Will this work?
I find the engine braking on diesel excessive . Having a CVT transmission this seem to compound the engine braking issues and even on steep hills I still require throttle or it will slow down more than I wish.
I want to experiment with fitting a one way drive or ratchet in the secondary drive small pulley . This will then remove all engine braking . If it works hopefully it will solve the over braking and may even improve the fuel consumption ,
I have used a sprag bearing on one side , these are a ball bearing race which has a set of cams that will freewheel in one direction but lock the bearing in the other direction.
On the other side of the pulley is a sealed bearing . The sprag bearing requires a key way both inner and outer to transmit the torque and prevent it slipping in it housing.
The unknown being if it will be able to cope with the torque, being belt drive it will help reduce the shock loading on the sprag bearing . I addition It may also just be to weird to ride !
[img]
The left pulley is a standard taper lock fitting the right one is modified with a one way drive sprag bearing
[/img]
[img]
This photo is looking down onto the secondary drive pulley behind the CVT pulley .
[/img]
I will fit it to the MK 5 bike currently under construction ...... So you will have to wait for the results!
I'm not sure I understand why you're experiencing severe engine breaking.
When you throttle off, the CVT driven sheaves should relax back down their ramps, allowing the CVT to sh*t to a higher ratio (lower engine revs). I admit that as the engine revs drop the centrifugal weights in the front sheaves will have less tendency to shift into a higher gear, but if you have the right balance of weights, ramps and springs then you shouldn't find the engine trying to rev too hard when you roll off the throttle...
My single Robin using the same CVT did have some engine braking and didn't actually " let go" until walking pace although I should imagine a multi cylinder engine may have more braking effect??
I'm getting a bit confused with your production line of bikes/marks but did you say you had altered the weights from standard? If so that may be the problem?
I looked at the subject for my single cylinder bike and concluded that most diesel engines of industrial origin rev to around the same revs whatever engine is used and the only difference is the power output.
My CVT was from an Aixam Kubota Z482 so I was pleased that the cvt take up was working fine and I just experimented with the rear sprockets.
Just a thought
gilburton wrote:My single Robin using the same CVT did have some engine braking and didn't actually " let go" until walking pace although I should imagine a multi cylinder engine may have more braking effect??
I'm getting a bit confused with your production line of bikes/marks but did you say you had altered the weights from standard? If so that may be the problem?
I looked at the subject for my single cylinder bike and concluded that most diesel engines of industrial origin rev to around the same revs whatever engine is used and the only difference is the power output.
My CVT was from an Aixam Kubota Z482 so I was pleased that the cvt take up was working fine and I just experimented with the rear sprockets.
Just a thought
Hi
My stock CVT from an Axiam holds the engine pretty much constant speed @ around 3200 rpm up hill or down hill and I find myself needing to apply throttle when going down hill ! I have now reduced the constant engine speed closer to a 2000 rpm but still I get lots of engine braking. So the idea is what happens if it's reduced to zero. Maybe it will be horrible to ride but I like the thought of it in traffic!
Cheers Tim
So this begs to question those with CVT bikes....... how much engine breaking do you get and when do you get into over breaking at the rear wheel ?
should you underpower/ (weaker breaking dialled in) at the rear breaks compared to a normal bike?
Hi
The same hill I romp down on a manual box with no throttle at 30 mph the CVT will bring me to a walking speed unless I keep some power on. so I want to experiment and remove the braking to zero and see if it improves the ride and maybe the mpg.
Cheers Tim
Last edited by Tim on Tue Feb 18, 2014 7:27 pm, edited 1 time in total.
Since this is about CVT..... might be best to be in the CVT thread. Future readers seeking CVT knowledge more liable to find it too if it was in there. Moderator will move it I guess if they agree
coachgeo wrote:Since this is about CVT..... might be best to be in the CVT thread. Future readers seeking CVT knowledge more liable to find it too if it was in there. Moderator will move it I guess if they agree
Hi
I am good with that I recon it would be better placed under CVt stuff .
Thanks Tim
gilburton wrote:My single Robin using the same CVT did have some engine braking and didn't actually " let go" until walking pace although I should imagine a multi cylinder engine may have more braking effect??
I'm getting a bit confused with your production line of bikes/marks but did you say you had altered the weights from standard? If so that may be the problem?
I looked at the subject for my single cylinder bike and concluded that most diesel engines of industrial origin rev to around the same revs whatever engine is used and the only difference is the power output.
My CVT was from an Aixam Kubota Z482 so I was pleased that the cvt take up was working fine and I just experimented with the rear sprockets.
Just a thought
Hi
I agree but I find the standard setup best for performance and I have reduce the engine rpm to get the engine back to being more fuel efficient and I find the higher rpm makes my bike noisy and a blurr of sound!
Possibly the real reason being I am just a sadoo that thinks what what if I just changed"...............?
The idea may not work but I will keep you updated when I have tried it.
Thanks Tim
Attachments
The left is the standard front CVT spring , the right is the lighter spring I fit keeping the engine operating at much reduced RPM .
Another thing to keep in mind about the industrial engines we are using is that, unless we have modified the fuel systems, they have all-speed governors. As such, the "throttle" setting Is really just an engine speed setting. So when you have to keep half throttle on down a hill, your injectors are only delivering a fraction of the fuel they are when you are running the same rpm under load. The point is that you likely aren't wasting as much fuel as it seems like..."I need to twist my throttle THIS much to go DOWN a hill? !"
However, I can appreciate your annoyance with the phenomenon.
If you are wondering whether you have an all-speed gov, just twist the throttle in neutral...any given throttle setting should correspond to a particular rpm all the way up to max rpm. If all you have is a rev limiter, a half twist of the throttle will likely run you right up to red line.
albertaphil wrote:Another thing to keep in mind about the industrial engines we are using is that, unless we have modified the fuel systems, they have all-speed governors. As such, the "throttle" setting Is really just an engine speed setting. So when you have to keep half throttle on down a hill, your injectors are only delivering a fraction of the fuel they are when you are running the same rpm under load. The point is that you likely aren't wasting as much fuel as it seems like..."I need to twist my throttle THIS much to go DOWN a hill? !"
However, I can appreciate your annoyance with the phenomenon......
not haven driven it yet... there then lies a question in my mind. Ok so you have a CVT....... going down hill... Speed wants to increase so you let off throttle to maintain speed...)..... engine rpm drops....... Primary clutch begins changing due to less gravitational forces based on lower engine RPM's, this causes changes in Secondary clutch too ending up with you in a lower gear ratio ...... therefore you start slowing down when you were actually wanting to maintain speed. (engine braking basically) Or am I wrong on that?
Does engine rpm stay at same place as before downhill but not cause of same fuel delivery via driver input at throttle but instead because of a matching reduction in throttle with downhill momentum to keep the rear tire at same RPM (which maintains bike speed). This means that same rear tire RPM spins engine at previous RPM as it was on flat ground moments earlier? (assuming the throttle response based on downhill momentum only lowered engine RPM's only enough to maintain speed)
Obviously in that case some diminishing return exist if throttle reduced more. With less thottle no longer allowing engine to match former travelling speed's even with assistance of downhill momentum, then engine RPM and thusly engine braking from additional lowering of throttle causes an unmatched point thus clutch ratios change further and engine breaking begin to decelerate you.
boy that is way more wordy than I want. anyway For any of above to happen the secondary must be able to push the primary and thusly the engine and Im not sure a CVT can do that. Im still green on the full concept of how they work.
Well all I can say from a single cyl point of view I never noticed this??
I haven't seen any comments on engine braking from the microcar forums?
Ok they might be slightly heavier but surely the same principal applies?
I haven't driven a dIesel bike with a cvt but I have driven quads and snowmobiles with cvts and heavy trucks with all speed govs and automatic transmissions. I think what is going on is that the combo of governors and cvts responds exactly opposite of you would expect when you go down a hill. Tim, can you confirm if the following is true...
When you drive your car with an auto transmission, you idle your way up the hill, and when you reach the top, gravity starts pulling you, you let off on the gas pedal, the transmission shifts into higher gears and you pick up speed effortlessly on the downhill with the engine revving slowly.
Most cvts are set up to "downshift" when a reverse torque goes through them, I.e. when the the wheel is pushing the engine precisely TO increase engine braking. And then your all-speed gov backs off the fuel for you when the load comes off the engine even though you haven't moved the twist grip (just as it would when running a generator or whatever it did before you put it in a bike) so as to maintain a constant engine speed.
So what you get is a situation where you are expecting the transmission to upshift and to be able to let right off the throttle when you are going down a hill but instead the transmission downshifts and you May even have to increase your throttle setting to prevent your transmission from downshifting further! Just remember that your increased throttle setting is only putting just enough fuel into the engine to prevent the secondary pulley of your cvt from driving your primary which would cause it to downshift. But it is all backwards from what you would expect from your experience of driving cars with automatics.
Hi
Yes I agree with your reasoning. The cvt in an overrun situation will try hold the engine at a constant rpm regardless of speed. If you encounter a very very steep hill it increase the speed of the bike but keep the engine rpm constant . On a slight hill the effect of the good engine braking will diminish the speed to keep the engine rpm constant , that is unless you combat this but opening the throttle a little .
It is true that when the engine is powering the bike the cvt holds the engine rpm fairly constant say 3000rpm however when in the overrun down hill mode the cvt will hold the engine rpm constant but at a slightly lower rpm at around 2500 to 2700 rpm . This I assume is due to the CVTs rear pulleys load direction favouring the direction of the ramp that provides the constant tension for the belt when the front cvt pulley is expanding or contracting .
I am surprised the CVt system work so well and seem reliable. The really amazing this is it ability to act as a clutch and drop the belt tension completely and yet be able to give a perfectly smooth take up or engagement .
I am chain driving the gear transmission on my bike because I couldn't buy a cvt that would fit the taper of my crankshaft, but I love the concept of the cvt. They are also really effective in quads and snowmobiles. You just have to be willing to give up the control you always thought you had when you we're jamming gears:-)
but did you say you had altered the weights from standard? If so that may be the problem?
