The schematic representation of a DC motor driven railway bogie is shown in the figure. The wheels are perfectly rigid and the track is perfectly flat, so there is no vertical excitation from the rail on the wheels and the wheels have no vertical velocity. Note that this is not coach or car-body; the coach is mounted on two such bogies with another set of secondary suspensions (air springs) placed in the V-grooves.
Check the pdf attached
Draw the bond graph model of the system