BOOST CONTROL [SKYACTIV-G 2.5T]

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Outline

• The PCM controls the boost pressure to improve the responsiveness of the turbocharger, the acceleration performance and fuel economy of the vehicle, and to reduce surge noise.

• The PCM controls the following 3 valves to obtain optimum boost pressure according to the driving conditions.

― Wastegate valve

― Air bypass valve

― Three way solenoid valve

• For details on the boost system and the opening/closing of each valve on the boost pressure control, refer to the INTAKE SYSTEM and EXHAUST SYSTEM. (See BOOST SYSTEM [SKYACTIV-G 2.5T].) (SeeDYNAMIC PRESSURE TURBO [SKYACTIV-G 2.5T]) (SeeEXHAUST MANIFOLD [SKYACTIV-G 2.5T])

Block Diagram

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Operation

• The PCM controls each of the following valves to obtain optimum boost pressure according to the engine operation conditions.

Wastegate valve control

• The PCM calculates the opening angle of the wastegate valve to realize the target boost pressure according to the engine operation conditions (output torque).

• The PCM performs feedback control of the wastegate valve to achieve the target boost pressure.

Target boost pressure

― The target boost pressure is calculated based on the engine speed and the charging efficiency^*1.

Actual boost pressure

― Directly detected by the boost pressure sensor.

*1 :Charging efficiency is the ratio of the actual amount of intake air to the maximum air charging amount (mass volume) of the cylinder. The value increases as the engine load increases.

• When the PCM determines that the actual boost pressure is high (excessive amount of exhaust gas) against the target boost pressure, it increases the wastegate valve opening angle. In addition, when the PCM determines that the exhaust gas flow during idling is high or when the selector lever is in the N or P position, it opens the wastegate valve.

• When the PCM determines that the actual boost pressure is low (amount of exhaust gas is less) against the target boost pressure, it decreases the wastegate valve opening angle to increase the amount of exhaust gas flowing to the turbine wheel. In addition when the PCM determines that the amount of exhaust gas is low during idling, or when the selector lever is in the D or R position, it closes the wastegate valve.

Air bypass valve control

• The PCM switches the energization to the air bypass valve according to the engine operation conditions.

• The PCM fully opens the air bypass valve to protect the parts during overboost.

Energization to air bypass valve

Implementation conditions

Air bypass valve operation conditions

ON

When any of the following conditions is met

• Vehicle speed decelerates based on driver's request

• Overboost determined

Fully open

OFF

Conditions other than above

Fully closed

Energization to air bypass valve	Implementation conditions	Air bypass valve operation conditions
ON	When any of the following conditions is met • Vehicle speed decelerates based on driver's request • Overboost determined	Fully open
OFF	Conditions other than above	Fully closed

Three way solenoid valve control

• The PCM switches the energization to the three way solenoid valve according to the engine operation conditions.

• The three way solenoid valve controls the opening/closing of the exhaust manifold variable valve to increase the turbocharger turbine operation force.

Energization to three way solenoid valve

Implementation conditions

Exhaust manifold variable valve operation conditions

ON

Conditions other than above

Fully closed

ONFF

When any of the following conditions is met

• Engine speed is 1,620 rpm or more

• Excessive amount of exhaust gas during idling

Fully open

Energization to three way solenoid valve	Implementation conditions	Exhaust manifold variable valve operation conditions
ON	Conditions other than above	Fully closed
ONFF	When any of the following conditions is met • Engine speed is 1,620 rpm or more • Excessive amount of exhaust gas during idling	Fully open