A tubular spring, such as a coil spring, a torsion-rod spring, and/or a stabilizer for motor vehicles, may comprise at least one metal tube element having a tube internal cross section, a tube internal diameter, a tube external diameter, a tube internal wall, and a tube wall thickness. At least one metal foam may be disposed in the tube internal cross section of the at least one metal tube element of the tubular spring in at least one part-region. The metal foam may be connected in an at least partially materially integral manner to the tube internal wall of the metal tube element. Further, the at least one metal tube element may have an at least partially martensitic structure.

An annular reference surface is formed around a through-hole of an eye portion. A distal-end-side curved portion is formed at a first corner portion, on an outer side of the annular reference surface. The thickness of the distal-end-side curved portion is reduced in a range of a length from the first flat surface toward the distal end surface. A hole-side curved portion whose thickness is reduced toward an inner surface of the through-hole is formed at a second corner portion, on an inner side of the annular reference surface. The length of the hole-side curved portion is less than the length of the distal-end-side curved portion. The hole-side curved portion is curved with a greater curvature than that of the distal-end-side curved portion.

A coil spring for use in a link-motion-type suspension includes a lower end turn portion, an upper end turn portion, and an effective portion of a cylindrical shape between the lower end turn portion and the upper end turn portion. Further, the coil spring includes a bowing control portion including a taper portion formed in at least one end turn portion of the lower end turn portion and the upper end turn portion. The taper portion has a shape whose thickness is reduced from the middle of the end turn portion toward a distal end of a wire along its length, and bowing of the effective portion is suppressed by absorbing a change in the inclination of a spring seat by the taper portion.

A plate assembly for a motor vehicle may include a first plate, a second arranged substantially parallel to the first plate, the second plate defining a plurality of perforations, and a mesh core including a plurality of wire bundles, the core arranged between the plates, wherein the mesh core is rigidly joined to an inner surface of each plate via the perforations.

A hollow stabilizer (1) according to the invention is formed in a hollow shape and includes a bent portion (1c1, 1c2, m1-m5). With a thickness of an inner side of the bent portion (1c1, 1c2, m1-m5) being larger than a thickness of an outer side of the bent portion (1c1, 1c2, m1-m5), a hardness of the outer side of the bent portion (1c1, 1c2, m1-m5) is higher than a hardness of the inner side of the bent portion (1c1, 1c2, m1-m5) through quenching by cooling down after heating by electrical heating.

A hollow stabilizer has a tubular shape and is provided with a torsion section that is provided to a vehicle and that extends in the vehicle width direction; an arm section that extends in the front-back direction of the vehicle; and bent sections that connect the torsion section and the arm section. The hardness of the outer surface of the bent inner sides of the bent sections of the hollow stabilizer is 70% or more with respect to the hardness of the outer surface of the arm section.

A method includes, providing a tubular member (10) used for a hollow spring, and applying the compressive residual stress to at least a portion of an inner surface of the steel tube by applying the compressive force to at least a portion of an outer surface of the tubular member (10) from a circumferential direction, and a fatigue life of the tubular member (10) is prolonged by applying the compressive residual stress to the inner surface of the tubular member (10). Applying the force to the outer surface of the tubular member (10) includes pressing the tubular member (10) with a die (1). The die (1) has a pressing surface (1a) shaped such that the compressive force can be applied to at least the portion of the outer surface of the tubular member (10) from the circumferential direction.

A stabilizer including: a main body for generating an elastic restoring force; and connecting portions formed on both ends of the main body and respectively connected to left and right suspension devices. Hardness of the connecting portions is lower than that of the main body. A method for manufacturing the stabilizer includes, in order, an entire body heat treatment process for heat treating an entire stabilizer and increasing hardness of the entire stabilizer, and a connecting portion softening process for heating the connecting portions and reducing the hardness of the connecting portions. The method for manufacturing the stabilizer thereby increases hardness of the main body and reduces the hardness of the connecting portions lower than that of the main body.

A method of manufacturing a hollow stabilizer includes a forming step of subjecting an element pipe to a bending process, to form a product shape including bent portions, and a quenching step of quenching the element pipe subjected to the bending process. In the quenching step, a cooling process is performed by immersing the element pipe made of steel in coolant and by spraying the coolant to an outer surface of the bent portion.

An electric resistance welded steel pipe for manufacturing a hollow stabilizer has a Lankford value in a pipe longitudinal direction of from 0.7 to less than 1.0. The electric resistance welded steel pipe is subjected to cold bending and then to a heat treatment including quenching and tempering to manufacture a stabilizer. The cold bending is cold rotary draw bending. When bent with a bend radius of from 1.0 times to 3.0 times an outer diameter of the pipe before cold bending, a flattening ratio is from 0% to 10%, a thickness reduction rate on a bending outside and a thickness increase rate on a bending inside are from 0% to 10%, and additionally, a circumferential length change of a bending center portion is from 0% to 10%. A Vickers hardness of the stabilizer after the heat treatment is adjusted to from 400 HV to less than 580 HV.