The brake is a device that can slow down, stop or keep the moving parts (or moving machinery) in a stopped state.It is a mechanical part that stops or decelerates moving parts in machinery.It is commonly known as brake.The brake is mainly composed of brake frame, brake parts and control devices.Some brakes are also equipped with automatic adjustment devices for brake clearance.In order to reduce the braking torque and structural size, the brake is usually installed on the high-speed shaft of the equipment, but large equipment with high safety requirements (such as mine hoist, elevator, etc.) should be installed on the low-speed shaft near the working part of the equipment.
The downstream industries of the industrial brake industry are mainly equipment manufacturing industries such as lifting and transportation machinery, metallurgical equipment, mining equipment, construction machinery, wind power and nuclear power equipment, ships and offshore heavy industry. Benefiting from the revitalization and development of these industries, the industrial brake industry will usher in another round of continuoushealthyDevelopment opportunities.China's industrial brake industry will still maintain an annual growth rate of 10% - 20% in the next few years.
According to the Prospects of the Analysis Report on Market Demand and Investment Planning of China's Brake Industry, the relevant deployment of promoting the leap forward development of key areas in the Twelfth Five Year Plan development specification outline, high-end equipment manufacturing, new energy, new materials and other strategic emerging industries will still be the key areas of China's vigorous development.The country's standardization of the equipment manufacturing industry will help promote the development of China's brake industry.In addition, as the economy continues to maintain stable growth in 2011, China's GDP will be 9.5% in 2011, and automobile production and sales are expected to continue to gain a large growth;In 2011, the total demand of the national automobile market is expected to reach 20 million vehicles.Based on comprehensive judgment, the growth rate of China's automobile sales in 2011 was 10% - 15%, which will drive the development of the demand market of the brake industry.It is estimated that the market size of China's brake industry will maintain an annual growth rate of 15% - 25% in the next five years.
With the revitalization and development of the equipment manufacturing industry, the output of domestic brakes has also increased significantly, and the sales revenue of the brake industry has increased synchronously;Due to the late start, weak technical foundation and limited capital investment, China's brake products are mainly low-end products. A few leading enterprises in the industry adhere to independent innovation, increase R&D investment, and are developing towards medium and high-end products with high technology content. The market share of medium and high-end brake products is gradually increasingThe profit margin of high-end brake enterprises is on the rise;For low-end product manufacturers, due to the large number of manufacturers and fierce competition, the price is declining. At the same time, the price of steel and other major raw materials fluctuates, and the growth rate of their profits is slowing down.[1]
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BrakeWith the development of modern industrial machinery, there are many new structural types, among which caliper disc brake, magnetic powder brake and electromagnetic brake are most widely used.The specific classification is as follows:
1. Friction brake can be divided into disc brake, external block brake, internal expansion shoe brake, belt brake, integrated belt brake, double shoe brake, multi shoe brake, simple belt brake, single disc brake, multi disc brake, fixed caliper brake, floating brake, etc.
2. Non friction brake, which can be divided into magnetic powder brake, magnetic eddy current brake, water eddy current brake, etc.
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Balanced booster brake
Balanced booster brake
The pursuit of balanced braking in prevention is the pursuit of balanced and consistent braking force of wheels when the vehicle brakes.The front wheels on both sides are consistent;It can prevent direction deviation, and the rear wheels on both sides are consistent;It can prevent side slip and tail flick.When the car brakes on ice and snow roads and wet roads, deviation and tail flick will cause the car to lose control in varying degrees. If both situations occur at the same time, normal road braking will also cause the car to lose control completely.Once the heavy transport vehicle is out of control, the consequences will be more serious.Therefore;In order to avoid major traffic accidents and ensure the safety of people's lives and property, heavy transport vehicles must resolutely eliminate all "unbalanced" car brakes.The brake deviates and the tail flicks.
Strong braking force
Total braking force=original braking force+self increasing force. When the balanced force increasing brake works, it is necessary to generate a self increasing braking force formed by the conversion of friction force into mechanical force. After the combination of the two braking forces, the total braking force can increase by about 40%. Therefore, China's first "brake" has a higher safety performance in dealing with heavy loads, steep slopes, and various dangerous roads.
Completely solve the problem of brake drum rupture
Broken brake drum will cause wheel braking failure, involving driving safety.All vehicles equipped with balanced booster brakes are amazed that the problem of brake drum rupture, which has been puzzling for a long time, has finally been successfully solved.Balanced braking;It can make the drum face evenly stressed, reduce the pressure stress per unit area, reduce the hot cracks, and the mechanical strength of the brake drum body is not easy to damage, so the fracture problem can be easily solved.In the future, brake drums will mainly be scrapped due to natural wear.The service life exceeds three times of the original brake.
The friction plate cannot be wasted
Brake pad of original brake;The maximum contact surface does not exceed 80%, and the wear degree of the two shoes is inconsistent. Replace all the shoes with the thinnest end in place.It's a pity to see the heavy scrap film.The contact surface of the balance brake is 100% from beginning to end, and the wear degree is even, and the thickness of the scrap plate is equal.In terms of wear volume or weight, one third more shall be worn off.Therefore, China's first "brake" saves more brake pads.
Maintenance of axle bearing mass
The brake is installed on the axle housing, the brake drum is installed on the wheel core, and the wheel core is installed on the half axle guide through the bearing, which is the automobile axle.Balanced braking axle eliminates the running stress bias and stress concentration of the driving mechanism, maximally maintains the bearing quality of the axle, saving money, time and high cost performance.
After the upgrading of the braking system of the transport vehicle, the performance will be greatly changed. The value of the brake drum and friction plate alone is more than three times of its value.In the process of long-term use, it can save a lot of material costs and maintenance costs as well as a lot of energy and time.The increased investment in refitting a pair of balancers is not enough to purchase half of the brake drums, which fully reflects the high cost performance and reduces the occurrence of failures.The service life of the wheel core, bearing and half shaft guide tube on the axle is doubled.
Service brake
The service brake (foot brake) is convenient for slowing down and stopping in the process of moving forward, not only to keep the car stationary.If the service brake fails, the parking brake shall be applied.When the vehicle stops stably, use the parking brake (hand brake) to prevent the vehicle from moving forward and backward.After parking, in addition to using the parking brake, the gear should be put in the first gear when parking on an upward slope (to prevent backward travel), and the gear should be put in the reverse gear when parking on a downward slope (to prevent forward travel).
In the industrial brake, the crane brake is both a working device and a safety device for the crane. In the lifting mechanism, the brake is used to stop the lifted or lowered goods stably at the required height, or to control the lifting or lowering speed. In the running or luffing mechanism, the brake can make the mechanism stop stably at the required position.
Hydraulic braking is stable, safe and reliable, convenient for maintenance, low power consumption, long service life, no noise, high frequency, etc.
The company's products are widely used in domestic lifting and transportation, port machinery, metallurgical machinery, railway machinery, hydraulic machinery, mining machinery and other industries.
Elevator brake
The brake is one of the safety parts of the elevator with frequent actions. It can stop the motor of the elevator when there is no power supply, and make the car stop effectively. The safe operation of the elevator is closely related to the working condition of the brake.A large number of accident cases show that one of the main reasons for elevator casualties is brake failure or design defects, which leads to the phenomenon of top punching, bottom sinking, car sliding, and even shearing.Therefore, it is particularly important to strengthen the safety inspection of elevator brakes.
1. Common problems, safety requirements and inspection of mechanical part of brake
1.1 Common problems in mechanical part of brake
The common problems of the mechanical part of the elevator brake are as follows.
(1) The stroke indicator collides with the movable indicator, and the designers of some manufacturers are not thoughtful about the uniqueness of the installation of the stroke indicator.
(2) Long term use causes the brake shoe to fall off, and the bonding is broken (some brakes are bonded rather than riveted).
(3) The sealing rubber is aged and cracked, and the brake is blocked due to falling foreign matters.
(4) The electromagnet core is rusted, causing the brake to jam.
(5) The design of the guide mechanism of the elevator iron core is unreasonable, and the connection between the copper bar and the iron core is broken at many places, causing the brake to jam.
(6) The elevator maintenance personnel did not check and maintain the brake properly.
1.2 Safety requirements and inspection of mechanical part of brake
In order to solve the above problems, relevant national regulations and standards have put forward corresponding safety requirements and inspection standards, which are detailed as follows.
(1) In case of power loss of elevator power supply or control circuit power supply for any reason, the brake shall generate enough braking torque to make the lift car stop reliably.Therefore, braking torque is its main parameter, which is used to ensure that the elevator in operation stops at the deceleration required by the standard.
Item 8.10 of Annex A of TSG T7001-2009 Elevator Supervision, Inspection and Periodic Inspection Rules - Traction and Forced Drive Elevator requires: "The lift car shall move up at normal running speed without load, cut off the power supply of motor and brake, and the lift car shall be reliably stopped without obvious deformation and damage."
During the inspection, when the lift car is unloaded and going up to the upper part of the travel at the normal operating speed, disconnect the main power switch and check the brake stop and deformation of the lift car.
During the inspection, the lift car carries 125% of the rated load and goes down at the normal operating speed. When the lift car runs to a lower landing, cut off the power supply of the motor and brake, and the lift car should be reliably stopped without obvious deformation and damage.Usually, the acceleration and deceleration tester is used to test and record the values on site, and the instrument can display the average deceleration.
(2) Article 12.4.2.1 of GB7588-2003 requires that: "All mechanical parts of the brake involved in applying braking force to the brake wheel or disc shall be assembled in two parts. If a group of parts does not work, there shall be sufficient braking force to slow down the car carrying the rated load at the rated speed. The iron core of the electromagnetic coil is considered as a mechanical part, while the coil is not."This standard can be understood as "all brake components involved in applying braking force to the brake wheel or brake disc shall be brake pads and compression springs or weights that generate braking force, which shall be divided into two groups according to the above provisions.At the same time, the iron core of the electromagnet that plays the role of opening the brake, which is opposite to the compression spring applying the braking force to the brake wheel, must also be correspondingly divided into two groups, and there can be no correlation between the two groups of iron cores, and their actions should be independent.This regulation does not emphasize two coils. If two coils are set, it means two sets of brakes. "Therefore, the hardware mentioned above shall meet the requirements during appearance inspection.During the function test, it is considered that one group of brake shoes will be opened, so that the car with rated load traveling down at rated speed will be pulled and powered off, and the other group of brake shoes will judge each other whether the car will slow down.
Since this requirement is proposed in GB7588-2003, and the elevator manufactured according to GB7588-1995 has only one brake electromagnet iron core, it can only be used as one group of brakes rather than two groups, so it does not meet the requirements of this condition.Therefore, during the actual inspection, the method of "new standard for new elevator, old standard for old elevator" is generally followed according to the date of departure.
(3) Article 12.4.2.4 of GB7588-2003 requires: "The elevator driving host equipped with manual emergency operation device shall be able to release the brake by hand and need to keep it released with a continuous force." During inspection, disconnect the main power supply of the elevator, install the disc wheel, 1-2 maintenance personnel hold the disc wheel, and another maintenance personnel use a brake release wrench to release the holding brake,Conduct rescue turning and releasing test.Of course, due to the different types of traction models from different manufacturers, the operation mode is slightly different.If it is an operating device with an operating force greater than 400N or a roomless elevator that is difficult to manually crank, it shall be equipped with an emergency electric operating device.
(4) For block brakes,Article 4.1.10 of GB10060-1993 Code for Acceptance of Elevator Installation requires: "The brake acts flexibly. When braking, the brake shoes on both sides should closely and evenly fit on the working surface of the brake wheel. When releasing the brake, they should leave synchronously. The average clearance at the four corners on both sides should not be more than 0.7 mm." Therefore, the rotating parts of the brake must be checked during inspection, and each pin shaft should rotate flexibly;The moving iron core shall operate without jamming when power is on or off;The brake arms on both sides of the brake shall act in the same way, that is, open or hold the brake at the same time.When the average clearance at the four corners of the brake is not more than 0.7mm on both sides, short circuit the upper limit switch, upper limit switch and buffer switch, and lift the empty car at slow speed to make the counterweight fully compacted on the buffer.Cut off the main power supply of the elevator, manually energize the brake control coil, open the brake, measure the clearance between the brake shoe and the brake wheel with a feeler gauge, and the average clearance at the four corners shall not be greater than 0.7mm.It should be noted here that the standard requires the average value of the clearance.
(5) Frequently check the wear of brake shoe (or brake pad).If the amount of wear is large, the contact surface between the brake shoe (or brake pad) and the brake wheel (disc) will be reduced, resulting in a reduction of the braking torque, resulting in unsafe hazards such as sliding.Figure 1 shows the brake shoe with severe wear.In structure, the force used by the brake shoe on the brake wheel or brake disc shall be symmetrical, and it will not produce additional load on the motor shaft and worm shaft.The brake shoe material shall be nonflammable and have a certain thermal capacity to ensure that the friction coefficient is basically unchanged when heating.It must be made of materials with sufficient strength and good quality. It is not allowed to use harmful materials, such as asbestos.
(6) Brake noise shall be tested separately
2 Safety requirements and inspection of electric part of brake
2.1 Safety requirements for electrical part of brake
Since the brake is electromechanical type, the inspection of the electrical part of the brake is also very important.
(1) Under the working voltage, operate according to the operating mechanism, load duration and cycle of the traction machine. When the brake reaches thermal stability, measure the temperature rise of the brake coil.The measurement method is resistance method in 8.6.2 of GB 755-2008 Rotating Electrical Machines - Rating and Performance.When Class B insulation is adopted, the temperature rise of brake coil shall not exceed 80K;When Class F insulation is adopted, the temperature rise of brake coil shall not exceed 105K.For brakes whose exposed surface temperature exceeds 6 (TC), warning signs shall be added to prevent burns.
(2) The withstand voltage test of the brake coil shall meet the requirement that 1000 V voltage shall be applied between the conductive part and the ground for 1 min without breakdown.
(3) The minimum pull in voltage and maximum release voltage of the brake electromagnet shall be measured after the brake temperature rise test.According to Elevator Traction Machine (GB/T 24478-2009), the minimum pull in voltage and maximum release voltage of brake electromagnet shall be lower than 80% and 55% of the rated voltage respectively.
(4) Newer brakes are equipped with band type brake monitoring switch. When the brake operates abnormally, the switch will act to protect the elevator from stopping, which provides guarantee for the safe and reliable operation of the brake.However, there is no relevant standard requirement. I hope it can be reflected in the standard in the future for maintenance and inspection.
(5) Another important point of the brake electrical part is the control circuit of the brake coil.According to the provisions of relevant standards, it can be summarized as follows: ① During normal operation, the brake should be kept in the released state under continuous energization. ②At least two independent electrical devices shall be used to cut off the brake current, regardless of whether these devices are integrated with the electrical device used to cut off the current of the elevator driving host. ③The so-called independence means that the two contactors have no mutual control relationship. The two contactors must be controlled by two independent signals, not by one signal. ④When the elevator stops, if the main contact of one of the contactors is not opened, the elevator shall be prevented from running again when the next running direction changes at the latest. ⑤When the elevator motor is likely to act as a generator, it shall be prevented from feeding power to the electrical device that controls the brake. ⑥After disconnecting the release circuit of the brake, the elevator shall be effectively braked without additional delay.The brake response time shall not be greater than 0.5s to prevent the elevator from backward pulling and sliding.The response time of the service brake, which is also used as the braking element of the lift car uplink overspeed protection device, shall meet the braking requirements of 9.10.1 in GB 7588-2003. ⑦If one contact in the circuit is stuck, the other contactor contact can still reliably disconnect the brake circuit to prevent the slide. ⑧It can monitor the failure that the contactor is not opened, so as to prevent another contactor from not opening and causing the slide.
2.2 Matters needing attention when checking the control circuit of brake coil
Through studying the standard and summarizing the experience in practice, the author believes that the following aspects should be paid attention to when checking the brake coil control circuit.
(1) Carefully consult the electrical schematic diagram and wiring diagram, and carefully analyze the number of electrical devices in the control circuit and their mutual independence.For example, in Figure 2, it can be found that XC, SC and YXC are not independent and have a mutual control relationship.
(2) Check the control circuit of the brake to confirm whether the brake current is cut off by more than two electrical devices.
(3) Analysis of the independence between the electrical devices that cut off the brake current.After determining that the number of electrical devices that cut off the brake current is not less than two, the independence between electrical devices should be further analyzed.
(4) After the review of electrical schematic diagram is completed, on-site inspection can be carried out.Generally, the following steps can be followed.
① First, check whether the equipment is consistent with the drawings. After confirming that the equipment is consistent with the drawings, complete the inspection of the remaining problems in the drawing review, such as the number and type of electrical devices.
② The elevator is powered on, the car is placed at the intermediate landing, and the elevator door is closed.
③ When the elevator is running, the machine room maintenance personnel use tools to hold down a contactor that has been pulled in to cut off the brake current.
④ The elevator stops at the same level.At this time, the main contact of the tested contactor should still be closed under the action of artificial external force, which can simulate the electric shock adhesion state.If the maintenance personnel in the car select the original departure floor, the elevator shall not operate.
⑤ During the above tests, personnel shall be assigned to stand beside the main power supply. In case of any accident, power shall be cut off immediately to stop the ladder.
During the above test, if the elevator cannot run when the running direction of the elevator changes, it can be determined that the electrical control system of the brake meets the requirements of the standard, and the test conclusion is qualified.
3 New function of brake
For elevators, brakes are both working devices and safety devices.With the development of technology and the improvement of energy conservation and environmental protection requirements, more and more permanent magnet synchronous gearless traction machines will replace the traditional worm gear traction machines, so it may not be necessary to install a separate uplink overspeed protection device. The brakes of this permanent magnet synchronous gearless traction machine (type test shall be conducted) have the uplink overspeed protection function.According to the requirements of Article 9.10 of GB 7588-2003, the car upward overspeed protection device is usually composed of speed monitoring element and deceleration actuating element, while the brake of permanent magnet synchronous gearless traction machine (all brake components involved in applying force to the brake wheel or disc are assembled in two parts, which are considered to have internal redundancy)It is used as a deceleration actuator to slow down or stop the elevator.Therefore, during the inspection, it is necessary to check whether the brake should have type test certificate and report with uplink overspeed protection function, whether the brake is directly and rigidly connected to the traction wheel, and whether there should be electrical devices to verify whether the brake works normally, but not connected to the safety circuit in series.The braking performance of its uplink overspeed protection shall also meet the relevant requirements of Article 9.10 of GB 7588 - 2003.
TSG T700 1-2009 requires the elevator manufacturer to provide the type test certificate of the driving host. The author has consulted some type test certificates and reports of the driving host, which all include the contents of the brake. Compared with the previous one, this one has an additional safety check in both mechanical and electrical parts.
classification
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friction
① Friction brakes.Brake by the friction between the brake and the moving parts.
② Non friction brakes.The structural forms of the brake mainly include magnetic powder brake (using the shear force generated by magnetic particle magnetization to brake), magnetic eddy current brake (adjusting the size of braking torque by adjusting the excitation current) and water eddy current brake.
Structural form of brake parts
It can also be divided into external block brake, internal tension shoe brake, belt brake, disc brake, etc;
Working status of brake parts
It can also be divided into the normally closed brake (usually in the tight brake state, the brake can be released by applying external force) and the normally open brake (usually in the loose brake state, the brake can be released by applying external force);
Operation mode
It can also be divided into brakes operated by manpower, hydraulic pressure, air pressure and electromagnetic force.
Function of braking system
The braking system can be divided into service braking system, parking braking system, emergency braking system and auxiliary braking system.Among the above braking systems, the service braking system and the parking braking system are required for every vehicle.
Brake control energy
The braking system can be divided into manual braking system, dynamic braking system and servo braking system.The braking system with the driver's body as the only braking energy is called the manual braking system;The system that brakes completely by the potential energy in the form of air pressure or hydraulic pressure converted from the power of the engine is called the power braking system;The braking system that uses both human power and engine power for braking is called servo braking system or power assisted braking system.
Braking energy transmission mode
The braking system can be divided into mechanical, hydraulic, pneumatic, electromagnetic and other types.The braking system that adopts more than two energy transmission modes at the same time is called the combined braking system.
working principle
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The general working principle of the braking system is to use the mutual friction between the non rotating elements connected to the body (or frame) and the rotating elements connected to the wheel (or transmission shaft) to prevent the rotation of the wheel or the trend of rotation.
Schematic diagram of working principle of braking system
A simple hydraulic braking system diagram can be used to illustrate the working principle of the braking system.A metal brake drum with the inner round surface as the working surface is fixed on the wheel hub and rotates with the wheel.On the fixed brake bottom plate, there are two supporting pins supporting the lower ends of the two arc brake shoes.The outer circular surface of the brake shoe is equipped with a friction plate.The brake bottom plate is also equipped with a hydraulic brake wheel cylinder, which is connected with the hydraulic brake master cylinder installed on the frame by an oil pipe 5.The piston 3 in the master cylinder can be operated by the driver through the brake pedal mechanism.
When the driver steps down the brake pedal to make the piston compress the brake fluid, the wheel cylinder piston presses the brake shoe toward the brake drum under the action of hydraulic pressure to reduce the rotating speed of the brake drum or keep it still.
When learning about the brake system of a certain model, you may often hear the words "front disc and rear drum" or "front disc and rear drum". What does it mean?Some readers ask questions about the automobile brake system via email, such as the difference between disc brake and drum brake, the difference between ventilated disc and solid disc, etc.
Many middle and low-end models with small engine displacement in the car market use the "front disc and rear drum" brake system, that is, the front wheel uses the disc brake, and the rear wheel uses the drum brake, such as the common FAW Volkswagen Jetta, Changan Suzuki Alto and Antelope, BYD Fryer, Dongfeng Yueda Kia Qianlima, Shanghai GM Sail, etc.First, let's briefly understand the drum brake that is often used by the rear wheel.
The difference in actual application is obvious, and disc brake is better than drum brake.Drum brake and disc brake have their own advantages and disadvantages.In terms of braking effect, there is little difference between disc brake and drum brake, because kinetic energy is converted into heat energy by braking.If the car body is small and light, drum brakes can be used for the rear wheels.
In terms of heat dissipation, the disc brake dissipates heat faster than the drum brake, and the ventilated disc brake has better heat dissipation effect;In terms of sensitivity, the disc brake will be higher, but in rainy days when the road is muddy, the braking effect will be greatly reduced when the brake drum is stuck with mud, which is also a disadvantage of the disc brake;In terms of cost, drum brake is lower than disc brake, and its service life is longer. Therefore, drum brake is often used in some middle and low-end vehicles, and four-wheel disc brake is basically used in middle and high-end vehicles.
From the point of view of economy and practicality, car designers generally adopt a hybrid form of front wheel disc brake and rear wheel drum brake.During the braking process of a four-wheel car, due to the effect of inertia, the front wheel load usually accounts for 70% - 80% of the total vehicle load, so the front wheel load is greater than the rear wheel load.In order to save costs, car manufacturers use front wheel disc brake and rear wheel drum brake.For medium and high class cars with four-wheel disc brake, the front wheel ventilated disc brake is used for better heat dissipation, and the rear wheel non ventilated disc brake is also the cost reason.After all, the manufacturing process of the ventilation plate is much more complicated, and the price is relatively expensive.With the development of material science and the reduction of cost, the disc brake has the tendency to gradually replace the drum brake in the field of cars.
Generally, the brake applies braking torque to the rotating element through the fixed element in the brake to reduce the rotating angular speed of the latter. At the same time, depending on the adhesion between the wheel and the ground, the brake force on the road surface is generated to slow down the vehicle.All brakes that generate braking torque by friction between fixed components and working surfaces of rotating components are friction brakes.Friction brakes used in automobiles can be divided into drum type and disc type.
The brake whose rotating element is fixed on the wheel or half axle, that is, the brake torque directly acts on the wheels on both sides is called wheel brake.The brake whose rotating elements are fixed on the transmission shaft of the transmission system and whose braking torque is distributed to the wheels on both sides through the drive axle is called the central brake.
Block type
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The brake for crane is composed of brake pad, brake arm, brake wheel and brake release.The brake wheel is usually installed on the rotating shaft of the mechanism as a half of the coupling. The symmetrically arranged brake arm is hinged with the fixed part of the frame. Two brake pads with friction materials on the inner side are movably hinged on the two brake arms. Under the action of the brake force on the brake release, the paired brake pads hold the brake wheel in a radial direction to produce brake torque.
When the power is connected, the iron core of the electromagnetic brake release attracts the armature to press the push rod, which pushes the left brake arm to swing to the left, and the main spring is compressed.At the same time, the auxiliary spring releasing the pressure pushes the right brake arm to the right, and the two brake booms drive the brake pad to separate from the brake wheel, so that the mechanism can move.When the power supply is cut off, the iron core loses magnetism and the attraction to the armature is eliminated, so the pressure of the armature on the push rod is relieved. Under the effect of the tension of the main spring, the two brake booms swing inward together, driving the brake pads to hold the brake wheel to produce brake torque;At the same time, the auxiliary spring is compressed.The braking torque is determined by the force of the main spring, and the auxiliary spring ensures the clearance between looseness.The braking performance of the block brake is largely determined by the performance of the brake release.
Brake system
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function
The functions of decelerating or even stopping a moving car, stabilizing the speed of a downhill car, and keeping a stopped car stationary are collectively referred to as braking;A series of special devices installed on the car so that the driver can apply a certain force on some parts of the car (mainly the wheels) from the outside (mainly the road surface) according to the road and traffic conditions, and brake the car to a certain extent. This controllable external force for braking the car is called braking force;Such a series of special devices are called braking systems.
The braking system used to slow down or even stop the running car is called the service braking system;The device used to make the stopped car stay in place is called parking brake system.These two brake systems are necessary for every car.[2]
component
Any braking system has the following four basic components:
1) The energy supply device includes various components for supplying and regulating the energy required for braking and improving the state of energy transmission medium.
2) Control device, including various components that generate braking action and control braking effect.
3) Transmission device, including various components that transmit braking energy to the brake
4) Brake, the component that generates the force (braking force) that obstructs the movement or movement trend of the vehicle, including the retarder in the auxiliary braking system.
classification
According to the braking energy, the service braking system can be divided into: the braking system with the driver's body as the only braking energy is called the human braking system;The power braking system is completely braked by the potential energy in the form of air pressure or hydraulic pressure converted from the power of the engine, and its braking source can be the engine driven air compressor or oil pump;The braking system that uses both human power and engine power for braking is called servo braking system.
The parking brake system can be manual or power type.Inertial braking system and gravity braking system are also specially used for trailers.
According to the transmission mode of braking energy, braking systems can be divided into mechanical, hydraulic, pneumatic and electromagnetic types.The braking system that adopts more than two energy transmission modes at the same time can be called combined braking system.
Drum type
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The rotating element is a brake drum, and its working surface is an inner cylindrical surface;The fixed element is the brake shoe, and its working surface is a cylindrical surface. The brake torque is generated by the friction force between the brake shoe and the brake drum.[3]
brief introduction
Drum braking is also called block braking, which is achieved by pressing the brake block on the brake wheel.Drum brake is an early designed brake system. Its brake drum design has been used on horse drawn carriages since 1902, and it was not widely used in the automobile industry until about 1920.The mainstream of drum brake is internally tensioned. Its brake pad (brake shoe) is located inside the brake wheel. When braking, the brake pad opens outward and rubs the inside of the brake wheel to achieve the purpose of braking.Compared with the disk brake, the heat dissipation of the drum brake is much worse. The stability of the brake force of the drum brake is poor. The brake force varies greatly on different roads, and it is not easy to control.However, due to poor heat dissipation performance, a large amount of heat will be accumulated during braking.Under the influence of high temperature, brake pads and wheel drums are prone to extremely complex deformation, braking recession and chattering, which will lead to the decline of braking efficiency.In addition, after using the drum brake for a period of time, the clearance of the brake shoe should be adjusted regularly, or even the entire brake drum should be removed to clean the accumulated brake powder.Of course, the drum brake is not useless. It is cheap, has large braking force, and conforms to the traditional design.In the braking process of a four-wheel car, due to the inertia, the load of the front wheels usually accounts for 70% - 80% of the total load of the car. The braking force of the front wheels is larger than that of the rear wheels, and the rear wheels play an auxiliary braking role. Therefore, in order to save costs, the car manufacturers use the brake method of the front disc and the rear drum.However, for heavy vehicles, because the speed is generally not very high, the durability of brake shoes is also higher than that of disc brakes, and the braking force is large, many heavy vehicles still use the four-wheel drum design.
advantage
Self braking effect: the drum brake has a good self braking effect. Because the brake makes the brake pad stretched out, the wheel rotation and the brake drum with the extension twist an angle (of course not big enough for you to easily see). The greater the tension (braking force) outside the brake pad, the more obvious the situation is. Therefore, the drum brake is generally used for large vehicles. In addition to the low cost,The difference between the drum brake of large cars and that of small cars may only be that large pneumatic assistance is used, while small cars use vacuum assistance to help brake.Low cost: drum brake has a lower level of manufacturing technology, and is also the first brake system used, so the manufacturing cost is lower than disc brake.
shortcoming
Because the brake lining of drum brake is sealed in the brake drum, the worn chippings of the brake lining cannot be removed, which affects the contact surface between the brake drum and the brake lining and affects the brake performance.The biggest disadvantage of drum brake is that it will slip after being exposed to rain in rainy days, which will cause brake failure. This is its most terrible leading shoe brake's increasing and decreasing force effect. Set the brake drum's rotation direction when the car is moving forward (this is called the brake drum's positive rotation).The supporting point 3 of the brake shoe 1 is at its front end, and the actuating force applied by the brake wheel cylinder 6 acts on its rear end, so the rotation direction of the brake shoe when it opens is the same as that of the brake drum.The brake shoe with this property is called the leading shoe.On the contrary, the supporting point 4 of the brake shoe 2 is at the rear end, and the driving force is applied to the front end. When the brake shoe 2 opens, its rotation direction is opposite to the rotation direction of the brake drum.Brake shoes with this property are called slave shoes.When the car drives backward, that is, when the brake drum rotates in the opposite direction, shoe 1 becomes the slave shoe, and shoe 2 becomes the leading shoe.When the brake drum rotates in the forward direction and reverse direction, the brake with a leading shoe and a trailing shoe is called the leading and trailing shoe brake.When braking, the actuating force applied by the two pistons is equal.Therefore, an additional radial force is generated on the brake drum during braking.The brake that the normal force from the two shoes on the brake drum cannot balance with each other is called unbalanced brake.When the one-way double leading shoe brake rotates in the positive direction of the brake drum, the brake with both leading shoes is called the double leading shoe brake, and its structure diagram is shown in the right figure.There are two main structural differences between the double leading shoe brake and the leading and trailing shoe brake. One is that the two brake shoes of the double leading shoe brake each use a single piston wheel cylinder, while the two shoes of the leading and trailing shoe brake share a double piston wheel cylinder;Second, the arrangement of the two sets of brake shoes, brake wheel cylinders and support pins of the double leading shoe brake on the brake floor is centrally symmetrical, while the arrangement of the brake shoes, brake wheel cylinders and support pins of the leading shoe brake on the brake floor is axisymmetric.The two-way double leading shoe brake is called the two-way double leading shoe brake, regardless of whether it is a forward brake or a reverse brake. Figure 5-42 is a schematic diagram of its structure.Compared with the leading and trailing shoe brake, the two-way double leading shoe brake has three characteristics in structure: first, it uses two double piston brake wheel cylinders;Second, both ends of the two brake shoes are supported by floating bearings, and the circumferential position of the fulcrum is also floating;Third, all fixed elements on the brake bottom plate, such as brake shoes, brake wheel cylinders, return springs, etc., are in pairs, and arranged symmetrically both axially and centrally.When the double slave shoe brake brakes forward, the brake whose two brake shoes are both slave shoes is called the double slave shoe brake, and its structure diagram is shown in Figure 5-44.The structure of this brake is very similar to that of the double leading shoe brake. The only difference between the two is that the relative motion directions of the fixed elements and the rotating elements are different.Although the forward braking effect of the double trailing shoe brake is lower than that of the double leading shoe brake and the leading trailing shoe brake, its efficiency is less sensitive to the change of friction coefficient, that is, it has good stability of braking efficiency.The fixed elements of double leading shoe, two-way double leading shoe and double trailing shoe brakes are arranged symmetrically in the center.If the clearance is adjusted correctly, the two normal resultant forces exerted by the two shoes on the brake drum can balance each other and will not cause additional radial load on the hub bearing.Therefore, these three brakes are all balanced brakes.See the right figure for the structure principle of one-way self amplification brake.The lower ends of the first brake shoe 1 and the second brake shoe 2 are respectively floated on both ends of the floating ejector rod 6.When the car is braked forward, the single piston wheel cylinder will apply the actuating force FS1 to the first shoe to press it against the brake drum 3.The first shoe is the leading shoe and is in balance under the action of various forces.The ejector rod 6 is floating, and the actuating force FS2, which is equal to the force S1 in the opposite direction, is applied to the second shoe.Therefore, the second hoof is also the leading hoof.The driving force and friction force acting on the first shoe are transmitted to the second shoe through the ejector rod, forming the second shoe driving force FS2.According to the force analysis of brake shoe 1, FS2 is greater than FS1. In addition, the force arm of force FS2 on the supporting point of the second shoe is also greater than that of force FS1 on the supporting point of the first shoe.Therefore, the braking torque of the second shoe must be greater than that of the first shoe.When reversing braking, the braking efficiency of the first shoe is much lower than that of the general leading shoe, and the second shoe does not work because it is not stimulated.The structure principle of two-way self amplification brake is shown in Figure 5-47.It is characterized by that when the brake drum rotates in the forward and reverse directions, it can play a self reinforcing role by the friction between the shoe drum.Its structure is different from the one-way self boosting type in that it mainly uses the double piston brake wheel cylinder 4, which can apply equal actuating force FS to both shoes at the same time.When the brake drum rotates in the positive direction (as shown by the arrow), the front brake shoe 1 is the first shoe, and the rear brake shoe 3 is the second shoe;When the brake drum rotates in the opposite direction, the situation is opposite.During braking, the first shoe receives only one actuating force FS, while the second shoe has two actuating forces FS and S, and S>FS.Considering that the opportunity of forward braking is far more than that of reverse braking, and the working load of the brake during forward braking is also far greater than that of reverse braking, the friction plate area of rear shoe 3 is larger.Cam brakes are used in the pneumatic braking systems of all domestic and some foreign vehicles, and most of them are designed as leading shoe brakes.During braking, the brake adjusting arm drives the camshaft to rotate under the action of the push rod of the brake chamber 6, so that the two brake shoes press against the brake drum and brake.Due to the central symmetry of the cam profile and the axial symmetry of the two shoe structure and installation, the displacement of the corresponding points on the two shoes caused by the rotation of the cam must be equal.This kind of leading and trailing shoe brake, which is actuated by a cam with fixed axis, is an equal displacement brake. The friction between the brake drum and the brake shoe makes the leading shoe end try to leave the brake cam, and the trailing shoe end is closer to the cam.Therefore, although the leading shoe has a potential boosting effect and the secondary shoe has a potential reducing effect, it is this difference that makes the driving force of the leading shoe with high braking efficiency less than that of the secondary shoe with low braking efficiency, so that the braking torque of the two shoes is equal.The arrangement of the two shoes in the wedge brake can be the leading and trailing shoe type.The actuating device of the brake wedge itself as the brake shoe actuator can be mechanical, hydraulic or pneumatic.The circular arc surfaces at the ends of the two brake shoes are respectively floated on the bottom surface of the straight groove on the outer end surface of the plunger 3 and plunger 6.The inner end faces of the plungers 3 and 6 are inclined planes, which contact the rollers 4 in the grooves on both sides of the spacer 5.When braking, the wheel cylinder piston 15 pushes the brake wedge 13 inward under the hydraulic action.The latter makes the second roller roll inwards along the oblique side of the plunger, and pushes the second plungers 3 and 6 outward to move a certain distance in the hole of the brake bottom plate 7, so that the brake shoe presses against the brake drum.Once the wheel cylinder hydraulic pressure is removed, this series of parts will return under the action of the brake shoe return spring.Guide pins 1 and 10 are used to prevent the two plungers from rotating.Summary of drum brakes The various drum brakes described above have their own advantages and disadvantages.In terms of braking efficiency, under the same basic structural parameters and working pressure of the wheel cylinder, the self boosting brake takes the first place because it makes the most full use of the friction potential, and the following are the double leading shoe type, the leading shoe type, and the double trailing shoe type.However, the friction coefficient between the hoof and the drum itself is an unstable factor, which can vary in a large range depending on the material, temperature and surface conditions (such as whether the brake drum and friction plate are stained with water, oil, sintering, etc.).The effectiveness of the self increasing brake depends most on the friction coefficient, so its effectiveness has the worst thermal stability.In the process of braking, the increase of braking torque of self boosting brake appears too rapid in some cases.The two-way self boosting brake is mostly used for the rear wheels of cars, one of the reasons is that it is convenient to charge the parking brake as well.The one-way self boosting brake is only used for the front wheels of medium and light vehicles, because the requirements for the effectiveness of the front wheel brake are not high when reversing brake.Although the braking efficiency of the double trailing shoe brake is the lowest, it has the best efficiency stability, so there are still a few luxury cars (such as the British Queen car) to ensure braking reliability.The leading shoe brake developed earlier, its efficiency and efficiency stability are in the middle, and it has the advantages of simple structure, so it is still widely used in various cars.
disc
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Exploded view of disc brake
There are two types: clamp disc type and full disc type, the former is more commonly used.The characteristics of caliper disc brake are as follows: the rotating element in the friction pair is the brake disc. The brake disc and the wheel hub rotate together. With the two end faces as the working surfaces, the fixed element is the brake caliper. The brake caliper presses the brake pad to the brake disc under the action of the brake wheel cylinder, thus generating the brake friction torque.Caliper disc brakes are widely used in passenger cars and light buses.
The disc brake is hydraulic type and controlled by hydraulic pressure. The main parts include brake disc, wheel cylinder, brake caliper, oil pipe, etc.The brake disc is made of alloy steel and fixed on the wheel, which rotates with the wheel.The wheel cylinder is fixed on the bottom plate of the brake, and the two friction plates on the brake caliper are respectively installed on both sides of the brake disc. The piston of the wheel cylinder is driven by the hydraulic pressure delivered from the oil pipe to push the friction plate to the brake disc for friction braking, which acts as if the rotating plate is clamped with pliers to force it to stop.The disc brake features fast heat dissipation, light weight, simple structure and convenient adjustment.The disc brakes used by many cars include flat brake discs, perforated brake discs and scoring brake discs. The scoring brake discs have good braking effect and ventilation and heat dissipation capacity.
The disc brake applies force along the brake disc, the brake shaft is free from bending moment, the radial dimension is small, and the braking performance is stable.
The rotating element in the friction pair of the disc brake is a metal disc working on the end face, which is called the brake disc.The fixed elements have a variety of structural types, which can be generally divided into two categories.One type is the brake block composed of friction block with small working area and its metal back plate. There are 2-4 brake blocks in each brake.These brake pads and their actuating devices are installed in the clamp shaped supports across both sides of the brake disc, and are collectively called brake calipers.The brake composed of brake disc and brake caliper is called caliper disc brake.The metal backing plate and friction plate of the other type of fixed components are also disc shaped, and all working surfaces of the brake disc can contact the friction plate at the same time. This kind of brake is called full disc brake.Caliper disc brakes were used only as central brakes in the past, but they are increasingly used as wheel brakes by cars and trucks at all levels.Only a few vehicles (mainly heavy vehicles) use full disc brakes as wheel brakes.Only the caliper disc brake is introduced here.The caliper disc brake can be divided into fixed caliper disc type and floating caliper disc type.[4]
characteristic
Compared with the drum brake, the disc brake has the following advantages: generally, there is no friction boosting effect, so the brake efficiency is less affected by the friction coefficient, that is, the efficiency is more stable;After immersion, the efficiency decreases less, and it can return to normal after only one or two braking;When the output braking torque is the same, the size and mass are generally small;The thermal expansion of the brake disc along the thickness direction is very small, which will not significantly increase the brake clearance like the thermal expansion of the brake drum, resulting in excessive brake pedal travel;It is easy to realize automatic clearance adjustment, and other maintenance and repair operations are also simple.For caliper disc brake, because the brake disc is exposed, it has the advantage of good heat dissipation.The disadvantage of the disc brake is its low efficiency, so the brake actuating pipeline pressure required for the hydraulic brake system is high, and servo devices are generally used.
Disc brakes have been widely used in cars, but most of them are only used as front wheel brakes, except for all wheels on some high-performance cars. They work with the drum brakes of the rear wheels, so that the car can have a higher directional stability when braking.On freight cars, disc brakes are also used, but they are far from being popularized.
advantage
Since the brake system is not sealed, the brake wear cannot be deposited on the brake. The centrifugal force of the disc brake can throw out all water, dust and other pollution to maintain a certain degree of cleanliness.In addition, since the disc brake parts are independent, it is easier to repair than the drum brake.
shortcoming
In addition to its high cost, disc brakes are basically superior to drum brakes. Disc brakes are also called disc brakes, which are named after their shape as the name implies.It is hydraulically controlled, and its main components include brake disc, wheel cylinder, brake caliper, oil pipe, etc.The brake disc is made of alloy steel and fixed on the wheel, which rotates with the wheel.The wheel cylinder is fixed on the bottom plate of the brake.The two friction plates on the brake caliper are respectively installed on both sides of the brake disc.The piston of the wheel cylinder is driven by the hydraulic pressure delivered from the oil pipe to push the friction plate to the brake disc for friction braking. It acts as if the rotating disc is clamped with pliers to force it to stop.The brake has the advantages of fast heat dissipation, light weight, simple structure and convenient adjustment.In particular, under high load, it has good heat resistance, stable braking effect, and is not afraid of mud and water. When driving in winter and bad road conditions, disc braking is easier to stop the car in a short time than drum braking.Some disc brakes also have many small holes on the brake disc to accelerate ventilation and heat dissipation to improve braking efficiency.In contrast, drum brake will accumulate a lot of heat during braking due to poor heat dissipation performance.Under the influence of high temperature, the brake shoe and wheel drum are prone to extremely complex deformation, braking recession and chattering, which will lead to the decline of braking efficiency.Of course, disc brakes have their own shortcomings.For example, the manufacturing requirements for the brake and brake pipeline are high, the friction plate has large consumption and high cost, and due to the small area of the friction plate, the relative friction working surface is also small, and the brake hydraulic pressure required is high, so it must be used by vehicles with power assisted devices, so it can only be used on light vehicles.The drum brake is relatively cheap and economical.
Fixed caliper disc type
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Fixed caliper disc brake.The brake caliper body 5 straddled on the brake disc 1 is fixed on the axle 6. It cannot rotate or move along the axis of the brake disc. The two pistons 2 in it are located on both sides of the brake disc 1.During braking, the brake fluid enters the two connected hydraulic cavities in the caliper body through the oil inlet 4 from the brake master cylinder (brake master cylinder), and presses the brake blocks 3 on both sides to the brake disc 1 that is fixedly connected with the wheels, thus braking occurs.
The brake has the following disadvantages: there are many oil cylinders, which makes the brake caliper structure complex;The oil cylinder is located on both sides of the brake disc and must be connected by the oil passage in the caliper or the external oil pipe across the brake disc, which makes the size of the brake caliper too large to be installed in the rim of modern cars;When the heat load is large, the brake fluid in the oil cylinder and the oil pipe or oil passage across the brake disc is easy to be heated and vaporized;If it is also used for parking brake, a mechanically actuated parking brake caliper must be installed.
Floating tong disc type
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For the floating caliper disc brake, the brake caliper body 2 is connected with the axle 7 through the guide pin 6 and can move axially relative to the brake disc 1.The brake caliper body is only equipped with an oil cylinder at the inner side of the brake disc, while the outer brake block is attached to the caliper body.When braking, the hydraulic oil enters the brake cylinder through the oil inlet 5, pushes the piston 4 and its friction block to move to the right, and presses it onto the brake disc, making the cylinder and the brake caliper body move to the left along the pin as a whole, until the friction block on the right side of the brake disc is also pressed onto the brake disc to clamp the brake disc and brake it.In contrast to the fixed caliper disc brake, the floating caliper disc brake has smaller axial and radial dimensions, and the brake fluid is less likely to vaporize when heated.In addition, when the floating caliper disc brake charges the service and parking brakes at the same time, it is only necessary to install some mechanical transmission parts of the parking brake near the cylinder of the service brake caliper to push the cylinder piston.Therefore, since the 1970s, the floating caliper disc brake has gradually replaced the fixed caliper disc brake.
Brake mechanism
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According to the different installation positions on the vehicle, the parking brake devices are divided into central parking brake devices and wheel parking brake devices.The brake of the former is installed on the transmission shaft, which is called the central brake;The latter shares a set of brakes with the service brake, which is simple and compact in structure and has been widely used in cars.
This brake combines a disc brake as the service brake and a drum brake as the parking brake.The outer rim of the double acting brake disc acts as the brake disc of the disc brake, and the middle drum acts as the brake drum of the drum brake.
When the parking brake is applied, pull the manual parking brake control lever in the cab to the brake position, drive it through a series of levers and cables, pull the lower end of the parking brake lever forward, rotate it around the flat head pin, and push the brake push rod to the left by the middle fulcrum to push the front brake shoe toward the brake drum.After the front brake shoe is pressed against the brake drum, the push rod stops moving, and the brake lever continues to rotate around the middle fulcrum.Then the upper end of the brake lever moves to the right to press the rear brake shoe against the brake drum to apply the parking brake.
When the brake is released, push the parking brake control lever back to the non braking position. The brake lever returns under the action of the pull rope return spring, and the brake shoe return spring pulls the two brake shoes together.
Self-adjusting device
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When the brake shoe is in the original position where it does not work, there should be a proper clearance between its friction plate and the brake drum. The set value is specified by the automobile manufacturer, which is generally between 0.25 and 0.5mm.If the clearance in any brake friction pair (hereinafter referred to as brake clearance) is too small, it is not easy to ensure that the brake is completely released, causing friction pair dragging;Too large will make the brake pedal travel too long, making it inconvenient for the driver to operate, and will also delay the time when the brake starts to work.However, during the operation of the brake, the constant wear of the friction plate will lead to the gradual increase of the brake clearance.In serious cases, even if the brake pedal is pressed to the lower limit position, sufficient braking torque will not be generated.Most cars are equipped with brake clearance self-adjusting devices, and some trucks still use manual adjustment.
Brake clearance adjustment is an important item in automobile maintenance and repair. According to different working processes, it can be divided into one time adjustment type and step adjustment type.
The right figure is a friction limit type clearance self-adjusting device installed in the brake wheel cylinder.The limiting friction ring 2 used to limit the inner limit position of the brake shoe when not braking is installed in the ring groove at the inner end of the wheel cylinder piston 3. The width of the ring groove or spiral groove on the piston is greater than the thickness of the limiting friction ring.The maximum axial displacement of the piston relative to the friction ring is the clearance between them.The clearance shall be equal to the wheel cylinder piston stroke required for full braking when the brake clearance is the set standard value.
When braking, the piston of the wheel cylinder moves outward. If the brake clearance increases to exceed the set value due to various reasons, when the piston moves outward to 0, full braking cannot be achieved, but as long as the wheel cylinder continues to push out the piston together with the friction ring until full braking is achieved.In this way, when the brake is released, the brake shoe can only return until the piston contacts the limit friction ring at the new position, that is, the brake clearance is the set value.
transmission
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Brake
In general, the composition of the mechanical transmission device of the parking brake system is shown in the right figure.The parking brake system shares rear wheel brakes 7 with the service brake system.When the parking brake is applied, the driver pulls up the parking brake control lever 1, tightens the parking brake control cable 3 through the balance lever 2, and actuates the two rear wheel brakes.Due to the one-way action of the pawl, after the pawl is engaged with the pawl tooth plate, the control lever cannot reverse, and the parking brake lever system can be reliably locked in the brake position.To release the brake, pull up the control lever a little, and then press down the pressing rod button 8 at the end of the control lever to make the pawl leave the pawl tooth plate through the pawl pressing rod.Then push the control lever down to the released brake position.The pawl can lock the whole parking mechanical brake lever system in the released brake position.The parking brake system must reliably ensure that the vehicle stops in place, which can only be achieved by mechanical locking method. Therefore, the parking brake system uses mechanical transmission device.
Hydraulic unit
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Brake
The service braking system of the car adopts hydraulic transmission device, which is mainly composed of brake master cylinder (brake master cylinder), hydraulic pipeline, brake wheel cylinder (brake wheel cylinder) in rear wheel drum brake, hydraulic cylinder in front wheel caliper disc brake, etc. See the right figure.In addition to metal pipes (copper pipes), the connecting oil pipes between the master cylinder and the wheel cylinder also use special rubber brake hoses.There are also various pipe joints between hydraulic components and oil pipes.Before braking, the hydraulic system is filled with specially prepared brake fluid.
Depress the brake pedal 4, and the brake master cylinder 5 will feed the brake hydraulic pressure into the brake wheel cylinder 6 and the brake caliper 2, pushing the brake block to the brake drum and brake disc.When the brake clearance disappears and the brake torque begins to be generated, the hydraulic pressure and pedal force can continue to increase until the brake is fully braked.During this process, due to the elastic expansion deformation of the oil pipe and the elastic compression deformation of the friction element under the hydraulic pressure, the pedal and wheel cylinder piston can continue to move for a certain distance.Release the pedal, and the brake shoe and wheel cylinder piston return under the action of the return spring to return the brake hydraulic pressure to the master cylinder.
Booster
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Brake
A vacuum booster is widely installed on cars as a brake booster, which uses the vacuum at the engine throat to help the driver operate the brake pedal.According to the number of vacuum booster diaphragms, the vacuum booster is divided into single diaphragm type and tandem diaphragm type.
Single diaphragm domestic cars all use this type of vacuum booster.
working process：
1. When the vacuum booster does not work (Fig. a), the spring 15 pushes the push rod together with the plunger 18 to the rear limit position (that is, the vacuum valve is opened), and the rubber valve 9 is pressed against the air valve seat 10 by the spring (that is, the air valve is closed).The front and rear cavities of the servo air chamber are interconnected through channel A, control valve cavity and channel B, and are isolated from the air.After the engine starts to work and the vacuum check valve is sucked open, a certain degree of vacuum will be generated in the left and right chambers of the servo air chamber.
2. When the brake pedal is pressed down, the air chamber diaphragm seat 8 is fixed at first, and the control force from the pedal mechanism pushes the control valve push rod 12 and the control valve plunger 18 forward relative to the diaphragm seat 8.When the clearance between the plunger and the rubber reaction plate 7 is eliminated, the control force will be transmitted to the brake master cylinder push rod 2 through the reaction plate 7 (as shown in the following figure).At the same time, the rubber valve 9 moves forward with the control valve plunger until it contacts the vacuum valve seat on the diaphragm seat 8.At this time, the front and rear chambers of the servo air chamber are isolated.
3. The control valve push rod 12 continues to push the control valve plunger forward until the air valve seat 10 on it is a certain distance away from the rubber valve 9.External air is filled into the rear chamber of servo air chamber (as shown in the figure below) to reduce its vacuum.During this process, the diaphragm 20 and the valve seat move forward continuously until the valve contacts the air valve seat again.Therefore, in any balance state, the stable vacuum degree in the rear chamber of the servo air chamber is an increasing function of the pedal travel.
electromagnetism
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Introduction to electromagnetic brake
Electromagnetic brake
The electromagnet is the key part of the electromagnetic brake, which has a great impact on the performance stability and reliability of the electromagnetic brake.When the car continuously uses the brake when going down a long slope or adopts emergency braking at high speed, the temperature of the working parts of the brake will rise sharply.When the temperature is high to a certain extent, the friction coefficient of the brake friction pair and the braking efficiency of the brake are reduced due to mechanical, physical and chemical factors. This phenomenon is called the thermal recession of the braking efficiency. The thermal recession resistance of the brake is one of the important indicators to evaluate the performance of the brake.In the following, the temperature field of electromagnet and friction ring in each period of time when going down a long slope is analyzed by using the finite element analysis method, and the accuracy of the analysis model and method is verified by tests.
The electromagnetic brake is the executive component of the whole braking system.The electromagnetic brake is installed on the wheels of the trailer.Its structure is shown in Figure 1.The whole brake is mainly composed of electromagnet, lever drive mechanism, front and rear brake shoes, bottom plate, friction ring and other parts.
A mechanical part that stops or decelerates moving parts in a machine.It is commonly known as brake.The brake is mainly composed of brake frame, brake parts and control devices.Some brakes are also equipped with automatic adjustment devices for brake clearance.In order to reduce the braking torque and structural size, the brake is usually installed on the high-speed shaft of the equipment, but large equipment with high safety requirements (such as mine hoist, elevator, etc.) should be installed on the low-speed shaft near the working part of the equipment.
Some brakes have been standardized and serialized and manufactured by professional factories for selection.
working principle
Electromagnetic brake
The friction ring rotates with the brake drum, and the electromagnet and the drive lever are connected together through a snap ring.At the beginning of braking, the controller sends out a braking signal, and the electromagnet is energized to generate electromagnetic attraction, which is adsorbed on the friction ring.Since the electromagnet is constrained by the drive lever, it slides relative to the friction ring, and the friction force acting on the electromagnet drives the connected drive lever to rotate around the fulcrum.The driven end of the lever opens the two friction shoes of the brake and presses them against the brake drum to generate braking torque.At the end of braking, the electromagnet is powered off, and the suction and friction force disappear. Under the pull of the return spring, the friction shoe leaves the brake drum to release the braking.
Electromagnetic brake is an ideal automatic actuator in modern industry, which mainly plays the role of transmitting power and controlling motion in mechanical transmission system.The utility model has the advantages of compact structure, simple operation, sensitive response, long service life, reliable use, easy remote control, etc.
It is mainly matched with series motors.It is widely used in metallurgy, construction, chemical industry, food, machine tools, stage, elevator, ship, packaging and other machinery, as well as in occasions such as (danger prevention) braking when power is off.
