Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
  • F01L—CYCLICALLY OPERATING VALVES FOR MACHINES OR ENGINES
  • F01L13/00—Modifications of valve-gear to facilitate reversing, braking, starting, changing compression ratio, or other specific operations
  • F01L13/0015—Modifications of valve-gear to facilitate reversing, braking, starting, changing compression ratio, or other specific operations for optimising engine performances by modifying valve lift according to various working parameters, e.g. rotational speed, load, torque
  • F01L13/0057—Modifications of valve-gear to facilitate reversing, braking, starting, changing compression ratio, or other specific operations for optimising engine performances by modifying valve lift according to various working parameters, e.g. rotational speed, load, torque by splittable or deformable cams

Definitions

• the present invention relates to a variable valve timing mechanism for an internal combustion engine.
• the present invention seeks to provide a variable valve timing mechanism which introduces lost motion into the valve train but which mitigates noise nd wear problems.
• a drive mechanism for transmitting driving torque from the crankshaft to a camshaft of an internal combustion engine and incorporating means for permitting a limited degree of rotation of one of the shafts relative to the other
• the drive mechanism comprising concentric drive and driven members connectible respectively to the crankshaft and the camshaft, and a lever pivotably supported on one of the members and having a force transmitting surface that is biassed by a spring to remain in contact at all times with a reaction surface on the other member, the position of the point of contact between the two surfaces being dependent upon the relative angular position of the drive and driven members and being operative to move progressively to vary the mechanical advantage of the lever as the shafts rotate relative to one another under the action of the torque reversals on the camshaft.
• the spring does not act directly between the drive and driven members but does so through a variable ratio lever.
• direct drive conditions when all the lost motion is taken up
• the point of contact between the drive surface of the lever and the reaction surface on the other member is nearly coincident with the pivot point of the lever, resulting in the effective lever arms having a very large ratio and increasing the drive torque transmitted.
• the torque on the camshaft is reversed by a valve spring acting on a cam
• the point of contact moves away from the pivot point of the lever, first reducing the transmitted torque and then allowing the reverse torque to accelerate the camshaft and make it lead the crankshaft within the permissible limited lost motion.
• the surface of the lever and the reaction surface with which it makes contact are profiled in such a manner that the surface of the lever rolls without slipping on the reaction surface. This avoids wear due to friction and reduces the lubrication requirements of the mechanism.
• the strength of the valve springs and the friction on the valve train determine the applied torque to effect the phase change and the rate of change of the phase during such torque reversal will also depend upon the moment of inertia of the drive mechanism.
• the amplitude of the phase change i.e. the extent to which the duration of the valve event is reduced, further depends on the time that the torque acts, in other words upon the engine speed.
• the valve springs and the moment of inertia are constant and the extent of variation will vary only and automatically with engine speed, assuming no change in friction. It is possible to apply a variable drag between the drive and driven members, for example by the use of a magnetic clutch, to reduce the phase change occurring at any given engine speed.
• Figure 1 is a transverse section through a drive mechanism, taken along the section line I-I in Figure 2, and
• Figure 2 is an axial section through the drive mechanism, taken along the section line II-II in Figure 1.
• a drive mechanism comprises a driven member 10 connected to the camshaft 12 of an engine, and a drive member 14 driven through a belt 16 by the engine crankshaft.
• the drive member 14 is journalled about the camshaft 12 and can rotate relative to it.
• the coupling between the drive and driven members 14 and 10 is effected by means of pins 18 in the driven member 10 about which there are pivoted two levers 20 that are both biassed to rotate in a clockwise direction as viewed in Figure 1 by helical springs 22.
• the pins 18 and levers 20 are located within a deep recess in the drive member 14 bounded by reaction surfaces 24 against which the levers 20 are urged by the springs 22.
• An electromagnetic clutch 30 is included to apply a controllable drag between the drive and driven members 14 and 10.
• a disk 32 is formed in close proximity to the drive member 14 and fixed for rotation with the camshaft 12 and an electromagnet 34 powered by a suitable control circuit 36 can apply a variable magnetic field to a thin film of magnetic fluid 38 disposed between the disk 32 and the drive member 14.
• the purpose of the clutch 30 is to apply a variable drag between the drive and driven members 14 and 10 to moderate the extent of phase change at any given engine speed.
• the illustrated embodiment incorporates a position sensor 40 that provides a position feedback signal to the control circuit 36 so that the phase change can be accurately closed loop controlled.
• both surface may ⁇ be curved or the reaction surfaces alone may be curved.

Landscapes

• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Valve Device For Special Equipments (AREA)
• Valve-Gear Or Valve Arrangements (AREA)

Applications Claiming Priority (3)

Publications (2)

Family

ID=10748875

Family Applications (1)

Country Status (4)

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Family Cites Families (4)

• 1994
  • 1994-01-15 GB GB9400748A patent/GB2285671A/en not_active Withdrawn
  • 1994-12-15 EP EP95905179A patent/EP0739444B1/de not_active Expired - Lifetime
  • 1994-12-15 DE DE69411193T patent/DE69411193T2/de not_active Expired - Fee Related
  • 1994-12-15 WO PCT/GB1994/002797 patent/WO1995019493A1/en active IP Right Grant

Non-Patent Citations (1)

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