Recently, Volkswagen Group's new energy vehicles broke the circle again! The reason for the circle break is not that they have adopted any zenith star black technology, but because of the ancient and backward - drum brake, which has "seen the light of day" on the Volkswagen ID series electric vehicles and even the Audi Q5-e-tron model.
According to the consistent views of netizens, the drum brake grade is low and the performance is poor. Models that pay attention to performance or material conscience and are generous will never be touched. The disc brake grade is high and the performance is good, so the "sincere" model should use the disc brake. Therefore, the "collective" drum brake of the new energy series of the Volkswagen Group has become the focus of the scolding.
"Media Teacher" explains volkswagen/Audi with drum brakes
It is to reduce drag and improve battery life
But recently I found that many media on the Internet are trying to make a "reasonable explanation" for the use of drum brakes by Volkswagen New Energy. One of the "more mainstream" statements caught my attention: there is a "return spring" in the drum brake, and after the brake is released, the brake pad will be "returned" under the action of the spring pull, so there is no contact between the brake pad and the brake drum, so there is no friction.
And the disc brake? There is no "return spring", after releasing the brake, the brake pad is only a very gentle "pull" on the surface of the brake disc (in their words, "loose and not far away"), still in contact with each other, although it is only a very gentle "pull", but there will always be resistance. - Professionally called "drag resistance".
In the words of those media: although the comprehensive performance of the disc brake is better than the drum brake, after all, the electric vehicle is more special, the electric vehicle is very sensitive to resistance, and the smaller the resistance of the wheel rolling, the more favorable it is to the endurance of the electric vehicle. Therefore, the Volkswagen ID series and Audi's choice of drum brakes makes some sense.
Disc brakes are more "advanced" than drum brakes
At least for cars, this statement does hold
OK！ The explanation given by the majority of "media teachers" is like this. So are they right? First of all, let's make one thing clear: drum brakes are indeed inferior to disc brakes – at least in the passenger car sector (the situation is completely different for freight vehicles).
Because the braking force of the disc brake is purely "linear", the amount of brake pedal you press, the force of the brake increases. The braking force of the drum brake is "non-linear", when you step on the brake pedal, the drum brake will "brake while adding force to itself, the more the brake is heavier" - this is the unique "self-enhancement" phenomenon of the drum brake (the specific principle we will not expand, after all, it is not writing a paper).
The phenomenon of "self-enhancement" is definitely a good thing for freight cars! Because of the existence of the "self-increasing force" phenomenon, a small drum brake can produce a very "brutal" braking force, and the freight vehicle is very heavy, so the larger the braking force, the better. Therefore, drum brakes are suitable for trucks.
But this is not necessarily the case for family cars: in addition to making the brake "foot feeling" worse, the phenomenon of "self-incrementing force" will also interfere with the work efficiency of the ABS/EBD system to a certain extent. Therefore, anyone who pursues the performance grade on the car will try to avoid drum brakes. If you don't understand the technical principle level of explanation, then just remember the simplest "logical rhetorical question": if the drum brake is better, then why not use the front wheel?
After explaining the first question, let's go back to the views of the "media teachers" on the use of drum brakes for Volkswagen/Audi New Energy. - They say that there is "residual resistance" in the disc brake, while the drum brake does not. Therefore, the drum brake for electric vehicles is a very advanced idea, and it is a design made to ensure endurance...
Then let's see if there is any "residual resistance" in the drum brake! "Media teachers" say that "there is no return spring in the brake", so what is the truth? It is true that many disc brakes do not have a return spring, but do you really believe that when we release the brake, the brake pads do not "return"?
In fact, the disc brake system, after releasing the brake pedal, the brake pad will also "return to position"! It's just that the amount of retraction is not as obvious as the drum brake. In the disc brake system, the high-elastic rubber sealing ring on the piston is used to do this work. —— After releasing the brakes, the sealing ring deforms under its own elastic force, "pulling the brake pads back into place".
Does the disc brake really not "return"?
Is it really "loose and not far away" so the resistance is large?
Of course, the "return volume" of the disc brake is very small, usually no more than 0.3 mm (that is, after the return, 3 strands of hair can be inserted between the brake disc and the brake pad). Therefore, after the disc brake is released, the brake pads and the brake discs are not in contact. It's just that the gap is small and looks like it's "shrugging"!
Therefore, the "residual resistance" of the brake is nonsense! The real reason for the "residual resistance" is the aging of the piston seal ring, or the poor lubrication of the caliper guide rail of the disc brake, which leads to the "unsmooth return" of the brake pads and leads to "dragging and grinding" (this is what the "media teachers" call "loose and not far away")
There are also many "brake pad separation circlips" for disc brakes
Car owners should be careful not to lose!
Of course, the probability of aging of the drum brake is much smaller, and it is indeed much more durable, which we also admit. Therefore, in order to prevent the brake pads from being "not smoothly returned", many new disc brakes have added "brake pad separation springs". It is to ensure that the brake pads can be correctly returned under the pull of the spring. Therefore, after the new disc brake adopts the "brake pad separation circlip", the "drag resistance" is not greater than the drum brake.
Of course, the shape of this "brake pad separation circlip" is very different from the traditional spring, so it is easy to lose. In fact, too many car repair shops have accidentally lost the "brake pad separation spring" when replacing the brake pad for customers, resulting in the abnormal "dragging" of the brake pad.
Then the customer will always hear the brake noise in the process of using the car, check and check and check and check the reason ("brake pad separation spring" is easy to ignore)... What's even more frightening is that I once heard some small workers in the auto repair industry claim that "it doesn't matter if this thing is installed or not"... Therefore, we recommend replacing the brake pads or try to find regular stores!
At the end of the article, we have to return to the Volkswagen/Audi use of drum brakes. Such a large enterprise, the grade of Audi Q5 is not low, why do you have to risk being scolded with a drum brake? ------------------------------------------------- It turned out that everything was for "weight loss"!
According to the data of the manufacturer of Volkswagen/Audi New Energy Drum Brake, they have reduced the weight of the rear brake for the Volkswagen Group by 30% with a simple drum brake structure! This is quite objective! Because in general, the front wheel of the civil car accounts for 70% to 80% of the brake load of the whole car, and the brake load borne by the rear wheel only accounts for 20% to 30% of the brake load of the whole vehicle. From this point of view, we don't need too high-end brake configurations at the rear. Therefore, it is acceptable for the rear wheel to brake with a drum, and this is the truth!
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