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EP-3431740-B1 - ENGINE SYSTEM AND CONTROL METHOD THEREFOR

EP3431740B1EP 3431740 B1EP3431740 B1EP 3431740B1EP-3431740-B1

Inventors

  • WATANABE, KOICHI
  • YUKI, KAZUHIRO

Dates

Publication Date
20260506
Application Date
20160314

Claims (4)

  1. An engine system comprising a 4-stroke engine using a gas as fuel and including a micro-pilot oil injection valve (11) to ignite a fuel-air mixture of gas and air in a combustion chamber, and including an output shaft of the engine that is connected to a propeller of a marine propulsion unit, wherein in an intake pipe of the engine, a turbocharger configured to perform turbocharging and an air cooler configured to cool air from the turbocharger before the air is supplied to the intake pipe are provided, the engine system comprising: a torque sensor (21) configured to measure a torque of the output shaft of the engine; a rotational speed sensor (20) configured to measure a rotational speed of the output shaft of the engine; a control unit (22) configured to obtain power of the output shaft from a torque measurement value by the torque sensor and a rotational speed measurement value by the rotational speed sensor, and configured to set change of a closing timing of an intake valve (8) of the engine when power of the output shaft of the engine is increased; and a variable intake valve timing mechanism (30) configured to change the closing timing of the intake valve according to the closing timing of the intake valve set by the control unit and configured to adjust advance amount of the closing timing of the intake valve from bottom dead center, characterized in that : control of lowering a compression ratio of a fuel-air mixture of the gas and air in the engine is performed by the variable intake valve timing mechanism according to an increase in rotational speed of the output shaft of the engine and an increase in power of the output shaft of the engine.
  2. The engine system according to Claim 1, wherein adjustment of the advance amount of the closing timing of the intake valve is performed continuously or by multiple stages by the variable intake valve timing mechanism.
  3. The engine system according to Claim 2, wherein the advance amount determined in the control unit is set from a value of the advance amount determined using as parameters a plurality of data on power and rotational speed of the output shaft which are previously measured.
  4. A control method for an engine system including a 4-stroke engine using a gas as fuel and including a micro-pilot oil injection valve (11) to ignite a fuel-air mixture of gas and air in a combustion chamber wherein in an intake pipe of the engine, a turbocharger configured to perform turbocharging and an air cooler configured to cool air from the turbocharger before the air is supplied to the intake pipe are provided, and an output shaft of the engine is connected to a propeller of a marine propulsion unit, the method comprising: a process of obtaining power of the output shaft of the engine from a torque measurement value of the output shaft measured by a torque sensor (21) and a rotational speed measurement value of the output shaft measured by a rotational speed sensor (20), and of setting change of a closing timing of an intake valve (8) of the engine when power of the output shaft of the engine is increased; and a process of mechanically changing the closing timing of the intake valve according to the set closing timing of the intake valve and of adjusting advance amount of the closing timing of the intake valve from bottom dead center, the method being characterized in that a compression ratio of a fuel-air mixture of the gas and air in the engine is lowered by mechanically changing the closing timing of the intake valve according to an increase in rotational speed of the output shaft of the engine and an increase in power of the output shaft of the engine.

Description

Technical Field The present invention relates to a 4-stroke engine system according to the preamble of claim 1 and a control method therefor. Background Art In the related art, as an example of an engine system using fuel gas, a dual fuel engine that can correspond to any one of fuel gas such as natural gas or the like and liquid fuel such as heavy fuel or the like is known. In addition, in an internal combustion engine, it is known that engine performance can be appropriately controlled using a variable valve timing mechanism, and an effect of lowering an effective compression ratio of a fuel-air mixture under the control is also known. For example, internal combustion engines including variable valve timing mechanisms are known in the following Patent Documents 1 to 6. For example, the variable valve timing apparatus disclosed in Patent Document 1 is installed in a gasoline engine and is configured to change a valve opening timing of an intake valve in an internal combustion engine. The internal combustion engine has a turbocharger and the variable valve timing apparatus and a target turbocharging pressure of the turbocharger is set, and when power of the internal combustion engine is within a predetermined high power range, a target valve closing timing is set such that an expansion ratio during a combustion cycle exceeds a compression ratio and that the expansion ratio approaches the compression ratio as the detected power of the internal combustion engine is increased. Accordingly, a limit at which knocking begins to occur is expanded by suppressing an increase in turbocharging pressure. Then, by employing a mechanism using two cams of a main intake cam and a sub intake cam and changing phases of the two cams, both of a valve opening timing and a valve closing timing are varied. In the dual fuel engine disclosed in Patent Document 2, during operation of a premixed combustion mode, a compression ratio is suppressed in order to prevent occurrence of knocking, and during operation of a diffusion combustion mode, the engine is operated at a higher compression ratio in order to improve thermal efficiency or fuel ignitability. An intake valve driving means and a crank angle detection means are provided, and upon the operation of the premixed combustion mode (a gas engine mode), a signal that advances a valve closing timing of an intake valve more than during the operation of the diffusion combustion mode is output. In the premixed combustion mode of Patent Document 2, the valve closing timing of the intake valve is set to a predetermined position of 60° to 70° before bottom dead center, and the advanced angular position is not varied during the premixed combustion mode. In addition, in an internal combustion engine disclosed in Patent Document 3, valve opening timing and valve closing timing of an exhaust valve are advanced by advance of the exhaust valve, thereby a part of an exhaust gas in a combustion chamber is flowed backward to an intake port, and thus, a combustion state of the internal combustion engine is improved. When it is assumed there is a torque detection means configured to detect an output torque output from an engine main body and that the detected output torque is smaller than a limit torque, execution of early closing control of the exhaust valve is prohibited. Accordingly, occurrence of torque fluctuation that causes deterioration of drivability, an engine stall, or the like is prevented. In addition, examples of specific configurations of the variable valve timing mechanism are disclosed in the following Patent Documents 4 to 6. As shown in FIGS. 11A and 11B, a driving mechanism of a variable valve timing mechanism 100 disclosed in Patent Document 4 includes a link mechanism 101 and an actuator 102. In the link mechanism 101, an exhaust valve swing arm 103 connected to a push rod of an exhaust valve of an engine is supported by a link shaft 104, and an intake valve swing arm 105 connected to a push rod of an intake valve is supported by a tappet shaft 106 of an eccentric shaft section that is eccentric from the link shaft 104. Each of the exhaust valve swing arm 103 and the intake valve swing arm 105 can be advanced and retracted by an eccentric cam 108a of a cam shaft 108. In addition, the link shaft 104 is connected to a piston rod 109 installed on the actuator 102. When positions shown in FIG. 11B are before a jumping-out operation of the piston rod 109, by performing the jumping-out operation of the piston rod 109 using the actuator 102, both of the swing arms 105 and 103 connected thereto are rotated toward one side. For this reason, a pivoting angle of both of the swing arms 105 and 103 can be controlled by the actuator 102 via the link mechanism 101. In addition, the variable valve timing mechanisms disclosed in Patent Documents 5 and 6 are disclosed in FIGS. 12 and 13 as another example. The same components as the variable valve timing mechanism 100 shown in FIG. 11 are designat