WO2002079615A1

WO2002079615A1 - Valve control mechanism and engines containing same

Info

Publication number: WO2002079615A1
Application number: PCT/GB2002/001545
Authority: WO
Inventors: Christopher Paulet Melmoth Walters
Original assignee: Walters Christopher Paulet Mel
Priority date: 2001-03-29
Filing date: 2002-03-28
Publication date: 2002-10-10
Also published as: GB0107892D0

Abstract

A valve control mechanism is disclosed which permits the engine timing to be varied as a non-linear function of axial camshaft (4) displacement. The mechanism utilises a coupling in which radially outwardly extending pegs (107) carried by a first member (80) cooperate with a variable angular pitch spline track (106) in a second member (88) positioned about said first member (80).

Description

TITLE

VALVE CONTROL MECHANISM AND ENGINES CONTAINING SAME

FIELD OF THE INVENTION

This invention relates to a valve control mechanism for an internal combustion engine, and to engines containing such a mechanism.

BACKGROUND OF THE INVENTION AND PRIOR ART

My British Patent No 2 190 140 describes and claims a valve control mechanism which comprises: a camshaft carrying a plurality of cams, the camshaft being mounted in a cam carrier and being arranged for a limited degree of axial movement and having associated with it means for effecting such movement, each of the cam surfaces having an outline, in a section plane containing the axis of the camshaft, which is not parallel to that axis, whereby in use the valve action is a function of the axial location of the camshaft within the range of permitted axial movement, the mechanism also comprising a cam follower for each cam, the cam follower comprising a one-piece body which reciprocates within a slideway and at one extremity acts upon the end of a valve stem through only a shim and has at the opposite extremity a trough of part- circular cross-section which receives a member in the form of a segment of a circular cylinder, the curved surface of which faces the interior surface of the trough, so that said member can turn with respect to said body, whilst a planar side surface of the member faces the cam surface. The present invention offers developments derived from this earlier valve control- mechanism.

My UK Patent Application NO 9925628.1 (2341659A) describes and claims, in or for use in an internal combustion engine, a valve control mechanism which comprises :

(1) a camshaft carrying a plurality of cams, the camshaft being mounted in, or being adapted to be mounted in, a cylinder head or cam carrier; and

(2) means for varying the rotational phase of the camshaft ;

characterised in that

(A) said rotational phase varying means comprises a piston housed and axially displaceable within a cylinder, the axial position of said piston being under hydraulic control, said piston being mechanically coupled to the camshaft, said mechanical coupling serving to translate the axial movement of said piston into rotational movement of said camshaft; and

(B) said piston is arranged so that its own axial displacement results additionally in axial displacement of the camshaft .

GB 2341659A thus discloses a valve control mechanism for an internal combustion engine, comprising a camshaft mounted in a camshaft support and drivable in rotation by an input member, the camshaft being axially displaceable relatively to the input member by means of a hydraulic cylinder and piston arrangement, the camshaft being coupled to the input member by a coupling mechanism which causes rotation of the camshaft relative to the input member upon axial displacement of the camshaft relative to the input number .

The embodiment disclosed in GB 2341S59A utilises a timing change device in the form of a helical spline with a constant helix angle which gives a constant (linear) change of valve timing with camshaft axial movement .

However, optimum engine performance is not necessarily achieved if the relationship between changes in valve lift (and/or opening duration) and timing changes is fixed.

According to the present invention the said rotation is a non-linear function of the said axial displacement.

The present invention thus enables a valve control mechanism to be constructed which varies valve timing as a non-linear function of valve lift and opening duration.

Thus, the combined lift/duration/timing change produced by a single axial movement of the camshaft results in the timing change varying non-linearly with axial movement. Therefore the (dyno optimised) optimal timing at particular lift and duration values of the inlet and exhaust camshaft profiles may more nearly approach the ideal compromise of the timing/duration/timing values at the particular engine speed or range of speeds such that the best engine performance/low emissions/ fuel economy trade-off is obtained.

The coupling mechanism may comprise a first member provided with a peg engaging a track provided on a second member, the track being helical and having a helix angle which varies along the axis of the helix. The variation in helix angle may occur discontinuously along the length of the track. For example the track may comprise two or more sections of constant, or approximately constant, helix angle, interconnected by bends in the track.

In a preferred embodiment in accordance with the present invention, the peg is one of a series of radially mounted specially shaped pegs mounted on a particular pitch circle diameter on the camshaft and at a specified longitudinal position. Each peg cooperates with a respective one of the tracks. The pegs may be free to rotate about their own axes in radially positioned holes in a carrier fixed to the camshaft. They are constrained in their longitudinal direction by engagement in the tracks, which are radially formed in the internal bore of the input member, which may be a pulley, gear wheel or sprocket wheel, within which the tracks are mounted. By virtue of this construction, the pegs are able to transmit rotary motion from the input member to the camshaft .

The or each peg preferably comprises a stem connected at one end to the first member and carrying an enlarged head at the other end. At least the head is rotatable relatively to the first member, and possibly the entire peg is rotatably positioned in a respective bore in the first member.

The head may have a generally rectangular profile as viewed lengthwise of the stem. The longer sides of the generally rectangular profile may be convex, with a curvature no less than the curvature of the sharpest bend in the track.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, and to show more clearly how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:

FIGURE 1 is a sectional view through part of an internal combustion engine in accordance with the invention of GB 2341659A, with certain parts omitted for the sake of clarity;

FIGURE 2 shows an alternative construction for part of the engine shown in Figure 1 ;

FIGURE 3 shows one component of the structure illustrated in Figure 2 ;

FIGURE 4 is a sectional view through part of an internal combustion engine incorporating a valve control mechanism in accordance with the present invention;

FIGURE 5 is a sectional view taken on the line V-V in Figure 4 ; FIGURE 6 is a fragmentary view taken' in the direction of the arrow VI in Figure 5 ;

FIGURE 7 shows a component of the coupling mechanism of Figure 5 ; and

FIGURE 8 is an end view of the component of Figure 7.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring to Figures 1-3 of the drawings, the engine of GB 2341659A and that of the present invention includes an overhead camshaft 4 supported in a cylinder head or cam carrier 41. The camshaft 4 carries a plurality of profiled cams 5. Each of the cams 5 cooperates with a half roller 16 which sits in a recess 19 formed on the upper surface of a rectangular cam follower body 6. The half roller 16 is in the form of a segment of a circular cylinder and is free to rotate about its longitudinal axis while seated in the recess 19. A valve stem 1 cooperates with each cam follower body 6 and is held in place by retainers 2 (only the upper retainer is shown in the drawings) and compression springs 3.

The preferred cam profiles are three dimensional, ie valve lift varies tangentially with cam angle in end view and varies along the camshaft linearly at each cam angle in side view. To achieve this, the line connecting the points of maximum radial extent of each cam 5 (ie the lower boundary of the cam as seen in Figure 1) is inclined to the camshaft axis. If desired, the profile of each cam may be such that the line connecting the points of maximum radial extent of the cam at opposite ends (in the direction of the camshaft axis) thereof is skewed to the axis of the camshaft so that the point of maximum radial extent at one end of the cam is angularly displaced about the camshaft axis relatively to the corresponding point at the other end of the cam. This applies equally to the present invention.

In the GB 2341659A engine, the front end of the camshaft 4 is connected to a piston 7 located within a cylinder 9. The chamber of the cylinder 9 is defined by a front plate 10 and by an annular flange 11 integral with the plate 10; the rear face 12 of the chamber is part of a housing 13 which is secured to the flange 11. The inner surface 14 of the housing 13 is provided with internal splines 19 which cooperate with external splines 8 on the camshaft 4 so that axial movement of the camshaft 4 relative to the housing 13 causes rotation of the camshaft.

The housing 13 acts as a carrier for the camshaft 4 at the splines 8 and, through the action of a bearing surface 40, constitutes an outer bearing for the front end of camshaft 4 within the cylinder head or carrier

41. An inner bearing for the front end of the camshaft 4 is provided by the outer diameter of splines 8 and the inner spline track diameter in the housing 13. A camshaft pulley 42 is supported on the cylinder head or cam carrier 41 by camshaft pulley bearings 39. The camshaft pulley bearings 39 can accept radial and axial loads and provide a stiffer than conventional means of mounting the camshaft pulley. The bearings 39 support the camshaft pulley 42 on a circular ring 43 which forms part of the cylinder head structure together with parts 41 and 44.

Referring now to Figures 2 and 3, an alternative to the splines 8, 19 is shown. In this embodiment, the coupling mechanism comprises a cylinder 18 connected to the camshaft 4. The outer surface of the cylinder 18 is formed with a plurality of helical grooves 20-27. These grooves carry bearing elements, eg ball bearings 28 (see Figure 2) . The balls 28 are held between thrust rings 29 and 30; these prevent the balls from moving excessively in the axial direction. They are received in longitudinally extending grooves formed in the inner surface of a housing 31. Consequently axial movement of cylinder 18 results in its partial rotation which in turn imparts a controllable degree of rotational advancement or retardation to the camshaft 4.

Axial movement of the piston 7 is caused by the supply of oil under pressure to chamber 9 via inlets 15 and 17; oil is supplied to these inlets from proportional programmable valves, e.g. "Moog" valves (not shown). By controlling the hydraulic pressures at inlets 15 and 17, piston 7 is caused to move axially within chamber

9, thereby moving the splines 8 (or cylinder 18) and the camshaft 4 by a corresponding axial amount . This movement, in turn, causes an additional rotational movement by means of the splines 8 (or the grooves 20- 27) thereby rotationally advancing or retarding the camshaft within pre-set limits (eg as defined by the number and disposition of the helical grooves 20-27 formed in cylinder 18) . The effect of axial movement of the camshaft 4 will be discerned from Figure 1 : movement to the right causes the valve stem 1 to rise relative to its previous position at the same point in its cycle, thus giving reduced valve lift and, if desired, a change in the duration of valve opening. The rotational advancement imparted by spline 8, 18 additionally advances the valve timing. Movement to the left reverses these effects .

The present invention has many features in common with the earlier invention discloses in GB 2341659A; this will be apparent from the foregoing description of Figures 1-3 together with the general form of construction illustrated by Figure 4. The particular features which distinguish the present invention from the arrangement of GB 2341659A will now be described with reference to Figures 4 to 8.

As shown in Figure 4, the camshaft 4 is provided at its front end with a carrier 80 and a piston 82 having a piston head 83 (corresponding to the piston 7 in Figure 1) . The carrier 80 and the piston 82 are secured to the camshaft 4 by a bolt 84.

The camshaft 4 is supported in the cylinder head or cam carrier 41 by camshaft bearings 86, of which only one is shown in Figure 4. An input member 88, in the form of a sprocket wheel having sprocket teeth 90, is supported on the cylinder head or cam carrier 41 by deep-groove roller bearings 39. The input member 88 carries, as well as the sprocket teeth 90, a toothed pulley wheel 92 for driving ancillary equipment. A body 94 is fixed to the input member 88 by screws 96. The body 94 projects into the carrier 80 and defines a cylinder 95 within which the piston 82 can move. A hydraulic manifold 98 is received in the body 94. The manifold 98 has internal oil supply and return passages 100, 102 which are connected to hydraulic control valves (not shown) . The passage 102 opens at a first end face of the manifold 98, within the cylinder 95 on one side of the piston head 83. The passage 100 communicates with a further passage 104 in the body 94, and so communicates with the cylinder 95 on the other side of the piston head 83. Thus, the piston and cylinder unit made of piston 82 and the body 94 is double-acting enabling the piston 82, and consequently the camshaft 4, to be driven under hydraulic pressure in both directions.

The internal surface of the input member 88 has an array of helically extending grooves or tracks 106. The carrier 80 has a corresponding number of pegs 107, each peg engaging a respective one of the grooves 106, as shown in Figure 5.

As shown in Figures 7 and 8, each peg comprises a stem 108 and a head 110. The head 110 is rotatable with respect to the carrier 80. This may be achieved by using a peg of which the stem 108 and head 110 are formed as a single piece, with the peg 107 being mounted rotatably in the carrier 80, or by mounting the head 110 rotatably on the stem 108, in which case the stem 108 may be rigidly secured with the carrier 80.

As shown in Figure 8, the head 110 is generally rectangular, with convex longer sides 112 and rounded corners 114. As shown in Figure. 6, the grooves 106 do not have a constant pitch angle, as is the case with the splines shown in Figures 1 to 3. Instead, the pitch angle varies in the direction of the camshaft axis. Consequently, the head 110 of each peg 107 rotates about the axis of the stem 108 as the peg moves along the grooves 106. As shown for the right-hand groove 106 in Figure 6, the groove has relatively straight sections 116, 117, 118 and 119 which are connected to one another by bends of varying curvature.

The result of the varying pitch angle of the helical grooves 106 is that the rate of change of the advancing or retarding of the valve timing is not linear with respect to the axial displacement of the camshaft 4 under the action of the piston 82.

Thus, in the present invention, the coupling mechanism between the camshaft 4 and the input member 88 comprises a series of radially mounted, specially shaped pegs 107 mounted on a particular pitch circle diameter on the camshaft 4 and at a specified longitudinal position, at least the heads 110 of the pegs 107 being free to rotate about their own axes in their radially positioned holes in the carrier 80 whilst being constrained in a longitudinal direction by their engagement in the radially formed variable angular pitch spline tracks 106 in the internal bore of the input member 88 within which they are mounted. By virtue of this construction, they are able to transmit rotary motion from the input member 88 to the camshaft 4. The variation in track helix angle with axial length is mainly restricted in a practical design sense by the length and shape of the rectangular head 110 of each peg 107 (see Figure 8) which must be able. to be compliant with its mating track and free to rotate about its own axis as the mating track varies in helix angle with axial camshaft movement .

Thus the camshaft 4 is rotated relative to the input member 88 owing to the axial movement of the camshaft thus varying the camshaft timing in a chosen and as required non-linear fashion within the practical constraints of the possible peg profile/track curvature "helical" geometry.

The rectangular head 110 or "slipper" of the pegs 107 is advantageously profiled such that the radii of curvature of the longer sides of the head 110, and the minimum radius of curvature of the varying track sides are generally equal so that the contact stress between the surfaces brought about by the shear force due to the transmitted torsional loads is reduced. In addition the radiussed front and rear corners of the head 110 and the ability of the heads to rotate ensure that there is a smooth axial movement of the heads 110 along their tracks 90 whilst the arrangement is variably torsionally loaded by the drive system (crankshaft and camshaft etc drive torques) .

The centrifugal forces acting on the pegs 107 as the camshafts 4 rotate are reacted by the peg upper surfaces engaging with the bottom of the flat spline track surfaces 106.

As system as described above may incorporate the following features: 1. The rectangular cam follower may possess any desired type of end of corner radii detail whilst maintaining its basic rectangular shape around the periphery that contains the rectangular half- roller.

2. The rectangular cam follower form advantageously allows the maximum can profile scrub radius (valve velocity) to be increased to allow larger valve lift area cam profiles to be designed which in turn improves engine performance. The scrub radius limit is not limited as in the conventional bucket system which is limited by the cylinder bore centres which control the valve positions and the bearing spacing and the bucket maximum diametral longitudinal proximities to themselves, dictated by the valve centre positions, and the bearing positions (bearing either between buckets or either side of the two buckets) .

3. The rectangular cam follower has an inherently higher solid valve train stiffness/mass ratio at maximum scrub (measured) than a conventional round bucket system which again allows a larger valve lift area cam profile to be designed which in turn improves engine performance .

The rectangular cam follower structure is therefore desirable to provide the larger velocity and the high valve train stiffness/mass ratio that allows the valve train dynamics to sustain the improved valve lift area profiles achievable with the increased velocities. 4. The rectangular cam follower may advantageously be made of a light alloy whilst the half-roller could be steel or ceramic if required to allow comparable valve train stiffness/mass ratios with current light -valve valve trains.

5. The_. line of action of the valve need not be aligned with the side wall of the rectangular follower but could be anywhere between the side wall and the centre on a structural web that connects the 2 sides of the bucket, thus reducing the sideways "overturning" load on the bucket and therefore reducing friction and wear whilst maintaining the optimum valve/follower/camshaft packaging for the larger camshaft axial movement possibility and thus allowing the maximum desirable cam profile variation for a particular design.

6. The valve clearance shimming could conveniently be alternatively achieved by the employment of a half roller that has an integral small amount of additional material above the roller centre line whose flat face is identical to the half roller and parallel to it (vertical sides) . The change in translational valve lift due to these variable half-roller thicknesses in an engine would be small and the servicing convenience of not removing the follower when valve shimming at service intervals would be a big advantage.

Claims

1. A valve control mechanism for an internal combustion engine, comprising a camshaft (4) mounted in a camshaft support (41) and drivable in rotation by an input member (88) , the camshaft (4) being axially displaceable relatively to the input member (88) by means of a hydraulic cylinder and piston arrangement (95, 83), the camshaft (4) being coupled to the input member (88) by a coupling mechanism (106, 107) which causes rotation of the camshaft (4) relative to the input member (88) upon axial displacement of the camshaft (4) relative to the input number (88) , characterised in that the said rotation is a nonlinear function of the said axial displacement.

2. A valve control mechanism as claimed in claim 1, characterised in that the coupling mechanism comprises a first member (80) provided with a peg (107) engaging a track (106) provided on a second member (88) , the track (106) being helical and having a helix angle which varies along the axis of the helix.

A valve control mechanism as claimed in claim 2, characterised in that the first member (80) is secured to the camshaft (4) and the second member (88) comprises the input member.

A valve control mechanism as claimed in claim 2 or 3, characterised in that the track (106) comprises a groove formed in an internal cylindrical surface of the second member (88) .

5. A valve control mechanism as claimed in any one of claims 2 to 4 , characterised in that the peg (107) is one of a plurality of pegs distributed equally about the first member (80) , each peg (107) engaging a respective track (106) in the second member (88) .

6. A valve control mechanism as claimed in any one of claims 2 to 5, characterised in that the or each peg (107) comprises a stem (108) connected at one end to the first member (80) and carrying an enlarged head (110) at the other end.

7. A valve control mechanism as claimed in claim 6, characterised in that the head (110) is rotatable relatively to the first member (80) .

8. A valve control mechanism as claimed in claim 6 or 7, characterised in that the head (110) has a generally rectangular profile as viewed lengthwise of the stem (108) .

9. A valve control mechanism as claimed in claim 8, characterised in that the longer sides (112) of the generally rectangular profile are convex.

10. A valve control mechanism as claimed in any one of claims 2 to 9, characterised in that the variation in helix angle occurs discontinuously .

11. A valve control mechanism as claimed in any one of the preceding claims, characterised in that the camshaft (4) is provided with cams (5) which operate valves, the axial displacement and rotation of the camshaft (4) relative to the input member (88) causing, in operation, variation in the timing lift of the valves and in the duration of opening of the valves .