Engine with sub combustion chamber

Abstract

To disclose technique that can start up an engine without occurrence of an accidental fire even when the engine is in a cold state, and after the start-up, can ignite the engine only with flame in a sub combustion chamber.SOLUTION: An internal electrode (center electrode) 22 is exposed inside a sub combustion chamber 15, and an external electrode (ground electrode) 24 is arranged below and outside the sub combustion chamber 15. A movable intermediate electrode 26 freely moving up and down is attached to a guide cylinder 25 provided on the bottom plate 15a of the sub combustion chamber 15. A lower end of a coil spring 29 is fixed to the lower end of the movable intermediate electrode 26, and the end of the upper end of the coil spring 29 is fixed to the bottom plate 15a. The coil spring 29 is made of a shape-memory alloy and is contracted at the start-up, and the movable intermediate electrode 26 moves up, and thus sparks are generated in a lower discharge gap 27. When the internal temperature of the sub combustion chamber 15 increases to secure fuel ignition, the coil spring 29 expands and the movable intermediate electrode 26 moves down, and sparks are generated in an upper discharge gap, which exhibits the function of the sub chamber.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to an engine having a sub-combustion chamber in a cylinder head.

Background Art

[0002] In engines such as gasoline engines and gas engines, it has been proposed to provide a sub-combustion chamber (sub-chamber) in the cylinder head. The sub-combustion chamber is used in combination with a spark plug, and the flame generated in the sub-combustion chamber is ejected from the injection hole into the main combustion chamber to ignite the main fuel. Since the flame generated in the sub-combustion chamber has excellent ignitability of the fuel, there is an advantage that even if the fuel of the air-fuel mixture is lean, it can be surely burned. Therefore, it has been attracting attention as a promising technology for improving fuel efficiency and promoting exhaust gas purification.

[0003] As means for igniting the air-fuel mixture in the sub-combustion chamber, there are a passive method in which the air-fuel mixture ejected from the intake port is taken into the sub-combustion chamber and ignited by a spark plug exposed inside the sub-combustion chamber, and an active method in which fuel is taken into the sub-combustion chamber from a dedicated path and this fuel is ignited by a spark plug. However, the former passive method has a simple structure and does not require a control device, so it is excellent in terms of cost and compatibility with actual machines.

[0004] On the other hand, as a problem of the passive method, there is a risk of poor ignitability of the fuel and misfire when the temperature of the air-fuel mixture is low, such as at cold engine start. As a countermeasure against this point, Patent Document 1 proposes a sub-combustion chamber structure provided with discharge gaps inside and outside the sub-combustion chamber.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] In the configuration of Patent Document 1, even if combustion does not occur inside the sub-combustion chamber, the fuel in the main combustion chamber can be ignited by the external discharge gap. Therefore, it is possible to prevent misfire and start and operate even in a cold state. However, since discharge is constantly occurring in the internal and external discharge gaps, there are problems such as a large current being required for ignition, leading to deterioration of fuel consumption, and there is a risk that the ignition device will become larger in size and the cost will increase.

[0007] Also, after leaving the cold state, the spark in the external discharge gap continues, and since ignition by the flame ejected from the sub-combustion chamber and ignition by the external discharge gap always coexist, there is a concern that turbulence may occur in the spread of the flame in the main combustion chamber, which may prevent stable combustion.

[0008] The present invention has been made to improve such a situation.

Means for Solving the Problems

[0009] The engine of the present invention is "An engine including a main combustion chamber provided in a cylinder head and a sub-combustion chamber having at least a part thereof exposed to the main combustion chamber, an internal electrode disposed inside the sub-combustion chamber, an external electrode exposed to the main combustion chamber, a movable intermediate electrode that moves between the internal electrode and the external electrode to selectively form a discharge gap inside and outside the sub-combustion chamber, and a drive member that moves the movable intermediate electrode." It has such a configuration.

[0010] The present invention can be developed in various ways. As an example, in claim 2, "The drive member is made of a material that deforms by heat, and in a state lower than a predetermined temperature, it raises the movable intermediate electrode to form a discharge gap outside the sub-combustion chamber, and when the temperature exceeds the predetermined temperature, it lowers the movable intermediate electrode to form a discharge gap inside the sub-combustion chamber." It has such a configuration.

[0011] In claim 2, specifically, a spring made of a shape memory alloy is used as the driving member, and the movable intermediate electrode can be moved to the side of the internal electrode or the side of the external electrode with a predetermined set temperature as a boundary. Alternatively, it is also possible to utilize thermal expansion or use a bimetal.

Advantages of the Invention

[0012] In the present invention, since the movement of the movable intermediate electrode selectively executes the spark inside the auxiliary combustion chamber and the spark outside the auxiliary combustion chamber, as in claim 2, at the start in the cold state, a spark is generated outside the auxiliary combustion chamber, and after getting out of the cold state, a spark is generated inside the auxiliary combustion chamber, thereby preventing misfire at the cold start and realizing stable start and operation.

[0013] And since only one of the internal and external discharge gaps generates a spark, there is no increase in power consumption, and it is possible to prevent deterioration of fuel efficiency, and there are no problems such as an increase in cost due to an increase in the size of the ignition device. Furthermore, after getting out of the cold state, the fuel in the main combustion chamber is ignited only by the flame generated in the auxiliary combustion chamber, so that the spread of the flame in the main combustion chamber can be stabilized and combustion can be stabilized.

[0014] As the driving means of the movable intermediate electrode, for example, it is also possible to use the movable intermediate electrode as a magnetic body, bias it in a direction away from the internal electrode with a spring, and attract it with an electromagnet at the cold start to temporarily generate a spark at the external electrode. However, if a configuration that uses a material that deforms with heat as in claim 2 is adopted for driving, there is an advantage that the movable intermediate electrode can be moved with a simple structure.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Figure 4

Best Mode for Carrying Out the Invention

[0016] (1). Basic Structure Next, embodiments of the present invention will be described with reference to the drawings. Hereinafter, the terms "front" and "rear" and "left" and "right" are used to specify directions. The front-rear direction is the crank axis direction, and the left-right direction is the direction orthogonal to the crank axis direction and the cylinder bore axis direction. Regarding the front and rear, the side where the timing chain is arranged is defined as the front, and the side where the transmission is arranged is defined as the rear.

[0017] This embodiment is applied to an automotive engine. The basic structure of the engine is the same as the conventional one, but for the sake of clarity, it will be described with reference to FIG. 1. The engine has, as basic elements, a cylinder block 1 and a cylinder head 3 fixed to the upper surface of the cylinder block 1 via a gasket 2. A plurality of cylinder bores 4 arranged in the crank axis direction are formed in the cylinder block 1.

[0018] On the other hand, a pentroof-type combustion chamber recess 5 facing the cylinder bore 4 is formed in the cylinder head 3. The main combustion chamber is formed by the cylinder bore 4 of the cylinder block 1 and the combustion chamber recess 5 of the cylinder head 3. Hereinafter, for the sake of convenience, the combustion chamber recess 5 is regarded as the main combustion chamber. A piston is slidably fitted in the cylinder bore 4, but its illustration is omitted. Note that the recess formed on the crown surface of the piston may also form a part of the main combustion chamber.

[0019] In the cylinder head 3, corresponding to each combustion chamber recess 5, a pair of intake ports 6 and a pair of exhaust ports 7 are formed on the left and right sides sandwiching the crank axis. The intake outlet hole of the intake port 6 is opened and closed by an intake valve 8, and the exhaust inlet hole of the exhaust port 7 is opened and closed by an exhaust valve 9. Each valve 8, 9 is biased in the closing direction by springs 10, 11.

[0020] The pair of intake ports 6 are independent over the entire length and open to the intake side surface 3a of the cylinder head 3. An intake manifold 12 is fixed to the intake side surface 3a of the cylinder head 3. A fuel injection injector 13 is mounted on the intake manifold 12 (or on the cylinder head 3) corresponding to each intake port 6. Note that the fuel injection injector 13 can also be mounted on the cylinder head 3.

[0021] Among the top surface parts of each combustion chamber recess 5 in the cylinder head 3, a plug hole (ignition hole) 14 is opened at a part surrounded by the intake outlet hole and the exhaust inlet hole, and an ignition plug 16 having a sub - combustion chamber 15 is screwed and mounted in the plug hole 14. In FIG. 1, the reference numeral 17 indicates a water jacket through which cooling water flows.

[0022] (2). Main part of the first embodiment As shown in FIG. 2, the ignition plug 16 has an outer cylinder 20 with external threads and a center electrode 21 disposed inside the outer cylinder 20 via an insulator. The lower end part of the center electrode 21 is an internal electrode 22 exposed below the outer cylinder 20. A sub - combustion chamber 15 formed in a downward - tapered trapezoidal cross - section is fixed to the lower end of the outer cylinder 20 by welding. A plurality (for example, 4 to 10) of spray holes 23 are formed at equal intervals in the circumferential direction on the outer peripheral wall of the lower end part of the sub - combustion chamber 15. The axis of each spray hole 23 is inclined with respect to the axis of the ignition plug 16, and the flame jets obliquely downward.

[0023] The sub-combustion chamber 15 is made of a conductive material, and an L-shaped external electrode (ground electrode) 24 is fixed to the bottom plate 15a by welding or the like. And, on the bottom plate 15a of the sub-combustion chamber 15, a vertically open guide cylinder 25 made of a non-conductor and formed in a cylindrical shape is fixed by laser welding, brazing, forced fitting, etc., and a columnar movable intermediate electrode 26 made of a highly conductive metal is arranged in the guide cylinder 25 so as to be slidable up and down. The guide cylinder 25 and the guide movable intermediate electrode 26 are formed concentrically with the internal electrode 22, and the tip of the external electrode 24 is located below the movable intermediate electrode 26.

[0024] When the movable intermediate electrode 26 rises to the extreme, its upper end abuts against the internal electrode 22, and a lower discharge gap 27 is formed between the lower end and the external electrode 24. When it descends to the extreme, its lower end abuts against the external electrode 24, and an upper discharge gap 28 is formed between the upper end and the internal electrode 22. Therefore, by the ascending and descending of the movable intermediate electrode 26, the lower discharge gap 27 and the upper discharge gap 28 are selectively formed.

[0025] Needless to say, the upper end of the guide cylinder 25 is set to a height that exposes the upper end portion of the movable intermediate electrode 26 that has risen to the extreme, and the lower end of the guide cylinder 25 is set to a height that exposes the lower end portion of the movable intermediate electrode 26 that has descended to the extreme. The lower end portion of the guide cylinder 25 protrudes slightly downward from the bottom plate 15a of the sub-combustion chamber 15, but it is also possible to set it to the same height as the lower surface of the bottom plate 15a.

[0026] A coil spring 29, which is an example of a driving member, is arranged on the lower surface portion of the bottom plate 15a in the sub-combustion chamber 15. The coil spring 29 is made of a shape memory alloy wire, and is set to contract in a state lower than a predetermined temperature and expand when exceeding the predetermined temperature. And, while the upper end of the coil spring 29 is fixed to the bottom plate 15a of the sub-combustion chamber 15 by welding or the like, the lower end of the coil spring 29 is formed on a ring 30 wound around the lower end of the movable intermediate electrode 26, and the ring 30 is fixed to the movable intermediate electrode 26 in an electrically insulated state.

[0027] Therefore, the movable intermediate electrode 26 moves up and down due to the expansion and contraction of the coil spring 29. When the coil spring 29 is fully extended, the lower end of the movable intermediate electrode 26 abuts against the external electrode 24, and when the coil spring 29 is fully contracted, the upper end of the movable intermediate electrode 26 abuts against the internal electrode 22.

[0028] As a means for fixing the ring 30 to the movable intermediate electrode 26 in an insulating state, for example, an annular groove having an arcuate cross section may be formed at the lower end of the movable intermediate electrode 26, and the ring 30 may be forcibly fitted into the annular groove via a heat-resistant insulating sheet. Alternatively, an insulating layer may be formed by firing a ceramic-based material or the like on the annular portion of the ring 30 or the movable intermediate electrode 26, and the ring 30 may be forcibly fitted into the annular groove.

[0029] (3). Summary of the First Embodiment The predetermined temperature at which the coil spring 29 changes between the extended state and the contracted state is a temperature at which the air-fuel mixture entering the inside of the sub-combustion chamber 15 can be heated to ignite smoothly by the spark. That is, the temperature of the recess 5 (main combustion chamber) for the combustion chamber and the temperature of the sub-combustion chamber 15 increase from the start of the engine, and accordingly, the temperature of the coil spring 29 also increases. However, the temperature of the coil spring 29 when the internal temperature of the sub-combustion chamber 15 has heated the air-fuel mixture to a state where ignition can be achieved smoothly by the spark at the upper discharge gap 28 is set as the predetermined temperature, and the coil spring 29 may be processed.

[0030] Furthermore, when the engine is started, the sub-combustion chamber 15 and the coil spring 29 are heated up. However, since the heating rate of these members is slower than the heating rate inside the recess 5 for the combustion chamber and the sub-combustion chamber 15, the predetermined temperature at which the coil spring 29 is deformed is much lower than the ambient temperature of the recess 5 for the combustion chamber. The specific temperature may be found using a device capable of measuring the temperature inside the combustion chamber.

[0031] Realistically, in a normal gasoline engine, even if it starts in a cold state, after 5 seconds have elapsed, the interior of the auxiliary combustion chamber 15 will heat up to a temperature where the air-fuel mixture can be reliably ignited. For example, it is possible to measure the surface temperature of the auxiliary combustion chamber 15 5 seconds after starting and set that temperature as the shape change temperature of the coil spring 29.

[0032] When using the coil spring 29 made of a wire-shaped shape memory alloy as the driving member as in the embodiment, it can be manufactured by the same processing method as a normal spring, so it is highly practical.

[0033] Note that there is an allowable value for realizing a spark in relation to the voltage for the gap of the discharge gap. When the voltage is constant, the spark will not occur if the gap is too small or too large. Therefore, the upper and lower discharge gaps 27, 28 are set to the interval where the spark occurs most efficiently under a predetermined voltage. And although it is possible that the movable intermediate electrode 26 is energized while it is descending, in this case, a current may be supplied so that the spark occurs in both discharge gaps. Since the increase in current is only for a very short time at startup, it will not deteriorate the fuel consumption to such an extent.

[0034] (4). Other Embodiments Next, other embodiments shown in FIGS. 3 and 4 will be described. In the second embodiment shown in FIG. 3, the auxiliary combustion chamber 15 is made of a sintered alloy, a thick portion is formed on the bottom plate 15a and a guide hole 31 is formed here. On the other hand, the movable intermediate electrode 26 is held by a cylindrical bush 32 made of a non-conductive material such as ceramic, and the cylindrical bush 32 is fitted into the guide hole 31 so as to be movable up and down. The cylindrical bush 32 is integrated with the movable intermediate electrode 26 by temporarily forming it in a state of holding the movable intermediate electrode 26 in an amorphous state and then firing it. A small-diameter portion 26a for preventing detachment is formed on the movable intermediate electrode 26.

[0035] On the other hand, an annular groove 33 is formed at the upper end of the cylindrical bush 32, and a conical spring 34 is used as a driving member. The small-diameter ring portion 34a of the conical spring 34 is forcibly fitted into the annular groove 33 of the cylindrical bush 32, and the large-diameter ring portion 34b of the conical spring 34 is fixed to the bottom plate 15a of the auxiliary combustion chamber 15 by welding or the like.

[0036] In this embodiment, the virtual center line O of each injection hole 23 is set to pass through the upper discharge gap 28, and the cylindrical bush 32 is set to be located below the virtual center line O in the lowered state. Therefore, the flame generated inside the auxiliary combustion chamber 15 passes through the injection hole 23 without being obstructed by the cylindrical bush 32 and scatters into the recess 5 for the combustion chamber. The external electrode 24 is integrally formed with the auxiliary combustion chamber 15, but it can also be manufactured separately and welded to the auxiliary combustion chamber 15.

[0037] In this embodiment, as shown in (B), the lower end of the cylindrical bush 32 is positioned above the lower surface of the bottom plate 15a when it has fully risen. However, it may be advisable to set the lower end of the cylindrical bush 32 to be flush with the lower surface of the bottom plate 15a or slightly below the bottom plate 15a when the cylindrical bush 32 has fully risen.

[0038] In this embodiment, since the conical spring 34 mainly heats up through the auxiliary combustion chamber 15, the temperature rise is slower than that in the first embodiment. Therefore, the shape change temperature is much lower than that of the coil spring 29 in the first embodiment.

[0039] In the third embodiment shown in Fig. 4(A), a guide hole 31 is formed in the bottom plate 15a of the auxiliary combustion chamber 15 in the same manner as in the second embodiment, and a conical spring 34 is used as a driving member. However, instead of using the cylindrical bush 32 as in the second embodiment, the movable intermediate electrode 26 is slidably inserted into the guide hole 31, and the small-diameter ring portion 34a of the conical spring 34 is forcibly fitted into the annular groove 33 formed in the movable intermediate electrode 26.

[0040] And in this embodiment, as a means for preventing conduction between the movable intermediate electrode 26 and the sub-combustion chamber 15, a heat-resistant non-conductive layer 35 such as a ceramic-based paint is formed on the outer peripheral surface (including the annular groove 33) of the movable intermediate electrode 26. The heat-resistant non-conductive layer 35 is preferably formed by firing. In this embodiment, there is an advantage that the structure is simplified.

[0041] The fourth embodiment shown in FIG. 4(B) is a modification of the third embodiment, and the difference from the third embodiment is that the conical spring 34 is arranged on the lower surface portion of the bottom plate 15a. Therefore, the annular groove 33 is formed at the lower end portion of the movable intermediate electrode 26. A recess 36 into which the conical spring 34 fits is formed on the lower surface of the bottom plate 15a.

[0042] 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, in each of the above embodiments, the sub-combustion chamber 15 is made of a conductor and has a grounding function. However, it is also possible to make the sub-combustion chamber 15 of a heat-resistant non-conductive material (or a material with a very low conductivity that can be practically regarded as a non-conductor), and fit the movable intermediate electrode into the guide hole formed therein so as to be able to move up and down. However, in this case, it is necessary to connect the external electrode and the outer cylinder with a conductive connection plate made of a conductor. A leaf spring can also be used as the driving member.

Industrial Applicability

[0043] The present invention can be embodied in an engine provided with a sub-combustion chamber. Therefore, it can be industrially utilized.

Explanation of Reference Numerals

[0044] 3 Cylinder head 5 Recess for combustion chamber 6 Intake port 14 Plug hole (ignition hole) 15 Sub-combustion chamber 16 Ignition plug 20 Outer cylinder 21 Central electrode 22 Internal electrode (exposed portion of the central electrode) 23 Injection hole 24 External electrode (grounding electrode) 25 Guide cylinder 26 Movable intermediate electrode 27 Lower discharge gap 28 Upper discharge gap 29 Coil spring as an example of a drive member 31 Guide hole 32 Cylindrical bush 33 Annular groove 34 Conical spring as an example of a drive member

Claims

1. An engine comprising a main combustion chamber provided in a cylinder head and a sub-combustion chamber having at least a part thereof exposed to the main combustion chamber, an internal electrode disposed inside the sub-combustion chamber, an external electrode exposed to the main combustion chamber, a movable intermediate electrode that moves between the internal electrode and the external electrode to selectively form a discharge gap inside and outside the sub-combustion chamber, and a drive member that moves the movable intermediate electrode. An engine with a sub-combustion chamber.

2. The drive member is made of a material that deforms by heat. In a state lower than a predetermined temperature, the drive member raises the movable intermediate electrode to form a discharge gap outside the sub-combustion chamber, and when the temperature exceeds the predetermined temperature, the drive member lowers the movable intermediate electrode to form a discharge gap inside the sub-combustion chamber. The engine with a sub-combustion chamber according to Claim 1.

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