Electronic Throttle Control Module: Description and Operation

Torque Based Electronic Throttle Control (ETC)

Overview

Torque Based Electronic Throttle Control (ETC) is a strategy that delivers a transmission output shaft torque (via throttle angle) based on driver demand (pedal position). It utilizes the Visteon Gen II electronic throttle body (replaces throttle cable).

Torque based ETC strategy was developed mainly to improve fuel economy. This is possible by not coupling the throttle angle to pedal position, which enables various fuel economy schemes and technologies.
Background "Why Torque Based ETC"

Torque based ETC enables aggressive automatic transmission shift schedules (earlier upshifts and later downshifts). This is possible by adjusting the throttle angle to achieve the same wheel torque during shifts. In other words the engine shifts can result is an engine lugging condition (low RPM and low manifold vacuum) while still delivering the same torque requested by the driver. It should be noted that the ETC system includes a wrench light on the instrument cluster that illuminates when a fault is detected. Faults are also accompanied by DTCS and the "Check Engine Soon" light.

It also enables many fuel economy/emission improvement technologies such as:

- VCT (deliver same torque during transitions)
- Continuously varying Transmission (CVT)
- Hybrid Electric Vehicle (HEV)

Torque based ECT also results is a less intrusive vehicle and engine speed limiting, along with smoother traction control.

Other generic benefits of ETC are:

- Eliminate cruise control actuators
- Eliminate ISC Bypass actuator
- Better airflow range
- Packaging (no cable)

Electronic Throttle Body

The Gen II electronic throttle body (Figure 148) has the following characteristics

1. The DC motor is driven by the PCM (requires two wires). The gear ratio from the motor to the throttle plate shaft is 17:1.
2. There are two designs; parallel and in-series. The parallel design has the motor under the bore parallel to the plate shaft. The motor housing is integrated into the main housing (in general this is more difficult to package). The in-series design has a separate motor housing that protrudes out and offers more packaging flexibility.
3. 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 (force of plunger spring is 2X main spring). Default angle is usually set to result in a top vehicle speed of 30 MPH (typically 7 to 8 degrees from hard-stop angle).
4. The closed throttle plate hard stop is used to avoid the throttle from binding is the bore (~0.75 degree). This hard stop is non-adjustable and is set to result in less airflow than the minimum engine airflow required at idle.
5. Unlike cable type throttle bodies, the intent for the ETB is not to have a hole in the plate or use plate sealant. The hole in the plate is not required with ETB because the required idle airflow is provided by the plate angle, which also is the reason there is no IAC.
6. The system has two throttle position sensors. Redundant throttle position signals are required for monitor reasons. TP1 has a negative slope (increasing angle, decreasing voltage) and 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 throttle position. The TP assembly requires four wires.

- 5 V Reference Voltage
- Signal Return (ground)
- TP1 voltage with negative voltage slope (5-0)
- TP2 voltage with positive voltage slope (0-5)

Accelerator Pedal Position Sensors (APPS)

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

1. There are three pedal position sensors required for safety monitor reasons. APP1 has a negative slope (increasing angle, decreasing voltage) and APP2 & 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 two VREF wires, two signal return wires and three signal wires (total of seven wires and pins) between the PCM and APPS assembly.
- 2- (5 V Reference Voltage)
- 2- (Signal Return "ground")
- APP1 voltage with negative voltage slope (5-0)
- APP2 voltage with positive voltage slope (0-5)
- APP3 voltage with positive voltage slope (0-5)

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 three pedal position signals ensure a correct input to the PCM, if any one signal has a fault. The PCM knows if a signal is wrong by calculating where it should be, inferred by the other signals. A safe value will be substituted for a faulty signal if two out of the three signals are bad.