GB2345739A

GB2345739A - Variable valve timing mechanisms connected in series via inverter

Info

Publication number: GB2345739A
Application number: GB0000282A
Authority: GB
Inventors: Peter Harry Parker
Original assignee: MG Rover Group Ltd
Current assignee: MG Rover Group Ltd
Priority date: 1999-01-14
Filing date: 2000-01-10
Publication date: 2000-07-19
Also published as: GB0000282D0

Abstract

An IC engine camshaft mechanism comprises first 18, second 19 and third 21 camshafts operating valves for respective cylinders by means of first, second and third variable valve timing mechanisms (VVT) providing respective camshaft cyclic speed variation given constant crankshaft driven member 25 speed. The first and second VVTs (32, 33 Figs. 3,4) are nested together and driven by a common input member (41). The second camshaft has a portion (23) extending coaxially through the first camshaft to take drive from its VVT and a further portion (123 Fig 5) extending coaxially through the third camshaft to drive the third VVT (132) input member (141) through an inverter (133), (a mirror of the second VVT) to invert the second camshaft speed variation such that the third VVT input member rotates at the same speed as the common input member.

Description

INTERNAL COMBUSTION ENGINE The invention relates to an internal combustion engine of the kind having at least two cylinders, 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 a respective camshaft for operating one of said groups of valves for each cylinder, each camshaft being arranged to be driven by a respective variable valve timing (VVlV) mechanism operative to provide a cyclic variation of the rotational speed of the respective camshaft during constant rotational speed of a respective input member driven by the crankshaft.

GB-A-2 336 888 and GB-A-2 336 889 describe internal combustion engines in which VVT mechanisms are provided for the inlet camshafts only. Two VVT mechanisms are at the end of the engine where a drive is taken from the crankshaft to the camshaft. The exhaust camshaft is a conventional, fixed timing, component, but also serves to transmit drive to a third WT mechanism at the end of the engine remote from the drive from the crankshaft to the camshaft.

In some cases it may be inconvenient to provide the additional drive from the exhaust camshaft to the VVT mechanism or mechanisms, e. g., because of installation constraints or because it is required to use VVT mechanisms on the exhaust camshaft.

It is an object of the present invention to provide an internal combustion engine including an alternative drive for a VVT mechanism.

According to the invention there is provided an internal combustion engine having at least two cylinders, 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 a respective camshaft for operating one of said groups of valves for each cylinder, each camshaft being arranged to be driven by a respective variable valve timing (VVT) mechanism operative to provide a cyclic variation of the rotational speed of the respective camshaft during constant rotational speed of a respective input member driven by the crankshaft, the input member of one of the WT mechanisms being arranged to drive the input member of another of the VVT mechanisms through said one VVT mechanism and an inverting mechanism which is operative to invert the cyclic variation in the rotational speed produced by said one VVT mechanism so that in use the input member of said other VVT mechanism rotates at the same speed as the input member of said one VVT mechanism.

In a preferred arrangement, at least first, second and third said cylinders are arranged in line, first, second and third said camshafts are provided for operating said one group of valves for the first, second and third cylinders respectively, first, second and third said WT mechanisms are provided for the first, second and third camshaft respectively and each of the first and second WT mechanisms has a common input member, the second camshaft having elongate portions each extending coaxially through the first and third camshafts respectively so that in n use drive is transmitted from the common input member to the input member of the third VVT mechanism through the second VVT mechanism, the second camshaft and the inverting mechanism.

Conveniently, each of the third VVT mechanism and the inverting mechanism comprises 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 third camshaft and the input member of the third VVT mechanism respectively 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 inverting mechanism having an input member which extends through an aperture in the intermediate driving member of the third WT mechanism and the input member of the third WT mechanism extending through an aperture in the intermediate driving member of the inverting mechanism, and means for moving the axisofrotationoftherespectiveintermediatedrivingmemberthrougha the axis of rotation of the respective intermediate driving member through a respective locus to respectively vary the valve timing and compensate for the valve timing variation of the second camshaft, the radially offset driving means of the third WT mechanism and the radially offset driven means of inverting mechanism being on the input member of the third WT mechanism and angularly offset from each other by substantially 90 .

Where the crankshaft has crank throws which are angularly spaced by an amount which is offset from 180 (the crankshaft offset), the locus for the inverting mechanism may be angularly offset from the locus for the third WT mechanism (the WT offset) by an amount which compensates for the crankshaft offset.

Normally, 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.

Each locus of the axis of rotation of the respective intermediate driving member may be generated by a respective eccentric which locates the respective intermediate driving member. Such an eccentric may be an eccentric sleeve which provides a bearing for the respective intermediate driving member. Each eccentric sleeve may have gear teeth meshing with a respective gear pinion on a common adjustment shaft. Alternatively, each eccentric sleeve may have gear teeth which mesh with a respective gear pinion, the gear pinions being on offset axes and coupled for rotation with a common adjustment shaft. In a further alternative, one eccentric sleeve is in use driven for rotary adjustment and is coupled to the other eccentric sleeve for rotation therewith.

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 being diametrically opposed.

The invention will now be described by way of example and with reference to the accompanying drawings, of which: Fig. l 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 rotated through 90 ; Fig. 5 is a partial cross-sectional view on line III-III of the cylinder head of the engine shown in Fig. 1 showing further parts of the camshaft drive mechanism in detail; and Fig. 6 is a view similar to Fig. 3 showing the camshaft drive mechanism rotated through 90 .

Referring to Figs. 1 to 6 and in particular to Figs. l 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 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 VVT mechanisms 32 and 33 for cylinders Nos. l 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.

Fig. 3 shows the details of the VVT mechanism 32 of cylinder No. 1 to better effect whereas Fig. 4 shows the details of the WT mechanism 33 of cylinder No. 2 to better effect. Both of the VVT mechanisms 32 and 33 of cylinders Nos. 1 and 2 are substantially as described in GB-A-2 336 888 to which reference should be made. The description immediately following is a summary of the main features.

Both VVT mechanisms 32 and 33 include a common input member 41 which is rotatable about substantially the same axis as the camshafts 18 and 19, being rotatable in a housing 46 attached to the cylinder head 14. VVT mechanism 32 of No. 1 cylinder includes an intermediate driving member 36 having 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 a radially offset driven means in the form of a driven peg 42 which is in driving engagement with slot 38. The intermediate driving member 36 is journalled in an eccentric sleeve 51 which is rotatable in the cylinder head about an axis offset from the axis of rotation of inlet camshaft 18.

WT mechanism 33 of No. 2 cylinder includes another intermediate driving member 54 having 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. Intermediate driving member 54 is journalled in another eccentric sleeve 51A about an axis offset from the axis of rotation of inlet camshaft 19 in an adapter bush 70 fixed in the cylinder head 14.

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.

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-A-2 268 570. This is achieved by rotating the eccentric sleeves 51 and 51A.

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 profile to compensate for this.

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 VVT mechanism 33 of cylinder No. 2 has the locus of the axis of rotation of its intermediate driving member 54 angularly offset by 30 from the locus of the axis of rotation of the intermediate driving member 36 of WT mechanism 32. The magnitude of this angular displacement or offset is one half of that of the crank offset (angle a) 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 30 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 WT mechanism 132 is provided for inlet camshaft 21 which is substantially the same as the WT mechanism 32 of cylinder No. l and to that extent the components shown in Figs. 5 and 6 are a mirror image of those shown in Figs. 3 and 4 and carry the same reference numerals but with the addition of 100. However, in order to provide drive to an input member 141, there is a drive from the inlet camshaft 19 of cylinder No. 2 by means of an inverting TQt-t'voTYY 3 ]'7 o nyol < aT rsic * t V\T *8cTm ) f cylinder No. 2. The VVT mechanism 132 and the inverting mechanism 133 are grouped together outboard of the camshaft 21 in a similar manner to the WT mechanisms 32 and 33 for cylinders Nos. 1 and 2.

Fig. 5 shows the details of the WT mechanism 132 of cylinder No. 3 to better effect whereas Fig. 6 shows the details of the inverting mechanism 133 to better effect. Again both the WT mechanism 132 and the inverting mechanism 133 are substantially as the WT mechanisms described in GB-A-2 336 888 (allowing for the mirror imaging) and reference should be made to that earlier description. The description immediately following is a summary of the main features.

The input member 141 is rotatable about substantially the same axis as the camshaft 21 in a housing 146 attached to the cylinder head 14. WT mechanism 132 includes an intermediate driving member 136 having a pair of diametrically opposed radially extending slots 137 and 138. Slot 137 is in driving engagement with a driving peg 139 which forms a radially offset driving means on the input member 141. An output member in the form of a bearing portion 143 of the inlet camshaft 21 of No. 3 cylinder has a radially offset driven means in the form of a driven peg 142 which is in driving engagement with slot 138. The intermediate driving member 136 is journalled in an eccentric sleeve 151 which is rotatable in the cylinder head about an axis offset from the axis of rotation of inlet camshaft 21..

The inverting mechanism 133 includes another intermediate driving member 154 having a pair of diametrically opposed radially extending slots 155 and 156.

Slot 155 is in driving engagement with a driven peg 157 on the input member 141 which is angularly offset from driving peg 139 by 90 . Slot 156 is in driving engagement with a driving peg 158 on a radially extending lobe 153 which is part of a further elongate portion 123 of the inlet camshaft 19 of cylinder No. 2.

Intermediate driving member 154 is journalled in another eccentric sleeve 151A rotatable in an adapter bush 170 fixed in the cylinder head 14.

The intermediate driving member 154 of the inverting mechanism 133 has an aperture 162 angularly spaced from the slots 137 and 138 to allow a boss 163 on the input member 141 to extend through with clearance, the boss 163 being drilled to receive the driving peg 139. An aperture 164 in intermediate driving member 136 is provided to partially accommodate the lobe 159 with clearance.

The inverting mechanism 133 effects a cyclic variation in the rotational speed provided by camshaft 19 by moving the axis of rotation of the respective intermediate driving member 154 relative to the axis of rotation of the inlet camshafts 19 by rotating the eccentric sleeves 151A and in a manner substantially as previously described. This cyclic variation is equal and opposite to the cyclic variation imparted to camshaft 19 by the VVT mechanism 33, the inverting mechanism 133 inverting the cyclic variation in the rotational speed of the camshaft 19 such that input member 141 rotates at the same speed as the common input member 41.

VVT mechanism 32 produces a cyclic variation in the speed of camshaft 21 by moving the axis of rotation of the respective intermediate driving member 136 relative to the axis of rotation of the inlet camshafts 21 by rotating the eccentric sleeve 151 and in a manner substantially as previously described. Again, rotary control of the eccentric sleeves 151 and 151A is achieved by rotation of respective gear pinions 166,166A on the control shaft 68, these meshing with gear teeth 167, 167A on the outer periphery of the respective eccentric sleeve.

To compensate for the crankshaft offset the inverting mechanism 133 has the locus of the axis of rotation of its intermediate driving member 154 also angularly offset by 30 from the locus of the axis of rotation of the intermediate driving member 136 of WT mechanism 132. Also, whilst the cam lobes of inlet camshaft 21 are angularly aligned with the driven peg 142, to compensate for the 30 offset of the eccentric sleeves 151,151A, there is a 30 offset in the opposite direction between the lobes of the camshaft 19 and the driving peg 158.

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 .

Instead of profiling the gear teeth 67,67A, 167,167A on the eccentric sleeves 51,51A, 151,151A, the control pinions 66,66A, 166,166A may run in separate bores, slightly displaced from each other. The pinions 66,66A, 166,166A 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, 166A may be omitted and the associated eccentric sleeve 51A, 151A rotationally coupled to the adjacent eccentric sleeve 51,151, e. g. by a peg in one sleeve which engages a radial slot in the other sleeve.

Although the WT mechanisms and the inverting mechanisms are based on those described in GB-A-2 336 888 they may be based on other VVT mechanisms, for example the VVT mechanisms described in GB-A-2 336 889.

Claims

CLAIMS 1. An internal combustion engine having at least two cylinders, 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 a respective camshaft for operating one of said groups of valves for each cylinder, each camshaft being arranged to be driven by a respective variable valve timing (VVT) mechanism operative to provide a cyclic variation of the rotational speed of the respective camshaft during constant rotational speed of a respective input member driven by the crankshaft, the input member of one of the VVT mechanisms being arranged to drive the input member of another of the WT mechanisms through said one WT mechanism and an inverting mechanism which is operative to invert the cyclic variation in the rotational speed produced by said one WT mechanism so that in use the input member of said other WT mechanism rotates at the same speed as the input member of said one WT mechanism.
2. An engine according to claim 1 wherein at least first, second and third said cylinders are arranged in line, first, second and third said camshafts are provided for operating said one group of valves for the first, second and third cylinders respectively, first, second and third said WT mechanisms are provided for the first, second and third camshaft respectively and each of the first and second VVT mechanisms has a common input member, the second camshaft having elongate portions each extending coaxially through the first and third camshafts respectively so that in use drive is transmitted from the common input member to the input member of the third VVT mechanism through the second VVT mechanism, the second camshaft and the inverting mechanism.
3. An engine according to claim wherein each of the third VVT mechanism and the inverting mechanism comprises a pair of radially offset driving means, a respective intermediate driva zig member arranged to be driven by a respective one of the offset driving mea s, a respective output member arranged to drive the third camshaft and the input member of the third VVT mechanism respectively and having a r r spective radially offset driven means arranged substantially radially opposi e the respective offset driving means and to be driven by the respective termediate driving member, the inverting mechanism having an input member which extends through an aperture in the intermediate driving member of the third WT mechanism and the input member of the third WT mechanism extending through an aperture in the intermediate driving member of the inverting mechanism, and means for moving the axis of rotation of the respective intermediate driving member through a respective locus to respectively vary the valve timing and compensate for the valve timing variation of the second camshaft, the radially offset driving means of the third WT mechanism and the radially offset driven means of inverting mechanism being on the input member of the third VVT mechanism and angularly offset from each other by substantially 90 .
4. An engine according to claim 3 wherein crankshaft has crank throws which are angularly spaced by an amount which is offset from 180 (the crankshaft offset), the locus for the inverting mechanism being angularly offset from the locus for the third VVT mechanism (the VVT offset) by an amount which compensates for the crankshaft offset.
5. An engine according to claim 4 wherein the camshafts are arranged to be driven at half engine speed and the magnitude of the VVT offset is one half the magnitude of the crankshaft offset.
6. An engine according to any of claims 3 to 5 wherein each locus is generated by a respective eccentric which locates the respective intermediate driving member.
7. An engine according to claim 7 wherein each eccentric is an eccentric sleeve which provides a bearing for the respective intermediate driving member.
8. An engine according to claim 7 wherein each eccentric sleeve has gear teeth meshing with a respective gear pinion on a common adjustment shaft.
9. An engine according to claim 7 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.
10. An engine according to claim 7 wherein one eccentric sleeve is in use driven for rotary adjustment and is coupled to the other eccentric sleeve for rotation therewith.
11. An engine according to any of claims 3 to 10 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.
12. An internal combustion engine having a camshaft drive mechanism substantially as described herein with reference to the accompanying drawings.