The Audi Q7: Suspension

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January 31, 2006

Source: Audi AG

Dynamic and safe

The dynamic suspension of the Audi Q7 uses sports technologies such as double wishbone suspension all round. At the same time, long spring travel, a ground clearance of 205 millimetres and robust components take into account the demands of off-road driving. In respect of dynamism, the driving performance of the Audi Q7 bears any comparison; and in terms of driving safety, it also sets the benchmark – on the road and on rough terrain. In addition to the standard steel chassis, adaptive air suspension is available.

The Audi Q7 is a classic illustration of Audi’s claim to offer optimum technical solutions in every model. As a performance SUV it harmoniously combines excellent driving comfort with a level of dynamism that is quite new for this category of vehicle. Even the slightly tail-heavy axle load distribution of
40 : 60 per cent between front and rear is a clear sign of its agile nature.

Audi supplies the Q7 with a conventional steel-spring suspension and hydraulic twin-tube shock absorbers as standard. Ground clearance here is around
205 millimetres to ensure good off-road handling. Spring travel is correspondingly long and comfortable. The long wheelbase of 3,002 millimetres guarantees straight-line stability at high speeds.

Wishbones of aluminium

To enhance ride comfort and driving dynamics, the double wishbones at the front of the Audi Q7 are made of aluminium. The upper triangular wishbone is a cast part, the lower is forged. The large gap between both wishbones guarantees precise wheel control. The mounting for the spring strut and upper wishbone is also made of aluminium.

The lower wishbone and anti-roll bar, made of high-strength steel tubing, are attached to a subframe of high-strength steel, on which the steering is mounted. The mounts are hydraulically damped – this minimises rolling noise and improves comfort even more.

servotronic with variable assistance

All Audi Q7 models are equipped as standard with speed-dependent servotronic steering. The purely hydraulic rack-and-pinion steering helps the driver to manoeuvre in or out of a parking space, and its directness and precision ensure good road contact and clear feedback at high speeds.

The servotronic is generally tuned for direct sporty response: depending on steering wheel angle, its ratio varies from around 10.0:1 to 16.5:1. When steering out of the central position, the steering responds more indirectly – this guards against nervous vehicle reactions at high speeds and makes minor corrections to maintain straight-line stability. If the steering wheel is at a greater angle, the control action is more direct and agile with a view to an active driving feel.

At the rear axle, the upper wishbone and the spring strut cross bar are made of forged aluminium. The tie bar is made of weight-optimised tailored rolled blanks, which thanks to steel plates of varying thicknesses, combine low weight with high rigidity for sections under particular load and strain.

All control arms are attached to a subframe which also supports the final drive. The spring struts are cardan-mounted on a separate wishbone of cast aluminium, which is attached to the body. Their marked inwardly tilted position reduces overall height and creates more room in the vehicle interior to accommodate the third row of seats.

The rubber-bonded metal mounts at the rear axle have been specially optimised to perform their respective purpose. Where loads occur in a longitudinal direction, their torsional rigidity is low to enhance ride comfort. Lateral forces on the other hand are firmly absorbed in the interests of driving stability.

Large wheels but extremely light

The Audi Q7 is fitted with 18-inch aluminium wheels as standard, with 235/60 tyres – on the eight-cylinder version with 255/55 tyres. The rims underneath are 7.5 inches wide (for the V6 engines) and 8 inches (for the V8).

Each can bear a wheel load of 900 kilograms while weighing only 11.3 and 12.0 kg respectively.

Wheels in other sizes (18, 19 and 20-inch) can be ordered as options. An optical highlight is the new 20-inch 5 twin-spoke cast aluminium wheel of two-colour design – with spoke flanks in anthracite and polished design elements. If the Audi Q7 is ordered as a 5-seater with 18-inch wheels, a full-size spare wheel is available. The initial equipment version comes from the assembly line with summer tyres suitable for on and off-road driving. Special 18-inch off-road tyres are available as an option.

Driving on air

The latest-generation adaptive air suspension is available as an option on the Audi Q7. The combination of air suspension and an electronically controlled damping system produces the perfect synthesis of sporty handling and supreme ride comfort.

The air suspension essentially comprises a compressor, two accumulators each with a capacity of around 10 litres and four electronically controlled dampers, integrated into the suspension struts. To ensure sensitive response the externally-guided bellows are made of a particularly thin material.

For normal driving, a choice of three different characteristics can be selected via the Multi Media Interface (MMI) operating system, ranging from very sporty to comfortable, namely Dynamic, Automatic and Comfort. The system control unit varies the air-spring and damping characteristics at the compression and rebound stage according to the mode selected and vehicle speed. The driving modes and height levels can be read off the MMI screen. The ride height also appears in the central driver information display.

More sportiness in dynamic mode

The Automatic mode is designed to offer the best handling performance in every situation. Alternatively, drivers requiring more comfort can select the Comfort mode, which has a particularly soft damping action. In both cases the body is at normal ride height up to 120 km/h, offering 180 mm ground clearance. In the Dynamic mode the suspension is lowered by 15 mm from the start – the lower centre of gravity ensures a more dynamic driving experience.

Irrespective of the mode selected, the body is automatically lowered on motorways to a ground clearance of 165 mm if the Audi Q7 travels for longer than 30 seconds at a speed of at least 120 km/h. From a speed of 160 km/h – maintained constantly for over 20 seconds – the body is lowered by another
15 mm to further optimise stability and aerodynamic drag. If the vehicle slows down, the air suspension lifts the body in two stages to restore the normal ride height – the thresholds for this being 130 and 70 km/h.

Particularly on country roads, the dynamics also benefit from an important innovative feature of adaptive air suspension – the dynamic roll stabilisation function. The system, using information provided by four sensors at the wheels and three additional sensors on the body, actively responds to steering input and body roll. By deliberately increasing the damping forces, it counteracts the rolling motion of the vehicle. In fast cornering manoeuvres, for example, the body remains horizontally stable.

Off-road mode up to 100 km/h

Off-road, the Audi Q7 driver can activate two additional modes: the off-road mode is 25 millimetres above normal ride height and can be used up to a speed of 100 km/h. The lift mode is even higher – with 35 millimetres of extra ground clearance (absolute value 240 mm), even major obstacles can be negotiated at moderate speeds.

Finally, two functions round off the range of options: via a button in the luggage compartment the driver can lower the loading lip by 71 millimetres, making it much easier to load heavy objects into the vehicle. There is even a special suspension mode for driving with a trailer.

The air suspension of the Audi Q7 also functions as a high-tech self-levelling suspension – it keeps the body at the ideal height, regardless of the load situation. Passengers benefit from a very smooth ride at all times.

New ESP with off-road expertise

The Audi Q7 is equipped with latest-generation stabilisation control technologies. The ESP incorporates a number of components – the anti-lock brake system ABS with electronic brake-force distribution EBD and hydraulic brake assist, the traction control system ASR and the electronic differential lock EDL.

To allow for the far-reaching scope of the performance SUV, the ESP has new features such as an off-road mode that can be activated by a switch. In this mode the system tolerates a certain amount of slip when braking or accelerating, which can often be of help on loose surfaces. Fluid control thresholds apply at lower speeds, whereas more and more priority is attached to driving stability as the speed increases.

For downhill driving there is a special assist function. Below 20 km/h it keeps the speed constant on steep downhill stretches, allowing the driver to fully concentrate on steering the vehicle. In addition to this, the rollover stabilisation program intervenes in the event of critical driving situations that might cause the vehicle to overturn and takes the necessary corrective braking action.

Fording depth of over 53 centimetres

With all these technologies – quattro permanent four-wheel drive, high-torque engines, long spring travel and high ground clearance – the Audi Q7 offers superior off-road capability. Its maximum possible climbing capacity is 31 degrees.

The ramp angle measures 21 degrees for vehicles with steel-spring suspension, 24 degrees for the Audi Q7 with air suspension. There is a similar difference in the angle of slope (23/25 degrees). If driving through water the Audi performance SUV can plunge in up to a depth of 500 (air suspension: 535) millimetres.

An off-road package for fans of a more cross-country look will be available at a later date. This includes painted front guards, underride protection plates of brushed stainless steel at front and rear, flared wheel arches and rocker panels.

More safety with the car-trailer combination

There is now a further additional function for the ESP in conjunction with the optional towing bracket. The trailer stabilisation system represents an invaluable safety bonus for driving with a trailer. It detects hazardous trailer vibration and sway from the start and stabilises the outfit by means of automatic brake intervention. Depending on how risky the situation is, the ESP brakes the front wheels only or all four wheels of the Audi Q7. Following drivers are warned accordingly by the brake lights.

The ESP is not the only system on the Audi Q7 to feature state-of-the-art technology – the hydraulic brake system also gives a strong performance. Even under extreme load it always guarantees exceptional deceleration. The four discs are internally ventilated and generous in size – those at the front axle are
350 millimetres in diameter and 34 millimetres thick; at the rear axle 358 mm on the 4.2 FSI and 330 mm on the TDI. The front brake calipers are cast from black anodised aluminium and feature a six-piston design.

Air ducts in the vehicle floor help to improve brake cooling. The smooth-finished discs are dirt-resistant – important for off-road driving. Here deflector shields protect the brake lines from damage caused by gravel impact.

The optional tyre pressure monitoring system makes another important contribution to driving safety. It constantly monitors the temperature and pressure of all four tyres. In the event of pressure loss it sends warning messages, varying in priority according to pressure levels, to the MMI screen.

The driver can call up the current tyre pressures on the screen at any time. The system serves as an early warning system to guard against accidents – 85 per cent of all burst tyres start off as unidentified slow punctures.

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