Apparatus for rotation of tailgate assembly

In a tailgate assembly, a connecting mechanism which joins one end of each side plate of the assembly to the frame of the vehicle carrying the assembly wherein pivoting of the dump body of the vehicle causes the connecting mechanism to rotate the tailgate assembly. The connecting mechanism includes a chain on each side of the body which is biased about the side of the body by a roller assembly that engages the chain to hold it away from the side and to limit its lateral movement along the length of the side.

TECHNICAL FIELD 
The invention generally relates to tailgate assemblies for off-road, 
heavy-duty trucks and more particularly relates to mechanisms for raising 
and lowering tailgates. 
BACKGROUND 
Because tailgate assemblies can be damaged by the difficult tasks performed 
by the off-road, heavy-duty trucks, the bodies of the trucks have 
traditionally been designed to function without tailgates. But, as a 
result of a desire to increase capacity, tailgate assemblies have been 
designed for addition of tailgates to the bodies which are capable of 
withstanding the harsh working environment of off-road trucks. For 
example, in U.S. Pat. No. 3,751,112 to Hagenbuch a tailgate assembly 
includes two side plates that are pivotally connected to the sides of the 
body. In order to raise the tailgate upon the pivoting of the body, a pair 
of outriggers mounted to the frame of the truck, secure one end of a pair 
of chains (or cables) which cause the tailgate to rotate when the body is 
dumped. 
By providing outriggers, the chains or cables which rotate the tailgate are 
attached at a point on the frame which extends out beyond the side of the 
body. By attaching one end of the chains at the end of the outriggers, the 
chains are not biased around the bottom edge of the body, which would 
cause damage to both the chains and the truck body. 
But, because the outriggers are a cantilever and extend from the frame to a 
point beyond the sides of the body, the outriggers may be plagued with 
problems under certain conditions. For instance, because of limited 
available space on the frames of some truck models, the area of the base 
of the outriggers (where they attach to the frame) may be smaller than 
desired. The strength of the outriggers may be compromised if the bases of 
the outriggers have areas too small for the outriggers to withstand the 
large forces exerted at the ends of the outriggers as the tailgate is 
rotated when the body pivots. As a result of the area of the base being 
too small, the outriggers may be susceptible to bending after repeated 
use. Finally, some manufacturers of trucks are reluctant to honor 
warranties if the frame of the truck has been subjected to welding as is 
required to mount the outriggers for the addition of a tailgate assembly. 
One attempt at eliminating the potential problems of the use of outriggers 
to raise tailgates has been to use a shortened outrigger which does not 
extend beyond the sides of the body. By shortening the outrigger, the 
weakening caused by cantilevering is reduced. Because these outriggers do 
not extend beyond the sides of the body, the chains (or cables) are biased 
against the bottom edge of the body. When the body is pivoted to a dump 
position, the chains move relative to the bottom edge of the body. In 
order to prevent damage of the body or the chains as the body pivots in 
dumping, an elongated roller is mounted on each side of the body in order 
to protect the truck body and reduce wear of the chain. 
Each roller is elongated because, as the body pivots, the chain changes 
position along the length of the sides of the body. As a result, in 
addition to the roller rotating as the chain pulls the tailgate to a 
raised position, the chain also walks along the length of the roller as 
the relative positions of the chain and roller change. Because of 
frictional forces, the chain does not walk smoothly along the length of 
the roller; instead, it moves in a jerking motion caused by the friction 
between the roller and chain holding it in a stationary lateral position 
until movement of the body and tailgate cause an angle in the chain which 
creates sufficient force to overcome the friction. As the body continues 
to pivot, the forces created by the bending chain increase until they 
again overcome the friction and the chain snaps to a new position. This 
jerking movement is extremely hard on both the rollers, the chains, the 
outrigger, the tailgate and the truck frame. As a result, the rollers and 
chains wear out quickly. 
To overcome the foregoing wear problem, it is known to use a cable 
connection instead of a chain. Because a cable is composed of multiple 
strands of wire, frictional forces between strands become substantial if 
the elongated rollers bend the cable at too great an angle. In order to 
reduce the angle, the shortened outriggers are provided. Although the 
amount of extension of these shortened outriggers reduces problems 
inherent in a cantilevered support off the truck frame, the problems 
remain. 
SUMMARY OF THE INVENTION 
The primary objection of the invention is to provide a mechanism for 
raising and lowering a tailgate assembly which does not have the foregoing 
disadvantages associated with both full truck width and shortened 
outriggers. In this connection, it is also an object of the invention to 
provide a mechanism for raising and lowering tailgate assemblies that 
fulfills the foregoing objective without introducing new disadvantages as 
exemplified by the foregoing prior attempts. 
It is another object of the invention to provide a tailgate assembly which 
can be easily added to existing truck bodies without compromising the 
structural integrity of the frame or body. 
Other objects and advantages will become apparent with reference to the 
following detailed description when taken in conjunction with the 
drawings. 
The invention provides an improved connecting mechanism joining the 
tailgate assembly of a dump body and the frame of the vehicle which 
function to rotate the tailgate assembly in response to pivoting of the 
dump body. In order to join the connecting mechanism to both the tailgate 
assembly and the frame, it is angled about the side sheets of the body. 
The connecting mechanism is biased away from the side sheets by a pair of 
roller assemblies mounted to the bottom sheet of the body of the tailgate 
assembly. In order to prevent repositioning of the connecting mechanism 
along the length of the side sheets as the body pivots and the tailgate 
rotates, the roller assembly includes means for limiting the lateral 
movement of the mechanism. The means resists lateral movement of the 
connecting mechanism, thereby biasing the mechanism in a plane parallel to 
the side plates. 
While the invention will be described in some detail with reference to a 
preferred embodiment, it is to be understood that it is not intended to 
limit the invention to such detail. On the contrary, it is intended to 
cover all alternatives, modifications and equivalents which fall within 
the spirit and scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring first to FIG. 1, there is shown the typical rear dump vehicle 
illustrated in the dump position. The rear dump vehicle includes a dump 
body 11 having a pair of side sheets 13 (one sheet shown only), a front 
sheet 15 and a bottom sheet 17. Furthermore, some rear dump vehicles 
include a canopy 19 coupled to the dump body 11. The canopy operates to 
protect a cab 21 when the rear dump vehicle is being loaded. The side 
sheets 13, the front sheet 15 and the bottom sheet 17 provide an open top 
wherein earth or other loaded material can be inserted in the dump body 
11. The dump body 11 is generally connected to the main frame 23 by a body 
pivot assembly 25 so that the body can be rotated about a body pivot pin 
25a for dumping the load. 
A tailgate assembly 27 is illustrated having a pair of side plates 29 (one 
of which is illustrated only) and a rear plate 31. The side plates 29 are 
pivotally connected to the side sheets 13 of the dump body 11 by a 
tailgate pivot pin 33. Consequently, the tailgate 27 can pivot about the 
pivot pin 33 to provide both a dump position (as shown in FIG. 1) and a 
load position (as shown in FIG. 2). The rear plate 31 of the tailgate 27 
is illustrated in FIG. 2 as extending beyond the rear portions of the side 
sheets 13. Furthermore, the rear plate 31 is shown substantially 
perpendicular to a ground surface. Consequently, the rear plate 31 when in 
the load position provides an increased volume for the dump body 11 in 
which loaded material can be placed. 
The forward edge of the side plates 29 of the tailgate assembly 27 have 
extension pieces 35 thereon which provide an anchor for a chain 37. At the 
opposite end of the chain 37, it is connected to an elongated mounting 
support 39. The mounting support 39 is in turn welded to a base section 40 
for the hoist cylinders 42. As an aid in describing relative movement of 
the dump body 11, the tailgate assembly 27 and the chain 37, a Cartesian 
coordinate system is illustrated with a Y-axis aligned parallel with the 
axis of rotation for the dump body and the X-axis parallel with the length 
of the vehicle. The Z-axis is substantially vertical. 
As the forward portion of the dump body 11 is raised by the hoist cylinders 
42, the dump body is pivoted about the body pivot pin 25a. Pivoting of the 
dump body 11 causes the chain 37 to become taut and, as a result, exerts a 
torque on the side plate 29 which causes counterclockwise rotation of the 
tailgate assembly 27 about the pivot pin 33. As illustrated in FIG. 1, 
pivoting of the dump body 11 causes the rear plate 31 to rotate to a 
position which substantially clears the normal maximum load height of 
loaded material carried in the dump body. Consequently, any material on 
the bottom sheet 17 of the dump body 11 can be discharged beneath the rear 
plate 31 of the tailgate assembly 27 and through the rear portion of the 
side sheets 13. 
The tailgate pivot pin 33 can be located at any desired position relative 
to the side plate 29 of the tailgate assembly 27 and the side sheets 13 of 
the dump body 11. However, a desired position for the tailgate pivot pin 
33 is in a position which causes a slight raising of the rear plate 31 of 
the tailgate assembly 27 to an angle approximately 90.degree. between the 
top of side sheets 13 and the top of side plate 29. A slight raising of 
the rear plate 31 provides increased clearance between the rear plate and 
the bottom sheet 17 for discharge of the loaded material. By placing the 
pivot pin 33 substantially forward from the rear of the side sheets 13 (as 
shown in FIG. 1), rotating motion of the surface of the rear plate 31 is 
upwardly and over the loaded material. 
The mounting support 39 is preferably an elongated, square and hollow 
tubing (e.g., steel) which is secured to the lowermost portion of the base 
section 40 which anchors one end of each of the hoist cylinders 42. 
Although the mounting support 39 eliminates the need for outriggers, the 
chain 37 can no longer maintain a straight line in the Y-Z plane, as it 
could when an outrigger was present. 
As best seen in FIG. 3, a straight line SL in the Y-Z plane connecting the 
extension piece 35 to the end 39a of the mounting support 39 cuts through 
the side walls 13 and the bottom 17. Therefore, the chain 37 must be 
biased around the edge 41 formed where the side 13 meets the bottom 17. In 
order to direct the chains 37 around their respective edges 41, a pair of 
roller assemblies 43 are mounted (e.g., welded) on the bottom sheet 17 and 
adjacent the edges 41 in order to engage the chains 37 and prevent 
scraping of the edges against the chains as they move relative to one 
another as the dump body 11 pivots. 
Referring more particularly to FIGS. 2 and 3, in the lowered position of 
the dump body 11, each of the chains 37 describe a straight line in the 
X-Z plane and an angled line in the Y-Z plane. The angling of the chain 37 
in the Y-Z plane is provided by a cylindrical roller 45 in each of the 
roller assemblies 43 which causes the chain to be biased away from the 
edge 41. Because the roller 45 is mounted for rotation about an axis 
r.sub.1 which is substantially transverse to the line formed by the chain 
37 in the X-Z plane, pivoting of the dump body 11 will cause the roller 45 
to rotate as the chain moves over the surface of the roller. 
In accordance with one important aspect of the invention, each of the 
roller assemblies include a second roller whose axis of rotation is 
approximately transverse to that of roller 45; when the chain is biased 
away from the edge 41 in the Y-Z plane by the roller 45 during pivoting of 
the dump body 11 and rotation of the tailgate assembly 27, the chain also 
is biased forwardly in the X-Z plane by the second roller so that the 
sliding of the chain along the length of the roller 45 is limited. Each of 
the second rollers is mounted in the roller assembly relative to the first 
roller 45 so as to engage the chain 37 as it begins to move laterally 
along the length of the surface of roller 45 in response to the pivoting 
of the dump body 11 and the rotation of the tailgate assembly 27. After 
the second roller engages the chain 37, further pivoting of the dump body 
11 will cause the chain 37 to angle about the second roller in the X-Z 
plane. Because the chain 37 is biased forwardly, the first roller 45 is 
able to hold the chain away from the edge 41 without being of a 
substantially longer length. In addition, by limiting the amount of travel 
of the chain 37 along the length of the roller 45, the wear caused by such 
lateral movement is substantially reduced. Because the chain no longer 
catches and releases in response to the frictional dynamics of the chain 
moving laterally over an elongated roller as in the prior art, the raising 
and lowering of the tailgate assembly 27 in accordance with the invention 
is much smoother than previously possible in tailgate assemblies without 
outriggers. 
Viewing the dump body 11 from the side and in its lowered position as 
illustrated in FIG. 2, the chain 37 appears as aligned substantially in a 
straight line. Actually, the chain 37 is angled in the Y-Z plane about the 
edge 41 by the first roller 45, as best seen in FIG. 3, whose axis of 
rotation r.sub.1 is in approximate parallel alignment with the edge 41. 
When the operator of the vehicle activates the hoist cylinders 42, the 
dump body 11 pivots, thereby causing the roller assembly 43 and the 
tailgate assembly 27 to rotate about the pivot pin 25a. As the dump body 
11 pivots toward its dump position shown in FIGS. 4 and 5, the extension 
piece 35 moves relative to the roller assembly 43 and the mounting support 
39. 
Since the chain 37 remains taut as the dump body 11 pivots, it attempts to 
maintain a straight line between the extension piece 35 and the mounting 
support 39. In attempting to maintain such a straight line, the chain 
moves along the length of roller 45 as the relative positions of the 
extension piece 35 and mounting support 39 change. Because roller 47 is 
mounted for rotation about an axis r.sub.2 that is transverse to the axis 
of rotation r.sub.1 for roller 45, when the chain 37 reaches the surface 
of the roller 47 it is prevented from traveling further along the length 
of roller 45, and it is biased by the surface of the roller so that 
continued pivoting of the dump body 11 causes the chain 37 to rotate the 
roller as the chain becomes angled in the X-Z plane as well as the Y-Z 
plane. 
Referring to FIG. 6, each of the roller assemblies 43 includes first and 
second metal plates 49 and 50 which are mounted on the edges to the bottom 
sheet 17 of the truck body 11. At the free ends of the plates 49 and 50, 
metal cross members 51 and 53 brace the plates so as to provide a sturdy 
open box structure. Spanning plates 49 and 50, the journals of roller 45 
are received by holes in the plates which are surrounded by bushings 62 
(only one is shown) mounted on the outside surface of each of the plates. 
Likewise, roller 47 spans the opposing cross members 51 and 53 with its 
journals being received by holes in each of the cross members which are 
surrounded by bushings 60 mounted on the outside surface of the members. 
To further support the roller assembly 43, struts 65 (only one is shown in 
FIG. 2) extend from the outside of the plates 49 and 50 to the surface of 
the bottom sheet 17. 
Each of the rollers 45 and 47 is constructed of large and small tubing 
concentrically positioned and capped at both ends by a donut-shaped metal 
piece. The foregoing construction creates a central bore through each 
roller 45,47 that receives an elongated rod that serves as a shaft about 
which the rollers rotate. The ends of the shafts serve as the journals 
which are received by the bushings 62 and 60. As a possible addition to 
the roller assembly, a layer of rubber may be vulcanized to its 
circumference in order to further improve the smoothness of the movement 
of the chain 37 over the surface of the roller. 
The extension piece 35, roller assembly 43 and mounting support 39 may be 
moved relatively to one another from their positions shown in the drawings 
in order to provide for varying degrees of tailgate rotation which 
maximizes the opening of the tailgate relative to the body. Because such 
repositioning may result in the chain 37 rubbing the plate 50 of the 
roller assembly 43, a third roller mounted in the assembly may prove 
necessary. By simply extending the length of the cross members 51 and 53 
and the length of the roller 45, the third roller can be added which is 
supported by the cross members on the forward side of the chain 37. The 
third roller may have an axis of rotation parallel with the axis of 
rotation r.sub.2 of the second roller 47. 
In keeping with the invention, the chain 37 may be a single continuous 
chain which reaches from one extension piece 35 to the other as best shown 
in FIGS. 3 and 5. For a continuous chain 37, the mounting 39 is preferably 
a conduit through which the chain passes. A single continuous chain 37 
responds to changes in the tension of the chain on each side of the body 
resulting from uneven tilting of the body. If this happens, the distance 
between the ends 39 of the mounting support 39 and the extension pieces 35 
will increase on one side and decrease on the other side. By making the 
chain 37 continuous, any shifting or tilting of the body 11 is compensated 
for by movement of the chain through the hollow of the support mounting 
39. 
If the chain 37 breaks, release of the chain's tension on both sides of the 
body can be avoided by limiting the chain's freedom of movement through 
the mounting support 39. For example, a short auxiliary chain may attach 
the chain 39 to the mounting support such that a break on one side will 
permit only a limited release of the tension on the opposing side because 
the auxiliary chain will hold the unbroken side to the mounting support. 
The preferred way of implementing the chains 37 is to provide two separate 
chains whose ends are secured to the ends 39a of the mounting support 39 
thus tending to stabilize the tilting of the body. In order to attach the 
ends of each separate chain 37 to the ends 39a of the mounting support, 
the ends 39a are formed by welding a metal plate (not shown) over each end 
of the mounting support 39. Two support brackets (not shown) are 
positioned to be standing on end with the metal plate as their base. These 
support brackets receive a nut and bolt assembly that also receives the 
last link of the chain 39. Because the last link is sandwiched between the 
two support brackets, the nut and bolt assembly secures the end of the 
chain 37 to the mounting support 39. 
From the foregoing, it will be appreciated that the connecting mechanism of 
the invention provides an effective means for raising and lowering a 
tailgate assembly for heavy-duty, off-road trucks without necessitating 
the use of an outrigger. Furthermore, the dual-roller assembly 43 allows 
the chain 37 to easily move relative to the dump body 11 without jumping 
and without requiring cumbersome accessory equipment in lieu of 
outriggers.