The Growing Need for Valve Actuation Systems
It is famously said, “necessity is the mother of invention.” This is certainly true of engine technologies, which only ever get invented because needs have to be met, and it’s now especially true of valve actuation systems because they help meet the increasing needs to improve fuel economy and reduce tailpipe emissions.
Not that Variable Valve Actuation (VVA) is an entirely new invention. In fact, a two-position-variable valve system is at the heart of Jacobs’ first engine brake, the legendary Jake Brake, which went into service in 1961! What’s changed since then is not the principle of exploiting valve timing or actuation for some kind of benefit, but how this is executed and at what point in the engine’s cycle. Differing valve actuation strategies and technologies are now employed to meet differing needs.
This diversification has been seen in recent years in the introduction of a range of new Jacobs technologies for medium- and heavy-duty engines. Fully-flexible VVA, Active Decompression Technology (ADT), Cylinder Deactivation (CDA), and the High Power Density (HPD) engine brake are distinct from one another in their primary objectives and strategies. These technologies do, however, share hardware and components proven over many millions of miles, and also have in common the ability to improve fuel economy and lower emissions.
Economy and emissions benefits are sometimes the primary aims of Jacobs technology, sometimes a bonus in addition to delivering some other advantage, but always worth having. And this ability to deliver dual benefits makes Jacobs’ technical solutions exceptional. Though there are widely-adopted technologies that improve fuel economy, and though there are widely-adopted technologies that lower emissions, Jacobs’ are unusual for simultaneously achieving both.
This is important because more fuel-efficient methods are needed for reducing nitrogen oxide (NOx) emissions. Engine manufacturers have typically met EPA 2010 and EU6 emissions legislation by employing cooled Exhaust Gas Recirculation (EGR) and Selective Catalytic Reduction (SCR), but both these solutions have disadvantages. EGR reduces exhaust temperatures to lower NOx, but in order to cool it before sending the exhaust back into the engine, it must go through a lot of plumbing and a heat exchanger. These parts have had issues with long-term reliability. If the right level of EGR is not used, excessive particulate matter can be produced which can hasten the clogging-up of diesel particulate filters.
The SCR system injects a small amount of an ammonia (NH3) and water solution (Diesel Exhaust Fluid – DEF) onto the SCR catalyst. This can only be done once the SCR catalyst has warmed up to temperatures around 200 ⁰C. The engine calibration can force the engine to run inefficiently in some warm-up modes to get the SCR system up to operating temperature. This inefficiency costs fuel economy. Purchasing the DEF liquid is another expense for the truck owner and can be considered part of the “fuel economy” of the vehicle.
Additionally, if the aftertreatment system is not quite up to temperature or doesn’t quite convert all of the DEF, “ammonia-slip” can occur where ammonia gas is exhausted from the tailpipe.
The SCR system’s use of fuel is greatest when engines start from cold or the aftertreatment cools down during low-load operation and needs to be heated back up. These are exactly the circumstances regulators now have in their sights. By 2024 the California Air Resources Board (CARB) is scheduled to tighten NOx emissions regulations for low-load drive cycles, and soon after, regulators in Europe and China are also expected to toughen their rules.
This means there’s a need for technologies that can quickly get heat into an aftertreatment system, then keep the system hot, without hurting fuel consumption. Ideally, technologies for exhaust thermal management should not only provide heat for the aftertreatment but allow the vehicle to have better fuel economy. These two objectives once seemed mutually exclusive, but Jacobs’ well-proven VVA and CDA technologies show that both can be achieved simultaneously.