On many cars, the accelerator pedal motion is communicated via the throttle cable, which is mechanically connected to the throttle linkages, which, in turn, rotate the throttle plate. The largest piece inside the throttle body is the throttle plate, which is a butterfly valve that regulates the airflow. Often, an engine coolant line also runs through it in order for the engine to draw intake air at a certain temperature (the engine's current coolant temperature, which the ECU senses through the relevant sensor) and therefore with a known density. The throttle body is usually located between the air filter box and the intake manifold, and it is usually attached to, or near, the mass airflow sensor. In fuel injected engines, the throttle body is the part of the air intake system that controls the amount of air flowing into the engine, in response to driver accelerator pedal input in the main. The components of a typical throttle body Some modern internal combustion engines do not use a traditional throttle, instead relying on their variable intake valve timing system to regulate the airflow into the cylinders, although the end result is the same, albeit with less pumping losses. It controls the engine power output, which may or may not reflect in a change of RPM, depending on the propeller installation (fixed-pitch or constant speed). In a reciprocating engine aircraft, the throttle control is usually a hand-operated lever or knob. An exception to this generalization is newer diesel engines meeting stricter emissions standards, where such a valve is used to generate intake manifold vacuum, thereby allowing the introduction of exhaust gas (see EGR) to lower combustion temperatures and thereby minimize NOx production. Because diesel engines do not need to control air volumes, they usually lack a butterfly valve in the intake tract. The power output of a diesel engine is controlled by regulating the quantity of fuel that is injected into the cylinder. When the throttle is partially closed, a manifold vacuum develops as the intake drops below ambient pressure. When a throttle is wide open, the intake manifold is usually at ambient atmospheric pressure. In a carbureted engine, it is found in the carburetor. In a fuel-injected engine, the throttle valve is placed on the entrance of the intake manifold, or housed in the throttle body. The throttle on a gasoline engine is typically a butterfly valve. This means that the operator does not have direct control over the flow of fuel and air the Engine Control Unit (ECU) can achieve better control in order to reduce emissions, maximize performance and adjust the engine idle to make a cold engine warm up faster or to account for eventual additional engine loads such as running air conditioning compressors in order to avoid engine stalls. Modern engines of both types (gas and diesel) are commonly drive-by-wire systems where sensors monitor the driver controls and in response a computerized system controls the flow of fuel and air. The further the pedal is pushed, the wider the throttle valve opens. This arm is usually directly linked to the accelerator cable, and operates in accordance with the driver, who hits it. The butterfly valve of the throttle is operated by means of an arm piece, loaded by a spring. Historically, the throttle pedal or lever acts via a direct mechanical linkage. The throttle of a diesel, when present, regulates the air flow into the engine. In a gasoline direct injection engine, the throttle regulates the amount of air allowed to enter the engine. For a gasoline engine, the throttle most commonly regulates the amount of air and fuel allowed to enter the engine. In a motor vehicle the control used by the driver to regulate power is sometimes called the throttle, accelerator, or gas pedal. In an internal combustion engine, the throttle is a means of controlling an engine's power by regulating the amount of fuel or air entering the engine. A cross-section view of a butterfly valve
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