Powered by compressed air (or nitrogen), air motors are simple in design, offer variable speed, and are relatively inexpensive compared to electric motors. A key feature is the fact that they are explosion proof.
Blue Earth Technology LLC has developed a new, air-driven motor that it says offers a few new twists on this venerable old technology. Inventor Roy Rafalski says that the speed range of a proof-of-concept model, bench tested for maximum rpm with no load and simple use of magnetic switches to open and close air control valves located at head and cap end of each cylinder to time pressure pulses, is in the 100 to 850 rpm range.
He believes a maximum speed of 4000 rpm could be maintained with an electronic-valve timing controller and alternative air valves, allowing the motor to compete directly with a gasoline engine of similar output.
Design News was not given a description of the proprietary internal structure of the motor, only a photo (below) showing the motor's exterior and the following explanation: "It is simply straight-line motion produced from the cylinder at the full force being transferred into the rotary crank mechanism."
Rafalski claims that it is the first air motor design to use air cylinders to provide rotary motion. Based on the presence of the two silencers it appears that they are used in a single-acting mode. By operating the cylinders in a double-acting mode, whereby air pressure is delivered to the cap end of one cylinder and the head end of the opposite, Rafalski claims that the output torque increases by approximately 88%, but air consumption also rises.
One unique feature is the apparent external commutation of the air flow by means of two solenoid valves shown at the end of the two cylinders. Coupled with a shaft angle sensor (not shown) and an external controller, this would allow a suitable control program to provide optimum performance at all output levels. By altering valve timing, this could allow regenerative braking with little extra hardware - similar to torque and speed control on railroad steam engines.
Asked about the intended method of sensing shaft position and controlling the air valves, Rafalski says that air delivery could be controlled several ways, -- electronically or mechanically. In order to maintain a constant speed, torque output, for industrial applications, the system would require constant pulse width modulation.