The invention relates to a combustion engine comprising a number of cylinders accommodating pistons which are capable of reciprocating movement, whereby at least two inlet ports to be opened and closed by means of inlet valves and at least one exhaust port to be opened and closed by means of an exhaust valve are provided for each cylinder, and whereby an inlet channel connects to each of the inlet ports of a cylinder, said inlet channels being in communication with an air inlet chamber, whilst means are provided by which the passage of one of said inlet channels can be opened or closed, as desired, which inlet channels of each cylinder are in communication with a separate air inlet chamber, which is in communication with an air supply chamber via at least two air supply channels having different lengths, whilst means are provided for opening or closing, as desired, the shorter of the two air supply channels during operation.

The term air inlet chamber is understood to mean the space forming the connection between the air inlet channels and the air supply channels. The air inlet chamber may also be a channel connecting the air inlet channels and the air supply channels, therefore.

Combustion engines exhibit resonance of the air in the inlet channels during operation, which is partly caused by the opening and closing of the inlet valves. It is possible to influence the charging of the cylinders with air by utilizing said resonance behaviour, since more air will be introduced into the respective cylinder when a flow of air towards the inlet valve takes place in the inlet channel than will be the case when a flow or air away from the inlet valve takes place in the inlet channel at the moment of opening of the inlet valve.

The utilization of inter alia this resonance behaviour with a view to increasing the efficiency of the engine is known per se.

In a similar combustion engine known from Japanese Patent Application No. 62-101.822 air can be supplied from the air supply chamber to the air inlet chamber either via the long air supply channel or via both air supply channels. The shorter air supply channel is to that end provided with a valve which can be jointly opened or closed with a valve present in the inlet channel. In the open position of the valves air flows into the cylinder through the shorter air supply channel and

the two air inlet channels. The long air supply channel is not closed thereby, so that also part of the air from the air supply chamber will flow to the inlet channels via the long air supply channel, which has an adverse effect on the air flow behaviour. The fact is that the resonance behaviour of the air between the air supply chamber and the air inlet chamber is thereby determined by the open short air supply channel as well as by the long air supply channel, which is undesirable.

The object of the invention is to obtain a combustion engine of the above kind, wherein the drawbacks of the known combustion engines can be avoided and wherein a particularly effective control, an efficient combustion and an economical fuel consumption of the engine can be effected while using an air inlet system of compact dimensions.

According to the invention this object can be achieved in that furthermore means are provided for opening or closing the longer of the two air supply channels during operation, as desired, whereby either the longer or the shorter air supply channel is open.

Since the supply of the combustion air takes place either through the longer or through the shorter of the two air supply channels, the air flow through the one supply channel cannot be influenced by the air flow through the other supply channel.

Depending on the operating conditions air can be supplied from the air supply chamber to the air inlet chamber via the long or via the short air supply channel and/or be introduced into the cylinder and the combustion space of said cylinder from the air inlet chamber via one or both inlet channels and the inlet ports connecting thereto.

In practice it has become apparent that this makes it possible to effect a very efficient control of the supply of combustion air to the various cylinders of the combustion engine, without any undesirable effects as a result of the air supply to the one cylinder being influenced by the air supply to the other cylinder occurring thereby, so that an effective air supply, air compression and fuel ignition optimally adapted to the operating conditions of the combustion engine can be realized during operation.

When little combustion air is required during operation, the supply of air can take place via a single inlet channel, whereby the combustion air can be caused to whirl about the central axis of the cylinder in the cylinder space, which appears to have an advantageous

effect on the combustion at a low rotational speed. When higher rotational speeds are used and the supply of air takes place via both inlet channels, a tumbling movement of the air in the cylinder space will be effected, which is advantageous in the case of said operating conditions. It is noted that from European Patent No. 0 225 620 a combustion engine is known wherein the inlet channels of each cylinder are in communication with a common chamber, to which two channels having different lengths are connected. A few of the longer channels are connected to a common air supply chamber, which is connected, via two channels -having different lengths, to a second air supply chamber. The second air supply chamber is in direct communication with the shorter channels connecting to the common chambers of the cylinders, which channels can be opened or closed as desired, in such a manner that combustion air can be supplied via both channels connected to a common chamber of a cylinder, or only via the longer of the two channels. The shorter of the two channels provided between the two air supply chambers can be opened or closed as desired, so that air can be supplied from the second air supply chamber to the first air supply chamber either via only the longer of the two channels provided between said chambers or via both channels provided between said chambers. This is a rather complicated construction, which takes up relatively much space, whilst an even supply of combustion air to the various cylinders cannot be controlled in an accurate manner.

One embodiment of the combustion engine according to the invention is characterized in that a valve mechanism is disposed near the connection of said air supply channels to said air inlet chamber, which valve mechanism can be adjusted from a first position, in which said valve mechanism closes the connection between the longer of the two air supply channels and the air inlet chamber and releases the connection between the shorter of the two air supply channels and said air inlet chamber, to a second position, in which said valve mechanism releases the connection be ^t ween the longer of the two air supply channels and the air inlet chamber and closes the connection between the shorter of the two air supply channels and said air inlet chamber.

In this manner one air supply channel can be opened, whilst the other air supply channel is simultaneously closed, by means of a single valve mechanism. Thus the two air supply channels can at no time be open or closed at the same time.

A further optimization of the combustion engine may be effected when means are provided by which the lifting height of the inlet valves can be controlled. Also this possibility of varying the lifting height of the inlet valves makes it possible to influence the supply of combustion air to the respective cylinders so as to obtain an optimum operation.

The invention will be explained in more detail below with reference to the accompanying Figures.

Figure 1 is a diagrammatic side view of a cyl inder space of a combustion engine with inlet and outlet channels connected thereto.

Figure 2 is a diagrammatic plan view of Figure 1.

Figure 3 diagrammatically shows the construction of the air inlet system.

Figure 4 shows a graph, wherein the rotational speed (number of revolutions) is plotted on the horizontal axis and wherein the average effective pressure (in bar), which is a measure for the load on the piston, is plotted on the vertical axis.

Figure 5 shows another embodiment of a device according to the invention. The invention applies to a usual 4-stroke combustion engine, which comprises four in-line cylinders 1 in the illustrated embodiment, but it will be apparent that the combustion engine may comprise fewer or more cylinders, whilst furthermore it will not be necessary for the cylinders to be arranged in-line, of course. Also V-arrangements of the cylinders or the like will be possible, of course.

Cylinder 1 is conventionally closed at one end by a cylinder head 2 which is diagrammatically indicated in Figure 1, which cylinder head comprises two inlet ports 3 and 4, one outlet port 5 and an ignition plug 6. As is indicated in Figure 2, cylinder head 2 may be divided into four quadrants 7 - 10 being arranged in clockwise succession, seen in plan view, whereby the two inlet ports 3 and 4 are arranged in successive quadrants 7 and 8, seen in clockwise direction, and outlet port 5 and ignition plug 6 are each arranged in a further quadrant 9 and 10 respectively.

The inlet and outlet ports can be opened and closed in a usual manner by means of inlet valves and outlet valves respectively.

Said valves and said means for opening and closing the valves are not shown, since valves and valve driving means of this type are generally known.

Inlet channels 11 and 12 connect to inlet ports 3 and 4 respectively, whilst an outlet channel 13 connects to outlet port 5.

The two inlet channels 11 and 12 of each cylinder, which have the same length, open into a common air inlet chamber 14. As will be apparent from Figure 3, the air inlet chambers 14 of the various cylinders 1 are separated from each other. Inlet channel 12 houses a valve 15, which can be pivoted about a pivot pin 16 between a first position, in which valve 15 closes the passage through inlet channel 12, and a second position, in which air can flow freely through inlet channel 11 during operation, and vice versa, as indicated by the double arrow P in Figure 3. Two air supply channels 17 and 18 connect to air inlet chamber 14, which channels connect said air inlet chamber to an air supply chamber 19. The length of the air supply channel 18 is considerably larger than the length of air supply channel 17 thereby. Air supply channel 18 may have a volute-like configuration, in order to make it possible to accommodate air supply channel 18 in a space of limited dimensions. In one embodiment that was used the length of the short air supply channel was ± 37.5 cm, for example, and the length of the long air supply channel 18 was ± 77 cm. It will be apparent, however, that these dimensions are not given by way of limitation and that the magnitude of said lengths will depend on the further construction of the engine, among other things.

A valve 20 is disposed near the connection of the two air supply channels 17 and 18 to air inlet chamber 14, which valve can pivot from the position illustrated in full lines in Figure 3, in which said valve 20 shuts off the connection between the short air supply channel 17 and air inlet chamber 14 and releases the connection between the long air supply channel 18 and air inlet chamber 14, to the position 20 ^' illustrated in dotted lines in Figure 3, in which the valve shuts off the connection between the long air supply channel 18 and air inlet chamber 14 and releases the connection between the short air supply channel 17 and air inlet chamber 14, and vice versa, as is indicated by means of the double arrow Q.

The supply of combustion air to air supply chamber 19 takes place in the direction according to arrow A and is regulated by means of a usual throttle valve, which, for example in the case of a combustion engine used in a motor vehicle, is controlled by an accelerator. In the illustrated combustion engine, which is for example to be fuelled by petrol or gas, the fuel is injected into the air inlet channel 11, near inlet port 3, in a usual manner by means not shown.

The mechanism for controlling the inlet valves of the engine is preferably constructed in such a manner that the lifting height of the valves can be varied, in which connection the use of two different cams for lifting each inlet valve may be considered, for example, so that the valve can be lifted from its seat over a first distance or be lifted from said seat over a second, larger distance, depending on the operating conditions. The aforesaid valves 15 and 20 as well as (possibly) the means for varying the distance over which the inlet valves are lifted from their seats are controlled by control means (not shown) in dependence on the operating conditions under which the engine works, such as the position of the throttle valve and the rotational speed of the engine, for example.

As is for example indicated in Figure 4, air may be supplied only to inlet port 3 via the short air supply channel 17 and air inlet channel 11 in operating range I, that is, an operating range with a comparatively low rotational speed and a comparatively small load. If the lifting height of the valves is adjustable thereby, the valve will preferably be lifted the smaller height.

In range II, with a comparatively low rotational speed and a higher engine power, air may be supplied only through the longer air supply channel 18, air inlet channel 11 and valve 3, whereby the valve will be lifted the larger height if the lifting height of the valve can be varied.

In range III, with a comparatively high rotational speed and a comparatively low engine power, air may be supplied through the short air supply channel 17 and the two air inlet channels 11 and 12, to which end valve 15 in channel 12 is open. The valves will thereby be lifted the small height from their seats if the lifting height of the valves is variable.

In range IV, with an increasing rotational speed and an increasing load, air may also be supplied through the short air supply channel 17 and the two channels 11 and 12, whereby the large lifting height of the valves will be used if the lifting height of the valves is variable. In range V, with a comparatively high rotational speed and higher engine power values, air may be supplied through the long air supply channel 18 and the two air inlet channels 11 and 12, whereby the large lifting height of the valves is used if said lifting height is variable. If air is supplied to a cylinder only through a single air inlet channel 11, the mixture of air and fuel will enter the cylinder at a point which is located eccentrically with respect to the central axis of the cylinder, which results in a whirling flow of the mixture of combustion air and gas about the central axis of the cylinder, as is indicated by arrow B in Figure 1.

If on the other hand air enters the cylinder through both inlet ports 3 and 4, the air will exhibit a greater tendency to tumble about an imaginary axis extending perpendicularly to the central axis of cylinder 1, as is indicated by means of arrow C. This leads to an advantageous result, since it has become apparent in practice that, in order to obtain an efficient combustion, it is advantageous for the mixture of combustion air and fuel to make a whirling motion about the central axis of the cylinder when low rotational speeds are used and to make the above-described tumbling movement when high rotational speeds are used. As a result of the above-described position of the ignition plug 6 an efficient ignition of the mixture of air and fuel will take place in both cases thereby.

It will be apparent that the operation as described above represents merely an example of a possible method of controlling the operation of the engine, in particular for controlling the supply of combustion air, and that many variations thereto are conceivable, depending on the construction of the engine. Furthermore the above operating ranges I-V will usually be less clearly defined with respect to each other than Figure 4 would suggest. Figure 5 shows another embodiment of a combustion engine according to the invention, with like parts being numbered alike. The combustion engine is provided with a air supply chamber 19, to which two

air supply channels 17 and 18 are connected, said air supply channels 17 and 18 being connected to an air inlet chamber 14 on a side remote from the air supply chamber 19. The air flow from air supply chamber 19 to air inlet chamber 14 through short air supply channels 17 is indicated by means of arrows P3, whilst the air flow through long air supply channels 18 is indicated by means of arrows P4. A tubular element 23, which is capable of pivoting movement about a pivot pin 22 from a position illustrated in full lines in Figure 5, in the direction indicated by arrow P2, to the position 23 ^' illustrated in dotted lines, is disposed near the transition between air supply channels 17 and 18 and air inlet chamber 14. In the position of tubular element 23 that is shown in Figure 5 said tubular element forms a connection between the relatively short air supply channel

17 and air inlet chamber 14. The long air supply channel 18 is closed by the wall of tubular element 23. When tubular element 23 pivots about pivot pin 22 in the direction indicated by arrow P2, the long air supply channel

18 is brought into open communication with air inlet chamber 14, whilst the short air inlet channel 17 is simultaneously closed. The tubular element extending between an air inlet channel and air inlet chamber 14 provides a continuous channel, as it were. This results in a relatively advantageous flow behaviour.