Abstract:
A multi-axle leaf spring suspension having a compliant equalizer. The leaf springs are mounted one behind the other on each side of the vehicle. Adjacent ends of the leaf springs are pivotally attached to the compliant equalizer. The compliant equalizer is pivotally mounted to a vehicle frame. The compliant equalizer comprises a pair of arms that are pivotally connected to each other in a scissor-like fashion. One end of each arm is pivotally connected to the end of a leaf spring. The other end of each arm is cooperatively arranged to contain and compress a spring member between them. The compliant equalizer reduces the magnitude of shocks that would be other wise transmitted to the suspension and frame by absorbing them through compression of the spring member.

Description:
FIELD OF THE INVENTION 
     The invention relates to multi-axle suspension systems, and more particularly to a multi-axle leaf spring suspension system having a compliant equalizer. 
     BACKGROUND OF THE INVENTION 
     Conventional multi-axle assemblies for trucks or trailers may comprise two or more axles. In the case of a two axle arrangement, four leaf springs are used. Two leaf springs are on each side of the frame. The remote ends of each pair of springs are usually supported within hanger brackets which are secured to the frame. The adjacent ends of each pair of springs are supported by a pivotally mounted equalizer. The equalizers are in turn supported by hanger brackets which are secured to the frame. 
     When the front wheels in the tandem suspension, for example, encounter a condition in the road producing a vertical movement of the front axle, the resultant deflection in the front springs is transmitted in part by the equalizer to the rear springs. This results in an equalizing effect in which any vertical displacement of either axle is distributed between the springs which minimizes the weight differential between the axles. 
     In the instance of a vehicle equipped with a prior art equalization tandem one problem concerns inadequate and abrupt load equalization from one axle to another. As one end of the equalizer rotates upwardly at the point at which the spring end contacts the leaf spring, the other end abruptly rotates downward. This action causes abrupt and unequal moments about the center pivot point of the equalizer; inequality increases as the range of equalizer movement increases. 
     The end results of improper load equalization are numerous. If the axle which encounters bumps and overloads is unpowered, a loss of traction can occur on the powered axle. The suspension components, and springs in particular, are subjected to higher stresses and therefore their service life is shortened appreciably. As the leaf springs are subjected to overload they progressively lose capacity to absorb energy and therefore transmit more energy through the mounting brackets to the vehicle frame. Increased input of energy into the vehicle frame can often contribute at given loads, speeds and highway conditions to damage to the vehicle. Further, wherever an unequal load distribution occurs within a tandem suspension, the axle which is overloaded transmits its load to the roadway in a manner that can be detrimental to the roadway. The foregoing arguments also apply to suspensions comprising more than two axles. 
     Representative of the art is U.S. Pat. No. 4,033,606 to Ward (1977) which discloses an equalized suspension system is provided for the truck of a truck-trailer combination of the tandem axle type. The suspension on each side of the vehicle includes independent semi-elliptic leaf springs mounted in tandem relationship one behind the other, and which are respectively connected at their midpoint to the forward and rearward axles. The remote ends of each spring are supported in rolling contact with respective roller assemblies housed by respective brackets which, in turn, are secured to the frame of the truck. An equalizer support bracket is provided between the adjacent ends of each pair of springs and an equalizer is pivotally supported within each equalizer support bracket. The adjacent ends of the springs are pivotally attached to shackles which, in turn, are pivotally mounted to the respective equalizers. 
     What is needed is a multi-axle leaf spring suspension system having a compliant equalizer. The present invention meets this need. 
     SUMMARY OF THE INVENTION 
     The primary aspect of the invention is to provide a multi-axle leaf spring suspension system having a compliant equalizer. 
     Other aspects of the invention will be pointed out or made obvious by the following description of the invention and the accompanying drawings. 
     The invention comprises a multi-axle leaf spring suspension having a compliant equalizer. The leaf springs are mounted one behind the other on each side of the vehicle. Adjacent ends of the leaf springs are pivotally attached to the compliant equalizer. The compliant equalizer is pivotally mounted to a vehicle frame. The compliant equalizer comprises a pair of arms that are pivotally connected to each other in a scissor-like fashion. One end of each arm is pivotally connected to the end of a leaf spring. The other end of each arm is cooperatively arranged to contain and compress a spring member between them. The compliant equalizer reduces the magnitude of shocks that would be other wise transmitted to the suspension and frame by absorbing them through compression of the spring member. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and form a part of the specification, illustrate preferred embodiments of the present invention, and together with a description, serve to explain the principles of the invention. 
         FIG. 1  is a side view of a prior art equalizer. 
         FIG. 2  is a side view of the inventive equalizer. 
         FIG. 3  is a top view of the inventive equalizer. 
         FIG. 4  is an end view of the inventive equalizer. 
         FIG. 5  is a side view of a prior art tandem suspension. 
         FIG. 6  is a side view of an inventive suspension. 
         FIG. 7  is a side view of an inventive suspension. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  is a side view of a prior art equalizer. Equalizer (A) comprises a frame (B). Leaf springs (not shown) are pivotally connected to the equalizer by a shaft (not shown) that engages hole (C) and by a shaft (not shown) that engages hole (D), each in a manner known in the art. The equalizer can be pivotally connected to a vehicle frame bracket by a shaft or pin (not shown) that engages frame (B) at hole (E). Equalizer (A) pivots about the shaft in hole (E) as the equalizer absorbs movement in the suspension. Grease zerk (F) may be used to lubricate the joint if necessary. 
       FIG. 2  is a side view of the inventive equalizer. The inventive equalizer comprises arm portions  10 ,  20 . Arm portion  10  comprises an arm  11  and arm  12 . Arm  11  and arm  12  extend substantially radially from pivot portion  13 . Arm  11  and arm  12  describe an angle (θ) between them which angle is centered with respect to pivot portion ( 13 ). 
     Arm portion  20  comprises an arm  21  and arm  22 . Arm  21  and arm  22  extend substantially radially from pivot portion  23 . Arm  21  and arm  22  describe an angle (θ) between them which angle is centered with respect to pivot portion ( 13 ). 
     Angle (θ) is in the range of approximately 10° to approximately 170°. In the preferred embodiment angle θ is in the range of approximately 30° to approximately 60°. 
     Arm portions  10  and  20  pivot with respect to each other in a scissor-like fashion on a common pivot. The common pivot comprises pivot portion  13  and pivot portion  23 . Pivot portion  13  and pivot portion  23  each pivotally engage shaft  130  when installed in a suspension, see  FIG. 6 . 
     A spring member  30  is disposed between arms  12  and  22 . Arms  12  and  22  are aligned with each other in order to capture and contain the spring member  30  which is compressively disposed between them. Protrusions  120  and  220  comprise means to retain spring member  30  between arm  12  and arm  22  in order to prevent lateral movement of spring member  30  during operation of the suspension and equalizer. In normal operation spring member  30  is in compression between arm  12  and arm  22 . 
     Spring member  30  absorbs load inputs to the equalizer as the suspension operates. Spring member  30  provides an additional compliant element in the overall suspension system. Hence, in addition to the leaf springs in a tandem axle system, spring member  30  provides another component having a spring rate that can be used to tune the suspension for a better ride. 
     Spring member  30  may comprise natural or synthetic rubber or other polymeric material. Spring member  30  may also comprise a torsion spring or any other spring which is suitable for the service. 
     An end of each connector ( 40 ,  50 ), see  FIG. 6 , pivotally connects through holes  24  and  14  respectively by way of a shaft that projects through each hole. The other end of each connector ( 40 ,  50 ) is connected to each leaf spring. 
       FIG. 3  is a top view of the inventive equalizer. Referring to axis B-B, portion  140  projects in an “L” shape across axis B-B to a position that is somewhat offset from arm  11 . Portion  240  projects in an “L” shape across axis B-B to a position that is somewhat offset from arm  21 . This arrangement makes the equalizer substantially symmetric about axis B-B which balances the forces experienced by the equalizer during operation, thereby negating any tendency that the equalizer would have to twist. 
     Spring member  30  is captured between arms  12 ,  22 . Arm  22  projects in an “L” shape from arm portion  25  across axis B-B. Arm  12  projects in an “L” shape from arm portion  15  across axis B-B. Hence, when viewed in plan each portion  10 ,  20  “interlocks” with the other in a complementary fashion with respect to axis B-B in order to give the equalizer a symmetric form with respect to axis B-B. This arrangement minimizes the overall size and thickness of the inventive equalizer. 
       FIG. 4  is an end view of the inventive equalizer from  4 - 4  in  FIG. 3 . Arm portion  10  and arm portion  20  symmetrically cooperate about axis B-B. Arm  22  is shown as having a circular form in this view, but may have any shape suitable to accommodate the shape of spring member  30 . Grease zerks (F) may be used to lubricate the joint. 
       FIG. 5  is a side view of a prior art tandem suspension. Leaf spring LS 1  is connected at one end to frame bracket F 2  and at the other end to a connector CO 1 . CO 1  is in turn connected to a shaft that is pivotally engaged through hole (D) in equalizer (A). Leaf spring LS 2  is connected at one end to frame bracket F 3  and at the other end to a connector CO 2 . CO 2  is in turn connected to a shaft that is pivotally engaged through hole (C) in equalizer (A). Equalizer (A) is pivotally connected to frame bracket F 1  by a shaft that is pivotally connected through hole (E). Frame brackets F 1 , F 2 , F 3  are each connected to a vehicle frame (not shown) in a manner known in the art. 
     Axle A 1  is connected to leaf spring LS 1  in a manner known in the art. Axle A 2  is connected to leaf spring LS 2  in a manner known in the art. Either axle may be powered as part of a drive train (not shown). 
     The prior art system shown in  FIG. 5  limits the pivot action of the equalizer (A) to a single rocking movement of the equalizer (A) about hole (E). 
       FIG. 6  is a side view of an inventive suspension. Equalizer  100  is pivotally connected to frame bracket F 1  by shaft  130 . It is understood that  FIG. 6  shows one side of a vehicle suspension, a like arrangement being present on the other side of the vehicle. 
     Leaf spring end LS 10  is pivotally connected to one end of connector  40 . Another end of connector  40  is pivotally connected to hole  24  by shaft  240 . Connector  40  displaces end LS 10  some distance from hole  24  thereby creating a linkage having another degree of freedom of movement over the prior art for leaf spring LS 1  and therefore for the suspension as well. 
     End LS 20  is pivotally connected to one end of connector  50 . Another end of connector  50  is pivotally connected to hole  14  by shaft  140 . Connector  50  displaces end LS 20  some distance from hole  14  thereby creating a linkage having another degree of freedom of movement over the prior art for leaf spring LS 2  and therefore for the suspension as well. 
     As a vehicle travels on a road the suspension absorbs movement of axles A 1  and A 2  by flexing of each of the leaf springs LS 1  and LS 2 , as well as by the relative movement of arm portions  10  and  20  through compression and expansion of spring member  30 . Further, equalizer  100  pivots about shaft  130  to absorb and transmit differential movement of the two axles. Spring member  30  acts as a shock absorber and also damps vibrations that may otherwise be transmitted to the vehicle frame though F 1 . 
     Since the compliant equalizer comprises two arm portions that pivot to a certain extent independently about the common pivot, the inventive suspension takes advantage of two pivot arms ( 10 ,  20 ) (were there is only one in the prior art equalizer (A)) that are connected through the spring member  30 . Hence, in the inventive suspension the end of each leaf spring (LS 10 , LS 20 ) moves somewhat independently of the other since each is only connected to a single arm portion ( 10 ,  20 ), thereby increasing the available range of movement of the suspension. However, equalizing loads are still transmitted through the equalizer, just in a less damaging manner by virtue of the compliant spring member. 
       FIG. 7  is a side view of an inventive suspension. In the case of a multi-axle suspension having more than two axles, the arrangement described herein is simply repeated for each additional axle, namely, another equalizer is disposed between each pair of leaf springs on each side of the vehicle as shown in  FIG. 6 . For example, in the case of a third axle A 3  mounted on leaf spring LS 3 , another equalizer  200  is pivotally mounted on frame bracket F 2 . Leaf spring LS 3  is connected at one end to connector  60  and thereby to equalizer  200 , and at the other end to frame bracket F 4 . Instead of being connected to frame bracket F 2  as in  FIG. 6 , an end of leaf spring LS 1  is connected to connector  70  and thereby to equalizer  200 . The suspension is otherwise as described in this specification. 
     Although forms of the invention have been described herein, it will be obvious to those skilled in the art that variations may be made in the construction and relation of parts without departing from the spirit and scope of the invention described herein.