CONTROL SYSTEM FOR INTERNAL COMBUSTION ENGINE, AND CONTROL METHOD FOR INTERNAL COMBUSTION ENGINE

FIELD OF THE INVENTION

[0001] The present invention relates to a control system for an internal combustion engine in which a filter which collects particulate matter within the exhaust is provided to an exhaust passage, and to a control method for the internal combustion engine.

BACKGROUND OF THE INVENTION

[0002] In Japanese Patent Application Publication No. JP-A-2004-44443, there is disclosed a technique related to an exhaust purification device for an internal combustion engine in which a filter which carries a NOx occlusion substance is provided to the exhaust passage. According to this publication, it is decided whether or not the filter is clogged, based upon change of the pressure within the exhaust passage at the upstream side of the filter when the exhaust flow amount has decreased so that it is necessary to perform reduction of the NOx which has been occluded in the NOx reduction substance.

DISCLOSURE OF THE INVENTION

[0003] The object of the present invention is to provide, for an internal combustion engine in which a filter which collects particulate matter within the exhaust is provided to an exhaust passage, a technique which can improve the stability of the combustion state.

[0004] A first aspect of the present invention relates to a control system for an internal combustion engine in which a filter which collects particulate matter (hereinafter

termed "PM") within the exhaust is provided in an exhaust passage. With this control system, along with increase of the amount of PM collected in the filter, it is possible to suppress elevation of pressure in the exhaust passage on the upstream side of that filter by increasing the opening amount of an exhaust throttle valve. [0005] In more detail, the present invention relates to a control system for an internal combustion engine, in which a filter which collects particulate matter within the exhaust is provided in an exhaust passage. This control system for an internal combustion engine includes a pressure detection means which detects an upstream side pressure, which is the pressure in the exhaust passage on the upstream side of the filter, and an exhaust throttle valve provided in the exhaust passage on the downstream side of the filter. When the operational state of the internal combustion engine is a steady operational state, the opening amount of the exhaust throttle valve is controlled so that the upstream side pressure detected by the pressure detection means becomes a constant value. [0006] Even if the operational state of the internal combustion engine is a steady operational state, the upstream side pressure is elevated when the amount of PM collected in the filter increases. At this time, it is possible to suppress elevation of this upstream side pressure by gradually increasing the opening amount of the exhaust throttle valve according to the increase of the amount of PM which is collected in the filter. [0007] Thus, when the operational state of the internal combustion engine is a steady operational state, the opening amount of the exhaust throttle valve is controlled so that the upstream side pressure becomes a constant value.

[0008] By doing this, it is possible to suppress excessive elevation of the upstream side pressure. Furthermore, it is possible to keep the influence exerted upon the combustion state of the internal combustion engine by the upstream pressure constant. Due to this, it is possible to make the combustion state of the internal combustion engine more stable.

[0009] The pressure detection means may be a pressure sensor which outputs an electrical signal corresponding to the upstream side pressure.

[0010] And it may be arranged for the pressure detection means to estimate the upstream side pressure based upon the operational state of the internal combustion engine.

[0011] The steady operational state may be the idling operational state after the end of the internal combustion engine warming up.

[0012] Or, the steady operational state may be the idling operational state after the temperature of the filter has decreased to normal temperature.

[0013] There may be further included a collected PM amount estimation means which estimates the amount of collected PM in the filter, based upon the opening amount of the exhaust throttle valve when the operational state of the internal combustion engine is a steady operational state.

[0014] As described above, the opening amount of the exhaust throttle valve is gradually increased according to increase of the amount of PM collected in the filter. Due to this, it is possible to estimate the amount of PM collected in the filter based upon the opening amount of the exhaust throttle valve.

[0015] In this case, it would also be acceptable to arrange to estimate the amount of PM collected in the filter, while not further providing any pressure difference detection device which detects the pressure difference in the exhaust passage between its side upstream of the filter and its side downstream thereof. [0016] There may be further included a pressure difference detection device which includes a pipe whose end portions are connected to the exhaust passage at the upstream side and the downstream side of the filter, and a pressure difference detection unit which is provided in the pipe and detects the pressure difference in the exhaust passage between the upstream side and the downstream side of the filter. [0017] Furthermore, a collected PM amount estimation means which estimates the amount of PM collected in the filter based upon the opening amount of the exhaust throttle valve may be taken as a first collected PM amount estimation means, and there may also be included a second collected PM amount estimation means which estimates the collected amount of particulate matter in the filter, based upon the pressure difference

detected by the pressure difference detection device.

[0018] At this time, if clogging of the pipe of the pressure difference detection device by PM has occurred, the value of the collected PM amount as estimated by the second collected PM amount estimation means increases, even though the amount of collected PM in the filter has not increased.

[0019] Thus, in the above described case, it may be decided that clogging of the pipe of the pressure difference detection device has occurred, if the value obtained by subtracting the amount of collected particulate matter which is estimated by the first collected PM amount estimation means from the collected amount of particulate matter which is estimated by the second PM amount estimation means is greater than or equal to a predetermined value.

[0020] Here, the predetermined value is a value which constitutes a threshold value, by which it is possible to decide that the collected amount of particulate matter as estimated by the second collected PM amount estimation means has increased due to the occurrence of clogging of the pipe of the pressure difference detection device.

[0021] A second aspect of the present invention relates to a control method for an internal combustion engine in which a filter which collects particulate, matter within the exhaust is connected to an exhaust passage. In this control method for the internal combustion engine, an upstream side pressure, which is the pressure in the exhaust passage on the upstream side of the filter, is detected. Furthermore, when the operational state of the internal combustion engine is a steady operational state, the opening amount of an exhaust throttle valve which is provided in the exhaust passage on the downstream side of the filter is controlled so that the upstream side pressure becomes a constant value. [0022] According to aspects of the present invention, for an internal combustion engine in which a filter which collects particulate matter within the exhaust is provided to an exhaust passage, it is possible to make the state of combustion more stable.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The foregoing and further objects, features and advantages of the invention will become apparent from the following description of preferred embodiments with reference to the accompanying drawings, wherein like numerals are used to represent like elements and wherein:

Fig. 1 is a schematic structural diagram of the intake and exhaust system of an internal combustion engine according to a first embodiment;

Fig. 2 is a flow chart showing a control routine for upstream side pressure control according to the first embodiment;

Fig. 3 is a flow chart showing a collected PM amount calculation routine according to the first embodiment;

Fig. 4 is a schematic structural diagram of the intake and exhaust system of an internal combustion engine according to a second embodiment; and Fig. 5 is a flow chart showing a pipe clogging decision routine according to the second embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] In the following, concrete embodiments of the control system for an internal combustion engine according to the present invention will be explained with reference to the drawings.

[0025] Here, the present invention will be explained by citing, as an example, the case in which it is applied to a diesel engine for driving a vehicle. Fig. 1 is a figure showing the schematic structure of the intake and exhaust system of an internal combustion engine according to a first embodiment.

[0026] The internal combustion engine 1 is a diesel engine for driving a vehicle. An intake passage 3 and an exhaust passage 2 are connected to this internal combustion engine 1. A particulate filter 4 (hereinafter simply termed a "filter") which

collects PM within the exhaust is provided in the exhaust passage 2. An occlusion reduction type NOx catalyst is carried upon the filter 4. It should be understood that the catalyst which is carried upon the filter 4 is not limited to being an occlusion reduction type NOx catalyst. For example, it could be a catalyst having an oxidant function, such as an oxidant catalyst.

[0027] Furthermore, in the exhaust passage 2, on the upstream side of the filter

4, there is provided a pressure sensor 5 which outputs an electric signal corresponding to the pressure within the exhaust passage 2 (the upstream side pressure). Furthermore, an exhaust throttle valve 6 is provided in the exhaust passage 2, on the downstream side of the filter 4.

[0028] To this internal combustion engine 1 which has the structure described above, there is provided an electronic control unit (ECU) 10 for controlling the internal combustion engine 1. This ECU 10 is a unit which controls the operational state of the internal combustion engine 1 according to the operating conditions of the internal combustion engine 1 or requests from the driver.

[0029] To this ECU 10 there are electrically connected the pressure sensor 5, a crank position sensor 7 which outputs an electrical signal corresponding to the rotational angle of the crank shaft of the internal combustion engine 1, and an accelerator opening amount sensor 8 mounted to the internal combustion engine 1 which outputs an electrical signal corresponding to the accelerator opening amount of the vehicle. And the output signals of these sensors are inputted to the ECU 10.

[0030] The ECU 10 calculates the rotational speed of the internal combustion engine 1 based upon the value detected by the crank position sensor 7. Furthermore, the ECU 10 calculates the load upon the internal combustion engine 1, based upon the value detected by the accelerator opening amount sensor 8.

[0031] Moreover, the exhaust throttle valve 6 and a fuel injection valve of the internal combustion engine 1 are electrically connected to the ECU 10. These are controlled by the ECU 10.

[0032] Now, the upstream side pressure control according to this embodiment

will be explained. In this embodiment, a reference pressure, which is a reference value for the upstream side pressure, and a reference opening amount, which is a reference value for the opening amount of the exhaust throttle valve 6, are set in advance according to the operational state of the internal combustion engine 1. Here, this reference pressure is a value at which no excessive influence will be exerted upon the combustion state in the internal combustion engine 1. Furthermore, the reference opening amount is an opening amount of the exhaust throttle valve 6 at which the upstream side pressure becomes equal to the reference pressure, when the filter 4 is in its initial state (its state in which no PM is collected therein). [0033] Suppose that the filter 4 is in its initial state and the operational state of the internal combustion engine 1 is a steady operational state. In this case, let the opening amount of the exhaust throttle valve 6 be taken as the reference opening amount corresponding to the operational state of the internal combustion engine 1 at this time. By doing this, it is possible to take the upstream side pressure as the reference pressure according to the operational state of the internal combustion engine 1 at this time.

[0034] However, PM within the exhaust is collected within the filter 4. Along with increase of this collected PM amount, the upstream side pressure gradually comes to be elevated, even though the operational state of the internal combustion engine 1 may be the steady operational state. [0035] When the upstream side pressure becomes excessively high, there is a fear that it may exert an excessive influence upon the combustion state in the internal combustion engine 1. Thus, in this embodiment, when the operational state of the internal combustion engine 1 is a steady operational state, the opening amount of the exhaust throttle valve 6 is controlled so as to maintain the value detected by the pressure sensor 5 at the reference pressure. In other words, the elevation of the upstream side pressure which accompanies the increase of the PM amount collected in the filter 4 is suppressed by gradually increasing the opening amount of the exhaust throttle valve 6 from the reference opening amount.

[0036] In the following, the control routine for upstream side pressure control

according to this embodiment will be explained based upon the flow chart shown in Fig. 2. This routine is stored in advance in the ECU 10, and is a routine which is repeated at predetermined intervals.

[0037] In this routine, first, in a step SlOl, the ECU 10 distinguishes whether or not the operational state of the internal combustion engine 1 is the steady operational state. If an affirmative decision has been made in this step SlOl, then the ECU 10 proceeds to the step S 102. However, if a negative decision has been made in the step

SlOl, then the ECU 10 terminates the execution of this routine.

[0038] In the step S 102, the ECU 10 derives a reference pressure PupO based upon the operational state of the internal combustion engine 1. In this embodiment, the relationship between the operational state of the internal combustion engine 1 and the reference pressure PupO is stored in advance as a map in the ECU 10.

[0039] Next, the ECU 10 proceeds to the step S 103, in which it controls the opening amount Qv of the exhaust throttle valve 6, so that the value Pup detected by the pressure sensor 5 becomes equal to the reference pressure PupO. In other words, if the value Pup detected by the pressure sensor 5 is higher than the reference pressure PupO, then the opening amount Qv of the exhaust throttle valve 6 is increased. After this, the ECU 10 terminates the execution of this routine.

[0040] According to this embodiment, it is possible to prevent excessive elevation of the upstream side pressure. Furthermore, by keeping the upstream side pressure at a constant value (the reference pressure), it is possible to keep the influence which this upstream side pressure exerts upon the combustion state of the internal combustion engine 1 constant. Due to this, it is possible to make the combustion state of the internal combustion engine 1 more stable. [0041] It should be understood that, in this embodiment, it would also be acceptable not to provide the pressure sensor 5, but instead to estimate the upstream side pressure based upon the operational state of the internal combustion engine, or the like.

[0042] Next, the method according to this embodiment for estimating the amount of PM collected in the filter 4 will be explained. As described above, in this

embodiment, when the operational state of the internal combustion engine 1 is in a steady operational state, then the opening amount of the exhaust throttle valve 6 is controlled so as to maintain the upstream side pressure at the reference pressure.

[0043] In other words, when the filter 4 is in its initial state, the opening amount of the exhaust throttle valve 6 is controlled to be equal to the reference opening amount. And, in correspondence to increase of the amount of PM collected by the filter 4, the opening amount of the exhaust throttle valve 6 gradually becomes greater. Due to this, it is possible to estimate the amount of PM collected by the filter 4 based upon the opening amount of the exhaust throttle valve 6. [0044] Now, a collected PM amount calculation routine, which calculates the amount of PM collected by the filter 4 according to this embodiment, will be explained based upon the flow chart shown in Fig. 3. This routine is stored in advance in the ECU 10, and is a routine which is executed at predetermined intervals.

[0045] In this routine, first, in a step S201, the ECU 10 distinguishes whether or not the operational state of the internal combustion engine 1 is the steady operational state. If an affirmative decision has been made in this step S201, then the ECU 10 proceeds to the step S202. However, if a negative decision has been made in the step S201, then the ECU 10 terminates the execution of this routine.

[0046] In the step S202, the ECU 10 subtracts the reference opening amount QvO for the exhaust throttle valve 6 corresponding to the operational state of the internal combustion engine 1 from the opening amount Qv of the exhaust throttle valve 6. By doing this, the opening amount increase amount δQv is calculated from the reference opening amount QvO for the exhaust throttle valve 6.

[0047] Next, the ECU 10 proceeds to the step S203, in which it calculates the amount Qpm of PM collected in the filter 4 from the opening amount increase amount δQv of the exhaust throttle valve 6. In this embodiment, the relationship between the opening amount increase amount δQv of the exhaust throttle valve 6 and the collected amount Qpm of PM in the filter 4 is obtained by experiment or the like, and these relationships may be stored in advance as a map in the ECU 10. Having calculated the

collected PM amount in the filter 4, the ECU 10 terminates the execution of this routine.

[0048] When estimating the amount of PM collected in a filter, there is a known method of providing a pressure difference sensor which detects the pressure difference in the exhaust passage between the upstream side and the downstream side of the filter, and of estimating the collected PM amount based upon the value detected by this pressure difference sensor.

[0049] However, according to the collected PM amount estimation method according to this embodiment, it is possible to estimate the amount of PM collected in the filter 4 while not additionally providing this type of pressure difference sensor. [0050] It should be understood that it would also be acceptable to initiate filter regeneration control, in order to eliminate PM from the filter 4, when the collected PM amount, as estimated by a collected PM amount estimation method like the one described above, reaches an upper limit value which has been determined in advance. As such filter regeneration control, there may be cited, by way of example, a method of supplying an unburned fuel component to the occlusion reduction type NOx catalyst which is carried upon the filter 4 by executing secondary fuel injection after the main fuel injection for the internal combustion engine 1.

[0051] Furthermore, it becomes difficult to suppress the increase of the upstream side pressure which accompanies increase of the amount of PM collected in the filter 4 by controlling the opening amount of the exhaust throttle valve 6 after the time point at which the exhaust throttle valve 6 has become in the fully open state or in the neighborhood of the fully open state. Thus, it is preferable to initiate execution of filter regeneration control when this state has come to pass.

[0052] In this embodiment, it is arranged to calculate the amount of PM collected in the filter 4 when the operational state of the internal combustion engine 1 is a steady operational state. However it would also be acceptable to perform this calculation of the amount of collected PM when, after warming up of the internal combustion engine I ₅ it is in the idling operational state.

[0053] Furthermore, after such filter regeneration control has been completed,

it would also be acceptable to calculate the remaining amount of PM in the filter 4 (the amount which it has been impossible to eliminate) by performing calculation of the collected PM amount when the engine is idling, after the temperature of the filter 4 has decreased to its normal temperature. [0054] Fig. 4 is a figure showing the schematic structure of the intake and exhaust systems of an internal combustion engine according to a second embodiment. The schematic structure of the intake and exhaust systems of the internal combustion engine according to this embodiment differs from that of the first embodiment, only in the aspect that a pressure difference sensor 11 is provided to the exhaust passage 2. With regard to the other structure thereof, the same reference numbers are appended to the same structures, and the explanation thereof will be curtailed.

[0055] The pressure difference sensor 11 comprises a pipe 12 and a pressure difference detection unit 13. The end portions of the pipe 12 are connected to the exhaust passage 2, one on the upstream side of the filter 4, and the other on its downstream side. And the pressure difference sensor 11 is provided partway along this pipe. This pressure difference sensor 11 detects the difference of pressures in the exhaust passage 2 between its side upstream of the filter 4 and its side downstream thereof (in the following, termed the "before/after filter pressure difference"). This pressure difference sensor 11 is electrically connected to the ECU 10. The output signal of the pressure difference sensor 11 is inputted to the ECU 10.

[0056] The more that the amount of PM collected in the filter 4 increases, the more does the before/after filter pressure difference increase. Due to this, in this embodiment, it is also possible to estimate the amount of PM collected in the filter 4 based upon the value detected by the pressure difference sensor 11. [0057] Sometimes PM flows into the pipe 12 of the pressure difference sensor

11. Thus, a pipe clogging decision method for deciding whether not clogging of the pipe 12 by PM has occurred will now be explained.

[0058] In this embodiment, just as with the first embodiment, the amount of PM which has collected in the filter 4, as estimated based upon the opening amount of the

exhaust throttle valve 6, is taken as a first collected PM amount estimated value. On the other hand, the amount of PM which has collected in the filter 4, as estimated based upon the value detected by the pressure difference sensor 11, is taken as a second collected PM amount estimated value. [0059] When the pipe 12 is clogged by PM, the value detected by the pressure difference sensor 11 is elevated even though the amount of PM collected in the filter 4 is not increased. In other words, the second collected PM amount estimated value comes to be increased.

[0060] Thus, if the second collected PM amount estimated value becomes a value which exceeds the first collected PM amount estimated value by a predetermined value, it is decided that clogging of the pipe 12 by PM has occurred. Here, this predetermined value is a value which constitutes a threshold value for being able to decide that the second collected PM amount estimated value has increase due to clogging of the pipe 12 having occurred. This predetermined value is a value which is determined in advance by experiment or the like.

[0061] In the following, the pipe clogging decision routine according to this embodiment when deciding whether or not clogging of the pipe 12 by PM has occurred will be explained based upon the flow chart shown in Fig. 5. This routine is stored in advance in the ECU 10, and is a routine which is repeated at predetermined intervals. [0062] In this routine, first, in a step S301, the ECU 10 distinguishes whether or not the operational state of the internal combustion engine 1 is the steady operational state. If an affirmative decision has been made in this step S301, then the ECU 10 proceeds to a step S302. However, if a negative decision has been made in the step S301, then the ECU 10 terminates the execution of this routine. [0063] In the step S302, the ECU 10 calculates a first collected PM amount estimated value Qpml.

[0064] Next, the ECU 10 proceeds to a step S303, in which it calculates a second collected PM amount estimated value Qpm2.

[0065] Next, the ECU 10 proceeds to a step 304, in which it distinguishes

whether or not the value δQpm which is obtained by subtracting the first collected PM amount estimated value Qpml from the second collected PM amount estimated value Qpm2 is greater than or equal to a predetermined value δQpmO. If an affirmative decision has been made in this step S304, then the ECU 10 proceeds to a step S305. However, if a negative decision has been made in the step S304, then the ECU 10 terminates the execution of this routine.

[0066] In the step S305, the ECU 10 decides that clogging of the pipe 12 by PM has occurred. In this case, the ECU 10 notifies the driver of the vehicle that clogging of the pipe 12 has occurred. Thereafter, the ECU 10 terminates the execution of this routine.

[0067] According to the routine explained above, it is possible to detect any anomaly in the pressure difference sensor 11.

[0068] It should be understood that, in this embodiment, when the second collected PM amount estimated value becomes greater than or equal to a threshold value for initiating the execution of filter regeneration control, it may be decided that clogging of the pipe 12 due to PM has occurred, if the first collected PM amount estimated value does not reach that threshold value.

[0069] While the invention has been described with reference to what are considered to be preferred embodiments thereof, it is to be understood that the invention is not limited to the disclosed embodiments or constructions. On the contrary, the invention is intended to cover various modifications and equivalent arrangements. In addition, while the various elements of the disclosed invention are shown in various combinations and configurations, which are exemplary, other combinations and configurations, including more, less or only a single element, are also within the spirit and scope of the invention.