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Superb question: Torque Converter at 0.0 L/KM?

Echelon

By Echelon,
in Conti Talk

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Echelon

Echelon

3rd Gear

Bro Koolaba, just a question, in trying your excellent fuel "stretching" method I am managing quite well in my fc. When I am on 5th gear or sometimes even 3rd gear when I release the accelerator the car will show 0.0 L/KM this is when the torque convertor is disengaged and no fuel is being pushed to the engine? Because immediately after that at a slow speed it will start to go up again. (Not sure if I explained it clearly)

 

So why does it do that?

 

Attached is a pic of my improvements in FC.Usually it is 540km of fuel available, it has incrementally been stretching the distance.

post-73-1190877520_thumb.jpg

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Moeykf

Moeykf

Neutral Newbie

bro, ur situation also applies to my octy. when i release my accelerator at speeds above 60km/h, reading is 0.0L....when it slows down to speeds of 40km/h and below, it will gradually increase even if i never step on the accelerator. think the highest will be like 30+L when it is at 10km/h and drops back to 0.0L when the vehicle comes to a stop.

 

till now i also got no idea wat does tat mean haha.

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Koolaba

Koolaba

1st Gear
(edited)

Hi,

 

The torque convertor in an automatic transmission is akin to the clutch in the manual transmission. The only difference being: torque convertors work on the principle of fluid coupling, whereas the driving and driven gears in a manual transmission are coupled mechanically. Fluid coupling is less effcient in the transmission of energy.

 

In any manual transmission car with a instantaneous FC meter, you will see 0.0l/100km once you release the accelerator with the clutch engaged (i.e. rpm does not drop to idling range). King and Drive, who drive manual Octavia 1.6 and 1.8T respectively, will be able to attest to this.

 

In the automatic transmission, the 0.0l/100km readout is present if and only if the following two conditions are present:

1. the torque convertor is locked

2. the accelerator pedal is not depressed at all

In such instances, the fuel cut-off design of the vehicle is active and no fuel is consumed at all.

 

If you see a instantaneous FC reading greater than 0.0l/100km, it indicates that the torque convertor is unlocked and thus uncoupled. This is similar to free-wheeling (aka coasting in neutral) in a manual transmission. The transmission control unit in the automatic transmission regulates the un/locking of the torque convertor. If the speed is too slow, the torque convertor needs to be decoupled so that the engine does not stall.

Edited by Koolaba
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Try_conti

Try_conti

2nd Gear

Just a quick question about 'no fuel consumed'. I don't think this is true as fuel is needed to keep the engine running.

 

If really no fuel consumed, the engine would have stalled.

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Echelon

Echelon

3rd Gear
  • Author

Well it has been good, in the past my fuel gauge needle at half tank only allows me 250km more of distance to travel, right now it is showing 320km amount of fuel to go, can I go from Sg-KL with this.....Hhaa...

 

Thanks Koolaba, learnt alot from you. [scholar]

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Echelon

Echelon

3rd Gear
  • Author

Wow yours is better, today I am at the 320km mark. Notice a drop when I stepped to overtake at the PIE and the turbo came on. But the method applied by bro Koolaba has been very helpful.

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Koolaba

Koolaba

1st Gear
(edited)

I have read the write-up in the owner's manual for a (manual transmission) Opel Combo on the fuel cut-off facility. It mentioned that no fuel is fed into the engine when fuel cut-off is activated. To lower the FC, the manual has prescribed that it is good practice not to allow the vehicle to free-wheel / coast to a stop i.e. with the clucth disengaged, gear shifted to neutral and rpm dropping to idling range.

 

If we relate this to the law of Physics, the engine will not stall as long as the following conditions are present:

- the driven wheels are moving, thus a momentum is present

- the cluth is engaged, thus the engine is still coupled to the rotating (moving) wheels

 

If you have driven a manual car, you will agree that the engine will stall if you do not depress the cluth pedal (hence disengaging the clucth). Due to the mechanical coupling (when the clutch is still engaged), the deccelerating wheels will also bring the engine to a halt.

 

I have shifted to the west. Feel free to arrange for a meet-up. We can get Viperphoenix to join us too.

Edited by Koolaba
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Falc

Falc

3rd Gear
the manual has prescribed that it is good practice not to allow the vehicle to free-wheel / coast to a stop i.e. with the clucth disengaged, gear shifted to neutral and rpm dropping to idling range.

 

I have read that too. Just to contribute abit ...

 

The rationale is by not disengaging the clutch, as the car slows, momentum is been used to drive your air-con, power steering etc. Hence, no extra fuel consumed by engine.

 

If you disengaged the clutch, the egine will be in idle mode, and in idle mode, the aircon and power steering are driven by the engine not by car's momentum, hence fuel is consumed.

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Koolaba

Koolaba

1st Gear

[nod]

 

On automatic transmission cars, the transmission control unit (not the driver) decides when to unlock/lock the torque convertor. This is one of the factors why automatic cars are less fuel efficient than the manual counterparts.

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Koolaba

Koolaba

1st Gear

One of the Superb owners, Soleution, has commented that rhe range (indicated on the MFA) is almost 800km when he travelled between Singapore and KL. He has no problems driving to and from KL on less than a full tank of petrol.

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Echelon

Echelon

3rd Gear
  • Author

That is incredible!! 800 km on one tank of petrol!Man I got to give that a try. What would be the recommended speed to be able to achieve that kind of FC?

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