Lying under the car, what can you see? | technology flow

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In the face of suit sales in 4S stores, exquisite men and women who are among the scenes of the auto show, how can they show their insiders and extraordinary? Don't open the hood and look like a fool, crouch down, bend down, bow your head, look around and peek at the bottom of the car, and then slowly get up, or slightly chin up, or sigh softly, turn your back and pace away, hiding your merits and names.

Some people are born under the car.

Whenever car lovers gather together, the last round of the training level cloud confrontation will always be leaning down to the side of the car to guide and study the things under the skirt. Whenever a new car is released for test drive appreciation, and the car media teachers flock to it, you will always see several straight male technical houses squatting there for a long time, as if they are attached to the straight steel breath, and do not want to be blinded by the superficial flashy fans.

Not every drop of milk is called Terensu, and not every squat is really purposeful.

Leaving aside the pretentious and deep performances, let's seriously explore what they can see and what they can see when they (we) crouch down and stick their heads under the car, as far as the naked eye can see.

Since we talk about "bottom", we naturally think about the chassis and suspension first. In our traditional understanding of the "three major pieces", the engine and transmission are now mostly blocked by the chassis guard plate, and the suspension system needs "moving space" after all. So from the bottom of the car perspective alone, you can at least roughly distinguish the basic structure of the front and rear suspension, as well as some of the more obvious suspension configurations.

More importantly, the old friends of our column should know that the terms such as "multi-link" used by car companies and the media are actually very broad in definition and have little reference value. And once you have mastered the naked eye to distinguish the "hanging", no matter how vague, chaotic, and indiscriminate the writing on the configuration table is, it will not be able to hide your crouching down.

The front suspension does not need to be said too much, and there are only two front suspension structures widely used in passenger cars today, namely the familiar MacPherson and double wishbone suspension. The former is sometimes referred to as the "spring-damped strut suspension", while some of the latter are referred to as "five-link suspension" due to differences in detail (you may wish to jump to "What's Wrong with No Suspension in the Electric Age?"). "), but on the whole can still be classified into these two categories.

The difference between McPherson and double wishbones has long been an enduring old topic in the Internet world (we have also participated in the column: "Why is double wisharm YYDS?"). 》）。

It's just as easy to tell the difference — you don't even need to actually look at the bottom of the car, crouch down and look through the gap between the top edge of the front tire and the bottom edge of the wheel arch. If all you can see is a damping spring pillar, then there is a high probability that it belongs to the McPherson front suspension; if you can witness a metal "wishbone" (which is actually the upper wishbone of the "double" wishbones), then the front double wishbone suspension is unmistakable.

Upper wishbones of the BMW iX front double wishbones

McPherson had only spring shock absorbers in this position

An exception is the so-called "low double wishbones", because the upper wishbones are lower, completely obscured by the wheels, and the "wishbones" cannot be seen in the gaps between the wheel arches. This double wishbone suspension is more common in more extreme high-performance vehicles, so it is not necessary to identify it. To distinguish between the low double wishbones and the McPherson suspension, the front wheel needs to be deflected at an angle, as will be mentioned below in the rear suspension section.

The rear suspension is varied. First of all, another old friend of everyone, the torque beam is not independent suspension. This is very simple, crouching down from the rear of the car to look at the rear axle, if there is a black steel beam that is coherent left and right, it can be concluded that it is the rear suspension of the torsion beam.

If the left and right are separated from each other, then enter the world of independent suspension.

The McPherson suspension can also be used on the rear wheels and is even sometimes tucked into the "multi-link" category. In fact, "multi-link" is not strictly defined, it only limits the number of connecting rods to "many", but any ≥ three links may be counted as multi-link. When the McPherson suspension is used in the rear axle, it requires at least two lateral linkages and a longitudinal arm (hence the early years as "double/triple rods", commonly known as "chopsticks").

Observe the front of the rear wheel from the bottom of the car side, and whether there is a longitudinal control arm extending from the rear wheel to the front of the car. If so, then it has a high probability, either the rear McPherson suspension or the rear E-type multi-link suspension. The latter is named after the "three horizontal and one vertical" structure similar to the letter E (but it does not look like it), and it is also called "four connecting rods".

The longitudinal arm of the Transgechi GS8 rear E-type multi-link suspension, visible on both sides

To distinguish between these two rear suspension structures with longitudinal arms, you need to go around the bottom of the rear and focus your attention on the inner knuckle of the rear wheel (what is the knuckle Please jump "What shaft is Tesla broken?"). 》）。 If the rear shock absorber and spring are one, and the lower end is fixed to the upper end of the rear steering knuckle, then the probability is the rear McPherson suspension; if the rear shock absorber and spring are independent of each other, and the lower end is connected to the connecting rod instead of the steering knuckle, it can basically be determined as an E-type multi-link.

The Transgechi GS8 rear E-type multi-link, paying attention to the separation of the spring and shock absorber, is connected to the connecting rod below

In an ancient Camry's rear MacPherson suspension, the red ring is a spring-loaded shock-damping integral pillar in the shadow connected to the upper end of the steering knuckle, and there is no connection on the connecting rod in the blue circle

This feature of the McPherson suspension can also be used to distinguish between the McPherson front axle and the low-profile double wishbone suspension. The front wheel deflects at an angle to look at the inside of the wheel, if the spring-dampened strut is fixed at the upper end of the steering knuckle, it is the McPherson suspension; if the strut is attached to the lower wishbones/connecting rods, it is most likely a double wishbones suspension, at this time you may wish to look carefully for where the upper wishbones are hidden.

The 991 GT3 has a low-profile double wishbone with the lower end attached to the lower wishbone

In the front McPherson of the BMW i3, the reeds connect the knuckles, and the joints are fixed dead

Speaking back to the rear wheel. If no longitudinal arm is found at the front of the rear wheel, nor is it a non-independent structure of the torsion beam, then congratulations, the rear suspension of the car in front of you may be more "advanced" (relative, and only structurally rather than specifically), with a rear H-arm multi-link or rear five-link structure.

Similar to the case with the front suspension, the rear five-link is actually related to the rear double wishbones, although the former is used more on the rear wheels of mainstream passenger cars. As the name suggests, five rods can be counted. However, in order to reduce the wind resistance, today's new cars generally use various guard plates, and even cover the lower connecting rod, so it is not easy to actually count.

BMW iX rear five links, you can see two, note the lower link with a guard plate

The H-arm multi-link has more recognizable features. Look down from the bottom of the rear and you'll notice a wide lower control arm with two hinges (H-shaped) on each side of the wheel and body. In addition, because the H arm is often too heavy if it is made of steel, most of the practical applications are silver aluminum.

Porsche Macan rear H-arm multi-link, note the difference in the appearance of the H-arm and the guard plate linkage in the upper five-link

In addition to the H-arm itself, in the H-arm multi-link suspension structure, you can only find at most two independent lateral linkages (arrows in the figure below).

If you lift the car, the H-arm will be more intuitive

After the above steps, and then excluding the H-arm multi-link, then the remaining probability is only the last possibility of the five links. In fact, the last five links are clear from the perspective of the structure diagram, but because the five connecting rods are relatively "ordinary", can be shaped into various "looks", and are likely to cover each other, from the perspective of the bottom of the car under which humans are crouched, it becomes less recognizable.

The rear five connecting rods of the ID.3, such a perspective needs to be confirmed with no longitudinal arm and non-H arm, picture: Autohome

Lexus LC rear five links, only four links can be seen in the picture, note that the red also serves as the rear steering lever

These laws are mainly for today's new cars, which are more than ten years and eight years old, because the interference of some "ancient" suspension structures is not fully applicable. For models listed in the past two years, familiar with the characteristics of the above suspension structures, you can basically recognize the basic structure of the front and rear suspensions of 90% of the load-bearing body models.

Of course, it needs to be emphasized again that structure is just structure, it is a foundation but does not determine the whole. From the perspective of crouching down to see the bottom of the car, you can also see some important suspension configurations more clearly, such as whether it is equipped with rear wheel steering, air springs, active anti-roll bars and so on.

Extreme Kr 001, very obvious air spring

In addition to the suspension, the body structure is sometimes strengthened under the car, especially in models with relatively low body stiffness such as convertibles and SUVs. For example, the BMW X3 28i below has two cable-stayed rods at the bottom of the rear to increase the stiffness of the body, and these two reinforcement bars are not available on some 25i models.

Of course, it is not advisable to judge the car with the naked eye. Don't say that it is a car consumer and a enthusiast, even if you have built a car for a lifetime and played with a car for a lifetime, it is unlikely that you can pat your chest and tell you that he can 100% predict what a car looks like with a glance. But on the other hand, looking at the problem dialectically, this is not to say that we cannot obtain any useful information based on our vision alone.

Although the basic structure of a suspension is only a structure, it is not only structural theory, but also to recognize that any kind of suspension has its own advantages, disadvantages and performance limitations. Coupled with the specifications of other suspension hardware, although it is impossible to derive a specific performance level, it is no problem to judge the general performance orientation and cost investment of a car.

The same is true of the body, power, braking, transmission, and other things we haven't talked about much. When you see the rear differential in the center of the rear axle covered with heat sinks, you know that this will not be a weak car; when you see the dense reinforcement of the rear wheel arch, you know that it will not be a low-end entry model with cast aluminum; when you see the hollow treatment on the aluminum suspension linkage, you should know that it is important to look at the lightweight of this car.

Spying on the bottom of the car is not a mysterious knowledge, but it also does not hide any martial arts secrets that are clear at a glance. Not every child who squats when he sees the car understands what he wants to see and what he can see, but not every straight man and woman who kisses the butt of the car and does not let go is just trying to give a new word to understand.