Vehicle twist axle assembly

The twist axle assembly includes a pair of spaced apart trailing arms and a twist beam of which extends in a first direction between the trailing arms. The twist beam includes a pair of end portions and a middle portion. The twist beam further has a pair of side walls and at least one additional wall that extends between the side walls. The side walls in the middle portion are generally parallel with the side walls of the end portions. The twist beam is generally hour-glass shaped with the middle portion having a first width and the end portions have a greater second width. The twist beam also tapers from the first width of the middle portion to the second widths of the end portions for gradually increasing a torsional stiffness from the middle portion to the end portions.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is related, generally, to vehicle twist axle assemblies.

2. Related Art

A twist beam rear axle suspension assembly, also known as a torsion axle assembly, is a type of automobile suspension system including a pair of trailing arms, each of which is coupled with a wheel of a vehicle and with an axle of the vehicle, and a twist beam which extends transversely between the trailing arms. During operation of the vehicle, the twist beam deforms in a twisting movement when one of the wheels moves relative to another, such as during vehicle body roll or when one of the wheels encounters, for example, a pothole or an obstacle in a road. The twisting movement of the twist beam absorbs this movement to make the ride more comfortable for occupants in the vehicle body.

In order to provide the twist axle assembly with desirable performance characteristics, the entire length of the twist beam is provided with a relatively low torsional stiffness as compared to the trailing arms, thereby allowing the trailing arms to pivot relative to one another. However, this configuration may result in abrupt changes in torsional stiffness about the twisting axis at the joints between the twist beam and the trailing arms, and these abrupt changes in the torsional stiffness of the twist axle assembly at these joints could compromise the structural integrity of the joints.

One approach to improve the structural integrity of the joints between the twist axle and the trailing arms is to vary the torsional stiffness of the twist axle so as to reduce the differences in the torsional stiffnesses of the twist beam and the trailing arms at the joints. For example, one type of twist beam is configured with a crush tube design where the center area is generally V-shaped with angled, double walls and opposite end portions have closed geometrical shapes. The V-shaped center portion has a relatively lower torsional stiffness than the rectangular or circular end portions, and the twist axis is also provided with intermediate sections which transition between the V-shaped center portion and the stiffer end portions. Another approach is to add pieces to the twist beam adjacent the trailing arms to make the transition more gradual.

SUMMARY OF THE INVENTION AND ADVANTAGES

One aspect of the present invention is for a twist axle assembly for use in a vehicle. The twist axle assembly includes a pair of spaced apart trailing arms and a twist beam of a single piece which extends in a first direction between opposite ends that are operably connected with the trailing arms. The twist beam includes a pair of end portions and a middle portion which extends between the end portions. The twist beam further has a pair of side walls and at least one additional wall that extends between the side walls. The twist beam is generally hour-glass shaped with the middle portion having a first width in a second direction that is generally transverse to the first directions and the end portions have a greater second width in the second direction. The twist beam also tapers from the first width of the middle portion to the second widths of the end portions for gradually increasing a torsional stiffness from the middle portion to the end portions.

In use, the reduced torsional stiffness of the twist beam in the middle portion causes the majority of the twisting stresses from relative rotation of the trailing arms to be absorbed by the middle portion of the twist beam. This has the effect of protecting the joints between the ends of the twist beam and the trailing arms from damage that could result from twisting in the end portions. Additionally, the generally parallel relationship between the side walls of the middle portion and the end portions allows the twist beam to be made very cost effectively through stamping.

According to another aspect of the present invention, the side walls of the middle portion are generally parallel with the side walls in the end portions.

According to yet another aspect of the present invention, the side walls of the middle portion are within three degrees of being exactly parallel with the side walls in the end portions.

According to still another aspect of the present invention, the twist beam has a top wall and a bottom wall, and the middle portion has an opening formed into the bottom wall for further reducing the torsional stiffness of the middle portion in comparison to the end portions.

According to a further aspect of the present invention, the side walls of the middle portion include a plurality of apertures for further reducing the torsional stiffness of the middle portion in comparison to the end portions.

According to yet a further aspect of the present invention, the twist beam is generally U-shaped with the wall extending between the side walls being a top wall.

According to still a further aspect of the present invention, the ends of the twist beam are secured with the trailing arms through welding.

According to another aspect of the present invention, at least a portion of each of the end portions of the twist beam has a closed geometric profile.

Another aspect of the present invention is related to a method of making a twist axle assembly for a vehicle. The method includes the step of providing a pair of trailing arms. The method continues with the step of stamping a workpiece of sheet metal into a twist beam. The as-stamped twist beam has a pair of end portions and a middle portion that extends in a first direction between the end portions. The twist beam further includes a pair of side walls and at least one additional wall that extends between the side walls. Also, the twist beam is generally hour-glass shaped with the middle portion having a first width in a second direction, which is generally transverse to the first direction, and the end portions have a greater second width in the second direction. The twist beam tapers from the first width of the middle portion to the second widths of the end portions for gradually increasing a torsional stiffness of the twist beam from the middle portion to the end portions. The method proceeds with the step of attaching the twist beam with the trailing arms.

According to another aspect of the present invention, the side walls in the middle portion of the twist beam are generally parallel with the side walls in the end portions.

According to still another aspect of the present invention, the twist beam has a top wall and a bottom wall, and the middle portion has an opening formed into the bottom wall for further reducing a torsional stiffness of the middle portion in has an opening formed into the bottom wall for further reducing the torsional stiffness of the middle portion in comparison to the end portions.

According to a further aspect of the present invention, the side walls of the middle portion include a plurality of apertures for further reducing the torsional stiffness of the middle portion in comparison to the end portions.

According to yet a further aspect of the present invention, at least a portion of each of the end portions of the twist beam has a closed geometric profile.

According to still a further aspect of the present invention, the step of attaching the twist beam with the trailing arms is further defined as welding the twist beam with the trailing arms.

DESCRIPTION OF THE ENABLING EMBODIMENT

Referring to the Figures, wherein like numerals indicate corresponding parts throughout the several views, a first exemplary embodiment of an improved twist axle assembly20for a vehicle suspension system is generally shown inFIGS. 1-6. The twist axle assembly20includes a pair of trailing arms22and a twist beam24(also known as a cross-member) that extends in a lateral direction (which, in use, corresponds with a lateral direction of a vehicle) between the trailing arms22. The trailing arms22are configured for attachment with opposing wheels of the vehicle, and in use, the trailing arms22pivot relative to one another in response to the vehicle rolling while cornering at speed or in response to the wheels encountering an object, such as a pot hole. The twist beam24resists the relative rotation of the trailing arms22to reduce roll and generally improve the performance of the vehicle's dynamics.

The twist beam24extends in a first direction between opposite ends and includes a pair of opposing end portions26and a middle portion28which extends between the end portions26. The exemplary twist beam24is generally symmetrical in shape about a lateral midpoint of the twist beam24. The end portions26of the twist beam24are connected with the trailing arms22for allowing the trailing arms22to rotate relative to one another during operation of the vehicle. The trailing arms22could have any suitable shapes or configurations. Both the twist beam24and the trailing arms22are preferably made of metal (such as, for example, steel, steel alloy, aluminum, aluminum alloys, magnesium, magnesium alloys, etc.).

Referring still toFIG. 2, in the exemplary embodiment, the end portions26of the twist beam24are provided with spaced apart side walls30that have U-shaped recesses32formed therein. The U-shaped recesses32are shaped similarly to outer mating surfaces on the trailing arms22for establishing so-called “glove” connections with the trailing arms22. Specifically, the trailing arms22are slid into the U-shaped recesses32on the end portions26, and then these two components are welded together (for example, through MIG welding, TIG welding, laser welding, etc.).

Referring now toFIG. 4, the exemplary twist beam24is generally hour-glass shaped in that it has a variable width along its length to vary a torsional stiffness of the twist beam24between the ends. Specifically, a portion of the middle portion28, including a lateral midpoint of the twist beam24, has a first width W1, and a portion of each of the end portions26has a second width W2that is greater than the first width W1adjacent the end portions26. The twist beam24transitions gradually from the lesser first width W1of the middle portion28to the greater second widths W2of the end portions26for gradually increasing the torsional stiffness of the twist beam24from the middle portion28to the end portions26. This is advantageous because, during use, the majority of the twisting of the twist beam24occurs in the middle portion28with the lower torsional stiffness, thereby improving the durability of the weld joints between the twist beam24and the trailing arms22by protecting the weld joints from damage that could occur from twisting in the end portions26.

As shown, the end portions26of the twist beam24have closed (or nearly closed) geometrical profiles, and the middle portion28has an open, and uncrushed, geometrical profile. Specifically, the end portions26have generally rectangular shapes with a top wall34and a bottom wall36that extend between the side walls30, and the middle portion28is generally U-shaped. In contrast to crushed tube-style twist beams, the exemplary middle portion28is single walled, and the open geometrical configuration is provided by an opening38in the bottom wall36. This configuration further reduces the torsional stiffness of the middle portion28in comparison to the end portions26to further protect the weld joints between the twist beam24and the trailing arms22. The opening38is generally elliptical or oval in shape such that the torsional stiffness of the twist beam24transitions gradually from a minimum torsional stiffness at an approximate midpoint of the middle portion28to the end portions26, and the opening38extends at least partially into the side walls30(as shown inFIGS. 5 and 6). As also shown inFIGS. 5 and 6, in the middle portion28, the side walls30of the exemplary twist beam24are provided with holes40, or openings, that are spaced from one another in the first direction to further reduce the torsional stiffness of the middle portion28in comparison to the end portions26and thereby further protect the weld joints between the twist beam24and the trailing arms22.

The side walls30in the middle portion28extend parallel or nearly parallel with one another and with the side walls30of the end portions26. Specifically, in the exemplary embodiment, the side walls30of the middle portion28are angled relative to the side walls30of the end portions26by less than approximately three degrees (3°). This angle range allows for a stamping die draft during the manufacturing of the twist beam24to allow for low cost and highly efficient manufacturing.

Referring now toFIGS. 7-12, a second exemplary embodiment of the twist axle assembly120is generally shown with like numerals, separated by a prefix of “1”, indicating corresponding parts with the first exemplary embodiment described above. The second exemplary embodiment is distinguished from the first exemplary embodiment in that the twist beam124is generally U-shaped along its entire length. That is, as shown inFIG. 10, the twist beam124of the second exemplary embodiment lacks a bottom wall. Since the twist beam124of this embodiment lacks a bottom wall, the opening138for reducing the torsional stiffness of the middle portion128is only in the side walls130. Similar to the first exemplary embodiment described above, at least a portion of the middle portion128of the twist beam124has a first width W1which is less than a second width W2at the end portions126. Additionally, the second embodiment is distinguished from the first embodiment in that while the side walls130of the middle portion128do extend in parallel with the side walls130of the end portions126, the side walls130of each of the end and middle portions128are angled relative to one another.

Another aspect of the present invention is a method of making a twist axle assembly20for use in a vehicle suspension system. The method includes the step of providing a pair of trailing arms22. The method continues with the step of stamping a workpiece (such as a generally planar blank) into a twist beam24with a pair of end portions26and a middle portion28that extends in a first direction between the end portions26. The twist beam24has a pair of side walls30and at least one additional wall that extends between the side walls30. The side walls30in the middle portion28are generally parallel with the side walls30in the in the end portions36. The twist beam24is generally hour-glass shaped with the middle portion28having a first width W1in a second direction, which is generally transverse to the first direction, and the end portions26have a greater second width W2in the second direction. The twist beam24tapers from the first width W1in the middle portion28to the second width W2of the end portions26for gradually increasing a torsional stiffness of the twist beam24from the middle portion28to the end portions26. The method proceeds with the step of attaching the end portions of the twist beam24with the trailing arms22.