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Although an overhead camshaft (OHC) engine also has overhead valves, the common usage of the term "overhead valve engine" is limited to engines where the camshaft is located in the engine block. In these traditional OHV engines, the motion of the camshaft is transferred using pushrods (hence the term "pushrod engine") and rocker arms to operate ...
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.
The ratio is determined by the ratio of the distances from the rocker arm's pivot point to the point where it touches the valve and the point where it touches the pushrod/camshaft. A rocker ratio greater than one essentially increases the camshaft's lift. Current automotive design favors rocker arm ratios of about 1.5:1 to 1.8:1.
A camshaft operating two valves. A camshaft is a shaft that contains a row of pointed cams in order to convert rotational motion to reciprocating motion.Camshafts are used in piston engines (to operate the intake and exhaust valves), [1] [2] mechanically controlled ignition systems and early electric motor speed controllers.
Pushrods are long, slender metal rods that are used in overhead valve engines to transfer motion from the camshaft (located in the engine block) to the valves (located in the cylinder head). The bottom end of a pushrod is mated to a lifter, upon which the camshaft makes contact. The camshaft lobe moves the lifter upwards, which moves the pushrod.
The lobed camshaft rhythmically presses against the lifter, which transmits the motion to the engine valve in one of two ways: through a pushrod which actuates the valve via a rocker mechanism (in an overhead valve (OHV) engine); via direct contact with the valve stem or rocker arm (in an overhead camshaft (OHC) configuration).
In an overhead valve engine the tappets (on right) are sandwiched between pushrods and the camshaft. In an internal combustion engine, a tappet (also called a 'valve lifter' or 'cam follower') [3] [4] [5] is the component which converts the rotation of the camshaft into vertical motion to open and close an intake or exhaust valve.
Since those days, lift, velocity, acceleration, and jerk curves for cams have been modelled by computer [6] to reveal that cam dynamics are not what they seemed. With proper analysis, problems relating to valve adjustment, hydraulic tappets , push rods, rocker arms, and above all, valve float , became things of the past without desmodromic drive.