Damped steering mechanism for a watercraft

A hydraulic damper is provided for a steering system, such as that of a boat or watercraft. A manually movable steering mechanism, such as a steering wheel, is connected to a piston and cylinder combination in such a way that rotation of the steering wheel causes relative movement between the piston and cylinder. Hydraulic fluid is disposed within the cylinder in such a way that movement between the cylinder and piston requires the hydraulic fluid to move from one portion of the cylinder to another portion of the cylinder. This fluid movement is conducted through a conduit which can be external to the cylinder or internal to the cylinder and extending through the piston.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention is generally related to a damping mechanism and, more 
particularly, to a hydraulically damped mechanism for the steering system 
of a boat. 
2. Description of the Prior Art 
Many different types of dampers are known to those skilled in the art. 
Dampers are typically used to slow the movement of one component in 
relation to another component. As such, dampers can be used to absorb 
vibration and other sudden motions. 
U.S. Pat. No. 5,257,828, which issued to Miller et al on Nov. 2, 1993, 
describes a method and apparatus for controlling damping in an electric 
assist steering system for vehicle yaw rate control. The electric assist 
steering system comprises a steering torque sensor and an electric assist 
variable reluctance motor operatively connected to a steering member. A 
motor control signal is provided in response to a value of the torque 
signal for control of the assist motor. A motor speed sensor senses speed 
of the power assist motor and a vehicle speed sensor senses the vehicle 
speed. A control circuit modifies the motor control signal in response to 
the sensed motor speed and the sensed vehicle speed signal so as to 
provide damping that is functionally related to both the motor speed and 
the vehicle speed for vehicle yaw rate control. 
U.S. Pat. No. 4,349,079, which issued to Leiber on Sep. 14, 1982, describes 
a power steering system for motor vehicles. The system comprises a 
measurement transducer for the steering direction in close relationship 
with a piston-cylinder unit which acts simultaneously as the steering 
damper and as the auxiliary force apparatus. The measurement transducer 
may also be integrated in the piston of the unit. The control of the 
hydraulic medium for the piston-cylinder unit takes place preferably via 
three position valves due to desired throttling in accordance with 
velocity of the return flow at a particular time. 
U.S. Pat. No. 4,736,962, which issued to Motrenec on Apr. 12, 1988, 
describes a steering stabilizer for vehicles. It is particularly 
applicable to handlebar controlled vehicles. The stabilizer utilizes a 
steering column housing having a cylindrical chamber therein. The steering 
column passes through the actual center of the chamber and hydraulic fluid 
is held within the chamber. A piston or vane is movable by the turning of 
the steering column and forces the hydraulic fluid through a restricted 
passageway whereby the turning of the handlebars is viscously damped. 
U.S. Pat. No. 5,052,528, which issued to Sullivan on Oct. 1, 1991, 
describes a steering knuckle damper. A limited stroke hydraulic actuator 
which may be located in the structure of a steered axle in a shallow blind 
bore is disclosed. The piston may be slidably received in the bore and is 
disposed by an adjustable protrusion secured to the steering system. 
Displacement of the piston causes hydraulic fluid to flow through an 
orifice from one side to the other. Resistance to flow of fluid through 
the orifice damps the motion of the piston and consequently the steering 
system. A spring returns the piston to an initial position when the 
steering system is removed from end of travel position. 
U.S. Pat. No. 5,603,391, which issued Class et al on Feb. 18, 1997, 
describes a damper valve for a power steering coupler. The invention 
relates generally to a damper valve for use on a coupler for hydraulic 
lines, and, in particular, those which connect a hydraulically actuated 
servomotor of a servo control to a servo valve. According to the 
invention, all the elements having a damping effect are arranged captively 
in the coupler. 
U.S. Pat. No. 5,607,035, which issued to Fulks et al on Mar. 4, 1997, 
describes a hydraulic damper. The damper is intended for use with a motor 
vehicle and comprises a longitudinally extending tube and a separately 
formed steering knuckle secured to the tube, wherein the tube is formed 
from extruded aluminum or aluminum alloy and the steering knuckle is 
formed from aluminum or aluminum alloy. The steering knuckle includes a 
tubular portion that overlies and is secured to a portion of the tube 
through the use of a groove in the tubular portion and a groove in the 
tube. Adhesive may be injected into the grooves to aid in securing the 
steering knuckle to the tube. 
U.S. Pat. No. 5,184,702, which issued to Schulze et al on Feb. 9, 1993, 
describes a hydraulic damper. The damper is designed as a piston-cylinder 
unit. The arrangement has a part forming a vibrational system by means of 
a spring. Vibrations acting on the damper arrangement are greater 
attenuated virtually only in the resonant range of the vibrational system 
because only in this case can vibrations of high amplitude be excited and 
a high dissipation of energy by way of hydraulic flows in channels and 
between cylinder chambers takes place. 
Newly developed steering systems for boats and other watercraft incorporate 
electronically controlled signals that eliminate the need for a direct 
mechanical or hydraulic connection between a steering wheel or other 
manually movable steering mechanism and the control surfaces which 
actually implement the steering command. For example, in an electrically 
controlled boat system incorporating either an outboard motor or a 
sterndrive, movement of a steering wheel by an operator can create 
electronic signals that result in the appropriate steering movement of the 
outboard motor or sterndrive, but the steering wheel is not directly 
connected to the outboard motor or sterndrive either hydraulically or 
mechanically. As a result, the operator feels virtually no resistance when 
the steering wheel is moved. In these types of steering systems, which are 
commonly referred to as "steer by wire" systems, the lack of feel or 
resistance in the steering wheel can lead to potentially dangerous 
circumstances. It would therefore be significantly beneficial if the 
steering mechanism of a boat or watercraft could be provided with a system 
that resists an operator's movement of the steering wheel in a manner that 
is similar to the natural resistance experienced by the operator of a boat 
or watercraft when a mechanical or hydraulic steering system is used. 
SUMMARY OF THE INVENTION 
A steering damper made in accordance with the present invention comprises a 
manually movable steering mechanism, such as a steering wheel, a cylinder, 
and a quantity of hydraulic fluid disposed within the cylinder. A piston 
is movable within the cylinder and a conduit connects a first portion of 
the cylinder in fluid communication with the second portion of the 
cylinder in order to allow the hydraulic fluid to flow from the first 
portion to the second portion in response to relative movement between the 
piston and the cylinder. The manually movable steering mechanisms is 
connected to a preselected one of the piston and cylinder to cause the 
relative movement between the piston and cylinder in response to movement 
of the manually movable steering mechanism. 
In a particularly preferred embodiment of the present invention, a valve is 
disposed in fluid communication with the conduit in order to affect the 
rate of flow through the conduit between first and second portions of the 
cylinder. The conduit can be disposed outside the cylinder or, 
alternatively, can be formed through the piston within the cylinder. In 
certain embodiments of the present invention, both types of conduits can 
be used. 
The manually movable steering mechanism can be attached in torque 
transmitting relation with either the cylinder or the piston to cause 
relative movement between the piston and cylinder in response to movement 
of the manually movable steering mechanism. 
A centering mechanism can be disposed within the cylinder in order to force 
the piston and the cylinder into a preferred position relative to each 
other when no manual force is exerted on the manually movable steering 
mechanism. The centering mechanism can comprise a spring that is disposed 
within the cylinder and in force transmitting relation with the piston.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Throughout the description of the preferred embodiment of the present 
invention, like components will be identified by like reference numerals. 
With the development of "steer by wire" control systems, a need arises for 
a method of providing a positive feel at the steering wheel in the absence 
of steering cables, hydraulic coupling systems, or other types of 
mechanical connections between the steering wheel and either the outboard 
motor or sterndrive. Without being coupled, either hydraulically or 
mechanically, to the outboard motor or sterndrive, the steering wheel 
would no longer experience the normal resistive forces in a manner similar 
to known systems. The operator could easily oversteer and experience 
difficulty in controlling the watercraft during steering maneuvers. Some 
means is necessary to simulate the feel of existing steering mechanisms, 
both mechanical and hydraulic, that are well known to those skilled in the 
art. 
Some steering dampers are known to those skilled in the art. These 
typically include a friction collar which resists rotation of a steering 
shaft. The amount of friction provided by these systems can be adjusted by 
turning a set screw that increases or decreases the force between the 
friction collar and the steering shaft. Unfortunately, friction dampers 
can become worn and require periodic adjustment. 
FIG. 1 shows a perspective view of one embodiment of the present invention. 
A steering shaft 10 is attached to a pinion gear 12 which, in turn, is 
disposed in meshing relation with a rack 14. A rod 18 is physically 
attached to a stationary object (not shown). Cylinder 20 is movable, in a 
left and right direction in FIG. 1, relative to the stationary shaft 18. A 
piston (not shown in FIG. 1) is disposed within the cylinder 20 and moves 
relative to the cylinder 20 in response to rotation of the steering shaft 
10. As the steering shaft 10 turns, pinion gear 12 meshes with the teeth 
of the rack 14 and forces the cylinder 20 to the left or right in response 
to the rotation of the steering shaft 10. A conduit 30 connects a first 
portion of the cylinder 20 in fluid communication with a second portion of 
the cylinder 20 to allow hydraulic fluid to flow to flow from the first 
portion to the second portion and vice versa. A valve 34 is disposed in 
fluid communication with the conduit 30 to control the flow of hydraulic 
through the conduit 30. An adjustment 38 is provided to affect the size of 
an orifice within the valve 34. By changing the size of the orifice by the 
adjustment screw 38, more or less resistance can be provided to the flow 
of hydraulic fluid through the conduit 30. This, in turn, has the effect 
of changing the resistance of movement of the cylinder 20 relative to the 
piston and the stationary shaft 18 to which the piston is attached. 
FIG. 2 is a sectional view of a cylinder 20, stationary rod 18, and conduit 
30. The valve 34 is shown with a schematically represented orifice 40. 
Inside the cylinder 20 is a piston 50. As can be seen, the piston 50 has 
another conduit 54 formed through its axial length. The location of the 
piston 50 within the cylinder 20 defines a first portion 61 and a second 
portion 62 of the cylinder 20. 
If the cylinder 20 is moved relative to the stationary rod 18, hydraulic 
fluid 66 must move from one side of the piston 50 to the other side of the 
piston 50 since the hydraulic fluid is incompressible. In FIG. 2, two 
conduits are provided for this movement. Some of the hydraulic fluid 62 
can move through the conduit 30 from one portion of the cylinder 20 to the 
other. In addition, hydraulic fluid 62 can also flow through the conduit 
54 that is formed through the piston 50. 
With continued reference to FIG. 2, a spring mechanism 70 is shown being 
disposed within the cylinder 20. In the embodiment of FIG. 2, two spring 
elements are provided, with one spring element being disposed on one side 
of the piston 50 and the other spring element being disposed on the 
opposite side of the piston 50. Although the spring mechanism is not 
required in all embodiments of the present invention, it can serve the 
purpose of centering the piston 50 within the cylinder 20. Therefore, when 
all force is removed from the system, the cylinder 20 will return to a 
central position with respect to the stationary shaft 18 and the piston 
50. 
In FIG. 3, the piston 50 is shown with four individual conduits 54 formed 
through its axial dimension. If the rod 18 is attached to a stationary 
object, as described above, movement of the cylinder 20 in the direction 
represented by arrow A will cause the volume of the first portion 61 to 
decrease while the second portion 62 increases. This requires hydraulic 
fluid to flow in the direction represented by arrows B from the first 
portion 61 to the second portion 62. The flow of the hydraulic fluid 
through the conduits 54 slows the relative movement between the cylinder 
20 and the piston 50. This slowing of the relative movement between the 
piston and the cylinder provides a natural feel for the boat operator as 
the steering wheel is turned. 
FIG. 4 is a schematic representation of a steering shaft 10, its attached 
pinion gear 12, a rack 14 attached to a cylinder 20, and a stationary rod 
18 which is rigidly attached to a stationary object that is schematically 
represented by the blocks identified by reference numeral 80. A steering 
wheel 84 is attached to the steering shaft 10 and can be used by a boat 
operator to rotate the steering shaft 10 and its attached pinion gear 12. 
This, in turn, causes the rack 14 and its attached cylinder 20 to move 
either left or right in FIG. 4, as represented by arrows C. Since the 
piston 50 (not shown in FIG. 4) is stationary and attached to the 
stationary rod 18, the cylinder 20 moves relative to the piston 50 and 
hydraulic fluid must pass through the conduits as described above in 
conjunction with FIGS. 1, 2, and 3. 
With continued reference to FIG. 4, a resolver 90 can be attached to the 
steering shaft 10 to provide a signal, on line 92, to an engine control 
unit 96. Even though the system in FIG. 4 represents a "steer by wire" 
system, the cylinder 20 and piston 50 provide a natural resistance to the 
movement of the steering wheel 84 by the operator. 
FIG. 5 shows an alternate embodiment of the present invention. In the 
embodiment of FIG. 5, the cylinder 20 is stationary and attached to a 
suitable structure through the use of legs 21. A piston 50 (not shown in 
FIG. 5) is disposed within the cylinder 20 and is movable relative to the 
cylinder 20. The piston 50 is attached to shaft 98 which, in turn, is 
attached to rack 14. The steering shaft 10 is attached to a pinion gear 12 
which is disposed in meshing relation with the rack 14. As the steering 
shaft 10 is rotated by a steering wheel 84 (not shown in FIG. 5), the rack 
14 is moved to the left or right in FIG. 5. This movement moves the rod 98 
which, in turn, moves the piston 50 within the cylinder 20. The same types 
of conduits, either the conduit 30 described above in conjunction with 
FIGS. 1 and 2 or the conduits 54 formed through the piston 50, can be used 
to allow a flow of hydraulic fluid from a first portion of the cylinder 20 
to a second portion of the cylinder 20, or vice versa. In the manner 
described above in FIG. 4, a resolver 90 can be used to provide a signal 
to an engine control unit 96 (not shown in FIG. 5). 
Although the present invention has been described in considerable detail 
and illustrated to show several embodiments of the present invention, it 
should be understood that alternative embodiments are also within its 
scope.