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Gearbox Question Grinding Me - hightower - 04-01-14

So, as you can guess from my other posts I've been looking at mechanics (the theory side anyway). I understand how the gearbox works, but have a grinding (pun intended) question.


Look at this animation: [Image: sequential-gearbox-animation.gif]




You see when the red and yellow dogs come together, that creates your drive. However, what I can't find the answer to is "what if the red and yellow gears come together when the dogs are inline with each other?"


Surely, rather than engaging gear the dogs will bounce off each other and you'd be in some sort of false neutral?

Re: Gearbox Question Grinding Me - hightower - 04-01-14

Upon further searching, I think the solution to this is synchro gearboxes. But not sure how they work, does anyone have a decent tutorial - tried searching but they all seem a bit naff at explaining.

Re: Gearbox Question Grinding Me - sadlonelygit - 04-01-14

Cant see the animation but put simply you have a driven gear and an idler gear. The driven gear generaly spins faster than the idler so eventually the dogs engage

Re: Gearbox Question Grinding Me - Fazerider - 04-01-14


I can't see your animation, but yes, in that condition the gear won't have engaged and you'll feel it "hasn't gone in". Bear in mind that the gear and dog will normally be rotating at slightly different speeds even if you've judged the required revs quite accurately. It's a gentle pressure that you are applying to the selector arm not a brief impact... after a tiny fraction of a second the dog will be aligned with the slot and be able to drop in.
It's why getting the gearbox into gear can be tricky when the engine isn't running, with no relative movement to help the dogs and gears align sometimes it won't go in unless you give the back wheel a nudge.


The slots the dog engages with are longer than the pinions on the dog itself, this increases the opportunity for the two to engage... this is where most of the slop in the gearbox drive train comes from (put it in gear and rotate the sprocket back and forth to feel it).


Synchomesh is an extra ring that drags on the gear to match speeds and blocks full engagement until the dogs are aligned. I don't think many bikes have those though, ours are simple crash boxes.

Re: Gearbox Question Grinding Me - nick crisp - 04-01-14

On the subject of gears, used to read about straight-cut gears, and how, particularly on Kawasakis of the time, they used to cause that characteristic whine Kwaks were known for. So what is a straight-cut gear, what other types are there, advantages/disadvantages/reasons for using one type or another?

Re: Gearbox Question Grinding Me - Fazerider - 04-01-14

(04-01-14, 02:48 PM)nick crisp link Wrote: On the subject of gears, used to read about straight-cut gears, and how, particularly on Kawasakis of the time, they used to cause that characteristic whine Kwaks were known for. So what is a straight-cut gear, what other types are there, advantages/disadvantages/reasons for using one type or another?
Straight cut gears are what we have. They're noisier because the whole width of the tooth touches its mating gear's tooth at the same time.
Helical cut ones mesh gradually. They're less efficient because some of the torque gets turned into an axial force.
Car gearboxes are generally helical except for first gear where that is the one used to provide reverse (introducing another gear wheel means it would be required to have the opposite cut) so that's why cars are extra whiney when in reverse. Dunno why older Kawasaki's should be particularly bad though.

Re: Gearbox Question Grinding Me - Fraser - 04-01-14

Early Kwakers and Triumph triples have straight cut primary gears, whines in all gears LOL

Re: Gearbox Question Grinding Me - mickvp - 04-01-14

Hightower,

I make gearboxes and transfer boxes for a living, I cant see your animation, but I imagine its just a basic representation of how involute forms mesh. Typical gears can be just the gear itself, but (in the case of most transfer boxes) a lot of gears have a set of secondary dog gears on one end. take this component that we make in work:

[Image: FTC1741-GEAR-HIGH-OUTPUT-LT230.jpg]

as you can see, there is a helical gear, and a dog gear on the same component. this is a high output gear (which is what will be driving when you are in the 2H or 4H range). there is another larger gear which faces this which is made in exactly the same fashion, this is the Low gear (which is what will be driving when you are in the 4L range) It looks like this:

[Image: FTC1084.jpg]

As you can see, its basically the same as the high gear, except there are more teeth, and the outside diameter is larger (which means it will provide a lot more torque, being bigger). the dog teeth on this component are identical to the ones on the high gear.

Now, both of these gear mate CONSTANTLY with their respective mating part (both gear mate to the same "cluster" gear - a cluster gear is simply a gear with more than one gear on the same part). the mating part looks like this:

[Image: FRC5426-GEAR-CLUSTER-LT230-TRANSFER-BOX.jpg]

So you can see this cluster has 3 gear on it. the smaller diameter gear is the one which mates to the larger low gear, the bottom gear (as you look at it) is which gear mates to the high gear, and the centre gear is the one which mates to the input gear, which is where all the drive comes from for the whole system (this would be take directly from the engine in the case of the gearbox).

You can see what the whole assembly looks like here:

[Image: lt230_a_big.jpg]

you might be wondering to yourself now, if these gear are all meshed together at the same time, how is it that only one set is driving at any one time? The answer to that lies in the dog teeth, which are attached to the high, and low gears. these dog gears mesh with a coupling sleeve assembly, which looks like this:

[Image: RTC4373-HIGH-LOW-GEAR-SLEEVE-AND-HUB.jpg]

what happens is inside the cabin, when you select a different gear ratio (be it a gear, or in this case, a range for your transfer box). the gear lever moves a selector rod which is attached to the coupling sleeve (you can see the bronze selector rod in the assembly picture above). this takes the drive off of one gear, and onto another one (either high, or low), as only one of these can be engaged at once due to the design of the coupling sleeve.

so moving the selctor switch engages either the high gear or low gear with the diff cage (this is the part the high/low/and coupling sleeves all slide over)

heres a video that helps explain it:

Gearbox operation with clutch

hopefully ive not made that too confusing for you.


Re: Gearbox Question Grinding Me - mickvp - 04-01-14

oh, and the gear type depends on application really. Straight cut involutes are the most common form of gears, followed closely by helical gears.

dog gears are generally not used for running together, they are used for meshing purposes mainly (they dont run together well due to the missing tooth nature of them).

bevel gears (straight or spiral) are used to transmit vertical force to horzontal rotation (and hypoid gears are a sort of curved teeth variation of this).

then there is planet gears, which are usually 2 or more planet gears surrounding a sun gear, which is all within a planet carrier (and/or annulus)

there are also a few type of lesser used worm gears (worm gears/herringbone gears).

As I say, the uses of each are basically to suit the applcations, helicals are used over straight cut gears as they are slightly stronger in terms of the forces that can be transmitted through them (to make a spur gear of the same strength as a helical, you would need to make it larger, which can be a problem if space is an issue)


Re: Gearbox Question Grinding Me - nick crisp - 04-01-14

(04-01-14, 03:08 PM)Fazerider link Wrote: [quote author=nick crisp link=topic=11205.msg119580#msg119580 date=1388843339]
On the subject of gears, used to read about straight-cut gears, and how, particularly on Kawasakis of the time, they used to cause that characteristic whine Kwaks were known for. So what is a straight-cut gear, what other types are there, advantages/disadvantages/reasons for using one type or another?
Straight cut gears are what we have. They're noisier because the whole width of the tooth touches its mating gear's tooth at the same time.
Helical cut ones mesh gradually. They're less efficient because some of the torque gets turned into an axial force.
Car gearboxes are generally helical except for first gear where that is the one used to provide reverse (introducing another gear wheel means it would be required to have the opposite cut) so that's why cars are extra whiney when in reverse. Dunno why older Kawasaki's should be particularly bad though.
[/quote]

Ta!  :thumbup

Some good info there Mick  :thumbup

I don't work on bikes much anymore, used to strip them down and rebuild now and again, so I understand the basics and how it works, but always good to have any knowledge gaps filled with a bit more detail.






Re: Gearbox Question Grinding Me - hightower - 04-01-14

Thanks for info, especially your detailed post MickVP - much appreciated. I thought I had gearbox down, and your post has confirmed that for me. It's fairly straight forward once you break it down and know what to look for.


My question was (and I'm hoping you have an answer MickVP)... my animation should be viewable now with any luck (original post). You can see the red and yellow gears come together, and they connect with the dogs on the inside. That's all well and good when one dog is not inline with another dog - they will slot in and start to drive. But when they are in line surely they bounce off each other and no gear is engaged?

Re: Gearbox Question Grinding Me - mickvp - 04-01-14

(04-01-14, 06:33 PM)hightower link Wrote: Thanks for info, especially your detailed post MickVP - much appreciated. I thought I had gearbox down, and your post has confirmed that for me. It's fairly straight forward once you break it down and know what to look for.


My question was (and I'm hoping you have an answer MickVP)... my animation should be viewable now with any luck (original post). You can see the red and yellow gears come together, and they connect with the dogs on the inside. That's all well and good when one dog is not inline with another dog - they will slot in and start to drive. But when they are in line surely they bounce off each other and no gear is engaged?

yes, I can see your animation now. and the answer lies in this picture:

[Image: RTC4373-HIGH-LOW-GEAR-SLEEVE-AND-HUB.jpg]

This outside sleeve you can see is what engages with the dog teeth. if you look closely you will see it doesnt have standard teeth on the face, it has loads of little circular caverns. The dog teeth engage inside these caverns, but only at the highest point of the cavern, if you try to engage it when its not at the highest point, nothing happens, it just wont engage properly (but as the gears are constantly in mesh and therefore spinning, it will only be a momentary delay before the dogs rotate round enough to be in line with the appropriate section of the coupling sleeve and it will snick in neatly).

I hope that makes sense. Basically, your simplistic animation, while right in theory, is not how the finished design looks, it has been manufactured differently to reduce the chance of the issue you describe Smile

Re: Gearbox Question Grinding Me - hightower - 04-01-14

So, if we were to split open our Fazer boxes what sort of gears would we expect to see (if anyone has pictures that'd be a massive help)


And thanks MickVP

Re: Gearbox Question Grinding Me - hightower - 04-01-14

Sorry, just to clarify my confusion - this gearbox says it is off a motorbike. Would we see something like that in a Fazer. And if so, that seems to have dogs that slot in to grooves - so what happens if when you change gear the dog misses a groove?


How a motorcycle transmission works

Re: Gearbox Question Grinding Me - mickvp - 04-01-14

yes, thats pretty standard motorcycle gearing. You need to remember, that although that fella is turning that by hand, at what? 50-60rpm? when its inside the gearbox and running it will be spinning much faster than that, so its a non-issue really. even if the dogs do meet in the way you describe, the gear will have rotated around enough to engage in under a second, so youll never notice. This is eliminated in cars with the advent of synchromesh (generally a small coneshape component that fits between the coupling sleeve and the relevant gear).

The lack of synchromesh (and the same issue you are asking about sort of) is also why you get that "clunk" when you engage first (because the gearbox is going from no engagement to engagement).

All that being said. in a motorcycle box like ours (or most modern motorcycle transmissions), it CAN still happen, making a bigger space between the dog teeth helps to reduce it though.



Re: Gearbox Question Grinding Me - hightower - 04-01-14

Thanks man, you've been so helpful.

Re: Gearbox Question Grinding Me - mickvp - 04-01-14

happy to help mate Smile

anything else, just pop up a thread/pm me and ill do my best to help you out if I can  :thumbup

Re: Gearbox Question Grinding Me - rustyrider - 04-01-14

Mick, those pictures of yours look like a Land Rover LT230 transfer box.  Do you work for LR or is it Borg Warner that make them?

Re: Gearbox Question Grinding Me - mickvp - 04-01-14

It is indeed the LT230 box. It gets made in Glasgow now at Albion Automotive (part of American Axle and Manufacturing) Smile


Re: Gearbox Question Grinding Me - Razgruff - 05-01-14

while on the subject of gears, and without trying to confuse the issue.
Are there any bike gearboxs that use twin counter shafts and have to be timed in like of some truck boxs, ?

Been a long time since I really looked at modern stuff,