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Publication Number:  FHWA-HRT-18-037    Date:  September 2017
Publication Number: FHWA-HRT-18-037
Date: September 2017


Eco-Drive Experiment on Rolling Terrain for Fuel Consumption Optimization

Chapter 4. Experimental Vehicle Platform

The CAV used in the field experiment is a part of FHWA’s automated vehicle fleet. Each vehicle was designed to be a complete research platform. (Please refer to Raboy and Ma (2017) for detailed introduction of the experimental vehicle platform.) Each research platform is outfitted with the following components:

The base system configuration for the FHWA CAVs is shown in figure 3. At the center of the vehicle control system is the in-vehicle Linux PC. PinPoint™ transmits real-time, high-accuracy GPS data to the in-vehicle computer. The DSRC OBU broadcasts BSMs and receives other vehicles’ BSMs and transmits this information through the Linux PC. The long-range radar transmits object data to the Linux PC. The MAB receives data from Linux PC, including BSMs from other vehicles, roadside units (RSUs), and radar data. The MAB control commands are speed recommendations from the control algorithm embedded in Matlab Simulink, which are then injected into the vehicle CAN bus.

This graphic shows the flow of data within the vehicle. In the top half of the image, an in-vehicle computer communicates with three peripherals: a PinPoint device (second row, left) provides accurate GPS data, a radar (top row) provides the distance and speed of surrounding objects, and a radio (second row, right) transmits the vehicle's BSM and receives BSMs from other vehicles. Black arrows indicate the flow of data to the in-vehicle computer. The in-vehicle computer communicates those data to a Realtime Processor (third row, center), which runs the vehicle Proportional-Integral-Derivative (PID) control algorithm (third row, left). The Realtime Processor then applies speed and wrench effort commands to the vehicle over the CAN bus (bottom row).

Source: FHWA
Figure 3. Data flow of the vehicle control systems (Ma, Leslie, and Zhou, 2018).

To enable the accurate measurement of fuel consumption, a fuel flow meter was installed to measure the amount of fuel delivered to the engine as a function of time. This flowmeter is accurate to better than ±1.0 percent over the whole 250:1 flow range, and repeatability is less than ±0.1 percent. The location was chosen based on the characteristics of the fuel system. This section of the fuel line is easily accessible, relatively low pressure (<100 psi), and away from the heat of the engine. The fuel system operates as a returnless system, meaning the in-tank fuel pump delivers the fuel required by the engine, and no fuel is returned to the tank. This simplifies the fuel flow measurement, but places additional restrictions on the location of the flowmeter. To ensure sufficient fuel pressure at the engine, the flowmeter was inserted upstream of the inline pressure sensor that is used to regulate the fuel pump. This would allow the vehicle’s closed-loop fuel pump controller to provide the appropriate fuel pressure at the engine.

The modified fuel system is shown in figure 4. To simplify modifications to the vehicle, a replacement fuel line was purchased and modified with the flowmeter. Then the original fuel line was removed and the modified fuel line was installed. The original fuel line was saved to be reinstalled at the conclusion of the experiment.

This diagram shows the modified fuel supply line, including the flow meter. A segment of the fuel line is enclosed in a grey box to show the flowmeter assembly that was installed. The flowmeter assembly includes the flowmeter and a pressure meter. Fuel flows from the tank (bottom left), clockwise through devices in the following order: fuel pump, metal tube, rubber tube, flowmeter, rubber tube, metal tube, pressure meter, metal tube, nylon tube, flex sensor, nylon tube, metal tube, engine compartment.

Source: FHWA
Figure 4. Installation of the fuel flowmeter.

The output of the flowmeter is a square wave with a frequency that is directly proportional to the flow of the fluid. The relationship (K-factor) for this model of flowmeter is 20,000 pulses per liter. With a built-in capability to measure frequency, pulse width, and duty cycle, the MAB is a logical choice to interface with this data source. Thus, the flowmeter was wired to the MAB and the software was modified to translate the square wave into a flow measurement.

Three 2013 Cadillac SRX from the CAV fleet in a parking lot.

Source: FHWA
Figure 5. CAV vehicle fleet.

Figure 5 shows the CAV fleet used in this experiment. Figure 6 shows the hardware components as installed in each of the FHWA CAVs. Figure 7 shows the ultrasonic fuel meter that is installed in the test vehicle’s fuel line.

This photo shows the vehicle control devices installed in the rear of a Cadillac SRX, including a hardened PC, MicroAutobox, Pinpoint, radio, and CAN interface.

Source: FHWA
Figure 6. Vehicle control devices.

This photo shows the fuel flowmeter installed in the fuel line under the vehicle. Rubber tubes are also visible connecting the flowmeter to other parts of the fuel supply line.

Source: FHWA
Figure 7. Fuel meter installed at vehicle fuel line.

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