ARD - Lucky Posted November 18, 2012 Report Share Posted November 18, 2012 Converter slip doesn't affect RPM but it does affect road speed. So given a particular RPM and gear ratio you won't know road speed accurately because the converter doesn't provide 1:1 input/output. I may be misunderstanding, is your circuit a piggy back to the factory TCU or a replacement to the factory TCU? The unit I built simply replaced the TCU as a whole so we may be talking apples/oranges.... Link to comment Share on other sites More sharing options...
Simply Volvo Posted November 18, 2012 Author Report Share Posted November 18, 2012 Im not sure what to call it. I guess it would be a piggy back. When your not in paddle shifter mode, my circuit just monitors the TCU and receives things like what gear your in and RPM, etc. When i want to enter paddle shifter mode, my circuit shuts off the TCU and takes full control of all the pins and such. This way i keep stock TCU functionality so people can still use the auto box but when they wanna shift gears, they can.The way i look at it is that Either way, if you use the speed sensor or calculate it there is going to be accuracy issues. Link to comment Share on other sites More sharing options...
ARD - Lucky Posted November 18, 2012 Report Share Posted November 18, 2012 Now I see, didn't realize your circuit was in addition to TCU, that makes more sense. Not sure how measuring road speed directly will have accuracy issues but either way sounds like you've got a plan! Link to comment Share on other sites More sharing options...
Simply Volvo Posted November 18, 2012 Author Report Share Posted November 18, 2012 Now I see, didn't realize your circuit was in addition to TCU, that makes more sense. Not sure how measuring road speed directly will have accuracy issues but either way sounds like you've got a plan! Im quite confused now, Earlier you said that you had trouble implementing the speed sensor because converter slip... I had trouble implementing that with sufficient precision since the converter slip is pretty considerable in the early RPM's, so for me road speed was necessary to accurately control RPM over shoot on downshifts. Were talking about the trans speed sensor, correct? Not road speed. Link to comment Share on other sites More sharing options...
ARD - Lucky Posted November 18, 2012 Report Share Posted November 18, 2012 I had trouble when it came to calculating road speed via RPM and gear ratio because of converter slip. Once I used the actual road speed signal coming in to the TCU then it was quite a bit easier. In earlier models (upto 95 IIRC) the road speed signal comes from the trans output sensor, in later 96-98 models the road speed comes from ABS. You'll have to review the schematic to see if the wiring pinout changes, I simply just don't remember In the end I found that the only way I could accurately tell for sure if a downshift was going to over rev the engine was to calculate an estimated rise in RPM via gear ratio change and then consider road speed against RPM with a known gear ratio to determine how close the converter was to it's stall speed. Accidental double tap downshifting probably won't be an issue if there's good debounce in the switch input and enough delay between registered shift requests on that pin so may be more worry than it's worth..? Link to comment Share on other sites More sharing options...
Simply Volvo Posted November 18, 2012 Author Report Share Posted November 18, 2012 I had trouble when it came to calculating road speed via RPM and gear ratio because of converter slip. Once I used the actual road speed signal coming in to the TCU then it was quite a bit easier. In earlier models (upto 95 IIRC) the road speed signal comes from the trans output sensor, in later 96-98 models the road speed comes from ABS. You'll have to review the schematic to see if the wiring pinout changes, I simply just don't remember In the end I found that the only way I could accurately tell for sure if a downshift was going to over rev the engine was to calculate an estimated rise in RPM via gear ratio change and then consider road speed against RPM with a known gear ratio to determine how close the converter was to it's stall speed. Ahh now that makes more sense! In my eyes it seems as though im only going to need to implement the trans speed sensor if i make it so you can program a table with custom shift points... but even then instead of doing shift points at a certain road speed i could do them at a certain RPM and or TPS values. I think it would be in my best bet to leave the transmission speed sensor out. With all of these changes(and yes they did change from trans mount to ABS), it may cause more problems then good. As for telling if the gear can be downshifted or not... Im gonna need to do some quick thinking before i post back what my strategy is. I believe you can just use RPM and gear ratio to tell if it can be downshifted or not. Link to comment Share on other sites More sharing options...
Simply Volvo Posted November 18, 2012 Author Report Share Posted November 18, 2012 So yes its hit me, I simply cannot just use RPM to determine vehicle speed. Below stall speed(2700) its going to be super inaccurate and in order to determine if you can downshift you need vehicle speed. So now i have two options... Implement the speed sensor... or Give the user the option to make it so if you want downshift protection you need to tap the downshift paddle twice. Personally i find downshift prevention annoying. The whole point of the paddles is so you have complete control over your gears. What do you guys think? Link to comment Share on other sites More sharing options...
Über855R Posted November 18, 2012 Report Share Posted November 18, 2012 My two immediate thoughts are: 1.) Downshift protection will protect the tranny. 2.) you don't have it on a manual... So it's not a must, but, see 1.) Link to comment Share on other sites More sharing options...
Simply Volvo Posted November 18, 2012 Author Report Share Posted November 18, 2012 My two immediate thoughts are: 1.) Downshift protection will protect the tranny. 2.) you don't have it on a manual... So it's not a must, but, see 1.) Yes but if you accidentally downshift, its only gonna be 1 gear. AKA 2nd to 1st, 3rd to 2nd or 4th to 3rd. You're never gonna downshift accidentally from 4 to 1st especially with the double tap downshift feature. Think about it. Anyway even if you do accidentally downshift, the torque converter works in the opposite direction, but not very good, so as rpms go up, it slips more and more so really it would only rev up to about 4k rpm so technically its impossible to over rev it. In gear one, the transmissions internal brakes dont even engage. Hence why I can idle while cruising at 70mph in 1st gear. Once you get into second gear, two of the brakes engage and since the torque converter doesnt work very well in reverse, the engine braking affect takes place, engine doesnt go over 4k to 5k and the car slows down. So with all that said, IMO only double downshift is required. Thoughts. Link to comment Share on other sites More sharing options...
Brad850 Posted November 18, 2012 Report Share Posted November 18, 2012 I see where uber855r is coming from and I believe it's a great idea but personally I wouldn't want it. Link to comment Share on other sites More sharing options...
Simply Volvo Posted November 18, 2012 Author Report Share Posted November 18, 2012 I see where uber855r is coming from and I believe it's a great idea but personally I wouldn't want it. Yeah it agree its a good way to prevent accidental downshifting. But i agree with you, i think double tapping would get annoying. Actually i think any form of downshift prevention would be annoying, but then again people need assurance who arnt comfortable with accidental downshift. Link to comment Share on other sites More sharing options...
Brad850 Posted November 18, 2012 Report Share Posted November 18, 2012 Would it be a hassle for you to make it available for the people that want it? Link to comment Share on other sites More sharing options...
Simply Volvo Posted November 18, 2012 Author Report Share Posted November 18, 2012 Would it be a hassle for you to make it available for the people that want it? No. The cool thing is as of now, software is going to be included like turbo tuner so people can change their settings and stuff... So there will be three options for Downshift protection 1. No protection 2. Double Tap 3. RPM algorithm. You can pick whichever suits you the best. Link to comment Share on other sites More sharing options...
Über855R Posted November 18, 2012 Report Share Posted November 18, 2012 There is no safety net for a manual. If you are stupid and put it in the wrong gear, you break something. So don't be stupid. That was where I got to in my thought process, then double tap for down seemed like stupidity insurance in an easy simple form. Link to comment Share on other sites More sharing options...
Simply Volvo Posted November 18, 2012 Author Report Share Posted November 18, 2012 There is no safety net for a manual. If you are stupid and put it in the wrong gear, you break something. So don't be stupid. That was where I got to in my thought process, then double tap for down seemed like stupidity insurance in an easy simple form. Well i already have RPM implemented, so i might as well implement a small RPM algorithm. It wont be super accurate but it will get the job done for people who want assurance. But yea that statement is true., though it is a lot harder to accidental shift in a manual. Link to comment Share on other sites More sharing options...
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