Fuel economy improvement of parallel hybrid electric vehicle using speed ratio control of continuously variable transmission
The global relationship between energy constraints and CO2 gas reduction forces auto engineers to develop efficient and environmentally friendly alternative powertrain technologies, including alternative powertrains. Parallel electric vehicles are considered the most in the short and medium term. Promising. HEVs have been shown to improve fuel economy and minimum additional cost requirements, and HEV drive trains can be mixed in parallel or in series. In terms of car applications, parallel hybrid drive structures have been introduced to the market in HEVs. In a parallel hybrid configuration, the mechanical connections between the components are not as optimized as in series mixing, but this disadvantage can be overcome with a continuously variable transmission (CVT), which allows the engine to be at a minimum fuel regardless of the vehicle speed. Consume operation. It can be seen that CVT has been applied to many parallel hybrid drive vehicles according to the powertrain standard. HEV can improve fuel economy in different aspects. One possibility is to improve the propulsion system and increase the transmission efficiency of different powertrain components, such as engine and motor. It is a way to achieve this requirement. Another method is to control the powertrain as a whole to optimize the fuel. The energy required by a particular engine is the integral of the fuel consumption of each component.
As we all know, the metal belt CVT uses CVT speed ratio control to provide a more efficient working level of an engine than a conventional multi-speed gear transmission. In terms of CVT ratio control, the CVT ratio is determined based on the engine optimum operating point and the vehicle speed. For an ideal transmission situation, the speed ratio can vary the engine operating point position on the optimal operating line (OOL) for minimum fuel consumption. However, in practice, there is a powertrain response lag caused by the driver's accelerator pedal input wheel torque, which causes a deviation between the actual engine operating point and the OOL. To overcome this response lag, many studies have been conducted, using additional flywheel and engine CVT combined control.
This paper recommends an improved CVT ratio control method to improve engine performance by considering the HEV powertrain response lag. In this method, the speed ratio is calculated based on estimating the vehicle speed in response to the lag, using this method. Since the power source of the HEV is a combination of an engine and a motor, in order to give a TVO, the torque of the engine and the motor should be obtained from the engine and motor characteristic graphs, respectively. The next step is to start simulation with a fixed CVT speed ratio i, which gives an acceleration line diagram for the time. Repeatedly changing the speed ratio and TVO for the known maximum acceleration a of the TVO and i, a three-dimensional acceleration TV speed can be obtained. In contrast to the figure, the figure is called the a' plot ", according to the "HEV" line as shown. The corrected CVT speed (5) can be obtained from the "line and equations (4) and (5), and the CVT is corrected. The speed ratio will soon change towards a larger speed ratio than that described in equation (2), which causes a rapid upshift.
However, if the downshift maneuvering requires fast acceleration performance, the rapid upshift causes a slow acceleration performance. In order to ensure the transmission capacity, the acceleration condition is: the positive CVT speed ratio control method can guarantee fuel economy rather than transmission, otherwise the conventional CVT speed ratio control method can be applied (2).
g 4. According to the test results, the response lag for finding the driving torque is 450 milliseconds. The response lag is measured from the TVO input (point A) to the drive torque starting point (point B), which is due to engine torque, air throttle, CVT, etc., as previously indicated, from the drive shaft to the wheel With additional response lag, the powertrain response lag may exceed 500 milliseconds in an actual vehicle.
In the HEV bench tester, the drive mode consists of moderate acceleration and constant speed, which is used to estimate the modified CVT speed ratio control method recommended in this study. The TOV accelerator pedal position Ap and the motor torque are as shown in (b) and (c). The TVO and motor torque are calculated by the HEV manipulation method based on the accelerator pedal position Ap. If the vehicle speed enters the normal speed range, the HEV driving mode is changed from the acceleration mode to the normal speed mode by the working method, and the motor stops assisting. (d) shows the CVT ratio response, and (e) shows the engine operating trace using conventional CVT ratio control for a given drive scheme. With the CVT ratio control, the engine speed is maintained within the range of (1)e 820-1590 rpm.
Show modified CVT speed ratio control HEV bench test machine test results. In this test, the estimated corrected CVT speed ratio response lag is 500 milliseconds. As shown in (a), the vehicle speed V tracks the speed Vd. The TVO(b), Ap(b) and motor torque (c) indicate Same as the conventional CVT speed ratio control response. However, it can be seen from the d circle that the CVT ratio shift is faster than the conventional CVT ratio because of the modified speed ratio control method. Thus the engine working trace (e) is converted to a lower engine speed range using a correction method.
The fuel economy of various test transmission modes was compared by the test results. It can be seen that the fuel economy obtained by the modified CVT speed ratio control method At=500 milliseconds is improved by 6.9% compared with the conventional CVT speed ratio control. However, the percentage of this improvement is only the ratio of the speed control of the HEV test (AT= 500 milliseconds) Fuel economy comparison Fig. shows the mitigation acceleration mode obtained. Therefore, it requires the performance of the modified CVT ratio control method to be evaluated throughout the transmission cycle, such as the Federal City Transmission Scheme (FUDS). Simulations are used to estimate FUDS performance due to certain limitations such as the difficulty of operating the FUDS test using the HEV bench tester power absorption capability in the deceleration mode. In the simulation, the vehicle parameters are listed in Table 1. In 0 and 11, the FUDS CVT speed ratio control method simulation results are first compared. In this simulation, the response lag is AT=500 milliseconds, and the vehicle speed can be seen (0a and 11a). Engine speed (0c and 11c) motor torque (0d and 11d) and battery SOD (0e and 11e) indicate that the two CVT ratio control methods are the same, but studies have shown that engine speed is controlled with a modified CVT ratio (1c) ) is smaller than the conventional control (0c), which causes the CVT speed ratio to rise and fall quickly (1b). At 1f, the engine trace obtained by the full FUDS with the modified CVT speed ratio control method can be found. For OOL, it is faster than the conventional CVT. More precise than control (0f).
Using modified CVT speed ratio control (~=500 milliseconds) HEV simulation results 圪 s 2 for different At fuel economy comparisons 2 compared different response lag AtHEV fuel economy, Ap700 milliseconds achieved the best fuel economy and improved fuel economy About 2.6% of the simulation, the final SOC remains within the original SOC ± 0.5% in order to compare fuel economy. As shown in Fig. 2, HEV fuel economy is the best. Increasing the corrected CVT speed ratio is used to calculate the powertrain response lag At. However, due to the fast shifting, the larger At may cause the vehicle to be slow. Therefore, a comparison between fuel economy and acceleration performance is required.
5 Conclusion The recommended CVT speed ratio control method improves the fuel economy of the parallel HEV powertrain response lag. In this method, the target CVT speed ratio is corrected by estimating the vehicle speed after the powertrain response lag, suggesting an acceleration line. Figure. The CVT speed ratio control method has used the HEV bench test machine to verify the head. According to the test results, it can be found that for the slow acceleration mode, the modified speed ratio control method obtains the engine working trace to the more efficient interval than the conventional CVT speed ratio control shift. It gives the best fuel economy. In addition, the HEV powertrain model is used to simulate the FUDS performance to evaluate the fuel economy of response lag to HEV. The simulation results show that the response lag is used to correct the CVT increase ratio to obtain the best fuel economy. However, in practical applications, a comparison between fuel economy and acceleration performance is required. (Liu Qing translated from Proc.IMechE.Vol.219
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