Alcohol-containing fuel engine system and vehicle

Abstract

In an alcohol-containing fuel engine system (1), an exhaust passage (12) includes a high-thermal-conductivity in-engine exhaust passage (121), a low-thermal-conductivity upstream exhaust passage (122), a catalyst (123), an intermediate exhaust passage (124), and a muffler (125). The high-thermal-conductivity in-engine exhaust passage (121) is configured such that the length (L1) thereof in an exhaust gas flow direction is less than the length (L2) of a most upstream part (1222) when the low-thermal-conductivity upstream exhaust passage (122) is divided into five portions of equal length, and is greater than the half of the length (L2) of the most upstream part (1222).

Description

Alcohol-containing fuel engine system and vehicle

[0001] The present invention relates to an engine system using an alcohol-containing fuel and a vehicle equipped with the same.

[0002] Alcohol-containing fuels, which contain alcohol, are known as fuels supplied to engines. There are several types of alcohol-containing fuels with different alcohol concentrations. Vehicles that can run on several types of alcohol-containing fuels are disclosed in, for example, Patent Documents 1 to 3.

[0003] Patent Document 1 discloses a vehicle equipped with two exhaust passages for its engine. When using alcohol-containing fuel with a high alcohol concentration, this vehicle directs exhaust gas from the engine through one exhaust passage and also directs it through the other exhaust passage by controlling an on-off valve, thereby suppressing an increase in exhaust pressure.

[0004] Patent Document 2 discloses a vehicle equipped with a concentration estimation unit that estimates the alcohol concentration contained in fuel supplied to the engine. In this vehicle, if the estimation of the alcohol concentration is incomplete during a cold start of the engine, the amount of intake air supplied to the engine is increased, and the alcohol-containing fuel supplied to the engine is controlled so that the air-fuel ratio becomes rich relative to the increased intake air amount.

[0005] Patent Document 3 discloses a vehicle equipped with a concentration detection means for detecting the alcohol concentration contained in fuel supplied to the engine, an exhaust passage through which exhaust gas flows from the engine, and a diversion passage for diverting a portion of the exhaust gas flowing through the exhaust passage. In this vehicle, the amount of exhaust gas diverted to the diversion passage is controlled according to the detected alcohol concentration. An injector is provided in the diversion passage. The injector injects alcohol-containing fuel into the exhaust gas flowing through the diversion passage, generating a mixed gas of the exhaust gas and the alcohol-containing fuel. The mixed gas is vaporized, etc., to reform the exhaust gas.

[0006] Japanese Patent Application Laid-Open No. 05-005428 Japanese Patent No. 5979060 Japanese Patent Application Laid-Open No. 2009-138695

[0007] Alcohol-containing fuels generate less heat when burned than gasoline. Therefore, in vehicles using alcohol-containing fuels, it is difficult to quickly raise the catalyst that purifies exhaust gases to its activation temperature. This is particularly true during cold starts, when starting a completely cold engine. Furthermore, in vehicles using multiple alcohol fuels with different alcohol concentrations, the amount of heat generated by combustion varies depending on the alcohol concentration. The difference in alcohol concentration causes variations in the temperature of the exhaust gas flowing into the catalyst. As a result, the time it takes for the catalyst to reach its activation temperature also varies. Furthermore, different alcohol concentrations result in different theoretical air-fuel ratios. Therefore, it is necessary to adjust the fuel injection amount for each alcohol concentration. However, this complicates fuel injection control and places greater constraints on fuel injection control.

[0008] An object of the present invention is to provide an engine system and vehicle using an alcohol-containing fuel that can quickly activate a catalyst while increasing the degree of freedom in fuel injection control.

[0009] The present inventors have studied a configuration for quickly activating a catalyst when using an alcohol-containing fuel. Exhaust gas emitted from an engine passes through an exhaust passage and is released into the atmosphere. The temperature of the exhaust gas decreases the further downstream in the exhaust passage. If a catalyst is installed downstream in the exhaust passage, i.e., farther from the engine, low-temperature exhaust gas flows into the catalyst. As a result, it becomes difficult to quickly activate the catalyst. Therefore, it is possible to install the catalyst upstream in the exhaust passage, i.e., near the engine, so that higher-temperature exhaust gas flows into the catalyst. However, because exhaust gas pressure is high upstream in the exhaust passage, the location of the catalyst more upstream in the exhaust passage is not necessarily the best.

[0010] The inventors have investigated the temperature variation of exhaust gas flowing into a catalyst when using multiple types of alcohol-containing fuel. One possible method for maintaining a constant temperature of exhaust gas flowing into the catalyst even when the alcohol concentration changes is to make the catalyst position adjustable. However, changing the catalyst position every time the type of fuel changes is cumbersome and unrealistic. Furthermore, in vehicles, particularly saddle-type vehicles, it is desirable not to change the catalyst position due to the catalyst placement space and appearance considerations. Another possible approach is to provide a bypass passage so that the length of the exhaust passage changes depending on the alcohol concentration. However, a bypass passage complicates the vehicle structure.

[0011] The inventor further investigated the temperature variation of exhaust gas flowing into the catalyst. One of the factors that causes the temperature of exhaust gas to decrease as it travels downstream in the exhaust passage is heat removal by the piping that makes up the exhaust passage. The exhaust passage is the passage through which exhaust gas passes from the engine's combustion chamber until it is released into the atmosphere, and is composed of an exhaust port, an exhaust pipe, etc. Exhaust gas emitted from the combustion chamber first passes through the exhaust port before exiting the engine. An exhaust pipe is connected to the exhaust port. Exhaust gas that leaves the exhaust port passes through the exhaust pipe and is released into the atmosphere. The inventor noticed that the exhaust passage is composed of at least two types of components: the exhaust port and the exhaust pipe.

[0012] The exhaust port is made of a material with high thermal conductivity for heat dissipation. The exhaust port is located, for example, inside the head cylinder of an engine. The head cylinder is a large component of a vehicle and has a large heat capacity. Therefore, heat from the exhaust port, which is heated by exhaust gas, is easily transferred to the head cylinder. On the other hand, the exhaust pipe is generally located outside the engine and made of a material with lower thermal conductivity than the exhaust port. In other words, if the exhaust port and the exhaust pipe are considered to be the same length, the exhaust gas passing through the exhaust passage loses a large amount of heat at the exhaust port. The inventors believed that if the amount of heat dissipated at the exhaust port, which has high thermal conductivity, and the amount of heat dissipated at the exhaust pipe, which has low thermal conductivity, could be controlled, the catalyst could be activated quickly even with alcohol-containing fuel, and the temperature variation of the exhaust gas flowing into the catalyst due to changes in alcohol concentration even when the catalyst is in the same position could be suppressed.

[0013] (1) An alcohol-containing fuel engine system of the present invention comprises: an engine including a combustion chamber for burning an alcohol-containing fuel; and an exhaust passage through which exhaust gas discharged from the combustion chamber flows, wherein the exhaust passage comprises: a high thermal conductivity internal-engine exhaust passage provided within the engine and connected to the combustion chamber, and through which exhaust gas discharged from the combustion chamber flows; a low thermal conductivity upstream exhaust passage provided outside the engine and connected to the downstream end of the high thermal conductivity internal-engine exhaust passage, and through which exhaust gas that has passed through the high thermal conductivity internal-engine exhaust passage flows; a catalyst that includes an upstream end provided at the same position as the downstream end of the low thermal conductivity upstream exhaust passage in the flow direction of the exhaust gas, and purifies the exhaust gas that has passed through the low thermal conductivity upstream exhaust passage; an intermediate exhaust passage provided downstream of the catalyst in the flow direction of the exhaust gas, and through which exhaust gas that has passed through the catalyst flows; and a muffler provided downstream of the intermediate exhaust passage in the flow direction of the exhaust gas, through which exhaust gas that has passed through the intermediate exhaust passage flows, and which reduces noise generated by the exhaust gas. the low thermal conductivity upstream exhaust passage is divided into five sections, namely, a most upstream section, an upstream section, an intermediate section, a downstream section, and a most downstream section, each having an equal length, in order from upstream in the flow direction of the exhaust gas; and the high thermal conductivity internal-engine exhaust passage is configured so that the length in the flow direction of the exhaust gas is shorter than the length of the most upstream section when the low thermal conductivity upstream exhaust passage from the downstream end of the high thermal conductivity internal-engine exhaust passage to the upstream end of the catalyst provided upstream of the muffler and the intermediate exhaust passage is divided into five sections, namely, a most upstream section, an upstream section, an intermediate section, a downstream section, and a most downstream section, each having an equal length, in order from upstream in the flow direction of the exhaust gas, and is longer than half the length of the most upstream section, so as to reduce the amount of heat of the exhaust gas that is removed by the high thermal conductivity internal-engine exhaust passage, which has a higher thermal conductivity than the low thermal conductivity upstream exhaust passage, and to suppress a difference in temperature of the exhaust gas flowing into the catalyst, which occurs when each of the plurality of alcohol-containing fuels with different alcohol concentrations is burned.

[0014] The above-described alcohol-containing fuel engine system can use multiple alcohol-containing fuels with different alcohol concentrations. Furthermore, in the alcohol-containing fuel engine system, the catalyst is located upstream of the muffler, i.e., closer to the combustion chamber in the exhaust gas flow direction. Furthermore, in the alcohol-containing fuel engine system, the length of the high-thermal conductivity internal exhaust passage is shorter than the length of the most upstream portion of the low-thermal conductivity upstream exhaust passage. That is, the length of the high-thermal conductivity internal exhaust passage, which easily absorbs the temperature of the exhaust gas, is set short. This configuration enables early activation of the catalyst even with alcohol-containing fuels, which have a lower calorific value than gasoline. It also reduces the amount of heat dissipated in the high-thermal conductivity internal exhaust passage, effectively reducing the total amount of heat dissipated in the high-thermal conductivity internal exhaust passage and the low-thermal conductivity upstream exhaust passage. As a result, even if the alcohol concentration in the fuel changes while the distance from the combustion chamber to the catalyst remains the same, variation in the temperature of the exhaust gas flowing into the catalyst is suppressed, thereby reducing the constraints on fuel injection control that is set for multiple alcohol concentrations. Therefore, the above-described alcohol-containing fuel engine system enables early activation of the catalyst while increasing the flexibility of fuel injection control.

[0015] (2) In the alcohol-containing fuel engine system of (1) above, the lower limit of the alcohol concentration in the alcohol-containing fuel is 0% by volume, and the high thermal conductivity engine exhaust passage is configured so that the length in the flow direction of the exhaust gas is shorter than the length of the most upstream portion and longer than half the length of the most upstream portion, so as to suppress the difference in temperature of the exhaust gas flowing into the catalyst when each of multiple types of alcohol-containing fuels, including those with an alcohol concentration of 0% by volume, is burned.

[0016] The above-described alcohol-containing fuel engine system can use not only fuels containing alcohol, but also fuels not containing alcohol (e.g., hydrocarbon fuels). The above-described alcohol-containing fuels include, for example, E0 and M0, and alcohol-containing fuels with alcohol concentrations of E0, M0, or higher can be used. When a large number of types of fuels are usable, the temperature of the exhaust gas flowing into the catalyst tends to vary widely. The above-described alcohol-containing fuel engine system (2) is particularly suitable for cases where such exhaust gas temperature variation tends to be large.

[0017] (3) In the alcohol-containing fuel engine system of (1) or (2) above, the exhaust passage may be configured to pass exhaust gas resulting from combustion of the alcohol-containing fuel supplied so as to make the air-fuel ratio rich during cold start through the high thermal conductivity internal engine exhaust passage configured so that the length in the flow direction of the exhaust gas is shorter than the length of the most upstream portion and longer than half the length of the most upstream portion.

[0018] It takes longer to heat a cold catalyst to its activation temperature than to heat a warmed catalyst to its activation temperature. Furthermore, compared to using an alcohol-containing fuel with a low alcohol concentration, the amount of heat generated is smaller when using an alcohol-containing fuel with a high alcohol concentration, and it takes longer to heat the catalyst to its activation temperature. In the alcohol-containing fuel engine system described above in (3), the alcohol-containing fuel is supplied to the engine so that the air-fuel ratio is rich during cold start. Additionally, variations in the temperature of the exhaust gas flowing into the catalyst due to differences in alcohol concentration are suppressed. In other words, a rich air-fuel ratio increases the amount of heat generated, and even with a fuel with a high alcohol concentration, a heat generation amount similar to that of a fuel with a low alcohol concentration can be obtained. Therefore, the above-described alcohol-containing fuel engine system enables early activation of the catalyst while increasing the flexibility of fuel injection control.

[0019] (4) In any of the alcohol-containing fuel engine systems (1) to (3) above, the high thermal conductivity engine-internal exhaust passage may be configured so that the length from the downstream end of the high thermal conductivity engine-internal exhaust passage to the upstream end of the catalyst is shorter than the length of the most upstream portion of the low thermal conductivity upstream exhaust passage, and is longer than half the length of the most upstream portion, by providing the catalyst upstream of the muffler and the intermediate exhaust passage in the flow direction of the exhaust gas, so that the length from the downstream end of the high thermal conductivity engine-internal exhaust passage to the upstream end of the catalyst is shorter than the length from the upstream end of the catalyst to the downstream end of the exhaust passage.

[0020] In the alcohol-containing fuel engine system described above in (4), the length of the portion of the exhaust path outside the engine upstream of the catalyst is shorter than the portion of the exhaust path downstream of the catalyst. In other words, the catalyst is located closer to the engine in terms of the entire exhaust path. Therefore, the above-described alcohol-containing fuel engine system can quickly activate the catalyst while increasing the degree of freedom in fuel injection control.

[0021] (5) In the alcohol-containing fuel engine system according to any one of (1) to (4), the high thermal conductivity engine internal exhaust passage may be made of aluminum or an aluminum alloy, and the low thermal conductivity upstream exhaust passage may be made of stainless steel, titanium, or a titanium alloy.

[0022] Aluminum or aluminum alloys have higher thermal conductivity than stainless steel, titanium, or titanium alloys. Aluminum or aluminum alloys are also lightweight. Therefore, aluminum or aluminum alloys are suitable as materials for high-thermal-conductivity internal exhaust passages installed inside engines. Stainless steel, titanium, or titanium alloys have high strength and excellent corrosion resistance. Therefore, stainless steel, titanium, or titanium alloys are suitable as materials for low-thermal-conductivity upstream exhaust passages installed outside engines.

[0023] (6) A vehicle of the present invention is equipped with any one of the alcohol-containing fuel engine systems (1) to (5) above.

[0024] Hereinafter, each configuration and terminology of the present invention will be explained.

[0025] An alcohol-containing fuel is a fuel composition containing alcohol as a major component. The term "major component" as used herein means that alcohol is not an impurity or an unavoidable mixture, and includes, for example, at least 1% by volume. An alcohol-containing fuel may also contain a hydrocarbon fuel. A hydrocarbon fuel may also be included as a major component. Examples of alcohols include, but are not limited to, methanol, ethanol, propanol, and butanol. The alcohol concentration (volume concentration) may be greater than 0% by volume or substantially 100% by volume. Examples of hydrocarbon fuels include, but are not limited to, gasoline. E0, E3, E10, E15, E20, E25, E85, and E100 may be used. E indicates the volume percent of ethanol in a gasoline-ethanol mixture. M0, M3, M10, M15, M20, M25, M85, and M100 may be used. M indicates the volume percent of methanol in a gasoline-methanol mixture. A mixture of a different composition but with an equivalent concentration may also be used. As long as it is applicable to the engine, the composition and alcohol concentration of the alcohol-containing fuel are not particularly limited.

[0026] The engine is not particularly limited as long as the lower limit of the alcohol concentration of the applicable alcohol-containing fuel is 0% by volume or higher. Examples of the lower limit include, in volume percent, 0, 3, 10, 15, 20, 25, 85, and 100. A lower limit of 20% by volume means that the engine is capable of using alcohol-containing fuel with an alcohol concentration of 20% by volume or higher. A lower limit of 20% by volume means that the engine is capable of using alcohol-containing fuel with an alcohol concentration of 20-100% by volume or higher. The smaller the lower limit, the more alcohol-containing fuels with various alcohol concentrations can be used. The engine may be configured so that the lower limit of the alcohol concentration of the applicable alcohol-containing fuel is 0% by volume. In other words, the engine may be capable of using hydrocarbon fuels that do not contain alcohol (e.g., gasoline). The engine may be configured so that the lower limit of the alcohol concentration of the applicable alcohol-containing fuel is 100% by volume. In other words, the engine may be capable of using fuel composed only of alcohol. The upper limit of the alcohol concentration is not particularly limited. In short, the engine may be adapted to use multiple types of alcohol-containing fuels with different alcohol concentrations. Regarding the number of cylinders, the engine may be, for example, a single-cylinder engine. The engine may be, for example, a two-cylinder engine. The engine may be, for example, an engine with two or more cylinders. If the engine has multiple cylinders (combustion chambers), at least one of the multiple exhaust passages may correspond to the exhaust passage described in the claims. The combustion chamber may have, for example, a cylindrical shape.

[0027] The exhaust passage is connected to, for example, a combustion chamber of an engine. The exhaust passage refers to, for example, a passage through which exhaust gas flows from the combustion chamber to the outside of a vehicle. The upstream end of the exhaust passage is located, for example, at a position where the combustion chamber and the exhaust passage are connected. The downstream end of the exhaust passage is located, for example, at a position where the exhaust gas is discharged into the atmosphere. The exhaust passage constitutes, for example, a continuous path from the combustion chamber to the exhaust gas being released into the atmosphere. The length of the exhaust passage does not change, for example, depending on the alcohol concentration of an alcohol-containing fuel. The exhaust passage may include a branch passage. The branch passage is, for example, an EGR (Exhaust Gas Recirculation) passage. The EGR passage branches off from, for example, a high thermal conductivity internal engine exhaust passage and connects to an intake passage. In such a configuration, the length of the high thermal conductivity internal engine exhaust passage does not include, for example, the length of the branch passage. More specifically, for example, if the exhaust passage includes an EGR passage, the length of the high thermal conductivity internal-engine exhaust passage is the length from the upstream end of the high thermal conductivity internal-engine exhaust passage connected to the combustion chamber to the downstream end of the high thermal conductivity internal-engine exhaust passage connected to the low thermal conductivity upstream exhaust passage, and does not include the length of the EGR passage. Furthermore, if the engine has multiple cylinders, the exhaust passage may include, for example, multiple low thermal conductivity upstream exhaust passages. The exhaust passage may include, for example, at least one exhaust manifold bundling multiple low thermal conductivity upstream exhaust passages. In such a configuration, the length of the low thermal conductivity upstream exhaust passage corresponds to the length of one low thermal conductivity upstream exhaust passage through which exhaust gas discharged from one combustion chamber passes, and does not include the lengths of other low thermal conductivity upstream exhaust passages. The exhaust passage may include, from upstream to downstream, for example, a high thermal conductivity internal-engine exhaust passage, a low thermal conductivity upstream exhaust passage, and an intermediate exhaust passage. The exhaust passage may also include, for example, a downstream exhaust passage provided downstream of a muffler. In addition, when the exhaust passage is configured by connecting multiple parts, the divisions of the passages do not have to coincide with the divisions (connections) of the parts. Furthermore, the length of each passage in the direction of exhaust gas flow refers to, for example, the length along the center line of each passage.

[0028] The high thermal conductivity internal-engine exhaust passage is provided, for example, within an engine. The high thermal conductivity internal-engine exhaust passage is separated from the combustion chamber, for example, by an exhaust valve. The high thermal conductivity internal-engine exhaust passage may, for example, extend linearly or may be curved. The high thermal conductivity internal-engine exhaust passage has, for example, a circular or substantially circular cross-sectional shape. The cross-sectional shape refers, for example, to the shape obtained by cutting the passage along a plane perpendicular to the flow direction of the exhaust gas (the extension direction of the high thermal conductivity internal-engine exhaust passage). The high thermal conductivity internal-engine exhaust passage has a higher thermal conductivity than, for example, a low thermal conductivity upstream exhaust passage. The high thermal conductivity internal-engine exhaust passage is made of, for example, aluminum or an aluminum alloy. A plurality of high thermal conductivity internal-engine exhaust passages may be provided, for example. For example, at least one high thermal conductivity internal-engine exhaust passage is provided for each combustion chamber. For example, at least one high thermal conductivity internal-engine exhaust passage is provided for each engine.

[0029] The upstream end of the high thermal conductivity internal-engine exhaust passage corresponds to, for example, the upstream end of the exhaust passage. The upstream end of the high thermal conductivity internal-engine exhaust passage is located, for example, at a position where the combustion chamber and the high thermal conductivity internal-engine exhaust passage are connected. The upstream end of the high thermal conductivity internal-engine exhaust passage is located, for example, at the position of the exhaust valve. The downstream end of the high thermal conductivity internal-engine exhaust passage is located, for example, at a position where the high thermal conductivity internal-engine exhaust passage and the low thermal conductivity upstream exhaust passage are connected. When multiple high thermal conductivity internal-engine exhaust passages are provided, at least two high thermal conductivity internal-engine exhaust passages may be combined. In this case, the downstream end of the high thermal conductivity internal-engine exhaust passage corresponds to the downstream end of a combined passage where at least two high thermal conductivity internal-engine exhaust passages are combined. In the exhaust gas flow direction, the length of the high thermal conductivity internal-engine exhaust passage is, for example, the length from the upstream end to the downstream end of the high thermal conductivity internal-engine exhaust passage. The length of the high thermal conductivity internal-engine exhaust passage is, for example, shorter than the longitudinal length of the head cylinder in which the combustion chamber is provided. The length of the high thermal conductivity engine internal exhaust passage is shorter than, for example, the length of the head cylinder in the left-right direction. The length of the high thermal conductivity engine internal exhaust passage is shorter than, for example, the shorter of the length of the head cylinder in the front-rear direction and the length of the head cylinder in the left-right direction. Note that the front-rear direction corresponds to the front-rear direction of a vehicle when the alcohol-containing fuel engine system is mounted on the vehicle. The same applies to the left-right direction.

[0030] In a cross-sectional view of the engine cut along a plane perpendicular to the central axis of the combustion chamber, the downstream end of the high thermal conductivity internal-engine exhaust passage is located, for example, within an imaginary circle. The radius of the imaginary circle corresponds, for example, to the diameter (bore) of the combustion chamber. The center of the imaginary circle is located, for example, at the end of the inner surface of the combustion chamber closest to the high thermal conductivity internal-engine exhaust passage in a cross-sectional view of the engine cut along a plane perpendicular to the central axis of the combustion chamber. This end corresponds, for example, to the front end or rear end of the inner surface of the combustion chamber in a cross-sectional view of the engine cut along a plane perpendicular to the central axis of the combustion chamber. This end may correspond, for example, to the left end or right end of the inner surface of the combustion chamber in a cross-sectional view of the engine cut along a plane perpendicular to the central axis of the combustion chamber. This end may correspond, for example, to the upper end or lower end of the inner surface of the combustion chamber in a cross-sectional view of the engine cut along a plane perpendicular to the central axis of the combustion chamber.

[0031] The high thermal conductivity internal-engine exhaust passage reduces the amount of heat lost from the exhaust gas in the high thermal conductivity internal-engine exhaust passage, compared to, for example, a high thermal conductivity internal-engine exhaust passage configured to be longer than the length of the most upstream portion of a low thermal conductivity upstream exhaust passage.The high thermal conductivity internal-engine exhaust passage suppresses the difference in temperature of the exhaust gas flowing into the catalyst, which occurs when multiple types of alcohol-containing fuels with different alcohol concentrations are burned, compared to, for example, a high thermal conductivity internal-engine exhaust passage configured to be longer than the length of the most upstream portion of a low thermal conductivity upstream exhaust passage.

[0032] The high thermal conductivity engine internal exhaust passage is not provided with a sensor for detecting, for example, the oxygen concentration in the exhaust gas. The sensor is, for example, an oxygen sensor or an air-fuel ratio sensor. The high thermal conductivity engine internal exhaust passage does not include a hole for a sensor for detecting, for example, the oxygen concentration in the exhaust gas. The sensor for detecting the oxygen concentration in the exhaust gas is provided, for example, in an exhaust passage outside the engine. The sensor for detecting the oxygen concentration in the exhaust gas is provided, for example, downstream of the downstream end of the high thermal conductivity engine internal exhaust passage in the exhaust passage. The sensor for detecting the oxygen concentration in the exhaust gas is provided, for example, upstream of the catalyst in the exhaust passage. The sensor for detecting the oxygen concentration in the exhaust gas may be provided, for example, downstream of the catalyst in the exhaust passage. The sensor for detecting the oxygen concentration in the exhaust gas is provided, for example, in the low thermal conductivity upstream exhaust passage.

[0033] The low thermal conductivity upstream exhaust passage is provided, for example, outside the engine. The low thermal conductivity upstream exhaust passage is provided, for example, so as to be exposed to the outside of the vehicle. The low thermal conductivity upstream exhaust passage is provided, for example, so as to be exposed to the atmosphere. The low thermal conductivity upstream exhaust passage may, for example, extend linearly or may be curved. The low thermal conductivity upstream exhaust passage has, for example, a circular or substantially circular cross-sectional shape. The low thermal conductivity upstream exhaust passage may, for example, have a lower thermal conductivity than the high thermal conductivity in-engine exhaust passage. The low thermal conductivity upstream exhaust passage is, for example, made of stainless steel. The low thermal conductivity upstream exhaust passage is, for example, made of titanium or a titanium alloy.

[0034] The upstream end of the low thermal conductivity upstream exhaust passage is located, for example, at a position where the high thermal conductivity internal-engine exhaust passage and the low thermal conductivity upstream exhaust passage are connected. The upstream end of the low thermal conductivity upstream exhaust passage is located, for example, at the downstream end of the high thermal conductivity internal-engine exhaust passage. The downstream end of the high thermal conductivity internal-engine exhaust passage is located, for example, at the upstream end of the catalyst. In the exhaust gas flow direction, the length of the low thermal conductivity upstream exhaust passage is, for example, the length from the upstream end to the downstream end of the low thermal conductivity upstream exhaust passage.

[0035] The length of the low thermal conductivity upstream exhaust passage is set, for example, within a range that does not cause sintering of the catalyst. The length of the low thermal conductivity upstream exhaust passage is set, for example, within a range that allows the catalyst to be heated to its activation temperature. Similarly, the length of the high thermal conductivity internal-engine exhaust passage is set, for example, within a range that does not cause sintering of the catalyst. The length of the high thermal conductivity internal-engine exhaust passage is set, for example, within a range that allows the catalyst to be heated to its activation temperature. Within these ranges, the high thermal conductivity internal-engine exhaust passage is configured so that its length in the exhaust gas flow direction is shorter than the length of the most upstream portion of the low thermal conductivity upstream exhaust passage and longer than half the length of the most upstream portion. While maintaining this relationship, the specific dimensions of the high thermal conductivity internal-engine exhaust passage and the low thermal conductivity upstream exhaust passage are set appropriately depending on, for example, the type of vehicle.

[0036] The intermediate exhaust passage is provided, for example, outside the engine. The upstream end of the intermediate exhaust passage is provided, for example, at the downstream end of the catalyst. The downstream end of the intermediate exhaust passage is provided, for example, at the upstream end of the silencer. The intermediate exhaust passage is made of, for example, the same material as the low-thermal-conductivity upstream exhaust passage.

[0037] The catalyst is, for example, a catalytic converter for simultaneously converting carbon monoxide, hydrocarbons, and nitrogen oxides emitted from an engine. The catalyst is, for example, a three-way catalyst. The catalyst has, for example, a metal honeycomb structure. The surface of the honeycomb structure is coated with a catalytic precious metal (e.g., Pt, Pd, Rh, etc.). The catalyst may be a dedicated product for alcohol-containing fuels or a general-purpose product that is also used for gasoline fuels. The catalyst is, for example, provided in an exhaust passage. The catalyst is, for example, provided between a low-thermal conductivity upstream exhaust passage and an intermediate exhaust passage. The catalyst is, for example, housed in a casing connecting the low-thermal conductivity upstream exhaust passage and the intermediate exhaust passage. The catalyst is, for example, provided upstream of a silencer. The catalyst is, for example, not provided within a silencer. For example, one or more catalysts may be provided in the exhaust passage. When multiple catalysts are provided in the exhaust passage, the catalyst referred to in the present invention refers, for example, to the catalyst located most upstream.

[0038] A vehicle is a device for transportation. A vehicle is configured to operate in a manned or unmanned (automated) manner. A vehicle can be a personal transportation vehicle. For example, a vehicle may be a public transportation vehicle such as a bus. Examples of personal transportation vehicles include automobiles and saddle-type vehicles. A vehicle may or may not have wheels. Examples of vehicles without wheels include ships with propellers, drones and helicopters with propellers, snowmobiles, and watercraft. A vehicle may or may not have a cabin. Examples of vehicles with a cabin include automobiles and helicopters. One example of a vehicle is a saddle-type vehicle. A saddle-type vehicle is a vehicle equipped with a saddle-type seat. A saddle-type vehicle is a vehicle configured so that a passenger sits astride a saddle. The saddle-type vehicle is not limited to scooter-type, moped-type, off-road-type, and on-road-type motorcycles, but also includes snowmobiles, watercraft, all-terrain vehicles (ATVs), etc. The saddle-type vehicle may have at least one front wheel and at least one rear wheel. The saddle-type vehicle is not limited to motorcycles, but may be a three-wheeled vehicle having a pair of front or rear wheels, or a four-wheeled vehicle having a pair of front and rear wheels, respectively. The saddle-type vehicle may be configured to be able to turn in a lean position toward the inside of a curve. Saddle-type vehicles that can turn in a lean position require agility, so responsiveness in traveling to a starting operation by the rider and acceleration performance at the time of starting are important. In a saddle-type vehicle that can turn in a lean position, high responsiveness to a starting operation contributes to handling stability at the time of starting. Other examples of vehicles include golf cars, caterpillar-type snowmobiles, and snowplows.

[0039] According to the present invention, it is possible to quickly activate the catalyst while increasing the degree of freedom in fuel injection control.

[0040] Fig. 1(A) is a schematic diagram showing an alcohol-containing fuel engine system of this embodiment, and Fig. 1(B) is a schematic diagram showing the relationship between a high thermal conductivity engine internal exhaust passage and a low thermal conductivity upstream exhaust passage. Fig. 2 is a cross-sectional view showing an engine of the alcohol-containing fuel engine system of this embodiment. Fig. 3 is a schematic diagram showing a modified example of the alcohol-containing fuel engine system of this embodiment.

[0041] A vehicle according to an embodiment of the present invention will be described below with reference to the drawings. Note that the embodiment described below is merely an example. The present invention should not be construed as being limited in any way by the embodiment described below.

[0042] 1A is a schematic diagram showing an alcohol-containing fuel engine system 1 according to the present embodiment. The alcohol-containing fuel engine system 1 includes an engine 11 and an exhaust passage 12.

[0043] The engine 11 includes a combustion chamber 111 and a high thermal conductivity internal engine exhaust passage 121. The combustion chamber 111 is a space in which an alcohol-containing fuel is burned. The alcohol-containing fuel is injected, for example, by an injector (not shown). The alcohol-containing fuel may be injected into an intake pipe or into the combustion chamber. The alcohol-containing fuel is mixed with air and ignited by an ignition device in the combustion chamber to burn. The combustion of the alcohol-containing fuel produces exhaust gas.

[0044] Exhaust gas discharged from the combustion chamber 111 flows through the exhaust passage 12. The exhaust passage 12 includes a low thermal conductivity upstream exhaust passage 122, a catalyst 123, an intermediate exhaust passage 124, and a muffler 125.

[0045] The high thermal conductivity internal-engine exhaust passage 121 is connected to the combustion chamber 111. Exhaust gas discharged from the combustion chamber 111 flows through the high thermal conductivity internal-engine exhaust passage 121. The high thermal conductivity internal-engine exhaust passage 121 has a curved tubular shape. The high thermal conductivity internal-engine exhaust passage 121 extends from the combustion chamber 111 to the outer surface of the engine 11. In other words, the high thermal conductivity internal-engine exhaust passage 121 is provided inside the engine 11. The high thermal conductivity internal-engine exhaust passage 121 is made of an aluminum alloy containing aluminum as a main component.

[0046] The low thermal conductivity upstream exhaust passage 122 is connected to the downstream end 1211 of the high thermal conductivity internal-engine exhaust passage 121. The low thermal conductivity upstream exhaust passage 122 is provided outside the engine 11. Exhaust gas that has passed through the high thermal conductivity internal-engine exhaust passage 121 flows through the low thermal conductivity upstream exhaust passage 122. The low thermal conductivity upstream exhaust passage 122 is made of stainless steel. The low thermal conductivity upstream exhaust passage 122 has a lower thermal conductivity than the high thermal conductivity internal-engine exhaust passage 121.

[0047] The catalyst 123 includes an upstream end 1231 that is provided at the same position as the downstream end 1221 of the low thermal conductivity upstream exhaust passage 122 in the flow direction of the exhaust gas. That is, the upstream end 1231 of the catalyst 123 is provided at the same position as the downstream end 1221 of the low thermal conductivity upstream exhaust passage 122. The catalyst 123 is a three-way catalyst. The catalyst 123 purifies the exhaust gas that has passed through the low thermal conductivity upstream exhaust passage 122.

[0048] The intermediate exhaust passage 124 is provided downstream of the catalyst in the flow direction of the exhaust gas. Exhaust gas that has passed through the catalyst 123 flows through the intermediate exhaust passage 124.

[0049] The silencer 125 is provided downstream of the intermediate exhaust passage 124 in the flow direction of the exhaust gas. The exhaust gas that has passed through the intermediate exhaust passage 124 flows through the silencer 125. The silencer 125 reduces the sound generated by the exhaust gas.

[0050] 1B is a schematic diagram showing the relationship between the high thermal conductivity internal-engine exhaust passage and the low thermal conductivity upstream exhaust passage. For illustrative purposes, the high thermal conductivity internal-engine exhaust passage 121 is depicted as a straight line. The low thermal conductivity upstream exhaust passage 122 is divided into five sections, each of which has the same length, from upstream to downstream in the exhaust gas flow direction: a most upstream section 1222, an upstream section 1223, an intermediate section 1224, a downstream section 1225, and a most downstream section 1226. The high thermal conductivity internal-engine exhaust passage 121 is configured such that its length L1 in the exhaust gas flow direction is shorter than the length L2 of the most upstream section 1222 of the low thermal conductivity upstream exhaust passage 122, but is longer than half the length L2 of the most upstream section 1222.

[0051] In this way, by appropriately adjusting the length L1 of the high thermal conductivity engine exhaust passage 121 and the length L2 of the low thermal conductivity upstream exhaust passage 122, the amount of heat lost from the exhaust gas in the high thermal conductivity engine exhaust passage 121, which has a higher thermal conductivity than the low thermal conductivity upstream exhaust passage 122, is reduced. In other words, the total amount of heat lost in the high thermal conductivity engine exhaust passage 121 and the low thermal conductivity upstream exhaust passage 122 can be effectively reduced. As a result, the temperature difference in the exhaust gas flowing into the catalyst 123 that occurs when multiple alcohol-containing fuels with different alcohol concentrations are burned is suppressed. The alcohol-containing fuel engine system 1 reduces the need for separate fuel injection controls for multiple alcohol-containing fuels with different alcohol concentrations. Therefore, the alcohol-containing fuel engine system 1 allows for early activation of the catalyst 123 while increasing the flexibility of fuel injection control.

[0052] 2 is a cross-sectional view showing the engine of the alcohol-containing fuel engine system of this embodiment. This figure shows the engine cut along a plane perpendicular to the central axis of the combustion chamber 111, as viewed from below. The downstream end 1211 of the high thermal conductivity internal-engine exhaust passage 121 is located within an imaginary circle A1. In the cross-sectional view of the engine cut along a plane perpendicular to the central axis of the combustion chamber 111, the center of the imaginary circle A1 is located at the end of the inner surface of the combustion chamber 111 closest to the high thermal conductivity internal-engine exhaust passage 121. It is located at the front end. The radius of the imaginary circle A1 corresponds to the diameter D1 (bore) of the combustion chamber.

[0053] 3 is a schematic diagram showing a modification of the alcohol-containing fuel engine system of this embodiment. The catalyst 123 may be provided upstream of the silencer 125 and the intermediate exhaust passage 124 in the exhaust gas flow direction so that the length L3 from the downstream end 1211 of the high thermal conductivity internal-engine exhaust passage 121 to the upstream end 1231 of the catalyst 123 is shorter than the length L4 from the upstream end 1231 of the catalyst 123 to the downstream end 126 of the exhaust passage 12.

[0054] 1: Alcohol-containing fuel engine system 11: Engine 111: Combustion chamber 12: Exhaust passage 121: High thermal conductivity engine internal exhaust passage 1211: Downstream end of high thermal conductivity engine internal exhaust passage 122: Low thermal conductivity upstream exhaust passage 1221: Downstream end of low thermal conductivity upstream exhaust passage 1222: Most upstream portion 1223: Upstream portion 1224: Intermediate portion 1225: Downstream portion 1226: Most downstream portion 123: Catalyst 1231: Upstream end of catalyst 124: Intermediate exhaust passage 125: Muffler 126: Downstream end of exhaust passage

Claims

1. An alcohol-containing fuel engine system comprising: an engine including a combustion chamber for burning an alcohol-containing fuel; and an exhaust passage through which exhaust gas discharged from the combustion chamber flows, wherein the exhaust passage includes: a high thermal conductivity in-engine exhaust passage provided in the engine and connected to the combustion chamber, through which exhaust gas discharged from the combustion chamber flows; a low thermal conductivity upstream exhaust passage provided outside the engine and connected to a downstream end of the high thermal conductivity in-engine exhaust passage, through which exhaust gas that has passed through the high thermal conductivity in-engine exhaust passage flows; a catalyst provided at a position of an upstream end at a downstream end of the low thermal conductivity upstream exhaust passage in the flow direction of the exhaust gas, for purifying the exhaust gas that has passed through the low thermal conductivity upstream exhaust passage; an intermediate exhaust passage provided downstream of the catalyst in the flow direction of the exhaust gas, through which exhaust gas that has passed through the catalyst flows; and a muffler provided downstream of the intermediate exhaust passage in the flow direction of the exhaust gas, through which exhaust gas that has passed through the intermediate exhaust passage flows and which reduces noise generated by the exhaust gas; the low thermal conductivity upstream exhaust passage is divided in the flow direction of the exhaust gas into five parts: an uppermost upstream part, an upstream part, a middle part, a downstream part, and a lowermost downstream part, each having an equal length; the high thermal conductivity in-engine exhaust passage is configured to reduce the amount of heat of the exhaust gas taken away by the high thermal conductivity in-engine exhaust passage having a higher thermal conductivity than the low thermal conductivity upstream exhaust passage, and to suppress the difference in temperature of the exhaust gas flowing into the catalyst when each of a plurality of types of the alcohol-containing fuels having different alcohol concentrations is burned, and the length of the high thermal conductivity in-engine exhaust passage in the flow direction of the exhaust gas is shorter than the length of the uppermost upstream part when the low thermal conductivity upstream exhaust passage from the downstream end of the high thermal conductivity in-engine exhaust passage to the upstream end of the catalyst provided upstream of the muffler and the intermediate exhaust passage is divided in the flow direction of the exhaust gas into five parts: an uppermost upstream part, an upstream part, a middle part, a downstream part, and a lowermost downstream part, each having an equal length, and is longer than half of the length of the uppermost upstream part.

2. The alcohol-containing fuel engine system according to claim 1, wherein a lower limit value of the alcohol concentration in the alcohol-containing fuel is 0% by volume, and the high thermal conductivity engine internal exhaust passage suppresses a temperature difference of the exhaust gas flowing into a catalyst when each of a plurality of types of the alcohol-containing fuels having an alcohol concentration including 0% by volume is burned, and is configured such that a length in a flow direction of the exhaust gas is shorter than a length of the most upstream portion and longer than half of the length of the most upstream portion.

3. The alcohol-containing fuel engine system according to claim 1 or 2, wherein the exhaust passage passes exhaust gas generated by combustion of the alcohol-containing fuel supplied so that an air-fuel ratio becomes rich at cold start, through the high thermal conductivity engine internal exhaust passage configured such that a length in a flow direction of the exhaust gas is shorter than a length of the most upstream portion and longer than half of the length of the most upstream portion.

4. The alcohol-containing fuel engine system according to any one of claims 1 to 3, wherein in a flow direction of the exhaust gas, the high thermal conductivity engine internal exhaust passage is configured such that a length from a downstream end of the high thermal conductivity engine internal exhaust passage to an upstream end of the catalyst is shorter than a length of the most upstream portion in the low thermal conductivity upstream exhaust passage configured such that the catalyst is provided upstream of the muffler and the intermediate exhaust passage and is shorter than a length from the upstream end of the catalyst to a downstream end of the exhaust passage and longer than half of the length of the most upstream portion.

5. The alcohol-containing fuel engine system according to any one of claims 1 to 4, wherein the high thermal conductivity engine internal exhaust passage is made of aluminum or an aluminum alloy, and the low thermal conductivity upstream exhaust passage is made of stainless steel, titanium or a titanium alloy.

6. A vehicle comprising the alcohol-containing fuel engine system according to any one of claims 1 to 5.

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