With the continuous progress of automotive industry technology, users have higher and higher requirements for vehicle performance. NVH performance is an important performance index of vehicle, and NVH performance is an important part of vehicle NVH performance. Strengthening the control of exhaust system noise is an effective way to solve the problem of vehicle noise. In this article, you will be introduced to the one-way silencing valve for automobile muffler, as shown in Figure 1. Because of the high cost, it is mainly used in some cars, and some economical cars have gradually begun to study and adopt this new technology. This paper introduces this new technology in detail.

Introduction of new automobile technology one-way silencing valve

Figure 1 check valve structure

1、 Advantages and disadvantages of check valve dual-mode muffler:

Advantages of single valve dual-mode muffler:

Generally, the silencer using one-way valve can reduce the noise by 5 ~ 10dB, and the power loss can be reduced by about 30%. See Figure 2.

When the noise and power loss are the same, the volume of the dual-mode muffler can be reduced by 5 ~ 10 liters.

Introduction of new automobile technology one-way silencing valve

Table 2 Comparison of noise and back pressure during valve opening and closing

The cost of single valve dual-mode automobile muffler can also be included in the disadvantages:

Cost increase: the built-in valve is about $5-10 and the external valve is about $10-20. The silencing valve is generally placed inside the muffler barrel or at the end of the exhaust tailpipe. The number of parts increases, the system reliability decreases and the maintenance is difficult.

Figure 3 air flow direction when the check valve is opened and closed.

2、 Classification of check valves for automobile silencers.

Introduction of new automobile technology one-way silencing valve

There are three common types of check valves (see Figure 4)

Adaptive valve driven by air flow.

It is applicable to the external pipeline for low-frequency noise modulation to improve the resonance mode in the pipeline. Thus, the structure of the muffler is simplified and the weight and volume of the muffler are reduced.

The active valve is electrically and actively controlled.

It is mainly used for resonance modulation of external pipe and rear tail pipe. During high-speed operation, it provides low back pressure and multi angle control through engine ECU, which has better adaptability to the engine.

 A built-in valve in the silencing package driven by air flow.

The automobile muffler factory produces this kind of muffler, which is mainly used for internal modulation of low-frequency boosting. The closing valve is used to achieve better silencing transmission loss, and reduce the back pressure when opening, which has good adaptability to idle working conditions.

Introduction of new automobile technology one-way silencing valve

Figure 4 structure comparison of three check valves

3、 Working principle of check valve.

Adding a silencing valve inside the muffler can effectively improve the noise performance of the vehicle at low speed, but there are two problems:

 Low speed and small flow NVH problems are prominent:

When the valve is in the silencing state, the valve does not open. At this time, the back pressure is large and the noise is low.

When the valve is in the pipeline, the opening of the valve decreases, reducing the diameter of the pipeline and reducing the noise of the tailpipe (see 5).

The pressure drop of high speed and large flow is prominent:

When the valve is in the muffler and the valve is opened, the back pressure decreases and the noise increases.

The valve opening is on the pipeline, which increases the valve opening, improves the pipe diameter, improves the back pressure, improves the order noise and reduces the air flow noise.

Introduction of new automobile technology one-way silencing valve

Figure 5 difference of tailpipe noise when one-way valve is opened

4、 Application example of check valve.

Install a check valve at the end of the tailpipe.

Applicable principles:

At low flow rate, the pressure increases slightly after closing, but the equivalent diameter of tailpipe is halved, and the noise is significantly reduced; When the flow is large, the check valve is fully opened, the back pressure is significantly reduced, the equivalent diameter of the tailpipe increases, the order noise increases, and the air flow noise decreases. Specific applications are listed in Figure 6.

Figure 6 example of one-way valve at the end of exhaust tailpipe

The check valve shall be applied to the intake pipe end of the rear silencer.

Applicable principles:

Shut down at low flow rate, the back pressure increases slightly, the air flow passes through the long channel, the sound loss increases and the noise decreases. Under large flow, the check valve is fully opened, the back pressure is significantly reduced, the air flow channel is reduced, the sound energy loss is reduced and the noise is increased. Specific applications are listed in Figure 7.

Figure 7 example of check valve inside silencer.

Due to the requirements for vehicle NVH performance and the improvement of requirements for environmental protection and fuel consumption, newly developed models will increasingly adopt new technologies, such as active noise reduction technology of exhaust system, electric supercharging technology of intake system, etc.