EP1314870A1

EP1314870A1 - Enhanced two-stroke endothermic engine

Info

Publication number: EP1314870A1
Application number: EP01830718A
Authority: EP
Inventors: Franco Lambertini
Original assignee: Morini Franco Motori SpA
Current assignee: Morini Franco Motori SpA
Priority date: 2001-11-21
Filing date: 2001-11-21
Publication date: 2003-05-28
Anticipated expiration: 2021-11-21
Also published as: ATE289003T1; DE60108886D1; EP1314870B1

Abstract

The enhanced two-stroke engine (1) comprises a crankcase (2), a cylinder (3) provided with an exhaust port (6), a series of transfer ports (7) communicating with the crankcase (2), the cylinder (3) further comprises at least an air inlet port (8) positioned in proximity to the exhaust port (6) and connected to a source (13) that supplies pure air towards the port (8), in such a way that the air allowed in by the port (8) creates an air barrier in front of the exhaust port (6); the pollution-abating action is based on three different principles: (i) shield against the egress of cool gases to the exhaust, (ii) oxidation and post-combustion in the exhaust system anticipating the operation of the catalyst, (iii) stratification of the charge of fuel-air mixture in the cylinder with globally leaner combustion with respect to traditional two-stroke engines.

Description

The present invention relates to an enhanced two-stroke endothermic engine.
More specifically, the two-stroke engine according to the present invention is provided with some constructive features that allow to reduce polluting emissions and fuel consumption.
The two-stroke engine according to the present invention finds advantageous application in the field of engines for small vehicles in general, such as mopeds, motorcycles, scooters, snowmobiles, or for portable tools such as chainsaws, lawn mowers, etc. Moreover, the present invention also finds application in the field of marine engines, for instance for outboard engines.
The main advantages of tradition two-stroke engines are the simplicity of construction, light weight and high specific power.
The main defects are their high consumption, polluting emissions caused above all by carbon monoxide and by unburned hydrocarbons and due mainly to incomplete combustion and to the escape from the exhaust of air-fuel mixture before it is burnt.
Such defects, and in particular the problem of the polluting emissions, are so severe that in many countries the laws that govern pollution control no longer allow the use of traditional two-stroke engines.
Some attempts to solve these problems provide for the application of fuel supply systems by direct injection into the combustion chamber, effected after shutting the exhaust port. The escape of fuel from the exhaust should thereby be avoided.
For instance, documents US-2 017 009, DE-26 19 136 and DD-213 471, disclose pump injectors able to perform direct injection into the combustion chamber of endothermic engines. These injection devices, however, are relatively complicated and have poor reliability. Their repair and servicing requires specialised technical personnel, specifically trained on the operation and maintenance of such devices.
Moreover, the direct injection into the combustion chamber, being at high pressure, is also rather costly to obtain, and can lead to metering difficulties, especially for small-displacement engines when used under partial loads. Furthermore, the time for injection is very short and it is therefore necessary to limit the maximum power of the engine, in order to perform the injection earlier, when the exhaust port is still open, thereby returning, however, to have the problems of the escape of unburned fuel from the exhaust.
In the final analysis, this type of solution is not suitable for small-displacement engines, with fairly high specific power and reduced cost.
Other attempts to eliminate the typical defects of traditional two-stroke engines are illustrated in patent application WO-00/55488 and in US Patent 4 848 279. Said documents disclose two-stroke engines provided with devices for injecting air into the combustion chamber or into the exhaust pipe.
However, these solutions are also not very satisfactory because of the complications they introduce: in the first case, a dual carburettor of a special type is necessary, whilst in the second case an additional source of high-pressure compressed air must be provided. In this case, too, the actual achievement of reduced pollution values is not certain.
The aim of the present invention is to obtain an enhanced two-stroke endothermic engine that allows to reduce the polluting emissions at the exhaust, meeting current and future pollution-abatement regulations.
Another aim of the present invention is to obtain a two-stroke endothermic engine that is simple to produce and that does not require complicated and unreliable devices, in such a way as not to alter the typical advantages of traditional two-stroke engines.
A further aim of the present invention is to obtain a two-stroke endothermic engine that is economical to produce and that can easily be repaired and serviced by traditional mechanics without requiring, on their part, specific training on the operation and maintenance of this type of engine.
In accordance with an aspect of the present invention, a two-stroke endothermic engine is provided as specified in claim 1. The dependent claims refer to preferred and advantageous embodiments of the invention.
Embodiments of the present invention, purely by way of non limiting indication, are described hereafter with the aid of the accompanying drawings, in which:

Figure 1 shows a partial cross section of the two-stroke engine of the present invention;
Figure 2 shows a partial longitudinal section of the engine of Figure 1;
Figure 3 shows a bottom view of the cylinder and of the crankcase, with some parts partially removed and sectioned, of the engine of the previous figures;
Figures 4 and 5 show a cross section of the cylinder and some sectioned details of the engine of the previous figures;
Figures 5 and 6 show some details of the engine of the previous figures;
Figures 8, 9 and 10 show some variations of details of the engine of the present invention.
Figures 11 through 18 show an operating sequence of the engine of the present invention.

In accordance with the figures of the accompanying drawings, the two-stroke engine is globally indicated with the number 1.
The engine 1 includes a crankcase 2, shown partially, a cylinder 3 mounted on the crankcase 2 and a head 4 for closing the cylinder 3. The head 4 is provided with a cap 4a for collecting the air-fuel mix around the ignition plug. Inside the cylinder 3 is able to slide a piston 5 which opens a series of ports for the operation of the engine according to the two-stroke cycle. The piston 5 is connected in conventional fashion, not shown herein, to a drive shaft by means of piston pin and connecting rod.
More specifically, the cylinder 3, having an axis 3', comprises at least an exhaust port 6, having an axis 6', and a series of transfer ports 7 communicating with the crankcase 2, which in turn comprises an intake and pre-compression chamber of the usual type, not shown herein, connected in known fashion, for instance by means of a blade valve, to a fuel supply device, for instance a carburettor (not shown herein).
The cylinder 3 further comprises at least an air inlet port 8 positioned in proximity to the exhaust port 6. Preferably, the cylinder 3 is provided with two air inlet ports 8 positioned to the side of the exhaust port 6. The air inlet ports 8 are connected to an air supplier-resonator device 9.
The supplier-resonator 9 comprises a resonance chamber 10 and at least a conduit 11 for connecting the resonance chamber 10 to the air inlet port or ports 8.
As shown in greater detail in Figures 2, 3, 4 and 5, the conduit or conduits 11 are made with such an inclination, in the part proximate to the cylinder 3, that a fluid egressing the port or ports 8 is oriented with an angle α relative to the axis 3' and towards the top of the cylinder 3 and with an angle β relative to the axis 6' of the exhaust port 6 and towards the centre of the cylinder.
The angle α can be between 20 and 75 degrees and it is preferably about 40 degrees (Figures 2 and 5) relative to the axis 3', whilst the angle β can be between 50 and 80 degrees and it is preferably 70 degrees relative to the axis 6'.
The resonance chamber 10 further comprises an opening 12 for admitting the air coming from a source 13 of air. The opening 12 can be provided with appropriate regulating means 14. In the illustrated example, the regulating means 14 comprise a blade valve 15, which in the practical execution can comprise a single blade, as shown in the drawings, or multiple blades.
The source of air 13 can provide air at atmospheric pressure or with a certain over-pressure, drawing it directly through filtering means (not illustrated herein).
In this latter case, in addition to the filtering means, it is necessary to provide means, which are wholly known and thus not illustrated herein, for increasing the pressure of the air, such as a compressor, a mechanically actuated pump of the membrane type or the like, or a pump that is actuated mechanically through the pressure waves of the gases in the exhaust system.
The air inlet ports 8 have relatively limited width relative to the other ports to increase outflow velocity in order to increase turbulence and the barrier effects, and they are located near the exhaust port 6.
Each air inlet port 8 is positioned relative to the exhaust port 6 and so dimensioned as to create a "blade" of pure air which, inside the cylinder 3, opposes the egress of the cool gases 20 coming from the transfer ports 7 and favours re-mixing (turbulence).
The resonance chamber 10 is positioned between the cylinder 3 and the crankcase 2 and comprises a closure wall 16 whereon is located the opening 12 and whereon is also mounted the blade vale 15.
In this area, between the cylinder 3 and the crankcase 2 is provided an insulating gasket 16a whose purpose is to protect the blade valve 15 from the heat coming from the cylinder and in particular from the exhaust manifold, located above the chamber 10.
The latter can be made with different volumes according to the characteristics of power to be obtained from the engine.
Larger resonance chambers 10 are suitable for engines with more "tourist-like" characteristics, i.e. engines with higher torque at low rpm settings, whilst smaller chambers 10 are suitable for "sportier" engines, i.e. engines with greater specific power.
It is also possible to realise a resonance chamber 10 whose volume can vary according to the rpm setting of the engine and hence it is possible to have a chamber 10 with greater volume at low rpm settings of the engine and of lesser volume at high rpm settings.
For example, one of the lateral walls of the chamber 10 can be translatable under the action of appropriate actuation means sensitive to the rpm setting of the engine. Said means can comprise centrifugal masses which rotate together with the drive shaft and which are displaced according to the velocity of rotation thereof. The displacement of the masses can thus be used to displace the lateral wall of the chamber 10.
The opening 12 comprises a supporting part 17 for the blade valve 15. The support part 17 can be integral with the wall 16 for closing the chamber 10 as shown in the figures.
The support function of the part 17 for the blade valve 15 is very important for the proper operation of the valve because it allows to maintain the blade bearing on an ample area, when the chamber 10 is under pressure. Without said part 17, the blade of the valve 15 would be subjected to flexure due to the relatively high pressure of the chamber 10, so that the blade valve 15 would deteriorate in a short time.
Figures 11 through 18 show an example of operation of the engine of the present invention according to the configuration of Figure 8. Moreover, the differences of operation with respect to the other engines configurations illustrated in Figures 9 and 10 will be described.
In Figure 11, the engine 1 is in the expansion phase after the combustion of the fuel-air mixture. The piston 5 during its descent opens the exhaust port 6 and the exhaust phase thus starts. The pressure inside the cylinder 3 drops from a few bar, by way of indication about 4-4.5, to a pressure of about 1.5 bar.
As indicated above, the chamber 10 can be supplied air from the source 13 of air at atmospheric pressure or with a certain over-pressure. Therefore, the chamber 10 can be at a pressure that is slightly lower than atmospheric pressure, i.e. about 0.8-0.9 bar, or when the chamber 10 is supercharged, at greater than atmospheric pressure.
The piston 5, continuing its descent, starts to open also the air inlet ports 8 as shown in Figures 12 and 13. The cylinder 3 is then placed in communication with the chamber 10.
The pressure of the gases inside the cylinder 3 exceeds that of the chamber 10, so the burned gases 18 in the cylinder 3, indicated by the arrows drawn in dashed lines, enter the chamber 10 until the pressure in the chamber 10 is equal to the pressure of the cylinder 3.
Figures 8, 9 and 10 show embodiments of the present invention in which the air inlet ports 8 have different heights in relation to the height of the exhaust port 6. These parameters allow to vary the operating characteristics of the engine of the present invention.
The relation between the height of the exhaust ports 6 and the height of the air inlet ports 8 is that as the height of the inlet ports 8 increases, so does the pressure level in the resonance chamber 10.
The variation of the height of the air inlet port 8 is a function of the effect to be obtained by the return wave towards the cylinder and hence of the characteristics of the engine, since the farther upwards the air inlet port 8 is situated, the higher the compression pressure of the air inside the chamber 10 will be, hence the higher will be the return effect of the air in the cylinder 3 and thus the stronger the barrier effect will be.
The height of the air inlet port 8 is, therefore, the result of a trade-off that is a function of the engine specifications: power/pollution/consumption.
Returning to the operation of the engine, Figure 14 shows a moment subsequent to the descent of the piston 5, in which the pressure level in the chamber 10 has dropped until becoming lower than the pressure level of the pure air, indicated with the arrows 19, coming from the air source 13.
If supercharging is provided, the pure air 19 enters in over-pressure through the means 14 for regulating the opening 12, whilst if the atmospheric feeding is provided for the chamber 10, the pure air 19 enters the chamber 10 because of a vacuum wave of the burned gases 18. The latter, returning outside through the ports 8, cause a vacuum in the chamber 10 which thus causes the intake of the pure air 19.
In any case, the waves of the exhaust gases 18 contribute to intake the pure air 19 into the resonance chamber 10 and subsequently to the egress of the pure air 19 partly mixed with the exhaust gases 18.
As indicated above, the regulating means 14 are practically obtained with a blade valve 15 of a known type, which allows automatically to regulate the ingress of the pure air 19. Alternatively, different regulating means 14 can be provided for admitting air into the chamber 10, such as commanded mitre or slide valves (not shown herein).
In regard to the inlet of pure air 19, both in case of aspirated intake, and in the case of supercharged intake, in the chamber 10 pressure waves are produced so that the burned gases 18 and the pure air 19, mixed to each other in the chamber 10 itself, vigorously return outside from the air inlet ports 8 in the cylinder 3.
Advantageously the chamber 10 is in proximity to the exhaust conduit, so that part of the heat of the exhaust gas is transmitted to the pure air 19 present in the chamber 10, and thanks to the heat the pure air 19 present in the chamber 10 undergoes such a temperature increase as to increase pressure and favour an oxidation effect of the cool gases 20 and a post-combustion effect.
The supercharging influences the quantity of pure air 19 that enters the chamber 10 and is mixed with the burned gases 18, but not substantially influence the return pressure in the cylinder because in any case the burned gases 18 that raise the pressure level entering the resonance chamber 10. In the final analysis, the result is always that of a strong flow of burned gases 18 and pure air 19 returning from the ports 8 towards the cylinder 3, which pulsates with a resonance rate that depends, among other factors, on the volume of the chamber 10.
The outflow from the ports 8, schematically shown by the arrows 19 and as indicated in Figures 14 and 15, encounters the cool gases 20 coming from the transfers 7 and creates an obstacle to their direct egress into the exhaust. The particular shape of the thin, elongated ports 8 and the orientation of the conduits 11 favours the antagonist and barrier effect against the flame front of the combustion and the cool gases 20 coming from the transfers 7. The possibility for the cool gases 20 to egress from the exhaust port 6 is, therefore, highly reduced.
In Figure 16, the piston 5 has reached the bottom dead center and the flow of pure air 19 and burned gases 18 continues to egress from the air inlet ports 8 and continues the barrier effect against the cool gases 20, and the flow of pure air 19 and burned gases 18 continues to egress from the exhaust port 6.
The effect of the pure air 19 in the exhaust is to favour the oxidation of any cool gases 20 and unburned gas which are along the exhaust pipe and to favour the effect of the catalyst.
In Figures 17 and 18, the piston 5 rises again and starts progressively to throttle the transfer ports 7, the exhaust ports 6 and the air inlet ports 8. The barrier action of the flow, coming from the air inlet ports 8, continues to prevent the egress of the cool gases 20 in the exhaust. Figure 18 shows that the transfer ports are already shut whilst the flow of pure air 19 and burned gases 18 of air coming from the ports 8 continues to enter the cylinder 3 and also to egress into the exhaust.
The pure air 19 that does not escape from the exhaust participates in the combustion of the engine. Thus, there is an additional pollution abating effect due to the stratification of the fuel charge with an area where the fuel-air mixture is richer, around the spark plug and an area where it is leaner, i.e. with more abundant air, around the air inlet ports 8. In this way a globally leaner combustion is obtained, with further advantages in pollution abatement terms.
To favour the combustion, the head 4 can have a cap 4a in eccentric position, offset to the side opposite the air inlet ports 8.
The pollution-abating action of the engine of the present invention therefore develops along three main points.
A barrier effect against the cool gases that prevents, or greatly decreases, their egress into the exhaust.
An ingress of pure air into the exhaust which favours the oxidation in the catalyst, if installed, at the exhaust and in any case favours a post-combustion of the exhaust gases and hence anticipates the operation of the catalyst, if installed.
Lastly, the possibility of obtaining a lean combustion thanks to the stratification of the fuel charge inside the cylinder 3.
The main advantages of the present engine are the economical construction which requires few additional components with respect to a traditional two-stroke engine.
The engine of the present invention is, in fact, based on a traditional two-stroke engine structure.
The additional devices, the resonance chamber 10, the air source 13, etc., are relatively simple and inexpensive. Moreover, their entire operation is intuitive and can be repaired and serviced also be mechanics without specific training.
The traditional characteristics of good specific power of two-stroke engines remain practically unaltered.
Moreover, the devices added to the engine of the present invention provide for flexible use, because they are suitable both for "tourist-like" engines and for "sportier" engines.
Lastly, the pollution-abating action of the devices added to the engine of the present invention remain unaltered over time because it has no parts subject to wear and it is certain because it is based on three different principles, combined and mutually enhancing: (i) barrier against the egress of cool gases to the exhaust, (ii) oxidation and post-combustion in the exhaust system, (iii) stratification of the charge of fuel-air mixture in the cylinder with globally leaner combustion relative to traditional two-stroke engines.

Key

1: engine
2: crankcase
3: cylinder
3': cylinder axis
4: head
4a: cap of the head 4
5: piston
6: exhaust port
6': axis of the exhaust port
7: transfer port
8: air inlet port
9: air supplier-resonator
10: resonance chamber
11: connection conduit
12: opening for the chamber 10
13: air source
14: means for regulating the opening 12
15: blade valve
16: wall for closing the chamber 10
16a: insulating gasket
17: part for supporting the blade of the blade valve 15
18: exhaust gases
19: pure air
20: cool transfer gases

Claims

Two-stroke endothermic engine (1) comprising a crankcase (2), a cylinder (3), having an axis (3'), at least an exhaust port (6) having an axis (6'), and a series of transfer ports (7) communicating with the base (2), the cylinder (3) being mounted on the crankcase (2), a head (4) for closing the cylinder (3), a piston (5) able to slide within the cylinder (3) able to open the series of ports (6, 7) for the operation of the engine (1) according to the two-stroke cycle, characterised in that the cylinder (3) comprises at least an air inlet port (8) positioned in proximity to the exhaust port (6) and connected to a source (13) that supplies air towards the port (8), in such a way that the air ingressing from the port (8) creates an air barrier in front of the exhaust port (6).
Engine as claimed in claim 1, characterised in that the air inlet port (8) is positioned between the exhaust port (6) and the transfer ports (7).
Engine as claimed in claims 1 or 2, characterised in that the air inlet port (8) is connected to a supplier-resonator device (9) through at least a conduit (11).
Engine as claimed in claim 3, characterised in that the conduit (11) or the conduits (11) have an inclination, in the part proximate to the cylinder (3) that is upward and toward the middle of the exhaust port side (6) of the cylinder (3) itself.
Engine as claimed in claim 4, characterised in that the conduit (11) or the conduits (11) have an angle α relative to the axis (3') and towards the top of the cylinder (3) measuring between 20 and 75 degrees.
Engine as claimed in claims 4 or 5, characterised in that the conduit (11) or the conduits (11) have an angle β relative to the axis (6') of the exhaust port (6) measuring between 50 and 80 degrees.
Engine as claimed in one of the claims from 3 to 6, characterised in that the supplier-resonator device (9) comprises a resonance chamber (10) provided with an opening (12) for the admission of pure air (19) coming from a source (13) of air.
Engine as claimed in claim 7, characterised in that the opening (12) is provided with regulating means (14).
Engine as claimed in claim 8, characterised in that the regulating means (14) comprise a blade valve (15) provided with one or more blades.
Engine as claimed in claim 9, characterised in that the opening (12) comprises a support part (17) for the blade valve (15).
Engine as claimed in one of the claims from 7 to 10, characterised in that the source (13) of air provides pure air 19 with over-pressure relative to atmospheric pressure.
Engine as claimed in one of the claims from 7 to 11, characterised in that the resonance chamber (10) is in proximity to the exhaust port (6) in such a way as to be heated by exhaust gases.
Engine as claimed in one of the claims from 9 to 11, characterised in that the blade valve (15) is thermally insulated from the cylinder (3) by means of a gasket (16a).