JP2007064012A - Variable stroke engine - Google Patents

Abstract

In a variable stroke engine, the number of parts is reduced and the engine can be downsized.
Timed transmission means for transmitting rotational power of a crankshaft with a reduction ratio of 1/2 between a camshaft and a crankshaft provided in a valve mechanism provided on an upper part of an engine body. The camshaft 36 is provided with a pivot shaft 50 having an axis that is eccentric from the rotational axis thereof.
[Selection] Figure 1

Description

  The present invention relates to a variable stroke engine, and in particular, is connected to a main connecting rod whose one end is connected to a piston via a piston pin, a crankshaft rotatably supported by a crankcase of an engine body, and the main connecting rod. A sub connecting rod connected to the other end, a control rod having one end connected to the sub connecting rod at a position shifted from the connecting position of the main connecting rod, and power transmission reduced by a reduction ratio of 1/2 from the crankshaft. The present invention relates to an improvement in a variable stroke engine that includes a pivot shaft that rotates about an eccentric axis and is connected to the other end of the control rod.

Conventionally, such a variable stroke engine is already known from, for example, Japanese Patent Application Laid-Open No. H10-228707. In addition to a control rod having one end connected to a sub connecting rod on an eccentric shaft provided on a rotating shaft having an axis parallel to the crankshaft. By connecting the ends, the stroke of the piston is changed.
JP 2003-314237 A

  By the way, in the variable stroke engine disclosed in Patent Document 1, the valve operating mechanism is configured to be an OHV type so that a rotating shaft that has a pivot shaft and is rotatably supported by a crankcase also serves as a cam shaft. If such an OHV type valve operating mechanism is used, not only the number of parts constituting the valve operating mechanism such as a push rod increases, but also the valve operating mechanism becomes relatively heavy so that high rotation speed is achieved. However, since there are many contact parts between the parts which comprise a valve operating mechanism, mechanical noise will become comparatively large.

  In order to solve such a problem, it is conceivable to employ an OHC type valve mechanism in which the camshaft is provided at the upper part of the engine body. However, such an OHC type valve mechanism is provided on the crankshaft. If the conventional timing transmission means consisting of a driven wheel, a driven wheel provided on the camshaft, and an endless transmission belt wound around the driving wheel and the driven wheel is simply applied, a pivot shaft is provided separately from the camshaft. Therefore, a mechanism for transmitting the rotational power of the crankshaft with a reduction ratio of 1/2 is required on the rotating shaft, which increases the number of parts and increases the size of the engine.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a variable stroke engine capable of reducing the number of parts and miniaturizing the engine.

  To achieve the above object, the invention according to claim 1 is connected to a main connecting rod whose one end is connected to the piston via a piston pin and a crankshaft rotatably supported by a crankcase of the engine body. And a sub connecting rod connected to the other end of the main connecting rod, a control rod having one end connected to the sub connecting rod at a position shifted from the connecting position of the main connecting rod, and a reduction ratio of 1/2 from the crankshaft. In a variable stroke engine having a pivot shaft that rotates around an eccentric axis by decelerated power transmission and to which the other end of the control rod is connected, a camshaft and a crank that are provided in a valve mechanism provided in an upper part of the engine body Between the shafts, the rotational power of the crankshaft is halved Provided timing transmission means for transmitting at a speed ratio, characterized in that the pivot shaft is provided having an axis offset from the axis of rotation to the camshaft.

  According to a second aspect of the present invention, in addition to the configuration of the first aspect of the invention, center lines of the main connecting rod and the control rod are arranged on the same plane.

  According to the configuration of the first aspect of the present invention, the rotational power decelerated from the crankshaft by the reduction ratio of 1/2 from the crankshaft is transmitted to the camshaft provided in the valve mechanism provided in the upper portion of the engine body by the timing transmission means. However, since the camshaft is provided with a pivot shaft, it is necessary to secure a space for arranging the rotation shaft as compared with the rotation shaft having the pivot shaft rotatably supported by the crankcase. The crankcase can be made compact and the engine height can be set low, and a reduction drive mechanism for driving the rotating shaft between the rotating shaft and the crankshaft is required. As a result, the axial length of the crankshaft can be shortened and the entire engine can be made compact. Moreover, the number of parts can be reduced by eliminating the need for a rotating shaft. Furthermore, the control rod is formed to have a relatively long length between the lower part and the upper part of the engine body. However, the control rod at the connecting point to the sub-connecting rod has a small amount of vibration and wear is reduced. The control rod, which can be suppressed and becomes heavier when it becomes relatively long, performs the counterweight function, and the dynamic balance of the crankshaft can be improved.

  According to the second aspect of the present invention, the main connecting rod, the sub connecting rod and the control rod can be compactly arranged in the direction along the axis of the crankshaft, and the distance between the bearings at both ends of the crankshaft can be shortened. it can. Furthermore, the load on the main connecting rod and the sub connecting rod due to the explosive force can be reduced by moving the control rod toward the crankshaft.

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

  1 and 2 show an embodiment of the present invention. FIG. 1 is a longitudinal side view of an engine, which is a cross-sectional view taken along line 1-1 of FIG. 2, and FIG. It is line sectional drawing.

  The engine is an air-cooled single-cylinder engine used for, for example, a work machine. An engine body 21 includes a crankcase 22, a cylinder block 23 protruding upward from the crankcase 22, and a head of the cylinder block 23. The cylinder head 24 is joined to the cylinder head 24, and the head cover 25 is joined to the cylinder head 24. In addition, the crankcase 22 is installed on the engine bed of various working machines by an installation surface 22 a on the lower surface of the crankcase 22.

  A crankshaft 27 integrally having a pair of balance weights 27a and 27b and a crank pin 27c connecting the balance weights 27a and 27b is rotatably supported on the crankcase 22.

  The cylinder block 29 is formed with a cylinder bore 29 into which the piston 28 is slidably fitted, and a combustion chamber 30 that faces the top of the piston 28 is formed between the cylinder block 23 and the cylinder head 24. In addition, an intake port 31 and an exhaust port 32 that can communicate with the combustion chamber 30 are formed in the cylinder head 24, and an intake valve 33 that opens and closes between the intake port 31 and the combustion chamber 30, and between the exhaust port 32 and the combustion chamber 30. An exhaust valve 34 for opening and closing the valve is disposed so as to be openable and closable.

  The valve operating mechanism 35 that opens and closes the intake valve 33 and the exhaust valve 34 includes a camshaft 36 that is rotationally driven from the crankshaft 27 at a reduction ratio of 1/2, an intake side cam 37 provided on the camshaft 36, and an exhaust. A side cam 38, an intake side rocker arm 39 that swings following the intake side cam 37, and an exhaust side rocker arm (not shown) that swings following the exhaust side cam 38. One end of the exhaust-side rocker arm is pivotably supported by the cylinder head 24 via a common swinging support shaft 41 having an axis parallel to the crankshaft 27, and the other end of the intake-side rocker arm 39 has an advancing / retreating position. A tappet screw 42 that is screwed so as to be adjustable is brought into contact with the upper end portion of the intake valve 33 and is screwed into the other end portion of the exhaust side rocker arm so that the advance / retreat position can be adjusted. Tappet screws (not shown) is brought into contact with the upper end portion of the exhaust valve 34.

  The camshaft 36 has an axis parallel to the crankshaft 27 and is rotatably supported between the cylinder head 24 and the head cover 25. Between the camshaft 36 and the crankshaft 27, the crankshaft 27 Is provided with a timing transmission means 45 disposed between one of the pair of balance weights 27a and 27b and the crankcase 22. The timing transmission means 45 is a drive sprocket fixed to the crankshaft 27. 46, a driven sprocket 47 provided on the camshaft 36, and a timing toothed belt 48 wound around the drive sprocket 46 and the driven sprocket 47. The cylinder block 23 and the cylinder head 24 include the timing toothed belt. Run 48 Belt chamber 49 which is formed.

  Between the intake side cam 37 and the exhaust side cam 38, the cam shaft 36 is integrally provided with a pivot shaft 50 having an axis that is eccentric from the rotational axis of the cam shaft 36. The piston 28 and the crankshaft 27 are connected via a link mechanism 51.

  The link mechanism 51 includes a main connecting rod 52 having one end connected to the piston 28 via a piston pin 55 and a sub connecting rod 53 connected to the crank pin 27c of the crankshaft 27 and to the other end of the main connecting rod 52. And a control rod 54 having one end connected to the sub connecting rod 53 at a position shifted from the connecting position of the main connecting rod 52 and the other end connected to the pivot shaft 50.

  The sub connecting rod 53 is formed so as to be in sliding contact with the half circumference of the crank pin 27 c, and a crank cap 56 that is in sliding contact with the remaining half circumference of the crank pin 27 c is fastened to the sub connecting rod 53.

  The other end of the main connecting rod 52 is rotatably connected to one end of the sub connecting rod 53 via the first pin 57. One end of the control rod 54 is rotatably connected to the sub connecting rod 53 via the second pin 58, and the pivot shaft 50 is fitted to the other end of the control rod 54 so as to be relatively slidable. A circular shaft hole 59 is provided.

  Moreover, the center lines of the main connecting rod 52 and the control rod 54 are arranged on the same plane perpendicular to the axis of the crankshaft 27, and the control rod 54 is provided in the cylinder block 23 adjacent to the cylinder bore 29. It penetrates so that 60 may be extended up and down.

  Thus, with the rotation of the reduction ratio of 1/2 of the pivot shaft 50 according to the rotation of the crankshaft 27, the link mechanism 51 makes the stroke of the piston 28 in the expansion stroke larger than the stroke in the compression stroke. The cycle thermal efficiency can be improved by operating in such a way as to allow more expansion work to be performed with the same amount of intake air mixture.

  Next, the operation of this embodiment will be described. Between the camshaft 36 and the crankshaft 27 provided in the valve mechanism 35 provided on the upper portion of the engine body 21, the rotational power of the crankshaft 27 is reduced at a reduction ratio of 1/2. A timing transmission means 45 for transmission is provided, and the camshaft 36 is provided with a pivot shaft 50 having an axis decentered from the rotation axis thereof, and a control rod 54 constituting a part of the link mechanism 51 on the pivot shaft 50. Are connected.

  That is, the camshaft 36 provided in the valve mechanism 35 provided in the upper part of the engine body 21 is transmitted with rotational power decelerated from the crankshaft 27 by a reduction ratio of 1/2 by the timing transmission means 45. Since the camshaft 36 is provided with the pivot shaft 50, it is not necessary to secure a space for arranging the rotating shaft, compared to the conventional one in which the rotating shaft having the pivot shaft is rotatably supported by the crankcase. As a result, the crankcase 22 can be made compact, the engine height can be set low, and a reduction drive mechanism for driving the rotation shaft between the rotation shaft and the crankshaft needs to be provided. Because there is no, the shaft length of the crankshaft 27 can be shortened and the whole engine can be made compact. Becomes, the rotary shaft can be reduced number of parts by eliminating the need.

  Further, the control rod 54 is formed to have a relatively long length between the lower part and the upper part of the engine body 21, but the amount of deflection of the control rod 54 at the connection point to the sub connecting rod 53 is reduced. As a result, the wear can be suppressed, and the control rod 54 that becomes heavier when it becomes relatively long can perform the counterweight function, so that the dynamic balance of the crankshaft 27 can be improved.

  Since the center lines of the main connecting rod 52 and the control rod 54 are arranged on the same plane, the main connecting rod 52, the sub connecting rod 53 and the control rod 54 can be arranged in a compact manner in the direction along the axis of the crankshaft 27. The distance between the bearings at both ends of the shaft 27 can be shortened. Further, the load on the main connecting rod 52 and the sub connecting rod 53 due to the explosive force can be reduced by the movement of the control rod 54 toward the crankshaft 27 side.

  Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various design changes can be made without departing from the present invention described in the claims. It is.

FIG. 3 is a longitudinal side view of the engine, and is a cross-sectional view taken along line 1-1 of FIG. FIG. 2 is a sectional view taken along line 2-2 of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 21 ... Engine main body 22 ... Crankcase 27 ... Crankshaft 28 ... Piston 35 ... Valve-operating mechanism 36 ... Camshaft 45 ... Timing transmission means 50 ... Pivot shaft 52 ... Main connecting rod 53 ... Sub connecting rod 54 ... Control rod 55 ... Piston pin

Claims (2)

  One end is connected to a main connecting rod (52) connected to the piston (28) via a piston pin (55) and a crankshaft (27) rotatably supported by a crankcase (22) of the engine body (21). And a sub connecting rod (53) connected to the other end of the main connecting rod (52) and a control having one end connected to the sub connecting rod (53) at a position shifted from the connecting position of the main connecting rod (52). A rod (54) and a pivot shaft (50) that rotates around an eccentric axis by power transmission decelerated from the crankshaft (27) with a reduction ratio of 1/2 and to which the other end of the control rod (54) is connected. ) Is provided with a valve mechanism (35) provided at the upper part of the engine body (21). Between the shaft (36) and the crankshaft (27), timing transmission means (45) for transmitting the rotational power of the crankshaft (27) at a reduction ratio of 1/2 is provided, and the camshaft (36) The variable stroke engine according to claim 1, wherein the pivot shaft (50) having an axis decentered from the rotation axis is provided.   The variable stroke engine according to claim 1, wherein center lines of the main connecting rod (52) and the control rod (54) are arranged on the same plane.

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