US3628518A

US3628518A - Internal combustion engines

Info

Publication number: US3628518A
Application number: US9250*[A
Authority: US
Inventors: Gordon Purves Blair; Mervyn Bradshaw Johnston
Original assignee: Birmingham Small Arms Co Ltd
Current assignee: Birmingham Small Arms Co Ltd
Priority date: 1968-09-12
Filing date: 1969-09-10
Publication date: 1971-12-21
Anticipated expiration: 1988-12-21
Also published as: FR2017908A1; ES371386A1; DE1945955A1; GB1241191A

Abstract

A rotatable sleeve with openings surrounds a stator having passages therethrough disposed in the induction passage of a two stroke cycle engine.

Description

nited States Patent 123/73 V, 123/80 BA 1 m2, 1 [51] Int.Cl 1101117/00, F011 7/12 [50] Field otsearch 123/190 A, 73 V, 80 B, 190 B,190C,190 D [56] References Cited UNITED STATES PATENTS 1,808,671 6/1931 Luycky .v 123/80 B1 1,920,924 8/1933 Gordon 123/190 A5 2,839,036 6/1958 Strang 123/73 V FOREIGN PATENTS 808,656 7/1951 Germany 123/73 V Primary Examiner-Wendell E. Burns Anorney-Norris & Bateman ABSTRACT: A rotatable sleeve with openings surrounds a stator having passages therethrough disposed in the induction passage of a two stroke cycle engine.

(Jordon PQJCVGS Blair aw? i acrvyn Biacshaw Jonnston INTERNAL COMBUSTION ENGINES This invention relates to internal combustion engines, particularly to multicylinder in-line internal combustion engines. The invention is particularly applicable to two-stroke cycle internal combustion engines.

One disadvantage of the piston-controlled porting of the conventional two-stroke cycle engines of the naturally aspirated type, such as for example, those used in motor cycles, is that the port timing is symmetrical. This applies particularly to the intake port where typical timings are 70 before to dead center (BTDC) opening and 70 after top dead center (ATDC) closing for low-speed engines and up to 100 (BTDC) opening and 100 ATDC closing for racing motorcycle engines. It will be evident that much fuel is lost from the intake port during the crankcase compression stroke particularly with the longer timing of 200 included angle.

Various methods of providing the desirable asymmetrical timing have been proposed but the disc valve (or Zimmerman valve) is generally regarded as being the most successful. The disc valve, in most constructions, allows for asymmetrical timing by having a thin steel disc, which rotates in the same plane as the flywheel, interrupt and allow passage of the intake flow which lies in the same plane as the crankshaft. It will be obvious that it then becomes difficult to couple more than two cylinders in line together, unless a 90 bend is accepted in the intake tract. For high specific power output engines this sharp bend is undesirable. An alternative arrangement is to arrange four cylinders somewhat in the shape of a square, this being in effect two two-cylinder engines with crankshafts geared together to construct a four-cylinder engine.

One of the objects of the present invention is to provide asymmetrically intake timed, multicylinder in-line two-stroke cycle engines without either 90 bends in the intake pipes or the use of geared crankshafts as above referred to.

According to a feature of the invention an internal combustion engine is provided with a stator having transverse induction passages therethrough surrounded by a rotor in which are openings and solid faces adapted to uncover the induction passages to allow the induction mixture to pass through the induction passages to the inlet ports of the engine and to be cut off as desired.

The stator is preferably in the form of a circular bar with transverse induction passages formed therein, at least one for each cylinder. The passages may conveniently be circular holes but other cross-sectional shapes may be used to give different intake characteristics. Each passage will of course be in line with each intake tract and may be so disposed as to assist in providing a desired directional flow.

The rotor is preferably in the form of a sleeve having suitable holes formed therein which when in register with the induction passages in the stator, allow the inlet mixture to pass into the engine cylinder. The size, shape and disposition of the holes in the rotor will depend on the port timing of each cylinder and the firing order of the'cylinders.

The rotor may be driven from the crankshaft by any convenient means, for example, by chain, gears or rubber-toothed timing belt. Preferably an extension to the crankcase is adapted to accommodate the stator-rotor assembly. The rotor is preferably mounted on antifriction bearings and is adapted to run clear of the housing and the stator.

In the general construction of an engine according to the invention, while it is acceptable for the connecting rod to pass through an extension of the bore the cylinder to the crankcase in conventional manner, it is preferred that the connecting rod pass through a slot in the metal of the crankcase. It is also preferred that two opposed transfer ports are used together with a rear transfer port, steeply inclined towards the cylinder head.

An embodiment of the invention, by way of example, is shown in the accompanying drawings, in which:

FIG. 1 is a plan section along line XX of FIG. 2 of a fourcylinder two-stroke cycle engine according to the invention,

FIG. 2 is an elevation section along line Y-Y of FIG. I, and

FIG. 3 is an elevation section along line Z-Z of FIG. I. Referring firstly to FIGS. I and 2, the four cylinders of a

twostroke engine

1, 2, 3, and 4 are arranged in in-line arrangement in cylinder block 5. A piston 6 is disposed within each cylinder such that the piston within cylinders 1 and 3 are at top dead center when the pistons within cylinders 2 and 4 are at bottom dead center. Connecting rod 7 connects the piston 6 to crankshaft 8 in conventional manner and passes through slot 9 in the wall 10 which substantially closes the bottom of each cylinder.

Cylinder head II is secured to the cylinder block 5 by means of nuts I2 screwed onto studs 13 screwed into the cylinder head and forms hemispherical combustion chamber 14 at the top of each cylinder. A sparking plug I5 is screwed into the threaded aperture 16 provided at the apex of each combustion chamber.

Exhaust pipes 17 are secured to the cylinder block 5 in alignment with exhaust ports 18 to conduct away the exhaust gas in conventional manner.

Inlet port 19 is situated at the lower end of the cylinder and has affixed in alignment with its outer opening a conventional carburetor 20. A valve, indicated at 21, is positioned in inlet port 19 and is adapted to open and close said port.

The valve assembly 21 is disposed within cylindrical bore 22 in the cylinder block, which bore runs the entire length of the cylinder block and intersects each inlet port 19 in exactly similar manner. The valve assembly 21 comprises a circular cross section stator 23 about which rotates a rotor 24 of cylindrical shape.

At one end of the valve assembly the stator 23 is provided with central boss 25 on which is mounted ball bearing 26 which is so arranged that the rotor 24 is held in spaced relationship with the stator 23 and the bore 22. The inner ball race 27 of ball bearing 26 is an interference fit on boss 25 and therefore remains stationary therewith and the outer ball race 28 rotates with the rotor 24. The boss 25 has a threaded end portion 29 of reduced diameter which is inserted through hole 30 in end plate 31 which is secured to the cylinder block and closes the end of bore 22. Nut 32 secures the boss 25 to the end plate 31.

At the other end of the valve assembly the rotor 24 is closed by integral end wall 33 from which projects central boss 34. Bearing 35 is assembled on boss 34 such that its inner race rotates therewith while its outer race is stationary and is located within counterbore 36 at the end of bore 22. Ball bearing 37 is located within recess 38 in end wall 33, its outer race rotating with the rotor and its inner race remaining stationary on boss 39 projecting from the end of stator 23. End plate 40 closes the end of bore 22 and has a hole 41 through which projects boss 34 of rotor 24.

A pulley 42 is located on the threaded end portion 43 of boss 34 and is clamped thereto by nut 44. The pulley 42, and hence the rotor 24, are driven from pulley 45 mounted on the crankshaft 8 by means of toothed belt 46. The driven/driver ratio is 2:1 such that the rotor 24 rotates once for every two revolutions of the crankshaft 8.

The use of

bearings

26, 35 and 37 produces a valve assembly in which there are no rubbing parts and which operates with the minimum of frictional losses. The valve requires very little power for its operation, particularly if the rotor is made from a light material such as aluminum.

The valve operates to open and close the inlet ports of the cylinders by means of apertures in the stator and the rotor which move into and out of alignment. The apertures in the stator 23 are in the form of circular cross section bores 47 of the same diameter, and aligned with, the inlet ports I9. In this embodiment there are, therefore, four bores 47 in the stator 23.

The rotor 24 has four pairs of diametrically opposed holes 48, each pair being positioned with its axis in the same plane as the axis of one of the bores 47 in the stator 23. The axes of the pairs of holes 48 associated with cylinders I and 3 are coplanar and are at right angles to the axes of the pairs of holes associated with cylinders 2 and 4. By this arrangement the inlet ports of cylinders l and 3 are fully open, that is holes 48 are aligned with bores 47, when the inlet ports of cylinders 2 and 4 are fully closed, that is with holes 48 and bores 47 completely out of alignment.

The operation and function of the valve in relation to the two piston strokes is as follows:

As the piston moves on the crankcase compression downstroke the valve starts to close. By virtue of the 2:1 relationship between the crankshaft and rotor speed of revolution, the 180 revolution of the crankshaft from the top dead center position to the bottom dead center position results in a 90 revolution of the rotor from the fully open to the fully closed position. The closure of the .inlet port during the crankcase compression stroke limits loss of fuel and increases the crankcase compression ratio and thus results in quick and efficient transference of the fuel mixture from the crankcase to the combustion chamber when the rear transfer port 49 and the side transfer ports 50 are uncovered by the piston. The wall at the bottom of the cylinder also tends to keep the crankcase compression ratio at a fairly high value.

As the piston moves on the crankcase induction upstroke the valve opens until it is fully open at top dead center and thus allows fuel mixture to be drawn from the carburetor into the crankcase.

it is apparent that the port timing of the engine according to the invention is not piston controlled and can be arranged to be asymmetric with relation to the piston movement as described in the above embodiment.

in a modification of the above-described embodiment the holes in the rotor are of rectangular shape and thus open and close the stator bore more quickly for any given rotor diameter.

The firing sequence of an engine according to the invention is not limited to that described above in which the cylinders fire in pairs and indeed it would be preferable to have in a four cylinder engine one cylinder firing every 90 rotation of the crankshaft. Obviously the disposition of the holes in the rotor can be arranged to suit any required firing sequence.

What we claim is: v

1. A two-stroke internal combustion engine comprising a cylinder block, at least one cylinder formed within said block and a piston reciprocally mounted within said cylinder, an induction passage in said block located adjacent one end of said cylinder for passing an induction mixture into said cylinder and an exhaust passage located adjacent the other end of said cylinder for exhausting combustion gases from said cylinder, a cylindrical valve chamber intersecting said induction passage, a cylindrical stator disposed concentrically within said chamber and having a passage therethrough aligned with and of substantially the same cross-sectional shape as said induction passage, means for holding said stator stationary, and a rotatable rotor in the form of a sleeve surrounding the stator having openings and solid faces adapted to uncover and cover the passage through said stator as said rotor rotates, and bearing means for rotatably mounting said rotor on said stator in spaced relationship therefrom.

2. A two-stroke internal combustion engine as defined in claim 1, said stator having an axial boss at each end thereof, and said bearing means comprising a bearing mounted on each said boss for permitting said rotor to rotate around said stator in spaced relation therefrom.

3. A two-stroke internal combustion engine as defined in claim 1, said stator holding means being connected to and fixing one end of said stator, and another bearing disposed between the end of the rotor, remote from the fixed end of said stator, and the wall of said valve chamber.

4. A two-stroke internal combustion as defined in claim 3, wherein said remote end of said rotor has an axial shaft protruding therefrom, said another bearing being disposed between said shaft and the wall of the valve chamber, and a pulley affixed to said shaft and adapted to impart rotational movement to said rotor.

5. A two-stroke internal combustion engine as defined in claim 1, wherein the passage through said stator is of circular cross section and the openings in said rotor are of rectangular shape.