How does humvee trans know what gear to be in

[Talns100]

I am working with a humvee h1 which has the 4L80E trans model.
How does the transmission control module know what gear to be in.
I know there are 4 sensors:
1. Throttle Position
2. The Gear Lever
3. Crank RPM
4. Transfer Case RPM

Am I right? How does that actually work?

 

[AAVP7]

Hello, and welcome to Steelsoldiers !

You are almost right about the sensors, but there are a few more (TISS, TOSS). You want to download this manual:

4L80 Troubleshooting Manual

This is a lot to read, but it is one of the best and exhausting Humvee manuals out there.

To answer your question: The transmission computer (TCM) computes the optimal gear from a bunch of sensors. Central are the TISS and TOSS sensors (Transmission Input Speed Sensor - Transmission Output Speed Sensor). The ratio between these, plus the Throttle Position Sensor TPS and the Crankshaft rpm sensor is then used to compute the gear to be in.

 

[Talns100]

Hello, and welcome to Steelsoldiers !

You are almost right about the sensors, but there are a few more (TISS, TOSS). You want to download this manual:

4L80 Troubleshooting Manual

This is a lot to read, but it is one of the best and exhausting Humvee manuals out there.

To answer your question: The transmission computer (TCM) computes the optimal gear from a bunch of sensors. Central are the TISS and TOSS sensors (Transmission Input Speed Sensor - Transmission Output Speed Sensor). The ratio between these, plus the Throttle Position Sensor TPS and the Crankshaft rpm sensor is then used to compute the gear to be in.

Wow thanks for the reply!
Do you know another manual which describes how the trans work and how is everything calculated to find the optimal gear?
I am trying to find more info about TISS and TOSS and how they calculate TCC Slip Speed.
And does the TCM takes the engine RPM into consideration?

 

[Talns100]

??

 

[NDT]

There is no military manual that describes the engineering of the 4L80E transmission, the design and the software is proprietary to GM, the Army just cares that it works and how to fix it. Surely however, someone on the internet has reverse engineered the transmission and has your answers, just not on SteelSoldiers, that I have seen.

 

[TOBASH]

Hello, and welcome to Steelsoldiers !

You are almost right about the sensors, but there are a few more (TISS, TOSS). You want to download this manual:

4L80 Troubleshooting Manual

This is a lot to read, but it is one of the best and exhausting Humvee manuals out there.

To answer your question: The transmission computer (TCM) computes the optimal gear from a bunch of sensors. Central are the TISS and TOSS sensors (Transmission Input Speed Sensor - Transmission Output Speed Sensor). The ratio between these, plus the Throttle Position Sensor TPS and the Crankshaft rpm sensor is then used to compute the gear to be in.

Thanks for posting this. My M1165 is not shifting so I guess I need to start testing and such. Let the good times roll.

 

[Mogman]

Thanks for posting this. My M1165 is not shifting so I guess I need to start testing and such. Let the good times roll.

Remember the very first thing is to make sure you have a working trans light when in run but not running.
If you don't you cannot proceed, you could have a bad light, a power issue (or other wiring issue) to the TCM or a bad TCM.
It is usually all down hill after getting a working trans light.
EDIT, if you have a working trans light then you have power to the TCM

 

[patracy]

Wow thanks for the reply!
Do you know another manual which describes how the trans work and how is everything calculated to find the optimal gear?
I am trying to find more info about TISS and TOSS and how they calculate TCC Slip Speed.
And does the TCM takes the engine RPM into consideration?

I doubt there will be anything like that in any military TM. The DOD had no part in designing/coding the TCM, they simply bought it. That said, there's a wealth of knowledge out there on the internet about the 4l80e and the logic to controlling it. And yes, the TCM (well any TCM) reads engine RPM, as well as output shaft rpm, and uses maps for gear selection based on that.

 

[Mogman]

Also when talking about the OEM TCM when you look remember this is an early "mechanical injection" version, think 6.2L, in the civy world by the time the 6.5L came out almost all 4l80Es installed used a completely different setup where the truck had an ECM, (all gassers also had ECMs) nothing at all in common with the HMMWV.

I am curious why you are interested in the actual programming, if custom or programmable shifting is desired unless you want to take the time to decipher the HEX data in the PROMs that is the only way to change the programming other than what EPROMs you can purchase.
If you want I should be able to send you the hex files from NA and turbo PROMs

 

[TOBASH]

Remember the very first thing is to make sure you have a working trans light when in run but not running.
If you don't you cannot proceed, you could have a bad light, a power issue (or other wiring issue) to the TCM or a bad TCM.
It is usually all down hill after getting a working trans light.
EDIT, if you have a working trans light then you have power to the TCM

Trans light is great. Shifting, not so much.

Shifts reverse well. Shifts first and second, then stops.

I will RTFM

Thanks!