned piston sliding space side in the aforementioned cylinder bore has a circumferential groove (e.g., circumferential groove 223 described later). The aforementioned piston is inserted from the aforementioned crankcase side into the aforementioned cylinder bore of the aforementioned cylinder body. The assembly method includes the following steps: a cylindrical clamp (e.g., cylindrical clamp 33 described later) that can fit with the aforementioned circumferential groove is installed on the outer periphery of the aforementioned piston; the aforementioned piston with the aforementioned cylindrical clamp installed is received from the aforementioned crankcase side into the aforementioned piston sliding space; the aforementioned cylindrical clamp is fitted with the aforementioned circumferential groove, thereby aligning the central axis of the aforementioned piston with the central axis of the aforementioned cylinder bore in the aforementioned piston sliding space; and, in the state where the aforementioned cylindrical clamp is fitted with the aforementioned circumferential groove, the aforementioned piston is slid inside the aforementioned cylindrical clamp and inserted into the aforementioned cylinder bore.

[0018] (The effect of the invention)

[0019] According to (1) above, since the crankcase has a piston sliding space that can accommodate the piston when the piston's central axis is aligned with the cylinder bore's central axis, the piston can be inserted into the cylinder bore from the crankcase side using this piston sliding space. Therefore, an engine that improves piston assembly workability can be provided.

[0020] According to (2) above, an engine can be provided in which the central axis of the piston can be easily aligned with the central axis of the cylinder bore by fitting a cylindrical clamp mounted on the outer periphery of the piston into the circumferential groove of the cylinder bore. Therefore, the workability of inserting the piston into the cylinder bore from the crankcase side is good, and the workability of piston assembly is further improved.

[0021] Based on (3) above, it is possible to provide a multi-cylinder opposed engine with improved piston assembly workability.

[0022] According to (4) above, the cylinder head and cylinder block are integrated, thereby reducing the number of parts in the engine block and reducing the cost of the engine.

[0023] According to (5) above, by fitting the tip of the cylindrical clamp into the circumferential groove of the cylinder bore within the piston sliding space of the crankcase, the central axis of the piston can be easily aligned with the central axis of the cylinder bore, and the piston can be inserted into the cylinder bore in this state. Therefore, the workability of inserting the piston into the cylinder bore from the crankcase side is good, and the assembly workability of the piston can be improved. Attached Figure Description

[0024] Figure 1 This is a perspective view of the engine in this embodiment.

[0025] Figure 2 This is a perspective view illustrating the engine block half of the engine according to this embodiment.

[0026] Figure 3 yes Figure 2 The image shows a side cross-sectional view of the engine block half.

[0027] Figure 4 yes Figure 3 An enlarged view of part A in the image.

[0028] Figure 5 This is a bottom view illustrating the situation where the piston of the engine of this embodiment is inserted into the cylinder bore.

[0029] Figure 6 This is a side cross-sectional view illustrating the insertion of the piston of the engine of this embodiment into the cylinder bore.

[0030] Figure 7 This is a perspective view illustrating the connection of the engine block halves of the engine in this embodiment to each other.

[0031] Figure 8 This is a perspective view illustrating an engine according to another embodiment, in which a cylindrical clamp is mounted on the piston.

[0032] Figure 9 It is a three-dimensional view of a piston fitted with a cylindrical clamp.

[0033] Figure 10 This is a side cross-sectional view of the engine block half of an engine according to another embodiment.

[0034] Figure 11 This is a side cross-sectional view illustrating an engine according to another embodiment, in which a piston fitted with a cylindrical clamp is inserted into the cylinder bore.

[0035] Figure 12 This is a perspective view illustrating the removal of a cylindrical clamp from an engine in another embodiment. Detailed Implementation

[0036] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Figure 1 This is a perspective view of the engine according to this embodiment. Engine 1 is a multi-cylinder opposed engine, configured such that engine block halves 2,2, each having two cylinder bores 221 for receiving pistons 3, are integrally assembled on the crankcase 23 side. Engine 1 of this embodiment has four cylinders. However, the number of cylinders in the engine is not limited to four, and the cylinder configuration is not limited to a configuration with opposing cylinders. Furthermore, since the two engine block halves 2,2 of engine 1 are actually identical in structure, the following description of the internal structure will refer only to one engine block halves 2.

[0037] like Figure 2 and Figure 3 As shown, the engine block half 2 is a one-piece molded product, having a structure that integrates the cylinder head 21, cylinder block 22, and crankcase 23. This engine block half 2 can be manufactured using metal materials such as aluminum (powder metal, metal wire, etc.) and employs a layered molding method.

[0038] In additive manufacturing using a 3D printer, for example, when using powdered metal as the metal material, the engine block half 2 is three-dimensionally stacked by repeatedly performing the following steps: melting and solidifying the shaped portion by irradiating the powdered metal dispersed on a substrate with a laser or electron beam as a heat source; and moving the substrate to disperse new powdered metal. According to additive manufacturing, even for engine block half 2 with a complex shape including a cylinder head 21, cylinder block 22, and crankcase 23, the entire engine block half 2 can be easily integrally molded using a 3D printer. However, the engine block half 2 of the engine 1 is not limited to being stacked using additive manufacturing.

[0039] like Figure 3 As shown, the engine block half 2 has two cylinder bores 221, 221 arranged side by side. The cylinder head 21 has an intake port 211 and an exhaust port 212 that communicate with the cylinder bores 221, 221 respectively. Therefore, as described in detail later, the piston 3 cannot be inserted into the cylinder bores 221, 221 from the side of the cylinder head 21.

[0040] The cylinder block 22 integrally has a water jacket 24 on the outside of the cylinder liner 222 that forms the cylinder bore 221. The water jacket 24 is formed from the cylinder block 22 to the cylinder head 21. The water jacket 24 uses coolant flowing in from the coolant inlet 241 to cool the area around the intake port 211 and exhaust port 212 of the cylinder head 21, as well as the area around the cylinder bore 221 of the cylinder block 22. The cooled coolant is discharged to the outside (e.g., radiator, etc.) from the coolant outlet 242.

[0041] The crankcase 23 is located on the opposite side of the cylinder head 21 relative to the cylinder block 22. A crankshaft housing 231 is formed inside the crankcase 23. The crankshaft housing 231 is the crankshaft 5 (see reference). Figure 7 The housing space contains the connecting rod 4 (refer to) that is connected to the piston 3. Figure 7 and Figure 9 One end of the crankshaft housing 231 is simultaneously connected to the two cylinder bores 221, 221 of the cylinder block 22.

[0042] The crankcase 23 has a plurality of crank bearings 232 located close to the cylinder bores 221, 221 of the cylinder block 22. The crank bearings 232 rotatably support the crankshaft 5 (see reference) housed within the crankshaft housing 231. Figure 7 Journal 51 (refer to) Figure 7 In this embodiment, three crank bearings 232 are provided on the crankcase 23 of one engine block half 2.

[0043] like Figure 3 , Figure 4 and Figure 5 As shown, three crank bearings 232 are arranged along the X direction of the parallel cylinder bores 221, 221 in the engine block half 2, and are positioned to clamp the cylinder bore 221 when viewed from the crankcase 23 side. The two crank bearings 232, 232 adjacent to each other on the left and right sides of the figure are arranged to overlap the extension lines of the cylinder bores 221, 221. That is, when the cylindrical cylinder bores 221, 221 extend towards the crankcase 23, the cylinder bores 221, 221 interfere with the aforementioned crank bearings 232, 232. Therefore, when the piston 3 is inserted from the crankcase 23 side into the cylinder bore 221, the aforementioned crank bearings 232, 232 become obstructions, and thus the piston 3 cannot be coaxially positioned below the cylinder bore 221 within the crankcase 23.

[0044] Therefore, in this embodiment, the crankcase 23 is designed to allow the piston 3 to be coaxially positioned below the cylinder bore 221, such as... Figure 3 and Figure 4As shown, piston sliding spaces 233 and 233, which can accommodate piston 3, are respectively provided below cylinder bores 221 and 221 in crankcase 23. The piston sliding spaces 233 and 233 are provided with cutouts 232a and 232a cut off from the cylinder bores 221 and 221 respectively on the crank bearings 232 and 232 arranged to overlap the extension lines of cylinder bores 221 and 221, thereby forming a continuous connection with the lower ends of cylinder bores 221 and 221.

[0045] like Figure 4 As shown, the height h1 of the piston sliding space 233 is at the axial height h2 of the cylindrical portion 31 of the piston 3 (see reference). Figure 6 The piston sliding space 233, due to the cylinder bore, allows the entire cylindrical portion 31 of the piston 3 to be housed within the piston sliding space 233 while the central axis J2 of the piston 3 is aligned with the central axis J1 of the cylinder bore 221.

[0046] Next, use Figure 5 , Figure 6 and Figure 7 The method of assembling engine 1 by inserting piston 3 into cylinder bore 221 from crankcase 23 side will be described.

[0047] like Figure 6 As shown, the piston 3 has a cylindrical portion 31 that constitutes the portion with the largest outer diameter in the piston 3. The cylindrical portion 31 has a plurality of piston rings 32, which are received within a plurality of grooves formed on the outer circumferential surface. Furthermore, in Figure 5 and Figure 6 In the text, the connection between piston 3 and crankshaft 5 (see reference) is omitted. Figure 7 Link 4 connecting the two (refer to) Figure 7 The illustration is shown.

[0048] like Figure 5 and Figure 6 As shown, piston 3 is inserted into cylinder bore 221 from the crankshaft housing 23 side of crankcase 23 (P1). At this time, piston 3 is inserted to a position that avoids the overlapping crank bearing 232. Thus, the central axis J2 of piston 3 is positioned away from the crank bearing 232 relative to the central axis J1 of cylinder bore 221.

[0049] Since the piston sliding space 233 can accommodate the entire cylindrical portion 31 of the piston 3, when the piston 3 is inserted into the piston sliding space 233, the piston 3 slides laterally toward the overlapping crank bearing 232 so that the central axis J2 is aligned with the central axis J1 of the cylinder bore 221 (P2).

[0050] Then, piston 3 is pushed upward toward cylinder bore 221 (P3) and housed within cylinder bore 221.

[0051] After inserting pistons 3 and 3 into the two cylinder bores 221 and 221 of one of the engine block halves 2, as follows: Figure 7 As shown, the remaining two pistons 3,3, connected by connecting rod 4 and crankshaft 5, are inserted into the two cylinder bores 221, 221 of the other engine block half 2 in the same manner as described above. Then, the two engine block half 2,2 are assembled as a single unit by connecting crankcases 23, 23 to each other.

[0052] Furthermore, as described above, when inserting the piston 3 from the crankcase 23 side into the cylinder bore 221, the central axis J2 of the piston 3 needs to be aligned with the central axis J1 of the cylinder bore 221 within the piston sliding space 233. However, since the tip of the cylindrical portion 31 of the piston 3 is difficult to see directly, the operation of aligning the central axes J1 and J2 requires skilled operation.

[0053] Therefore, refer to Figures 8-12 Another embodiment of the engine 1, in which the central axis J2 of the piston 3 can be easily aligned with the central axis J1 of the cylinder bore 221, will be described. Figures 8-12 In the text, parts marked with the same symbols as in the above embodiments indicate parts with the same structure. Detailed descriptions refer to the descriptions of the above embodiments, and some parts may be omitted in the following description.

[0054] First, before inserting piston 3 into cylinder bore 221, as follows Figure 8 and Figure 9 As shown, a cylindrical clamp 33 is installed on the outer periphery of the cylindrical portion 31 of the piston 3, on which the piston ring 32 is mounted. The cylindrical clamp 33 is composed of two clamp halves 331, 331, which are each formed as a semicircular arc corresponding to half of the outer periphery of the cylindrical portion 31, i.e., a range of 180°. The clamp halves 331 have mounting portions 332, 332 that bulge outward from both ends. The two clamp halves 331, 331 are combined to form a circle to clamp the cylindrical portion 31, and are mounted on the entire circumference of the cylindrical portion 31 by making their mounting portions 332, 332 adjacent to each other. The outer diameter of the cylindrical clamp 33 mounted on the cylindrical portion 31 is larger than the inner diameter of the cylinder bore 221. The adjacent mounting portions 332, 332 are fixed to each other by clamps or other fixing fixtures (not shown).

[0055] The piston ring 32, which is disposed on the outer periphery of the cylindrical portion 31 of the piston 3, protrudes slightly from the outer peripheral surface of the cylindrical portion 31 in order to slide on the inner wall surface of the cylinder bore 221. The cylindrical clamp 33, which is mounted on the outer periphery of the cylindrical portion 31, compresses the piston ring 32 radially inward so that the outer diameter of the piston ring 32 is approximately aligned with the outer diameter of the cylindrical portion 31.

[0056] like Figure 8As shown, each clamp half 331, 331 of the cylindrical clamp 33 has a segment 333, 333 at its tip on the travel direction side when inserted into the cylinder bore 221. The clamp half 331, 331 are assembled into a circle, and the segment 333 is provided around the entire circumference of the cylindrical clamp 33. The segment 333 is formed into a tapered shape with its diameter gradually decreasing towards the tip. When the cylindrical clamp 33 is mounted on the cylindrical portion 31 of the piston 3, the segment 333 protrudes upward from the upper end face 31a of the cylindrical portion 31 and is coaxially arranged with the cylindrical portion 31.

[0057] Figure 10 An engine block half 2A according to another embodiment is illustrated. Circumferential grooves 23 and 223, respectively, for fitting a cylindrical clamp 33, are pre-formed on the cylinder bores 221 and 221 of the engine block half 2A. The circumferential grooves 223 are disposed at the lower end of the cylinder bore 221 adjacent to the piston sliding space 233 of the crankcase 23, and are provided around the entire circumference of the inner periphery of the cylinder bore 221. The circumferential grooves 223 have a tapered shape, which expands towards the piston sliding space 23 and aligns with the tapered shape of the segment 333 of the cylindrical clamp 33.

[0058] like Figure 11 As shown, the piston 3, equipped with the cylindrical clamp 33, is received in the piston sliding space 233 from the crankcase 23 side. At this time, the mounting portions 332, 332 of the cylindrical clamp 33 are arranged in a direction orthogonal to the arrangement direction X of the cylinder bores 221, 221. Therefore, the mounting portions 332, 332 of the cylindrical clamp 33 will not interfere with the crank bearing 232 of the crankcase 23. Furthermore, the piston sliding space 233 has a size that can accommodate the entire cylindrical portion 31 of the piston 3 in the state where the cylindrical clamp 33 is installed.

[0059] Subsequently, as described above, piston 3 slides laterally within piston sliding space 233. During this sliding movement, piston 3 is pressed in and moved by the segment 333 of cylindrical clamp 33 abutting against the periphery of the lower end of cylinder bore 221. Therefore, if the position of segment 333 coincides with the position of circumferential groove 223, cylindrical clamp 33 is guided by segment 333 into a conical shape within circumferential groove 223 and engages with it. Thus, the central axis J2 of piston 3... Figure 11 (Not shown in the diagram) and the central axis J1 of cylinder bore 221 ( Figure 11 Alignment (not shown in the image).

[0060] Subsequently, with the cylindrical clamp 33 engaged with the circumferential groove 223, the piston 3 is pushed upward toward the cylinder bore 221. Since the outer diameter of the cylindrical clamp 33 is larger than the inner diameter of the cylinder bore 221, when the piston 3 is pushed upward, the lower end of the cylindrical clamp 33 remains in contact with the cylinder bore 221, and only the cylindrical portion 31 of the piston 3 slides inside the cylindrical clamp 33 and is inserted into the cylinder bore 221. Thus, the piston 3 is inserted into the cylinder bore 221 with its central axis J2 reliably aligned with the central axis J1 of the cylinder bore 221. Because the segment 333 of the cylindrical clamp 33 mounted on the piston 3 engages with the circumferential groove 223 of the cylinder bore 221, the central axes J1 and J2 are naturally aligned with each other; therefore, skilled operator practice is not required.

[0061] like Figure 12 As shown, after all pistons 3 are inserted into cylinder bores 221 and the two engine block halves 2A, 2A are assembled into one unit, the cylindrical clamp 33 is removed outward from the openings 234, 234 on the sides of each crankcase 23, 23. Alternatively, the cylindrical clamp 33 can be removed outward from the openings 234 of each engine block half 2A before the two engine block halves 2A, 2A are assembled into one unit.

[0062] The engine 1 according to the above embodiments achieves the following effects. Specifically, the engine 1 includes: a cylinder block 22 having a cylinder bore 221 that internally houses a piston 3; and a crankcase 23 integral with the cylinder block 22 and having a crank bearing 232 arranged to overlap the extension line of the cylinder bore 221. The crankcase 23 has a piston sliding space 233, which, by cutting the crank bearing 232 from the cylinder bore 221 side, allows the piston 3 to be housed with its central axis J2 aligned with the central axis J1 of the cylinder bore 221. Therefore, since the crankcase 23 has a piston sliding space 233 that allows the piston 3 to be housed with its central axis J2 aligned with the central axis J1 of the cylinder bore 221, the piston 3 can be inserted from the crankcase 23 side into the cylinder bore 221 using this piston sliding space 233. Thus, the assembly workability of the piston 3 is improved.

[0063] The engine 1 shown in the above embodiment has a circumferential groove 223 on the periphery of the piston sliding space 233 side in the cylinder bore 221. The circumferential groove 223 can engage with a cylindrical clamp 33 mounted on the outer periphery of the piston 3 when the piston 3 is inserted into the cylinder bore 221. Accordingly, by engaging the cylindrical clamp 33 mounted on the outer periphery of the piston 3 with the circumferential groove 223 of the cylinder bore 221, the central axis J2 of the piston 3 can be easily aligned with the central axis J1 of the cylinder bore 221. Therefore, the workability of inserting the piston 3 into the cylinder bore 221 from the crankcase 23 side is good, and an engine 1 with further improved piston 3 assembly workability can be provided.

[0064] The engine 1 shown in the above embodiment is a multi-cylinder opposed engine. The crankcases 23, 23 of the engine block half 2, 2A, which integrate the cylinder block 22 and the crankcase 23, are connected to each other, and the pistons 3 are arranged opposite each other. Accordingly, a multi-cylinder opposed engine with improved piston 3 assembly workability can be provided.

[0065] The engine 1 shown in the above embodiment has a cylinder head 21 on the opposite side of the cylinder block 22 from the crankcase 23, and the cylinder head 21 is integrated with the cylinder block 22. By integrating the cylinder head 21 with the cylinder block 22, the number of parts in the engine block half 2,2A can be reduced, and the cost of the engine 1 can be reduced.

[0066] The engine 1 assembly method shown in the above embodiments includes: a cylinder block 22 having a cylinder bore 221 that houses a piston 3; and a crankcase 23 integrated with the cylinder block 22 and having a crank bearing 232 arranged to overlap the extension line of the cylinder bore 221. The crankcase 23 has a piston sliding space 233, which can accommodate the piston 3 with the central axis J2 of the piston 3 aligned with the central axis J1 of the cylinder bore 221 by cutting the crank bearing 232 from the cylinder bore 221 side. The piston sliding space 233 side end in the cylinder bore 221 has a circumferential groove 223, and the piston 3 is inserted into the cylinder bore 221 of the cylinder block 22 from the crankcase 23 side. The assembly method includes the following steps: a cylindrical clamp 33 that can engage with the circumferential groove 223 is installed on the outer periphery of the piston 3; the piston 3 with the cylindrical clamp 33 installed is received from the crankcase 23 side into the piston sliding space 233; by engaging the cylindrical clamp 33 with the circumferential groove 223, the central axis J2 of the piston 3 is aligned with the central axis J1 of the cylinder bore 221 in the piston sliding space 233; and, with the cylindrical clamp 33 engaged with the circumferential groove 223, the piston 3 is slid inside the cylindrical clamp 33 and inserted into the cylinder bore 221. Accordingly, within the piston sliding space 233 of the crankcase 23, by engaging the tip of the cylindrical clamp 33 with the circumferential groove 223 of the cylinder bore 221, the central axis J2 of the piston 3 can be easily aligned with the central axis J1 of the cylinder bore 221, and the piston 3 can be inserted into the cylinder bore 221 in this state. Therefore, the workability of inserting the piston 3 into the cylinder bore 221 from the crankcase 23 side is good, and the assembly workability of the piston 3 is improved.

[0067] Figure Labels

[0068] 1. Engine

[0069] 2.2A Engine Block Half

[0070] 21 Cylinder head

[0071] 22 cylinder block

[0072] 221 Cylinder bore

[0073] 223 Circumferential Groove

[0074] 23 Crankcase

[0075] 232 Crank Bearing

[0076] 233 Piston sliding space

[0077] 3 Pistons

[0078] 33 Cylindrical clamp

[0079] J1 Cylinder Bore Center Axis

[0080] J2 piston center axis

Claims

1. An engine comprising: a cylinder block having a cylinder bore internally receiving a piston; and a crankcase integral with the cylinder block and having a crankshaft bearing; the engine being characterized in that... Furthermore, the aforementioned crank bearing is configured to overlap the extension line of the aforementioned cylinder bore, and the surface of the aforementioned cylinder bore side at the aforementioned overlapping portion has a cut-out portion cut off from the aforementioned cylinder bore side. The aforementioned crankcase has a piston sliding space formed by the aforementioned cutout on the aforementioned crank bearing, which can accommodate the aforementioned piston while the central axis of the aforementioned piston is aligned with the central axis of the aforementioned cylinder bore.

2. The engine according to claim 1, wherein, The piston sliding space side of the aforementioned cylinder bore has a circumferential groove at its end periphery. When the piston is inserted into the aforementioned cylinder bore, the circumferential groove can engage with a cylindrical clamp mounted on the outer periphery of the aforementioned piston.

3. The engine according to claim 1 or 2, wherein, The engine is a multi-cylinder opposed engine, wherein the aforementioned crankcase of the engine block half, which is an integrated cylinder block and crankcase, is connected to each other, and the aforementioned pistons are arranged opposite to each other.

4. The engine according to any one of claims 1 to 3, wherein, The cylinder head is located on the opposite side of the aforementioned crankcase, relative to the aforementioned cylinder block. The aforementioned cylinder head and the aforementioned cylinder block are integrated.

5. The engine according to claim 1 or 2, wherein, The aforementioned piston sliding space is a space capable of accommodating the aforementioned piston and allowing the aforementioned piston to slide in a direction intersecting with the aforementioned central axis of the piston, so that the state in which the central axis of the aforementioned piston is misaligned with the central axis of the aforementioned cylinder bore is changed to the state in which the aforementioned central axis of the aforementioned piston is aligned with the aforementioned central axis of the aforementioned cylinder bore.

6. A method for assembling an engine, the engine comprising: a cylinder block having a cylinder bore internally receiving a piston; and a crankcase integral with the cylinder block and having a crank bearing; Furthermore, the aforementioned crank bearing is configured to overlap the extension line of the aforementioned cylinder bore, and the surface of the aforementioned cylinder bore side at the aforementioned overlapping portion has a cut-out portion cut off from the aforementioned cylinder bore side. The aforementioned crankcase is provided with a piston sliding space, which is formed by the aforementioned cutout portion of the aforementioned crank bearing. This piston sliding space is capable of accommodating the aforementioned piston and allows the aforementioned piston to slide in a direction intersecting with the central axis of the piston, so that the state in which the central axis of the aforementioned piston is misaligned with the central axis of the aforementioned cylinder bore changes to a state in which the central axis of the aforementioned piston is aligned with the central axis of the aforementioned cylinder bore. The piston has a circumferential groove at its end on the sliding space side in the aforementioned cylinder bore, and the piston is inserted from the crankcase side into the aforementioned cylinder bore of the aforementioned cylinder block. The assembly method is characterized by the following steps: A cylindrical clamp that can fit into the aforementioned circumferential groove is installed on the outer periphery of the aforementioned piston; The piston, which is equipped with the aforementioned cylindrical clamp, is received from the aforementioned crankcase side into the aforementioned piston sliding space; The aforementioned cylindrical clamp is fitted into the aforementioned circumferential groove, thereby aligning the central axis of the aforementioned piston with the central axis of the aforementioned cylinder bore within the aforementioned piston sliding space; and, With the aforementioned cylindrical clamp engaged with the aforementioned circumferential groove, the aforementioned piston slides inside the aforementioned cylindrical clamp and is inserted into the aforementioned cylinder bore.

7. The engine assembly method as described in claim 6, wherein, The aforementioned crankcase has an opening on the side. After the piston is inserted into the cylinder bore, the cylindrical clamp is removed from the opening.

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