Note: Descriptions are shown in the official language in which they were submitted.
106B3~5
E].ECTRIC TROLLING MOTOR APPARATUS
_
Back~round of the Invention
This invention relates to an elec~ric ~rolling
motor apparatus and particularly to such a motor having a
solid state motor control circuit including automatic safety
means for protecting the motor under varying, operating envi-
ronments.
Small electric trolling motors have been widely
employed for propelling of small fishing boats and the like.
Trolling is at extremely low boat speeds and, consequently,
small electric motor driven outboard units o a relatively
low horsepower are readily adapted to this application.
Thus, a boat will normally not have to be propelled in excess
of two and one-haLf miles per hour during trolling. Conse-
quently, electric trolling motors may be relatively lightweightunits which can be readily, manually carried to and from the
boat s~ructure.
The electric trolling motors generally include a
tubular housing member in the form of a pipe-like element
which is provided with a suitable pivotal mounting bracket
for attachment to the transom of the boat. A tiller handle
is provided at the upper end for pivoting within the brac~et
for steering of the boat. A lower propeller unit is secured
to the lower end of the mounting unit for immersion within the
water for actual powering or propulsion of the boat. Generally,
the electric motor is housed within the lower propeller unit
of the outboard motor unit. The lower propeller unit is her-
metically sealed to permit the direct immersion into the body
of water. Various controls are provided for controlling the
speed of the electric motor by varying the current supplied
to the motor.
~'~
~.~
106~3385
The motor is energized generally ~rom a battery
located within the boat structure and connected to the motor
by suitable electrical cables extended downwardly through the
mounting housing or conduit. Conventionally, such outboard
electric motors are of a permanent magnet type motor with
the speed controlled by adjusting the current supply to the
rotor. Various electrical control systems have been pro-
vided for varying the power supplied to the motor and thereby
the driving force or speed.
Solid state controls for electric motors and the
like may advantageously be applied to an electric trolling
motor where efficient control of the motor energization is
highly desirable to minimize the load on the battery and
thereby establish a reasonably long operating period. Solid
state controls may also advantageously be located directly
within the lower, propeller housing by providing appropriate
means to locate the solid state components for efficient
cooling.
Solid state switch elements are sensitive to
overloading conditions and, consequently, have presented
particular problems in connection with trolling motors and
the like where severe loading conditions may be encountered.
Thus, trolling mot:ors are often operated in heavy weedy water
and severe loads may be placed on the electric motor. Perma-
nent magnet motors tend to maintain a constant speed by in-
creasing ~he current drawn from the source, such motors,
therefore, produce a heavy stall current and/or voltage within
the electrical circuit. Further, under certain conditions
very high starting current surges are encountered in permanent
magnet motors. Consequently, compensation must be made to
-- ~0683~35
, . :,
momentarily accept or to compensate for such loads.
Further, the lncreased current conditions may result
in abnormally dangerous temperature conditions, as
solid state devices are notoriously temperature sensitive.
With the development o~ sophisticated solid state
igni~ions and the like for conventional outboard motors, the
, servicing o~ solid state circu~ts is more readily available,
However, such servicing may not be available in remote areas and
~ the solid state components, particularly power transistors and the
like, are relatively expensi~e Failure of the electronic circui-'
try almost makes repair on site impossible and thus, in essence,
strands the operator with only manual means for return of the boat.
The trolling motor application, thereore, pre
- sents a rather severe operating environment for the control
systems. There remains a very significant demand for a
versa~ile'solid st:ate control for a submersible trolling
motor which has safe operationaltresponse under the usual
conditions encount:ered and which establishes a long operat-
ing lie with mini.mal chance of malfunction or failure.
Summary of the Present Invention
The present invention is directed to an electric
trolling motor having a solid state control circuit with
means which provide a continuous monitoring of the circuit
and motor operaticm and includes means to respond thereto
to prevent adverse or damaging energizing conditions. The
present invention by providing a continuous and reliable
monitoring means Ls particularly adapted to mounting within
the motor housing o~ the lower propeller u,nit.
Generally, in accordance with the present invention
30,
1(~68385
a solid state power control means is provided having a low
voltage input controlling the output power circuit connec-
tion for supplying of varying current to the motor> and
particularly includes means to monitor the current, the
voltage and the temperature of the power switch means. In
accordance with a particularly unique aspect of the present
~ invention, the several elements conjointly control the
; energizing circuit: to individually and conjointly respond
to the several conditions such that an extremely high
level of any one of the parameters will provide a first
compensating response and selected lower sensed levels of
any two or more parameters to effect a similar compensating
response.
Generally, in accordance with a particularly prac-
tical and optimum construction, the control circuit in-
cludes a solid state amplification means to control the
.
current flow to the motor, such as a power transistor means
and a driver or control transistor means connected as a
voltage regulator to the motor and in a fold-back current
2Q supply to~provide voltage regulation of the motor over a
limited range and an~overriding limit control which main-
tains current to the motor under all operating and stall
conditions but at such a level as to prevent destruction of
the power transistor means and the associated circuitry. The
power transis~or and driver transistor means is generally
connected as a constant voltage source to the motor over
a selected current range to maintain an essentially con-
stant voltage to the motor regardiess of load current re-
quirements and thus maintaining an essentially constant
speed regardless of the propeller loading or the motor loading.
Thus a relatively constant speed will be maintained even
1068385
though in the presence of weed entanglement of the pro-
peller, varying degrees or extremes of frictional loading
of the gearing and bearings within the motor unit and the
like and particularly provides for very smooth, slow speed
running. The constant voltage condition, however, is
limited to a selected, safe current range and the circuit
includes multiple paràmeter self-protecting, compensating
means to positively reduce the current under canditions
which would tend to damage the control system. The self-
protecting, compensating means includes a sensing amplifier-having a summing input for the several individual sensors
of voltage, current and temperature. The output of the
sensing amplifier is summed with a speed control signal
and applied to the power stage to control the voltage
applied across the motor. The motor current is advantage-
ously sensed by a resistor connected in series with the
power transistor and across the input means to the sensing
amplifier. The resistor has a low resistance value so as
to develop a voltage propor~ional to current without signi-
ficantly reducing the voltage supplied to the power transis-
tor means and to the motor. A voltage dividing network is
connected across the power transistor means to continuously
monitor the transistor voltage and provide a voltage signal
which is summed with the current signal by series connecting
a part of the network in series with the current sensing
resistor to the input means. In addition, a temperature
sensitive means is thermally coupled to the power transistor
means to thereby continuously monitor its tempera~ure and
produce à signal which is added at the summing point in
accordance with I:he temperature of the power transistor.
In this manner7 lhe control summing point continuously
~6~31Y5
monitors the three most significant parameters of the solid
state control switch means and correspondingly activates
the control amplifier such as a transistor to modulate the
speed input signal to the input or speed summing point to
the power stage.
The power s~age consists of two opposite-~olarity
transistors connected in a compounded configuration with a
base input connected to the control summing point and with
the motor connecled in the collector circuit to the battery
in an input power loop and the emitter connected to the re-
turn side of the battery to ~form with the motor an output
loop.
The several resistor elements of the sensing network
are particularly selected to establish a control signal at
the control summing point which will modulate and activate,
after a selected current level, the sensing transistor in
accordance with the relative magnitude of the individual
parameters. An e~tremely high level of any single sensed
parameter will effectively modulate the operation of the
regulator by reducing the bias of the power stage. A some-
what lower sense,d level of the combination of any two of
the parameters similarly reduces the bias and finally sens-
ing of all three parameters at a further reduced level will
also similarly reduce the bias to the power stage in the same
manner and to a similar degree. The summing system thus de-
velops a series of similar current versus voltage curves for
different constant temperatures each of which, in essence,
encloses the same operating area for that particular tempera-
ture. The circuit thus maintains a continuing monitor:ing
and control to maintain the circuit operating within the
proper parameters or power characteristics.
~L0683~5
Further, in order to further protect the solid
state control when it is mounted within lower propeller unit,
a unique circuit support is provided within the housing to
maintain efficient cooling, particularly of the solid state
S power ampli~ier means. In a particularly unique and novel
constructio.n.of this aspect of the present invention, the
forward end or nose cone of the lower propeller housing ~nit
is formed with a cooling platorm connected to the sidewall
by suitable interconnecting heat transfer elements which ma~
be integrally formed in the usual cast constructions. The
platform is located inwardly of the open.end of the nose
cone with a suitable propeller shaft bearing unit secured
within the outer open end. The solid state circuit board is
secured to the platform with an opening surrounding at least
a portion of the platform and with the power transistor means
. in irm abutment with the platform to establish maximum heat
transfer characteristics. In a particularly novel and unique
construction, the platform is formed with a pair of.back-to-
back and interconnected triangular-shaped portions connected
back-to-back by a small bridging portion to define a platform
generally corresponding but slightly smaller than.the configura-
tion of the mounting frame of the conventional solid state
power transistor and further defining a pair of central re-
cesses to the opposite sides thereof. The circuit board is
formed with a corresponding configured opening which is some-
what larger ~han the platform and is adapted to telescope
over the platform but is somewhat smaller than the mounting
frame A central thin, insulator member abuts the raised
platform with the power transistor bolted onto the insulated
platform to maintain firm, physical interengagement to the
housing with a consequent excellent heat transfer.
- The present inventor has found that the raised
platform within the forward end of the housing maintains a
--7--
10683~35
highly desired and satisfactory cooling characteristic,
contributing significantly to the safe and long operaking
life of the circuit~ The cooling, particularly in combina-
tion with the continuous power and temperature monitoring,
essentially eliminates the destruction of the electronic
circuitry as a result of the energization of the motor.
The present invention thus provides a highly
improved, electric trolling motor employing a solid state
motor control for the efficient variable control of the
motor speed.
- - Brief Description of the Drawings
The drawings furnished herewith illustrate the
best mode presently contemplated by the inventor for carrying
out the subject invention in which the above advantages and
features are clearly disclosed as well as others which will
be readily understood from the following description of the
embodiments shown.
In the drawings:
Fig. 1 is a side elevational view of the lower
propeller unit of a trolling motor with parts broken away
and sectioned to more clearly illustrate details of construc-
tion of the present invention;
Fig. 2 is a trans~erse, vertical, sectional view
taken generally on Line 2-2 of Fig. l;
Fig. 3 is an exploded view showing principal com-
ponents of the illustrated embodiment of the invention;
Fig. 4 is a vertical, sectional view taken generally
on line 4-4 of Fig. 2;
Fig. 5 is a schematic illustration of a self-
protecting, continuously monitoring, energiæing circuit for
~136~;i 8~i
the trolling motor illustrating a preferred embodiment of
the present invent:Lon; and
Fig. 6 ls a diagrammatic illustration of voltage
and current characteristics with changing temperature condi-
tions of the circuit shown in Fig. S.
Descr~ption of the Illustrated Embodiment
.
Re~erring to the drawings and particularly to Fig.
l, a trolling motor is illustrated including a lower propeller
unit l secured to the lower end of a vertical mounting hous-
ing 2. A tlller handle assembly or unit 3 is secured to theupper end of the mounting housing 2. Housing 2 is sho~n in
the form of a conventional threaded pipe-like member threaded
at the opposite ends for connection to units l and 3. A
swivel bracket mount unit 3a will be secured to the housing
2 for mounting of the trolling motor to the transom of a boat,
not shown. The lower propeller unit l will, of course, be
located below the boat and thus immersed within the water
while the ~iller handle assembly 3 will be located within the
boat for convenient manual turning of the lower propeller unit l
and for controlling the speed and direction of the boa~.
The lower propeller unit l includes an electric motor 4 in-
cluding a rotor S centrally located within a permanent magnet
stator 6. The motor 4 is rotatably mounted within the lower
unit l with the rotor shaft coupled to drive a propeller 7
through a suitable gear means, not shown, within the aft end
o~ the propeller unit, in accordance with conventional practice.
A battery 8 is conventionally provided within the ~oat and
connected through the control unit 3 and suitable connecting
leads 8a to provide an adjustable current supply to the motor
4 for varying the speed of the motor. The speed of permanent
-9
3385
magnet motor 4 is controlled by varying the power supplied
to the rotor 5. In accordance with the present invention,
the power is supplied to the motor through a novel, solid
state control circuit or unit 9 which is uniquely mounted
within the lower propeller housing unit 1. The solid state
control unit 9 is connected by the three connecting leads
8a to provide power to the motor rotor 5 in accordance
with a preset, ad;justable speed control signal which is set
by the operator at the tiller asse~bly 3.
More particularly, the illustrated embodimen~ o
the lower propelLer unit 1 includes a central, cylindrical
housing portion 10 within which the permanent magnet stator
6 ie secured in any suitable and well-known manner. An aft
propeller housing :ll and a forward or front nose cone housing
12 are secured to the opposite ends of the cylindrical hous-
ing 10 by a pair of suitable connecting bolt members 12a to
form a unitary, water-tight housing. The rotor 5 is located
within the housing 10 and rotatably supported at the opposite
ends in suitable bearing members within the aft and front
cone housings 11 and 12. Any suitable bearing support struc-
ture can be provided within the aft housing 1~ and no detail
thereof is shown. The forward nose cone housing 12 includes
a radial bearing 13 located within the open end thereof and
which is provided with a corresponding cylindrical end open-
ing portion to locate the bearing 13 with the housing sec-
tions 10 through 1~ interconnected by the bolts 12a. The end
of the rotor shaft 14 is journaled in bearing 13 and termi-
nates in spaced relation to the outer end of the cone housing
12 to define a front nose cone chamber 15 within which the
control unit 9 is :Located, and ~miquely mounted to provide
-10-
0683~35
eficient cooling of the solid state circuit components.
Generally, control unit 9 includes a circuit mounting
board 16 which is secured to a platform 17 within the
chamber 15 in the outermost end of the nose cone 12. A
5 solid state power amplifying means such as a power tran-
sistor unit 18 is affixed to the outer face of the circuit
board 16 in heat transfer relation to platform 17, with
other interrelatecl control components such as resistors,
capacitors and the like. The power transistor unit 18 in-
10 cludes a mounting plate or flange 19 in accordance with the
usuaL construction and in the-illustrated embodiment of the
invention. The unit 9 is secured in place by suitable attach-
ment screws 20 or bolts which extend through the flan~e of
the circuit board and thread into the platform 17 to firmly
15 mou~t the circuit board and simul~aneously hold the unit
t 18 in cooling engagement with the platform 17.
More particularly, as shown in Figs. 2 - 4, the
platform 17 includes a central, solid core portion which
is integrally cast with the nose cone 12 located coaxially
20 of the lower propulsion unit 1. A plurality of radially
distributed arms 21 connect the core portion to the outer
cone wall and defi.ne a star or spider-shaped platform sup-
port. The plateform 17 is integrally formed with the upper
surface of the core portion and arms 21 as a raised platform
25 having a pair of generally triangular portions 22 and 23
interconnected by a neck portion to define a pair of cen-
trally located recesses 24. Portions 22 and 23 generally de-
fine a raised platform conforming or complementing the con-
figuration of the mounting flange 19 of the solid state tran-
30 sistor unit 18. P,ppropriate bolt holes 25 are provided to
the opposite ends of the platform 17 in accordance with
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683~35
mounting flange openings to appropriately receive the
mounting bolts 20 as most clearly shown in Fig. 3.
The circuit board 16 generally is formed of a
suitable insulating material and may advantageously be a
S well-known fiberglass, reinforced plastic.
The fiberglass circuit board 16 has a centrally
located opening 27 with central locating arms 28 essen-
tially correspond:ing to the configuration defined by the
triangular-shaped platform portions 22 and 23 and the re-
cesses 24. The opening 27 is slightly larger than theplatform 17 and in assembly telescopes and r~tes therewith.
The opening 27 is slightly smaller than the mounting flange
19 whic~ overlaps the board and is interconnected thereto
by leads 29a which extend through the board and are bent
over. The board 16 is thereby also located in the plan
spaced fram the upper sur~ace of the base portion 15 The
plate 19,' of course, is provided with appropriate openings
for passage of the attachment bolts 20. In the assembled
relation, the board 16 telescopes over the pla~form por-
tions 22 and 23. The transistor unit 18 is secured in
abutting, overlying relationship by bolts 20 to pla~form
portions 22 and 23 with a thin, insulating member 30 there-
between. Insulating washers 30a are provided for bolts 20
to completely insulate the transistor unit 18 from the bolts
20 and therefore from the platform. The thin member 30
maintains good thermal conductivity for heat within the
power amplifier unit 18 to the platform 17 and therefore to
the nose cone 12 for efficient switch cooling.
The circuit cor~onents 31 for interconnection of
motor 4 and amplifier unit 18 to éach other and to the leads
-12-
8 3 ~ ~
8a are located to the outer side of the circuit board 16
and in the illustrated embodiment of the invention are
connected by suitable leads which project downwardly
through suitable openings 31a in the circuit board to the
underside thereo. Suitable solder connecting lines 31b
are formed to the undersurface of the circuit board 16
to provide the necessary circui~ interconnections. The
locating arms 28 of the circuit board 16 are particularly
provided with appropriate openings to provide circuit con-
nection to the emitter and base terminals of the power
-transistor means 18. - -- -- -
The depth of the platform portions 22 and 23 is
grea~er than the depth of the opening 27 to the insulatc~r
28 and the circuit board is thus held in spaced relation
to the base unit 16 to prevent short-circuiting of the
circuit components. The board, of course, is sufficiently
rigld to~prevent the deflection with the base unit.
Further, after the assembly of the circuit board
and power transistor unit 18 to the pIatform 17 the nose
cone 12 is fiLled with a suitable encapsulating material
32 such as a heat conductive epoxy to the level of the
bearing support portion for bearing 13. The material 32
serves to conduct heat from the several circuit board com-
ponents as well as to physically support the asse~bly
within the nose c:one.
The circuit board 16 may be completely pre-
assembled and readily mounted within the nose cone 12
wlth the power transistor unit 18 through the common
attachment bolts 20. The location within the nose cone
12 and in engagement with the wall of the nose cone as
-13-
68385-
well as the heat conductive epoxy 32 provides for a
rapid transfer of the heat generated within the unit to
the nose cone and thus to the water to provide e~ficient
cooling. The construction and arrangement particularly
adapts the temperature sensitive, solid state control
circuit to the mounting within the motor housing.
A particularly unique control is illustrated
in Fig. 5, wherein the rotor 5 of the motor 4 is con-
nected directly to the positive side of the battery 8
by one of the leads 8a and the opposite side is con-
-nected to ground through an electronic control circuit
33 which ~ay be mounted on circuit board 16.
The speed control input to the circuit 33 is
derived from a small potentiometer 34 having an adjust-
able tap 35 connected as the input to the control cir-
I cuit 33. Thus, the potentiometer 34, in accordance
with conventional practice, may be connected directly
across the batte:ry 8 with the voltage signal determined
by the setting of the potentiometer tap 35. The poten-
tiometer may be a very small resistor element mounted
within the upper unit 3 and with the tap provided with
a suitable control knob or lever 35a. Turning of the
knob 35a varies the signal supplied to the control cir-
cuit 33.
The preslent invention is further, particularly
directed to a trolling motor including the unique con-
trol circuit 33 to further protect the control circuit
under operating condit:ions. Generally, in the embodi-
ment of the invention illustrated in Fig. 5, the power
control transistor unit 18 is shown as an NPN power
-14-
- ~)683~35
transistor 18 having its collector to emitter c;rcuit
connected in series with the motor rotor 4 and the
ground side of the battery 8. A control transistor
36 of a:PNP construction has its emitter to collector
circuit connected between the collector and base of the
transistor 18 and its base connected 8S the input signal
to the adjustable po~entiometer tap 35 in series with
a current limi~ing resistor 37. The transistor 18, in
accordance with conventional practice, will be a suit-
able high powered transistor for carrying of the motor
- load current-while the transistor 36 is a relatively
low-power transistor for providing control current to
the transistor 18 in response to the input voltage
signal at tape 35 with the transistor 18 providing the
desired linear response. Such a transistor connection
produces a very large current gain with an essential
unity voltage ga.in. The input impedance is high while
the output impedance is low, and the combination pro-
vides a highly d.esirable and unusually satisfactory
powèr ampli~ier-;means.
A self-protecting parameter sensing circuit
branch 38 is connected between the.common junction
of the resistor 37 and the base of tranæistor 36 to
de~ine a summing point 39 for summing the speed control
signal with a power transistor protecting signal and
to thereby conjointly control the voltage applied
across motor 4. In particular, the circuit simul-
taneously establishes a limited voltage regulation
for supplying a varying current and power to the
motor rotor 4 over a given speed range and then
-15-
~L0683~35
positively limil:ng the curxent through the power
transistor 18 to a level which will prevent damaging
thereo.
More particularly, the branch circuit 38
includes a control transistor 40 having the emitter
to collector circuit connected between the summing .
point 39 and motor 4 to provide a protective control
signal to the summing point 39 in accordance with a
sensed signal appearing at the base of transistor 40.
The base connection defines a common summing
point or node to sum the-several sensed parameters
including a motor current signal with a transistor
volta~e parameter signal and a power transistor
temperature signal, as follows.
A current sensing resistor 41 is connected in
series with the rotor 4 to the collector side of the
power transistor 18. The resistor 41 is a very low
valued resistance so as to introduce a minimum voltage
drop into the series circuit. For example, the re-
sistor 41 may typically be of the order of less than
one-tenth ohm and in one embodiment was .035 ohm,
which will, however, develop a voltage signal directly
- proportional to the current therethrough and provide
therefore a control signal proportional to the motor
current. The positivç side of the resistor 41 is
connected to the emitter of the PNP control transis-
tor 40, while the negative side is connected in series
with a voltage sensing resistor 42 to a common summing
point or node 43 at the ~ase of the transistor 40.
More particular:ly, the resistor 42 is connected in
-16-
6838S
series with a resistor 44 directly across the collec-
tor to emitter of. the power transistor 18. A signal
directly proporti.onal to the voltage across the power
transistor 18 appears across resistor 42-44 with the
junction of the two resistors 42 and 44 connected at the
common summing node 43. A voltage signal is therefore
developed at the summing point 43 proportional to the
voltage across the power transistor 18.
Finally, the temperature parameter of the
: 10 power switch means 18 is sensed by heat sensitive means
-such as a thermistor 45 which,-as illustrated, includes
a temperature sensitive resistor 46 connected in parallel
. with the voltage dividing resistor 44. The thermistor
46 is mounted to the unit 19 and coupled to the power
transistor 18 through the metallic conduction as shown
at 47. The thermistor 45 is heated in accordance with
the temperature of the power transistor 18 and results
in a direct related corresponding change in the voltage
signal at the su~ing point 43.
In summary the combination of the current sens-
ing resistor 41j the voltage sensing resistors 42 and
44 and the heat sensing thermistor 46 provides continu-
ous monitoring of the three most significant parameters
in connection with solid state power units.
The circuit is completed by a Zener diode 48
and a blocking di.ode 49 connected across the rotor 4
to provide transient protection. Similarly, in accordance
with conventional practice, a protective diode 50 may
be connected across the transistor and a stabilization
capacitor 51 connected across the base to collector
0683 !35
circuit as shown~ The Zener diode 48 functions to protec-t
the circuit in the event that the battery 8 is connected wi-th
reversed polarity~ Blocking ~iode 49 functions to protect the
- circuit from damaging transient voltages, back-biasing voltages
and the like across the motor.
The power transistor 18 functions as a voltage
regulator over a limited current range, as follows.
The potential of the speed control tap 35 varies the
potential applied to the base of the control transistor
36 and determined the conductivity of the power transis-
tor 18. Thus, as the tap 35 approaches ground potential,
conductivity will increase and the current supplied to
the motor increases to establish a corresponding in-
creased motor voltage.
The voltage between the tap 35 and the positive
side of the battery is equal essentially to the motor
-
~voltage in series with the drop acrc)ss the small cur-
rent sensing resistor 41 and the emitter to base iunction
drop of the control transistor 36. As previously noted
the drop across the resistor 41 is minimal and the drop
across emitter-to-base circuit of a transistor is
normally of the order of 7/lO o~ a volt and thus is alsa
minimal. For practical analysis, the motor voltage can,
therefore, be assumed to correspond essentially to the
potentiometer voltage input to the transistor unit 18
with the current varying to maintain the motor potential.
With the potentiometer tap 35 set to the lower
end and thus effectively at ground or zero potential,
the regulator input signal appearing at the summing
point 39 is effectively zero and essentially the full
-18-
~)683~35
power source potential is impressed across ~he motor.
Conversely, when the tap is set to the opposite end
of the potentiometer 34 and thus directly to the posi-
tive side of the battery, the full power source potential
is applied to the input summing point 39 and essentially
the total source potential is exhibited across the re-
gulator resulting in the turn-off or setting the motor
potential essentially at zero thereby effectively turn-
ing the motor off. As the tap 35 is moved ~rom the top
side to approach ground, the voltage applied to the motor
-circuit proportionately increases. As the voltage appli-
ed to the motor increases, the current flow through the
motor circui~ and thus to the transistor 36 will increase
tending to further drive the transistor 18 on to maintain
the voltage across the motor 4 and thereby control the
speed to maintain an essentially constant speed. The
particular current range over which this action will
occur is controlled particularly by the value of the re-
; sistance and the beta or gain of the transistors 18 and
36. For example, in a practical trolling motor construc-
tion employing a small permanent magnet motor of 1/4
horsepower, the unit was established to provide a normal
two amp, slow speed current in the motor circuit. With
a heavy load on the motor, the circuit increases the
amperage up to six amperes to hold the load voltage and
the speed constant in the presence of propeller weed
entanglement, and the like.
In addition to this limited voltage regulation,
the sensing circuit 38 superimposes a continuous monitor-
ing of the circuit parameters to maintain safe circuitoperation.
-19-
~068385
The sensing amplifier transistor 40, in parti-
cular, provides an additional signal at the summing
point 39 and effectively operates, when turned-on, to
provide an increased controlsignal to the regulating
power transistor unit 18. A signal from transistor 40
effectively increases the voltage across the regulator
with a reduction in the motor voltage and current through
the series power circuit to limit the current.
The individual sensing o~ the three power regu-
lator parameters are sum~Lated at the summing point 43as previously-discussed, and conjointly provides a con-
trol as follows.
The transistor 40 functions as a control ampli-
fier means and when turned on increases the potential at
the base of the transistor 36 which through the foLlower
action of its emitter increases the regulator potential
and reduces the motor potential. T:his results in a cor-
responding decrease in the speed. The sensing ampli~ier
transistor 40 in this manner functions to modulate the
driving speed of the motor to maintain a safe current
; condition in the motor circuit. The extent to which the
motor speed is modulated or reduced is dependent upon
the amount the control transistor 40 is driven on.
More particularly the control transistor 40 is a
current amplifier which conducts after the base to emitter
potential is exceeded in accordance with conventional func-
tioning. There are essentially three current paths to
ground for the base including the voltage sensing resistor
44, the thermal-sensing resistor 46 and the resistor 42
in series with the power transistor 18.
-20-
~068385
As the motor 4 is loaded, the transistor 18 re-
sponds to effectively draw and supply maximum current to
the rotor 5. The back EMF of the motor 4 will also de-
: crease, tending to further increase the current level.
The heavy increase in current through resistor 41 signi-
ficantly above, for example,l6 amperes establishes a turn-
; on voltage across resistor 41 sufficient to turn-on the
sensing transistor 40. Thus, as the motor current in-
creases in response to the action of the voltage regulation
of transistor unit 18, the voltage across resistor 41 in-
creases. At a selected current level,.the voltage drop
: reaches ~he emitter to base drop of transistor 40 which,
in response to any further increase in load or motor current,
conducts to ground through resistor 37 and potentiometer 34.
This increases the! potential at the base, and essentially
simulates moving of tap 35 from ground to reduce the con-
ductivity,of power switch unit 18 and thereby reduce the
current through the load circuit.
Generally, the system is selected such that the
normaL maximum regulating current will not turn on the tran-
sistor and that the current level must rise significantly.
- However, if the voltage across the transistor simultaneously
rises, the transistor 18 may.be damaged or destroyed. For
example, heavy weed entangelement may tend to stall or heav-
ily load the motor with a resulting drop across the rotor 5and a corresponding increase voltage drop across the tran-
sistor 35. Such a combination of maximum regulated current
and high voltage could be destructive. The present invention
includes a voltage monitor means which in the illustrated em-
bodiment includes the series-connected resistor 42 and 44
connected across l:ransistor 18.
. -2~-
~6~3385
In particular) as the load current rises because
of weed entanglement and the like, the voltage across the
rotor 5 decreases and the voltage across transistor 18 in-
creases. This increased potential appears across the volt-
age dividing network and particularly a proportional levelappears across the resis~or 42. The base of transistor
40 relative to the emitter thus becomes more negative and
the transistor 40 is driven on in accordance with both the
current and voltage signals. The transistor 40 provides an
output signal at control sensing point or node 39 which, in
turn, is reflected as an increased potential at the base of
the control transistor 36. As previously noted an increased
potential at the base of the emitter-follower connected
transistor 36 reduces the conductivity of transistor 18 with
the voltage across the rotor 5 reduced and the voltage across
the transistor increased. The current through the major power
motor circuit or loop is significantLy reduced thereby.
For example, stalling of the motor will result in
application o essentially the entire source potential across
the motor circuit. Such a high voltage and associated high
stall current wou].d rapidly destroy the power transistor 18.
Thi~ is prevented in the present invention, however, by sig-
nificantly reducing the current and thereby holding the power
dissipation requirements of the transistor 18 below the de-
struction level.
This heavy current stall condition can generate sig-
nificant heat within the power transistor 18 even when operat-
ing at the normal decreased current level. If allowed to
exist for more than a few minutes, the maximum safe operating
temperature of the transistor would be exceeded. However, in
the illustrated embodiment, the sensing unit 45 responds to
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10683~5
the temperature of transistor 18 and decreases with
increasing temperature. Therefore, as the transistor
18 power dissipation and temperature increases, the parall-
el resistance of resistor ~4 and 45 decreases and increases
the current drive of the transistor 40, as a result of the
connection to the summing point ~3. As a result a still
higher potential appears at the summing point 39, and
therefore the base of the emitter-~ollower transistor 36,
to urther decrease the current drive to the motor and
the power transistor 18.
; Generally, under normal propeller operating con-
ditions, the thermistor 45 functions to minimize and mai~-
tain the current below the destructive level while main-
taining some current to the motor tending to maintain
rotation of the propeller and movement of the boat.
If, or any reason, the motor 4 is stalled out of
water, t,he power transistor unit 18 inthe absence of nor-
mal water cooling will rapidly heat to a very significant
level, decreasing the resistance to a level capable of
completely shutting down the system. Under all normal
operations, however, the system will reduce the power dis-
sipated in the transistor 18 to a safe level and maintain
a continuous propelling force in the trolling motor.
The operating power transistor 18 temperature
limitation is typically as shown in Fig. 6 wherein tem-
perature related operating current and voltage traces 52,
53 and 54 are shown defining sae operating conditions for
the transistor 18. Thus each of the curves is generally of
a similar configuration or shape but is offset with the
larger or higher curve 52 corresponding to a lower
23-
~6838~
temperature and the smallest curve 54 indicative of
the highest temperature with 53 corresponding to an inter-
mediate temperature. For example, the illustrated curves
are typical of sa~e operating conditions for twenty-five,
fifty and seventy-five degree operating temperatures of
the power transi'stor 18.
Applicant has found that the illustrated e~bodi-
ment of the invention employing the limited voltage regu~
lation to establish a constant voltage source wi.th fluctu-
ating load current to hold the constant speed in combina-
~-tion with the overriding limit--monitor in response to the
. significant parameters produces a relatively inexpensive
and reliable trolling motor solid state control. The
circuit thus controls the speed of the motor with the
constant voltage system under normal operation conditions
l~ allowing certain limited current f:Luctuation after which
the continuously monitored protect:ion permits continued.
- functioning of the trolling motor at a somewhat reduced
performance level which is directly proportional to the
20 relative danger level of the adverse or damaging condi- .
tions encountered. The unit may, there~ore, be conveniently
mounted within the lower unit and advantageously may be
mounted in accordance with the illustrated embodiment
thereof.
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