GB2577398A

GB2577398A - A Rotary valve internal combustion engine

Info

Publication number: GB2577398A
Application number: GB1912714.1A
Authority: GB
Inventors: Lawes Keith; Mason Brian
Original assignee: RCV Engines Ltd; Kaaz Corp
Current assignee: RCV Engines Ltd; Kaaz Corp
Priority date: 2018-09-06
Filing date: 2019-09-04
Publication date: 2020-03-25
Also published as: GB201912714D0

Abstract

A rotary valve internal combustion engine comprising a combustion chamber defined in part by the piston and the combustion end of the cylinder, a valve housing (Fig. 1, 8) fixed at an outer portion of the combustion end of the cylinder and defining a bore, and a rotary valve 5 rotatable about an axis (Fig. 1 5a) in the bore, the valve having in a wall part thereof a port giving fluid communication to and from the combustion chamber via inlet 27 and exhaust 28 ports in the valve housing. The engine has a carburettor 29 and an exhaust muffler 30 mounted on opposite sides of the engine, when the engine is at TDC, the valve port is angled towards the carburettor, and the centrelines of the inlet and exhaust ports are offset at an angle allowing for the muffler and carburettor to be parallel to the crankshaft centreline 31.

Description

A rotary valve internal combustion engine The present invention relates to a rotary valve internal combustion engine, particularly but not exclusively, for a manually held machine such as a horticultural grass trimmer or hedge trimmer, in which the control of the intake and exhaust gases of combustion is achieved by means of a rotary valve.

A rotary valve internal combustion engine comprising: a piston connected to a crankshaft and that reciprocates in a cylinder, the cylinder having a combustion end, a combustion chamber being defined in part by the piston and the combustion end of the cylinder, a valve housing fixed at an outer portion of the combustion end of the cylinder and defining a bore and a rotary valve rotatable about a rotary valve axis in the bore in the valve housing, the rotary valve having a hollow valve body having an interior volume forming a part of the combustion chamber, wherein the interior volume of the hollow valve body is subjected to combustion gases throughout the combustion process, and further having in a wall part thereof a port giving, during rotation of the valve, fluid communication successively to and from the combustion chamber via inlet and exhaust ports in the valve housing.

The present invention seeks to provide such an engine suitable for use with a horticultural machine. designed to be held and operated manually by an operator. The term horticultural machine is intended to include hand-held machines for use in horticulture, gardens and forestry for such purposes as grass trimmers, hedge trimmers, brush cutters, clearing saws, shredders, blowers vacuum collectors, mist blowers, and chainsaws.

According to the present invention there is provided a rotary valve internal combustion engine comprising: a piston connected to a crankshaft and that reciprocates in a cylinder, the cylinder having a combustion end, a combustion chamber being defined in part by the piston and the combustion end of the cylinder, a valve housing fixed at an outer portion of the combustion end of the cylinder and defining a bore and a rotary valve rotatable about a rotary valve axis in the bore in the valve housing, the rotary valve having a hollow valve body having an interior volume forming a part of the combustion chamber, wherein the interior volume of the hollow valve body is subjected to combustion gases throughout the combustion process, and further having in a wall part thereof a port giving, during rotation of the valve, fluid communication successively to and from the combustion chamber via inlet and exhaust ports in the valve housing, the engine having a carburettor for controlling the air/fuel mix into the engine and an exhaust muffler for the exhaust gases, wherein the port layout is arranged to position the exhaust muffler and carburettor on opposite sides of the engine, the port angles being arranged such that the main body of the carburettor and main body of the muffler are substantially parallel to the centreline of the engine, wherein when the engine is at top dead centre, the valve port is angled a predetermined number of degrees from the crankshaft axis said angular offset reducing the radial offset of the inlet port that is required to achieve a mounting flange for the carburettor that is substantially parallel to the centreline of the engine, the centreline of the inlet port is offset towards the operator a predetermined number of degrees from a radial line from the cylinder axis, said angular offset allowing the mounting flange for the carburettor to be substantially parallel to the centreline of the engine, and the centreline of the exhaust port is offset a predetermined number of degrees from a radial line from the cylinder axis, said angular offset allowing the main body of the muffler to be substantially parallel to the centreline of the engine using an angled mounting flange.

Preferred embodiments of the present invention will now be described by way of example with reference to the accompanying drawings, in which:-Figure 1 shows a cross-sectional view of a single cylinder air cooled spark ignition rotary valve internal combustion engine, and Figure 2 shows a part-sectional plan view of an embodiment of the engine for use with a manually held and operated horticultural machine such as a strimmer or hedge trimmer, and Figure 3 shows a side view of part of the engine shown in Figure 2.

Figure 4 there is shown a sectional view of part of the engine of Figure 1 illustrating the air/fuel inlet tract Referring now to Figure 1, there is shown a single cylinder air cooled engine. The engine has a cylinder housing containing the cylinder 2. A piston 1 is connected in the conventional manner to a crankshaft 3 mounted for rotation in a crankcase 14 for reciprocation in the cylinder 2. The upper part of the cylinder 2 is closed by a combustion chamber 4 in a combustion chamber housing. The combustion chamber housing has an inlet port 27 for the flow of inlet air/fuel mix into the combustion chamber and an exhaust port 28 for venting the exhaust gas out of the combustion chamber 4, the gas flows being controlled by a rotary valve 5. In this embodiment, the valve 5 is rotatable in a valve housing 8 in the combustion chamber housing about an axis 5a which is co-axial with the axis of the cylinder 2. In other embodiments, the axis of rotation of the valve body is offset from the axis 5a of the cylinder 2.

At its end remote from the combustion chamber 4, the rotary valve 5 has a concentric drive shaft 6 carrying a single race ball bearing 7 which rotatably supports the valve 5 in the valve housing 8. The valve driveshaft 6 is secured to a coaxial driven gear 9 which meshes with a drive gear 10 of a drive arrangement 11 through which the driven gear 9 and hence the rotary valve 5 is connected to the crankshaft 3. The drive arrangement 11 includes a drive shaft 12 which is located in a channel or tube 17 in the cylinder housing and mounted for rotation in an upper bearing 18 adjacent the drive gear 10 and a lower bearing 13 adjacent the crankshaft 3. The driveshaft 11 carries a bevel gear 15 which meshes with a corresponding bevel gear 16 secured on the crankshaft for rotation with the crankshaft 3. Thus, the rotation of the crankshaft 3 and hence the piston movement is coordinated with the rotation of the rotary valve 5 so that the engine operates on the conventional four stroke cycle. To achieve this, the diameter of the driven gear 9 is twice that of the drive gear 10 so that the rotary valve 5 rotates at half engine speed. The rotary valve 5 comprises a generally cylindrical rotary valve body 5 rotatable about a rotary valve axis 5a with a close sliding fit in the bore in the valve housing 8, the rotary valve 5 having a hollow valve body having an interior volume 19 forming a part of the combustion chamber. The valve has a generally cylindrical body part comprising the valve body 19 itself which is slightly larger in diameter than the shaft 6, which forms a shoulder 14 against which the inner race of the ball bearing 7 is located. The valve body 19 extends into the combustion chamber and has in its interior a volume 20 which forms part of the combustion chamber 4 and which is subject to combustion gases at all stages of the combustion process.

The shaft 6 part of the rotary valve 5 is only slightly smaller in diameter than the valve body 19 to provide the shoulder 14. The shaft is solid to provide a good path for conducting heat from the valve body 19 to the exterior.

The rotary valve body 19 has a port 21 which, during rotation of the valve, enables fluid communication successively to and from the interior volume of the valve and hence the combustion chamber via the inlet and exhaust ports in the valve housing. In this embodiment the port 21 is in the form of a recess formed in the lower peripheral edge 22 of the wall 23 of the valve body adjacent to the combustion chamber 4 the recess extending upwardly from this lower edge of the wall of the valve to form the port 21 in the side of the valve Ignition is provided by a spark plug secured into a plug bore 25 formed in the valve housing 8 and extending into the valve bore.

Referring now to Figure 2, there is shown a plan view of an engine intended for a horticultural machine such as a grass trimmer or a hedge trimmer which is manually held and operated by an operator where the engine is positioned to one side and/or behind the operator. In such machines, it is a requirement that the exhaust and exhaust muffler is located away from the operator and a carburettor for controlling the air/fuel mix through the inlet is located towards the operator. This is due to the heat of the exhaust and fact that the operator may be required to adjust the carburettor. A carburettor with airbox assembly 29 is attached to the inlet port 27, and an exhaust muffler 30 is connected to the exhaust port 28. Ideally, both the carburettor airbox assembly 29 and the exhaust muffler 30 should be substantially parallel to the centreline of the crankshaft. the inlet and exhaust ports should be straight rather than curved to enable diecasting of the cylinder 2. Straight ports and exhaust muffler/carburettor airbox positions simplify manufacture, neaten the appearance of the engine and make the engine easier to package within a typical horticultural machine. However, in order to provide the correct valve timing of the engine, which is determined by the position of the inlet and exhaust openings in the valve housing, this will require both the inlet ports and exhaust ports to be angled away from their ideal angle which is aligned with a radius running from the cylinder axis.

More-over as any restriction in flow in the inlet port due to a non-radial port angle will have a greater effect on engine power than the equivalent restriction in the exhaust port, the ports are angled such that the inlet port is closer to the ideal radial angle than the exhaust port.

In this embodiment, the top dead centre timing point is angled towards the inlet side from the centreline of the crankshaft by 10°, in other words when the piston is at top dead centre the centreline of the valve port is pointing 10 degrees towards the side of the engine nearest the operator. This enables the inlet port opening within the valve housing to be moved round 10 degrees towards the operator. This enables the inlet port 27 to be closer to the ideal radial angle than the exhaust port. The inlet port 27 is then angled a further 11° from the radial axis of the cylinder axis with the result that the mounting flange of the carburettor airbox assembly 29 is substantially parallel to the centreline of the engine.

The centreline of the exhaust port 28 is offset 15° from the radial axis. The exhaust muffler has an angled flange 33 which mates with the exhaust port 28 so as to allow the main body of the exhaust muffler to be aligned substantially with the centreline 31 of the engine.

The exhaust muffler 13 is having a two-part shell construction of the muffler and a flange to mate with the angled exhaust port. This has the advantage of avoiding the use of a separate tube or pipe between the exhaust port and the muffler body.

As shown in up Figure 2, the inlet side of the cylinder has a curved panel 34 which serves to guide cooling air around the rear of the cylinder to provide a cooling flow around the rear of the cylinder.

A closure plate 35 at the rear of the engine, shown in Figure 3, forms a lower face of the cooling air flow passage, which forces the cooling air to exit from the rear of cowl, rather than short circuiting down into the cooling air intake.

Referring now to Figure 4 there is shown a sectional view of part of the engine of Figure 1 illustrating the air/fuel inlet tract. Part of the outer casing 29 of the engine comprises an air box 30, also known as a plenum chamber, which is divided by a wall 33 into an unfiltered air volume into which ambient air enters through inlet passages 31, and a filtered air volume 32.

The dividing wall 33 contains a filter 34 through which air from the unfiltered side passes into the filtered air side volume 32. The inlet tract has a tuning pipe 35 secured to the carburettor. The tuning pipe 35 leads from the air inlet 36 of the carburettor 28 through a curved path passing through the unfiltered volume in the airbox, through the dividing wall and into the filtered air volume 32. In one form, the tuning pipe 35 passes through the filter itself. The inlet 37 to the tuning pipe 35 is located in the filtered volume 32 and is flared outwardly to improve the flow of air into the tuning pipe 35 and hence into the engine. The curved path maximises the length of the tuning pipe which increases the efficiency of the engine without causing a significant change to the overall size of the engine.

Although shown as a simple curve, it will be appreciated that the tuning pipe may have a more complex shape and may follow a serpentine path.

It is to be understood that the features of the various embodiments described herein may be combined with each other, unless specifically noted.

Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations may be substituted for the specific embodiments shown and described without departing from the scope of the present invention. This application is intended to cover any adaptions or variations of the specific embodiments discussed herein. Therefore, it is intended that this invention be limited only by the claims and the equivalents thereof.

Claims

CLAIMS1. A rotary valve internal combustion engine adapted for use in a hand-held machine, the engine comprising: a piston connected to a crankshaft and that reciprocates in a cylinder, the cylinder having a combustion end, a combustion chamber being defined in part by the piston and the combustion end of the cylinder, a valve housing fixed at an outer portion of the combustion end of the cylinder and defining a bore and a rotary valve rotatable about a rotary valve axis in the bore in the valve housing, the rotary valve having a hollow valve body having an interior volume forming a part of the combustion chamber, wherein the interior volume of the hollow valve body is subjected to combustion gases throughout the combustion process, and further having in a wall part thereof a port giving, during rotation of the valve, fluid communication successively to and from the combustion chamber via inlet and exhaust ports in the valve housing, the engine having a carburettor for controlling the air/fuel mix into the engine and an exhaust muffler for the exhaust gases, the port angles being arranged such that the main body of the carburettor and main body of the muffler are on opposite sides of the engine and substantially parallel to the centreline of the crankshaft wherein when the engine is at top dead centre, the valve port is angled a predetermined number of degrees towards the operator, said angular offset reducing the radial offset of the inlet port that is required to achieve a mounting flange for the carburettor that is substantially parallel to the centreline of the engine, the centreline of the inlet port is offset towards the operator a predetermined number of degrees from a radial line from the cylinder axis, said angular offset allowing the mounting flange for the carburettor to be substantially parallel to the centreline of the engine, and the centreline of the exhaust port is offset a predetermined number of degrees from a radial line from the cylinder axis, said angular offset allowing the main body of the muffler to be substantially parallel to the centreline of the engine using an angled mounting flange.
2. A rotary valve internal combustion engine according to claim 1, wherein the radial offset is smaller for the inlet port than the exhaust port.
3. A rotary valve internal combustion engine according to claim 1 or 2 wherein the exhaust muffler has an angled flange that mates with a corresponding mounting of the exhaust port so that the main body of the exhaust muffler is aligned substantially with the centreline of the engine.
4. A rotary valve internal combustion engine according to any one of the preceding claims wherein an air guide panel guides the inlet cooling air around the cylinder towards the rear face of the cylinder.
5. A rotary valve internal combustion engine according to any one of the preceding claims wherein a closure plate at the rear of the engine forces the cooling air to exit from the rear of cowl rather than short circuiting down into the cooling air intake.
6. A rotary valve internal combustion engine according to any one of claims 1 to 5, wherein the engine has an airbox containing a curved tuning pipe leading from the air inlet of the engine into a filtered air volume part of the airbox.
7. A rotary valve internal combustion engine according to claim 6, wherein the engine has a carburettor and a tuning our now you are you are you are a you are a you are, the tuning pipe being secured to the air inlet of the carburettor.
8. A rotary valve internal combustion engine according to claim 6 or 7, wherein the airbox is divided into an unfiltered volume and filtered volume by a dividing wall, the dividing wall containing a filter through which air passes from the unfiltered volume to the filtered volume, the tuning pipe air inlet being located in the filtered volume.
9. A rotary valve internal combustion engine according to claim 6, wherein the tuning pipe passes from the carburettor through the unfiltered volume and through the dividing wall into the filtered volume.
10. A rotary valve internal combustion engine according to claim 6, wherein the tuning pipe passes through the filter in the dividing wall.
11. A rotary valve internal combustion engine according to claim 6, wherein the tuning pipe has a serpentine profile along its length.
12.. A manually held horticultural machine having an engine as claimed in any one of claims 1 toll.