Semi-active Muffler System Based On HQ Tube

Taking the low frequency noise as the research object, this paper briefly introduces thebasic principles of HQ tube, and then a new type of semi-active muffler is designed using theresonance conditions. The controller reads the sensor signals based on different characteristicsof the noise source, control signals are sent to the valves and the stepping motor to adjust thelength difference of the pipeline to get a good noise reduction. The muffler could realize theautomatic control of the noise under steady and the instable condition through the sensor,controller, the valves and stepper motor. Then the test bench is built. And the control system isstudied here, including the analysis of the control model, the realization of control strategy ofthe valves and the stepping motor. The control procedure of the muffler is implemented byDSP, and then the simulation of the control system was taken. The correctness of the programand each module validated the feasible of the control strategy, which proved that this controlsystem could be applied to actual control of the test bench.In the conditions without flow, the acoustic characteristics testing have been done usingthe control systems. The valves and the stepping motor have a rapid response, for a givenfrequency noise source, the valves and the stepping motor could achieve the appropriate statuscorresponding to frequency in control. The control results are the same as the required systemstate. It proved the accuracy of programs which could control the valves and the steppingmotor, and the feasibility of the control system. So the precise control of semi-active muffleris achieved. Then the measurement of the TL and IL were taken. From the analysis of the TLmeasurement results, this semi-active noise control device has a good noise control effect oflow frequency noise and the harmonic frequency noise corresponding to the low frequency,the maximum noise reduction closes to35dB. For the IL, the sound pressure level of the noisehas been reduced after passing through the muffler. This semi-active noise control device hasa good noise control effect of low frequency noise, it has an average of11dB noise reductionin the entire range of35-100Hz in this measurement conditions.