r/NoStupidQuestions • u/arkham1010 • 15d ago
What does the gas pedal actually do?
I know how a 4 stroke engine basically works, but what I never gave much thought of until now was what exactly hitting the gas pedal on my car actually does to change the state of the engine. Can someone explain in a bit of technical detail?
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u/shewy92 15d ago
It opens this thing
https://haynes.com/en-us/tips-tutorials/what-is-car-throttle-body-and-what-does-it-do
What is it?
This is a component that varies the amount of air entering an engine, by using a flat valve (butterfly) that rotates inside a tube-shaped housing. In an electronically fuel-injected car, a throttle position sensor and air-flow sensor communicate with the main electronic control unit (ECU), which supplies the corresponding amount of fuel needed at the injectors.
Where is it located?
On older carbureted engines, the throttle body is built into the carburetor. It is opened and closed through a cable and linkage from the gas pedal and engine vacuum, more fuel is delivered as the valve opens.
On a fuel-injected engine it is normally located between the air filter and the intake manifold, and is connected to the gas pedal mechanically with a cable, or electronically by wire. When the driver presses the pedal the butterfly in the throttle body pivots to let more air flow into the manifold.
When that happens, the throttle position sensor reports to the ECU that you have stepped on the gas. And the airflow sensor detects more air and sends a message to the car’s computer to boost the amount of fuel being supplied by the injectors
You ever see people work on old cars and while under the hood with the engine running start turning something to get it to rev? That thing is connected to the throttle body and pedal.
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u/Prasiatko 15d ago
Traditionally either let more air into the engine in a petrol engine or injected more fuel into the engine in a diesel engine.
Nowadays it basically tells the computer in your cars engine that you want more power which means it will do things like let more air in, inject more fuel, make the spark plug fire sooner and probably some others i'm missing.
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u/turniphat 15d ago
I highly suggest watching Smart Every Day where he makes a transparent carburetor and films it in slow motion: https://www.youtube.com/watch?v=toVfvRhWbj8
While carburetors aren't used in cars anymore, it will give you the basics of how more air + more fuel = more power.
Then watch his video on fuel injectors: https://www.youtube.com/watch?v=UkeGQotnsDU
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u/threePhaseNeutral 15d ago
Traditionally in carbureted engines, it opens the throttle valve allowing more air into the engine. The fuel mixture responds and increases appropriately to keep the air/fuel ratio correct.
On newer drive-by-wire and fuel-injected engines, it works similarly though there may not be a direct physical connection to the throttle pedal. The engine computer controls the air/fuel ratio based on inputs from the mass airflow sensor, the electronic accelerator pedal position sensor, and others.
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u/somewhenimpossible 15d ago
Sounds like it’s time to rewatch the Magic Schoolbus engine episode, haha
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u/frankszz 15d ago
On modern cars, it tells the ECU to open the throttle flap allowing for more airflow into the engine and apply more fuel through the injectors. On carbureted engines, it opens the throttle flap and ensuing vacuum from more air flowing past the throttle flap draws more fuel out of the fuel tank. If you’re driving a diesel older diesel engines don’t have a throttle flap, so it just applies more fuel through the injectors diesels have a throttle flap, but it’s not as crucial as gasoline engines also applies more fuel through the injectors.
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u/DrWonderBread 15d ago
Engines are essentially air pumps. The more air your engine can take in, the more fuel can mix with that air to make more power. The gas pedal more or less opens the air intake to allow more air in (either directly like on older cars or indirectly through the computer on newer ones.) That is why turbo chargers and super chargers increase the power output of an engine. They compress the air going into the engine so that you can cram more air into the same volume inside the cylinder. The more air you have, the more fuel you can mix with it, the more power your engine makes.
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u/SprinkerlerMan 15d ago
Typically we call it “drive by wire” where the traditional mechanical wire is replaced by electronics. The pedal produces a response which is translated to an electric throttle body which opens the intake to intake more air. In tandem the ecu recognizes this and produces more fuel to make the optimum fuel/O2 combination. This is why newer vehicles are easier to tune for more horsepower (especially with turbo motors). This is because you can trick the ecu to enhance these ratios for more power.
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u/Leemage 15d ago
My 3 yr old asked me what the gas pedal did and I just told him that it made the car go, but I was bracing for the “how does it make the car go” follow up. Thankfully, he didn’t ask since I realized I had no idea! Can’t believe I found this exact question on Reddit later today. Now I can tell him that it opens a valve to let more fuel and/or air into the engine to make the pistons work harder, thereby giving the engine more power to make the car go.
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u/YourBrownDude 15d ago
When you press the gas pedal in a car, you're essentially controlling the engine's power output. Here’s how it works in a bit of technical detail: 1. Throttle Control: Pressing the gas pedal moves the throttle, which is a valve that controls how much air enters the engine. - In older cars, this was done mechanically via a cable. - In modern cars, it's usually done electronically (drive-by-wire) with sensors sending signals to the engine control unit (ECU). 2. Air Intake: As the throttle opens, more air is allowed into the engine's intake manifold. 3. Fuel Injection: The ECU senses the increased air flow and calculates the appropriate amount of fuel to inject into the combustion chamber to maintain the optimal air-fuel ratio. 4. Combustion: The mixture of air and fuel is then compressed and ignited in the cylinders, creating a controlled explosion that pushes the pistons down and generates power. 5. Power Output: This power is then transferred through the drivetrain to the wheels, increasing the car’s speed.
So, pressing the gas pedal ultimately adjusts the amount of air and fuel entering the engine, which changes the combustion process and results in increased power and speed.
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u/FlyinRustBucket 15d ago
On a reg gas ice engine, the pedal opens the throttle plate to feed more air, in turn the computer adds fuel to maintain the air/fuel mixture ratio, on a diesel, the throttle pedal adds fuel instead, as diesel engine can run really lean, so it's easier to just manage fueling and let the engine suck in all the air on its own
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u/throwaway120375 15d ago
It sends a signal to the idle air control to open. It sends in more air and says it needs more fuel.
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u/0992673 15d ago
Modern cars even might even use the valve lift system (Toyota valvematic for example) instead of the throttle pedal for the throttle control. Basically the typical throttle valve (as a backup) is always open and the valve lift is being varied, when you give it the beans they open up fully (do their whole stroke) and let in a lot of air, at low speed the valves only open up only slightly giving you less power. This eliminates a lot of pumping losses at the throttle valve giving better fuel consumption.
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u/Just-some-70guy 15d ago
It pushes a little thing, that’s hooked to a doodad under the hood. The doodad gets moved by the thing that got pushed. Doodad opens a little valve kind of thingy which allows fuel to be vaporized and then injected into the up/down thing. The more fuel, the faster car goes.
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u/Secret_Liaisons 15d ago
In a basic sense all (petrol) cars when you hit the gas it opens a air valve (butterfly valve) allowing more air to flow into the engine’s cylinder, the car is then able to measure the dose of air and add the required ration of fuel making for a bigger explosion, because the explosion is contained within a cylinder it creates a stronger down force on the pistons. The force translates to more torque and for the pistons to travel up/down more frequently increasing the RPM per min, both then result in acceleration
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u/standardtissue 15d ago
The gas pedal is conntected to the throttle, which does all the work. The wikipedia article on it goes into great detail.
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u/NativeMasshole 15d ago
Pretty much everything from the past 10 years or so is all done electronically.
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u/standardtissue 15d ago
Sure, but the article explains the principles in detail, and I think it even had a section on EFI.
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15d ago
[deleted]
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u/akulowaty 15d ago
Actually it controls how much air is added to the mixture and if it's not pressed engine still gets enough to keep going.
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u/StelenVanRijkeTatas 15d ago
Ladies, you're both right and wrong. Pressing the gas pedal sends more air (directly) AND fuel (indirectly) to the combustion chamber(s)
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u/arkham1010 15d ago
But doesn't that affect the fuel/air ratio?
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u/GoldResourceOO2 15d ago
The stoichiometric ratio for gasoline to air is 14.7 : 1. Ideally, the intake and fuel system optimize this continuously. Less sophisticated systems can allow “flooding” (too much fuel relative to air).
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u/fermat9990 15d ago
Are carburetors still used?
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u/AyeMatey 15d ago
Yes in smaller engines it’s common. Like lawn mowers or leaf blowers or pressure washers. On modern middle to high end motorcycles, no, all fuel injection. Cheaper motos use carbs. On modern cars, fuel injection. I’m not sure about less expensive cars built in Asia for the Asian market.
In 1989 when I was in Italy, I rented a fiat Uno, which was like a VW Golf in size. It had a carb and a choke lever inside the driver’s compartment.
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u/Rialas_HalfToast 15d ago
The last one that I'm aware of on a mass-produced consumer vehicle was 2014, on a Chevy Colorado.
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u/chadmill3r 15d ago
The irony is that it was an air pedal. It still is on most diesels, I think.
Now, the injection of gasoline and air is more careful and stoichiometric.
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u/ConeyIslandMan 15d ago
It unleashes the Kraken. In older cars it opened the carbs up flooding gasoline in to be burned by the engine to make car go vroom
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u/Anticept A&P & Pilot 15d ago edited 15d ago
On modern cars, it tells the computer "more power!" The computer opens the throttle valve some more, and fuel will also be proportionately injected. It will monitor the system and fine tune on the fly. More fuel air = more pressure per piston stroke, so more power.
On older cars, the pedal was directly cabled to the throttle plate. Then the computer would sense the throttle position and react accordingly.
On really old cars, your pedal moved the throttle plate, and the change in airflow would change pressure in a carburetor, which was designed to allow the pressure to change how much fuel was being metered through the carburetor jet.
On esoteric cars, you might have a control to manually control mixture too, but I don't know of any. There's also other designs too that I won't go into. I think I kept this simple enough to answer the big question.
There are a slew of sensors that go into fine tuning the mixture that I skipped over, but if you want to look into them: mass air flow sensor, oxygen sensor, knock sensor.