13 replies to this topic

[chrisuofc]

I asked a question recently about double decluthing and recieved a lot of help. Thanks
I have another question now. How do you shift without the clutch (both up and downshifts)?
Thanks

[John Galt]

Match the revs perfectly with what the engine speed would normally be in the new gear at whatever rate of speed you're at.

Example: In my old honda, I would shift from 2nd to 3rd at around 42 mph. I knew that in 3rd gear at 42, the engine speed would be 3500 rpm. Pull the lever from 2, rev to 3500, and slide it up to 3 delicately.

Same goes for downshifting. You have to know your car very well, or you'll grind the synchros into oblivion.

[Jezztor]

Yup - there we go. To check where you can shift for a particular gear, select the gear and idle at a certain RPM. Clutch in, but keep the accelerator where it is. If RPM stays the same, let the clutch back out and see if the car a) loses speed because of gearchange and b) see if RPM is still the same, on your gauge.

[Billy Gunn]

Well if only it were that simple for an F1 car!!

The engine speed has to be decelerated enough to get the gear dogs out of mesh, but not too much so that the overun side of the dogs drag. At this point the gears can be moved out of mesh, without damage to the dog undercuts. Get this bit wrong and you finish up with all your dogs lying in the bottom of the box ~ symptoms jumping out of gear on accel when you pull it out of gear too early, or jumping out of gear on overun if you do it too late!

Now to reinsert into the next gear we need to know if we are changing up or down, let's say we're going up a gear (3rd to 4th) the engine speed will be targetted to get the correct 'synching'. If it goes OK ~ no problem, but if it doesn't go (and this may be monitored by the gearbox selector drum potentiometer reading), the process will have to be gone through again - known as a retry. For downshifts the engine will have to be throttle blipped to speed up the mainshaft cogs to ensure correct 'synching'.

This is without going into the complex startegies such as 'skip' shifting where 2 gears are dropped at a time, such that one may downchange from 6th to 4th to 2nd.

Get the control system wrong for this part of the exercise and you will be eating gearbox internals like no one would believe. I heard of one team back in '97 that changed their EMS supplier and went through a whole of the previous seasons quantity of gear sets in winter practice alone - that before the seasons opening race!!

Times for these shifts are incredibly fast - a single upshift can occur in less than 20 millisecs, down skip shifts in under 30 millisecs. It was once calculated that a lap of Silverstone with two identical cars one with a 'slow shifter' (app. 80 millisecs) to one doing fast shifts (less than 20 millisecs) would see the fast shifter doing a lap some .5 sec faster for no other reason than the shift speed!

Billy G

'yerdontgetowtfernowt'

[H. Eckener]

Here is a good read
http://www.hewland-e...k/svga/help.htm

[desmo]

If any of you have the chance I recommend reading SAE Paper 2201-01-1162, "Analysis of a F1 Car Hydraulic Circuit Dynamic Behavior" which while primarily dealing with the title subject, also by necessity has some intersting insights into how the upshift and downshift strategies were implemented for the 1999 Minardi. Here's a bit:

"The down-shift is composed by two distinct and successive phases of clutch and gear selector actuation, separated by a phase of partial opening of the throttle valves imposed by the drive by wire (commonly called kicker). In this way, the engaging of a lower gear can occur only when the primary and the secondary shaft of the gearbox are synchronized, thus having the proper rotational speed.

"The first actuator involved in the down cycle is the driveby wire that, starting from the minimum displacement position imposed by the decelerating regime, is forced by the ECU to assume a working position corresponding to the 50% of the maximum angular displacement; then, the drive by wire maintains this position for 1.2 tmax. Contemporarily, the clutch actuator undergoes to a working cycle similar to that shown in figure 6, while the gear selector is forced to assume the neutral position between 6 th and 5 th gears. After the time interval necessary to synchronize the primary and secondary shaft of the gearbox, about 1.0 tmax, the second phase of the down cycle begins and the gear selector is forced to engage the lower gear. After the engagement, the ECU forces the drive by wire to assume the minimum displacement position, corresponding to 10% of the maximum angular displacement. At the end of this phase, requesting about 0.9 tmax, the system returns in the initial condition, and it is ready to begin a new down cycle."

[lateralforce]

Is it just me or is it only in a Honda that it's easy to change gear without depressing the clutch pedal??

[chrisuofc]

I heard that too, but I'm not sure why. I've driven a few Hondas, and I've always found their clutches difficult. I learned on an '84 Porsche 944, and now I drive an '88 944. Maybe it's just because they're so different. Does anyone know why japanese clutches are supposedly so easy to drive?

[Garagiste]

Speaking from experience, VWs are also easy to clutchless shift. I once drove a Golf about 70 odd miles without the benefit of the left hand pedal.

[Hammer]

Originally posted by lateralforce
Is it just me or is it only in a Honda that it's easy to change gear without depressing the clutch pedal??

In my experiance it has more to do with the accuracy of the gear shift mechanism itself, and also the internal design of the gearbox.... some cars are just great and you never need the clutch, whilst others can be dreadful. However, using ATF or very low viscosity gearbox oil can make a world of difference.

Ciao..

Hammer.

[jacobyte]

Originally posted by Billy Gunn
Well if only it were that simple for an F1 car!!

The engine speed has to be decelerated enough to get the gear dogs out of mesh, but not too much so that the overun side of the dogs drag.

It's not the engine speed, but the load on the engine. A dog-change box will change faster at higher rpm, so the driver just needs to take the load off the throttle for almost no time at all and the next gear will engage almost instantaneously (I don't know the precise time in ms, as I'm just a driver!).

[Billy Gunn]

jocobyte quoted:-

"It's not the engine speed, but the load on the engine."

Yea- but you reduce the load on the gearbox! not the engine, and to do that you reduce the engine power, .... and to do that you can either close the throttles, cut fuel or cut spark .....all actions will have the effect of reducing engine speed. QED

'yerderntgitowtfernowt'

[lumepo03]

The clutch is there for aa reason and it is better to use it and replace it once a decade then to have to do periodic replacements on gearbox internals. Just match the rpm of the gear you want to go to and it will slot in. Like JYStewart says "clutch material is cheap to replace".

[Fizzicist]

There's a wonderful tale of Martin Brundle being terribly pleased with himself after his Tyrrell debut, when he was called into Ken's office.

Ken Tyrrell then upended a box of mangled cogs and shafts and said to him "You drove very well Martin, this is what's left of your gearbox. Do be more careful with it next time!"