A disc brake is a type of brake that uses a caliper to press the pair of pads against the disk or "rotor" to create friction. This action inhibits the rotation of the shaft, such as the vehicle's axle, either to reduce the rotational speed or to hold it still. The energy of motion is converted into waste heat which must be dissolved.
Hydraulically activated disc brakes are the most common form of brake for motor vehicles, but the principles of disc brakes apply to almost all rotating axes.
Video Disc brake
Design
The development of type disc brakes started in England in the 1890s. In 1902, Lanchester Motor Company designed the brakes that were visible and operated in a manner similar to the modern disc brake system even though the disc was thin and the cable activated the brake pad. Other designs are not practical or widely available in cars for 60 years. Successful applications began in the aircraft before World War II, and even the German Tiger tank was fitted with discs in 1942. After the war, technological advances began to arrive in the 1950s, leading to a critical demonstration of excellence in the 1953 24 Hour Le Mans race, which required braking from high speed several times per lap. The Jaguar racing team won, using disc brake-equipped cars, with much of the credit awarded to superior brake performance over rivals equipped with drum brakes. Mass production began with the 1955 CitroÃÆ'¡n DS.
Compared to drum brakes, disc brakes offer better stoppage performance as the disks are more easily cooled. As a result discs are less susceptible to faded brakes that are caused when brake components overheat. Disc brakes also recover faster than submersion (wet brakes are less effective than dry ones).
Most drum brake designs have at least one leading shoe, which gives a servo effect. In contrast, disc brakes have no self-servo effect and the braking force is always proportional to the pressure placed on the brake pad by the braking system through the brake servo, braking pedal, or lever. This tends to give the driver a better "feel" and help to avoid future congestion. Drums are also susceptible to "bell mouthing" and trapping of lining materials used in assembly, both causing various braking problems.
Disks are usually made of cast iron, but may in some cases be made of composites such as reinforced carbon or ceramic matrix composites. It's connected to the wheel and/or axis . To slow the wheel, the friction material in the form of brake pads, mounted on the brake calipers, is mechanically, hydraulically, pneumatically, or electromagnetically applied to both sides of the disc. Friction causes the disc and the connected wheels to slow down or stop.
Maps Disc brake
History
Initial experiment
The development of disc brakes began in England in the 1890s.
The first caliper-type disc brakes were patented by Frederick William Lanchester at his Birmingham factory in 1902 and successfully used on Lanchester cars. However, the limited choice of metal in this period means that it has to use copper as a braking medium that works on the disc. The current bad road condition, no more than a dusty and rough road, meant that the copper quickly made the system impractical.
Successful applications began in aircraft and tanks before and during World War II. In the UK, the Daimler Company used disc brakes on the Daimler Armored Car of 1939, the disc brakes, made by the Girling company, are required because in four-wheel drive vehicles (4x4), the epicyclic final drive is in the wheel hub and therefore leaves no space for conventional hub-mounted drum brakes.
At Argus Motoren Germany, Hermann Klaue (1912-2001) has a patented disc brake in 1940. Argus-supplied wheels are equipped with disc brakes for example. to Arado Ar 96. The German Tiger I heavy tank, introduced in 1942 with a Argus-Werke disk 55 cm on each drive shaft.
American Crosley Hot Shot is often given credit for the first production disc brakes. For six months in 1950, Crosley built the car with this brake, then returned to the brake drum. The lack of adequate research leads to reliability issues, such as sticking and corrosion, especially in areas that use salt on winter roads. Conversion drum brakes for Hot Shots are quite popular. Disk Crosley is a Goodyear development, a caliper type with ventilated discs, originally designed for aircraft applications.
Chrysler developed a unique braking system, offered from 1949 to 1953. Instead of a dish with a pressed caliper on it, the system uses a double expansion disc that scrubs the inner surface of the cast-iron brake drum, which is duplicated as a brake home. The disk spreads to create friction against the inner drum surface through the standard wheel cylinder action. Because of the cost, the brakes were only standard on Crown Chrysler and the City and State of Newport in 1950. They were optional, however, at other Chryslers, priced around $ 400, at a time when the overall Crosley Hot Shot sold for $ 935. The wheel was built by the Automated Specialties Expertise Company (Ausco) St. Joseph, Michigan, under the inventor's patent H.L. Lambert, and was first tested in Plymouth 1939. The Chrysler disc is "self-energizing," in which some of its own braking energy contributes to the braking effort. This is done by a small ball mounted in an oval hole that leads to the brake surface. When the disc makes initial contact with the friction surface, the ball will be forced up the hole which forces the disc to separate further and adds braking energy. This is made for lighter braking pressure compared to calipers, avoiding fading brakes, encouraging better operation, and providing one-third more friction surfaces than a standard twelve-inch Chrysler drum. The present-day owner considers Ausco-Lambert to be very reliable and powerful, but acknowledges his toughness and sensibility.
First use in race
The first use of disc brakes in racing was in 1951, one of the BRM Type 15 uses the Girling set produced, the first for Formula One cars. Reliable caliper type disc brakes then appeared in 1953 in the Jaguar C-Type racing car. This brake helped the company to win the 1953 24 Hours of Le Mans, developed in the UK by Dunlop. That same year, the Austin-Healey 100S aluminum body, of which 50 were made, was the first car sold publicly to have disc brakes, fitted to all 4 wheels.
Mass production
The first mass production use of modern disc brakes was in 1955, at the CitroÃÆ'¡n DS, which featured brake discs of the caliper type among many innovations. This disc is installed near the transmission, and is supported by the vehicle's central hydraulic system. The model went on to sell 1.5 million units over 20 years with the same brake setup.
The Jensen 541, with four-wheel disc brakes, was followed in 1956. Triumph showcased the 1956 TR3 with disc brakes to the public, but the first production car with Girling disc brakes was made in September 1956.
The most popular disc brakes on sports cars when first introduced, because these vehicles are more demanding about the performance of the brakes. Discs have now become more common in most passenger vehicles, although many (especially light vehicles) use drum brakes on the rear wheels to keep costs and weights down as well as to simplify the provision for parking brakes. When the front brakes do most of the braking effort, this can be a reasonable compromise.
Many of the initial implementations for the car lies the brakes on the inside of the driveshaft, near the differential, while most current brakes are located inside the wheel. The inboard location reduces the weight of the unsprung and removes the source of heat transfer to the tire.
Historically, brake discs are produced worldwide with a strong concentration in Europe and America. Between 1989 and 2005, the manufacture of brake discs migrated to China.
In the US.
After 10 years of absence, the US built another production car equipped with disc brakes - Studantier Avanti 1963 (Bendix system is optional on some other Studebaker models). Front disc brakes became standard equipment in 1965 at Rambler Marlin (Bendix units are optional on all Rambler Classic and Ambassador models of American Motors), as well as on Ford Thunderbird and Lincoln Continental. The four-wheel disc brake system was also introduced in 1965 at Chevrolet Corvette Stingray.
Motorcycles
The first motorcycle that uses disc brakes is a racing vehicle. MV Agusta was the first to offer small disc brake bikes to the public on a small scale in 1965, on a relatively expensive touring motorcycle, using mechanical brake relations. In 1969 Honda introduced the more affordable CB750, which features a hydraulically actuated disc brake (and rear drum brakes), and sold in large quantities. Disc brakes are now common on motorcycles, mopeds and even mountain bikes.
Brake disc
The disc brake (or rotor) is the rotating part of the wheel brake disc assembly, which is passed through the brake pads. The material is usually a gray iron, a kind of cast iron. Disc design is somewhat varied. Some are only solid, but others are hollowed with fins or propellers that join together two disk contact surfaces (usually included as part of the casting process). The weight and strength of the vehicle determine the need for ventilated discs. The "ventilated" disk design helps remove the heat generated and is commonly used on heavier front discs.
Discs for motorcycles, bicycles, and many cars often have holes or slits that cut the discs. This is done for better heat dissipation, to help surface water dispersal, to reduce noise, reduce mass, or to cosmetic marketing.
Slotted discs have shallow drains that are worked into the disc to help remove dust and gas. Slotting is the preferred method in most racing environments to remove gas and water and to degrade brake pads. Some discs are drilled and placed. Slotted discs are generally not used on standard vehicles because they quickly use brake pads; However, the removal of this material is beneficial for racing vehicles because it makes the pads soft and avoids the vitrified surfaces. On the road, drilled or hollow discs still have a positive effect in wet conditions because the holes or gaps prevent the film from building water between discs and pads.
A floating dish is lined, rather than rigid, to the center as a way of avoiding thermal stress, cracking and curling. This allows the disk to expand in a controlled symmetrical manner and with unwanted heat transfer to the hub.
Motorcycles and scooters
Lambretta introduced the first high volume production of single disc brakes, floating, front, enclosed in ventilated and cable-driven alloy cabs, in 1962 TV175, followed by a range-topping GT200 in 1964. The 1969 Honda CB750 introduced hydraulic disc brakes in scale large to the public wide motorcycle, following the lesser-known MV Agusta 600 1965, which has a cable operated mechanical actuation.
Unlike car disc brakes buried in the wheel, bicycle disc brakes are in the airflow and have optimal cooling. Although cast iron discs have a porous surface that provides superior braking performance, such discs are rusty in rain and become unsightly. Therefore, motorcycle discs are usually made of stainless steel, drilled, bent or wavy to disperse rainwater. Modern motorcycle discs tend to have a floating design in which the discs "float" on the coils and can move slightly, allowing a better centered disk with fixed calipers. The floating disk also avoids disc warping and reduces heat transfer to the wheel hub. Calipers have evolved from simple single piston units to two, four and even six-piston. Compared to cars, motorcycles have a higher center of mass: the ratio of wheelbase, so they experience heavy transfer during braking. The front brake absorbs most of the braking force, while the rear brake works primarily to balance the motorcycle during braking. Modern sport bikes typically have large twin front discs, with single back discs that are much smaller. Very fast or heavy bikes may have discarded discs.
Early disc brakes (as in the early fours of Honda and Norton Commando) place the calipers on top of discs, in front of the fork sliders. Although this gives better brake pads, it is now almost universal practice to put the caliper behind the slider (to reduce the angular momentum of the fork assembly). The rear disc caliper can be mounted on top (eg BMW R1100S) or below (eg Yamaha TRX850) swing arm: the low stand is slightly better for CG purposes, while the top placement makes the caliper cleaner better and is protected from roadblocks.
Modern developments, especially in reversed ("upside down" or "USD") forks are radial mounted caliper. Although this is fashionable, there is no evidence that they improve braking performance, nor does it increase the rigidity of the fork. (Lack of fork buffer option, USD fork is best corroborated by too large front axle).
Bicycle
Mountain bike disc brakes can range from simple, mechanical (wired) systems, to costly and powerful multi-piston hydraulic disc systems, commonly used on racing bikes downhill. Improved technology has seen the creation of discs discarded for use on mountain bikes, similar to those in cars, which were introduced to help avoid fading heat in alpine descendants quickly. Although less common, discs are also used on road bikes for all-weather cycling with predictable braking, though drums are sometimes preferred because it is more difficult to break in crowded parking, where discs are sometimes bent. Most disc brakes are made of steel. Stainless steel is preferred because of its anti-rust properties. The disc is thin, often about 2 mm. Some use two-piece floating discs, others use floating calipers, others use floating pads in the calipers, and some use a single moving pad that creates a caliper slide on its mount, pulling another pad into contact with the disc. Because the "motor" is small, the unusual bicycle brake feature is a retractable cushion to remove the drag when the brakes are released. Instead, most other brakes drag the bearings lightly when removed so as to minimize initial operational trips.
Heavy vehicles
Disc brakes are increasingly being used on very large and heavy road vehicles, where the previous large brake drum is almost universal. One reason is that the lack of self-help from the discs makes the braking power more predictable, so the peak brake power can be raised without more risk of braking induced braking or grooved on the articulated vehicle. Others are less fade disc brakes when it is hot, and in heavy vehicle air and rolling drag and braking the engine is a small part of the total braking force, so the brakes are used louder than on lighter vehicles, and the faded drum brakes can occur in one stop. For this reason, a heavy truck with disc brakes can stop at about 120% distance from a passenger car, but with a drum stop it takes about 150% of its distance. In Europe, remote regulation basically requires disc brakes for heavy vehicles. In the US, drums are allowed and are usually preferred because of lower prices, although the total lifetime costs are higher and the service intervals are more frequent.
Rail and airplane
Still larger discs are used for rail cars and some airplanes. Passenger and light rail vehicles often use disc brakes from the wheel, which helps ensure free cooling air flow. However, on some modern passenger cars, like the Amfleet II car, the inboard disc brakes are used. This reduces wear and tear of debris, and also provides protection from rain and snow, which will make the discs slippery, and unreliable. However, there is still plenty of cooling for reliable operation. In contrast, some aircraft have brakes fitted with very little cooling and the brakes get hot enough at the stop, but this is acceptable because there is time for cooling, and where the maximum braking energy is highly predictable.
Automotive use
For automotive use, disc brake discs are usually made from a material called gray iron. SAE maintains specifications for the manufacture of gray iron for various applications. For normal light car and light truck applications, the SAE J431 G3000 specification (replaced to G10) determines the range of hardness, chemical composition, precise tensile strength, and other properties necessary for usage purposes. Some race cars and aircraft use brakes with carbon fiber discs and carbon fiber pads to reduce weight. The wear rate tends to be high, and braking can be poor or grabby until the brakes are hot. For this reason, many performance-oriented vehicles or trucks that pull something overweight are equipped with perforated or ventilated rotors. This kind of increase eliminates excessive heat and removes contaminants that can interfere with the grip. Usually performance rotor is installed as an aftermarket upgrade or comes as part of a performance package at a given trim level from the factory. The main drawback of vented and slotted rotors is high wear.
Racing
In racing cars and high-performance cars, other disk materials have been used. Reinforced carbon discs and bearings inspired by aircraft braking systems as used on Concorde were introduced in Formula One by Brabham in conjunction with Dunlop in 1976. Carbon-carbon braking is now used in most top-level motorsport around the world, reducing unsprung weight, giving better friction performance and improved structural properties at high temperatures, compared to cast iron. Carbon brakes are sometimes applied to road cars, by French sports car manufacturer Venturi in the mid-1990s for example, but must reach very high operating temperatures before they become truly effective and are not very suitable for road use. The extreme heat generated in this system is easily visible during night racing, especially on shorter tracks. It is not uncommon to be able to see the cars, either directly or on the television and see the red disc brakes light up during the application.
Ceramic composite
Ceramic discs are used on some high performing cars and heavy vehicles.
The first development of modern ceramic brakes was made by British engineers working in the railway industry for TGV applications in 1988. The goal was to reduce the weight, the number of brakes per axis, as well as provide stable friction from very high speed and all temperatures. The result is a carbon fiber reinforced ceramic process which is now used in various forms for automotive, rail, and aircraft brake applications.
Due to the high heat tolerance and mechanical strength of ceramic composite discs, they are often used on exotic vehicles where the cost is not expensive for applications. They are also found in industrial applications where light weight ceramic discs and low maintenance properties justify the cost relative to alternatives. Composite brakes can withstand temperatures that will allow steel discs to be bent.
Porsche's Composite Ceramic Brakes (PCCB) are silicon carbon fibers, with very high temperature capability, 50% weight reduction over iron discs (thereby reducing vehicle unsprung weight), significant reductions in dust generation, substantially improved maintenance intervals, and increased power resistant in corrosive environments than conventional iron discs. Found on some of their more expensive models, this is also an optional brake for all street Porsches at an additional cost. This is generally acknowledged by bright yellow paint on six-piston aluminum calipers matched to discs. The disk is internally sourced like cast iron, and drilled cross.
Setup mechanism
In automotive applications, the piston seal has a square cross section, also known as a square piece seal.
As the piston moves in and out, the seal pulls and stretches across the piston, causing the seal to twist. The distortion seal is about 1/10 millimeters. The piston is allowed to move freely, but the slightest drag caused by the seal stops the piston from its complete withdrawal to the previous position when the brake is released, and thus picks up the slack caused by brake pad wear, eliminating the need for the springs back.
In some rear disc calipers, the parking brake activates a mechanism inside the caliper that performs some of the same functions.
Disk damage mode
Discs are usually damaged in one of four ways: scar tissue, cracks, curls or excessive rusting. The service shop will occasionally respond to any disk problem by replacing the entire disk, This is done especially where the cost of the new disc is actually lower than the labor cost to coat the old disc. This is mechanically unnecessary unless the disc has reached the minimum recommended thickness of the manufacturer, which makes it unsafe to use it, or the rusty propellers are very severe (ventilated discs only). Most leading vehicle manufacturers recommend skimming disc brakes (US: turning) as a solution to run-out, vibration and brake problems. The machining process is carried out in a brake lathe, which removes a very thin layer from the disk surface to clean out minor damage and restore a uniform thickness. The necessary disk machining will maximize the mileage out of the current disc on the vehicle.
Run-out
Run-out is measured using a dial indicator on a fixed rigid base, with the tip perpendicular to the surface of the disc brake. Usually measured about 1 / 2 at (12.7 mm) from the outer diameter of the disk. Disk spins. The difference between the minimum and maximum values ​​on a dial is called a lateral run-out. Run-out hub/disc assembly specifications common to passenger vehicles is about 0.002 in (0.0508 mm). Runouts can be caused by deformation of the disk itself or by runouts on the surface of the underlying wheel hub or by contamination between the disk surface and the surface of the underlying hub installation. Determining the root cause of the displacement indicator (lateral escape) requires disassembling the disc from the hub. Disc face runout due to hub face runout or contamination will usually have a period of 1 minimum and 1 maximum per revolution of brake discs.
Discs can be done to eliminate variations in thickness and lateral run-out. Machining can be done in situ (on-car) or off-car (bench lathe). Both methods will eliminate the thickness variation. On-car machining with the right equipment can also eliminate the lateral run-out due to non-perpendicular hub-face.
Faulty fittings can distort the disc (warp); a disk retaining bolt (or wheel nut/lug, if the disc is only placed in place by the wheel, as in many cars) should be tightened progressively and evenly. The use of air tools to tighten the wheel nuts can be a bad practice, unless the key moments are also used for final toning. The vehicle manual will show the right pattern to tighten as well as the torque rating for the bolts. Lug nuts should not be tightened in a circle. Some vehicles are sensitive to applied force bolts and tightening should be done with the moment lock.
Often an uneven transfer pad is confusing for disc warping. In fact, the majority of brake discs diagnosed as "warped" are actually uneven product pad transfer materials. Uneven transfer pads will often cause variations in disk thickness. When a thicker part of the disk passes between the pads, the pads will move away and the brake pedal will rise slightly; this is a pedal pulsation. The thickness variations can be felt by the driver when approximately 0.17 mm (0.0067 inches) or larger (on the car discs).
This type of thickness variation has many causes, but there are three main mechanisms that contribute most to the multiplication of the thickness of the disc connected to an uneven transfer pad. The first is the incorrect selection of brake pads for the given application. Effective bearings at low temperatures, such as when braking for the first time in cold weather, are often made of materials that unravel unevenly at higher temperatures. This uneven decomposition results in the uneven deposition of material to the brake discs. Another cause of uneven material transfer is an improper break on pad/disk combination. For proper rest, the disc surface should be refreshed (either by machining the contact surface or by replacing the disk as a whole) each time the pad is replaced on the vehicle. Once this is done, many brakes are applied many times in a row. It creates smooth, even interface between pad and disk. When this is not done properly, the brake pads will see an uneven distribution of voltage and heat, resulting in uneven, random-looking material pad deposition. The third major mechanism of uneven material pad transfer is known as "imprinting pad." This occurs when the brake pad is heated to the point that the material begins to break and moves to the disc. In properly damaged brake systems (with properly selected pads), this transfer is natural and is actually a major contributor to the braking force generated by the brake pads. However, if the vehicle stops and the driver continues to use the brakes, the pads will deposit the material layer in the form of brake pads. This small thickness variation can initiate an uneven transfer pad cycle.
After the disc has a certain degree of thickness variation, uneven pad deposition can accelerate, sometimes resulting in changes in the crystal structure of the metal that make up the disk in extreme situations. When the brakes are applied, the pads slide on the surface of the varied disk. When the pads pass through the thick part of the disc, they are forced out. The driver's feet applied to the brake pedal naturally resist this change, and thus more force is applied to the pads. The result is a thicker part looking at higher levels of stress. This causes an uneven surface heating disc, which causes two major problems. When the disc brake heats up unevenly, it also expands unevenly. The thick part of the disc expands over the thinner part as it sees more heat, and thus the thickness difference is magnified. Also, uneven heat distribution results in an uneven transfer of pad material. The result is that the thicker and warmer parts receive more pad material than the cooler-cooler parts, contributing to the further increase in the thickness of the discs. In extreme situations, this uneven warming may actually cause the crystal structure of the disk material to change. When the hotter part of the disc reaches very high temperatures (1,200-1,300 Â ° F or 649-704 Â ° C), the metal can undergo phase transformations and the dissolved carbon in the steel can precipitate to form carbon-known carbide regions as a cementite. This iron carbide is very different from cast iron the rest of the disc is made up of. It's very hard, very fragile, and does not absorb heat well. Once cementite is formed, the integrity of the disk is compromised. Even if the disc surface is worked, the cementite inside the disc will not use or absorb heat at the same rate as the surrounding cast iron, causing uneven thickness and uneven disk heating characteristics to return.
Scars
Scars (USA: Scoring) can occur if brake pads are not replaced immediately when they reach the end of service and are considered obsolete. Once enough of the friction material has worn, the steel pad support plate (for glued bearings) or rivet nails (for glued pads) will directly bear on the wear surface of the disc, reduce braking power and make scratches on the disc. Generally discs with sufficient scores, which operate satisfactorily with existing brake pads, will be used with new pads. If scarring is deeper but not excessive, it can be repaired by treating the surface layer of the disc. This can only be done multiple times because the disk has minimum rated secure thickness. Minimum thickness values ​​are usually thrown into the disk during manufacture on the hub or disk edge. In Pennsylvania, which has one of North America's most stringent safety inspection programs, automotive discs can not pass safety inspections if the score is deeper than.015 inches (0.38 mm), and should be replaced if machining will reduce the disk in below its minimum safe thickness.
To prevent scarring, it is wise to periodically check the brake pads for use. Tire rotation is a logical time for inspection, since rotation should be done regularly based on vehicle operating time and all wheels must be removed, allowing ready visual access to the brake pads. Some types of wheels and brake settings will provide enough open space to see the pads without removing the wheel. When practicable, the pads that are near the wear point should be replaced immediately, since full wear leads to unsafe scarring and braking. Many disc brake pads will include a kind of soft steel spring or pull tab as part of the pad assembly, which is designed to start dragging on the disc when the pad is almost obsolete. The result is a loud enough metal throttle, reminding the user of the vehicle that service is needed, and this usually will not hurt the disc if the brakes are immediately serviced. A set of bearings may be considered for replacement if the thickness of the pad material is equal to or less than the supporting steel thickness. In Pennsylvania, the standard is 1/32 ".
Cracking
Cracking is mostly restricted to drilled disks, which can develop small cracks around the edges of the holes drilled near the edge of the disc due to uneven disk expansion levels in heavy duty environments. Manufacturers who use drill discs as OEMs usually do so for two reasons: appearance, if they determine that the average owner of the vehicle model will prefer a temporary display with less emphasis on hardware; or as a function to reduce unsprung weight on the brake assembly, assuming engineering that enough mass of brake discs to absorb the temperature and racing pressure. The brake disc is a heat sink, but the loss of heat sink mass can be offset by an increase in surface area to radiate far heat. Small hairline cracks may appear on any metal discs that are drilled as normal wear mechanisms, but in severe cases discs will fail catastrophically. No fixes are possible for cracks, and if the crack becomes severe, the disc should be replaced. This crack occurs due to the phenomenon of low cycle fatigue as a result of repeated hard braking.
Connecting
Discs are generally made of cast iron and a number of normal surface rust. The disc contact area for brake pads will remain clean with regular use, but vehicles that are stored for a long time can develop significant rust in the contact area which can reduce the braking power temporarily until the rusty layer fades away again.. Rust can also cause warping of discs when the brakes are re-activated after storage because the differential heating between the remaining no-man's areas is covered by bearings and rust around most of the surface of the disc area. Over time, ventilated brake discs can develop severe corrosion of rust inside the ventilation gap, sacrificing structural strength and requiring replacement.
Caliper
Brake calipers are assemblies that accommodate brake pads and pistons. Pistons are usually made of plastic, aluminum or chrome plated steel.
The calipers are of two types, floating or fixed. The calipers remain immobile relative to the disk and thus are less tolerant of disk imperfections. It uses one or more opponent piston pairs to clamp from each side of the disc, and is more complex and expensive than floating calipers.
Floating calipers (also called "sliding caliper") move according to the disk, along the lines parallel to the disk rotation axis; a piston on one side of the disc pushes the inner brake pads to make contact with the braking surface, then pulls the caliper body with the outer brake pads so that pressure is applied to both sides of the disc. The floating caliper (single piston) design is subject to a sticking failure, caused by dirt or corrosion that enters at least one mounting mechanism and stops normal movement. This may cause the caliper pads to rub on the disc when the brakes are not involved or pull it at an angle. Sticking may occur due to rare use of the vehicle, boot seal failure or rubber that allows entry of debris, dry grease in the mounting mechanisms and subsequent water vapor accidents that cause corrosion, or some combination of these factors. The consequences can be a reduction in fuel efficiency, extreme heating of the disk or excessive wear on the affected pad. Sticky front calipers can also cause steering vibrations.
Another type of floating caliper is the swinging caliper. Instead of a pair of horizontal bolts that allow the caliper to move straight in and out respectively to the body of the car, the caliper swings using one, vertical pivot shaft located somewhere behind the central axis. When the driver presses the brake, the brake piston pushes the inner piston and rotates the entire caliper inside, when viewed from above. Because the piston angle of the swing caliper changes relative to the disk, this design uses a narrow wedge-shaped wedge on the back on the outside and is narrower on the inside front.
Various types of brake calipers are also used on bicycle rim brakes.
Piston and cylinder
The most common caliper design uses a single hydraulically actuated piston in a cylinder, although high performance brakes are used as much as twelve. Modern cars use different hydraulic circuits to drive the brakes on each set of wheels as a security measure. The hydraulic design also helps to double the braking power. The number of pistons in the caliper is often referred to as the number of 'pots', so if the vehicle has a 'six pot' calipers it means each caliper has six pistons.
Brake failure may occur due to piston failure to pull back, which is usually a consequence of not operating the vehicle during prolonged outdoor storage in poor condition. In high mileage vehicles, piston seals may leak, which must be repaired immediately.
Brake pads
The brake pads are designed for high friction with the brake pad material embedded in the disc in the coating process while wearing evenly. Friction can be divided into two parts. They are: adhesive and abrasive.
Depending on the nature of the pad and disk material as well as the configuration and usage, the usage level of pad and disk will vary greatly. The properties that determine material wear and tear involve a trade-off between performance and longevity.
The brake pads usually have to be replaced regularly (depending on the pad material, and the drivestyle), and some are equipped with a mechanism that reminds the driver that replacements are required, such as a thin piece of soft metal that rubs against the disk when the pads are too thin causing the brakes to scream, in the pad material that shuts off the electrical circuit and turns on the warning light when the brake pad is thin, or the electronic sensor.
Generally the road-going vehicle has two brake pads per caliper, while up to six are mounted on every race caliper, with friction properties varying in a staggered pattern for optimum performance.
Early brake pads (and upholstery) contain asbestos, producing dust that should not be inhaled. Although new bearings can be made of ceramic, Kevlar, and other plastics, inhaling brake dust is still to be avoided regardless of the material.
Common issues
Squeal
Sometimes loud noises or high loud noises occur when the brakes are applied. Most squeal brakes are generated by vibrations (resonant instability) of the brake components, especially pads and discs (known as force-coupled excitations). This squeal type should not have a negative impact on the performance of the brake discs. Techniques include adding gap bearings to the point of contact between the caliper piston and the pads, the bond insulator (damper) to the backplate pad, the brake shims between the brake pad and the piston, etc. All must be coated with a very high temperature, high solids lubricant to help reduce the squeal. This allows metal to metal parts to move independently of each other and thus eliminate the buildup of energy that can create audible frequencies as brakes scream, groan, or growl. It is inherent that some pads will be more screaming given the type of pad and use case. Bearings that are usually rated to be very high temperature resistant for long periods tend to produce large friction that causes more noise during brake applications.
Cold weather combined with high moisture in the morning (dew) often aggravates the screams of the brakes, although screams generally stop when the coating reaches the usual operating temperature. This stronger influence of the bearings is intended to be used at higher temperatures. Brake dust can also cause a screaming and commercial brake cleaning product designed to remove dirt and other contaminants. Bearings without the right amount of transfer material can also be screamed, this can be fixed with bedding or re-bedding brake pads to disc brakes.
Some wear layer indicators, which lie either as a semi-metal layer inside a brake pad material or with an external "sensor", are also designed to scream when layers need replacing. Typical external sensors are essentially different from the sounds described above (when the brakes are applied) because the noise of the wearing sensors usually occurs when the brakes are not in use. The wear sensors can only create a shrill under braking when it first shows wear and tear but is still a very different sound and pitch.
Judder or shimmy
Rem judder is usually felt by the driver as a small to heavy vibration that is transferred through the chassis during braking.
The judder phenomenon can be classified into two distinct subgroups: hot (or thermal ), or cold judder.
Hot judder is usually produced as a result of longer and more moderate braking than high speeds where the vehicle does not stop completely. This usually happens when the rider slows down from a speed of about 120 km/h (74.6 mph) to about 60 km/h (37.3 mph), which results in heavy vibrations transmitted to the driver. This vibration is the result of uneven heat distribution, or hot spots . Hot spots are classified as concentrated thermal areas that alternate between the two sides of the disk distorting them in such a way as to produce sinusoidal waves around the edges. After brake pads (friction material/brake linings) come into contact with sinusoidal surfaces during braking, heavy vibrations are induced, and can produce hazardous conditions for people driving a vehicle.
Cold judder, on the other hand, is the result of uneven disc disc patterns or variations in disc thickness (DTV). This variation on the surface of the disk is usually the result of extensive use of the road vehicle. DTV is usually associated with the following causes: waviness and surface roughness of the disc, misalignment of the axis (runout), elastic deflection, wear and transfer of friction material. Each type can be mounted potentially by ensuring a clean mounting surface on both sides of the brake disc between the hub of the wheel and the brake disc hub prior to use and attention to printing after extended use by allowing the brake pedal to be very depressed at the end of heavy use. Sometimes the bed in the procedure can clean and minimize DTV and put a new transfer layer even between pad and disc brakes. However it will not eliminate hot spots or run out of excess.
Dust
Source of the article : Wikipedia
0 Comments