"As the next generation engine series of Honda, the new 2.0L gasoline engine equipped with accord plug-in hybrid vehicle has the characteristics of low fuel consumption and good emission performance. Variable valve timing and lift electronic control system is adopted, with 2 specific cams (i.e. power cam and fuel economy CAM). The duration of power cam action is short, which is used for high-power output and engine starting; The fuel economy cam action lasts for a long time, and the Atkinson cycle effect can be obtained by delaying the inlet valve closing timing. Cooled exhaust gas recirculation (EGR) technology is also adopted, and the control system is improved to achieve the goal of low fuel consumption. Firstly, the new control system which can ensure the pressure difference between the front and rear of EGR valve improves the control performance of EGR flow. Secondly, the torque control is improved to predict the engine torque drop caused by ignition delay. Driveability and fuel economy remain at the same level under extremely harsh conditions. Finally, the control technology based on changing the operating point of atmospheric pressure is adopted, which can maintain low fuel consumption even if the environment changes. A new type of fast preheating system for catalytic converter for hybrid electric vehicle is developed. In the engine starting stage, the engine load is controlled by changing the motor operation, which can effectively preheat the catalytic converter, so as to reduce the exhaust emission to a level that can meet the Sulev 20 standard of ultra-low emission vehicle.
0 Preface
In the process of global motorization, it is one of the responsibilities of automobile manufacturers to provide products that pay attention to the environment. Every company is trying to develop various technologies, such as fuel cell vehicles, pure electric vehicles, hybrid electric vehicles, and turbocharged cylinder reduction enhanced engines.
Honda has been selling hybrid electric vehicles with integrated motor assist systems. This system has the advantages of simple structure, compact layout and light weight, and is suitable for small cars. At the end of 2012, Honda began to sell the accord plug-in hybrid vehicle, which adopts a new dual motor hybrid system, improves the power and can be used for medium-sized cars.
Honda has developed a new gasoline engine for the accord plug-in hybrid vehicle. As part of the new engine series "earth dream technology", the engine will also be used in the accord full hybrid electric vehicle launched in the autumn of 2013.
1. Development objectives
In the development of new gasoline engine, the most important problem is fuel consumption. In order to reduce the fuel consumption of hybrid electric vehicles, it is necessary to understand the operating area of the engine, which is determined by the driving mode of the vehicle. The vehicle has three different driving modes (Figure 1).
The three driving modes are pure electric drive, hybrid drive and engine drive. In the pure electric drive mode, the engine does not work, and the vehicle only uses the energy of the battery. The hybrid drive mode is applicable to the high load state of normal driving. The vehicle operates with the electric energy generated by the engine. In this mode, the engine operates according to the best fuel consumption curve. The engine driving mode is applicable to high-speed cruise, and the vehicle speed exceeds 80km / h. In high-speed cruise, direct engine drive is more efficient than using the motor in the hybrid system. At this time, the engine is running at medium load. The operating area of the engine is shown in Figure 2.
2 engine performance
2.1 engine specifications
The main technical specifications of the new gasoline engine are listed in Table 1, and the outline is shown in Figure 3. The cylinder diameter of the existing 2.0L gasoline engine is the same as that of the new model.
The new gasoline engine adopts double overhead camshaft, and VTEC and evtc technology are applied on the intake side. The top pressure rocker arm with hydraulic clearance adjuster is used on the exhaust side to reduce mass and friction. In order to compensate the air flow performance after adopting strong tumble airway, the inlet valve diameter is expanded by 1mm.
In order to reduce the height of the engine, the cylinder offset is adjusted. Reduce the diameter of crankshaft main journal to reduce friction loss. The compression ratio is 13.0, and Atkinson cycle and cooling EGR system are adopted. In order to improve fuel economy, electric water pump is adopted. Due to the need to take into account the power performance, fuel consumption and cost, the inlet injection mode is selected instead of the direct injection mode in the cylinder.
2.2 power performance of engine
The dynamic performance of the new gasoline engine is shown in Figure 4. The maximum power is 105kW when the engine speed is 6200r / min. when the speed exceeds 2500r / min, the maximum torque reaches 165n · M.
2.3 fuel consumption
Fig. 5 shows the improvement of fuel economy. The operation area of the new gasoline engine is in the low fuel consumption area. Compared with the existing engine, the fuel consumption is reduced by 10%. The fuel consumption rate curve is shown in Figure 2. At the operating point of engine speed 2500r / min and torque 120N · m, the fuel consumption rate is 214G / (kW · h).
3 engine hardware technology
3.1 VTEC system
VTEC system is adopted on the intake side of the valve train. This is a mature technology of Honda, and its structure is shown in Figure 6. Each cylinder has 3 cams and 3 rocker arms. The cams on both sides are power cams and the center is fuel economy cam. When the power cam is used, VTEC is closed and the three rocker arms work independently; When using the fuel economy cam, the VTEC opens and the three rocker arms are locked together by the synchronizing pin. In order to ensure variable control under low oil pressure after engine starting, hydraulic VTEC mechanism is adopted.
The valve lift curve of the cam is shown in Fig. 7, and its operating area is shown in Fig. 8. The action duration of the power cam is short (valve lift 1mm, crankshaft angle 196 ° CA), which is only used when the engine is started and high power output is required. The action duration of fuel economy cam is long (valve lift 1mm, crankshaft angle 240 ° CA), which is used in normal driving requiring low fuel consumption.
In this study, the effect of VTEC system is verified from the aspects of power output, fuel consumption and initial emission. First, the power difference between the two cams is shown in Fig. 9. Due to the long duration of the fuel economy cam, it can not be used at high engine speed, so the maximum power output is obtained through the power cam. When the engine speed is below 3000r / min, the difference of maximum torque is only about 5N · M. However, the effect of using fuel economy cam at the maximum torque operating point is poor, which is due to the long action duration and a large amount of exhaust backflow. In order to obtain high torque, the EGR rate needs to be reduced. Therefore, the power cam has good fuel economy in the high torque region.
Secondly, the fuel consumption performance of the two cams is shown in FIG. 10. In the high load area, the fuel consumption rate of the two cams is the same; However, in other regions, the fuel economy cam has a slightly lower fuel consumption rate. Because of its long duration, Atkinson cycle effect can be used to reduce pump gas loss.
The initial emission performance is shown in figures 11 and 12. Figure 11 shows the covariance of the average indicated pressure relative to the ignition timing under the same inlet valve closing timing. Because the power cam has a smaller valve overlap angle, its combustion is more stable than the fuel economy cam, so a longer ignition delay can be allowed. Figure 12 shows the hydrocarbon (HC) emission of two kinds of cams under different ignition timing. The influence of ignition delay is very large. The HC emission of power cam is 50% of that of fuel economy cam, and it also helps to reduce the initial emission when the engine starts.
As mentioned above, the two cams differ in power, fuel consumption and initial emission. The power cam performs well in power output and emission performance, while the fuel economy cam performs well in fuel consumption. If VTEC system is not adopted, the compromised cam profile must be selected, and all kinds of performance will deteriorate. The advantages of VTEC system are brought into full play here.
3.2 cooling EGR
Since the hybrid operation is limited to the high load area, it is a reasonable choice to use the cooling EGR system to improve fuel economy [2]. However, cooling EGR will slow down the combustion speed. In order to maximize the effect of cooling EGR, combustion must be improved. For this purpose, a high-intensity tumble inlet port (FIG. 13) is designed to make the main intake air flow enter the exhaust side of the combustion chamber. Change the side of the inlet and redesign from below the inlet. The flow simulation results of the newly developed inlet and the existing inlet are shown in FIG. 14. The flow at the bottom of the valve is reduced, and the main intake air flows through the upper part of the valve to produce high-intensity tumble in the cylinder. The tumble ratio of the newly developed inlet is 1.40, while that of the existing inlet is 0.73. The engine test results are shown in FIG. 15. The high tumble ratio improves the average indicated pressure covariance and reduces the indicated fuel consumption rate at the optimal point by 5g / (kW · h).
It is necessary to optimize the fuel consumption under high load conditions in hybrid drive mode and medium load conditions in engine drive mode. The relationship between effective fuel consumption rate, intake valve closing timing and EGR rate under high load and medium load conditions is shown in figures 16 and 17. Under high load conditions, closing the intake valve in advance and increasing the EGR rate to the combustion limit can make the effective fuel consumption rate reach the best value. Under medium load conditions, there is an optimal balance between delaying intake valve closing and introducing EGR to reduce pump air loss. This shows that the correction strategy of fuel consumption changes with the change of engine load. Adjusting intake valve closing timing and EGR rate according to engine load can improve fuel economy under high load and medium load conditions. Thanks to VTEC system, it is possible to achieve this goal by adopting fuel economy cam which is conducive to reducing fuel consumption.
4 engine control system
The concept of the new gasoline engine is to improve fuel economy by using cooled recirculated exhaust gas in high load areas. However, this practice reduces the combustion stability. Therefore, it is largely affected by environmental changes such as external temperature, atmospheric pressure and humidity. In the conventional engine control system, only the device with one boundary can be used, and the ability of hardware can not be brought into full play.
In order to obtain good fuel economy, a new engine control system is developed. The system can be adjusted according to the changes of the external environment.
4.1 EGR control
Generally, the purpose of EGR in gasoline engine is to reduce pump loss and improve emission performance. Therefore, EGR is mainly used in low load and medium load areas. However, the design concept of new gasoline engine is to introduce EGR in high load area, so controlling EGR flow becomes more important. Generally speaking, when the differential pressure is close to zero, the sensitivity of valve flow increases sharply. Therefore, it is difficult to control the flow with valves. In order to ensure the accuracy of EGR flow, a new engine control system is constructed, which can keep the specific differential pressure unchanged no matter how the environment changes.
4.2 torque control
In high compression ratio engines, torque is often reduced by delaying ignition to avoid deflagration. Especially in the high load area under high temperature, the deflagration tendency is stronger. The torque characteristics of the new gasoline engine are shown in Figure 20. In the high load area under high temperature conditions, the engine torque is reduced. Torque reduction leads to poor driveability and increased fuel consumption. Therefore, the problem must be solved by accurately estimating the amount of torque reduction. The researchers created a new torque estimation model (Figure 21). By measuring the external conditions, setting the ignition delay, and controlling various working conditions accordingly, the torque drop can be compensated, so as to ensure the balance between driveability and fuel consumption under harsh driving conditions.
4.3 operation point control
The operating curve is a curve connected with the optimal fuel consumption point of each engine speed. Make the engine run according to the operation curve shown in Figure 2, and low fuel consumption can be obtained in hybrid drive mode. The operating curve is located in the high load area with cooled EGR. The total gas filling of the cylinder is at a high level. Regardless of atmospheric pressure, it must be maintained Δ PLMT invariant
When the atmospheric pressure drops, the EGR rate drops below the normal condition, and the fuel economy becomes worse. Therefore, the fuel consumption values under different atmospheric pressures were measured (Fig. 22). The results show that when the atmospheric pressure decreases, the fuel economy decreases sharply under the same load, which means that the optimal fuel consumption curve moves with the change of atmospheric pressure.
Therefore, a control system that can change the operation curve according to atmospheric pressure is developed (Fig. 23). Firstly, two operation curves under normal conditions and high altitude conditions are prepared. Insert the measured atmospheric pressure parameters into two operation curves to establish the best operation curve. In this way, the best fuel consumption performance can be maintained regardless of the change of atmospheric pressure.
5sulev 20 standard
Considering the environment, fuel consumption and exhaust emission are important parameters. The goal of this development is to meet sulev20 standard. With the new catalytic converter preheating control, the hybrid electric vehicle can be preheated quickly. Figure 24 shows the exhaust system of the new model, and figure 25 shows the control mode of the new engine. After the engine is started, keep the engine under low load immediately to reduce the exhaust emission before the catalytic converter is preheated. After the near engine catalytic converter is preheated, the starting motor is used to increase the engine load and exhaust energy, so as to speed up the preheating speed of the catalytic converter under the far vehicle body. At this time, the increased exhaust gas due to the increase of engine load is purified by the preheated near engine catalytic converter. Therefore, the emissions of non methane organic gases and nitrogen oxides can be maintained below the Sulev 20 standard limit (Figure 26).
6 Conclusion
(1) The new gasoline engine adopts Atkinson cycle and cooling EGR system again, and is combined with VTEC system. The maximum power is 105kW and the fuel consumption rate is 214G / (kW · h), which is 10% better than the existing engine.
(2) By developing a new engine control system, the original fuel consumption performance and driveability can be maintained in case of environmental changes: EGR gas flow control can ensure the adjustment to the specified differential pressure no matter how the external conditions change; The torque control realized by on-board calculation can accurately estimate the starting engine torque; No matter how the atmospheric pressure changes, the operating point control can track the optimal fuel consumption curve.
(3) A new catalytic converter preheating control system using motor load to control engine operation is developed, which can meet the requirements of Sulev 20 standard., Read the full text“
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