Engine

Cap segment surfaces (9a) and (9b) of a larger-diameter end portion (7) of a connecting rod (5) are positioned at an upper and a lower portions of a crank pin (8) and are inclined from a right upper portion of the larger-diameter end portion (7) of the connecting rod (5) to a left lower portion thereof. A cap (10) is attached by connecting rod bolts (11a) and (11b), head portion (12a) and (12b) of which are arranged vertically along the inclination direction of the cap segment surfaces (9a) and (9b). With a piston (24) existing at a bottom dead center, a weight connection portion (15a) of an upper rotary balancer (4a) is provided with a recess (13a) at a portion oriented leftwards and downwards which comes to face the head portion (12a) of the upper connecting rod bolt (11a).

BACKGROUND OF THE INVENTION

1. Technical Field of the Invention

The present invention relates to an engine.

2. Description of Related Art

An example of the conventional engines, as shown inFIG. 11, arranges a pair of upper and lower rotary balancers104aand104bon a right horizontal side of a crank shaft103and provides an opening141of a cylinder block122on a right horizontal side of the paired upper and lower rotary balancers104aand104b, which opening is closed by a closure142, at a specific observation position with a cylinder102oriented horizontal on a left side of a center axis101of the crank shaft103, when seen in a direction parallel to the center axis101of the crank shaft103as well as the present invention.

As shown inFIG. 11, at the specific observation position, with a piston124existing at a bottom dead center, the pair of the upper and lower rotary balancers104aand104bhave weight connection portions115aand115bpositioned on respective left horizontal sides of their rotation centers143aand143b. A gap144is formed between the both weight connection portions115aand115bwhen the piston124exists at the bottom dead center.

As shown inFIG. 14, at the specific observation position, with a larger-diameter end portion107of a connecting rod being present at a stroke intermediate position above the center axis101of the crank shaft103, while the upper rotary balancer104ahas the weight connection portion115apositioned above the center143aof its rotation, the lower rotary balancer104bhas the weight connection portion115bdisposed below the center143bof its rotation. A gap146is formed between the both weight connection portions115aand115bwhen the larger-diameter end portion107is present at the stroke intermediate position.

This conventional technique is different from the present invention on the following points.

As shown inFIG. 11, at the specific observation position, with a center axis106of the connecting rod oriented horizontal, a pair of upper and lower cap segment surfaces109aand109bof the larger-diameter end portion107of the connecting rod are positioned at an upper and a lower portions of a crank pin108and are made vertical. A cap110is attached by a pair of an upper and a lower connecting rod bolts111aand111b, head portions112aand112bof which are arranged vertically along the paired upper and lower cap segment surfaces109aand109b.

And as shown inFIG. 12, at the specific observation position, with the piston124existing at a position just after it has passed the bottom dead center, while the upper rotary balancer104ahas the weight connection portion115aarranged at a left lower portion of the rotation center143a, the lower rotary balancer104bhas the weight connection portion115bdisposed at a left upper portion of the rotation center143b. A gap144ais formed between the both weight connection portions115aand115bjust after the piston124has passed the bottom dead center. The upper connecting rod bolt111ahas the head portion112aopposed to the gap144afrom its right lower portion and has an axis an extension line145aof which goes rightwards and downwards to pass through the gap144aand the opening141.

As shown inFIG. 13, at the specific observation position, with the piston124being present at a position just before it passes the bottom dead center, while the upper rotary balancer104ahas the weight connection portion115aarranged at a left upper portion of its rotation center143a, the lower rotary balancer104bhas the weight connection portion115bpositioned at a left lower portion of its rotation center143b. A gap144bis formed between the both weight connection portions115aand115bjust before the piston124passes the bottom dead center. The lower connecting rod bolt111bhas the head portion112bopposed to the gap144bfrom its right upper portion. This lower connecting rod bolt111bhas an axis an extension line145bof which goes rightwards and upwards to pass through the gap144band the opening141.

And as shown inFIG. 14, at the specific observation position, with the larger-diameter end portion107of the connecting rod existing at an stroke intermediate position above the center axis101of the crank shaft103, the lower connecting rod bolt111bhas the head portion112bopposed to the gap146from its right portion. This connecting rod bolt111bhas the axis the extension line145bof which goes rightwards and upwards to interfere with the upper weight connection portion115a.

This conventional technique has the following problems.

<Problem 1> There Occurs Stagnation in the Work for Attaching and Detaching the Cap.

As shown inFIGS. 12 to 14, when conducting a predetermined maintenance work of the piston124or the like, there is a case where the closure142is removed and the paired connecting rod bolts111aand111bare removed by a socket wrench147to detach the cap110while retaining the paired rotary balancers104aand104bassembled to the cylinder block122, and after the predetermined maintenance work has been completed, the cap110is attached to assemble the connecting rod bolts111aand111bby the socket wrench147. In such a case, the lower connecting rod bolt111bcannot be detached and attached at once to result in stagnating the work for attaching and detaching the cap110.

More specifically, in the case of detaching the cap110, first, after the engine has been brought into such a state that the piston124has just passed the bottom dead center as shown inFIG. 12, the straight socket wrench147is inserted into the cylinder block122through the opening141and a socket148at its leading end is inserted from the gap144aalong the extension line145aof the axis of the upper connecting rod bolt111a. The upper connecting rod bolt111ahas the head portion112afitted into the socket148. Then the socket wrench147is rotated to dismantle the upper connecting rod bolt111a. Next, after the engine has been brought into such a state that the piston124is just before passing the bottom dead center as shown inFIG. 13, the same socket wrench147is inserted through the opening141and the socket148at its leading end is inserted from the gap144balong the extension line145bof the axis of the lower connecting rod bolt111band the head portion112bof the lower connecting rod bolt111bis fitted into the socket148. The socket wrench147is rotated to once loosen the lower connecting rod bolt111b. Subsequently, after the engine has been brought into the stroke intermediate state as shown inFIG. 14, both hands are inserted from the opening141to the cylinder block122via the gap146. While supporting the cap110by one hand, the lower connecting rod bolt111bis dismantled by the other hand.

Next, in the case where the cap110is attached after having conducted the predetermined maintenance work, first, the engine is brought into the stroke intermediate state as shown inFIG. 14. Then the cap110and the lower connecting rod bolt111bare held by both hands and are inserted from the opening141to the crank pin108via the gap146. While supporting the cap110by one hand so that it dose not fall, the lower connecting rod bolt111bis once temporarily fastened by the other hand. Subsequently, after having brought the engine into such a state that the piston124is just before passing the bottom dead center as shown inFIG. 13, the straight socket wrench147is inserted from the opening141into the cylinder block122and the socket148at the leading end is inserted from the gap144balong the extension line145bof the axis of the lower connecting rod bolt111b. The head portion112bof the lower connecting rod bolt111bis fitted into the socket148and the socket wrench147is rotated to rigidly fasten the lower connecting rod bolt111b. Next, the engine is brought into such a state that the piston124has just passed the bottom dead center as shown inFIG. 12and thereafter the same socket wrench147has the socket148at the leading end, fitted onto the head portion112aof the upper connecting rod bolt111a, which is inserted into the cylinder block122through the opening141. The socket148at the leading end is inserted from the gap144ato the cap110with the upper connecting rod bolt111a. The upper connecting rod bolt111ais attached.

<Problem 2> The Engine is Produced at a High Cost.

When an engine of high exhaust amount is produced by borrowing a cylinder block122to be used for an engine of low exhaust amount and making a radius123from the center axis101of the crank shaft to a center of the crank pin108larger than that of the engine of low exhaust amount and making a dimension127from a center of a piston pin125to a piston head top surface126smaller than that of the engine of low exhaust amount, if the engine of high exhaust amount maintains such a structure that the cap segment surfaces109aand109bform a vertical surface as well as the engine of low exhaust amount, while the engine is in operation, the head portion112aof the upper connecting rod bolt111ainterferes with an upper portion128aof the crank shaft103in the crank case128. Therefore, conventionally, in the case of producing the engine of high exhaust amount, there was prepared a separate cylinder block which is exclusively used for the engine of high exhaust amount and prevents the head portion112aof the upper connecting rod bolt111afrom interfering with the upper portion128a, without using the cylinder block122to be used for the engine of low exhaust amount. This entails a high production cost of the engine of high exhaust amount.

The present invention has an object to provide an engine capable of solving the problems. More specifically, the present invention provides an engine which enables a cap to be attached and detached quickly and can reduce the production cost.

SUMMARY OF THE INVENTION

As exemplified inFIG. 1, when seen in a direction parallel to a center axis1of a crank shaft3, at a specific observation position with a cylinder2oriented horizontal on a left side of the center axis1of the crank shaft3, there are arranged on a right horizontal side of the crank shaft3a pair of upper and lower rotary balancers4aand4b, on a right horizontal side of which an opening41of a cylinder block22is provided. The opening41is closed with a closure42.

At the specific observation position, with a piston24existing at a bottom dead center, the paired upper and lower rotary balancers4aand4bhave the respective weight connection portions15aand15barranged on a left horizontal side of the respective centers43aand43bof the rotary balancers4aand4b. A gap44is formed between the both weight connection portions15aand15bwhen the piston24exists at the bottom dead center.

As exemplified inFIG. 2, at the specific observation position, with a larger-diameter end portion7of a connecting rod5being present at a stroke intermediate position above the center axis1of the crank shaft3, the upper rotary balancer4ahas the weight connection portion15aarranged above the rotation center43athereof and the lower rotary balancer4bhas the weight connection portion15bdisposed below the rotation center43bthereof. A gap46is formed between the both weight connection portions15aand15bof the paired upper and lower rotary balancers4aand4b.

As exemplified inFIG. 1, at the specific observation position, with a center axis6of the connecting rod oriented horizontal, a pair of upper and lower cap segment surfaces9aand9bof the larger-diameter end portion7of the connecting rod5are positioned at an upper and a lower positions of the crank pin8and are inclined from a right upper portion of the larger-diameter end portion7to a left lower portion thereof. A cap10is attached by a pair of upper and lower connecting rod bolts11aand11b, head portions12aand12bof which are arranged vertically along the inclination direction of the paired upper and lower cap segment surfaces9aand9b.

At the specific observation position, with the piston24existing at the bottom dead center, the weight connection portion15aof the upper rotary balancer4ais provided with a recess13aat a left lower portion which will oppose to the head portion12aof the upper connecting rod bolt11a.

At the specific observation position, with the piston24being present at the bottom dead center, the upper connecting rod bolt11ahas the head portion12aopposed to the recess13afrom its right upper portion and to the gap44from its right lower portion. The upper connecting rod bolt11ahas an axis an extension line45aof which goes rightwards and upwards to pass through the gap44and the opening41.

As shown inFIG. 2, at the specific observation position, with the larger-diameter end portion7of the connecting rod arranged at the stroke intermediate position above the center axis1of the crank shaft, the lower connecting rod bolt11bhas the head portion12bfacing the gap46from its right portion. The connecting rod bolt11bhas an axis an extension line45bof which goes rightwards and downwards to pass through the gap46and the opening41.

The engine as set forth in each of claims1to8is adaptable to a horizontal engine having the cylinder2oriented horizontal, a vertical engine having the cylinder2oriented vertical, and an inclined engine having the cylinder2oriented slant. In any case, observation is made at the specific observation position with the cylinder2oriented horizontal on the left side of the center axis1of the crank shaft when seen in a direction parallel to the cylinder axis1of the crank shaft to judge if it satisfies the featuring matter stated in each of claims.

Especially, claim2concerns an engine where at the specific observation position, as exemplified inFIG. 1, with the piston24existing at the bottom dead center, the weight connection portion15aof the upper rotary balancer4ahas a left upper portion provided with the other recess13bwhich will become vertically symmetric with respect to the recess13aand is sandwiched by the both recesses13aand13bto form a capital letter “T” in section.

As exemplified inFIG. 1, especially the invention of claim3makes an inner surface of the recess13aarcuate at the specific observation position. The invention of claim4forms the lower rotary balancer4binto the same structure as that of the upper rotary balancer4a. As illustrated inFIG. 6, the invention of claim5is adapted to an engine where the upper rotary balancer4ahas a bearing17internally fitted into a bearing hole16closed at its inner end. As shown inFIG. 1, the invention of claim6relates to an engine where an oil reservoir18is formed below the connecting rod5and a lower surface20of the larger-diameter end portion, which runs axially of the lower connecting rod bolt11b, is connected to a lower surface21of the connecting rod5which runs along the center axis6of the connecting rod, without bypassing via an angled shoulder of the larger-diameter end portion7of the connecting rod5when it is adapted to a horizontal engine which rotates the larger-diameter end portion7of the connecting rod in a clockwise direction19at the specific observation position.

As exemplified inFIG. 6, the invention of claim7concerns an engine which enables an oil pump36to supply oil to a space between the crank pin8and the larger-diameter end portion7of the connecting rod5. As exemplified inFIG. 1, the invention of claim8concerns an engine where at the specific observation position, with the center axis6of the connecting rod5oriented horizontal, the pair of upper and lower cap segment surfaces9aand9bof the larger-diameter end portion7of the connecting rod are positioned at the upper and lower portions of crank pin8and are inclined so that they have a vertical line oriented in a direction defined through rotating it by an angle of 20 degrees to 40 degrees in the clockwise direction.

EFFECT OF THE INVENTION

INVENTION OF CLAIM1

<Effect 1> The Cap Can be Attached and Detached Quickly.

As exemplified inFIGS. 3 and 4, when conducting the maintenance of the piston24or the like, there is a case where with the paired rotary balancers4aand4bassembled to the cylinder block22, the pair of connecting rod bolts11aand11bare removed by a socket wrench47to detach the cap10and thereafter the cap10is assembled to attach the pair of upper and lower connecting rod bolts11aand11bby the socket wrench47. In this case, the paired upper and lower connecting rod bolts11aand11bcan be detached and attached at once. This results in the possibility of promptly attaching and detaching the cap10.

More specifically, when the cap10is removed, first, after the engine has been brought into a state where the piston24is present at the bottom dead center as shown inFIG. 3, the straight socket wrench47is inserted into the cylinder block22through the opening41and the socket48at its leading end is inserted from the gap44along the extension line45aof the axis of the upper connecting rod bolt11a. The head portion12aof the upper connecting rod bolt11ais fitted into the socket48and the socket wrench47is rotated to dismantle the upper connecting rod bolt11aat once. At this time, even if the head portion12aof the upper connecting rod bolt11aextremely approaches the weight connection portion15aof the upper rotary balancer4a, the recess13aenables the socket48to avoid the interference with the weight connection portion15aof the upper rotary balancer4a. Next, after the engine has been brought into a state where the larger-diameter end portion7is present at the stroke intermediate position as shown inFIG. 4, the same socket wrench47and one hand are inserted into the cylinder block22through the opening41and the gap46. The head portion12bof the lower connecting rod bolt11bis fitted into the socket48at the leading end of the socket wrench47. Then while supporting the cap10by one hand so that it does not fall, the socket wrench47is rotated to dismantle the lower connecting rod bolt11bat once.

Next, when the cap10is attached after the predetermined maintenance work, first, the engine has been brought into the state where the larger-diameter end portion7is present at the stroke intermediate position as shown inFIG. 4. Then the socket wrench47has the socket48into which the head portion12bof the lower connecting rod bolt11bis fitted. While having the cap10by one hand and the socket wrench47by the other hand, these are inserted toward the crank pin8through the opening41and the gap46. While supporting the cap10by one hand so that it does not fall, the socket wrench47is rotated by the other hand to attach the lower connecting rod bolt11bat once. Subsequently, after the engine has been brought into the state where the piston24is present at the bottom dead center as shown inFIG. 3, the head portion12aof the upper connecting rod bolt11ais fitted into the socket48of the same socket wrench47, which is inserted toward the cap10through the opening41and the gap44to attach the upper connecting rod bolt11aat once.

<Effect 2> It Is Possible to Produce the Engine at a Lower Cost and to Enable the Larger-Diameter End Portion of the Connecting Rod to Avoid the Interference with the Constituent Parts of the Engine.

When the engine of high exhaust amount is produced by borrowing the cylinder block22to be used for the engine of low exhaust amount as exemplified inFIG. 7and making the radius23from the center axis1of the crank shaft3to the center of the crank pin8larger than that of the engine of low exhaust amount and making the dimension27from the piston pin25to the piston head top surface27smaller than that of the engine of low exhaust amount as shown inFIG. 1, if the structure of the present invention is adopted for the engine of high exhaust amount, the engine can be produced at a lower cost. More specifically, as exemplified inFIG. 1, if the structure of the present invention is adopted for the engine of high exhaust amount, as shown inFIG. 10, while the engine is in operation, the head portion12aof the upper connecting rod bolt11adoes not interfere with the upper portion28aof the crank shaft3and the other portions in the crank case28without using smaller ones for the larger-diameter end portion7of the connecting rod5and the connecting rod bolt11a. Thus a high explosion pressure accompanying the attempt to increase the exhaust amount can be received by the larger-diameter end portion7of the connecting rod5and the connecting rod bolt11awithout problem, which in turn enables the engine of high exhaust amount to be produced by using the cylinder block22to be used for the engine of low exhaust amount with the result of reducing the production cost of the engine.

Further, the cap segment surfaces9aand9bare inclined from the right upper portion to the left lower portion, which results in hardly forming an angled shoulder at the larger-diameter end portion7of the connecting rod5. Thus even if the engine of high exhaust amount as exemplified inFIG. 1is produced by borrowing the cylinder block22of the engine of low exhaust amount illustrated inFIG. 7, the larger-diameter end portion7of the connecting rod5can avoid the interference with the constituent parts (for example, a valve operating cam shaft39and the like) of the engine arranged at the same positions as those of the engine of low exhaust amount.

<Effect 3> Lubricating Performance is High Within the Crank Case.

As exemplified inFIG. 1, the oil sprinkled within the crank case28is splashed back by the inner surface of the recess13aof the upper rotary balancer4ato come to be fine oil mist, which floats within the crank case28. This enhances the lubricating performance within the crank case28.

INVENTION OF CLAIM2

<Effect 4> The Lubricating Performance Becomes Higher Within the Crank Case.

As illustrated inFIG. 1, since there is provided the other recess13bwhich is vertically symmetric with respect to the recess13a, when compared with the case where only the recess13ais provided, there are more portions which splash back the oil, with the result of producing more oil mist to further enhance the lubricating performance within the crank case28.

<Effect 5> It is Possible to Secure a Necessary Strength for the Rotary Balancer.

As illustrated inFIG. 1, the weight connection portion15ais sandwiched by the recesses13aand13bto form a capital letter “T” in section. This results in securing a necessary strength for the rotary balancer4a.

INVENTION OF CLAIM3

<Effect 6> It is Possible to Enhance the Strength of the Connection Portion.

As exemplified inFIG. 1, since at the specific observation position, the recess13ahas its inner surface made arcuate, the connection portion15can have a higher strength than the case where the recess13ahas a bent inner surface, by an amount corresponding to the absence of the concentration of stress.

INVENTION OF CLAIM4

<Effect 7> The Lubricating Performance is More Enhanced Within the Crank Case.

As exemplified inFIG. 1, there are more portions which splash back the oil than the case where only one rotary balancer4ais provided with the recess13a, which results in producing more oil mist. This more enhances the lubricating performance within the crank case28.

<Effect 8> The Upper and Lower Rotary Balancers can be Made Common to Each Other

As illustrated inFIG. 1, the upper and lower rotary balancers are formed into the same structure to result in making the upper and lower rotary balancers common to one anther. This prevents the upper and lower rotary balancers from being attached by mistake and besides facilitates the control of parts.

INVENTION OF CLAIM5

<Effect 9> The Lubricating Performance is Remarkably Improved.

As illustrated inFIG. 6, in the case where the rotary balancer4ahas the bearing17internally fitted into the bearing hole16closed at its inner end, originally oil mist hardly invades the bearing17of the rotary balancer14aand therefore a high lubricating performance is unexpectable. However, in the case of the present invention, more oil mist is produced within the crank case8with the result of being able to obtain a high lubricating performance. Thus the lubricating performance is remarkably improved.

INVENTION OF CLAIM6

<Effect 10> The Oil is Consumed in a Smaller Amount and the Larger-Diameter End Portion of the Connecting Rod can Avoid the Interference with the Constituent Parts of the Engine.

As shown inFIG. 1, when adapting this invention to a, horizontal engine where the oil reservoir18is formed below the connecting rod5and at the specific observation position, the larger-diameter end portion7of the connecting rod5is rotated in the clockwise direction19, the lower surface20of the larger-diameter end portion7, which runs axially of the lower connecting rod bolt11bis connected to the lower surface21of the connecting rod5, which runs along the center axis6of the connecting rod5without bypassing via the angled shoulder of the larger-diameter end portion7of the connecting rod5. In consequence, when compared with the case where they are connected to each other through such angled shoulder, the oil invades from the cylinder2to a combustion chamber in quantity reduced by an amount in which such shoulder would have splashed the oil or the waved oil within the oil reservoir18over the cylinder2. This results in decreasing the oil consumption amount.

Further, the larger-diameter end portion7of the connecting rod5does not have the angled shoulder. Thus even if the engine of high exhaust amount as shown inFIG. 1is produced by borrowing the cylinder block22of the engine of low exhaust amount as shown inFIG. 7, the larger-diameter end portion7of the connecting rod5can avoid the interference with the constituent parts of the engine (for example, the valve operating cam shaft39and the like) arranged at the same positions as those of the engine of low exhaust amount.

INVENTION OF CLAIM7

<Effect 11> The Lubricating Performance is High Within the Crank Case.

As exemplified inFIG. 6, the oil can be supplied by the oil pump36to the space between the crank pin8and the larger-diameter end portion7of the connecting rod5. Therefore, when the oil which has leaked out of the space between the crank pin8and the large-diameter end portion7of the connecting rod is sprinkled around the crank shaft3upon the rotation of the same, part of the sprinkled oil is splashed back by the inner surface of the recess13aof the rotary balancer4ato become fine oil mist, which floats within the crank case28. This enhances the lubricating performance within the crank case28.

INVENTION OF CLAIM8

<Effect 12> It is Possible to Put the Invention into Practice Without any Trouble.

As exemplified inFIG. 1, the paired upper and lower cap segment surfaces9aand9bare positioned at the upper and lower portions of the crank pin8and are inclined so that they are oriented in a direction defined through rotating their vertical line by an angle of 20 degrees to 40 degrees in the clockwise direction19. Therefore, the invention can be put into practice without any trouble.

More specifically, with the inclination angle of less than 20 degrees, there is a likelihood that the head portion12aof the upper connecting rod bolt11ainterferes with the upper portion28aof the crank case28unless the larger-diameter end portion7of the connecting rod5and the upper connecting rod bolt11aare made quite small. Further, with the inclination angle of not less than 40 degrees, the socket48of the socket wrench47which has been inserted through the gap44cannot be fitted onto the head portion12aof the upper connecting rod bolt11a. On the other hand, with the inclination angle within the range of 20 degrees to 40 degrees, even if the larger-diameter end portion7of the connecting rod5and the upper connecting rod bolt11aare formed large enough to withstand the high explosion pressure of the engine of high exhaust amount, there occurs no problem and therefore the invention can be put into practice without any trouble.

DESCRIPTION OF PREFERRED EMBODIMENTS

An embodiment of the present invention is explained based on the drawings.

In this embodiment, an explanation is given for an engine of high exhaust amount. The engine of high exhaust amount is produced by borrowing the cylinder block to be used for an engine of low exhaust amount.

Any one ofFIGS. 1 to 6explains an engine of high exhaust amount according to the embodiment of the present invention. An explanation is given by utilizing a horizontal diesel engine in this embodiment.

This engine is outlined as follows.

As shown inFIG. 5, when seen in a direction parallel to a center axis1of a crank shaft3, at a specific observation position with a cylinder2oriented horizontal on a left side of the center axis1of the crank shaft3, a pair of upper and lower rotary balancers4aand4bare arranged on a right horizontal side of the crank shaft3. A cylinder block22comprises a crank case28, an oil reservoir18disposed below the crank case28, a cylinder liner attaching portion30on a left side of the crank case28and a cylinder jacket31surrounding the cylinder liner attaching portion30. As shown inFIG. 1, the crank case28accommodates the crank shaft3and the pair of upper and lower rotary balancers4aand4b. The cylinder block22has a right end wall provided with an opening41, through which connecting rod bolts11aand11bcan be assembled and detached. A closure21covers the opening41and is attached detachably by bolts42aand42b. The paired upper and lower balancers4aand4bare arranged vertically symmetric with respect to a horizontal plane which passes by the center axis1of the crank shaft3.

The paired upper and lower rotary balancers4aand4bare primary balancers each of which makes one rotation while the crank shaft3makes one rotation. At the specific observation position, while the crank shaft3rotates in a clockwise direction19, the upper rotary balancer4arotates in a counter-clockwise direction and the lower rotary balancer4brotates in the clockwise direction. As shown inFIG. 5, the cylinder block22has a left end to which a cylinder head32is assembled. A head cover37is assembled to the cylinder head32. At an upper portion of the cylinder block22, a radiator33which communicates with the cylinder jacket31is arranged above the cylinder jacket31and a fuel tank34is disposed above the crank case28.

As shown inFIG. 5, used for the cylinder2is a cylinder liner2aattached to the cylinder liner attaching portion30. A piston24is internally fitted into the cylinder liner2a. The crank shaft3is interlockingly connected to the piston24through a connecting rod5. A valve operating cam shaft39is arranged at a left lower portion of the crank shaft3below the cylinder liner2a. As shown inFIG. 6, a smaller-diameter end portion35of the connecting rod5is connected to the piston24by a piston pin25. A larger-diameter end portion7of the connecting rod5is connected to the crank shaft3by a crank pin8. An oil pump36can supply oil to a journal portion3aof the crank shaft3and the crank pin8. Further, the upper rotary balancer4ais provided with a weight connection portion15abetween weight portions14and14. This cylinder block22has a front end portion, to which a gear case37is assembled. This gear case37accommodates a timing transmission gear38. As shown inFIG. 1, at the specific observation position, with the piston24existing at a bottom dead center, the paired upper and lower rotary balancers4aand4bhave the respective weight connection portions15aand15bpositioned on left horizontal sides of centers43aand43bof the respective balancers. A gap44is formed between the both weight connection portions15aand15bwhen the piston24is present at the bottom dead center. As illustrated inFIG. 2, at the specific observation position, with the larger-diameter end portion7of the connecting rod5existing at a stroke intermediate position above the center axis1of the crank shaft3, the upper rotary balancer4ahas the weight connection portion15apositioned above the rotation center43aof the balancer4aand the lower rotary balancer4bhas the weight connection portion15barranged below the rotation center43bof the balancer4b. A gap46is formed between the both weight connection portions15aand15bof the paired upper and lower rotary balancers4aand4bwhen the larger-diameter end portion7is present at the stroke intermediate position.

The connecting rod5is constructed as follows.

As shown inFIG. 1, at the specific observation position, with a center axis6of the connecting rod5oriented horizontal, a pair of upper and lower cap segment surfaces9aand9bof the larger-diameter end portion7of the connecting rod5are positioned at an upper and a lower portions of the crank pin8and are inclined from a right upper portion of the larger-diameter end portion7of the connecting rod5to a left lower portion thereof. A cap10is attached by a pair of upper and lower connecting rod bolts11aand11b, head portions12aand12bof which are vertically arranged along the inclination direction of the paired upper and lower cap segment surfaces9aand9b. A lower surface20of the larger-diameter end portion7, which runs axially of the lower connecting rod bolt11bis connected to a lower surface21of the connecting rod5, which runs along the center axis6of the connecting rod5, without bypassing via an angled shoulder of the larger-diameter end portion7of the connecting rod5. The lower surface20of the larger-diameter end portion7makes an obtuse angle with the lower surface21of the connecting rod5.

The upper rotary balancer4ais constructed as follows.

As shown inFIG. 1, at the specific observation position, with the piston24existing at the bottom dead center, the weight connection portion15aof the upper rotary balancer4ais provided with a recess13aat a left lower portion which opposes to the head portion12aof the upper connecting rod bolt11a. An oil pump36as shown inFIG. 6can feed oil to a space between the crank pin8and the larger-diameter end portion7of the connecting rod5.

Further, as shown inFIG. 1, at the specific observation position, with the piston24being present at the bottom dead center, the recess13ais made to face the head portion12aof the upper connecting rod bolt11afrom a right upper portion thereof and the gap44from a right lower portion thereof. This upper connecting rod bolt11ahas an axis an extension line45aof which goes rightwards and downwards to pass through the gap44and the opening41. The recess13ahas a lower corner angled portion13copposed to a right upper corner angled portion12cof the head portion12aof the upper connecting rod bolt11afrom the just right horizontal portion thereof. Moreover, while the engine is in operation, the recess13enables the rotary balancer4ato avoid the interference with the head portion12aof the upper connecting rod bolt11a. Therefore, when the piston is at the bottom dead center, the upper connecting rod bolt11ahas the head portion12aextremely close to the weight connection portion15aof the upper rotary balancer4a. However, when detaching and attaching the upper connecting rod bolt11a, the recess13aprevents the socket48of the socket wrench47from interfering with the weight connection portion15aof the upper rotary balancer4a.

Additionally, as shown inFIG. 2, at the specific observation position, with the larger-diameter end portion7of the connecting rod5existing at the stroke intermediate position above the center axis1of the crank shaft3, the lower connecting rod bolt11bhas the head portion12bopposed to the gap46from its right portion. The connecting rod bolt11bhas an axis an extension line45bwhich goes rightwards and downwards to pass through the gap46and the opening41.

As shown inFIG. 1, at the specific observation position, with the piston24being present at the bottom dead center, the weight connection portion15aof the upper rotary balancer4ais provided at its left upper portion with the other recess13bwhich becomes vertically symmetric with respect to the recess13a. The weight connection portion15ais sandwiched by the both recesses13aand13bto form a capital letter “T” in section. As illustrated inFIG. 1, at the specific observation position, either of the recesses13aand13bhas its inner surface made arcuate. Therefore, it is sufficient if the weight connection portion15ais carved only by a small amount as if it were carved along a locus of the upper connecting rod bolt12a. The lower rotary balancer4bhas the same structure as that of the upper rotary balancer4a. As shown inFIG. 6, the bearing17of the upper rotary balancer4ais internally fitted into the bearing hole16closed at its inner end. This is same to the bearing of the lower rotary balancer4b.

Further, as shown inFIG. 1, at the specific observation position, with the center axis6of the connecting rod5oriented horizontal, the paired upper and lower cap segment surfaces9aand9bof the larger-diameter end portion7are positioned at the upper and lower portions of the crank pin8and are inclined in a direction defined through rotating their vertical line by 30 degrees in the clockwise direction. This angle is preferably 20 degrees to 40 degrees and more preferably, 20 degrees to 35 degrees.

The above-mentioned engine is produced by the following procedures.

According to this method, the engine of high exhaust amount is produced by borrowing a cylinder block22and a valve operating cam shaft39to be used for the engine of low exhaust amount as shown inFIG. 7and making a radius23from a center axis1of a crank shaft3to a center of a crank pin8larger than that of the engine of low exhaust amount and making a dimension27from a center of a piston pin25to a piston head top surface26smaller than that of the engine of low exhaust amount as shown inFIG. 1. Further, an outer diameter of a piston24is made larger than that of the engine of low exhaust amount as well as inner and outer diameters of a cylinder liner2a.

The engine of low exhaust amount is common to the engine of high exhaust amount in the following main structures.

As shown inFIG. 7, when seen in a direction parallel to the center axis1of the crank shaft3, at the specific observation position with the cylinder2oriented horizontal on a left side of the center axis1of the crank shaft3, a pair of upper and lower rotary balancers4aand4bare arranged on a right horizontal side of the crank shaft3. The pair of upper and lower rotary balancers4aand4bhave a right horizontal side provided with an opening41, which is covered with a closure42.

At the specific observation position, with the piston24existing at the bottom dead center, the paired upper and lower rotary balancers4aand4bhave respective weight connection portions15aand15bpositioned on a left horizontal sides of centers43aand43bof the respective balancers. And a gap44is formed between the both weight connection portions15aand15bwhen the piston24is present at the bottom dead center.

Like inFIG. 2, at the specific observation position, with a larger-diameter end portion7of a connecting rod5being present at a stroke intermediate position above the center axis1of the crank shaft3, the upper rotary balancer4ahas the weight connection portion15apositioned above its rotation center43aand the lower rotary balancer4bhas the weight connection portion15barranged below its rotation center43b. A gap46is formed between the both weight connection portions15aand15bof the paired rotary balancers4aand4bwhen the larger-diameter end portion7of the connecting rod5is present at the stroke intermediate position. The valve operating cam shaft39is disposed at a left lower portion of the crank shaft3below a cylinder liner2a. The same cylinder block22and the same valve operating cam shaft39are used. The paired rotary balancers4aand4bare arranged in the same manner as well as the valve operating cam shaft39. InFIGS. 7 to 14, the same elements as those of the engine of high exhaust amount as shown inFIGS. 1 to 6are designated by the same reference characters.

The engine of low exhaust amount is different from the engine of high exhaust amount on the following structures.

As shown inFIG. 7, at the specific observation position, with the center axis6of the connecting rod5oriented horizontal, the paired upper and lower cap segment surfaces9aand9bof the larger-diameter end portion7of the connecting rod5are positioned at an upper and a lower portions of the crank pin8and are made vertical. A cap10is attached by a pair of upper and lower connecting rod bolts11aand11b, head portions12aand12bof which are vertically arranged along the formation direction of the paired upper and lower cap segment surfaces9aand9b. The paired upper and lower rotary balancers4aand4bare not provided with such recesses as used in the engine of high exhaust amount. The piston24and the cylinder liner2aare different from those of the engine of high exhaust amount in dimension. In short, an outer diameter of the piston24is smaller than that of the engine of high exhaust amount as well as inner and outer diameters of the cylinder liner2a. In addition, as shown inFIG. 7, the radius23from the center axis1of the crank shaft3to the center of the crank pin8is made smaller than that of the engine of high exhaust amount and the dimension27from the center of the piston pin25to the piston head top surface26is made larger than that of the engine of high exhaust amount.

The engine of high exhaust amount is produced by the following concrete method.

The engine as shown inFIGS. 1 to 6is produced by employing the cylinder block22and the valve operating cam shaft3to be used for the engine of low exhaust amount as shown inFIGS. 7 to 9as main borrowed parts and utilizing the piston24, the cylinder liner2a, the connecting rod5, the crank shaft3, and the paired upper and lower rotary balancers4aand4bas exclusive parts. As for the other parts such as the cylinder head32, the radiator33, the fuel tank34and the like, they are borrowed from the engine of low exhaust amount. Since the cylinder liner2ahas the outer diameter made larger than that of the engine of low exhaust amount, the cylinder liner attaching portion30has its inner surfaced carved more than in the case of the engine of low exhaust amount to widen the inner diameter.

When borrowing the cylinder block22and the valve operating cam shaft39to be used for the engine of low exhaust amount as shown inFIG. 7, as illustrated inFIG. 1, at the specific observation position, with the valve operating cam shaft39arranged at a position lower than the center axis1of the crank shaft3, the lower surface20of the larger-diameter end portion7, which runs axially of the lower connecting rod bolt11b, is connected to the lower surface21of the connecting rod5which runs along the center axis6of the connecting rod5, without bypassing via an angled shoulder of the larger-diameter end portion7of the connecting rod5, thereby enabling the larger-diameter end portion7of the connecting rod5to avoid the interference with the valve operating cam shaft39arranged in the same manner as in the engine of low exhaust amount.

In the case of adopting the above-mentioned production method, as shown inFIG. 10, the head portion12aof the upper connecting bolt11aand a shoulder40at an upper portion of the larger-diameter end portion7of the connecting rod5do not interfere with the upper portion28aof the crank shaft3in the crank case28. The lower surface20of the larger-diameter end portion7of the connecting rod5does not interfere with the valve operating cam shaft39arranged in the same manner as in the engine of low exhaust amount as well.

As illustrated inFIG. 10, differently from the embodiment of the present invention, in the event that a connecting rod of the same structure as that of the conventional technique is used, the head portion112aof the upper connecting rod bolt interferes with the upper portion28aof the crank shaft3in the crank case28and the shoulder140at a lower portion of the larger-diameter end portion of the connecting rod interferes with the valve operating cam shaft39arranged in the same manner as in the engine of low exhaust amount.