Application of the hottest air pressure anti lock

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The application of pneumatic anti lock braking system in commercial vehicles

recently, Wall Street reported that the U.S. government made a proposal to equip all vehicles with anti lock system ABS after reviewing a series of traffic accidents caused by Firestone tires two years ago. At the same time, the Research Report of the insurance industry also released the data that installing ABS on all cars can reduce fatal traffic accidents by 9%. It can be seen that ABS is of great significance in improving driving safety

pneumatic ABS has a wide development space in the field of commercial vehicles because of its good compatibility with the original pneumatic braking system of commercial vehicles and certain cost advantages (compared with hydraulic ABS). The pneumatic anti lock braking system developed and produced by companies such as WABCO and Knorr-Bremse has achieved a milestone leap in pneumatic braking technology. In recent years, with the rapid development of China's freight and passenger transport business and the introduction of a large number of foreign advanced commercial vehicle technologies, the application of pneumatic ABS in domestic commercial vehicles has gradually increased, and shows a trend of rapid popularization like car hydraulic ABS. According to the data of Beijing International Automobile Exhibition in 2002, many domestic commercial vehicles (including Dongfeng Tianlong large truck) participating in the exhibition have been equipped with pneumatic ABS system, and some of them are even equipped with the internationally advanced vebco fourth generation commercial vehicle pneumatic ABS (i.e. type D). This paper will briefly introduce the application of the pneumatic anti lock braking system in the commercial vehicle engineering, in which the processor can quickly change the position of the extrudate of the two extruders in the coextrusion structure

composition of pneumatic ABS

the braking force control principle of pneumatic anti lock braking system (referred to as pneumatic ABS) is similar to that of hydraulic anti lock braking system, that is, through the impact modified wheel speed sensor widely used in PVC products to detect the rotational speed of the wheel. When the wheel has a sliding/locking trend or phenomenon, the ABS electronic control unit ECU adjusts the braking force of the corresponding wheel in real time according to the signal transmitted by the wheel speed sensor, To avoid wheel sliding/locking, so as to improve the steering maneuverability and driving stability of the vehicle under emergency braking conditions, ensure that the driver can carry out effective emergency avoidance maneuvers and reduce the emergency braking distance under most road conditions

the pneumatic ABS system is mainly composed of electronic control unit ECU, regulating valve, wheel speed sensor, ABS fault indicator and diagnostic system

electronic control unit ECU

electronic control unit ECU is the core component of pneumatic ABS control system, and it is also the main component to measure the performance and functional level of ABS system. According to different installation types, ECU is mainly divided into cab mounted and frame mounted. ECU is connected with wheel speed sensor, regulating valve, power supply, indicator light and fault diagnosis connector. During braking, ECU adjusts the braking force of the corresponding wheel in real time by controlling the action of the regulating valve according to the wheel speed pulse signal fed back by the wheel speed sensor (whether there is a sliding/locking trend), so as to eliminate the locking tendency of the corresponding wheel in time

when the pneumatic ABS system fails, the ECU will transmit the fault information to the ABS fault indicator in real time and convert it into the corresponding fault code. ECU also has the function of on-board fault automatic diagnosis

for commercial vehicles equipped with retarder, when the pneumatic ABS system enters the working state, the retarder control system stops the action of the retarder after receiving the signal sent by ECU; When ABS stops working, ECU triggers the retarder to enter the normal working state again

regulating valve

during the operation of the pneumatic braking system, the ABS regulating valve plays a role in regulating the gas pressure in the brake chamber. When the control command of ABS ECU is not received, the regulating valve allows the compressed gas to pass freely, and the gas pressure does not decay at this time. The action of ECU control regulating valve is mainly divided into changing the gas pressure to the brake chamber or maintaining the existing pressure of the air pressure pipeline

a typical ABS regulating valve assembly consists of two regulating valves and a relay valve. If ABS has traction control function, a traction control valve will be integrated into the ABS regulating valve assembly. When the regulating valve adopts an independent structure, the regulating valve should be arranged behind the relay valve in the air pressure pipeline and as close to its corresponding brake chamber as possible to ensure the best control effect

the independent regulating valve usually has three air ports, namely, air inlet, air outlet and exhaust port

- the supply port receives compressed gas from the quick release valve or relay valve

- the delivery port inputs the compressed gas into the brake chamber

- the exhaust port releases the compressed gas from the brake chamber

the basic principle of ECU controlling the regulating valve is as follows: when the wheel tends to lock, ECU sends a control command to trigger the solenoid coil, drive the air inlet to close and the exhaust port to open; When the gas discharged from the exhaust port is enough to eliminate the locking tendency of the wheels, the ECU triggers the exhaust port to close and decides whether to keep the air inlet closed to maintain the existing pressure according to the current braking condition, or open the air inlet to increase the air pressure in the brake chamber and cycle the above actions

wheel speed sensor

wheel speed sensor is composed of two main components: trigger gear ring (exciter) and signal pickup (pickup), as well as related wires and mounting brackets

trigger ring gear is simply a ring with a toothed notch. The most common trigger gear ring uses 100 equal teeth, but the specific number of teeth is ultimately determined by the system design

signal pickups are commonly referred to as sensors. The signal pickup is a package, which can be mainly divided into rod pickup and right angle pickup according to its appearance. When the ring gear is triggered to rotate in front of it, the pickup generates the corresponding electronic pulse, and the ECU recognizes the speed and acceleration/deceleration rate of the corresponding wheel according to the pulse signal. The slight increase of the distance between the pickup and the ring gear will lead to the sudden decline of the pulse signal strength. Therefore, the wheel speed sensor is a whole composed of the pickup and the ring gear with a fixed distance between them, and its spacing distance must be maintained within the mandatory parameters specified by the automobile manufacturer

wheel speed sensors have various installation types. In the most common commercial vehicle pneumatic ABS, the pickup is installed on the flange of the wheel shaft end, and the ring gear is installed on the wheel assembly (or integrated with the wheel assembly)

the system structure of pneumatic ABS depends on the number of wheel speed sensors and regulating valves used. The most common pneumatic ABS of commercial vehicles can be divided into:

- 4 sensors/4 regulating valves (4s/4m)

- 6 sensors/4 regulating valves (6s/4m)

- 6 sensors/6 regulating valves (6s/6m)

the most common pneumatic ABS of trailers are 2s/1m, 2s/2m, 4s/2m and 4s/36. The accuracy of microcomputer software analysis data is m

abs fault indicator

commercial vehicles equipped with pneumatic ABS must also be equipped with yellow indicators that can display most ABS faults. The internal (CAB) ABS indicator light must be installed within the range that the driver can see directly, usually on the instrument panel

abs automatic on-board fault diagnosis

although the ABS automatic on-board fault diagnosis device is not a mandatory item in laws and regulations, almost all pneumatic ABS of commercial vehicles have automatic diagnosis function. Usually, the automatic diagnosis system indicates the fault of the ABS system through the ABS fault indicator installed in the cab or the LED installed on the ECU. Maintenance personnel can diagnose ABS system faults through the following methods:

- flashing signal of ABS indicator light or LED light

- read the fault codes stored in the system by the special diagnostic tool through the interface under the instrument panel

traction control system

the function of traction control system TCS (traction control system) is to prevent the wheel from slipping/spinning when starting or accelerating on a smooth road. At present, various manufacturers have different names for this system, mainly including: automatic traction. Its composition structure includes: grating ruler, measuring range, stepping electromechanical gravity Control ATC, automatic anti-skid adjustment ASR and TCS, etc. TCS attempts to restore the traction function of the corresponding wheels by braking the pulley or reducing the engine output torque. Unlike ABS, TCS can automatically apply braking force to the corresponding wheels without the driver pressing the brake pedal

tcs is not a mandatory item of commercial vehicle regulations, but TCS helps pneumatic ABS improve the traction of the vehicle on the premise of avoiding driving wheel slip. TCS is a common option of ABS, and its electronic control part is integrated with the pneumatic ABS electronic control unit ECU. When the wheel speed sensor detects that the speed of a wheel is higher than the speed of the other wheel on the same axle, the ECU quickly and automatically applies braking force to the corresponding wheel, that is, the ECU directly triggers the regulating valve to open, and the compressed air enters the brake chamber to brake until the corresponding wheel recovers its balance, which actually plays the function of drive axle differential lock. However, when the wheels at both ends of an axle slip at the same time, the abs/tcs electronic control unit ECU will immediately send the command to reduce the engine output torque to the engine control unit ECU through the controller area can, and the engine ECU will eliminate the slip by controlling the opening of the throttle (reducing the engine output torque)

advantages of pneumatic ABS

compared with conventional pneumatic braking, pneumatic ABS benefits from the fast response electronic control system and the ABS regulating valve close to the wheel, so it has more agile and accurate braking force control. The main advantages of commercial vehicles equipped with pneumatic ABS include:

- improving the control ability of vehicles under bad road conditions

- shorten vehicle emergency? Braking distance of vehicle

- reduce freight costs while reducing traffic accidents

- stabilize the risk cost

- low installation and maintenance cost (compared with hydraulic ABS) and little environmental pollution

how to drive pneumatic ABS commercial vehicles

pneumatic ABS is different from hydraulic ABS, so some operating skills for hydraulic ABS are not applicable to pneumatic ABS. When braking commercial vehicles equipped with air pressure ABS, in addition to maintaining the stability and rationality of the braking force when stepping on the brake pedal, additional attention should be paid to the following matters:

- the specific braking operation is the same as that of the air pressure braking system without ABS

- in case of emergency braking, what is the use point? method. For fast-moving pneumatic ABS commercial vehicles, continuous death? It is still possible to cause the vehicle to have out of control braking accidents such as braking deviation or tail flicking

- when pneumatic ABS starts the anti lock function, the driver will not feel the pulse rebound (feedback) force of the brake pedal like hydraulic ABS or special circulating braking noise

- in the braking process, the braking force of the applied pedal shall be adjusted in time according to the state of the vehicle and the pedal feedback force, so as to ensure that the vehicle is in a controlled braking state

common faults of pneumatic ABS system

the statistical data of WABCO company shows that the ten common faults that lead to the display of pneumatic ABS fault indicator are as follows:

- the wire near the fixing clip of the frame is scratched or broken

- the sharp object of the frame or the wire near the frame mounted regulating valve is broken or? Erosion

- the protective cover of the connecting wire of the sensor or regulating valve is damaged

- connector corrosion and poor sealing or damage of connecting parts

- the connector pin is damaged or the seal of the connector itself cannot meet the sealing requirements of the service environment

- poor contact of terminal component connector

- excessive air gap of wheel speed sensor

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