Clutchless shifting a dog gearbox. 1

[dodyryda]

this question is kinda related to thread78-142609. basically we are looking to install a jerico dog box in our circuit race car and are looking to incorporate a flat shift device so we can shift at full throttle on upshifts. From what i understand i will need a microswitch on the shifter and so as soon as the shifter moves the ignition will cut to reduce the load and enable the shift to take place. We have a 2 stage msd ignition on the car so i can wire this microswitch into the 2 step limiter to provide the ignition cut.
my question is firstly where can i source a suitable microswitch to detect shifter movement i.e has anyone setup something to this.. also obviously as we'll be clutching on down shifts i don't want this shifter movement to cut the ignition so i figured by wiring a clutch switch in to the circuit if the clutch is depressed it would bypass the shifter microswitch... just wondering whether anyone had a similar setup and could advise .....

cheers....

 

[BrianPetersen]

It's done with roadrace or dragrace motorcycles all the time. In that application, the switch is in the shift linkage rod between the foot lever and the shift shaft which goes into the gearbox.

Here's a common one.

http://www.powercommander.com/powercommander_iii_usb/powercommander_quick_shifter.aspx

If you are using an automotive H pattern shifter, things are a bit more complicated ...

 

[dodyryda]

Thanks for your almost instant reply! ..yeah this is the problem .. it's a H pattern shifter external rail 4 speed so just wondering on how to mount the switch, what do you think about the clutch switch to disable circuit for downshifts,, sound about right?

 

[BrianPetersen]

Never done anything of the sort with an H pattern because every motorcycle gearbox is sequential and that's all I deal with. In that case it works simply by only switching when the rod is in compression (or tension, depending on which way the linkage works). F1 and World Rally gearboxes do it by shifting with pneumatics or hydraulics, and they're sequential, so the computer can control what's going on. Trouble with an H pattern is you don't really know what the driver's going to do, how fast he's going to pull the next gear into engagement, and if he misses the gate on shifting from 2 to 3 the shift might take longer.

With an external rail, for sure you can put force transducers in both shift rails, detecting both compression and tension - no other choice. If you want to do full throttle shifts you'll probably also need to know if the transmission is in neutral between gears because of different time to shift between 2-3 (between gates) and 3-4 (same gate). Clutch pedal switch to disable the system should work. Beyond that, can't help, never seen it done.

If the base of the shift linkage is tied to the transmission with a locating rod (many rod-shifted transverse gearboxes are like this) then you might be able to cut the number of switches in half by putting the switches on that rod instead of on each rail, since whatever force is going through each rail is going opposite through that rod. If there's no such rod but you can get access to where the base of the shifter is mounted, you might be able to do something similar.

 

[pontiacjack]

If I understand you right, you're planning to use a dog-ring-shifted Jerico box. Have you talked with Jerico (Jerry Hemingson) about upshifting? I believe that all of their dog-ring boxes are termed "clutchless", and that drag racers use them as such- full-throttle upshifts, no clutching, and no ignition-interrupt. I'm not one of those racers, so please let me know if I'm misinformed.
I do have a little experience with the dog-rings, from using a 4th-gear-only Jerico as a foolproof IN/OUT box in my blown-alky mini pulling tractor. I wanted to avoid the hassle of an input-shaft-brake for when the slipper clutch drags, and it works well- makes it easy for me to believe the "clutchless" upshifting claims.

 

[evelrod]

Just out of curiosity, why would you want to pull a 'power shift' in a "non" drag race car? I've used several dog boxes such as Jerico, JKD, etc. in road race cars over the years.
One thing I learned the hard way, when I pull an upshift, just 'blip' the throttle and on downshifts, use the clutch...I've never broken a box using this method (knock wood), at least not yet. Full power shifts are tough on equipment. I did a few on my drag cars back in the late 50's, early 60's. I also rebuilt a lot of drive trains.

Rod

 

[patprimmer]

I agree with Rod

In drag racing the small fraction of a seconds gain and the very short required service life makes full power shifting viable in drag racing, but for any other forms of racing, the extra weight of the stronger components needed to withstand full power shifts for the duration of a race meeting will negate the small time savings.

Regards

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Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Newmanite]

Ever thought about putting it in the "handle or "knob" of the gear selector? Recess an area within the knob and fit a switch.Have a look at truck gear knobs they have a switch incorporated in them for their splitter box gearing.

 

[patprimmer]

I think some European attempts at semi automatic transmissins in the 60s had servo or solenoid operated clutches and a pressure activated switch in the gear lever so that if the lever was moved back or forward, the switch contacted and disengaged the clutch. It was important NOT to leave your hand resting on the shifter.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[dodyryda]

thanks for you input .. think i've worked out a system that will work...