Go Back   Team-BHP > Under the Hood > Technical Stuff


Reply
 
Thread Tools Search this Thread
Old 16th March 2011, 21:18   #61
Distinguished - BHPian
 
Join Date: Jul 2009
Location: Kolkata
Posts: 3,506
Thanked: 2,072 Times
Default re: RPM shoots up when changing gears

Quote:
Originally Posted by DerAlte View Post
That has already been taken care of in the first few cm after the jet in carb engine. No effect by the time it reaches cylinder. Even in GDI it hardly has any effect in the cylinder.
It is now a cold charge.

For what?
Equilibrium.

In the end it all boils down to actual time available for cooling or heating - duty cycle is an abstraction.
Far more than an abstraction. If the freq of the stimulus is far higher than the observable change in the result, it saves you from a whole lot of (sometimes very) complex mathematics. I think in todays IT/ electronics dominated age, should have called it PWM!

PS: Sutripta - we are seriously OT wrt the thread title. Shouldn't we move all the OT stuff to a new thread?
I agree. But you are the Mod!
Quote:
Originally Posted by SS-Traveller View Post
...and this is what I found additionally. Does this apply to all cars, or just Hyundai?
I find that quoted explanation very iffy. First, it is a turbocharged petrol. Secondly think why our old faithful Ambassadors would vent blue smoke when we suddenly snapped the throttle shut. (Actually, Ive seen this even more in Omnis on restart)

Quote:
Originally Posted by SPIKE ARRESTOR View Post
PS- @Nitrogary, Sutripta, SS da, can we have a separate thread on calibrations? Would be a good topic for discussion.
Hi Spike, a very warm welcome!

Quote:
Originally Posted by SS-Traveller View Post
Maintenant, quel professeur devrais-je croire?
Keep the faith (in yourself) and to thyself be true. Don't believe (blindly) false prophets, sorry professors (false or otherwise). Question everything!

Regards
Sutripta

Last edited by Sutripta : 16th March 2011 at 21:20.
Sutripta is offline   Reply With Quote
Old 16th March 2011, 23:41   #62
Senior - BHPian
 
DerAlte's Avatar
 
Join Date: Mar 2007
Location: Bangalore
Posts: 8,076
Thanked: 2,876 Times
Default re: RPM shoots up when changing gears

Quote:
Originally Posted by SS-Traveller View Post
... Maintenant, quel professeur devrais-je croire?
Vous devez croire seulemant Le Professeur, parce que - malheureusement - je ne suis pas!

Quote:
Originally Posted by SS-Traveller View Post
... With an increase in crankcase pressure ...
Full OHT - how? what caused it?

Last edited by DerAlte : 16th March 2011 at 23:56.
DerAlte is offline   Reply With Quote
Old 17th March 2011, 00:16   #63
Distinguished - BHPian
 
SS-Traveller's Avatar
 
Join Date: Jan 2009
Location: New Delhi
Posts: 6,629
Thanked: 10,863 Times
Default re: RPM shoots up when changing gears

Quote:
Originally Posted by SS-Traveller View Post
With an increase in crankcase pressure...
Quote:
Originally Posted by Sutripta View Post
...think why our old faithful Ambassadors would vent blue smoke when we suddenly snapped the throttle shut. (Actually, Ive seen this even more in Omnis on restart)
Simple question, Sutripta, and a reasonably simple answer, I think, but I'll leave it to you to answer. It will also answer...
Quote:
Originally Posted by DerAlte View Post
...how? what caused it?
...but...
Quote:
Originally Posted by DerAlte View Post
Full OHT
= Oral Hydration Therapy?
SS-Traveller is offline   Reply With Quote
Old 17th March 2011, 06:36   #64
Distinguished - BHPian
 
Join Date: Jul 2009
Location: Kolkata
Posts: 3,506
Thanked: 2,072 Times
Default re: RPM shoots up when changing gears

Quote:
Originally Posted by DerAlte View Post
Vous devez croire seulemant Le Professeur, parce que - malheureusement - je ne suis pas!
Heureusement - je ne suis pas!
Guys, could we lay off this on a public forum.

Quote:
Originally Posted by SS-Traveller View Post
Simple question, Sutripta, and a reasonably simple answer, I think, but I'll leave it to you to answer. It will also answer...

...but...

= Oral Hydration Therapy?
But do you agree?

Regards
Sutripta
Sutripta is offline   Reply With Quote
Old 17th March 2011, 10:11   #65
Distinguished - BHPian
 
SS-Traveller's Avatar
 
Join Date: Jan 2009
Location: New Delhi
Posts: 6,629
Thanked: 10,863 Times
Default re: RPM shoots up when changing gears

Quote:
Originally Posted by Sutripta View Post
But do you agree?
About blue smoke from the tailpipe on an overrunning engine in Ambys and Omnis? Absolutely. But I'd like you to put the answer about the why here in your own words.
SS-Traveller is offline   Reply With Quote
Old 17th March 2011, 10:31   #66
Senior - BHPian
 
DerAlte's Avatar
 
Join Date: Mar 2007
Location: Bangalore
Posts: 8,076
Thanked: 2,876 Times
Default re: RPM shoots up when changing gears

Quote:
Originally Posted by SS-Traveller View Post
... = Oral Hydration Therapy? ...
No, OHT = Over Head Transmission (went over the head)! Needs Oral Re-hydration anyhow after that.
Quote:
Originally Posted by Sutripta View Post
Heureusement - je ne suis pas aussi!
Mais non, je ne crois pas que, monsieur!
Quote:
Originally Posted by Sutripta View Post
Guys, could we lay off this on a public forum.?...
D'accord. But, no fun when done off the forum, non?

Last edited by DerAlte : 17th March 2011 at 11:19.
DerAlte is offline   Reply With Quote
Old 17th March 2011, 11:14   #67
Senior - BHPian
 
DerAlte's Avatar
 
Join Date: Mar 2007
Location: Bangalore
Posts: 8,076
Thanked: 2,876 Times
Default re: RPM shoots up when changing gears

Quote:
Originally Posted by Sutripta View Post
... Far more than an abstraction. ...
An abstraction, nevertheless. Once a phenomenon has been abstracted, anything beyond is still abstraction, not a reversible process to relate to the details.

Quote:
Originally Posted by Sutripta View Post
... I think in todays IT/ electronics dominated age, should have called it PWM! ...
Inappropriate simile / example. PWM can be / is deliberately controlled (modulation, thereby controlling the controlled element / system - like heater on/off -> oven temperature). In your use case, equilibrium temperature of cylinder innards is a result of (not directly controllable) variable conditions.

Achieving deterministic results (like preventing burnout) in such variable conditions is by human "do's and don'ts" - to be ignored at one's own peril. Much before that, the system is actually overdesigned - a measure of how much the human can ignore before there is a catastrophic failure. Dr. Porsche and his team worked towards reducing overdesign without compromizing system reliability.

Quote:
Originally Posted by Sutripta View Post
... Re: the actual thread starters problem, the best answers will come from the ECU coders (as to what has been done) and from their seniors as to why that has been done. ...
Principle of Management by Exclusion.
DerAlte is offline   Reply With Quote
Old 17th March 2011, 11:28   #68
Distinguished - BHPian
 
Join Date: Jul 2009
Location: Kolkata
Posts: 3,506
Thanked: 2,072 Times
Default re: RPM shoots up when changing gears

Quote:
Originally Posted by SS-Traveller View Post
But I'd like you to put the answer about the why here in your own words.
OK. Here goes. (Like all good disinformation pieces, it will be based on truths, halftruths, lies, speculation, ...)
One of the most difficult to lubricate systems in a OHV/ OHC IC engine is the valvegear. Because that which will be adequate at low speeds will overlubricate at higher speeds.
An overrunning engine with throttle snapped shut generates pretty high vacuum, greatly increasing the drawing in of lube oil/ vapours. In a turbocharged engine, the pressue diff between WOT and throttle snapped shut will be even more. And I would think lubrication would be more than the NA case.

Quote:
Originally Posted by DerAlte View Post
No fun when done off the forum, non?
OK, lets continue with the fun and games. As long as people don't charge us for impersonation!

Regards
Sutripta
Sutripta is offline   Reply With Quote
Old 17th March 2011, 11:55   #69
Distinguished - BHPian
 
SS-Traveller's Avatar
 
Join Date: Jan 2009
Location: New Delhi
Posts: 6,629
Thanked: 10,863 Times
Default re: RPM shoots up when changing gears

Quote:
Originally Posted by DerAlte View Post
No, OHT = Over Head Transmission (went over the head)! Needs Oral Re-hydration anyhow after that.
D'accord. But, no fun when done off the forum, non?
Off-public-forum or on, it's always great fun! Bring on the splash lube and let's all rehydrate.
Quote:
Originally Posted by DerAlte View Post
...the system is actually overdesigned - a measure of how much the human can ignore before there is a catastrophic failure. Dr. Porsche and his team worked towards reducing overdesign without compromizing system reliability.
System reliability, catastrophic failure, overdesigning of systems... somewhere along the way, I think we lost newbie BHPian lambdaplus, whose not-so-complicated query was about whether his Fiesta (and other cars) show a jump in RPM when shifting gears, is normal or not.
Quote:
Originally Posted by lambdaplus View Post
...noticed something while driving...
Whenever you shift gears, the rpm goes a bit high!
I mean:
You are at 1300 rpm and press clutch (to change,say, from 1st to 2nd), the rpm goes to 1400-1500 rpm while you are changing!

Advantage:
You don't loose torque while gear shifts. You have revved your car to 2000 rpm and you change gears so that you can achieve higher speeds.
I'm not sure how much of a plus this is quantitatively, but it certainly it gives a good feeling while drive!
@Lambdaplus: Stop laughing your head off silently! You're the person to answer your own query, and since your Occupation: Automotive Engineer @ Bosch was missed by us all, why don't you now come forward and tell us? As Sutripta said,
Quote:
Originally Posted by Sutripta
Re: the actual thread starters problem, the best answers will come from the ECU coders (as to what has been done) and from their seniors as to why that has been done. Anything mysterious, you can blame on 'these newfangled emission c**p.'

Last edited by SS-Traveller : 17th March 2011 at 11:57.
SS-Traveller is offline   Reply With Quote
Old 17th March 2011, 15:05   #70
Senior - BHPian
 
DerAlte's Avatar
 
Join Date: Mar 2007
Location: Bangalore
Posts: 8,076
Thanked: 2,876 Times
Default re: RPM shoots up when changing gears

Quote:
Originally Posted by Sutripta View Post
... generates pretty high vacuum, greatly increasing the drawing in of lube oil/ vapours. In a turbocharged engine, ... even more. And I would think lubrication would be more than the NA case. ...
Knew as much, but didn't want to talk as I am not an engine-vengine type. Was stumped by the "pressure is higher in crankcase" - yes it is, but only numerically correct, not logic. In overrun, the work that is done on the pistons (momentum -> energy transfer via transmission; wouldn't happen if not in gear) causes the relative vacuum in the cylinder, which pulls lube vapours through the gaps in the rings.

In a TC engine, vacuum would be lesser - higher manifold pressure than non-TC - isn't it?

Quote:
Originally Posted by SS-Traveller View Post
... somewhere along the way, I think we lost newbie BHPian lambdaplus, ...
That was my reference to we being seriously OT. I will move out the OT posts to another thread.

Quote:
Originally Posted by SS-Traveller View Post
... @Lambdaplus: ... answer your own query, ...
a. non-Bosch injection in Fiesta b. Lambdaplus dare not talk about Bosch injection and c. quite likely he wouldn't have been allowed anywhere near by the system.

@Lambdaplus, you can do a lot without revealing, but that would need you to take interest personally and visit the test labs (or use the simulator).
DerAlte is offline   Reply With Quote
Old 17th March 2011, 18:40   #71
Distinguished - BHPian
 
SS-Traveller's Avatar
 
Join Date: Jan 2009
Location: New Delhi
Posts: 6,629
Thanked: 10,863 Times
Default re: RPM shoots up when changing gears

Quote:
Originally Posted by DerAlte View Post
(I am not an engine-vengine person)...
Quote:
Originally Posted by DerAlte View Post
...I am not an engine-vengine type.
Could you elaborate further on this ?
Quote:
Originally Posted by DerAlte View Post
In a TC engine, vacuum would be lesser - higher manifold pressure than non-TC - isn't it?
Why should the turbo reduce vacuum inside the induction manifold with the throttle valve closed (petrol engine)? Isn't the turbo supposed to breathe more air into the induction manifold 'distal' to the throttle valve? Once the throttle valve closes, the turbo cannot pump any more air into the manifold any more than atmospheric air can get in. Different scenario in a diesel intake manifold though, I think.
Quote:
Originally Posted by DerAlte View Post
That was my reference to we being seriously OT. I will move out the OT posts to another thread.
Let's get lambdaplus's opinion first. I suppose he may not agree!
Quote:
Originally Posted by DerAlte View Post
a. non-Bosch injection in Fiesta b. Lambdaplus dare not talk about Bosch injection and c. quite likely he wouldn't have been allowed anywhere near by the system.
OHT. I thought he is an automotive engineer.
SS-Traveller is offline   Reply With Quote
Old 18th March 2011, 12:10   #72
Senior - BHPian
 
DerAlte's Avatar
 
Join Date: Mar 2007
Location: Bangalore
Posts: 8,076
Thanked: 2,876 Times
Default re: RPM shoots up when changing gears

Quote:
Originally Posted by SS-Traveller View Post
Could you elaborate further on this ? ...
Colloquial phrase on TBHP for all who focus on engine & mechanicals, i.e. all who are not ICE, tyre, detailing, etc.!

Quote:
Originally Posted by SS-Traveller View Post
... Isn't the turbo supposed to breathe more air ...
Oooo medical term - 'distal'! Turbo 'blows' more air - it is the engine which is breathing and wheezing!. More air = more pressure, isn't it? So, if in the induction / suction stroke more air went in, at the BDC pressure is higher in the cylinder (relative to NA)? Beyond the next TDC (end of compression stroke, no fuel involved so no firing before TDC), when - in overrun - the piston is being drawn back there is still relative higher pressure? Higher pressure = lesser vaccuum?

Quote:
Originally Posted by SS-Traveller View Post
... I thought he is an automotive engineer.
Of course he is an automotive engineer. But that, mon ami, due to the qaida-kanoon in some companies, neither means universal accessibility to information / knowledge (work constrained to limited function), nor leave and license to disseminate the same. That is why my suggestion - personal interest / passion; that is the only way to go beyond constraints.

Last edited by DerAlte : 18th March 2011 at 12:12.
DerAlte is offline   Reply With Quote
Old 18th March 2011, 17:00   #73
Distinguished - BHPian
 
SS-Traveller's Avatar
 
Join Date: Jan 2009
Location: New Delhi
Posts: 6,629
Thanked: 10,863 Times
Default re: RPM shoots up when changing gears

Quote:
Originally Posted by DerAlte View Post
Colloquial phrase on TBHP for all who focus on engine & mechanicals, i.e. all who are not ICE, tyre, detailing, etc.!
Understood. Engines are your Achilles' heel while ICE, tyre and detailing are your forte.
Quote:
Originally Posted by DerAlte View Post
Oooo medical term - 'distal'!
Dozens of terms, from 'nose' to 'tail', 'injection' to 'shoulder', heck, even 'nuts' - the medics knew them first before the engineer-vengineer did.
Quote:
Originally Posted by DerAlte View Post
Turbo 'blows' more air - it is the engine which is breathing and wheezing!.
The turbo blows when the revs are high, and softly breathes out when idling. Relative expression. Medics do understand blowing out to be exhalation too, esp. where those millions-of-years-old models are concerned. Even engines sound asthmatic, don't they? It's all about GIGO (gas-in, gas-out). Lo.
Quote:
Originally Posted by DerAlte View Post
More air = more pressure, isn't it? So, if in the induction / suction stroke more air went in, at the BDC pressure is higher in the cylinder (relative to NA)? Beyond the next TDC (end of compression stroke, no fuel involved so no firing before TDC), when - in overrun - the piston is being drawn back there is still relative higher pressure? Higher pressure = lesser vaccuum?
True - for the first few revolutions of the engine after throttle closure. As the throttle snaps shut, the turbo has already boosted the pressure inside the intake manifold, but cannot boost any further (manifold sealed off from turbo by throttle valve) ==>> inlet stroke of each cylinder takes in the air at higher pressure ==>> cylinder goes through the cycle (I-C-P-E) ==>> pumps out air into exhaust manifold ==>> pressure in intake manifold reduces with each revolution ==>> partial vacuum ==>> sucks out oil past valve guides and oil control rings ==>> increased emissions. Keep the throttle slightly open by ECU control even though the accelerator pedal is 'off', and emissions reduce.
Quote:
Originally Posted by DerAlte View Post
Of course he is an automotive engineer. But that, mon ami, due to the qaida-kanoon in some companies, neither means universal accessibility to information / knowledge (work constrained to limited function)...
OMG. Managers, rules, for-your-eyes-only secret files, need-to-know information... What do engineers learn in engineering colleges?

Last edited by SS-Traveller : 18th March 2011 at 17:03.
SS-Traveller is offline   Reply With Quote
Old 18th March 2011, 19:16   #74
Senior - BHPian
 
DerAlte's Avatar
 
Join Date: Mar 2007
Location: Bangalore
Posts: 8,076
Thanked: 2,876 Times
Default re: RPM shoots up when changing gears

Quote:
Originally Posted by SS-Traveller View Post
Understood. Engines are your Achilles' heel while ICE, tyre and detailing are your forte.
Incorrect. Engines are not my Achilles heel - just that I don't focus on them (any more). And I am not into tyre and detailing.

Quote:
Originally Posted by SS-Traveller View Post
... (manifold sealed off from turbo by throttle valve) ==>> inlet stroke of each cylinder takes in the air at higher pressure ==>> cylinder goes through the cycle (I-C-P-E) ==>> pumps out air into exhaust manifold ==>> pressure in intake manifold reduces with each revolution ==>> partial vacuum ==>> sucks out oil past valve guides and oil control rings ==>> increased emissions. Keep the throttle slightly open by ECU control even though the accelerator pedal is 'off', and emissions reduce.
A-ha, appadiya?
1. ECU cannot hold the throttle open - there is no actuator, only a sensor there. Putting an actuator can be catastropic. Also, throttle doesn't seal - there is a minimum flow
2. So by your logic, there is generally no difference in the vaccuum between NA and TC engines? Throttle closes shut in either case

Quote:
Originally Posted by SS-Traveller View Post
... OMG. Managers, rules, for-your-eyes-only ... What do engineers learn in engineering colleges?
Jo tan laagi, so tan jaani! All that has a purpose / objective, and "method in madness" and all that.

Engg. College? Precious little of relevance to current practices and technology. The main reason why a new engineer straight out of college is not productively deployable. Completely different from Med - at least a new doctor is productive (not efficient or skillful - that takes time) straight away. Neither will he run away, nor will he kill the patient. That is something that one cannot be certain with Engg. (O bhai @lambda, please do not take offense - not a comment on your abilities).
DerAlte is offline   Reply With Quote
Old 18th March 2011, 21:25   #75
Distinguished - BHPian
 
SS-Traveller's Avatar
 
Join Date: Jan 2009
Location: New Delhi
Posts: 6,629
Thanked: 10,863 Times
Default re: RPM shoots up when changing gears

Quote:
Originally Posted by DerAlte View Post
Engines are not my Achilles heel - just that I don't focus on them (any more).
Blurred engines? Progressive lenses recommended.
Quote:
Originally Posted by DerAlte View Post
A-ha, appadiya?
You're quite the linguist, Sir. Hercule Poirot and Sherlock Holmes would be put to shame.
Quote:
Originally Posted by DerAlte View Post
1. ECU cannot hold the throttle open - there is no actuator, only a sensor there.
And in drive-by-wire accelerator pedals?
Quote:
Originally Posted by DerAlte View Post
Putting an actuator can be catastropic.
How and why so?
Quote:
Originally Posted by DerAlte View Post
Also, throttle doesn't seal - there is a minimum flow
Can someone confirm that please? Carburettor throttles are 100% leakproof when new.
Quote:
Originally Posted by DerAlte View Post
2. So by your logic, there is generally no difference in the vaccuum between NA and TC engines? Throttle closes shut in either case
Non. Inferences being drawn, Sir, where none exist - it is certainly not my logic.
Quote:
Originally Posted by DerAlte View Post
Engg. College? Precious little of relevance to current practices and technology. The main reason why a new engineer straight out of college is not productively deployable. Completely different from Med - at least a new doctor is productive (not efficient or skillful - that takes time) straight away. Neither will he run away, nor will he kill the patient. That is something that one cannot be certain with Engg.
Very interesting & intuitive observation. An absolute eye-opener for me AFA engineering colleges are concerned.
SS-Traveller is offline   Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
RPM shoots up when clutch depressed rao_battula Technical Stuff 83 27th September 2016 15:28
Can Engine RPM/Speed shoots up automatically in AT vehicle shaktideep Technical Stuff 6 22nd February 2011 16:39
Esteem 2002 - RPM Fluctuation (Blip) After Changing Gears genesis Technical Stuff 7 28th July 2009 10:25
Not changing gears !!! shirishindurkar Technical Stuff 27 14th September 2007 18:29
RPM shoots up... gkrishn Technical Stuff 11 21st July 2005 23:02


All times are GMT +5.5. The time now is 01:59.

Copyright 2000 - 2017, Team-BHP.com
Proudly powered by E2E Networks