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Reducing criteria pollutants while reducing greenhouse gases is an active area of research for commercial on-road vehicles as well as for off-road machines. The heavy duty on-road sector has moved to reducing NOx by 82.5% compared to 2010 regulations while increasing the engine useful life from 435,000 to 650,000 miles by 2027 in the United States (US). An additional certification cycle, the Low Load Cycle (LLC), has been added focusing on part load operation having tight NOx emissions levels. In addition to NOx, the total CO2 emissions from the vehicle will also be reduced for various model years. The off-road market is following with a 90% NOx reduction target compared to Tier 4 Final for 130-560 kW engines along with greenhouse gas targets that are still being established. The off-road market will also need to certify with a Low Load Application Cycle (LLAC), a version of which was proposed for evaluation in 2021.

Current heavy duty diesel valvetrains are not able to utilize hydraulic lash adjusters (HLA) in conjunction with an engine brake. During a braking event the engine brake introduces substantial lash into the vehicle valvetrain. The HLA reacts by pumping out to take up the lash encountered during braking, thereby preventing the valves from properly seating at the end of the cycle. Jacobs Vehicle Systems has developed a new mechanism to allow the inclusion of an engine brake into a valvetrain equipped with hydraulic lash adjusters. The fulcrum system maintains a load on the hydraulic lash adjuster during engine brake operation preventing the HLA from extending. HLA are appealing to engine manufacturers because they allow for simpler manufacturing, less maintenance, reduced NVH and valve motion enhancements. This paper describes the design, simulation and testing of the lashless valvetrain with engine brake including the next steps in the development of the valvetrain.

Heavy duty valvetrains have evolved over the last 20 years with the integration of engine braking into the valvetrain. Jacobs Vehicle Systems have developed the High Power Density (HPD) engine brake that increases retarding powe, especially at low engine speed. The system works by converting the engine from a 4 stroke during positive power into a 2 stroke for retarding power. This more than doubles the retarding power at cruise engine speeds reducing the need to downshift in order to control the vehicle, compensates for reduction in natural vehicle retarding due to aerodynamic and friction enhancements, and enables the same vehicle retarding power with a smaller displacement engine as engine downsizing becomes prevalent. This paper describes lessons learnt during a recent vehicle demonstration project undertaken by Jacobs including performance, durability, integration with the engine powertrain, controls development, calibration, management of air system and transient operation.