EP0097665B1 - Variable timing for four stroke engine - Google Patents

Abstract

A device for internal combustion engines, particularly car engines, allows to vary the opening duration and the lift of the timing valves. The variation results from the utilization of all or part of the profile of the alternating cam (9) of which the motion about the axis (14) is provided by the rotating leading cams (10, 11) by contact of the rollers (12) and is transmitted to the roller (8) which acutates with its shaft (13) the rocker arm (3) of the valve (6) returned by the spring (7). The adjustment is carried out by positioning the sprocket wheel (8) by means of the support arms (15) of the shaft (13) which are keyed to the control shaft (14) by means of pins (16).

Description

The present invention relates to a device for internal combustion engines which makes it possible to vary the opening time and the lifting of the dispensing valves.

Mechanical valve controls having these adjustment possibilities are the subject of patents but not of practical applications, because of certain major characteristics which are very limiting. For most of these mechanisms, in fact, the origin of the movement comes from a rod-crank system. The resulting drawbacks are highlighted by the schematic representation, given in FIG. 1 appended to the present application, of an embodiment of the state of the art, known from document FR-A-2472078. With reference to this FIG. 1, the variable opening of the valve 6, whose spring 7 ensures the return, is obtained by using all or part of the profile of the static cam 5 positioned for this purpose. The roller 4, actuated by the rod 1 of the crankshaft 2, and subjected to to and fro on the profile of the static cam 5, transmits the movement to the latch 3 actuating the valve 6. The amplitude of the reciprocating movement remaining constant, the extent of the useful part of the profile of the static cam 5 varies in the opposite direction to that of the neutral part. The laws of opening and closing of valve 6 are roughly symmetrical.

Drug. static 5 here occupies the position corresponding to the greatest duration of opening and lifting of the valve 6. The link 1, the roller 4, the latch 5, the valve 6 and the spring 7 determine, in the representation in solid line, the maximum lifting position of the valve 6, and, in dotted lines, the positions of opening start and end of closing of the valve 6.

The range of movement of the valve 6 is greater than 150 degrees, which represents, for a four-stroke engine where the shaft 2 rotates at half speed, a cam angle greater than 300 DV (DV: Degrees related to the crankshaft ; at the motor output shaft).

• AOA (Afance ouverture admission) : 45 DV
• RFA (Retard fermeture admission) : 75 DV.

Such a long valve opening time 6 is only used on sports engines, and may give rise, for example, to the following setting:

• AOA (Afance opening admission): 45 DV
• RFA (Admission closing delay): 75 DV.

It is therefore found that, even for a significant maximum opening time of the valve 6, less than half of the stroke of the crankshaft 2 is useful.

Also taking into account the constraints imposed by the realization of the profile of the static cam 5, the stroke of the crankshaft 2 as well as the amplitude of the corresponding reciprocating movement are too great and lead to an embodiment of which it is sufficient to analyze the excessive bulk for justify its unsuitability on modern engines known for their compactness.

• - des premiers moyens à came munis d'une came menante entraînée en rotation autour d'un premier axe de rotation, pour produire un mouvement primaire alternatif,
• - des seconds moyens à came munis d'une came alternative à laquelle le mouvement primaire est transmis de sorte que la came alternative produise un mouvement secondaire de levée de soupape, pour lever la soupape à l'encontre d'un ressort de rappel, et par l'intermédiaire d'au moins un organe d'actionnement de la soupape, du type poussoir, linguet, ou basculeur,
• - des moyens à galet interposés entre l'organe d'actionnement et un profil de la came alternative, et munis d'un galet en contact avec ledit profil, pour transmettre audit organe d'actionnement le mouvement secondaire que lesdits moyens à galet reçoivent de la came alternative, et
• - des moyens de commande permettant de faire coopérer le galet avec une partie plus ou moins importante du profil de la came alternative en provoquant un déplacement relatif entre ledit galet et ladite came alternative,
• - ladite came alternative étant une came oscillant autour d'un second axe de rotation et portant au moins un organe de contact, du type galet, qui est en contact avec ladite came menante pour transmettre ledit mouvement primaire de cette dernière à ladite came alternative.

On the other hand, document DE-A-2 629 554 discloses a valve control device for an internal combustion engine, making it possible to vary the opening and closing times as well as the lifting of at least a valve of an internal combustion engine, of the type comprising a kinematic chain which comprises:

• - first cam means provided with a driving cam driven in rotation about a first axis of rotation, to produce an alternative primary movement,
• - second cam means provided with an alternative cam to which the primary movement is transmitted so that the alternative cam produces a secondary valve lifting movement, in order to lift the valve against a return spring, and by means of at least one valve actuating member, of the pusher, latch, or rocker type,
• - roller means interposed between the actuating member and a profile of the reciprocating cam, and provided with a roller in contact with said profile, for transmitting to said actuating member the secondary movement that said roller means receive from the alternative cam, and
• control means making it possible to make the roller cooperate with a more or less significant part of the profile of the alternating cam by causing a relative displacement between said roller and said alternating cam,
• - Said alternative cam being a cam oscillating around a second axis of rotation and carrying at least one contact member, of the roller type, which is in contact with said driving cam to transmit said primary movement of the latter to said alternative cam.

In this known embodiment, the adjustment mode consists in off-centering a driving camshaft, so as to cause a relative rotation of the alternating cam relative to a latch acting on the valve.

The eccentricity of the driving camshaft is a means of adjustment which makes it impossible to use a single camshaft for intake and exhaust and which, above all, still leads to an embodiment which is much too bulky.

• - lesdits moyens à galet comprennent également un axe autour duquel ledit galet est monté rotatif, et ces moyens à galet ne sont en contact, d'une part, avec ledit profil de la came alternative que par ledit galet, qui roule sur ce profil et reçoit ledit mouvement secondaire de ladite came alternative, et, d'autre part, avec ledit organe d'actionnement que par ledit axe, qui glisse sur ledit organe d'actionnement et lui communique ledit mouvement secondaire, et
• - lesdits moyens de commande comprennent des organes de support qui se fixent en position réglable autour dudit second axe de rotation et qui présentent des rainures de guidage dans lesquelles ledit axe du galet est engagé et guidé par ses deux extrémités, de sorte que le changement de la position desdits organes de support, et donc du galet, autour dudit second axe de rotation provoque un changement de la position relative entre ledit galet et ladite came alternative, et fait ainsi varier la levée de soupape et ses instants d'ouverture et de fermeture.

The invention makes it possible in particular to eliminate these drawbacks and achieves this object with a valve control device of the type presented above, and which is characterized in that said first axis of rotation is fixed and said alternative primary movement is invariable for all adjustment ensured by the control means, and in that:

• said roller means also comprise an axis around which said roller is mounted to rotate, and these roller means are in contact, on the one hand, with said profile of the alternating cam only by said roller, which rolls on this profile and receives said secondary movement from said alternating cam, and, on the other hand, with said action member only by said axis, which slides on said actuating member and communicates said secondary movement to it, and
• - Said control means comprise support members which are fixed in adjustable position around said second axis of rotation and which have guide grooves in which said axis of the roller is engaged and guided by its two ends, so that the change of the position of said support members, and therefore of the roller, around said second axis of rotation causes a change in the relative position between said roller and said reciprocating cam, and thus varies the valve lift and its opening and closing instants .

The invariable laws of the back and forth of the reciprocating movement can be rigorously symmetrical or very distinct; it follows that the opening and closing phases of the valve are respectively symmetrical or clearly asymmetrical. For very short valve openings, it is desirable to limit the maximum valve lift in order to avoid considerable efforts in the distribution elements. However, from a sufficient valve opening time, it is possible to keep or very gradually change the maximum lift and essentially increase the range of movement.

The invention offers the greatest possible choice for the law of alternative primary movement, the minimized amplitude of which is entirely used by the alternative cam of the valve lifting movement during the longest opening time. This advantageous property results from the existence of the stop range of the reciprocating movement, corresponding to the neutral part of the rotating cam. The size of the device is thus reduced in large proportions.

Note also that the freedom left for the law of reciprocating movement greatly facilitates the tracing of the reciprocating cam of the secondary valve lift movement.

Finally, by maintaining the axis of rotation of a driving camshaft fixed, it is possible to control from this, the intake and exhaust valves and thus keep the small footprint of the distribution engines classic single overhead camshaft. The rotating driving cam, at the origin of the alternating and invariable primary movement, achieves a unilateral or bilateral connection.

In the case of a unilateral connection, formed by said first cam means, this unilateral connection is such that said driving cam pivots said alternative cam in a direction around said second axis of rotation, and at least one elastic member of said connection unilateral exerts an elastic restoring force tending to rotate said alternating cam in the other direction around said second axis of rotation. This or these elastic members, adapted to the various embodiments of the invention, is or are, depending on the case, of compression, traction, bending or torsion.

For the most universal embodiment, the driving cam takes the form of a disc cam.

In the case of a bilateral connection, formed by said first cam means, this bilateral connection is such that said driving cam pivots said alternative cam in a direction around said second axis of rotation, and this bilateral connection comprises a cam follower , integral in rotation with said driving cam about said first axis of rotation, and making said alternating cam pivot in the other direction around said second axis of rotation, by means of at least one contact member, of the roller type or pad, carried by said alternative cam and in contact with said cam follower.

The use for example of a grooved cam is to be avoided, in particular because of the machining disadvantages.

In an advantageous embodiment, the change of the relative position between said roller and said alternative cam is obtained by moving said guide grooves in a direction extending parallel to a neutral part of said profile of the alternative cam, and said axis of the roller is in contact, during the closing of said valve, with a part of said actuating member which has a profile in an arc of a circle concentric to said neutral part of said profile of the alternating cam.

Preferably, said axis of the roller has, at each of its two ends, two parallel flats engaged in the corresponding guide groove and in contact with this groove, which is straight and extends substantially radially with respect to said second axis of rotation, so as to laterally maintain said axis of the roller with respect to said control means. In addition, said valve actuating member advantageously has a U-shaped profile which laterally holds said roller, and preferably this actuating member is in contact with said roller axis on a contact zone of the latter which has a radius of curvature greater than that of said axis, outside of said contact zone. Advantageously, said axis of the roller is equipped with an anti-wear pad having, in its central part, a clearance allowing the passage of the roller which laterally holds said pad, the latter also having, at each of its two ends, two faces d support in the form of arcs of a circle coming into contact, one with a gutter formed in the axis of the roller to receive the corresponding end of the anti-wear pad, and the other against said actuating member, so that, during the lifting of the valve, two rotations occur simultaneously around the bearing faces, one in said gutter of the axis, and the other on said actuating member. Finally, it is possible that the actuating member of the valve comprises a gear, interposed between said roller means, which are remote from the valve, and a rocker which is close to the valve.

• la figure 1 est une représentation schématique d'une réalisation de l'état de la technique déjà prise en considération ci-dessus,
• la figure 2 correspond à une vue de droite d'un exemple de réalisation selon l'invention,
• la figure 3 représente une vue principale transversale de l'exemple de la figure 2,
• la figure 4 correspond à une vue de gauche de l'exemple de réalisation des figures 2 et 3,
• les figures 5 et 6 montrent un galet de réglage et son axe de rotation équipé d'un patin anti-usure, et destiné à être utilisé dans l'exemple de réalisation des figures 2 à 4, et
• la figure 7 représente schématiquement une variante de l'exemple de réalisation des figures 2 à 4.

Other advantages and characteristics of the invention will emerge from the description given below, without implied limitation, of an exemplary embodiment and of a variant, with reference to the appended drawings in which:

• FIG. 1 is a schematic representation of an embodiment of the state of the art already taken into consideration above,
• FIG. 2 corresponds to a right view of an exemplary embodiment according to the invention,
• FIG. 3 represents a main transverse view of the example of FIG. 2,
• FIG. 4 corresponds to a view on the left of the exemplary embodiment of FIGS. 2 and 3,
• FIGS. 5 and 6 show an adjustment roller and its axis of rotation equipped with an anti-wear pad, and intended to be used in the embodiment of FIGS. 2 to 4, and
• FIG. 7 schematically represents a variant of the exemplary embodiment of FIGS. 2 to 4.

In the embodiment of the invention shown in _" Figures 2, 3 and 4, the cam 9 of the valve lift movement 6 is driven, around the axis 14, of an alternating oscillating movement, resulting from the transformation of the movement leading from rotation of the disc cam 10 and of the disc cam follower 11. The contacts with the aforementioned disc cams 10-11 are made by means of pads with suitable profiles, as shown in 12 BIS in the figure. 7, or even rollers 12, as shown in FIG. 3, the rolling of which on the cams 10 ensures non-slip contact. The roller 8 receives the cam lifting movement 9 and transmits it by its axis 13, to the latch 3 actuating the valve 6. The neutral part of the alternating cam 9 as well as the top of the latch 3 in contact with the axis 13 of the roller 8, are arcs of circles whose centers coincide with the axis 14 during the closing of the valve 6. The U-shaped profile of the latch 3 maintains the n lateral of the roller 8. The adjustment is made by positioning the roller 8 differently by a rotation about the axis 14. Each law of the roller 8 corresponds to a law of movement of the valve 6.

In the present embodiment, the support arms 15 of the axis 13 of the roller 8 are made integral by "bicycle 16" keys to the control shaft 14. The valve 6 is shown in the constantly closed position, but during the upward movement. of the roller 8, the ends of the axis 13 describe the guide grooves 15a machined in the arms 15, generally radially with respect to the axis 14. The two parallel flats (the dishes 13b) produced at each end of the axis 13 in contact with the aforementioned grooves 15a, make the stresses negligible, and at the same time ensure the lateral retention of the axis 13. In order also to reduce the stresses in contact with the axis 13 and above the latch 3, it is possible in a conventional manner, to increase within certain limits the radius of curvature under the axis 13 at the aforementioned contact. From this point of view, the search for the best reliability by endurance tests has demonstrated the entirely satisfactory behavior of the variant of the axis 13 equipped with the anti-wear pad 17 and shown in FIGS. 5 and 6.

The elements 13 and 3, in contact with each face of the shoe 17, have the same radius of curvature as the latter. The shoe 17 therefore consists of two bearing faces 17a and 17b, in the form of arcs of circles, around which two rotations take place simultaneously during the lifting of the valve 6; one in the gutter 13a of the axis 13 and the other on the top of the latch 3. In its central part, the shoe 17 has a clearance necessary for the passage of the roller 8. This arrangement in the center provides lateral support of the shoe 17 via the roller 8.

In accordance with the usage in engines, the invention indifferently uses latches or rockers 3 (FIGS. 2 to 4) or rocker arms, such as the rocker arm in FIG. 7, to collect the reactions of the cams attacking the valves, and, moreover, references, such as the reference 18, as shown in FIG. 7, when it is a question of moving the camshaft 10, 11 away from the valves 6.

In fact, the variant shown diagrammatically in FIG. 7 is a variant in which the camshaft 10, 11 is located away from the valve 6 by means of a reference 18. In this variant, the reference 18 is placed downstream of the variation mechanism which, housed near the camshaft 10, 11, is therefore remote from the valve 6.

Claims (10)

1. Valve control device for an internal combustion engine, for varying the opening and closing moments as well as the lift of at least one valve (6) of an internal combustion engine, and comprising a kinematic chain including :

- first cam means having one driving cam (10) rotating around a first rotation axis for producing an alternating primary movement,

- second cam means having an alternating cam (9) to which the primary movement is transmitted so that the alternating cam (9) produces a valve lift secondary movement for lifting the valve (6) against the action of a return spring (7), with the help of at least one valve actuating member (3), like a push-rod, a lever or a rocker arm,

- roller means (8, 13) interposed between the actuating member (3) and a profile of the alternating cam (9), and having a roller (8) in contact with said profile, for transmitting to said actuating member (3) the secondary movement that said roller means receives from the alternating cam (9), and

- control means (14, 15, 16) allowing to cause the roller (8) to cooperate with a more or less important portion of the alternating cam profile (9) in providing a relative displacement between said roller (8) and said alternating cam (9),

- said alternating cam (9) being a cam oscillating around a second rotation axis (14) and bearing at least one contact member, like a roller (12) or a shoe (12 bis), which is in contact with said driving cam (10) for transmitting said primary movement from the latter to said alternating cam (9), characterized in that said first rotation axis is a fixed axis and said alternating primary movement is an invariable movement for any adjustment provided by the control means (14, 15, 16) and in that

- said roller means further comprises an axis (13) around which said roller (8) is rotatably mounted, and this roller means is in contact, on the one hand, with said alternating cam profile only by means of said roller (8), which rolls on this profile and receives said secondary movement from said alternating cam (9), and, on the other hand, with said actuating member (3) only by means of said axis (13) which slides on said actuating member (3) and communicates to it said secondary movement, and

- said control means includes support members (15) which are adjustably fastened around said-second rotation axis (14) and present guide grooves (15a) in which said roller axis (13) is engaged and guided by its two ends, so that the changing of the support members position, and thus the roller (8) position, around said second rotation axis (14) causes a changing of the relative position between said roller (8) and said alternating cam (9), and thus changes the valve (6) lift and the valve opening and closing moments.

2. Valve control device as in claim 1, characterized in that said first cam means is in the form of an unilateral linkage in which said driving cam (10) pivots said alternating cam (9) in one direction around said second rotation axis (14) and in which at least one resilient member produces an elastic return force tending to pivot said alternating cam (9) in the other direction around said second rotation axis (14).

3. Valve control device as in claim 1. characterized in that said first cam means is in the form of a bilateral linkage in which said driving cam (10) pivots said alternating cam (9) in one direction around said second rotation axis (14), and which comprises a return-cam (11), integral in rotation with said driving cam (10) around said first rotation axis, and pivoting said alternating cam (9) in the other direction around said second rotation axis (14), through at least one contact member, like a roller (12) or a shoe (12 bis), borne by said alternating cam and in contact with said return-cam (11).

4. Valve control device as in any of claims 1 to 3, characterized in that said changing of the relative position between said roller (8) and said alternating cam (9) is obtained by displacing said guide grooves (15a) in a direction extending parallel to a neutral portion of said alternating cam profile.

5. Valve control device as in claim 4, characterized in that said roller axis (13) is in contact, while said valve (6) is closing, with a portion of said actuating member (3) having a part circular profile which is concentric with said neutral portion of said alternating cam profile.

6. Valve control device as in any of claims 1 to 5, characterized in that said roller axis (13) presents at each of its two ends, two parallel flat surfaces (13b) engaged in the corresponding guide grooves (15a) and in contact with this groove, which is rectilinear and extends substantially radially with respect to said second rotation axis (14), so as to laterally maintain said roller axis (13) with respect to said control means.

7. Valve control device as in any of claims 1 to 6, characterized in that said valve actuating member (3) has a U-shapped profile which laterally maintains said roller (8).

8. Valve control device as in any of claims 1 to 7, characterized in that said actuating member (3) is in contact with said roller axis (13) along a zone of contact of the latter which has a radius of curvature greater than that of said axis (13) outside of said zone of contact.

9. Valve control device as in any of claims 1 to 8, characterized in that said roller axis (13) is equipped with an anti-wear shoe (17) having, in its central portion, a clearance allowing the roller (8) to pass so that said roller (8) laterally maintains said shoe (17), the latter having further, at each of its two ends, two bearing surfaces in the shape of arcs of cercle (17a, 17b), one of which (17b) engages a groove (13a) formed in the axis (13) of the roller (8) for receiving the corresponding end of the anti-wear shoe (17), and the other (17a) engages said actuating member (3), so that, during valve lift, two rotations take place simultaneously around the bearing surfaces (17a, 17b), one in said groove (13a) of the axis (13) and the other on said actuating member (3).

10. Valve control device as in any of claims 1 to 8, characterized in that the valve actuating member comprises a bell crank lever (18) interposed between said roller means (8, 13) which is away from said valve (6), and a rocker arm (20) which is close to the valve (6).

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