Note: Descriptions are shown in the official language in which they were submitted.
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LIFT AXLE SUSPENSION
TECHNICAL FIELD
[0001] This relates to a lift axle suspension.
BACKGROUND
[0002] The use of a lift axle suspension enables a driver of a vehicle to
lift one or more
axles in order to selectively transfer more weight to the tires that remain on
the ground. This
may be done when the vehicle is unloaded in order to increase traction,
provide more
controlled braking, to increase fuel mileage, and to save tire wear.
[0003] Examples of lift axle suspensions include United States patent no.
6,997,464
(Yakimishyn) entitled "Lift Axle Suspension" and United States patent no.
7,303,201
(Yakitnishyn) entitled "Air Suspension System for a Vehicle".
SUMMARY
[0004] There is provided a lift axle suspension for a tandem trailer. The
tandem trailer
comprises at least a first axle and a second axle. The lift axle suspension
comprises a first
suspension air bag mounted to act as suspension for the first axle, a second
suspension air bag
mounted to act as suspension for the second axle, and a lift air bag that,
when pressurized,
applies a lifting force to lift the second axle relative to the first axle. A
first pneumatic circuit
connects the supply of compressed air to each of the first suspension air bag
and a diverter
valve. The flow of compressed air through the first pneumatic circuit is
controlled by a height
selector valve that is opened and closed based on the ride height of the
trailer. The diverter
valve has a first position that supplies compressed air to the second
suspension air bag and a
second position that supplies compressed air to a pressure regulator that
limits air pressure to
a predetermined pressure. A second pneumatic circuit connects a supply of
compressed air to
the lift air bag. The flow of compressed air through the first pneumatic
circuit is controlled by
a pilot valve that is opened when the diverter valve is in the second
position.
[0005] According to another aspect, the pilot valve may be pneumatically
actuated, and
the pilot valve may be opened when air pressure is applied to the regulator.
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[0006] According to another aspect, the supply of compressed air may
comprise a
pneumatic air cylinder connected to the first and second pneumatic cylinders.
[0007] According to another aspect, the second pneumatic circuit
comprises an override
switch that closes the second pneumatic circuit.
[0008] In other aspects, the features described above may be combined
together in any
reasonable combination as will be recognized by those skilled in the art.
BRIEF DESCRIPTION OF THE CRAWINGS
[0009] These and other features will become more apparent from the
following
description in which reference is made to the appended drawings, the drawings
are for the
purpose of illustration only and are not intended to be in any way limiting,
wherein:
FIG. 1 is a side elevation view of a prior art lift axle with the axle in a
lowered
position.
HG. 2 is a detailed, partial side elevation view of the fulcrum and first end
of a
lever as illustrated in FIG. 1.
FIG. 3 is a side elevation view of the lift axle assembly illustrated in HG.
1, with
the axle in a raised position.
HG. 4 is a side elevation view of a lift axle assembly.
HG. 5 is a side elevation view of an alternate lift axle assembly with the
axle in a
raised position.
FIG. 6 is a side elevation view of the lift axle assembly illustrated in FIG.
5, with
the axle in a lowered position.
DETAILED DESCRIPTION
[0010] A prior art lift axle suspension, generally identified by
reference numeral 10, will
first be described with reference to FIG. 1 through 3.
[0011] Referring to FIG. 1, pivot arm 12 having pivotal end 14 that is
pivotally attached
to vehicle frame 16 by pivot arm bracket 18. Remote end with adapter 20 is
attached to axle
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with wheels 22 and is actuated by first suspension air bag 24 shown in
extended mode. All
elements 12 through 24 are shown as basic lift axle suspension 26. Preferred
embodiment 10
comprises lever 28 having a first end 30 and second end 32 which rotates about
fulcrum 34
which is attached to frame 16 by lever bracket 36. An adjustable sling 38
adapts first end 30
to axle with wheel 22. Referring to FIG. 2, lever 28 is further adapted with a
plurality of
adjustably positioned fulcrum points 40 and a sling adjusting mechanism 42.
Referring to
FIG. 1, second end 32 is actuated by lift air bag 44 shown in deflation mode.
Air supply 46
provides pressure through connection hoses 48a ¨ 48d. Pressurized air is
channelled through
load leveler valve 50 to air diverter 52 and regulator 54.
[0012] Referring to FIG. 3, axle with wheels 22 is shown in the elevated
position relative
to any other axle with wheels at ground level 56. Lift air bag 44 is shown in
extension mode
and first suspension air bag 24 is shown in deflation mode.
[0013] In operation, the weight and contact height of select axles with
wheels 22 in
multiple, tandem-axle type vehicles may be changed by changing the settings of
load leveler
valve 50, air diverter 52 and regulator 54. Depending upon the need, air will
be diverted to
lift air bag 44 which in turn actuates second end 32 of lever 28 causing lever
28 to rotate
about the fulcrum 34 and, in turn, lift first end 30. First end 30 then exerts
upward pressure
on adjustable sling 38, lifting axle with wheel 22 which, in turn, lifts
remote end with adapter
20 which is now able to deflate and compress first suspension air bag 24 by
exhausting air to
atmosphere through diverter valve 52. The result is an elevated wheel position
relative to
ground level 56 such that the tires on axles with wheels 22 that are part of
lift axle
suspensions 10 are conserved.
[0014] Further, should the need to adapt the lift axle suspension 10 to a
different vehicle,
an operator may select one of adjustably positioned fulcrum points 40 and
adjust the sling by
operating sling adjustment mechanism 42.
,
[0015] In order to allow for safe operation of a lift axle, the prior art
lift axle suspension
10 described above was designed to ensure that the safe operating load limit
could not be
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exceeded when a trailer is being operated in the "lift" or "up" mode. In the
lift axle mode,
diverter 52 is set to supply air to lift bag 44, which causes corresponding
air bag 24 to be
compressed and axle 22 to be raised. Regulator 54 is set to prevent the
pressure in line 48d
from exceeding a maximum value. With diverter 52 in the "up" position, this
also limits the
pressure in lines 48a that connects suspension bag 24a to load leveller valve
50 and line 48b
that connects load leveller valve 50 to diverter 52 thereby reducing the lift
capacity of air bag
24a related to the "always down" axle 22a. This ensures that the load limit,
as set by
regulation, the manufacturer, or the user to ensure the lift axle is operated
within safe
operating ranges. As the load on rear axle 22a, or "always down" axle,
increases, the air
pressure required to maintain the desired ride height will increase. However,
regulator 54 will
prevent the air pressure from exceeding the maximum value when diverter 52 is
set to supply
pressure along line 48d. As the load on the trailer is increased beyond the
safe operating load
limit, the trailer deck will continue to lower as regulator 54 prevents the
air pressure from
increasing to maintain the ride height. This will either draw the operator's
attention to the
problem, and at high enough pressures, will prevent the axles from being
lifted outside the
safe operating range.
[0016] Referring now to FIG. 5, a modified lift axle suspension 100 is
shown. In this
embodiment, similar reference numbers have been used for similar components.
It will be
understood that, even though the reference numbers are the same, the operation
of some
components may be different. Some of these differences are described below,
while other
differences will be implicitly understood by those skilled in the art,
including changes in the
design based on different operating ranges or specifications. As can be seen,
lever 28 on
modified lift axle 100 does not require the same mechanical advantage to raise
axle 22 in the
lift mode when compared to lift axle suspension 10 described previously. It
was previously
found that such a mechanical advantage was required when lift bag 44 was
supplied with a
lower air pressure. However, in the present system, diverter 52 is able to
supply lift bag 44
with air up to the pressure found in air supply 46 such that a mechanical
advantage is not
required. As such, the presently described system can be installed with
different types of lift
axles that use a wide range of lever designs to lift and hold lift axle 22 in
the "up" position.
[0017] Modified lift axle suspension 100 permits lift bag 44 to be
operated at higher
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pressures. This may be desirable, for example, when lift bag 44 is from a
different system
that has been designed to require a higher pressure, such a pressure up to the
pressure of air
supply 46. As the pressure allowed by regulator 54 will be inherently less
than the maximum
pressure of air supply 46. This higher pressure may be required due to a
different design or
5 position of lift bag 44 that may not benefit from the mechanical
advantage of using a lever as
in the embodiment depicted in FIG. 4, or if a greater lifting force is
desired, such as to hold
lift axle 22 in the raised position more securely in order to prevent any wear
that may result
from vibrations or other movement.
[0018] As shown, lift axle suspension 100 has a pilot valve 102 on line 104
that connects
air supply 46 to lift bag 44. Pilot valve 102 moves between an open position
to supply lift bag
44 with air from air supply 46 and a closed position that isolates lift bag 44
from air supply
46. As shown, pilot valve 102 is a pneumatic valve that is connected to
airline 48d via line
106 and configured such that, when diverter 52 is in the "on" or "lift"
position, in which line
48c is vented and air is supplied to line 48d, the air pressure is applied to
pilot valve 102 via
line 106, causing it to move to the open position. Pilot valve 102 will be set
to be actuated at
a lower pressure than regulator 54, and also lower than the normal operating
pressure of
suspension bag 24a associated with the "always down" axle 22a. Preferably,
pilot valve 102
is also configured to vent line 104 and deflate lift bag 44 when in the closed
position.
[0019] Other types of pilot valves 102 may also be used, such as an
electronic valve or a
mechanical valve that moves with diverter 52. A pneumatic valve is preferred
as it provides a
fails safe. In the event that hydraulic pressure is lost, pilot valve 102 will
close, and lift bag 44
will not be energized. Other locks or checks may also be used, such as switch
108, which
provides an override to shut off the lift system. As depicted, switch 108 may
be used to force
diverter 52 to supply air to line 48c instead of 48d and is connected to
diverter 52 by a line
110, which may be a pneumatic, mechanical, or electrical connection. For
example, if
diverter 52 is normally biased to the position that pressurizes suspension bag
24 and is pushed
to the lift position by a control line of pressurized air, switch 108 may vent
the control line,
allowing the internal bias to return diverter 52 to the suspension position by
supplying air to
suspension air bag 24 along line 48c. At the same time, switch 108 may also
vent line 104a to
disconnect and vent lift bag 44 from air supply 46.
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[0020] Similarly to lift axle suspension 10, modified lift axle
suspension 100 uses
regulator 54 to limit the maximum pressure applied to suspension bag 24a for
the always-
down axle 22a. However, by connecting lift bag 44 to air source 46 separately
from regulator
54, the pressure applied to lift bag 44 is not limited to the maximum pressure
allowed by
regulator 54.
[0021] Referring to FIG. 5 and FIG. 6, the increased pressure applied to
lift bag 44 may
also allow for the removal of the second pivot lever 28 used in the embodiment
of FIG. 4. As
shown in FIG. 5, when axle 22 is in a raised position, lift bag 44 is
expanded. As the
maximum pressure is greater than the maximum pressure allowed by regulator 54,
lift bag 44
applies sufficient force to pivot arm 12 about pivotal end 14 to raise the
front axle 22.
Referring to FIG. 6, when lift bag 44 is compressed, axle 22 can be lowered to
ground surface
56.
[0022] In this patent document, the word "comprising" is used in its non-
limiting sense to
mean that items following the word are included, but items not specifically
mentioned are not
excluded. A reference to an element by the indefinite article "a" does not
exclude the
possibility that more than one of the elements is present, unless the context
clearly requires
that there be one and only one of the elements.
[0023] The scope of the following claims should not be limited by the
preferred
embodiments set forth in the examples above and in the drawings, but should be
given the
broadest interpretation consistent with the description as a whole.
