Subaru Two-Stage Twin Turbo Operation

i Menu

The Subaru two-stage twin turbocharger system is composed of the primary and secondary turbochargers, the air-cooled intercooler, the exhaust gas supply control valve, the intake air control valve, the air bypass valve, the supercharged-pressure relief valve, the differential pressure sensor, the solenoid box, etc.

The twin turbocharger system uses two small turbochargers. While engine speed is low, the single turbo charging is provided by the primary turbocharger. When the engine speed becomes high, twin turbo charging is provided by both primary and secondary turbocharger. In this way, supercharging is started from low speeds, so that there is less turbocharger lag, while the torque at low engine speed is improved, and at the high engine speed range, higher output can be obtained as compared with the single turbocharger system. By optimally controlling the switching between single turbo charging and twin turbo charging, the Subaru two-stage twin turbocharger system actualizes a smooth transitional torque characteristic from medium to high speeds.


Valve status according to engine operating condition

  Idling Single turbocharging range Secondary turbocharger preparation rotation range Twin turbocharger range
1. Wastegate valve Closed Operation Closed Operation
2. Exhaust gas supply control valve Closed Closed Operation Fully open
3. Supercharged pressure relief valve Closed
atmospheric pressure
Closed
atmospheric pressure
Operation
atmospheric pressure
Closed [ 1 ]
4. Intake air control valve Closed
negative Pressure
Closed
negative Pressure
Closed
negative Pressure
Operation
atmospheric pressure

[ 1 ] The supercharged pressure relief valve opens when low octane fuel is used


Solenoid status according to engine operating condition

  Idling Single turbocharging range Secondary turbocharger preparation rotation range Twin turbocharger range
5. Wastegate duty solenoid OFF – valve closed Duty control – valve open OFF – valve closed Duty Control – valve open
6. Exhaust gas supply control duty solenoid OFF – valve closed
atmospheric pressure
OFF – valve closed
atmospheric pressure
Duty control – valve open
Duty positive pressure
OFF – valve open
positive pressure
7. Exhaust gas supply control solenoid
(positive pressure)
OFF – valve closed
Sends atomospheric pressure to 6
OFF – valve closed
Sends atomospheric pressure to 6
ON – valve open
Sends positive pressure to 6
ON – valve open
Sends positive pressure to 6
8. Exhaust gas supply control solenoid
(negative pressure)
OFF – valve closed OFF – valve closed OFF – valve closed
Sends negative pressure to the negative chamber of 2
ON – valve open
Sends negative pressure to the negative chamber of 2
9. Intake air control solenoid OFF – valve open
Sends negative pressure to 4
OFF – valve open
Sends negative pressure to 4
OFF – valve open
Sends negative pressure to 4
ON – valve closed
Sends atmospheric pressure to 4
10. Supercharged pressure relief valve #1 solenoid
(negative pressure)
OFF – valve closed OFF – valve closed OFF – valve closed OFF [ 2 ] – valve closed
11. Supercharged pressure relief valve #2 solenoid
(positive pressure)
OFF – valve closed OFF – valve closed OFF – valve closed ON – valve open
Sends positive pressure to 3

[ 2 ] Superchared pressure relief valve #1 solenoid will turn ON when low octane fuel is used
Arabic Numerals in the table correspond to the numbers attached to the front of the parts name