AU592990B2

AU592990B2 - Improvements relating to controlling emissions from two stroke engines

Info

Publication number: AU592990B2
Application number: AU57898/86A
Authority: AU
Inventors: Christopher Kim Schlunke
Original assignee: Orbital Engine Co Pty Ltd
Current assignee: Orbital Engine Co Pty Ltd
Priority date: 1985-05-24
Filing date: 1986-05-23
Publication date: 1990-02-01
Anticipated expiration: 2006-05-23
Also published as: AU5789886A

Description

5929.m90 COMMONWEALTH OF AUSTRALIA PATENTS ACT 1952-69 LODGED AT SUB-OFFICE COMPLETE SPECIFICATIJJ 3MA18 (ORIGINL) I Nelbournej Class I Ft. Class Application Number: PH- 729 Lodged: 24.0 5.19 Fornpetea Specification Lodged: t

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II 4 p46I NM of Applicant: Address of Applicant: Artual Inventor: Address for Service: ORBITAL ENGINE COMPANY PROPRIETARY LIMITED 4 Whipple Street, Balcatta$ Western Australiia, Australia CHRI:STOPHER JIM SCHLUNKE, FDWD. WATERS SONS, )O QUEEN STREET, MELBOURNE, AUSTRALIA, 3000, Complete $pecification for the ivention entited: IMPROVEMENTS RELATING TO CONTROLLING EMISSIONS FROM TWO STROKE ENGINES The following stitement Is a full description of this Ii~ention, Including the best method of performing It known to us IMPROVEMEnS REIATING TO CONTROLLING 2MISSIONS FROM 'M STROI EN GINES This invention relates to internal combustion engines operating on the two stroke cycle and is particularly directed to controlling the cc~bustion process so that the harmful components of the engine exhaust are kept within permissible limits.

Engines operating on the two stroke cycle have been recognised as exhibiting poor performance in both the area of fuel consumption and the level of harmful emissions in the engine exhaust. However, there are substantial benefits to be obtained by wider use of engines S, operating on the two stroke cycle, firstly, because of the their relatively simple construction, and secondly because of their S'relatively high power to weight ratio. There is accordingly a need to Sdevelop a two stroke engine wherein the exhaust emissions can be brought within the acceptable limits laid down by the various government bodies throughout the world, particularly for automotive and marine applications.

In a conventional crankcase ccmpression two stroke engine a pre-mixed charge of fuel and air is delivered to or prepared in the crankcase and is subsequently transferred to the combustion chamber through an inlet or transfer port or ports which communicates the combustion chamber with the crankcase, as the piston reciprocates in the cylinder. Having regard to the extent and nature of movement of the pre-mixed charge between the time of its initial formation and its final compressed state in the combustion chamber, immeiately prior to ignition, a high degree of mix between the fuel ind the air takes place. This results in a relatively even distribution of the fuel throughout the air charge in the combustion chamber and is commonlv r 'erred to as a homogeneous charge. Accordingly, any part of this pre-mixed charge which passes to the exhaust system in an unburnt condition is relatively high in hydrocarbon and represents an emission control problem. The unburnt charge may pass to the exhaust system by a "short circuiting,' gas flow between the transfer and exhaust ports and also from unburst charge remaining after cambustion ceased.

U' 2- After a homogeneous charge of the correct fuel/gas ratio has been ignited, such as by a spark from a spark plug, combustion will spread through the charge so long as the charge temperature is sufficient to not extinguish the flame front. In an engine the charge is subjected to various quenching effects, such as contact with the cylinder walls, that can lowcer the temperature of that part of the charge in close proximity thereto. Accordingly, it is practice to use a somewhat rich fuel/gas mixture to promote ccmbustion further into the quenched areas of the charge. This can in some engines reduce the actual quantity of unburnt charge but that unburnt portion is rich in fuel, and hence HC, and so counter-acts to varying degrees the benefit of extending the flame-front.

It has also been proposed to stratify the fuel distribution in an engine charge so that the charge cloer to the point of ignition is a richer in fuel and the charge is progressively leaner as the distance I t rt from the ignition point increases. This means that the parts of the charge furthermost from the ignition point, and hence most 1-ely not to combust, are lean in respect of fuel and hence also HC. However, a S lean mixture is more susceptible to extinguishing of the flame-front and therefore a great proportion of the charge may remain unburnt with ur' resultant increase in HC.

United States Patent No. 3817227 by Onishi is directed to improving the combustion efficiency of a two stroke cycle engine and [purification of the exhaust gas therefrom. The Onishi specification discloses an engine wherein a pre-mixed fuel-air charge is delivered by the crankcase compression through transfer ports to the engine cylinder. Because of the manner of preparation of the fuel-air charge it is of a pre-mixed form and will be substantially a homogeneous charge when delivered to the engine cylinder.

The Onishi specification proposes to control the velocity of the fuel-air charge entering the cylinder, and thereby orAtrol the extent 1 of mixing of the incxming fuel/air charge with the tresidual exhaust gas remaining in the engine cylinder frcm the previous engine cycle. It is stated in the Onishi specification that, by reducing the velocity of Ii 3 the incoming fuel/air mixture, a form of stratification between the fuel/air mixture and the residual exhaust gas is achieved, and this prevents the exhaust gas leaning-out the fuel/air mixture and so I reducing the ccmbustibility thereof, and concentrates the incoming fuel-air mixture in the recess provided in the cylinder head.

The control of the velocity of the incoming gas mixture as proposed by Onishi is achieved by coupling the conventional throttle valve in the air intake passage with a similar throttle valve in exhaust passage slightly downstream of the exhaust port. The i mechanical linkage coupling the two throttle valves is arranged to S, provide a non-linear but fixed relation between the movement of the I~ exhaust throttle valve in response to the movement of the intake r throttle valve, This fixed relationship is illustrated graphically in t Fig. 6 of the Onishi specification and described with reference to that graph.

It will be appreciated that in a pre-mixed charged engine as described by Onishi the throttle position on the air intake primarily lt ,determines the engine load. At lowc load the intake throttle is near closed and at maximum load it is fully open independent of engine speed. Accordingly, the control system proposed by Onishi's does not f account for the engine speed at which the particular load is being experienced.

It is considered that the inability of the proposal by Onishi to take acount of the engine speed would seriously detract from it's ability to effectively control exhaust emissions, particularly hydrocarbons. It is well known that the scavenging process of two stoke engines, including the velocity of the incoming fuel-air charge and the outgoing exhaust gases, is significantly influenced by the Smagnitude and frequency of the pressure pulses in the exhaust system, and these in turn are highly influenced by and dependent on the engine speed. The throttling of the exhaust port as proposed by Onishi will influence the pressure pulses in the exhaust system and hence influence tbe velocity of gas movements in the cylinder. However, as this throttling is not related to engine speed its effectivness will be reduced, and under certain circumstances my be detrimental to achieving the reqilred gas flow condition in the engine cylinder.

0 1 1 4 It is therefore the principal object of the present invention to provide a method of operating a two stroke internal combustion engine whereby the combustion process may be controlled throughout the working range of the engine to produce an acceptable exhaust emission level particularly in regard to hydrocarbons.

With this object in view there is provided a method of operating an internal combustion engine on the two stroke cycle to control the level of contaminants in the exhaust gases, the engine havz;ig a cylinder, a piston mounted to reciprocate in the cylinder, said piston and cylinder defining a combustion chamber that cyclically varies in volume as the piston recip- 15 rocates, an air inlet port providing communication between the combustion chamber and a source of air, and an exhaust port providing communication between 4t 1 the combustion chamber and an exhaust duct, said inlet J* and exhaust ports being arranged to be opened and closed by the piston as it reciprocates in the .cylinder, said method comprising admitting a charge of air to the combustion chamber through the inlet port, compressing the charge of air in the combustion chamber by the movement of the piston after the inlet and exhaust ports have been closed, injecting a metered quantity of fuel into the air charge in the combustion chamber, igniting said fuel charge, and exhausting the products of combustion through the exhaust port after expansion in the combustion chain- t ber, sensing the engine load and engine speed while the engine is operating, and regulating the mass of the products of combustion retained in the combustion chamber at closure of the ports so hydrocarbons present In the exhausted products of combustion are within selected limits by r n

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7 1 4a controlling the flow of gases through the exhaust port while open in relation to engine speed and load to regulate the gas flow through the combustion chamber over the range of engine speeds and loads, said controlling including adjusting the degree of throttling of the exhaust port through a range of values between a minimum and a maximum, for each combination of engine load and speed said degree of throttling of the exhaust port being preset and determined in accordance with the selected limits for hydrocarbons present in the exhausted products.

Conveniently the control of the flow of the gas is achieved by controlling the flow through both of the inlet and exhaust ports, which not only individually controls the flow through each port but, since in the engine cycle there are periods when both ports are open, has also a synergistic effect, as both ports influence the pressure conditions in the combustion chamber and hence the gas flow therein and therethrough.

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Also, the control of the flow in the exhaust port influeces the pressure pulses in the exhaust system, which ray be used to control the scavenging of the onbustion chamber an4/or the retention of the charge therein.

Preferably the control of the gas flow in the cmbustion chamber is by the use of respective throttle devices in association with each of the inlet and exhaust ports, and controlling the throttle devices by an electronic control unit (ECU) that receives signals in response to engine load and speed. The throttle devices, particularly the one associated with the exhaust port may be arranged to also effect a variation in the timing of the port opening and closing.

It is necessary in order to _btain the required control of the [.combustion chamber gas .chaxe, aml so contro, the exhaust emission levels, to have independent control of the flow through the inlet and t exhaust ports. Within the operating speed range of the engine it is necessary to be capable of opening the exhaust throttle as the inlet throttle is opened, or the fueling rate (load) is increased at one particular speed, while at another speed the exhaust throttle is restricted as the inlet throttle is opened. It may also be necessary at oe speed in the operating speed range to open and then restrict the exhaust throttle as the inlet throttle is opened to respond to an increasing air requirement. It is therefore appreciatei that there is ino fixed or consistent relation between inlet and exhaust throttle positions over the load-speed range of the engine.

This independent but related control of the inlet and e~baust port throttling gives the required flexibility in control of the pressure fluctuations at the exhaust port and corresponding flexibility in tk control of the scavenging process. It is necessary to be capable of varying the pressure fluctuations in both timing and n ingnitude with both engine speed and load, so as to achieve th!e, reqaired variation in amount of exhaust gas retained in the combustionL chamber and hence control the HC emissions.

A further advantage can be achieved by variation of the exhaust 'i iJ I1 -6port opening and closing timing which also influences the timing of the pressure fluctuations at the exhaust port. Exhaust port timing control is also useful in improving torque in the low speed range while also maintaining control of the level of exhaust emisoions.

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V V *t I The use of direct injection of the metered quantity of fuel into the combustion chamber, enables the establishment of a fuel distribution within the air charge in a stratified form, with the richer mixture being in close proximity to the ignition point, and the mixture progressively leaning out as the distance frcm the point of injection increases. This enables the overall fuel-air ratio to be decreased so the engine runs leaner, and yet the mixture in the vicinity of the igniter is sufficiently rich to ensure reliable ignition of the fuel-air charge. Also, as the mixturE is richer in the vicinity of initial ignition, the mixture in the remaining portion of the cmbustion chamber charge will resultantly be leaner, and will be substantially leaner than a homogeneous pre-mixed charge. Accordingly, if the flame is extinguished before it has moved through the full extent of the fuel in the combustion chamber, cdue to various quenching effects, the unburnt portion of the charge will be very lean and will therefore contain a reduced HC, and thyus the HC content of the exhaust gas will be reduced.

The benefits of the stratification of the fuel in the air charge are further enhanced by the presently proposed control of the gas flow through the inlet and exhaust ports regulating the quantity of exhaust gas retained in the combustion chamber at the closing of the exhaust port. This retained exhaust gas is at a relatively high temperature and accordingly will raise the temperature of the new charge enterir.

the combustion chamber on the next cycle. The resulting temperatre increase of the new fuel/gas charge will improve the flamability o' the lean portion of the charge, so that the flaie front will extend further into the lean portion of the charge, and consequently the final quantity of unburnt fuel is reduced with a corresponding reduction in HC in the exhaust gases.

7 -7- The quantity of retained exhaust gas is controlled in accordance with .the engine load and speed, so that, at all points in the engine operating range, the amount of heat available from the retained exhaust gas is sufficient to raise the charge temperature to achieve the acceptable level of HC in the released exhaust gas. It will be appreciated that retaining part of the ex-ust gas in the engine cylinder results in the gas being at a higher temperature than if part of the exhaust gas was recycled into the incoming air charge.

It is recognised that in a conventional two stroke cycle eriine the portion of the exhaust gas that would normally leave the cylinder late in the exhaust period has a relatively high HC content.

i' Accordingly the retention of that portion of the exhaust gas or part t 4 thereof in the cylinder contributes significantly to HC emission control.

It has previously been recognised that the mixing of exhaust gas with the air/fuel mixture does contribute to the reduction in the NOx 1 contaminant in an engine exhaust gas. In many prior proposals, exhaust gas has been mixed with the air/fuel mixture to obtain a substantially hamogeneous charge. However, an increase in the proportion of exhaust gas in a homogeneous charge can lead to instability in the engine operation. In particular, it has been shown that the air/fuel ratio at which lean misfirs is experienced in a engine becomes richer as te amount of exhaust gas in the total charge increases.

Ihe combustion process and mixture preparation proposed by the present invention enables the benefit of NOx reduction by the presence of exhaut gases in the engine charge with a reduced effect of this exhaust gas on the stability of the engine. his is achieved by the fact that the exhaust gases are not recirculated into the incoming fuel air charge, but are retained in the ca~bustion chamber at the conclusion of the previous cycle. The retained exhaust gas is thus mixed to a lesser degree with the fresh charge of air, resulting in a degree of stratification of the iresh charge and the retained exhaust gases, with the fresh charge being acentrated in the areas closer to the point of injection of the fuel. This contributes to the re stable operation of the engine, which of course, is further assisted by the stratified form of the fuel charge. The ccmbined effect is that the fuel is pr,=ipally stratified in the fresh air charge, which in turn is stratified in relation to the retained exhaust gases.

In a conventional engine having a homogeneous charge of fuel, air and exhaust gas, a significant part of the NOx formation derives from the early part of the ombustion as the flame front travels frm the ignition point. This is due primarily to the high temperature attained during this period, and also the relatively high proportion of the cycle time in which these temperature conditions prevail. Also in an engine with a conventional stratified fuel charge where the overall air/fuel ratio is near stoichiametry and the stratification is from rich to lean with respect to the ignition point, then NOx formation occurs primarily during the mid portion of the combustion cycle, where the flame temperature and hence the suitability for NOx generation is 1 high due in part to the relatively high fuel/air ratio, and where there t is good oxygen availability and a considerable period of tre available ti ,under 1cPvonitions most suitable for the prcnotion of NOx formation.

j The control of the preparation of the cylinder charge as A presently proposed provides a charge that is not homogzex either from the point of view of fuel and air or retained exhaust gases. The charge has the fuel stratified with a fuel rich region close to the ignition point, and the retained exhaust gas stratified with an exhaust gas lean region also close to the ignition point. This distribution of fuel, air ar-A exhaust gas provides for a concentration of fuel and air in the region of ignition so a generally leaner overall fuel/gas ratio (gas comprises air plus retained exhaust gas) may be used without sacrifice in ignitability. Despite this overall leaner mixture, and the high temperature prevailing in the early part of the ombustion cycle, the fuel/gas ratio close to the ignition point is sufficieotly rich to be readily ignited and is not conducive to NOx formation.

During the mid part of the cacustion gase, where high NOx formation is experienced in a normal stratified fuel engine, the present process exhibits a leaning of the fuel/air ratio and a lowering of the temperature, with an increase in exhaust gas content of the cmbusting mixture. This ocmbination of conditions are also not conducive to NOx formation. In the final part of the ciustion phase the high concentration of exhaust gas due to the stratification thereof in the ~rd -9carbustion chamber will suppress the formation of NOx.

The foregoinq disclosure emphasises how the regulation of the charge distribution in the combustion chamber can be used, to acdhieve control of the formation of HC and NOx during the canmbustion process.

This regulation of the charge distribution may be achieved by selected control of the degree of throttling of the inlet and exhaust ports and of the exhaust port timing of the engine. The throttling may be effected by appropriate valves at the inlet and exhaust port or in the ducts or passages communicating therewithl.

Conveniently, the inlet is restricted by providing a lutterfly type throttle valve in a port through which the air is drawn into the engine crankcase prior to being oampressed in the crankcase to be Sdelivered via a transfer passage or passages to the cmbustion chamber.

SThis arrangement is selected Lcause of the space constraints on Slocating a suitable valve in the intenal transfer passage closer to J athe actual cmbustion chamber. Also, it is cammon for more than one transfer port to be provided for each ccmbstion chamber, and it uld be necessary to provide a valve in each such t\ansfer port. The exhaust restriction may similarly be achieved by a valve in the exhaust port.

The movements of the respective valves may b- effected by Srespective motors which may be electrically operated and controlled electronically. t~he valves may be operated by suitable solenoids or stepper motors controlled by an ECU (electronic control unit).

S Psition sensors may be provided to supply feedback to the ECU relative Sto the actual position of the relevant valve to improve the accuracy of the positioning of the valve.

It will be appreciated that the strategy required to achieve any particular level of contaminants the exhaust gasses an/or fuel consuption will vay for each different engine, firstly because the basic physical gecmetry of the engine influenes the ocabustion process. Factors such as the size and location of the inlet and exhaust ports, the orientation of the inlet ports, and cylinder head and piston crown shape each exhibit varying degrees of influence on the A

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gas flow in the cylinder and the comnbustion process. Secondly the exhaust system downstream of the exhaust port will influence gas flow in the cylinder by reason of the pressure pulses created at the exhaust port which may vary in timing and magnitude.

Accordin'y, the degree of restriction of the gas flows in the inlet and exhaust ports must be detenined experimentally for each engine design over the load and speed range of its operation. The degree of restriction will also be related to the required level of contaminants in the exhaust and/or the required fuel consunmption. In soame applications the fuel ecoonay of the engine may be more irportant than exhaust contaminant level and so tha control strategy would be different to that where exhaust contaminant level were to be strictly controlled.

The following discussion of the effects of the restriction of flow in the exhaust and inlet ports of an engine will give an Sappreciation of how these flows can be controlled to regulate the t quantity of exhaust gas retainled in the combustion chamber. The discussion relates to a three cylinder two stroke cycle engine of 1200 cc capacity operating over the speed runge of 800 to 3000 RPM and load range of 0 to 25 Nm. The engine has direct in-cylinder fuel injection and crazkcase compression air Pr4ply.

1. Very lo se d 00 to 100 RP) In this region the pressure )v1sations in the exhaust system have a relatively long period in which to declty and are of a very low magnitude and so pulses in the exhaust system geerally have little influence on the flo through the exhaust port and hence the control of exhaust gas retention lemel. At high loads the inlet port is only partly throttled and the $Wau-* 1 fully throttled so that tie area available for drzwdtzy e front the exhaust sytem bAdk into th Qtse s ctin ctir ia Iuced.

At low loads the inlp4 p" 4 d1, ond the engine is not sensitive to the deW ttling, And the tiMirq is cptimised for hit ds, The exhauct port is preferably thrott,i rove echaust gas purity.

i hus in the very low speed region a typical operation of throttling of the inlet and exhaust ports is: High .Loads: open inlet port throttle and close exhaust ort throttle to reduce exhaust gas retention in combustion chamber.

Low Loads: close inlet port throttle:- increases exhaust gas retention in ccmbustion chamber, open inlet port throttle, (1 reduces exhav'st gas retention, exhaust port throttle irrelevant.

2. Lw Speeds (1000 to 2000 RPM) In this region the exhaust port throttle ts closed at both high and low loads, primarily to reduce the effect of undesirable pulses returning from the exhaust system. Closing the exhaust 1 port throttle charnges the time of arrival and magnitude of the pulse at the exhaust port.At these speeds throttling of the S, exhaust port changes the timing of the returning pulse so lower pressure levels can be achieved in the cmbustion chamber at exhaust port closure. This in turn means that the inlet port throttle can be closed for the same air flow into ane engine or altenatively the inlet port throttle can be left untouched and higher vacuum achieved, often with a slight increa.e in air flow.

Reduced pressure in the ccmbustion chamber at exhaust port closure also means less exhaust gas diluent is present, and therefore the exhaust gas/fuel ratio is richer, but exhaust gas/air ratios may be higher as the dilution levels are lower.

These features are exhibited at both high and low lcads because of the stremth of the speed depedent returning pressure pulse in tlia exhaust system.

|Thus in the low speed region a typical operation of the inlet and exhaust throttles at all loads are: Close the exhaust port throttle to reduce quantity of exhaust gas retained.

Close the inlet port throttle to increase the amount of exhct i gas retained.

At full load (outside the range requiring emission control) the exhaust port is opened to a precise speed dependent value, as the

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I I If, timing of the positive pulse in the exhaust system is forced closer to that desired for full load performance.

3. Medium (2000 to 3000 RPM) In this region the exhaust throttle can very accurately control the pressure at exhaust port closure, because of the timing and strength of a pressure pulse in the exhaust system. This will be the general case because the ragnit:nde and adjustability of the pressure fluctuations will i#prove as speed increases, due to the decreased amount of attenutation arising fram the reduced time between pulses, and the higher gas veloc-ities and pressures developed.

At light loads the mechanism for exhaust gas retention control is the same as that mantioned above for low speeds. The preferred exhaust throttle setting moves fram fully closed at light loads to fully open at hjqh loads because this moves the pressure pulse such that a positive pulse arrives during the transfer port closure to exhaust port closure period. This reduces the quantity of exhaust gas in the cylinder, because the fresh charge can normally escape through the Lxhaust port at these higher speeds and throttle settings, and the pressure pulse prevents this frn occuring. nus, the trapped charge purity level is high. The inlet throttle settings at these loads are generally critical because HC and NOx is improved as the eitne is throttled.

Thuz! in the medium speed range a typical operation of throttling of the inlet and exhaust ports is: Iow Loads: throttling the exhaust port reduces retained gas.

Inlet port throttling increases retained gas.

High Loads: reduction of the throttling of the exhaust port decreases retained exhaust gas. Increasing the throttling of the inlet port increases retained exhaust gas.

It is to be understood that the above described operating strategy is to be taken as a typical exanplk,, and it may be varied generally or in specific areas to suit differig requirments, engines, I L

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The invention will be more readily understood from the following dascription of typical operating strategies for the control of the exhaust port throttling, and of one practical arrangement of a two stroke engine incorporating controlled inlet and exhaust port throttling.

In the drawings: Fig. 1 is a three dimensional map of exhaust throttle valve position plotted against speed and load.

Fig. 2 is a chart of preferred positions of the exhaust port throttle at a range of points in the load and speed range of an engine.

Fig. 3 is a chrt similar cc Fig 2 showing the effects of variations in the exhaust port throttle position at various points in the load mi speed range of the engine.

Fig. 4 is a graph ccsparing the HC emission of an engine operated in accordance with this invention and prior proposed engines.

Fig. 5 is a longitudinal section view of a single cylinder engine ecipped to operate in accordance w'.th the present invention.

Fig. 6 is a sectional view through the cylinder and exhaust throttle as incorporated in the engine shown in Fig. Fig. 7 is a simplified logic diagram of the electronic control system enployed to regulate t'he position of the exhaust throttle and control fueling and ignition of the engine.

Fig. 1 is a three dimensional rap showing a typical plot of exhaust port throttle setting over the speed and load operating range of the 1200 cc capacity three cylinder two stroke engine. p;w6sly rzfereez to ir the rap has been developed for operation of the cnwine within the specific exhaust emission requirement for passer er autamcbiles operated in the U.S.A.

Tue control of the exhaust port position is controlled by a s,gnal from an EWJ which receives input signals indicating the engine speed ad the air nass consumption of the engine which is indicative of engine load. The LOU has stored therein a rap as represented by Fig.

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9 4 4 4*4 4 at t~a 44 a 4 -14- 1 and, from the speed and load input signals, determines from the map the required degree of throttling of the exhaust port and issues an appropriate signal to a drive mechanism coupled to a valve in the exhaust port.

It is to be particularly noted from Figure 1 that a substantial degree of throttling of the exhaust port is required over the low to medium load range and a minimum degree of throttling in the high load range. The degree of throttling increases rapidly at high loads in the highei: part of the low speed range, and then progressively decreases through the medium speed range to the high speed range. The significant change in the exhaust port throttling at high loads between the very low and high load speeds arises from the effects of the tuned exhaust system.

It is therefore to be understood that the adjustment of the exhaust port can also be used to regulate the effects of a tuned exhaust sysem when operating at speeds out of the e •tuned speed range, It is well-known to use a tuned exhaust system on two stroke internal combustion engines, so that the arrival time of high and low pressure pulses at the exhaust port can be arranged to improve scavenging of the exhaust gases And entrapment of the fresh charge in the combustion chamber.

However, tuned exhaust systems are speed dependent and with any particular exhaust system, the correct or near correct tining of the pressure pulses at the exhaust port is only achieved over a relatively narrow range of engine speeds.

E The control of the gas flow through the exhaust port and/or S't the inlet port, and the timing of the exhaust port opening, as currently proposed, can be used to vary the performance S of the tuned exhaust system when engine operating conditions are such that the normal performance of the tuned exhaust system may operate adversely to the control of contaminanta in the exhaust gas. 1n i J nrpeto h rs hrei h obsincabr 1 By way of example the throttling of the gas flow through the exhaust port may be varied to modify the high pressure pulses in the exhaust system at the time of closure of the exhaust port, so as to reduce the extent that fresh charge air is returned to the cylinder and thereby increase the ratio of exhaust gas to fresh charge gas trapped in the combustion chamber. Alternatively, if a low pressure pulse is present at the exhaust port at the time of closing thereof, which would normally lower the pressure in the combustion chamber, the degree of throttling of the flow through the inlet port may be reduced, and the exhaust port throttled to an extent to substantially close the port, thereby also bringing about an increase in the ratio of trapped exhaust gas to fresh charge air. It will therefore 15 be understood that the control of the throttling of the exhaust port may be used to modify the effects of a tuned exhaust system, both within or outside of the tuned speed range, the modification may either enhance or counter the effects of the tuned exhaust system, as may be necessary for engine performance or contaminant control.

The map shown in Figure 1 has been determined from test information obtained with the three cylinder two stroke engine previously referred to and, as stated hereinbefore, the physical geometry of the porting and combustion chamber of the engine, and other facts, will influence the required degree of throttling of the exhaust port over the engine speed and load range. However, the general trends of variations of the exhaust port throttling as represented in Figure 1 will apply to crankcase compression, direct fuel-injected two stroke engines.

There is shown in Figure 2 a chart of the preferred settings of the exhaust port throttle valve in the engine to which the map in Figure 1 applies. In this engine the exhaust port has an area of 1570 sq mm when unthrottied and 200 sq mm when fully throttled. The degree of throttling of D- 31 bp- Flow -UIN" the e-haust port is represented in the chart by numerals ranging from 0 to 10, in linear proportion to the degree of throttling and with 10 indicating the fully throttled position. The exhaust port throttle settings are shown for a range of speeds from 1000 to 4000 RPM and torques from 0 to 30 Nm.

Figure 3 is a chart, for the same engine as referred to above in relation to Figure 2, showing actual air flows through the exhaust port for exhaust throttle settings at typical speeds within the range shLwn in Figure 2. At selected points on the chart a graph is drawn showing air flow against flow through the exhaust for the extent of opening of the exhaust port expressed as a percentage of the movement between the minimum and maximum open position of the exhaust port. (The origin of each graph corresponds to the t r t II i t V t 16 4.

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444 9 49 94 4 4*4 4 relevant point on the chart). The centre figure or. each graph is the throttle setting showvn in Fig. 2 and the figures on either side repivsent a variation of 10% in the throttle opening on either side of that setting. The left hard figures are for an increase in the extent of throttling and the right hand for a decrease in throttling. It will be noted fran Fig. 3 that in the speed range of 1500 to 3000 RPM and torque range 10 to 30Rii the 10% variation in exhaust port throttling has a significant effect on th.e gas flow. through the exhaust port. As this gas flowt is indicative of gas flow~s in the coebustion chamtber, and hence the rate of exhaust gas retained, the chart in Fig. 3 illustrates the imp~ortance of correct and accurate control of the exhaust port throttling.

In regard to Figs 1, 2 and 3 it is to be understood that the throttle in the air intake passage is positioned by an operator actuated control, such as. an accelerator pedal or the like, to set the engine load demarid.

The engine load having been so establizhed the position of the throttle in the exhaust port is determined frozu a i,,ap, such as in Fig.

1, for the then current speed of the engine, am' the exhaust throttle morved to that position. Accordingly in this control strategy the ECU previously referred to does not control the position of the throttle, in the air intake passage, but receives a signal responsive to that position as one ipuit, and a signal corresponding to the engine speed, and determines the required position of the exhaust port throttle.

In a more advanced control strategy the position of the throttle in the air intake is also controlled by the ECU by way of a nip of the same format as Fig. 1, plotting that throttle position against engine load aid speed. A map such as is Fig. 1 is also s! red in the EmJ plotting exhaust throttle position against load and speed. The Eaj receives an operator initiated signal indicating the engine load denmand, and a signal related to the engine speed, and from these signals determines from the respective maps the correct position of the intake and exhaust throttles.

Fig 4 is a graph showjing the rate of hydrocarbon emission against Powier output for three different engine setups. Plot A is the level of 4 44 9.

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-17- HC in grams per kilowatt hour obtained ip conventional crankcase ocmpression, car±'retted two stroke engine~pontrolled throttling of the inlet port. Plot B is the level of HC obtained with basically the same engine when operated in accordance, with the present invention, that is when the engine is fitted with direct in-cylinder fuel injection creating a stratified fue-l charge and has throttle controls on the exhaust port and inlet port operated in accordance with the present invention. Both Plot A and B are based on an engine speed of 2000 RPM aid Plot C ha's been mo~delled to the same spec,, Plot C been developed as representative of the level of HC control cbtaied in another two stroke engine wherein the inlet and exhaust ports PAre throttled in a fixed relaltion in accordance with enine load and independent of engine speed. The Plot c was ckbtained 4 44 fromi information published by Ricardo ccaiany Engineers (1927) 4, Limited relating to the engine control system developed by the Nippon Clean Enine QtVany, this being the engine the subject of Patent No. 3817227. Mhe Ricardo publication is entitled A Stud~y of Stratified Charge Engines for Light Duity Power Plants Report No.

460/3/74/011,/A. The mater3, used to produce plot c is taken from Fig 7-7 on Page 272.

Although Plot C represents a substantial inprovarent aver Plot A the HC levels Plot C are- far in excess of acceptable lavelt for engines used in autamoive passenger vehicles und~er both United States and Australian standards. Hc~wer Plot B indicates a level that ir-,d j. ccIPlY With both of these standards and represents a HC le1 inth a4 range of 3 to 4 grams per miles on the driving cycle set down in these standards.

Referring now to Fig. 5 of the drawings, there is depicted a longitud~inal cross-sectional, view of a two stoke cycle internal c~hostion engine erploying crankcase oV~ressikn for the delivery of the air charge to the cylinder. It is, however, to b~e urderstood that the present invention ray be aj ,ied to two stroke engines wheroin the air supply is delivered fromn an alternative pressure source such as a ,~AN turbocharger or supercharger. the engine coiprises a crakcase 10 in

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zz LL 0I 18 which is journalled a crankshaft 11 for rotation about its axis and which is coupled by the connecting rod 12 to the piston 13. The piston 13 reciprocates in the cylinder 14 to induce rotation of the crankshaft 11 and, with the cylinder head 15 provides a variable volume conbustion chamber.

At substantially diametricly opposite locations in the cylinder there are provided a transfer port 20 and an exhaust port 21, ich are opened and closed by the piston as it reciprocates in the cylinder.

The exhaust port 21 cammunicates with an exhaust system 22 which carries the exhaust gas to a suitable discharge point to atmosphere.

The transfer port 20 is in cmmmnication with the interior of the crankcase 10 via the transfer passage 25. The air induction duct 26 cucmmunicates with the interior of the crankcase 10. The reed valve 28 is prodded in the duct. 26 to open and close in response to the a a ,pressure conditions in the crankcase

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The throttle valve 30 is mxunted in the exhaust port for pivotal nmmet about the axis 31 so that it may vary the effective crces-sectional area of the exhaust port 21.

,The exhaust port throttle valve 30 has a control edge 33 which extends in the circumferential direction of the internal face of the cylinder 14 and accordingly as the valve 30 pivots on the axis 31, the edge 33 varies the effective height of the exhaust port in the axial d'irection of 'the cylinder. It will thus be appreciated that the plivotal noveent of the exhaust throttle valve 30 not only results in a throttling of the exhaust port but will also vary the timing of the opening and closing of the exhaust port 21.

More details of the exhaust port throttle valve 30 ar, shn in Fig. 6 wherein it is to be noted that the pivot axis 31 of the throttle valve 30 is imlined to the general direction of the control edge 13 of the throttle valve. This results in the end 35 of the control edge being at a greater radius, with respect to the pivot axis 31, than the other end 136 of the control edge. This inclined arrangement between he c)ntrol edge 33 and the pivot axis 31 of the -19exhaust port throttle valve enables the throttle valve to be initially set up with the control edge 33 parallel to the upper edge of the oxhaust port 21 although upon angular movement of the throttle valve, the control edge 33 will take up a progressively increas Iq anglar relation to the top edge of the exhaust port. T4s enables the effective open area of the exhaust port to be varied at a greater rate than the variation of the height of the exhaust port. Accordingly, different rates of variation can be obtained in the exhaust port area and exhaust port timing. The extent of variation between these rates is controlled by the angle of inclination between the control edge 33 and the pivot axis 31 of the exhaust port throttle valve.

f' Irk The air flow to the engine is regulated by the dual throttle valve assembly 29 ccnprising two side by side passages 38 and 39 each K, having a respective throttle valve 40 and 41, coupled to operate in S uanison over at least part of their range of travel. The passages 38 and 39 lead to the plenham chanber 42 from which air is distributed to the crankcase 10, or in the case of a multi cylinder engine to respective crankcase cartments one asociated with each cylinder.

In a multi cylinder construction there would also be a reed valve 28 for each crankcase ccmarbmt.

The air supply to the dual throttle unit 29 passes through the filter box 44 in which there is located an air flow sensor. The throttle valves 40 and 41 in the air passages 38 and 39 are coupled via the drive system 45 and linkage 47 to the driver operated accelerator pedal 48.

The cylinder -head 15 includes a cavity 50 into which the majority of the air charge is ccunressed when the piston is at the top dead centre position of its travel in the cylinder. Projecting into the cavity is a convenional spark plug 51 and a fuel injection nozzle 52 being part of a fuel meterJxg and injection unit 53. The exhaust throttle control valve 30 is coupled through the driver system 55 to the motor 57.

A temerature gauge 58 is provided in the water cooled galleries 20 56 of the cylinda- head and the crankshaft speed and position sensor 59 is coupled to the crankshaft to provide an input to the electronic control unit (ECU) 60. The signal fra the air flow sensor in the filter box 44 and frau tme tenperature sensor 58 are also supplied to the ECU 60. line sensor 59 determines the speed of rotation of the engine crankshaft and issues an appropriate signal to the ECU. This signal also provides a base fron which the position of the piston in the engine cycle can be determined.

It will be appreciated that t>hse three inputs to the ECJ provide the necessary aiformation to enable the required load and the engine speed to be determined as well as the position of the piston in its 4 reciprocating movnt in the cylinder. nie input from the tenperature sensor in the cylinder head provides information to indicate the state of operation of the engine such as whether it is starting up from cold or whether it is running at its normal regulated tenperature. From these inputs the ECU determines, from appropriate maps stored in the J ECJ, the fuel requirements of thc engine together with the correct time in the engire cycle to effect injection of the fuel into the engine cylinder and to activate the spark plug. In addition the Eau from a *map such as Fig. 1, determines the appropriate position of the exhaust 4, port control valve so as to obtain the desired gas flow through the cylinder to achieve the desired level of emissions in the eaxhaust 4 44 gases. The ECU is ues to the motor 57 an appropriate signal to activate the exhaust valve in the determined position.

Fig. 7 of the drawings illustrates in a somewhat siplified form the logic diagram of the ECU which shall row be described. The air flow sensor 61, which corresponds to the sensor referred to previously, is located in the air flow path to the throttle 62 whereby the air flow sensor will provide a reading directly related to the rate of air supply to the engine. The output from the air flow sensor is a voltage varying in accordance with the rate of air flow and this signal is, initially converted to a -form acceptable to the by the converter 64. The converted air flow signal is then processed with a signal from the sensor 59 indica.ng the engine speed in revolutions per minute, so as to achieve an output APC which indicates the quantity of air per

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-21cylinder per engine cycle being delivered to the engine. This APC K signal is then feed to four maps preprogramned into the ECU, the maps being an air fuel ratio map AFR, an ignition timing map 1T, a fuel injection timing map FIT, andl an exhaust valve position map )LWP. Each of these raps also receives a signal from the sensor 59 ind~icating the RSM of the engine and the position of the piston within the engine cycl e sutn outputsga frau the air fuel ratio meap is intgraed iththeairpercyindr pr ccle sinalbythe divider 67 to provide c signal indicating the fuel requirement of the engine per cylinder per cycle FPC, which is in turn supplied to the fuel metering and injection unit 53 to control the quantity of fuel injected into each cylinder per cycle. The ouitput from the ignition timing map is fed to ai ignition timing controller 65 so that the spark plug will spark at the point in the engine cycle as has been determined frau the spark timing map having regard to the engine speed and air flowM.

Similarly the output from the fuel injection timing map is fed to the fuelmeitering and injection unit 53 to set the tire in the cylirder cycle at which injection im ccmmnod ani termixiated. Finally the ouitput from the exhaust valve position map is feed to the motor 57 to place the exhaust port control valve 30 in the required position as has been determined in relation to the air per cylinder per cycle (engine load) and engine speed inputs to the exhaust map. It is preferable for the motor 57 to have a position feed back system whereby a signal is ireturned to the EWL inlicaing the actual position of the exhaust valve, whereby a further correctiLon may be made to the ro~tor 57 if the actual position does not correspond to that determined by the output from the exhaust valve position map. The timing of the injection of the fuel is controlled from the injection timing rap andl the ECIJ.

Alternatively a port may be controlled by a valve actuatable under the control of the ECU.

A fuel metering and injection method and device suitable for me~tering and delivering fuel to an engine operating in accordance with.

the inrvention. herein are described in detail, in Australian Patent Application No. 32132/84, the disclosure of tich is hereby 22 incorporated by reference for the teaching of the fuel metering and injection method and device therein.

An alternative fuel metering ard injection method d device is desc.-ibed in Australian Patent Application 46758/85, the disclosure of which is hereby incorporated by reference for the teachir of the fuel metering and injection method and device therein.

In a modification of the control strategy the air flow sensor 61 is replaced by an operator actuated engine load demard signal generator, that will provide a signal input to the ECJ that is directly fuel demand related.

41 It has previously been stated that the fuel is injected into the comustion chamber to form a stratified air-fuel distribution with the area in the immediate vicinity of the ignition device fuel rich. The fuel is preferably delivered to the comstion chamber entrained in air to promote a high degree of atomisation of the fuel Conveniently the fuel metering and injector unit 53 includes a chamber in which a metered quantity of fuel is collected, and the fuel is delivered from that chamber to the c=nbustion chamber by a pulse of air. The pulse of air may automatically open a port to establish communication between the chamber holdix the fuel and the combustion cammber, and the stratification of the fuel in the air within the cxcafustion chamber is by a preferred shaping of the cavity in the cylinder head, and the regulation of the extent of penetration of the fuel into the air charge in the combustion chamber.

A particularly advantageous shape of the cavity 50 is disclosed in the United States Patent Application lodged the same day as this arplication and entitled Improvements Relating to Two Stroke Cycle Internal Ccabustion Engines, inventors Christopher Kim Schlunke, and Robert Max Davis, the disclosure of which is hereby incorporated by reference for the teaching -of the cylinder head cavity shape.

!7 -I I -22a- The method and the engine of the present invention will be of advantage when used in connection with an engine mounted for propulsion of a boat, such as an outboard marine engine, or an engine mounted for propulsion of a vehicle, although it should be understood that the invention is not limited to these applications.

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Claims

1. A method of operating an internal combustion engine on the two stroke cycle to control the level of contaminants in the exhaust gases, the engine having a cylinder, a piston mounted to reciprocate in the cylinder, said piston and cylinder defining a combustion chamber that cyclically varies in volume as the piston reciprocates, an air inlet port providing communication between the combustion chamber and a source of air, and an exhaust port providing communication between the combustion chamber and an exhaust duct, said inlet and exhaust ports being aranged to be opened and closed by the piston as it reciprocates in the cylinder, said method comprising admitting a charge of air to the combustion chamber through the inlet port, compressing the charge of air in the combustion chamber by the movement of the piston after the inlet and exhaust ports have been closed, injecting a metered quantity of fuel into I, I the air charge in the combustion chamber, igniting said fuel j: tcharge, and exhausting the products of combustion through the exhaust port after expansion in the combustion chamber, sensing the engine load and engine speed while the engine is operating, and regulating the mass of the products of combustion retained in the combustion chamber at closure of the ports so hydrocarbons present in the exhausted products of combustion are within selected limits by controlling the flow of gases through the exhaust port while open in Hrelation to engine speed and load to regulate the gas flow Sthrough the combustion chamber over the range of engine 5 speeds and loads, said controlling including adjusting the degree of throttling of the exhaust port through a range of j values between a minimunm :nd a maximum, for each combination of engine load and speed said degree of throttling of the exhaust port being preset -nd determined in accordance with the selected limits for hydrocarbons present in the exhausted products. 2' w W a% "K w i F. -1 24

2. A method of operating an internal combustion engine on the two stroke cycle to control the level of contaminants in the exhaust gases, the engine having a cylinder, a piston mounted to reciprocate in the cylinder, said piston and cylinder defining a combus- tion chamber that cyclically varies in volume as the piston reciprocates, an air inlet port providing communication between the combustion chamber and source of air, and an exhaust port providing communi- cation between the combustion chamber and an exhaust duct, said inlet and exhaust ports being arranged to be opened and closed by the piston as it reciprocates in the cylinder, said method comprising admitting a charge of air to the combustion chamber through the inlet port, compressing the air in the combustion chamber by the movement of the piston after the inlet and exhaust ports have been closed, injecting a me- terid quantity of fuel into the air charge in the combustion chamber, igniting said fuel charge, and exhausting the products of combustion through the exhaust port after expansion in the combustion cham- ber, sensing independently the engine load and the engine speed while the engine is operating, and regu- lating the mass of the products of combustion retained in the combustion chamber at closure of the exhaust port so hydrocarbons present in the exhausted products of combustion are within selected limits by: C controlling the air flow through the inlet port into the combustion chamber in accordance with the sensed engine load; and controlling the flow of gases through the exhaust port in relation to speed and load, including adjusting the degree of throttling of the exhaust port f t l J vr through a range of values between a minimum and a maximum, for each combination of engine load and speed, said degree of throttling of the exhaust port being preset and determined in accordance with the selected limits for hydrocarbons present in the ex- hausted products; said controlling of the flows through the inlet and exhaust ports regulating gas flow through the combustion chamber over the .full range of engine speeds and loads.

3. A method of operating an engine as claimed in claim 1 wherein the flow of air into the combustion chamber and the flow of products of combustion from the combustion chamber are controlled to achieve said regulation of the mass of products of combustion retained.

4. A method of operating an engine as claimed in claim 1 or 2 wherein the controlling of the flow of gases in the combustion chamber includes adjusting the timing of the opening and closing of the exhaust port in relation to engine speed and load. S 5. A method of operating an engine as claimed in S, claim 1 wherein the control of the gas flow in the a e combustion chamber is effected by independently con- trolling the flow of air into the combustion chamber and the flow of products of combustion from said chamber, the flow of air being controlled in a prede- termined relation to the sensed engine load and the flow of exhaust gas being controlled in a predeter- TRAZ. mined relation to the sensed engine speed and engine fc load. Vo .K -26

6. A method of operating an engine as claimed in any one of claims 1 to 5, wherein the fuel is injected into the combustion chamber to form a stratified fuel air charge in the combustion chamber.

7. A method of operating an engine as claimed in claim 6 wherein the metered quantity of fuel is in- jected into the combustion chamber entrained in a gas.

8. A method of operating an engine as claimed in claim 5, wherein the controlling of the flow of the products of combustion from said chamber includes adjusting the timing of the opening and closing of the exhaust port in response to the sensed engine speed. t

9. An internal combustion engine operating on the $it, two stroke cycle comprising a cylinder, a piston mounted to reciprocate in the cylinder, said piston and cylinder defining a combustion chamber that cycli- cally varies in volume as the piston reciprocates, an air inlet port providing communication between the combustion chamber and a source of air, and an exhaust S port providing communication between the combustion ,Jd ,chamber and an exhaust duct, said inlet and exhaust C ports being arranged to be opened and closed by the p't r piston as it reciprocates in the cylinder, means to inject fuel directly into the combustion chamber, and means for regulating the mass of the products of combustion retained in the combustion chamber at the closure of the exhaust port so hydrocarbons present in the exhausted products of combustion are within selected limits, said regulating means including means to control the flow of gases through the exhaust port in relation to engine speed and load including adjust- 26a ment of the degree of throttling of the exhaust port through a range of values between a maximum and a minimum, as said regulating means being so arranged that for each combination of engine load and speed the throttling of the exhaust port is, adjusted to a preset degree determined in accordance with the selected limits for hydrocarbons present in the exhausted products. r r V C C t 417' Q' C 27 An internal combustion engine as claimed in claim 9 wherein said means to control the flow of gases include a first means to contril the flow of air into said chamber, a second means to control the flow of products of combustion from said chamber, and means operable in response to the engine load and engine speed to actuate said first and second means in a predetermined relation to regulate the mass of prod- ucts of combustion retained in the combustion chamber at the closure of the ports. fi 11. An internal combustion engine as claimed in S• claim 9 wherein said means to control the flow of gases includes a first means to control the flow of air into said chamber, a second means to control the ,flow or products of combustion from said chamber, S: r( means operable to actuate one of said first and second %ti control means in a predetermined relation to the engine load, and means operable to actuate the other one of said first and second control means in a prede- c' -termined relation to engine load and engine speed to regulate the mass of products of combustion retained in the combustion chamber at closure of the ports.

12. An internal combustion engine as claimed in Sclaim 9 wherein the means to control the flow of gases includes means to adjust the timing of the opening and closing of the exhaust port in relation to engine speed and load.

13. An internal combustion engine as claimed in j' claim 10 or 11 wherein one of said first and second t IR.44., means is operable to adjust the timing of the opening '^and closhg of the exhaust port in relation to engine speed and load. "A I -28-

14. An internal combustion engine as claimed in claim 9 including means to sense the engine speed and issue a signal representative of the engine speed, means to sense the engine load, an electronic control unit arranged to receive said speed and load signals and adapted to determine from said signals the required gas flow through the exhaust port and issue a signal representative of said gas flow, and means arranged to receive said gas flow signal and operable in response thereto to control the flow through the exhaust port. An internal combustion engine as claimed in claim 14 wherein said means operable in response to said gas flow 4, signal controls the degree of throttling of the exhaust port. 4 0

16. An internal combustion engine as claimed in any one of claims 9 to I, wherein means are provided to inject a metered quantity of fuel into an air charge in the combustion chamber each engine cycle.

17. An internal combustion engine as claimed in claim r 16 wherein said injection means are adapted to inject the *4 fuel in a manner to form a stratified fuel air charge in the combustion chamber. g(I tr j OFF1CI w1r -29-

18. An internal combustion engine as claimed in claim 17 wherein said injection means are operable to inject said fuel into said chamber entrained is a gas. DATED this 12th day of October, 1989. ORBITAL ENGINE COMPANY PTY LTD WATERMARK PATENT ATTORNEYS SUITE 18 159 ADELAIDE TERRACE EAST PERTH WA 6004 t t is t t 4