Retarding ignition timing during gear shift

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Healey3000
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Retarding ignition timing during gear shift

Post by Healey3000 »

Hi,

The vehicle I'm working on has a gearbox with a hydraulic overdrive. Inputs to the decision whether to engage the O/D or not are 1) a third/fourth gear sensor, 2) dash on/off switch and a 1/4 throttle switch. There is some twisted logic regarding disengagement, etc. but that's a topic for another thread.

It is considered good practice to press the clutch before O/D engagement and release but that takes away from the seamless use of the O/D. With MS3, one could set up I/O logic, using the various inputs to control the overdrive. To make shifts smooth, I'm wondering whether modern transmission techniques of retarding ignition during a shift can be implemented in MS3.

Possible with Launch Control? Any other ideas (like opening or closing a secondary air passage to "blip" the throttle)?

Thanks.
dontz125
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Re: Retarding ignition timing during gear shift

Post by dontz125 »

Blipping the throttle is used to raise the revs during a downshift - NOT what you want when upshifting to O/D. Take a look at Sequential Shift Cut, used with bikes and other vehicles that shift up and down, not in an H; when the shift signal is received (thumb button, sensor in the shift linkage) the ignition is cut for ~ 100msec, unloading the transmission and allowing the gear dogs to rearrange themselves. It might work for your purposes, it might not.
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Re: Retarding ignition timing during gear shift

Post by jsmcortina »

Have a look at the "torque convertor lockup" feature, that might do what you are looking for - except for the retarding.

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Healey3000
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Re: Retarding ignition timing during gear shift

Post by Healey3000 »

dontz125 wrote:Blipping the throttle is used to raise the revs during a downshift - NOT what you want when upshifting to O/D. Take a look at Sequential Shift Cut, used with bikes and other vehicles that shift up and down, not in an H; when the shift signal is received (thumb button, sensor in the shift linkage) the ignition is cut for ~ 100msec, unloading the transmission and allowing the gear dogs to rearrange themselves. It might work for your purposes, it might not.
Hi,

I actually would need both blip up and blip down as it is recommended going in and out of O/D. I'll take a look at SSC.

Thanks.
Healey3000
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Re: Retarding ignition timing during gear shift

Post by Healey3000 »

jsmcortina wrote:Have a look at the "torque convertor lockup" feature, that might do what you are looking for - except for the retarding.

James
Hi James,

I will take a look; thanks.

Can MS3 be commanded to retard ignition x degrees for y msec via an I/O line? That way, I can build the O/D logic using a separate uC and simply send MS3 an I/O command. MS3 retards timing, the uC triggers the O/D solenoid and then MS3 resumes proper timing.

Perhaps a second table for ignition timing (like you have for an alternative fuel table)? The second table could be an offset from the original table and by flipping tables momentarily, retarded timing can be effected.

Thanks.
Healey3000
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Re: Retarding ignition timing during gear shift

Post by Healey3000 »

jsmcortina wrote:Have a look at the "torque convertor lockup" feature, that might do what you are looking for - except for the retarding.

James
Hi James,

Can a "retard" field be easily added to the torque converter lockup feature? User selects a degree value from 0 to some maximum. When MS3 triggers the output line, it first retards and then sets the bit?

I know, easy for me to say.

Thanks.
OrangeAlpine
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Re: Retarding ignition timing during gear shift

Post by OrangeAlpine »

If this is a Laycock unit, I think you want to avoid the momentum of the vehicle revving the engine. That puts a big shock load on the transmission output shaft as the shift is very abrupt. If that is the case in your application, you do want to retard ignition, but blip the throttle on both upshift and downshift. That is recommended in the Sunbeam Alpine owners manual.

Bill
Healey3000
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Re: Retarding ignition timing during gear shift

Post by Healey3000 »

OrangeAlpine wrote:If this is a Laycock unit, I think you want to avoid the momentum of the vehicle revving the engine. That puts a big shock load on the transmission output shaft as the shift is very abrupt. If that is the case in your application, you do want to retard ignition, but blip the throttle on both upshift and downshift. That is recommended in the Sunbeam Alpine owners manual.

Bill
Hi Bill,

Yes it is a Laycock unit. In the original implementation, the O/D does not disengage unless you apply throttle; a bit of a blip perhaps. I can see why that is required, as it helps bring the revs up to meet the drive shaft's change. I don't follow why it would be necessary when upshifting; wouldn't you want to have the engine drop revs in anticipation?

The question now is how best to use MS3's capabilities? The O/D option is certainly more sophisticated than the original so there must be a good way to use the TPS and MAP windows to shift up and down. Being able to retard timing would be terrific and I hope that James can find a way to add that capability.
OrangeAlpine
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Re: Retarding ignition timing during gear shift

Post by OrangeAlpine »

If you are driving along, say 50 mph in fourth gear, let off the gas and engage the O.D., there would be a driveline shock very similar to a downshifting. The car would suddenly be changine the engine speed.

I can see an argument for spark retard if the throttle is near wide open and upshifting. That would alleviate the upshift shock. Otherwise I think retard is a bad idea.

Bill
Healey3000
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Re: Retarding ignition timing during gear shift

Post by Healey3000 »

OrangeAlpine wrote:If you are driving along, say 50 mph in fourth gear, let off the gas and engage the O.D., there would be a driveline shock very similar to a downshifting. The car would suddenly be changine the engine speed.

I can see an argument for spark retard if the throttle is near wide open and upshifting. That would alleviate the upshift shock. Otherwise I think retard is a bad idea.

Bill
Engaging the O/D would be like upshifting, wouldn't it?

Here's an interesting article on driving the Laycock. It makes sense that ideally, you should have no change in road speed when O/D is either engaged or disengaged. Rpm should change to compensate. That is what we do when driving a manual transmission vehicle, after all.
OrangeAlpine
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Re: Retarding ignition timing during gear shift

Post by OrangeAlpine »

No. The O.D. clutch action is very abrupt, much like side stepping the clutch. Imagine driving along at 50 mph in 4th, declutch, shift to third, let your foot off the gas and side step the clutch. That is essentially what your doing when you upshift with a closed throttle.

Yes, when you shift gears manually the rpms match the road speed, but you aid the process coordinating the throttle and clutch. Once agin, the Laycock has virtually no clutch action. It is either "on" or "off". It is literally a switch.

Bill
OrangeAlpine
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Re: Retarding ignition timing during gear shift

Post by OrangeAlpine »

Just realized that I suffered a major brain fart while typing the above. I should have said:

While "crusing" at 40 in third, quickly shift to fourth and side step the clutch.

The results will be approximately the same, only the stresses on the drivetrain will be reversed. Sorry 'bout that.

Bill
Healey3000
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Re: Retarding ignition timing during gear shift

Post by Healey3000 »

OrangeAlpine wrote:Just realized that I suffered a major brain fart while typing the above. I should have said:

While "crusing" at 40 in third, quickly shift to fourth and side step the clutch.

The results will be approximately the same, only the stresses on the drivetrain will be reversed. Sorry 'bout that.

Bill
Agreed. Is there then no solution to eliminating or reducing shock during O/D on/off? Perhaps pressing the clutch every time before engaging or disengaging the O/D is the only way, that is, treat it like a true gear. That sort of takes away from the "fun".

Using an electronic throttle would solve this, I think. Drop RPM simultaneously with engaging O/D, like a rev-matched clutchless shift.
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