A permanent magnet enhanced electromagnetic valve actuator

Abstract: An electromagnetic valve actuator (10) for actuating movement of a valve (12) in a vehicle engine is disclosed. The actuator (10) includes a valve assembly operatively connected to the valve for movement therewith. The valve assembly includes a shaft (14) connected to the valve (12), two armature plates (16,18) operatively associated with the shaft (14) each armature plate (16,18) having a permanent magnet as an integral part. An electromagnetic coil (24) is positioned between the two armature plates (16,18) for electromagnetically pushing and pulling the armature plates (16,18) and two springs (26,28) are engaged with the two armature plates (16,18) for biasing them in opposing directions. The permanent magnets are used to assist the electromagnetic coil (24) in holding the valve (12) in a desired position to reduce power consumption.

Description: The present invention relates to an electromagnetic valve actuator and in particular to an electromagnetic valve actuator for opening and closing a valve in a vehicle engine. In a vehicle engine, a valve is controlled to open and close so that a cylinder may perform intake, compression, expansion, and exhaust operations. In one example of a drive apparatus for opening and closing valves, a camshaft, which is configured by disposing cams for vale opening and closing on one shaft, is provided on the upper portion of the engine or on one side face thereof. A crankshaft, which translates the piston motion to rotational motion, and the camshaft which operates the vales are connected by means such as a belt or chain. The camshaft is driven in synchronism with the crankshaft of the engine. The valves are opened by the cam lobes on the camshaft via a link mechanism such as a rocker arm or push rod. The valve normally is held in the closed position by a spring. In another example of a drive apparatus for opening and closing an intake exhaust valve, an intake camshaft having an intake valve opening profile, and an exhaust camshaft having an exhaust valve opening profile are disposed on the upper portion of an engine, the cam lobe of the intake camshaft pushes the axial end face of the intake valve directly, and the cam lobe of the exhaust camshaft pushes the axial end face of the exhaust valve directly, thereby opening the intake/exhaust valve. This conventional drive apparatus for opening and closing the intake/exhaust valve results in an increase in engine size because the camshaft and link mechanism must be added onto the engine. Furthermore, since the camshaft and link mechanism are driven by the output shaft (crankshaft) of the engine, some of the engine output is consumed by frictional resistance when the camshaft and link mechanism are driven. This reduces the effective output of the engine. Further, the actuation timing of the intake/exhaust valve is fixed and cannot be altered during engine operation. Hence, the valve actuation timing is a compromise between low and high engine rpm. As a consequence, the engine output torque is not optimum neither at low nor at high engine rpm. In order to solve the foregoing problems, various systems for driving an intake/exhaust valve to open and close the same by electromagnetic force from an electromagnet, without relying upon a camshaft, have been proposed, such as in U.S. Patent Nos. 4,955,334 and 4,829,947. These patents teach the use of a single armature plate which is movable by a pair of electromagnetic coils positioned on opposing sides of the plate. US patent number 6,318,312 describes a valve actuator for an internal combustion engine including an electromagnetic coil and two springs. The valve actuator comprises a shaft connected to the valve and two armatures operatively connected to the shaft for movement therewith The electromagnetic coil is positioned between the two armatures for electromagnetically pushing and pulling the armatures. The two springs bias the valve in opposing directions towards the open and closed positions respectively. It is an object of this invention to provide an improved electromagnetic valve actuator. According to a first aspect of the invention there is provided an electromagnetic valve actuator for actuating movement of a valve between full open and full closed positions in a vehicle engine, the actuator comprising a valve actuator assembly, an electromagnetic coil and two springs, the valve actuator assembly comprising a shaft connected to the valve and two armature plates operatively connected to the shaft for movement therewith, wherein the electromagnetic coil is positioned between the two armature plates for electromagnetically pushing and pulling the armature plates and each of the two springs is engaged with a respective one of the two armature plates for biasing the armature plates in opposing directions, current supply means being provided to supply first and second holding currents of respective polarity to the electromagnetic coil to hold the valve in the full open and full closed positions respectively, characterised in that each armature plate includes a permanent magnet operative to assist the electromagnetic coil in holding the valve in a desired full open or full closed position to reduce power consumption, the current supply means supplying to the electromagnetic coil a current of a polarity reversed relative to the holding current to open or to close the valve, which reversed polarity current is reduced as the valve approaches the full open or full closed position to soften the landing of the armature plates on the electromagnetic coil. One of the armature plates may be operatively connected to the shaft via abutment with a plate fixed to the shaft, the armature plate being slidingly engaged with the shaft. One of the armature plates may be fixed directly to the shaft. Each of the permanent magnets may be a permanent magnet sheet connected to a ferromagnetic plate. The permanent magnets may be arranged such that like poles face the electromagnetic coil. According to a second aspect of the invention there is provided a method of controlling and electromagnetic valve actuator according to the first aspect of the invention, characterised in that the method comprises supplying first and second holding currents of respective polarity to the electromagnetic coil to hold the valve in the full open and full closed positions respectively, selectively energising the electromagnetic coil positioned between the two armature plates to push and pull the armature plates to effect opening and closing movement of the valve and reducing the energising of the electromagnetic coil as the valve approaches the full open or full closed position to soften the landing of the armature plates on the electromagnetic coil. Said energising step may comprise providing a negative current to bias the armature plates in one direction, and a positive current to bias the armature plates in an opposite direction. The method may further comprise reversing the current to the electromagnetic coil for a short period of time as the valve approaches a closed position to reduce landing velocity. According to a third aspect of the invention there is provided an internal combustion engine having two or more reciprocating valves wherein at least one of the reciprocating valves is actuated by an electromagnetic valve actuator in accordance with the first aspect of the invention. The invention will now be described by way of example with reference to the accompanying drawing of which:- Figure 1 shows a schematic longitudinal cross-sectional view of an electromagnetic valve actuator in accordance with the present invention, with a valve in a closed position; Figure 2 shows a schematic longitudinal cross-sectional view of the electromagnetic valve actuator assembly of Figure 1, with the valve in an open position; Figure 3 shows a schematic longitudinal cross-sectional view of the electromagnetic valve actuator of Figure 1, with the valve in a fully open position; Figure 4 shows a schematic longitudinal cross-sectional view of the electromagnetic valve actuator of Figure 1, with the valve in a nearly closed position; and Figure 5 shows a graphical illustration of an electromagnetic coil current control scheme to actuate opening and closing of the valve assembly of Figures 1-4 in accordance with the present invention. Referring to Figures 1-5, an electromagnetic valve actuator 10 and electromagnetic coil current control scheme are shown for opening and closing a valve 12 for the vehicle engine 13. The electromagnetic valve actuator 10 includes a valve actuator assembly connected to the valve 12 for movement therewith. The valve actuator assembly includes a shaft 14 and first and second armature plates 16, 18 operatively associated with the shaft 14 for moving the shaft 14 and the valve 12. As shown in Figure 1 a shaft 20 connects the first and second armature plates 16,18 together, such that the second armature plate 18 is engageable with a plate 22 connected to the shaft 14, for driving the shaft 14 and the first armature plate 16 is directly fixed to the shaft 14. More specifically the armature plate 18 is operatively connected to the shaft 14 via abutment with the plate 22 which is fixed to the shaft 14. The armature plate 18 is slidingly engaged with the shaft 14 and the system must have "lash" or clearance between valve shaft 14 and the armature plate 18 to ensure that the poppet valve 12 can fully seat or close. Each armature plate 16, 18 includes a permanent magnet in the form of a permanent magnet sheet connected to a ferromagnetic plate. An electromagnetic coil 24 is positioned between the two armature plates 16,18 for electromagnetically pushing and pulling the armature plates 16,18. First and second springs 26,28 are engaged with the two armature plates 16,18 for biasing the armature plates 16,18 in opposing directions. The actuation of the actuator 10 is described below. In Figure 1, the fixed electromagnetic coil 24 is holding the lower armature plate 18 to compress the upper spring 26. The lower spring 28 then expands to close the valve 12. The plates 16,18 use permanent magnets with a North-South (N-S, top-to-bottom) configuration in the upper plate 16 and a South-North (top-to-bottom) configuration in the lower plate 18 so that like poles face the electromagnetic coil 24. In this position, a negative holding current is applied to the coil 24, as shown in Figure 5 (see "A" in Figure 5), giving the electromagnetic coil 24 a North pole on its lower surface (as viewed in Figure 1), thereby enhancing the closing force by pulling on the South pole of the lower armature plate 18. This ultimately reduces the electrical power required to hold the valve 12 in the closed position, and therefore reduces fuel consumption. Referring to Figure 2, when the valve opens, the current in the electromagnetic coil 24 is reversed (see "B" in Figure 5) so that the electromagnet 24 has South pole on its lower surface. This creates an opposing force between the electromagnet and the lower armature plate 18 which supplements the opening force normally provided by the upper spring 26. Additionally, the positive coil current creates an attractive force between the North pole of the upper surface of the electromagnet 24 and the South pole of the upper armature plate 16. This increases the opening speed of the valve 12, and therefore improves the volumetric efficiency of the engine at higher speeds. As the valve approaches the full open position, the current is reduced (see "C" in Figure 5) to minimize the closing force and soften the abutment or landing of the upper armature plate 16 on the coil 24. If the armature speed and inertia are high, a negative current (see "D" in Figure 5) may be applied to the coil 24 for a short time to further reduce the abutment or landing velocity to a level below that possible for an armature without permanent magnets. Referring to Figure 3, when the valve reaches the fully open position, the current is held at a positive level (see "E" in Figure 5) where the magnetic forces balance the spring forces. Again, the permanent magnet enhances the force and therefore reduces the electrical power required to hold the valve 12 open. Referring to Figure 4, the valve closing process is similar to the opening process. The coil current is reversed (see "F" in Figure 5) to create a South pole on the upper surface of the electromagnet 24 (as viewed in the Figures). This repels the South pole of the upper armature plate 16. The North pole on the lower surface of the coil 24 attracts the South pole on the lower armature plate 18. The additional attractive and repulsive forces created by the permanent magnets supplement the closing force provided by the lower spring 28. As the valve approaches the full closed position, the current magnitude is reduced (see "G" in Figure 5) to minimize the closing force and soften the landing of the upper armature plate 16 on the coil 24. If the armature speed and inertia are high, a positive current (see "H" in Figure 5) may be applied for a short time to further reduce the landing velocity. The control scheme is shown in Figure 5 in which the dashed line indicates valve position, and the solid line indicates the current through the electromagnetic coil 24.

Claims: An electromagnetic valve actuator (10) for actuating movement of a valve (12) between full open and full closed positions in a vehicle engine, the actuator (10) comprising a valve actuator assembly, an electromagnetic coil (24) and two springs (26,28), the valve actuator assembly comprising a shaft (14) connected to the valve (12) and two armature plates (16,18) operatively connected to the shaft (14) for movement therewith, wherein the electromagnetic coil (24) is positioned between the two armature plates (16,18) for electromagnetically pushing and pulling the armature plates (16,18) and each of the two springs (26,28) is engaged with a respective one of the two armature plates (16,18) for biasing the armature plates (16,18) in opposing directions, current supply means being provided to supply first and second holding currents of respective polarity to the electromagnetic coil (24) to hold the valve in the full open and full closed positions respectively; characterised in that each armature plate (16,18) includes a permanent magnet operative to assist the electromagnetic coil (24) in holding the valve (12) in a desired full open or full closed position to reduce power consumption, the current supply means supplying to the electromagnetic coil (24) a current of a polarity reversed relative to the holding current to open or to close the valve, which reversed polarity current is reduced as the valve approaches the full open or full closed position to soften the landing of the armature plates on the electromagnetic coil (24). An actuator as claimed in claim 1, wherein the polarity of the electromagnetic coil (24) is again reversed near to the open and closed positions of the valve (12) so as to further reduce valve landing speed. An actuator as claimed in claim 1 or in claim 2, wherein each of the permanent magnets is a permanent magnet sheet connected to a ferromagnetic plate. An actuator as claimed in any of claims 1 to 3, wherein the permanent magnets are arranged such that like poles face the electromagnetic coil (24). A method of controlling and electromagnetic valve actuator as claimed in any of claims 1 to 4, characterised in that the method comprises supplying first and second holding currents of respective polarity to the electromagnetic coil (24) to hold the valve in the full open and full closed positions respectively, selectively energising the electromagnetic coil (24) positioned between the two armature plates (16,18) to push and pull the armature plates (16,18) to effect opening and closing movement of the valve (12) and reducing the energising of the electromagnetic coil (24) as the valve approaches the full open or full closed position to soften the landing of the armature plates on the electromagnetic coil (24). A method as claimed in claim 5 wherein said energising step comprises providing a negative current to bias the armature plates (16,18) in one direction, and a positive current to bias the armature plates (16,18) in an opposite direction. A method as claimed in any of claims 5 or 6, wherein the method further comprises reversing the current to the electromagnetic coil (24) for a short period of time as the valve approaches a closed position to further reduce landing velocity. An internal combustion engine having two or more reciprocating valves (12) characterised in that at least one of the reciprocating valves (12) is actuated by an electromagnetic valve actuator (10) as claimed in any of claims 1 to 4.

Inventors: CURTIS ERIC WARREN, HAGHGOOIE MOHAMMAD, MEGLI THOMAS WILLIAM, CURTIS, ERIC WARREN, HAGHGOOIE, MOHAMMAD, MEGLI, THOMAS WILLIAM
Applicants: FORD GLOBAL TECH INC, FORD GLOBAL TECHNOLOGIES, INC.
Application year: 2001
Main classification: F01L9
IPC codes: F01L9