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:

• A proprietary longitudinal controller – a set of custom electronic control units (ECUs) that enable fully automatic control of vehicle acceleration and braking by integrating directly with the existing vehicle ACC system.
• A dSPACE MicroAutoBox (MAB) II controller – a specialized real-time computing platform that provides commands to the longitudinal controller (dSPACE, Inc., 2018). This is accessed via dSPACE ControlDesk through a MATLAB/Simulink library (MathWorks, 2018).
• An Arada LocoMate – a dedicated short-range communications (DSRC) onboard unit (OBU) that enables the transmission and reception of Basic Safety Messages (BSMs) (Arada Systems, 2018).
• A Linux-based, in-vehicle, secondary computer that integrates with the MAB. This computer gathers vehicle measures, operates the algorithms, and communicates with the human machine interface (HMI).
• PinPoint™ – a special GPS device that fuses data from multiple sensors—including GPS—to create far more reliable positioning, velocity, orientation, and time metrics (Torc, 2018). This suite of sensors is always active, weighing all data to ensure accurate positioning even if GPS data are unavailable or inaccurate.
• TerraStar Service – a data services provider that enables accurate and efficient positioning solutions (TerraStar, 2018). The service uses a satellite-based positioning technique known as precise point positioning (PPP) that delivers an accuracy of a few centimeters globally using just a single receiver and without the need for a dedicated communications channel.

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.

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.

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.

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.

Source: FHWA
Figure 6. Vehicle control devices.

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