Electromagnetic force valve driving apparatus

Abstract: A valve driving apparatus includes a reciprocally movable magnetic pole (3) connected to an inlet/exhaust valve (4), a fixed magnetic pole (12) opposing one end of the movable magnetic pole, and a spring (32) biasing the inlet/exhaust valve in the closing direction at all times. When the inlet/exhaust valve is released, the one end of the movable magnetic pole and the fixed magnetic pole are energized to have the same polarity and the inlet/exhaust valve is driven in the opening direction by a repulsive force acting between the two magnetic poles. The inlet/exhaust valve is held at a position where the repulsive force and spring force balance each other. The inlet/exhaust valve is caused to begin moving in the closing direction by eliminating the repulsive force. The two magnetic poles are excited again immediately before the valve is seated, thereby reducing the travelling speed in the closing direction to mitigate seating shock.

Description: This invention relates to an electromagnetic force valve driving apparatus for opening and closing the inlet/exhaust valve of an engine by an electromagnetic force produced by an electromagnet. In one example of a conventional drive apparatus for opening and closing an inlet/exhaust valve, a camshaft on which cams for inlet and exhaust are disposed is provided on the upper portion of the engine or on one side thereof. A crankshaft and the camshaft are connected by rotary transmission means such as a belt, and the camshaft is driven rotationally in synchronism with the rotational phase of the engine. The cam face of the camshaft and the axial end face of the valve are connected via a link mechanism such as a rocker arm or push rod. The inlet/exhaust valve, which is biased in the closing direction at all times by a valve spring, is driven in the opening direction by the link mechanism which acts to push the axial end face of the valve. This conventional drive apparatus for opening and closing the inlet/exhaust valve results in a large-size engine because the camshaft and link mechanism must be included. Also, since the camshaft and link mechanism are driven by the output shaft of the engine, some of the engine output is consumed by frictional resistance when the camshaft and link mechanism are driven. This diminishes the effective output of the engine. Furthermore, the timing of the inlet/discharge valve cannot be altered during engine operation. Since the valve timing is adjusted in conformity with the rotational speed of the engine, engine output and efficiency decline when the engine is running at a speed (rpm) different from the prescribed speed. In order to solve the foregoing problems, an apparatus for driving an inlet/exhaust valve by an attractive force acting between a movable magnetic pole connected to the inlet/exhaust valve and a magnetic pole of a fixed electromagnet has been disclosed in JP-A-58-183805, and JP-A-61-76713. In these apparatus, the distance between the magnetic pole of the electromagnet and the movable magnetic pole is at a maximum at the moment that the attractive force starts acting upon the movable magnetic pole. Consequently, the attractive force between the magnetic pole of the electromagnet and the movable magnetic pole is at a minimum at this time. Accordingly, acceleration of the movable magnetic pole immediately after it starts moving is low, and therefore the size of the opening of the valve operatively associated with the movable magnetic pole is small. Furthermore, since the distance between the electromagnet and the movable magnetic pole is large even in the case where a braking force is applied to the movable magnetic pole just prior to valve seating in order to mitigate shock when the valve is seated, as described in the specification of JP-A-61-76713, the braking force is too small to reduce the seating shock sufficiently. JP-A-58-101206 partially solves this problem by a construction in which is provided an electromagnetic force valve driving apparatus for opening and closing an inlet/exhaust valve of an engine, comprising a magnetic member on the inlet/exhaust valve for reciprocable movement therewith; first and second cooperating electromagnets, the first of which has a magnetic pole opposing one side of the movable magnetic pole, the second electromagnet having a magnetic pole which opposes the other side of the magnetic pole member; a spring which acts to close the valve; and energizing control means for energizing said first and second electromagnets to open and close the inlet/exhaust valve. A similar system is shown in US-A-4392632 in which there is described a system for slowing the valve just before it seats, by causing a repulsive force to act between the magnets employed. The present invention has been devised in view of the foregoing points and its object is to provide an electromagnetic force valve driving apparatus in which the magnetic force that acts upon the valve is maximised when the valve starts moving and when the valve is seated. According to the present invention, there is provided an electromagnetic force valve driving apparatus for opening and closing an inlet/exhaust valve of an engine, the apparatus comprising: a magnetic pole member connected to an inlet/ exhaust valve for reciprocable movement therewith; a first electromagnet having first and second opposed poles, the first pole opposing one end of the magnetic pole member; a second electromagnet comprising a yoke member, the valve being movable relative to the yoke member, the yoke member having an upper magnetic pole opposing the one end of the movable magnetic pole member and a lower magnetic pole opposing the other end of the movable magnetic pole member, the second pole of the first electromagnet being a peripheral pole which opposes the first pole of the first electromagnet and the upper pole of the second electromagnet; a spring for urging the valve closed, the spring subjecting said movable magnetic pole member to a force which moves it in the direction of the one end thereof; and, energising control means for energising said first electromagnet and including a programmable control unit for adjusting the timing of valve opening, the energising means energising said first and second electromagnets to open the inlet/exhaust valve and to cause a repulsive force to act between the one end of said movable magnetic pole and the first pole immediately before it is seated. The present invention is characterised over JP-A-58-101206 by various features, including the peripheral second pole of the first electromagnet. With the electromagnetic force valve driving apparatus of the present invention, a repulsive force is caused to act between the one end of the movable magnetic pole and the upper fixed magnetic pole when the inlet/exhaust valve is released. The repulsive force drives the inlet/exhaust valve in the opening direction. After the movable magnetic pole has been held for a prescribed period of time at a position where the repulsive force and spring force are in balance, energisation is terminated so that the inlet/exhaust valve is closed by the force of the spring. Energisation is resumed for a prescribed period of time just prior to seating of the valve, thereby decelerating the valve in the closing direction to mitigate seating shock. Thus, in accordance with the present invention, there can be provided an electromagnetic force valve driving apparatus for high output and superlative fuel economy in which driving of the inlet/exhaust valve in the opening direction and braking of the valve at seating are achieved by an electromagnetic force, and a high drive force in the opening direction as well as a large acceleration at seating are obtained. As a result, the degree to which the inlet/exhaust valve opens is enlarged, i.e., the inlet/exhaust resistance is diminished. One example of apparatus according to the present invention will now be described with reference to the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof. Figure 1 is a block diagram illustrating an embodiment of the present invention; Figure 2 is a view showing a valve drive section; and, Figure 3 is a diagram showing the relationship between amount of valve movement and time. An engine 6 has an inlet valve for opening and closing the inlet port of a cylinder, and a discharge valve for opening and closing the discharge port of the cylinder. The discussion that follows will deal primarily with the inlet valve. Numeral 4 denotes the inlet valve, which is formed of a heat-resistant, light weight ceramic. It is also permissible to form the inlet valve 4 of a heat-resistant alloy, as in the prior art. The inlet valve 4 is axially supported by a valve guide 41 so as to be slidable in the axial direction and has a bevelled portion which is seated on a valve seat 42 disposed at the outlet of an intake conduit 43, thereby closing the inlet port. A movable magnetic pole 3 comprising a magnetic material is fixedly secured to the axial end portion of the inlet valve 4 by a fixing member 33. The axial end portion of the movable magnetic pole 3 is formed to have a radially projecting end magnetic pole 31. An upper electromagnet 1 is disposed in close proximity to the end magnetic pole 31 on the upper side thereof and comprises a central magnetic pole 12 opposing the end magnetic pole 31, a peripheral magnetic pole 13 opposing the central magnetic pole 12, and an upper coil 11 for producing magnetic lines of force in the central magnetic pole 12 and peripheral magnetic pole 13. A lower electromagnet 2 is provided about the outer periphery of the movable magnetic pole 3 and comprises an upper magnetic pole 23 opposing the peripheral magnetic pole 13 and the end magnetic pole 31, a lower magnetic pole 22 opposing the outer peripheral surface of the movable magnetic pole 3, and a lower coil 21 for generating magnetic lines of force in the upper magnetic pole 23 and the lower magnetic pole 22. A spring 32 for applying an upwardly directed force to the inlet valve 4 via the movable magnetic pole 3 is disposed between the end magnetic pole 31 and the lower magnetic pole 22. The upper coil 11 and the lower coil 21 are connected to an input/output interface 54 within a control unit 5. Connected to the input/output interface 54 in addition to the upper coil 11 and lower coil 21 is a rotary sensor 61 provided in close proximity to the output shaft of the engine 6. The control unit 5 comprises, in addition to the input/output interface 54 which supervises signal input/output with the external equipment, a ROM 52 in which programs and data are stored in advance, a CPU 51 for performing processing under control of the programs stored in the ROM 52, a RAM 53 for temporarily storing input signals and the results of processing, and a control memory 55 for controlling the flow of signals within the control unit 5. The operation of the apparatus according to the invention will now be described. Figure 2 is a view illustrating the upper electromagnet 1 and lower electromagnet 2, which constitute the valve drive section. The cross-section hatching in Figure 1 has been removed from Figure 2. During ordinary operation, the inlet valve 4 is urged upwardly by the spring 32 and held at a position where it is seated on the valve seat 42. When the rotational phase of the engine 6 sensed by the rotation sensor 61 represents the time for opening the inlet valve 4, a current is passed through the upper coil 11 in such a manner that a North (N) pole is produced in the central magnetic pole 12 and a South (S) pole in the peripheral magnetic pole 13. Concurrently, a current is passed through the lower coil 21 as well to produce an N pole in the lower magnetic pole 22 and an S pole in the upper magnetic pole 23. Since the end magnetic pole 31 opposes the upper magnetic pole 23, an N pole is produced in the end magnetic pole 31 by the S pole generated in the upper magnetic pole 23. Accordingly, the central magnetic pole 12 and the end magnetic pole 31 are identical in polarity and repel each other, as a result of which the inlet valve 4 is driven downwardly. Since the distance between the central magnetic pole 12 and end magnetic pole 31 at the moment the foregoing driving operation begins is minimum in terms of the vertical stroke of the inlet valve 4, the downwardly directed driving force produced by the electromagnetic repulsion is at a maximum. When the inlet valve 4 is thus driven downwardly to increase the distance between the end magnetic pole 31 and central magnetic pole 12, the repulsive force decreases and the upwardly directed force produced by the spring 32 increases. The inlet valve 4 stops at a position where the downward repulsive force and the upward spring force balance each other. Supply of current to the upper coil 11 and lower coil 21 is interrupted at a first predetermined time from the moment the inlet valve 4 is opened. As a result, the downward repulsive force vanishes and only the upwardly directed force produced by the spring 32 remains. Accordingly, the inlet valve 4 is driven upwardly. Immediately before the inlet valve is seated on the valve seat 42, namely at a second predetermined time clocked from the moment the first time period elapses, a current is again passed through the upper coil 11 and lower coil 21 in such a manner that N poles are produced in the central magnetic pole 12 and end magnetic pole 31. Owing to the supply of current, a downwardly directed repulsive force acts upon the inlet valve 4 to reduce the velocity of its upward movement, thereby mitigating shock produced when the valve 4 is seated on the valve seat 42. At a third set time, set in advance as the time required for deceleration, supply of current to the upper coil 11 and lower coil 21 is interrupted again. As a result, the inlet valve 4 is maintained in the seated position on the valve seat 42 by the spring 32. A table giving the correlation between each set time period and engine rpm is stored in the ROM 52 beforehand. The first, second and third times mentioned above are obtained by calculating the set time corresponding to engine rpm from the rpm of the engine 6, which is sensed by the rotation sensor 61, and the correlation table. The opening and closing of the valve will now be described with reference to Figure 3. Figure 3 shows so-called cam profile curves, in which the horizontal axis represents the opening timing of the inlet valve 4, and the vertical axis represents the amount of valve movement. The curves in this diagram indicate the change in the amount of movement of the inlet valve with the passage of time. The curve indicated by the solid line is that according to the present invention, while the curve indicated by the dashed line is that obtained with the conventional apparatus using electromagnets. In the conventional apparatus associated with the curve indicated by the dashed line, the valve is driven by an attractive force produced electromagnetically. Consequently, the attractive force is at a minimum at the moment the force begins to act, and the distance over which the electromagnetic force acts diminishes with movement of the valve, as a result of which the attractive force increases. Accordingly, acceleration immediately after the start of movement is low. On the other hand, in the apparatus of the present invention, the acceleration is high immediately after the valve begins moving, as described above. The area defined between the profile curve and the horizontal axis indicates the degree of valve opening. It will be understood that this area, as obtained with the apparatus of the present invention, is larger than that of the prior art by the amount indicated by the shaded portions. Accordingly, the apparatus of the present invention is such that inlet/discharge resistance at the opening of an inlet/discharge valve is smaller than in the prior art apparatus and the performance of the engine 6 is improved over the prior-art apparatus. As well as the table giving the correlation between the set times and engine rpm mentioned above, a map giving the correlation between engine rpm and valve opening timing is stored in the ROM 52 in advance, and engine output and efficiency can be improved over the entire region of engine rpm by altering the valve opening timing as the rotational speed of the engine 6 changes. In addition, it is possible to perform cylinder control to increase or decrease the number of operating cylinders by driving or stopping the inlet/exhaust valves of each cylinder attendant upon a rise or fall in the rpm of the engine 6. Although the present invention has been described primarily with regard to an inlet valve, it is obvious that the drive apparatus according to the invention can be similarly applied to an exhaust valve.

Claims: An electromagnetic force valve driving apparatus for opening and closing an inlet/exhaust valve of an engine, the apparatus comprising: a magnetic pole member (3) connected to an inlet/exhaust valve (4) for reciprocable movement therewith; a first electromagnet (1) having first and second opposed poles (12,13), the first pole (12) opposing one end (31) of the magnetic pole member (3); a second electromagnet (2) comprising a yoke member, the valve (4) being movable relative to the yoke member, the yoke member having an upper magnetic pole (23) opposing the one end (31) of the movable magnetic pole member (3) and a lower magnetic pole (22) opposing the other end of the movable magnetic pole member (3), the second pole (13) of the first electromagnet (1) being a peripheral pole which opposes the first pole (12) of the first electromagnet (1) and the upper pole (23) of the second electromagnet; a spring (32) for urging the valve closed, the spring subjecting said movable magnetic pole member (3) to a force which moves it in the direction of the one end (31) thereof; and, energising control means (5) for energising said first electromagnet and including a programmable control unit (5) for adjusting the timing of valve opening, the energising means energising said first and second electromagnets to open the inlet/exhaust valve and to cause a repulsive force to act between the one end (31) of said movable magnetic pole (3) and the first pole (12) immediately before it is seated. Apparatus according to claim 1, wherein the control unit (5) has a memory (52) in which can be stored a map of the times at which said first and second electromagnets are to be energised relative to the rotational speed of said engine. Apparatus according to claim 1 or claim 2, wherein the timing of the valve is varied with the engine speed.

Inventors: KAWAMURA HIDEO, KAWAMURA, HIDEO
Applicants: ISUZU CERAMICS RES INST, ISUZU CERAMICS RESEARCH INSTITUTE CO., LTD.
Application year: 1990
Main classification: F01L9
IPC codes: H01F7, F16K31, F01L9