The world is sometimes weird. When you are responsible for something and want to do it well, no one cares whether it is good or bad, right or wrong. When you are not in the right place, others will swarm with problems. The one who appeared in front of you, I realized that I might have met the PUA in the workplace. Regarding the bushing, I have talked about many details casually before. People who understand are bored, and those who don`t understand are struggling to read. This also violates my original intention of writing the bushing article, so I plan to write a bushing case. Let's explain it to facilitate everyone's understanding.
Back to the basic concept, is it difficult to make bushings? Not difficult to do! If you just want to make a bush with no problem with fatigue, then you find a reliable supplier, and then choose the most similar model from their technical accumulation, and use "the fatigue adjustment may be problematic" in front of the performance team. Lie down comfortably for this reason, and the leader cooperates. It should be no problem to be a salted fish. But if you want to see the stars and the sea, and plan to work out an ideal suspension with the tuning team, it will be difficult to reach the sky by selecting the model alone. Here we have to develop from zero to one based on the performance requirements and the capabilities of the supplier. The layout of the bushings should be developed before all the structural parts, and the margin for adjustment can be considered as a real entry.
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So the question is, how big is the suspension performance gain between the good and bad bushings? Is it cost-effective to invest in manpower and material resources? The answer is yes. Let's take a look at the adjustment parts of the chassis first, there are not many things that have room to play tricks. The spring plays a supporting role, depending on the stiffness changes. Most of them are straight springs and eccentric springs. At most, they are looking for a variable stiffness spring. The rest is to go to the electronic control. This is a joke without hundreds of millions of development costs; stability The rod is also called the anti-roll rod. Its contribution is to control the lateral angle of the vehicle. To be more technical, it can only be said that the performance of the tight test bushing improves the line stiffness efficiency and the hollow rod lightweight; the shock absorber is the most effective thing. It converts the suspension motion vibration from mechanical energy to thermal energy. The core is to adjust the valve system during the adjustment process. Most of them are based on selection and matching, and they are also electronically controlled, which is very expensive. As for the bushings, there are about 20 bushings in total. The difference between good and bad is no more than 100 yuan. The development cost is several million to the sky, but it can greatly improve the comfort and reduce the rubber lag by reducing the torsional stiffness and dynamic stiffness. Improve maneuverability. If the bushing can be developed positively, the suspension performance is destined to jump out of the dilemma that fatigue is only 600 minutes long, and it will provide greater support and improvement to the performance department, which is extremely cost-effective.
Firstly. Here we need to classify the bushings in different positions. The first category is torsion beam and trailing arm bushings, which take into account handling and comfort performance. The movement is extremely complicated. Fatigue is considered to be qualified. As for the best chasing performance, It is a luxury; the second category is the front swing arm comfort bushing and the rear sub-frame bushing, which are mainly comfortable, with moderate fatigue difficulty, and performance has the opportunity to make some new tricks; the third category is other swing arms Bushings. These bushings are mainly manoeuvrability, and the impact on the suspension is not as obvious as the previous four bushings. They need to be optimized on a system-by-system basis, so they are relatively simple.
Here we will use three examples to explain (it will be divided into three chapters, anyway, it will be written, whether you post it depends on my mood~especially the performance of the white prostitution~), let's take the development of four-bar bushing as an example ( The stiffness is not real and is for reference only).
A rod bushing required stiffness: radial 12000N/mm, vertical 500N/mm, torsion 1.5N.m/° Fastener M14 aluminum
B-rod bushing required stiffness: radial 2000N/mm, vertical 500N/mm, torsion 1.5N.m/° Fastener M14 aluminum
C-rod bushing required stiffness: radial 14000N/mm, vertical 500N/mm, torsion 1.5N.m/° Fastener M14 aluminum
D rod bushing required stiffness: radial 9000N/mm, vertical 500N/mm, torsion 1.5N.m/° Fastener M14 aluminum
First of all, we clarify our input. We can see the radial stiffness of the four bushings. The stiffness of bushing B is much lower than that of other parts. We need to confirm the static load to confirm whether there is excessive movement at this point and avoid The three harder points do not move, and the soft points are fatigued due to excessive exercise.
Assuming that there is no problem, take point A as an example. Before we choose the structure and rubber, we need to clarify our design ideas. What are the hidden attributes of the core of the suspension link bushing? In my personal opinion, the minimum torsional stiffness and rubber hysteresis should be provided while the stiffness requirements are met. Then, before pursuing these properties, the fatigue problem is the first mountain we must cross.
Rubber has a very strange characteristic. It is compressive and not tensile, and all fatigue failures are tensile (except for aging). We can avoid it in two ways. One is the structural design to avoid excessive stretch of the rubber, and the other is to select the formula with the best fatigue performance. Traditional bushing development often has a fixed structure and size, and the rubber material is also fixed. However, the force of the vehicle is different, so it can only meet the pure fatigue performance. Now we need to jump out of the traditional design and no longer use the bushing layout size as a constant , And then use the compound with the best comprehensive performance as a constant.
Then after the idea is determined, we return to the structural design. First of all, we do not have a hollow direction, the rigidity is large, and the torsion requirement is small. We can choose the structure with a middle frame insert (if you still think of the inner frame drum type and high torsional rigidity, then you can only say that you know the performance of the vehicle. Too little. The superposition of torsional stiffness will produce parasitic stiffness. Although the model has elastic characteristics, it actually reflects many viscous characteristics. Too high contribution rate of parasitic stiffness will make the rear suspension always have a feeling of screwing force).
The first is the inner frame, M14 fasteners, aluminum. We can calculate the cross-sectional area that meets the crushing requirements, and then combine the friction coefficient and static load to determine whether the two ends need to be frosted or knurled. I will not elaborate on the design details here. This needs to be designed in accordance with the specific capabilities of the supplier. The auto factory focuses on auditing, then we can get the outer diameter of the inner frame: A=14 (bolt size) + 0.5 (assembly space, combined with specific needs) Adjustment) + wall thickness (satisfying crushing, process failure, etc.) + X. Then combine the width of the interface to define the height of the inner skeleton to complete the inner skeleton design.
When it comes to the rubber part, thickness is the core of the performance of the bushing, and it is also a concentrated experience of the supplier's capabilities. First of all, we must clarify which variables are related to the stiffness of the bushing: it is proportional to the modulus of the rubber, inversely proportional to the thickness of the rubber, and proportional to the height of the rubber. Most of the rubber materials with the best fatigue performance in China are controlled at 60 Shore hardness, while most of them abroad are around 45-50. The corresponding rubber thickness is, for example, 8mm and 6mm, then the difference begins to appear: the 60HA solution will naturally be higher than the 45HA solution due to the hardness limit of the formula, which will have a negative effect on the comfort, and more Thick glue may bring more lag, and for suspension and other stiffness conditions, it will make the control more sluggish. Of course, this does not take into account the requirement of a linear section of rigidity for the bushing. If there is a requirement for a linear section, the thickness of the rubber is already fixed, and the rubber is also fixed.
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Most of the exoskeleton has a fixed thickness, which can meet the requirements of press-in force and extrusion force, and the length needs to be defined. In fact, the length of the exoskeleton is strongly related to the length of the rubber. We need to judge the movement position of the exoskeleton in combination with the static load and the vertical stiffness curve of the bushing. Under the maximum tolerance, there will be no collision noise.
In all cases, we have obtained the following dimensions: inner skeleton outer diameter + rubber thickness + adhesive thickness + outer skeleton thickness, the outer diameter of a bushing has been determined, and the configuration is the most comprehensive performance Good rubber compound. Many careful young men have discovered, why can't domestic suppliers use 45HA rubber? Because of the diameter reduction, the closed-end bushing will have two diameter reductions, one after vulcanization, to eliminate stress concentration, and one is to press in the swing arm sleeve to provide extrusion force and squeeze rubber. After previous calculations, the difference between the outer diameter of 60HA and 45HA compounds is 6mm or more, and for every 1mm reduction in outer diameter, the increase in press-in force is exponential. Therefore, foreign suppliers have worked hard to increase the amount of shrinkage, such as opening linings. Set or something
In fact, at this point, we have a qualified swing
Arm Bushing layout, which has low dynamic stiffness and hysteresis, and the best fatigue performance. But if this is enough, it can only mean that you are not pursuing. The students who have participated in the adjustment know that the adjustment team will change the bushing hardness to optimize the actual performance of the vehicle. After two rounds, the rubber may enter a hardness range with high fatigue risk, so we really have to lie down again. Let performance compromise? Or let the project give a grinding fee to change the space of the swing arm or the sub-frame? I don't want either. We have already reserved this X genius margin when calculating the outer diameter of the inner frame. For example, the two adjustments are to reduce the hardness. Our compound has become 39HA or even lower. We can replace the stiffness with 45HA. We only need to ensure that the outer diameter remains unchanged, and the inner skeleton minus the thickness of X In this way, the internal skeleton will not fail, and it will also make room for the change of the compound, and the overall performance such as fatigue will be back to the best.
