not limited to any particular prime mover engine 18 is sized to be able to propel the motor vehicle 10 and its load at a desired speed along a level highway drive the auxiliaries of the motor vehicle and may have a small amount of additional available power for supplying kinetic energy to flywheel 20 engine 18 drives flywheel 20 through drive connection 26 drive connection 26 may be any convenient drive connection including direct coupling shaft or chain drive furthermore in view of the relatively small amount of power transmitted some belt drives are also feasible flywheel 20 is a cylindrical structure having top wall 28 bottom wall 30 and cylindrical side wall 32 see fig2 and 3 flywheel 20 is mounted on central shaft 34 which is mounted for rotation in the body 12 of motor vehicle 10 for dynamic considerations discussed below the flywheel 20 is preferably mounted near the longitudinal and transverse center of the motor vehicle in view of that location it is sometimes convenient to mount engine 18 elsewhere and drive it through drive connection 26 otherwise engine 18 can be directly mounted on top of flywheel 20 flywheel 20 has liquid 36 therein liquid 36 is preferably water because of its weight and viscosity inexpensive character and wide availability when water is used it may carry anti rust and lubricity additives as well as anti freeze additives for those cases where.