A watercraft propulsion system includes a propulsion unit to be driven by an engine. The engine includes a cylinder block, an air intake channel, an exhaust channel, a supercharging device, and a fuel injector. The watercraft propulsion system includes the engine, the propulsion unit to be driven by the engine, a rotation speed sensor to detect a rotation speed of the engine, an air intake pressure sensor to detect an air intake pressure of the engine, and a controller. The controller is configured or programmed to compute a command fuel injection amount so that the engine performs a combustion operation at an air/fuel ratio in a lean-burn range (lean-combustion range) according to the rotation speed detected by the rotation speed sensor and the air intake pressure detected by the air intake pressure sensor, and to drive the fuel injector based on the computed command fuel injection amount.

An engine system provided to a vehicle having an accelerator pedal is provided. When an engine operation range is determined to shift to a first range (where an electromagnetic clutch is disengaged) from a second range (where the clutch is engaged) after an opening of the accelerator pedal increases at a rate below a given reference rate, the clutch is switched from ON to OFF after a given basic stand-by period passes from the shift. When the engine operation range is determined to shift from the second range to the first range after the accelerator pedal opening increases at the given reference rate or above, the clutch is switched from ON to OFF after a given acceleration stand-by period (longer than the basic stand-by period by a given added period) passes from the shift.

The present disclosure relates to dual compression engine boosting systems utilizing both a turbocharger and a supercharger and control systems relating to relative activation and deactivation of the boosting devices. Various Exhaust Gas Recirculation (EGR) configurations are also disclosed for the dual compression engine boosting systems.

A watercraft propulsion system includes a propulsion unit to be driven by an engine. The engine includes a cylinder block, an air intake channel, an exhaust channel, a supercharging device, and a fuel injector. The watercraft propulsion system includes the engine, the propulsion unit to be driven by the engine, a rotation speed sensor to detect a rotation speed of the engine, an air intake pressure sensor to detect an air intake pressure of the engine, and a controller. The controller is configured or programmed to compute a command fuel injection amount so that the engine performs a combustion operation at an air/fuel ratio in a lean-burn range (lean-combustion range) according to the rotation speed detected by the rotation speed sensor and the air intake pressure detected by the air intake pressure sensor, and to drive the fuel injector based on the computed command fuel injection amount.

The invention relates to a method for determining the pressure P.sub.avcm upstream of a mechanical compressor (3) equipped with a double supercharging circuit of a combustion engine. The pressure P.sub.avcm is determined by a dynamic model based on a law of conservation of flow rate in the volume upstream of the mechanical compressor. The model links the pressure P.sub.avcm upstream of the mechanical compressor (3) to a temperature T.sub.avcm upstream of the mechanical compressor (3), to a boost pressure P.sub.sural and boost temperature T.sub.sural on the intake side of the engine, and to an openness Bypass of the bypass valve (4).

A straddle-type vehicle comprises a supercharging device which compresses intake-air, an air-intake chamber which is disposed downstream of the supercharging device, a pressure rising suppressing valve which is actuated by a pressure and connected to an inner space of the air-intake chamber, the pressure rising suppressing valve being configured to open the inner space of the air-intake chamber to a relief passage, in a case where a difference between a preset pressure in a pilot space and a pressure in the air-intake chamber reaches a predetermined value or more, a control valve which is electrically actuated and is capable of performing switching of a space to be in communication with the pilot space, between a high-pressure space and a low-pressure space; and a valve controller which provides to the control valve an operation command for controlling the control valve.

A determination is made whether or not the condition that the amount V of condensed water remaining in an intake passage has exceeded a predetermined upper limit has been met, based on an input parameter associated with the amount V. If, during an engine operation in an unsupercharged mode, a determination is made that the condition has been met, a condensed water discharging operation of a supercharger is performed such that the condensed water remaining is discharged to a cylinder of the engine through operation of the supercharger.

An engine system is provided, which includes a supercharger driven by a crankshaft of an engine, an electromagnetic clutch disconnectably connecting the crankshaft to the supercharger, and a controller configured to output a control signal to the electromagnetic clutch. The controller includes a processor configured to execute an uphill-angle detecting module to detect an uphill angle during traveling of a vehicle, an uphill determining module to determine whether the detected uphill angle is above a given first uphill angle, and a boost controlling module to, when the detected uphill angle is above the first uphill angle, control the electromagnetic clutch to connect the crankshaft to the supercharger even when a target torque of the engine is within a not-boosting range.

An engine system provided to a vehicle having an accelerator pedal is provided. When an engine operation range is determined to shift to a first range (where an electromagnetic clutch is disengaged) from a second range (where the clutch is engaged) after an opening of the accelerator pedal increases at a rate below a given reference rate, the clutch is switched from ON to OFF after a given basic stand-by period passes from the shift. When the engine operation range is determined to shift from the second range to the first range after the accelerator pedal opening increases at the given reference rate or above, the clutch is switched from ON to OFF after a given acceleration stand-by period (longer than the basic stand-by period by a given added period) passes from the shift.

An engine system is provided, which includes a supercharger driven by a crankshaft of an engine, an electromagnetic clutch disconnectably connecting the crankshaft to the supercharger, and a controller configured to output a control signal to the electromagnetic clutch. The controller includes a processor configured to execute an uphill-angle detecting module to detect an uphill angle during traveling of a vehicle, an uphill determining module to determine whether the detected uphill angle is above a given first uphill angle, and a boost controlling module to, when the detected uphill angle is above the first uphill angle, control the electromagnetic clutch to connect the crankshaft to the supercharger even when a target torque of the engine is within a not-boosting range.