GB2395751A

GB2395751A - Internal Combustion Engine EGR Pipe Assembly

Info

Publication number: GB2395751A
Application number: GB0227721A
Authority: GB
Inventors: Stuart Morrison
Original assignee: Ford Global Technologies LLC
Current assignee: Ford Global Technologies LLC
Priority date: 2002-11-28
Filing date: 2002-11-28
Publication date: 2004-06-02
Also published as: WO2004048767A1; GB0227721D0

Abstract

An exhaust gas recirculation pipe assembly 112 includes an inlet end fitting 125 for connection to an engine exhaust manifold, an outlet end fitting 127 for connection to an EGR control valve, with a flexible tube 135 having a convoluted portion 137 between end portions 136 attached to the end fittings 125 and 127. A liner tube 141 extends generally coaxially through the flexible tube 135 to conduct EGR flow from the inlet end fitting 125 to the outlet end fitting 127, one end being rigidly secured to an end fitting. The other end in close non-abutting proximity to the other end fitting. A substantial radial clearance or annular gap 151 between the liner tube 141 and the flexible tube 135 protects the flexible tube from the main flow of EGR gas and thus keeps the convoluted portion 137 below the temperatures at which hot salt corrosion tends to occur.

Description

239575 1

Internal Combustion Engine EGR Pine Assembly The invention relates to exhaust gas recirculation (EGR) pipe assemblies for internal combustion engines.

Fig.1 of the accompanying drawings is a perspective view showing an internal combustion engine 11 with a typical EGR pipe assembly 12. The engine 11 is a V8 type 5 and has an engine block comprising a crankcase and cylinder block 13 and cylinder heads 14 and 15. An inlet duct for the supply of air into the engine includes a pair of inlet manifolds 16, one for each bank of cylinders, which in Fig.1 are largely obscured by other parts of the air intake system, e.g. intercoolers etc. Each inlet manifold 16 is of generally conventional form and is fast with a respective cylinder head 14, 15. Exhaust ducts in the 10 form of two exhaust manifolds 17 and 18, one for each bank of cylinders, are provided to duct exhaust gas away from the engine 11 through the usual arrangement of exhaust pipes, catalyst assemblies and silencers. A respective EGR control valve 21 is fast with each inlet manifold 16 and is supplied with exhaust gas from a respective exhaust manifold 17 by the respective EGR pipe assembly 12. In Fig.1 the EGR control valve 21 and 15 associated EGR pipe assembly 12 for only one bank of cylinders is visible, the corresponding components for the other bank of cylinders being substantially identical.

Each EGR pipe assembly 12 comprises an inlet body or end fitting rigidly connected to the exhaust duct, an outlet body or end fitting rigidly connected to the inlet duct, an EGR passage in the inlet body for the flow of EGR gas from the exhaust duct, an EGR passage 20 in the outlet body for the flow of EGR gas into the inlet duct and a flexible gas-tight tube including a convoluted portion generally coaxial with the EGR passages and having its ends welded or brazed to the end fittings.

A problem with the typical EGR pipe assembly 12 is that the convoluted pipe portion can reach temperatures of around 750 C. Such temperatures, when combined with the 25 stresses induced by thermal expansion and contraction of the various engine, exhaust and

EGR components, are liable to cause hot salt corrosion which shows as grain boundary etching or erosion in the material of the convoluted pipe (typically stainless steel) and failure may occur after prolonged use.

The problem is recognised in US-A-5158061 and US-A-5609144 which both show the 5 use of a telescopic liner pipe to help protect the convoluted pipe. Whilst this may be satisfactory for many purposes, both proposals require the use of metal on metal sliding contact in the liner pipe which can give rise to unwanted wear and noise generation.

It is an object of the present invention to provide an EGR pipe assembly which avoids the problem outlined above.

10 According to one aspect of the invention there is provided an exhaust gas recirculation (EGR) pipe assembly for an internal combustion engine having an engine block and inlet and exhaust ducts fast with the engine block, the EGR pipe assembly comprising an inlet body adapted to be rigidly connected to the exhaust duct, an outlet body adapted to be rigidly connected to the inlet duct, an EGR passage in the inlet body for the flow of EGR 15 gas from the exhaust duct, an EGR passage in the outlet body for the flow of EGR gas into the inlet duct, a flexible gas- tight tube generally coaxial with the EGR passages and having one end sealed and secured to the inlet body and the other end sealed and secured to the outlet body and a liner tube extending generally coaxially and with a substantial radial clearance through the flexible tube to conduct EGR flow from the inlet body to the outlet 20 body, wherein the liner tube is rigidly secured at one end to one of said bodies and has its other end in close non-abutting proximity to the other end of said bodies. A quantity of stagnant EGR gas is trapped between the liner tube and the flexible tube so that the flexible tube is appreciably cooler than it would otherwise be but there is no sliding or other abutting contact of the liner tube with the other of the inlet and outlet bodies to cause wear 25 or rattles during normal use of the engine.

Conveniently, said other end of the liner tube has a small axial clearance with the adjacent body. Otherwise, said other end of the liner tube may extend into the EGR passage of the adjacent end fitting with a substantial radial clearance.

According to another aspect of the invention there is provided an internal combustion 5 engine having an engine block, inlet and exhaust ducts fast with the engine block and an EGR pipe assembly according to said one aspect of the invention connected between the exhaust duct and the inlet duct. Typically, the inlet duct includes an EGR control valve, the outlet body being directly connected to the EGR control valve The invention will be described by way of example and with further reference to the 10 remainder of the accompanying drawings, of which: Fig.2 is a side elevation of an EGR pipe assembly according to the invention; Fig.3 is a cross-section on the line lil-lil in Fig.2; Fig.4 is a view in the direction of arrow "A" in Fig.2; and Fig.5 is a scrap section based on Fig.3 showing a modification 15 Referring to Figs. 2 to 4, there is shown an EGR pipe assembly 112 which is a direct replacement for that shown in Fig.1 and which includes an inlet body or end fitting 125 having a flange 126 for connection to the exhaust manifold 17, an outlet body or end fitting 127 having a flange 128 for connection to the EGR control valve 21. Each flange 126,128 has holes 131, 132 for fixing screws or studs, the holes 131 in flange 126 being elongated 20 to allow for easy assembly to the exhaust manifold 17 without imposing a torsional load in the EGR pipe assembly 112. Each end fitting 125, 127 has a through passage, conveniently referred to as an EGR passage 133, 134, the EGR passage 133 in the inlet end fitting 125 being for the flow of EGR gas from the exhaust manifold 17 and the EGR passage 134 in the outlet end fitting 127 being for the flow of EGR gas into the EGR control 25 valve 21 and hence into the inlet manifold 16.

- 4 A flexible gas-tight tube 135 having plain cylindrical end portions 136 and an intermediate convoluted portion 137 has its ends sealed and secured to the end fittings 125 and 127 by, brazing, welding or other convenient means and is generally coaxial with the EGR passages 133 and 134. A significant length of each end portion 136 extends over the 5 adjacent cylindrical end portion of the respective end fitting 125, 127 for location and alignment. A liner tube 141 extends generally coaxially through the flexible tube 135 to conduct EGR flow from the inlet end fitting 125 to the outlet end fitting 127, the end adjacent the inlet end fitting being inserted into a matching end bore 142 in the EGR passage 133 and rigidly secured by brazing. The other end of the liner tube 141 is in close 10 non-abutting proximity to the outlet end fitting 127, its end face 143 having a small axial clearance "b" with the adjacent end face 144 of the end fitting 127. The adjacent end of the EGR passage 134 in the outlet end fitting 127 has a generally cylindrical recess 145.

There is a substantial radial clearance or annular gap 151 between the outer surface of the liner tube 141 and the inner surface of the flexible tube 135. The liner tube 141, the flexible 15 tube 135 and the end fittings 125,127 are typically made from stainless steel, type T321.

In use on the engine 11, the EGR pipe assembly 112 is required to accommodate the dimensional variations in distance and angle between the interface of the flange 126 with the exhaust manifold 17 and the interface of the flange 128 with the EGR valve 21 as the engine is operated between extremes such as full load, idle and static cold soak. The 20 convoluted portion 137 of the tube 135 flexes to accommodate these dimensional variations but the liner tube 141 stays rigid with the inlet end fitting 125 so that its end adjacent the outlet end fitting 127 moves relative to it, such movement being unrestricted by virtue of the clearance "b". If the clearance "b" is taken up, e.g. by thermal expansion of the liner tube 141 or movement of one end fitting 125 towards the other 127, the recess 25 145 can accommodate such dimensional variations by providing additional radial clearance.

- 5 EGR gas passing through the EGR pipe assembly 112 heats the end fittings 125, 127 and the liner tube 141 to a temperature of around 750 C. However, the annular gap 151 between the liner tube 141 and the flexible tube 135 protects the flexible tube from the main flow of EGR gas, the gas trapped in the space formed by the annular gap being 5 relatively stagnant. The flexible tube 135 can dissipate heat by radiation and by convection to the surrounding atmosphere so that its temperature, particularly in the convoluted portion 137, is very much lower, typically 550 C maximum. This keeps the convoluted portion 137 below the temperatures at which hot salt corrosion tends to occur, even though the amount of flexing in the flexible tube 135 is the same. The relatively low temperature of the flexible 10tube 135 and the unstressed nature of the liner tube 141 avoids the use of high grade, high cost stainless alloys. Under all operating conditions of the engine 11 there is no contact of the liner tube 141 with any other of the components of the EGR pipe assembly 112 (except where it is secured in the inlet end fitting 125) so there is no opportunity for wear or noise from components in abutting or sliding contact.

15In the modification shown in Fig.5 the recess 145 is deeper than that shown in Figs. 2 to 4 and the adjacent end of the liner tube 141 extends part way into the recess.

While the liner tube 141 has been shown and described as being secured in the inlet end fitting 125, it might, in some circumstances, be fitted in the outlet end fitting 127, with appropriate modifications which might include making the adjacent end of the EGR 20 passage in the inlet end fitting of smaller diameter to form a nozzle which directs the flow into the liner tube. Such an arrangement should not unduly create flow in the space formed by the annular gap 151 between the flexible tube 135 and the liner tube 141.

Claims

- 6 CLAIMS

1. An exhaust gas recirculation (EGR) pipe assembly for an internal combustion engine having an engine block and inlet and exhaust ducts fast with the engine block, the EGR pipe assembly comprising an inlet body adapted to be rigidly connected to the exhaust duct, an outlet body adapted to be rigidly connected to the inlet duct, an EGR passage in the inlet body for the flow of EGR gas from the exhaust duct, an EGR passage in the outlet body for the flow of EGR gas into the inlet duct, a flexible gas-tight tube generally coaxial with the EGR passages and having one end sealed and secured to the inlet body and the other end sealed and secured to the outlet body and a liner tube extending generally coaxially and with a substantial radial clearance through the flexible tube to conduct EGR flow from the inlet body to the outlet body, wherein the liner tube is rigidly secured at one end to one of said bodies and has its other end in close non-abutting proximity to the other end of said bodies.

2. An EGR pipe assembly according to claim 1 wherein said other end of the liner tube has a small axial clearance with the adjacent body.

3. An EGR pipe assembly according to claim 1 wherein said other end of the liner tube extends into the EGR passage of the adjacent end fitting with a substantial radial clearance.

4. An EGR pipe assembly according to and preceding claim wherein the liner tube is rigidly secured at said one end to the inlet body.

5. An EGR pipe assembly according to any preceding claim wherein the flexible tube is convoluted.

- 7

6. An internal combustion engine having an engine block, inlet and exhaust ducts fast with the engine block and an EGR pipe assembly according to any preceding claim connected between the exhaust duct and the inlet duct.

7. An engine according to claim 6 wherein the inlet duct includes an EGR control valve, the outlet body being directly connected to the EGR control valve.

8. An EGR pipe assembly substantially as described herein with reference to the accompanying drawings.