Injector in EFI system

The injector is a key part of the gasoline EFI. It controls the final injection of the fuel. If something goes wrong, the engine will work abnormally or stop working immediately.

If the injector is installed in the position of the original carburetor and combined with the throttle valve, this form is called single-point electronic fuel injection. Its advantages are low cost and simple maintenance. The disadvantage is that the distance between the injection point and each cylinder is short. Unequal resulting in uneven fuel distribution, the cold engine starts to easily adhere to the wall of the intake manifold.

If the injector is installed on the intake pipe of each cylinder, this form is called a multi-point electronic fuel injection device, which is the most popular form of gasoline EFI engine. Its advantage is that each cylinder has its own injector. The injector is as close as possible to the intake valve, avoiding the disadvantage of single-point electronic fuel injection. The disadvantage is high cost and complicated maintenance.

At present, most automotive engines use multi-point EFI, and a small number of economic vehicles use single-point EFI. If the old carburetor engine was converted to an electronic fuel injection, a single point of electrospray was used.

The general automobile electronically controlled gasoline injection device consists of three parts: the fuel supply part, the gas supply part, and the control part. The fuel supply consists of fuel tank, gasoline pump, fuel filter, pressure regulator and fuel injector. The petrol pump takes gasoline out of the fuel tank and filters the impurities through the petrol filter. The pressure is increased by the pressure regulator to make the petrol pressure higher than that of the petrol pump. The negative pressure of the intake manifold is sent to the injectors of each cylinder via the pipeline. The injector is equivalent to a switch and the control switch is the ECU (Electronic Control Unit).

The injector is controlled by an electromagnetic coil, and the on-off of the solenoid current is controlled by the ECU. The ECU performs processing based on the signal fed back by the sensor and sends an electrical signal to the injector, which determines the time for the injector to open and to inject gasoline. This interval is called the "pulse width" of the injector. The electromagnetic coil of the injector generates a magnetic field after being energized. Under the influence of the magnetic field, the plunger is sucked up against the spring force, and the valve body is taken out of the valve seat. Gasoline is ejected from the nozzle opening under pressure; when the electromagnetic coil is powered off, the magnetic field disappears. The plunger moves down under the action of the spring force, and the valve body closes the nozzle opening against the valve seat, so that the gasoline will not get out. The valve body is divided into two types, a ball valve and a needle valve. In order to ensure the accuracy of the injection, the ball valve or the needle valve and the valve seat require high machining accuracy, and the lift of the valve body is minute, only about 0.1 mm. Due to the action of the pressure regulator, the injector is in front of the high pressure oil circuit and the rear is the low pressure of the intake manifold. The pressure difference forms a negative pressure, ensuring that the fuel forms a mist spray near the intake valve.

Although the multi-point electronic fuel injection system has one injector per cylinder, the injection amount of the injector is determined by the pulse width, that is, the injection amount depends on the injector opening time. But specific to different fuel injection forms, and not all the same, there is a general multi-ignition oil injection system (MPI) and sequential fuel injection system (SFI) points.

In the MPI system, the injectors are divided into several groups and the same group of injectors are opened at the same time. For example, the injectors of a 4-cylinder machine are divided into two groups, each with two injectors. These two groups of injectors inject fuel in turn, and the engine crankshaft has a group of injectors for each revolution. The injectors of this system are connected in parallel. The ECU sends the same signal to all injectors in the same group. The injectors are turned on and off at the same time. The programming is simple and the electronic circuit is simplified, but it is different for the engine. The lack of random changes in operating conditions will result in the retention of oil and gas in the intake manifold.

Each injector in the SFI system is directly connected to the ECU and controlled separately. It can be precisely done that the injector is opened just before the intake valve opens, and the fuel injector can be adjusted instantaneously between two injection periods. The features to adapt to changes in different operating conditions. Therefore, SFI is the most accurate and ideal method for multi-point electronic fuel injection systems. Many car engines currently use this method.

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