A hollow coil spring is made of a hollow wire in which a terminal sealed portion is formed on an end portion of the wire. The terminal sealed portion has a rotationally symmetric shape in which an axis passing through the center of the wire is the symmetric axis. The hollow coil spring includes an end wall portion, and an end face arc-shaped curved surface. The end wall portion includes an end face perpendicular to the axis. A distal-end-center closure portion is formed on the axis at the center of the end wall portion. A spring seat includes a base member and a sheet member. An end turn portion of the hollow coil spring is in contact with the sheet member. The end face of the end turn portion is opposed to a stopper wall of the spring seat.

The invention relates to a method for manufacturing a coil spring and for determining a propelling condition for a shot medium. In a case where it is confirmed that the coating film remains in a third step, at least one or more of conditions of the shot peening treatment including a propelling speed of the shot medium, a propelling time of the shot medium, a material of the shot medium, and an average particle diameter of the shot medium are changed and the second step and the third step are repeated until the coating film does not remain. In a case where it is confirmed that the coating film does not remain in the third step, the condition of the shot peening treatment in the second step in which the coil spring is obtained with no remaining coating film is determined as the propelling condition for the shot medium.

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.

Automotive leaf springs are produced from low-hardenability and specified hardenability steel, with identical and different length, width and thickness and constant or variable cross section profile, that are subjected to through-surface hardening and low tempering. The ideal critical diameter of hardening, carbon content and hardened layer depth depend on the thickness of constant cross section profile leaf and maximum and minimum thicknesses of variable cross section profile leafs. Adherence to the optimum correlations of parameters indicated make it possible to produce leaf springs with the highest mechanical properties and longevity.

A method of producing a stabilizer (10) of a motor vehicle, such that the stabilizer includes a torsion bar (11) and longitudinal links (12, 13). The longitudinal links (12, 13) are in each case connected to the torsion bar (11) by welding, and the longitudinal links (12, 13) and the torsion bar (11) are heat-treated before welding. Each longitudinal link (12, 13) is welded at one end to the torsion bar (11) on both sides, in each case, by a respective multilayer weld seam (14), and each weld seam (14) is made with unequal widths such that the width of the weld seam (14) adjacent to the torsion bar (11) is shorter than its width adjacent to the respective longitudinal link (12, 13).

A semi-finished product (31) includes a first curved portion on one end of a plate-shaped bridge portion (33), and a second curved portion (37) on the other end of the bridge portion (33). The second curved portion (37) includes at the end a second lock portion (51) to lock with a first lock portion (41). The bridge portion (33) and the inner circumferential surfaces of the first and second curved portions (35, 37) are pressure-contacted and caulked on the outer circumferential surface of the stabilizer bar (11) by first and second dies (61, 62). At least one of the inner circumferential surfaces (31c) of the first and second curved portions (35, 37) and the outer circumferential surface of the stabilizer bar opposed to the inner surfaces (31c) is formed with an anti-slippage portion (38). The inner circumferential surfaces (31c) of the first and second curved portions (35, 37) and the outer circumferential surface of the stabilizer bar (11) have an anti-slippage material (Co) therebetween.