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Smoothing engines with torque reserves

by Steven St. Laurent on

Normally, the term “torque reserve” brings up visions of the Dodge Demon’s 808-horsepower, drag-race-focused powertrain and its various tricks. But torque reserve can also be used to make ordinary cars, using two-stage valve lift (normal and high performance), smoother.

The reason for having a low-valve-lift mode is to increase efficiency, by reducing pumping losses.  The high-lift mode increases the valves’ ability to move a lot of air quickly, for higher performance.  The change in valve lift modes is fast, but EGR and throttle changes are not, resulting in some roughness, which this system is designed to overcome.

FCA US’ latest patent covers a system which monitors the valvetrain, EGR, and intake pressure. When it sees the valve system about to go from high to low lift, the system creates a torque reserve, then releases it during the transition to smooth out the change. The system can apparently be adapted for cam phasing, two-phase oil pumps, MultiAir systems, or other systems, and can include a second torque reserve for the next transition.

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