The reliability of locomotive braking system is the basis of ensuring traffic safety, which plays an important role in increasing train carrying capacity and improving train running speed. The application of linear displacement sensor in locomotive box brake unit is of great significance for on-line monitoring of brake device status and wheel set wear.

The locomotive box brake unit is mainly composed of brake transmission device, brake cylinder and brake shoe clearance adjustment device. When the locomotive is braked, it is realized by charging and exhausting the brake cylinder. When inflation, the piston rod moves, and the brake shoe pressure produces mechanical friction on the wheel tread to form a braking force. When exhausting, the piston rod will reset automatically under the action of the return spring. Locomotive brake device mainly has the following problems: brake shoe is made of cast iron, long-term braking will produce serious wear, there is the hidden danger of brake failure; the long-term use of return spring has the defect of mechanical fatigue, wheel tread and brake shoe are bonded, which can cause the wheel to heat up rapidly, and finally cause braking delay; long-term braking will cause wheel set ellipticity and lateral stability Reduce the risk of locomotive derailment.

The linear displacement sensor is used for locomotive braking device. One sensor rod is connected with the brake shoe bracket of the brake device, which can produce relative displacement with the brake shoe movement, and the other sensor probe is close to the wheel set tread. The current signal with good anti-interference performance is often selected as the output signal of the sensor, which is transmitted to the control unit for processing through a / D conversion. The upper computer software can set the initial parameters such as the thickness of brake shoe, the thickness of wheel tread, the ellipticity of wheel set and the normal reset displacement of brake. When the locomotive is running, the data such as displacement variation and train speed collected by sensors are transmitted to the central processing unit. After calculation by the central processing unit and compared with the set value, if the measured value exceeds the set value range, it will drive the sound and light alarm device to achieve the purpose of real-time monitoring.

When the locomotive is braked and reset, two linear displacement sensors are driven by the connecting shaft of brake shoe support rod and brake shoe bracket to produce corresponding displacement. After system processing, it can quickly judge whether the brake is normal reset, whether there is wheel sticking phenomenon, and whether the displacement deviation is too large after automatic reset. According to the displacement change of linear displacement sensor, wheel hub diameter and train running speed, the wheel tread wear can be calculated. If the warning value is exceeded, the problems such as brake reset fault, brake shoe wear, braking condition, wheel hub wear and other problems can be timely fed back and handled to ensure driving safety.