A stabilizer includes bend sections. With respect to positions in a circumferential direction of a radial cross section of each of the bend sections, a center of an inside of a bend is defined as 0, and a center of an outside of the bend is defined as 180. The bend sections each include a bend interior section located at 0, a bend exterior section located at 180, a first side section located at 90, and a second side section located at 270. The bend interior section has compressive residual stress from a surface to a first depth. The bend exterior section has compressive residual stress to a second depth. The first side section has compressive residual stress to a third depth. The second side section has compressive residual stress to a fourth depth.

A method of manufacturing a suspension coil spring includes forming first shot peening indentations on a surface of a wire by projecting first shots toward the wire and forming a compressive residual stress portion to which a compressive residual stress is imparted from the surface of the wire to a first depth, and projecting ball shots as second shots toward a lower end turn portion by an ultrasonic apparatus. A size of each ball shot is larger than a size of each first shot. The method includes forming second shot peening indentations on a surface of the lower end turn portion, and a deep residual stress portion in the lower end turn portion, a compressive residual stress of the deep residual stress portion imparted from the surface of the wire to a second depth that is deeper than the first depth.

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.

A stabilizer includes a stabilizer bar and a rubber bush. The stabilizer bar includes a bar body made of a steel and a coating film covering the bar body. The coating film is formed on the surface of the bar body by using a resin having a water contact angle of more than 65. By performing surface treatment for reducing the contact angle of the coating film present on an attachment part, the contact angle of the attachment part is changed to 65 or less. A pre-cured liquid adhesive agent is applied to an inner surface (adhesion surface) of the rubber bush. After a region including the attachment part of the stabilizer bar is heated, the rubber bush is overlaid on the attachment part. The adhesive agent is cured in a state where the rubber bush is pressed.

A method of manufacturing a suspension coil spring includes forming first shot peening indentations on a surface of a wire by projecting first shots toward the wire and forming a compressive residual stress portion to which a compressive residual stress is imparted from the surface of the wire to a first depth, and projecting ball shots as second shots toward a lower end turn portion by an ultrasonic apparatus. A size of each ball shot is larger than a size of each first shot. The method includes forming second shot peening indentations on a surface of the lower end turn portion, and a deep residual stress portion in the lower end turn portion, a compressive residual stress of the deep residual stress portion imparted from the surface of the wire to a second depth that is deeper than the first depth.

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.

According to an embodiment, a coil spring is formed of a wire which is helically wound, and includes an end turn portion and an effective portion, and a surface of the wire in the end turn portion includes an area which is softer than a surface of the wire in the effective portion.

A hollow spring member and hollow spring member production method can be provided, which can save the time and energy necessary for carburization, thus requiring no dedicated carburizing furnace or the like for carburization, and further can make the interior space of a steel tube a rust-prevention atmosphere. A hollow stabilizer for a vehicle includes a steel tube sealed at one end and another end thereof and a carburizing gas sealed in the interior space of the steel tube.

A terminal sealed portion is formed on an end portion of a hollow rod made of steel. An enclosed space is formed on an inner side of the hollow rod. At an end of the enclosed space, a terminal gap is formed. A volatile powdered rust inhibitor is supplied in the enclosed space. As the volatile powdered rust inhibitor is vaporized, the enclosed space is turned into a rust-inhibiting atmosphere. As the vaporized component of the volatile powdered rust inhibitor is adsorbed to an inner surface of the enclosed space, an inner surface rust-inhibiting film is formed. The vaporized component also enters inside the terminal gap, and forms a terminal rust-inhibiting film.

On an end portion of a hollow rod, which is a material of a hollow coil spring, a terminal sealed portion is formed. The terminal sealed portion has a rotationally symmetric shape in which an axis passing through the center of the rod is a symmetric axis. The terminal sealed portion includes an end wall portion, and a distal-end-center closure portion formed on the axis. In the distal-end-center closure portion, a distal end opening portion of the spin-formed rod is joined together and formed as an integral part. On the axis at the inner surface of the end wall portion, a recess having a rotationally symmetric shape in which the axis is the symmetric axis is formed. A thickness of the recess of the end wall portion is reduced toward the axis.