Chery explains how Stockman’s diesel PHEV actually works

The chief engineer of the Chery Stockman ute has explained its unusual diesel plug-in hybrid system, revealing why the Chinese brand rejected an electric-only rear axle in favour of traditional mechanical four-wheel drive. Plus, Chery says it has solved the famous difficulties of developing diesel plug-in hybrid engines by using a smaller electric motor to rapidly bring the combustion engine to an ideal temperature to keep the diesel particulate filter (DPF) clear. Technical boss Mark Qi said that while the system would prioritise EV mode for low-speed driving, when the diesel engine was required, it would run at higher revs and for longer than petrol PHEV engines to tackle soot build-up and exhaust temperature challenges. But the fuel won’t go to waste, Qi said, because the excess energy would be directed to charging the Stockman’s 34-kilowatt-hour battery pack during DPF regeneration.

Qi told carsales that repeated cold and brief diesel engine operation can leave exhaust gases too cool for effective DPF regeneration, encouraging soot accumulation.

Instead of simply bolting an electric motor onto an existing diesel engine, Chery says it has engineered a new solution from the ground up in association with engine component supplier EVL.

Electric propulsion in the Stockman is intended to mainly cover low-speed, cold-running duties that typically cause excessive particulate production in normal diesel engines.

The smaller of the Stockman’s two electric motors, a P1 integrated starter generator (ISG), is used to rapidly start and bring the diesel engine to a more useful operating speed.

By contrast to rival diesel utes, which Qi noted idle at 700–800rpm, the Stockman will instead idle above 1000rpm when required.

The aim is to almost instantly establish conditions in which the Stockman’s diesel can function properly, including generating sufficient heat for DPF burn-off.

Once the Stockman’s diesel engine has started, it won’t turn off instantly when driver demands drop, as typically experienced with petrol plug-in hybrid vehicles.

Instead, hybrid management software will keep the diesel running for longer, doing double duty for DPF regeneration and driving a generator to recharge the 34kWh battery.

Qi said owners would find DPF regeneration largely imperceptible.

While he said the team had considered exhaust gas recirculation (EGR) issues, he did not suggest that EGR deposits had been entirely eliminated.

Meanwhile, the Stockman’s bigger electric motor is a P2.5 unit integrated within the four-speed transmission. It can propel the ute electrically or assist the diesel.

Specific power and torque for the electric drive motor are not yet known. Ford’s Ranger PHEV uses a 75kW P2.5 motor for the same purpose.

The Stockman differs substantially from the Shark 6’s electrically driven rear axle. Qi wanted the diesel to be able to drive both axles mechanically, which he said is particularly useful on steep ascents when weight shifts to the rear wheels.

BYD’s competing solution removes the propshaft and transfer case, reducing mechanical complexity but taking away the ability for the combustion engine to drive the rear wheels.

The Stockman’s diesel PHEV configuration promises to combine 96km of electric driving range with the promise of long-distance driving range and mechanical off-road hardware, but there’s no doubt it is a complex solution.

Whether the protections engineered into the system to prevent DPF and EGR issues are effective will no doubt be a hot-button topic once Stockman units make their way into customer hands next year.

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