Passenger car braking system

Contents

Contents

Legend List _______________________________________

Introduction of _________________________________________________________

1 Overview of diagrams and structures of passenger car braking systems _____

2 Description of operation, adjustments and technical characteristics of the designed unit ______________________________________________

3 Design calculation of the braking system ______________________________

   3.1 Calculation of braking dynamics ____________________________________

   3.2 Calculation of brakes __________________________________

   3.3 Parameters of braking mechanisms loading ________________

   3.4 Calculation of the main brake cylinder ___________________________

   3.5 Calculation of vacuum amplifier ___________________________________   42

   3.6 Calculation of parking braking system __________________________

4 Check calculation of the braking system ____________________________

   4.1 Checking the vehicle for compliance with UNECE Regulation No. 13 _____

   4.2 Calculation of anti-lock system (ABS) _______________________

   4.3 Calculation of disc brake clamp ___________________

   4.4 Calculation of brake disc attachment bolts on the ________________ cut

5 Conclusion of the ____________________________________________________ 

6 List of literature used ________________________________

Legend List

AP - the active area of the piston of the hydraulic amplifier;

AS - the area of a rod of the main brake cylinder;

AGTC - area of the main brake cylinder;

AKTCi - area of the wheel brake cylinder;

a is the distance between the front axle and the centre of gravity of the vehicle;

Bi - brake conversion factor;

B is the width of the tire profile;

b is the distance between the rear axle and the centre of gravity of the vehicle;

C - specific heat capacity;

Dομi - coordinates of brake diagram;

D - diameter of brake disc;

dII - outer diameter of the tyre;

dy - diameter of hydraulic amplifier piston;

dGTC - diameter of the main brake cylinder;

db - brake drum diameter

dCi - wheel brake cylinder diameter;

E - modulus of elasticity;

FCP - bolt shear force;

Fοi - braking force of the i-th bridge;

ΑFH - total area of brake linings;

FHi- area of the brake linings of the i-th bridge;

FS - pressure force;

FNR - spring force;

FTP - friction force;

FSMAX - maximum force on the rod;

FP - force on pedals;

Fj - vehicle inertia force;

f is friction coefficient of friction linings;

G - full weight of the car;

G2 - weight on the rear axle of the motors4

g - acceleration of free fall;

H is the height of the car;

H/B is the ratio of the width of the tyre profile to its height;

h - distance between the point of force application to the block from the hydraulic cylinder to the block support point;

hg is the height of the center of gravity of the car;

hGTZ - rod stroke of the main brake cylinder;

J - moment of cross section inertia;

j - car deceleration;

jPR - limit deceleration of the car;

Kti - brake conversion factor;

kY - hydraulic gain;

L - wheelbase of the car;

Li - specific friction operation;

l is the distance from the centre of the drum to the block support point;

Mοi - brake torque of the i-th bridge;

MT2MAX - maximum braking torque on the rear axle of the car;

n - number of rear axle wheels;

p - pressure in hydraulic drive of braking system;

pSYS- pressure generated by hydraulic amplifier pump;

RZi - the reaction of the road acting on the iy bridge of the car;

RB - drum radius;

rH - internal radius of friction linings of disc braking mechanism;

rB - outer radius of friction linings of disc braking mechanism;

r0 - rolling radius of the car wheel;

rS - friction radius of disc braking mechanism;

Qmi - mass of ventilated brake disc or brake drum;

q - specific load on brake linings;

qS - specific load in contact of friction pairs;

S - drum wall thickness;

SB - cut area of one bolt; 

SPMAX - maximum brake pedal stroke; 

∆ti - heating of brake disc or drum in one braking;

VGTC - maximum volume of the main braking mechanism;

Vmax - the initial speed of the car when determining the specific friction operation;

UP - Gear ratio from the pedal to the rod of the main brake cylinder;

W - moment of section resistance;

Z - relative deceleration of the car;

α - angle of cover plates coverage;

[beta] - brake distribution coefficient;

β - drive deformation coefficient;

χ - specific load of the back bridge;

∆KTTs - stroke of brake cylinder piston;

∆GTTs - clearance between GTZ and pusher;

δ - opening of the bracket;

¼ P - drive efficiency;

μ- friction coefficient of friction brake linings;

ρ - the average specific pressure upon a drum wall;

σ - the flexural tension of a bracket of the disk brake mechanism;

tCP - bolt shear stress;

ψ - specific load of the back bridge;

F is the distribution indicator.

Introduction

The purpose of the course project is to consolidate the theoretical knowledge acquired during the training process, and acquire practical skills in calculating the real brakes of a passenger car, as well as familiarize yourself with the existing brake schemes; The current standards and requirements for vehicle braking.

The objective of the project is to design the braking mechanisms of the Lexus GS300 car, which involves studying the design decisions of real-life braking mechanisms, and adopting on their basis the design of the braking mechanisms for the designed car. Get acquainted with the production of brakes and their features. Design the front and rear axle brakes of the vehicle and inspect the designed vehicle according to the requirements detailed in UNECE Regulation No. 13. 

Overview of diagrams and structures of passenger car braking systems

In modern automotive industry , car safety is inconceivable without effective braking control, which, in accordance with the requirements of the EEC member countries, should consist of the following brake systems (TS):

 - main (working), which provides deceleration of the passenger car not less than 5.8 m/s2 , moving with - speed not more than 80 km/h with a force on the pedal less than 50 kg; 

 - auxiliary (emergency), providing deceleration of at least 2.75 m/s2; - parking, which can be combined with emergency.

Drum brake

Drum brakes drum is applied to the wheel hub, and braking takes place with the aid of brake pads, expansion against the inside of the drum. A drum brake in which friction is caused by a plurality of boots or gaskets which are pressed against the inner surface of the rotary drum. The drum brake was invented in 1902 by Louis Renault, although less complex drum brakes were used by Maybach a year earlier . In the first drum brakes, shoes are mechanically driven with levers and rods or cables . Since the mid 1930s, shoes have been operated with oil pressure in a small cylinder wheel and pistons (as in the picture), although some vehicles have continued with purely mechanical systems for decades. Some designs have two wheel cylinders. Shoes in drum brakes are susceptible to wear and brakes must be adjusted regularly until the 1950s by the introduction of separate drum brakes . Self adjustment brakes work, the ratchet mechanism deals with how manual brakes are used . If the hand drive travel of the lever exceeds a certain amount, Rachet turns out to be a screw that moves the brake pads to the drum . In 1960 and 1970, the brake drums on the front wheels of cars were gradually replaced by disc brakes and now many cars use disc brakes on all wheels. Another type of drum brake where the friction belt is wrapped around outside the drum and tightened . This type preceded the modern drum brake, and then was often used for parking brake on the central shaft . This type of belt brake is also used in automatic transmissions and aerobic cycling equipment exercises. The drum brakes from the inner shoe have a particularly disadvantageous position when the drums are heated by abrupt braking the diameter of the drum increases by expanding the material and the brake should be further reduced by effective braking . This increase in motion pedal is known as BRAKES and can cause brakes to fail in extreme circumstances. For this reason, drum brakes have been replaced in most modern cars and light trucks with at least the front wheel (often already four wheels) disc brakes.

Drum brakes are still used in some modern cars due to the weight and cost of benefits. Advanced hybrid car technology with drum rear brakes is the Toyota Prius. (Hybrid vehicles significantly reduce everyday wear on the brake system due to their energy recovery of motor generators). Early type of brake pads contained by ASBESTA  . When working with the braking system of old cars, care must be taken so as not to inhale dust is present in the braking system.

Disc brake

With disc brakes, the disc is applied to the wheel hub, can be clamped between 2 brake shoes. On passenger cars, both of these systems are hydraulic . The brake pedal acts as the master cylinder. Hydraulic lines and hoses connect the master cylinder to brake cylinders on wheels. Most modern cars either disc brakes on the front wheels and drum brakes on the rear, or disc brakes on all 4 wheels. Disc brakes require more force to control them. The brake amplifier assists the driver by increasing the force applied to the master cylinder when the brake is on. Disc brake device for decelerating or stopping wheel rotation . The brake disc (or  rotor in English), usually made of steel, has a connection with the wheel or axle. To stop the wheel, the brake shoe (installed in a device called a brake caliper ) is compressed by mechanical or hydraulic force on both sides. Friction causes disk and gives wheels to slow down or stop. Cars, motorcycles, bicycles and some use disc brakes. Disc brakes were most popular on sports cars when they were first introduced, since these vehicles are more demanding on brakes. Many early implementations are located stationary brake discs, a number of differential, but most of the discs today are located inside the wheels . (Fixed places reduce CAR WEIGHT and eliminate heat source in tyres, important in Formula One Racing.) The discs have now become the standard in most passenger cars, although some retain the use of drum brakes on the rear wheels to maintain costs and weights, as well as to simplify the position of the parking brake or emergency braking. As the front brakes perform most of the braking force, it can be a reasonable compromise.  

Since only disc brakes are used in the designed braking system of the studied car, in the future we will consider only the latter.

Brakes of the most important safety parts in vehicles . In general, all vehicles have their own safety devices to stop their car. Brakes function to slow down and stop wheel rotation . To stop the wheel, the brake shoes are forced mechanically against the disc rotor on both surfaces . They are mandatory for all modern cars and for the safe operation of vehicles. In short, the brakes convert the kinetic energy of the car into thermal energy, thereby slowing down its speed.

The brakes have been reconfigured and improved since their invention. The increase in speed, as well as the growing weight of the machine, made these improvements significantly . The faster the car goes and the heavier it is, the harder it is to stop. The effective braking system required to accomplish this task with the complex term where the material should be lighter than before and the performance of the brake should be improved. modern cars often use a combination of disc brakes and drum brakes. For a normal passenger car, as a rule, disc brakes are located on the front two wheels and drum brakes on the two rear wheels. Clearly shows that, together with steering and tyres, they are the most important accident prevention systems in the present vehicle, which must operate reliably under different conditions . However, the performance of the braking system depends on the design itself, as well as the right to choose the material . It is important to do some analysis on the rotor disc brake, which was designed to predict the behavior of the system than to follow with some improvements. 

Today, there is a lot of software that has been developed to satisfy vehicle finite element modeling and analysis, components such as MSC.ADAMS (Automatic Dynamic Mechanical Systems), CATIA, MSC Patran/NASTRAN, ANSYS, DYNA and ABAQUS. Most software is used in a wide range of industries, such as automotive, oil and gas, aerospace, marine, heavy engineering debt, construction, electromechanical and general engineering industries. As part of this project, the CATIA package design and the ABAQUS and MSC PATRANNASTRAN package finite elements will be used to create the model and run the selected components.

Disk Design

The most common automotive braking systems today are disc brakes. It follows that the main element of this type of brake is the brake disc to which the actuator force is applied. Since existing car brakes use friction as the main principle of operation, there is a shoe covered with a layer of friction material between the disc and the brake mechanism. As is known, the increase in the efficiency of any brakes is prevented by the temperature in the friction pair. The more intense the car brakes, the more heat is released and the more parts of the brake mechanism are heated. For a conventional brake shoe, this results in a loss of friction properties by reducing the friction coefficient. 

You can go further and find that the heat from the shoe is transferred not only to the air, but also to the actuator itself - the bracket (caliper), the heated pistons of which are able to bring the brake fluid to a boil. This can lead to the formation of air bubbles in the liquid and, as a result, its loss of elastic properties and the "failure" of the brake pedal. The most logical thing will be to increase the boiling point of the brake liquid and make shoes that can not reduce the coefficient of friction with an increase in temperature. This is exactly what the designers of the brake systems did, and now there are pads operating in the range from 200 degrees and above. The disk is also heated, which leads to a violation of the shape of its working surface, its warping, which results in an axial run-out of the disk transmitted to the steering wheel and brake pedal. To begin with, consider the reason for the deformation of the disk under the influence of temperature. Typically, a conventional brake disc is a rim integrally formed with a U-shaped hub. When heated, a disk resembling a hat in a section conditionally tends to turn "inside out" due to the difference in lengths of the outer and inner contours. The inner one is larger, therefore, and the linear thermal expansion is also larger. This leads to the fact that the "hat" raises fields. It is the series of such lifts and lowers during cooling that leads to deformation of the disk. In order to reduce this effect, flaps are made on the disks at the points of connection of the rim with the hub from the outside or other measures are carried out that increase the length of the outer contour. And what if you make the disk more massive, then it certainly will not die. A good idea, just imagine what unsprung mass such a car will have, and the presence of an additional flywheel on each wheel will make braking problematic, adding the need to "extinguish" their inertia. In addition, the problem of heat dissipation remained. So on the stage came a disc with internal ventilation or just ventilated. It immediately made it possible to increase braking efficiency due to more favorable temperature conditions for the friction pair. The ventilated disc has a substantially enlarged surface from which it imparts heat to the environment. And if you bring additional cooling air to the brake disc, then you can even forget about overheating the brakes. The ventilated brake disc also reduces the temperature load on the hub bearing. 

The expansion of the heat dissipation surface is also facilitated by perforation of the discs, in which the rim has more than one dozen through holes with countersink. Through holes made along the entire working plane of the disk reduce the weight of the disk, contribute to a more effective decrease in its temperature during operation (which reduces the risk of warpage), and remove gases formed when the blocks friction against the disk. Also, the perforation does not allow the brake shoe to "float" when water enters the working surface of the disk in the rain or when passing through puddles. Water found in the path of the block is extruded into the disk, from where it is ejected outside under the influence of centrifugal force. Here lies the danger to perforated discs. Water on the sometimes hot brake disc can cause catastrophic consequences for its integrity, it can crack and even burst. The holes will become additional stress concentrators and the starting points of these very cracks. Therefore, claims of increased efficiency of perforated discs should often be considered as an advertising move. However, there are production cars in which such disks are standing and feel good for all the time of operation, being replaced only due to wear and tear. Such a picture can be observed, in particular, on Ferrari and Porsche cars. The fact is that the diameter of the holes is not large, their location is combined with the configuration of the inner blades of the disk, and the disk itself, as a rule, is thick-walled and of large diameter. This reduces the risk of cracking, but the more correct solution is the grooves on the working surface of the disc. In addition to water, the grooves remove the gaseous products of the "life" of the shoe and wear products. The grooves are directed depending on the rotation of the disk or symmetrical, which allows you to put the disk on the left and right sides of the car. This applies to the blades within the disc. The conventional vented disc has radially spaced blades, which makes the left and right brake discs the same, but there are discs with inclined blades for better removal of heated air. In this case, the left disk is a mirror copy of the right and vice versa. Indicating all these advantages of the grooves, one cannot but say why they were originally developed. Again, motorsport with its increased brake loads required effective cleaning of the brake pads. The fact is that when working at high loads, the brake pads are very quickly covered with a thin layer of coke - burnt and spent friction material. If it is not forcibly removed, the block turns into a slippery ski. Grooves, splines practically cut this spent layer, updating the block. This allows you to maintain the operability of the pads throughout the race. Given all the above, it can be considered that for ordinary urban cars, brake discs with splines, of course, are the subject of pride of the owner, but at the same time the reason for the more frequent change of brake pads.

Now we have reached the major league of brake discs - ventilated teams. Of course, there are solid discs with directed blades, but there are not many of them. This is due to the need to have complex tooling for the left and right disks, which not every manufacturer can go to. As a result, the disk on one side ejects air outside, and on the other, grabs it and tries to squeeze it from the center into the wheel arch. 

The demountable discs (Figure 4) are initially divided into left and right and have a fastening flange for the hub, which is usually made of high-quality aviation aluminum. This design allows even more heat dissipation, which favorably affects the performance of the brakes and the heat loading of the hub bearings. It is understood that such a disk is lighter than its integral counterpart. There are pitfalls here too. The most dangerous is the difference in the thermal deformation coefficients of the disc and hub materials. To solve this problem, slots are made on the hub, but the so-called floating disks can be called the most effective way to combat this phenomenon. Their essence is the absence of a rigid connection between the disk and the hub, while the disk can move relative to the hub usually in the axial direction within a few tenths of a millimeter. Floating discs have a significant drawback - they are afraid of dirt, which can deprive them of mobility, so they are mainly used in ring motorsport.

Recently, carbon-ceramic and carbon-carbon composite brakes have been used in racing, sports machines, and even high application speed train cars. This should not be confused with ceramic brake pads for use with standard steel discs that are simply high quality brake pads . The carbon-carbon brake discs consist of carbon fiber in the carbon matrix using excellent thermal conductivity of graphite. Among other things, they were used in the aircraft brakes. Moisture can reduce the braking power of carbon-carbon brakes. Another serious problem with carbon-carbon is its reactivity at a high temperature . In addition, the carbon-carbon pads are not performed in full force until they reach 300 ° C (572 ° F). Above 500 ° C (932 ° F), carbon reacts with air and burns, and even at the normal brake temperature there will be some burning of the outer layers. This can be reduced by coating the disc, sometimes with carbon-ceramic.

Carbon-ceramic brake discs consist of carbon fiber in a silicon carbide (C/ SiC ) matrix. Carbon ceramic brakes are light and have a very high heat capacity and thermal conductivity, which makes them ideal as brake discs can withstand more than 1600 ° C (2912 ° F). They are also very expensive and require special pads, delegating them for use mainly on high end applications such as Porsche Carrera GT. The lifetime of carbon-ceramic brakes is limited to cracking, which is due to the different expansion rate between carbon and silicon carbide. These cracks slowly pass air in contact with carbon as a result of combustion.

Early Lotus Elise models came with aluminum metal composite matrix (MMC), brake discs . These brakes were also a light and cost-effective alternative to graphite/ceramic variations available, but they cannot work at the same temperatures . However, for the manufacturer of these disks are closed, and Lotus was forced to switch to iron.

Disc Material

Most often, brake discs are made of cast iron. The popularity of this material is explained by good friction properties and low production costs. In addition to these advantages, cast iron has a number of significant disadvantages that limit its use in certain types of vehicles - sports cars and motorcycles. With regular intense braking, which causes a significant increase in temperature (400 C and above), it is possible to warp the disk, and if water, for example, from a puddle, enters its overheated surface in such modes, the cast-iron disk is covered with a network of cracks and sometimes even crumbles. In addition, such discs are very heavy, and after long parking, their working surface is covered with rust crust. To avoid these shortcomings, discs, to a greater extent motorcycle and much less often automobile, began to be made of stainless steel. The weaker friction properties of this material were compensated by an increase in the diameter of the discs and their working surface. To make this responsible part of the braking system, ordinary steel is also used, which, like stainless steel, is not so sensitive to temperature differences and has slightly worse friction properties than cast iron. In the 70s, carbon plastic brake discs began to be installed on sports cars - carbon. Having overcome the growth period, carbon brakes left their metal colleagues far behind. Dish yourself: the weight of the carbon brake disc is an order of magnitude less than metal, the coefficient of friction is an order of magnitude higher, and the operating range limited on conventional 500600 C brakes extends far beyond the 1000 C mark. The carbon disks do not warp, and the decrease in unsprung and rotating masses positively affects the driving performance of the car. Nevertheless, the way to ordinary road cars such brakes have so far been ordered. The cost of a set of carbon brakes can reach the cost of a new small-class car, and they start working normally only after good heating: before that, the friction coefficient of the brakes is even lower than usual! We must not forget about the convenience of deceleration control: if everything is simple and clear with traditional brakes, then it is extremely difficult to control the deceleration here. In fact, under normal conditions, carbon brakes will be an analogue of the go/stand switch.

Ceramic brakes have more rosy prospects in the automotive industry. They do not have such a staggering coefficient of friction as carboxylic, but have a number of advantages. Ceramics have much more possibilities than metal or various composites. This material has excellent resistance to high temperatures, high resistance to corrosion and wear, low specific gravity and high strength. But there is more to come. Ceramic brake discs, compared to similar parts made of gray cast iron, are 50% lighter. The weight, for example, of the PORSCHE 911 ceramic brake disc is twice as light as usual, which means that the unsprung masses, and therefore the load on the suspension, are smaller. The so-called gyroscopic effect is also reduced when the body rotating at high speed resists changing the direction of rotation. In addition, the use of ceramics allows you to increase the coefficient of friction by 25%, and at the same time dramatically increase the efficiency of braking in a hot state. Another advantage is incredible durability. Ceramic discs usually do not require replacement for 300,000 km. Unfortunately, there are also shortcomings. First, cold ceramic discs stop the machine worse than cold metal brake discs. Secondly, ceramics do not work well at very low temperatures. Thirdly, such disks creak unpleasantly when working. And finally, in the fourth, their price is just exorbitant.

Brake pads

Brake pads are the most important element of the braking system. It is on them that the effectiveness of the brakes depends. Good, correct pads will not only perform their functions for a long and reliable time, but also keep the brake disc or drum intact for many years. On the contrary, bad, poor-quality pads can ruin the brake disc by making deep ditches in it, etc. Brake pads are different. Moreover, we are not talking about design and design, but primarily about the material of friction linings, which actually carry out braking. Frictional mixtures today there is a great many. Each company has its own recipe and its own ingredients. The mixture may comprise 15 or more different components. Their proportions are clearly maintained. Any change in the proportion of a component can significantly change the properties of future brake linings, up to their complete inoperability

The base of the friction mixture is a reinforcing component. It is on it that the strength, heat resistance and stability of the braking properties of the product depend. In recent years, stable types of friction products have developed, which have come to their name, precisely based on their reinforcing component. Asbestos, non-asbestos and organic (based on organic fibers) components are isolated. The former, as the name shows, use asbestos as a reinforcing element. The harmful nature of this material for man has already become a parable in the pagan. Many car repair and maintenance manuals say that changing asbestos-containing brake pads and even removing wheels (if you have such brakes) is necessary extremely carefully, taking care in advance to protect the respiratory and visual organs. Nonzasbestos are friction material in which other components play the role of reinforcing component. It can be steel wool, copper, brass chips, various polymer compositions, etc. In budget blocks, manufacturers use a mixture of organic and inorganic fibers, balancing between the coefficient of friction, wear resistance and the final price of the block. In the case of expensive pads, although intended for road vehicles, manufacturers may include granules of soft metals and artificial graphite, Kevlar and carboxylic fibers, thus increasing the thermal stability of the friction material. The most modern friction materials at the moment are made on the basis of organic fibers. Such pads have the best braking properties. It is not for nothing that they are installed on modern Formula1 cars, where the brake loads (by the standards of city cars) are simply prohibitive. After all, they have to reduce the speed of the car from 300 to 60 km/h in a matter of seconds or even a fraction of a second. Unfortunately, like any high-tech and knowledge-intensive products, the cost of such pads is available only to such "money" types of motorsport. And once again remember the warmth. The pads should also be cooled, but unlike the discs, they just should not pass heat through themselves. Heating themselves, they will definitely begin to warm the working brake cylinders, and they, in turn, brake fluid, and if it boils, the brakes will stop working, with all the ensuing consequences. That is why it is so important to provide a thermal barrier between the friction linings and the metal base of the brake pad.

Anti-lock braking system (ABS)

The anti-lock braking system (known as ABS, from the German name "Antiblockiersystem," provided to it by its inventors on Bosch) is a system on cars that prevents wheel blocking during braking. The purpose of this is twofold:

to allow the driver to support steering as well as

reduce the braking distance.

A typical ABS consists of:

central electronic unit,

four speed sensors (one per wheel), and

two or more hydraulic valves on the circuit brakes.

The electronic unit constantly monitors the speed of rotation of each wheel . When it senses that one or more wheels rotate more slowly than others (provided it is brought to lock) it moves the valves to reduce the pressure on the braking system, effectively reducing the braking force on that wheel.

Efficiency

With high grip properties, such as bitumen, whether wet or dry, most ABS equipped cars are able to achieve a better braking path (that is, less) than those that would not be possible without the interests of ABS . A moderate experienced driver without ABS could, using braking intonation, to match the performance of a novice driver with ABS equipped vehicles . However, for a significant number of drivers, ABS will improve their braking path in a variety of conditions . Recommended a technician for non-specialist drivers in an ABSequipped car, in typical complete braking of a state of emergency, to press the brake pedal as densely as possible and, if necessary, guide around obstacles . In such situations, ABS will significantly reduce the chances of drift and subsequent loss of control, especially with heavy vehicles.

In gravel and snow, ABS tends to increase braking distance . On these surfaces, lock the wheels to dig and stop the vehicle faster. ABS prevents this from happening. Some ABS controllers reduce this problem by slowing down cycling time, thus allowing the wheels to repeatedly briefly lock and unlock . The main advantage of ABS on such surfaces is to increase the driver's ability to maintain control of the car rather than skid, although loss of control remains more likely on soft surfaces like gravel or slippery surfaces like snow or ice.

When activated, ABS causes the brake pedal to make the pulse noticeable . As most drivers rarely or never brake hard enough to cause a brake lock, and a significant number of rare bothered to read the car's manual, this cannot be detected before an emergency. When drivers still arise extraordinary, which leads to their brake stiff and thus encounter this pulsating for the first time, many of them believe to reduce the pressure pedal and thus lengthen the brake path, which contributes to a higher accident rate than the head of ABS emergency stop capability otherwise promise. Some manufacturers Therefore, "Brake Assist" systems are implemented that define the driver trying to stop the collapse and maintain braking forces in this situation . However, ABS significantly improves safety and control of drivers on the roads in situations where they know not to release the brakes when they feel a pulsating ABS.

It is worth noting that the heavier the car, the more it will benefit from ABS. This is particularly true for vehicles with less complex hydraulic braking systems, where they are difficult to control as easily as with more advanced braking systems. Conversely, lighter cars, especially sports cars with a highly developed brake system without ABS can outbrake comparable vehicles, even with ABS.

Thrust monitoring system

ABS equipment can also be used to realize vehicle acceleration thrust. If, when accelerated, the tire loses ground grip, the ABS controller can detect the situation and apply brakes to reduce acceleration so that the thrust is restored . Manufacturers often offer this as a separately priced option, although the infrastructure is mainly in conjunction with ABS. More complex versions of this can also control throttle levels and brakes simultaneously, which leads to the fact that Continental Teves terms Electronic Stability Control or that Bosch terms " Electronic Stability Program" (ESP).

Brake Assist

Dynamic Brake Control

Another electronic system - DBC, Dynamic Brake Control was developed by BMW engineers. It is similar to the Brake Assist systems, which are used, for example, on MercedesBenz and Toyota cars. The DBC system accelerates and amplifies the process of increasing pressure in the brake actuator in case of emergency braking and provides - even with insufficient pedal pressing force - a minimum braking path. Based on the data on the pressure rise rate and the force applied to the pedal, the computer determines the occurrence of a dangerous situation and immediately sets the maximum pressure in the braking system, thereby significantly reducing the braking path of your car. Control unit additionally takes into account car speed and level of brake wear. The DBC system uses the principle of hydraulic amplification, not the vacuum principle. Such a hydraulic system provides better and much more accurate dosing of the braking force in case of emergency braking. Besides. The DBC computer is associated with ABS and DSC (Dynamic Stability Control) systems. 

Cornering Brake Control (Figure 7) - braking control system in turns.

The EBD system is designed to redistribute braking forces between the front and rear wheels, as well as the wheels of the right and left sides of the car, depending on the driving conditions. EBD operates as part of a traditional 4-channel electronically controlled ABS. When braking a straight-moving car, the load is redistributed - the front wheels are loaded, and the rear wheels, in turn, are unloaded. Therefore, if the rear brakes develop the same force as the front brakes, the possibility of locking the rear wheels will increase. Using wheel speed sensors, the ABS control unit detects this moment and adjusts the applied force. It should be noted that the distribution of forces between the axles during braking depends significantly on the weight of the load and its placement. The second situation, when the interference of electronics becomes useful, occurs during braking in the turn. In this case, the outer wheels are loaded and the inner wheels are unloaded, respectively, there is a risk of their blocking. Based on the signals of the wheel sensors and the deceleration sensor (or acceleration sensor), the EBD determines the braking conditions of the wheels and by means of a combination of valves controls the liquid pressure supplied to each of the wheel mechanisms .

Sensotronic Brake Control (SBC) (Figure 9).

Developed by Mersedes engineers, today it is perhaps the most advanced braking system installed serially on modern cars. The principal difference of the SBC system is the electronic interaction system between the brake pedal and the braking mechanisms. When pressing the brake pedal, the microcomputer, using information from various systems and sensors, estimates the speed of transferring the leg from the gas pedal to the brake pedal, the force of pressing the pedal, the included gear, the features of the road surface, the trajectory of movement, speed, loading of the car and other parameters. As a result, an optimal braking force is given, and each wheel is different. If motion parameters change, forces are instantly redistributed. Like the systems described above, SBC helps the driver with intense braking and cornering. The system is able to work in the "cork" mode, when the electronics themselves stop the car, as soon as the driver has removed his foot from the gas pedal, and the "soft stop" function provides smooth braking without "clues." There are many other advantages associated with the introduction of the SBC system: the reaction time of the brake pads after pressing the brake pedal has decreased significantly, due to the fact that with a sharply dropped gas, SBC recognizes the critical situation and presses the pads to the brake disc in advance; in rainy weather, when there is a risk of moisture falling on the brake mechanisms, which leads to a decrease in brake efficiency, SBC slightly retains the wheels, drying the discs, so the brake efficiency remains; no vibration on the brake pedal during ABS operation. This is not only an increase in comfort. On the driver's simulator, the Mercedes conducted a special study and found out that two-thirds of drivers are confused when ABS comes into play with intense braking and the brake pedal begins to vibrate. At best, they stop building up the force on the pedal, and at worst, they completely reduce it. Tests showed that when braking on a snowy road, only the absence of vibrations during the operation of ABS allowed to reduce the braking distance by more than two meters!

Actuators of KnorrBremse brake cylinders (Figure 10)

 Application Modular approach KnorrBremse on the brake cylinder design for buses, trucks and trailers means that it can offer solutions for almost every type of situation, size, performance and design of the cylinder. The modular approach means that we drastically reduced the number of individual components, reducing customers spare parts and maintenance.

ABS (anti-lock system) (Figure 11)

ABS (anti-lock system) prevents wheel locking during braking, while ASR (push-pull rods) ensure that none of the wheels on the driven axle backs during acceleration . The ASR thus acts as a differential of increased friction, providing optimal traction regardless of the state of the road surface.

 Application Having pioneered the development of ABS systems for trucks, it goes without saying that KnorrBremse offers ABS and ASR systems for all types of vehicles and their trailers.

Adaptive cruise control system

To facilitate the task of the driver in heavy traffic, the KnorrBremse has developed an adaptive cruise control system (ACC), which automatically maintains at the desired distance from the vehicle ahead, depending on the speed at which it moves.

Brake lining unit

- Single and double unit versions available - Durable design for a variety of climates - Cost-effective solution for multiple applications

Brake actuators

- Closing force from 10 kN to 110 kN, with extremely compact and lightweight design - Integration of special features like emergency gear release, speed sensors, etc.

-Compact, lightweight design

- Simple  trolley installation

- Low life cycle cost

Brake discs

- Wheels or mounting axes - Steel, grey iron, iron graphite, aluminium or fibre reinforced ceramic - Split or rings of non-cleavable friction - Modular design

- High tech materials, e.g. with Isobar ® high temperature brake pads - Low wear - Easy to replace

 The Disc Brake feature slows the car down by applying the force of the brake cylinder to the brake disc. KnorrBremse has established new standards with a pneumatic brake disc for trucks with a gross mass of 6 t to 44 t or more . The advantages over conventional systems are: reduced weight, compact design, even wear of pads, ease of maintenance, reduced costs and increased safety.

Knorr-Bremse disc brakes (Figure 19)

KnorrBremse 's position as a leading supplier of disc brakes and full braking systems for trucks was further anchored to further technological developments such as all-in-one brake calipers, splined discs from intermediate elements and split discs to facilitate disc replacement

 Description of operation, adjustments and technical characteristics of the designed unit

The object of the study of this course project is the Lexus GS300 car. In this car, all the brake mechanisms are disc, therefore, the description of drum brakes does not make sense. Only disc brakes will be described.

The disc braking mechanism is very effective, as it dissipates heat perfectly. It is for this reason that disc brakes are installed on the front and rear wheels of the car.

Cast iron brake disc fixed on wheel hub. Brake bracket with brake shoes rigidly coupled with front suspension strut. Pistons of working cylinders of brake bracket press brake shoes against brake disc under action of brake fluid pressure, causing its braking due to friction forces.

 Description of braking mechanisms operation:

When the driver presses the brake pedal, the master brake cylinder converts this motion to brake fluid pressure. This pressure is transferred by incompressible fluid to the four wheel brakes.

In a brake system with disc brakes, when the brake pedal is pressed, the brake shoes are pressed with a force against the brake disc. In the process of braking, the kinetic energy of a moving car turns into heat due to friction.

 Description of brake adjustments:

To stop a car weighing one ton, moving at a speed of 130 km/h, you need to spend significant power, about 150 kW (200 hp). This power in the form of heat at a temperature of 300... 800 C ° should be scattered through a small area (about a few square centimeters) of brake pads!

Wear control: Brake pad material is softer than brake disc material and will therefore wear out faster. Therefore, brake pads should be regularly monitored and replaced as soon as their thickness is reduced to 2mm. When the brake pads wear, there is a risk of damaging the brake disc, in addition, the driver risks losing control of the car during sharp braking.

The brake disc is a responsible part of the brake mechanism. At each braking, it is subjected to significant loads and, therefore, must meet very high technical requirements.

BRAKE DISCS MUST ALWAYS BE IN EXCELLENT CONDITION SO THAT BRAKE SHOES CAN PERFORM THEIR TASK WITH MAXIMUM EFFICIENCY!

 Therefore, it is recommended to monitor the condition of the brake discs each time the brake pads are replaced. If the service surface of the brake disc has deep scratches, if it is curved, cracked or oxidized, it must be replaced immediately. After replacement of brake discs it is required to replace with new and brake pads. It is necessary to replace two discs of the same axis simultaneously in order to avoid asymmetry of braking.

The brake fluid is an incompressible fluid that transmits force from the brake pedal to the four wheel brakes by means of the master brake cylinder. Too old brake fluid can lead to a loss of braking efficiency, especially when braking is intense (for example, in mountains). It is recommended to replace the brake fluid every 2 years to prevent corrosion damage to the brake line.

Check calculation of braking system

Vehicle braking systems shall be tested in the following sequence:

1) Calculation of braking dynamics of the car.

2) Calculation of braking mechanisms.

3) Check the distribution of braking forces for compliance with UNECE Regulation No. 13.

4) Calculation of brake drive.

5) Calculation of brake drive devices.

6) Calculation of additional brake drive devices and interconnected systems.

7) Calculation of parking braking system.

Calculation of braking dynamics

To brake the vehicle with maximum efficiency, while maintaining stability and controllability, it is necessary to ensure a certain distribution of braking forces between the bridges. An optimal distribution is considered such that during the braking process all the wheels of the car are simultaneously brought to the blocking boundary. The required change in brake force ratios is determined by a change in normal reactions to the wheels of individual bridges during braking .

Conclusion

During the course project, the braking system of the Lexus GS300 passenger car was designed in 1991, the brake dynamics of the car in the loaded and loaded condition were calculated, and the parameters of the braking mechanisms were selected and calculated. The vehicle was checked for compliance with UNECE Regulation No. 13 and ABS was calculated. Parameters of wear resistance and heat resistance of brake mechanisms were calculated, i.e. specific load on brake linings, specific friction operation, heating of brake disk in one braking was determined. Strength calculation of parts: braces of disc braking mechanism and bolts of brake disc attachment was performed. 

All the obtained numerical values ​ ​ of the above-described calculated values ​ ​ do not exceed the permissible limits.