I know the impala ss and a few trucks are getting the DOD but I was just wondering if this system was self contained in the pcm or what? How hard would it be to use on of these engines in a transplant provided you got all the wiring/pcm etc?

figured it would be a good discussion post

 

Displacement on Demand (DoD) System Description
To provide maximum fuel economy under light load driving conditions, the engine control module (ECM) will command the displacement on demand (DoD) system to deactivate engine cylinders 1 and 7 on the left bank, and cylinders 4 and 6 on the right bank, switching to a V4 mode. The engine will operate on 8 cylinders, or V8 mode, during engine starting, engine idling, and medium to heavy throttle applications.

When commanded ON, the ECM will determine what cylinder is firing, and begin deactivation on the next closest DoD cylinder in firing order sequence. The Gen IV engine has a firing order of 1-8-7-2-6-5-4-3. If cylinder number 1 is on its combustion event when DoD is commanded ON, the next cylinder in the firing order sequence that can be deactivated is cylinder number 7. If cylinder number 5 is on its combustion event when DoD is commanded ON, then the next cylinder in the firing order sequence that can be deactivated is cylinder number 4.

Cylinder deactivation is accomplished by not allowing the intake and exhaust valves to open on the selected cylinders by using special valve lifters. The deactivation lifters contain spring loaded locking pins that connect the internal pin housing of the lifter to the outer housing. The pin housing contains the lifter plunger and pushrod seat which interfaces with the pushrod. The outer housing contacts the camshaft lobe through a roller. During V8 mode, the locking pins are pushed outward by spring force, locking the pin housing and outer housing together causing the lifter to function as a normal lifter. When V4 mode is commanded ON, the locking pins are pushed inward with engine oil pressure directed from the valve lifter oil manifold (VLOM) assembly solenoids. When the lifter pin housing is unlocked from the outer housing, the internal pin housing will remain stationary, while the outer housing will move with the profile of the camshaft lobe, which results in the valve remaining closed. One VLOM solenoid controls both the intake and exhaust valves for each deactivating cylinder. There are 2 distinct oil passages going to each DoD lifter bore, one for the hydraulic lash-adjusting feature of the lifter, and one for controlling the locking pins used for cylinder deactivation.

Although both intake and exhaust valve lifters are controlled by the same solenoid in the VLOM, 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 upwards 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. However, when DoD 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.

By deactivating the exhaust valve first, this allows the capture of a burnt air/fuel charge or exhaust gas charge in the combustion chamber. The capture of exhaust gases in the combustion chamber will contribute to a reduction in oil consumption, noise and vibration levels, and exhaust emissions when operating in V4 mode. During the transition from V8 to V4 mode, the fuel injectors will be turned OFF on the deactivated cylinders. The ignition system secondary voltage or spark is still present across the spark plug electrodes on the deactivated cylinders. If all enabling conditions are met and maintained for DoD operation, the ECM calibrations will limit cylinder deactivation to a cycle time of 10 minutes in V4 mode, and then return to V8 mode for 1 minute.

Switching between V8 and V4 mode is accomplished in less than 250 milliseconds, making the transitions seamless and transparent to the vehicle operator. The 250 milliseconds includes the time for the ECM to sequence the transitions, the response time for the VLOM solenoids to energize, and the time for the DoD valve lifters to deactivate, all within 2 revolutions of the engine crankshaft.

The DoD system consists of the following components:

• The valve lifter oil manifold (VLOM) assembly

• Eight DoD valve lifters, 2 per deactivating cylinder

• The engine oil pressure regulator valve for DoD operation

• Gen IV DoD engine block

• The ECM

 

It works pretty well, almost undetectable as it switches. I don't see why some enterprising individual couldn't put one of these in a hybrid of some sort!

 

So how does the piston move if the chamber is closed? Wouldn't that result in huge parasitic loss or "engine braking" while compressing and expanding the exhaust gases every stroke? That must be why the system is not active during idle.

 

The sequence starts by deactivating an exhaust valve first but when it does it captures a partial burnt air/fuel charge in that cylinder.....it isn't pumped all the way out of the cylinder. That allows a certain amount of pressure to remain which keeps the pressure on the rings and in turn doesn't let oil get past them into the cylinder. This residual pressure also helps to minimize vibration, noise and also keeps the emissions level down. Clever boys they have in the engineering department, eh??

 

Maybe I am over simplifying it in my mind but why didn't they just cut the fuel injectors and let the values run normally.

Mark

 

You are correct it has nothing to do with not allowing valves to open or close. It deactivates the injector and spark for that specific combustion chamber. Just like limp mode in the northstar V-8's. Not allowing the valves to open and close would break components from all the pressure not being able to be released

 

...aahhhh but they DO keep the valves from opening, the secret is in the TIMING of the deactivation. The injector is disabled but the secondary ignition still throws a spark in the deactivated cylinder. If they just flat closed the valves you are right, the thing would sound like a bowling ball in a washing machine!