Abstract:
A lift axle suspension for a tandem trailer has first and second suspension air bags for first and second axles. There is 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 supplies compressed air to the first suspension air bag and a diverter valve and is controlled by a height selector valve that is opened and closed based on the ride height of the trailer. The diverter valve selectively supplies compressed air to the second suspension air bag and a pressure regulator that limits air pressure to a predetermined pressure. A second pneumatic supplies compressed air to the lift air bag and is controlled by a pilot valve.

Description:
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 U.S. Pat. No. 6,997,464 (Yakimishyn) entitled “Lift Axle Suspension” and U.S. Pat. No. 7,303,201 (Yakimishyn) 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. 
         [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 DRAWINGS 
         [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: 
           [0010]      FIG. 1  is a side elevation view of a prior art lift axle with the axle in a lowered position. 
           [0011]      FIG. 2  is a detailed, partial side elevation view of the fulcrum and first end of a lever as illustrated in  FIG. 1 . 
           [0012]      FIG. 3  is a side elevation view of the lift axle assembly illustrated in  FIG. 1 , with the axle in a raised position. 
           [0013]      FIG. 4  is a side elevation view of a lift axle assembly. 
           [0014]      FIG. 5  is a side elevation view of an alternate lift axle assembly with the axle in a raised position. 
           [0015]      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 
       [0016]    A prior art lift axle suspension, generally identified by reference numeral  10 , will first be described with reference to  FIG. 1 through 3 . 
         [0017]    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 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  48   a - 48   d . Pressurized air is channelled through load leveler valve  50  to air diverter  52  and regulator  54 . 
         [0018]    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. 
         [0019]    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. 
         [0020]    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 . 
         [0021]    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 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  48   d  from exceeding a maximum value. With diverter  52  in the “up” position, this also limits the pressure in lines  48   a  that connects suspension bag  24   a  to load leveller valve  50  and line  48   b  that connects load leveller valve  50  to diverter  52  thereby reducing the lift capacity of air bag  24   a  related to the “always down” axle  22   a . 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  22   a , 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  48   d . 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&#39;s attention to the problem, and at high enough pressures, will prevent the axles from being lifted outside the safe operating range. 
         [0022]    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. 
         [0023]    Modified lift axle suspension  100  permits lift bag  44  to be operated at higher 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 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. 
         [0024]    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  48   d  via line  106  and configured such that, when diverter  52  is in the “on” or “lift” position, in which line  48   c  is vented and air is supplied to line  48   d , 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  24   a  associated with the “always down” axle  22   a . Preferably, pilot valve  102  is also configured to vent line  104  and deflate lift bag  44  when in the closed position. 
         [0025]    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  48   c  instead of  48   d  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  48   c . At the same time, switch  108  may also vent line  104   a  to disconnect and vent lift bag  44  from air supply  46 . 
         [0026]    Similarly to lift axle suspension  10 , modified lift axle suspension  100  uses regulator  54  to limit the maximum pressure applied to suspension bag  24   a  for the always-down axle  22   a . 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 . 
         [0027]    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 . 
         [0028]    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. 
         [0029]    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.