ZF's 8HP70 8-speed transmission is a key upgrade on Land Rover's 2012 model year Discovery 4. The new transmission directly contributes to an improvement in CO2 emissions: in 3.0-litre V6 diesel form the new Discovery has slightly more power than before, but generates less CO2.
Already used by Land Rover in the Range Rover and Range Rover Sport, the 8HP70 transmission contributes to lower fuel consumption and CO2 emissions in several ways:
- with eight ratios available, the gaps between gears are smaller but the overall spread of ratios is wider - giving a higher top gear which reduces cruising fuel consumption
- the hydraulic system is more efficient, reducing demand on the hydraulic pump which reduces energy wastage
- Transmission Idle Control automatically selects neutral when the Discovery is stationary
- the torque converter lock-up activates at lower speeds and operating temperatures to reduce slip and improve efficiency
- the transmission selects lower gears when the ambient temperature is cold to aid warm-up
The new transmission will change gear in just 200ms, which is said to equal the smoothness of a dual-clutch transmission, "while providing a more sophisticated driving experience."
Further benefits of the new transmission include:
- in hot conditions the transmission selects lower gears to run the air conditioning pump faster, cooling the cabin more effectively
- closer ratios and rev-matched downshifts improve smoothness of gearchanges
- adaptive controls detect driving style and road conditions, avoiding unwanted gearshifts (for example in the middle of a sequence of bends) and selecting the optimum gears for entry and exit of corners
- 'skip shifts' miss out up to six intermediate gears if necessary for more rapid response when overtaking
The 8HP70 in the Discovery 4 is controlled using a Jaguar-style rotary selector, together with gearshift paddles behind the steering wheel. To avoid confusion, the selector knob for the Terrain Response system is replaced by a switch.
"The new 8-speed transmission is a perfect match for our 3.0-litre diesel engine. The additional ratios combined with skip shifts mean the engine is always working in the most efficient part of its operating range," said Paul Walker, chief programme engineer.
