Land Rover Discovery: Four-Wheel Ddrive Systems - Vehicles Without- Active Driveline / Description and Operation

COMPONENT LOCATION - ALL WHEEL DRIVE SYSTEM - VEHICLES WITH OUT ACTIVE DRIVE LINE

1. Power Transfer Unit (PTU)
2. Driveshaft
3. Active On-Demand coupling
4. Rear differential

POWER TRANSFER UNIT (PTU) - VEHICLES WITHOUT ACTIVE DRIVELINE

1. Transmission
2. Power Transfer Unit (PTU)

OVERVIEW

Vehicles without the active driveline system have conventional mechanical differentials for the for the front and rear torque output to the halfshafts.

The front differential is located within the manual or automatic transmission.

The rear differential is located in its own housing and is attached to the rear subframe.

The non-active driveline system comprises a front differential, a Power Transfer Unit (PTU), a two-piece driveshaft, an active on-demand coupling and a rear differential.

The full-time intelligent system continuously varies the front/rear torque split using an electronically-controlled active on-demand coupling to provide variable torque AWD (all-wheel drive) when required.

The PTU is located at the rear of the engine and is attached directly to the right side of the transmission casing. A bracket on the PTU attaches the unit to the engine cylinder block.

The PTU is common to both the GTDi 2.0L Petrol and TD4 2.2L Diesel engines.

The PTU transfers the output from the transmission and distributes it to the rear wheels via a two-piece driveshaft to the active on-demand coupling and the rear differential. The active on-demand coupling controls the torque output to the rear differential. The front halfshafts are driven from the transmission front differential, not the PTU.

For details of the active on-demand coupling and the rear differential: For additional information, refer to: Rear Drive Axle and Differential (205- 02A, Description and Operation).

DESCRIPTION

Power Transfer Unit (PTU) Sectional View

1. Right halfshaft
2. Collar
3. Vee seal
4. Oil seal
5. Angular contact ball bearings (2 off)
6. Crown wheel drive gear
7. Casing
8. O ring seal
9. Tube shaft seal
10. Halfshaft dust seal
11. Housing
12. Drain plug
13. Pinion gear
14. Taper roller bearing (2 off)
15. Collapsible spacer
16. Drive flange
17. Pinion nut
18. Oil seal and flinger
19. Transmission casing
20. Transmission front differential

Power Transfer Unit (PTU)

1. Driveshaft mounting flange
2. Power Transfer Unit (PTU)
3. Drive collar (fitted to Transmission differential housing output spline - part of transmission not PTU)
4. Transmission mounting flange
5. Breather tube
6. Engine mounting bracket (GTDi 2.0L Petrol shown)
7. Right halfshaft dust seal

The crown wheel drive gear is mounted longitudinally across the PTU. The gear is a low-offset hypoid bevel gear configured for minimal power loss across the speed range. The left end of the gear has splines which mate with corresponding splines in the transmission front differential output sleeve. The drive gear is hollow which allows for the fitment of the right halfshaft. The halfshaft is located through the hollow drive gear and mates with splines in the side gear of the transmission's front differential. The halfshaft is driven by the transmission front differential and receives no drive from the PTU.

The crown wheel is supported in the PTU casing on opposing angular contact ball bearings which are pressed into a housing and sealed with an O ring seal. The housing is fitted with a triple edge oil seal on the outer end of the housing which directs dirt and moisture away from the area of the drive gear. Another seal is fitted which prevents the ingress of dirt and moisture between the drive gear and right halfshaft.

The pinion gear is locked in the PTU casing at 90 degrees to the crown wheel drive gear. The pinion gear is supported in the casing on opposing taper roller bearings. The pinion gear is retained in the casing with a preload nut. The outer end of the pinion gear is splined and mates with the driveshaft output flange. The flange is secured with a nut which is screwed onto the pinion gear.

A collapsible spacer is located between the outer taper roller bearing and a shoulder on the pinion gear. The spacer collapses under pressure applied by the pinion nut and pre-loads the pinion bearings to the correct setting when the nut is torque tightened to a predetermined value.

OPERATION - VEHICLES WITH OUT ACTIVE DRIVE LINE

The Power Transfer Unit (PTU) is driven via the differential carrier in the front differential in the main transmission and supplies drive to the rear differential via the driveshaft. The torque transferred is then determined via the active on-demand coupling on the rear differential.

The front left and right halfshafts are connected to the side gears in the transmission front differential. No drive from the PTU is passed to the front halfshafts.

Active Driveline SystemGearshift Cable Adjustment

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