Abstract:
An ignition system for a gasoline engine comprising an ignition coil to which an electric current is supplied from a battery through a transistor. The transistor is so controlled as to turn on and off in response to switching off and on of a contact breaker. A current flowing through the breaker points of the contact breaker is increased temporarily in accordance with the operating conditions of the engine for preventing fouling or damage of the breaker points due to contaminants deposited thereon.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to an ignition system for a gasoline engine. 
     2. Description of the Prior Art 
     Generally, in ignition systems of the type in which the interrupting signal from the contact breaker of the distributor is amplified by a transistor, means are provided for minimizing the amount of current applied to the contact breaker so as to enhance the durability (increase the wear-life) of the contact breaker contacts. This however, gives rise to the possibility of causing fouling or poor conductivity of the contact points due to the points being stained by lubricating oil used on the sliding parts in the distributor or other factors. As a countermeasure to avoid this, attempts have been made to use a lubricating oil which is less liable to inhibit conduction; an alternative measure has been to increase the voltage or current applied to the contact points to a certain elevated level. But increased current invites a reduction in the durability of the contact points. 
     SUMMARY OF THE INVENTION 
     In view of the above, the present invention proposes an improved ignition system in which the amount of current supplied to the interrupter is increased only when the gasoline engine is operating under a certain special condition, in order to thereby improve the durability of the contact points contacts and to prevent fouling. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a circuit diagram showing one embodiment of the present invention; and FIG. 2 is a circuit diagram showing another embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The invention will now be described in detail by way of some preferred embodiments thereof with reference to the accompanying drawings. 
     Referring first to FIG. 1, an embodiment of the present invention is shown where the value of current supplied to the contact points is controlled in correspondence with the starting condition of the engine. A battery 1, grounded at its cathode, is connected at its anode to the primary winding of an ignition coil 3 through a main switch 2. The secondary winding of ignition coil 3 is grounded through a spark plug 4. The connecting point of the primary and secondary windings of ignition coil 3 is connected to the collector of an NPN type transistor 5, the emitter of which is connected to ground. Resistors 6 and 7 are connected in series to the base of transistor 5 to supply an electric current or voltage from the battery 1 to transistor 5 through the main switch 2. The base electrode of transistor 5 is grounded through a resistor 8 and also through a contact 10 of a contact breaker 9. The main switch 2 is connected to the junction point of resistors 6 and 7 through a switch 11 and is further connected to one of the terminals of an engine starting motor 13 through a switch 12, the other terminal of starting motor 13 being grounded. A screw-like spline, which is meshed with a pinion 14, is formed at one end of the revolving shaft of starting motor 13. Pinion 14, in turn, is arranged to mesh with a gear 15 of the engine. A lever 16 for controlling axial movement of pinion 14 is also provided. 
     The main switch 2 is connected to the coil of an electromagnet 18 which operates lever 16 through a starter switch 17. When starter switch 17 is closed, an electric current flows to the coil to energize electromagnet 18 to let the lever 16 pivot clockwise about its axis, causing the pinion 14 to mesh with the gear 15 and at the same time closing switches 11 and 12. 
     Now the engine is rotated by the starting motor 13, while the transistor 5 becomes conductive and nonconductive repetitively as the contact points 10 of the interrupter 9 is opened and closed successively. At the instant when the transistor 5 becomes nonconductive, a high voltage develops in the secondary winding of the ignition coil 3 to generate sparks in the spark plug 4 to start operating the engine. During this period, since the resistor 6 is shortcircuited by the closure of the switch 11, a high voltage is applied or a large current flows to the contact points 10. 
     When the rotational frequency of the engine becomes greater than that of the starting motor 13, the pinion 14 moves to the right on the spline of the motor shaft and disengages from the gear 15 of the engine. This rightward movement of the pinion 14 causes the lever 16 to swing counterclockwise against the magnetic force of the electromagnet, consequently opening the switches 11 and 12. Now the starting motor 13 is disconnected from the battery 1 and the engine proceeds into a normal operating condition. When the switch 11 is opened, the contact points 10 becomes connected to the battery 1 through both resistors 6 and 7, with the result that a a current smaller than that applied at the time of engine starting is applied to contact points 10. 
     FIG. 2 shows another embodiment where the value of current supplied to the contact points 10 is controlled in accordance with the vacuum pressure of the engine carburetor. As in the embodiment of FIG. 1, the battery 1 is connected through a main switch 2 to an ignition coil 3, spark plug 4, transistor 5, resistance 8 and contact points 10 of contact breaker 9. In this case, however, a resistance 19 and a switch 20 (which are connected in series) and a resistance 21 are connected between the main switch 2 and the base of the transistor 5; switch 20 is provided with a diaphragm 23 adapted to close switch 20 when the vacuum pressure of the engine carburetor 22 is small. Owing to this arrangement, when the vacuum pressure is large, electric current flows only to the resistors 8 and 21, and only a small current flows or a low voltage is applied to the points 10. However, if the vacuum pressure of the carburetor 22 is reduced, such as at the time of acceleration, the switch 20 is closed by the diaphragm 23 to connect the resistance 19 in parallel to the resistance 21, thereby reducing the effective resistance between battery 1 and contact point 10 in a known manner, so that the contact point 10 is supplied with a current greater than that applied when the negative suction pressure is high. 
     Thus, according to the present invention, as is apparent from the foregoing description, the current supplied to the contact points is increased at the time of starting of the engine or when the vacuum pressure of the carburetor is low to thereby prevent fouling or damage of the contact points, and during the other condition of engine operation, the current supplied to the interrupter contact is reduced to enhance the durability and increase the life of this contact. Therefore, the interrupter contact is less likely to be fouled or damaged, as by lubricating oil or the like and is also free from damage by high current.