Undulating washer or wave-shaped spring with a defined progressive characteristic spring rate

An axially acting undulating washer or wave-shaped spring consisting of a closed annular member which comprises a central x-axis and which is periodically undulating across the circumference, wherein a wave line extends between a plurality of identical minima and identical maxima, said minima and maxima forming contact points relative to axis-normal contact faces in an unloaded state of the annular member, said annular member comprising first wave line portions starting from each minimum and maximum in each circumferential direction, which first wave line portions having a flattened form in an unloaded state compared to respective wave line portions at maxima and minima of a cosine wave,

• said annular member further comprising second wave line portions directly adjoining the first wave line portions, which second wave line portions having a steepened form compared to said cosine wave
• wherein, under an increasing axial load on the annular member, said first wave line portions are deformed at a first spring rate and flattened to contact the contact faces, and
• wherein, after flattening of the first wave line portions, said second wave line portions are deformed at a second spring rate which is higher than the first spring rate.