CA1068385A - Electric trolling motor apparatus - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
An electric trolling motor apparatus includes a solid state motor control housed within the lower propeller unit to establish a constant speed in combination with continuous monitoring to prevent damaging current levels.
The forward nose cone of the unit has an inner transverse platform with cast radial ribs and with a shape to receive the slightly smaller mounting frame of a power transistor with a pair of central lateral recesses. A circuit board is formed with a corresponding configured opening. The transistor is bolted to the platform for heat transfer and supports the circuit board. The transistor is connected as a voltage regulator to maintain an essentially constant voltage and resulting speed of the motor. A self-protecting, compensating means positively reduces the current under conditions which would tend to damage the control system.
A sensing amplifier has a summing input connected to in-dividual sensors of the voltage, current and temperature parameters of the power transistor and an output summed with the speed signal to the transistor and provide an overriding motor current control. An extremely high level of any single sensed parameter effectively reduces the input to the tran-sistor regulator. A somewhat lower sensed level of the com-bination of any two of the parameters similarly responds and sensing of all three parameters at a further reduced level also similarly responds to reduce the motor speed.

Description

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.

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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 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 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 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 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 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 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 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 - ~)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 ~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 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 ~)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.

~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.

~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 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 ~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.

Claims (22)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An outboard motor apparatus comprising a lower propeller unit having a motor, a solid state motor control circuit unit mounted within the lower propeller unit, said circuit unit including a regulator means to regulate the current to the motor and maintain a constant voltage across the motor in accordance with the setting of an input signal, and a limiting means forming a part of said circuit unit and monitoring a plurality of the operating parameters of said regulator means and coupled to said regulator means to change the input signal to reduce the performance of the motor and prevent said parameters from reaching levels sufficient to damage the regulator means.

2. The motor apparatus of claim 1 wherein said regulator means includes a power transistor and a control transistor, an adjustable resistance means establishing a speed signal voltage, an input means of the control transistor being connected in series with the adjustable resistance means and the motor, said power transistor having an input means connected in series with the output means of the control transistor to a common ground and said power transistor having an output means connected in series between said common ground and the motor whereby said power transistor conducts sufficient current to maintain a constant motor voltage and speed, said limiting means being connected to the control transistor and responsive to selected abnormal power transistor current and voltage to reduce the speed signal voltage to the control transistor and thereby to the power transistor.

3. The motor apparatus of claim 1 wherein said circuit unit includes a solid state power switch means having a control signal input means and power output means, and said limiting means including temperature sensitive means coupled to the power switch means to limit the current to the motor.

4. The motor apparatus of claim 1 wherein said limiting means includes a current sensing means connected to sense the current through the regulator means, a voltage sensing means connected to sense the voltage across the regulator means, temperature sensing means coupled to the regulator means to sense the temperature thereof, and summing means coupled to all said sensing means and operable to conjointly control the regulator means to reduce the current flow through the regulator means in accordance with selected abnormal levels of the current, voltage and temperature.

5. The motor apparatus of claim 4 wherein said regulator means includes a power transistor and said current sensing means includes a current sensing resistor connected in series with the power transistor and said voltage sensing means includes a pair of series connected voltage sensing resistors connected across the power transistor, the connec-tion of said voltage sensing resistors defining a signal summing node, said temperature sensing means including a tem-perature sensitive resistor connected in parallel with one of said voltage sensing resistors, and said limiting means includes a sensing amplifier means having an input terminal means connected to said summing node.

6. The motor apparatus of claim 4 wherein said regulator means includes a power transistor, and a control transistor, an adjustable resistance means establishing a speed signal voltage, an input means of the control transis-tor being connected in series with the adjustable resistance means and the motor, said power transistor having an input means connected in series with the output means of the control transistor to a common ground and said power transistor having an output means connected in series between said com-mon ground and the motor whereby said power transistor is connected to conduct sufficient current to maintain a constant motor voltage and speed, said summing means establish-ing a voltage signal and connected to oppose said speed signal voltage to thereby reduce the voltage level below the constant voltage and reduce the current.

7. The motor apparatus of claim 1 wherein said regulator means includes a solid state amplifying element having a control signal input means and power output means, said lower propeller unit includes a forward end housing section having an outer housing wall defining an inner chamber, said chamber including a platform structure integrally attached to said housing wall and terminating in an intermediate wall portion, said control unit including a circuit board secured to said amplifying element, and means securing said amplifying element abutting the platform struction to firmly support the circuit board with the amplifying element in supporting relation to said intermediate wall portion and with the heat within the amplifying element being conductively transferred to said wall portion.

8. In the trolling motor of claim 7 wherein said amplifying element includes a housing having a mounting flange, said wall portion is a raised portion conforming essentially to said mounting flange and slightly smaller than the mounting flange, said raised portion having edge recesses located in accordance with the input connections to the power amplifying element, and said circuit board having an opening with edge projecting arms and said opening generally corresponding in shape to said platform and being slightly smaller than said raised portion including said recesses and located to mate with said raised portion and recesses.

9. Outboard motor apparatus having a lower propeller unit secured to a boat mounting member and an upper tiller handle unit, said lower propeller unit being sealed and housing a permanent magnet electric motor with a variable energized rotor for controlling the speed of the motor, said motor being constructed for energization from a battery, a solid state motor control circuit unit mounted within the lower propeller unit, said control circuit unit comprising a solid state power transistor means connected in series with said rotor between a first and a second battery input means, said solid state power transistor means having a control signal input means, a speed setting voltage means establishing an input signal and connected to said control signal input means, circuit means connected to said power transistor means and to said motor to define a voltage regulator means to regulate the current to the rotor and maintain a constant voltage across the rotor in accordance with the setting of said input signal, and a current limit means forming a part of the control circuit unit and monitoring a plurality of the operating parameters of said power transistor means and coupled to said power transistor means of said regulator means, said current limit means being responsive to abnormal parameters to override said voltage regulator means and change the input signal to reduce the performance of the motor and prevent said parameters from reaching levels sufficient lo damage the power transistor.

10. The motor apparatus of claim 9 wherein the current limit means includes a current sensor, a voltage sensor and a temperature sensor, each of said sensors being operable to establish a voltage signal, summing means to establish a voltage signal proportional to the sum of the sensors voltage signals, and an amplifying means having an input means connected to said summing means and an output means connected to said control signal input means and oper-able when conducting to reduce the voltage at said control signal input means and thereby limit the current and protect said power transistor means against high current, high voltage, high temeprature and combinations thereof.

11. The motor apparatus of claim 9 wherein said circuit means includes an input control transistor connected in an emitter follower connection with an input means connected to the motor and battery in series with said speed setting voltage means in an input power loop, and said power transistor means is a power transistor having an input means connected in series with the output of the control transis-tor, said power transistor having a power output means connected in series with the motor and battery input means in an output power loop.

12. The motor apparatus of claim 11 wherein said current limit means includes a current sensing resistor in series between the power transistor and the motor, a sensing amplifier having an input means connected across said current sensing resistor in series with an input resis-tor with a signal sensing node defined between the amplifier and the input resistor, said sensing amplifier having output means connected between the motor and the input means of the control transistor to modulate the voltage of the vol-tage regulator means, a voltage sensing resistor connected across said power transistor in series with said input resistor and current sensing resistor to establish a voltage related signal at said sensing node, and a temperature responsive resistor coupled to said power transistor and con-nected in parallel with said voltage sensing resistor to establish a temperature related signal at said sensing node, said sensing amplifier being responsive to any one sensed selected abnormal parameter and lesser combination of abnormal parameters to modulate the input voltage to and reduce the conductivity of the power transistor.

13. The motor apparatus of claim 9 whrein said rotor has one motor input connected to the first battery input means and having a second motor input, said current limit means including a current sensing resistor connected to said second motor input, said power transistor means is a power transistor having a collector and emitter one of which is connected to said sensing resistor and the opposite of which is connected to the second battery input means, a control transistor of an opposite polarity from the power transistor and having an emitter and collector and having a control base and forming a base emitter junction connected in series with the sensing resistor and with an emitter to collector junction connected in series with the base of the power transistor, said speed setting voltage means including an adjustable resistor connected to said first and second battery input means and having an adjustable output tap, a series resistor connected between the tap and the control base, said current limit means including a pair of voltage sensing resistors connected in series across said power transistor with the connection of said resistors defining a signal sum-ming node and with one sensing resistor connected to the second battery input means, a thermistor coupled to said power transistor and connected in parallel with the voltage sensing resistor connected to the second battery input means, and said current limit means including a transistor having an emitter and collector between the second motor input of the rotor and the base of the control transistor and having a base connected to said sensing node.

14. The motor apparatus of claim 13 wherein said rotor includes a rotor shaft, a bearing for said shaft, said lower propeller unit includes a cone-shaped forward end housing section having an end portion for supporting the bearing and the rotor shaft and defining an inner chamber, said chamber including a platform structure integrally attached to said housing section and terminating in a transverse wall portion spaced from said shaft and shaft bearing, said power transistor having a heat conductive mounting flange member, a circuit board abutting said transverse wall portion and having a central portion slightly smaller and corresponding to said mounting flange member, means securing said circuit board to said power transistor, means securing said mounting flange member in electrically insulating and heat conductive abutting relation to said wall portion to firmly clamp the power transistor to said transverse wall portion and with the heat within the transistor being conductively transferred to said transverse wall portion, said circuit board including the components of said current limit means to the face opposite the transverse wall portion, and a heat conductive resin encasing said circuit board and components.

15. The motor apparatus of claim 14 wherein said transverse wall portion includes a raised platform conform-ing essentially to said transistor mounting flange member, said platform having centrally located edge recesses, said power transistor having input connections aligned with said recesses, and said circuit board having projecting arms slightly smaller than said recesses and located to mate with said recesses.

16. The motor apparatus of claim 1 wherein the lower propeller unit includes a cup-shaped hollow forward end housing section including a solid outer housing wall having an open end and defining an inner chamber, a plat-form structure integrally attached to said housing wall within said chamber and terminating in a transverse mounting wall portion spanning the open end of the housing section, said circuit unit including a circuit board having control circuit components mounted thereon and said regulator means including a power amplifier means firmly clamped abutting said transverse mounting wall portion with heat within the amplifier means being conductively transferred to said transverse mounting wall portion and to said housing wall.

17. The motor apparatus of claim 16 wherein said amplifier means includes a mounting flange, said transverse mounting wall portion is a raised platform conforming essentially to the mounting flange of said amplifier means, said portion being smaller than said mounting flange and having edge recesses located in accordance with the input connections to the power amplifier means, and said circuit board having an opening with projecting arms and being constructed to closely telescope over the raised platform portion with the arms mating with said recesses.

18. The motor apparatus of claim 16 including a heat conductive insulating material filling the chamber to encapsulate said circuit board to carry the heat to said end housing section.

19. The motor apparatus of claim 18 wherein said end housing section includes a shaft bearing secured within the open end of the housing in spaced relation to the transverse wall portion and said heat conductive insulating material.

20. A solid state control circuit unit for an outboard motor apparatus including an electric motor in a lower propeller unit and said motor having a variably energized rotor to control the speed, said control circuit unit being constructed to be located in said lower propeller unit and comprising first and second battery input means, regulator means encircling a power amplifier unit having input means in series with an adjustable voltage means for connection to battery input means in an input power loop and having output means for series connection with the rotor and the battery input means in an output power loop, said power amplifier unit operating to regulate the current to the rotor and maintain a constant voltage on the rotor to establish a constant speed, a sensing amplifier having output means connected between the rotor and the input means of the power amplifier unit to modulate the voltage of the adjustable voltage means and thereby automatically adjust the constant voltage to limit the current drawn, and current limit means to sense a plurality of the operating parameters of the power amplifier unit and coupled to the regulator means to charge the input signal to sensing amplifier to reduce the performance of the motor and prevent said parameters from reaching levels sufficient to damage the regulator means.

21. The control circuit unit of claim 20 wherein said current limit means includes a current sensing resistor connected in series with the power amplifier unit, said sensing amplifier having an input means connected across said sensing resistor in series with an input resistor with a signal sensing node defined at the connection to the resistors, a voltage sensing resistor connected across said power amplifier unit in series with said input resistor to establish a voltage related signal at said sensing node, and a temperature responsive resistor coupled to said power amplifier unit and connected in parallel with said voltage sensing resistor to establish a temperature related signal at said sensing node, said sensing amplifier being respon-sive to any one sensed selected abnormal parameter and to a lesser combination of abnormal parameters to modulate the input voltage to and reduce the conductivity of the power amplifier unit and thereby limit the current in the output power loop.

22. The control circuit unit of claim 20 wherein said rotor has one rotor input connected to one battery input means and having a second rotor input, said current limit means including a current sensing resistor connected to said second rotor input, said power amplifier unit including a power transistor having a collector and emitter one of which is connected to said sensing resistor and the opposite of which is connected to the second battery input means, said power amplifier unit further including a power transistor and a control transistor of a polarity opposite the power transistor and having an emitter and collector connected be-tween the sensing resistor and the base of the power transis-tor and having a control base, said adjustable voltage means including an adjustable resistor connected across said battery input means and having an adjustable output tap, a series resistor connected between the tap and the control base to complete said input power loop, said current limit means including a pair of voltage sensing resistors connected in series across said power transistor with the connection of said voltage sensing resistors defining a signal summing node, a thermistor coupled to said power transistor and connected in parallel with the voltage sensing resis-tor connected to the second battery input means, and said sensing amplifier being a transistor having an emitter and collector between the second rotor input of the rotor and the control base of the control transistor and having a base connected to said signal summing node.