GB2336888A - Internal combustion engine having variable valve timing. - Google Patents

Abstract

A variable valve timing (VVT) mechanism for a 3 cylinder or V6 internal combustion engine has inlet valves operated by first and second camshafts (18, 19, see Figure 1), the second camshaft 19 having an elongate portion 23 extending coaxially through the first camshaft 18. First and second variable valve timing mechanisms 32, 33 are driven by a common input member 41 having a pair of offset pegs 39 that are radially offset by 90‹, engaging a slot 37 in a intermediate driving member 36. This intermediate driving member in turn drives output members 43, 59 on the further camshaft by corresponding, diametrically opposed peg 42 and slot 38. The axis of rotation of each intermediate driving member is moveable, by eccentric sleeves 51, 51A, through a respective locus to vary the valve timing. The loci of the first and second VVT mechanisms are offset to compensate for the crankshaft offset.

Description

2336888 INTERNAL COMBUSTION ENGINE The invention relates to an internal

combustion engine of the kind having an engine block which defines at least first and second cylinders arranged in line, a crankshaft, a first group of valves comprising inlet valves for each cylinder, a second group of valves comprising exhaust valves for each cylinder and a camshaft drive mechanism comprising first and second camshafts which in use extend parallel to the crankshaft for operating one of said groups of valves for the first and second cylinders respectively, the second camshaft having an elongate portion extending coaxially through the first camshaft, a first variable valve timing (VVT) mechanism arranged so that in use drive is transmitted from the crankshaft to the first camshaft and a second WT mechanism arranged so that in use drive is transmitted from the crankshaft to the second camshaft through the elongate portion, each WT mechanism comprising a common input member for driving connection to the crankshaft and having a pair of radially offset driving means, a respective intermediate driving member arranged to be driven by a respective one of the offset driving means, a respective output member arranged to drive the respective camshaft and having a respective radially offset driven means arranged substantially radially opposite the respective offset driving means and to be driven by the respective intermediate driving member, the output member of the second WT mechanism extending through an aperture in the intermediate driving member of the first WT mechanism and the input member of the first WT mechanism extending through an aperture in the driving member of the second WT mechanism, and means for moving the axis of rotation of the respective intermediate driving member through a locus to vary the valve timing.

An internal combustion engine of the kind referred to above is described in GB 2 268 570 and in particular a four cylinder in-line engine is described.

This engine, by implication, has a conventional four throw crankshaft in which the throws for cylinders Nos.1 and 2 are angularly spaced by 180 to give an even 1-3-4-2 firing order. As a result of the 1800 crankshaft spacing the offset driving means of the common input member are offset by 90 and the locus of the axis of rotation of each intermediate driving member is the same. The locus is created by rotation of an eccentric sleeve which acts as a bearing for the intermediate driving members and is common to both.

The camshaft drive mechanism described in GB 2 268 570 can be applied to other types of engine where there are 2, 3 or 4 cylinders in line in a single bank but there are difficulties where the cranks of two adjacent cylinders which share a common WT input member are not angularly spaced by 18T but by a different angle. For example, a three cylinder in line engine or a V6 engine would have the cranks of cylinders Nos.1 and 2 spaced by 120 intervals and a V8 would have the cranks of cylinders Nos.1 and 2 (and Nos.5 and 6) spaced by 90 and 270 (cylinders numbered according to DIN 73 021, i.e. counting from the front (non driving) end; left bank = Nos.1-3 (V6), Nos.14 (V8); right bank = Nos.4-6 (V6), Nos.5-8 (VS)). This means that the angular relationship between the components of the two WT mechanisms has to be different from that of the 4 cylinder in line engine. The present invention addresses this problem.

According to the invention there is provided an internal combustion engine having an engine block which defines at least first and second cylinders arranged in line, a crankshaft having crank throws which are angularly spaced by an amount which is offset from 180 (the crankshaft offset), a first group of valves comprising inlet valves for each cylinder, a second group of valves comprising exhaust valves for each cylinder and a camshaft drive mechanism comprising first and second camshafts which in use extend parallel to the crankshaft for operating one of said groups of valves for the first and second cylinders respectively, the second camshaft having an elongate portion extending coaxially through the first camshaft, a first variable valve timing (VVT) mechanism arranged so that in use drive is transmitted from the crankshaft to the first camshaft and a second WT mechanism arranged so that in use drive is transmitted from the crankshaft to the second camshaft through the elongate portion, each VVT mechanism comprising a common input member for driving connection to the crankshaft and having a pair of radially offset driving means which are angularly offset from each other by substantially 90', a respective intermediate driving member arranged to be driven by a respective one of the offset driving means, a respective output member arranged to drive the respective camshaft and having a respective radially offset driven means arranged substantially radially opposite the respective offset driving means and to be driven by the respective intermediate driving member, the output member of the second WT mechanism extending through an aperture in the intermediate driving member of the first WT mechanism and the input member of the first WT mechanism extending through an aperture in the intermediate driving member of the second WT mechanism, and means for moving the axis of rotation of the respective intermediate driving member through a respective locus to vary the valve timing, the locus for the second WT mechanism being angularly offset from the locus for the first WT mechanism (the WT offset) by an amount which compensates for the crankshaft offset.

In a four stroke engine where the camshafts are arranged to be driven at half engine speed the magnitude of the WT offset is one half the magnitude of the crankshaft offset.

Conveniently the locus of each WT mechanism is generated by a respective eccentric which locates the respective intermediate driving member, in which case each- eccentric may be an eccentric sleeve which provides a bearing for the respective intermediate driving member. Each eccentric sleeve may have gear teeth which mesh with a respective gear pinion on a common adjustment shaft. Alternatively each eccentric sleeve may have gear teeth meshing with a respective gear pinion, the gear pinions being on offset axes and coupled for rotation with a common adjustment shaft or one eccentric sleeve may be driven for rotary adjustment and other eccentric sleeve be coupled for rotation therewith.

Each offset driving means conveniently comprises a respective peg which engages one respective slot or groove in the respective intermediate driving member and each offset driven means comprises a respective peg which engages another respective slot or groove in the respective intermediate driving member, the slots or grooves being diametrically opposed.

The invention will now be described by way of example and with reference to the accompanying drawings, of which:- Fig.1 is a diagrammatic perspective view of one embodiment of an internal combustion engine according to the invention and incorporating a camshaft drive mechanism; Fig.2 is a perspective diagram of the crankshaft and cylinders of the engine shown in Fig. 1; Fig.3 is a partial cross-sectional view on line III-III of the cylinder head of the engine shown in Fig.1 showing parts of the camshaft drive mechanism in detail; Fig.4 is a view similar to Fig.3 showing the camshaft drive mechanism 5 rotated through 90; Fig.5 is a perspective view of one of the components shown in Figs. 3 and 4; Fig.6 is an elevation of another of the components shown in Figs. 3 and 4; Fig.7 is a diagram showing on an enlarged scale the geometry of a WT mechanism incorporated in the camshaft drive mechanism shown in Figs. 1 to 6; and Fig.8 is a diagram showing part of Fig.6 on a further enlarged scale and with further detail.

Referring to Figs.1 to 6 and in particular to Figs.1 and 2, an internal combustion engine 11 includes an engine block 12 comprising a crankcase 13 integral with a cylinder block and a cylinder head 14. A crankshaft 15 is journalled in the crankcase and has a drive pulley 16 for a toothed belt 17 at one end and carries a flywheel (not shown) at the other end for transmitting the engine output, e.g. through a clutch to a gearbox. The cylinder block defines a bank of three cylinders 20 in line which, in the conventional manner, will be referred to as Nos. 1 to 3, starting at the drive pulley end.

The cylinder head 14 carries inlet and exhaust valves (not shown) for the engine. The inlet valves are operated by three inlet camshafts 18, 19 and 21 for cylinder Nos. 1, 2,and 3 respectively. The inlet camshafts 18 and 19 of cylinders Nos. 1 and 2 are nested, that is inlet camshaft 19 has an elongate portion 23 which extends coaxially through a bore 24 in inlet camshaft 18. Inlet camshafts 18 and 19 are both driven by a toothed pulley 25.

An exhaust camshaft 26, extending parallel to the inlet camshafts 18, 19, and 21, is common to all three cylinders and is driven by another toothed pulley 27, pulleys 25 and 27 being driven by the toothed belt 17 and having twice the number of teeth as the drive pulley 16 so as to rotate at half crankshaft speed. The exhaust camshaft 26 acts as a layshaft to transmit drive through another toothed belt 28 and through another pair of pulleys 29 and 31 to the inlet camshaft 21 of cylinder No. 3, pulley 31 having the same number of teeth as pulley 29.

The inlet camshafts 18, and 19, of cylinder Nos.1 and 2 are each driven through a respective variable valve timing (VVT) mechanism, indicated generally at 32, and 33 respectively (Figs 3 & 4). The WT mechanisms 32 and 33 for cylinders Nos.1 and 2 are grouped together outboard of the camshafts 18 and 19 where they are driven by the drive pulley 16 and toothed belt 17.

^ 8 ^ Fig.3 shows the details of the WT mechanism 32 of cylinder No.1 to better effect whereas Fig.4 shows the details of the VVT mechanism 33 of cylinder No.2 to better effect.

Both V57T mechanisms include a common input member 41 which is rotatable about substantially the same axis as the camshafts 18 and 19, being carried by ball bearings 45 in a housing 46 attached to the cylinder head 14. Pulley 25 is spigotted onto the input member 41 and is retained by a cap screw 47.

WT mechanism 32 of No.1 cylinder includes an intermediate driving member 36 which defines a pair of diametrically opposed radially extending slots 37 and 38. Slot 37 is in driving engagement with a driving peg 39 which forms a radially offset driving means on the input member 41. An output member in the form of a bearing portion 43 of the inlet camshaft 18 of No. 1 cylinder has radially offset driven means in the form of a driven peg 42 which is in driving engagement with slot 38. Pegs 39 and 42 drive through rectangular drive blocks 44 each of which is rotatable on its respective peg 39 or 42 and is a close sliding fit in the appropriate slot 37 or 38.

The cylinder head 14 defines a bore 49 whose axis is offset from the axis of rotation of inlet camshaft 18. An eccentric sleeve 51 is rotatable in the bore 49 and provides the outer race of a needle roller bearing 52. The inner race of bearing 52 is the outer diameter of intermediate driving member 36 so that the driving member is journalled in the eccentric sleeve 51.

WT mechanism 33 of No.2 cylinder includes another intermediate driving member 54 which defines a pair of diametrically opposed radially extending slots 55 and 56. Slot 55 is in driving engagement with another driving peg 57 on the input member 41 which is angularly offset from driving peg 39 by 90. Slot 56 is in driving engagement with another driven peg 58 on another output member in the form of a radially extending lobe 59 which is part of the elongate portion 23 of the inlet camshaft 19 of cylinder No.2. Pegs 57 and 58 drive through rectangular drive blocks 61 in a similar manner to pegs 39 and 42.

Intermediate driving member 54 is journalled in another eccentric sleeve 51A by another needle roller bearing 53. Eccentric sleeve 51A is rotatable in a bore 49A of an adapter bush 70 which is fixed in the cylinder head 14. Bore 49A is the same diameter as bore 49 and has its axis offset from the axis of rotation of inlet camshaft 19. However, its axis is not in line with that of bore 49 as will be described in more detail later.

The intermediate driving member 54 of WT mechanism 33 has an aperture 62 angularly spaced from the slots 37 and 38 to allow a boss 63 on the input member 41 to extend through with clearance, the boss 63 being drilled to receive the driving peg 39. An aperture 64 in the driving member 36 is provided to partially accommodate the lobe 59 with clearance. Fig.5 shows the driving member 36 in detail perspective.

Each WT mechanism 32, 33 produces a cyclic variation in the speed of the respective camshaft by moving the axis of rotation of the respective intermediate driving member 36, 54 relative to the axis of rotation of the inlet camshafts 18, 19 in a manner substantially as described in GB 2 268 570. This is achieved by rotating the eccentric sleeves 51 and 51A. Eccentric sleeve 51 is shown in more detail and on an enlarged scale in Fig.6 with some features of eccentric sleeve 51A superimposed. The outer diameter of sleeve 51 which rotates in the bore 49 is represented by D1 and the inner diameter which provides the outer race of the needle roller bearing 52 is represented by D2. The eccentricity of sleeve 51 is represented by E and this dimension is made substantially equal to the offset between the axis of rotation of the inlet camshafts 18, 19 and the axis of bore 49. Sleeve 51' is exactly similar, its outer diameter which rotates in bore 49A being shown dotted and represented by D1a.

Rotary control of each eccentric sleeves 51 and 51A is achieved by rotation of a respective gear pinion 66, 66A which meshes with gear teeth 67, 67A on the outer periphery of the respective eccentric sleeve. The pinions 66, 66A are part of a control shaft 68 which extends from one end of the cylinder head 14 to the other and is driven by a rotary servomotor (not shown). The pinions 66, 66A on the control shaft 68 are axially aligned, the gear teeth 67 on the eccentric sleeves 51, 51A being profiled to compensate for this.

The effect of rotating eccentric sleeve 51 is shown in Figs 7 and 8. In Fig.7 the pegs 39 and 42 of WT mechanism 32 of cylinder No.1 are shown diagrammatically and the line of motion of the inlet valves is indicated by a line V-V. Point 0 corresponds to the axis of rotation of the input member 41 and the inlet camshaft 18; point P corresponds to the axis of rotation of intermediate driving member 36. The dimension 0-P is conveniently referred to as the eccentricity of intermediate driving member 36 for a particular setting of eccentric sleeve 51 and is to be distinguished from the eccentricity E of the.eccentric sleeve which is represented as dimension P-A where A is the axis of the bore 49 in which eccentric sleeve 51 rotates. Points P and A are also shown in Fig.6.

The effect of varying the angular position of eccentric sleeve 51 is seen in Fig.8. When sleeve 51 is rotated point P moves through a locus as represented by circle L in Fig.8. When point P is coincident with point 0 then the axes of rotation of the input member 41, camshaft 18 and intermediate driving member 36 all coincide and the drive from the input member to the camshaft is without any cyclic variation. When the eccentric sleeve 51 is moved such that P is at point P2 the eccentricity 0-P is at a maximum.

The three cylinder engine 11 has even firing intervals so that the throws of the crankshaft 15 are spaced at 120. This means that the crank throws of cylinders Nos. 1 and 2 are offset from 180 by 60', as depicted in Fig. 2 by the angle a which is conveniently referred to as the crankshaft offset. To compensate for this the WT mechanism 33 of cylinder No.2 has the locus La of the axis of rotation of its intermediate driving member 36 angularly offset from the locus L by 30 as depicted by the angle P in Fig. 8. This is achieved by angular displacement of the bores 49, 49A. The magnitude of the angle 0 is one half of that of the angle (x because the WT mechanism rotates at one half of crankshaft speed.

The cam lobes of inlet camshaft 18 are angularly aligned with the driven peg 42. However to compensate for the 3011 offset of the eccentric sleeves 51, 51A, there is a 30' offset in the opposite direction between the lobes of the camshaft 19 and the driven peg 58.

For No.3 cylinder a single VVT mechanism is provided for inlet camshaft 21 and is driven by pulley 31. This is substantially the same as the WT mechanism 32 of cylinder No.1 but can be simplffied to the extent that the driving peg 39 does not have to be mounted on a boss 63 so as to extend through the intermediate driving member of an adjacent ','VT mechanism.

1 It will be appreciated that the common input member 41, the intermediate driving members 36, 54 and the inlet camshafts 18 and 19 can be common with a corresponding four cylinder in line engine similar to that described in GB 2 268 570, except for the need for an angular difference in the alignment of the cams and the driven pegs on at least one of the camshafts.- Although the invention has been described with reference to a three cylinder engine, the cylinder banks in a V6 engine will be exactly similar, each bank having crank throws angularly spaced at 120. For a VS engine having adjacent crank throws angularly spaced at 90 and 270 (a crankshaft offset of 90') the invention can be applied in the same way but the WT offset P is 45. The VS engine will have two WT mechanisms at each end of four cylinders.

Instead of profiling the gear teeth 67 on the eccentric sleeves 51, 51A, the control pinions 66, 66A may run in separate bores, slightly displaced from each other. The pinions 66, 66A would be coupled by a peg and slot or some other form of coupling which allows for shaft misalignment (e.g. an Oldham coupling). -Alternatively, one pinion 66A may be omitted and eccentric sleeve 51A be rotationally coupled to eccentric sleeve 51, e.g. by a peg in one sleeve which engages a radial slot in the other sleeve.

Claims (8)

1. An internal combustion engine having an engine block which defines at least first and second cylinders arranged in line, a crankshaft having crank throws which are angularly spaced by an amount which is offset from 180 (the crankshaft offset), a first group of valves comprising inlet valves for each cylinder, a second group of valves comprising exhaust valves for each cylinder and a camshaft drive mechanism comprising first and second camshafts which in use extend parallel to the crankshaft for operating one of said groups of valves for the first and second cylinders respectively, the second camshaft having an elongate portion extending coaxially through the first camshaft, a first variable valve timing (VVT) mechanism arranged so that in use drive is transmitted from the crankshaft to the first camshaft and a second WT mechanism arranged so that in use drive is transmitted from the crankshaft to the second camshaft through the elongate portion, each WT mechanism comprising a common input member for driving connection to the crankshaft and having a pair of radially offset driving means which are angularly offset from each other by substantially 90', a respective intermediate driving member arranged to be driven by a respective one of the offset driving means, a respective output member arranged to drive the respective camshaft and having a respective radially offset driven means arranged substantially radially opposite the respective offset driving means and to be driven by the respective intermediate driving member, the output member of the second WT mechanism extending through an aperture in the intermediate driving member of the first WT mechanism and the input member of the first WT mechanism extending through an aperture in the intermediate driving member of the second WT mechanism, and means for moving the axis of rotation of the respective intermediate driving member through a respective locus to vary the valve timing, the locus for the second WT mechanism being angularly offset from the locus for the first WT mechanism (the WT offset) by an amount which compensates for the crankshaft offset.
2. 2. An engine according to claim 1 wherein the camshafts are arranged to be driven at half engine speed and the magnitude of the WT offset is one half the magnitude of the crankshaft offset.
3. 3. An engine according to claim 1 or claim 2 wherein the locus of each WT mechanism is generated by a respective eccentric which locates the respective intermediate driving member.
4. 4. An engine according to claim 3 wherein each eccentric is an eccentric sleeve which provides a bearing for the respective intermediate driving member.
5. 5. An engine according to claim 4 wherein each eccentric sleeve has gear teeth meshing with a respective gear pinion on a common adjustment shaft.
6. 6. An engine according to claim 4 wherein each eccentric sleeve has gear teeth meshing with a respective gear pinion, the gear pinions being on offset axes and coupled for rotation with a common adjustment shaft.
7. An engine according to claim 4 wherein one eccentric sleeve is in use driven for rotary adjustment and is coupled to the other eccentric sleeve for rotation therewith.
8. 8. An engine according to any preceding claim wherein each offset driving means comprises a respective peg which engages one respective slot or groove in the respective intermediate driving member and each offset driven means comprises a respective peg which engages another respective slot or groove in the respective intermediate driving member, the slots or grooves being diametrically opposed.

   An internal combustion engine having variable valve timing mechanisms substantially as described herein with reference to the accompanying drawings.