Overload protection control circuit for marine engines

Claim 1

An overload protection circuit for a marine engine comprising: (a) servo-positioning means including a double-acting piston device and gear means connected thereto and operable thereby for setting propeller pitch, either forward or reverse, in accordance with the predominating one of respective opposing fluid pressure signals acting on opposite sides of said piston device; (b) relay valve means including a pair of opposingly arranged pressure chambers; (c) first conduit means for transmitting an operator-initiated fluid pressure speed control signal to one of said pressure chambers of said relay valve means and to a fuel rack positioner device, said fuel rack positioner being effective for producing a backfeed fuel rack position signal transmitted to the other of said pressure chambers of said relay valve means, (d) said relay valve means being operable for producing a fluid pressure propeller pitch correction signal, in accordance with the ratio of said speed control signal and said fuel rack position signal, and transmitting said correction signal to one side of said opposite sides of said double-acting piston device and effecting both direction and degree of propeller pitch accordingly; (e) second conduit means for transmitting an operator-initiated fluid pressure propeller pitch control signal to the other side of said opposite sides of said piston device and cooperating with said correction signal for setting the position of the piston device and consequently propeller pitch in accordance with the relationship of the respective fluid pressure signals acting concurrently on said opposite sides, (f) said piston device being operable to assume a neutral position in which propeller pitch is zero when the pressures acting on said opposite sides are equal; and (g) overload limiting valve means interposed in said second conduit means between said relay valve means and said servo-positioning means, said overload limiting valve means having a preset pressure limit and being operable responsively to said correction signal at a pressure exceeding said pre-set pressure limit, to a certain supply position in which said fluid pressure pitch control signal is communicated concurrently to both said opposite sides of said piston device for effecting operation thereof to its said neutral position in which propeller pitch is reduced to zero.