Electronic throttle unit
The throttle unit is mounted on the engine intake manifold, the location can vary depending on engine type. 5 cylinder turbocharged engines and 6 cylinder engines have the throttle unit mounted under the intake manifold. Others have it mounted on the side of the intake manifold. The throttle unit's primary task is to control the amount of air to the engine from the request from the Engine control module (ECM).
The Electronic throttle module (ETM) is in the throttle unit, which means that it works as its own control module on the high speed side of the CAN.
The connection to the CAN takes up two of the six pins in the throttle unit's connector, the remaining four are taken up by:
- Voltage supply, 12 V via the engine control system's system relay.
- Ground terminals, separated from the engine control system's other ground terminals.
- Information about the brake pedal's position from the brake lamp switch.
- Information about the position of the accelerator pedal from the accelerator pedal unit's PWM sensor.
In order for the Electronic throttle module (ETM) to carry out the main task of controlling the air flow to the engine, the voltage supply, ground and contact with the CAN is sufficient. The other two signals about the position of the brake pedal and the accelerator pedal are used as a safety function in case a problem should occur with CAN communication. This makes it possible to continue driving, but with reduced driveability. The signals are used, among other things, to carry out a plausibility check of the desired throttle angle that comes from the Engine control module (ECM) via CAN.
In addition, the throttle unit consists of a further number of components such as throttle housing, throttle disc, throttle spindle, torque motor, throttle position sensor (potentiometers), spring unit etc.
In one end the throttle unit contains a stepless torque motor that is directly operated on the throttle spindle. The torque motor is supplied with 12 V and controlled by the Electronic throttle module (ETM). In the other end there is the throttle's spring unit and the mechanical stop for the smallest and largest throttle openings.
Outside the torque motor and the spring unit, out on the relevant end there is a throttle position sensor (potentiometer). The two position sensors are mechanically connected to each other via the throttle spindle.
- Rotational hub with contacts.
- Contacts, x 2
- Contact track, 2 grooves.
For safety reasons, two position sensors send the same signal about the position of the throttle to the electronic throttle module (ETM).
If the signal from one of the position sensors is missing or faulty, the electronic throttle module (ETM) is still able to calculate the position of the throttle using the signal from the other position sensor. This maintains the driveability of the car.
Depending on the type of fault, the throttle system can reconfigure its own software (limp-home mode) and can react in different ways.
The throttle is a so called "ball zone throttle" which means that the throttle housing's mating surfaces are "spherical" and provide a better solution per opening angle. This gives more accurate flow control from idling position up to approximately 20 % open throttle. The effect is a smoother start at throttle opening / acceleration.
A number of plausibility checks are carried out by the Engine control module (ECM) to determine whether the throttle unit and Electronic throttle module (ETM) works as intended or not.