Abstract:
A skid steer loader has an interlock system that is responsive to sensor input to lock out such as operation of lift and tilt cylinders of the skid steer loader when the input indicates a condition has not been met. The loader is provided with a cab that has an operator entrance and egress door, and a door latch and a latch striker on the cab are provided with a sensor that senses when the cab door is closed and latched. The lockout prevents carrying out the functions when the door is not closed and latched.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an interlock system for determining whether a door or cover is closed and latched. When a door on a cab on an industrial vehicle, such as a skid steer loader, is unlatched, a lock out signal to disable components of the vehicle is provided until such time as the cab door is again closed and latched. 
     Skid steer loaders are operated with rollover protection cabs, and in inclement weather, either hot or cold, the cab can be enclosed, and a door provided on the operator entrance opening. It has been found that because of the compact nature of skid steer loader, in particular, if the door is fully opened and the lift arms of the loader are operated, the door can become damaged by the lift arms. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a sensor for determining when a latch on a door or other hinged cover is closed and latched to provide a signal indicating the door or cover is properly latched closed. The signal is used, as disclosed, as a signal to an interlock system, and when the latch is not properly secured with the door closed, that is, when the door is ajar or open, controls for operation of some secondary system, such as the lift arm and bucket tilt cylinder of a loader, are disabled. 
     A switch used for determining when the door is closed and latched can be a magnetic reed switch or a Hall effect sensor, with a magnet mounted on a latch striker or bolt secured to the frame of the cab. The sensor is positioned on the door so that unless the door latch is adjacent to and in alignment with the magnet on the striker bolt, that is, fully seated or secured, there will be no enabling signal to permit operation of the selected system, for example, the lift and tilt cylinders of the loader, that are used for operation of the lift arms. 
     The skid steer loaders that are made by Bobcat Company, a business unit of Ingersoll-Rand Company presently include a interlock control system that prevents operation of the vehicle in response to selected sensor inputs indicating a selected condition. The sensor of the present invention is designed to provide an input to such a system so that when the door is in place on the cab, an additional signal from the latch sensor is needed to enable the operation of the lift arms and bucket cylinders of the skid steer loader. The same arrangement can be used for locking our functions on other vehicles or systems that have a door or cover that should be closed and latched before the selected functions are enabled. 
     The present door shown will provide an input to similar interlock systems where a controller is disabled when the sensor signal indicates that a door or cover is not closed and latched. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic perspective view of a skid steer loader having an interlock system made according to the present invention; 
         FIG. 2  is a fragmentary perspective view of a typical door and latch arrangement; 
         FIG. 3  is an enlarged, exploded rear perspective view of a door frame and latch assembly as viewed from the interior of the cab; 
         FIG. 4  is an enlarged exploded perspective view showing a typical latch assembly from an exterior of a cab door having a sensor system of the present invention installed; 
         FIG. 5  is a rear view of the latch from the interior of the cab showing the striker and the door latch in a latched position with parts broken away; 
         FIG. 6  is a schematic rear view of a latch having a modified sensor, showing the latch and a sensor from an interior of the cab; 
         FIG. 7  is a side sectional view of  FIG. 6 ; and 
         FIG. 8  is a fragmentary detailed view of a latch striker of  FIG. 6 , with parts broken away. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A skid steer loader  10  is shown in  FIG. 1 , and it has a frame  12 , supported on wheels  14 , and further it has a pair of pivoting lift arms  16  that are operated with hydraulic actuators  18 . The lift arms support a tilting bucket  15  that is raised with the lift arms and tilted using a tilt hydraulic cylinder or actuator  17 . The skid steer loader has a cab  20 , as shown, and in this instance, a door assembly  22  (see  FIG. 2 ) is provided on the cab. The door can hinge between an open and closed position. An engine  24  is used for providing power to a hydraulic system including a hydraulic pump  26  connected to a lockout valve  36 , and providing power to a set of actuator hydraulic valves  28  and then to the various hydraulic components such as the lift arm actuator  18  and bucket tilt actuator  17 . Drive hydraulic motors  30  are used for driving the wheels  14  in a conventional manner. 
     A drive interlock system  32 , is provided as is disclosed in U.S. Pat. No. 5,425,431 in greater detail. The specification of U.S. Pat. No. 5,425,431 is incorporated by reference. The interlock system  32  has logic controls that, among other functions, enables or disables the operation of actuator hydraulic valves  28 , through a lockout valve  36  and it also can control operation of drive motors  30  (or other drive), through a drive lockout  31 . Operation of the lift arm cylinders or actuators  18 , and the tilt cylinders or actuators  17  is enabled only when lockout valve  36  is open. 
     In the present invention, whenever a door is installed on a cab, a circuit is closed by a normally closed switch or sensor  56  on the door latch, that will be more fully explained, unless the door is closed and a door latch is secured or latched. The closing and latching of the door assembly  22  relative to the cab frame around the door opening on the cab  20  provides a signal to the interlock system  32  by opening the switch or sensor  56  so the lockout valve  36  is enabled or open and the actuator valves  28  receive hydraulic fluid under pressure. The valves  28  can then be operated to provide hydraulic fluid to the cylinders  18 , and  17 . 
     If desired, the door latch switch or sensor can be used to control other functions of a vehicle, such as operating the drive lockout  31  to prevent the vehicle or loader from moving until the door is closed and latched. Interlock valve  36  must be open in order for hydraulic fluid under pressure to be provided to the hydraulic valves  28 . When interlock valve is closed or disabled it completely shuts off the operation of the selected components or functions of the machine including hydraulic cylinders. The lift actuators  18  and tilt actuator  17  are disabled until the door is closed and latched. Other inputs  33 , as disclosed in U.S. Pat. No. 5,425,431, also may be needed to enable valve  36  and drive lockout  31 . 
     The door  32  is hinged as at  40 , along one side relative to the cab, and is positioned in a door opening frame shown at  42 . The door assembly  22  is generally made with an exterior peripheral frame in which a transparent panel is supported a shown in U.S. Design Pat. No. D437,275. The door has a handle panel portion  44  that includes a latch assembly plate  46 . 
     The latch assembly plate  46  supports a conventional door latch assembly  48 , that is operated from a push button handle  50 , also of conventional design. The push button on the handle engages a lever  50 A on the interior of the door that operates cams to open the door. An operator handle  53  in the cab  20  permits the operator to open the door. The handle  50  is securely clamped onto the latch plate  46 . 
     Movement of the push button on handle  50  operates against lever  50 A so cams move in a conventional manner and open or separate a pair of spring loaded latch dogs  52 , that are pivotally mounted between a plate  49  as supported in a latch housing  58 , and an outer wall  59  of the latch housing  58 . The details of the latch operator are not shown, but the push buttons and lever operate to open or separate the latch dogs  52 , which are spring loaded to a closed position. 
     The latch housing  58  is used to also support a normally closed latch sensor or switch  56  that is mounted on a bracket  57  which is attached to an inner side of plate  49 . The closed switch  56  closes a circuit and provides a signal to the interlock system controller  32  to close lockout valve  36  whenever a door is installed. The latch housing wall  59  and plate  49  have U-shaped openings or notches  60  that are open on the interior side of the latch and that will receive a latch striker bar  62  that is mounted onto the door opening frame wall  65  on the cab. An end  63  of the latch striker bar  62 , extends through an opening in wall  65 , forming part of the door opening frame on the cab and is held fixed on the wall  65  with a nut in a normal manner. 
     The latch striker bar  62  is a cylindrical shaft. The latch dogs  52  will cam on the latch striker bar and the spring load on the latch dogs permits them to separate to fit over the striker bar  62  and latch in place when the door is fully closed. 
     The latch striker carries a permanent, preferably high strength, magnet  66  on a head end  67  of the striker bar. The magnet  66  is suitably positioned to be aligned with an adjacent sensor or switch  56  only when the door is in closed and latched position. The notches  60  in wall  49  are open so the magnetic field from magnet  66  affects notch or sensor  56  when the door is closed and latched. The magnet  66  is held in a recess in the head end  67  of the striker bar  62 , which can be seen in  FIG. 5  where the head end  67  of the striker bar  62  has been broken away. When the door is closed and latched, the normally closed sensor or switch  56  will be shifted in state or position to open due to the presence of the magnetic field from the magnet  66 . 
     The sensor  56  can be a magnetic reed switch, or can be a Hall effect sensor with the actuating magnet  66  carried in the striker bolt or bar  62 . 
     The sensor leads are extended along the door frame  40  that is used for supporting the glass in the door, and the leads are connected with a coupler  70  on the door that connects to a connector  71  on the frame  12  of the loader that leads to the controller  32 . 
     In many instances, an industrial vehicle will be operated without a door, and thus, the present arrangement is designed to permit operation of the loader lift and tilt cylinders when a door is not used. The wiring on the loader body can remain in place and the lift and tilt cylinders will be operable. 
     When a door is not originally present or is taken off, the coupler  70  is separated from connector  71  and the circuit to the interlock controller is open. The normally closed switch or sensor  56  is removed with the door. With the circuit open, there is no signal from the door circuit that causes the controller  32  to close the interlock valve  36 . 
     The switch or sensor  56  is normally closed as stated, and when the door is installed, the coupler  70  is connected to connector  71  on the frame  12 . The switch  56  is closed and the controller  32  causes the valve  36  to move to position to block operation of the loader lift and tilt actuators. When the door is removed and the coupler  70  and connector  71  separate, the sensor or switch  56  is no longer in the circuit so the circuit is open and the interlock valve  36  is not closed by the door latch circuit. 
     When the door  23  is in place, the door  22  preferably has to be closed and latched so that the sensor component  56  on the door is operated (opened) by the component on the striker or on a fixed portion on the cab, such as a door frame to “enable” the interlock valve  36 . 
     It also should be noted that the latch can be on the cab, and a fixed striker positioned on the door. When desired, the sensor arrangement can be selected to sense a door closed, but not fully latched position. The door position could be one where it was known that the door was not going to interfere with, or be in the way of, the lift arm movement. 
       FIGS. 9 and 10  show a modified form of the invention schematically. A latch plate  76  that mounts onto a door  78  is shown in latched position, with latch dogs  80 . A striker cylinder or bar  82  is held in the latch dogs. The striker bar is mounted onto a fixed cab frame wall  84 . 
     In this form of the invention, the striker bar  82  has a flange  88  that carries locating pins  90  that are not symmetrical about the axis of the striker bar, and which will fit in provided receptacles  92  in the cab frame wall to make sure that the positioning of the magnet  94  is correct for alignment with a Hall effect sensor  96  that is supported on the latch housing  98 . 
     The magnet  94 , as shown in  FIG. 9 , is inserted into a cross hole or bore  100  in the striker bar. Hole  100  is of size to receive the magnet  94 . A smaller diameter cross bore  102  is provided in alignment with the bore  100 , so that the magnet can be either pushed out or pounded out of hole  100  for replacement. 
     The Hall effect sensor  96  is connected to the interlock system  32  so that when the door is on the loader but is not closed sufficiently the lift and tilt actuators and other selected power components are disabled, as previously explained. Variations in sensors thus can be made, and variations in magnet mounting also can be provided. 
     The strength of the magnet field, and the sensitivity of the sensor can be selected so that mounting one or both of the sensor components adjacent the latch and/or striker will provide a door position signal that will enable the lift arms when the door will not be in the path of the lift arms. 
     In automotive applications, a door striker for a door latch is used and the same sensor system can be utilized. Some door latches operate so that if tripped but not fully latched, the door latches have to be reset by operating the door latch before the door can be fully closed and latched. The sensor system of the present invention is preferably sensitive to the fully closed and latched position of the door and will not permit operation of the controlled function until both door closing and latching occurs. However, as pointed out, in some applications a signal indicating the door is in a closed or newly closed position is satisfactory. 
     Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.