## 3 Driving Behavior Characterization for Fuel-Consumption Scenarios
### Fuel-Consumption Obtainment by Simulation  
An important step of this work is the obtainment of a meaningful set of fuel consumption data, as mentioned in precedent paragraphs. This step was found to be needed, since the Uyanik dataset lacked the engine's engine control unit (ECU) data regarding fuel injection or intake airflow.  
Several alternatives were studied in order to obtain and measure fuel control unit data, finally choosing a simulation environment. We selected the Gamma Technologies GT-Suite environment [47], since it does not only allows element-by-element simulation of mechanical systems, but also enables users to run macroscopic approximated models of complete automobiles. Thus, while the former requires an exact parameterization of each mechanical element and link of the engine, the latter allows us to fit a pre-elaborated model based on telemetry (such as speed, acceleration, brake, or selected gear) as well as on car manufacturer information, such as gear ratios, tire dimensions, or wheelbase (see Figure 3).  
Figure 3: Flow of real-world telemetry-based fuel consumption simulation. It has macroscopic car parameters (gear ratios, tyre dimensions, and wheelbase) and telemetry (gas pedal, brake pedal, speed, selected gear, and accelerations) as inputs. The model returns the simulated fuel flow as output.  
Finally, the gear ratios were computed while using data about RPM and vehicle speed, available for each instant. We computed the speed/rpm ratio sample-by-sample and matched it with each gear's ratio. When computed ratios did not match with any of the gear ratios, we assumed that the driver was operating the clutch pedal.  
Once the car parameters were successfully extracted, we elaborated on the model that is displayed in Figure 4. In this model, four main elements can be identified for the car itself, the vehicle, transmission, engine, and ECU blocks, while the driver is modeled by another one. These blocks contain the characteristic parameters of their corresponding real-world counterparts.  
* Vehicle comprises data regarding car wheelbase, wheel radius, friction coefficients, aerodynamics, weight, inertia, and final transmission ratio.
* Transmission incorporates individual ratios for each of the user-selectable gears, as well as clutch parameters.
* Engine consists of parameters such as engine displacement, engine type (4-stroke or 2-stroke), minimum operation speed, or fuel characteristics.
* ECU controls the maximum engine RPM, idle speed, and fuel injection cutoff and restart points.
* Driver wraps the telemetry data related to the handling of the car, such as selected gear, accelerator pedal state, brake pedal state, clutch, and desired speed.  
Several checks were performed on the simulation model in order to verify that the returned results provide an acceptable emulation of the real car performance. Thus, given a set of selected gears, as displayed in Figure 5a, the application of the driver operation of the accelerator and brake pedals, along with the dynamics of the car restricted to a set of measured accelerations, brings out the simulated RPM and vehicle speed red curves of Figure 5b,c, respectively. As can be seen, these red curves are almost totally overlapped with the blue ones, which represent the real world-collected data, with relative errors of 1.83% for RPM and of 0.44% for speed. These low relative errors mean that the simulation faithfully emulates the real car behavior and, consequently, that the returned fuel consumption simulated data is useful for carrying out estimations in order to verify the proposed SOM-based models and extracting conclusions.  
Figure 4: Block diagram of real-world telemetry-based fuel consumption simulation of Uyanik Renault Mégane 1.5 dCi Sedan 74 kW. It has macroscopic car parameters (gear ratios, tyre dimensions, and wheelbase) and telemetry (gas pedal, brake pedal, speed, selected gear, and accelerations) as inputs. The model returns the simulated fuel flow as output.