Connection between two shaft ends, positioned coaxially one behind the other, of a gas shuttle valve in an internal combustion engine and a valve actuator

Abstract

The present invention relates to a connection between two shaft ends (8, 10), situated coaxially one behind the other, of a gas exchange valve (1) of an internal combustion engine and a piston rod (2) of a valve actuator (4), where at least one coupling member (14) at least partially surrounds the shaft ends (8, 10).

Description

BACKGROUND INFORMATION

[0001] The present invention starts out from a connection between two shaft ends, situated coaxially one behind the other, of a gas exchange valve of an internal combustion engine and of a valve actuator, where at least one coupling member according to the definition of the species set forth in Patent claim 1 at least partially surrounds the shaft ends.

[0002] Such a connection is known from EP 0 279 265 B1, where the coupling member includes two half-shells whose radially external peripheral surfaces are cylindrical and whose radially internal peripheral surfaces are conical in a manner complimentary to the piston rod ends of the valve actuator, which are tapered conically with respect to one another, and to a shaft of the gas exchange valve. To prevent the two half-shells from falling apart, a cylindrical coupling sleeve held to the half-shells by the axial prestress force of a valve spring supported on the bottom of the screw sleeve is pushed over them, the shaft of the gas exchange valve extending through an opening in the bottom of the screw sleeve. The two shaft ends, which are tapered relatively to each other, have at the extremity flanges that are widened in a plate-like manner and grip the coupling member formed by the half-shells from behind, so that the two shaft ends are connected to one another by the coupling member in a form-locking manner. At the form-locking junction between the conical runout of the shaft ends and the extreme flanges, the cross section is weakened in each case by a distinct groove, which has a negative effect on the fatigue strength of the connection. This represents a significant disadvantage especially with regard to the high number of load changes that gas exchange valves of internal combustion engines are subjected to.

SUMMARY OF THE INVENTION

[0003] Due to the frictionally engaged connection between the coupling member and the shaft ends, no undercuts are necessary that as groove-like indentations would weaken the cross section of the shaft ends and/or of the coupling member. Consequently, the connection of the present invention is distinguished by a high degree of fatigue strength.

[0004] According to a particularly preferred measure, the prestress applied to the coupling member by the tensioning member is adjustable. For this purpose, the tensioning member includes at least two conical tensioning sleeves able to be axially screwed against one another and having conical surfaces that are able to be wedged against conical tensioning surfaces formed on the radially external peripheral surface of the coupling member, a defined radial prestress being able to be generated between the coupling member and the shaft ends as function of the degree of tightening of the conical tensioning sleeves. This is advantageous above all with regard to the surface conditions that may differ depending on the gas exchange valve or the valve actuator and to the correspondingly different friction coefficient in that the radial prestress necessary for slip-free static friction locking may be adjusted.

[0005] Viewed in the circumferential direction, the coupling member has a multi-part design and preferably includes at least two half pipe-shaped coupling wedges, which complement one another to form a sleeve, each coupling wedge having on its outer peripheral surface two tensioning surfaces situated radially one behind the another and expanding conically with respect to one another, each tensioning surface being assigned to one conical surface of one of the conical tensioning sleeves. Both conical tensioning sleeves are expediently provided with a contact surface for a screw tool.

[0006] According to a further refinement, positioning projections and positioning recesses that preferably intermesh with play are provided on the coupling member and on each shaft end for positioning the coupling member on the shaft ends. This ensures that the coupling member is tensioned in a defined position with respect to the shaft ends, and a balanced surface covering results. On the other hand, the loose intermeshing of the positioning projections and recesses reduces fatigue strength-lowering notch stresses. According to a preferred measure, the radially internal, cylindrical peripheral surface of the coupling wedges has annular protuberances that extend in the circumferential direction, each annular protuberance being assigned to an annular groove of a shaft end. The annular protuberances and annular grooves have an essentially semicircular cross section, the inner radius of the annular grooves being greater than the outer radius of the annular protuberance in order to prevent direct material contact as much as possible and to keep the notch stresses caused by the annular grooves as low as possible.

[0007] Finally, the connection between the valve actuator and the gas exchange valve is preferably situated in an accessible region outside of a valve actuator housing. Therefore, in the event that repairs are needed, it is very easy to replace a gas exchange valve or a valve actuator, and it is not necessary to dismantle the valve actuator.

[0008] Advantageous further refinements and improvements of the invention specified in claim 1 are rendered possible by the additional measures specified in the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] An exemplary embodiment of the present invention is represented in the drawing and explained in detail in the following description. The figures show:

[0010] FIG. 1 shows a lateral view of a cross section of a preferred specific embodiment of a connection of the invention between a shaft end of a gas exchange valve of an internal combustion engine and a piston rod of a valve actuator;

[0011] FIG. 2 shows a view of a cross section along line II-II from FIG. 1;

[0012] FIG. 3 shows an enlarged view of detail A from FIG. 1.

DETAILED DESCRIPTION

[0013] Only a gas exchange valve 1 of a valve mechanism of an internal combustion engine is shown in FIG. 1 that is actuated by a piston rod 2 of a valve actuator 4 such that it performs upward and downward opening and closing movements. For this purpose, piston rod 2 of valve actuator 4 and a shaft 6 of gas exchange valve 1 are situated coaxially one behind the other, a shaft end 8 of piston rod 2 and a shaft end 10 of shaft 6 of gas exchange valve 1 being situated opposite one another. Piston rod 2 and shaft 6 of gas exchange valve 1 preferably have the same diameter. To be able to transfer the pressing motion and/or pulling motion of piston rod 2 to gas exchange valve 1, a coupling member 14 is provided that at least partially surrounds shaft end 8 of piston rod 2 as well as shaft end 10 of gas exchange valve 1. Viewed in the circumferential direction, coupling body 14 preferably has a multi-part design and includes two half pipe-shaped coupling wedges 16, 18, which complement one another to essentially form a sleeve, as is best seen in the sectional view in FIG. 2. The radially internal peripheral surfaces of both coupling wedges 16, 18 are cylindrical and have the same radius as piston rod 2 and shaft 6 of gas exchange valve 1. Viewed in the circumferential direction, both coupling wedges 16, 18 do not connect to one another without gap, but a narrow opening 20 remains at both joints, so that there is a circumferential compensation for both coupling wedges 16, 18 when a radial pressure is exerted on them from the outside.

[0014] As can best be seen in FIG. 1, intermeshing positioning projections and positioning recesses are provided on coupling member 14 and on each shaft end 8, 10 for positioning coupling member 14 on shaft ends 8, 10. This ensures that coupling member 14 is situated in a defined position with respect to both shaft ends 8, 10 and that a balanced surface covering results. According to the preferred specific embodiment, each radially internal, cylindrical peripheral surface of both coupling wedges 14, 16 has two annular protuberances extending in the circumferential direction, a top annular protuberance 22 engaging with a circumferential annular groove 24 formed on shaft end 8 of piston rod 2, and a bottom annular protuberance 26 engaging with an annular groove 28 in a shaft end 10 of gas exchange valve 1. Annular protuberances 22, 26 and annular grooves 24, 28, which are assigned to one another, have an essentially semicircular cross section as can be seen in enlarged view A in FIG. 3 in particular. Annular protuberances 22, 26 do not abut against annular grooves 24, 28 of the shaft ends since their inner radius is greater than the outer radius of annular protuberances 22, 26.

[0015] Both half pipe-shaped coupling wedges 16, 18 have on their radially external peripheral surface tensioning surfaces 30, 32 disposed one behind the other and expanding conically toward one another in order to be able to tension coupling wedges 16, 18 radially with respect to both shaft ends 8, 10. For this purpose, a tensioning member, preferably two conical tensioning sleeves 34, 36, which are able to be axially screwed against each other and have conical surfaces 38, 40, is provided that is able to be wedged against tensioning surfaces 30, 32 of coupling wedge 16, 18, a defined radial prestress being able to be produced between coupling wedges 16, 18 and both shaft ends 8, 10 as a function of the screwing degree of the two conical tensioning sleeves 34, 36. Since the motion of piston rod 2 of valve actuator 4 is to be transferred to gas exchange valve 1 in a slip-free manner, the prestress must be so great that there is always static friction between coupling wedges 16, 18 and shaft ends 8, 10 under the forces acting during operation. Of the two tensioning surfaces 30, 32 of a coupling wedge 16, 18, a top tensioning surface 30 is assigned in each case to a conical surface 38 of top conical tensioning sleeve 34, and a bottom tensioning surface 32 is assigned in each case to a conical surface 40 of bottom conical tensioning sleeve 36. Top conical tensioning sleeve 34 is able to be screwed into bottom conical tensioning sleeve 36 in that radially external peripheral surface of top conical tensioning sleeve 34 is provided with an external thread 42, and the radially internal peripheral surface of bottom conical tensioning sleeve 36 is provided with an internal thread 44 having the same diameter. Both conical tensioning sleeves 34, 36 are provided at their ends facing away from one another with a contact surface 48, 50 for a screw tool. Threads 42, 44 are consequently outside of the force flux that arises when the valve is actuated and extends from piston rod 2 over the two coupling wedges 16, 18 to shaft 6 of gas exchange valve 1 and is only subjected to the static prestress for procuring the friction locking between coupling wedges 16, 18 and shaft ends 8, 10. Since annular protuberances 22, 26 of both coupling wedges 16, 18 do not rest against annular grooves 24, 28 of shaft ends 8, 10, the form locking portion generated by coupling wedges 16, 18 being radially pressed outweighs the form locking portion caused by the mutually assigned annular protuberance/annular groove pairings in the case of the coupling of piston rod 2 and shaft 6 of gas exchange valve 1. Consequently, the annular protuberance/annular groove pairings are foremost used to fix coupling member 14 to shaft ends 8, 10 and can, therefore, have small dimensions. Consequently, their stress concentration at shaft ends 8, 10 and their influence on the fatigue strength of the connection is minimal.

[0016] As seen in FIG. 1, the described connection between piston rod 2 of valve actuator 4 and shaft 6 of the gas exchange valve is situated outside of a valve actuator housing 52 of valve actuator 4 in an easily accessible region, so that valve actuator 4 and gas exchange valve 1 are both easy to assemble and disassemble as individual modules.

[0017] According to a further specific embodiment, coupling member 14 is also able to be designed as a one-piece sleeve instead of as a two-piece sleeve, a continuous slit extending in the axial direction needing to be provided in this case in the wall of the sleeve in order to enable compensating motion of the one-piece sleeve in the circumferential direction when radial prestress is applied from the outside by the wedge effect of conical tensioning sleeves 34, 36.

Claims

1. A connection between two shaft ends (8, 10), situated coaxially one behind the other, of a gas exchange valve (1) of an internal combustion engine and a piston rod (2) of a valve actuator (4), where at least one coupling member (14) at least partially surrounds the shaft ends (8, 10), wherein the coupling body (14) is radially tensioned with respect to the two shaft ends (8, 10) by at least one tensioning member (34, 36) to produce static friction locking between each shaft end (8, 10) and the coupling member (14) that transfers the actuating motion of valve actuator (4) to gas exchange valve (1) in a slip-free manner.

2. The connection as recited in claim 1, wherein the tensioning member includes at least two conical tensioning sleeves (34, 36), which are able to be axially screwed against one another, having conical surfaces (38, 40), which are able to be wedged against conical tensioning surfaces (30, 32), which are formed on the radially external peripheral surface of coupling member (14), thereby making it possible to generate a radial prestress producing the static friction locking between the coupling member (14) and the shaft ends (8, 10).

3. The connection as recited in claim 2, wherein viewed in the circumferential direction, the coupling member has a multi-part design and preferably includes at least two half pipe-shaped coupling wedges (16, 18), which complement one another to form a sleeve, each one having on its radially external peripheral surface two tensioning surfaces (30, 32) situated one behind the other and expanding conically toward one another, each tensioning surface (30, 32) being assigned to a conical surface (38, 40) of one of the conical tensioning sleeves (34, 36).

4. The connection as recited in claim 2 or 3, wherein both conical tensioning sleeves (34, 36) are provided with a contact surface (48, 50) for a screw tool.

5. The connection as recited in one of the preceding claims, wherein positioning projections (22, 26) and positioning recesses (24, 28) preferably intermeshing with play are provided on the coupling member (14) and each shaft end (8, 10) for positioning the coupling member (14) with respect to the shaft ends (8, 10).

6. The connection as recited in claims 3 through 5, wherein the coupling wedges (16, 18) have on their radially internal, cylindrical peripheral surface at least two annular protuberances (22, 26), which extend in the circumferential direction, at least one annular protuberance (22, 26) being assigned to one annular groove (24, 28) of a shaft end (8, 10).

7. The connection as recited in claim 6, wherein the annular protuberances (22, 26) and annular grooves (24, 28) have an essentially semicircular cross section, the inner radius of the annular grooves (24, 28) being greater than the outer radius of the annular protuberances (22, 26).

8. The connection as recited in one of the preceding claims, wherein it is situated in an accessible region outside of a valve actuator housing (52).