GB2261025A - Four-stroke engine inlet and exhaust valving - Google Patents

Abstract

A combustion chamber 7 communicates through a port 11 with a secondary chamber 12. Opening and closing of the port 11 is controlled by a trumpet valve 13. The secondary chamber 12 has an inlet port 17 which is controlled by an oscillating valve 18 to open and close communication with an air pressure passage 19. An oscillating valve 21 opens and closes communication between an exhaust port 20 in the secondary chamber 12 and an exhaust passage 22. The valves are synchronised so that during the inlet stroke valves 13 and 18 are open to admit air under pressure to the combustion chamber while valve 12 is closed; during the compression stroke and during power stroke valves 18 and 21 are open for air flow through the secondary chamber 12 to exhaust 22 while the valve 13 is closed and during the exhaust stroke valve 18 is closed while valves 13 and 21 are open for exhaust from the combustion chamber. Preferably at the end of the exhaust stoke, the valve 18 is opened to admit air under pressure to the combustion chamber to scavenge exhaust gases remaining in that chamber. <IMAGE>

Description

TITLE "An internal combustion engine" TECHNICAL FIELD & BACKGROUND ART The present invention relates to an internal combustion engine of the kind having a piston axially reciprocable in a piston cylinder with a combustion chamber formed between the piston and cylinder to be expanded and contracted during reciprocation. More particularly, the invention concerns engines generally known as of the fourstroke type in which combustive fluid, typically comprising petroleum spirit (gasoline) or diesel oil, is admitted to the combustion chamber and fired in known manner for reciprocating the piston sequentially through successive inlet, compression, power and exhaust strokes.

It is well known with four-stroke engines to provide valve controlled ports in a wall of the combustion chamber and which are controlled in their opening and closing in synchronisation with the piston reciprocation for one or more of the ports to open for the admission of air into the combustion chamber during the inlet stroke as that chamber expands, to close to seal the combustion chamber during the compression and power strokes in which the combustive fluid is fired and to open during the exhaust stroke for the combustion gases to be displaced from the combustion chamber through one or more of the ports to an exhaust.

With a view to improving engine efficiency in the rate of gas exchange for increased flow of air into the combustion chamber during the inlet stroke and rapid exhaustion of combustion gases during the exhaust stroke, it is usual to provide several of the aforementioned valve controlled ports so that the area of the porting is relatively large for the gas exchange. In current automobile four-stroke engines there are typically four valve control ports for each piston cylinder in the engine. The provision of such a multi-valve porting arrangement is a relatively expensive facility and is inconvenient to manufacture, install and maintain in the restricted space available in the wall of the combustion chamber. It is also found that the efficiency of the gas exchange is not improved in proportion to the increase in the number of valve control ports which are provided.Furthermore, it is found that the valve controlled ports in the combustion chamber become heated during use and maintain this heat with consequent inefficiency in the engine. It is an object of the present invention to provide an internal combustion engine of the four-stroke type which alleviates the aforementioned disadvantages.

STATEMENT OF INVENTION & ADVANTAGES According to the present invention there is provided an internal combustion engine having a piston axially reoiprocable in a piston cylinder; a combustion chamber formed between the piston and its cylinder and which is expanded and contracted during reciprocation of the piston; means for admitting combustive fluid to the combustion chamber for firing to reciprocate the piston sequentially through successive inlet, compression, power and exhaust strokes; a main port for providing communication between the combustion chamber and a secondary chamber; first valve means controlling said main port for opening and closing said communication therethrough; an inlet port for providing communication between an air inlet passage and the secondary chamber; second valve means controlling said inlet port for opening and closing said communication therethrough; an exhaust port for providing communication between the secondary chamber and an exhaust passage; third valve means controlling said exhaust port for opening and closing said communication therethrough, and control means synchronising opening and closing of said first, second and third valve means whereby in said inlet stroke during expansion of the combustion chamber the inlet and main ports are open to admit air to the combustion chamber and the exhaust port is closed; in said compression stroke during contraction of the combustion chamber and in said power stroke during expansion of the combustion chamber the inlet and exhaust ports are open for air flow through the secondary chamber from the air inlet to exhaust and the main port is closed, and in said exhaust stroke during contraction of the combustion chamber the inlet port is closed and the main and exhaust ports are open for combustion gases from firing of the combustive fluid to flow from the combustion chamber by way of the secondary chamber to exhaust.

By the present invention air flow into the combustion chamber and exhaust of combustion gases from the combustion chamber is effected by way of the secondary chamber under control of the first valve means while the ingress of air to, and egress of air and/or combustion gases from, the secondary chamber is controlled by the second and third valve means. Consequently the first valve means can be formed as a single displaceable valve member which controls opening and closing of the main port, The latter preferably being formed as a single aperture in the wall of the combustion chamber. The main valve is preferably a conventional trumpet valve member controlling a single aperture in the wall of the combustion chamber for gas exchange purposes to and from the combustion chamber.

Such a single aperture permits the main port to be considerably larger in its through-flow area than conventional engine valve arrangements having two or more gas exchange ports in the combustion chamber; this may simply be illustrated by comparing a single circular main port of a given diameter in the engine of the present invention with known internal combustion engines having two gas exchange ports in the combustion chamber each having a diameter half that of the aforementioned given diameter where the aperture area for gas exchange through flow will be greater by the present invention in the ratio of approximately 2:1.Furthermore, when the main port is closed by the first valve means during the compression and power strokes of the piston, both the inlet port and exhaust port are opened by their respective second and third valve means to permit air, preferably under pressure, from the air inlet to flow through the secondary chamber and over the closed first valve means to exhaust. This latter flow of air has the advantage that it provides a cooling effect on the valves, particularly the first valve means and the third valve means which is subjected to heating from hot exhaust gases. Furthermore the flow of clean air into the exhaust subsequent to the exhaust stroke serves to reduce the density of the combustion gases emitted during the exhaust stroke.

Preferably during and immediately or shortly before termination of the exhaust stroke, the second valve means is controlled to open the inlet port for air to be admitted through the secondary chamber to the contracting combustion chamber and flow therethrough by way of the secondary chamber to exhaust. This preferred feature has the advantage that it permits efficient purging of exhaust gases from the combustion chamber prior to the piston attaining its inner dead centre and reversing to expand the combustion chamber in its inlet stroke.

Usually the air inlet will communicate with an air pressure source such as a compressor or supercharger for optimum efficiency although it will be appreciated that for certain vehicle engines adequate air flow may be achieved by movement of the vehicle. Usually the secondary chamber and main port will be located adjacent to the combustion chamber in axial alignment with the piston cylinder although it will be appreciated that the secondary chamber and the main port in the combustion chamber can be offset on the piston cylinder as convenient for engine design.

Preferably at least one, and desirably both, of the second valve means and third valve means comprises a valve component having a through port and which is rotatably mounted in a valve seating whereby rotary movement of the valve component opens and closes communication, by way of the through port, from its associated passage to the secondary chamber. The valve component is preferably substantially cylindrical (for convenience of manufacture and installation) and is mounted for rotation about its longitudinal axis in a substantially complementary cylindrical valve seating while the through port is in the form of a flow passage extending substantially diametrically through the cylindrical valve component.A further preference is that the aforementioned valve component is controlled for rotary reciprocation in its valve seating so that its through port is reciprocated arcuately in opening and closing communication between its associated passage and the secondary chamber. Desirably an outer end of the through port is in constant communication with its associated passage while an inner end of the through port adjacent to the secondary chamber progressively opens or closes communication with the secondary chamber during rotary reciprocation of the valve component. This latter arrangement permits rapid and efficient opening and closing movement to be achieved.

The first valve means, especially when in the form of a linearly displaceable trumpet valve, may be controlled for its opening and closing movements by means well known in the art of internal combustion engine valves which usually have the valve displaceable against a spring loading under control of a rotating cam shaft. The second and third valve means may be similarly controlled from a rotating cam shaft; for example where valve meanshas a valve component mounted for rotary reciprocation as above described and preferred, the valve component may be spring loaded against arcuate displacement in one sense of direction and which arcuate displacement is determined by a rotating cam shaft. It will be appreciated that the opening and closing control of the respective valve means may be achieved by other means known in the art, such as electronically or by desmodromic control.It will also be appreciated that the timing for open and closing of the respective valves and the synchronisation of this with the reciprocation of the piston, admission of combustion fuel/fluid to the combustion chamber and firing of that fluid in conventional manner will be well known to those skilled in the art of internal combustion engine design.

DRAWINGS One embodiment of a four-stroke internal combustion engine constructed in accordance with the present invention will now be described, by way of example only, with reference to the accompanying illustrative drawings, in which:- Figure 1 is a section through part of the engine showing a piston in its cylinder and associated engine valves disposed for the piston to move in its inlet stroke; Figures 2 to 6 are similar sections to that of Figure 1 and show the disposition of the engine valves for the piston to move sequentially through successive compression, power and exhaust strokes following the inlet stroke of Figure 1, and Figure 7 is an exploded view diagrammatically illustrating a control mechanism for the engine valves.

DETAILED DESCRIPTION OF DRAWINGS The part of the internal combustion engine, which may be for petroleum spirit (gasoline) or diesel oil fuel, as shown in Figures 1 to 6 will undoubtedly be familiar to those conversant with four-stroke engines and conventional engine components necessary for running the engine to provide an output drive to a crank shaft have not been shown and, in general, will not be discussed as such a discussion is considered superfluous to the understanding of the present invention.

The engine has a cylinder block 1 having a cylinder 2 within which is axially slidable a piston 3. Mounted on the block 1 and sealed thereto through a gasket 4 is a cylinder head 5. A cavity 6 in the head 5 coincides with the cylinder 2. A combustion chamber 7 is formed between the cavity 6, a crown face 8 of the piston 3 and any axial part length of the cylinder 2 adjacent to the cavity 6 and which is exposed from the piston crown 8. A rod 9 is connected by a gudgeon pin 10 to a skirt 3A of the piston to inter-connect the piston with a crank shaft (not shown) to which rotary drive is imparted in conventional manner during reciprocating axial displacement of the piston in its cylinder.

It will be appreciated that the engine will usually have a plurality of pistons which are driven in respective cylinders and appropriately synchronised to impart drive to the crank shaft in a manner well known in the art.

A circular port 11 in the wall of the cavity 6 and coaxial with the cylinder 2 provides communication between the combustion chamber 7 and a relatively smaller secondary chamber 12 in the cylinder head 5. The port 11 has an annular valve seating 11A and is opened or closed by a head 13 of a trumpet valve member 14 which head 13 is axially displaceable in the combustion chamber 7 to seal against the valve seating llA. A stem 15 of the valve member 14 extends through a bush 16 in the head 5 co-axially with the cylinder 2 to be linearly and axially displaceable for opening and closing the port 11.

The secondary chamber 12 has an inlet port 17 which can be progressively opened or closed by a rotary inlet valve 18 to communication with an inlet passage 19 and therethrough with a source of air under pressure such as a super-charger or compressor (not shown). The secondary chamber also has an exhaust port 20 which can be progressively opened or closed by a rotary exhaust valve 21 to communication with an exhaust passage 22. The rotary valves 18 and 21 are similarly formed, each comprising a cylindrical valve body 23 which is mounted in a cylindrical and complementary seating 24 in the cylinder head 5 for rotation about its longitudinal axis. The valve body 23 has a passage or through port 25 which extends, generally, diametrically therethrough. The valve body 23 of each valve 18 and 21 is controlled (in a manner which will be hereinafter discussed) to exhibit rotary reciprocation about its longitudinal axis so that its through port 25 is reciprocated arcuately. From Figure 1 it will be seen that the through port 25 is tapered to converge as it approaches an inner end 25A adjacent the chamber 12 from an outer end 25B thereof. The aforementioned rotary reciprocation of the valve members 23 and the tapered configuration of the through ports 25 is arranged so that the outer ends 25B of the through ports and in constant communication with their respectively associated passages 19 and 22 while the inner end 25A of the through ports can open to communicate with the respectively associated inlet port 17 or exhaust port 20 or be closed by the cylindrical seatings 24 for the valve members.

The cylinder head 5 will include means (not shown) for injecting or otherwise introducing combustive fuel into the combustion chamber 7 for firing (typically by a spark plug in the case of a petroleum spirit engine) to power the piston in a manner which is well known in the art for fourstroke piston engines.

The sequence for operation of the piston and cylinder structure and its associated engine valves as above described will now be considered for a cycle of four successive strokes of the piston 3 which is axially displaceable in its cylinder between a top (or inner) dead centre TDC and bottom (or outer) dead centre BDC where the TDC corresponds to the combustion chamber 7 being at its minimum volume and the BDC corresponds to the combustion chamber being at its maximum volume.

In Figure 1 the piston 3 has passed through the TDC and commenced an inlet stroke to expand the combustion chamber 7. At the commencement of the inlet stroke the port 11 remains fully open (by the trumpet valve 13) from the prior exhaust stroke while inlet valve 18 is fully open for pressurised air in the passage 19 to communicate with the inlet port 17 and exhaust valve 21 is closing by rotary movement of its valve member 23 in the direction of arrow A (closing communication between the exhaust port 20 and the exhaust passage 22). Consequently the combustion chamber 7 is filling with clean air derived from the passage 19 and through the secondary chamber 12.

From Figure 1 the piston 3 moves through its BDC to reverse and commence a compression stroke as shown in Figure 2 at which time the trumpet valve 13 has displaced against its valve seating llA to close the port 11 and seal the combustion chamber. The valve member 23 of the inlet valve 18 is rotating in the direction of arrow B to partially close the inlet port 17 to communication with air pressure in the passage 19 while the valve member 23 of the exhaust valve 21 has reversed and is rotating in the direction of arrow C to progressively open communication between the exhaust port 20 and the exhaust passage 22.

As the rotary valve 21 opens, air flow is permitted from the passage 19 and successively through the valve 18, secondary chamber 12 and valve 21 to exhaust so that the stream of air over the trumpet valve 13 in the secondary chamber 12 provides a cooling effect on that valve and also on the valves 18 and 21. During the compression stroke fuel is injected directly into the compression chamber 7.

Following the end of the compression stroke, the piston 3 passes through its top dead centre and commences a power stroke as shown in Figure 3. The compressed air/fuel mixture in the combustion chamber 7 is fired, usually immediately before the piston reaches TDC, to drive the piston for the power stroke. As shown in Figure 3 the rotary exhaust valve 21 is fully open while the rotary inlet valve 18 is partially open to maintain the air flow through the secondary chamber 12 over the valve 13.

When the piston 3 approaches the end of its power stroke as shown in Figure 4, the rotary inlet valve 18 recommences its rotation as indicated by the arrow D to progressively close the inner end 25A of its through port and thereby progressively close air flow from the passage 19 to the secondary chamber 12 while exhaust valve 21 is maintained fully open and the trumpet valve 13 is closed.

Following the power stroke and reversal of the piston through its bottom dead centre BDC, the piston commences an exhaust stroke shown in Figure 5 and the trumpet valve 13 is displaced to open port 11 while the rotary inlet valve 18 is fully closed and the rotary exhaust valve 21 is fully open. Consequently, as the combustion chamber 7 contracts, the combustion or exhaust gases are displaced from that chamber through the port 11, secondary chamber 12 and exhaust valve 21 to the exhaust passage 22.

Towards the end of the exhaust stroke and immediately or shortly before the piston reaches its top dead centre TDC and reverses and while the trumpet valve 13 is open, the valve member 23 of the rotary inlet valve 18 commences movement as indicated by arrow D in Figure 6 to progressively open the inlet port 17 to communication with pressurised air in the passage 19 while the exhaust port 20 maintains communication through its associated exhaust valve 21 with the exhaust passage 22 (although the valve member 23 of the exhaust valve 21 has commenced movement in a direction indicated by arrow E for its inner end 25A to progressively close communication between the exhaust port 20 and the exhaust passage 22).Consequently as the piston approaches the end of its exhaust stroke, air under pressure from the passage 19 is admitted to the secondary chamber 12 and by way of the open port 11 to the contracting combustion chamber 7 from which it can pass through the exhaust valve 21 to the exhaust passage 22.

This stream of air through the combustion chamber 7 scavenges from that chamber exhaust gas which may otherwise remain at the end of the exhaust stroke. Following the exhaust stroke and reversal of the piston at its top dead centre, a further inlet stroke commences as above described with reference to Figure 1 for a successive four-stroke cycle.

Although the drawings are diagrammatic, it will be appreciated that the single trumpet valve 13 in the wall of the combustion chamber 7 will permit the port 11 to have a relatively large diameter for efficient and rapid gas exchange therethrough. Also as both of the rotary valves 18 and 21 are remote from the combustion chamber 7, the sealing of the valve members 23 in their seatings 24 is less critical than, for example, the sealing between the trumpet valve 13 and its seating llA. There is also the advantage that following the successive exhaust and compression strokes and with the inlet and exhaust valves 18 and 21 open as shown in Figure 3, the stream of clean air from the passage 19 directly through the secondary chamber 12 to the exhaust passage will serve to dilute the previously emitted exhaust gases to reduce the emission of the engine. Furthermore, the scavenging of the exhaust gases from the contracting combustion chamber as discussed with reference to Figure 6 permits substantially uncontaminated fuel and air mixtures to be introduced into the expanding combustion chamber in its inlet stroke; it is believed that such mixtures will burn cleaner than if contaminated with exhaust gas with consequential fuel efficiency and lower emissions. It is also believed that the pressurised induction of air will permit increased engine torque thus allowing for higher gearing in a vehicle which may be driven by the engine, improved economy and reduced drive-by noise.

The reciprocating rotary valves 18 and 21 may open and close rapidly to provide accurate control and synchronisation of the gas flow through those valves and it will be appreciated that the through passages 25 and their inner and outer end ports will be formed to provide the required gas flow characteristics.

The control of the trumpet valve member 14 and reciprocating rotary valves 18 and 21 and the synchronisation in the operation of those valves can be achieved by various control systems which may be mechanical, electrical or actuated by fluid pressure. An example of a simple control system for the engine valves is shown in Figure 7 comprising a rotating cam shaft 30 having three cam shaped lobes 30A, 30B and 30C associated with the piston and cylinder so that during their rotation the lobes respectively control operation of the trumpet valve member 14 and the reciprocating rotary valves 18 and 21.

Conveniently the cam shaft 30 is located on the centre line of the valve stem 15 of the trumpet valve and the trumpet valve is controlled in conventional manner during rotation of the lobe 30A with the cam shaft whereby a bucket type cam follower with shim adjustment retained by a spring retainer provides the appropriate and required displacement to the valve member 14 against spring loading of that valve member. The control for the rotary valves 18 and 21 is effected in a similar manner and, for convenience, the rotary valve member 23 for the inlet valve 18 only has been shown in Figure 7 for control by the cam lobe 30B (it being realised that control of the valve member 23 for the rotary exhaust valve 21 will be achieved, with appropriate sequencing, similarly from the cam lobe 30C).In Figure 7 the cylindrical valve member 23 is provided with a generally tangentially or radially extending finger part 31 which is spring loaded through a compression coil spring 32 relative to the head 5 to be biased in its rotary motion in the direction of arrow F of Figure 7. The valve member 23 has a seating 32 within which is located one end 33 of a push rod 34. The opposite end 35 of the push rod is received within a cam follower 36 which reacts through a shim 37 on the cam shaft lobe 30B. From Figure 7 it will be seen that with the rod 34 engaged in its respective seatings and the cam follower 36 acting against the lobe 30B, the arcuate movement or rotation of the valve member 23 will be determined by the profile of the rotating cam lobe 30B against, or under, the spring loading 32. By adjustment in the thickness of the shim 37, variations in the rotary movement of the valve member can be provided and thereby variations in the timing at which the through port 25 of that member opens or closes the inlet port 17.

Although the crown 8 of the piston 3 is shown as a flat face, it will be appreciated that the crown 8 may be recessed as indicated at 100 in Figure 1 in defining part of the combustion chamber 7. With such a recess 100, the trumpet valve head 13 may be arranged to be received in that recess as the piston 3 is at or towards TDC on its exhaust and inlet strokes.

Claims (13)

1. An internal combustion engine having a piston axially reciprocable in a piston cylinder; a combustion chamber formed between the piston and its cylinder and which is expanded and contracted during reciprocation of the piston; means for admitting combustive fluid to the combustion chamber for firing to reciprocate the piston sequentially through successive inlet, compression, power and exhaust strokes; a main port for providing communication between the combustion chamber and a secondary chamber; first valve means controlling said main port for opening and closing said communication therethrough; an inlet port for providing communication between an air inlet passage and the secondary chamber; second valve means controlling said inlet port for opening and closing said communication therethrough; an exhaust port for providing communication between the secondary chamber and an exhaust passage; third valve means controlling said exhaust port for opening and closing said communication therethrough, and control means synchronising opening and closing of said first, second and third valve means whereby in said inlet stroke during expansion of the combustion chamber the inlet and main ports are open to admit air to the combustion chamber and the exhaust port is closed; in said compression stroke during contraction of the combustion chamber and in said power stroke during expansion of the combustion chamber the inlet and exhaust ports are open for air flow through the secondary chamber from the air inlet to exhaust and the main port is closed, and in said exhaust stroke during contracting of the combustion chamber the inlet port is closed and the main and exhaust ports are open for combustion gases from firing of the combustive fluid to flow from the combustion chamber by way of the secondary chamber to exhaust.

2. An engine as claimed in claim 1 in which during said exhaust stroke and prior to the termination of that stroke, said second valve means is controlled to open the inlet port for air to be admitted to the contracting combustion chamber and flow therethrough by way of the secondary chamber to exhaust.

3. An engine as claimed in either claim 1 or claim 2 in which the secondary chamber is located substantially in axial alignment with the piston cylinder.

4. An engine as claimed in any one of the preceding claims in which the main port consists of an aperture which communicates between the combustion chamber and the secondary chamber and the first valve means comprises a single displaceable valve member which engages in a valve seating in the combustion chamber to close the aperture and is displaceable from said seating to open the aperture.

5. An engine as claimed in claim 4 when appendant to claim 3 in which said aperture is substantially concentric with the piston cylinder.

6. An engine as claimed in either claim 4 or claim 5 in which the valve member is a linearly displaceable trumpet valve.

7. An engine as claimed in any one of the preceding claims in which at least one of the second valve means and third valve means comprises a valve component having a through port and which is rotatably mounted in a valve seating whereby rotary movement of the valve component opens and closes communication by way of its through port between its associated passage and the second chamber.

8. An engine as claimed in claim 7 in which the valve component is substantially cylindrical and is mounted for rotation about its axis in a substantially complementary cylindrical valve seating and said through port comprises a flow passage extending substantially diametrically through the valve component.

9. An engine as claimed in either claim 7 or claim 8 in which the valve component is controlled for rotary reciprocation in its valve seating for its through port to be reciprocated arcuately in opening and closing said communication.

10. An engine as claimed in claim 9 in which the through port has an outer end which is in constant communication with its associated passage and an inner end adjacent to the secondary chamber which progressively opens or closes to communication with the secondary chamber during said rotary reciprocation.

11. An engine as claimed in either claim 9 or claim 10 in which the valve component is spring loaded to be biased in one sense of its rotary displacement and control means is provided for rotating the valve component in the opposite sense of its rotary displacement against said spring biasing.

12. An engine as claimed in claim 11 in which said control means comprises a lobe of a rotating cam shaft.

13. An internal combustion engine substantially as herein described with reference to the accompanying illustrative drawings.