Ramps in the TRA, how they work and how they effect performance.

[tollen77]

These principles are difficult to disprove although I know of one individual who will try hard to do so.

Me, me! (hand waving in the air)

Nah, the principles are accurately stated, and one thing about the TRA, it does make you think!

I doo find it interesting that people can read the principles and then don't know why they are correct.

Take the "Spring force can determine rpms in either clutch. More spring force = higher rpms." statement. Anyone think about why this works in isolation? It works because all the bigger spring does is suck up a portion of the force that the flyweight is generating. The engine hp gets a chance to escape in the form of higher RPM, because the HP hasn't changed (non mountain sled). To take it to the extreme you could have a spring from the front end of a Buick car in the TRA, and if you can add enough weight to the arms that clutch will move, but why would you want to doo that? Now you need a different ramp profile to match the spring rate of the Buick spring.

This is all fine on a lake, but change the weight of the sled or the HP curve and the tuning starts all over again.

Heat is another great friend of the TRA. The TRA loves to make heat. So anytime the tuning of the clutch is off a little the engine HP will escape in the form of heat, and poof! No more belt. All clutches produce heat. The difference is they do not overheat as quickly or as severely as the TRA. I'm thinking it was the rubber wiggle mount of the TRA outer hub that lets the TRA scrub the belt to make it so hot so quick. If the belt was loose enough to slip, then the secondary would be broken or stuck.

I don't see where there is a tuning solution for the TRA on a sled where the weight changes and the HP constantly changes through out the day. Can't be done.

The principles are correct, just the TRA is no good.

"Take the "Spring force can determine rpms in either clutch. More spring force = higher rpms." statement. Anyone think about why this works in isolation? It works because all the bigger spring does is suck up a portion of the force that the flyweight is generating. The engine hp gets a chance to escape in the form of higher RPM, because the HP hasn't changed (non mountain sled). To take it to the extreme you could have a spring from the front end of a Buick car in the TRA, and if you can add enough weight to the arms that clutch will move, but why would you want to doo that? Now you need a different ramp profile to match the spring rate of the Buick spring."


I'm with you there YDPC. Increasing spring forces doesn't seem like a very efficient way to reduce belt squeeze. Though, many have argued that it's neccessary to prevent over-sensitivity to load. I'm still on the fence as to what is best. Though hopefully another season of experimenting will push me one way or the other.


As for the TRA being no good... I think you've made your point pretty clear that you're not a fan. Hey, that's fine with me. Though I'm not sure what saying, "TRA sucks, TRA sucks!" really adds to the conversation.



.

 

[tollen77]

@tollen 77

When you break down into principle form, then it does not matter what brand oem or aftermarket clutch you speak of.

The hat you wear right now, says "snowmobile" specifically "skidoo".
I am going to take my snowmobile hat off and put on my "Automotive" hat.
.....I am not thinking snowmobile, I am thinking "Car" one of my fave cars is a 350 hp "Nissan Murano"

---------------------------------------------------------------

Example (The clutches stop upshifting - mph ceases)
The question is designed to achieve a yes or no answer - any other answer is non-responsive.

Regarding Primary clutch - IF the clutches stop upshifting, THEN does the belt continue to move across the sheave face on the primary? yes or no?

Regarding Secondary clutch - IF the clutches stop upshifting, THEN does the belt continue to move across the sheave face on the secondary? yes or no?

-----​

"Regarding Primary clutch - IF the clutches stop upshifting, THEN does the belt continue to move across the sheave face on the primary? yes or no?"

Not sure I totally understand which direction the belt is moving in your question, but here it goes. If the clutch stops upshifting then the belt will no longer rise in the primary. The clutch continues to spin, of course and so the belt continues to spin, though over a smaller 'sprocket' than at full shift.

Are you saying that there is more friction created between the belt and the sheave face at anything less than full shift than is created right at full shift? If that's the case, that explains why anything less than ideal RPM would create excessive heat.



.

 

[Dynamo^Joe]

If a clutch stops "up shifting" I would tend to believe there is no motion.

Remember how early natives started fires?
If you rub a stick in one spot back and forth hard enough and long enough, in "one location" from the continuous use in one location "range", would the stick get hot enough to ignite? yes or no?
Would the stick ignite from excessive temperature? yes or no?

From what I understand when the clutch stops up shifting, motion of the belt ceases, it ceases to move across the sheave face.
While under full throttle(continuous energy input), the belt dwells in one location "range" on the sheave face.(no motion output)
If you continue to apply energy without motion increase - something is bound to happen, the energy is expelled somewhere - more than likely "heat"
Would continuous application of this calibration cause heat? yes or no?

The longer the belt dwells in one location, heat increases.

The more frequent the belt stops up shifting (rpm fluctuation) the more times the belt stalls in a "range" on the primary clutch, heat increases.

I quote only reputable sources, this information is not me
---The #1 cause of heat is rpm fluctuation.

Evidence of RPM fluctuation is excessive heat.

Here is the big question - What causes rpm fluctuation?

 

[jaws136]

RPM fluctuation on a mountain sled would be caused by inconsistant load on the mountain, snow condition, incline, whatever to your clutch set-up right? So the first place to combat this in the CVT is helix right? As you shift up you want to have the right ammount of "stall" of that torque load for the motor to keep rpms at peak. That is how i'm seeing it.

My question is this, stall is great for the transitional loads to keep motor running rrr's let's say you are set-up great for control of that inconsistant load and never come off of peak rpm's, then you go to a smooth relatively consistant hill where much more speed can be reached, is there a relation to having a low cam angle here in relation to top speed? Say at 8250rpms a straight 40 would reach 55mph and a straight 36 only reach 48mph???? Or are helix numbers irrelevant to the limit of top speed?

 

[tollen77]

If a clutch stops "up shifting" I would tend to believe there is no motion.

Remember how early natives started fires?
If you rub a stick in one spot back and forth hard enough and long enough, in "one location" from the continuous use in one location "range", would the stick get hot enough to ignite? yes or no?
Would the stick ignite from excessive temperature? yes or no?

From what I understand when the clutch stops up shifting, motion of the belt ceases, it ceases to move across the sheave face.
While under full throttle(continuous energy input), the belt dwells in one location "range" on the sheave face.(no motion output)
If you continue to apply energy without motion increase - something is bound to happen, the energy is expelled somewhere - more than likely "heat"
Would continuous application of this calibration cause heat? yes or no?

The longer the belt dwells in one location, heat increases.

The more frequent the belt stops up shifting (rpm fluctuation) the more times the belt stalls in a "range" on the primary clutch, heat increases.

I quote only reputable sources, this information is not me
---The #1 cause of heat is rpm fluctuation.

Evidence of RPM fluctuation is excessive heat.

Here is the big question - What causes rpm fluctuation?

OK, so when either clutch hold the belt at the same level for an extended period of time belt friction creates excessive heat in that spot. That makes sense. But would this scenario not happen more frequently from the engine maintaining the same RPM for an extended period???

It seems that RPM variation should actually cool the clutch, though this isn't happening. Why???


.

 

[DaveB]

OK, so when either clutch hold the belt at the same level for an extended period of time belt friction creates excessive heat in that spot. That makes sense. But would this scenario not happen more frequently from the engine maintaining the same RPM for an extended period???

It seems that RPM variation should actually cool the clutch, though this isn't happening. Why???


.

If you'll let me play (I asked my Mom...she said it was OK)...maintaining the RPM the same does not mean the clutches stay in the same shift-out point. The secondary is "load sensing" and moves in and out with the changes to the load on the track....incline, decline, softer snow, harder snow, powder, etc.

RPM variation doesn't cool the clutches because the secondary twists to open and close....the belt always slips a bit there. Plus when your belt is low in the primary, the primary has less surface area of grip than the secondary and it takes a little more grab for the primary to get a hold of the belt. Guys that "winggg, wingggg, wingggg", the throttle all the time will always get warmer clutches than those who do not.

 

[Dynamo^Joe]

tollen77;OK, so when either clutch hold the belt at the same level for an extended period of time belt friction creates excessive heat in that spot. That makes sense.

tollen77; But would this scenario not happen more frequently from the engine maintaining the same RPM for an extended period???
---What scenario? Your question needs more detail, I don't know what you are thinking of? Scenario of what?

---Are you calibrating with part throttle or full throttle? I calibrate with full throttle. I observe the sled and measure under condition that allows full throttle. Guys who help me tune perform tests under full throttle position.
I try to test in areas where the sled can be operated, performing a certain few tests where there is a minimum time in seconds the sled must see full throttle.

tollen77;It seems that RPM variation should actually cool the clutch, though this isn't happening. Why???
---Before we move on, can you explain why fluctuating rpms cool clutches.


Quotes 09 handbook - Pg 119.
In calibrating clutches, the objective will be to maintain as horizontal line as possible between low ratio and high ratio. This shift speed must be as close as possible to the engine peak hp rpm. aka - Calibrate with a clicker number that will allow straight shift / rpms.

 

[YamaDoo PolCat]

If you'll let me play (I asked my Mom...she said it was OK)...maintaining the RPM the same does not mean the clutches stay in the same shift-out point. The secondary is "load sensing" and moves in and out with the changes to the load on the track....incline, decline, softer snow, harder snow, powder, etc.

RPM variation doesn't cool the clutches because the secondary twists to open and close....the belt always slips a bit there. Plus when your belt is low in the primary, the primary has less surface area of grip than the secondary and it takes a little more grab for the primary to get a hold of the belt. Guys that "winggg, wingggg, wingggg", the throttle all the time will always get warmer clutches than those who do not.

Good post Mr.B. There is one more source of heat in the TRA and that is the flex mounted rubber hub riveted to the one side of the clutch. It acts like an isolator, AND an obital sander. It gets hot! The rubber is suspended by the big spring, so any resonance in the spring makes the rubber wiggle and scrub the belt. The hotter the clutch, the softer the rubber and the heat increases as more movement is generated by that soft wiggly rubber mounted sheave. BOOM, by by belt.

Here's a quote for Tollen, the TRA sucks! I'm just shocked that BRP makes such a great sled, and then puts a clutch like that on for the mountain sleds... It is not good enough.

 

[YamaDoo PolCat]

tollen77;
Quotes 09 handbook - Pg 119.
In calibrating clutches, the objective will be to maintain as horizontal line as possible between low ratio and high ratio. This shift speed must be as close as possible to the engine peak hp rpm. aka - Calibrate with a clicker number that will allow straight shift / rpms.

Maintain a horizontal line? Those books.... flatlanders.

 

[tollen77]

If you'll let me play (I asked my Mom...she said it was OK)...maintaining the RPM the same does not mean the clutches stay in the same shift-out point. The secondary is "load sensing" and moves in and out with the changes to the load on the track....incline, decline, softer snow, harder snow, powder, etc.

RPM variation doesn't cool the clutches because the secondary twists to open and close....the belt always slips a bit there. Plus when your belt is low in the primary, the primary has less surface area of grip than the secondary and it takes a little more grab for the primary to get a hold of the belt. Guys that "winggg, wingggg, wingggg", the throttle all the time will always get warmer clutches than those who do not.

"maintaining the RPM the same does not mean the clutches stay in the same shift-out point. The secondary is "load sensing" and moves in and out with the changes to the load on the track....incline, decline, softer snow, harder snow, powder, etc."

"RPM variation doesn't cool the clutches because the secondary twists to open and close....the belt always slips a bit there."


Right Dave, very good point and all of this makes a lot of sense once you look at it this way. Thanks for clarifying.


"Plus when your belt is low in the primary, the primary has less surface area of grip than the secondary and it takes a little more grab for the primary to get a hold of the belt."


I believe that a lot of the lost contact area when the belt is down low is made up by the improved geometry of the TRA. From what I understand, the TRA provides more pinch down low than most othe clutches at the expense of providing relatively less pinch when the belt is up higher in the clutch. I'm not going to live and die by that statement, but that's what I've been told. If true, this added squeeze should go some way to make up for the loss of contact area, no?

Either way, it appears the RPM that Joe is referring to is not so much engine RPM but rather secondary RPM changes due to changes in snow load. Does that make sense?

This still doesn't totally jive with what Joe said earlier.


"- The #1 cause of system high temperature is "RPM FLUCTUATION"
An engine has "rated rpms" An engine has "torque point rpms"

IF you run a system at less than rated rpms, THEN temperatures will increase. (The clutches stop upshifting - mph ceases to increase)

IF you run a system at more than rated rpms, THEN temperatures will increase. (The clutches stop upshifting - mph increases ONLY by virtue of increased engine rpm)"


What am I missing here???



.

 

[tollen77]

tollen77;OK, so when either clutch hold the belt at the same level for an extended period of time belt friction creates excessive heat in that spot. That makes sense.

tollen77; But would this scenario not happen more frequently from the engine maintaining the same RPM for an extended period???
---What scenario? Your question needs more detail, I don't know what you are thinking of? Scenario of what?

---Are you calibrating with part throttle or full throttle? I calibrate with full throttle. I observe the sled and measure under condition that allows full throttle. Guys who help me tune perform tests under full throttle position.
I try to test in areas where the sled can be operated, performing a certain few tests where there is a minimum time in seconds the sled must see full throttle.


tollen77;It seems that RPM variation should actually cool the clutch, though this isn't happening. Why???
---Before we move on, can you explain why fluctuating rpms cool clutches.


Quotes 09 handbook - Pg 119.
In calibrating clutches, the objective will be to maintain as horizontal line as possible between low ratio and high ratio. This shift speed must be as close as possible to the engine peak hp rpm. aka - Calibrate with a clicker number that will allow straight shift / rpms.

Hey, I'm just trying to understand this. I think DaveB did a good job of explaining why a belt moving up and down the clutch makes more heat and looking at it that way makes a lot of sense. I assumed that by moving the belt up and down through fluctuating RPMs that the belt heat created by clamping forces would be distributed over a larger portion of the clutch. Clearly, that's wrong since I wasn't accounting for the belt slipping as the clutches moved.


Joe said;
"--What scenario? Your question needs more detail, I don't know what you are thinking of? Scenario of what?

---Are you calibrating with part throttle or full throttle? I calibrate with full throttle. I observe the sled and measure under condition that allows full throttle. Guys who help me tune perform tests under full throttle position.
I try to test in areas where the sled can be operated, performing a certain few tests where there is a minimum time in seconds the sled must see full throttle."


Any scenario where the belt stays in the same position on the clutch. Clearly that part doesn't matter any more though so lets just go with WOT. As for where I'm calibrating, I'm not calibrating anything.... just trying to understand clutching a little better.



.

 

[tollen77]

Here's a quote for Tollen, the TRA sucks! I'm just shocked that BRP makes such a great sled, and then puts a clutch like that on for the mountain sleds... It is not good enough.

Ha, that's funny man. You're relentless.

 

[DaveB]

I dealt with him all last year....your turn. hahaha.

 

[shortstop20]

Maintain a horizontal line? Those books.... flatlanders.

What would you suggest?

 

[Dynamo^Joe]

Maintain a horizontal line? Those books.... flatlanders.

Your 07R is rated at 8150 rpms.

2 Questions....

1. When you are going up a hill, are there ever times where you are on the throttle wide open for more than 8 seconds? yes or no?

2. While applying full throttle, when you are going up a snow hill in the steep and deep want your engine to run:
a) more than 8150?
b) less than 8150?
c) at 8150 rpms?

Only pick one letter, a, b or c.

thanks
Joey

 

[Dynamo^Joe]

Good post Mr.B. There is one more source of heat in the TRA and that is the flex mounted rubber hub riveted to the one side of the clutch. It acts like an isolator, AND an obital sander. It gets hot! The rubber is suspended by the big spring, so any resonance in the spring makes the rubber wiggle and scrub the belt. The hotter the clutch, the softer the rubber and the heat increases as more movement is generated by that soft wiggly rubber mounted sheave. BOOM, by by belt.

There is no mechanical connection with the "cushion" to the governor cup.
There is a plate that is fastened to the governor cup.

The cushion is laminated with glue to the plate on the governor cup.
This is called a "Cushion Drive". The splined shaft connects to the female portion of the governor cup. This cushion is held on the aluminum cup by virtue of friction - the rubber is laminated onto the disc, the disc is held on by force of the torque of the clutch bolt.

The pictures I show here are failure due to lack of clutch bolt torque. A guy thought that 75 lbs was too much so he repeatedly torqued at 45 lbs and upon a sudden shock to the track load while under full throttle, the cushion sheared - due to the lack of friction that the torque of the clutch bolt applies.
You are better off with slight more bolt torque than less bolt torque.

When the clutch is spinning the rollers push out against the ramps, the ramps are connected to the governor cup. Under full throttle the clutch is like a solid piece of aluminum even though power transmit through the rubber cushion.

The cushion is under torque and flex so little almost not measurable. The little bit that the clutch is flexible reduces the "natural frequency" that the crankshaft rings at and prevents crankshaft failure due to cracking, also prevents failure of the ignition stator due to stator natural frequency. The design of the clutch is very deep that it is built with an inherent quality it will reduce if not eliminate engine component failure due to vibration.

 

[Original Tetonice]

If you'll let me play (I asked my Mom...she said it was OK)...maintaining the RPM the same does not mean the clutches stay in the same shift-out point. The secondary is "load sensing" and moves in and out with the changes to the load on the track....incline, decline, softer snow, harder snow, powder, etc.

RPM variation doesn't cool the clutches because the secondary twists to open and close....the belt always slips a bit there. Plus when your belt is low in the primary, the primary has less surface area of grip than the secondary and it takes a little more grab for the primary to get a hold of the belt. Guys that "winggg, wingggg, wingggg", the throttle all the time will always get warmer clutches than those who do not.

Ditto to the throttle winng,wingg, wingg...with every wingg the TRA arm/rollers works harder as it shifts on any ramp.

By the way the TRA is a vey simple clutch to operate and shouldn't be discouraged by the scienctific discovery being displayed.

OT

 

[YamaDoo PolCat]

What would you suggest?

Vertical. Horizontal is another market segment called trails.

 

[shortstop20]

I don't think you are understanding what that post was supposed to mean. He is talking about getting a horizontal, "straight" shift of the clutches. In other words they start shifting at peak RPM's/HP and keep shifting at peak RPM/HP and the RPM's do not deviate away from peak HP.

If you had a vertical shift the clutches would start shifting below, at, or above peak RPM/HP and then keep shifting as the RPM's went up, which is not the correct way to do it unless you don't want your sled to be as fast as it could. Trail or mountain riding is irrelevant, you still want to keep a straight shift in my experience.

 

[YamaDoo PolCat]

Your 07R is rated at 8150 rpms.

2 Questions....

1. When you are going up a hill, are there ever times where you are on the throttle wide open for more than 8 seconds? yes or no?

2. While applying full throttle, when you are going up a snow hill in the steep and deep want your engine to run:
a) more than 8150?
b) less than 8150?
c) at 8150 rpms?

Only pick one letter, a, b or c.

thanks
Joey

Hey Joey, how you dooin'?

Answers,

1. Going up hill? Man the flipper is taped! A hard run seems to last for-ever. In the deep powder going up the Box you are probably pinned for 2 or 3 minutes. It is an avalanche prone area and you want to make the safety zones. I knew I should not have tried it with the TRA last year, but got stupid. You've probably seen this picture before. It was spooky switching that belt out, especially with the guddamm kevlar wrapped around everything. I had to let my buddies go play by themselves for a while. I didn't have any more belts and could not hold the throttle open safely for long enough to be safe in there.

Average full throttle, in less snow, would be 20 to 40 seconds. Just sitting here watching the clock and visualizing a couple common runs. Elevation 4,500 to 7,500.

2. a) I want the tach to indicate 8,200RPM, until I loose sight of it under the snow. After that all you can go by is the steady engine tone. When ever you let off the throttle you can wipe the guages before the next run. But even if you can't see the guage you are always listening for that sweet tone. If you hear the engine tone change you better start looking for a parking spot. It may be a belt problem, too much snow on the intake or engine trouble. So get the sound of 8,200 RPM in your head and keep it. You want to hear lots of it. When that TRA starts wobbling the engine RPM around, it used to drive me nuts!

When there is less snow and you are just playing a long hill and the engine RPM is good, you listen for the track speed. You can hear the "whooph" as the track flies over tank traps and stuff in the hill and it has a particular sound and feel when the track speed is going to kick ***. The engine tone should never change, but you can hear the track changing speed as the clutches shift up and down as the load feed back from the track changes.

That's why I get such a kick out of people talking about extra pinch on the belt. The tension on the belt of course must be at whatever design value it is rated for, but after that the belt is free to move according to the load, and the HP given to handle that load. The belt isn't going to slip worth worring about.

Darn, I'm rambling.

Anyway that's what we need in the mountains, a great clutch combo and there is nothing matter with the stock BRP 07 roller secondary and stock helix.