The asphalt spreading truck must check its driving speed when carrying out asphalt penetration work, and feed back the speed signal to the controller to determine the amount of asphalt spreading. When the current speed is high, the controller controls the asphalt pump output to increase, and when the speed slows down, the controller controls the asphalt pump output to decrease to make the asphalt permeable layer uniform and in line with the construction requirements of the asphalt permeable layer project.

1.Existing problems
At present, most asphalt spreading trucks use the following two methods to check the driving speed of the vehicle:
One is to use a manufactured speed radar, and the other is to use a limit switch.
Speed ??radar has the advantages of small size, solid structure, convenient installation, and accurate detection, but it is relatively expensive.
In order to reduce the manufacturing cost of asphalt spreading trucks, some companies use limit switches to check the speed of asphalt spreading trucks.
The limit switch speed limiting device is installed on the gearbox output shaft of the asphalt spreader truck. It mainly consists of a speed limiter wheel, a limit switch, a mounting support frame, etc. When the asphalt spreader truck is driving, the limit switch checks the magnetic induction of the speed limiter wheel. Outputs differential signals and outputs speed data signals.
Driving will cause vibration, and the vibration of the car will cause the limit switch and the speed limiter wheel to collide with each other, causing the speed test to be inaccurate. As a result, the sprayed bitumen is not uniform and the amount of bitumen spread is inaccurate. Sometimes the car vibrates too much, causing the limit switch to be damaged.
2. Improvement methods
Regarding the shortcomings of using limit switches to check the speed, we decided to use the speed sensor of the chassis of this car to check the speed. The speed sensor of this car is a component, which has the advantages of accurate detection, small size, easy installation, and strong anti-interference.
The magnetically induced speed limiting wheel is located in the rotating shaft protective sleeve and is not easy to be damaged. The selected components not only solve the common fault hazard of collision between the sensor and the flange piece, but also reduce the limit switch, flange piece and installation support frame, thereby reducing manufacturing costs and improving the installation efficiency of the electronic control system.