Bentley develops W12 cylinder deactivation

  • 13-Mar-2015 02:06 EDT
Bentley Flying Spur W12.jpg

For Bentley's new W12 cylinder deactivation, the engine control unit deactivates one bank of six cylinders while leaving the valves to operate as normal.

Luxury car manufacturers around the world are devising multiple solutions for improving fuel economy and emissions while maintaining the high-performance multi-cylinder engines their customers have traditionally expected. One of the those solutions is cylinder deactivation.

Bentley already has two methods of cylinder deactivation on its 6.75-L and 4.0-L V8 engines but, as Rolf Frech, Member of the Board for Engineering, explained at the 2015 Geneva Motor Show, the complexity of the 6.0-L W12’s layout (essentially two narrow-angle V6s on a common crankshaft) and cylinder firing demanded a third solution.

“It was clear that we couldn’t use either of the solutions we currently employ as that would have demanded a new cylinder head," he said. "So we asked how can we do that with an intelligent arrangement?”

The challenge is that when cylinders are switched off they cool down, as does the catalytic converter, resulting in spikes of exhaust emissions. “The complication was to develop intelligent management just to switch the cylinders off and switch them back on with the right timing and change to the other six,” he said.

In essence, the engine control unit simply deactivates one bank of six cylinders while leaving the valves to operate as normal.

“The big advantage of this is not only about reducing CO2 on the normal test, but in daily use,” Frech explained. The significant gains are under part-throttle cruising conditions.

“If you make it into a real six-cylinder, you don’t have any problems with balance," he noted. "There was something of an issue with exhaust boom, but we have countered that with some modifications to the exhaust.”

By doing it in this manner, the inlet and exhaust sensors determine when to switch between each bank, ensuring the cylinders remain hot. It also fulfills U.S. OBD requirements.

The engine also receives a power increase, from 567 to 582 hp (423 to 434 kW), with rated torque also rising from 516 to 531 lb·ft (700 to 720 N·m). The greater output is accompanied by claimed improvements to fuel economy of up to 5% (combined fuel economy is 16.6 U.S. mpg) and lower CO2 emissions of 329 g/km.

Looking to future applications, Frech revealed that there would be “other opportunities” with W12-powered vehicles, including possible individual cylinder deactivation and electric-motor assistance for the forthcoming Bentayga SUV due later this year.

HTML for Linking to Page
Page URL
Rate It
4.00 Avg. Rating

Read More Articles On

Start of production for the plug-in hybrid Chrysler Pacifica minivan begins in late 2016, marking a milestone as Fiat Chrysler Automobiles (FCA)'s first mass-produced PHEV.
Volvo is using a blast of compressed air as a relatively simple solution to boost torque delivery of its new D5 diesel powering the V90 wagon.
Validation testing of the new 2-step VCR by several OEMs has been successful to date and is expanding, as the industry examines more sophisticated solutions to meet CO2 regulations.
What does it cost to replace an EV battery at the retail level? For a BMW i3 a new battery will set owners back about $16,000, according to Dr. Christian Cozzarini, BMW Department Head, Environmental Engineering, who spoke at the 2016 CAR Management Briefing Seminars.

Related Items

Technical Paper / Journal Article
Training / Education
Training / Education
Training / Education
Training / Education
Technical Paper / Journal Article