GB2336889A - Variable valve timing mechanism for 3 cylinder and V6 engines - Google Patents

Abstract

A 3 cylinder or V6 engine has first and second cylinders and a crankshaft with crank throws angularly spaced by 240‹. Inlet valves for the first and second cylinders are operated by respective first and second camshafts 18, 19, the second camshaft having an elongate portion 23 extending coaxially through the first camshaft. First and second variable valve timing (VVT) mechanisms 32, 33 comprise a common input member 41 having a pair of driving pegs 39, 57 which each engage in a slot in a respective intermediate driving member 36, 54. Each driving member in turn drives a respective output member 43, (59, fig. 6) on the respective camshaft by means of a corresponding peg and slot (38, 42 fig. 4 ad 56, 58 fig. 6). The axis of rotation of each intermediate driving member is movable by a eccentric sleeve 51 to vary the valve timing. The driving pegs are spaced by 120‹.

Description

INTERNAL COMBUSTION ENGINE 2336889 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 1800 to give an even 1-3-4-2 firing order. As a result of the 180 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 180' 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 -3 according to DIN 73 021, i.e. counting from the front (non driving) end; left bank = Nos.1-3 (V6), Nos.14 (VS); 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 5 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 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 spaced by 90 plus an offset angle (the input offset) which compensates for the crank offset, 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 spaced at 180' plus an offset angle (the drive offset) and arranged to be driven by the respective intermediate driving member, the output member of the second VVT 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 intermediate driving members through a locus to vary the valve timing.

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

Conveniently 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 in each intermediate driving member being spaced by 180 plus the amount of the drive offset.

Conveniently the amount of the drive offset is equal to the amount of the input offset. In particular, in a four stroke engine where the camshafts are arranged to be driven at half engine speed and the crankshaft offset is 60', the drive offset is conveniently 30'..

The locus of each WT mechanism may be generated by an eccentric which locates the intermediate driving members, in which case the eccentric may be an eccentric sleeve which provides a bearing for the intermediate driving members.

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 in Fig.1 showing parts of the camshaft drive mechanism in detail; Figs.4, 5 and 6 are views similar to Fig.3 each with the camshaft drive mechanism rotated to different positions to show further detail; Fig.7 is a perspective view of one of the components shown in Figs.3 to 6; Fig.8 is an elevation of another of the components shown in Figs.3 and 4; Fig.9 is a diagram showing the angular relationship of certain elements of the camshaft drive mechanism shown in Figs. 1 to 8; and Figs.10, 11, 12 are diagrams similar to Fig 9 each showing the angular relationship of certain of the parts shown in Figs.3 to 7.

Referring to Figs.1 to 8 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.

" 7 " An exhaust camshaft 26 extends 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 (M) mechanism, indicated generally at 32, and 33 respectively (Figs 3 & 4). The M 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.

Figs.3 and 4 show the details of the WT mechanism 32 of cylinder No. 1 to better effect whereas Figs.5 and 6 show the details of the WT mechanism 33 of cylinder No.2 to better effect.

Both WT 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 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 driving peg 42 which is in driving engagement with slot 38. Pegs 39 and 42 transmit drive through rectangular drive blocks 44 each of which is rotatable on its peg 39 or 42 and is a close sliding fit in the appropriate slot 37 or 38.

The housing 46 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 is also journalled in eccentric sleeve 51 by another needle roller bearing 53 and which has a pair of diametrically opposed radially extending slots 55 and 56. Slot 55 is in driving engagement with 1 9 - another driving peg 57 on the input member 41 which is angularly offset from driving peg 39. 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.

An aperture 62 angularly spaced from the slots 37 and 38 in intermediate driving member 54 allows a boss 63 on the input member 41 to extend through with clearance, the boss 63 being drilled to receive the peg 39. Similarly, an aperture 64 in intermediate driving member 36 is provided to partially accommodate the lobe 59 with clearance. Fig.7 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 sleeve 51 which is shown in more detail and on an enlarged scale in Fig.8. The outer diameter of sleeve 51 which rotates in the bore 49 is represented by D l and the inner diameter which provides the outer race of the needle roller bearings 52 and 53 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.

Rotary control of the eccentric sleeve 51 is achieved by rotation of a gear pinion (not shown) which meshes with gear teeth 67 on the outer periphery of the eccentric sleeve. The pinions are part of a control shaft (not shown) which extends from one end of the cylinder head 14 to the other and is driven by a rotary servomotor (not shown).

In Fig.8 point P corresponds to the axis of rotation of intermediate driving member 36 and point A is the axis of the bore 49 in which eccentric sleeve 51 rotates. The dimension P-A represents the eccentricity E of the eccentric sleeve 51. When the eccentric sleeve 51 is rotated point P moves through a locus substantially as described in GB 2 268 570.

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 15throws of cylinders Nos. 1 and 2 are offset from 180 by 6T, as depicted in Fig.2 by the angle a which is conveniently referred to as the crankshaft offset. For No. 3 cylinder a single WT 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 simplified to the extent 20 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 WT mechanism.

To compensate for the crankshaft offset, the WT mechanism 33 of cylinder No.2 has its drive peg angularly spaced from drive peg 39 of cylinder No. 1 by 120. In the case of the four cylinder engine with no crankshaft offset (as described in GB 2 268 570), the drive pegs are angularly spaced by 90', this being the appropriate phase difference for a four stroke engine with a camshaft rotating at half crankshaft speed. Hence the 120 spacing of the drive pegs 39 and 57 in the three cylinder engine amounts to 900 plus 30', which additional amount (i.e. 30') can conveniently be referred to as the input offset. Also in the case of the four cylinder engine, the driven pegs on the camshafts are each at substantially 180' to the respective drive peg, the slots in the intermediate driving members being diametrically opposed. This allows the clearance apertures required in each intermediate driving member to accommodate the drive peg or driven peg of the other intermediate driving member to be spaced at 90 to the slots. In the case of the three cylinder engine, the 120spacing of the drive pegs 39 and 57 means that intermediate drive members with diametrically opposed slots cannot be conveniently used. This is because the clearance apertures would have to be at 60' to one of the slots, making it difficult to accommodate components (pegs, drive blocks and intermediate driving members) which meet strength and wear requirements.

- 12 In the engine described above with reference to Figs.1 to 8, the above difficulty is overcome by spacing the driven pegs 42 and 58 from the respective drive pegs 39 and 57 by 180' plus an offset angle, conveniently referred to as the drive offset. The drive offset is conveniently the same as the input offset, i.e. 30'. Fig.9 shows the angular relationship of all the drive pegs and driven pegs and additionally shows the positions of the drive peg 39A for No.3 cylinder and the corresponding driven peg 42A. The input offset is depicted by the angle P and the drive offset by the angle 0. The angular relationships are further illustrated in Figs.10 to 13. Fig.10 shows the drive pegs 39 and 57, Fig.11 shows the drive pegs 39 and 57 and driven peg 58 in relation to intermediate drive member 54 of WT mechanism 33 (No. 2 cylinder), Fig.12 shows the driven pegs 42 and 58 and drive peg 39 in relation to intermediate drive member 36 of WT mechanism 32 (No.1 cylinder) and Fig.13 shows the driven pegs 42 and 49 in relation to the bearing portion 43 on camshaft 18 and the lobe 59 on camshaft 19. The magnitude of the angle P is one half of that of the angle (x because the WT mechanism rotates at one half of crankshaft speed.

It will be appreciated that the eccentric sleeve, its gear drive mechanism and many other components 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 driving pegs and the slots in the intermediate driving members.

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. Similarly, the invention may be applied to the 3 cylinder or V6 engine irrespective of firing 5 order or the location (front or rear) of the camshaft drive For a V8 engine having adjacent crank throws angularly spaced at 90' and 270' (a crankshaft offset of 90') the invention may be applied in the similar way but to a limited extent only. For three of the adjacent end pairs of cylinders in each bank the firing intervals will be 270 and the invention can be applied with an input offset P of 45 and a drive offset chosen as convenient for positioning the apertures in the intermediate drive members. For the remaining adjacent end pair of cylinders the firing intervals will be 90 and the invention cannot be readily applied. In such a case the invention of our co-pending application GB filed herewith (case P2350) may be applied, conveniently at the rear of the engine. A copy of the specification of co-pending application GB (case P2350) is appended hereto for cross -reference.

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 spaced by 900 plus an offset angle (the input offset) which compensates for the crank offset, 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 spaced at 180' plus an offset angle (the drive offset) and arranged 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 intermediate driving members through a locus to vary the valve timing.
2. An engine according to claim 1 wherein the camshafts are arranged to be driven at half engine speed and the magnitude of the input offset is one half the magnitude of the crankshaft offset.
3. 3.

   An engine according to claim 1 or claim 2 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 in each intermediate driving member being spaced by 180' plus the amount of the drive offset.
4. 4. An engine according to any preceding claim wherein the amount of the drive offset is equal to the amount of the input offset.
5. 5.

   An engine according to claim 2 or any of claim 3 and 4 when dependent upon claim 2 wherein the crankshaft offset is 60'and the drive offset is 3T.
6. 6. An engine according to any preceding claim wherein the locus of each WT mechanism is generated by an eccentric which locates the intermediate driving members.
7. An engine according to clanin 6 wherein the eccentric is an eccentric sleeve which provides a bearing for the intermediate driving members.
8. 8. An internal combustion engine having variable valve timing mechanisms substantially as described herein with reference to the accompanying drawings.