ELEGANT SIMPLICITY

The S70 and V70 AWD's behave like a conventional front-drive vehicles on dry roads. But when road conditions deteriorate or become slippery, Volvo 's AWD system automatically switches into four-wheel drive without the driver having to shift levers or push buttons. The Volvo engineering and design philosophy has always dictated that any new feature or technology is only of value if it does not complicate the driving experience. So engineers have designed a simple, user-friendly AWD system that makes driving more sure-footed and safer under most adverse road or weather conditions. It automatically makes traction transfer decisions so quickly that a driver never needs to think about selecting either front wheel drive or all-wheel-drive models. Volvo 's AWD combine the single most desirable feature of an SUV platform during take-off traction, with superior ride, handling, comfort, safety engineering, performance and fuel economy.

HOW Volvo 'S AWD WORKS

Engine power can be diverted to rear wheels through a transfer differential located adjacent to the transmission. Power can be split to either the front or rear wheels in varying amounts as road conditions dictate and without driver intervention.

Viscous Coupling
The viscous coupling, which is located ahead of the rear differential, appears as a long tube filled with silicone oil and contains a large number of discs. The viscous clutch is designed to use the silicon oil's viscosity to transfer power via the discs to the rear wheels when the front wheels start to spin. Every other disc is connected to the front wheel part of the shaft and the alternating discs are connected to the rear differential. When the discs revolve at a different rate the silicone oil in which the discs rotate becomes more viscous and thus increases the pressure. As this pressure increases, torque is transferred to the rear wheels. If the viscous coupling is subjected to intensive slipping, the silicone oil and discs become very hot. At this point, the coupling locks-up to prevent any slippage.

Freewheel Unit
Volvo has also engineered into the drive line system a freewheel component. This unit disengages the rear drive during braking and/or coasting help ensure optimum braking performance. With this feature, the ABS braking system does not need modification. Another refinement, when it comes to this freewheel, is that it also has a lock-up function. This means that Volvo 's AWD system is always in four-wheel driven when it reverses.

Rear Drive Unit
The rear drive unit is similar to the one used for the S90N90 series, but uses coil springs rather than a mono-leaf composite spring. The choice of this unit, rather than engineering a completely new one, is a clever bit of engineering. The drive unit was fitted with minor modifications, required virtually no re-engineering, and created only minor changes in manufacturing, which means that all the good characteristics S90N90 are transplanted into this vehicle. And this also turns out to be a very cost effective solution to a potentially tricky problem. The axle housing assembly consists of two sections of cast aluminum bolted together. This assembly houses the drive unit and Multi-link rear suspension, shock absorbers, and anti-roll bar. This independent rear suspension unit mounts into the S70 and V70 chassis without major modifications or loss of interior cargo space. The rear drive unit delivers a high degree of rear wheel traction while providing excellent road noise isolation, passenger comfort, and driving pleasure.

FRONT AND REAR TRACTION CONTROL

Volvo engineers have also incorporated a locking differential for the rear axle drive unit, and Traction Control System (TRACS) for the front drive unit to help ensure that the correct amount of power is distributed as needed at low speeds. The locking rear differential senses minute differences in rear wheels rotational speed and at speeds less than 25 mph automatically locks both rear wheels to transfer engine power to help maintain traction. TRACS, based on an ABS feed back system, is designed to work at speeds of less than 25 mph and is especially useful in helping to prevent front wheel spin at vehicle launch. Both these systems, locking rear differential and front wheel TRACS, working together help to prevent wheel spin, thereby helping to ensure maximum take-off traction control on most slippery road surfaces.

GROUND CLEARANCE AND RIDE HEIGHT

Ground clearance difference between Volvo 's V70 and the V70 XC is about I inch for a total of 6.5 inches clearance at the vehicle's lowest point. Ground clearance between the V70 AWD and V70 R AWD and the S70 GLT AWD as compared to non-AWD models is virtually identical. While the mission of the XC is to help provide optimum traction on loose road surfaces during highway and dirt/gravel travel, the 6.5 inches of clearance is quite respectable when comparing it to most SUVs and is surprisingly good for a passenger wagon. While consideration for ground clearance is important for off-road vehicles, many in fact have ground clearances only slightly higher than the XC.

Vehicle height between models varies. All non-AWD V70 share the same ride height of 56.2 inches. The S70 GLT AWD, V70 AWD and V70 R AWD also share the same 57.2 inches height. The V70 XC AWD is slightly 2 inches higher than its non-AWD cousins with a total of 58.3 inches of vehicle height.

AN INTELLIGENT ALTERNATIVE

The overall result of this design is an intelligent AWD system that provides a conventional front-drive with all its responsiveness and advantages. But when driving conditions suddenly change, the AWD platform is transformed into a four-wheel drive vehicle with the traction advantage of a SUV. All without the inherited discomforts normally associated with traditional truck-like 4X4s.