Ships – Steering mechanism – Fluid pressure
Reexamination Certificate
2001-08-20
2003-05-20
Swinehart, Ed (Department: 3617)
Ships
Steering mechanism
Fluid pressure
Reexamination Certificate
active
06564739
ABSTRACT:
FIELD OF THE INVENTION
This application relates to a steering system for marine vessels employing a modified helm pump having a rotary encoder mechanically coupled to its input shaft. The system is operable in either power steering or manual hydraulic steering modes.
BACKGROUND OF THE INVENTION
Many small marine vessels, such as fishing boats, have manual hydraulic rather than power steering. Such vessels are controlled by rotating a steering wheel which causes delivery of hydraulic fluid from a helm pump directly to one or more steering cylinders which control the position of the vessel's rudder. The disadvantages of manual steering are well recognized. For example, the steering wheel must typically be rotated a large number of revolutions in order to change the direction of the vessel. Generally speaking, the larger the vessel, the more effort is required to steer manually.
Other steering problems may arise in large marine vessels such as tankers (which typically include power steering systems). The primary problem is that it is not possible to effectively steer such vessels from the wheelhouse if the power system fails. Rather, the pilot must instruct remote operators in the steering gear flat or compartment to manually alter the position of the steering cylinders. If this back-up voice communication system fails, or if the pilot's instructions are misunderstood or misinterpreted, safe control of the vessel may be lost.
Steering systems are known in the prior art having a primary electric control and a hydraulic back-up control. U.S. Pat. No. 4,736,811, Marsden et al., dated Apr. 12, 1988 relates to a steering system primarily designed for large earth moving construction and industrial vehicles rather than watercraft and hence it does not employ a helm pump. The steering system includes a steering wheel having a rotatable shaft coupled thereto. A sensor is provided for detecting the angular velocity of the shaft and directing an electrical signal to a control box. The control box, in turn, directs an electrical signal commensurate to the input signal from the sensor to energize a solenoid actuated pilot valve which in turn actuates the hydraulic steering system. The hydraulic steering circuit is disabled when the electrically controlled circuit is activated.
Since the Marsden et al. steering control system relates to land vehicles, a time delay between rotation of the steering wheel and adjustment of the steering control actuator is not permissible. Accordingly, in the Marsden et al. system a main pilot operated steering valve is provided for ensuring full flow of pressurized fluid to a steering piston in both the electric and hydraulic modes. The position of the steering wheel thus corresponds to an absolute steering position in both modes.
The Applicant has previously developed a steering signal conversion manifold specifically designed for watercraft for converting a manual hydraulic steering signal into a proportional electrical signal. The Applicant's conversion manifold is the subject of U.S. Pat. No. 5,146,745, the text and drawings of which are incorporated herein by reference. The manifold is connectable between a hydraulic fluid supply, such as a conventional helm pump, and a hydraulic steering cylinder controlling the operation of a steering tiller. The manifold includes a rotary actuator responsive to variations in flow of hydraulic fluid from the helm pump. In particular, the rotary actuator comprises a rotor shaft having a potentiometer mounted at one end thereof. In operation, when the steering wheel is turned in the power steering mode, hydraulic fluid is diverted from the helm pump into the manifold resulting in rotation of the manifold rotor shaft. This in turn causes the potentiometer to generate an electrical signal representative of the change in position of the rotary actuator and hence proportional to the manual hydraulic steering signal. In alternative embodiments of the invention, signal generating devices other than a potentiometer may be used for generating a proportional electrical signal, such as a hall effect device or an optical encoder.
While the steering signal conversion manifold of the '745 Patent is useful for its intended purpose and has exhibited commercial success, the Applicant has recognized that the same benefits may be achieved by other means. In the present invention, means for generating an electronic signal are coupled directly to the helm pump input shaft upstream from the hydraulic fluid supply lines. The signal generating means may comprise, for example, an optical encoder which generates signals responsive to rotation of the input shaft as the steering wheel is rotated. This arrangement is more versatile than the prior art system since the electronic signals generated do not necessarily correlate with absolute steering positions. Further, since the signal generating device is coupled directly to the pump input shaft, there is no time delay initiating the steering commands in the power steering mode.
Electric helms are known in the prior art which resemble a standard helm pump. However, when the steering wheel is turned a potentiometer sends an electrical signal to an amplifier controlling a power unit rather than pumping hydraulic fluid from the helm. No hydraulic back-up system is available in the event of power failure.
The need has arisen for a modified helm pump having a standard input shaft and dual hydraulic and electronic output. The invention may be conveniently retrofitted into existing vessels to provide power steering, and may also be readily installed in larger vessels to provide back-up, emergency manual steering.
SUMMARY OF THE INVENTION
In accordance with the invention, a marine helm pump assembly is provided comprising a helm pump for actuating the flow of hydraulic fluid and a first signal generator mounted on the helm pump. The helm pump includes a chamber for holding a supply of the hydraulic fluid; a single rotatable input shaft connectable to a steering wheel; and first and second fluid ports in communication with the chamber for enabling flow of the hydraulic fluid into and out of the helm pump in response to changes in position of the input shaft. The first signal generator is mounted on the helm pump and is operatively coupled to the input shaft for producing digital steering signals representative of changes in position of the input shaft.
Preferably the first signal generator is connected to the input shaft by means of a direct mechanical connection. For example, the signal generator may be mounted directly on the input shaft or may be coupled to the input shaft by means of a spur gear or belt connector. The signal generator may comprise, for example, an incremental optical encoder. Alternatively, a hall effect device or potentiometer may be employed. The assembly may further include a second signal generator also coupled to the input shaft in a similar manner for redundancy purposes.
A steering system for a marine vessel is also described enabling both electric power and manual hydraulic steering. The system includes a helm pump having a primary hydraulic fluid supply and a rotatable input shaft, the input shaft being connectable to a steering actuator, such as a steering wheel. In response to changes in position of the input shaft the helm pump pumps hydraulic fluid from the primary hydraulic fluid supply into hydraulic fluid supply lines connectable to a hydraulic steering cylinder for controlling the position of the vessel's rudder. A first signal generator is mounted on the helm pump and is operatively coupled to the input shaft for producing digital steering signals representative of changes in position of the input shaft.
Preferably the steering system further comprises a bypass manifold in fluid communication with the helm pump and the steering cylinder and located therebetween. The bypass manifold is adjustable between a first position permitting flow of hydraulic fluid between the helm pump and the steering cylinder and a second position blocking flow of hydraulic
Jastram Engineering Ltd.
Oyen Wiggs Green & Mutala
Swinehart Ed
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