The present invention relates to a muffler for an exhaust system of an internal combustion engine.
Mufflers are used, for example, as components of exhaust systems of motor vehicles in general, and in particular as components of exhausts systems of cars. For specific types of cars, e.g. sports cars, it is desirable that the sound exiting the exhaust system has a sportive characteristic including sound components which are experienced as having a certain “roughness” (aggressive sound). Roughness sensitivity of humans is highest for amplitude modulated sound where the frequency of the envelope is in the range of 50 Hz to 100 Hz, although also envelope frequencies outside this range may contribute to the experienced roughness, too.
It is known that many so-called “engine orders” contribute to the amplitude modulated sound emitted by the engine, with an engine order being defined as corresponding to one revolution of the crank shaft. By way of example, at 3000 rpm (revolutions per minute) of the crank shaft the first engine order is 50 Hz (i.e. the first engine order corresponds to the rotational frequency of the crank shaft). In particular the “higher engine orders” (second and higher engine orders), that is to say multiples of the first engine order are known to contribute to the amplitude modulated sound which is responsible for the experienced roughness. Therefore, to achieve a sportive sound characteristic it is important that the higher engine orders are contained in the sound exiting the exhaust system.
To preserve the higher engine orders in the sound coming from the engine and allowing these higher engine orders to exit the exhaust system to create the sportive sound, a known two-branch exhaust component comprises a conventional muffler arranged in a first branch of the two-branch exhaust component and a bypass pipe arranged in the second branch of the two-branch component. The muffler in the first branch comprises a relatively voluminous casing in the inner space of which attenuating elements may be arranged for attenuating all types of sound passing through the inner space of the muffler and thus very substantially reducing the overall noise emitted by the engine, so that the noise exiting the exhaust system is very substantially reduced. The bypass pipe in the second branch is essentially a conventional pipe which is sized and shaped to allow the higher engine orders to pass through thus forming an acoustic bypass. The two branches are re-joined again downstream of the muffler.
While this is an acceptable and well-working constructional approach for an exhaust component from the perspective of achieving a reduced overall sound level emitted from the exhaust system and at the same time providing for a sportive sound characteristic, this constructional approach suffers from some disadvantages.
A first disadvantage is that due to the comparatively large surface of the casing of the muffler, cooling of the muffler by the ambient air is much more effective than cooling of the bypass pipe which has a comparatively small surface that is exposed to the ambient air. Accordingly, thermal expansion caused by the hot exhaust gas flowing through the two branches may lead to different lengths of the two branches. Since the two-branch component is typically mounted between an upstream exhaust pipe and a downstream exhaust pipe this different thermal expansion must be compensated for to avoid a too high thermal stress in the material which may otherwise result in that the component may get broken. To compensate for the different thermal expansions, at least one flexible element (e.g. a kind of metallic bellows) is arranged in the branch of the bypass pipe. However, such flexible elements are comparatively difficult to manufacture and are costly. A further disadvantage of the described two-branch component is that the construction is rather voluminous so that mounting of the component to the chassis of a car is comparatively space-consuming. A further disadvantage of this constructional approach is that pressure losses are generated in the two Y-joints splitting the exhaust pipe to form the two branches and re-joining the two branches again.
A further known exhaust component comprises a muffler comprising a casing and a pipe extending through the casing. The pipe comprises one or more branch conduits branching off of the pipe wall. The branch conduit(s) open(s) out into the interior of the casing. While this constructional approach is more compact than the constructional approach discussed above, it suffers from the disadvantage that pipes comprising one or more branch conduits branching off of the pipe wall are comparatively difficult and expensive to manufacture. An additional disadvantage is that the cut-off frequency of the high pass filter so formed cannot easily be tuned within the desired bandwidth without departing from the range of typical dimensions of the branched pipes.
Therefore, it is an object of the invention to provide a muffler that overcomes the above-described disadvantages while at the same time allowing higher engine orders to pass through so that the sound exiting the exhaust system has a sportive sound characteristic.
In accordance with the invention, this object is achieved by a muffler for an exhaust system of an internal combustion engine as it is characterized by the features of the independent claim. Further advantageous aspects are the subject of the dependent claims.
In accordance with the invention, the muffler for an exhaust system of an internal combustion engine comprises: a casing having an inner space, an inlet pipe for sound to enter the muffler, an outlet pipe for sound to exit the muffler, and a separation wall arranged to extend from the inlet pipe to the outlet pipe and being embodied in a manner such as to define first and second acoustical ducts extending through the casing to allow sound propagating along the first acoustical duct to enter the inner space of the casing and to thereafter exit the inner space of the casing again, and to allow sound propagating along the second acoustical duct to acoustically bypass the inner space of the casing, wherein the muffler, including the inner space of the casing, the inlet pipe, the outlet pipe and the separation wall, is sized and shaped to form a high pass filter having a cut-off frequency which is in the range of 200 Hz to 800 Hz.
The muffler according to the invention allows for tuning of the cut-off frequency in the afore-mentioned range by changing the size or shape (or both) of the inner space, the inlet pipe and the outlet pipe, and their arrangement relative to one another. As a result thereof, the (relevant) higher engine orders are allowed to pass through in order to preserve the sportive sound characteristic.
The separation wall can be embodied differently, as will be explained further below, as long as it establishes two different acoustical ducts, so that one portion of the sound propagates through a first acoustical duct comprising a duct-volume (inner space of the casing)-duct arrangement, whereas another portion of the sound propagates through a second acoustical duct which is acoustically bypasses the inner space of the casing of the muffler. For example, the separation wall may be embodied as an inner pipe, or it may be embodied as a transverse separation wall arranged within a continuous pipe forming the inlet and outlet pipe, without these embodiment being exhaustive. The inlet and outlet pipes as well as the separation wall (embodied as inner pipe or as transverse separation wall) can be made of very thin metal so as to allow the reduction of weight when compared with prior art constructional approaches. Such weight reduction ultimately results in reduced fuel consumption and reduced CO2 emissions, thus being more favourable with respect to environmental aspects. Also, pressure losses like those caused by the Y-joints before and after the two branches in the prior art construction discussed above do not occur, thus further reducing fuel consumption and CO2 emissions.
In accordance with one aspect of the invention, the inlet pipe has an internal inlet pipe opening (into the inner space of the casing) for sound propagating along the first acoustical duct to enter the inner space of the casing, and the outlet pipe has an internal outlet pipe opening (out of the inner space of the casing) through which sound may exit the inner space of the casing. The separation wall includes an inner pipe arranged to extend at least from the internal inlet pipe opening to the internal outlet pipe opening.
This is a so-called “pipe-in-pipe” construction. For example, the inlet pipe as well as the outlet pipe can be fixedly attached (e.g. through welding) to the casing, so that the muffler can be attached to the exhaust system by connecting the inlet pipe to the upstream exhaust pipe and the outlet pipe to the downstream exhaust pipe. A part of the sound enters the inner space of the casing through the internal inlet pipe opening of the inlet pipe and exits from the inner space of the casing through the internal outlet pipe opening of the outlet pipe. The inner pipe forms an acoustical bypass that extends at least between the internal inlet opening of the inlet pipe and the internal outlet opening of the outlet pipe.
The “pipe-in-pipe” construction of the muffler according to the invention is a compact space-saving construction. Elements for compensating different thermal expansion which are difficult to manufacture and which are costly can be avoided. Moreover, no branch conduits branching off of a pipe wall are needed and, accordingly, the “pipe-in-pipe” construction—apart from the casing—comprises only simple conventional pipes, so that the muffler and its components are easy to manufacture.
Again, the muffler according to the invention, including the inner space of the casing, the inlet pipe, the outlet pipe and the inner pipe, is sized and shaped such that the muffler as a whole forms a high pass filter the cut-off frequency of which can be tuned such that the (relevant) higher engine orders are allowed to pass through so as to preserve the sportive sound characteristic. The inner pipe may form a duct which is acoustically separated from the inner space of the casing and may even be hermetically separated from the inner space of the casing, or may form a duct which is to some extent connected to the inner space of the casing, for example by comprising a number of holes provided in its wall. In any event, each of the measures is applied such that the cut-off frequency is such that the (relevant) higher engine orders are allowed to pass through so as to preserve the sportive sound characteristic.
According to a further aspect of the invention, the inner pipe has an overall length such that the inner pipe extends through the internal inlet pipe opening into the inlet pipe by a first insertion length and through the internal outlet pipe opening into the outlet pipe by a second insertion length. This makes sure that the part of the sound propagating through the inner pipe enters the inner pipe at a location upstream of the internal inlet opening of the inlet pipe. Likewise, the sound that has passed through the inner pipe exits the inner pipe at a location downstream of the internal outlet opening of the outlet tube. The insertion length can be used, for example, for tuning the cut-off frequency of the high pass filter since that portion between the location in the inlet tube where the inner pipe starts and the location of the internal inlet pipe opening as well as that portion between the internal outlet pipe opening and the location where the inner pipe ends in the outlet pipe both form an acoustical inductance.
According to one aspect of the invention, the inner pipe is fixed either only to the inlet pipe or is fixed only to the outlet pipe, and the outlet pipe or the inlet pipe to which the inner pipe is not fixed has a larger cross-sectional size than the cross-sectional size of the inlet pipe or outlet pipe to which the inner pipe is fixed.
When the mufflers are mounted to the chassis of a car, in operation they are exposed to mechanical vibrations. Since the inner pipe is fixed only to the inlet pipe or only to the outlet pipe the free end of the inner pipe (that end which is not fixed) may vibrate. In order to avoid mechanical contact between the free end of the inner pipe and the respective inlet pipe or outlet pipe upon vibration, the cross-sectional size of the respective inlet pipe or outlet pipe is sufficiently large, since such mechanical contact would result in rattling noises which are undesirable and may also negatively affect the lifetime of the muffler.
According to another aspect of the invention which may or may not be combined with the afore-mentioned aspect, the inner pipe is fixed either only to the inlet pipe or is fixed only to the outlet pipe. The inner pipe comprises a bent portion which is bent towards the center of the internal outlet pipe opening or towards the center of the inlet pipe opening to which the inner pipe is not fixed. This is also a constructive approach to avoid unintended rattling noises. The term “bent portion” includes every type of bending curvature which is technically feasible and is not limited to a particular bending method. The term “bent towards the center” includes every form which increases the distance between the inner pipe and the wall of the inlet pipe or the outlet pipe.
According to yet another aspect of the invention, the inner pipe is fixed to both, the inlet pipe and the outlet pipe. The inner pipe comprises a compensation element for compensating the thermal expansion of the inner pipe which is fixed to the inlet pipe and to the outlet pipe. Fixation of the inner pipe to both the inlet pipe and the outlet pipe provides for an increased mechanical stability of the inner pipe when compared to a single connection of the inner pipe to only one of the inlet pipe and outlet pipe. On the other hand, such fixation of the inner pipe to both the inlet pipe and the outlet pipe may cause problems upon thermal expansion and may cause high thermal stresses in the inner pipe or may cause the inner pipe to deform, since the cooling of the casing by the ambient air is much more efficient than the cooling of the inner pipe. The compensation element allows for compensation of the larger thermal expansion of the inner pipe while maintaining the advantage of the increased stability provided for by the fixation of the inner pipe to both, the inlet pipe and the outlet pipe.
In accordance with a further aspect of the invention, the inlet pipe has a first longitudinal axis and the outlet pipe has a second longitudinal axis. The first longitudinal axis and the second longitudinal axis are arranged parallel to one another (but not coincident). By arranging the inlet pipe and outlet pipe parallel to one another, the internal inlet opening and the internal outlet opening are offset relative to each other. The offset between the internal inlet pipe opening and the internal outlet pipe opening allows to fix the inner pipe to either the inlet pipe or to the outlet pipe, and at the same time due to the offset outlet pipe or inlet pipe, respectively, the free end of the inner pipe is arranged sufficiently spaced from the outlet pipe or the inlet pipe so as to avoid mechanical contact.
According to a further aspect of the invention, the inner pipe has a screw-shaped outer contour having an outer diameter such that the inner pipe firmly fits into the inlet pipe and into the outlet pipe. The screw shaped outer contour on one hand provides for a firm fit of the inner pipe in the inlet pipe and the outlet pipe. The firm fit is established along the entire part of the outer contour of the inner pipe which is arranged in the inlet pipe and the outlet pipe. A portion of the sound propagates through the “grooves” of the screw-shaped outer contour and enters the inner space of the casing (assuming that the outer contour is at least partially arranged in the inlet pipe). Upon exiting the inner space of the casing, this portion of the sound passes along the “grooves” of the screw-shaped outer contour. The other portion of the sound propagates through the inner pipe.
According to another aspect of the invention, the inlet pipe and the outlet pipe are formed by a continuous pipe completely extending through the casing and having at least one opening for sound to enter into and to exit from the inner space of the casing. The term “continuous pipe” is meant to describe a pipe that completely extends through the entire casing so that one end of the continuous pipe can be connected to an upstream exhaust pipe of the exhaust system and the other end of the continuous pipe can be connected to a downstream exhaust pipe of the exhaust system. Instead of having an inlet pipe having a dedicated internal inlet opening through which sound enters the inner space of the casing and an outlet pipe having a dedicated internal outlet opening through which sound exits the inner space of the casing, the continuous pipe which completely extends through the inner space comprises at least one opening (in its otherwise closed wall) for sound to enter into and exit the inner space through said at least one opening. The inner pipe is arranged in the said continuous pipe. This embodiment may impart good stability to the muffler with respect to vibrations that occur in operation (i.e. when being mounted to the chassis of the car).
According to one aspect of the invention, the continuous pipe is a single continuous pipe and comprises an integral compensation element for compensating thermal expansion of the single continuous pipe. The single continuous pipe is a single piece (which is either made from one single piece or which is made of two or more pieces which are welded together to form a single piece after welding, or which is joined by another suitable joining technique such as e.g. brazing) and does not have any flexible joints or separations in longitudinal direction. This may lead to thermal stress in the single continuous pipe which is connected to the casing, since cooling of the casing through the ambient air is much more effective (due to the large surface of the casing) than cooling of the single continuous pipe extending through the interior of the casing which has a much smaller surface which additionally is not exposed to the ambient air, so that the thermal expansion of the single continuous pipe is larger than that of the casing. To avoid such thermal stress in the single continuous pipe, the single continuous pipe comprises an integral compensation element, which may for example be embodied as metal bellows which can be made separately and welded between two pipe pieces so as to form a single continuous pipe having an integral compensation element.
According to another aspect of the invention, the continuous pipe comprises separate first and second pipes, and further comprises a compensation element slidably connecting the first and second pipes to form the continuous pipe. The first pipe and the second pipe are connected by the slidable compensation element so that the connection element does not have to be integral with the single continuous pipe. Such slidable connection element is easy to manufacture. The compensation element allows linear movement of the first pipe and the second pipe relative to one another in order to compensate for the different thermal expansions of the casing and the first and second pipes.
In accordance with yet another aspect of the invention, the inlet pipe or the outlet pipe or the continuous pipe (whichever is applicable) comprises projections extending inwardly from an inner wall of the inlet pipe or the outlet pipe or the continuous pipe. The projections are distributed circumferentially at different angular positions on the inner wall and protrude inwardly for a depth such as to fixedly mount the inner pipe. In principle, the shape and number of projections for fixedly mounting the inner pipe is not limited but can be chosen to provide a fixed support for the inner pipe so that the inner pipe is fixedly mounted to prevent it from vibrating when the muffler is in use. For example, multiples of three projections angularly spaced along the inner circumference of the continuous outer pipe by 120° may be provided. The three projections of a triple of projections angularly spaced by 120° advantageously are also spaced from one another in the longitudinal direction of the continuous pipe in order to reduce backpressure when compared to an arrangement of three projections of a triple of projections which are all arranged at the same longitudinal position.
In accordance with yet another aspect of the invention, the inner pipe forms a duct which is acoustically separated from the inner space of the casing, and in particular the inner pipe may be configured to hermetically separate the duct from the inner space. The term “acoustically separated” may also include cases in which there is a very small “leakage” between the duct and the inner space of the casing so that exhaust gases passing through the duct may to a very small extent (only a few percent) enter into the casing even though they travel through the duct. The term “hermetically separate” is to be understood in the sense that there is no such exhaust gas “leakage” anymore.
When discussing the pipe-in-pipe construction it has been outlined that generally the inner pipe may be acoustically separated or may even be hermetically separated from the inner space of the casing, or that it may be connected to the inner space of the casing. Both constructional options are possible, and this has to be taken into consideration when tuning the cut-off frequency of the high pass filter.
According to another aspect of the invention, the inlet pipe and the outlet pipe are formed by a continuous pipe completely extending through the casing, however, the separation wall is a transverse wall arranged within the continuous pipe so as to partition the continuous pipe into the first and second acoustical ducts. The continuous pipe has at least one opening in its wall at a location allowing sound propagating through the first acoustical duct to enter into and exit from the inner space of the casing.
This constructional approach is not a pipe-in-pipe construction but rather partitions the interior of one continuous pipe (with or without compensation element) into two partitions with the aid of the transverse wall. This constructional approach has a reduced number of separate parts since it does no longer have an inner pipe but nevertheless provides a duct which is acoustically separated from the inner space of the casing.
Further advantageous aspects of the invention become apparent from the following description of embodiments of the muffler according to the invention with reference to the schematic drawings in which:
Further advantageous aspects of the invention become apparent from the following description of embodiments of the muffler according to the invention with reference to the schematic drawings in which:
The muffler may form a component of an exhaust system of an internal combustion engine by connecting inlet pipe 3 to an upstream exhaust pipe (not shown) through which exhaust gas coming from the engine enters the muffler. The exhaust gas flows through inlet pipe 3 and a portion of the exhaust gas stream enters inner space 11 of the casing 1 through internal inlet pipe opening 31 (first acoustical duct 581 for the sound) while another portion of the exhaust gas stream flows through inner pipe 22 (second acoustical duct 21 for the sound). For exiting inner space 11, the exhaust gas flows through internal outlet pipe opening 41 into outlet pipe 4 which is connected to the downstream exhaust pipe, and from there further towards the end pipe of the exhaust system. That portion of the sound propagating in the exhaust gas along the first acoustical duct is acoustically attenuated in the inner space 11 of casing 1 in the manner well-known in the art. For attenuation of the sound, the size and shape of the casing 1 can be adapted to provide an inner space 11 in which the sound propagating through the exhaust gas interferes in a manner such as to get attenuated. Additional acoustic attenuation elements (not shown in
The size of the inner space 11 of the casing 1, of the inlet pipe 3, of the outlet pipe 4, of the inner pipe 22, as well as the insertion length b of the inner pipe 22 into the inlet pipe 3 as well as the insertion length c of the inner pipe 22 into the outlet pipe 4 are chosen such that the muffler as a whole acts as a high pass filter having a desired cut-off frequency. This cut-off frequency is chosen such that higher engine orders are allowed to pass through the muffler as a whole. Since the higher engine orders are known to be important for the sportive sound characteristic, they are thus preserved in the sound emitted from the exhaust system downstream of the muffler.
In this manner, a compact muffler is formed by having inner pipe 22 (or more generally the separation wall 2) extend through the inner space of the casing 1 and still preserving the higher engine orders in the sound emitted by the exhaust system to achieve a sportive sound characteristic. At the same time, the compact muffler is easy and comparatively inexpensive to manufacture.
Further embodiments of the muffler according to the invention in which the one end of inner pipe 22 is fixed to inlet pipe 3 and in which the other end of inner pipe 3 is a free end are shown in
Fixation of the inner pipe 22 to inlet pipe 3 (embodiment shown in
Returning to
While not being exhaustive, two embodiments how such slip joint may be realized are shown in
Exhaust gas and together with it the sound generally propagates along two different acoustical ducts. The first acoustical duct includes a spiral channel 25 extending helically along the outer surface of inner pipe 22, the spiral duct being formed by the “grooves” of the screw-shaped outer contour 28. The sound propagating along this first acoustical duct then enters inner space 11 of casing 1 and continues to propagate along spiral channel 25 formed by the “grooves” of the screw-shaped outer contour 28 of inner pipe 22 arranged in outlet pipe piece 401. Once it exits the spiral channel 25, it further propagates through outlet pipe pieces 401 and 400.
The second acoustical duct is formed by the interior of inner pipe 22. This duct is acoustically separated from the afore-described first acoustical duct and bypasses the inner space 11 of casing 1. As the sound exits inner pipe 22 it comes together with the sound that has propagated through the “grooves” of the screw-shaped outer contour 28, and the sound then further propagates through outer outlet pipe pieces 401 and 400. Again, the muffler as a whole forms the high pass filter having the desired cut-off frequency.
In the embodiment shown in
In the embodiment of
In the embodiment shown in
In
In
In
This kind of fixation of the inner pipe 22 is not limited to the fixation of the inner pipe 22 to the inner wall 37 of inlet pipe 3 but is also applicable to a fixation of the inner pipe 22 to the outlet pipe 4. Also, it is applicable to the fixation of inner pipe 22 to the continuous pipe 5 completely extending through the inner space of the casing.
Embodiments and aspects of the invention have been described with the aid of the drawings. However, various modifications and changes to these embodiments are possible without departing from the general teaching underlying the invention. In particular, combining features of different embodiments is conceivable as long as such combination of features is not contradictory. Therefore, the invention is not to be understood as being limited to the described embodiments, but rather the scope of protection is defined by the appended claims.
Number | Date | Country | Kind |
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12180707.7 | Aug 2012 | EP | regional |
This application is a Continuation of U.S. Ser. No. 13/967,121, filed 14 Aug. 2013, which claims benefit of European Patent Application No. 12180707.7, filed on 16 Aug. 2012, and which applications are hereby incorporated herein by reference. To the extent appropriate, a claim of priority is made to each of the above disclosed applications.
Number | Date | Country | |
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Parent | 13967121 | Aug 2013 | US |
Child | 14964803 | US |