INJECTION AMOUNT LEARNING DEVICE AND INJECTION AMOUNT LEARNING METHOD FOR INTERNAL COMBUSTION ENGINE

BACKGROUND OF THE INVENTION 1. Field of the Invention

[0001] The invention relates (o an injection amount learning device for an internal combustion engine which executes the injection amount learning in an internal combustion engine, and an injection amount learning method therefor.

2. Description of the Related Art

[0002] This kind of technology is described in, for example, Japanese Patent Application Publication No. 2000-282926 (JP-A-2000-282926), Japanese Patent Application Publication No. 2002-38997 (JP-A-2002-38997), and Japanese Patent Application Publication No. 2005-16486 (JP-A-2005- 16486). Japanese Patent Application Publication No. 2000-282926 (JP-A-2000-282926) describes a technology in which the speed change ratio (or gear ratio) of a continuously variable transmission is controlled so that the engine is in a high-load operation state, and the state of variation of the amount of fuel injection is learned. Japanese Patent Application Publication No. 2002-38997 (JP-A-2002-38997) describes a technology in which the pilot injection amount and the injection timing are learned and corrected separately for each cylinder. Japanese Patent Application Publication No. 2005-16486 (JP- A-2005-16486) describes a technology in which if a characteristic value of emission, generated torque, etc., deviates from a predetermined range, the learned injection amount is altered so that the characteristic value is contained in the predetermined range. Furthermore, other technologies relevant to the invention are described in Japanese Patent Application Publication No. 2002-30958 (JP-A-20O2-30958), and Japanese Patent Application Publication Xo. 2003-83140 (JP-A-2003-83140).

[0009] In the technologies described in the foregoing patent literatures, however, it sometimes happens that during deceleration or the like of a vehicle, the fuel injection at

the time of injection amount learning causes an engine rotation (torque) fluctuation, resulting in a jerky thrust feel.

SUMMARY OF THE INVENTION [0004] The invention provides an injection amount learning device and an injection amount learning method capable of appropriately performing an injection amount learning while restraining the occurrence of a jerky thrust feel during deceleration of the vehicle.

[0005] In a first embodiment of the invention, an injection amount learning device for an internal combustion engine includes: a first learning portion that, during deceleration of a vehicle, performs an injection amount learning on a fuel injection valve by performing injection of a very small amount of fuel from the fuel injection valve to a cylinder of the internal combustion engine; and a control portion that controls the vehicle so that a torque fluctuation or a rotation fluctuation brought about by the injection of the very small amount of fuel is cancelled out when the injection amount learning is performed.

[0006] The foregoing injection amount learning device for an internal combustion engine is suitably utilized to execute the injection amount learning in the internal combustion engine. Concretely, the first learning portion performs the injection amount learning by injecting a very small amount of fuel from the fuel injection valve to the corresponding cylinder of the internal combustion engine during deceleration of the vehicle. Besides, at the time of the foregoing injection amount learning, the control portion controls the vehicle so that the torque fluctuation or the rotation fluctuation brought about by the injection of the very small amount of fuel is cancelled out Therefore, it becomes possible to appropriately perform the injection amount learning with regard to the fuel injection valve while restraining the occurrence of a jerky thrust feel during deceleration of the vehicle.

[0007] In the injection amount learning device of the first aspect, the internal combustion engine may be constructed so that output of the internal combustion engine

is transmitted to a continuously variable transmission, and the control portion may shift the speed change ratio of the continuously variable transmission so that the torque fluctuation or the rotation fluctuation brought about by the injection of the very small amount of fuel is cancelled out by brake torque of the internal combustion engine. [0008] In this aspect, the control portion increases the brake torque (deceleration brake torque) by, for example, shifting the speed change ratio so that the rotation speed of the interna] combustion engine becomes higher. Therefore, it becomes possible to appropriately cancel out the torque fluctuation or the rotation fluctuation brought about by the fuel injection that produces engine output is cancelled out by the brake torque. [0009] In the foregoing injection amount learning device, the first learning portion may alter a learned value for use in the injection amount learning based on whether or not the torque fluctuation or the rotation fluctuation is cancelled out by the control portion shifting the speed change ratio. Therefore, the injection amount learning with regard to the fuel injection valve can be accurately performed. [0010] In the foregoing injection amount learning device, the control portion may shift the speed change ratio of the continuously variable transmission so that the internal combustion engine reaches a rotation speed at which the torque fluctuation or the rotation fluctuation that is greater than or equal to a predetermined value occurs when the very small amount of fuel is injected. Therefore, the rotation speed of the engine can be appropriately set at a speed at which the torque fluctuation or the rotation fluctuation can be accurately detected. Thus, it becomes possible to accurately perform the injection amount learning with regard to the fuel injection valve.

[0011] Besides, the control portion may include a computation portion that detects the torque fluctuation or the rotation fluctuation, and the predetermined value may be determined based on a computing capacity of the computation portion.

[0012] In the foregoing injection amount learning device, the vehicle may be constructed as a hybrid vehicle, and the control portion may change an amount of regeneration performed by an electric motor provided in the hybrid vehicle so that the torque fluctuation or the rotation fluctuation brought about by the fuel injection from the

fuel injection valve is cancelled out by the regeneration performed by the electric motor. This also makes it possible to appropriately perform the injection amount learning with regard to the fuel injection valve while restraining the occurrence of a jerky thrust feel in the vehicle. [0013] In the injection amount learning device of the first embodiment for the internal combustion engine, the internal combustion engine may include a catalyst provided on an exhaust passageway, an adding valve that adds fuel into the exhaust passageway at an upstream side of the catalyst, a first EGR passageway that returns exhaust gas from a location on the exhaust passageway at a downstream side of the catalyst to a location on an intake passageway at an upstream side of a compressor of a turbocharger, and a first EGR valve provided on the first EGR passageway, and the injection amount learning device may further include a second learning portion that performs the injection amount learning on the adding valve based on a rotation fluctuation or a torque fluctuation that is bought about by injecting fuel from the adding valve, and the second learning portion may control the first EGR valve to a fully open state when the injection amount learning on the adding valve is performed, and may perform the injection amount learning on the adding valve when exhaust gas from fuel injected from the adding valve returns to the cylinder through the first EGR passageway. This construction will make it possible to accurately perform the injection amount learning with regard to the adding valve.

[0014] In the foregoing injection amount learning device, the second learning portion may perform the injection amount learning on the adding valve after the injection amount learning by the first learning portion ends. The control portion may cause the fuel injection valve on which the injection amount learning by the first learning portion has ended to inject fuel when the second learning portion performs the injection amount learning on the adding valve. Therefore, the accuracy of the detection of the rotation fluctuation or the like can be improved, and it becomes possible to further accurately perform the injection amount learning with regard to the adding valve.

[0015] Furthermore, the second learning portion may stop the injection amount

learning on the adding valve when exhaust gas from fuel injected for a first time from the fuel injection valve has returned to an intake side through the first EGR passageway. This makes it possible to prevent false learning in the injection amount learning, and makes it possible to improve the accuracy of the injection amount learning, [0016] A second embodiment of the invention is an injection amount learning method for an internal combustion engine. The injection amount learning method includes: performing an injection amount learning on a fuel injection valve by performing injection of a very small amount of fuel from the fuel injection valve to a cylinder of the internal combustion engine when it is determined that the vehicle is decelerating; and controlling the vehicle so that a torque fluctuation or a rotation fluctuation brought about by the injection of the very small amount of fuel is cancelled out. This makes it possible to appropriately perform the injection amount learning with regard to the fuel injection valve while restraining the occurrence of a jerky thrust feel during acceleration of the vehicle.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The foregoing and further objects, features and advantages of the invention wfll 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 block diagram showing a general construction of a vehicle to which an injection amount learning device for an internal combustion engine in accordance with an embodiment of the invention is applied;

FIGS. 2A and 2B are diagrams for describing a method of shifting the speed change ratio of transmission in the first embodiment;

FIG 3 is a diagram showing a concrete example of the brake torque during deceleration of the vehicle;

FIG 4 is a flowchart showing an injection amount learning process in accordance with the first embodiment;

FIG S is a diagram for describing an injection amount learning method in accordance with a second embodiment;

FIG 6 is a flowchart showing an injection amount learning process in accordance with the second embodiment; FIGS. 7 A and 7b are diagrams for describing an injection amount learning method in accordance with a third embodiment;

FIG 8 is a flowchart showing an injection amount learning process in accordance with the third embodiment;

FIG 9 is a flowchart showing an injection amount learning process in accordance with a fourth embodiment;

FIG 10 is a flowchart showing an injection amount learning process in accordance with a fifth embodiment; and

FIG 11 is a block diagram showing a general construction of a vehicle to which an injection amount learning device for an internal combustion engine in accordance with a modification in the invention is applied.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0018] Preferred embodiments of the invention will be described hereinafter with reference to the drawings. [0019J [DEVICE CONSTRUCTION] FIG 1 is a block dfagram showing a general construction of a vehicle 100 to which an injection amount learning device for an internal combustion engine in accordance with an embodiment of the invention is applied. In FIG 1, solid-line arrows show flows of intake and exhaust, and broken-line arrows show the input/output of signals. [0020] The vehicle 100 mainly includes an engine 10, a fuel injection valve IS, a rotation speed sensor 16, a continuously variable transmission (CVT) 17, an intake passageway 20, an air flow meter (AFM) 21, a throttle valve 22, a rurbocfaarger 23, an intercooler (IC) 24, an exhaust passageway 25, an adding valve 26, a catalyst 30, a high-pressure EGR device 50, a low-pressure EGR device 51, and an ECU (Engine

Control Unit) 7.

[0021] Intake air introduced from outside passes through the intake passageway 20.

The throttle valve 22 adjusts the amount of flow of intake air that passes through the intake passageway 20. The intake passageway 20 is provided with a compressor 23a of a turbocharger 23 that supercharges intake gas. The intake passageway 20 is also provided with an intercooler 24 that cools the intake gas.

[00221 The engine 10 is supplied with intake gas from the intake passageway 20, and with fuel from the fuel injection valve IS. The engine 10 generates a traveling power for the vehicle 100 by burning a mixture of the supplied intake gas and fuel in a combustion chamber. The engine 10 corresponds to, for example, a diesel engine or the like. The fuel injection valve 15 is constructed as a nozzle that injects fuel into a cylinder of the engine 10, and is controlled in the injection amount, the injection timing, etc., by a control signal S15 supplied from the ECU 7.

[0023] The output of the engine 10 is output via the continuously variable transmission 17 (hereinafter, also referred to as "the CVT"). The CVT 17 is a mechanism capable of continuously shifting the speed change ratio, and is controlled in the speed change ratio (or gear ratio) and the like by a control signal S 17 supplied from the ECU 7. The engine 10 is provided with the rotation speed sensor 16 that detects the rotation speed of the engine 10 (engine rotation speed). The rotation speed sensor 16 supplies the ECU 7 with a detection signal S 16 that corresponds to the detected rotation speed. In addition, the vehicle 100 is also provided with various sensors other than the foregoing sensor. Descriptions of portions that are not particularly relevant to the embodiment are omitted herein.

[0024] The exhaust gas produced by combustion in the engine 10 is discharged via the exhaust passageway 25. The exhaust passageway 25 is provided with a turbine 23b of the turbocharger 23 that is rotated by energy of exhaust gas, and also with the catalyst 30 capable of purifying exhaust gas. Besides, the exhaust passageway 25 is provided with the adding valve 26 that adds fuel into the exhaust passageway 25 at an upstream side of the catalyst 30. The adding valve 26 is constructed as a nozzle that adds fuel

into the exhaust passageway 25, and is controlled by a control signal S26 supplied from the ECU 7.

[0025] The vehicle 100 is equipped with the high-pressure EGR device 50 that returns exhaust gas from the upstream side of the turbine 23b to the downstream side of the compressor 23a, and the low-pressure EGR device 51 that returns exhaust gas from the downstream side of the turbine 23b and the catalyst 30 to the upstream side of the compressor 23a. The high-pressure EGR device 50 has a high-pressure EGR passageway 31, and a high-pressure EGR valve 33. The high-pressure EGR passageway 31 is a passageway that connects a location on the exhaust passageway 25 that is upstream of the turbine 23b and a location on the intake passageway 20 that is downstream of the intercooler 24. Besides, the high-pressure EGR valve 33 provided on the high-pressure EGR passageway 31 controls the amount of exhaust gas that is returned. On the other hand, the low-pressure EGR device 51 has a low-pressure EGR passageway 35, an EGR cooler 36, and a low-pressure EGR valve 37. The low-pressure EGR passageway 35 is a passageway that connects a location on the exhaust passageway 25 that is downstream of the catalyst 30, and a location on the intake passageway 20 that is upstream of the compressor 23a. The EGR cooler 36 provided on the low-pressure EGR passageway 35 cools the exhaust gas to be returned, and the low-pressure EGR valve 37 provided on the low-pressure EGR passageway 35 controls the amount of exhaust gas that is returned. The low-pressure EGR valve 37 is controlled by a control signal S37 supplied from the ECU 7. Incidentally, the low-pressure EGR passageway 35 functions as a first EGR passageway, and the low-pressure EGR valve 37 functions as a first EGR valve.

[002(S] The ECU 7 is constructed of a CPU (Central Processing UniiX a ROM (Read-Only Memory), a RAM (Random Access Memory), etc. The ECU 7 acquires output of various sensors (not shown) provided in the vehicle 100, and performs controls of various component elements of the vehicle 100 on the basis of the acquired sensor outputs. In this embodiment, the ECU 7 mainly performs an injection amount learning in which, during deceleration of the vehicle 100, a very small amount of fuel is injected

from the fuel injection valve IS, and the amount of injection from the fuel injection valve 15 is corrected on the basis of the rotation fluctuation that occurs due to the injection of a very small amount of fuel (that corresponds the detection signal S 16 acquired from the rotation speed sensor 16), or the like. More specifically, at the time of execution of this S injection amount learning, the ECU 7 performs such a control that the torque fluctuation or rotation fluctuation due to the fuel injection from the fuel injection valve 15 is cancelled out.

[0027] Thus, the ECU 7 functions as an injection amount learning device for an internal combustion engine in the invention. Concretely, the ECU 7 operates as a first learning portion, a control portion, and a second learning portion. Incidentally, although the ECU 7 also controls other component elements of the vehicle 100, portions that are not particularly relevant to the embodiment are omitted from the description.

[0028] [INJECTION AMOUNT LEARNING METHOD] Hereinafter, injection amount learning methods in accordance with embodiments which are performed by the ECU 7 will be concretely described.

[0029] (FIRST EMBODIMENT) First, an injection amount learning method in accordance with a first embodiment will be described.

[0030] As described above, at the time of the fuel cut during deceleration of the vehicle 100, the ECU 7 performs the injection amount learning with regard to the fuel injection valve 15 by injecting a very small amount of fuel from the fuel injection valve

15. In the first embodiment, the ECU 7, at the time of injection amount learning, performs a control so that the torque fluctuation or rotation fluctuation that occurs when the small amount of fuel is injected from the fuel injection valve 15 is cancelled out

Concretely, the ECU 7 performs a control of shifting the speed change ratio of the CVT 17 so that the torque caused by the fuel injection from the fuel injection valve 15 is cancelled out by the brake torque of the engine 10 (engine brake torque, or deceleration brake torque). For example, the ECU 7 shifts the speed change ratio so that the engine rotation speed becomes higher, whereby the brake torque of the engine 10 is increased, that is, the friction of the engine 10 is increased. This brake torque makes it possible to

cancel out the torque fluctuation or rotation fluctuation that occurs due to the injection of the small amount of fuel so that the engine output becomes optimal at the time of the torque fluctuation. Therefore, it becomes possible to appropriately perform the injection amount learning of the fuel injection valve IS while restraining the occurrence of a jerky thrust feel or the like during deceleration of the vehicle 100.

[0031] With reference to FIGS. 2 and 3, the injection amount learning method in accordance with the first embodiment will be described.

[0032] FIGS. 2A and 2B are diagrams for concretely describing the method of shifting the speed change ratio. FlG 2A shows a relation of the engine rotation speed and the vehicle speed with the speed change ratio. Concretely, in FIG 2A, the horizontal axis shows the engine rotation speed, and the vertical axis shows the vehicle speed. When the injection amount learning is performed, the ECU 7 shifts the speed change ratio so that the engine rotation speed heightens as shown by a hollow arrow Al in FIG 2A. FTG 2B shows a relation between the engine rotation speed (horizontal axis) and the brake torque (vertical axis) of the engine 10. It can be understood from FIG. 2B that in the case where the speed change ratio is shifted so that the engine rotation speed heightens as shown by a hollow arrow A2, the brake torque tends to increase as shown by a hollow arrow A3.

[0033] FIG 3 is a diagram showing a concrete example of the brake torque of the engine 10 during deceleration of the vehicle. In FIG 3, the brake torque is shown in the positive direction, and the torque produced by combustion is shown in the negative direction. Furthermore in FIG 3, the torque produced by combustion is shown by hatching.

[0034] In FIG 3, bar (a) shows the torque that occurs when the injection amount learning is not performed (at the time of ordinary control) during deceleration of the vehicle 100. During the ordinary control, the brake torque Bl occurs. In this case, torque from combustion does not occur, and therefore a negative torque that corresponds to the brake torque Bl is produced from the vehicle. Bar (b) in FIG 3 shows the torque that occurs when during deceleration of the vehicle 100, only the control of injecting the

very small amount of fuel only for tbe injection amount learning (that is, a control such that the torque caused by the fuel injection is cancelled out is not performed). In this case, while the brake torque Bl as shown by bar (a) is generated basically, a torque B2 caused by the injection of the very small amount of fuel of injection for the injection amount learning is also generated. Therefore, a negative torque B3 obtained by subtracting the torque B2 caused by the fuel injection from the brake torque Bl is produced from the vehicle 100. In this case, it can be said that the negative torque B3 smaller than the negative torque Bl corresponding to the brake torque Bl as shown in bar (a) in FIG 3 is produced from the vehicle 100. Therefore, it is considered that a jerky thrust feel occurs at the time of the injection amount learning.

[0035] In FIG 3, bar (c) shows the brake torque produced when, during deceleration of the vehicle 100, the control in accordance with the first embodiment is executed at the time of the injection amount learning (i.e., the control of shifting the speed change ratio so that the torque caused by the fuel injection is cancelled out by the brake torque is executed). By performing the foregoing control of shifting the speed change ratio, a brake torque B4 is produced. That is, the brake torque B4 that is larger than the brake torque Bl shown by bar (a) in FIG 3 is produced. Besides, a torque B5 is brought about by the very small amount of fuel injection. Therefore, a negative torque B6 obtained by subtracting the torque B5 caused by the fuel injection from the brake torque B4 is produced from the vehicle 100. In this case, it can be said that the negative torque B6 substantially equal to the negative torque Bl corresponding to the brake torque Bl as shown by bar (a) in FIG 3 is produced from the vehicle 100. Therefore, it can be considered that in the case where control in accordance with the first embodiment is executed, there occurs substantially no jerky thrust feel at the time of the injection amount learning.

[0036] FIG 4 is a flowchart showing an injection amount learning process in accordance with the first embodiment. This process is repeatedly executed by the ECU 7.

[0037] Firstly, in step SlOl, the ECU 7 determines whether or not the vehicle 100 is

in a deceleration state and in a fuel-cut state. In this embodiment, the case where the vehicle is in the deceleration state and in the fuel-cut state is used as a condition for executing the injection amount learning, in order to accurately perform the injection amount learning. If the vehicle is in the deceleration state and in the fuel-cut state (YES in step SlOl), the process proceeds to step S 102. If the vehicle is not in the deceleration state or the fuel-cut state (NO in step SlOl), the process returns to step SlOl.

(0038] In step S 102, the ECU 7 starts the injection of the very small amount of fuel from the fuel injection valve 15 in order to perform the injection amount learning with regard to the fuel injection valve IS. Then, the process proceeds to step S103. [0039] In step S 103, the ECU 7 determines whether or not the rotation fluctuation (amount of the torque increase) caused by the injection of the very small amount of fuel is stored. If the rotation fluctuation obtained at the previous time of learning is stored (YES in step S 103), the process proceeds to step S 104. If the rotation fluctuation is not stored (NO in step S103), the process exits the flow shown in the chart. [0040] In step S 104, the ECU 7 performs the control of shifting the speed change ratio of the CVT 17 so that the rotation fluctuation (amount of the torque increase) obtained in step S103 is cancelled by the brake torque of the engine 10. Concretely, the ECU 7 performs the control of shifting the speed change ratio so that the amount of the torque increase is cancelled out at the time of the injection amount learning by increasing the brake torque. That is, the speed change ratio is shifted so that the amount of torque increase caused by the injection of the very small amount of fuel and the amount of increase in the brake torque of the engine 10 become substantially equal. After the foregoing process ends, the process exits the flow shown in the chart.

[0041] According to the foregoing injection amount learning process, it is possible to properly perform the injection amount learning with regard to the fuel injection valve 15 while restraining the jerky thrust feel at the time of the injection amount learning,

[0042] (SECOND EMBODIMENT) Next, an injection amount learning method in accordance with the second embodiment will be described.

[0043] In the second embodiment, too, the control of shifting the speed change ratio

of the CVT 17 is executed so that during execution of the injection amount learning, the torque fluctuation or rotation fluctuation caused by the fuel injection from the fuel injection valve 15 is cancelled out, as in the foregoing first embodiment The second embodiment is different from the first embodiment in that the injection amount learning is performed on the basis of whether or not the torque fluctuation or rotation fluctuation caused by the fuel injection from the fuel injection valve 15 is cancelled out by performing the foregoing control of shifting the speed change ratio. That is, in the second embodiment, the ECU 7 performs the injection amount learning on the basis of whether or not the rotation fluctuation brought about by the fuel injection from the fuel injection valve IS is substantially equal to the learned value (the rotation fluctuation obtained at the previous time of learning) when the speed change ratio is shifted.

[0044] FIQ S is a diagram for concretely describing an injection amount learning method in accordance with the second embodiment In FIQ 5, the horizontal axis shows time, and the vertical axis shows the rotation fluctuation of the engine 10. Herein, description will be made in conjunction with a case where the vehicle 100 is in the deceleration state and in the fuel-cut state.

[0045] A graph shown by reference character Cl shows an example of a result from the case where only the speed change ratio of the CVT 17 is shifted at a time tl (more specifically, the case where the speed change ratio is shifted ao that the brake torque increases), without performing the fuel injection from the fuel injection valve 15. In this case, it can be understood that the rotation fluctuation occurs in the negative direction, that is, the rotation fluctuation decreases. In contrast, the graph shown by C2 shows an example from the case where the fuel injection from the fuel injection valve 15 for the purpose of the injection amount learning is performed at the time tl and where the rotation fluctuation caused by the fuel injection is not cancelled out In this case, it can be understood that the rotation fluctuation occurs in the positive direction, that is, the rotation fluctuation increases. For example, in the case where the brake torque increased by shifting the speed change ratio is smaller than the torque brought about the fuel injection, the rotation fluctuation tends to increase.

[0046) On the other hand, the graph shown by C3 shows an example from the case where the fuel injection from the fuel injection valve 15 for the purpose of the injection amount learning is performed at the time tl and where the rotation fluctuation caused by the fuel injection is cancelled out. In this case, it can be understood that there is δ substantially no change in the rotation fluctuation. This can be considered to be because the brake torque increased by shifting the speed change ratio and the torque brought about by the fuel injection are substantially equal.

[0047] In the second embodiment, the ECU 7 performs the injection amount learning of the fuel injection valve IS on the basis of the rotation fluctuation brought about by the fuel injection from the fuel injection valve IS, that is, on the basis of whether or not the rotation fluctuation brought about by the fuel injection is cancelled out.

[0048] FIG 6 is a flowchart showing an injection amount learning process in accordance with a second embodiment. This process is repeatedly executed by the ECU 7.

[0049] The process of steps S201 to S204 is substantially the same as the foregoing process of step SlOl to S 104 (see FIG 4), and the description thereof will be omitted. Herein, the process from step S20S on will be described.

[0050] In step S205, the ECU 7 determines whether or not the rotation fluctuation caused by the fuel injection from the fuel injection valve IS is cancelled out by the control of shifting the speed change ratio in step S204. In other words, the ECU 7 determines whether or not the rotation fluctuation of the engine 10 obtained following the performance of the fuel injection from the fuel injection valve IS and the control of shifting the speed change ratio in CVT 17 is substantially equal to the learned value (the rotation fluctuation obtained at the previous time of learning). If the rotation fluctuation has been cancelled out (YES in step S205). the process exits the flow shown in the chart In this case, it can be said that there is no need to alter the learned value. On the other hand, in the case where the rotation fluctuation is not cancelled out (NO in step S205), the process proceeds to step S206.

[0051] In step S206, the ECU 7 alters the learned value for use for the next time of learning, with regard to the present rotation amount and the torque fluctuation calculated from the rotation fluctuation. After the foregoing process ends, the process exits the flow shown in the chart. [0052] On the other hand, if in step S203 it is determined that the rotation fluctuation

(amount of the torque increase) brought about by the fuel injection from the fuel injection valve IS at the previous time of (earning is not stored (NO in step S203), the process proceeds to step S207. In this case, it can be said that the learned value (rotation fluctuation) at the previous time of learning is not stored for some reason. In step S2O7, the ECU 7 predicts the rotation fluctuation brought about by the fuel injection from the fuel injection valve IS, and performs the control of shifting the speed change ratio of the

CVT 17 so that the predicted rotation fluctuation is cancelled out by the brake torque of the engine 10. For example, the ECU 7 determines the speed change ratio by referring to a map in which the rotation fluctuation, the speed change ratio, etc., are associated with the very small injection amount beforehand. After the foregoing process ends the process proceeds to step S208.

[0053] In step S208, the ECU 7 determines whether or not the rotation fluctuation caused by the fuel injection from the fuel injection valve IS has been cancelled out by performing the control of shifting the speed change ratio in step S207. Io other words, it is determined whether or not the rotation fluctuation actually brought about by the fuel injection from the fuel injection valve IS is substantially equal to the rotation fluctuation predicted in step S207. Concretely, ECU7 observes the rotation speed of the engine 10 based on the output of rotation speed sensor 16, and determines whether or not the rotation fluctuation is maintained within a predetermined range. If the rotation fluctuation has been cancelled out (YES in step S208), the process exits the flow shown in the chart. OQ the other hand, if the rotation fluctuation has not been cancelled out (NO in step S208), the process proceeds to step S206. In this case, the ECU 7 alters the learned value for use at the next time of learning, with regard to the present rotation fluctuation and the torque fluctuation calculated from the rotation fluctuation (step S206),

16

as described above.

[0054] According to the foregoing injection amount learning process, it is possible to accurately perform the injection amount learning with regard to the fuel injection valve 15 while restraining the occurrence of a jerky thrust fee) at the time of the injection amount learning.

[0055] (THIRD EMBODIMENT) Next, an injection amount learning method in accordance with a third embodiment will be described.

[0056] The third embodiment is different from the foregoing first and second embodiments in that, at the time of the injection amount learning with regard to the fuel injection valve IS, a control of shifting the speed change ratio of the CVT 17 is performed so as to bring about an engine rotation speed at which a torque fluctuation or a rotation fluctuation greater than or equal to a predetermined value can be provided by the injection of a very small amount of fuel. That is, in the third embodiment, the control of shifting the speed change ratio is performed so as to obtain an engine rotation speed that makes it possible to accurately detect the torque fluctuation or the rotation fluctuation caused by the injection of the very small amount of fuel from the fuel injection valve 15. The speed change ratio is shifted in this manner because the torque fluctuation or the rotation fluctuation brought about by the fuel injection from the fuel injection valve 15 differs depending on the engine rotation speed. [0057] In one example, the ECU 7 shifts the speed change ratio of the CVT 17 so that the engine rotation speed reaches a minimum speed at which the torque fluctuation (rotation fluctuation) caused by the injection of the very small amount of fuel becomes substantially maximum, in order to achieve both good detection accuracy for the torque fluctuation (rotation fluctuation) and good fuel economy. In another example, taking into account the computing capacity (amount of load, calculation routine speed) of the ECU 7, the speed change ratio of the CVT 17 is shifted so as to bring about an engine rotation speed at which the rotation fluctuation can be detected by the ECU 7 as accurately as possible for a fixed number of times of performing fuel injection.

[00581 FIQL 7 is a diagram for concretely describing an injection amount learning

method in accordance with the third embodiment. FlG 7 A shows a relation between the engine rotation speed (horizontal axis) and the amount of rise in the rotation speed (vertical axis) in the case where the amount of fuel injection is fixed. It can be understood from FIG 7A that if a speed ratio shift is performed so that the engine rotation speed decreases, the amount of rise in the rotation speed increases. By increasing the amount of rise in the rotation speed through the shifting of the speed change ratio in this manner, it becomes possible to accurately perform the injection amount learning with regard to the fuel injection valve IS while restraining the deterioration of fuel economy. [00591 FIG TB shows time along the horizontal axis, and shows the rotation fluctuation along the vertical axis. In this case, the graphs shown by reference characters Dl and D2 show the rotation fluctuations that occur in the case where at a time t2, fuel injection is performed a fixed number of times. Besides, the graph shown by Dl is assumed to have been obtained in a situation of a higher engine rotation speed than the graph shown by D2. From FIG 7B it can be understood that as for the graph shown by Dl, the number of measurements obtained is not sufficient for the rotation fluctuation, in comparison with the graph shown by D2. In the case where the engine rotation speed is high, the number of points of measurement of the engine rotation speed tends to decreases, due to the computing capacity of the ECU 7. hi this embodiment, taking into account the computing capacity of the ECU 7, the speed change ratio can be shifted so as to bring about an engine rotation speed at which the rotation fluctuation can be accurately detected with a fixed number of times of fuel injection.

[0060] FIG 8 is a flowchart showing an injection amount learning process in accordance with the third embodiment This process is repeatedly executed by the ECU 7. The process of steps S301 to S302 is the same as the foregoing process of steps S 101 to S102 (see FIG 4), and the description thereof will be omitted. In the following description, the process of step S303 will be described.

[0061] In step S303, the ECU 7 performs a control of shifting the speed change ratio of the CVT 17 so as to bring about an engine rotation speed at which the torque

fluctuation can be accurately detected. Concretely, the ECU 7 shifts the speed change ratio so as to obtain a minimum engine rotation speed at which the torque fluctuation

(rotation fluctuation) caused by the injection of the very small amount of fuel becomes substantially maximum, in order to achieve both good detection accuracy for the torque fluctuation (rotation fluctuation) and good fuel economy. After the foregoing process ends, the process exits the flow shown in the chart. Incidentally, instead of shifting the speed change ratio so as to obtain a minimum engine rotation speed at which the torque fluctuation becomes substantially maximum, it is permissible to shift the speed change ratio so as to bring about an engine rotation speed at which the rotation fluctuation can be accurately detected, taking into account the computing capacity of the ECU 7 (the amount of load, the calculation routine speed). That is, the speed change ratio may also be shifted to a ratio that makes it possible to obtain an engine rotation speed that allows the ECU 7 to obtain a sufficient number of measurements.

[0062] According to the foregoing injection amount learning process, it becomes possible to appropriately set an engine rotation speed that allows accurate detection of the torque fluctuation or the rotation fluctuation by shifting the speed change ratio of the

CVT 17. Hence, it becomes possible to accurately perform the injection amount learning with regard to the fuel injection valve 15.

[0063] Incidentally, the injection amount learning method in accordance with the third embodiment and the foregoing injection amount learning method in accordance with the first embodiment may be combined. Concretely, the control of shifting the speed change ratio of the CVT 17 may be performed so that the engine rotation speed becomes a rotation speed that allows accurate detection of the torque fluctuation or the rotation fluctuation caused by the injection of the very small amount of fuel and also so that the torque fluctuation or the rotation fluctuation caused by the fuel injection from the fuel injection valve 15 is cancelled out by the brake torque of the engine 10. That is, the control of shifting the speed change ratio may be performed so as to bring about an engine rotation speed that allows accurate detection of the rotation fluctuation or the like and that WTEU not impair the brake torque of the engine 10. Furthermore, the injection

amount learning may also be performed in a manner described in the second embodiment, oα the basis of whether or not the rotation fluctuation or the torque fluctuation caused by the fuel injection from the fuel injection valve 15 is cancelled out, besides through the control of shifting the speed change ratio. [0064] (FOURTH EMBODIMENT) Next, an injection amount learning method in accordance with a fourth embodiment will be described.

[0065] The fourth embodiment is different from the foregoing first to third embodiments in that the injection amount learning with regard to an adding valve 26 provided on the exhaust passageway 25 is performed instead of the injection amount learning with regard to the fuel injection valve 15. That is, in the fourth embodiment, an injection amount learning or correcting the amount of injection from the adding valve 26 is performed. Specifically, in the fourth embodiment, at the time of performing the injection amount learning, the low-pressure EGR valve 37 is controlled to a fully open state. Furthermore, the injection amount learning with regard to the adding valve 26 is executed when the CO ₂ attributed to the fuel injected from at least the adding valve 26 flows into the cylinder. Concretely, at the time of the fuel-cut during deceleration of the vehicle 100, the ECU 7 performs the injection amount learning on the basis of the rotation fluctuation or the torque fluctuation brought about by injecting fuel from the adding valve 26. This rotation fluctuation or torque fluctuation tends to occur as CO ₂ attributed to the fuel injected from the adding valve 26 passes through the low-pressure EGR passageway 35 and flows into the cylinder and therefore the CO ₂ increases the loss by compression in the cylinder, and therefore increases the friction of the engine 10.

[0066] FIG 9 is a flowchart showing an injection amount learning process in accordance with a fourth embodiment This process is repeatedly executed by the ECU 7.

[0067] Firstly, in step S401, the ECU 7 determines whether or not the vehicle 100 is in the deceleration state and in the fuel-cut state. In this embodiment, in order to restrain the influence caused by the fuel injection from the fuel injection valve 15 and the rotation fluctuation during deceleration of the vehicle 100, the case where the vehicle is

in the deceleration state and in the fuel-cut state is used as a condition for executing the injection amount learning with regard to the adding valve 26. If the vehicle is in the deceleration state and in the fuel-cut state (YES in step S401), the process proceeds to step S4O2. If the vehicle is not in the deceleration state or the fuel-cut state (NO in step S401), the process returns to step S401.

[0068] In step S402, the ECU 7 starts the fuel injection from the adding valve 26 in order to perform the injection amount learning with regard to the adding valve 26. Furthermore, the ECU 7 controls the low-pressure EGR valve 37 to the fully open state. This control is performed for the purpose of returning the CO2 or unburaed fuel attributed to the fuel injection from the adding valve 26, to the intake side. After the foregoing process ends, the process proceeds to step S4O3.

[0069] In step S403, the ECU 7 determines whether or not the CO ₂ attributed to the injection from the adding valve 26 has flown into the cylinder via the low-pressure EGR passageway 35. For example, the ECU 7 performs the foregoing determination on the basis of the amount of time needed for CO ₂ or the like to flow into the cylinder (which is found from the length or the like of the low-pressure EGR passageway 35, the intake passageway 20, etc.). If the COj attributed to the fuel injected by the adding valve 26 has flown into the cylinder (YES in step S403), the process proceeds to step S404. If such CO ₂ has not flown into the cylinder (NO in step S403), the process returns to step S403.

[0070] In step S404, the ECU 7 performs the injection amount learning with regard to the adding valve 26 on the basis of the rotation fluctuation that occurs in the engine 10. Concretely, on the basis of the obtained rotation fluctuation, correction with regard to the amount of injection from the adding valve 26 is performed. Incidentally, in the case where the CO ₂ attributed to the fuel injected from the adding valve 26 is returned into the cylinder, the CO ₂ increases the loss by the compression, and therefore increases the friction of the engine 10, so that the foregoing rotation fluctuation occurs. After the foregoing process ends, the process exits the flow shown in the chart

[0071] According to the foregoing injection amount learning process, it becomes

possible to accurately perform the injection amount learning with regard to the adding valve 26.

[0072] Incidentally, the injection amount learning method in accordance with the fourth embodiment and the injection amount learning method in accordance with the first embodiment may be combined. Concretely, in the case where the foregoing injection amount learning with regard to the adding valve 26 is performed and also the injection amount learning with regard to the fuel injection valve 15 is performed, the control of shifting the speed change ratio of the CVT 17 can be performed so that the torque fluctuation or the rotation fluctuation caused by the fuel injection from the fuel injection valve IS is cancelled out by the brake torque of the engine 10. Furthermore, the injection amount learning method in accordance with the fourth embodiment and the injection amount learning method in accordance with the second and third embodiments may be combined. That is, in the case where the injection amount learning with regard to the fuel injection valve 15 is performed, it is permissible to use at least one of the injection amount learning method in accordance with the second embodiment and the injection amount learning method in accordance with the third embodiment

[0073] (FIFTH EMBODIMENT) Next, an injection amount learning method in accordance with a fifth embodiment will be described.

[0074] In the fifth embodiment, the injection amount learning with regard to the adding valve 26 provided on the exhaust passageway 25 is performed as in the fourth embodiment. However, the fifth embodiment is different from the fourth embodiment in that the injection amount learning with regard to the adding valve 26 is performed after the injection amount learning with regard to the fuel injection valve 15 has ended, and that the injection amount learning with regard to the adding valve 26 is performed by injecting fuel from the fuel injection valve 15 with regard to which the injection amount learning has ended (i.e., the fuel injection valve 15 whose accuracy has been guaranteed). This is performed for the following purpose. That is, by performing the fuel injection from the fuel injection valve 15 provided for the cylinder with regard to which the injection amount learning has ended, combustion is performed under a situation where

the factor that affects the rotation fluctuation is only COj that is circulated from the low-pressure EGR passageway 3S ₁ so that the rotation fluctuation caused by the fuel injection from the adding valve 26 becomes large. Thus, the detection accuracy is improved. [0075] Furthermore, in the fifth embodiment, when the exhaust gas from the fuel injected for the first time from the fuel injection valve 15 is returned from the low-pressure EGR passageway 35 to the intake air side, the injection amount learning with regard to the adding valve 26 is stopped, that is, the fuel injection from the fuel injection valve 15 is stopped. This is performed because when the exhaust gas from the fuel injected for the first time from the fuel injection valve 15 is returned to the intake side, the EGR gas produced due to the adding valve 26 and the combustion makes the CO ₂ concentration different from the original level. That is, this is performed in order to secure an accuracy in the injection amount learning.

[0076] FIG 10 is a flowchart showing an injection amount learning process in accordance with the fifth embodiment. This process is repeatedly executed by the ECU 7.

[0077] The process of step S501 is the same as the process of the foregoing step S401 (see FlG 9), and will be omitted from description. In step S502, the ECU 7 determines whether or not the injection amount learning with regard to the fuel injection valve 15 has ended. If the injection amount learning has ended (YES in step S502), the process proceeds to step S503. In this case, in the process that follows, a process for performing the injection amount learning with regard to the adding valve 26 is executed. On the other band, if the injection amount learning has not ended (NO in step S502), the process proceeds to step S508. In this case, the ECU 7 firstly executes the injection amount learning with regard to the fuel injection valve 15 (step S508). That is, the amount of fuel injected from the fuel injection valve 15 is corrected. After the process of step S508 ends, the process exits the flow shown in the chart.

[0078] In step S503, the ECU 7 starts the fuel injection from the adding valve 26, and fully opens the low-pressure EGR valve 37, as in the foregoing process of step S402

(see FlG 9). Then, the process proceeds to step S504. In step S504, the ECU 7 determines whether or not the CO ₂ injected by the adding valve 26 has flown into the cylinder via the low-pressure EGR passageway 35, as in the foregoing process of step S403 (see FIG 9). If the CO ₃ attributed to the fuel injected by the adding valve 26 has flown into the cylinder (YES in step S504% the process proceeds to step SS05. If such CO ₂ has not flown into the cylinder (NO in step S504), the process returns to step S504.

[0079] In step S505, the ECU 7 executes the fuel injection from the fuel injection valve 15 whose accuracy has been guaranteed, in accordance with the gas that has flown into the cylinder after being circulated through the low-pressure EGR passageway 35. That is, the ECU 7 causes the fuel injection valve 15, with regard to which the injection amount learning has ended, to inject fuel when the injection amount learning with regard to the adding valve 26 is performed. Due to this operation, the combustion in the cylinder can be performed in a situation where the factor that affects the rotation fluctuation is only CO ₂ that is circulated through the low-pressure EGR passageway 35, $0 that the rotation fluctuation caused by the fuel injection from the adding valve 26 can be made large. Hence, it becomes possible to improve the detection accuracy for the rotation fluctuation. After the foregoing process ends, the process proceeds to step

S506.

[0080] In step S506, the ECU 7 determines whether or not the exhaust gas from the fuel injected for the first time from the fuel injection valve 15 has been returned to the intake side through the low-pressure EGR passageway 35. For example, the ECU 7 performs this determination on the basis of the time that is needed for the exhaust gas to return to the intake side. If the exhaust gas from the fuel injected from the fuel injection valve 15 has been returned (YES in step S506), the process proceeds to step S507. If the exhaust gas has not been returned (NO in step S506), the process returns to step

S506.

[0081] In step S507, the ECU 7 stops the injection amount learning with regard to the adding valve 26, that is, stops the fuel injection from the fuel injection valve 15. In this case, since the exhaust gas from the fuel injected for the first time from the fuel

injection valve IS has been returned to the intake side, the EGR gas produced due to the adding valve 26 and the combustion makes the CO ₂ concentration different from the original level. Therefore, the ECU 7 stops the injection amount learning with regard to the adding valve 26 in order to secure an accuracy of the injection amount learning, that is, in order to prevent false learning. After the foregoing process ends, the process exits the flow shown in the chart. Incidentally, the injection amount learning may be restarted when the CO ₂ concentration determined only by the fuel injection from the adding valve 26 is reached

[0082] According to the foregoing injection amount learning process, it becomes possible to prevent false learning in the injection amount learning with regard to the adding valve 26 and therefore improve the accuracy of the injection amount learning with regard to the adding valve 26.

[0083] Besides, the injection amount learning method in accordance with the fifth embodiment and the foregoing injection amount learning method in accordance with the first embodiment may be combined. Concretely, in the case where the foregoing injection amount learning with regard to the adding valve 26 is performed and also the injection amount learning with regard to the fuel injection valve IS is performed, the control of shifting the speed change ratio of the CVT 17 can be performed so that the torque fluctuation or the rotation fluctuation caused by the fuel injection from the fuel injection valve 15 is cancelled out by the brake torque of the engine 10. Furthermore, the injection amount learning method in accordance with the fifth embodiment and the injection amount learning method in accordance with the second and third embodiments may be combined. Concretely, in the process of step S508 (see FIG 10X at least one of the injection amount learning processes shown in the first to third embodiments (see FIGS. 4, 6 and 8) can be executed.

[0084] [MODIFICATIONS] Although in the foregoing embodiments, the torque fluctuation or the rotation fluctuation caused by the fuel injection from the fuel injection valve IS is cancelled out by performing the control of shifting the speed change ratio of the CVT 17 at the time of the injection amount learning, this is not restrictive. In a

different example, at the time of the injection amount learning, the torque fluctuation or the rotation fluctuation caused by the fuel injection from the fuel injection valve can be cancelled out by performing a control of changing the amount of regeneration of an electric motor provided in a hybrid vehicle (a motor MG 1 described below). That is, in a modification, the torque caused by the fuel injection from the fuel injection valve is offset by causing an electric motor provided in a hybrid vehicle to perform the regenerative operation.

[0085] FIG 11 is a block diagram showing a general construction of a vehicle 100a to which an injection amount learning device for an internal combustion engine in accordance with a modification is applied.

[0086] The vehicle 100a mainly includes an ECXJ 7a, an axle shaft 110, wheels 120, an engine 10a, electric motors MGl, MG2, a planetary gear 300, an inverter 400, and a battery SOO. The vehicle 100a is constructed as a so-called series-parallel hybrid vehicle. [0087} The axle abaft 110 is a portion of a power transmission system that transmits power from the engine 10a and the motor MG2 to the wheels 120. The wheels 120 are wheels of the vehicle 100a, and FIG 1 shows only left and front wheels for simplification of description. The engine 10a is constructed of a gasoline engine or the like, and functions as a main motive power source of the vehicle 100a. Besides, the engine 10a is provided with a fuel injection valve ISa that injects fuel into a cylinder of the engine 10a.

[0088] The motor MGl is constructed so as to function mainly as a generator for charging the battery 500 or as a generator for supplying electric power to the motor MG2. The motor MG2 is constructed so as to function as an electric motor that adds to the output of the engine 10a. Each of the motor MGl and the motor MG2 is constructed as, for example, a synchronous motor generator, and includes a rotor that has on its outer peripheral surface a plurality of permanent magnets, and a stator on which three-phase coils that form a rotating magnetic field are provided. The planetary gear (planetary gear mechanism) 300 is constructed so as to be capable of distributing output of the

engine 10a to (he motor MGl and the axle shaft ItO, and functions as a power splitting mechanism.

[0089] The inverter 400 is a DOAC converter that controls the input/output of electric power of the battery 500 with respect to the motor MGl and the motor MG2. For example, the inverter 400 is constructed so as to be capable of supplying the DC

(direct-current) electric power extracted from the battery 500 to the motor MG2 after converting if into an AC (alternating-current) electric power, or of supplying the AC electric power generated by the motor MGl to the motor MG2, and also to be capable of supplying the AC electric power generated by the motor MGl to the battery SOO after converting it into a DC electric power. The battery SOO is a rechargeable storage battery constructed so as to be capable of functioning as an electric power source for driving the motor MGl and the motor MG2.

[0090] The ECU 7a is constructed of a CPU (Central Processing Unit), a ROM (Read-Only MemoryX a RAM (Random Access Memory), etc. (which are not shown). Basically, the ECU 7a performs the injection amount learning with regard to the fuel injection valve 15a by injecting a very small amount of fuel from the fuel injection valve 15a during deceleration of the vehicle 100a, similarly to the foregoing ECU 7. Specifically; at the time of the injection amount learning, the ECU 7a performs a control of f*»"gi"g the amount of regeneration performed by the motor MGl so that the torque fluctuation or the rotation fluctuation brought about by the fuel injection from the fuel injection valve 15a is cancelled out

[0091] Furthermore, as in the second embodiment, the ECU 7a can perform the injection amount learning with regard to the fuel injection valve ISa on the basis of whether or not the torque fluctuation or the rotation fluctuation caused by the fuel injection from the fuel injection valve ISa is cancelled out by the regeneration performed by the motor MGl. Furthermore, the ECU 7a, as in the third embodiment, can perform a control so that the torque fluctuation or the rotation fluctuation caused by the fuel injection from the fuel injection valve 15a is accurately detected. Moreover, besides executing the injection amount learning with regard to the fuel injection valve 15a as

described above, the ECU 7a can also execute the injection amount learning with regard to an adding valve (not shown) that is provided on the exhaust passageway as in the foregoing fourth and fifth embodiments. As described above, the ECU 7a functions as an injection amount learning device for an internal combustion engine in accordance with the invention.