5.2.2. General information about system of injection "Common Rail"
Arrangement of elements of system of injection of "Common Rail" on the diesel 4-cylinder engine
Basic element of system of injection of fuel is the fuel pump which is installed on all diesel engines. Injection pressure to 1350 bars is necessary for increase in power up to 160 kW at the cylinder.
Many systems of injection of diesel fuel, in particular, of direct injection (Dl) are in recent years developed. At the same time the task not only increases in engine capacity, but also reduction of fuel consumption and noise and decrease in toxicity of the fulfilled gases was pursued. In comparison with earlier used systems the system of injection of Bosch "Common Rail" fuel (accumulator fuel system) for direct injection of fuel (Dl) provides higher flexibility at adaptation to a power supply system of the diesel engine, for example:
– an extensive scope (for automobile and commercial cars with output powers of 30 kW on the cylinder, as well as for trucks of big loading capacity, locomotives and vessels with output powers of 200 kW on the cylinder;
– high pressures of injection of fuel to 1400 bars;
– changes of injection at start of the engine;
– possibility of control, main and late injection;
– provides compliance of pressure of injection to an operating mode of the engine.
Functioning of system of injection
The distinctive characteristic of system with the general pipeline "Common Rail" (accumulator fuel system) consists in division of the knot creating pressure and fuel injection knot.
The basis of system is made by the tank (accumulator). Pressure of injection does not depend on amount of injectable fuel and frequency of rotation of a bent shaft of the engine. The fuel reserve under pressure is in the accumulator of high pressure "Common Rail" and is ready to injection. The amount of injectable fuel is defined upon the demand of the driver, and pressure of injection calculates the control unit (ECU) on the basis of information from various sensors. ECU transmits the excitement signal to the nozzle solenoid meaning the beginning of supply of fuel to precisely determined moment. The amount of injectable fuel is defined by the period of opening of a spray and pressure in system. ECU and sensors of system of injection of fuel include:
– sensor of frequency of rotation of a bent shaft;
– sensor of position of the camshaft;
– sensor of provision of a pedal of an accelerator;
– pressure sensor in system with the general pipeline;
– sensor of temperature of cooling liquid;
– air consumption measuring instrument.
On the basis of information from above-mentioned sensors and the requirement of the driver (the provision of a pedal of an accelerator) ECU defines the instant operational characteristic of the engine and car in general. The block processes the signals developed by sensors and transferred on communication lines and on the basis of this information operates system of injection in the mode of the opened or closed contour. Frequency of rotation of a bent shaft of the engine is measured by the sensor of frequency of rotation of a bent shaft, and the sensor of position of the camshaft defines the sequence of injection of fuel (phase length). The electric signal from a potentiometer of provision of a pedal of an accelerator transmits ECU a signal of extent of pressing by the driver an accelerator pedal.
The measuring instrument of a consumption of air transmits ECU a signal with data on an instant stream of air that allows to calculate process of full combustion of fuel with the minimum content of harmful substances in the fulfilled gases. As the engine is equipped with a turbocompressor and adjustment of increase in pressure of pressurization, the additional sensor also measures this pressure. At a low external temperature and the cold ECU engine defines the moment of injection and other parameters corresponding to the particular operational treatment. Depending on the car and increase in requirements to safety and comfort for information transfer of ECU additional sensors can be used. In the drawing the example of the diesel 4-cylinder engine with system of injection of Common Rail fuel is shown.
The shown arrangement of elements does not correspond to their real arrangement.
The main functions of system consist in ensuring injection of the required amount of fuel at strictly certain moment and under necessary pressure. It ensures not only smooth functioning of the diesel engine, but also economic consumption of fuel.
Additional functions in the closed contour and function of management without feedback serve in an operating mode for reduction of toxicity of the fulfilled gases and fuel consumption and are used for improvement of safety, comfort and convenience.
For example: recirculation of the fulfilled gases (EGR), adjustment of pressure of pressurization of air, gear shifting, an electronic immobilizer, etc. The CAN system provides data exchange with other systems of the car. At diagnostic check of the car it is possible to take the data which are in a reserve of data of system.