By Mark Sealy
|This integrated valve block controls turbocharger wastegate emissions to help meet 2010 EPA diesel-engine standards. Multiple proportional valves can be configured in custom housings to meet a variety of performance and design requirements. |
As requirements for commercial vehicles get more demanding, the diesel engine is rapidly becoming a far more sophisticated platform. Requirements driving this advance include emissions regulations, fuel efficiency standards, and higher user expectations for drivability and reliability. Meeting these demands requires control systems and associated actuators able to maximize the performance of specific vehicle systems.
This trend is particularly apparent in emissions-control systems requiring turbocharger control, exhaust gas recirculation (EGR), and exhaust brakes for after-treatment thermal management. Over the past 15 years, diesel engine boosting systems have transitioned from single, passive turbochargers with simple mechanical waste gates to multistage or variable geometry turbochargers (VGT) with proportional actuation requiring fast, precise, and repeatable position control. The same is true for EGR valves and exhaust brakes.
Electropneumatic control technology has kept pace with advances in engine-boosting systems. For example, Norgren has developed a family of proportional-pneumatic control valves that reside on the engine, providing precise closed-loop control while withstanding high vibration and elevated temperatures.
Advantages of pneumatics
Some engineers hesitate to use pneumatic systems because of old misconceptions about response times, accuracy, and air consumption. However, constant improvements in speed and accuracy mean there are components and systems to meet virtually any requirement. Current-generation proportional valves have a response time as low as 150 msec, a speed comparable to electric actuators. Next-generation pneumatic proportional valves will further reduce air consumption and improve durability.
At the same time, the inherent characteristics of pneumatics deliver significant advantages. Pneumatic controls are generally a simpler, more familiar technology for maintenance personnel. They typically generate more force or torque, so are better suited to cope with real-life problems such as static friction in flap valves due to corrosion or poor fuel quality. The fact that they use less complicated electronic controls and require no water cooling and no gears also contributes to their simplicity and reliability.
Pneumatic systems are especially attractive in diesel engines because of their durability despite a rugged operating environment.
Pneumatic components also give designers a lot of flexibility in meeting performance and configuration demands. Suppliers with a wide range of products and specialized engineering capabilities can meet requirements from the simplest 2-port, 2-position valve to integrated platforms with sophisticated closed-loop proportional valves.
Electropneumatic control systems are well-suited for the demanding performance and space requirements of today’s heavy-duty diesel engines. The electronic “brains” can be mounted away from the engine, while the valves do their jobs close to the action. Systems can be configured for simple open-loop control to open or close a valve. More and more often, though, designers are taking advantage of closed-loop systems.
|Compared with a series of individual valves, a “plug-and-play” unit reduces the number of electrical and pneumatic connection points and the potential for installation errors or leaks. It also operates in a smaller footprint. |
The electronic controller in a closed-loop system not only directs component operation, but it collects data used to monitor operations and signal problems. It can be programmed to measure pressure, position, and flow at any point in the process. This capability for continuous monitoring and self-adjusting give closed-loop systems high accuracy. The feedback loop also makes this system well suited for on-board diagnostics, as the controller can monitor both the performance and condition of the pneumatics and collect and store data for maintenance and regulatory reporting.
Multi-function valve block
Electronic control of individual valves offers all the benefits described above, but integrating multiple valves and other components into a single cast-aluminum housing or manifold significantly enhances the value of the system. This is clearly seen in the example of the multi-function control valve block (MCVB) for controlling turbocharger waste gate emissions and exhaust brakes in heavy-duty truck engines.
Previous designs relied on standalone valves, each with its own housing, pneumatic connections, wiring, and mounting hardware. The new version consolidates several proportional valves, a pressure regulator, pressure sensor, and all the associated fittings into a single cast-aluminum housing with one connector.
The MCVB magnifies the advantages inherent in electropneumatic control systems. It is easier to install a “plug-and-play” unit than individual valves. Fewer electrical and pneumatic connection points mean fewer chances for installation errors and leaks.
The unit’s rapid-response valves adjust the air/fuel mix quickly to control emissions while still giving the driver the engine response and power required. And the high-accuracy valves deliver precise positioning, so the electronic controller does not need to continuously make corrections and adjustments.
|This exploded view shows consolidated multiple proportional valves, a pressure regulator, a pressure sensor, and all the associated fittings into a single cast aluminum housing with a single connector. |
The integrated unit uses common input and exhaust circuits. And it consolidates four modules into one – reducing the total number of components by 30%. The MCVB also requires less mounting hardware and has a significantly smaller footprint, compared with individual valves. This gives designers more options for placement and more space for other equipment.
Mounting components into a single unit has another advantage: Instead of qualifying each component and validating its performance, the MCVB comes as one comprehensive, pretested unit.
Variations on a theme
The MCVB was developed by Norgren’s Engineering Advantage custom-engineering group to meet specific requirements for 2010 EPA emissions standards. But an integrated electropneumatic platform can be adapted for any variety of applications. Many aspects can be modified to meet performance and durability requirements and fit a specific design configuration.
For example, components can mount inside a complex cast block, as with the MCVB. Or a laminar manifold can permit connections in three dimensions, reducing the size while adding capabilities. Multiple operations can be consolidated within one unit and connections configured to match up with other engine components.
Materials options include aluminum for light weight or stainless steel for chemical or salt environments. Even lightweight composites or plastic housings can be used for certain under-the-hood applications. Likewise, seals are specified based on the operating environment.
Integrated electropneumatic engine-control systems can be designed to withstand most any aggressive environment, making them valuable not only for trucks but for heavy equipment, rail, and construction applications. And co-developing an integrated system with an expert pneumatics supplier lets OEMs focus scarce engineering resources on their own core competencies and bring products to market faster.
Looking to the future
Controlling inlet air, charge air, and exhaust gas are all fundamental requirements met by electropneumatic controls, and these actuation systems for diesel engines will continue to improve. Beyond that, there are opportunities for this technology in the shut-off and control of compressed natural gas (CNG), liquefied petroleum gas (LPG), and liquefied natural gas (LNG), and in the control and regulation of urea emissions-control systems.
Demands for even better fuel efficiency and further reduction in CO2 emissions will bring new waste-heat recovery systems to market. And trends towards bio fuels and hybrid vehicles continue to create new opportunities for advanced fluid and motion control.
Mark Sealy is Engineering Director, and David Shrader is Global Business Development Manager, Commercial Vehicle Sector, Norgren, Littleton, Colo. For more information, visit www.norgren.com/usa and www.engineeringadvantage.com.