Four-cycle internal combustion engines use cams to let a fresh gas/air mixture into the engine and exhaust gases out. A four-stroke motor as used in nearly every automobile has one intake valve and one exhaust valve for every cylinder. Sophisticated four-stroke engines with advanced valve-timing operations (such as phase shifting) use cam control solenoids and actuators for both intake and exhaust valves. Because the control solenoid controls the cam actuator, they are sometimes called a cam actuator solenoid.
Four-stroke engines transfer power or torque through a crankshaft to the drivetrain. The crankshaft, known as the "bottom end" of the engine, must be synchronised with the valves, which are linked by a timing chain (or other mechanical drive) and one or more cams; this assembly along with the cylinders and pistons is known as the "top end" of the engine. The bottom and top ends of the engine are synchronised so that if one is turned 180 degrees, the other is turned 180 degrees.
Phase Shifting & Variable Valve Timing
Most four-stroke engines use one or more fixed cams. A cam profile is connected by a timing chain to the crankshaft and it determines when intake and exhaust valves open and close relative to the movements of the crankshaft, which in turn move the pistons. Complex engines approximate variable valve timing by adjusting the position of one or crankshaft assemblies during the engines operation, shifting the cam timing in the process.
For these sophisticated valve-trains to work, an on-board computer must sense the position of the cam to give it feedback and tell it when to move or shift and how much. An exhaust cam actuator solenoid is the apparatus that takes a computer signal and mechanically invokes the actuator to shift the position of the exhaust cam.
Cars that have these kinds of sophisticated valve-trains are either technically advanced modern cars or race cars. Modern cars that use cam actuator solenoids are likely to have on-board computers attached to sensors that can provide mechanics with engine failure codes. For example, GM's Trailblazer and Envoy can give codes that indicate problems with the exhaust cam actuator control solenoid.
- The Free Dictionary: Definition of Actuator by the Free Online Dictionary, Thesaurus and Encyclopedia.
- Your Dictionary: Definition of solenoid at Your Dictionary.com
- Chevy High Performance Magazine: Tech Article: Camshaft Basics
- Great Auto Help: Cam Actuator Solenoid Valve: GM Description Operation: Codes