GM Inside News Forum banner
1 - 1 of 1 Posts

· Premium Member
9,965 Posts
Discussion Starter · #1 ·

Envoy XL Denali Includes Fuel-Saving Displacement on Demand Feature

CHICAGO -A new, Gen IV version of the professional grade Vortec 5300 V-8 engine is standard in the 2005 GMC Envoy Denali and Envoy XL Denali. The fuel-saving Displacement on Demand (DOD) feature will be included with the Envoy XL Denali later in 2005.

DOD technology enables fuel economy gains of up to 8 percent in certain light-load driving conditions by reducing the number of cylinders engaged in the combustion process. It also helps reduce emissions. The Envoy XL Denali is one of the first trucks in GM's portfolio to be equipped with the sophisticated system.

"DOD is another demonstration of the versatility, strength and performance of the legendary small-block V-8 engine," said Sam Winegarden, chief engineer of small-block engines. "It maintains broad, usable torque that SUV customers depend on, delivering it in a technologically advanced manner that reduces fuel consumption and emissions - it's definitely a win-win scenario."

Enabled by GM's E40 engine control module (ECM), DOD saves fuel by using only half of the engine's cylinders during most normal driving conditions. The system automatically and seamlessly deactivates and reactivates cylinders during a variety of driving conditions. The engine always starts and idles on eight cylinders, but once certain criteria are met while driving, the controller can alternate the engine's operation between eight and four cylinders. The engine always operates with all eight cylinders during load-intensive driving situations such as brisk acceleration, load carrying or towing. Fuel economy gains depend on driving style and load-carrying conditions.

The E40 ECM uses sensors to determine when conditions are optimal for cylinder deactivation - alternate cylinders are deactivated, effectively creating a V-4 engine. The cylinders are deactivated by the closing of the intake and exhaust valves, which cuts off the air and fuel needed for combustion. The pistons continue pumping, but pump only cooling air.

The E40 ECM can tell what the engine is doing at any point in a cycle, including the last cylinder fired and the position of the valvetrain, which helps interpret information to control fuel injection, electronic spark control and electronic throttle control. Using the same information, algorithms manage the cylinder deactivation and reactivation process. The process happens instantly and seamlessly, with the engine capable of constantly switching between V-8 and V-4 modes without the driver noticing.

Although electronics control when to deactivate the cylinders, the valves' mechanical shut-off is the result of clever two-stage hydraulic lifters. Developed by Eaton Corp., the lifters have an inner and outer section - with one telescoping into the other. The two sections are coupled or uncoupled via a locking pin. When cylinder deactivation is initiated, hydraulic pressure is used to move the pin and collapse the lifter, which closes the valve. When the cylinder is reactivated, the removal of hydraulic pressure causes the locking pin to return to its latched position and restore the lifter's normal function. The special lifters are only used with the valves designated for deactivation - the other four cylinders' valves have conventional hydraulic lifters.

"From behind the wheel, there's no indication or sensation that the operating mode of the engine has changed," said Winegarden.

Solenoids in the lifter oil manifold assembly operate to deliver high-pressure oil to the switching lifters, which activates the locking pins. Oil circulation and pressure does not vary, regardless of the engine's operational mode. Lifter design and pushrod length are the same for every cylinder, but camshaft lobe profiles differ for cylinders designated to be deactivated.

Because the vibration and acoustic dynamics of the V-8 and V-4 modes are different, engineers tuned the exhaust system to accommodate both. Additionally, special exhaust and engine mounts were designed for the multiphase engine operation.

The E40 ECM controller also is used to increase manifold pressure in V-4 mode so the engine can maintain a V-8 torque load.

Gen IV improvements

In addition to DOD, the Gen IV Vortec 5300 all-aluminum V-8 brings a host of other refinements suited to the Envoy Denali and Envoy XL Denali models' premium market positions. The engine is estimated at 290 horsepower and 325 lb.-ft. of torque - including the DOD version, which also supports tow capacities comparable to non-DOD-equipped engines.

Based on the architecture of the successful Gen III small-block introduced in GM trucks in 1999, the Gen IV engine incorporates several significant design changes:

- New casting for iron and aluminum blocks with redesigned oil galleries to support DOD oiling requirements.
- Knock sensor locations moved out of lifter valley to provide room for DOD lifter oiling solenoids.
- Camshaft sensor relocated from the rear of the block to the front of the block provides room for new oil galleries.
- Higher capacity oil pump accommodates increased oil circulation requirements of DOD.
- Ignition has smaller, more efficient coils that require less energy to produce a comparable spark.
- Returnless fuel system for improved evaporative emissions.
- Larger throttle body angled upward for improved water drainage.
- Electronic throttle control on all models for improved throttle response and DOD signaling.
- E40 ECM operates DOD, ETC and other engine functions.
- Separate controller for transmission.

The Gen IV Vortec 5300 benefits from continual improvements incorporated into later versions of the Gen III engine, including iridium-tip long-life spark plugs; pistons with floating wrist pins; a redesigned water pump with improved sealing; and a stronger, long-life timing chain.

Gen IV engines share the deep skirt engine block design of previous GM truck engines. Extending below the crankshaft centerline, the rigid block contributes to world-class smoothness and strength. It also allows cross-bolted main bearing caps for additional strength and dimensional accuracy.

The engines' similarities also include the balanced cylinder head design, which promotes optimal performance and efficiency with identical airflow and energy direction to each cylinder. A tall intake manifold plenum helps draw a longer, tuned path for incoming air to build low-rpm torque, allowing the engine to make torque at low rpm and sustain it over a broad rpm band.

GMC, a division of General Motors Corporation, markets the Sierra, Yukon, Envoy, Savana, Safari and GMC medium duty trucks and the all-new Canyon midsize pickup. GMC's lineup of professional grade trucks delivers outstanding capabilities. GMC sold nearly 580,000 vehicles in 2003, setting a divisional sales record for the 10th time in eleven years.
1 - 1 of 1 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.