Amid the evolving regulatory landscape, the humble power take-off has found itself repurposed as a way of reducing truck emissions. Richard Simpson investigates

Legislative and environmental pressures are increasing focus on truck power take-off (PTO) systems. The first of these is the ban on using ‘red’ (duty rebated) diesel to drive ancillary equipment such as fridges and pumps on trucks. Having to burn full-price ‘white’ (DERV) in an auxiliary donkey engine pretty much destroys the economic case for having the engine in the first place.

The second pressure comes from the introduction of battery-electric trucks. The rise of EVs opens the opportunity to use electrical power taken directly from the vehicle’s traction batteries to drive equipment as an alternative to mechanical power. This setup is particularly welcome, because a chassis filled with batteries imposes considerable constraints on the siting of mechanically driven equipment, as Volvo Truck’s product manager John Comer points out. “On an electric truck, the chassis space ‘belongs’ to the truck manufacturer,” he explains. “You can’t move batteries ‘out of the way’ to accommodate other equipment the way you can re-site a fuel tank, for example.”

Nevertheless, Volvo’s heavy electric trucks, which retain the standard I-Shift automated transmission, also feature the I-Shift’s two mechanical PTO points, which can deliver up to 150KW of power. But a more compact solution is a 40kW electrical power take-off, which draws direct from the truck’s traction batteries. This unit is available across the entire Volvo Trucks battery line-up from the FL to the FH. Space constraints mean this component is mounted by the rear axle on FL and FE models, and behind the cab on the bigger FM and FH trucks. It is possible, in theory, to relocate the unit, but its cooling needs must be accommodated, Comer says. “But for applications such as tippers and mixers, the location behind the cab is pretty much ideal,” he confirms.

“A gearbox-driven PTO is 90% efficient, compared to 98% from an electric PTO,” says Comer. PTOs of any kind will inevitably compromise electric vehicle range, but he points out they are just one of many systems making calls on the traction batteries. “Every system in an electric truck is ultimately powered by PTO from traction batteries, from the power-steering to the dash cam.”

Volvo customers choosing diesel have a further PTO option. All Volvo engines, from five to 16 litres, have the capability to drive another PTO direct from the engine’s rear-mounted timing-gear. This can be specified with an output of 600 or 1,000Nm, as required.


One application for the timing-gear driven PTO, which can also be specified from new on any make of truck, but is also retrofittable to existing Volvo, Renault and Scania trucks, is a Hultsteins Ecogen unit. This item generates electricity to power a trailer fridge unit, instead of the usual donkey engine.

Graham Usher, UK managing director of Hultsteins, says that the system saves the fuel and emissions from the fridge engine by using hydraulic pressure produced by the PTO to power an alternator. It produces 26kW of 400V current. “It’s a beneficial parasite, producing a lot of useful extra power at a very small cost in terms of additional fuel consumption,” he explains. “And not only is the additional fuel burned by the truck’s engine very small compared to what would be burned by a separate engine, the exhaust gas is passed through the truck’s very sophisticated after-treatment system, which removes all but a tiny fraction of harmful emissions. Ecogen can power any diesel-electric fridge-trailer as it plugs in via the trailer’s ‘shore-power’ socket and the diesel engine remains fitted to the trailer, so it does not compromise flexibility on a mixed fleet or preclude control of the trailer temperature.”

Usher explains that not only does Ecogen save fuel and cut pollution, it also saves wear and tear on the trailer because of the reduced run times of the motor. “There’s no need for the diesel engine to run when the trailer is attached to an Ecogen-equipped tractor,” he says. “This can transform the reliability of an expensive trailer that is eight or nine years old with high diesel engine hours – and might otherwise be becoming uneconomic to operate.

“The front-end cost of fridge trailers is rising all the time, and high interest rates are forcing rental, leasing and HP prices up even more,” continues Usher. “It only costs £800 to £1,500 to specify the engine PTO on a new truck – and it effectively future-proofs it against any restrictions that may be applied to the use of donkey engines in the coming years. Ecogen can cut the trailer’s operating cost by 60–80%.”

The environmental benefit is considerable, maintains the Hultsteins man. “Yes, you can get an all-electric fridge trailer – and about 100 were sold in the UK last year – and the additional costs are understood to exceed £40,000. But there are approximately 35,000 fridge trailers operating in the UK, and 3,000 to 3,500 are replaced each year,” he reveals. “It could take 25-30 years to get all the diesel-electric fridge trailers out of the UK fleet, so there are great benefits from installing Ecogen on tractors in fridge fleets now to help reduce carbon, cost and scope 3 emissions.

“We’ve installed quite a few on gas-powered trucks, which gives an ever greater reduction in CO2 than using it on a diesel truck,” he adds.


Usher is investigating further uses beyond refrigeration for the Ecogen unit. “One application is Tarmac ‘hot-boxes’. Current designs use gas burners with external naked flames,” he explains. “When you think about it, this is not very environmentally friendly and raises potential safety issues. If underbody gas fires were invented today, would they be permitted? Instead, we could use Ecogen to power an electric heating element that would keep the Tarmac hot and ready for use without the pollution and danger of naked flames.”

Another deployment of the Ecogen unit is for the transportation of electric cars with flat batteries. “We could literally charge recovered vehicles on the go,” he asserts.

Operators specifying trucks for specialist tasks such as road-sweeping – and gully emptying and jetting – should consider selecting an Allison fully automatic transmission in place of the manufacturer’s standard offering, says Nathan Wilson, Allison’s sales manager for UK and Ireland.

“Most truck transmissions have rear- or side-mounted PTO points, but the Allison has an aperture for either side and a third PTO aperture at ‘one o’clock’ on the top of the bell-housing,” says Wilson. “All three PTO options connect to the transmission’s turbine shaft, which rotates at engine speed irrespective of the truck’s road speed.

“Where you have complex bodywork with multiple powered functions, this can be a real advantage both in terms of designing the layout and operating the vehicle,” he adds.

The manufacturer of roadsweepers that normally use a secondary engine can replace the donkey engines that power the equipment and choose an Allison transmission, says Wilson. The advantages? Reduced capital and operating costs and less environmental impact. “We are also seeing companies that retrofit existing ICE vehicles with electric power including Allison transmissions in their conversions as not only do they enhance road performance, but they also offer the opportunity to install low-cost mechanical PTOs,” he confirms.

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