WO2001018365A1

WO2001018365A1 - Arrangement at a silencer and method for reduction of noise from a gas flow

Info

Publication number: WO2001018365A1
Application number: PCT/SE2000/001695
Authority: WO
Inventors: Ahmed El-Bahrawy
Original assignee: Volvo Personvagnar Ab
Priority date: 1999-09-06
Filing date: 2000-09-04
Publication date: 2001-03-15
Also published as: SE9903168L; SE9903168D0; SE521329C2

Abstract

An arrangement for providing a noise silencing unit (3) for reducing noise from a gas through flow, which comprises at least a first flow path for said gas flow and a detection arrangement in connection with said first flow path for detecting the pressure of the gas flow. Further the arrangement comprises a switching arrangement with an adjustable throttle for blocking the first flow path to a first opening degree at detecting a pressure which is below a predetermined first limit value (p0), whereby the throttle is arranged for opening to a second opening degree if the first limit value (p0) is exceeded, and the throttle is arranged for opening to a third opening degree at detecting a pressure exceeding a predetermined second limit value (p1). The first opening degree corresponds to less than about 15% of the complete sectional area of the first flow path at the throttle, and that the second opening degree corresponds to more than about 30% and less than about 60% of the complete sectional area, and the third opening degree corresponds to more than about 90% of the complete sectional area.

Description

Title

Arrangement at a silencer and method for reduction of noise from a gas flow

Technical area The present intention relates to an arrangement at a silencer, according to the preamble of the following claim 1. In particular, the invention is intended to be used as, or in connection with, a silencer intended for an exhaust system in a motor vehicle. The invention also relates to a method for reduction of noise from a gas flow, according to the preamble of the following claim 14.

The background of the invention

Vehicles being driven with assistance of a combustion engine normally also comprise an exhaust system being used for leading away the contaminants of the engine exhausts, which are generated at the combustion of the engine fuel. In this context, there is a general desire to lead away the exhausts of the vehicle while as little noise as possible is generated by the gas flow.

Contemporary exhaust systems, intended for example for passenger cars, comprise an exhaust pipe, at least an exhaust silencer and normally also a catalytic converter. Concerning the silencer, it is used for balancing out pulsations of the gas flow and thereby making them so inaudible as possible. In such a way, the noise level of the gas flow may be decreased.

In addition the requirement of a low noise level, requirements are also set forth to create the exhaust system as small as possible, since passenger cars have further reduced building-in volume available.

For complying with the requirement of the noise reducing capacity of a silencer in an exhaust system, it is previously known to arrange this so that it can switch between different conditions, where a first condition is characterised by a low engine load. When this condition exists, the gas flow may be lead along a certain flow path with a particular good noise reduction capacity. This gives a low noise level of the exhaust system, in particularly when the vehicle stands still and is driven in idle. When said first condition does not exist, the gas flow may be lead along another flow path in the exhaust system. According to known technique, the gas flow may be switched between the different flow paths with assistance of an electromechanical or pneumatic regulator, which is provided with an input signal from the actual engine. Then the gas flow may be switched between the different flow paths with the assistance of such a regulator.

A substantial drawback of the arrangement known in the present technical area, refers to the fact that there is a risk that too a high backpressure in the exhaust system occurs at a high engine load and speed. This may in turn lead to reduced engine power, which of course is a drawback, in particular, at working conditions, which are characterised by high engine speeds. A further drawback is that known systems require a relatively large building-in volume, which is a problem, particularly in relation to contemporary passenger cars having a very limited available space.

Thus, there is a need of reversible arrangements at the silencer units, which, in particular, gives an effective noise reduction, a small building-in volume and a low backpressure at high speeds.

The patent application no. SE 9704221-2 of the applicant describes an improved arrangement for reducing noise of a gas through flow which provides the advantages mentioned above. The arrangement according to SE 9704221-2 comprises a first flow path and a second flow path for the gas flow, and also a switching arrangement for alternating control of the gas flow along the first flow path and the second flow path, respectively. Further the arrangement described comprises a detection arrangement for detecting the pressure of the gas flow, whereby the switching arrangement comprises an adjustable throttle valve for blocking the first flow path when detecting a pressure, which is below a predetermined limit value, so that the gas flow is lead through the second flow path, and further the throttle is arranged to be opened if the limit value is exceeded, so that the gas flow is lead along the first flow path.

However, there remains a need of arrangements which, having a minimum space requirement and lowest possible weight, can achieve an ever more efficient silencing of noise. Summary of the invention

Thus, the object of the present invention is to provide a further improved arrangement at, or as in itself provides, a noise silencing unit, in particular intended for an exhaust system of a motor vehicle, at which the problem above is solved. This object is obtained by means of an arrangement, which features appear in the following claim 1, and a method the features of which appear in the following claim 14.

The arrangement according to the invention provides or comprises a silencing unit for reducing noise of a gas through flow. The arrangement comprises at least a first flow path for the gas flow, and a detection arrangement in connection with the first flow path for detecting the pressure of the gas flow. Further the arrangement comprises a switching arrangement with an adjustable throttle for blocking the first flow path to a first opening degree when detecting a pressure which is below a predetermined first limit value. Further the throttle is arranged for opening to a second opening degree if the first limit value is exceeded, and for opening to a third opening degree when detecting a pressure exceeding a predetermined second limit value. Thereby, the first opening degree corresponds to less than about 15% of the complete sectional area of the first flow path at the throttle, while the second opening degree corresponds to more than about 30% and less than about 60% of the complete sectional area, and the third opening degree corresponds to more than about 90% of the complete sectional area.

According to the invention, a number of advantages are obtained in relation to the arrangements previously known. Firstly, it should be established that the invention, by means of the particularly adjusted opening characteristics of the throttle, admits a very efficient noise reduction at a low engine load, and moreover a low pressure drop at increasing engine load. A further advantage is that the invention gives a very low back pressure of the gas flow in the working operations which are characteristic at high engine speeds, i.e. when the throttle mentioned above is opened to the third opening degree. By the fact that the invention uses the available pressure which exists at the inlet of the noise reducing unit, good possibilities are given as well to a simple and effective control of the position of the throttle. An additional advantage of the invention is that it requires a very small building-in volume in a vehicle. In a particularly preferred embodiment of the arrangement according to the invention, the first opening degree corresponds to more than about 8% and less than about 12% of the complete sectional area of the first flow path. This embodiment makes it possible to completely or partly replace a silencer unit of an engine vehicle with the arrangement according to the invention which requires a minimum space and obtains a very low weight, since a first opening degree within the range indicated above, enables idling without use of any particular flow paths provided for idling or the like.

Further preferred embodiments of the invention appear in the following dependent claims.

Description of the figures

The invention will be described more in detail in the following with reference to an embodiment and the enclosed drawings, where:

Fig. 1 substantially shows a perspective view of an arrangement according to a preferred embodiment of the present invention,

Fig. 2. shows a simplified sectional view of a silencer unit according to a preferred embodiment of the invention,

Fig. 3 shows a simplified sectional view of a throttle arrangement according to a preferred embodiment of the invention, and

Fig. 4. shows a graph illustrating a particularly preferred opening characteristic of a throttle, which is a part of the arrangement according to the invention.

Preferred embodiment

In figure 1 an arrangement, according to the present invention, is shown in principle, in which the embodiment as shown in fig.l is intended to be arranged at a silencer unit 3 for reducing noise of a gas through flow.

The arrangement according to the invention comprises at least a first flow path 4, 5, 6 for the gas flow and also a detection arrangement 12 which is connected to the first flow path for detecting the pressure of the gas flow. Further the arrangement comprises a switching arrangement 7, 11 with an adjustable throttle valve 7 for blocking the first flow path 4, 5, 6 to a first opening degree when detecting a pressure which is below a predetermined limit value p₀. Thereby the throttle 7 is arranged to open to a second opening degree if the first limit value p₀ is exceeded, and for opening to a third opening degree when detecting a pressure which exceeds a predetermined second limit value p,.

According to the invention, the first opening degree thereby corresponds to less than about 15% of the complete sectional area of the first flow path 4,5,6 at the throttle, while the second opening degree corresponds to more than about 30% and less than about 60% of the complete sectional area, and the third opening degree corresponds to more than about 90% of the complete sectional area.

By means of the opening characteristic of the throttle 7 specified above, a number of the purposes indicated above and the advantages of the present invention are obtained.

In a particularly preferred embodiment of the invention, the first opening degree corresponds to more than about 8% and less than about 12% of the complete sectional area of the first flow path at the throttle.

As previously it has been mentioned, moreover the particularly preferred embodiment makes it possible to completely or partly replace a silencer unit of an engine vehicle with the arrangement according to the invention which requires a minimum of space and obtains a very low weight, since a first opening degree within the range indicated above enables idling without use of any particular flow paths provided for idling or the like.

The preferred first opening degree is particularly preferably obtained by means of the fact that the throttle 7 is provided with a hole (not visible in the figures) with an adjustable size. However, it is also possible with embodiments where the first opening degree aimed at is obtained by giving the throttle a diameter being less than the diameter of the first flow path, or by providing the throttle is provided with apertures, rim notches or the like. Further the desired first opening degree may be obtained by tilting the throttle to some degree, i.e. opened, at the blocking of the first flow path. In the particularly preferred embodiment of the arrangement according to the invention, the opening of the throttle 7 from the second to the third opening degree is arranged to occur during an increase of the pressure from the second limit value p„ which is less than about 1,0 kPa.

Further in the particularly preferred embodiment, the switching arrangement 7, 11 the exhaust cut-out 7 is arranged for a substantially linear opening movement between the first and the second opening degree and/or between the second and third opening degree, and reversed also for a substantially linear blocking movement.

Tests have proven that a linear opening movement and reversed blocking movement as well, i.e. the movement of the throttle to a closed position, altogether provides the best compromise between noise reduction effect and (undesired) effect loss at for instance different speeds of a combustion engine.

It has also been shown to be particularly preferred that the opening of the throttle from the second to the third opening degree runs as quickly as possible, i.e. that the graph shown in fig.4 rises as quickly as possible from p, and upwards. The reason for this is that the flow noise of the gas flow dominates at high speeds and gas flow velocities/- pressures. Since such flow noise may not be considerably reduced by means of throttling this is unnecessary at high pressures, and would only cause of undesired effect losses at pressures, which are higher than p,.

In the particularly preferred embodiment, the first limit value p₀ corresponds to a pressure of the gas flow which is between 7 and 9 kPa, while the second limit value (p_{) corresponds to a pressure of the gas flow which is between about 11 and 13 kPa. These pressure ranges are considered to be optimum for many combustion engines, but it is, however, possible having alternative embodiments of the arrangement according to the invention using other pressure ranges.

The arrangement according to the invention is, as evident from above, particularly preferred in itself, such as appeared above, a silencer unit that completely or partly replaces conventional silencers in an exhaust system. In a preferred embodiment, which is illustrated in the enclosed figures 1 and 2, the arrangement according to the invention is, however, arranged at a silencer in an exhaust system of an engine vehicle. In this embodiment the arrangement comprises a first connection pipe 1 arranged to be connected together with an (not shown) exhaust pipe for feeding a gas flow of a combustion engine not shown located in the vehicle. Hereby the exhausts flow in the direction being indicated with arrows in figure 1. Further the arrangement shown comprises a second connection pipe 2 established to be connected to an additional (not shown) exhaust pipe being arranged to lead the gas flow further out in the atmosphere. Thus, it is realised that the first connection pipe 1 is arranged upstream in relation to the second connection pipe 2 concerning the flow of the gas flow through the system.

Between the two connection pipes 1,2 in the embodiment described, a silencer unit 3 is provided. According to what is evident from figure 1 this comprises a first perforated pipe section 4, which is connected to and constitutes an extension of the first connection pipe 1. The first perforated pipe section 4 is substantially cylindrically shaped and is connected to an intermediate, not perforated pipe section 5, which in its turn is connected to a second perforated pipe section 6 of the same type as the first perforated pipe section 4. Finally, the second perforated pipe section 6 is connected to the second connection pipe 2. It is also possible having embodiments of the invention where no such perforated pipe sections exist.

According to what will be described in detail below, the intermediate section 5 of the described embodiment contains an adjustable throttle 7, preferably in shape of a circular disc. Further the pipe sections 4, 5, 6 are preferably shaped and dimensioned in such a way which is advantageous concerning its noise reducing characteristics. For instance, either of the pipe sections 4, 5, 6 may be tuned by an appropriate choice of volume, sectional area etc. to function as a high pass filter, which enables reducing noise which arises in the gas flow flowing through. As a complement to such a shaping, the pipe sections 4, 5, 6, respectively, may also comprise noise reducing materials, e.g. in the form of mineral wool or the similar. The perforated pipe sections 4,6 are connected to a second silencing volume 8 via their perforations, which silencing volume 8 is shaped as a substantially cylindrically housing with a somewhat larger diameter than the perforated sections 4, 6 and the intermediate section 5. The silencing volume 8 is preferably arranged substantially concentrically in relation to the pipe sections 4, 5, 6 and thus surrounding these sections. The silencing volume 8, thus constituting a part of the silencing unit 3, is dimensioned in a corresponding way as the pipe sections 4, 5, 6, so as to provide a noise reducing effect for exhausts flowing through. As a complement to this, the silencer volume 8 may also comprise noise-reducing materials, e.g. mineral wool. As evident from above, it is also possible having embodiments of the invention where no such particularly silencing volumes exist.

In the embodiment described, the gas flow of the engine may be controlled by means of the opening degree of the throttle either along a first flow path or along a second flow path, depending on whether certain predetermined conditions exist in the present engine. In closer detail, these conditions are characterised in that the engine is driven with proportionately low load and speed or proportionately high load and speed, respectively. Thereby, these conditions may be detected by means of detecting the pressure existing from the gas flow, which gas flow comes into the silencer 3. The first flow path is defined by the first perforated pipe section 4, the intermediate section 5 and the second perforated pipe section 6. According to what will be described in detail below, the gas flow is guided along this first flow path at a relatively high load and high speed of the engine. Contrary hereto, the second flow path is defined by the first perforated pipe section 4, the silencing volume 8 and the second perforated section 6 as well. The gas flow is guided along the second flow path at a relatively low load and low speed of the engine. Thus in the embodiment described, the first opening degree of the throttle may be 0%, i.e. the throttle may completely close the first flow path, since the second flow path still admits the passage of the gas flow past the throttle. As apparent from above, no second flow path exists in the particularly preferred embodiment, but the gas flow may instead pass the throttle having an opening degree which is larger than 0 % via the first flow path only. For controlling the gas flow along one of the two flow paths, the throttle 7 mentioned above, is used, which in the embodiment described constitutes a switching arrangement for alternating switching between the two conditions mentioned above. For this object, the throttle 7 is suspended on an shaft spindle 9, which in turn is pivotably suspended in the intermediate section 5 and has its extension substantially perpendicular to the longitudinal direction of the intermediate section 5. The pivotably axle 9 may be controlled to be rotated with assistance of a lever arm 10, which in turn is joined to a draw rod 11. This draw rod 11 constitutes a part of a particular valve arrangement 12, which according to the embodiment is a type of diaphragm valve and will be described in greater detail below. A pressure pipe 13 is also connected to the valve arrangement 12, which pressure pipe 13 helps exhausts under pressure to become deflected from the first connecting pipe 1 and further to the valve arrangement 12, which is indicated with a dotted arrow in figure 1. With assistance of the valve arrangement 12 the existing pressure level of the gas flow is used for controlling the throttle 7.

The appearance and the function of the silencing unit 3, of the embodiment described, appear in the figure 2. This figure shows a somewhat simplified sectional view, seen from the side, from which appears that the throttle 7 may be brought in a position where the intermediate section 5 is blocked for passage of the entering gas flow, i.e. the throttle is lead to the first opening degree. In this position the gas flow, in the embodiment described, is forced into the surrounding silencer volume 8 by the perforations of the first perforated section 4. The gas flow is fed along the silencer volume 8 and further out through the perforations in the second perforated section 6 to the second connecting pipe 2. The throttle 7 is brought in the position, shown in figure 2, at a condition which is characterised of low load and low speed of the actual engine, which corresponds to a proportionately low gas flow and pressure of the gas flow. In an opposite way according to the invention, the throttle 7 may be brought into an open position at a high load and a high speed of the actual engine, i.e. the throttle may be brought to the second opening degree, or to the third opening degree at very high load. This leads to that the gas flow follows the flow path which is defined by the perforated sections 4, 6 and the intermediate section 5, i.e. substantially without passing through the silencer volume 8. The function of the valve arrangement 12 will now be described in particular with reference to figure 3, which is a somewhat simplified sectional view. With assistance from a two-way arrow, which is indicated in the figure, the draw rod 11 is arranged so it can be displaced upwards and downwards inside a housing 14 which further surrounds the valve arrangement 12. The housing 14 is substantially formed as a cylindrical container, and also comprises a rigid intermediate wall 15 and two diaphragms 16,17. The diaphragms 16, 17 are produced of an elastic material, preferably of rubber or another material with the corresponding characteristics.

The housing 14, the intermediate wall 15 and the diaphragms 16,17 together define four different chambers 18, 19, 20 and 21, respectively. The first chamber 18 is delimited by the housing 14 and the first diaphragm 16, and composes a chamber to which the pressure pipe 13 is connected. Thus, a certain pressure exists in this first chamber 18, which size depends on the gas flow and the pressure in the first connecting pipe 1 (see figure 1), and thus also of the current operating condition of the actual engine.

The second chamber 19 is delimited by the first diaphragm 16 and the intermediate wall 15, and is connected to the surrounding atmosphere via an opening 22. Thus, atmospheric pressure always exists in the second chamber 19.

The third chamber 20 is delimited by the intermediate wall 15 and the second diaphragm 17, while the fourth chamber 21 is delimited by the second diaphragm 17 and the interior bottom surface of the housing 14. The fourth chamber 21 is connected to the surrounding atmosphere via an additional opening 23. Thus, atmospheric pressure always exists in the fourth chamber 21.

A first spring 24 is arranged between the first diaphragm 16 and the intermediate wall 15, which spring preferably constitutes a helix spring. This spring 24 is arranged so as it exerts a force against the first diaphragm 16, whereby this aims to adopt the condition shown in figure 3. This condition corresponds to that the draw rod 11 is in its top position, which in turn corresponds to that the throttle 7 (compare figure 1) is in its closed position, i.e. lead to the first opening degree. Further it is valid, that the draw rod 11 is shaped with an extension which constitutes a substantially cylindrical section 25 with elongation inside the housing 14. More in detail, the cylinder 25 runs through a hole 26 in the topside of the housing 12 and through a hole 27 in the first diaphragm 16. The cylinder 25 is fixedly connected to the first diaphragm 16 as far as that the cylinder 25 (and thus also the draw rod 11) is effected to be displaced upwards or downwards at a corresponding effect with a pressure force against the first diaphragm 16. Further the cylinder 25 is provided with at least a through hole 28, constituting a connection between the interior of the cylinder 25 and the first chamber 18.

The cylinder 25 has its extension through a hole 29 in the intermediate wall 15 and through an additional hole 30 in the second diaphragm 17. Analogously to what has been stated above, the cylinder 25 is connected to the second diaphragm 17 so that the cylinder 25 (and thus also the draw rod 11) is effected to be displaced upwards or downwards at the corresponding effect on the second diaphragm 17.

The end section of the cylinder 25, i.e. the end section of the cylinder 25 which is turned away from the draw rod 11, is provided with an internal circular projection 31 according to what is shown in figure 3. This projection 31 is arranged to co-operate with an internal valve comprising a piston 32 being arranged to be able to be displaced along the interior of the cylinder 25. By this fact the outer dimensions of the piston 32 substantially correspond to the interior dimensions of the cylinder 25. Further the piston 32 is spring resilienced and comprises a second spring 33 for this object, preferably in shape of a helical spring. In this way, the piston 32 may be influenced by spring force so it aims to abut the said projection 31, by means of one of the end sections of the second spring 33 presses against the underside of the piston 32. The opposite end section of the second spring 33 is fixedly connected with the lower end section of the cylinder 25.

The lower end section of the cylinder 25 is completed with an opening 34 to the fourth chamber 21. Moreover the piston 32 is connected with a cylindrical casing 35 having its extension through the second spring 33 and through the said opening 34. The casing 35 is provided with a through-going hole 36 as in the condition which is shown in figure 3 defines a connection between the third chamber 20 and the fourth chamber 21 , together with the opening 34 and an additional hole 37 in the cylinder 25.

If the topside of the piston 32 is influenced by a pressure of such a magnitude that the spring force of the second spring 33 is exceeded, the piston 32 will be pressed down along the cylinder 25, i.e. out of the sealing contact with the projection 31. This leads to the fact that the piston 32 and the housing 35 connected with the piston 32 are displaced downwards in relation to the cylinder 25. Finally, the piston 32 and the casing 35 will have been displaced as far down that the hole 36 in the casing 35 is located below the hole 34 in the end section of the cylinder 25. Simultaneously, the piston 32 will have been pressed down so far that it is on the same level as the hole 37 or even further down. In this way the connection is blocked between the third chamber 20 and the fourth chamber 21. By this time, a connection moreover appears between the first chamber 18 and the third chamber 20. This connection is defined by the hole 28, the interior of the cylinder 25 and the hole 37. In this condition the both diaphragms 16, 17 will be effected of the pressure as is exists in the suction hose 13.

The function of the invention will now be described in detail. In the case that the present engine is driven with a proportionately low load and low engine speed, a relatively low gas flow exists through the first connection pipe 1. This also leads to a relatively low pressure in the suction hose 13 as well as in the first chamber 18. Hereby is also valid that the first spring 24 is manufactured with a rigidity which is tuned so, at this relatively low pressure, that it is capable of keeping the first diaphragm 16 in a substantially unaffected condition, i.e. in the condition which is shown in figure 3. This condition constitutes a position, in that way, where the draw rod 11 is in a first end position which corresponds to that the throttle 7 is in a closed position, i.e. the throttle 7 is lead to the first opening degree, and completely blocks the intermediate section 5 for passage of the gas flow in the embodiment described. This leads in its turn that the gas flow is forced to pass along the flow path which comprising the surrounding silencer volume 8. The noise being generated by the gas flow will then be silenced by means of the gas flow passes through the silencing material in the silencing volume 8. This working condition order gives a very effective silencing exhaust noise, which in particular may be used when the present vehicle is still and driven in idle.

As the load and the speed of the engine increases an even higher pressure will exist in the first chamber 18 (cf. figure 3). This also leads to the fact that an even higher pressure effect against the first diaphragm 16. Finally when the pressure exceeds a predetermined limit value p₀, corresponding to the spring force which is provided by the first spring 24, the first diaphragm 16 will start being pushed in direction to the second chamber 19, which means that the draw rod 11 is also pulled downwardly. This leads to the fact that the throttle 7 starts to become opened in direction to the second opening degree.

During the course of events, the second diaphragm 17 will also be influenced via the cylinder 25, since these two components are connected to each other. If the pressure in the first chamber 18 later rises sufficiently enough, finally the pressure against the topside of the piston 32 (compare figure 3) will exceed a certain predetermined value pi which coπesponds to the spring force which is provided by the second spring 33. This leads to the fact that the piston 32 is displaced out off abutment to the projection 31, and is successively pressed down along the cylinder 25. When the piston 32 has been displaced so far as it is at least partly located below the opening 37 in the cylinder 25, a connection comes up between the first chamber 18 and the third chamber 20. This leads to that the present gas pressure also effects against the second diaphragm 17. A pressure of the same magnitude then influences the both diaphragms 16, 17, which provide an increased force against the draw rod 11 and thus also an increase of the opening velocity of the throttle 7. Finally the throttle 7 will be completely open (i.e. with an extension which is substantially parallel with the longitudinal direction of the intermediate section 5), which makes that the gas flow flows through the flow path which is defined by the perforated sections 4, 6 and the intermediate section 6, substantially without passing the silencer volume 8. This working condition, i.e. with the throttle lead to the third opening degree, leads to the fact that the gas velocity through the silencer 3 is decreased, which also reduces the pressure drop and the flow noise. Altogether an effective noise silencing is received while very low back pressure comes up in the exhaust system when the throttle 7 is lead to the third opening degree and thus is completely open.

When the pressure against the diaphragms 16, 17 reduces, on account of reduced load of the engine, the draw rod 11 will return to the position where the throttle is closed, which occurs as a consequence of the force of the first spring 24. Moreover the piston 32 will return to the position 32 where it abuts the projection 31.

The function of the invention will now be explained further with reference to figure 4. This figure shows a diagram illustrating the opening degree of the throttle 7 as a function of the pressure p which exists in the suction hose 13, and thus, as effects against the valve arrangement 12. As long as the pressure p is below the limit value p₀, as mentioned above, the throttle 7 will remain closed in the first opening degree. When the pressure exceeds p₀ the spring force of the first spring 24 will be overcome, which leads to that the cylinder 25 and also the draw rod 11 are pressed downward. This leads to that the throttle 7 starts to be opened to the second opening degree. By the diagram it is evident that the opening rate during this phase is substantially constant, i.e. the opening occurs linearly. If the pressure is further increased and exceeds the second limit value p„ the both diaphragms 16, 17 will be effected with the same pressure, which leads to a more rapid opening rate of the throttle 7 in relation to the increase of the pressure. Finally the throttle 7 will be lead to the third opening degree and thus in a completely open condition. Altogether the invention gives a compliant, preferably step- by-step linear, control of the transition between completely closed throttle and completely open throttle, whereby a relatively low opening rate changes into a very high opening time as the second limit value p is exceeded. According to the preferred embodiment of the invention, two diaphragms 16, 17 are used (compare to figure 3) which may be effected according to the course of events described above. By means of an appropriate dimension of these diaphragms and besides the valve arrangement 12 a back pressure is obtained, which is substantially constant and independent of the speed of the engine in the present exhaust system. Thereby the invention may be adjusted to the pressure course as is present in the exhaust system (i.e. within the working range of the engine), so that an optimal control of the back pressure is obtained. Thus, the valve aπangement 12 constitutes a detection arrangement for detecting the pressure present in the incoming gas flow, and for controlling the throttling of the gas flow depending on if the pressure is below or exceeds a first limit value p₀ or a second limit value p,.

The invention is not restricted to the embodiment described above and shown in the drawings, but may be varied within the scope of the following claims. For instance the silencer volume, through which the gas flow is lead, may alternatively be a side flow running along a certain pipe connection. Moreover the invention may principally give a good function concerning the function of the throttle at a valve arrangement only using one diaphragm.

The invention is not restricted to be used at exhaust systems. According to a possible embodiment of the invention, it may for instance be used for silencing noise at the inlet side of the engine. In this case, the silencer unit is arranged at the inlet pipe of the engine. A suction hose is then arranged as a connection between the inlet pipe and the valve arrangement according to the invention, so that the valve aπangement detects the pressure in the inlet side. Further the valve aπangement according to the invention, according to this embodiment aπanged with a reversed function, so that in time as an under pressure is built up on the inlet side of the engine, the flow through the inlet pipe is controlled via a certain silencer volume at a low under pressure and directly through the inlet pipe (without passing through the silencer volume) at a high under pressure. This aπangement gives an effective silencing of the inlet noise of the engine.

According to an embodiment of the invention, the valve aπangement 12 described above may principally be replaced by a pressure detecting sensor which is connected to a control unit, which in its turn is aπanged to control the throttle 7.

As an alternative to the draw rod 11 described above and the lever arm 10, the throttle 7 may alternatively be opened and be closed with assistance of an electric engine.

It is also possible with embodiments of the invention where the throttle is controlled according to the opening characteristics according to the invention in another appropriate way, for instance mechanically, pneumatically or with assistance from an electronically control system.

Finally, it is pointed out that the invention may be used for noise silencing in relation to other applications besides exhaust systems.

Claims

1. Arrangement at a noise silencing unit (3) for reducing noise from a gas through flow, which comprises at least a first flow path (4, 5, 6) for said gas flow and a detection aπangement (12) in connection with said first flow path for detecting the pressure of the gas flow, whereby said aπangement comprises a switching aπangement (7, 11) with an adjustable throttle (7) for blocking the first flow path (4, 5, 6) to a first opening degree at detecting a pressure which is below a predetermined first limit value (p₀), whereby the throttle (7) is arranged for opening to a second opening degree if the first limit value (p₀) is exceeded, and the throttle (7) is arranged for opening to a third opening degree at detecting a pressure exceeding a predetermined second limit value (p , characterised in that the first opening degree coπesponds to less than about 15% of the complete sectional area of the first flow path (4, 5, 6) at the throttle (7), and that the second opening degree coπesponds to more than about 30% and less than about 60% of the complete sectional area, and the third opening degree corresponds to more than about 90% of the complete sectional area.

2. Arrangement as claimed in claim 1, characterised in that the first opening degree coπesponds to more than about 8% and less than about 12% of the complete sectional area.

3. Aπangement as claimed in claim 1 or 2, characterised in that the opening of the throttle (7) from the second to the third opening degree is aπanged for occurring during an increase of the pressure from the second limit value (pj) which is less than about 1,0 kPa.

4. Arrangement as claimed in claim 1, 2 or 3, characterised in that the switching aπangement (7, 11) of the throttle (7)is arranged for a substantially linear opening motion between the first and the second opening degree and/or between the second and third opening degree, and reversed also for a substantially linear blocking motion.

5. Arrangement as claimed in any of the proceeding claims, characterised in that the first limit value (p₀) coπesponds to a pressure of the gas flow lying which is 7 and 9 kPa, while the second limit value (p,) coπesponds to a pressure of the gas flow which is between about 11 and 13 kPa.

6. Aπangement as claimed in any of the proceeding claims, characterised in thatthe detection aπangement (12) comprises a valve (12) which is connected with the inlet (1) to the silencing unit (3) via a connection (13) and which is aπanged for said control of the switching aπangement (7,11).

7. Aπangement as claimed in claim 6, characterised in that the said valve aπangement (12) at least comprises an elastic diaphragm (16) aπanged to be effected by said pressure, and that the diaphragm (16) is connected with a connection element (10,11) for transferring the motions of the diaphragm to said throttle (7).

8. Arrangement according to claim 7, characterised in th at the valve aπangement (12) comprises a second diaphragm (17), which is connected to said connection element (10,11) and an interior valve (32,22) being aπanged to be opened at a pressure exceeding said predetermined second limit value (p,), whereby said connection (13) is put in connection with both the diaphragms (16, 17).

9. Arrangement according to claim 8, characterised in that the said interior valve (32, 33) comprises a spring resilience piston (32) which is aπanged to be effected by said pressure and displaceable arranged in relation to said connection element (11).

10. Arrangement as claimed in any of the proceeding claims, characterised in that the aπangement except said first flow path (4,5,6) for said gas flow also comprises a second flow path (4,8,6), which at least partly constitutes a side flow (8) to the first flow path (4,5,6).

11. Arrangement according as clamed in claim 10, characterised in that said side flow (8) is constituted by a silencing volume (8) being substantially concentrically aπanged in relation to the first flow path (4, 5, 6).

12. Arrangement as claimed in claim 11, characterised in that the silencing element (3) comprises two perforated, silencing pipe section (4,6) to be connected to the gas flow to and from, respectively, said silencing volume (8).

13. Engine vehicles comprising an aπangement as claimed in any of the claims 1-11, for silencing noise of a gas flow generated of a combustion engine of an engine vehicle.

14. Method at a silencer unit (3) for reducing noise from a gas flow flowing through, comprising:

controlling the gas flow through at least a first flow path (4, 5, 6) detecting the pressure of said gas flow,

blocking the first flow path (4,5,6) to a first opening degree when detecting a pressure which is below a predetermined first limit value (p₀),

opening said first flow path (4,5,6) to a second opening degree if the said first limit value (p₀) is exceeded,

opening said first flow path (4,5,6) to a third opening degree at detecting a pressure which exceeds a predetermined second limit value (p_x),

characterised in that the first opening degree corresponds to less than about 15% of the complete sectional area of the first flow path (4, 5, 6) at the throttle (7), and that the second opening degree coπesponds to more than about 30% and less than about 60% of the complete sectional area, and the third opening degree coπesponds to more than about 90% of the complete sectional area.

15. Method as claimed in claim 14, characterised in that the first opening degree coπesponds to more than about 8% and less than about 12% of the complete sectional area.

16. Method as claimed in claim 14 or 15, characterised in that the opening of the throttle (7) from the second to the third opening degree occurs during an increase of the pressure from the second limit value (p,) which is less than about 1,0 kPa.

17. Method as claimed in claim 14, 15 or 16, characterised in that the opening of the throttle (7) from the first and the second opening degree and/or between the second and third opening degree occur substantially linearly.

18. Method as claimed in any of the claims 14-17, characterised in that the first limit value (p₀) coπesponds to a pressure of the gas flow which is between 7 and 9 kPa, and that the second limit value (p_x) coπesponds to a pressure of the gas flow which is between about 11 and 13 kPa.

19. Method as claimed in any of the claims 14-18, characterised in, that: said detecting the pressure of the gas flow comprises effect of at least an elastic diaphragm (16), and that the motions of the diaphragm (16) is lead to a throttle (7) aπanged for said blocking and opening, respectively, of the first flow path (4, 5, 6).

20. Method according to any of the claims 14-19, characterised in, that it comprises: effect of a first diaphragm (16) when the pressure exceeds a first limit value (p₀), and effect of a second diaphragm (17) together with said first diaphragm (16) when the pressure exceeds a second limit value (p_j).