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Old 02-28-2010, 08:27 AM   #1
tommygun6644
 
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AFM: how does it works?

How does the engine shut off 4 cylinders?
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Old 02-28-2010, 08:39 AM   #2
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http://www.ls1tech.com/forums/5322427-post3.html

http://www.fastfieros.com/tech/dod_oil_path.htm


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Old 02-28-2010, 08:40 AM   #3
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Cylinder Deactivation (Active Fuel Management) System Description




To provide maximum fuel economy under light load driving conditions, the engine control module (ECM) will command the cylinder deactivation system ON to deactivate engine cylinders 1, 7, 6, and 4, 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 cylinder deactivation is commanded, the ECM will determine what cylinder is firing and begin deactivation on the next closest deactivated cylinder in firing order sequence. For example, if cylinder number 1 is on its combustion event when cylinder deactivation 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 cylinder deactivation 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, when all cylinders are active, 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 cylinder deactivation 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 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 cylinder deactivation 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 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.

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 cylinder deactivation mode.

During the transition from V8 to V4 mode, the fuel injectors will be turned OFF on the deactivated cylinders. To help prevent spark plug fouling, 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 cylinder deactivation operation, the ECM calibrations will limit cylinder deactivation to a cycle time of 10 minutes in V4 mode, then return to V8 mode for 1 minute.

Switching between V8 and V4 modes 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 valve lifters to deactivate, all within 2 revolutions of the engine crankshaft.

Valve Lifter Oil Manifold (VLOM) Assembly
The cylinder deactivation system uses an electro-hydraulic actuator device called the valve lifter oil manifold (VLOM) assembly. The VLOM is bolted to the top of the engine valley, below the intake manifold assembly. The VLOM consists of 4 electrically operated normally closed solenoids. Each solenoid controls the application of engine oil pressure to the intake and exhaust valve lifters on the cylinders selected to deactivate. Engine oil pressure is routed to the VLOM assembly from an internal oil passage on the rear of the cylinder block.

All 4 VLOM solenoids are connected in parallel to a fused ignition 1 voltage circuit, supplied by the powertrain relay. The ground or control circuit for each solenoid is connected to a low side driver internal to the engine control module (ECM).

When all enabling conditions are met for cylinder deactivation, the ECM will ground 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 VLOM into 8 separate vertical passages in the engine lifter valley. The 8 vertical passages, 2 per cylinder, are connected to the valve lifter bores of the cylinders to be deactivated. When vehicle-operating conditions require a return to V8 mode, the ECM will turn OFF the control circuit 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 housing of the VLOM incorporates several bleeds in the oil passages to purge any air trapped in the VLOM or engine block.

To help control contamination to the hydraulic circuits, a small replaceable oil screen is located in the VLOM oil inlet passage, below the oil pressure sensor. The oil pressure sensor is a 3-wire sensor which provides oil pressure information to the ECM.

During service, use extreme care in keeping the VLOM assembly free of any contamination or foreign material.

Cylinder deactivation may be inhibited for many reasons including the following:

• Engine coolant temperature out of range for cylinder activation

• Engine vacuum out of range

• Brake booster vacuum out of range

• Transmission gear incorrect or shift in progress

• Accelerator pedal out of range or rate of pedal application to fast

• Engine oil pressure and temperature out of range

• Engine speed of range

• Vehicle speed out of range

• Minimum time in V8 mode not met

• Maximum V4 mode time exceeded

• Decel fuel cutoff active

• Reduced engine power active

• Torque management active

• Catalytic converter over temperature protection active

• Piston protection active, knock detected

• Cylinder deactivation solenoid driver circuit faults
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Last edited by camaro1; 02-28-2010 at 08:50 AM.
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Old 02-28-2010, 08:42 AM   #4
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Oil flow is cut to 4 of the 8 cylinder's lifters. Fuel and spark is also cut. And your running on 4 instead of 8. With no oil pressure in those lifters, those valves stay closed. There is a manifold with solenoids in the lifter valley controlling this.

An absolutely moronic feature, just my opinion. If I want a 4 banger, I'd buy a 4 banger.
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Old 02-28-2010, 08:53 AM   #5
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I stuck my head out the window the other day when the engine had shut off to 4cyl, and it sounded terrible! Now I'm embarrassed everytime I go slowly by a group of people walking. I've been as low as 18mph and had AFM activate! This feature should be only 60mph and above or something like that. I cut off my rear mufflers, not thinking about AFM, and it sounds terrible in 4cyl mode.
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Old 02-28-2010, 09:09 AM   #6
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Thanks for all the info all.

My grandfather was actually asking me the other day, I had no idea.
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Old 02-28-2010, 10:36 AM   #7
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Quote:
Originally Posted by Russell James View Post
Oil flow is cut to 4 of the 8 cylinder's lifters. Fuel and spark is also cut. And your running on 4 instead of 8. With no oil pressure in those lifters, those valves stay closed. There is a manifold with solenoids in the lifter valley controlling this.

An absolutely moronic feature, just my opinion. If I want a 4 banger, I'd buy a 4 banger.
Moronic? You are joking right? This is a HUGE engineering accomplishment to avoid you having to pay a 4 digit guzzler tax on your Camaro.

Now it's fair for you to say you would pay it, but not many would. It would certainly impact sales if every Automatic Camaro had to add over a grand to the sticker.

So I can certainly understand your not liking the feature.................but moronic?
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Old 02-28-2010, 02:02 PM   #8
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Originally Posted by Number 3 View Post
Moronic? You are joking right? This is a HUGE engineering accomplishment to avoid you having to pay a 4 digit guzzler tax on your Camaro.

Now it's fair for you to say you would pay it, but not many would. It would certainly impact sales if every Automatic Camaro had to add over a grand to the sticker.

So I can certainly understand your not liking the feature.................but moronic?
Thankfully don't have it in my Camaro, mines an M6. Had it in my Silverado, absolutely hated it. There were some speeds and roads near me where it was constantly kicking in and out of. Heck, even in my subdivision at 15 mph, it would kick to 4 cyl.. bwaaaaaaaaaaaa. start slowing down, so you give it a little gas and it kicks out, get back to a steady speed and it kicks in again bwaaaaaaa... just fricken annoying.

I was ready to sell my truck until I tried a handheld tuner and shut it off.
Love the truck now and it gets about the same mileage. I wouldn't call shutting off oil flow to a lifter any great technology advancement. It's a solenoid. Many manufacturers use some variation of it. I'd be impressed with it if it were seamless and unnoticeable. In my truck it was annoying has heck. So no, not impressed with the technology.
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Old 02-28-2010, 02:48 PM   #9
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i didn't really care for it either way when i got my camaro...now after having it for almost 1,000 miles..i'm not really liking it that much anymore. i think i'm gonna get a tuner and tune it off. my camaro is my dd and where i drive to/from work it turns on a lot and it sounds terrible! it's not really helping me with gas mileage either...i'm getting like 13.4 mpg.
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Old 02-28-2010, 03:36 PM   #10
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At least it works better than the 4-6-8 in the Caddilac.
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