downshifting in a cvt
#1
01-28-2005, 03:38 PM
downshifting in a cvt
i had a few questions, but focusing on one has let the others slip...
does downshifting into sport, or even a gear lower while going down a steep hill have adverse effects on a cvt transmission? i have heard that the if going too fast (say over 25) puts a lot of strain on the transmission. if anyone could compare this to downshifting in a 5-speed manual (this was my preferred way to slow down my old nova) it would be greatly appreciated.
does downshifting into sport, or even a gear lower while going down a steep hill have adverse effects on a cvt transmission? i have heard that the if going too fast (say over 25) puts a lot of strain on the transmission. if anyone could compare this to downshifting in a 5-speed manual (this was my preferred way to slow down my old nova) it would be greatly appreciated.
#3
01-28-2005, 05:53 PM
What car are we talking about? I don't really know much about automobiles in general. The Prius is a CVT, but I don't think it actually has a transmission (okay, I'm definitely showing my ignorance). Anyway, on the Prius it's either in Drive or Braking mode.
#4
01-28-2005, 06:40 PM
What you don't want to do is take a CVT (with ICE off) out of "N" and slam it in gear going over 20ish. Just letting your foot off the gas will cause a CVT to start regen and it should automatically downshift.
Last edited by lakedude; 01-31-2005 at 06:36 PM.
#5
01-28-2005, 06:47 PM
Jason
The Prius has a planetary gear set like an old 3 speed bike but way newer/better/cooler. Instead of 3 fixed ratios like the ole 3 speed a Prius uses the planetary gear as a "split power device" to blend the power from both the engine (ICE) and one of the motors. How fast and which direction the motor turns determine the final gear ratio. With the electric motor spinning one way the system is geared down like shifting into a low gear. At some point the motor stops and turns the other way, which makes the ratio taller like shifting a car into overdrive. I'll edit in a link in case you care.
Too late to stop me:
http://home.earthlink.net/~graham1/M...Understanding/
http://home.earthlink.net/~graham1/M...PowerTrain.htm
http://home.earthlink.net/~graham1/M...plitDevice.htm
The Toyota split power device is the heart of the whole system and it is brilliant!
The Prius has a planetary gear set like an old 3 speed bike but way newer/better/cooler. Instead of 3 fixed ratios like the ole 3 speed a Prius uses the planetary gear as a "split power device" to blend the power from both the engine (ICE) and one of the motors. How fast and which direction the motor turns determine the final gear ratio. With the electric motor spinning one way the system is geared down like shifting into a low gear. At some point the motor stops and turns the other way, which makes the ratio taller like shifting a car into overdrive. I'll edit in a link in case you care.
Too late to stop me:
http://home.earthlink.net/~graham1/M...Understanding/
http://home.earthlink.net/~graham1/M...PowerTrain.htm
http://home.earthlink.net/~graham1/M...plitDevice.htm
The Toyota split power device is the heart of the whole system and it is brilliant!
Last edited by lakedude; 01-28-2005 at 06:55 PM.
#6
01-29-2005, 03:59 PM
don't worry jason because im all for acknowledging my ignorance when it comes to cars. what my main question should have stated is:
is it detrimental to the cvt on a 05 hch to take the shifter and click it down one to "S", and if you'd like to slow down even more, to limit the gear ratios and bring it down one more into (i believe it is) "L". i compare it to downshifting because i used to drive stick, but i believe all it does is to limit the gear ratios; but when going down hill it will allow the engine/transmission to work together to slow the vehicle.
any reason for me not to do this, and perhaps if georgia could chime in... how do you utilize the coasting trick if you shouldn't place the car from neutral into drive going over 20 (40). people definitely get a bit angry when you slow down to 40 on the highway.
is it detrimental to the cvt on a 05 hch to take the shifter and click it down one to "S", and if you'd like to slow down even more, to limit the gear ratios and bring it down one more into (i believe it is) "L". i compare it to downshifting because i used to drive stick, but i believe all it does is to limit the gear ratios; but when going down hill it will allow the engine/transmission to work together to slow the vehicle.
any reason for me not to do this, and perhaps if georgia could chime in... how do you utilize the coasting trick if you shouldn't place the car from neutral into drive going over 20 (40). people definitely get a bit angry when you slow down to 40 on the highway.
#8
01-31-2005, 03:37 PM
one thing i have found that helps when shifting back into drive from a neutral coast (in a cvt) is to slightly press down on the accelerator and bring the rpms up to around 1500 (depending on the sped of course). this seems to completely eliminate the jerk when you "slam" the car back into drive. unfortunately this doesn't work when you reboot and have auto stop running. that is definitely a back roads trick to be utilized under special and practiced circumstances.
#9
01-31-2005, 04:32 PM
Ridiculously Active Enthusiast
Join Date: Mar 2004
Location: Atlanta, Ga
Posts: 1,797
Thanks Andrew, sorry for the late response but my crazy Alltel DSL quit again.
You're right, you can put your CVT back into D from N at any speed as long as the engine is still running. Correct again, if you've shut down (reboot) the engine while rolling in N then expect a jerk through the drivetrain. Above 40 it gets to be severe, and above about 50MPH it is down right alarming.
As mentioned we have to make the best judgements, and I'll do that only at around 2:00-3:00AM on the deserted rural highways I drive.
A couple of months after I first bought my CVT I forgot the 40MPH rule and rebooted to roll down a 3-mile decline on a 65MPH limit freeway.
This was not wise.
I had to restart going 55-60MPH and the jerk was so severe that something "screamed" under the hood and had a terrible feel about it.
Even today I wonder if I damaged the metallic belt in any way?
Needless to say I haven't done that since, and is why I always mention the 40MPH rule for a reboot.
About downshifting...I don't think any damage will come to the CVT for this but I always try to time out a good regen instead.
if georgia could chime in
As mentioned we have to make the best judgements, and I'll do that only at around 2:00-3:00AM on the deserted rural highways I drive.
A couple of months after I first bought my CVT I forgot the 40MPH rule and rebooted to roll down a 3-mile decline on a 65MPH limit freeway.
This was not wise.
I had to restart going 55-60MPH and the jerk was so severe that something "screamed" under the hood and had a terrible feel about it.
Even today I wonder if I damaged the metallic belt in any way?
Needless to say I haven't done that since, and is why I always mention the 40MPH rule for a reboot.
About downshifting...I don't think any damage will come to the CVT for this but I always try to time out a good regen instead.
Last edited by Hot_Georgia_2004; 01-31-2005 at 04:39 PM.
#10
02-01-2005, 01:18 PM
outstanding georgia, i appreciate the speedy reply and as always; your knowledge is greatly appreciated.
i'm definitely starting to pick up the techniques, a combination of the research i've done and plain ole driving experience. currently have a tank of about 170 miles and still averaging above 60mpg. the goal is to keep the whole tank this way but its going to be a hard time running, especially with my 05 hch's gauge being 3 whole mpg off :/
perhaps the dealer can give me some information on why this is so?
take care and thanks again!
i'm definitely starting to pick up the techniques, a combination of the research i've done and plain ole driving experience. currently have a tank of about 170 miles and still averaging above 60mpg. the goal is to keep the whole tank this way but its going to be a hard time running, especially with my 05 hch's gauge being 3 whole mpg off :/
perhaps the dealer can give me some information on why this is so?
take care and thanks again!
