ELECTROMAGNETICALLY DRIVEN VALVE CONTROLLER

Abstract: The controller electromagnetically controls the valves that open and close intake and exhaust ports through which the interior of the cylinder of an engine is communicated with the exterior. When the engine is in operation so far, it is not allowed to change the timings for opening and closing the valves. Thus, the opening and closing timings have been so set that a high efficiency is obtained when the engine is operated at a predetermined number of revolutions. The intake and exhaust valves are opened and closed by the electromagnetic force to change the opening and closing timings depending upon the number of revolutions of the engine.

Description: Technical Field The present invention relates to a control system for electromagnetically controlling the operation of a valve which opens and closes an intake/exhaust port through which the interior and exterior of an engine cylinder communicate with each other. Background Art Conventional control systems for controlling the opening and closing intake and exhaust valves operate as follows: When fuel is burned in a combustion chamber, the piston is lowered to cause the connecting rod to rotate the crankshaft. A camshaft disposed in the cylinder head is driven by the crankshaft and a timing belt, and the intake and exhaust valves are opened and closed by rocker arms held against cam surfaces of the camshaft. Since the timing with which the intake and exhaust valves are opened and closed cannot be altered during operation of the engine, the valve opening and closing timing is preset such that the engine operates with high efficiency when it rotates at a predetermined speed. More specifically, the timing with which the intake valve is opened is selected as a crankshaft angle ranging from 20° to 30° before the top dead center (TDC), and the timing with which it is closed is selected as a crankshaft angle ranging from 50° to 60° after the bottom dead center (BDC). The timing with which the exhaust valve is opened is selected as a crankshaft angle ranging from 50° to 60° before the bottom dead center (BDC), and the timing with which it is closed is selected as a crankshaft angle ranging from 20° to 30° after the top dead center (TDC). With the conventional settings for the timing with which the intake and exhaust valves are opened and closed, since the intake valve remains open even after the bottom dead center (BDC), when the engine is operating at a speed lower than the above predetermined speed, a air-fuel mixture which has once been drawn into the cylinder is discharged back out of the cylinder through the intake port as the piston moves upwardly, resulting in a reduction in the engine output power. After the top dead center (TDC), the exhaust valve remains still open for a certain period of time. Therefore, an unburned air-fuel mixture introduced from the intake port does not stay in the cylinder, but is discharged through the cylinder from the exhaust port, resulting in poor fuel economy. Valve control systems having electromagnetic means, rather than camshafts, for driving intake and exhaust valves are disclosed in Japanese Laid-Open Patent Publication Nos. 58-183805 corresponding to the preamble of claim 1. and 61-76713. However, the disclosed valve control systems are not designed to solve the above problems. In view of the aforesaid problems, it is an object of the present invention to provide a control system for an electromagnetically driven valve, which prevents an air-fuel mixture from being discharged back from or through a cylinder even when the engine operates at low speed, so that the engine can produce an increased output power with increased fuel economy. According to the present invention, there is provided a control system for controlling the opening and closing timings of an electromagnetically driven intake/exhaust valve of an internal combustion engine, comprising: a magnetic plate coupled to the intake/exhaust valve, the magnetic plate being reciprocally movable with the valve; electromagnets having fixed magnetic poles confronting end faces of the magnetic plate in directions in which the magnetic plate is reciprocally movable; and, valve opening/closing means for energizing the electromagnets to produce attractive forces acting between the magnetic plate and the fixed magnetic poles for thereby opening and closing the intake/exhaust; characterised by: a rotation sensor for detecting the rotational speed of the engine; timing varying means for varying the timings with which the intake/exhaust valve is opened and closed by the valve opening/closing means, in directions toward the top dead center and the bottom dead center when the rotational speed as detected by the rotation sensor is reduced; and, a spring coupled to the intake/exhaust valve for closing the valve when the engine is stopped and damping the opening of the valve to reduce the shock applied thereto. The intake/exhaust valve is electromagnetically opened and closed by the control system according to the present invention. In operation, the rotational speed of the engine is detected. When the rotational speed of the engine is low, the intake/exhaust valve is opened and closed at timings near the top dead center (TDC) and the bottom dead center (BDC). As the engine rotational speed increases, the intake/exhaust valve is opened and closed at timings far from the top dead center (TDC) and the bottom dead center (BDC). In a full range of engine rotational speeds, therefore, the air-fuel mixture is prevented from being discharged back from or through the cylinder, and the engine output power and efficiency are increased. One example of a valve controller according to the present invention will now be described with reference to the accompanying drawings in which: Fig. 1 is a block diagram showing a control system for an electromagnetically driven valve according to an embodiment of the present invention; Fig. 2 is a diagram showing a table illustrating the relationship between engine rotational speeds and timings with which a valve is opened and closed; and Fig. 3 is a diagram showing the relationship between crankshaft angles and distances which the valve moves. Best Mode for Carrying Out the Invention An embodiment of the present invention will hereinafter be described with reference to the drawings. Fig. 1 is a block diagram showing a control system for an electromagnetically driven valve according to an embodiment of the present invention. An intake valve 8 is made of a light heat-resistant material such as ceramic or a heat-resistant alloy. A magnetic member 57 is mounted on the end of the stem of the intake valve 8. The intake valve 8 is held by a valve guide 51 which guides the intake valve 8 for axial movement. A spring 58 is disposed around the stem between the valve guide 51 and the magnetic member 57 for urging the intake valve 8 to move upwardly. An upper circular electromagnet 52 is disposed a predetermined distance upwardly from the magnetic member 57, and a lower circular electromagnet 53 is disposed a predetermined distance downwardly from the magnetic member 57. The upper and lower electromagnets 52, 53 have respective coils connected to an input/output interface 56c in a control unit 56. To the input/output interface 56c, there is also connected a rotation sensor 55 for detecting the rotational speed of the engine 54 and the crankshaft angle thereof. The control unit 56 also includes, in addition to the input/output interface 56c, a CPU 56a for carrying out arithmetic operations based on a program and a table representing the relationship between engine rotational speeds and valve opening/closing timings, which are stored in a ROM 56d, a RAM 56e for temporarily storing data, and a control memory 56b for controlling the operation of the blocks of the control unit 56. Operation of the control system according to the present invention will be described below. The rotational speed of the engine 1 which is detected by the rotation sensor 55 is sent through the input/output interface 56c and temporarily stored in the RAM 56e. Then, a valve opening/closing timing is determined from the engine rotational speed stored in the RAM 56e, using the table stored in the ROM 56d, the table indicating the relationship between engine rotational speeds and valve opening/closing timings. The table is shown by way of example in Fig. 2. In Fig. 2, the horizontal axis represents the engine rotational speed which increases to the right, and the vertical axis represents the crankshaft angle. The timing (IC) with which the intake valve 8 is closed indicates a crankshaft angle after the bottom dead center (BDC), and the timing (IO) with which the intake valve 8 is opened indicates a crankshaft angle before the top dead center (TDC). As shown in Fig. 2, when the engine rotational speed decreases, the closing timing (IC) approaches the bottom dead center (BDC), and the opening timing (IO) also approaches the top dead center (TDC). While the table shown in Fig. 2 shows the engine rotational speeds and the opening/closing timings, a correction for causing the opening/closing timings to approach the top and bottom dead centers as the engine load is reduced may be added to the table. When the opening/closing timings for the intake valve 8 are determined from the table, drive signals are transmitted to the upper and lower electromagnets 52, 53 based on the crankshaft angle as detected by the rotation sensor 55. The relationship between crankshaft angles and distances which the valve moves is shown in Fig. 3. The lower curve represents a cam profile curve of the camshaft. The vertical axis represents the distance L which the valve moves, the distance L corresponding to the lift of the cam profile, and the horizontal axis represents the crankshaft angle. The lower curve is indicated between the opening timing (IO) and the closing timing (IC) of the intake valve 8. The upper portion of Fig. 3 shows a condition EU in which the upper electromagnet 52 is energized, a condition EB in which the lower electromagnet 53 is energized, and attractive forces Fa, Fb, Fc, Fd produced by these electromagnets. Since the electromagnetic attractive forces are inversely proportional to the square of the distance between the electromagnets and the magnetic member, the curves Fa, Fb, Fc, Fd are guadratic curves. When the intake valve 8 is closed, the coil of the upper electromagnet 52 is continuously energized to keep the intake valve 8 closed, so that the intake valve 8 remains attracted upwardly through the magnetic member 57. When the crankshaft angle reaches IO, the upper electromagnet 52 is de-energized to cancel the upward attractive force, and the lower electromagnet 53 is energized to generate the downward attractive force Fa to open the intake valve 8. The intake valve 8 is attracted downwardly, starting to be driven in the opening direction to open the intake port. When the crankshaft angle increases a predetermined first angle from IO, the lower electromagnet 53 is de-energized, and the upper electromagnet 52 starts being energized. The upper electromagnet 52 generates the upward attractive force Fb in the valve closing direction. The speed at which the intake valve 8 moves is now reduced. At the time an angle ϑc has elapsed from IO, the intake valve 8 is stopped at a maximum distance Lm which it has traversed. Upon elapse of ϑc, the current passing through the upper electromagnet 52 is varied to change the upward attractive force from Fb to Fc. When the crankshaft angle increases a predetermined second angle, which is greater than ϑc, from IO, the upper electromagnet 52 is deenergized, and the lower electromagnet 53 is energized. The speed at which the intake valve 8 moves upwardly is reduced by the downward attractive force Fd. Therefore, the shock with which the intake valve 8 is seated is lessened. The spring 58 is provided in order to prevent the intake valve 8 from being lowered downwardly when the control system is not in operation at the time the motor vehicle is at rest, for example. The spring 58 normally urges the intake valve 8 upwardly, and the urging force of the spring 58 is selected such that it will not affect the attractive forces Fa, Fd of the lower electromagnet 53. The process from IO until the distance L traversed by the valve is maximized will be described below using equations. If it is assumed that then engine rotational speed is indicated by N (RPM), the crankshaft angle by ϑ (deg), and the time by t (Sec), then the following relationship is satisfied: ϑ = 6Nt. It is assumed that the acceleration applied to the intake valve is indicated by α, the distance traversed by the intake valve by L, the attractive force by F, and the valve mass by m, then the distance L and the attractive force F are expressed as follows: L = ½αt² F = mα. Therefore, during a period of time in which the downward acceleration α₁ is imposed by the lower electromagnet 53, the attractive force Fa is given by: Fa = mα₁, hence, α₁ = Fa/m. When the intake valve is accelerated up to ϑn with the acceleration α₁, the speed Va of the valve and the distance La traversed by the valve are given, using the accumulation of small times ▵t, as follows: Since the crankshaft angle is ϑc from the valve closing condition until the distance L traversed by the valve is maximum, the valve has to be decelerate and its speed has to be reduced to 0 during the interval of ϑc - ϑn. Therefore, the lower electromagnet 53 is de-energized and at the same time the upper electromagnet 52 is energized to give an upward acceleration αb to the intake valve, thus decelerating the intake valve. The upward attractive force Fb produced by the upper electromagnet 52 is given by: Fb = mαb, and therefore, the speed V of the intake valve while it is decelerating is expressed by: The attractive force Fb is determined so that the speed becomes V = 0 at the position in which the crankshaft angle is ϑc. The maximum distance Lm traversed by the valve is expressed as follows: For closing the valve, the same arithmetic operations as those described above may be carried out. While the present invention has been described with respect to the intake valve, the present invention is also applicable to an exhaust valve except that the timings with which it is closed and opened are different. Industrial Applicability The control system according to the present invention controls the opening and closing of an intake/exhaust valve of an engine when the valve is electromagnetically opened and closed. The rotational speed of the engine is detected, and the opening and closing timings of the intake/exhaust valve are varied as the rotational speed increases or decreases, so that the efficiency and output power of the engine are made greater than those of conventional engines in a full range of engine rotational speeds.

Claims: A control system for controlling the opening and closing timings of an electromagnetically driven intake/exhaust valve of an internal combustion engine, comprising: a magnetic plate (57) coupled to the intake/exhaust valve, the magnetic plate being reciprocally movable with the valve; electromagnets (52, 53) having fixed magnetic poles confronting end faces of the magnetic plate in directions in which the magnetic plate is reciprocally movable; and, valve opening/closing means for energizing the electromagnets to produce attractive forces acting between the magnetic plate and the fixed magnetic poles for thereby opening and closing the intake/exhaust; characterised by: a rotation sensor (55) for detecting the rotational speed of the engine; timing varying means for varying the timings with which the intake/exhaust valve is opened and closed by the valve opening/closing means, in directions toward the top dead center and the bottom dead center when the rotational speed as detected by the rotation sensor is reduced; and, a spring (58) disposed around the intake/exhaust valve stem for closing the valve when the engine is stopped. A control system according to claim 1, wherein the intake/exhaust valve is made of ceramic. A control system according to claim (1), wherein said valve opening/closing means attracts said magnetic plate in the direction to open the valve immediately before said intake/exhaust valve is seated, so that a shock caused when the intake/exhaust valve is seated will be lessened. A control system according to claim (1), further including a load sensor for detecting a load on said internal combustion engine, said timing varying means varying the timings with which the intake/exhaust valve is opened and closed by said valve opening/closing means, in directions toward the top dead center and the bottom dead center when the load on the engine as detected by said load sensor is reduced. A control system according to claim (1), wherein said fixed magnetic poles comprise a pair of fixed magnetic poles having different polarities.

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: F02D13, F01L9