Abstract:
The present invention is a control system for a vehicle that utilizes a powered attachment such as a material spreader. Such a device requires the use of a high current drawing motor, which in turn requires the ability to control the flow of high amperage current. The high current switching circuitry is mounted on or near the electric motor to prevent the heat generated by the circuitry from posing any type of hazard. A low current control is placed within the cab of the vehicle and serves to remotely control the switching circuitry.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to controls for accessories attached or mounted to vehicles and more specifically to a cab mounted control for controlling a high current power source for an electric motor which drives an accessory such as a spreader for sand or salt that is coupled to a vehicle. 
     2. Description of the Related Art 
     There are many devices that are coupled with a vehicle that require a separate motor to control and operate the device. For instance, a spreader is often mounted on a vehicle to aid in the deposition of granular material such as salt, seed, fertilizers, chemical agents, sand or the like onto a surface as the vehicle travels over it. The spreader is connected to a material supply bin, which is usually gravity fed. As the material falls through the spreader, its is distributed by an auger or similar driving device. The auger is powered by an electric motor which is controlled by the operator in the cab of the vehicle. The operator can start, stop and control the speed of the spreader by so controlling the motor. The speed of the spreader controls the distribution characteristics of the material being spread. 
     Traditionally, the electric motor requires a relatively high current power source to adequately drive the spreader. Therefore, the motor control circuitry employed must be able to handle such a high current load. Obviously, any type of circuitry capable of handling such a level of current is appropriate. Generally, the power control circuit is mounted in the cab of the vehicle. The operator then actuates a control which will turn on, turn off and vary the speed of the electric motor by varying the amount of current which ultimately reaches the motor. 
     While this arrangement provides all of the necessary control the operator may require, it also creates several areas of concern. In order to make such an arrangement functional, relatively heavy gauge wire must be run through the firewall of the vehicle and into the cab. In and of itself, this is a modification which many vehicle owners may be hesitant to make as a correspondingly large hole must be cut. Furthermore, the cab and spreader are usually located on opposite ends of the vehicle. As such, a long length of this heavy gauge wire must be utilized. This adds significantly to the cost of such a system. In order to locate the power control circuitry remotely from the motor and driver device, rather large and very expensive high current handling electrical plugs must be utilized, further increasing the overall cost. These plugs are used to couple the high current wire to a control box that contains the MOSFET and also to couple the wire to a junction with the electric motor. In addition, the length of the wire reduces the efficiency of the system due to the voltage drop-off encountered. Finally, the size of the wire makes it difficult to conceal. As such, the exposed wire is subject to abrasions and inadvertent cutting. 
     The most significant concern, however, is the relatively large amount of heat that is generated by a MOSFET (or similar component) located within the cab of a vehicle, when handling high current loads. The heat generated by the control circuitry represents a fire hazard and severely limits the design parameters available during installation. Typically, the cab mounted circuitry occupies almost 2 square feet of space. It is difficult to place such a large device within the cab of a vehicle because the heat produced will often adversely affect the surrounding components. A large number of the items within the cab are made of plastic and are thus subject to melt. Wiring proximate the control circuit can also be damaged by the heat and thus short circuit. This causes obvious mechanical/electrical problems and also creates a risk of fire. If the circuitry can be mounted in a location that does not affect components in the cab, it will prevent the operator from being able to fully utilize the cab. That is, anything brought into the cab must be carefully placed to avoid contact with the control circuit. 
     As such, the heat generated by previous power control circuits is of significant concern. There has been no way to minimize this heat generation as those components which can handle the required current levels must necessarily dissipate this heat in some manner. Presently, such systems must simply be installed within the cab of the vehicle, in a location which hopefully minimizes the exposure of sensitive elements to the high levels of heat generated. The heat is simply allowed to dissipate into the surrounding air. Such installation presumes that the airflow within the cab will be sufficient to prevent the control circuitry from overheating. This is often incorrect, and as a result, the control circuitry may be prone to overheating, thus amplifying the above described concerns. Since the space inside the cabs of vehicles is so limited, the placement of the control is extremely problematic. As a result, vehicle owners must risk serious damage to their vehicles and forego the use of significant amounts of space within the cab in order to simply control an attachment which is mounted on the vehicle. 
     Therefore, there exists a need to provide an accessory control unit for high current drawing vehicle accessories that is electrically efficient and thermally isolated. 
     SUMMARY OF THE INVENTION 
     The present invention places all the high current switching circuitry within the accessory at or near the electric motor. A low current control line is run from the cab of the vehicle to the switching circuitry, thus giving the operator full control over the electric motor without having the physically intrusive high current wires inside the cab of the vehicle. Since the power is brought directly to the motor, as opposed to a long control line run, the system is more efficient. 
     Locating the switching circuitry within the accessory prevents the heat generated by the circuitry from posing any hazard within the cab of the vehicle. In addition, the circuitry can be directly connected to the casing of the electric motor. Generally, the casing is an aluminum shell, which acts as a heat sink to the switching circuitry. The circuitry can be placed on the inside of the motor casing to conserve space. Alternatively, the circuitry can be mounted to the outside of the motor casing, or even adjacent to it, thus allowing the present system to be more easily retrofit into existing devices. 
     In one embodiment of the present invention, a MOSFET is used to control the high current flow to the electric motor. The MOSFET is mounted on the inner wall of the motor casing. A low current control within the cab actuates the MOSFET, which in turn controls the flow of current to the electric motor. In a preferred embodiment, a photovoltaic isolator is used to control the MOSFET. The photovoltaic isolator includes a variable LED and a photovoltaic generator. The intensity of the LED is varied by the cab control. The LED is located proximate to the photovoltaic generator that is coupled to the gate of the MOSFET. As the intensity of the light emitted by the LED increases, the photovoltaic generator increases the voltage at the gate, thus controlling the MOSFET in a known way. Alternatively, the MOSFET may be controlled directly through the actuation of a variable resistor or similar element, which directly controls the voltage generated at the gate. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram representing the control system of the present invention coupled with a vehicle. 
     FIG. 2 is schematic drawing of the control system with the circuitry mounted within the housing of an electric motor (shown in cross section). 
     FIG. 3 is a circuit diagram of the control system of the present invention utilizing a photovoltaic controller. 
     FIG. 4 is a circuit diagram of the control system of the present invention utilizing a variable resistor. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 1 illustrates the control system  10  as it is coupled with a vehicle  14  and an accessory. The vehicle  14  is representative of any type of vehicle to which a powered material handler, such as spreader  20 , may be attached. The vehicle  14  can range from a small personal vehicle, such as a pickup truck, to a larger commercial vehicle such as a dump truck used by road servicing crews. A housing  12  containing the accessory is coupled to the vehicle  14 . This connection is represented by coupling  18 . The housing  12  could be mounted directly to the vehicle as either a permanent or removable attachment or could simply be pulled behind as a trailer. Within the housing  12  is the actual spreader  20 . The spreader  20  includes some form of material handling device, such as an auger and is attached to a material supply container (either within the spreader  20  or within the vehicle  14 ). An electric motor  22  is mounted within the spreader  20  and has a drive shaft  34  (FIG. 2) which is coupled to the material handling device. A high current switching circuit, such as MOSFET  24 , is mounted on the electric motor  22 . 
     A control  26  is mounted within the cab  16  of the vehicle  14 . The control  26  is electrically connected to MOSFET  24  with a relatively thin, low current control line  28 . The control  26  allows an operator to turn the electric motor  22  on, off and vary its speed by controlling the MOSFET  24 , which in turns controls the amount of current supplied to the motor  22 . 
     FIG. 2 schematically illustrates the control system  10  of the present invention in its most preferred form. High amperage current is supplied to the electric motor  22  by an alternator  38  (or similar power supply). Current is ultimately delivered to the coils  32  of the electric motor  22 , which in turn causes the drive shaft  34  to rotate and deliver motive force to the actual spreader itself. The positive feed of the alternator  38  is coupled to the positive terminal  36  of the MOSFET  24 . The MOSFET  24  is of sufficient capacity to handle the high current load. In a preferred embodiment, the MOSFET  24  has a  100  Amp capacity. The positive output of MOSFET  24  is coupled, via positive lead  42 , through junction  40  to the motor coil  32 . The MOSFET  24  is flushly mounted to an inner side of the aluminum motor housing  30 , which acts as a heat sink for the MOSFET  24 . The positive terminal  36  of the MOSFET  24  extends through the motor housing  30 . Alternatively, the MOSFET could be mounted to the outer surface of the electric motor  22 . This makes installation easier and allows this system to be retrofit into existing devices. Control  26  receives power from a low current power supply  44 . The control  26  is coupled to the MOSFET  24  via control line  28 . As the control  26  is varied, the amount of current that flows from the alternator  38 , through MOSFET  24  and ultimately to the coils  32  is correspondingly varied. while it is preferable to mount the MOSFET  24  to an inner surface of the motor  22 , it is to be understood that the present invention contemplates locating the MOSFET  24  (or equivalent circuitry) anywhere proximate the electric motor  22 . That is, MOSFET  24  can be mounted on an outer surface of the motor  22  or on a structure located proximate to the motor  22 , so long as the efficiency of the circuit is maintained, heat generation is controlled, and the cab controls are connected remotely via a low current control line. 
     FIG. 3 is a circuit diagram illustrating one way of controlling electric motor  22  using a photovoltaic isolator. The photovoltaic isolator includes LED  46  and photovoltaic generator  48 . One example of such a photovoltaic isolator is that produced by International Rectifier, Series PVI, particularly the PVI 1050 or the PVI 5100. Control  26  serves to control the amount of current reaching LED  46 . As such, the control  26  will turn on, turn off and vary the intensity of LED  46 . As is known, LED  46  will only require a minimal current supply. The LED  46  is located proximate to a photovoltaic generator  48 . As the LED  46  varies in intensity, the photovoltaic generator  48  causes a corresponding variance in the voltage applied to the gate of the MOSFET  24 . By controlling the voltage applied to the gate, the amount of current which flows from the voltage source  50  (such as alternator  38 ) to the electric motor  22  is also controlled. The combination of the LED  46  and the photovoltaic generator  48  also act as an isolator to physically separate the low current control line from the high current switching circuit. 
     Alternatively, as shown in FIG. 4, a variable resistor  52  may be substituted for the LED  46 /photovoltaic controller  48  combination. The variable resistor  52  is actuated directly by the controller  26 , and varies the amount of low amperage current passing to ground. This may be accomplished in any of the known ways, such as employing a rheostat, a potentiometer, or the like. Once again, by varying the amount of voltage applied to the gate of the MOSFET  24 , the amount of current flowing from the voltage source  50  to the electric motor  22  is correspondingly varied. 
     While the above embodiments have been shown and described to include a MOSFET, the present invention contemplates the use of any type of high current switching circuitry. That is, by locating the switching circuitry close to the motor, and away from the cab, and remotely controlling the circuitry from the cab, the problems associated with any of these switching arrangements are minimized. 
     Those skilled in the art will further appreciate that the present invention may be embodied in other specific forms without departing from the spirit or central attributes thereof. In that the foregoing description of the present invention discloses only exemplary embodiments thereof, it is to be understood that other variations are contemplated as being within the scope of the present invention. Accordingly, the present invention is not limited in the particular embodiments which have been described in detail therein. Rather, reference should be made to the appended claims as indicative of the scope and content of the present invention.