Throttle Control

Throttle Control







To ensure that the correct throttle angle is reached, the engine control module (ECM) controls the throttle shutter in the throttle unit (6/120), mainly using the signal from:
- accelerator pedal (AP) position sensor (7/51)
- clutch pedal sensor (7/123) via central electronic module (CEM) (4/56)
- stop lamp switch (3/9)
- the throttle position (TP) sensor on the electronic throttle unit (6/120)
- brake pedal sensor (7/124) via brake control module (BCM) (4/16).

Additional signals and parameters are used to ensure optimum throttle control. By example by compensating for:
- the load from the air conditioning (A/C) compressor
- the load from the transmission depending on the selected gear mode (automatic)
- engine coolant temperature (ECT).

In a combustion engine, the difference between the minimum and maximum airflow is considerable. The smaller air flows need more thorough regulation (for example during idle air trim), so the throttle position (TP) sensor signal 1 is amplified approximately 4 times in the engine control module (ECM) before it reaches the Analog/Digital converter in the engine control module (ECM). This means that there are three, two real and one fictitious, input signals available to the engine control module (ECM). These signals are used to determine the position of the throttle disc and to control the throttle motor to the correct throttle angle.

Because the signal is amplified, it reaches its maximum value at approximately a quarter of maximum deployment.

The engine control module (ECM) primarily uses the signal from throttle position (TP) sensor 1 as a measurement of throttle opening. The signal from throttle position (TP) sensor 2 is mainly to check that throttle position (TP) sensor 1 is working. The engine control module (ECM) then uses the signal to calculate a throttle angle (actual value). This is the actual throttle angle. The value for the actual throttle angle is used by those functions in the engine control module (ECM) which depend on this information so that the throttle can be correctly regulated.

There is an adaptation (learning) in the engine control module (ECM) so that the control module can calculate how the damper motor needs to be controlled. See "Adaptation of the electronic throttle unit" below. This adaptation occurs automatically when necessary. The engine control module (ECM) moves the throttle disc to the different positions and reads off and registers the actual values from the throttle position (TP) sensors.

The throttle angle is regulated so that the actual angle (actual value) is the same as the angle calculated by the engine control module (ECM) (desired value). The engine control module (ECM) also uses the values that were stored during adaptation of the throttle angle, and the actual signals from the throttle position (TP) sensor.

The damper motor is deployed by the integrated power stage in the engine control module (ECM) using a pulse width modulation (PWM) signal. The torsion from the opening and return springs in the electronic throttle unit is also used. If the engine control module (ECM) detects a fault in the electronic throttle unit so that the throttle disc cannot be controlled, the springs in the throttle unit will turn the throttle disc to the limp home position (return position). This return position is calibrated to provide a throttle angle large enough to allow the car to be driven to a workshop, although with considerably reduced drivability.

Throttle angle
The engine control module (ECM) also monitors the throttle unit signals from the throttle position (TP) sensors, to ensure that these signals are within the parameters and correspond to the same throttle angle.

If the difference between the signals exceeds a set limit the maximum value is selected as the actual value (which means that the throttle disc is controlled down). If the engine control module (ECM) detects a fault in both throttle position sensors, the electronic throttle unit power stage is switched off. The throttle switches to limp home mode (return position). Diagnostic trouble codes (DTC) are stored in the engine control module (ECM) if faults are detected in the throttle position (TP) sensors.

Adaptation of the throttle unit
Adaptation of the electronic throttle unit is carried out automatically when requested by the engine control module (ECM). Adaptation is carried out to check the function of the electronic throttle unit, and, if necessary, to update the values obtained from the throttle position (TP) sensors etc. during regulation, as these values can change somewhat over the service life of the throttle unit. Diagnostic trouble codes (DTC) are stored in the engine control module (ECM) if faults are detected in the electronic throttle unit.