Vehicles equipped with internal combustion engines

Abstract

To provide a vehicle capable of effectively preventing or avoiding a fuel-lean state even when an air-fuel ratio fluctuates during transition to high-load operation.SOLUTION: A vehicle 2 mounted with an internal combustion engine comprises: an exhaust gas purification device 20 mounted with a catalyst to purify exhaust gas emitted from an internal combustion engine 4; oxygen sensors 30 and 32 to detect a residual oxygen concentration in the exhaust gas; and a control device 40 executing feedback control of an air-fuel ratio related to fuel supplied to the internal combustion engine 4 on the basis of the residual oxygen concentration. The control device 40 corrects the air-fuel ratio by setting a lower limit value for reducing an amount of the fuel for a predetermined period after transition to high-load operation. Thus, the vehicle is capable of suppressing an NOx emission by preventing or avoiding a fuel-lean state even when the air-fuel ratio fluctuates during the transition to the high-load operation.SELECTED DRAWING: Figure 2

Description

Technical Field

[0004] , , , , , , ,

[0006] , , , ,

[0005] , , , , , , ,

[0001] The technology disclosed in this specification relates to a vehicle equipped with an internal combustion engine.

Background Art

[0002] In a vehicle equipped with an internal combustion engine, an exhaust gas purification device including a catalyst is provided for oxidizing and reducing components in the exhaust gas to purify it. Such a vehicle includes an oxygen sensor for detecting the residual oxygen concentration in the exhaust gas, estimates the mixing ratio of air and fuel (hereinafter referred to as the air-fuel ratio) in the internal combustion engine based on the residual oxygen concentration, and performs feedback control to correct the fuel and maintain the air-fuel ratio within a certain range.

[0003] Feedback control controls the fuel amount regardless of the driving load to control the air-fuel ratio. It is known that when shifting to high load of the engine, the amount of NOx emissions tends to increase because the fuel is reduced and controlled to the lean side by feedback control. For example, Patent Document 1 describes setting a correction coefficient for feedback control so that the air-fuel ratio tends to the rich side during a shift to high load operation such as acceleration. Thereby, the amount of NOx emissions is suppressed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, when shifting to high load operation, a phenomenon (air-fuel ratio roughness) may occur in which the detected air-fuel ratio fluctuates greatly and its amplitude becomes large. In setting the correction coefficient, when air-fuel ratio roughness occurs, it may not be possible to sufficiently avoid the fuel lean state.

[0006] This specification provides a vehicle that can effectively suppress or avoid a lean fuel condition even when air-fuel ratio fluctuations occur during high-load operation. [Means for solving the problem]

[0007] The technology disclosed herein relates to a vehicle equipped with an internal combustion engine. The vehicle includes an exhaust gas purification device equipped with a catalyst for purifying exhaust gas emitted from the internal combustion engine, an oxygen sensor for detecting the residual oxygen concentration in the exhaust gas, and a control device that performs feedback control to control the air-fuel ratio of the fuel supplied to the internal combustion engine based on the residual oxygen concentration. The control device corrects the air-fuel ratio by setting a lower limit for reducing the fuel for a predetermined period after transitioning to high-load operation.

[0008] According to this vehicle, even if air-fuel ratio fluctuations occur for a certain period after transitioning to high-load operation, the air-fuel ratio can be corrected to prevent it from becoming too lean by setting a lower limit for fuel reduction. Therefore, NOx emissions can be reduced by effectively suppressing or avoiding the lean fuel state caused by conventional feedback control. [Brief explanation of the drawing]

[0009] [Figure 1] This is a diagram showing the configuration of the vehicle. [Figure 2] This figure shows an example of the air-fuel ratio lower limit control process performed by the control device. [Figure 3] This is a diagram showing the configuration of a hybrid vehicle. [Modes for carrying out the invention]

[0010] Hereinafter, embodiments of the vehicle 2 of this disclosure will be described with reference to the drawings as appropriate. The vehicle 2 shown in Figure 1 comprises an engine 4, an exhaust gas purification device 20, oxygen sensors 30 and 32, and a control device 40 that controls the engine 4.

[0011] Engine 4 is an example of an internal combustion engine as used herein, and is not particularly limited to any internal combustion engine that can be mounted and used in a vehicle. Engine 4 in Figure 1 is a gasoline engine that uses gasoline as fuel. Although not shown, Engine 4 includes a combustion chamber, a fuel injection mechanism, a fuel tank, an intake mechanism for air which is the combustion gas, and an exhaust mechanism for exhaust gas.

[0012] The exhaust gas purification device 20 is installed in the exhaust passage of the exhaust gas exhaust mechanism of the engine 4. The exhaust gas purification device 20 includes a catalytic converter 22 containing a known three-way catalyst that oxidizes hydrocarbons and carbon monoxide, which are components of incomplete combustion, and reduces NOx, which is a by-product. The exhaust gas purified by passing through the catalytic converter 22 is discharged into the atmosphere.

[0013] Oxygen sensors 30 and 32 detect the residual oxygen concentration in the exhaust gas from the engine 4. Oxygen sensor 30 is located upstream of the catalytic converter 22, and oxygen sensor 32 is located downstream of the catalytic converter 22.

[0014] The control device 40 performs various controls on the engine 4, including air-fuel ratio control (fuel injection control). The control device 40 is typically configured as a computer equipped with a processor such as a CPU and memory. The control device 40 controls various operations of the engine 4 based on input signals from various sensors, including oxygen sensors 30 and 32, and input devices related to the operating load provided by the user.

[0015] Next, the air-fuel ratio lower limit control process by the control device 40 will be described with reference to Figure 2. Figure 2 shows a flowchart as an example of the air-fuel ratio lower limit control process. The processor repeatedly executes this process at a predetermined number of clock cycles. The processor also separately performs feedback control of the normal air-fuel ratio based on the residual oxygen concentration detected by the oxygen sensors 30 and 32.

[0016] The processor monitors whether the timing for transitioning to high-load operation has arrived for engine 4, such as during acceleration (step S10). The processor determines that the timing for transitioning to high-load operation has arrived when the high-load operation conditions were not met during the previous process execution, but are met during the current process execution. High-load operation conditions are set by, for example, whether any or more input values ​​such as engine speed, accelerator opening, intake air load ratio, and intake air volume exceed predetermined reference values. Typically, when the engine speed and / or intake air load ratio did not exceed the reference values ​​during the previous process execution, but exceed these reference values ​​during the current process execution, the processor determines that the timing for transitioning to high-load operation has arrived.

[0017] When the processor determines that the timing for transitioning to high-load operation has arrived, the processor clears the post-high-load operation transition counter (hereinafter simply referred to as the post-high-load operation transition counter), which has already started and is continuing to count, and terminates this process (step S20). The post-high-load operation transition counter is started separately when the timing for transitioning to high-load operation is determined in step S10, and continues to count until the timing for transitioning to high-load operation is determined again.

[0018] The high-load transition counter is set to correspond to the period after transitioning to high-load operation during which a lean air-fuel ratio state is likely to occur or an air-fuel ratio fluctuation phenomenon is likely to occur due to feedback control. The high-load transition counter may be, for example, a counter value that directly corresponds to a predetermined elapsed time since the transition to high-load operation, or a counter value that corresponds to the cumulative amount of air flowing into the engine 4 since the transition to high-load operation.

[0019] In step S10, for example, when the high-load operation conditions were satisfied during the previous process and are also satisfied in the current process, the processor cannot determine that it is the timing of the transition to high-load operation. That is, when the processor has already transitioned to high-load operation, it determines whether it is within a predetermined period after the transition to high-load operation based on the post-high-load transition counter (step S30).

[0020] When the processor determines that it is within a predetermined period after the transition to high-load operation based on the post-high-load transition counter (when YES), it newly sets a lower limit value (guard value) when reducing the fuel by feedback control (step S40). This lower limit value is set, for example, to a value that can suppress NOx when the air-fuel ratio is controlled to be fuel-lean by feedback control. Such a lower limit value can be set, for example, based on measured values or simulations. The lower limit value of the air-fuel ratio feedback correction rate is set to, for example, 0% or -5%.

[0021] By setting the lower limit value when reducing the fuel, even if the air-fuel ratio is controlled to the fuel-lean side by feedback control, the fuel is not reduced beyond the set lower limit value, so the fuel-lean state is suppressed or avoided, and the NOx emission amount can be suppressed. Also, even if air-fuel ratio roughness occurs during the transition to high-load operation, the fuel-lean state is surely suppressed or avoided regardless of the air-fuel ratio roughness.

[0022] When the processor cannot determine that it is within a predetermined period after the transition to high-load operation based on the post-high-load transition counter (when NO), the processor ends this process. This is because when the post-high-load transition counter exceeds a predetermined value and is not within the predetermined period after the transition to high-load operation, there is no longer a need to consider an increase in NOx emissions or air-fuel ratio roughness due to fuel-lean side control of the air-fuel ratio.

[0023] The processor repeatedly executes this air-fuel ratio lower limit value control process, monitors the arrival of the high-load operation transition timing, and sets the lower limit value of fuel reduction as necessary.

[0024] As described above, according to the vehicle 2, within a predetermined period after the high-load operation transition of the engine 4, a new lower limit value of fuel reduction is set to suppress the control towards the lean fuel side by feedback control. By doing so, even if air-fuel ratio fluctuations occur, the NOx emission amount due to the lean fuel state during high-load operation can be suppressed.

[0025] In the above description, the vehicle 2 is assumed to include only the engine 4 as its driving device. However, in a hybrid vehicle (HBEV) 62, a similar lower limit value of fuel reduction can also be set in the feedback control of the engine 4.

[0026] An example of the hybrid vehicle 62 shown in FIG. 3 is presented. Elements common to the vehicle 2 are denoted by the same reference numerals. The hybrid vehicle 62 includes a generator 7, a driving motor 72, an inverter 74, and a battery 76. The generator 7 is connected to the engine 4 via a power transmission mechanism not shown. The generator 7 is electrically connected to the battery 76 via the inverter 74. The electric power generated by the generator 7 is supplied to the battery 76 via the inverter 74.

[0027] The driving motor 72 is connected to drive wheels not shown via a power distribution mechanism and a speed reduction mechanism not shown. The driving motor 72 is driven using the electric power supplied from the battery 76 via the inverter 74. The control device 40 controls the operations of each element of the hybrid vehicle 62.

[0028] In such hybrid vehicles 62, a separate trigger process is executed to determine whether to start the air-fuel ratio lower limit control process shown in Figure 2. This trigger process starts the air-fuel ratio control process shown in Figure 2 only under conditions where assistance from the drive motor 72 is not possible during high-load operation. In this process, for example, the processor monitors whether there are situations where the battery output is limited, such as when the power for assistance from the drive motor 72 is below a predetermined value, when the battery temperature is above a predetermined temperature, or when the temperature is below a predetermined temperature. When the processor determines that the conditions for assistance from the drive motor 72 are not possible are met, it starts the air-fuel ratio lower limit control process described above and terminates this trigger process. On the other hand, when the processor does not meet the conditions for assistance from the drive motor 72, that is, when motor assistance is available, it does not start the air-fuel ratio lower limit control process described above and terminates this trigger process. This trigger process is executed repeatedly at a predetermined number of clock cycles.

[0029] In this way, even in the hybrid vehicle 62, when the assistance of the drive motor 72 cannot be used when transitioning to high-load operation, even if an air-fuel ratio disturbance occurs, the lean fuel condition in the engine 4 can be suppressed or avoided, thereby suppressing NOx emissions. [Explanation of Symbols]

[0030] 2: Vehicle, 4: Engine, 20: Exhaust gas purification system, 22: Catalytic converter, 30, 32: Oxygen sensor, 40: Control device, 62: Hybrid vehicle, 70: Generator, 72: Drive motor, 74: Inverter, 76: Battery

Claims

[Claim 1] A vehicle equipped with an internal combustion engine, An exhaust gas purification device equipped with a catalyst for purifying exhaust gas discharged from the internal combustion engine, An oxygen sensor for detecting the residual oxygen concentration in the exhaust gas, A control device that performs feedback control to control the air-fuel ratio of the fuel supplied to the internal combustion engine based on the residual oxygen concentration, Equipped with, The control device corrects the air-fuel ratio by setting a lower limit value for reducing the amount of fuel for a predetermined period after transitioning to high-load operation, such that NOx can be suppressed when the air-fuel ratio is controlled to be lean by feedback control.

Images