This application claims benefit of Ser. No. 17/182,504.5, filed on 21 Jul. 2017 in the European Patent Office and which application is incorporated herein by reference. To the extent appropriate, a claim of priority is made to the above disclosed application.

FIELD OF THE INVENTION

The present invention relates to a method for forming a collar in a muffler housing of a muffler for an internal combustion engine.

BACKGROUND

Due to increasing flexibility requirements as well as the requirements to have common components for different vehicle platforms, mufflers, in particular rear mufflers, tend to be designed to accommodate the space below the trunk in a direction transverse to the driving direction. Such transverse muffler also allows for very easy design and integration of two tail pipes which are arranged on each side of the back of the vehicle. The transverse muffler is then located at the rear of the car beneath the trunk in a direction parallel to the rear axle. Although this arrangement allows the use of the distance between the two wheels, hence allowing a muffler length of up to 800 mm and more, this arrangement, however, requires that the height of the transverse muffler has to be reduced, in order to maintain the trunk capacity, when compared to the longitudinal mufflers oriented from front to rear in the direction of the vehicle (driving direction of the vehicle). Such flat shape of a transverse rear muffler allows the muffler to fit under the bottom floor of the trunk of the car with minimal trunk volume loss.

In order to allow easy integration of the transverse muffler with the exhaust system, side entry—meaning an exhaust pipe entry through the muffler housing on the longitudinal side of the muffler conveying the exhaust gases from the internal combustion engine to the muffler—of the exhaust pipe through the wall of the muffler shell into the muffler is of particular interest as the exhaust pipe(s) upstream of the transverse rear muffler conveying the exhaust gases into the rear muffler are typically positioned in the middle tunnel underneath the car. It is therefore beneficial that the exhaust tube enters the transverse rear muffler through the muffler shell of the muffler in order to prevent additional exhaust pipe length and additional bends (curved pipe portions) leading to additional backpressure, costs and reduced compactness of the exhaust system. Alternatively, side exit, meaning an exit pipe emanating from the muffler housing on the longitudinal side of the muffler for discharging the exhaust gasses from the muffler, may be required.

For allowing leak-tight and secure connection, the formation of such side entry or side exit includes the formation of a collar for connecting the exhaust tube or the exhaust pipe to the transverse muffler. In particular, the side entry will be located on the side of the flat transverse muffler where the radius of curvature of the muffler shell is small. Problems occur, however, during formation of the collar at such highly curved positions, such as rupture of the muffler shell sheet and reproducibility of the tubular connection regarding, for example, tube welding.

Therefore, making the collar hole on the side of the transverse muffler is a technical challenge, especially for very flat mufflers where the collar has to be made in an area of the muffler shell where the radius of the muffler shell is very small and hence strongly curved. In extreme cases, the diameter of the collar, which needs to fit the diameter of the exhaust pipe, is only marginally smaller than the height of the muffler itself. Such a situation particularly occurs for exhaust systems for powerful engines with high mass flow rates which need large pipe diameters.

Current methods to generate collars are based on stamping and drawing, making use of a punch (or die) to be pulled in one or more linear strokes, for example several dies with increasing diameter.

The existing methods have drawbacks for making collars in highly curved sheets such as in flat transverse mufflers with a collar situated in the curved region of the muffler shell. One drawback is that the material the muffler shell is made of, generally steel, cannot flow sufficiently from the highly curved muffler shell to the corner when pulling the die through the hole. Extreme thinning occurs up to the rupture limit where the collar starts to crack. When a crack occurs in the collar, the muffler shell or even the entire muffler has to be scrapped because the connection between the muffler and the exhaust tube would not be durable and leak-tight. In order to avoid cracks, multiple dies having increasing diameters may be used in a step-by-step process, thereby stepwise forming the collar. Such step-by-step process, described in the following for a rolled shell muffler, involves multiple process steps during which each die has to be first introduced into the inner space (interior) of the muffler through the end cap openings where the end caps close the muffler at a later stage, because the die, having a diameter larger than the side entry hole, cannot be introduced into the inner space (interior) of the muffler through the side entry hole. This requires that the collar is formed while the interior components (e.g. baffles) of the muffler are not yet inserted (i.e. before stuffing). At this stage, the muffler housing is not supported by the baffles, for example, and can therefore be easily deformed during formation of the collar. Such deformation of the muffler housing is not acceptable and the muffler housing has to be scrapped. Therefore, this procedure is a very time-consuming and very expensive multiple step process which does not ensure proper collar formation without cracks. Even in case the collar is formed without cracking, the end circumference of the collar is crenated due to the large deformations caused. Crenations are generally roughness of the collar mouth and initiations of cracks around the collar that are generated by the collar forming step with the state of the art methods.

Crenations have a negative impact on the durability of weld connections between the exhaust pipe and the side entry collar, making additional steps of machining necessary to eliminate crenations. Besides such additional machining step being time-consuming and expensive, the metal burrs or particles generated by machining are not desired, as they may get trapped in the end product. Such metal burrs or particles may then cause rattling noises in the muffler. Removal of machining burrs, constantly cleaning the tools etc., once again increase the complexity and the costs of the production.

It is therefore an object of the present invention to overcome the drawbacks of existing methods of making collars.

In order to overcome these problems, the present invention suggests a method as it is specified by the features of the independent claim. Embodiments of the method according to the invention are the subject of dependent claims.

SUMMARY OF THE INVENTION

The invention relates to a method for forming a collar in a muffler housing for a muffler for an internal combustion engine, the method comprising:providing a muffler shell made of a metal sheet and forming a muffler housing, the muffler shell having an exhaust gas opening,providing a collar forming head having a rotational axis and at least two movable expanders,introducing the collar forming head into the muffler housing, wherein the expanders are in a retracted position, by moving the retracted collar forming head along the rotational axis through the exhaust gas opening in the muffler shell, wherein the retracted collar forming head has a largest diameter smaller than a largest diameter of the exhaust gas opening in the muffler shell,moving the expanders of the collar forming head introduced into the muffler housing radially away from the rotational axis of the collar forming head from the retracted position to an expanded position, in which the largest diameter of the expanded collar forming head radially to the rotational axis is larger than the largest diameter of the exhaust gas opening,rotating the collar forming head around the rotational axis of the collar forming head,bringing the rotating expanded collar forming head in contact with the metal sheet adjacent to and surrounding the exhaust gas opening in the muffler shell by moving the expanded collar forming head along the rotational axis in a direction outwardly from the interior of the muffler housing,forming an outwardly projecting collar around the exhaust gas opening by flaring the edge of the metal sheet surrounding the exhaust gas opening outwardly and increasing the size of the exhaust gas opening by moving the expanded collar forming head along the rotational axis (in a direction outwardly from the interior of the muffler housing to the exterior of the muffler housing).

The smallest diameter of the exhaust gas opening is the largest diameter of a circle or cylinder which is confined by the exhaust gas opening. The largest diameter of the exhaust gas opening is the smallest diameter of a circle or cylinder which confines the exhaust gas opening. In particular, these diameters are measured in a plane projecting radially away from and perpendicular to the rotational axis of the collar forming head.

When the exhaust gas opening has an elongation and the collar forming head is not circular and has a largest diameter smaller than a largest diameter of the exhaust gas opening in the muffler shell, but larger than the smallest diameter of the exhaust gas opening, the collar forming head is introduced into the exhaust gas opening in a position in which the elongation of the collar forming head is in the direction of the elongation of the exhaust gas opening. Particularly, however, the largest diameter of the collar forming head may be smaller than the smallest diameter of the exhaust gas opening in the muffler shell.

The expanders of the collar forming head may be moved in a radial direction away from the rotational axis. This movement may be performed in a direction perpendicular to the rotational axis or alternatively inclined at an angle relative the direction perpendicular to the rotational axis.

The exhaust gas opening may be the raw opening before any collar formation has been done or an already existing collar formed in a previous step of the collar formation in case of stepwise formation of the collar.

The rotation of the collar forming head has to occur at the stage of bringing the expanded collar forming head in contact with the metal sheet adjacent to and surrounding the exhaust gas opening. The collar forming head may, however, already rotate at any time before this step.

The method according to the invention allows for very efficient and reliable collar formation in a muffler housing while reducing the risks of cracks. This method is particularly advantageous for double layered muffler shells forming the muffler housing. In particular, the rotation of the expanders allows a very gentle formation of the collar in order to form a collar of excellent quality.

The method allows for collar formation in a muffler housing of a rolled envelope type muffler (muffler housing made of one muffler envelope—which may comprise one or more layers of metal sheet—rolled to form the muffler housing) or half-shell type mufflers (muffler housing made from two muffler shell halves joined together). In the half-shell type muffler, either one shell half or both shell halves have an exhaust gas opening. Outwardly projecting collars may be formed on one or more of the exhaust gas openings either for the half-shell type muffler or for the rolled envelope type muffler.

In case of a half-shell type muffler, the muffler housing comprises two shell halves which are joined together to form the muffler housing. When referring to the muffler shell or to the muffler housing, it is to be understood that the muffler shell or the muffler housing may be formed by two half-shells.

The collar formation may be particularly performed in one step. This means that the collar is particularly formed without incremental step-by-step formation of the collar. The diameter of the collar forming head has the diameter of the final collar to be formed during the step of collar formation.

According to a further aspect of the method according to the invention, the method further comprises the step of inserting muffler interior components into the muffler housing which is performed prior to the step of forming the outwardly projecting collar.

The insertion of the muffler interior components prior to the step of forming the collar allows for a very efficient manufacturing process of the muffler and reduces the risk of distortions of the muffler housing which is supported by the muffler interior components.

According to yet a further aspect of the method according to the invention, the method further comprises a step of inserting the muffler interior components into the muffler housing which is performed after the step of forming the outwardly projecting collar

The insertion of the muffler interior components after collar formation is particularly advantageous in case an internal pipe is already attached to the muffler interior before insertion into the muffler housing. In case of a half-shell type muffler, for example, the muffler interior components may then be easily introduced into one of the half shells of the muffler, before the second half shell is joined to the first half shell to close the muffler. Insertion of the muffler interior after collar formation may also be advantageous in case of an internal pipe having a bend as introduction into the interior space of the muffler housing is simplified.

Still in accordance with a further aspect of the method according to the invention, the method comprises inserting an internal pipe into the muffler housing through the outwardly projecting collar. The insertion of the internal pipe may be done from the inside (interior space of the muffler housing) of the muffler housing through the outwardly projecting collar towards the exterior of the muffler housing (in this case before the insertion of the muffler interior components) or from the outside of the muffler housing through the outwardly projecting collar into the inner space of the muffler housing (in this case either before or after the insertion of the muffler interior components).

The internal pipe penetrates into the housing of the muffler for introducing exhaust gas into or for discharging exhaust gas from the muffler. The internal pipe may have a plurality of punched apertures along the circumference. Thus, the high frequencies contained in the exhaust noise are reduced and the exhaust noise is tuned to a low noise in low and middle frequency bands. The internal pipe particularly protrudes outwardly from the collar mouth over a distance of up to 10 mm, particularly up to 5 mm, very particularly from 1 mm to 3 mm.

Yet in accordance with another aspect of the method according to the invention, forming the outwardly projecting collar around the exhaust gas opening comprises the formation of a collar wall and after the step of inserting of the internal pipe the internal pipe is expanded to contact the wall of the outwardly projecting collar.

The step of expanding the internal pipe to contact the wall of the outwardly projecting collar is also referred to as calibration. The calibration allows for a leak-tight joint in the muffler manufactured. Additionally, the calibration allows for reproducibly and durably joining the pipes in the muffler manufactured either by mechanical locking, such as ridge lock, or by welding.

According to still a further aspect of the method according to the invention, the method comprises the step of inserting an external pipe into the internal pipe through the outwardly projecting collar.

The external pipe is, for example, an inlet exhaust tube conducting the exhaust gases from the internal combustion engine to the muffler or a tail pipe for discharging the exhaust gases from the muffler. The external pipe is particularly welded to the outwardly projecting collar. Particularly, when the internal pipe projects outwardly from the collar mouth, the weld will join the external pipe, the internal pipe and the outwardly projecting collar.

According to a further aspect of the method according to the invention, the step of providing a muffler shell comprises forming a rolled envelope muffler housing made from the muffler shell.

According to an alternative aspect of the method according to the invention, the step of providing a muffler shell comprises providing two muffler shell halves for forming a muffler housing made from two muffler shell halves, and wherein the exhaust gas opening is provided in at least one of the muffler shell halves.

In case of a half-shell type muffler, the step of forming an outwardly projecting collar is particularly performed after the step of inserting the muffler interior components into muffler housing and joining the two muffler shell halves to form a closed muffler housing. This sequence allows for the formation of the outwardly projecting collar on a particularly stiff muffler housing. The muffler interior components include, for example, baffles and pipes.

In accordance with a further aspect of the method according to the invention, the step of providing a muffler shell comprises providing at least one flat metal sheet comprising the exhaust gas opening, and rolling the metal sheet to form the muffler housing or deep drawing the metal sheet to form at least one of two shell halves.

In accordance with another aspect of the method according to the invention, the step of providing a muffler shell comprises providing two flat metal sheets and deep drawing the metal sheets to form two shell halves and forming the exhaust gas opening during the deep drawing step in at least one of the shell halves.

Still in accordance with a further aspect of the method according to the invention, the step of providing a muffler shell comprises providing at least one flat metal sheet, rolling the metal sheet to form the muffler housing or deep drawing the metal sheet to form at least one of two shell halves, and subsequent to the rolling or deep drawing step forming the exhaust gas opening.

In accordance with a still further aspect of the method according to the invention, the step of providing a muffler shell comprises providing a muffler shell with an elongated exhaust gas opening adapted to form a collar having a planar mouth in a direction radial to the rotational axis.

A planar mouth with a smooth edge having no crenations allows a reliable, reproducible and durable joint connection with the exhaust pipe, e.g. by robot welding, thereby minimizing manual weld repairing.

Hence, a planar mouth is particularly advantageous for collar forming on mufflers when two tubes and a collar are welded together at the same time with one weld. The internal tube which is inserted into the muffler through the formed collar has a straight cut and slightly protrudes from the collar mouth. The external tube (e.g. the intermediate tube in the tunnel, or the tailpipe) is inserted inside of the internal tube (typically over a depth of 15 to 30 mm). The planar mouth of the collar allows easy welding along the cut of the internal tube, such that by welding the internal tube, the external tube and the collar mouth are joined together by the weld.

The method according to the invention avoids machining of the collar for the reliable connection of the exhaust pipe to the collar. Furthermore, this method prevents burrs and particles from the machining to enter the interior of the muffler, leading to additional steps of removal of the debris from the muffler. In particular, the elongated exhaust gas opening may be elliptical or oval and is designed and tuned to avoid machining subsequent to the collar forming step.

In accordance with another aspect of the method according to the invention, the step of forming an outwardly projecting collar comprising a collar mouth at the end of the collar, in a direction away from the muffler shell, comprises forming a collar mouth having a circular shape.

In particular, providing a collar forming head comprises providing a collar forming head having expanders configured to be moved into various expanded positions, thereby varying the diameter of the expanded collar forming head.

Such configuration allows for a flexible use of the method which is then adapted for the formation of collars for diverse exhaust pipes with different diameters to be connected to the side entry of the muffler. Additionally, this method allows for incremental step-by-step formation of the collar by increasing stepwise the diameter of the collar forming head.

The step of introducing a collar forming head in a retracted position into the muffler housing of the muffler, moving the expanders of the collar forming head to an expanded position and bringing the rotating expanded collar forming head in contact with the metal sheet surrounding the exhaust gas opening in the muffler shell may alternatively be repeated for a step-by-step formation of the collar by step-by-step increase of the diameter of the collar forming head.

The steps are, in the incremental process, repeated until the final diameter of the collar is reached. This incremental method is facilitated by the particular use of the collar forming head. In addition to the rotation of the collar forming head, the incremental method allows for an even more gentle formation of the collar in the muffler housing.

The step of forming an outwardly projecting collar comprising a collar mouth at the end of the collar, in a direction away from the muffler shell, may comprise forming a collar mouth having a circular shape. The collar mouth may alternatively be elongated and have an elliptical or oval shape, for example.

The step of providing a collar forming head may particularly comprise providing a collar forming head movable along the rotational axis towards and away from the exhaust gas opening in the muffler shell and having expanders configured to engage portions of said muffler shell adjacent to and surrounding the exhaust gas opening to form a collar, a mounting portion holding the expanders on the collar forming head, the expanders being configured for a movement radially of the rotational axis between a retracted position and an extended collar forming position.

The step of providing a collar forming head may comprise providing a collar forming head, an actuator for moving said collar forming head relatively to the exhaust gas opening in the muffler shell into and away from the exhaust gas opening along an axis, expanders adapted to engage portions of the muffler shell adjacent to and surrounding the exhaust gas opening to form a collar, and a mounting portion movably holding the expanders on the collar forming head configured for a movement axially and radially with respect to the rotational axis between a retracted position and an extended collar forming position, wherein at least portions of the expanders come to lie under the edge of the muffler shell adjacent to the exhaust gas opening in the expanded position.

The expanders may be inclined with respect to the rotational axis.

Each and every feature described herein, and each and every combination of two or more of such features, is included within the scope of the present invention provided that the features included in such a combination are not mutually inconsistent. In addition, any feature or combination of features may be specifically excluded from any embodiment of the present invention.

