Toyota all-wheel drive. Torsen AWD

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© Toyota-Club.Net
Feb 2020

Offer to somebody to continue the associative series "four-wheel drive"... "torsen"... - most likely, you will hear "Audi". Although it is Toyota, who owns the "Torsen" brand via JTEKT now, and Toyota use such LSDs for more than two decades.

The first Torsen center differential was installed on large Toyota SUVs in 2002, and the scheme we are considering firstly presented in 2006 for top Lexus series, but it became relatively mass only since the mid-2010s at Crown family models.

This type transfer box designation is "LF1A", it is combined with an 8- or 10-speed automatic transmissions (AA80F/AGA0F) or hybrid transmissions (L110F/L210F/L310F).

Crown AWS211.2152014-2018
Crown AZSH212018-..
Lexus IS AVE352015-..
Lexus LS USF45.462006-2017
Lexus LS UVF45.462006-2017
Lexus LS GVF552017-..
Lexus LS VXFA552017-..

Transfer (LF1A). 1 - front drive gear, 2 - input shaft, 3 - oil pump, 4 - front output shaft, 5 - front driven gear, 6 - intermediate gear, 7 - rear output shaft, 8 - flange, 9 - center differential

Drive type - full-time all wheel drive.

Center differential - cylindrical, asymmetrical, LSD (limited slip differential) type Torsen Type-C.

The planetary gear carrier (with 8 planet gears) is connected to the transmission output shaft. It rotates front drive via sun gear and rear drive via epicycle.

1 - epicycle, 2 - bearing, 3 - sun gear, 4 - planet gear, 5 - carrier, 6 - rear output shaft, 7 - washer plate, 8 - front drive gear, 9 - input shaft

When cornering, the rotational speeds of the sun gear and epicycle are different, so the planet gears rotate on its axis. Due to spiral teeth, a separating force is produced that pressed the planets against the carrier wall. Friction resistance occurs and stops the planet gears, and makes the gear on the low-speed side to rotate. Speed difference between the sun gear and the epicycle is reduced, the drive torque is distributed from to the low-speed rotation side.

1 - sun gear, 2 - epicycle, 3 - carrier, 4 - planet gear. a - front output shaft revs, b - rear output shaft revs, c - input revs, d - planet gear is pressed to the carrier (limited slip)

The torque distribution ratio between the front and rear wheels depends on driving conditions:
Straight (front/rear output speed is equal)40:6040:60
Cornering (front > rear output speed)31:6950:50
Cornering (front < rear output speed)48:5230:70

• When straight driving the rotation speeds do not differ, the torque is transmitted to the front and rear wheels without planet gears rotation, the torque distribution ratio is 40:60.

Straight driving. 1 - sun gear, 2 - planet gear, 3 - epicycle, 4 - carrier. a - input torque, b - output torque (front), c - output torque (rear)

• If the speed of the front wheels is higher than the rear ones, the sun gear rotates faster than the epicycle, the torque distribution ratio is 31:69 - suppressing front wheel skid and improving cornering ability.

Distribution 31:69. 1 - sun gear, 2 - planet gear, 3 - epicycle, 4 - carrier. a - input torque, b - output torque (front), c - output torque (rear)

• If the speed of the front wheels is lower than the rear ones, then the sun gear rotates slower than the epicycle, the torque distribution ratio is 48:52 - suppressing rear wheel skid and ensuring vehicle stability during cornering.

• Deceleration while cornering adds friction created by sun gear pressed to the washer plate. If at the same time the speed of the front wheels is higher than the rear, then the torque distribution ratio is 50:50, if on the contrary - 30:70. As a result, vehicle stability during deceleration while cornering ensured.

Distribution 50:50. 1 - sun gear, 2 - planet gear, 3 - epicycle, 4 - carrier. a - pressure to washer plate, b - input torque, c - output torque (front), d - output torque (rear)

For lubrication of the components a trochoid oil pump is integrated in the front case driven, driven by the front drive intermediate gear shaft.

Oil pump. 1 - front case, 2 - drive rotor, 3 - driven rotor, 4 - plate, 5 - drive shaft

Transfer box capacity - 0.7 l, recommended fluid - Toyota Transfer gear oil LL80 (08885-02806) or Toyota Differential Gear Oil LX 75W-85 GL-5.

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