SUMMARY: Diesel injection systems in history page 2 Generality page 3 Hydraulic layout page 4 Electrical layout page 5 High pressure pump pages 6-7 Rail page 8 Pressure control (hints) page 9 Injector page 10 Solenoid injectors pages 11-12 Piezo injectors (indirect drive) page 13 Piezo injectors (direct drive) page 14 ECU - injection strategy (hints) pages 15-16-17 Diesel injection systems in history In-line pumps Distributor pump VE Mechanical injection Distributor pump VP Pump-injector Electronic injection Common Rail 2 Generality The system common rail (CR) is now the fuel system of the fuel mostly used in compression ignition engines Major advantages over predecessors: Pressure Injection independent of the rotation regime of the engine Flexible control of injection pressure (pressure range 300 2200bar) Flexible and accurate control of the injection quantity Possibility of several injections per cycle depending on the operating condition Flexibility in the timing of the injections of TDC engine Alfa Romeo 156 1.9JDT the first car equipped with the common rail system (1997) 3 Hydraulic layout Pressure regulatorr Pressure sensor High pressure pump Rail High pressure circuit Low pressure circuit Filter Electro injector Tank Booster pump Main components of the hydraulic layout: Low-pressure pump (usually installed inside the tank) Fuel-filter Pompa high pressure Rail Pressure sensor installed on the rail Flow regulator (FMV) or pressure regulator (PCV) Injectors 4 Electrical layout Pressure regulator Electronic control unit High pressure pump Rail Pressure sensor Feed pump The engine control unit (ECU) has as its main function is to manage the system injection: Monitors the pressure inside the rail (injection pressure) Controls the flow regulator or the pressure regulator Controls the injectors managing the duration, the number and timing of the injections 5 High pressure pump The high-pressure pump receives the fuel from the low pressure circuit and sends it to the rail at pressures are in the range 300 to 2200 bar depending on the operating condition of the engine and on which the system is installed. It is generally composed of a shaft with eccentric (1) realizes that by rotating the suction stroke and the delivery of a number of pumping elements (3). The pump is lubricated by the fuel itself and on it you can be installed of devices for adjusting the delivery pressure. 6 High pressure pump Pump CP1 with integrated pressure regulator to the outlet (PCV) Pump CP4 with flow regulator integrated suction (FMV) CR 1° generation A pressure regulating valve electronics (PCV) is installed on the high pressure side of the pump. It is controlled by the control unit to adjust the injection pressure by downloading or less fuel from the high pressure circuit. CR 2° generation A flow control valve electronics (FMV) is installed on the low pressure side of the pump. It is controlled by the control unit to regulate the inflow of fuel to the pump in relation to the injection pressure required. 7 Rail Pressure sensor Pressure regulator The rail is an accumulator fuel to which are connected the high-pressure pump and the injectors. On it is installed a pressure sensor that the control unit uses to monitor the injection pressure (PRAIL). It may also be present a pressure regulator (PCV), if it is not already present on the pump. Is there any configuration of the system where the regulator on rail is coupled to the flow control (FMV) installed on the pump. 8 Pressure control (hints) How realize the conditions of the mapping for a given operating condition? The control unit must be able to adjust the pressure inside the rail to obtain the value required by mapping (PRAIL). Reading of the pressure inside the rail by means of the integrated pressure sensor. Control the pressure in the rail by adjusting the flow rate sucked by the high pressure pump. Comparison of the detected pressure with the required value in the corresponding map for a given operating condition. Control the pressure in the rail by recirculating or less part of the fuel in the tank. 9 Injector The injectors are classified according to the type of drive according to the type of hydraulic layout. In the solenoid-operated injector, Solenoid injectors an electromagnetic force, generated in a solenoid crossed by Operate: current, is exploited to actuate the injector. In the piezo injectors utilizes the inverse Piezoelectric injectors piezoelectric effect, that is the capacity of the piezoelectric material to deform when subjected to an electric voltage. The electric drive is not directly connected to the pin, there is Injectors indirectly actuated interposed a pilot valve. Injectors direct actuated Hydraulic layout: The electric drive is directly connected to the needle through a mechanical linkage. 10 Solenoid injectors Injectors are indirectly actuated, the solenoid controls a pilot valve the opening of which causes an imbalance of the forces acting on the needle such as to allow the lifting. Pilot valve A B 1) 2) 3) 4) 5) 6) 7) 8) 9) 10) 11) injector at rest injector operating Fuel recirculation Electrical connector Solenoid Input fuel (by rail) Ball valve Hole A Hole Z Control chamber Control rod High pressure line Pin 11 Solenoid injectors Because of the complex internal hydraulic circuit and the presence of mechanical parts with a not negligible inertia, the injection is not synchronized with the electrical command supplied to the injector from the engine control. 12 Piezo injectors (indirect drive) The piezoelectric actuator, the extension of which is amplified hydraulically, it acts on a pilot valve which opens to download the environment upstream of the needle, which then will rise due to the effect of the pressure of the fuel in the delivery chamber. The layout of the valve is such that the leaking fuel are much lower than those of the injectors solenoid seen previously. Fuel recirculation Piezoelectric actuator Input fuel Hydraulic amplifier Pilot valve Pulverizer Pilot valve Hole A Control chamber Bypass Hole Z Pin 13 Piezo injectors (direct drive) The piezoelectric actuator is directly connected to the pin by means of a mechanical linkage, then NOT is no pilot valve. Advantages: 1) The dynamics of the injector is improved; 2) It is not necessary to recirculate fuel to actuate the injector(efficiency ). Disadvantages: 1) The piezoelectric actuator must be larger in order to generate the forces necessary to raise the needle; 2) It is necessary to control the injectors with very high voltages (≈ 160 volts) that may require a special shielding of the electric circuit of the injection system 14 ECU - injection strategy (hints) Mapping unit The basic strategy of injection include: Reading throttle position (load); Reading of the speed of rotation of the engine (rpm); Reading maps of control: 1. Depending on the load and the speed of rotation is chosen, the related map, the amount of fuel to be injected to the cycle (mb) and the injection pressure (PRAIL); 2. Based on the amount to be injected (sc) and the injection pressure (PRAIL) is chosen, from another map, the duration of the electrical command to be supplied to the injectors (ET). 15 ECU - injection strategy (hints) After choosing injection pressure and duration of the electrical control to the injectors, the control unit must choosing a number of other parameters with the aim to maintain the engine in top possible conditions, minimizing (to the extent possible) the emission of pollutants and fuel consumption. In addition the unit constantly monitors the conversion efficiency of the devices of aftertreatment of the exhaust gas (oxidizing catalyst, DPF, DeNOx) using, when appropriate, strategies regeneration. 16 ECU - injection strategy (hints) 17 Rabotti Srl Technological partnership
