Nissan Patents Emissions Device For Engine Stop/Start Changeovers

Nissan has recently patented a new variable valve timing (VVT) mechanism for use in series hybrids. The unit looks like it could eventually be attached to the brand’s “e-Power” vehicles with an emphasis on reducing emissions upon startup. While less exciting than power adders, the system may help keep combustion vehicles on the road a while longer as government regulators keep raising the threshold on what can legally leave your tailpipe.

Spotted by CarBuzz, the patent is supposed to work with a VVT system on the exhaust cam — specifically whenever the hybrid needs to start running the combustion engine again.

From CarBuzz:

E-Power, in case you aren't familiar, relies on the combustion engine as a generator, powering electric motors instead of driving the wheels directly. But that means, depending on the power requirements and type of driving you're doing, the combustion engine itself isn't always running. The problem the patent addresses is that when the engine regularly stops and starts, a regular exhaust gas recirculation (EGR) system resets its valve to closed when the engine switches off. When the engine starts again, there's a moment on restart when the engine is pushing fuel that hasn't been burned through the system straight through the exhaust rather than recirculating a portion of exhaust gas back into the intake to burn off any petrol that didn't combust the first time round. This is bad news for emissions testing.

Essentially, the patented system always restarts with the EGR system recirculating due to valve overlap with the engine's variable valve timing (VVT) system. When the engine is running and the oil pressure is up within the VVT actuator, the VVT system maximizes retardation on the exhaust timing, creating maximum permissible overlap between exhaust and intake valve timing. But Nissan's patent describes a locking pin mechanism, which engages the moment the engine is switched off, holding the exhaust timing in this position without the need for oil pressure to do so.

ECUs have ensured that cars idle higher upon startup for decades. Prior to that, vehicles came with a manually adjusted choke that could be fiddled with as the engine approached its optimal temperature.

Initially essential to help prevent engine stalls, the concept now doubles as a way to help with emissions. The faster an engine warms up, the sooner it can achieve optimized combustion. In fact, you may have noticed that newer models actually idle higher upon cold startups than vehicles from a few years back. Once the catalytic converter and multitude of sensors are up to temperature, they can begin to communicate with the computer on how best to run the engine in order to reduce emissions — keeping government regulators happy.

While we can debate all day about whether running a totally cold engine at higher engine speeds is better for the longevity of the motor, taking into account modern oil viscosity and pressures, it’s inarguable that manufacturers want to meet emissions as soon as possible for testing purposes.

What’s different today is that loads of vehicles come with stop/start functionality (people broadly dislike) that’s designed to reduce emissions. However, on certain hybrid systems this may also result in those engines going cold or potentially wasting fuel and producing extra emissions between changeovers. Nissan is simply trying to address the issue by not allowing the vehicle to temporarily run rich and doing what it can to get the catalytic converted back up to temperature as quickly as possible.

Your author couldn’t care less about that and would frankly rather have an automobile running with excess fuel (rich) than too much air (lean). However, Nissan’s new patent is alleged to come with other benefits. It’s supposed to help limit the mechanical load on oil pumps during engine startup due to not needing to send lubricants through the VVT system. That theoretically could extend the life of your oil pump and may even help to get better oil pressure for other essential components. Nissan likewise suggested that the tech could also be applied to the intake side of the valvetrain, potentially resulting in less-harsh restarts.

A lot of the above had to be translated from Japanese. But that’s what Nissan seems to be trying to convey in the patent filing. However, those kinds of benefits always feel like mild coping, as oil pressure concerns likely wouldn’t be an issue if we weren’t starting and stopping the engine (which effectively just exists to recharge the battery on e-Power hybrid systems) for the primary purpose of satisfying emissions.

With hybrids becoming increasingly common on dealer lots, it may not be worth complaining. Rough transitions between gas and electric propulsion have become common complaints among today’s drivers and this may be a good way to address them. There’s likewise nothing obvious tying this patent specifically to series hybrids, as it should work more-or-less the same with a more-traditional parallel hybrid or plug-in hybrid (PHEV) system.

It could theoretically be used on the stop/start systems found on non-hybrid gasoline powertrains, too. But there might not be much reason to bother, as those engines don’t typically see enough downtime on trips for it to matter.

If the new patent works as suggested within the filing and manages to extend the lifespan of hybrid powertrains, then we might as well throw Nissan a giant parade. But we’re likewise skeptical of introducing additional complexity to vehicles, particularly when it’s chiefly in service of satisfying emissions. There’s a difficult balance that has to be maintained between appeasing regulators and satisfying customers. Lately, consumers seem to be getting the short end of that stick and that makes it hard not to be a little cynical. But we’ll likewise be curious to see how this tech performs when and if it’s applied.

[Images: Sadi-Santos/Shutterstock; WIPO]

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