The Trammel Engine is an internal combustion (IC) engine based on a well known motion mechanism, called a Trammel mechanism or an ellipsograph, which serves the function of coupling a linear oscillating motion to a rotational motion. In the traditional piston engine this function is performed by the crankshaft, connecting rod and piston (gudgeon) pin.

It can be easily proven that if the output of the Trammel engine has a constant angular velocity the piston pairs performs a true sinusoidal motion, equivalent of a traditional piston engine with an infinitely long connecting rod. It can also be easily proven that under the same circumstances the center of mass of the piston pairs (and the linkage) performs a steady circular motion, thus being simple to balance fully.

The challenge, in taking advantage of this mechanism in an engine with significant power, is to design an appropriate linkage. Three problems in particular seem to have held back such a design, namely connecting the rotational output from the front and back of the engine, the number of components needed to mechanically actuate the overhead valves and eliminating the inherent piston to cylinder side-loads, that the combustion pressure would generate. That there would be large side-loads can be visualized from fig.1 by fixing the center point of the linkage in space, applying a downward force to the top piston and realizing that the rotation of the linkage would result in a push of the vertical piston pair to the right and push of the horizontal piston pair upwards.

Fig.1 shows a conceptual drawing of the Trammel engine consisting of two perpendicular rigid piston pairs, connected through the outer pivot points of a clockwise rotating linkage having also a center pivot point performing a counter-clockwise circular orbit and through which a rotational output can be captured.

In the absence of the impacts of rocking pistons, there is the potential of applying brittle ceramic coating (thermal and anti friction) on the cylinder walls improving the efficiency.

The lack of friction between pistons and cylinders (friction between piston rings and cylinders is unchanged), which now is captured in a planetary gear, has a surprisingly large effect on the internal friction. The resulting fuel savings compared to a comparable 4-cylinder engine has been calculated and is shown in the figure below, which also can be interpreted as relative torque increase. Averaged over the working range for typical automotive use this corresponds to a fuel saving (or torque increase) of about 15%.

Fig.2 shows the calculated fuel saving of the Trammel engine relative to a similar 4-cylinder engine. High RPM and low load provides the most benefit.

A low cost mechanism overcoming the problems described previously has been designed and is patented (see references). A theory for the main internal forces has been developed and is documented in a compendium and in the patent. The first iteration is manufactured and has been successfully powered externally. The mechanical drawings for the second iteration of the basic engine are in the process of being done and a SAE paper on the subject has been written and was presented at Future of Transportation Technology (FTT) conference in Costa Mesa CA 1999. 

As can be seen from figure 1, a 4-cylinder configuration of the engine is the most natural, but others can be easily envisioned, such as 8-cylinders consisting of two "stacks" of 4-cylinders and down to two cylinders, accomplished by reducing each piston pair to a piston plus a guided counterweight, pump or the like, ensuring the center of mass is at the outer pivot point of the linkage (center of piston journal bearing).

In order to make the prototypes better than the best of near future traditional engines, some key components are necessary, namely an electronically controlled valve mechanism and comprehensive engine management hardware and software. Furthermore recent technological trends suggest the flywheel, alternator and starter can be substituted by an integrated starter-alternator-damper ISAD at the location of the traditional flywheel.

The Trammel mechanism has among other the following advantages relative to the traditional piston-connecting rod-crankshaft design:

Relative to the Wankel engine the following advantages are obtained:

*  RotaPower, designed by Moller International, Davis, CA is a compact Wankel engine with very low claimed emission. If true, this must be primarily due to their patented thermal/friction coating in which case the coating could be applied to any engine with the same relative improvement.

With the addition of computer controlled electro-magnetic actuated valves the following advantages, relative to both a Wankel and traditional piston engines without these valves, are obtained:

With the addition of a computer controlled ISADâ system the following advantages, relative to both a Wankel and traditional piston engines without this system, are obtained:

Fig.3 is a graphical representation of the expected improvement provided by the Trammel engine, using the best contemporary ICSI engine as a baseline (Std+EM-valve means standard engine with computer controlled electromagnetic valves).

In summary, the Trammel engine can be expected to be better than both future traditional piston and Wankel engines. More specifically better most and equal some of the critical design parameters for automotive IC engines such as low brake specific fuel consumption (bsfc), emission (HC, CO, NOx), NVH, high power density, broad-bandedness (wide RPM range) and expected low manufacturing cost, serviceability, durability, long service intervals and clean uncluttered appearance.

Recently Honda has shown natural gas vehicle based on a 1.6 liter gasoline engine with only few internal modification accomplishing 1/10th of ULEV emission. The Trammel engine is no more difficult to convert to natural gas.

I have now entered into a collaboration with Ginler Technologies who in parallel pursued the Trammel engine and simultaneous with the issuance of my patent arrived a the same idea of offloading the piston cylinder forces through a planetary gear. Their approach was to use an external shaft to index the front and back of the engine components. Patent number 5,189,994 and 6,006,619 captures their ideas.

It is expected that the engine needs three design iterations, at a duration of one year each, before a commercially attractive prototype will materialize.

Some references: 

"The Internal Combustion Engine in Theory and Practice", C.F. Taylor, MIT Press, 1992.
"Cruciform Engine", P. Gibbons, Costa Mesa, CA, Patent # 4,850,313, July 25, 1989.
"Electronic Valve Timing", L.A. Gould, W.E. Richeson and F.L. Erickson, Philips Industrial Electronics Company. Automotive Engineering, April 1991.
"Electro-magnetically Actuated Valve", F. B. Morinigo and K.O. Stuart, Aura Systems, El Segundo, CA, Patent # 5,222,714, June 29, 1993.
"Electro-magnetically Valve Actuator Drives Variable Valvetrain", M. Gottschalk. Design News, Nov.1993.
"Camless Engine", M.M. Schecter and M.B. Levin. SAE Technical Paper # 960581, Feb. 26-29, 1996.
"ISADâ A Computer Controlled Starter-Alternator-damper-System", Klaus-Peter Zeyen and Thomas Pels. SAE Technical Paper # 972660, Aug. 6-8, 1997.
"The Integrated Starter Alternator Damper: The First Step Toward Hybrid Electric Vehicles", C. Peter Cho - Delco Remy America Inc. William B. Wylam - Delco Remy America Inc. SAE Technical Paper # 2000-01-1571, Future Car Congress, April 2000.
"Near-Zero Emission Natural Gas Vehicle, Honda Civic GX", Toshiuki Suga, Ben Knight and Sakuji Arai. SAE Technical Paper # 972643, Aug. 6-8, 1997.
"Soft Landing Electro-magnetically Actuated Engine Valve", R.E.Diel et Al., Ford Global Technologies, Patent # 5,730,091, March 24, 1998.
"Internal Combustion Engine Equipped with Electromagnetic Valve Driving Apparatus and Head Structure Thereof", T.Izuo, Toyota Japan, Patent # 5,720,242, February 24, 1998.
"Internal Combustion Engine", L.Pedersen, Patent # 5,782,213, July 21, 1998.
"Trammel Engine Crank Mechanism", L.G.Pedersen, SAE Technical Paper # 2000-01-3073  SP-1559.

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