Valve timing mechanisms

Abstract

A variable valve timing mechanism for an internal combustion engine including at least one valve-actuating camshaft driven from a crankshaft is described. The valve timing mechanism comprises a movable member which is arranged in use to be rotatable by the crankshaft and movable in translation relative to the camshaft in dependence upon an engine operating condition such as engine load or speed. The movable member is connected to the crankshaft by an eccentric linkage such that movement of the movable member relative to the camshaft varies the angular position of the camshaft relative to the crank and also varies the rate of angular movement of the camshaft, thereby varying the valve timing.

What is claimed is: .[.1. A valve timing mechanism for an internal combustion engine including at least one valve-actuating camshaft driven from a crankshaft, said camshaft having at least one cam element fixedly mounted thereon, the mechanism comprising, a movable member arranged in use to be rotatable by the crankshaft and movable in translation relative to the camshaft in dependence upon an engine operating condition, the movable member being connected to the camshaft by an eccentric linkage such that movement of the movable member relative to the camshaft varies the angular position of the camshaft about its axis of rotation relative to the angular position of the crankshaft about its axis of rotation and also varies the rate of angular movement of the camshaft, relative to the angular velocity of the crankshaft thereby varying the valve timing..]. .[.2. An internal combustion engine comprising at least one cylinder, at least one inlet and at least one exhaust valve for the or each cylinder, camshafts, said camshafts having at least one cam element fixedly mounted thereon for opening the inlet and outlet valves of the or each cylinder, a crankshaft, and means for driving the camshafts from the crankshaft, the driving means comprising a movable member rotatable by the crankshaft and connected to at least one camshaft by an eccentric linkage, and the rotatable member being movable in translation relative to said at least one camshaft in dependence upon an operating condition of the engine, movement of the movable member causing the eccentric linkage to vary the angular position of the camshaft about its axis of rotation relative to the angular position of the crankshaft about its axis of rotation and also to vary the rate of angular movement of the camshaft relative to the angular velocity of the crankshaft, thereby varying the valve timing..]. .[.3. An internal combustion engine according to claim 2, comprising means for moving the rotatable member in dependence upon engine load..]. .[.4. An internal combustion engine according to claim 2, comprising means for moving the rotatable member in dependence upon engine speed..]. .[.5. An internal combustion engine according to claim 2, comprising means for moving the rotatable member in dependence upon engine load and speed..]. .[.6. An internal combustion engine according to claim 2, wherein the movable member is supported on a pivotal arm..]. .[.7. An internal combustion engine according to claim 2, wherein the movable member is supported on a slide..]. .[.8. An internal combustion engine according to claim 6, wherein the position of the movable member is controlled by a piston and cylinder arrangement comprising a control piston the position of which is dependent upon an engine operating condition, a main piston in which the control piston is slidably received, and a cylinder in which the main piston is received, a linkage being provided between the main piston 
     
        and the support for the movable member..]. .[.9.  An internal combustion engine according to claim 6, wherein the pivotal arm supports two rotatable members one of which drives the inlet valve camshaft and the other of which drives the outlet valve camshafts, the two rotatable members rotating at the same rate as each other..]. .[.10. An internal combustion engine according to claim 9, wherein the rotatable members are meshed together and one of them is driven by a gear train from the crankshaft, one gear in the train being pivotal about the same axis as the pivotal arm..]. .[.11. An internal combustion engine according to claim 2, wherein the or each movable member comprises a plate provided with a radial slot which slidably receives a follower supported eccentrically by the camshaft..]. .[.12. An internal combustion engine according to claim 2, comprising four in-line cylinders, and four in-line inlet valve camshafts, each camshaft controlling at least one valve of a respective cylinder, and the camshafts being arranged in pairs on opposite side of a single drive means with one camshaft of each pair being driven by a shaft extending through the other camshaft of the pair..]. .[.13. An internal combustion engine according to claim 2, the timing mechanism being such that the inlet valve timing may be altered to open an inlet valve nearer to top dead centre while simultaneously the inlet valve timing is altered to close the inlet valve nearer to bottom dead centre, and the exhaust valve timing may be altered to open an exhaust valve nearer to bottom dead centre while simultaneously the exhaust valve timing is altered to close the exhaust valve nearer to top dead centre..]. .[.14. An internal combustion engine according to claim 13, wherein the degree of alteration to the position of inlet valve opening at any particular instant can be different to the degree of alteration to the position of inlet valve closing at the same particular instant..]. .[.15. An internal combustion engine according to claim 13, wherein the degree of alteration to the position of exhaust valve opening at any particular instant can be different to the degree of alteration to the position of exhaust valve closing at the same particular instant..]. .[.16. An internal combustion engine according to claim 13, wherein the degree of alteration to the inlet valve opening and closing at any particular instant can be different to the degree of alteration to the exhaust valve opening and closing at the same particular instant..]. .[.17. An internal combustion engine according to claim 2, wherein inlet and exhaust valves are driven by the 
     
     
        same movable member..]. .Iadd.18.  A valve timing mechanism for an internal combustion engine including a crankshaft;   at least one cylinder;   an inlet valve and an outlet valve for said cylinder;   means defining first and second axes of rotation;   an inlet camshaft mounted to rotate about said first axis of rotation and carrying an inlet valve cam to operate said inlet valve, and an exhaust camshaft mounted to rotate about said second axis of rotation and carrying an exhaust valve cam to operate said exhaust valve;   a member movable in dependence upon an engine operating condition;   a driving mechanism driven from said crankshaft and mounted on said movable member;   means defining third and fourth axes of rotation;   said driving mechanism comprising   a first rotary member, mounted to rotate about said third axis and eccentrically-connected to said inlet camshaft, said third axis being parallel to but displaceable relative to said first axis, and   a second rotary member, mounted to rotate about said fourth axis and eccentrically-connected to said exhaust camshaft, said fourth axis being parallel to but displaceable relative to said second axis;   said third and fourth axes being fixed to said movable member and relative to each other, whereby said movement of said movable member varies the said eccentricity of said connections between said first rotary member and said inlet camshaft and said second rotary member and said exhaust camshaft, thereby varying the rate of angular movement of said camshafts relative to the angular movement of said crankshaft and so varying the timing of said inlet and exhaust valves. .Iaddend. .Iadd.19. A valve timing mechanism according to claim 18 in which said third and fourth axes are coincident and said first and second rotary members are combined in a single rotary member, mounted on said movable member and eccentrically connected both to said inlet camshaft and to said exhaust camshaft.   
     
     
        .Iaddend. .Iadd.20.  A valve timing mechanism for an internal combustion engine including a crankshaft;   at least one cylinder;   an inlet valve and an outlet valve for said cylinder;   means defining first and second axes of rotation;   an inlet camshaft mounted to rotate about said first axis of rotation and carrying an inlet valve cam to operate said inlet valve, and an exhaust camshaft mounted to rotate about said second axis of rotation and carrying an exhaust valve cam to operate said exhaust valve;   mechanism movable in dependence upon an engine operating condition;   driving means driven from said crankshaft and mounted on said movable mechanism;   means defining third and fourth axes of rotation;   said driving means comprising a first rotary member, mounted to rotate about said third axis and eccentrically-connected to said inlet camshaft, said third axis being parallel to but displaceable relative to said first axis, and   a second rotary member, mounted to rotate about said fourth axis and eccentrically-connected to said exhaust camshaft, said fourth axis being parallel to but displaceable relative to said second axis;   said third and fourth axes being at a constant spacing-apart relative to each other, whereby said movement of said movable member varies the said eccentricity of said connections between said first rotary member and said inlet camshaft and said second rotary member and said exhaust camshaft without varying said spacing-apart of said third and fourth axes, thereby varying the rate of angular movement of said camshafts relative to the angular movement of said crankshaft and so varying the timing of said   
     
     
        inlet and exhaust valves. .Iaddend. .Iadd.21.  A valve timing mechanism according to claim 20 in which said inlet camshaft and said exhaust camshaft are coaxial. .Iaddend. .Iadd.22. A valve timing mechanism according to claim 20 in which said inlet camshaft and said exhaust camshaft are parallel to and laterally spaced from each other. .Iaddend. .Iadd.23. A valve timing mechanism according claim 20 in which said third and fourth axes are coincident and said first and second rotary members are combined in a single rotary member, eccentrically connected both to said inlet camshaft and to said exhaust camshaft. .Iaddend. .Iadd.24. A valve timing mechanism according to claim 20 in which said driving means comprises two separate rotary members mounted to rotate about parallel but spaced-apart axes. .Iaddend. .Iadd.25. A valve timing mechanism according to claim 20 in which said mechanism movable in dependence upon an engine 
     
     
        operating condition comprises a sliding member. .Iaddend. .Iadd.26.  A valve timing mechanism according to claim 20 in which each of said eccentric connections between said first rotary member and said inlet camshaft, and said second rotary member and said exhaust camshaft, comprises a radial slot formed in the respective rotary member and slidably-receiving a follower supported eccentrically by the respective said camshaft. .Iaddend. .Iadd.27. A valve timing mechanism according to claim 20 comprising four in-line cylinders and four in-line inlet camshafts, each said inlet camshaft controlling at least one inlet valve of a respective cylinder, and the said inlet camshafts being arranged in pairs on opposite sides of a single said driving means with one camshaft of each pair being driven by a shaft extending through the other camshaft of the pair. .Iaddend. .Iadd.28. A valve timing mechanism according to claim 20 in which the inlet valve timing may be altered to open an inlet valve nearer to top dead center while simultaneously the inlet valve timing is altered to close the inlet valve nearer to bottom dead center, and the exhaust valve timing may be altered to open an exhaust valve nearer to bottom dead center while simultaneously the exhaust valve timing is altered to close the exhaust valve nearer to top dead center. .Iaddend. 
     
     
        .Iadd.29.  A valve timing mechanism according to claim 28, wherein the degree of alteration to the position of inlet valve opening at any particular instant can be different to the degree of alteration to the position of inlet valve closing at the same particular instant. .Iaddend. .Iadd.30. A valve timing mechanism according to claim 28, wherein the degree of alteration to the position of exhaust valve opening at any particular instant can be different to the degree of alteration to the position of exhaust valve closing at the same particular instant. .Iaddend. .Iadd.31. A valve timing mechanism according to claim 28 wherein the degree of alteration to the inlet valve opening and closing at any particular instant can be different to the degree of alteration to the exhaust valve opening and closing at the same particular instant. .Iaddend. .Iadd.32. A valve timing mechanism according to claim 20 in which said mechanism movable in dependence upon an engine operating condition comprises a pivoted arm. .Iaddend. .Iadd.33. A valve timing mechanism according to claim 32, wherein the position of the pivoted arm is controlled by a piston and cylinder arrangement comprising a control piston the position of which is dependent upon said engine operating condition, a main piston in which said control piston is received, and a cylinder in which the main piston is received, a linkage being provided 
     
     
        between said main piston and said pivoted arm. .Iaddend. .Iadd.34.  A valve timing mechanism according to claim 32 in which said driving means comprises two separate rotary members, mounted on said pivoted arm to rotate at the same rate as each other and about parallel but spaced-apart axes. .Iaddend. .Iadd.35. A valve timing mechanism according to claim 34 wherein said two separate rotary members are meshed together and one of them is driven by a gear train from said crank shaft, one gear in the said train being pivotal about the same axis as the pivoted arm. .Iaddend.