GB2274679A - I.c.engine exhaust port control and engine balancing apparatus - Google Patents

Abstract

The drive from the crankshaft 19 to the exhaust port shutters 20, 21, 22 includes or drives out of balance weights 25, 26 for engine balancing. The drive may include a chain or gears. The motor 37, controlled in response to engine speed, inlet manifold depression or temperature, determines the extent of shutter movement in synchronism with piston reciprocation. The weight 26 may provide a drive pulley for a water pump. <IMAGE>

Description

APPARATUS FOR CONTROLLING THE AREA OF AN EXHAUST PORT OF AN INTERNAL COMBUSTION ENGINE AND FOR BALANCING THE INTERNAL COMBUSTION ENGINE The present invention relates to apparatus for regulating the aperture of an exhaust port in an internal combustion engine and for balancing the internal combustion engine.

The invention will be discussed with particular reference to two-stroke engines, but should not be considered to be limited to such engines. The invention could be used with any engine having an exhaust port open and closed by the piston in a cylinder during its reciprocal motion.

In International Publication No. Wool/17348 an internal combustion engine is described which has a piston reciprocating within the cylinder with an exhaust port allowing communication of the cylinder with an exhaust passage. Moveable shutter means is provided to vary the effective area of the exhaust port. Sensor means generate signals corresponding to operation characteristics of the engine and the signals are processed by a control unit which controls the shutter means accordingly. In an embodiment shown in the publication the shutter means varies the effective area of the exhaust port in timed relation with the reciprocal motion of the piston. The invention described has the effect of improving engine performance, reducing fuel emissions and improving engine efficiency.

The invention described in WO91/17348 would typically be used in a two-stroke engine. A common configuration of two-stroke engine for an automobile is a three cylinder arrangement. Three cylinder engines suffer from vibration problems since it is impossible to balance out the rocking couple.

Commonly, balancer shafts are provided which are driven in timed relationship with the piston motion of the engine to provide a balancing effect to cancel the out of balance forces generated by piston motion.

Accordingly, the present invention provides an internal combustion engine comprising a cylinder; a piston reciprocating within the cylinder, a crankshaft connected to the piston and driven by the reciprocal motion of the piston; shutter means provided to vary the effective area of the exhaust port and drive means which forms a driving connection between the shutter means and the crankshaft; wherein the drive means drives the shutter means to vary the effective area of the exhaust port in timed relationship with the reciprocal motion of the piston, characterised in that balancing means is provided to balance the engine during operation, the balancing means being included in the drive means or being driven by the drive means.

The applicant has appreciated that apparatus for controlling the aperture of an exhaust port such as described in WO91/17348 can easily be adapted to provide an elegant solution to the balancing problem, without the need for a balancer shaft to be separately driven from the crankshaft of the engine.

The present invention will be described with reference to the accompanying drawings in which; Figure 1 is a schematic representation of an engine of one embodiment of the invention, Figure 2 is a schematic detailed view of part of the engine of Figure 1, Figures 3A to 6A are simplified diagrammatic cross-sections of a piston and cylinder of the engine of Figure 1 showing the arrangement at different stages during the cycle, Figures 3B to 6B are simplied diagrammatic cross-sections of a piston and cylinder of an engine of Figure 1 showing the same sequences as Figures 3A to 6A but with the engine adjusted to account for a change in operating characteristic of engine, Figure 1 shows schematically a three cylinder two-stroke internal combustion engine. The engine has three cylinders 10, 11 and 12. Pistons (not shown in Figure 1) reciprocate within the cylinders.The pistons are connected via connecting rods 13, 14 and 15 and gudgeon pins 16, 17 and 18 to a crankshaft 19.

The three cylinders 10, 11 and 12 respectively have exhaust ports 20, 21 and 22 which are opened and closed by the pistons in the cylinders during reciprocal motion of the pistons.

The crankshaft 19 has a pulley 23 mounted thereon which is connected by a belt 24 to a second pulley 25.

The cylinders 10, 11 and 12 are provided with exhaust port shutters 26, 27, 28 for varying the aperture of the exhaust ports 20, 21 and 22.

Turning to Figure 2 of the application, we will consider in detail the operation of the exhaust port shutter 28. The exhaust port shutter 28 is mounted on a shaft 29 which is mounted in suitable bearing means in the cylinder block of the engine. The shaft 29 is mounted to a link 30 and rotates upon rotation of the link. The link 30 is connected at one end thereof to the shaft 29 and is pivotally connected at the other end thereof to a second link 31. The link 31 is pivotally connected at one end thereof to the link 30 and at the other end thereof to two further links 32 and 33.

The link 32 is pivotally connected at one end thereof to the links 31 and 33 and at the other end thereof to a control link 34.

The link 33 is pivotally connected at one end to the two links 31 and 32 and at the other end is eccentrically mounted upon a shaft 35.

The shaft 35 runs along the longitudinal length of the engine (as can be seen in Figure 1) and is mounted by suitable bearing means in the cylinder block of the engine. The pulley 25, already mentioned, is mounted on the shaft 35 and the shaft 35 rotates with rotation of the pulley 25.

The link 34 is mounted on a second shaft 36 which extends along the longitudinal length of the engine (as can be seen in Figure 1). The shaft 36 is mounted in suitable bearing means in the cylinder block of the engine and is connected to an electric motor 37. The electric motor 37 is electrically controlled by a controller 38. The controller 38 is in turn connected to sensors 39 and 40.

The sensor 39 is an engine speed sensor which measures the rotational speed of the engine. The sensor 40 is a sensor connected to the inlet manifold of the engine which measures the depression in the inlet manifold to generate a signal indicative of engine load.

A further sensor 41 is provided which is connected either in the oil or water circuit of the engine to measure engine temperature.

Referring now to figures 3A to 6A, the method of operation of the shutter 28 can be seen. The Figure 3A shows a piston 42 which reciprocates in the cylinder 12. A plurality of transfer ports 43 are shown and a transfer passage 44. In the preferred embodiment of the engine shown in the figures the engine is a crankcase scavenge two-stroke internal combustion engine and therefore the transfer passages (such as passage 44) which are linked to the transfer ports 43 will connect the cylinder 12 with the crankcase of the engine so that fuel/air mixture in the crankcase of the engine pressurised by the piston 43, 42 during downward motion can be delivered to the combustion chamber defined in the cylinder 12.

The exhaust port shutter 28 can be seen mounted in an exhaust passage 25 which opens on to the cylinder 12 via the exhaust port 22. The exhaust port shutter 28 is mounted to oscillate into and out of the exhaust passage 25 to vary the effective area of the exhaust port 22.

The plurality of connecting links illustrated in Figure 2 can be seen also in Figure 3A.

The Figure 3A shows the piston 42 at a point when the piston and the skirt thereof just cover the exhaust port 22. Typically this occurs when the output crankshaft 19 has rotated 900 from the point at which the piston 42 is at its top dead centre position. The piston completely covers the transfer ports 43. The shutter 28 is withdrawn into the wall of the exhaust passage. The gases in the cylinder 12 have been combusted.

Figure 4A shows the pistion 42 at a point when it is moved downward from its position in Figure 3A, on rotation by roughly 280 of the output crankshaft 19. Since the crankshaft 19 is connected via the pulleys 23 and 25 and belt 24 to the shaft 35, the rotation of the crankshaft 19 causes rotation of the shaft 35. Due to the nature of the eccentric mounting of the link 33 to the shaft 35, the rotation of the shaft 35 between the position of the shaft in position 3A and the position of the shaft in Figure 4A does not cause the exhaust port shutter 28 to move down into the exhaust passage 25 to reduce the area of the exhaust port 22. The exhaust port 22 as shown in the Figure 4A has been uncovered by the piston 42 and hence combusted gases present in the cylinder at high pressure flow out of the cylinder through the exhaust port 22.

Figure 5A shows the piston 42 in its bottom dead centre position. The piston 22 has uncovered the transfer port 43 and pressurised fuel/air mixture can enter the cylinder 12 through the transfer ports 43.

The pressurised fuel/air mixture drives remaining combusted gases from the cylinder 12 into the exhaust passage 25 in a scavenging process common in two-stroke engines.

The motion of the piston from its position shown in Figure 4A to the position shown in Figure 5A has resulted in rotation of the crankshaft 19 and thus rotation of the shaft 35. The rotation of the shaft 35 has caused the exhaust port shutter member 28 to move downwardly into the exhaust passage 25 and reduce the aperture of the exhaust port 22. The reduction of the aperture of the exhaust port 22 helps prevent the excessive loss of fuel/air mixture during scavenging process.

In Figure 6A the piston is moving upwardly within the cylinder and the piston has just closed the transfer ports 43. This would typically occur at 0 roughly 242 of crankshaft rotation from top dead centre. The motion of the piston from its position shown in Figure 5A to its position shown in Figure 6A has resulted in crankshaft rotation and thus rotation of the shaft 35. The rotation of the shaft 35 has caused the shutter member 28 to move down to its lowest position. At its lowest position, the lowermost point of the shutter member 28 is at the same level as or just below the highest point of the transfer ports 43.The piston 42 and the exhaust port shutter 28 together act to seal off the exhaust passage 25 so that none or very little of the fuel/air mixture in the cylinder 12 is expelled through the exhaust passage 22 by the piston 42 in its further upward motion. This reduces exhaust emissions and/or fuel consumption and also enables a longer period of compression of the fuel/air mixture allowing a higher peak pressure to be achieved and greater engine thermal efficiency.

The sequence of Figures 3A and 6A shows the operation of the shutter member at high engine speed or loads. The sequence of Figures 3B to 6B show the same piston positions as shown in Figures 3A to 6A, but show the operation of the shutter member 28 at lower engine speeds.

At lower engine speeds the piston will be moving more slowly and therefore the time that the piston takes to move from the position in its downward stroke at which it clears the upper lip of the exhaust port 22 to the time at which it reaches the same position during the upward stroke is longer than at higher engine speeds. Considering the integral of the area of the port 22 opened by the piston 42 over time for each stroke as the "time/area" for the engine, it should be appreciated that an engine requires a certain time/area for adequate blow down/scavenging.

In the past, the size of an exhaust port 22 would be chosen so that adequate time/area for blow down/scavenging was allowed at high engine speeds.

The exhaust port size however was not the best size for the engine operating at low speeds, because the size of the aperture 22 was larger than required by the engine at low engine speeds; the piston 42 moving slower and thus a smaller port area being required to achieve a desired time/area.

In the present invention means are provided for varying the area of the port 22 with engine speed and load. These means comprise the controller 38 which receives signals indicative of engine speed and load and controls the electric motor 37 to rotate the shaft 36. The controller is programmed such that at low engine speeds the shaft 36 is rotated such that the shutter member 28 is never fully retracted into the walls of the exhaust passage 25. Instead as can be seen in figures 3B and 4B, in its upper position exhaust port shutter 28 reduces the effective area of the exhaust port 22 (when compared with the total possible area of the exhaust port 22). The reduction delays the opening of the cylinder 12 to the exhaust passage 25 in terms of crankshaft degrees of motion of the piston during its downward motion.Thus at lower speeds the apparatus provides a longer expansion stroke than at higher speeds.

As can be seen by comparing Figures SA and 5B the shutter member 28 in low speed operation reduces the aperture 22 to a far greater degree during the scavenging period of the engine than in the high speed operating condition of the engine. By reducing the port area the exhaust port shutter reduces exhaust emissions at low speeds and increases engine efficiency.

It can be seen by comparing Figures 6A and Figure 6B that the lowermost position of the shutter 28 is the same for all engine speeds and loads. In its lowermost position the engine exhaust port shutter 28 has a position which is level with or just below the uppermost part of the transfer ports 43, for all engine speed and loads. This is done by positioning links 34 and 32 relative to each other such that rotation of link 34 by the shaft 36 causes the point of pivotal connection of the links 32 and 34 to move along an arc of fixed radius from the positions of the point of pivotal connection of the links 31 and 33 when the shutter member 28 is at its lowest point.

Looking at Figure 6B the pivot point A shown in the drawing is the point of pivotal connection of links 32 and 34 at high engine speeds and the point B shown in the drawing is the point of pivotal connection of the links 32 and 34 at very low engine speeds (points A and B being the extreme positions). It can be seen from the dotted line 50 that the pivot point of the two links 32 and 34 moves along an arc at constant radius from the point C shown in the drawings.

It is beneficial to configure the exhaust port shutter operating mechanism such that the lower level of the exhaust port shutter 28 always occupies a position at or below the upper level of the transfer ports for all engine speeds and loads because it is required at all engine speeds or loads that the exhaust port 22 is effectively shut as soon as the piston 22 closes the transfer ports 43 during upward motion.

The controller 38 is also programmed to vary shutter operation with engine temperature (as measured by the sensor 41), to reduce exhaust emissions at low temperatures.

All of the above features were known from the publication W091/17348 wherein a full description is given.

The present invention differs from the invention described in WO91/17348 because the pulley 25 provided on the shaft 35 is a balancing member in that it is deliberately arranged with an uneven distribution of mass to provide an out of balance force on the engine. Furthermore, the shaft 35 is also provided with an out of balance disc member 26 at the end of the shaft distanced from the pulley 25.

As can be clearly seen in Figure 1 pulley 25 is provided with a cut-out portion 51 on one side of a diameter 52 of the pulley. The out of balance disc member 26 is the same shape and size as the pulley 25, but is provided with a cut-out portion 53 which is 0 180 out of phase with the cut-out portion 51, the cut-out portion 53 being a mirror image of the cut-out portion 51.

In the arrangement of the engine shown in Figure 1 the engine is a three cylinder engine and the motion of the pistons in the cylinders 10, 11 and 12 will generate a rotating couple. This occurs because the piston in the cylinder 12 is 2400 out of phase (in terms of degrees of crankshaft rotation), with the piston in the cylinder 10. This causes out of balance forces to act upon the crankshaft 19 and the engine block of the engine which tend to cause a rocking of the engine about a pivot axis running through the centre cylinder 11.

The present invention cures the out of balance problem by providing the out of balance pulley 25 and disc member 26. The pulley 25 and disc member 26 provide an out of balance rocking force on the engine in an opposite sense to the out of balance rocking forces provided by the piston-motion. Thus the out of balance forces generated by the rotation of the pulley 25 and disc member 26 cancel the out of balance forces generated by the motion of the pistons within the cylinders 10 and 12 and a balanced engine is provided.

It is preferable that the pulley 25 and disc member 26 are provided as distant from each other as possible. The distance of the pulley 25 and disc member 26 from each other should be as great as possible to keep the out of balance masses as small as possible. In practice, the pulley 25 and disc member 26 will preferably be provided outside of the engine cylinder block at the very ends of the shaft 35 (although both could be situated inside the block or one inside and one outside if required).

The arrangement works effectively since the shaft 35 is rotated at engine speed in timed relationship to the rotation of the shaft 19 so that the out of balance forces generated by the rotation of the pulley 25 and disc member 26 are in time with the out of balance forces generated by the motion of pistons within the cylinders 10, 11 and 12.

It will be appreciated that the present invention provides an arrangement which provides variable assymetrical exhaust port opening timing and provides balancing. The arrangement provides balancing without the need for a separate balancing shaft to be included in the engine in addition to the exhaust shutter operating means.

Whilst in the preferred embodiment described above the motion of the shutters 26, 27 and 28 is variable with engine speed and load, the invention could also include modification of any exhaust port shutter system which has members driven in timed relationship to the motion of the pistons within the cylinders. For instance, the motion of the exhaust port shutter 26, 27 and 28 might be fixed for all engine speeds or loads or temperatures.

Whilst the preferred embodiment of engine described above has three cylinders the apparatus of the invention could be used to provide balancing in all types of ported engine, from one cylinder engines upwards.

In a single cylinder engine the pulley shaft would preferably be provided with a pulley shaft having a pulley and a disc member mounted thereon which both generate out o-f balance forces in phase with each other and 1800 out of phase with the primary forces generated by piston motion.

The phase relationship required between the forces generated by the out of balance members of the arrangements of the inventions will vary between applications with the nature of the engines concerned.

It should be appreciated that the arrangements of the invention provide balancing to primary out of balance forces and/or couples. In a two cylinder 0 engine having a 180 crankshaft the two pistons are in primary force balance but a rocking couple is generated by piston motion. Therefore in such an application the apparatus of the engine would be configured to provide only a correcting couple.

In preferred embodiments of the apparatus of the invention the out of balance disc member described above will be used as a pulley for a belt driving an engine ancillary such as a water pump.

It should be appreciated that whilst in preferred embodiments of the invention the out of balance disc member provided on the pulley shaft will be the same size and mass as the pulley or the shaft this is not critical and is preferred only to ease manufacture. If both out of balance members on the pulley shaft are designed for being driven by or for driving belts then it might well be desirable to have one member larger than the other. However it is preferred for reasons of balance that the product of the out of balance mass of one member with the radial distance of its centre of gravity from the axis of rotation of the shaft is the same as the product of the mass of the other member with the distance of its centre of gravity from the axis of rotation of the shaft.

It should also be appreciated that whilst in the preferred embodiment described above the shaft 35 is driven to rotate by means of pulleys and belts, the shaft could be connected by gears to the crankshaft 19 or the pulley 61 could be driven by a chain.

It should further be appreciated that whilst it is preferred that the shutter means for varying the effective area of the exhaust port comprises an oscillating shutter member pivotally mounted in the exhaust passage, the shutter means could equally well take the form of a variety of other arrangements, e.g.

a guillotine valve oscillating into and out of the exhaust passage or a rotary valve mounted for rotation in the exhaust passage.

Claims (17)

CLAIMS:

1. An internal combustion engine comprising a cylinder; a piston reciprocating within the cylinder, a crankshaft connected to the piston and driven by the reciprocal motion of the piston; shutter means provided to vary the effective area of the exhaust port and drive means which forms a driving connection between the shutter means and the crankshaft; wherein the drive means drives the shutter means to vary the effective area of the exhaust port in timed relationship with the reciprocal motion of the piston, characterised in that balancing means is provided to balance the engine during operation, the balancing means being included in the drive means or being driven by the drive means.

2. An internal combustion engine as claimed in Claim 1 wherein the drive means includes a shaft which rotates in timed relationship with the crankshaft and the balancing means are provided on the shaft or are driven by the shaft.

3. An internal combustion engine as claimed in Claim 2 wherein the shaft is connected to the crankshaft and a plurality of pivotally connected links are connected between the shutter means and the shaft; wherein the balancing means comprises a first balancing member mounted on the shaft which generates a balancing force for balancing the engine.

4. An internal combustion engine as claimed in Claim 3 wherein the first balancing member is a pulley which has an uneven distribution of mass, the pulley being connected by belt means or chain means to the crankshaft.

5. An internal combustion engine as claimed in Claim 3 wherein the first balancing member is a gear which has an uneven distribution of mass, the gear being connected by connecting gear means to the crankshaft.

6. An internal combustion engine as claimed in any one of Claims 2 to 4 wherein the shaft extends longitudinally of the engine parallel to the crankshaft and the balancing means comprises a first balancing member and a second balancing member rotated by the shaft, the first and second balancing members being spaced apart along the length of shaft.

7. An internal combustion engine as claimed in Claim 6 and having a plurality of in line cylinders wherein the first and second balancing members are both mounted on the shaft, the first balancing member and the second balancing member being spaced further apart than the foremost and hindmost cylinders of the plurality of in line cylinders.

8. An internal combustion engine as claimed in Claim 6 or Claim 7 wherein the second balancing member is identical in size to the first balancing member and is arranged to provide a balancing force in a direction opposite to the balancing force provided by the first balancing member.

9. An internal combustion engine as claimed in any one of Claims 6, 7 or 8 wherein the second balancing member is connected by transmission means to an engine ancillary.

10. An internal combustion engine as claimed in any one of Claims 2 to 9 having a plurality of in line cylinders each having an exhaust port opened and closed by pistons reciprocating within the cylinders, wherein shutter means is provided for the exhaust port of each cylinder and each shutter means is connected to and driven by the shaft.

11. An internal combustion engine as claimed in Claim 10 having three cylinders in line.

12. An internal combustion engine as claimed in any one of the preceding claims wherein the shutter means oscillates in the exhaust port between a first position in which the exhaust port has a first effective area and a second position in which the exhaust port has a second smaller effective area.

13. An internal combustion engine as claimed in Claim 12 further comprising sensor means for sensing engine speed or load or temperature and control means connected to the sensor means, the control means adjusting the first position of the shutter means to vary the first effective area of the exhaust port with changes in engine speed or load or temperature.

14. An internal combustion engine as claimed in any one of the preceding claims wherein the drive means comprises a shaft connected to the crankshaft which rotates in timed relationship with the crankshaft; and connection means connected between the shaft and the shutter means, the connection means oscillating the shutter means on rotation of the shaft; characterised in that the shaft rotates at engine speed and two out of balance members are provided on the shaft for rotation therewith, the out of balance members generating a balancing force for the engine.

15. An internal combustion engine as claimed in claim 14 wherein the magnitude of the product of the out of balance mass of a first out of balance member with the distance of the centre of gravity of the first balance member from the shaft is equivalent to magnitude of the product of the out of balance mass of the second out of balance member with the distance of the centre of gravity of the second out of balance member from the shaft.

16. An internal combustion engine as claimed in Claim 6 or 7 having one piston reciprocating in one cylinder wherein the first and second balancing members both provide a balancing force in the same direction to balance the out of balance forces generated by the piston.

17. An internal combustion engine susbstantially as hereinbefore described with reference to and as shown in the accompanying drawings.