The Gray-Hawley muffler (Fig. 249) is used on a number of commercial cars and consists of two cast heads which support three cylindrical sheet metal tubes. The gases enter the inner one of the three members from the exhaust pipe. They expand in this chamber and then pass through fine perforations at the opposite end in the partition wall into the intermediate chamber, and thence through similar perforations at the rear end of the innermost portion wall into the outer chamber from which they escape at the further end. The path of the gases is shown by the arrow-heads in this illustration.
The United States trucks are equipped with the muffler shown in Fig. 250 which is similar to the one previously mentioned. The gases take the same path and are expanded in a similar manner. However, they are discharged through perforations at the center of the outer chamber, as this muffler is mounted crosswise at the rear end of the subframe. Into the head, which connects with the exhaust pipe, a cut-out is placed. This cut-out consists of a poppet valve, held to its seat by a spring and bell crank pivoting in a bracket operated through suitable linkage from the operator's seat. When this cut-out is opened by raising the valve from its seat, the greater part of the gases take the path of the least resistance, which is through the valve opening in>tead of passing through the various expansion chambers.
Fig. 249. The Gray-Hawley Muffler.
Fig. 230. The U. S. Muffler with Cutout.
The Riker muffler (Fig.251) is somewhat similar to those depicted above. except that the inner chamber is perforated at both ends and the outlet is of a different shape. Both end plates or heads are provided with Hat surfaces to which the supporting brackets are bolted. The front head has an opening against which a flat valve is held through the pressure exerted by a coiled spring attached to the end of a bell crank and the head. The bell crank supports. the valve, which is raised from its seat when the cut-out pedal is depressed. Both exhaust and outlet pipes are attached to the muffler heads by flanges and belts.
The Powell muffler is also used by some makers of commercial vehicles. This consists of a number of pressed steel cups, the open ends of which are flanged out so as to fit over the closed end of the adjacent section or cup. Each of the cups 1 are perforated and through these perfor-ations the adjacent chaining communicate. Cups B and C are used at the rear end and are so arranged as to form a somewhat tortuous passage for the gases. This is accomplished by a series of small perforations in cup B while cup C has a large central hole. Three tie rods hold the various sections together, which permits using any number of cups to meet the requirements of each individual engine to which the muffler may be fitted. Fig. 252 shows this muffler as applied to the Mogul trucks, and Fig. 253 illustrates its application to the Knox tractor, in which it is mounted crosswise at the front end of the frame.
Fig. 251. Riker Muffler and Cutout.
Fig. 252. The Powell Muffler.
A pressed steel muffler has recently been introduced by Gueder, Paeschke & Frey Co., which is used on the Denby trucks. This is illustrated in Fig. 254, and consists of a number of pressed steel cups placed in a steel shell and electrically welded. This makes a very light construction and the claim is made that it weighs but five pounds. The gases enter at the forward end and pass through conical-shaped cups which are so spaced that an expansion chamber is formed between them. The remaining cups are of similar shape, but reversed in position and also provide limited expansion chambers between them. The first of these is perforated, while the second has but one large central hole, and the third has but half the number of perforations of the first one. The outlet, instead of having one large central opening, is also perforated, so that the gases escape in continuous streams.
Fig. 255 depicts another popular type of muffler known as the "Dunco" which operates on a principle of automatic adjustment which is that of the well-known steam ejector. A portion of the exhaust gases pass directly through a central tube to a high speed jet, at the outlet of that tube, and induce a partial vacuum behind them, thus drawing the remaining gases through baffle plates or cones in the muffler. It is claimed that this muffler is self-adjusting to variations in speed, and the frequency of injector impulses varies directly as the speed of the engine, so that the pull of the ejector is always proportional to the volume of gas to be drawn through and discharged. The heads arc mal-leable' callings and tie rods hold the entire construction together, so that it is very simple to lake the muffler apart for cleaning.
Fig. 253. The Knox Tractor Muffler.
Fig. 254. The G. P. & F. Muffler.
Fig. 255. Draco Ejector Type Muffler.
The Maxim silencer (Fig. 266) incorporates a somewhat different principle in which but one tubular member is used. The interior construction is of a peculiar built spiral chamber, which, it is claimed, can not clog or collect carbon. The gases enter at one end and pass from inlet to outlet without obstructions of any kind. This continuous channel has the peculiarity of circular or helical form, and, owing to the centrifugal force of the fast moving gases, these gases whirl to the outer periphery, traveling an approximate distance of three and one half times the length of the muffler. Slow moving gases will remain at the center and gradually move forward to the outlet. The heads are malleable, while the shell is made of sheet steel, seamed and electrically welded to prevent bursting.
The Oldberg muffler (Fig. 257) has a series of expansion chambers, The gases enter the center member and, due to the arrangement of the perforations, immediately start to pass out and around to the opposite side. Each alternate tube is placed eccentrically with respect to the axis of the muffler. The perforations in each tubular member are arranged in two rows throughout their length. The total area of these perforations is greatly in excess of the area of the exhaust pipe connecting with the muffler. The sound waves are interrupted by passing half of the gases around each side of the tubular members, the two streams coming together on the opposite side of the preceding chamber.
The mufflers described above apply to four and six cylinder engines, while Fig. 258 illustrates the I.H.C. construction for their two-cylinder engines. It consists of an inner and outer shell with cast heads retained by a single tie rod. The gases enter the outer chamber near its center through exhaust pipes from each cylinder. They expand in this outer chamber and pass through perforations in the walls of the inner member, whence they escape at both ends, as the muffler is mounted crosswise at the rear end of the frame. The outlets and mounting brackets are cast integral with the muffler heads. The end view illustrates the method of retaining the exhaust pipes with packing joints.
The exhaust system begins with the exhaust manifold of the engine and includes the exhaust pipe, cut-out and muffler. Practice differs with the various makers however. What has been outlined in this and previous chapters on the engine serves to give a general idea of the subject.
Fig. 256. The Maxim Silencer.
Fig. 257. The Old Berg Muffler.
Fig. 258. The I. H. C. Muffler for Two-Cylinder Opposed Motor.