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The Freelander2 Full-Time Intelligent 4x4 System
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By MartinW at 2007-12-13 09:04
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Thursday, 22 June 2006
An innovative full-time intelligent 4x4 transmission is fundamental to delivering Freelander 2’s class-leading breadth of capability. Its front-rear torque split varies continuously to suit dynamic conditions. Only a small amount of torque is fed to the rear wheels under normal conditions, such as on a straight tarmac road, but in tough off-road situations, almost all the engine torque can be fed to the rear wheels, if required. This is an ideal arrangement that always offers maximum grip in difficult conditions, yet minimises rear drive – and therefore rotational losses and, in turn, fuel consumption – when not required.
"The torque balance adapts continuously," says chief programme engineer Andrew Foster. "So, for example, if you encounter mud or snow on the road, torque distribution between front and rear can be adjusted, to give you optimal traction and primary safety at all times."
The intelligent 4x4 system has been developed in conjunction with Haldex, whose acclaimed centre-coupling technology continuously alters the front-rear torque split, normally through a hydraulically operated multi-plate wet clutch. However, Land Rover wanted an electronically controlled centre coupling – linking the propshaft to the rear differential – that could pre-engage at rest to reduce wheelspin from standing starts, engage quickly when traction loss was detected and disengage quickly without compromising stability control systems. The system also had to transmit the necessary torque to achieve Freelander 2’s off-road traction demands.
The result is used exclusively on Freelander 2, and proactively engages full-time 4x4 rapidly and completely. A new high-pressure pre-charge pump charges the hydraulic system as soon as the engine is started, allowing for full-time 4x4 from rest. It also reduces the time taken to achieve full torque once wheel-slip has been detected – within 15 degrees of wheel-slip rotation (compared with over 60 degrees of wheel-slip rotation with more conventional units).
The Freelander 2’s Haldex unit is designed to allow up to 1500 Nm of torque transmission. An accumulator also speeds up the unit’s response. Full torque transmission can be achieved in just 150 milliseconds. In effect, the new Haldex coupling gives the proactive engagement benefits of full-time 4x4 and the efficiency and fuel economy of an on-demand system. Representing the best of both worlds, it is ideal for a compact 4x4 such as Freelander 2.
Terrain Response Enhances Go-Anywhere Ability
Terrain Response is one of the core Land Rover technologies that gives the Freelander 2 its outstanding breadth of capability. Standard on all but the entry model, it adapts the responses of the vehicle’s engine, gearbox, centre coupling and chassis systems to match the demands of the terrain. It optimises driveability and comfort, as well as maximising traction.
On the Freelander 2, there are four Terrain Response settings which the driver can choose via a rotary control:
General Driving – provides a broad span of ability suitable for most on-road driving and easier off-road conditions
Grass/Gravel/Snow – for slippery conditions, on-road or off-road
Mud and Ruts
Sand
"Each of the settings optimises Freelander 2’s suite of electronic and mechanical controls to suit the chosen terrain," says Andrew Foster. "It’s like having an off-road expert to assist."
Terrain Response also controls the following range of stability and traction aids:
Dynamic Stability Control (DSC): is designed to help stop torque to a wheel after loss of traction, but in some off-road situations torque feed is still desirable, even when traction is being lost. Terrain Response automatically adjusts the DSC so that appropriate torque is maintained
Electronic Traction Control and Anti-lock Brakes: these slip and braking control systems are all adjusted and tuned by Terrain Response to offer optimum grip, braking power and safety on the chosen terrain
Hill Descent Control (HDC): the latest generation of the award-winning Land Rover technology that automatically restricts speed downhill, using the anti-lock brakes, and improves driver control on slippery descents. HDC is automatically engaged on appropriate Terrain Response programmes. Downhill speed rates vary according to which surface is selected
Terrain Response also changes the setting of the electronic centre coupling, to optimise 4x4 drive in tough conditions. It works continuously, and made its production debut in the Land Rover Discovery 3 in 2004.
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