【導(dǎo)讀】天津工程師范學(xué)院20xx屆本科生畢業(yè)設(shè)計(jì)。設(shè)計(jì)的目的和意義。隨著汽車保有量的增加，同時(shí)也帶來了能源

　　

【正文】 CU about how far the driver has depressed the pedal, in other words about his (her) torque requirement. The airmass meter provides the ECU with data on the instantaneous air flow in order that bustion can be adapted so as to ply with the emissions regulations. Insofar as the engine is equipped with an exhaustgas turbocharger and boostpressure control, the boostpressure sensor also measures boostpressure. At low outside temperatures and with the engine cold, the ECU applies the data from the coolanttemperature and airtemperature sensors to adapt the set point values for start of injection, post injection, and further parameters to the particular operating conditions. Depending upon the vehicle in question, in order to ply with the increasing demands for safety and fort, further sensors and data lines provide inputs to the ECU. Basic functions The basic functions control the injection of the diesel fuel at the right moment, in the right quantities, and with the correct injection pressure. They ensure that the diesel engine not only runs smoothly, but also economically. 天津工程師范學(xué)院 20xx 屆本科生畢業(yè)設(shè)計(jì) 30 Auxiliary functions Auxiliary closed and openloop control functions serve to improve both the exhaustgas emission and fuelconsumption figures, or are used for increasing safety, fort, and convenience. Examples here are ExhaustGas Recirculation (EGR), boostpressure control, vehiclespeed control (cruise control), and electronic immobilizer etc. The CAN bus system permits the exchange of data with other electronic systems in the vehicle (. ABS and electronic transmissionshift control). During vehicle inspection in the workshop, a diagnosis interface permits evaluation of the stored system data. Injection characteristics Conventional injection characteristics With conventional injection systems, using distributor and inline injection pumps, fuel injection today prises only the main injection phasewithout pilot and postinjection phases. On the solenoidvalvecontrolled distributor pump though, developments are progressing towards the introduction of a pilotinjection phase. In conventional systems, pressure generation and the provision of the injected fuel quantity are coupled to each other by a cam and a pump plunger. This has the following effects upon the injection characteristics: The injection pressure increases together with increasing speed and injected fuel quantity, During the actual injection process, the injection pressure increases and then drops again to the nozzle closing pressure at the end of injection, The consequences are as follows: Smaller injected fuel quantities are injected with lower pressures than larger injected fuel quantities, The peak pressure is more than double that of the mean injection pressure, and In line with the requirements for efficient bustion, the rateofdischarge curve is practically triangular. The peak pressure is decisive for the mechanical loading of a fuelinjection pump’s ponents and drive. On conventional fuelinjection systems it is decisive for the quality of the A/F mixture formation in the bustion chamber. Injection characteristics with Common Rail Compared to conventional injection characteristics, the following demands are made upon an ideal injection characteristic: 天津工程師范學(xué)院 20xx 屆本科生畢業(yè)設(shè)計(jì) 31 Independently of each other, injected fuel quantity and injection pressure should be definable for each and every engine operating condition (provides more freedom for achieving ideal A/F mixture formation) At the beginning of the injection process, the injected fuel quantity should be as low as possible (that is, during the ignition lag between the start of injection and the start of bustion). These requirements are plied with in the Common Rail accumulator injection system with its pilot and maininjection features. The Common Rail system is a modular system, and essentially the following ponents are responsible for the injection characteristic: Solenoidvalvecontrolled injectors which are screwed into the cylinder head, Pressure accumulator (rail), and Highpressure pump. The following ponents also required in order to operate the system: Electronic control unit(ECU), Crankshaftspeed sensor, and Camshaftspeed sensor (phase sensor). For passengercar systems, a radialpiston pump is used as the highpressure pump for pressure generation. Pressure is generated independently of the injection process. The speed of the highpressure pump is coupled directly to the engine speed with a nonvariable transmission ratio. In parison with conventional injection systems, the fact that delivery is practically uniform, means that not only is the Common Rail highpressure pump much smaller, but also that its drive is not subject to such high pressureloading peaks. The injectors are connected to the rail by short lines and, essentially, prise a nozzle, and a solenoid valve which is energized by the ECU to switch it on (start of injection). When the solenoid valve is switched off (deenergized) injection ceases. Presuming constant pressure, the injected fuel quantity is directly proportional to the length o f time the solenoid valve is energized. It is pletely independent of the engine or pump speed (timecontrolled fuel injection). The required highspeed solenoid switching is achieved by using high voltages and currents. This means that the solenoidvalve triggering stage in the ECU must be designed accordingly. 天津工程師范學(xué)院 20xx 屆本科生畢業(yè)設(shè)計(jì) 32 The start of injection is controlled by the angletime control system of the EDC (Electronic Diesel Control). This uses a sensor on the crankshaft to register engine speed, and a sensor on the camshaft for phase detection (working cycle). Pilot injection Pilot injection can be advanced by up to 90 crankshaf