Marine propulsion systems with variable-pitch screw propellers

Abstract

Marine propulsion equipment for installation in a ship or boat comprises a screw propeller with variable-pitch blades, mounted on one end of a propeller shaft whose other end is coupled to the output flange of a reversible speed-reduction gearbox. A pitch control rod is connected at one end through a linkage to the blades and extends within an axial bore in the shaft, the rod being longitudinally movable by a hydraulic actuator between predetermined limiting positions corresponding respectively to a coarse-pitch setting and a fine-pitch setting of the screw blades. The actuator is of piston-and-cylinder type interposed between the output shaft of the gearbox and the adjacent end of the propeller shaft as a part of the drive train. The actuator cylinder is formed either in a half-coupling which connects the shaft to the gearbox output flange, or in a separate tubular capsule which is itself connected between the half-coupling and the gearbox output flange. The piston of the actuator is rigidly secured, directly or via an intermediate piston rod, to the end of the pitch control rod remote from the propeller. Pressurized hydraulic fluid is admitted through a longitudinal passage in the output shaft of the gearbox, under the control of, for example, a solenoid-operated valve, into the actuator cylinder to drive the piston and pitch control rod in the direction towards the propeller into a limiting position corresponding to a fine-pitch forward setting of the blade angle, against the force of return spring means. When the actuator is de-pressurized, the return spring means returns the piston and pitch control rod to a second limiting position corresponding to a coarse-pitch forward setting of the blade angle. The limiting positions are determined by stops at opposite ends of the cylinder against which the piston abuts.