Abstract:
An air suspension system for a multi-axle vehicle has an air bag system including at least one air bag operatively associated with the vehicle wheels on selected wheel and axle sets to control relative movement between each of the selected wheels and a supporting frame structure of the vehicle. The system has an air-flow control arrangement to control the flow of air into each air bag to thereby control the relative movement of the wheels and vehicle frame structure. A pressurizing arrangement is provided to maintain a selected, predetermined pressure in the air bag system when the vehicle is at rest to thereby maintain a desired vehicle height. The pressurizing arrangement includes a valve to admit pressurized air to or exhaust air from the air bag system to maintain the predetermined vehicle height. The valve is actuated by a link associated with a rocker member connected to spaced axles of the vehicle.

Description:
This application is a Continuation-in-Part of U.S. patent application Ser. No. 10/409,001 filed on Apr. 8, 2003, which is a Continuation-in-Part of U.S. patent application Ser. No. 09/744,529 filed on Jan. 25, 2001, which is the National Stage of Application No. PCT/AU99/00605 filed on Jul. 29, 1999, which claims priority to Australian Application No. PP 4916 filed on Jul. 29, 1998, Australian Application No. PP 5450 filed on Aug. 25, 1998 and Australian Application No. PP 9076 filed on Mar. 9, 1999, and which application(s) are incorporated herein by reference. 

   FIELD OF THE INVENTION 
   This invention relates to a vehicle suspension incorporating linked air bags and relates particularly to a suspension system, which can be used for load transport vehicles, such as trucks, trailers, coaches and other road vehicles. However, the principles of the invention may be adapted for use with any wheeled vehicle, including tracked vehicles. 
   BACKGROUND OF THE INVENTION 
   Suspension systems incorporating air bags have previously been proposed. Air bag suspensions have been used on trucks, trailers, buses, coaches and the like for many years, and they generally provide an improved ride on highway surfaces, particularly relatively smooth highway surfaces. 
   When used on multi-axle vehicles, or when multiple air bags are used in conjunction with single axles on vehicles, it has previously been proposed to provide air bags on each side of the vehicle with the air bags connected by a tube or other connector of relatively small cross sectional area which restricts the flow of air between the tubes to a relatively low flow rate. The tube enables the air bags to be inflated relatively equally to provide an even height for the suspension of the vehicle above the ground. 
   Previously proposed air bag systems, however, have been shown to experience difficulty in providing adequate vehicle suspension when the vehicle is driven over rough terrain, particularly when such suspension systems have been used in conjunction with multi-wheeled, multi-axle vehicles. For example, for a coach having a multi-axle, rear suspension system, passing over a kerb, raised road section or the like, movement of the forward set of wheels over the impediment causes a consequent movement of the rear wheels lifting the rear wheels off the ground surface. Naturally, if drive is provided to the rear wheels of the dual rear axle suspension system, the vehicle can be stranded. A similar problem can arise with trucks or other vehicles with lazy axles when travelling over uneven roads, or when traversing relatively rough terrain. This may occur, for example, with farm related vehicles such as in attempting to load livestock or handling relatively large quantities of hay, straw, farming equipment, earthmoving equipment or the like. 
   With previously proposed air bag suspension systems, the air bags are generally supplied with air from an air tank using a relatively small diameter, low flow rate air tube connecting the tank to the air bags. This whole purpose of the connecting tube is to enable the air bags to be inflated and deflated, to vary the height of the vehicle above the ground depending on load conditions. The low flow rate air tubes are not designed or constructed to transfer air between air bags in response to sudden changes in pressure within the air bags and they do not quickly equalise the pressure within and between the air bags. This can cause difficulties, particularly with air bag suspension systems used in multi-axle vehicles, where it can be difficult to drive onto a ramp or the like as the valve, which is set to control the vehicle height, will react to the relative movement of one axle to thereby cause air to flow into the air bags thus causing one set of wheels to be lifted off the ramp. If that set of wheels is the set of driving wheels, further progress along the ramp may be prevented. 
   Another difficulty encountered with previously known air bag suspension systems is known as “tramp”. When a multi-axle vehicle encounters a rough or uneven road surface, such as a railway crossing, a cattle grid or the like, the vehicle suspension is caused to oscillate (tramp) for a substantial period of time. Such oscillation may cause damage to the road&#39;s surface as well as unduly stress a fully loaded vehicle. 
   Attempts have been made to overcome known difficulties using air bags for vehicle suspension systems. Australian Patent No 567664 discloses an air bag suspension whereby an air tank is mounted in the vehicle chassis directly above the air bags, and short, large diameter air ducts connect each air bag to the air tank. This system has as its aim to maintain the air pressure in each air bag relatively constant irrespective of the position of the vehicle axle to thereby reduce excessive vehicle body movement. The specification also discloses the elimination of restricting flow air lines connecting the air bags to the air tank. Each side of the vehicle has its own air tank connected to the air bags on that side of the vehicle, with the air tanks optionally being connected. 
   However, this proposal does not solve the problems referred to above as, when a vehicle axle moves upwardly due to an irregularity in a road surface, air in the air bag and the air tank is compressed. When the irregularity in the road surface has been passed, the pressure in the air tank and air bag would force down the axle with great speed thereby forcing the vehicle tyre onto the road surface with a great impact. Because of the resilience of the vehicle pneumatic tyre, the rebound would be sufficient to again compress air in the air bag and air tank, thereby commencing a cycle of tramping. Shock absorbers or dampers are thereby required in such a system to counteract the effects of the tramping. Such shock absorbers or dampers add to the vehicle suspension costs and provide further stress points in the vehicle suspension. 
   Australian Patent Application No 69220/87 proposes the damping of shock loads on the suspension system by providing a secondary air tank mounted within the primary air tank and communicating through a restrictive opening. The secondary air tank and restrictive opening combine to assist in the dampening of shock loads on the suspension. However, with the speed of operation, the large volume of air in the air tank and the large size of openings between the air bags to the air tank means that no effective dampening of tramping occurs and the system is unable to cope with uneven loads and uneven terrain. 
   U.S. Pat. No. 3,063,732 discloses a vehicle suspension system incorporating both leaf and air spring assemblies in combination. The specification discloses the use of air bags on a dual axle suspension with front and rear air bags connected by a hollow sub-frame to serve as pneumatic reservoirs. The system is also provided with height control valves on each side of the suspension so that the air bags on each side are independently inflated in accordance with load conditions. The air suspension is used in conjunction with leaf springs on each end of each axle. However, this suspension system does not provide means for controlling tramp or otherwise damping suspension oscillations. Further, the ride height on both sides of the vehicle need to be adjusted to change the level travel height for any given load. 
   BRIEF DESCRIPTION OF THE INVENTION 
   According to one aspect of the present invention there is provided an air suspension system for multiple axles of a multi-axle vehicle, comprising an air bag system including at least one air bag operatively associated with vehicle wheels on selected axle sets to control relative movement between each of the selected wheels and a supporting frame structure of the vehicle, an air-flow arrangement to control the flow of air at least into each air bag, pressurising arrangement to maintain a selected, predetermined pressure in the air bag system when the vehicle is at rest, the pressurising arrangement including a valve to admit pressurised air to or exhaust air from the air bag system to maintain a predetermined vehicle height, wherein the valve is actuated by a link associated with a rocker member connected to spaced axles of the vehicle. 
   In one embodiment of the invention, the link is connected to the rocker member approximately mid-way between the connections of the rocker member to the respective spaced axles. Preferably, relative movement in one direction between the point of connection of the link to the rocker member and the vehicle supporting frame structure actuates the valve to admit pressurised air to the air bag system. 
   In one arrangement where the vehicle has three or more axle and wheel sets, two valves are used to maintain a predetermined vehicle height, each valve being actuated by separate links extending from points along rocker members mounted between adjacent axle sets. 
   In a preferred arrangement, the selected predetermined pressure is selectively variable to vary the vehicle height subject to load on the vehicle supporting frame structure. 
   The pressurising arrangement may also include a source of pressurised air, a low flow-rate air connection between the source of pressurised air and the air bag system, with the or each valve being connected to the low flow-rate air connection. With this arrangement, the pressurising arrangement is substantially unresponsive to valve actuation caused by relative movement of the rocker member and the supporting frame structure of the vehicle during vehicle operation when it is not at rest. 
   In one form, the rocker member comprises an elongated element mounted substantially longitudinally relative to the supporting frame structure of the vehicle, the element having attachment means at or adjacent each end for mounting the respective end portions thereof to respective spaced axle sets. 
   In one preferred system according to the invention, the air suspension system includes a high flow-rate air tube on each side of the vehicle connected to air bags on each side that are associated with adjacent axle and wheel sets. The system further includes air flow controlling means between the respective air bags and the associated high flow-rate air tube which regulates the flow of air from the high flow-rate air tube into the air bags generally in proportion to the air flow rate to thereby control the rate of air pressure build-up in the air bags when air flows from the high flow-rate air tube into the air bag, the high flow-rate air tube forming a manifold to which air is passed in a manner that is substantially un-regulated by the air-flow controlling means when air pressure in the air bag increases above that in the manifold. 
   The high flow rate air tubes associated with each opposed air bag are interconnected by a low flow rate connection to restrict flow of air between the high flow rate air tubes. Air is able to flow to and from the air bags to the manifold as a result of a sudden pressure increase in a respective air bag resulting, for example, from a vehicle wheel encountering a bump in a road surface. Such sudden pressure increase, however, is not passed from one manifold to the other due to the low flow rate connection restricting air flow between manifolds. Further, because the valve link is subject to movement only when the centre of the rocker member moves relative to the vehicle support frame structure, and the valve is connected to the source of pressurised air via a low flow-rate air tube, the selected, predetermined pressure in the air bag system is substantially unchanged. 
   Preferably, the air flow controlling means comprises a reduced diameter connection at one end, or each end, of the manifold. In a particular form, the air flow controlling means comprises the end wall of the manifold defining a shoulder between the manifold wall and the connection to the respective air bag. Such a shoulder acts to regulate the flow of air entering the connection from the manifold. It is believed that the regulation is as a result of turbulence developed, and the turbulence is proportional to the flow rate of air into the respective connection such that the regulation is proportional to the pressure difference between that of the air bag to which air is flowing and the manifold. Such regulation enables the system of the invention to react appropriately to road surface irregularities at any given vehicle speed. It is found that the rate of increase in pressure in one air bag and the transference of air from that air bag to the manifold and thus to the other air bag together with the controlled rate of flow of the air to the other air bag stabilises the rate of inflation of the other air bag to either totally obviate tramp or to substantially minimise rebound. Still further, it is found that the controlled rate of transference of air from the manifold to an air bag avoids development of suspension harmonic vibrations and/or oscillations which can give rise to unstable vehicle operation. 
   In one form of the invention, the pressurising means admits pressurised air from a tank, an air pump or the like, to the air bag system, and exhausts air from the air bag system through a restricted outlet, or low flow-rate air tube, to maintain the selected, predetermined vehicle height. As indicated, the pressurising means is unresponsive to sudden pressure changes in the air bag system during vehicle operation, and is used primarily to control and adjust the height of the vehicle within predetermined limits for any given load. 
   It will be understood that, in its preferred forms, the or each height valve is actuated by the link connected to the rocker member extending between adjacent axle sets of a multi-axle set of the vehicle. The link is connected to the rocker member at a point approximately mid way along the length of the rocker member whereby only relative movement between the midway connection point and the vehicle supporting frame structure causes actuation of the valve. This means that normal movement of the suspension during vehicle operation will generally not result in operation of the height valve. 
   The air suspension system of the present invention is adapted to be installed in existing vehicles as well as being incorporated into vehicles during manufacture. For incorporation into existing vehicles, an air suspension kit is provided comprising the necessary number of air bags, the appropriate high flow rate air tubes to connect to the respective air bags, the connectors to connect the high flow rate air tubes to the air bags, and system pressurising means incorporating an air tank or the like and a height control valve. The height control valve is connected to the high flow rate air tubes by a low flow rate connection so that changes in air pressure in the manifolds is not transferred between the manifolds. 

   
     DESCRIPTION OF DRAWINGS 
     In order that the invention may be fully understood embodiments thereof will now be described with reference to the accompanying drawings wherein: 
       FIG. 1  is a schematic side view of a vehicle structure fitted with an air suspension system in accordance with a first embodiment of the invention; 
       FIG. 2  is a plan view of the air bag suspension system embodiment of  FIG. 1 ; 
       FIG. 3  is a schematic side view of a second embodiment of the invention; 
       FIG. 4  is a side view illustrating a height valve for use with embodiments of the invention, 
       FIG. 5  is a view similar to  FIG. 4 , but illustrating an embodiment of the invention applied to a tri-axle vehicle structure, 
       FIG. 6  is a similar view to that of  FIG. 5  showing a further embodiment of the invention, and 
       FIG. 7  is a schematic longitudinal sectional view of a high flow rate air tube for use with embodiments of the invention. 
   

   DESCRIPTION OF PREFERRED EMBODIMENTS 
   Referring to the drawings,  FIG. 1  shows one embodiment of the present invention for use with a vehicle having a pair of adjacent axles  22  mounting front and rear wheels  12  and  14 . The vehicle incorporates a chassis member  10  on each side of the vehicle carrying a suspension mounting  16  for the front and rear axle and wheel sets. A trailing suspension arm  18  is mounted to each mounting bracket  16  by respective pivot pins  20 . The axle  22  of each wheel set is mounted to the opposed suspension arms  18 . Each suspension arm  18  is Z-shaped and engages over the respective axle  22  to form a mounting for respective front and rear air bags  24  and  25  which engage between the suspension arm  18  and the chassis  10 . The nature and operation of air bags in vehicle suspensions is well known and will not be described in further detail. 
   In this embodiment, a high flow rate air tube  26  extends between the respective front and rear air bags  24  and  25  and is connected thereto by connectors  27 . The high flow rate air tubes  26  on each side of the vehicle enable air to be transferred between the respective front and rear air bags in the event that the front and rear wheels  12  and  14  move upwardly or downwardly with respect to the chassis  10 . Thus, if the front wheel  12  moves upwardly relative to the chassis  10 , through the tire encountering a bump in a road surface, the air bag  24  is compressed increasing the pressure of air in that air bag. Air is then able to move from that air bag to the rear air bag  25  through the high flow rate air tube  26 . Similarly, if the rear wheel  14  moves upwardly relative to the chassis  10  increasing the pressure in the rear air bag  25 , air moves through the high flow rate air tube  26  into the front air bag  24 . 
   This movement of air between the respective front and rear air bags is independent on each side of the vehicle, and enables all wheels of the vehicle structure to carry loads substantially equally, even when wheels are moving upwardly and downwardly relative to the chassis due to road irregularities and the like. If either or both of the front and rear wheel pairs  12  and  14  are driven wheels, the air bag system of this embodiment ensures that the appropriate downward pressure on the suspension arms  18 , and thus the axles  22 , enable the wheel sets  12  and  14  to have appropriate traction on the ground surface. In this way, it is possible for both wheel sets  12  and  14  to retain positive contact with the ground surface. The high flow rate air tube  26  is capable of transferring a relatively large volume of air relatively quickly between the respective front and rear air bags  24  and  25 , thereby decreasing load on the vehicle suspension system, including vehicle shock absorbers, if fitted. 
   As indicated, the passage of air through the high flow rate air tube  26  occurs in both directions, depending on which of the front and rear air bags  24  and  25  has the greater or lesser internal pressure resulting from relative movement of the vehicle wheels  12  and  14 . The high flow rate air tube  26  is connected to the respective air bags by connectors  27  which, together with the high flow rate air tube  26 , controls the rate of flow through the high flow rate air tube  26 . In this embodiment, the diameter of the high flow rate air tube  26  is approximately 2 inches and the diameter of the connectors  27  is between one half inch and one and one half inches. These relative dimensions, however, will vary with different embodiments of the invention, different air bag structures and sizes and the number of air bags used in an air suspension system. 
   As shown in  FIG. 2 , the high flow rate air tubes  26  on each side of the vehicle are interconnected by a low flow rate air tube  28  which is connected via low flow rate tube  31  to a height valve  29  mounted on the vehicle chassis  10 . A rocker member  32  extends between the front and rear axles  22 , and a vertically extending link  33  is connected between the rocker member  32  and the height valve  29 . With this arrangement, any change in height between the mid point of the rocker member, to which the link  33  is connected, and the height valve  29  results in movement of the link  33  to actuate the height valve. An air tank  34 , supplied with air from an air pump (not shown) through the inlet tube  36  contains air under pressure for pressurising the air bags. Movement of the link  33  causes the height valve  29  to either admit air into the air bag system through the low flow rate line  31  and low flow rate interconnecting tube  28 , or to exhaust air from the system. Thus, if the height between the mid point of the rocker member  32  and the valve  29  decreases, as a result of an increase in load on the vehicle chassis  10 , the valve actuates to increase the pressure in the air bags  24  to restore the height to the predetermined set position. The pressure in the air bags  24  and  25  is, therefore, adjusted in accordance with the vehicle mass and load. However, because the low flow rate air tube  28  and air supply tube  31  conveys air at a low flow rate, minimal transference of air occurs between the high flow rate air tubes  26  on opposite sides of the vehicle due to relative movement of the vehicle wheels and chassis during operation of the vehicle. Further, by placing the connection of the link  33  to the mid point of the rocker member  32 , up and down movements of the front and rear wheel sets over a road bump or the like does not effect the relative position of the mid point link connection sufficiently to cause substantial or effective actuation of the valve  29 . 
   Referring to  FIG. 3 , the arrangement shown is similar to that of  FIGS. 1 and 2  except that each axle  222  is associated with two air bags  224 ,  225 . With this arrangement, each of the front and rear air bags  224  and  225  are interconnected by a high flow rate air tube  226 , with the end bags being connected to the tube  226  by connectors  215  and  217  whilst the intermediate bags of each pair  224 ,  225  are connected to the tube by connectors  228  and  230 , respectively. It will be understood that relative vertical movement of the front and rear wheel sets  212  and  214  results in a transference of air from one of the pairs of air bags  224 ,  225  to the other, but only half the air transferred passes through the section of high flow rate air tubes  226  interconnecting those air bags of each pair. In this embodiment, a suspension saddle  218  connects the respective air bags with the front and rear axles  222 . Air fittings  215  and  217  are used to connect the high flow rate air tube  226  to the respective air bags  224 ,  225 . The air fittings  215 ,  217  act to regulate the flow of air to prevent uncontrolled air flow between the air bags, to obviate resonant or harmonic pressure transference through the system. 
   The air bags shown in this embodiment are pressurised in a manner similar to that shown in the previous embodiment. Thus, a rocker member (not shown) extends between the front and rear axles  222 , and a vertically extending link (not shown) is connected between the rocker member and the height valve, as more particularly shown in  FIG. 4 . 
   Referring to  FIG. 4 , the vehicle chassis  310  is carried by front and rear wheel sets  312 ,  314  utilising an air bag system according to either of the previous embodiments. In the arrangement illustrated, the wheels  312 ,  314  are driven through differentials  319 ,  321  with drive shafts  323  and  327 . 
   A height valve rocker member  333  is connected between the differential  319  and  321 . The height valve  334  is carried on cross member  313  and serves to automatically control the inflation of both front and rear air bag systems as previously described. The valve  334  is actuated by a link  336  which is connected substantially mid point of a rocker member  333  mounted between the differentials  319  and  321 . With this arrangement, if the wheels  312 ,  314  pass along a sloping ramp in a reversing mode, rear wheels  314  lift but front wheels  314  lower. Therefore, there is little or no movement of the centre of the rocker member  333  and the link  336  attached thereto. The valve may be arranged so that minimal movement of the mid point of the rocker member  333  may cause minimal movement of the link  336  but insufficiently to actuate the valve  334 . Otherwise, air bags may be inflated or deflated inappropriately as a result of movement of a vehicle on or off a ramp or the like. By using the mid point between the axles of the front and rear wheel sets  312  and  314 , the valve  334  is not actuated inappropriately. However, if both differentials,  319 ,  321  move up and down in relative unison, the rocker member  333  will cause the valve  334  to be actuated as required so that air is either added to or removed from the air bag system. 
   It will be understood that the pressure within the air bag system may be adjusted to take account of a load on the vehicle. Thus, with a “no load” condition, the pressure may be reduced to lower vehicle height. Conversely, when the vehicle is fully loaded, the pressure will be set to ensure a proper ride height for the vehicle. 
     FIG. 5  shows a further embodiment wherein the vehicle chassis  310  is carried on a tri-axle wheel set having driven front and middle wheel sets  312 ,  314 , and a rear wheel set  315 , all of which use an air bag system according to the previous embodiment. In the arrangement illustrated, as in  FIG. 4 , the wheels  312 ,  314  are driven through differentials  319 ,  321  with drive shafts  323  and  327 . The wheel set  315  is carried on axle  322  in a manner similar to that shown in  FIG. 1 . 
   A height valve rocker member  333  is connected between the differential  319  and  321  and a second rocker member  333 ′ is connected between the differential  321  and the axle  322 . A height valve  334  is carried on first cross member  313  while a second height valve  334 ′ is mounted on the second cross member  313 ′, both valves operating in parallel to automatically control the inflation of three pairs of air bags (not shown) to establish the desired ride height. As in  FIG. 4 , the valve  334  is actuated by a link  336  which is connected substantially mid point of the rocker member  333  mounted between the differentials  319  and  321 . The second, rearward valve  334 ′ is connected to the mid-point of the rocker member  333 ′ by the link  336 ′. 
   In a further form of the invention shown in  FIG. 6 , only a single valve  334 ′ is provided for a tri-axle suspension arrangement, and the rocker member  333 ′ extends between the rear axles  322  and  321 . With this arrangement, a separate air bag  325 , shown in dashed outline, is manually inflatable to lift the front axle  312  from the ground when the vehicle chassis  310  is lightly loaded, or unloaded so that the chassis is carried by the rear wheel sets only. 
   Referring to  FIG. 7 , there is illustrated a high flow rate air tube  452  which is adapted to be used with any of the embodiments of the invention but which will be described with reference to its use in the embodiment shown in  FIGS. 1 and 2 . 
   The high flow rate air tube  452  of this embodiment is formed from a relatively flexible, pressure hose, such as a hydraulic hose. In the embodiment illustrated, the hydraulic hose is of two inches diameter and is preformed with crimped ends joined to the smaller diameter connector tubes  27  which connect the high flow rate air tube  452  to the respective front and rear air bags  24  and  25  on each side of the vehicle. The connector tubes may have a diameter of between about 0.25 and 0.8 times the diameter of the high flow rate air tube. A hydraulic hose is a preferred form of high flow rate air tube as it is designed and constructed to resist collapsing if the outside pressure exceeds the inside pressure. 
   The hydraulic hose, being flexible, is also able to be located relative to a vehicle chassis  10  so as to be positioned over and around structural members, suspension arms and the like. The relatively large diameter, high flow rate air tube  452  constitutes a manifold  450  with the smaller diameter end connectors  27  through which air is passed from one or other of the air bags  24 ,  25  during vehicle operation. The change in diameter between the large diameter manifold  450  and the smaller diameter connections  27  forms a shoulder  453  at each end of the manifold  450 . Air flow through the manifold, indicated by flow lines  458 , becomes turbulent where it strikes a shoulder  453  and the air is forced to flow back on itself as it abuts the shoulder  453 . This air flow back results in a control or regulation of the air flow from the manifold  450  into the end connector  27  and the air bag  25 , when air is flowing in the direction as shown. 
   The air flow through the manifold  450  is generally proportional to the pressure difference between the air bags  24  and  25 , such as that caused by the front vehicle wheels  12  moving upwardly relative to the chassis  10  as a result of a bump in the road surface. The flow rate through the manifold  450  and out into the air bag  25  is regulated by the back flow of air impeding the flow of air out of the manifold  450 . Such impeding of the flow of air flowing into the air bag  25  prevents rapid transferral of air from one air bag to the other and therefore provides a damping effect to significantly reduce or eliminate tramping by reducing the rate of rise of pressure in air bag  25 . The control or regulation also prevents over transfer of air between air bags that could otherwise result in the air pressure in the air bag to which air is transferred rising above that of the other air bag. Such over transfer can give rise to oscillations, whereby air moves backward and forward between the air bags through the high flow air tube which sometimes resonates causing uncontrolled vehicle pitching. 
   It will be understood that when the air pressure in the air bag  25  becomes greater than that in the air bag  24 , air flows in the reverse direction to that shown in  FIG. 7 . It will also be understood that the back flow of air caused by the shoulder  453  when air flows out of the manifold  450  in one direction or the other provides a variable regulation of the air flow in accordance with the air flow rate through the manifold. The regulation enables the system of the invention to react appropriately to road surface irregularities at any given vehicle speed. The rate of increase in pressure in one air bag and the rate of transference of air from that air bag to the manifold and thus to the other air bag together with the controlled rate of flow of the air to the other air bag stabilises the rate of inflation of the other air bag to either totally obviate tramp or to substantially minimise rebound. 
   A port  456  may be formed at one or other end of the high flow rate air tube  452  to facilitate connection of the tube  452  with the low flow rate air tube  28  providing pressurised air to the system, as shown in  FIG. 2 . Alternatively, such a port may be positioned approximately centrally along the length of the flexible high flow rate tube  452 . 
   With the present invention, it may be possible to use an air bag suspension system without the use of normal dampers or shock absorbers. Alternatively, reduced capacity dampers or shock absorbers may be used thus significantly reducing costs of suspension component. The damping effect resulting from use of the present invention dramatically reduces suspension oscillation or resonance. Therefore, suspension components, including springs, mounting points and the like are subjected to less stress than would otherwise occur over the life of a vehicle.