Exhaust Silencer for Internal Combustion Engines

The present invention relates to an exhaust silencer for internal conbustion engines, especially for those used on motor vehicles and tractors.

At present, exhaust silencers used on motor vehicles and tractors work generally on the principle of consuming the energy of exhaust flows and equalizing fluctuations of the exhaust pressure. Therefor, silencers are commonly designed into such structures that make exhaust flows pass through a series of channels having reducing and expanding sections repeatedly, with frequent flow direction changs, or divide the exhaust flow into smaller streams flowing along rough surfaces. Such strutures did reduce noises to some extent. However, the backpressure of the exhaust tends to increase due to the blocked exhaust flow. The faster the engine runs, the greater the exhaust flow resistance will be, consequently the more loss of power output, and more fuel consumption. When an engine runs at its maximum speed, the loss of its power output due to the above causes can be as high as 5-10%. There is wide interest in providing a silencer have good performance with little influence on engine output is widely concerned.

The U.S. Pat. No. 4,203,503 and U.S. Pat. No. 4,209,076 disclosed a type of exhaust silencer, in which exhaust flows first enter a resonant cavity which absorbs sound energy, then enter an expansion cavity to expend the sound energy further, finally go out into the atmosphere. But in a silencer of such a type, exhaust flows are still blocked, exhaust flow resistance remains relatively large, thus the noise depressing effect and the saving of engine power output can not reach the desired level.

The object of the present invention is to provide for motor vehicles and tractors an exhaust silencer of a low backpressure type that reduces noises across a wide band and keeps fuel consumption relatively low.

According to the present invention, an exhaust silencer for motor vehicles and tractors has a cylindrical shell which is sealed at its both ends by a front lid and a rear lid, and the inside of which is divided by spacers into several separate chambers of different volumes, on each of the said lids an opening is formed for fixing a trumpet-like diverging pipe and tail pipe respectively, the geometric central axises of the said openings being identical with the axis of the cylindrical shell. The said trumpet pipe is either connected to a front pipe or integrally made therewith. Inside the cylindrical shell there are a group of core tubes, the walls of which are punched with flanged holes forming converging passages for communicating the inner channels of the tubes with the chambers. Each of the core tubes extends from a front chamber to a rear chamber through the spacers via a series of corresponding holes, which are equally arranged along circles having aligned centers and a common diameter on every spacer. In the front and rear chambers the core tubes deflect gradually inwardly toward section centers of the bigger end of the trumpet pipe and the front end of the tail pipe at inclining angles of 3.degree.-5.degree. and 5.degree.-10.degree. respectively. The ends of the deflected portions of each core tubes are adapted to have sectorial cross sections and are assembled together, so as to be inserted directly into the bigger end of the trumpet to form an integral counection therewith in the front chamber, and to be connected with the front end of the tail pipe and the rear lid plane in the rear chamber. The front pipe, the bunch of the core tubes, and tail pipe having successive inner flow channels of substantially equal cross section areas. The outlet edge of the tail pipe has substantially a sinewave profile, inside the tail pipe there are disposed some flow-dividing plates.

The exhaust gases discharged from the engine exhaust pipe pass through the front pipe of the silencer, then flow into the core tubes via the corresponding end openings of sectorial cross sections thereof by dividing the main flow into several smaller streams. By the principle of resistance silencing, when exhaust flows reach the flanged holes on each core tubes, sound waves are reflected backwardly to sound sources, thus suppressing the noise. Dividing the main flow into thinner substreams enables the ratio of expansion to rise greatly, and via the openings of the flanged holes on the core tubes small streams of exhausts flow into and from the said chambers in which the core tubes extend, causing the pressure of the exhaust flows to change greatly, too. The above said two desirable facts contribute not only to increase considerably the degree of noise reduction but to decrease the smoke density of the exhausts as well. The latter benifit is obtained because the soots in the exhaust flows deposit down to the chambers on their way through the punched portions of the core tubes as a result of expansion and centrifugalization of the flows at the openings of the flanged holes. In order to depress noises of middle and low frequencies, resonant chambers with different volumes are provided, while a certain volume of sound-absorbing material is provided in the last chamber to fill the space around the punched portions of the core tubes extending therethrough, so as to depress the high-frequency component of noises effectively. The punches on the walls of the core tubes have flanges which form passages converging outwardly to the chambers and which help to keep the flow resistance of the inner walls of the core tubes relatively low. The flow-dividing plates disposed in the tail pipe are used mainly to prevent resonance that might otherwise happen when exhaust flows are accumulating. The outlet of the tail pipe has an edge of substantially sinewave profile, which helps to discharge the exhausts into the atmosphere evenly.

The present invention is advantageous in that:

1. The fact that the front pipe, the bunch of the core tubes, and the tail pipe have successive inner flow channels of substantially equal cross section areas assures the discharge of exhausts to take place at a substantially constant flow rate, enabling reduction of losses induced by the high exhaust back-pressure, and hence the reduction in the loss of engine output and in oil consumption.

2. The exhaust flows divide into substreams by flowing through a bundle of core tubes instead of flowing through a single tube, thus reducing the noise level effectively.

3. Since the exhausts flow freely and continually through the inner chambers, and the soots in the exhausts diffuse into the inner chambers of the silencer on their way through the punched portions of the core tubes, the effect of off-engine cleaning of exhausts can be obtained, with the smoke density of exhausts considerably decreased.

4. The punches on the walls of the core tubes are so shaped that their flanges form passages converging radially outwardly, thus the inner walls of the core tubes are generally smooth, which have relatively low resistance and enable substantially free flows of exhausts.

5. The ability of allowing exhausts to flow continually at substantially constant volume rates extends the service lives of silencers and enables engines to run in good working cycles.

Some performance data of the silencers according to the present invention are listed in the Table I, in which is shown a comparision of noise levels and fuel consumptions between the silencers made according to the present invention and silencers of conventional types, testing on Jie. Fang CA-10B trucks, load capacity 4 ton.

Now, a prefered embodiment of the present invention will be described in detail by refering to the following drawings:

FIG. 1 is a longitudinal section view taken from a silencer of the type according to the present invention, having 4 chambers and 8 core tubes;

FIG. 2 is an end view taken along the arrow A in the FIG. 1, showing the assembly of the sectorial sectional ends of the core tubes at the connected portion of trumpet pipe and front pipe;

FIG. 3 is a plan view of a spacer, showing the arrangement of openings for core tubes;

FIG. 4 is a cross section of a core tube, taken from the section C--C in FIG. 1, showing the flanged holes on the tube wall;

FIG. 5 is a development of the tail pipe, showing the arrangement of flow-dividing plates therein, and a sinewave profile at the outlet edge thereof;

FIG. 6 is a perspective view of an end portion of core tube, showing the sectorial section thereof.

Refer now to FIG. 1, in which a silencer embodying the present invention is shown, the said silencer has 4 chambers and 8 core tubes therefor:

The rear end of the front pipe 1 of a diameter D.sub.1 is welded to the smaller end of the trumpet pipe 3. The ends of eight core tubes 5 of a diameter d are assembled together and inserted directly into the bigger end of the trumpet pipe 3 and welded therewith, with the channel in the trumpet pipe 3 being divided into eight sub-channels of sectorial sections by the correspondingly shaped ends of the eight core tubes 5, accordingly. From the welded point the eight core tubes 5 depart from each other and extend radially forwardly to the front spacer 4, each at an inclining angle of 3.degree.-5.degree. with respect to the longitudinal axis of the cylindrical shell, then the eight tubes 5 deflect to the direction parallel to the longitudinal axis of the cylindrical shell and extend further through the openings correspondingly formed on each of the front spacer 4, middle spacer 6, and rear spacer 8. From the rear spacer 8 the eight core tubes deflect and extend toward the longitudinal axis of the shell at an inclining angle of 5.degree.-10.degree., and finally meet with one another at the entrance of the tail pipe 11, with their end of sectorial sections being assembled together and welded to the corresponding edges of the flow-dividing plates 12 disposed in the tail pipe 11. The flow-dividing plates 12 consist of eight flat plates, the dimensions of each plates are so determined that when they extend longitudinally in the tail pipe 11 with their front end edges welded to the ends of the core tubes 5, their rear end edges lie in a predetermined spiral surface, and their longitudinal edges keep apart from the inner wall of the tail pipe 11 by a small gap. The tail pipe 11 has a diameter D.sub.2, the outlet edge of the development of the pipe 11 has substantially a sinewave profile.

The walls of each the core tubes 5 are punched with holes, the ratio of the punched area to the wall surface area of each tube is 30%-50%. Said holes have flanges forming passages converging radially outwardly to the chambers inside the cylindrical shell, and in the said chambers groups of the said holes on each core tube 5 are axially staggered to those on the adjacent core tubes, all of the said core tubes 5 extend through the openings uniformly arranged along circles having aligned centers and a common diameter on each spacer (4,6,8).

The front pipe 1, the bunch of the eight core tubes 5, and the tail pipe 11 are so dimensioned that the cross section areas of their inner channels have substantially the following relation: ##EQU1##

According to the best mode of the present invention, it is advantageous to have

D.sub.1 =D.sub.2 =60 mm.

and

d=22 mm.

The assembly described above is disposed in the cylindrical shell 7, the front end and rear end thereof are closed by the front lid 2 and the rear lid 10, respectively. The rear chamber, i.e. the one between the rear spacer 8 and the rear lid 10 is filled with sound-absorbing materials 9, such as glass wool.

The noise level of a truck having a load capacity of 4-5 tons is decreased to 80-83 dB (A) when the truck is equipped with the silencer of the type according to the present invenion. In addition, because the silencer of the present invention assures a relatively low exhaust back pressure, the loss of power output is reduced, hence there is lower oil consumption (see Table 1). Further, the smoke density and pollutant emissions are also reduced.