Load distribution system for road vehicles having wheel axles supported by pneumatic suspension

A load distribution system for a road vehicle comprises a main wheels suspension which is preferably the steering wheels suspension and an auxiliary wheels suspension. The system includes air-inflatable balloons in the auxiliary suspension and an air compressor to feed the balloons. A weight sensor constantly measures the weight carried by the main suspension and sends corresponding signals to a computer. The system further comprises a control assembly for the auxiliary suspension constructed to receive pressure air from the compressor and feed it to the auxiliary suspension balloons. The control assembly is connected to the computer which is programmed to respond to the weight variations by correspondingly adjusting the pressure in the balloons of the auxiliary suspension in order to let the auxiliary suspension carry any extra weight which exceeds a preselected maximum weight to be carried by the main suspension.

BACKGROUND OF THE INVENTION 
1. Field of the invention 
The present invention relates to a system for use on a load transportation 
vehicle, having an auxiliary axle with a suspension of the pneumatic type, 
which system is capable of automatically and accurately distributing the 
load to be carried by the vehicle between at least one of the main axle, 
preferably the front one, and the auxiliary axle, whenever the latter is 
needed. 
2. Description of the prior art 
Vehicles to which the invention particularly applies are those equipped 
with retractable auxiliary wheels between the front steering wheels and 
the rear wheels; the auxiliary retractable wheels being intended to carry 
a surplus load when brought to ground-engaging position. Both suspensions 
for the steering wheels and for the auxiliary wheels include inflatable 
balloons either exclusively or in combination with spring blades. 
As is known, it is of prime importance that the steering wheels not be 
overloaded or underloaded at any time so that the driver may be able 
constantly to control steering of the vehicle properly. This is 
particularly so whenever the vehicle carries a surplus load at which time 
the auxiliary wheels have to be used and the load distributed so that the 
steering wheels are neither overloaded or underloaded. Apart from 
difficulties in driving, the driver may be penalized, at a load-measuring 
station along the road, for having an overloaded axle. 
At the present time, it is possible for the vehicle driver to inflate or 
deflate the suspension balloons manually to try to reach the best possible 
load distribution between the steering and auxiliary wheels, but this can 
only be done manually, as aforesaid. There is indeed absolutely no way for 
him to assess with any accuracy whether or not the load distribution has 
been done properly except by means of his own experienced perception of 
the vehicle behaviour as sensed through the steering column. It will be 
appreciated that such an adjustment is quite subjective and therefore may 
lead to dangerous situations, not to mention rendering driving more 
difficult. 
SUMMARY OF THE INVENTION 
An object of the invention is consequently to provide a load distribution 
system wherein the distribution can be made fully automatically and with 
accuracy, the driver having no part to play in the operation. 
With this object in view, the invention proposes a load distribution system 
for a road vehicle, which system comprises a main suspension and an 
auxiliary suspension including air-inflatable balloons fed by an air 
compressor. A weight sensor constantly measures the weight carried by the 
main suspension and sends corresponding signals to a programmed computer. 
The system further comprises a control assembly for the auxiliary wheels 
suspension constructed to receive pressurized air from the compressor and 
feed it to the auxiliary suspension balloons. The control assembly is 
connected to the computer which is programmed to respond to the weight 
variations by correspondingly adjusting the pressure in the balloons of 
the auxiliary suspension in order to let the auxiliary suspension carry 
any extra weight which exceeds a preselected weight to be carried by the 
main suspension. 
Preferably, the main suspension is the front wheels suspension. Preferably 
also, the control assembly comprises an air pressure controller 
operatively connected to the balloons of the auxiliary suspension, to the 
computer and to the air compressor for feeding pressure air to the 
balloons under control of the computer. 
The control assembly may also include lifting and lowering means for moving 
the wheels of the auxiliary suspension between a ground-engaging position 
of the wheels and a retracted position. 
According to a particular feature of the invention, means are also proposed 
for feeding pressure air to the air brakes of the auxiliary wheels up to a 
given pressure that is proportional and preferably equal to the pressure 
of the air fed to the balloons of the auxiliary suspension. In this 
manner, the pressure applied by the driver on the air brakes of the 
auxiliary suspension can never exceed that corresponding to the load 
carried by the wheels of the auxiliary suspension. 
A description now follows of a preferred embodiment of the invention having 
reference to the appended drawings.

DESCRIPTION OF A PREFERRED EMBODIMENT 
Referring to FIG. 1, there is shown a truck having front steering wheels 1, 
rear wheels 3 and retractable auxiliary wheels 5 between the front and 
rear wheels, the auxiliary wheels being intended for carrying any load in 
surplus of the usual load carried by the truck and borne by the front and 
rear wheels. 
The steering wheels 1 are mounted on a transverse axle beam 7 connected, at 
its ends, to a frame beam 9 of the truck by means of a pair of like 
suspensions 11 which may be conventional as long as it includes pneumatic 
balloons. Rear wheels 3 are mounted on the front beam 9 in a similar 
manner but need not include pneumatic balloons. 
The front suspensions 11 shown in FIG. 1 are of the combined pneumatic and 
blade-spring type such as disclosed in Applicant's copending application 
Ser. No. 07/349,107, filed on May 9, 1989. The one illustrated in FIG. 1 
comprises a blade spring 13 fixed to the axle beam 7 and pivoted at one 
end to a bracket 15 of the adjacent frame beam 9. The other end is 
slidably received in a lever 17 pivoted at one end to a bracket 19 and 
fixed, at its other end, to an inflatable air balloon 20 secured to and 
beneath the frame beam 9. 
Each auxiliary wheel 5 is similarly mounted on the beam 9 of the truck body 
frame through a suspension 21 of a conventional type including an air 
inflatable balloon 23 and air brakes 25. The suspensions 21 further 
include conventional lifting and lowering means 27 (FIG. 2) capable of 
moving the wheels 5 between a ground-engaging position and a retracted 
position. Such means 27 can be pneumatic and part of the system of the 
invention or hydraulic and connected to the hydraulic circuitry of the 
truck. 
A computerized pneumatic circuit 29 connected to the front and auxiliary 
suspensions 11, 21, integrates the various components of the load 
distribution system, as made according to the invention and illustrated in 
FIG. 2 to which reference is now made. 
As shown, an air compressor 31 sends pressurized air to the balloons 20. 
A weight sensor 37 operatively connected to all of the balloons 20 and to 
the computer 35 constantly assesses the weight supported by the 
steering-wheels suspension. It may include a conventional pressure gauge 
capable of measuring the air pressure in the balloons 20 or it may include 
a ruler device measuring the linear lag or deflection of the suspension. 
It may also include sensor means for evaluating the effective load and 
calculating its distribution over the axles. In all cases, the 
measurements made are directly proportional to the weight supported by the 
steering-wheels suspension 11 and are transformed into corresponding 
weight signals sent to the computer 35 which compares them to the 
preselected weight, acceptable to the steering wheels; the computer 
establishing weight variations from these signals with respect to the 
acceptable weight. 
The system in FIG. 2 further comprises an assembly 39 for controlling the 
action of the auxiliary-wheels suspension 21. It is operatively connected 
to the computer 35, to the air compressor 31, and to the balloons 23 of 
the auxiliary-wheels suspension through pipings 41, 43. It is constructed 
for receiving pressure air from the air compressor 31 and for feeding it 
to the balloons 23. The computer 35 is programmed for responding to the 
weight variations in the balloons 20 by correspondingly adjusting the 
pressure in the balloons 23 in order to maintain constant the preselected 
weight to be carried by the steering wheels 1 of the suspension 11. For 
this purpose, the control assembly has an air pressure controller 45 which 
is operatively connected to the balloons 23, through pipings 41, 43, so as 
to transfer, under the control of the computer 35, pressurized air to the 
balloons 23 at a pressure commensurate to the weight variations in the 
balloons 20. 
The control assembly 39 additionally comprises the aforesaid means 27 for 
lifting and lowering the auxiliary wheels 5 between a ground-engaging 
position and a retracted position as aforesaid. Where these means, which 
could involve power jacks, are pneumatic, they are connected to the air 
compressor 31 and to the computer 35 for complete computer-controlled 
operation. They may, on the other hand, be hydraulically operated and be 
part of the hydraulic circuit of the vehicle. 
Where the means 27 are pneumatic and a surplus load is detected on the 
steering wheels by the weight sensor 37, the computer orders their 
actuation to apply the auxiliary wheels to the ground and pressurized air 
to be sent to the balloons 23, which, by their inflation, lift the vehicle 
so that the auxiliary wheels 5 gradually pick up the surplus load thereby 
gradually reducing the load on the steering wheels 1 until the preselected 
load thereon is reestablished. In this manner, the computer 35 is able 
constantly to keep the load on the steering wheels at the preselected 
weight by shifting any overload thereon to the auxiliary wheels. There is 
no longer any need for the driver to make approximate and hazardous 
adjustments. 
Let us assume, for instance, that the proper load, for good driving 
condition, to be supported by the steering wheels corresponds to a 
pressure of 80 psi in the balloons 20. Suppose now that a surplus load is 
added which brings the total load to an equivalent of 145 psi, which load 
is distributed to all wheels including the steering wheels 1 and the rear 
wheels 3. The steering wheels 1 are thus overloaded. The sensor 11 then 
sends signals to the computer 35 which orders actuation of the control 
assembly 39 causing the means 27 to lower the auxiliary wheels 5 to the 
ground and inflation of the balloons 23. As the latter lifts the vehicle, 
the auxiliary wheels 5 gradually pick up part of the surplus load, 
reducing, by the same token, the load applied to the front wheels 1 until 
the load on them is finally reduced to the acceptable one corresponding to 
80 psi in the balloons 20. Any further addition of load on the steering 
wheels over the acceptable one is immediately removed from them by 
corresponding inflation of the balloons 23. 
As an added feature, the system of the invention may provide for supplying 
air to the air brakes 25 at a pressure that is always proportional to the 
one corresponding to the load carried by the auxiliary wheels to prevent 
freezing of the brakes and skidding of the vehicle. For this purpose, and 
as shown in the embodiment of FIG. 2, a control valve 51 is connected to 
the piping 41 to receive air from it which will be at the same pressure as 
that in the balloons 23. This valve 51 is mounted in line onto a 
pressurized air supply line 47 leading from the air compressor to the air 
brakes 25, just upstream the pedal-operated air-brake control valve 53 of 
said air brakes 25. In this manner, the braking force allowed by the 
vehicle operator can never exceed the pressure allowed by the control 
valve 51 in the line 47, which pressure is proportional to force carrying 
the load in the balloons 23. 
Although, in the above description of a preferred embodiment of the 
invention, reference has been made to the front wheels suspension as a 
"main" suspension whose load is to be controlled, the invention as claimed 
hereinafter is of broader application. Indeed, use could also be made of 
the rear suspension or of any intermediate suspension in the case of 
multiaxles vehicle as "main" suspension, the basic aim of the invention 
being exclusively to balance the weight over the axles. 
Although in the above description and appended claims, reference has been 
made exclusively to air-inflatable balloons supplied by an air compressor, 
the invention is intended also to encompass any similar suspension using 
another fluid instead of air.