1. Field of the Invention
This invention relates to an expander/prime mover for extracting heat and mechanical energy from a pressured gas, particularly to a piston type expander having dual, independent rotatable mechanical outputs.
2. Description of the Prior Art
The great majority of rotary engines designed for operation by a pressured gas have utilized linearly reciprocating pistons and cylinders. Similarly, many expanders have resorted to the use of linearly reciprocating pistons and cylinders. In most instances known to Applicant, the pistons have been connected to a crankshaft and in this manner, the reciprocating movements of all the pistons produced by expansion of a pressured gas in the cylinders is converted into a rotational power output, while the gas is concurrently cooled.
The utilization of a crankshaft inherently involves expensive precision manufacturing operations in order to ensure the balance of the crankshaft. Additionally, the successive power strokes of each piston are delayed by an interval determined by the rotational speed of the crankshaft, since this determines the time required for the piston to return from its bottom dead center position to its top dead center position in its respective cylinder. For this reason, the utilization of fluid pressure engines is primarily confined to low torque, high speed applications. It inherently does not have the ability to generate a substantial torque at low speeds due to the substantial delay in the successive expansions of the pressured gas charges supplied to each cylinder. Additionally, there is the well known deficiency involved in every crankshaft of the effective moment arm of the piston force varying cyclically from zero to a maximum and then back to zero as the piston proceeds through its entire power stroke.
In co-pending application Ser. No. 634,846, filed July 26, 1984 and assigned to the assignee of this application, there is disclosed an apparatus for producing a mechanical rotating output by expansion of a pressured gas in a plurality of cylinders arranged on a circular support in an equally spaced array about the axis of a rotatable shaft to which the cylinder support is secured. The pistons cooperating with the cylinders are secured to one rotary element of a unidirectional (over-running) clutch which is constructed so that movement of the pistons in one direction relative to the cylinders is prevented while movement of the pistons in the opposite direction is permitted. A load driving element is connected to the rotatable shaft on which the cylinders are mounted and hence an intermittent rotational power output is provided by such shaft due to the reaction forces intermittently acting on the cylinders.
In co-pending application Ser. No. 678,439, filed Dec. 5, 1984 and assigned to the assignee of this application, a plurality of cylinders are mounted in a peripherally spaced array about the axis of a power output shaft, but the support structure for the cylinders is rigidly secured to one of the bearing supports for the shaft. The cooperating piston elements are again connected to a rotatable element of a unidirectional (over-running) clutch mounted on the shaft and impart a periodic rotation to the power output shaft through the unidirectional (over-running) clutch, but can move back to their positions relative to the cooperating cylinders free of any connection to the rotating power output shaft.
In both of these prior art constructions, the open inner ends of the peripherally spaced array of cylinders communicate with a fluid pressure chamber within which a small pressure is maintained, sufficient to return the piston (or the cylinders), as the case may be, to their power stroke initiating positions wherein the pistons are disposed adjacent the outer closed end of the cylinders, ready to receive another charge of pressured gas. This necessarily involves a slight loss in mechanical efficiency of the expander due to the mechanical effort required to return the relatively light weight pistons to their power stroke initiating positions in the cylinders. If the pistons can be rapidly returned to their power stroke initiating positions relative to the cylinders while developing a useful mechanical output, obviously, the overall efficiency of the expander can be improved.