WO1998038419A1

WO1998038419A1 - A direct electronic fuel injection system for two-stroke internal combustion engines

Info

Publication number: WO1998038419A1
Application number: PCT/IB1998/000186
Authority: WO
Inventors: Pierluigi Marconi
Original assignee: Bimota SpA
Current assignee: Bimota SpA
Priority date: 1997-02-28
Filing date: 1998-02-16
Publication date: 1998-09-03
Anticipated expiration: 1999-08-28
Also published as: ITBO970113A0; ZA981677B; AU5777398A; IT1291231B1; ITBO970113A1

Abstract

The invention relates to a fuel injection system (1) for a two-stroke internal combustion engine (10) of the type comprising a cylinder (2) with an internal cavity (2') of a substantially cylindrical shape and having on its side wall (11) a number of intake ports (15, 16, 17) and exhaust ports (12, 13); a reciprocating piston (3) that slides coaxially within the cavity (2') of the piston (2); a cylinder head (6) connected to one end of the cylinder (2) and defining inside it a combustion chamber (7) that communicates with the cavity (2'). The cylinder head (6) mounts at least one fuel mixture ignition device (9). The system (1) comprises an electronic unit (20) that cyclically activates an injector (19), which is mounted in the side wall (11), when the exhaust ports (12, 13) are substantially closed, the axis (32) of the injector (19) making with the plane normal to the cylinder axis an angle (β) of between 15° and 35°, while the angle (α) which the axis (32) of the injector (19) makes with the axis (12') of the exhaust port (12) is between 180° and 360°.

Description

A direct electronic fuel injection system for two-stroke internal combustion engines

Technical Field

The present invention relates to a direct electronic low- pressure fuel injection system for two-stroke internal combustion engines . Hereafter, without restricting the scope of the invention, reference will be made to a fuel injector for two-stroke internal combustion engines with controlled ignition, that is to say, of the type equipped with a spark plug and a device for producing the spark across the electrodes of the spark plug. However, the fuel-air mixture can also be ignited by compression through conventional devices designed to appropriately vary the engine compression ratio in such a way as to ignite the fuel-air mixture.

Background Art

A fuel delivery system for two-stroke internal combustion engines of the above type is described in the publication "INGENIEURS DE 'AUTOMOBILE" No.11, 1st November 1977, BOULOGNE, FRANCE , pages 717-723. This publication describes a two-stroke engine with a small cylinder capacity (50-120 cm³) equipped with an electronic injection device where the injector is fitted inside the side wall of the cylinder.

In the engine described in the above document, the axis of the injector is perpendicular to the axis of the cylinder and the injector is located diametrically opposite the main exhaust port.

Since the injector axis is perpendicular to the cylinder axis, the jet of fuel delivered by the injector strikes the cylinder wall in the area opposite the injector. This wall, being relatively cool, tends to condense the fuel on it, preventing the fuel and air from mixing effectively and thus increasing the amount of fuel that escapes combustion. Moreover, since the injector nozzle is located under the upper edge of the exhaust port, all the fuel must be delivered while the exhaust port is still open, that is to say, while the cylinder exhaust stroke is still in progress. Therefore, the separation of burnt gases from the fuel-air mixture still to be burnt is left to the special flows created within the cylinder, said flows being separable by means of aerodynamic screens .

These conditions are strongly influenced by the dimensional ratios and capacity of the cylinder and by the fuel and gas flows passing into the engine, and require lengthy and costly experiments in order to achieve good results in terms of fuel consumption, power and pollutant emissions.

Also, changing one of the engine parameters, even just a little, makes it necessary to change the injection components and to carry out a new set of experiments.

Disclosure of the Invention

The aim of the present invention is to overcome the disadvantages just mentioned by providing a fuel delivery system for two-stroke internal combustion engines which, on account of the position of the injector and the type of electronic drive, can be adapted to suit a wide range of cylinder capacities, dimensional ratios and power outputs of two-stroke engines and, in addition to this, permits a discernible reduction in the amount of unburnt fuel discharged from the exhaust.

According to the invention, it is not necessary to substitute the constructional components of the system but only to change the position of the injector and reprogram the software of the unit that controls fuel delivery.

Other advantages of the present invention are a lowering of atmospheric pollution to a degree comparable to that of a four- stroke engine and a substantial reduction in fuel consumption compared to two-stroke engines with conventional fuel delivery systems.

Another advantage of the system made in accordance with the present invention is that it uses only components that are normally available on the market and is therefore economical to manufacture and to maintain.

The invention, as characterized in the claims, provides a fuel delivery system applied to a two-stroke internal combustion engine of the type comprising a cylinder with an internal cavity of a substantially cylindrical shape and having on its side wall in at least one first area an air intake port and, in at least one second area, a main exhaust port and secondary exhaust ports for the discharge of combustion gases; a reciprocating piston that slides coaxially within the cavity of the cylinder; a cylinder head connected to one end of the cylinder and defining inside it a combustion chamber that communicates with the cavity, the cylinder head mounting at least one fuel mixture ignition device that extends towards or into the combustion chamber; a crankshaft connected to the piston by a conrod and a pin; the fuel delivery system comprises an injector that is mounted in the side wall and has a fuel delivery nozzle located in a third area of said cavity; the axis of the injector making an angle with the axis of the exhaust port; a first electronic unit that cyclically activates the injector; said fuel delivery system is characterized in that the axis of the injector makes with a plane normal to the axis of the cylinder an angle β of between 15° and 35°, in that the angle α ranges between 180° and 360° and in that said electronic control unit cyclically activates the injector during each revolution of the crankshaft at an instant t when the exhaust ports are substantially closed; the values of the angle α, of the angle β and of the injector cyclic activation time t being defined in accordance with the functional parameters of the engine depending on the dimensional ratios, displacement and capacity of the engine without having to act on the architecture of the engine and on the dimensional ratios.

In a preferred embodiment of the present invention, the distance between the injector nozzle and a plane normal to the longitudinal axis of the cylinder and delimiting the cylinder itself in the proximity of the cylinder head ranges between the values of the products of the piston stroke multiplied by the constants 0.20 and 0.70. Further characteristics and advantages of the system made according to the present invention are more apparent from the detailed description which follows with reference to the accompanying drawings which illustrate a preferred embodiment of the invention and in which:

Figure 1 is a schematic cross section, partly in the form of a block diagram, through the line I-I in Fig. 2, of the fuel delivery system and of a portion of the two-stroke internal combustion engine made according to the present invention; and Figure 2 is a plan view of the upper portion of the two- stroke internal combustion engine illustrated in Fig. 1.

With reference to the accompanying drawings, the numeral 1 denotes as a whole a two-stroke internal combustion engine 10 of which only the upper portion is illustrated in the interests of brevity.

In the description which follows, this portion of engine, when referred to as a whole, will simply be called "the engine" for short .

The engine 10 essentially comprises a cylinder 2 with a vertical axis, this cylinder 2 being delimited by a side wall 11.

A piston 3, illustrated at its top dead centre in the drawings, slides axially within an axial cavity 2' in the cylinder 2 and is fitted to the top of a conrod 4 by means of a piston pin 5 whose axis is horizontal and normal to the plane illustrated in the drawings. The conrod 4 is in turn connected to a crankshaft lOg.

The numeral 6 denotes a cylinder head connected to a flat horizontal face at the top end of the cylinder 2 by screw fastening means (not illustrated) and of which a part facing the internal cavity of the cylinder 2 is equipped with a substantially hemispherical combustion chamber 7. The cylinder head 6 has a threaded through hole 8 accommodating a spark plug 9 connected to a conventional electronic unit, schematically illustrated as a block 29, capable of producing sparks across the electrodes of the spark plug 9. The side wall 11 of the cylinder 2 has, in a first portion of it, labelled Zl in Fig. 1, two main intake or transfer ports

15, made diametrically opposite each other (of which only one is illustrated) , a pair of secondary intake or transfer ports 16 (of which only one is illustrated) and an intake port 17, also called "fifth port", located between the secondary ports 16. The intake ports 15, 16 and 17 communicate with the interior of the intake chamber or casing 10c of the engine 10 in a manner that is not illustrated, being entirely conventional.

The side wall 11 of the cylinder 2 also has, in a second portion of it, labelled Z2 in Fig. 1, a main exhaust port 12, with axis 12', and two exhaust ports 13 located on opposite sides of the exhaust port 12 (of which only one is illustrated) . The exhaust ports 13 are usually called "secondary exhaust ports" and communicate indirectly with an exhaust pipe 14, while the exhaust port 12 communicates directly with it. The distance between the upper edges of the exhaust ports 12 and 13 and the horizontal plane delimiting the top of the cylinder 2 is labelled LS .

A third portion of the side wall 11 of the cylinder 2, labelled Z3 in Fig. 1, has a through hole 18 which accommodates, coaxially secured in it, an injector 19 having an axis 32.

The axis 32 of the injector 19 intersects the axis of the cylinder 2 and makes with a horizontal plane below the inlet points of the hole 18 in the cylinder 2 an angle β, preferably ranging from 15° to 35°. The angle OC which the injector axis 32 makes with axis 12' of the exhaust port ranges from 180° to 360° and is preferably 360°. In the latter case, the hole 18 and the injector 19 are located above the exhaust port 12, as illustrated in Fig. 1.

The fuel delivery system 1 includes the injector 19, equipped with a nozzle 21. The fuel delivery system 1 also includes a customary electronic unit that controls the injector 19.

The control unit is represented as a block 20 and is designed to control the operation of the injector 19 in such a way as to activate it at an instant t when the crankshaft lOg has, for different running speeds (RPM) of the engine 10, rotated through a given angle (+ 30° depending on the speed) measured from the top dead centre position of the piston 3 , as shown in the table of experimental values below: INJECTION TIMING (Y) RPM (X) INJECTION TIMING (Y) RPM (X)

180° 1000 108° 6500

180° 1500 102° 7000

180° 2000 98° 7500

180° 2500 93° 8000

172° 3000 84° 8500

158° 3500 82° 8750

144° 4000 80° 9000

141° 4500 78° 9250

130° 5000 72° 9500

128° 5500 68° 9750

120° 6000 65° 10000

The timing angles shown in the table above indicate the instant at which a control signal is generated by the electronic control unit 20 to activate the injector 19 and are calculated to take into account the minimum mechanical time delay from the moment the activation signal is transmitted to that in which the injector 19 responds by opening its fuel nozzle 21.

Preferably, the nozzle 21 of the injector 19 is set apart from the horizontal plane delimiting the top of the cylinder 2 by a length A whose lower and upper limit values are determined by the following mathematical relation: 0.20*STROKE < A < 0.70*STROKE, where STROKE is the distance travelled by the piston 3 inside the cavity 2' of the cylinder 2.

With reference to Fig. 1, the fuel delivery system 1 comprises a customary sensing device 22, represented schematically as a block, capable of monitoring the angular position of the throttle valve (not illustrated) located in the air intake duct (not illustrated) to the engine 10 with respect to a fixed reference and of sending a signal to the electronic control unit 20 according to the angle measured. In other terms, the sensing device 22 is capable of measuring the variable degree to which said air intake duct is opened. The numeral 23 denotes another customary sensing device, also represented schematically as a block, capable of monitoring the speed of rotation of the engine 10 and of sending a signal to the electronic control unit 20 according to the rotation speed detected. Similarly, the numeral 24 denotes a sensing device used to detect the air pressure inside the intake box (not illustrated) of the engine 10 and to send a signal to the electronic control unit 20 according to the pressure detected. Another sensing device, labelled 25, measures the temperature of the engine cooling liquid and sends a signal to the electronic control unit 20 according to the temperature measured. The numeral 26 denotes a device that measures the ambient air temperature, the numeral 27 a device that measures the voltage across the terminals of the battery (not illustrated) connected to the engine 10, and lastly, the numeral 28 a sensor designed to sample the exhaust gases and to return a signal to the electronic control unit 20 reflecting the percentage of unburnt substances in the emissions.

The numeral 30 denotes a flow control element, represented schematically, consisting of a gate valve located along the path followed by the exhaust gases discharged from the engine 10 through the exhaust ports 12 and 13 and capable of vertical movement through the agency of an actuator consisting, for example, of a stepping motor 31, driven by the electronic control unit 20.

The control unit 20 can also be connected to the control unit 29 of the ignition system so as to achieve integrated control of ignition and fuel supply.

As to the operation of the engine 10, this will be immediately apparent to a person skilled in the art from the foregoing description and few comments are required. The salient feature is that, during each revolution of the engine 10, the injector 19 directs a metered quantity of fuel into the combustion chamber 7 of the engine 10, the timing of which is shown in the table above, said quantity being determined by the electronic control unit 20 on the basis of the software it is programmed with and according to the signals sent to it by the above mentioned sensing devices 22, 23, 24, 25, 26, 27 and 28. Also significant is the fact that the stepping motor 31, controlled by the electronic unit 20, can vary the size of the openings of the exhaust ports 12 and 13. Lastly, experiments have shown that the geometry of the combustion chamber 7 plus the fact that the positioning of the injector 19 is directly correlated with the start of the injection phase ensure that any fuel dispensed by the injector 19 before the exhaust ports are completely closed immediately reaches the crown of the piston 3 where the heat evaporates it, causing it to ascend towards the spark plug 9 and thus preventing unburnt fuel from escaping through the exhaust ports 12 and 13.

From the foregoing description, it appears clear that the fuel delivery system made in accordance with the present invention fully achieves the aims mentioned above, witness the fact that it requires the use of only commercially available components and is easily adaptable to engines with different dimensional, displacement and power specifications. The adaptation of the fuel delivery system 1 is effected without having to substitute the components of the system but by just changing the position of the injector 19 in the engine 10 and modifying the related control software.

As to their impact on the environment, two-stroke engines equipped with fuel delivery systems 1 have been shown to compare favourably with four-stroke engines.

Moreover, by preventing the emission of unburnt fuel into the atmosphere, the fuel delivery system 1 applied to a two-stroke engine has permitted the achievement of fuel economies of up to 60%.

The invention described can be subject to modifications and variations without thereby departing from the scope of the inventive concept. Moreover, all the details of the invention may be substituted by technically equivalent elements.

Claims

1. A fuel delivery system (1) applied to a two-stroke internal combustion engine (10) of the type comprising a cylinder (2) with an internal cavity (2') of a substantially cylindrical shape, the cylinder (2) having on its side wall (11) in at least one first area (Zl) an air intake port (15, 16, 17) and, in at least one second area (Z2), a main exhaust port (12) with an axis (12') and secondary exhaust ports (13) for the discharge of the combustion gases; a reciprocating piston (3) that slides coaxially within the cavity (2') of the cylinder (2); a cylinder head (6) connected to one end of the cylinder (2) and defining inside it a combustion chamber (7) that communicates with the cavity (2'), the cylinder head (6) mounting at least one fuel mixture ignition device (9) that extends towards or into the combustion chamber (7) ; a crankshaft (lOg) connected to the piston (3) by a conrod (4) and a pin (5); said fuel delivery system (1) comprising an injector (19) that is mounted in the side wall (11) and has a fuel delivery nozzle (21) located in a third area (Z3) of said cavity (2'); the axis (32) of the injector (19) making an angle ( ) with the axis (12') of the exhaust port (12); a first electronic unit (20) that cyclically activates the injector (19); and being characterized in that

- the axis (32) of the injector (19) makes with a plane normal to the axis of the cylinder (2) an angle (β) of between 15° and 35°;

- in that the angle (α) ranges between 180° and 360°; - and in that said electronic control unit (20) cyclically activates the injector (19) during each revolution of the crankshaft (lOg) at an instant t when the exhaust ports (12, 13) are substantially closed; the values of the angle (α) , of the angle (β) and of the injector (19) cyclic activation instant t being defined in accordance with the functional parameters of the engine (10) depending on the dimensional ratios, displacement and capacity of the engine without having to act on the architecture of the engine and on the dimensional ratios.

2. The fuel delivery system according to claim 1, characterized in that the distance (A) between the injector (19) nozzle (21) and a plane normal to the longitudinal axis of the cylinder (2) and delimiting the cylinder (2) itself in the proximity of the cylinder head (6) ranges between the values of the products obtained by multiplying the stroke of the piston (3) by the constants 0.20 and 0.70.

3. The fuel delivery system according to claim 2, characterized in that the distance (A) between the injector (19) nozzle (21) and a plane normal to the longitudinal axis of the cylinder (2) is less than the smaller distance (LS) between the exhaust port and said normal plane.

4. The fuel delivery system according to any of the foregoing claims characterized in that it comprises a first sensing device

(22) capable of measuring the variable degree to which said air intake duct is opened and of sending a signal to the first electronic control unit (20) according to the angle measured.

5. The fuel delivery system according to any of the foregoing claims characterized in that it comprises a second sensing device

(23) capable of monitoring the speed of rotation of the engine (10) and of sending a signal to the first electronic control unit (20) according to the rotation speed detected.

6. The fuel delivery system according to any of the foregoing claims characterized in that it comprises a third sensing device

(24) used to detect the air pressure inside an intake box of the engine (10) and to send a signal to the first electronic control unit (20) according to the pressure detected.

7. The fuel delivery system according to any of the foregoing claims characterized in that it comprises a fourth sensing device (25) used to measure the temperature of the cooling liquid in the engine (10) and to send a signal to the first electronic control unit (20) according to the temperature measured.

8. The fuel delivery system according to any of the foregoing claims characterized in that it comprises a fifth sensing device (26) capable of measuring the ambient air temperature and of sending a signal to the first electronic control unit (20) according to the temperature measured.

9. The fuel delivery system according to any of the foregoing claims characterized in that it comprises a sixth sensing device (27) capable of measuring the voltage across the terminals of a battery connected to the engine (10) and of sending a signal to the first electronic control unit (20) according to the voltage measured.

10. The fuel delivery system according to any of the foregoing claims characterized in that it comprises a seventh sensing device (28) capable of sampling the exhaust gases and of returning a signal to the electronic control unit (20) reflecting the percentage of unburnt substances in the emissions from the engine (10) .

11. The fuel delivery system according to any of the foregoing claims characterized in that it comprises a second electronic control unit (29) which can be connected to the first electronic unit (20) and which is designed to control the ignition device (9) •

12. The fuel delivery system according to any of the foregoing claims characterized in that it comprises first flow control means (30) designed to vary the size of the opening of the exhaust port (12, 13), first actuating means (31) driven by the electronic control unit (20) being envisaged to actuate the first flow control means (30) .

13. The fuel delivery system according to any of the foregoing claims characterized in that the injector (19) is activated at an instant t when the crankshaft (lOg) has, for different running speeds (RPM) of the engine (10) , rotated through a given angle measured by the first electronic control unit (20) with a tolerance of ± 30° from the top dead centre position of the piston (3), as shown in the table below:

INJECTION TIMING (Y) RPM (X INJECTION TIMING (Y) RPM (X)

180° 1000 108° 6500

180° 1500 102° 7000

180° 2000 98° 7500

180° 2500 93° 8000

117722°° 33000000 84° 8500

158° 3500 82° 8750

144° 4000 80° 9000

141° 4500 78° 9250

130° 5000 72° 9500

112288°° 55550000 68° 9750

120° 6000 65° 10000

14. A two-stroke internal combustion engine equipped with a fuel delivery system such as that described in the foregoing claims.

15. A motor vehicle comprising a two-stroke internal combustion engine according to claim 14.

16. A method for delivering fuel to a two-stroke internal combustion engine (10) of the type comprising a cylinder (2) with an internal cavity (2') of a substantially cylindrical shape, the cylinder (2) having on its side wall (11) in at least one first area (Zl) an air intake port (15, 16, 17) and, in at least one second area (Z2), a main exhaust port (12) and secondary exhaust ports (13) for the discharge of the combustion gases; a reciprocating piston (3) that slides coaxially within the cavity

(2') of the cylinder (2); a cylinder head (6) connected to one end of the cylinder (2) and defining inside it a combustion chamber

(7) that communicates with the cavity (2'), the cylinder head (6) mounting at least one fuel mixture ignition device (9) that extends towards or into the combustion chamber (7) ; a crankshaft

(lOg) connected to the piston (3) by a conrod (4) and a pin (5); said method comprising the stages of providing the engine (10) with an injector (19) that is mounted in said side wall (11); positioning a fuel delivery nozzle (21) in the injector (19) substantially facing a third area (Z3) of the cavity (2'); and cyclically activating the injector (19) by means of an electronic control unit (20) , and said method being characterized in that the activation of said injector (19) occurs at an instant t when the crankshaft (lOg) has, for different running speeds (RPM) of the engine (10) , rotated through a given angle, with a tolerance of ±30°, measured from the top dead centre position of the piston (3), as shown in the table below:

INJECTION TIMING (Y) RPM (X) INJECTION TIMING (Y) RPM (X)

180° 1000 108° 6500

180° 1500 102° 7000

180° 2000 98° 7500

180° 2500 93° 8000

172° 3000 84° 8500

158° 3500 82° 8750

144° 4000 80° 9000

141° 4500 78° 9250

130° 5000 72° 9500

128° 5500 68° 9750

120° 6000 65° 10000

AMENDED CLAIMS

[received by the International Bureau on 23 June 1998 (23.06.98); original claim 1 amended; remaining claims unchanged (1 page)]

1. A fuel delivery system (1) for two-stroke internal combustion engines (10) ; the engines (10) of the type comprising a cylinder (2) with an internal cavity (2') of a substantially cylindrical shape, the cylinder (2) having on its side wall (11) in at least one first area (Zl) an air intake port (15, 16, 17) and, in at least one second area (Z2) , a main exhaust port (12) with an axis (12') and secondary exhaust ports (13) for the discharge of the combustion gases; a reciprocating piston (3) that slides coaxially within the cavity (2') of the cylinder (2); a cylinder head (6) connected to one end of the cylinder (2) and defining inside it a combustion chamber (7) that communicates with the cavity (2'), the cylinder head (6) mounting at least one fuel mixture ignition device (9) that extends towards or into the combustion chamber (7) ; a crankshaft (lOg) connected to the piston (3) by a conrod (4) and a pin (5) ; said fuel delivery system (1) comprising an injector (19) that is mounted in the side wall (11) and has a fuel delivery nozzle (21) located in a third area (Z3) of said cavity (2'); the axis (32) of the injector (19) making an angle ( ) with the axis (12') of the exhaust port (12) and an angle (β) with a plane normal to the axis of the cylinder (2) of between 15° and 35°; a first electronic unit (20) that cyclically activates the injector (19) which supplies a metered quantity of fuel into the combustion chamber (7) ; and being characterized in that the angle ( ) ranges between 180° and 360°; said electronic control unit (20) cyclically activates the injector (IS) during each revolution of the crankshaft (lOg) at an instant t when the exhaust ports (12, 13) are substantially closed; it is applicable to two-stroke engines having a wide range of cylinder capacities, dimensional ratios, power specifications, the injector (19) cyclic activation instant t and the metered quantity of fuel being determined by the electronic control unit (20) on the basis of a software defined in accordance with the values of the angle (α) , of the angle (β) and the functional parameters of the engines (10), without the necessity of substituting constructional components of the system or having to act on the architecture of the engine and on the dimensional ratios thereof.