21 replies to this topic

[Hellenic tifosi]

I have followed a lot of gearbox discussions here and I can say that I understand the function of gearboxes pretty well. I also understand the purpose of blipping the throttle during downshifts(I also practice it at my road car), but I would like to know how is this acheived in case of a sequential gearbox. In a normal transmission, you can stop at neutral during the gearchange, but in a F1-type gearbox this is not possible. However, Formula1 cars are supposed to be automatically matching the revs during dowshifting. Can anyone explain to me what is happening?

[DEVO]

A sequential gearbox has a clutch just like a standard transmission... a sequential gearbox also has neutral as well... only you can't get to it directly as in a standard transmission. So the keyword is clutch. The clutch acts like neutral when pressed, therefore allowing you to change gears. Now if you match your revs correctly you can bypass the clutch all together with both sequential and standard transmissions. Something I wouldn't recommend.

[Hellenic tifosi]

DEVO, let me explain myself better. IN a normal gearbox, one has to make the following moves: Press the clutch and move to neutral - relase the clutch - match the revs - press the clutch and move to the selected gear. In a sequential gearbox, I don't think you can leave the car into neutral so as to match the revs.

[Mark Beckman]

Originally posted by Hellenic tifosi

1/ DEVO, let me explain myself better. IN a normal gearbox, one has to make the following moves: Press the clutch and move to neutral - relase the clutch - match the revs - press the clutch and move to the selected gear.

2/ In a sequential gearbox, I don't think you can leave the car into neutral so as to match the revs.

1/ Your kidding arent you ?? What do you drive, a 1955 Mack truck with a non-synchromesh crash gearbox ?

2/ Sequential is only a description of the method of gear selection and means when you perform the action of moving the gearshifter, wether manually or by computer, the next gear will be selected, ie: 4th will come after 3rd on upshifts, in difference to a traditional automotive selector system that any gear can be selected from any other gear.

In any gearbox there is always a moment of neutral between gears and with the lack of inertia in a racecar with a sequential shifter and close ratio gearbox there is ample time to match rpm to the next gear and this is generally performed without declutching (and without thinking).

For you information, motorcycles have had sequential gearboxes just about forever.

[Hellenic tifosi]

Well, I drive a modern car, but i just like the feeling of making a perfect downchange! Of cousre I don't do it all the time, just when I am into it! Maybe the fact that my first car was an old Autobianchi has something to do with it....

Now, concerning the function of sequential gearboxes, I was aware of their differences with the normal ones, but what I didn't know was that there is enough time to blip the throttle during the gearchange. It seems to me now that this is done DURING the selector drum's rotation, isn't it? In any case, thank you very much for the clarification!

[Mark Beckman]

Originally posted by Hellenic tifosi


1/ Now, concerning the function of sequential gearboxes, I was aware of their differences with the normal ones, but what I didn't know was that there is enough time to blip the throttle during the gearchange. It seems to me now that this is done DURING the selector drum's rotation, isn't it? In any case, thank you very much for the clarification!

2/ Well, I drive a modern car, but i just like the feeling of making a perfect downchange! Of cousre I don't do it all the time, just when I am into it! Maybe the fact that my first car was an old Autobianchi has something to do with it....

1/ DURING the rotation of the selector drum (or rotating plate), the drum with its grooves moves the fork to a neutral position, it then either continues to move that same fork or another fork to the next gear, but there is most certainly a moment of the gearbox being in complete neutral between each gear.

2/ Ok I'll tell you how to change gear properly, it will take you a little while to get used to it but you'll change gears twice as fast and twice as smooth, even in an Autobianchi ;)

Firstly drive down the road normally accelerating, we shall say we are in 2nd gear about to change into 3rd.

Now ease off on the throttle and simply push your gearlever into the neutral position,

THIS IS DONE WITHOUT TOUCHING THE CLUTCH !!

You will find that the gearstick will move very easily into neutral from any gear just as you start to decelerate, (if it goes into neutral with a bang then you are lifting off to severly before attempting to move the gearstick, it should happen at the same time).

Now you should be coasting along, in neutral.

If your not sure you can drive at a constant speed in, say 2nd gear on a flat road, neither accelerating nor decelerating and simply move the lever into neutral without moving the throttle, you will find it moves into neutral very easily, dont be scared you are not hurting anything.

Now you will be coasting along, but with the engine revving (you can release the throttle now!).

Now simply select your next gear, 3rd in this case, by pressing the clutch pedal in and selecting your gear which you will find amazingly easier to do.



OK, practice this for a few weeks and hopefully what you will end up naturally doing is as you start to lift the throttle, you start to depress the clutch pedal at the same time as you are selecting neutral with the gear lever.

By the time you have selected neutral, the clutch has travelled far enough to be disengaged allowing the next gear to be selected while the engine revs have dropped enough to match the next gear speed.

It may sound confusing but its very easy to learn and as I said, very fast and smooth.



Downchanges work the same, except the throttle is working the opposite way, just as you "blip" the throttle to match revs, you start the operation as described, downchanges will take much longer to perfect though.

Have fun :-)

[Hellenic tifosi]

Mark, I think that I now understand exactly how the matching of the revs is done in sequential transmissions. Thank you very much.

Concerning your propositions for gear changes, I find them very interesting. Given that by now I am able to double clutch when downshifting, and that matching the revs is no big deal, I will do my best to master the technique as soon as possible!

[Mark Beckman]

Check back in a few days, I know where theres some great drawings to help explain a particular sequential gearbox.

[BRIAN GLOVER]

Let me put in my two cents worth.
The locking method for gears on the main shaft on a gearbox is done in a number of ways. The motorcycle way, as found in F1 cars, locks the gear to the shaft with a dog cam that needs pressure from a fork or lever to 'sieze' the gear to the shaft via a wedge effect of the cam. The mecanism stays locked without the use of splines. Motorcycles shifts are notoriously clunky and earlier bikes would slip out of gears with throttle shut off. This method does not neccessarey have to be sequential, but the transmission works smoother that way, and shift mecanisms are designed accordingly. Rally cars have this type of transmission.

Another way of locking the gear to the shaft, as found on passenger cars, is a dog collar/sincro assy units, which rotates at the same rpm as the shaft, because of an interference fit to splines on the main shaft. This collar, pushes dogs onto a sincro ring, via a fork, which is attached to the gear lever,which inturn, siezes the gear to the ring which causes the gear to rotate at the same rpm as the shaft.

The collar has teeth that line up with teeth on the sincro ring which line up with teeth on the gear and locks the assembly to the shaft via the splines.
The grooves on the brass sincro ring retain oil which allows slippage of 3 to 5 degrees before siezure for alignment purposes. Other types of sincro rings have wet clutch linings bonded to steal instead of silicon bronze units, but also slip before locking.

It is not a good idea to double declutch with with these types of sincro mechanisms, in fact ZF forbids it, because if you sincronize the rpm of the gear and the shaft thru the use of the double declutching method, the sincro ring's teeth may not be aligned with the teeth on the gear, which causes damage to the sharp edges of these teeth and can block a shift. Slow gear changes will become difficult also.
If you are in favour of spirited driving, like a lot of lunatcs who are members of this forum are, you may however assist the sincros by delaying the shift slightly after double declucthing so that slippage can occur. Under no circumstances should you not use the clutch with these types of transmissions.

Big trucks have no sincromesh, so double de clutching is essential. Shifts can be made without the clutch with this type of transmission, however,with careful use of the throttle. It is always a good idea at least, to bring the shift to neutral with the use of the clutch in this type of transmission.

On race or street cars and bikes, the gas is blipped with the clutch disingaged during down shifts, not only to assist with the shift, but to keep the car settled when the clutch is released to prevent sudden engine braking. Unloading the transmission by dis engaging the clutch, allows much lighter loads on shift and locking mechanisms. Always use the clutch if you are paying for it.

F1 car shifts are done with computers. The new Enzo Ferrari has normal type sincro rings. There are manufactures that have sequential shift mecanisms, which employ dog cams in all gears but for first, because of the same problems motorcycles have at stop lights.
Ferrari 360's F1 shifters have a normal gearbox, and the shifts are seqential and the cluth and throttle and hydraulic shifts are controlled electronically. The Enzo and the F360 have different transmissions to the F1 car.
These cars are not fun to drive in rush hour traffic.



[QUOTE]Originally posted by Mark Beckman
[B]

1/ Your kidding arent you ?? What do you drive, a 1955 Mack truck with a non-synchromesh crash gearbox ?

[jetsetjim]

Formula1 cars are supposed to be automatically matching the revs during dowshifting. Can anyone explain to me what is happening?

I hope this answers the question you were originally asking..

F1 gearboxes are all now hydraulically actuated, electronically controlled shifting mechanisms. The baisc theory behind the shift system is the same as for a conventional sequential box with a selector barrel as described by others in this thread.

What sets F1 boxes apart from conventional boxes is the electronics used to control the shift. As most people are aware, most of the teams (not all though, I hasten to add...) now have systems which allow the driver to change gear without using the clutch on downshift (a lot do still use the clutch on upshift to take the shock out of the system). It also has to be remembered that F1 throttles are all now fly-by-wire, so can be controlled by electonics.

The electronics on the car allow the drivers to "flat shift" up through the box. As the driver selects the next gear, with his foot still full on the accelerator, the electonics automatically reduce the throttle, and then through a combination of spark cuts, fuel ******/advance, clutch actuation and selector barrel movement, selects the next gear. All this happens in less than 0.1sec, so is unnoticable to the human ear.

On downshifts, the electronics again control throttle, fuel, etc to ensure clean changes. Again a spark cut is usually involved, and this time the throttle is automatically "blipped" to the optimum revs for the downshift. As the throttle blips and the engine revs rise, the gears will simply slot into mesh without any damage.

Admittedly, this is a very simplified version of what goes on.. and the trick to quick and smooth gearchanges is timing of all the relevant sequences... That is where the electronics wizzkids earn their money!

p.s

Big trucks have no sincromesh, so double de clutching is essential

Brain.. I've had my HGV licence for 7 years, and have yet to come across a large truck without Synchro gears... Double declutching isn't needed these days.. most do it just to make the ride smoother.

[Mark Beckman]

Originally posted by BRIAN GLOVER

1/ The locking method for gears on the main shaft on a gearbox is done in a number of ways. The motorcycle way, as found in F1 cars, locks the gear to the shaft with a dog cam that needs pressure from a fork or lever to 'sieze' the gear to the shaft via a wedge effect of the cam. The mecanism stays locked without the use of splines.
2/ Motorcycles shifts are notoriously clunky and earlier bikes would slip out of gears with throttle shut off.

Maybe you said this but our languages are a bit different......

1/ The gears are totally free at all times to move on the shaft, they are never locked on the shaft, it is the shift drum or the quadrant that is notched in various methods that has a spring loaded plunger or roller that fits into those notches that holds the drum/quadrant in place, that holds the fork in place, that holds the gear in place. Motorcycle/racing boxes in this case are nearly always straight cut gears and therefore have no thrust to deal with and little pressure is required to hold them in place.

2/ Motorcycle shifts are not notoriously clunky, only certain manufacturers who couldnt be bothered to do better and with a little work can have them shifting a lot smooother. It also depends on application, a gear with 3 large dogs is going to clunk compared to a 4 or 5 dog gear. Earlier bikes slip out of gear usually because they are old!
Earlier bikes had their dogs ground square to the face of the gear (modern bikes are slightly undercut) and from the very first time you used them they are wearing towards eventually having a positive angle on them forcing them apart under load. When I rebuild a gearbox, usually 2 or 3 per month, I send the gears to an engineer who grinds a -2 degree undercut on the dogs for me so they actually pull together underload.

[WGD706]

What makes a sequential gearbox more preferential to a regular 'H' pattern?
Is there less time spent between gears?

[blkirk]

Have you ever tried to downshift 5-4 and get 5-2 instead? Or how about a 4-5 upshift that became a 4-3 downshift instead?

With a sequential transmission, unless something breaks, you absolutely cannot miss a shift.

-B

[BRIAN GLOVER]

Originally posted by jetsetjim


F1 gearboxes are all now hydraulically actuated,

or air


. As most people are aware, most of the teams (not all though, I hasten to add...) now have systems which allow the driver to change gear without using the clutch on downshift (a lot do still use the clutch on upshift to take the shock out of the system). .

The last F1 car to have a clutch pedal, was Alesi's Benneton. A button is used for the clutch at starts or differnt types of electronic launch sequences.

Brain.. I've had my HGV licence for 7 years, and have yet to come across a large truck without Synchro gears... Double declutching isn't needed these days.. most do it just to make the ride smoother.

I am refering to class 8 rigs known as semis in the States. I know of none with sincromesh transmissions.

[Mark Beckman]

I've rebuilt a few Roadrangers (Eaton Fuller), mostly 10 and 13 speeders, which would be the most common large truck gearbox of all and they didnt use synchromesh, but its over 15 years since I did one and I have never worked on a European large truck gearbox.

[DEVO]

Originally posted by Hellenic tifosi
Mark, I think that I now understand exactly how the matching of the revs is done in sequential transmissions. Thank you very much.

Concerning your propositions for gear changes, I find them very interesting. Given that by now I am able to double clutch when downshifting, and that matching the revs is no big deal, I will do my best to master the technique as soon as possible!

In most modern day cars you do not need to double clutch in order to match revs. In my car the first 3 gears are synchromeshed. So the car does the matching for me.

[jetsetjim]

or air

Tyrrell were the last team to use pneumatics for the gearshift, back in 1998. Every team now uses hydraulics, as it gives a much faster response than pneumatics ever could.

he last F1 car to have a clutch pedal, was Alesi's Benneton. A button is used for the clutch at starts or differnt types of electronic launch sequences

Sorry.. I didn't give the best explanation... when I said that teams still use the clutch on upshift.. I meant that it is all controlled electronically... Everyone now runs paddle operated clucthes for starts, but once the car is running, electronics control all the clutch movements.

I am refering to class 8 rigs known as semis in the States. I know of none with sincromesh transmissions

I am surprised to find that those things are so antiquated! The equivalent over here is Class 1, and they have had Synchro boxes for donkey's years.. I can't understand why there would be the difference, as the engine characteristics between US and European engines are very similar..

[Mark Beckman]

Originally posted by jetsetjim




I am surprised to find that those things are so antiquated! The equivalent over here is Class 1, and they have had Synchro boxes for donkey's years.. I can't understand why there would be the difference, as the engine characteristics between US and European engines are very similar..

Cause they work perfectly and are bullet proof (Eaton Fuller Roadrangers).

Leave sleeping dogs lay.

[jetsetjim]

Now now Mark.. Calm Down... No need to take it all personally!! Jeez......

All I said was that I was surprised that those vehicles still used old technology.. Synchro boxes have been the norm for years in Europe, and I would have thought that the newer trucks in the US would now have them, more in the interest of comfort than anything else. (Straight cut "crash boxes" without Synchro can be notoriously noisy and produce a lot of mechanical "whine")

Ok, they may be bullet-proof and ultra-reliable.. but so are the 'boxes on the European trucks...

[Mark Beckman]

Originally posted by jetsetjim
Now now Mark.. Calm Down... No need to take it all personally!! Jeez......

All I said was that I was surprised that those vehicles still used old technology.. Synchro boxes have been the norm for years in Europe, and I would have thought that the newer trucks in the US would now have them, more in the interest of comfort than anything else. (Straight cut "crash boxes" without Synchro can be notoriously noisy and produce a lot of mechanical "whine")

Ok, they may be bullet-proof and ultra-reliable.. but so are the 'boxes on the European trucks...

Huh ?? I was just answering your comment.

"Leave sleeping dogs lay" is just an old expression, means the same as "if it aint broke dont fix it" and I was refering to why they still use a non sychro mesh gearbox, not anything you said

[jetsetjim]

My apologies Mark..

I misinterpreted what you were saying.. The phrase "Leave sleeping dogs lay" has a different meaning over here... We use the phrase "Let sleeping dogs lie".. which is commonly used to bury an arguement.. hence my misunderstanding.

[Mark Beckman]

Forums are full of language misunderstandings, its half the fun sometimes