Interpretation of highlights of Dongfeng Nissan’s new sunshine technology

Dongfeng Nissan’s new Sunshine sedan had its premiere at the Guangzhou Auto Show in December 2010. The car adopted a brand-new model platform and was modeled L02B. Not only has it greatly improved vehicle power, equipped with a HR15DE dual-injector engine and the world’s first CVT with planetary gears, it has also made breakthroughs in information technology applications. In addition, this model also explores the potential in many details, significantly improving the overall performance of the vehicle without increasing costs. Here is a brief introduction to some of the car’s technical highlights.

1.Engine

(1) Fuel injector

The engine model used in this model is HR15DE. This engine uses dual injectors for fuel injection for the first time (Figure 1). Its notable features are: it not only improves the atomization effect of fuel, but also increases the area of ​​contact between fuel and air when entering the cylinder, allowing the mixture to be better gasified, resulting in more complete combustion and higher engine efficiency. high.

The fuel pressure in the injector rail of this engine is 350 kPa, which is higher than the fuel pressure of ordinary engines. This can make the fuel atomization effect better, and the fuel atomization diameter can be reduced to 30 μm, while the fuel atomization diameter of ordinary injectors is generally above 70 μm. Each injector has 18 injection holes, which is 6 more injection holes than ordinary injectors, so that the static flow rate of a single injector can reach 157 ml/min at 300 kPa. Then, when working with dual injectors, the fuel flow can reach 314 ml/min. It can be seen that such an injector design can not only ensure good atomization, but also have sufficient fuel flow, so that the engine control system can control freely under various working conditions.

(2) Lubrication system

In addition to the lubrication task, the engine’s lubrication system also plays an auxiliary role in cooling. The lubricating oil is injected from the cylinder block to the bottom of the piston (Figure 2). The heat in the combustion chamber can be transferred to the lubricating oil through the top of the piston, and the lubricating oil takes away this part of the heat and dissipates it. This reduces the temperature of the combustion chamber, thereby improving the engine’s anti-knock capability. When the engine requires large torque output, the tendency of knocking will increase due to the increase in the mixture inhaled in the cylinder. However, due to the above measures, the tendency of engine knocking is reduced, so that the engine does not need to delay ignition to avoid knocking. This makes the engine’s power response more perfect.

(3) Cylinder head and piston

This engine enhances the turbulence effect through the design of the cylinder head and piston top (Figure 3). When the intake airflow passes through the cylinder head air passage, the air passage is moderately throttled near the valve door, which can increase the airflow velocity at the valve door without excessively increasing the intake resistance. The accelerated airflow hits the specially designed groove on the top of the piston, effectively creating turbulence. The inertia of the air flow is used to make the mixture flow annularly in the cylinder. This extends the gasification distance of the mixed gas within a limited time, thus improving the gasification effect, making combustion more complete and improving fuel economy.

(4) Three-way catalytic converter

The three-way catalytic converter of this engine has also changed in details. It changes the frame shape of the honeycomb holes from the traditional square to a hexagonal one (Figure 4). We know that under the same circumference, the circular area is the largest, so generally speaking, the honeycomb holes of the three-way catalytic converter are circular to maximize the passage capacity of the air flow. Because a hexagon is closer to a circle than a square, the former can increase the diameter of the central hole if the diagonal lengths of the frame are the same. This improvement measure not only reduces the airflow resistance of the catalytic converter, but also saves the use of rare metals and reduces costs. The exhaust airflow is improved without affecting the purification performance, thereby increasing the engine power output. Since the ventilation performance of the three-way catalytic converter has been improved, the exhaust back pressure can be reduced. In order to fully realize the benefits of this improvement, the new engine also increased the diameter of the exhaust manifold from 30.8 mm to 32 mm (Figure 5) to improve the performance of the engine’s power output.

2.CVT transmission

This model uses a new generation CVT, model number RE0F11A. In the past, small-displacement vehicles of the Dongfeng Nissan brand could only be matched with the RE0F08B type CVT transmission due to installation space limitations, and their maximum input torque was only 120 N?m; for large-displacement vehicles, they needed to be matched with the RE0F08A type CVT transmission. Its maximum input torque is 150 N?m. Now, RE0F11A is smaller than RE0F08B, but its maximum input torque has reached 150 N?m, and the transmission range has also been increased (Figure 6). Therefore, RE0F11A can replace the previous two CVTs and be installed on any vehicle on the V platform. So, how does this CVT transmission achieve high torque in a small size?

(1) Auxiliary gearbox

RE0F11A is the world’s first CVT that uses an auxiliary gearbox (Figure 7), and its transmission range is also the largest so far. We know that in order for a CVT to transmit greater torque, the contact area between the transmission belt and the pulley must be increased (Figure 8), which means that the CVT pulley must be large enough, but this will inevitably increase the volume of the transmission. In order to solve this contradiction, RE0F11A uses an auxiliary gearbox to reduce the torque burden carried by the pulley. This CVT takes advantage of the continuous shifting characteristics of the pulley to cover up the shifting feeling of the auxiliary gearbox, fully retaining the unique shifting feeling of a CVT. Practice has proved that as long as the torque ratio of the CVT pulley and the auxiliary gearbox is properly matched, it is possible to achieve small-volume and high-torque transmission.

The transmission ratio of a conventional CVT changes continuously (Figure 9, in the figure: n-engine speed, k-transmission ratio, v-vehicle speed), while the transmission ratio of an automatic transmission changes step-wise (Figure 10). The transmission process of the auxiliary gearbox is the same as that of the automatic transmission, and the transmission is also achieved through a planetary gear row (Figure 11). In order to achieve the overall transmission effect of a conventional CVT, RE0F11A uses the reverse change of the CVT pulley transmission ratio to compensate for the change in the transmission ratio of the auxiliary gearbox at the moment of shifting (Figure 12), so that there is no sudden change in the overall transmission ratio of the transmission. It can be seen from the figure that the engine speed and vehicle speed do not change at the moment when the auxiliary gearbox shifts gears.

In order to avoid shifting shock, at the moment when the auxiliary gearbox shifts, the transmission controls the CVT input shaft torque to remain unchanged, so that the engine speed does not jump. However, the inertia of the auxiliary gear exists objectively. Therefore, the torque of the output shaft is first reduced and then restored at the moment of the auxiliary gearbox shifting to buffer the shift impact (Figure 13). Although the traction force of the vehicle will change at this time, by using the inertia of the vehicle itself, as long as the change rate of the traction force is controlled within a certain range (Figure 14), the driver will not feel the impact of the shift at all. For example, at a certain shift moment, the traction force change is 0.03 N. According to the CVT shift curve, the traction force slope at this time is 0.1 N/s. Then as long as the duration of the auxiliary gearbox shift moment is controlled to 0.3 s, The driver will not notice the gear change. In this way, the driving feeling of the vehicle is exactly the same as that of a conventional CVT.

(2) Structural features

Not only that, this CVT has also been improved in many aspects. In order to reduce the stirring resistance of the transmission oil, a certain distance is maintained between the rotating parts and the transmission oil level (Figure 15). This measure alone can improve fuel economy by 30%. Due to the reduced size of the pulleys, the overall mass of the transmission is reduced by 13%. The adoption of an ultra-thin torque converter shortens the overall length of the transmission by 10%, which saves valuable installation space for front-wheel drive vehicles. The torque converter’s lock-up clutch uses a low-stiffness buffer to make the transmission smoother. In addition, the lock-up range of the lock-up clutch has been expanded and lock-up occurs at lower vehicle speeds, further improving fuel economy. The transmission oil pump uses a high-efficiency oil pump, which can adjust the oil pressure according to the working conditions of the transmission. These details all reflect the designers’ increased awareness of energy conservation and environmental protection. The auxiliary gearbox and shift control clutch are integrated parts, making them work more stably and reliably.