Method for operating an internal combustion engine system

Abstract

The invention relates to a method for operating an internal combustion engine system (2), wherein the internal combustion engine system (2) is provided with an air intake duct (3), an exhaust gas duct (4) and an exhaust gas recirculation (EGR) system (5), wherein the EGR system (5) comprises an EGR conduit (6) that fluidly connects the exhaust duct (4) and the intake duct (3), and wherein a gas feeding device (7) configured to feed exhaust gas from the exhaust duct (4) to the intake duct (3) is arranged in the EGR conduit (6). The method is characterized in that it comprises the step of: providing a flushing liquid in the EGR conduit (6) upstream of the EGR gas feeding device (7) so as to flush and clean the EGR gas feeding device (7). The invention also relates to an internal combustion engine system (2) configured for being operated by such a method and to a vehicle (1) provided with such an engine system (2). The invention further relates to means for controlling the above method.

Claims

1. A method for operating an internal combustion engine system, wherein the internal combustion engine system is provided with an air intake duct, an exhaust gas duct and an exhaust gas recirculation (EGR) system, wherein the EGR system comprises an EGR conduit that fluidly connects the exhaust duct and the intake duct, and wherein a gas feeding device configured to feed exhaust gas from the exhaust duct to the intake duct is arranged in the EGR conduit, the method comprises: detecting an indication of accumulated deposits of soot, hydrocarbons or other contaminants in the gas feeding device by determining whether a rotational friction of a rotary member of the gas feeding device exceeds a threshold value; and providing a flushing liquid in the EGR conduit upstream of the EGR gas feeding device so as to flush and clean the EGR gas feeding device as the flushing liquid follows the exhaust gas towards and into the EGR gas feeding device, wherein the detecting the indication of accumulated deposits is carried out before the providing the flushing liquid in the EGR conduit.

2. The method according to claim 1, wherein the method further comprises the steps of: condensing exhaust gas in or downstream an EGR cooling device arranged in association with the EGR conduit so as to form an EGR condensate, and using the EGR condensate as the flushing liquid.

3. The method according to claim 2, wherein the method further comprises the step of: controlling the operation of the internal combustion engine system so as to produce more EGR condensate than during normal operation of the internal combustion engine system.

4. The method according to claim 3, wherein the step of producing more EGR condensate comprises one or more of the following steps: increasing the efficiency of the EGR cooling device; increasing the mass flow of the exhaust gas flowing through the EGR conduit; increasing the fraction of fuel in an air-fuel mixture that is combusted in the internal combustion engine system; and/or operating the EGR system while the internal combustion engine system has a temperature that is lower than a normal operation temperature.

5. The method according to claim 1, wherein the step of providing the flushing liquid in the EGR conduit upstream of the EGR gas feeding device comprises the step of: introducing at least part of the flushing liquid into the EGR conduit via a flush liquid channel arranged in fluid communication with a flush liquid tank and the EGR conduit.

6. The method according to claim 1, wherein the method is carried out during cold start of the internal combustion engine system.

7. The method according to claim 1, wherein the gas feeding device is configured to feed exhaust gas by means of at least one rotating member.

8. The method according to claim 1, wherein the gas feeding device is configured to feed exhaust gas by means of a displacement pump, preferably a Roots type blower having a pair of rotors provided with meshing lobes.

9. The method according to claim 1, wherein the determination of the rotational friction comprises one or more of the following steps: measuring a torque applied to the rotary member, measuring a driving power, such as a drive motor current, of a drive source arranged to drive the gas feeding device and rotate the rotary member, measuring an actual rotational speed of the rotary member, measuring a response time of the rotary member between a change in driving power and a resulting change of rotational speed.

10. The method according to claim 1, wherein, in case an indication of accumulated deposits is detected, the method further comprises the step of: operating the rotary member in a reversed rotational direction, opposite to a rotational direction used under normal operational conditions.

11. The method according to claim 10, wherein the rotary member is operated in the reversed rotational direction in a pulsed manner during a short period, wherein the pulsed reversed operation is followed by continued operation in the normal operational rotational direction.

12. The method according to claim 11, wherein the short period during which the rotary member is operated in the reversed direction is less than 10 s, preferably less than 5 s.

13. The method according to claim 11, wherein the method comprises the step of: repeating the step of operating, in a pulsed manner, the rotary member in a reversed rotational direction.

14. The method according to claim 11, wherein the method comprises the step of operating the rotary member in a pulsed manner alternately in the reverse rotational direction and the normal rotational direction.

15. A method according to claim 1, wherein, in case an indication of accumulated deposits is detected, the method further comprises the step of: increasing a drive power of a drive motor arranged to drive the gas feeding device and the rotary member to a power level higher than a power level used under normal operational conditions.

16. A method according to claim 1, wherein, in case an indication of accumulated deposits is detected, the method further comprises the step of: guiding the flow of exhaust gas in the EGR conduit in a bypass conduit arranged in fluid communication with the EGR conduit upstream and downstream of the gas feeding device.

17. A method according to claim 1, wherein the method further comprises the step of: increasing the temperature of the exhaust gas flowing through the gas feeding device.

18. A method according to claim 17, wherein the method comprises the step of: operating the internal combustion engine system so as to increase the temperature of the exhaust gas and/or reducing a cooling effect of an EGR cooling device arranged in the EGR conduit upstream of the gas feeding device.

19. The internal combustion engine system defined in claim 1, including an electronic control unit configured to perform the method of claim 1.

20. The internal combustion engine system according to claim 19, wherein the engine system comprises a flush liquid channel arranged in fluid communication with a flush liquid tank and the EGR conduit, wherein the flush liquid channel is arranged to allow introduction of flushing liquid in the EGR conduit upstream of the EGR gas feeding device so as to allow flushing and cleaning of the EGR gas feeding device.

21. The internal combustion engine system according to claim 19, wherein the engine system comprises an EGR cooling device arranged in association with the EGR conduit.

22. A vehicle comprising the internal combustion engine system according to claim 19.

23. A non-transitory computer readable medium carrying a computer program comprising program code for controlling the steps of claim 1 when said program product is run on a computer.

24. A control unit for controlling an internal combustion engine system, the control unit being configured to control the steps of the method according to claim 1.

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 is a schematic view of a vehicle/truck provided with an internal combustion engine system according to the invention,

(4) FIG. 2 is a schematic view of the internal combustion engine system according to FIG. 1,

(5) FIG. 3 is a schematic sectional view of a gas feeding device in the form of a Roots type blower, and

(6) FIG. 4 is a flow diagram for an exemplary embodiment of the inventive method.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE INVENTION

(7) FIG. 1 shows a schematic view of a truck 1 provided with an internal combustion engine system 2 according to the invention.

(8) FIG. 2 shows a schematic view of the internal combustion engine system 2 according to FIG. 1. The engine system 2 is provided with an air intake duct 3, an exhaust gas duct 4 and an exhaust gas recirculation (EGR) system 5. Intake air 3a is compressed in a turbo compressor 3b before entering the intake duct 3. Exhaust gas 4a leaves the schematically illustrated engine system 2 after having passed through an exhaust turbine 4b that drives the turbo compressor 3b. The air intake duct 3 guides air to a plurality of cylinders 21 (in this example six) arranged in an engine block 20 and the exhaust duct 4 leads the exhaust gas away from the cylinders 21 and the engine block 20.

(9) In line with conventional engine systems each cylinder 21 is provided with a piston (not shown) as well as intake and exhaust valves (not shown), wherein the pistons are connected to a crankshaft (not shown) further connected to driving wheels of the vehicle 1 via various transmissions (not shown). Fuel supply and exhaust gas aftertreatment equipment is not shown in the figures.

(10) The EGR system 5 comprises an EGR conduit 6 that fluidly connects the exhaust duct 4 and the intake duct 3. To provide for a flow of EGR when the pressure is higher in the intake duct 3 than in the exhaust duct 4 a gas feeding device 7 configured to feed exhaust gas from the exhaust duct 4 to the intake duct 3 is arranged in the EGR conduit 6. The gas feeding device 7 is in this example a Roots type blower (see FIG. 3). A drive motor 9, in this case an electric motor, is arranged to drive the gas feeding device 7, which in this case means that the drive motor 9 is arranged to rotate rotary members 71, 72 of the gas feeding device 7 (see FIG. 3).

(11) The EGR system 5 further comprises: an EGR valve 12 for opening/closing of the EGR conduit 6 (the gas feeding device 7 can also function as EGR valve, see below); an EGR cooling device 8 arranged to allow for cooling of the exhaust gas flowing through the EGR conduit 6; an EGR bypass conduit 10 arranged in fluid communication with the EGR conduit 6 upstream and downstream of the gas feeding device 7 so as to allow for an EGR flow that by-passes the gas feeding device 7; and a bypass valve 11 arranged in the EGR bypass conduit 10.

(12) FIG. 2 further indicates an optional flush liquid channel 13 arranged to fluidly connect an optional flush liquid tank 14 with the EGR conduit 6 upstream of the EGR gas feeding device 7 for introduction of a flushing liquid into the EGR conduit 6. The channel 13 and tank 14 may be used as an alternative or complement to the provision of flushing liquid directly in the EGR conduit 6 by means of condensation as will be described below.

(13) The engine system 2 further comprises a control unit (not shown) configured to control parts and functions of the engine system 2 and to control e.g. all method steps described in this disclosure. The control unit receives information from various sensors (not shown) arranged in the engine system 2. The principle function of control units for controlling operation of internal combustion engines and engine systems is well known in the art.

(14) During normal operation of the engine system 2 the pressure is higher in the intake duct 3 than in the exhaust duct 4, the EGR valve 12 is open, the bypass valve 11 is closed, and the gas feeding device 7 feeds exhaust gas through the EGR conduit 6 from the exhaust duct 4 to the intake duct 3. The gas feeding device 7 can function as an EGR valve by e.g. turning it off and lock it in a stationary (non-rotating) position that substantially prevents through-flow. This is done by controlling the electric drive motor 9. The EGR valve 12 is thus in this example not necessary. When the gas feeding device 7 is turned off and locked, opening of the bypass valve 11 allows for a flow of exhaust gas through the EGR bypass conduit 10. The gas feeding device 7 may be turned off but set in a mode that allows through-flow, i.e. the rotary members 71, 72 of the Roots blower are allowed to rotate.

(15) FIG. 3 shows a schematic view of the gas feeding device 7 arranged in the EGR conduit 6, wherein the gas feeding device 7 is in the form of a Roots type blower having first and second rotary members 71, 72 provided with meshing lobes 71a, 71b, 72a, 72b configured to rotate inside a surrounding housing 73. Roots type blowers are well known as such. In some Roots type blowers each rotary member is provided with more than two lobes. In relation to FIG. 3 an incoming EGR flow in the EGR conduit 6 passes an inlet at the left and is displaced (as indicated by the arrows) by the rotary members 71, 72 to an outlet at the right and further into the EGR conduit 6 downstream of the gas feeding device 7 (towards the intake duct 3 and the cylinders 21 as indicated in FIG. 1).

(16) FIG. 4 shows a flowchart of an example of a method of operating the internal combustion engine system 2 where a flushing liquid in the form of EGR condensate is provided in the EGR conduit 6 upstream of the gas feeding device 7 for the purpose of flushing and cleaning of the EGR gas feeding device 7.

(17) The example of FIG. 4 comprises the steps of: S1—starting the engine system 2 (cold start), including operating the EGR system 5 (i.e. opening the EGR valve 12 if closed, starting the gas feeding device 7 and operating the EGR cooling device 8); S2—providing flushing liquid/EGR condensate in the EGR conduit 6 upstream of the EGR gas feeding device 7 by operating the engine system 2 so that EGR exhaust gas condenses in or downstream the EGR cooling device 8; and S3—flushing and cleaning the EGR gas feeding device 7 by allowing the flushing liquid/EGR condensate to follow the recirculated exhaust gas towards and into the EGR gas feeding device 7 where it will remove at least some of any deposited material.

(18) Steps S2 and S3 are carried out more or less simultaneously. Typically, step S3 does not require any particular action to be taken. Steps S2 and S3 may be regarded as one common step.

(19) Step S2 may start almost immediately after step S1 depending on the situation, such as initial temperature of engine system and initial setting on parameters for controlling the operation of the engine system 2. If EGR condensate is not produced in sufficient amounts in step S2 this step can comprise the action of controlling the engine system 2 to produce more EGR condensate by e.g. increasing the efficiency of the EGR cooling device 8, increasing the mass flow of the exhaust gas flowing through the EGR conduit 6 and/or increasing the fraction of fuel in an air-fuel mixture that is combusted in the internal combustion engine system 2.

(20) Steps S2 and S3 may be terminated after a certain time period or when the engine system 2 has reached a certain temperature (e.g. when the temperature of an engine cooling medium/water has reached a certain temperature).

(21) In a variant of the above example step S2 is preceded by the step of: S1′—detecting an indication of accumulated deposits of soot, hydrocarbons or other contaminants in the gas feeding device 7 by determining whether a rotational friction 30 of the rotary member 71, 72 of the gas feeding device 7 exceeds a threshold value,

(22) which, if the threshold value in step S1′ is exceeded, can be followed by steps S2 and S3.

(23) In this variant the engine system 2 may be operated under normal operating conditions during performance of step S1′. Whereas steps S2 and S3 in the example above are initiated as a response to cold start conditions (i.e. as a response to e.g. a low engine cooling medium temperature), these steps (S2 and S3) are carried out as a response to a high rotational friction of the rotary member 71, 72 of the gas feeding device 7 in the variant involving step S1′. Steps 2 and 3 may also be initiated as a response to e.g. the lapse of a certain time period since flushing of the gas feeding device 7 was carried out last time.

(24) As a complement or alternative to steps S2 and S3 in case the threshold value in step S1′ is exceeded, one or more of the following steps is/are possible: operating the rotary member 71, 72 in a reversed rotational direction, opposite to a rotational direction used under normal operational conditions; increasing a drive power of the drive motor 9 arranged to drive the gas feeding device 7 and the rotary member 71, 72 to a power level higher than a power level used under normal operational conditions; guiding the flow of exhaust gas in the EGR conduit 6 in the bypass conduit 10; and/or increasing the temperature of the exhaust gas flowing through the gas feeding device 7.

(25) These complementing or alternative steps are further described above.

(26) As to the determination of the rotational friction of the rotary member 71, 72 of the gas feeding device 7 it may comprise one or more of the following steps: measuring a torque applied to the rotary member 71, 72; measuring a driving power, such as a drive motor current, of the drive motor 9; measuring an actual rotational speed of the rotary member 71, 72; measuring a response time of the rotary member 71, 72 between a change in driving power and a resulting change of rotational speed.

(27) As an alternative or complement to the provision of a flushing liquid by generating EGR condensate directly in the EGR conduit 6 used in step S2, it is possible to introduce flushing liquid into the EGR conduit 6 from the flush liquid tank 14 via the flush liquid channel 13. The flush liquid tank 14 may contain previously accumulated EGR condensate or another liquid.

(28) It is to be understood that the present invention is not limited to the embodiments described above and illustrated in the drawings; rather, the skilled person will recognize that many changes and modifications may be made within the scope of the appended claims.