Dissection of a TS-2- How it works and how they were made

[raygreenwood]

I did post this to add to a thread in the bay bus forum which is a great thread.
You should check it out. I posted a separate thread here because all of us need these just as bad as the type 2 and 3 guys and a lot of 411/412 guys may not follow many threads in the bay forum.
Here is that thread: https://www.thesamba.com/vw/forum/viewtopic.php?t=789175

Ok, so I noted in the bay forum thread that many years ago I cut open one of these. Even though that was many years ago, compared to the one I cut open last night, it was a relatively new one probably made in mid to late 90’s.

I crudely described what I remember in that one. It had a small thermistor soldered onto the wire on one end and onto the inside of the steel sensor body on the other and it was filled with a ceramic heat insulator mastic.

I do not remember if it was Bosch but it was most probably whatever brand that Beck Arnley was selling at that time, either a German repro or a made in Italy repro.
I remember it worked well BUT….because it only had shrink tube instead of the nice OEM polypropylene or nylon strain relief it eventually cracked and wore through and shorted to ground at the ire to sensor body joint.

This one was an original Bosch sensor with both Bosch and VW logo stamped on it. Part #s on it are
022 906 041 and 0280 130 012.

This was made before VW/Bosch superseded to 022 906 041A and then eventually to 311 906 041A. This came out of one of my engines and that puts its age to 1972 or 1973.

I have to say that seeing what I saw back then and seeing what I seei nthis one, this part has probably changed how it was produced several times over its production life.

The way this one is made is impressive. Bosch did not use a “store bought” thermistor sensor, cannister shaped or otherwise….that was soldered or pressed into the sensor body in any way.
They MANUFACTURED the sensor inside of the drilled out sensor body. Impressive….and had to be expensive. A whole lot of steps went into making these.

Behold!

So, this is the TS-2 I am cutting open. It lost the outer terminal but it was also screwy in resistance readings.

With the polypropylene strain relief pulled off. By the way, this is the only way these should be done.
The current versions of these sensors using heat shrink are NOT good enough strain relief.

This is the sensor cleaned up with a brass wheel. Notice the joint where the arrow is. The stem sticking out is a separate part from the body. The top of the sensor body is swaged around it.

Here it is with the swage cuff sliced off. This is VERY different inside from what I have seen before on newer versions of this sensor.

Notice the thin insulating sleeve inside of the bore

So, from right to left you have a fully insulated wire going through a steel ferrule that is crimped very lightly just for mechanical hold.

That clipped brush of that wire is sticking through a crimped seat (still insulated from the body of the sensor) that holds the spring.
On the end of that spring, you see a little cylindrical pellet. Then you see the nylon insulating sleeve that was inside of the bore. Then you see the sensor body.

Here is a detail of that metal pellet. At first I thought is was crimped or soldered on . Nope!

It comes right off. Its laying in the right hand foreground.

The face of the spring seat is on the left and the pellet is on the right. You can see the contact mark.

Looking down in the bore we see a machined surface. The rest of the bore walls are rusted but not whatever is at the bottom.

So, I sectioned the bore and on the right you can see that it is a swaged in ground disc. It looks to be nickel plated which means it will never rust. On the left you can see the contact face of the pellet on that disc.

Sorry for the poor focus. I was hand holding the scope and did not have time to set up the rack and pinion. This is the spring seat where it makes connection with the wire.

Here is a detail once the spring is popped off of how the wire passes through the outer stem and is insulated and how the current is passed to the spring inside and then to the pellet.

Here is a sketch of how its laid out.

And….the “thermistor” is that little cylindrical pellet. The inner plate is just a rust proof ground plate. The spring is designed to keep constant contact pressure between the thermistor and ground to make sure there is as little resistance variation as possible. This is something we find everyday in all sorts of electronics.

This is why if you cannot have a hard soldered connection either because you cannot solder where it needs to be or the soldered connection will not survive heat cycling or vibration….you use a spring tensioned connection just like modern fuel injector female connectors that you see in every system from L-jet to now (except GM’s 80’s and 90’s sh*t wagons).

So….

Here is that little thermistor pellet trapped between my taped down VOM probes.

What would you think it’s going to read?

Yep….2300 ohms on the button! The readings scroll around a little bit because pressure needs to be constant but that’s pretty damn good!

These could be easily and cheaply built with a modern store bought thermistor. But if you want them to work right and live you have to start with the right range of thermistor (or one that is close that you can add a resistor or potentiometer to) and you have to properly connect it to ground and you have to properly insulate it and it needs to be a thermistor that can handle 400+ degrees.
Ray

[Lars S]

Nice work Ray!
Never thought there was so much in that tiny one...learned a lot@

Lars S
_________________
Porsche 914 -72, Bahia Red daily driver
VW411 2-d -70, White, sold
VW412 4-d, -73, Gold Metallic, daily driver
Suzuki T500, -69, Candy Gold, sold
Suzuki K50, -77, Black, daily driver
BMW R69S -69, White, sold
Husqvarna 118cc, -47, Black, Sold

[nogoodwithusernames]

So what goes bad in there to make them go out of spec? Spring loses tension?
_________________
71 Squareback, 1.7l T4 w/ crank trigger fuel and spark
(Conversion thread https://www.thesamba.com/vw/forum/viewtopic.php?t=732508&highlight= or https://shoptalkforums.com/viewtopic.php?f=1&t=151375&sid=f0542d44a322d290c29d6609fac7f215 )
74 914, 2.0L w/ D-Jet

-Derek

[raygreenwood]