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This is with respect to non synchromesh, sequential transmission. Ducati along with several after market systems, implement clutchless downshifts by automatically applying a slight throttle to unload the gear.

Ducati Quick Shift up/down (DQS)
Flatshifter Blip Clutchless Downshift Kit

I understand how clutchless upshifts work.
For clutchless downshifts - while I understand the concept behind blipping the throttle while coasting, engine braking and hard braking helps unload the gear, I do not understand how how this could be achieved perfectly.
I want to understand how this process is automated - timing, logical order of events etc. (Main question)

  1. I believe a sensor on the gear shifter (strain guage) gives input to the controller of the riders intention to downshift.

  2. The controller slighty blips the throttle to unload the gear and engage the lower gear. The blip also helps in revving the newly engaged gear and possibly helps reduce RPM mismatch resulting in smoother engine braking.
    Am i correct in the above two statements? How is the amount of blip calculated (is it rev dependent or is it not so sensitive)? Is there any tendency to upset the bike (by working in opposition to braking)?

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  • What would be the process for clutchless downshifts when the throttle is being applied , ie no engine braking. E.g you're accelerating in a higher gear and want to shift down?
    – chilljeet
    Commented Apr 22, 2015 at 11:14

1 Answer 1

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Background

The Ducati transmission type is a constant mesh sequential.

There is a ride by wire system that controls the the throttle butterfly's.

Ride by wire is necessary in order for the ECU to regulate power based upon various maps the rider can select.

Process

The clutchless downshift is similar to the clutchless upshift in that it is essentially doing the opposite of the latter.

1. Foot depresses shift lever

2. Grounding switch detects beginning of shift

3. ECU sends signal to throttle body actuator

4. Throttle body actuator momentarily opens butterfly in the throttle body

  • Engine receives enough fuel to momentarily unload force on dog and slot gear relationship in transmission

  • Dog and slot in the gear relationship has force being transmitted through them unloaded and are now able to be separated

5. Riders continued depression of the shift lever forces the shift drum to begin to turn.

6. Shift fork slides unloaded gear out of position/Other gear shift fork slides the next gear into position (these two events are occurring simultaneously).

7. Butterfly closes in throttle body

8. Force from rear wheel that's transferred through the chain and the secondary shaft loads gear with force.

9. Deceleration continues with engine braking engaged and the transmission under load again.

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    excellent. I'm interested in point no. 4 . How is the amount by which the throtlle has to be opened decided (what all other inputs are needed)? Can this technique be implemented manually by the rider as easily and safely as I believe clutchless upshifts are?
    – chilljeet
    Commented Apr 15, 2015 at 5:53
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    I've come to the conclusion there isn't a need for perfect rev-matching as blipping the throttle reduces engine braking (apart from unloading the gear), significantly reducing shock load.
    – chilljeet
    Commented Apr 22, 2015 at 11:10

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