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 a transmission output shaft torque (via throttle angle) based on driver demand (pedal position). It utilizes an electronic throttle body, the PCM and a accelerator pedal assembly to control throttle opening and engine torque. The ETC system basically replaces the standard cable operated accelerator pedal, idle air control (IAC) motor, 3-wire throttle position sensor (TPS) and mechanical throttle body
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, and by calculating this desired torque, the system prevents engine lugging (low RPM and low manifold vacuum) while still delivering the performance and torque requested by the driver.
It also enables many fuel economy/emission improvement technologies such as:
- VCT (deliver same torque during transitions)
- Hybrid Electric Vehicle (HEV)
Torque based ETC 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 Idle Air Control (IAC) Bypass actuator
- Better airflow range
- Packaging (no cable)
- More responsive powertrain at altitude and improved shift quality
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.
Electronic Throttle Body (ETB)
The Gen II electronic throttle body (Figure 133) 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 2 times stronger than the main spring). Default angle is usually set to result in a top vehicle speed of 30 MPH (48 Km). Typically this throttle angle is 7 to 8 degrees from the hard-stop angle.
4. The closed throttle plate hard stop is used to avoid the throttle from binding in the bore (approximately 0.75 degree). This hard stop setting 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 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 IAC bypass actuator.
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 sensor 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 system monitoring. 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.
Electronic Throttle Body And Accelerator Pedal Assembly:
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 value will be substituted for a faulty signal if two out of the three signals are bad.
Electronic Throttle Control System Strategy
GEN II ETC System:
As stated earlier the torque based ETC strategy was developed mainly to improve fuel economy and to accommodate Variable Cam Timing. This is possible by not coupling the throttle angle to the drivers pedal position. By uncoupling the throttle angle (produce engine torque) from pedal position (driver demand). This allows the powertrain control strategy to optimize fuel control and transmission shift schedules while delivering the requested wheel torque. ETC is used on the 2004 MY Lincoln LS and Ford Thunderbird, Explorer/Mountaineer, and the new light-duty F-series.
The ETC monitor system is distributed across two processors within the PCM: the main powertrain control processor unit (CPU) and a monitoring processor called an Enhanced-Quizzer (E-Quizzer) processor. The primary monitoring function is performed 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 specified amount, the IPC takes appropriate mitigating action.
ETC System Failure Mode And Effects Management, Part 1:
ETC System Failure Mode And Effects Management, Part 2:
Since the IPC and 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 it determines that the IPC function is impaired in any way, it takes appropriate Failure Mode and Effects Management (FMEM) actions.
Electronic Throttle Monitor Operation:
Electronic Throttle Monitor Operation, Part 1:
Electronic Throttle Monitor Operation, Part 2:
Accelerator and Throttle Position Sensor Inputs
Accelerator Pedal Position Sensor Check:
Accelerator Pedal Position Sensor Check:
Throttle Position Sensor Check:
Throttle Position Sensor Check:
Throttle Plate Position Controller (TPPC) Outputs
Throttle Plate Controller Check 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 via a 312.5 Hz duty cycle signal. The TPPC interprets the duty cycle signal as follows:
- 0% <= DC < 5% - Out of range, limp home default position.
- 5% <= DC < 6% - Commanded default position, closed.
- 6% <= DC < 7% - Commanded default position. Used for key-on, engine off.
- 7% <= DC < 10% - Closed against hard-stop. Used to learn zero throttle angle position (hard-stop) after key-up.
- 10% <= DC <= 92% - Normal operation, between 0 degrees (hard-stop) and 82%, 10% duty cycle = 0 degrees throttle angle, 92% duty cycle = 82 degrees throttle angle.
- 92% < DC <= 96% - Wide Open Throttle, 82 to 86 degrees throttle angle.
- 96% < DC <= 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 positive or negative voltage to the Electronic Throttle Body Motor.