Four Key Functions of the Camshaft in an Internal Combustion Engine

The camshaft (or camshafts) performs four core functions: it opens and closes the intake valves at precise times; opens and closes the exhaust valves at precise times; mechanically drives or actuates certain auxiliary components (such as a fuel pump, vacuum pump, and—on older engines—the ignition distributor); and provides a positional/timing reference for engine management and variable valve timing systems. These roles ensure correct breathing, combustion efficiency, and reliable synchronization with the crankshaft.

What the Camshaft Does

At the heart of the valvetrain, the camshaft converts rotational motion into the controlled linear motion that actuates valves, while also serving as a mechanical and timing hub for related systems. The following list outlines the four primary functions it performs in most engine designs, from classic pushrod layouts to modern overhead-cam engines with variable valve timing.

• Times and actuates the intake valves: Cam lobes lift followers/lifters to open intake valves, controlling when and how far they open (lift) and for how long (duration) to regulate the air (or air-fuel) charge entering the cylinder.
• Times and actuates the exhaust valves: Complementary lobes open the exhaust valves to expel combustion gases, including any designed overlap with intake events to improve scavenging and efficiency.
• Drives or actuates auxiliary components: A cam lobe or cam-driven gear can power ancillary devices—commonly a mechanical fuel pump (including modern high-pressure gasoline direct-injection pumps), a vacuum pump, and, on older spark-ignition engines, the ignition distributor.
• Provides a timing reference/interface for control systems: The camshaft’s indexed position (read by a camshaft position sensor) synchronizes sequential fuel injection and ignition timing with the crankshaft; in engines with variable valve timing/phasing, the camshaft also interfaces with phasers to alter valve timing dynamically for performance, efficiency, and emissions.

Together, these functions ensure the engine breathes properly across the rev range, that auxiliary devices receive mechanical drive when needed, and that electronic controls have the precise positional data required for accurate, real-time management.

How These Functions Influence Performance and Reliability

Valve timing, lift, and duration governed by the camshaft directly shape torque delivery, peak power, fuel economy, and emissions. Aggressive profiles and longer duration raise high-rpm power but can compromise idle quality, while variable valve timing mitigates this trade-off by shifting cam phasing as conditions change.

Cam-driven auxiliaries reduce the need for separate drive systems, simplifying packaging and ensuring robust, synchronous operation. Meanwhile, accurate cam position data is essential for sequential fuel injection and ignition; any timing error—due to chain/belt stretch or worn lobes—can degrade drivability, raise emissions, or cause mechanical damage.

Modern vs. Older Engines

Modern overhead-cam engines often use dual camshafts (DOHC) and electronically controlled cam phasers to independently optimize intake and exhaust events. Many gasoline direct-injection engines mount a high-pressure fuel pump on the intake cam. Older pushrod engines typically use a single camshaft in the block to operate both intake and exhaust valves via lifters and pushrods, and the same shaft may drive a mechanical fuel pump and the ignition distributor.

Summary

The camshaft’s four functions are to actuate the intake valves, actuate the exhaust valves, drive key auxiliaries, and provide a precise timing reference for engine control and variable valve timing. These roles work together to determine how efficiently the engine breathes, how reliably it runs, and how well it balances power, economy, and emissions across operating conditions.