An eccentric has a geometric center offset from a rotating shaft axis. Projecting that center onto a fixed line gives an ideal simple-harmonic displacement. This calculator evaluates that ideal projection from entered throw, angles and speed.
Valve Motion Eccentric Interactive Calculator
Enter eccentric throw, crank angle, angular advance and shaft speed. Results describe an ideal eccentric-center projection—not actual valve travel, valve events, strap/rod kinematics, loads, bearing behavior or equipment suitability.
Equation Used
- Throw is the entered offset between shaft and eccentric centers.
- Position is the ideal projection of that offset at entered crank angle plus advance.
- Peak-to-peak travel is twice entered throw for the eccentric-center projection.
- Peak speed is the amplitude times constant angular speed.
- The animation is a geometric cue, not a rigid strap-and-rod closure.
- Valve lap, lead, port geometry, linkage ratios, rod angularity, friction, clearance, loads, acceleration forces, lubrication, wear, strength, operating limits and safety are omitted.
Documented Eccentric-and-Strap Topology
U.S. Patents 326,398 and 455,872 document steam-engine valve mechanisms using an eccentric, strap and eccentric rod to transmit motion toward a valve. Patent 747,109 likewise identifies a crankshaft-mounted valve-operating eccentric, eccentric strap and rod. These sources support the topology, not a universal valve-motion waveform.
What This Calculator Represents
The tool treats only the rotating eccentric-center offset and its projection on a fixed line. It reports the ideal projection at entered phase, twice the offset as peak-to-peak projection, and the ideal peak projection speed at constant RPM.
Ideal Eccentric-Centre Projection
position x = e cos psi
peak-to-peak projection = 2e
angular speed omega = 2 pi n / 60
ideal peak speed = e omega
Historical steam-engine texts describe eccentric throw in relation to valve travel, but actual valve travel depends on the intervening linkage.
Worked Ideal Example
At 50 mm entered throw, 0 degree crank angle and 120 degree advance, the ideal projection is -25.0 mm and phase is 120 degrees. The peak-to-peak center projection is 100 mm. At 200 RPM the ideal peak projected speed is about 1,047 mm/s.
Model Boundary
- Calculated: eccentric-center phase, ideal projection, peak-to-peak projection and ideal peak speed.
- Illustrated: shaft axis, offset center, generic strap disc, rod and slider cue.
- Not calculated: actual strap/rod closure, link ratio, valve events, lap, lead, port opening, forces, inertia load, bearing pressure, clearance, lubrication, wear, strength, settings or safety.
Frequently Asked Questions
Is twice the throw always actual valve travel?
No; it is the ideal eccentric-center peak-to-peak projection.
Does angular advance prove valve timing?
No.
Is peak speed an actual measured valve speed?
No; it is the ideal projected-center maximum.
Does the animation close the eccentric rod geometry?
No.
Can the calculator set lap or lead?
No.
Can it size a strap, bearing or lubricator?
No.
References
- U.S. Patent 326,398: eccentric, strap, rod and valve-motion topology.
- U.S. Patent 455,872: eccentric, eccentric strap, eccentric rod and valve-rod motion transfer.
- U.S. Patent 747,109: crankshaft-mounted valve-operating eccentric, strap and rod.
- Practical Stationary Engineering: historical definition of eccentric throw and valve travel.
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