CTIS Theory questions.

[motomacguyver]

I have a few questions on CTIS Theory, not how to operate it, not how to remove and replace parts per the TM (I read that part). I’m interested in how it’s supposed to work at the design level so we can troubleshoot our problems more intelligently.

So here are my questions, and some observations of my own.

1st Question, What is the “signal” for the wheel valves to let air out? There is only one air line in/out and no electrical connection to the wheels, so this must be done pneumatically. How?

2nd Question, After raising the air pressure in the wheels, does the CTIS manifold “purge” the air out of the lines? I think it does, because the CM automotive web site says they took great pain to make sure the wheel bearing seals are not under pressure most of the time. Verification would be great.


3rd Question, Is the CTIS manifold capable of checking and filling pressures one circuit at a time? (There are 3 lines running out of the manifold, one for each axel.) Or is it able to “gross fill” all three circuits, and then isolate individual circuits and fine tune the pressures?




Finally, here is my reason for asking these questions.

When I deflate the tires, (go from highway to X-country) I get varying tire psi's, when I inflate, the tire psi is stable until it gets up to pressure, then the CTIS must purge the air lines, (the CTIS manifold seems like it lets out a lot of air at this point, maybe 20 seconds worth), and then my tire psi's are all over the place. This must be the tire valves not deflating correctly? Am I correct in this assumption?

Thanks in advance.

 

[rickf]

I am going to jump in here just to se where this goes. I do not have a CTIS but I have heard all the complaints and these are some very good questions.

Rick

 

[Stalwart]

Looks like they really over thought the plumbing on the A3, are you sure it not a British design? On my Hummer H1, it is simple, all lines are charged from the front/rear/all/off wheel selector to the tires ALL the time. I guess they thought a Private was too busy to select his own tire pressure via a simple rocker switch.

 

[glcaines]

I'm really glad you posted this. I was going to start a similar thread, but never got around to it. As I mentioned in my recent PM, I am having some issues with my CTIS as well. The TM has a lot of good information, but does NOT explain how the CM Automotive CTIS system works. I've found virtually nothing on the theory of operation for this system. I really hope this thread goes somewhere. I'm currently working on my CTIS system and I'll provide information as I gain knowledge.

 

[Stalwart]

It would be very simple to modify the system using 2 air solenoid valves, either 2 gages or a two needle gage, a selector valve and a rocker switch. Simple, elegant and would work as long as the seals work in the hubs. You could also get over any leakage worry while driving using a adjustable pressure regulator.

 

[mktopside]

Looks like they really over thought the plumbing on the A3, are you sure it not a British design? On my Hummer H1, it is simple, all lines are charged from the front/rear/all/off wheel selector to the tires ALL the time. I guess they thought a Private was too busy to select his own tire pressure via a simple rocker switch.

And hummers blow inner hub seals all the time because of that design.

The CM system is a really intelligent and not all that complicated of a setup. The only reason it gets confusing is because of the computer integration.

Not saying they aren't prone to problems, but I don't see those issues being related to the design of the system.

 

[mktopside]

I have a few questions on CTIS Theory, not how to operate it, not how to remove and replace parts per the TM (I read that part). I’m interested in how it’s supposed to work at the design level so we can troubleshoot our problems more intelligently.

So here are my questions, and some observations of my own.

1st Question, What is the “signal” for the wheel valves to let air out? There is only one air line in/out and no electrical connection to the wheels, so this must be done pneumatically. How?

2nd Question, After raising the air pressure in the wheels, does the CTIS manifold “purge” the air out of the lines? I think it does, because the CM automotive web site says they took great pain to make sure the wheel bearing seals are not under pressure most of the time. Verification would be great.


3rd Question, Is the CTIS manifold capable of checking and filling pressures one circuit at a time? (There are 3 lines running out of the manifold, one for each axel.) Or is it able to “gross fill” all three circuits, and then isolate individual circuits and fine tune the pressures?




Finally, here is my reason for asking these questions.

When I deflate the tires, (go from highway to X-country) I get varying tire psi's, when I inflate, the tire psi is stable until it gets up to pressure, then the CTIS must purge the air lines, (the CTIS manifold seems like it lets out a lot of air at this point, maybe 20 seconds worth), and then my tire psi's are all over the place. This must be the tire valves not deflating correctly? Am I correct in this assumption?

Thanks in advance.

I can't answer factually, but I'll give it my best shot.

1: it seems to me that the system sends an air charge to the wheel valve at a specified PSI far above tire pressure, to move a piston and spring to the "fill/check" position, to fill the tires. To deflate them, it charges the line to a higher pressure that moves the piston further, blocking off the fill port, and venting line pressure and tire pressure out a larger port. That is why the system needs 90psi to operate, because it's high enough to operate the wheel valves, but high enough above the tire pressure to where the wheels valves aren't affected by the tire pressure.

This is speculation on my part, I don't really know.

My CTIS doesn't fill my tires equally, but it fills them close enough to where it really doesn't matter from a mobility standpoint.

 

[Stalwart]

I've only had slow leakage problems over MANY months. I just go by the many posting about A3 owners problems and the issues they seem to have with them. I'm a really big fan of computerization, but sometimes engineers take a design a bit too far with too many critical components.

They must be using an air equivalent of a hydraulic fuse.

 

[mktopside]

I've only had slow leakage problems over MANY months. I just go by the many posting about A3 owners problems and the issues they seem to have with them. I'm a really big fan of computerization, but sometimes engineers take a design a bit too far with too many critical components.

They must be using an air equivalent of a hydraulic fuse.

I think the biggest problem with CTIS is that there are no TMs on it, no PMCS standards, and no real knowledge on how to adjust parts of the system to tune it to do what you want.....or non adjustability in various parts of it. It's too soldier proof.

My biggest gripe with it is that it uses more air to operate than it puts in the tires.

 

[motomacguyver]

I've only had slow leakage problems over MANY months. I just go by the many posting about A3 owners problems and the issues they seem to have with them. I'm a really big fan of computerization, but sometimes engineers take a design a bit too far with too many critical components.

They must be using an air equivalent of a hydraulic fuse.

I had slow leakage problems also, this happened even with the CTIS off. Took the truck to a heavy truck tire shop that had a guy there that used to be military, and they would work on the wheels/tires. We found slow leaks on 4 of 7 tires. Replacing the wheel "O" rings and the valve stem "O" rings and then the slow leak problem was gone. Also while the wheels/tires were off the truck they did a soap bubble test and none of the CTIS valve were leaking at that time. Now all the tires hold air with the CTIS off.

 

[glcaines]

I have dismantled one of my A3 wheels. The grommet under the valve stem is supposed to be torqued to 40-65 lb-ft according to TM 9-2320-386-24-1-1. The brass nut on mine was only finger tight. Interestingly, that tire was not leaking air. I suspect the rest of mine are similarly loose. The rubber becomes old and cracked and relaxes with age. It is also very important not to move the valve stem when installing and removing fittings to the CTIS as this can loosen the nut.

 

[AceHigh]

Great stuff! I can tell you the manifold is usually at zero PSI. I took the manifold off and all the tires stayed full. To me the big problem with it is changing tires, takes a few extra steps.

 

[3dAngus]

Basic Layout

 

[3dAngus]

A little bigger...

 

[motomacguyver]

I can't answer factually, but I'll give it my best shot.

1: it seems to me that the system sends an air charge to the wheel valve at a specified PSI far above tire pressure, to move a piston and spring to the "fill/check" position, to fill the tires. To deflate them, it charges the line to a higher pressure that moves the piston further, blocking off the fill port, and venting line pressure and tire pressure out a larger port. That is why the system needs 90psi to operate, because it's high enough to operate the wheel valves, but high enough above the tire pressure to where the wheels valves aren't affected by the tire pressure.

This is speculation on my part, I don't really know.

My CTIS doesn't fill my tires equally, but it fills them close enough to where it really doesn't matter from a mobility standpoint.

This is interesting, however, I wonder if it may work in reverse. By sending a low pressure pulse to open the tire valves. Some of the reasoning is that, we are sure the air comes and goes thru the same hose. And the brakes want/need at least 60 psi to work, so that would explain the 90 psi?

When the CTIS dumps air the tire psi will be from 45 to 15 psi. (on different wheels) and the exaust valve, exausts for 20-30 seconds, and then I think the CTIS system tries to refill.

Thanks for your input, this is speculation on this end also.

 

[Stalwart]

OK, I think I got it. If you install an air fuse like devise out at the tire this could be easily achived:

http://www.norgren.com/document_resources/DE/10.7.001.pdf

With something that could be as small as 1-2" long this device with nothing more than a housing, a ball (or a shuttle valve with seal) and a small spring. This would allow the system to to drop to atmospheric pressure, while the tire remains inflated. The valve would close as soon as the air in the manifold and piping dropped QUICKLY and the air pressure on the ball (or valve) would overcome spring pressure and seal off the tire (like a check valve). You'd need a large dump valve but that is easy! When the tire pressure needed to be dropped, the ECU tells the air controller to send air through the manifold and piping and bring it up to normal tire pressure. Since there is spring pressure against the ball, the ball would unseat and then air could then be removed at a reduced rate, just below the threshold of the ball overcoming spring pressure.

 

[Rustygears]

I too have a semi-working CTIS on my A3. Being an experienced heavy equipment mechanic as well as an engineer, I contacted the folks at CM to see if they could assist and provide additional troubleshooting insight as well as understanding so I could document better for all of us how to troubleshoot the system beyond the TM direction to swap stuff until it works. I for one cannot afford the expense and waste of time doing shotgun troubleshooting. CM's idea was for me to drive the truck to their facility for them to investigate. They also said they were developing documents for subassembly repair and enhanced troubleshooting for the military. They weren't willing to share. It may be a simple system, but in my opinion this vendor sucks based upon their willingness to help. Ask John Deere for help with a 60 year old tractor - they send original parts drawings so you can fabricate a now unavailable part. What a contrast. I paid CM a fortune for their equipment via my tax dollars. I never paid John Deere a penny (not even postage). I know who I will seek to patronize in future!

 

[3dAngus]

Rustygears, what you just told me is the government did not procure drawings data. When on contract to DOD, these contractors get a fee for developing data and drawings and providing that to the government. Government engineers write up the technical end of the contract, and specify what data they want. Logistic Officers, or Program Managers, then order on seperate Contractual Data Requirements Listing, the individually procured data the government gets based on need, and cost. Either of the need (weak justification) or cost (monies currently in budget) can get that particular data item stripped off of the contract. The contractor then holds off on the government procured data until the government comes back with another contract to procure it. If the contractor gives it out in the meantime, they can lose a lucrative government contract, often worth six figures for this data, which includes drawings and tech orders, with detailed troubleshooting procedures and schematics. I'm certain that is what you encountered. I have seen it all my life.

 

[renovate7]

I talked to CTIS a while ago and am going to take a stab at this, trying to keep it simple, for my sake...First, under mormal conditions there is no air pressure from the the CTIS to the wheels, each wheel valve is closed. The wheel valves are preset for the lowest pressure you want the tires to operate at, say on an A3 30 psi. When air above this pressure is sent to the wheel the valve opens and the tire inflates/deflates to what ever pressure is sent to it...If your at 50 psi and want to deflate to 40 psi, 40psi is sent to the wheel. The valve opens and the tire deflates to 40 psi. If your at 35 psi and want to go to 50 psi, 50 psi is sent to the wheel, the valve opens and the tire inflates to 50 psi. The CTIS senses when the pressure is reached and shuts off. If you send less than the factory preset pressure the valve won't open...There are 3 output lines, one for each axle, with a T at each axle for each tire. I think the CTIS can operate each axle independently but not each tire. If you have a tire going flat the CTIS won't automaticaly sense it. That is why the system is designed to turn on/off at preset times, every so many minutes. It will send whatever pressure it is currently set at, say 50psi, to each wheel. If a wheel is below that it will inflate it to that pressure. I can't remember but I think it then alerts you to the fact one tire has a problem...Hope all this is clear.

 

[motomacguyver]

I talked to CTIS a while ago and am going to take a stab at this, trying to keep it simple, for my sake...First, under mormal conditions there is no air pressure from the the CTIS to the wheels, each wheel valve is closed. The wheel valves are preset for the lowest pressure you want the tires to operate at, say on an A3 30 psi. When air above this pressure is sent to the wheel the valve opens and the tire inflates/deflates to what ever pressure is sent to it...If your at 50 psi and want to deflate to 40 psi, 40psi is sent to the wheel. The valve opens and the tire deflates to 40 psi. If your at 35 psi and want to go to 50 psi, 50 psi is sent to the wheel, the valve opens and the tire inflates to 50 psi. The CTIS senses when the pressure is reached and shuts off. If you send less than the factory preset pressure the valve won't open...There are 3 output lines, one for each axle, with a T at each axle for each tire. I think the CTIS can operate each axle independently but not each tire. If you have a tire going flat the CTIS won't automaticaly sense it. That is why the system is designed to turn on/off at preset times, every so many minutes. It will send whatever pressure it is currently set at, say 50psi, to each wheel. If a wheel is below that it will inflate it to that pressure. I can't remember but I think it then alerts you to the fact one tire has a problem...Hope all this is clear.

Thanks, this is the best description yet.

On a side note, does anyone have a used, take off wheel valve they would donate/sell cheap so I can take it apart and rebuild one at a time so my truck isn't down for a period of time? Thanks.