Ericsson’s Patent Model of a Cross-Compound Steam Engine – ca 1849

Description:

This model was filed with the application to the U.S. Patent Office for Patent Number 6,844 issued to John Ericsson of New York, New York on November 6, 1849. The patent was titled “Arrangement of Engine for Using Steam Expansively.” In a common engine design of the time, high pressure steam from a boiler was introduced to the engine’s cylinder for only a portion of the stroke. The steam “cut-off” valve was then closed, and the steam’s expansive force did the remainder of the work for that stroke. This saved fuel because of the reduced need for continuous high-pressure steam.

The goal of Mr. Ericsson’s invention was to improve the ability of an engine to use the expansive force of steam for efficiency while still providing uniform power throughout the stroke of the engine. In his design the resistance applied to the piston rod by the load on the engine decreased in the exact ratio of the decreasing pressure of the steam as it expanded in the cylinder. He achieved this by using two cylinders of differing sizes and exhausting the steam from the smaller cylinder into the larger. At the same time, steam pressure was balanced on both sides of the piston of the smaller cylinder. The relative sizes of the cylinders were carefully chosen to equalize the force on the engine’s crankshaft. The patent application claimed that this equal force was maintained even with the steam expanded by a factor of over twenty. This was a significant improvement over existing designs.

Mr. Ericsson was a prolific inventor; his inventions included many types of steam engines and associated apparatus as well as air engines. He was the designer of the USS Monitor for the North during the Civil War and designed its engine as well as numerous other marine steam engines.

The patent model as shown in the image is constructed of wood. All of the key elements of the patent are illustrated by the model including the arrangement of the crankshafts and the steam valves and their operating mechanisms. Diagrams showing the complete design of the patent can be found in the patent document online at the United States Patent and Trademark Office website, www.uspto.gov.