DEVICE FOR STEP-DRIVING VALVES

Abstract: A device for step-driving valves to open and close the intake and exhaust valves of an engine utilizing the electromagnetic force generated by an electromagnet. To an intake or exhaust valve (8) is coupled a magnetic member (3) that moves reciprocally and that has toothed magnetic pole in parallel with the reciprocating direction. There are further provided fixed magnetic poles (4c, 4d, 6c, 6d) opposed to the toothed magnetic pole and arranged in parallel with the reciprocating direction. The intake or exhaust valve (8) is opened and closed by the electromagnetic attractive and repelling force acting among the toothed magnetic pole and the fixed magnetic poles (4c, 4d, 6c, 6d). When the intake or exhaust valve (8) is opened and closed, therefore, there develops no change in the distance among the toothed magnetic pole and the fixed magnetic poles (4c, 4d, 6c, 6d). The valves are therefore opened and closed stably.

Description: Technical Field The present invention relates to a system for actuating intake and exhaust valves in stepped movement with a linear stepping motor disposed on a stem end of the intake and exhaust valves of an engine. Background Art Some conventional actuating systems for opening and closing intake and exhaust valves include a single camshaft which has cams for the intake and exhaust valves, the camshaft being disposed above or laterally of an engine. The camshaft is operatively connected to the crankshaft of the engine by a rotation transmitting means such as a belt, so that the camshaft can rotate synchronously with the rotation of the engine. The valves have stems whose ends are pressed by cam surfaces of the camshaft through a link mechanism such as rocker arms or push rods. The intake and exhaust valves are normally closed by springs, and can be opened when their stem ends are pressed by the cam surfaces. Alternatively, an intake camshaft having cams for acting on intake valves and an exhaust camshaft having cams for acting on exhaust valves are disposed above an engine. The intake and exhaust valves are opened when the stem ends of the intake valves are directly pushed by the cam surfaces of the intake camshaft and the stem ends of the exhaust valves are directly pushed by the cam surfaces of the exhaust camshaft. Therefore, the above conventional actuating systems for opening and closing intake and exhaust valves include camshafts and link mechanisms added to the engine, which is thus necessarily large in size. Since the camshafts and the link mechanisms are driven by the output shaft of the engine, the engine output power is partly consumed due to the frictional resistance produced when the camshafts and the link mechanisms are driven by the engine. As a result, the effective engine output power is reduced. The timing with which the intake and exhaust valves are opened and closed cannot be altered during operation of the engine, but the valve opening and closing timing is preset such that the engine operates with high efficiency when it rotates at a predetermined speed. Therefore, the engine output power and efficiency are lower when the engine rotates at a speed different from the predetermined speed. To solve the above problems, there have been proposed valve actuating systems for opening and closing intake and exhaust valves under electromagnetic forces from electromagnets, rather than with camshafts, as disclosed in Japanese Laid-Open Patent Publications Nos. 58-183805 and 61-76713. However, with the electromagnets disclosed in the above two publications, the distance between the electromagnet and the magnetic body varies when the intake and exhaust valves are actuated, resulting in an abrupt change in electromagnetic forces and highly unstable operation of the intake and exhaust valves. JP-A-60/109678 discloses a solenoid proportional control valve in which a spool having teeth is moved by a pair of electromagnets between which is positioned a permanent magnet. JP-A-61/88760 discloses a linear motor. In view of the aforesaid problems, it is an object of the present invention to provide a system for actuating a valve in stepped movement with a linear stepping motor disposed on a stem end of intake and exhaust valves, rather than with a camshaft, so that the valves can be opened and closed stably with respect to the movement thereof. According to the present invention, there is provided an engine intake/exhaust valve actuating system for actuating intake and exhaust valves of an engine in stepped movement, the system comprising: a magnetic body coupled to an engine valve, the magnetic body being reciprocally movable and having a plurality of tooth-like magnetic poles juxtaposed at equal intervals in the direction in which the magnetic body is reciprocally movable; a plurality of fixed upper magnetic poles and a plurality of fixed lower magnetic poles disposed in confronting relation to the tooth-like magnetic poles, the fixed magnetic poles being spaced at intervals different from the intervals of the tooth-like magnetic poles in the direction in which the tooth-like magnetic poles are juxtaposed; a plurality of excitation coils, each fixed magnetic pole having an excitation coil wound therearound for selectively generating magnetic lines of force through said fixed magnetic pole; a permanent magnet connecting and extending over the upper and lower fixed magnetic poles for influencing the generation of magnetic lines of force from the fixed magnetic poles; and, energization control means for energizing the excitation coils to open and close the valve by controlling the generation of magnetic lines of force through each of the fixed magnetic poles. With the system according to the present invention, the intake/exhaust valve is opened and closed under attractive and repelling forces acting between the tooth-like magnetic poles juxtaposed on the magnetic body coupled to the intake/exhaust valve and the fixed magnetic poles confronting the tooth-like magnetic poles. Since opening and closing forces acting on the intake/exhaust valve remain unchanged irrespective of movement of the intake/exhaust valve, stable opening and closing forces are applied to the intake/exhaust valve. In the drawings: Fig. 1 is a block diagram showing a system for actuating a valve in stepped movement according to an embodiment of the present invention; Fig. 2 is an enlarged view of the stem end of an intake valve; Figs. 3(a) through 3(e) are diagrams showing the conditions of magnetic lines of force at the time the valve is moved; and Fig. 4 is a diagram showing the relationship between the crankshaft angle and the distance which the valve moves. Best Mode for Carrying Out the Invention An embodiment of the present invention will hereinafter be described in detail with reference to the drawings. Fig. 1 is a block diagram showing an actuating system according to an embodiment of the present invention, and Fig. 2 is an enlarged view of the stem end of an intake valve. An engine 1 has an output shaft, adjacent to which there is disposed a rotation sensor 2 for detecting the rotational speed and phase of the output shaft and converting the detected speed and phase into a signal. The engine 1 has intake and exhaust ports which are opened and closed by intake and exhaust valves, respectively. Of these intake and exhaust valves, the intake valve will mainly be described below. An intake valve 8 is made of a highly strong and lightweight material such as ceramic. The intake valve 8 has a stem axially slidably supported by a valve guide 9. A valve seat 11 is mounted in the intake port of an intake passage. The intake port is closed when the head of the intake valve 8 is closely held against the valve seat 11. The stem end of the intake valve 8 is fitted in a scale 3 which is made of a magnetic material and having teeth on its peripheral surface at a pitch P, the teeth serving as magnetic poles. Around the scale 3, there are disposed left and right upper electromagnets 4 each having fixed magnetic poles 4c, 4d spaced from each other by a distance of 1.5 P, and left and right lower electromagnets 6 each having fixed magnetic poles 6c, 6d spaced from each other at a distance of 1.5 P, the upper and lower electromagnets 4, 6 being spaced from each other by a distance of 1.75 P. The upper and lower electromagnets 4, 6 are joined to each other by permanent magnets 5. Coils 4a, 4b, 6a, 6b are disposed respectively around the fixed magnetic poles 4c, 4d, 6c, 6d. The coils on the fixed magnetic poles 4c, 4d and the coils on the fixed magnetic poles 6c, 6d are respectively connected in series with each other. The upper electromagnets 4 on the lefthand and righthand sides of the intake valve 8 are connected such that they are supplied with the same electric power signal, and the left and right lower electromagnets 6 are also connected such that they are supplied with the same electric power signal. A spring 7 is disposed between the slider 3 and the valve guide 9 for preventing the intake valve 8 from dropping when the electromagnets are de-energized. Wires for supplying the electric power signals to the upper and lower electromagnets 4, 6 are connected to an input/output interface 10d in a control unit 10. The rotation sensor 2 is also connected to the input/output interface 10d. The control unit 10 includes, in addition to the input/output interface 10d, a RAM 10c for temporarily storing data and the results of arithmetic operations, a ROM 10b for storing a program and various relation maps, a CPU 10a for effective arithmetic operations according to the program stored in the ROM 10b, and a control memory 10e for controlling the flow of signals in the control unit 10. Operation of the actuating system according to the present invention will be described below. Figs. 3(a) through 3(e) show the conditions of magnetic lines of force at the stem end of the intake valve 8. Figs. 3(a) through 3(e) illustrate the righthand portion of the intake valve 8. Those of the coils 4a, 4b, 6a, 6b which are energized are indicated by the solid lines, and those which are de-energized are indicated by the broken lines. In the position of Fig. 3(a) where the intake valve is being closed from the open condition, only the upper electromagnet 4 is energized. The upper electromagnet 4 is energized in a direction to produce an N pole on the tip of the fixed magnetic pole 4c. The coils 4a, 4b of the upper electromagnet 4 are connected in series to each other. Since, however, the magnetic lines of force generated by the fixed magnetic poles 4c, 4d are oriented in opposite directions upon energization of the upper electromagnet 4, the magnetic lines of force generated by the coil 4b cancel out the magnetic lines of force generated by the permanent magnet 5, and no pole is produced on the tip of the fixed magnetic pole 4d. The magnetic lines of force generated by the coil 4a are in the same direction as the magnetic lines of force generated by the permanent magnet 5, so that an N pole is produced on the tip of the fixed magnetic pole 4c, and an S pole is produced on the tooth of the scale 3 which confronts the fixed magnetic pole 4c. At this time, the coils 6a, 6b of the lower electromagnet 6 are not energized. As the shortest distance between the fixed magnetic pole 6c and the tooth of the scale 3 is equal to the shortest distance between the fixed magnetic pole 6d and the tooth of the scale 3, both the fixed magnetic poles 6c, 6d produce S poles of the same strength. Then, as shown in Fig. 3(b), the upper electromagnet 4 is de-energized, and the coils 6a, 6b of the lower electromagnet 6 are energized in a direction to produce an S pole on the tip of the fixed magnetic pole 6d. Since the coils 6a, 6b are connected such that the magnetic lines of force generated by the fixed magnetic poles 6c, 6d upon energization of the coils 6a, 6b are oriented in opposite directions, no pole is produced on the tip of the fixed magnetic pole 6c. Therefore, as shown, a stable condition is reached in the position in which the fixed magnetic pole 6d and the tooth of the scale 3 confront each other. This position is reached when the scale 3 has moved from the position shown in Fig. 3(a) upwardly by a distance of ¼ P. Then, as shown in Fig. 3(c), the lower electromagnet 6 is de-energized, and the upper electromagnet 4 is energized in a direction to produce an N pole on the tip of the fixed magnetic pole 4d. This direction of energization is opposite to the direction of energization shown in Fig. 3(a). Now, a stable condition is reached in a position in which the fixed magnetic pole 4d and the tooth of the scale 3 confront each other, i.e., when the scale 3 has moved from the position shown in Fig. 3(b) upwardly by a distance of ¼ P. Then, as shown in Fig. 3(d), the upper electromagnet 4 is de-energized, and the lower electromagnet 6 is energized in a direction to produce an S pole on the tip of the fixed magnetic pole 6c, i.e., in a direction opposite to the direction shown in Fig. 3(b). The scale 3 now moves upwardly by a distance of ¼ P, and a stable condition is reached in a position in which the fixed magnetic pole 6c and the tooth of the scale 3 confront each other. Then, as shown in Fig. 3(e), the electromagnets are energized in the same manner as shown in Fig. 3(a), reaching a stable condition in a position in which the fixed magnetic pole 4c and the tooth of the scale 3 confront each other. Through the above steps shown in Figs. 3(a) through 3(e), the scale 3 moves upwardly by a distance of P. The above steps are repeated to move the scale 3 upwardly. It can obviously be understood that the intake valve 8 can be moved downwardly by reversing the above steps. Fig. 3 shows the relationship between the crankshaft angle and the distance traversed by the valve. The horizontal axis of the graph indicates the crankshaft angle, and the vertical axis indicates the distance by which the valve moves. The relationship achieved by the inventive system is indicated by the solid-line curves, and the relationship achieved by the conventional system is indicated by the broken-line curve. When the crankshaft angle detected by the rotation sensor 2 reaches the timing to open the valve, the valve is controlled so as to move in the opening direction. When the timing to close the valve is reached, the valve is controlled to be seated on the valve seat 11. When the valve is actuated by the conventional cam, the movement of the valve is uniquely determined. According to the present invention, the distance traversed by the valve can be varied as desired as illustrated. The ROM 10b may store a map of engine rotational speeds and distances traversed by the valve. The distance traversed by the valve can be varied depending on the engine rotational speed detected by the rotation sensor 2, using the map. Since a plurality of valves in a multicylinder engine can individually be controlled, the number of cylinders that are in operation can be increased or reduced depending on the rotational speed of the engine. While the intake valve has been described above, the actuating system of the present invention is also applicable to the exhaust valve, which is omitted from illustration. Industrial Applicability As described above, the system for actuating a valve in stepped movement according to the present invention is used as a system actuating intake and exhaust valves of an engine, and suitable for use with an engine which is required to vary the timing to open and close the intake and exhaust valves depending on changes in an operating condition such as the engine rotational speed.

Claims: An engine intake/exhaust valve actuating system for actuating intake and exhaust valves of an engine in stepped movement, the system comprising: a magnetic body (3) coupled to an engine valve (8), the magnetic body being reciprocally movable and having a plurality of tooth-like magnetic poles juxtaposed at equal intervals in the direction in which the magnetic body is reciprocally movable; a plurality of fixed upper magnetic poles (4c,4d) and a plurality of fixed lower magnetic poles (6c,6d) disposed in confronting relation to the tooth-like magnetic poles, the fixed magnetic poles being spaced at intervals different from the intervals of the tooth-like magnetic poles in the direction in which the tooth-like magnetic poles are juxtaposed; a plurality of excitation coils (4a,4b,6a,6b), each fixed magnetic pole having an excitation coil wound therearound for selectively generating magnetic lines of force through said fixed magnetic pole; a permanent magnet (5) connecting and extending over the upper and lower fixed magnetic poles for influencing the generation of magnetic lines of force from the fixed magnetic poles; and, energization control means (10) for energizing the excitation coils to open and close the valve by controlling the generation of magnetic lines of force through each of the fixed magnetic poles. A system according to claim 1, wherein the valve is made of ceramic. A system according to claim 1 or claim 2, wherein the energization control means produces combined electromagnetic forces acting between the tooth-like magnetic poles and the fixed magnetic poles in an opening direction, thereby lessening shocks produced when the valve is seated. A system according to any of claims 1 to 3, wherein the timing established by the energization control means to open and close the valve is variable as the rotational speed of the engine (1) varies.

Inventors: KAWAMURA HIDEO - OKADA -CHOME, KAWAMURA, HIDEO 13-5, OKADA 8-CHOME
Applicants: ISUZU CERAMICS RES INST, ISUZU CERAMICS RESEARCH INSTITUTE CO., LTD.
Application year: 1989
Main classification: F01L9
IPC codes: F16K31, F01L9, H02K41