GB2442813A

GB2442813A - Camshaft assembly with moveable cam lobe

Info

Publication number: GB2442813A
Application number: GB0623923A
Authority: GB
Inventors: Riccardo Meldolesi
Original assignee: Powertrain Technology Ltd
Current assignee: Powertrain Technology Ltd
Priority date: 2006-10-14
Filing date: 2006-11-30
Publication date: 2008-04-16
Anticipated expiration: 2026-11-30
Also published as: GB0620446D0; GB0623923D0; GB2442813B

Abstract

A camshaft assembly comprises a fixed cam 1 and a moveable cam lobe 2 integral with a cylindrical stem 3 which runs in a cylindrical hole 26 in the fixed cam 1. The moveable cam lobe 2 is locked in its active position by hydraulic pressure which is directed into a chamber 10 formed by the base of the stem 3 and the base of the hole 26. and maintained by a one-way valve. When it is required to move the cam to its inactive position the pressure is released by means of a sliding piston 6 mounted in the stem 3 which uncovers a port 14 through which the oil can exit. In another embodiment of the invention the moveable cam lobe 2 is retained in its active position by a lower level of hydraulic pressure and in its retracted position by a higher level of hydraulic pressure. The movable lobe 2 can provide an extra exhaust valve opening event for internal EGR.

Description

VALVE MEChANiSMS WITH HYDRAUUCALLY ACTUATED SECONDARY OPENING

Field of the invention

The present mvenflon relates to the camshaft of an internal combustion engine or compressor having one or more cylinders and at least one inlet or exhaust valve per cylinder operated by a variable valve lift mechanism which provides two switchable modes of valve opening for either the inlet or exhaust valve(s); i.e. either a single event profile or a double event profile.

Some definitions and terminology are now provided to help subsequent explanations.

Terminology & Definitions A cam profile is a description of the radial distance from the centre of rotation of a prismatic element to the periphery of the prismatic element, usually defined at angular increments around the centre of rotation of the prismatic element.

Lift refers to the movement of the valve away from its closed position and, with reference to a cam profile, the lift may be referred to as a displacement from the surface of the prismatic element where it is at its minimum distance from the centre of its radius of rotation. Usually this minimum distance is constant over a significant angle. Within that angular sector, the prismatic surface is often called the base circle. Usually the valve is closed when the contact between cam and follower is located on the cam base circle.

A cam follower is a device which makes contact with the cam profile and which is moved by the cam and, in turn, operates a valve. The valve lift profile results from the movement of the cam follower, which is in turn operated by the cam profile. A follower may for example, be a bucket tappet or a rocker.

Open period refers to the angular portion, usually measured in degrees, when the cam profile exceeds the base circle radius. This portion of the cam profile is the lifting portion.

A sequential cam profile is one in which a single cani contains two lifting portions and two falling portions which activate the valve in sequence during one camshaft revolution.

Selective assembly is a manufacturing method in which parts of an assembly are selected having dimensions within certain tolerance limits so that the overall assembly of parts achieves certain desired and usually critical dimensions.

A naturally aspirated engine is one using ambient air without any precompression prior to entering the cylinders.

A pressured charged engine is one in which the ambient air is precompressed by some type of compressor prior to entering the cylinders, in order to increase the mass flow into the engine, and therefore increase the engine power.

Background

It is well known that the emissions, from internal combustion engines, of oxides of nitrogen., NOx, can be reduced by reducing the temperature of combustion. An effective means of achieving that is the introduction of exhaust gas recirculation (EGR) into the combustion chamber before the start of combustion. This can be achieved by introducing the EUR with the combustion mixture through the inlet valve or, more simply, by allowing some of the exhaust gas to return to the combustion chamber through the exhaust valve but during the induction stroke. In some diesel engines the exhaust cam has 1 of 7 a sthall additional lobe or bump on a portion of the base circle of the cam profile. The effect of the extra small lobe is to cause the exhaust valve to open momentarily and by a small amount during the induction stroke. That allows a small volume of exhaust gas to enter the combustion chamber. While this is desirable under light engine loads it becomes a problem under full load or near lull load conditions. The introduction of exhaust gas into the combustion chamber limits the amount of oxygen that is present and so reduces the possible maximum power output of the engine In an internal combustion engine the valve lift i.e. the length of movement of the valve along its axis between its closed and open 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 operating conditions.

This invention provides the benefits of a cam profile with an extra lifting portion (valve event) under light load conditions while providing no extra lifting portion under full load conditions. That is to say that it is a system allowing variable valve actuation and, therefore, enabling the introduction of EGR through the exhaust valve during the inlet stroke. Alternatively, it is possible to introduce exhaust to the cylinder by momentarily opening the inlet valve during the exhaust stroke so that exhaust enters the induction system and then returns to the combustion chamber when the inlet valve re-opens.

There are many types of mechanism providing variable valve actuation. This invention relates to the type which uses a camshaft with fixed and moveable cams such that at least one fixed cam per valve or valve pair is used for a first operational mode while a second moveable cam may be optionally either engaged to provide a secondary valve opening event for that same valve for a second operational mode, or the moveable cam disengaged so that it does not provide a secondary valve opening event.

Pnor 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. Those embodiments are aimed at systems which provide 2 discrete profiles which are used, in a mutually exclusive fhshion under different operating conditions.

Patent application GB 0613727.7 relates to the superposition of a first and second cam profile to form a third cam profile which is a sequence of the first and second cam profiles so that the valve connected to these cam profiles will either follow the first cam profile, or will follow the first and second cam profiles in sequence. The system uses fixed and slideable cams in which the slideable cams latch in their active positions using hydraulically actuated pins which are retained in the latching position using hydraulic pressure and are retracted using spring force.

The subject of the present invention is a system providing the benefits of sequential profiles using fixed and slideable cams with a simplified switching mechanism which does not require the operation of sliding pins.

Summary of the invention

hi its broadest sense, the invention comprises a camshaft assembly comprising a fixed cam 1 which is rigidly attached to a camshaft and a moveable cain lobe 2 which is moveable in a direction substantially orthogonal to the axis of rotation of said camshaft between a first position in which it actuates a cam follower and a second position in which it does not actuate the said cam follower characterised in that moveable cam lobe 2 is retained in its first position by the action of fluid pressure.

2 of 7 This invention is described, with various embodiments, in the following figures and text.

Brief Description of Figures

The preferred embodiments will now be described with reference to the following figures: Figure 1 -Cross section of embodiment with venting to the cam profile, in the second or inactive position.

Figure 2 -Cross section of embodiment venting to the cam profile, in the first or active position.

Figure 3 -Cross section of embodiment with venting to the centre of the camshaft, in the second or inactive position.

Figure 4 -Cross section of embodiment with venting to the centre of the camshaft, in first or active position.

Figure 5 -Cross section of embodiment with normally extended actuation, in the second or inactive position.

Figure 6-Cross section of embodiment with normally extended actuation, in first or active position.

Detailed Description of the Preferred Embodiments

Figure 1 shows a first embodiment of the invention with a moveable cam lobe 2 slideably located within a fixed cam] which is mounted on a camshaft (not shown). Moveable cam lobe 2 is slideably located within the base circle portion of fixed cam 1 providing a sequential profile. Cam lobe 2 has substantially flat side faces (not shown) and is integral with or fixed to stem 3 which is a substantially cylindrical sliding member and which incorporates piston 6 which is slideable in a direction substantially orthogonal to the major axis of stem 3 and within bush 7. The camshaft rotates about a longitudinal axis (not shown) and the moveable cam is able to slide, along axis 24 which is in a direction substantially orthogonal to the camshaft axis. Fixed cam I has a base circle portion 21 of its profile and a lifting portion 25 of its profile. Moveable cam lobe 2 is shown in its second or inactive position in which it does not come into contact with the cam follower (not shown). When it is required to activate moveable cam lobe 2, the pressure of the oil (or other hydraulic fluid) in supply channel 5 and hole 4 is increased and pressure is applied to piston 6 overcoming the force from spring 16 and causing piston 6 to move away from hole 4. Piston 6 is shown in its second position in which port 15 is blocked. In moving away from that position piston 6 displaces oil which escapes through port 17 past ball 18 which is lifted from its seat against the pressure from spring 19. The oil passes through hole 23 in retaining cap 20 into the volume exterior to the camshaft assembly. Piston 6 continues to move until it covers port 14 and uncovers port 15. At this point oil passes from hole 4 through port 15 causing ball 13 to be lifted from its seat against the force from spring 12 so that high pressure oil passes through holes 27 in retaining cap 11 and fills chamber 10. The pressure of the oil in chamber 10 causes stem 3 to move away from chamber 10 taking moveable cam lobe 2 towards its active position. Stem 3 continues to move until the top surface of spacer 8 comes into contact with the bottom surface of bush 7. At this point moveabte cam lobe 2 is locked in its active position, by the action of hydraulic pressure, as shown in Figure 2. Part of the surfIce of stem 3 forms a part of the boundaiy of chamber 10 which contains pressurised fluid.

In Figure 2, moveable cam lobe 2 is shown m its first or active position in which moveable cam profile 22 is active as it is able to make contact with the cam follower (not shown) moving the follower to cause the inlet or exhaust valve to open (lift) by a small amount. The assembly method for the components shown, which may also be applied to Later embodiments, may be as follows. Moveable cam lobe 2 and stem 3 with its internal components assembled are fitted into bush 7. Spacer 8, which is optional, and circip 9 are fitted to stem 3. The assembly is then pressed into hole 26, to a measured depth in fixed cam 1, so that cam profile 22 is in the correct position when moveable cam lobe 2 is in the active position.

3 of 7 Still referring to Figure 2, when it is required to return moveable cam lobe 2 to its second or inactive position the oil pressure in hole 4 is reduced until the force from spring 16 is able to overcome the oil pressure. At this point piston 6, which is shown in its first position, moves towards hole 4 under the action of the spring force. When port 14 is uncovered oil passes from chamber 10 through ports 14 and 17 past ball 18, which is lifted from its seat against the pressure from spring 19, and into the volume outside the camshaft assembly. Moveable cam lobe 2 is then pushed towards its inactive position by the next contact with the cam follower (not shown).

Ball 13 and spring 12 act as a one-way valve allowing oil to enter chamber 10 by means of port 15 but not allowing it to exit by that route. Other one-way valve means are possible for this application. It is also possible to orientate the axis of spring 12 differently or position ball 13 and its seat differently in for example, in cases where there are high centrifugal loads due to high camshaft rotational speeds.

For example (referring to Figure 1) the major axis of spring 12 may be substantially parallel to the major axis of spring 16. Ball 13 may be replaced by a conical member acting upon a conical shaped seat. Centrifugal force would in this case cause relatively little effect on the operation of the one-way valve. Another way of reducing the effect of centrifugal force on the operation of the one-way valve would be to position it closer to the centre of rotation of fixed cam 1.

Figure 3 shows a second embodiment of the invention in which oil is vented back to a channel in the camshaft. Figure 3 shows moveable cam lobe 2 in its inactive position. When it is required to activate moveable cam lobe 2, the pressure of the oil in hole 4 is increased and pressure is applied to piston 6 overcoming the force from spring 16 and causing piston 6 to move away from hole 4. In doing so piston 6 displaces oil which escapes through port 30 past ball 31 which is lifted from its seat against the pressure from spring 32. The oil passes through hole 33 in retaining cap 34 into cavity 35. Cavity is connected to a channel (not shown) in the camshaft (not shown). As in the previous embodiment high pressure oil is transferred to chamber 10 causing stem 3 to move away from cavity 10 until moveable cam lobe 2 reaches the active position.

Figure 4 shows moveable cam lobe 2 retained in its first or active position by the pressure of oil in cavity 10. When it is required to return moveable cam lobe 2 to its second or inactive position the oil pressure in hole 4 is reduced until the force from spring 16 is able to overcome the oil pressure. At this point piston 6 moves towards hole 4 under the action of the spring force. When port 14 is uncovered oil passes from chamber 10 through ports 14 and 30 past ball 31, which is lifted from its seat against the pressure from spring 32, and into cavity 35. Moveable cam lobe 2 is then pushed towards its inactive position by the next contact with the cam follower (not shown).

Referring to Figures 3 and 4, the position and orientation of port 30, and hole 36 (containing the assembly of ball 31, spring 32, and retaining cap 34) may be varied within stem 3 or nioveable cam lobe 2. It may, for example, be advantageous to position hole 36 such that the expelled oil issues from one of the side faces (not shown) of moveable cam lobe 2.

In the above embodiments of the invention, moveable cam lobe 2 is locked in its active position by the action of fluid pressure and unlocked when the fluid pressure is reduced to a lower level. In the following embodiment of the invention, moveable cam lobe 2 is retained in its first or extended position by a relatively low level of oil pressure and retained in its second or retracted position when oil pressure rises to a higher level. The former embodiments can be described as "normally retracted" and the latter embodiment can be described as "normally extended".

Figure 5 shows a "normally extended" embodiment of the invention in the second or inactive position.

High pressure oil in hole 4 connects with cavity 41 causing piston 42 to be held in the position shown against force from spring 50. Oil in spring cavity 53 ts vented via hole 51 and channel 52 to prevent a hydraulic lock. With piston 42 in the position shown circumferential groove 49 aligns with holes 48 and 59 allowing the passage of oil around piston 42. As stem 3 moves from the active position (See Figure 6) towards the inactive position as shown in Figure 5, oil is displaced from chamber 45 through hole 48, circumferential groove 49, hole 59 and via one way valve 62 to channel 55 and supply hole 4.

4 of 7 The movement of moveable cam lobe 2 and stem 3 towards the mactive position is caused by contact between moveable cam 2 and the cam follower (not shown). The force exerted on moveable cam lobe 2 by that contact is sufficient to pressurise the oil in chamber 45 to a significantly higher level than the maximum oil pressure in hole 4. The pressure difference between the oil in chamber 45 and hole 4 is sufficient, at that time, to allow oil to flow as described. In the position shown in Figure 5, moveable cam lobe 2 and stem 3 axe unable to move back towards the active position because oil is prevented from filling chamber 45 by one-way valve 62. There are several possible well known arrangements for one way valves but in the example shown in this case, ball 57 blocks hole 59 by means of force exerted by spring 56. Chamber 61 is connected via channel 55 to hole 4 at any point within the scope of movement of stem 3. The oil leaving chamber 45 is directed back to a channel in the camshaft (hole 4) in preference to being vented directly to the exterior of the camshaft assembly. This is a means of preventing air from being introduced into the oil.

Figure 6 shows a "normally extended" embodiment of the invention in the first or active position.

When moveable cam 2 is required to be extended to its active position, pressure of the oil m hole 4 is reduced to a lower level (compared to the level described with reference to Figure 5) but remains significantly above the general air pressure surrounding the camshaft assembly. Piston 42 moves towards the position shown in Figure 6 by virtue of the force from spring 50. En that position circumferential groove 49 aligns with holes 54 and 62 allowing the passage of oil from hole 4 to chamber 45 past ball 47 which is lifted from its seat against the force from spring 46. The pressure of oil in chamber 45 rises to a level significantly above the air pressure surrounding the camshaft assembly which causes stem 3 and moveable cam 2 to move from the position shown in Figure 5 to the position shown in Figure 6 while oil continues to flow into chamber 45. In the active position, the pressure of the oil in chamber 45 is sufficient to lock moveable cam 2 in position against the force of contact with the cain follower (not shown).

The axis of travel of the moveable cam lobe 2 is typically within an angular arc that spans up to 270 degrees from the angular positions of the zero lift points. The zero lift points are defined as the start and end points of the base circle portion of the fixed cam profile.

Although moveable cam lobe 2 has been described as being actuated by oil (hydraulic pressure), it may also be actuated by pressure from another medium such as air (pneumatic pressure).

The invention, as described with reference to all previous figures, may be optionally used on the inlet valves or exhaust valves. When the invention is applied to the inlet valves, the additional profile would usually be timed to open during the exhaust stroke. When the invention is applied to the exhaust valves, the additional profile would usually be timed to open during the induction stroke.

This invention is applicable to both spark ignition and compression ignition engines which may either be naturally aspirated or pressure charged. of 7

Claims

Clahns I A camshaft assembly comprising a fixed cam 1 which is rigidly

attached to a camshaft and a moveable cam lobe 2 which is moveable in a direction substantially orthogonal to the axis of rotation of said camshaft between a first position in which it actuates a cam follower and a second position in which it does not actuate the said cam follower characterised in that moveable cam lobe 2 is retained in its first position by the action of fluid pressure.
2 A camshaft assembly as claimed in Claim 1 in which moveable cam lobe 2 is slideably located within the base circle portion of fixed cam I providing a sequential profile.
3 A camshaft assembly as claimed in any previous claim in which moveable cam lobe 2 is integral with or rigidly attached to stem 3 which is substantially cylindrical in shape and which incorporates pIston 6,42 which is slideable in a direction substantially orthogonal to the major axis of stem 3.
4 A camshaft assembly as claimed in any previous claim in which moveable cam lobe 2 is retained lii its first position by a first level of fluid pressure and its second position by a second level of fluid pressure in which the first level of fluid pressure is lower than the second level of fluid pressure.
A camshaft assembly as claimed in Claims 1 to 3 in which moveable cam lobe 2 is locked in its active position, by the action of fluid pressure and unlocked when the said fluid pressure is reduced to a lower level.
6 A camshaft assembly as claimed in any previous claim in which part of the surface of stem 3 forms a part of the boundary of chamber 10, 45 which contains pressurised fluid.
7 A camshaft assembly as claimed in any previous claim in which piston 6, 42 slides between a first position in which it allows pressurised fluid to enter chamber 10 and a second position in which it allows pressurised fluid to leave chamber 10.
8 A camshaft assembly as claimed in any previous claim in which piston 6, 42 has a circumferential groove 49 allowing the passage of fluid around said piston.
9 A camshaft assembly as claimed in any previous claim in which stem 3 engages with a substantially cylindrical bush 7, 58 which is press fitted into hole 26, 60.
A camshaft assembly as claimed in any previous claim in which fluid is held within chamber 10, 45 by means of ball 13,47 held against its seat by spring 12, 46.
11 A camshaft assembly as claimed in any previous claim in which fluid is held within chamber 10, 45 by at least a single one-way valve.
12 A camshaft assembly, as claimed in any previous claim in which the fluid is air. p..

S p. p.

S

S p..

S

12 A camshaft assembly as claimed in any previous claim in which the fluid leaving chamber 10, 45 is directed into a channel in the camshaft.

13 A camshaft assembly, as claimed in any previous claim in which the fluid is oil.

14 A camshaft assembly, as claimed in any previous claim in which the fluid is air.

6 of 7 Amended Claims have been Filed as follows Claims I A camshaft assembly comprising a fixed cam I which is rigidly attached to a camshaft and a inoveable cam lobe 2 which is slideably located within the base circle portion of fixed cain I providing a sequential profile and which is moveable in a direction substantially orthogonal to the axis of rotation of said camshaft between a first position in which it actuates a cam follower and a second position in which it does not actuate the said cam follower, and moveable cam lobe 2 is locked in its first position by the action of fluid pressure, characterised in that moveable cam lobe 2 is integral with or rigidly attached to stem 3 which is substantially cylindrical in shape and which incorporates piston 6, 42 which is slideable in a direction substantially orthogonal to the major axis of stem 3.

2 A camshaft assembly as claimed in Claim i in which moveable cam lobe 2 is locked in its first position by a first level of fluid pressure and locked in its second position by a second level of fluid pressure in which the first level of fluid pressure is lower than the second Level of fluid pressure.

3 A camshaft assembly as claimed in Claim i in which moveable cam lobe 2 is locked in its active position by the action of fluid pressure and unlocked when the said fluid pressure is reduced to a lower level.

4 A camshaft assembly as claimed in any previous claim in which part of the surface of stem 3 forms a part of the boundary of chamber 10,45 which contains pressurised fluid.

A camshaft assembly as claimed in any previous claim in which piston 6, 42 slides between a first position in which it allows pressurised fluid to enter chamber 10 and a second position in which it allows pressurised fluid to leave chamber 10.

6 A camshaft assembly as claimed in any previous claim in which piston 6, 42 has a circumferential groove 49 allowing the passage of fluid around said piston.

7 A camshaft assembly as claimed in any previous claim in which stem 3 engages with a substantially cylindrical bush 7,58 which is press fitted tnto hole 26,60.

S A camshaft assembly as claimed in any previous claim in which fluid is held within chamber 10,45 by means of ball 13, 47 held against its seat by spring 12, 46.

9 A camshaft assembly as claimed in any previous claim in which fluid is held within chamber 10,45 by at least a single one-way valve.

A camshaft assembly as claimed in any previous claim in which the fluid leaving chamber 10, is directed into a channel in the camshaft.

11 A camshaft assembly, as claimed in any previous claim in which the fluid is oil.