vehicle

Abstract

To enable a catalyst to appropriately function.SOLUTION: A vehicle includes: an engine; a catalyst for purifying gas to be discharged from the engine; an oxygen concentration detection section for detecting an oxygen concentration in the catalyst; and a control device. The control device includes: one or a plurality of processors; and one or a plurality of memories each connected to the processor. The processor executes processing including determination of whether or not stop of the engine is prohibited on the basis of the state of the engine and a detection result from the oxygen concentration detection section.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a vehicle.

Background Art

[0002] For example, Patent Document 1 discloses a hybrid vehicle that controls an engine based on the temperature of a catalyst. In such a hybrid vehicle, when a stop condition is satisfied and the temperature of the catalyst is below a threshold value, the engine is stopped, and when the stop condition is satisfied and the temperature of the catalyst is higher than the threshold value, the operation of the engine is continued.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] For example, in a hybrid vehicle, in a situation where the engine is stopped and the vehicle is running by a motor, an operation may be performed to repeatedly depress and release an accelerator pedal within a short period of time. At this time, depending on the driving scene, due to the depression and release of the accelerator pedal, the start and stop of the stopped engine may be frequently repeated within a short period of time.

[0005] Here, when the engine is stopped, oxygen that is not burned in the cylinder and is discharged from the exhaust port reaches the catalyst, thereby increasing the oxygen concentration in the catalyst. If the start and stop of the engine are repeated within a short period of time, before the oxygen concentration in the catalyst sufficiently decreases, the increase in the oxygen concentration in the catalyst due to the stop of the engine is repeated, and the oxygen concentration in the catalyst becomes high. When the oxygen concentration in the catalyst becomes higher than the oxygen concentration at which the catalyst can purify NOx, the catalyst cannot appropriately purify NOx.

[0006] Therefore, the present invention aims to provide a vehicle capable of properly utilizing a catalyst. [Means for solving the problem]

[0007] above To solve the aforementioned problem, a vehicle according to one embodiment of the present invention is provided. The engine and A catalyst for purifying the gas emitted from the aforementioned engine, The oxygen concentration detection unit detects the oxygen concentration in the catalyst, Control device and Equipped with, The control device is One or more processors, One or more memory connected to the processor, It has, The neutral air-fuel ratio is an air-fuel ratio within a predetermined range, including the stoichiometric air-fuel ratio. A predetermined first threshold is set to an oxygen concentration corresponding to the boundary value on the lean atmosphere side within the range of the neutral air-fuel ratio. A predetermined second threshold is set to an oxygen concentration corresponding to the stoichiometric air-fuel ratio within the range of the neutral air-fuel ratio. The aforementioned processor, If the engine is started and the oxygen concentration in the catalyst detected by the oxygen concentration detection unit is higher than the first threshold, the engine will not be stopped. After the engine shutdown is prohibited, if the oxygen concentration in the catalyst detected by the oxygen concentration detection unit falls below the second threshold, the prohibition on engine shutdown is lifted. Execute the process that includes this. To solve the above problems, a vehicle according to one embodiment of the present invention is provided. The engine and A catalyst for purifying the gas emitted from the aforementioned engine, The oxygen concentration detection unit detects the oxygen concentration in the catalyst, Control device and Equipped with, The control device is configured to: include one or more processors; one or more memories connected to the processor; and is configured to: The neutral air-fuel ratio is an air-fuel ratio within a predetermined range including the theoretical air-fuel ratio. The processor is configured to: when the engine is started and the oxygen concentration in the catalyst detected by the oxygen concentration detection unit is higher than a predetermined first threshold value, prohibit the engine from stopping; when the engine is prohibited from stopping, control the engine so that the air-fuel ratio in the engine becomes lower than the upper limit value of the neutral air-fuel ratio; after the prohibition of the engine stop, when the oxygen concentration in the catalyst detected by the oxygen concentration detection unit becomes equal to or lower than a predetermined second threshold value, release the prohibition of the engine stop; and execute a process including the above operations.

Advantages of the Invention

[0008] According to the present invention, it is possible to cause the catalyst to function properly.

Brief Description of the Drawings

[0009] [Figure 1] FIG. 1 is a block diagram showing the configuration of a vehicle 1 according to the present embodiment. [Figure 2] FIG. 2 is a diagram for explaining problems when the start and stop of the engine 12 are frequently repeated within a short period of time. [Figure 3] FIG. 3 is a diagram for explaining the operation of the vehicle control unit of the present embodiment. [Figure 4] FIG. 4 is a flowchart for explaining the operation flow of the vehicle control unit of the present embodiment.

Embodiments for Carrying Out the Invention

[0010] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings. The specific dimensions, materials, numerical values, etc. shown in such embodiments are merely examples for facilitating the understanding of the invention, and do not limit the present invention unless otherwise specified. In this specification and the drawings, elements having substantially the same functions and configurations are denoted by the same reference numerals to omit redundant descriptions, and elements not directly related to the present invention are omitted from the illustration.

[0011] FIG. 1 is a block diagram showing the configuration of a vehicle 1 according to the present embodiment. The vehicle 1 is a hybrid vehicle including a motor 10 and an engine 12 as drive sources.

[0012] The motor 10 has a rotor. Although not shown, the motor 10 is electrically connected to a battery through an inverter. The rotor of the motor 10 rotates according to the electric power supplied from the battery. The vehicle 1 is configured to be able to transmit the driving force according to the rotation of the rotor of the motor 10 to an axle and wheels.

[0013] The engine 12 has an intake port 20 and an exhaust port 22. Although not shown, the engine 12 has a cylinder and a piston disposed in the cylinder.

[0014] When the intake port 20 is opened, air is introduced into the cylinder through the intake port 20. Further, fuel is injected into the cylinder. In the cylinder, a mixture of air and fuel burns, causing the piston to slide in the cylinder. The vehicle 1 is configured to be able to transmit the driving force according to the sliding of the piston of the engine 12 to an axle and wheels via a crankshaft.

[0015] In addition to the motor 10 and the engine 12, the vehicle 1 includes an exhaust pipe 24, a catalyst 26, an A / F sensor 28, an O2 sensor 30, an accelerator pedal sensor 32, and a vehicle control device 34.

[0016] The exhaust pipe 24 is connected to the exhaust port 22. When the exhaust port 22 is opened, the gas inside the cylinder is discharged through the exhaust port 22 into the exhaust pipe 24. The exhaust pipe 24 functions as an exhaust passage through which the gas discharged from the engine 12 flows.

[0017] The catalyst 26 is located in the middle of the exhaust pipe 24. The catalyst 26 purifies the gas emitted from the engine 12. For example, the catalyst 26 is a three-way catalyst or an LNT (Lean NOx Traps). A three-way catalyst is composed of, for example, platinum (Pt), palladium (Pd), and rhodium (Rh), and removes hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx) from the gas emitted from the engine 12. An LNT purifies nitrogen oxides (NOx) from the gas emitted from the engine 12 and also captures particulate matter.

[0018] The A / F sensor 28 is located between the exhaust port 22 and the catalyst 26 in the exhaust passage. In other words, the A / F sensor 28 is located upstream of the catalyst 26 in the gas flow in the exhaust passage. The A / F sensor 28 detects the air-fuel ratio of the gas discharged from the exhaust port 22. The air-fuel ratio indicates the ratio of air to fuel.

[0019] The O2 sensor 30 is located in the exhaust passage on the side opposite the exhaust port 22 to the catalyst 26. In other words, the O2 sensor 30 is located downstream of the catalyst 26 in the gas flow path of the exhaust passage. The O2 sensor 30 detects the oxygen concentration of the gas after it has passed through the catalyst 26. Therefore, the O2 sensor 30 functions as an oxygen concentration detection unit that detects the oxygen concentration within the catalyst 26.

[0020] Here, the air-fuel ratio at or near the stoichiometric air-fuel ratio, that is, the air-fuel ratio within a predetermined range including the stoichiometric air-fuel ratio, is sometimes called the neutral air-fuel ratio. Also, the atmosphere of a mixture or gas when its air-fuel ratio is lower than the neutral air-fuel ratio is sometimes called a rich atmosphere. In a rich atmosphere, there is an excess of fuel and a leaner amount of air compared to the atmosphere at the stoichiometric air-fuel ratio. Also, the atmosphere of a mixture or gas when its air-fuel ratio is higher than the neutral air-fuel ratio is sometimes called a lean atmosphere. In a lean atmosphere, there is a leaner amount of fuel and an excess of air compared to the atmosphere at the stoichiometric air-fuel ratio.

[0021] When the air-fuel ratio is greater than the neutral air-fuel ratio, the oxygen concentration becomes higher than the oxygen concentration at the neutral air-fuel ratio. For example, when the air-fuel ratio of the gas in catalyst 26 is greater than the neutral air-fuel ratio, the atmosphere of the gas in catalyst 26 becomes lean, and the oxygen concentration in catalyst 26 becomes higher than the oxygen concentration in catalyst 26 when the air-fuel ratio of the gas in catalyst 26 is neutral.

[0022] When the air-fuel ratio is lower than the neutral air-fuel ratio, the oxygen concentration becomes lower than the oxygen concentration at the neutral air-fuel ratio. For example, when the air-fuel ratio of the gas in catalyst 26 is lower than the neutral air-fuel ratio, the atmosphere of the gas in catalyst 26 becomes a rich atmosphere, and the oxygen concentration in catalyst 26 becomes lower than the oxygen concentration in catalyst 26 when the air-fuel ratio of the gas in catalyst 26 is the neutral air-fuel ratio.

[0023] The O2 sensor 30 outputs a voltage according to the oxygen concentration in the catalyst 26. Hereafter, the voltage output from the O2 sensor 30 may be referred to as the O2 sensor voltage. When the gas atmosphere in the catalyst 26 is lean, that is, when the oxygen concentration in the catalyst 26 is higher than the oxygen concentration at a neutral air-fuel ratio, the O2 sensor voltage will be lower than the O2 sensor voltage at a neutral air-fuel ratio. On the other hand, when the gas atmosphere in the catalyst 26 is rich, that is, when the oxygen concentration in the catalyst 26 is lower than the oxygen concentration at a neutral air-fuel ratio, the O2 sensor voltage will be higher than the O2 sensor voltage at a neutral air-fuel ratio. From this, the oxygen concentration in the catalyst 26 can be determined based on the O2 sensor voltage.

[0024] The accelerator pedal sensor 32 detects the amount of movement of the accelerator pedal.

[0025] The vehicle control device 34 has one or more processors 40 and one or more memories 42 connected to the processors 40. The processors 40 include ROM in which programs are stored and RAM as a work area. The processors 40 cooperate with the programs contained in the memories 42 to function as a vehicle control unit 50 and control the entire vehicle 1.

[0026] The vehicle control unit 50 controls the fuel injection amount based on the detection result of the A / F sensor 28. The vehicle control unit 50 also obtains the amount of accelerator pedal operation from the accelerator pedal sensor 32 and derives the requested driving force requested by the driver based on the obtained accelerator pedal operation amount and the speed of the vehicle 1. The vehicle control unit 50 controls the motor 10 and engine 12 based on the requested driving force.

[0027] For example, if the requested driving force is less than a predetermined driving force, the vehicle control unit 50 stops the engine 12 and controls the vehicle 1 to run using only the driving force of the motor 10. Specifically, the vehicle control unit 50 controls the frequency of the inverter based on the requested driving force to drive the motor 10 at a rotational speed corresponding to the requested driving force. The predetermined driving force may be set to any value less than or equal to the upper limit of the driving force that the motor 10 can generate.

[0028] On the other hand, if the requested driving force is greater than or equal to a predetermined driving force, the vehicle control unit 50 drives the engine 12 in addition to the motor 10, and controls the vehicle 1 to move using both the motor 10 and the engine 12, thereby realizing the requested driving force with the driving forces of both the motor 10 and the engine 12. For example, the vehicle control unit 50 determines the distribution of the driving force between the motor 10 and the engine 12 based on the requested driving force. The vehicle control unit 50 rotates the motor 10 at a rotational speed corresponding to the driving force allocated to the motor 10, and drives the engine 12 at a rotational speed corresponding to the driving force allocated to the engine 12.

[0029] Here, we assume a situation where the engine 12 is stopped and the vehicle 1 is running solely on the motor 10. In this situation, the driver may repeatedly press and release the accelerator pedal in a short period of time. Depending on the driving scene, pressing the accelerator pedal may cause the required driving force to change from below a predetermined driving force to above a predetermined driving force, and releasing the accelerator pedal may cause the required driving force to change from above a predetermined driving force to below a predetermined driving force, and this process may be repeated frequently in a short period of time. As a result, the engine 12 will be started and stopped frequently in a short period of time.

[0030] Figure 2 illustrates the problems that arise when the engine 12 is started and stopped frequently in a short period of time. In the example in Figure 2, the range of oxygen concentrations corresponding to the neutral air-fuel ratio is shown in hatching, as indicated by the time chart of oxygen concentration in the catalyst 26.

[0031] At time point T1 in Figure 2, the amount of accelerator pedal operation detected by the accelerator pedal sensor 32 increases, the required driving force becomes greater than or equal to a predetermined driving force, the engine 12 starts, and the engine speed increases.

[0032] Suppose that at time T2, following time T1, the amount of accelerator pedal operation decreases and the required driving force falls below the predetermined driving force. In that case, the vehicle control unit 50 performs an operation to stop the engine 12 at time T2.

[0033] At time T2, the vehicle control unit 50 stops the injection of fuel into the cylinder and stops the combustion of the fuel-air mixture in order to stop the engine 12. However, even though the fuel injection stops, the piston does not stop immediately and continues to slide due to inertia. Then the sliding motion of the piston decreases, and at time T3, after time T2, the piston stops, and the engine 12 is stopped.

[0034] Between time point T2 and time point T3, that is, from the time fuel injection is stopped until the engine 12 is completely stopped, intake air is drawn in through the intake port 20 and exhaust air is drawn in through the exhaust port 22 in conjunction with the sliding of the piston. During this time, since combustion of the air-fuel mixture is stopped, the oxygen in the air supplied through the intake port 20 is not burned and is discharged through the exhaust port 22.

[0035] The oxygen that is emitted without being burned reaches the catalyst 26 through the exhaust passage. As a result, the oxygen concentration in the catalyst 26 at time T3 when the engine is stopped is higher than the oxygen concentration in the catalyst 26 before the engine is stopped, such as at time T2. For example, the oxygen concentration in the catalyst 26 at time T3 when the engine is stopped is higher than the oxygen concentration corresponding to the neutral air-fuel ratio.

[0036] Based on these phenomena, the vehicle control unit 50 controls the engine 12 during operation from time T1 to time T2 so that the air-fuel ratio within the engine 12 is slightly richer than the stoichiometric air-fuel ratio within the range of the neutral air-fuel ratio. As a result, the gas emitted from the engine 12 and reaching the catalyst 26 causes the oxygen concentration within the catalyst 26 to be slightly lower than the oxygen concentration corresponding to the stoichiometric air-fuel ratio within the range of the neutral air-fuel ratio during engine operation. This reduces the degree to which the oxygen concentration within the catalyst 26 increases when the engine is stopped. However, even with this measure, as shown in the example in Figure 2, the oxygen concentration within the catalyst 26 when the engine is stopped may exceed the range of the oxygen concentration corresponding to the neutral air-fuel ratio.

[0037] In the example shown in Figure 2, the engine 12 is restarted at time T4, after time T3. The oxygen concentration in the catalyst 26 at time T4 is approximately the same as the oxygen concentration in the catalyst 26 at time T3, and is higher than the oxygen concentration corresponding to the neutral air-fuel ratio. If the oxygen concentration in the catalyst 26 is higher than the oxygen concentration corresponding to the neutral air-fuel ratio while the engine 12 is running after time T4, the vehicle control unit 50 controls the engine 12 so that the air-fuel ratio in the engine 12 becomes slightly lower than the neutral air-fuel ratio. As a result, the amount of oxygen supplied from the engine 12 to the catalyst 26 decreases compared to when the air-fuel ratio in the engine 12 is the neutral air-fuel ratio, and the oxygen concentration in the catalyst 26 gradually decreases from the oxygen concentration in the catalyst 26 at time T4.

[0038] In the example shown in Figure 2, assume that at time T5, before the oxygen concentration in the catalyst 26 has sufficiently decreased, the amount of accelerator pedal operation decreases and the required driving force falls below a predetermined driving force. At time T5, the vehicle control unit 50 performs an operation to stop the engine 12. As a result, from time T5 until time T6, when the engine 12 has finished stopping, the unburned oxygen that is discharged reaches the catalyst 26 through the exhaust passage. Consequently, the oxygen concentration in the catalyst 26 at time T6 becomes higher than the oxygen concentration in the catalyst 26 at time T3.

[0039] Furthermore, in the example in Figure 2, the engine is restarted at time T7, after time T6. The oxygen concentration in the catalyst 26 at time T7 is approximately the same as the oxygen concentration in the catalyst 26 at time T6. The oxygen concentration in the catalyst 26 after time T7 gradually decreases from the oxygen concentration in the catalyst 26 at time T7.

[0040] Assuming that, similar to time T5, at time T8, before the oxygen concentration in catalyst 26 has sufficiently decreased, the accelerator pedal input decreases and the required driving force falls below a predetermined driving force, causing the engine 12 to stop. In this case, from time T8 to time T9, when the engine 12 has finished stopping, unburned oxygen is discharged and reaches catalyst 26 through the exhaust passage. As a result, the oxygen concentration in catalyst 26 at time T9 is higher than the oxygen concentration in catalyst 26 at time T6.

[0041] Thus, if the engine 12 is started and stopped repeatedly in a short period of time, the oxygen concentration in the catalyst 26 does not decrease to the oxygen concentration corresponding to the neutral air-fuel ratio, and in some cases, the oxygen concentration in the catalyst 26 may even increase.

[0042] Furthermore, if the oxygen concentration within the catalyst 26 exceeds the oxygen concentration at which the catalyst 26 can purify NOx, the catalyst 26 will no longer be able to properly purify the NOx in the gas emitted from the engine 12. For example, in the example shown in Figure 2, during engine operation from the start of the engine 12 at time T7 to the completion of engine shutdown at time T9, the oxygen concentration within the catalyst 26 is higher than the oxygen concentration at which NOx can be purified. As a result, in the example shown in Figure 2, NOx is not properly purified by the catalyst 26 between time T7 and time T9, and the amount of NOx emitted is higher compared to between time T1 and time T3, or between time T4 and time T6.

[0043] To address these problems, the operation of the vehicle control unit 50 of the vehicle 1 according to this embodiment will be described below with reference to Figure 3.

[0044] Figure 3 is a diagram illustrating the operation of the vehicle control unit 50 of this embodiment. In the oxygen concentration time chart in the catalyst 26 of Figure 3, the range of oxygen concentration corresponding to the neutral air-fuel ratio is indicated by hatching. Similarly, in the O2 sensor voltage time chart in Figure 3, the range of O2 sensor voltage corresponding to the neutral air-fuel ratio is indicated by hatching.

[0045] At time T11 in Figure 3, the amount of accelerator pedal operation detected by the accelerator pedal sensor 32 increases, the required driving force becomes greater than or equal to the predetermined driving force, the engine 12 starts and the engine speed increases.

[0046] Suppose that at time T12, following time T11, the amount of accelerator pedal operation decreases and the required driving force falls below the predetermined driving force. In that case, the vehicle control unit 50 performs an operation to stop the engine 12 at time T12.

[0047] Assume that at engine startup at time T11, the O2 sensor voltage is within the range corresponding to the neutral air-fuel ratio, that is, the oxygen concentration in the catalyst 26 is the oxygen concentration corresponding to the neutral air-fuel ratio. In this case, the vehicle control unit 50 controls the engine 12 so that the oxygen concentration in the catalyst 26 is maintained at the oxygen concentration corresponding to the neutral air-fuel ratio. As a result, during the operation of the engine 12 from time T11 to time T12, the oxygen concentration in the catalyst 26 is maintained at the oxygen concentration corresponding to the neutral air-fuel ratio. If the oxygen concentration in the catalyst 26 is the oxygen concentration corresponding to the neutral air-fuel ratio at engine startup, the vehicle control unit 50 may also control the engine 12 so that the air-fuel ratio in the engine 12 is slightly richer than the stoichiometric air-fuel ratio within the range of the neutral air-fuel ratio during operation. In this case as well, the oxygen concentration in the catalyst 26 is maintained at the oxygen concentration corresponding to the neutral air-fuel ratio during operation of the engine 12.

[0048] From time T12 until time T13, when the engine 12 has finished stopping, unburned oxygen is discharged and reaches the catalyst 26 through the exhaust passage. As a result, the oxygen concentration in the catalyst 26 increases from time T12 to time T13. The oxygen concentration in the catalyst 26 at time T13 becomes higher than, for example, the oxygen concentration corresponding to the boundary value on the lean atmosphere side of the oxygen concentration corresponding to the neutral air-fuel ratio. Here, the boundary value on the lean atmosphere side corresponds to the maximum value of the oxygen concentration corresponding to the neutral air-fuel ratio.

[0049] Furthermore, between time point T12 and time point T13, the O2 sensor voltage decreases in conjunction with the change in oxygen concentration within the catalyst 26. At time point T13, the O2 sensor voltage becomes lower than, for example, the O2 sensor voltage corresponding to the lean atmosphere boundary value among the O2 sensor voltages corresponding to the neutral air-fuel ratio. Note that the lean atmosphere boundary value here corresponds to the minimum value among the O2 sensor voltages corresponding to the neutral air-fuel ratio.

[0050] In the example shown in Figure 3, the engine 12 is restarted at time T14, after time T13. The oxygen concentration in the catalyst 26 at time T14 is approximately the same as the oxygen concentration in the catalyst 26 at time T13. Also, the O2 sensor voltage at time T14 is approximately the same as the O2 sensor voltage at time T13.

[0051] In this embodiment, the vehicle control unit 50 acquires the oxygen concentration in the catalyst 26 when the engine 12 is started at time T14. The vehicle control unit 50 determines whether the acquired oxygen concentration in the catalyst 26 is greater than a predetermined first threshold Th1a when the engine 12 is started.

[0052] The predetermined first threshold Th1a is set to the oxygen concentration corresponding to the boundary value on the lean atmosphere side among the oxygen concentrations corresponding to the neutral air-fuel ratio, as shown by the dashed line in the oxygen concentration time chart in catalyst 26 in Figure 3. Note that the first threshold Th1a is not limited to this example and may be set to any oxygen concentration less than or equal to the maximum oxygen concentration at which catalyst 26 can purify NOx.

[0053] Furthermore, as shown by the dashed line in the O2 sensor voltage time chart in Figure 3, a predetermined threshold Th1b is set with respect to the O2 sensor voltage. The threshold Th1b for the O2 sensor voltage corresponds to the first threshold Th1a for the oxygen concentration in the catalyst 26. The threshold Th1b is set, for example, to the O2 sensor voltage corresponding to the boundary value on the lean atmosphere side among the O2 sensor voltages corresponding to the neutral air-fuel ratio. Note that the threshold Th1b is not limited to this example, and may be set to any O2 sensor voltage as long as it corresponds to the first threshold Th1a for the oxygen concentration in the catalyst 26.

[0054] In this embodiment, the vehicle control unit 50 turns on the engine stop prohibition flag when the engine 12 is started and the oxygen concentration in the catalyst 26 is higher than the first threshold Th1a. The engine stop prohibition flag is a flag that indicates whether or not to prohibit the stopping of the engine 12. When the engine stop prohibition flag is on, the vehicle control unit 50 prohibits the stopping of the engine 12 and continues to drive the engine 12, regardless of whether the conditions for stopping the engine 12 have been met.

[0055] More specifically, when the engine 12 is started, the vehicle control unit 50 acquires the O2 sensor voltage from the O2 sensor 30 as an indicator of the oxygen concentration in the catalyst 26. If the acquired O2 sensor voltage is lower than the threshold Th1b, the vehicle control unit 50 turns on the engine stop prohibition flag. Note that the threshold Th1b corresponds to the first threshold Th1a, and since a lower O2 sensor voltage indicates a higher oxygen concentration, the condition that the O2 sensor voltage is lower than the threshold Th1b corresponds to the condition that the oxygen concentration in the catalyst 26 is higher than the first threshold Th1a.

[0056] In Figure 3, since the engine 12 is running at time T14, the vehicle control unit 50 acquires the O2 sensor voltage at time T14. Since the O2 sensor voltage at time T14 is lower than the threshold Th1b, the vehicle control unit 50 turns on the engine stop prohibition flag at time T14. The engine stop prohibition flag remains on until it is turned off.

[0057] While the engine 12 is running after time T14, the vehicle control unit 50 controls the engine 12 so that the air-fuel ratio inside the engine 12 is slightly lower than the neutral air-fuel ratio, so the oxygen concentration inside the catalyst 26 decreases after time T14.

[0058] Furthermore, after time point T14, the O2 sensor voltage increases in conjunction with the change in oxygen concentration within catalyst 26.

[0059] In the example shown in Figure 3, at time T15, after time T14, the amount of accelerator pedal operation decreases and the required driving force falls below the predetermined driving force. However, because the engine stop prohibition flag is in the ON state, even if the required driving force falls below the predetermined driving force, the vehicle control unit 50 prohibits stopping the engine 12 and continues to drive the engine 12.

[0060] While the engine 12 is running, it is controlled so that the air-fuel ratio within the engine 12 is slightly lower than the neutral air-fuel ratio. Therefore, as the engine 12 continues to run, the oxygen concentration within the catalyst 26 continues to decrease. By continuing to run the engine 12, the oxygen concentration within the catalyst 26 can be brought up to the oxygen concentration corresponding to the neutral air-fuel ratio.

[0061] Furthermore, as the engine 12 continues to run, the O2 sensor voltage continues to rise in conjunction with the change in oxygen concentration within the catalyst 26. By continuing to run the engine 12, the O2 sensor voltage can be brought up to the O2 sensor voltage corresponding to the neutral air-fuel ratio.

[0062] In this embodiment, the vehicle control unit 50 continuously acquires the oxygen concentration in the catalyst 26 even after the engine 12 is prohibited from being stopped. The vehicle control unit 50 determines whether the acquired oxygen concentration in the catalyst 26 has fallen below a predetermined second threshold Th2a.

[0063] The predetermined second threshold Th2a is set to an oxygen concentration corresponding to a target air-fuel ratio within the neutral air-fuel ratio range, for example, as shown by the dashed line in the oxygen concentration time chart in the catalyst 26 in Figure 3. The target air-fuel ratio is set to, for example, the stoichiometric air-fuel ratio, but may be set to any air-fuel ratio within the neutral air-fuel ratio range. The second threshold Th2a is set to a value smaller than the first threshold Th1a, for example. Note that the second threshold Th2a may be set to a different value from the first threshold Th1a, or it may be set to the same value as the first threshold Th1a.

[0064] Furthermore, as shown by the dashed line in the O2 sensor voltage time chart in Figure 3, a predetermined threshold Th2b is set with respect to the O2 sensor voltage. The threshold Th2b for the O2 sensor voltage corresponds to a second threshold Th2a for the oxygen concentration in the catalyst 26. The threshold Th2b is set to the O2 sensor voltage corresponding to the target air-fuel ratio within the neutral air-fuel ratio range. Note that the threshold Th2b is not limited to this example and may be set to any O2 sensor voltage as long as it corresponds to the second threshold Th2a for the oxygen concentration in the catalyst 26. The threshold Th2b is set to a value greater than, for example, the threshold Th1b. Note that the threshold Th2b may be set to a different value from the threshold Th1b, or it may be set to the same value as the threshold Th1b.

[0065] In this embodiment, the vehicle control unit 50 releases the prohibition on stopping the engine 12 when the oxygen concentration in the catalyst 26 falls below a predetermined second threshold Th2a, after the engine 12 has been prohibited from stopping, or in other words, when the engine stop prohibition flag is in the ON state.

[0066] More specifically, even when the engine stop prohibition flag is ON, the vehicle control unit 50 sequentially acquires the O2 sensor voltage from the O2 sensor 30 as an indicator of the oxygen concentration in the catalyst 26. If the acquired O2 sensor voltage is above the threshold Th2b, the vehicle control unit 50 turns off the engine stop prohibition flag. Since the threshold Th2b corresponds to the second threshold Th2a, and a higher O2 sensor voltage indicates a lower oxygen concentration, the condition that the O2 sensor voltage is above the threshold Th2b corresponds to the condition that the oxygen concentration in the catalyst 26 is below the second threshold Th2a.

[0067] In Figure 3, it is assumed that at time T16, following time T15, the accelerator pedal operation amount increases and the required driving force becomes equal to or greater than the predetermined driving force. Then, in Figure 3, it is assumed that at time T17, following time T16, the O2 sensor voltage becomes equal to or greater than the threshold Th2b. When the O2 sensor voltage becomes equal to or greater than the threshold Th2b, the oxygen concentration in the catalyst 26 is within the range of the neutral air-fuel ratio. In other words, the neutralization of the atmosphere in the catalyst 26 is complete.

[0068] The vehicle control unit 50 turns off the engine stop prohibition flag at time T17 when the O2 sensor voltage becomes equal to or greater than the threshold Th2b. Since the neutralization of the atmosphere in the catalyst 26 is completed at time T17, the vehicle control unit 50 may control the engine 12 from time T17 onward so that the air-fuel ratio becomes a target air-fuel ratio within the range of the neutral air-fuel ratio.

[0069] At time point T17, the accelerator pedal is pressed hard, and the required driving force is greater than or equal to the predetermined driving force. Therefore, in Figure 3, even if the engine stop prohibition flag is turned off at time point T17, the engine 12 continues to drive.

[0070] At time T18, following time T17, if the amount of accelerator pedal operation decreases and the required driving force falls below a predetermined driving force, the vehicle control unit 50 performs an operation to stop the engine 12 because the engine stop prohibition flag is in the off state. Then, at time T19, following time T18, the engine 12 has finished stopping.

[0071] Furthermore, if the requested driving force is less than a predetermined driving force at the time the engine stop prohibition flag is turned off, the vehicle control unit 50 may stop the engine 12 at the time the engine stop prohibition flag is turned off.

[0072] As described above, the vehicle control unit 50 of this embodiment decides whether or not to prohibit stopping the engine 12 based on the state of the engine 12 and the detection result of the oxygen concentration detection unit. The state of the engine 12 here refers to the operating state, such as whether the engine 12 is running or stopped. By prohibiting stopping the engine 12 and continuing to run the engine 12, the vehicle control unit 50 can suppress an increase in the oxygen concentration in the catalyst 26 even if the accelerator pedal is repeatedly pressed and released in a short period of time. As a result, the catalyst 26 can function properly and NOx emissions can be appropriately suppressed.

[0073] Figure 4 is a flowchart illustrating the operation flow of the vehicle control unit 50 in this embodiment. When a predetermined interrupt timing occurs at a predetermined interval, the vehicle control unit 50 executes the series of processes shown in Figure 4.

[0074] When a predetermined interrupt timing occurs, the vehicle control unit 50 acquires the oxygen concentration in the catalyst 26 (S10). More specifically, the vehicle control unit 50 acquires the O2 sensor voltage from the O2 sensor 30 as an indicator of the oxygen concentration in the catalyst 26.

[0075] Next, the vehicle control unit 50 determines whether or not the engine 12 has started (S11). For example, if the engine 12 was not running at the previous interrupt timing, but was running at the current interrupt timing, the vehicle control unit 50 determines that the engine 12 has started.

[0076] If engine 12 does not start (NO in S11), the vehicle control unit 50 proceeds to step S14. Note that "engine 12 did not start" includes both the case where engine 12 is stopped and the case where engine 12 continues to run. If engine 12 is not running at the current interrupt timing, it can be determined that engine 12 is stopped, i.e., engine 12 did not start. Also, if engine 12 is running at both the previous interrupt timing and the current interrupt timing, it can be determined that engine 12 continues to run, i.e., engine 12 did not start.

[0077] If the engine 12 is started (YES in S11), the vehicle control unit 50 determines whether the acquired oxygen concentration is higher than a predetermined first threshold Th1a (S12). More specifically, the vehicle control unit 50 determines whether the O2 sensor voltage acquired as an indicator of oxygen concentration is lower than threshold Th1b, which corresponds to the first threshold Th1a. If the O2 sensor voltage is lower than threshold Th1b, it corresponds to the oxygen concentration being higher than the first threshold Th1a.

[0078] If the oxygen concentration is higher than the first threshold Th1a, in other words, if the O2 sensor voltage is lower than the threshold Th1b (YES in S12), the vehicle control unit 50 turns on the engine stop prohibition flag (S13) and proceeds to step S14. The turned-on engine stop prohibition flag remains on until it is turned off. After the engine has started, even if the required driving force falls below a predetermined driving force, the engine will not stop and will maintain its driving state as long as the engine stop prohibition flag remains on.

[0079] On the other hand, if the oxygen concentration is below the first threshold Th1a, in other words, if the O2 sensor voltage is above the threshold Th1b (NO in S12), the vehicle control unit 50 proceeds to step S14. In this case, the engine stop prohibition flag is not turned on, so the engine 12 is not prohibited from stopping. As a result, the started engine 12 then stops when the required driving force falls below a predetermined driving force.

[0080] In step S14, the vehicle control unit 50 determines whether the acquired oxygen concentration is less than or equal to a predetermined second threshold Th2a (S14). More specifically, the vehicle control unit 50 determines whether the O2 sensor voltage acquired as an indicator of oxygen concentration is greater than or equal to the threshold Th2b corresponding to the second threshold Th2a. If the O2 sensor voltage is greater than or equal to the threshold Th2b, it corresponds to the oxygen concentration being less than or equal to the second threshold Th2a.

[0081] If the oxygen concentration is below the second threshold Th2a, in other words, if the O2 sensor voltage is above the threshold Th2b (YES in S14), the vehicle control unit 50 turns off the engine stop prohibition flag (S15) and terminates the series of processes. When the engine stop prohibition flag is turned off, the prohibition against stopping the engine 12 is released.

[0082] On the other hand, if the oxygen concentration is higher than the second threshold Th2a, in other words, if the O2 sensor voltage is lower than the threshold Th2b (NO in S14), the vehicle control unit 50 terminates the series of processes.

[0083] When the engine stop prohibition flag is turned off, if the requested driving force is equal to or greater than a predetermined driving force, the vehicle control unit 50 continues to drive the engine 12, and then stops the engine 12 when the requested driving force falls below the predetermined driving force. Also, when the engine stop prohibition flag is turned off, if the requested driving force is less than a predetermined driving force, the vehicle control unit 50 stops the engine 12 at that time. Even if the engine 12 is stopped, the vehicle 1 can still be driven by the driving force of the motor 10.

[0084] As described above, in the vehicle 1 of this embodiment, whether or not to prohibit stopping the engine 12 is determined based on the state of the engine 12 and the detection result of the oxygen concentration detection unit. In the vehicle 1 of this embodiment, by prohibiting stopping the engine 12, even if the accelerator pedal is repeatedly pressed and released in a short period of time, the engine 12 can continue to run until the atmosphere inside the catalyst 26 is neutralized. As a result, in the vehicle 1 of this embodiment, it is possible to suppress the oxygen concentration inside the catalyst 26 from becoming higher than the oxygen concentration at which the catalyst 26 can purify NOx.

[0085] Therefore, according to the vehicle 1 of this embodiment, it is possible to make the catalyst 26 function properly.

[0086] Furthermore, in the vehicle 1 of this embodiment, if the engine 12 is started and the oxygen concentration in the catalyst 26 detected by the oxygen concentration detection unit is higher than a predetermined first threshold Th1a, the engine 12 is prohibited from being stopped. This makes it possible to more effectively suppress the increase in oxygen concentration in the catalyst 26 in the vehicle 1 of this embodiment.

[0087] Furthermore, in the vehicle 1 of this embodiment, after the stopping of the engine 12 is prohibited, the prohibition on stopping the engine 12 is released when the oxygen concentration in the catalyst 26 detected by the oxygen concentration detection unit falls below a predetermined second threshold Th2a. As a result, in the vehicle 1 of this embodiment, it is possible to avoid the engine 12 continuing to run unnecessarily after the atmosphere in the catalyst 26 has been neutralized, thereby suppressing a decrease in fuel efficiency.

[0088] Embodiments of the present invention have been described above with reference to the attached drawings, but it goes without saying that the present invention is not limited to these embodiments. It is clear to those skilled in the art that various modifications or alterations can be conceived within the scope of the claims, and these will naturally also fall within the technical scope of the present invention. [Explanation of Symbols]

[0089] 1 vehicle 12 Engines 26 Catalyst 30 O2 sensors 34 Vehicle control system 40 processors 42 memory

Claims

1. The engine and A catalyst for purifying the gas emitted from the aforementioned engine, The oxygen concentration detection unit detects the oxygen concentration in the catalyst, Control device and Equipped with, The control device is One or more processors, One or more memories connected to the processor, It has, The neutral air-fuel ratio is an air-fuel ratio within a predetermined range, including the stoichiometric air-fuel ratio. A predetermined first threshold is set to an oxygen concentration corresponding to the boundary value on the lean atmosphere side within the range of the neutral air-fuel ratio. A predetermined second threshold is set to an oxygen concentration corresponding to the stoichiometric air-fuel ratio within the range of the neutral air-fuel ratio. The aforementioned processor, If the engine is started and the oxygen concentration in the catalyst detected by the oxygen concentration detection unit is higher than the first threshold, the engine will not be stopped. After the engine shutdown is prohibited, if the oxygen concentration in the catalyst detected by the oxygen concentration detection unit falls below the second threshold, the prohibition on engine shutdown is lifted. A vehicle that performs a process that includes the following.

2. The engine and A catalyst for purifying the gas emitted from the aforementioned engine, The oxygen concentration detection unit detects the oxygen concentration in the catalyst, Control device and Equipped with, The control device is One or more processors, One or more memories connected to the processor, It has, The neutral air-fuel ratio is an air-fuel ratio within a predetermined range, including the stoichiometric air-fuel ratio. The aforementioned processor, If the engine is started and the oxygen concentration in the catalyst detected by the oxygen concentration detection unit is higher than a predetermined first threshold, the engine will not be stopped. With the engine being prohibited from being stopped, the engine is controlled so that the air-fuel ratio within the engine falls below the upper limit of the neutral air-fuel ratio. After the engine shutdown is prohibited, if the oxygen concentration in the catalyst detected by the oxygen concentration detection unit falls below a predetermined second threshold, the prohibition on engine shutdown is lifted. A vehicle that performs a process that includes the following.

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