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The lobe separation angle (LSA, also called lobe centreline angle) is the angle between the centreline of the intake lobes and the centreline of the exhaust lobes. [23] A higher LSA reduces overlap, which improves idle quality and intake vacuum, [22] however using a wider LSA to compensate for excessive duration can reduce power and torque ...
The cam can be seen as a device that converts rotational motion to reciprocating (or sometimes oscillating) motion. [clarification needed] [3] A common example is the camshaft of an automobile, which takes the rotary motion of the engine and converts it into the reciprocating motion necessary to operate the intake and exhaust valves of the cylinders.
Intake, induction or suction: The intake valves are open as a result of the cam lobe pressing down on the valve stem. The piston moves downward increasing the volume of the combustion chamber and allowing air to enter in the case of a CI engine or an air-fuel mix in the case of SI engines that do not use direct injection.
Camshafts normally have one lobe per valve, with a fixed valve duration and lift. Although many modern engines use camshaft phasing, adjusting the lift and valve duration in a working engine is more difficult. Some manufacturers use systems with more than one cam lobe, but this is still a compromise as only a few profiles can be in operation at ...
For twin-cam or DOHC engines, VCT was used on either the intake or exhaust camshaft. (Engines that have VCT on both camshafts are now designated as Ti-VCT.↓) The use of variable camshaft timing on the exhaust camshaft is for improved emissions, and vehicles with VCT on the exhaust camshaft do not require exhaust gas recirculation (EGR) as retarding the exhaust cam timing achieves the same ...
The mechanism is a coaxial shaft arrangement where the outer shaft carries the main body of the cam lobe. The main body of the cam lobe is in its maximum duration form. Typically the main lobe body would have a duration of about 450°. The lobe is very long axially, about 45 mm (1.8 in), and its profile consists of conventional opening and ...
Properly optimizing the valve duration avoids undue stresses to the camshaft lobes and tappets. 'Valve bounce' is a related condition where the valve does not stay seated because of the combined effects of the valve's inertia and resonance of metallic valve springs that reduce the closing force and allow the valve to re-open partially.
The hydraulic lifter, situated between the camshaft and each valve, is a hollow steel cylinder encasing an internal piston. This piston is held at the outer limit of its travel with a strong spring. The lobed camshaft rhythmically presses against the lifter, which transmits the motion to the engine valve in one of two ways: