Control device for multi-cylinder engine

Abstract

To achieve both deterioration diagnosis of an exhaust gas sensor and control of engine braking.SOLUTION: A control device (35) for a multi-cylinder engine (10) has an exhaust gas sensor (28) installed on the downstream side of a catalyst (26). The control device for the multi-cylinder engine is provided with a deterioration diagnosis unit (37) that performs deterioration diagnosis on the exhaust gas sensor, and a brake control unit (36) that controls engine braking when the vehicle is decelerating. The deterioration diagnosis unit diagnoses the deterioration of the exhaust gas sensor while fuel is cut off from all cylinders, and the brake control unit reduces the number of cylinders for which fuel is cut off, thereby mitigating engine braking. The deterioration diagnosis of the exhaust gas sensor takes priority over the engine brake mitigation control, and fuel is cut off from all cylinders.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a control device for a multi-cylinder engine. [Background technology]

[0002] The engine control device is equipped with a fault diagnosis function (OBD2: On Board Diagnostic 2). The conditions for performing the fault diagnosis require that the exhaust gas sensor installed downstream of the catalyst be diagnosed for deterioration. A known method for diagnosing the deterioration of the exhaust gas sensor downstream of the catalyst is to monitor the response speed of the exhaust gas sensor during fuel cut (see, for example, Patent Document 1). In the deterioration diagnosis method described in Patent Document 1, the diagnosis is made based on various conditions, such as the response speed of the output value of the exhaust gas sensor downstream of the catalyst, when fuel is cut off, until it transitions from a rich-side set value to a lean-side set value. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 3560263 Summary of the Invention [Problem to be solved by the invention]

[0004] Some vehicles are equipped with an engine brake control that controls the effectiveness of the engine brake when the vehicle is decelerating, and the strength of the engine brake (the magnitude of deceleration) can be selected from three levels using a switch on the vehicle. The strength of the engine brake is controlled by adjusting the throttle opening when the accelerator is fully closed and the number of cylinders for which fuel is cut off. If a mode in which engine braking is reduced (a mode with small deceleration) is selected, some cylinders will not be subjected to fuel cut-off, and deterioration diagnosis of the exhaust gas sensor will not be performed accurately.

[0005] The present invention has been made in view of the above points, and an object of the present invention is to provide a control device for a multi-cylinder engine that can simultaneously perform deterioration diagnosis of an exhaust gas sensor and engine brake control. [Means for solving the problem]

[0006] One embodiment of the present invention provides a control device for a multi-cylinder engine in which an exhaust gas sensor is installed downstream of a catalyst, and includes a deterioration diagnosis unit that performs a deterioration diagnosis on the exhaust gas sensor, and a brake control unit that controls engine braking when the vehicle decelerates, wherein the deterioration diagnosis unit diagnoses deterioration of the exhaust gas sensor while fuel is cut off from all cylinders, and the brake control unit reduces the number of cylinders for which fuel is cut off to ease the engine braking, so that the deterioration diagnosis of the exhaust gas sensor takes priority over the engine brake easing control, thereby cutting fuel from all cylinders, thereby solving the above-mentioned problem. [Effects of the Invention]

[0007] According to the control device for a multi-cylinder engine of one aspect of the present invention, engine braking is alleviated by not cutting fuel to some cylinders, but during the exhaust gas sensor deterioration diagnosis, the engine brake mitigation control is disabled and fuel is cut to all cylinders. As a result, exhaust gas sensor deterioration can be accurately diagnosed, and both exhaust gas sensor deterioration diagnosis and engine brake control can be achieved. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic diagram of an engine according to an embodiment of the present invention; [Figure 2] 10A and 10B are diagrams illustrating an example of the operation of the engine brake mitigation control according to the present embodiment. [Figure 3] 10 is an example of a flowchart of a first priority control according to the present embodiment. [Figure 4] 10 is an example of a flowchart of a second priority control according to the present embodiment.

[0009] In one embodiment of the present invention, a multi-cylinder engine includes an exhaust gas sensor installed downstream of a catalyst. The control device for this multi-cylinder engine includes a deterioration diagnosis unit that performs a deterioration diagnosis on the exhaust gas sensor and a brake control unit that controls engine braking during vehicle deceleration. The deterioration diagnosis unit diagnoses the exhaust gas sensor for deterioration while fuel is cut off from all cylinders, and the brake control unit reduces the number of cylinders for which fuel is cut off, thereby mitigating engine braking. While engine braking is mitigated by not cutting fuel to some cylinders, exhaust gas sensor deterioration diagnosis takes priority over engine brake mitigation control, and engine brake mitigation control is disabled during exhaust gas sensor deterioration diagnosis, resulting in fuel being cut off from all cylinders. This allows for accurate diagnosis of exhaust gas sensor deterioration, enabling both exhaust gas sensor deterioration diagnosis and engine brake control to be achieved. [Example]

[0010] The control device for a multi-cylinder engine of this embodiment will be described below with reference to the accompanying drawings, in which: Figure 1 is a schematic diagram of the engine of this embodiment;

[0011] As shown in Figure 1, engine 10 is a multi-cylinder engine (a four-cylinder engine in this embodiment) having multiple cylinders. An intake valve 12 and an exhaust valve 13 are provided for each cylinder in a cylinder head 11 of engine 10. The intake valve 12 opens and closes an intake port 15 connected to an intake pipe 14, and the exhaust valve 13 opens and closes an exhaust port 17 connected to an exhaust pipe 16. The opening and closing of the intake valve 12 causes intake air to be drawn from the intake pipe 14 through the intake port 15 into a combustion chamber 18, and the opening and closing of the exhaust valve 13 causes burned exhaust gas to be discharged from the combustion chamber 18 through the exhaust port 17 into the exhaust pipe 16.

[0012] A fuel injection valve 21 is attached to the intake pipe 14, and fuel is injected from the fuel injection valve 21 toward the intake port 15. An electronically controlled throttle body 22 is provided in the intake pipe 14 upstream of the fuel injection valve 21. A throttle valve 23 is supported in the throttle body 22, and the amount of intake air sent to the intake port 15 is adjusted according to the opening of the throttle valve 23. In addition, an actuator 24 and a throttle sensor 25 are provided in the throttle body 22. The actuator 24 opens and closes the throttle valve 23, and the throttle sensor 25 detects the opening of the throttle valve 23.

[0013] A catalyst 26 is attached to the exhaust pipe 16, and air pollutants in the exhaust gas are purified as the exhaust gas passes through the catalyst 26. A first oxygen sensor 27 is installed in the exhaust pipe 16 upstream of the catalyst 26, and a second oxygen sensor (exhaust gas sensor) 28 is installed in the exhaust pipe 16 downstream of the catalyst 26. The first oxygen sensor 27 detects the oxygen concentration in the exhaust gas, and the second oxygen sensor 28 detects the oxygen concentration of the exhaust gas that has passed through the catalyst 26. The detection result of the first oxygen sensor 27 is used for feedback control of the fuel injection amount, and the detection result of the second oxygen sensor 28 is used for diagnosing deterioration of the catalyst 26.

[0014] An ECU (Electronic Control Unit) 35 is connected to the saddle-ride type vehicle as a control device, and the ECU 35 comprehensively controls each part of the engine 10. In addition to the fuel injection valve 21, the actuator 24, the throttle sensor 25, and the first and second oxygen sensors 27 and 28, sensors such as an accelerator position sensor 31 and an engine brake operation switch 32 are also connected to the ECU 35. An electric signal corresponding to the amount of operation of an accelerator grip 33 is input from the accelerator position sensor 31 to the ECU 35, and the ECU 35 operates the actuator 24 to adjust the opening of the throttle valve 23.

[0015] The operation switch 32 accepts an operation by the rider to select an engine braking mode. In this embodiment, the engine braking mode is selected from an OFF mode and first to third modes. In the OFF mode, engine braking is not reduced, in the first mode, engine braking is slightly reduced, in the second mode, engine braking is further reduced, and in the third mode, engine braking is greatly reduced. When the vehicle decelerates, engine braking is strongest (great deceleration) in the OFF mode, and engine braking is weakest (smallest deceleration) in the third mode.

[0016] The ECU 35 also includes a brake control unit 36 ​​that controls engine braking when the vehicle is decelerating, and a deterioration diagnosis unit 37 that performs a deterioration diagnosis on the second oxygen sensor 28. The brake control unit 36 ​​controls the strength of the engine braking that occurs when the accelerator grip 33 is fully closed by a combination of adjusting the opening of the throttle valve 23 and adjusting the number of cylinders for which fuel is cut off by the fuel injection valve 21. In other words, when the accelerator grip 33 is fully closed, the throttle valve 23 opens, reducing pumping loss and mitigating engine braking, and fuel is injected into some of the cylinders, thereby mitigating engine braking.

[0017] In this embodiment, when the third mode is selected as the engine braking mode by the operation switch 32, the brake control unit 36 ​​controls the fuel injector 21 when the accelerator grip 33 is fully closed to reduce the number of cylinders for which fuel is cut off. There are cylinders for which fuel cut-off is not applied, and engine braking is alleviated (deceleration is reduced). Note that when the first or second mode is selected as the engine braking mode by the operation switch 32, the brake control unit 36 ​​controls the fuel injector 21 when the accelerator grip 33 is fully closed to cut fuel in all cylinders, and the throttle valve 23 is opened to alleviate engine braking.

[0018] The ECU 35 performs a fault diagnosis on each part of the vehicle, and as part of the fault diagnosis, the deterioration diagnosis unit 37 diagnoses the deterioration of the second oxygen sensor 28. In this case, the response speed and output value of the second oxygen sensor 28 are monitored while fuel is cut off in all cylinders, and if the response speed or output value of the second oxygen sensor 28 falls outside the allowable range, the second oxygen sensor 28 is diagnosed as having deteriorated. As described above, when the engine brake mode is the third mode, fuel is not cut off in some cylinders, but in the deterioration diagnosis of the second oxygen sensor 28, fuel cut is required in all cylinders to improve the diagnostic accuracy.

[0019] Therefore, in this embodiment, the deterioration diagnosis of the second oxygen sensor 28 is prioritized over the engine braking mitigation control in the third mode, and fuel is cut off for all cylinders, thereby avoiding competition between the engine braking mitigation control and the deterioration diagnosis of the second oxygen sensor 28. In this case, when the conditions for performing the deterioration diagnosis of the second oxygen sensor 28 are met, the deterioration diagnosis of the second oxygen sensor 28 may be prioritized over the engine braking mitigation control in the third mode. Furthermore, until one deterioration diagnosis of the second oxygen sensor 28 is completed during one driving cycle, the deterioration diagnosis of the second oxygen sensor 28 may be prioritized over the engine braking mitigation control in the third mode.

[0020] Each process of the ECU 35 may be implemented by software using a processor, or may be implemented by a logic circuit (hardware) formed in an integrated circuit or the like. When a processor is used, the processor reads and executes programs stored in memory to perform various processes. As the processor, for example, a CPU (Central Processing Unit) is used. Furthermore, the memory is configured by one or more storage media such as a ROM (Read Only Memory) or a RAM (Random Access Memory) depending on the application.

[0021] The ON / OFF operation of the engine brake mitigation control in the third mode will be described with reference to FIG. 2. FIG. 2 is a diagram showing an example of the operation of the engine brake mitigation control in this embodiment. Note that (A) of FIG. 2 shows a first priority control that prioritizes the deterioration diagnosis when the conditions for performing the deterioration diagnosis of the second oxygen sensor are met. (B) of FIG. 2 shows a second priority control that prioritizes the deterioration diagnosis until the deterioration diagnosis of the second oxygen sensor is completed. Note that the following description will explain the first and second priority controls, but either the first or second priority control may be adopted in the control device for a multi-cylinder engine in this embodiment.

[0022] As shown in FIG. 2, braking is performed during one driving cycle from the start to the end of driving, and vehicle speed changes. In the first priority control shown in FIG. 2(A), the third mode engine brake mitigation control is ON. For example, if the conditions for performing the deterioration diagnosis of the second oxygen sensor 28 are met at time t1, the third mode engine brake mitigation control is turned OFF even when the accelerator grip 33 is fully closed. Fuel is cut off for all cylinders, and the deterioration diagnosis of the second oxygen sensor 28 is performed. When the deterioration diagnosis of the second oxygen sensor 28 is completed, the third mode engine brake mitigation control is turned ON again, and fuel is injected into some of the cylinders when the accelerator grip 33 is fully closed.

[0023] Furthermore, for example, if the conditions for performing a deterioration diagnosis of the second oxygen sensor 28 are met at time t2, the third-mode engine brake mitigation control is turned OFF even when the accelerator grip 33 is fully closed. Fuel is cut off to all cylinders and a deterioration diagnosis of the second oxygen sensor 28 is performed. When the deterioration diagnosis of the second oxygen sensor 28 is completed, the third-mode engine brake mitigation control is turned ON again, and fuel is injected into some of the cylinders when the accelerator grip 33 is fully closed. In this way, when the conditions for performing a deterioration diagnosis are met, the second oxygen sensor 28 takes priority over the third-mode engine brake mitigation control, and after the deterioration diagnosis of the second oxygen sensor 28 is performed, the third-mode engine brake mitigation control takes priority.

[0024] The first priority control minimizes (in this embodiment, only once) the number of times that the engine brake mitigation control is disabled during one driving cycle. The conditions for performing a deterioration diagnosis of the second oxygen sensor 28 include, for example, that no other sensors that affect the deterioration diagnosis are faulty, that the heater of the second oxygen sensor 28 is energized to a certain level or more, that the second oxygen sensor 28 is activated, that the catalyst temperature is sufficiently high, that the engine speed is above a certain level, that the intake pipe differential pressure is below a certain level, that fuel is cut off for all cylinders, and that the voltage of the second oxygen sensor 28 immediately before the fuel cut is above a certain level. It may be determined that the conditions for performing a deterioration diagnosis are met when at least one of these various conditions is met.

[0025] 2(B), the third mode engine brake mitigation control is turned OFF from the start of driving, and fuel is cut off to all cylinders when the accelerator grip 33 is fully closed. For example, when a deterioration diagnosis of the second oxygen sensor 28 is performed and the deterioration diagnosis of the second oxygen sensor 28 is completed at time t3, the third mode engine brake mitigation control is turned ON, and fuel is injected to some of the cylinders when the accelerator grip 33 is fully closed. Also, for example, when the deterioration diagnosis of the second oxygen sensor 28 is completed at time t4, the third mode engine brake mitigation control is turned ON, and fuel is injected to some of the cylinders when the accelerator grip 33 is fully closed.

[0026] In this way, until one deterioration diagnosis of the second oxygen sensor 28 is completed during one driving cycle, the deterioration diagnosis of the exhaust gas sensor takes priority over the third mode engine brake mitigation control. After the deterioration diagnosis of the second oxygen sensor 28 is completed, the third mode engine brake mitigation control takes priority (starts). Due to the second priority control, the third mode engine brake mitigation control is turned OFF until the deterioration diagnosis of the second oxygen sensor 28 is completed, and after the deterioration diagnosis of the second oxygen sensor 28 is completed, the third mode engine brake mitigation control is always ON, making it easy to understand the control switching.

[0027] The operation flow of the priority control of the degradation diagnosis will be described with reference to Figures 3 and 4. Figure 3 is an example of a flowchart of the first priority control of this embodiment. Figure 4 is an example of a flowchart of the second priority control of this embodiment.

[0028] First, the first priority control will be described. As shown in Fig. 3, when the accelerator grip 33 is fully closed (step S01), the ECU 35 determines whether the engine braking mode is the third mode (step S02). If the engine braking mode is not the third mode (No in step S02), the engine braking mode is determined to be the first or second mode, and fuel is cut off in all cylinders (step S07). If the engine braking mode is the third mode (Yes in step S02), the ECU 35 determines whether the deterioration diagnosis of the second oxygen sensor 28 has not been completed (step S03) to avoid conflict with the deterioration diagnosis of the second oxygen sensor 28.

[0029] If the deterioration diagnosis of the second oxygen sensor 28 has been completed (No in step S03), priority is given to the third mode of engine braking mitigation control, and the brake control unit 36 ​​cuts fuel to only specific cylinders to mitigate engine braking (step S06). If the deterioration diagnosis of the second oxygen sensor 28 has not been completed (Yes in step S03), the ECU 35 determines whether the engine braking mode set by the brake control unit 36 ​​is inactive (step S04). If the engine braking is already active (No in step S04), the brake control unit 36 ​​cuts fuel to only specific cylinders to mitigate engine braking (step S06).

[0030] If the engine braking mode is not active (Yes in step S04), the ECU 35 determines whether the conditions for performing a deterioration diagnosis of the second oxygen sensor 28 are met (step S05). If the conditions for performing a deterioration diagnosis are not met (No in step S05), priority is given to the reduction control of engine braking in the third mode, and the brake control unit 36 ​​cuts fuel to only specific cylinders to reduce engine braking (step S06). If the conditions for performing a deterioration diagnosis are met (Yes in step S05), priority is given to the deterioration diagnosis of the second oxygen sensor 28, and fuel is cut to all cylinders (step S07).

[0031] When the deterioration diagnosis unit 37 performs a deterioration diagnosis on the second oxygen sensor 28 and the deterioration diagnosis is completed (Yes in step S08), the ECU 35 stores information indicating that the deterioration diagnosis has been completed in memory (step S09). Once the deterioration diagnosis on the second oxygen sensor 28 is completed, the determination in step S03 becomes No until one driving cycle is completed, and the engine braking reduction control in the third mode takes priority. In other words, during the engine braking reduction control, fuel cut is not performed on all cylinders for the deterioration diagnosis of the second oxygen sensor 28.

[0032] Next, the second priority control will be described. As shown in Fig. 4, when the accelerator grip 33 is fully closed (step S11), the ECU 35 determines whether the engine braking mode is the third mode (step S12). If the engine braking mode is not the third mode (No in step S12), the engine braking mode is determined to be the first or second mode, and fuel is cut off in all cylinders (step S16). If the engine braking mode is the third mode (Yes in step S12), the ECU 35 determines whether the deterioration diagnosis of the second oxygen sensor 28 has not been completed (step S13) to avoid conflict with the deterioration diagnosis of the second oxygen sensor 28.

[0033] If the deterioration diagnosis of the second oxygen sensor 28 has been completed (No in step S13), priority is given to the third mode of engine braking mitigation control, and the brake control unit 36 ​​cuts fuel to only specific cylinders to mitigate engine braking (step S15). If the deterioration diagnosis of the second oxygen sensor 28 has not been completed (Yes in step S13), the ECU 35 determines whether the engine braking mode set by the brake control unit 36 ​​is inactive (step S14). If the engine braking is already active (No in step S14), the brake control unit 36 ​​cuts fuel to only specific cylinders to mitigate engine braking (step S15).

[0034] When the engine brake mode is not active (Yes in step S14), the ECU 35 prioritizes the deterioration diagnosis of the second oxygen sensor 28 and cuts fuel to all cylinders (step S16). When the deterioration diagnosis unit 37 performs the deterioration diagnosis of the second oxygen sensor 28 and the deterioration diagnosis is completed (Yes in step S17), the ECU 35 stores information indicating that the deterioration diagnosis has been completed in memory (step S18). Once the deterioration diagnosis of the second oxygen sensor 28 is completed, the determination process in step S13 becomes No until one driving cycle is completed, and fuel is not cut to all cylinders during the engine brake mitigation control in the third mode.

[0035] As described above, according to the control device for a multi-cylinder engine of this embodiment, engine braking is alleviated by not cutting fuel to some cylinders, but the engine braking mitigation control is disabled and fuel is cut to all cylinders during deterioration diagnosis of the second oxygen sensor 28. As a result, deterioration of the second oxygen sensor 28 is accurately diagnosed, and it is possible to achieve both deterioration diagnosis of the second oxygen sensor 28 and engine braking control.

[0036] In this embodiment, fuel is cut off for all cylinders during engine braking mitigation control in the third mode, but the throttle valve may be opened to mitigate engine braking during deterioration diagnosis of the second oxygen sensor. This enables engine braking mitigation control to be enabled during deterioration diagnosis of the second oxygen sensor, and makes it possible to mitigate engine braking without reducing the accuracy of the deterioration diagnosis of the second oxygen sensor.

[0037] In this embodiment, the deterioration diagnosis of the second oxygen sensor is prioritized over the engine brake mitigation control when the conditions for the deterioration diagnosis of the second oxygen sensor are met or when the deterioration diagnosis of the second oxygen sensor is completed once during one driving cycle, but the trigger for the priority control is not particularly limited. For example, the deterioration diagnosis of the second oxygen sensor may be prioritized over the engine brake mitigation control manually, or the deterioration diagnosis of the second oxygen sensor may be prioritized over the engine brake mitigation control depending on the driving time or driving environment.

[0038] Furthermore, in this embodiment, the engine braking mode has three stages, namely, the first to third modes, but the engine braking mode may have four or more stages, or may have two or less stages.

[0039] Furthermore, in this embodiment, the second oxygen sensor is exemplified as the exhaust gas sensor, but the exhaust gas sensor may be any sensor that can be diagnosed for deterioration in a state where fuel is cut off from all cylinders.

[0040] Furthermore, the multi-cylinder engine control device of this embodiment is not limited to the saddle-ride type vehicle described above, but can also be applied to other vehicles such as ATVs (All Terrain Vehicles), jet skis, etc. Note that the saddle-ride type vehicle is not limited to all vehicles in which the driver rides while straddling the seat, but also includes scooter-type vehicles in which the driver does not straddle the seat.

[0041] As described above, the first aspect is a control device (ECU 35) for a multi-cylinder engine (engine 10) having an exhaust gas sensor (second oxygen sensor 28) installed downstream of a catalyst (26), the control device including: a deterioration diagnosis unit (37) that performs a deterioration diagnosis on the exhaust gas sensor; and a brake control unit (36) that controls engine braking during deceleration of the vehicle. The deterioration diagnosis unit diagnoses the deterioration of the exhaust gas sensor while fuel is cut off for all cylinders, and the brake control unit reduces the number of cylinders to which fuel is cut to ease the engine braking. The deterioration diagnosis of the exhaust gas sensor takes priority over the engine braking easing control, and fuel is cut off for all cylinders. With this configuration, engine braking is eased by not cutting fuel for some cylinders, but during the exhaust gas sensor deterioration diagnosis, the engine braking easing control is disabled and fuel is cut off for all cylinders. As a result, the deterioration of the exhaust gas sensor is accurately diagnosed, and it is possible to achieve both the deterioration diagnosis of the exhaust gas sensor and engine braking control.

[0042] In the second aspect, when the condition for performing the deterioration diagnosis of the exhaust gas sensor in the first aspect is satisfied, the deterioration diagnosis of the exhaust gas sensor takes priority over the engine brake mitigation control, and fuel is cut off for all cylinders. With this configuration, the occurrence of the engine brake mitigation control being invalid during one driving cycle is minimized.

[0043] In the third aspect, in the first aspect, the deterioration diagnosis of the exhaust gas sensor is prioritized over the mitigation control of the engine brake, and fuel is cut off for all cylinders until one deterioration diagnosis of the exhaust gas sensor is completed during one driving cycle. With this configuration, the mitigation control of the engine brake is disabled until the deterioration diagnosis of the exhaust gas sensor is completed, making it easy to understand the control switching.

[0044] In a fourth aspect, in any one of the first to third aspects, the brake control unit opens the throttle valve (23) to ease the engine braking, and is capable of opening the throttle valve to ease the engine braking during the deterioration diagnosis of the exhaust gas sensor. With this configuration, the engine braking easing control can be enabled during the deterioration diagnosis of the exhaust gas sensor, and the engine braking can be eased without reducing the accuracy of the deterioration diagnosis of the exhaust gas sensor.

[0045] Although the present embodiment has been described, other embodiments may be those in which the above-described embodiments and modifications are combined in whole or in part.

[0046] Furthermore, the technology of the present invention is not limited to the above-described embodiments, and various changes, substitutions, and modifications may be made without departing from the spirit of the technical idea. Furthermore, if the technical idea can be realized in a different way due to technological advances or other derived technologies, it may be implemented using that method. Therefore, the claims cover all embodiments that may fall within the scope of the technical idea. [Explanation of symbols]

[0047] 10: Engine 21: Fuel injection valve 23: Throttle valve 26: Catalyst 28: Second oxygen sensor (exhaust gas sensor) 35: ECU (control unit) 36: Brake control unit 37: Deterioration diagnosis unit

Claims

1. A control device for a multi-cylinder engine in which an exhaust gas sensor is installed downstream of a catalyst, a deterioration diagnosis unit that performs a deterioration diagnosis on the exhaust gas sensor; a brake control unit that controls engine braking when the vehicle is decelerating, the deterioration diagnosis unit diagnoses deterioration of the exhaust gas sensor during fuel cut of all cylinders, The brake control unit reduces the number of cylinders to which fuel is cut to alleviate engine braking, A control device for a multi-cylinder engine, characterized in that fuel is cut off to all cylinders by giving priority to the deterioration diagnosis of the exhaust gas sensor over the mitigation control of the engine brake.

2. 2. The control device for a multi-cylinder engine according to claim 1, wherein when the conditions for performing the deterioration diagnosis of the exhaust gas sensor are met, the deterioration diagnosis of the exhaust gas sensor is prioritized over the mitigation control of the engine brake, and fuel is cut off for all cylinders.

3. 2. The control device for a multi-cylinder engine according to claim 1, wherein the deterioration diagnosis of the exhaust gas sensor is prioritized over engine brake mitigation control until one deterioration diagnosis of the exhaust gas sensor is completed during one driving cycle, and fuel is cut off to all cylinders.

4. The brake control unit opens a throttle valve to reduce engine braking, 4. The control device for a multi-cylinder engine according to claim 1, wherein the throttle valve is opened to reduce engine braking during the deterioration diagnosis of the exhaust gas sensor.

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