A mixed intake two-stroke engine and reed valve therefor

Abstract

 A two-stroke engine of mixed induction type comprises a first duct (19) for direct induction or intake of the mixture into the cylinder chamber (16) and at least one further duct for induction or intake by reeds, the further duct(s) is (are) provided in the cylinder and opens (open) into the cylinder chamber (16) and/or into the transfer ducts (24). The engine is equipped with a reed valve also forming the subject of the invention, and comprising a free central passage (52) and at least one further passage (54) provided with reed actuator (55).

Description

[0001] This invention relates to a combined or mixed intake two-stroke engine (i.e. an engine with intake by piston valve and reed valve comprising a first duct for direct intake sf the mixture into the cylinder chamber and one or more additional ducts for intake by reeds. Such engines are used, for example, in the motorcycle environment, but also for industrial engines, as engines for motarsaws, small tractors, etc.

[0002] The invention also relates to a reed valve for mixed intake two-stroke engine of the type above set forth.

[0003] Lately, in the field of two-stroke engines for motorcycles a "mixed" type of intake has been developed, having over other conventional intake systems the advantage of very little mixture blow-back at low r.p.m. and a high filling degree throughout the rotational range of the engine.

[0004] A prior art engine of mixed intake system type has an intake duct branching off in the engine cylinder; a first branch thereof directly enters the cylinder chamber; and the second branch diverges from the first branch and terminates in the engine block; a reed valve is placed on this second branch. This known engine has the disadvantage that the intake system also involves the engine block, which is a highly costly part; accordingly, as a whole the engine is remarkably expensive.

[0005] Engines are also known that use only one (and accordingly not mixed) type of intake through reed valves; particularly, they have the reed valve(s) interposed on a single intake duct and the whole intake occurs through the reeds. These engines have the disadvantage of a not high filling degree at low r.p.m. due to the impediment to the passage of the sucked-in flow caused by the resistance to the opening of the obturating reeds.

[0006] In order to overcome such disadvantages of the prior art a two-stroke engine and valve according to this application have been devised. In addition to the usual intake duct provided in the cylinder and opening into the cylinder chamber, the engine comprises one or more additional intake ducts provided in the cylinder and opening into the cylinder transfer ducts. Such additional ducts are branches of the usual duct, and according to a further preferred feature of the invention a seat is formed at the branching location for a reed valve or "reed holder" which also forms part of the invention. The valve has a first free passage intended to be placed at said intake duct and one or more additional passages provided with flow regulating reeds intended to be placed at said additonal ducts.

[0007] Generally, but not necessarily, this reed holder or reed support is of a tapered shape, such as a frustrum of pyramid having four or more sides, wherein the first passage is axial, while the other passages are provided on one or more faces or sides of the pyramid.

[0008] This novel engine and reed holder structure allows without any changes to use blocks already in use for other types f engines and enables to provide a mixed intake type of engine of easier construction and reduced cost relative to such engines at present commercially available under same performances.

[0009] A more detailed description of the invention will now be given with reference to the accompanying drawings, wherein unrestrictive exemplary embodiments thereof are shown, and in which:

Fig. 1 is a partially schematic axial sectional view through a first embodiment of a two-stroke engine unit according to this application, shown at two operating positions;

Fig. 2 is a sectional view taken along line 2-2 of Fig. 1, wherein the piston has been omitted;

Fig. 3 is a perspective view of a first embodiment for a reed valve or reed holder according to the invention, with a reed assembly and limiting device shown in a broken away view;

Fig. 4 is a perspective view similar to Fig. 3, showing a second type of reed holder;

Fig. 5 is a fragmentary sectional view similar to that of . Fig. 1, showing a second embodiment of the engine unit; and

Fig. 6 is a sectional view taken along line 6-6 of Fig. 5.

[0010] Referring to Figs. 1 and 2, a two-stroke engine 10 according to the invention comprises a cylinder 11, at the top closed by a cylinder head 12, and a piston 13. Both said cylinder 11 and head 12 are shown as provided in a known manner with cooling fins 11' and 12', respectively. The head 12 has a bore 14 for a sparking plug (not shown). The cylinder is internally provided with a liner 15 defining an inner chamber 16 having said piston 13 sliding therein. Through said cylinder and relevant liner provision is made for an exhaust duct 18 and an intake or suction duct 19, which may be of any known configuration, for example (Fig. 2) branching off to open into the cylinder chamber in two separate ports 19'.

[0011] Cylinder 11 is secured to a block 20 forming a crankcase-pump assembly 21. The chamber of this crankcase-pump assembly 21 communicates with said cylinder chamber 12 through transfer ducts 24 opening by transfer ports 25 into the power stroke chamber of the cylinder. The connecting rod of the piston is shown at 27 and drives the driving shaft shown at 28.

[0012] Reference numeral 30 designates a carburettor of any known suitable type, and reference numeral 31 designates a resilient mount for the carburettor, which mount is also of known type.

[0013] According to the present application, one or more (two in this embodiment) additional intake ducts 40 and 41 have been provided in cylinder 11, and branch off from the primary duct 19 and, in this case, each open into a transfer duct 24. At the branching of the intake duct, a seat 42 is provided for a reed holder or reed valve 50, forming a further feature of the present invention and which will now be described.

[0014] This reed valve 50 comprises a body 51 which in the preferred embodiment, is in the shape of a frustrum of pyramid having four sides, but which could be of any number of sides, or could be in the shape of a frustrum of cone having one or more flattened sides. Said body 51 has a through aperture or free axial passage 52, and on one or more sides has further apertures or passages 54 provided with resilient reed shutters 54. In the embodiment shown in Fig. 3, for use on an engine as in Figs. 1 and 2, said body member 51 has apertures 54 on two opposite sides, the apertures being in number of two on each side. The reeds 55 are of well known type and are provided with rigid opening limiting devices or stoppers 56, each reed and relevant stopper being secured to said body member 51 by a fastening means 57. The reed valve is also provided with a flange 58 or other means for attachment to the cylinder and may be provided with a tubular extension for attachment to the carburettor mount, if desired. The valve may be made of metal material and provided with seals 59 on one or more walls, for example in rubber injection.

[0015] The design of the valve shown in Fig. 3 is suitable for mounting on an engine as that in Figs. 1 and 2.

[0016] Therein there is shown that the free axial passage 52 of the valves is arranged at the cylinder intake duct 19, while the additional passages 54 of the valve, provided with reed shutter, are arranged at additional intake ducts 40 and 41. Accordingly, the engine operates by mixed intake.

[0017] A further exemplary embodiment of a reed valve according to the present application is shown in Fig. 4, while the embodiment of the engine on which such a valve is mounted is shown in Figs. 5 and 6. In Fig. 4, the reed valve 150 has a body member 151 of frustrum of pyramid shape with free axial passage 152 and additional passages or apertures 154 on the four sides, provided with reed shutter 155 and opening limiting devices 156. The other elements of valve 150 do not substantially differ from the corresponding elements of valve 50, and will not be described in detail.

[0018] The engine 110 of this second embodiment comprises elements similar to those of engine 10 of the first embodiment, and the similar elements are shown in Figs. 5 and 6 with the same reference numerals of Figs. 1 and 2 added by 100, and will not be described in detail.

[0019] The cylinder 111 of engine 110 has provided therein a first intake duct 119, and additional intake ducts 140 and 141 shown in Fig. 6, and 144 and 145 shown in Fig. 5. While said first intake duct 119 is supplied through the free passage 152 of the valve, the other ducts 140, . 141, 144 and 145 are supplied through the reeded apertures 154. It will be seen that while ducts 140 and 141 open into the cylinder transfer ducts, ducts 144 and 145 directly open into the chamber defined by the cylinder liner.

[0020] Obviously, changes and modifications can be made to the . foregoing description, it being however considered that all of those changes and modifications as devisable by those skilled in the art are within the range of the present application.

Claims

1. A two-stroke engine of mixed intake system type, 'the engine comprising a first duct (19) for direct suction of the mixture in the cylinder chamber (16) and at least one additional duct for suction by reeds, characterized in that all of said ducts (19, 40, 41; 140, 141) are provided in the cylinder.

2. An engine according to Claim 1, wherein some ducts (140, 141) of said additional ducts open into the cylinder chamber.

3. An engine according to Claim 1, wherein some ducts (40, 41) of said additional ducts open into the cylinder transfer ducts (24).

4. An engine according to Claim 1, wherein said additional ducts branch off from said first duct and at the branching location a reed valve or reed holder (50; 150) is mounted and has a free passage (52; 152) which is arranged at said first duct and one or more passages (54; 154) provided with reeds (55; 155) which are arranged at said one or more additional ducts.

5. A reed valve for two-stroke engine of mixed intake type, characterized by comprising a free central passage (52; 152) and at least one additional passage (54; 154) provided with reed shutter (55; 155).

6. A reed valve according to Claim 5, said valve having a body member (51; 151) of tapered shape with said free passage at axial position and said reeded passage(s) on the side surface.

7. A reed valve according to Claim 5, said valve being in the shape of a frustrum of pyramid having a plurality of sides, with said free passage at axial position and said passage(s) with reed shutter on at least one of the pyramid sides.

8. A reed valve according to Claim 5, further comprising a flange for attachment to the engine cylinder body.

9. A reed valve according to Claim 5, further comprising a substantially tubular extension for attachment to a carburettor.

Drawing