On December 30, 2021, many engineers from Li Auto's NVH team went to work with suitcases to prepare for the upcoming New Year's Day holiday, and the NVH team, including Ji Xiangdong, senior director of Li Auto's R&D and R&D operations, reported to Li Xiang on the L9 NVH solution under development.
"We thought that the plan to achieve the set goal was scolded by Brother Xiang, who felt that the noise performance of the L9 range extender did not meet his expectations at all." Ji Xiangdong said.
Initially, Li Xiang proposed for the R&D team to develop the NVH of the L9 to reach the level of the X7 based on his own BMW X7. From the perspective of engineering feasibility, the R&D team set a target of 85% of the core indicators of nearly 200 NVH indicators to surpass the BMW X7.
As a result, Ji Xiangdong issued a military order to "solve the problem within one month, otherwise 'roll up and leave'".
Ji Xiangdong said in reviewing this experience, on the one hand, the boss's expectations are not in line with the indicators that our engineers said, and on the other hand, from the perspective of feasibility, 85% of the surpass is a good result.
This also shows that on the one hand, Li Xiang is a "product manager" who has very strict requirements for products, and on the other hand, NVH is a complex, fragmented, and even subjective project, even if the professional engineering team believes that the product that achieves the goal may not be able to satisfy users.
Recently, at the Li Auto NVH Technology Day, Li Auto showed a "hearing threshold statistics" chart, in which the data of the yellow line is Li Xiang himself, which can be seen that compared with the insensitive people, Li Xiang's perception of sounds of each frequency is closer to the sensitive people (low decibels/dB sounds can be heard).
With such a product manager as the boss, for Ji Xiangdong, who was nicknamed "fungus" by his colleagues, it may be understandable to be "scolded".
Of course, perhaps it is precisely because of Li Xiang's sensitivity to sound that Li Auto can finally achieve a performance that surpasses the industry in terms of NVH.
Stacking, stacking does not produce excellent NVH
NVH, which is the abbreviation of Noise, Vibration, and Harshness, is also the abbreviation of quietness in the general sense.
How can I improve NVH performance? Perhaps the most straightforward way is to use more soundproofing and sound-absorbing materials, double-laminated glass, and better tires...... However, in fact, NVH is a complex system engineering, and even compared with the acceleration and braking, space size, and configuration form of the vehicle, which can be measured by a unified dimension, NVH is still a highly subjective index.
On the one hand, as mentioned above, everyone's perception of sound is different, and the same noise performance may be completely different for different users. On the other hand, NVH involves too many areas of vehicle development, more than 30% of the more than 10,000 parts of the whole car are related to NVH performance, and involve different driving dynamics, environment, temperature, weather, etc., it is not as simple as adding a few more pieces of soundproof cotton.
This is not like zero hundred acceleration, which can theoretically be solved by only a stronger power system; Stockpiling alone can improve NVH with half the effort, and may also affect other aspects of the vehicle's performance.
Or even some unexpected questions.
Towards the end of the development of the ideal L9, Li Xiang found that the road noise of the L9 test car on rough asphalt roads was very obvious, and it was not as calm as the BMW X7 sound. In order to solve this sound problem, which even the team did not perceive, the team went through four shifts and 24 hours a day, and finally came up with the most reasonable solution, that is, to increase the resonant block.
However, this solution, which the team thought could definitely solve the road noise problem, made the team very hesitant when making the final decision, not because of performance, time, or cost, but because of public opinion. After all, a resonant block in a prominent position on the upper wishbone is likely to be caught by the "do-gooders" in the future (and indeed it is).
Of course, in the end, under Li Xiang's decision, this resonant block design was used in the L9 production car.
This incident may be an "extreme" case in solving NVH, but it also shows that even if the engineering team does not consider the cost of "stacking" at all, it will take a lot of technicians and testing costs to solve the problem, and even if the problem is solved at the technical level, it must also consider the possible potential public opinion risks.
In fact, in the case of building a car, any problem that can be solved only by "spending money" is always the simplest problem. NVH, even if you have industry-wide simulation technology software, you still need rich experience; Even if you can identify problems, you still need to balance complex metrics, time, and costs within R&D; Even if you can solve all kinds of noise at any cost, you still need the cooperation of the supplier.
This is the case with the refrigerator on the Ideal L series and the cooling fan on the MEGA.
In a sense, it has opened up the ideal of the market segment of "refrigerators, color TVs, and large sofas", and in the development of L9 car refrigerators, it actually encountered great NVH challenges. Before the L9, few car companies would use compressors to refrigerate the refrigerator, although the cooling effect is better, but the noise is greater, not to mention that the L9 refrigerator is placed in the center of the cockpit, which is more sensitive to noise.
What's more, all the car refrigerator suppliers on the market can't come up with ready-made product solutions that can satisfy the ideal team.
Therefore, the ideal team helps suppliers to develop products together, from the compressor body to the bracket, fan and other details, to find the source of noise and optimize it. At the same time, the NVH team ended up adding a 360° soundproofing package to the entire refrigerator. The supplier of this set of solutions has subsequently received the needs of many other car companies, "The name is the same refrigerator as the ideal." ”
And on the ideal MEGA, in order to achieve 5C supercharging with a supercharging power of more than 500 kilowatts, the ideal once again became a crab eater.
Overcharging requires a lot of heat dissipation from the vehicle, and only by keeping the battery temperature in the right range can the charging power be kept as high as possible. To this end, the Ideal MEGA is equipped with a large fan with a power of 1,100 watts and a diameter of 535 mm, which is the first of its kind for family electric vehicles, which in the past were mostly only used in large-displacement diesel commercial vehicles.
As a result, the finished product from the supplier behaved like a small motorcycle, and the "bump" sound was completely unacceptable to the NVH team. However, as a supplier of the industry's leading enterprises, it did not cooperate, and also listed Mercedes-Benz GLE, Land Rover Range Rover, which also planned to use high-power fans, and did not put forward such needs.
So the NVH team decided to do their own simulation and come up with an optimization plan, but the first step was to get the confidential data of the fan blade shape that was not disclosed to the OEM, and it went through several rounds of twists and turns. Subsequently, based on the original plan, the ideal team proposed a new optimization scheme for the number of blades, blade spacing, blade shape, and even the shape of the windshield. In the end, after several rounds of simulation and verification, the team found the current nine-piece bionic wavy blade solution.
And this blade scheme was also "reversed" by the supplier.
A little "obsessive-compulsive" spirit
In a list of NVH results, the Li MEGA occupies the first place in the 3th gear of 40 km/h, 80 km/h and 120 km/h, and even the Li ONE launched in 2019 can lead many newer BEVs in the list.
Li Auto's ability to achieve such extreme performance in the NVH field is of course inseparable from Li Xiang's sensitive hearing and "obsessive-compulsive disorder" requirements at the beginning.
During the development of the L9, it was not uncommon for the engineering team to find fault with the needs only to be found faulty by Li Xiang.
In June 2022, Li Xiang found that the trial car he drove would have noisy high-frequency noise after turning on the air conditioner, even similar to the central air conditioning at home. At that time, it was actually very close to the scheduled August 30 delivery time of the ideal L9.
In fact, this is distributed between 4000hz and 8000hz, and most of the colleagues in the NVH team can't hear it, but in order to solve this problem, the team urgently tested and adjusted, and finally optimized the refrigerant expansion valve in the thermal management system, which will lead to an increase in the cost of more than 140 yuan per car after L9 mass production.
If the cumulative delivery of the ideal L9 exceeds 200,000 units, this alone will reduce the profit by nearly 30 million yuan.
But the reason why the team quickly made the decision to make changes is because the younger the person, the more sensitive they are to high-frequency noises, which are heard by small children. The ideal car, which is positioned as a "mobile home", naturally hopes that every member of the car can get the best riding experience.
And this persistent spirit and accumulation of experience have been summarized on the ideal MEGA.
Ideal MEGA from the exterior styling, to the body structure; From the use of soundproofing materials to the design of various components, the NVH experience is fully considered.
As we all know, the drag coefficient of the Ideal MEGA is only 0.215, which is the lowest among MPVs. However, the low drag coefficient pursued from the beginning of the design is not equivalent to the excellent NVH.
For example, the styling design of the exterior rearview mirror has undergone more than 30 rounds of optimization iterations, and 12 key parameters have been adjusted. We saw several models from the first version to the final version at the event, and after careful comparison, we can clearly find the changes in their design, but this change is not likely to affect the overall beauty of the shape. This is also the result of the joint trade-off and optimization between the styling design team and the NVH engineering team.
For details like the roof lidar, through the adjustment of the NVH team, this lidar that protrudes on the surface of the car body finally contributes to the interior noise of the car to 0.
If you remove the body skin, you can see how much MEGA has put into the structure and sound package.
For example, a three-horizontal and four-vertical frame structure is added to the bottom of the body to improve the rigidity of the body and reduce vibration, so that the experience of the footsteps of passengers in each row is improved, and the final floor vibration transfer function of MEGA is 4.2 times better than that of the industry.
For example, in terms of third-row riding experience, mainstream MPVs usually use ordinary tempered glass in the rear corner window, including the ideal MEGA at the beginning of the design, which also uses this mainstream scheme.
However, in the simulation stage, the NVH team found that the hidden slide cavity and the bright strip step position of the corner window will generate high-frequency generation under the impact of airflow, while the large-area tempered glass has a "high-frequency coupling rate range", which is more sound transparent near the coupling frequency.
The team chose to optimize the slope of the corner window steps and supplement the sealing of the inner cavity of the slide rail, but the problem of insufficient sound insulation still existed, and the team was not satisfied during the actual vehicle test.
In fact, the third-row ride comfort of MPVs is relatively poor by "default" in the industry, but in order to achieve an "equal" experience for the whole family, Ideal proposes a more expensive solution of using acoustic laminated glass.
PVB acoustic laminated glass has stronger sound insulation ability, and there is no "high-frequency coupling rate range", but at this time, many hard molds for body interior and exterior decoration have been started, and the cost of replacing materials is huge, and the new scheme has only been verified by theoretical analysis and glass bench, and has not been tested by real vehicles.
Eventually, however, the NVH team leader decided to replace the glass material, a decision that nearly 1.5 times the cost of the MEGA bike.
Perhaps from a business point of view, such "obsessive-compulsive" behavior seems to be more like the "self-touch" of engineers, but the feedback and praise from users for the comfort of the third row is more important for the long-term reputation of the company and the product.
Large corporate perspective
There may be many levels of car building, and the appearance design and configuration parameters may be the easiest to achieve, but in contrast, NVH may be the most "thankless".
In fact, for this difficult but hard-working project, the R&D center of Li Auto has also built a supporting modal laboratory, a soundproof suite laboratory, a vehicle semi-anechoic room and an intelligent listening room, and verified the use of various acoustic materials through a large number of experimental simulations.
Is it worth it?
But if we pull the timeline to a wider range, we will find that although the involution of "refrigerators, color TVs, and large sofas" on the market is becoming more and more intense, there are more and more competing products that look like ideals, but are much cheaper. However, Li Auto is still the strongest sales volume among the new power brands.