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(11) | EP 3 318 734 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | MECHANISM FOR ACTUATING ENGINE VALVES |
| (57) A mechanism for actuating engine cams comprising at least one camshaft (1) that includes
two cams (2 and 3) for each valve (8) to be actuated, and a rocker arm (9) is arranged
between said pair of cams and the valve which has two supports (10 and 11), which
rest in opposite directions on the cams (2 and 3).
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Field of the invention
[0001] The present invention relates to a mechanism for actuating engine valves, especially for actuating the inlet and outlet valves of an internal combustion engine, the mechanism of which includes at least one camshaft and a series of tilting rocker arms about a shaft that is parallel to the shaft of the camshaft.
[0002] The object of the invention is to provide a system for actuating engine valves, via a camshaft, which reduces the number of pieces necessary, between the camshaft and the valves to be actuated, in order to cause and control the movement of said valves.
Background of the invention
[0003] The camshaft is a mechanism that is used in internal combustion engines to control the opening and closing of the inlet and outlet valves and consists of a shaft on which several cams, as many as there are valves in the engine, are mechanised, each cam being intended to actuate one valve. The cams are mechanised on the shaft with the corresponding phase angle to open the different engine cylinders in accordance with the envisaged working order.
[0004] The characteristic common to the different types of camshafts is that the number of cams coincides with the number of engine valves.
[0005] Certain embodiments may have two camshafts, one for actuating the inlet valves and another for actuating the outlet valves.
[0006] Actuating the valves, from the corresponding cams, is carried out through a series of intermediate elements, such as rods, tappets, rocker arms and springs, which complicate both the mounting of the assembly and the operation and maintenance thereof.
Description of the invention
[0007] The aim of the present invention is to resolve the presented problems via an actuation mechanism made in such a way that it enables the intermediate components that are traditionally arranged between the camshaft and the engine valves, in order to actuate said valves, to be removed.
[0008] An object of the invention is to provide a mechanism that enables the opening and closing operations of the engine valves to be carried out with a single rocker arm per valve and without any of the other pieces that move between the camshaft and the valves, which enables the actuation of said valves to be carried out smoothly, noiselessly and without the need for adjustments.
[0009] The mechanism of the invention comprises at least one camshaft and series of rocker arms, one for each engine valve.
[0010] The camshaft comprises two cams for each valve to be actuated and a rocker arm to actuate the valve is arranged between each pair of cams and the valve to be actuated. This rocker arm has two supports, each one facing and resting on a cam, in opposite directions in both supports.
[0011] The two cams are positioned angularly with respect to one another on the camshaft such that when said camshaft rotates they are actuated alternately and in opposite directions on the two supports of the rocker arm, such that they cause the alternate tilting of said rocker arm and therefore moving the associated valve in the opening and closing directions.
[0012] The two cams of each pair of cams are angularly positioned with respect one another on the camshaft such that their actuation on the supports of the rocker arm is synchronised with the necessary opening and closing movements of the valve to be actuated.
[0013] In this way, in the actuation mechanism, the only mobile element between the camshaft and the valves to be actuated constitutes the rocker arm of each valve.
[0014] According to a preferred embodiment, the cams have a circular contour with different diameters, coaxial to the camshaft, the cam with the largest diameter having a peripheral hollow, the bottom of which coincides with the circular contour of the cam with the smallest diameter, whilst the cam with the smallest diameter has a peripheral projection, the top of which coincides with the circular contour of the cam with the largest diameter, the hollow and the projection being located in diametrically opposed positions and having a trajectory of equal length.
[0015] With this make-up in each 360 degree rotation of the camshaft, the two cams of each pair of cams responsible for actuating a valve act through the corresponding rocker arm and in a synchronised manner on said valve, in order to make it open and close, without the involvement of any other intermediate element.
[0016] The rocker arm may consist of a tilting lever that forms two supports on one side, each one facing one of the cams of each pair of cams responsible for actuating one valve and both supports being positioned such that they receive the actuation of the two cams in opposite directions. This lever may act directly on the valve to be actuated or through an auxiliary pin.
[0017] The invention may be applied to mechanisms that include one or two camshafts. In the first case, the single shaft moves the inlet and outlet valves, each one with a pair of cams and through a single rocker arm, and in the second case, one shaft for the inlet valves and another for the outlet valves, also with two cams and one rocker arm per valve.
[0018] The arrangement of the two cams per valve makes it possible for a single rocker arm to carry out the opening and closing movement of each valve, without any other intermediate element, which enables the mechanism of the invention to be mounted between cylinders with a small diameter.
[0019] Due to its simplicity, the mechanism of the invention does not require complicated mounting, adjustment and maintenance operations and its operation is smooth and noiseless.
[0020] The mechanism is arranged above the cylinder head and may be mounted and dismounted without having to dismount said cylinder head.
Brief description of the drawings
[0021] A non-limiting exemplary embodiment is schematically shown in the accompanying drawings, where:
Figure 1 is a partial front view of the camshaft, according to direction A of figure 2, with two cams for actuating one valve.
Figure 2 is a side view of the assembly of figure 1.
Figure 3 is a side view of a mechanism made according to the invention, which includes the camshaft of figures 1 and 2.
Figure 4 is a similar view to that of figure 3, showing a possible embodiment variant.
Detailed description of an embodiment
[0022] Figures 1 and 2 show the make-up of the camshaft that forms part of the mechanism of the invention.
[0023] In accordance with the invention, the camshaft (1) includes two cams (2 and 3) for each valve to be actuated. In the example represented, the cams (2 and 3) have a circular contour with different diameters. The cam (2) with the largest diameter has a peripheral hollow (4), the bottom (5) of which coincides with the circular contour of the cam (3) with the smallest diameter, for example along the length of a section (5). As for the cam (3) with the smallest diameter, it has a peripheral projection (6), the top of which coincides with the circular contour of the cam (2) with the largest diameter, for example along the length of a section (7). The peripheral hollow (4) has a trajectory or length equal to that of the peripheral projection (6) and the section (5) of the hollow (4) is also of equal length to that of the section (7) of the projection (6).
[0024] The hollow (4) and the projection (6) have angularly offset, diametrically opposed positions and have a trajectory of equal length.
[0025] Figure 3 shows a mechanism that includes the camshaft (1) of figures 1 and 2. This mechanism includes a rocker arm (9), between the pair of cams (2 and 3) and the valve to be actuated (8), which has two supports (10 and 11). The support (10) is facing and resting on the cam (2). As for the support (11), it is facing and resting on the cam (3), in the opposite direction to the support (10). The rocker arm (9) tilts about the shaft (12), located on the end of said rocker arm.
[0026] The rocker arm (9) may carry a pin (13) through which said cam is connected to the valve (8) to be actuated, in order to cause the movement thereof between the closing and opening positions.
[0027] With this make-up, when the camshaft (1) rotates in the direction of the arrow "D", from the position shown in figure 3, the projection (6) pushes and moves the support (11) in the direction of the arrow "C", sliding along the length of the section (15) until it reaches the top (7), forcing the cam (9) to rotate about the shaft (12) in the direction of the arrow "D", causing the actuation of the valve (8) in an opening or closing direction. At the same time, the support (10) slides through the profile of the hollow (4) until it reaches the bottom (5). By continuing to rotate the camshaft (1), the support (11) moves along the length of the top (7) of the projection (6) and the support (10) along the length of the bottom (5) of the hollow (4). Continuing the rotation of the camshaft (1), the support (10), when it slides over the upward section (16), is pushed and moved in the direction of the arrow "F", in the opposite direction to direction "C" that the support (11) was moved in, forcing the cam (9) to rotate about the shaft in the direction opposite to that of arrow "D", causing the actuation of valve (8) in the direction opposite that that which was mentioned above. At the same time, the support (11) moves downwards on the profile of the projection (6).
[0028] This cycle, wherein the supports (10 and 11) are moved alternately in opposite directions, in order to also actuate the valve (8) in opposite opening and closing directions, is generated in each 360 degree rotation of the camshaft.
[0029] The cams (2 and 3) are positioned angularly on the camshaft (1) such that the actuation thereof on the supports (10 and 11) is synchronised with the movement of the pin (13), which is required for the opening and closing of the valve (8), in the precise moments and periods for the operation of the engine.
[0030] The supports (10 and 11) may take the form of rollers that facilitate the movement on the cams (2 and 3).
[0031] Figure 4 shows an embodiment variant wherein the rocker arm (9) acts on the valve (8) from the free end (14) thereof, and the tilting shaft (12) is located at an intermediate point, this embodiment being especially intended for high cylinder capacity engines, whilst the embodiment of figure 3 is preferably intended for small cylinder capacity engines.
1. A mechanism for actuating engine valves comprising at least one camshaft (1) and a
series of rocker arms (9) that tilt about a shaft (12) parallel to the shaft of the
camshaft, characterised in that the camshaft (1) comprises two cams (2 and 3) for each valve (8) to be actuated and
a rocker (9) to actuate the valve is arranged between said two cams and the valve,
which has two supports (10 and 11), each one facing and resting on a cam, in opposite
directions; the two cams (2 and 3) of which are positioned angularly with respect
to one another on the camshaft (1) such that they act alternately and in opposite
directions on the supports (10 and 11) of the rocker arm (9), causing the alternate
tilting of said rocker arm and therefore the movement of the associated valve (8)
in the opening or closing direction.
2. The mechanism according to claim 1, characterised in that the two cams (2 and 3) have a circular contour with different diameters, the cam
(2) with the largest diameter having a peripheral hollow (4), the bottom (5) of which
coincides with the circular contour of the cam (3) with the smallest diameter, whilst
the cam with the smallest diameter (3) has a peripheral projection (6), the top (7)
of which coincides with the circular contour of the cam (2) with the largest diameter,
the hollow and projection of which are located in diametrically opposed positions
and having a trajectory of equal length.
3. The mechanism according to claim 1, characterised in that the rocker arm (9) acts on the valve (8) through an intermediate pin (12), located
between the supports (10 and 11) and the tilting shaft (12).
4. The mechanism according to claim 1, characterised in that the tilting point (12) of the rocker arm is located between the supports (10 and
11) and the actuation point (14) on the valve.