Lloyd, R., "Hydro-Mechanical Transmission Implements Regenerative Braking for the Postal LLV Trucks and a Hydraulic Hybrid Passenger Vehicle at a Lower Cost than a Conventional Vehicle," SAE Technical Paper 2015-01-1096, 2015, doi:10.4271/2015-01-1096.
The frequent stops of the typical postal delivery vehicle make it an attractive application for regenerative braking. The hydro-mechanical automatic transmission described in SAE paper 2014-01-1717 contains all the functions necessary to implement hydraulic regenerative braking including the accumulator and reservoir. This paper describes the substitution of the hydro-mechanical transmission for the present transmission of the postal LLV vehicles and estimates the performance benefits. The result represents a low impact path for the US Postal Service to extend the useful life of the LLV vehicles and increase the mpg by approx. 100%.A cost comparison between a convention ICE mid-sized passenger sedan and a similar size gas/hydraulic hybrid vehicle illustrates the cost advantage of the hydraulic approach using the new transmission design. Besides lower cost, the vehicle will have greater initial acceleration and 25%+ better mpg. Hydraulic regenerative braking has twice the overall efficiency of energy recovery and greater startup torque than electric regenerative braking. Its ability to handle higher peaks of braking energy, means more of the braking energy can be captured than with the electric systems.