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Car Parts

Feb 2023

Each time you get into a car, you interact with feats of electrical and mechanical engineering that have been continuously refined over the past 100 years. Today, there are almost 300 million cars in the United States, and automotive manufacturers are constantly pushing the envelope to make transportation more sustainable, easier to use, and safer. Cars are so much more than our way of getting from point A to point B; they’re woven into the fabric of our lives and are filled with complexity—both visible and hidden. 

To understand the hidden side of this complexity, we used our industrial CT scanner to see inside a few of the most essential and familiar car parts. Let’s dive in.

Want to go deeper on CT for automotive applications? Join us for an interactive walkthrough on March 7.

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TOYOTA, 2015-2017

The airbag is the more common name for the Supplemental Restraint System (SRS)—supplemental because it’s intended to support seatbelts in keeping passengers safe. In the event of a crash, they need to slow down a passenger’s forward motion as evenly and as quickly as possible. If the car’s computer senses sudden deceleration (usually the equivalent of hitting a brick wall at 10 to 15 mph), it activates a chain of events in the blink of an eye.

The vinyl panel on the front of the airbag unit is designed to break apart instantly when the airbag expands, without creating stray debris that could injure the driver. There’s an indented break line running across this airbag’s front cover.

The airbag itself is folded into two neat coils, tightly packed above and below this line. It’s coated with cornstarch or talcum powder to keep it pliable and ready to unfurl at all times.

In this view, we’ve adjusted the opacity to show only metal components. There’s a big metal cylinder in the center of the airbag assembly. Now we'll see what's inside...

When the car’s computer detects a crash, it sends current through an igniter that heats up this inflator cylinder filled with pellets of sodium azide, a solid chemical propellant similar to rocket fuel. The sodium azide burns rapidly and releases harmless nitrogen gas to inflate the airbag in less than one-twentieth of a second. The bag is fully inflated for only one-tenth of a second and almost completely deflated by three-tenths of a second after the initial impact.
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Fuel cap

STANT, 2006

The fuel cap is much more than just the gateway to your gas tank. A defective one can trigger your check engine light and even cause you to fail a state vehicle inspection. The fuel cap serves a dual purpose: it prevents contamination of your fuel and protects the atmosphere by preventing smog-forming volatile organic compounds (VOCs) from leaking out of your tank. When fuel starts evaporating on a hot day, a cap in good working order helps the vehicle’s evaporative emissions canister capture vapors to be consumed later by the engine when needed.

Who doesn’t love the satisfying click the fuel cap makes when you twist it shut? This torque limiting feature lets you know that the o-ring has been sealed and prevents you from overtightening, making it easy to open back up the next time you refuel. Denser than the outer plastic, a series of tabs with raised edges run along a ring of grooves and catch when the cap has been sufficiently tightened.

But the real point of the fuel cap is to secure the opening to your vehicle’s gas tank. This cap comes equipped with a ring lipped on the inner and outer edges to create a strong seal when driven down by a screw-like component.

However well-engineered the torque limiting feature and sealing mechanisms may be, a plastic part like this one can still have hidden vulnerabilities, visible only to a CT scanner. This one happens to have some air bubbles that got stuck in its molten plastic during the injection molding process, resulting in a phenomenon known as porosity. A part with high porosity has less material integrity and could end up failing prematurely.

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Combination switch


Windshield wipers, headlights, and hazard lights are important safety systems in any car. Drivers want controls that are easily accessible, intuitive, and reliable. Automakers aim to achieve that while also producing controls that are inexpensive to manufacture and install during vehicle assembly. As one of the car’s primary tactile interfaces, a combination switch has to be robust enough to survive tens of thousands of cycles.

Starting at the end of the switch, we can see a few springs and ball bearings inside the assembly. These provide tactile feedback and hold controls at discrete positions corresponding to different windshield wiper speeds as well as the on/off state of the cruise control. In contrast, the windshield wiper fluid dispenser switch features a push-and-return functionality that requires constant engagement.

Putting your turn signal on gives you instant tactile and audible feedback so that you can keep your eyes on the road. You feel and hear the latch click, and it stays switched until you or the steering wheel’s movement tells it that the turn is complete.

The housing at the base of the switch contains a complex assembly of latches and springs that generate this familiar sequence and turn a flick of your finger into a group of blinking lights on the outside of your car.
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Engine piston

GM, 2013-2020

An internal combustion engine converts thermal energy released by burning fuel into mechanical work to propel the car. Your car’s engine has multiple cylinders—typically four, six, or eight, each with a piston. Contrary to popular belief, unless something goes wrong, the combustion reaction in a gasoline engine is not actually an explosion. A turbulent flame that travels outward from the spark plugs toward the cylinder's wall releases heat, raising the pressure inside the cylinder. The piston is a moving wall in the combustion chamber and transmits force from a violent chemical reaction—much hotter than the piston’s melting temperature—to the crankshaft via the connecting rod. This particular piston has been engineered to improve power, increase efficiency, and reduce unwanted emissions. 

This piston has three rings, each with a distinct role. The topmost ring seals the combustion chamber and prevents leakage beyond what’s needed for oil transport. The middle scraper ring scrapes excess oil off the cylinder wall as the piston travels down. And the bottom oil control ring regulates the amount of oil on the wall to lubricate the piston’s journey up and down.

To allow excess oil to drain away, the control ring groove has three tiny holes leading back to the oil reservoir.

On the interior of the piston, there’s a cooling loop that runs around the interior circumference of the piston. The engine injects oil into that ring from below, and although the oil is hot enough to boil water, it’s cool enough to lower the piston’s temperature and prevent engine damage.

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