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Old 3rd March 2014, 14:33   #151
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Default Re: Automated Manual Transmission (AMT): The new buzz in India

Quote:
Originally Posted by Sutripta View Post

How does one gradually lock a TC?

Can gears be changed with the TC locked?
The TC 's are set to lock when the slip is below a particular limit, usually just under 10%. The locking feels like another shift, and you notice the rpm drop.

In a car with 5 speed TC auto the sequence as like this C1 C2 C3 C4 C5 L5.
So the feel that you get is that of a 6 speed gearbox. The next gear is usually selected when converter slip is usually below 10% and after final gear is selected the lock is applied.

In a bus with a 6 speed TC auto box the sequence is 2C (1C 1L 2C) 2L 3L 4L 5L.
That is the bus starts in 2C and then locks up 2L and then shifts in locked mode only to 3L 4L 5L. If driver throttles to stall limit without a start up, then it shifts down to 1C and sequence starts from there.
In heavier vehicles the engine torque to vehicle weight ratio is low, so shift shock slows the engine and gives only a negligible jerks to the vehicle.
In a car the jerk would be very high.
I have heard that the auto industry is working towards a 9 speed very closed ratio gearbox which will shift in locked mode and ratios will be so close that shift shock will be negligible.

Rahul
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Old 3rd March 2014, 15:52   #152
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Default Re: Automated Manual Transmission (AMT): The new buzz in India

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Originally Posted by Rahul Rao View Post
The TC 's are set to lock when the slip is below a particular limit, usually just under 10%. The locking feels like another shift, and you notice the rpm drop.

In a car with 5 speed TC auto the sequence as like this C1 C2 C3 C4 C5 L5.
So the feel that you get is that of a 6 speed gearbox. The next gear is usually selected when converter slip is usually below 10% and after final gear is selected the lock is applied.

In a bus with a 6 speed TC auto box the sequence is 2C (1C 1L 2C) 2L 3L 4L 5L.
That is the bus starts in 2C and then locks up 2L and then shifts in locked mode only to 3L 4L 5L. If driver throttles to stall limit without a start up, then it shifts down to 1C and sequence starts from there.
In heavier vehicles the engine torque to vehicle weight ratio is low, so shift shock slows the engine and gives only a negligible jerks to the vehicle.
In a car the jerk would be very high.
I have heard that the auto industry is working towards a 9 speed very closed ratio gearbox which will shift in locked mode and ratios will be so close that shift shock will be negligible.

Rahul
Thanks Rahul,
On cars, if your driving 40 - 50 km/h, so your autobox is in say third gear, driving steadily along, can't you lock up? Or would that cause to big a jerk? Your electronics (ECU etc) should be able to make it a virtually 'jerk free event' shouldn't it? The ECU can calculate exactly how mucht the RPM and the fuel injection needs to be adjusted when it locks.

I've also driven numerous (small) autobox cars that have an overdrive button. I'm very familiar with overdrives on manual boxes, (just about all the Triumphs I've owned had one) but on the autoboxes it always puzzled me. On some of these autoboxes the o/d button would work in any gear, rather then only on the high(est) gear. Made me wonder if it wasn't some sort of convertor lock up as well, just "advertised" as overdrive because that sounds much cooler.

Jeroen
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Old 3rd March 2014, 18:31   #153
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Default Re: Automated Manual Transmission (AMT): The new buzz in India

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Originally Posted by Jeroen View Post
On cars, if your driving 40 - 50 km/h, so your autobox is in say third gear, driving steadily along, can't you lock up? Or would that cause to big a jerk? Your electronics (ECU etc) should be able to make it a virtually 'jerk free event' shouldn't it?
A condition where you have 40-50 kph cruising with converter locked up in 3rd compared to a condition where you have 40-50 kph cruise with converter in 4th with some amount of slip and torque multiplication may work out to be only marginally less efficient. But converter multiplication may provide instant power if required. Some cars like Mercedes E200 compressor have lock up in upper two gears instead of only top.
Designers probably give more importance to smoothness than efficiency in cars and more to initial torque multiplication and efficiency in trucks and buses.
If you see Torque converters and CVT's you get same or even better efficiency than manuals if you drive with a lite foot. Here the converter gives only about 50% multiplication at start, and achieves close to 0 multiplication at 10% slip at just above idling RPM, and then locks up all further ratio changes are taken up by the CVT unless you brake and come to a dead halt, or max CVT multiplication ratio is not enough to keep the engine speed from falling close to idling speed.

Quote:
Originally Posted by Jeroen View Post
On some of these autoboxes the o/d button would work in any gear, rather then only on the high(est) gear. Made me wonder if it wasn't some sort of convertor lock up as well, just "advertised" as overdrive
I don't know how this actually functions, if some one has gone through the software of the TCU they will be able to tell us.

Rahul
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Old 3rd March 2014, 20:51   #154
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Default Re: Automated Manual Transmission (AMT): The new buzz in India

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so shift shock slows the engine and gives only a negligible jerks to the vehicle.
Shift shock or lock shock?

If one wants the best times for acceleration, what would be the best strategy: shift with TC locked, or unlocked. (This can't be reasoned through. Need figures.)

Quote:
Originally Posted by Rahul Rao View Post
Here the converter gives only about 50% multiplication at start, and achieves close to 0 multiplication at 10% slip at just above idling RPM, and then locks up all further ratio changes are taken up by the CVT unless you brake and come to a dead halt, or max CVT multiplication ratio is not enough to keep the engine speed from falling close to idling speed.
Any difference (esp. in stall ratio) in a TC for CVT as opposed to conventional slushbox?

When did the lockup TC first start coming in the industry?

Your thoughts on luxury (International definition, not Indian. ie = powerful) cars having say 8 speed gearboxes.

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Sutripta
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Old 3rd March 2014, 21:28   #155
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Default Re: Automated Manual Transmission (AMT): The new buzz in India

Well It will be shift shock and not lock shock, as the Autoboxes in buses shift up without the converter dis engaging. The ecu momentarily cuts the throttle when upshift is triggered and the engine generates less or negligible torque for that extremely short period of time, and so the engines RPM gets suppressed and the shear mass of the 16 Ton bus dose not jerk at all. You note the shift only due to change in engine note.

Best acceleration will be achieved with converter in high slip mode a fraction below the stall RPM, not in locked mode.

I'm not sure about difference in TC's for CVT as opposed to the conventional slushboxes.

The TC lock was developed as a Jugad by a engineer in Indian Railways in one of the maintenance sheds I think at Ludhiyana (I will confirm his name and the location later)
he noticed that the efficiency of DHMU trains (Diesel Hydraulic Multiple Unit) which have hi multiplication Torque converters (as high as 8:1 multiplication as opposed to 1.5:1 in cars) was good when torque multiplication process was on, but when there was no multiplication, even then there was noticeable slip which caused oil heating and fuel loss.
Unluckily he (or probably Indian railway) started the patient process only for Torque converters used in trains, and this idea was picked up by almost all manufacturers of torque converters for heavy trucks and buses sometime in the 90's. Every one developed it in different ways, but Allison and ZF were the first to provide locks in low gears, and shift with lock on.
This lock later came down to heavier SUV's and finally cars.

The fact that buses with manual transmissions and those with Autoboxes with TC lock return the same highway mileage shows that this technology cannot be abandoned in favor of DSG etc, and better management software may show us very efficient conventional automatics.

Rahul
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Old 3rd March 2014, 22:11   #156
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Default Re: Automated Manual Transmission (AMT): The new buzz in India

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Originally Posted by Rahul Rao View Post
Best acceleration will be achieved with converter in high slip mode a fraction below the stall RPM, not in locked mode.
Hard data (along with engine torque curves, and rolling resistance data) would be illuminating. For cars preferably.

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Old 3rd March 2014, 22:41   #157
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Default Re: Automated Manual Transmission (AMT): The new buzz in India

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Best acceleration will be achieved with converter in high slip mode a fraction below the stall RPM, not in locked mode.
Are you sure? This would imply that engines produce their highest torque just before stalling??

What is high slip mode? Can you set that?

Jeroen
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Old 4th March 2014, 10:17   #158
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Default Re: Automated Manual Transmission (AMT): The new buzz in India

@ Sutripta
I am not working in the automobile engineering field but in Air conditioning and refrigeration business, so I don't have the required data in hand. Will try to acquire it. In my previous job I worked on adaptation of HVAC for Cars minibuses etc, when we were working on Main engine driven Ac units for Buses (Remember pre Volvo buses had under slung auxiliary engines for Ac) there were others working on gearboxes manual as well as auto and changes in final drive etc. I discussed things with them and gained some knowledge in the field.

@ Jeroen Stall RPM is not the speed at which a engine stalls, but the maximum RPM to which a engine can achieve when you press the brake as well as the throttle fully.
If same engine is used in an car as well as an SUV, the car may have a converter with less torque multiplication (say 1.5:1), while the SUV may have one with more torque multiplication (say 2.5:1).
In this case the Stall Rpm of the SUV's converter will be much lesser than in the car. The SUV will be able to accelerate with a higher load, and may be even be able to pull out a stuck trailer without the engine redlining but acceleration will be slower.
The Car engine will accelerate to a higher RPM, and give better 0 to 100 timing, but this acceleration will fall if we load the car.http://en.wikipedia.org/wiki/Torque_converter

In India we see measly engines with Torque converters and notice only the dis advantage of it, but if you try to drive a larger car with converter only then will you be able to feel both advantage as well as dis advantage of one.

Get behind the wheels of a torque converter RWD Pre ASR era car, press the brake and floor the throttle, and then release the brake, and experience the immense acceleration the torque multiplication provides. You may even receive tyre squealing acceleration upto 60kph or more. Eg a Pre 2001 petrol Merc Automatic.

Rahul

PS to Post 155 Converter locks existed since early 1920's, but were impractical and jerky so seldom used. The one developed by the Indian Railway engineer was the first practically usable one.
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Old 4th March 2014, 14:48   #159
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Default Re: Automated Manual Transmission (AMT): The new buzz in India

[quote=Rahul Rao;3382819Get behind the wheels of a torque converter RWD Pre ASR era car, press the brake and floor the throttle, and then release the brake, and experience the immense acceleration the torque multiplication provides. You may even receive tyre squealing acceleration upto 60kph or more. Eg a Pre 2001 petrol Merc Automatic.

.[/QUOTE]

My Jaguar XJR does just fine by flooring the throttle. 400BHP on the rear wheels gets me to 100km/h in 5 seconds. Admittedly, I have never tried to keep it on the brake and fully depress the throttle. Sort of manual launch control, its quick enough as it is!

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Old 4th March 2014, 21:15   #160
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Default Re: Automated Manual Transmission (AMT): The new buzz in India

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@ Sutripta
I am not working in the automobile engineering field but in Air conditioning and refrigeration business, so I don't have the required data in hand.
OK.

Quote:
Get behind the wheels of a torque converter RWD Pre ASR era car, press the brake and floor the throttle, and then release the brake,
Known as torquing up the system.
Manufacturers frown on it. And oftentimes does not give the best launches.

Quote:
PS to Post 155 Converter locks existed since early 1920's, but were impractical and jerky so seldom used. The one developed by the Indian Railway engineer was the first practically usable one.
Don't know about IR contribution to the lockup TC, but for cars the thought has been there in every engineers head. Was just not important enough before the oil shock of the 70s. And even then it remained only on paper for a long time.

Question for the experts: When should a TC unlock? When an auto is driven in 'manual' mode?

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Sutripta
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Old 5th March 2014, 20:44   #161
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Default Re: Automated Manual Transmission (AMT): The new buzz in India

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Can % slip be actively controlled?

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Sutripta
No but there are things the TCM can do to influence it. The % slip is a function of deficiency in supply:demand
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Old 5th March 2014, 22:10   #162
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Default Re: Automated Manual Transmission (AMT): The new buzz in India

Where would TC lockup figure in the system designers list of priorities? Would it be an actively sought goal, or lock only if certain conditions are met on their own?

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The % slip is a function of deficiency in supply:demand
Meaning?

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Old 6th March 2014, 17:29   #163
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From a design point of view it helps to increase full efficiency and to decrease engine noise. So I guess it depends how relevant that is and what the realistic gain could be.

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Old 8th March 2014, 01:51   #164
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Default Re: Automated Manual Transmission (AMT): The new buzz in India

Maruti Suzuki To Launch Alto K10, Wagon R With AMT. Alto would be in 2014 and Wagon R in 2015.

http://www.motorbeam.com/cars/maruti...h-amt-gearbox/
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Old 8th March 2014, 07:19   #165
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Default Re: Automated Manual Transmission (AMT): The new buzz in India

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Where would TC lockup figure in the system designers list of priorities? Would it be an actively sought goal, or lock only if certain conditions are met on their own?

Regards
Sutripta
We are digressing but it depends on the design objective. If its FE at any cost, then TC lockup as early and often as you can to the determent of NVH, acceleration & shift quality

Last edited by Mpower : 9th March 2014 at 02:32.
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