Transparent All-wheel-drive Ford Transit revealed at Hanover Commercial Vehicle Show
By Mike Hanlon
September 22, 2006
September 23, 2006 - A new all-wheel-drive (AWD) Ford Transit has been revealed this week at the Hanover Commercial Vehicle Show in Germany. The AWD system automatically provides stepless torque flow to the front wheels when required on slippery surfaces. This new derivative is specifically targeted at customers who frequently face low friction surfaces, adding more flexibility and reliability to their transportation needs and will be rushed into production for sale in the first quarter of 2007. The 'intelligent' system increases traction without affecting road performance or ground clearance and was developed for the needs of utility companies, hotels, agricultural and forestry companies and police forces.
The Transit's AWD system is available with the 2.4-litre 140 PS Duratorq TDCi diesel engine equipped with a six-speed manual transmission.
Under normal driving conditions, the Ford Transit AWD uses rear wheel drive only. However, should road surfaces become slippery with rain, snow, ice or split friction, a loss of traction might occur and the rear wheels are likely to slip. Ford's mechanical torque sensor will automatically engage the two clutches inside the front transmission, which at the same time limits the rear axle's overspeed and transfers torque towards both front wheels for additional traction. At the same time the de-stabilising effect of spinning rear wheels is being re-balanced from oversteering to a neutral driving behaviour by the physical torque flow to the front wheels.
A core element of the system is a hydraulically controlled torque sensor inside the front axle transmission. By sensing speed difference between front and rear axles, the integrated oil pump will continuously lock the multi plate clutch to one of the front wheels and gently convert torque to the front wheel.
The system is completely mechanical and free of wear – no service is required during its lifetime, apart from oil level control inside the clutch housings. Another core element of the system is an Eaton-type oil pump inside each of the clutch housings. It uses a small volume of oil to engage the clutches whenever required (transmission oil type 75W-90 BO).
As long as the front wheels rotate on dry and solid ground at the same speed as the rear wheel drive axle, both clutch pumps remain static and the entire hydraulic system is without function – the clutch locking system remains without pressure and both clutches are open. In case of minor speed differences typical for cornering situations, the pumps begin to rotate gently and pump a small amount of oil through the valves of the clutch system, without closing them for straight torque transmission.
As soon as the rear wheel drive shows significant slip, both clutches inside the system engage as the inner rotor and outer rotor begin to rotate at different speeds. At an appropriate speed difference the two hydraulic valve systems close the clutch system to each front wheel, delivering enough torque to either wheel to stabilize the drive situation and reduce overspeed effects at the rear axle.
Once all wheel speeds are adjusted to a close to identical level, the system disengages automatically by releasing oil pressure from the clutch system. In order to adjust the clutch system to different oil temperatures – which may vary from -40 °C to around 100 °C – a viscosity compensation valve is embedded into the system.
The AWD system is purely mechanical and operates automatically so that the driver is not distracted by having to engage the system. In slippery conditions the system simply increases drive to the front wheels, enhancing the vehicle's overall road performance.
Drive is taken off the transmission main shaft via a helical gear set towards the front differential. A system of mechanical multiplate clutches combined with an hydraulic freewheel mechanism feeds power forward when required.
The smooth and intelligently controlled torque flow to the front wheels via the freewheeling hydraulic unit ensures that the Transit's well proven driving dynamics are maintained even under slippery conditions. Standard ground clearance is also retained as a bulky differential housing is not needed with this compact and lightweight AWD system.
Compared with the standard rear wheel drive Transit, the additional front axle weight is just 50 kg – the rear axle weight does not change.
The Ford Transit AWD will be offered with rear wheel drive, single rear wheel vehicles across a broad range of cab-styles including single and double chassis cab and minibuses, plus the Transit panel van range. Low, medium or high roof derivatives will be available and short, medium or long wheelbase.
Key customers for the new model are those frequently encountering low friction surfaces and bad weather conditions. Transit AWD has improved off road capability but does not include raised ground clearance, therefore retaining standard load heights.
The new Transit AWD is perfectly suited for authorities like police, forest wardens, rescue services and fire brigades, providing the reassurance and confidence to handle situations which are beyond the capabilities of a standard vehicle. Transit ambulances fitted with the AWD system, for example, will be more able to ensure ongoing mobility in adverse conditions and deliver patients safely where previously they may have been delayed.
Utility companies will also benefit from the capabilities of the Transit AWD, as they will be surefooted performers for field and track work (for example crossing a muddy field track to fix a pylon). Ultimately this saves time and means that utility resources can be more effectively deployed.
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