Control device for internal combustion engines

Abstract

Regardless of differences in intake air volume during fuel cut-off, it suppresses torque shock at the start of fuel cut-off. [Solution] When cutting fuel during accelerator release, the time required TX for the torque to decrease to the F / C permitted torque TP after accelerator release is calculated based on the F / C target air amount GA*, which is the target value of the intake air amount during fuel cut, and the engine water temperature THW, which is the coolant temperature of the internal combustion engine (S100~S130). Then, when the elapsed time after accelerator release is equal to or greater than the required time TX (S140: YES), fuel cut is initiated (S150).

Description

Technical Field

[0001] The present invention relates to a control device for an internal combustion engine mounted on a vehicle.

Background Art

[0002] In an internal combustion engine mounted on a vehicle, when the driver releases the accelerator pedal and the vehicle is coasting, fuel cut of the internal combustion engine is performed to suppress fuel consumption. In Patent Document 1, at the time of fuel cut, when the engine torque estimated based on the gear stage of the transmission and the vehicle speed drops below a certain value, the fuel injection of the internal combustion engine is stopped to suppress the occurrence of torque shock.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In internal combustion engines equipped with a filter device in the exhaust passage to collect particulate matter (PM) in the exhaust, a filter regeneration process is sometimes performed during fuel cut-off to burn the PM accumulated on the filter device and regenerate it. To efficiently burn PM during this filter regeneration process, it is necessary to supply more fresh air to the filter device during fuel cut-off than during normal fuel cut-off. Therefore, during filter regeneration, the throttle opening during fuel cut-off may be larger than during normal fuel cut-off. When the throttle opening is larger, the pumping loss of the internal combustion engine is smaller than when it is smaller, so the decrease in engine torque after releasing the accelerator is delayed. However, the engine torque estimation result cannot reflect the effect of the difference in intake air volume after releasing the accelerator, based only on the transmission gear and vehicle speed. Therefore, when filter regeneration is performed, fuel injection is stopped when the engine torque is higher than expected. Conversely, if the amount of intake air during fuel cut-off is less than normal, fuel injection is stopped when the engine torque is lower than expected. Therefore, with the conventional technology described above, if the amount of intake air is changed during fuel cut-off, it may not be possible to sufficiently suppress the occurrence of torque shock at the start of fuel cut-off. [Means for solving the problem]

[0005] A control device for an internal combustion engine that solves the above problems is a control device for an internal combustion engine that cuts off fuel when the accelerator is released, and is configured to calculate the time when the engine torque falls below a predetermined value based on a target value of the intake air amount during the fuel cut, and to start the fuel cut at the calculated time. [Effects of the Invention]

[0006] The control device for the internal combustion engine described above has the effect of suppressing torque shock at the start of fuel cut-off, regardless of the difference in intake air volume during fuel cut-off. [Brief explanation of the drawing]

[0007] [Figure 1] Figure 1 is a schematic diagram showing the configuration of one embodiment of a control device for an internal combustion engine. [Figure 2] Figure 2 is a flowchart of the process performed by the control device shown in Figure 1 when initiating fuel cut-off. [Figure 3] Figure 3(a) shows the transition of the F / C permission flag, Figure 3(b) shows the transition of the F / C flag, Figure 3(c) shows the transition of the engine speed NE, and Figure 3(d) shows the transition of the engine torque TE at the start of fuel cut in an internal combustion engine to which the control device of Figure 1 is applied. [Modes for carrying out the invention]

[0008] Below, one embodiment of a control device for an internal combustion engine will be described in detail with reference to Figures 1 to 3. <Configuration of the control system for an internal combustion engine> First, the configuration of this embodiment will be described with reference to Figure 1. The internal combustion engine 10 to which the control device of this embodiment is applied is mounted on a hybrid vehicle. The internal combustion engine 10 is connected to the wheels 23 via a motor 20, a transmission 21, and a differential 22.

[0009] The internal combustion engine 10 comprises a cylinder 11 in which the air-fuel mixture is burned, an intake passage 12 which is the path for introducing intake air into the cylinder 11, and an exhaust passage 13 which is the path for discharging exhaust gas from the cylinder 11. The internal combustion engine 10 in Figure 1 has four cylinders 11, but the number of cylinders 11 is arbitrary. A throttle valve 14 is installed in the intake passage 12 to adjust the intake air amount GA of the internal combustion engine 10. A filter device 15 is installed in the exhaust passage 13 to collect PM (particulate matter) in the exhaust gas. Furthermore, the internal combustion engine 10 is individually provided in each cylinder 11 with an injector 16 that injects fuel into the intake air used for combustion in the cylinder 11, and an ignition device 17 that ignites the air-fuel mixture in the cylinder 11 by spark discharge.

[0010] The control device for the internal combustion engine 10 is configured as an ECM (Engine Control Module) 30, which includes a CPU (Central Processing Unit) 31 and a ROM (Read-Only Memory) 32. The ROM 32 stores programs and data used to control the internal combustion engine 10. The ECM 30 performs various processes for controlling the internal combustion engine 10 by executing programs read from the ROM 32 by the CPU 31. The ECM 30 receives detection signals from sensors such as an airflow meter 33, a crank angle sensor 34, a water temperature sensor 35, an accelerator pedal sensor 36, and a vehicle speed sensor 37. The airflow meter 33 is a sensor that detects the intake air volume GA of the internal combustion engine 10. The crank angle sensor 34 is a sensor that detects the rotation angle of the crankshaft, which is the output shaft of the internal combustion engine 10. The water temperature sensor 35 is a sensor that detects the engine water temperature THW, which is the coolant temperature of the internal combustion engine 10. The accelerator pedal sensor 36 is a sensor that detects the accelerator opening degree ACC, which is the amount the driver of the hybrid vehicle presses down on the accelerator pedal. The vehicle speed sensor 37 is a sensor that detects the vehicle speed SPD, which is the driving speed of the hybrid vehicle.

[0011] The ECM30 controls the internal combustion engine 10 by determining the throttle opening (the opening degree of the throttle valve 14), the fuel injection amount from the injector 16, and the ignition timing of the air-fuel mixture by the ignition device 17, based on the detection results of each sensor. In controlling the internal combustion engine 10, the ECM30 also calculates the engine speed NE, which is the rotational speed of the crankshaft, based on the detection results of the crank angle sensor 34. Furthermore, the ECM30 calculates the engine load ratio KL based on the engine speed NE and the intake air volume GA. The engine load ratio KL represents the charging efficiency of the intake air of cylinder 11.

[0012] <Fuel cut-off control> The ECM30 performs a fuel cut, stopping the fuel supply to the internal combustion engine 10 when the hybrid vehicle is coasting. In this embodiment, the ECM30 performs a fuel cut by stopping fuel injection from the injectors 16 of each cylinder 11 when the predetermined F / C permission conditions are met. In this embodiment, the F / C permission conditions are that all of the following are met: the accelerator is off, the engine speed NE is equal to or greater than the predetermined F / C start speed, and the vehicle speed SPD is equal to or greater than the predetermined F / C start vehicle speed. The ECM30 determines that the accelerator is off when the accelerator opening ACC is less than or equal to the predetermined accelerator off opening. The accelerator off opening is set to "0" or a very small accelerator opening ACC close to "0".

[0013] On the other hand, the ECM 30 terminates the fuel cut and restarts combustion of the internal combustion engine 10 when the predetermined F / C recovery conditions are met after the fuel cut has started. In this embodiment, the F / C recovery conditions are that any of the following are met: the accelerator opening ACC exceeds the accelerator off opening, the engine rotation speed NE is less than or equal to the predetermined F / C recovery rotation speed, or the vehicle speed SPD is less than or equal to the predetermined F / C recovery vehicle speed. The F / C recovery rotation speed is set to a rotation speed lower than the F / C start rotation speed, and the F / C recovery vehicle speed is set to a speed higher than the F / C start vehicle speed.

[0014] Furthermore, the ECM30 may also perform a filter regeneration process to burn and purify PM accumulated in the filter device 15 during fuel cut-off. When the ECM30 performs filter regeneration, it performs fuel cut-off with a larger intake air volume GA than during normal fuel cut-off. Specifically, when the ECM30 performs filter regeneration, it sets the F / C target air volume GA* to a larger value than during normal fuel cut-off. The F / C target air volume GA* represents the target value of the intake air volume GA during fuel cut-off. When the F / C permission conditions are met, the ECM30 controls the throttle opening to an opening that makes the intake air volume GA equal to the F / C target air volume GA*. The ECM30 performs filter regeneration when the F / C permission conditions are met while the amount of PM accumulated in the filter device 15 is equal to or greater than a predetermined regeneration judgment value.

[0015] <Fuel cut-off initiation process> Next, with reference to Figure 2, the details of the processes performed by the ECM30 during the period from the fulfillment of the F / C authorization conditions to the commencement of fuel cut will be explained. Figure 2 shows the processing procedure of the ECM30 from the fulfillment of the F / C authorization conditions to the commencement of fuel cut. The ECM30 starts the process shown in Figure 2 in response to the fulfillment of the F / C authorization conditions. After the F / C authorization conditions are fulfilled, the ECM30 starts reducing the intake air amount GA to the F / C target air amount GA*.

[0016] When the F / C permission conditions are met, the ECM30 first acquires the initial torque TE0, the F / C target air volume GA*, and the engine water temperature THW in step S100. The initial torque TE0 represents the value of the engine torque TE when the F / C permission conditions are met, i.e., when the accelerator is released. During load operation of the internal combustion engine 10, the ECM30 estimates the engine torque TE based on the engine speed NE and the engine load ratio KL, etc. The ECM30 then acquires the estimated value of the engine torque TE just before the accelerator is released as the value of the initial torque TE0.

[0017] In the next step S110, the ECM 30 calculates the F / C torque TE* based on the F / C target air quantity GA* and the engine coolant temperature THW. The F / C torque TE* represents the engine torque TE during fuel cut. When a small value is set for the F / C target air quantity GA*, the ECM 30 calculates the F / C torque TE* to be a smaller value than when a large value is set. Also, when the engine coolant temperature THW is low, the ECM 30 calculates the F / C torque TE* to be a smaller value than when it is high.

[0018] In the subsequent step S120, the ECM 30 calculates the value of the torque decay rate γ based on the initial torque TE0 and the F / C torque TE*. The torque decay rate γ represents the decay rate of the engine torque TE after the accelerator is turned off. When the difference between the initial torque TE0 and the F / C torque TE* is large, the ECM 30 calculates the value of the torque decay rate γ to be a larger value than when it is small.

[0019] In the next step S130, the ECM 30 calculates the value of the required time TX until the engine torque TE drops to the predetermined F / C permission torque TP after the accelerator is turned off, based on the initial torque TE0 and the torque decay rate γ. The F / C permission torque TP represents the upper limit value of the engine torque TE at the start of fuel cut, such that the torque shock generated in response to the start of fuel cut remains within an acceptable magnitude. Specifically, the ECM 30 calculates the quotient obtained by dividing the difference between the initial torque TE0 and the F / C permission torque TP by the torque decay rate γ as the value of the required time TX.

[0020] After that, the ECM 30 waits until the elapsed time after the accelerator is turned off becomes equal to or more than the required time TX (S140: YES), and sets the F / C flag. The F / C flag is a flag indicating that fuel cut is in progress according to the setting. After starting fuel cut according to the setting of the F / C flag, the ECM 30 ends the process at the start of fuel cut shown in FIG. 2.

[0021] <Operation of the Embodiment> When the F / C permission condition is satisfied in response to the accelerator being off, the ECM30 reduces the intake air volume GA of the internal combustion engine 10 to the F / C target air volume GA*. When performing fuel cut with filter regeneration processing, the ECM30 sets a larger value for the F / C target air volume GA* than in the case of normal fuel cut without filter regeneration processing.

[0022] On the other hand, in the fuel cut start process, the ECM30 calculates the F / C torque TE*, which is the engine torque TE during fuel cut, based on the F / C target air volume GA* and the engine coolant temperature THW. The F / C torque TE* becomes smaller as the pumping loss and friction loss of the internal combustion engine 10 during fuel cut become larger. The pumping loss of the internal combustion engine 10 during fuel cut becomes larger as the F / C target air volume GA* becomes smaller. Also, the friction loss of the internal combustion engine 10 becomes larger as the engine coolant temperature THW becomes lower. Therefore, the F / C torque TE* becomes smaller as the F / C target air volume GA* becomes smaller or as the engine coolant temperature THW becomes lower. By basing on the F / C target air volume GA* and the engine coolant temperature THW, the ECM30 calculates the F / C torque TE* in a manner that reflects the difference in pumping loss and friction loss during fuel cut.

[0023] The rate of decrease of the engine torque TE after the accelerator is off, that is, the torque decay rate γ, becomes larger as the decrease in the engine torque TE associated with the reduction of the intake air volume GA becomes larger. That is, the torque decay rate γ becomes larger as the difference between the initial torque TE0, which is the engine torque TE at the time of accelerator off, and the F / C torque TE* becomes larger. The ECM30 calculates the torque decay rate γ based on the difference between the initial torque TE0 and the F / C torque TE* in a manner that reflects this relationship. Strictly speaking, the ECM30 calculates the linear approximation value of the decay rate of the engine torque TE during the period when the engine torque TE is decreasing after the accelerator is off as the value of the torque decay rate γ.

[0024] In this embodiment, the engine torque TE after the accelerator is released is treated as a value that decreases over time from the initial torque TE0 at a rate corresponding to the torque decay rate γ. The formula for calculating the engine torque TE after the accelerator is released in this case is given by equation (1). In the equation, "t" represents the elapsed time after the accelerator is released. From equation (1), equation (2) can be derived to calculate the time TX required for the engine torque TE to decrease to the F / C permitted torque TP after the accelerator is released. The ECM 30 determines the start timing of the fuel cut based on the time TX calculated using equation (2). Therefore, in the internal combustion engine 10 to which the control device of this embodiment is applied, regardless of the difference in intake air volume GA and engine water temperature THW during the fuel cut, the fuel cut is started when the engine torque TE falls below the F / C permitted torque TP.

[0025]

number

[0026] Figure 3 shows the control behavior at the start of fuel cut in the control device of this embodiment. Figure 3(a) shows the transition of the F / C permission flag, Figure 3(b) shows the transition of the F / C flag, Figure 3(c) shows the transition of the engine rotational speed NE, and Figure 3(d) shows the transition of the engine torque TE.

[0027] In the following explanation, a fuel cut without filter regeneration, performed when the engine water temperature THW has risen to the temperature at which the internal combustion engine 10 is fully warmed up, will be referred to as a normal fuel cut. In contrast, a fuel cut without filter regeneration, performed when the engine water temperature THW is lower than the temperature at which the internal combustion engine 10 is fully warmed up, will be referred to as a low-temperature fuel cut. Furthermore, a fuel cut accompanied by filter regeneration, performed when the engine water temperature THW has risen to the temperature at which the internal combustion engine 10 is fully warmed up, will be referred to as a fuel cut during filter regeneration. Figures 3(b) and 3(d) show the changes in the F / C flag and engine torque TE when a normal fuel cut is performed, with solid lines. Figures 3(b) and 3(d) also show the changes in the F / C flag and engine torque TE when a low-temperature fuel cut is performed, with dashed lines. Furthermore, Figures 3(b) and 3(d) show the changes in the F / C flag and engine torque TE when fuel cut is performed during filter regeneration, indicated by dashed lines.

[0028] In Figure 3, at time t1, the F / C permission condition is met by releasing the accelerator, and the F / C permission flag is set. The ECM30 reduces the intake air volume GA to the F / C target air volume GA* in response to the F / C permission condition being met. In the case of fuel cut during filter regeneration, a larger value is set for the F / C target air volume GA* than in the case of fuel cut under normal conditions or at low water temperature.

[0029] In Figure 3, the initial torque TE0 is the same in all three situations, but the engine torque TE during fuel cut, i.e., F / C torque TE*, is different in each of the three situations. In Figure 3, the value of F / C torque TE* during normal fuel cut is "TE2". In contrast, in the case of fuel cut at low water temperature, the friction loss is large, so the F / C torque TE* is a smaller value than "TE2", which is "TE3". Also, in the case of fuel cut during filter regeneration, a larger value is set for the F / C target air amount GA* than during normal fuel cut, resulting in smaller pumping losses during fuel cut. Therefore, the F / C torque TE* in the case of fuel cut during filter regeneration is a larger value than the value of "TE2" during normal fuel cut, which is "TE1".

[0030] Due to these differences in F / C torque TE*, the torque decay rate γ after releasing the accelerator also differs in the three situations described above. In Figure 3, the torque decay rate γ in the case of fuel cut at low water temperature is greater than in the case of normal fuel cut, while the torque decay rate γ in the case of fuel cut during filter regeneration is smaller than in the case of normal fuel cut. As a result, the timing at which the engine torque TE drops below the F / C permitted torque TP also differs in the three situations described above. In Figure 3, in the case of normal fuel cut, the engine torque TE drops below the F / C permitted torque TP at time t3. In contrast, in the case of fuel cut at low water temperature, the engine torque TE drops below the F / C permitted torque TP at time t2, which is earlier than time t3, and in the case of fuel cut during filter regeneration, the engine torque TE drops below the F / C permitted torque TP at time t4, which is later than time t3.

[0031] In response to this, the ECM30, as described above, uses the F / C target air volume GA* and engine water temperature THW to determine the timing at which the engine torque TE falls below the F / C permitted torque TP, reflecting the change in torque damping rate γ due to the difference between them. The ECM30 then initiates fuel cut at the determined timing. Therefore, in all three situations described above, fuel cut is initiated at the appropriate time when the engine torque TE falls below the F / C permitted torque TP.

[0032] <Effects of the Embodiment> The control device for the internal combustion engine 10 in this embodiment provides the following effects. (1) When the F / C target air volume GA* is small, the pumping loss of the internal combustion engine 10 during fuel cut is greater than when it is large, so the engine torque TE decreases more quickly after the accelerator is released. In response to this, when the ECM 30 performs fuel cut when the accelerator is released, it calculates the time when the engine torque TE falls below a predetermined value (F / C permitted torque TP) based on the F / C target air volume GA*, and starts the fuel cut at that calculated time. Therefore, regardless of the difference in intake air volume GA during fuel cut, the torque shock at the start of fuel cut can be suppressed.

[0033] (2) When the engine water temperature THW is low, the friction loss of the internal combustion engine 10 is large, causing the engine torque TE to decrease more quickly after the accelerator is released. In response to this, the ECM 30 calculates the time when the engine torque TE falls below a predetermined value, based on the engine water temperature THW in addition to the F / C target air amount GA*. Therefore, regardless of the difference in engine water temperature THW, the torque shock at the start of fuel cut can be suppressed.

[0034] (3) The ECM30 calculates the torque decay rate γ, which is the decay rate of the engine torque TE after the accelerator is released, based on the initial torque TE0 (engine torque TE when the accelerator is released), the F / C target air volume GA*, and the engine water temperature THW. Then, based on the initial torque TE0 and the torque decay rate γ, the ECM30 calculates the time when the engine torque TE falls below the F / C permitted torque TP. Therefore, it can accurately calculate the time when the engine torque TE falls below the F / C permitted torque TP.

[0035] (4) When the ECM 30 performs filter regeneration to burn off particulate matter accumulated in the filter device 15 installed in the exhaust passage 13 of the internal combustion engine 10 during fuel cut-off, the F / C target air amount GA* is set to a larger value than during normal fuel cut-off. By increasing the intake air amount GA during fuel cut-off, the amount of oxygen supplied to the filter device 15 is increased, thereby promoting the combustion and purification of particulate matter.

[0036] (Other embodiments) The above embodiment can be implemented with the following modifications. The above embodiment and the following modifications can be combined with each other to the extent that they do not contradict each other technically.

[0037] If the warm-up of the internal combustion engine 10 is included in the conditions for executing fuel cut, the influence of engine water temperature THW on the change in engine torque TE after the accelerator is released becomes small. Therefore, in such cases, the torque decay rate γ may be calculated based only on the initial torque TE0 and the F / C target air volume GA*, without using the engine water temperature THW. In other words, the engine torque TE after the accelerator is released may be estimated based only on the F / C target air volume GA*, without using the engine water temperature THW.

[0038] In the above embodiment, the engine torque TE after the accelerator is released may be sequentially estimated, and fuel cut may be initiated when the estimated value falls below the F / C permitted torque TP. For example, the engine torque TE after the accelerator is released may be estimated using equation (1) based on the initial torque TE0, the torque decay rate γ, and the elapsed time after the accelerator is released.

[0039] In the above embodiment, the torque damping rate γ was first determined, and the engine torque TE after the accelerator was released was estimated as a value that gradually decreases from the initial torque TE0 with a gradient corresponding to the torque damping rate γ. The engine torque TE after the accelerator was released may be estimated in other ways. For example, the engine torque TE after the accelerator was released may be estimated based on the F / C target air volume GA* and the engine rotational speed NE, or based on the F / C target air volume GA*, the engine water temperature THW and the engine rotational speed NE.

[0040] In the above embodiment, the F / C target air volume GA* was switched depending on whether filter regeneration was performed or not, but the F / C target air volume GA* may be switched in a different manner.

[0041] The fuel cut-off start control in the control device of the above embodiment can also be applied to internal combustion engines 10 with configurations different from those shown in Figure 1. For example, it can be applied to internal combustion engines installed in hybrid vehicles different from those shown in Figure 1, or to internal combustion engines installed in engine vehicles that do not have a motor as a drive source. [Explanation of Symbols]

[0042] 10...Internal combustion engine, 11...Cylinder, 12...Intake passage, 13...Exhaust passage, 14...Throttle valve, 15...Filter device, 16...Injector, 17...Ignition device, 20...Motor, 21...Transmission, 22...Differential, 23...Wheel, 30...ECM (Engine Control Module), 31...CPU, 32...ROM, 33...Airflow meter, 34...Crank angle sensor, 35...Water temperature sensor, 36...Accelerator pedal sensor, 37...Vehicle speed sensor.

Claims

1. A control device for an internal combustion engine that performs fuel cut when the accelerator is released, the control device for an internal combustion engine that calculates the time when the engine torque falls below a predetermined value based on a target value of intake air amount during the fuel cut, and starts the fuel cut at the calculated time.

2. A control device for an internal combustion engine according to claim 1, which determines the decay rate of the engine torque after the accelerator is released based on the initial torque, which is the engine torque when the accelerator is released, and the target value of the intake air volume, and calculates the time when the engine torque becomes less than or equal to the predetermined value based on the initial torque and the decay rate.

3. The control device for an internal combustion engine according to claim 1, which calculates the time when the engine torque falls below a predetermined value based on the target value of the intake air volume and the coolant temperature of the internal combustion engine.

4. A control device for an internal combustion engine according to claim 3, which determines the decay rate of the engine torque after the accelerator is released based on the initial torque, which is the engine torque when the accelerator is released, the target value of the intake air volume, and the coolant temperature, and calculates the time when the engine torque becomes less than or equal to the predetermined value based on the initial torque and the decay rate.

5. The control device for an internal combustion engine according to claim 1, wherein when filter regeneration for combustion purification of particulate matter accumulated in a filter device installed in the exhaust passage of the internal combustion engine is performed during fuel cut-off, the target value of the intake air amount is set to a value greater than that during normal fuel cut-off.

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