Electronic Throttle Control Module: Description and Operation

TORQUE BASED ELECTRONIC THROTTLE CONTROL (ETC)

Overview
The Generation II (Gen II) torque based electronic throttle control (ETC) is a hardware and software strategy that delivers an engine output torque (through throttle angle) based on driver demand (pedal position). It uses an electronic throttle body, the PCM, and an accelerator pedal assembly to the control throttle opening and engine torque. The ETC system basically replaces the standard cable operated accelerator pedal, idle air control (IAC) valve, 3-wire throttle position (TP) sensor, and mechanical throttle body.

Electronic Throttle Body (ETB)
The Gen II electronic throttle body has the following characteristics:
1. The DC motor is driven by the PCM (requires 2 wires). The gear ratio from the motor to the throttle plate shaft is 17:1.
2. Two springs are used: one is used to close the throttle (main spring) and the other is in a plunger assembly that results in a default angle with no power applied. This is for limp home reasons (the force of the plunger spring is 2 times stronger than the main spring). The default angle is usually set to result in a top vehicle speed of 48 km/h (30 mph). Typically this throttle angle is 7 to 8 degrees from the hard-stop angle.
3. The closed throttle plate hard stop is used to prevent the throttle from binding in the bore (~0.75 degrees). This hard stop setting is non-adjustable and is set to result in less airflow than the minimum engine airflow required at idle.
4. Unlike cable type throttle bodies, the intent for the ETB is to not have a hole in the throttle plate or to use plate sealant. The hole is not required in the ETB because the required idle airflow is provided by the plate angle in the throttle body assembly. This plate angle controls idle and idle quality and eliminates the need for an IAC valve.
5. The system has 2 throttle position sensors. Redundant throttle position signals are required for monitor reasons. The TP1 has a negative slope (increasing angle, decreasing voltage) and the TP2 has a positive slope (increasing angle, increasing voltage). During normal operation the negative sloped TP sensor (TP1) is used by the control strategy as the indication of the throttle position. The TP sensor assembly requires 4 wires:
- 5 volt reference voltage (ETCREF)
- Signal return (ETCRTN)
- TP1 voltage with negative voltage slope 5 volts to 0 volts
- TP2 voltage with positive voltage slope 0 volts to 5 volts

Accelerator Pedal Position (APP) Sensors

Electronic Throttle Body (ETB) And Accelerator Pedal Assembly:

The ETC strategy uses pedal position as an input to determine the driver demand.

1. There are 3 pedal position sensors required for system monitoring. The APP1 has a negative slope (increasing angle, decreasing voltage) and APP2 and APP3 both have a positive slope (increasing angle, increasing voltage). During normal operation APP1 is used as the indication of pedal position by the strategy.
2. There are 2 VREF signals (ETCREF1 and ETCREF2), 2 signal returns (ETCRTN1 and ETCRTN2), and 3 signals (APPS1, APPS2, and APPS3) between the PCM and APP assembly.
- 5 volt reference voltage circuits (2)
- Signal return (ground) circuits (2)
- APP1 voltage with negative voltage slope 5 volts to 0 volts
- APP2 voltage with positive voltage slope 0 volts to 5 volts
- APP3 voltage with positive voltage slope 0 volts to 5 volts

3. The pedal position signal is converted to pedal travel degrees (rotary angle) by the PCM. The software then converts these degrees to counts, which is the input to the torque based strategy.
4. The 3 pedal position signals provide a correct input to the PCM should any one signal have a fault. The PCM knows if a signal is wrong by calculating where it should be, inferred from the other signals. A value is substituted for a faulty signal if 2 out of the 3 signals are bad.

Electronic Throttle Control (ETC) System Strategy

GEN II ETC System:

ETC System Failure Mode And Effects Management (Part 1):

ETC System Failure Mode And Effects Management (Part 2):

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 of 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.

Accelerator and Throttle Position Sensor Inputs

Accelerator Pedal Position Sensor Check:

Throttle Position Sensor Check:

Throttle Plate Position Controller (TPPC) Outputs

Throttle Plate Controller Check Operation:

Electronic Throttle Monitor Operation:

The purpose of the TPPC is to control the throttle position to the desired throttle angle. It is a separate chip embedded in the PCM. The desired angle is communicated from the main CPU over a 312.5 Hz duty cycle signal. The TPPC interprets the duty cycle signal as follows:
- Less than 5% - Out of range, limp home default position.
- Greater than or equal to 5% but less than 6% - Commanded default position, closed.
- Greater than or equal to 6% but less than 7% - Commanded default position. Used for key on, engine off.
- Greater than or equal to 7% but less than 10% - Closed against hard-stop. Used to learn zero throttle angle position (hard-stop) after key-up.
- Greater than or equal to 10% but less than or equal to 92% - Normal operation, between 0 degrees (hard-stop) and 82 degrees, 10% duty cycle equals 0 degrees throttle angle, 92% duty cycle equals 82 degrees throttle angle.
- Greater than 92% but less than or equal to 96% - Wide Open Throttle, 82 to 86 degrees throttle angle.
- Greater than 96% but less than or equal to 100% - Out of Range, limp home default position.

The desired angle is relative to the hard-stop angle. The hard-stop angle is learned during each key-up process before the main CPU requests the throttle plate to be closed against the hard-stop. The output of the TPPC is a voltage request to the H-driver (also in PCM). The H-driver is capable of providing a positive or negative voltage to the electronic throttle body motor.