Abstract:
A material handling lift for moving a load horizontally over a surface and vertically with respect to that surface and a suspension system for the material handling lift. The material handling lift includes a frame with wheels for traveling over the surface. At least one of the wheels is a drive wheel mounted on a vertically-oriented steering column. The steering column is connected to the frame by a parallelogram type suspension system which includes swing arms that are pivotally connected to the frame. A stabilizer bar is connected between the free ends of the swing arms and a shock dampener is connected between the frame and a swing arm. The suspension system helps dampen the shock of traveling over uneven terrain, helps to keep the steering column vertical and the wheels of the vehicle on the ground thereby helping to maintain constant traction with the surface and control of the steering, braking and acceleration of the vehicle. Furthermore, the suspension system aids in providing constant steering effort for the vehicle, regardless of the weight of the load carried.

Description:
BACKGROUND OF THE INVENTION 
   TECHNICAL FIELD 
   This invention generally relates to vehicles for lifting and transporting materials. More particularly, the invention relates to power-driven walk-behind vehicles that are used to move loads both horizontally over a surface and vertically with respect to the surface. Specifically, the invention relates to a vehicle which includes a suspension system connecting the drive wheel to the frame of the vehicle and which enables the vehicle to travel over an uneven surface. 
   BACKGROUND INFORMATION 
   Power-driven walk-behind vehicles, such as powered pallet jacks, powered material transfer trucks and powered pallet stackers are commonly used in the manufacturing and retailing industries for moving heavy loads from one location to another within a factory or store and for stacking products on top of each other. When the powered vehicle travels across even terrain, all of its wheels remain in contact with the ground surface and the weight of the vehicle is distributed across all of the wheels. The vehicle is, therefore, able to move forward at a relatively constant speed. If, however, the vehicle travels over uneven terrain, one of the wheels may enter a small hole or depression in the surface and this may cause other wheels to be temporarily lifted off the ground surface. This causes a hesitation in the forward motion of the vehicle and causes the drive wheel to lose traction and the operator momentarily loses control of steering, acceleration and braking. Similarly, if the vehicle travels over a small bump in the terrain, some of the wheels may lift off the ground causing additional force to be placed on the drive wheel and additional strain on the motor. This is particularly problematic if the drive wheel of the vehicle is the wheel which travels over the bump and some or all of the side wheels are temporarily lifted off the ground. This greatly increases the strain on the motor and thereby reduces the motor&#39;s life and greatly increases the operator&#39;s steering effort. Furthermore, powered vehicles are designed to carry heavy loads and these loads have to be positioned correctly in order to maintain the vehicle&#39;s center of gravity in a particular location for safe operation. If wheels are lifted off the ground, the vehicle&#39;s center of gravity may be shifted to an unsafe position and the vehicle may tip over putting the vehicle, operator and load at risk. 
   There is therefore a need in the art for a material handling lift vehicle that is able to negotiate both even and uneven terrain without being prone to having some of its wheels lift off the ground and which can therefore maintain substantially constant traction and continuous operator control, i.e., steering, acceleration and braking, regardless of surface conditions or weight of load being carried. 
   SUMMARY OF THE INVENTION 
   It is therefore an object of the present invention to provide a material handling lift vehicle with a suspension system connecting its drive wheel to the vehicle frame. The suspension system adjusts the drive wheel&#39;s relative position when the vehicle travels over uneven terrain so that the vehicle&#39;s wheels are all kept in contact with the ground. The suspension system also holds the steering rod, onto which the drive wheel is mounted, in a substantially vertical position when the vehicle is traveling over uneven terrain. 
   The material handling lift vehicle includes a frame that has side wheels mounted on it to travel over the ground surface. At least a portion of the frame holds the load thereon. A drive wheel is received on an axle mounted at one end of a steering column. A parallelogram type suspension connects the steering column to the frame. The parallelogram type suspension includes at least one pair of swing arms that extend outwardly from the frame and are pivotally connected thereto, a stabilizer bar fixedly connected between the swing arms and at least one shock absorber or dampener connected at one end to the frame and pivotally connected at the other end to the swing arms. A plate extends between the stabilizer bar and the steering column and is fixedly connected thereto. When the drive wheel travels over the uneven surface, rotational movement in the suspension system causes a vertical movement in the steering column and thus any shocks to the system are dampened. Consequently, all the wheels of the vehicle tend to remain in contact with the surface over which the vehicle is traveling regardless of the condition of that surface. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The preferred embodiments of the invention, illustrative of the best mode in which applicant has contemplated applying the principles, are set forth in the following description and are shown in the drawings and are particularly and distinctly pointed out and set forth in the appended claims. 
       FIG. 1  is a side elevational view of a material handling lift vehicle in accordance with the present invention; 
       FIG. 2  is a partial cross-sectional side elevational view of the material handling lift vehicle with the hood removed to show the suspension system of the present invention connected to the steering column; 
       FIG. 3  is a partial front elevational view of the material handling lift vehicle and suspension system shown in  FIG. 2 ; 
       FIG. 4  is a partial top view of the material handling lift vehicle and suspension system; 
       FIG. 5  is a partial cross-sectional side elevational view through line  5 - 5  of  FIG. 4 , showing the shock dampener in greater detail; 
       FIG. 6  is a partial cross-sectional side elevational view through line  6 - 6  of  FIG. 4 , showing the stabilizer bars and their connection to the outer surface of the steering column housing; 
       FIG. 7  is a partial cross-sectional side elevational view through line  7 - 7  of  FIG. 4 , showing the connection of the housing to the steering column; 
       FIG. 8  is a partial cross-sectional front elevational view through line  8 - 8  of  FIG. 4 , showing the stabilizer bars in greater detail; 
       FIG. 9  is a partial cross-sectional front elevational view through line  9 - 9  of  FIG. 4 , showing the connection of the upper and lower swing arms to the bracket mounted on the frame; 
       FIG. 10  is a partial top view of the material handling lift vehicle moving toward a depression in the ground surface; 
       FIG. 11  is a partial cross-sectional side elevational view of the material handling lift vehicle as shown in  FIG. 10 , showing the suspension system in its rest position as it travels over a relatively flat surface; 
       FIG. 12  is a partial cross-sectional side elevational view of the material handling lift vehicle showing the drive wheel entering a depression in the ground surface and showing the related movement in the positions of the suspension system components; 
       FIG. 13  is a partial cross-sectional side elevational view of the material handling lift vehicle after it has exited the depression in the surface and showing the suspension system returning to its rest position; 
       FIG. 14  is a partial cross-sectional side elevational view of the material handling lift vehicle approaching a bump in the surface over which it is traveling; 
       FIG. 15  is a partial cross-sectional side elevational view of the material handling lift vehicle showing the drive wheel riding over the bump in the surface and showing the related movement in the suspension system; and 
       FIG. 16  is a partial cross-sectional side elevational view of the material handling lift vehicle with the suspension system returning to its rest position after negotiating the bump in the ground surface. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to  FIGS. 1-9 , there is shown a material handling lift vehicle, generally indicated at  10 . Material handling lift vehicle  10  includes a frame, generally indicated at  12 , onto which is mounted a power unit (not shown), a support  16  and a load carrying platform  18 . Two pairs of laterally spaced side wheel assemblies  19  and  21 , having wheels  20  and  22  respectively, are provided on the underside of frame  12 . A non load-bearing drive wheel assembly  24  is connected to a steering column  26  and is positioned intermediate side wheel assemblies  19  and  21 . Drive wheel  24  is provided with a parallelogram-style suspension system, generally indicated at  27 . Both the power unit (not shown) and suspension system  27  are covered by a hood  28  for protection and to make material handling lift vehicle  10  more aesthetically pleasing. 
   Still, referring to  FIGS. 1-9 , frame  12  includes a horizontal portion  12   a  and a vertical portion  12   b  ( FIG. 2 ). A plurality of pairs of support brackets  30 ,  32  and  34  are mounted on vertical section  12   b  and extend outwardly therefrom at substantially ninety degrees thereto. Brackets  30  and  32  connect frame  12  and steering column  26  together via components of suspension system  27  as will be hereinafter described. Brackets  34  connect the side wheel assemblies  19 ,  21  to frame  12 . 
   Steering column  26  is an elongated tubular member having a longitudinal axis indicated by line X-X′ ( FIG. 2 ). A steering column cap  36  is screwed onto one end of steering column  26  and a handle  37  extends outwardly from cap  36  to enable an operator to move stacker  10 . A mount plate  38  is welded onto the opposite end of steering column  26 . An axle support flange  40  extends downwardly from mount plate  38  and supports an axle  42  which extends outwardly from mount plate  38  and through the bore (not shown) of drive wheel  24 . Axle  42  lies substantially at ninety degrees to the longitudinal axis X-X′ of steering column  26 . A housing  44 , having a central bore  46  ( FIG. 4 ), is coaxially disposed around a portion of steering column  26  intermediate cap  36  and mount plate  38 . Housing  44  is spaced a distance above mount plate  38  and between a pair of collars  48  and  50  ( FIG. 7 ) and is connected to steering column  26  at bearing assemblies  52 . 
   In accordance with one of the main features of the invention and referring to  FIGS. 2-9 , suspension system  27  includes a pair of laterally spaced upper swing arms  54 , a pair of laterally spaced lower swing arms  56 , an upper stabilizer bar  58 , a lower stabilizer bar  60  and a pair of shock dampeners  62 . When these components are connected together and to frame  12 , they are arranged to form a parallelogram-style suspension system for maintaining steering column  26  substantially vertical and to reduce the tendency of steering column  26  to move from a vertical position when drive wheel  24  travels over an uneven surface. Steering column  26  is disposed within the parallelogram formed by upper and lower swing arms  54 ,  56 ; stabilizer bars  58 ,  60  and frame  12 . 
   Upper and lower swing arms  54 ,  56  are of substantially the same length and each arm has a longitudinal axis extending from a first end  54   a  and  56   a  to a second end  54   b  and  56   b , respectively. In  FIG. 2 , the longitudinal axis of upper swing arm  54  is indicated by the line Y-Y′ and the longitudinal axis of lower swing arm  56  is indicated by the line Z-Z′. First end  54   a  of each upper swing arm  54  is provided with an aperture  64  ( FIG. 9 ). A sleeve  66  is received through aperture  64  and a pin  68  pivotally connects first end  54   a  of each upper swing arm  54  between a pair of brackets  30 , such as pair  30   a  or  30   b  ( FIG. 9 ). Similarly, first end  56   a  of each lower swing arm  56  is provided with an aperture  70  and a sleeve  72  and pin  74  are received therethrough to pivotally connect each lower swing arm  56  to a pair of brackets  30   a  or  30   b . Upper swing arms  54  are disposed vertically above lower swing arms  54  on brackets  30 . 
     FIG. 8  shows that upper stabilizer bar  58  is positioned between the second ends  54   b  of upper swing arms  54 . Upper stabilizer bar  58  includes a tubular member  76 , a rod  78  and bearing assemblies  80 . Tubular member  76  includes annular shoulders  77  for engaging bearing assemblies  80 . Rod  78  has threaded ends  78   a  and  78   b  which extend outwardly from tubular member  76 . Each threaded end  78   a ,  78   b  is received through an aperture  82  in second end  54   b  of one of upper swing arms  54 . A nut  84  is screwed onto each threaded end  78   a ,  78   b  to pivotally connect upper swing arms  54  to upper stabilizer bar  58 . Lower stabilizer bar  60  is substantially identical in structure and function to upper stabilizer bar  58 . Lower stabilizer bar  60  is disposed between lower swing arms  56  and the threaded ends  86   a ,  86   b  of rod  86  are each received through an aperture  88  in second end  56   b  of one of lower swing arms  56  and are secured therein by a nut  90 . Tubular member  92  is pivotally connected between second ends  56   b  of lower swing arms  56  via bearing assemblies  93 . Tubular member  92  includes annular shoulders  95  which engage bearing assemblies  93 . Upper and lower swing arms  54 ,  56  lie substantially parallel to each other when upper and lower stabilizer bars  58 ,  60  are secured thereto. Upper and lower swing arms  54 ,  56  are connected to brackets  30  in such a way that they are separated from each other by a small gap  94 . Upper and lower stabilizer bars  58 ,  60  lie substantially parallel to each other and at right angles to the longitudinal axes Y-Y′, Z-Z′, of the upper and lower swing arms  54 ,  56 . 
   Referring to  FIGS. 4 ,  7  and  8 , a pair of laterally spaced plates  96  are provided to connect upper stabilizer bar  58  to housing  44 . A second pair of laterally spaced plates  98  are provided to connect lower stabilizer bar  60  to housing  44 . Plates  96  and  98  each have an arcuate first end complementary sized and shaped to engage the outer surfaces of tubular members  76 ,  92 , respectively. The first ends of plates  96  and  98  are welded to tubular members  76 ,  92 , respectively. Plates  96  and  98  abut the outer surface of housing  44  ( FIG. 4 ) and are welded thereto. Plates  96 ,  98  lie substantially parallel to the longitudinal axes Y-Y′, Z-Z′, of upper and lower swing arms  54 ,  56 . Upper and lower stabilizer bars  59 ,  60  are therefore rigidly connected to steering column  26  and, consequently, when steering column  26  moves vertically up and down as drive wheel  24  travels over a surface  100 , upper and lower stabilizer bars  58 , 60  move in unison with steering column  26  about bearing assemblies  80 . 
   Referring to  FIGS. 2-5 , shock dampeners  62  are provided to dampen the reciprocating motion of steering column  26  and to maintain constant traction and steering effort and control when drive wheel  24  travels over uneven areas of surface  100 . A first end  62   a  of each shock dampener  62  is pivotally connected, via a spacer  102  and pin  104 , through an aperture (not shown) in one of upper swing arms  54 . The second end  62   b  of each shock dampener  62  is pivotally connected between a pair of brackets  32  by a pin  106 . Shock dampeners  62  preferably are of the type having a spring biased piston rod  63  that reciprocates in and out of a cylinder  65 , but could equally be of any other known type of shock dampener without departing from the spirit of the present invention. 
   Referring to  FIGS. 10-13 , in use, material handling lift vehicle  10  may be driven over surface  100  in the direction of the arrow “A”.  FIG. 11  shows the position of upper and lower swing arms  54 ,  56  when surface  100  is flat and even and all wheels of vehicle  10  engage surface  100  in the same plane. Upper and lower swing arms  54 ,  56  extend outwardly from and generally normal to frame  12   b  and lie substantially normal to the longitudinal axis X-X′ of steering column  26 . As vehicle  10  continues to move in the direction of the arrow “A”, drive wheel  24  enters a small depression  108  in surface  100 . If steering column  26  was not provided with suspension system  27 , drive wheel  24  would lose contact with surface  100  and traction, control and forward motion of vehicle  10  would be impeded. However, steering column  26  is provided with suspension system  27  and, consequently, when drive wheel  24  enters depression  108 , steering column  26  moves vertically downwardly in the direction of arrow “B” toward surface  100  ( FIG. 12 ) causing drive wheel  24  to remain in contact with the surface  110  of depression  108 . As upper and lower stabilizer bars  58 ,  60  are rigidly attached to housing  44 , they move downwardly in the direction of arrow “B” when steering column  26  moves downwardly in the direction of arrow “B”. This causes second ends  54   b  and  56   b  of upper and lower swing arms  54 ,  56 , respectively, to move in an arc “C”, thereby moving first end  62   a  of each shock dampener  62  downwardly. This, in turn, drives piston rods  63  into cylinders  65  in the direction of arrow “D”. As vehicle  10  continues to move in the direction of the arrow “A”, drive wheel  24  exits depression  108  and steering column  26  moves upwardly in the direction of arrow “E” ( FIG. 13 ). The upward motion of steering column  26  is transferred to upper and lower stabilizer bars  58 ,  60  and thereby to second ends  54   b  and  56   b  of upper and lower swing arms  54 ,  56 , causing them to begin to move in an arc indicated by arrow “F”. The release of the downward thrust on piston rods  63  allows them to rebound in the direction of arrow “G” and this allows upper and lower swing arms  54 ,  56  to return to their rest position. Wheels  20  and  22  remain in contact with surface  100  when drive wheel  24  travels into and out of depression  108 . The forward motion of vehicle  10  in the direction of the arrow “A” is therefore not interrupted or impeded, traction and control are not lost and no additional stress is placed upon the power unit (not shown) even though vehicle  10  is traveling over an uneven surface. 
   Referring to  FIGS. 14-16 , suspension system  27  is also useful for assisting vehicle  10  to negotiate bumps  114  in surface  100  without wheels  20 ,  22  lifting off surface  100  and stressing power unit (not shown) and increasing steering effort. Vehicle  10  moves in the direction of arrow “H”. When vehicle  10  is traveling over a flat or even section of surface  100 , upper and lower swing arms  54 ,  56  are in the rest position where their longitudinal axes lies at ninety degrees to the longitudinal axis of steering column  26 . As vehicle  10  continues in the direction “H”, drive wheel  24  travels upwardly onto bump  114  and, as it does so, it causes steering column  26  to be forced upwardly in the direction of the arrow “I”. Upper and lower stabilizer bars  58 ,  60  move upwardly in the direction of the arrow “I” with steering column  26 . Second ends  54   b  and  56   b  of upper and lower swing arms  54 ,  56  are moved in an arc “J”, causing piston rod  63  to be drawn out of cylinder  65  in the direction of arrow “K”. This allows the wheels  20  and  22  to remain in contact with surface  100  while drive wheel  24  moves over bump  114 . Drive wheel  24  is therefore not carrying any additional weight of vehicle  10  as it travels over bump  114  and power unit (not shown) is therefore not additionally stressed and traction is maintained and steering effort remains constant. When drive wheel  24  rolls off bump  114  and returns back to the flat even surface  100 , steering column  26  moves downwardly in the direction of arrow “L” ( FIG. 16 ). The movement in steering column  26  causes downward movement in upper and lower stabilizer bars  58 ,  60 , and thereby causes upper and lower swing arms  54 ,  56  to move in an arc “M”. Piston rods  63  consequently rebound in the direction of arrow “N”. This returns upper and lower swing arms  54 ,  56  to their rest position. The entire time that drive wheel  24  is traveling over bump  114  the wheels  20 ,  22  remain in contact with surface  100 . 
   It will be understood that modifications may be made to vehicle  10  without departing from the spirit of the present invention. Material handling lift vehicle  10  is shown to include a motor to raise and lower the load carrying platform and to move the vehicle across the terrain. Vehicle  10  may, alternatively, be provided with a hand-cranked winch, to raise and lower platform, and a handle used to push the unit across the terrain by hand. Additionally, the shock dampener is shown as being attached to the upper swing arm, but it could alternatively be connected to the lower swing arm by inserting a pin (not shown) through aperture  116 . Upper and lower stabilizer bars may be manufactured with a pair of laterally spaced slots therein to receive plates instead of having a concavely shaped front edge for receiving the convexly shaped stabilizer bar. Furthermore, while the bolt passing through the stabilizer bar is shown as having threaded ends that are secured with nuts to the swing arms, it will be understood that other rods and fasteners could be utilized, such as a pin with a cooperating cotter pin. It will also be understood that while the suspension system is disclosed as connecting the drive wheel to the frame, such a system could also be mounted on any or all of the side wheels. 
   In the foregoing description, certain terms have been used for brevity, clearness, and understanding. No unnecessary limitations are to be implied therefrom beyond the requirement of the prior art because such terms are used for descriptive purposes and are intended to be broadly construed. 
   Moreover, the description and illustration of the invention is an example and the invention is not limited to the exact details shown or described.