GB2190140A

GB2190140A - Valve lift mechanism

Info

Publication number: GB2190140A
Application number: GB08628154A
Authority: GB
Inventors: Christopher Paulet Mel Walters
Original assignee: CHRIS WALTERS
Current assignee: CHRIS WALTERS
Priority date: 1986-05-01
Filing date: 1986-11-25
Publication date: 1987-11-11
Also published as: GB8610727D0; GB2190140B; GB8628154D0

Abstract

A cam (5) on a camshaft (4) has a cam surface (5a) the outline of which, in a section plane containing the axis (4a) of the camshaft, is not parallel to that axis (4a). The camshaft can be moved lengthwise by applying oil to one side of a piston (7) which does not rotate with the camshaft. This movement is opposed by a spring (11) or by applying oil to the opposite side of the piston. The cam follower is a half- roller (16) and a body (6) which receives it in a part-cylindrical trough so that the half-roller can rotate about its axis (16a). Its flat surface engages the cam surface (5a) and the extent to which it pushes the body (6) downwardly depends upon the angle through which the cam has turned from a particular position and the extent and direction of the lengthwise movement of the camshaft from a particular position. The body (6) acts against lifting springs (3) to press downwardly a valve (1) of an engine.

Description

SPECIFICATION Valve lift mechanism This invention relates to internal combustion engines and, more particularly, is concerned with a valve for the inlet and/or exhaust valves of such an engine.

Conventionally, a poppet valve internal combustion engine will have one or more overhead camshafts each of which includes a plurality of cams disposed to act on cam followers which in turn act on valve stems so that rotation of the cams causes reciprocal movement of the valves. In section perpendicular to the axis of the camshaft, each cam conventionally has a pear-drop shape and is symmetrical in the direction of the camshaft axis.

With such an arrangement, valve action is independent of parameters such as engine speed, richness of the fuel mixture and engine load. Hence it is impossible to optimise factors such as engine torque, fuel economy and exhaust emissions under varying load conditions and engine speed with such conventional valve arrangements.

An object of the present invention is to provide a modified camshaft and valve lift mechanism for the inlet and/or exhaust valves of an internal combustion engine which modified system enables valve action to be modified as a function of one or more predetermined parameters.

According to the present invention, there is provided in or for use in an internal combustion engine, a valve lift mechanism which comprises (i) an overhead camshaft carrying a plurality of cams, the camshaft being mounted in a cam carrier and being arranged for a limited degree of axial movement; and (ii) means for effecting axial movement of the camshaft, wherein the cam profiles are such that, at least over part of the cam circumference, the contact line on the cam surface is non-parallel to the cam axis, whereby in use valve action is a function of the axial location of the camshaft within the range of permitted axial movement.

Preferably, axial movement of the camshaft is effected by fluid pressure acting on a cylinder and piston arrangement. Conveniently, oil under pressure is fed to such a cylinder and acts against a piston which is connected to the camshaft via a thrust race. Means is provided, at the drive end of the camshaft, for ensuring that the camshaft may be driven regardless of the extent of its axial displacement. Conveniently, the drive end of the camshaft will carry a spline or ball spline shaft which cooperates with a driving pulley, gear or sprocket. Thus the camshaft can move axially through the drive medium while still allowing the shaft to be driven.

The action of a camshaft in accordance with this invention is preferably transmitted to the valves of the internal combustion engine in which it is fitted by means of cam followers which include half rollers which have a flat upper surface which makes contact with the cam profile line and which are free to rotate about an axis which is normal to a plane containing the camshaft axis and the axis of movement of the valve with which the follower is associated. The half rollers can conveniently take the form of segments of a circular cylinder. At least the flat surface of each half roller should be formed of an extremely hard material, preferably one with a low thermal expansion coefficient. Conveniently, the half rollers are seated in rectangular follower bodies.

The valve mechanism can be used with the device for varying the phase of a camshaft as described in copending Patent Application No.

8624358 entitled "Camshaft Phase Angle Variation", the contents of which are herein incorporated by reference.

According to a second aspect of the present invention, there is provided an internal combustion engine which comprises: (1) an overhead camshaft; (2) a cam carrier in which said camshaft is retained and further including a cylinder and piston arrangement coaxial with said camshaft, one end of said piston being secured to said camshaft; (3) means for supplying a fluid under pressure to said cylinder so as to act upon the piston and hence to cause axial displacement of said camshaft; (4) means operable to oppose axial displacement of the camshaft resulting from the action of said fluid under pressure; (5) a plurality of cams carried by said camshaft, each cam over at least part of its circumference having a profile which, in section through the axis of the camshaft, is non-parallel to said axis;; (6) a plurality of cam followers each comprising a follower body having mounted therein, for cooperation with a respective one of said cams, a half roller which has a planar surface for contact with the cam profile line and which is free to rotate about an axis normal to a plane containing the axis of the camshaft and the axis of movement of the valve with which the respective follower is associated; and (7) a valve having a stem held in valve retainers and acted upon by said cam follower.

Said means operable to tend to oppose axial displacement of the camshaft can be, for example, biasing means acting axially on the camshaft or further means for supplying a fluid under pressure to act upon the piston in a direction opposite to that of the fluid of the first mentioned fluid supplying means.

For a better understanding of the invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: FIGURE 1 is a sectional view of the cam carrier/head casting of an internal combustion engine including a camshaft and valve arrangement in accordance with the present invention; FIGURE 2 is a section on the line X-X of Figure 1; FIGURE 3 is a plan view of a cam follower illustrated in Figure 2; and FIGURE 4 is a sectional view as in Figure 1 but with a modified camshaft and valve arrangement; FIGURE 5 is a schematic diagram showing a combined modified valve lift mechanism and camshaft phase angle varying device.

Referring now to Figures 1 to 3 of the drawings, the valve lift mechanism of the present invention comprises a cam carrier/head casting 10 in which is mounted an overhead camshaft 4. Coaxial with camshaft 4 and connected thereto via a thrust race 8 is a piston 7. Piston 7 is located for axial movement within a cylinder 9; an inlet channel 18 communicates with that end of cylinder 9 remote from camshaft 4.

The camshaft 4 carries a plurality of profiled cams of which one such cam 5 is illustrated.

The cam profiles are 3-dimensional, i.e. valve lift varies tangentially with cam angle in end view and varies along the camshaft axis linearly at each cam angle in side view. The cam surface 5a makes contact with a half roller 16 which is seated in a rectangular cam follower body 6. Half roller 16 is in the form of a segment of a circular cylinder and is free to rotate about an axis 16a (see Figure 3). At least the flat surface of half roller 16 is formed of a temperature resistant material of extreme hardness-e.g. the ceramic material Syalon. Cam follower body 6 acts against the upper end of stem 1a of a valve 1 through adjusting shims 17. Valve 1 is held within cam carrier 10 by retainers 2 and compression springs 3 and is constrained in all directions except in the axial direction in which the valve undergoes reciprocal movement.

Overhead camshaft 4 is driven by a drive gear 14 which is located in cam carrier 10 between thrust washers 15. Gear 14 is connected to camshaft 4 via a spline 13. Compression springs 11 act against camshaft 4 via a thrust race 12, tending to urge the camshaft axially to the left as seen in Figure 1.

The sectional view of Figure 1 is taken in a plane containing the axis 4a of camshaft 4 and the axis of movement of valve 1. The axis of rotation 1 6a of half roller 16 is perpendicular to the plane of Figure 1.

Figure 2 is an equivalent full section along the lines X-X of Figure 1, and thus is in a plane perpendicular to camshaft axis 4a and containing the axis of movement of valve 1.

Figure 2 shows that the cam surface 5a is profiled-that is, over part of its circumference, the contact line is not parallel to the cam axis 4a. This is also apparent from Figure 1 where the line of contact between cam surface 5a and half roller 16 is oblique with respect to axis 4a.

In use, camshaft 4 is able to undergo axial displacement to a limited extent, this being determined by the gap in cylinder 9 beyond the end face of piston 7 when springs 11 are fully compressed. During operation of an engine incorporating the valve lift mechanism as illustrated, oil under pressure is supplied via inlet 18 to cylinder 9. The pressure within cylinder 9 urges piston 7 to the right as seen in Figure 1, thus causing axial displacement of camshaft 4 to the right against the restraining action of springs 11. At any given time, the axial position of camshaft 4 will determine the action of valve 1. Hence by selecting a predetermined 3-dimensional cam profile, the valve opening point, duration and lift can all be controlled by the extent of axial displacement of camshaft 4.Because half roller 16 is free to rotate about axis 1 6a while seated on cam follower body 6, proper contact with cam surface 5a is always maintained.

The oil under pressure supplied to inlet 18 may be provided by a pump which is fed from the main engine oil supply by a bleed-off valve which is actuated by a solenoid or other electronic means which in turn is controlled by a microprocessor. In this way, it is possible to adjust the camshaft lift diagram to engine speed and load requirements, the microprocessor being programmed or mapped within the designed lift/duration range.

Referring now to Figure 4, a modified valve lift mechanism is shown. In Figure 4 like reference numerals designate like parts as in Figures 1 to 3. In this modified mechanism, the spring 11 and thrust bearing 12 are no longer required, and that end of the camshaft can be arranged to communicate with the camshaft phase varying device referred to above. In the modified mechanism, the piston 7 is replaced by a shorter piston 71 having a piston rod 27 fixediy secured thereto (or integral therewith as illustrated) in a non rotatable manner. Seals 20, 26 are provided for the piston 71 and the rod 27 respectively. A chamber 29 is formed between the seals 20 and 26, and there is a further inlet 19 leading into the chamber 29.

A disc 22 is threaded into the cylinder head casting 10 and seals the chamber 29 with an 'o' ring seal 21.

The rod 27 is threaded at an end 30 and is screwed into a bearing carrier 23. The rod 27 is locked against rotation by pin 28. The bearing carrier 23 is mounted on the camshaft 4 via a crossed cylindrical roller bearing 81 which is capable of transmitting two way axial loading imposed on the camshaft 4 from the piston 71, and camshaft axial loads arising from the profiles of the cam 5. This enables the camshaft to be moved axially in both directions, while being free to rotate without causing rotation of the piston rod. Circlips 24 and 25 retain the bearing 81 in the rearwards direction and shoulders in the carrier 23 and on the camshaft 4 provide bearing retention in the opposite direction.

Referring now to Figure 5, operation of the modified valve lift mechanism will be described. Operation of the camshaft phase varying device on the left hand side of Figure 5 will not be described in detail herein since it is described in the copending application referred to above.

A high pressure oil pump 32 serves to introduce oil from an oil sump 33 into a cylinder 91 corresponding to that designated by reference numeral 9 in Figure 1, and into the chamber 29 formed between the piston 71 and the seals, via a relief valve 34 and pressure gauge 40. Respective return feeds are provided for the cylinder 91 and chamber 29 via respective solenoid or "quick-acting" electrohydraulic servo valves 35, 36 for the return of oil to the sump 23.

The modified mechanism enables the camshaft to be moved axially with a faster response time than the arrangement described above with reference to Figures 1 to 3, enabling it to follow more closely changes in engine speed and load during use. This provides an even more effective electronically controlled engine management system for optimising engine output, emmissions and fuel economy. Control of the axial movement of the camshaft in the modified mechanism is effected by a microprocessor 27, which controls the servovalves 35, 36 to open one or the other to permit oil to flow from cylinder 91 or chamber 29 according to the direction and magnitude of camshaft movement required. A linear transducer 38 senses the axial movement of the camshaft to provide a feedback signal to the microprocessor 37 to control that movement.

Claims

1. In or for use in an internal combustion engine, a valve lift mechanism which comprises (i) an overhead camshaft carrying a plurality of cams, the camshaft being mounted in a cam carrier and being arranged for a limited degree of axial movement; and (ii) means for effecting axial movement of the camshaft, wherein the cam profiles are such that, at least over part of the cam circumference, the contact line on the cam surface is non-parallel to the cam axis, whereby in use valve action is a function of the axial location of the camshaft within the range of permitted axial movement.

2. A mechanism as claimed in claim 1, in which axial movement of the camshaft is effected by fluid pressure acting on a cylinder and piston arrangement.

3. An internal combustion engine which comprises: (1) an overhead camshaft; (2) a cam carrier in which said camshaft is retained and further including a cylinder and piston arrangement coaxial with said camshaft, one end of said piston being secured to said camshaft; (3) means for supplying a fluid under pressure to said cylinder so as to act upon the piston and hence to cause axial displacement of said camshaft; (4) means operable to oppose axial displacement of the camshaft resulting from the action of said fluid under pressure; (5) a plurality of cams carried by said camshaft, each cam over at least part of its circumference having a profile which, in section through the axis of the camshaft, is non-parallel to said axis;; (6) a plurality of cam followers each comprising a follower body having mounted therein, for cooperation with a respective one of said cams, a half roller which has a planar surface for contact with the cam profile line and which is free to rotate about an axis normal to a plane containing the axis of the camshaft and the axis of movement of the valve with which the respective follower is associated; and (7) a valve having a stem held in valve retainers and acted upon by said cam follower.

4. An engine as claimed in claim 3, in which said means operable to tend to oppose axial displacement of the camshaft comprises biasing means acting axially on the camshaft.

5. An engine as claimed in claim 3, in which said means operable to tend to oppose axial displacement of the camshaft comprises further means for supplying a fluid under pressure to act upon the piston in a direction opposite to that of the fluid of the first mentioned fluid supplying means.

6. A valve lift mechanism substantially as hereinbefore described with reference to or as shown in the accompanying drawings.

CLAIMS Amendments to the claims have been filed, and have the following effect: New claims have been filed as follows:

7. In or for use in an internal combustion engine, a valve-control mechanism which comprises a camshaft carrying a plurality of cams, the camshaft being mounted in a cam carrier and being arranged for a limited degree of axial movement and having associated with it means for effecting such movement, the cam surface having an outline, in a section plane containing the axis of the camshaft, which is not parallel to that axis, whereby in use the valve action is a function of the axial location of the camshaft within the range of permitted axial movement, the mechanism also comprising a cam follower for each cam, the cam follower comprising a one-piece body which reciprocates within a slideway and at one extremity acts upon the end of a valve stem through only a shim and has at the opposite extremity a trough of part-circular cross-section which receives a member in the form of a segment of a circular cylinder, the curved surface of which faces the interior surface of the trough, so that the said member can turn with respect to said body, whilst a planar side surface of the member faces the cam surface.

8. A mechanism according to claim 7 in which said member is exactly a half-cylinder with no laterally-projecting parts which would make its width greater than the diameter of said circular cylinder.

9. Apparatus including a valve of an internal combustion engine, a cam mounted on a camshaft and a cam follower including a body which is mounted in a guideway and serves to displace the valve as the cam is turned, said body having two opposite side surfaces which are planar and parallel to one another and slide on two opposite parallel and planar surfaces of the guideway, characterised in that externally the body is elongate as seen when looking in the direction in which it slides.

10. Apparatus according to claim 9, characterised in that externally the body is substantially rectangular as seen when looking in the direction in which it slides.

11. Apparatus according to claim 9 or 10, characterised in that the body does not contact the cam, but is formed with a trough of part-circular cross-section in which a member in the form of a segment of a circular cylinder is mounted so that its curved surface faces the interior surface of the trough and a planar side surface on the member faces the cam surface.

12. Apparatus according to claim 11, characterised in that said member is exactly a halfcylinder with no laterally projecting parts.

13. An engine according to claim 8, in which a microprocessor controls, in dependence upon engine speed and load, valves controlling the flow of oil from chambers on opposite sides of a piston which is coupled to the camshaft so as to displace it lengthwise but not rotate with it.