GB2214567A - I.C. engine variable timing valve gear - Google Patents

Abstract

The rocking angle of a follower 30 between the cam 41 and the valve is variable to adjust the timing of valve opening and closure. The follower 30 rocks about the cam axis and the position between A and C of the pivot 37 of the rocking mechanism determines the rocking angle. The mechanism lever 36 may be rocked by an eccentric 34 on the camshaft or a separate crankshaft-driven eccentric (3, 12, 28, Figs 1 to 8). <IMAGE>

Description

UARIABLE VALVE TIMING BY ROCKING CAM FOLLOWER This invention relates to internal combustion engines.

Typical motor vehicle engines must oPerate ouer a wide range of speed and load conditions. To achieue a low fuel consumption in both urban driving and motorway driving conditions, engine design must compromise between high speed high load efficiency and low speed low load efficiency. The parameters which restrict the flexibility of an engine most greatly are the timings of the inlet and exhaust valve opening and closing events. These are normally fixed to give a reasonable spread of power and effic iency coupled with a legal uolume of emissions. This usually results in an engine that never achieues its maximum potential efficiency.

The improvements in performance and emissions output that can be achieued by an engine with fulls variable valve timing are well known by engine manufacturers. Seueral mechanisms that produce uariable valve timing have alreadY been produced and run on deuelopment engines; but none are currently exPloited commer cially. This is because the mechanisms that provide sufficient uariation to achieue all the benefits of uariable valve timing haue proued to haue wear Problems or haue produced imperfect valve motions.There is therefore a requirement for a durable mechanism that can provide fully uariable valve timing and a perfect valve motion.

According to the invention each intake and exhaust valve of an internal combustion engine is actuated by a mechanism consisting of: a cam, a driven cam follower whose angle uaries cyclically as the cam rotates; a tappet that interposes between the cam follower and the valve; and a normal valve spring arrangement.

There is also a mechanism to drive the cyclical rocking of the cam follower which can be uaried in either phase or magnitude or both.

The driven cam follower will be termed the "rocking cam follower" and abbreviated to RCF for the purpose of this description.

The RCF has a plane surface that interacts with the cam and a profiled surface that interacts with the tappet and is profiled to maintain an operating clearance between cam and follower when the cam is not operating the valve for all possible positions of the rocking cam follower. The rocking cam follower is oscillated in a controlled manner such that the position of the cam at which valve opening besins and valve closing finishes; varies precisely according to the setting of the control mechanism.

The primary effect of the RCF is to change the length of period of the cam in terms of degrees cam rotation and hence crankshaft rotation. n secondary effect which maY be used is to change the phase angle of the cam relative to crankshaft rotation. The two effects combined allow value opening and closing events to be changed br different amounts.

The invention will now be described bY was of example with reference to the accompanying drawings: Fig. 1 shows a side elevation of one arrangement of the invention The adjusting mechanism is not shown for clarity and onlY Part of the valve installation is shown as it is conventional.

Fig.2 shows a top elevation of Fis.1 denoted by arrow 'N'.

Fig.3 shows a front elevation of Fig.1 denoted br arrow 'B'. It is elaborated to show more of the adjusting mechanism which in this case is a simple eccentric pivot.

Fig.4 shows a side elevation of a second arrangement of the invention.

Fig.5 shows a front elevation of Fig.4 denoted by arrow 'C'.

Fig.6 shows an arrangement of four gear wheels fixed to the camshaft and the eccentric drive shaft which could be used to change the phase of rotation of the eccentric drive. Operation of the control rod gives up to 18 degrees of phase angle change.

Fig.7 shows a side elevation of a third arrangement of the inuention.

Fig.8 shows a,front elevation of Fig.7 denoted by arrow 'D'.

Fig.9 shows a side elevation of a fourth arrangement of the inuention.

Fig. 1 shows a front elevation of Fig.9 denoted bY arrow 'E'.

Fig.11 shows a side elevation of a fifth arrangement of the inuention.

Fig. 12 shows a plan uiew of section 'F-F' of Fig.11. The arrangement shown is for an engine with 4 ualues per cylinder where 2 ualues are operated bY 2 cams simultaneously.

Figures 1 to 12 show for example 5 different methods of driving the RCF. In each case the camshaft is driven by the crankshaft in any conventional manner; and the valve and spring arrangement and means for adjusting tappet clearance bs metal shim are normal. In all cases the cam is rigidly attached to the camshaft and rotates in fixed phase with the crankshaft. The arrangements shown could be used equally for intake and exhaust ualues.

Operation of the rocking cam follower is now described with reference to Fig. 1.

In this arrangement the RCF (1) pivots about the axis of rotation of the camshaft (2) and is driven bY an eccentric drive (3). The magnitude of the rocking motion is controlled by the position of pivot < 4). fls cam (5) rotates anticlockwise it interacts with plane surface < 6) of RCF (t) which is simultan eousls oscillatins annularly about a central position at the same frequency as the camshaft is rotating.As the cam (5) interacts with plane surface (6) of the RCF, the profiled surface (7) of the RCF interacts with surface (8) of the valve tappet (9) to oPerate the valve. The resulting valve motion is a function of the rotation of the cam and the rotation of the RCF. With the control mechanism set for low speed at position (a) valve opening is delayed bY an angle Ca) as shown and the RCF moues in the opposite direction to the cam to shorten its period of operation and allow the valve to close approximately e degrees earlier.With the control mechanism set for mid speed at position (b) the rocking motion of the RCF is very small and the cam period is unaffected bY the RCF. With the control mechanism set for high speed at position (c) the Phase of the oscillation of the RCF reuerses compared to setting (a) which causes the oPposite effect i.e. valve opening is aduanced and valve closing is retarded giving a longer valve period.

The locus (a-c) of pivot (4) controls the amplitude of oscillation of the RCF and also the position of the centre of oscillation. In this arrangement the centre of oscillation defines the phase of the cam relative to cam rotation. For examPle, to achieue a phase aduance at high speed; the centre (11) of locus (a-c) (see also Fig. 3) would be fixed at a lower point thus moving point (c) towards the cam causing the RCF to oscillate about a new position shifted clockwise. In practise locus (a-c) would be arranged to provide the optimum change in valve timing.

Operation of the RCF with a fixed amplitude of oscillation will now be described with reference to Fig.4.

In this arrangement a fixed eccentric drive (12) rotates at the same sPeed as cam (13) but in the opposite direction. The angle (#) of the RCF (14) at the points of valve opening and valve closing is controlled by: the eccentricity (15) of the drive; the separation between the camshaft (13) and follower drive shaft (12), and the phase of rotation of the eccentric drive relative to the camshaft. Value timing is uaried by changing the phase of rotation of the eccentric drive shaft (12). Fig.4 shows the mechanism set in the low sPeed position i.e. valve opening is delayed and cam period reduced.In the high speed position eccentric drive (12) would be aduanced in Phase bY 18B degrees causing valve opening to advance and the cam period to be extended.

Operation of the RCF with a uariable eccentric drive will now be described with reference to Fig.7.

In this arrangement the RCF (25) pivots about the axis of rotation of the camshaft (26) and is driven bY a variable eccentric drive (27). The angle C) of the RCF is controlled by: the separation of the camshaft (26) and eccentric drive shaft (28), the Phase of rotation of the eccentric drive shaft; and the eccentricity of the eccentric drive (29).As the shaft separation and phase of rotation are fixed; the angle (e) of the RCF at the point of valve opening and valve closing can be uaried bY moving the centre of the eccentric drive (27) along locus Ca-c). Position (a) on locus (a-c) corresponds to a low sPeed setting and would cause valve opening to be declared and cam period to be shortened. Position (b) corresponds to a mid speed setting at which the amplitude of oscillation of the RCF would reduce to zero and valve motion would not be affected by the RCF. Position (c) corresponds to a high sPeed position at which value opening would be aduanced and cam period extended.

Operation of the RCF with direct drive from the camshaft will now be described with reference to Fig.9.

In this arrangement of the invention the RCF (16) pivots about an adjustable control bar (17) and is driven bY an eccentric drive (18) machined onto the camshaft (19). The ansle (t) of the RCF at the point of valve opening and valve closing is controlled bY the eccentricity C2) of the drive (18), and the position of the control bar (17) relative to the camshaft (19).

In this arrangement moving control bar (17) towards (a) on locus (a-c) would aduance valve opening and extend cam period.

Moving control bar (17) towards (c) on locus (a-c) would delay valve opening and reduce cam period.

UPPer surface (21) of tappet (22) is profiled such that it can interact with profiled surface (23) of the RCF to maintain a uniform clearance between follower (16) and tappet (22) when the cam (24) is not operating for all settings of control bar (17).

Operation of the RCF with the sliding joint separated from the rotating joint will now be described with reference to Fig.11 and Fig. 12.

In this arrangement of the invention the RCF C3) is mounted in a seParate body (31) that is capable of oscillating annularly, thus the bodY (31) may be mounted on fixed bearings (32) and the RCF maY be mounted bY a simple sliding joint (33).

Body (31) is driven by an eccentric (34) machined onto camshaft (35) acting through a uariable leuer mechanism (36). Adjustable pivot bar (37) can be moued along locus (a-c) to vary the amplitude of oscillation of the RCF. The drive is transmitted to body (31) through connecting rod (38) which slides through a bearing (39) in fixed mounting C4e).

Control bar (37) is shown in the low sPeed position (a); and cam (41) is shown in the valve closing position. In this position valve opening is delayed and valve closing is aduanced to shorten cam period. With control bar (37) in mid position (b), RCF oscillation would be very small and valve motion would be unmodified by the RCF. With control bar (37) in high sPeed position (c), the direction of oscillation would be reuersed causing valve opening to advance and valve closing to be retarded giving a longer cam period.

Control bar (37) position also controls the position of the centre of oscillation of the RCF thus locus (a-c) can be arranged to provide a change in the Phase of operation of the cam. For instance if point (c) on locus (a-c) were moued to the right; the centre of oscillation of the RCF would be moued anticlockwise causins an aduance in the phase of operation of cam (41) relative to camshaft rotation.

For each of the example arrangements of the invention shown a timing control deuice is required. AnY well known method may be used such as a hydraulic or electric motor. To gain full advantage of uariable valve timing this would be controlled by a microprocessor programmed to give the optimum balance between emissions and economy for any particular engine speed and load.

This invention is concerned with achieving control of the duration and timing of valve operation using a rocking cam follower driven at the same frequencY as the camshaft which rocks either about the axis of rotation of the camshaft or about the centre of an adjustable pivot bar mounted parallel to the camshaft. n person skilled in the art will readily be able to propose uariations of the essential invention; for example: bY combining different features from the examPles shown to achieue a different arrangement, or bY choosing a different method of driving the rocking cam follower; or bY changing the arransement to suit a particular engine design.

Claims (9)

1. A valve actuating mechanism for the inlet and/or exhaust valves of an internal combustion engine comprising of for each valve, a cam and cam follower, and between each cam and cam follower an additional rocking cam follower whose surface which cooperates with the cam is plane and capable of rotation about the axis of the cam to change the relative angle between the cam and the plane surface so that the angular position of the rocking cam follower defines the opening and closing times of the valve, and as the rocking cam follower interacts with the cam it slides radially relative to the cam to operate a second cam follower and the valve, and the surface of the rocking cam follower which interacts with the said second cam follower is profiled such that when the cam is not operating for all possible angles of the rocking cam follower a constant clearance is maintained between the rocking cam follower and the base radius of the cam.

2. A valve actuating mechanism as claimed in claim 1 in which the rocking cam follower pivots about a bearing surface that is integral with the cam shaft and concentric with the axis of rotation of the cam shaft.

3. A valve actuating mechanism as claimed in claim 1 in which the rocking cam follower pivots about a bearing surface that is detached from the camshaft and concentric with the axis of rotation of the camshft.

4. A valve actuating mechanism as claimed in claim 1 in which the rocking cam follower pivots about a bearing surface that is integral with the camshaft and eccentric to the axis of rotation of the camshaft.

5. A valve actuating mechanism as claimed in any of claims 1 to 4 in which the rocking cam follower rocks in phase with the cam rotation and valve timing is controlled by changing the magnitude of the rocking motion.

6. A valve actuating mechanism as claimed in any of claims 1 to 5 in which the rocking cam follower rocks and valve timing is controlled by changing the phase of the rocking motion relative to rotation of the cam.

7. A valve actuating mechanism as claimed in any of claims 1 to 6 in which the rocking cam follower is held at a fixed angle by the control mechanism to control the opening and closing times of the valve without changing the cam period.

8. A valve actuating mechanism constructed and operating substantially as described in Figures 1 to 12 of the accompanying drawings.

9. An internal combustion engine incorporating a valve actuating mechanism as claimed in any of claims 1 to 8.