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Hardenbrook and Rice's 1904 patent became the template for Gade engines. The ported exhaust shown in the patent drawing (referenced as item no. 90) is on top of the cylinder, but Gade engines had it on the right side of the cylinder.

Gas Engine Patents of Note

The air-cooled Gade engine is a bit of an enigma. Casual
inspection reveals a basic air-cooled horizontal engine with an
atmospheric inlet valve and a mechanically actuated exhaust valve.
The confusion comes upon noticing the placement of the muffler just
beyond the midpoint of the cylinder. For many people, this
automatically suggests a two-stroke engine, yet this surely has to
be a four-stroke owing to its use of intake and exhaust valves.
Then it runs, puffing exhaust from both the muffler and an
unchecked port in the cylinder head.

Ported Exhaust

That basic feature is arguably the Gade’s best-known
mechanical attribute, and it was spelled out in the patent
application filed in 1902 by Frank Hardenbrook and William Rice.
Patent no. 760,333 was awarded in 1904, and engines manufactured by
Gade Bros. Manufacturing Co., Iowa Falls, Iowa, hit the market the
same year using the patented design.

The novelty behind the Gade engine lay in its use of a ported
exhaust, a design copied and simultaneously developed by at least a
few other companies. The impetus behind the design was the desire
for a cooler-running engine. The Gade’s governor is set up to
hold the exhaust valve open on overrun. As with any atmospheric
intake, this means the engine will not pull a fuel/air charge as
there is no pressure differential to open the valve. But with the
ported design, this also introduced an additional cooling
mechanism.

With the exhaust valve held open, the engine draws fresh air
through the exhaust port during over-run. This air in turn travels
through the cylinder and vents through the port. Some quantity of
air then pulls back into the cylinder through the port and vents
through the exhaust valve. This combined current of fresh air draws
heat away, keeping running temperatures at tolerable levels – and
without the use of an auxiliary fan.

The port also supplies a secondary intake tract. The vacuum
created during the intake stroke means the pressure inside the
cylinder is less than atmospheric. When the port is exposed at the
bottom of the intake stroke, a small charge of air enters the
cylinder, mixing with the fuel/air mixture drawn through the intake
valve.

With the ported design the lion’s share of combustion gases
are released at the bottom of the power stroke. Importantly, this
means less work for the engine, since the piston doesn’t have
to push the hot exhaust gases through the poppet valve set in the
cylinder head. This means less strain on corresponding valve train
components and theoretically, at least, a more reliable engine.

Know of an interesting patent? Contact Gas Engine Magazine at:
1503 SW 42nd St., Topeka, KS 66609-1265; rbackus@ogdenpubs.com

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