With the advent of winter, the temperature drops sharply, and trucks with air braking system begin to show typical seasonal faults: no air injection, no return of braking, braking failure, which brings us a lot of trouble, and some even lead to serious accidents. Therefore, it is very important to conduct a comprehensive investigation on the vehicle air braking system before winter. After years of improvement and upgrading, the basic structure of the domestic mainstream truck air braking system has not changed much, but new components such as ABS sensor and air dryer have higher requirements for the braking system, which also needs special attention.
Through the case investigation of truck drivers and some accidents, some serious accidents, such as Trailer fire and brake failure, are related to the braking system, and often small faults and parts eventually lead to major disasters. Some faults are caused by the system not being checked or using fake parts. These parts are intact at that time, which is easy to cause illusion. The following describes the key points of inspection and ordinary replacement of accessories from several aspects.
When checking the exhaust port of the pressure relief valve at ordinary times, pay attention to whether the oil contamination is serious. In case of serious oil contamination, repair the air compressor and replace it if necessary.
Pay special attention to whether the oil lubricating oil pipe of the air compressor is in good condition, and pay attention that the oil pipe cannot be welded, repaired and loaded, and whether there is other force and vibration during installation. The fracture of lubricating oil pipe is easy to cause serious failure of air pump and engine. The oil pipe shall be standby on the vehicle for replacement. Check whether the air inlet pipeline of the air compressor is intact and ensure that the air inlet is clean and sealed. (different types of air compressors for different engines)
During cold start in winter, when the water temperature does not reach 60-80 ℃, it is strictly prohibited to run the engine with a large throttle, so as to avoid cylinder pulling and excessive wear of the air compressor due to poor lubrication, oil channeling and carbon deposition in the cylinder head (air compressor).
It is difficult to distinguish the performance of the dryer from the appearance. Because the dryer completes a working cycle, it needs two actions of “water absorption and drainage”. In addition to selecting a high-quality dryer, it is necessary to check whether the system works normally. If there is serious oil stain under the exhaust port, it indicates that the molecular sieve of the dryer is seriously polluted by oil stain, has completely failed and does not have the function of water absorption.
Check the back blowing performance of the dryer. During the pressure relief action of the normally working dryer, the compressed air in the back blowing tank or air receiver will back blow the molecular sieve of the dryer to discharge water. At this time, there is a “puff” sound at the exhaust port and water vapor is discharged. If there is no exhaust action, check the dryer base, pressure limiting valve and four circuit protection valve, and replace them if necessary.
The air inlet temperature end inspection can be completed by temperature measurement test paper. When it is higher than 65 ℃, the filter performance of the dryer will decline or even fail. In particular, some batches of Dongfeng Tianlong tractors need to be equipped with spiral pipes to achieve the purpose of cooling.
The snow water splashed by tires in winter is very easy to freeze the electrical circuit, resulting in short circuit and pull open circuit of the circuit. After wrapping the line with fresh-keeping film, apply a small amount of grease or lubricating oil to prevent moisture condensation.
The air pressure sensor of air reservoir and ABS solenoid valve are also wrapped with fresh-keeping film to prevent signal failure and false alarm caused by icing. This is a trick commonly used by bus drivers in the north.
“Movable” gas pipeline refers to a kind of gas pipeline in motion, such as the gas pipeline connecting the brake cylinder to both ends of the frame and the spiral gas pipeline from the trailer to the main vehicle. This kind of tracheal material is special, and it is prone to fatigue, crack and even fracture after long-term exercise.
The “movable” gas pipeline cannot be replaced by hydraulic pressure resistant oil pipe. This is because the hydraulic oil pipe has a steel wire lining layer and has a certain range of bending deformation. For example, the front and rear axle slave pump pipeline has large expansion action, and the mixed hydraulic pipe is prone to internal cracks. The high-quality gas pipe shall be a special rubber gas pipe, with a steel wire protective layer on the outside and lined with cord fabric reinforcing layer. The external steel wire layer can disperse the external deformation and stress and prevent scraping interference.
Special attention shall be paid to the interface of trailer gas pipe, especially the “sub large pipe” of inferior PVC material, which is often mixed, with poor low-temperature performance, extremely brittle and easy to crack and fracture.
If the inferior “sub large pipe” is installed between the wheel cylinder and the emergency relay valve, if the air leakage is not detected in time, it will cause braking failure. In particular, the crack of the parking brake pipeline leaks air, and the spring makes the brake bite, resulting in the overheating of the brake hub. According to statistics, 70% of the semi-trailer fires are caused by air circuit faults, which is not alarmist.
Pay special attention to whether there is air leakage at the air pipe interface of the slave cylinder. The inspection of the parking brake pipeline needs to be carried out when the brake is released. Take anti slip measures for the vehicle. Under the condition of ensuring safety, check one by one. Do not overheat the brake hub and cause fire due to poor brake return caused by air pipe leakage.
The brake return action is divided into active and passive return. The passive return refers to the mechanism such as shoe return spring and shoe fixing pin in the brake hub. The active return action is affected by many components. First, press the brake pedal with enough compressed air, and quickly release the pedal. Pay attention to the exhaust condition of relay valve or quick release valve. If the bleeding is slow, it shall be repaired and replaced in time. Most valve body damage is related to oil stain and water inflow. Pay attention to check the dryer.
Pay attention to check whether the return spring of the brake cylinder is broken or material fatigue. Do not underestimate this small spring. According to the lever principle, the force of the return spring will be greater than that of the passive return tension spring of the shoe. If necessary, replace the high-strength return spring to improve the reaction time and reliable return of braking action. In addition, the small spring ensures good braking return, which will save more fuel and completely improve the braking bite.
The passive return part refers to various parts in the brake hub. The shoe return tension spring needs to be checked up and down with a crowbar. If there is no elasticity and fatigue elongation, it needs to be replaced in time. In order to avoid the poor return of the lower shoe for a long time, interference and friction with the brake hub, resulting in high temperature, and the false appearance of astringency in the adjustment of the brake pad clearance, which cannot be adjusted correctly.
Pay attention to whether the fixed pin of camshaft and brake shoe in the brake drum can move easily. If it is astringent, it needs to be removed, polished and derusted, and replaced if necessary. If the movement is too large, replace the brake shoe bushing or assembly.
Many truck users like to use “brake king”. This kind of violation increases the brake air pressure, which is like inducing poison to quench thirst. The advantages and disadvantages of brake pads are often ignored, which will affect the braking performance. For example, the fake BPW axle brake pad can not reach 40% of the friction of the original pad, the brake is overheated, and the brake hub is scrapped in advance.
The riveting of brake pads requires special equipment. Manual riveting or bolt fixation is easy to loosen. Note that the use of brake king is prone to serious accidents such as brake pad fracture and looseness, which is also the main cause of brake hub fire, which is often easy to ignore.
If the brake hub is used for a long time, the edge will “moss”. It is normal. The main body of the brake hub has no cracks and the interior is smooth. It can be repaired within 3mm for normal use. The redundant convex groove is flattened with a grinder, and the thickened brake pad can be used continuously to save economic cost.
Note that vehicles equipped with “brake king” cannot be used. This is due to uneven braking force, resulting in uneven inner surface of hub, rubbing and cracking of brake pad and hub.
When the inner diameter of the brake hub becomes larger, replace the “camshaft increasing roller” to restore the braking force. It should be noted that after replacing the increasing wheel, the braking action curve will also change, which is prone to poor return. Especially after the brake pad clearance is too large, it is necessary to adjust the brake clearance in time. At this time, the passive return tension spring of the shoe is limited, The return spring of the slave cylinder needs to be strengthened.
Brake system inspection is particularly important before winter, involving crooked goods such as brake king, inferior brake pipe and dryer. You can’t be lazy at ordinary times, let alone all rely on repairmen. As the saying goes, “a good car needs seven maintenance and three repair”. You should be aware of your car’s problems. Today’s 6-axle semi-trailer and 12 braking units need to be checked carefully. This is not the era of cycling. The behemoth driving 18 wheels can not be despised. There is no profound theory, only the necessary knowledge. The serious and careful spirit of the older generation is still useful. Remember.