JP7566825B2 - Independent throttle type 2-4 cylinder engine unit - Google Patents

Description

The present invention relates to an independent throttle type 2-4 cylinder engine unit.

As one type of internal combustion engine, an independent throttle type multi-cylinder engine is known. In an independent throttle type multi-cylinder engine, an independent intake passage is provided for each of the multiple cylinders. A throttle valve is provided in each intake passage. By opening and closing the throttle valve of each intake passage, a mixture of fuel and air flows into each cylinder. Such an independent throttle type multi-cylinder engine is disclosed, for example, in Patent Document 1.

Patent No. 4400402 specification

The objective of the present invention is to improve the accuracy of detecting imbalances in the air-fuel ratio between cylinders using a single sensor in an independent throttle type 2-4 cylinder engine unit, which is based on the premise that the amount of air supplied to each cylinder varies.

(1) An independent throttle type 2-4 cylinder engine unit according to an embodiment of the present invention includes 2-4 cylinders each forming a combustion chamber together with a piston, a crankshaft that rotates by burning fuel in the combustion chamber, 2-4 independent exhaust pipes provided corresponding to each of the 2-4 cylinders and through which exhaust gas from the corresponding cylinder flows, a collective exhaust pipe including a collector section where the 2-4 independent exhaust pipes are collected and a catalyst provided downstream of the collector section in the exhaust gas flow direction, a pre-catalyst sensor provided at the collector section of the collective exhaust pipe for detecting the oxygen ratio or oxygen concentration in the exhaust gas flowing into the catalyst from each of the 2-4 cylinders, and a control device. The crankshaft is configured so that at least one combustion interval in the rotation cycle of the crankshaft is 240 degrees or more in crank angle, thereby reducing interference between exhaust gases flowing into the catalyst from each cylinder corresponding to each combustion constituting at least one combustion interval. The control device is configured to detect imbalances in the air-fuel ratio between cylinders 2-4 using the results of the pre-catalyst sensor detecting the oxygen ratio or oxygen concentration in the exhaust gas with reduced interference flowing into the catalyst from each of cylinders 2-4 at the collection point.

In the independent throttle type 2-4 cylinder engine unit, a pre-catalyst sensor is provided in the collecting section. Since exhaust gas from each independent exhaust pipe flows into the collecting section sequentially, the pre-catalyst sensor can detect the oxygen ratio or oxygen concentration in the exhaust gas flowing into the catalyst from each cylinder. In the independent throttle type 2-4 cylinder engine unit, the combustion interval from one combustion to the next combustion is 240 degrees or more in crank angle. A combustion interval of 240 degrees or more is a long period that occupies more than 1/3 of the rotation cycle (720 degrees) of the crankshaft in a four-stroke engine, for example. The period from when the exhaust gas generated by one combustion flows into the collecting section to when the exhaust gas generated by the next combustion flows into the collecting section is long, which makes it difficult for exhaust gases discharged from different cylinders to mix in the collecting section, making it easy for the pre-catalyst sensor to detect the oxygen ratio or oxygen concentration in the exhaust gas discharged from each cylinder. The control device can use the oxygen ratio or oxygen concentration in the exhaust gas with reduced interference detected by the pre-catalyst sensor to determine whether the air-fuel ratio of the mixture supplied to each cylinder is rich or lean. Therefore, in an independent throttle type 2-4 cylinder engine unit that assumes that the amount of air supplied to each cylinder varies, it is possible to improve the accuracy of detecting imbalance in air-fuel ratio between cylinders using a single sensor.

(2) In the independent throttle type 2-4 cylinder engine unit described above in (1), the pre-catalyst sensor may be a pre-catalyst oxygen sensor that detects the oxygen ratio in the exhaust gas flowing into the catalyst from each of the 2nd to 4th cylinders.

In general, an air-fuel ratio sensor or an oxygen sensor is used to detect cylinder-to-cylinder imbalance in air-fuel ratio. An air-fuel ratio sensor detects the oxygen concentration in the exhaust gas continuously or linearly. An oxygen sensor detects the oxygen ratio in the exhaust gas as a binary value, lean or rich. In the independent throttle type 2-4 cylinder engine unit described above in (2), the pre-catalyst sensor is composed of an oxygen sensor. Therefore, the amount of detection data is reduced and it is less expensive than when an air-fuel ratio sensor is used.

The term "2-4 cylinder engine unit" is, for example, a general term for an engine and an intake and exhaust system. The 2-4 cylinder engine unit includes, for example, an engine that generates power for driving a vehicle in which the 2-4 cylinder engine unit is installed. The engine is an internal combustion engine. The engine is not an electric motor. The engine is, for example, a reciprocating engine. The engine is, for example, a four-stroke engine. The engine is, for example, preferably a gasoline engine in which fuel is burned by a spark plug. The engine may be, for example, a diesel engine in which fuel is burned by compressed air. The engine is, for example, an in-line, V-type, or horizontally opposed 2-4 cylinder engine. The engine is, for example, preferably a naturally aspirated engine. The engine includes, for example, 2-4 cylinders, a piston, and a crankshaft. The 2-4 cylinder engine unit may be a hybrid engine unit including an engine and an electric motor. The hybrid engine unit may be, for example, a parallel type hybrid engine unit or a series type hybrid engine unit.

The "independent throttle type 2-4 cylinder engine unit" is mounted, for example, on a tilting vehicle. The tilting vehicle is a transportation device. The tilting vehicle is a vehicle driven by a person. The tilting vehicle includes, for example, a vehicle body that tilts to the left when the tilting vehicle turns left and tilts to the right when the tilting vehicle turns right. The tilting vehicle is, for example, a motorcycle. The tilting vehicle is not limited to motorcycles, and may be, for example, a three-wheeled motor vehicle or a four-wheeled motor vehicle. The tilting vehicle has, for example, at least one front wheel and at least one rear wheel. The tilting vehicle is not particularly limited, and examples thereof include scooter-type, moped-type, off-road-type, and on-road-type tilting vehicles.

The independent throttle type 2-4 cylinder engine unit is mounted, for example, on a saddle-type vehicle. A saddle-type vehicle is a type of vehicle in which the driver sits astride the saddle. In a saddle-type vehicle, the left foot of the seated driver is positioned to the left of the center in the left-right direction of the saddle-type vehicle, and the right foot is positioned to the right of the center in the left-right direction of the saddle-type vehicle. The above-mentioned motorcycle and three-wheeled motor vehicle are each an example of a saddle-type vehicle. Further, an example of a saddle-type vehicle is an ATV (All-Terrain Vehicle). An ATV is an example of a saddle-type four-wheeled motor vehicle. Furthermore, a saddle-type vehicle may not have wheels, for example. An example of such a saddle-type vehicle is a snowmobile. A snowmobile has, for example, a track belt instead of wheels. However, the independent throttle type 2-4 cylinder engine unit may be mounted on a four-wheeled motor vehicle that is not a tilting vehicle. In a four-wheeled motor vehicle that is not a tilting vehicle, for example, the two-four cylinder engine unit is disposed at the front or rear of the vehicle. The front and rear are not disposed at positions that overlap with the driver when viewed from the top and bottom of the vehicle. The rotation speed of the crankshaft of a two-four cylinder engine unit mounted on a four-wheeled motor vehicle that is not a tilting vehicle is, for example, low during normal operation. The maximum value of the rotation speed of the crankshaft of a two-four cylinder engine unit mounted on a four-wheeled motor vehicle that is not a tilting vehicle is lower than, for example, a tilting vehicle and a saddle-type vehicle.

An independent throttle type 2-4 cylinder engine unit includes, for example, multiple intake passages through which air passes to supply each of the 2-4 cylinders. An independent throttle type 2-4 cylinder engine unit includes, for example, the same number of intake passages as the 2-4 cylinders. The multiple intake passages are, for example, independent of each other. Each of the multiple intake passages is connected to a corresponding cylinder. However, the multiple intake passages may be combined together at an intake port that takes in outside air.

An independent throttle type 2-4 cylinder engine unit includes, for example, a throttle valve provided in each of a plurality of intake passages. The plurality of throttle valves, for example, adjust the amount of air flowing into the corresponding cylinders. The plurality of throttle valves are, for example, controlled simultaneously. The plurality of throttle valves may also be controlled individually. The openings of the plurality of throttle valves are, for example, controlled to be the same at a nominal value. The openings of the plurality of throttle valves may also be controlled to be different at a nominal value.

An independent throttle type 2-4 cylinder engine unit includes, for example, an injector provided in each of a plurality of intake passages for injecting fuel. Each of the plurality of injectors is provided, for example, downstream of the throttle valve in the flow direction of the intake air. Each of the plurality of injectors is, for example, electronically controlled. Each of the plurality of injectors injects fuel, for example, into the intake passage. Each of the plurality of injectors does not inject fuel directly into a cylinder, for example.

An example of an independent throttle type 2-4 cylinder engine unit is a 2-4 cylinder engine unit of an unequal interval combustion type and an independent throttle type. An unequal interval combustion type and an independent throttle type 2-4 cylinder engine unit means an engine unit configured so that all combustion intervals expressed in crank angles are not equal in the rotation cycle of the crankshaft. The combustion interval expressed in crank angle means the rotation angle of the crankshaft from the combustion in one cylinder as a reference (crank angle is 0 degrees) to the combustion in another cylinder that will next perform combustion. For example, consider a 4-stroke 2-cylinder engine unit of an unequal interval combustion type and an independent throttle type. In this engine unit, if the combustion in the first cylinder is taken as a reference, combustion occurs in the second cylinder when the crankshaft has rotated 270 degrees since the combustion in the first cylinder. Combustion occurs again in the first cylinder when the crankshaft has rotated 450 degrees since the combustion in the second cylinder. In this case, the two-cylinder engine unit with variable combustion intervals and independent throttle has a combustion interval of 270 degrees and 450 degrees in crank angle. The two-cylinder engine unit with variable combustion intervals and independent throttle may have a combustion interval of 180 degrees and 540 degrees in crank angle. The three-cylinder engine unit with variable combustion intervals and independent throttle has a combustion interval of 180 degrees, 270 degrees, and 270 degrees, for example. The four-cylinder engine unit with variable combustion intervals and independent throttle has a combustion interval of 270 degrees, 180 degrees, 90 degrees, and 180 degrees in crank angle, for example.

The independent throttle type 2-4 cylinder engine unit may be an equal interval combustion type and independent throttle type 2-3 cylinder engine unit. The equal interval combustion type and independent throttle type 2-3 cylinder engine unit means an engine unit configured so that all combustion intervals expressed in crank angles are equal in the rotation cycle of the crankshaft. The equal interval combustion type and independent throttle type 2-3 cylinder engine unit does not include, for example, an equal interval combustion type engine unit with four or more cylinders.

Each of the "two to four cylinders" has, for example, a cylindrical internal space. Each of the two to four cylinders houses a piston in the internal space. Each of the two to four cylinders' internal spaces, together with the piston, form a combustion chamber in which a mixture of fuel and air is burned. The piston reciprocates as the mixture is burned in each combustion chamber.

The "crankshaft" includes, for example, a journal, a crank pin that is eccentric with respect to the journal, and a crank arm that connects the journal and the crank pin. The crankshaft is connected to a piston, for example, via a connecting rod. The connecting rod connects the piston and the crank pin. The crankshaft converts, for example, the reciprocating motion of the piston into rotational motion.

Each of the "two to four independent exhaust pipes" is connected to a corresponding cylinder. Each of the two to four independent exhaust pipes is connected to, for example, an exhaust port provided in each of the two to four cylinders. For example, substantially only exhaust gas from a corresponding cylinder flows through each of the two to four independent exhaust pipes. Exhaust gas from cylinders not corresponding to each of the two to four independent exhaust pipes does not substantially flow through each of the two to four independent exhaust pipes. Exhaust gas from two or more cylinders does not substantially flow through each of the two to four independent exhaust pipes. At the upstream end of each of the two to four independent exhaust pipes (the connection portion with the exhaust port of the engine), each independent exhaust pipe is, for example, independent from each other. Each of the two to four independent exhaust pipes is, for example, independent from each other until it reaches a collecting portion. Note that the two to four independent exhaust pipes may merge with some of the two to four independent exhaust pipes before reaching the collecting portion. In other words, a merging portion may be interposed between some of the independent exhaust pipes and the collecting portion. The two to four independent exhaust pipes are connected to a collecting exhaust pipe. The 2-4 independent exhaust pipes are, for example, the portions of the exhaust gas path from the corresponding cylinders to the collective portion of the collective exhaust pipe. Each of the 2-4 independent exhaust pipes includes, for example, a straight portion that extends in a straight line. Each of the 2-4 independent exhaust pipes includes, for example, a curved portion that extends in a curved line. When an independent throttle type 2-4 cylinder engine unit is mounted on a vehicle, the 2-4 independent exhaust pipes are longest in the vertical direction of the vehicle, compared to the front-rear and left-right directions.

The exhaust gas is generated, for example, by burning a mixture of intake air and fuel taken in from outside the vehicle equipped with an independent throttle type 2-4 cylinder engine unit. The exhaust gas may be generated by burning a mixture of intake air, exhaust gas, and fuel. In other words, the independent throttle type 2-4 cylinder engine unit may employ an EGR system (Exhaust Gas Recirculation system) that re-intakes at least a portion of the exhaust gas.

An "exhaust pipe collector" is, for example, an exhaust pipe that combines two to four individual exhaust pipes into one. The exhaust pipe collector is located downstream of the two to four individual exhaust pipes in the flow direction of the exhaust gas. The exhaust pipe collector includes a collector section and a catalyst.

The "collection section" is, for example, the section where 2-4 independent exhaust pipes join together. Exhaust gas from, for example, 2-4 cylinders flows through the collection section. The collection section is, for example, the section from the downstream ends of the 2-4 independent exhaust pipes to the catalyst. The collection section includes, for example, a branching section where the 2-4 independent exhaust pipes join together, and a straight section that extends in a straight line downstream from the branching section in the flow direction of the exhaust gas.

The "catalyst" is provided, for example, in a portion downstream of the collecting portion in the exhaust pipe. The catalyst is provided, for example, in the exhaust pipe. The catalyst purifies the exhaust gas flowing through the exhaust pipe. The catalyst has, for example, an oxygen storage capacity. The catalyst is, for example, a three-way catalyst. The catalyst may be an oxidation catalyst, a nitrogen oxide selective reduction catalyst, a nitrogen oxide storage reduction catalyst, or the like. The catalyst does not have to be an oxidation-reduction catalyst. The catalyst may be an oxidation catalyst or a reduction catalyst that purifies the exhaust gas only by oxidation or reduction. The catalyst oxidizes or reduces, for example, the hydrocarbons, carbon monoxide, and nitrogen oxides in the exhaust gas. The catalyst may oxidize or reduce any one or two of the hydrocarbons, carbon monoxide, and nitrogen oxides. The catalyst oxidizes, for example, the hydrocarbons to water and carbon dioxide. The catalyst oxidizes, for example, the carbon monoxide to carbon dioxide. The catalyst reduces, for example, the nitrogen oxides to nitrogen and oxygen. The catalyst includes, for example, a substrate and a precious metal having an exhaust gas purification function provided on the substrate surface. Precious metals include, for example, platinum, palladium, and rhodium.

For example, only one "pre-catalyst sensor" is provided in the exhaust pipe. For example, the pre-catalyst sensor is provided in the collecting section of the exhaust pipe. For example, the pre-catalyst sensor is provided in the straight section of the collecting section. For example, the pre-catalyst sensor detects the oxygen ratio or oxygen concentration in the exhaust gas before it is purified by the catalyst. For example, the pre-catalyst sensor detects the oxygen ratio or oxygen concentration in the exhaust gas that flows in sequentially from each of two to four cylinders. In other words, the pre-catalyst sensor detects the oxygen ratio or oxygen concentration in the exhaust gas discharged from all two to four cylinders, for example.

The pre-catalyst sensor is, for example, a pre-catalyst oxygen sensor that detects the oxygen ratio in the exhaust gas. The oxygen ratio is, for example, an index that expresses the oxygen concentration in the exhaust gas in a binary value. In other words, the pre-catalyst oxygen sensor detects only whether the oxygen ratio in the exhaust gas is high or low. The pre-catalyst oxygen sensor detects that the oxygen ratio in the exhaust gas is high, for example, when the oxygen ratio in the exhaust gas exceeds a predetermined threshold. The pre-catalyst oxygen sensor detects that the oxygen ratio in the exhaust gas is low, for example, when the oxygen ratio in the exhaust gas is equal to or lower than a predetermined threshold. The threshold used to detect that the oxygen ratio is high and the threshold used to detect that the oxygen ratio is low may be set separately. The pre-catalyst oxygen sensor has, for example, a sensor element portion made of a solid electrolyte body mainly made of zirconia. When the sensor element portion is, for example, heated to a high temperature and activated, the pre-catalyst oxygen sensor detects the oxygen ratio in the exhaust gas.

The pre-catalyst sensor is, for example, a pre-catalyst air-fuel ratio sensor that detects the oxygen concentration in the exhaust gas. The oxygen concentration is, for example, a continuous or linear value. The pre-catalyst air-fuel ratio sensor detects, for example, changes in the oxygen concentration in the exhaust gas in a continuous or linear manner.

The air-fuel ratio of the mixture supplied to each cylinder is determined based on the oxygen ratio or oxygen concentration detected by such a pre-catalyst sensor. A state in which there is an excess of fuel relative to the target air-fuel ratio is said to be rich. A state in which there is an excess of air relative to the target air-fuel ratio is said to be lean. The target air-fuel ratio may be a value or range that includes the stoichiometric air-fuel ratio, or may be a value or range that is slightly deviated from the stoichiometric air-fuel ratio. The pre-catalyst sensor is, for example, electrically connected to a control device. The pre-catalyst sensor sends, for example, the detected oxygen ratio or oxygen concentration to the control device as a detection result. More specifically, the pre-catalyst sensor sends, for example, an electrical signal indicating the detected oxygen ratio or oxygen concentration to the control device.

The "control device" is, for example, an ECU (Electronic Control Unit). The control device includes, for example, a processor such as a CPU (Central Processing Unit) or a DSP (Digital Signal Processor). The control device may include, for example, a non-volatile memory in which one or more programs including part or all of the arithmetic processing executed by the control device are recorded. The control device realizes detection of at least cylinder-to-cylinder imbalance in air-fuel ratio, for example, by the processor reading and executing one or more programs recorded in the non-volatile memory.

The control device performs feedback control of the fuel supplied to each of the 2-4 cylinders individually so that the air-fuel ratio of the mixture of fuel and air supplied to each of the 2-4 cylinders becomes the target air-fuel ratio, for example, using the detection result corresponding to each cylinder received from the pre-catalyst sensor. More specifically, the control device determines the air-fuel ratio in each of the 2-4 cylinders using the detection result received from the pre-catalyst sensor. The control device performs feedback control to correct the amount of fuel supplied to each of the 2-4 cylinders so as to eliminate the determined result. That is, the control device increases the amount of fuel supplied when it determines that each of the 2-4 cylinders is lean, and decreases the amount of fuel supplied when it determines that each of the 2-4 cylinders is rich. However, the control device does not have to eliminate the determined result in one feedback control. The control device controls the amount of fuel supplied to each of the 2-4 cylinders so that, for example, when viewed in a predetermined period, it alternates between rich and lean with respect to the target air-fuel ratio as a whole. That is, the control device controls the amount of fuel supplied to each of the second to fourth cylinders so that the air-fuel ratio in each of the second to fourth cylinders is maintained at or substantially at the target air-fuel ratio.

As described above, in an independent throttle type 2-4 cylinder engine unit, it is assumed that the amount of air supplied to each cylinder varies. For example, the control device controls the fuel supplied to each cylinder individually to keep the air-fuel ratio in each cylinder within a predetermined range from the target air-fuel ratio, even though the amount of air supplied to each cylinder varies. However, suppose that the air-fuel ratio in a certain cylinder deviates significantly from the target air-fuel ratio beyond the allowable range due to some factor. In this case, the air-fuel ratio varies significantly between the 2-4 cylinders, and the components in the exhaust gas differ from those expected, which also affects the purification function of the catalyst. Therefore, in such a case, it is desirable to notify the driver of the vehicle equipped with the independent throttle type 2-4 cylinder engine unit that the air-fuel ratio deviates significantly from the target air-fuel ratio.

Therefore, for example, in at least one of the two to four cylinders, when the Nth air-fuel ratio determination result is the same as the N-1th determination result, the control device calculates an integrated correction amount that is larger than the correction amount used in the N-1th feedback control. The "large integrated correction amount" here means that if the N-1th fuel correction amount is an increase, the Nth fuel correction amount is increased compared to the N-1th fuel correction amount, and if the N-1th fuel correction amount is a decrease, the Nth fuel correction amount is decreased compared to the N-1th fuel correction amount. The control device increases the integrated correction amount for each feedback control until the Nth determination result differs from the N-1th determination result. For example, the control device compares the calculated integrated correction amount with a predetermined threshold value. For example, when the integrated correction amount is equal to or smaller than the threshold value, the control device executes feedback control to correct the amount of fuel supplied to the target cylinder using the integrated correction amount. For example, if the cumulative correction amount is greater than a threshold value, the control device determines that an abnormality in the air-fuel ratio has occurred in that cylinder. In this way, when the control device detects an abnormality in the air-fuel ratio in at least one of the two to four cylinders, this is referred to as detecting an imbalance in the air-fuel ratio between cylinders. The abnormality referred to here is when the amount of fuel correction by feedback control exceeds a predetermined threshold value. For example, when the control device detects an imbalance in the air-fuel ratio between cylinders in at least one cylinder, it executes a process for notifying the driver or the like to inspect the two- to four-cylinder engine unit. Note that the feedback control and the method of detecting imbalance between cylinders described here are merely examples, and are not limited to these examples.

The control device is configured to detect the imbalance of the air-fuel ratio between two to four cylinders, for example, by using at least the detection result of the pre-catalyst sensor detecting the oxygen ratio or oxygen concentration in the exhaust gas flowing into the catalyst from each cylinder corresponding to each combustion constituting the widest combustion interval at the crank angle. In a two-cylinder engine unit of the non-uniform combustion interval type, the widest combustion interval is, for example, a combustion interval of 450 degrees or 540 degrees. This combustion interval of 450 degrees or 540 degrees is the interval from the second combustion in a rotation cycle of the crankshaft to the first combustion in the next rotation cycle. In a three-cylinder engine unit of the non-uniform combustion interval type, the widest combustion interval is, for example, a combustion interval of 270 degrees. This combustion interval of 270 degrees is the interval from the second combustion to the third combustion in a rotation cycle of the crankshaft, or from the third combustion to the first combustion in the next rotation cycle. In a four-cylinder engine unit of the non-uniform combustion interval type, the widest combustion interval is, for example, a combustion interval of 270 degrees. This 270 degree combustion interval is the interval from the first combustion to the second combustion in a crankshaft rotation cycle.

The above and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the embodiments of the present invention taken in conjunction with the accompanying drawings. As used herein, the term "and/or" includes any or all combinations of one or more of the associated listed items. As used herein, the use of the terms "including," "comprising," or "having" and variations thereof, identifies the presence of the described features, steps, operations, elements, components, and/or equivalents thereof, but may include one or more of the steps, operations, elements, components, and/or groups thereof. Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs. Terms such as those defined in commonly used dictionaries should be interpreted to have a meaning consistent with the meaning in the context of the relevant technology and the present disclosure, and should not be interpreted in an ideal or overly formal sense unless expressly defined herein. In the description of the present invention, it is understood that a number of techniques and steps are disclosed. Each of these has separate benefits, and each can also be used with one or more, or in some cases all, of the other disclosed techniques. Thus, for the sake of clarity, this description will refrain from unnecessarily repeating all possible combinations of individual steps. Nevertheless, the specification and claims should be read with the understanding that all such combinations are within the scope of the present invention and claims. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be apparent to one skilled in the art that the present invention can be practiced without these specific details. The present disclosure is to be considered as an example of the present invention, and is not intended to limit the present invention to the specific embodiments illustrated in the following drawings or description.

The present invention can improve the accuracy of detecting imbalances in the air-fuel ratio between cylinders using a single sensor in an independent throttle type 2-4 cylinder engine unit, which is based on the assumption that the amount of air supplied to each cylinder varies.

FIG. 1(A) is a schematic diagram of the vicinity of the combustion chamber of an independent throttle type two-cylinder engine unit of this embodiment, FIG. 1(B) is a schematic diagram of the entire independent throttle type two-cylinder engine unit of this embodiment, and FIG. 1(C) is a diagram showing the relationship between combustion timing and crankshaft rotation speed in the independent throttle type two-cylinder engine unit of this embodiment. FIG. 2 is a flowchart showing a process for detecting an imbalance in air-fuel ratio among cylinders according to this embodiment. FIG. 3 is a diagram showing an example of a change in the fuel correction amount when an imbalance between cylinders occurs in a certain cylinder of the two-cylinder engine unit of this embodiment.

Below, an independent throttle type 2-4 cylinder engine unit according to an embodiment of the present invention will be described with reference to the drawings. Note that the embodiment described below is merely an example. The present invention should not be interpreted in any way as being limited by the embodiment described below.

Figure 1 (A) is a schematic diagram of the vicinity of the combustion chamber of an independent throttle type two-cylinder engine unit of this embodiment. The two-cylinder engine unit 1 is an independent throttle type and non-uniform combustion interval type two-cylinder engine unit. The two-cylinder engine unit 1 has two cylinders 11A, 11B and a crankshaft 12.

The two cylinders 11A, 11B each form a combustion chamber 112 together with a piston 111. The two cylinders 11A, 11B are arranged in series. The two cylinders 11A, 11B each have a cylindrical internal space that forms a part of the combustion chamber 112. The pistons 111 each have a cylindrical shape. The pistons 111 are each arranged in the internal space of the corresponding cylinder 11A, 11B and reciprocate. The pistons 111 are each connected to the crankshaft 12 via a connecting rod. A combustion chamber 112 is formed in each of the two cylinders 11A, 11B. The combustion chambers 112 each connect to an intake pipe. In each combustion chamber 112, a mixture of fuel and air flowing in from the intake pipe is burned. The combustion of the mixture generates exhaust gas.

Figure 1(B) is a schematic diagram of the entire independent throttle type two-cylinder engine unit of this embodiment. The two-cylinder engine unit 1 further includes two independent exhaust pipes 13A, 13B, a collective exhaust pipe 14, a pre-catalyst sensor 15, and a control device 16.

Two independent exhaust pipes 13A, 13B are provided corresponding to two cylinders 11A, 11B, respectively. The two independent exhaust pipes 13A, 13B are independent of each other. Exhaust gas from the corresponding cylinders 11A, 11B flows through each of the two independent exhaust pipes 13A, 13B. The downstream ends of the two independent exhaust pipes 13A, 13B are each connected to a collective exhaust pipe 14.

The exhaust manifold 14 includes a manifold 141 where the two independent exhaust pipes 13A, 13B join together, and a catalyst 142 that is provided downstream of the manifold 141 in the exhaust gas flow direction. Exhaust gas from each of the two cylinders 11A, 11B flows through the manifold 141. The catalyst 142 is, for example, a three-way catalyst. The catalyst 142 purifies the exhaust gas that flows through the exhaust manifold 14.

One pre-catalyst sensor 15 is provided in the collecting section 141 of the collecting exhaust pipe 14. The pre-catalyst sensor 15 detects the oxygen ratio or oxygen concentration in the exhaust gas flowing into the catalyst 142 from each of the two cylinders 11A, 11B. In this embodiment, the pre-catalyst sensor 15 is a pre-catalyst oxygen sensor that detects the oxygen ratio (rich/lean) in the exhaust gas flowing into the catalyst 142 from each of the two cylinders 11A, 11B. The pre-catalyst sensor 15 is electrically connected to the control device 16. The pre-catalyst sensor 15 sends the detected oxygen ratio to the control device 16 as a detection result.

Figure 1 (C) shows the relationship between combustion timing and crankshaft rotation speed in an independent throttle type two-cylinder engine unit of this embodiment. The crankshaft 12 is configured so that at least one combustion interval X1 in the rotation cycle of the crankshaft 12 is 240 degrees or more in crank angle. This reduces interference between exhaust gases flowing into the catalyst 142 from each cylinder 11A, 11B corresponding to each combustion that constitutes at least one combustion interval X1.

The control device 16 is configured to detect an imbalance in the air-fuel ratio between the two cylinders 11A and 11B using the detection results of the pre-catalyst sensor 15 detecting the oxygen ratio or oxygen concentration in the exhaust gas with reduced interference flowing into the catalyst 142 from each of the two cylinders 11A and 11B at the collection section 141.

<Detection of air-fuel ratio imbalance between cylinders>
2 is a flowchart showing the process of detecting an imbalance in the air-fuel ratio between the cylinders according to the present embodiment. The control device 16 performs the process of detecting an imbalance in the air-fuel ratio between the cylinders for each of the two cylinders 11A and 11B. Here, it is assumed that the two-cylinder engine unit 1 is already in operation.

First, the control device 16 acquires the oxygen ratio in the exhaust gas in the collection section 141 detected by the pre-catalyst sensor 15. The control device 16 acquires the oxygen ratio from the pre-catalyst sensor 15 periodically or irregularly (step S11).

Next, the control device 16 determines whether the air-fuel ratio in each cylinder 11A, 11B is rich or lean with respect to the target air-fuel ratio based on the detection results obtained from the pre-catalyst sensor 15 (step S12).

Then, the control device 16 compares the judgment result with the previous judgment result. For example, when the control device 16 acquires the oxygen ratio detected by the pre-catalyst sensor 15 for the first time after the operation of the two-cylinder engine unit 1, the control device 16 determines that the first judgment result is different from the previous judgment result because the previous (0th) judgment result does not exist. In other words, the control device 16 compares the Nth judgment result with the N-1th judgment result (step S13).

When the Nth judgment result and the N-1th judgment result for a certain cylinder differ (NO in step S13), the control device 16 executes feedback control to correct the amount of fuel supplied to the cylinder being judged by a predetermined initial correction amount so as to cancel the Nth judgment result. However, feedback control using the initial correction amount does not require the next N+1th judgment result to be different from the Nth judgment result. For example, when the N-1th judgment result for a certain cylinder is lean and the Nth judgment result is rich, the control device 16 reduces the amount of fuel supplied by a predetermined amount so that the N+1th judgment result becomes lean (to cancel the rich judgment) (step S14).

The control device 16 controls the fuel supplied to each cylinder 11A, 11B so that the air-fuel ratio judgment result for each cylinder 11A, 11B alternates between rich and lean at a certain interval. This allows the air-fuel ratio in each cylinder 11A, 11B to be maintained close to the target air-fuel ratio. However, even if such feedback control is performed, there are cases where the rich or lean air-fuel ratio is not improved due to some factor.

If the Nth judgment result and the N-1th judgment result are the same (YES in step S13), the control device 16 calculates the cumulative correction amount (step S15).

Next, the control device 16 compares the calculated cumulative correction amount with a predetermined threshold value (step S16).

If the cumulative correction amount is equal to or less than the threshold value (NO in step S16), the control device 16 executes feedback control to correct the amount of fuel supplied to the cylinder being judged by the calculated cumulative correction amount so as to eliminate the Nth judgment result (step S17).

After performing feedback control using the cumulative correction amount, if the new judgment result is different from the previous judgment result (NO in step S13), the control device 16 performs feedback control again using the initial correction amount to eliminate the new judgment result. On the other hand, if the new judgment result is the same as the previous judgment result even after performing feedback control using the cumulative correction amount (YES in step S13), the control device 16 calculates a new cumulative correction amount that is larger than the previous cumulative correction amount (step S15). That is, if the richness or leanness of the air-fuel ratio is not improved even after performing feedback control using the cumulative correction amount, the control device 16 increases the cumulative correction amount for each feedback control. Note that the initial cumulative correction amount and the change amount of the correction amount for each feedback control may be predetermined. As a result of repeating such feedback control, the calculated cumulative correction amount may exceed a threshold value.

If the cumulative correction amount is greater than the threshold value (YES in step S16), the control device 16 determines that an imbalance in the air-fuel ratio between the cylinders being judged has occurred (step S18).

Figure 3 is a diagram showing an example of the change in the fuel correction amount when an imbalance between cylinders occurs in a cylinder of the two-cylinder engine unit of this embodiment. In the diagram, the horizontal axis indicates time, and the vertical axis indicates the correction amount of fuel supplied to the target cylinder 11A in feedback control. Also, it is assumed that the target cylinder 11A is normal in period T1, and that an imbalance between cylinders in the air-fuel ratio occurs in the target cylinder 11A in period T2. For reference, the judgment result of the air-fuel ratio for the target cylinder is also shown. Each arrow in the judgment result column represents one judgment.

At the beginning of period T1, the control device 16 determines that the air-fuel ratio of the target cylinder 11A is lean multiple times in succession based on the detection results obtained from the pre-catalyst sensor 15. In this case, the control device 16 repeatedly executes feedback control using the integrated correction amount A1. The control device 16 increases the integrated correction amount A1 for each feedback control. In other words, the control device 16 increases the amount of fuel supplied to the target cylinder 11A for each feedback control.

Then, the control device 16 determines that the air-fuel ratio of the target cylinder 11A is rich. In this case, the control device 16 executes feedback control using the initial correction amount A2. The control device 16 executes feedback control to eliminate the lean result of the previous determination. In other words, the control device 16 reduces the amount of fuel supplied to the target cylinder 11A by the initial correction amount.

Then, the control device 16 judges the air-fuel ratio of the target cylinder 11A to be rich several times in succession. In this case, the control device 16 reduces the fuel supplied to the target cylinder 11A by the integrated correction amount A1 for each feedback control. Since the target cylinder 11A is normal during period T1, the control device 16's judgment result of the air-fuel ratio for the target cylinder 11A, when viewed over a certain period of time, alternates between rich and lean overall. As a result, the air-fuel ratio in the target cylinder 11A is maintained at a value close to the target air-fuel ratio.

During period T2, the control device 16 continues to determine the air-fuel ratio of the target cylinder 11A based on the detection result obtained from the pre-catalyst sensor 15. However, during period T2, since an imbalance in the air-fuel ratio between cylinders occurs in the target cylinder 11A, the determination result may not be resolved even if feedback control is performed. For example, as shown in the figure, immediately after the boundary line L where the imbalance in the air-fuel ratio between cylinders occurs, feedback control (feedback control using an integrated correction amount) is performed to reduce the fuel supplied to the target cylinder 11A. Since the amount of fuel supplied to the target cylinder 11A decreases with each feedback control due to the execution of this feedback control, if feedback control is repeated multiple times, the control device 16 should determine that the air-fuel ratio of the target cylinder 11A is lean.

However, because some abnormality has occurred in the target cylinder 11A, the air-fuel ratio determination for the target cylinder 11A remains rich. Therefore, the cumulative correction amount increases with each feedback control, and the amount of fuel supplied to the target cylinder 11A continues to be reduced.

However, a threshold is set in advance for the cumulative correction amount used in the feedback control. When the calculated cumulative correction amount exceeds the threshold, the control device 16 determines that an imbalance in the air-fuel ratio between the cylinders occurs in the target cylinder 11A. When the control device 16 detects an imbalance between the cylinders, it executes a process to notify the driver or the like to inspect the engine unit.

In the above explanation, the independent throttle type 2-4 cylinder engine unit is a 2-cylinder engine unit 1. However, the independent throttle type 2-4 cylinder engine unit may be a 3-cylinder or 4-cylinder engine unit. In short, the type of the 2-4 cylinder engine unit is not particularly limited as long as at least one combustion interval is 240 degrees or more in the crankshaft rotation cycle.

The embodiments and modifications described and/or illustrated in this specification are intended to facilitate understanding of the present disclosure and are not intended to limit the ideas of the present disclosure. The above-mentioned embodiments and modifications may be modified or improved without departing from the spirit of the present disclosure. The spirit of the present disclosure includes equivalent elements, modifications, deletions, combinations (e.g., combinations of features across the embodiments and modifications), improvements, and changes that may be recognized by a person skilled in the art based on the embodiments disclosed in this specification. The limitations in the claims should be interpreted broadly based on the terms used in the claims and should not be limited to the embodiments and modifications described in this specification or in the prosecution of this application. Such embodiments and modifications should be interpreted as non-exclusive. For example, in this specification, the terms "preferably" and "good" are non-exclusive and mean "preferably but not limited to" and "good but not limited to".

1: 2-cylinder engine unit 11A, 11B: Cylinder 111: Piston 112: Combustion chamber 12: Crankshaft 13A, 13B: Independent exhaust pipe 14: Collective exhaust pipe 141: Collecting section 142: Catalyst 15: Pre-catalyst sensor 16: Control device X1: Combustion interval

Claims (2)

The independent throttle type 2-4 cylinder engine unit is
Two to four cylinders, each of which forms a combustion chamber with a piston,
a crankshaft that rotates as fuel is combusted in the combustion chamber;
Two to four independent exhaust pipes provided corresponding to the two to four cylinders, respectively, through which exhaust gas from the corresponding cylinders flows;
a collecting exhaust pipe including a collecting section where the two to four independent exhaust pipes are collected and a catalyst provided downstream of the collecting section in a flow direction of the exhaust gas;
a pre-catalyst sensor provided at the collecting portion of the collecting exhaust pipe for detecting an oxygen ratio or an oxygen concentration in the exhaust gas flowing into the catalyst from each of the second to fourth cylinders;
A control device,
the crankshaft is configured so that at least one combustion interval in a rotation cycle of the crankshaft is equal to or greater than 240 degrees in crank angle, thereby reducing interference between the exhaust gases flowing into the catalyst from the cylinders corresponding to the combustions constituting the at least one combustion interval;
The control device is configured to detect an imbalance in the air -fuel ratio between cylinders by detecting an abnormality in the air-fuel ratio in at least one of the two to four cylinders provided in the independent throttle type 2-4 cylinder engine unit using a detection result obtained by the pre- catalyst sensor at the collecting portion of the oxygen ratio or oxygen concentration in the exhaust gas flowing into the catalyst from the two to four cylinders , whereby the interference is reduced by making at least one combustion interval equal to or greater than 240 degrees in crank angle. 2. The independent throttle type 2-4 cylinder engine unit according to claim 1,
The pre-catalyst sensors are pre-catalyst oxygen sensors that detect the oxygen ratio in the exhaust gas flowing into the catalyst from each of the second to fourth cylinders.

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