Abstract:
A control system for controlling the opening and closing of the tailgate of a dump truck includes an actuator unit which is mounted on the truck box or tailgate. The actuator unit controls the degree of opening of the tailgate during the unloading operation and therefore the rate at which the material is discharged from the truck box. A positional feedback unit produces an output signal indicating the movement of the tailgate between open and closed positions. This signal is displayed on a control panel of a control unit in the truck cab. An operator in the truck cab can therefore control opening and closing of the tailgate and can monitor the position of the tailgate. The control system effects an accurate metering of material from the truck box.

Description:
FIELD OF THE INVENTION 
     This invention relates to a control system for controlling the position of the tailgate of a dump truck as material is dumped from the truck. 
     BACKGROUND OF THE INVENTION 
     In conventional dump truck design, a truck operator usually upon reaching the dump site is first required to adjust the tailgate chains which limits the amount the tailgate opens during the dumping operation. The operator then returns to the cab and via the console unlatches the tailgate, elevates the truck box and begins the application of material from the truck box. 
     However, if the adjustment of the tailgate chains was incorrect, if the chains had become entangled, or if something in the material was restricting discharge of the material from the truck box, the operator would then be required to leave the cab to readjust or disentangle the chains, or clear the restriction impeding the flow of material from the truck box. Since the truck box is elevated, the material load within the truck box is now applying pressure to the tailgate chains, and it becomes almost impossible to adjust the chains without shifting the material within the truck box (lowering the truck box) away from the tailgate. 
     In the event the operator attempts to adjusts the chains without shifting the load (lowering the box), severe injury to the operator may result due to the forces involved. In order to readjust the chains, the operator must be standing at the rear end of the truck. When an operator attempts to readjusts the chains, the operator&#39;s focus is changed from operating an entire material handling system (dump truck) to making a point of application adjustment (adjusting the tailgate). When the operator is required to leave the cab, the operator is much more vulnerable to ground traffic. Further, when making such a readjustment of the tailgate chains, the operator may also give up a strategic vantage point thereby losing sight of the overall conditions developing around the operating environment. 
     The amount of man and equipment hours lost in adjusting the tailgates of conventional dump trucks is a major consideration. The hours lost in adjusting and readjusting the tailgate in these conventional dump trucks are impossible to recover. 
     SUMMARY OF THE INVENTION 
     An object of this invention is to provide a novel control system for variably controlling and continuously monitoring the position of the tailgate of a conventional dump truck as material is discharged from the truck. The novel control system allows the material discharged from the truck box or body to be variably adjusted by an operator in the cab and thereby allows accurate metering of the material from the truck. 
     The amount of travel or degree of opening of the tailgate is controlled by an actuator unit which may be mounted on the tailgate, dump box or tailgate hinge shaft. Operation of the actuator unit is accomplished via a control unit in the truck cab. The output signals produced by a positional feedback unit located on or adjacent the tailgate are received by the control unit allow the operator to not only precisely control the position of the tailgate but to also continuously monitor the position of tailgate as it shifts between closed and open positions. This arrangement provides the operator with real time information with respect to the position of the tailgate from a location (truck cab) remote from the tailgate. 
     Further, this control system enhances operator safety and substantially reduces the time lost during adjustments required in the conventional dump truck operation. 
    
    
     BRIEF DESCRIPTION OF THE FIGURES OF THE DRAWINGS 
     FIG. 1 is a side elevational view of a conventional dump truck incorporating the novel control system with certain parts thereof broken away for clarity; 
     FIG. 2 is a fragmentary view of portion of the dump truck box illustrating one embodiment of the actuator unit; 
     FIG. 3 is a schematic view of one embodiment of the control system; 
     FIG. 4 is a fragmentary perspective view of a portion of the truck box and tailgate illustrating another embodiment of the actuator unit; 
     FIG. 5 is a fragmentary perspective view similar to FIG.  4  and illustrating a further embodiment of the actuator unit; 
     FIG. 6 is a fragmentary perspective view similar to FIG. 4 but illustrating another embodiment of the actuator unit with the tailgate in the closed position; 
     FIG. 7 is a fragmentary perspective view of the embodiment of FIG. 6 illustrating the tailgate in the partially opened position; 
     FIG. 8 is a fragmentary perspective view of the embodiment of FIG. 6 but illustrating the actuator unit disengaged from latching pin on the truck box; 
     FIG. 9 is a fragmentary perspective view similar to FIG.  4  and illustrating a further embodiment of the actuator unit with the tailgate in the closed latched position; and 
     FIG. 10 is a fragmentary perspective view of the embodiment of FIG.  9  and illustrating the tailgate disengaged from the actuator unit. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings, and more particularly to FIG. 1, it will be seen that a conventional dump truck, designated generally by the reference numeral  10 , and incorporating the novel control system is thereshown. The dump truck  10  includes a cab  11  mounted on a chassis  12  which also pivotally mounts a conventional open top, generally rectangular or parallelepiped shaped truck body or box  13 . Although the pivot mount for the truck box  13  is not shown, the pivot mount is of conventional construction and is positioned in the usual location rearwardly of the rear dual wheels. The truck box is adapted to contain material which is to be unloaded through the rear end at a selected application site. 
     During conventional operation of a dump truck, such as that shown in FIG. 1, the truck box  13  will contain the material to be unloaded. The operator will drive to the application site and adjust the chains to limit the amount the tailgate may open. It will be appreciated that the tailgate swings open by action of gravity as the truck box is elevated. Note the phantom line configuration of FIG.  1 . 
     The driver will then unlatch the gate via a console in the cab and then move the truck slowly forward as material is discharged from the truck box  13 . The rate at which the material is discharged from the truck box is determined by the opening defined between the tailgate and truck box  13 . If the rate of discharge is incorrect, the driver must leave the cab to readjust the setting of the chains. Thus, the operator is exposed to the dangers of ground traffic, and possible injury if readjustment is attempted when the truck box  13  is elevated. These kinds of stoppages are also time consuming. 
     The present control system overcomes these problems and affords a substantial savings in man hours. The control system, schematically shown in FIG. 3, includes an actuator unit  21 . 
     In the embodiment of FIGS. 1-3, the actuator unit  21  includes a pair of identical actuators each mounted on one side wall  13   a  of the truck box  13 . A compartment  13   b  containing each actuator is located at the rear end portion of a side wall  13   a  and is closed by a suitable cover plate  13   c.    
     Each actuator includes a hydraulic cylinder  22  having a piston therein connected to a piston rod  23  having an outer end positioned between and pivotally connected by a pivot  25  to a pair of arms  24  The arms  24  are pivotally connected to a sidewall  13   a  of the truck box  13  by a pivot  26 . The arms  24  are fixedly connected to one end of an arm of a L-shaped latching member  27 . The other arm  29  of the L-shaped latching member  27  extends angularly from the arm  28 . The L-shaped latching member  27  has a locking notch  31  on the inner surface thereof located at the juncture of the arms  28  and  29 . Each latching member  27  engages one of a pair of pins  30  secured to the lower side edge portion of the tailgate  16 . 
     It will be seen that when the piston rods  23  are extended, each L-shaped latching member will be moved to the position illustrated in FIG. 1, and pins  30  on the tailgate will be positioned in the locking notches  31 . The tailgate  16  will then be locked in a closed position. When the piston rod is shifted in a retracting direction, the L-shaped latching members  27  will be pivoted from the latching position of FIG. 1 in a direction to allow progressive opening of the tailgate  16  if the truck box is elevated. Complete retraction of the piston rods allow the pins  30  on the tailgate to move free of the respective latching members  27 . 
     The control system  20  is also provided with a positional feedback unit  35  which, in the embodiment shown, is a linear potentiometer. The linear potentiometer positional feedback unit  35  is a commercial unit of well-known construction and a detailed showing is not required. The linear potentiometer is positioned within the cylinder  22  and senses the position of the piston/rod  23  and ultimately the position of the tailgate  16  during movement of the tailgate. In the embodiment shown, the linear potentiometer is a Model No. 6300 Series Internal Position Sensor manufactured by Duncan Electronics, a Division of BEI Electronics Co. 
     The hydraulic cylinder and piston actuator unit  21  may be a commercial model including the WT Series manufactured by Bailey Hydraulics, Inc. The linear potentiometer may be incorporated in the hydraulic unit when purchased. It is pointed out that other commercial linear potentiometers may be used instead of Model 6300 manufactured by Duncan Electronics. 
     The feedback unit  35  may also be an inductive or capacitive proximity sensor and target arranged in a linear or radial pattern depending on the design of the actuator unit. Suitable inductive or capacitive proximity sensors are those manufactured by Turck Products. Acceptable inductive or capacitive proximity sensors and target sensors are also manufactured and sold by Baumer Electric of Germany. Optical encoders may also be used as the feedback unit. 
     The control system  20  also includes a control unit or console  36  which is mounted in the cab  11  of the truck for easy access by a truck operator. The control unit  36  includes a housing  37  which contains the electric components and which presents a control panel  37   a . The control panel  37   a  has a pair of normally open switches  38  and  39 . 
     The switches are electrically connected to a solenoid valve  33  by electrical conductors  41 . A pair of conduits intercommunicate the solenoid valve  33  with the hydraulic cylinder  22 . It will be appreciated that there is a hydraulic system for each hydraulic cylinder. The solenoid valve  33  is also connected in communicating relation by a supply conduct  34  to the conventional hydraulic fluid supply of the truck. It will be seen that when switch  38  is closed, hydraulic fluid which be directed by the solenoid valve  33  into the cylinder  22  to cause the piston rod  23  to be extended thereby moving the tailgate  16  in a closing or latching direction. Conversely, when switch  39  is closed, the solenoid valve  33  will direct fluid to the cylinder  22  to cause retraction of the piston rod and movement of the tailgate in an opening direction. 
     The control panel  37   a  is also provided with directional indicators  42  and  43  which indicate the direction the tailgate will move if switch  38  or switch  39  is closed. The control panel  37   a  further includes a tailgate position indicator  44  which includes a plurality of LEDs (light emitting diodes)  45  arranged in an arcuate pattern and provided with a number sequence, each number located adjacent an LED. A stationary representation  46  of the tailgate in a partially open position is also provided. The letter designation L indicates the locked position and letter designation F indicates unlatched or free. Electrical conductors  40  electrically connect the positional feedback unit to the electrical components of the tailgate position indicator  44 . 
     During operation of control system illustrated in FIG. 1-3, the operator, upon reaching an application site, will close switch  39  until the tailgate position indicator  44  indicates the desired open position of the tailgate. The truck box  13  will then be raised and the material will be applied in the conventional manner as the truck is moved forwardly. Ready adjustment of the position of the tailgate  16 , for any reason, can be accomplished by merely actuating the switches  38  or  39 . The operator may therefore continuously monitor and control the position of the tailgate from the safety of the cab. The novel control system allows controlled, metered application of the material to be discharged from the truck box  13 . 
     Referring now to FIG. 4, a different embodiment of the actuator unit  51  is thereshown. The actuator unit  51  includes a reversible rotary hydraulic motor  52  whose output shaft (not shown) is fixedly connected to an angular shaped latching member  53 . The latching member  53  includes an arm  54  which is fixed to the output shaft of the rotary hydraulic motor. An arm  55  is integral with arm  54  and engages and retains the locking pin  30  of the tailgate  16  when the tailgate is in a closed position or in a partially open position for discharge of material from the truck box. 
     A positional feedback unit  56  is mounted on the hydraulic motor  52  and comprises a rotary potentiometer similar to that of FIG. 1-3. The positional feedback unit  56  continuously senses the angular position of the latching member, and, hence the position of the tailgate  16 . Output signals from the positional feedback unit  56  are transmitted to the control unit  36 . 
     The output shaft of the rotary hydraulic motor  52  are positioned in a compartment in the sidewall  13   a  of the truck box and the arm  54  projects outwardly of a rear opening  13   d  in the compartment. It will be seen that rotation of the output shaft of the hydraulic motor in one direction will move the latching member in a latching direction and movement in the opposite direction will move the latching member  53  in an unlatching or free direction. 
     Referring now to FIG. 5, another embodiment of the actuator system is thereshown and includes a pair of hydraulic rams including a pair of cylinders  64  mounted on the rear surface of the tailgate. The cylinders are connected to a source of hydraulic fluid under pressure and are provided with pistons and piston rods. The piston rods are provided with teeth to define a rack, each rack engaging a pinion gear within a housing. The pinion gears drive a shaft  63 , the outer ends of which are journaled in suitable bearing  65 . 
     Angular latching members  66  are affixed to the ends of the shaft  63  for movement therewith. Each angular latching member  66  includes an arm  67  fixedly connected to an end of the shaft  63  and an arm  68  which is engagable with a locking pin  69  positioned within a compartment  13   b  and closed by a cover plate  13   c . The locking pins  69  are therefore mounted on the truck box  13  and the latching member  66  is mounted on the tailgate. The pins  69  are located within the compartments  13   b  which are provided with rearwardly facing openings  13   d . It will be seen that when the cylinder and piston units are actuated the shaft will be selectively rotated in one direction or the other. Rotation of the shaft  63  opens and closes the tailgate  16 . 
     Although not shown in the drawings, a positional feedback unit is provided and is positioned within the hydraulic motor housing. The positional feedback unit is a commercially available rotary potentiometer which sends output signals to the control unit  36 . The position of the tailgate can be controlled and monitored at all times by an operator. 
     Referring now to FIGS. 6,  7  and  8 , it will be seen that another embodiment of the actuator unit  71  is thereshown. The actuator unit  71  will include a hydraulic actuator system like that of embodiment of FIG. 5 mounted on the rear surface of a tailgate  16  and having an output shaft  73  projecting from opposite sides thereof. The ends of the shaft  73  are journaled in suitable bearings  75  mounted on the rear surface of the tailgate  16 . 
     Sectional latching members  76  are secured to the outer ends of the output shaft  73  and are moveable therewith. Each latching member  76  includes an arm  77  affixed to the outer end of the output shaft  73 . The arm  77  is pivoted to an elongate arm  78  by a pivot  79 . The outer end of the arm  78  is provided with a latching recess  78   a  and the outer end portion of arm  77  is provided with a stop element  77   a  projecting outwardly from one longitudinal edge thereof. 
     The truck box  13  is provided with locking pins  80  located within a compartments closed by cover plates  13   c . It will be noted that when output shaft  73  is rotated in one angular direction, the sectional latching member will be moved in direction to close the tailgate  16 , and when moved in the opposite direction, the tailgate will be moved in an opening direction. When the tailgate  16  is moved from a closed or latched position (FIG.  6 ), in an opening direction, the sectional latching members  76  will be extended from a folded position to an unfolded position. 
     In FIG. 6, the sectional latching members will be in a folded side-by-side relation similar to a toggle linkage. The arms  77  and  78  will progressively unfold in an opening direction until the arm  78  engages a stop element  77   a  on arm  77 . Relative movement between the arms ceases when this occurs. In the completely unlatched position, the tailgate will swing free (FIG.  8 ). As the arms unfold, the arm  78  will disengage from the pin  80 . Conversely, when the arms  77 ,  78  move to the folded position (FIG.  6 ), the arms will move relative to each other until the latching recess  78   a  engages pin  80 . 
     The positional feed back unit (not shown) will be a commercial rotary potentiometer like that of FIG.  5  and positioned with a housing. 
     Referring now to FIGS. 9 and 10, it will be seen that a further embodiment of the actuator unit  81  is thereshown. The actuator unit includes a double acting hydraulic cylinder  82  having a piston rod  83  extending therefrom. The outer end of the piston rod  83  is bent to define a latching element  84 . The piston rod  83  extends through a housing  85  which has a cylindrical opening therein through which the piston rod extends. The cylindrical opening or bore in the housing  85  is provided with a spiral groove (not shown) therein for receiving a pin on the piston rod. The interaction of the pin and spiral groove cause the piston to rotate during linear movement thereof. 
     It will be seen that when the piston is retracted (FIG.  9 ), the latching element  84   s  will engage the tailgate and hold the tailgate in a closed and latched position. When the piston rod  83  is extended, the tailgate will be allowed to progressively move in an opening direction. The piston rod  83  will simultaneously rotate about its longitudinal axis during this linear movement until the latching element  84  disengages from the tailgate  16  allowing the tailgate to swing free (FIG.  10 ). 
     Although not shown in the drawings, the actuator unit will be provided with a positional feedback unit. In the embodiment of FIGS. 9 and 10, the positional feedback unit comprises a commercially available linear potentiometer positioned within the cylinder  82  and electrically connected to the control unit. In all of the embodiments, control of the position of the tailgate is controlled by an operator in the cab while continuously monitoring the disposition of the tailgate. 
     From the foregoing description, it will be seen that a number of embodiments of the control system have been illustrated and described. It is pointed out that the actuator unit of the control system can be mounted on the tailgate, dump box or hinge (shaft mount) of the tailgate. In the embodiments shown, the actuator units have been shown as mounted on the dump box or tailgate. 
     Although the actuator units have been illustrated as hydraulically actuated, other power systems may also be used. Electric and pneumatic power system or a combination of electric, pneumatic and hydraulic power systems may be used. The control system may be sold as a kit for retrofitting dump trucks or it may be sold as OEM equipment on newly produced trucks. Although the control system is preferably to be used with dump trucks, the control system may also be used with trailers or similar vehicles in which the material is pushed from a tailgate opening while the vehicle remains horizontal. Although the control unit of the present embodiments has been illustrated as visually perceptible to an operator, an audible system may also be used. A combination of visual and audible control system may be employed. Finally, it will be seen that the present control system provides the operator constant real time information about the position of the tailgate thereby allowing the operator to adjust the tailgate for optimum application of the material being unloaded.