TRAILING ARM SUSPENSION WITH WRAPPER COMPRESSION AXLE MOUNTING

Abstract: A vehicle suspension system for mounting ground-engaging wheels to a vehicle frame (10) where two arms (18) are secured to opposite sides of the frame and a wheel-carrying axle (12) is suspended between the arms. The axle is secured to the arms by a wrapper plate (34) partially surrounding the axle, adapter plates (39) mounted to the interior surface of the wrapper plate and at least one bolt (38) to compress the wrapper about the axle and the adapter plate against the axle. In this configuration, the wrapper plate supports and strengthens the axle. The wrapper plate generally conforms to the profile of that portion of the axle which it surrounds. The axle can be square, oval, hexagon, octagon, rectangular or D-shaped in cross section. The wrapper plate and the adapter plates exert substantially transverse forces on the axle. An aperture (42) is formed in the wrapper plate in the side thereof in a location corresponding to the vertical midpoint of the adjacent side of the axle. A circular washer (44) is welded to the axle on each side thereof in registry with the apertures in the side of the wrapper plate to prevent lateral translation of the wrapper plate with respect to the axle.

Description: TRAILING ARM SUSPENSION WITH WRAPPER COMPRESSION AXLE MOUNTING BACKGROUND OF THE INVENTION Technical Field This invention relates to vehicle suspension systems for mounting ground-engaging wheels to a vehicle frame, and, more particularly, to a trailing arm suspension axle in which a wheel-carrying axle is secured to a trailing arm. In one of its aspects, the invention relates to a method of mounting an axle support assembly on an axle for ground-engaging wheels. Description of Related Art In U.S. Patent No. 4,693,486 to Pierce, et al. (issued September 15, 1987), a trailing arm suspension has an axle secured to a trailing arm by a wrapper plate partially surrounding the axle, a bolt is utilized to compress the wrapper plate about the axle so that the wrapper plate supports and strengthens the axle, and a circular plug weld attaches the wrapper plate to the axle. The U.S. Patent No. 3,547,215 to Bird (issued December 15, 1970) discloses a trailing arm suspension wherein a square axle is typically welded to a bracket which is, in turn, secured to the trailing arm of the vehicle suspension structure. The weldment securing the axle to the bracket is usually made at the midpoint of the side of the axle where vertical bending moment stresses are neutral. Axles are typically welded to the brackets in order to attach the axle to the bracket under high loading conditions. The axle is welded to the axle bracket by a line weld on either side of the bracket. Because it is a line weld, the weldment has "ends" at which stresses are concentrated and at which cracks may initiate. The U.S. Patent No. 5,116,075 to Pierce discloses a trailing arm suspension with a wrapper compression axle mounting similar to the Pierce et al. '486 patent except that the aperture in the wrapper plate is eliminated and blocks are welded to the axle adjacent the wrapper plate to prevent lateral translation of the wrapper plate with respect to the axle. Although this arrangement is relatively satisfactory, it has been found that the blocks may give rise to stress cracks at the points where the blocks are welded to the axle. It has been found that the highest stress points in this suspension were at the edges of the wrapper plate where the blocks are positioned and that these stresses cause the greatest strains on the axle at that point. It has further been found that at the axial midpoint of the wrapper on the vertical center of the axle, minimal strains on the axle appear. SUMMARY OF THE INVENTION The invention relates to a vehicle suspension system for mounting ground-engaging wheels to a vehicle frame and to a method for mounting an axle support assembly to an axle. The suspension system comprises at least two substantially rigid arms secured to opposite sides of the frame. The arms are secured to the vehicle frame through substantially aligned pivot mounts. At least one wheel-carrying axle is mounted to the arms. A wrapper plate having an elongated planar complementary surface wraps around the axle at least 180°. Opposite sides of the wrapper plate extend beyond the lower portion of the axle. At least one bolt extends through the wrapper plate at the depending opposite sides thereof for diametrically compressing opposite sides of the axle. According to the invention, the wrapper plate has at least one aperture positioned in a side of the wrapper plate in a position at about the vertical midpoint of the axle. A washer is welded to the axle and is in register with the wrapper plate aperture to prevent lateral shifting of the wrapper plate with respect to the axle. Preferably, the washer is annular shaped and is welded to the axle through welds at a central opening in the washer. In a preferred embodiment, the wrapper plate aperture is at an axial central portion of the wrapper plate. BRIEF OF DESCRIPTION OF THE DRAWINGS The invention will now be described in detail with reference to the accompanying drawings wherein: FIG. 1 is a fragmentary, side elevational view of a vehicle frame having mounted thereon a suspension system according to the invention; FIG. 2 is an enlarged, fragmentary side sectional view of the suspension shown in FIG. 1; FIG. 3 is a sectional view taken along line 3-3 in FIG. 2; and FIG. 4 is a sectional view taken along line 4-4 in FIG. 3. DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings and to FIG. 1 in particular, a vehicle frame 10 has an axle 12 and ground-engaging wheels 14 (shown in phantom lines) suspended therefrom by a suspension system 16 according to the invention. The front of the vehicle is to the left of the frame as viewed in FIG. 1. Suspension system 16 includes, at each side of the vehicle frame 10, a trailing arm 18 pivotally mounted to a hanger bracket 20 depending from frame 10. The hanger 20 has a pivot pin 22 at the lower end thereof for pivotably supporting the forward end of trailing arm 18. Trailing arm 18 comprises a hollow rectangular member for supporting the axle 12. The forward end of trailing arm 18 is pivotably mounted at pivot pin 22. The trailing arm 18 extends rearward along the vehicle frame 10. The rear end of the trailing arm 18 is secured to an air spring 24. Trailing arm 18 has a slight downward bend intermediate between its forward and rear ends. A forward bushed pin 26 and a rear bushed pin 28 extend through trailing arm 18 near the slight downward bend therein for supporting an axle support assembly 30 while permitting limited articulation between the axle support assembly 30 and the trailing arm 18. The upper portion of the air spring 24 is fixedly secured to the vehicle frame 10. In operation, vertical movement of the ground-engaging wheels 14 is translated through axle 12 to the axle support assembly 30. Vertical movement of axle support assembly 30 is translated to trailing arm 18 through forward bushed pin 26 and rear bushed pin 28. Referring to FIG. 3, a bushing 29 encases bushed pins 26, 28. The limited articulation permitted between axle support assembly 30 and trailing arm 18 by the bushing 29 of forward bushed pin 26 and rear bushed pin 28 cushions the vertical movement of the trailing arm 18 and controls the roll rate of the suspension by permitting axle support assembly 30 to make small vertical and conical displacements relative to trailing arm 18. Significant vertical displacement of axle support assembly 30 causes the vertical displacement of trailing arm 18. Vertical movement of trailing arm 18 is permitted by the pivotal connection of the forward end of trailing arm 18 at the pivot pin 22. The vertical movement of trailing arm 18 is cushioned and restrained by air spring 24 and a shock absorber (not shown). The axle support assembly 30 comprises a pair of side plates 32 disposed on either side of trailing arm 18, a U-shaped wrapper plate 34 depending from the side plates 32, a reinforcing plate 36, a bolt 38 and adapter plates 39. The bolt 38 passes through the end of the U-shaped wrapper plate 34 for compressing the sides of the wrapper plate 34. Each side plate 32 comprises a vertical plate having openings at the upper portion thereof to receive forward bushed pin 26 and rear bushed pin 28. The forward bushed pin 26 and rear bushed pin 28 extend through trailing arm 18 and through corresponding openings in the pair of side plates 32 disposed on either side of trailing arm 18 to secure side plates 32 to trailing arm 18 thereby supporting the axle support assembly 30 while permitting limited articulation between the side plates 32 and trailing arm 18. In addition, each side plate 32 has a U-shaped opening adapted at the lower portion thereof to receive in complimentary fashion the bight portion of U-shaped wrapper plate 34. The side plate 32 thereby acts to both provide a surface to which wrapper plate 34 may be secured as by welding and also acts to reinforce wrapper plate 34. Wrapper plate 34, as seen in FIG. 3, is a saddle-shaped plate. As seen in FIG. 2, the wrapper plate 34 is a of U-shaped cross-section. The bight portion of the wrapper plate 34 is disposed upwardly within side plates 32 and the open end of wrapper plate 34 extends downwardly. Wrapper plate 34 is secured to side plates 32 by suitable means such as welding. Wrapper plate 34 is shaped to snugly receive the axle 12 having a square, rectangular or other non-circular cross sectional configuration with a small space between the upper surface of the axle and the inside surface of the wrapper plate 34. As can be seen in FIG. 3, wrapper plate 34 has an aperture 40 in the bight portion of the U-shaped wrapper plate 34 to reduce the overall weight of the axle support assembly 30, to increase the flexibility of the wrapper plate 34 and to provide trailing arm clearance. Wrapper plate 34 includes bolts 38 extending through the sides of the U-shaped wrapper plate 34. When assembled, the bolts 38 are positioned beneath the axle 12 and are adapted to place the side of the U-shaped wrapper plate 34 in compression against the axle 12 when the bolts 38 are tightened. Adapter plates 39 are incorporated to enhance the gripping effect of the wrapper plate 34 on the axle 12. The adapter plates 39 are fixedly attached to the interior surface of wrapper plate 34 at a point just below the opening in wrapper plate 34 for bolts 38. The adapter plates 39 are U-shaped in cross section with two upstanding leg portions 31 and a bight portion 33. The adapter plates 39 are mounted such that the upper surface of the two upstanding leg portions 31 contact the lower surface of the axle 12. Axle support assembly 30 also includes a reinforcing plate 36 secured as by welding to side plate 32 and wrapper plate 34 for supporting and reinforcing wrapper plate 34. A shock absorber bracket 37 is provided at the inner side plate 32 for securing a lower portion of a shock absorber (not shown) to dampen oscillations of the axle 12. Although the axle support assembly 30 is described in the preferred embodiment as a plurality of plates fixedly attached to one another by suitable means such as welding, it can also be easily understood that a single axle support assembly could be formed by a casting. According to the invention, the wrapper plate includes at least one and preferably two apertures 42 in the sides thereof at a position at approximately the vertical midpoint of the axle 12. An annular washer 44 is welded to the axle at a vertical midpoint of the axle 12 and in register with the aperture 42. The washer 44 has a central aperture 46. Preferably, the washer 44 is welded to the axle at the aperture 46 through welds 48. The external diameter of the washer 44 closely resembles the interior diameter of the aperture 42 and extends into the aperture to prevent relative lateral shifting between the wrapper plate 34 and the axle 12. The welding of the washer 44 to the axle 12 at the midpoint of the axis and centrally with respect to the wrapper plate 34 minimizes the stresses between the wrapper plate and the axle 12 to prevent shifting of the wrapper plate 34 with respect to the axle 12. If desirable, the apertures 42 in the wrapper plate 34 can be axially offset from one another and the washers 44 can likewise be welded to the axle at axially displaced locations with respect to each other. In operation, the axle 12 is secured within the wrapper plate 34 by first inserting the axle 12 into the U-shaped complementary wrapper plate 34 and then clamping the axle 12 forcibly into wrapper plate 34. Bolt 38 is tightened until the wrapper plate 34 is snug against axle 12. Then, the adapter plates 39 are fixedly attached as by welding to the interior surface of the wrapper plate 34 such that the upstanding leg portions 31 contact the lower surface of the axle 12. With the adapter plates 39 securely in place, the bolt 38 is further tightened to create compressive forces on the axle 12. As the bolt 38 is tightened, as shown in FIG. 2, the sides of the wrapper plates exert a first diametric compressive force on the complementary sides of the axle 12 in the direction of arrow Fl. The tightening of bolt 38 also causes the depending ends of the U-shaped wrapper plate 34 to bend or flex inward. This inward bending results in a slight rotation of the bottom of the wrapper plate about the bottom corners of the axle 12 to introduce a horizontal component of movement into the bottom end of the wrapper plate 34. This inward bending of wrapper plate 34 at the ends thereof results in the application of a vertical component of force F2, on axle 12 by adapter plates 39. Thus, the horizontal force on the ends of the U-shaped wrapper plate 34 is translated into a second compressive force F2, which is transverse to the first force Fl. The transverse compression force F2 exerted by the adapter plates 39 on the axle along with the compression force Fl exerted along the internal faces of wrapper plate 34 provide sufficient gripping strength for the axle support assembly 30 on the axle 12, and strengthens the axle against torsional stresses and bending stresses. As illustrated in FIG. 3, the washer 44 is aligned with the opening 42 in the wrapper plate 34. Preferably, the wrapper plate 34 contains two apertures, one on each side of the axle and further comprises two washers 44, each in register with an aperture. The washers 44 are positioned in the apertures 42 and are welded in place by plug welds 48 between the washer and the axle 12. As illustrated in FIG. 3, the welds 48 are positioned preferably in the central opening 46 of the washer 44. The welding of the washer 44 onto the axle 12 should take place after the U-shaped wrapper plate 34 is completely attached to the axle 12. Other axle shapes such as D-shaped, hexagon, octagon, and rectangular can be used in accordance with the invention by simply modifying the configuration of the wrapper plate to conform to the cross section of the axle. The invention overcomes the problem of potential stress fractures at the ends of the wrapper plate and provides a simple and expedited method of assembling a suspension system according to the invention with a minimum of effort. The suspension system is more effective than the suspension systems of the prior art. Reasonable variation and modification are possible within the scope of the foregoing disclosure without departing from the spirit of the invention which is defined in the appended claims.

Claims: CLAIMS The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows: 1. In a vehicle suspension for mounting ground-engaging wheels to a vehicle frame, the suspension system comprising at least two substantially rigid arms secured to opposite sides of the frame through substantially aligned pivot mounts; at least one wheel-carrying axle mounted to said arms through a wrapper plate having an elongated planar complementary surface wrapping at least 180° around said axle and depending opposites sides extending beyond said axle; and at least one bolt for diametrically compressing said axle by drawing said opposite sides of said wrapper plate toward each other; the improvement comprising; an aperture in at least one side of the wrapper plate; a washer in the aperture and welded to the axle; the lateral dimension of the washer generally conforms to the lateral dimension of the aperture to prevent lateral shifting of the wrapper plate with respect to the axle. 2. A vehicle suspension system according to claim 1 wherein the aperture in the wrapper plate is circular in configuration and the washer is circular in configuration. 3. A vehicle suspension system according to claim 2 wherein the washer is annular in configuration and the washer is welded to the axle at a central opening in the washer. 4. A vehicle suspension system according to claim 1 wherein the aperture is positioned at an axial central portion of the wrapper plate. 5. In a method for mounting an axle support assembly on an axle for ground-engaging wheels comprising the steps of; inserting an axle in an elongated planar complementary surface of a wrapper plate having at least one aperture; inserting a bolt through opposite sides of said wrapper plate; tightening said bolt until said wrapper plate makes contact with the opposite sides of the axle; the improvement which comprises: placing a washer in the at least one aperture in the wrapper plate, and welding the washer to the axle. 6. A method for mounting an axle support assembly on an axle for ground-engaging wheels according to claim 5 wherein the washer has a cross dimension approximately equal to a cross dimension of the at least one aperture to prevent lateral shifting of the wrapper plate with respect to the axle. 7. A method for mounting an axle support assembly on an axle for ground-engaging wheels according to claim 6 wherein the washer is annular in configuration and the welding step comprises placing a weld bead in a central opening of the washer.

Inventors: PIERCE WILLIAM C, PIERCE, WILLIAM, C.
Applicants: NAI NEWAY INC, PIERCE WILLIAM C, NAI NEWAY, INC., PIERCE, WILLIAM, C.
Application year: 1995
Main classification: B60G9
IPC codes: B60G9, B60G21