The second age of Disco

New cars can be deceptive. Often the gleaming new styling hides the same old mechanicals. The opposite is true of Land Rover’s Discovery. At first glance the model, which goes on sale this month, looks hardly different from the old one. Underneath, though, most things have changed and so have most of the external panels. […]

New cars can be deceptive. Often the gleaming new styling hides the same old mechanicals.

The opposite is true of Land Rover’s Discovery. At first glance the model, which goes on sale this month, looks hardly different from the old one. Underneath, though, most things have changed and so have most of the external panels. ‘The evolution that hides a revolution’ is how Rover describes it.

What hasn’t changed is the ladder chassis and beam axle arrangement of the old model. It has not followed the pioneering route of the Freelander, which broke with tradition and used independent suspension and monocoque construction. It surprised traditionalists with its on-road refinement and off-road ability.

Discovery’s performance on and off road has been improved using electronics. The suspension has been reconfigured around the Rover-designed Active Cornering Enhancement system. Off-road, the Discovery benefits from Hill Descent Control, first used in the Freelander.

Diesel models are fitted with a new Rover five-cylinder engine using LucasVarity’s electronic unit injector system. The long-lived petrol V8 is further enhanced. The body is lengthened to allow for a forward-facing third row of seats.

Excessive body roll was one of the main complaints about the old Discovery. This posed a dilemma for chassis engineers. ‘Fitting a very thick anti-roll bar would give good roll performance but this is not so good off-road,’ says chassis engineer Magnus Campbell. ‘In cross-articulation, when the front and rear axles want to swing in opposite directions on uneven ground, a very stiff anti-roll bar limits that and you lose traction.’

The solution is Active Cornering Enhancement, designed to achieve increased articulation off-road and angles of roll on the road which are of executive saloon-standard. It uses hydraulic activators which are electronically controlled to apply an opposing force to resist body roll during cornering, but not to resist single wheel bump inputs.

The system eliminates roll up to lateral accelerations of 0.4g and allows reduced roll at higher figures, so that feedback is still provided to the driver. The system is inactive at speeds below 2mph, allowing maximum cross-articulation. Assistance builds up to 100% between 2 10mph on normal roads.

The heart of the system is two accelerometers, one under the floor and one in the roof lining, which send signals to the appropriate side of the hydraulic system via an electronic control unit. Off-road, differences in the accelerometer readings measure the roughness of the terrain and, for a given speed, roll control is reduced according to the roughness. The system can also detect side slopes and will keep the body parallel to the ground.

Rover worked closely with its suppliers on ACE but was responsible for the overall system design, including the development of algorithms for the electronic unit. It owns 10 of the 11 patents applied for on the system.

There was an emphasis on using proven technology and components the electronic control unit is a modified version of Rover’s MEMs engine management chip, for example. The pump, however, is a radial piston type optimised to minimise power consumption.

Electronics figure large in the new Discovery, with its braking system performing several functions apart from the now common anti-lock braking function which controls the braking force applied to each wheel depending on the adhesion between the tyre and road surface.

Electronic brake distribution optimises the braking balance between front and back. This eliminates the need for a pressure control valve to the rear brakes, needed to counteract the tendency of the rear wheels to lock under heavy braking as the vehicle weight is thrown forward.

Traction control limits the torque delivered to each wheel by applying the brakes to a slipping wheel. The new system can sense differences in wheel speed between opposite sides and front to back. This removes the need for a manually selected centre differential lock or viscous coupling between front and back axles. On the new Discovery, the system has been modified to operate even when the vehicle is being driven on no throttle important for off-road driving.

Hill Descent Control was introduced on the Freelander to make up for the absence of the usual low-range gearbox. The Freelander’s Hill Descent Control uses the traction control system to apply the brakes and limit the speed to between 4.4mph and 8.8mph.

Land Rover engineers found HDC provided more accurate control of target speed. ‘Engine braking is applied equally to all the wheels, and if a wheel spins you lose the braking from that wheel. HDC controls this,’ says ABS engineer Jo Lopes. ‘Also, HDC biases the braking effort to the downhill axle, improving stability.’

Diesel versions of the Discovery feature the all-new Rover Td5 turbocharged 2.5-litre, five-cylinder engine. Before the BMW takeover, the engine was planned as one of a family of modular four, five and six-cylinder engines; BMW approved just the Td5 as a dedicated Land Rover engine to replace the unit used in Tdi Discoveries.

A key feature is the use of LucasVarity electronic unit injectors for the first time in a four-wheel drive vehicle. Unit injectors combine the fuel pump and injector in one unit, suiting the original modular philosophy but providing other advantages.

The injectors each incorporate a camshaft-driven pump to pressurise the fuel, coupled with precise electronic control of the injector itself. High fuel pressures are possible, giving more power and better combustion at high revs. Another innovative feature is that fuel pressure is used to positively close the injector, rather than relying on springs. This gives a rapid, clean end to injection.

Both these factors contribute to low levels of NOx, hydrocarbon and particulate emissions, so that the engine can meet all emissions legislation in the world without an exhaust catalyst. Rover also claims class-leading fuel consumption.

Noise is reduced, especially at low speeds. The engine develops more torque and more power across the rev range, with an impressive 315Nm of torque at 1,950rpm.

Rover engineer Les Wilkins says that compared to common rail injection unit injectors are capable of much higher pressures 1,500 bar to common rail’s 1,350 bar, with the possibility of increasing to 2,000 bar if needed to meet future emission targets. These pressures are all contained within the injector without the need for a pressurised fuel line running alongside the engine.

The disadvantages are that a bespoke cylinder head design is needed; also common rail delivers fuel at a constant pressure, whereas with unit injectors, the pressure depends on engine revs.

The car’s electrics have been redesigned. ‘The old architecture was at crisis point and was too complex to assemble at line speed,’ says Land Rover electrics engineer Mark Wise. The amount of wiring is reduced by using a controller area network bus for communications between electronic control units. An ‘intelligent’ fuse box groups together fuses and relays.

‘At the end of the line you swipe a bar code on the build card and it automatically tells the car what it is,’ says Wise. It also allows various customer options to be specified, or unspecified, by the dealer such as a number of features related to the door locking system, or making the wipers wipe automatically when the windscreen washers are selected.

Internally, extra passengers in the new Discovery get a better deal. The occasional rear seats, a factory fit option, still fold away below the rear side windows but, unlike the old Discovery, they fold out to face forward. Each third-row passenger gets a full three-point seat belt, with head restraints that fold down from the roof. The seats, their locking mechanism and the head restraints are all the subject of patent applications.

Priced at £25,000 35,000, the new model will be pitched more upmarket than the outgoing one, competing with the Mercedes M Class and Toyota Land Cruiser Colorado. Rover says BMW quality has been raised to BMW standards. It hopes to sell 120,000 annually compared with a total of 400,000 of the original Discovery since 1987.

Peter Fry, team leader for body structures, sums it up: ‘What we’ve learned from BMW is that attention to detail truly makes a quality car.’