Abstract:
An exhaust system provides the benefits of equal or near equal length exhaust pipes for vehicles (for example with transverse engines) having differing length exhaust pipes connected with a single muffler. In accordance with the invention, the muffler has separate first and second internal inlet pipes which have lengths differing by a predetermined length dimension equal or nearly equal to the difference in exhaust pipe lengths. The inlet pipes are connected so that the total lengths of the pairs of inlet pipes and connected exhaust pipes provide a total length of exhaust flow path which is generally equal for gas flow from both engine banks to the interior of the muffler. An optional feature is dual restricted and valve-controlled outlet flow paths which maintain a minimum back pressure at low flows to aid EGR distribution and allow high flow rates at low back pressure for high performance output of the engine with a performance sound.

Description:
TECHNICAL FIELD 
     This invention relates to vehicle exhaust systems, in particular to systems having unequal length exhaust pipes and to a muffler including unequal length internal inlet pipes for equalizing the length of connected pairs of pipes delivering exhaust gas flow to the muffler interior. 
     BACKGROUND OF THE INVENTION 
     In automotive vehicles with longitudinally-mounted engines having exhaust systems with dual exhaust pipes leading to a single muffler, the dual exhaust pipes may have essentially equal lengths. Such systems tend to deliver to the muffler exhaust gas having similar sound wave and gas flow patterns, which generally results in a pleasant sound quality of the engine exhaust note. 
     On the other hand, transverse-mounted engines may have exhaust systems with dual exhaust pipes leading from opposite front and rear cylinder banks of the engine to a single muffler. In such systems the exhaust pipes may have a difference in length that is in excess of one meter. This difference yields sound wave additions and cancellations, causing the quality of the exhaust note to be substantially inferior to those systems that have nearly equal length geometries. The result is typically a “raspy” quality to the exhaust note. 
     A further characteristic of high flow low back pressure exhaust systems is that, when the exhaust flow rates are low, the back pressure is reduced and the systems are subject to pulsations which interfere with equal internal distribution of recirculated exhaust gas (EGR) to the cylinders. 
     Accordingly, a system is desired which improves the sound quality of exhaust systems for vehicles with transversely-mounted engines and other systems with differing dual exhaust pipe lengths. Preferably, the system could also improve EGR distribution at low exhaust flow rates without causing excessive exhaust back pressure at high exhaust flow rates. 
     SUMMARY OF THE INVENTION 
     The present invention provides an active muffler and vehicle exhaust system, particularly for transverse engines but applicable to other vehicle engines. The system provides the benefits of equal or nearly length exhaust pipe systems of longitudinally-mounted engines to exhaust systems where unequal length exhaust pipes are utilized. 
     In accordance with the invention, a single exhaust muffler is provided with separate first and second internal inlet pipes which have lengths differing by a predetermined length dimension. The difference in lengths is made equal, or nearly equal, to the difference in the lengths of exhaust pipes extending from the associated engine exhaust outlets to the single exhaust muffler. The inlet pipes are connected so that the total lengths of the pairs of inlet pipes with their corresponding connected exhaust pipes provide total lengths of exhaust flow paths which are approximately equal for gas flow from both engine banks to the interior of the muffler. 
     An optional additional feature of the muffler is the provision of dual outlet flow paths for the exhaust gas. These include a restricted gas flow path which is always open and a low restriction flow path controlled by a back pressure valve which closes the passage at low exhaust gas flow rates. The exhaust gas back pressure is thus raised at low flows so that EGR distribution to the cylinders is improved. The valve is opened at higher exhaust flow rates so that back pressure in the muffler is reduced, allowing the passage of exhaust gas through a high flow low back pressure system. This provides for high performance output of the engine, undiminished by excessive back pressure in the manifold. The dual outlet paths may also provide a performance sound to the high flow exhaust note. 
    
    
     These and other features and advantages of the invention will be more fully understood from the following description of certain specific embodiments of the invention taken together with the accompanying drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic view illustrating the arrangement of an exhaust system for a transverse-mounted vehicle engine connected with a muffler having equalizing inlet pipes according to the invention; 
     FIG. 2 is a pictorial view illustrating an exemplary arrangement of internal pipes and chambers for a muffler according to the invention; and 
     FIG. 3 is a pictorial view from the inlet end showing the back pressure valve mounting within the manifold of FIG.  2 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring first to FIG. 1 of the drawings in detail, numeral  10  generally indicates an automotive vehicle, such as an automobile, having a longitudinal axis  12 . An engine  14  is mounted in a forward portion of the vehicle and disposed transversely, with the axis  16  of the engine crankshaft, not shown, lying normal to the longitudinal vehicle axis  12 . The engine is of the V-type, having left and right cylinder banks  18 ,  20 , respectively. The engine is mounted conventionally with its front end facing the right side of the vehicle so that the left cylinder bank  18  lies toward the front of the vehicle while the right cylinder bank  20  lies toward the rear of the vehicle. 
     The vehicle  10  is provided with an exhaust muffler  22  having an outer shell  24  enclosing first and second internal inlet pipes  26 ,  28 , respectively. The inlet pipes extend through a front wall  30  of the muffler to connection with a mounting flange  32 . 
     The left and right engine cylinder banks  18 ,  20  include exhaust outlets  34 ,  36 , respectively, displaced toward the front and rear of the vehicle. A first exhaust pipe  38  connects the rear exhaust outlet  36  with the first inlet pipe  26  of the muffler through a mounting flange  40  connected with the manifold mounting flange  32 . A second exhaust pipe  42  connects the front exhaust outlet  34  with the second inlet pipe  28 , also through the mounting flanges  40 ,  32 . 
     Because of the relatively close spacing between the rear engine exhaust outlet  36  and the mounting flange  40 , the first exhaust pipe  38  is relatively short. On the other hand, the second exhaust pipe  42 , connecting the forward exhaust outlet  34  with flange  40 , is substantially longer, by a predetermined length dimension, than the first exhaust pipe  38 . The difference in pipe lengths is due not only to their being mounted on opposite rear and forward sides of the engine but also to the necessary routing of the second exhaust pipe  42  around the engine to the flange  40  mounted behind the engine. 
     In accordance with the invention, the total length of the short first exhaust pipe  38  and its connected second inlet pipe  26  within the muffler is made approximately equal to the length of the longer second exhaust pipe  42  and the connected second inlet pipe  28  within the muffler. This is accomplished by extending the length of the first inlet pipe  26  within the muffler by the differential dimension so that the total length of the pair of pipes  38 ,  26  is approximately equalized with the total length of the pair of pipes  42 ,  28 . This length extension is accomplished, as shown schematically in FIG. 1, by a return loop  44  in the first inlet pipe  26  so that the length of pipe  26  within the muffler is longer than that of the second inlet pipe  28  by the predetermined length dimension. 
     While approximately equal exhaust pair lengths are generally preferred at present, some systems may have acceptable, or even preferable, sound or may better meet packaging requirements, with substantial length variations between the two pairs of connected pipes. Such variations could be as small as 6 inches or 15 mm or as great as 15 percent of the total length of the longer of the pipe pairs within the scope of the broader aspects of the invention. 
     The schematic illustration of FIG. 1 shows in simple form the looped internal form of the longer inlet pipe  26  which makes up for the shorter length of the connected exhaust pipe  38  to provide essentially equal length pairs of connected exhaust and inlet pipe assemblies. However, the illustration of the muffler  22  in FIG. 1 does not show the tuning and quieting components of the muffler, but shows the inlet pipes  26 ,  28  as extending completely through the muffler and out a rear wall  46  without any obvious connection with resonance chambers within the muffler. Thus, FIG. 1 is illustrative of the manner in which the connecting pipes of the exhaust system are substantially equalized in length but does not indicate other features of the muffler construction. 
     Referring to FIGS. 2 and 3, pictorial views of an actual muffler  48  embodying various features of the invention are shown. Muffler  48  includes an outer shell  50  shown with its upper portion removed to display the interior of the muffler. The interior volume is divided by a plurality of bulkheads  52  into a series of chambers including an inlet chamber  54 , a transfer chamber  56 , a low flow chamber  58 , a high flow and resonance chamber  60 , a resonance chamber  62  and an outlet chamber  64 . 
     A first inlet pipe  66  enters the manifold interior through a front wall  68  and is formed with a return loop  70  that passes through several of the chambers, returning to the inlet chamber  54 . Here, the loop  70  again turns rearward and is joined by a connector  72  with a relatively short second inlet pipe  74 . The passages of the two inlet pipes are thus joined together and connected with a distribution pipe  76 . 
     Pipe  76  includes two serially-spaced outlets including a restricted, low flow outlet  78  and a low restriction, high flow outlet  80 . The low flow outlet  78  comprises a ring of a limited number of perforations in the distribution pipe wall, forming a restricted flow path for exhaust gas from the distribution pipe  76  to the low flow chamber  58 . The high flow outlet  80  comprises a substantially greater number of small perforations through the wall of the distribution pipe  76  connecting the pipe interior with the high flow chamber  60 . 
     The low flow chamber  58  communicates with the end of a first connector pipe  82 , which extends toward the rear of the muffler and connects with a single outlet pipe  84  extending through the rear wall  86  of the muffler. The high flow outlet  80  connects through the high flow chamber  60  with a high flow inlet  88  in a longitudinal transfer pipe  90 . This transfer pipe also has a perforated resonance outlet  92  to the resonance chamber  62  and has an open opposite end  94  communicating with the transfer chamber  56 . A door valve  96  closes the open end  94  of the transfer pipe and is openable by exhaust pressure and temperature, or by suitable control means, to permit high gas flow from the open end  94  of the pipe  90 . A second connector pipe  98  also includes an open end  100  which opens into the transfer chamber  56 . Pipe  98  extends rearward from the transfer chamber to a connection with the first connector pipe  82  in the outlet chamber  64  where the two pipes join the single outlet pipe  84  extending through the rear wall  86  of the manifold. 
     In operation, exhaust gas flows from the rear exhaust outlet, not shown, of the engine, through a short first exhaust pipe  102  to the first inlet pipe  66 , where it travels around the return loop  70  until it joins the short second inlet pipe  74  at the connector  72 . Concurrently, exhaust flow from the front exhaust outlet, not shown, of the engine passes through the long exhaust pipe  104  and the second inlet pipe  74  into connector  72 , where it joins exhaust flow from the first inlet pipe  66 . 
     Exhaust gas from the connector  72  passes through the restricted low flow outlet  78  of the distribution pipe  76  into the low flow chamber  58 . It then enters into the open end of the first connector pipe  82  and is carried to the rear of the muffler and into the single outlet pipe  84 . 
     At low exhaust gas flows, as occurs during low speed and low load engine operation, the control door valve  96  remains closed, blocking the outlet  94  of the transfer pipe  90 . In this condition, the high flow chamber  60  acts as a resonance chamber which absorbs pulsations in the gas flow within the volume of the chamber  60  as well as through the transfer of gas from the high flow outlet  80  to the high flow inlet  88  of the transfer pipe  90 . Some of this gas passes through the resonance outlet  92  into the resonance chamber  62  so that chambers  62  and  60  both contribute to muffling of the sound generated by the exhaust gas flow during low speed and load, low gas flow operation of the engine. 
     When the engine speed and load increase, so that back pressure in the exhaust system reaches a predetermined higher value, the control valve  96  is opened, either through a valve actuator, not shown, or by the action of the back pressure, assisted by gas temperature which reduces the closing force of the valve return spring. Then a substantially increased free flow of exhaust gas passes through the open end  94  of the transfer valve into the transfer chamber  56  and into the open end  100  of the second connector pipe  98 . Pipe  98  carries the exhaust gas to the single outlet pipe  84  where it is mixed with gas from the first inlet pipe  66  for exhaust from the vehicle. When the valve  96  is opened, the resistance to flow in the muffler is substantially reduced, so that a larger flow of exhaust gas through the muffler is permitted without a large increase in exhaust. back pressure. Thus, maximum performance of the engine at higher speeds and loads is assured. 
     Operation of the control valve  96  is designed to maintain a minimum exhaust back pressure in the inlet pipes  66 ,  74  of the muffler during low gas flow at low speed and load engine conditions. The back pressure increases internal recirculation of exhaust gas (EGR) to the engine cylinders so that equal distribution of the recirculated exhaust gas to the cylinders may be maintained. At higher speeds and loads, opening of the control valve  96  maintains a controlled back pressure within the muffler so that exhaust gas recirculation remains at a controllable level while high performance of the engine with high gas flow and low back pressure within the muffler is maintained. 
     While the invention has been described by reference to certain preferred embodiments, it should be understood that numerous changes could be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the disclosed embodiments, but that it have the full scope permitted by the language of the following claims.