GB2449092A

GB2449092A - Gas sealing system in a rotary heat exchanger

Info

Publication number: GB2449092A
Application number: GB0708945A
Authority: GB
Inventors: Thomas Tsoi Hei Ma
Original assignee: Individual
Current assignee: Individual
Priority date: 2007-05-10
Filing date: 2007-05-10
Publication date: 2008-11-12
Also published as: GB0708945D0

Abstract

A gas sealing system in a rotary heat exchanger comprising a matrix 10 rotating in a housing 14 and having at least two sets of entry and exit ducts 22, 22', 24, 24' facing opposite ends of the matrix 10, the gas sealing system comprising a controlled end clearance 50 between an end face of the rotating matrix 10 to prevent leakage of fluid between end faces of the matrix 10, the end clearance 50 being controlled by a bearing assembly comprising a bearing 52 sandwiched between a first flange 54 fixed to an end of the matrix 10 and a second flange 56 that is urged towards the first flange 54 by a spring 62 and permits the bearing 52 and flanges 54, 56 to move axially as an integral unit due to progressive movement of the matrix 10 (thermal expansion) or dynamic shaking (vibrations) of the matrix 10 under resonance conditions to maintain the end clearance constant while being subjected to pulsating pressures. Bearing 52 may be balls, tapered or tapered plain bearing (53, fig 5). Second flange 56 may form part of the housing 14 (fig 3) provided with tension springs (64) constructed as bellows holding the bearing assembly together. The matrix 10 may be rotated by pulleys (72, 74, fig 4) and a belt (76) wrapped around the matrix 10 or a ring gear mounted on the perimeter of the matrix 10. Inlet and outlets 22 - 24' may be connected to flexible telescopic pipes.

Description

GAS SEALING SYSTEM IN A ROTARY EGR DISPENSER

Field of the invention

The present invention relates to the design of a rotary EGR dispenser in a reciprocating internal combustion engine.

Background of the invention

GB1136122 and US6161528 provide teaching in the gas sealing system of a rotary heat exchanger or regenerator.

The heat exchanger comprises a housing having inlet and outlet apertures for the heat-exchange gases and a flow guiding matrix which is rotatable in the housing and through which the gases can flow. A sealing means is necessary to prevent leakage of the gases between the end faces of the rotating matrix and the adjacent end walls of the housing.

In GB1136122, the sealing means is a controlled gap of less than half the hydraulic diameter of the flow guiding channels of the matrix. Because of differential thermal expansion, this gap could vary, increasing leakage if the gap increases, and risking contact causing damage of the fragile matrix if the gap closes. To minimise the change in the width of the gap, both the housing and the matrix are made of ceramic material of similar thermal expansion.

In US6161528, the sealing means is a spring-loaded contact sliding member of solid lubricating material which does not damage the fragile matrix but the contact pressure would cause friction and wear and increase the power requirement for rotating the matrix.

GB0600643.,1 describes a rotary EGR dispenser for a reciprocating internal combustion engine where some exhaust gases are recirculated back to the intake system of the engine by means of a rotary gas exchanger. In this case, the effectiveness of the end seals becomes even more important in face of pulsating pressure conditions inside the gas exchanger which is connected to the reciprocating engine exhaust and intake ducts.

S

Summary of the invention

with the aim of improving the gas sealing system especially in GB0600643.l, there is provided according to the present invention a gas sealing system in a rotary EGR dispenser for a reciprocating piston internal combustion engine, the EGR dispenser comprising a housing containing a rotating matrix and having at least two sets of entry and exit ducts each set facing opposite ends of the rotating matrix, a said matrix of thin wall structure having a plurality of flow passages aligned substantially parallel with the axis of rotation of the matrix for guiding an engine exhaust gas stream and an engine intake air stream along the separate sets of entry and exit ducts from one end of the matrix to the other end of the matrix, and means for rotating the matrix at a sufficient speed for a substantial volumetric gas exchange to occur between the exhaust gas stream and the intake air stream thereby dispensing a predetermined quantity of EGR to the engine, the gas sealing system comprising a very small minimum end clearance between the unexposed end faces of the rotating matrix butting with the end walls of the housing for preventing to all intents and purposes any gas leakage at the perimeters of the entry and exit ducts and maintaining different gas pressures within the respective sets of ducts, and at least one end support assembly for controlling the end clearance by means of a bearing-race sandwiched between a first flange fixed to the end of the matrix and a second flange fixed to a floating end wall of the housing carrying the entry and exit ducts, wherein the floating end wall is free to move axially relative to an axial section of the housing and is urged by a spring with sufficient spring load towards the first flange such that the bearing-race and flanges move as an integral unit with no free play while following any progressive movement of the matrix without dynamic shaking of the matrix under resonance conditions as the matrix rotates thereby maintaining a substantially constant end clearance while being subjected to pulsating pressures inside the EGR dispenser.

Whilst an analogous gas sealing system is described in GB852204 for a rotary regenerative air pre-heater used commonly in a steady flow gas turbine, the present invention is predicated upon the realisation that in a rotary EGR dispenser for a reciprocating internal combustion engine, there are strong pressure waves traversing back and forth along the engine exhaust ducts and the engine intake ducts and hence inside the rotary EGR dispenser caused by the reciprocating strokes of the internal combustion engine cycle. Such pressure waves propagating inside the gas exchanger could cause severe flapping of any lightly spring-loaded sealing component as well as rapid shaking of the matrix if there is free play in the end supports of the rotating matrix resulting in loss in gas seal and fall in line pressure which are dynamically induced under resonance conditions allowed by the free play. This effect has not been experienced in the steady flow heat exchanger or heat regenerator used in the gas turbine and external combustion hot air engine, and has not been anticipated in GB852240 which merely aimed at preventing touching of the rotor ends under steady flow conditions with allowance for a certain amount of free play. The gas sealing system of the present invention does not rely on sealing strips or flaps and does not allow free play in the end supports of the rotating matrix thus preventing dynamic shaking of the matrix, making it the preferred system for use in a rotary EGR dispenser of a reciprocating internal combustion engine in order to ensure good gas seals even under severe pulsating pressure conditions found inside the EGR dispenser.

Preferably, the end clearance is less than half the hydraulic diameter of the flow guiding channels of the rotating matrix. This provides excellent seal while the matrix is free to rotate without touching the end walls.

The hydraulic diameter is hereby defined as being equal to the area of the cross-section of the channel multiplied by four and divided by the length of the perimeter of the cross-section.

In the invention, a tubular shell is provided for enclosing the rotating matrix and permitting sliding fit with the second flange of the bearing-race assembly at each end of the tubular shell, and at least one compression spring is provided for holding the bearing-race assembly together within the shell against end-caps in the shell.

Alternatively, the end wall carrying the second flange is extended to form part of an axial section of the housing, and the two end walls and said sections of housing are pulled towards one another by a tension spring thereby holding the bearing-race assembly together. In this case, the tension spring may be constructed as a flexible bellow completely enclosing the rotating matrix.

A bearing-race is therein defined as a ring support for free rotation around a circular track, and may comprise various bearing means such as ball bearing, roller bearing or plain bearing. In the invention, the bearing-race also provides lateral support of the flow guiding matrix for rotation within the housing. The driving means for rotating the matrix may be a shaft along the axis of the matrix or a belt or gear around the body of the matrix.

Finally, to cope with vibrations transmitted from the external connections, flexible or telescopic pipe sections may be provided connecting the entry and exit ducts of the housing to the engine.

Brief description of the drawings

The invention will now be described further by way of example with reference to the accompanying drawings in which Figure 1 is a schematic sectional view of a gas sealing system of the present invention in a rotary EGR dispenser which includes a compression spring, Figure 2 is a schematic plan view of Figure 1 showing the rotating matrix and bearing-race at the first flange, Figure 3 is a schematic sectional view of an alternative gas sealing system in a rotary EGR dispenser which includes a tension spring, Figure 4 is a schematic sectional view of a rotating matrix driven by a pulley and belt, Figure 5 is a schematic sectional view of a gas sealing system in a rotary EGR dispenser with an alternative design for the bearing race, and Figure 6 is a schematic plan view of Figure 5 showing the rotating matrix and bearing-race of Figure 5.

Detailed description of the preferred embodiment

Figure 1 shows a rotary EGR dispenser for a reciprocating piston internal combustion engine. The EGR dispenser comprises a cylindrical housing 14 having entry and exit ducts 22, 22' and 24, 24' at the ends of the housing 14 for counter-flow of an engine exhaust gas stream and an engine intake air stream, a flow guiding matrix 10 which is rotatable in the housing 14 and through which the respective gas streams can flow, and sealing means (gap 50) for preventing leakage of gases between the end faces of the rotating matrix 10 and the adjacent end walls of the housing 14. The width of the controlled gap 50 (which is largely exaggerated in the drawing) is less than half the hydraulic diameter of the flow guiding channels of the matrix 10.

This provides excellent seal while the matrix is free to rotate without touching the end walls.

Typically, the flow guiding channels in the rotating matrix 10 is constructed of extruded ceramic honeycomb or wrapped metallic foil. The wall thickness of the channels is in the order of 0.1 mm and the hydraulic diameter in the range of 0.3 to 1.0 mm. Thus the width of the sealing gap should not exceed the range of 0.15 to 0.5 mm and this should not be allowed to change significantly even though the overall dimension and the position of the matrix relative to the housing could vary, both progressively due to differential thermal expansion and dynamically due to pressure wave action found inside the EGR dispenser.

Furthermore, because of the extremely fragile construction of the channels, any uncontrolled touching of the ends of the channels could cause damage of the thin walls and should be avoided. On the other hand, the cylindrical block of the matrix with internal honeycomb structure is very strong and can transmit large forces via metal sleeves and flanges fixed to it by cement or by shrink-fit.

The width of the gap 50 is controlled by a bearing ball-race 52 sandwiched between a flange 54 fixed to the end of the matrix 10 and a flange 56 fixed to a floating end wall of the housing carrying the ducts 22, 24' in one end wall and 22', 24 in the other end wall. The flange 56 is free to move axially relative to an axial section of the housing 14 and is urged by a spring 62 towards the flange 54 thus following the position of the flange 54 while allowing the flange 54 to rotate relative to the flange 56 supported by the ball-race 52 which is fixed substantially in the same plane as the controlled gap 50. The spring 62 has sufficient spring load such that the bearing ball-race assembly 52, 54, 56 has no free play and moves as an integral unit along the axial housing while maintaining a constant width of the gap 50 even though the gap position may have moved progressively. As a result, because there is no free play in the end support of the rotating matrix, dynamic shaking of the matrix cannot take place even in face of strong pressure pulsations that are present inside the EGR dispenser so that good gas seals can always be maintained.

In Figure 1, a tubular shell l4a forms the axial housing enclosing the rotating matrix 10 and permitting sliding fit with the flange 56 of the bearing ball-race assembly 52, 54, 56 at each end of the tubular shell 14a.

A compression coil spring 62 is provided at one end of the housing 14 for holding the bearing ball-race assembly together within the shell against end-caps 14b in the shell.

In this case the rotating assembly is forced directly against the bottom end-cap of the housing so that the position of the sealing gap at the lower end of the matrix is fixed while the position of the sealing gap 50 at the upper end of the matrix 10 could move substantially but the width of the gap 50 would remain the same controlled by the height of the balls in the ball-race 52 constituting part of an integral ball-race assembly 52, 54, 56.

In Figure 3, the end wall carrying the flange 56 is extended to form part of an axial section 14c of the housing, and the two end walls and said sections of housing are pulled towards one another by a tension spring 64 thereby holding the bearing ball-race assembly 52, 54, 56 together against any pressure wave travelling in either direction along the housing. The tension spring 64 may be constructed as a flexible bellow completely enclosing the rotating matrix 10.

In Figures 2 and 4, the bearing ball-race assembly 52, 54 also provides lateral support of the matrix 10 for rotation within the housing 14. A driving means for rotating the matrix 10 is shown comprising pulleys 72, 74 and belt 76 wrapped around the body of the matrix 10.

Alternatively a ring gear (not shown) mounted at the perimeter of the matrix may be used. As a further alternative, a central drive shaft (not shown) mounted within the matrix may be provided. The driving means may be connected to an electric motor or an engine drive train.

It should be noted that whilst a flat bearing ball-race is shown in the Figures 1, 2 and 3, a tapered bearing roller-race could be used to similar effect. As a further alternative, a tapered plain bearing race 53 of solid lubricant material may be used as shown in figures 5 and 6.

Finally, to cope with vibrations transmitted from the i external connections, flexible or telescopic pipe sections may be provided connecting the entry and exit ducts of the housing to the engine.

The gas sealing system of the present invention does not rely on sealing strips or flaps and does not allow free play in the end supports of the rotating matrix thus preventing dynamic shaking of the matrix under resonance conditions, making it the preferred system for use in a rotary EGR dispenser of a reciprocating internal combustion engine especially one that is turbocharged in order to ensure good gas seals even under severe pulsating pressure conditions found inside the EGR dispenser caused by the reciprocating strokes of the internal combustion engine cycle. Such pressure waves propagating inside the gas exchanger have not been experienced in the prior art steady flow heat exchanger or heat regenerator used in the gas turbine and external combustion hot air engine where there are only small pressure pulsations hence no special provision is necessary to prevent dynamic shaking of the matrix.

Claims

1. A gas sealing system in a rotary EGR dispenser for a reciprocating piston internal combustion engine, the EGR dispenser comprising a housing containing a rotating matrix and having at least two sets of entry and exit ducts each set facing opposite ends of the rotating matrix, a said matrix of thin wall structure having a plurality of flow passages aligned substantially parallel with the axis of rotation of the matrix for guiding an engine exhaust gas stream and an engine intake air stream along the separate sets of entry and exit ducts from one end of the matrix to the other end of the matrix, and means for rotating the matrix at a sufficient speed for a substantial volumetric gas exchange to occur between the exhaust gas stream and the intake air stream thereby dispensing a predetermined quantity of EGR to the engine, the gas sealing system comprising a very small minimum end clearance between the unexposed end faces of the rotating matrix butting with the end walls of the housing for preventing to all intents and purposes any gas leakage at the perimeters of the entry and exit ducts and maintaining different gas pressures within the respective sets of ducts, and at least one end support assembly for controlling the end clearance by means of a bearing-race sandwiched between a first flange fixed to the end of the matrix and a second flange fixed to a floating end wall of the housing carrying the entry and exit ducts, wherein the floating end wall is free to move axially relative to an axial section of the housing and is urged by a spring with sufficient spring load towards the first flange such that the bearing-race and flanges move as an integral unit with no free play while following any progressive movement of the matrix without dynamic shaking of the matrix under resonance conditions as the matrix rotates thereby maintaining a substantially constant end clearance while being subjected to pulsating pressures inside the EGR dispenser.

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2. A gas sealing system as claimed in claim 1, wherein the end clearance is less than half the hydraulic diameter of the flow guiding channels of the rotating matrix.

3. A gas sealing system as claimed in claim 1 or 2, wherein a tubular shell is provided for enclosing the rotating matrix and permitting sliding fit with the second flange of the bearing-race assembly at each end of the tubular shell, and at least one compression spring is provided for holding the bearing-race assembly together within the shell against end-caps in the shell.

4. A gas sealing system as claimed in claim 1 or 2, wherein the end wall carrying the second flange is extended to form part of an axial section of the housing, and the two end walls and said sections of housing are pulled towards one another by a tension spring thereby holding the bearing-race assembly together.

5. A gas sealing system as claimed in claim 4, wherein the tension spring is constructed as a flexible bellow completely enclosing the rotating matrix.

6. A gas sealing system as claimed in claim 1 or 2, wherein the bearing-race assembly additionally provides lateral support of the flow guiding matrix for rotation within the housing.