August 2009 listing of the Audi A6L 2.7TDI cars, FAW – Volkswagen Audi brand in the domestic launch a diesel version of the model. The car equipped with 2.7 L V6 turbocharged direct injection diesel engine (Figure 1), advanced technology and manufacturing processes, making this engine power or fuel economy (about one hundred kilometers 6.8 L) and in terms of emissions ( Euro IV on) have performed extremely well. In order to facilitate the majority of maintenance personnel to understand the car, this article will briefly introduce the diesel engine.
FIG 1
A mechanical part
FIG. 2
Audi 2.7TDI diesel engine cylinder is made of GGV-40 (vermicular graphite cast iron), the cylinder center distance of 90 mm. Open crankcase in disposition crankshaft center, (FIG. 2) by a ladder frame fixed to the crankshaft in the crankcase. A crankcase vertically separated, as well as to strengthen the rigidity of the crankcase lower body is made of an aluminum material. Engine ultraviolet – honing processing method of laser irradiation, so that the cylinder surface finer and improve the friction properties of the running surface, and thus reducing oil consumption.
1. Crank Mechanism (FIG. 3)
Figure 3
The engine crankshaft forged from a quenched and tempered steel, using four main bearing supported on the main bearing support, breaking linkage bearing material and tris (lower) connected to the crankshaft by sputtering bearing (upper), four main bearings form a bearing frame, can enhance the overall engine strength. Bags using a valveless piston box (FIG. 4), the combustion chamber is located in the middle of the piston, oil injected into the cooling passage through the annular piston. Valveless bag box-like structure can reduce harmful gas emissions while using the inner annular oil passage, the lower the operating temperature of the piston.
Figure 4
The cylinder head 2.
In order to reduce noise, the engine uses separate head cover (FIG. 5) , between the camshaft and the drive spur gear employed. Crankshaft through a chain drive intake camshaft, the intakeA camshaft driven by the exhaust camshaft spur gear.
Figure 5
the engine combustion noise by various measures have been much reduced, but the mechanical gear noise becomes relatively apparent, to overcome this further noise and improve the smooth running of the engine. The engine uses a simple and effective structure.
Figure 6
As (FIG. 6), a spur gear is straight-toothed employed (usually helical gear), a spur gear width shrink fitting portions secured together with the camshaft, there are six projections on the front side of the inclined surface, the narrow portion of the spur gear (spur gear motion) wide with six inner cylindrical protrusion bevel gear corresponding to the recess. A determined axial force is generated by the disc spring, the coned disc spring so that the narrow long pinion gear with respect to the radial and axial movement occurs, the shim for adjusting an axial force. Using the slope to help enable short pinion gear with respect to the width of an axial force (or axial motion) is converted into a radial force (or radial movement), so that the two gear portions are staggered to achieve the backlash compensation, 2 gear teeth operation is achieved without a gap.
an exhaust camshaft driven by an intake camshaft via a spur gear, four valves per cylinder to ensure optimum charging efficiency, the roller with a hydraulic clearance compensation rocker friction-free drive can reduce fuel consumption and exhaust emissions, and noise reduction. The exhaust camshaft high pressure molding, to reduce its mass about 3.5 kg.
If a leak occurs in the area of the copper ring of the injector, the high pressure leak (16.5 MPa) the gas can escape from the combustion chamber through an exhaust passage. The upper portion of the cylinder head exhaust passage of the exhaust manifold. This measure prevents the impeller side of the combustion chamber to produce high pressure into the crankcase ventilation through the supercharger, turbocharger resulting in seal damage or dysfunction crankcase.
3. The chain drive
Figure 7
The engine uses a drive in the form of a chain drive (FIG. 7), a single row chain – a bushing chain (chain uniaxial), disposed on the transmission side. Each chain drive TotalTo have their own hydraulic, spring-loaded with a chain tensioner and the chain guide. Chain is improved, i.e., the wrap angle becomes large sprocket, the chain guide member is reduced, thereby reducing the driving force of the chain (to reduce the internal friction losses).
Second, the electronic control part
An air supply system 1.
The air supply system of a diesel engine of the Audi 2.7TDI by the air cleaner, brake booster, boost in the cold, low-pressure pump, EGR cooler, an engine speed sensor, camshaft position sensor, a coolant temperature sensor, air quality sensor, diesel injection system control unit, the throttle body, an exhaust gas recirculation solenoid valve, the boost pressure limiting solenoid valve, the EGR cooler switching valve, and an intake flap motor inlet flap motor 2 (Figure 8).
Figure 8
(1) a throttle body
is a stepless adjustment of the throttle valve, it is possible to realize a high EGR rate. Engine stall throttle valve closed, to prevent the engine vibration. And intake throttle flap opening speed when cut to compensate for checking the air quality sensor and an oxygen sensor.
(2) vortex flap (FIG. 9)
Figure 9
vortex flap, and by the throttle valve the pressure from the functional viewpoint of the structure of the motor is the same. Flap vortex action to provide a sufficient amount of inflation at different loads and speed conditions. To reduce emissions, the air flow vortex in the cylinder and combustion processes have to be an exact match, this may be achieved by continuous variation of the angle vortex flap. When the vortex flap closed, air enters only through the tangential inlet cylinder may be a low load, form a strong swirling motion at low speed, to produce a good effect combustion in the combustion chamber, but also produces fewer emissions. When the swirl flap is opened, air is drawn into the cylinder through the opening to the airway and cutting scroll airways, so that a large amount of air enters the combustion chamber to produce a good effect of a pneumatic cylinder. The engine control unit constantly receiving the feedback signal of the current position of the flap, the flap if a fault occurs, the adjustment is no longer achieved. It should be noted that the vortex flap can not be opened and closed manually, this will causeIts damage.
2. The fuel supply system
10
composition of the fuel supply system of an engine as Audi 2.7TDI (FIG. 10) shows. Previous difference is employed a secondary pump, which makes the system high voltage peaks of up to 180 MPa.
(1) high pressure pump
11
CP4.2 new high-pressure pump can produce a pressure of about 180 MPa, and a high pressure provided by the fuel pump fuel pump G6 and electric auxiliary pump. The high pressure pump 2 pumps the piston by a cam shaft with dual cams alternately driven (FIG. 11). The new high-pressure pump advantages are: the use of roller pusher can reduce fuel consumption; tape drive (high pressure pump) uniform load; can greatly improve the efficiency by adjusting the intake side of the fuel metering valve.
(2) fuel metering valve N290 (inside the high-pressure pump)
The fuel metering valve action N290 is to determine the amount of fuel delivered to the high-pressure pump, further need to determine how much oil is compressed, by changing the duty cycle of the control pressure and the piston position changes. When N290 is not energized, the solenoid valve opens, at this time the minimum cross-section leading to the high pressure pump, a solenoid valve may be adjusted by a section of a fuel load and speed. When N290 is energized, the solenoid valve is closed, the control pressure increases so that the control piston moves in a direction to increase the cross section leading to the high pressure pump. Since the engine is canceled mechanical gear pump, and therefore directly returned to the tank from the fuel spill solenoid valve.
(3) The fuel pressure sensor
sensor measures the actual pressure of the fuel pressure within the high pressure system, and conversion to the engine control unit is a voltage signal. The core of the fuel pressure sensor is a steel membrane, the membrane is attached to the strain gage steel, as long as the pressure acting on one side of a steel membrane, the deformation resistance of the strain changes its resistance. The engine control unit provides a voltage of 5 V for the sensor, when the pressure increases, the strain resistance is reduced, i.e., the signal voltage will rise. The engine control unit may calculate an appropriate value according to the actual pressure signal voltage.
(4) common rail injector
12
The precise control of the injector, the jet engine Audi 2.7TDI oil actuator module (FIG. 12) which utilizes the piezoelectric effect. The piezoelectric effect is, if the piezoelectric crystal element is compressed or stretched, will produce an alternating voltage, whereas, if the voltage applied to the piezoelectric element, the crystal structure may be stretched. Pressure of the liquid may be generated by performing the deformation of the longitudinal direction of the element module and transmitted to the switching valve.
Audi 2.7TDI engine each working stroke of the injector switch valve may be opened five times, all carried out under the same injection pressure, the injection point and the injection quantity variation are elastic and not with the camshaft position bind to each other, according to the pre-injection and spray characteristics (emissions and noise) can be realized after many times. The highest speed in the transmission, from 3 300 r / min starting, the preliminary ejection will be closed. Purpose is to spray the particulate filter regeneration, if not the particle filter is installed no post spray.
(5) rail orifice
a pressure wave generated when closing the injector, the pressure wave transmitted to the fuel rail, and then reflected back from the rail. This would injector needle and needle seat have a greater damage. To attenuate the pressure wave, in front of the engine mounting a fuel injector orifice, the needle valve to reduce impact on the valve seat. An orifice in the rail is mechanically pushed.
(6) of the glow plug
13
The engine control unit controlling the heating time by the duty control unit, and calculates heating mode, heating the starting time and duration (FIG. 13). Heating mode comprising: before heating, the heating startup preparation, start heating and after heating.
The heating time control means by pulse-width signal voltage of 3 ~ 7 V to individually driving each glow plug, the maximum pre-heating time is 2 S. If the glow plug is damaged, stored fault codes.
3. The exhaust gas recirculation system
the exhaust gas recirculation system is mainly composed of an exhaust gas recirculation cooler, and the cooled exhaust gas temperature sensor bypass flap 4 (G98) (Figure 14).
14
(1) a bypass flap
When the engine cold state, the bypass valve is opened, then exhaust gases directly into the cylinder, the engine rapid warming. When the engine enters a normal operating temperature, the bypass valve is closed, then the exhaust gas recirculation cooler V400 pump starts working. V400 radiator outlet cooling liquid introduced into the cooler, the exhaust gas is further cooled, so that, to further improve the combustion chamber and a pneumatic effect of reducing NOx emissions. When
satisfies the following condition, the bypass flap opens, the exhaust gas without water cooling.
① engine temperature is below 55 ℃.
② tank outlet temperature below 18 ℃ or above 70 ℃.
③ the engine is idling.
④ After the temperature of the exhaust gas after the exhaust gas recirculation cooler below 120 ℃.
⑤ ambient temperature is below 16 ℃.
In addition, design for safety, if the vacuum plugging, i.e. closing the bypass flap (water-cooling) under the return action of the spring.
(2) λ (excess air ratio) adjustment
Audi 2.7TDI engine with wideband oxygen sensor with an adjustable heater ([lambda] sensor). Always work diesel engine, able to work in a more lean mixture state of the engine in the oxygen-rich state, the data is adjusted by the amount of exhaust gas recirculation λ sensor, and correcting emissions, exhaust gas recirculation rate can increase until the smoke limit, Thus the engine operates at a high exhaust gas recirculation rate, which makes the engine without a particle filter, the exhaust can reach Europe ⅳ standard. At the same time, also as the [lambda] sensor signals based on the reliability of inspection of the air flow meter by using a [lambda] value calculating module calculates the air mass, and then compared with the value of the air flow meter and corrected.
(Lee Min-DPRK)