GB2428274A

GB2428274A - I.c. engine valve actuation mechanism with independently variable timing and lift

Info

Publication number: GB2428274A
Application number: GB0514496A
Authority: GB
Inventors: Jean-Pierre Pirault; Samuel Lesley; Martin Love; Riccardo Meldolesi
Original assignee: Powertrain Technology Ltd
Current assignee: Powertrain Technology Ltd
Priority date: 2005-07-14
Filing date: 2005-07-14
Publication date: 2007-01-24
Anticipated expiration: 2025-07-14
Also published as: GB2428274B; GB0514496D0

Abstract

The invention comprises an internal combustion engine in which variable valve timing and lift are provided by means of an oscillating link 40 actuated by a connecting rod 20 and crank mechanism 14 connected to the main engine crankshaft 18. The oscillating link 40 oscillates about a control point 35 substantially at one end of the link and the other end of the link is connected to a valve actuation mechanism. Two control shafts 30,22 with eccentrically mounted pins are connected to the control point, via separate links 36,39 rotatably attached to the pins, such that rotation of one or both shafts causes movement of the control point. The movement is controllable in two dimensions and has the effect of varying period and lift independently.

Description

Improvements to internal combustion engine valve-actuation mechanisms

Field of the invention

The present invention relates to a variable valve-actuation mechanism of an internal combustion engine having one or more cylinders and at least one inlet valve and at least one exhaust valve per cylinder.

Background

In an internal combustion engine the valve timings i.e. the points at which the valve starts to open and finishes closing are traditionally fixed in relation to the instantaneous positions of the crankshaft. The time between those two events, expressed in terms of degrees of rotation of the main engine crankshaft, is generally known as the period and is, therefore, also fixed, in those engines. Similarly the valve lift i.e. the length of movement of the valve along its axis between its open and closed positions, is traditionally also fixed for all engine operating conditions. However, it is increasingly desirable and increasingly common to be able to provide valve timings and lifts that can be varied according to engine conditions.

There are many types of mechanism providing variable valve-actuation. This invention relates the type which uses a link (one per valve) which oscillates about a control point at one of its ends. The valve is actuated via a mechanism at the other end of the link. The oscillation is driven by a crank and connecting rod methanism which is rotatably attached to the link. Variation in timing and lift are provided by movement of the control point. The extent to which timing and lift can be varied independently depends upon the degree of flexibility of movement of the control point, in two dimensions. This invention enables improvements in the mechanisms used to provide that flexibility and hence the effectiveness of the independent control of valve timing and lift.

Prior art

Patent application GBO4I 3944.0 discloses an oscillating valve-actuation mechanism of the type described above in which an oscillating link is oscillated about one end, the control point, under the action of a crankshaft and connecting rod. Moving the control point changes the valve opening period and the maximum valve lift. GBO4I 3944.0 also shows a means of moving the control point through an arc which is a one- dimensional movement along a prescribed line. This provides variations in the valve opening period and the maximum valve lift. However, these variables cannot be controlled independently. For optimum efficiency of the engine, it is of further benefit to be able to vary valve lift and period independently and hence provide the control point with movement that is two-dimensional and not limited to a single line. GBO4I 3944.0 also discloses means of providing two-dimensional movement.

However, these are relatively complex devices. Providing a simpler and reliable means of achieving two-dimensional movement of the control point is the subject of the present invention.

Summary of the invention

The broadest aspect of the invention comprises a variable valve-actuation mechanism including an oscillating link rotatably connected to a connecting rod which in turn is rotatably connected to a crankshaft such that said oscillating link oscillates about a control point comprising a pin which is connected by a first control link to a first control shaft and by a second control link to a second control shaft, each control shaft being rotatable about its own axis and each having an offset pin by which it is connected to its respective control link such 1 of5 that rotation of the said control shafts causes two-dimensional movement of the said control point.

This invention is described, with various embodiments, in the following figures and text.

Brief description of figures

Figure 1 - a side view of the mechanism Figure 2 - a graph of the characteristics of the mechanism

Detailed description of the preferred embodiments

Specific embodiments of the invention will now be described with reference to the accompanying figures, in which: Figure 1 shows an embodiment of the invention which operates on poppet valve 2 via roller follower 8. The valve is shown at maximum lift. Crankshaft 18 rotates about axis 16 and has an eccentric 14. Crankshaft 18 is driven synchronously by the main engine crankshaft (not shown) and, therefore, has a substantially constant angular relationship to that crankshaft.

Connecting rod 20 has one end mounted on eccentric 14, and the other end mounted on second pin 42 of oscillating link 40. First pin 38 of oscillating link 40 is mounted at the control point 35 about which oscillating link 40 oscillates as crankshaft 18 rotates. When crankshaft 18 is in the position shown, where axis 19 of connecting rod 20 passes through axis 16 of crankshaft 18, then the valve 2 is at the maximum possible lift for that particular position of control point 38. Cam link 56 has one end mounted on third pin 52 and the other end mounted on cam pin 10, which is mounted on cam lever 12. Camshaft 46 oscillates about camshaft axis 48 when cam lever 12 is oscillated by cam link 56. In this view, anticlockwise movement of camshaft 46 causes cam 54 to move anticlockwise, and, because cam 54 is in contact with roller 6 of roller follower 8, it makes roller follower 8 move clockwise about spherical end 58 of hydraulic backlash adjuster 60 thereby making valve 2 move along its axis to the open position.

There are two control shafts, first control shaft 30 and second control shaft 22, and two links, first control link 36 and second control link 39. First control shaft 30 is attached to lever 32 which contains pin 34. Second control shaft 22 is attached to eccentric 27. First control link 36 has one end mounted on pin 34 and the other end mounted on first pin 38 which is mounted at the control point 35. Second control link 39 has one end mounted on eccentric 27 and the other end mounted on first pin 38. When either first control shaft 30 or second control shaft 22 or both control shafts are rotated about their respective axes 28 and 24, control point 38 moves relative to camshaft 46 and crankshaft 18, thereby changing the geometry of the assembly and thereby changing the valve- opening period relative to the angular position of the engine crankshaft (not shown) and the maximum lift of the valve.

In the preferred embodiment the position of first control shaft 30 is such that first control link 36 is substantially parallel to the axis 44 of oscillating link 40 and second control shaft 22 is in a position which puts second control link 39 substantially perpendicular to the axis 44 of oscillating link 40. By this means the movement of the control point in the X direction 41 and the Y direction 37 can be operated substantially independently thereby providing control of the opening period and the maximum lift of the valve, in accordance with Figure 2.

Figure 2 shows how, by varying the X and Y coordinates of the control point, the valve opening period and the maximum valve lift may be controlled. Line 1 represents a typical envelope of maximum practical movement of the control point. Lines 2, 3 and 4 represent lines of constant peak lift in which 2 is a smaller peak lift than 3 which is a smaller peak lift 2 of 5 than 4. Lines 5, 6 and 7 represent lines of constant period in which 5 is a smaller period than 6 which is a smaller period than 7. Referring to Figures 1 and 2 it can be seen that moving control point 38 in the general direction of oscillating link axis 44, changes, mainly, the opening period. Moving control point 38 transverse to the oscillating link axis 44, changes both the opening period and the maximum lift, It can be seen that it is possible to keep maximum lift constant while varying the period. To do this it is necessary to move control point 38 along one of (or substantially parallel to) the lines of constant maximum lift 2, 3 and 4. It is also possible to keep the valve opening period constant while varying the maximum valve lift. To do this it is necessary to move control point 38 along one of (or substantially parallel to) the lines of constant period 5, 6 and 7. It is also possible to vary both variables simultaneously by moving control point 38 in a manner not parallel to either sets of lines.

Hence the described variable-valve-actuation mechanism provides the ability to vary valve opening period and maximum valve lift independently to optimise the performance of the engine over its whole range of loads and speeds. This is done by varying the angular positions of the first control shaft and the second control shaft.

It should be noted that the requirements to vary valve timing and maximum lift vary between diesel and gasoline engines and, to a lesser extent, from engine to engine. Hence the program controlling the movements of the first control shaft and the second control shaft will be different for each engine.

In engines having two adjacent valves in each cylinder whose opening characteristics are required to be identical, it is possible to have one cam for each of the valves, on the camshaft, and thereby to drive both valves with one valve-actuation mechanism. However, in engines having two adjacent valves in each cylinder whose opening characteristics are not required to be identical, two adjacent valve-actuation mechanisms will be required. In the latter case, it is possible to provide one valve with high lift and the adjacent valve with low lift to generate high swirl or turbulence in the incoming air, thereby speeding up combustion at light loads and low speeds.

Although the preferred embodiment is applied to an oscillating link with the control point substantially at one end, it may also be applied to an oscillating link with the control point substantially in the centre with the point of attachment of the connecting rod substantially at one end so that oscillation is a rocking motion about the control point.

The valve-actuation mechanism may be applied equally to the inlet and the exhaust valves of an engine, via either direct acting bucket tappets or rolling element finger followers.

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Claims

Claims A variable valve-actuation mechanism including an oscillating link

rotatably connected to a connecting rod which in turn is rotatably connected to a crankshaft such that said oscillating link oscillates about a control point comprising a pin which is connected by a first control link to a first control shaft and by a second control link to a second control shaft, each control shaft being rotatable about its own axis and each having an offset pin by which it is connected to its respective control link such that rotation of the said control shafts causes two-dimensional movement of the said control point.
2 An oscillating valve-actuation mechanism as described in claim I in which the axis of one of the two control links, is substantially in line with the axis of the oscillating link and the axis of the other control link, is substantially perpendicular to the axis of the oscillating link.
3 An oscillating valve-actuation mechanism for an internal-combustion engine comprising an oscillating link having a longitudinal axis, a first pin at one end of the link, a third pin at the other end of the link, and a second pin between the first and third pins; a crankshaft rotating about a crankshaft axis, driven synchronously by the engine, and having an eccentric member; a connecting rod; a cam link; a camshaft oscillating about a camshaft axis and having a cam and a cam pin; and a poppet valve: they are arranged so that the connecting rod is connected at one end to the eccentric on the crankshaft and at the other end to the second pin on the oscillating link, the cam link is connected at one end to the third pin on the oscillating link and at the other end to the cam pin; the oscillating link oscillates about the first pin, the control point, under the action of the crankshaft and connecting rod; the oscillating link causes the cam link to oscillate, which in turn causes the camshaft to oscillate, thereby causing the cam to oscillate about the camshaft axis; the oscillating cam acts on the poppet valve either directly or indirectly to make the valve open and close: in addition there are two control shafts, a first shaft and a second shaft, each rotatable about its own control-shaft axis; each control shaft having an offset pin; and two control links, a first control link and a second control link; the first control link is connected at one end to the first shaft pin and at the other to the control pin on the oscillating link, the second control link is connected at one end to the second shaft pin and at the other to the control pin on the oscillating link: whereby, when either the first shaft or the second shaft or both shafts are rotated about their axes, the control point on the oscillating link moves relative to the camshaft and the crankshaft, thereby changing the duration of the opening period and the maximum height of the lift of the poppet valve.
4 A variable valve-actuation mechanism substantially as herein described, with reference to Figure 1.

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