Question about the SRM

IDZRVIT · 05-31-2013, 11:26 AM

Quote:

Originally Posted by theDreamer

You do know electrons, which is the basis for computation, travel at a much faster rate of speed and are beating you in your shifts. What is probably happening with you is that on your upshifts you are above its 'increase' limit meaning it sees no reason to raise the RPM when you upshift. Different shifting style.

And you also realize that those elctrons are sent through wires to a fuel injector (after the computer has determined the TPS opening and compared that parameter with a few others in order to produce the corect voltage signal to that injector) that has to open and introduce fuel into the cylinder on a compression stroke (gotta wait for the right stroke and there are four of them), fuel then is compressed, more electrons sent to the ignition to fire a plug which then needs to create the spark at a precise moment as the piston moves up the cylinder, and this will will ignite the air/fuel mixture to start the combustion process which will expand as it burns (fuel doesn't explode as some do believe) and force the piston back down the cylinder under load which will then rotate the crankshaft and the crank sensor will send electrons back through the wiring to the tach sensor which will then be converted to a mechanical force to rotate the needle in the tach. Yes, it happens fast but not as fast as you are trying to make this out. Probably best measured in 1/100 ths of a second or even 1/10 ths but not in a couple of nano-seconds.

Edit: There is a process which has to be completed from the time you move that shifter out of gear to the time you visually see the result at the tach.

theDreamer · 05-31-2013, 11:36 AM

You understand for the initial 'bump' in RPM it is purely electronic right?
It is just sensors & the ECU making adjustments, once you go into engagement of a gear is when the motor, fuel, etc is played with.

IDZRVIT · 05-31-2013, 12:31 PM

Quote:

Originally Posted by theDreamer

You understand for the initial 'bump' in RPM it is purely electronic right?It is just sensors & the ECU making adjustments, once you go into engagement of a gear is when the motor, fuel, etc is played with.

This can turn out to be a good discussion on how SRM works. Yes, I can see where the computer could be programmed to add fuel (increase in engine speed) if left in neutral for a small period of time during the upshift process or anticipating such but is that true? I know the purpose of SRM is to eliminate heel-toe for downshifts but you don't heel-toe for upshifts. There is no reason to. If I'm already at say 3500 rpm and for ready to upshift and the computer detects this as I move the shifter into the next higher gear, why would it want to increase the rpm? If the revs drop several hundred rpm (foot off gas, clutch in.....) and the shift is completed at say 3100 rpm without SRM, why would the computer want to increase the revs to say 3900 rpm if I wasn't planning on accellerating any more because I've reached my cruising speed? To me, that would cause a slight unwanted surge in speed. If that is what this discussion is about and I have explained this scenario correctly for SRM interaction in an upshift, then this would be a safety issue, no?

SS_Firehawk · 05-31-2013, 12:51 PM

Quote:

Originally Posted by theDreamer

You do know electrons, which is the basis for computation, travel at a much faster rate of speed and are beating you in your shifts. What is probably happening with you is that on your upshifts you are above its 'increase' limit meaning it sees no reason to raise the RPM when you upshift. Different shifting style.

Dreamer, you are my hero, I thought the same thing... but you were sooooo much nicer about it than what was in my mind

theDreamer · 05-31-2013, 02:23 PM

Quote:

Originally Posted by IDZRVIT

This can turn out to be a good discussion on how SRM works. Yes, I can see where the computer could be programmed to add fuel (increase in engine speed) if left in neutral for a small period of time during the upshift process or anticipating such but is that true? I know the purpose of SRM is to eliminate heel-toe for downshifts but you don't heel-toe for upshifts. There is no reason to. If I'm already at say 3500 rpm and for ready to upshift and the computer detects this as I move the shifter into the next higher gear, why would it want to increase the rpm? If the revs drop several hundred rpm (foot off gas, clutch in.....) and the shift is completed at say 3100 rpm without SRM, why would the computer want to increase the revs to say 3900 rpm if I wasn't planning on accellerating any more because I've reached my cruising speed? To me, that would cause a slight unwanted surge in speed. If that is what this discussion is about and I have explained this scenario correctly for SRM interaction in an upshift, then this would be a safety issue, no?

Yes, it is true that the system will increase RPM on a shift up. I am trying to locate a few articles but it was discussed with Nissan and they said the Revmatch works on both up & down shifts to help 'smooth out' shifts.
Now the questions we would have to look at is how it determines this smoothness factor and what issues it could cause on an upshift.
I would presume the upshift rev is more of a safety net for the transmission. Meaning that it keeps the parameters inline with what it wants to be around so if you are off by 100 it will do a slight bump to bring it up for you but this could cause the driver to have some jutter if not prepared or ready.

This would be a fantastic test on a bone stock car.
Do some slow 1-2 shifts and 3-4 and record the RPM gauge and OBD2 readings/logs and then some faster higher RPM shifts and do some data comparisons. The shift speed factor can come into play and can be controlled a bit but will just need a driver who is steady.

Quote:

Originally Posted by SS_Firehawk

Dreamer, you are my hero, I thought the same thing... but you were sooooo much nicer about it than what was in my mind

I seem to be the nice guy on the forum.

IDZRVIT · 05-31-2013, 08:05 PM

Dreamer, next time I'm driving the wife's Z I will pay a bit more attention to my upshifts/revs and see if they increase at all. I think both of the Z's my wife has had were built on a Wednesday.

IDZRVIT · 06-04-2013, 08:58 AM

OK, so here's how my Z's SRM works. It revs up when downshifting. It doesn't do anything during an upshift. This is the way it should work for reasons stated in my previous post. If a car revs during an upshift I will speculate the driver is slow to get off the gas pedal when depressing the clutch causing the car to rev.

theDreamer · 06-04-2013, 09:02 AM

Ok, finally found the article: 2009 Nissan 370Z's SynchroRev Match Explained - Tech Dept. - Car Reviews - Car and Driver

Quote:

The gearshift sensors monitor gear position as well as side-to-side shifter movement and are sensitive enough that you can hold down the clutch pedal and watch the revs jump precisely to the right rpm if you merely hint at moving the shift lever to a lower gear. But it’s not just for downshifts; SRM also sticks the engine speed at the targeted rpm during upshifts to prevent any lumpiness that might result from letting the revs drop too low.

JARblue · 06-04-2013, 09:55 AM

Quote:

Originally Posted by IDZRVIT

OK, so here's how my Z's SRM works. It revs up when downshifting. It doesn't do anything during an upshift.

Dreamer has, imo, very clearly explained why you are not experiencing SRM engine revs during upshift - it's your manner of driving. Not to mention the link that he provided is quite informative. If you accelerate in 1st, then put the shift knob in neutral and let go (so it centers between 3rd & 4th gears), the tach needle will eventually drop to around your normal idle RPM. To then shift to 2nd would require an increase in RPMs for a smooth shift; with SRM ON, it will rev match for you when you move the shift knob to the 2nd gear gate regardless of whether you let the clutch out or not.

Quote:

Originally Posted by IDZRVIT

This is the way it should work for reasons stated in my previous post. If a car revs during an upshift I will speculate the driver is slow to get off the gas pedal when depressing the clutch causing the car to rev.

Why shouldn't it work that way? If I wait a hair too long to reengage the clutch and the RPMs drop slightly lower than the ideal for the gear shift, I'd rather SRM jump in and rev up for me a hair than make the car jerk cause of a mistimed clutch engagement. I understand your point about slow shifts, but you don't seem to get that SRM is supposed to do that. Under casual driving I would say it's better to let SRM correct your slow clutch engagement by increasing RPMs than engaging the clutch too quickly before the RPMs have dropped sufficiently.

I used SRM to learn how the car wants to shift. Now that I know how much the RPMs drop on an upshift in different gears and at different speeds and acceleration rates, I leave it off and make smooth shifts (most of the time) without SRM's aid.

IDZRVIT · 06-06-2013, 10:45 AM

OK, so I played around a bit with the manual. If shifted normally or quickly, here is what I observed. In a downshift, the engine revs. In an upshift, the engine does not rev but hangs or "sticks". Again, it would be a poor design to have it rev. That said, I noticed that if the gear shift is put into neutral and let it stay there for more than a second or two, the rpms drop down towards idle speed. Then, whether you select an upshift or downshift, the engine will rev to match the proper speed for the engagement of that gear. No one should be shifting like this i.e. taking more than a second to get into the next gear. That's why I found it odd that anyone would notice engine revving during an upshift.

blackcherry20 · 06-06-2013, 11:41 AM

Quote:

Originally Posted by gomer_110

The clutch in our cars is notorious for feeling strange compared to other cars but this is normal. You will get used to it.

kind of clunky even (at 15k)...

05-31-2013, 11:36 AM	#17 (permalink)
theDreamer A True Z Fanatic Join Date: Feb 2009 Location: Texas Posts: 30,879 Drives: 370z Rep Power: 4210	You understand for the initial 'bump' in RPM it is purely electronic right? It is just sensors & the ECU making adjustments, once you go into engagement of a gear is when the motor, fuel, etc is played with. iceman21_23 likes this. __________________ theDreamer's Z // Fast Intentions // Uprev // GTM // HKS // TEIN theDreamer's Silvia // URAS // GREDDY Houston Zs // Facebook // Twitter // Instagram

05-31-2013, 08:05 PM	#21 (permalink)
IDZRVIT A True Z Fanatic Join Date: May 2009 Location: Halifax Posts: 1,659 Drives: '13 CTS-V, '76 Vette Rep Power: 27	Dreamer, next time I'm driving the wife's Z I will pay a bit more attention to my upshifts/revs and see if they increase at all. I think both of the Z's my wife has had were built on a Wednesday. __________________ "America.... still builds rockets!" Vette: 355 cid, 400 rwhp '13 CTS-V Coupe: 6.2L LSA, 556HP

06-04-2013, 08:58 AM	#22 (permalink)
IDZRVIT A True Z Fanatic Join Date: May 2009 Location: Halifax Posts: 1,659 Drives: '13 CTS-V, '76 Vette Rep Power: 27	OK, so here's how my Z's SRM works. It revs up when downshifting. It doesn't do anything during an upshift. This is the way it should work for reasons stated in my previous post. If a car revs during an upshift I will speculate the driver is slow to get off the gas pedal when depressing the clutch causing the car to rev. __________________ "America.... still builds rockets!" Vette: 355 cid, 400 rwhp '13 CTS-V Coupe: 6.2L LSA, 556HP

06-06-2013, 10:45 AM	#25 (permalink)
IDZRVIT A True Z Fanatic Join Date: May 2009 Location: Halifax Posts: 1,659 Drives: '13 CTS-V, '76 Vette Rep Power: 27	OK, so I played around a bit with the manual. If shifted normally or quickly, here is what I observed. In a downshift, the engine revs. In an upshift, the engine does not rev but hangs or "sticks". Again, it would be a poor design to have it rev. That said, I noticed that if the gear shift is put into neutral and let it stay there for more than a second or two, the rpms drop down towards idle speed. Then, whether you select an upshift or downshift, the engine will rev to match the proper speed for the engagement of that gear. No one should be shifting like this i.e. taking more than a second to get into the next gear. That's why I found it odd that anyone would notice engine revving during an upshift. __________________ "America.... still builds rockets!" Vette: 355 cid, 400 rwhp '13 CTS-V Coupe: 6.2L LSA, 556HP

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