Dog leg gearboxes

[jogi730]

I take it this type of g/b is stronger than usual type. How do they work in a road going car. Is it worth the upgrade?
Cheers
Chris

[4WheelDrifter]

Do you mean dog engagement? AFAIK they can be used in a road car. Quicker gear changes with or without the use of the clutch. I'm not sure if they are stronger though.

[ThatGUY]

A dog box does not have syncros. And i don't know about all but they have straight cut gears also. They are way much more stronger than standard gear boxes. AFAIK they are used on all the rally car. If you don't have really high power i doubt it is worth it. You would have to rev mach all gear changes as there is no syncros.

Andrew

[rotoryboy]

If you don't have really high power i doubt it is worth it.
Andrew

You've not seen Chris's car then

[ThatGUY]

Oh crap. I didn't pay attention. LOL I seen a run from GTI I think.
It would be nice then. You should be able to do harder launches with a dog box.

Andrew

[4WheelDrifter]

You can use just straight cut gears with a syncro box, if you want the box to be stronger, and you don't mind the noise. I thought the dogs replaced the syncros and allow engagement at any speed.

[s2avant95M]

i used to have a dog leg gearbox in my lotus sunbeam, well i assume by dog leg you mean first gear is where 2nd normally is.....

[4WheelDrifter]

Does that mean i'm on the wrong track here?

[rotoryboy]

Does that mean i'm on the wrong track here?

No I think your right

[S2central.net]

Huh WTF - its a 'dog' gearbox. Such gears are stronger than normal roadgoing gears. It has nothing to do with synchromesh. Only downside is increased noise - ever wondered why full race/rally cars have that nice transmission whine. Such noise doesn't sell road cars. Reckon on paying LOTS of money to find a dog box that will fit the S2.

Paul

[4WheelDrifter]

I wondered how a dog leg was going to benifit Chris.

[meep]

Huh WTF - its a 'dog' gearbox. Such gears are stronger than normal roadgoing gears. It has nothing to do with synchromesh. Only downside is increased noise - ever wondered why full race/rally cars have that nice transmission whine. Such noise doesn't sell road cars. Reckon on paying LOTS of money to find a dog box that will fit the S2.

Paul

No.

The word dog box comes from the Dog rings that you have insted of syncromesh rings. The whining sound is straight cut gears as oposed to helical cut gears that you have in a normal box. Ill try and find some pics.

Edit:

Straight cut gears


Helical cut gears



Syncromesh Ring.

It works in the way that you have a ring that slides over the "groves" locking the 2 together. As seen in this picture they are slightly angular allowing the ring to slowly sync the 2 kogs.

Dog ring.

Insteed of the the syncromesh you see in this picture that there is simply dog teeth and holes in the other kog for it to lock into. This is quite brutal and you want to be swift when shifting since the dog teeth will wear VERY fast if they are just pushed in abit when the slack has been taken out.

Edit2:
There is also something called dog LEG gearbox. This is in regards to the shift pattern wich is the following.

R..2..4
1..3..5

A couple more sport oriented BMWs and Mercedes has this shift pattern.


Ohh yea hello btw forgot that, kinda new here

[jogi730]

Glad people spotted the deliberate mistake .
I did in fact mean a straight dog box so forgive me.
So this box would be no good for normal road use? BAck to drawing board again then...lol
Cheers
Chris

[Keeper of The Kitten]

Aww, everyone else got here before me!

Yes, dog leg gearshift merely refers to the positioning of the lever in an "H" pattern system - the reason it was originally employed (and was heavily employed in single seaters) is that 1st really didn't get used again after the car is moving, so with the common 5-spd gearboxes of the time the lever only needed moving across the gate once. This reduced the hand movement required by the driver and also reduced the required clearance in the cockpit. 1st gear can be quite difficult to engage in the single seat cars and some drivers even needed to use both hands to get the car into gear. Used extensively in Hewland and Staffs boxes and others of that ilk. We had Staffs based designs in our F3 cars in the 90s. These days a lot of cars like that use sequential shift and sometimes paddle switches, and F3 has returned to allowing the use of 6-spd (sequential lever).

Dog engagement gears as posted above use the sliding wheels with face teeth - these are dog clutches, which cannot be "slipped" - they are either engaged or disengaged. They have a slight undercut (you can see it in the last pic above) which holds them when the gear is loading them (acceleration) and it slips out when the load is momentarily cut - this used to be done by careful throttle control, but when we were running in F3 it became popular to employ a switch that cut the ignition instead. This took the form of a driver operated button because the rules dictated against anything being automatically controlled. We had the button on the steering wheel but it was also tried on top of the lever. In sportscars we later tried a device which used a microswitch action on the gearknob, sensing the pull loads (worked on sequential only). I'd say a manual ignition cut can allow very quick shifting - you lean on the lever a bit as you approach the shift point, and press the button when you want to change.

Straight cut gears can be used on road cars - they are noisier (whining, a bit like McLaren when things aren't going their way), but the friction is heavily reduced because there is no angular slippage between the meshing teeth. The gear strength can be greater too, but that's to do with tooth profiles (root thickness) and materials as much as anything else.

The gears and dog rings in racing boxes get regular inspection and renewal so they can be a lot narrower for lower weight and friction (and more compact gearbox architecture) because they don't need to last very long. Our priorities with a road going car would tend to be a good value strong gearbox that's going to last a while, hence we live with a bit more weight and thicker gears.

I'm intrigued by the new-ish Zero Shift system that replaces dog rings with separate "bullets" (see latest copy of Racecar) - it can effectively engage two gears at once but uses ramping that allows the "bullets" to disengage from the gear which is being overtaken by the next gear engaged. This system allows totally seamless power shifting (with developments going on to further smooth things), even the Audi DSG system cannot maintain a constant acceleration curve whereas this system can - we need to get these guys to consider developing a version for a proper car - you know, an S2 with a 6-spd?!!

__MDC__

[Graham]

And not forgeting another advantage of the spur gear is that it practically has no axial thrust as the gears act directly against each other cancelling out the thrust generated by helical gears