JP2019143528A - Two-stroke engine - Google Patents

Abstract

To provide a two-stroke engine that varies a compression ratio during operation.SOLUTION: A two-stroke engine includes: a cylinder having a combustion chamber; a piston sliding inside the cylinder; and a crankshaft interlocking with the piston. The crankshaft includes: a main shaft; and a crank arm provided toward an outer side in a radial direction from the main shaft and having a variable distance in the radial direction from the main shaft.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a two-stroke engine.

  For example, Patent Document 1 discloses a two-stroke engine mounted on a ship or the like. Such a two-stroke engine includes a piston and a cylinder in which the piston slides. When the piston is moved to the top dead center, the combustion gas in the cylinder is compressed and self-ignited.

JP2013-7320A

  In the two-stroke engine having such a configuration, it is conceivable to operate at a high compression ratio in order to improve the combustion efficiency. However, since the optimal compression ratio varies depending on the operating conditions and the composition of the supplied fuel, it is required to change the compression ratio during combustion during operation.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to make the compression ratio variable during operation in a two-stroke engine.

  As a first means for solving the above-mentioned problems, the present invention is a two-stroke engine having a cylinder having a combustion chamber, a piston sliding in the cylinder, and a crankshaft interlocked with the piston. The crankshaft includes a main shaft and a crank arm that is provided radially outward from the main shaft and is capable of changing a distance in the radial direction from the main shaft.

  According to the present invention, the position of the top dead center in the cylinder of the piston can be changed via the piston rod by changing the distance between the main shaft and the crank pin in the main shaft radial direction during operation. Thereby, the volume of a combustion chamber changes and it becomes possible to change a compression ratio.

1 is a schematic cross-sectional view of a two-stroke engine according to an embodiment of the present invention.

  Hereinafter, an embodiment of an engine system according to the present invention will be described with reference to the drawings. In the following drawings, the scale of each member is appropriately changed in order to make each member a recognizable size.

The engine system 100 of this embodiment is mounted on a ship such as a large tanker, for example, and has an engine 1 and a control unit 200 as shown in FIG.
The engine 1 is a multi-cylinder uniflow scavenging diesel engine (two-stroke engine), a gas operation mode in which a gaseous fuel such as natural gas is burned together with a liquid fuel such as heavy oil, and a diesel operation mode in which a liquid fuel such as heavy oil is burned. And have. In the gas operation mode, only gaseous fuel may be burned. Such an engine 1 includes a cylinder portion 2, a fuel injection valve 3, a piston 4, an exhaust valve unit 5, a piston rod 6, a crosshead 7, a connecting rod 8, a crankshaft 9, a hydraulic pump. 10.

  The cylinder portion 2 includes a cylindrical cylinder liner 2a having a combustion chamber R1, a cylinder head 2b in which an exhaust port H is formed and connected to an unillustrated exhaust reservoir, a lower portion of the cylinder liner 2a, and a cylinder liner. And a cylindrical cylinder jacket 2c into which the lower end of 2a is inserted. The cylinder jacket 2c is provided with a scavenging port S and a scavenging chamber R2, and is connected to a scavenging reservoir.

  The fuel injection valve 3 is a valve device provided in the cylinder head 2b. The fuel injection valve 3 injects liquid fuel toward the combustion chamber R1 during operation with liquid fuel. In addition, the fuel injection valve 3 injects a small amount of liquid fuel toward the combustion chamber R1 as pilot fuel at the time of start-up when operating with gaseous fuel.

  The piston 4 has a substantially cylindrical shape, and is connected to a piston rod 6 to be described later and disposed inside the cylinder liner 2a. The piston 4 slides in the cylinder liner 2a with the piston rod 6 due to pressure fluctuations in the combustion chamber R1.

  The exhaust valve unit 5 includes an exhaust valve 5a, an exhaust valve housing 5b, and an exhaust valve drive unit 5c. The exhaust valve 5a is provided inside the cylinder head 2b, and closes the exhaust port H in the cylinder part 2 by the exhaust valve drive part 5c. The exhaust valve housing 5b is a cylindrical housing that houses the end of the exhaust valve 5a. The exhaust valve drive unit 5 c is an actuator that moves the exhaust valve 5 a in a direction along the stroke direction of the piston 4.

  The piston rod 6 is a long member having one end connected to the piston 4 and the other end connected to the crosshead 7. The crosshead 7 has a crosshead pin (not shown). The crosshead 7 is connected to the end of the piston rod 6 and the end of the connecting rod 8, and transmits the linear motion of the piston 4 to the connecting rod 8.

  As shown in FIG. 1, the connecting rod 8 is a long member that is connected to the crosshead pin 7 a and connected to the crankshaft 9. The connecting rod 8 converts the linear motion of the piston 4 transmitted to the cross head pin 7a into rotational motion.

  The crankshaft 9 is a member that is connected to the piston 4 via the piston rod 6 and the connecting rod 8 and interlocks with the piston 4, and has a main shaft 9a, a plurality of crank arms 9b, and a crankpin 9c. . The main shaft 9a is a long member having a substantially cylindrical shape and having a rotation shaft at the center. Further, the main shaft 9a is connected to a turbine or the like (not shown) via a gear, and transmits rotational motion to the turbine or the like.

The crank arm 9b has a movable part 9d and a fixed part 9e. The movable portion 9d has a recess that forms the hydraulic chamber R3, and is joined to the crankpin 9c at the end. The movable portion 9d is provided with a relief channel (not shown) that communicates with the hydraulic chamber R3. The relief flow path is provided with a relief valve controlled by the control unit 200. The fixed portion 9e is a member having one end inserted into the hydraulic chamber R3 and one end joined to the main shaft 9a. Such a crank arm 9b protrudes radially outward from the main shaft 9a, and two crank arms 9b are paired and connected by a crank pin 9c.
The crank pin 9c is a cylindrical member joined to the movable portion 9d of the crank arm 9b and connected to one end of the connecting rod 8.

  The hydraulic pump 10 is a pump that supplies hydraulic oil to the hydraulic chamber R3 based on an instruction from the control unit 200, and is fixed to the outside as a separate body from the crankshaft 9. For example, a part of the cooling oil supplied to the piston 4 is supplied to the hydraulic pump 10 as hydraulic oil.

  The control unit 200 is a computer that controls a fuel supply amount and the like based on an operation by a ship operator. The control unit 200 controls the hydraulic pump 10 to change the volume of the hydraulic chamber R3 and change the compression ratio.

  In such an engine system 100, when increasing the compression ratio, the control unit 200 drives the hydraulic pump 10 to supply hydraulic oil to the hydraulic chamber R3. Thereby, the movable part 9d is lifted from the fixed part 9e, and the length of the crank arm 9b is extended. Therefore, the top dead center of the piston 4 connected to the crank pin 9c via the connecting rod 8 and the piston rod 6 moves further upward, and the compression ratio is increased.

  Further, when the compression ratio is lowered, the control unit 200 opens the relief valve of the relief flow path communicating with the hydraulic chamber R3, and releases the hydraulic oil in the hydraulic chamber R3 to the outside. As a result, the movable portion 9d comes into close contact with the fixed portion 9e, and the length of the crank arm 9b is shortened. Therefore, the top dead center of the piston 4 connected to the crank pin 9c via the connecting rod 8 and the piston rod 6 moves downward, and the compression ratio is lowered.

  According to this embodiment, the distance between the main shaft 9a and the crank pin 9c in the radial direction of the main shaft 9a can be changed by changing the length of the crank arm 9b. The position can be changed. Therefore, it is possible to easily change the compression ratio during operation.

  As mentioned above, although preferred embodiment of this invention was described referring drawings, this invention is not limited to the said embodiment. Various shapes, combinations, and the like of the constituent members shown in the above-described embodiments are examples, and various modifications can be made based on design requirements and the like without departing from the spirit of the present invention.

  In the above embodiment, the length of the crank arm 9b is changed by the hydraulic chamber R3 provided in the crank arm 9b, but the present invention is not limited to this. A device such as a jack may be provided between the movable portion 9d and the fixed portion 9e of the crank arm 9b, and the length of the crank arm 9b may be changed.

  In the above embodiment, the crank arm 9b is provided with the movable portion 9d on the crank pin 9c side, but the present invention is not limited to this. For example, the connecting position of the crank pin 9c in the crank arm 9b may be moved radially outward by a hydraulic cylinder or the like. Similarly, the connecting position of the main shaft 9a in the crank arm 9b may be moved radially inward by a hydraulic cylinder or the like. Even in these cases, the relative distance between the main shaft 9a and the crankpin 9c changes as in the above embodiment, so that the top dead center position of the piston 4 changes and the compression ratio can be changed.

DESCRIPTION OF SYMBOLS 1 Engine 2 Cylinder part 2a Cylinder liner 2b Cylinder head 2c Cylinder jacket 4 Piston 5 Exhaust valve unit 5a Exhaust valve 5b Exhaust valve housing 5c Exhaust valve drive part 6 Piston rod 7 Crosshead 8 Connecting rod 9 Crank shaft 9a Main shaft 9b Crank arm 9c Crank pin 9d Movable part 9e Fixed part 100 Engine system 200 Control part H Exhaust port R1 Combustion chamber R2 Scavenging chamber S Scavenging port

Claims (1)

A two-stroke engine having a cylinder having a combustion chamber, a piston sliding in the cylinder, and a crankshaft interlocking with the piston;
The crankshaft has a main shaft and a crank arm provided radially outward from the main shaft and capable of changing a distance in the radial direction from the main shaft.

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