High-pressure rail (Common Rail) electronic injection technology refers to the complete integration of the generation of injection pressure and the injection process in a closed-loop system composed of a high-pressure oil pump, a pressure sensor and an electronic control unit (ECU). A separate oil supply method. It uses a high-pressure oil pump to deliver high-pressure fuel to the company oil supply pipe (Rail). It achieves precise control through the oil pressure in the company oil supply pipe, so that the pressure of the high-pressure oil pipe (Pressure) has nothing to do with the engine speed. It can greatly reduce the degree of change of diesel engine oil supply pressure with engine speed.
At present, there are three major companies in the world that are developing and producing diesel engine high-pressure rail systems, Japan Denso, Germany Bosch and the United States Ford. The rail system separates fuel pressure generation and fuel injection. If the unit pump diesel injection technology is compared to a revolution in diesel technology, the rail system can be called a rebellion because it deviates from the traditional Diesel systems are similar to sequential gasoline injection systems. The rail system opens up new ways to reduce diesel engine emissions and noise.
Due to its strong technical potential, today various manufacturers have set their sights on the third generation of axle rail systems - piezoelectric (piezo) axle rail systems, piezoelectric actuators Instead of a solenoid valve, more precise injection control is achieved. Without the oil return pipe, the structure is simpler. The pressure is elastically adjustable from 200 to 2000 Pa. The minimum injection volume can be controlled at 0.5mm3, which reduces smoke and NOX emissions.
The increasingly serious energy crisis has become the focus of the world's internal combustion engine industry, making diesel engines more and more popular among users. Compared with gasoline engines, diesel engines have many advantages: they can reduce CO2 exhaust emissions by 20% to 25%, have better acceleration performance at lower speeds, average fuel consumption is 25% to 30% lower, and can provide more driving pleasure. Therefore, someone boldly predicted the development trend of diesel engines in global automobile production and divided the proportion of diesel engines in world automobile production by region. However, compared with gasoline engines, emission control of diesel engines is another difficulty. In order to meet emission standards, the advanced fuel injection system of diesel engines - high-pressure injection rail technology has become the focus of attention of industry insiders. A few years ago, high-voltage rail technology was dominated by foreign investment, but now this situation has been broken.
The improvement of emission standards will inevitably promote the development of engine technology
On December 30, 2005, Beijing took the lead in implementing the National III emission standards. On July 31, 2006, new vehicles in the Shanghai bus and taxi industries implemented the National III emission standards. On September 1, 2006, Guangzhou began to implement the National III emission standards. On July 1 this year, the country will fully implement the National III emission standards. By 2010, the country will implement the National IV emission standards.
The improvement of emission standards will inevitably promote the development of engine technology. For gasoline engines, it is not difficult to meet current emission standards because the technology is relatively mature and there is after-treatment. For diesel engines, since most of them still have mechanical fuel systems and the development history of diesel engine direct injection technology is relatively short, the engine must be redesigned to meet emission standards. Currently, most of our country uses imported technologies to meet the current emission standards (National III), but some companies are also conducting independent research and development, such as China FAW Wuxi Oil Pump Nozzle Research Institute, Chengdu Witte, etc. Under the requirements of more stringent emission standards, in addition to the electronically controlled fuel system, many new technologies have also been introduced into the engine. Ricardo, a world-famous automobile research and development institution, recommends engine technical requirements at each emission stage. It can be seen that the rail system is one of the most inherited and sustainable fuel injection systems due to its unique advantages.
High-pressure injection rail systems have been widely used abroad
After the diesel fuel injection system developed from mechanical control to electronic control, the electronic injection system has undergone three changes , namely position fuel injection system, time fuel injection system and time pressure fuel injection system (first rail system). The high-pressure injection rail system realizes the separation of pressure establishment and injection process, thereby making the control process more flexible, more accurately achieving precise control of small oil volumes, and better achieving multiple injections.
Since Japan Denso Corporation published a paper on the ECD-U2 high-voltage rail system in 1991, foreign fuel system manufacturers have invested huge amounts of money and manpower in developing rail systems. Bosch released a high-pressure rail system for cars in 1995, using a radial piston rotor fuel supply pump and the injector solenoid valve using a ball valve structure. At present, Bosch's first rail system has been commonly used in European passenger cars and light vehicle diesel engines, such as Germany's Daimler-Benz C series cars, Italy's Alfa Remeo 156 cars, and Germany's Volkswagen Audi 3.3L V8 turbo Diesel engines, the Duramax 6600 diesel engine jointly produced by General Motors of the United States and Isuzu of Japan, and the ISBe3.9L and 5.9L fully electronically controlled diesel engines of Cummins of the United States, etc. Delphi and Siemens launched the MultecDCR1400 rail system for cars in 1998 and 2000 respectively, which used a radial piston rotor fuel supply pump. Delphi's injector solenoid valve was designed inside the injector, making the injector larger. Small and compact; Siemens injectors use piezoelectric actuators, which have shorter response times; and the first generation product of ECD-U2 was researched and developed by Japan Denso Company in 1991, and was matched with Hino's J08C diesel engine and Isuzu's 6HK1 in 1995 Diesel engine, after years of improvement and perfection, the latest product has been used in the ECD-U2P system of cars.
Currently, axle rail fuel injection systems are widely used. Bosch has produced 25 million axle rail systems and invested in the construction of a technology center and factory in Wuxi, Jiangsu, achieving localization. Production. Great Wall Motors and Bosch have developed high-pressure rail diesel engines. In addition, Audi, Mercedes-Benz, Huatai and other brands have also launched cars using rail systems. Some universities, research institutes and enterprises in our country have also achieved unique research results through cooperation or independent research and development, and dozens of patents have been published. Therefore, our country has accumulated certain experience in electronically controlled direct injection diesel engines, but generally speaking, there is still a gap with foreign countries, mainly reflected in the quality control of manufacturing technology and mass production. In addition, the supporting system related to the domestic rail system is not perfect, and some parts still rely on imports, such as single-chip microcomputer chips, rail pressure sensors, etc.
Foreign companies no longer have an absolute advantage in competing with Chinese companies
Compared with gasoline engines, the gap between domestic electronically controlled diesel engines and foreign countries is relatively small. This is due to two reasons: first, most of my country's original diesel engine vehicles have their own brands; second, my country's diesel engine vehicles have low comfort requirements and low prices, so foreign companies do not have an advantage in competing with Chinese companies.
With the improvement of emission standards, diesel engines must adopt electronically controlled injection systems. At present, domestic diesel electronic control systems mainly include rails, single pumps, etc. Compared with foreign advanced technologies, although they do not yet have equivalent strength, they have good development momentum. For example, the rail system developed by Wuxi Oil Pump and Nozzle Research Institute has been used in Wuxi buses. At the same time, there are a large number of domestic companies engaged in the research and development of electronically controlled diesel engines. Therefore, the domestic electronically controlled diesel engine market will definitely make a difference in the future. The prices of products provided by foreign companies are relatively high, and the supply price depends on the batch size. As the batch size of electronically controlled diesel engines in my country is not large at present, it is difficult for them to get a satisfactory price.
At the same time, in terms of after-sales service and parts supply, domestic independent brand systems also have obvious advantages. The competitiveness of domestically independently developed electronically controlled fuel systems is mainly reflected in the following aspects: First, they are cheap and economical. The batch sizes are smaller. Secondly, for light truck products, if the batch size is not large, we can choose the PM-type inline pump + electronic governor + cooling EGR solution with high injection pressure to match the rail technology. This is also our advantage. Also, for medium and heavy-duty vehicles, technical routes such as independent rails and single pumps have been implemented in the National III stage.
Of course, domestic electronically controlled diesel engine systems still face many challenges, such as immature manufacturing processes and small batch sizes; it is difficult to guarantee fuel quality; and the level of diesel engine post-processing technology is not high. But these will pass over time and will be gradually resolved soon.