Bucket Dump Hesitates

[patrickg]

Rich, My meager understanding of working a diesel engine would cause me to look at the torque curve (T versus RPM). Then I would ensure that I was safely above the RPM where max torque can be produced. Note I say "can" not "is". If you don't apply a load there is very low torque irrespective of the RPM. Anyway the idea is to not lug the little diesel engine. Staying above the max torque RPM helps in this way: As load increases and torque demand goes up RPM does fall. If in the process of falling it takes you to a place on the torque curve where more torque is available then the RPM loss becomes less and less as the torque peak is approached. Like springs getting stiffer and stiffer as more and more overload leaves are engaged (assuming progressive engagement overloads).

If you try to work the engine near or below the max torque RPM then a little increase in load and you are below max torque point (on the part of the curve with a negative slope). As load increases torque goes down, a rapidly degenerating situation where you will if you persist, potentially damage the engine, or likely just kill it, like I do when ramming a dirt pile with the FEL while running too low of RPM. By the time I get off the HST pedal and stop trying to get the bucket to roll back the engine has died. I hate running at PTO speed due to noise etc but I need more practice running closer to the torque peak instead of well above it such as at PTO speed. Hopefully I will learn the deft touch or buy the outrageously expensive active noise cancelling ear muffs and try not to think about all those parts threshing about and racing back and forth in that little engine. (Why not a small turbine, no repiprocating mass!) Hope this helps. If you are partially confused by my comments, drop me a line and I'll finish the job.

Patrick

 

[Bird]

Darin, when they talked about carbon buildup at idle, I think they're talking about less than 1000 rpm. I wouldn't be concerned about the carbon buildup at 1200-1600 rpm (anybody disagree?). But then Patrick has already told you about the torque curve.

Bird

 

[RichS]

Hey Patrick, Still computing that... Give me a second.... Nope one more.... /w3tcompact/icons/tongue.gif Ok. got it.
Just kidding....
Good point about the torque curve. Every make/brand and size engine is different and therefore it is not a one speed {rpm} takes all type of situation. As much as that would make all of our lives easier but less exciting! /w3tcompact/icons/smile.gif What would we have to talk about then! /w3tcompact/icons/frown.gif
I understand your philosophy, however that little voice in my head keeps telling me. "MAN CRANK UP THOSE RPM'S, I DON'T THINK THE NEXT TOWN CAN HEAR YOU!"
Besides my wallet is screaming, "ALL RIGHT GIVE ME SOME FLOW!!!".
Seriously, I know the engine is rated to run at RPM speed for hours on end. But the problem is not in the engine, it is in my own disconcertion running the engine where it is most appropriate to run it. You are right it has an auto-governing system that seems to decrease the RPM as load increases. However, I have not gotten completely proficient yet on changing throttle level as work increases/decreases. As time goes on, I hopefully will come to an agreement with my little tractor as to what is best


Rich S.

 

[frank_f15]

knight: keep the rpms up and be careful of the positioning of the control handle. sometimes u are trying to do 2 things at one time. it coulld be a valve problem, but i found that it sometimes ,is operator problem(like me) but be sure and let the dealer check it out.

 

[DarinRay]

Thanks Bird and if anyone else has any comments then thank you too /w3tcompact/icons/laugh.gif. And wow Patrick that is some explanation I just wish I could sound and be that smart.

Darin

 

[patrickg]

RichS, Often posted values (like inflation pressure molded into the sidewall of a tire) or a redline or the PTO mark on the tach seem to attract folks like moths to a flame. How many times have you heard someone say they run the manufacturer's recommended tire pressure? The pressure on the side wall is a maximum cold inflation pressure not a normal running pressure. The max load rating is also molded into the sidewall. Who do you know that carries sand bags or other weight arround to ensure they follow the manufacturer's load recommendation? If you aren't loading the tires to the max then you don't need max pressure (for ordinary driving). Superstition and missunderstanding abound.

Meanwhile back to RPM: Some implements "need" PTO RPM or close to it to have the kinetic energy (moving inertia) to carry through the hard spots (look at the size of the external flywheels on some antique tractors, same idea achieved differently).

To get more specific toward our case(with small "c"): Our little diesel is governed but the effect I was describing isn't it. The loss of RPM as load increases is not the result of an active control but a result of basic physics. Higher loading tends to slow the engine as it has to do more work. If we are operating at an RPM above max torque (like we definitely should be) then as RPM drops more torque is available. The result is like this: as we increase loading one loading unit at a time, RPM drops less and less for each step as the available torque continues to INCREASE as RPM drops. U N T I L we reach the max torque RPM and then each unit of increased loading causes a larger and larger RPM drop which if we don't do something will lug or stall the engine.

Manufacturers, Kubota included, brag about the steep slope of their torque curve because it is a benefit (when operating above max torque RPM). It is what "powers" you through a hard spot box blading or whatever. Steeper is stiffer, more resistance to being slowed down by increased loading. B U T if you get on the backside of the curve, oh well, shame on you.

To recap: PTO speed I S above max torque speed and will work fine. However, if the particular job doesn't demand max or near max HP, then dropping the R's a tad can be a good thing, quieter, less wear on engine and hydraulics, keeps hydraulic actions as slow as my thinking.

I seem to be able to roll the FEL bucket while raising or lowering it while pulling forward or back and turning while trying to not hit the vinyl siding on the new house with rear implement/counterweight while not driving into trench and not driving over fresh non-compacted cross trench and tipping over FOR about an hour at RPMs between 2300 and 2600(PTO) then I just can't juggle that many balls at the same time, something has to give as I slide into cognitive overload. So I reduce RPM and proceed a bit less frantically and drag the bucket across the ground less because I got distracted by something else. So far I haven't crashed into the house but that has been partly luck.
Maybe it is my crude control actions B U T at high RPM my FEL gets pretty violent (out takes from Godzilla movie).

If this hasn't totally confused everyone, just say, I'll try to finish the job.

Patrick

 

[patrickg]

Thanks for the kind words Darin but if I was smart I wouldn't have nearly turned my tractor over twice this morning. Once when I "gently" rammed the dirt pile while back filling trenches and rolled the bucket back. Worked fine the first 5 times. This time I got into some dirt that had solidified or something and as the bucket rolled back the right rear tire went into the air. I very slooooooly rolled it back just a tad to see if it would break out and the tire went higher (as did the pucker factor in a non linear fashion). I tried to slowly slowly do everything in reverse that had got me to this "interesting position". (For a guy who helped train pilots to recover from "unusual attitudes" only by reference to instruments, I sure am easily disturbed by unusual attitudes in a tractor.) The wheel went higher. Backed up real real slow and it leveled out. Whew! Undaunted by the recent experience, my heart beating again, adrenilin rush subsiding, a couple buckets later I whipped the wheel and punched the hydrostat pedal to the metal in reverse. Rt rear tire went into the air and tractor leaned more than immediatley preceeding interesting experience. I didn't have time to think (don't know what I would have thought of with so little experience on tractor) but sort of instinctively got off the go pedal and the braking action of the left rear acted as a fulcrum to my high CG and plopped the tractor back down on terra firma. Lesson learned. Yes, familiarity (even supposed familiarity) will get you in trouble. I promise to be a better citizen in the future. All the tilt meters in the world with or without alarms would not have helped. Sometimes you just have to remind yourself to not do something stupid. I am sort of "PRO TILTOMETER" I'm sure I would have one if Kubota or the tilt meter guy would tell me how much tilt is too much tilt. One day I will do the CG determining exercise and figure the safe "bank angles" and "climb and dive angles too".

Until then I'll make haste more slowly.

Patrick

 

[hayden]

Kevin,

I've experienced exactly what you are describing on both a B2400 and B2910. There's a post somewhere on this topic.

What I've found is that after you lift your bucket load and go to dump, you can do one of three things:

1) Dump in "slow speed" only. This is the first detent position to the right on the loader control.

2) Dump in "slow speed" then proceed to "fast speed". This is done by going to the first detent for a second or so, then proceeding to the full right position.

3) Go directly to the "fast speed" without pausing in the first detent position.

What you describe happens most often (at least to me) in case #2 when you first do a slow dump then speed up. The "fast speed" is a regenerative cycle where oil is delivered to both ends of the cylinder, and movement results from one end overpowering the rod end due to the difference in surface area to apply pressure against. The extra speed comes form the oil expelled from the overpowered side being used to further push the opposite end.

I've taken mine to the dealer and they talked to Kubota and the answer back is that it's normal. I've seen it on at least two machines now so I kind of believe it. I've never come up with a solid explanation of what's happening, but it seems to be related to the transition from non-regenerative to regenerative cycle, and I expect involves expelling air from the system because, acording to physics, fluids are not compressible, so for moving fluid to not be causing movement in the cylinder means it must be filling a void somewhere.

I've just learned to live with it. Doing slow dumps only or going rapidly to fast dump seems to avoid the pregnant pause.

Peter

 

[frank_f15]

peter: i could not have said it better. my 2400 acts just like u described. slow dump is fine, fast dump is fine, but sometimes the transition between slow dump and fast dump, causes a slight hesitation. not always,but sometimes. always wonder if there is something wrong with unit. seems like, it is normal.

 

[Knight9]

Thanks all for the feedback. I had 2 more loads delivered and spread them out yesterday. I really concentrated on what I was doing and not being sloppy with the movement of the control. The bucket dump hesitation still happened a few times but not nearly as much. I hadn't read the notes about the slow/fast dump before I did this work. I'll pay particular attention to it next time.

Will probably still show the dealer what I've seen happening when we do the 50 hr maintenance, but I'm certainly less concerned about it now.

Thanks again. When I get around to getting a digital camera I'll be sure to post photos of where all the dirt went!! I better get one heck of a nice lawn after all that work! /w3tcompact/icons/wink.gif/w3tcompact/icons/smile.gif

Kevin