An air motor is described having a variable volume air chamber 10 controlled by a reciprocating piston 12, intake and exhaust ports to and from the air chamber 10 controlled by respective cyclically actuated intake 14 and exhaust 18 valves for receiving compressed air from a compressed air storage tank 20 and discharging expanded air to the ambient atmosphere. The air motor is characterised in that it operates according to a four stroke cycle with an additional pair of air metering strokes prior to the expansion and exhaust strokes of the air motor, the pair of air metering strokes comprising an intake stroke during which compressed air from the compressed air storage tank 20 is admitted at substantially constant air tank pressure into an increasing volume of the air chamber 10 and a return displacement stroke during which some of the admitted compressed air in the air chamber 10 is returned at substantially the same air tank pressure from a decreasing volume of the air chamber 10 back to the compressed air storage tank 20. The pair of air metering strokes controls the quantity of compressed air retained in the air chamber 10 at the beginning of the expansion stroke of the air motor by the difference in mass flow transferred into and out of the air chamber 10 during the intake and return strokes respectively.
MA THOMAS TSOI-HEI [GB]; ZHAO HUA [GB]
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