Diesel’s US Correspondent, Steve Sturgess looks at new developments in the engine brake world, as Jacobs finds a use for its lost motion technology.
Around the end of the ‘90s, as Cummins readied its unique dual overhead camshaft Signature 600, now the ISX, and International Engine showcased an entirely camless engine design, the other poppet-valve expert organisation, Jacobs, was working on ‘lost motion’ valve trains that would enable variable valve timing and cylinder cutout.
Jacobs, of course, is the long-time manufacturer of the diesel engine compression brake that was invented by Clessie Cummins, founder of the eponymous engine company. He was part of the crew that piloted the first Cummins-powered truck, an Indiana from Cummins’ home state, on a North American crossing in 1931 to demonstrate the fuel efficiency and reliability of the Cummins U-model diesel engine.
On the last leg to Los Angeles, Cummins had been warned about the steep downgrade of the ‘Cahone’ Pass. He sailed past the sign announcing the Cajon Pass without recognising its unique Spanish pronunciation and ran away down the grade, trying to slow the truck by gearing down and only just missing the caboose of a freight train crossing the highway as they did back then.
After that frightening experience, Clessie Cummins vowed to design a retarding device for the diesel, which he did after Cummins removed him from the company. And the Jacobs Chuck Manufacturing Company became the manufacturer.
In the years since, Jacobs has grown to understand a lot about poppet valves and their actuation, partnering and sharing its technology with many engine introductions like the ISX and the Daimler Heavy Duty Engine Platforms that currently power Freightliner, Western Star, Mercedes-Benz and Fuso trucks around the world.
The lost motion that I saw on a special visit to the Connecticut-based Jacobs nearly 30 years ago has now reached fruition with technology that may prove essential to meet the next round of North American heavy-duty diesel emissions and fuel-economy mandates. It includes cylinder cutout for light loaded, steady-state cruise with up to 20 per cent fuel savings.
Lost motion enables modification of the valve movement from the strict motion of the cam profile. Normally, the valve-train follows the cam profile, but by involving lost motion by way of an electro-hydraulic actuation, the lift of the valve, duration of opening and actual time within the limits of the cam profile can all be modified. Honda has been a big proponent of the technology in its VVT engines, which are outstanding for their power and frugality.
Jacobs first lost-motion product, which launched at the last IAA show in Hannover, Germany, is the CDA or cylinder deactivation. This technology disables engine valves in selected cylinders which allows a large engine to have the fuel economy of a smaller engine. Also, higher exhaust temperatures in the still operating cylinders maintain after-treatment temperatures at low load conditions and start-up, resulting in faster engine and after-treatment system warm-up
Other benefits from the control for the CDA include Improved combustion and fuel consumption in the firing cylinders. It minimises cooling of the after-treatment during coasting.
The actuation is through a hydraulic mechanism integrated into pushrod or valve bridge and is modular with Jacobs High Power Density engine brake technology. Interestingly, the exhaust valve can be timed to give a two-cycle braking mode for additional retardation.
An interesting option that can be integrated is a lifting of the exhaust valve as the engine shuts down. This eliminates the distinctive shake of the big diesel as it rapidly comes to a stop and can prove tiresome to a driver who is trying to sleep through a stop-start heating/battery regeneration series of cycles.
Jacobs is working with a number of engine makers on upcoming designs, said Robb Janak, director of new technology for Jacobs Vehicle Systems in a recent exclusive interview. The CDA will integrate into the valvetrains of future engines, the first of which may appear as early as 2024. And while the technology can work on any individual cylinder, Janak says most work is being done on six-cylinder engines with three cylinders equipped with the deactivation and the whole six featuring improved engine braking and the ‘no-shake’ option.
