Throttle

This article relies largely or entirely on a single source. Relevant discussion may be found on the talk page. Please help improve this article by introducing citations to additional sources. Find sources: "Throttle" – news · newspapers · books · scholar · JSTOR (February 2019)

A throttle is a mechanism by which

is managed by constriction or obstruction.

An engine's power can be increased or decreased by the restriction of inlet gases (by the use of a throttle), but usually decreased. The term throttle has come to refer, informally, to any mechanism by which the power or speed of an engine is regulated, such as a car's accelerator pedal. What is often termed a throttle (in an aviation context) is also called a thrust lever, particularly for jet engine powered aircraft. For a steam locomotive, the valve which controls the steam is known as the regulator.

Internal combustion engines

In an

engine, the throttle regulates only the amount of air allowed to enter the engine. The throttle of a diesel, when present, regulates the air flow into the engine.

Historically, the throttle pedal or lever acts via a direct

mechanical linkage

. The butterfly valve of the throttle is operated by means of an arm piece, loaded by a spring. This arm is usually directly linked to the accelerator cable, and operates in accordance with the driver, who hits it. The further the pedal is pushed, the wider the throttle valve opens.

Modern engines of both types (gas and diesel) are commonly

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.

The throttle on a gasoline engine is typically a

develops as the intake drops below ambient pressure.

The power output of a diesel engine is controlled by regulating the quantity of fuel that is injected into the cylinder. Because diesel engines do not need to control air volumes, they usually lack a butterfly valve in the intake tract. 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.

In a

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 result is the same, albeit with less pumping losses.

Throttle body

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 throttle body is usually located between the

) and therefore with a known density.

The largest piece inside the throttle body is the throttle plate, which is a butterfly valve that regulates the airflow.

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. In cars with electronic throttle control (also known as "drive-by-wire"), an electric actuator controls the throttle linkages and the accelerator pedal connects not to the throttle body, but to a sensor, which outputs a signal proportional to the current pedal position and sends it to the ECU. The ECU then determines the throttle opening based on the accelerator pedal's position and inputs from other engine sensors such as the engine coolant temperature sensor.

When the driver presses on the accelerator pedal, the throttle plate rotates within the throttle body, opening the throttle passage to allow more air into the intake manifold, immediately drawn inside by its vacuum. Usually a mass airflow sensor measures this change and communicates it to the ECU. The ECU then increases the amount of fuel injected by the injectors in order to obtain the required

(TPS) is connected to the shaft of the throttle plate to provide the ECU with information on whether the throttle is in the idle position, wide-open throttle (WOT) position, or somewhere in between these extremes.

Throttle bodies may also contain valves and adjustments to control the minimum airflow during

, the Idle Air Control Valve (IACV), that the ECU uses to control the amount of air that can bypass the main throttle opening to allow the engine to idle when the throttle is closed.

The most basic carbureted engines, such as single cylinder Briggs & Stratton lawn-mower engines, feature a single small throttle plate over a basic carburetor with a single venturi. The throttle is either open or closed (although there is always a small hole or other bypass to allow a small amount of air to flow through so the engine can idle when the throttle is closed), or some intermediate position. Since air velocity is crucial to the functioning of a carburetor, to keep average air velocity up, larger engines require more complex carburetors with multiple small venturis, typically two or four (these venturis are commonly called "barrels"). A typical "2-barrel" carburetor uses a single oval or rectangular throttle plate, and works similarly to a single venturi carburetor, but with two small openings instead of one. A 4-venturi carburetor has two pairs of venturis, each pair regulated by a single oval or rectangular throttle plate. Under normal operation, only one throttle plate (the "primary") opens when the accelerator pedal is pressed, allowing more air into the engine, but keeping overall airflow velocity through the carburetor high (thus improving efficiency). The "secondary" throttle is operated either mechanically when the primary plate is opened past a certain amount, or via engine vacuum, influenced by the position of the accelerator pedal and engine load, allowing for greater air flow into the engine at high RPM and load and better efficiency at low RPM. Multiple 2-venturi or 4-venturi carburetors can be used simultaneously in situations where maximum engine power is of priority.

A throttle body is somewhat analogous to the carburetor in a non-injected engine, although it is important to remember that a throttle body is not the same thing as a throttle, and that carbureted engines have throttles as well. A throttle body simply supplies a convenient place to mount a throttle in the absence of a carburetor venturi. Carburetors are an older technology, which mechanically modulate the amount of air flow (with an internal throttle plate) and combine air and fuel together (venturi). Cars with fuel injection don't need a mechanical device to meter the fuel flow, since that duty is taken over by injectors in the intake pathways (for multipoint fuel injection systems) or cylinders (for direct injection systems) coupled with electronic sensors and computers which precisely calculate how long should a certain injector stay open and therefore how much fuel should be injected by each injection pulse. However, they do still need a throttle to control the airflow into the engine, together with a sensor that detects its current opening angle, so that the correct air/fuel ratio can be met at any RPM and engine load combination. The simplest way to do this is to simply remove the carburetor unit, and bolt a simple unit containing a throttle body and fuel injectors on instead. This is known as single-port injection, also known by different marketing names (such as "throttle-body injection" by General Motors and "central fuel injection" by Ford, among others), and it allows an older engine design to be converted from carburetor to fuel injection without significantly altering the intake manifold design. More complex later designs use intake manifolds, and even cylinder heads, specially designed for the inclusion of injectors.

Multiple throttle bodies

Most fuel injected cars have a single throttle, contained in a throttle body. Vehicles can sometimes employ more than one throttle body, connected by linkages to operate simultaneously, which improves

, can use a separate throttle body for each cylinder, often called "individual throttle bodies" or ITBs. Although rare in production vehicles, these are common equipment on many racing cars and modified street vehicles. This practice harks back to the days when many high performance cars were given one, small, single-venturi carburettor for each cylinder or pair of cylinders (i.e. Weber, SU carburettors), each one with their own small throttle plate inside. In a carburettor, the smaller throttle opening also allowed for more precise and fast carburettor response, as well as better atomization of the fuel when running at low engine speeds.

Other engines

.

Throttling of a

. They are also useful in situations where the airspeed of the vehicle must be limited due to aerodynamic stress in the denser atmosphere at lower levels (e.g. the Space Shuttle). Rockets characteristically become lighter the longer they burn, with the changing ratio of thrust:weight resulting in increasing acceleration, so engines are often throttled (or switched off) to limit acceleration forces towards the end of a stage's burn time if it is carrying sensitive cargo (e.g. humans).

In a jet engine, thrust is controlled by changing the amount of fuel flowing into the combustion chamber, similar to a diesel engine.

Lifespan of the throttle in cars

The lifespan of the throttle is not set since it highly depends on the driving style and specific vehicle. The throttle tends to be quite dirty after 100-150 thousand kilometers, and it is necessary to clean it up. The malfunction of the throttle could be indicated by illuminated EPC warning light.^[2] This is usually the case with modern Volkswagen Group vehicles. Vehicles not equipped with the EPC warning light indicate issues with the throttle by illuminated check engine symbol.

Symptoms of the throttle malfunction could vary from poor idle, decreased engine power, poor mileage, bad acceleration, and so on. The effective way to increase the throttle's lifespan is through regular maintenance and cleaning.^[3]

See also

• Adapted automobile

References

External links