Patent Grant
10844827
The present application claims the benefit of priority of Japanese Patent Application No. 2018-127422 filed on Jul. 4, 2018, the disclosure of which is incorporated herein by reference.
This disclosure relates generally to an ignition device for internal combustion engines.
Typical ignition devices for internal combustion engines work to create combustion of an air-fuel mixture within a combustion chamber using sparks developed by a spark plug. An initial flame arising from the combustion of the mixture expands to achieve normal combustion of the mixture.
In order to ensure stability in achieving the above normal combustion, multiple ignition systems are known which are designed to produce a plurality of ignition events in each cycle of an operation of the internal combustion engine, that is, per compression stroke in the internal combustion engine.
Usually, when a flow of air-fuel mixture within a combustion chamber is created at a high speed, it will disturb growth of a flame kernel, thus resulting in a difficulty in improving the ignitability of the mixture. Specifically, when a high-speed flow of the mixture is created, a plurality of flames produced by multiple ignitions will be moved by the flow of the mixture away from a spark gap of the spark plug within a short period of time. This disturbs a thermal exchange among the plurality of flames which usually combine and grow together. It is, thus, difficult to enhance the ignitability of the mixture.
An increase in ignition energy in order to enhance the ignitability of the mixture will, however, result in acceleration of mechanical wear of electrodes of the spark plug, which leads to a decrease in service like of the spark plug, or require an ignition coil of the spark plug to have an increased sized. The increase in ignition energy is, therefore, undesirable.
It is an object of this disclosure to provide an ignition device which is designed to improve the ignitability of mixture in an internal combustion engine without increasing the ignition energy.
According to one aspect of the invention, there is provided an ignition device for an internal combustion engine which comprises: (a) a spark plug equipped with a housing, a center electrode retained inside the housing, and a ground electrode which defines a spark gap between itself and the center electrode; and (b) a controller which controls an operation of the spark plug. The spark plug is mounted in an internal combustion engine with a head of the housing protruding from an inner surface of a combustion chamber into the combustion chamber. The head of the housing protruding into the combustion chamber has at least a portion located downstream of the spark gap in a mixture flow within the combustion chamber. The controller works to perform a plurality of sequential events of discharge in the spark plug in each cycle of an operation of the internal combustion engine.
The spark plug 10 of the ignition device is, as described above, mounted in the internal combustion engine with the head of the housing protruding from the inner surface into the combustion chamber. The protruding head of the housing has at least a portion located downstream of the spark gap in the mixture flow within the combustion chamber. This creates a stagnating region which is located adjacent and downstream of the protruding portion and where the mixture flow has a lower flow velocity. In the stagnating region, the mixture flow is circulated in a swirling or eddy form. The mixture which has flowed near the spark gap and passed the protruding head is sucked into the stagnating region.
The controller is configured to activate the spark plug to achieve a plurality of ignitions in each operation cycle of the internal combustion engine. This sequentially develops flames near the spark gap in each operation cycle of the internal combustion engine. Each of the flames is moved or drifted by the mixture flow attracted into the stagnating region, so that it stays near the stagnating region within the combustion chamber. This causes the first flame to collide with the second flame which has occurred following the first flame, so that they are combined or mixed. This facilitates growth of a flame within the combustion chamber and enhances the ignition of the mixture.
In the above way, the flames and are mixed to create a grown flame, thereby facilitating the ignition of the mixture without need to increase the ignition energy within the whole of the combustion chamber.
The above structure of the ignition device is capable of improving the ability of the spark plug to ignite the mixture without need for increasing the ignition energy.
In this disclosure, symbols in brackets represent correspondence relation between terms in claims and terms described in embodiments which will be discussed later, but are not limited only to parts referred to in the disclosure.
The present invention will be understood more fully from the detailed description given hereinbelow and from the accompanying drawings of the preferred embodiments of the invention, which, however, should not be taken to limit the invention to the specific embodiments but are for the purpose of explanation and understanding only.
In the drawings:
Prior to describing preferred embodiments, the discussion will refer to prior art multiple ignition systems which are designed to produce a plurality of ignition events in each cycle of an operation of the internal combustion engine, that is, per compression stroke in the internal combustion engine. For instance, Japanese Patent No. 4239607 teaches a controller to control multiple ignitions as a function of a growth rate of a flame kernel.
Usually, when a flow of air-fuel mixture within a combustion chamber is created at a high speed, it will disturb growth of a flame kernel, thus resulting in a difficulty in improving the ignitability of the mixture. Specifically, when a high-speed flow of the mixture is created, a plurality of flames produced by multiple ignitions will be moved by the flow of the mixture away from a spark gap of the spark plug within a short period of time. This disturbs a thermal exchange among the plurality of flames which usually combine and grow together. It is, thus, difficult to enhance the ignitability of the mixture.
An increase in ignition energy in order to enhance the ignitability of the mixture will, however, result in acceleration of mechanical wear of electrodes of the spark plug, which leads to a decrease in service like of the spark plug, or require an ignition coil of the spark plug to have an increased sized. The increase in ignition energy is, therefore, undesirable.
The ignition device 1 includes the spark plug 10 and the controller 100 which works to control an ignition operation of the spark plug 10.
The spark plug 10 includes the housing 2 (also called a metal shell), the center electrode 3 retained inside the housing 2, and the ground electrode 4 which defines the stark gap 11 between itself and the center electrode 3.
In use of the spark plug 10, the housing 2 is, as illustrated in
The housing 2 has the protruding head 21 extending from the base-side inner surface 721 to the top side Z1. The protruding head 21 is arranged at least to have a portion located downstream of the spark gap 11 in a flow of an air-fuel mixture (which will also be referred to as a mixture flow F) within the combustion chamber 72.
The controller 100, as demonstrated in
The spark plug 10 has the center electrode 3 disposed inside the hollow cylindrical housing 2 through the cylindrical porcelain insulator 5. The center electrode 3 has a head protruding from the housing 2 and the porcelain insulator 5 to the top side Z1.
The ground electrode 4, as clearly illustrated in
The ground electrode 4, as clearly illustrated in
The protruding head 21 extends continuously along the whole of a circumference of the spark plug 10. In other words, the protruding head 21 occupies the entire circumference of the housing 2 and is exposed from the base-side inner surface 721 to the combustion chamber 72 (i.e., toward the top side Z1). In this embodiment, a portion of the spark plug 10 which is inserted into the combustion chamber 72 in the axial direction of the spark plug 10 is also referred to as the top side Z1, while the opposite side is also be referred to as the base side Z2.
The base-side inner surface 721 of the combustion chamber 72 is, as clearly illustrated in
The ignition device 1 in this embodiment may be used as an igniter for internal combustion engines mounted in vehicles, such as, automobiles.
The ignition device 1 is designed to have mounted therein an ignition coil, not shown, and apply a high-voltage, as developed at the ignition coil, to the spark plug 10 to create electric sparks in the spark gap 11. Such a spark-creating time, in other words, a time at which the high-voltage is applied to the spark plug 10 is controlled by the controller 100.
The ignition coil is equipped with a primary coil and a secondary coil which are magnetically connected together. The controller 100 works to control a primary current flowing in the primary coil, thereby controlling a secondary current flowing in the secondary coil. Specifically, cutting off the primary current flowing to the primary coil will result in induction of a secondary voltage in the secondary coil, which is, in turn, applied as the high-voltage to the spark plug 10, thereby causing sparks to be created in the spark gap 11, so that the secondary current flows in the spark gap 11.
The controller 100, as described above, works to perform a plurality of ignitions in the spark plug 10 in each cycle of the operation of the internal combustion engine 250. Specifically, the controller 100, as demonstrated in
In other words, an ignition energy (i.e., electrical energy) is delivered from the ignition coil to the spark plug 10 at a plurality of sequential times in each cycle of the operation of the internal combustion engine 250. A discharge interval Δt that is a time interval between adjacent events of the ignitions in the spark plug 10 is selected to be 2 msec. or less. In this embodiment, the two ignitions are performed in each cycle of the operation of the internal combustion engine 250.
The amounts of the ignition energy consumed by the two ignitions are selected to be substantially identical with each other.
The embodiment offers the following beneficial advantages.
The spark plug 10 of the ignition device 1 is, as described above, mounted in the internal combustion engine 250 with the head of the housing 2 protruding from the base-side inner surface 721 to the top side Z1 within the combustion chamber 72. The protruding head 21 of the housing 2 has at least a portion located downstream of the spark gap 11 in the mixture flow F within the combustion chamber 72. This, as illustrated in
The controller 100 is, as already described with reference to
In the above way, the flames B1 and B2 are mixed to create a larger flame, thereby facilitating the ignition of the mixture without need to increase the ignition energy within the whole of the combustion chamber 72.
The spark gap 11 and the upright portion 41 are, as viewed in the axial direction of the spark plug 10 in
The protruding head 21 extends continuously along the whole of a circumference of the spark plug 10. This facilitates arrangement of at least a portion of the protruding head 12 downstream of the spark gap 11 in the direction of the mixture flow F regardless of orientation of the spark plug 10 mounted in the internal combustion engine 250 and also enables the housing 2 to be formed in a simple shape, thereby resulting in a decrease in production cost of the spark plug 10.
The structure of the spark plug 10 in this embodiment is, as described above, capable of enhancing the ability of the spark plug 10 to ignite the mixture without increasing the ignition energy.
Specifically, the controller 100 works to terminate the first occurring secondary current P1 that is an earlier one of two successive secondary currents halfway before the first occurring secondary current P1 is fully completed.
The second secondary current P2 is, like in the first embodiment illustrated in
Specifically, the controller 10, as illustrated in
The above turning on of the ignition signal IGt will cause the primary oil to flow in the ignition coil again, thereby interrupting the secondary current to the spark plug 10. The electrical energy is, therefore, stored in the ignition coil again. Specifically, the electrical energy is added to that remaining in the ignition coil without being fully consumed by the first discharge. This enables the electrical energy, as required to produce the secondary current P2 (i.e., the second spark), to be stored in the ignition coil within a decrease period of time.
Afterwards, the controller 100 turns off the ignition signal IGt to interrupt the primary current, so that the secondary current P2 is delivered to the spark plug 10 again. This creates the second spark in the spark plug 10.
Other arrangements are identical with those in the first embodiment, and explanation thereof in detail will be omitted here. In the second and following embodiments, the same or similar reference numbers, as employed already, will refer to the same or similar parts.
The controller 100 in the second embodiment is, as apparent from the above discussion, designed to decrease a time interval (i.e., the discharge interval Δt) between the end of the first discharge (i.e., the end of the first secondary current P1) and the start of the second discharge (i.e., the start of the second secondary current P2). In other words, the controller 100 intentionally interrupts or stops the first discharge before it is fully completed to save the electrical energy in the ignition coil. This results in a decrease time it takes to charge, in the ignition coil after the end of the first discharge (i.e., occurrence of the first spark in the spark gap 11), an amount of electrical energy which is required to develop the second discharge (i.e., the second spark in the spark gap 11).
The second discharge (i.e., the second spark) is, therefore, started after the passage of a short amount of time (i.e., the discharge interval Δt) following the termination of the first discharge. This causes the plurality of flames B1 and B2 arising from sequential events of sparks to be produced close to each other, thereby facilitating the mixing of the flames B1 and B2. This more improves the ability of the spark plug 10 to ignite the mixture.
The second embodiment also offers substantially the same other beneficial advantages as in the first embodiment.
Specifically, the shield wall 211 extends from an end of a major body of the housing 2 into the combustion chamber 72. The shield wall 211 is located more downstream than the spark gap 11 is in the direction of the mixture flow F within the combustion chamber 72. The shield wall 211 constitutes the protruding head 21. The shield wall 211 protrudes from the base-side inner surface 721 toward the top side Z1 within the combustion chamber 72.
The shield wall 211 is curved in the circumferential direction of the housing 2 and occupies a portion of an entire circumference of the end of the major body of the housing 2. In other words, the shield wall 211 extends from the portion of the entire circumference of the housing 2 inwardly into the combustion chamber 72, that is, a base end of the spark plug 10 which is located outside the combustion chamber 72. The shield wall 211, as illustrated in
In use, the spark plug 10 is mounted in the internal combustion engine 250 with the shield wall 211, as viewed in the axial direction Z, located downstream of the spark gap 11 in the mixture flow F within the combustion chamber 72.
The shield wall 21, as clearly illustrated in
Other arrangements are identical with those in the first embodiment.
The use of the shield wall 21 enables a degree to which the head of the spark plug 10 protrudes into or is exposed to the combustion chamber 72 to be decreased, especially, on an upstream side of the spark gap 11 in the mixture flow F. This facilitates the ease with which the mixture flow F reaches the spark gap 11, which elongates a spark. The shield wall 211 occupies only a portion of the circumference of the housing 2, thereby resulting in a decrease in overall size of the housing 2. This results in a decrease in loss of an initial flame caused by being cooled by the housing 2 including the shield wall 211, thereby minimizing a risk of a misfire in the combustion chamber 72.
The third embodiment also offers substantially the same other beneficial advantages as in the first embodiment.
We conducted experimental tests on the ignition device 1 in the first embodiment.
Specifically, we mounted the spark plug 10, as demonstrated in
In the tests, an air-fuel mixture whose air-fuel ratio is 26 was injected into the simulating combustion chamber 82 to create the mixture flow F moving at a velocity of 5 m/s. The spark plug 10 was mounted in the fluid bench 8 at the same orientation as that in the first embodiment relative to the mixture flow F. The protruding head 21 of the housing 2 was exposed to the simulating combustion chamber 82 by about 5 mm. In other words, the protruding head 21 protruded by the distance a of about 5 mm (see
In the discharge pattern No. 1, the spark plug 10 was activated to perform a single event of discharge in each cycle.
In the discharge patterns No. 2 to No. 8, the spark plug 10 was activated to perform two sequential discharge events in each cycle. The discharge intervals Δt in the discharge patterns No. 1 to No. 8 are listed in table 1 below.
In each discharge pattern, an amount of electrical energy delivered to the spark plug 10 in each cycle was about 80 mJ.
We observed states of combustion of the mixture in the discharge patterns No. 1 to No. 9. Specifically, we took images of the states of combustion through the monitor window 84 of the fluid bench 8 with a high-speed camera using schlieren techniques. The images derived using the schlieren techniques (which will also be referred to below as schlieren images) do not always match outlines of flames, but a portion of the schlieren image where combustion reaction is more active usually appears darker or deeper. Dark portions of the schlieren images match combusted portions of the mixture or flames. In the following discussion, the dark portions of the schlieren images will also be referred to as flames for convenience sake.
The schelieren images were took three times: 10 msec. 15 msec. and 40 msec. after start of the discharge in the spark plug 10. In the discharge patterns No. 2 to 9 where the two sequential events of discharge were performed, the above times are based on the start of the first event of the discharge.
The schlieren images in the discharge patterns in some of the discharge patterns No. 1 to No. 9 are illustrated in
The schlieren images show that the flame is first moved by the mixture flow F downstream (i.e., the right side in the images) away from the spark plug 10 and then expands to create a flow of the flame back to the spark plug 10. Particularly, in the discharge patterns No. 2 and No. 3, the flame expands greatly. This shows that two sequential events of the discharge performed at the decreased discharge interval Δt facilitate the expansion of a flame.
We also more objectively evaluated the schlieren images in the discharge patterns according to index combustion velocities. We classified locations of leading portions of the flames moving back to the spark plug 10 in 40 msec. after the start of the discharge into five types. Specifically, the leading portions of the flames moving back to the spark plug 10 which lie between the center of the monitor window 84 and the spark plug 10 are labeled as the level 3. The leading portions of the flames lies over the spark plug 10 are labeled as the level 4. The leading portions of the flames lies upstream (i.e., the left side in the drawings) of the spark plug 10 are labeled as the level 5. There are no schlieren images to which the levels 1 and 2 are applicable. The levels 1 and 2 will, therefore, not be referred to in this disclosure.
Results of the evaluation using the index combustion velocities are represented by the above table 1 and
Table 1 and the graph in
The regulation of the discharge interval Δt may be achieved in the following way. The controller 100 may change the discharge interval Δt as a function of a speed of or a load on the internal combustion engine 250. Usually, when the speed of the internal combustion engine 250 is increased, it will result in an increase in velocity of the mixture in the combustion chamber. The discharge interval Δt is, therefore, preferably shortened with an increase in speed of the engine 250. When the load on the engine 250 is decreased, it will result in a decrease in temperature in the combustion chamber. The discharge interval Δt is, therefore, preferably shortened with a decrease in load on the engine 250. The controller 100 may regulate the discharge interval Δt in the above way using a sensor measuring the velocity of the mixture in the combustion chamber or temperature in the combustion chamber.
The controller 100 may alternatively shorten the discharge interval Δt with a decrease in amount of electrical energy for the discharge in the spark plug 10.
While the present invention has been disclosed in terms of the preferred embodiments in order to facilitate better understanding thereof, it should be appreciated that the invention can be embodied in various ways without departing from the principle of the invention. Therefore, the invention should be understood to include all possible embodiments and modifications to the shown embodiments which can be embodied without departing from the principle of the invention as set forth in the appended claims.
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