ations ▁can ▁be ▁found ▁in ▁vehicle ▁or ▁fly w heel ▁manufact urer ' s ▁published ▁documentation . ▁Other ▁failure ▁modes ▁are ▁sever ely ▁gro oved / dam aged ▁cl utch ▁m ating ▁surface , ▁gre ase ▁loss , ▁and ▁crack ing . ▁ ▁Types ▁▁ ▁The ▁main ▁type ▁is ▁called ▁a ▁planet ary ▁DM F . ▁The ▁planet ary ▁g ear ▁and ▁the ▁t ors ional ▁dam per ▁are ▁incorpor ated ▁into ▁the ▁main ▁ ▁fly w heel . ▁For ▁this ▁purpose , ▁the ▁main ▁fly w heel ▁is ▁divided ▁into ▁primary ▁and ▁secondary ▁pin ion - connected ▁masses , ▁and ▁between ▁them ▁there ▁are ▁four ▁different ▁types ▁of ▁bent ▁spr ings : ▁ ▁Ind ividual ▁bent ▁spring ▁ ▁The ▁simplest ▁form ▁of ▁the ▁bent ▁spring ▁is ▁the ▁standard ▁single ▁spring . ▁ ▁One - phase ▁bent ▁spr ings ▁in ▁parallel ▁ ▁The ▁standard ▁spr ings ▁are ▁called ▁parallel ▁spr ings ▁of ▁one ▁phase . ▁These ▁consist ▁of ▁an ▁outer ▁and ▁an ▁inner ▁spring ▁of ▁almost ▁equal ▁lengths ▁and ▁connected ▁in ▁parallel . ▁The ▁individual ▁characteristic ▁curves ▁of ▁the ▁two ▁spr ings ▁are ▁added ▁to ▁form ▁the ▁characteristic ▁curve ▁of ▁the ▁spring ▁pair . ▁ ▁Two - phase ▁bent ▁spr ings ▁in ▁parallel ▁ ▁In ▁the ▁case ▁of ▁two - stage ▁spring ▁there ▁are ▁two ▁cur ved ▁parallel ▁spr ings , ▁one ▁inside ▁the ▁other , ▁but ▁the ▁internal ▁spring ▁is ▁shorter ▁so ▁that ▁it ▁acts ▁later . ▁The ▁characteristic ▁curve ▁of ▁the ▁outer ▁spring ▁is ▁adapted ▁to ▁increase ▁when ▁the ▁engine ▁is