Electronic Throttle Control (ETC) System Strategy
The ETC strategy was developed mainly to improve fuel economy. This is possible by not coupling the throttle angle to the drivers pedal position and by uncoupling the throttle angle (produce engine torque) from pedal position (driver demand). This allows the powertrain control strategy to optimize fuel control while delivering the requested wheel torque.
The ETC monitor system is distributed across 2 processors within the PCM: the main powertrain central processing unit (CPU) and a monitoring processor called an enhanced quizzer (E-Quizzer) processor. The primary monitoring function is carried out by the independent plausibility check (IPC) software, which resides on the main processor. It is responsible for determining the driver demanded torque and comparing it to an estimate of the actual torque delivered. If the generated torque exceeds driver demand by a specified amount, the IPC takes appropriate action.
Since the IPC and the main controller share the same processor, they are subject to a number of potential, common failure modes. Therefore, the E-Quizzer processor was added to redundantly monitor selected PCM inputs and to act as an intelligent watchdog and monitor the performance to the IPC and the main processor. If the E-Quizzer determines that the IPC function is impaired in any way, it takes appropriate failure mode and effects management (FMEM) actions.
| Effect | Failure Mode (1) | ||
|---|---|---|---|
| No Effect on Driveability | A loss of redundancy or loss of a non-critical input could result in a fault that does not affect driveability. The caution light turns on, but the throttle control and torque control systems will functions normally. | ||
| Disable Speed Control | If certain failures are detected, speed control is disabled. Throttle control and torque control continues to function normally. | ||
| RPM guard with Pedal Follower | In this mode, torque control is disabled due to the loss of a critical sensor, PCM, or hybrid system fault. The throttle is controlled in pedal follower mode as a function of the pedal position sensor input only. A maximum allowed RPM is determined based on pedal position (RPM guard.) If the actual RPM exceeds this limit, spark and fuel are used to bring the RPM below the limit. | ||
| RPM guard with Default Throttle | In this mode, the throttle plate control is disabled due to the loss of throttle position, the throttle plate position controller, or other major electronic throttle body fault. A default command is sent to the TPPC, or the H-bridge is disabled. Depending on the fault detected, the throttle plate is controlled or springs to the default (limp home) position. A maximum allowed RPM is determined based on pedal position (RPM guard.) If the actual RPM exceeds this limit, spark and fuel are used to bring the RPM below the limit. | ||
| RPM guard with High Forced Idle | This mode is caused by the loss of 2 or 3 pedal position sensor inputs due to sensor, wiring, or PCM faults. The system is unable to determine driver demand, and the throttle is controlled to a fixed high idle airflow. There is no response to the driver input. The maximum allowed RPM is a fixed value (RPM guard). If the actual RPM exceeds this limit, spark and fuel are used to bring the RPM below the limit. | ||
| Shutdown | If significant processor fault is detected, the monitor forces vehicle shutdown by disabling all fuel injectors. | ||
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