GB2305706A

GB2305706A - A cam arrangement for an internal combustion engine

Info

Publication number: GB2305706A
Application number: GB9619881A
Authority: GB
Inventors: Alfred Beier; Dietrich Distler; Christian Heimermann
Original assignee: Volkswagen AG
Current assignee: Volkswagen AG
Priority date: 1995-09-28
Filing date: 1996-09-24
Publication date: 1997-04-16
Anticipated expiration: 2016-09-24
Also published as: FR2739411B1; FR2739411A1; DE19638330A1; GB9619881D0; GB2305706B

Abstract

A cam arrangement for an internal combustion engine, comprises a camshaft formed from an inner shaft 1 and from cam elements 2 arranged thereon, each cam element comprising a sleeve-shaped carrier having cam discs 4, 5 mounted thereon. The cam elements are mounted on the inner shaft 1 so as to be pivotable to a limited extent, and are divided in the axial direction into two cam element parts 2a, 2b, axial pivotability being limited by a stop 8 running in an oil-filled recess 9. To achieve different closing flanks of the gas exchange valves actuated by cam discs 4, 5 of the cam elements 2, supply ducts 11, 12, which match with the recess 9 and which branch off from a longitudinal duct 10 of the inner shaft 1, and which carry pressure oil, have different cross-sections. A sealing ring 13, divides the oil filled recess 9 between the two cam element parts 2a, 2b, and a throttle bore 20 may be provided in the stop. Various oil passage configurations (figures 3a to 4c) are disclosed.

Description

DESCRIPTION A CAM ARRANGEMENT FOR AN INTERNAL COMBUSTION ENGINE The present invention relates to a cam arrangement for an internal combustion engine.

A cam arrangement of the relevant generic type is known from DE-43 22 246 Al, two cams located at an axial distance from one another being arranged on a carrier element designed in the form of a sleeve. This sleeve is arranged coaxially relative to an inner shaft and, during production, can be pushed onto the latter.

This known arrangement affords many advantages in terms of the manufacture of a camshaft, since the individual cams or the entire cam element can be manufactured independently of the inner shaft. In principle, it serves for the purpose of influencing the closing flanks of gas exchange valves in dependence on rotational speed.

Furthermore, it is known, in principle, from DE-32 34 640 C2 and from DE-41 00 087 Al to damp the pivoting movement of cams, arranged movably relative to an inner shaft, by an arrangement of bores provided, if appropriate, with throttle diaphragms. In this case, the pivoting cams have oil-filled recesses which extend over a limited circumference and into which a nose fixedly connected to the inner shaft and having these bores or throttle diaphragms extends. A cam arrangement of the relevant generic type having this type of limited pivotability, is also disclosed in DE43 22 246 Al.

An aim of the present invention is to provide a cam arrangement for an internal combustion engine, in which, in as simpler way as possible in terms of construction, by means of pivoting cams, closing flanks differing in dependence on rotational speed, of gas exchange valves assigned to a cylinder of the internal combustion engine and serving for inlet and/or exhaust, are achieved.

According to the present invention there is provided a cam arrangement for an internal combustion engine, comprising a camshaft formed from an inner shaft and from cam elements arranged thereon, for the periodic actuation of gas exchange valves, each cam element having at least two cam discs located at an axial distance from one another on a sleeve-shaped carrier element which has a continuous cylindrical bore for coaxially receiving the inner shaft this cam element being held on the inner shaft so as to be pivotable to a limited extent, a stop effective between the cam element and inner shaft limiting the pivoting range and, for this purpose, engaging into an oilfilled recess in the cam element the cam element being designed so as to be divided in the axial direction, each part cam element formed thereby carrying at least one cam disc and being pivotable to a limited extent independently of the other part cam element in each case.

The present invention provides a cam element assigned to a cylinder of an internal combustion engine which has at least one division in the axial direction, so that the part cam elements thereby obtained are each pivotable to a limited extent independently of one another. The advantages in terms of production which can be carried out separately from the inner shaft and in terms of mounting on the inner shaft are preserved in full, but, in addition, there is the advantage that the gas exchange valves actuated by the part cam elements have, on their closing flank, valve elevation curves which deviate from one another. In use on a camshaft serving an inlet, a controlled charge movement can be achieved thereby, since the inlet valves actuated in each case by the part cam elements have an opening duration of differing length.

In an advantageous embodiment of the present invention, this deviating pivotability of the part cam elements can be achieved, for example, in that the cam element is not divided symmetrically, but the axial extent of the part cam elements achieved thereby are different from one another. A different damping behaviour is thereby achieved within the oil-filled recess, since the displaceable oil volumes of the two part cam elements differ from one another.

In addition to or irrespective of this, the supply ducts of the part cam elements, the said supply ducts carrying pressure oil, branching off from a longitudinal duct formed in the inner shaft and supplying the recess, can have different throughflow resistances and/or designs or arrangements from one another, with the result that a damping behaviour different in each case is once again established. For this purpose, the supply ducts can have cross-sectional areas, outflow orifices and positionings differing from one another and/or, in addition, non-return valves.

The ducts provided with a non-return valve provide damping abruptly at the commencement of each cam pivoting movement, whereas damping commences gradually in the other cases.

In addition to the constructive measures mentioned, the entire damping behaviour of the part cam elements is influenced by the valve-spring forces of the gas exchange valves, actuated by the cam discs, and by the masses moved at the same time.

The cam arrangement according to the present invention can advantageously be used in any valvecontrolled internal combustion engine having at least two identical inlet and/or exhaust valves, whilst, for example in the case of three valves serving for inlet, one part cam element can have two cam discs for the synchronous actuation of two of the three inlet valves and the other part cam element can have one cam disc for actuating the third inlet valve. Furthermore, it is possible, whilst preserving a constructional unit, to provide more than one division on a cam element, in order thereby to set separate damping properties in each case, for example for the abovementioned three inlet valves.

The present invention will now be further described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 shows a side view of a cam arrangement constructed according to the present invention, Fig. 2 shows a section along the line II - II in Fig. 1.

Fig. 3a, b, c show different versions of a detail of Fig. 2, and Figs. 4a, b, c show top views of the versions according to Figs 3a to c.

A cam arrangement for an internal combustion engine comprises a camshaft, formed from an inner shaft 1 and from cam elements 2 arranged thereon, for the periodic actuation of gas exchange valves (not shown) designed as inlet or exhaust valves, with cup tappets 3 being interposed. The cam elements 2 have a plurality of cam discs 4, 5 located at an axial distance from one another on a sleeve-shaped carrier element 6 which has a continuous cylindrical bore 7 for coaxially receiving the inner shaft 1.

The cam element 2 is held on the inner shaft 1 so as to be pivotable relative thereto to a limited extent, a stop 8 effective between the cam element 2 and inner shaft 1 and fixed to the inner shaft 1, limiting the pivoting range. The cam discs 4, 5 have a recess 9 into which the stop 8 engages and can move as the cam discs 4, 5 pivot, the length of recess 9 limiting the pivoting range.

The inner shaft 1 has a longitudinally extracting duct 10 carrying pressure oil and supply ducts 11, 12 branching off radially from the latter and opening into the recess 9.

The cam element 2 is designated so as to be divided in the axial direction of the camshaft, part cam elements 2a and 2b formed thereby each being assigned a cam disc 4 and 5. Arranged coaxially relative to the inner shaft 1 between the two part cam elements 2a, 2b is a sealing ring 13 which separates the oil-filled recess 9 between these two part cam elements 2a, 2b in an oil-tight manner. As is evident from Fig. 1, the axial extents of the part cam elements 2a, 2b differ from one another, with the result that the part cam element 2a carrying the cam disc 4 is assigned a portion of larger area of the stop 8 than the other part cam element 2b.

To acheive different dampings of the part cam elements 2a, 2b, the supply ducts, 11, 12 have throughflow resistances deviating from one another, this being achieved according to Fig. 1, for example, by means of different cross-sectional areas.

Furthermore, these supply ducts 11, 12 can be modified in terms of their relative position in relation to the recess 9 and in terms of their number and/or their geometrical design at their outflow orifices. Various versions for this purpose are shown in Figures 3a to 3c and 4a to 4c. Thus, in each case, Figure 3 shows the longitudinal duct 10 of the inner shaft 1, one of the supply ducts 11, 12, their outflow orifices 14 into the recess 9 and the stop 8 which is designed cylindrically here and which is movable together with the inner shaft 1 between stop faces 15, 16 of the recess 9.

So that, even at elevated rotational speeds, the recess 9 can be filled satisfactorily with damping oil in the short period of time available, the size of the outflow orifice 14 must not be fall below a specific value. On the other hand, the distance in the circumferential direction which the stop face 15 covers until the outflow orifice 14 is closed completely should be as short as possible, in order to achieve damped pivoting also for high rotational speeds. In this case, damping does not commence before closure of the outflow orifices 14, the stop face 15 moving only slightly in relation to the inner shaft 1 in higher rotational speed ranges.

These contradictory requirements with regard to the size of the outflow orifices 14 and the available time span can be satisfied, for example according to Figures 3b and 4b, by means of a mutually parallel arrangement of a plurality of supply ducts. According to Figures 3c and 4c, the supply duct 11, which has no or only a slight overlap with the recess 9 when the stop 8 bears on the stop face 16, can open into a groove 17 which extends only slightly in the longitudinal direction of the recess 9, but which makes a sufficient outflow area available.

In order to prevent damping from commencing too abruptly in a jolt-lik.e manner during the complete closing of the outflow orifice 14, a microduct 18 tapering in the circumferential direction can be formed on the latter according to Figures 3a and 4a.

For further influencing the damping, according to Figure 2, which, in relation to Figure 1, shows a cam disc S rotated in the direction of the arrow during run-off from the cup tappet 3, a non-return valve 19 can be arranged on one or in both supply ducts 11, 12.

Furthermore, in addition, throttle bores 20 of specific cross-section, assigned to the part cam elements 2a, 2b, can be arranged in the stop 8. By means of the non-return valves 19 which are advantageously designed as ball valves, a comparatively rapid commencement of damping can be brought about, since, in the event of the least relative movement of the cam element 2, the ball is induced to close as a result of the diminishing oil pressure.

Furthermore, the achievable damping characteristics can be influenced by the design of the nonreturn valve 19. For example, a Teflon ball has lower inertia than a steel ball, with the result that, in turn, a more rapid closure movement can be achieved.

Moreover, rapid closing can be achieved by means of a comparatively short travel of the ball, which, if appropriate, can be arranged in a spring-assisted manner. If too rigid damping occurs in specific rotational speed ranges as a result of the abovementioned measures with regard to ball mass, spring assistance and closing travel, the non-return valve 19 can additionally be provided with a bypass 21 comparable in its effect to the throttle bore 20.

Whereas, in the solution with a throttle bore 20 in the stop 8, the oil quantity which has passed through is lost to the pressure-oil circuit as leakage oil and, to that extent, places an increased power demand on the oil pump, a solution which is more favourable in terms of overall efficiency is possible by means of the abovementioned bypass 21, since pressure oil forced back through this is fed once again to the pressure-oil circuit. In contrast to Figure 2, this bypass 21 can be arranged anywhere between the recess 9 and longitudinal duct 10. The relative position of such a bypass 21 in relation to the recess 9 determines the damping character.The advantage of an arrangement in the vicinity of the stop 8 is that, during the filling of the recess 9, the oil volume flow is additionally fed through this bypass 21, thus assisting the return movement of the cam element 2 into its initial position. In an arrangement distant from the stop 8, damping is preferably reduced towards higher rotational speeds.

When the abovedescribed cam arrangement is in operation, the two cam discs 4, 5 run synchronously on their associated cup tappets 3 in the direction of rotation indicated in Figure 2, the stop 8, which is fixedly connected to the driving inner shaft 1, bearing on the matching stop face 16 of the cam discs 4, 5.

When the cam discs 4, 5 run off, as shown in Figure 2, the valve spring (not shown) presses the respective cup tappet 3 upwards, with the result that the angular speed of the cam discs 4, 5 deviates briefly from that of the inner shaft 1 and the stop 8 runs through the recess 9 in dependence on rotational speed at most until the opposite stop face 15 is reached. By virtue of the abovedescribed measures in the form of the different supply ducts 11, 12, of the non-return valve 19, of the throttle bore 20, of the bypass 21 and of the differing axial extent of the part cam elements 2a, 2b, a different damping behaviour of these elements can be set. Consequently, in the gas exchange valves actuated by the cam discs 4 or 5, closing flanks different from one another are obtained.

It may be pointed out that the axial retention of the cam element 2 constituting a constructional unit can be implemented, in contrast to Figure 1, where it occurs by means of retaining sleeves 22, 23, also, for example, by means of an overlapping arrangement of those parts of the carrier element 6 which are assigned to the two part cam elements 2a, 2b. In this case, for example, one portion of the carrier element 6 can engage over the other and engage into this positively, but so as to allow rotation.

Claims

1. A cam arrangement for an internal combustion engine, comprising a camshaft formed from an inner shaft and from cam elements arranged thereon, for the periodic actuation of gas exchange valves, each cam element having at least two cam discs located at an axial distance from one another on a sleeve-shaped carrier element which has a continuous cylindrical bore for coaxially receiving the inner shaft this cam element being held on the so as to be pivotable to a limited extent, a stop effective between the cam element and inner shaft limiting the pivoting range and, for this purpose, engaging into an oil-filled recess in the cam element, the cam element being designed so as to be divided in the axial direction, each part cam element formed thereby carrying at least one cam disc and being pivotable to a limited extent independently of the other part cam element in each case.

2. A cam arrangement as claimed in claim 1, in which a longitudinal duct for carrying pressure oil is provided in the inner shaft, supply ducts branching off radially from the latter and opening into the recess, at least one supply duct being arranged for each of the part cam elements, the said supply ducts having throughflow resistances deviating from one another.

3. A cam arrangement as claimed in claim 1 or claim 2, in which the axial extents of the part cam elements differ from one another.

4. A cam arrangement as claimed in claim 2 or claim 3, in which a sealing ring separating the recesses of the part cam elements from one another in an oil-tight manner and coaxially surrounding the inner shaft is arranged in the region of the division of the cam element.

5. A cam arrangement as claimed in claim 2 or claim 3, insofar as claim 3 refers back to claim 2, in which the supply ducts have cross-sectional areas which differ from one another.

6. A cam arrangement as claimed in claim 2 or claim 3, insofar as claim 3 refers back to claim 2, in which involved the supply ducts have outflow orifices which differ from one another.

7. A cam arrangement as claimed in claim 2 or claim 3, insofar as claim 3 refers back to claim 2, in which the part cam elements are each assigned a number of supply ducts each number differing from the other.

8. A cam arrangement as claimed in claim 2 or claim 3, insofar as claim 3 refers back to claim 2, in which at least one of the supply ducts has a non-return valve.

9. A cam arrangement as claimed in one or more of the preceding claims, in which the part cam elements each carry a number of cam discs, each number differing from the other.

10. A cam arrangement as claimed in one or more of the preceding claims, in which the cam element is designed so as to multiply divided in the axial direction.

11. A cam arrangement for an internal combustion engine, constructed and arranged substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

Amendments to the claims have been filed as follows

1. A cam arrangement for an internal combustion engine, comprising a camshaft formed from an inner shaft and from cam elements arranged thereon, for the periodic actuation of gas exchange valves, each cam element having at least two cam discs located at an axial distance from one another on a sleeve-shaped carrier element which has a continuous cylindrical bore for coaxially receiving the inner shaft this cam element being held on the inner shaft so as to be pivotable to a limited extent, a stop effective between the cam element and inner shaft limiting the pivoting range and, for this purpose, engaging into an oilfilled recess in the cam element, the cam element being designed so as to be divided in the axial direction, each part cam element formed thereby carrying at least one cam disc and being pivotable to a limited extent independently of the other part cam element in each case.