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A hydraulic tappet, also known as a hydraulic valve lifter or hydraulic lash adjuster, is a device for maintaining zero valve clearance in an internal combustion engine. Conventional solid valve lifters require regular adjusting to maintain a small clearance between the valve and its rocker or cam follower. This space prevents the parts from ...
A hydraulic tappet, also known as a "hydraulic valve lifter" and "hydraulic lash adjuster", contains a small hydraulic piston that becomes filled with pressurised engine oil. [4] [11] The piston acts as a hydraulic spring that automatically adjusts the tappet clearance according to the oil pressure. Although the movements of the piston are ...
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. Today [ when? ] most automotive engines use overhead cams , driving a flat tappet to achieve the shortest, lightest weight, and most inelastic path from cam to ...
The stiff springs are needed to overcome the weight of the rocker arms and hydraulic self-adjusting tappets used and thereby prevent valve float, which they do up to around 6700 rpm. The stiff valve springs add more friction and pressure to the already high-friction "flat tappet" design.
Depending on the design used, the valves are actuated by a rocker arm, finger, or bucket tappet. Overhead valve engines use rocker arms, which are actuated from below indirectly (through the pushrods) by the cam lobes. Overhead camshaft engines use fingers or bucket tappets, which are actuated from above directly by the cam lobes. [3]
A tappet between valve and cam is a contact surface on which the cam slides to open the valve. Many engines use one or more camshafts "above" a row (or each row) of cylinders, as in the illustration, in which each cam directly actuates a valve through a flat tappet.
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In contrast, MultiAir uses managed hydraulic fluid to provide variable valve control. Control of a MultiAir engine's intake valves works via a valve tappet (cam follower), moved by a mechanical intake cam, which is connected to the intake valve through a hydraulic chamber, controlled by a normally open on/off solenoid valve. [11]
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