Route profile analysis to determine suitability of electric postal delivery vehicles

An instrumentation system and computer program were developed that allow the U.S. Postal Service to determine which postal routes are suitable for electric delivery vehicles. The instrumentation system provides route data. The route data and electric vehicle characteristics are used in the computer program to calculate vehicle energy and power requirements for the particular route. The performance characteristics of electric vehicles are contained in an input data file to the computer program. The instrumentation system is designed for use during normal mail delivery with gasoline-powered vehicles. The system is powered by the vehicle battery. Minimum operator interaction and inexpensive maintenance-free sensors are featured in the design. Route grade is determined from a pendulum measurement corrected for vehicle acceleration. Acceleration is determined from a measurement of the distance traveled. The value of road grade obtained in this manner is in excellent agreement with civil survey data. The distance transducer utilizes an electro-optical sensor and a rotating disk driven by the speedometer gear to provide a resolution of 3 mm. A microprocessor provides timing and data management. Data are recorded on a cassette tape. The instrumentation system is compact and readily installed or removed in a "survey" delivery vehicle. Calibration requirements are minimal. Since postal delivery routes are closed, i.e., they begin and end at the same location (elevation), the bias error in initial orientation of the pendulum can be reduced to zero during data reduction. After the tape is inserted by the operator at the beginning of a run, and identification information is keyed in, data are automatically recorded in 50-s blocks. If the vehicle is not in motion during a data block period, no data are recorded for that period. Route data on the cassette tape are reduced in subroutine CARAIN which converts the binary data to engineering plots of time, speed, acceleration, road grade, and elevation vs distance. The program CARA determines whether a specific electric vehicle can complete the route, subject to energy and power limitations. Output plots of battery power and battery state of charge vs time are provided. If battery power or motor torque limitations are exceeded, this fact is noted, but otherwise disregarded, as the calculation proceeds to the end of the route or to a set minimum value of battery state of charge. Battery state of charge is determined by a first-order-system method developed at Purdue University; the results compare well with battery test data. CARA was validated by comparing performance predictions with test data obtained with electric postal delivery vehicles. Acceptance test results indicate that a useful route profile analysis system has been developed.