Symmetrical AWD or SAWD is an all-wheel drive system in Subaru vehicles, which has been in use since 2003. It is installed on all models of the brand, except for the BRZ and Kei models. It improves vehicle steerability and stability on slippery surfaces. It also enables faster acceleration on dry roads and optimizes off-road capability.
How it works
The distinguishing feature of the SAWD system is its symmetrical arrangement. The engine's crankshaft, gearbox, propshaft, and center and axle differentials are all arranged along the vehicle's longitudinal axis. This helps lower the center of gravity and provides better vehicle weight distribution. The result is better vehicle handling and comfort for the driver and other occupants.
The SAWD system is available in different versions. Manual transmission versions are commonly fitted with a bevel gear center differential and a viscous coupling for locking. With equal traction on all wheels, engine torque is distributed evenly to both axles. The viscous coupling then engages when either one begins to slip and most of the torque is redistributed to the axle that has the best traction. Versions with more powerful engines offer a self-locking rear differential with viscous coupling.
In vehicles with an automatic transmission or continuously variable transmission, the SAWD works with a multi-plate clutch and a gerotor pump. It distributes the torque to the axles depending on the road conditions. An electronically controlled multi-plate clutch with positive locking is sometimes used for this process.
Features of the SAWD system
| Transmission Type | Subaru Models | Differential Characteristics |
| Manual | Outback BL, BP, BR, BS; Impreza GR, CH, G3, GG; GJ, GP; Legacy BL, BP, BR, BM. | The center differential has a bevel gear engaged by a viscous coupling and often a reduction gear. The rear differential can also be equipped with locking via a viscous coupling. |
| Automatic transmission | Legacy BL, BP, BR, BM; Tribeca B9. | In a center differential, an asymmetric differential with planetary gear set and multi-plate clutch is used. If necessary, one wheel can be supplied with full engine power via the driving dynamics control. |
| Lineartronic CVT | Outback BL, BP, BR, BS; Impreza GR, CH, G3, GG; GJ, GP; Legacy BL, BP, BR, BM. | An electronically controlled multi-plate clutch is used to distribute torque to the axles instead of a center differential. Axle differentials are often of the open type. |