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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.
In four-stroke cycle engines and some two-stroke cycle engines, the valve timing is controlled by the camshaft. It can be varied by modifying the camshaft, or it can be varied during engine operation by variable valve timing. It is also affected by the adjustment of the valve mechanism, and particularly by the tappet clearance.
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.
Oil under constant pressure is supplied to the lifter via an oil channel, through a small hole in the lifter body. When the engine valve is closed (lifter in a neutral position), the lifter is free to fill with oil. As the camshaft lobe enters the lift phase of its travel, it compresses the lifter piston, and a valve shuts the oil inlet.
In most piston engines, the camshaft(s) are mechanically connected to the crankshaft. The crankshaft drives the camshaft (via a timing belt, timing chain or gears), which in turn actuates the intake and exhaust valves. [1] These valves allow the engine to inhale air (or an air/fuel mixture) and exhale the exhaust gasses. [2]
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 ...
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 ...