Clearing The Air

Sensors, diagnostics and controls advance to help trap emissions.

August 1, 2016

Terry Costlow

Peering inside aftertreatment systems helps John Deere determine how sensors can help improve efficiency.

They’re not as certain as death and taxes, but tighter emissions regulations have become a constant presence in off-highway vehicle development programs. Design teams continue to focus on meeting mandates or fine-tuning engine and aftertreatment systems to improve efficiency even when regulators give them a respite.

Perkins continuously strives to understand engine usage so engines can be made more efficient.

The European Union’s Commission National Emission Ceilings and the California Air Resources Board’s Mobile Source Strategy are both tightening requirements, though new regulations won’t take effect for a few years. That’s giving design teams a chance to refine their designs.

“We’re in a regulatory lull, so companies are looking at making things cheaper or squeezing out better performance,” said Dave Rodgers, Engines Business Unit Director at Ricardo. “They’re not looking at components, most people are looking at the complete aftertreatment system, how it’s architected and constructed.”

Advanced emission controls systems that include the engine and aftertreatment systems are being revised to save space, cut cost and improve performance. Though mechanical elements are being updated, many of the changes come in sensors and electronic controls.

“Areas of most focus, and potential benefit, include combustion and aftertreatment, particularly in terms of characterizing the large set of kinetic reactions that govern pollutant production and subsequent reactions,” said Alan Chewter, Senior Manager, Powertrain Systems, at IAV Automotive Engineering. “Additionally, since it is necessary to coordinate control of several actuators simultaneously to achieve stability and optimal performance, multi-input multi-output (MIMO) controller structures are common.”

Sharper sensors

Monitoring gas flow is critical as Tenneco devises ways to share information and reduce emissions.

The digital side of electronic controls leverage the gains of microprocessors used in autos and consumer products, so advances in that segment of design are fairly predictable. But that’s not the case in sensors.

Finding high-performance sensors that can operate in harsh off-highway environments is not always simple. As requirements become more stringent, the need for sensor improvements will increase.

“Electronic controls will really come into play as we go to Tier 5,” Rodgers said. “In Europe, that may be complicated because there’s no set level for grams per liter, it’s for particulate size. Sensor technology is not really there for that.”

Engineers at Ricardo are testing engines and aftertreatment systems to see how size and performance can be improved.

Design teams have made solid advances in recent years, for example using NO_x sensors to tighten control of tailpipe NO_x emissions. But many system developers are asking sensor suppliers for a range of advances so they can push state of the art further. Improvements could lengthen the time between chemical refills and regeneration cycles.

“New sensor technologies are being developed in the industry for detecting soot loading and ash loading in the diesel particulate filter (DPF), and for detecting ammonia storage levels in the selective catalytic reduction (SCR) system,” said Jason Schneider, manager of product engineering at John Deere Power Systems (JDPS). “These sensors could lengthen the time between active DPF regenerations, lengthen the time between ash cleaning service intervals and provide a better management of tailpipe NO_x emission control.”

Copious communication

Electronic controllers are providing more advanced diagnostics that can be used to reduce emissions. (Cummins)

Regardless of the type of sensors being used, technologists note that sharing data from sensors and related controllers can improve performance. This focus on sharing comes into play from the start of vehicle design. When all electronic modules communicate freely, engineers can locate computing power where it’s most effective.

“The sharing of sensor information, modeled parameters and data allows for the distribution of controls through the system,” said Ben Patel, Vice President, Clean Air, Global Research & Development at Tenneco. “For example, in an SCR-coated DPF (SDPF) system, the engine may already be calculating the soot loading in the SDPF and measuring soot post-DPF. If that modeled and measured data is shared with the SCR model, it allows the model to be more accurate without the cost of developing a separate model for soot-loading.”

Taking an overarching look at vehicle performance early in the design cycle helps at every level. When all factors are considered from the concept phase through completion, developers can reduce engine size. That helps trim emissions while reducing weight and cost.

“The real benefits of electronics are around the deep integration of the engine into the vehicle,” said David Costura, New Technology Manager at Perkins. “By understanding what the vehicle is trying to accomplish and what its constraints are, the engine can be developed and customized to get every last bit of power, fuel economy and response within the emissions limits.”

John Deere is developing prognostics to help reduce downtime.

As planners have determined the size of the engine, they have to examine its interactions with the aftertreatment system. There are trade-offs between the two, where there’s something of a battle between what engines emit and aftertreatment systems cleanse.

“Improved controls can result in reduced components in the engine; you can let the aftertreatment system clean it up and do the work that the engine used to have to do,” Rodgers said. “But that’s harder on a larger engine.”

Close links and tight communications aren’t limited to engines and aftertreatment systems. Engines and hydraulic systems make good use of networks to share data so engines can deliver the necessary power while running the engine at the best rpm levels.

“The more specific and detailed information that can be shared between power-producing and -consuming functions on a vehicle system, the more opportunities there are for optimal control, and real time trade-off between competing objectives to be achieved,” IAV’s Chewter said.

The ability to share data can be used by companies to examine real-world usage. That should help as they develop next-generation equipment that can burn fuel more efficiently even as usage patterns change. Enhanced network communication may also be used to teach operators to utilize equipment more effectively, which can further trim emissions.

“As the controls architecture and hardware capability grows, we have more opportunity to use all the data available around the engine,” Costura said. “We can look at the way the engine is operated by application, operator or even worksite to monitor performance, coach the operator to improve efficiency or even drive the development of custom ratings.”

Prognostics and remote diagnostics

One benefit of having more electronic controls is that understanding faults becomes simpler. Diagnostic capabilities have become a central factor in electronic systems as developers marry the power of microprocessors with larger memory capacities, making it possible to look at events leading up to a fault.

Vehicle control systems are getting better at monitoring their own performance, constantly checking to see if each component is performing within expected parameters. Diagnostic systems are also getting better at fully analyzing any problem and presenting data that can shorten repair times.

“In some cases the more significant challenge is ensuring the system is operating properly and that the information the system receives from the sensors can be trusted, the on-board diagnostics,” said Maurice Dantzler, Function and Component Architecture Director, Cummins Emission Solutions. “We also see a strong desire to have good fault isolation capability to reduce repair costs. From a downtime perspective, we are seeing a push for self-diagnosis of the system while in operation. So when the vehicle arrives at the shop, the diagnosis is done and isolated to a component for a quick fix.”

As diagnostic technologies advance, developers are focusing on more ways to minimize unscheduled downtime. Some companies are working on prognostics as a way to predict pending breakdowns and plan repairs in a more strategic way. Others are utilizing telematics to give remote managers more capabilities to arrange maintenance and repair shutdowns.

“Greater emphasis is given to prognostics and remote diagnostics,” said JDPS’ Schneider. “These allow service repairs to be scheduled at a time convenient to the operator, resulting in increased efficiency and reducing costly work disabling failure modes.”

While diagnostic systems continue to improve, these advances are only made by overcoming significant challenges. The number of sensors and controllers on vehicles continues to grow, increasing the job of diagnostic functions that monitor them. The vehicle’s control systems also perform more tasks, many of them are more precise than the jobs done in prior generations. All these factors make it more difficult to analyze what’s going on.

“As systems become more complex and based on physical models of real systems, diagnostics opportunities improve,” Chewter said. “However, in competition with this is the fact that systems operate at higher levels of efficiency: lower emission levels, higher catalyst conversion efficiencies, etc. These factors can act to reduce the final diagnostic system performance.”

That doesn’t mean that progress is slowing down. Engineers continue to work on techniques that let systems fix some of the problems they identify. This is another way to reduce unscheduled downtime.

“Improved diagnostics would be able to identify temporary fail modes and request corrective action to recover,” Dantzler said. “For example, if a system has deposits, a special regeneration could be initiated to clear the deposits and get the system to a normal functioning state. This helps the system prevent the chances of going into an irrecoverable mode.”