GB2480240A

GB2480240A - Turbocharged diesel engine with long-route EGR and an auxiliary intake compressor

Info

Publication number: GB2480240A
Application number: GB1007741A
Authority: GB
Inventors: Alberto Vassallo; Federico Luigi Guglielmone; Federico Ferrero
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2010-05-10
Filing date: 2010-05-10
Publication date: 2011-11-16
Also published as: GB201007741D0

Abstract

A turbocharged Diesel engine (1) comprises a main compressor 40 located in the intake pipe 2 and driven by a turbine 41 located in the exhaust pipe 3; a long-route exhaust gas recirculation (LR-EGR) conduit 60 fluidly connected between a point 32 of the exhaust pipe 3 downstream the turbine 41 to a point 22 of the intake pipe 2 upstream the main compressor 40, and an auxiliary compressor 70 located in the intake pipe 2 downstream the linking point 22 of the intake pipe 2 with the LR-EGR conduit 60. The auxiliary compressor 70 may be driven electrically. A bypass conduit 71 around the auxiliary compressor 70 may have a bypass valve 72 that is opened when the auxiliary compressor 70 is activated. The auxiliary compressor 70 may be activated when engine load increases. A short-route EGR conduit 50 may also be provided.

Description

IVRBOCIRD DIESEL ENGINE

TEICAL FIELD

The present invention relates to a turbocharged Diesel engine of a motor vehicle, in particular to a turbocharged Diesel engine provided with a long route exhaust gas recirculation (LR-EGR) conduit.

BUND

A turbocharged Diesel engine generally comprises an intake manifold, an exhaust manifold, an intake pipe for conveying fresh air from the environment to the intake manifold, an exhaust pipe for conveying the exhaust gas from an exhaust manifold to the environment, and a turbo- charger comprising a compressor located in the intake pipe, for com-pressing the induction air, and a turbine located in the exhaust pipe, for driving said compressor.

A turbocharged Diesel engine further comprises an intercooler, also called as charge air cooler, located in the intake pipe downstream the compressor, for cooling the induction air before it reaches the intake manifold.

In order to reduce the polluting emissions, a turbocharged Diesel en-gine generally ca-nprises a diesel oxidation catalyst (DEC) located in the exhaust pipe downstream the turbine, for degrading residual hy- drocarbons and carbon oxides contained in the exhaust gas, and a di-esel particulate filter (DPF) located in the exhaust pipe downstream the DOC, for capturing and removing diesel particulate matter (soot) from the exhaust gas.

P turbocharged Diesel engines can further comprise an exhaust gas re-circulation (EGR) system, for selectively routing back exhaust gas from the exhaust manifold into the intake manifold, in order to re-duce the production of nitrogen oxides (NO) during the combustion processes.

Conventional EGR systems comprise a short route EGR (SR-EGR) conduit that fluidly connects the exhaust manifold with the intake manifold, a SR-EGR cooler located in the SR-EGR conduit, for cooling the ex-haust gas flowing therein, and a SR-EGR valve for regulating the flow rate of exhaust gas through the SR-EGR conduit.

Improved EGR systems further comprise a long route EGR (LR-EGR) con-duit, which fluidly connects the exhaust pipe downstream the DPF with the intake pipe upstream the compressor of the turbocharger, a LR-EGR cooler located in the LR-EGR conduit, and a LR-EGR valve for regulat-ing the flow rate of exhaust gas through the LR-EGR conduit.

While these improved EGR systems effectively reduce the NOX production when the engine load is at a steady state, their efficiency is dras-tically reduced when the engine load rapidly increases, such as for example when the Diesel engine is requested to accelerate the motor vehicle.

This behaviour is generally caused by the turbo-lag to which the tur- bocharger of the Diesel engine is subject during engine load increas-ing transients.

As a matter of fact, the turbo-lag is the time taken for the exhaust gas driving the turbocharger to come to high pressure, and taken for the turbocharger to overcome its rotational inertia and reach the speed necessary for the compressor to operate properly.

During a turbo-lag, the cairessor of the turbocharger is generally not able to supply the boost pressure necessary for the Diesel engine to promptly accelerate the motor vehicle, thereby impairing both the comfort and the driveability level.

Moreover, the compressor of the turbocharger is generally not even able to draw from the LR-EGR conduit the proper flow rate of exhaust gas necessary for the Diesel engine to effectively reduce the produc-tion of NO.

As a consequence, a plot representing the NO production of a turbo-charged Diesel engine generally shows several spikes that coincide with the engine load increasing transients.

These NO spikes can be handled by means of an improved aftertreatment system, for example by providing the exhaust pipe of the turbocharged Diesel engine with a Lean NQ trap (LNT) or a Selective Reduction Cat-alyst (SCR).

However, this solution increases the cost of the aftertreatment sys-tern, so that it is generally not applicable to city cars and other motor vehicles of economic class.

In view of the above, it is an object of an embodiment of the present invention to reduce the production of NO of a turbocharged Diesel en-gine, principally during the engine load increasing transients.

Another object is to achieve this goal with a simple, rational and rather cheap solution.

DISCLOSURE

These and/or other objects are attained by the characteristics of the embodiments of the invention as reported in independent claims. The dependent claims recite preferred and/or especially advantageous fea-tures of the embodiments of the invention.

An embodiment of the invention provides a turbocharged Diesel engine comprising an intake pipe, an exhaust pipe, a main compressor located in the intake pipe, which is driven by a turbine located in the ex-haust pipe, a LR-EGR conduit that fluidly connects a linking point of the exhaust pipe downstream the turbine to a linking point of the in-take pipe upstream the main compressor, and an auxiliary compressor located in the intake pipe downstream the linking point of the intake pipe with the LR-EGR conduit.

In this way, the auxiliary compressor increases the flow rate of ex-haust gas from the LR-EGR conduit, in particular during the engine load increasing transients, thereby allowing the turbocharged Diesel engine to produce a reduced amount of NO.

At the same time, the auxiliary canpressor increases the boost pres-sure of the induction gas, namely the fresh air eventually mixed with recirculated exhaust gas, thereby improving the performances of the Diesel engine and therefore the comfort and the driveability of the motor vehicle.

Moreover, the auxiliary compressor speeds up the raising of the ex-haust gas pressure, reducing the turbo-lag of the main compressor driven by the turbine.

As a consequence of this benefits, the displacement of a turbocharged Diesel engine according to the present embodiment of the invention can be strongly reduced, without dramatically worsening the perfor-mances and the polluting emissions.

A turbocharged Diesel engine so downsized can be mounted on a city car or other economic motor vehicle, so as to guarantee an acceptable comfort and driveability level, without the need of an expensive af-tertreatment system.

According to an aspect of the invention, the auxiliary compressor is electrically driven.

An electrically driven compressor is generally quite simple to be ma-naged, and does not require important modifications of the layout of the turbocharged Diesel engine.

According to another aspect of the invention, the auxiliary compres-sor is located downstream the main compressor.

This aspect of the invention allows a better package of the auxiliary compressor and increases the turbo-lag benefits.

In fact, the auxiliary compressor could be placed also upstream the main compressor.

However, this latter layout generally causes higher volume capacity effects, which reduce the turbo-lag benefits of the auxiliary corn-pressor, and causes also package drawbacks due to the proximity of the LR-EGR control and mixing valve.

According to a further aspect of the invention, the auxiliary com-pressor is located upstream a charge air cooler.

This aspect has the advantage of simplifying the package of the aux-iliary compressor.

Nonetheless, the auxiliary compressor could be placed also downstream the charge air cooler.

According to still another aspect of the invention, the turbocharged Diesel engine can comprise a bypass conduit connecting a point of the intake pipe downstream the auxiliary compressor to another point of the intake pipe between the auxiliary compressor and the linking point of the intake pipe with the LR-EGR conduit.

This bypass conduit allows the induction gas to bypass the auxiliary corrressor when the latter is not operating, so as to avoid an exces-sive pressure drop.

The turbocharged Diesel engine can further comprise a bypass valve located in the bypass conduit.

This bypass valve can be advantageously used for opening and closing the bypass conduit, depending on whether the auxiliary compressor is operating or not.

nother embodiment of the invention provides a method for operating the turbocharged Diesel engine described above.

The method comprises the steps of monitoring an engine load of the turbocharged Diesel engine, of activating the auxiliary compressor if the engine load is increasing, and of deactivating the auxiliary can-pressor if the engine load is at a steady state.

By activating the auxiliary compressor when the engine load increas-es, the method solves the drawbacks related to the turbo-lag of the main compressor driven by the turbine.

By deactivating the auxiliary caipressor when the engine load is at a steady state, the method saves the energy necessary for the auxiliary compressor to operate, thereby improving the global efficiency of the turbocharged Diesel engine.

According to an aspect of the invention, the method comprises the further steps of closing the bypass conduit, if the auxiliary com- pressor is activated, and of opening the bypass conduit, if the aux-iliary canpressor is deactivated.

By opening the bypass conduit if the auxiliary compressor is deacti-vated, the induction gas bypasses the auxiliary compressor so as not to be subjected to an excessive pressure drop.

By closing the bypass conduit if the auxiliary compressor is acti- vated, the induction gas is forced to pass through the auxiliary com-pressor, and is prevented to flow back through the by pass conduit causing a short circuit.

The method according to the invention can be carried out with the help of a computer program comprising a program-code for carrying out all the steps of the method described above, and in the form of a computer program product canprising the computer program.

The computer program product can be embodied as the previously dis- closed turbocharged Diesel engine, which is equipped with an ECU con-nected to the auxiliary compressor, a data carrier associated to the ECU, and the computer program stored in the data carrier, so that, when the ECU executes the computer program, all the steps of the me-thod described above are carried out.

The method can be also embodied as an electromagnetic signal, said signal being modulated to carry a sequence of data bits which represent a computer program to carry out all steps of the method.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described, by way of example, with reference to the accanpanying drawings.

Figure 1 schematically illustrates a turbocharged Diesel engine ac-cording to an embodiment of the invention.

Figure 2 is a flowchart illustrating a method for operating the Die-sel engine of figure 1.

DEThILED DEScRIPTION

The present invention is hereinafter disclosed with reference to a turbocharged Diesel engine 1 of a motor vehicle.

The turbocharged Diesel engine 1 comprises an intake manifold 10, an exhaust manifold 11, an intake pipe 2 for feeding fresh air frait the environment into the intake manifold 10, an exhaust pipe 3 for dis- charging the exhaust gas fran the exhaust manifold 11 into the envi-ronment, and a turbocharger 4 which comprises a main compressor 40 located in the intake pipe 2, for compressing the air stream flowing therein, and a turbine 41 located in the exhaust pipe 3, for driving the main compressor 40.

The turbocharged Diesel engine 1 further comprises an intercooler 20, also referred as Charge Air Cooler (CAC), located in the intake pipe 2 downstream the main compressor 40, for cooling the air stream be-fore it reaches the intake manifold 10, and a valve 21 located in the intake pipe 2 between the OAC 20 and the intake manifold 10.

The turbocharged Diesel engine 1 further comprises a diesel oxidation catalyst (DOC) 30 located in the exhaust pipe 3 downstream the tur-bine 41, for degrading residual hydrocarbons (1-IC) and carbon oxides (CO) contained in the exhaust gas, and a diesel particulate filter (DPF) 31 located in the exhaust pipe 3 downstream the DOC 30, for capturing and removing diesel particulate matter (soot) from the ex-haust gas.

In order to reduce the emission of nitrogen oxides (NOr), the turbo-charged Diesel engine 1 comprises an exhaust gas recirculation (EGR) system, for routing back and feeding exhaust gas into the intake manifold 10.

The EGR system comprise a first EGR conduit 50 for fluidly connecting the exhaust manifold 11 directly with the intake manifold 10, a first EGR cooler 51 located in the first EGR conduit 50, for cooling the exhaust gas flowing therein, and a first electrically controlled valve 52 located in the first EGR conduit 50, for regulating the flow rate of exhaust gas through the first EGR conduit 50.

Since the first EGR conduit 50 directly connects the exhaust manifold 11 with the intake manifold 10, it is also generally referred as short route EGR (SR-EGR) conduit and it is employed for routing back exhaust gas having high pressure.

The EGR system further comprise a second EGR conduit 60, which fluid-ly connects a linking point 32 of the exhaust pipe 3 with a linking point 22 of the intake pipe 2, and a second EGR cooler 61 located in the second EGR conduit 60, for cooling the exhaust gas flowing therein.

The linking point 32 is located downstream the DPF 31, while the linking point 22 is located downstream an air filter 23 and upstream the main compressor 40.

The flow rate of exhaust gas through the second EGR conduit 60 is de-termined by an electrically controlled three-way valve 62, which is located in the linking point 22.

The second EGR conduit 60 is generally referred as long route EGR (LR-EGR) conduit, and it is employed for routing back exhaust gas having lower temperature and lower pressure than the exhaust gas routed back buy the SR-EGR conduit 50.

The turbocharged Diesel engine 1 further comprises an electrically driven auxiliary compressor 70, which is located in the intake pipe 2 downstream the main compressor 40 and upstream the CAC 20, a bypass conduit 71, which fluidly connects a point 73 of the intake pipe 2 between the main compressor 40 and the CAC 20 to another point 74 of the intake pipe 2 between the auxiliary compressor 70 and the main compressor 40, and a bypass valve 72 located in the bypass conduit 71, for selectively open and close the bypass conduit 71.

The turbocharged Diesel engine 1 is operated by an engine control unit (ECU) 80, which is generally provided for generating and apply-ing control signals to the valves 52 and 62, in order to route back the exhaust gas through the SR-EGR conduit 50 and/or through the LR- EGR conduit 60, for activating and deactivating the auxiliary com-pressor 70, and for opening and closing the bypass valve 72 of the bypass conduit 71.

In particular, the ECU 80 manages the operation of the auxiliary com-pressor 70 according to the iterative control procedure illustrated in figure 2.

The procedure provides for monitoring the engine load during the op-eration of the turbocharger Diesel engine 1.

As a matter of fact, this step can be performed by monitoring any pa-rameter related to the engine load, such as for example the indicated mean effective pressure (IMEP) or the speed of the motor vehicle on which the turbocharged Diesel engine 1 is mounted.

Afterwards, the control procedure provides for evaluating if the en-gine load is increasing.

If the engine load increases, the turbocharger 4 is generally sub-jected to the turbo-lag, so that it generally produces a weak boost pressure and is unable to draw the proper amount of exhaust gas from the LR-EGR conduit 60.

For this reason, the control procedure provides for activating the auxiliary compressor 70 and for keeping it activated, when the engine load increases.

In this way, the auxiliary compressor 70 increases the flow rate of exhaust gas from the LR-EGR conduit 60, in order to reduce the quan- tity of Nc< produced by turbocharged Diesel engine 1 below an allowa-ble level.

At the same time, the auxiliary compressor 70 increases the boost pressure of the induction gas, namely a mixture of fresh air arid re-circulated exhaust gas, thereby improving the performances of the turbocharged Diesel engine 1 and therefore the comfort and the dri-veability of the motor vehicle.

Furthermore, the auxiliary compressor 70 speeds up the raising of the pressure in the exhaust pipe 3, advantageously reducing the turbo-lag to which the turbocharger 4 is subjected.

While the auxiliary compressor 70 is activated, the control procedure further provides for closing the bypass valve 72.

In this way, the induction gas flowing towards the intake manifold 10 is forced to pass through the auxiliary compressor 70 and, at the same time, the induction gas charged by the auxiliary compressor 70 is prevented to flow back through the bypass conduit 71 causing a short circuit.

Once the engine load does not increase, particularly when the engine load reaches a steady state, the control procedure provides for deac-tivating the auxiliary compressor 70.

In this way, the main compressor 40 takes care of drawing the entire flow rate of exhaust gas fran the LR-EGR conduit 60, as well as of providing the induction gas with the proper boost pressure.

As a matter of fact, the turbocharger Diesel engine 1 operates in a conventional mode, without any additional electricity consumption due to the auxiliary compressor 70.

While the auxiliary compressor 70 is deactivated, the control proce-dure further provides for opening the bypass valve 72, so that the induction gas flowing towards the intake manifold 10 is forced to pass through the bypass conduit 71, thereby avoiding excessive pres-sure drop.

This control procedure for operating the turbocharged Diesel engine 1 can be managed with the help of a computer program comprising a pro-grain-code for carrying out all the steps described above.

The computer program is stored in a data carrier 81 associated to the ECU 80.

In this way, when the ECU 80 executes the computer program, all the steps of the embodiments of the method described above are carried out.

While at least one exemplary embodiment has been presented in the foregoing surrrnary and detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only exam- ples, and are not intended to limit the scope, applicability, or con- figuration in any way. Rather, the forgoing summary and detailed de-scription will provide those skilled in the art with a convenient road map for implementing at least one exemplary embodiment, it being understood that various changes may be made in the function and ar-rangement of elements described in an exemplary embodinnt without departing from the scope as set forth in the appended claims and in their legal equivalents.

REEFERS

1 Turbocharged Diesel engine 2 Intake pipe 3 Exhaust pipe 4 Turbocharger Intake manifold 11 Exhaust manifold Charge air cooler 21 Valve 22 Linking point of the intake pipe 23 ir filter

DOC

31 DPF 32 Linking point of the exhaust pipe Main compressor 41 Turbine driving the main compressor SR-EGR conduit 51 EGR cooler 52 Valve LR-EGR conduit 61 EGR cooler 62 Three-way valve Auxiliary compressor 71 Bypass conduit 72 Bypass valve 73 Point of intake pipe 74 Point of intake pipe

ECU

81 Data carrier cIIMs

Claims

1. Turbocharged Diesel engine (1) comprising an intake pipe (2), an exhaust pipe (3), a main compressor (40) located in the intake pipe (2), which is driven by a turbine (41) located in the exhaust pipe (3), a LR-EGR conduit (60) that fluidly connects a linking point (32) of the exhaust pipe (3) downstream the turbine (41) to a linking point (22) of the intake pipe (2) upstream the main corripressor (40), and an auxiliary cnpressor (70) located in the intake pipe (2) down-stream the linking point (22) of the intake pipe (2) with the LR-EGR conduit (60).

2. Turbocharged Diesel engine (1) according to claim 1, wherein the auxiliary compressor (70) is electrically driven.

3. Turbocharged Diesel engine according to claim 1, wherein the aux-iliary compressor (70) is located downstream the main compressor (40)

4. Turbocharged Diesel engine (1) according to claim 1, wherein the auxiliary compressor (70) is located upstream an charge air cooler (20)

5. Turbocharged Diesel engine (1) according to claim 1, ccxrtprising a bypass conduit (71) connecting a point (73) of the intake pipe (2) downstream the auxiliary compressor (70) to another point (74) of the intake pipe (2) between the auxiliary compressor (70) and the linking point (22) of the intake pipe (2) with the LR-EGR conduit (60).

6. Turbocharged Diesel engine (1) according to claim 5, catiprising a bypass valve (72) located in the bypass conduit (71).

7. Method for operating a turbocharged Diesel engine (1) according to any claim from 1 to 6, comprising the steps of: -monitoring an engine load of the turbocharged Diesel engine (1), -activating the auxiliary compressor (70) if the engine load is in-creasing, and -deactivating the auxiliary compressor (70) if the engine load is at a steady state.

8. Method according to claim 7, comprising the further steps of: -closing the bypass conduit (71), if the auxiliary compressor (70) is activated, and -opening the bypass conduit (71), if the auxiliary compressor (70) is deactivated.

9. Computer program canprising a computer-code for carrying out a method according to any claim fran 7 to 8.

10. Computer program product on which the computer program according to claim 9 is stored.

11. Turbocharged Diesel engine (1) according to any claim from 1 to 6, comprising an ECU (80) connected to the auxiliary canpressor (70), a data carrier (81) associated to the ECU (80), and a canputer pro-gram according to claim 9 stored in the data carrier (81).

12. Pn electromagnetic signal modulated as a carrier for a sequence of data bits representing the computer program according to claim 9.