Abstract:
A low voltage interrupt for an electric winch prevents voltage decay of a battery due to excessive operation of the winch. If the battery voltage decays below a threshold, the low voltage interrupt disables the winch, allowing an alternator to recharge the battery. A voltage sense circuit determines the voltage of the battery. The sensed voltage is compared to a predetermined threshold. If the sensed voltage decays below the threshold, the low voltage interrupt generates an interrupt signal. The interrupt signal causes a relay to actuate, thereby interrupting current to the winch.

Description:
FIELD OF THE INVENTION 
   The present invention relates to an electric winch, and more particularly to compensating for a low voltage condition in a battery and/or charging system of an electric winch. 
   BACKGROUND OF THE INVENTION 
   Winches used to pull or lift heavy loads support a wide range of applications and assume a variety of sizes and types. Electrically-powered winches require a voltage supply to power the winch motor. A vehicle may incorporate a winch and power the winch with the vehicle battery and/or electrical system. 
   Frequent and excessive operation of the winch may result in an undue demand of current from the electrical supply. The current used by the winch may exceed the current supplied to the battery by a vehicle alternator. Continuous operation of the winch under this condition may cause the battery voltage to decay. Low battery voltage may cause performance issues with the winch or other electromechanical devices in the system. For example, low battery voltage reduces the speed of the winch motor, causing the motor to run for a longer period of time in order to pull a given load. Consequently, more heat is generated in the motor. Additionally, the battery may not be able to provide sufficient voltage to start the vehicle. 
   SUMMARY OF THE INVENTION 
   A low voltage interrupt system for an electric winch comprises an electrical supply that provides current to the electric winch. A voltage sense circuit determines a voltage of the electrical supply. A controller compares the voltage to a threshold voltage and generates an interrupt signal if the voltage is below the threshold voltage for a first period. A relay actuates in response to the interrupt signal, thereby interrupting the current to the electric winch. 
   In another aspect of the invention, a low voltage interrupt method for an electric winch comprises providing a current from an electrical supply to the electric winch. A voltage of the electrical supply is determined. The voltage is compared to a low voltage threshold. An interrupt signal is generated if the voltage is less than the low voltage threshold for a first period. The interrupt signal is received at a relay. The relay interrupts the current in response to the interrupt signal. 
   Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
       FIG. 1  is a functional block diagram of a low voltage interrupter circuit according to the present invention; 
       FIG. 2  is a circuit diagram of a low voltage interrupter circuit according to the present invention; 
       FIG. 3  graphically illustrates a battery voltage signal and a low voltage interrupt signal according to the present invention; and 
       FIG. 4  is a flow diagram of a low voltage interrupter algorithm according to the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements. 
   A low voltage interrupter system  10  for an electric winch includes a voltage sense circuit  12  and a switch  14  as shown in  FIG. 1 . The voltage sense circuit  12  senses a voltage from a battery  16 . The battery  16  supplies electrical power to various electro-mechanical devices in a vehicle having a winch system. For example, the battery  16  provides electrical power to vehicle accessories such as head lights, tail lights, the HVAC blower motor, and radio, as well as the voltage sense circuit  12 , a winch driving circuit  18  including a solenoid pack, and an electric winch  20 . As is known in the art, the battery  16  may provide electrical power to additional devices of the winch system. 
   The battery  16  is charged by an alternator  22  of a vehicle (not shown). However, operation of the winch  20  may drain the voltage of the battery  16  at a rate faster than the alternator  22  can charge the battery  16 . For example, the battery  16  may provide a system voltage of approximately 12 v. Operation of the winch  20  may cause the battery  16  to provide a voltage less than 12 v. As a result, certain electrical or electro-mechanical functions in the system may not perform as desired. The performance or reliability of the battery  16  may be reduced due to a lower operating voltage. Similarly, the operating speed of the winch  20  may be reduced. 
   The voltage sense circuit  12  senses the voltage of the battery  16  to determine if the voltage is below a threshold voltage. The voltage sense circuit  12  is operable to sense the effective voltage of the battery  16  at any location in the winch system. If the voltage sense circuit  12  determines that the voltage of the battery  16  is below the threshold voltage, the voltage sense circuit  12  generates a low voltage interrupt signal  24 . The switch  14  actuates to an open position in response to the low voltage interrupt signal  24 . If the switch  14  is in an open position, the solenoid pack  18  does not receive electrical power from the battery  16 . Therefore, operation of the winch  20  is interrupted. While the operation of the winch  20  is interrupted, the alternator  22  is able to charge the battery  16  more effectively. 
   Referring now to  FIG. 2 , the low voltage sense circuit  12  comprises a microcontroller unit  30 . The microcontroller unit  30  includes an analog-to-digital (A/D) converter that samples the voltage from the battery  16 . The microcontroller unit  30  differentiates the actual voltage of the battery  16  from other voltages of the electrical system. Other factors affecting the voltage signal include a transient voltage caused by winch inrush current or ripple voltage caused by alternator rotation. Microcontroller, sampling, and other computational functions may be performed on an integrated circuit, as shown, or each may be performed by a dedicated circuit as is known in the art. 
   The winch driving circuit  18  selectively provides electrical energy to rotate a winch armature  32  in a first direction or a second direction as is known in the art. Additionally, the winch driving circuit  18  is operable to provide no electrical energy to the armature  32 , thereby halting the operation of the winch. The winch driving circuit  18 , for example, includes four solenoids  34 ,  36 ,  38 ,  40  in an H-bridge configuration. A voltage signal applied at solenoid pack terminals  56 ,  58  affects the operation of the solenoids  34 ,  36 ,  38 ,  40 . For example, a voltage applied at a first terminal  56  energizes solenoids  36  and  38 . Energizing solenoids  36  and  38  causes current to flow from an input terminal  42  in a direction  44 . Current flow in direction  44  through a field  46  causes the armature  32  to rotate in a first direction  48 . Conversely, a voltage applied at a second terminal  58  energizes solenoids  34  and  40 . Energizing solenoids  34  and  40  causes current to flow from the input terminal  42  in a direction  50 . Current flow in direction  50  through the field  46  causes the armature  32  to rotate in a second direction  52 . 
   The switch  14  comprises, for example, a relay  54 . The relay  54  provides a connection between the solenoid pack terminals  42 ,  44  and a ground  59 , allowing current to flow selectively through the solenoids  34 ,  36 ,  38 ,  40 . The relay  54  receives the low voltage interrupt signal  24  from the microcontroller unit  30 . The low voltage interrupt signal  24  defaults to a first state wherein the relay  54  is closed. For example, the low voltage interrupt signal  24  may default to 0 v. If the voltage from the battery  16  drops below the threshold voltage, the microcontroller unit  30  causes the low voltage interrupt signal  24  to a second state. As a result, the relay  54  opens. With the relay  54  in an open position, all of the solenoids  34 ,  36 ,  38 ,  40  are de-energized. Therefore, the armature  32  does not receive electrical energy from the winch driving circuit  18 , causing operation of the winch to halt. 
   The low voltage interrupt signal  24  is generated in response to the voltage signal  60  from the battery as shown in  FIG. 3 . At time t 1 , the voltage signal  60  is approximately equal to or slightly above the threshold voltage  62 . For example, a nominal voltage of the voltage signal  60  may be 12 v, and the threshold voltage  62  may be 10 v. The low voltage interrupt signal  24  is a first state at time t 1 . While the voltage signal  60  provided by the battery is a DC voltage, the operation of the alternator may cause a ripple voltage  64  in the voltage signal  60 . In certain circumstances, the ripple voltage  64  may cause the voltage signal  60  to drop below the threshold voltage  62 . The voltage signal  60  may be rectified or filtered to minimize the effect of the ripple voltage  64 . 
   An inrush current causes a transient voltage  66  at time t 2 . The inrush current is a result of the beginning of the operation of the winch. The alternator is not able to charge the battery enough to compensate for the voltage required by the winch. Therefore, the voltage signal  60  begins to decay. At time t 3 , the microcontroller senses that the voltage signal  60  has decayed below the threshold voltage  62 . The microcontroller causes the voltage interrupt signal  24  to change from the first state to a second state. For example, the voltage interrupt signal  24  may change from 0 v to 5 v. When the voltage interrupt signal  24  is the second state, the relay of  FIG. 2  is energized, interrupting the current through the solenoids. The relay is energized for a predetermined period  68  to allow the alternator to charge the battery. For example, the predetermined period  68  may be 30 seconds. After the predetermined period  68  is elapsed, the microcontroller determines if the voltage signal  60  is still below the threshold voltage  62 . If the voltage signal  60  is below the threshold voltage  62  after the predetermined period  68 , the microcontroller continues to energize the relay. Alternatively, the relay may be energized until the microcontroller senses that the voltage signal  60  is charged above the threshold voltage  62 . 
   A low voltage interrupter algorithm  80  is shown in  FIG. 4 . The algorithm  80  starts at the power-up of the vehicle or winch system. A startup timer is initialized at step  82 . The startup timer ensures that the algorithm  80  does not initiate a low voltage interrupt prematurely. The electrical system of the vehicle may be unstable immediately after power-up, resulting in an unstable voltage signal. At step  84 , the algorithm  80  determines if a proper startup period has elapsed. In an exemplary embodiment, the startup period is 50 ms. If the startup timer has not reached 50 ms, step  84  is repeated. After the startup timer reaches the proper period, the algorithm  80  continues to step  86 . 
   At step  86 , the algorithm  80  determines if the voltage signal from the battery is below the low voltage threshold. If the voltage signal is not below the low voltage threshold, the algorithm continues to step  88 . If the voltage signal is below the low voltage threshold, the algorithm  80  determines if the voltage signal bas been below the low voltage threshold for a low voltage period at step  90 . In an exemplary embodiment, the low voltage period is 600 ms. During operation of the winch, system noise or voltage transients may cause the voltage signal to fall below the low voltage threshold temporarily. The low voltage period ensures that the algorithm  80  does not initiate a low voltage interrupt due to a temporary voltage drop. If the voltage signal is not below the low voltage threshold for 600 ms, the algorithm  80  continues to check the voltage signal at step  86 . If the voltage signal is below the low voltage threshold continuously for 600 ms, the algorithm  80  disables the winch motor at step  92 . 
   A flag is set at step  94  to indicate that the algorithm  80  initiated a low voltage interrupt. An interrupt timer is checked at step  96  to determine if the low voltage interrupt has been active for a disable period. The interrupt timer ensures that the winch motor is disabled for the disable period before allowing the algorithm  80  to re-enable the winch motor. In the preferred embodiment, the disable period is 30 seconds. If the disable period has not elapsed, the algorithm  80  checks the voltage signal again at step  86 . If the voltage signal is still below the low voltage threshold, the algorithm  80  continues through to step  96  to recheck the disable period. If the voltage signal is not below the low voltage threshold, the algorithm  80  determines if the flag was previously set at step  88 . If the flag was set, the algorithm  80  continues to step  96 . If the flag was not set, the algorithm  80  returns to step  86 . 
   If the disable period is elapsed at step  96 , the algorithm  80  rechecks the voltage signal at step  98 . If the voltage signal is still below the low voltage threshold, the algorithm  80  returns to step  92 . If the voltage signal is above the low voltage threshold, the algorithm  80  enables the winch motor and clears the flag at step  100 . The algorithm then continues to check for a low voltage signal at step  84 . In alternative embodiments, the algorithm  80  may require that the voltage signal increase to a second threshold. For example, the algorithm  80  may continue with the winch motor disabled until the voltage signal attains a specific voltage level above the low voltage threshold. 
   The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.