If you’ve seen Predator (1987), you’re familiar with the alien being that was capable of destroying Schwarzenegger’s entire military rescue team, and very nearly took out the Austrian bodybuilder himself. Meanwhile, if you know the WJ Grand Cherokee, you’re aware that it’s a popular SUV that served in the Jeep product line from 1999 to 2004. But what do these two have in common?
Would you believe—it’s the ability to sense heat via infrared! The Predator was able to see in the thermal range of the electromagnetic spectrum. It picked up thermal-range infrared radiation which allowed it to track its human prey through the dense jungle. The WJ Grand Cherokee, on the other hand, uses its thermal IR sense for altogether more peaceful means, as do some following models.
Yes, when equipped with the Automatic Zone Control HVAC system, the Grand Cherokee came equipped with two infrared thermal sensors, or thermopiles. One is aimed at the driver, the other, the passenger. It was a rather unique way of determining just how hard to run the heating or cooling to serve the occupants of the vehicle.
Most automatic climate control systems use a little fan to suck the interior air over a small temperature sensor, usually a thermistor. This allows the HVAC system to know the temperature of the air inside the vehicle, and adjust its output to help reach the desired set point. But Jeep engineers realized this was missing the point. We don’t so much care about how hot or cool the air in the car is. We care about how hot or cool we are.
To find this out, the Jeep’s climate control needed a way to sense the temperature of the occupants at a distance. Nobody’s getting in their car and putting on a temperature sensor probe, after all, so it had to be done wirelessly. Enter the infrared thermopile. This is a small device that can pick up infrared radiation in the thermal part of the electromagnetic spectrum. See, objects emit infrared radiation depending on their temperature. The hotter something is, the more IR it puts out. Capture this radiation, which is essentially just light that’s too long in waveform for us to see with our eyes, and you can determine an object’s temperature to a fairly good degree of accuracy, subject to some complicated assumptions we won’t get into here.
A single thermopile can capture infrared radiation at a distance and spit out an electrical signal that correlates to temperature. You’re probably more familiar with them then you think. A thermopile is the sensor used in non-contact thermometer guns that you might have used to check the temperature of engine components or a catalytic converter. If you go ahead and take a bunch of thermopiles and put them into a rectangular array, you can actually create a crude thermal camera. Proper thermal cameras, such as those used in the filming of Predator, essentially have an array of hundreds or thousands of individual sensors that pick up IR to create a higher-resolution image. But at its heart, it’s the same idea—using infrared radiation to measure the heat of an object at range.
By my research, Jeep used this system in the WJ model from 1999 to 2004, in vehicles equipped with “Infrared Dual-Zone Climate Control.” The thermopiles were mounted behind a small plastic lens between the two temperature control knobs, which is largely transparent to infrared waves. It’s an interesting fact that materials that block visible light may not block IR, and vice versa. For example, we consider glass transparent when it comes to visible light, but it’s excellent at blocking IR radiation in the thermal spectrum.
Infrared thermopile sensors also appeared in the climate control for the WK model, built from 2006 to 2010. However, the controls had a different physical layout. It has single round sensor window in the center, and the manual specifically notes that this area should be kept free of debris to avoid impeding its operation.
On the WK design, the small round hole on the climate controls makes it look like the sensor is pointing straight out of the dash. Whereas, if there were sensors aimed at the driver and passenger, you’d expect there to be obviously two of them, and that they’d be pointing at a clear angle towards each seating position. I could be wrong, and the sensor we see on the WK could have two separate elements each with a certain viewing angle, but I’d have to tear one down to be sure. Sadly, I couldn’t get my hands on a WK climate control unit prior to publication.
It seems that the system fell out of favor with Jeep in time, as strange features often do. When the WK2 model arrived in 2011, the manual failed to mention anything about infrared sensors, unlike previous generations. However, there’s a chance it does still have a thermopile sensor—the little round nubbin in the middle of the fan speed control looks like it could maybe be serving that purpose.
So why would Jeep abandon this innovative feature? The most likely reason is simplicity and cost. Buying an off-the-shelf interior temperature sensor and doing what every other automaker was doing was probably cheaper. Directly sampling the occupant’s surface temperature does sound nifty, it’s true, but it probably didn’t make much difference to how the climate control really worked in practice. Regular systems from other automakers seemed to satisfy customers just fine, and I’ve never heard anyone crowing that their Jeep understood them on a deeper, more personal level.
I’m always a big fan of weirdness in automobiles. I love that someone at Jeep had this totally bonkers idea of using thermopiles to sense people’s heat instead of just measuring the internal air temperature with a thermistor. Even more so, I love that the rest of the company ran with it. It sounds like something straight out of a 1980s Mercedes S-Class, but nope—it was good old Jeep doing it in the late ’90s.
Here’s to the rich world of automobiles, and everything they teach us about science and engineering. I can’t wait to find the next bit of weird vehicular ephemera, and you bet I’ll find a way to tie it to a 1980s action movie, too.
Image credits: Jeep, eBay, S-Twins, Predator (1987) via screenshot, NASA, Reduction Revolution, element 14
This is common in Dodge as well. Had it in my Magnum and Chargers.
*Me, getting too hot, staring at my thermopile window, waiting for AC* DO IT! DO IT NOW! WHAT ARE YOU WAITING FOR???
This is interesting and might have addressed one of my big pet peeves with auto climate control, which is that I want very different behavior when I get in the car dripping with sweat from a bike ride in the summer versus when I get in the car freezing cold after a long time outside on a winter day (or, for a less obvious example, dripping with sweat because I overdressed for a snowshoe hike on a cold day). Just measuring the cabin temperature doesn’t tell you whether I’m comfortable or not, this might.
Of course, this would all be solved if they’d just bring back temperature knobs so I can tell the car what I want instead of it guessing. Alas.
I feel the same way – the way sun is hitting me makes a huge difference in what I want the HVAC to do. A few days ago I had the car blowing cold air while driving in the sun, turned west and wasn’t in the sun anymore and had to crank the heat up because I was cold. I love my manual 3 knob HVAC, i dont find it a chore to set to what I want, just like I don’t find it a chore to select my own gears – I like to be in control of my vehicle.
At least my income doesn’t put me at risk of buying a car with the HVAC in a screen.
Sun (or better: light) sensors have been used used in automatic AC sistems for a looooong time!
There was a sun sensor in my Renault Clio with auto AC in 2004. That was a small and cheap car even for European tastes and it was far from luxury at that time.
If this technology was put in this car at the time, it was used in bigger and more expensive cars for ages by then 🙂
Yeah, I believe both of my vehicles with auto climate control have sun sensors, but they still don’t work quite right. I end up having to tweak the temp setting when the sun goes down or if I turn so the sun is coming in different windows.
Yes, I totally get this!
My BMW was designed with this in mind. It has a big “MAX COLD” button (actually instead of cold it’s just a snowflake) that you hit when you need to chill the fuck down ASAP
The climate control system in the WK2 Jeep GC is the same one that was used in the first generation LX cars.
https://i.pinimg.com/736x/f3/00/3c/f3003cfe734afa90556cc7bec3364a8f.jpg
Thanks to an aftermarket upgrade my SAAB 96 knows what body temperature is supposed to be, what range of air temperature is generally considered to be the comfort zone, what the freezing temperature of water is, and the fact that 0 is zero:
https://live.staticflickr.com/65535/52892377355_83ceb08ced_c.jpg
As far as I can tell, however, the car itself remains perfectly indifferent to all of this information. In its defense, it’s not clear what it could do in the absence of air conditioning anyway. Or a heater. I probably shouldn’t have removed the heater.
Whoa! I need to know more about this thing
It’s… not that fancy. It’s just a thermometer combined with a cobalt chloride humidity indicator (the pink/blue ring, blue in the photo). It’s not hooked up to anything which is why it makes no difference to the operation of the car.
Better than Volvo’s heartbeat sensor
Did you leave a baby in your car *or* is their a stalker in your backseat?
In our case its the dogs who set off the alarm – you have to hit a button to see the heartbeat thing
I feel like next you’ll be telling us that Sunbeam Alpines had an innovative seat positioning system that actually would allow a vengeful muscleman and a miscast comedian’s daughter to fit comfortably?
I did not understand the reference, what am I, Captain America?
I like you Lewin. That’s why I’m going to kill you last.
(note to autopian overlords: this is empathically not a threat against our beloved Australian, it’s just a killer quote from an Austrian in a Lewin-spec movie. I know if David read this w/o the note, he might get worried)
I, on the other hand, got that reference.
The older I get, the more I enjoy Growth Arnold stuff (compared to Peak Arnold like Predator or Total Recall) like it and Raw Deal. So silly, fairly low budget, and he plays it all straight – no winks/nods – still.
Wait!? I just assumed most cars read interior temperature this way. Although I have never felt like I get great temperature control in my WJ. I also feel like it has the worlds loudest blower fan. I don’t know how they engineered something that can simultaneously wail and move such little air.
Counterpoint: it may just be faulty.
That could be the case. I might have to do some digging into this as we approach the summer.
nope! most cars don’t read your temperature with an infrared sensor, they do it this way:
https://www.theautopian.com/what-are-those-weird-three-little-slots-on-your-dash-for/
Fascinating. Thanks for the deep dives, this is the kind of detailed information I love from the Autopian.
Sounds like an extremely expensive body thermometer.
“Doctor, can you squeeze me in today? My car said I’m running a fever.”
I’m curious how well this worked if someone was wearing a big, bulky jacket.
My thoughts exactly. I’m sure that’s part of the reason it disappeared. Maybe it only read faces, but I bet it would get confused when the jacket was blue and the face was red (in the thermal image).
The further from the thermopile, the greater area that it’s reading (and effectively averaging) over. I suspect for most people the thermopile was probably getting a vague torso reading, and yes – I think it would be thrown off by a shiny thick jacket that could be quite cool vs. the wearer’s body temp inside
But, if it leaks oil, can it be killed? According to David Tracy probably not, hopefully it could make it to the choppa.
Ugh, I own a wj with this system. It seems to do a great job at regulating temperature, but it’s hateful in that it will almost always at some point turn on the AC during the drive without you noticing even when it’s in the 40s, 50s, etc outside. If you’re like me and hate needlessly running the compressor when it isn’t needed, it drives you bonkers having to manually turn it off when you finally notice the LED has illuminated on the AC button. It will then stay off the rest of your trip, but it will re-enable at some random point the next time you’re driving. I hate it. That and the auto-temp system has a 100% fail rate of doors in the hvac case breaking, necessitating a dash pull.
Pretty sure the WJ didn’t come with the IR sensors. I’ve had both a ZJ and WJ with dual climate controls. And, yeah, I had to pull the whole dash out of the WJ a couple of times.
WJ definitely did come with the IR sensors on the automatic climate control system, but the sensor is not located where the image in this article says it is. The IR sensor on the WJ is located in the little circle between the two temp control knobs. The dark gray panel at the top of the control panel is where the selected temperature is displayed. I know this because I was working for DaimlerChrysler as a technical training instructor when the WJ was in production. The WJ version of the system did cause some complaints, too: people often did not feel comfortable at what they thought was a reasonable temperature setting of 68-72 degrees F. You may have needed to set it at 63 degrees or 77 degrees (for example) in order to feel comfortable, which some people just could not understand. If I recall correctly, Chrysler eventually came up with a revised calibration so that the temperature displayed on the control panel looked more reasonable to most people. My 2008 Grand Caravan also has an IR sensor climate control system, but with 3 sensors in order to control the rear zone as well. I’ve owned it since new, and it seems to work fine. The thing about the bulky jacket is true in my experience: I find that the system skews “too warm” if I drive the car with a heavy jacket on, and I need to set the comfort temp to a very low value (in the low 60’s) in order to stay comfortable.
Thank you for the correction – I’ll fix this.
I love learning about old technology that was so advanced and clever, but got phased out for whatever unknown reason. This sounds like something I’d love to see in a new LC500. Imagine, if you will, a luxury GT convertible, where it’s nearly impossible to maintain or measure a specific cabin temperature due to the roof’s abbsence. Here, this infrared tech could enable smart climate control to strategically use the LC500’s MANY vents to keep the driver’s body at an optimal temperature without any guesswork as to how much warm/cold air it’s losing or how hard the sun is beating on the occupant’s brow.
I’ve got an even better idea for the luxury trucks that we all loved discussing this week: A moisture sensor in the seat that detects how heavily the user’s crack is sweating from
climbing into the second-story cabinhauling bricks and automatically cranks the A/C up until the aforementioned crack is as dry as James May’s delivery. (but seriously I’d love cooled seats with a crack-moisture-sensor in any car)IR is also very good at capturing the wicked soul of satanic dogs, like seen on the picture above
OK, but the WK2 pic you have up HAS the IR sensor, it’s just now in the center of the Fan knob. That’s what that shiny circle in the middle is.
Mopar isn’t he only one to use this style sensor for their auto temp control. Ford has been switching to using these, mounted in the windshield, facing the interior, since about 2020.
Yeah, bit of a letdown with the details on this article. The headline says “one generation“, but if the WJ, WK, and WK2 have had it — that’s three generations of Grand Cherokees. The photo of the WJ’s HVAC control panel points to the window for the digital display, but I believe that’s incorrect — the infrared sensor is that oval between the temperature dials.
And you’re right, Chrysler (or its supplier) isn’t the only one using this kind of sensor — even my old F56 Mini Cooper had an IR lens on the HVAC panel, along with the F/G-series BMWs using similar parts.
I love these articles that shine some light on the technical stuff that nobody really cares about, but a little more accuracy would be nice.
Had a 2006 Chrysler Pacifica that had this same thermopile setup. Didn’t seem to work any better than regular climate control. It also had those odd Chrysler “Auto-Hi” and “Auto-Lo” settings, which kind of defeats the point of an “Auto” setting.
If you want accurate body temps, you need to insert a thermometer into the nose and down the esophagus, and another into the rectum. I am sure customers would pay extra for the latter.
Some customers, not all.
“What brings you to the ER today?”
“Temperature sensor in my car broke off.”
“Shouldn’t that be an issue for your mechanic?”
“The car’s already in the shop, but the mechanic wasn’t willing to fish the sensor out.”
I love that they didn’t use this needlessly complicated system because they had to do it, but because they wanted to try it out. This is the kind of end user testing that is ok in cars. If it fails, nobody dies. At worst the subjects wind up with goosebumps or swamp ass.
Some OEM’s still use them: https://www.audiworld.com/forums/q5-sq5-mkii-discussion-218/what-little-dot-drivers-seat-heater-button-3065373/
What? No.
I don’t want an engineer to guess at how cold I wanna be through some IR magic. I wanna crank that and have my nips freeze off.
Set desired body temperature to hypothermic. Problem solved!
(To be clear, I want this feature, along with the ability to have it attempt to make me hypothermic.)
Brilliant. What we really need is an environmental nipple sensor! The settings range from Florida (warm and flat) to Himalayas (cold and peaky).
Does one just clamp the sensor in place?
Handheld
I love reading about some of the seriously weird ways automakers tried to solve issues! Thanks!