EP1239136A1 - Cylinder head for a combustion engine comprising an upper part forming a cylinder head cover carrying a camshaft - Google Patents

Abstract

The cylinder head (10), especially for a motor vehicle i.c. engine, consists of a main section that fits on top of the cylinder block and a cover (30). The main section has a cavity containing the valve actuating mechanism, and the cover carries the camshaft (18') between fixed (34a) and detachable (34b) bearing halves. The fixed bearing halves are made in the cylinder head cover and are designed to take all the forces to which the camshaft is subjected, the cover being in the form of a block with appropriate rigidity, and the detachable bearing halves fitted to its lower face by screws (36').

Description

The invention relates to a cylinder head of a heat engine, especially for a motor vehicle.

The invention relates more particularly to a cylinder head heat engine, in particular for a motor vehicle, comprising a main part, forming a cylinder head body, intended to be mounted on a cylinder block of the engine and comprising an upper part, forming a cylinder head cover, type in which the cylinder head has a recess which is intended to receive valve actuating elements from the motor and which opens into an upper face of the body cylinder head, to which the cylinder head cover, the elements valve actuation comprising a camshaft fixed to the by means of bearings each consisting substantially of one half fixed in the cylinder head and a half added in the form of a bearing cap.

In an internal combustion engine cylinder head, air / fuel mixture intake and exhaust burned are controlled by respective valves, actuated by a camshaft, i.e. a single camshaft, either by two camshafts.

In most recent production vehicles, the or the camshafts are mounted "at the head", that is to say the closest possible valves, so in the cylinder head.

Each camshaft is positioned and rotatably mounted in the cylinder head by means of plain bearings, generally in aluminum or aluminum alloy, each of which is made a half bearing, called a "fixed" half, formed directly in the cylinder head and completed by an attached bearing cap, or a part which incorporates this function, which should therefore be fixed on the cylinder head.

To provide the necessary lubrication between the shaft to cams, usually made of steel, and aluminum bearings, oil supply lines are practiced in the cylinder head, so as to lead to the right of the landings.

This results in a certain number of constraints for the design and construction of the cylinder head. In particular, the half-bearings "fixed" produced at the level of the cylinder head are obtained during of the manufacture thereof by molding. Therefore, their forms and their positions depend on the constraints of achieving the cylinder head, namely that it must present on the one hand adequate passages for the elements of the distribution, as well as passages for the cylinder head fixing screws on the cylinder block of the motor.

In particular, we seek to place the bearings of the shaft at cams as much as possible in the middle between two cylinders successive of the engine, but the cylinder head must also be fixed on the engine block precisely in the same region intermediate between the cylinders, so you have to plan practically in the same transverse plane of the cylinder head four or six vertical holes, two for fixing the cylinder head to the engine cylinder block and two or four for fixing the or bearing caps. This is not always possible.

In addition, taking into account the orientation of the half-bearings fixed in the cylinder head, almost all of the forces that develop between the camshaft and the valves are precisely directed in the opposite direction to these fixed half-bearings, so they have to be cashed in by the bearing caps reported. It should therefore be taken into account when designing and the realization of these bearing caps, as well as their fixing on the rest of the cylinder head.

In a very compact architecture, as is the case small displacement engines, the location of these half bearings fixed becomes an important problem, and we may have to opt for non-optimal technical solutions, whether cost, mass, or technical performance. As example, we may indeed have to choose a spacing, considered in the axial direction of the camshaft, more important as necessary between the landings, with the corollary that it will then necessary to make the camshaft more rigid, therefore more heavy and bulkier.

Another solution could consist in decoupling the half-bearings "fixed" from the rest of the cylinder head, but with for consequence which is added between the cylinder head and each half-bearing an interface, i.e. also operations of additional manufacturing, and it is then necessary to provide a tightness at this interface.

Finally, the numerous conduits, channels, recesses and holes thus formed in the cylinder head, and in particular in the cylinder head body, significantly reduce its rigidity, and it is therefore frequently necessary that the cylinder head cover fixed on the upper face of the cylinder head body has rigidity suitable for imparting to the assembly formed by the cylinder head body and the cylinder head cover sufficient rigidity. Attaching this cylinder head cover also requires corresponding tapped holes for fixing screws.

The object of the invention is therefore to propose a cylinder head in which the mounting of the camshaft, or camshafts, does not have the aforementioned drawbacks, without however increase the complexity of the realization of the cylinder head, nor increase production costs.

In accordance with the invention, this objective is achieved with a cylinder head of the type indicated in the introduction, characterized in that that said fixed bearing halves are made in the cylinder head cover.

• les moitiés fixes de paliers réalisées dans le couvre-culasse présentent une orientation propre à encaisser sensiblement la totalité des efforts subis en fonctionnement par l'arbre à cames ;
• le couvre-culasse est réalisé sous forme d'une poutre présentant une rigidité propre à compléter celle du corps de culasse ;
• la fixation des chapeaux de palier est effectuée sous la face inférieure du couvre-culasse qui est lui-même en appui sur la face supérieure du corps de culasse ;
• deux taraudages formés dans le couvre-culasse pour des vis de fixation d'un chapeau de palier et deux perçages formés dans le corps de culasse pour des vis de fixation de la culasse sont agencés sensiblement dans un même plan axial du moteur, entre deux cylindres de celui-ci ;
• l'arbre à cames comporte un perçage central pour la distribution de lubrifiant aux paliers de l'arbre à cames ;
• chaque chapeau de palier comporte des trous de passage pour des vis de fixation, et le couvre-culasse comporte des taraudages pour lesdites vis ;
• chaque chapeau de palier comporte un doigt de positionnement en saillie, qui vient se loger lors du montage dans un trou de forme correspondante dans la face inférieure de la poutre couvre-culasse.

According to other characteristics of the invention:

• the fixed halves of bearings made in the cylinder head cover have an orientation capable of absorbing substantially all of the forces undergone in operation by the camshaft;
• the cylinder head cover is made in the form of a beam having a rigidity capable of supplementing that of the cylinder head body;
• the fixing of the bearing caps is carried out under the lower face of the cylinder head cover which is itself in abutment on the upper face of the cylinder head body;
• two threads formed in the cylinder head cover for screws for fixing a bearing cap and two holes formed in the cylinder head body for screws for fixing the cylinder head are arranged substantially in the same axial plane of the engine, between two cylinders of it;
• the camshaft has a central bore for the distribution of lubricant to the bearings of the camshaft;
• each bearing cap has through holes for fixing screws, and the cylinder head cover has threads for said screws;
• each bearing cap has a projecting positioning finger, which is housed during mounting in a correspondingly shaped hole in the underside of the cylinder head cover beam.

• la figure 1 est une vue en coupe schématique fragmentaire, par un plan axial vertical parallèle aux axes des cylindres, d'une première culasse selon l'état de la technique ;
• la figure 2a est une vue en coupe d'une deuxième culasse selon l'état de la technique, prise suivant la ligne 2a-2a de la figure 2b ;
• la figure 2b est une vue en élévation partielle de dessus de la culasse de la figure 2a ;
• la figure 3a est une vue en coupe d'une culasse selon l'invention, prise suivant la ligne 3a-3a de la figure 3b, dans une représentation analogue à celle de la figure 2a ; et
• la figure 3b est une vue en élévation partielle de dessus de la culasse de la figure 3a.

Other characteristics and advantages of the invention will appear on reading the detailed description which follows, for the understanding of which reference will be made to the appended drawings, in which:

• Figure 1 is a fragmentary schematic sectional view, through a vertical axial plane parallel to the axes of the cylinders, of a first cylinder head according to the prior art;
• Figure 2a is a sectional view of a second cylinder head according to the prior art, taken along line 2a-2a of Figure 2b;
• Figure 2b is a partial elevation view from above of the cylinder head of Figure 2a;
• Figure 3a is a sectional view of a cylinder head according to the invention, taken along line 3a-3a of Figure 3b, in a representation similar to that of Figure 2a; and
• Figure 3b is a partial elevational view of the cylinder head of Figure 3a from above.

In all of the figures, we used the same references to designate identical or filling elements the same functions, if necessary accompanied by an index (a, b, etc.), or of the sign ['] (prime) or ["] (second).

In addition, in the present description, the expressions "vertical", "below", etc. refer to the orientation of the elements of a heat engine as shown in FIGS.

In Figure 1, we see a vertical section of a cylinder head according to the state of the art, comprising a main part or cylinder head body 10 whose lower face 12 is intended to be fixed on a cylinder block (not shown) of an engine thermal, which is therefore arranged below the cylinder head in the representation of figure 1.

In the lower region of the cylinder head body 10 are provided with intake (or exhaust) passages 14 intended for the flow of the admitted air / fuel mixture to the engine cylinders, or respectively to the gas flow burns which escape from the cylinders.

These passages 14 are controlled by valves 16, and these are actuated by at least one camshaft 18, of which we only see the cross section, which extends in the direction longitudinal of the motor, here perpendicular to the plane of the Fig. The camshaft 18 carries cams 20, only one of which is visible here, distributed along its length and each associated with one engine intake or exhaust valves 16.

As is well known, the profile of the cams 20 and their respective angular positions around the shaft 18 are chosen in the desired manner to obtain the temporal succession adequate valve openings / closings which correspond to the engine operating cycles (intake - compression - expansion - exhaust).

Cams 20 are only used to control the lowering movement of the valves 16, by pressing the valve stems 22 pointing upwards. The return of valves 16 up in the closed position is secured using springs 24 prisoners between the cylinder head body 10 and cups 26 fixed on the valve stems 22

The camshaft 18-20 is housed in a recess longitudinal 28 provided in the upper face 32 formed in the above the cylinder head body 10, which is capped by a part upper forming cylinder head cover 30, fixing the latter being ensured by pressing its lower face 33 on the face upper 32 of the cylinder head body 10. The camshaft 18 is mounted in the cylinder head by bearings each of which is designated as a whole by the reference 34, composed of a half-bearing lower 34a "fixed" formed integrally with the cylinder head body itself, and an added upper half-bearing 34b, known as "hat bearing ", fixed on the cylinder head body corresponding to the fixed lower half-bearing 34a by screws 36, thus completing the bearings 34. For the passage of the screws 36, the bearing cap has holes 37.

Figure 1 shows that the realization of the cylinder head is complex, especially since it still has to house passages for draining the engine coolant, threaded housings for fixing the spark plugs (petrol engines) or glow plugs (engines diesel) or injectors (injection engine), similarly only passages and ducts for the lubricant supplied to bearings 34 of the camshaft 18-20.

We also see in this figure that the cylinder head cover 30 is not not just a simple "cover" to close the upper recess of the cylinder head body 10, but that it is brought to fulfill an important rigidification function of the body cylinder head which no longer has the necessary own rigidity, given the multiple recesses and passages mentioned which through.

It is also clear that the lower half-bearings 34a receive almost no effort in operation, but that the upper half-bearings 34b collect practically all forces, mainly due to return springs 24. It is therefore necessary take this into account for their sizing, and that of their fixation.

On the other hand, the apparently satisfactory aspect for tradesmen, this is where the realization of the half-bearings lower directly from material in the cylinder head body during its molding seems to impose itself as being the solution the simpler and less expensive.

Now observing Figures 2a and 2b, we realize that this solution often leads to difficult technical choices. Indeed, it is here about a cylinder head which carries two camshafts (not themselves represented in the figure, but symbolized by their axes 18 'and 18 "), as is usual in modern engines, especially small displacement engines which we seek to obtain the greatest possible power.

In the section of figure 2a the lower half-bearings 34a 'and 34a "are moved relatively far up and towards the outside, if we refer to a longitudinal and vertical plane median of the motor, symbolized by the line L-L in the view in elevation of figure 2b. Correspondingly, the half-bearings upper 34b 'and 34b "are made of material with a common component which also forms the cylinder head cover 30. This solution has in this respect at least the advantage that the integration of upper half-bearings 34b 'and 34b "in the cylinder head cover is homogeneous with its stiffening function.

However, the geometric constraints are such that, as shown in Figure 2b, the threads 38 for the screws 36 for fixing the upper half-bearings must be advanced axially (i.e. in the L-L direction) so far that they are almost at the same level as an engine cylinder (VS). The intermediate zones between the cylinders are indeed reserved for the holes 40 intended for the fixing screws of the cylinder head on the cylinder block, which can never be placed elsewhere since they are essential for sealing the cylinder head on the cylinder block.

We will now refer to Figures 3a and 3b which represent a cylinder head according to the present invention, of new in section and partial elevation.

Here, the cylinder head body 10 itself no longer ensures directly the mounting function of the camshaft (symbolized by its axis 18 '). This function is taken over by the party upper forming cylinder head cover 30, produced here practically in the form of a "beam" in which the half-bearings are formed "fixed" upper 34a, with the necessary rigidity counts given the efforts they take, and here too in a way that is well compatible with the stiffening function devolved to the cylinder head beam 30.

The lower half-bearings 34b are added parts, fixed under the cylinder head cover beam 30. Because they take almost no effort in operation, they can be as tight as possible, just like their fixing screws, to simply close the corresponding bearing 34.

The advantages of this solution are manifold. First location, since it is no longer necessary to provide half-bearings fixed formed in the cylinder head body, there is a more great freedom for its design. Nor is it necessary to provide holes in the cylinder head body for fixing the bearing caps, which also leads to more great freedom of design.

In this regard, since the threads 38 'for the screws fixing 36 'of the bearing caps 34b are provided in the cylinder head cover 30 and no longer in the cylinder head body 10, there is no obstacle to providing that these tappings 38 'formed in the beam and the holes 40 formed in the body of cylinder head 10 for the bolts fixing the cylinder head to the cylinder block are arranged substantially in the same axial plane of the engine, between two cylinders thereof.

Of course, there must be threads in the cylinder head 42 for fixing screws 44 of the cylinder head cover beam 30 on the cylinder head body 10. Thanks to the inherent rigidity of the beam 30, it will be possible to provide these tappings 42 at locations practically any, in which they do not interfere with other parts of the cylinder head or mechanical assembly camshaft / valves.

In particular, when enough material remains, we can spare the threads 42 also substantially in the same plane as the cylinder head fixing screws, i.e. between two successive engine cylinders (C).

For the lubrication of bearings 34, nothing prevents provide in the cylinder head body 10, and / or in the cylinder head cover beam 30, lubricant distribution ducts, such as by example the same lubricant that is used for mechanical elements of the engine, these conduits leading to the upper half-bearings 34a.

It may however be advisable to provide lubrication through the center of the camshaft. In this case, it includes an axial hole (not shown) closed at both ends, which extends over the entire length concerned by the bearings, and radial holes at each of the bearings. food axial drilling in pressurized lubricant is carried out via a bearing at the end of the camshaft, sparing in the periphery of it a shallow groove and piercings radials which make it communicate with the axial bore.

It should also be noted that keeping the load-bearing "fixed" half-bearings on the cylinder head cover beam does not lead, during assembly, to possible cumulations of harmful tolerances between the camshaft - which depends on the cylinder head cover - on the one hand, and the rest of the mechanism valves - which depends on the cylinder head body - on the other hand.

Indeed, the bearing spans are machined to the dimensions "in situ" finals. That is to say, we proceed to the blank assembly bearing caps on the beam and then beam on the cylinder head body, and we take advantage of the fact that it exists at the end of breech (in the axial direction) anyway an opening for the subsequent passage of the end of the camshaft that it is connect to its drive mechanism (chain, gear, or toothed belt), to introduce the final machining tool axial direction and make it pass successively through the bearings.

The very small games which can then result from disassembly and reassembly are immaterial. The only ones games which we cannot totally overcome are the games axial, i.e. in the direction of the length of the shaft to cams. These games however remain here in the range of those that we see in the cylinder heads of classic construction and do represent no discomfort.

As an option, each bearing cap 34b has a projecting positioning finger 50, which is housed during mounting in a hole 52 of corresponding shape in the face lower 33 of the cylinder head cover beam 30.

Claims (8)

Cylinder head (10) of a thermal engine, in particular for a motor vehicle, comprising a main part or cylinder head body (10) intended to be mounted on a cylinder block of the engine and covered by a cylinder head cover (30), of the type in which the cylinder head has a recess (28) which is intended to receive actuating elements (18-20) of engine valves and which opens into an upper face (32) of the cylinder head body (10), on which is fixed said cylinder head cover (30), the valve actuating elements comprising a camshaft (18) fixed by means of bearings (34) each consisting substantially of a fixed half (34a) in the cylinder head and of a half attached in the form of a bearing cap (34b),
characterized in that said fixed bearing halves (34a) are made in the cylinder head cover (30). Cylinder head according to claim 1, characterized in that the bearing halves (34a) produced in the cylinder head cover (30) have an orientation capable of absorbing substantially all of the forces undergone in operation by said camshaft (18). Cylinder head according to either of Claims 1 and 2, characterized in that the cylinder head cover (30) is produced in the form of a beam having a rigidity capable of supplementing that of the cylinder head body (10). Cylinder head according to any one of claims 1 to 3, characterized in that the fixing of the bearing caps (34b) is carried out under the underside (??) of the cylinder head cover (30). Cylinder head according to any one of claims 1 to 4, characterized in that two threads (38 ') formed in the cylinder head cover (30) for fixing screws (36') of a bearing cap (34b) and two holes (40) formed in the cylinder head body (10) for the cylinder head fixing screws are arranged substantially in the same axial plane of the engine, between two cylinders thereof. Cylinder head according to any one of claims 1 to 5, characterized in that the camshaft has a central bore for distribution of lubricant to the bearings of the camshaft (18). Cylinder head according to any one of Claims 1 to 6, characterized in that each bearing cap (34b) has passage holes (37) for fixing screws (36 '), and the cylinder head cover (30) has threads (38 ') for said screws (36'). Cylinder head according to any one of claims 1 to 7, characterized in that each bearing cap (34b) comprises a projecting positioning finger (50), which is received during mounting in a hole (52) of corresponding shape in the lower face (33) of the cylinder head cover beam (30).

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