Composite multi-axle suspension for vehicles

A multi-axle suspension system for large motor homes, buses and like vehicles provides load dividing, improved vehicle stability and handling, a smoother ride and a driver selectable range of variable braking. The system also maintains an optimum chassis frame height under varying vehicle loading. A tag axle behind the vehicle drive axle includes a trailing arm which rotates upwardly or downwardly in response to an increase or decrease in vehicle loading. Such rotation operates a control linkage of a pressurized fluid control valve to supply additional fluid to or exhaust fluid from a spring device having supportive engagement with the vehicle chassis frame. A constant portion of the vehicle load is maintained on the tag axle at all times.

BACKGROUND OF THE INVENTION 
The present invention arises as a result of a long-felt need for an 
improved suspension system for multi-axle vehicles, such as large motor 
homes and buses. Because of their weight and high centers of gravity, 
vehicles of this type tend to lack stability on the highway, are 
frequently deficient in braking performance and handling compared to other 
vehicles on the road, and provide less than optimum ride from a comfort 
standpoint. The present invention in terms of a broad objective seeks to 
substantially eliminate or dramatically improve upon the above and other 
known deficiencies of prior art suspension systems for vehicles of the 
class mentioned. 
The prior art contains many teachings on vehicular suspension systems which 
seek mainly to maintain the vehicle in a level stance under varying 
conditions of loading and/or braking. The known prior art suspensions for 
vehicles of the type on which the present invention is employed compensate 
for changes in vehicle loading by maintaining the chassis frame at a 
design elevation under all conditions of loading between empty and fully 
loaded. The prior art suspension systems do not possess the ability to 
improve dramatically the fore/aft or lateral stability of the vehicle 
within the range of normal and highway speeds, so that emergency lane 
changing, braking and like maneuvers can be safely carried out. The 
present invention possesses the above and other capabilities which are 
absent in the prior art. 
A further and more specific object of the invention is to provide an 
improved suspension for motor homes, buses and the like in which the 
provision of a tag axle in association with the drive axle of the vehicle 
and a fluid-pressure operated spring means constantly divides the total 
vehicle load between the drive axle and tag axle, maintaining a constant 
portion of the load on the tag axle at all times and under all variations 
in static and dynamic loading between an empty vehicle and a fully loaded 
vehicle. This load dividing capability of the invention forms the basis of 
the greatly improved handling and stability of the vehicle, more effective 
braking, greater passenger comfort and avoidance of loss of road traction 
when the tag axle rolls up onto a curb or other elevated surface resulting 
in lifting of the vehicle drive or traction wheels. 
Other features and advantages of the invention will become apparent to 
those skilled in the art during the course of the following description. 
SUMMARY OF THE INVENTION 
In achieving the stated objectives of the invention and eliminating the 
deficiencies of the prior art, the present invention embodies a preferably 
torsion-type tag axle assembly securely bracketed to the vehicle chassis 
frame in tandem relationship to the vehicle drive axle and behind the 
same. The tag axle assembly includes independently sprung wheels journaled 
on vertically swingable arms of the axle assembly which are operatively 
connected through adjustable linkages with a pair of pressurized fluid 
control and distribution valves receiving fluid from an on-board supply. 
The two valves can deliver the pressurized fluid to, or exhaust fluid 
from, a pair of connected pressurized fluid springs, such as air springs, 
supportively engaged with the chassis frame of the vehicle and being 
themselves supported on parts of the drive axle structure. In operation, a 
constant comparatively small portion of the total vehicle load is 
maintained on the tag axle assembly and the movements of the tag axle 
swinging arms through the valve operating linkages and fluid control and 
distribution valves distributes any increased vehicle load between the 
vehicle drive axle and front axle, thus diminishing variations in the 
center of gravity of the vehicle.

DETAILED DESCRIPTION 
Referring to the drawings in detail wherein like numerals designate like 
parts throughout the same, a motor home 20 or like vehicle is equipped 
with a composite multi-axle suspension system according to the present 
invention, which system includes near the rear of the vehicle a drive axle 
21 and a tandem tag axle 22. Preferably, but not necessarily, the tag axle 
22 is of the type disclosed in U.S. Pat. Nos. 3,208,168 and 3,436,069, 
issued to Henschen. Other forms of tag axles can be employed, if desired. 
In the Henschen-type axle 22, the two wheels 23 thereof are independently 
sprung and are journaled independently on two trailing parallel vertically 
swingable arms 24. The arms 24 carry spindles 25 for the two wheels 23. 
The forward ends of the arms 24 are secured to square shafts 26 disposed 
inside of a square tube 27 in accordance with the referenced Henschen 
patents, resilient cushioning elements 28 being held between the square 
shaft 26 and square tube to provide torsional resistance to the rising or 
falling of each arm 24 independently from a neutral position. The ends of 
the Henschen tag axle square tube 27 are securely attached to the chassis 
rails 29 of the vehicle by brackets 30. Preferably, the swingable arms 24 
are snubbed by shock absorbers 31 connected between extensions 32 of the 
arms 24 and attachment points 33 on the brackets 30. 
Each independent arm 24 of the tag axle 22 is pivotally connected at 34 to 
an adjustable operating linkage 35 including a lever arm 36 connected to 
the rotary spool element of a pressurized fluid control and distribution 
valve 37. Each valve 37 is secured by a bracket 38 to an adjacent 
stationary support surface on the vehicle chassis frame. The valve 37 is 
of a commercial type manufactured by Nelson Metal Products, Midland-Ross 
Corp., 2950 Prairie St., Grandville, Mich. 49418, No.H450-13 and -14, left 
hand and right hand. 
Each valve 37 receives pressurized fluid, preferably compressed air, from 
an on-board source, not shown, through a delivery line 39. Each valve has 
an exhaust or return line 40 and a pressurized fluid delivery or outlet 
line 41 leading to and connected with an inlet fitting 42 of one of a pair 
of air springs 43. The air springs 43 per se are conventional and are 
preferably of the kind manufactured and sold by Firestone Industrial 
Products, Noblesville, Ind., as No. 1T14F-4, or an equivalent device. 
The two air springs 43 are supported on an underslung transverse horizontal 
beam 44 suspended by adjustable brackets 45 from the two leaf spring 
assemblies 46 which support the adjacent chassis rails 29 of the vehicle 
at the drive axle 21. As shown in the drawings, the rear end portions of 
the leaf springs 46 have been cut off at 47 and the brackets 45 are welded 
directly to the foreshortened rear end portions of the leaf springs. The 
tops of the air springs 43 engage a sturdy cross member 48 of the chassis 
frame of the vehicle and are suitably attached thereto. As will be further 
discussed, when the air springs 43 receive air through the lines 41 from 
the valves 37, they exert an upward lifting force on the vehicle chassis 
and when the air is exhausted from the springs 43 through the valves 37 
and their exhaust lines 40, the lifting force exerted by the air springs 
on the chassis frame is relieved. 
The two air springs 43 are functionally interconnected by a line 49 so that 
they may function as one spring. They can also act as independent springs, 
depending upon the time related functioning of the interconnecting line 
49. The two air springs are near and somewhat inwardly of the opposite 
side rails 29 of the chassis frame. 
The operation of the load proportioning suspension system for vehicles 
according to the invention is briefly as follows: 
FIG. 4 of the drawings depicts a desired vehicle stance under any loading 
within design parameters. Typically, a motor home 20 of the class to which 
the invention is applied could weigh 12,000 pounds empty and 16,000 pounds 
fully loaded. On increasing the vehicle load, additional weight is applied 
to the ground contact points, two of which points are indicated in FIG. 4 
at FA and FG where the tag axle wheels 23 and drive axle wheels 50 make 
contact with the ground. The normal distance from the top of chassis rails 
29 to the ground may be 28 inches. When the load on the vehicle is 
increased, the new or additional force at the point FA moves upwardly 
through the wheel 23 to spindle 25 causing the trailing arm 24 to rotate 
upwardly in the "loading" direction around the axis of square shaft 26 of 
the torsion axle 22. This movement of the arm 24 displaces the linkage 
connection 34, 35, 36 upwardly, moving the spool of valve 37 to the "fire" 
position. This allows compressed air from the line 39 to flow through the 
line 41 to the associated air springs 43, via line 49, it being understood 
that two air springs, two valves 37, two valve linkages 34, 35, 36, and 
two independently sprung tax axle arm 24 are involved. 
The air springs 43 are then extended vertically and, being solidly 
supported on the beam 44, displace the chassis frame of the vehicle 
including rails 29 upwardly. This upward movement of the chassis frame 
relieves or reduces loading at the ground contact point FA. This 
diminished force or load allows the trailing arm 24 to rotate downwardly, 
or return to its original or specific load location. The load on the tag 
axle 22 is now at its original predetermined desired loading, which might 
be 3000 pounds. This tag axle loading is maintained constant in the 
described operation of the invention, in accordance with a very important 
objective of the invention of automatically dividing the vehicle load 
between the tag axle 22, the drive axle 21 and the front wheels of the 
vehicle 20. The increased load applied to the total vehicle 20 has now 
distributed itself automatically between the front and drive axle 
structures of the vehicle, thereby diminishing center of gravity 
variations. A decrease in loading on the vehicle will induce actions, or 
reactions, exactly opposite to those described above. 
The above-described load dividing capability of the suspension system 
provides, among others, the following important advantages over the prior 
art: a smoother ride with improved handling, stability and braking; 
emergency lane changing can be carried out with remarkable stability and 
safety; and squatting or nose diving of the vehicle under braking is 
minimized. 
A very important benefit derived from the invention is the prevention of 
lost traction due to lifting of the traction wheels 50 when the tag axle 
wheel or wheels 23 ascend a curb or incline. When this occurs, with the 
invention installed and operating, the system operates substantially as 
described to deliver pressurized fluid to the air springs 43, lifting the 
chassis frame, and transferring more weight onto the drive axle wheels 50 
while relieving weight on the tag axle wheels 23 at point FA and quickly 
placing the desired weight or loading on the tag axle, such as 3000 
pounds. This mode of operation is initiated when the tag axle wheels 
ascend a curb or incline, resulting in swinging one or both of the arms 24 
upwardly in the "loading" direction as previously described. Since the two 
air springs 43 are interconnected to function as one spring, it matters 
not whether one or both of the independently sprung arms 24 is elevated to 
operate the system. 
Similarly, when one or both tag axle wheels 23 descend into a ditch, the 
suspension system is quickly self-correcting within the limits of 
suspension design movement to restore the proper portion of the load, such 
as 3000 pounds, to the tag axle which load has momentarily diminished when 
the tag axle wheels enter a ditch or depression. The descending of the 
wheels 23 under these conditions and the resulting lowering of an arm or 
arms 24 causes the valve 37 to exhaust fluid from the air springs 43, 
relieving the lifting force on the chassis frame, reducing the force or 
weight at the point FG and transferring some of this weight to the tag 
axle wheels 23 now in a ditch or depression to maintain the optimum 
division of the load. This obviously stabilizes the vehicle and correctly 
distributes the vehicle weight, thus enabling the driver more readily to 
clear the ditch or depression. 
It should be noted here that another advantage of the invention, derived 
from using the Henschen axle according to the referenced patents, is the 
minimizing of the unsprung vehicle load, due to the fact that the Henschen 
axle is very lightweight although extremely sturdy and reliable. 
Still another advantage of the invention is the provision of a driver 
selectable range of variable braking forces on the tag axle 22 
proportional to brake pedal effort. This is enabled by utilizing a 
conventional trailer brake control device and adapting the same to the 
hydraulics of the normal motor home brake system. This control device has 
a limited range of adjustment for the braking force applied to the tag 
axle wheels 23, which neither allows freewheeling nor equalized braking 
compared to the braking of drive or traction wheels 50. With minimum but 
proportional braking on the tag axle wheels, the vehicle maintains maximum 
directional stability on all types of road surfaces and weather 
conditions. With maximum but proportional driver selected braking, the 
vehicle is able to maximize the braking force of the vehicle applied to 
the road. The driver is enabled to realize total vehicle brake 
effectiveness under varying conditions of driving through the use of the 
system. 
It is to be understood that the form of the invention herewith shown and 
described is to be taken as a preferred example of the same, and that 
various changes in the shape, size and arrangement of parts may be 
resorted to, without departing from the spirit of the invention or scope 
of the subjoined claims.