Abstract:
The invention relates to a suspension system for installation between a chassis and dual axles of a vehicle. The suspension system includes an equalizer beam pivotally linking the axles together. A trailing arm support member is pivotally attached to a hanger bracket on the chassis. A suspension saddle is secured to the trailing arm support member to provide pivotal support for an equalizer beam. Air springs are located between the chassis and the trailing arm support member.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a continuation of U.S. Ser. No. 09/145,472, filed Sep. 2, 1998, U.S. Pat. No. 6,224,074. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates to vehicle suspension systems for dual axle vehicles in which the axles are attached to equaliser beams or more commonly known as walking beams, so that the vehicle load is transferred to the road surface either equally, or in proportion, to the position of the beam pivot to the beam centre. 
     Various vehicle suspensions have been developed for dual axle vehicles in which the axles are attached to walking beams with a springing medium located between the beam pivot and the vehicle chassis to absorb shocks caused by uneven road conditions. Additionally a mechanical connection system is used between the walking beam and the chassis to firstly transmit tractive effort and torque; secondly to absorb braking effort and torque; and thirdly to constrain the lateral relationship of the axles with the chassis. In the case where the springing mechanism uses steel springs, the spring is usually a multi-leaf semi elliptical type or a taper leaf type, having an eye at the forward end and a slipper surface at the rear end. The spring and its associated saddle then performs all or part all of the required functions of the mechanical connection system. In the case where the springing mechanism uses rubber springs, or air springs, the mechanical connection systems are usually vertical drive pins and load cushions located in vertical aligned rubber bushings. 
     Air suspensions are generally recognised as having desirable features including superior ride comfort for the driver; enhanced impact protection for the vehicle and cargo; and reduced road impact and consequent road wear. Air suspension with walking beams and vertical drive pins have the benefits of previously mentioned desirable features reduced because the vertical drive pins and associated bushings tend to restrict vertical freedom of the suspension. 
     BRIEF SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a suspension system which combines the advantages of both a walking beam suspension which incorporates air spring(s). 
     A further object of the invention is to provide a suspension system which provides a simple way of converting an existing walking beam suspension from mechanical springing to air springing. 
     With these objects in view the present invention in a first aspect provides a suspension system for installation between a chassis and dual axles of a vehicle, said suspension system including an equaliser beam pivotally linking said axles together, a trailing arm support member pivotally attached to a hanger bracket on said chassis, a suspension saddle secured to said trailing arm support to provide pivotal support for said equaliser beam and air spring means located between said chassis and said trailing arm support member. 
     Preferably said trailing arm support member is formed from a steel fabrication, a nodular iron casting or a spring steel. In a preferred embodiment said suspension saddle is located below said trailing support member and said air spring means is located on the opposing side of said trailing support member. In a practical embodiment the pivotal attachment of said trailing arm support member to said hanger bracket includes a releasable offset cam member to provide axle alignment adjustment. 
     In a further aspect of the invention there is provided an axle adjustment system for vehicle suspension, said axle adjustment system including a hanger bracket for attachment to the chassis of said vehicle, a suspension element pivotally attached to said hanger bracket, a pivot pin releasably located within said hanger bracket and having a cam element for engagement with said suspension element whereby rotation of said pivot pin causes relative movement between said suspension element and said hanger bracket. 
    
    
     In order that the invention may be clearly understood there shall now be described by way of a non-limitative examples only preferred constructions of the invention incorporating the principal features of the present invention. The description is with reference to the accompanying illustrated drawings in which: 
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     FIG. 1 is a side view of a first embodiment of a vehicle suspension made in accordance with the invention; 
     FIG. 2 is an exploded perspective view of the components of the vehicle suspension shown in FIG. 1; 
     FIG. 3 is a cross-sectional view along and in the direction of arrows  3 — 3  shown in FIG. 1; 
     FIG. 4 is a cross-sectional view along and in the direction of arrows  4 — 4  shown in FIG. 1; 
     FIG. 5 is a cross-sectional view along and in the direction of arrows  5 — 5  shown in FIG. 1; 
     FIG. 6 is a side view of a second embodiment of a vehicle suspension made in accordance with the invention; and 
     FIG. 7 is a similar view to that of FIG. 1 of the third embodiment of a vehicle suspension made in accordance with the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     For illustrative purposes, the suspension systems  10 , 12  in FIGS. 1 to  5  and FIG. 6 respectively are shown installed on a tandem axle vehicle. To avoid duplication of description identical reference numerals will be used for identical components in both embodiments. Since each suspension in the systems is identical to the other, only one need be described. The vehicle is the kind having a left side rail frame member  14 , a right side rail frame member  16 , a forward axle  18  and a trailing axle  20 . It will be understood that the suspensions illustrated for the left side of the vehicle is duplicated with the same kind of suspension on the right side of the vehicle. 
     An equaliser beam  22  (also known as a walking beam) is formed as a steel or nodular iron casting, a steel or aluminium alloy forging or a steel fabrication. The beam  22  has a pivot centre hole  24  and pivot bushing shells  26 . Each bushing shell  26  includes a beam end bush  28  which incorporates a compliant rubber element  30  and a steel centre  32  that provides for attachment to axles  18 , 20  through an axle bracket  34 . An adjustment method for axle alignment is provided by adjustment shims  36 . The use of such shims are well known in the art. In the inset shown as “A” in FIG.  2  and in FIG. 5 an alternate beam end bush design is shown that does not incorporate the axle alignment feature of shims  36 . This alternative uses an adaptor assembly  38  for attachment to the axles  18 , 20  via axle brackets  34 . Assembly  38  includes a support sleeve  40 , end plugs  42 , threaded fastener  44  and nut  46 . 
     Located in pivot centre hole  24  is a pivot bush  48  which allows for articulation of axles  18 , 20  and also transfers the vertical force from the vehicle weight and horizontal forces of tractive effort and braking, through to wheels, tires and the ground surface. Pivot bush  48  usually has a steel inner sleeve  50 , compliant rubber element  52  and an steel outer sleeve  54 . The outer sleeve  54  is a press fit in the pivot centre hole  24  and the inner sleeve  50  extends at each end to accept a respective clamp  56  to locate the pivot bush  48  and beam  22  assembly in a suspension saddle  58 . If desired, a lubricatable bronze bushing arrangement could be used to replace the steel and rubber bush  48 . A tubular steel cross tube  60  fits into each of the inner sleeves  50  to maintain alignment of one beam relative to the other. One cross tube  60  is used per vehicle. 
     Suspension saddle  58  is made as a steel or nodular iron casting or alternatively can be a welded steel fabrication. Lugs  62  are an optional item for this type of saddle and are used as a location face for a trailing arm support member  64  in the form of a spring member which fits on to the saddle  58 . Two saddles  58  are used per suspension, one each side of the vehicle. Spring member  64  is the main support member which acts as a beam member. Spring member  64  can be constructed as a leaf spring assembly with from one to several leaves (as shown). To hold the leaves together a bolt  65  and nut  67  are used. An eye  66  of spring member  64  is pivoted at the front end to a frame hanger bracket  68  fixed to frame member  14 . Spring member  64  is clamped to the suspension saddle  58  with bolts  70  at approximately a centre position and has air springs  72  mounted between the centre and the rear of spring member  64 . Two spring members  64  are used per suspension, one each side of the vehicle. 
     An adaptor plate  74  is mounted on top of spring member  64  and acts to support the air springs  72 . Each air spring  72  has a mounting bracket  76  to allow attachment to frame members  14 , 16 . Bracket  76  is secured to the top plate  77  of air spring  72  with top plate  77  abutting a respective one of frame members  14 , 16 . In a further embodiment saddle  58 , spring member  64  and adaptor plate  74  can be manufactured in one piece. This can be in the form of a steel, aluminium alloy or nodular iron casting, or as a welded steel fabrication. The air springs  72  can be the industry standard sleeves, rolling lobes or convoluted types. In the embodiment shown in FIGS. 1 to  5  two air springs  72  are shown per side. In the embodiment shown in FIG. 6 only two air springs  72  are used ie one each side of the vehicle. The number of air springs  72  used can vary to suit requirements. The air spring(s)  72  of each side are connected in series to equalise the pressure. Alternately, it is possible to isolate the air springs on the right side from those on the left side as an aid to roll stability. 
     Hanger bracket  68  is manufactured as a steel or nodular iron or aluminium alloy casting or a steel fabrication. The lower part  78  of hanger bracket  68  is the upper half of a split cap arrangement, designed to locate, house and restrain a suspension pivot pin  88 . Pivot pin  88  may be cylindrical and provide no suspension adjustment or be shaped as shown to provide adjustment. Clamps  80  form the lower half of the split cap arrangement secured by threaded studs  82  which are screwed into hanger bracket  68 . Washers  86  and nuts  84  hold clamps  80  in position. An alternative arrangement to this would be the use of a bolt passing through clamps  80  to be threaded directly into hanger bracket  68 . 
     In the embodiment shown pivot pin  88  allows adjustment of axle alignment. A pivot bush  90  is an interference fit in eye  66  of spring member  64 . Pivot pin  88  includes a an eccentric element  92  which is located between support pins  94  and offset therefrom to provide a cam member. Eccentric element  92  is located within pivot bush  90  and can rotate therein. Support pins  94  are clamped by the split cap functions of lower part  78  of hanger bracket  68  and clamps  80 . A square hole  96  is designed to accept the square bar of a wrench or turning bar (not shown) so that the eccentric element  92  can be rotated about the diametral axis of support pins  94 , inside the split cap housing (when loosened). This rotation moves the diametral axis of eccentric element  92  which in turn moves the spring member  64  of the suspension to provide the adjustment. Square hole  96  may be incorporated into an insert or could alternatively be any polygonal hole, the criteria being that a key arrangement inserted into the hole can transmit torque to eccentric element so that it can be rotated, when the nuts  84  of the split cap are loosened. This adjustment system is not restricted to this embodiment as it can be readily incorporated in any spring, trailing arm or other axle attachment arrangement for suspension. Vehicle suspensions benefit from having an alignment adjustment system to allow wheels and tires to be aligned, relative to the vehicle direction of travel, to provide for optimum tire life. 
     A longitudinal torque rod or linkage  98  will control driving and braking torque of the forward driven (or non driven) axle  18 . One forward longitudinal torque rod  98  would be used per suspension. A further longitudinal torque rod or linkage  100  controls driving and braking torque of the rearmost drive (or non driven) axle  20 . A transverse rod  102  (sometimes referred to as a Panhard rod) controls lateral movement of the axles  18 , 20  relative to the chassis. Two transverse rods  102  are used per suspension, one for each of the two axles. A spacer and shim pack  104  provides lateral alignment adjustment of transverse rods  102 , if required. In an alternate design an “A”-frame arrangement or “V”-rod can be substituted for the two longitudinal torque rods  98 , 100  and the two transverse rods  102 . A height control valve  106  is used to maintain a constant ride height for the suspension. Normally the suspension will use a single height control valve  106  but an alternative may use two valves as an aid to roll stability. Two valves would normally be used, one each side, when the left and right air springs are isolated from each other. A hydraulic shock absorber (damper)  108  provides hydraulic control of suspension movement. The suspension will normally have 4 shock absorbers  108 , 110  per suspension, ie two per axle (as shown in FIG. 1) but an alternative would be for two shock absorbers  108  (as shown in FIG. 2) fitted to rear axle  108  only. 
     In FIG. 7 there is shown a further embodiment where the same reference numerals have been used to avoid duplication of description. In this embodiment trailing arm support  64  (FIG. 1) is in the form of a steel fabrication  120 . It may also be formed as a nodular iron casting. Fabrication  120  is T-shaped in cross-section and has suspension saddle(s)  126  secured thereto. The horizontal arm  124  of fabrication  120  has the air springs  72  secured thereto. Shock absorber  108  is coupled to the free end  122  of trailing arm support  120  and to frame member  14 . 
     The invention can also be used to convert existing suspensions to the new type of suspension. Examples of suspensions that can be converted are the following Hendrickson model series: AR series, R series, RT/RT2 series, RTE/RTE 2  series, RU series, RUE series, U/U2 series, UE/UE2 series, RS series, SR series and VS series. 
     Whilst there has been described in the foregoing description preferred constructions of a suspension system incorporating certain features of the present invention, it will be understood by those skilled in the technology concerned that many variations or modifications and details of design or construction may be made without departing from the essential features of the present invention.