An automatically-engaged part-time front-wheel-drive system is now being offered in Europe on DAF CF and XF 4x2 tractor units.
DAF Trucks will also add the switchable front-drive to other chassis configurations in Europe later this year.
It says that the hydraulic front-wheel-drive system is designed for "trucks that clock up most of their mileage on the road, but are sometimes required to drive offroad or in slippery conditions."
The new PXP (Paul Extra Power) drive has been developed in league with German special vehicle conversion operation Paul Nutzfahrzeuge. It's available in Europe on DAF tractor units powered by either the PACCAR MX-11 or MX-13 engines.
DAF points out that permanent all-wheel-drive for only occasional use "means a considerable cost in terms of acquisition, maintenance and fuel consumption.
"However, it is sometimes very important to have extra traction to tackle ditches, sandy roads, unpaved tip-sites and steep inclines."
A switch on the dashboard puts the switchable drive on standby in potentially tricky situations. If the vehicle then experiences slip from the powered wheels, PXP is automatically activated. The greater the amount of rear-wheel slip, the more traction the front wheels provide.
The system is available in the first four forward gears and the first and second reverse gears. At speeds above 20km/h (and/or in 5th gear or higher) PXP switches back to standby mode. The system activates itself again at lower speeds and whenever use is required.
To make the switchable FWD possible, each front axle wheel hub is equipped with a hydraulic motor, producing torque of 6435Nm or more at a maximum system pressure of 360 bar. This ensures optimal performance and optimal longevity and reliability. 
A unique feature is that the motors are driven by a hydraulic pump fitted directly onto the engine PTO, saving both weight and space. The hydraulic pump can also drive components like cranes, hook arms, stabilisers or skip loader systems for maximum efficiency. This means that only one hydraulic tank is required, which also results in less weight and more space.
The PXP system demonstrates DAF's ability to provide optimal solutions for every transport requirement, it says.