Clutchless gear changes
Discussion
This is my first post so I will say hi to everyone first, I am currently in my final year of a mechanical engineering degree so I have a fair degree of knowledge on the workings of gearboxes and the like. However the one thing I have never managed to get my head around is how bike gearboxes and race car boxes can carry out clutchless upshifts without there being expensive graunching noises. If any one could explain this to me in "relatively" straighforward way I would greatly appreciate it, cheers.
Alex
Alex
Not just bikes and exotica! I used to do it in my old Citroen CX when I got tired! Some gearboxes are better at it than others but the synchromesh is the key (unless you're REALLY good)! Imagine you're pootling along in (say) 2nd and you want to go to third. The trick is to make sure the gearbox isn't transmitting any torque as you change. That means acceleration OR engine braking. If you get the car on a completely neutral throttle and push the gear lever from 2nd to neutral (the easy bit) then allow the revs to drop as close to what they would be at the same road speed in third as possible and hold the gear lever against the synchro for third. You will feel a bit of resistance - just keep a gentle pressure on it and once the synchro mesh equalises the speed of the two shafts, the lever will just "snick" into third. It gets easier as you go up the box. You can go down the box in the same way but you obviously need to increase the revs. Again, if you hold the gear lever against the synchros and increase the engine revs, the lever will "pop" into the gear as soon as the internal speeds equalise. Depending on how knackered your gearbox is, it might complain a bit and I'm sure it shortens the life of the synchros (unless you're some sort of driving "god"! Find an old knacker and go and practice!
Bikes and race boxes are whats known as 'dog' boxes where the drive is transferred from the hub to the gear via dog teeth on the face of the gear. Bear in mind you still have to lift or cut engine power momentarily to pull the dog ring out of 1st say and slam it into 2nd however theres no braking effect as with synchros and once its in, its transmitting drive, so it gives a very quick shift albeit, not always the smoothest.
Matt
Matt
busa_rush said:
Isn't it about time somebody invented a new type of gearbox that could change gear instantly without lifting off the power?
Isn't that called zero shift..?
>> Edited by busa_rush on Sunday 12th February 00:13
Yes, the zeroshift is a remarkable invention. www.zeroshift.co.uk/systemanime.htm
Dragsters up shift with no power cut!
The way that they do it is to have dogs with a negative retaining angle on the overrun side of the dog - if you lift off it would come out of gear. They then have a shift mechanism that allows you to engage two gears at once. So when you engage a higher gear, the lower one pops out of gear automaticaly.
The way that they do it is to have dogs with a negative retaining angle on the overrun side of the dog - if you lift off it would come out of gear. They then have a shift mechanism that allows you to engage two gears at once. So when you engage a higher gear, the lower one pops out of gear automaticaly.
GreenV8S said:
arhhh.. ,a granny shifter are you ????? FULL throttle shifts can be done with just about any manual car/van
Just about any grossly underpowered and car/van maybe!
Not at all,(just incase of crossed wires, you cant have clutch-less full throttle shifts)
Any gearbox that is not 'notchy'/difficult to shift should work no matter what HP.
I've not driven a TVR so don't know how good/bad it shifts, let me have a drive of yours & I'll soon tell you if it would work on yours & then show you
Have a look at this vid , its a street car with 700bhp running 9.5sec. 1/4 miles
www.hotrod.com/eventcoverage/pump_gas_chevelle_lg.mov
(requires quicktime to view)
>> Edited by MartinD on Tuesday 14th February 11:52
Barbarossa said:
................ They then have a shift mechanism that allows you to engage two gears at once. So when you engage a higher gear, the lower one pops out of gear automaticaly.
Not sure what box your thinking of , but most/all ? manual box's you physically cant engage 2 gears at once , to get the next gear it has to come out of one gear to get the next.
Sure your not thinking of a trans brake on an auto box ?
Full throttle up shift (without a FTGS controller) implies that the engine is running against the rev limiter when you engage the clutch. Normally you wouldn't do this because it would stuff the transmission, and if the transmission held it would be a huge disruption to the car and probably either spin the wheels or send you off backwards. But if the car was grossly underpowered the need to get as much energy out of the engine as possible might outweigh the need to keep everything smooth and maintain traction.
I did experiment with a home-made FTGS controller at one point and it worked well, but I could never pursuade myself to trust it. If it had ever failed, things would have got ugly. There's only one time I'd do a full throttle gear change that that's changing down under acceleration. Even that takes care otherwise you just spin the wheels or twist the transmission in half.
I did experiment with a home-made FTGS controller at one point and it worked well, but I could never pursuade myself to trust it. If it had ever failed, things would have got ugly. There's only one time I'd do a full throttle gear change that that's changing down under acceleration. Even that takes care otherwise you just spin the wheels or twist the transmission in half.
James murray (megasquirt guru) has been playing around with flat shift (full throttle shift) NOT clutchless shifting. Essentially all it does is retard or cut the ignition when you hit the clutch.
www.msefi.com/viewtopic.php?p=79713
www.msefi.com/viewtopic.php?p=79713
There are several add-ons that allow flat shifting.
Most use a switch on the clutch pedal to initiate either a full ign cut for a determined period, or a half rev limiter for teh duration the switch is engaged.
I use the former, although still havent really felt the need to abuse the car that much lol.
Most use a switch on the clutch pedal to initiate either a full ign cut for a determined period, or a half rev limiter for teh duration the switch is engaged.
I use the former, although still havent really felt the need to abuse the car that much lol.
My system brought in a secondary rev limiter, but only if the revs were over a threshold before the clutch was depressed (so I could still blip on down shifts). I was disappointed that none of the usual aftermarket guys had anything like this in any of their rev limit/traction control/launch control/etc systems.
Gassing Station | Engines & Drivetrain | Top of Page | What's New | My Stuff