AU679287B2

AU679287B2 - Two-stroke engine of the spark ignition type

Info

Publication number: AU679287B2
Application number: AU81567/94A
Authority: AU
Inventors: Yoichi Ishibasi; Takaharu Kurosaki; Kenjiro Saito; Yuji Tsushima
Original assignee: Honda Motor Co Ltd
Current assignee: Honda Motor Co Ltd
Priority date: 1993-12-18
Filing date: 1994-12-19
Publication date: 1997-06-26
Anticipated expiration: 2014-12-19
Also published as: KR0130021B1; TW284825B; KR950019190A; AU8156794A

Description

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-1- TWO-STROKE ENGINE OF THE SPARK IGNITION TYPE This invention relates to a two-stroke engine of the spark ignition type, in which fresh air in a combustion chamber can be compressed and self ignited at least in a low load operating state to effect activated heat atmosphere combustion, wherein the fresh air in the combustion chamber can be ignited, in a transition operating state between the activated heat atmosphere operating state and an ordinary spark ignition combustion operating state, by spark ignition at a timing earlier than the spark ignition timing in the ordinary spark ignition combustion operating state to stabilise the combustion condition to eliminate abnormal combustion noise or harmful effects of heat.

In a two-stroke engine of the spark ignition type with a carburettor where fresh air obtained by mixing fuel with air in advance is supplied into a combustion chamber, an exhaust port and a scavenging port which are opened and closed by a piston are formed on an inner circumferential face of a cylinder bore. Fresh air pressurised in a oO.e crank chamber is supplied into a cylinder chamber through the scavenging port while burnt gas in the cylinder chamber is expelled through the exhaust port, and the fresh air compressed in the cylinder chamber is ignited by means of an ignition plug.

In such a conventional two-stroke engine of the spark ignition type as described above, if the exhaust port is made large in order to set the output power and the efficiency in a high speed, high load operating state to a high level, then, in a low oeload operating state, the amount of unburnt hydrocarbons in the exhaust gas is increased due to blow-by of fresh air or unstable combustion, resulting in low fuel efficiencies.

In order to eliminate this, an engine has previously been developed in which an exhaust control valve acting as an exhaust air passage opening ratio adjustment means is actuated to provide a given exhaust air passage opening ratio in response to the engine speed and the throttle valve opening to control the in-cylinder pressure when the exhaust opening is closed up by the piston an appropriate amount, at least in a low load operating state, so that fresh air in a combustion chamber can be activated by heat [N:\libtt]00391:HRW I I I _II energy of burnt gas remaining in the combustion chamber to cause the fresh air in the combustion chamber to be compressed and self ignited at an ignition timing preferable for operation of the engine.

The combustion in which the ignition timing preferable for operation of an engine is positively controlled to cause activated heat atmosphere combustion to take place in this manner is hereinafter referred to as AR combustion, and the operating state in which such AR combustion takes place will be hereinafter referred to as AR operating state.

In such a two-stroke engine of the spark ignition type in which AR combustion can take place as described above, an ignition plug generates a spark at a predetermined ignition timing regardless of the operating condition of the engine, and since the amount of fresh air taken in is small in an AR combustion operation which makes use of heat energy of burnt gas, as apparent from a characteristic diagram of FIG. 6, when the engine speed Ne (rpm) is higher than a very low speed, the output power is low 15 compared to that in an ordinary combustion operation in which ignition firing takes place, but in a transition operating state A between the ordinary combustion operating *state and the AR combustion operating state, ordinary combustion and AR combustion take place in a mixed manner.

If, in the AR combustion operating state, the exhaust air passage opening ratio 20 is set appropriately in response to the comparatively low engine speed and the o comparatively small throttle valve opening by way of the exhaust control valve, then compression self ignition in which the ignition timing is stabilised takes place without being influenced by the spark ignition timing by the ignition plug. However, in the transition operating state A in which ordinary combustion and AR combustion take place in a mixed condition as described above, in a particular engine revolution, fresh air activated by heat energy of burnt gas is ignited by compression self ignition at an early timing to cause a sudden combustion reaction so that, as shown at the middle and lower parts of FIG. 8, a great pressure variation and a high in-cylinder pressure are provided, but in a subsequent engine revolution, the ignition timing is delayed by a [N:\libtt]00391:HRW I I drop in expansion end temperature due to the early ignition, and a small pressure variation and a low in-cylinder pressure are provided, Such phenomena take place alternately, and the ignition timing is not stabilised and high exhaust noise is produced.

Meanwhile, in the claim of the official gazette of Japanese Patent Laid-Open Application No. Showa 53-109007, it is recited: "an operation method for a spark ignition engine, characterised in that a cylinder which is normally operated with spark ignition is operated upon particular operation such that both of an intake air flow and an exhaust air flow or only the exhaust air flow is restricted so as to effect operation with compression ignition, and upon transition to the compression ignition operation, said cylinder is operated with spark ignition at a compulsorily advanced ignition timing", which is understood as meaning the ignition timing is advanced in a transition operating state between an ordinary combustion operating state and an AR combustion operating state within a single cylinder. However, since, upon transition to the compression self ignition operation (different from the AR combustion operation) in which the compression self ignition timing is not controlled, the exhaust air flow is restricted so as to effect a compression self ignition operation within one of two cylinders while only the ignition timing is advanced without restricting the exhaust air flow within the other cylinder, combustion is started prior to the top dead centre to cause an excessively early ignition condition. Consequently, the occurrence of harmful heat effects or abnormal combustion noise is invited.

It is the object of the preser: invention to overcome or substantially ameliorate the above disadvantages.

There is disclosed herein a two-stroke engine of the spark ignition type ooooo S0 wherein a fresh charge, obtained in advance by mixing fuel into air, is supplied into a combustion chamber and the fresh charge in said combustion chamber can be compressed and self ignited at least in a low load operating state to effect activated heat atmosphere combustion, said engine comprising: exhaust air passage opening ratio adjustment means for adjusting an opening ratio of an exhaust air passage to control a compression starting in-cylinder pressure; [N:\lAibtt]00391:HRW U I I SO

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0 5 ignition timing adjustment means for adjusting an ignition timing; and control means for driving said exhaust air passage opening ratio adjustment means to an exhaust air passage opening ratio determined from at least engine speed and throttle valve opening parameters to adjust the compression starting in-cylinder pressure to a predetermined compression starting timing in-cylinder pressure with which the fresh charge in said combustion chamber can be compressed and self ignited at an ignition timing preferable to operation of said engine, said control means also being for operating said ignition timing adjustment means in a transition operating state between the activated heat atmosphere combustion operating state and an ordinary spark ignition combustion operating state to cause spark ignition to occur at a timing earlier than a spark ignition timing in the ordinary spark ignition combustion operating state to control a combustion starting timing by the spark ignition to a timing in the proximity of the top dead centre.

Since the preferred form of the present invention is constructed in such a manner as described above, in the transition operating state between the AR combustion operating state and the ordinary combustion operating state, spark ignition by the ignition plug can be caused to take place at a timing earlier than the spark ignition timing in the ordinary spark ignition combustion operating state to ignite fresh air in the combustion chamber without depending upon compression self ignition. Consequently, 20 the combustion condition can be made substantially fixed in any stroke, and the exhaust noise can be held at a low level and harmful heat effects can be eliminated.

The present invention can exhibit a superior effect particularly with a twostroke engine of the spark ignition type wherein the ignition delay period is long due to a strong pulsation disturbance in an exhaust air passage in which an exhaust air passage opening ratio adjustment means comprises a butterfly valve.

A preferred form of the present invention will now be described by way of example with reference to the accompanying drawings, wherein: FIG. 1 is a vertical sectional side elevational view showing, in vertical section, a cylinder portion of a two-stroke engine of the spark ignition type which includes a [N:\libtt]00391:KEH y o- 0 combustion control apparatus of the present invention; FIG. 2 is a side elevational view of the cylinder portion showing the same side as in FIG. 1; FIG. 3 is a horizontal sectional plan view taken along line III-I in FIG. 1; FIG. 4 is a schematic view showing an outline of the embodiment shown in FIG. 1; FIG. 5 is a drawing showing a control map; FIG. 6 is a characteristic diagram showing an operating condition of the engine with the engine speed indicated on the abscissa axis and with the average effective io pressure indicated on the ordinate axis; FIG. 7 is a characteristic diagram illustrating the condition among the combustion timing, the in-cylinder pressure variation and the in-cylinder pressure in the embodiment of the present invention; and FIG. 8 is a characteristic diagram illustrating the condition among the combustion timing, the in-cylinder pressure variation and the in-cylinder pressure of a conventional two-stroke engine of the spark ignition type.

S" "In the following, an embodiment of the present invention shown in FIGS. 1 to 4 will be described.

A two-stroke engine 1 of the spark ignition type which includes a throttle valve control apparatus according to the present invention is carried on a motorcycle (not shown), and in the two-stroke engine 1 of the spark ignition type, a cylinder block 3 and a cylinder head 4 are successively placed one on the other above a crank case 2 and S. integrally coupled to each other.

A piston 6 is fitted for upward and downward sliding movement in a cylinder bore 5 formed in the cylinder block 3, and the piston 6 and a crank 8 are connected to each other by a connecting rod 7 so that the crank 8 is driven to rotate by upward and downward movement of the piston 6.

Further, an intake air passage 10 is connected to a crank chamber 9 in the crank case 2, and a carburettor 11 and a reed valve 13 are interposed in series in the [N:\libtt]00391:HRW

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intake air passage 10. A throttle valve 12 of the piston type of the carburettor 11 is connected to a throttle drum 16 by way of a rod 14 and a lever 15. The throttle drum 16 is connected to a throttle grip by way of a wire not shown so that, when the throttle grip is twisted in one direction, the throttle valve 12 is raised to increase the throttle valve opening.

Furthermore, the intake air passage 10 is connected to the crank chamber 9 of the crank case 2, and scavenging ports 17 and an exhaust port 18 are opened to an inner periphery of the cylinder bore 5. The scavenging ports 17 are connected to the crank chamber 9 by way of scavenging air passages 19 while the exhaust port 18 communicates with an exhaust air passage An ignition plug 22 is provided in a recessed portion of the combustion chamber 21 above the cylinder bore 5. Fresh air mixed with fuel supplied from the carburettor 11 is drawn, by way of reed valve 13, into the crank chamber 9, which has i' •been put into a negative pressure condition upon an upward stroke of piston 6, and then 15 compressed upon a downward stroke. Then, when the piston 6 moves down from the scavenging ports 17 to open the scavenging ports 17, the compressed fresh air is supplied into the combustion chamber 21, and as a result of the admission of the compressed fresh air, part of the combusted gas in the combustion chamber 21 is expelled into the exhaust air passage 20 by way of the exhaust port 18. When the scavenging ports 17 and then the exhaust port 18 are closed as a result of upward movement of the piston 6, the air/fuel mixture in the combustion chamber 21 is compressed upon the upward movement of the piston 6, and in the proximity of the top dead centre, ignition by means of an ignition plug 22 or self ignition by heat energy of Sthe remaining gas of the previous combustion cycle takes place.

Further, an exhaust control valve 23 serving as exhaust air passage opening ratio adjustment means is provided in the proximity of the exhaust port 18, and the exhaust control valve 23 is fitted in a gap 26, located between a recessed portion 24 provided on the cylinder block 3 and having an arcuate vertical section and an exhaust air passage member 25 formed with a cross section of a substantially similar shape as [N:\libtt]00391:HRW c I' I I that of the recessed portion 24. The gap 26 has a substantially constant width, and the exhaust control valve 23 is supported for upward and downward rocking motion around a centre line c. A drive lever 28 shown in FIG. 2 is integrally mounted on a drive shaft 27 integral with the exhaust control valve 23, and the drive lever 28 is connected to a pulley 31 of an exhaust control servomotor 30 by way of a drive cable 29 so that the exhaust control valve 23 is driven to be rocked upwardly or downwardly by the exhaust control servomotor 30 so as to be set to a required exhaust opening ratio 0 e between 0 and 100%.

Also, the exhaust control valve 23 is formed so as to have a generally channelshaped horizontal cross section, and a side face arm portion 23b of the exhaust control valve 23 is fitted in a gap portion 32 positioned outwardly of the exhaust air passage so that the side face arm portion 23b, but not arcuate portion 23a of the exhaust control valve 23 for closing the exhaust port 18, will not have a negative influence upon a flow of exhaust gas.

In FIG. 4, which diagrammatically shows the essential parts of the two-stroke engine 1 of the spark ignition type, the throttle valve opening 0 th of the throttle valve 12 which is manually operated is detected by a throttle valve opening sensor 33 formed from a potentiometer or a like element and which sends an input to an exhaust control valve CPU 38.

B. B Further, the engine speed Ne detected by an engine speed sensor 34, an intake air pressure Pi detected by an intake air pressure sensor 35, a cooling water temperature Tw detected by a water temperature gauge 36, an in-cylinder maximum pressure generation timing, an ignition timing or a compression starting pressure PEC detected by an in-cylinder sensor 37, connection/disconnection of the clutch, a gear position of the transmission and so forth are inputs to the CPU 38.

The CPU 38 determines an operating condition of the two-stroke engine 1 of the spark ignition type from those input values and generates various control signals. In particular, the CPU 38 operates in accordance with the control map of FIG. 5 which defines the exhaust opening ratio 0 e in accordance with the engine speed Ne and the [N:\libtt]00391:HRW I st throttle valve opening 0 th, and transmits to the exhaust control servomotor 30 a drive signal AOe at which the exhaust opening ratio 0 e based on the map is provided.

The exhaust air passage opening ratio 0 e in the map of FIG. 5 provides a value at which gas filled in the cylinder can be ignited at an ignition timing most preferable for operation of the two-stroke engine 1 of the spark ignition type.

Further, the ignition plug 22 gernerates, in an ordinary combustion operating state, a spark, for example, at 100 (crank angle) prior to the top dead centre, and when it is determined by the CPU 38 based on the map shown in FIG. 6 from an engine speed Ne and an average effective pressure PME detected by the engine speed sensor 34 and the in-cylinder sensor 37 that the engine 1 is operating in the transition operating state A between the ordinary combustion operating state and the AR combustion operating state, the ignition timing of the ignition plug 22 is advanced in response to a control signal of the CPU 38 so that a spark is generated at 20' prior to .the top dead centre.

15 Since the embodiment shown in FIGS. 1 to 4 is constructed in such a manner as described above, in an operating state in which the engine speed Ne is high, the exhaust control valve 23 is rocked upwardly to open the throttle opening to a substantially fully open condition so that the exhaust air passage opening ratio 0 e is set •substantially to approximately 100%, and a spark is generated from the ignition plug 22 at 10' prior to the top dead centre. Thus, the two-stroke engine 1 of the spark ignition type is operating in an ordinary combustion operating condition in which such spark ignition takes place.

S:Then, as the engine speed Ne decreases or as both of the engine speed Ne and Sthe throttle valve opening 0 th decrease, the exhaust control valve 23 is rocked downwardly so that the exhaust port 18 is restricted to reduce the exhaust air passage opening ratio 0 e, and when the transition operating state A between the ordinary combustion operating state and the AR combustion operating state is entered, the ignition timing of the ignition plug 22 comes to 200 prior to the top dead centre. Thus, although the combustion timing would vary to a great extent among different [N:\libtt]00391:HRW LL IL I l;s revolutions of the engine, as shown at the uppermost part of FIG. 8, if the ignition timing of the ignition plug 22 otherwise remained at 100 prior to the top dead centre, the combustion starting timing relative to top dead centre is substantially constant as shown at the uppermost part of FIG. 7, and the pressure variation and the maximum pressure are decreased as shown at middle and lower parts of FIG. 7, resulting in reduction in combustion noise and elimination of harmful effects of heat by abnormal combustion.

Then, as the engine speed Ne further decreases, or as both of the engine speed Ne and the throttle valve opening 0 th decrease, the exhaust control valve 23 is further rocked downwardly so that the exhaust port 18 is further restricted and the exhaust air passage opening ratio '9 e is further reduced. Consequently, fresh air in the combustion chamber 21 is compressed and self ignited at an ignition timing most preferable for operation of the engine without being influenced remarkably by ignition of the ignition plug 22, and an AR combustion operating state commences.

Further, also in another transition operating state B between the AR combustion operating state and an irregular combustion operating state, since the ignition timing by the ignition plug 22 is advanced by 100 (crank angle) compared to the ignition timing in the ordinary combustion operating state, the irregular combustion Scondition is moderated, and the amount of unburnt hydrocarbons discharged is reduced.

While, in the embodiment described above, the exhaust control valve 23 is used as exhaust air passage opening ratio adjustment means, a butterfly valve may be interposed for opening and closing movement in the exhaust air passage oOO •g [N:\Iibtt]00391:HRW Il~'d

Claims

1. A two-stroke engine of the spark ignition type wherein a fresh charge, obtained in advance by mixing fuel into air, is supplied into a combustion chamber and the fresh charge in said combustion chamber can be compressed and self ignited at least in a low load operating state to effect activated heat atmosphere combustion, said engine comprising: exhaust air passage opening ratio adjustment means for adjusting an opening ratio of an exhaust air passage to control a compression starting in-cylinder pressure; ignition timing adjustment means for adjusting an ignition timing; and control means for driving said exhaust air passage opening ratio adjustment S•means to an exhaust air passage opening ratio determined from at least engine speed and throttle valve opening parameters to adjust the compression starting in-cylinder °°pressure to a predetermined compression staiting timing in-cylinder pressure with which the fresh charge in said combustion chamber can be compressed and self ignited at an ignition timing preferable to operation of said engine, said control means also being for operating said ignition timing adjustment means in a transition operating state between the activated heat atmosphere combustion operating state and an ordinary spark ignition combustion operating state to cause spark ignition to occur at a timing earlier S°than a spark ignition timing in the ordinary spark ignition combustion operating state to control a combustion starting timing by the spark ignition to a timing in the proximity of the top dead centre.

2. The engine of claim 1, wherein said exhaust air passage opening ratio **o adjustment means comprises an exhaust control valve.

3. The engine of claim 2, wherein said exhaust control valve has an arcuate vertical cross section and a substantially channel shaped horizontal cross section, said exhaust control valve fitting within a gap provided between a recessed portion of a cylinder block of said engine and an exhaust air passage member.

4. The engine of claim 2, wherein said exhaust control valve is a A butterfly valve. butterfly valve. [N:\libtt]00391:KEH I- I I The engine of any one of claims 2 to 4, wherein said exhaust control valve is attached to a drive shaft and is adapted for rotation about an axis of said drive shaft.

6. The engine of claim 5, wherein an exhaust control servomotor is operatively connected to said drive shaft for rotating said drive shaft, thereby adjusting the position of said exhaust control valve and adjusting said exhaust air passage opening ratio.

7. The engine of any one of claims 1 to 6, wherein said control means comprises a CPU.

8. The engine of claim 7, wherein said CPU receives input signals for determining any one or more of the group of engine parameters consisting of: engine speed; intake air pressure; cooling water temperature; in-cylinder maximum pressure generation timing; ignition timing; compression start pressure; clutch position; and transmission gear position. 15 9. The engine of claim 7 or claim 8, wherein said driving said exhaust air passage opening ratio adjustment means comprises transmitting an output signal from said CPU to said exhaust air passage opening ratio adjustment means. An engine substantially as hereinbefore described with reference to SFigs. 1 to 7. DATED this Fifteenth Day of December 1994 S* Honda Giken Kogyo Kabushiki Kaisha 25 Patent Attorneys for the Applicant SPRUSON FERGUSON [N:\libtt]00391:HRW I I ILII rl Two-Stroke Engine of the Spark Ignition Type ABSTRACT A throttle valve opening Oth of a manually operated throttle valve 12 is detected by a throttle valve opening sensor 33 formed from a potentiometer or the like while an engine speed Ne is detected by an engine speed sensor 34, and the sensor signals are transmitted as inputs to a CPU 38. The CPU 38 operates in accordance with a control map of which determines an exhaust air passage opening ratio 0 e in response to the engine speed Ne and the throttle valve opening 0 th, and transmits to an exhaust control servomotor 30 a drive signal AOe to provide an exhaust air passage opening ratio 0 e based on the control map. Also, an ignition plug 22 generates, in an ordinary combustion operating state, a spark at 100 (crank angle) prior to the top dead centre. When it is determined by the CPU 38 that the engine is operating in a transition operating state A between the ordinary combustion operating state and an AR combustion operating state, a spark is generated at 200 prior to the top dead centre in response to a control signal of the CPU 38. 15 FIG. 4 0 09 C C C o C.. C C 0 o 111INV ~y l~71Z.A 11