Abstract:
A non-torque reactive trailing arm air suspension system for vehicle driven axle using a spherical joint means between trailing arm and axle as one of four nodes of four bar mechanism disposed on both sides of vehicle that maintains substantially constant pinion shaft angle during vehicle operation. Four bars L 1,  L 2,  L 3,  L 4  are formed by 1) hanger bracket, 2) link rod, 3) driven axle with its attachments and 4) trailing arm respectively. In one of the preferred embodiments as disposed on one vehicle side, first end ( 42 ) of trailing arm ( 10 ) is pivotally connected to top of hanger bracket ( 06 ) which is attached to frame rail ( 04 ). Mid-portion ( 44 ) of trailing arm is “spherically” connected to axle top. Air spring ( 24 ) and shock absorber ( 26 ) are disposed between second end ( 46 ) of trailing arm and frame rail ( 04 ). One end of link rod ( 14 ) is pivotally connected to hanger bracket bottom and other end is pivotally connected to axle bottom.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application Ser. No. 61/460,105, filed Dec. 27, 2010. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not Applicable 
       THE NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT 
       [0003]    Rajakumar Subbarayalu Greensboro North Carolina 
         [0004]    Gowthaman Subbarayalu Fremont California 
       INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC 
       [0005]    Not Applicable 
       BACKGROUND OF THE INVENTION 
       [0006]    1) Field of the Invention 
         [0007]    This invention relates to vehicle trailing arm air suspension system, more particularly to driven axles. Driven axles of trucks carry invariably an input shaft also called pinion shaft to which is connected a propeller shaft to transmit power from engine to differential assembly from where power is distributed to wheels on either sides of axle. A cardan type universal joint generally joins propeller shaft to pinion shaft. Angle of pinion shaft is set in a truck around an ideal design angle to achieve low included angle, called ‘joint working angle’, between propeller shaft axis and pinion shaft axis. During rotary power transmission from propeller shaft to pinion shaft, a low included angle will induce low rotational variation of pinion shaft that will in turn reduce inertial vibrations excited in the driveline system. Maintaining angle of pinion shaft axis around its set ideal design angle in various positions of jounce and rebound is a challenge when the trailing arm is clamped to axle. Change in pinion shaft axis angle from its ideal design angle will increase driveline induced vibrations in vehicle and also reduce life of driveline components. A substantially constant pinion shaft angle maintained around ideal design angle would result in low universal joint induced vibrations and longer life of parts in driveline. 
         [0008]    During vehicle acceleration, coasting deceleration, and braking, a driven axle is subjected to equal and opposite torsional reactions, about axle lateral axis also called wheel axis, in response to drive torque and braking torque. Torsional resilience, about axle lateral axis, is generally incorporated in suspension systems. In a suspension where a trailing arm is “rigidly” clamped to axle, due to this torsional resilience, reaction torque on axle changes pinion shaft angle unless this reaction torque is suitably countered. A wide variety of prior art suspensions with objective of countering the reactive torque on axle based on four bar mechanism have been proposed and are examined in the following paragraphs. 
         [0009]    2) Description of Related Art 
         [0010]    In Patent U.S. Pat. No. 7,168,718, Bjorn O. Svartz discloses a suspension where joint between lower control arm and axle is a pivot joint  31 . All numbers in this paragraph refer to numbers used by Bjorn O. Svartz in U.S. Pat. No. 7,168,718 and has no equivalent relationship to invention disclosed herewith. He states in column 5 line 38 to 40, “The lower control arm passes under and is clamped to the rigid axle  6  by means of a pair of U-shaped clamps  27 ,  28 .” Since lower control arm is ‘clamped’ to rigid axle the pivot  31  will be an additional connection to axle making the pivoting action redundant. This would make the arrangement a rectangular structure of four links  21 - 31 ,  31 - 42 ,  42 - 43  and  43 - 21  than a mechanism. Even if some assistance is drawn from resilient bushes in joints, the suspension would lack sufficient travel of axle because of clamping lower control arm to rigid axle. As will be understood by those skilled in the art, in a trailing arm suspension, wherein axle is connected to trailing arm around its mid length and arm ends connected to frame either directly or through an air spring, the trailing arm can be equated to a simply supported beam. Substantially concentrated upward load is applied to trailing arm at axle connection while frame rail connections exert downward load. In such a beam, maximum bending moment occurs around the point of upward force application. Corresponding stress on the beam due to this bending moment will need to be borne by material around upward force application point. In a control arm like that of  20 , material around load application point  31  experiences maximum bending moment. Having a through hole at this point in a trailing arm would weaken the region around the through hole. This is primarily because a pivot joint like  31  needs a through hole in the trailing arm to receive pin or bush to be connected to axle. 
         [0011]    In his patent U.S. Pat. No. 4,132,433, Willetts proposes a vehicle suspension wherein a trailing arm, mentioned as longitudinally-extending beam member  420 , is connected to a rigid axle by a pivot joint as seen in his  FIG. 2  and  FIG. 3 . To accommodate this pivot and outer sleeve  452 , the trailing arm has a through hole as shown in his  FIG. 3 . This hole in trailing arm has the disadvantage of weakening the section of beam around the pivot joint. 
         [0012]    Dudding et al. proposes a non-reactive trailing arm air suspension via patent U.S. Pat. No. 6,945,548 that has a pivot joint between trailing arm and axle. The trailing arm has a through bore at pivot joint  36  between trailing arm and axle where the highest bending moment would be experienced by the trailing arm. 
         [0013]    Another feature generally found in prior art non-reactive trailing arm air suspensions that have a pivoted trailing arm front end is, the portion of trailing arm between front pivot and axle joint is vertically non-resilient. While air spring and shock absorber, which are generally disposed rearward of axle in such a trailing arm air suspension of a driven axle, substantially absorb shocks and energy by way of work done at the rear end of trailing arm, not enough energy is absorbed in suspension portion forward of axle. Elastomeric bushing in the front pivot absorbs very marginal energy as negligible work is done at that pivot. The joint between trailing arm and frame hanger bracket invariably experiences shocks that are transmitted to suspended mass causing occupant discomfort and requiring additional measures to counter negative effects of shocks on suspended mass. 
         [0014]    In Patent U.S. Pat. No. 6,390,485, Robert L. Caden describes a trailing arm air suspension wherein trailing arm is connected to axle by a pivot joint  56  that is outside the trailing arm body which is desirable as the trailing arm does not have a through hole. This also has the advantage of absorbing shocks both forward and rearward of axle. Robert achieves the non-torque reactive aspect of suspension by a mechanism built by an upper torque rod  74  for first link, a combination of frame and hanger bracket for the second link, a lower torque, rod for the third link and axle for the fourth link. The torque rods  74  and its associated mounting brackets can be avoided if the front portion of trailing arm is made to function as a link that counters reaction torque. 
         [0015]    Therefore in a non-torque reactive trailing arm suspension, it is desirable not to have a through hole around the area where axle is connected to trailing arm, to avoid weakening the structure. 
         [0016]    It is further advantageous to have a non-torque reactive trailing arm air suspension wherein substantial energy absorption takes place forward of axle by the trailing arm which trailing arm portion between axle joint and hanger bracket joint functions as one link of a four links mechanism, which mechanism achieves non-torque reactive aspect of suspension. 
         [0017]    One of the objectives of this invention is to provide a non-torque reactive trailing arm air suspension wherein is provided a trailing arm which mid-portion that is connected to axle does not have a through hole as a means for connecting to axle. 
         [0018]    Another objective of this disclosure is to provide a non-torque reactive trailing arm air suspension that is based on four bar mechanism that uses a spherical joint between axle and trailing arm, which spherical joint acts as one of four nodes of four bar mechanism and which spherical joint does not require the trailing arm to have a through hole. 
         [0019]    Yet another objective of this invention is to provide a non-torque reactive trailing arm air suspension that uses a rolled and formed trailing arm which trailing arm first end is connected to hanger bracket by a pivot joint and uses the length of rolled and formed trailing arm between hanger bracket pivot joint and trailing arm axle joint as one of four links of four bar mechanism, which link portion has a partial length of trailing arm that is vertically resilient. 
         [0020]    A ‘torque reactive’ trailing arm air suspension functionally attached to a driven axle has a pair of trailing arm assemblies, comprising pairs of hanger brackets, trailing arms, their attachments to axle and hanger brackets, air springs and shock absorbers. Front end of trailing arm of each assembly is generally pivotally connected to hanger bracket or longitudinally sliding and vertically restrained in hanger brackets. In the version of longitudinally sliding front end of trailing arm, the axle is connected to hanger bracket generally by additional tie link between axle and hanger bracket. This additional tie link is generally pivotally connected to hanger bracket and axle. Middle portion of trailing arm is generally “rigidly” clamped to one side of axle or pivotally connected to axle. The trailing arm generally extends behind axle where it is connected to one end of an air spring and to one end of a shock absorber. Other ends of air spring and shock absorber are connected to frame rail. Front portion of trailing arm bears partial suspended weight of vehicle. Rear portion of trailing arm bears partial suspended weight of vehicle through the air spring that is connected to frame rail. Rigidly clamped attachment of trailing arms to axle combined with pivoted or vertically-restrained-sliding of front end of trailing arm in the hanger bracket makes the suspension inherently reactive to torque induced by traction force and wheel braking torque. Due to resilience in the suspension system, this reaction on axle changes pinion shaft angle of driven axle. Effect of reaction on axle is more pronounced during vehicle acceleration from stop and during vehicle hard braking. While it is an industry practice to set angle of pinion shaft to its ideal design angle that substantially cancels joint working angle of all cardan joints in driveline system, a ‘rigidly axle mounted trailing arm set up’ generally does not maintain factory set pinion shaft angle during jounce and rebound of axle and during acceleration and braking. 
         [0021]    In prior art ‘torque reactive’ trailing arm air suspensions where the trailing arm is rigidly clamped to axle, structural strength of trailing arm is preserved but the suspension is rendered ‘torque reactive’. In prior art ‘non-torque reactive’ a trailing arm air suspensions where the trailing arm uses a through hole as a means of pivotally connecting trailing arm to axle, the region around the hole experiences substantially high bending stress and the presence of through hole around that area further weakens the structure. In prior art non-torque reactive trailing arm air suspensions where the trailing arm does not have through hole but pivotally connects trailing arm to axle, an additional link and its mounting brackets are required to make a non-torque reactive suspension. 
       BRIEF SUMMARY OF THE INVENTION 
       [0022]    The disclosed invention is a vehicle trailing arm air suspension system and more particularly a truck driven axle air suspension system. One of the preferred embodiments of this invention is based on ‘ four bar mechanism’ also called ‘ four link mechanism’, the four links are represented by 1) a hanger bracket, 2) a link rod, 3) driven axle along with its attachments to connect mid-portion of trailing arm and second end of link rod and 4) a trailing arm of preferably spring steel. The invention uses a spherical joint constructed to spherically connect trailing arm and axle which joint is one of four joints of four bar mechanism. The invention as applied to a single driven axle comprises a pair of trailing arm assemblies each disposed on both sides of vehicle. Each assembly comprises a hanger bracket, a trailing arm with its attachments to hanger bracket and axle, a link rod with its attachments to hanger bracket and axle, an air spring and a shock absorber. It must be noted that ‘longitudinal direction’ means the direction of normal vehicle travel, ‘axle’ means the axle assembly consisting of a driven-axle with attachments that are necessary on the axle to connect to trailing arm and link rod. Also it must be noted that ‘frame’ or ‘vehicle frame’ means a frame assembly consisting of oppositely spaced and longitudinally oriented frame rails that are parallel to each other and connected by a series of transversely oriented cross members functionally attached to the inboard side of frame rails along their length. ‘Rolled’ means a metal working process in which a part is shaped to required form by repeatedly passing a preformed metal part between rollers till the required form is obtained. ‘Formed’ means the process in which a shape of a part is obtained by such operations as bending, drawing that does not require removal of material. The term ‘ node’ means the joining point or axis of two links in a mechanism. 
         [0023]    A hanger bracket is rigidly attached to outboard of the frame rail by a plurality of fasteners. Trailing arm is a longitudinally disposed beam of varying rectangular section of solid spring steel having a formed hole at its first end, a mid-portion and a second end. Trailing arm has a vertically resilient part between first end and mid-portion. In the preferred embodiment the trailing arm is provided with a step near to the second end to accommodate an air spring between second end and frame rail. First end of the trailing arm is pivotally connected to top of hanger bracket. The axes of pivots as discussed in this invention are generally perpendicular to a longitudinal vertical plane. In this text a longitudinal vertical plane is an imaginary plane that is oriented vertically in the direction of vehicle motion. The pivoted connection between the first end of the trailing arm and the hanger bracket acts as one of four nodes of four bar mechanism. 
         [0024]    Mid-portion of the trailing arm is “spherically” connected to top of driven axle providing a spherical joint between mid-portion of trailing arm and top of axle. A spherical segment-top and a spherical segment-bottom are each made out of hemispherical steel blocks of suitable size. On the base of each hemispherical block is provided a centrally located through-slotted cavity, its web parallel to base, its depth from base of hemisphere being substantially equal to half vertical height of mid-portion of trailing arm and its width being substantially equal to horizontal lateral width of mid-portion of trailing arm. These slot cavities cooperatively receive half vertical thickness of the mid-portion of trailing arm when the slotted hemispherical blocks are fastened base to base to form a slotted sphere around mid-portion of trailing arm. The web surface of the slots in the spherical segments are keyed to their corresponding horizontally disposed matching surfaces on mid-portion of trailing arm to prevent relative movement between the spherical segments and the trailing arm. The spherical segment-top and spherical segment-bottom are preferably fastened together at inboard and outboard sides of the trailing arm. A block-top and a block-bottom each made out of rectangular steel block are provided with hemispherical cavities to cooperatively receive corresponding spherical segments when assembled base to base. Suitable slots are provided in the blocks to have sufficient clearance around trailing arm during operation. The blocks together are rigidly attached to top of axle by clamping them to the axle preferably using two U-shaped bolts one each on inboard and outboard of trailing arm. All four spherical surfaces of spherical segments and blocks have a common center. Required clearance is provided between the spherical cavities of the blocks and spherical surfaces of the segments to allow for suitable journal bushing. Sliding clearance is provided between the segments and bushings. The arrangement forms a limited articulation spherical joint between axle and mid-portion of trailing arm. The center of the spherical joint thus formed act as one of four nodes of four link mechanism. 
         [0025]    A link rod is disposed between hanger bracket and axle. First end of a link rod is pivotally connected to bottom end of hanger bracket. Other end of link rod is pivotally connected to a bottom bracket which bottom attached to bottom of axle with the same U-shaped bolts used to clamp blocks to axle. Bottom bracket has holes to receive pins to pivotally connect second end of link rod to bottom bracket. The link rod forms one of the links of four bar mechanism and its pivoted ends form two nodes of four bar mechanism. 
         [0026]    In operation, the hanger bracket functions as ‘ground link’ of the four bar mechanism. Axle, with its connections to trailing arm and link rod, functions as the ‘driven link’ of four bar mechanism. Four bar mechanism thus formed is geometrically arranged to achieve required ideal design angle of pinion shaft. Lengths of opposite links are preferably maintained equal to achieve substantially constant pinion shaft angle during jounce and rebound motion of axle. This arrangement of four bar mechanism makes the axle substantially non-reactive to drive torque and brake torque. Drive torque and brake torque induced reactive torque on axle, about axle axis, are substantially countered by the link rod and the portion of trailing arm between spherical joint and pivoted first end of trailing arm. Second end of trailing arm is connected to one end of an air spring and to one end of a shock absorber. Other end of the air spring and the shock absorber are connected to the frame rail. To control the lateral motion of the axle during jounce and rebound, one end of a tie rod is pivotally attached to the frame rail and the other end of the tie rod is pivotally attached to the axle. Vertically resilient portion of trailing arm between first end and mid-portion and air spring act as energy absorption elements of suspension. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0027]      FIG. 1  is a perspective view illustrating the trailing arm suspension according to the present invention pertaining to a single driven axle shown assembled on a truck frame. 
           [0028]      FIG. 2  is a perspective view illustrating the trailing arm suspension according to the present invention pertaining to a single driven axle without tires, shown assembled on a truck frame. 
           [0029]      FIG. 3  is a view of the invention pertaining to a single driven axle viewed from left side of truck. 
           [0030]      FIG. 4  is the longitudinal vertical section of the invention through the spherical joint center  50 . 
           [0031]      FIG. 5  illustrates the perspective View ‘A’, side view ‘B’ and top view ‘C’ of trailing arm, segment-top and segment-bottom assembled to mid-portion of the trailing arm. 
           [0032]      FIG. 6  is the perspective view of the invention pertaining to a tandem driven axle shown assembled on a truck frame when viewed down at an angle. 
           [0033]      FIG. 7  is the general view of the invention for a tandem driven axle without tires shown assembled on a truck frame. 
           [0034]      FIG. 8  is the left side view of the invention for a tandem driven axle, with axle and inter-axle propeller shaft. 
           [0035]      FIG. 9 through 14  shows longitudinal vertical sections of various embodiments of the invention as contemplated presently. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0036]      FIG. 1  illustrates portion of truck chassis showing general arrangement of the suspension according to the invention as applied to a single driven axle. Frame rails  03  and  04  are parallel and oppositely spaced steel channels, their longer dimension, length, oriented longitudinally in the direction of normal drive motion of truck. Frame rails  03  and  04  are joined laterally by multiplicity of cross members fastened to inboard sides of frame rails  03  and  04 . Only the cross member  51  relevant to suspension is shown. Hanger brackets  05  and  06  are shown mounted to out-board sides of frame rails  03  and  04 . Propeller shaft  101  is shown connected to driven axle  150  by a cardan type universal joint  102 . Wheels  08  are shown mounted on either side of axle  150 . During vehicle operation, power from vehicle&#39;s power source (not shown) is transmitted to wheels through a multiplicity of propeller shafts (not shown) between power source and propeller shaft  101  and through gears (not shown) in driven axle  150 . Driven axle  150  contains the pinion shaft (not shown) which is in the path of power transmission to wheels  08 . 
         [0037]      FIG. 2  illustrates portion of truck showing general arrangement of the suspension according to the invention applied to a single driven axle  150  shown without wheels.  56  is a longitudinal vertical plane oriented in the direction of vehicle drive motion passing through vehicle lateral center. Components are numbered such that odd numbers represent those parts belonging to right hand side trailing arm assembly and even numbers represent parts belonging to left hand side trailing arm assembly with the exception of  150 ,  101 ,  102 ,  51 ,  38 ,  52 , and  56 . The pairs of numbers after the occurrence of another pair of numbers in a sentence in this text need to be considered as being in order respectively. 
         [0038]    Hanger brackets  05 , 06  are rigidly attached to the outboard sides of frame rails  03 , 04  respectively by a plurality of fasteners. The fasteners also fasten a cross member  51  between frame rails. First end  41 ,  42  ( FIG. 4 ) of trailing arm  09 , 10  are shown pivotally connected to top of hanger brackets  05 , 06  by pivot pins  11  (not visible in the Figure) and  12 . The axes of pivot pins  11  and  12  are substantially collinear, and substantially perpendicular to the longitudinal vertical plane  56 . First end of link rods  13 , 14  are shown connected to lower end of the hanger brackets  05 , 06  by pivot pins  15 , 16 . Axes of pivot pins  15 , 16  are substantially collinear, and substantially perpendicular to the longitudinal vertical plane  56 . Second end of link rods  13 , 14  are pivotally connected to bottom brackets  17 , 18  by pins  27 , 28  respectively. Axes of pivot pins  27 , 28  are substantially collinear and substantially perpendicular to the longitudinal vertical plane. Bottom brackets  17 , 18  are rigidly attached to lower portion of axle  150  one on each side of axle by U-shaped bolts  19 ,  21  on the right side and  20 ,  22  on the left side. A second end  45 ,  46  of the trailing arms  09 , 10  is attached to one end of air springs  23 , 24  by suitable bracketry and fasteners. One end of shock absorbers  25 ,  26  is attached to the second end  45 ,  46  of trailing arm  09 , 10  by suitable bracketry and fasteners. Second end of the air springs  23 , 24  and second end of shock absorbers  25  and  26  are attached to frame rails  03 , 04  by suitable bracketry and fasteners. The figure also illustrates axle axis  48  extending from left to right of axle  150 . 
         [0039]      FIG. 3  illustrates side view of general arrangement of the invention as applied to single driven axle  150 , viewed from left hand side of vehicle. In the drawing, front of vehicle is to the left and rear of vehicle is to the right. Components are numbered such that odd numbers represent those parts belonging to right hand side trailing arm assembly and even numbers represent parts belonging to left hand side trailing arm assembly with the exception of  150 ,  101 ,  102 ,  37 ,  38 ,  47 ,  48 ,  51 ,  52 ,  55 , and  56 . This illustration need to be correlated with  FIG. 4  for better understanding. Pinion shaft axis  47  is generally in the fore aft direction parallel to the longitudinal vertical plane  56 . Pinion shaft axis  47  is set at an angle β° in reference to horizontal ground plane  37  to achieve required ‘joint working angle’ α° between propeller shaft axis  55  and pinion shaft axis  47 . In the figure the pinion shaft axis is shown horizontal, though the orientation varies according to various vehicle requirements. Hanger bracket  06  is shown partially cut for the purpose of showing universal joint  102 . Horizontal plane  52  that is represented by a dashed line in this view is shown passing through axle axis  48 . 
         [0040]      FIG. 4  shows partial view of section through a plane parallel to longitudinal vertical plane  56  and passing through nodal center  50  of spherical joint which is formed between trailing arm  10  and axle  150 . Odd numbers represent those parts that belong to right hand side trailing arm assembly with exception of axle  150 , and even numbers represent those parts belonging to left hand side trailing arm assembly. In this figure front of vehicle is towards left. For sake of clarity, only left side trailing arm suspension assembly is illustrated. This figure shows connection details of mid-portion  44  of trailing arm  10  to top of axle  150  by an assembly comprising trailing arm  10 , block-top  34 , block-bottom  36 , spherical segment-top  30  and spherical segment-bottom  32 . The illustration shows suspension assembly  154  comprising hanger bracket  06 , pin  12 , trailing arm  10 , segment-top  30 , segment-bottom  32 , block-top  34 , block-bottom  36 , U-shaped bolts  20 , 22 , bottom bracket  18 , pin  28 , link rod  14 , and pin  16 . The suspension assembly  154  is shown attached to left frame rail  04 . Suspension assembly  154  is also shown connected to axle  150 . The portion of trailing arms  09 , 10  between  41 , 42  and  43 , 44  is the vertically resilient portion  57 , 58  of the trailing arms. To highlight the purpose of  FIG. 4 , the details of fastening hanger bracket to frame rail  04  are not shown. Air spring  24  is disposed between second end  46  of trailing arm  10  and frame rail  04 . Shock absorber  26  is shown disposed between second end  46  of trailing arm and frame rail  04 . In the illustration, spherical segment-top  30  and spherical segment-bottom  32  are shown keyed in matching depressions in trailing arm  10 . Convex spherical surface ‘ 30   a ’ of segment-top  30  cooperatively engages with matching concave spherical surface ‘ 34   a ’ in block-top  34 . Similarly, convex spherical surface ‘ 32   a ’ of spherical segment-bottom  32  cooperatively engages with concave spherical surface ‘ 36   a ’ in block-bottom  36 . Suitable spherical shapes of bushing (not shown) material interface between spherical surfaces of segment-top  30  and block-top  34  and between spherical surfaces of segment-bottom  32  and block-bottom  36 . Spherical surfaces  30   a,    34   a,    32   a  and  36   a  in the assembly are arranged to have a common center point  50 . This ensures the assembly acts as a single spherical joint. Unlike a pivot joint which has one degree of rotational freedom about an ‘axis’, a spherical joint has three degrees of rotational freedom about a ‘point’ ( 50 ).  FIG. 4  also illustrates the four bar links. Distance between pin  12  and pin  16  of hanger bracket  06  represents ground link L 1  of four bar mechanism. Dimension of link rod  14  between pin  16  and pin  28  represents second link L 2 . Distance between pin  28  and spherical joint center  50  on top of axle  150  represents driven link L 3 . Link L 3  is formed by bottom bracket  18 , axle  150 , block-bottom  36 , block-top  34 , segment-bottom  32 , segment-top  30 , mid-portion  44  of trailing arm of which  18 ,  150 ,  36 , and  34  are clamped together as shown by U-shaped bolts  20 , 22 . The four bar mechanism is completed by link L 4  formed between nodal center  50  of spherical joint and pin  12 . Pin  12  forms the first pivot joint between first end  42  of trailing arm and hanger bracket  06 , pin  16  forms the second pivot joint between hanger bracket and one end of link rod  14 , pin  18  forms the third pivot joint between other end of link rod  14  and axle  150  by cooperatively disposed bottom bracket  18 . Fourth node of the four bar mechanism is the spherical joint center point  50  formed between trailing arm  10  and axle  150  with cooperatively disposed segments  30 , 32  and blocks  34 , 36  and mid-portion  44  of trailing arm  10 . First ends  41 , 42  of trailing arm  09 , 10  , vertically resilient front portion  57 ,  58  of trailing arms and second ends  45 ,  46  of trailing arms are shown. 
         [0041]      FIG. 5  illustrates the trailing arm  10 , segment-top  30  and segment-bottom  32  assembled together. Spherical surface  30   a  of segment-top and spherical surface  32   a  of segment-bottom is shown in this figure. In this illustration the spherical surfaces  30   a  and  32   a  are convex in shape. The figure also shows front end  41  with formed to obtain a hole  59 , mid-portion  44  and second end  46  of the trailing arm. 
         [0042]      FIG. 6  Figure illustrates portion of truck showing general arrangement of the invention on tandem driven axles. The suspensions in these axles are akin to that of single driven axle and definitions and assembly arrangements are common to single driven axle suspension 
         [0043]      FIG. 7  illustrates portion of truck showing general arrangement of the suspension on tandem driven axles without tires. The figure shows the first driven axle  151  and second driven axle  152  connected at universal joints  103  and  105  by an inter axle propeller shaft  104 . Suspension in these axles are akin to that of single driven axle and definitions and assembly arrangements are common to single driven axle suspension. 
         [0044]      FIG. 8  illustrates the left side view showing general arrangement of the suspension on tandem driven axles. 
         [0045]      FIG. 9  shows one of the preferred embodiments of the invention. This is an over slung suspension arrangement wherein the trailing arm is above axle  150 . In this embodiment, the spherical joint center  50  is above the axle  150 . This embodiment is the same as explained in  FIG. 4 . The spherical joint is formed by two convex spherical surfaces of spherical segment-top  30  and segment-bottom  32  and two concave spherical surfaces of block-top  34  and block-bottom  36 . 
         [0046]      FIG. 10  shows a variant of embodiment in  FIG. 9  wherein the trailing arm  10  is under slung on axle  150 . In this embodiment the spherical joint center  50  is below the axle  150 . 
         [0047]      FIG. 11  shows another embodiment of the invention where the spherical joint center  50  is above axle  150  and above the over slung trailing arm. In this arrangement the block-top  34  has a spherical projection  54  cooperatively engaging with spherical cavity in spherical segment-top  30 . Spherical segment-bottom  32  cooperatively engages with spherical surface of block-bottom  36 . 
         [0048]      FIG. 12  shows a variant of embodiment in  FIG. 11  where the spherical joint center  50  is below axle  150  and above under slung trailing arm. The spherical joint arrangement is similar to that explained in  FIG. 11 . 
         [0049]      FIG. 13  shows another embodiment of the invention where the spherical joint is formed by 1) spherical segment-top  30 , 2) a spherical ball  40 , 3) block-top  34 , 4) spherical segment-bottom  32  and 5) block-bottom  36 . The spherical joint center  50  is above axle  150  and above over slung trailing arm. This arrangement is a variant of that described in ‘FIG.  11 ’ in that the spherical projection  54  in block-top is substituted by a spherical ball  40  which cooperatively engages concave spherical surfaces in spherical segment-top  30  and block-top  34 . 
         [0050]      FIG. 14  shows a variant of embodiment shown in  FIG. 13  where the spherical joint arrangement is similar to that explained in  FIG. 13 . Spherical joint center  50  is below axle and above the under slung trailing arm. 
         [0051]    Although the above description relates to specific preferred embodiments as presently contemplated by the inventor, it will be understood that the invention in its broad aspect includes mechanical and functional equivalents of the elements described herein.