JP2012137003A - Piston structure of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piston structure for sufficiently cooling a piston, and capable of preventing engine oil from intruding in a combustion chamber.SOLUTION: This piston structure of an internal combustion engine includes the piston 37 reciprocatably arranged in a cylinder 25, and a connecting rod 40 connected to a lower part of the piston 37 via a piston pin 38. The piston structure includes a crown part 46 for constituting a top surface 51 of the piston 37, and a skirt part 47 extending toward the lower part from the outer periphery of the crown part 46. The rib 54 is formed only on one side from the center of the crown part 46 on a reverse surface 48 of the crown part 46, and a piston jet 60 is arranged so that the engine oil can be injected toward the reverse surface 48 of the crown part 46 on the opposite side of the rib 54-forming side.

Description

  The present invention relates to a piston structure applied to an internal combustion engine.

  In general, in an internal combustion engine used in a vehicle such as a motorcycle or an automobile, the reciprocating motion of a piston provided in a cylinder is transmitted to a crankshaft through a connecting rod, and the crankshaft rotates to allow the vehicle to travel. It becomes.

  As shown in FIG. 6, the piston 71 used in the internal combustion engine as described above includes a crown portion 73 that constitutes the top surface 72 of the piston 71 and a skirt portion 74 that extends downward from the outer periphery of the crown portion 73. And a pair of pin boss portions 76 (only one pin boss portion 76 is shown in FIG. 6) provided on the back surface 79 of the crown portion 73 and provided with a pin hole 75 in the center portion. The piston 71 and the connecting rod can be connected by the piston pin 77 held in the pin hole 75 described above.

  The piston 71 having such a configuration has a problem that the piston 71 is deformed by a reaction force received from the cylinder in the expansion process (fuel explosion process). Further, with the deformation of the piston 71 described above, the piston pin 77 is also stressed, and the piston pin 77 is deformed.

  Conventionally, the strength of the piston 71 is increased by installing bridge ribs 78 between a pair of pin boss portions 76 on both sides of the piston pin 77 as shown in FIG. And the deformation of the piston pin 77 was prevented.

  By the way, in the internal combustion engine having the above-described configuration, each part of the internal combustion engine becomes a high temperature state by the heat energy absorbed by the internal combustion engine in the expansion process described above, and the piston 71 is also constantly heated. In order to suppress the high temperature of the piston 71, conventionally, a so-called piston jet that cools the piston 71 by spraying engine oil toward the piston 71 has been used (for example, “oil jet of Patent Document 1”). Device 11 ").

  In general, the portion of the piston 71 that is most likely to reach a high temperature is the central portion of the crown portion 73 that is close to the center position of the explosion. In the conventional piston structure, in order to efficiently cool the center of the crown portion 73, the nozzle of the piston jet is inclined, and engine oil is blown from the inclined nozzle to the back surface 79 of the crown portion 73, whereby the piston Engine oil was passed between 71 and the piston pin 77.

JP 2009-1917779 A

  However, when the configuration in which the engine oil is passed between the piston 71 and the piston pin 77 is applied to the piston 71 as shown in FIG. 6, the engine oil that has cooled the center of the crown portion 73 is relatively cooled. Reaches the skirt portion 74 that does not require (see a one-dot chain line arrow in FIG. 6), and adheres to the cylinder through the skirt portion 74. The engine oil adhering to this cylinder is scraped off into the crankcase by a piston ring or the like attached to the piston 71 in general, but slightly remaining engine oil enters the combustion chamber formed above the piston 71, There is a risk of increasing harmful substances such as hydrocarbons and nitrogen compounds contained in the exhaust gas from the internal combustion engine.

  Further, in the configuration of the prior art, at the time of manufacturing the piston 71, it is necessary to cut the upper part of the bridge rib 78 (see the two-dot chain line in FIG. 6) obliquely after die cutting (window cutting), which increases the cost. Leads to.

  In view of the above circumstances, an object of the present invention is to provide a piston structure capable of sufficiently cooling the piston and preventing engine oil from entering the combustion chamber.

  The present invention is a piston structure of an internal combustion engine comprising a piston provided in a cylinder so as to be able to reciprocate, and a connecting rod connected to the lower side of the piston via a piston pin, the top surface of the piston being And a skirt portion extending downward from the outer periphery of the crown portion, and a rib is formed on the back surface of the crown portion only on one side from the center of the crown portion. A piston jet is provided so that engine oil can be injected toward the back surface of the crown portion on the side opposite to the forming side.

  By adopting such a configuration, the engine oil can be passed through the center of the crown portion of the piston, and the piston can be sufficiently cooled. Further, the engine oil can be prevented from adhering to the skirt portion by the rib, and accordingly, the engine oil can be prevented from entering the combustion chamber.

  Further, the rib may be formed to extend downward from an upper tangent line between two upper and lower tangent lines connecting the lower end of the skirt portion on the rib forming side and the outer peripheral surface of the piston pin. .

  By adopting such a configuration, it is possible to reliably prevent the engine oil that has collided and scattered from the back surface of the crown portion from adhering to the skirt portion, and it is more effective for the engine oil to enter the combustion chamber. Can be suppressed.

  Further, the rib may be formed closer to the piston pin side than the skirt portion, and may be formed at the same position as the lower end of the piston pin or extending downward from the lower end.

  By adopting such a configuration, the engine oil that has collided with the back surface of the crown portion and splashed can be rebounded by the rib and adhered to the piston pin, and the piston pin can be well lubricated.

  According to the present invention, it is possible to sufficiently cool the piston and prevent engine oil from entering the combustion chamber.

1 is a left side view of a motorcycle according to an embodiment of the present invention. It is a left view which shows the engine which concerns on one Embodiment of this invention. It is sectional drawing which shows the principal part of the engine which concerns on one Embodiment of this invention. It is a bottom view which shows the piston which concerns on one Embodiment of this invention. It is AA sectional drawing of FIG. It is sectional drawing which shows the piston which concerns on a prior art example.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In the present embodiment, a case where the piston structure of the internal combustion engine according to the present invention is applied to an off-road type motorcycle 1 will be described. Hereinafter, the directions of up and down, left and right, and front and rear indicate directions viewed from the driver who rides the motorcycle 1.

  First, the outline of the motorcycle 1 will be described with reference to FIG. The motorcycle 1 is provided with a vehicle body frame 2 constituting a framework. The vehicle body frame 2 is, for example, a twin tube type, and includes a head pipe 3 disposed at the front upper end of the vehicle body frame 2, a pair of left and right main frames 4 extending rearward and downward from the head pipe 3, A cradle frame 5 provided below the main frame 4 and a pair of left and right seat rails 6 extending from the rear portion of the main frame 4 toward the rear upper side are mainly configured.

  A pair of left and right front forks 7 are supported on the head pipe 3 so as to be rotatable left and right. A front wheel 8 is pivotally supported at the lower end of the front fork 7, and a front fender 10 is provided above the front wheel 8. A handle bar 11 is fixed to the upper end of the front fork 7 in the left-right direction, and handle grips 12 are provided at the left and right ends of the handle bar 11.

  A fuel tank 13 is provided between the pair of left and right main frames 4, and side covers 14 are provided so as to cover both the left and right sides of the fuel tank 13. A driver seat 15 is provided behind the fuel tank 13 from above the rear of the pair of left and right main frames 4 to above the seat rail 6, and an engine (internal combustion engine) 16 is mounted below the fuel tank 13. ing.

  A pivot shaft 17 is installed at the lower rear part of the pair of left and right main frames 4, and a front end portion of a swing arm 18 is supported on the pivot shaft 17 so as to be swingable in the vertical direction. A rear wheel 20 is pivotally supported at the rear end of the swing arm 18, and a rear fender 21 is provided above the rear wheel 20. A muffler 22 is provided between the rear wheel 20 and the rear fender 21, and a rear side cover 23 is provided so as to cover the left and right sides of the muffler 22.

  Next, the outline of the engine 16 will be described with reference to FIGS. The engine 16 is, for example, a DOHC-type water-cooled single-cylinder engine. As shown in FIG. 2, as shown in FIG. A cylinder 25, a cylinder head 26 provided above the cylinder 25, and a cylinder head cover 27 that covers the upper surface of the cylinder head 26 are provided.

  As shown in FIG. 3, a combustion chamber 28 is provided between the cylinder head 26 and the cylinder 25. An intake port 31 to which an intake valve 30 is attached is provided on the rear side (right side in FIG. 3) of the combustion chamber 28. The intake port 31 communicates with an intake port 32 provided at the rear portion of the cylinder head 26, and a throttle body (not shown) is connected to the intake port 32. The air-fuel mixture from the throttle body is supplied to the combustion chamber 28 via the intake port 32 and the intake port 31. As is clear from the above description, in the present embodiment, the rear side of the engine 16 is the intake side.

  An exhaust port 34 to which an exhaust valve 33 is attached is provided in front of the combustion chamber 28 (left side in FIG. 3). The exhaust port 34 communicates with an exhaust port 35 provided at the front portion of the cylinder head 26. The exhaust port 35 is connected to the above-described muffler 22 (see FIG. 1) via an exhaust pipe 36 (see FIG. 1), and exhaust from the combustion chamber 28 is exhausted to the exhaust port 34, the exhaust port 35, the exhaust pipe 36. And it can discharge | emit to the back of the motorcycle 1 through the muffler 22. FIG. As is clear from the above description, in this embodiment, the front side of the engine 16 is the exhaust side.

  A piston 37 is accommodated in the cylinder 25 so as to be able to reciprocate, and a small end 41 of a connecting rod 40 is connected to the lower side of the piston 37 via a piston pin 38 (details will be described later). A crank pin 45 of a crankshaft 44 is connected to the large end 42 of the connecting rod 40 via a bearing 43. A magneto (not shown) for power generation is provided at the left end of the crankshaft 44, and a magnet cover 39 is provided so as to cover the magnet (see FIG. 2).

  Next, the configuration of the piston 37 will be described mainly with reference to FIGS. 4 and 5. Note that the upper, lower, left, and right sides in FIG. 4 correspond to the left, right, front, and rear of the piston 37, respectively.

  The piston 37 has a bottomed cylindrical shape, and includes a crown portion 46 provided at the upper end of the piston 37, a pair of front and rear skirt portions 47 extending downward from the outer periphery of the crown portion 46, and front and rear sides of the back surface 48 of the crown portion 46. And a pair of left and right pin bosses 50 provided in the direction.

  The crown portion 46 constitutes the top surface 51 of the piston 37, and the top surface 51 partitions the lower end of the combustion chamber 28 (see FIG. 3). A plurality of annular ring grooves 52 are provided on the outer periphery of the crown portion 46, and a piston ring (not shown) is configured to be attached to the ring grooves 52.

  The front end portions of the pair of pin boss portions 50 are respectively connected to the left and right end portions of the front skirt portion 47, and the rear end portions of the pair of pin boss portions 50 are respectively connected to the left and right end portions of the rear skirt portion 47. Thus, a space 53 surrounded by a pair of front and rear skirt portions 47 and a pair of left and right pin boss portions 50 is formed at the center in the left-right direction of the piston 37. The bottom surface of the space 53 is opened.

  The space 53 is partitioned into a front portion 55 and a rear portion 56 by ribs 54 formed on the back surface 48 of the crown portion 46. The rib 54 is provided only on one side (the rear side in the present embodiment) from the center of the crown portion 46, and is provided between the pair of pin boss portions 50. The rib 54 is formed to extend downward from the upper tangent line X of two upper and lower tangent lines X and Y connecting the lower end of the skirt portion 47 on the rib 54 forming side and the outer peripheral surface of the piston pin 38. (See two-dot chain lines X and Y in FIG. 5). Further, the rib 54 is formed closer to the piston pin 38 side than the skirt portion 47 and extends downward from the lower end of the piston pin 38 (see the two-dot chain line Z in FIG. 5).

  A pin hole 57 is provided in the left-right direction at the center in the front-rear direction of the pair of pin boss portions 50. And in the state which inserted the small end part 41 of the connecting rod 40 in the front side part 55 of the space 53, the small end hole 58 (refer FIG. 3) provided in the small end part 41 of the connecting rod 40, and the pin hole of each pin boss | hub part 50 By connecting the piston pin 38 to 57, the connecting rod 40 is connected to the lower side of the piston 37 via the piston pin 38.

  A piston jet 60 is provided below the front portion of the piston 37. The piston jet 60 is capable of injecting engine oil toward the back surface 48 of the crown portion 46 on the side opposite to the rib 54 formation side (front side in the present embodiment), as indicated by a dotted arrow in FIG. The position and inclination of the nozzle 61 are adjusted.

  When the mixture is exploded in the combustion chamber 28 in the configuration as described above, the piston 37 is pushed down by the pressure of the explosion (see arrow P in FIG. 3) and connected to the piston 37 via the connecting rod 40. The crankshaft 44 rotates. The rotation of the crankshaft 44 is transmitted to the rear wheel 20 so that the motorcycle 1 can travel.

  Moreover, each part of the engine 16 becomes a high temperature state by the heat energy absorbed by the engine 16 in the above-described explosion process, and the piston 37 is also heated. Therefore, in order to suppress the high temperature of the piston 37, engine oil is jetted from the piston jet 60 toward the back surface 48 of the crown portion 46 to cool the piston 37.

  At this time, a rib 54 is formed only on the rear side 48 on the back surface 48 of the crown portion 46, and a piston jet 60 is provided so that engine oil can be injected toward the front side of the back surface 48 of the crown portion 46. Therefore, the engine oil passes through the center of the back surface 48 of the crown portion 46 (see the dashed line arrow in FIG. 5). Thereby, sufficient cooling of piston 37 is attained.

  Further, the rib 54 can prevent the engine oil from adhering to the intake side (rear) skirt portion 47, so that the engine oil adheres to the cylinder 25 through the skirt portion 47, and the inside of the combustion chamber 28. It is possible to prevent intrusion. Further, excessive engine oil is prevented from being supplied to the intake side (rear side) by the rib 54, and the cooling effect of the central portion and the front portion of the crown portion 46 can be improved.

  Further, in the present embodiment, the rib 54 is formed extending downward from the upper tangent line X (see FIG. 5), so that the engine oil that collides with the back surface 48 of the crown portion 46 and scatters is taken into the intake side ( It is possible to reliably prevent the rear skirt 47 from adhering, and to more effectively suppress the engine oil from entering the combustion chamber 28.

  Further, in this embodiment, the rib 54 is formed closer to the piston pin 38 side than the skirt portion 47 on the intake side (rear side), and the rib 54 extends downward from the lower end of the piston pin 38. (See FIG. 5). Therefore, the engine oil that collides and scatters on the back surface 48 of the crown portion 46 can be rebounded by the rib 54 and attached to the piston pin 38, and the piston pin 38 can be lubricated well.

  In this embodiment, the rib 54 is formed so as to extend downward from the lower end of the piston pin 38 as described above. However, even if the rib 54 is provided at the same position as the lower end of the piston pin 38, the above-described piston pin is provided. The effect of improving the lubricating performance of 38 can be obtained.

  Further, the rib 54 is installed between the pin boss portions 50 as described above, so that the connection rigidity between the pin boss portions 50 can be increased, and the deformation of the pin boss portion 50 due to the inertia force of the reciprocating motion of the piston 37 or the explosion pressure is effective. Can be suppressed. Therefore, the rigidity of the entire piston 37 can be dramatically increased, and the deformation amount of the entire piston 37 can be reduced.

  Further, when the air-fuel mixture is exploded in the combustion chamber 28 as described above, a reaction force is generated from the cylinder 25 to the piston 37 by the pressure of the explosion, and a side pressure is applied to the rear (thrust side) skirt portion 47 (FIG. 4). (See arrow a). Along with this, pressure is generated in a direction in which the pin boss portions 50 on the left and right sides of the rear portion 56 of the space 53 are separated from each other (see arrow b in FIG. 4), which may promote deformation of the pin boss portion 50. is there. However, in the present embodiment, since the rib 54 is provided on the rear side to which the above-described side pressure is applied, it is possible to effectively prevent the pin boss portion 50 from being deformed by the pressure accompanying the side pressure. As described above, in the present embodiment, the rib 54 is provided on the rear side (thrust side) on which the side pressure is easily applied, so that the deformation of the pin boss portion 50 can be surely prevented even with the rib 54 on only one side.

  Further, the exhaust side of the engine 16 is usually higher in temperature than the intake side. In this regard, in the present embodiment, the rib 54 is provided only on the rear side that is the intake side, and the rib 54 is not provided on the front side that is the exhaust side. Therefore, it is possible to concentrate the engine oil on the central portion of the crown portion 46 that tends to become high temperature and the exhaust side, and it is possible to further improve the cooling performance of the piston 37 by the engine oil.

  Further, in the present embodiment, the rib 54 is provided on the back surface 48 of the crown portion 46, so that an additional process such as a cutting process required in the above-described conventional technique is not required. Therefore, it is possible to provide the piston 37 capable of realizing high strength and high cooling performance by a simple manufacturing process.

  In the present embodiment, as shown in FIG. 5, the lower end of the pin boss portion 50 and the lower end of the rib 54 are substantially the same height. However, in other different embodiments, the rib 54 is lower than the lower end of the pin boss portion 50. It is also possible to set so that the lower end of is at a high position.

25 cylinder 37 piston 38 piston pin 40 connecting rod 46 crown portion 47 skirt portion 48 back surface 51 top surface 54 rib 60 piston jet

Claims (3)

A piston structure of an internal combustion engine comprising a piston provided in a cylinder so as to be capable of reciprocating, and a connecting rod connected to the lower side of the piston via a piston pin,
A crown portion constituting the top surface of the piston, and a skirt portion extending downward from the outer periphery of the crown portion,
On the back surface of the crown portion, a rib is formed only on one side of the center of the crown portion, so that engine oil can be injected toward the back surface of the crown portion on the side opposite to the rib forming side. A piston structure for an internal combustion engine, wherein a piston jet is provided.   The rib is formed so as to extend downward from an upper tangent of two upper and lower tangents connecting the lower end of the skirt portion on the rib forming side and the outer peripheral surface of the piston pin. The piston structure of the internal combustion engine according to claim 1.   The rib is formed closer to the piston pin side than the skirt portion, and is formed at the same position as the lower end of the piston pin or extending downward from the lower end. 2. A piston structure of an internal combustion engine according to 1.