Nissan X-TRAIL - All New Chassis | Part Five

Nissan X-TRAIL

Nissan X-TRAIL

THE GENUINE ARTICLE AT A GLANCE

  • All-new chassis
  • Genuine SUV credentials, with:
  • Latest 4x4-i intelligent four-wheel drive system
  • Advanced hill start and descent controls
  • Enhanced on-road comfort and handling

Nissan has resisted the temptation to soften the X-TRAIL’s go-anywhere attitude and instead has made it even more capable.

All X-TRAILs are equipped with Nissan’s ALL-MODE 4x4 system which operates in two-wheel drive only to minimise fuel consumption and switches into four-wheel drive mode as and when the vehicle detects it is needed, or manually selected by the driver. The SPORT and AVENTURA models get the very latest intelligent edition known as ALL-MODE 4x4-i.

The primary improvements that have led to the development of ALL-MODE 4x4-i are the inclusion of sensors monitoring side, front and rear G forces, yaw rates and steering angles. They improve the X-TRAIL’s stability and offer added dynamic reassurance in marginal conditions by sending the power to the wheel with most grip. That applies in normal road conditions to reduce under- and oversteer, as well as off-road.

The X-TRAIL’s ALL-MODE 4x4-i system works in tandem with the other advanced on-board systems, such as the eighth generation electronic stability program (ESP), traction control (TCS), anti-lock brakes (ABS) and electronic brakeforce distribution (EBD).

In addition, ALL-MODE 4x4-i works in parallel with two further electronic systems designed to give the driver greater control when driving down steep inclines (Downhill Drive Support or DDS) or when starting off uphill (Uphill Start Support or USS).

EASY TO USE

ALL MODE 4x4-i is exceptionally easy to operate. Controlled via a large two position, three mode rotary knob situated behind the gear lever on the centre console, the system allows the driver to choose between two- (front-) wheel drive or fully automatic four-wheel drive: thanks to the improvements in the technology, the ‘AUTO’ setting is regarded as the default mode. The third ‘LOCK’ setting is for use off-road.

Once in AUTO mode, ALL-MODE 4x4-i constantly monitors all the sensors and uses yaw rate feedback to ensure ideal distribution of the engine torque between front and rear axles – as much as 50 per cent of that available can be sent to the back wheels if needed.

ALL-MODE 4x4-i includes a predictive mode, which anticipates the risk of wheel spin based on throttle position and engine torque, and transfers torque to the rear before the front wheels start to lose grip. Four-wheel drive systems on most other compact SUVs do not have the benefit of ALL-MODE 4x4-i’s predictive capability.

FUN TO DRIVE

On road, it translates into a car that is more fun to drive. It has more neutral handling as understeer is virtually eliminated regardless of vehicle speed while high speed stability and steering feedback are also enhanced. The system also works
exceptionally well on low grip and split mm surfaces when the constant monitoring of grip levels guarantees traction where it’s needed.

Off-road capability is enhanced by the ability to lock the system to ensure torque is split equally between both axles for ultimate grip. Set by twisting the rotary knob beyond the AUTO position (to which the switch reverts once set), LOCK operates at speeds of up to 40 km/h (25mph), above which it is automatically over-ridden. The setting is also over-ridden each time the engine is re-started, when the system automatically reverts to AUTO mode.

There are times when driving off-road that wheelspin can be an advantage – for finding grip in mud and snow for example – and as a further refinement on the new X-TRAIL, ESP can be deactivated to permit wheelspin.

HOW IT WORKS

When operating under normal conditions in AUTO mode, engine torque is transferred to the transmission and the front transfer case. The transfer case, in turn, is in constant mesh with the propshaft, driving the shaft but not the rear wheels at this stage.

All the while, sensors linking the engine’s ECU, wheel speed, steering angle, plus longitudinal and lateral G and yaw rates monitor and anticipate wheel slippage.

Just ahead of the rear final drive is an electronically-controlled coupling which enables drive to be fed through both front and rear axles. Its main clutch is connected to the propshaft, while a control clutch connects to the rear drive.

The control clutch features a cam system comprising two plates with asymmetric grooves on both faces, separated by a series of ball bearings. To activate rear-wheel drive, the control clutch is engaged by an electromagnet which causes one of the plates to be slowed down, allowing the bearings to move to one end of the grooves.

This forces the plates to separate which in turn applies pressure to the main clutch, and torque is transmitted between the two to supply drive to the rear wheels. The main clutch transmits torque relative to the current applied to the electromagnet and the resulting engagement pressure. A torque-limiter prevents excessive torque being sent to the rear wheels.

When LOCK is selected, the control unit supplies the maximum amount of current to the electromagnet. This causes the control clutch cam plates to apply maximum pressure to the main clutch to give a fixed 50/50 torque split at lower speeds.

ALL MODE offers further sophistication during everyday driving. Even in 2WD mode some torque is transferred to the rear wheels under certain circumstances, namely during hard acceleration when the electromagnetic clutch is engaged by 50%, and if massive slippage occurs at the front wheels, in which case the clutch is engaged by 75%.

If AUTO is selected, under light acceleration the electromagnetic clutch is engaged by up to 50%, dividing the torque to suit the conditions. During hard acceleration, the unit is fully engaged (100%) to allow the maximum permissible front/rear torque split of 50/50.

And when the X-TRAIL is being driven in AUTO at fairly constant speeds, a small drag current is supplied to the electromagnet to ensure that the system is ready to act instantaneously.

Finally, when the ABS is operated, the coupling is de-energised so that the front and rear axles can be controlled individually.

HILL HELPERS

Two further features of the new ALL-MODE 4x4-i are Downhill Drive Support and Uphill Start Support. DDS is engaged manually when the system is in LOCK mode and uses the anti-lock brakes to maintain a controlled descent speed of 5 mph. With the system looking after the vehicle speed, the driver can concentrate on steering the safest path. DDS works not only if the X-TRAIL is driving downhill in 1st gear but also when reversing down a descent.

USS, in contrast, operates automatically both on- and off-road. It comes into play when the X-TRAIL starts off from rest in any gear on an incline of 10 per cent or more, and prevents the vehicle from rolling backwards for the second or so it takes a driver to move his foot from the brake to the throttle. USS also works when reversing up a hill.

NEW SUSPENSION LAYOUT

To match its new four-wheel system, X-TRAIL has a new chassis and suspension system. Based on the Alliance C-platform, which also underpins the recently launched Nissan QASHQAI, X-TRAIL has fully independent suspension for improved on-road comfort without compromising off-road ability.

Strut-type front suspension with combined coil-over-strut assemblies and a forward lower link is mounted on a sub-frame. The sub-frame has compliant rubber mounts to isolate road noise and vibration from the platform, improving both general refinement and ride comfort. A front anti-roll bar is attached directly to the strut assembly for more effective control of body roll under cornering.

At the rear, a fully independent multi-link system has been used for precise handling and high-speed stability. Attached to the vehicle via a rigid rear subframe to keep unwanted noise and vibrations to a minimum, the compact assembly features an aluminium rear upper link to reduce weight: the saving is in the region of 4kg. The design also ensures minimal intrusion into the trunk area.

Friction control dampers are fitted to the front and rear suspension set-ups. Within the damper, a tiny valve controls the flow of oil according to the speed of the piston movement. This means that ride comfort is improved, but handling responsiveness is not compromised as the dampers react to different piston movement characteristics within the damper to give optimum damping control.

LARGER ALL ROUND

Dimensionally, new X-TRAIL is marginally bigger all round than the original. Like QASHQAI it sits on a 2630mm wheelbase – up 5mm – while overall length has increased by 175mm to 4630mm. Rear track has also increased slightly from 1530mm to 1535mm.

The all-important off-road dimensions, however, show X-TRAIL remains very capable with a minimum ground clearance of 200mm, approach and departure angles of 29 deg and 23 deg respectively and a ramp angle of 20 deg. Wading depth is 350mm.

TREK models are shod with 215/65R16 tyres on 16 inch alloys, other models with 215/60R17 tyres on 17 inch alloy wheels.

ELECTRIC POWER STEERING

Handling and manoeuvrability are aided by the adoption of electric power steering (EPS). This state-of-the-art system offers greater assistance at lower speeds with more steering feel provided as speeds rise. Tuned for European tastes, the system checks speed inputs every 40 milliseconds and is speed sensitive to 0.006 mph. It provides a strong self-centering action at lower engine speeds for easier town driving and greater feel at higher speeds.

Its brushless DC motor results in lower friction losses which, in turn, means reduced wear and lower service costs while the lack of a hydraulic pump means there are fuel consumptions benefits, too.

Disc brakes all round with standard ABS, Brake Assist and Electronic Brake Force Distribution ensure powerful and secure stopping performance. Brake Assist maintains maximum deceleration during an emergency stop while EBD constantly alters the front/rear balance to achieve optimum brake performance, automatically compensating for differing load conditions.

Nissan X-TRAIL | Part Six
Published 12 December 2007 Melanie Carter

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