Title of Invention	TWO-STROKE INTERNAL COMBUSTION ENGINE
Abstract	A two-stroke internal combustion (IC) engine 100 is disclosed. The two-stroke IC engine 100 includes a cylinder 102 having a booster port 118 in a wall of the cylinder 102, a piston 106 reciprocating inside the cylinder 102, and a crankcase 112 having a combustion chamber 134 and an intake port 138 for introducing an air-oil mixture inside the crankcase chamber 134. The piston 106 is provided with an opening 132 in a piston wall and in the proximity to a piston crown 130. The opening 132 in the piston 106 aligns with the booster port 118 when the piston 106 is at a bottom dead center FIG. 1

Title of Invention

TWO-STROKE INTERNAL COMBUSTION ENGINE

Abstract

A two-stroke internal combustion (IC) engine 100 is disclosed. The two-stroke IC engine 100 includes a cylinder 102 having a booster port 118 in a wall of the cylinder 102, a piston 106 reciprocating inside the cylinder 102, and a crankcase 112 having a combustion chamber 134 and an intake port 138 for introducing an air-oil mixture inside the crankcase chamber 134. The piston 106 is provided with an opening 132 in a piston wall and in the proximity to a piston crown 130. The opening 132 in the piston 106 aligns with the booster port 118 when the piston 106 is at a bottom dead center FIG. 1

Full Text	TECHNICAL FIELD The subject matter described herein, in general, relates to an internal combustion engine and in particular, relates to a two-stroke internal combustion engine. BACKGROUND In conventional two-stroke diesel engines, fuel and air are provided separately for combustion. The air is first compressed to a high pressure in a combustion chamber and the fuel is then sprayed in an atomized state in the combustion chamber for combustion. The compression of the air to a high pressure and the combustion of the fuel inside the combustion chamber generate a lot of heat thus increasing the temperature inside the engine. As a result, all the components inside the engine, including pistons, connecting rods, and piston pins connecting the piston and the connecting rod, are exposed to high temperatures, the phenomenon being termed as high thermal loading. Particularly, the piston pin, which is in direct contact with the piston, tends to receive heat load from the piston crown by conduction. This heat load can cause high thermal stresses that result in over-heating and wear over a period of time, thereby effecting the functioning and life of the engine. Additionally, the over heating may also result in piston seizure, i.e., a sudden stalling of the engine, caused by the piston becoming stuck in a piston bore. Another factor influencing the high thermal load is the friction between various components such as the piston pin and the connecting rod. To keep the engine running, the piston, the piston pin, and the connecting rod are in continuous reciprocating or rotary motion. These components of a conventional slider-crank mechanism are critical for smooth output from such engines and in this process, these components bear significant proportion of thermal and mechanical loads. Therefore, these components need proper lubrication and cooling in order to prevent damages induced due to friction and high thermal loading. In addition, as the piston pin also requires high load carrying capacity, it becomes essential to protect the piston pin from the aforesaid damages. In conventional systems having large engines, the lubrication and cooling of the piston, the piston pins, the bearings, and the small end is provided through coolants, lubricants or a combination thereof present in a central reservoir. In one system, the central reservoir is incorporated in the piston itself along with passages communicating between the central reservoir and a coolant channel present in the piston body. The passages are used to transfer the coolant and the lubricant from the central reservoir to the coolant channel for cooling and lubricating the piston, and to move the heated coolant and lubricant from the coolant channel back to the reservoir. The coolant channel is further connected to a central cavity in the piston body through drain passages for lubricating various components, such as the piston pin and the small end of the connecting rod, connected to the piston. However, such a cooling and lubricating system complicates the design of the piston due to the incorporation of the coolant channel, the central reservoir, the central cavity, and various passages inside the piston. Moreover, the maintenance of the cooling and lubricating system inside the reservoir is difficult. In small or medium sized engines, lubricant used for large end pressure-fed bearings is passed through a hole drilled in the connecting rod to the small end of the connecting rod. This is used for cooling and lubrication of the small end. Such a design is also complicated and does not provide the required extent of cooling. SUMMARY The subject matter described herein is directed to a two-stroke internal combustion (IC) engine having a cylinder, an intake port, a crankcase chamber receiving an air-oil mixture from the intake port, a piston pin, and a piston reciprocating inside the cylinder. A wall of the piston is provided with an opening located at a location above the piston pin and in proximity to a piston crown. The opening aligns with a booster port in a wall of the cylinder such that the air-oil mixture entering the crankcase chamber flows through the opening to the booster port. As the air-oil mixture flows through the piston, it passes over a piston pin of the piston, thus cooling and lubricating the piston pin. With this kind of an arrangement, the high thermal load on the piston pin is reduced, and the size and the mass of the piston pin can also be reduced. Additionally, the piston pin is located at an optimum distance from the piston crown, thus resulting in higher durability, optimum reciprocating masses and longer life of the piston pin. Further, the optimum distance of the piston pin from the piston crown provides a narrow passage for the flow of air-oil mixture ensuring that the air-oil mixture passes over the piston pin before entering the booster port. These and other features, aspects, and advantages of the present subject matter will be better understood with reference to the following description and appended claims. This summary is provided to introduce a selection of concepts in a simplified form. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. BRIEF DESCRIPTION OF DRAWINGS The above and other features, aspects, and advantages of the subject matter will be better understood with regard to the following description, appended claims, and accompanying drawings where: Fig. 1 illustrates a cross sectional view of an exemplary two-stroke internal combustion (IC) engine 100, according to one embodiment of the present subject matter. Fig. 2 illustrates a flow of an air-oil mixture in a piston in the exemplary two-stroke IC engine 100 of fig. 1, according to an embodiment of the present subject matter. DETAILED DESCRIPTION The subject matter described herein is directed to a two-stroke internal combustion (IC) engine, such as a diesel engine, interchangeably referred to as an engine. In such engines, air is compressed to high pressures inside a combustion chamber of a cylinder to achieve high temperatures. Due to the high temperatures, a fuel injected in the combustion chamber gets ignited. The combustion of fuel further increases the temperature inside the engine and adversely affects components of the engine such as a piston, a connecting rod, and a piston pin connecting the piston and the connecting rod. An extremely high temperature inside the engine is a necessity; however, extreme temperatures can adversely affect the components of the engine, especially the piston pin and the piston, and can be detrimental to the life and efficiency of the engine. Therefore, the following description relates to an arrangement for providing flow of an air-oil mixture inside the piston and the cylinder for cooling and lubricating the piston pin, thereby reducing wear and tear of the piston pin due to high thermal loading. Additionally, the size and the mass of the piston pin are reduced and the piston pin is located at an optimum distance from the piston crown, thus resulting in higher durability, optimum reciprocating masses and longer life of the piston pin. Fig. 1 illustrates a cross sectional view of an exemplary two-stroke internal combustion (IC) engine 100, hereinafter interchangeably referred to as an engine 100, according to one embodiment of the present subject matter. In said embodiment, the IC engine 100 is a diesel engine. The engine 100 includes a cylinder 102 having a cylinder head 104, a piston 106, a piston pin 108, a connecting rod 110, a crankcase 112, a crankshaft 114, and a combustion chamber 116. The combustion chamber 116 is the region between the piston 106 and the cylinder head 104. The cylinder 102 further includes a booster port 118 in a cylinder wall, a coolant passage 120 in proximity to the booster port 118, a nozzle 122 located on the cylinder head 104, scavenge ports (not shown in this figure), and an exhaust port 124. The connecting rod 110 has a small end 126 and a big end 128. The small end 126 is connected to the piston 106 using the piston pin 108, whereas the big end 128 is connected to the crankshaft 114 housed inside the crankcase 112. Here, the terms "small end" and "big end" reflect a convention for identifying location or association of the term with the piston 106 and the crankshaft 114 respectively, rather than necessarily absolute or relative size of the joint. In one implementation of said embodiment, the piston 106 has a hollow region defined by a piston wall and a piston crown 130. The piston wall has an opening 132 located above the centre of the piston pin 108 and in proximity to the piston crown 130. Additionally, the size and the mass of the piston pin 108 can be reduced and the piston pin 108 is located at an optimum distance from the piston crown 130, such as at a distance equal to 0.5 to 0.7 times the diameter of the piston 106. Such a location of the piston pin 108 provides a narrow passage between the piston pin 108 and the piston crown 130. Reducing the size and the mass of the piston pin provides optimum reciprocating masses thus ensuring a longer life of the piston pin. The piston 106 reciprocates inside the cylinder 102 between a top dead center (TDC) and a bottom dead center (BDC). The TDC is in proximity to the cylinder head 104 and the BDC is in proximity to the crankcase 112. The location of the booster port 118 and the opening 132 is such that the opening 132 in the piston wall aligns with an opening of the booster port 118 when the piston 106 is at BDC. Further, the crankcase 112 is provided with a crankcase chamber 134, a one-way valve 136 hereinafter referred to as an intake valve, and an intake port 138 for introducing a mixture of fuel-free air and a lubricating oil mist, interchangeably referred to as an air-oil mixture, directly into the crankcase chamber 134 as indicated by an arrow 140. In one embodiment, the intake valve 136 is a reed valve, which restricts the flow of the air-oil mixture in a single direction from the intake port 138 to the crankcase chamber 134. The intake valve 136 prevents a reverse flow of the air-oil mixture, i.e., it prevents the air-oil mixture from moving out of the crankcase chamber 134 into the intake port 138. The air-oil mixture is received by the crankcase chamber 134 when the piston 106 starts moving upwards, i.e., towards the TDC. When the piston 106 starts moving upwards, the intake valve 136 opens and the air-oil mixture starts entering the crankcase chamber 134 from the intake port 136 and fill the crankcase chamber 134 and the space between the crankcase chamber 134 and the hollow region of the piston 106. As the piston 106 reaches the TDC the intake valve 136 closes thus stopping additional air-oil mixture from entering the crankcase chamber 134. As the piston 106 reaches the TDC, combustion of fuel, for example diesel, takes place inside the combustion chamber 116. The gases thus produced expand in volume to push the piston 106 down towards the BDC. The downward movement of the piston 106 compresses the air-oil mixture between the hollow region of the piston 106 and the crankcase chamber 134. Compression of the air-oil mixture is facilitated by using the reed valve as the intake valve 124, as it prevents the air-oil mixture form escaping into intake port 138 during the compression. The piston 106 continues to move downwards compressing the air-oil mixture, until it reaches the (BDC). At this instant, the opening 132 is substantially aligned with a first section of the booster port 118. The downwards movement of the piston 106, forces some of the compressed air-oil mixture, present inside the crankcase chamber 134, to escape to the combustion chamber 116 through the scavenge ports. Whereas, rest of the compressed air-oil mixture trapped inside the crankcase chamber 134 and the hollow region of the piston 104 are forced to rush through the opening 132, into the booster port 118. Since the opening 132 is above the piston pin 108 and is offset with respect to the piston pin 108, the air-oil mixture is forced to move in the narrow region over the piston pin 108 towards the booster port 118. The movement of the air-oil mixture over the piston pin 108 provides lubrication and cooling effect to the piston pin 108 and the small end 126. As the air-oil mixture lubricates the piston pin 108 and the small end 118, the concentration of the lubricating oil in the air-oil mixture gets substantially reduced thus preventing any effect of the lubricating oil in the combustion. The booster port 118 facilitates the transfer of the air-oil mixture from the hollow region of the piston 106 towards the combustion chamber 116 as indicated by arrows 142 and 144. The arrow 142 indicates the flow of air-oil mixture in the first section of the booster port 118 from the opening 132 and the arrow 144 indicates the flow of air-oil mixture in a second section of the booster port 118 and into the combustion chamber 116. The two-sections of the booster port 118 are mentioned to indicate change in direction of flow of the air-oil mixture in the booster port 118 prior to entry into the combustion chamber 116. Fig. 2 illustrates a cross-sectional view 200 of the IC engine 100, particularly the cylinder 102 and the piston 106, showing the flow of the air-oil mixture according to an embodiment of the present subject matter. As discussed earlier, the opening 132 is near the piston crown 130. Thus, when the opening 132 of the piston 106 is aligned with the booster port 118, the air-oil mixture is already compressed to the maximum limit inside the crankcase chamber 134 and the hollow region of the piston 106. In this position of the piston 106, the air-oil mixture flows in the direction shown by the arrows 202, 204, and 206 around the piston pin 108 such that the air-oil mixture absorbs the heat from the piston 106 and the piston pin 108. The heat load may be generated due to the reciprocating movement of the piston 106 and the combustion taking place inside the combustion chamber 116 above the piston crown 130, as discussed earlier. Additionally, the lubricating oil mist in the air-oil mixture lubricates the piston pin 108, the small end 126, and a bearing 208 provided between the piston pin 108 and the small end 126. Droplets of the lubricating oil adhere to the piston pin 108 and the piston 106 resulting in better and prolonged lubrication and effective working of both the components. The lubricating oil reaches the bearing 208 through small passages, such as passages 210-1 and 210-2, provided in the small end 126. The bearing 208 is provided for facilitating smooth relative movement between the connecting rod 110 and the piston pin 108, while ensuring that gas load and inertia load can be supported reliably at this joint of the connecting rod for the desired life of the connecting rod. The bearing 208 may be either a full-complement bearing or a caged needle-roller bearing. The piston pin 108 may be a fixed pin, a semi-floating pin, or a full-floating pin. Further, the air-oil mixture entering the booster port 118 is cooled by coolant present in the coolant passage 120. A coolant such as water or a mixture of water and glycol is circulated inside the coolant passage 120. The cooling of the air-oil mixture in the booster port 118 also increases the density of the air-oil mixture that enables higher mass flow rate of the air-oil mixture to the combustion chamber 116. Increase in the mass flow rate of the air-oil mixture facilitates improved filling of the combustion chamber 116 which in-turn could help to obtain higher output from the engine 100. The cooled air-oil mixture flows into the combustion chamber 116 through the booster port 118 and mixes with the rest of the air-oil mixture that had flown inside the combustion chamber 116 through scavenge ports 212. As the piston 106 moves upwards again, the air-oil mixture in the combustion chamber 116 is compressed to a high pressure, increasing the temperature inside the combustion chamber 116. As the piston 106 reaches TDC, the fuel is sprayed into the combustion chamber 116 by the nozzle 122. The fuel burns and the gases thus produced expand in volume to push the piston 106 towards the BDC. When the piston 106 travels downwards the exhaust gases produced during combustion are emitted via the exhaust port 124. While certain features of the claimed subject matter have been illustrated and described herein, many modifications, substitutions, changes, and equivalents will now occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes that fall within the true spirit of the claimed subject matter. I/We claim: 1. A two-stroke internal combustion (IC) engine (100) comprising: a cylinder (102) having a cylinder wall; a piston (106) adapted to reciprocate inside the cylinder (102), the piston (106) having a piston wall and a piston crown (130); a piston pin (108) connecting the piston (106) to a small end (126) of a connecting rod (110); a crankshaft (114) connected to a big end (128) of the connecting rod (110); and a crankcase (112) housing the crankshaft (114), wherein the crankcase (112) includes a crankcase chamber (134) and an intake port (138), and wherein the intake port (138) introduces an air-oil mixture into the crankcase chamber (134); characterized in that, the cylinder (102) has a booster port (118) in the cylinder wall; and the piston (106) has an opening (132) in the piston wall, wherein the opening (132) is provided in proximity to the piston crown (130) and above the piston pin (108), wherein the opening (132) is aligned with the booster port (118) when the piston (106) is at a bottom dead center. 2. The two-stroke IC engine (100) as claimed in claim 1, wherein a section of the booster port (118) opens in a combustion chamber (116). 3. The two-stroke IC engine (100) as claimed in claim 1, wherein the cylinder (102) comprises a coolant passage (120) in proximity to the booster port (118) such that a coolant circulating inside the coolant passage (120) cools the air-oil mixture flowing through the booster port (118). 4. The two-stroke IC engine (100) as claimed in claim 3, wherein the coolant is selected from the group consisting of water and a mixture of water and glycol. 5. The two-stroke IC engine (100) as claimed in claim 1, wherein the two-stroke IC engine (100) is a diesel engine. 6. The two-stroke IC engine (100) as claimed in claim 1, wherein the piston pin (108) is selected from the group consisting of a fixed pin, a semi-floating pin, and a full-floating pin. 7. The two-stroke IC engine (100) as claimed in claim 1, wherein a bearing (208) is provided between the piston (106) and the small end (126), and wherein the small end (126) includes passages (210-1, 210-2) to lubricate the bearing (208). 8. The two-stroke IC engine (100) as claimed in claim 7, wherein the bearing (208) is selected from the group consisting of a full-complement bearing and a caged needled-roller bearing. 9. A vehicle comprising a two-stroke internal combustion (IC) engine (100) as claimed in any of the preceding claims. 10. A method comprising: introducing an air-oil mixture inside a crankcase chamber (134); compressing the air-oil mixture inside the crankcase chamber (134) and a hollow region of a piston (106); and aligning an opening (130) in a piston wall of the piston (106) with a booster port (118) in a cylinder (102) to force the air-oil mixture to flow over the piston pin (108) and enter the booster port (118) through the opening (132), wherein the flow of the air-oil mixture cools and lubricates the piston pin (108), a small end (126), and a bearing (208).

Full Text

TECHNICAL FIELD

The subject matter described herein, in general, relates to an internal combustion engine and in particular, relates to a two-stroke internal combustion engine.

BACKGROUND

In conventional two-stroke diesel engines, fuel and air are provided separately for combustion. The air is first compressed to a high pressure in a combustion chamber and the fuel is then sprayed in an atomized state in the combustion chamber for combustion. The compression of the air to a high pressure and the combustion of the fuel inside the combustion chamber generate a lot of heat thus increasing the temperature inside the engine. As a result, all the components inside the engine, including pistons, connecting rods, and piston pins connecting the piston and the connecting rod, are exposed to high temperatures, the phenomenon being termed as high thermal loading. Particularly, the piston pin, which is in direct contact with the piston, tends to receive heat load from the piston crown by conduction. This heat load can cause high thermal stresses that result in over-heating and wear over a period of time, thereby effecting the functioning and life of the engine. Additionally, the over heating may also result in piston seizure, i.e., a sudden stalling of the engine, caused by the piston becoming stuck in a piston bore. Another factor influencing the high thermal load is the friction between various components such as the piston pin and the connecting rod.

To keep the engine running, the piston, the piston pin, and the connecting rod are in continuous reciprocating or rotary motion. These components of a conventional slider-crank mechanism are critical for smooth output from such engines and in this process, these components bear significant proportion of thermal and mechanical loads. Therefore, these components need proper lubrication and cooling in order to prevent damages induced due to friction and high thermal loading. In addition, as the piston pin also requires high load carrying capacity, it becomes essential to protect the piston pin from the aforesaid damages.

In conventional systems having large engines, the lubrication and cooling of the piston, the piston pins, the bearings, and the small end is provided through coolants, lubricants or a combination thereof present in a central reservoir. In one system, the central reservoir is incorporated in the piston itself along with passages communicating between the central reservoir and a coolant channel present in the piston body. The passages are used to transfer the coolant and the lubricant from the central reservoir to the coolant channel for cooling and lubricating the piston, and to move the heated coolant and lubricant from the coolant channel back to the reservoir. The coolant channel is further connected to a central cavity in the piston body through drain passages for lubricating various components, such as the piston pin and the small end of the connecting rod, connected to the piston.

However, such a cooling and lubricating system complicates the design of the piston due to the incorporation of the coolant channel, the central reservoir, the central cavity, and various passages inside the piston. Moreover, the maintenance of the cooling and lubricating system inside the reservoir is difficult. In small or medium sized engines, lubricant used for large end pressure-fed bearings is passed through a hole drilled in the connecting rod to the small end of the connecting rod. This is used for cooling and lubrication of the small end. Such a design is also complicated and does not provide the required extent of cooling.

SUMMARY

The subject matter described herein is directed to a two-stroke internal combustion (IC) engine having a cylinder, an intake port, a crankcase chamber receiving an air-oil mixture from the intake port, a piston pin, and a piston reciprocating inside the cylinder.

A wall of the piston is provided with an opening located at a location above the piston pin and in proximity to a piston crown. The opening aligns with a booster port in a wall of the cylinder such that the air-oil mixture entering the crankcase chamber flows through the opening to the booster port. As the air-oil mixture flows through the piston, it passes over a piston pin of the piston, thus cooling and lubricating the piston pin. With this kind of an arrangement, the high thermal load on the piston pin is reduced, and the size and the mass of the piston pin can also be reduced. Additionally, the piston pin is located at an optimum distance from the piston crown, thus resulting in higher durability, optimum reciprocating masses and longer life of the piston pin. Further, the optimum distance of the piston pin from the piston crown provides a narrow passage for the flow of air-oil mixture ensuring that the air-oil mixture passes over the piston pin before entering the booster port.

These and other features, aspects, and advantages of the present subject matter will be better understood with reference to the following description and appended claims. This summary is provided to introduce a selection of concepts in a simplified form. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.

BRIEF DESCRIPTION OF DRAWINGS

The above and other features, aspects, and advantages of the subject matter will be better understood with regard to the following description, appended claims, and accompanying drawings where:

Fig. 1 illustrates a cross sectional view of an exemplary two-stroke internal combustion (IC) engine 100, according to one embodiment of the present subject matter.

Fig. 2 illustrates a flow of an air-oil mixture in a piston in the exemplary two-stroke IC engine 100 of fig. 1, according to an embodiment of the present subject matter.

DETAILED DESCRIPTION

The subject matter described herein is directed to a two-stroke internal combustion (IC) engine, such as a diesel engine, interchangeably referred to as an engine. In such engines, air is compressed to high pressures inside a combustion chamber of a cylinder to achieve high temperatures. Due to the high temperatures, a fuel injected in the combustion chamber gets ignited. The combustion of fuel further increases the temperature inside the engine and adversely affects components of the engine such as a piston, a connecting rod, and a piston pin connecting the piston and the connecting rod.

An extremely high temperature inside the engine is a necessity; however, extreme temperatures can adversely affect the components of the engine, especially the piston pin and the piston, and can be detrimental to the life and efficiency of the engine. Therefore, the following description relates to an arrangement for providing flow of an air-oil mixture inside the piston and the cylinder for cooling and lubricating the piston pin, thereby reducing wear and tear of the piston pin due to high thermal loading.

Additionally, the size and the mass of the piston pin are reduced and the piston pin is located at an optimum distance from the piston crown, thus resulting in higher durability, optimum reciprocating masses and longer life of the piston pin.

Fig. 1 illustrates a cross sectional view of an exemplary two-stroke internal combustion (IC) engine 100, hereinafter interchangeably referred to as an engine 100, according to one embodiment of the present subject matter. In said embodiment, the IC engine 100 is a diesel engine. The engine 100 includes a cylinder 102 having a cylinder head 104, a piston 106, a piston pin 108, a connecting rod 110, a crankcase 112, a crankshaft 114, and a combustion chamber 116. The combustion chamber 116 is the region between the piston 106 and the cylinder head 104. The cylinder 102 further includes a booster port 118 in a cylinder wall, a coolant passage 120 in proximity to the booster port 118, a nozzle 122 located on the cylinder head 104, scavenge ports (not shown in this figure), and an exhaust port 124. The connecting rod 110 has a small end 126 and a big end 128.

The small end 126 is connected to the piston 106 using the piston pin 108, whereas the big end 128 is connected to the crankshaft 114 housed inside the crankcase 112. Here, the terms "small end" and "big end" reflect a convention for identifying location or association of the term with the piston 106 and the crankshaft 114 respectively, rather than necessarily absolute or relative size of the joint.

In one implementation of said embodiment, the piston 106 has a hollow region defined by a piston wall and a piston crown 130. The piston wall has an opening 132 located above the centre of the piston pin 108 and in proximity to the piston crown 130. Additionally, the size and the mass of the piston pin 108 can be reduced and the piston pin 108 is located at an optimum distance from the piston crown 130, such as at a distance equal to 0.5 to 0.7 times the diameter of the piston 106. Such a location of the piston pin 108 provides a narrow passage between the piston pin 108 and the piston crown 130. Reducing the size and the mass of the piston pin provides optimum reciprocating masses thus ensuring a longer life of the piston pin.

The piston 106 reciprocates inside the cylinder 102 between a top dead center (TDC) and a bottom dead center (BDC). The TDC is in proximity to the cylinder head 104 and the BDC is in proximity to the crankcase 112. The location of the booster port 118 and the opening 132 is such that the opening 132 in the piston wall aligns with an opening of the booster port 118 when the piston 106 is at BDC.

Further, the crankcase 112 is provided with a crankcase chamber 134, a one-way valve 136 hereinafter referred to as an intake valve, and an intake port 138 for introducing a mixture of fuel-free air and a lubricating oil mist, interchangeably referred to as an air-oil mixture, directly into the crankcase chamber 134 as indicated by an arrow 140. In one embodiment, the intake valve 136 is a reed valve, which restricts the flow of the air-oil mixture in a single direction from the intake port 138 to the crankcase chamber 134. The intake valve 136 prevents a reverse flow of the air-oil mixture, i.e., it prevents the air-oil mixture from moving out of the crankcase chamber 134 into the intake port 138. The air-oil mixture is received by the crankcase chamber 134 when the piston 106 starts moving upwards, i.e., towards the TDC. When the piston 106 starts moving upwards, the intake valve 136 opens and the air-oil mixture starts entering the crankcase chamber 134 from the intake port 136 and fill the crankcase chamber 134 and the space between the crankcase chamber 134 and the hollow region of the piston 106. As the piston 106 reaches the TDC the intake valve 136 closes thus stopping additional air-oil mixture from entering the crankcase chamber 134.

As the piston 106 reaches the TDC, combustion of fuel, for example diesel, takes place inside the combustion chamber 116. The gases thus produced expand in volume to push the piston 106 down towards the BDC. The downward movement of the piston 106 compresses the air-oil mixture between the hollow region of the piston 106 and the crankcase chamber 134. Compression of the air-oil mixture is facilitated by using the reed valve as the intake valve 124, as it prevents the air-oil mixture form escaping into intake port 138 during the compression.

The piston 106 continues to move downwards compressing the air-oil mixture, until it reaches the (BDC). At this instant, the opening 132 is substantially aligned with a first section of the booster port 118. The downwards movement of the piston 106, forces some of the compressed air-oil mixture, present inside the crankcase chamber 134, to escape to the combustion chamber 116 through the scavenge ports. Whereas, rest of the compressed air-oil mixture trapped inside the crankcase chamber 134 and the hollow region of the piston 104 are forced to rush through the opening 132, into the booster port 118. Since the opening 132 is above the piston pin 108 and is offset with respect to the piston pin 108, the air-oil mixture is forced to move in the narrow region over the piston pin 108 towards the booster port 118.

The movement of the air-oil mixture over the piston pin 108 provides lubrication and cooling effect to the piston pin 108 and the small end 126. As the air-oil mixture lubricates the piston pin 108 and the small end 118, the concentration of the lubricating oil in the air-oil mixture gets substantially reduced thus preventing any effect of the lubricating oil in the combustion. The booster port 118 facilitates the transfer of the air-oil mixture from the hollow region of the piston 106 towards the combustion chamber 116 as indicated by arrows 142 and 144. The arrow 142 indicates the flow of air-oil mixture in the first section of the booster port 118 from the opening 132 and the arrow 144 indicates the flow of air-oil mixture in a second section of the booster port 118 and into the combustion chamber 116. The two-sections of the booster port 118 are mentioned to indicate change in direction of flow of the air-oil mixture in the booster port 118 prior to entry into the combustion chamber 116.

Fig. 2 illustrates a cross-sectional view 200 of the IC engine 100, particularly the cylinder 102 and the piston 106, showing the flow of the air-oil mixture according to an embodiment of the present subject matter. As discussed earlier, the opening 132 is near the piston crown 130. Thus, when the opening 132 of the piston 106 is aligned with the booster port 118, the air-oil mixture is already compressed to the maximum limit inside the crankcase chamber 134 and the hollow region of the piston 106. In this position of the piston 106, the air-oil mixture flows in the direction shown by the arrows 202, 204, and 206 around the piston pin 108 such that the air-oil mixture absorbs the heat from the piston 106 and the piston pin 108. The heat load may be generated due to the reciprocating movement of the piston 106 and the combustion taking place inside the combustion chamber 116 above the piston crown 130, as discussed earlier. Additionally, the lubricating oil mist in the air-oil mixture lubricates the piston pin 108, the small end 126, and a bearing 208 provided between the piston pin 108 and the small end 126. Droplets of the lubricating oil adhere to the piston pin 108 and the piston 106 resulting in better and prolonged lubrication and effective working of both the components.

The lubricating oil reaches the bearing 208 through small passages, such as passages 210-1 and 210-2, provided in the small end 126. The bearing 208 is provided for facilitating smooth relative movement between the connecting rod 110 and the piston pin 108, while ensuring that gas load and inertia load can be supported reliably at this joint of the connecting rod for the desired life of the connecting rod. The bearing 208 may be either a full-complement bearing or a caged needle-roller bearing. The piston pin 108 may be a fixed pin, a semi-floating pin, or a full-floating pin.

Further, the air-oil mixture entering the booster port 118 is cooled by coolant present in the coolant passage 120. A coolant such as water or a mixture of water and glycol is circulated inside the coolant passage 120. The cooling of the air-oil mixture in the booster port 118 also increases the density of the air-oil mixture that enables higher mass flow rate of the air-oil mixture to the combustion chamber 116. Increase in the mass flow rate of the air-oil mixture facilitates improved filling of the combustion chamber 116 which in-turn could help to obtain higher output from the engine 100.

The cooled air-oil mixture flows into the combustion chamber 116 through the booster port 118 and mixes with the rest of the air-oil mixture that had flown inside the combustion chamber 116 through scavenge ports 212. As the piston 106 moves upwards again, the air-oil mixture in the combustion chamber 116 is compressed to a high pressure, increasing the temperature inside the combustion chamber 116. As the piston 106 reaches TDC, the fuel is sprayed into the combustion chamber 116 by the nozzle 122. The fuel burns and the gases thus produced expand in volume to push the piston 106 towards the BDC. When the piston 106 travels downwards the exhaust gases produced during combustion are emitted via the exhaust port 124.

While certain features of the claimed subject matter have been illustrated and described herein, many modifications, substitutions, changes, and equivalents will now occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes that fall within the true spirit of the claimed subject matter.

I/We claim:

1. A two-stroke internal combustion (IC) engine (100) comprising:

a cylinder (102) having a cylinder wall;

a piston (106) adapted to reciprocate inside the cylinder (102), the piston (106) having a piston wall and a piston crown (130);

a piston pin (108) connecting the piston (106) to a small end (126) of a connecting rod (110);

a crankshaft (114) connected to a big end (128) of the connecting rod (110); and

a crankcase (112) housing the crankshaft (114), wherein the crankcase (112) includes a crankcase chamber (134) and an intake port (138), and wherein the intake port (138) introduces an air-oil mixture into the crankcase chamber (134); characterized in that, the cylinder (102) has a booster port (118) in the cylinder wall; and the piston (106) has an opening (132) in the piston wall, wherein the opening (132) is provided in proximity to the piston crown (130) and above the piston pin (108), wherein the opening (132) is aligned with the booster port (118) when the piston (106) is at a bottom dead center.

2. The two-stroke IC engine (100) as claimed in claim 1, wherein a section of the booster port (118) opens in a combustion chamber (116).

3. The two-stroke IC engine (100) as claimed in claim 1, wherein the cylinder (102) comprises a coolant passage (120) in proximity to the booster port (118) such that a coolant circulating inside the coolant passage (120) cools the air-oil mixture flowing through the booster port (118).

4. The two-stroke IC engine (100) as claimed in claim 3, wherein the coolant is selected from the group consisting of water and a mixture of water and glycol.

5. The two-stroke IC engine (100) as claimed in claim 1, wherein the two-stroke IC engine (100) is a diesel engine.

6. The two-stroke IC engine (100) as claimed in claim 1, wherein the piston pin (108) is selected from the group consisting of a fixed pin, a semi-floating pin, and a full-floating pin.

7. The two-stroke IC engine (100) as claimed in claim 1, wherein a bearing (208) is provided between the piston (106) and the small end (126), and wherein the small end (126) includes passages (210-1, 210-2) to lubricate the bearing (208).

8. The two-stroke IC engine (100) as claimed in claim 7, wherein the bearing (208) is selected from the group consisting of a full-complement bearing and a caged needled-roller bearing.

9. A vehicle comprising a two-stroke internal combustion (IC) engine (100) as claimed in any of the preceding claims.

10. A method comprising:
introducing an air-oil mixture inside a crankcase chamber (134);

compressing the air-oil mixture inside the crankcase chamber (134) and a hollow region of a piston (106); and

aligning an opening (130) in a piston wall of the piston (106) with a booster port (118) in a cylinder (102) to force the air-oil mixture to flow over the piston pin (108) and enter the booster port (118) through the opening (132), wherein the flow of the air-oil mixture cools and lubricates the piston pin (108), a small end (126), and a bearing (208).

Documents:

http://ipindiaonline.gov.in/patentsearch/GrantedSearch/viewdoc.aspx?id=mQlnI5ZPV7mWEZaTpq0LOA==&loc=egcICQiyoj82NGgGrC5ChA==

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Patent Number

279351

Indian Patent Application Number

2396/CHE/2008

PG Journal Number

03/2017

Publication Date

20-Jan-2017

Grant Date

18-Jan-2017

Date of Filing

29-Oct-2008

Name of Patentee

TVS MOTOR COMPANY LIMITED

Applicant Address

JAYALAKSHMI ESTATE, 24 (OLD # 8), HADDOWS ROAD CHENNAI - 600 006

Inventors:

#	Inventor's Name	Inventor's Address
1	PATTABIRAMAN VENUGOPALAN	JAYALAKSHMI ESTATE, 24 (OLD # 8), HADDOWS ROAD CHENNAI - 600 006
2	HARNE VINAY CHANDRAKANT	JAYALAKSHMI ESTATE, 24 (OLD # 8), HADDOWS ROAD CHENNAI - 600 006

PCT International Classification Number

F02F3/00, F02F3/24

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA