GB2310003A

GB2310003A - Combustion chamber for in-cylinder direct fuel injection, spark ignition engine

Info

Publication number: GB2310003A
Application number: GB9702648A
Authority: GB
Inventors: Akira Akimoto
Original assignee: Fuji Jukogyo KK; Fuji Heavy Industries Ltd
Current assignee: Subaru Corp
Priority date: 1996-02-09
Filing date: 1997-02-10
Publication date: 1997-08-13
Anticipated expiration: 2017-02-10
Also published as: JPH09209762A; JP3681080B2; DE19705023B4; DE19705023A1; GB2310003B; GB9702648D0

Description

2310003

-1DESCRIPTION

COMBUSTION CHAMBER FOR IN-CYLINDER DIRECT FUEL INJECTION ENGINE The present invention relates to the construction of combustion chamber for an in-cylinder direct fuel injection type spark ignition engine and more particularly to the construction of a cylinder head and a piston which readily produce a.tumble flow and to a disposition of a spark plug and a fuel injector so as to optimize the combustion of fuel sprayed from a fuel injector.

Generally, in this type of engine the combustion strategy can be selectively switched to.either of two combustion strategies, a stratified charge combustion and a homogeneous combustion. The stratified charge combustion is obtained by achieving charge stratification at the later stage of the compression stroke and forming ignitable mixture gases around the spark plug and the homogeneous charge combustion is achieved by mixing fuel injected during the intake stroke with intake air.

As an example of the technology of the combustion chamber suitable for both stratified charge combustion and homogeneous charge combustion, the inventor of the present i n v e n - tion has proposed a Japanese Patent Application Laid-open No. Toku-Kai- Hei 6-42352 in which an fuel injector is disposed in a v e rt i c 4.1 position at the top centre o f the combustion chamber and a cavity is formed at the top surface of the piston in the counter direction to the injection direction of the fuel injector. Further, in this invention an electrode of the spark plug is disposed in the vicinity of the nozzle of the fuel injector.

According to this combustion chamber structure, in a stratified charge combustion, the end portion of fuel whose injection terminates immediately before the ignition t i m i n g i s ignited by the s p a r k plug or a i r - f u e 1 mixtures impacted on and reflected by the cavity of the piston are i g n i t e d j u s t at t h a t i g n i t i o n t i m i n 9, whereby combustion stability is secured. On the other hand, in a homogene- ous charge combustion, since fuel, starts to be injected at a rather early stage of the intake stroke, homogeneous air-fuel aixtures can be obtained. Furthermore, according to this combustion chamber, since the fuel injector is provided in a vertical position at the top centre of the combustion chamber, sprayed fuel is prevented from sticking to the cylinder wall surface, thereby avoiding an adverse effect on combustion due to so-called fuel quenching.

In order to obtain a stable combustion by forming ignitable air-fuel mixtures at t h e i g n i t i o n p o i n t of t h e spark plug, a best finishing timing of fuel injection (BITI) where ignition is optimum has a characteristic shown by a broken line in Fig. 13. As understood by the characteristic Line, the best fuel injection timing has a very weak corre lation with respect to the fuel injection amount (or engine load) and consequently it is understood that the finishing timing of fuel injection is allowed to be kept constant with respect to the ignition timing.

However, as shown in Fig. 14, when the fuel injec- tion timing becomes advanced (rendered early) with respect to the ignition timing, since injected fuel is more premixed with air, HC and NOx emissions increase up to a given advance angle and then thereafter gradually decrease. On the con- trary, when the fuel injection timing becomes retarded(rendered 1 a t e) with respect to the ignition timing, sinceinjected fuel is burned in droplets, smoke emissions increase due to the lack of vaporization of fuel. Further, there is a tenden- cy f o r the timing of smoke generation to come early as the fuel injection amount increases. Consequently, according to a best injection timing control (BITE), it is necessary from the aspect of emissions (smoke, CO, HC and NOx) that the fuel injectiontiming be advanced with an increase of the fuel injection amount (engine load).

As.a result of this, in a stratified charge combustion, it is clearly understood that the BITI control focused on ignitabitityhas a different control area from the BITE control focused on emissions countermeasures.

-4 However, in case of a combustion chamber wherein a flat cavity la is formed on the top surface of the piston as shown in Fig. 15, if the fuel injection (finishing) timing is established early, fuel sprayed from the fuel injector 2 is diffused around after being impacted on the cavity. Resultant I y, f u e 1 spray does n o t reach the neighbourhood of the electrode 3a of the spark plug 3 and ignitable air-fuel m i xtures can not be formed around the e I ect rode 3a, ( e a d i n g to misfires or incomplete combustion. Therefore, in case of a n e n g i n e havi ng a pi ston conf i gurat i on 1 i ke thi s, i t i s necessary to bring the injection finishing timing close to the ignition timing and to ignite an end portion of sprayed fuel. That is to say, it is understood that there is a limit in advancing the fuel injection (finishing) timing according to the fuel injection amount.

To solve this problem, i'.has been proposed for the flat cavity la at the top surface of the piston to be modified to a curved shape so that fuel injected from the fuel injector curls up along the curved surface of the cavity. This idea enables the formation of an ignitable air-fuel mixture around the electrode of the spark plug and the fuel injection timin to some degree. However, this method of relying upon the fueL spray configuration, is still inadequate to securd i g n i t a b 1 e air-fuel mixtures around the spark plug when the fuel injection timing is further advanced.

Generally, in case of stratified charge combus- t i o n, ai r-f uel mixtures around the electrode of the spark plug become overrich or cause a lack of vaporization as a mean air-fuel ratio comes near the stoichiometric air-fuel r a t i o, i. e., the injection amount i s increased and this results in generation of, smoke. CO and HC emissions. This means that there is a given rich Limit in the mean air- fuel ratio at stratified charge combustion. On the other hand, in case of homogeneous charge combustion, since the overall mixture gases are homogenized, there is also a given lean limit under which ignition is impossible.

It is known that the stratified charge combustion is fit for low and medium load operations and homogeneous charge ccrmbustion is f i t f o r h i g h Load operations. E n g i n e loads vary continuously during operation. Further, in the in-cylinder direct fuel injection engine airfuel ratios are established variably according to changing engine loads. Therefore,in the case where the rich limit of the stratified charge combustion is located at a leaner side than the Lean limit of homogeneous charge combustion, each time the operating area of the engine varies, the air-fuel ratio is changed discontinuously, t h a t i s, when changing f rom stratified charge combustion to homogeneous charge combustion, a swift change occurs in the ri ch direction of ai r-f uel ratio and when changing f rom homogeneous charge combustion to stratified charge combustion, a rapi d change occurs to the 1 e a n s i d e.

Thus, the situation in which the air-fuel ratio is changed discontinuously each time the combustion strategy varies results in deteriorated emissions and unacceptable driveability. This situation will be described with reference to Fig. 13.

In order to retain the continuity of air-fuel ratio (assuming that intake air amount is constant), i f the injection amount at stratified charge combustion is established at the same level P, as the lean limit P3 of homogeneous charge combustion, there occur inconveniences such as a generation of smoke emissions and an increase of CO emissions the point P 1 On the other hand, if the injection amount is established at the rich limit P 2 so as to avoid these inconveniences when switching from stratified charge combustion to homogeneous charge combustion, the injection amount is increased fxom P 2 to P 3 abruptly and this brings about a discontinuity of engine output against engine load.

Accordingly, the present invention i obviate the disadvantages of the known art.

It is an object of the present invention to provide a construction of combustion chamber for an in-cylinder direct fuel injection spark ignition engine capable of estab1 i s h i n g a wide range of i n j e c t i o n finishing timing at stratified charge combustion according to the fuel injection s intended to amount without an adverse effect on emissions and always obtaining a stable ignition performance.

It is a further object of the present invention to provide a construction of combustion chamber capable of securing a continuity of engine load when switching from stratified charge combustion to homogeneous charge combustion so as to obtain a good driveability.

A combustion chamber for an in-cylinder direct fuel injection spark ignition engine comprises:

a fuel injector disposed between the intake valve side roof and the exhaust valve side roof and slightly inclined toward the exhaust valve side; an intake port provided on an intake port side roof at an acute angle including zero degree with respect to an extended line from an exhaust side roof so as to form a tumble flow of intake air along the exhaust side roof; a piston cavity with a curbed surface formed on the top surface of a piston so as to reflect fuel spray injected from a fuel injector together with that tumble flow in the direction of the intake side roof; and an electrode of a spark plug projected from the intake side roof so as just to collide with the tumble flow including fuel spray.

In accordance with a second aspect of the present invention, there is provided a combustion chamber for an in-cylinder direct fuel injection spark ignition engine having a roof on an intake valve side, a roof on an exhaust valve side, an intake valve provided in said intake valve side roof for introducing intake air therethrough, an exhaust valve provided in said exhaust valve side roof for discharging exhaust gas therethrough, a piston, a cylinder and a spark plug, the combustion chamber comprising:

a fuel injector disposed between said intake valve side roof and said exhaust valve side roof and inclined at a first inclination angle toward said intake valve side with respect to an axis of said cylinder; an intake port provided on said intake valve side roof at a second inclination angle with respect to an axis of said cylinder so as to hit said intake air directly against said piston and form a tumble flow of said intake air; a piston cavity with a curved surface formed on the top surface of said piston so as to reflect a fuel spray injected from said fuel injector together with said tumble flow of said intake air in the direction of said exhaust valve side roof; and an electrode of said spark plug projecting from said exhaust valve side roof so as to be exposed to said tumble flow and said fuel spray reflected by said piston cavity.

By way of example only, specific embodiments of the present invention will now be described with reference to the accompanying drawings, in which:Fig. 1 is a schematic drawing showing a combustion -gchamber of an in-cylinder direct fuel injection spark ignition engine according to a first embodiment of the present invention; Fig. 2 is a side view showing the construction of a combustion chamber of the first embodiment of the present invention; Fig. 3 is a top view of the combustion chamber of the first embodiment of the present invention; Fig. 4 is a side view of showing a state of fuel spray ately before ignition timing in the chamber of Fig. 1; Fig. 5 is a side view showing a state of fuel spray impacted on a piston cavity in the chamber of Fig. 1; Fig. 6 is a side view showing a state of fuel spray when there is no tuTible flow during acceleration in the chamber of Fig. 1; Fig. 7 is a side view showing a state of fuel spray when there occurs a t umble flaw during acceleration in the chamber of Fig. 1; Fig. 8 is a diagram showing a relationship between combustion stability and injection timing; Fig. 9 is a diagram showing a relationship between a driveable zone and a best injection timing; Fig. 10a is a diagram showing a comparison of a rate of combustion fluctuation between a piston with a flat top surface and a piston with a curved cavity; Fig. 10b is a diagram showing a comparison of a smoke density between a piston with a flat top surface and a piston with a curved cavity; Fig. 10c emssions between a piston with a curved Fig. 10d emissions between a piston with a curved Fig. Ila rate of combustion direction of tumble is a diagram showing a comparison of NOx piston with a flat top surface and a cavity; is a diagram showing a comparison of HC piston with a f lat t o p surface and a cavity; is a diagram showing a comparison of a fluctuation according to a rotational flow and a tumble rate; F i g. 11 b i s a diagram showing a comparison of smoke den-sity according to a rotational direction of tumble flow and a tumble rate; Fig. Ilc is a diagram showing a comparison of NOx emissions according to a rotational direction of tumble flow and a tumble rate; Fig. Ild is a diagram showing a comparison of HC emissions according to a rotational direction of tumble flow and a tumble rate; Fig. 12 is schematic drawing showing a combustion chamber according to a second embodiment of t h e present invention; Fig. 13 is a diagram showing a relationship bet w e e n f u e 1 i n j e c t i o n finishing t i m i n g and f u e 1 i n j e c t i o n amount according to the prior art;

Fig. 14 is a diagram showing a relationship between the amount of emissions and fuel injection timing; and Fig. 15 is a schematic drawing showing a combustion chamber of an in- cyLinder direct fuel injection spark ignition engine according to the prior art.

An example of a combustion chamber of an in-cylind e r d i r e c t f u e 1 i n j e c t i o n e n 9 i n e i s presented i n F i 9. 1 through Fig. 7. This example indicates a combustion chamber of a DOHC engine with four valves. In these drawings, numeral 11 denotes a cylinder, numeral 12 denotes a cylinder head, numeral 13denotes apiston, and numeral 14denotes acombustion chamber which is formed by a top surface 13a of the piston 13 positioned at top dead centre, an inner wall of the cylinder 11 and a bottom surface of the cylinder head 12.

A concave 12a is formed at the bottom surface of the cylinder head 12. The concave 12a belongs to a so-called pentroof type in this embodiment. A top portion 12b is formed at the top of the concave 12a slightly away from the cylinder centre (line A). A fuel injector 15 is disposed near the centre of the top portion 12b with its nozzle 15a facing the combustion chamber 14. An intake port 16 is provided at the intake side pentroof 12c of the concave 12a respectively on both sides of the fuel injector 15 and an exhaust port 17 is provided at an exhaust side pentroof 12d of the concave 12a respectively on both sides of the fuel injector 15.

Further, a squish area 18 is formed at the bottom of both pentroofs 12c, 12d.

Further, an intake valve 21 and an exhaust valve 22 are provided in the intake port 16 and in the exhaust port 17 respectively. The intake valve 21 is driven by an intake cam 19 and the exhaust valve 22 is driven by an exhaust cam 20. As shown in Fig. 1, the intake port 16 has a straight shape and extends parallel to an extended line L,, of the exhaust side pentroof 12d or inclined at an acute angle y upward with respect to the extended line L,,. Preferably the acute angle y is in the range from 0 to 15 degrees. Further, the intake port 16 has an inclination angle 0 (preferably from 0 to 20 degrees) with respect to the axis of the cylinder 11. Intake air is guided through the thus constituted intake port 16 and flows into the combustion chamber 14 along the exhaust side pentroof 12d, causing a tumble flow turning anticlockwise in the combustion chamber 14 as shown in Fig. 1.

Further, in this embodiment, the fuel injector 15 whose centre line is shown by a line B is inclined toward the exhaust port 17 at an inclination angle a (positive anticlockwise on the drawing) with respect to the axis of the cylinder 11 so as to obtain a more effective fuel spray. The angle a is preferably in the range from 20 to -5 degrees.

A cavity 13b with a curved surface is formed on the top surface 13a of the piston 13. The cavity 13b has such a shape and location as to be able to guide the tumble flow along the curved surface and to turn it toward the intake side pentroof 12c smoothly. As illustrated by a one-dot chain line in Fig. 3, the cavity 13b is located directly under the fuel injector 15 and at a position slightly offset to the side of the exhaust port 17.

An electrode 23a of a spark plug 23 projects from the intake side pentroof 12c between the intake ports 16 and 16 so as to collide with the tumble flow reflected by the cavity 13b and to be exposed to fuel spray when fuel is i n j e c t e d Generally, there is an expertised technical term, a tumble rate, to express an intensity of tumble flow numericalty. The tumble rate is defined as a number of rotations of intake air per one revolution of the crank shaft and it is determined depending o n miscellaneous factors s u c h a s a n inclination angle of the intake port 16, a configuration of the combustion chamber 14, a configuration of the piston 13 and the like. In this embodiment, the tumble rate is determined primarily by the inclination angle of the intake port 16, and the position and curvature of the cavity 13b of the piston 13. According to experiments by the inventor, it has been found that tumble rates ranging from 0.5 to 1.7 produce a most favourable result. That is to say, with a tumble rate smaller than 0.5, the tumble flow decays before the compression stroke, resulting in failure to form a good airf u e 1 m i x t u r e. On the other hand, with a tumble rate larger than 1.7, the tumble flow is so strong that intake air reflected from the cavity 13b of the piston 13 is spread around towards the cylinder wall, resuttantly sprayed fuel is diffused in the stream of the scattering tumble flow and an ignitable air- fuel mixture is not formed around the electrode 23a of the spark plug 23. Consequently, it is desirable that the tumble rate be established within a range of 0.5 to 1.7.

Further, according to experiments by the inventor, it is known that the combination of the inclination angle a ranging from 20 to -5 degrees and the acute angle y ranging from 0 to 15 degrees brings the most favourable effects to the formation of tumble flow. Further, with respect to the size and location of the cavity 13b, it is known that its diameter d (millimetre) calculated according to the following formula bears a most favourable result.

d = D x 0.5 - k where D (millimetre) is a piston diameter and k is a constant (millimetre) ranging 'from 0 to 5 millimeterms. Further, its depth e and its offset amount s from the cylinder axis should take values ranging from 5 to lomillimetres and from 0 to 5 millimetreS respectively.

Next, an operation of thus constituted combustion chamber wilt be described.

Under stratified charge combustion at an extremely low load, the engine is operated with the BITI control where- by stable combustion is obtained. In this case, since the best fuel injection timing is set near the ignition timing, sprayed f u e 1 i t s e 1 f m a k e s air-fuel m i x t u r e g a s around t h e electrode 23a of the spark plug 23 and this mixture gas is ignited at the ignition timing. At extremely low load, gas s p e e d is very low and therefore air-fuel m i x t u r e i s n o t -15affected by the configuration of the piston cavity 13b.

Further, at the BITE control equivalent to a constant speed running (RIL load), as shown in Fig. 8, f u e 1 injection is finished earlier than the BIT1 control, therefore, fuel spray at the end of injection is impacted on the piston cavity 13b and a flow of fuel spray curls up therefrom. Thus, ignitable air-fuel mixture is formed around the electrode 13b of the spark plug 13, as illustrated in Fig. 5. A one-dot chain line (b) in Fig. 8 presents an ignitabi lity of fuel injected at the same timing as in a case of a piston cavity with a fLat surface (see Fig. 15). In the case of a pisfon with a f lat surface, f u e 1 s p r a y is diffused around toward the cylinder bore without being reflected upward, and as a result an ignitable mixture gas is not formed around the electrode 23a of the spark plug 23. Therefore, in this case the BITE control can not be conducted due to poor comb u s t i o n.

Furthermore, at the BITE control equivalent to an acceleration load, the fuel injection finishing timing comes earlier as shown in Fig. 8. In this case, early injection timing fosters diffusion or vaporization of sprayed fuel. F i 9. 6 indicates an example of the combustion chamber in which air-fuel mixture lies on the allover surface of the piston cavity 13b. If a tumble f low is given to this state, these air-f uet mixtures curt up toward the electrode 23a of the spark plug 23, forming an ignitable mixture gas around -16the e 1 ect rode 23a j ust when i gni t ion i s app 1 i ed. Thus, as shown in Fig. 8, the BITE control i s available even when ignition is applied early during acceleration equivalency. According L y, a c cordi ng to t h is embodiment, combustion can be k e p t stable over a broad area r a n g i n 9 f rom the misfiring limit (a) on the Late side to the misfiring limit (d) on the ear ly side. The mi sf i ri ng 1 i mi t (a) i s a 1 imit 1 i ne whose Left area indicates an area causing misfire due to the proximity of the injection timing to the ignition timing, namely, due to the breakage of discharge passes of the spark plug 23 by fuel spray.

Fig. 10a through Fi g. 10d show examples of compari son data between a pi ston with a f Lat top surf ace and a piston with a curved cavity in combustion or emissions characteristiz.

As understood f rom those comparison data, i n the case of a piston with a curved cavity, establishing the fuel injection finishing timing early has no adverse effect on combustion until a rather early timing. In this case the fuel injection timing can be established within a broad range. On the other hand, in case of a pi ston with a f lat top surf ace an early establishment of the fuel injection finishing timing i ncurs Poor combustion or mi sf i re because an ignitable ai rfuel mixture gas is not formed around the electrode of the spark plug. Consequently, in this case the selectable range of the fuel injection finishing timing is very narrow.

Referring to F i g. lla through F i g. 11 d, t h e s e drawings show differences of combustion and emissions characteristic with respect to a rotational direction of tumble flow and a tumble rate.

Comparing the tumble flow rotating in the direction of this embodiment with the one rotating in an inverse d i r e c t i o n, the tumble flow having an inverse rotational direction is proved to be inferior in the aspect of ignitabiLity for the reason that the inverse tumble flow blows out in an opposite direction to the electrode of the This tendency becomes more remarkable as the fuel timing becomes earlier. With respect to an effect rate, it is proved that there is a certain optimal the tumble rate. According to experiments by the it has been proved that the optimal value of tumble.0 in case of configurations of the combustion and the piston cited in this embodiment. Further it fuel spray spark plug i n j e c t i o n of tumble vat ue i n inventor, r a t e i s 1 chamber has been proved that a stable ignition can be obtained within a range of 0.5 to 1. 7 of tumble rate. That is to Say, if the tumble rate is smaller than 0.5, it is proved that the tumble flow is deteriorated before reaching the compression stroke, having no use in the formation of air-fuet mixture. Further, if the tumble rate is larger than 2.0, it is proved that the tumble flow is so strong that fuel spray is diffused and as a result an ignitable air-fuet mixture is not formed around the electrode of the spark plug.

Fig. 9 shows a driveable range of ai r-f uel ratio versus to the fuel injection timing by diagonal shading when the BITE control is conducted. The a i r-f ue 1 ratio and the f u e 1 i n j e c t i o n f i ni sh i ng t i m i n 9 in ea c h d r i v i n g a r e a a r e determined by miscellaneous limits such as discharge pass breakage by fuel spray, generation of smoke, combustion fluctuation and the like. As understood from this diagram, with 1 the air- fuel ratio and the injection timing within this driveable range, the BITE control can be retained and the air-fuel ratio can be changed continuously, ranging from the stratified charge combustion to the homogeneous charge combustion, without having an adverse effect on the ignitability and combustibility of the engine.

F i g. 12 depicts a second embodiment according to the present invention.

In the second embodiment, the spark plug 23 is relocated from the intake port side to the exhaust port side 17 and its electrode 23a projects into the combustion chamber 14 from between two exhaust valves 22 and 22. In this case, since an inclination angle e (positive clockwise on the drawing) of the intake port 16 with respect to the cylinder axis is designed to be smaller than that of the first embcdiment, the tumble flow is generated in an adverse direction to the tumble direction according to the first embodiment, i.e. in a clockwise direction as shown in this drawing. Preferably the angle 8 is in the range from 0 to 20 degrees. That is, the intake air introduced through the intake valve 21 first hits the top surface 13a of the piston 13 and then the tumble flow is generated by the piston 1 -19cavity 13b of the piston 13. The tumble flow curls up from the piston cavity 13b in the direction of the pentroof 12d of the exhaust s i d e. The fuel spray injected from the fuel injector 15 collides with the tumble f tow and forms air-fuel mixtures there. In this embodiment, the fuel injector is inclined at an inclination angle Xslightly tamard the intake port 16 so as to obtain a more effective fuel spray. In this embodiment, the inclination angle O,Of the fuel injector 15 is preferably in the range frcm 5 to -20 degrees. Thus, ignitable mixture gas is fcm& around the electrode 23a of the spark plug 23.

This disposition of the spark plug 23 on the exhaust port side has the advantage of permitting the enlargement of the diameter of the intake valve, compared with the first embodiment. In this embodiment too, it is desirable that the tumble rate is established to a value ranging from 0.5 to 1.7.

In summary, acco rdi ng to the f i rst embodi ment o f the present invention, intake air introduced into the combustion chamber is guided along the pentroof on the exhaust port s i de and then a f t er co 11 i di ng wi th the curved pi ston cavi ty on the top of the piston, the tumble flow curls up toward the vicinity of the electrode of the spark plug. On the other hand, according to the second embodiment, intake air is introduced into the combustion chamber and then after directly colliding w i t h t h e curved piston cavity, t h e t u m b 1 e f low curls up toward the vicinity of the electrode of the spark p 1 u g. When the injection timing is relatively t a t e, i. e., when it is relatively close to the ignition timing ( s t r a t i - fied charge combustion area), air-fuel mixture is formed in t h e v i c i n i t y o f t h e electrode of t h e s p a r k p 1 u 9 b y t h e sprayed fuel itself and that gas mixture is ignited by the spark plug. When the injection timing is relatively early, i. e., w h e n i t i s relatively far from the ignition timing (stratified charge combustion area), sprayed fuel is reflect ed by the piston cavity and the reflected fuel spray forms mixture gas around the electrode of the spark plug. Then, the mixture gas is ignited at the specified ignition timing. When the injection timing is earlier still (in this area, there is a stratified charge combustion at t h e e a r 1 y stage and t h e r e is a homogeneous charge combustion at t h e 1 a t t e r s t a 9 e 9-prayed fuel is trapped by the piston cavity, t h e trapped fuel is mixed with therising tumble flow and the mixture gas reaches the vicinity of the electrode of t h e spark plug. Then, the mixture gas is ignited at the specified ignition timing. The transfer from stratified charge combus tion to homogeneous charge combustion is continuously carried out. Thus, throughout all operating conditions of the engine, a stable ignitabi lity and a stable combustion performance can be achieved. The stable combustion leads to suppression of unac ceptable HC, CO, NOx and smoke emissions and a smooth ' transfer from stratified charge combustion to homogeneous charge combustion contributes to good driveability.

Further, by means of establishing the rotational number of the tumble f low per one engine revolution between 0.5 and 1.7, ignitable air-fuel mixture is achieved around the electrode of the spark plug not to deteriorate the tumble flow during the compression stroke and further not to diffuse fuel around.

In accordance with the first embodiment, the large arrow indications (4) in Figs. 1,2, and 7 show the induced air flow from upper surfaces of the intake pipe 16 and the combustion chamber 14 to the cavity 13 of the piston 13, and the tumble flow occurs in the counter-clockwise direction. Therefore, the induced air mixes effectively with the fuel injected from the upper side.

In accordance with the second embodiment, the large arrow indication (4) in Fig. 12 shows the air induced into the combustion chamber 14, i.e., into the cavity 13 of the piston 13. The tumble flow occurs in the clockwise direction. Therefore, the induced air mixes effectively with the fuel injected from the upper side and efficiently ignited by the electrode 23a of the spark plug 23 for an optimum combustion.

While the presently preferred embodiments of the present invention have been shown and described, it is to be understood that these disclosures are for the purpose of illustration and that various changes and modifications may be made without departing from the scope of the invention.

i

Claims

-22CLAIMS

1 A combustion chamber for an in-cylinder direct fuel injection spark ignition engine having a roof on an intake valve side, a roof on an exhaust valve side, an intake valve provided in said intake valve side roof for introducing intake air therethrough, an exhaust valve provided in said exhaust valve side roof for discharging exhaust gas there through, a piston, a cylinder and a spark plug, the ction chamber canprising:

a f uet injector disposed between said intake valve side roof and said exhaust valve side roof and inclined at a f i r s t i n c 1 i n a t i o n a n 9 L e toward said exhaust valve side with respect to an axis of said cylinder; an intake port provided on said intake valve side roof at an acute angle (including zero degrees) upward with respect to an extended line from said exhaust valve side roof so as to form a tumble f low of said intake air along said exhaust valve side roof; a piston cavity with a curved surface formed on the top surface of said piston so as to reflect a fuel spray injected from said fuel injector together with said tumble flow of said intake air in the direction of said intake valve side roof; and n electrode of said spark plug projecting from said intak: valve side roof so as to be exposed to said tumble flow and said fuel spray ref lected by said piston c a v i t y.

2. A combustion chamber for an in-cylinder direct fuel injection spark ignition engine having a roof on an intake valve side, a roof on an exhaust valve side, an intake valve provided in said intake valve side roof for introducing intake air therethrough, an exhaust valve provided in said exhaust valve side roof for discharging exhaust gas therethrough, a piston, a cylinder and a spark plug, the combustion chamber comprising:

3. A combustion chamber as claimed in claim 1 or claim 2, wherein said tumble flow rotates at a rotation ranging from 0.5 to 1.7 per one rotation of said amount engine.

4. A combustion chamber as claimed in any of claims 1 to 3, wherein said first inclination angle ranges from 20 to -20 degrees.

5. A combustion chamber as claimed in claim 4, wherein said first inclination angle ranges from 20 to -5 degrees.

6. A combustion chamber as claimed in claim 4, wherein said first inclination angle ranges from 5 to 20 degrees.

7. A combustion chamber as claimed in claim 1 or any of claims 3 to 6 when appendant to claim 1, wherein said acute angle ranges from 0 to 15 degrees.

8. A combustion chamber as claimed in claim 2 or any of claims 3 to 6 when appendant to claim 2, wherein said second inclination angle ranges from 0 to 20 degrees.

9. A combustion chamber substantially as herein described, with reference to, and as illustrated in, Figs. 1 to 12 of the accompanying drawings.

10. An in-cylinder direct fuel injection spark engine comprising a combustion chamber as claimed in any of the preceding claims.

11. A vehicle comprising an engine as claimed in claim 10.