Method for controlling an internal combustion engine system

Abstract

The invention relates to a method for controlling 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) is arranged in the EGR conduit (6), said gas feeding device (7) being configured to feed exhaust gas from the exhaust duct (4) to the intake duct (3) during operation of the engine system (2). The method is characterized in that it comprises the step of: detecting a risk of freezing of condensed water in the EGR conduit (6), and, in case such a risk is detected and in case the gas feeding device (7) is not in operation, operating the 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 controlling 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 in a form of a positive displacement pump is arranged in the EGR conduit, said gas feeding device being configured to feed exhaust gas from the exhaust duct to the intake duct during operation of the engine system, characterized in that the method comprises the step of: detecting a risk of freezing of condensed water in the EGR conduit, detecting non-operation of moving parts of the gas feeding device, and, in case such a risk is detected and the moving parts of the gas feeding device is not in operation, operating the gas feeding device to pump the condensed water out by the moving parts of the gas feeding device.

2. Method according to claim 1, wherein the step of detecting the freezing risk comprises the step of determining a temperature in or close to the gas feeding device.

3. Method according to claim 2, wherein the step of determining the temperature comprises at least two temperature determinations carried out at different points in time so as to allow a determination of a change of the temperature in or close to the gas feeding device.

4. Method according to claim 1, wherein the step of detecting the freezing risk comprises the step of determining a humidity in the EGR conduit.

5. Method according to claim 1, wherein the step of operating the gas feeding device is carried out so as to pump any condensed water out from the EGR conduit and from the gas feeding device.

6. Method according to claim 1, wherein the step of operating the gas feeding device is carried out by operating the gas feeding device in a low-power mode in which the capability of the gas feeding device to feed gas is smaller than during normal operational conditions but where moving parts of the gas feeding device are kept in motion.

7. Method according to claim 6, wherein the step of operating the gas feeding device in the low-power mode comprises the step of: determining whether a rotational friction of a rotary member of the gas feeding device exceeds a threshold value, and, in case the threshold value is exceeded, 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 normally used in the low-power mode.

8. Method according to claim 1, wherein the method is carried out within a threshold time interval after switching off the internal combustion engine system.

9. Method according to claim 1, wherein the method is carried out within an arbitrary interval after switching off the internal combustion engine system.

10. 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.

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

12. The method according to claim 1, wherein the engine system comprises a drive motor arranged to drive the gas feeding device.

13. An internal combustion engine system 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 in a form of a positive displacement pump is arranged in the EGR conduit, said gas feeding device being configured to feed exhaust gas from the exhaust duct to the intake duct during operation of the engine system, characterized in that the engine system is configured to control the steps of claim 1.

14. A vehicle comprising an internal combustion engine system according to claim 13.

15. A computer program product comprising program code means for controlling the steps of claim 1 when said program is run on a computer.

16. A computer readable medium carrying a computer program comprising program code means for controlling the steps of claim 1 when said program product is run on a computer.

17. A control unit for controlling an internal combustion engine according to claim 13, the control unit being configured to perform the steps.

18. The method according to claim 12, wherein the drive motor is an electric motor.

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 4a 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 25 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 30 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 35 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) 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.

(13) 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.

(14) 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 25 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).

(15) FIG. 4 shows a flowchart of an example of a method of controlling the internal combustion engine system 2 in a situation where the general operation of the engine system 2 has been switched off some time ago (i.e. pistons, valves, turbo compressor 3B etc. do not move, no air is fed through the intake duct 3, no exhaust gas is produced, the gas feeding device 7 is not in operation but is operable, etc.). The exemplified method illustrates detection of a risk of freezing of condensed water in the EGR conduit 6 (that might damage the gas feeding device 7) and which action that is taken if such a risk is detected. Further actions are discussed below.

(16) The step of switching off the general operation of the engine system 2 is carried out before the exemplified method.

(17) The example of FIG. 4 comprises the steps of: S1—determining a first temperature T1 in or close to the gas feeding device 7 at a first point in time t1; S2—determining a second temperature T2 in or close to the gas feeding device 7 at a second point in time t2, which is later (e.g. 5 min) than the first point in time t1; S3—determining whether T2 is below a pre-set threshold level (e.g. 3° C.) and whether T2 is less than T1 (i.e. whether the temperature is decreasing);
in case T2 is below the pre-set threshold level and T2 is less than T1, S4—operating the gas feeding device 7 so as to pump any condensed water out from the EGR conduit 6 or at least out from the gas feeding device 7.

(18) Various options are possible after step S4 and what to do depend on the particular application and situation.

(19) In some engine systems, depending e.g. on where the gas feeding device 7 is positioned 30 in the EGR system 5, and in some situations, depending e.g. on how the engine system 2 was operated before switching off and on the values of T1 and T2, it may be that the freezing risk, or at least that the risk of having the gas feeding device 7 damaged due to freezing, is eliminated after step S4. In such a case the method has fulfilled its purpose and can be terminated.

(20) In other cases it may be suitable to repeat the method (where the already determined T2 may form the “first temperature” so that only S2, S3 and, possibly, S4 are repeated, with a new “second temperature” determined in S2). Further repetitions are possible.

(21) In still other cases step S4 may be followed by operating the gas feeding device 7 in a low-power mode in which the capability of the gas feeding device 7 to feed gas is smaller than during normal operational conditions but where the rotary members 71, 72 of the gas feeding device 7 are kept in motion. This “creep mode” is further described above. During operation in low-power (“creep”) mode it is suitable to determine whether a rotational friction of at least one of the rotary members 71, 72 exceeds a threshold value, since increased rotational friction might be an indication on that ice has begun to be formed in the gas feeding device 7. The rotational friction can be determined in several ways as described above. In case the threshold value is exceeded, it is suitable to increase a drive power of the drive motor 9 arranged to drive the rotary members 71, 72 to a power level higher than a power level normally used in the low-power mode. This will remove water/ice from the gas feeding device or at least keep the rotary members 71, 72 in motion and prevent them from getting stuck/freezing up.

(22) 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.