| Operation of electronic throttle system |
| With the electronic throttle system the throttle valve is not actuated by a cable connected to the accelerator pedal. There is no mechanical link between the accelerator and the throttle valve. |
| The position of the accelerator pedal is communicated to the engine control unit by two accelerator position senders (variable resistors, both fitted in a single housing) which are connected to the accelerator pedal. |
| The position of the accelerator pedal (driver input) is one of the principal input variables for the engine control unit. |
| The throttle valve is actuated by a servomotor (throttle valve positioner) in the throttle valve module over the full range of engine speeds and load conditions. |
| The throttle valve is actuated by the throttle valve positioner in line with the specifications of the engine control unit. |
| When the ignition is on and the engine is not running, the engine control unit operates the throttle valve positioner in exact accordance with the signals from the accelerator position senders. For example, when the accelerator is pressed down half way, the throttle valve positioner opens the throttle valve by an equivalent amount, i.e. about half way. |
| When the engine is running (under load) the engine control unit can open and close the throttle valve freely (i.e. independently of the signals being sent by the accelerator position sender). |
| Thus, for example, the throttle valve may already be fully open even though the accelerator is only pressed down half way. This has the advantage of preventing throttling losses at the throttle valve. |
| Under certain engine load conditions there is also a significant improvement in emission levels and fuel consumption. |
| The engine control unit can provide the optimum combination of throttle valve opening and charge pressure in order to generate the required torque. |
| It would be inappropriate to think of the “electronic throttle system” as only comprising one or two components. The electronic throttle system actually contains all the components used to determine, control and monitor the position of the throttle valve, e.g. the accelerator pedal position sender, the throttle valve module, the EPC warning lamp and the engine control unit...). |
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