The chassi spring (the so-called miniblock spring) is a barrel compression spring with inconstant wire diameter. Depending on the application, it is either designed with a progressive or a linear characteristic.
Its optimum utilization of material allows for both low dead weight and low package space.
Typical areas of application: suspension springs, power springs for brake actuators, valve springs.
Click on the miniatures to enlarge the FEM deflection simulations: