High lift tag axle for trucks

A high lift tag axle for a concrete mixer truck or the like is pivotally attached to the rear of the truck through a pair of tag arms each having a lever arm, with a linkage arrangement interconnecting each lever arm to the truck frame, and a hydraulic cylinder connected to said linkage arrangement to align the linkage arrangement in a plane sufficient to lock the lift axle in a downward position where the wheels engage the road surface, and whereby the hydraulic cylinder can pivot as the linkage arrangement sufficient to pivot the tag axle into a position whereby the wheels are raised off of the road surface.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates generally to vehicular trucks, and more to a new and 
improved high lift tag axle for transit mixers, i.e. concrete mixer trucks 
and the like, which will not only permit an increase in the legal payload 
of the truck or mixer unit, but does not rely on a complicated hydraulic 
system to hold the tag axle in either the lowered or raised position. 
Rather, the tag axle of this invention utilizes a mechanical lock-down 
arrangement so that all ground forces are transmitted through the physical 
structure thereof and not the hydraulic system. In addition, the tag axle 
of this invention can be raised to an exceptionally high position so that 
it is not obstructive to complete access to the rear of the truck for the 
purpose of discharging concrete and the like. 
2. The Prior Art 
It is well known that most federal, state and local highways have load 
limits which limit the weight of vehicles traveling thereon. While there 
are total over-all weight limits per vehicle, many highways regulations 
also provide for load limits per vehicle axle. This is particularly true 
in the case of bridges where in addition to overall weight limits per 
vehicle, there are also weight limits to prevent localized weight 
concentrations. In this regard, the Federal Highway Administration has 
issued a "Bridge Gross Weight Formula", commonly referred to as the 
"bridge formula", which specifies load limits on the basis of bridge load 
carrying classifications, and provides formulas for determining load 
limits based not only on the basis of weight per axle, but also on the 
basis of distances between axles and the total over-all span between the 
front axle and the rearmost axle. The essence of the bridge formula is to 
prevent heavy loads from being concentrated on few closely spaced axles. 
Therefore, the total overall weight limit for many truck designs can be 
increased, to a limit, if the weight is spread over more axles spread 
further apart. While the federal bridge formula is applicable only to 
federal highway, many states have adopted the bridge formula into their 
own highway load limit regulations. 
The use of auxiliary axles on trucks for providing additional load-bearing 
wheels is well known in the art. Particularly on tandem and tri-axle 
trucks, it is common practice to provide a hydraulic or spring actuated 
lift for one of the rear axles, so that it can or will be lifted from the 
road surface when the load is light and the additional load-bearing wheels 
are not needed. 
In the case of transit mixers, i.e. concrete mixer trucks, there has been 
considerable interest and development in the art of "lift axles" or "tag 
axles", which are separate axle assemblies added to the rear of the truck. 
Such tag axles include a mechanism for lowering the unit so that the 
wheels will engage the road surface at some point behind the rearmost 
tandem axle, so that the legal load carrying capacity of the transit mixer 
can be significantly increased and yet satisfy the bridge formula. This 
increased load carrying capacity is effected not only by virtue of the 
fact that the load is spread over more axles, but also because the 
distance between the front and rearmost axles is significantly increased. 
Utilization of such a tag axle can permit a conventional tandem axle 
transit mixer, having a legal load limit of about seven cubic yard of 
concrete, to be legally increased to nine or even ten cubic yards. 
Ideally, the tag axle is utilized to carry such heavy loads only when the 
transit mixer is traveling on public roadways and needed for the purpose 
satisfying the bridge formula or other load limits. In off-the-road use, 
however, such tag axles are not beneficial, and are therefore provided 
with means for lifting the tag axle from the roadway surface. In lifting 
the tag axle off the roadway, the load on the front axle is reduced to 
permit easier steering, the load is increased on the drive axles to 
increase traction, the truck's maneuverability is increased by reducing 
its overall wheel base, and the truck can be positioned closer to forms 
and other unloading sites to facilitate the discharge of concrete. 
One disadvantage of some tag axles in current use, is that they cannot be 
raised sufficiently to get them out of the way to facilitate access to the 
discharge end of the truck. These tag axle units are based on folding 
linkage which hydraulically pulls the tag axle up under the discharge 
chute only inches from the road surface, so that the operator must work 
around the tag axle in discharging the concrete from the mixer. Other 
designs are known, however, which do raise the tag axle well above the 
discharge chute and above the head of the operator so that it is not an 
obstruction to the operator's discharge activities. 
All the tag axles in current use utilize a hydraulic system for activating 
the tag axle from one position to the other, and in addition rely on the 
hydraulic system for maintaining the tag axle in contact with the road 
surface, if not also for maintaining the tag axle in its lifted, off the 
road position. In fact, many of the tag axle units available commercially, 
rely on the hydraulic system to provide a "spring" suspension or shock 
absorbing feature to the tag axle, so that the ground loads are 
transmitted to, and borne entirely by, the hydraulic system. These 
hydraulic systems must therefore be adapted to very heavy duty use, and 
typically include pressure regulating controls so that the "hold down" 
pressure applied to the tag axle is adjustable for controlling that 
pressure in proportion to the load weight on the truck. It is readily 
apparent that the demands on the hydraulic system are significant, as the 
system is constantly active and under excessive pressure while the tag 
axle is being utilized, if not also while the tag axle is in the raised, 
off the road position. Accordingly, such tag axles tend to be rather 
expensive, and subject to frequent hydraulic system difficulties, failure 
and repairs. 
SUMMARY OF THE INVENTION 
This invention is predicated upon the conception and development of a 
simple and inexpensive improved tag axle, which, although hydraulically 
operated to move it from one position to the other, does not rely on the 
hydraulic system to maintain the tag axle in either position. Instead, a 
unique hydraulically operated linkage system is utilized to raise and 
lower the tag axle as necessary to move it from one position to the other, 
while the linkage system itself locks the tag axle into position for 
engagement with the road surface with virtually no load on the hydraulic 
system once it is in proper position. In the raised, off the road 
position, the wheels and axle are raised high above the operator's head so 
that they will not be an obstruction, and such that the tag axle's weight 
is borne entirely by its steel support structure, again with virtually no 
load on the hydraulic system. Accordingly, the unique tag axle of this 
invention will permit the use of a far less robust and costly hydraulic 
system consisting of one or two simple hydraulic cylinders, without the 
need for any pressure regulating controls associated with the hydraulic 
system.

DETAILED DESCRIPTION OF THE INVENTION 
Reference to FIG. 1-3 will illustrate one embodiment of this invention 
wherein a partial side view of a concrete mixer truck is illustrated, 
showing the extreme rearward portion comprising the truck frame 10, the 
rearmost wheels 12, the rearward portion of concrete mixer 14, the rear 
mixer bearing support 16, the mixer charging hopper 18, and the mixer 
discharge chute 20, all of which are pursuant to prior art practices. The 
tag axle according to this invention is shown at 30, which comprises in 
part, a pair of tag arms 32 pivotally connected through pins 34 to 
vertical plates 36 welded to the rearmost portions of the truck frame 10. 
While only one such tag arm 32, pin 34 and so forth are shown in any of 
the figures, it should be appreciated that only one side of the truck is 
illustrated. Therefore, most elements of the tag axle assembly described 
herein will, except for the wheel axle 38, consist of matching left and 
right elements, unless otherwise noted. The drawings, however, illustrate 
only the left element on the left side of the truck. 
While the forward ends of tag arms 32 are pivotally connected to the truck 
frame 10 as noted above, the rearward portions support the tag wheels 40 
with tires 42 mounted thereon. Tag wheels 40 are rotatably supported on 
opposite ends of wheel axle 38, which extend from one tag arm 32 to the 
other. It should be apparent that there is only one wheel axle 38. 
The rearward end of each tag arm 32 is provided with a load support 
extension 44, which extends rearwardly when the tag axle is in the 
downward position, and a pivot support plate 46 extending downwardly from 
the forward end of load support extension 44. A pivot arm 48 is pivotally 
secured to each pivot support plate 46, so that it will extend rearwardly, 
generally parallel to load support extension 44. Wheel axle 38 is secured 
to the underside of each pivot arms 48 with U-bolts 50, while pneumatic 
air bags 52 are secured above wheel axle 38 and positioned between 
extensions 44 and pivot arms 48. Pneumatic air bags 52 are preferably of 
the type that can be selectively pressurized so that the load supported by 
the tag axle can be controlled to the extent desired. As can be seen, when 
the tag axle 30 is in the down position to carry its share of the load, 
the wheels 40 tires 42 and axle 38 will have some freedom to move with 
respect to the rigid tag arms 32 by virtue of air bags 52 which provide 
some degree of spring suspension and shock absorption. 
As show in FIG. 3, a preferred embodiment of this invention would include 
self steering capabilities, such as a single tie rod 56, connected to a 
spindle 58 at each wheel 42, as well as shock absorbers 60. Techniques for 
providing self steering capabilities to trailer wheels is well known in 
the prior art, and therefore, need not be detailed here, suffice it to say 
that the tag axle of this invention may or may not include such a feature, 
and if it is included, there are several well known techniques for 
effecting such capabilities. In addition to self steering capabilities, 
the tag wheels are also preferably provided with brakes (not shown), 
ideally hydraulic or air brakes connected to, and controlled by, the 
truck's brake system, as well as fenders and tail lights (not shown). 
Since such brake systems fenders and tail lights are well known in the 
prior art, they have not been shown in the attached drawings so that the 
drawings can be kept as simple as possible to facilitate an understanding 
of this invention. 
Actuation of the tag axle 30 between its downward, on the road position and 
its upward, off the road position, is effected by hydraulic cylinder or 
cylinders 70, having a base end pivotally secured to truck frame 10 at pin 
72, while its reciprocating end is secured to angular link plates 74 at 
pin 76. While only one such hydraulic cylinder 70 is all that is 
necessary, particularly if it is centered between the tag arms 32, two 
such hydraulic cylinders 70 can be utilized, one each secured adjacent to 
each tag arm 32, if they are interconnected to operate in unison. 
While the two extreme positions of all the linkage elements are shown in 
FIGS. 1 and 2, FIGS. 4 and 5 show the relationship in more detail, with 
FIG. 4 showing the linkage relationship when the tag axle 30 is in the 
down position engaged with the roadway, and FIG. 5 showing the linkage 
relationship when the tag axle 30 is in the up, off the road position. 
Reference to FIG. 4 will illustrate that when the tag axle is in the 
downward, on the road position, hydraulic cylinder 70 is in the extended 
position, so that it has pushed angled link plates 74, pivoting on 
stationary pins 75, to their fully horizontal position with the upper 
surfaces of link plates 74 abutting against the lower surface of load 
stops 80. Load stops 80 can be any sort of solid member secured to truck 
frame 10 which are adapted to limit the counter-clock movement (as shown 
from the left side of the truck) of link plates 74 as shown. Preferably, 
load stops 80 are solid steel blocks presenting a plainer surface against 
which the upper surface of link plate 74 can by positioned. 
With further reference to FIGS. 4 and 5, each tag arm 32 is rigidly 
secured, such as by welding, to a pivotal lever arm 82, so that both will 
pivot in unison at pin 34. Since each pivotal lever arm 82 is welded to 
the associated tag arm 32, these two elements could be formed as a single 
element if so desired. Is should be apparent therefore, that when lever 
arms 82 are pivoted in either direction at pins 34 through a given angle, 
tag arms 32 will pivot therewith through the same angle, or visa versa, as 
can be seen by contrasting FIG. 4 with FIG. 5. The upper end of lever arms 
82, extending away from tag arms 32, are pivotally secured to pins 84, 
while the rearward ends of link plates 86 are also pivotally secured to 
pins 84. As should be apparent, any translational movement of link plates 
86 pushing or pulling on pins 84, will cause pivotal motion of lever arms 
82, as well as tag arms 32. The other ends of link plates 86, i.e. the 
forward ends, are secured to pins 88, which are also secured to rotatable 
ends of angled link plates 74. 
To explain the operation of the linkage, it should first be appreciated 
that pins 75 and 34 are rigidly secured to the truck frame so that they 
cannot move, but will permit rotation of the link plates and arms 
rotatably secured thereto. Pins 84 and 88, on the other hand, are 
connected only to the link plates or the lever arm as shown, and 
therefore, are not only capable of permitting rotational movement of the 
links and arms secured thereto, but are also subject to translational 
movement, to the extent permitted by the linkage. As shown in FIG. 4, it 
can be seen that when the tag axle is in the downward position for 
engaging the tires 42 with the road surface, angled link plates 74 are 
being held by hydraulic cylinder 70 against load stops 80, so that pins 88 
and 84 are necessarily aligned in a horizontal plane with pins 75. When 
hydraulic cylinder 70 is activated and withdrawn, angled link plates 74 
will be caused to rotate downward, pivoting on pins 75, away from load 
stops 80 (clockwise as shown) so that pins 88 will move through the same 
arc, pulling on link plates 86, which in turn pull on pin 84. This 
movement of pins 84 will cause lever arm 82 and tag arms 32 to rotate the 
tag axle into an upward position, (counterclockwise as shown). FIG. 5 
illustrates the tag axle 30 in its fully raised position, as a result of 
the above described actions. 
In the fully upward position, as shown in FIG. 5, the weight of the tag 
axle is borne almost entirely by pins 34, so that there is no significant 
load on hydraulic cylinder 70. The only load on hydraulic cylinder 70, 
will be the result of those forces which will tend to rotate the tag axle 
rearwardly, such as wind forces when the truck is in motion, and modest 
gravitational forces which may result from the fact that the center of 
mass of the tag axle may not directly over, or forward of, pins 34. These 
forces on hydraulic cylinder 70 can, however, be completely eliminated by 
providing a means for locking the tag axle in it upward position, such as 
a latch or pin 90 which will lock at least one tag arm 32 to the mixer 
bearing support 16. 
In the fully downward position, as illustrated in FIG. 1 and 4, it can be 
seen there is still no significant load on hydraulic cylinder 70. The load 
imposed on wheels 40 and tires 42, is transmitted back through tag arms 32 
to the above described linkage and load stop 80. Since pins 75, 88 and 84, 
are aligned in a plane with angled link plates 74 biased against load stop 
80, all ground forces acting on the tag axle, will be borne by these 
members, and the only load on hydraulic cylinder 70 will be that required 
to keep angled link plates 74 biased against load stop 80. For this 
reason, it is essential that pins 75, 88 and 84 be aligned in a plane so 
that any force tending to rotate the tag axle 30, will be absorbed 
entirely by the linkage and load stop 80, without any tendency to rotate 
angled link plate 74 away from load stop 80. While the plane in which pins 
75, 88 and 84 lie is shown to be horizontal, it is not essential that it 
be horizontal, as long as the pins can be locked in a plane so that the 
ground loads are absorbed entirely by the linkage without causing any 
rotational movement of any link. 
Since the above described linkage is preferably duplicated on each side of 
the truck, duplicate links and pivot arms should be provided, one set on 
each side of the truck. However, since the linkage members must be 
properly aligned to operate in unison, single elongated pins 75, 34, 84 
and 88 can be utilized which span across the rear of the truck from one 
set of linkage elements to the other. Use of single pins spanning the rear 
of the truck will assure that they are properly aligned from left to 
right. This may be particularly desirable for fixed pins 34 and 75, which 
must be secured to the truck frame. It is a rather simple matter to mount 
these rotatable pins, i.e. pins 34 and 75 within bearings secured within 
housings welded to the truck frame. This will provide the advantage that 
the links will operate in unison and eliminate the possibility that they 
could move other than in synchronized unison and thereby cause an 
undesirable binding and twisting in the tag axle alignment. In the event 
that only one hydraulic cylinder 70 is utilized, it is preferable that it 
be spaced midway between the tag arms 32 and associated linkage so that 
loading thereon will be uniform. In this event it will be necessary that 
one pin 76 be provided which spans between the pair of angled links 74, 
with the hydraulic cylinder attached at its midpoint. 
While it is of course necessary that suitable bearings be provided at pins 
75, 35, 84 and 88 to minimize friction and permit easy rotation of the 
linkage members on the respective pins, the provision of such bearings is 
readily within the skill of the art and need not be detailed here. 
In operation it can be seen that the tag axle, when put in the downward 
position with the tires engaged with the road surface, will have the tag 
arms 32 locked into a preset position, and held in that position by the 
linkage lock assembly. All ground loads transmitted through the tag arms 
32 are shared by the components of the linkage assembly, and not the 
hydraulic cylinder 70. Once the tag axle is lowered and locked into 
position, air bags 52 should be pressurized to effect the desired ground 
load through the axle and tires. The air pressure in air bags 52 is 
usually set to a value of from 60 to 100 psi depending on the desired 
ground load, which is usually from 6,000 to 12,000 pounds, which, of 
course, includes the weight of the tag axle. The air bags 52 also act as 
shock absorbers eliminating the need for accumulators. 
In view of the above disclosure it is apparent that numerous modifications 
and other embodiments of the tag axle could be made without departing from 
the spirit of the invention. As already noted, the tag axle can be 
optionally provided with self-steering capability, wheel brakes, fenders, 
tail lights and the like. In addition, other forms and shapes of the 
component parts could be utilized depending on the truck being fitted with 
the tag axle. While the above description has been limited to the 
application of a tag axle on a concrete mixer truck, it should be apparent 
that the tag axle of this invention could be installed on trucks utilized 
in other forms of service, and the tag axle of this invention should not, 
therefore, be limited to use on concrete mixer trucks. 
In addition to the above, it should be realized that the linkage 
arrangement as depicted, is only one example of how the linkage can be 
arranged, as clearly other arrangements could be utilized without 
departing from the spirit of this invention. For example, the hydraulic 
cylinder, or what ever means is utilized to pivot the linkage, could be 
connected to link plate 86 instead of 74, or the pivotal motion could be 
effected in the opposite direction, so that the load stop 80 is under the 
linkage. In addition, additional linkage members could be provided if 
desired for any reason, provided that the pivot pins thereof can be 
aligned in a plane to lock the tag axle in position as described. While 
the plane can be positioned in other locations, the plane should of course 
be sufficiently tangent to the arc of motion of the pin 84 in lever arm 82 
so that the linkage will be aligned keep the lever arm 82 from moving. All 
that is essential is that the tag arms have a lever means for lifting the 
tag arms, and that a linkage arrangement be secured to that lever which is 
capable of being locked in a plane sufficient to hold the tag axle in the 
downward position, while also being pivotal to raise the tag axle. Clearly 
therefore, there are a great number of differing arrangements that could 
be created if desired.