CLL(Capacitor long life)capacitor filtering to reduce the current spikes
In any DC motor/Gen. there are multiple coils generally equal to the number of commutator segments.
when a brush passes over a comm. segment the current is reversed in that coil from say +I to -I.
If inductance of that coil is say L henry then voltage induced in the coil= 2*L*dI/dt.
dI/dt is decided by the speed of the machine.
If say L=5 mH and current is 1 Amp. and current changed from +I to -I in 0.1 millisecond then the voltage induced=2*1*5*10^-3/0.1*10^-3=10000 Volts which would instaniously develop  (figure are deiberately taken on the higher side!) and may break the air gap between the segment(now the segment is away brom the brush) and sparking will be seen between the segment and brush. This happens with every segment.
a capacitor forms a tank circuit between coil inductance and forms a  voltage having a lower rate of rise   across capacitor CVc=It means Vc=I.t/C
7.If C=1 micro Fd then Vc=1*0.2*10^-3/1*10^-6=200 volts. (p. note that all the values are illustrtive just to show he effect of capacitior.)
vtingole