EP0155261B2 - Valve timing gear for an internal-combustion engine - Google Patents

Abstract

In an internal combustion engine with a cylinder (1), the cylinder head (2) has four valves (3, 4) inclined towards each other and arranged to be radially aligned with respect to the combustion chamber, pairs of the valves being operable by a common camshaft (6) by means of conical cams (7). To make it possible to use such a valve control for high rotational speeds, too, bucket type tappets (8) are displaceably mounted between the radially aligned valves (3, 4) and the conical cams (7) in the cylinder head (2).

Description

The invention relates to a valve control for a reciprocating piston internal combustion engine according to the introductory part of independent claim 1.

In order to ensure advantageous combustion, hemispherical combustion chambers are sought in internal combustion engines which require a valve arrangement that is radially oriented with respect to the combustion chamber. A particularly advantageous gas exchange is achieved with favorable utilization of the combustion chamber in that two intake and two exhaust valves are provided for each cylinder and that the valves of the same function are diametrically opposed to one another with respect to the cylinder axis. Due to the radial alignment of the valves, camshafts are mainly used for valve actuation, from which the valve lift is derived via bumpers and rocker arms. In such a valve arrangement, the transmission of the lifting movement of conventional control cams of overhead camshafts to the valves is only possible using complex drag and angle levers. Despite the use of camshafts below, a corresponding valve control for high-speed internal combustion engines cannot be guaranteed, because due to the masses to be moved, exact valve timing cannot be transmitted. Because of the comparatively low flutter limit of the valves, it is impossible to reach high engine speeds.

In JP-A-5 399 121, two cam shafts are arranged above the four radially aligned valves, the cams of which have a bevel cut corresponding to the respective valve angle. In this schematic representation, however, no solution is offered for the transmission of the cam stroke to the valve.

With JP-U-57 107 903 the teaching is imparted to keep the reciprocating masses small by tappets between the conically shaped cams and the valves in the case of inclined valves. Due to the inclined position of the valve, the cup tappet is overrun off-center by the cranked cam during its stroke movement. As the valve angle increases, this leads to an unsatisfactory contact pattern and ultimately to the destruction of this component.

In order to avoid a complex drive connection between the camshaft and the valves in the case of valves arranged at an angle to one another, it is also known (GB-A 266 442) to design the cams as conical and to have them act directly on the spring plate of the valves.

A disadvantage of this construction, however, is that the transverse forces transmitted from the conical cams to the spring plates must be removed via the valve guide, which leads to premature wear of the valve guides. In addition, since there is a relative displacement of the cams with respect to the spring plates in the direction of the line of contact between the cams and the spring plates during a stroke, the spring plates are loaded by a tilting moment, which excludes the use of such a valve control for valves with a larger angle of inclination, so that these are known Construction for valves which are radially oriented with respect to the combustion chamber is unusable.

To reduce the overall length of an in-line engine, it is further known (DE-B 953 672) to alternately tilt the valves arranged in a row one behind the other in opposite directions and to drive them via a common camshaft with conical cams, the cam lobe being lifted via a rocker arm each is transferred to the valve stem in order to avoid the transfer of transverse forces to the valve stems. This known construction is complex because of the rocker arms between the conical cams and the valves, the problem being that the rocker arms are supported in such a way that the transverse forces that occur can be absorbed without having to accept premature wear of the rocker arm bearings. In addition, in this known construction the distance of the individual valves from one another is limited by the desired limitation of the overall length, so that a radial alignment of the valves with respect to the combustion chamber is not possible.

GB-A 375 459 shows an internal combustion engine with two pairs of valves arranged at an angle to one another and radially oriented with respect to the combustion chamber, which can be actuated by means of conically designed cams. The transfer of the stroke of the conically shaped cams to the valves takes place, similarly to GE-A 242 919, via rocker arms, so that the disadvantages described in connection with DE-B 953 672 occur.

From GE-A 558779 an internal combustion engine with two valves per cylinder is known, which are actuated by a common camshaft arranged above the valves. 5 of GB-A 558779 there is also shown an arrangement of the valves in which the axes of the valves do not run parallel but inclined to one another. The cam associated with the valve inclined to the axis of the camshaft is conical. In the GB-A 558 779, tappets which are guided in the cylinder head are provided between the cams - including the conical cams - and the valve, which act on the valve stem via an adjustable screw. These tappets of GB-A 558 779 are not cup tappets because they are not cup-shaped and coaxially enclose the valve spring and the valve disk to save overall height. The tappets of GB-A 558 779 are simple sliding cylinders whose high weight caused by the complex valve clearance compensation does not allow the speeds required by modern engines.

Cup tappets for transferring the cam movement to valves are known (cf. L. Apfelbeck “Paths to high-performance engines” Motorbuch Verlag Stuttgart 1979, chapters V and VII).

The object of the invention is to avoid these deficiencies and to improve a valve control of the type described at the outset in such a way that its advantages can also be used for high-speed internal combustion engines, without having to accept the disadvantages of the prior art.

The invention solves this problem with the features of claim 1.

The provision of bucket tappets between the conical cams and the valves means that the additional mass to be moved via the cam drive can be kept comparatively small, so that the achievable engine speed is not restricted in this regard. In addition, the cup tappet, which is arranged coaxially to the valve stem, can be guided in a bore of the cylinder head that receives the valve spring, so that the transverse forces transmitted from the conical cams to the cup tappet can be transferred to the cylinder head in a simple manner without valve loading. Because of the comparatively large diameter of the guide bore for the bucket tappet, the additional load on the tappet guide due to the transverse forces occurring remains within permissible limits, the space required for guiding the bucket tappet being advantageously met by the space available with a radial valve arrangement.

The possible guide length for the cup tappets ensures that the tilting moments that occur during a cam stroke are transferred to the cup tappets. According to the invention, these tilting moments can be avoided if, in the rotational position for the maximum stroke, the cams are pre-curved against the associated bucket tappet from a plane normal to the axis. This means that the bucket tappet is not over-centered even when the cam stroke is full. With a corresponding adjustment to the respective geometrical conditions, the cam curvature can easily achieve that the bucket tappet is always loaded in the center, which allows the individual valves to tilt the bucket tappet without tilting even when the angle of inclination is comparatively large.

Due to the axial displaceability of the cams, any desired valve clearance can be set in a simple manner,

because with an axial displacement of the cams the distance between the control surface of the cams and the tappet changes. There is therefore no need to adjust the valve clearance, for example by means of washers between the tappet and the valve stem.

One possibility of arranging the cams in an axially adjustable manner is to mount the cams on the camshaft in an axially adjustable manner. The respective axial position of the cams can be secured, for example, by shaft nuts. A further possibility of adjusting the valve clearance can be obtained in that the camshaft is divided and that the partial shafts each having a cam are axially adjustable per se. In this case, the partial shafts of the camshaft must be held axially to fix the set valve clearance, which can be achieved in different ways.

The arrangement of individually adjustable partial shafts also allows independent adjustment of the valve clearance if the partial shafts of the camshaft are hydraulically adjustable. Particularly simple design conditions can be ensured in this way that the partial shafts are acted upon hydraulically via a check valve in each case in order to reduce the valve clearance, because the axial position of the respective partial shaft is retained with the closing of the check valve following an adjustment.

The transmission of the cam stroke to the valve stems via a bucket tappet which is displaceably mounted in the cylinder head finally enables the formation of a flow channel for a cooling medium between the two camshafts in the arrangement of four radially arranged valves, to which a common camshaft with conical cams is assigned in pairs advantageous cooling of the cylinder head can also be provided in the area of the spark plug.

• Fig. 1 eine erfindungsgemäße Ventilsteuerung für eine Brennkraftmaschine im Schnitt nach der Linie III-III der Fig. 3,
• Fig. 2 eine Konstruktionsvariante in einem der Fig. 1 entsprechenden Schnitt,
• Fig. 3 einen Schnitt nach der Linie II-II der Fig. 4 und
• Fig. 4 eine schematische Draufsicht auf einen Zylinderkopf mit vereinfachter Darstellung der erfindungsgemäßen Ventilsteuerung.

The subject matter of the invention is shown in the drawing, for example. Show it

• 1 is a valve control according to the invention for an internal combustion engine in section along the line III-III of FIG. 3,
• 2 shows a construction variant in a section corresponding to FIG. 1,
• Fig. 3 is a section along the line II-II of Fig. 4 and
• Fig. 4 is a schematic plan view of a cylinder head with a simplified representation of the valve control according to the invention.

The internal combustion engine shown consists essentially of a cylinder 1, the cylinder head 2 of which has two intake valves 3 and two exhaust valves 4, the arrangement being such that the valves with the same function are diametrically opposed with respect to the cylinder axis. The valves 3, 4 are aligned radially with respect to the combustion chamber, which is closed off by a spherical cap, so that the axes of the valve stems 5 intersect at the center of the ball defining the spherical cap. These valves 3 and 4 are assigned in pairs to a camshaft 6 which carries conically shaped cams 7. The cam stroke is transmitted to the valve stems 5 via a cup tappet 8, which is cup-shaped and coaxially encloses the valve spring 9 and the spring plate 10. This tappet is in a bore 11 of the cylinder head 2 guided coaxially to the valve stems 5 so that the transverse forces transmitted from the conical cams 7 to the tappets 8 can be transferred to the cylinder head 2 via the wall of the bore 11. Since the bucket tappet 8 lies loosely on the valve stem 5, only a power transmission in the direction of the axis of the valve stem 5 is possible, but not transversely to it.

As can be seen in particular from FIGS. 1 and 2, the conically shaped cams 7 are pre-curved in the rotational position for the maximum stroke in the raised area from a plane normal to the axis against the associated bucket tappet 8, so that the bucket tappet 8 does not become eccentric from the cam during the stroke can be overrun. The load on the bucket tappet 8 therefore remains central in every stroke position.

To adjust the valve clearance, the camshaft 6 is divided into two partial shafts 6a and 6b according to FIG. 1, each part being axially displaceably mounted in the cylinder head 2. These two part shafts 6a and 6b are connected to one another in a rotationally fixed but axially displaceable manner via an axially fixed coupling piece 12, namely there is a multi-groove connection between the part shafts 6a, 6b and the coupling piece 12. The desired valve clearance is set by an axial adjustment of the partial shafts 6a, 6b, washers 13 of corresponding thickness in the form of half rings are inserted between the coupling piece 12 and the shaft collars 14 for fixing the position before the partial shafts are axially clamped together with the coupling piece 12 via a tension bolt 15 become. The centrifugal forces that occur due to the centrifugal forces 13 being prevented are prevented by an axially projecting edge projection of the shaft collars 14 that surrounds the washers on the outside. The adjustment of the valve clearance can therefore be carried out without complex and time-consuming dismantling and installation work, without the need to readjust the valve timing.

The construction illustrated in FIG. 2 even allows an independent valve clearance adjustment in that the partial shafts 6a, 6b of the camshaft 6 are acted upon hydraulically. For this purpose, the partial shafts 6a, 6b are connected to pressure cylinders 16, which can be supplied with pressure oil from the lubrication system of the engine via channels 17 provided in the coupling piece 12 and check valves 19 inserted into axial through bores 18 of the partial shafts. If a cam 7 moves in the area of its base circle over the bucket tappet 8, any play that may exist between the cam and the bucket tappet is compensated for, because the pressure oil can flow via the check valve 19 to the pressure cylinder 16 and can axially adjust the partial shaft in the sense of a play reduction. until the check valve closes again due to the pressure building up in the pressure cylinder 16, so that the partial shaft is held in its axial position. Leakage losses which are noticeable by a pressure reduction in the pressure cylinder 16 when the cam moves in the area of its base circle over the tappet are immediately compensated for, because in such a case the check valve 19 opens again. The hydraulic action on the partial shafts 6a, 6b in the sense of a reduction in play between the cup tappets 8 and the cams 7 thus causes the cup tappets 8 to be in constant contact with the cams 7, which has an advantageous effect on the smooth running and the load on the cams and the cup tappets.

As can be seen in particular in FIG. 3, a flow channel 20 for a cooling medium can be kept free between the two camshafts 6 and the valves 3 and 4 assigned to these camshafts, which also creates favorable cooling conditions in the area of the central spark plug 21, especially in air-cooled engines .

Claims (6)

1. Valve control for a reciprocating piston internal combustion engine with at least one cylinder (1) and with four valves (3, 4) arranged inclined to one another in the cylinder head (2) operated by cams (7) of two cam shafts (6) in radial arrangement with respect to the combustion chamber of the cylinder (1), of which two are actuated by one of the two cam shafts (6) and the other two by the other cam shaft (6), wherein, for each valve (3,4), a separate conically constructed cam (7) is provided and each valve (3, 4) has, in each case, a valve spring (9) and a spring carrier (10), characterised in that each cam shaft (6) is arranged above the cylinder head (2) and that between each valve (3,4) and the respective cam (7) there is provided a cup tappet (8) arranged coaxially with the valve (3,4) slidably guided in the cylinder head (2) which is constructed in a pot shape, which surrounds the valve spring (9) and the spring carrier (10) coaxially and engages directly on the respective cam (6) and that

   in the rotational position for the maximum stroke, the cams (7) in the lifting region are precurved out of a plane normal to the axis towards the respective cup tappet (8) and

   the cams (7) are axially adjustable.
2. Valve control according to Claim 1, characterised in that the cams (7) are mounted axially adjustably on the cam shaft (6).
3. Valve control according to Claim 1, characterised in that the cam shaft (6) is divided and that the partial shafts (6a, 6b), having in each case one cam (7), are themselves axially adjustable.
4. Valve control according to Claim 3, characterised in that the partial shafts (6a, 6b) of the cam shaft (6) are hydraulically adjustable.
5. Valve control according to Claim 4, characterised in that the hydraulic loading of the partial shafts (6a, 6b) takes place in the sense of a diminution of the valve play via, in each case, a check valve.
6. Valve control according to one of Claims 1 to 5, characterised in that between both of the cam shafts (7), a flow channel (20) is provided for a cooling medium.

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