## 2 Target Vehicle and Data
### Target Data  
The TMED type HEV shown in Figure 1 drives the vehicle using MG2 in EV driving mode and drives the vehicle mainly using the engine and MG2 in HEV driving mode. According to a power distribution strategy, an HCU drives the vehicle in EV mode or HEV mode. Therefore EV\(\leftrightarrow\)HEV mode transitions can occur when the vehicle is driving. For an HEV\(\rightarrow\)EV mode transition, an HCU gives an EV mode transition command, and then an engine clutch is disengaged with a clutch pressure drop. Additionally, an EV\(\rightarrow\)HEV mode transition is accomplished through the following process [46].  
1. Cranking an engine using MG1 or MG2;
2. Speed synchronization of both sides of the engine clutch (engine and traction motor speed synchronization);
3. Engine clutch engagement and transition to HEV mode.  
This paper tried to detect anomalies related to this engine clutch engagement/disengagement occurring in EV\(\leftrightarrow\)HEV mode transitions.  
Table 1 shows the cases of representative anomalous behavior for such data. An engine clutch engagement failure is the case when the speed difference between an engine and a motor occurs at higher than a certain level, although an HCU applies an engine clutch command to be fully engaged. The engine clutch disengagement failure is the case when the speed difference between an engine and a motor occurs lower than a certain level because the clutch is not released correctly, although an HCU applies an engine clutch command to be released. The clutch pressure command following failure is the case when the clutch pressure does not follow a clutch pressure command from the HCU or TCU (transmission control unit). We collected actual vehicle test data, including the following anomalous behavior cases, and trained the models to detect anomalies with these data.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Case** & **Description** \\ \hline Engine clutch & The speed difference between an engine and a motor exceeds a certain level, although an HCU applies an engine clutch command to be fully engaged. \\ Engine clutch & (This case is that the engine clutch is not fully engaged as intended. For the target vehicle, as the engine clutch \\ engagement failure & connects the engine and the motor, there should be no speed difference between the engine and the motor when HCU commands the engine clutch as full engagement in normal conditions.) \\ \hline Engine clutch & The speed difference between an engine and a motor is less than a certain level over a certain time, although an HCU applies an engine clutch command to be released/open and an engine operating mode command to be off for EV mode. \\ Engine clutch & (This case is that the engine clutch is not released as intended in EV mode. As a result, the speed difference is small as the engine clutch still connects the engine and the motor. In normal conditions, there should be a speed difference between the engine and the motor because the motor has speed according to the vehicle speed and the engine speed is zero due to the engine off command.) \\ \hline Clutch pressure command & The difference between a clutch pressure command value and a clutch pressure sensor value exceeds a certain level over a certain time. \\ following failure & (This case is that the engine clutch pressure does not follow a command. In normal conditions, the difference between the pressure command and pressure sensor value should be small enough. When the pressure command changes significantly, hydraulic generation delay can slightly increase this difference, but the duration should not be long.) \\ \hline \hline \end{tabular}
\end{table}
Table 1: Representative anomalous behaviors in engine clutch engagement/disengagement.  
Figure 2: Parallel HEV structures classification.