| Lock-torque converter to improve city and towing mileage
- Click HERE for Original Thread
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| azyva |
Hello everyone.
I own 2004 MDX, and I have a discussion subjet I would like to run by you.
BACKGROUND INFO (skip to the BIG QUESION below if you know about torque converters)
I have been reading many threads in this forum about gaz mileage. I have also been experimenting a lot with different driving habbit.
One of my conclusions is that a significant amount of gaz energy is wasted heating the ATM fluid within the torque converter (TC for short) of the vehicule. This is true for essentially all vehicules equiped with automatic transmissions.
The MDX, like may other modern vehicles, is equipped with a locking TC which mechanically locks the input and output shafts together so that power transfer does not involve ATM fluid pressure between the turbine and the pump inside the TC. With a little bit of practice, you can easily tell with the TC locks up or unlocks by looking at the RPM or simply "feeling" the engine.
This locking occurs at the discretion of the ECU, typically at constant cruising speed above a certain minimum speed. When accelerating (or when climbing a hill, or when towing), the ECU generally unlocks the TC so as to let the engine run at higher speed and thus provide more power. If the acceleration (or hill slope) is very gentle, le ECU may let the TC locked.
Now, in my the experiments, I was able to cause de ECU to lock the TC sooner than it typically would by accelerating very gently from traffic signs (stops and lights), and playing a bit with the gaz pedal, so as to tell the ECU that I do not require heavy acceleration. This has resulted in significant improvement in gaz mileage. My wife, who do not care much about all this stuff, get around 13 MPG in city driving. I can get around 17. On highway, when I not in a hurry, I get between 24 and 26.
BIG QUESTION
What if the MDX provided a switch that when activated, would force de locking of the TC? I am sure that this way, our city (or towing) mileage could improve significantly.
Of course, Acura or other car maker would not offer such a device since incorrectly using it could harm the transmission. In particular:
- The TC must be unlocked before stopping the vehicule (otherwise, the engine would stall);
- I guess the TC must be unlocked when the transmission shifts gear (otherwise, it may have difficulty synchronizing, such as when you do not use the clutch to shift gear on a manual transmission);
- I guess the locking mechanism in the TC has a maximum torque it can sustain. I believe it is not as strong as the clutch in a manual transmission as it is only meant to improve gaz mileage at cruising speed with no stress on the vehicule. It may very well be that when towing a heavy load, it would somehow slip.
But I would be ready to experiment with this.
First of all, what do you think about all this? Any opinions? Suggestions?
Second, in order to try this, I would need to know the wiring diagram coming out of the ECU of the vehicle. I do not have the MDX service manual, and here in Montreal, it costs around 220 $ (Canadian). Quite a bit for an experiment which may not be fruitful. Would anyone out here own such a manual and be kind enough to inclure scans of the page or pages which describe the wiring diagram of the ECU, particularly the part related to the automatic transmission control?
Thanks in advance,
David |
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| G. COLTON |
What you have found is that being gentle with your acceleration at stop signs/lights improves fuel mileage. This gentle acceleration is good regardless of what the torque converter does. The same is true of highway driving. When accelerating be gentle.
When driving on the highway it is not uncommon to average 24-26mps if you drive in the range of 60-65mph. Out of the interstate I usually drive 75 and average 21. If I an driving to Pensacola on a 4 lane road at 60 mph is is not at all unusual to average 24mpg even with traffic and a few lights.
Good driving.
G |
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| eRauL |
quote:
Originally posted by G. COLTON
...
When driving on the highway it is not uncommon to average 24-26mps if you drive in the range of 60-65mph. Out of the interstate I usually drive 75 and average 21. If I an driving to Pensacola on a 4 lane road at 60 mph is is not at all unusual to average 24mpg even with traffic and a few lights.
...
G
I got my little Mazda to 40mpg one week by, dangerously, tailgating those 18 wheelers on my way to work :1:
Who needs Hybrid? :2: |
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| mysweetjorge |
quote:
Originally posted by azyva
The MDX, like may other modern vehicles, is equipped with a locking TC which mechanically locks the input and output shafts together so that power transfer does not involve ATM fluid pressure between the turbine and the pump inside the TC. With a little bit of practice, you can easily tell with the TC locks up or unlocks by looking at the RPM or simply "feeling" the engine.
This locking occurs at the discretion of the ECU, typically at constant cruising speed above a certain minimum speed. When accelerating (or when climbing a hill, or when towing), the ECU generally unlocks the TC so as to let the engine run at higher speed and thus provide more power. If the acceleration (or hill slope) is very gentle, le ECU may let the TC locked.
David
Can you tell by the sound it produces if the torque converter mechanism has locked or unlocked itself? Or does it ever produce any sound at all per your tests?
I seem to get bothered by a clicking sound coming from the front driver's side noticeably by the engine's firewall.
The moment I hear the clicking sound as soon as the MDX starts to move, it would accelerate as if it were carrying a load.
However, if no clicking sound is produced, acceleration is smooth as silk.
I'm just curious to know if this sound has got something to do with the torque converter pre-maturely locking up or not at all.
Thanks. |
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| azyva |
mysweetjorge,
The locking or unlocking of the torque converter does not produce any sound in my case. I know when it engages or disengages simply by looking at the RPM, or hearing the engine sound when everything else is quiet.
When the torque converter locks up, the RPM decreases a bit, and this decrease is not sufficient to be attributable to the transmission shifting gear.
Also, the torque converter will generally refuse to lock up at low speed when the vehicule is accelerating, even gently.
As far as the clicking soud is concerned, I also do hear a faint click when the vehicule is coming to a stop, just before it immobilizes. I did not notice, but probably it does the same immediately after starting to move.
This very faint click comes from a mechanical lock within the transmission shift stick that prevents the stick from being put into reverse while the vehicule is still moving.
Following my initial request my my initial post, if anyone on this forum happens to have the Acura MDX service manual, I would be very interested in having a copy of the electrical wiring information related to the transmission control. In return, I promise I to share my experiences in trying to manually control the locking and unlocking of the torque converter. Thanks.
David |
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| SuperTech |
Perform this little "experiment" of yours, and consider your powertrain warranty null and void. Yes, the entire powertrain, and not just isolated to the transmission.
Honda engineers have programmed the points for the TC solenoid locking and unlocking to ensure the best possible fuel mileage without harming the engine or transmission. By forcing the TC into lockup at slow speeds around town (or even worse, towing), you will probably be lugging the motor to maintain the same level of acceleration that you're already used to when the TC was allowed to "slip" and multiply torque like it's supposed to. Not to mention, if you have the TC forced in lockup and feed it too much throttle, it may try to downshift on you when you weren't expecting it. And unless you're extremely ready to hit the button to unlock it before it does, you will have a harsh shifts that will eventually destroy the transmission and weaken other components of the drivetrain.
The short version is this. The ECU and the people who programmed it are smarter than you. Leave it alone. If you do...when something breaks (and it will), all repairs will be on your nickel. And we do have ways to tell if electronics have been tampered with. |
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| azyva |
Thanks SuperTech for your honest and informed feedback. I appreciate it.
I do understand the implications of manually controlling the locking of the torque converter, and I know it is a very delicate thing to do, and I in no way believe to be smarter than the engineers who have programmed the ECU.
The main reason for my interest in this subject is the following.
I use my MDX for towing a camping trailer during summer times (I live in Quebec). I believe the trailer and all the stuff in it weighs somewhere between 3500 and 4000 pounds. Its dry weight is 3250 pounds. According to the vehicle specifications, this is a little bit over the limit of 3500 pounds for a (relatively) flat nosed trailer.
My experience towing this trailer is that at normal cruising speeds (between 90 and 100 km/h, or 55 to 60 mph), the ECU generally refuses to lock the torque converter, unless I've got really favorable conditions (back wind and/or closely following a trailer bigger than mine). This results in:
- Degraded fuel economy ;
- Heat build up within the torque converter housing and the ATF fluid (I cannot mesure this, but this is my guess). The temperature sensor actually never came on.
But I generally feel it would not take much for the torque converter to lock up. I feel the engine, in 4th speed, would be able to sustain a lower RPM with a locked torque converter, resulting in much better fuel economy, and less strain on the transmission.
I would greatly appreciate your feedback on this. I am a little bit worried about damages to the transmission. Are my worries justified?
As a side note, I did a full ATF fluid change at the end of last summer, and plan to do one every year, which amounts to around 5000 towing km.
Regards,
David |
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| SuperTech |
quote:
Originally posted by azyva
My experience towing this trailer is that at normal cruising speeds (between 90 and 100 km/h, or 55 to 60 mph), the ECU generally refuses to lock the torque converter, unless I've got really favorable conditions (back wind and/or closely following a trailer bigger than mine). This results in:
It's not going into lockup at times because the ECU is detecting too much throttle and wants to allow torque multiplication so your added throttle input will actually have some results other than slowing down since you've got too much load. When the RPMs are low like that in 5th gear, it doesn't take very much for it to come out of lockup. If it stayed locked up, the engine would lug which is not good to do.
If you don't have the ATF cooler, get one. If you're towing to the capacity of the vehicle, it's stupid not to have one. Another reason is that any transmission warranty claim can be denied if they see you've been towing with no cooler.
Fact is this. If towing was really a main conern for you...a V8 equipped full size SUV would have been better. The MDX's 3.5L V6 just doesn't have enough torque in the low end to effectively tow and still get acceptable mileage. But say...a new 2007 Tahoe with a big powerful V8 with more torque than horsepower would be better suited to tow. And even loaded with a trailer, might even pull down better mileage than the MDX. Even better, a 3/4 ton turbodiesel equipped pickup. Those seem to take the least amount of mileage penalty for towing/hauling heavy loads. |
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| azyva |
quote:
If you don't have the ATF cooler, get one. If you're towing to the capacity of the vehicle, it's stupid not to have one. Another reason is that any transmission warranty claim can be denied if they see you've been towing with no cooler.
My MDX is equipped with the factory towing package (hitch and coolers).
I am still wondering if the vehicle is able/designed tow my type of load for long distances at cruising speeds without the torque converter being locked.
quote:
If towing was really a main conern for you...a V8 equipped full size SUV would have been better.
The MDX came before the trailer. We initially had a popup tent, and decided to upgrade, hoping to still be able to keep the MDX.
A bigger vehicle would be too cumbersome for me, given that the MDX is used mostly as a familly car, not a towing vehicle.
Thanks. |
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| SuperTech |
quote:
Originally posted by azyva
I am still wondering if the vehicle is able/designed tow my type of load for long distances at cruising speeds without the torque converter being locked.
Try towing in D4 then. The additional RPM might allow the computer to allow lockup. Of course, the gain in fuel mileage you may get with the TC locked would be offset by the extra RPM of being in a lower gear.
The way you've been using the vehcile so far seems OK. Just be sure to monitor the condition of the ATF frequently. |
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| azyva |
SuperTech,
As per the owner's manual recommendations, I do always tow in D4, never in D5. Actually, even if I were in D5, the load is such that the computer generally keeps the transmission in 4th gear.
But even in D4, even with the extra RPM, the TC does not lock. If it were locked, the RPM would be around say 2000. Unlocked, it reads around 2400. So there is around 400 RPM whipping the ATF fluid.
My question still holds. Do you believe the vehicle is designed to sustain such a condition for long distances?
And one last question: Does the TC stay unlocked to avoid damaging itself, or simply to allow the engine to run at higher RPM and thus provide more torque? I mean, would the locking mechanism in the TC be able to sustain the torque imposed by the load? Or would it risk slipping? Is the locking mechanism mechanical using some kind of metal latch, or is it more like a manual transmission clutch?
Thank you so much for your kind feedback. Really appreciated.
David |
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| SuperTech |
That must be quite a load then. Not just the weight, but the aerodynamic drag must also create more load.
As long as the A/T Temp light never comes on, you're operating in normal parameters. Would I want to tow something like that say, 1000 miles? No.
To answer your last question. The TC stays unlocked to allow more torque to be transmitted to the gears. If you were to forcibly lock it, there wouldn't be a risk of slipage. But you would be lugging the engine. What locks the TC is an electromagnetic solenoid that either closes or opens a path for ATF pump pressure to flow. There is another solenoid that regulates line pressure based on engine load to lengthen transmission life by allowing just enough pressure to avoid slipping. (Kinda like a vacuum modulator on an old transmission) |
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