Load signal potentiometer G157

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Load signal potentiometer G157

Post by Deylan » Tue Jun 23, 2009 7:37 pm

The load signal potentiometer is in essence a Throttle Position Sensor (TPS), it effectively informs the DIGISWING control unit the position of the accelerator pedal, and thus, the DIGISWING control unit uses this information to master the clutch operation, and also determine when to switch the engine off (i.e., when the throttle is closed).

It can be adjusted by altering the adjustment screw. Do not confuse this with the residual volume screw. If in doubt seek advice from an expert who knows what he is doing and respects the electronic nature of the vehicle. Once this is adjusted the engine idling speed will most likely need to be adjusted to correct specifications. See "Cold starting aid" for idle speed specifications. Basic setting will also probably need to be carried out.

If this switch fails the control unit can substitute data from the engine speed sender to determine throttle position, ecomatic mode is fully disabled, both ecomatic control lamp K110 [k110] and engine running control lamp K111 [k111] are illuminated, clutch behaviour is delayed when pulling away and choppy/uncomfortable.

Additional notes:

When the vehicle is operating in this emergency running programme, the engine must be revved up to approximately 1500RPM before the clutch will take up drive, this is to guarantee that that the accelerator pedal is being operated and the driver is intending to pull away, rather than a slightly out of adjustment engine idling speed, which would cause the car to move off unintentionally. Because of this the car tends to drive off with a lurch - this is due to the fact that the engine speed sender and load signal potentiometer data directly influences the clutch control algorithm when pulling away, however, because the emergency programme simply prohibits clutch operation below approx. 1500RPM, once 1500RPM is attained the clutch is suddenly operated to a predefined stored value corresponding to that amount.

It is apparent that the load signal potentiometer plays a very important part in clutch closure operation when accelerating off and during gear change. The goal of the control unit is to close the clutch near to when the engine revolutions match what they will be when they are connected, and when pulling away, to ensure clutch slip is not too high or low, to reduce wear on the clutch and increase driving comfort. One might assume most of this calculation is done through monitoring engine RPM in relation to the gearbox input shaft speed, actually, it seems that the load signal potentiometer is playing a big part in how much clutch slip occurs. Presumably, the reasoning behind this is that the clutch position should correspond with engine torque produced, as opposed to engine RPM. For example, if the accelerator pedal is pressed down hard, the clutch can be closed further and quicker than it could be when it is pressed lightly, even at the same engine RPM, due to the increased torque produced by the engine.

Therefore if excessive clutch slip is encountered during pulling away in 1st gear, or when changing gear, or "jolting", then it is quite possible the problem lies within a worn potentiometer.

Another condition that can be encountered by a faulty load signal potentiometer or, one in require of basic setting, is when one is driving along in ecomatic mode and lifts off throttle towards the fully closed position, but not totally, the clutch seems to be opened and the engine revs jump up. This is because the control unit has assumed that the driver has lifted his foot off the accelerator totally and therefore it needs to enter overrun, however this not the case, the control unit realises this by the increase of engine RPM and re-closes the clutch. Resetting to basic setting may fix this issue however if it reoccurs it is quite possible that the potentiometer is worn and therefore it's resistance at a given position is not consistent, therefore throwing out the adaption. This could also be caused by a loose or slack cable.
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