Improved timing system for internal combustion engines with high specific power

Abstract

 A control device for valves for internal combustion engines (10) in which the two groups (11) of valves, one for intake (10) and one for exhaust (11) are controlled each by a camshaft (15, 17) and in which said camshaft (15, 17) directly controls through an interposed guide socket (14, 18) the homologous valves aligned thereunder and, through a "finger" rocker arm (20), those outside said alignment.
Said valves (10, 11) (both intake and exhaust) are advantageously arranged equidistant from the centre of the combustion chamber and with the axes of the homologous valves parallel. The cams (24) of said camshafts (17) which control said "finger" rocker arms (20) have a lift reduced by one rho as compared with the cams (19) which directly control the remaining valves while the transmission ratio of said "finger" rocker arms (20) is 1/rho so as to cause all the homologous valves to open and close in unison and with the same amplitude of movement.

Description

[0001] It is known that to secure high specific powers in internal combustion engines it is necessary to increase to a maximum the cross section areas of the valve passages and in particular the intake valve passages. But this requirement conflicts with the limitation of the diameter of the cylinder in which the valves are to be housed and with the requirement of having to make valves as light as possible to limit the inertia thereof and thus reach high engine revolution speeds.

[0002] The search for possible solutions to the problems mentioned has led to the adoption of several valves for each cylinder in order to allow smaller and hence lighter valves while at the same time realizing a better ratio of the cylinder diameter to the overall cross section area of the valve passages.

[0003] In engines with a certain level of specific power it is now common practice to adopt the construction solution of two intake valves and two exhaust valves, thus producing engines with four valves per cylinder, which represent a good compromise between the various requirements mentioned above.

[0004] The construction of engines with more than four valves per cylinder would lead to a further reduction of the weight and/or an increase of the total cross section area of the valves. Such a construction however conflicts with the problem of the design of the valve operating device. Indeed, in the case of engines with four valves per cylinder control of the valves in groups of two for intake and two for exhaust can be realized simply by using two camshafts each of which drives two exhaust or two intake valves arranged with the stems parallel, the latter condition making it possible to realize a combustion chamber with optimal shape for engine performance. But if an engine is to be built with more valves, e.g. three intake and two exhaust and it is desired to maintain simplicity of construction and reliability in controlling the intake and exhaust valves with a single camshaft, the three intake valves must be arranged with at least one of them having the stem out of parallel with the other two so as to bring the upper parts of said stems all on the same axis and thus capable of being driven by a single camshaft, since it would be impossible to arrange the three valves on the same axis directly because of lack of space and also due to the design of the combustion chamber. A similar problem arises if it is desired to build an engine with more than two exhaust valves. All this involves a reduction in the designer's freedom of choice regarding the form of the combustion chamber and consequently leads in the end to a reduction in the engine's performance compared with the performance theoretically possible.

[0005] The general purpose of the present invention is to avoid the drawbacks mentioned above by a device for controlling the valves of an internal combustion engine which would provide control of the valves in a simple manner if they are more than two in number for exhaust and/or similarly more than two for intake, by means of a single camshaft for each group of intake of exhaust valves and with the axes of the valves of each of said groups mutually parallel to permit design of a combustion chamber with optimal characteristics.

[0006] To achieve said purpose in accordance with the invention it was thought to design a device for the control of the valves of internal combustion engines of the type placing in each cylinder two groups of valves, one group for intake and one group for exhaust, each controlled by a single camshaft characterized in that said camshaft controls directly through an interposed guide socket the intake or exhaust valves aligned thereunder and through a "finger-type" rocker arm those outside of said alignment.

[0007] To make clearer the explanation of the present invention and its advantages compared with the known art reference is now made to the annexed drawings in which is shown schematically a possible application of the principles of the invention to a five-valve engine. In the drawings:

FIG. 1 represents schematically the top view of a possible arrangement of five valves on one cylinder,

FIG. 2 shows a schematic side view of a valve control device arranged as in FIG. 1, and

FIG. 3 represents a schematic top view of the control device of the valves shown in FIG. 2.

[0008] With reference to the figures the device which will now be described is an example of a possible application of the principles of the present invention to an engine having five valves per cylinder divided in three intake valves 10 and two exhaust valves 11. As shown in FIG. 1, to secure a good combustion chamber and good coefficients of efflux, which are linked with filling, the five valves are arranged symmetrically on the cylinder 12 with regard to the axis of said cylinder and equidistant therefrom. As may be seen in FIG. 2 the exhaust valves 11, which are arranged with their stems 13 parallel, are controlled, each through a guide socket 14, by a single camshaft 15, while the intake valves 10, which are also parallel with their stems 16, are controlled by a second camshaft 17. The two intake valves 10 most distant from each other are each controlled directly through a guide socket by lateral cams 19 of said shaft 17 while the central intake valve 10 is controlled through a "finger" rocker arm 20 which is pivoted at one of its ends by means of a ball pin 21 to a part 22 integral with the cylinder 12 while its other end 23 rests on the free end of the stem 16 of said central valve. Said "finger" rocker arm 20, which is placed in the space between the two guide sockets 18 (as may be seen clearly in FIG. 3) is in turn controlled by another cam 24 of the camshaft 17 placed centrally with respect to the two side cams 19 of said shaft which controls the intake valves 10 most distant from one another. Said other cam 24 has lift reduced by a certain ratio rho with respect to the two laterals 19 while the "finger" rocker arm 23 achieves a transmission ratio of 1/rho in such a manner as to cause the central intake valve to open and close in unison and with the same amplitude of movement as the two lateral intake valves.

[0009] According to the innovative principles of the invention there is thus secured with extreme simplicity (in practice adding a single "finger" rocker arm) the advantage of being able to arrange the valves in the best positions by freeing them from the severe limitation of alignment with the respective controlling camshaft. Naturally the above construction example has been described here only as an example of the innovative principles of the invention and is to be so considered. Indeed said principles can be applied not only to the intake valves but also to the exhaust valves, constructing for example an engine with six valves per cylinder or indeed an engine with any number of intake and exhaust valves for each cylinder wherein those with homologous operation and arranged on the same axis are controlled directly by one camshaft while the others, with the same function but outside of said axis, are controlled by "finger" rocker arms arranged for example as described above.

[0010] Whatever the number of valves selected the advantages of the application of the principles of the present invention are substantial, it being possible to control all the valves having homologous operation by a single camshaft while at the same time it is possible to arrange the valves on an ideal circumference concentric with the cylinder and with a relative orientation at will (in particular valves having homologous operation with the axes mutually parallel) securing the advantage of being able to make chambers with optimal shape for combustion quality but also facilitating the solution of construction problems. Furthermore it is possible to use guide sockets of normal dimensions for the valves controlled directly by the camshaft since the "finger" rocker arm occupies little transverse space and, allowing considerable design freedom, can be inserted in the space between said guide sockets to reach the valves to be controlled.

Claims

1. A control device for valves for internal combustion engines of the type comprising in each cylinder (12) two groups of valves, one for intake (10) and one for exhaust (11), each controlled by a single camshaft (17, 15) characterized in that said camshaft (17, 15) controls directly through an interposed guide socket (18, 14) the valves aligned thereunder and through a "finger" rocker arm (20) those outside said alignment.

2. A device in accordance with claim 1 characterized in that said valves (10, 11) are arranged on a circumference concentric with the combustion chamber of said cylinder (12).

3. A device in accordance with claim 1 or 2 characterized in that the stems (16, 13) of the valves of each one of the two said groups (10, 11) are parallel.

4. A device in accordance with any of the above claims characterized in that at least one of said "finger" rocker arms (20) is inserted in the space between two of said guide sockets (18).

5. A device in accordance with any one of the above claims characterized in that the lift of the cam (19) of said camshaft (17) directly controlling said valves (10) differs from that of the cams (24) controlling said "finger" rocker arms in a relationship equal to the transmission relationship of said 'finger" rocker arm (20).

Drawing