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.
| 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
| 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