The design of engine port is jointly developed by CFD and port laboratory. The macro-flow field in the cylinder of a four-valve gasoline engine with dual intake ports is mainly tumble. In order to reduce the intake resistance and form a strong tumble flow in the cylinder, a bifurcated intake port is adopted. The intake port has only one inlet on the cylinder head, and it is divided into two forks before entering the combustion chamber, which lead to two intake valves respectively, which can improve its flow coefficient and tumble speed in the cylinder at the same time. For the roof-shaped combustion chamber, the intake valve and exhaust valve are symmetrically arranged on both sides, and the airflow entering the cylinder from the air inlet forms a turnover motion while sinking and rotating around the horizontal axis. The average tumble ratio of 477F inlet is higher than 0.65.
The perfect air distribution further reduces the cyclic variation COV when the engine is idling, and at the same time, the HC and CO in the original emission are also greatly reduced, which reduces the cost of tail gas aftertreatment.
The position of the ignition nozzle of the spark plug is biased to the exhaust side, which is conducive to discharging the exhaust gas near the spark plug to release ignition energy, effectively shortening the flame propagation distance, reducing heat loss, accelerating the flame area expansion rate and combustion rate, and greatly improving the violence resistance of the engine.
The design compression ratio of the engine 10.5 and the excellent intake flow field make the 477F engine burn fully and the speed is extremely fast.
Advanced combustion system and optimized cam profile, valve timing and intake pipe design greatly improve the charging efficiency of the engine at low speed, reaching the first torque peak at 3000 rpm and the second torque peak at 5000 rpm, with excellent torque output characteristics. Excellent torque characteristics and optimal matching of gearbox make the whole vehicle not only adapt to low-speed and complex urban road conditions, but also meet the requirements of high-speed power output of expressway. In the early stage of engine development, 477F firmly took the design route of fully reducing friction.
The SOHC four-valve engine used in the 477F is half of the camshaft of the popular DOHC four-valve valve mechanism, so the SOHC engine has the advantages of high reliability, high mechanical efficiency and low cost. The experimental comparison shows that the FMEP camshaft of 477F engine is 0.03Bar smaller than the typical double overhead camshaft. Its rocker arm adopts embedded hydraulic tappet structure, which is also completely designed and developed independently, creating a precedent for independent development of hydraulic rocker arm in China and breaking the embarrassing situation that hydraulic rocker arm can only be designed and developed by foreign suppliers.
Compared with the traditional rocker arm valve train, the 477F adopts a more advanced roller rocker arm (the friction pair between cam and rocker arm is roller contact). The splashing oil in the oil pool of cylinder head brings good lubrication to the roller, reduces friction resistance and increases mechanical efficiency. Single overhead camshaft (SOHC) manufactured by QT700 drives both intake valve and exhaust valve, with compact structure, low cost and small resistance moment. Even at the rated speed of 6 150RPM, the rotating torque of the whole valve train is only 20Nm.
The route to fully reduce friction resistance is also reflected in the in-depth study of friction pairs and the optimal combination of friction pairs on the basis of ensuring engine reliability. The piston ring adopts advanced thin ring technology, and the matching cylinder wall adopts low friction mesh processing technology, which reduces the wear resistance and increases the oil control ability of the piston ring. The engine can meet the requirements of engine fuel consumption and fuel consumption rate under various complex working conditions.
Crankshaft adopts narrow journal design, and with newly developed bearing bush, it ensures support strength and greatly reduces friction resistance. The experimental data show that the friction work of 477F engine is better than that of 1.3L engine below 3000rpm, and the FMEP is much lower than that of the general 1.5L four-valve engine.
For crankshaft, friction loss is mainly caused by crankshaft and bearing bush pair. The friction loss of crankshaft and bearing bush consists of two parts, namely, hydrodynamic loss and contact friction loss.
Liquid power loss is the liquid friction of lubricating oil between crankshaft and bearing bush when the engine is running, which is determined by the combustion situation in the cylinder, the linear speed of crankshaft rotation and the quality of lubricating oil. The linear velocity can be reduced by reducing the diameter of the crankshaft. 477F crankshaft adopts crankshaft strengthening technology. On the premise of meeting the requirements of crankshaft strength, the journal diameter is reduced by 15%, and the purpose of lightweight crankshaft is realized.
According to the final development results, at 6200rpm, the peak value of friction work decreased from 1320W to 780W, and the total friction work loss of bearings decreased by 34.8%. Exhaust system:
In order to respond to the national policy of energy saving and emission reduction and give full play to the engine's potential, we use CFD to calculate the engine exhaust manifold with pre-catalyst, and optimize the uniformity coefficient, velocity distribution, Mach number, pressure distribution and pressure gradient flowing into the catalyst.
Air intake system:
In order to improve the charging efficiency, reasonably organize fuel injection and oil-gas mixing to improve fuel consumption and emissions, the intake manifold and fuel injection target have been carefully calculated and developed.
Through multiple rounds of adjustment and matching, the organization of fuel injection and air intake is perfectly combined, and the mixture is formed reasonably, laying a solid foundation for reducing fuel consumption and improving emissions;
The length, diameter and direction of the intake manifold play an important role in the torque, power and fuel consumption of the engine. After several rounds of CAE and CFD calculation and optimization, the most reasonable related parameters are selected to improve the inflation efficiency. The optimization of design and development covers every component. Taking water pump and oil pump as examples, the mechanical efficiency of the engine is further improved by adopting plastic impeller of water pump and optimizing the characteristics of oil pump.
Water pump: the water seal of the water pump adopts double SiC structure, which reduces the dynamic contact pressure of the sealing surface and effectively controls the pressure fluctuation of the contact surface; After several rounds of CAE analysis and optimization experiments, the weight of the impeller was reduced from 152 g of metal to 27 g of plastic, with a weight reduction of more than 82%. Together, the shaft power consumed by the water pump decreases by 30.6% at the rated engine speed, and the efficiency of the water pump near the rated engine torque point increases by 4%.
When the inlet water temperature, inlet and outlet water pressure difference and pump water flow are equal, the power consumption of pump shaft is compared with the increase of pump speed. After optimization, with the increase of rotating speed, the rising trend of shaft power consumption is greatly slowed down, and the higher the rotating speed, the more obvious the energy saving is.
When the inlet water temperature, inlet and outlet water pressure difference and pump water flow are equal, with the increase of pump speed, the efficiency of the pump is compared. After optimization, with the increase of rotating speed, the efficiency of the pump increases with the increase of rotating speed, and the higher the rotating speed, the more obvious the efficiency improvement. The average amplitude is above 2%.