Analysis of the control strategy of range extender system on the vehicle NVH performance

2.1. First operating point selected

Before the operation of range extender, the vehicle runs in pure electric mode, and the NVH performance level of the vehicle is basically the same as that of pure electric vehicles. The starting process of the range extender will inevitably cause the increase in the vibration and noise in the vehicle, which is different from the engine start and stop of the traditional internal combustion engine, the main differences are: 1) The first operating point of the range extender is often higher than the idle speed of the conventional fuel vehicle engine , and need to provide additional external output power; 2) The ignition speed of the range extender is higher than that of the traditional internal combustion engine, this is because the start of the range extender is often dragged by the generator, and the generator has a larger power and torque than the starter. Therefore, the range extender start process can quickly pass through the resonance area of the range extender mount system to reach the isolation area. In this article, we mainly discuss the impact of the first operating point of the range extender on the NVH performance of the vehicle.

The first working point selected after the range extender starts is mainly based on the vehicle's minimum power and fuel economy requirements. At present, the initial speed of the prototype vehicle is 1200 rpm according to the demand, and the other speed points (1400 rpm/1800 rpm/2400 rpm) are designed mainly for evaluate the effect of different speed points on NVH performance.

The vibration of the seat rail is basically equivalent at operating points of 1400 rpm/1800 rpm/2400 rpm. When the operating point is 2400 rpm, there is a significant peak after the startup is completed.

2.2. Transition mode between different operating points

The transition mode between different operating points of the range extender will affect the noise and vibration in the vehicle. The specific transition mode is shown in Fig. 3, which mainly includes three ways: 1) The speed and power increase simultaneously; 2) The speed remains unchanged first, the power is increased, and then the speed is increased; 3) The power is kept unchanged, the speed is increased, and then the power is increased.

Fig. 1Sound pressure of different operation points

Fig. 2Seat rail vibration of different operation points

Fig. 3Different transition mode of operating points

Fig. 4Sound pressure of different transition mode

Fig. 5Seat rail vibration of different transition mode

These three modes of transition tests were performed on a engineering prototype vehicle. The test results are shown in Figs. 3-5. When mode 1 is used, the vibration and noise will reach the maximum value after the completion of transition. When mode 2 is used, the vibration and noise will have secondary peak value, the sound pressure level in the vehicle is basically the same as that in mode 1, and the vibration of seat rail level in the vehicle is lower than that in mode 1. When mode 3 is adopted, there is no obvious secondary peak in the whole transition process, the vibration and noise peak at the maximum power point, and the overall vibration and noise are lower than mode 1.Among the three modes, mode 3 NVH performances better than mode 1 and mode 2.

2.3. Transition rate between different operating points

The transition rate between different operating points of the range extender will also affect the noise and vibration in the vehicle. The test results of different transition rates are shown in Fig. 6-7, where the initial speed is 1800 rpm, the target speed is 2400 rpm, the transition rate is 100 rpm/s, 200 rpm/s, 300 rpm/s, and the corresponding transition time is 6S/3S/2S. When the transition rate is 200 rpm/s and 300 rpm/s, there are obvious sound pressure peaks after the completion of the speed transition. The sound pressure level of 300 rpm/s is still higher than 100 rpm/s and 200 rpm/s in the following time, and 100 rpm/s has a good level, but correspondingly, the transition time is longer, which may affect the subjective feeling of driving.

Fig. 6Sound pressure of different transition rate

Fig. 7Seat rail vibration of different transition rate

The vibration of the seat rail in the vehicle has the optimal vibration value at 300 rpm/s. Under the two operating conditions of transition rate of 100 rpm/s and 200 rpm/s, the peak vibration value is significantly higher than 300 rpm/s, and the time span is 3 s and 2 s.

2.4. Confirmation of the operating points

In the engineering prototype vehicle stage, the optimization and confirmation of the operating point of the range extender can quickly identify the NVH problem in the vehicle state, and ensure the frequency avoidance between the ignition order frequency of the range extender and the frequency of key components of the vehicle body, such as subframe, steering wheel, body panels, etc. The vibration and noise test results of the range extender operate under different loads and speeds are shown in Figs. 8-9. Among them, purple refers to the power line of 20 kW of the distance increaser, black refers to the power line of 30 kW of the distance increaser, and gray refers to the power line of 40kW of the distance increase.

From the test data, the sound pressure of the right ear of the driver has peaks in the two speed ranges, 1) 2200-2400 rpm, 2) above 3000 rpm, and the vibration of the seat rail has a peak around 1400 rpm, and vibration problems also exist at 1200 rpm under 80 % and 90 % load. Therefore, from the perspective of NVH control of the vehicle, it is recommended that 1) the speed of the range extender need to avoid 1300-1500 rpm, 2000-2450 rpm, and the maximum operating speed of the range extender is required to be less than 2800 rpm; 2) When the range extender load is above 80 %, the range extender speed should also avoid 1100 rpm-1200 rpm.

Fig. 8Sound pressure of different throttle percentage

Fig. 9Seat rail vibration of different throttle percentage