GB2427897A

GB2427897A - I.c. engine camshaft with fixed and slideable cams switchable between high-lift and low-lift modes

Info

Publication number: GB2427897A
Application number: GB0513357A
Authority: GB
Inventors: Riccardo Meldolesi; David J Lacy; Samuel Lesley
Original assignee: JEAN PIERRE PIRAULT
Current assignee: JEAN PIERRE PIRAULT
Priority date: 2005-06-30
Filing date: 2005-06-30
Publication date: 2007-01-10
Anticipated expiration: 2025-06-30
Also published as: GB2427897B; GB0513357D0

Abstract

An i.c. engine has a valve actuation system in which poppet valves are operated via a camshaft with fixed cams 24 and slideable cams 46. The fixed cams 24, integral with the camshaft core 48, provide low valve lift and the slideable cams 46 are extended by springs 54 to provide high lift. Hydraulic pressure is used to move locking pistons 32a, 32bwhich protrude into the slideable cam 46 against the force of springs 22a, 22b to lock each slideable cam 46 in its extended position. In the retracted position, the hydraulic pressure is reduced and the slideable cam is locked in position by a spring-loaded locking pin 10 mounted in the slideable cam 46 which protrudes into a corresponding hole 50 in the camshaft core. Thus the pin 10 locates in a separate hole 50 in the camshaft core 48 not used by the pistons 32a. 32b enabling the difference between high and low lift to be much smaller than previously possible and allowing the system to be used with rocker or finger follower cam actuation systems. Alternatively, the cam may be locked by the pistons in the low lift mode and by the pin in the high lift mode. A mechanical actuator may engage the pistons instead of hydraulic pressure.

Description

IMPROVEMENTS TO VARIABLE VALVE TIMING MECHANISMS

Field of the invention

The present invention relates to the camshaft of an internal combustion engine having one or more cylinders and at least one inlet valve per cylinder operated by a variable valve timing mechanism which provides two switchable modes of valve lift; low-lift and high-lift.

Background

In an internal combustion engine the valve lift i.e. the length of movement of the valve along its axis between its open and closed positions, is traditionally fixed for all engine operating conditions. However it is increasingly desirable and increasingly common to be able to provide valve lifts that can be varied according to engine conditions.

There are many types of mechanism providing variable valve lift. This invention relates to the type which uses a camshaft with separate fixed and slideable cams for each valve such that, typically, two fixed cams per valve are used for low-lift operation while a slideable cam is locked below (i.e. towards the centre of the camshaft) the level of the fixed cams and the slideable cam is locked in a higher position (i.e. away from the centre of the camshaft) for high-lift operation.

Prior Art

UK patent GB2385888 and UK applications GB 0106891.5 and GB 0501164.8 describe camshaft assemblies having fixed cams which provide low lift and slideable cams which provide high lift. Technical paper SAE 2005-01-0769 describes a further embodiment having fixed cams with 3 mm lift and slideable cams with 10.2 mm lift. That embodiment contains two pistons for latching the slideable cam in its high-lift position and a single locking pin for latching the slideable cam in its low-lift position.

This arrangement works satisfactorily when the cams operate directly on bucket tappets fitted to the poppet valves, and when the two positions of the slideable cam are separated by a distance such as 7.2 mm, for example. However, when the cams operate on the poppet valves via a rocker or finger follower having a ratio of 2:1, for example, then the distance between the two positions of the slideable cam is too small to be achieved by the arrangement of pistons and locking pins shown in the SAE paper. The invention described herein shows another arrangement of the pistons and locking pin which permits the two positions of the slideable cam to be significantly closer and, hence, may be used with finger or rocker follower arrangements.

Summary of the invention

In its broadest aspect, the invention is a camshaft comprising a moveable cam, a shaft, a first locking member and a second locking member, the moveable cam being moveable relative to the shaft between a first position and a second position, a first aperture being provided in the shaft for receiving the first locking member to lock the moveable cam in said first position and a second aperture being provided in the moveable cam for receiving the second locking member to lock the moveable cam in said second position.

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

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Brief Description of Figures

Preferred embodiment will now be described with reference to the following figures: Figure 1 - Cross section of camshaft assembly at high lift.

Figure 2- Cross section of camshaft assembly at low lift.

Detailed Description of the Preferred Embodiments

In figure 1 slideable cam 46 is shown in its high-lift or second, position relative to the camshaft core 48, with chamber 52 between them. The profile 4 of the slideable cam 46 projects beyond the profile 6 of the fixed low-lift cam 24. The core 48 has parallel faces 36a and 36b which form a slideway for the slideable cam 46. On the right side of slideable cam 46 is a hole 18a in which is an insert 20a with an extended lip 34a. Lip 34a forms a stop against which the outside diameter of insert 38a is in contact. This ensures that piston 32a is aligned with the bore of insert 28a which allows piston 32a to be pushed in a direction away from the camshaft core 48 under the influence of hydraulic pressure from oil or another pressunsed fluid, in axial hole, or channel, 44 which overcomes the force applied by spring 22a. Similarly, pressure in channel 44 pushes piston 32b in the opposite direction against the force of spring 22b. With pistons 32a and 32b in the positions shown, slideable cam 46 is locked in the high-lift position and pistons 32a and 32b transfer cam contact forces to the camshaft core 48. Piston 40 also has hydraulic pressure applied to it but it cannot move because it is out of alignment with hole 8. Similarly, pin 10 cannot move under the action of spring 12. Piston 40 serves as a seal to prevent hydraulic pressure from leaking via slideway 36a. Vent hole 56 allows the pressure in chamber 52 to be maintained at the same level as in the space external to the camshaft to avoid hydraulic lock.

In figure 2 slideable cam 46 is shown in its low-lift, or first, position relative to the camshaft core 48. The profile 4 of the slideable cam 46 lies entirely within the profile 6 of the fixed low- lift cam 24. The transition from high lift to low lift occurs as follows: hydraulic pressure in axial channel 44 is relieved, allowing springs 22a and 22b to push pistons 32a and 32b out of engagement with inserts 28a and 28b. Caps 26a and 26b limit the travel of springs 22a and 22b. When pistons 32a and 32b are disengaged, the force generated between the slideable cam 46 and the finger follower (not shown) overcomes centrifugal force and the force of spring 54, and slideable cam 46 slides into its low-lift position. With slideable cam 46 in the low-lift position, spring 12 pushes pin 10 towards camshaft core 48 into engagement with chamfer 2 around hole 50, and in doing so pushes piston 40 towards the centre line of camshaft core 48. Pin 10 contacts only the upper part of chamfer 2, i.e. on the side nearest to spring 54, and locks slideable cam 46 in its low-lift position.

In the preferred embodiment first and second positions are low lift and high lift positions respectively but it is possible for the first position to be the high lift position and the second position to be the low lift position. Although the preferred embodiment uses two pistons per slideable cam to lock the slideable cam in the extended or high-lift position it is also possible to use a single piston per slideable cam to lock it in the high-lift position. This can be located either on the side of the camshaft core 48 where pin 10 is located or on the opposite side of the camshaft core 48. Alternatively, the piston or pistons may be used to lock the cam in the retracted, or low-lift, position and a locking pin may be used to lock it in the high-lift or extended position. Whichever position of locking pin is used, it can be disengaged by fluid pressure acting on a piston or other resilient member. Another possible embodiment uses a mechanical actuator, rather than hydraulic pressure, to engage the piston or pistons.

2 of 7 An important difference between the preferred embodiment of the invention described here and the prior art described in SAE paper 2005-010769 is that, instead of engaging with the bore of insert 38a, at the lowlift position, pin 10 engages with new aperture 50. New piston serves to disengage the pin 10 when the cam is moved to the high-lift position. This allows the distance between the low-lift and high-lift positions of slideable cam 46 to be significantly smaller and, typically, as small as 3 mm.

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Claims

Claims 1. A camshaft comprising a moveable cam, a shaft, a first locking

member and a second locking member, the moveable cam being moveable relative to the shaft between a first position and a second position, a first aperture being provided in the shaft for receiving the first locking member to lock the moveable cam in said first position and a second aperture being provided in the moveable cam for receiving the second locking member to lock the moveable cam in said second position.
2. A camshaft as claimed in claim 1, wherein the moveable cam provides a high-lift profile when it is in said second position.
3. A camshaft as claimed in claim I or claim 2 further comprising a first resilient member for displacing the first locking member into the first aperture.
4. A camshaft as claimed in claim 1, 2 or 3 further comprising a piston for displacing the first locking member out of the first aperture.
5. A camshaft as claimed in claim 4, wherein the piston is movable in response to the supply of a pressurised fluid.
6. A camshaft as claimed in claim 4, wherein the piston is movable by means of a mechanical actuator.
7. A camshaft as claimed in any one of the preceding claims, wherein the second locking member is movable into the second aperture in response to the supply of a pressurised fluid.
8. A camshaft as claimed in any one of the preceding claims, wherein the second locking member is movable into the second aperture by means of a mechanical actuator.
9. A camshaft as claimed in claim 5 or claim 7, wherein a channel is provided in the shaft for supplying pressurised fluid to the piston and/or second locking member.
10. A camshaft as claimed in any one of the preceding claims further comprising a second resilient member for displacing the second locking member out of the second aperture.
11. A camshaft as claimed in any one of the preceding claims, wherein the moveable cam is biased towards said second position.
12. A camshaft as claimed in any one of the preceding claims, wherein a third aperture is provided in the moveable cam for receiving a third locking member also to lock the moveable cam in said second position.
13. A camshaft as claimed in claim 10, wherein the second and third locking members are co-axial.
14. A camshaft as claimed in any one of the preceding claims, further comprising a stop member for limiting movement of the moveable cam relative to the shaft.
15. A camshaft as claimed in claim 12, wherein the stop member is provided on the moveable cam.
16. A camshaft as claimed in any one of the preceding claims, wherein the moveable cam is provided with a vent.

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17. A camshaft as claimed in any one of the preceding claims wherein the moveable cam is provided between a first fixed cam and a second fixed cam.
18. A camshaft as claimed in claim 17, wherein the first and second fixed cams have a low- lift profile.
19. A camshaft as claimed in any one of the preceding claims, wherein the distance between said first and second positions is less than or equal to 6mm.
20. A kit of parts for assembling a camshaft as claimed in any one of the preceding claims.
21. A shaft assembly for mounting at least one moveable cam, the shaft comprising an aperture for receiving a first locking member to lock the moveable cam in a first position, and a second locking member for locking the moveable cam in a second position, wherein the aperture and the second locking member are offset in a transverse direction.
22 A shaft assembly as claimed in claim 21 further comprising a piston for displacing the first locking member out of said aperture.
23. A shaft assembly as claimed in claim 21 or claim 22 further comprising a channel for supplying a pressunsed fluid to the second locking member and/or the piston.
24. A moveable cam for mounting on a shaft, the moveable cam comprising a first locking member for locking the moveable cam in a first position relative to the shaft, and an aperture for receiving a second locking member to lock the moveable cam in a second position, the moveable cam further comprising a stop member for limiting the movement of the moveable cam relative to the shaft.
25. A moveable cam for mounting on a shaft, the cam having a vent to allow fluid to vent from one side of the cam to the other.
26. A camshaft providing variable valve lift by means of fixed and slideable cams whereby the said fixed cam is integral with the camshaft core and provides low lift when the said slideable cam is retracted and the said slideable cam creates high lift when in its extended position and the said slideable cam is locked, when in its extended position, by one or more pistons located in one or more holes in the said camshaft core protruding into one or more corresponding holes in the said slideable cam acting under the influence of hydraulic pressure, and in which the said slideable cam is locked when in the retracted position by a latching pin which protrudes into a separate latching pin hole in the camshaft core, not used by the said piston or pistons.
27 A camshaft assembly as claimed in claim 26 in which the camshaft core contains two piston holes, each of which contains a piston, each of which locates in a corresponding hole in the slideable cam when the said slideable cam is in the retracted position.
28. A camshaft assembly as claimed in claim 27 in which the two piston holes in the camshaft core are coaxial and the two corresponding piston holes in the slideable cam are coaxial.
29. A camshaft assembly as claimed in any one of the preceding claims in which the sides of the parallel-sided camshaft core contain recesses, the piston holes in the said camshaft core contain bushes which project into the recesses, and each of the piston holes in the said slideable cam contain an insert with a projecting lip arranged so that the said projecting lip contacts the outside diameter of the said bush to form a stop to hold of 7 the said slideable cam in its high-lift position, thereby allowing the pistons to slide into engagement with the said holes in the said slideable cam under the influence of hydraulic pressure.
30. A camshaft assembly as claimed in claims 26 to 29 in which the piston holes in the slideable cam contain springs to push the pistons out of engagement with the slideable cam when the hydraulic pressure is released.
31. A camshaft assembly as claimed in claims 26 to 30 in which the latching pin hole in the camshaft core contains a slideable piston, acted upon by pressure in the axial hole.
30. A camshaft assembly as claimed in any one of the preceding claims in which the chamber between the slideable cam and the core is vented to the space external to the camshaft assembly via a hole.
33. A camshaft substantially as herein described, with reference to Figures 1 and 2.
34. A cam substantially as herein described, with reference to Figures 1 and 2.

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