Abstract:
A lift truck includes an operator compartment having a center operating position providing an operator with a first field of view and an off center operator position providing the operator with a second field of view. A pair of forks extend away from the operator compartment. Each of the forks include a distal end. A pair of base legs extend away from the operator compartment and space laterally outwardly from the pair of forks away from a central axis of the truck. Each of the base legs include a distal end. A pair of mast columns is interposed between the operator compartment and the forks. A portion of the first field of view is blocked by the mast columns and a portion of the second field of view is blocked by the mast columns. The distal ends of the forks and the distal ends of the base legs are visible in the first field of view and the second field of view.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is a continuation of U.S. patent application Ser. No. 12/106,802, filed Apr. 21, 2008, which is a continuation of U.S. patent application Ser. No. 11/467,754, filed Aug. 28, 2006, now U.S. Pat. No. 7,398,859, which is a continuation of U.S. patent application Ser. No. 10/634,377 filed Aug. 5, 2003, now U.S. Pat. No. 7,096,999, all of which are fully incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The field of the invention is industrial lift trucks, and particularly lift trucks with telescopic masts. 
         [0003]    A lift truck typically is a battery powered vehicle having an operator compartment with controls that enable the operator to drive the truck and to hoist materials and carry them quickly throughout a factory or warehouse. An upright telescopic mast is attached to the forward end of the truck and with a carriage, or forks, supporting materials can be hoisted by extending the telescopic mast upward. 
         [0004]    An exemplary lift truck is shown in  FIGS. 1 and 2 . It includes an operator compartment  10 , a battery  11  and outriggers, or baselegs,  12 A and B. A three section, telescopic mast  20  attaches to the front of the truck and includes a base section  21  and two telescopic sections  22  and  23 . As shown best in  FIG. 2 , the lower telescopic section  22  (referred to in the art as the “outer” telescopic section) is nested within the base section  21  and the higher telescopic section  23  (referred to in the art as the “inner” telescopic section) is nested inward of the outer telescopic section  22 . 
         [0005]    A fork carriage  13  is slidable mounted to the inner telescopic section  23  and it is moved up and down thereon by carriage free lift cylinders  13 A and B via chains  13 C which pass over pulleys  13 D. The outer telescopic section  22  is moved relative to the base section  21  by a main lift cylinder  22 A located midway between the left and right mast sections. Lift chains (not shown in  FIGS. 1 and 2 ) fastened to the base section  21 , extending over pulleys at the top of the outer telescopic section  22 , and fastened to the bottom end of the inner telescopic section  23  provide a simultaneous and coordinated movement of the inner telescopic section  23  relative to the outer telescopic section  22 . Operation of the main lift cylinder  22 A using controls in the operator compartment  10  may thus extend or contract the two telescopic sections  22  and  23 . Operation of the carriage free lift cylinders  13 A and B from the operator compartment  10  also controls the precise height of the fork carriage  13 . 
         [0006]    These mast elements plus the associated hydraulic hoses and electrical cable provide obstructions which limit the operator&#39;s field of view when looking forward towards the forks from the operator compartment  10 . This is particularly true when the mast is lowered and all the cylinders  22 A,  13 A and  13 B are disposed directly in front of the operator. 
         [0007]    Many efforts have been made to improve the operators&#39; field of view when looking forward through the mast. These include shortening the main lift cylinders as disclosed in U.S. Pat. Nos. 4,191,276 and 4,261,438 so that it does not obstruct view when the mast is lowered, shifting the location of the main lift cylinder to one side as disclosed in U.S. Pat. No. 4,355,703; shifting the location of the single main lift cylinder to one side and shifting a single carriage free lift cylinder to the other side as disclosed in U.S. Pat. No. 4,506,764; and shifting the location of the two carriage free lift cylinders to locations nearer the mast uprights to increase visibility as described in U.S. Pat. Nos. 4,369,861; 4,365,693; 4,030,568 and 4,441,585. Yet another approach disclosed in U.S. Pat. No. 4,585,093 is to locate the two carriage free lift cylinders substantially behind the mast uprights and provide two main lift cylinders which are also behind the respective mast uprights. This is carried one step further in U.S. Pat. No. 6,505,710 in which the two main lift cylinders are formed into the base section of the mast. 
         [0008]    A significant constraint on the design of a lift truck mast structure is its fore to aft dimension. The length of a lift truck is a very important characteristic, since turning radius is directly related to length. The productivity of a truck and operator is directly related to the turning radius since in the tight confines of factories and warehouses a smaller turning radius translates to less back-and-forth jockeying of the truck. The elimination of one or more inches in the length of a truck therefore has significant economic significance. 
       SUMMARY OF THE INVENTION 
       [0009]    The present invention is a lift truck in which the mast elements and associated lift elements are arranged to maximize the operator&#39;s field of view when looking forward from the operator compartment. In a preferred embodiment, an operator compartment provides an operator with a center operating position providing the operator with a first field of view and an off center operator position providing the operator with a second field of view. A pair of forks extend away from the operator compartment. Each of the forks include a distal end. A pair of base legs extend away from the operator compartment and space laterally outwardly from the pair of forks away from a central axis of the truck. Each of the base legs include a distal end. A pair of mast columns is interposed between the operator compartment and the forks. A portion of the first field of view is blocked by the mast columns and a portion of the second field of view is blocked by the mast columns. The distal ends of the forks and the distal ends of the base legs are visible in the first field of view and the second field of view. 
         [0010]    A general object of the invention is to maximize the operator&#39;s field of view from both operating positions. In one embodiment, this objective is accomplished by nesting the mid rail members in the base rail members and mounting the lift chain pulleys forward of the top rail members, the two obstructing profiles of the mast columns are minimized when viewed from the operator compartment. 
         [0011]    Another aspect of the invention is the arrangement of the main lift cylinders and a pair of free lift cylinders. The free lift cylinders are mounted to the top rail members and positioned substantially behind the mast columns and laterally inward from the main lift cylinders. Operation of the free lift cylinders raises and lowers a carriage slidably mounted to the inner telescopic section. The lateral location of the free lift cylinders is asymmetric with respect to the truck center line to provide clearance for a hose pulley which the left cylinder supports without reducing operator visibility. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a perspective view of a typical prior art lift truck; 
           [0013]      FIG. 2  is a cross-sectional view through the mast of the prior art lift truck in  FIG. 1 ; 
           [0014]      FIG. 3  is a side elevation view of a lift truck which employs the present invention; 
           [0015]      FIGS. 4A and 4B  are perspective views of the mast structure of the lift truck of  FIG. 3 ; 
           [0016]      FIGS. 5A ,  5 B and  5 C are perspective views of the respective base section, outer telescopic section and inner telescopic section of the mast structure of  FIG. 4 ; 
           [0017]      FIG. 6  is a partial top plan view of the lift truck of  FIG. 3  showing the arrangement of mast elements according to a preferred embodiment of the invention; 
           [0018]      FIG. 7  is a top view of the lift truck of  FIG. 3  with sight lines indicating the operator&#39;s field of view through the mast structure; 
           [0019]      FIG. 8  is a perspective view of the inner telescopic section with attached free lift cylinders, and 
           [0020]      FIG. 9  is a partial perspective view of the inner telescopic section with slidably mounted fork carriage. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0021]    Referring particularly to  FIG. 3 , a lift truck which employs a preferred embodiment of the invention includes a power unit  110  having an operator&#39;s compartment  112  located to the rear and a battery compartment  114  located at the forward end. The battery supplies power to a traction motor drive (not shown) which rotates a steerable drive wheel  116  to propel and steer the lift truck. A pair of laterally spaced baselegs  118  indirectly connect to, and extend forward from the power unit  110 , and each baseleg includes wheels  120  which support the truck. 
         [0022]    A mast  122  connects to the front end of the power unit  110  and extends vertically upward therefrom. The mast  122  supports a fork carriage  124  which can be elevated to different heights as will be described in detail below. The mast  122  is comprised of three telescopic sections which are shown best in  FIGS. 4A and 4B . These include a base section  126 , an outer telescopic section  128 , and an inner telescopic section  130 . Rollers mounted to the sections  126 ,  128  and  130  enable those sections to slide with respect to each other to allow the mast to be raised and lowered. These mast elements form two spaced mast columns which obstruct the operator&#39;s view when looking forward from the operator compartment. It is an objective of this design to reduce the profile of these mast columns and the associated mast elements to maximize the operator&#39;s forward field of view. 
         [0023]    As shown best in  FIG. 5A , the base section  126  is comprised of a pair of spaced, base rail members  132  and  134  connected together at their bottom ends by a base crosstie  136  and at their upper ends by a pair of crossties  138  and  140 . The crossties  138  and  140  include a set of louvers which provide the desired structural rigidity and which are oriented at an angle which minimizes obstruction of the operator&#39;s view. The crosstie  140  also serves to support a protective guard  142  (see  FIG. 3 ) above the operator. The base crosstie  136  attaches to the front of the power unit  110  and serves as a means for fastening the mast structure to the power unit  110 . 
         [0024]    Referring particularly to  FIG. 5B , the outer telescopic  128  is comprised of a pair of spaced, upright mid rails  144  and  146  connected at their lower ends by a lower crosstie  148 . An upper crosstie  150  extends rearward from the upper ends of the mid rails  144  and  146  and then laterally across the space between the mid rails  144  and  146  to maintain their parallel alignment. The rearward extending portions of the crosstie  150  also provides a connection point for a pair of main lift cylinders to be described in more detail below. 
         [0025]    Referring particularly to  FIGS. 5C and 8 , the inner telescopic section  130  is comprised of a pair of spaced, upright top rails  152  and  154  connected at their lower ends by a lower crosstie  156  and connected at their upper ends by an upper crosstie  158 . Upper crosstie  158  extends rearward and presents a horizontal platform having openings therein which enable the upper ends of a pair of free lift cylinders  160  and  162  to extend. The lower ends of free lift cylinders  160  and  162  mount to ears  164  and  166  that extend rearward from the top rails  154  and  152  adjacent the lower crosstie  156 . The upper cylinder ends connect to a rear flange  202  of the top rails  152  and  154  near their top ends. As will be described in detail below, the free lift cylinders  160  and  162  are hydraulically operated in response to commands from the operator to extend and retract rods  168  and  170  to raise and lower the fork carriage  124  that is slidably mounted to the top rails  152  and  154 . 
         [0026]    Referring particularly to  FIGS. 8 and 9 , free lift chain pulleys  171  and  173  are mounted to the top ends of the respective free lift cylinder rods  168  and  170 . Free lift chains  175  and  177  extend over the respective pulleys  171  and  173  and one end of each chain is anchored to the rear side of respective free lift cylinders  160  and  162 . The other end of each free lift chain drapes down the front side of their respective cylinders  160  and  162  and attaches to the back of the fork carriage  124 . When the rods  168  and  170  of the free lift cylinders  160  and  162  are extended, the pulleys  171  and  173  move upward and the forward ends of the chains  175  and  177  are raised a corresponding amount to slide the fork carriage  124  upward on the inner telescopic section  130 . 
         [0027]    As shown in  FIG. 9 , the fork carriage  124  requires hydraulic hoses and cable  179  to operate a reach and retract mechanism mounted therein. These hoses and cable  179  extend over a hose pulley  181  which is mounted above the chain pulley  171  on the left free lift cylinder  160 . One end of each hose and cable  179  is anchored on the rear side of the free lift cylinders  160  and the other end connects to the hydraulic and electrical circuits in the fork carriage  124 . 
         [0028]    As shown best in  FIGS. 4A and 4B , the telescopic mast structure is raised and lowered by a pair of main lift cylinders  172  and  174 . The lower ends of the cylinders  172  and  174  are fastened to the base section  126  adjacent each end of base crosstie  136 . Rods  176  and  178  extend upward from respective main lift cylinders  172  and  174  and fasten to the upper crosstie  150  on outer telescopic section  128 . When the lift cylinders  172  and  174  are hydraulically operated in response to commands from the operator, the outer telescopic section  128  is lifted and lowered with respect to the base section  126  to extend and retract the mast. 
         [0029]    As shown best in  FIG. 5B , the telescopic motion of the outer telescopic section  128  in response to operation of the main lift cylinders  172  and  174  also operates the inner telescopic section  130  through a pair of lift chains  180  and  182 . The lift chains  180  and  182  are supported by pulleys  184  and  186  mounted at the upper ends of respective mid rails  144  and  146  with their axes of rotation oriented in the fore and aft direction. An outboard end  188  of each lift chain  180  and  182  is connected to the inner telescopic section  130 , and an inboard end  190  of each lift chain  180  and  182  is connected to the base section  126 . When the outer telescopic section  128  is telescoped upward by the main lift cylinders  172  and  174 , the pulleys  184  and  186  are lifted upward therewith, and the outboard ends  188  of the lift chains  180  and  182  also lift, or telescope upward to lift the inner telescopic section  130 . Thus, the inner and outer telescopic sections  130  and  128  slide in unison when the main lift cylinders  172  and  174  are operated to extend or retract the mast. 
         [0030]    Referring particularly to  FIG. 6 , the shape and location of the above mast assembly elements are designed to maximize the operator&#39;s field of view when looking forward through the mast. Looking at the left mast column, the C-shaped base rail  134  formed by a web and forward and rear flanges substantially encloses the I-shaped mid rail  146  which nests therein. The I-shaped mid rail  146  has a web with a forward and rear flange. The I-shaped top rail  154  formed by a web and forward and rear flanges is immediately inboard the base rail  134  with their respective rear flanges  200  and  202  substantially aligned. The lift chain pulley  186  is mounted in the web  204  of the mid rail  146  and it is disposed forward of the top rail  154 . The resulting assembly of mast elements is compact in the lateral direction without lengthening the truck in the fore/aft direction. The right side of the mast is a mirror image of the left side, although other elements now to be described are not necessarily symmetrically arranged. In addition to the compact arrangement of elements, the left and right mast columns provide protection for the lift chains  180  and  182 . 
         [0031]    Referring still to  FIG. 6 , other elements of the mast are also arranged to maximize the operator&#39;s field of view. The main lift cylinders  172  and  174  are positioned directly behind the respective base rails  134  and  132 . By using two main lift cylinders  172  and  174  rather than one, their diameters may be reduced such that they do not significantly increase truck length when moved behind the mast. The right side free lift cylinder  162  is positioned directly behind the top rail  152  so as not to increase the lateral dimension of the right mast column. On the other hand, the left side free lift cylinder  160  is positioned behind and inboard the rear flange  202  of the top rail  154 . This arrangement allows the free lift cylinder  160  to be moved forward approximately 0.25 inches so that the much larger hose pulley  181  that supports the hoses and cable  179  can be moved forward into the viewing “shadow” of the left mast column. 
         [0032]    Another asymmetry between the left mast column and right mast column is a set of hose pulleys  205  disposed behind the left mast column, between the main lift cylinder  172  and the free lift cylinder  160 . As shown in  FIG. 5B , these pulleys  205  are mounted to a support bracket  207  that extends downward from the upper crosstie  150  on outer telescopic section  128 . The hoses which these pulleys  205  support hang down through the extended height of the outer telescopic and are positioned laterally in the viewing shadow of the left mast column so as to not provide an additional obstruction to the operator&#39;s field of view. As will be explained below, this asymmetric arrangement of the left and right mast columns provides a maximum field of view for an operator who is positioned to the right of the central fore and aft axis  208  of the lift truck shown in  FIG. 7 . 
         [0033]    Referring particularly to  FIG. 7 , an operator positioned in the operator&#39;s compartment can assume a number of different positions which provide different fields of view when looking forward through the mast. When the operator takes a centered forward stance his field of view emanates from point  206  which is located near the fore and aft central axis  208  of the lift truck. Two regions  210  and  212  are blocked from view by the left and right mast columns when the operator is in this position. 
         [0034]    The operator can also take a right forward position, in which his field of view emanates from a point  214  far to the right of the central axis  208 . Two regions  216  and  218  are blocked from view by the left and right mast columns when the operator is in this position. It should be apparent that by shifting between these two operator positions the forward field of view extends to all but two, small triangular areas  220  and  222 . Most importantly, the forks  224  are in complete view as are the ends of both baselegs  118 . This expanded field of view facilitates driving the truck in confined spaces and placing loads on the forks  224 .