WO2009048411A1

WO2009048411A1 - Valve bridge in a combustion engine

Info

Publication number: WO2009048411A1
Application number: PCT/SE2008/051115
Authority: WO
Inventors: Morgan Halldin; Jairo De Lima Souza
Original assignee: Scania Cv Ab (Publ)
Priority date: 2007-10-12
Filing date: 2008-10-02
Publication date: 2009-04-16
Also published as: SE531707C2; DE112008002712B4; SE0702291L; DE112008002712T5

Abstract

The present invention relates to a valve yoke (8) for a combustion engine, which is adapted to transmitting a control movement from a rocker arm (6) to two valves (9) in a combustion space (10). The valve yoke (8) comprises a first contact surface (8al) adapted to being in contact with the rocker arm (6), two second contact surfaces (8bl) each adapted to being in contact with one of the two valves (9), and a control duct (12) which has a first aperture (12a) for accommodating a control element (13). The control duct (12) comprises a second aperture (12b) and the valve yoke (8) comprises an external surface constituting a lubrication path (14a-c) which extends from a peripheral surface (8al) of the valve yoke where this is availability of lubricant to the second aperture (12b) of the control duct.

Description

Valve bridge in a combustion engine

BACKGROUND TO THE INVENTION, AND STATE OF THE ART

The present invention relates to a valve yoke for a combustion engine according to the preamble of claim 1.

Combustion engines often have more than one inlet valve and one exhaust valve per combustion space. In such cases it is possible to use a valve yoke for simultaneously transmitting control movements from a rocker arm to two inlet valves or to two outlet valves. A valve yoke usually comprises a wear washer which serves as the valve yoke's contact surface with the rocker arm. The rocker arm may comprise a so-called elephant foot which serves as the rocker arm's contact surface. Valve yokes usually have two arms protruding in opposite directions which each have at an outer end portion a downward-facing contact surface adapted to transmitting the valve yoke's movements to the valves. A conventional valve yoke also comprises a control duct for accommodating a correspondingly shaped control pin. The purpose of the control duct and the control pin during operation of the combustion engine is to provide control of the valve yoke so that it is subjected to linear reciprocating movements which can be converted to opening and closing movements of the valves.

During operation of the combustion engine, the valve yoke performs rapid linear reciprocating movements relative to the control pin. The surfaces of the control pin and the surfaces of the valve yoke which define the control duct are thus substantially continuously subject to loads. It is therefore very important that the friction between the surfaces of the control duct and the surfaces of the control pin be continuously kept at a very low level. If such is not the case, the surfaces will be subject to rapid wear impairing the continuing ability of the control pin to control the movements of the valve yoke. If the friction becomes too great there is also risk of shearing. SUMMARY OF THE INVENTION

The object of the present invention is to provide a valve yoke for a combustion engine which is so configured that the friction between the surfaces which define a control duct of the valve yoke and the surfaces of a correspondingly shaped control element which controls the movement of the valve yoke is continuously kept at a very low level during operation of the combustion engine.

This object is achieved with the valve yoke of the kind mentioned in the introduction which is characterised by the features indicated in the characterising part of claim 1. The valve yoke thus comprises an external surface which defines a lubrication path which leads a lubricant from a peripheral surface where there is availability of lubricant to a second aperture of the control duct. The result is a simple and effective way of supplying lubricant to the control duct. The lubricant supplied is thereafter distributed in the control duct in such a way that a thin layer of lubricant is formed between the adjacent surfaces of the control duct and of the control element. The presence of such a layer of lubricant leads to the friction between the surfaces of the control duct and of the control element being very low during operation of the combustion engine. The risk of wear and shearing in this region of the valve yoke is thus substantially entirely eliminated. The lubricant may be a suitable lubricating oil. The lubrication path has with advantage a substantially continuous slope downwards along its whole extent in the assembled state of the valve yoke. This means that the lubricant runs downwards along the whole lubrication path by force of gravity. The second aperture is preferably situated in an upper portion of the control duct. Thus the lubricant can also be led downwards into and be distributed in the control duct by force of gravity. When the valve yoke and the control duct move downwards relative to the control element during operation of the combustion engine, the result is a progressively reduced space in the control duct above the control element to accommodate any surplus lubricant. This surplus lubricant can be pushed out via the second aperture. The second aperture can thus be used both for leading lubricant to the control duct and for leading surplus lubricant out from the control duct. According to a preferred embodiment of the present invention, the lubrication path has an extent from a region situated in or close to the first contact surface of the valve yoke. Conventional rocker arms normally have an internal lubrication passage which leads to close to this contact surface with the valve yoke in order to provide lubrication and cooling of this contact region. There is thus always availability of lubricant close to the valve yoke's contact surface with the rocker arm. By arranging an initial stretch of the lubrication path in this region, lubricant can substantially continuously be led on from this region to the control duct of the valve yoke.

According to another preferred embodiment of the present invention, the valve yoke comprises a first contact portion comprising said first contact surface, a control portion comprising said control duct and an arm structure connecting the first contact surface to the control portion. Such an arm structure makes it possible for the first contact portion and the control portion to be arranged at a vertical distance from one another. With advantage, the arm structure connects the first contact portion to the control portion in such a way that the second aperture of the control duct is situated at a position substantially vertically below the first contact portion when the valve yoke is in an assembled state. Thus both the first contact portion and the control portion can be placed centrally. The control portion is with advantage tubular.

According to another preferred embodiment of the present invention, said first contact portion comprises surfaces adapted to constituting at least one stretch of said lubrication path. Such a portion may form an initial stretch of the lubrication path which leads lubricant to the first contact surface of the valve yoke. With advantage, the first contact portion comprises an upper surface which has a recess in which an initial stretch of the lubrication path is situated. Thus the lubricant does not have to run particularly far over the upper surface from the first contact surface of the valve yoke to reach the initial stretch of the lubrication path. Said arm structure preferably comprises surfaces adapted to constituting at least one stretch of said lubrication path. As the arm structure connects the first contact portion and the control portion, it is very advantageous for the lubrication path to be provided along the upper surfaces of the arm structure. The arm structure may comprise two first arms which protrude in different directions from the first contact portion and two second arms which connect the first arms to the control portion. The first arms may have a shape of an inverted V and the second arms a shape of a V. Both the first arms and the second arms thus have sloping surfaces which can be used for constituting the lubrication path.

According to another preferred embodiment of the present invention, the arm structure is connected to two second contact portions which comprise the second contact surfaces. With advantage, the two second contact portions are arranged on opposite sides of the first contact portion and on opposite sides of the control portion. The arm structure comprises with advantage surfaces adapted to constituting at least one stretch of a further lubrication path which extends from a region situated in or close to the first contact surface of the valve yoke to one of the second contact portions. The contact surfaces of the valve yoke with the valves may thus also be provided with lubrication so that they do not become worn down. The arm structure preferably comprises surfaces adapted to constituting two parallel part-paths for lubricant, the one parallel part-path ending with a guiding surface adapted to leading lubricant towards the second aperture, and the second parallel part-path being adapted to leading lubricant towards one of the second contact portions. The parallel part-paths having different dimensions makes it possible for the distribution of the amount of lubricant between the control duct and the second contact portions to be controlled. The lubrication path comprises with advantage a chamfered portion of the first contact portion which defines an initial stretch of the lubrication path. With such a chamfered portion the lubrication path can start relatively near to the contact surface. The lubricant which spreads in different directions over the upper surface of the first contact portion therefore needs only to be led a relatively short distance along the upper surface before it reaches the chamfered portion which defines a beginning of the lubrication path. Thus a relatively large proportion of the lubricant supplied can be led to the lubrication path.

BRIEF DESCRIPTION OF THE DRAWINGS A preferred embodiment of the invention is described below by way of example with reference to the following drawings, in which:

Fig. 1 depicts a number of motion-transmitting components which comprise inter alia a valve yoke for transmitting control movements to two valves in a combustion space, Fig. 2 depicts the valve yoke in Fig. 1 in more detail.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

Fig. 1 depicts part of a combustion engine provided with a low camshaft 1 which rotates at a speed related to the speed of the combustion engine. The camshaft 1 has a peripheral control surface 2 provided with at least one cam. A valve lifter 3 is adapted to being in continuous contact with the control surface 2. A pushrod 4 fitted substantially vertically has a lower end articulatedly connected to the valve lifter 3 and an upper end articulatedly connected to a component 5 which is firmly mounted on a rocker arm 6. The articulating upper connection of the pushrod 4 comprises a ball seat connected to a ball-shaped portion 5a of the component 5. The component 5 has an adjusting screw 5b and a nut 5c for adjustable fastening of the component 5 to a first end 6a of the rocker arm 6. The rocker arm 6 is supported for pivoting at a middle portion about an articulation 7. The rocker arm 6 has at a second end 6b on the opposite side of the articulation 7 a contact surface Ob₁ adapted to being in contact with a contact surface Sa₁ of a valve yoke 8. The contact surface Ob₁ of the rocker arm may take the form of a surface of a so-called elephant foot. The rocker arm 6 has a schematically depicted lubrication passage 6c which has an outlet in or close to the contact surface Ob₁ of the rocker arm. The lubrication passage 6c is part of the combustion engine's ordinary lubrication system.

The valve yoke 8 is adapted to transmitting all the control movements to two valves 9 in a combustion space 10 in the combustion engine. Only one of the two valves 9 is visible in Fig. 1. The valves 9 may be two inlet valves whose purpose is to control the supply of air to the combustion space 10, or two exhaust valves whose purpose is to control the evacuation of exhaust gases from the combustion space 10. Each of the valves 9 is connected to a valve spring 11 which endeavours to move the valves 9 towards a closed position. The valve lifter 3, the pushrod 4, the component 5, the rocker arm 6 and the valve yoke 8 are components of a motion-transmitting mechanism whose purpose is to convert control movements from the control surface 2 of the camshaft to simultaneous opening movements of the valves 9 against the action of the respective valve springs 11.

The configuration of the valve yoke 8 is most clearly illustrated in Fig. 2. The valve yoke 8 comprises a first contact portion 8a which has a substantially planar surface constituting the upper surface of the valve yoke in an assembled state. The upper surface of the first contact portion 8a comprises a wear washer comprising the aforesaid contact surface Sa₁. The valve yoke 8 comprises two second contact portions 8b which each have a downward- facing contact surface Sb₁ adapted to being in contact with a contact surface 9a of the respective valve 9. The valve yoke 8 is provided with an arm structure which comprises two upper arms 8c. The upper arms 8c extend in opposite directions downwards from the first contact portion 8a. Each of the upper arms 8c connects the first contact portion 8a to one of the contact portions 8b. The upper arms 8c have upper surfaces sloping downwards from a connection with the first contact portion 8 a to a connection with the second contact portion 8b. The arm structure also comprises two lower arms 8d which extend in opposite directions obliquely upwards from a tubular guiding portion 8e of the valve yoke 8. The two lower arms 8d connect the guiding portion 8e to the first arms 8c. The lower arms 8d have upper surfaces which slope downwards towards the guiding portion 8e when the valve yoke is an assembled state. The guiding portion 8e comprises an internal space which forms a control duct 12 adapted to accommodating a control pin 13 with a corresponding shape. The control pin is stationarily installed in the combustion engine. The purpose of the control duct 12 and the control pin 13 is to provide the valve yoke 8 with control such that a linear movement in a vertical direction is imparted to it during operation of the combustion engine. The control duct 12 has here a constant cross-sectional area with a circular shape. However, the control duct 12 may have some other shape. The control duct 12 has a lower aperture 12a for accommodating the control pin 13 and an upper aperture 12b. The arm structure 8c, 8d connects the first contact portion 8a and the guiding portion 8e so that the upper aperture 12b of the control duct is situated substantially vertically below the first contact portion 8a when the valve yoke 8 is an assembled state. The upper aperture 12b has with advantage a cross-sectional area at least as large as the cross-sectional area of the control duct 12.

The rocker arm 6 thus comprises a lubrication passage 6c which has an outlet aperture in or close to the contact surface Ob₁ of the rocker arm. Via the lubrication passage 6c, lubricant is supplied to a first contact region between the contact surface Ob₁ of the rocker arm and the upper contact surface Sa₁ of the valve yoke. The friction between the contact surfaces Ob₁, Sa₁ in the first contact region can thus be kept at a low level. The planar upper surface of the first contact portion 8a changes, at one portion of its periphery, to a chamfered portion 8a₂. The chamfered portion 8a₂ is intended to initiate a flow of lubricant from the contact surface 8ai along a number of lubrication paths which extend along the external surface of the valve yoke. The upper surface of the first portion 8a comprises two peripheral recesses 8a₃ in the chamfered portion 8a₂. Each of the peripheral recesses 8a₃ defines an initial stretch of a lubrication path. The lubrication paths comprise initial part-paths 14a in the form of substantially vertically directed surfaces of the first contact portion 8a. The initial part-paths 14a thus have a relatively steep slope downwards from the upper surface of the first portion 8 a. The initial part-paths 14a change to two parallel part-paths Hb₁, 14b₂ formed on the upper surfaces of the first arms 8c. The parallel part-paths Hb₁, 14b₂ slope downwards from the first contact portion 8 a. One of the parallel part-paths Hb₁ also has a side slope so that it slopes downwards towards a free side edge. By this side slope the respective part-paths Hb₁ are provided with an end in a wedge-shaped guiding surface 8f which has a different slope than the part-paths Hb₁. The guiding surfaces 8 f constitute upper portions of the lower arms 8d. Each of the guiding surfaces 8f constitutes an initial stretch of a final part-path Hc₁ which slopes downwards towards the upper aperture 12b of the control duct. The parallel part-paths Hb₂, however, continue with an unchanged slope to the second contact portions 8b. An initial stretch of a further lubrication path is also formed between the two peripheral recesses 8a₃ in the chamfered portion 8a₂. The further lubrication path comprises an initial part-path 14d in the form of substantially vertically directed surfaces of the first contact portion 8a. The initial part-path 14d is situated vertically above the lower arms 8d close to the upper aperture 12b of the control duct.

During operation of the combustion engine, control movements are transmitted from the control surface 2 to the valves 9 via the components 3, 4, 5, 6, 8 of the motion- transmitting mechanism. To open the valves 9, the rocker arm 6 is pivoted anticlockwise about the articulation 7, as illustrated in Fig. 1, so that the valve yoke 8 is pressed down by the rocker arm 6. As the valve yoke 8 is mounted on the control pin 13 via the control duct 12, it imparts a linear movement downwards. The contact surfaces 8b i of the valve yoke thereupon press the valves 9 down against the action of the valve springs 11. The two valves 9 are thus provided with simultaneous opening movements. When the valve lifter 3 has passed the tip of the cam on the control surface 2, the rocker arm 6 pivots back clockwise about the articulation 7. The valve springs 11 exert a force which maintains the contact between the contact surfaces 9a, 8b _\ of the valves 9 and of the valve yoke 8 and between the contact surfaces Sa₁ , Ob₁ of the valve yoke 8 and of the rocker arm 6.

The lubricant from the rocker arm 6 which is supplied to the contact surface Sa₁ spreads in various directions over the upper surface of the first contact portion 8a. However, the lubricant needs only to be led a relatively short distance along the upper surface before it reaches the chamfered portion 8a₂ which defines a beginning of the aforesaid lubrication paths. A relatively ample flow of lubricant can thus be achieved inter alia along the symmetrically arranged first part-paths 14a. The lubricant runs from the first part-paths 14a to the parallel part-paths Hb₁, Hb₂ which are thus defined by the upper surfaces of the first arms 8c. A certain proportion of the lubricant which runs along the side-sloping part-paths Hb₁ runs down over the side edges of the upper arms 8c and down onto the final part-path Hc₁ which itself leads the lubricant towards the upper aperture 12b of the control duct. The portion of the lubricant which reaches the guiding surfaces 8f is led by them towards the upper aperture 12b of the control duct via the final part-path Hc₁. The lubricant led along the non side-sloping part-paths 14b₂ is led all the way to the second contact portions 8b. The lubricant runs thereafter downwards to the second contact surfaces 8b _ls where it provides lubrication and cooling. By such a supply of lubricant the friction in the second contact regions can be kept at a continuously low level during operation of the combustion engine. The lubricant led over the chamfered portion 8a₂ and along the initial part-path 14d arranged between the recesses 8a₃ drops down onto the part-path 14ci below. At least part of this lubricant is led into the control duct via its upper aperture 12b.

The control duct 12 and the control pin 13 thus control the valve yoke 8 so that linear movements are imparted to it in alternate directions. The adjoining surfaces between the control duct 12 and the control pin 13 are therefore continuously subject to mutual loads. For this reason it is very important that the friction between these surfaces be likewise kept at a low level to prevent wear and risk of shearing. According to the present invention, part of the lubricant from the first contact portion 8ai is therefore led along well-defined lubrication paths on the external surfaces of the valve yoke to the second aperture 12b of the control duct. The lubricant is thereafter led into the control duct 12 and along its wall surfaces, where it forms a thin layer of lubricant between the adjoining surfaces of the control duct 12 and of the control pin 13. The presence of such a layer of lubricant results in very low friction between the adjacent surfaces of the control duct 12 and of the control pin 13 when they undergo mutual movements. The risk of wear and shearing is therefore substantially eliminated in this region. When the valve yoke 8 and the control duct 12 move downwards relative to the control pin 13, the clear space in the control duct 12 above the control pin 13 is progressively reduced. When the clear space has been reduced to a level such that it is substantially completely full of lubricant, the surplus lubricant is led out through the upper aperture 12b of the control duct. The fact that the upper aperture 12b of the control duct has at least the same cross-sectional area as the control duct 12 affords assurance that no surplus lubricant will remain in the control duct and brake the movement of the valve yoke 8 when the control pin 13 reaches the upper portion of the control duct 12. The surplus lubricant is led out to an external region situated close to an upper portion of the valve yoke 8. The invention is in no way limited to the embodiment illustrated in the drawings but may be varied freely within the scopes of the claims. In the embodiment example, control movements are transmitted from a low camshaft to the valve yoke. Control movements might equally well be transmitted from a high camshaft to the valve yoke.

Claims

1. A valve yoke (8) for a combustion engine, which is adapted to transmitting control movements from a camshaft (1) to two valves (9) in a combustion space (10), which valve yoke (8) comprises a first contact portion (8a) comprising a first contact surface (8aO adapted to being in contact with a rocker arm (6), two second contact surfaces (Sb₁) each adapted to being in contact with one of the two valves (9), a control portion (8e) comprising a control duct (12) which has a first aperture (12a) for accommodating a control element (13), and an arm structure (8c, d) connecting the first contact portion (8a) to the control portion (8e), characterised in that the valve yoke (8) comprises an external surface which constitutes at least one lubrication path (14a-d) extending from a region situated in or close to the valve yoke's first contact surface (Sa₁) where there is availability of lubricant to a second aperture (12b) of the control duct, and that the arm structure (8c, d) connects the first contact portion (8a) to the control portion (8e) in such a way that the second aperture (12b) of the control duct is situated at a position substantially vertically below the first contact portion (8a) when the valve yoke (8) is in an assembled state.

2. A valve yoke according to claim 1, characterised in that said first contact portion (8a) comprises surfaces adapted to constituting at least one stretch (14a, 14d) of said lubrication path.

3. A valve yoke according to claim 1 or 2, characterised in that said arm structure (8c, d) comprises surfaces adapted to constituting at least one stretch of said lubrication path (14bi, Hc₁).

4. A valve yoke according to any one of the foregoing claims, characterised in that said arm structure comprises two first arms (8c) protruding in different directions from the first contact portion (8a), and two second arms (8d) connecting the first arms (8c) to the control portion (8e).

5. A valve yoke according to any one of the foregoing claims, characterised in that the arm structure (8c, d) is connected to two second contact portions (8b) which comprise the second contact surfaces (8b]).

6. A valve yoke according to claim 5, characterised in that the arm structure (8c) comprises surfaces adapted to constituting at least one stretch of a further lubrication path which extends from the region situated in or close to the valve yoke's first contact surface (Sa₁) to at least one of the second contact portions (8b).

7. A valve yoke according to claim 6, characterised in that the arm structure (8c, d) comprises surfaces adapted to constituting two parallel part-paths (Hb₁, 14b₂) for lubricant, that one parallel lubrication path (Hb₁) ends with a guiding surface (8f) adapted to leading lubricant towards the second aperture (12b), and that the other parallel part-path (14b₂) is adapted to leading lubricant towards one of the second contact portions (8b).

8. A valve yoke according to any one of the foregoing claims, characterised in that the lubrication path comprises a chamfered portion (8a₂) of the first contact portion (8a) which defines an initial stretch of the lubrication path.