FR3024061A1 - METHOD AND PRESS FOR SIMULTANEOUSLY FREQUENCING VALVE SEATS IN A MOTOR VEHICLE MOTOR CYLINDER HEAD - Google Patents

Abstract

The invention relates to a method and a simultaneous hooping press of at least two valve seats (1), each seat (1) being pressed in abutment in a respective housing of a motor cylinder head by a nose (5). with a support (4, 4a) for each seat (1), the support (4, 4a) having a bearing area (6a) on the seat (1) running under the action of the nose (5). ), characterized by a relative freedom of movement in the stroke of the bearing areas (6a) relative to each other or to each other so that when a seat (1) abuts in its housing, the pressing force is transferred to the other supports (4, 4a) and so on until the last seat (1) associated abuts. Application in the field of motor vehicles.

Description

The present invention relates to a process for simultaneous shrinking of the valve seats in a motor vehicle engine cylinder head as well as the press for the implementation of the invention. BACKGROUND OF THE INVENTION of the process. [0002] The guides and the valve seats are most often hooped in a bore previously precisely machined in the body of the cylinder head of an internal combustion engine, the hooping having for mission, on the one hand, to ensure good heat transfer to the walls of the cylinder head and, secondly, to ensure the proper positioning of guides and seats to ensure proper operation of the distribution. The establishment is generally provided with a press to exert the necessary force to the fitting, assisted in some cases by prior cooling of the seats and / or liquid nitrogen guides and / or a preheating of the breech for cases where hooping is important. For reasons of productivity and also space, especially with the generalization of cylinder heads with four valves per cylinder, it is often used a press that simultaneously moves several seats at a time. In this pressing process, it is very important to ensure that each seat is well plated on the bottom of its housing, otherwise there is a risk that during operation the combination of differential expansions between seat and cylinder head and the repeated forces of the valve falling on its seat do not cause a migration of the seat to the bottom of its housing when it was not plated correctly during the initial assembly of the cylinder head. Thus, a good operation of the distribution requires to ensure precise positioning of the parts between them if we want both to respect at best the law of lifting of a valve dictated by the cam law and reduce the noise in operation while ensuring the minimum clearance necessary to ensure the proper closing of the valve whatever the engine temperature conditions and anticipate any wear on the seats between seat and valve. Thus, it is conventional to adopt a cold clearance of the order of 0.10 to 0.25 mm with a tolerance of ± 0.05 mm or to use a hydraulic retrofit device which avoids the adjustment operation. [000s] It is easy to see that it is imperative to guarantee that, during the operation of fitting the seats, the latter have been pushed fully into their housing, otherwise there is a risk that in operation, under the combined action of the differential expansion between the aluminum of the cylinder head and the seat steel and the repeated axial force related to the closing of the valve on its seat, the seat does not end up filling the game that remained between seat and housing fund. This would cause functional clearance to be canceled with a significant risk of valve leakage and rapid deterioration of its range resulting in loss of compression. When the spacing between the various valves is sufficient to implement an individual press piston for each station, it is easy to ensure correct plating of each guide by adjusting a final level of sufficient effort to ensure 15 fitting even in the case of the maximum dispersions of the parts involved in the hooping, combined with a control of the race which ensures that the seat is at the bottom of the housing and that it has not seized during the journey. However, in the case of a low center distance, it is not always possible to implement two contiguous press heads and it is then necessary to fit two seats with one and the same press. [001 0] If the seat has not been correctly plated, during the initial assembly of the cylinder head, there may be a risk of loss of the functional clearance between pusher or rocker and valve if the distribution has no catch-up hydraulic or if the migration exceeds the hydraulic catch-up range. This results in a loss of tightness of the valve, the consequences of which are a loss of performance, a significant risk of merging of the range on the valve or even of no starting of the engine. [001 1] Therefore, the problem underlying the invention is to ensure, during a process of hooping in parallel of several valve seats, each seat to abut in a respective housing of a cylinder head. a motor vehicle engine, that each of the valve seats is systematically in effective support at the bottom of its housing at the end of the hooping process. To achieve this objective, it is provided according to the invention a simultaneous hooping process of at least two valve seats, each seat being pressed in abutment in a respective housing of a motor vehicle engine cylinder head by a press nose having a support for each seat, the support having a bearing area on the seat performing a stroke under the action of the press nose, characterized by a relative freedom of movement in the stroke of the zones of support relative to each other so that, when a seat abuts in its housing, the pressing force is transferred to the other supports and so on until that the last associated seat is at the bottom of his dwelling. The technical effect is to carry out a press frettage by ensuring that each of the valve seats is always supported at the bottom of its housing. This is achieved by a differential stroke between the different media installed on the press. This has been made possible by integrating advantageously at each support installed on the press a hydraulic device for individualizing the movement at each of the valve seats to fret. Advantageously, the pressing force is reported by a hydraulic system common to all the supports with an internal hydraulic pressure to the system 15 increasing proportionally to the rise of the pressing forces, a seat arriving in abutment at the bottom of its housing causing a depression of its support zone in the press nose and stopping of its descent while the support zones of the other supports continue their descent until all the seats arrive in abutment. [0015] Advantageously, the hydraulic system is purged prior to its operation, the bearing zones being towards the half-way position of their support at the beginning of the hooping process. The invention also relates to a press for the implementation of such a hooping process having a press nose transmitting a pressure to the supports of a respective seat, characterized in that each support comprises a cylinder in which A piston is movable, the piston carrying the bearing zone on the associated seat, the cylinders of the supports being connected by a hydraulic circuit connected to the nose ensuring at all times an equal internal hydraulic pressure between the supports. Thus, it is integrated with each support a hydraulic system equivalent to a hydraulic lifter device, passive type, which in general is not very demanding in space, little subject to wear and ensures a good equality of effort between the different media. [0018] Advantageously, the hydraulic circuit opens into each cylinder by a grooves system with seals providing a sealed connection between each cylinder and the hydraulic circuit outside the cylinders. Advantageously, the hydraulic circuit comprises a portion housed in the nose 5 press, channels from the cylinder of each support. Advantageously, each channel serves as purge circuit of the hydraulic circuit. Advantageously, the seal between piston and cylinder is provided for each piston by an O-ring seal groove. [0022] Advantageously, each support is in the form of a base containing the cylinder in its interior. Advantageously, a threaded closure ring is disposed on the base for its closure. Other features, objects and advantages of the present invention will appear on reading the detailed description which follows and with reference to the accompanying drawings given by way of non-limiting examples and in which: FIG. a diagrammatic representation of a longitudinal section of a hooping press with the fretted valve seats positioned on the press, the press being according to the state of the art; - FIG. 2 is a schematic representation of a longitudinal section; of a frettage press with the fretted seats positioned on the press, the press being according to the present invention; - Figure 3 is a diagrammatic representation of a longitudinal section of a shrink press support with the seat to FIG. 4 is a diagrammatic representation of a top view of a portion of a pressurized portion of a press according to the present invention; FIG. A shrink press according to the present invention with a seat positioned on the press; FIG. 5 is a diagrammatic representation of an exploded view of the various elements of a support forming part of a press according to the present invention. It should be borne in mind that the figures are given by way of example and are not limiting of the invention. They are schematic representations of principle intended to facilitate the understanding of the invention and are not necessarily at the scale of practical applications. In particular, the dimensions of the various elements illustrated are not representative of reality. Figure 1 shows a hooping press according to the state of the art. In this figure, it is shown a press for the implementation of a simultaneous hooping process of at least two valve seats 1. It may be that the valve seat 1 is coupled with a guide during pressing but this is not mandatory. This is also valid for a press according to the present invention. Each seat 1 is pressed in abutment in a respective housing of a motor vehicle engine cylinder head by a press nose 5 having a support 3, 10 3a or tip for each seat 1. The support 3, 3a presents a bearing zone on the seat 1 running under the action of the nose 5 press. Each support 3, 3a can be fixed to the press nose 5 by an insert 10, 10a respectively. According to this state of the art, the press nose 5 is rigid, that is to say that there is no device in the press that ensures that each of the 15 seats 1 is systematically in support of the bottom of its housing, that is to say allow a differential stroke between the two supports 3, 3a installed on the press. Comparing FIG. 2 of a press according to the present invention with the press of the state of the art shown in FIG. 1, in the hooping method according to the invention of at least two valve seats 1, there is relative freedom of movement in the course of the bearing areas of the supports 4, 4a with respect to each other, when there are only two supports 4, 4a or with respect to each other when there are more than two supports. Thus, when a seat 1 is in abutment in its housing for a support 4, 4a respectively, the pressing force is transferred to the other supports 4, 4a and so on 25 until the last seat 1 associated is in abutment at the bottom of its housing, the relative freedom of movement being obtained hydraulically. In Figure 2, it is shown two supports 4, 4a which is not limiting, this number of support 4, 4a can be higher. In practice, the seat 1 can be held by retractable balls housed in the support 4, 4a. According to one embodiment of the present invention, the pressing force is transferred by a hydraulic system common to all the supports 4, 4a with a hydraulic pressure internal to the system increasing proportionally to the rise of the forces of the invention. pressing. Advantageously, the hydraulic system can be purged prior to its operation, the bearing zones being approximately halfway through their support 4, 4a. When a valve seat 1 reaches the abutment at the bottom of its housing, this causes a depression of its support zone 6a in the nose 5 of press and the stop of its descent while the bearing zones 6a other supports 4, 4a continue their descent until all the seats 1 arrive in abutment. The support zones of which one associated with a support is referenced 6a in FIG. 5 are carried directly or indirectly by a piston 6. [0035] Such a hydraulic system can be likened to a hydraulic lifting device. The contribution of an embodiment of the present invention to the state of the art consists in replacing each of the two rigid seat supports 3, 3a installed at the nose 5 of the press, as shown in FIG. cylinder / piston assemblies associated with a hydraulic connection ensuring at all times an equal internal pressure between the two supports 4, 4a, as for example shown in FIG. 2. [0036] Referring to FIGS. 2 to 5, a press for the implementation of a hooping process with a press nose 5 transmitting a pressure to the supports 4, 4a of a respective valve seat 1 has each of its support 4, 4a comprising a cylinder 7 in which is movable a piston 6. It is this piston 6 which forms the bearing zone against the associated seat 1. The cylinders 7 of the supports 4, 4a are connected by a hydraulic circuit 8 connected to the press nose 5 ensuring at all times an equal internal hydraulic pressure between the supports 4, 4a. A portion of the supports 4, 4a, namely the respective piston 6, is therefore movable relative to the pressing nose 5. In an embodiment according to the present invention, when the press is at rest, the internal hydraulic pressure in the hydraulic circuit 8 is zero taking as zero reference the atmospheric pressure. When the press is in action, the internal hydraulic pressure in the hydraulic circuit increases in proportion to the rise in the fitting forces of the valve seats 1 into their housing. When one of the two seats 1 comes into abutment against its seat, the movement of the piston 6 of the support 4, 4a associated with the seat stops and the other piston, in Figure 2, continues its course at a double speed of the descent of the press nose 5 until reaching in turn its stop. At this time, the internal hydraulic pressure will reach its maximum, corresponding to the maximum force setting of the press relative to the sum of the section of the pistons 6 of the seat supports 1. [0039] This is valid for a number of supports 4, 4a greater than two. However, in which case, the speed is not doubled but increased according to the number of pistons 6 continuing their race. As can be seen in FIG. 3, the hydraulic circuit 8 can open into each cylinder 7 by a groove system 9 with sealing seals providing a tight connection between each cylinder 7 and the external hydraulic circuit 8. 7. As can be seen in FIGS. 2 and 4, the hydraulic circuit 8 can comprise a portion housed in the press nose 5 common to all the supports 4, 4a, channels 12, 12a starting from the cylinder 7 of each support 4, 4a to join the common portion of the hydraulic circuit 8. The channels 12, 12a of the support 4, 4a can advantageously pass through the insert 10, 10a of the support 4, 4a. Referring again to all Figures 2 to 5, on the one hand, it is appropriate, during the preparation of the tooling to ensure a perfect purge of the hydraulic system to avoid any air buffer that would decrease the stroke by compression of trapped air. Each channel 12, 12a can serve as purge circuit of the hydraulic circuit 8 and in particular of the inside of the cylinder 7 of each support 4, 4a. On the other hand, it should be ascertained that, when the purge is carried out, all the pistons 6 are situated substantially in the middle of their stroke so as to guarantee that the hydraulic system is capable of compensating the dispersions races that will be necessary to ensure the abutment on all media 4, 4a of the press. This race dispersion will be essentially related to the dispersions of housing machining depth and thickness between the seats 1 of the valve. The seal between the piston 6 and the cylinder 7 is ensured for each piston 6 by a sealing groove for an O-ring. As can be seen more particularly in Figures 2 and 5, each support 4, 4a may comprise a base 13 comprising inside the cylinder 7. A threaded closure ring 11 may be arranged on the base 7 for its closure. The main advantage of the present invention is to ensure a good plating of the valve seats in their housing in the cylinder head and thus to eliminate the losses of functional games related to a subsequent migration of the seat in operation. This allows a relaxation of the tolerances of machining depth of the housing and height tolerances of the seats before fitting, so a preparation work less demanding housing and reduced, to the extent that the final machining 10 of the scope the seat is always made after fitting and will compensate for these dispersions. The invention is not limited to the described and illustrated embodiments which have been given only as examples.

Claims (10)

REVENDICATIONS1. Method for simultaneous shrinking of at least two valve seats (1), each seat (1) being pressed in abutment in a respective housing of a motor vehicle engine cylinder head by a press nose (5) having a support (4, 4a) for each seat (1), the support (4, 4a) having a bearing zone (6a) on the seat (1) running under the action of the press nose (5), characterized by a relative freedom of movement in the path of the bearing zones (6a) relative to each other or to each other so that when a seat (1) abuts in its housing, the pressing force is transferred to the other supports (4, 4a) and so on until the last seat (1) associated is in abutment at the bottom of its housing. 2. Method according to claim 1, wherein the pressing force is transferred by a hydraulic system common to all the supports (4, 4a) with an internal hydraulic pressure to the system increasing in proportion to the rise in pressing forces, a seat (1) reaching a stop at the bottom of its housing causing a depression of its bearing zone (6a) in the nose (5) press and the stop of its descent while the bearing zones (6a) of the others supports (4, 4a) continue their descent until all the seats (1) come to a stop. 3. Method according to claim 2, wherein the hydraulic system is purged prior to its operation, the bearing zones (6a) being towards the half-stroke position of their support (4, 4a) at the beginning of the hooping process. . 4. Press for implementing a hooping method according to any one of claims 1 to 3, having a nose (5) press transmitting a pressure to the supports (4, 4a) of a seat (1 ), characterized in that each support (4, 4a) comprises a cylinder (7) in which is movable a piston (6), the piston (6) carrying the bearing zone (6a) on the seat (1) associated, the cylinders (7) of the supports (4, 4a) being connected by a hydraulic circuit (8) connected to the nose (5) ensuring at all times an equal internal hydraulic pressure between the supports (4, 4a). 5. Press according to claim 4, wherein the hydraulic circuit (8) opens into each cylinder (7) by a system of grooves (9) with seals providing a sealed connection between each cylinder (7) and the hydraulic circuit (8) outside the cylinders (7). 3024061 10 6. Press according to claim 4 or 5, wherein the hydraulic circuit (8) comprises a portion housed in the nose (5) press, channels (12, 12a) from the cylinder (7) of each support (4, 4a). The press of claim 6, wherein each channel (12, 12a) serves as a purge circuit of the hydraulic circuit (8). 8. Press according to any one of claims 4 to 7, wherein the seal between piston (6) and cylinder (7) is provided for each piston (6) by an O-ring sealing groove. Press according to claim 8, wherein each support (4, 4a) is in the form of a base (13) containing the cylinder (7) in its interior. 10. Press according to claim 9, wherein a threaded closure ring (11) is disposed on the base (7) for closing.