Hiscox’s double-grooved eccentric uses a push-rod end that traverses crossed grooves and follows different radial paths on alternate revolutions. His gas-engine text describes operating one exhaust valve in a four-cycle engine. It is not the separate intake-and-exhaust follower arrangement previously described here.
Linear actuator checks for Double-grooved Eccentric Valve Gear for a Four-cycle Gas Engine
An actuator-driven version of double-grooved eccentric valve gear for a four-cycle gas engine should be reviewed for stroke, linkage angle, and peak force. The mechanism may feel light through most of the travel and still bind or spike in force at one position.
For cam-driven motion, look for dwell, rapid lift, and shock loading. A linear actuator may simplify positioning, but it will not naturally reproduce a cam profile unless the control system is designed for it.
If the application needs synchronized motion, feedback should be treated as a requirement rather than an accessory. Two open-loop actuators wired together can drift apart when friction, load, or mounting geometry differs between sides.
- Map actuator stroke to the actual output travel before choosing a model.
- Check for binding, changing leverage, and peak load near the ends of travel.
- Decide whether timed motion is acceptable or position feedback is required.
For a FIRGELLI design review, calculate the load case with the FIRGELLI actuator force calculator and plan the switching or controller arrangement with the linear actuator wiring diagram generator. If an actuator or cylinder is already installed, the linear actuator replacement finder helps keep the comparison tied to real dimensions.
Crossed-Groove Eccentric · Alternate-Revolution Valve Motion
Follow one traversing follower through crossed grooves. Compare a selected exhaust-valve event occurring once per two direct shaft revolutions.
Equation Used
- One exhaust event per two shaft revolutions.
- One follower traverses the intended crossed-groove route.
- Transverse motion is a selected cosine path.
- Radial lift is a selected cosine event; acceleration joins dwell discontinuously.
- Crosshead and barrel centre-path rendering are explanatory selections.
Not two independently phased intake/exhaust cams. No engine-specific timing, wear or strength rating.
One follower changes tracks
The original figure shows two adjacent grooves with a crossover. The follower end traverses between them, so the path repeats after two shaft turns. In the gas-engine description, one section has a smaller radial path than the other, allowing the exhaust-valve rod to be operated on alternate revolutions.
The main view exposes the groove centre paths through a translucent barrel. The follower moves both transversely and radially. An illustrated sliding crosshead transfers radial motion to a single valve while accepting the transverse movement. This transfer detail is a reconstruction choice, not a dimensioned assembly taken from the source.
The unwrapped view separates the two branches and shows their crossover. A complete circuit follows the blue branch for one revolution and the gold branch for the next. The selected radial lift occurs once during that two-revolution circuit.
The source does not provide a manufacturing profile or the follower guidance at the crossing. The animation assumes the follower continues along its intended route; it does not establish a groove-switching or anti-jamming design.
Compare an alternate-revolution exhaust event
This calculator explores the four-cycle use stated by Hiscox. Enter a selected lift, transverse range, direct shaft speed and valve-event duration. It reports event rate, elapsed time and the peak speeds and acceleration of the chosen motion law.
The demonstration is phased from a track seam, not engine top dead centre. It does not specify an actual intake or exhaust opening angle relative to a piston, gas flow, power rating or valve-spring requirement.
Explicit reconstruction law
Let θ be direct shaft rotation over a 4π-radian cycle, S the total transverse travel and H the maximum radial lift. Transverse position is x=−(S/2)cos(θ/2). It changes lanes after one shaft revolution and returns after two.
On the active revolution choose an event centred at θ=π/2, of duration D radians. Between θ₀=π/2−D/2 and θ₀+D, put u=(θ−θ₀)/D and h=(H/2)[1−cos(2πu)]. Outside that event and throughout the alternate revolution, h=0. The allowed event durations keep lift away from the crossover.
With shaft speed n rpm and ω=2πn/60 rad/s, event rate is n/2 per minute and cycle time is 120/n seconds. Open time is D/ω. Peak radial speed is Hπω/D; peak radial acceleration magnitude is 2Hπ²ω²/D². Peak transverse speed is Sω/4.
The cosine event has zero velocity at its endpoints, but acceleration changes when it joins the dwell. These numbers are kinematics of the chosen law, not a jerk-limited cam design, spring-force calculation or allowable-speed rating.
6 mm lift at 240 shaft rpm
At 240 rpm the selected circuit repeats every 0.5 seconds and gives 120 valve events per minute. A 120° event lasts 0.08333 seconds.
For 6 mm maximum lift, peak radial speed is about 226.195 mm/s and peak acceleration magnitude is about 17,054.676 mm/s². With 14 mm transverse travel, peak transverse speed is about 87.965 mm/s.
Doubling shaft speed doubles both peak speeds and quadruples peak acceleration. Changing the transverse range changes only the transverse path and its speed; it does not change the selected valve lift.
Keep the historical principle and selected design separate
The two-track crossover and alternate radial paths come from the source. The cosine lift event, dimensions, timing origin, translucent rendering and sliding crosshead are explicit explanatory choices.
The original page’s generic half-speed intake/exhaust story, specific engine-brand examples, service-life figures and wear thresholds were not supported by this drawing. They have been replaced by the actual alternate-revolution principle and a declared calculation model.
A working design still needs a follower that negotiates the crossover, groove widths and depths, pressure-angle and contact checks, lubrication, valve return, clearances and an engine timing reference. This page does not calculate those details.
Double-grooved eccentric questions
Are there separate intake and exhaust followers?
Not in the source arrangement reviewed here. One traversing follower operates an exhaust-valve rod on alternate turns.
Does the illustrated shaft turn at half engine speed?
No half-speed shaft is added in this direct-drive reconstruction. The crossed path supplies the two-revolution repetition.
Why does the follower move sideways?
It traverses from one groove branch to the other.
Is the 120° default an engine specification?
No. It is an adjustable duration for the selected cosine event, without a defined piston TDC.
Does the crossover work without special guidance?
The source is not detailed enough to establish that. The animation assumes the intended route; a working follower and groove junction require additional design.
Primary references
Gardner D. Hiscox, Mechanical Movements, Powers, Devices and Appliances, no. 437, printed page 122: crossed grooves and alternating rod throws.
Hiscox, Gas, Gasoline and Oil Engines, printed pages 98–99, figure 28D: traversing push-rod end and different groove radii for alternate-revolution exhaust operation. The numerical groove law used here is a declared reconstruction, not a tracing of a dimensioned historical cam.
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