At the Technology and Maintenance Council of the American Trucking Associations, what Diesel News’ US Correspondent, Steve Sturgess, found the most interesting was an Eaton roll out of upcoming fuel economy technologies that included NO products or services. It was fascinating for that.
A lesser known side of Eaton’s business is the manufacture of valves and valve trains for the passenger car side. As such, it has a wealth of collective experience in making poppet valves go up and down in gasoline and diesel engines. It is putting a lot of that knowledge on the line to help engineers and designers of next generation heavy-duty engines that will have to up their game to meet United States greenhouse gas (GHG) emissions regulations that go into their second phase for heavy-duty engines in 2021 but get really tough in 2024. Similar regulations will phase in with Europe’s Euro VII in the same timeframe, so the technology will have wide application.
The technology employed varies the valve timing through the four-stroke cycle. Dr Mihai Dorobantu, Eaton’s director of technology planning, said Eaton could tackle NOx in Selective Catalytic Reduction (SCR) after treatment or in-engine. Or both. In-engine there are trade-offs. Varying timing to mimic the Miller cycle reduces CO2. As well, the reduced pumping losses of this approach also reduce CO2, but all this increases cost and the overall fragility of the engine.
After treatment reduces NOx and works well at medium to high loads, said Dr Dorobantu, reducing 98-99 percent of the engine-out NOx. But it doesn’t work well at low load or idle. One solution is to increase the amount of catalysts to lower NOx but that’s a very expensive decision, in terms of cost, weight and space. The answer is to manage exhaust temperature at low load.
Eaton’s Variable Valve Activation (VVA) adds or subtracts motion in the valve train, modifying cam profile on the fly to command different valve behaviour. Dorobanto said this allows for keeping the basic cam profile, and adding mechanical modifiers.
The Eaton solution is to apply late intake valve closing to keep the inlet valve open past cam-closing. This gets more air into the cylinder to mimic the Miller cycle. On the exhaust side, opening the exhaust valve earlier than the cam profile means exhaust gases remain hot and this hotter exhaust improves the low-load and idle after treatment efficiency. The same capsule can open the exhaust valve at the top of compression to work as the retarder. The cam-profile modifiers can be in the valve train or rocker arms.
These modifying actuators can also eliminate manual setting of valve lash, which is done on diesels at 20,000 to 30,000 miles (30,000 to 50,000km) as wear on the valve seat and other valve train components allows for a drift out of correct adjustment and correct timing. Dorobanto says Eaton is working on hydraulic valve lifters as used in gasoline engines to allow lash to be constant over engine life and across all cylinders for optimised operation.
The bounty of VVA does not stop there. There is also an opportunity to introduce cylinder deactivation which means less engine displacement at low load. It doesn’t work as a fuel-save on diesels, though. But it does keep the exhaust stream hot by preventing the cool exhaust gas at no- or part-load blowing past the catalysts and reducing the efficiency of the after treatment performance.
Further, VVA can double the braking horsepower by closing the exhaust valve during the exhaust stroke. The trend to lower truck aerodynamic losses, lower rolling resistance tires and downsped engines is dictating a need for more braking. Getting two brake strokes per cycle instead of just one is a good way to achieve this, he said.