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How do cams control valves in an automobile engine?
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Six simple machines for transforming energy into work.
In an automobile engine, the camshaft acts as the mechanical controller for the intake and exhaust valves. It features irregularly shaped disks called cams, or cam lobes, which convert the shaft's rotary motion into the linear, up-and-down motion required to open and close the valves at precise intervals.1
The camshaft is synchronized with the crankshaft via gears, chains, or belts, typically rotating at half the crankshaft's speed in a four-stroke engine. As the cam lobe rotates, it pushes against a tappet (or lifter). Depending on the engine design, this motion is transferred in one of two ways:12
- Cam-in-block: The motion travels from the lifter through a pushrod to a rocker arm, which then pivots to depress and open the valve.13
- Overhead camshaft: The camshaft is positioned directly above the valves, eliminating the need for pushrods and allowing for higher engine speeds.12
Once the cam lobe rotates past the lifter, the valve's spring forces it to close, ensuring the combustion chamber remains sealed.13