Fuel regulating device and vehicle

Abstract

To appropriately prevent shortening of a service life of a catalyst due to suppression of an overspeed of an engine.SOLUTION: A fuel regulating device includes an ECU 10 and a catalyst downstream oxygen sensor SE4. The ECU 10 controls a fuel injection device 61 for operating an engine 5. The catalyst downstream oxygen sensor SE4 is provided downstream of a three-way catalyst 53 in an exhaust system mounted to the engine 5 and detects oxygen concentration of an exhaust gas. When the engine speed reaches a first speed that is recognized as overspeed, the ECU 10 regulates a fuel supply amount so that the engine speed lowers. When the engine speed lowers to reach second speed, the fuel supply amount to the engine 5 is returned to a normal amount. Then, when the engine speed is continuously maintained within a monitoring range, the fuel supply amount is regulated on the basis of the detection result obtained by the catalyst downstream oxygen sensor SE4. The monitoring range is a range that includes the second speed and is lower than the first speed.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a fuel regulating device that regulates the amount of fuel supplied to an engine, and to a vehicle. [Background technology]

[0002] A control that stops the supply of fuel to the engine to prevent the engine speed from becoming excessively high (hereinafter, referred to as over-rev limit control) is known. In the over-rev limit control, for example, when the engine speed reaches a predetermined first rotation speed, the supply of fuel to the engine is stopped. Thereafter, when the engine speed drops to a predetermined second rotation speed that is lower than the first rotation speed, the supply of fuel to the engine is resumed.

[0003] Assume that after the over-rev limit control is ended, for example, the throttle valve is maintained in a fully open state. In this case, the engine speed increases from the second rotation speed and reaches the first rotation speed again. As a result, the over-rev limit control is performed again, and the supply of fuel to the engine is stopped. In this way, the repeated stopping and restarting of the fuel supply to the engine may increase the temperature of a catalyst provided in the exhaust system of the engine, and accelerate the deterioration of the catalyst. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2012-241691 A Summary of the Invention [Problem to be solved by the invention]

[0005] Patent Document 1 describes a fuel supply device that supplies fuel so that the air-fuel ratio of the gas flowing into the three-way catalyst becomes leaner than the theoretical air-fuel ratio after fuel supply to the engine is resumed in order to suppress the catalyst from becoming too hot due to repeated over-rev limit control as described above. However, in reality, it is difficult to appropriately adjust the amount of fuel supplied to the engine without causing the engine to misfire.

[0006] An object of the present invention is to provide a fuel adjustment device and a vehicle that can appropriately prevent a catalyst from becoming short in life due to suppression of engine overspeed. [Means for solving the problem]

[0007] A fuel adjustment device according to one aspect of the present invention includes a control unit that controls an engine driving unit that operates an engine, and an oxygen sensor that is provided downstream of a catalyst that purifies exhaust gas in an exhaust system attached to the engine and detects an oxygen concentration of the exhaust gas, the engine driving unit including a fuel supply unit that supplies fuel to the engine, and the control unit operates the engine driving unit according to second conditions different from the first conditions so that the engine rotation speed decreases when the engine rotation speed reaches a first rotation speed by increasing in a state in which the engine driving unit operates according to a first condition. and when the rotation speed of the engine reaches a second rotation speed lower than the first rotation speed from the first rotation speed while the engine driving unit is operating according to the second condition, returning the operating condition of the engine driving unit from the second condition to the first condition, and adjusting the fuel supply amount of the fuel supply unit based on the detection result of the oxygen sensor when the rotation speed of the engine is continuously maintained within a monitoring range from a point in time when the operating condition of the engine driving unit is returned from the second condition to the first condition, the monitoring range is a range that includes the second rotation speed and is lower than the first rotation speed.

[0008] A vehicle according to another aspect of the present invention includes the engine, the exhaust system, the catalyst provided in the exhaust system, the engine drive unit, the above-mentioned fuel adjustment device, and drive wheels driven by the engine. Effect of the Invention

[0009] According to the present invention, it is possible to appropriately prevent the catalyst from having a shortened life due to suppression of engine overspeed. [Brief description of the drawings]

[0010] [Figure 1] 1 is a right side view of a motorcycle according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a block diagram showing a control system of the motorcycle shown in FIG. [Diagram 3] 4 is a flowchart of a fuel adjustment process according to one embodiment of the present invention. [Figure 4] 3 is a flowchart showing details of a process executed by the CPU of FIG. 2 when fuel feedback control is ON. [Diagram 5] 4 is a time chart for explaining a specific example of the operation of the engine according to the fuel adjustment process of FIG. 3. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] A fuel adjustment device and a vehicle including the same according to an embodiment of the present invention will now be described with reference to the drawings. As an example of the vehicle, a motorcycle will be described.

[0012] 1. Outline of motorcycle configuration Fig. 1 is a right side view of a motorcycle according to an embodiment of the present invention. Fig. 1 shows a state in which the motorcycle 100 stands vertically relative to the road surface. The motorcycle 100 in Fig. 1 includes a metal body frame 1. The body frame 1 includes a head pipe 1h and a plurality of frame members. The head pipe 1h is located at the front of the vehicle, and the plurality of frame members are provided to extend from the head pipe 1h toward the rear of the vehicle.

[0013] A front fork 2 is provided on the head pipe 1h so as to be rotatable around the axis of the head pipe 1h. A front wheel 3 is rotatably supported on the lower end of the front fork 2. A handlebar 4 is provided on the upper end of the front fork 2. An accelerator grip 4g is provided on the handlebar 4 so as to be operable by the rider.

[0014] The body frame 1 supports the engine 5 so as to be located below the head pipe 1h. In this embodiment, the engine 5 is provided integrally with a transmission (not shown) to form an engine unit. The body frame 1 also supports a fuel tank 8 so as to be located above the engine 5 and behind the head pipe 1h. The body frame 1 also supports a seat 9 so as to be located behind the fuel tank 8.

[0015] An ECU (Electronic Control Unit) 10 is provided between the engine 5, the fuel tank 8, and the seat 9. The ECU 10 includes a CPU (Central Processing Unit) 10a (FIG. 2), a ROM (Read Only Memory) 10b (FIG. 2), and a RAM (Random Access Memory) 10c (FIG. 2). The ROM 10b is, for example, a non-volatile memory, and stores a system program, a fuel adjustment program, and information associated with these programs. The RAM 10c is, for example, a volatile memory, and is used as a working area for the CPU 10a and temporarily stores various data. The CPU 10a realizes various functions by executing the fuel adjustment program stored in the ROM 10b. The various functions realized by the CPU 10a will be described in detail later.

[0016] The fuel adjustment program in this embodiment may be provided in a form stored in a computer-readable recording medium and installed in the ROM 10b or a storage device connectable to the ECU 10. In addition, if the ECU 10 is connectable to a communication network, the fuel adjustment program may be distributed from a server connected to the communication network and installed in the ROM 10b or the storage device while the ECU 10 is connected to the communication network.

[0017] A rear arm 6 is provided so as to extend rearward from a lower center of the body frame 1 in the front-rear direction of the motorcycle 100. The rear arm 6 is supported by the body frame 1 using a pivot shaft (not shown). A rear wheel 7 is rotatably supported at the rear end of the rear arm 6. The rear wheel 7 serves as a drive wheel and is rotated by power generated by the engine 5.

[0018] The engine 5 has an intake port for supplying an air-fuel mixture into the combustion chamber and an exhaust port for discharging burned gas from the combustion chamber. An intake pipe 60 is connected to the intake port of the engine 5. A fuel injector 61 (FIG. 2) and a throttle valve 62 (FIG. 2) are provided in the intake pipe 60. One end of an exhaust pipe 51 is connected to the exhaust port of the engine 5. A muffler 52 is connected to the other end of the exhaust pipe 51. A three-way catalyst 53 is disposed inside the muffler 52. The three-way catalyst 53 purifies exhaust gas from the engine 5. The three-way catalyst 53 may be provided inside the exhaust pipe 51 instead of the muffler 52.

[0019] 2. Over-rev limit control and fuel feedback control In motorcycle 100 according to this embodiment, the over-rev limit control described in the Background Art is performed to prevent the rotation speed (engine rotation speed) of engine 5 from becoming excessively high. Specifically, in this embodiment, as the over-rev limit control, when the engine rotation speed increases and reaches a first rotation speed, the supply of fuel to engine 5 is stopped until the engine rotation speed decreases to a second rotation speed lower than the first rotation speed. Note that the first rotation speed and the second rotation speed are determined according to the type of engine 5 so that the engine 5 is not damaged or malfunctions due to the rotation speed becoming excessively high.

[0020] Assume that, for example, the throttle valve 62 is maintained in a fully open state after the over rev limit control. In this case, the supply of fuel to the engine 5 is resumed, causing the engine speed to increase. When the engine speed reaches the first speed, the over rev limit control is performed again.

[0021] If fuel is not supplied to the engine 5 during over-rev limit control, the gas (exhaust gas) discharged from the engine 5 will contain a large amount of oxygen. As a result, the oxygen in the exhaust gas is stored in the three-way catalyst 53 through a reduction reaction. On the other hand, if a large amount of fuel is supplied to the engine 5 after over-rev limit control, the amount of oxygen contained in the exhaust gas will decrease. As a result, the stored oxygen is released from the three-way catalyst 53 through an oxidation reaction.

[0022] If an increase in engine speed and a decrease in engine speed due to over-rev limit control are repeated in a short cycle, there is a possibility that the oxygen concentration in the exhaust gas of the engine 5 will fluctuate greatly and regularly as described above. In other words, there is a possibility that the air-fuel ratio of the exhaust gas of the engine 5 will fluctuate greatly and regularly. In this case, strong reduction reactions and strong oxidation reactions will occur repeatedly in the three-way catalyst 53. This may cause the temperature of the three-way catalyst 53 to rise excessively, accelerating the deterioration of the three-way catalyst 53.

[0023] Therefore, in this embodiment, when the engine rotation speed is within a specific monitoring range after the over-rev limit control, control is performed to reduce the occurrence of oxidation reactions in the three-way catalyst 53. The monitoring range is set to a range lower than the first rotation speed and including the second rotation speed.

[0024] The above control (control for reducing the occurrence of oxidation reactions in the three-way catalyst 53) is feedback control that adjusts the amount of fuel supplied to the engine 5 based on the oxygen concentration of the exhaust gas flowing downstream of the three-way catalyst 53. In the following description, this feedback control will be referred to as fuel feedback control.

[0025] 3. Control system of motorcycle 100 Fig. 2 is a block diagram showing a control system of motorcycle 100 of Fig. 1. As shown in Fig. 2, motorcycle 100 according to this embodiment includes, as a control system configuration, ECU 10, fuel injector 61, throttle actuator 63, accelerator sensor SE0, throttle sensor SE1, intake pressure sensor SE2, crank sensor SE3, and catalyst downstream oxygen sensor SE4. In this embodiment, the configuration including ECU 10 and catalyst downstream oxygen sensor SE4 corresponds to the fuel adjustment device of the present invention.

[0026] The accelerator sensor SE0 is provided on the handlebar 4 in Fig. 1. The accelerator sensor SE0 detects the amount of operation of the accelerator grip 4g by the driver (accelerator opening degree), and outputs an electrical signal indicative of the detected accelerator opening degree.

[0027] The throttle actuator 63 adjusts the opening degree (throttle opening degree) of the throttle valve 62 to adjust the amount of air led from an air cleaner (not shown) to the engine 5. The fuel injection device 61 injects fuel into an intake port of the engine 5 so that an air-fuel mixture is led to a combustion chamber of the engine 5. In this way, fuel is supplied to the engine 5. The throttle sensor SE1 is provided near the throttle valve 62. The throttle sensor SE1 detects the opening degree of the throttle valve 62 and outputs an electrical signal indicative of the detected throttle opening degree.

[0028] The intake pressure sensor SE2 is provided in a portion of the intake pipe 60 downstream of the throttle valve 62. The intake pressure sensor SE2 detects the pressure (intake pressure) in the intake pipe 60 as the intake state of the engine 5, and outputs an electric signal indicating the detected intake pressure. The crank sensor SE3 is provided in the vicinity of the engine 5. The crank sensor SE3 detects the rotation speed (engine rotation speed) of the crankshaft of the engine 5, and outputs an electric signal indicating the detected engine rotation speed.

[0029] The catalyst downstream oxygen sensor SE4 is provided in a portion of the muffler 52 downstream of the three-way catalyst 53. The catalyst downstream oxygen sensor SE4 detects the oxygen concentration of the exhaust gas after it is discharged from the engine 5 and purified by the three-way catalyst 53, and outputs an electrical signal indicating the detected oxygen concentration. As described above, the three-way catalyst 53 may be provided in the exhaust pipe 51 instead of the muffler 52. Therefore, when the three-way catalyst 53 is provided in the exhaust pipe 51, the catalyst downstream oxygen sensor SE4 may be provided in the exhaust pipe 51 so as to be located in a portion downstream of the three-way catalyst 53.

[0030] The ECU 10 includes a CPU 10a, a ROM 10b, and a RAM 10c. The CPU 10a has, as functional units, a rotation speed determination unit 11, an oxygen concentration determination unit 12, an engine control unit 13, a feedback control unit 14, and an information storage unit 15. These functional units of the CPU 10a are realized by the CPU 10a executing a fuel adjustment program stored in the ROM 10b. Note that some or all of the multiple functional units of the CPU 10a may be realized by hardware such as electronic circuits.

[0031] When the power supply of the motorcycle 100 is turned on, the information holding unit 15 reads at least a part of the information from the plurality of pieces of information stored in the ROM 10b and holds the read information. The information held in the information holding unit 15 includes a "first condition for engine control", a "second condition for engine control", a "monitoring range", a "first rotation speed", a "second rotation speed", a "third rotation speed", and a "specified reduction amount for fuel feedback control".

[0032] In the following description, the operating state of the engine 5 when the over-rev limit control is not performed is referred to as a normal operating state. In this embodiment, the normal operating state of the engine 5 is, for example, a state in which the engine speed is determined at least in accordance with the magnitude of the accelerator opening or the throttle opening.

[0033] The "first condition for engine control (hereinafter, referred to as the first condition)" includes information indicating the amount of fuel supplied to the engine 5 (the amount of fuel to be supplied to the engine 5 per cycle) when the engine 5 is in a normal operating state. Specifically, the first condition includes, for example, a map indicating a predetermined relationship between the throttle opening, the engine speed, and the amount of fuel supplied to the engine 5. Alternatively, the first condition includes a map indicating a predetermined relationship between the pressure in the intake pipe 60 (intake pressure), the engine speed, and the amount of fuel supplied to the engine 5. According to these maps, when the engine 5 is in a normal operating state, the amount of fuel supplied to the engine 5 is adjusted based on the throttle opening or the intake pressure and the engine speed.

[0034] The "second condition for engine control (hereinafter referred to as the second condition)" includes information indicating the amount of fuel supplied to engine 5 during over-rev limit control. In this embodiment, the amount of fuel supplied to engine 5 during over-rev limit control is 0. According to this second condition, during over-rev limit control, fuel is not supplied to engine 5 regardless of the throttle opening and intake pressure.

[0035] The "monitoring range" is a range of engine rotation speeds. In this embodiment, the "monitoring range" is set to a range equal to or higher than a "third rotation speed" described later and lower than the "first rotation speed". The "first rotation speed" is a rotation speed that is a reference for starting over-rev limit control for the engine 5 in a normal operating state, and defines the upper limit of the "monitoring range" as described above. The "second rotation speed" is a rotation speed that is a reference for ending the over-rev limit control and returning the engine 5 to a normal operating state, and is set within the above-mentioned "monitoring range". The "third rotation speed" is a rotation speed lower than the "second rotation speed" and is the lower limit of the "monitoring range".

[0036] The "prescribed reduction amount for fuel feedback control (hereinafter referred to as the prescribed reduction amount)" is used to gradually reduce the amount of fuel supplied to the engine 5 during the above-mentioned fuel feedback control. A specific method for using the prescribed reduction amount will be described later.

[0037] The rotation speed determination unit 11 acquires the engine rotation speed by receiving the output of the crank sensor SE3. Moreover, when the engine 5 is in a normal operating state, the rotation speed determination unit 11 determines whether or not the engine rotation speed has reached a first rotation speed by increasing the engine rotation speed. Moreover, during over-rev limit control of the engine 5, the rotation speed determination unit 11 determines whether or not the engine rotation speed has reached a second rotation speed by decreasing the engine rotation speed. Furthermore, the rotation speed determination unit 11 determines whether or not the engine rotation speed continues to be within the monitoring range after the over-rev limit control of the engine 5.

[0038] The oxygen concentration determination unit 12 receives the output of the catalyst downstream oxygen sensor SE4. As a result, the oxygen concentration determination unit 12 determines whether the oxygen concentration of the exhaust gas after being purified by the three-way catalyst 53 is higher than the oxygen concentration corresponding to the stoichiometric air-fuel ratio (hereinafter referred to as the reference concentration) based on the detected oxygen concentration. In other words, the oxygen concentration determination unit 12 determines whether the air-fuel ratio of the exhaust gas flowing downstream of the three-way catalyst 53 is higher than the stoichiometric air-fuel ratio (whether it is lean).

[0039] The engine control unit 13 receives the output of the accelerator sensor SE0 to obtain the accelerator opening degree, and controls the throttle actuator 63 based on the accelerator opening degree, thereby adjusting the throttle opening degree.

[0040] Moreover, the engine control unit 13 receives the output of the throttle sensor SE1 to obtain the throttle opening degree, and receives the output of the intake pressure sensor SE2 to obtain the intake pressure of the engine 5. Furthermore, the engine control unit 13 receives the output of the crank sensor SE3 to obtain the engine rotation speed.

[0041] Here, it is assumed that the first condition stored in the information holding unit 15 includes a map showing the relationship between the throttle opening, the engine speed, and the amount of fuel supply. In this case, the engine control unit 13 sets the amount of fuel supply to the engine 5 based on the first condition, the acquired throttle opening, and the acquired engine speed when the engine 5 is in a normal operating state. Furthermore, the engine control unit 13 controls the fuel injection device 61 based on the set amount of fuel supply.

[0042] On the other hand, it is assumed that the first condition stored in the information holding unit 15 includes a map showing the relationship between the intake pressure, the engine speed, and the fuel supply amount. In this case, the engine control unit 13 sets the fuel supply amount to the engine 5 based on the first condition, the acquired intake pressure, and the acquired engine speed when the engine 5 is in a normal operating state. In addition, the engine control unit 13 controls the fuel injection device 61 based on the set fuel supply amount. In this way, the amount of fuel supplied to the engine 5 per cycle is appropriately adjusted.

[0043] In addition to the above example, the engine control unit 13 sets the amount of fuel supplied to the engine 5 to 0 based on the second condition stored in the information storage unit 15 during over-rev limit control of the engine 5. In other words, the supply of fuel to the engine 5 is stopped.

[0044] After over-rev limit control of engine 5, feedback control unit 14 performs fuel feedback control when the engine rotation speed continues to be within the monitoring range. Specifically, based on the detection result of oxygen concentration determination unit 12, feedback control unit 14 gradually adjusts the amount of fuel supplied to engine 5 so that the oxygen concentration of exhaust gas flowing downstream of three-way catalyst 53 becomes higher than the reference concentration. As a result, during fuel feedback control, if the air-fuel ratio of exhaust gas is not lean, the amount of fuel supplied to engine 5 is gradually reduced from the amount of fuel supplied set according to the first condition to an amount at which engine 5 does not misfire.

[0045] 4. Fuel adjustment processing 3 is a flowchart of a fuel adjustment process according to one embodiment of the present invention. The fuel adjustment process is started by the CPU 10a of the ECU 10 executing a fuel adjustment program in response to starting the engine 5. In the following description, performing the fuel feedback control of the engine 5 is referred to as turning on the fuel feedback control, and not performing the fuel feedback control of the engine 5 is referred to as turning off the fuel feedback control.

[0046] In the initial state, the first condition, the second condition, the monitoring range, the first rotation speed, the second rotation speed, the third rotation speed, and the specified reduction amount in Fig. 2 are stored in the information storage unit 15. Also, in the initial state, the fuel feedback control of the engine 5 is in the OFF state.

[0047] 3, when the fuel adjustment process is started, the engine control unit 13 drives the engine 5 under the first condition (step S11). That is, the engine control unit 13 sets the amount of fuel supplied to the engine 5 based on the map of the first condition and the outputs of the various sensors (SE0 to SE3), and controls the fuel injection device 61. This maintains the operating state of the engine 5 in a normal operating state.

[0048] Next, the rotation speed determination unit 11 determines whether or not the engine rotation speed has increased to reach a first rotation speed based on the output of the crank sensor SE3 (step S12). If the engine rotation speed has not reached the first rotation speed, the process of step S12 is repeated. On the other hand, when the engine rotation speed reaches the first rotation speed, the engine control unit 13 drives the engine 5 under the second condition (step S13). That is, the engine control unit 13 sets the amount of fuel supplied to the engine 5 to 0 based on the second condition (fuel cut). In this way, the over-rev limit control is started in step S13, and the engine rotation speed decreases.

[0049] Next, the rotation speed determination unit 11 determines whether or not the engine rotation speed has reached the second rotation speed due to a decrease in the engine rotation speed based on the output of the crank sensor SE3 (step S14). If the engine rotation speed has not reached the second rotation speed, the process of step S14 is repeated. On the other hand, if the engine rotation speed reaches the second rotation speed, the engine control unit 13 drives the engine 5 under the first condition (step S15), similarly to the process of step S11. In this way, the over-rev limit control ends in step S15. At this time, the engine rotation speed becomes lower than the first rotation speed by a certain speed (the difference between the first rotation speed and the second rotation speed).

[0050] Next, the rotation speed determination unit 11 determines whether or not the engine rotation speed is within the monitoring range based on the output of the crank sensor SE3 (step S16). If the engine rotation speed is not within the monitoring range, the rotation speed determination unit 11 returns the process to be executed to the process of step S12. On the other hand, if the engine rotation speed is within the monitoring range, the feedback control unit 14 turns on the fuel feedback control using the catalyst downstream oxygen sensor SE4 (step S17). The details of the process performed by the CPU 10a when the fuel feedback control is on will be described later.

[0051] Next, the rotation speed determination unit 11 determines whether or not the engine rotation speed is within the monitoring range based on the output of the crank sensor SE3, similar to the process of step S16 (step S18). If the engine rotation speed is not within the monitoring range, the feedback control unit 14 turns off the fuel feedback control (step S19) and returns the process to be executed to the process of step S12.

[0052] On the other hand, when the engine rotation speed is within the monitoring range in step S18, the rotation speed determination unit 11 determines whether or not the engine rotation speed has reached the first rotation speed due to an increase in the engine rotation speed, similar to the process of step S12 (step S20). When the engine rotation speed has not reached the first rotation speed, the rotation speed determination unit 11 returns the process to be executed to the process of step S18. On the other hand, when the engine rotation speed reaches the first rotation speed, the feedback control unit 14 turns off the fuel feedback control (step S21) and returns the process to be executed to the process of step S13.

[0053] Fig. 4 is a flowchart showing details of the processing performed by the CPU 10a in Fig. 2 when the fuel feedback control is on. The series of processing shown in Fig. 4 is started when the fuel feedback control is switched from off to on in the processing of step S17 in Fig. 3.

[0054] When the fuel feedback control is turned on in the process of step S17, the oxygen concentration determination unit 12 determines whether or not the oxygen concentration of the exhaust gas is higher than the reference concentration based on the output of the catalyst downstream oxygen sensor SE4 (step S31). If the oxygen concentration of the exhaust gas is higher than the reference concentration, that is, if the air-fuel ratio of the exhaust gas is lean, the process of step S31 is repeated.

[0055] On the other hand, when the oxygen concentration of the exhaust gas is equal to or lower than the reference concentration, that is, when the air-fuel ratio of the exhaust gas is stoichiometric or rich, the feedback control unit 14 reduces the amount of fuel supplied to the engine 5 from the set amount by a specified reduction amount (step S32). Specifically, the amount of fuel supplied to the engine 5 is adjusted to an amount obtained by reducing the amount of fuel supplied set in accordance with the first condition by a specified reduction amount. This adjustment process can also be called a correction process of the amount of fuel supplied set in accordance with the first condition. Thereafter, the feedback control unit 14 advances the process to be executed to step S31.

[0056] The above-mentioned processing of steps S31 and S32 is continuously executed at predetermined time intervals until the fuel feedback control is turned off by the processing of step S19 or step S21 in Fig. 3. According to the processing of steps S31 and S32, when the air-fuel ratio of the exhaust gas is stoichiometric or rich, the air-fuel ratio of the exhaust gas is gradually adjusted to be lean, for example, every predetermined number of cycles. As a result, even if the over-rev limit control is repeated in a short cycle, the change in the reaction occurring in the three-way catalyst 53 is gradually stabilized.

[0057] In this way, the air-fuel ratio of the exhaust gas is maintained lean, thereby reducing the occurrence of oxidation reactions in the three-way catalyst 53. As a result, a rapid increase in temperature of the three-way catalyst 53 caused by repeated strong oxidation reactions and strong reduction reactions in the three-way catalyst 53 is suppressed.

[0058] 5. Specific example of engine 5 operation with fuel adjustment processing Fig. 5 is a time chart for explaining a specific example of the operation of the engine 5 by the fuel adjustment process of Fig. 3. Three items related to the operation of the engine 5 are shown on the left side of Fig. 5. The three items are "engine speed", "engine control conditions", and "fuel feedback control", and are arranged vertically in this order from the top row (first row) to the bottom row (third row).

[0059] To the right of each item, the change in state corresponding to that item is shown in chronological order using a common time axis. To the right of the first item "Engine speed," an example of the change in engine speed over time is shown using a graph with the engine speed on the vertical axis and time on the horizontal axis.

[0060] In the first graph, the symbols "rs1", "rs2", and "rs3" on the vertical axis represent the first rotation speed, the second rotation speed, and the third rotation speed, respectively. Also, the white arrow MR shown in the first graph represents the range equal to or higher than the third rotation speed rs3 and lower than the first rotation speed rs1 as the monitoring range.

[0061] To the right of the item "Conditions for engine control" in the second row, it is shown whether the conditions used to drive the engine 5 are the first conditions or the second conditions at each point on the time axis. To the right of the item "Fuel feedback control" in the third row, it is shown whether the fuel feedback control is on or off at each point on the time axis.

[0062] At time t11 in the initial state, the engine 5 is in a normal operating state and the engine speed is lower than the third rotation speed rs3. In this case, the engine 5 is driven according to the first condition and the fuel feedback control is turned off.

[0063] For example, assume that the driver continues to operate the accelerator grip 4g from time t11 to time t21 (described later) to maintain the accelerator pedal at full throttle. In this case, as time t11 passes, a large amount of air-fuel mixture is introduced into the engine 5, causing the engine speed to increase.

[0064] When the engine speed increases and reaches the first rotation speed rs1 at time t12, the over-rev limit control is started. Specifically, the conditions used for driving the engine 5 are changed from the first conditions to the second conditions by the processes of steps S12 and S13 in FIG. 3. As a result, the engine 5 is driven in accordance with the second conditions. When the engine 5 is driven in accordance with the second conditions, fuel is not supplied to the engine 5. As a result, the engine speed drops.

[0065] When the engine speed reaches the second rotation speed rs2 at time t13 due to the decrease in the engine speed, the over-rev limit control is terminated by the process of step S14 in FIG. 3. Furthermore, the conditions used for driving the engine 5 are changed from the second conditions to the first conditions by the process of step S15 in FIG. 3. Furthermore, the engine speed is within the monitoring range MR at time t13. In this case, the fuel feedback control is turned on by the control of steps S16 and S17 in FIG. 3. As a result, the air-fuel ratio of the exhaust gas is adjusted to be lean, and a large amount of mixture is introduced into the engine 5. As a result, the engine speed is increased while maintaining a state in which it is within the monitoring range MR.

[0066] After that, when the engine speed reaches the first rotation speed rs1 again at time t14, the fuel feedback control is turned off by the processing of steps S20 and S21 in Fig. 3. Also, the condition used for driving the engine 5 is changed again from the first condition to the second condition by the processing of step S13 in Fig. 3, and the over-rev limit control is started. As a result, the engine speed decreases again.

[0067] When the engine rotation speed decreases and reaches the second rotation speed rs2 at time t15, the over-rev limit control is terminated by the process of step S14 in Fig. 3. Moreover, the condition used for driving the engine 5 is changed again from the second condition to the first condition by the process of step S15 in Fig. 3.

[0068] In the example of Fig. 5, the accelerator opening is maintained at full open from time t11 to time t21 as described above. As a result, the processes performed at time t12 and t13 are similarly repeated at time t14 and t15 as described above. In addition, the processes performed at time t12 and t13 are similarly repeated at time t16 and t17, and similarly repeated at time t18 and t19. Furthermore, the process performed at time t12 is similarly repeated at time t20.

[0069] Here, it is assumed that at time t21, the driver reduces the amount of operation of the accelerator grip 4g to 0, thereby reducing the accelerator opening. In this case, the engine speed further decreases from time t21. After that, at time t22, when the engine speed falls below the third engine speed rs3, that is, when the engine speed falls outside the monitoring range MR, the fuel feedback control is turned off by the processes of steps S18 and S19 in FIG. 3.

[0070] 6.Effects (a) In the above-described motorcycle 100, when the engine 5 is driven according to the first condition and the engine speed reaches the first rotation speed rs1, the over-rev limit control is performed. As a result, the engine 5 is driven according to the second condition, and the engine speed decreases. Therefore, over-revving of the engine 5 is suppressed.

[0071] When the engine speed drops to the second rotation speed rs2, the conditions used for driving the engine 5 are returned from the second conditions to the first conditions. In this state, if the engine speed is maintained within the monitoring range MR, there is a high possibility that the engine speed will reach the first rotation speed rs1 again in a relatively short time. As a result, if the over-rev limit control is performed periodically, strong oxidation reactions and strong reduction reactions may occur alternately in the three-way catalyst 53, and the temperature of the three-way catalyst 53 may become excessively high.

[0072] Therefore, in the above-described motorcycle 100, when the engine speed continues to be in the monitoring range MR after the over-rev limit control, the fuel feedback control based on the output of the catalyst downstream oxygen sensor SE4 is turned on. As a result, when the engine speed continues to be in the monitoring range MR after the over-rev limit control, the air-fuel ratio of the exhaust gas is adjusted to be lean, and the reaction occurring in the three-way catalyst 53 is limited to the reduction reaction.

[0073] Here, the reason for using the output of the catalyst downstream oxygen sensor SE4 in the fuel feedback control will be explained. There is a large variation in the oxygen concentration in the exhaust gas immediately after it is discharged from the engine 5. Therefore, even if the oxygen concentration of the exhaust gas immediately after it is discharged from the engine 5 is detected, the detection result will be unstable. It is difficult to appropriately adjust the air-fuel ratio of the exhaust gas using the unstable detection result.

[0074] In contrast, the three-way catalyst 53 functions as a filter that reduces variations in the oxygen concentration in the exhaust gas flowing through the exhaust pipe 51 and the muffler 52. Therefore, the catalyst downstream oxygen sensor SE4 can obtain a more stable detection result for the oxygen concentration in the exhaust gas than when an oxygen sensor provided upstream of the three-way catalyst 53 is used. As a result, in the fuel feedback control, the amount of fuel supplied by the fuel injector 61 is appropriately adjusted based on the detection result of the catalyst downstream oxygen sensor SE4. As a result, the life of the three-way catalyst 53 is appropriately prevented from being shortened due to the suppression of overspeed of the engine 5.

[0075] (b) Furthermore, according to the above fuel feedback control, it is not necessary to use an additional map to determine the fuel supply amount for protecting the three-way catalyst 53 after the over-rev limit control. This makes it possible to prevent the life of the three-way catalyst 53 from being shortened in a simple manner without requiring the troublesome task of creating an additional map.

[0076] (c) The monitoring range MR is set to a continuous range equal to or higher than a third rotation speed rs3 that is lower than the second rotation speed rs2 and lower than the first rotation speed rs1. In this case, even if the engine rotation speed temporarily becomes lower than the second rotation speed rs2 after the over-rev limit control is terminated, the fuel feedback control is performed as long as the engine rotation speed does not drop to the third rotation speed rs3. This makes it possible to more appropriately control the reaction occurring in the three-way catalyst 53.

[0077] (d) In the fuel feedback control, the amount of fuel supplied is adjusted every predetermined number of cycles until the air-fuel ratio of the exhaust gas becomes lean. Therefore, the amount of fuel supplied can be appropriately adjusted without accurately determining the degree of deviation between the actual air-fuel ratio of the exhaust gas and the stoichiometric air-fuel ratio. Therefore, an inexpensive oxygen sensor capable of detecting only whether the oxygen concentration is higher than the oxygen concentration corresponding to the stoichiometric air-fuel ratio can be used as the catalyst downstream oxygen sensor SE4.

[0078] 7. Other embodiments (a) In the above embodiment, the second condition includes information indicating that the amount of fuel supplied to the engine 5 during over rev limit control is 0, but the present invention is not limited to this. The second condition may include information indicating that the amount of fuel supplied to the engine 5 during over rev limit control is a specific value greater than 0. In this case, the specific value greater than 0 is set to a value lower than the value of the amount of fuel supplied that should be set based on the map of the first condition when the engine 5 is in a normal operating state. This makes it possible to gently reduce the engine speed during over rev limit control.

[0079] (b) In the above embodiment, the second condition includes information indicating that the amount of fuel supplied to the engine 5 during over rev limit control is zero, but the present invention is not limited to this. The second condition may include information for adjusting the opening of the throttle valve 62 in addition to, or instead of, the information for adjusting the amount of fuel supplied. For example, the second condition may include information for setting the opening of the throttle valve 62 to a value significantly smaller than when the engine 5 is in a normal operating state. Even in this case, the engine speed can be forcibly reduced during over rev limit control.

[0080] (c) In the above embodiment, the monitoring range MR, which serves as the basis for performing fuel feedback control, is set to a range that is equal to or greater than the third rotational speed rs3 and lower than the first rotational speed rs1, but the present invention is not limited to this.

[0081] The monitoring range MR may be set to a range equal to or greater than the second rotation speed rs2 and lower than the first rotation speed rs1, instead of a range equal to or greater than the third rotation speed rs3 and lower than the first rotation speed rs1. In other words, in the above embodiment, the second rotation speed rs2 and the third rotation speed rs3 may be set to the same value.

[0082] (d) In the motorcycle 100 according to the above embodiment, the CPU 10a has the information storage unit 15 as a functional unit, but the present invention is not limited to this. Each piece of information stored by the information storage unit 15 is stored in advance in the ROM 10b. Therefore, the other functional units (11, 12, 13, 14) of the CPU 10a may read and store information required for processing by the other functional units from the ROM 10b as appropriate. In this case, the information storage unit 15 becomes unnecessary.

[0083] (e) In the motorcycle 100 according to the above embodiment, a catalyst downstream oxygen sensor SE4 is used to perform fuel feedback control. As the catalyst downstream oxygen sensor SE4, an oxygen sensor that detects only whether or not the oxygen concentration in the gas is higher than the oxygen concentration corresponding to the stoichiometric air-fuel ratio may be used, or an air-fuel ratio sensor that detects the oxygen concentration in the gas in more detail may be used.

[0084] (f) The above-described embodiment is an example in which the present invention is applied to a motorcycle. However, the present invention is not limited to this and may be applied to other saddle-ride vehicles, such as three-wheeled motor vehicles or ATVs (All Terrain Vehicles), or other vehicles other than saddle-ride vehicles, such as three-wheeled motor vehicles and four-wheeled motor vehicles.

[0085] 8. Correspondence between each part of the embodiment and each component of the claims The following describes an example of the correspondence between each component of the claims and each component of the embodiment. Various other elements having the configuration or function described in the claims may be used as each component of the claims.

[0086] In the above embodiment, engine 5 is an example of an engine, fuel injection device 61, throttle valve 62 and throttle actuator 63 are examples of an engine drive section, ECU 10 is an example of a control section, exhaust pipe 51 and muffler 52 are examples of an exhaust system, three-way catalyst 53 is an example of a catalyst, catalyst downstream oxygen sensor SE4 is an example of an oxygen sensor, and fuel injection device 61 is an example of a fuel supply section.

[0087] In addition, the first rotational speed rs1 is an example of a first rotational speed, the second rotational speed rs2 is an example of a second rotational speed, the monitoring range MR is an example of a monitoring range, a configuration including the ECU 10 and the catalyst downstream oxygen sensor SE4 is an example of a fuel adjustment device, the third rotational speed rs3 is an example of a third rotational speed, the rear wheel 7 is an example of a drive wheel, and the motorcycle 100 is an example of a vehicle.

[0088] 9. Summary of the embodiment (1) The fuel adjustment device according to the first paragraph is A control unit that controls an engine drive unit that operates the engine; an oxygen sensor provided downstream of a catalyst that purifies exhaust gas in an exhaust system attached to the engine, the oxygen sensor detecting an oxygen concentration in the exhaust gas; the engine drive unit includes a fuel supply unit that supplies fuel to the engine; The control unit is operating the engine driving unit under a second condition different from the first condition such that, when the rotation speed of the engine increases to reach a first rotation speed in a state in which the engine driving unit operates under a first condition, the rotation speed of the engine decreases; when the rotation speed of the engine reaches a second rotation speed lower than the first rotation speed from the first rotation speed while the engine driving unit is operating according to the second condition, returning the operating condition of the engine driving unit from the second condition to the first condition; adjusting a fuel supply amount of the fuel supply unit based on a detection result of the oxygen sensor when a rotation speed of the engine is continuously maintained within a monitoring range from a point in time when the operating condition of the engine driving unit is returned to the first condition from the second condition; The monitoring range includes the second rotational speed and is lower than the first rotational speed.

[0089] According to the fuel regulating device, when the engine rotation speed reaches the first rotation speed while the engine driving unit is operating according to the first condition, the operating condition of the engine driving unit is switched. The engine driving unit operates according to the second condition, and the engine rotation speed decreases. Therefore, the engine rotation speed is prevented from becoming excessively high beyond the first rotation speed. In other words, over-revving of the engine is suppressed.

[0090] When the engine speed drops to the second speed, the operating conditions of the engine driving part are returned from the second condition to the first condition. If the engine speed is then maintained within the monitoring range, the engine speed is likely to reach the first speed again in a relatively short time. If the operating conditions of the engine driving part are repeatedly switched, a regular fluctuation in the air-fuel ratio of the gas flowing from the engine to the exhaust system may occur. If the oxidation reaction and the reduction reaction in the catalyst are alternately repeated in association with the fluctuation in the air-fuel ratio, the temperature of the catalyst may become excessively high.

[0091] In order to prevent the temperature of the catalyst from becoming excessively high without causing the engine to misfire, it is preferable to reduce the intensity of at least one of the oxidation and reduction reactions. The reaction occurring in the catalyst and its degree are determined, for example, by the air-fuel ratio of the mixture supplied to the engine. Therefore, if the oxygen concentration of the gas exhausted from the engine is known, the air-fuel ratio of the mixture supplied to the engine can be appropriately adjusted based on the oxygen concentration.

[0092] There is a large variation in the oxygen concentration in exhaust gas immediately after it is discharged from the engine. Even if the oxygen concentration of exhaust gas immediately after it is discharged from the engine is detected, the detection result will be unstable. It is difficult to appropriately adjust the air-fuel ratio of the mixture using the unstable detection result.

[0093] In contrast, the catalyst functions as a filter that reduces the variation in oxygen concentration in the exhaust gas flowing through the exhaust system. According to the above configuration, the oxygen concentration in the exhaust gas from the engine is detected by an oxygen sensor located downstream of the catalyst. In this case, a stable detection result can be obtained for the oxygen concentration in the exhaust gas, and the amount of fuel supplied by the fuel supply unit is appropriately adjusted based on the detection result of the oxygen sensor. Therefore, it is possible to appropriately and selectively cause oxidation and reduction reactions in the catalyst. As a result, the catalyst's lifespan is appropriately prevented from being shortened due to the suppression of engine overspeed.

[0094] (2) In the fuel adjustment device according to the first paragraph, The control unit is When adjusting the fuel supply amount of the fuel supply unit, the fuel supply unit may be adjusted so that an amount of fuel is supplied to the engine that is different from the fuel supply amount corresponding to the first condition and the fuel supply amount corresponding to the second condition.

[0095] In this case, the amount of fuel supplied to the engine can be more appropriately adjusted based on the detection result of the oxygen sensor.

[0096] (3) In the fuel adjustment device according to paragraph 1 or 2, the first condition includes setting an amount of fuel to be supplied from the fuel supply unit to the engine to a first supply amount, The second condition may include setting the amount of fuel to be supplied from the fuel supply unit to the engine to zero or to a second supply amount lower than the first supply amount.

[0097] In this case, in the control for suppressing the overspeed of the engine, fuel is not supplied to the engine or the amount of fuel supplied to the engine is reduced, thereby decreasing the rotation speed of the engine.

[0098] (4) In the fuel adjustment device according to any one of paragraphs 1 to 3, Adjusting the amount of fuel supplied by the fuel supply unit based on the detection result of the oxygen sensor may include feedback controlling the fuel supply unit so that the oxygen concentration detected by the oxygen sensor is higher than the oxygen concentration corresponding to the theoretical air-fuel ratio.

[0099] In this case, when the engine rotation speed is maintained within the monitoring range after the operating conditions of the engine drive unit are returned from the second condition to the first condition, the oxygen concentration of the exhaust gas is increased by feedback control based on the detection result of the oxygen sensor. When the air-fuel ratio of the exhaust gas is maintained lean, the reaction occurring in the catalyst is limited to the reduction reaction. As a result, the repetition of strong oxidation reaction and strong reduction reaction in the catalyst is suppressed, and the temperature of the catalyst is prevented from becoming excessively high.

[0100] (5) In the fuel adjustment device according to the fourth paragraph, Feedback controlling the fuel supply unit may include determining whether or not the oxygen concentration detected by the oxygen sensor is higher than the oxygen concentration corresponding to the stoichiometric air-fuel ratio, and reducing the fuel supply amount of the fuel supply unit by a specified reduction amount from a preset fuel supply amount when the detected oxygen concentration is equal to or lower than the oxygen concentration corresponding to the stoichiometric air-fuel ratio.

[0101] In this case, when the air-fuel ratio of the exhaust gas is not lean, the fuel supply amount is reduced by a specified reduction amount, for example, every predetermined number of cycles, so that the change in the reaction occurring in the catalyst is gradually stabilized.

[0102] In this case, the amount of fuel supplied is adjusted stepwise until the air-fuel ratio of the exhaust gas becomes lean, so that the amount of fuel supplied can be appropriately adjusted without accurately determining the degree of deviation between the actual air-fuel ratio of the exhaust gas and the stoichiometric air-fuel ratio. Therefore, an inexpensive oxygen sensor capable of detecting only whether the oxygen concentration is higher than the oxygen concentration corresponding to the stoichiometric air-fuel ratio can be used.

[0103] (Item 6) In the fuel adjustment device according to any one of items 1 to 5, The monitoring range may be a continuous range equal to or greater than a third rotational speed lower than the second rotational speed and lower than the first rotational speed.

[0104] In this case, even if the engine speed temporarily becomes lower than the second rotation speed after the operating condition of the engine driving part is returned to the first condition from the second rotation speed, the fuel injection amount of the fuel supply part is adjusted as long as the engine speed does not decrease to the third rotation speed, thereby making it possible to more appropriately control the reaction occurring in the catalyst.

[0105] (Article 7) The vehicle referred to in paragraph 7 is The engine; The exhaust system; The catalyst provided in the exhaust system; The engine drive unit; A fuel adjustment device according to any one of claims 1 to 6, and a drive wheel driven by the engine.

[0106] The vehicle includes the above-mentioned fuel adjustment device, and therefore the catalyst life is prevented from being shortened due to the control for suppressing the engine overspeed. [Explanation of symbols]

[0107] 1...body frame, 1h...head pipe, 2...front fork, 3...front wheel, 4...handle, 4g...accelerator grip, 5...engine, 6...rear arm, 7...rear wheel, 8...fuel tank, 9...seat, 10...ECU, 10a...CPU, 10b...ROM, 10c...RAM, 11...rotation speed determination unit, 12...oxygen concentration determination unit, 13...engine control unit, 14...feedback control unit, 15...information storage unit, 51...exhaust pipe, 52...muffler, 53...three-way catalyst, 60...intake pipe, 61...fuel injector, 62...throttle valve, 63...throttle actuator, 100...motorcycle, MR...monitoring range, SE0...accelerator sensor, SE1...throttle sensor, SE2...intake pressure sensor, SE3...crank sensor, SE4...catalyst downstream oxygen sensor, rs1...first rotation speed, rs2...second rotation speed, rs3...third rotation speed,

Claims

1. A control unit that controls an engine drive unit that operates the engine; an oxygen sensor provided downstream of a catalyst that purifies exhaust gas in an exhaust system attached to the engine, the oxygen sensor detecting an oxygen concentration in the exhaust gas; the engine drive unit includes a fuel supply unit that supplies fuel to the engine; The control unit is operating the engine driving unit under a second condition different from the first condition such that, when the rotation speed of the engine increases to reach a first rotation speed in a state in which the engine driving unit operates under a first condition, the rotation speed of the engine decreases; when the rotation speed of the engine reaches a second rotation speed lower than the first rotation speed from the first rotation speed while the engine driving unit is operating according to the second condition, returning the operating condition of the engine driving unit from the second condition to the first condition; adjusting a fuel supply amount of the fuel supply unit based on a detection result of the oxygen sensor when a rotation speed of the engine is continuously maintained within a monitoring range from a point in time when the operating condition of the engine driving unit is returned to the first condition from the second condition; The monitoring range includes the second rotational speed and is a range lower than the first rotational speed.

2. The control unit is 2. The fuel adjustment device according to claim 1, wherein the fuel supply unit adjusts a fuel supply amount to supply an amount of fuel to the engine that is different from a fuel supply amount corresponding to the first condition and a fuel supply amount corresponding to the second condition when adjusting the fuel supply amount of the fuel supply unit.

3. the first condition includes setting an amount of fuel to be supplied from the fuel supply unit to the engine to a first supply amount, 3. The fuel adjustment device according to claim 1, wherein the second condition includes setting the amount of fuel to be supplied from the fuel supply unit to the engine to zero or a second supply amount lower than the first supply amount.

4. 3. The fuel adjustment device according to claim 1, wherein adjusting the fuel supply amount of the fuel supply unit based on the detection result of the oxygen sensor includes feedback controlling the fuel supply unit so that the oxygen concentration detected by the oxygen sensor becomes higher than the oxygen concentration corresponding to the theoretical air-fuel ratio.

5. 5. The fuel adjustment device according to claim 4, wherein the feedback control of the fuel supply unit includes determining whether or not an oxygen concentration detected by the oxygen sensor is higher than an oxygen concentration corresponding to a stoichiometric air-fuel ratio, and reducing an amount of fuel supplied by the fuel supply unit from a preset fuel supply amount by a specified reduction amount when the detected oxygen concentration is equal to or lower than the oxygen concentration corresponding to the stoichiometric air-fuel ratio.

6. 3. The fuel adjustment device according to claim 1, wherein the monitoring range is a continuous range that is equal to or greater than a third rotational speed that is lower than the second rotational speed and is lower than the first rotational speed.

7. The engine; The exhaust system; The catalyst provided in the exhaust system; The engine drive unit; A fuel adjustment device according to claim 1 or 2, and a drive wheel driven by the engine.

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