New V8 Engines Feature Dynamic Fuel Management

The all-new 2019 Silverado 1500 and Sierra 1500 offer two new V8 engines: the 5.3L V8 (RPO L84) and the 6.2L V8 (RPO L87). (Fig. 1)

Fig. 1

These new engines deliver the power demanded by truck owners — the 5.3L V8 has a power output of 355 horsepower and 383 lb.-ft. of torque and the 6.2L V8 (Fig. 2) develops 420 horsepower and 460 lb.-ft. of torque — while optimizing fuel economy.

Fig. 2

One of the enhancements to the efficiency of the new engines is the new Dynamic Fuel Management (DFM) system, which is the successor to Active Fuel Management (AFM). AFM alternated between 8 cylinder and 4 cylinder modes, but DFM actively turns off any number of cylinders in a variety of combinations, allowing the engine to run on 17 different cylinder patterns.

DFM is powered by a sophisticated controller that continuously monitors the vehicle’s accelerator pedal and runs a complex sequence of calculations to determine how many cylinders are required to meet the driver’s power demand. The DFM controller can make this determination 80 times per second. Switching between V8 and DFM modes is accomplished in less than 250 milliseconds, or within two revolutions of the crankshaft, making the transition seamless and transparent to the driver.

 

Valve Lifter Operation

Cylinder deactivation is accomplished by not allowing the intake and exhaust valves to open on the selected cylinders by using special valve lifters. (Fig. 3) The deactivation lifters contain spring loaded locking pins that connect the internal pin housing of the lifter to the outer housing.

Fig. 3

When cylinder deactivation is commanded, the ECM will determine what cylinder is firing and begin deactivation on the next closest deactivated cylinder in the firing order sequence. Although both intake and exhaust valve lifters are controlled by the same solenoid, the intake and exhaust valves do not become deactivated at the same time. Cylinder deactivation is timed so that the cylinder is on an intake event.

During an intake event, the intake cam lobe is pushing the valve lifter upward to open the intake valve against the force of the valve spring. The force exerted by the valve spring is acting on the side of the lifter locking pins, preventing them from moving until the intake valve has closed. When the intake valve lifter reaches the base circle of the camshaft lobe, the valve spring force is reduced, allowing the locking pins to move, deactivating the intake valve.

When cylinder deactivation is commanded on, the exhaust valve for the deactivated cylinder is in the closed position, allowing the locking pins on the valve lifter to move immediately and deactivate the exhaust valve.

When all enabling conditions are met for cylinder deactivation, the ECM will actuate the high and low control of each solenoid control circuit in firing order sequence, allowing current to flow through the solenoid windings. With the coil windings energized, the solenoid valve opens, redirecting engine oil pressure through the valve lifter oil solenoid valves into 16 separate vertical passages in the engine lifter valley. The 16 vertical passages — two per cylinder — are connected to the valve lifter bores of the cylinders to be deactivated.

When operating conditions require a return to V8 mode, the ECM turns off the control circuits for the solenoids, allowing the solenoid valves to close. With the solenoid valves closed, engine oil pressure in the control ports is exhausted through the body of the solenoids into the engine block lifter valley. The oil passages of the valve lifter oil solenoid valves incorporate several bleeds in the oil passages to purge any air trapped in the engine block.

 

Valve Lifter Oil Solenoid Valve Operation

DFM uses eight valve lifter oil solenoid valves (one for each cylinder) that are mounted in the engine block valley under the engine block valley cover. (Fig. 4) Each solenoid controls engine oil pressure to the intake and exhaust valve lifters on the cylinders selected to deactivate. Engine oil pressure is routed to the lifter oil gallery from an internal oil passage on the rear of the cylinder block.

Fig. 4

When an oil control solenoid valve is commanded open, pressurized oil forces the lifter locking pins (Fig. 5, E) inward. The pushrod (Fig. 5, A) remains in a constant position and does not travel upward and downward. The outer body of the lifter (Fig. 5, C) moves upward and downward independently from the pin housing (Fig. 5, D). The valve lifter spring (Fig. 5, B) retains tension on the valve train components to eliminate valve train noise.

Fig. 5

With DFM, the engines are able to better balance power needs with fuel efficiency. During an industry-standard test schedule, the 2019 Silverado 2WD with the 5.3L V8 and DFM operated with fewer than eight active cylinders more than 60 percent of the time, 9 percent more than a comparably equipped 2018 model with AFM.

 

– Thanks to Dave MacGillis and Sherman Dixon

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