Brake Assebly for bulldozer spare parts

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Description

Increasing the driving speed of bulldozers is one of the main technical measures to improve production efficiency, but there must be a braking system with good performance to ensure driving safety. The braking performance directly affects the safety of driving. Many bulldozer accidents are caused by poor braking performance. Therefore, the braking performance of the bulldozer must be checked frequently. If the braking performance is found to be degraded, the braking must be timely The system is adjusted or repaired to improve braking performance. But how to test the braking performance of bulldozers simply and quickly has always been a relatively difficult task. At present, the commonly used inspection methods include visual inspection, test drive and special instrument inspection. The first two methods are simple to operate, but have large errors. They can only roughly estimate the braking performance of the bulldozer, cannot obtain specific data, and lack a unified evaluation standard; the latter is expensive and complicated to operate, and it is not suitable for mobile measurement. In fact, the braking performance of the bulldozer mainly depends on the braking torque, so the braking torque can be used as a standard to measure the performance of the braking system. This paper proposes a method for measuring braking torque and corresponding measuring instrument controlled by a single-chip microcomputer. This instrument can accurately measure the dynamic torque of the bulldozing mechanism, and is small in size and can be moved for measurement. It can be used for the supervision and maintenance department of the agricultural machinery supervision department. Provide scientific basis for the maintenance of the equipment.

1. Measuring principle

The measuring device consists of a jack, a base, a steel wire rope, a tension sensor and a measuring instrument. The jack is fixed on the base and is used to lift the wheels. The function of the wire rope is to apply a moment to the wheel on the outer edge of the wheel. One end of the wire rope is tied to the wheel through a hole in the hub, and the other end is connected to the tension sensor along the wheel, and the tension sensor is connected to the base. The tensile force sensor converts the strain signal of the tensile force into an electrical signal, which is transmitted to the measuring instrument through the shielded wire, and the measuring instrument performs signal amplification, analog-to-digital conversion and data display.

When measuring, first push the jack up to make the wheel slightly off the ground. At this time, the wheel should be able to rotate freely. If it does not rotate, it indicates that the gap between the brake shoe and the brake drum is too small and needs to be adjusted or repaired. Turn the wheel to make the wire rope taut, then step on the brake and continue to lift the jack, the wire rope is gradually tightened. When the torque generated by the rope pulling force exceeds the braking torque of the brake, the wheels start to slip. At this time, the maximum braking torque M of the brake is equal to the torque produced by the rope pulling force, namely:

M=F.r

F-the pulling force of the wire rope

r-bulldozer wheel radius

The pulling force of the steel wire rope is converted into an electric signal by the pulling force sensor, which is processed, recorded and displayed by the measuring instrument as required. For a certain type of bulldozer, the radius of the wheel is usually constant, so the rope pulling force can also be used to directly measure the braking performance of this type of bulldozer.

2. The hardware design of the measuring instrument

The hardware of the measuring instrument is composed of signal amplification module, A/D analog-to-digital conversion module and CPU processing module. The measuring instrument realizes the amplification processing of the weak signal and converts it into a digital quantity, calculates the braking torque and displays the measurement result.

1. Signal amplification module

The output signal of the tension sensor (SENSOR) is a pair of common-mode voltage signals. The voltage difference (ΔV) is very small, usually only a few millivolts, so it must be amplified. The amplifying module is composed of high-precision amplifier ICL7650, which adopts differential input amplifying mode. ICL7650 is a CMOS-type chopper-stabilized zero-stabilized integrated operational amplifier. It adopts a dynamic zeroing method to eliminate the offset and temperature drift of the operational amplifier. It has high precision and is very close to an ideal operational amplifier in performance. For the circuit parameters, the common mode signal sent by the tension sensor can be differentially amplified by 100 times.

2. A/D analog-to-digital conversion module

The core of the analog-to-digital conversion module is the ICL7109 A/D converter. ICL7109 is a double integral A/D converter. The data output is a 12-bit binary number with high resolution and strong anti-interference ability. At the same time, it has good compatibility with the microprocessor interface, and its data line and control line can be directly connected with the microprocessor bus.

3. CPU processing module

The CPU processing module is composed of a microprocessor, a row and column keyboard (KEY) and a liquid crystal display (LCD). The 89C51 single-chip microcomputer is used as the microprocessor of the measuring instrument. This single-chip microcomputer chip has a 4K electrically erasable program memory, which has high integration and strong processing capacity. The 89C51 reads the sampled data of the A/D converter and processes the data at a rate of 30 times per second. The working mode, control commands and some operating parameters of the measuring instrument are input by the row and column keyboard, and the operating results are output from the liquid crystal display.

Three, software design

In order to achieve the purpose of reliably measuring braking force, it is necessary to design corresponding measurement software. The measurement software includes the following functions.

1. Self-check function

Plug in the power, the software is started, first run the self-check program. The self-check program scans the various hardware of the measuring instrument to check whether the hardware works normally and whether the sensor signal can be input, etc. If the measuring instrument is working normally, it will display "P——" on the display and wait for the command to be received, otherwise it will give an alarm and output an error code.

2. Zero adjustment function

When the tension sensor is not under force, its output differential signal (ΔV) is not necessarily zero, but a constant, so the measuring instrument must have a zero adjustment function, and the result of the measurement should be subtracted from this initial constant. The zero adjustment function is used as follows: remove the tension applied to both ends of the tension sensor, press the "track" key to enter the measurement state, and the result displayed at this time is the initial constant. Press the "Zero" key on the keyboard, and the zero program will automatically subtract the initial constant from the measurement result, and the measuring instrument will display ‘0’.

3. Correction function

After the measuring instrument is used for a period of time, the output signal of the tension sensor and the signal processing of the amplifier will have a slight linear change, that is, linear error. In order to ensure the measurement accuracy of the braking force, it is necessary to calibrate the measuring instrument regularly, so a calibration function is designed in the software. The calibration function is used as follows: Press the "tracking" key to enter the measurement state. Hang a certain weight object (50-100kg is appropriate) on the tension sensor. The weight of the object has been weighed in advance. At this time, the measured result should be equal to the weight of the object. If it is not equal, it indicates that there is a linear error and needs to be corrected. Press the "calibration" key on the keyboard, and then input the actual weight of the object, and then press the "confirm" key to realize the calibration of the measuring instrument, and the calibration parameters are automatically saved in the single-chip microcomputer.