9/14/2023 0 Comments Dodge variable valve timing![]() ![]() When the rpm level drops below 4,500, the oil pressure solenoid shuts off, blocking off the oil pressure and returns the engine to the normally operated two intake valves. This higher lobe gives the engine the needed boost in power at an rpm higher than 4,500. ![]() This, in-turn, “locks” the normally used two intake valves together with a set of pins that are pushed outward into the two intake rockers and transfers their motion to a higher eccentric lobe (operated by the middle rocker arm). The i-VTEC system uses an oil pressure solenoid activated electrically by the PCM to allow oil to pass into the rocker arm between the two normal rockers. Honda’s term for a variable valve system is i-VTEC. If you encounter a vehicle that has higher than normal NOx levels, or a burnt or damaged pre-catalyst, make sure the VVT solenoid and exhaust camshaft position sensor are operating properly. This controls combustion temperatures and the production of NOx. ![]() Modern variable valve timing systems are doing the same job as the EGV valve, only better.Ī VVT system is able to control the timing of the exhaust valve so that the right amount of inert exhaust gases remain in the combustion chamber for the next combustion cycle. This process lowers the combustion temperature to under 2,500° F, above which NOx gases are formed, hurting both the environment and a vehicle’s performance.ĮGR systems work, but they are not able to react fast enough or precise enough for modern engines and emissions standards. The elimination of the EGR valve is the result of the VVT’s ability to control gases entering and exiting the combustion chamber.ĮGR systems are designed to reduce smog-causing nitrous oxides (NOx) by recirculating a portion of the exhaust gases from each cylinder of the engine back into the intake manifold. One item that’s going the way of the smog pump is the Exhaust Gas Recirculation (EGR) valve. This is all the result of the configuration and shape of the exhaust ports and manifolds, all of which work together and make the whole process seamless. ![]() This slight intake valve opening creates low pressure and aides the piston in pushing out the remaining gases and getting ready for the next turn of the crankshaft. Leaving the intake valve partially open at the right point also allows fresh air to enter the cylinder while the exhaust valve is doing its job of removing the already-burnt gases. This reduces the exertion from the crankshaft and piston and provides a smoother, more even-running engine at every rpm level. Pushing the exhaust gas out of a cylinder requires some of the force that is generated during the combustion stroke. Opening the exhaust valve when there is still some pressure left in the cylinder allows a small portion of the exhaust gas to escape before the piston starts its upward travel. One great advantage of the VVT system is the way it can take the force needed to expel the burnt mixture out of the exhaust valve. This also enables an increase in miles per gallon throughout the engine’s power band by controlling valve timing and making the engine more fuel-efficient. Now an engine can produce both low- and high-end performance without any erratic idle condition or high-end loss. With variable valve timing, the valve duration can be matched to the engine speed, torque requirements and valve overlap. Because these engines are designed to have maximum performance at the top end, the cam is “cut” for better performance at the high end, so sacrifices are made at the idle end.) On a conventional engine, both the exhaust and intake valves’ open or closed position depends on their fixed position relative to the chain or belt that’s driven by the crankshaft. The pattern and timing cannot be altered, so there’s no way to increase or decrease the amount of valve lap when both valves are open at the same time.Īs engines go, some have great low-end performance, while others have better top-end performance. (If you’ve ever heard an old street rod or dragster popping and rumbling at an idle, you’ve heard the lope from the cam. But, they are part of a larger diagnostic picture that includes everything from the throttle body to the oxygen sensor. Most vairable valve timing components are non-serviceable and have integrated sensors. These systems are simple from a diagnostic perspective. Now, the VVT is playing a direct role in vehicle emissions and the way gases are burned in the combustion camber. These systems offered higher performance from smaller displacement engines at higher rpm.Īs these vehicles exceeded their new car warranties, technicians learned the ins and outs of these systems and how regular oil changes could increase the life of VVT components. By the early 1990s, almost all import automotive manufacturers had a successful variable valve timing (VVT) system in production. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |