Information
-
Patent Grant
-
6350164
-
Patent Number
6,350,164
-
Date Filed
Friday, March 31, 200024 years ago
-
Date Issued
Tuesday, February 26, 200222 years ago
-
Inventors
-
Original Assignees
-
Examiners
Agents
- Fletcher, Yoder & Van Someren
-
CPC
-
US Classifications
Field of Search
US
- 114 150
- 114 151
- 114 144 B
- 440 6
- 440 38
-
International Classifications
-
Abstract
A technique is provided for steering and navigating a watercraft. The technique provides for dual electric motor propulsion units aft of a transverse centerline of the watercraft. A forward thruster system is provided forward of the transverse centerline. The rear drive units provide components of thrust for navigating the craft through straight-ahead settings and turning settings. The forward thruster system provides additional thrust components for moving the watercraft in a “sliding” direction, and for providing additional turning thrust. The system is particularly well suited to slow-speed navigation, such as for recreational fishing, as well as for close quarters navigation and docking.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to the field of steering and navigation systems for watercraft, and particularly for pleasure craft. Even more particularly, the invention relates to a technique which employs dual electric motor stem drives in conjunction with a forward thruster for a range of navigational controls.
2. Description of the Related Art
Various systems and configurations have been proposed and are currently in use for navigating watercraft. Depending upon the size and use of the watercraft, these systems include both internal combustion-driven propulsion units, and electric motor drives. In the former case, outboard motors may be mounted to a transom of a boat, and used alone or in tandem to produce the desired thrust for navigating the boat for its intended use. Similarly, inboard motors typically include an internal combustion engine housed within a compartment of the hull, with a driven propeller extending through the hull to propel the boat in a similar manner.
Electric motor drives for watercraft have been developed, and are particularly well suited to slow-speed and special purpose applications. For example, trolling motors and electric outboards are available for slow-speed navigation, and are well suited to fishing boats, wherein quiet operation is essential. Indeed, electric motor drives are the favored solution for such activities, and are typically used in tandem with outboard or inboard motor systems to provide flexibility and to enhance the utility of the craft for a wide range of activities.
While propulsion systems of the type described above are generally suitable for many uses, they are not without drawbacks. For example, internal combustion engine-driven systems are simply unsuitable for applications in which low noise levels, low emission levels, and low speed navigation are important. Similarly, conventional electric propulsion systems often do not provide a desired degree of navigational flexibility, and suffer from a tendency to become entangled in weeds or other plants growth, to contact submerged objects and obstructions, and so forth. Moreover, conventional trolling motor systems typically require that a drive unit and directional unit be rigidly mounted to a deck surface, both during deployment and when stowed. Consequently, a second of the deck becomes essentially unusable and is severely obstructed. These systems also detract from the aesthetic appeal of the watercraft, and may provide an unacceptable level of aerodynamic drag, both when deployed and when stowed.
There is a need, therefore, for an improved propulsion and navigation system for watercraft, particularly for pleasure craft. There is, at present, a particular need for a system which would eliminate or reduce the need for deck encumbrances, while providing effective low-speed navigation and steering. Furthermore, there is a need for a system which can be retrofitted to existing boat designs, as well as incorporated into new designs, controlled through relatively intuitive control devices, and provide as user-friendly a navigation system as possible.
SUMMARY OF THE INVENTION
The invention provides a navigation system for a watercraft designed to respond to these needs. The system may be retrofitted to existing boat designs, but is particularly well suited to new designs which specifically incorporate its features integrally with other hull and control elements. The technique makes use of a series of propulsion units which operate in cooperation. In particular, a pair of electric motor propulsion systems are provided in the stern region of the watercraft and may be driven at various speeds and directions to produce resultant thrust components for navigating the craft. A forward thruster unit compliments the rear propulsion units to produce thrust components which are at least partially transverse to a longitudinal centerline of the craft. That is, the forward thruster unit enables the craft to be navigated in lateral directions, either through turns (i.e. rotation of the hull) or through “sliding” type movement (i.e. lateral movement without rotation of the hull).
The resulting system and controls enable a wide range of navigational commands. For example, the system may be employed for relatively slow-speed navigation during activities such as fishing. In this type of operation, the technique allows for replacement or reduced dependency on conventional trolling motor or electric outboard systems. Moreover, the technique facilitates navigation into tight areas, such as between trees, stumps, and similar obstacles in a manner heretofore unavailable through conventional propulsion systems. Similarly, the technique allows for simplified docking by providing a high degree of low-speed navigability.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing and other advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings in which:
FIG. 1
is a perspective view of a watercraft incorporating certain features in accordance with the present technique;
FIG. 2
is a diagrammatical plan view of the watercraft of
FIG. 1
illustrating the layout of a propulsion system comprising electric motor drives positioned in a stern region of a hull;
FIG. 3
is a diagrammatical representation of the stern region of the watercraft of
FIG. 2
illustrating components of thrust produced by the propulsion units;
FIG. 4
is a diagrammatical side view of one of the units shown in
FIG. 3
illustrating an exemplary vertical offset;
FIG. 5
is a top plan view of the stern region of the watercraft illustrated in the previous figures, showing the placement of the propulsion units within cavities formed within the hull;
FIG. 6
is a rear elevational view of the stern region shown in
FIG. 5
with the propulsion units in place, illustrating a manner in which the props may be lodged within recesses formed in the hull;
FIG. 7
is a bottom plan view of the stern region shown in
FIG. 5
illustrating the placement of the propulsion unit props within recesses of the hull;
FIG. 8
is a partial sectional view along line
8
—
8
of
FIG. 7
illustrating the position of one of the propulsion units within the recess formed in the hull;
FIG. 9
is a partial sectional view along line
9
—
9
of
FIG. 7
, again illustrating the placement of one of the propulsion units within the hull;
FIG. 10
is a plan view of one of the propulsion units illustrated in the previous figures, removed from the hull for explanatory purposes;
FIGS. 10
a
and
10
b
are perspective and exploded views, respectively, of a preferred embodiment of a propulsion unit for use in the present technique where a rigid transmission arrangement can be employed;
FIG. 11
is a perspective view of a control unit, in the form of a foot pedal control, for inputting operator commands used to navigate the watercraft by powering the propulsion units illustrated in the foregoing figures;
FIG. 12
is a diagrammatical representation of certain of the control input devices associated with the control unit of
FIG. 11
in connection with a control circuit for regulating speed and direction of the propulsion units;
FIG. 13
is a graphical representation of drive signals applied to the propulsion units illustrated in the foregoing figures during a trim adjustment procedure;
FIG. 14
is a flow chart illustrating exemplary steps in a trim procedure for adjusting thrust or speed offsets between propulsion units of the type illustrated in the foregoing figures;
FIG. 15
is a graphical representation of drive signals for a propulsion system of the type illustrated in the foregoing figures;
FIGS. 16-18
are graphical representations of exemplary drive signal relationships used to navigate a watercraft through control of propulsion units as illustrated in the foregoing figures;
FIG. 19
is a side view of a forward thruster system for use in the watercraft in accordance with aspects of the present technique;
FIG. 20
is a top view of the system of
FIG. 19
installed in the craft hull; and
FIG. 21
is a partially broken away side view of the system of FIG.
19
.
DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS
Turning now to the drawings and referring first to
FIG. 1
, a watercraft
10
is illustrated that includes various features in accordance with the present technique. While the present technique is not necessarily limited to any particular type of craft, it is particularly well suited to smaller pleasure craft, such as fishing boats, ski boats, pontoon boats, and so forth. In the embodiment illustrated in
FIG. 1
, the watercraft
10
has a single hull
12
on which a deck
14
is fitted. The hull and deck may be formed as separate components and later assembled along with the other elements needed to complete the watercraft. The watercraft then presents a bow
16
and a stern
18
, with a transom
20
being provided in the stern region for supporting various components as described below. A cabin
22
may be formed in the deck section
14
, and an operator's console
24
allows for control of the watercraft, such as for navigating to and about desired areas in a lake, river, offshore area or other body of water. When floated on a body of water, the watercraft generally has a waterline
26
below which the propulsion devices described below are positioned.
In the embodiment illustrated in
FIG. 1
, a primary propulsion system, designated generally by reference numeral
28
, includes a conventional outboard motor
30
secured to transom
20
. Alternatively, more than one such outboard may be provided, or an inboard motor may be provided partially within the watercraft hull. As will be appreciated by those skilled in the art, such outboard motors and inboard motors typically include an internal combustion engine for driving a prop. Navigation of the system is controlled by adjustment of a rudder or of the annular position of the outboard
30
, such as by means of a steering wheel
32
.
Also as shown in
FIG. 1
, a secondary propulsion system
34
is provided in the stern region
18
, as well as a forward thruster system
300
. In the illustrated embodiment, the secondary propulsion system
34
includes first and second propulsion units
36
and
38
. Each propulsion unit is provided in the stern region on either side of the outboard motor
30
. As described more fully below, each propulsion unit
36
and
38
includes an electric motor
40
positioned within the hull, a support and power transmission assembly
42
(see, e.g., FIG.
10
), extending from the electric motor to an outboard surface of the hull, and a prop
44
positioned outside the hull and driven by the electric motor. Also as described more fully below, the prop
44
of each propulsion unit is preferably positioned within a recess
46
formed integrally within the hull. The electric motors, then, are positioned within one or more inner cavities
48
formed by the hull and generally included between the hull section of the watercraft and the deck
14
. The motors may be enclosed within compartments, and accessed via doors or hatches in the deck (not shown).
While in the present embodiment the preferred positions of the propulsion units are in the stern region, it should be noted that other positions may be provided in accordance with certain aspects of the present technique. For example, the propulsion units may be positioned adjacent to lateral sections of the hull, to produce components of thrust directed laterally and in fore-and-aft directions.
Also as illustrated in
FIG. 1
, a forward thruster system
300
is provided for complimenting the secondary propulsion system
34
. As described more fully below, the forward thruster system
300
includes a thruster drive
302
which displaces water through a conduit
304
extending from side-to-side in the hull. Apertures
306
provide for intake and discharge of water to produce a desired laterally-directed thrust.
In the diagrammatical representation of
FIG. 2
, the propulsion units
36
and
38
are shown in their positions in accordance with a present embodiment, as is thruster system
300
. As will be appreciated by those skilled in the art, watercraft
10
generally presents a longitudinal centerline
50
and a transverse centerline
52
orthogonal to longitudinal centerline
50
. The propulsion units are positioned at locations
54
and
56
which are symmetrical with respect to longitudinal centerline
50
. In the illustrated embodiment, each of the propulsion units is oriented so as to produce a thrust which is directed both in a fore-and-aft orientation, as well as in a direction oblique with respect to the longitudinal centerline
50
. In the present embodiment, the thrust, as generally represented by arrows
58
and
60
, may be created in either direction so as to propel the watercraft forward (in the direction of the bow) or reverse (in the direction of the aft) and to turn the watercraft as desired. Thus, in the diagram of
FIG. 2
, a resultant thrust
62
may be said to be available generally along longitudinal centerline
50
, with this thrust being oriented at various angles, as represented by reference numeral
64
, by relative control of the propulsion units.
In addition to the propulsion units
36
and
38
, thrust components are produced by the thruster system
300
. In the illustrated embodiment, thruster system
300
is provided forward of the transverse centerline
52
, and generally symmetrically with respect to the longitudinal centerline
50
of the watercraft. The thruster drive
302
thus draws water through one of the apertures
306
and expels water through the opposite aperture to produce laterally-directed thrust components
61
. In operation, the forward thruster system may be driven in cooperation with the rear propulsion units to produce a resultant thrust
63
, tending to slide the watercraft laterally to the left or to the right. Alternatively, the thruster system and the propulsion units may be driven cooperatively to turn the watercraft in a resultant thrust as indicated at reference numeral
64
. It should be noted, however, that in specific applications, the propulsion units
36
and
38
may be driven separately from the forward thruster system, or the forward thruster system may be driven without operation of the propulsion units.
The components of the thrust produced by the propulsion units are illustrated diagrammatically in somewhat greater detail in
FIGS. 3 and 4
. As shown in
FIG. 3
, the propulsion units
36
and
38
are positioned in the stern region and the props are oriented so as to produce the thrust
58
and
60
at oblique angles with respect to the centerline
50
. In a present embodiment, the angle of the thrust produced with respect to the centerline, as represented by reference numeral
66
in
FIG. 3
, is approximately 45°. As will be appreciated by those skilled in the art, however, other angles may be employed and the relative speeds of the propulsion units, as described below, controlled appropriately to produce a resultant thrust to navigate the watercraft. In addition to the offset angle with respect to centerline
50
, the propulsion units may be disposed so as to produce a thrust which is offset with respect to a horizontal plane, as illustrated in FIG.
4
. The angle
68
, generally inclined downwardly in an aft direction with respect to a horizontal plane, is approximately 8° in a present embodiment.
Referring again to
FIG. 3
, as the propulsion units are driven at desired speeds as described below, the thrust
58
and
60
produced by the units may be resolved into two orthogonal components of thrust as indicated by reference numerals
70
and
72
. More particularly, a first component
70
of the thrust is generally oriented parallel to centerline
50
, to propel the watercraft in the forward or reverse direction. The orthogonal component
72
of the thrust serves to orient the watercraft angularly, such as to turn the watercraft when being displaced forward or reverse, or with no or substantially no forward or reverse displacement at all.
In addition to the components of thrust produced by propulsion units
36
and
38
, thrust components
61
are produced by the thruster system
300
. As noted above, these thrust components may be produced in conjunction with those provided by the propulsion units, so as to provide turning or sliding movement of the watercraft hull. Alternatively, thrust components
61
may be produced without additional thrust by the propulsion units. It should also be noted that while in the illustrated embodiment the thrust components
61
produced by the thruster system are generally orthogonal to the longitudinal axis
50
of the watercraft, various angular orientations may be assumed. For example, the forward thruster system may direct thrust having both transverse components and components generally aligned with the longitudinal axis of the watercraft. Thus, resultant thrusts may be achieved which essentially do not displace the watercraft in a forward or aft direction, but provide only lateral sliding movement, such as for docking.
The propulsion units in the illustrated embodiment may be conveniently mounted within the stern region of the watercraft, being secured to a wall section of the hull shell, as illustrated in
FIGS. 5-9
. More particularly, the electric motor
40
of each propulsion unit, which is coupled to a control unit to receive drive signals as described below, is mounted within the inner cavity
48
formed within the hull, and may be conveniently supported on the support and power transmission assembly
42
. In the illustrated embodiment, a relatively planar section
74
of the hull shell is designed to receive a mounting plate
76
(see, e.g.,
FIG. 8
) which is fixed to the support and power transmission assembly
42
, and generally forms a part thereof. In
FIG. 5
, the right propulsion unit has been removed to illustrate an exemplary configuration of wall section
74
for receiving and supporting the propulsion unit. In this exemplary embodiment, an aperture
78
is formed through the hull shell wall and extends from the inner cavity to the surface defining recess
46
(see, e.g., FIG.
6
). Additional apertures
80
may be provided around aperture
78
for receiving fasteners used to secure the mounting plate to the hull.
While the foregoing structure of the hull and the position of the propulsion units are desired, it should be appreciated that the addition of the propulsion units to the watercraft may be an optional feature available at or after initial sale or configuration of the craft. For example, where a user does not desire the secondary propulsion system including the propulsion units positioned within the recesses of the hull, the recesses may nevertheless be formed in the hull to accommodate the propulsion units which may then be added to the watercraft, such as in the form of kits without substantial reworking of the hull. In such case, the apertures
78
and
80
may simply be covered by sealing plates or similar assemblies, generally similar or identical to mounting plate
76
, which are left in place until the propulsion units are mounted. The recesses
46
formed in the hull will not adversely affect the performance of the hull, even when the propulsion units are not mounted as illustrated. Alternatively, a cap or plate could be placed over the recesses to partially or completely cover the recesses, where desired.
As shown in
FIG. 6
, each propulsion unit is preferably mounted in the hull such that the prop
44
is substantially or completely protected by the bounds of the recess. Each recess is therefore defined by an inner wall
84
which forms part of the outboard wall or surface of the hull shell. In the illustrated embodiment, the recesses have an open bottom
86
and an open aft region
88
such that water may be displaced through the recess by rotation of the prop. It may also be noted in
FIG. 6
that, when placed in use, the uppermost limits of each recess preferably lie below waterline
26
.
The shape, orientation and contours of the recesses are preferably designed to promote desired water flow to and from the props of the propulsion units. In the partial bottom plan view of
FIG. 7
, each recess is illustrated as including, in addition to the open aft region
88
and open bottom
86
, an upper or top surface
90
. The top surface
90
may be substantially planar, such as forming a part of the wall through which the propulsion units extend and to which the propulsion units are securely mounted, facilitating mounting and sealing. Moreover, a section of the upper or top surface
90
preferably forms an integral cavitation plate
92
. As will be appreciated by those skilled in the art, such a cavitation plate serves a general purpose of maintaining water flow over the props during use, so as to prevent or reduce the entrainment of air through the recess, or the creation of air bubbles due to localized low pressure regions formed by rotation of the props. In general, the integral cavitation plates
92
may be angularly oriented downwardly in a fore-to-aft direction so as to direct water in a steady and smooth stream generally oriented in the same direction as the props themselves.
FIGS. 8 and 9
represent somewhat simplified sections through one of the recesses shown in FIG.
7
. Again, the support and power transmission assembly
42
of the propulsion unit extends through aperture
78
to position the prop
44
within the recess. The recess then guides water displaced by the prop, guiding the flow of water by the surfaces of the recess between the open bottom region
86
and the open aft region
88
. The top surface of the recess then forms the cavitation plate which reduces entrainment of air and bubbling of the water during operation.
FIG. 10
illustrates a present embodiment for each propulsion unit
36
and
38
. In the illustrated embodiment, the propulsion units include a motor
40
coupled to drive the prop
44
through the intermediary of the support and transmission assembly
42
. While any suitable motor may be employed, in the present embodiment, a switched reluctance motor is used by virtue of its high efficiency, relatively small size and weight, variable speed controllability, reversibility, and so forth. The motor is coupled to a control circuit via a network bus
144
as described in greater detail below. The motor is supported on a motor support bracket or plate
94
which may be fixed to the support and power transmission assembly
42
.
The support and power transmission assembly
42
both provides support for the motor and prop, and accommodates transmission of torque from the motor to the prop. In the illustrated embodiment, assembly
42
includes a support tube
96
made of a rigid tubular material, such as stainless steel. Within tube
96
a flex shaft assembly
98
is provided, extending from motor
40
to prop
44
. As will be appreciated by those skilled in the art, such flex shaft assemblies generally include a flexible sheath in which a flexible drive shaft is disposed coaxially. The sheath is held stationary within the support tube, while the flexible shaft is drivingly coupled to a drive shaft
100
of motor
40
. Mounting plate
76
may be rigidly fixed to support tube
96
, such as by welding. This connection of the plate to the support tube provides for the necessary mechanical support, as well as a sealed passage of the support tube through the support plate. A seal or gasket
102
is provided over the support plate to seal against the hull shell when the propulsion unit is installed. Fasteners
104
permit the seal
102
and support plate to be rigidly fixed to the watercraft hull. As will be appreciated by those skilled in the art, while in the illustrated embodiment the support plate and the gasket are provided on an inner surface of the hull, a similar support plate and gasket may be provided on the outer surface of the hull, or plates and gaskets may be provided on both the inner and outer surfaces of the hull.
The prop assembly
106
is secured at a lower end of support tube
96
. In the illustrated embodiment, prop assembly
106
is a freely extending propeller which rotates without a shroud. However, where desired, an additional shroud or various alternative propeller designs may be provided. Prop assembly
106
further includes a driven shaft
108
which is drivingly coupled to the flex shaft assembly
98
. Bearing and seal assemblies
110
are provided at either end of the support tube and provide for rotational mounting of the flex shaft assembly and of the motor and prop shafts, and seal the interior of the support tube from water intrusion.
FIGS. 10
a
and
10
b
represent a second preferred embodiment for the propulsion units
36
and
38
wherein a straight or rigid transmission shaft is employed for transmitting torque. As illustrated in
FIG. 10
a,
the propulsion unit includes a motor
40
and support and power transmission assembly
42
, with a mounting plate
76
extending therebetween. As described above, mounting plate
76
is provided for facilitating fixation of the propulsion units to the hull and for interposition of a seal between the plate and the hull. Motor
40
is mounted on a motor support
94
which, in turn, is secured to a modified support tube or housing
96
. In the illustrated embodiment, a 90° gear transmission
107
provides for translating torque from motor
40
about 90° for driving prop assembly
106
.
Referring to the exploded view of
FIG. 10
b,
motor
40
is secured to the support tube or housing
96
as illustrated, and a straight or rigid transmission shaft
101
extends between the gear transmission
107
and the motor. Moreover, a driven shaft
108
extends from the gear transmission to drive a sealed propeller shaft assembly
109
. In the illustrated embodiment, assembly
109
may include seals, a driven shaft, and a retaining and sealing plate for preventing the intrusion of water into the gear transmission housing. Bearing assemblies
110
support the shafts in rotation within the assembly. The arrangement of
FIGS. 10
a
and
10
b
is particularly well suited to placements wherein sufficient space is available for mounting of the electric motor inboard, with the gear transmission positioned outboard. It will be noted that space constraints are substantially reduced by the arrangement, and mounting surfaces and recess sizes may be similarly reduced.
As will be appreciated by those skilled in the art, various modifications may be made to the propulsion unit described above. For example, while the motor may be positioned in a completely external propulsion unit along with the prop assembly, in the preferred embodiment illustrated, the electric motor may be preserved in the dry cavity and compartment of the hull, while nevertheless providing the torque required for rotating the prop. Similarly, alternative fixation arrangements may be envisaged, such as plates or support assemblies with brackets which are fixed either to the prop assembly itself, or to various points along the support and power transmission assembly, or directly adjacent to the electric motor.
Referring now to a presently preferred configuration for the forward thruster system
300
,
FIGS. 19
,
20
and
21
illustrate several views of the arrangement. The thruster system includes thruster drive
302
which preferably comprises a direct current electric motor such as a switched reluctance motor. Thruster drive
302
is directly coupled to a transmission assembly
308
which serves to transmit torque from the thruster drive to a prop assembly
310
disposed within conduit
304
. A support flange
312
is provided on a support housing
314
of the transmission assembly for supporting the thruster drive. Connections between the thruster drive are provided in a manner similar to that described above with reference to the drive motors of the propulsion units.
The transmission assembly
308
further includes an upper support member
316
which may include a bearing for an output shaft
318
of drive motor
302
. A coupling
320
is secured to this output shaft. A second interface element
322
, which may similarly include a bearing, serves to support a driven shaft
324
in rotation. Coupling
320
links shafts
318
and
324
to one another such that torque may be transmitted from the thruster drive to the prop assembly
310
through these elements. An interface flange
326
serves to support the transmission assembly
308
on the conduit
304
. Where desired, separate support elements may be provided for fixing the entire structure to an internal support arrangement of the hull (not shown).
The prop assembly
310
includes a gear transmission
328
which translates the rotation of shaft
324
through 90° to drive a pair of props
332
and
334
. While a single prop may be employed for this purpose, the use of a pair of counter-rotating props provides for additional thrust and symmetry of the unit in its configuration and operation. The prop assembly
310
may include support struts
330
which position the gear transmission
328
within the conduit and support these components during operation.
In operation, the thruster drive
302
receives control signals from the control circuitry, preferably in cooperation with the rear propulsion units to drive the props at desired speeds and directions. In a presently preferred configuration, thruster drive
302
is bi-directional, such that the props may displace water in either direction through conduit
304
.
As illustrated in
FIG. 20
, the thruster system
300
may be configured as a stand-alone system which is positioned within and functions with mating features of the watercraft hull. In the configuration illustrated in
FIG. 20
, apertures
306
are formed in the watercraft hull
312
, and extend into cylindrical flanges or extensions
336
. The conduit
304
of the thruster system is then positioned between these extensions
336
, and sealed to the extensions via couplings or collars
338
. Thus, when driven, water is drawn into one of the apertures
306
, propelled through the conduit
304
under the influence of propellers
332
and
334
, and expelled through the opposite aperture to produce the desired thrust.
The foregoing arrangement is illustrated in a partial-breakaway view in FIG.
21
. Again, thruster drive
302
is driven through the intermediary of transmission assembly
308
to drive props
332
and
334
in rotation. Thrust components
61
are thereby produced at either end of the conduit
304
.
It should be noted that in certain configurations, economies may be realized by configuring the thruster system
300
with the same components as those used for the rear propulsion units. In particular, in a presently preferred configuration, many of the components of the thruster system
300
are substantially identical to those of the propulsion unit configuration illustrated in
FIGS. 10
a
and
10
b.
Control of the propulsion units may be automated in accordance with various control algorithms, but also preferably allows for operator command inputs, such as via a control device as illustrated in FIG.
11
.
FIG. 11
illustrates an exemplary operator control
112
formed as a base
114
on which a foot control
116
is positioned. While the operator inputs may be made through an operator's console, such as console
24
shown in
FIG. 1
, the operator control
112
of
FIG. 11
provides for hands-free operation, similar to that available in conventional trolling motor and electric outboard systems. However, the operator control
112
of
FIG. 11
includes additional features not found in conventional devices.
In the embodiment illustrated in
FIG. 11
, the operator control
112
includes a series of switches and inputs for regulating operation of the propulsion units
36
and
38
. By way of example, an on/off switch
118
is provided for enabling the system. A variable speed set or control input
120
is provided for regulating the relative thrust level or velocity of the propulsion system as described more fully below. Continuous forward and continuous reverse switches
124
and
126
are provided for selecting fixed and continuous forward and reverse operation. Momentary forward and momentary reverse switches
128
and
130
allow the operator to rapidly and temporarily reverse the direction of rotation of the propulsion units. Moreover, foot control
116
may be rocked towards a toe region
132
or toward a heel region
134
to provide a steering input. Similarly, the foot control
116
may be rocked or slid to the left and to the right as indicated at reference numerals
131
and
133
, respectively, to provide for “slide left” and “slide right” commands. As described more fully below, such commands may coordinate operation of the forward thruster system and the rear propulsion units, or only of the forward thruster system, to provide for lateral or docking-type motion. In a preferred embodiment, the foot control
116
is biased toward a centered position with respect to the steering inputs such that the operator must forcibly depress the foot control towards the toe region or the heel region to obtain the desired left or right steering input, or move the foot control to the left or to the right for the “slide” commands. By way of example, depressing the foot control
116
towards toe region
132
produces a “steer right” command, while depressing the heel region
134
produces a “steer left” command.
FIG. 12
illustrates diagrammatically the arrangement of switches within operator control
112
and the manner in which they are coupled to a control circuit for regulation of the speeds of motors
40
of the propulsion units. In particular, the on/off switch
118
may be selected (e.g., closed) to provide an on or off command to enable or energize the system. Speed setting
120
, which may be a momentary contact switch or a potentiometer input, provides a variable input signal for the speed control within a predetermined speed control range. A momentary contact switch
122
provides for setting a trim adjustment or calibration level as described more fully below. The continuous forward and continuous reverse switches
124
and
126
provide signals which place the drive in continuous forward and continuous reverse modes wherein the propulsion units are driven to provide the desired speed set on the speed setting input
120
. Momentary forward and momentary reverse switches
128
and
130
are momentary contact switches which cause reversal of the propulsion units from their current direction so long as the switch is depressed. Slide right and slide left switches
137
and
139
, are provided beneath or adjacent to right and left regions of the foot control
116
to provide signals for lateral “sliding” motion. Finally, steer right and steer left switches
136
and
138
, provided beneath the toe and heel region
132
and
134
of the operator control are momentary contact switches which provide input signals to alter the relative rotational speeds or settings of the propulsion units and thruster system, such as depending upon the duration of time they are depressed or closed.
The control inputs illustrated diagrammatically in
FIG. 12
, are coupled to a control circuit
142
via communications lines
140
. The communications lines
140
transmit signals generated by manipulations or settings of the control inputs to the control circuit. In a presently preferred embodiment, control circuit
142
includes a microprocessor controller, associated volatile and non-volatile memory, and signal generation circuitry for outputting drive signals for motors
40
. Moreover, while illustrated separately in
FIG. 12
, control circuit
142
may be physically positioned within the operator control package. Appropriate programming code within control circuit
142
translates the control inputs to determine the appropriate output drive signals. As described more fully below, the drive signals may be produced within a predetermined range of speed settings. Upon receiving speed set commands, forward or reverse continuous drive commands, momentary forward or momentary reverse commands, slide left or slide right commands, or steer left or steer right commands, control circuit
142
determines a level of output signal (e.g., counts from a preset available speed range) to produce the desired navigation thrust as commanded by the operator. Drive signals for the motors of the propulsion units and forward thruster system are then conveyed via a network bus
144
, such as a control area network (CAN), for driving the respective motors. By way of example, functional components for use in control circuit
142
may include a standard microprocessor, and motor drive circuitry available from Semifusion Corporation of Morgan Hill, Calif. A CAN bus interface for use in control circuit
142
may be obtained commercially from Microchip Technology, Inc. of Chandler, Ariz.
It should be noted that, while in the foregoing arrangement, control inputs are received through the operator control only, various automated features may also be incorporated in the system. For example, where electronic compasses, global positioning system receivers, depth finders, fish finders, and similar detection or input devices are available, the system may be adapted to produce navigational commands and drive signals to regulate the relative speeds of the propulsion units to maintain navigation through desired way points, within desired depths, in preset directions, and so forth.
While the propulsions units
36
and
38
are generally similar and are mounted in similar positions and configurations, various manufacturing tolerances in the mechanical and electrical systems may result in differences in the thrust produced by the units, even with equal control signal input levels. The propulsion units and the propulsion system are therefore preferably electronically trimmed or calibrated to provide for equal thrust performance over the range of speed and direction settings.
FIGS. 13 and 14
illustrate a present manner for carrying out the electronic trim adjustment procedure. In particular,
FIG. 13
illustrates graphically a manner in which the drive signals to the motors
40
of the propulsion units
36
and
38
may be sequentially adjusted during the calibration procedure to determine a nominal offset or trim setting.
FIG. 14
illustrates exemplary steps in control logic for carrying out this process.
FIG. 13
illustrates drive signals to motors
40
of the propulsion units graphically, with the magnitude of the drive signals being indicated by vertical axis
146
and time being indicated along the horizontal axis
148
. In the trim calibration process, designated generally by reference numeral
170
in
FIG. 14
, once the operator depresses the trim set input
122
(see
FIG. 12
; a visual or audible indictor may provide feedback of entry into the trim calibration process), an initial speed setting is provided, as shown by trace
150
in
FIG. 13
, to drive the motors at a preset initial speed, as illustrated at step
172
of FIG.
14
. It is contemplated that the calibration should be carried out in a relatively calm body of water with little or no current or wind, and with no input to drive the forward thruster system. Depending upon manufacturing and operating tolerances and variations of the propulsion units, different thrusts may be produced. Such differences in thrust may also result from the inherent torque or moment of the props associated with the propulsion units. These factors may, in practice, cause the watercraft to deviate from a “straight-ahead” setting, veering to the left or to the right. At step
174
in
FIG. 14
, the operator then manually steers the system, such as by depressing the toe or heel regions of the operator input, to correct for the error in the direction of setting. In graphical terms, as shown in
FIG. 13
, this manual correction occurs at reference numeral
152
, resulting in a decrease in the drive signal level
154
to one of the motors, with an increase in the drive signal level
156
to the other motor. A first offset
158
thus results from the differences in the two drive signal levels. As noted above, where the signals are computed by the control circuitry in terms of counts over a dynamic range, the initial offset
158
may be a relatively small number of counts.
At step
176
of
FIG. 14
, the operator determines whether the tracking provided by the new setting is sufficient (i.e. steers the watercraft in a straight-ahead direction). If the trim is not sufficiently corrected, an additional manual steering correction may be made, as represented at reference numeral
160
in FIG.
13
. This additional correction leads to a further decrease
162
in the drive signal applied to one of the motors, with a corresponding increase
164
in the drive signal applied to the other motor. The offset or correction difference
166
is correspondingly increased. Note that the operator could also decrease the trim difference if the previous steering adjustment overcompensated for the steering error. Once the operator has determined that the system is properly set to guide the watercraft in the desired direction (e.g., straight-ahead), the settings are stored, as indicated at step
178
in
FIG. 14
, by depressing the trim set input
122
(see FIG.
12
). At such time, as shown graphically at reference numeral
168
in
FIG. 13
, the then-current offset
166
is stored in the memory of the control circuit, such as in the form of a number of counts over the dynamic range of the drive signals. This value is then used in future navigation of the system, to alter the relative speed settings of the propulsion units, providing accurate and repeatable steering based upon known command inputs. As will be appreciated by those skilled in the art, while the offset between the speed settings may be constant and linear (i.e. based upon a linear relationship between the rotational speed and the resultant thrust), the foregoing technique may be further refined by providing for variable or non-linear adjustment (e.g., computing a varying offset depending upon the relative speed settings).
As noted above, components of thrust produced by propulsion units
36
and
38
, and by thruster system
300
, may be employed to drive the watercraft in a variety of directions and to turn and navigate the watercraft as desired.
FIGS. 15-18
illustrate a series of steering scenarios which may be envisaged for driving and turning the watercraft by relative adjustment of rotational speeds and directions of the propulsion units and thruster system.
FIG. 15
represents levels of drive signals applied to the motors of the propulsion units and thruster system for driving the watercraft first in a forward direction, then in a reverse direction. As shown in
FIG. 15
, at a time t
1
, the operator depresses the continuous forward input
124
, causing the control circuit to output drive signals which ramp up as indicated by trace
180
to a level corresponding to the speed setting on input
120
. While the rate of ramp up or ramp down of the drive signals may be controlled independently, in the embodiment illustrated in
FIG. 15
, the ramp rate is set, such as in terms of a number of counts per second over the dynamic range of the drive signals. Once the desired speed setting is reached, the drive signal levels off as indicated by trace
182
. At the same time, if lateral movement is desired, or if a forward turn is to be executed, a drive signal
183
is applied to the forward thruster system. It should be noted that, where a trim setting has been stored in the memory of the control circuit
142
, this trim setting will generally be applied to offset the drive signals applied to the propulsion units accordingly. However, in
FIGS. 15-18
, the offset is assumed to be zero for the sake of simplicity.
Continuing in
FIG. 15
, by way of example, the operator may depress the continuous reverse input
126
at time t
2
. Depressing the continuous reverse input results in a decline in the drive signal level as indicated by trace
184
until a point is reached at which the speed of the propulsion units is substantially zero, and the motors are reversed. This transition point is indicated at reference numeral
186
in FIG.
15
. Thereafter, the speed of the propulsion units is ramped upwardly in amplitude again, but in a reverse direction until a time t
3
, where the speed set on input
120
is again reached, but in the reverse direction. Trace
188
of
FIG. 15
indicates a continuous speed control in the reverse direction. Again, where lateral movement is desired, or where a turn is to be executed, a control signal
189
may be applied to the forward thruster system. At time t
4
in
FIG. 15
, a zero speed setting is input via the operator control, resulting in a ramp toward a zero drive signal setting at time t
5
. A subsequent “slide” command at time t
6
results in another drive signal
190
applied to one or both propulsion units, with a cooperative drive signal
191
applied to the forward thruster system.
The momentary forward and momentary reverse inputs
128
and
130
function in a generally similar manner. That is, when depressed, with the continuous forward or reverse functions operational, selection of the momentary input in the opposite direction results in a relatively rapid ramp downwardly (i.e. toward a zero thrust level) followed by a rapid reversal, so long as the input is held closed. These momentary or temporary changes in signals to the propulsion units may be accompanied by signals applied to the forward thruster system. Once the input is released, the drive signals return to their previous directions and levels. If the continuous function is not operational, the motors are turned on (i.e., driven) and their speed is ramped quickly in the momentary input direction.
FIGS. 16 and 17
represent exemplary scenarios for steering the watercraft in one direction, followed by return to a previous setting. As illustrated first in
FIG. 16
, an initial speed input
192
is provided, causing the propulsion units to drive the watercraft in a straight-ahead direction. At time t
1
, an operator command is received to steer the watercraft from the initial direction, to the left or to the right. Depending upon the predetermined ramp rate, or upon an operator-set ramp rate, the signals applied to the propulsion units are increased as indicated at reference numeral
194
and decreased as indicated at reference numeral
196
. The relative rotational speeds then produce components of thrust which cause the watercraft to steer left or steer right. By way of example, an increase in the rotational speed, and thus the thrust, of the right propulsion unit, accompanied by a decrease in the rotational speed, and thus the thrust, of the left propulsion unit, will cause the watercraft to steer toward the left. Where the steer command is maintained, such as by holding the operator command toe or heel region depressed, the declining drive signal may cross the zero axis, resulting in reversal of the rotational direction of the corresponding motor, as indicated at reference numeral
186
in FIG.
16
. In the scenario of
FIG. 16
, the ramp rate following this reversal continues until the system reaches a maximum turn setting at time t
2
(which may correspond to forward and reverse settings different from those shown in FIG.
16
). Thereafter, the steering setting will remain constant, until the steering input is removed at time t
3
. During this time, an additional drive signal may be applied to the forward thruster system, as indicated by trace
197
. Depending upon the relative thrust components, these signals may produce lateral translational or tuning motion of the craft. In the scenario illustrated in
FIG. 16
, a rapid ramp rate is then assumed, as indicated by traces
198
, until the straight-ahead settings are obtained at time t
4
. It will be appreciated, however, that the control input resulting in return to the initial straight-ahead setting could have continued, resulting in steering the watercraft in the opposite direction, by reversal of the relative speed and direction settings of the propulsion units.
In the scenario of
FIG. 17
, the speed of only one of the propulsion units is adjusted, while the speed of the other propulsion unit remains relatively unchanged, and the forward thruster provides no thrust. Thus, following an initial setting
192
, a command input is received at time t
1
to steer the watercraft either to the left or to the right. In the scenario of
FIG. 17
, such a steer command is followed by a rapid ramp down to a zero speed level, as indicated by trace
200
, followed by a more gradual ramp down, as indicated by trace
202
. At a time t
2
, a steering command is received to return to the initial setting, resulting in a rapid ramp up to the initial setting as indicated by trace
206
. During the adjustment to the single propulsion unit, as indicated by traces
200
,
202
and
206
, the remaining propulsion unit was maintained at a fixed speed, as indicated by trace
204
.
Steering commands and adjustments of the type described above, may also be made and maintained as indicated in FIG.
18
. In the scenario of
FIG. 18
, drive signals applied to the propulsion units begin at an initial level as indicated by reference numeral
192
. At time t
1
, a steering command is input to navigate the watercraft to the left or to the right. The command results in rapid ramping up of the drive signal to a first of the propulsion units, as indicated by reference numeral
208
, and ramping down of the drive signal to the opposite propulsion unit is indicated by trace
210
. While both of the drive signals may have maintained the propulsion units rotating in the same direction, in the example of
FIG. 18
, trace
210
crosses the zero axis, resulting in reversal of the rotational direction of the second propulsion unit. Thereafter, speeds of the propulsion units are maintained at constant levels, as indicated by traces
212
. At the same time, a drive signal may be applied to the forward thruster system to provide additional turning thrust, as indicated at trace
213
. The watercraft is thus rapidly steered to the left or to the right, and maintained at the new steering setting (i.e. left or right turn) until later command inputs are received.
It should be appreciated that the various scenarios for steering presented in
FIGS. 15-18
are offered by way of example only. In practice, and with specific propulsion units, props, hull designs, and so forth, optimal ramp rates, maximum drive command levels, and so forth, may be determined. Moreover, as noted above, where the output thrust of the propulsion units is not linearly related to the rotational speed of the motors, adjustments may be made in the levels of the drive signals to provide predictable, repeatable and intuitive steering adjustments based upon the command inputs.
While the invention may be susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and have been described in detail herein. However, it should be understood that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the following appended claims.
Claims
- 1. A propulsion system for a watercraft, the watercraft including a hull having a longitudinal centerline and a transverse centerline, the system comprising:a forward propulsion unit disposed forward of the transverse centerline and configured to produce thrust directed transverse to the longitudinal centerline; first and second aft propulsion units mounted to the hull at symmetrical locations and at angled orientations with respect to the longitudinal centerline, each aft propulsion unit being configured to produce at least a thrust component parallel with the longitudinal centerline; and a system controller coupled to the forward and aft propulsion units and configured to control operation of the propulsion units to produce a resultant thrust for navigating the watercraft.
- 2. The system of claim 1, wherein the forward propulsion unit includes an electric motor and a prop drivable by the electric motor.
- 3. The system of claim 2, wherein the electric motor of the forward propulsion unit is bi-directional.
- 4. The system of claim 1, wherein each of the aft propulsion units includes an electric motor and a prop drivable by the respective electric motor.
- 5. The system of claim 1, wherein the forward propulsion unit produces thrust directed substantially perpendicular to the longitudinal centerline.
- 6. The system of claim 1, wherein each of the aft propulsion units produces a thrust component directed generally parallel to the longitudinal centerline and a thrust component directed generally transverse to the horizontal centerline.
- 7. The system of claim 1, wherein the forward propulsion unit includes an tubular flow conduit and configured to draw water from one side of the transverse centerline and to discharge water on an opposite side of the transverse centerline.
- 8. The system of claim 7, wherein the forward propulsion unit includes a prop disposed within the flow conduit for displacing water through the conduit during operation.
- 9. The system of claim 1, wherein the system controller includes a foot-operated input device for receiving operator navigation commands.
- 10. The system of claim 1, wherein each propulsion unit includes an electric motor disposed within an inner cavity of the hull and drivingly coupled to a power transmission drive train to drive a respective prop through the hull.
- 11. A watercraft comprising:a hull having a longitudinal centerline and a transverse centerline; a forward propulsion unit including an electric motor drivingly coupled to a prop, the forward propulsion unit being disposed forward of the transverse centerline and configured to produce thrust directed transverse to the longitudinal centerline; first and second aft propulsion units each including an electric motor drivingly coupled to a prop, the aft propulsion units being mounted to the hull at symmetrical locations and at angled orientations with respect to the longitudinal centerline, each aft propulsion unit being configured to produce at least a thrust component generally parallel with the longitudinal centerline and a thrust component generally transverse to the longitudinal centerline; and a system controller coupled to the forward and aft propulsion units and configured to control operation of the propulsion units to produce a resultant thrust for navigating the watercraft.
- 12. The watercraft of claim 11, wherein the electric motor of each propulsion unit is disposed within an inboard cavity of the hull, and wherein each propulsion unit includes a power transmission drive train extending through the hull to drive the respective prop.
- 13. The watercraft of claim 12, wherein at least one of the power transmission drive trains includes a flexible shaft coupled between the respective electric motor and the respective prop.
- 14. The watercraft of claim 11, wherein the hull includes first and second integral recesses for receiving at least the first and second props of the first and second aft propulsion units, respectively.
- 15. The watercraft of claim 11, wherein the forward propulsion unit includes a conduit extending across the longitudinal centerline of the hull for channeling water displaced by the forward propulsion unit prop during operation.
- 16. The watercraft of claim 11, wherein the system controller includes an operator input device for receiving operator navigation commands, and wherein the system controller is configured to generate drive signals for the electric motors of the forward and aft propulsion units based upon the operator navigation commands.
- 17. The watercraft of claim 11, wherein the electric motors of the forward and aft propulsion units are bi-directional.
- 18. The watercraft of claim 11, wherein the resultant thrust is produced by driving the electric motors of at least the first and second aft propulsion units at different speeds.
- 19. The watercraft of claim 11, wherein the resultant thrust is produced by driving the electric motors of the first and second aft propulsion units in different rotational directions.
- 20. A watercraft comprising:a hull having a longitudinal centerline and a transverse centerline; a forward propulsion unit including an electric motor drivingly coupled to a prop, the forward propulsion unit being disposed forward of the transverse centerline and configured to produce thrust directed transverse to the longitudinal centerline; first and second aft propulsion units each including an electric motor drivingly coupled to a prop, the aft propulsion units being mounted to the hull at symmetrical locations with respect to the longitudinal centerline, each aft propulsion unit being configured to produce at least a thrust component generally parallel with the longitudinal centerline and a thrust component generally transverse to the longitudinal centerline, wherein the props of the first and second aft propulsion units are directed to produce respective thrusts directed downwardly and inwardly towards the longitudinal centerline of the hull; and a system controller coupled to the forward and aft propulsion units and configured to control operation of the propulsion units to produce a resultant thrust for navigating the watercraft.
- 21. The watercraft of claim 20, wherein the props of the first and second aft propulsion units are disposed to produce respective thrusts directed inwardly at less than 45 degrees with respect to the longitudinal centerline and downwardly at less than 10 degrees.
- 22. A watercraft comprising:a hull having a longitudinal centerline and a transverse centerline; a primary propulsion system including an internal combustion engine drivingly coupled to a propeller for producing thrust to displace the hull on a body of water; and a secondary propulsion system including: a forward electric propulsion unit including an electric motor drivingly coupled to a prop, the forward propulsion unit being disposed forward of the transverse centerline and configured to produce thrust directed transverse to the longitudinal centerline; first and second aft electric propulsion units each including an electric motor drivingly coupled to a prop, the aft propulsion units being mounted to the hull at symmetrical locations and at angled orientations with configured to produce at least a thrust component generally parallel with the longitudinal centerline and a thrust component generally transverse to the longitudinal centerline; and a system controller coupled to the forward and aft propulsion units and configured to control operation of the propulsion units to produce a resultant thrust for navigating the watercraft.
- 23. The watercraft of claim 22, wherein the primary propulsion system includes an outboard motor.
- 24. The watercraft of claim 22, wherein the electric motor of each propulsion unit of the secondary propulsion system is disposed within an inboard cavity of the hull, and wherein each propulsion unit includes a power transmission drive train extending through the hull to drive the respective prop.
- 25. The watercraft of claim 22, wherein the hull includes first and second integral recesses for receiving at least the first and second props of the first and second aft propulsion units, respectively.
- 26. The watercraft of claim 22, wherein the primary propulsion system is disposed generally along the longitudinal centerline of the hull and the first and second aft propulsion units are disposed on either side of the primary propulsion system in a stern region of the hull.
- 27. The watercraft of claim 22, wherein the forward propulsion unit includes a conduit extending across the longitudinal centerline of the hull for channeling water displaced by the forward propulsion unit prop during operation.
- 28. The watercraft of claim 22, wherein the system controller includes an operator input device for receiving operator navigation commands, and wherein the system controller is configured to generate drive signals for the electric motors of the forward and aft propulsion units based upon the operator navigation commands.
- 29. The watercraft of claim 22, wherein the electric motors of the forward and aft propulsion units are bi-directional.
- 30. A method for steering a watercraft, the watercraft including a hull having a longitudinal centerline and a transverse centerline, the method comprising the steps of:applying forward drive signals to a forward propulsion unit disposed forward of the longitudinal centerline, forward propulsion unit including an electric motor and a prop drivingly coupled to the electric motor; applying aft drive signals to first and second aft propulsion units disposed symmetrically and angularly about the longitudinal centerline, each aft propulsion unit including an electric motor and a prop drivingly coupled to the respective electric motor; and whereby the forward and aft drive signals produce components of thrust from each of the forward and aft propulsion units to provide a desired resultant thrust for steering the watercraft.
- 31. The method of claim 30, wherein the forward propulsion unit displaces water from one side of the longitudinal centerline to an opposite side of the longitudinal centerline.
- 32. The method of claim 30, wherein the aft propulsion units each produce a component of thrust directed generally parallel to the longitudinal centerline and a component of trust directed generally transverse to the longitudinal centerline.
- 33. The method of claim 30, wherein the aft drive signals drive the electric motors of the first and second aft propulsion units in rotation at different speeds.
- 34. The method of claim 30, wherein the aft drive signals drive the electric motors of the first and second aft propulsion units in rotation in different directions.
- 35. The system of claim 1, wherein the angled orientations of the first and second aft propulsion units are symmetrical with respect to the longitudinal centerline.
- 36. The system of claim 35, wherein the angled orientations of the first and second aft propulsion units are directed inwardly toward the longitudinal centerline and outwardly from the hull.
- 37. The system of claim 1, wherein the first and second aft propulsion units are mounted to the hull angularly with respect to a horizontal plane passing through the longitudinal and transverse centerlines.
- 38. The system of claim 11, wherein the angled orientations of the first and second aft propulsion units are directed inwardly toward the longitudinal centerline and outwardly from the hull.
- 39. The system of claim 11, wherein the first and second aft propulsion units are mounted to the hull angularly with respect to a horizontal plane passing through the longitudinal and transverse centerlines.
- 40. The system of claim 22, wherein the first and second aft propulsion units are mounted to the hull angularly with respect to a horizontal plane passing through the longitudinal and transverse centerlines.
- 41. The method of claim 30, wherein the first and second aft propulsion units are mounted to the hull angularly with respect to a horizontal plane passing through the longitudinal and transverse centerlines.
US Referenced Citations (6)