Engine

Abstract

To simultaneously achieve improvement in ignitability and compactification in an auxiliary intake air passage in an engine provided with an auxiliary intake air passage for fuel heating in an intake device.SOLUTION: In an engine with even numbered cylinders such as two cylinders and four cylinders, a branch pipe 19 of an intake manifold 4 is formed so that two each of independent branch passages 23a and 23b are formed, and an auxiliary intake air passage 5 of a meandering type or the like for heating is arranged between the adjacent independent inside branch passages 23a. An outlet passage 34 of the auxiliary intake air passage 5 is communicated with the two independent inside branch passages 23a. A space between the two independent inside branch passages 23a can be used effectively as an arrangement space for the auxiliary intake air passage 5. Since the outlet passage 34 of the auxiliary intake air passage 5 is close to an intake port 7, an air-fuel mixture is supplied to a cylinder bore 1 without lowering its temperature, thereby being able to improve ignitability.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an engine equipped with an intake device having a fuel heating function.

Background Art

[0002] In a spark ignition engine such as a gasoline engine, as a fuel injection mode, there are a port injection method of injecting fuel into the intake port and a direct injection method of injecting fuel into the cylinder. The port injection method has advantages such as a simple injector structure and cost reduction due to low fuel injection pressure, and the ability to improve the mixing property of intake air and fuel, and is widely used.

[0003] On the other hand, as a problem of the port injection method, at cold start, the volatility of the fuel becomes insufficient and it is difficult to suppress PM and HC (it is difficult to sufficiently reduce PN). In particular, when the fuel is non-gasoline such as ethanol-based, the above problem appears significantly due to low volatility.

[0004] Therefore, it has been conventionally proposed to heat (warm up) the intake air at cold start to enhance the ignitability, and an example thereof is disclosed in Patent Document 1. That is, Patent Document 1 provides an electric heater immediately downstream of the throttle valve, heats the air-fuel mixture passing through the throttle valve with the heater, and the heated air-fuel mixture is led from the intake pipe to the cylinder head. In Patent Document 1, the fuel injection injector is arranged upstream of the throttle valve.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] Patent Document 1 provides a throttle valve in the middle of the intake passage on the downstream side of the air cleaner. In the case of a multi-cylinder engine, it is presumed that an intake manifold equipped with a surge tank is arranged on the downstream side of the throttle valve.

[0007] Then, Patent Document 1 utilizes the basic structure of the intake device as it is and arranges a heater directly below the throttle valve. However, since the intake passage is designed to have less flow resistance, in the configuration of Patent Document 1, there is a problem that the opportunity for the air-fuel mixture to contact the heater is small and the heating efficiency of the air-fuel mixture is poor.

[0008] That is, in Patent Document 1, the heater is merely arranged so as to surround the axis of the passage through which the air-fuel mixture travels straight. Therefore, it is considered that most of the air-fuel mixture passes through without contacting the heater. Thus, it can be said that the heating efficiency is poor. In other words, since Patent Document 1 uses the basic structure of the intake device as it is, it is necessary to consider not to impede the flow of the air-fuel mixture during normal operation. Then, the opportunity for the air-fuel mixture to contact the heater is small and the heating efficiency is poor.

[0009] Also, the throttle valve is usually of the butterfly type, and Patent Document 1 also adopts the butterfly type. However, during cold start (first idle), the throttle valve is usually at an intermediate opening degree between fully closed and fully open. Therefore, it cannot be said that the air-fuel mixture flows at a uniform density directly below the throttle valve. For this reason, a phenomenon in which the air-fuel mixture contacts only a part of the heater is also assumed, and a further decrease in heating efficiency is a concern.

[0010] Furthermore, there is a certain distance from the outlet of the throttle valve to the intake valve. If a heater is arranged directly below the throttle valve as in Patent Document 1, a phenomenon occurs in which the heat of the air-fuel mixture is taken away by the intake passage even when the air-fuel mixture is heated by the heater, and the efficiency of the heater deteriorates further.

[0011] Regarding these problems, it can be said that an auxiliary intake passage with a heating function that operates only during cold start should be installed in parallel. In this case, it is required to arrange the auxiliary intake passage so that it does not interfere as much as possible and to prevent the heated air-fuel mixture from cooling down. The present invention aims to disclose an intake technology that meets such requirements.

Means for Solving the Problems

[0012] The present invention is directed to an engine, which "has adjacent first and second cylinders, an independent intake passage corresponding to the first cylinder, an independent intake passage corresponding to the second cylinder, and a common intake passage for sending intake air to both independent intake passages via a throttle valve, and an auxiliary intake passage with a heating function for flowing the air-fuel mixture in a fully closed or slightly open state of the throttle valve is arranged between the two independent intake passages, and an outlet passage of the auxiliary intake passage communicates with the two independent intake passages." is configured as such.

[0013] The present invention can be developed in various ways. As an example, in claim 2, in claim 1, "a switching valve for switching between a state where the outlet passage of the auxiliary intake passage communicates with the two independent intake passages and a state where it does not communicate with the two independent intake passages is arranged, and the switching valve is controlled not to communicate with the two independent intake passages when intake air is supplied from the throttle valve to the two independent intake passages, and to communicate with the two independent intake passages when intake air is not supplied from the throttle valve to the two independent intake passages." is configured as such.

[0014] In the present invention, the auxiliary intake passage can adopt various structures, and the Tesla valve-shaped serpentine passage disclosed in Japanese Patent Application No. 2023-11960 by the inventor of the present application is suitable. Further, in the present invention, the independent intake passage includes both a branch pipe provided in the intake manifold and an intake port formed in the cylinder head. Therefore, the auxiliary intake passage may be arranged only at the location of the branch pipe of the intake manifold, or only at the location of the intake port of the cylinder head, or may be arranged so as to straddle both the branch pipe and the intake port.

[0015] Generally, an engine is provided with two intake ports as a set corresponding to one cylinder, and there are two modes: a mode in which injectors are arranged for the two intake ports respectively, and a mode in which the inlet portions of the two intake ports are communicated and fuel is injected from one injector into the two intake ports. However, the present invention can be applied to any of them. Further, the present invention can be applied to engines with an even number of cylinders, such as a two-cylinder engine or a four-cylinder engine.

Advantages of the Invention

[0016] In the present invention, an auxiliary intake passage is arranged separately from the main intake system used in the normal operating state, and the heated air-fuel mixture is sent to the cylinder from the auxiliary intake passage only under limited conditions such as during cold start. Therefore, the air-fuel mixture can be firmly heated during cold start without hindering the smoothness of normal operation using the main intake system. That is, the auxiliary intake passage can be designed to efficiently heat while maintaining an appropriate flow rate in the air-fuel mixture. Therefore, even with a fuel having poor volatility such as an ethanol-based fuel, smooth cold start can be achieved.

[0017] In particular, when a Tesla valve-shaped serpentine passage is adopted as the auxiliary intake passage, the contact opportunity of the air-fuel mixture with the heater can be significantly increased. Therefore, the fuel can be surely heated and volatilized, and the heating efficiency per unit amount of electric power can be significantly increased, which is particularly suitable.

[0018] In the present invention, since the auxiliary intake passage is disposed between adjacent independent intake passages, space can be effectively utilized, and problems such as objects hitting the auxiliary intake passage can be prevented or significantly reduced. It is also possible to integrate the auxiliary intake passage with the independent intake passage. By integrating in this way, handling and assembly can be facilitated, which is more preferable.

[0019] Furthermore, since the auxiliary intake passage is disposed between adjacent independent intake passages, the outlet at the end of the auxiliary intake passage can be brought as close as possible to the cylinder. For this reason, the air-fuel mixture heated and raised in temperature can be sent into the cylinder without being cooled down, and the purpose of improving ignitability can be achieved. This point can be said to be a remarkable effect of the present invention.

[0020] In the present invention, the auxiliary intake passage communicates with both independent intake passages. Therefore, the communication hole opens into the independent intake passage in a state like a horizontal hole. And when the air-fuel mixture is not supplied to the auxiliary intake passage, the auxiliary intake passage is in a closed state. So, basically, intake air does not flow into the auxiliary intake passage from the communication hole. However, if a switching valve is provided as in claim 2, the phenomenon of intake air flowing backward into the auxiliary intake passage in the normal operating state where intake air flows through the throttle valve can be surely prevented.

Brief Description of the Drawings

[0021]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0022] Next, embodiments of the present invention will be described with reference to the drawings. This embodiment is applied to a two-cylinder vertical engine mounted on an automobile. Hereinafter, for convenience of explanation, the front-rear, left-right, and up-down directions are used. The front-rear direction is the cam axis direction (crank axis direction), the left-right direction is a substantially horizontal direction orthogonal to the cam axis direction, and the up-down direction is the vertical direction. Regarding the front and rear, the side where the timing chain is arranged in the engine is the front, and the side where the transmission is arranged is the rear. The front-rear direction is shown in FIG. 1.

[0023] (1). Basic Structure As shown in FIG. 1, the engine of this embodiment includes a cylinder block 2 in which two cylinder bores (cylinders) 1 are formed, a cylinder head 3 fixed to the upper surface of the cylinder block 2, an intake manifold 4 fixed to the intake side surface 3a of the cylinder head 3, and an auxiliary intake passage 5 provided integrally with the intake manifold 4.

[0024] In the cylinder head 3, a pentroof-type combustion chamber recess 6 opening toward the cylinder bore 1 is formed, and a pair of front and rear intake ports 7a and 7b are opened in the combustion chamber recess 6. That is, an independent inner intake port 7a located inside in the front-rear direction and an independent outer intake port 7b located outside in the front-rear direction are opened. The intake ports 7a and 7b are opened and closed by intake valves 8 respectively. Main injectors 9 are arranged above the intake ports 7a and 7b respectively. The main injector 9 is attached to the attachment hole 10 via a sealing means (not shown) such as an O-ring. In addition, a delivery pipe 11 having a longitudinal length in the front-rear direction is connected to each main injector 9.

[0025] In Fig. 1, the intake valve camshaft is indicated by reference numeral 12, and the cam cap is indicated by reference numeral 13. The intake valve 8 is pushed by the camshaft 12 via a cap-shaped head case (not shown). Further, in Fig. 2, the ignition hole is indicated by reference numeral 14, the intake valve arrangement hole is indicated by reference numeral 15, and the exhaust valve arrangement hole is indicated by reference numeral 16. In Fig. 3, the exhaust port is indicated by reference numeral 17, and the exhaust valve is indicated by reference numeral 17a. In the embodiment, as clearly shown in Figs. 2 and 3, the pair of intake ports 7a and 7b are each independently open to the intake side surface 3a of the cylinder head 3.

[0026] The intake manifold 4 includes a surge tank 18 that is long in the front-rear direction, two branch pipes 19 branched from the surge tank 18, and a common flange 20 provided at the tips of the two branch pipes 19. The intake manifold 4 is a synthetic resin molded product and is formed hollow by joining a plurality of parts by vibration welding or the like, as is well known. Needless to say, the common flange 20 is fixed to the intake side surface 3a of the cylinder head 3 with bolts (and nuts).

[0027] An intake receiving seat 21b for fixing a throttle body 21a incorporating a throttle valve is provided at the rear end of the surge tank 18 so as to open substantially upward. An intake duct 21c is connected to the inlet of the throttle body 21a. The start end of the intake duct 21c is connected to the clean chamber outlet of the air cleaner or the compressor chamber outlet of the exhaust turbocharger. In the present embodiment, the intake duct 21c and the surge tank 18 constitute the common intake passage described in the claims.

[0028] The interior of the two branch pipes 19 and the common flange 20 is divided by a partition wall 22 into two passages, an independent inner branch passage 23a and an independent outer branch passage 23b. The independent inner branch passage 23a communicates with the inner intake port 7a, and the independent outer branch passage 23b communicates with the outer intake port 7b. The intake ports 7a, 7b and the independent branch passages 23a, 23b are slightly inclined so as to be lower toward the cylinder bore 1. In the present embodiment, the inner and outer intake ports 7a, 7b and the independent branch passages 23a, 23b constitute the independent intake passages described in the claims.

[0029] (2). Auxiliary Intake Passage The auxiliary intake passage 5 is configured as a meandering intake passage in the shape of a Tesla valve, and is disposed between adjacent independent inner branch passages 23a in the pair of branch pipes 19. At the start end of the auxiliary intake passage 5, an intake inlet 24 to which an auxiliary intake duct (not shown) is flange-joined is arranged to open substantially upward. The auxiliary intake duct is connected to a clean chamber of an air cleaner (not shown). As shown by the dashed-dotted line in FIG. 1, a switching valve 25 for interrupting the inflow of intake air is provided at the location of the intake inlet 24. The illustrated switching valve 25 is a solenoid valve of a type in which a spool (valve body) 25a moves forward and backward. The switching valve 25 can also be arranged at the end of the auxiliary intake passage 5, an air cleaner, an auxiliary intake duct, or the like.

[0030] At the location of the intake inlet 24, the nozzle 27 of the auxiliary injector 26 faces. Therefore, an air-fuel mixture is generated by fuel injection from the auxiliary injector 26. Needless to say, a fuel hose is connected to the auxiliary injector 26. The auxiliary injector 26 and the switching valve 25 are controlled by a control device (ECU).

[0031] From the end of the intake port 24, a first curved portion 28 through which the air-fuel mixture flows in a straight-ahead manner and a linear first auxiliary passage 29 facing in a direction intersecting the flow direction of the air-fuel mixture branch off, and the ends of both merge with each other. From the confluence of the first curved portion 28 and the first auxiliary passage 29, a second curved portion 30 through which the air-fuel mixture flows in a straight-ahead manner and a second auxiliary passage 31 facing in a direction intersecting the flow direction of the air-fuel mixture branch off.

[0032] The end of the second curved portion 30 and the end of the second auxiliary passage 31 merge with each other. From the confluence of the second curved portion 30 and the second auxiliary passage 31, a third curved portion 32 through which the air-fuel mixture flows in a straight-ahead manner and a third auxiliary passage 33 facing in a direction intersecting the flow direction of the air-fuel mixture branch off. Then, the third curved portion 32 and the third auxiliary passage 33 merge with each other, and an outlet passage 34 is connected here.

[0033] The first curved portion 28 and the first auxiliary passage 29, the second curved portion 30 and the second auxiliary passage 31, and the third curved portion 32 and the third auxiliary passage 33 each form D-shaped loop passages 35, 36, 37. Most of the air-fuel mixture generated at the intake port 24 flows into the first curved portion 28 with straight-ahead property, and most of the air-fuel mixture that has passed through the first curved portion 28 and the first auxiliary passage 29 flows into the second curved portion 30 with straight-ahead property, and most of the air-fuel mixture that has passed through the second curved portion 30 and the second auxiliary passage 31 flows into the third curved portion 32 with straight-ahead property.

[0034] The first curved portion 28, the second curved portion 30, and the third curved portion 32 each have a J-shaped form, and an electric heater 38 is disposed on the inner surface of the first curved portion 28 as a heating function. The heater 38 can adopt various modes such as a sticking type or an embedding type.

[0035] The auxiliary intake passage 5 is formed hollow by welding two members manufactured by injection molding. In this case, it is possible to manufacture the auxiliary intake passage 5 as an independent unit, but it is preferable to form a hollow structure using the parts that make up the intake manifold 4. The heater 38 is joined to the parts before the welding process. The cross-sectional shape of the auxiliary intake passage 5 can adopt various forms such as circular, oval, and angular, but in order to effectively utilize the space between adjacent independent inner branch passages 23a, it can be said that angular or oval shapes are preferable.

[0036] In this embodiment, the air-fuel mixture flows through the first loop passage 35, the second loop passage 36, and the third loop passage 37 in this order. However, since it flows into each of the curved portions 28, 30, 32 with straightness, the air-fuel mixture mainly flows into each of the curved portions 28, 30, 32 in the loop passages 35 to 37. On the other hand, since each of the auxiliary passages 29, 31, 33 branches in a direction intersecting the flow direction of the air-fuel mixture, the inflow amount of the air-fuel mixture is small.

[0037] And each of the curved portions 28, 30, 32 is J-shaped, and since the discharge direction of the air-fuel mixture intersects the auxiliary passages 29, 31, 33, resistance is exerted to prevent the air-fuel mixture from being discharged from each of the curved portions 28, 30, 32. For this reason, the air-fuel mixture tends to stay at each of the curved portions 28, 30, 32.

[0038] Therefore, it is difficult for the air-fuel mixture to flow from the intake port 24 toward the outlet passage 34. As a result, a certain amount can flow without the need for a valve. That is, the serpentine auxiliary intake passage 5 has a flow rate self-regulating function. By changing the cross-sectional areas of the curved portions 28, 30, 32 and the auxiliary passages 29, 31, 33, or by adjusting the outlet directions of the curved portions 28, 30, 32, the flow resistance of the air-fuel mixture can be tuned to adjust the flow rate.

[0039] The outlet passage 34 of the auxiliary intake passage 5 opens to adjacent independent inner branch passages 23a in the two branch pipes 19. Therefore, the air-fuel mixture heated in the auxiliary intake passage 5 flows into the inner intake port 7a via the independent inner branch passages 23a.

[0040] (3). Summary In this embodiment, at cold start, the throttle valve is held fully closed or slightly closed, the switching valve 25 is opened, and a predetermined amount of fuel is continuously injected from the auxiliary injector 26. The outlet passage 34 of the auxiliary intake passage 5 opens into two independent inner branch passages 23a. However, since the two pairs of intake valves 8 open and close alternately, the heated air-fuel mixture flows alternately into one and the other of the two independent inner branch passages 23a (flows alternately into one and the other of the two independent inner intake ports 7a).

[0041] That is, precisely, since there is always a differential pressure between the start end of the auxiliary intake passage 5 and the two independent branch passages 23, the air-fuel mixture also tends to flow into the independent branch passage 23a communicating with the intake port 7a where the intake valve 8 is not open. However, when the intake valve 8 is open, since the suction force of the independent branch passage 23a communicating with that intake port is large, the air-fuel mixture in the auxiliary intake passage 5 preferentially flows into the independent inner branch passage 23a corresponding to the independent intake port 7a where the intake valve 8 is open. Therefore, even if the air-fuel mixture is continuously generated in the auxiliary passage 5, most of the air-fuel mixture flows alternately into one and the other of the two independent inner intake ports 7a corresponding to the opening of the intake valve 8.

[0042] As described above, when the intake valve 8 is open, the suction action of the corresponding independent inner intake port 7a and the independent inner branch passage 23a becomes higher. Therefore, by performing fuel injection by the auxiliary injector 26 corresponding to the intake timing of the two cylinder bores 1 (cylinders), it is possible to send the entire amount of the air-fuel mixture to the cylinder bore 1 where the intake valve 8 is open. That is, by matching the generation timing of the air-fuel mixture in the auxiliary intake passage 5 and the intake timing of the cylinder bore 1, the entire amount (or almost the entire amount) of the air-fuel mixture generated in the auxiliary intake passage 5 can be intensively sent to the cylinder bore 1 where the intake valve 8 is open.

[0043] And as a feature of the present embodiment, first, since the auxiliary intake passage 5 has a meandering Tesla valve shape, the contact opportunity between the heater 38 and the fuel particles can be increased, promoting the vaporization of the fuel. Therefore, the heating efficiency per unit amount of electric power is significantly higher than that in Patent Document 1.

[0044] Next, since the auxiliary intake passage 5 is disposed between adjacent independent inner branch passages 23a, the auxiliary intake passage 5 can be arranged by effectively using the dead space. Therefore, the auxiliary intake passage 5 can be made compact. Further, since the outlet passage 34 is located at the end of the independent inner branch passage 23a, the heated air-fuel mixture can be quickly supplied to the cylinder bore 1. Therefore, even with a fuel having poor volatility such as ethanol-based fuel, cold start can be smoothly performed.

[0045] In the present embodiment, the air-fuel mixture flows into the inner intake port 7a and does not flow into the outer intake port 7b. However, since the throttle valve is closed, intake air does not flow into the cylinder bore 1 from the outer intake port 7b. Only the air-fuel mixture passing through the inner intake port 7a flows into the cylinder bore 1. Therefore, inside the cylinder bore 1, the fuel is further refined and dispersed due to the tumble effect or the like, enabling complete combustion.

[0046] The operating time of the auxiliary intake passage 5 may be set in consideration of various factors such as the type of fuel and the outside air temperature. That is, roughly, it often takes about 2 to 3 minutes for the inner surface temperature of the intake port 7a to rise to a level where it can sufficiently evaporate the fuel after cold start. Therefore, when starting the engine in a completely cold state and there is time margin during idling, it is preferable to use the auxiliary intake passage 5 for several minutes after starting. When there is still residual heat in the intake port 7a, such as when restarting the engine without much time elapsed since it was stopped, it can be said that the use of the auxiliary intake passage 5 may be for a short time.

[0047] When the vehicle must be driven without much time elapsing after starting, it is necessary to prioritize fuel injection by the main injector 9 to ensure output, so the use of the auxiliary intake passage 5 may have to be short. Therefore, various information such as the outside air temperature, the engine temperature (for example, the coolant temperature), and the driving mode should be taken into the ECU to control the transition from the operation of the auxiliary intake passage 5 to normal operation. Therefore, the operation time of the auxiliary intake passage 5 can be set from several seconds to several minutes.

[0048] At the time of starting, an amount of air-fuel mixture necessary for idling is supplied. However, if fuel is supplied from the auxiliary intake passage 5 so that the fuel injected first during cranking is used for the first explosion, there is no emission of unburned fuel, so there are no environmental problems and it is suitable.

[0049] For safety, the heating effect of the auxiliary intake passage 5 will be described in more detail. The air-fuel mixture is heated by the heater 38 at the first curved portion 28 of the auxiliary intake passage 5. Due to the synergistic effect of the tendency of the air-fuel mixture to stay at the first curved portion 28 and the air-fuel mixture being strongly pressed against the heater 38 by centrifugal force, the temperature of the entire air-fuel mixture can be efficiently and accurately increased.

[0050] The auxiliary intake passage 5 of the embodiment is composed of three loop passages 35 to 37, but it can also be configured as a single-stage type with only one loop passage or a two-stage type with two loop passages. Also, when there are a plurality of loop passages, it is possible to make their sizes and cross-sectional areas different. Furthermore, when there are a plurality of curved portions, it is also possible to provide heaters for the plurality of curved portions. Also, the heater 38 may be arranged over the entire inner surface of one curved portion.

[0051] (4). Other Embodiments Figure 4 shows another embodiment (modification). In the second embodiment shown in Fig. 4(A), a switching valve 25 is arranged in the outlet passage 34 of the auxiliary intake passage 5. The switching valve 25 in this example includes a valve body 41 that slides from above to open and close the outlet passage 34, and the valve body 41 is biased in the closing direction by a spring 42. And a linear movable iron core 43 provided on the valve body 41 is slid up and down by an electromagnetic coil 44. When the auxiliary intake passage 5 is in operation, the electromagnetic coil 44 is energized to control the opening of the outlet passage 34.

[0052] In this second embodiment, the switching valve 25 switches the outlet passage 34 between a state in which it communicates with two independent inner branch passages 23a and a state in which it does not communicate. That is, in a state where intake air is supplied from the throttle valve to the inner and outer intake ports 7a, 7b and the independent branch passages 23a, 23b, the outlet passage 34 does not communicate with the two independent inner branch passages 23a, and in a state where intake air is not supplied from the throttle valve to the inner and outer intake ports 7a, 7b and the independent branch passages 23a, 23b, the outlet passage 34 is controlled to communicate with the two independent inner branch passages 23a. Therefore, the phenomenon that intake air flows into the auxiliary intake passage 5 in the warm-up operation state where the auxiliary intake passage 5 is not in operation can be more reliably prevented.

[0053] Figs. 4(B) and (C) also show examples of the switching valve 25. In this example, a rotary three-way valve body 45 is used, and the three-way valve body 45 is rotated by a rotary solenoid or the like, so that the outlet passage 34 is switched between a state in which it communicates with two independent inner branch passages 23a (the state in Fig. 4(B)) and a state in which it does not communicate (the state in Fig. 4(C)). The three-way valve body 45 can also be slid in the axial direction. That is, the three-way valve body 45 is formed into a part with a T-shaped hole and a part without a T-shaped hole, and it can also be switched between a state in which the T-shaped hole communicates with the outlet passage 34 and the like and a state in which the outlet passage 34 and the like are blocked by the solid part without a hole.

[0054] The fourth embodiment shown in FIG. 4(D) is an alternative example of the outlet passage 34. In this embodiment, the outlet passage 34 penetrates through the common flange 20, and a lateral passage 46 communicating with two inner intake ports 7a is formed on the intake side surface 3a of the cylinder head 3. In this example, the structure of the intake manifold 4 can be simplified. In order to prevent the phenomenon that the once-vaporized fuel touches the cold metal cylinder head and cools down and condenses into a liquid (mist), a heat insulating material 47 is provided in the lateral passage 46.

[0055] The fifth embodiment shown in FIG. 4(E) extends the outlet passage 34 up to the common flange 20, and two bifurcated communication holes 48 leading to the two inner intake ports 7a are provided in the cylinder head 3. Since the communication holes 48 are inclined, the inflow property of the air-fuel mixture into the inner intake ports 7a is excellent, and the backflow prevention function during normal operation is also high. Although not shown, it is preferable to attach a heat insulating pipe to the communication holes 48 for the above purpose. Also in the examples of FIGS. 4(D) and 4(E), it is preferable to arrange the switching valve 25 at the end of the auxiliary intake passage 5.

[0056] As described above, the embodiments of the present invention have been described, but the present invention can be embodied in various other ways. For example, it can be applied to a 4-cylinder or 6-cylinder engine, and the present invention can be applied by combining two cylinders into one set. The auxiliary intake passage 5 does not have to be serpentine. When the serpentine auxiliary intake passage has a plurality of curved portions, the heater can be arranged at one or a plurality of arbitrary curved portions.

[0057] The auxiliary intake passage can also be arranged only at the location of the intake port, or in a state straddling the intake port and the branch pipe. When fixing the intake manifold to the cylinder head, it is also possible to provide flanges independently for each branch pipe. In the case of a single type in which two intake ports converge at the entrance and fuel is injected by a single main injector, the branch pipe also has a single structure, so the auxiliary intake passage may be arranged between adjacent branch pipes.

Industrial Applicability

[0058] The invention of the present application can be embodied in an engine equipped with a heating type intake device. Therefore, it can be used industrially.

Explanation of reference numerals

[0059] 2 - cylinder double block 3 - cylinder head 4 - intake manifold 5 - auxiliary intake passage 7a, 7b - intake ports (independent intake passages) 8 - intake valve 9 - main injector 18 - surge tank forming part of the common intake passage 19 - branch pipe 20 - common flange 21a - throttle body 21b - intake receiver seat to which the throttle body is attached 21c - intake duct forming the common intake passage 23a, 23b - independent branch passages (independent intake passages) 24 - intake inlet 25 - switching valve 26 - auxiliary injector 34 - outlet passage

Claims

1. adjacent first and second cylinders, an independent intake passage corresponding to the first cylinder, an independent intake passage corresponding to the second cylinder, and a common intake passage for sending intake air through a throttle valve to both independent intake passages, an auxiliary intake passage with a heating function for flowing a mixture in a fully closed state or a slightly open state of the throttle valve is arranged between the two independent intake passages, and an outlet passage of the auxiliary intake passage communicates with the two independent intake passages, an engine.

2. a switching valve for switching between a state of communicating with the two independent intake passages and a state of not communicating with the two independent intake passages is arranged in an outlet passage of the auxiliary intake passage, and the switching valve is not communicated with the two independent intake passages in a state where intake air is supplied from the throttle valve to the two independent intake passages, and is controlled to communicate with the two independent intake passages in a state where intake air is not supplied from the throttle valve to the two independent intake passages, the engine according to Claim 1.

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