| Electronic acceleration: operation |
| With the EPC system the throttle valve is not operated by a cable. There is no mechanical connection between accelerator and throttle valve. |
| The position of the accelerator is transmitted to the engine control unit by two accelerator position senders (variable resistors together in a housing) which are connected to the accelerator pedal. |
| The position of the accelerator (driver's requirement) is the main input value for the engine control unit. |
| The throttle valve is operated over the complete revolution and load range by an electric motor (throttle valve positioner) in the throttle valve control unit. |
| The throttle valve is operated by the throttle valve positioner which is controlled by the engine control unit. |
| When the engine is not running and the ignition is switched on the engine control unit moves the throttle valve exactly as prescribed by the accelerator pedal position sender. This means that when the accelerator is depressed halfway the throttle valve positioner opens the throttle valve by the same amount, the throttle is then approximately half open. |
| 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. |
| In this way, the throttle valve can, for example, be open completely even if the accelerator is only half way down. This avoids choking losses caused by the throttle valve. |
| 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. |
| It is incorrect to believe that the “EPC” is comprised of one or two components only. The electronic acceleration is a system that contains all of the elements that determine the throttle valve position, regulating and surveying, for example the accelerator position sender, the throttle control unit, the EPC indicator light, the engine control unit. |
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