| Operation of electronic throttle system |
| In the EPC, the throttle is not operated by a control cable from the accelerator. There is no mechanical link between the accelerator and the throttle valve. |
| The position of the accelerator is transmitted to the engine control unit by 2 accelerator position senders (variable resistors together in a housing) which are connected to the accelerator pedal |
| The position of the accelerator (decided by the driver) is one of the main input parameters to 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 position device actuates the throttle valve according to the commands it receives from 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 position device 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 or close the throttle valve independently of the accelerator pedal position sender. |
| For example, the throttle valve might already be fully open even though the accelerator is only pressed down half way. The advantage of this is that losses through bottlenecks caused by the throttle are avoided |
| After evaluating the torque requirements of various components (e.g. air conditioning, automatic gearbox, ABS/ESP and so on), the engine control unit calculates the optimal throttle valve opening angle for the respective situation |
| This also gives vastly improved consumption and exhaust emission levels at certain load conditions |
| „EPC“ is a system, which is comprised of all components which have an influence, control or monitor the position of the throttle valve, e.g. the accelerator pedal position sender, the throttle valve control unit, the EPC warning lamp, the engine control unit. |
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