Exhaust gas pressure regulator for a combustion engine

Abstract

An exhaust gas pressure regulator for a combustion engine includes a regulator housing and an inner diffuser assembly arranged inside the regulator housing so that an exhaust gas flow duct is formed between an inner surface of the regulator housing and an outer surface of the inner diffuser assembly. The inner diffuser assembly includes a front portion and a regulating piston that is moveable relative to the front portion and the regulator housing between an idle position in which the exhaust gas flow duct is open, and a pressurized position in which the regulating piston at least partly closes the exhaust gas flow duct. The inner diffuser assembly includes at least one throttled flow passage between the gas flow duct and an exhaust gas pressure chamber defined by the regulating piston and an interior surface of the front portion.

Claims

1. An exhaust gas pressure regulator for a combustion engine, the regulator comprising a regulator housing and an inner diffuser assembly arranged inside the regulator housing so that an exhaust gas flow duct is formed between an inner surface of the regulator housing and an outer surface of the inner diffuser assembly, wherein the inner diffuser assembly includes a front portion and a regulating piston that is moveable relative to the front portion and the regulator housing between an idle position in which the exhaust gas flow duct is open, and a pressurized position in which the regulating piston at least partly closes the exhaust gas flow duct, wherein the inner diffuser assembly comprises at least one throttled flow passage between the gas flow duct and an exhaust gas pressure chamber defined by the regulating piston and an interior surface of the front portion, wherein the inner diffuser assembly comprises a sealing ring that is configured to partly seal a flow passage between the regulating piston and the front portion of the inner diffuser assembly so that the at least one throttled flow passage is provided by means of a calibrated flow leakage past the sealing ring, and in that the at least one throttled flow passage is configured to form a low-pass filter for dynamic pressure pulsations in the exhaust gas flow duct, wherein the at least one throttled flow passage is configured such that an average pressure level within the exhaust gas pressure chamber corresponds to an average exhaust gas pressure level of an exhaust gas stream at an inlet to the throttled flow passage, and/or a total throttled flow passage is configured such that a degree of pressure attenuation of high frequency components of the dynamic pressure pulsations in the exhaust gas flow duct is at least 6dB.

2. The exhaust gas pressure regulator according to claim 1, wherein a total throttled flow passage of the inner diffuser assembly has a flow area in the range of 0.5-10 mm2.

3. The exhaust gas pressure regulator according to claim 1, wherein a total amount of effective surface area of the regulating piston accessible by exhaust gas in the exhaust gas flow duct for exerting an axial force on the regulating piston towards an outlet of the regulating housing is less than 75% of a total amount of effective surface area of the regulating piston accessible by exhaust gas within the exhaust gas pressure chamber for exerting an axial force on the regulating piston towards the outlet of the regulating housing.

4. The exhaust gas pressure regulator according to claim 1, wherein the front portion is stationary arranged in the regulator housing.

5. The exhaust gas pressure regulator according to claim 1, wherein both an internal cross-sectional area defined by an inner surface of a regulator housing and an outer diameter of the inner diffuser assembly increases in an axial direction towards an outlet of the exhaust gas pressure regulator, and the inner diffuser assembly is arranged concentrically inside the inner surface, of a regulator housing.

6. The exhaust gas pressure regulator according to claim 1, wherein the regulating piston is urged towards the idle position by a force of a mechanical spring device.

7. The exhaust gas pressure regulator according to claim 1, wherein the regulating piston comprises a sleeve portion in sliding contact with an exterior side of the front portion of the inner diffuser assembly, and the sleeve portion (131) protrudes into the exhaust gas flow duct when the regulating piston is in the pressurized position for at least partly closing the exhaust gas flow duct.

8. The exhaust gas pressure regulator according to claim 1, wherein the inner diffuser assembly comprises a stationary shaft, and the regulating piston is slidingly arranged on the shaft.

9. The exhaust gas pressure regulator according to claim 1, wherein the sealing ring is a metal piston ring.

10. The exhaust gas pressure regulator according to claim 9, wherein the metal piston ring in a mounted state has a gap between circumferential ends of the piston ring.

11. The exhaust gas pressure regulator according to claim 10, wherein a circumferential length of an arc-shaped gap between the circumferential ends of the piston ring is in the range of 2-50 mm.

12. The exhaust gas pressure regulator according to claim 1, wherein the exhaust gas pressure regulator further comprises a control pressure chamber defined by the regulating piston, a nozzle unit and a shaft, wherein a pressurized medium within the control pressure chamber is arranged to exert a force on the regulating piston towards the pressurized position.

13. The exhaust gas pressure regulator according to claim 12, wherein the pressure regulator further comprises a pressure medium flow passage for supplying pressurized medium from an outside pressure medium source to the control pressure chamber.

14. The exhaust gas pressure regulator according to claim 1, wherein the front portion of the inner diffuser assembly has a closed end facing an exhaust gas flow inlet of the exhaust gas pressure regulator, and an open end facing an exhaust gas outlet of the exhaust gas pressure regulator, wherein an annular damping member is provided between an axial abutment surface of the regulating piston and an opposite axial abutment surface of the front portion of the inner diffuser assembly for damping impact forces between the regulating piston and the front portion of the inner diffuser assembly.

15. The exhaust gas pressure regulator according to claim 14, wherein the front portion of the inner diffuser assembly has a conical shape with a generally increasing outer diameter in an axial direction from the closed end towards to the open end, and the opposite axial abutment surface of the front portion of the inner diffuser assembly is located in a radially outer region located near or at the open end.

16. The exhaust gas pressure regulator according to claim 14, wherein the annular damping element is a metal textile bushing.

17. An exhaust gas system for an internal combustion engine, wherein the exhaust gas system comprises a gas pressure regulator according to claim 1 located downstream of a first turbine unit and upstream of a second turbine unit.

18. The exhaust gas system according to claim 17, wherein the inner diffuser assembly forms a nozzle for the second turbine unit.

19. The exhaust gas system according to claim 17, wherein the second turbine unit is a turbo-compound unit.

20. The exhaust gas system according to claim 17, wherein the first turbine unit is a turbo-charger unit.

21. A combustion engine comprising an exhaust gas system according to claim 17.

22. A vehicle comprising a combustion engine according to claim 21.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) With reference to the appended drawings, below follows a more detailed description of embodiments of the invention cited as examples.

(2) In the drawings:

(3) FIG. 1 shows an example vehicle suitable for having a combustion engine with an exhaust gas pressure regulator according to the disclosure;

(4) FIG. 2 shows an example embodiment of an combustion engine having an exhaust gas pressure regulator according to the disclosure;

(5) FIG. 3 shows a schematic example embodiment of an exhaust gas pressure regulator according to the disclosure;

(6) FIG. 4 shown a part of the exhaust gas pressure regulator of FIG. 3 in more detail;

(7) FIG. 5 shows an example embodiment of a sealing ring according to the disclosure;

(8) FIG. 6 shows the schematic example embodiment of an exhaust gas pressure regulator of FIG. 3 with the regulation piston in a pressurized state;

(9) FIG. 7 shows an alternative embodiment of the throttled flow passage; and

(10) FIG. 8 shows schematic example pressure patterns of the pressure outside and within the exhaust gas pressure chamber.

DETAILED DESCRIPTION

(11) Various aspects of the disclosure will hereinafter be described in conjunction with the appended drawings to illustrate and not to limit the disclosure, wherein like designations denote like elements, and variations of the described aspects are not restricted to the specifically shown embodiments, but are applicable on other variations of the disclosure.

(12) With reference to FIG. 1, the disclosure concerns an exhaust gas pressure regulator for a combustion engine, wherein the combustion engine for example may be located in a vehicle such as a truck 1 for pulling a trailer. The truck typically comprises a chassis 4, front and rear wheels 3, a driver's cabin 8 and connector device 6 for connecting a trailer vehicle to the truck 1. The combustion engine may however alternatively be installed in other types of vehicles, such as buses, construction machinery, or the like.

(13) FIG. 2 schematically shows an example embodiment of piston engine 10 having the exhaust gas pressure regulator according to the disclosure. The piston engine 10 includes an engine block 20 with six cylinders 22, which are in fluid communication with an air intake manifold 23 and an exhaust manifold 21. The engine further comprises a turbo-charger unit 50 for increasing the output power of the combustion engine 1, as is well-known to the person skilled in the art of combustion engines. Hot exhaust gas having high-speed and high-pressure flows from the cylinders 22 via the exhaust manifold 21 and exhaust pipe 40 to a turbine wheel 28 of the turbo charger unit 50 and forces the turbine wheel 28 to rotate with a high speed. Exhaust air is subsequently conveyed via a regulator inlet pipe 33 to an exhaust gas pressure regulator 100 and turbo compound unit 60. The turbine wheel 28 of the turbo charger unit 27 is rotationally connected to an air intake compressor wheel 29 of the turbo charger unit 27 via a turbine shaft 30. The compressor wheel 29 compresses air that is sucked into turbo charger unit 27 via an inlet passage 31 and forwards the charge air to the intake manifold 23 via an inlet pipe 32.

(14) The turbo compound unit 60 provides an additional torque to a crankshaft 24 of the engine 10. An exhaust gas pressure regulator 100 is arranged between the turbo-charger unit 50 and the turbo-compound unit 60.

(15) Before turning to particular details of the exhaust gas pressure regulator 100, some general comments on the functionality of the present embodiment will be given. As exhaust gas is flowing out from the engine block 20, the energy of the exhaust gas will be used in the turbo-charger unit 50 for compressing the air before it is introduced in the cylinders 22. The exhaust gas will thereafter flow through the exhaust gas pressure regulator 100 which in its idle position serves to diffuse the exhaust gas flow before it flows through the turbo-compound unit 60. A part of the remaining energy of the exhaust gas flowing out from the exhaust gas pressure regulator 100 will cause a turbine of the turbo-compound unit 60 to rotate, which rotation is coupled to the crankshaft 24 via a transmission 12 and hydraulic convener 13, thus adding torque for driving the vehicle. The crankshaft 24 is subsequently connected to a transmission 14 for adapting gearing before transmitting output torque to the driving wheels via a power train output shaft 15. Further components, such as a catalytic converter and a silencer (not shown), are normally also provided in an exhaust pipe 11 located downstream of the turbo-compound unit 60 in order to form a complete exhaust system for the engine 10.

(16) The exhaust gas pressure regulator 100 is controllable for adjusting the amount of exhaust gas flowing through. During normal operation the exhaust gas pressure regulator 100 is in its idle position whereby no restriction in the exhaust gas flow is provided. However, in some situations it is desirable to compress the exhaust gas exiting the cylinders, e.g. during braking or engine heat mode for increasing the temperature of the exhaust gas. If this is the case the exhaust gas pressure regulator changes its position into an operational position for at least partly blocking the exhaust gas flow.

(17) Now turning to FIG. 3, which schematically shows an example embodiment of an exhaust gas pressure regulator 100 according to the disclosure. Exhaust gas is introduced at art inlet end 102 and flows through the pressure regulator to an outlet end 104. An exhaust gas flow duct 106 is formed between the inlet end 102 and the outlet end 104, which flow duct serves to diffuse the exhaust gas as will be further explained below. The exhaust gas flow duct 106 forms an annular conduit which has an outer periphery being defined by an inner surface 107 of the regulator housing 108 and, and an inner periphery being defined by an outer surface 109 of the inner diffuser assembly 110, which is arranged inside the arranged inside the regulator housing 108. Hence, the outer diameter of the inner diffuser assembly 110 is less than the inner diameter of the regulator housing 108, such that exhaust gas flows in the volume formed between these two components 108, 110, i.e. in the exhaust gas flow duct 106.

(18) The regulator housing 108 has a longitudinal extension such that it extends in the same direction as an exhaust gas flow, i.e. from the inlet end 102 towards the outlet end 104. The diameter of the regulator housing 108 is preferably varying along its longitudinal direction, such that the cross-sectional area is increasing along the exhaust gas flow direction 101. Correspondingly, the inner diffuser assembly 110 has a longitudinal extension such that it extends in the same direction as the exhaust gas flow. The diameter of the inner diffuser assembly 110 may vary along its longitudinal direction such that the cross-sectional area is increasing along the exhaust gas flow.

(19) The inner diffuser assembly 110 may thus have a conical shape, or a shape slightly deviating from a strict conical shape as indicated in FIG. 3 in which a bell shape is presented. Correspondingly, the regulator housing 108 may have a conical shape, or a shape slightly deviating from a strict conical shape as indicated in FIG. 3, in which a semi dome shape is shown.

(20) The regulator housing 108 and the inner diffuser assembly 110 are preferably arranged such that the width of the annular gas flow duct 106 is substantially constant, or slightly increasing, along the longitudinal extension when the exhaust gas pressure regulator 100 is in its idle position. However, as the diameter of the regulator housing 108 and the diameter of the inner diffuser assembly 110 are increasing along the exhaust gas flow direction, the volume of the gas flow duct 106 will increase along the exhaust gas flow direction 101 whereby a diffusion of the exhaust gas will be provided.

(21) The inner diffuser assembly 110 comprises a centrally arranged stationary shaft 105, a regulator piston 130 that is slidingly arranged on the shaft 105, and a conical front portion 111 stationary and permanently connected to the shaft 105.

(22) The regulating piston 130 that is moveable relative to the front portion and the regulator housing between an idle position in which the exhaust gas flow duct is open, and a pressurized position in which the regulating piston at least partly closes the exhaust gas flow duct

(23) An outlet end 142 of the shaft 140 is fixedly attached to a nozzle unit 150 which forms the outlet end 104 of the exhaust gas pressure regulator 100. The nozzle unit 150 further includes a cylindrical portion 152 extending towards the inlet end 102. The cylindrical portion 152 is configured to slidingly support an outer surface of the regulating piston 130. Hence, the piston 130 is arranged coaxially on the shaft 105 and the outer periphery of the piston 130 is sealed against the cylindrical portion 152 of the nozzle unit 150 by means of a seal 141.

(24) The nozzle unit 150 further has an outer portion 154, arranged radially outwards of said cylindrical portion 152 and forming a circumferential support structure surrounding the cylindrical portion 152. The outer portion 154 forms the outer portion of the outlet end 104 of the exhaust gas pressure regulator 100 and is connected to the regulator housing 108.

(25) In the disclosed embodiment the regulator housing 108 includes an outer annular flange 143 that is configured be connect the exhaust gas pressure regulator 100 to an outlet pipe 34 located downstream of the regulator 100 or alternatively directly to an inlet portion of the turbo-compound unit 60. Alternatively, the flange may be provided on the outer portion 154 of the nozzle unit 150 instead.

(26) In the disclosed embodiment the exhaust gas pressure regulator 100 further comprises an outer annular flange 147 that is configured to connect the exhaust gas pressure regulator 100 to an inlet pipe 33 located upstream of the regulator 100 or alternatively directly to an outlet portion of turbo-charger unit 50.

(27) In the disclosed example embodiment of the exhaust gas pressure regulator 100 the outer annular flange 147 is provided on an individual part 148 of the exhaust gas pressure regulator 100, which individual part 148 is connected with the regulator housing 108 by means of a corrugated metal tube 149. This design enables a large degree of freedom in relative motion between the individual part 148 and regulator housing 108, and vibrations are largely prevented from being transferred between the regulator housing 108 and individual part 148. The regulator may thus comprise three individual parts forming the outer surface of the regulator 100, namely the individual part 148, a regulator housing 108 and a nozzle unit 150.

(28) The regulating piston 130 is urged towards the idle position by the force of a mechanical spring 122, which is configured to abut an internal surface 113 of the conical front portion 111 and a first axial side surface 112 of the regulating piston 130.

(29) The exhaust gas pressure regulator 100 further comprises a control pressure chamber 164 configured for receiving pressurised air or the like for controlling the position of the regulating piston in the axial direction 118, and thereby also the desired backpressure in gas flow duct 106 is attained. The control pressure chamber 164 is defined by a second axial side surface 119 of the regulating piston 130, a portion of the nozzle unit 150 that faces the second axial side surface 119 of the regulating piston, an inner surface of the cylindrical portion 152 of the nozzle unit 150, and an outer surface of the shaft 105.

(30) One or more hollow connector elements 156 may be provided for connecting the outer portion 154 of the nozzle unit 150 with the inner diffuser assembly 110. The at least one hollow connector element 156 is arranged for allowing pressurized air to flow from a pressurised air source into the control pressure chamber 164 of the inner diffuser assembly 110. Feeding channels are thus arranged in one or n ore of the connector elements 156 for guiding the pressurized air into the closed cavity 164, but alternative solutions for feeding pressurized air icy the control pressure chamber are possible. When for example pressurized air is supplied via the air inlet 162, a force urging the piston 130 away from the idle position and towards a pressurized position will be generated.

(31) When the exhaust regulator 100 is located upstream of turbo-compound unit 60 or a second turbo charger unit, the connector elements 156 may form guide vanes that are arranged to guide the exhaust flow into a desired flow direction.

(32) The regulating piston 130 further comprises a sleeve portion 131 in sliding contact with an exterior side of the front portion 111 of the inner diffuser assembly 110. Thereby, an exhaust gas pressure chamber 132 is defined by the inner surface 133 of the substantially conical front portion 111, the first axial side surface 112 of the piston 130 and an outer surface of the shaft 105.

(33) The regulating piston 130 is moveable relative to the front portion 111 and the regulator housing 108 between an idle position in which the exhaust gas flow duct 106 is open, and a pressurized position in which the regulating piston 130 at least partly closes the exhaust gas flow duct 106. The closing is performed by controlling the regulating to move towards its pressurized position, thereby rendering the sleeve portion 131 of the regulating piston 130 to move into the exhaust gas flow duct 106, such that the exhaust gas flow duct 106 becomes at least partly closed. The sleeve portion 131 may consequently be referred to as a valve sleeve, and the regulating control piston 130 can move axially for regulating the flow area of the exhaust gas flow duct 106 by means of the valve sleeve, against the effect of the helical compression spring 122.

(34) A annular damping element 172 may be provided between an axial abutment surface of the regulating piston 130 and an opposite axial abutment surface 173 of the front portion 111 of the inner diffuser assembly 110 for damping impact forces between the regulating piston 130 and the front portion 111 of the inner diffuser assembly 110. The annular damping element 172 may be a metal textile bushing. An advantage of locating the annular damping element 172 at the radially outer portion of the front portion 111 a relatively large area of the annular damping element is accomplished, thereby reducing the impact stress on the damping element 172 and mating surfaces.

(35) In the idle position of the regulating valve (see FIG. 3), a distal portion 134 of the sleeve portion 131 may be configured to form part of the outer surface 109 of the inner diffuser assembly 110. In the active control position (see FIG. 6), an inner wall surface of the sleeve portion 131 protrudes into the exhaust gas flow duct 106 between the front portion 111 and the cylindrical portion 152 of the nozzle unit 150.

(36) The inner diffuser assembly 110 comprises at least one throttled flow passage 144 for enabling pressure equalization of the pressure within the gas flow duct 106 and the exhaust gas pressure chamber 132. In the embodiment of FIG. 3, the throttled flow passage 144 is formed by a passage at the location 135 of the sliding contact between the sleeve portion 131 and the exterior side of the front portion 111 of the inner diffuser assembly 110.

(37) Thanks to the throttled flow passage 144 the pressure within the exhaust gas pressure chamber 132 is substantially static when the regulating piston is arranged in a fixed position.

(38) With reference to FIG. 4, which corresponds to schematic magnification of the location 135 of the sliding contact, the exterior side of the front portion 111 of the inner diffuser assembly 110 comprises a groove 136, in which a sealing ring 137 is located. The dimensions of the front portion 111 of the inner diffuser assembly 110 and an interior side of the sleeve portion 131 are also selected such that a radial gap is also formed between an exterior side 138 of the front portion 111 and at interior side of the sleeve portion 131. The gap is part of the flow passage 144. The size of the gap is sufficient for enabling a leakage flow between the gas flow duct 106 and the exhaust gas pressure chamber 132. The total flow area resulting from the gap may be at least 50 mm2, specifically at least 100 mm2, or in the range of 50-1000 mm2.

(39) According to one example embodiment, the sealing ring 137 may be configured to at least partly seal the flow passage 144 between the regulating piston and the front portion of the inner diffuser assembly so that the a the flow passage 144 is throttled. This partly sealing of the flow passage 144 may for example be performed by means of a calibrated flow leakage past the sealing ring 137. One example solution for accomplishing the calibrated flow leakage past the sealing ring 137 is to provide sealing ring in form of a piston ring that has an annular gap 145 between circumferential ends of the piston ring.

(40) By selecting an appropriate circumferential length 146 of the arc-shaped gap between the circumferential ends of the piston ring it is possible to calibrate the level of flow leakage past the sealing ring. For example, the appropriate circumferential length 146 of the arc-shaped gap between the circumferential ends of the piston ring may be in the range of 2-50 mm, specifically in the range of 3-25 mm, and more specifically in the range of 5-20 mm.

(41) Due to the provision of the flow passage 144 a pressure balancing of the exhaust gas pressure regulator 100 is achieved, so that this automatically adjusts itself by self-regulation.

(42) When the exhaust gas pressure regulator 100 is activated, i.e. when pressurized media is supplied to the control pressure chamber 164, the regulating control piston 130 begins to move axially against the effect of the helical compression spring 122, and the sleeve portion 131 begins to protrude into the exhaust gas flow duct 106 until it has reached its pressurized position, in which it at least partly closes the exhaust gas flow duct 106. The pressurized position of the regulating piston 130 is shown in FIG. 6. The supplied pressure medium may for example have a pressure in the range about 0.5-10 bar.

(43) As a result, the pressure rises upstream of the regulating piston 130 (with a certain delay as the gas is compressible). The pressure upstream of the regulating valve is propagated with a certain delay into the exhaust gas pressure chamber 132 via the throttled flow passage 144. Upon approaching a pressure balance between the pressure within the control pressure chamber 164 and the exhaust gas pressure chamber 132, the regulating piston 130 will displace towards the idle position, such that a certain flow of exhaust gas is allowed past the sleeve portion 131. As a result, the pressure upstream of the sleeve portion 131 decreases. Soon a pressure balance will arise and the regulating piston 130 finds a position of equilibrium. The exhaust gas pressure regulator 100 described above is thus self-regulating and automatically provides a backpressure level in similar to the control pressure level.

(44) At the equilibrium position the pressure within the control pressure chamber 164 and the exhaust gas pressure chamber 132, will be approximately the same due to the fact that the effective surface areas of the regulating piston, i.e. the first axial side surface 112 and the second axial side surface 119, are nearly identical, bearing in mind that the pressure exerted by the spring is relatively small.

(45) The solution using the sealing ring 137 for accomplishing the desired calibrated low passage 144 between the gas flow duct 106 and the exhaust gas pressure chamber 132 is advantageous because the flow area of the flow passage can easily be adapted by means of mounting a different piston ring. However, the advantage of the disclosure in terms of increased reliability and reduced damages to the regulator 100 may alternatively be obtained by other means of accomplishing a calibrated flow passage. For example, the front portion 111 of the exhaust gas pressure regulator 100 may be provided with an aperture 161 at an appropriate location for enabling the desired calibrated flow passage 144 between the gas flow duct 106 and the exhaust gas pressure chamber 132, as schematically illustrated in FIG. 7. The size of the aperture 161 is thus relevant for obtaining the desired pressure throttling effect. The aperture may alternatively be provided in the shaft 105 or another part forming a wall of the exhaust gas pressure chamber 132.

(46) During for example engine braking the reciprocating motion of the pistons of the combustion engine generates a regular periodical pressure pattern in the exhaust gas flow with a certain frequency. A simplified example of such a regular periodical pressure pattern 165 in the exhaust gas flow is schematically shown in FIG. 8. The pressure pattern may have a certain amplitude 166 and a certain periodical length 167. A real life pressure pattern will most likely have a regular periodical pressure pattern that is less similar to a sinus function.

(47) The regular periodical exhaust gas pressure patterns may coincide or be a multiple of a resonance frequency of the regulating piston 130 and spring 122 assembly in the pressurized position, or an intermediate state between the idle position and pressurized position. Consequently, there is a risk that the regulating piston 130 starts oscillating with a high amplitude at certain engine operating conditions, thereby potentially damaging the regulating piston 130, the spring 122 and/or the nozzle 150 of the regulator 100.

(48) The sensitivity of the regulating piston for being influenced by the periodical pressure pattern can be reduced by reducing the amplitude 166 of the pressure pattern. This may be performed by reducing the effective surface area of the regulating piston 130 that is exposed to the exhaust gas pressure pattern 165. However, simply reducing the effective surface area may result in that the desired self-regulation of the regulating piston is lost or at least impaired.

(49) The solution according to the disclosure includes providing the regulator 100 with an exhaust gas pressure chamber 132 that exhibits about the same average pressure as the exhaust gas pressure pattern 165 but with a reduced amplitude, and having at least a portion of the effective surface area of the regulating piston 130 being exposed to the small amplitude pressure of the exhaust gas pressure chamber 132. Thereby, the amount of effective surface area of the regulating piston 130 that is exposed to the high amplitude exhaust gas pressure pattern 165 is reduced while maintaining the self-regulation functionality of the regulator 100.

(50) Accomplishing an exhaust gas pressure chamber 132 that exhibits about the same average pressure as the exhaust gas pressure pattern 165 but with a reduced amplitude may be performed by providing the inner diffuser assembly 110 with at least one throttled flow passage 144 for enabling pressure equalization of the pressure within the gas flow duct 106 and the exhaust gas pressure chamber 132. The throttled flow passage is configured to filter the large amplitude pressure pattern of the exhaust gas while still allowing an equalizing of the pressure of the gas flow duct 106 and the exhaust gas pressure chamber 132. The filtration and pressure equalization is performed by providing a controlled leakage area between the gas flow duct 106 and the exhaust gas pressure chamber 132. Thereby, large amplitude pressure pattern cannot propagate into the exhaust gas pressure chamber 132 without first losing a certain level of energy (amplitude). However, for avoiding too long delay until pressure equilibrium has been attained after a transient change, the leakage area cannot be too small.

(51) With a proper selected leakage flow the effective piston surface area that is exposed to the high amplitude pressure patterns of the exhaust as may be significantly decreased, depending on the proportion of the effective surface area of the regulating piston being exposed to high amplitude pressure pattern and low amplitude pressure.

(52) In the example embodiment of FIG. 3, the effective surface area of the regulating piston 130 that is exposed to high amplitude pressure pattern of the exhaust gas is shown with dotted force vectors 168, and the effective surface area of the regulating piston 130 that is exposed to low amplitude pressure pattern of the exhaust gas pressure chamber 132 is shown with solid force vectors 169. In the example embodiment of FIG. 3, the proportion of the total amount of effective surface area of the regulating piston that may be exposed to the high amplitude exhaust gas in the exhaust gas flow duct is significantly less 50%.

(53) The term effective surface area of the regulating piston herein refers to the surface of the regulating piston that may induce an axial force on the regulating piston when exposed to a pressure medium.

(54) A schematic and simplified illustration of the pressure pattern 170 within the exhaust gas pressure chamber 132 is illustrated in FIG. 8 for a regulator 100 having a certain leakage flow 144. In this ideal illustration, the amplitude 171 is significantly reduced (dampened) and the average pressure is substantially identical to the average pressure of the gas exhaust flow. The at least one throttled flow passage is thus configured to essentially form a low-pass filter for the dynamic pressure pulsations in the exhaust gas flow duct, where the high frequency pressure variations, such as for example pressure variations having a frequency above 10 Hz, specifically above 1 Hz, are damped. Thereby, the pressure within the exhaust gas pressure chamber 132 will mainly exhibit a low frequency pressure variation, such as for example below 10 Hz, specifically below 1 Hz. Pressure variations with such low frequency may be considered representing mainly the average pressure in the exhaust gas flow duct over a certain time period.

(55) The throttled flow passage may preferably be configured such that a degree of pressure attenuation of the high frequency components, i.e. frequencies above for example 10 Hz, specifically above 1 Hz, of the dynamic pressure pulsations in the exhaust gas flow duct is at least 6 dB, specifically at least 10 dB, and more specifically at least 20 db. The amplitude of the example pressure pattern 170 within the exhaust gas pressure chamber 132 Shown in FIG. 8 is damped with about 20 dB.

(56) As already described briefly, the exhaust gas pressure regulator 100 may preferably be used for braking of a vehicle without necessarily using the friction brakes. When a driver pushes down the brake pedal, a specific braking force is requested. An ECU of the vehicle may then calculate a corresponding air pressure which forces the regulating piston 130 to move, whereby the regulating piston 130 may at least partly close the exhaust gas duct 106 of the exhaust gas pressure regulator 100. For such application, the air pressure may for example be in the range of 1 to 10 Bars, overcoming the spring force as well as the exhaust gas pressure.

(57) In another application, the exhaust gas pressure regulator 100 is used in engine heat mode when it is desired to increase the temperature of the exhaust gas. In such case, an ECU of the vehicle will calculate the desired through flow of exhaust gas for providing the desired temperature, and subsequently apply a corresponding pressure level in the control pressure chamber 164

(58) Although the exhaust gas pressure regulator 100 has been described to operate in series with a turbo-charger unit 50 and a turbo-compound unit 60, it is readily understood that other applications may also be suitable for the proposed exhaust gas pressure regulator 100. Preferably, the presented exhaust gas pressure regulator may be arranged in any application where a radial turbine, e.g. of a turbo-charger unit, is followed by an axial turbine, e.g. of a turbo-compound unit or a further turbo-charger unit. Further, the exhaust gas pressure regulator 100 may be used in association with all kinds of piston engines, from one cylinder and upwards, and with two-stroke or four-stroke engines, for road vehicles, marine equipment, etc. Also, although a pneumatic system for operating the exhaust gas pressure regulator 100 has been described, other means such as mechanical and or hydraulic may also be implemented.

(59) The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. It is appreciated that various features of the above-described examples can be mixed and matched to form a variety of other alternatives. As such, the described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes that come within the meaning and range of equivalency of the claims are to be included within their scope.

(60) Reference signs mentioned in the claims should not be seen as limiting the extent of the matter protected by the claims, and their sole function is to make claims easier to understand.