Patent GB-770842-A (GB)
Title: Improvements in or relating to exhaust silencing apparatus for internal combustion engines
IPC: F01N1/08
Filed: 1955-06-16
Abstract: 770,842. Exhaust-silencers. LEISTRITZ, H. K. June 16, 1955 [June 19, 1954; Sept. 20, 1954; Oct. 8, 1954], No. 17470/55. Class 7 (2). A silencing chamber having an inlet at one end and closed by a baffle C at the other end is bounded by a casing B diverging from the inlet, and a second silencing chamber S has an end thereof applied against the baffle. A pipe D' which passes through an aperture D in the baffle and extends into both chambers is of smaller cross-sectional area than the inlet of the chamber and has a divergent mouth E terminating between two plates F<SP>1</SP>, F<SP>2</SP> forming an open-sided, wedge-shaped deflector F, the apex N of the deflector being directed towards but spaced from the inlet, and the base of the deflector being spaced from the baffle. As shown in Fig. 1, the casing B is conical in form, or alternatively is cylindrical and increases stepwise in diameter towards the baffle C and the mouth E of the pipe D is rigidly connected to the deflector F at a distance from the edges Q, R of the plates F<SP>1</SP>, F<SP>2</SP>, the crosssectional area F<SP>5</SP> between those edges being smaller than the total cross-sectional area F<SP>3</SP> between the edges and the casing B; the area of the baffle C is greater than four times the cross-sectional area of the inlet E<SP>1</SP> of the mouth E. The gas stream is split by the edge N into two components, one component travelling along the plate F<SP>2</SP> in a direction substantially parallel to the original direction of flow indicated by the arrow M, and the other component being deflected by the plate F<SP>1</SP> which extends at an angle of less than 45 degrees to the direction of flow M; a small component of the gas passes through perforations O in the plate F<SP>1</SP> and directly into the mouth E. The gas streams flowing over the plates are deflected by the baffle C in a direction opposite to that of the gas flowing into the chamber and enter the side openings of the deflector F introduction of the gas into the mouth E being assisted by the pressure drop existing between the two silencing chambers. In a modification, the casing B, Fig. 2, comprises a cylindrical part B<SP>3</SP>.and a divergent section B<SP>1</SP>, and the upper plate F<SP>2</SP> of the deflector F extends parallel to the axis of the chamber. A pipe T forming a continuation of the exhaust pipe but having a crosssectional area smaller than that of the latter, is provided with groups of perforations U<SP>1</SP>, U<SP>2</SP>, the gas flowing from the perforations U<SP>1</SP> entering the space V between the pipe and the casing and the remaining gas leaving the pipe through the perforations U<SP>2</SP> below the plate F<SP>1</SP>.The silencer unit S comprises acoustic chambers K<SP>1</SP>, K<SP>2</SP>, K<SP>3</SP>, the pipe D<SP>1</SP> opening into the chamber K<SP>1</SP> and the latter being connected to the chamber K<SP>2</SP> by a pipe D<SP>2</SP> of less cross-sectional area than that of the chamber K<SP>1</SP>. The chamber K<SP>3</SP> communicates with the chamber K<SP>2</SP> via a pipe D<SP>3</SP> of smaller cross-sectional area than the chamber K2, and with the atmosphere via a pipe D<SP>4</SP>. There may be one, two or more than three chambers K according to the sound frequencies to be attenuated. In a further modification, Fig. 3 (not shown), the casing consists of a divergent portion followed by a cylindrical section of the same diameter as that of the silencing chamber S, and extending from the edge N of the deflector F to the wall of the casing is a perforated step-like baffle plate substantially equal in width to that of the deflector; the pipe D' opens into the chamber S and a pipe D<SP>5</SP> of smaller cross-sectional area leads to the atmosphere or to another silencing unit. In a still further modification, the inclined plate, Fig. 4 (not shown), of the deflector F extends to the wall of the casing B and the gas flows past the sides of that plate ; the plate, Fig. 5 (not shown), may be perforated.