Development of a Braking Energy Regeneration System for City Buses

In order to improve the fuel economy of city buses, which start and stop frequently, a system has been developed that stores braking energy in a hydraulic accumulator and uses the energy when the vehicle is in its start and acceleration modes.

Through microcomputer control of the entire power train and energy storage system, the following goals are achieved:

1. 1.
   By applying currently available transmission technologies to the conventional power train system, all component functions are controlled so as to minimize the losses over the driving cycle.
2. 2.
   By applying a regenerative braking system, as much vehicle kinetic energy as possible is recovered and stored, and,
3. 3.
   The energy stored is used so as to achieve maximum overall efficiency.

A test vehicle functioning in city conditions achieved a 30% fuel economy gain.

Other advantages of this system are that brake wear is greatly reduced and clutch life is significantly extended since the vehicle can start in motion using only hydraulic energy.