Abstract:
Monitoring the temperature of the brush of the motor on an electric winch during operation and restricting the operation of the motor within a cooling range in order to minimize downtime and maximize runtime.

Description:
PRIORITY CLAIMS 
     The present application is a continuation-in-part of U.S. Provisional Patent Application No. 62/038,062, entitled System and Method for Thermal Protection of an Electric Winch, filed on Aug. 15, 2014 which is incorporated herein by reference. 
    
    
     1. FIELD OF THE INVENTION 
     The present invention relates generally to a system and method for controlling the motor of an electric winch. More particularly, the present invention relates to a system and method that prevents thermal damage to the motor of an electric winch while optimizing run time. 
     2. BACKGROUND OF THE INVENTION 
     Electric winches typically have lighter load ratings and shorter duty cycles when compared to hydraulic winches of comparable size. When fully loaded, electric winches can only be operated a short time before heat builds up to dangerous levels in the motor. This heat buildup can cause permanent damage to the motor and winch if left unchecked. However, electric winches are lighter and less expensive to install than hydraulically driven winches. This cost advantage has led to increased interest in the use of electric winches in applications where a hydraulic winch has traditionally been used. 
     What is needed, therefore, is a system or method for protecting an electric winch from damage caused by overheating. 
     Further what is needed is a system and method that optimizes runtime in the duty cycle of an electric winch. 
     DESCRIPTION OF THE INVENTION 
     The present invention achieves its objectives by monitoring the temperature of the electric motor. Various locations on the electric motor may be monitored for temperature during operation. In the preferred embodiment, the temperature of the brush of the electric motor is monitored during operation. The brush is a key component of the electric motor and is the site where much of the heat from operation is generated. Thus, if the brush does not overheat the rest of the motor will not overheat. 
     The temperature can be monitored by different types of devices. In the preferred embodiment, the temperature is monitored using a thermocouple. Thermocouples provide accurate temperature readings in the form of an electronic signal that can be readily interpreted and used by various electronic devices. Further, they are responsive to changes in the temperature. They do not have any thermal mass themselves that must also cool before they can sense the change in the brush. 
     In the preferred embodiment, the electronic signal is transmitted to a control circuit or other electronic control device. Initially, the winch and brush start at or near ambient temperature. This is typically well below 176° C. When the temperature of the brush reaches 212° C., the controller circuit terminates operation of the winch motor. This is accomplished by the opening of a relay or solenoid thus terminating the connection between the voltage supply source and the motor. This provides time for the motor to cool. Once the temperature of the brush reaches 176° C. the control circuit closes the relay. This returns the power supply to the motor and reinstates operation of the motor. This operating range may vary based on the metallurgy of the brush and motor and other cooling characteristics. These variations would be necessary to match the optimum range in the cooling curve. 
     Thus, in operation the motor is initially operable as long as the temperature of the brush is less than 212° C. Once the temperature of the brush reaches 212° C. the operation is terminated until it drops to 176° C. Thereafter, the temperature range of the brush needed for operation is 176° C. to 212° C. 
     This operating temperature range provides a couple of advantages. First, damage to the motor from heat buildup only occurs at temperatures in excess of 212° C. So no damage occurs to the motor or winch. Second, the cooling curve of an electric motor is steepest from 212° C. down to 176° C. The rate of cooling slows significantly at temperatures below 176° C. So by having 176° C. as the bottom of the temperature operating range the entire “fast” section of the cooling curve are utilized. The motor and winch are returned to service quickly. This maximizes up time and minimizes down time in the duty cycle. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Preferred embodiments of the invention will now be described in further detail. Other features, aspects, and advantages of the present invention will become better understood with regard to the following detailed description, appended claims, and accompanying drawings (which are not to scale) where: 
         FIG. 1  is a schematic of an electric winch incorporating the preferred embodiment of the present invention; 
         FIG. 2  is a flow chart of the operation of the present invention; and 
         FIG. 3  is the temperature vs. time cooling chart for the electric motor of the winch. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S) 
     Turning now to the drawings wherein like reference characters indicate like or similar parts throughout,  FIGS. 1-3  illustrates the preferred embodiment of the present invention. The electric winch  20  is seen in  FIG. 1 . It has an electric motor  22 , gear train  24 , spool  26  and control module  28 . Power from the motor  22  is transferred to the spool  26  via the gear train  24 . The gear train  24  provides a mechanical advantage for the motor  22  in rotating the spool  26 . 
     The control module  28  controls operation of the electric motor  22 . Line  30  is paid out and retrieved through rotation of the spool  26 . Direction of rotation of the spool  26  is changed by changing the direction of rotation of the motor  22 . The motor  22  is typically a direct current or DC motor. Thus by changing the polarity of the power the direction of rotation can be changed. The polarity of the power is controlled by the control module  28 . 
     The motor  22  has brushes  32  which transfer the electrical power to the field windings  34 . The brushes  32  are the most heat intensive piece of the motor  22 . In the preferred embodiment the temperature of at least one of the brushes  32  is monitored by a temperature sensor  36 . While other temperature sensors  36  may be used, the preferred embodiment uses a thermocouple  38  to monitor this temperature. The thermocouple  38  is coupled or otherwise attached to the brush  32 . The temperature reading of the brushes  32  is fed to the control module  20 . 
     As best seen in  FIG. 2 , the cooling range or fastest cooling temperature range for the electric motor  22  is from 212° C. down to 176° C. By using 212° C. as the upper limit of the operating limit and cooling range and then reinstating operation once the temperature of the electric motor  22  reaches 176° C. or the lower limit of the cooling range, the amount of shut down cooling time is minimized and the amount of operating time is maximized. The exact temperatures of the upper and lower limits of the cooling range may vary depending upon the materials used for the motor  22  and the design of the motor  22  and its housing. 
     When the operation of the winch  20  is started it is at ambient temperature. This would most likely be anywhere from −30° C. to 45° C. The operation of the winch  20  continues uninterrupted until the temperature of the motor  22 , as measured by the temperature sensor  36  in the brush  32 , reaches 212° C. At that point, the control module  28  suspends operation of the motor  22 , and in turn, the winch  20 , until the temperature of the motor  22  reaches 176° C. At this point, the control module  28  reinstates operation of the motor  22 , and in turn, the winch  20 . Operation of the winch  20  continues uninterrupted until the temperature of the motor  22  reaches 212° C. At that point, the cooling cycle is initiated taking the motor  22  and winch  20  out of service until the lower temperature (176° C.) is reached. 
     It should be noted, the gear train  24  could be planetary or traditional. Further, other types of temperature sensor  36  could be used with the present invention in lieu of the thermocouple. 
     The foregoing description details certain preferred embodiments of the present invention and describes the best mode contemplated. It will be appreciated, however, that changes may be made in the details of construction and the configuration of components without departing from the spirit and scope of the disclosure. Therefore, the description provided herein is to be considered exemplary, rather than limiting, and the true scope of the invention is that defined by the following claims and the full range of equivalency to which each element thereof is entitled.