Previous life of subframe
The subframe does not appear with the load-bearing body. Most of the early load-bearing bodies were semi-load-bearing structures, such as the semi-load-bearing body structure built by Chrysler in 1960, and the suspension can be directly installed on the frame.
Going forward, although the frame is removed, the suspension is directly connected to the load-bearing body. The advantages are light weight and low cost, but the car body is directly impacted by the ground and the comfort is not good. I feel this way when I sit on Chery QQ. The information transmission on the road is too straightforward, straighter than the steel straight man.
Of course, this can't blame a model of Chery QQ.
Small cars such as Chang 'an Benben, Hafei Lubao and Changhe Big Dipper are not installed. Even around 20 10, there are many models under 60,000 without sub-frames.
Therefore, the Great Wall Elf, Geely Panda, BYD F0 and Haval M 1 are the first representative models to be used, and they often use them as selling points.
Of course, this should be praised, because with the subframe, the suspension can be assembled on the subframe to form an assembly, and then installed on the car body together.
This can reduce the introduction of road vibration, improve the connection stiffness of suspension system and make the chassis more compact.
On the other hand, it also promotes the safety that everyone pays attention to.
There are three main load-bearing paths in the front cabin of an automobile: 1) anti-collision beam-front longitudinal beam-longitudinal beam extension beam; 2) Front longitudinal beam -A-pillar-roof beam; 3) Sub-frame-longitudinal beam floor extension-central passage and bottom beam. With the function of the auxiliary frame, the force transmission channel is equal to one more, and it also reaches the central channel and bottom beam with the best bearing capacity.
At this stage, the sub-frame has gradually dropped from the D-class car to the A-class car market, and most models have been equipped with sub-frames. Because of the cost, the front subframe is often equipped, and the rear subframe is still relatively common in mid-to high-end models.
▲ Rear subframe of Audi A6
Take Link 03 as an example, its rear subframe is very complete, on the one hand, it is a differential with rear axle for four-wheel drive models; On the one hand, as a sports car, a complete rear subframe can improve the ultimate bearing capacity of the vehicle.
Where does the price difference of the subframe come from?
Due to various reasons, the form of suspension has formed a set of relatively fixed price trends. For example, the former McPherson+rear torsion beam is mostly used for 65438+ million-class models; At the level of 0.2 million/200 thousand, the rear suspension is mostly multi-link, and it will be further classified according to the type, material and quantity of the link.
The sub-frame is similar, and the classification mainly includes spindle beam, H-type and full-frame. Because of the structural form, material and molding method, the price will be higher and higher.
However, just as we often discuss which kind of suspension is better, the differences between different sub-frames cannot be restored only by the above distinction, so it is necessary for us to say a few key points.
1) comfort difference
As mentioned above, the subframe can make the chassis more complete and slow down the impact, so the primary ability is to improve comfort. In this respect, the advantage of full-width subframe is the most prominent.
However, the soft and hard adjustment of the subframe will also directly affect the comfort. If the suspension of the subframe is designed to be soft, it can isolate the vibration generated when the car is driving, but it will reduce the support stiffness, especially when turning at high speed. Rigid subframe suspension can bring high connection stiffness, but the isolation of vibration and noise is very limited.
In addition, whether the subframe is equipped with reinforcements or not and the arrangement of reinforcements will also have an impact on this. For example, the structure shown below and the connection of two triangles can more effectively disperse the longitudinal force borne by the subframe to the left and right longitudinal beams.
To sum up, the structural form of the subframe determines the upper limit of comfort, but its soft and hard adjustment and reinforcement design are also very important. These details are difficult for us to see intuitively when buying a car. I suggest you test drive more and watch chassis analysis.
2) differences in security
The impact resistance of the whole frame subframe can be improved because of the addition of longitudinal beams. For example, as shown in the figure below, two longitudinal beams directly connected to the radiator of the water tank are installed in front of the front subframe, which brings the advantage that in the event of a frontal collision accident, the two longitudinal beams will bear the frontal collision impact force together with the front beam, and play a positive role in dispersing and guiding the impact force.
In view of the high-speed collision in front of the vehicle, some sub-frames will also adopt a drop-off design. This design is also common in full-frame subframes. When a serious frontal collision occurs at high speed, the front subframe absorbs kinetic energy and disconnects from the car body, so that the engine sinks smoothly and will not be squeezed into the cockpit, which increases the deformation and energy absorption space of the engine room.
▲ The subframe falls off in the collision, the collision energy is released, and the powertrain can sink.
Of course, the H-beam subframe used in the Lectra series has a similar shedding design, so we can't deny the safety level of other subframes with one stick. The full-frame subframe has greater advantages because it can participate in the collision earlier.
3) Differences in Lightweight
The huge subframe will increase the weight of the car. In order to balance the above characteristics, the advantages of aluminum alloy subframe appear.
Interrupt a little anecdote. In 20 18, Magna International cooperated with Ford Motor Company to develop a carbon fiber subframe, which is 34% lighter than the stamped steel subframe. The high plasticity of carbon fiber greatly simplifies the process. The original 45 metal parts were replaced by two molded parts and four metal parts, and the number of parts decreased by 87%.
Originally hit it off, I intend to take the lead in using it on Ford Fusion to test the feasibility of this scheme. However, contrary to expectations, this kind of carbon fiber subframe can only absorb 5% of the impact kinetic energy, and it needs to be mixed with high-strength steel and other metals to alleviate the impact force. Everyone knows what happened afterwards. Ford Fusion announced in the middle of 20 19 that it would stop production in North America in 2020, and this short-lived project died.
Therefore, lightweight is indeed necessary, but at this stage, the aluminum alloy subframe is still the most advanced solution.
4) Difference in durability
Generally speaking, the durability of the subframe is trustworthy. In order to ensure safety, the subframe will be designed with a series of durability tests. For example, because the subframe will be stressed when braking, it is necessary to design a braking force durability test.
1. The durability test shall be carried out under the following conditions:
1) The load point is the central installation point of the ball pins of the lower swing arms on both sides, and the load is applied along the longitudinal X direction of the whole vehicle;
2) Both ends are loaded laterally at the same time, and the loading direction is as shown in figure 1. The loading is carried out under 0.8g starting condition and 0.8g braking condition, which is about 6000N N.
3) The test loading frequency f is 3Hz；;
The test requirement is that after 300 thousand cycles of durability test, the sample is not allowed to produce obvious permanent deformation or cracks.
Or for the impact on the subframe when turning, as well as the fatigue test of turning lateral force.
2. Carry out fatigue test according to the following conditions:
1) The load point is the central installation point of the ball pins of the lower swing arms on both sides, and the load is applied in the Y direction along the transverse direction of the vehicle;
2) Both ends are simultaneously loaded laterally. The loading direction is shown in figure 1, and the loading force is 0.8g when turning. The test range is about 6000 Newton. ..
3) The test loading frequency f is 3Hz；;
According to the test requirements, after 300 thousand cycles of durability test, the sample is not allowed to produce obvious permanent deformation or cracks.
As far as Che Tejun is concerned, the double-layer stamped steel plate structure is better than the welded or bolted structure. In concrete form, in fact, the performance of Yuanbao beam, H-shaped and full-frame structure is not bad, but the full-frame structure will be better in height, which is related to more force transmission channels and more complete structure. For example, a new generation of Land Rover found that the steel full-frame subframe is very large, and the rigidity of the car body brought by this result is unmatched by urban SUVs.
To sum up the above points, the form of the sub-frame is indeed a penny for a penny, but the primary difference of this kind of accessories lies in the presence or absence, and then the improvement of experience. For10 ~150,000 models, in fact, there is no need to be too picky about its configuration level. Of course, if the design of conscience can be given, it is naturally commendable.
Write it at the end
Thanks to the progress of technology, the allocation rate of sub-frames has become higher and higher, and all of them can ensure good durability. Although Yuanbaoliang subframe is enough for ordinary family cars, we hope to get a more advanced subframe form based on the principle of more advanced experience. After all, whether the chassis is whole, comfortable or not, and even safe or not is directly related to it.
After this article, I believe everyone has found that the sub-frame is indeed a penny for a penny, but the same type of sub-frame will still be used differently because of the different details, which is also the place where manufacturers can reflect the level and conscience of making cars.
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This article comes from car home, the author of the car manufacturer, and does not represent car home's position.