JP2005139946A - Engine capable of two cycle operation - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To efficiently use exhaust gas energy in an exhaust gas type supercharger in an engine capable of two cycle operation and provided with the exhaust gas type supercharger. <P>SOLUTION: The engine 10 is provided with a lead valve 50 as a reverse flow preventing means between a combustion chamber 15 and the exhaust gas type supercharger 40 in an exhaust gas passage 17 discharging combustion chamber gas in a combustion chamber to outside. Exhaust gas discharged from an inside of the combustion chamber 15 once is prevented from flowing reversely into the combustion chamber 15 during scavenging period by being provided with the lead valve 50. Consequently, exhaust gas energy can be efficiently transmitted to a turbine 42 of the exhaust gas type supercharger 40 and supercharging can be done efficiently. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an engine capable of two-cycle operation, and more particularly to a technique for efficiently using exhaust energy.

  Self-ignition operation of a lean air-fuel mixture is known as an engine operation technique with high fuel efficiency and low NOx emission. Further, it is known that the two-cycle operation is more advantageous than the four-cycle operation during the self-ignition operation. In order to sufficiently reduce the NOx emission amount in such a two-cycle self-ignition operation, it has been proposed to increase the excess air ratio with a supercharger. As the supercharger used for two-cycle operation, there are generally an exhaust supercharger that uses exhaust energy from the engine and a mechanical supercharger that uses the output of the engine. It is more advantageous than a mechanical supercharger in that there is no mechanical energy loss (see, for example, Patent Document 1).

JP-A-3-151532

  However, since the two-cycle operation does not have independent strokes for exhaust and intake, the exhaust valve (or exhaust port) and the intake valve (or intake port) are opened at the same time in the period before and after bottom dead center, and gas exchange is performed. Requires a scavenging stroke to perform. That is, the exhaust valve is opened and blowdown is performed while the piston is moving from the top dead center to the bottom dead center due to the explosion pressure in the combustion chamber. Then, after the blow-down period has elapsed, the intake valve is opened while scavenging is started while the exhaust valve is open. Further, the exhaust valve is closed after the scavenging period.

  For this reason, a phenomenon occurs in which the high-pressure exhaust discharged from the combustion chamber to the exhaust port during the blow-down period flows back into the combustion chamber where the chamber pressure has decreased during the scavenging period. As a result, there is a problem in that the energy of the high-pressure exhaust discharged during the blowdown period cannot be sufficiently transmitted to the turbine of the exhaust supercharger, and the exhaust supercharger cannot be used efficiently.

  An object of the present invention is to efficiently use exhaust energy in an exhaust supercharger in an engine capable of two-cycle operation equipped with an exhaust supercharger.

  In order to solve the above-described problems, the present invention provides an engine capable of two-cycle operation including a piston that slides in a cylinder formed in a cylinder block and a cylinder head that is joined to the cylinder block. The engine according to the present invention is disposed on the exhaust passage, a combustion chamber defined by the cylinder, an upper surface of the piston, and the cylinder head, an exhaust passage communicating with the combustion chamber, An exhaust supercharger driven by exhaust from the combustion chamber, and an exhaust backflow prevention means disposed between the combustion chamber and the exhaust supercharger on the exhaust passage. Features.

  According to the engine configured as described above and capable of two-cycle operation, the exhaust once discharged from the combustion chamber can be prevented from flowing back into the combustion chamber, so that the exhaust energy can be efficiently exhausted. Can be communicated to. Further, it is possible to prevent the exhaust gas from flowing back into the combustion chamber and hindering the intake of fresh air from the intake valve.

  In the engine capable of two-cycle operation according to the present invention, the exhaust supercharger may be a supercharger with a motor assist mechanism in which driving by the exhaust is assisted by an electric motor. In such a case, even if sufficient exhaust energy cannot be obtained, the exhaust supercharger can be sufficiently driven by the electric motor. Further, since the exhaust energy can be efficiently transmitted to the exhaust type supercharger, the required auxiliary amount of the driving force by the electric motor can be reduced, and the driving energy of the electric motor can be reduced.

  In the engine capable of two-cycle operation according to the present invention, the exhaust backflow prevention means may be a reed valve. In such a case, the reed valve can easily prevent the backflow of exhaust gas into the combustion chamber, and can efficiently transmit the exhaust energy to the exhaust supercharger.

  In the engine capable of two-cycle operation according to the present invention, the exhaust backflow prevention means may be a rotary valve and a control device for the rotary valve. In such a case, by controlling the opening and closing of the rotary valve, it is possible to prevent the exhaust gas from flowing back into the combustion chamber and to efficiently transmit the exhaust energy to the exhaust type supercharger.

  Hereinafter, an engine capable of two-cycle operation according to the present invention will be described based on examples with reference to the drawings.

  The configuration of the engine according to the embodiment of the present invention will be described with reference to FIG. FIG. 1 is an explanatory diagram showing a schematic configuration of an engine according to an embodiment of the present invention. The engine 10 according to the present embodiment is an engine capable of two-cycle operation in at least a part of the operation region.

  The engine 10 according to this embodiment includes a cylinder block 20 having a plurality of cylinders 22 therein, a piston 24 inscribed so as to slide up and down in the cylinder 22, a cylinder head 30 disposed on the upper surface of the cylinder block 20, An exhaust supercharger 40 driven by exhaust, a control device (ECU) that controls the entire engine 10, and a reed valve 50 that functions as exhaust backflow prevention means are provided. A combustion chamber 15 is defined by the upper surfaces of the cylinder 22, the cylinder head 30 and the piston 24.

  The cylinder head 30 has an exhaust port 31 and an intake port 32 for each cylinder 22. Each exhaust port 31 is connected to a branch end of the exhaust pipe 16, and the exhaust port 31 and the exhaust pipe 16 constitute an exhaust passage 17 communicating with the combustion chamber 15. On the exhaust passage 17, a turbine 42 and a catalyst device (not shown) of the exhaust supercharger 40 are arranged from the upstream side.

  On the other hand, a branch end of the intake pipe 12 is connected to each intake port 32, and the intake port 32 and the intake pipe 12 constitute an intake passage 13 communicating with the combustion chamber 15. On the intake passage 13, a surge tank 60, an intercooler 62, a compressor 44 of an exhaust supercharger 40, and an air cleaner (not shown) are arranged from the downstream side.

  The cylinder head 30 includes, for each cylinder 22, an electromagnetically driven exhaust valve 34 for opening and closing the exhaust port 31 at an arbitrary timing, an electromagnetically driven intake valve 33 for opening and closing the intake port 32 at an arbitrary timing, A fuel injection valve 36 for directly injecting fuel into the combustion chamber 15 and a spark plug 35 for spark ignition are arranged.

  The exhaust supercharger 40 includes a turbine 42 that is rotationally driven by exhaust energy, a compressor 44 that is coaxial with the turbine 42 and compresses intake air, and a motor assist mechanism 46. As described, the turbine 42 is disposed on the exhaust passage 17 and the compressor 44 is disposed on the intake passage 13. The motor assist mechanism 46 assists the drive of the compressor 44 by the electric motor when the compressor 44 cannot be sufficiently driven only by the exhaust energy transmitted through the turbine 42 and a necessary supercharging pressure cannot be obtained.

  The reed valve 50 is disposed on the exhaust passage 17 on the upstream side of the turbine 42 as an exhaust backflow prevention means. For example, a well-known reed valve used in an intake system of a two-cycle engine that compresses a mixture of fuel and air in a crank chamber can be used. FIG. 2 is a cross-sectional view of the reed valve 50. FIG. 3 is an end view of the reed valve as viewed from the direction of the arrow Y1 in FIG.

  The reed valve 50 includes a valve main body 52 fixed to the housing 55, a metal thin plate lead piece 53, and a metal stopper 51. One end of the lead piece 53 and the stopper 51 is fixed to the valve main body 52 by a screw body 56. The valve body 52 has a valve hole 54, and the lead piece 53 is arranged so as to cover the valve hole 54. The stopper 51 is for restricting the maximum opening of the lead piece 53. In FIG. 3, the housing 55 and the stopper 51 are not shown in order to make the drawing easier to see. The lead piece 53 is in an open state (53a) with respect to the flow in the arrow Y2 direction in FIG. 2, and is in a closed state (53) with respect to the flow in the reverse direction. As a result, the reed valve functions as a backflow prevention means.

  The ECU is composed of a known microcomputer, and controls the electromagnetically driven intake valve 33, the electromagnetically driven exhaust valve 34, the ignition plug 35, the fuel injection valve 36, and the motor assist mechanism 46 according to the operating state, The entire operation of the engine 10 is controlled.

  Next, the operation of the engine 10 according to the present embodiment will be described with reference to FIGS. 4A to 4C are explanatory views conceptually showing the operation of the engine 10 according to the present embodiment. FIGS. 5A and 5B are explanatory views for explaining the operation of the reed valve 50 in the engine 10 according to this embodiment. FIG. 6 is an explanatory diagram illustrating changes in the pressure in the combustion chamber of the engine 10 and the pre-turbine pressure of the engine 10 according to this embodiment, and the open / closed states of the intake valves and the exhaust valves. In FIG. 6, the horizontal axis indicates the crank angle (time), and the vertical axis indicates the combustion chamber pressure, the turbine pre-pressure, the lift amount of the intake valve and the exhaust valve, respectively.

  In the two-cycle operation, the intake valve 33 and the exhaust valve 34 are opened and closed at an appropriate timing during one rotation of the crankshaft, so that the expansion stroke, the exhaust stroke (blowdown), the scavenging stroke, the intake stroke, and the compression stroke are performed. Switch one after another.

  For convenience of explanation, the description will be made from the state in which the air-fuel mixture in the combustion chamber 15 is burned. When the air-fuel mixture burns, high-pressure combustion gas is generated in the combustion chamber 15, and a force that pushes down the piston 24 acts on the piston 24. As shown in FIG. 4A, in the expansion stroke, the piston 24 descends, whereby the pressure generated in the combustion chamber 15 is converted into torque and output from the crankshaft 28 as power. (Period indicated by Tf in FIG. 6).

  The exhaust valve 34 is opened and blow-down is performed at an appropriate timing when the piston 24 is lowered to a certain degree (a period indicated by Tb in FIG. 6). The combustion gas is confined in the combustion chamber 15 at a high pressure, and the pressure Ps in the combustion chamber is higher than the pressure Pex in the exhaust passage. Therefore, even when the piston 24 is descending, the exhaust valve 34 is opened. The combustion gas is discharged into the exhaust passage 17 due to the pressure difference (see FIG. 4B). The discharged high-pressure combustion gas is used as drive energy for driving the turbine 42 of the exhaust supercharger 40 and pressurizing the intake air by the compressor 44. As shown in FIG. 6, immediately after the start of blowdown, when the high-pressure combustion gas is discharged, the pre-turbine pressure increases rapidly, and thereafter, the pre-turbine pressure starts to decrease as the pressure in the combustion chamber decreases.

  Subsequently, the intake valve 33 is opened at an appropriate timing, and the process proceeds to a scavenging stroke (a period indicated by Ts in FIG. 6). The air pressurized by the exhaust type supercharger 40 flows into the combustion chamber 15 from the intake passage 13, and the combustion gas remaining in the combustion chamber 15 is discharged to the exhaust passage 17 (FIG. 4 (c). )reference).

  Thus, in the two-cycle operation, the exhaust valve must be kept open for a certain period for the scavenging stroke even after the high-pressure exhaust is discharged at the time of blowdown. During this scavenging stroke, the pressure Ps in the combustion chamber may decrease due to the lowering of the piston and the intake pressure, and may be lower than the pressure Pex in the exhaust passage.

  At this time, in the conventional configuration (without a reed valve), as shown in FIG. 5 (b), a phenomenon occurs in which exhausted exhaust gas flows back into the combustion chamber 15. When this reverse flow phenomenon occurs, the pressure in the exhaust passage decreases, and as a result, the pre-turbine pressure decreases rapidly.

  In contrast, in the present embodiment, a reed valve 50 that allows only flow in the direction of the supercharger is disposed on the exhaust passage 17 between the combustion chamber 15 and the turbine 42 of the exhaust supercharger 40. Therefore, as shown in FIG. 5A, the exhaust gas that has once passed through the reed valve 50 does not flow back into the combustion chamber 15. As a result, a decrease in the pre-turbine pressure during the scavenging period is suppressed.

  As a result, in the engine 10 according to the present embodiment, as indicated by the curve P1 in FIG. 6, the turbine pre-pressure during the scavenging period is the turbine during the scavenging period in the conventional configuration indicated by the curve P2 in FIG. Keeps high compared to pre-pressure.

  As described above, according to the engine capable of two-cycle operation according to the present embodiment, since the reed valve 50 is provided on the exhaust passage 17, the pressure Ps in the combustion chamber becomes lower than the pressure Pex in the exhaust passage. Even in this case, the backflow of exhaust gas from the exhaust passage 17 into the combustion chamber 15 can be easily prevented. As a result, exhaust energy (drive energy) can be efficiently transmitted to the exhaust supercharger 40. At the same time, it is possible to prevent the exhaust gas from flowing backward into the combustion chamber 15 and hindering the intake of fresh air from the intake passage 13.

  Further, according to the engine 10 according to the present embodiment, the exhaust energy can be efficiently transmitted to the turbine 42 of the exhaust type supercharger 40, so that the necessary auxiliary amount of the driving force of the turbine 42 by the electric motor is reduced. The amount of energy consumed by the electric motor can be reduced.

・ Modification:
As mentioned above, although the Example of this invention was described, this invention is not limited to the said Example at all, In the range which does not deviate from the meaning, implementation in a various aspect is possible. For example, the following modifications are possible.

  In the above embodiment, the reed valve is provided as the backflow preventing means, but a rotary valve may be used. FIG. 7 is an explanatory diagram showing a schematic configuration of an engine according to a modification. In this modification, a rotary valve 70 is incorporated in the cylinder head 30. The rotary valve 70 can be rotated by an electric actuator (not shown), and the exhaust passage 17 can be freely opened and closed by rotating the rotary valve 70 under the control of the ECU. Therefore, the rotary valve functions as a backflow prevention device by controlling the rotary valve 70 to be closed only at the timing when the above-described backflow phenomenon occurs. As a result, even in this configuration, an effect equivalent to that of the embodiment can be obtained.

  In the above embodiment, the engine is a two-cycle engine that performs a spark ignition operation. However, an engine that performs a self-ignition operation that does not require a spark plug, or a self-ignition operation and spark ignition controlled by an ECU. An engine capable of switching operation may be used. Of course, a variable cycle engine that can be switched between a 4-cycle operation and a 2-cycle operation may be used.

It is explanatory drawing which shows schematic structure of the engine which concerns on the Example of this invention. 3 is a cross-sectional view of a reed valve 50. FIG. FIG. 3 is an end view of the reed valve 50 as viewed from the direction of arrow Y1 in FIG. 2. It is explanatory drawing which showed notionally the operation | movement of the engine 10 which concerns on an Example. It is explanatory drawing explaining the effect | action of the reed valve 50 in the engine 10 which concerns on an Example. It is explanatory drawing showing the opening-and-closing state of the pressure in a combustion chamber of the engine 10 which concerns on an Example, the pressure before a turbine, and an intake valve and an exhaust valve. It is explanatory drawing which shows schematic structure of the engine which concerns on the modification of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Engine which can operate 2 cycles 12 ... Intake pipe 13 ... Intake passage 15 ... Combustion chamber 16 ... Exhaust pipe 17 ... Exhaust passage 20 ... Cylinder block 22 ... Cylinder 24 ... Piston 26 ... Connecting rod 28 ... Crankshaft 30 ... Cylinder head DESCRIPTION OF SYMBOLS 31 ... Exhaust port 32 ... Intake port 33 ... Electromagnetic drive type intake valve 34 ... Electromagnetic drive type exhaust valve 35 ... Spark plug 36 ... Fuel injection valve 40 ... Exhaust type supercharger 42 ... Turbine 44 ... Compressor 46 ... Motor assist mechanism 50 ... Reed valve 51 ... Stopper 52 ... Valve body 53 ... Lead piece 54 ... Valve hole 55 ... Housing 56 ... Screw body 60 ... Surge tank 62 ... Intercooler 70 ... Rotary valve

Claims (4)

An engine capable of two-cycle operation comprising a piston that slides in a cylinder formed in a cylinder block, and a cylinder head that is joined to the cylinder block,
A combustion chamber defined by the cylinder, the upper surface of the piston, and the cylinder head;
An exhaust passage communicating with the combustion chamber;
An exhaust supercharger disposed on the exhaust passage and driven by exhaust from the combustion chamber;
Exhaust backflow prevention means disposed between the combustion chamber and the exhaust supercharger on the exhaust passage;
An engine capable of two-cycle operation. The engine capable of two-cycle operation according to claim 1,
The exhaust supercharger is a supercharger with a motor assist mechanism that is assisted by the exhaust by an electric motor, and is an engine capable of two-cycle operation. The engine capable of two-cycle operation according to claim 1 or 2,
The exhaust backflow prevention means is an engine capable of two-cycle operation, which is a reed valve. The engine capable of two-cycle operation according to claim 1 or 2,
The exhaust backflow prevention means includes a rotary valve,
An engine capable of two-cycle operation which is a control device for the rotary valve.

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