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Sanderson Engine Receives Patents on Mechanism for High-Efficiency Engine; Possible Hydraulic Hybrid Application

Cutaway drawing of the Sanderson engine.

Sanderson Engine Development Company (SED), which is developing a new engine that allows the conversion between reciprocating and rotational motion without the use of a conventional crankshaft, has been awarded three patents on critical elements of its technology.

The patents cover a piston assembly, an associated piston connecting joint, and a variable compression ratio mechanism. The piston joint and associated components are core components of the Sanderson Rocker Arm Mechanism (SRAM) invented by Robert and Albert Sanderson.

Among the applications for the engine currently being investigated is an integral hybrid hydraulic engine capable of powering a hydraulically-driven automobile.

In its simplest terms, the Sanderson Mechanism developed by SED is a variable-stroke system for single and multi-cylinder piston engines, using a patented configuration of universal joint and rocker arms to achieve remarkably low friction, small size, and high power-to-weight ratio. Other features are simple variable stroke adjustment, and very low noise and vibration.

The stroke is variable on all pistons simultaneously from a singe point control, easily controlled during engine operation even under all engine operating conditions. This feature is particularly valuable in increasing engine efficiency through higher CR, and reducing emissions, for example during cold-start and other conditions.

Sanderson prototype. Click to enlarge.

The SRAM concept allows the design and construction of a single integrated engine that incorporates a built-in hydraulic drive. This permits the elimination of numerous components normally required in hydraulically actuated vehicles such as log skidders and other commercial equipment.

Other potential applications being investigated for SRAM technology include pumps, compressors, refrigeration equipment, electric generators, agricultural and construction equipment, and hydraulic windmill systems.

The patent for the piston assembly  covers both single- and double-ended pistons that are connected to a unique rocker arm mechanism in a manner that enables the engine’s compression ratio to be changed by varying the piston stroke while the engine is operating. The patent covers the application of the variable combustion ratio technology to various types of engines including two- and four-stroke, diesel, multi-fuelled, steam powered, and others.

The patent for the piston joint covers a new type of sliding joint assembly that couples a single- or double-ended piston to the Sanderson rocker arm, which in turn permits the virtual elimination of piston side-load, thus reducing friction, heat, and engine wear. The piston joint represents one of the principal breakthrough technologies of the Sanderson Rocker Arm Mechanism.

The patent for the piston assembly includes the incorporation of a drive gear and associated components to enable varying the stroke of a piston between zero and maximum stroke. This permits the compression ratio of an engine to be changed while the engine is running.

John Fox, president of Sanderson Engine Development, said that the company is working toward licensing its SRAM technology to several vertical industry segments.

With escalating gasoline prices, SRAM engines will enable accelerated development of ultra high-efficiency vehicles that are much lighter than today’s automobiles and may reach previously unattainable levels of fuel efficiency. SRAM engine technology could achieve up to 75 miles per gallon or more in a mid-sized sedan or SUV.

—John Fox




Wait, 75mpg in a full sized SUV, under what conditions? If that's highway mileage, wouldn't it correspond to ~40-60% BTE?

perry hawkins

whats the point the oil compies will only raise the price accordly so you will never see cost benfit.i don't see the consumer getting more than 20 economic miles per gallon!the OIL COMPANIES WON'T STAND FOR IT!


New engines architectures have been proposed for over a centuries. Aside for the turbine none have managed to approached the popularity of the standard piston engine with crankshaft.


An absolutely wonderful mechanical engineering exercise that will never make it to production because its too late on the scene. At best it's four to five years before it can be built in quantities. GHGs were not discussed specifically; what the CO2 output? After all this is still an ICE with the same faults all ICEs have; albeit a more efficient one.

The talk of continuing the high CG point, unsafe, SUVs is scary especially when there is much to be gained by making cars lower and lighter. Quick-charge, medium-range BEVs are the correct autos for the majority of users with mass transit used for holiday and vacation trips.


People have been showing variable compression engines for years - eg Saab showed an engine with 8:1 to 14:1 VC. VC itself isn't new.


P Schager

They should have mentioned its potential when operated on high-octane altfuels such as ethanol or propane. As a flex-fuel engine, just the variable-CR capability should make it a much better performer, able to exploit the higher compression ratio available when running with that fuel instead of gasoline (given beefier bearings) and thus give miles-per-gallon that better show the potential of the fuel. Drivers with such an engine would save money when choosing either alternative fuel, so subsidies would not be needed anymore.

If it works, that's worth the price of admission. I'd check with the proponents of those fuels for development support, rather than auto manufacturers (who little care).

Because the pistons have no side forces, your chances would seem to be better of increasing the compression and operating temperature beyond previous limits set by lubrication. New NOX aftertreatments should enable this, and so you minimize all other pollutants while raising efficiency enough more to make it all worthwhile.

Like with a free-piston engine, it might make sense to put linear generators on the piston shafts to produce at least some output electrically, while bypassing the mechanical losses of the rocker system, for a hybrid or a range extender.


With a series hybrid, you could have an opposing piston design with no crankshaft and just linear alternators.

Then you oppose the vibration with an identical opposing phase pair. This configuration has been used in Stirling engine designs for quite a while.

Mike McCarthy

Second the motion on "just linear alternators" but to eliminate vibration, wouldn't you need at least two opposing pairs - - one pair on top, and the second pair, reversed opposing, on bottom (cylinders looked at from the end, upper left, upper right, lower left, lower right)?


Think of it as two of these "boxer" designs side by side and head to head. The two boxers are 180 degrees out of phase with each other.


It looks like a variation on a Scotch-yoke where the rotational motion is parallel to the pistons rather than perpendicular.

Does that rocker arm twist as the pistons move? What restricts it's movement? How do you start such a thing?


In four cylinder Stirling engines, they use a "swash plate". It is a plate that turns linear motion into rotary motion.


"Quick charge" is a nice concept and wish. That just doesn't and won't exist. Spend a few and compute it for yourself.


Having variable compression and variable torque is a great prize for sure.Can this supply the extra efficiency?
Otherwise the usual limitations and possibilities apply.
The arrangement is very similar to a(Sunbeam) sheep shearing hand piece, only the shears convert (cable drive) rotary motion to back and forth sliding action.
The torque and slides have fixed dimension.
does the job in this application.

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