One of Volkswagen’s star cars at the recent Tokyo Motor Show was the 2012 Passat Alltrack. More than an all-wheel-drive Passat Estate, this, it says, has real off-road ability. Open to order in April, it arrives in July. At its heart is the Haldex 4x4 system – now much more sophisticated than a part-time 4x4 device.
The motor vehicle’s classic drivetrain evolved before the First World War. A front-mounted engine “face forward” (radiator ahead) and drive out of the back to a gearbox which transmitted power by way of a propeller shaft to the rear axle.
The motor vehicle’s classic drivetrain evolved before the First World War. A front-mounted engine “face forward” (radiator ahead) and drive out of the back to a gearbox which transmitted power by way of a propeller shaft to the rear axle.
The first successful four-wheel drive light utility vehicle was the US Army’s World War II Willys Jeep. The conventional 4x4 system uses a transfer box through which drive is diverted and distributed to all four wheels. It remains the set-up for serious on/off road dual purpose vehicles including SUVs and luxury off-roaders.
In 1982 Audi invented the Quattro 4x4 system. A hollow shaft running through the transmission did away with the transfer case and auxiliary axle for drive to the front wheels – to the benefit of cost, weight and efficiency. A bevel gear distributed power equally front and rear (later variably) but no low ratio gear set.
Electronics paved the way for the Haldex system. Front wheel drive with the engine placed transversely across the axle had become the mainstream motor car layout. Space was gained elsewhere but, under the bonnet, it was tight. The Haldex solution was to run a prop shaft from the engine but locate the multi-plate clutch for the auxiliary drive at the end of it integrated with the rear axle.
An electric pump supplies oil to this unit and a rise in the oil pressure forces the clutch plates together. The more this happens the more drive is directed to the rear wheels – continuously variable but can be 100% RWD if needs be. It is part-time (“on-demand”) 4WD – there might be a trickle of torque to the rear axle (say 10% sometimes) but until the process begins the car’s “default mode” is FWD.Best of both worlds is the idea – economy and lower emissions of 4x2 in normal conditions but 4x4 there when you need it. The current iteration is Haldex IV but a Haldex V unit, lighter and yet more pro-active has been exhibited. It already senses signs of slip or abnormality (steering, yaw angle, etc.) fairly early on and brings in the rear axle to try to counter a slide or loss of traction pretty promptly.
Additional rear drive is there for fast acceleration or lane changing and cornering even in dry conditions. It’s useful for powerful front drive cars not just for traction (when the front axle would struggle to cope with all the torque) but also steering and handling generally. No low ratio of course but it’s quite an asset off-road.
The Haldex unit is used by a raft of major manufacturers and has become the ‘generic’ term for this kind of 4x4. Haldex AB of Sweden sold its Four Wheel Drive Transmission division to USA’s Borg Warner at the end of last year. A major player in this area it now covers almost every type of 4x4 configuration.
Most compact SUVs are, basically, ‘jacked-up’ front-drive hatches. The Haldex device allows some 4x4 credibility at (relatively) little cost. Electronic input can enhance off-road capability and Land Rover does this for its Freelander and Range Rover Evoque line-up. So does VW/Audi with the Tiguan/Q3.
With saloons and estates, Volvo, Vauxhall and Skoda recently expanded the range of Haldex 4x4 variants beyond top-performning V60 T6, Insignia VXR and Superb V6 to a broader range of Diesel models. Volkswagen UK offered it on the V6 Passat VI – but not with the current Passat VII from 2010.
Elsewhere 4x4 versions of the Passat 2.0 TDI 140 & 170 are available. VW calls its Haldex cars “4MOTION” and a Passat 4MOTION here has been mulled over for some time. Now, inspired no doubt by Audi’s Allroad quattro 4x4 and Skoda’s Scout variants, it’s decided to go for a more bespoke Estate-SUV crossover.
Length and width stay the same but the Alltrack is raised a useful 30mm. This should reduce the risk of grounding and new front and rear ‘bumpers’ aid approach and departure angles. More to the point is the “Off-Road Driving Programme” which (up to 18mph) adapts the ABS braking, electrionic differential, torque and hill descent controls to the terrain.
If Skoda’s application of this (Yeti/Octavia) is any indication, it should be good. Volkswagen UK have (thankfully) spared us any fake 4x2 FWD variants and the two models offered are both Diesel engined: 2.0 TDI 140 or 170. The former mated to a 6 speed manual gearbox, the latter hitched to VW’s DSG Dual-Clutch Automatic (also 6 speed). Prices will be announced closer to the on-sale date but the cheaper 140 with manual gearbox stands out as the clear car of choice.
By Huw Thomas
First published in Welsh Farmer, the newspaper for the National Farmers union of Wales
In 1982 Audi invented the Quattro 4x4 system. A hollow shaft running through the transmission did away with the transfer case and auxiliary axle for drive to the front wheels – to the benefit of cost, weight and efficiency. A bevel gear distributed power equally front and rear (later variably) but no low ratio gear set.
Electronics paved the way for the Haldex system. Front wheel drive with the engine placed transversely across the axle had become the mainstream motor car layout. Space was gained elsewhere but, under the bonnet, it was tight. The Haldex solution was to run a prop shaft from the engine but locate the multi-plate clutch for the auxiliary drive at the end of it integrated with the rear axle.
An electric pump supplies oil to this unit and a rise in the oil pressure forces the clutch plates together. The more this happens the more drive is directed to the rear wheels – continuously variable but can be 100% RWD if needs be. It is part-time (“on-demand”) 4WD – there might be a trickle of torque to the rear axle (say 10% sometimes) but until the process begins the car’s “default mode” is FWD.Best of both worlds is the idea – economy and lower emissions of 4x2 in normal conditions but 4x4 there when you need it. The current iteration is Haldex IV but a Haldex V unit, lighter and yet more pro-active has been exhibited. It already senses signs of slip or abnormality (steering, yaw angle, etc.) fairly early on and brings in the rear axle to try to counter a slide or loss of traction pretty promptly.
Additional rear drive is there for fast acceleration or lane changing and cornering even in dry conditions. It’s useful for powerful front drive cars not just for traction (when the front axle would struggle to cope with all the torque) but also steering and handling generally. No low ratio of course but it’s quite an asset off-road.
The Haldex unit is used by a raft of major manufacturers and has become the ‘generic’ term for this kind of 4x4. Haldex AB of Sweden sold its Four Wheel Drive Transmission division to USA’s Borg Warner at the end of last year. A major player in this area it now covers almost every type of 4x4 configuration.
Most compact SUVs are, basically, ‘jacked-up’ front-drive hatches. The Haldex device allows some 4x4 credibility at (relatively) little cost. Electronic input can enhance off-road capability and Land Rover does this for its Freelander and Range Rover Evoque line-up. So does VW/Audi with the Tiguan/Q3.
With saloons and estates, Volvo, Vauxhall and Skoda recently expanded the range of Haldex 4x4 variants beyond top-performning V60 T6, Insignia VXR and Superb V6 to a broader range of Diesel models. Volkswagen UK offered it on the V6 Passat VI – but not with the current Passat VII from 2010.
Elsewhere 4x4 versions of the Passat 2.0 TDI 140 & 170 are available. VW calls its Haldex cars “4MOTION” and a Passat 4MOTION here has been mulled over for some time. Now, inspired no doubt by Audi’s Allroad quattro 4x4 and Skoda’s Scout variants, it’s decided to go for a more bespoke Estate-SUV crossover.
Length and width stay the same but the Alltrack is raised a useful 30mm. This should reduce the risk of grounding and new front and rear ‘bumpers’ aid approach and departure angles. More to the point is the “Off-Road Driving Programme” which (up to 18mph) adapts the ABS braking, electrionic differential, torque and hill descent controls to the terrain.
If Skoda’s application of this (Yeti/Octavia) is any indication, it should be good. Volkswagen UK have (thankfully) spared us any fake 4x2 FWD variants and the two models offered are both Diesel engined: 2.0 TDI 140 or 170. The former mated to a 6 speed manual gearbox, the latter hitched to VW’s DSG Dual-Clutch Automatic (also 6 speed). Prices will be announced closer to the on-sale date but the cheaper 140 with manual gearbox stands out as the clear car of choice.
By Huw Thomas
First published in Welsh Farmer, the newspaper for the National Farmers union of Wales
RSS Feed