EXHAUST SYSTEM FOR AN ENGINE

Abstract

Exhaust system for an engine (10), comprising: a first volume element (20, 34); a first and a second exhaust pipe (36, 38) which are connected to the first volume element (20,34) and extend downstream from it, wherein the first exhaust pipe (36) has a first length (L1); a second volume element (20, 40) connected to the first and second exhaust pipes (36, 38) and downstream of the first volume element (20, 34); and a valve (46, 202) which is arranged in the second exhaust pipe (38) at a distance (D) from the first volume element (20, 34), wherein the distance (D) is smaller than the first length (L1), wherein the second pipe (38) is a first resonator for the first pipe (36), and is formed by a first section of the second pipe (38) between the first volume element (20, 34) and the valve (46, 202) in a closed position; wherein a second section of the second tube (38) between the second volume element (20, 40) and the valve (46, 202) is a second resonator for the first tube (36) when the valve (46) is in the closed position, where the valve is a first valve (202), the distance (D) is a first distance (D1); the exhaust system further includes: a second valve (204) which is arranged in the second exhaust pipe (38) at a second distance (D2) from the first volume element (20, 34), wherein the second distance (D2) is another fraction of the first length (L1), wherein the second distance (D2) is greater than the first distance (D1), and wherein the second pipe (38) is a third resonator for the first pipe (36), wherein the first valve (202) is in an open position and the second valve (204) is in a closed position.

Description

TECHNICAL FIELD

[0001] Various embodiments relate to an exhaust system for an internal combustion engine in a vehicle. BACKGROUND

[0002] Exhaust systems for internal combustion engines direct exhaust gases produced during the combustion process in the engine out into the surrounding environment. Exhaust systems typically include sections of piping. These pipes contain standing pressure waves that amplify the noise from the exhaust system based on the frequency of the standing wave and harmonics.

[0003] An exemplary exhaust system is disclosed in JP H04-109 038 A. In detail, this document shows an exhaust system with a main muffler and an auxiliary muffler arranged in a first center pipe, an opening valve arranged between the main muffler and the auxiliary muffler in the first center pipe, and a second center pipe communicating with the main muffler and the auxiliary muffler.

[0004] Another exhaust system is known from document JP H04- 66 722 A. SUMMARY

[0005] In one embodiment, an exhaust system for an engine includes a volume element and first and second exhaust pipes connected to and extending downstream from the volume element. The first exhaust pipe has a first length (L1). A valve is disposed in the second exhaust pipe at a distance (D) from the volume element. The distance D is less than L1, such that the second pipe acts as a resonator for the first pipe when the valve is in a closed position.

[0006] In another embodiment, an exhaust system for an engine comprises first and second exhaust pipes arranged as dual exhaust pipes, and a volume element connected to and downstream of the first and second exhaust pipes. The first exhaust pipe has a first length (L1). A valve is arranged in the second exhaust pipe at a distance (D) from the volume element. The distance (D) is a fraction of L1, such that the second pipe is a resonator for the first pipe when the valve is in a closed position.

[0007] In yet another embodiment, a method for controlling exhaust noise is provided. A valve is disposed in a first exhaust pipe at a distance (D) from a volume element, wherein the first pipe and a second exhaust pipe are connected to the element for dual exhaust flow, and wherein D is less than a length of the second pipe. The valve is closed so that the first pipe provides a resonator for the second pipe to counteract the standing wave in the second pipe. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic diagram of an engine and an exhaust system according to one embodiment; Fig. Figure 2 illustrates a schematic graphic representation of pressure waves in the exhaust system of the Fig. 1; Fig. Figure 3 is a graph illustrating sound pressure levels based on engine speed; Fig. 4 is a schematic diagram of an engine and exhaust system according to another embodiment; Fig. 5 is a schematic diagram of an engine and exhaust system according to yet another embodiment; and Fig. 6 is a schematic diagram of an engine and exhaust system according to another embodiment. DETAILED DESCRIPTION

[0008] As required, detailed embodiments of the present disclosure are provided herein; however, it should be understood that the disclosed embodiments are merely exemplary and may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or reduced to show the details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for one skilled in the art to variously employ the present disclosure.

[0009] Fig. 1 illustrates an internal combustion engine 10 and an associated exhaust system 12. The engine 10 may be an internal combustion engine, such as a compression ignition engine or a spark ignition engine. The engine 10 may have one or more cylinders and, in the present non-limiting example, is shown as having six cylinders. The cylinders in the engine may be arranged in an in-line configuration, a V configuration, or another configuration. In some embodiments, the engine 10 is used as the sole propulsion motor in a vehicle, such as a conventional vehicle or a stop / start vehicle. In other embodiments, the engine 10 may be used in a hybrid vehicle where an additional propulsion motor, such as an electric motor, is available to provide additional power to propel the vehicle.

[0010] The engine 10 includes at least one controller 14 and various sensors configured to provide signals to the controller for use in controlling the air and fuel supply to the engine, ignition timing, power and torque output from the engine, the exhaust system, and the like. Engine sensors may include, among others, an oxygen sensor in the exhaust system 12, an engine coolant temperature sensor, an accelerator pedal position sensor, an engine manifold pressure (MAP) sensor, an engine position sensor for crankshaft position, a mass air flow sensor in the intake manifold, a throttle position sensor, an exhaust gas temperature sensor in the exhaust system 12, and the like.

[0011] The controller 14, as well as any circuit or other electrical device disclosed herein, may include any number of microprocessors, integrated circuits, memory devices (e.g., FLASH, random access memory (RAM), read-only memory (ROM), electrically programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), or other suitable variations thereof), and software that cooperate with one another to perform the operation(s) disclosed herein. In addition, any one or more of the electrical devices disclosed herein may be configured to execute a computer program embodied in a non-transitory computer-readable medium programmed to perform any number of functions disclosed herein.

[0012] The exhaust system 12 is fluidly connected to the engine 10 for venting and directing exhaust gases from cylinders within the engine to the atmosphere. The exhaust system 12 includes one or more exhaust manifolds 16 connected to the exhaust ports of the engine cylinders. Piping 18 within the exhaust system 12 connects various components or devices of the exhaust system 12.

[0013] The exhaust system 12 includes one or more volume elements 20, i.e., mufflers or silencers, for noise control. The muffler or silencer is an acoustic device for noise control or noise reduction. The muffler or silencer acts to reduce the volume of the sound pressure generated by the engine. The exhaust system 12 may also include one or more emissions control systems (not shown), such as a three-way catalyst, a catalytic converter, a particulate filter, and the like. In some examples, the exhaust system 12 may also include other devices and systems (not shown), such as an exhaust gas recirculation (EGR) system and / or a compression device, such as a turbocharger.

[0014] When the engine is operating and exhaust gases flow through the exhaust system 12, pressure waves develop in the piping 18 of the exhaust system 12. The noise of the engine 10 and the exhaust system 12 may vary based on the pulsating exhaust pressure waves in the piping 18 and the exhaust system 12, which form acoustic waves. The noise may vary with engine speed and / or load and exhaust flow rates. The exhaust pressure waves include fundamental frequency and higher-order harmonics, and the engine exhaust system 12 may also exhibit tones based on the operating conditions of the engine 10 and the geometry of the exhaust system 12. The noise from the engine exhaust system 12 may oscillate at a primary resonant frequency and higher-order harmonic frequencies in the acoustic spectrum based on the operating conditions of the engine and exhaust system.

[0015] The volume elements 20 may include various mufflers, silencers, or other devices to reduce engine exhaust noise, for example, by diverting pressure waves in the exhaust gases. Each volume element 20 may include a muffler with reactive elements such as a series of tubes, baffles, and chambers, a muffler with acoustic filler material to absorb noise, or a combination thereof. The volume elements 20 have a larger effective cross-sectional area than a cross-sectional area of ​​the piping 18 to act as a node for the standing wave in the connected piping 18. Note that as the cross-sectional area or diameter of one of the tubes increases, the backpressure decreases, and the effectiveness of the muffler also decreases.

[0016] At least a portion of the exhaust system 12 is arranged as a dual exhaust system. In a dual exhaust system, the sections of the pipe 18 are arranged for parallel exhaust flow through a first and a second section of the pipe. The engine 10 may provide a single flow of exhaust gases to the exhaust system 12 from a single manifold 16 or may provide first and second separate exhaust gas flows to the exhaust system 12, for example, using two exhaust manifolds 16, as shown.

[0017] In Fig. 1, a first stream of exhaust gases flows through a pipe section 30 and into a volume element 20, such as a first muffler 34. A second stream of exhaust gases flows through a pipe section 32 and into the muffler 34. In other examples, a single stream of exhaust gases may flow from the engine 10 and into the muffler 34. The first and second exhaust streams may mix within the muffler 34.

[0018] The tube section 36 and the tube section 38 exit the muffler 34 and connect the muffler 34 to a silencer 40 or other muffler or volume element. The tubes 36, 38 extend downstream of the muffler 34. The tube 36 has a first length (L1) and the tube 38 has a second length (L2). In one example, the tubes 36, 38 have the same diameter and substantially the same length. For example, the tube 36 may be the same length as the tube 38 or may be within 5-10 percent of the length of the tube 38. In other examples, the tubes 36, 38 may differ in diameter and / or length.

[0019] Exhaust gases flowing from pipes 36, 38 into muffler 40 can mix within the muffler. From muffler 40, exhaust gases are directed to the outside environment, for example, using first and second exhaust tailpipes 42, 44 arranged as dual exhaust tailpipes. In other examples, a single exhaust tailpipe may be provided.

[0020] A valve 46 is arranged in the pipe 38. Likewise, as in Fig. 1, the tube 36 is shown without a corresponding valve such that flow through the tube 36 is unrestricted and the tube 36 is valveless. The valve 46 is connected to the controller 14 to control the position of the valve. In one example, the valve 46 may be a two-position valve and controlled between an open position and a closed position. In other examples, the valve 46 may be controlled to a specific position between an open and a closed position for variable flow therethrough. The valve 46 provides a variably sized orifice for flow through the tube 38, with the orifice size ranging from zero in a closed valve position to the diameter of the tube 38 in an open position.

[0021] The valve 46 is positioned within the tube 36 at a specific location and is spaced from each volume element 20. The valve 46 is disposed a distance (D) from a volume element, where D is a fixed or predetermined fraction of L1 or D is a function of the length L1. In an example where the tubes 36, 38 have substantially equal lengths, the valve 46 is disposed a distance (D) from both volume elements 34, 40. The valve 46 may also be disposed within the tube 36 to dampen and control a target resonant frequency. It should be noted that in other systems, flow through a tube may be controlled using a valve disposed adjacent to or connected to a volume element, which does not result in a noise-reducing resonator as contemplated in the present disclosure.

[0022] The controller 14 controls the position of the valve 46. When the valve 46 is in a partially or fully open position, exhaust gases from the muffler 34 flow through both exhaust pipes 36, 38 and to the muffler 40. When the valve 46 is in a closed position, exhaust gases from the muffler 34 flow only through the exhaust pipe 36 and to the muffler 40. The pipe 38 acts as one or two resonators for the pipe 36 when the valve 46 is in the closed position based on the exhaust system configuration, and acts to reduce or eliminate the standing wave in the pipe 36.

[0023] In the present example, as in Fig. 1, the valve 46 is arranged at a distance (D) that is half the length L1 of the tube 36, where L1 and L2 are equal. As such, the tube 38 acts as a quarter-wave resonator for the tube 36, with the closed valve 46 acting as the end wall of the resonator. A first portion 48 of the tube 38 between the first volume element 34 and the valve 46 forms a first resonator or first tuner for the tube 36 when the valve 46 is in the closed position. A second portion 50 of the tube 38 between the second volume element 40 and the valve 46 forms a second resonator or second tuner for the tube 36 when the valve 46 is in the closed position. In this configuration, the first and second resonators 48, 50 are each a quarter-wave resonator for the tube 36.

[0024] The tubes 36, 38 extend between the volume elements 34, 40 such that the volume elements 34, 40 each form a node for pressure waves within the first and second tubes 36, 38. When the valve 46 is closed, the first resonator formed by the tube section 48 is fluidly connected to the volume element 34 at one of the nodes for the pressure wave in the first tube 36, and adjacent to the junction of the tube 36 with the volume element 34. When the exhaust gases leave the muffler 34 with the valve closed, an acoustic wave, a standing wave, or a pressure wave is formed in the tube 36. The first resonator formed by the tube 38 also forms a standing wave that is phase-shifted from the wave formed in the tube 36 based on the distance D of the valve 46 from the element 34 and is reflected back toward the node on the muffler 34 by the closed valve 46.If D is half of L1, so that the resonator is a quarter-wave resonator, the standing wave in the resonator is one hundred and eighty degrees out of phase with the wave in the tube 36. The standing wave from the first resonator offsets the standing wave in the first tube 36 at the node of the muffler 34 and reduces the exhaust noise.

[0025] When the valve 46 is closed, the second resonator formed by the tube section 50 is fluidly connected to the volume element 40 at another of the pressure wave nodes in the first tube 36, and adjacent to the junction of the tube 36 and the volume element 40. As the exhaust gases exit the muffler 34 with the valve 46 closed, an acoustic wave, a standing wave, or a pressure wave is formed in the tube 36. The exhaust gases may flow from the tube 36, through the volume element 40, and into the second resonator formed by the section 50. The second resonator formed by the tube 38 also forms a standing wave that is out of phase with the wave formed in the tube 36 based on the distance D of the valve 46 from the element 40 and is reflected back toward the node on the element 40 by the closed valve 46.When D is half of L1 and the resonator is a quarter-wave resonator, the standing wave in the resonator is one hundred and eighty degrees out of phase with the wave in the pipe 36. The standing wave from the second resonator further offsets the standing wave in the first pipe 36 at the node of the muffler 40, further reducing the exhaust noise.

[0026] Fig. Figure 2 illustrates a schematic representation of the standing wave in tube 36, as well as the offsetting quarter wave provided by one of the resonators of the other tube 38 when the valve 46 is in a closed position. The standing wave in tube 36, indicated by line 60, extends between two nodes 62, 64 provided by the volume elements 34, 40. The quarter standing wave, shown by line 66, is 180° out of phase with line 60, thereby canceling at least some of the acoustic noise generated by the standing wave 60 in the first tube 36. In further examples, as described below, the second tube 38 and valve 46 can be used to control or offset higher-order harmonics, with a second-order harmonic in tube 36 shown for illustration by line 68.

[0027] According to one example, first and second resonators provided by tube 38 and valve 46 are tuned to offset the resonance in tube 36 in a frequency range of 50 to 1500 Hertz, although other frequency ranges are also contemplated. The position of valve 46 and the length of the resonators are based on the length of the other tube and the target tuning frequency to offset a standing wave. The primary or first resonance in tube 36 can be calculated as the speed of sound divided by the length of tube 36.The speed of sound can be calculated based on the exhaust gases flowing through pipe 36 and can be estimated using the equation for the speed of sound for an ideal gas using the universal gas constant (R = 8.314 J / mol-K), the molecular weight of the gas (kg / mol), the adiabatic gas constant associated with the exhaust gases, and the absolute temperature of the exhaust gases (K). In one example, the first and second resonators formed by pipe 38 and valve 46 provide a 100 Hertz resonator for pipe 36 at its primary harmonic resonance, with higher-order harmonics occurring at 300 Hz, 500 Hz, and 700 Hz.

[0028] In general, tubular elements, such as tubes 36, 38, amplify acoustic energy due to their physical properties, primarily their length. In conventional systems, the resonances in tubular elements may require additional volume elements tuned to the resonant frequency of the tube, for example, by adding additional mufflers to an exhaust system, thereby adding cost, weight, and packaging space within a vehicle. In the present disclosure, the addition of a valve 46 to the exhaust system provides an exhaust system 12 with tuned exhaust sound and without the need for additional mufflers or other volume elements to address resonance noise issues.The double tubes 36, 38 and the valve 46 can result in improved noise reduction with the tubes 36, 38 each directly connected to a common volume element 20, thereby reducing or eliminating branched connections that would complicate noise propagation and reduction.

[0029] When the valve 46 is in an at least partially open state, the valve 46 can additionally provide further benefits by: adding turbulence to the flow of exhaust gases to reduce the transmission of acoustic waves, providing an expansion ratio across the valve to provide a pressure drop and reduce the transmission of acoustic waves, and redirecting flow to alternative elements in the system. The valve 46 provides the ability to change a flow element such as the tube 38 into one or more tuning elements, such as the first and second resonators, to address the inherent resonance of a second flow element or tube 36.

[0030] The controller 14 controls the position of the valve 46 based on engine operating conditions. Low flow of exhaust gases through the tubes 36, 38, such as during engine idle or light load, may result in increased resonance in the tubes 36, 38 because the volume elements, such as the muffler 34, are less effective. In one example, the controller 14 controls the valve 46 to a closed position depending on an engine condition, such as engine speed and / or engine load, for example, using a lookup table or equation. The controller 14 may receive signals from various sensors indicative of engine operating conditions, such as throttle position, MAF, accelerator pedal position, and the like, to control the position of the valve 46.The controller 14 may send a signal to the valve 46 to close the valve in response to the engine condition being below a predetermined value and to open the valve in response to the engine condition being above the predetermined value.

[0031] In another example, the controller 14 controls the valve 46 to a partially open state to provide a reduced flow through the pipe 38 compared to the pipe 36. The controller 14 may control the valve 46 to provide a volumetric flow through the pipe 38 that is 15%, 10%, 5%, or less of the volumetric flow through the other pipe 36. As such, the partially open valve 46 acts to dampen the noise in the pipe 36 and the exhaust system 12 by reducing the noise across a broader spectrum, thereby providing further exhaust sound tuning.

[0032] Fig. Figure 3 shows sound pressure levels (A-weighted decibels, 5 dB (A) per division) plotted with increasing engine speed (revolutions per minute, 500 rpm per division). Line 100 represents the noise from the exhaust system 12 in Fig. 1 without a valve 46 or if the valve 46 remains open over all engine speeds. As in Fig. 3, at low engine speeds, such as idle speed or low loads, the noise increases to a peak or spike, as shown by the area 102.

[0033] An engine exhaust noise tuning guide may specify that the engine noise should not exceed a profile, as shown by line 104, to control the noise or to meet various regulatory standards or customer expectations. Line 106 illustrates the exhaust system 12 of the Fig. 1, wherein the valve 46 is controlled between an open and a closed position. In region 108, at idle speed or low engine load, the valve 46 is closed by the controller 14 such that all exhaust gas flow between the volume elements 34, 40 is via the tube 36, and the tube 38 forms a first and second quarter-wave resonator for the tube 36. As can be seen, the noise from the exhaust system in region 108 is significantly reduced and actually provides a valley or dip compared to the no-valve peak in region 102. It should be noted that if the valve 46 were not fully closed, the noise in region 108 would be dampened, with a wider and shallower dip or valley. At higher engine speeds, e.g., in region 110, the valve 46 is opened to allow higher flow rates of exhaust gases to flow through both tubes 36, 38 and to the environment.

[0034] Fig. Figure 4 illustrates an exhaust system 150 based on a variation of the exhaust system 12 as described above with reference to Fig. 1. Elements that are the same or similar to those described above with reference to Fig. 1 are provided with the same reference number.

[0035] The first and second exhaust pipes 36, 38 are arranged in a dual-pipe parallel flow configuration and are connected to and downstream of a volume element 20, such as a muffler 34. The first pipe 36 includes a first muffler 152 or other volume element, and the second pipe 38 includes a second, separate muffler 154 or other volume element. The two mufflers 152, 154 are arranged downstream of the muffler 34. The valve 46 is arranged in the second pipe 38 a distance (D) downstream of the volume element 34. The distance (D) is a function of the length (L1) of the first pipe and, in one example, half the length of the first pipe 36, such that a portion 156 of the pipe 38 acts as a quarter-wave resonator for the first pipe 38 when the valve 46 is in a closed position.

[0036] In the present example, the lengths of the first and second tubes 36, 38 may be the same or different. Since the first and second tubes are connected by only a single volume element 34, the tube 38 provides only a single resonator for the tube 36. The valve 46 in the closed position prevents exhaust gases from flowing through the muffler 154.

[0037] Fig. Figure 5 illustrates an exhaust system 200 based on a variation of the exhaust system 12 as described above with reference to Fig. 1. Elements that are the same or similar to those described above with reference to Fig. 1 are provided with the same reference number.

[0038] The first and second exhaust pipes 36, 38 are arranged in a double-pipe parallel flow configuration and are connected to and downstream of a volume element 20, such as a muffler 34. The first and second pipes 36, 38 may be connected to a common muffler 40 downstream as shown or may be connected to separate mufflers as described with reference to Fig. 4 described.

[0039] A first valve 202 is disposed in the tube 38 at a first distance (D1) from the volume element 34. A second valve 204 is disposed in the tube 38 at a second distance (D2) from the volume element 34. The valves 202, 204 may be similar to the valve 46 described above. The controller 14 independently controls the positions of each of the valves 202, 204 based on the operating conditions of the engine and exhaust system to tune exhaust noise and reduce certain harmonics or standing waves in the tube 36.

[0040] The distance D1 of the first valve 202 is based on a fixed or predetermined fraction of L1, such that D1 is a function of the length L1. When the first valve 202 is closed, the portion of the tube 38 between the muffler 34 and the valve 202 provides a resonator for the tube 36 of length D1. Note that with the valve 202 closed and the valve 204 open, the remaining portion of the tube 38 between the valve 202 and the muffler 40 provides another resonator of length (L2-D1) tuned to offset a different frequency for the tube 36.

[0041] The distance D2 of the second valve 204 is based on a different fixed or predetermined fraction of L1, such that D2 is another function of the length L1. The distance (D2) is greater than the distance (D1). When the second valve 204 is closed, the portion of the tube 38 between the muffler 40 and the valve 204 provides a resonator of length (L2-D2) for the tube 36. Note that with the valve 202 open and the valve 204 closed, the portion of the tube 38 between the valve 204 and the muffler provides another resonator of length (D2) tuned to offset a different frequency for the tube 36. The distances D1, D2 may be proportional to each other.

[0042] An additional combination of resonators can be provided with the two valves 202, 204 in the closed position, such that a section of the tube 38 between the muffler 34 and the valve 202 provides a resonator of length (D1) for the tube 36, and another section of the tube 38 between the muffler 40 and the valve 204 provides another resonator of length (L2-D2) for the tube 36. The distances (D1) and (L2-D2) can be the same or can vary from each other based on the lengths L1, L2 of the tubes 36, 38 and the target frequencies for tuning.

[0043] The controller 14 controls the positions of the valves 202, 204 based on the engine state or engine operating conditions to control the noise to a profile based on the available combinations of resonators from the positions of the valves 202, 204. For example, with the engine idling, the controller 14 may open the valve 202 and close the valve 204 to provide a longer resonator of length D2 from the portion of the pipe 38 from the muffler 34 to the valve 204. As the engine speed and / or load increases, the controller 14 may close the valve 202 and either hold the valve 204 in a closed position or open the valve 204 to provide a shorter resonator of length D1 from a portion of the pipe 38 between the muffler 34 and the valve 202. Generally, the controller controls the valves to vary the length(s) of the resonator orof the resonators as engine speed and / or load increases, and open all valves at higher engine speeds and / or loads to allow exhaust gases to flow unrestrictedly through pipe 38. Additional valves may be added to pipe 38 to provide additional resonators for use in tuning the exhaust system; however, the additional valves may add weight, cost, and complexity to the system, and the associated benefits may need to be reconsidered.

[0044] Fig. 6 illustrates an exhaust system 250 based on a variation of the exhaust system 200 as described above with reference to Fig. 5. Elements that are the same or similar to those described above with reference to Fig. 1 and Fig. 5 are provided with the same reference number.

[0045] The first and second exhaust pipes 36, 38 are arranged in a double-pipe parallel flow configuration and are connected to and downstream of a volume element 20, such as a muffler 34. The first and second pipes 36, 38 may be connected to a common muffler 40 downstream as shown or may be connected to separate mufflers as described with reference to Fig. 4 described.

[0046] A first valve 252 is disposed in the tube 38 at a first distance (D1) from the volume element 34. A second valve 254 is positioned in the tube 36 at a second distance (D2) from the volume element 34. The valves 252, 254 may be similar to the valves 46, 202, and 204 described above. The controller 14 controls the positions of the valves 252, 254 based on the operating conditions of the engine 10 and the exhaust system 250 to tune the exhaust sound and to control certain harmonics or the standing wave similarly as described above with respect to the Fig. 1 and Fig. 5, except that one of the two valves 252, 254 is always open during engine operation to provide a path for exhaust gases from the engine 10 to the surrounding environment. Therefore, the controller 14 prevents both valves 252, 254 from closing simultaneously.

[0047] The distance D1 of the first valve 252 is based on a fixed or predetermined fraction of the length L1 of the other tube 36, so that D1 is a function of the length L1. When the first valve 202 is closed, the portion of the tube 38 between the muffler 34 and the valve 202 provides a resonator for the tube 36 of length D1. With a common muffler 40, the remaining portion of the tube 38 between the muffler 40 and the valve 252 provides another resonator of length (L2-D1) for the tube 36 when the valve 252 is in a closed position. If the tubes 36, 38 are of equal length and D1 is located at the point halfway between them, the tube 36 can provide two quarter-wave resonators for the tube 36.If the tubes 36, 38 have different lengths, the distance D1 is based on the length L1 of the tube 36 and can be set as half of L1 to provide one quarter-wave resonator and another resonator tuned to a different frequency.

[0048] The distance D2 of the second valve 254 is based on a fixed or predetermined fraction of L2 of the tube 38. When the second valve 254 is closed, the portion of the tube 36 between the muffler 34 and the valve 254 provides a resonator for the tube 38 of length D2. With a common muffler 40, the remaining portion of the tube 36 between the muffler 40 and the valve 254 provides another resonator of length (L1-D2) for the tube 38 when the valve 254 is in a closed position. If the tubes 36, 38 are of equal length, D2 can be located at a point other than halfway to provide a resonator with a different frequency than valve 252.If the tubes 36, 38 have different lengths, the distance D2 is based on the length L2 of the tube 38 and can be set as half of L1 to provide a quarter-wave resonator and another resonator tuned to a different frequency.

[0049] Fig. 6 also illustrates a variation in accordance with the present disclosure wherein the engine 10 includes a single manifold or header 256 connected to the muffler 34, or wherein the muffler 34 includes a single exhaust inlet upstream of the dual exhaust pipes 36, 38. Note that some emission control devices or other devices or systems are not shown, but would be disposed between the exhaust manifold 256 and an upstream volume element, such as the muffler 34.

[0050] Although exemplary embodiments are described above, these embodiments are not intended to describe all possible forms of the disclosure. Instead, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the disclosure. In addition, the features of various embodiments may be combined to form further embodiments of the disclosure.

Claims

[1] Exhaust system for an engine (10), comprising: a first volume element (20, 34); a first and a second exhaust pipe (36, 38) connected to and extending downstream from the first volume element (20, 34), the first exhaust pipe (36) having a first length (L1); a second volume element (20, 40) connected to the first and second exhaust pipes (36, 38) and downstream of the first volume element (20, 34); and a valve (46, 202) arranged in the second exhaust pipe (38) at a distance (D) from the first volume element (20, 34), the distance (D) being less than the first length (L1), the second pipe (38) being a first resonator for the first pipe (36) and being formed by a first portion of the second pipe (38) between the first volume element (20, 34) and the valve (46, 202) in a closed position; wherein a second portion of the second tube (38) between the second volume element (20, 40) and the valve (46, 202) is a second resonator for the first tube (36) when the valve (46) is in the closed position, wherein the valve is a first valve (202), the distance (D) is a first distance (D1); wherein the exhaust system further comprises: a second valve (204) disposed in the second exhaust pipe (38) at a second distance (D2) from the first volume element (20, 34), the second distance (D2) being a different fraction of the first length (L1), the second distance (D2) being greater than the first distance (D1), and the second pipe (38) being a third resonator for the first pipe (36), the first valve (202) being in an open position and the second valve (204) being in a closed position. [2] The exhaust system of claim 1, wherein the distance (D) is half of the first length (L1) such that the first resonator is a quarter wave resonator for the first tube (36). [3] The exhaust system of claim 1, wherein the second pipe (38) has a second length (L2), the second length (L2) being equal to the first length (L1). [4] The exhaust system of claim 1, wherein a diameter of the first exhaust pipe (36) is equal to a diameter of the second exhaust pipe (38). [5] The exhaust system of claim 1, further comprising a controller (14) for closing the valve (46, 202) in response to an engine condition being below a predetermined value and for opening the valve (46, 202) in response to the engine condition being above the predetermined value. [6] The exhaust system of claim 1, wherein the distance (D) is half of the length (L1) such that the first resonator and the second resonator are each a quarter-wave resonator for the first tube (36). [7] The exhaust system of claim 6, wherein the second tube (38) between the second volume element (20, 40) and the second valve (204) serves as a fourth resonator for the first tube (36), the second valve (204) being in the closed position. [8] The exhaust system of claim 1, wherein exhaust gases flow through the second exhaust pipe (38) when the valve (46, 202) is in an open position. [9] The exhaust system of claim 1, wherein the first exhaust pipe (36) is valveless. [10] The exhaust system of claim 1, wherein the first volume element (20) is one of a muffler (34) and a silencer (40). [11] The exhaust system of claim 1, further comprising a controller (14) for controlling the valve (46, 202) to a partially open state to reduce flow through the second pipe (38), to attenuate and broaden the standing wave in the first pipe (36), and to adjust the exhaust noise. [12] The exhaust system of claim 1, further comprising a controller for closing the valve (46, 202) to counteract a standing wave in the first pipe (36) at a particular frequency and thereby tune the exhaust noise to a predetermined level. [13] An exhaust system for an engine (10), comprising: a volume element (20, 34, 40); first and second exhaust pipes (36, 38) connected to and extending downstream of the volume element (20, 34, 40), the first exhaust pipe (36) having a first length (L1) and the second exhaust pipe (38) having a second length (L2); a first valve (252) disposed in the second exhaust pipe (38) at a distance (D1) from the volume element (20, 34, 40), the distance (D1) being less than the first length (L1), the second pipe (38) being a resonator for the first pipe (36) when the first valve (252) is in a closed position; and a second valve (254) disposed in the first exhaust pipe (36) at a distance (D2) from the volume element (20, 34, 40), the distance (D2) being a fraction of the second length (L2), the first exhaust pipe (36) being a resonator for the second pipe (38) when the second valve (254) is in a closed position; wherein at least one of the first valve (252) and the second valve (254) is in an open position during engine operation. [14] The exhaust system of claim 13, wherein the second length (L2) is equal to the first length (L1) and the distance (D1) is greater than the distance (D2). [15] Exhaust system according to claim 13, wherein the distance (D1) is greater than the distance (D2). [16] The exhaust system of claim 15, further comprising a controller configured to close the first valve (252) and open the second valve (254) when an engine condition is below a first threshold. [17] The exhaust system of claim 16, wherein the controller is further configured to close the second valve (254) and open the first valve (252) when the engine condition is between the first threshold and a second threshold that is greater than the first threshold. [18] The exhaust system of claim 17, wherein the controller is further configured to open the first and second valves (252, 254) when the engine condition is above the second threshold.

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