Introduction of Short-term Precise Control Function (CVO) of High-pressure Injector

From: http://www.sinocmpinjector.com
CVO Function to Start the Engine

With the increasing shortage of energy in various countries, major OEMs have chosen to increase system injection pressure as one of the technical solutions to improve GDI engine emissions. High rail pressure can fully atomize the fuel, and with proper airflow movement, the quality of the mixture can be greatly improved. A more homogeneous mixture can make the combustion process more complete and thorough, and the emissions will be reduced. In addition, advanced fuel injection strategies are more inclined to use multiple injections at large loads and some special conditions (such as catalyst heating), and also use the highest system injection pressure at part load. These technological trends require that injectors work more in the small pulse width area.

Picture 1. Needle valve lift curve in the small
 pulse width area of the injector

However, for all high-pressure injectors of the solenoid valve type, the injection accuracy with a small pulse width is difficult to guarantee. This is mainly because when the pulse width is small, the needle valve is not fully opened, and the fuel injection amount is very sensitive to the lift of the needle valve. Small          changes in lift may cause large changes in the fuel injection amount. Figure 1 is the actual needle valve lift curve of a certain batch of high-pressure solenoid valve injectors (same model) working in a small pulse width region. It can be seen from the figure that under the same excitation pulse width, There is also a significant deviation in the needle valve movement of batch injectors, and these differences will inevitably result in different injection quantities.

Picture 2. CVO control effect

CVO Improves Injection Accuracy of Injectors

In order to improve the injection precision of the small pulse width area of the high-pressure injector, Bosch has developed the short-term precise control function of the injector. For a certain injector, the fuel injection quantity corresponds to the needle valve lift curve. The CVO function is to control the fuel injection quantity by adjusting the needle valve lift to the target position. The correspondence between the fuel injection amount and the needle valve lift was obtained from the CVO system test bench. Figure 2 shows the comparison effect with and without CVO (CVO3 is applicable to the 350bar system). It can be seen from the figure that the CVO function can significantly improve the injection accuracy of the injector in the small pulse width area (ballistic area, transition area), Improved injection accuracy for large pulse width areas.

Impact of CVO on Engine Performance

For engines that have integrated the CVO function, because the injection accuracy can be guaranteed, the calibration strategy does not need to deliberately avoid small pulse width areas, which provides the possibility for the implementation of a more effective calibration idea. The following figure shows the comparison results of the emissions of an engine with or without CVO.

Picture 3. Comparison of the presence and absence of
CVO emissions for an engine under different operating
conditions

As can be seen from Figure 3, for the engine, without changing the calibration strategy, due to the reliable fuel injection accuracy, the injection dispersion of each cylinder under the heating condition of the catalyst becomes smaller, and the combustion stability is significantly enhanced. The PN and HC emissions have dropped significantly. Under partial load conditions, the original two injections at 120 bar can now achieve three injections at 200 bar. The fuel atomization is more complete and the wet wall effect is reduced. Under the premise of ensuring the same gaseous emissions, PN emissions are effectively reduced. Under certain WLTC acceleration conditions, the CVO function can ensure the accuracy of each injection of multiple injections, the wet wall effect is reduced, and PN and HC are reduced to a certain extent.

Although the above shows that engine emissions with integrated CVO function will be improved, the CVO function itself is not a function for emissions. The development of CVO is only to improve the injection accuracy. The improvement of injection accuracy can make more effective and advanced calibration Strategies and ideas were realized, which in turn led to improvements in emissions. CVO escorts development of gasoline engine technology.

With stricter regulations on emissions intensity in various countries, CVO has become the main technical method for GDI gasoline engines equipped with 350bar systems to solve the problem of fuel injection accuracy. Facing more stringent regulatory requirements in the future, the next-generation GDI gasoline engine is likely to develop in the direction of higher system pressure, more frequent, and more complex fuel injection strategies. In this technology trend, CVO functions will become increasingly important.

Picture 4. Schematic diagram of the
CVO system test bench

In order to better serve foreign customers, United Electronics has established a CVO system test bench (a schematic diagram of the bench structure is shown in Figure 4). This test bench is a reliable tool for obtaining the true characteristics of the injector and the basic calibration data of the CVO. Must go through. With the use of the test bench, United Electronics has now built a comprehensive CVO working capability including systems and software and hardware, which will greatly improve the efficiency of foreign project testing and save development time and costs.