Abstract:
A system for moving a step assembly in response to maneuvers of an articulated work vehicle. The step assembly moves to avoid interference with the vehicle&#39;s wheels or tracks. A push rod assembly provides actuation to the step assembly in response to the vehicle motions.

Description:
FIELD OF THE INVENTION 
     The invention generally relates to work vehicles having a step assembly provided to facilitate ingress and egress to an operator cab. In particular, the invention relates to an articulated work vehicle having a moveable step assembly. The step assembly moves in response to vehicle maneuvers, to avoid interference with the vehicle propulsion system. 
     BACKGROUND OF THE INVENTION 
     Work vehicles, including, but not limited to, agricultural work vehicles such as tractors and combines as well as construction equipment vehicles such as loaders and backhoes, can be configured as articulating vehicles, that is having a pivot intermediate the work vehicle&#39;s front end and rear end. A central pivot serves to improve maneuverability of large or long work vehicles. Such work vehicles may be configured using a system of wheels, a system of tracks, or a combination thereof, to propel the work vehicle. The use of a pivot in a work vehicle has many advantages including maneuverability at a work site, such as a farm field or a construction site, and maneuverability on public roads during transport from work site to work site. 
     Large work vehicles often require a system of steps by which an operator may gain access to the operator station from the ground, or gain access to the ground from the operator station. It is desirable for the system of steps to remain stable and usable throughout operation of the vehicle so that a person may gain access to or exit from the operator station during reasonably slow operation of the work vehicle. 
     It may be desirable to locate a step assembly adjacent the vehicle pivot. The region adjacent the vehicle pivot provides added complexity in mounting sensitive and complicated equipment due to the vehicles movement in the pivot area. Therefore, due to the simplicity of the step assembly and proximity of pivot region to the operator station, it may be desirable to mount a step assembly in the pivot region. 
     Placing any equipment in the pivot region provides difficulties because the equipment may interfere with the tires or tracks of the work vehicle when the vehicle makes a turn. Therefore, there is a need for a system of moveable steps whereby the steps move in response to the turn of the work vehicle. For example, if the steps were located on the right side of the tractor adjacent the pivot, a right hand turn would cause interference between the steps and the wheels or tracks of the work vehicle. Therefore, there is a need for a step assembly that moves away from the interference area during a right hand turn. It would be advantageous to have the step assembly remain fixed while the tractor is going substantially in a straight line or during a left hand turn (if the steps are mounted on the right hand side, and right hand turn if the steps are mounted on the left hand side) in which there is no interference between the step assembly and the tracks or wheels. 
     SUMMARY OF THE INVENTION 
     One embodiment of the present invention relates to a moveable step apparatus including a step mount, a step assembly moveably interconnected with the step mount, an actuator mount, and an actuator coupled with the step assembly and with the actuator mount. The actuator provides a force to the step assembly, in response to a motion communicated to the actuator, to selectively move the step assembly relative to the step mount. 
     Another embodiment of the present invention includes an articulated vehicle having a moveable step assembly. The articulated vehicle includes a front vehicle section, a rear vehicle section, a pivotable joint interconnecting the front vehicle section and the rear vehicle section, a step mount interconnected with the vehicle on one of the front vehicle section and the rear vehicle section, a step assembly movably interconnected with the step mount, an actuator mount interconnected with the vehicle, and an actuator interconnected with the step assembly and with the vehicle. The pivotable joint facilitates steering of the vehicle. The actuator provides a force to the step assembly in response to a vehicle motion communicated to the actuator, to selectively move the step assembly relative to the vehicle. 
     A further embodiment of the present invention provides an articulated vehicle having a moveable step assembly. The articulated vehicle includes a front vehicle section, a rear vehicle section, and a pivotable joint interconnecting the front vehicle section and the rear vehicle section. The articulated vehicle further includes a step mount interconnected with the vehicle on one of the front vehicle section and the rear vehicle section, a step assembly movably interconnected with the step mount, a first push arm interconnected with the step assembly, an arm mount interconnected with the vehicle, a second push arm interconnected with the arm mount and interconnected with the first push arm, a sleeve interconnected with the first push arm and the second push arm, a slider substantially fixed to the sleeve and slidable with respect to the second push arm, and a spring engaging the second push arm and the slider. The pivotable joint facilitates steering of the vehicle. The first push arm and the second push arm are forced to move in response to steering actions of the vehicle and the step assembly is forced to move in response to motions of the first push arm. 
     Another embodiment of the present invention includes a push arm assembly including a first rod coupled with the step assembly, a second rod coupled with the actuator mount, and a spring engaging the first rod and the second rod. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will become more fully understood from the following detailed description, taken in conjunction with the accompanying drawings, wherein like reference numerals refer to like parts, in which: 
     FIG. 1 is a perspective view of a work vehicle in a right hand turn position showing the step assembly in a non-interfering position; 
     FIG. 2 is a perspective view of a step assembly showing the step assembly connected to a push arm assembly; 
     FIG. 3 is a top plan view of the work vehicle in a nominally straight position showing the step assembly in a nominal position; 
     FIG. 4 is a top plan view of the work vehicle in a right hand turn position similar to FIG. 1 showing the step assembly in a non-interfering position; 
     FIG. 5 is a top plan view of the push arm assembly; and 
     FIG. 6 is an exploded perspective view of the push arm assembly depicted in FIG.  5 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Turning now to FIG. 1, a tractor  10  is shown, representative of work vehicles such as agricultural or construction vehicles. Tractor  10  is depicted having rear tracks  12 , front tracks  14 , a front tractor section  20 , and a rear tractor section  30 . Front tractor section  20  and rear tractor section  30  are connected via pivot  40  located intermediate front tractor section  20  and rear tractor section  30 . Front section  20  has an operator station  22 , an operator platform  24 , and an operator entrance  26 . Rear tractor section  30  has an engine compartment  32 , a rear hitch  34 , a load bin  36 , a movable step assembly  50 , step platform  54 , and push rod assembly  60 . 
     Tractor  10  can be configured to be used as a harvester, whereby harvesting equipment is attached to rear hitch  34  and the fruits of the harvest are deposited in load bin  36 . Engine (not shown) in engine compartment  32  transmits a propulsive force by an appropriate drive train to rear and front tracks  12  and  14  that propel vehicle  10 . Movable steps  50  are mounted to or mounted adjacent to step platform  54 . Push rod assembly  60  is coupled to movable step assembly  50 , on a first end, and coupled to pivot  40 , on a second end. 
     FIG. 1 depicts tractor  10  in a right hand turn position. FIG. 1 also depicts step assembly  50  being mounted on the right side of tractor  10 . FIG. 4 further depicts tractor  10  in a right hand turn similar to FIG.  1 . Referring now to FIG. 3, tractor  10  is depicted in a nominally straight position whereby front tractor section  20  and rear tractor section  30  are substantially aligned. As shown in FIG. 3, movable step assembly  50  is in its nominal position. In its nominal position, step assembly  50  is substantially aligned with a first surface  56  of step platform  54 . As depicted in FIG. 4, step assembly  50  is shown in its alternate position, being substantially aligned with second surface  58  of step platform  54  so as not to interfere with rear tracks  12  and front tracks  14 . FIG. 5 depicts tractor  10  in a left hand turn position. Because, in a preferred embodiment, step assembly  50  is configured to be on the right side of tractor  10 , a left hand turn does not cause interference between step assembly  50  and rear track  12  or front tracks  14 . Therefore, it is desirable to have step assembly  50  remain in its nominal position, that is, substantially aligned with first surface  56  of step platform  54  during a left hand turn. It should however be noted that step assembly  50  could be configured on the left side of vehicle  10 . With step assembly  50  on the left side of vehicle  10 , step assembly  50  would move in response to a left hand turn and be in a nominal position while traveling substantially straight or performing a right hand turn. 
     Referring now to FIG. 2, step assembly  50  is shown coupled to push rod assembly  60 . Movable step assembly  50  has a multiplicity of stair treads  51 , a set of stair stringers or supports  52 , a set of rails  53 , a support arm  55 , and a step pivot  57 . Stair treads  51  are connected to and supported by stair supports  52 . Likewise, handrails  53  are connected to and supported by stair stringers  52 . Support arm  55  is connected to stair supports  52  on a first end and rotatably mounted to step assembly pivot  57  on a second end. 
     Referring now to FIG.  5  and FIG. 6, push arm assembly  60  has a first push rod  64 , a second push rod  68 , a spring  72 , a slide  76 , and a sleeve  80 . First push rod  64  has a pivot coupling  65  on a first end, the pivot coupling having a bushing  66 . As depicted in FIG. 6 bushing  66  is held in place by means of a second bushing  96  and two washers  94  and  98 . First push rod  64  also has a stop  67 , the stop being intermediate a first end  61  and a second end  62  of first push rod  64 . Second push rod  68  has a pivot coupling  69  at a first end, the pivot coupling having a bushing  70 . As depicted in FIG. 7 bushing  70  is held in place by a second bushing  90  and two washers  92  and  93 . Second push rod  68  also has a chamber  71  including at least two sides  77  and an end  78  having a rod aperture (not shown). The second end of first push rod  64  enters the rod aperture in end  78  of second push rod  68 . Sleeve  80  extends substantially the entire length of chambers  71 , and second end of rod  64  is encased therein. Sleeve  80  extends through an aperture  87  in slide  76 . Slide  76  is free to move along the length of chamber  71  while being retained to slide within chambers  71  and being mounted to sleeve  80  by a washer  88  and a nut  86 . Second end of rod  64  and sleeve  80  extend through spring  72 , spring  72  being situated substantially within chambers  71 . A first end  79  of spring  72  engages end  78  of chamber  71 . A second end of  81  of spring  72  engages slide  76 . 
     As depicted in FIG. 2 pivot coupling  65  of first push rod  64  is pivotally attached to a link  83 . Link  83  is rotatably mounted to step assembly pivot  57 . Pivot coupling  69  of second push rod  68  is rotatably mounted to clevis  85 . 
     In operation, when interference is an issue, as depicted in FIGS. 1 and 4, clevis  85  is configured to change position relative to the steering angle, as depicted in FIG.  4 . The movement of clevis  85  causes end  78  of second push rod  68  to engage and abut stop  67  of first push rod  64 . When end  78  pushes against stop  67  force is transmitted to coupling  65  of first push rod  64 . This force causes step assembly  50  to pivot about fixed axis  57  moving step assembly  50  into its alternate position, substantially aligned with surface  58 . 
     When tractor  10  returns to its nominal or straight position as depicted in FIG. 3, clevis  85  is substantially aligned with front tractor section  20 . Also, step assembly  50  returns to its nominal position, substantially aligned with surface  56 . 
     When a left hand turn of tractor  10  is made interference of rear tracks  12  and front tracks  14  with step assembly is not an issue. Therefore, it is desirable to have step assembly  50  substantially aligned with first surface  56 . When tractor  10  undergoes a left hand turn, as well as a nominal straight position, as shown in FIG. 3, first push rod  64  and second push rod  68  separate creating a gap between stop  67  and end  78 . Spring  72  is configured to make up the displacement between the two rods while allowing step assembly  50  to remain in place while clevis  85  and connecting link  83  rotate in opposite directions. During a left hand turn, slide  76  that is connected to sleeve  80  slides along sides  77  of chamber  71  thereby compressing spring  72 , and thereby creating an elongated push arm assembly  60 . 
     Push arm assembly  60  allows step assembly  50  to rotate when the vehicle makes a turn in one direction. In the figures shown, step assembly  50  rotates during a right hand turn and stays substantially stationary when the vehicle goes straight or engages in a left hand turn. Push arm assembly  60 , therefore, serves to keep step assembly  50  stable and sturdy during operation of the tractor, thereby allowing ingress and egress from operator station  22 . It is desirable to provide some amount of preload to spring  72  so that steps  50  are securely held in place, however, the preload should be low enough to prevent the steps from interfering with rear tracks  12  and front tracks  14  during a right hand turn. 
     In an alternative embodiment of the present invention, movable step assembly  50  may be moved, when interference is in issue, by an electric actuator or hydraulic actuator. An electric sensor may be used to measure steering angle at pivot  40  or alternatively on the steering column. The electrical sensor may be a potentiometer, a linear voltage displacement transducer, or other suitable sensor device. The sensor sends a signal to a control unit whereby the control unit provides an electric signal to a direct drive motor which causes the stair assembly to move. In a similar embodiment, the electrical sensor can be configured to send a signal to a control unit, the control unit communicating a signal to an electronic valve, the valve being connected to a hydraulic system, the hydraulic system having a hydraulic actuator. When appropriate, the hydraulic actuator is caused to move, thereby moving step assembly  50 . Furthermore, in other embodiments of the present invention a hydraulic cylinder may act on a mechanical linkage to provide movement to step assembly  50 . Also, when using a hydraulic actuator, an actuator input can be applied to the hydraulic cylinder through a mechanical linkage system or through an electromechanical system. 
     Turning more specifically to clevis  85 , this clevis is configured to provide 2-axes of rotation, one axis along the longitudinal axis of section  20  and the other axis perpendicular to the longitudinal axis. This arrangement permits sections  20  and  30  to both twist and pivot relative to each other. Alternatively, link  83  could also be configured to provide such 2-axis rotation. 
     Although only a few exemplary embodiments of this invention have been described above, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. As is readily indicated, the invention can be employed in a variety of ways and on a variety of articulated work vehicles. Further, the type of actuation mechanism and sensor mechanisms used may be varied in so far as they continue to accomplish functions related to selective step assembly movement. Further, the steps could be located on different sides and sections of the vehicle. Accordingly, all such modifications are intended to be included within the scope of the invention as defined in the following claims. Other substitutions, modifications, changes and omissions may be made in the design, operating conditions and arrangement of preferred and alternative embodiments without departing from the spirit of the invention as expressed in the appended claims.