Flat Foot Shift RPM

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ciphermonk
Posts: 23
Joined: Fri Nov 04, 2016 8:47 pm

Flat Foot Shift RPM

Post by ciphermonk »

Morning all,

I've been looking through my calibration trying to find where the RPM is specified for the engine to hold between flat foot shifts. Any idea where I can find that?

I've been looking through Gear Cut and see "Cut Enable Engine Speed" but I imagine that's strictly for enabling the feature? Not actually specifying the RPM that the engine will goto during a FFS event. Not finding anything in help (F1) for this portion of the calibration.

In "Ramp Out (Start of Cut Sequence)" I see that the Ignition Retard is set to 10 degrees for each gear. Is this how the cut is accomplished? Instead of specifying an RPM target, you simply specify how much to retard the timing when the clutch pedal is in and TPS is above 60%?

What am I missing?
stevieturbo
Posts: 1321
Joined: Sun Dec 07, 2008 2:04 pm

Re: Flat Foot Shift RPM

Post by stevieturbo »

Because that is not how most normal shift cuts are designed.

What you seem to be seeking is a lower rpm limit based on a switch input, not an actual shift cut strategy which cuts the engine momentarily to allow a flat shift via a dog or sequential box.

A reduced rpm limit on its own has far less ability to actually cut engine speed given weight of flywheel and general momentum.

What gearbox are you using, what are you using to initiate the cut etc ?
ciphermonk
Posts: 23
Joined: Fri Nov 04, 2016 8:47 pm

Re: Flat Foot Shift RPM

Post by ciphermonk »

Thanks for replying stevieturbo. I'm running a 6 speed H pattern gearbox.

I guess what I'm trying to prevent is total loss of boost between shifts. I'm looking for the functionality that allows me to keep the pedal to the floor between shifts yet prevents the engine from overspeeding to redline.

The cut would be initiated by pushing in the clutch pedal. When I take my foot off the clutch (I.e next gear engaged) functionality would return to normal.

I'm trying to understand how the Syvecs accomplishes this.
stevieturbo
Posts: 1321
Joined: Sun Dec 07, 2008 2:04 pm

Re: Flat Foot Shift RPM

Post by stevieturbo »

AFAIK and how I did use open loop cuts for mine for a short time.

The switch trigger will initiate the gear cut. "Power" will "ramp out" as you determine. This will then be a cut to the levels you have asked for the time period you have asked.
Then power will ramp back in, again as you have set this.

Clearly if the gearshift does not go to plan and you miss gears....power will resume after the time period regardless of whether you are in gear or not. But the ecu has no way to determine if you are actually in gear or not for a closed loop shift.

Now whilst I havent tried this bit...."End of request ends cut" for my description above is set to No

Possibly if you set this to Yes...it might get closer to what you are seeking but I havent tried an open loop shift like that so cant comment. But it would still be fuel/spark cuts and/or timing retards for the cut period, as opposed to any attempt to target a specific rpm.

Obviously switch position on the clutch pedal will affect how it all comes together too. I actually fitted a pressure sensor on the hydraulic line so I could simply alter the switch point on the ecu without having to move a mechanical switch.

But as I also had a habit of going from 2nd into 1st instead of 3rd...I stopped trying any flat shifts lol.
Mark_r33
Posts: 26
Joined: Sat Jan 18, 2014 7:14 pm

Re: Flat Foot Shift RPM

Post by Mark_r33 »

Stevie,

I was thinking of the same thing regarding the pressure sensor in the clutch line, how well does it work?

Do you have a log of a full clutch displacement vs pressure? I'm interested to see how non linear it is to displacement. I understand that you probably won't have a log with actual displacement displayed, but just a graph showing a full stroke of clutch pedal to the floor over time would be cool to look at.

I saw a video on youtube of somebody testing a clutch lines pressure (pretty terribly) and it seemed to peak and then drop again, which made sense, but ultimately put me off the idea. My next idea was to use one of those cheap landrover air suspension height pots to measure the pedal displacement instead.
stevieturbo
Posts: 1321
Joined: Sun Dec 07, 2008 2:04 pm

Re: Flat Foot Shift RPM

Post by stevieturbo »

The graph will vary depending how fast you operate the pedal really.

So from a point of view of triggering a flat shift....it should be pretty reliable as you'd trigger the open loop cut on the up-voltage somewhere....where you decide.
But at least it is something you can easily adjust, whereas a switch on the pedal would require more trial and error.

On the S6 I had it configured as the gearcutvoltage input, the S8 seems to be more configurable as you can tie the clutch switch input to an analogue signal and set the threshold that way.
Although havent actually looked if you can then use the clutch switch input as the trigger. Either way, there are options and it can trigger via a pressure sensor.
Short glimpse a section of a hillclimb, going 2-1 into a chicane, then 1-2, 2-3 so 3 clutch operations, logged at 50hz. Latter 2 approx 0.4s duration from rest to rest.
Most of the falling edge side of things would exhibit the little step on the way down. As to how far my diaphragm goes over centre etc...no idea.
Initial 2-1 downshift, clutch operation is much slower.
No flat shifting etc anywhere here

clpr graphs.jpg
clpr graphs.jpg (284.59 KiB) Viewed 24508 times
Mark_r33
Posts: 26
Joined: Sat Jan 18, 2014 7:14 pm

Re: Flat Foot Shift RPM

Post by Mark_r33 »

Brilliant, thanks for sharing that buddy that shows it perfectly.

That's a lot more consistent than I thought it would be too, to be fair. The 2-1 being much slower than the 1-2 and 2-3 are still all within a reasonable range regarding peak pressures, I'm liking this idea again now. Interesting on the little blip bit on release, must be the pressure plate landing back on the friction disc?

I've also had enough of trying to get switches to work well, bending brackets and fitting springs to the switch head.

I was looking at using something like these as an alternative, attached to pedal or even the throw out arm directly if you have one;

http://www.ebay.co.uk/itm/Land-Rover-Ra ... SwezVWvqvx
stevieturbo
Posts: 1321
Joined: Sun Dec 07, 2008 2:04 pm

Re: Flat Foot Shift RPM

Post by stevieturbo »

You could use any manner of sensors on the pedal really, no reason why that couldnt be adapted.

I just used pressure because it was simple as my clutch is hydraulic. It's a 100bar KA sensor, but there are probably cheaper ones out there.

Like you with previous setups I'd microswitches then mucked about trying to get them to switch at the right time etc etc Just a PITA.

But the hydraulic can also give some indication of what's going on with the clutch vs just a simple pedal pot. Might not always understand what is going on...but I'm sure it is more useful.
stevieturbo
Posts: 1321
Joined: Sun Dec 07, 2008 2:04 pm

Re: Flat Foot Shift RPM

Post by stevieturbo »

Some of these would be cheaper and I'd think a 50 bar or thereabouts would cover most clutches, when I bought the 100bar I'd no notion of what sort of pressures I'd see in there.

eg cheaper options

http://uk.rs-online.com/web/c/automatio ... 43&sra=oss

Fairly typical pressure sensors....although maybe not always most user friendly thread options. I got the KA in M10x1.0 so same as most brake fittings although as it didnt have a tapered seat needed to adapt a brake fitting on the clutch line so it would seal on a copper washer
Mark_r33
Posts: 26
Joined: Sat Jan 18, 2014 7:14 pm

Re: Flat Foot Shift RPM

Post by Mark_r33 »

Wow, that's cheap, thanks for sharing those little gems!

I see what you mean on the threads. They have a 7/16"-20 with 45* flare listed in the datasheet, I wonder if RS can provide the full range of them?

Thanks again for all your help here buddy, I'll definitely be giving this a go now
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