EP0505231B1 - Hydraulic control for variable amplitude lift mechanism of at least one internal combustion engine valve - Google Patents

Description

The present invention relates to a valve lifting mechanism with amplitude or variable opening law, for example for an internal combustion engine, and relates more particularly to a hydraulic control device for such a mechanism.

Particularly known from document EP-A-0462853, which belongs to the state of the art referred to in Article 54 (3) EPC, mechanisms for lifting at least one intake or exhaust for internal combustion engine, in which a control device acts on a movable articulation pivot of at least one latch to vary the amplitude of the lift and / or the valve opening law.

In these applications, a valve lifting mechanism has more particularly been described in which at least one latch, articulated on at least one pivot and displaceable by means of a cam, causes the valve lifting when it moves, at least a pivot being fixed and a pivot being mobile, under the effect of the control device between two positions called active and rest respectively, the valve being alternately actuated by a latch articulated on a fixed pivot according to the so-called rest position of the movable pivot and by a latch articulated on the movable pivot according to its active position, so as to vary the amplitude of the lifting by changing the position of the movable pivot.

Generally, the control devices comprise a control shaft on which are provided cams whose rotation causes the displacement of the movable pivot between its rest position and its active position.

On the other hand, document EP-A-405 927 describes a device corresponding to the preamble of claim 1, with at least two catches.

The object of the invention is to propose a new control device for a valve lifting mechanism by means of which it is possible to reduce the number and the mass of the moving parts, as well as to obtain a greater amplitude variation of the valve lift.

To this end, the subject of the invention is a device for controlling the lifting mechanism of at least one valve in which at least two catches, each of which is articulated on a pivot and cooperates with a cam to cause the valve to be lifted, at at least one pivot being mobile under the effect of the device between two respectively active and rest positions, characterized in that, the valve being alternately actuated by a latch articulated on a fixed pivot according to the rest position of the movable pivot and by a latch articulated on the movable pivot according to its so-called active position, so as to vary the amplitude of the lift by changing the position of the movable pivot, the movable pivot is secured to a sliding support in a fixed body, a locking finger mounted sliding in a transverse bore of the support coming into the active position with regard to a bore of the same diameter formed in the fixed body and a sliding piston housed in the bore of the fixed body that can be pushed hydraulically to move the finger until it engages in the bore of the fixed body, thereby locking the support in the active position of the pivot.

Advantageously, an elastic member is housed in the bore of the fixed body, and exerts on the finger in the active position a force opposite to the pushing of the piston, so that at the interruption of the pushing, the finger and the piston are returned to a position which allows the support of the movable pivot to slide.

In addition, it is possible that each latch is constantly kept in contact with its respective cam by means of return members.

In this case, one of the abovementioned return means consists of at least one spring disposed between the fixed body and the sliding support so as to urge the latch articulated on the movable pivot against the corresponding cam.

Preferably, at least one of the return members is constituted by a spring fixed on the one hand to the pawl and on the other hand to a fixed part for pressing the pawl against the corresponding cam.

In addition, the device comprises means for adjusting the clearance of each latch.

Then the adjustment means consist of pellets of appropriate thickness, arranged between the latch and a valve and by locknuts respectively mounted on the threaded rod of each of the fixed pivots.

It is advantageous that the pivot pins of the latches are mounted on the fixed body, the movable pivot being constituted by a shaft with an axis substantially parallel to the above-mentioned bores and housed in a boss integrated in the sliding support.

It is also possible that recesses are formed on at least one moving part such as the sliding support and the latches.

However, other advantages and particularities of the invention will emerge more clearly from the detailed description of an embodiment given only to As an example, which follows and refers to the accompanying drawings, in which.

Figure 1 is a sectional view along a plane perpendicular to the camshaft, of an internal combustion engine cylinder head equipped with the valve lift amplitude variation control device according to the invention.

FIG. 2 is a partial and simplified view according to arrow II in FIG. 1.

FIG. 3 is a view similar to FIG. 1, in section along the line III-III of FIG. 2.

Figure 4 is a schematic perspective view of a lifting mechanism of two valves, equipped with the device according to the invention and shown with the movable pivot in the rest position.

Figure 5 is a partial section along the line V-V of Figure 2, with the support of the movable pivot in the rest position.

Figure 6 is a view similar to Figure 4 with the movable pivot in the active position.

Figure 7 is a view similar to Figure 5 with the movable pivot support in the active position.

With particular reference to FIG. 1, it can be seen that a cylinder head 1 of an internal combustion engine comprises a duct 100, for example of intake or exhaust.

A valve 2 is slidably mounted in a guide barrel 3 fixed on the cylinder head 1. A cup 4 is fixed on the rod 2a of the valve 2 and a spring helical 6 is mounted between the cylinder head 1 and this cup 4 so as to permanently urge the valve 2 towards its closed position of the conduit 100, that is to say with its head 2c in sealed support against a valve seat 110 of cylinder head 1.

There is shown in Figures 4 and 6 a variable amplitude lifting mechanism which acts on two valves 2. The lifting mechanism consists of three lugs mounted pivoting relative to the cylinder head 1, and three cams integral with the same tree designated in 7.

Two straight lugs F are respectively mounted on pivots 13 and 14 fixed relative to the cylinder head 1. Each straight latch F is moved using a low profile cam B, during the rotation of the shaft 7.

A T-shaped central latch M is articulated on a pivot 15 movable relative to the cylinder head 1, and cooperates with a high profile cam H. The central latch M comprises a longitudinal part 35 which extends parallel to the lugs F and a transverse part 10 on which the latches F come to bear. A control device which will be described later makes it possible to move the movable pivot 15 between a so-called rest position (FIG. 4) and an active position (FIG. 6).

By virtue of this displacement of the pivot 15, the valves 2 are alternately actuated by the lugs F under the effect of the low cams B- and by means of the transverse part 10 of the latch M- when the movable pivot is in the rest position , and by the latch M under the effect of the high cam H when the movable pivot is in the active position. It is thus possible to vary the amplitude of the lifting of the valves 2 by changing the position of the movable pivot 15.

Before proceeding to the description of the control device, it should first of all be specified that the device according to the invention can be applied to most of the prior art variable valve lift mechanisms, and in particular to those described in the patent applications cited above. The content of these requests is integrated here by the reference therein, in order to simplify the description.

In the figures we see that in the control device according to the invention, the movable pivot 15 is mounted on a sliding support 50 which is itself housed in a guide groove 52 formed in a fixed body 51 and substantially orthogonal to the shaft 7. The fixed body 51 is immobilized on the cylinder head 1 using fixing screws V, such as that which is visible in FIG. 1.

A locking finger 60 is slidably mounted in a transverse bore 56 of the support 50. When the sliding support 50 is in the active or high position of the movable pivot 15 as shown in FIGS. 6 and 7, the transverse bore 56 comes to view a bore 66 of identical diameter formed in the fixed body 51. In this position, the bores 56 and 66 constitute a cylindrical recess passing right through the sliding support 50 and the fixed body 51. This cylindrical recess 56, 66 s extends in a direction substantially parallel to the axis of the camshaft 7. A sliding piston 61 is housed in the part of the bore 66 of the fixed body 51 which is located in line with the fixed pivot 14.

A pipe formed in the cylinder head 1 has been designated by the reference 40, which is connected to the cylindrical bore 66 via a pipe 41 produced by drilling in the fixed body 51. It can be seen in FIG. 1 that an O-ring 43 is disposed between the pipe 40 and the pipe 41 to seal between the cylinder head 1 and the fixed body 51. The pipes 40, 41 allow the connection of the bore 66 to a source of pressurized fluid such as oil. The reference 63 designates in FIGS. 5 and 7 a plate which is fixed to the fixed body 51 so as to close off the end of the bore 66 where the pipe 41 opens out. This plate 63 comprises a pin 64 projecting into the bore 66 and acting as a stop for the piston 61 when the support 50 is in the rest position of the movable pivot 15, shown in FIG. 5. The stop pin 64 makes it possible to prevent the piston 61 from closing off the pipe 41 The locking finger 60 has a length identical to the width of the sliding support 50. Thus, when the finger 60 is fully housed in the bore 56, the support 50 can freely slide from bottom to top, as shown by the arrows C in FIGS. 4 and 5. Furthermore, when the bore 56 is facing the bore 66 and that pressurized oil is supplied by the line 41, as indicated by the arrow A in FIG. 7, a hydraulic thrust moves the piston 61 and the d locking pin 60 to the left. For this purpose, the mounting of the piston 61 in the bore 66 must be carried out in a sealed manner. In the position shown in Figure 7, the finger 60 is engaged in the bore 66 and the piston 61 protrudes into the bore 56 of the sliding support 50. This gives a symmetrical locking of the support 50 which ensures good distribution of forces due to the action of the cam H on the latch M.

The reference numeral 55 designates an elastic member. The elastic member 55 is constituted by a helical spring housed in the part of the bore 66 which is opposite the piston 61. This elastic member 55 is disposed between a cylindrical pad 53 and a perforated washer 54. The perforated washer 54 is fixed in the bore 66 while the cylindrical pad 53 is slidably mounted therein. A guide rod 58 is fixed to the cylindrical pad 53 and extends coaxially to the bore 66 so as to pass through the opening of the perforated washer 54. When the support 50 is in the active position of the movable pivot 15, the member elastic 55 exerts via the cylindrical buffer 53 a force on the finger 60 which is opposite to the thrust exerted on the latter by the piston 61. Thus, as soon as the supply of pressurized oil is interrupted, the elastic member 55 pushes the locking finger 60 until the piston 61 abuts against the pin 64, to allow the support 50 to slide. Note in FIG. 7, that when the finger 60 is in the locking position of the support 50, the end of the guide rod 58 bears against the cylinder head 1, thus constituting a stop which makes it possible to immobilize the finger 60 and the piston 61 while ensuring the locking symmetry which has been explained above.

Each latch F and M is constantly maintained in contact with its respective cam B, H, by means of return members, which will now be described. The straight tabs F are kept in contact with the cams B using tension springs 70 and 71. The springs 70 and 71 are fixed on the one hand to the free end of each tab F and on the other hand to a fixed part secured to the cylinder head 1. More precisely, the upper ends of the springs 70 and 71 are hooked to a rod 72 each end of which is fixed to the cylinder head 1. The lower ends of the springs 70 and 71 are respectively hooked to lugs 70f and 71f. The 70f hooking lug is integrated into the latch F which is articulated on the fixed pivot 14, while the tab 71f is integrated into the latch F which is articulated on the fixed pivot 13. Thus, each latch F is constantly stressed in the direction of the arrows D visible in FIG. 6, to press against the corresponding cam B.

The catch M which is articulated on the movable pivot 15 is constantly kept in contact against the cam H by means of return means constituted by helical springs 73 and 74, arranged between the support 50 and the fixed body 51. As visible on the FIG. 3 in particular, the support 50 has substantially the shape of a T. The part corresponding to the vertical bar of the T is slidably housed in the guide groove 52 of the fixed body 51. The part corresponding to the transverse bar of the T is constituted by two support legs 59 perpendicular to the groove 52. The spring forming return means 73 is housed in a bore in the body 51 and projects from the upper face of the latter so as to come into abutment against the leg 59 which is in line with part 35 of the latch M. The spring 74 is housed in another bore of the fixed body 51 and bears by its upper end against the other tab 59 of the support 50. Thanks to this mounting, the springs orts 73 and 74 exert on the legs 59 of the support 50 a force oriented in the direction of the arrows C in FIG. 4, which urges the latch M against the corresponding cam H, by means of the movable pivot 15.

It will be understood that the springs 73 and 74 constantly stress the support 50 towards a position in which the locking finger 60 is facing the bore 66 of the fixed body 51. Thus when the back of the cam H is in contact with the latch M, the support 50 is automatically placed in the active position of the pivot 15. According to the example illustrated in FIG. 3, the pivot 15 is constituted by a shaft whose axis is substantially parallel to the axis 7 and to the bores 56,66. This shaft 15 is housed in a boss integrated into the support 50 and projecting from the latter between the tabs 59 described above.

It will also be noted here that all the pivots 13, 14 and 15 of articulation of the latches F and M are mounted on the fixed body 51, constituting with it, equipped with the support 50, the finger 60, the piston 61 and the springs 55, 73 and 74, a module assembled before mounting on the cylinder head. This covering several aligned cylinders of the engine, a single pipe 40 parallel to the shaft 7 supplies several modules respectively associated with each cylinder. The operating clearance of the latches F which are articulated on the fixed pivots 13 and 14 can be adjusted using adjustment means constituted by lock nuts 16 and 17, respectively. The locknuts 16 and 17 are mounted on the threaded rod by which the fixed pivots 13 and 14 are fixed on the body 51, and bear when tightened against the upper face of the fixed body 51. As shown in the figure 1, the adjustment of the clearance of the latches is also obtained by interposing pads 76 of appropriate thickness between the valve stem 2a and the transverse part 10 of the latches M.

As shown in Figures 1 and 2, there are provided on various moving parts of the recesses to reduce the moving masses. The sliding support and the latches F and M are hollowed out at E.

The operation of the control device which has just been described will now be briefly explained. When the engine operating conditions require a significant lifting of the valves 2, the pipe 40 of the cylinder head is put in communication with the source of pressurized oil. As soon as the bores 56 and 66 are facing one another, the finger 60 and the piston 61 are hydraulically pushed towards the locking position of the support 50 shown in FIG. 7, the oil under pressure reaching into the 'bore 66 of the fixed body 51. Then, since the pivot 15 is maintained in its active position, the high cam H acts on the latch M and causes a lifting of the valves 2 of large amplitude. Conversely, if it is preferable to obtain a valve lift of lesser amplitude, the hydraulic thrust exerted on the piston 61 is interrupted. Then, the sliding support 50 is unlocked by the spring 55, and as soon as the nose of the cam H comes into contact with the latch M, the movable pivot 15 and the sliding support 50 move as indicated in C in FIG. 5. Consequently, it is the low profile cams B which act on the catches F and cause via the transverse part 10 of the catcher M which is deactivated, a lifting of the valves whose amplitude is reduced. In other words, while the low profile cams B move the catches F and cause the valves 2 to lift, the high profile cam H exerts on the catcher M an effort which has the sole effect of sliding the support 50 against the stress exerted by the springs 73, 74.

As a variant, the respective profiles of cams B and H provide, in addition to or instead of different amplitudes, different durations of valve lift, so that the law of opening thereof varies according to whether the movable pivot is in active position or in rest position.

Consequently, a control device for a valve lifting mechanism has been produced, by means of which it is possible, compared with prior devices, to reduce the number and mass of the moving parts, as well as to obtain a greater variation in duration or amplitude of the valve lift.

The realization with pre-assembled modules allows a simplification of manufacture and assembly, providing reliability and low cost price of the mechanism.

It will also be specified here that the device according to the invention can also allow the lifting of a single valve, and that the lifting mechanism can comprise a number of catches other than three.

Claims (9)

1. Device for the control of a lifting mechanism of at least one valve, wherein at least two arms each one of which is pivoted onto a pivot and co-operates with a cam to cause the valve lift, at least one pivot being movable under the effect of the device between two active and rest positions, respectively, characterized in that, the valve being alternately actuated by an arm (F) pivoted onto a stationary pivot according to the rest position of the movable pivot and by an arm (M) pivoted onto the movable pivot (15) according to its so-called active position so as to vary the amplitude of the lift by changing the position of the movable pivot (15), the movable pivot (15) is made fast to a support (50) sliding in a stationary body (51), a locking finger (60), slidably mounted in a transverse bore (56) of the support (50) moving into an active position in front of a bore (66) of the same diameter formed in a stationary body (51) and a sliding piston (61) accommodated in the bore (66) of the stationary body being adapted to be hydraulically pushed to displace the finger (60) until its insertion into the bore (66) of the stationary body thereby locking the support (50) in the active position of the pivot (15).
2. Device according to claim 1, characterized in that an elastic member (55) is housed within the bore (66) of the stationary body (51) and exerts upon the finger (60) in the active position a force opposite to the thrust of the piston (61) so that upon the discontinuance of the thrust, the finger (60) and the piston (61) are urged back into a position which allows the support (50) of the movable pivot (15) to slide.
3. Device according to one of claims 1 or 2, characterized in that each arm (F, M) is constantly kept in contact with its respective cam (B, H) owing to return members (70, 71, 73, 74).
4. Device according to claim 3, characterized in that one of the aforesaid return means is constituted by at least one spring (73, 74) disposed between the stationary body (51) and the sliding support (50) so as to act upon the arm (M) pivoted onto the movable pivot (15) against the corresponding cam (H).
5. Device according to one of the claims 3 or 4, characterized in that at least one of the return members is constituted by a spring (70, 71) fastened on the one hand, to the arm (F) and on the other hand, to a stationary portion (72) for pressing the arm (F) onto the corresponding cam (B).
6. Device according to one of claims 1 to 5, characterized in that it comprises means (16, 17, 76) for adjusting the play of each arm (M, F).
7. Device according to claim 6, characterized in that the adjusting means are constituted by pads (76) of suitable thickness disposed between the arm (M) and a valve (2) and by check-nuts (16, 17) mounted onto the threaded shank of each one of the stationary pivots (13, 14).
8. Device according to one of claims 1 to 7, characterized in that the pivots (13, 14) for pivoting the arms (F) are mounted onto the stationary body (51), the movable pivot (15) being constituted by a shaft with an axis substantially parallel to the aforesaid bores (56, 66) and accommodated in a boss integrated into the sliding support (50).
9. Device according to one of the foregoing claims, characterized in that recesses are formed onto at least one movable part such as the sliding support (50) and the arms (F, M).

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