Land Rover Discovery: Planetary Gear Trains

1. Gear set 1
2. Gearset 2
3. Gear set 3
4. Gear set 4

The planetary gear trains used on the 9HP48 transmission comprise four planetary gear sets; GS1, GS2, GS3 and GS4.

Engine torque is transferred, via operation of single or combinations of multiplate clutches, multiplate brakes and two dog clutches, to the four planetary gear trains. The gear trains are controlled by reactionary inputs from the multiplate clutches to produce the nine forward gears and one reverse gear. The gear ratios are as follows:

Sun gear S2 of gear set GS2 has additional internal gearing and also operates as the ring gear R1 of gear set GS1.

Ring gear R3 is connected to planet carrier PC1 and PC2 and therefore rotates in the same direction and speed as the planet carrier.

Gear sets GS3 and GS4 are connected via a joint sun gear S3/S4 as a Simpson planetary gear set.

Ring gear R4 is connected to planet carrier PC3 and therefore rotates in the same direction and speed as the planet carrier.

Final output from the transmission occurs via gear set GS4 via a spur gear to the differential.

POWER FLOW

Operation of the transmission is controlled by the TCM which electrically activates various solenoids to control clutches to achieve the required transmission gear selection. The sequence of solenoid activation is based on programmed information in the TCM memory and physical transmission operating conditions such as vehicle speed, throttle position, engine load and the TCS position.

1. Torque converter lock-up clutch
2. Torque converter
3. Torque converter one-way clutch
4. Multiplate cutch 'E'
5. Dog clutch 'F'
6. Planetary gears P4
7. Ring gear R4
8. Ring gear R3
9. Planetary gear P3
10. Sun gear S4
11. Sun gear S3
12. Dog clutch 'A'
13. Sun gear S1
14. Planetary gear P1
15. Ring gear R1
16. Sun gear S2
17. Planetary gear P2
18. Ring gear R2
19. Multiplate brake 'D'
20. Multiplate brake 'C'
21. Multiplate clutch 'B'

Solenoid Operation

The following table shows the clutches that are closed to achieve the required gear ratios.

X = Clutch closed

In neutral, all of the solenoids are de-energized and the clutches and brakes are all disengaged, with the exception of dog clutch 'F' which is engaged when the transmission is in neutral. This allows rotation from the input shaft to rotate the planetary gear sets without transferring any drive to the differential.

Drive ClutchesPark Lock

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