Lt250r motor vibration with alternating current
How does cylinder deactivation work?
The link @cory is the description from the service manual. Just one repetition and I'll add some pictures and additional information.
Cylinder deactivation is achieved by not opening the intake and exhaust valves 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 reciprocating piston and the push rod seat that are connected to the push rod. The outer housing contacts the cam of the camshaft via a roller. During the V8 mode, the locking pins are pushed outward by spring force, which locks the pin housing and the outer housing together and the lifter functions as a normal lifter. When the V4 mode is turned on, the locking pins are pushed in with engine oil pressure directed by the solenoid valves of the valve lifter oil manifold assembly (VLOM). When the lift pin housing is unlocked from the outer housing, the inner pin housing remains stationary while the outer housing moves with the profile of the cam lobe, causing the valve to remain closed. A VLOM solenoid controls both the inlet and outlet valves for each deactivation cylinder. There are two different oil channels for each bore of the cylinder deactivation lifter, one for hydraulic clearance adjustment of the lifter and one for controlling the locking pins used for cylinder deactivation.
Although both the intake and exhaust valve lifters in the VLOM are controlled by the same solenoid, the intake and exhaust valves are not deactivated at the same time. The deactivation of the cylinder is timed so that the cylinder is in an intake event. During an intake event, the intake cam pushes the valve lifter upward to open the intake valve against the force of the valve spring. The force exerted by the valve spring acts on the side of the lock pins on the lifter and prevents them from moving until the inlet valve closes. When the intake valve lifter reaches the base circle of the cam on the camshaft, the valve spring force is reduced, which allows the locking pins to move and deactivate the intake valve. However, when cylinder deactivation is turned ON, the exhaust valve for the deactivated cylinder is in the closed position, allowing the locking pins on the valve lifter to immediately move and deactivate the exhaust valve.
By deactivating the exhaust valve for the first time, a burned air / fuel charge or exhaust gas charge in the combustion chamber can be detected. Trapping exhaust gases in the combustion chamber helps reduce oil consumption, noise and vibration levels, and exhaust emissions in V4 mode. During the transition from V8 to V4 mode, the injectors on the deactivated cylinders are switched off. The secondary voltage or the spark of the ignition system is still applied to the spark plug electrodes of the deactivated cylinders. If all of the enable conditions for cylinder deactivation operation are met and maintained, the ECM calibrations limit cylinder deactivation in V4 mode to a cycle time of 10 minutes and then return to V8 mode for 1 minute.
Cylinder deactivation (Active Fuel Management)
General Motors Active Fuel Management's engine control system provides the ability to achieve maximum fuel consumption by deactivating 4 of the engine's 8 cylinders under certain low-load driving conditions. The engine typically operates with 8 cylinders in V8 mode during starting, idling and with medium or heavy throttle. When the ON command is on, the engine control module (ECM) controls the active fuel management system and deactivates cylinders 1 and 7 on the left bank and cylinders 4 and 6 on the right bank, forcing V4 mode. See description of lubrication and cylinder deactivation system (Active Fuel Management).
Oil distributor for valve lifters
The valve lifter oil distribution assembly is bolted to the top of the engine block below the intake manifold assembly. The oil distributor consists of 4 electrically operated and normally closed magnets. Each solenoid directs the pressurized engine oil flow to the intake and exhaust valve lifters of the active fuel management system. The oil pressure relief valve located in the oil pan for active fuel management regulates the engine oil pressure to the lubrication system and to the oil distributor.
When the fuel management active mode enable conditions are met, the ECM grounds each solenoid control circuit in firing order so that current can flow through the solenoid windings. When the windings are energized, the solenoid valves open and direct pressurized engine oil through the valve lift oil manifold into 8 vertical passages in the engine block lift valley. The 8 vertical passages, 2 per cylinder, direct pressurized oil directly to the valve lift bores of the cylinders to be deactivated. If the vehicle's operating conditions call for a return to V8 mode, the ECM will turn off the ground circuit for the solenoids, allowing the solenoid valves to close. When the solenoid valves are closed, the remaining oil pressure is released through the vent channels of the valve lifter's oil manifold into the bottom of the engine block lifter. The oil manifold housing contains multiple oil vent passages that continuously remove trapped air from the manifold and engine block.
In order to control the contamination in the hydraulic system of the active fuel management, there is a small replaceable oil filter in the oil inlet channel of the oil distributor of the valve tappet. The oil pressure sensor monitors engine oil pressure and provides information to the ECM.
Active fuel management valve lifters
In V8 mode, the valve lifters of the active fuel management function similarly to the valve lifters of the inactive fuel management. The active fuel management oil manifold solenoid valves are in the closed position with no pressurized oil being directed to the valve lifters. The push rod moves up and down to operate the rocker arm and valve. The spring-loaded locking pins of the lifter are extended outwards and mechanically lock the pin housing to the outer body of the valve stem.
When the active fuel management system is turned ON, the ECM directs the oil manifold solenoids to open pressurized oil and direct it to the valve lifters. The oil flows through the valve lifter oil manifold and the engine block oil galleries and enters the valve lifter inlet port.
In V4 mode, pressurized oil pushes the locking pins inwards. The push rod stays in a constant position and does not move up and down. The outer body of the lifter moves up and down independently of the pen housing. The valve lift spring maintains tension on the valve train components to prevent valve train noise.
When the active fuel management system is turned OFF, the ECM instructs the oil manifold solenoids to close, stopping pressurized oil flow to the valve lifters. The oil pressure in the lifter decreases and the locking pins move outward to mechanically lock the pin housing and the outer body.
The active fuel management engine block contains additional functions to support the operation of the active fuel management system. Engine oil pressure is routed from an oil gallery in the rear of the cylinder block to the valve lifter oil manifold assembly. Cylinders 1, 4, 6 and 7 each have 2 vertical oil channels cast in block. The vertical oil passages allow oil to flow from the manifold assembly to the valve lifter bores.
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