Auotmatic sans torque converter

[thundair]

Is it possible to eliminate the torque converter and valve body then use external hydraulics to select shift.

I may be reaching but I have a request to prototype a 6 speed 8" in dia and 18" long transmission.

I dont know how I get into these I am mostly doing PSRU's for small aircraft engine conversions.

Thanks in advance

 

[Fabrico]

It's been done for at least 40 years on popular US transmissions, mostly for boats but also for drag cars. Shifting is usually handled by an aftermarket reverse pattern, manual shift, valve body.

As far as using an external valve body, it's certainly doable, but several items pertaining to shifting, fluid flow, and lubrication would have to be addressed.

 

[patprimmer]

I think a "T" model Ford had a manually controlled 2 speed plus reverse epicyclic gear box. They were introduced quite a long time ago.

Regards

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[crysta1c1ear]

Antonov displayed a friction launch 6AT at the Paris motorshow in the 1990s, and ZF did the same with a 7AT at the Frankfurt motorshow in 2003. Sachs make electronically controlled clutches to launch AMT vehicles from minicars to heavy trucks.

I went round a race track yesterday in a car with 6AT and no torque convertor. First gear was selected by activating a brake on a planetary gearset. Vehicle launch was by activating it gradually. The change to second just released the brake on the planetary gear and activated another brake on another planetary gearset. Overlapping the two brakes gave a powershift gearchange like the overlapping of clutches on a dual clutch transmission.

 

[GregLocock]

Or you could take a manual box and fit an auto shifter. Probably easiest to do to a constant mesh sequential box, but it has been done on a H selector as well.

The size you give is a touch on the narrow side, the length is fine, depending very much on the power and cooling requirements.

Cheers

Greg Locock

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

 

[Warpspeed]

Why not just use one of the modern electronic auto gearboxes ? These boxes have no internal hydraulic "brain", just some external electrical connections to the internal gear selecting "dumb" hydraulic solenoids.

So basically you just bolt up a dead standard modern electronic gearbox, and provide your own electrical (or electronic) interface to whatever gear selection method you choose to use. The choice of either running a torque converter or a clutch with this, is also up to you.

It would have all the advantages of a full manual box, but with electrical gear selection.

 

[thundair]

Warpspeed and crysta1c1ear

I think you've got the picture....I am stuck with the diameter that will exclude sliding gears in a conventional tranny.

I am hoping to design around existing components something good for 300 foot pounds of torque.

I have watched the mechanic apply air to a port to check the clutches,and was looking to use a micro switch to apply my hydraulic input to each clutch set to shift at the appropriate rpm.

Reverse is in there. I know that, but I will have to work that out later, after I confirm feasibility.


Thanks to all for the input this forum is truly a brain trust.


Cheers

 

[Fabrico]

A diameter of 8" should not be a problem if you stick to normal automatic transmission (planetary) components. There is alot more involved than simply blasting hydraulic fluid into a hole to apply a clucth. Fluid flow and pressure has everything to do with making the shifts livable for the transmission and the occupants. It needs to be speed (RPM/Governer) and throttle (TPS/MAP/Modulator) sensitive. And don't forget precise control of fluid being released from certain clutches and band servos.

As an alternative, you could simply blast away but use the clutch for each and every shift.

Eliminating the torque converter and adding a manual shift charistics would seem to negate any advantage such a transmission might have.

 

[thundair]

Fabrico

Thanks for the feed back as you can tell I am out of my element as usual......The parameters of this trans are multiple paddle shift and not sequential... plus the size I mentioned before.....My hope was to use the internal clutches to bypass the flywheel clutch and pressure plate.

Cheers

 

[Warpspeed]

These dumb electronic auto transmissions would violently "blast" fluid for gear changes in the way suggested, but only if you hard switch the control solenoids.

The solenoids can be pulse width modulated (PWM'ed) to open or close more gradually. This can all be mapped into a suitable microprocessor control system along with speed and engine load to make gear changes as smooth or as fast as is required.

That is more or less how the manufacturers do it these days anyway. It is just that their control processor may be completely unsuitable for your application, but the bare gearbox should work fine.

By completely eliminating the torque converter and clutch, it will put a LOT more heat and wear into the transmission during gear changes, especially if the changes are slowed down. In a heavy and/or powerful vehicle, transmission life may be shortened considerably.

 

[GregLocock]

I used to have a little box that gave me direct manual selection of gears in a slush box. This also had a lock-up clutch in the TC. It was possible to drive the car entirely using this box, but equally a thoughtless gear change with the TC locked would stretch the bands.



Cheers

Greg Locock

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

 

[thundair]

The car weight is 1280# with a 300HP V6 if you have seen this new trend of exoskeleton framed cars (bare bones) that is what the money is trying to build.

Warpspeed ...You are right about the violent reaction to slaming a clutch on and off. It looks a lot differnet when it is not under load setting on a shelf...

I am better with air/hydraulics there maybe a way to soften the engagement that way.

I like the microprocessor control but not sure how that will work with the pseudo race car look and feel..

 

[WHRVSC]

Oval track cars have been using Powerglides without a torque converter for a long time. They use a direct drive from the crank hub to the front pump. There are 3 methods that have been used to get the car moving:

1.An external valve to dump the hydraulic pressure,
2.An internal valve actuated by a slave cylinder attached to a hydraulic clutch pedal and lastly,
3.The valve body is modified with a bleed controlled by a carburetor jet in one gear. When the car is put into that gear, enough fluid is bled off to keep the gear from engaging. As the engine is rev’ed pressure builds up and the clutch engages. Once the car is moving the transmission is shifted into the race gear.

TCI make a lot of the units

Hope it helps.

 

[Warpspeed]

thundair, there may be a ways to lessen the impact of violent gear changes.

My first thoughts would be to fit a dry clutch, and hard shift the gearbox, but only while the clutch was disengaged. The loads on the box during actual ratio changes would then be no greater than with normal synchromesh in a manual box. Internal ratio changes could be made very fast indeed. The gearbox hydraulic solenoids might be activated via switch contacts fitted to the clutch linkage. So getting the exact timing and positioning of the clutch right for shifting should not be too difficult. Gears could then be changed as fast as the clutch was cycled, with a lot less stress on the box.

I recall something like this has been fitted to long distance trucks a long time ago. Pressmatic pre-selection I think it was called. The driver pushed a button to select any one of maybe 20 available gears, long before he actually wanted to shift. As soon as he reached his desired Rpm point he simply cycled the clutch. The truckers loved it. This was not sequential, any gear sequence could be selected.

Originally Porsche never offered a conventional automatic transmission in the 911, but used a peculiar scheme called the "sportmatic transmission" on some models. This was their standard four speed manual transaxle gearbox, but the conventional dry clutch was operated from a giant vacuum actuator. This looked rather like a standard vacuum brake booster mounted on top of the bellhousing. There was no clutch pedal. Whenever you placed your hand on the gear leaver, the clutch disengaged. I have never driven one myself, but apparently gears could be changed very smoothly by just moving the gear lever.

An entirely different way would be to use a standard H pattern gear lever, but with electrical output only. As you physically move the gear lever, the spool valves in the transmission move in exact proportion. This could be done fairly simply with PWM control of the spool valves. The faster you move the gear lever, the faster it shifts. A microprocessor could oversee the whole action, and there could then be some built in limits and safety features.

 

[crysta1c1ear]

Are you looking for a transmission or thinking of making one?
If you are thinking of making one, have you any idea of the time and effort involved? Companies spend hundreds of millions designing transmissions and getting them into production. If you are just looking to buy something, then it might be a case of accepting whatever has the right dimensions rather than debating the various technologies.

If the basic design is planetary, and if you are only going to get two ratios from a planetary gearset, then you'd need three, as 2*2 is only 4. 2*2*2=8 so you'd get 8 ratios, but if some of the ratios coincide, or are close enough that a ratio becomes effectively unusable, then that can reduce the number of gears to less than 8. One of the ratios from a planetary gearset is typically 1, direct drive.

Say you have ratios a,b,c, and that c is an overdrive which roughly cancels one of the other gears, say c~=1/a. Then you have 6 useful ratios.
1,a,b,c,ab,ac,bc,abc is 8 ratios.
However, ac~=1 and abc~=b so you are down to 6 ratios.

You said: I may be reaching but I have a request to prototype a 6 speed 8" in dia and 18" long transmission.
So what you are saying is broadly similar to saying can you get a 2 speed unit in an 8" diameter 6" long package [18"/3=6"], assuming you are prepared to daisy chain three 2-speed units. These units could be similar in design but with different numbers of teeth to give the different ratios, an overdrive unit just being a reduction unit facing the other way round so that input and output are swapped.

I think you might be biting off more than you can chew if you want to do this yourself.

 

[Warpspeed]

Lenco air shift (or manual) two speed planetary transmissions have been used for many years on very high powered drag and circuit racing cars. It is not uncommon to stack these one behind the other for an increased number of ratios. That would be one off the shelf solution.

Here is a multi speed manual Lenco:

http://www.lencoracing.com/st12.html

And here is a picture of the air shift version:

http://www.racingjunk.com/post/637817/Lenco-CS-1-3-speed-transmission-W-reverser.html

 

[GregLocock]

Although it is not likely to help with your diameter problem, a Ravigneaux is a relatively straightforward and practical way of getting more ratios in a compact unit.

Cheers

Greg Locock

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

 

[thundair]

Warpspeed
Thanks for your input I am confident this can be done but maybe not by me. The few gear boxes I have designed are mostly aircraft and always planetary but dedicated ratios.

crysta1c1ear
Yes we intend to manufacture the housing and controls but not any of the gear sets nor engineer the loads. The hope is to find a suitable trans and use the components from a used one to prototype and if it works we will buy new for the production models.

The one scary part for me is that I have never built an engine coupled trans without some buffer.
Most PSRU’s (power supply reduction unit) use some kind of harmonic damping.
I believe I could get away without using it on the driveshaft side but not on the engine side.
It maybe possible to use the loaded drive springs in the clutch plate without the clutch.

 

[thundair]

Greg
Still trying to get my head around the Ravigneaux gear set it looks like another set of planets.

I found this and will try to dig deeper

ZF 6HP26 Six-Speed Automatic
The transmission is based on the Lepelletier gear set, which is constructed by connecting a planetary gear to a Ravigneaux gear - a double planetary gear set commonly used in four-speed automatics.

Thanks to all

Cheers

 

[GregLocock]

Took me a couple of days!

Cheers

Greg Locock

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