A car engine basically has thousands of mini explosions happening inside of it, is has parts moving very fast and generating tons of heat, and experiences extreme temperature fluctuations on a daily basis. Yet it is the part that usually dies last in a car.
How do they make them last so long and why are we unable to make other parts of the car as long lasting, such as tires and brakes?
In: 638
Do not specifically to the question of why the engine lasts so long, but why tires and brakes specifically DONT last long. It’s because they MUST wear.
So in order to stop your car, your brake pads rub against your brake rotors. This rub creates friction. More friction results in material lost.
So imagine you have a spinning wood disk. You can either stop the wheel using a piece of wood, that’s smooth, or a piece of wood with sand paper. Which one will stop the wooden wheel faster? The sandpaper. But it wears the wood wheel faster. In essence that’s how brakes work.
Tires are the same principle. Need more grip? Need more friction. More friction = more wear
>why are we unable to make other parts of the car as long lasting
Engine design minimizes friction in order to increase efficiency and reduce wear on the components. Contrary, tyres and brakes are based on friction. Friction creates heat and shreds tiny pieces off material. So, engines promote motion and they need to eliminate friction to do that, but tyres and brakes have the opposite goal: provide stickiness by sacrificing materials.
For example, train wheels are made of metal and they can last for very long. But they don’t care about lateral grip because the tracks provide the turning forces. Car tyres are always a compromise between efficiency and grip. Make them softer, you get more performance. Make them harder, you get more efficiency (due to less friction losses) and they last longer.
There are brakes that will last potentially the life of the car. At least when it comes to brake rotors. However, carbon ceramic rotors cost something like $3,000 -$15,000
All the parts of an engine are designed to reduce friction as much possible. Everything is oiled, everything is machined to very specific tolerances to be smooth and uniform and not stick.
Tires and Brakes are designed to increase friction as much as possible. They are designed to be sticky, for tires to stick to the road to direct the car, for breaks to be able to dissipate the momentum of the car as heat.
Because they are sticky little bits wear away as they are used. So eventually they have to be replaced. The really astonishing thing is how long they actually last.
Most of the answer is oil. There’s a thin film of oil that separates the moving parts of your engine and reduces friction to almost zero. The heat is mostly absorbed by engine coolant (antifreeze), which is then cooled by the radiator.
By contrast, your brakes operate by taking the car’s kinetic energy and turning it into heat. They do that by rubbing two materials together, which naturally causes wear and tear. Some electric vehicles are changing that with regenerative braking, but most brake systems just have to wear out in order to function.
The tires also operate by rubbing on the pavement to make the car start, stop, and turn. There’s no real way to prevent wear on them, because that’s just how they work. If you put a film of oil on your tires, they wouldn’t wear out as fast, but your car wouldn’t be controllable.
The critical moving parts of the engine are oil lubricated and sealed inside the engine.
The oil provides a protective coating against contact with water and oxygen, and more importantly against metal on metal contact.
The purpose of the oil is to prevent solid surfaces from contacting each other, which would have lots of friction, wear, and heat. Heat would accelerate the wear, and the engine would seize. This happens when an engine isn’t properly lubricated.
Tires and brakes serve a much different purpose.
Tires NEED to be outside the vehicle for reasons I hope are rather obvious. That means no protection from weather, UV, or oxygen. That’s one of the reasons tires are black. Black pigments do a better job of blocking UV radiation from damaging the tire.
If we wanted tires and brakes to last longer, we could devise systems that coat them in oil. I’m hoping it’s also obvious why that might be a bad idea. The purpose of the tires and brakes *require* friction. Friction comes with wear and heat and more wear. There’s no way around it.
We can make harder tires that wear slower, but they wouldn’t grip as well.
In addition to friction and wear being part of the design, there are other design factors such as cost.
Brake rotors are chunks of metal that are going to wear away and undergo intense heat cycles. Under normal use, they’re *going to wear*. They’re in quite literally the worst possible environment – close to the road, getting wet, in contact with road salt, and undergoing intense heat cycles. Given that they’re going to be a wear item anyways, cost is a big factor. Cast iron doesn’t stand up well to corrosion and exposure, but it’s cheap and has all the other good properties.
Another reason engines last long is because oil changes are the one piece of maintenance that every car driver knows about. They’re the most frequent, they’re inexpensive, and even easy enough to do at home. Other service is not only more difficult, but it’s simply not required as frequently. As a result, it’s easier to forget about and be overdue on.
Two things: lubrication and engineering.
The parts are made of the correct materials, with the right dimensions and surface finishes. That combined with forced lubrication makes it work.
You’re right, it looks like a miracle that an engine lasts ten minutes, let alone years. That’s just the nature of the materials and the design, they can handle the punishment. It’s taken decades of refinement and billions of dollars to get them as reliable as they are. It takes a lot of really smart people a lot of time to figure these things out.
Here’s a mind-blowing fun fact. An internal combustion engine powered car has about 2,000 parts in its drive train. A comparable electric vehicle as about 20 parts.
Let that sink in.
No oil. No valves. No gears. No fuel injectors. No service and maintenance. No revenue to fix things that break by design. EVs are going to radically transform the automotive industry.
First of all, quick clarification – what happens inside a cylinder are NOT mini explosions, under normal operation, what happens are controlled burns. An explosion is a sudden and violent release of energy; a controlled burn is a fast but gradual release. Mini explosions are called ping and it can be catastrophic.
With regards to high temperatures, yes combusion can reach thousands of degrees, but since they only last for fractions of a seconds this is why parts won’t melt.
As long as your cooling system can transfer the heat out at a fast enough rate that engine can go on living.
Others have given very good answers, so I won’t repeat them here. As far as making stuff like brakes last longer, fiction is your enemy. Metal on metal parts inside an engine run on a thin film of oil, but anywhere where energy conversion happens through friction you are limited to how much longevity that component will achieve.
EDIT: fat fingered my response, fixed some grammar
There have been better longer lasting engine designs that were shelved by the auto industry in favor of cars that break quicker so they can resell more. Toyota is experimenting with new engine types that are a bit closer to the old shelved designs that GM didn’t use.
Latest Answers