An internal combustion engine of the said type is a thermodynamic engine in which a fuel mixture is burned in a cylinder. The heat energy is converted into mechanical work by the pressure of the combustion gas acting on a movable piston in the cylinder. The piston has a rectilinear alternating motion which is transformed into a rotary motion by means of a crank mechanism. The shaft in the crank mechanism is also the energy outlet of the engine.

The processes inside the cylinder take place in series, which comprise air and fuel supply, compression, combustion, expansion and expulsion of combustion gas. Each piston stroke in the series represents one stroke of the four-stroke cycle. Internal combustion engines are categorised according to stroke type, namely two-stroke and four-stroke engines. As mentioned, the invention relates to four-stroke engines.

In four-stroke engines, valve-controlled overhead or side intake and exhaust ports or openings are provided in the cylinder for the intake and exhaust of a fuel mixture and combustion gas, respectively.

Intake valves and exhaust valves are controlled by a valve gear. Such valve gears comprise camshafts which act directly or indirectly (levers) on the valves. The camshaft (s) is/are driven from the engine shaft.

A number of advanced valve gears exist, but they all have in common that they require a relatively large number of components and that the valves are subjected to great loads and resultant wear. The space in a cylinder also sets limits for the size of the valve ports, where, for example, in the case of overhead valves there is only a limited area (the cylinder surface) available. Side valves provide better space, but common to all valve arrangements is that the camshaft, valve springs, valve gears etc. require space and are subject to inner friction. The valve springs in particular have a speed limiting effect. Heat generation and vibrations are also a problem The object of the present invention is to provide a four-stroke engine which is lighter (lower weight), can be made smaller (more compact), and can be manufactured more cheaply than the four-stroke engines known to date.

Therefore, according to the invention, an arrangement as defined in patent claim 1 is proposed. Additional features of the invention are disclosed in the dependent patent claims.

It should be mentioned that piston-controlled ports are known in the case of two-stroke engines, and it is also known to use check valves, but then in the form of reed valves, in two-stroke engines, in the intake/flushing system. However, as mentioned, these known check valves are incorporated in the flushing system which is typical for two-stroke engines, where the crankcase is used as a mixing chamber for air and fuel before it passes into the cylinder chamber above the piston, the check valve then preventing flow back to the carburettor.

The use of one (or more) piston-controlled intake openings or ports in a cylinder wall in a four-stroke engine, optionally with a check valve in the intake, yields surprising advantages, as the intake system is simpler, and also allows further advantages in the rest of the motor design.

Special features of the invention and its advantages will be explained in more detail below, in a description of an exemplary embodiment of the invention, with reference to the drawings wherein: Figures la-e are purely schematic illustrations of an arrangement according to the invention and its mode of operation; and Figure 2 shows a section of the upper engine area, on a larger scale.

The purely schematic figures show only the parts that are essential for the understanding of the invention. Non-illustrated details are well-known to the skilled person and do not differ from structural details used for four-stroke internal combustion engines.

Figure 1 shows a four-stroke internal combustion engine comprising a cylinder 1, a crankcase 2 and a cylinder head 3. Arranged in the cylinder 1 is a reciprocating piston 4, which is connected via a connecting rod 5 to the crankshaft 6 supported in the crankcase 2, indicated by means of a circle on the drawing. An intake for fuel mixture is indicated by means of the reference numeral 7, and an exhaust valve is indicated by means of the reference numeral 8.

An opening 9 in the cylinder head 3 for the positioning of a spark plug/ignition element (not shown) is merely indicated.

The illustrated internal combustion engine works in a known way for a four-stroke engine. During an intake stroke the crank mechanism draws the piston from its top position to its bottom position. Air and fuel are then drawn in through the intake. In the next stroke, the compression stroke, the crank mechanism presses the piston from its bottom position to its top position. The intake valve closes and the fuel blend is compressed. During the third stroke, the working stroke, the ignited fuel mixture expands, pushing the piston from its top position to its bottom position. Towards the end of the stroke, the exhaust valve opens. During the fourth stroke, the exhaust stroke, the crank mechanism moves the piston from its bottom position to its top position. The exhaust valve is open. The combustion gas is then expelled from the cylinder. There then follows a new intake stroke etc.

According to the invention, the engine has a new and advantageous intake system 7.

An opening or port 10 is made in the cylinder wall of the cylinder 1, see in particular Figure 2. This port 10 is connected through a duct 11, merely indicated in the figure, to a carburettor (not shown). Provided in the duct/port 10/11 is a check valve 12, in the form of two flat tongues 13 and 14 which cooperate with a valve seat 15.

In the exemplary embodiment, the exhaust valve 9 is in the form of a rotary valve, with a rotary body 16 that has a diametrical duct 17, which can be brought into alignment with an exhaust port 18 in the cylinder 1 and an exhaust gas pipe 19. The rotary body 16 rotates with the crankshaft with the aid of a non-illustrated transmission belt, at a transmission ratio of 1: 4. The rotary valve, i. e. , the rotary body 16 thus runs at half the speed of an ordinary camshaft. One of the advantages of a rotary body of this kind is the reduced speed, with fewer tensions in and a longer life for the transmission belt.

The use of such rotary valves in motors is known and the rotary valve per se does not represent any novelty. However, its position in the cylinder wall, below the piston sealing rings 20 in the upper position of the piston 4, yields a substantial advantage.

The terminating compression and explosion (combustion) takes place against the cylinder head 3 and against the piston 4, and not directly against the rotary valve 9,16.

The intake valve 7 will not be affected either, as it is located in the cylinder wall below the piston ring area 12 at the start of the working stroke.

The sealing rings 20, i. e. , piston springs and the oil spring, are locked (not shown) so that the spring openings do not enter the ports 10, 18 as the piston 4 passes them.

The mode of operation of the new arrangement according to the invention will now be described in more detail with reference to the figures.

In Figure 1 a, the piston 4 is shown on its way down in the working stroke. The exhaust valve 9 is closed. The intake valve 7 is also closed, the flat tongues 13,14 bearing against the valve seat 15, and the piston also covers the intake port 10. Intake of oil from the crankcase is thus prevented.

In Figure 1b the piston 4 is on its way up in the exhaust stroke, after having passed its lower dead centre. The exhaust valve 9 is open. The intake valve 7 is still closed.

In Figure lc the piston 4 is on its way down in the intake stroke. Both the exhaust valve 9 and the intake valve 7 are closed. In Figure ld the piston 4 is shown in its lower dead centre, in a terminated intake stroke. The intake valve 7 is open ; it opens as soon as the negative pressure in the cylinder chamber comes into effect, as the piston 4 starts to uncover the port 10, the flat tongues then swinging out from the seat 15. The fuel mixture flows into the cylinder 1 above the piston 4.

In Figure 1 e the piston 4 has reached its upper dead centre in the compression stroke.

The intake valve is closed as a consequence of the rise in pressure and the piston 4 also covers the port 10. The exhaust valve 9 is closed. After the piston has passed its upper dead centre, ignition is initiated in a known way and the piston begins its working stroke (Figure la).

Surprisingly, it has been found that the relatively late opening of the intake 7 does not represent a disadvantage. It is also easily compensated for because the positioning of the intake port 10 in the cylinder wall now allows the possibility of a larger port opening (cross-sectional area), with increased rate of admission. It is also possible to have more than one port 10 in the cylinder wall. The check valve 12 works quickly and independently and does not require any mechanical or hydraulic valve control.

The notable advantage of the invention is the simplified intake system, without mechanical controls, as the intake valve is piston-controlled and automatic. The invention also permits other simplifications, such as in the exhaust valve, which can

advantageously be made as a simple rotary valve, although ordinary or conventional exhaust valves can be used.

It is not shown, but the piston-controlled intake opening may also be used without a diaphragm or check valve, but in that case there is a compressor which ensures that there is pressure above atmospheric in the intake duct.

The check valve must be positioned in the intake duct as close to the piston as possible, to avoid power loss.

The new intake system has no effect on the electronic control units used in a modern engine, such as lambda probe catalytic converters.

All told, a lighter, less bulky and cheaper four-stroke engine is obtained. The engine's combustion is not limited as in an ordinary overhead valve engine where the size of the valves will be limited by the diameter of the cylinder. The result is a better combustion/effect and cleaner exhaust.

The invention can also be implemented as an additional feature in a conventional overhead valve four-stroke engine in order to achieve better admission and better engine output.

Commonly known metal materials suitable for such valve environments, for example, may be used as the material in the check valve, i. e. , the flat tongues 13,14. One possible material is a Kevlar-based material.