Cars are complex, and automakers regularly add even more features. But what’s the story behind them? From wipers that know when it’s raining; to tires that tell you when they’re low, we explain the mysteries behind modern vehicles
How does the day-night mirror work?
Okay, but how about exterior auto-dimming mirrors?
How does the gas pump know to shut off when your tank’s full?
Is there an underground tank for each grade of gasoline?
Am I getting exactly the grade I ordered?
Does the pump hose on the gauge indicate the filler location?
Why don’t all auto-down windows also have auto-up?
How do my tires know they’re low on air?
How do 360-degree camera displays work?
How does adaptive cruise control keep me away from other vehicles?
How do automatic high-beam headlamps dim themselves?
How do HID high-beam headlamps work?
How do rain-sensing wipers know it’s raining?
How does my climate control adjust the heat or cold?
What's in the Vehicle Identification Number (VIN)?
It was obvious on older vehicles: you flipped the mirror up or down to reduce the glare of headlights behind you. But a modern mirror doesn’t move at all when you push the tab on it—or does it?
What you’re actually looking at in today’s cars is a piece of glass, with the mirror in behind. The mirrored surface still moves, but it’s inside the housing. When you flip it into the “night” position, the surface points up toward the vehicle’s ceiling, and headlights reflect in the glass and so look dimmer.
Some vehicles have auto-dimming interior or exterior mirrors, which automatically adjust to headlights from behind. Most of these systems use two sensors, one pointed forward and the other rearward, to measure ambient light and detect glare from headlights. The mirror contains two pieces of glass sandwiching electrochromic gel. When the sensors detect headlights, electric current is sent to the gel, which darkens in response.
Take a look at the nozzle next time you’re at the gas station. Near the end of it, you’ll see a little hole that’s connected to a very small pipe inside the nozzle. Once you start pumping gas, air is drawn through the tube. When the fuel in the tank rises to the level of the hole, the air stops flowing. This in turn triggers the nozzle to stop the flow of fuel.
Not quite. You’ll see three grades on the pump, but at many stations, there are only two fuel tanks buried below. One contains regular 87-octane fuel, while the other is filled with 91-octane. If you buy either of those, the gas pump draws from the appropriate tank. But if you select mid-grade 89-octane fuel, the pump pulls an equal amount from each tank and then blends them before dispensing the final mixture, which it continuously monitors to be sure the ratio is correct.
That depends on what the last driver bought. The pump hose is always full, and it contains about 500 millilitres of fuel. Your first half-litre will be whatever was in it from the last purchase, and when you hang up the nozzle, the next driver will get a half-litre of whatever you selected.
This one makes the rounds of the Internet on a regular basis: that if your gas gauge doesn’t have an arrow pointing to the side your gas filler is on, the position of the hose on the fuel pump icon will tell you if it’s on the right or left. However, it’s a myth. There’s always a 50-50 chance it’s right, and if yours is, that’s only a coincidence.
You’ll find auto-down windows on many vehicles, which go all the way down after you’ve pushed the button once, without having to hold it. But not all of them are auto-up, which may seem odd: it’s just reversing the motor, right? It all has to do with safety. Auto-down isn’t an issue, but an auto-up window has to have a sensor in case it’s closing when someone has an arm or other body part in the way. That adds to the cost and complexity, which is why the two directions aren’t always bundled together.
Tire pressure monitoring systems, or TPMS, are found on most new cars these days (they’re mandatory in the U.S., but not in Canada). They warn when a tire drops below approximately 25 percent of its recommended pressure, and they can tell because there are pressure sensors inside the tires. Most of them are attached to the valve stem, like this one, but you may also find them strapped to the inside of the rim. Some early systems didn’t use sensors, relying instead on the anti-lock brake and electronic stability control systems to indicate a tire that was spinning at a different rate.
While rearview cameras show you what’s behind as you’re backing up, 360-degree surround systems give you a “bird’s-eye” view from overhead. The vehicle not only has a camera on the back, but also on the grille, along with wide-angle cameras on the mirrors. A computer stitches the four images together and superimposes them around an image of the vehicle in the middle, giving the illusion of a single camera hovering over the roof and looking down.
These systems measure the distance between the vehicle and the car in front, and adjust the brake or throttle accordingly. It’s most common for these systems to use radar to detect vehicles ahead and determine how far away they are, but some use sonar. There’s also LIDAR, a laser-based system that, at least for now, is primarily used in prototype autonomous cars.
Found on a number of models, and increasingly on lower-cost ones, automatic high-beam headlamps dim themselves when they sense headlights or taillights of a vehicle up ahead, and then go back to full brightness once the road ahead is clear. Depending on the system, it uses a camera or a sensor, usually mounted near the top of the windshield, to monitor ambient light, street lamps, and oncoming headlamps. It then determines the light intensity and how fast you’re moving toward it, and dips the high-beams as necessary. It sounds futuristic, but General Motors actually introduced a similar system, called the Autronic Eye, in 1952!
High-intensity discharge (HID) headlamps, also known as xenon lamps, light up when an electronic arc travels through the xenon gas inside them. But since it takes a few seconds to reach their full output, they’re not really suited for the immediate on-off of high-beam headlamps. On some vehicles, the HID lights act solely as low-beams, while halogen bulbs are used for high-beams. But some pricier vehicles have “bi-xenon” headlamps: a shield covers a portion of the light pattern for low-beam, and flips up to allow full intensity for high-beams. Listen closely, and you’ll hear a little click from the lamps as the shield flips up or down.
Rain-sensing wipers not only come on when it’s raining, but they speed up or slow down in response to the intensity. The system uses an optical sensor mounted on the inside of the windshield that projects infrared light onto the glass. A dry windshield reflects most of the light back to the sensor, indicating that the wipers aren’t necessary. Raindrops alter the reflection, telling the system to turn the wipers on and to increase the wiper speed when more drops increasingly break up the reflective pattern.
It’s all done with doors! Hot air is warmed by the heater core, which uses hot coolant from the engine, while cold air comes from the air conditioning system. A fan blows that into the cabin, while a temperature blend door that’s controlled by a thermostat opens or closes to direct just the right amount of warmed or chilled air into the cabin. If you’ve set the temperature below what’s available, another door opens and vents the excess to the outdoors.
The 17-digit number starts off with the country of manufacture: 1 for the U.S., 2 for Canada, 3 for Mexico, J for Japan, W for Germany, etc. Various letters and numbers also identify the brand, the model, engine size, the factory where it was built and its sequence on the assembly line, and the model year. There’s also a series of numbers, unique to each vehicle, which help to identify it for such purposes as recalls or theft recovery.