Throttle

To regulate the required output power of petrol engines, the supplied air and fuel flow is regulated. The air flow is controlled by a throttle valve to the intake manifold.

Background

Engines generate a negative pressure during the intake stroke ( first cycle) by the moving piston in the cylinder down. Through this, ambient air is sucked.

Gasoline gasoline engines need an ignitable fuel -air ratio to ever work (see lambda control ). To vary the engine speed and power, can not simply be added to the fuel is less, but the total amount of mixture to be adjusted. Therefore, the amount of fresh air is adjusted by the throttle and dependent on a certain amount of fuel added.

Injection or carburetor put the intake air with the amount of fuel that can be combustible mixture. However, it will be no gaseous mixture but a mixture of fresh air with very finely atomized fuel.

Because the fuel -air mixture is regulated in the crowd, one speaks of a quantitative mixture regulation.

Construction

The throttle valve located in the intake duct between the air filter and the fan-shaped branching intake manifold of the engine. Exceptions are, inter alia, Racing engines and engines (eg BMW M3 ), in which a throttle valve is in sporty production vehicles at each cylinder.

Carburettor engines it is located in the carburetor, fuel-injection engines with the throttle body. There are central injections in which the injection nozzle is located in front of the throttle valve is in multipoint injections usually per cylinder in the intake manifold, a nozzle, that is, after the throttle valve.

The throttle valve is usually only a circular plate which is mounted rotatably on a vertical axis disposed in a cylindrical tube and in the closed state closes the tube. Possible, but not very common are from the circular shape deviating throttle. Furthermore, there are also devices having a plurality of throttle valves. However, this supply not a cylinder, but (like a flap ) is still first the intake tract from which the air to be distributed to the individual cylinders. When an engine is equipped with such units, the number of which is identical with the throttle valve of the cylinder, the units are connected directly with the intake ports of the engine and not passed through a collection tube. Almost all recreational marine engines were and are so constructed. Such a system can also be implemented as a register operation to obtain a more comfortable drive motor.

By pressing the accelerator pedal, the throttle valve is opened. The opening of the flap is done not necessarily directly related to the pedal position. Can be engaged by a control unit active in the opening of the door in particular by the electronic transmission of the accelerator pedal position of the throttle valve. Both the speed of the opening as well as the position of the flap as a function of the pedal position can be influenced. The aim here is to improve the drivability with powerful engines, or to increase the driving comfort for the occupants.

Since the throttle valve completely closes the pipe cross-section in neutral, the engine will die due to lack of air for combustion. Over the years, various systems were used to provide the necessary amount of air for idling the engine. The easiest way was there a mechanical stop which leaves open the flap a piece. Function in a similar idle screws. This seal, an additional bore, the air passes in addition to the throttle valve. Depending on the position of the screw can be doing the engine idle speed adjust. However, these systems require additional means for increasing idling at a cold start. This was achieved by an auxiliary air valve at the Bosch K -Jetronic for example. With the advent of fully electronic fuel injection systems, the amount of air for the idle by a servomotor (so-called idle control or idle control valve) is provided, which can raise and lower active and at any time the idle speed. Modern vehicles with electronic throttle often do not require additional idle controller, throttle valve while also actively controlled by the control unit for idling regulation.

If it exists, the current position of the throttle valve via a throttle valve potentiometer which is attached directly to the throttle valve axis, directed to the engine control unit. This computes the proper fuel injection amount in conjunction with a number of other values. A special position it takes, for example, a Bosch KE -Jetronic. These works - depending on the application - only with a full load switch or with an idle switch that transmits a signal for influencing the engine characteristics map to the controller.

Drives

In "classic" engines, the throttle valve is actuated directly by the accelerator, such as a cable or linkage, in modern electronically controlled engines happens via an electric actuator ( DC motor with gearbox, rarely direct drive without gear or stepper motors ). Languages ​​spoken by E- gas ( electronic accelerator ) or drive-by -wire.

In engines with carburettors or retrofitted gas facilities according to the Venturi principle, the throttle valve is at a location of the suction funnel behind the venturi, where it merges into a cylindrical cross-section. For injection it is in the throttle body.

High performance and racing engines use a throttle valve per cylinder, while engines with a lower power output per liter to make do with a total of a throttle valve.

Valvetronic

Developed by BMW Valvetronic fully variable valve train controls the amount of mixture over the stroke of the intake valves. Thus, the throttling losses of the throttle valve to be avoided and higher efficiencies. The reduced throttling losses may be achieved by a better mixture preparation and thus possible higher internal EGR rate, which is generated by a smaller negative pressure in the cylinder.

Diesel engines

Conventional diesel engines are inherently, because of the different type of mixture preparation, no throttle. In order to still be able to use a vacuum brake booster, vacuum pump must be used.

Modern diesel engines will continue to have a throttle, this however, is only to reduce the shaking when you turn off the engine. In operation, the door is always open. This " butterfly " is referred to as intake manifold.

For diesel engines that drive the reduction of nitrogen oxide in the exhaust gas shares a high exhaust gas recirculation rate, there is also a throttle valve. This will be closed during part load operation partly to reduce the fresh air supply, thus enabling a higher proportion of exhaust gases in the cylinder chamber.

In diesel engines ( and Others VW, BMW) with particulate filters, a throttle valve is installed, which is used for active regeneration of the particulate filter. It is used only during the regeneration phases of the particle filter.

A special feature represented pre-chamber diesel engines from Daimler cars, these possessed a throttle to regulate the vakuumpneumatisch acting diesel injection pump depends on the speed and power the brake booster or the pneumatic central vacuum.