Method of and apparatus for controlling a variable pitch steering propeller

BACKGROUND OF THE INVENTION

This invention relates to a method of and an apparatus for controlling a variable pitch propeller, and particularly for controlling a steering propeller located in a tunnel extending athwart the hull of a ship.

Steering propeller installations of the kind referred to above, such as that described and shown in, for example, U.S. Pat. No. 3,002,486, provide a turning effect on the ship by the action of a steering propeller that drives a stream of water through a tunnel athwart the ship. The steering propeller is usually driven by an electric motor, although other sources of driving power may be used. The blades of the steering propeller are mounted to a hub in a manner such that their pitch may be adjusted, generaLly by means of a hydraulic adjusting mechanism comprising a hydraulic cylinder and piston arranged in the hub and equipment for providing and controlling the delivery of a hydraulic fluid to the cylinder. The hydraulic adjusting mechanism is usually arranged for remote control from the bridge of the ship. By adjustment of the blades, the steering propeller can be set to different pitches, from maximum pitch in one direction to maximum pitch in the opposite direction, without reversing the direction of rotation of the propeller.

A steering propeller, especially one located in a tunnel athwart the hull, is often operated under conditions which vary considerably as a result of such changing factors as the direction of movement of the ship relative to the water and is also subject to intrusion of foreign objects, e.g., ice or debris into the tunnel which affect operation. Because steering propeller installations known heretofore are, in principle, arranged for direct setting of the propeller pitch from the bridge, there is always a risk that the pitch may be set to values which, under certain conditions of operation, will overload the driving motor of the steering propeller or means that the propeller installation may not be utilized in the most efficient way. An overload may cause motor breakdown and consequent lost steering ability.

SUMMARY OF THE INVENTION

There is provided, in accordance with the invention, a method of and an apparatus for controlling the steering effect of a controllable pitch steering propeller by which any desired steering effect is obtained under all operating conditions, without any risk that the driving motor of the steering propeller will be overloaded.

The energy requirement for powering a steering propeller is determined by the pitch and the speed of the propeller as well as by the operating conditions, for example, the speed and direction of the ship relative to the water and the presence of obstacles such as ice or debris in the tunnel. One aspect of the invention is a solution for the problem of how to limit the power consumption of the steering propeller to values that do not exceed the safe-operating power of the driving motor and that provide for the intended steering effect.

The method, according to the invention, involves, basically, the control of the pitch-setting mechanism of the propeller blades in accordance with a signal from a control device representing the difference between, on one hand, a “reference value” signal indicative of a desired output of the driving power of the steering propeller and, on the other hand, an actual load” signal indicative of the actual power output of the driving motor or engine.

Apparatus according to the invention comprises a manually adjustable controller that generates a “reference value” signal corresponding to the desired output of the steering propeller and a load-monitoring device associated with the motor powering the propeller that produces an “actual load” signal corresponding to the actual power output of the motor and a comparator that receives the signals from the controller and the load-monitoring device and produces from then a control signal which is used to control the hydraulic pitch-setting mechanism of the propeller blades in such a way that the propeller blades will be set to a pitch corresponding to the desired output.

The transverse thrust for steering a ship, which is produced by the steering propeller, is mainly determined by the power consumed by the steering propeller. It is therefore advantageous to control this power directly within the proper limits allowed for the motor. When the steering propeller is driven by an electric AC motor, as it is in most cases, the supply voltage and operating speed will be essentially constant and the motor output load-sensing device may therefore comprise a current transformer connected in the power supply line to the motor, since the motor power output under those conditions is proportional to the current.

DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention, reference may be made to the following description of an exemplary embodiment of the method and apparatus, taken in conjunction with the accompanying drawing, which is a schematic illustration of the embodiment of the apparatus.

DESCRIPTION OF AN EXEMPLARY EMBODIMENT

The embodiment of the control system, according to the invention, is depicted in the drawing in association with a marine steering system that comprises a propeller 1 mounted in a transverse tunnel through the hull of a ship (not shown) and driven by an electric motor 9 through an appropriate gear system 7. The blades S of the propeller are mounted on a hub 3 in such a manner as to be rotatable about radial axes, relative to the hub, to provide pitch settings ranging from a maximum pitch to provide propulsion in one direction to a maximum pitch providing propulsion iri the other direction. The pitch of the propeller blades 5 is altered and is maintained in any selected position by a hydraulic pitch-setting mechanism Il composed of a hydraulic cylinder 13 having a double-acting piston 15 and supplied from a source of hydraulic pressure 21 through a controllable valve 17, such as a solenoid valve. The hydraulic pressure source 21 may be connected, by way of the hydraulic lines 23 to the cylinder 13 selectively to deliver pressure to either side of the piston 15 in accordance with the position of the valve. If the valve 17 is set so that hydraulic pressure is delivered to the left side of the piston, the pitch of the propeller blades 5 is changed in one direction, an similarly the delivery of hydraulic pressure to the right side of the piston alters the propeller pitch in the other direction. In either case, the fluid pressure is bled from the cylinder through the nonactive supply conduit 23. Various specific designs for the hydraulic pitch-setting mechanism and the coupling of the mechanism to the propeller blades have been proposed and used, and the control system, according to the invention, may be used with a variety of different specific designs.

The activation of the steering system and the control of its operation is preferably accomplished from the bridge of the ship, and to that end, a controller 25 is provided on the bridge. The controller includes a start-stop switch 26, or any other suitable medium for starting and stopping the motor 9 and activating the control system when it is desired to use the steering system to maneuver the ship. The starting apparatus is operated at the bridge and initiates the starting sequence provided by the motor start control 28, which may be any suitable form of starting circuitry, usually relay circuitry, for starting and running the motor 9 up to speed. As will be described below, the steering control system ensures that the propeller blades are in a neutral (zero pitch) position during motor starting, so that the load on the electric drive motor is at a minimum until the motor has reached operating speed.

The controller 25 is provided with a suitable device for generating a variable reference signal representing a desired

3,589 3 propulsion output, or loading, of the propeller so that a desired steering effect is obtained. Such a device may include any suitable electrical or electronic components or circuits capable of developing a continuously variable electrical signal; it may comprise, for example, an autotransformer of 5 which the output is a continuously variable alternating current signal. At the controller 25 on the bridge, a control lever is adjusted by the operator to select any desired propeller loading over a range corresponding to a maximum propeller power output in one direction to a maximum power output in the other direction (i.e., full starboard or full port steering effect). Thus, once the steering system is activated, movement of the lever 27 to any position results in the development of a corresponding reference signal on the conductor 25α, which in turn controls the desired steering propeller output and direction. However, an appropriate interlock between the motor start control and the controller prevents operation of the control system until the motor 9 has reached operating speed. The maximum reference signal generated by the controller 25, for either pitch direction, is limited to a value that provides a propeller power output that is not in excess of a safe-operating load on the motor 9. As will be apparent below, the controller thus establishes a maximum power load on the motor and prevents overloading and the consequent possibility of damage to or burnout of the motor.

The power output of the motor is continuously monitored and a signal produced that is compared with the reference signal set on the controller 25. When an electric motor of the type operating at a constant voltage and constant speed is used, i.e., a synchronous motor, the power monitor 33 may comprise a current amplifier receiving an AC signal from a current transformer (not shown) in the line (s) between the power supply and motor armature. The power monitor 33 provides a continuous signal indicative of the actual power output of the motor, such signal being appropriately termed an “actual load” signal. The actual load signal from the power monitor 33 and the reference signal from the controller 25 are compared in a comparator 29, which may be of any of a number of electrical or electronic devices that are, per se, well known in the art, such as voltage, phase or polarity detecting relay circuits. The comparator 29 detects any difference between the actual load signal and the reference signal and produces an output signal on the conductor 30, representative of an error or correction value, and the correction signal is used to operate the solenoid valve 17 in an appropriate manner to deliver hydraulic pressure to the hydraulic cylinder to alter the pitch in the manner required to match the actual propeller output with the preset control value selected at the controller 25. For convenience, the actual load signal from the power monitor 33 may be referred to as the first signal, the reference signal from the controller 25 may be referred to as the second signal, and the correction signal from the comparator 29 may be referred to as the third signal.

For example, if it is desired to establish a maximum steering effect in the starboard direction, the controller operating lever 27, which is a manually operable control located on the bridge of the ship, is moved to an indicated position, such that the controller generates a reference signal corresponding to the maximum output of the propeller to provide propulsion in the starboard direction. Assuming that the motor has been started up and is running at speed, the reference signal on the conductor 25α and the signal from the power monitor 33 (representing the actual power being delivered by the motor) are compared in the comparator. Inasmuch as the motor is then running at approximately a no-load, or minimum load, condition with the propeller pitch at neutral, an error signal is generated and is applied to the solenoid valve 17 to shift the valve to a position providing delivery of hydraulic pressure to the part of the cylinder appropriate to drive the piston in a direction to adjust the blade pitch for starboard thrust. As the propeller blade pitch is changed, the load on the motor increases and the actual load signal from the monitor 33 similarly increases; but as long as there is an error signal at the

830 comparator output, the pitch of the propeller will continue to increase. When the actual load signal attains a value matching the reference signal, which means that the motor load corresponds to the desired propulsion output of the propeller, the error signal decreases to a minimum value and the solenoid valve is shifted to a position shutting off the hydraulic line, thereby leaving the propeller pitch set to the proper position.

If there should be a change in the operating conditions in the tunnel, such as might be caused by the intrusion of ice or 1® debris, which would increase the motor above the maximum safe-operating load at the existing propeller pitch, an increased error signal is generated in the comparator and is supplied to the solenoid valve to reduce the propeller pitch until 5 there is again a balance between the motor output and the present propeller output. When a balanced condition is again established, the error signal again drops to its minimum value, and the propeller blades remain set in the new, readjusted pitch position.

2q Accordingly, the control system, according to the invention, provides for the maintenance of a preestablished propeller power output regardless of the conditions under which the propeller is operating and in accordance with any change in the conditions in the steering propeller tunnel. The propeller blade pitch will be altered appropriately by the control system without manual correction by the operator to maintain a desired propulsion output in a given direction, but in no case placing a demand on the motor in excess of a safe-operating load.

As a further safety feature, the apparatus of the invention also includes a system for ensuring that the motor cannot be started when the propeller blades are in any position other than a neutral pitch position, thus providing for starting the motor under a minimum load condition. In particular, the ap35 paratus includes a pitch position monitor 35, which may be any suitable electromechanical or electrical device. Inasmuch as the piston occupies a position in the cylinder that is directly related to the pitch position of the propeller blades, the position of the piston in the cylinder provides a convenient indica40 tor and mechanical arrangement for monitoring the pitch position. The pitch position monitor 35 may be arranged to be under the control of the controller 25 so that an any time the controller is operated to start the motor the pitch position monitor is also energized. The monitor is preferably arranged 45 to provide an interlock signal, on a conductor 36, which renders the motor start control 28 inoperative. If the propeller blades are in any position other than a neutral position, the motor start control is thus overridden. In the meantime, the pitch position monitor 35 also generates a signal indicative of the propeller pitch position, and that signal is supplied to a comparator 29α, which may actually be a subcomponent of the main comparator 29.

The controller 25 is arranged automatically to provide, at 55 such time as the motor power is turned off, a reference signal and to conduct the signal to the comparator 29α. Such reference signal is representative of the desired pitch, usually neutral position, of the propeller blades during motor start-up. The comparator 29α compares that reference signal with the gQ pitch position monitor signal and produces an error signal which controls the operation of the solenoid valve 17. The reference signal is established at a value sufficient to produce in the comparator an error signal for any position of the propeller blades other than the desired position of the blades 65 during motor starting. The error signal is connected to the solenoid valve over the conductor 31 and actuates the valve appropriately to provide hydraulic pressure delivery to the cylinder in a manner such as to actuate the hydraulic mechanism and move the propeller blades to the starting posi70 tion.

Preferably, the controller is designed to carry out the starting, or zero pitch, adjustment automatically whenever the steering system is turned off. This can be accomplished in a number of ways, such as by providing a timer or latching relay 75 to maintain the pitch position monitor and hydraulic pressure

3,51 5 equipment in operation for either a sufficient time to complete a centering operation or until such time as the centering operation is completed with automatic shut-off. In the simplest case, the comparator 29a may be made operable only when the start-stop switch 26 is in the “off” position, during which time the comparator 29 is inoperative. Accordingly, the propeller blades are moved to a neutral pitch position when the steering system is shut down and are therefore in a position for starting up when the steering system is activated again.

The embodiment of the invention described above is intended to be merely exemplary, and those skilled in the art will be able to make numerous variations and modifications of it without departing from the spirit and scope of the invention. Thus, the particular units described above may be replaced by equivalent units of different types, but operating in substantially the same manner. Moreover, the system may be adapted to propeller power sources of other types, such as a direct current motor or a diesel engine, by providing an appropriate type of unit to monitor and produce a signal indicative of the output power.