The world is so unfair to brakes
The world is too unfair to brakes: except for the so-called "failure", people rarely look at it.
Like many things in the world, "stopping" is sometimes harder than "moving", and it is often harder to stop than run fast. For people who change cars from racing cars to play cars, brakes may even be one of the upgrades with the highest priority and the fastest effect.
In the early years, consumers would still pay attention to the difference between disc brakes and drum brakes. As drum brakes were eliminated at mainstream prices and disappeared for a while, only the performance-oriented high-end market still cared about details such as the number of caliper pistons, ventilation holes and so on. But in fact, even if it is not a "high game", the braking system is worth your while.
What can the front or rear of the caliper show?
Today's modern passenger cars have basically entered the era of disc brakes (the reverse movement of individual drum brakes will not be mentioned for the time being). What everyone is familiar with is the diameter of the brake disc and the size of the caliper, which can explain the excellent braking performance of a car. Poor, and thus imply the level of the overall performance of the vehicle.
In addition to these more intuitive and actual ratios, the orientation of the front wheel brake calipers will also reveal some additional vehicle information. Generally speaking, the front wheel calipers of transverse engine front drive vehicles are mostly located on the front side of the vehicle, while the front calipers of longitudinal engine rear drive vehicles are mostly located on the rear side (of course there are no shortage of exceptions).
This difference is mainly related to the cabin layout of fuel vehicles.
The engine of a front-wheel drive vehicle with a transverse engine is usually located in front of the front wheel axle, and because the transverse arrangement occupies a large transverse space, the front wheel steering rod is usually arranged behind the front wheel axle, which results in most of the front wheel brake calipers (the front of the car) direction).
This is not an ideal arrangement for the dynamic performance of the vehicle.
With the tie rods located behind the wheel contact point, the outer wheel with more steering pressure receives a push rather than a more consistent pull, which has a natural detrimental effect on steering stability. Therefore, today's Zhiji L7, Weilai ET5, etc. have begun to promote and emphasize the selling point of their own steering rod front.
Since the rear-wheel drive vehicle with a longitudinal engine has a gearbox and a transmission shaft running through the center of the vehicle, the front wheel steering gear and the steering rod are no longer easy to arrange behind the wheel axle, and most of them will choose the front steering rod. Therefore, the steering rod occupies the space in front of the wheel steering knuckle, and the front brake calipers tend to be arranged on the rear side (rear direction)。
Kia Stinger removes engine, transmission makes it difficult to rear steering rod
As for the brake itself, the front-mounted calipers are facing away from the front of the car, which is not ideal when using the airflow during driving to dissipate heat; on the contrary, the rear-mounted calipers have certain natural advantages in heat dissipation. Rear-mounted front-wheel calipers are also helpful for the weight distribution of the vehicle, especially for high-performance sports cars with lighter vehicles and larger brake ratios. Rear-mounted front-wheel calipers + front-mounted rear-wheel calipers are almost standard operations.
In the era of electric vehicles, many of the exclusive pure electric platforms that really let go of their hands and feet have left behind the structural constraints of the era of fuel vehicles. Although Volkswagen’s MEB platform is still positioned as an economical car, the ID.3 and ID.4 not only adopt a rear-drive configuration, but also use a steering gear/steering rod at the front and calipers at the rear for the front wheels. Better arrangement.
Floating or not, depends on what you say
"Float" is a word that comes up a lot in the rim jargon about braking. For the two most important parts of the disc brake system: the brake disc and the caliper, the meaning of the word floating is different.
For brake discs or brake discs, "floating disc" is an advanced type that is different from conventional fixed brake discs. Conventional brake discs generally have a single-piece structure, and the central part does not actually participate in braking friction, so the volume change is relatively small during the entire working process; however, the outer ring part will heat up sharply under intense braking, and its volume will expand significantly.
Differences in temperature and expansion between the inner and outer parts can cause pulling and deformation that can affect performance and safety.
Then there is a floating brake disc, the wheel mounting part of the inner ring is separated from the brake friction part of the outer ring, and different materials are usually selected (for example, carbon ceramics are used for the outer ring). The connection structure between the two has an expansion allowance, which allows the outer ring to heat up and expand under severe friction, increasing the working limit of the braking system.
For brake calipers, fixed calipers, or fixed calipers and opposing calipers, are an advanced choice compared to conventional floating calipers. Conventional calipers will only have pistons on one side (usually the inner side of the wheel), especially for ordinary family cars with low performance requirements. Naturally, the single-piston calipers used can only be one-sided pistons.
The reason why the conventional single-side piston (not necessarily single-piston) caliper is called "floating" is because of its working principle: at the beginning of the braking force establishment, the brake pad on the side of the piston is pushed out to contact the brake disc first, and then the top of the piston When the action stops, the caliper as a whole "floats" inward to make the outer brake pad contact the brake disc, so it is called a floating caliper
。
This structure only relies on mechanical action, and the outer part of the caliper does not need to arrange oil pipelines, and the structure is relatively simple; but it is obvious that the braking force on both sides is not uniform enough, which affects the braking effect and makes the brake oil more likely to overheat. Floating calipers are generally It is understandable that it is only used for domestic models.
For higher performance requirements, a fixed caliper with pistons on both sides is required, which is often called an opposing caliper. When pistons are arranged on both sides, the brake disc can be clamped inward from both sides at the same time, and naturally there is no need to allow the caliper to have the ability to "float", that is, the fixed caliper is commonly known as the fixed caliper.
The advantages and disadvantages of fixed calipers are not difficult to see. Contrary to floating calipers, it can provide more average and stable braking force, and the performance limit is higher; but it needs to leave more space on the outside of the brake disc, especially inside the calipers. The outer side requires a more complicated oil circuit arrangement, and the cost is naturally higher.
As the trend of electrification advances, the previous disc brake problems are put aside first, and drum brakes unexpectedly return to the field of vision. Volkswagen has adopted drum brakes on the rear wheels of the MEB platform (the configuration already on the market), and as expected, it has received a lot of dislike. However, the weakening of the rear wheel braking system of electric vehicles with rear motors is a phenomenon in line with technological evolution.
The third-generation Formula E electric racing car, which will be launched in 2023, directly and completely cancels the rear wheel (hydraulic) brakes, and relies entirely on the kinetic energy of the rear motor to recover the braking force. The front-drive configuration of Volkswagen MEB (unlisted) no longer has a rear motor. Although the applicable model positioning is lower than ID.3 and ID.4, it uses rear disc brakes instead.
When the "electrified brake" of kinetic energy recovery enters the game, the trivial matter of stopping is not razored, but tends to become more complicated.