Helper Spring. Shock Absorber. Suspension, Coil Spring and Torsion Spring.
A component (mounted in the center of the spring) which cushions the spring as it is compressed.

Fits XC90

Suspension Coil Spring
Your coil springs are not especially prone to failure, but if they have been cut, clamped, or heated to have the vehicle lowered, your 1991 Volvo might benefit from replacing the strut springs. Excessive rust can make the springs more prone to failure. Contact your local Volvo service department to have your suspension system evaluated.