Monovalve 4-Stroke Diesel Engine Patent

Patent Page: C.A. Winslow's patent for a monovalve engine.

C.A. Winslow's monovalve diesel

C.A. Winslow’s 1933 patent for a monovalve 4-stroke diesel engine.

Image courtesy U.S. Patent Office

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In the quest for durability and dependability, the old dictum “less is more” has been the hallmark of many successful engine designs. In the early 1930s, San Francisco, California, inventor Charles A. Winslow pursued the idea of using a single poppet valve – a monovalve – to control both intake and exhaust flow to create a new range of efficient and dependable diesel engines.

The idea wasn’t new – Rudolf Diesel patented a monovalve engine in 1895 – but prior to Winslow’s engine, few monovalve designs had made it beyond the drawing board. In late 1932, Winslow secured development funding and built a working single-cylinder prototype of his monovalve engine, setting up the American Diesel Engine Co. in the old Standard Gas Engine Co. factory in Oakland, California. Based on the success of that prototype, Winslow took his design into limited production with a range of 2- and 4-cylinder engines. A 6-cylinder engine was apparently proposed, but whether one was built is unknown.

Designed with an eye toward industrial and marine use, where steady engine speeds are the rule, Wilson’s engine held a single valve open for 444 degrees for each working cycle of 720 degrees of crankshaft rotation. Closed on compression and combustion, the single valve lifted for the exhaust stroke and stayed open until the end of the intake stroke. As the exhaust rushed out at high speed, it created a vacuum in a venturi in the combined intake and exhaust manifold, drawing in fresh air behind the exiting exhaust. As the exhaust rushed out, the fresh intake air rushed in behind it and was then drawn into the cylinder as the piston began its downward stroke. The valve then closed and the 4-stroke cycle was repeated. Winslow claimed the design benefited engine durability as the incoming air charge cooled the single valve, prolonging working life.

Interestingly, this was one of the few known flathead diesel engines, and would appear to have depended upon the flathead design, with the single valve placed alongside the cylinder and the combustion chamber concentrated above the valve and only partially extending into the cylinder. It was also somewhat unique in requiring no glow plugs or other heating aides for starting, which was by electric starter.

As patented, Winslow’s engine included a hydraulic valve lifter and an oil pressure operated fuel pump. In the event of low oil pressure the hydraulic lifter would partially collapse, resulting in noisy valve operation and reduced power output, a signal to the operator of needed engine attention. Further, in the event of a total loss of pressure the fuel pump would stop functioning altogether. Winslow’s design also included a crankshaft-driven induction fan – essentially a compressor – to deliver the incoming air charge.

Apparently, some of those features were dropped in production. American Diesel literature specified standard Bosch diesel fuel pumps and gave valve adjustment specifications, suggesting a conventional setup. A subsequent 1938 patent showed a revamped overhead valve design, but it doesn’t appear any were built to that specification.

Just how many engines were produced by Winslow’s American Diesel Engine Co. is unknown, but it couldn’t have been many. California engine and tractor historian Jack Alexander knows of four survivors, and recently acquired a 4-cylinder 75 hp Model 4-75 G stationary. Those numbers suggest that whatever the design’s merit, it was never built in large enough numbers to significantly impact the market.

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