Once upon a time, the design of a car engine seemed much clearer. An old carburetor had a float chamber, jets, a diffuser, and a mechanical connection to the accelerator pedal. Turn the throttle — the engine received more air, the vacuum pulled in more gasoline, and the engine started to develop more power.
With an injected engine, the same part has not disappeared. The throttle valve is still in the intake tract, but its role has changed. The accelerator pedal no longer directly meters fuel: it determines how much air the engine should receive, and the electronic control system calculates and supplies the necessary amount of gasoline.
This difference well explains how a modern gasoline engine regulates power and why it simultaneously needs a throttle, injectors, sensors, and an electronic control unit.
What the accelerator pedal actually regulates
The throttle valve is a round plate installed in the intake tract before the intake manifold. When the pedal is pressed, it opens wider, increasing the amount of air that can enter the engine.
Air itself does not replace fuel. It is necessary for gasoline combustion and acts as an oxidizer. The more air enters the cylinders, the more fuel can be burned with it, and the more energy can be obtained from the working process.
Therefore, the principle can be presented very simply: the driver actually sets the desired amount of air for the engine, and the control system then decides how much gasoline needs to be added. This is similar to a bonfire that is given more oxygen: the flame becomes more intense, but at the same time, the amount of fuel must also increase.
In a carbureted system, both processes were mechanically linked. A modern injector has separated these functions: the throttle regulates airflow, and the injectors meter fuel.
How the carburetor gave way to the injector
In a carburetor, fuel mixture preparation occurred without complex electronics. Air passed through a diffuser, creating a vacuum in that area, and thanks to it, gasoline flowed from the float chamber.
The result was a fairly simple device: a change in airflow automatically affected the amount of fuel entering the engine. The wider the throttle opened, the more air passed through the system, and the more gasoline was drawn into the flow.
But this scheme had limitations. A carburetor cannot account for all engine operating parameters with the same precision as an electronic system. As a result, the mixture composition changed depending on the mode, temperature, and other conditions.
Electronic injection allowed for much more precise fuel metering. Gasoline now enters the engine through injectors, and their operation is controlled by an electronic unit.
An injector is an electromagnetic valve. The control unit opens it for a certain time, allowing a calculated amount of fuel to enter the engine.
How the control unit knows how much gasoline is needed
The electronics do not choose the injector opening duration randomly. Data from numerous sensors are used for calculation, constantly informing the control unit about what is happening with the engine.
One of the key parameters is the amount of incoming air. A mass airflow sensor can be used to determine this. By receiving information about the airflow, the electronic unit calculates the necessary amount of fuel.
But even this is not enough for maximally precise mixture control. The result needs to be checked after fuel combustion, and here another crucial element of the system appears — the lambda probe.
How the engine checks its own mixture
The lambda probe is installed in the exhaust system and monitors the oxygen content in the exhaust gases. Based on this indicator, the electronic unit receives information about how well the mixture composition corresponds to the required mode.
If there is a lot of oxygen in the exhaust, the system determines that the mixture was lean, meaning there was insufficient fuel relative to air. In this case, the control unit increases fuel supply.
If there is little oxygen, this indicates a rich mixture. Then the amount of injected gasoline is reduced.
This results in a closed feedback system:
- sensors determine engine operating parameters;
- the control unit calculates the necessary amount of fuel;
- injectors supply the calculated dose;
- the lambda probe checks the result by the exhaust composition;
- the electronics correct the next operating cycle.
This principle is called lambda control. The system constantly receives feedback and adjusts the mixture composition depending on current conditions.
Why not make the accelerator pedal control fuel
At first glance, it seems logical to connect the accelerator pedal directly to the injectors. The driver pressed harder — the engine received more gasoline. But such a scheme would be much less convenient for a modern car.
The main reason is that the engine constantly has to maintain the correct air-fuel ratio. If you simply increase the fuel supply without controlling the airflow, the mixture will quickly cease to correspond to the required mode.
Therefore, it is much more convenient to use the throttle as a means of controlling the amount of air, and to meter fuel separately and automatically. Electronics can take into account many parameters at once and change the injection duration much more accurately than a simple mechanical connection.
There is another reason. A modern engine operates in far more than one mode. Idling, acceleration, constant speed driving, operation under load, turbocharging, exhaust gas recirculation — all these require different operating parameters for the power unit.
As a result, electronic control allows for simultaneously considering many factors, rather than linking the pedal position to a single mechanical parameter.
What has changed compared to the carburetor
In a carbureted engine, the throttle valve position directly affected the amount of air and, through vacuum, the fuel supply. The system was predominantly mechanical and therefore structurally simpler.
In an injected engine, an electronic intermediary appeared between pressing the pedal and the amount of fuel. It receives information about the engine's condition, calculates the required dose, and controls the injectors.
This allowed for significantly more precise control of the mixture composition. And the driver does not have to independently account for engine temperature, load, exhaust composition, or other parameters.
What this scheme provides
Electronic injection combined with feedback from the lambda probe provides several important results.
First — fuel efficiency. Electronics can maintain the necessary mixture composition depending on the engine's operating mode and not supply excess fuel where it is not needed.
Second — reduction of harmful emissions. Control of the mixture composition allows for more effective use of the catalytic converter and maintenance of its necessary operating conditions.
Third — the ability to control engine power and modes. Depending on the situation, the control unit changes injection parameters: during acceleration, conditions differ from constant speed driving, and under load, the engine operates differently than at idle.
Therefore, the modern accelerator pedal has actually become a means of setting the engine's operating mode, rather than a direct mechanical tap for fuel supply. The driver tells the engine how much power it needs by changing the throttle opening request, and then the electronic system itself determines how much air and fuel are necessary to achieve the desired result.
This is why the familiar throttle valve from the old carburetor has been preserved in the injected engine, but its role in the overall system has become completely different. Previously, it was part of the mixture preparation mechanism, and now it is one of the elements of a complex electronic engine control system.