GB2459694A

GB2459694A - Exhaust gas recirculation

Info

Publication number: GB2459694A
Application number: GB0807923A
Authority: GB
Inventors: Philip James Newman
Original assignee: Ford Global Technologies LLC
Current assignee: Ford Global Technologies LLC
Priority date: 2008-05-01
Filing date: 2008-05-01
Publication date: 2009-11-04
Anticipated expiration: 2028-05-01
Also published as: CN201439733U; GB0807923D0; GB2459694B

Abstract

A method of exhaust gas recirculation (EGR) and an EGR circuit (40) for an internal combustion engine having at least one cylinder (11) with an exhaust system having an exhaust emission after-treatment means (19,21) for exhaust gases from the cylinder(s), an air supply system including a main turbocharger (14) for supplying fresh air to the cylinders, the EGR circuit including conduit (41) connecting the downstream side of the emission after-treatment means (19,21), via a controllable EGR valve (48), to the fresh air supply to the charger (14), and an exhaust gas flow pump (42), also a turbocharger, which is located in said conduit (41) to supply a desired gas flow for mixing with the air supply system up stream of the charger (14).

Description

Exhaust Gas Recirculation

Field

This invention relates to exhaust gas recirculation circuits of the type used with internal combustion engines.

S

Background of the Invention

Exhaust gas recirculation (EGR) systems or circuits are used to both maximise vehicle fuel efficiency and to reduce the noxious emissions from the vehicle exhaust system. With vehicle emission regulations becoming more stringent and the need for vehicles to become "greener" there is a continuous need to reduce emissions in particular NO gases from engines, in particular diesel engines. One means of reducing exhaust gas emissions is the use of catalytic converters which may be coupled with the recirculation of exhaust gases in which exhaust gases in the exhaust manifold are passed to the inlet manifold using high exhaust gas back pressure. A problem with tighter regulations on emissions is that the increasing exhaust gas back pressure needed to give sufficient back flow may begin to effect fuel efficiencies. Another disadvantage of recirculation from the exhaust manifold is that the re-circulated gas may contain soot, water vapour and unused fuel which may foul an exhaust gas cooling system when fitted, and inlet manifold. Furthermore, if there is a failure due to system leakage, EGR valve failure etc., this may lead to overloads on other components such as particulate filters or catalytic converters.

Conventionally, EGR systems for turbo charged diesel engines have used the higher differential pressure before the turbocharger turbine wheel to re-circulate the exhaust gases to the inlet manifold. This is not always sufficient to reduce the NO emissions.

Alternatively mechanical pumps may be used in the EGR system but these add to the operating load on the engine.

Other EUR systems draw the re-circulating exhaust gases from downstream of the turbocharger turbine, through a particulate filter and then feed the gases to the front of the main turbocharger for passage to the cylinders. A disadvantage with this system is that the gas flow may be insufficient to reduce the NO emissions.

The present invention seeks to ameliorate the above problems.

Statements of Invention

According to a first aspect of the present invention there is provided an exhaust gas recirculation (EUR) circuit for an internal combustion engine having at least one cylinder with an exhaust system having an exhaust emission after-treatment means for exhaust gases from the cylinder(s), an air supply system including a main air induction charger for supplying fresh air to the cylinders, the EGR system including conduit connecting the downstream side of emission after-treatment means, via a controllable EUR valve, to the fresh air supply to the charger, wherein an exhaust gas flow pump is located in said conduit to supply a desired gas flow for mixing with the air supply system to the air induction charger.

Preferably the air induction charger is a turbocharger driven by exhaust gases from the cylinder(s) The gas flow pump may also be in the form of a turbocharger driven by exhaust gases from the cylinder(s) and preferably the turbine of the pump turbocharger may be bypassed to limit the EGR gas flow in the conduit to the main charger. The use of this type of pump imposes no extra loads on the engine and therefore does nor substantially effect fuel consumption and ensures sufficient EUR mass flow at low speeds and engine loads.

The exhaust gases from the cylinders may also be diverted directly from the exhaust manifold to the air supply system forming a second shorter EGR circuit.

Preferably the conduit upstream of the gas flow pump may be selectively connected via valve means with the conduit between the EUR valve and the exhaust gas flow pump forming a re-circulation route when the EGR valve is closed.

According to another aspect of the present invention there is provided an internal combustion engine, preferably a diesel engine, having an EGR circuit according to the first aspect of the present invention.

According to a further aspect of the present invention there is provided a method for exhaust gas recirculation (EGR) circuit for an internal combustion engine having at least one cylinder with an exhaust system with an exhaust emission after-treatment means for exhaust gases from the cylinder(s), and an air supply system including a main air induction charger for supplying fresh air to the cylinders, wherein in said method exhaust gases are diverted downstream of the emission after-treatment means and re-circulated to the fresh air supply to the charger by means of an exhaust gas flow pump, preferably also operated by exhaust gases from the cylinders.

Description of the Drawings

The Invention will be described by way of example and with reference to the accompanying drawings in which: Fig.1 is a schematic drawing of an internal combustion engine S having an EGR circuit according to the present invention, and Fig. 2 is a schematic drawing of an internal combustion engine with a second EGR circuit also according to the present hwention.

Detailed Description of the Invention

With reference to Fig 1, there is shown a schematic diagram of an internal combustion engine 10 of a motor vehicle. The invention is applicable to both diesel engines and petrol engines. The engine shown in Fig.1 of the present example is a diesel engine. The internal combustion engine 10 has a plurality of cylinders 11, in this example six cylinders but there may be any desired number of cylinders arranged in a V configuration.

The cylinders are supplied with fresh air via an air filter 13, conduit 12 and an air induction charger 14 in the form of a turbocharger. The high pressure side of the turbocharger compression wheel 15 delivers air through conduit 12B to an engine inlet manifold 16 via an intercooler 17, preferably an air to air intercooler. The cylinders 11 have a piston (not shown) reciprocal within the bore of the cylinder and at least one inlet valve (not shown) and at least one exhaust valve (not shown), the inlet valves being each connected to an air inlet manifold 16 and the exhaust valves being connected to a respective exhaust manifold branch 18A or 18B, as is well known. The manifold branches 18A, 18B merge into a single exhaust conduit 31, which conducts exhaust gases to an exhaust emission after-treatment device 19, for example a catalytic converter in the form of a diesel oxygen converter. A diesel particulate filter 21 is arranged downstream of the after-treatment device 19.

The exhaust gases from the exhaust manifold branch 1 8A are used to drive the turbine 22 of the main turbocharger 14 which is located in the conduit 31 immediately downstream of the exhaust manifold branches 18 A & B. The exhaust gases are re-circulated back to the fresh air inlet system via an exhaust gas recirculation (EGR) circuit or system 40. The EGR system 40 comprises a long ioop EGR circuit having a conduit 41 which interconnects with the exhaust gas conduit 31 downstream of the particulate filter 21 with the fresh air supply system via an exhaust gas flow pump 42.

The pump 42 is in turn connected to the fresh air intake conduit 12A by conduit 43. The conduit 41 passes through an intercooler 47 and an EGR valve 48 which are located upstream of the pump 42. The intercooler 47 if required typically comprises a water/air or air/air intercooler. The EGR valve 48 opens or closed the long ioop EGR system.

The pump 42 is preferably in the form of a small output turbocharger, the turbine 44 of which is driven by exhaust gases from the exhaust manifold branch 18B. The pump 42 should produce a sufficient depression at its compressor wheel 45 to draw the required exhaust gas flow rate from the exhaust conduit 31. The output from the compressor 45 may be limited by an exhaust gas by-pass 51 controlled by a by-pass valve 52. The gas flow from the compressor wheel 45 through the conduit 43 to the fresh air supply system may pass through a further intercooler 46 if required, and a first recirculation valve 49. The exhaust gas from the compressor 45 may be re-circulated back to the compressor 45 via a conduit 54 and a second recirculation valve 55.

When the long loop EGR is not needed, the valve 48 will be closed off and although the turbine 44 of the pump 42 is still revolving, the gases from the compressor 45 will be re-circulated.

The added benefits of the long loop EGR is that the exhaust gas re-circulated is clean of soot and fuel and therefore fouling is drastically reduced giving improved durability. The EGR gas provided to the engine is considerably cooled compared to the conventional short loop system which can give up to 20-30% reduction in NOx emissions for the same re-circulated exhaust gas mass flow rate. The mixing of the EGR to the fresh air into the engine will ensured as mixing occurs in the compressor wheel 15 of the main turbocharger 14 and in the length of conduit prior to the inlet manifold. Since the EGR is now deployed to the front of the main turbocharger compressor wheel, the main turbocharger unit will operate at an improved efficiency which will result in an improved fuel economy.

Additionally the transient response of the unit will be improved over a standard short loop circuit, where the air mass flow over the compressor wheel is reduced when the short loop EGR is active. In the event of an EGR system failure, this system gives two further advantages over the short loop system in that the EGR gases can be monitored at different locations over the long loop EGR and therefore any deviations from the norm are captured.

In the case of an overloaded particulate filter, which gives high exhaust system back pressure, the EGR flow rate is not affected, whereas a short ioop would unavoidably increase the EGR flow rate. This increases the system robustness against further system damage.

When the EUR long ioop is not utilised and the EGR valve 45 in conduit 41 is closed, the gas flow from the compressor 45 is re-circulated via the conduit 54 with the first recirculation valve 49 closed and the second recirculation valve 55 open.

S As a back-up, the EUR system may further include a conventional short loop comprising conduit 56 passing from the exhaust manifold branch 18B to the inlet manifold 16 via a passageway an intercooler 57 and a second EUR valve 58 so that the short loop is opened/closed by the valve 58. The valves 48, 49, 52, 55 and 58, are made from a suitable high temperature resistant material typically a corrosion resistant metallic compound of the type conventionally used for exhaust gas recirculation valves.

The valves 48,49,52,55 and 58 are operably controlled by a programmable ECU 23 (engine control unit) and which is connected to the fuel injectors (not shown) and to a plurality of other engine condition sensors shown schematically as sensor 28. The engine condition sensors 28 may include, but are not limited to, sensors which monitor engine position, engine speed, manifold static pressure, mass air flow into the manifold, engine temperature, air temperature, cam shaft position (inlet and exhaust), inlet manifold tuning valves, barometric pressure, EUR amount, YCT position, torque demand, gear position etc..

The condition of the valves i.e. open/closed is controlled by the programmable ECU 28 dependant upon the various sensed conditions and required engine control.

With reference to Fig.2, there is shown an EUR system which is substantially similar to the system shown in Fig.1, excepting that the system is utilised on an internal combustion engine having cylinders in an in-line configuration or V configuration. The same reference numbers will be applied to the same components that are shown in Pig. 1 The exhaust manifold 18 is connected by conduit 13 Ito the turbine of the exhaust gas flow pump 42. The gas exiting the turbine 44 of the gas flow pump 42 is fed by conduit 3lto the turbine 22 of the main turbocharger 14 as before. The exhaust gases are then passed through the diesel oxygen catalyst 19 and the particulate filter 21.

The EUR long loop is again provided by conduit 41 extending from downstream of the particulate filter 21 to the depression side of the compressor 45 on the pump 42. The gases from the compressor 42 are pumped via conduit 43 as before to the fresh air inlet supply conduit 12A. The speed limiter for the turbine 44 of the pump 42 is provided by a by-pass conduit 154 connected between the EUR conduit 43 and the conduit 41 downstream of the turbine 44. The EUR gases from the pump 42 are pumped to the fresh air supply conduit 12A as before and again a recirculation circuit is provided by valves 49, 55 and conduit 154 in the event that the EUR valve 48 is closed.

Again an additional short loop EGR may be provided by conduit 156 connecting the exhaust manifold 18 with the inlet manifold 16.

As before the system is operated by an ECU connected to the valves 48, 49, 58 and 152.