Abstract:
An interlock circuit on a mowing vehicle or tractor deactivates the engine if a signal from a single backup sensor is interrupted. The mowing vehicle or tractor has an engine, an electric power source to provide electric current to a magneto and an ignition, a transmission connected to the engine and having forward, neutral and reverse operations, a controllable tool drive (PTO) connected to the engine for powering an accessory, and a single backup sensor to provide a signal if no object is detected behind the vehicle. A reverse sensing switch is movable between a first position if the transmission is in forward or neutral, and a second position if the transmission is in reverse. A PTO switch is movable between an on condition for activating the PTO and an off position for deactivating the PTO.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates generally to interlock circuits for vehicles such as lawn and garden tractors, and more specifically to interlock circuits for selectively disabling operation of the engine and/or an accessory drive such as a PTO when an obstacle is sensed behind the vehicle.  
       BACKGROUND OF THE INVENTION  
       [0002]     Vehicles such as lawn and garden tractors may have PTO driven accessories, such as a lawn mower deck, that may be shut off when the vehicle is operated in reverse. For example, when a vehicle is shifted into reverse with the PTO running, an interlock circuit with a reverse gear switch may disconnect the PTO drive and/or stop the engine. The interlock circuit may prevent all operation of PTO driven accessories while the vehicle is operated in reverse.  
         [0003]     In recent years, interlock circuits have been proposed to include sensors that permit limited operation of the PTO when the vehicle is operated in reverse, but stop PTO operation if the sensor detects an object behind the vehicle. Various types of sensors have been proposed for detecting obstacles behind the vehicle, including but not limited to ultrasonic, infrared, or photoelectric sensors.  
         [0004]     Some interlock circuits may include two or more sensors, such as those described in U.S. Pat. Nos. 6,021,373; 6,044,632; 6,130,607; and 6,173,233. There is a need for a simple, low-cost interlock circuit for use with a single sensor to detect objects behind a vehicle.  
         [0005]     Additionally, interlock circuits proposed for sensors that detect obstacles behind riding lawn mowers and similar vehicles may not provide any assurance that the sensor is operational. There is a need for an interlock circuit that will provide assurance that the sensor is working and/or working correctly.  
         [0006]     Additionally, an interlock circuit for a sensor that detects obstacles behind a vehicle is needed that will allow the operator to override and continue using the implement in reverse even if an object is detected behind the vehicle.  
         [0007]     Additionally, an interlock circuit for a sensor that detects obstacles behind a vehicle is needed that may be reset and provide a non-intrusion signal after an object clears the field of view.  
       SUMMARY OF THE INVENTION  
       [0008]     An interlock circuit for a vehicle such as a lawn and garden tractor may be connected to a single sensor that detects objects behind the vehicle when the vehicle is in reverse with the PTO engaged. If no object is detected, the interlock circuit receives a non-intrusion signal from the sensor. If an object is detected by the sensor within a specified vision area, the interlock circuit shuts off the engine. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]      FIGS. 1   a  and  1   b  show a schematic of an interlock system for a vehicle such as a tractor or riding mower, that is responsive to a backup sensor according to a first embodiment.  
         [0010]      FIG. 2  is a state diagram for an interlock system according to a first embodiment. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0011]     Referring to  FIGS. 1   a  and  1   b , therein is shown a circuit schematic for a vehicle such as a tractor or riding mower having an ignition switch  10  with switch input terminals  12  and  14  connected to ground, and an input terminal  16  connected to the source of electrical power  18  on the vehicle. The switch  10  includes an off (uppermost) position, a run (center) position), and a start (lowermost) position. A closed path is provided from the terminal  12  to the terminal  22  only when the switch  10  is in the off position as shown. The output terminal  26  is connected to the input terminal  16  and to the source of power  18  when the switch  10  is in the run or the start position. The terminal  24  is connected to ground through the terminal  14  only when the switch  10  is in the start position.  
         [0012]     The terminal  22  is connected by line  32  to a magneto shut-down terminal and to the switched input terminal of a magneto relay  38  to assure engine kill when the ignition switch  10  is moved to the off position. The terminal  26  is connected through a fuse  42  to a switched power line  46  and to the switched input terminal of a start relay  48 . The start relay  48  is activated and powers a line  52  to the starter when certain pre-selected conditions on the vehicle are satisfied and the switch  10  is moved to the start position.  
         [0013]     The switched power line  46  is connected to a central input terminal  56  ( FIG. 1   b ) of a PTO switch  60  having off, on, and momentary on positions and additional input terminals  62  and  64 . The PTO switch  60  is biased to the on position when in the momentary on position. When the PTO switch  60  is in the off position and the park brake is in the on position, a first output terminal  66  is connected to an output terminal  158  of a park brake switch  70  to provide power from the switched power line  46  to line  156  to allow the engine to start and run. When the PTO switch is in the off position, output terminal  71  of the PTO switch  60  is connected to line  141 .  
         [0014]     When the PTO switch is in the on or momentary on position, output terminal  72  is connected to line  94  to provide a closed path from the switched power line  46  to the activation coil of an electric PTO clutch  80 .  
         [0015]     When the PTO switch is in the momentary on position, output terminal  84  is connected to a second output terminal  142  of the park brake switch  70  via blocking diode  180 , to line  141  to PTO relay  126 , and to a line  106  to relay structure  100 , to latch relay structure  100  ( FIG. 1   a ) when the vehicle is in a reverse gear. This is a manual latch system to allow mowing in reverse.  
         [0016]     The relay structure  100  includes bypass latching relay  102  having a control input  104  connected by a line  106  to the input terminal  64  of the PTO switch  60 . The relay structure  100  also includes an unlatching relay  110  having a control input  112  connected by the line  98  to the output terminal of the reverse sensing switch  90  so that when the line  94  is powered and the vehicle is out of reverse (switch  90  closed) the unlatching relay will be activated. The latching relay  102  includes a switched output  116  having a terminal connected via line  95  to the input terminal of reverse sensing switch  90 . The opposite terminal of the switched output  116  is connected through a blocking diode  120  to a PTO control input  122  of a PTO relay  126 . The PTO control input  122  is also connected via blocking diode  130  and the line  98  to the output terminal of reverse sensing switch  90 . The PTO relay will activate only if the reverse sensing switch  90  is closed (vehicle not in reverse) with power applied to the input of the switch  90  (PTO switch  60  is on and brake switch  70  is off), or if the latch relay  102  is activated (PTO switch  60  is in the momentary on position) with the line  95  powered, or if the reverse sensing switch  90  is open (vehicle in reverse) and the backup sensor relay  200  is closed. The output terminal of the switched output  116  is connected by a diode  132  to the upper terminal of the switched output  136  of the unlatching relay  110 , so when the relay  110  is in the position shown (not activated), a closed path is provided between the switched output  116  of the latching relay  102  and the control input  104  of the relay  102  to bootstrap the relay  102  in the on position, provided the line  94  is powered and the relay  110  remains inactivated. Once the vehicle is taken out of reverse so switch  90  closes, the relay  110  activates to interrupt bootstrapping on of the relay  102 .  
         [0017]     To bootstrap the latch relay  102  to the on condition after interruption requires opening of the reverse sensing switch  90  by placing the vehicle in the reverse condition and temporarily moving the PTO switch  60  to the momentary on position while the PTO relay  126  is activated. Once activated by movement of the PTO switch  60  to the momentary on position, the latch  102  will remain activated until the unlatch relay  110  is deactivated by closing the switch  90 .  
         [0018]     The PTO relay  126  includes a switched output having one terminal  140  connected by a line  141  to the output terminal  71  of the PTO switch  60  and to the output terminal  142  of the reverse sensing switch  90 . An opposite terminal  143  is connected by a line  144  to the vehicle ignition. The terminal  143  and line  144  are also connected to a switched output  146  of an ignition relay  150 . The relay  150  includes a control input  152  connected by a blocking diode  154  and a line  156  to an input terminal  62  of PTO switch  60  to provide a current path from the switched power line  46  to the ignition relay control input through terminal  68  of the brake switch  70 , and terminals  66 ,  62  of the PTO switch if the brake is on and the PTO switch is off.  
         [0019]     A second path from the switched power line  46  to the control input  152  of the ignition relay  150  includes an operator presence or seat switch  166  connected to the line  159 , a delay circuit  168  connected to the switch  166 , and a blocking diode  172  connected to the delay circuit  168 . The second path with switch  166  provides activation of the ignition relay  150  when the operator is at his station on the vehicle and switched power is on. The delay circuit  168  prevents nuisance interruptions of engine operation caused by seat bounce or the like.  
         [0020]     The magneto grounding relay  38  includes a control input  182  connected to the ignition relay control input  152  to ground the magneto when the input  152  is unpowered to assure engine kill when power is interrupted to the terminal  152 , for example, shortly after opening of the switch  166  when the operator leaves his station.  
         [0021]     The start relay  48  has a control input  192  connected by the line  156  to the upper terminal  62  of the PTO switch so that the starter can only be activated if the terminal  62  is powered, that is, if the PTO switch  60  is off and the brake switch  70  is on, as shown. The switch  10 , when in the start position, grounds one side of a control coil of the start relay  48  via diode  196  and terminal  24  to provide cranking power to the starter if the line  156  is powered (PTO off and brake on).  
         [0022]     In operation, the operator assures that the PTO switch  60  is off and the brake switch  70  is on so that upon movement of the ignition switch  10  to the start position, the magneto relay  38  activates to unground the magneto and the ignition relay  150  activates to provide power to the ignition coil. The start relay  48  activates to turn the starter. Once the engine is running and the ignition switch  10  is in the run position with the operator at his station (the switch  166  is closed), the ignition and magneto relays will remain activated by the operator presence circuit when the vehicle is placed in a forward gear and the brake switch  70  is moved to the on position.  
         [0023]     The control input of the PTO relay  126  receives an activation signal through the closed reverse sensing switch  90  (vehicle not in reverse), line  98  and diode  130 . To initialize PTO operation, the operator must first make sure that the PTO switch  60  is in the off position (as shown) with brake switch  70  closing the connection between terminals  88  and  142  (brake off) so that a closed path is provided through switches  60  and  70  via terminals  56 ,  72  and  142 ,  88  from the powered line  46  to the line  94 . Reengagement of the PTO relay  126  and the PTO  80  after shutdown requires that the PTO switch  60  first be moved to the off position. With the PTO relay on and the PTO switch  60  in the on position, the PTO is activated via line  141  through terminals  56 ,  72  and line  94 . With the brake off and the switch  70  providing a closed path from the line  142  to the line  46 , the PTO relay  126  will be bootstrapped to the on condition through the switch  90 , the line  98  and the diode  130 .  
         [0024]     When the vehicle is placed in reverse (reverse sensing switch  90  is open), the backup sensor relay  200  provides a current path from the switched power line  46  which keeps the engine operating while in reverse if no object is detected by the sensor. Current is provided to magneto relay  38  and ignition relay  150 . For example, the current path may be from line  46  through brake switch  70  (in the off state) to the PTO relay coil  126 , and from line  46  to ignition relay  150  to line  146 , line  143  through PTO relay  126  to line  141 , through seat switch  166  to line  159 , through time delay circuit  168  and diode  172  to ignition relay  150  through line  152 , and magneto relay  38  through line  182 .  
         [0025]     In the state diagram shown in  FIG. 2 , the blocks represents states of an interlock circuit for a vehicle such as a tractor or riding mower. The symbol “!” preceding a word or phrase indicates that the condition is not true. For example, “!REVERSE” indicates that the vehicle is not in reverse.  
         [0026]     Block  100  represents a state in which the engine is off, the magneto is stopped, and the start (crank) and fuel switches are off. In block  100 , the PTO switch may be off as shown in block  101 , or on as shown in block  102 . If the PTO is off as shown in block  101 , a key or start switch may be used to turn the magneto switch to the run position, and turn on the start (crank) and fuel switches as shown in block  103 . In block  103 , the brake switch is on, the reverse sensing switch indicates the vehicle is not in reverse, and the PTO switch is off. Otherwise, if the brake switch is off, or the reverse sensing switch indicates the vehicle is in reverse, or the PTO switch is on, the magneto, start and fuel switches are turned off and the interlock circuit returns to the state shown in block  101 .  
         [0027]     Block  104  represents a state of the interlock circuit in which the engine is running. The magneto is in the run position. However, if the brake is off and the seat or operator presence switch indicates no operator, the magneto, start and fuel switches are turned off and the interlock circuit returns to the state of block  101 . When the engine is running in block  104 , the PTO may be off as shown in block  105 , or the PTO may be on as shown in block  106 .  
         [0028]     Block  106  represents a state of the interlock circuit in which the PTO switch is on. To enter block  106  and activate the PTO, the seat or operator presence switch must indicate an operator is present, and the reverse sensing switch must indicate the vehicle is not in reverse. In block  106 , the reverse implement option switch may be unlatched as shown in block  107 , or latched as shown in block  109 . If the reverse implement option switch is latched as shown in block  109 , the PTO may be on while the vehicle is in reverse.  
         [0029]     Block  109  represents a state in which the PTO is on and the reverse implement option switch is latched. To go from block  107  to block  109 , the vehicle may be shifted into reverse and a backup presence detector must provide a true signal as shown in block  108 . The true signal indicates no object is detected behind the vehicle. In block  108 , if the backup presence detector provides a false signal indicating an object is detected behind the vehicle, a sensor malfunction, or otherwise stops providing an appropriate signal, the magneto is stopped immediately to kill the engine as shown in block  102 .  
         [0030]     Block  110  represents a state of an interlock circuit in which the key is turned to the off position, the fuel and PTO are turned off, and the magneto is turned to the stop position. The magneto and fuel solenoid may be shut off at once, or a delay may be provided to prevent engine after bang at shut down due to unburned fuel entering the muffler. For example, a delay may allow the spark plugs to continue to fire and burn up fuel for a set period such as two seconds after the key switch is shut off and the fuel solenoid is turned off. Delay circuit  168  shown in  FIG. 1A  may be used to provide this capability.  
         [0031]     If the vehicle is in reverse with the PTO on as shown in block  109 , and the sensor detects something in the field of view behind the vehicle, the engine will shut down, returning to block  102 . In one embodiment, an operator, while remaining seated, may cause the engine to recover before it stops spinning. For example, the engine may recover if the operator shifts out of reverse to neutral or forward before the engine stops spinning. Alternatively, the engine may recover if the operator activates a PTO override switch before the engine stops spinning, thus moving from being latched as shown in block  109  to unlatched as shown in block  107 . If the operator leaves the seat with the brake off and/or the PTO running, the engine will commence to shut down. The engine may recover if the operator sits back in the seat before the engine stops spinning.  
         [0032]     A backup presence detector may be mounted at or near the rear of the vehicle. Various different sensors may be used, including but not limited to ultrasonic, infrared, or photoelectric sensors. With the PTO on while the vehicle is in neutral or forward, the backup presence detector does not affect machine operation.  
         [0033]     When in reverse with the PTO engaged, the backup presence detector may provide a non-intrusion signal unless an object is detected in the specified vision area of the sensor behind the vehicle. The interlock circuit includes logic or machine control that looks for a non-intrusion signal from the backup presence detector. If no intrusion is detected in the specified vision area, the backup presence detector provides a non-intrusion signal to the interlock system so that the vehicle engine will continue to run. If, while the vehicle is in reverse and the PTO is engaged, the backup presence detector detects an object in its specified vision area, the sensor will provide a signal which will cause the vehicle engine to shut down.  
         [0034]     In one embodiment, the operator of the vehicle may shift the vehicle transmission from reverse to neutral or forward before the engine stops, so that the interlock control system may recover the engine to a running state. When shifted to neutral or forward, reverse sensing switch  90  will bypass the backup sensor relay  200  and return power to line  98  through diode  130  to PTO relay  126 , and to line  141  through seat switch  166 , line  159  to delay network  168 , and to ignition relay  150  which restores power to lines  146  and  143 .  
         [0035]     In one embodiment, the vehicle operator may manually activate the reverse implement option (RIO) and bypass the back up sensor, thus returning the engine to a running state. The RIO may be activated by moving PTO switch  60  to the momentary on position, connecting line  46  to line  84 , providing power to the latch network  100 , through diode  120  to PTO relay  126 , and also through diode  180  to line  141 , through seat switch  166  to line  159 , through delay  168  and diode  172  to ignition relay  150 .  
         [0036]     Having described the preferred embodiment, it will become apparent that various modifications can be made without departing from the scope of the invention as defined in the accompanying claims.