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I couldn’t find this discussed in any Gen V LT1 articles or addressed in any other CF posts, and it may be a dumb question, but here goes…

The Motor Trend article (which has been pointed out by various other CF posters) has 50 or so images at the end. Take a look at image #25 (click to enlarge) which is titled “2014 Chevrolet Corvette 6.2L LT1 LOMA 2 150x150 photo.”

http://wot.motortrend.com/next-gen-l...ch-280365.html

What is all that apparatus on the underside of what I would call the valley cover plate?

ZeeOSix

Maybe knock sensors, since there seems to be an electrical connetor associated with that hardware. Maybe one knock sensor for each pair of cylinders?

Mdm23

That's the Active Fuel Management system (AFM). That's what they're calling the cylinder deactivation on the C7. Notice it's right under all the direct injection stuff. It will cut fuel to half the cylinders during light load driving. The writeup that I read said the cylinder cutout wont be noticeable (let's hope so). There's actually an animation of it on YouTube.

glhs386

Otherwise known as the IRG: Internet Rage Generator.

MikeyTX

My ex wife was also an IRG in her own right. Internal Rage Generator

Badluck33

In my 1992 I drove my Car for over 500 miles with out even knowing that cylinders 2 & 7 were off.

MPG went close to 30. Power was there but was also noticeably different when all 8 were working together.

CSixDude

I believe that is the Spark Ignition Direct Injection (SIDI) pump.

rcallen484

Uhhhhhh, sure

boraxman

CSixDude

I take that back. The SIDI pump is connected to the fuel rail at the front of the engine. You can see it in this photo.



The item that you asked about actually gets mounted face down in the valley.



The cylinder deactivation is supposedly done in the lifters themselves, so maybe these are the solenoids that interface with the lifters to control when they deactivate. That's my best guess at this point anyway. Somehow they appear to interface with the lifter so that the valve can be held open so the cylinder won't have any compression when shut off (or deactivated).

Katech_Zach

You are correct. It is the controller for cylinder deactivation via lifters.

JoesC5

Just the opposite. When the AFM is engaged(running on four cylinders), the valves are in the closed position. The lifter is going up and down(following the cam lobe) but the lifter is not pushing the pushrod.

CSixDude

That seems like it would cost a lot of HP and poor fuel economy because the deactivated cylinder would be dragging down the engine on every compression stroke. Wouldn't you want to have a valve cracked open to relieve compression?

Katech_Zach

I know it sounds counter-intuitive, but with both valves closed you're not pumping or compressing anything. There is a vacuum in the cylinder on the intake stroke with the intake valve closed.

CSixDude

I suppose if they timed the system so that both valves initially closed with the piston at the mid point, it would then only be half full of air, and so it would minimize both the suction and compression sides of the intake and compression strokes, and then some of the energy would return on the back side of the cycle when it expands against the receding piston, acting a bit like a spring being stretched and compressed.

I know that other auto manufactures that previously have used cylinder deactivation used a "pop off" valve in the head to relieve pressure. Maybe this is the new way of doing it. I'd sure like to know more about the details of how the system functions.

JoesC5

Who has used a "pop off valve"? Where is the "pop off valve" located. The cylinder head combustion chamber is allready pretty full with the intake/exhaust valves and the spark plug. The Chrysler AFM system is the same as GM's.

Katech_Zach

AFM description and operation from 2012 Camaro:


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.

Manifold absolute pressure (MAP) and the conditions listed below determine when cylinder deactivation is enabled.
• Engine has been running for greater than 30 s
• Engine speed is between 700 and 2800rpm
• Engine oil pressure is between 187–455 kPa (27–66 psi)
• Engine coolant temperature is between 40–129°C (100–264°F)
• Engine oil temperature is between 16–128°C (61–263°F)
• Throttle angle is 6% or less
• Ignition voltage is greater than 11 V
• Transmission is not in first, second, or reverse gear
• Vehicle speed is greater than 25 kph (15.5 mph)
• Brake booster pressure is greater than 42.0 kPa (6 psi)
• Vehicle is not in fuel shut of mode
• Vehicle is not in heater performance mode
• Vehicle is not in tip in bump acceleration mode
• Vehicle is not in oil aeration mode
• Vehicle is not in low range (if equipped)

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 out of range
• Vehicle speed out of range
• Minimum time in V8 mode not met
• Maximum V4 mode time exceeded
• Decel fuel cutoff is active
• Reduced engine power is active
• Torque management is active
• Catalytic converter over temperature protection is active
• Piston protection is active, knock detected
• Cylinder deactivation solenoid driver circuit faults

CSixDude

I believe Chrysler used to use a pop off valve in one of their older designs. I haven't kept up with the new designs, so I'm not real familiar with how they do it now.

CSixDude

EXCELLENT! Thanks for posting this. It explains several things.


So the valve lifter oil manifold and VLOM solenoids must be what is shown in this photo.


Interesting. I need to think about this some and wrap my head around it. It sounds like its going to depend some on where the piston is in its cycle when it is deactivated, and they are just sacrificing whatever losses they get on the compression stroke and hoping most of it will be returned on the back side of the stroke.

JoesC5

When did Chrysler have a displacement on demand engine before the 2005 Hemi? The Chrysler DoD system from 2005 to today has always been the same design system as the AFM from GM. No "pop off valves".

With the valves closed, when one cylinder's piston is moving upward, compressing the trapped air, another piston in another cylinder is moving downward and the compressed air is pushing down on the piston.