GB2117047A - Intake and exhaust flow control valves in two-stroke engines - Google Patents

Abstract

The gas flow to the engine crank chamber or cylinder inlet ports and/or from the cylinder exhaust ports is controlled by blade valve members 1 rotating in opposite directions which cooperate to close or open the flow paths including the ports. Projections 36 on one member 1 may engage in recesses 38 in the other or one of the members may have edge grooves (41, Figs 9 and 10) to effect sealing. <IMAGE>

Description

SPECIFICATION Two-stroke internal combustion engine This invention relates to two-stroke internal combustion engines.

In high performance two-stroke internal combustion engines of the crankcase scavenged kind for use on motor cycles it is now common to provide some form of disc-type inlet valve for controlling opening and closing of the or each inlet port. Such inlet valves enable power in excess of 220 BHP per litre to be obtained from a twostroke engine.Although the timing varies somewhat from one design of engine to another, when power is required at about 11,000 RPM the disc-type inlet valve will generally commence to open about 20 to 25 degrees before the transfer port closes so that for a time all three ports (inlet, transfer and exhaust) will be at least partially open and the low pressure wave generated in the exhaust system will act to draw fuel/air mixture through the carburettor before the upward movement of the piston has begun to have much effect, thus wasting fuel. To take full advantage of induction ramming, disc-type inlet valves of the kind aforesaid are generally timed to close later, e.g., about 70 degrees after top dead centre, but could be earlier for slower speeds with a consequent gain in fuel economy.

Engines fitted with disc-type inlet valves have a number of disadvantages. For a start the fuel/air/ lubricant mixture entering through the inlet port tends to miss the big-end bearing completely and to be obstructed by the broad shank of the connecting rod, which can result in incompiete lubrication particularly of the big-end bearing.

Another disadvantage is that a disc-type inlet valve requires to be mounted on a free end of the mainshaft and the cylinders in a multi-cylinder engine must be arranged with this in view. Thus in a four cylinder engine four crank assemblies will normally be required which are geared together and each of which carries a disc-type inlet valve at a free end thereof. A further disadvantage is that the use of disc-type inlet valves increases the width of the engine, particularly of twin cylinder engines, thus adversely affecting the aerodynamics of a motor cycle fitted with such an engine. Moreover, in order to keep the width of the engine to a minimum a very short air intake pipe has to be used which subjects the carburettor to violent pulse flow, which is undesirable.To increase the length of the air intake tract would mean introducing bends therein and this is detrimental to good gas flow. Further disadvantages are that owing to the position of the disc-type valve on the wall of the crankcase it is difficult to direct the fuel/air/lubricant mixture entering the engine in the best direction and it is difficult to obtain a high primary compression ratio. Finally, disc-type inlet valves are not suitable for use on two-stroke internal combustion engines of the piston port kind.

The present invention has as its object to provide a two-stroke internal combustion engine having improved inlet and/or exhaust valve means.

The present invention provides a two-stroke internal combustion engine having at least one inlet and/or exhaust port and valve means for opening and closing the or each said port, the valve means comprising a pair of flat blade-like members mounted for rotation in opposite directions about their longitudinal axes between a position in which they cooperate to close the port and a position in which the port is open, and drive means for rotating said blade-like members in timed relation to the operation of the engine.

Preferably said blade-like members are mounted for continuous rotation in opposite directions and at the same speed when the engine is in operation so that they close the said port once and open the port once during each 1800 of rotation, said drive means being adapted to rotate the blade-like members at half the speed of the engine.

Each of said blade-like members preferably has a cylindrical bearing portion at each end thereof, and preferably integral therewith, whereby it is journalled in a valve housing, e.g., provided either by the crankcase or the cylinder block of the engine depending upon whether valve is an inlet or an exhaust valve and whether the engine is of the crankcase scavenged or cylinder port kind.

Where the engine is a multi-cylinder engine having aligned cylinders, e.g., a 1800 twin cylinder engine, then a single pair of rotatable member may serve two or more cylinders. In such a case each rotatable member may comprise a plurality of blade portions separated by an intermediate cylindrical bearing portion or portions.

Advantageously the said blade-like members are mounted so that the longitudinal axes thereof extend substantially parallel to the crankshaft of the engine and said drive means is such as to drive the blade-like members from the crankshaft of the engine.

The invention will be more particularly described with reference to the accompanying diagrammatic drawings, in which: Figure 1 is a fragmentary front elevation, partly in section, of inlet valve means for use in a twostroke internal combustion engine according to the present invention, Figure 2 is a fragmentary cross-section of the valve means shown in Figure 1, Figure 3 is a perspective view, partly in section, of the cylinder block, crankcase and inlet valve means of a twin-cylinder two-stroke internal combustion engine according to the present invention, Figure 4 is a sectional elevation through one cylinder of a two-stroke internal combustion engine according to the present invention having both inlet and exhaust valve means, Figure 5 is a view similar to Figure 4 and showing a modification of the engine shown in Figure 4, Figure 6 is an end view of the engine of Figure 4 or Figure 5 and illustrates the drive to the inlet and exhaust valve means, Figures 7 and 8 are end and perspective views respectively of a pair of modified valve members for use in an engine according to the present invention, and Figures 9 and 10 are end and perspective views respectively of another pair of modified valve members for use in an engine according to the present invention.

Referring to Figures 1 and 2 it will be seen that the valve means illustrated therein comprises a pair of rotary valve members V each having a flat blade-like portion 1 and a cylindrical bearing portion 2 at opposite ends thereof whereby they are jounalled for rotation in opposite directions about their longitudinal axes in a valve housing provided by a crankcase 3 of a two-stroke engine of the crankcase scavenged kind so as to control the opening and closing of an inlet port 4 in the crankcase 3. The members V extend with their longitudinal axes substantially parallel to the crankcase (not shown) of the engine and are so arranged that when in the position shown in Figures 1 and 2 the inlet port 4 will be open and when rotated through 900 will cooperate to close the inlet port 4.

The members V each carry a stub shaft 5 supported in a bearing 6 in a wall 7 of the crankcase 3. Gear wheels 8 fixedly mounted on the stub shafts 5 are in meshing engagement with one another so that when one of the members V is rotated in one direction as indicated by the arrow A in Figure 2 the other member V will be caused to rotate in the opposite direction as indicated by the arrow B in Figure 2. One of the stub shafts 5 extends through the wall 7 of the crankcase 3 as shown at 5a and has mounted on the end thereof a toothed sprocket 9 whereby it may be connected for drive to the crankcase of the engine by means of a flexible endless drive member such as a toothed belt (not shown).Since the members V will open and close the inlet port 4 twice during each 3600 of rotation the belt and sprocket drive from the crankshaft will be such as to drive the members V at half the speed of the engine.

Referring now to Figure 3 of the drawings it will be seen that the engine illustrated therein is a 1 800 twin-cylinder two-stroke engine of the crankcase scavenged kind having a cylinder block 10 providing two aligned cylinders 11 and a crankcase 12 having an inlet port 13 associated with each of the cylinders 11. For opening and closing the inlet ports 1 3 a pair of rotary valve members 14 are provided each of which comprises two flat blade-like portions 1 5 and 1 6 separated by an intermediate cylindrical portion 17. The blade-like portions 1 5, 1 6 of each member 14 lie in planes at right-angles to one another whereby when the portions 1 5 of the members 14 are cooperating to close the inlet port 13 of one cylinder the inlet port 1 3 of the other cylinder will be open, and vice versa.

As in the embodiment of Figures 1 and 2, the members 14 extend with their longitudinal axes substantially parallel to the crankshaft (not shown) of the engine and are rotatable in opposite directions at half the engine speed by suitable drive means from the crankshaft of the engine.

The engine illustrated in Figure 4 comprises a cylinder block 1 8 and a cylinder head 19 defining a cylinder 20 and a crankcase 21. The crankcase 21 has an inlet port 22 therein which communicates with the cylinder 20 whilst the cylinder block 18 has an exhaust port 23 therein which also communicates with the cylinder 20.

Inlet valve means 24 is provided for opening and closing the inlet port 22 whilst exhaust valve means 25 is provided for opening and closing the exhaust port 23. The valve means 24 and 25 are each as illustrated in Figures 1 and 2 except that the exhaust valve means 25 is mounted in bearings (not shown) in the cylinder block and not in the crankcase. As shown in Figure 4 the flat blade-like members 1 of the valve means 24 and 25 are angularly rotated through 900 with respect to one another so that when the inlet valve means 24 is fully closed (as shown) the exhaust valve means 25 will be fully open and vice versa.

The engine illustrated in Figure 5 is substantially the same as that illustrated in Figure 4 except that a transfer passage 26 is formed in the cylinder block which communicates the inlet port 22 with a transfer port 27.

Referring now to Figure 6, in which like reference numerals are used as have been used in Figures 1, 2, 4 and 5, it will be seen that each of the valve means 24 and 25 has mounted on a slub shaft 5a thereof a toothed pulley 9 which is driven by means of a toothed endless belt 28 from a double toothed pulley 29 mounted on a projecting end portion 30 of the crankshaft of the engine. It will also be seen from Figure 6 that an air intake 31 is provided which communicates with the inlet port 22 and that an exhaust pipe 32 is provided which communicates with the exhaust port 23.

Although in the illustrated embodiments a belt and pulley drive is provided for transmitting drive from the crankshaft of the engine to the rotary valve members it will be understood that other forms of drive can be provided if desired, such as, for example, a rotary cable drive or a shaft drive.

Figures 7 and 8 illustrate a modification wherein the rotary valve member flat blade-like portion 1 of one rotary valve member 35 has diametrically extending projections 36 thereon whilst the flat blade-like portion 1 of the other rotary valve member 37 has diametrically opposed recesses 38 therein for receiving the projection 36 when the rotary valve members 35, 37 are in closed position as shown in Figure 7. The projections 36 may be formed integrally with the rotary valve member 35 or may be formed separately, e.g., from a suitable metal, rubber or plastics material, and bonded or otherwise secured to the rotary valve member 35.

In the embodiment shown in Figures 9 and 10 the flat blade-like portion 1 of one of the rotary valve members 40 has grooves 41 in each of the end surfaces 42 thereof which provide a labyrinth seal with the plain end surfaces 43 of the flat blade-like portion 1 of the other rotary valve member 44 when the rotary valve members 40, 44 are in closed position as shown in Figure 9.

In all of the embodiments described above the rotary valve members are arranged with clearance between them, even when closed, and with clearance between the rotary valve members and the valve housing in which they are mounted.

Generally these clearances should not exceed 0.508 mm (0.020 inch) except in the case of the embodiments of Figures 7, 8, 9 and 10 where the clearance between the rotary valve members can be slightly more. If desired the stub shaft 5 of at least one of the rotary valve members can be used to drive a fuel injector. This enables a very compact arrangement of inlet valve and fuel injector to be obtained.

Whilst the engines described in the illustrated emodiments are of the crankcase scavenged kind it will be readily appreciated to those skilled in the art that the inlet valve means described is equally applicable to two-stroke engines of the piston port kind. The port timings in two-stroke engines of the piston port kind are symmetric (as opposed to asymmetric for the crankcase scavenged kind) and accordingly such engines are prone to blow back through the inlet tract at low engine speeds with consequent loss of charge and low speed power.

A piston port engine according to the present invention avoids these losses and provides an increase in power at low speeds and better fuel economy.

Because the blade-like valve members of the engines of the present invention rotate in opposite directions they provide rapid opening and closing of the or each inlet and/or exhaust port. The engines of the present invention when fitted with the described inlet valve also avoid or mitigate the many disadvantages of engines fitted with disctype inlet valves.

Claims (14)

1. A two-stroke internal combustion engine having at least one inlet and/or exhaust port and valve means for opening and closing the or each said port, the valve means comprising a pair of flat blade-like members mounted for rotation in opposite directions about their longitudinal axes between a position in which they cooperate to close the port and a position in which the port is open, the drive means for rotating said blade-like members in timed relation to the operation of the engine.

2. A two-stroke internal combustion engine according to claim 1, wherein said blade-like members are mounted for continuous rotation in opposite directions and at the same speed when the engine is in operation so that they close the port once and open the port once during each 1 800 of rotation, said drive means being adapted to rotate the blade-like members at half the speed of the engine.

3. A two-stroke internal combustion engine according to claim 1 or 2, wherein each of said blade-like members has a cylindrical bearing portion at each end thereof whereby it is journalled in a valve housing.

4. A two-stroke internal combustion engine according to claim 3, wherein said valve housing is provided by the crankcase or cylinder block of the engine

5. A two-stroke internal combustion engine according to any one of the preceding claims, wherein the engine is a multi-cylinder engine having aligned cylinders and wherein a single pair of flat blade-like members serves two or more cylinders.

6. A two-stroke internal combustion engine according to claim 5, wherein said pair of flat blade-like members each comprises a plurality of flat biade-like portions separated by an intermediate cylindrical bearing portion or portions.

7. A two-stroke internal combustion engine according to any one of the preceding claims, wherein said blade-like members are mounted so that the longitudinal axes thereof extend substantially parallel to the crankshaft of the engine and said drive means is such as to drive the blade-like members from the crankshaft of the engine.

8. A two-stroke internal combustion engine according to claim 7, wherein said drive means is adapted to transmit drive from the crankshaft to one of said blade-like members and wherein drive is transmitted from said one blade-like member to the other blade-like member.

9. A two-stroke internal combustion engine according to claim 8, wherein said blade-like members each have a stub shaft at one end thereof on which is mounted a gear wheel, said gear wheels being in meshing engagement to transmit drive from said one blade-like member to the other blade-like member.

10. A two-stroke internal combustion engine according to claim 7, 8 or 9, wherein said drive means comprises sprockets mounted on the crankshaft and one of said blade-like members and a flexible endless drive member extending around said sprockets.

11. A two-stroke internal combustion engine according to any one of the preceding claims, wherein one of said blade-like members has a longitudinally extending diametrical projection on each of the end surfaces thereof and wherein the other blade-like member has a longitudinally extending recess in each of the end surfaces thereof for receiving a said projection on said one member when the blade-like members are in closed position.

12. A two-stroke internal combustion engine according to any one of claims 1 to 10, wherein one of the blade-like members has longitudinally extending grooves in each of the end surfaces thereof which provide a labyrinth seal with the plain end surfaces of the other blade-like member when the blade-like members are in closed position.

1 3. A two-stroke internal combustion engine according to any one of the preceding claims, wherein the valve means is inlet valve means and wherein a fuel injector is associated with the inlet valve means and is driven thereby.

14. A two-stroke internal combustion engine substantially as herein described with reference to Figures 1 and 2, Figure 3, Figure 4, Figure 5, Figure 6, Figures 7 and 8 or Figures 9 and 10 of the accompanying drawings.