Title of Invention

"TORSION BEAM SUSPENSION"

Abstract

A torsion beam suspension incorporating paired trailing arms disposed apart from each other in the lateral direction of a vehicle, having front ends pivotally supported by a car body and rear ends for rotatively supporting wheels; and a torsion beam extending in the lateral direction of the vehicle and integrally connecting the trailing arms to each other. The torsion beam has a U-shape cross section formed of a U-shape warped portion, an upper flat portion and a lower flat portion and substantially opened in the longitudinal direction of the vehicle, the lower flat portion has a width in the longitudinal direction of the vehicle which is larger than the width of the upper flat portion in regions adjacent to the two ends of the torsion beam, and each of the regions includes a portion which is most easily deformed when a lateral force acts on the wheels.

Full Text

The present invention relates to a suspension of a vehicle, such as an automobile, and more particularly, to a torsion beam suspension. BACKGROUND In general, the torsion beam suspension incorporates paired trailing arms disposed apart from each other in the lateral direction with respect to the car axis, pivotally supported by the car body at front portions thereof and having rear portions for rotatively supporting wheels. Moreover, the torsion beam suspension incorporates a torsion beam extending in the lateral direction of the vehicle and having two ends welded to the paired trailing arms by welding. When the right and left wheels are bounded and rebounded in opposite phases, the right and left trailing arms are vertically and pivotally moved in opposite directions around the front ends thereof. As a result, the torsion beam is elastically twisted by the trailing arm so that the force for preventing the bounding and rebounding of the wheels is generated. As an example of the torsion beam suspension of the foregoing type, a torsion beam suspension has been disclosed in Japanese Utility-Model Laid-Open No. 58-90814. According to the foregoing disclosure, a torsion beam has a U-shape cross section formed of a U-shape warped portion, an upper flat portion and a lower flat portion and opened substantially in the rear (longitudinal) direction of the vehicle. Moreover, the width of the lower flat portion in the longitudinal direction of the vehicle is larger than the width of the upper flat portion in the longitudinal direction of the vehicle over the length of the torsion beam. The torsion beam suspension disclosed as described above is arranged so as to increase the strength of the lower flat portion of the torsion beam, on which tensile stress is exerted when a downward load is exerted on the vehicle. Therefore, the durabilit\ of the torsion beam can be improved as compared with a structure that the width of each of the upper flat portion and the lower flat portion in the longitudinal direction is the same. In a case of a usual torsion beam suspension, portions adjacent to the two ends of the torsion beam are most likely deformed when great lateral force acts on the vehicle when, for example, the vehicle collides with a curbstone. The torsion beam suspension disclosed as described above and incorporating the torsion beam, which has the predetermined cross sectional shape over the length thereof however, suffers from a problem of an unsatisfactory weight efficiency from a viewpoint of improving the strength against the lateral force of the wheel. Further, since the center of shearing of the cross section of the torsion beam is lowered, there arises another problem in which the roll steer of the vehicle tends to become oversteer. The main object of the present invention is to improve the weight efficiency relating to increase in the strength against lateral force of the wheels and prevent oversteering of roll steering of the vehicle. To achieve the said objective, this invention provides a torsion beam suspension including paired trailing arms disposed apart from each othef in the lateral direction of a vehicle, having front ends pivotally supported by a car body and rear ends for relatively supporting wheels, and a torsion beam extending in the lateral direction of the vehicle and integrally connecting the trailing arms to each other, characterized in that the torsion beam is defined by a U-shape cross section formed of a U-shape warped, portion, an upper flat portion and a lower flat portion, substantially opened in the longitudinal direction of the vehicle, and the lower flat portion has a width in the longitudinal direction of the vehicle which is larger than the width of the upper flat portion in regions adjacent to the two ends of the torsion beam. Since the foregoing embodiment has the structure in which the torsion beam has the U-shape cross section formed of a U-shape warped portion, an upper flat portion and a lower flat portion and substantially opened in the longitudinal direction of the vehicle and the lower flat portion has a width in the longitudinal direction of the vehicle which is larger than the width of the upper flat portion in regions adjacent to the two ends of the torsion beam, the strength of the portion adjacent to each of the two ends of the torsion beam which is most likely to be deformed when lateral force acts on the wheels can effective!) be increased. Therefore, the weight efficiency for increasing the strength of the torsion beam can be improved as compared with the conventional structure. Further, the depth of the U-shape cross section at each of the two ends of the torsion beam is gradually enlarged in a direction toward each of the two ends of the torsion beam, and the region includes a boundary portion between a portion in which the depth of the U-shape cross section is constant and a portion in which the depth of the U-shape cross section is gradually enlarged. As a result of the foregoing structure, the boundary portion which is one of portions which are most likely to be deformed when lateral force acts on the wheels can reliably be strengthened without lowering the center of shearing of the other regions. Further, the torsion beam has a cut portion formed in the bottom of the U-shape cross section at a position adjacent to each of the two ends thereof, and the region includes the portion in which the cut portion has been formed. As a result, the cut portion which is one of portions which are most likely to be deformed when lateral force acts on the wheels can reliably be strengthened without lowering of the center of shearing of the other regions. A structure may be employed in which the depth of the U-shape cross section at each of the two ends of the torsion beam is gradually enlarged in a direction toward each of the two ends of the torsion beam, and the cut portion is formed in the vicinity of a boundary portion between a portion in which the depth of the U-shape cross section is constant and a portion in which the depth of the U-shape cross section is gradually enlarged. The region may include the boundary portion and the portion in which the cut portion has been formed. Further, the width of the lower flat portion in the longitudinal direction of the vehicle is maximum in substantially the central portion in the region, and the width is gradually reduced in a direction toward each of the two ends of the region. The said region includes a portion, which is most easily deformed when a lateral force acts on the wheels. According to the second embodiment of the present invention, there is provided a torsion beam suspension including paired trailing arms disposed apart from each other in the lateral direction of a vehicle, having front ends pivotally supported by a car body and rear ends for rotatively supporting wheels, and a torsion beam extending in the lateral direction of the vehicle and integrally connecting the trailing arms to each other, characterized in that the torsion beam has a U-shape cross section substantially opened in the longitudinal direction of the vehicle, and the length of the torsion beam in a direction perpendicular to the lengthwise direction is made such that the length of an end downward of the bottom portion of the U-shape cross section is longer than the length of a portion upward of the bottom portion in a region adjacent to each of the two ends of the torsion beam. The foregoing embodiment has the structure in which the torsion beam has a U-shape cross section substantially opened in the longitudinal direction of the vehicle. Moreover, the length of the torsion beam in a direction perpendicular to the lengthwise direction is made such that the length of an end downward of the bottom portion of the U-shape cross section is longer than the length of a portion upward of the bottom portion in a region adjacent to each of the two ends of the torsion beam. Therefore, the portion adjacent to each of the two ends of the torsion beam which is one of portions which axe most likely to be deformed when lateral force acts on the wheels can reliably be strengthened. The length of the end downward of the bottom portion of the U-shape cross section is maximum in substantially the central portion of the region, and the length is gradually reduced in a direction toward each of the two end of the region. The said region includes a portion which is most likely to be deformed when a lateral force acts on the wheels. According a third embodiment of the present invention, there is provided a torsion beam suspension including paired trailing arms disposed apart from each other in the lateral direction of a vehicle, having front ends pivotally supported by a car body and rear ends for rotatively supporting wheels, and a torsion beam extending in the lateral direction of the vehicle and integrally connecting the trailing arms to each other, characterized in that the torsion beam has a U-shape cross section defined by a U-shape warped portion, an upper flat portion and a lower flat portion and substantially opened in the longitudinal direction of the vehicle, and the lower flat portion has a width in the longitudinal direction of the vehicle which is larger than the width of the upper flat portion in regions in which change in the section modulus of the torsion beam is greater than the section modulus of the other portions. The foregoing embodiment has the structure in which the torsion beam has a U-shape cross section formed of a U-shape warped portion, an upper flat portion and a lower flat portion and substantially opened in the longitudinal direction of the vehicle; and the lower flat portion has a width in the longitudinal direction of the vehicle which is larger than the width of the upper flat portion in regions in which the change in the section modulus of the torsion beam is greater than the section modulus of the other portions. Therefore, the region which is most likely to be deformed when lateral force acts on the wheels can effectively be strengthened. According to the first to third embodiments, the center of shearing of the regions of the torsion beam except for the predetermined region is not lowered, as compared with the structure in which the lower flat portion has a width in the longitudinal direction of the vehicle which is larger than the width of the upper flat portion over the length of the torsion beam. Therefore, roll-steering and over-steering of the vehicle can be prevented. The invention will now be described with reference to the accompanying drawings. FIG. 1A is a plan view showing an embodiment of a torsion beam suspension according to the present invention, and FIG. IB is a rear view showing the embodiment; FIG. 2 is an enlarged and partial plan view showing a right-hand trailing arm and a portion of a torsion beam; FIG. 3 is an enlarged and partial rear view showing the right-hand trailing arm and a portion of the torsion beam; FIG. 4 is an enlarged and partial side view showing the right-hand trailing arm and a portion of the torsion beam; FIG. 5 is a partial plan view showing an enlarged right-half portion of the torsion beam; FIG. 6 is a partial rear view showing an enlarged right-half portion of the torsion beam; FIG. 7 is a partial bottom view showing an enlarged right-half portion of the torsion beam; FIG. 8 is an enlarged cross sectional view taken along line VIII-VIII shown in FIG. 5; FIG. 9 is an enlarged cross sectional view taken along line IX -IX shown in FIG. 5; FIG. 10 is an enlarged cross sectional view taken along line X-X shown in FIG. 5; FIG. 11 is an enlarged cross sectional view taken along line XI-XI shown in FIG. 5; FIG. 12 is a front view showing a pin for joining the lower end of a shock absorber according to the embodiment; FIG. 13 is a front view showing the pin; FIG. 14 is a partial plan view similar to FIG. 5 and showing an enlarged right-half portion of the torsion beam of the embodiment of the torsion beam suspension according to the present invention; FIG. 15 is an enlarged cross sectional view taken along line XV-XV shown in FIG. 14; FIG. 16 is an enlarged cross sectional view taken along line XVI-XVI shown in FIG. 14; FIG. 17 is an enlarged cross sectional view taken along line XV1I-XVII shown in FIG. 14;and FIG. 18 is an enlarged cross sectional view taken along line XVII1-XVIII shown in FIG. 14. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to figs. 1A, IB and 2 to 4 of the drawings, reference numerals 10L and 10R represent left and right trailing arms disposed apart from each other in the lateral direction of the vehicle. Reference numeral 12 represents a torsion beam extending in a lateral direction of the vehicle. The trailing arms 10L and 10R are made of substantially S-shape tubular members formed of steel. The torsion beam 12 is formed of a steel plate having substantially U-shape cross section. Spring seat members 14L and 14R are welded to the trailing arms 10L and 10R at positions on the inside of the vehicle. The trailing arms 10L and 10R are disposed to the rear of the torsion beam 12. The trailing arms 10L and 10R are pivotally supported by a car body (not shown) by rubber bush units 18L and 18R integrally secured to the front end of the trailing arms 10L and 10R and incorporating axes 16L and 16R. Brackets 20 serving as wheel carriers are secured to the rear ends of the trailing arms 10L and 10R. The brackets 20 support wheels (not shown) rotatively around rotation axes 22. In the embodiment shown in the drawings, the U-shape cross section of the torsion beam 12 is structured to be opened from the front end of the trailing arm to the rear end of the same, that is, opened rearwards. The depth of the U-shape cross section is constant in the central portion of the torsion beam 12, the depth being gradually enlarged toward the two ends of the torsion beam 12. As a result, warped front ends 12A of the torsion beam are gradually and forward displaced toward the two ends thereof. The two ends of the torsion beam 12 have welded portions 24 which are integrally connected to the trailing arms 10L and 10R. In the embodiment shown in the drawings, rear portions of the torsion beam 12 have portions 12B projecting in the rear direction of the vehicle and outward direction of the vehicle, as shown in FIG. 2. The central portions of the two ends of the torsion beam 12 in the longitudinal direction of the vehicle extend in the longitudinal direction of the vehicle. Thus, a space between each of the central portions of the two ends in the longitudinal direction of the vehicle and the portion 12B forms substantially a circular-arc shape. In the embodiment shown in the drawings, the torsion beam 12 is formed into a wedge shape slightly projecting upwards. Also a torsion bar 26 disposed on the inside of the U-shape cross section of the torsion beam 12 and secured to the trailing arms 10L and 10R at the two ends thereof is formed into the wedge shape slightly projecting upwards to correspond to the torsion beam. FIGS. 5 to 7 are a partial plan view, a partial rear view and a partial bottom view each showing the right-half portion of the torsion beam 12 by enlarging the foregoing portion. FIGS. 8 to 11 are enlarged cross sectional views taken along lines VIII-VIII, IX-IX, X-X and XI-XI shown in FIG. 5, respectively. As can be understood from the foregoing drawings, the U-shape cross section of the torsion beam 12 is formed of a U-shape warped portion 28, an upper flat portion 30 and a lower flat portion 32. In the central portion of the torsion beam 12 in the lateral direction, a front end 12A of the U-shape warped portion 28 is positioned upward of a central plane 34 in the vertical direction. The front end 12A is gradually lowered in the direction toward the two ends of the torsion beam 12. At the two ends of the torsion beam 12, the front end 12A is substantially positioned at the position of the central plane 34 in the vertical direction. The width Wu of the upper flat portion 30 in the longitudinal direction of the vehicle is constant over the length of the torsion beam 12. As a result, a ridge 36 between the U-shape warped portion 28 and the upper flat portion 30 extends straight in the lateral direction when viewed from the upper position of the vehicle. On the other hand, the width Wl of the lower flat portion 32 in the longitudinal direction of the vehicle is constant in the central portion of the torsion beam 12. Moreover, the width Wl is substantially the same as the width Wu in the foregoing central portion. Note that the width Wl is gradually changed in each region 12E between a position 12D, which is an intermediate position of a region 12C in which the depth of the U-shape cross section is constant, and the two ends of the torsion beam 12. In the embodiment shown in the drawings, the width Wl of the lower flat portion 32 in the longitudinal direction of the vehicle is maximized at each of positions 12H more adjacent to the two ends as compared with a boundary 12G between the region 12C and a region 12F in which the depth of the U-shape cross section is gradually enlarged. The width Wl is gradually reduced from the position 12H in the direction toward the position 12D and the two ends. The position 12H is a position between the position 12D and each of the two ends of the torsion beam. Therefore, the ridge 38 between the U-shape warped portion 28 and the lower flat portion 32 straight extends laterally in the central portion of the torsion beam 12 when the ridge 38 is viewed from upper and lower positions of the vehicle. On the other hand, the ridge 38 extends to form the hypotenuse of a triangle in the region 12E, the vertex of which is the position 12H. A hole 40 and an elongated hole 42 in the form of cut portions are formed at the front end 12A in a region 12F having the U-shape cross section, the depth of which is gradually enlarged at a position adjacent to the 12H. The elongated hole 42 extending along the front end 12A inclirtes with respect to the horizontal direction As described above, the depth of the U-shape cross section of the torsion beam 12 is gradually enlarged in the region 12F. Moreover, the hole 40 and the elongated hole 42 are formed at the front end 12A at positions adjacent to the position 12H. Therefore, the portion in the vicinity of the position 12H is a portion in which the section modulus of the U-shape cross section of the torsion beam 12 is changed greatly as compared with the other portions, that is, a portion which can most likely to-be-deformed when lateral force acts on the wheels. The bracket 20 secured to the rear end of each of the trailing arms 10L and 10R incorporates a wheel support wall 44A extending in the longitudinal direction of the vehicle, a front wall 44B formed integrally with the wheel support wall 44A and extending substantially in the inboard direction (in the left-hand direction in FIG. 2) of the wheels and a rear wall 44C. The bracket 20 is the member formed into a substantially U-shape facing side. The outer end of an inclined wall 44D formed integrally with the wheel support wall 44A and extending downward and inward, the front wall 44B and the lower end of the rear wall 44C are welded to the trailing arm so that the brackets 20 are integrally secured to the corresponding trailing arm. In the embodiment shown in the drawings, the rear wall 44C is positioned in a portion of the rear end of the trailing arm extending substantially in the longitudinal direction of the vehicle. On the other hand, the front wall 44B is positioned at a position at which warping in the inboard direction starts when the front wall 44B is viewed in the direction from the rear end of the trailing arm to the front end. The portion of the front wall 44B in the outboard portion (right-hand portion in FIG. 2) extends in the lateral direction of the vehicle. The portion of the extending front wall 44B in the inboard portion is inclined rearward when the front wall 44B is viewed from a position upward of the vehicle. In this embodiment shown in the drawings, a pin 46 for joining the lower end of a shock absorber (not shown) is secured to the rear end of each of the trailing arms. As shown in FIG. 9, the pin 46 is formed of a central large-diameter portion 46A, a small-diameter portion 46B formed more outboard as compared with the large-diameter portion 46A and formed into a stepped shape and a small-diameter portion 46C formed more inboard as compared with the large-diameter portion 46A. A male-thread portion 46D is formed at the leading end of the small-diameter portion 46C. The pin 46 is inserted into holes provided for a wall 48 formed at the rear end of the trailing arm in the inboard portion and a wall 50 in the outboard portion. The outer end of the large-diameter portion 46A is welded to the wall 48, while the outer end of the small-diameter portion 46B is welded to the wall 50. Thus, the pin 46 is secured to the rear end of the trailing arm. In this embodiment shown in the drawings, the inner end of the pin 46 is positioned downward as compared with the outer end of the pin 46. As a result, an extending axis 52 of the pin 46 is inclined with respect to the horizontal direction. Referring to FIGS. 3 and 9, an alternate long and short dash line 54 indicates the axis of the shock absorber (not shown) which extends vertically with respect to the axis 52. In this embodiment structured as described above, the torsion beam 12 has the U-shape cross section constituted by the U-shape warped portion 28, the upper flat portion 30 and the lower flat portion 32. The region 12E, in which the width Wl of the lower flat portion 32 in the longitudinal direction of the vehicle is larger than the width Wu of the upper flat portion 30 in the longitudinal direction of the vehicle, includes the region in which the section modulus of the U-shape cross section of the torsion beam 12 is greatly changed as compared with the other portions. That is, the region 12E includes the portion in the vicinity of the position 12H which is the position which is most likely to be deformed when lateral force acts on the wheels. As compared with the structure in which the width Wl is the same as the width Wu over the length of the torsion beam 12, the strength of the portion which is most likely to be deformed when lateral force acts on the wheels can reliably be increased. In this embodiment shown in the drawings, the width Wl is largest at the position 12H, the width Wl being gradually reduced in a direction from the position 12H to the position 12D and to the two ends. As compared with the structure in which the width Wl is larger than the width Wu over the length of the torsion beam 12, a degree of lowering of the center of shearing of the U-shape cross section of the torsion beam can be moderated. As a result, oversteering of roll steering of the vehicle can be prevented. In the embodiment shown in the drawings, the depth of the U-shape cross section of the torsion beam 12 is gradually enlarged in the region 12F as described above. The front end 12A adjacent to the position 12H has the hole 40 and the elongated hole 42 in the form of cut portions. As a result, the position which is most easily deformed when lateral force acts on the wheels is the portion in the vicinity of the position 12H. Therefore, when the width Wl is set as described above, the portion, the strength of which is increased, can reliably be made to be the position which is most likely to be deformed. When the torsion beam of the torsion beam suspension having the U-shape cross section is twisted owning to bounding and rebounding of the right and left wheels in the opposite phases, highest stress is generally exerted on the ends of the opening portions of the U-shape cross section at the two ends of the torsion beam. In the embodiment shown in the drawings, each of the rear portions at the two ends of the torsion beam 12 has the portion 12B projecting in the rear and outward directions. Moreover, also the welded portion 24 is provided for the outer end of the portion 12B. As compared with the structure in which the portion 12B is not provided, the stress which acts on the rear portion of the two ends of the torsion beam 12 can reliably be held. As a result, the durability of the suspension can be improved. As shown in FIG. 3, lateral force F and moment M are, in addition to the longitudinal directional force, acting on the bracket 20, which is the wheel carrier, when the vehicle runs. Therefore, the force for separating the welded portions of the lower ends of the front wall 44B and the rear wall 44C acts on the foregoing welded portions. The foregoing force is largest at the inboard ends of the welded portions. Therefore, the durability of the bracket has been improved by elongating the lengths of the front wall and the rear wall or by decreasing the rigidity of the bracket. However, the former method encounters elongation of the welded portion and, therefore, the cost is raised. The latter method encounters decrease in the rigidity of the suspension. In the embodiment shown in the drawings, the outboard portion of the front wall 44B of the bracket 20 extends in the lateral direction of the vehicle. Moreover, the inboard portion of the extending front wall 44B inclines to the rear of the vehicle. Therefore, when the lateral force F and the moment M act on the bracket 20, the separating force acts on the lower welded portion of the front wall 44B. Moreover, the force for deforming the outboard portion of the front wall 44B in the lateral direction of the vehicle acts on the foregoing outboard portion of the front wall 44B. Therefore, as compared with the conventional structure in which the front wall 44B extends in the lateral direction of the vehicle, the force that acts on the inboard end of the lower welded portion of the front wall 44B can be reduced. As a result, the durability of the bracket can be improved. Thus, the necessity of elongating the length of each of the front wall and the rear wall and decreasing the rigidity of the bracket can be eliminated As a result, increase in the cost and decrease in the rigidity can be prevented. In the embodiment shown in the drawings, only the inboard portion of the front wall 44B is inclined to the rear of the vehicle. The inboard portion of the rear wall 44C may be inclined. The inboard portions of both of the front wall 44B and the rear wall 44C may be inclined. In the latter case, it is preferable that the inboard portions of the front wall 44B and the rear wall 44C are inclined in opposite directions. In the embodiment shown in the drawings, the pin 46 for joining the lower end of the shock absorber incorporates the small-diameter portion 46B with the stepped portion located closer to the outboard side than the large-diameter portion 46A. In case of the conventional structure (a pin 46') having a small-diameter portion formed into a tapered shape as shown in FIG. 10, a small-diameter portion of the material obtained by forging has to be cut to form a tapered portion 46E. On the other hand, the structure of the pin according to the embodiment shown in the drawings, the pin can be manufactured only by forging. As a result, the pin can be manufactured at low costs. Since the small-diameter portion 46B of the pin 46 has a shoulder portion interposed between the stepped regions, locating of the pin with respect to the rear end of the trailing arm can appropriately be performed by using a jig. As a result, the pin can be joined efficiently as compared with the conventional structure. The structure of the bracket 20 and that of the pin 46 according to the embodiment shown in the drawings may be applied to a torsion beam suspension which is not provided with the torsion beam 12 according to the present invention. Also in this case, the foregoing operation and effects can be realized. Although the invention has been described in its preferred form and structure with a certain degree of particularity, it is understood that the present disclosure of the preferred form can be changed in the details of construction and in the combination and arrangement of parts without departing from the spirit and the scope of the invention. The foregoing embodiment has the structure in which the torsion beam 12 has the U-shape cross section formed of the U-shape warped portion 28, the upper flat portion 30 and the lower flat portion 32. The length of the torsion beam in the direction perpendicular to the lengthwise direction of the torsion beam has to be made such that the length of the end of a portion downward of the bottom portion of the U-shape cross section is, in the predetermined region, longer than the length of the end upward of the bottom portion. If the foregoing requirement is met, the U-shape cross section of the torsion beam may be formed into a parabolic shape or a semi-elliptic shape, as shown in FIGS. 15 to 18 which correspond to FIGS. 8 to 11. In FIG. 14, portions corresponding to those shown in FIGS. 15 to 18 are given the same reference numerals as those shown in FIGS. 15 to 18. In the foregoing embodiment, the width Wl of the lower flat portion 32 in the longitudinal direction of the vehicle is gradually changed in the region 12E. The ridge 38 between the U-shape warped portion 28 and the lower flat portion 32 extends to form the hypotenuse of a triangle having the vertex at the position 12H. If the width Wl at the' position 12H is maximum, the ridge 38 may extend to form a curve as shown in FIG. 14 which corresponds to FIG. 5. Also in FIG. 14, the portions corresponding to those shown in FIG. 5 are given the same reference numerals as those shown in FIG. 5. In the foregoing embodiment, each of the trailing arms 10L and 10R is formed into substantially the S-shape. The trailing arm may be formed into an arbitrary shape. The U-shape cross section of the torsion beam 12 according to the embodiment shown in the drawing is opened rearwards. The direction of opening of the U-shape cross section may arbitrarily be determined except for the rearward direction. In the foregoing embodiment, no gusset is provided for each of the two ends of the torsion beam 12. The structure according to the present invention may be applied to a suspension having the gussets at the two ends of the torsion beam. In the foregoing case, it is preferable that the predetermined region includes the inner end of the gusset. WE CLAIM: 1. A torsion beam suspension comprising paired trailing arms disposed apart from each other in the lateral direction of a vehicle, having front ends pivotally supported by a car body and rear ends for rotatively supporting wheels; and a torsion beam extending in the lateral direction of the vehicle and integrally connecting said trailing arms to each other, characterized in that: said torsion beam is defined by a U-shape cross section formed of a U- shape warped portion, an upper flat portion and a lower flat portion, opened in the longitudinal direction of the vehicle, and said lower flat portion has a width in the longitudinal direction of the vehicle which is larger than the width of said upper flat portion in particular regions adjacent to the two ends of said torsion beam, a difference in a width in longitudinal direction of the vehicle between the lower flat portion and the upper flat portion in the particular region is larger than a difference in a width in longitudinal direction of the vehicle between the lower flat portion and the upper flat portion out of the particular region 2. • A torsion beam suspension as claimed in claim 1 wherein the depth of the U- shape cross section at each of the two ends of said torsion beam is enlarged in a direction toward each of the two ends of said torsion beam, and said region comprises a boundary portion between a portion in which the depth of the U-shape cross section is constant and a portion in which the depth of the U-shape cross section is enlarged. 3. A torsion beam suspension as claimed in claim 1 wherein said torsion beam has a cut portion formed in the bottom of the U-shape cross section at a position adjacent to each of the two ends thereof, and said region comprises the portion in which the cut portion has been formed. 4. A torsion beam suspension as claimed in claim 3 wherein the depth of the U- shape cross section at each of the two ends of the torsion beam is enlarged in a direction toward each of the two ends of said torsion beam, and said cut portion is formed in the vicinity of a portion in which the width of the lower flat portion is largest. 5. A torsion beam suspension as claimed in claim 1 wherein the width of said lower flat portion in the longitudinal direction of the vehicle is maximum in the central portion in the region, and the width is reduced in a direction toward each of the two ends of the region. 6. A torsion beam suspension as claimed in claim 5 wherein the region comprises the boundary portion and the portion in which the cut portion has been formed. 7. A torsion beam suspension as claimed in claim 1 comprising paired trailing arms disposed apart from each other in the lateral direction of a vehicle, having front ends pivotally supported by a car body and rear ends for rotatively supporting wheels; and a torsion beam extending in the lateral direction of the vehicle and integrally connecting said trailing arms to each other, wherein said torsion beam has a U shaped cross section opened in the longitudinal direction of the vehicle and the length of the torsion beam in a direction perpendicular to the lengthwise direction is made such that the length of an end downward of the bottom portion of the U-shape cross section is longer than the length of a portion upward of the bottom portion in a region adjacent to each of the two ends of the said torsion beam. 8. A torsion beam suspension as claimed in claim 7 wherein the length of the end downward of the bottom portion of the U-shape cross section is maximum in the central portion of the region, and the length is reduced in a direction toward each of the two end of the region. 9. A torsion beam suspension as claimed in claim 7 wherein the region comprises a portion, which is most easily deformed when a lateral force acts on the wheels. 10. A torsion beam suspension as claimed in claim 1 comprising paired trailing arms disposed apart from each other in the lateral direction of a vehicle, having front ends pivotally supported by a car body and rear ends for rotatively supporting wheels; and a torsion beam extending in the lateral direction of the vehicle and integrally connecting said trailing arms to each other, wherein said torsion beam has a U shaped cross section defined by a U-shape warped portion, an upper flat portion and a lower flat portion and opened in the longitudinal direction of the vehicle; and opened in the longitudinal direction of the vehicle and said lower flat portion has a width in the longitudinal direction of the vehicle which is larger than the width of said upper flat portion in regions in which change in the section modulus of said torsion beam is greater than the section modulus of the other portions. 11. A torsion beam suspension substantially as herein described with reference to and as illustrated in the accompanying drawings.

Documents:

1277-del-1999-abstract.pdf

1277-del-1999-claims.pdf

1277-del-1999-correspondence-others.pdf

1277-del-1999-correspondence-po.pdf

1277-del-1999-description (complete).pdf

1277-del-1999-drawings.pdf

1277-del-1999-form-1.pdf

1277-del-1999-form-19.pdf

1277-del-1999-form-2.pdf

1277-del-1999-form-3.pdf

1277-del-1999-form-5.pdf

1277-del-1999-gpa.pdf

1277-del-1999-petition-138.pdf

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