For the ideal harmonic reference used here, valve displacement from mid-position is x = r sin(θ + δ). Opening of the displayed positive-direction port is max(0, x − s), where s is outside lap. Total peak-to-peak valve travel is 2r.
Single-Eccentric Valve Gear · Ideal Harmonic Reference
Explore an ideal single-eccentric harmonic displacement reference and one directional lap-controlled port opening.
Equation Used
- The eccentric-to-valve relationship is represented by an ideal harmonic projection.
- Port opening refers only to the displayed positive-direction port.
- Eccentric setting follows the selected convention 90°+advance.
- Finite-rod angularity, the opposite port, flow, pressure, loads, wear and tolerances are excluded.
Valve displacement is measured from mid-position. Outside lap affects port opening, not the displacement coordinate.
Ideal eccentric projection and translating valve
The animation projects a rotating eccentric pin onto the valve axis and places a guided valve at that ideal harmonic coordinate. This is a transparent displacement construction, not a claim that a finite eccentric rod has zero angularity.
What the calculator determines
Select eccentric radius r, crank angle θ, angular advance δ and outside lap s. The calculator reports ideal displacement from mid-position, positive-direction port opening, peak-to-peak travel and the conventional eccentric setting 90° + δ.
Selected ideal harmonic convention
x = r sin(θ + δ); positive-port opening = max(0, x − s); travel = 2r; eccentric setting = 90° + δ.
Selected-input arithmetic
At r = 6 mm, θ = 0°, δ = 30° and s = 1.5 mm, x = 3.0 mm and the selected positive-direction port opening is 1.5 mm.
Reference model only
The model excludes finite-rod angularity, opposite-port opening, inside lap, lead at dead centers, cutoff, release, compression, steam flow, pressure, forces, wear, backlash and manufacturing tolerances.
Questions
Is displacement measured after subtracting lap?
No. Displacement is measured from valve mid-position; lap is subtracted only when calculating the displayed directional opening.
Does this calculate complete valve events?
No.
References & Further Reading
- Wikipedia contributors. Slide valve. Wikipedia
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