Conn, if you've ever read any of my posts in any of the multiple threads on the subject of AWD, you'll know I utterly hate when people think AWD makes them invincible. As I said I agree with you. Your first post was just a bit pompous and frankly irritating to all of us who had been having a nice civilized discussion up until then.
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AWD question
- Thread starter Martyd
- Start date
For any one interested how the Nissan Xtrail system works, links for both the T30 and T31.
http://www.x-trail-uk.co.uk/viewtopic.php?f=42&t=4764
http://www.x-trail-uk.co.uk/viewtopic.php?f=43&t=3754
http://www.x-trail-uk.co.uk/viewtopic.php?f=42&t=4764
http://www.x-trail-uk.co.uk/viewtopic.php?f=43&t=3754
T31 ALL MODE 4x4-i
Intelligent four-wheel drive system.
At the heart of the new X-TRAIL lies a sophisticated electronically controlled
‘intelligent’ four-wheel drive system called ALL MODE 4x4-i. It is the latest
version of the Nissan developed ALL MODE system that has been central to the
success of iconic off-road vehicles such as Pathfinder as well as the original XTRAIL.
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 over steer, as
well as off-road.
The X-Trail’s ALL MODE 4x4-i system works in tandem with the other advanced onboard
systems, such as the eighth generation electronic stability program, (ESP), traction
control (TCS), anti-lock brakes (ABS) and electronic brake force 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
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 the available can be sent to the back wheels if needed.
X-TRAIL-UK
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 under steer 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 mμ 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 wheel spin 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 wheel spin.
How it works X-TRAIL-UK
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 prop shaft, 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 prop shaft, 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.
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 7 km/h. 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. X-TRAIL-UK
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.
X-TRAIL-UK.
NISSAN X-TRAIL T30
X-TRAIL is also available with a choice of two petrol engines, displacing 2.0 and 2.5-litres respectively. Both are members of Nissan’s
QR range of all-alloy engines and both have four cylinders, twin overhead camshafts, 16 valves and CVTC (Continuous Valve Timing
Control). Offering good levels of refinement and ample power and torque, both units provide quiet and smooth on-road performance and
off-road ability.
The 2.0-litre unit develops 140PS and 192Nm of torque to give a maximum speed of 110mph with 0-62mph taking just 11.0 seconds in
two-wheel drive guise. Combined fuel consumption is 31.0mpg.
Broadly similar in layout, the 2.5-litre version offers more performance all round. Power rises to 165PS and torque to 230Nm. Maximum
speed increases to 118mph with 0-62mph taking 9.9 seconds (automatic 111mph and 11.1 seconds, respectively). At 30.1mpg
(automatic 29.4mpg) average fuel consumption is on a par with the 2.0-litre version.
Emissions from both petrol models are also commendably low; the 2.0 litre achieves 217g/km, for example.
Both engines have been designed not just for strong performance but also for excellent refinement with potential vibrations minimised
and low friction materials being used wherever possible. The aluminium block has a ladder-frame construction, which improves strength
while also reducing weight and resonance. Further weight reduction is achieved by the adoption of a resin intake manifold.
Low friction materials and lightweight items like the valve springs and the silent running timing chain all combine to offer a refined
response under all engine loads. Any vibration is then countered by the twin chain-driven balancer shafts.
SMOOTHER SHIFTING
So wide is the spread of torque from the diesel engine that it is matched with a slick six-speed manual transmission as standard. Five
close-ratio lower gears are topped by a ‘long’ overdrive top gear for optimum motorway cruising where the resulting low engine speeds
mean better economy and less noise.
For the petrol engines, Nissan has used a typically slick shifting five speed. A four speed automatic is an option on the 2.5 litre unit. It’s a
high-efficiency E-flow unit which offers better fuel figures than previous generation boxes. A mechanical lock-up on fourth gear improves
fuel consumption on longer journeys. With a drive-by-wire throttle and electronic throttle chamber (ETC) both sensitive to throttle
depression speed, the gearbox works out whether the driver wants high or low response rates and at what engine speed the gearbox
should change up or down.
DYNAMIC TECHNOLOGY
“By equipping X-TRAIL with the most advanced four-wheel drive system on the market and matching it with the
most up-to-date traction and stability control system available, we have developed a genuinely versatile SUV
that offers freedom of mobility with no compromise.”
ADVANCED ELECTRONICALLY CONTROLLED ALL MODE 4x4
At the heart of X-TRAIL lies some of the most sophisticated technology available anywhere on the 4x4 market. Developed by Nissan,
the ALL MODE 4x4 system allows secure and relaxed driving under all conditions, both on- and off-road, with advanced electronics
taking care of all traction needs.
In essence, ALL MODE 4x4 ensures X-TRAIL has grip at all times no matter how severe the conditions. But unlike some other
X-TRAIL-UK
automatic four-wheel drive systems, ALL MODE uses advanced electronics to ensure drive is transferred between wheels and axles the
instant a problem arises. Via the electronic throttle control, the system is able to anticipate low traction situations, and engage fourwheel
drive before traction is lost.
Only by using electronic sensors can this happen instantaneously: other systems might sound similar on paper, but usually operate via a
dual pump system, whereby the slipping of one pair of wheels pumps up the system to bring in the other pair. Because a wheel has to
slip for anything to happen, there’s a delay of several wheel rotations before traction is restored by which time the car could well be
stuck.
Nissan’s ALL MODE system anticipates loss of traction meaning that it only takes a few degrees of a single wheel rotation for torque to
be reapportioned.
Fig.1: Schematic of the X-TRAIL’s ALL MODE system
MODE ONE: 2WD
In X-TRAIL, the system has three modes, selected via a rotary switch on the dashboard. Under normal road conditions, eg around town
or on a dry motorway, the X-TRAIL should be run in ‘2WD’ – with the front wheels doing the ‘driving’. Lower fuel consumption and tyre
wear (or lack of) result. But should the system detect massive slip from the front wheels, ‘AUTO’ is selected till normal traction is
X-TRAIL-UK
resumed.
MODE TWO: AUTO
Should the driver’s pace quicken, the road surface become less firm or the weather deteriorate due to rain, snow or ice, it’s time to
switch to ‘AUTO’ in which the system is left to its own devices. A green warning light immediately illuminates under the speedo to show
that automatic four-wheel drive has been selected. This can be done at any speed and allows ALL MODE to apportion torque to each
axle based on a number of inputs, eg acclerator opening, wheel speed sensor, engine speed, G sensor and the brakes.
Torque can be redirected as much as 100 per cent front (with 0 per cent to rear) or up to 43 per cent rear (57 per cent front) almost
immediately and as required. The percentage split is constantly varying anyway. Keen drivers may even wish to leave their X-TRAIL in
‘AUTO’ all the time. Left in Auto, the system will automatically compensate for unexpected slippery conditions on-road, such as wet
leaves in autumn, early morning winter ice or loose gravel at any time of the year. It also adds the benefit of better fuel economy in 2WD
with the safety of 4WD when needed.
MODE THREE: LOCK
The X-TRAIL offers a further four-wheel drive mode, ‘LOCK’, in which the centre clutch locks to divide drive 57:43 (front to rear), a ratio
chosen because that’s how the car’s weight is apportioned over its front and rear axles. This is for serious off road use or for extreme
conditions such as when starting off on an incline covered in deep snow or driving through deep mud. You don’t even have to press
‘AUTO’ when the conditions become kinder because the car will do it for you.
HOW IT WORKS
When operating in 2WD or AUTO, engine torque is transferred to the transmission and to the front transfer case, and the transfer case
in turn is in constant mesh with, and driving the propellor shaft (but not the rear wheels) at all times. Sensors linking the engine’s ECU
and the anti-lock brakes, meanwhile, constantly monitor and anticipate wheel slippage.
Located just ahead of the rear final drive is an electronically-controlled coupling (Fig.2) which enables drive to be fed through both front
and rear axles. Its main clutch is connected to the propeller shaft, while a control clutch connects to the rear drive. X-TRAIL-UK
Fig 2: The ALL MODE system’s electronically-controlled coupling
The control clutch features a cam system comprising two plates with asymmetric grooves on both faces, separated by a series of ball
bearings. In order to activate rear-wheel drive, the control clutch is engaged by an electromagnet and this causes one of the plates to be
slowed down, causing the ball 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 give rear-wheel drive (Figs. 3 and 4). The main clutch
transmits torque relative to the current applied to the electromagnet and the resulting engagement pressure. X-TRAIL-UK
Fig.3: The electronically-controlled coupling operating in two-wheel drive.
The unit ’s clutch is not engaged at this point.
Fig. 4: The electromagnetic clutch is activated and torque is transmitted to the rear wheels.
X-TRAIL-UK
Fig. 5: When ALL MODE is switched to ‘Lock’, maximum current is supplied to the electromagnet. This
results in maximum pressure to the main clutch to give a 53/47 front/rear split in transmitted drive.
If the system is switched to AUTO, and in certain circumstances 2WD, then the instant ALL MODE anticipates wheel slippage when
encountering unexpected slippery conditions on-road, such as mud, wet leaves or ice, the coupling is automatically activated and drive
is correctly apportioned, the maximum torque spilt being 53/47 front-to-rear. 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 (Fig.5). This causes the control
clutch cam plates to apply maximum pressure to the main clutch to give a 53/47 split in transmitted drive, and this is available up to a
speed of approximately 18 mph. Over this speed, the system reverts to Auto operation, switching back to Lock when the X-TRAIL is
slowed.
X-TRAIL-UK
Fig. 6: This diagram shows the engagement of the electromagnetic clutch unit under a variety of
conditions.
100 % indicates that maximum torque split is taking place, ie 53% front and 47% rear.
ALL MODE offers further sophistication during everyday driving (Fig. 6). 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 53/47.
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.
MONOCOQUE CONSTRUCTION
X-TRAIL uses a monocoque construction for low weight whilst maintaining, excellent torsional rigidity. The suspension system is
attached to the shell via two sturdy subframes, insulated from the body to reduce noise, vibration and harshness. The front suspension
is by MacPherson strut and coils with the independent rear suspension using parallel links.
X-TRAIL-UK
Light and stiff – it features an aluminium transverse link – the rear suspension is designed to move the rear wheel trajectory backwards
on compression, rather than forward, thus minimising tyre impact when an obstacle is hit and providing a compliant ride under all
conditions.
Its long travel benefits off road ability but doesn’t compromise on-road comfort: X-TRAIL has been benchmarked against premium
passenger cars.
With a commanding driving position, excellent manoeuvrability, fine handling and comfort and a tight turning circle – 10.6m – X-TRAIL is
as easy to drive on-road as it is able off-road. Manoeuvrability is especially important when towing and an X-TRAIL 2.0 will lug 1.5
tonnes of braked trailer, the 2.2dCi and manual 2.5 an even heavier 2 tonnes.
The vital off-road statistics are an approach angle of 29 degrees, departure 26 degrees (2.2 dCi 25 degrees) and a ramp angle of 21
degrees (2.2 dCi 23 degrees). Minimum ground clearance is 200mm, with a maximum 48 degree tilt angle.
SAFETY
ACTIVE AND PASSIVE SAFETY
As the system is electronic, ALL MODE 4x4 is fully integrated with X-TRAIL’s array of electronic traction aids, collected together under
the ESP+ banner. Standard on Aventura models, ESP+ offers more than traditional stability systems and is ideally suited to a dual role
vehicle such as X-TRAIL.
The ABS sensors, steering angle sensor, G-sensor, yaw rate sensor, ALL MODE 4x4 controller and drive-by-wire throttle all
communicate with each other to detect a loss, or potential loss of traction on any wheel. ESP+ works by determining the intentions of the
driver through the steering wheel position sensor on the steering column and through the wheel speed sensors at the wheels. It then
calculates how the car should ideally be behaving, and compares this with what it’s actually doing monitored through the yaw rate
sensor (measures turning velocity about the vertical axis of the vehicle), wheel speed sensors and the lateral acceleration sensor, and
then calculates what needs to be done to marry the two. Stability is restored by varying any, or as many as is necessary of the following:
brake pressure to individual wheels (using the ABS and EBD), the mode of four-wheel drive and engine output.
An Active Brake Limited Slip Differential, also controlled by the ABS sensors, applies the brakes to any wheel that has lost traction and,
in so doing, transfers drive to the opposite wheel on the same axle.
As a result of this integrated approach, ESP+ can either apply the brake or redirect torque to any individual wheel independently, thus
controlling understeer and oversteer on the road and ensuring maximum traction is maintained off-road or when the going gets slippery.
X-TRAIL-UK
Fig.7: Intervention of ESP+ during understeer.
(1) With ESP+ (2) Without ESP+
(3) Braking force (4) Balancing yaw movement
Fig.8: Intervention of ESP+ during oversteer.
(1) Without ESP+ (2) With ESP+
(3) Braking force (4) Balancing yaw movement
In simple terms, at the onset of understeer (Fig.7) the rear wheel on the inside of the bend is braked which turns the vehicle back in the
direction of the bend; since the front wheels have insufficient grip, ESP mostly uses the rear brakes since more grip is available here.
During oversteer (Fig.8), the rear end needs to be brought into line and this is achieved by braking the front wheel on the outside of the
bend. Again, ESP mostly uses the front brakes as more grip is available here.
X-TRAIL offers particularly short stopping distances thanks to ventilated disc brakes front and rear and are controlled by the latest
generation four-channel, five-sensor ABS system which incorporates Nissan Brake Assist for maximum emergency stopping power and
Electronic Brakeforce Distribution for even braking under all conditions.
The combination of ALL MODE 4x4 and ESP+ means X-TRAIL has one of the most advanced active safety systems available on any
passenger car. It is backed up by a computer-analysed structure giving excellent passive safety protection with highly effective crumple
zones front and rear. Twin front SRS airbags are standard on all grades along with head and thorax side bags. Front seats are equipped
with active headrests, three point belts with pretensioners and load limiters, while ISOFIX child seat fastenings and three point
harnesses in the rear are also standard.
They are links to PDF files with lots of illustrations, so if interested perhaps joining the xtrail club may be worth while.
Apologies if not all the above makes sense, lacking the drawings etc.
Intelligent four-wheel drive system.
At the heart of the new X-TRAIL lies a sophisticated electronically controlled
‘intelligent’ four-wheel drive system called ALL MODE 4x4-i. It is the latest
version of the Nissan developed ALL MODE system that has been central to the
success of iconic off-road vehicles such as Pathfinder as well as the original XTRAIL.
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 over steer, as
well as off-road.
The X-Trail’s ALL MODE 4x4-i system works in tandem with the other advanced onboard
systems, such as the eighth generation electronic stability program, (ESP), traction
control (TCS), anti-lock brakes (ABS) and electronic brake force 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
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 the available can be sent to the back wheels if needed.
X-TRAIL-UK
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 under steer 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 mμ 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 wheel spin 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 wheel spin.
How it works X-TRAIL-UK
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 prop shaft, 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 prop shaft, 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.
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 7 km/h. 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. X-TRAIL-UK
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.
X-TRAIL-UK.
NISSAN X-TRAIL T30
X-TRAIL is also available with a choice of two petrol engines, displacing 2.0 and 2.5-litres respectively. Both are members of Nissan’s
QR range of all-alloy engines and both have four cylinders, twin overhead camshafts, 16 valves and CVTC (Continuous Valve Timing
Control). Offering good levels of refinement and ample power and torque, both units provide quiet and smooth on-road performance and
off-road ability.
The 2.0-litre unit develops 140PS and 192Nm of torque to give a maximum speed of 110mph with 0-62mph taking just 11.0 seconds in
two-wheel drive guise. Combined fuel consumption is 31.0mpg.
Broadly similar in layout, the 2.5-litre version offers more performance all round. Power rises to 165PS and torque to 230Nm. Maximum
speed increases to 118mph with 0-62mph taking 9.9 seconds (automatic 111mph and 11.1 seconds, respectively). At 30.1mpg
(automatic 29.4mpg) average fuel consumption is on a par with the 2.0-litre version.
Emissions from both petrol models are also commendably low; the 2.0 litre achieves 217g/km, for example.
Both engines have been designed not just for strong performance but also for excellent refinement with potential vibrations minimised
and low friction materials being used wherever possible. The aluminium block has a ladder-frame construction, which improves strength
while also reducing weight and resonance. Further weight reduction is achieved by the adoption of a resin intake manifold.
Low friction materials and lightweight items like the valve springs and the silent running timing chain all combine to offer a refined
response under all engine loads. Any vibration is then countered by the twin chain-driven balancer shafts.
SMOOTHER SHIFTING
So wide is the spread of torque from the diesel engine that it is matched with a slick six-speed manual transmission as standard. Five
close-ratio lower gears are topped by a ‘long’ overdrive top gear for optimum motorway cruising where the resulting low engine speeds
mean better economy and less noise.
For the petrol engines, Nissan has used a typically slick shifting five speed. A four speed automatic is an option on the 2.5 litre unit. It’s a
high-efficiency E-flow unit which offers better fuel figures than previous generation boxes. A mechanical lock-up on fourth gear improves
fuel consumption on longer journeys. With a drive-by-wire throttle and electronic throttle chamber (ETC) both sensitive to throttle
depression speed, the gearbox works out whether the driver wants high or low response rates and at what engine speed the gearbox
should change up or down.
DYNAMIC TECHNOLOGY
“By equipping X-TRAIL with the most advanced four-wheel drive system on the market and matching it with the
most up-to-date traction and stability control system available, we have developed a genuinely versatile SUV
that offers freedom of mobility with no compromise.”
ADVANCED ELECTRONICALLY CONTROLLED ALL MODE 4x4
At the heart of X-TRAIL lies some of the most sophisticated technology available anywhere on the 4x4 market. Developed by Nissan,
the ALL MODE 4x4 system allows secure and relaxed driving under all conditions, both on- and off-road, with advanced electronics
taking care of all traction needs.
In essence, ALL MODE 4x4 ensures X-TRAIL has grip at all times no matter how severe the conditions. But unlike some other
X-TRAIL-UK
automatic four-wheel drive systems, ALL MODE uses advanced electronics to ensure drive is transferred between wheels and axles the
instant a problem arises. Via the electronic throttle control, the system is able to anticipate low traction situations, and engage fourwheel
drive before traction is lost.
Only by using electronic sensors can this happen instantaneously: other systems might sound similar on paper, but usually operate via a
dual pump system, whereby the slipping of one pair of wheels pumps up the system to bring in the other pair. Because a wheel has to
slip for anything to happen, there’s a delay of several wheel rotations before traction is restored by which time the car could well be
stuck.
Nissan’s ALL MODE system anticipates loss of traction meaning that it only takes a few degrees of a single wheel rotation for torque to
be reapportioned.
Fig.1: Schematic of the X-TRAIL’s ALL MODE system
MODE ONE: 2WD
In X-TRAIL, the system has three modes, selected via a rotary switch on the dashboard. Under normal road conditions, eg around town
or on a dry motorway, the X-TRAIL should be run in ‘2WD’ – with the front wheels doing the ‘driving’. Lower fuel consumption and tyre
wear (or lack of) result. But should the system detect massive slip from the front wheels, ‘AUTO’ is selected till normal traction is
X-TRAIL-UK
resumed.
MODE TWO: AUTO
Should the driver’s pace quicken, the road surface become less firm or the weather deteriorate due to rain, snow or ice, it’s time to
switch to ‘AUTO’ in which the system is left to its own devices. A green warning light immediately illuminates under the speedo to show
that automatic four-wheel drive has been selected. This can be done at any speed and allows ALL MODE to apportion torque to each
axle based on a number of inputs, eg acclerator opening, wheel speed sensor, engine speed, G sensor and the brakes.
Torque can be redirected as much as 100 per cent front (with 0 per cent to rear) or up to 43 per cent rear (57 per cent front) almost
immediately and as required. The percentage split is constantly varying anyway. Keen drivers may even wish to leave their X-TRAIL in
‘AUTO’ all the time. Left in Auto, the system will automatically compensate for unexpected slippery conditions on-road, such as wet
leaves in autumn, early morning winter ice or loose gravel at any time of the year. It also adds the benefit of better fuel economy in 2WD
with the safety of 4WD when needed.
MODE THREE: LOCK
The X-TRAIL offers a further four-wheel drive mode, ‘LOCK’, in which the centre clutch locks to divide drive 57:43 (front to rear), a ratio
chosen because that’s how the car’s weight is apportioned over its front and rear axles. This is for serious off road use or for extreme
conditions such as when starting off on an incline covered in deep snow or driving through deep mud. You don’t even have to press
‘AUTO’ when the conditions become kinder because the car will do it for you.
HOW IT WORKS
When operating in 2WD or AUTO, engine torque is transferred to the transmission and to the front transfer case, and the transfer case
in turn is in constant mesh with, and driving the propellor shaft (but not the rear wheels) at all times. Sensors linking the engine’s ECU
and the anti-lock brakes, meanwhile, constantly monitor and anticipate wheel slippage.
Located just ahead of the rear final drive is an electronically-controlled coupling (Fig.2) which enables drive to be fed through both front
and rear axles. Its main clutch is connected to the propeller shaft, while a control clutch connects to the rear drive. X-TRAIL-UK
Fig 2: The ALL MODE system’s electronically-controlled coupling
The control clutch features a cam system comprising two plates with asymmetric grooves on both faces, separated by a series of ball
bearings. In order to activate rear-wheel drive, the control clutch is engaged by an electromagnet and this causes one of the plates to be
slowed down, causing the ball 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 give rear-wheel drive (Figs. 3 and 4). The main clutch
transmits torque relative to the current applied to the electromagnet and the resulting engagement pressure. X-TRAIL-UK
Fig.3: The electronically-controlled coupling operating in two-wheel drive.
The unit ’s clutch is not engaged at this point.
Fig. 4: The electromagnetic clutch is activated and torque is transmitted to the rear wheels.
X-TRAIL-UK
Fig. 5: When ALL MODE is switched to ‘Lock’, maximum current is supplied to the electromagnet. This
results in maximum pressure to the main clutch to give a 53/47 front/rear split in transmitted drive.
If the system is switched to AUTO, and in certain circumstances 2WD, then the instant ALL MODE anticipates wheel slippage when
encountering unexpected slippery conditions on-road, such as mud, wet leaves or ice, the coupling is automatically activated and drive
is correctly apportioned, the maximum torque spilt being 53/47 front-to-rear. 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 (Fig.5). This causes the control
clutch cam plates to apply maximum pressure to the main clutch to give a 53/47 split in transmitted drive, and this is available up to a
speed of approximately 18 mph. Over this speed, the system reverts to Auto operation, switching back to Lock when the X-TRAIL is
slowed.
X-TRAIL-UK
Fig. 6: This diagram shows the engagement of the electromagnetic clutch unit under a variety of
conditions.
100 % indicates that maximum torque split is taking place, ie 53% front and 47% rear.
ALL MODE offers further sophistication during everyday driving (Fig. 6). 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 53/47.
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.
MONOCOQUE CONSTRUCTION
X-TRAIL uses a monocoque construction for low weight whilst maintaining, excellent torsional rigidity. The suspension system is
attached to the shell via two sturdy subframes, insulated from the body to reduce noise, vibration and harshness. The front suspension
is by MacPherson strut and coils with the independent rear suspension using parallel links.
X-TRAIL-UK
Light and stiff – it features an aluminium transverse link – the rear suspension is designed to move the rear wheel trajectory backwards
on compression, rather than forward, thus minimising tyre impact when an obstacle is hit and providing a compliant ride under all
conditions.
Its long travel benefits off road ability but doesn’t compromise on-road comfort: X-TRAIL has been benchmarked against premium
passenger cars.
With a commanding driving position, excellent manoeuvrability, fine handling and comfort and a tight turning circle – 10.6m – X-TRAIL is
as easy to drive on-road as it is able off-road. Manoeuvrability is especially important when towing and an X-TRAIL 2.0 will lug 1.5
tonnes of braked trailer, the 2.2dCi and manual 2.5 an even heavier 2 tonnes.
The vital off-road statistics are an approach angle of 29 degrees, departure 26 degrees (2.2 dCi 25 degrees) and a ramp angle of 21
degrees (2.2 dCi 23 degrees). Minimum ground clearance is 200mm, with a maximum 48 degree tilt angle.
SAFETY
ACTIVE AND PASSIVE SAFETY
As the system is electronic, ALL MODE 4x4 is fully integrated with X-TRAIL’s array of electronic traction aids, collected together under
the ESP+ banner. Standard on Aventura models, ESP+ offers more than traditional stability systems and is ideally suited to a dual role
vehicle such as X-TRAIL.
The ABS sensors, steering angle sensor, G-sensor, yaw rate sensor, ALL MODE 4x4 controller and drive-by-wire throttle all
communicate with each other to detect a loss, or potential loss of traction on any wheel. ESP+ works by determining the intentions of the
driver through the steering wheel position sensor on the steering column and through the wheel speed sensors at the wheels. It then
calculates how the car should ideally be behaving, and compares this with what it’s actually doing monitored through the yaw rate
sensor (measures turning velocity about the vertical axis of the vehicle), wheel speed sensors and the lateral acceleration sensor, and
then calculates what needs to be done to marry the two. Stability is restored by varying any, or as many as is necessary of the following:
brake pressure to individual wheels (using the ABS and EBD), the mode of four-wheel drive and engine output.
An Active Brake Limited Slip Differential, also controlled by the ABS sensors, applies the brakes to any wheel that has lost traction and,
in so doing, transfers drive to the opposite wheel on the same axle.
As a result of this integrated approach, ESP+ can either apply the brake or redirect torque to any individual wheel independently, thus
controlling understeer and oversteer on the road and ensuring maximum traction is maintained off-road or when the going gets slippery.
X-TRAIL-UK
Fig.7: Intervention of ESP+ during understeer.
(1) With ESP+ (2) Without ESP+
(3) Braking force (4) Balancing yaw movement
Fig.8: Intervention of ESP+ during oversteer.
(1) Without ESP+ (2) With ESP+
(3) Braking force (4) Balancing yaw movement
In simple terms, at the onset of understeer (Fig.7) the rear wheel on the inside of the bend is braked which turns the vehicle back in the
direction of the bend; since the front wheels have insufficient grip, ESP mostly uses the rear brakes since more grip is available here.
During oversteer (Fig.8), the rear end needs to be brought into line and this is achieved by braking the front wheel on the outside of the
bend. Again, ESP mostly uses the front brakes as more grip is available here.
X-TRAIL offers particularly short stopping distances thanks to ventilated disc brakes front and rear and are controlled by the latest
generation four-channel, five-sensor ABS system which incorporates Nissan Brake Assist for maximum emergency stopping power and
Electronic Brakeforce Distribution for even braking under all conditions.
The combination of ALL MODE 4x4 and ESP+ means X-TRAIL has one of the most advanced active safety systems available on any
passenger car. It is backed up by a computer-analysed structure giving excellent passive safety protection with highly effective crumple
zones front and rear. Twin front SRS airbags are standard on all grades along with head and thorax side bags. Front seats are equipped
with active headrests, three point belts with pretensioners and load limiters, while ISOFIX child seat fastenings and three point
harnesses in the rear are also standard.
They are links to PDF files with lots of illustrations, so if interested perhaps joining the xtrail club may be worth while.
Apologies if not all the above makes sense, lacking the drawings etc.
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