JP2008138607A - Stroke characteristic variable engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve mounting rigidity of an actuator to an engine body, in a stroke characteristic variable engine allowing a moving stroke of a piston to be varied by connecting a piston and a crank shaft to a control shaft through a stroke variable link mechanism, and operating the stroke variable link mechanism by driving the control shaft by an actuator. <P>SOLUTION: A housing HU of the actuator AC is fastened to high-rigidity bearing walls 50a and 52a cast in crank bearing members 50 and 52 supporting the crank shaft 30 by fastening members 56. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an improvement in a stroke characteristic variable engine, in particular, a control shaft for operating a variable stroke link mechanism driven by an actuator.

Conventionally, the piston and crankshaft are connected to the control shaft via a variable stroke link mechanism, and this control shaft is driven by an actuator to operate the variable stroke link mechanism to change the moving stroke of the piston. Variable engines are known. (Refer to Patent Documents below.)
JP 2002-47955 A

  By the way, in such a conventional variable stroke characteristic engine, an actuator that operates the variable stroke mechanism is attached to the crankcase. However, since the actuator includes a drive source such as a motor, The weight and bulk are large, especially when the input load to the actuator is large, the actuator is inevitably increased in weight and size. If it is attached to the crankcase as before, the actuator In order to eliminate this possibility, there is a problem that the crankcase needs to be reinforced, which increases the weight, size, and cost of the engine body itself.

  The present invention has been made in view of such circumstances, and provides a novel variable stroke characteristic engine in which the attachment rigidity is increased by attaching the actuator using a highly rigid member of the engine body. With the goal.

In order to achieve the above object, according to the first aspect of the present invention, a piston and a crankshaft are connected to a control shaft via a stroke variable link mechanism, and the control shaft is driven by an actuator to operate the variable stroke link mechanism. In a variable stroke characteristic engine that operates and makes the moving stroke of the piston variable,
The housing of the actuator is attached to a crank bearing member that supports a crankshaft.

  To achieve the above object, according to a second aspect of the present invention, in the first aspect of the present invention, the actuator housing is mounted across the plurality of crank bearing members. .

  In order to achieve the above object, according to a third aspect of the present invention, in the first or second aspect of the present invention, the crank bearing member is formed integrally with a lower block constituting the engine main body, and more than the lower block. A highly rigid and highly rigid bearing wall is cast, and the housing of the actuator is supported by the lower block by a fastening member fastened to the highly rigid bearing wall.

  To achieve the above object, according to a fourth aspect of the present invention, the actuator housing and the high-rigidity bearing wall according to the third aspect are fastened together with the crank bearing member by the fastening member. It is characterized by that.

  According to the first aspect of the invention, since the housing of the actuator is attached to a highly rigid crank bearing member that supports the crankshaft, the attachment rigidity of the actuator is greatly improved.

  According to the invention of claim 2, since the actuator housing is mounted across a plurality of highly rigid crank bearing members, the mounting rigidity of the actuator is further improved, and the actuator housing includes a plurality of housings. It acts as a connecting member for connecting the crank bearing member, and the support rigidity of the crankshaft is also improved.

  Further, according to the invention of claim 3, the crank bearing member is formed integrally with the lower block constituting the engine body, and a high-rigidity bearing wall having higher rigidity than the lower block is cast, Since the housing of the actuator is supported by the lower block by the fastening member fastened to the high-rigidity bearing wall, the fastening rigidity of the actuator to the engine body is greatly improved, and the mounting rigidity of the actuator and the rigidity of the lower block are increased. Both improve.

  Furthermore, according to the invention of claim 4, since the housing of the actuator and the high-rigidity bearing wall are fastened together with the crank bearing member by the fastening member, the fastening rigidity of the actuator to the lower block is increased. In addition to the improvement, the number of fastening members can be reduced to reduce the number of parts, and further the increase in size in the direction crossing the crankshaft of the engine body can be suppressed.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be specifically described below based on examples of the present invention shown in the accompanying drawings.

  First, a first embodiment of the present invention will be described with reference to FIGS.

  1 is a schematic overall perspective view of a variable stroke characteristic engine, FIG. 2 is a view taken in the direction of arrow 2 in FIG. 1, FIG. 3 is a cross-sectional view taken along line 3-3 in FIG. 1 is a sectional view taken along line 4-4 in FIG. 1 (low compression ratio state), FIG. 5 is a sectional view taken along line 5-5 in FIG. 2, and FIG. 6 is a sectional view taken along line 6-6 in FIG. 7 is an enlarged vertical view taken along line 7-7 in FIG. 5, and FIG. 8 is a cross-sectional view taken along line 8-8 in FIG.

  1 to 4, a variable stroke characteristic engine E according to the present invention is for an automobile and is placed horizontally in an engine room of an automobile (not shown) (the crankshaft 30 is arranged laterally with respect to the traveling direction of the automobile). ). When the engine E is mounted on a vehicle, as shown in FIG. 2, the cylinder is slightly tilted backward, that is, its cylinder axis LL is slightly tilted backward with respect to the vertical line V-V.

  The variable stroke characteristic engine E is an in-line four-cylinder OHC type four-cycle engine. The engine body 1 includes a cylinder block 2 in which four cylinders 5 are provided in parallel in the lateral direction, and the cylinder block. The cylinder head 3 is integrally coupled to the two deck surfaces via the gasket 6, the upper block 40 (upper crankcase) is integrally formed at the lower portion of the cylinder block 2, and is integrally coupled to the lower surface thereof. The lower block 41 (lower crankcase) is provided, and the crankcase 4 is formed by the upper block 40 and the lower block 41. A head cover 9 is integrally crowned on the upper surface of the cylinder head 3 via a sealing material 8, and an oil pan 10 is integrally coupled to the lower surface of the lower block 41 (lower crankcase). .

  Pistons 11 are slidably fitted to the four cylinders 5 of the cylinder block 2, and four combustion chambers 12 are provided on the lower surface of the cylinder head 3 facing the top surfaces of the pistons 11. An intake port 14 and an exhaust port 15 communicating with those combustion chambers 12 are formed. An intake valve 16 is provided in the intake port 14 and an exhaust valve 17 is provided in the exhaust port 15 so as to be opened and closed. On the cylinder head 3, a valve operating mechanism 18 for opening and closing the intake valve 16 and the exhaust valve 17 is provided. The valve mechanism 18 swings on an intake side cam shaft 20 and an exhaust side cam shaft 21 that are rotatably supported by the cylinder head 3, and on an intake side and exhaust side rocker shafts 22, 23 provided on the cylinder head 3. The intake side and exhaust side camshafts 20 and 21 and the intake side and exhaust side rocker arms 24 and 25 connected to the intake valve 16 and the exhaust valve 17 so as to be pivotally supported are provided. According to the rotation of the shafts 20 and 21, the intake side and exhaust side rocker arms 24 and 25 are swung against the valve closing force of the valve springs 26 and 27 to open and close the intake valve 16 and the exhaust valve 17 at a predetermined timing. Can be operated.

  As shown in FIG. 2, the intake-side and exhaust-side camshafts 20, 21 are interlocked with a crankshaft 30 described later via a conventionally known timing transmission mechanism 28, and according to the rotation of the crankshaft 30, It is driven at half the rotational speed. The valve mechanism 18 is covered with a head cover 9 that is integrally crowned on the cylinder head 3. The cylinder head 3 is provided with a cylindrical plug insertion cylinder 31 corresponding to the four cylinders, and a spark plug 32 is inserted into the plug insertion cylinder 31.

  The timing transmission mechanism 28 is covered with a chain case 29 that is fixed to the end surface of the engine body 1 in the crankshaft direction. The plurality of intake ports 14 corresponding to the four cylinders 5 are opened toward the front surface of the engine body 1, that is, the front side of the vehicle, and an intake manifold 34 of the intake system IN is connected thereto. Since the intake system IN has a conventionally known structure, a detailed description thereof will be omitted.

  A plurality of exhaust ports 15 corresponding to the four cylinders 5 are opened toward the rear surface of the engine body 1, that is, toward the rear side of the vehicle, and an exhaust manifold 35 of the exhaust system EX is connected thereto. Since the exhaust system EX has a conventionally known structure, a detailed description thereof is omitted.

  As shown in FIGS. 3 and 4, the crankcase 4 including the upper block 40 (upper crankcase) at the lower part of the cylinder block 2 and the lower block 41 (lower crankcase) is more forward than the cylinder 5 part of the cylinder block 2. A projecting variable link mechanism LV (described later) is provided in the crank chamber CC of the projecting portion 36 so as to make the moving stroke of the piston 11 variable. The front surface 90 is provided with an actuator AC that drives the front surface 90, and this actuator AC is disposed below the crankshaft 30.

  As shown in FIGS. 3 to 5 and FIG. 8, a lower block 41 is fixed to the lower surface of the upper block 40 formed integrally with the lower portion of the cylinder block 2 with a plurality of connecting bolts 42. The journal shaft 30J of the crankshaft 30 is rotatably supported by a plurality of journal bearing portions 43 formed on the mating surfaces of the upper block 40 and the lower block 41 (see FIG. 8).

  As shown in FIG. 5, the lower block 41 is cast and molded into a closed cross-sectional structure having a square shape in plan view. End crank bearing members 50 and 51 are provided at the left and right ends, and an intermediate portion thereof is provided. The left and right intermediate crank bearing members 52 and 53 are further provided with a central crank bearing member 54 at the center thereof, and the journal shaft 30J of the crankshaft 30 is rotatably supported by these crank bearing members 50 to 54. Is done.

  Next, referring back to FIGS. 3 and 4, the structure of the variable stroke link mechanism LV that changes the compression ratio between the high compression ratio and the low compression ratio by changing the top dead center / bottom dead center positions of the piston 11. More specifically, as described above, the intermediate portions of the triangular lower link 60 swing on the plurality of crank pins 30P of the crankshaft 30 rotatably supported on the mating surfaces of the upper block 40 and the lower block 41, respectively. It is freely pivotally connected. One end (upper end) of the lower link 60 is pivotally connected to the lower end (large end) of an upper link (connecting rod) 61 pivotally connected to the piston pin 13 of the piston 11 via a first connecting pin 62. The upper end of the control link 63 is pivotally connected to the other end (lower end) of each lower link 60 via the second connecting pin 64. The control link 63 extends downward, and an eccentric pin 65P of a crank-shaped control shaft 65 (detailed later) is pivotally connected to the lower end of the control link 63. An actuator AC fixed to the lower front surface of the engine body 1 is linked to and connected to the control shaft 65, and the control shaft 65 is driven to swing within a predetermined angle range by driving the actuator AC. The control link 63 is driven to swing by the phase shift of the eccentric pin 65P. Specifically, the control shaft 65 swings between a first position shown in FIG. 3 (the eccentric pin 65P is a lower position) and a second position shown in FIG. 4 (the eccentric pin 65P is an upper position). Is possible. In the first position shown in FIG. 3, the eccentric pin 65P of the control shaft 66 is positioned below, so that the control link 63 is pulled down and the lower link 60 swings clockwise around the crank pin 30P of the crankshaft 30. As a result, the upper link 61 is pushed up, and the position of the piston 11 becomes higher than the cylinder 5, and the engine E enters a high compression ratio state. Further, in the second position shown in FIG. 4, since the eccentric pin 65P of the control shaft 65 is positioned upward (higher than the first position), the control link 63 is pushed up and the lower link 60 is cranked. The shaft 30 swings around the crank pin 30P in the counterclockwise direction, the upper link 61 is pushed down, the position of the piston 11 becomes lower than the cylinder 5, and the engine E enters a low compression ratio state. As described above, by the rotation control of the control shaft 65 by a predetermined angle, the control link 63 is swung, the motion constraint condition of the lower link 60 is changed, and the stroke characteristics including the top dead center position of the piston 11 are changed. Thus, it becomes possible to arbitrarily control the compression ratio of the engine E.

  Thus, the above-described upper link 61, the first connecting pin 62, the lower link 60, the second connecting pin 64, and the control link 63 constitute a variable stroke link mechanism LV.

  As shown in FIGS. 6 and 7, the control shaft 65, which is connected to the control link 63 and operates the variable stroke link mechanism LV, is similar to the crankshaft 30, and a plurality of journal shafts 65J and eccentric pins 65P connect the arm 65A. Are connected to each other through a crank shape. The control shaft 65 is connected to an actuator AC at one end, and is reciprocated within a predetermined angle range by the actuator AC. The control shaft 65 is arranged in parallel with the crankshaft 30, and is freely rotatable between the lower block 41 and a bearing block 70 fixed to the lower surface of the crankshaft 30 by a plurality of connecting bolts 68. It is supported by.

  The bearing block 70 that supports the control shaft 65 includes a connecting member 71 that extends in the axial direction of the control shaft 65 and a plurality of bearing walls that are connected to the connecting member 71 in an upright manner at intervals in the longitudinal direction. 72 and is cast and formed in a block shape to ensure high rigidity, and is formed on the mating surface of the upper surfaces of the plurality of bearing walls 72 and the lower surfaces of the crank bearing members 50 to 54 of the lower block 40. A plurality of journal shafts 65J of the control shaft 65 are rotatably supported by the bearing portions via surface bearings.

  As shown in FIGS. 5 and 6, among the plurality of crank bearing members 50 to 54 of the lower block 41, the adjacent end crank bearing member 50 and intermediate crank bearing member 52 have high-rigidity bearing walls 50 a and 52 a. It is integrally formed by casting, and uneven surfaces 55 are formed on both outer side surfaces in the width direction of these high-rigidity bearing walls 50a and 52a, so that the strength of casting connection with the crank bearing members 50 and 52 is increased. . For example, when the crank bearing members 50 and 52 are formed of an aluminum alloy material, the high-rigidity bearing walls 50a and 52a are formed of an iron material or a fiber reinforced composite material (FRM).

  As shown in FIG. 6, the upper surfaces of the high-rigidity bearing walls 50 a and 52 a are in direct contact with the lower surface of the upper block 41, and are fastened to the upper block 41 by a plurality of fastening bolts 57. A semicircular lower half of the journal bearing portion 45 of the crankshaft 30 is formed on one side of the upper surface of the high-rigidity bearing walls 50a and 52a, and a half of the journal bearing portion of the control shaft 65 is formed on the other side of the lower surface. A circular upper half is formed. The crankshaft 30 and the control shaft 65 are supported by high-rigidity bearing walls 50a and 52a.

  Further, the rigidity of the crankshaft 30 and the control shaft 65 is ensured by casting the high-rigidity bearing walls 50a and 52a specifically for the adjacent end crank bearing member 50 and intermediate crank bearing member 52. However, as will be described later, the mounting rigidity of the housing HU of the actuator AC can be increased.

  The bearing block 70 fastened to the lower surface of the lower block 41 and supporting the control shaft 65 in cooperation with the lower block 41 may be formed of the same material as the lower block 41, and the high rigidity You may form with the same material as the bearing walls 50a and 52a.

  As shown in FIGS. 1 to 6, the actuator AC that drives the control shaft 65 is integrally supported on the front surface 90 of the lower block 41 of the engine body 1 so as to be biased toward one side in the direction of the crankshaft 30. The housing HU of the actuator AC is fixed to the front surface 90 of the lower block 41 by a plurality of fastening bolts 56 that pass through the housing HU and the lower block 41 and are fastened to the high-rigidity bearing walls 50a and 52a. Therefore, the housing HU of the actuator AC is attached to the housing HU using the high-rigidity bearing walls 50a and 52a, and the attachment rigidity can be increased. Further, the housing HU of the actuator AC and the high-rigidity bearing walls 50a and 52a are fastened to the lower block 41 by the plurality of fastening members 56, so that the number of fastening members 56 can be reduced.

  As the actuator AC, a conventionally known actuator such as a vane hydraulic motor, an electric motor, or a hydraulic cylinder is used. As shown in FIGS. 1 to 5, the drive sector gear 67 fixed to the outer end of the output shaft 66 of the actuator AC is meshed with the driven sector gear 68 fixed to the outer end of the control shaft 65. Accordingly, the control shaft 65 can be rotated forward and backward within a predetermined angle range, and the stroke variable link mechanism LV can be driven. The driving and driven sector gears 67 and 68 are covered with a cover body 69 that is bolted to the end face of the engine body 1 via a chain case 29.

  As described above, according to the first embodiment, the actuator AC is attached to the high-rigidity crank bearing members 50 and 52, so that the attachment rigidity can be improved. By fastening to the highly rigid bearing walls 50a and 52a into which the members 50 and 52 are cast, the mounting rigidity can be further improved.

  Further, since the housing HU of the actuator AC is mounted across the plurality of highly rigid crank bearing members 50 and 52, the mounting rigidity of the actuator AC is further improved, and the housing HU of the actuator AC has a plurality of crank bearings. It acts as a connecting member for connecting the members 50 and 52, and the support rigidity of the crankshaft 30 is also improved.

  Further, the crank bearing members 50 and 52 are formed integrally with the lower block 41 constituting the engine body 1, and high-rigidity bearing walls 50a and 52a having higher rigidity than the lower block 41 are cast therein. Since the housing HU of the actuator AC is supported by the lower block 41 by the fastening member 56 fastened to the rigid bearing walls 50a and 52a, the fastening rigidity of the actuator AC to the engine body 1 is greatly improved, and the actuator AC Both the mounting rigidity and the rigidity of the lower block 41 are improved.

  Furthermore, since the housing HU of the actuator AC and the high-rigidity bearing walls 50a and 52a are fastened together with the crank bearing members 50 and 52 by the fastening member 56, the fastening rigidity of the actuator AC to the lower block 41 is high. In addition to the improvement, the number of fastening members 56 can be reduced to reduce the number of parts, and further the increase in size of the engine body 1 in the direction across the crankshaft 30 can be suppressed.

  Next, a second embodiment of the present invention will be described with reference to FIGS.

  9 is a schematic perspective view of the engine body, FIG. 10 is a cross-sectional view taken along line 10-10 in FIG. 11, FIG. 11 is a cross-sectional view taken along line 11-11 in FIG. 10, and FIG. FIG. 13 is a cross-sectional view taken along line 12-12, and FIG. 13 is a cross-sectional view taken along line 13-13 in FIG. 10, and the same reference numerals are given to the same elements as those in the first embodiment.

  In the second embodiment, the actuator AC is fixed to the lower front portion of the engine body 1, that is, the front surface 90 of the lower block by a plurality of fastening bolts 56.

  As shown in FIGS. 9 and 10, left and right end crank bearing members 50 and 51 and intermediate crank bearing member 52, excluding central bearing member 54, among a plurality of crank bearing members 50 to 54 formed on lower block 41. 53 are selected, and high-rigidity bearing walls 50a, 51a, 52a, 53a (same as the high-rigidity bearing walls 50a, 52a of the first embodiment) are cast and formed on these high-rigidity bearing walls 50a-53a. The actuator AC is fixed by a plurality of fastening bolts 56 to be fastened. That is, as shown in FIG. 11, the plurality of fastening bolts 56 are formed from the outside of the actuator AC by a plurality of fastening bolts 56 penetrating the housing HU and the crank bearing members 50 to 53 (lower block 41). Fastened to 50a-53a. Thereby, the mounting rigidity of the actuator AC to the engine main body 1 is increased, and the housing HU of the actuator AC and the high-rigidity bearing walls 50a to 53a are fastened to the lower block 41 by the fastening bolt 56.

  As shown in FIG. 10, the housing HU of the actuator AC is divided into a first housing HU <b> 1 and a second housing HU <b> 2, which are integrally coupled by a plurality of connecting bolts 101. A drive shaft 100 extending in the direction of the crankshaft 30 is connected to the output shaft 66 of the actuator AC. The drive shaft 100 is rotatably supported in the housing HU via a bearing, and a pair of drive sector gears 67 are fixed to an intermediate portion thereof. These drive sector gears 67 are respectively meshed with a pair of driven sector gears 68 fixed to the intermediate portion of the control shaft 65. When the actuator AC is driven, the control shaft 65 is fixed to a predetermined position as in the first embodiment. Drive forward and reverse at the rotation angle of.

  As shown in FIG. 12, the cover covering the control shaft 65 is formed integrally with the chain case 29, and the increase in the number of parts is suppressed.

  A coil spring 102 is provided at one end of the drive shaft 100. The coil spring 102 has one end engaged with the drive shaft 100 and the other end engaged with a fixed portion such as the lower housing 41, and urges the drive shaft 100 to rotate in one direction. The compression ratio of the link mechanism LV can be quickly changed. In the second embodiment, since the control shaft 65 is urged by the coil spring 102 via the drive shaft 100 in the rotational direction toward the high compression ratio, the compression ratio from the low compression ratio to the high compression ratio is increased. Changes will be made quickly.

  According to the second embodiment, the housing HU of the actuator AC is connected to the crank bearing members 50 to 53 by the fastening members 56 respectively fastened to the high-rigidity bearing walls 50 a to 53 a cast into the crank bearing members 50 to 53. Since it is fixed to 53, the mounting rigidity of the actuator AC to the engine body 1 is increased.

  Thus, according to the second embodiment, the same operational effects as the first embodiment can be obtained.

  Next, a third embodiment of the present invention will be described with reference to FIG.

  FIG. 14 is a cross-sectional view (corresponding to FIG. 6) of the mounting portion of the actuator to the engine body, in which the same elements as those in the first embodiment are denoted by the same reference numerals.

  The third embodiment is a case where the crank bearing members 50 to 53 are used as bearing caps, and a deep skirt portion 4 'is integrally extended downward in the crankcase 4 of the cylinder block 2, and its lower end. The oil pan 10 is fixed to. Crank bearing members 50 to 53 fixed to the crankcase 4 are accommodated in the deep skirt portion 4 '. The bearing members 50 and 52 (or 50 to 53) and the housing HU of the actuator AC are fastened and fixed to the crankcase 4 by a plurality of fastening bolts 56.

  As mentioned above, although the Example of this invention was described, this invention is not limited to the Example, A various Example is possible within the scope of the present invention.

  For example, in the above-described embodiment, the case where the present invention is applied to a variable compression ratio engine that changes the top dead center of the piston by changing the phase of the eccentric pin on the control shaft has been described. It is also applicable to.

Schematic overall perspective view of engine with variable stroke characteristics 2 arrow view of FIG. Sectional view along line 3-3 in FIG. 1 (high compression ratio state) Sectional view along line 4-4 in FIG. 1 (low compression ratio state) Sectional view along line 5-5 in FIG. Cross-sectional view along line 6-6 in FIG. Enlarged vertical view along line 7-7 in FIG. Sectional view along line 8-8 in FIG. Schematic perspective view of the engine body Sectional drawing which follows the 10-10 line of FIG. Sectional drawing which follows the 11-11 line of FIG. Sectional drawing which follows the 12-12 line of FIG. Sectional view along line 13-13 in FIG. Sectional view of the actuator mounting part on the engine body (corresponding to FIG. 6)

Explanation of symbols

1 .... Engine body 11 ... Piston 30 ... Crankshaft 41 ... Lower block 50 ... Crank bearing member (End crank bearing member)
50a ·········· Highly rigid bearing wall 51 ··········· Crank bearing member (end crank bearing member)
51a... High rigidity bearing wall 52... Crank bearing member (intermediate crank bearing member)
52a... High rigidity bearing wall 53... Crank bearing member (intermediate crank bearing member)
53a .... High rigidity bearing wall 56 .... Fastening member 65 ... Control shaft AC ... Actuator LV ... Variable stroke Link mechanism
HU ... Housing

Claims (4)

The piston (11) and the crankshaft (30) are connected to a control shaft (65) via a stroke variable link mechanism (LV), and the control shaft (65) is driven by an actuator (AC) to change the stroke. In the variable stroke characteristic engine that operates the mechanism (LV) and makes the moving stroke of the piston (11) variable,
The actuator (AC) housing (HU) is attached to a crank bearing member (50, 52; 50, 51, 52, 53) that supports the crankshaft (30), and has variable stroke characteristics. engine.   The housing (HU) of the actuator (AC) is mounted across a plurality of the crank bearing members (50, 52; 50, 51, 52, 53). The variable stroke characteristics engine described.   The crank bearing member (50, 52; 50, 51, 52, 53) is formed integrally with the lower block (41) constituting the engine body (1), and has a higher rigidity than the lower block (41). The rigid bearing wall (50a, 52a; 50a, 51a, 52a, 53a) is cast, and the fastening member (56) is fastened to the high-rigidity bearing wall (50a, 52a; 50a, 51a, 52a, 53a). The stroke characteristic variable engine according to claim 1 or 2, wherein a housing (HU) of the actuator (AC) is supported by a lower block (41). The housing (HU) of the actuator (AC) and the high-rigidity bearing walls (50a, 52a; 50a, 51a, 52a, 53a) are crank bearing members (50, 52; 50, 51) by the fastening members (56). 52, 53), the stroke characteristic variable engine according to claim 3.

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