Paddle Shifters & the L99- Help

[bobscogin]

Originally Posted by Dragoneye

There's no increased load, or extra wear that would require an extra warranty, or some sort of protection.

With no combustion occurring, or valve opening/closings on the deactivated cylinders, I'd think there would be *less* wear and load than on the firing cylinders.

Bob

[swifttal]

Originally Posted by bobscogin

With no combustion occurring, or valve opening/closings on the deactivated cylinders, I'd think there would be *less* wear and load than on the firing cylinders.

Bob

The valves still open and close - the cam that pushes the push rods which contacts the lifters to open/close valves doesn't magically swap out or anything - the fuel to those cylinders just simply cuts off

[bobscogin]

Originally Posted by swifttal

The valves still open and close - the cam that pushes the push rods which contacts the lifters to open/close valves doesn't magically swap out or anything - the fuel to those cylinders just simply cuts off

From what I've read, the valves stay closed on the deactivated cylinders. This is accomplished via the solenoid bank controlling oil flow to those lifters. If the valves still open/close on deactivated cylinders, you'd have tremendous pumping losses as the air moved in and out. By keeping them closed, the power loss from cylinders compressing the air is offset by the decompressing air forcing the piston down on the cylinders that are on the downstroke. The net loss is practically zero because the decompressing air contributes energy that was lost in compression, whereas if the deactivated cylinders were moving air in and out --- well, that would eat up a lot of power.

Bob

[Mr. Wyndham]

Originally Posted by bobscogin

From what I've read, the valves stay closed on the deactivated cylinders. This is accomplished via the solenoid bank controlling oil flow to those lifters. If the valves still open/close on deactivated cylinders, you'd have tremendous pumping losses as the air moved in and out. By keeping them closed, the power loss from cylinders compressing the air is offset by the decompressing air forcing the piston down on the cylinders that are on the downstroke. The net loss is practically zero because the decompressing air contributes energy that was lost in compression, whereas if the deactivated cylinders were moving air in and out --- well, that would eat up a lot of power.

Bob

Excellent explanation!

[bobscogin]

Originally Posted by Dragoneye

Excellent explanation!

Found this article on GM's site that explains it. Note the statement that the cam lobes on the deactivating cylinders have a different profile. That's interesting.

"A sophisticated engine controller determines when to deactivate cylinders, allowing the engine to maintain vehicle speed in lighter-load conditions such as highway cruising. The process is seamless and virtually imperceptible. When the cylinders are deactivated the V-8 engine effectively operates as a V-4, with alternate cylinders on each cylinder bank disabled. The engine returns to V-8 mode the instant the controller determines the vehicle speed or load requires additional power. When the V-6 engine is in AFM mode the left bank of cylinders are shut down. The key to AFM's efficiency and smooth operation is a set of special two-stage hydraulic valve lifters, which allows the lifters of deactivated cylinders to operate without actuating the valves.

The valve lifters have inner and outer bodies, which normally operate as a single unit. When the engine controller determines cylinder deactivation conditions are optimal, the outer body moves independently of the inner body on the disabled cylinders' lifters. The outer body moves in conjunction with camshaft actuation, but the inner body does not move, holding the pushrod in place. This prevents the pushrod from actuating the valve, thereby halting the combustion process. Solenoids in the engine lifter valley operate to deliver high-pressure oil to the switching lifters, activating a release pin to separate the inner and outer bodies. Oil circulation and pressure do 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.

The engine's electronic throttle control (ETC) also is used to increase manifold pressure in V-4 mode so that the engine can maintain a V-8 torque load."