Characteristics of battery ignition system and circuit breaker
Characteristics of battery ignition system
The battery ignition system is composed of ignition coil, spark plug, circuit breaker, distributor, ignition switch, high-voltage wire, etc. it belongs to inductive energy storage ignition system. The ignition characteristics of the battery ignition system can be summarized as follows.
(1) The ignition energy stored in the ignition coil is directly proportional to the square of the primary current. When the primary current is constant, the larger the primary inductance is, the more ignition energy is stored.
(2) Due to the existence of primary inductance, the primary current changes exponentially. That is, after the contact is closed, the primary current will not increase to a certain value immediately due to the use of back EMF, but gradually increase from zero. When the closing time is infinite, the primary current reaches a certain extreme value.
The closing time depends on the speed of the engine and the closing angle of the contacts. When the contact closing angle is constant, the closing time is inversely proportional to the engine speed. It is not difficult to see that the higher the engine speed, the smaller the primary current and the smaller the ignition energy. This is not only a prominent characteristic of the battery ignition system, but also an insurmountable disadvantage.
(3) It is precisely because of the existence of inductance that the ignition coil will induce not only the secondary back EMF but also the primary back EMF at the moment when the contact is disconnected, resulting in sparks between the contacts and ablating the contacts.
(4) The emergence of back emf will not only cause sparks between contacts, but also reduce the rate at which the primary current is cut off and the rising rate of secondary EMF. This is the reason why the battery ignition system is very sensitive to carbon deposition on the spark plug.
In view of this prominent feature of the battery ignition system, people take corresponding countermeasures, including finding a way from the structure of the circuit breaker.
Structural characteristics of battery breaker
The breaker is mainly composed of cam, contact pair, ignition advance device, etc. The cam of the circuit breaker repeatedly controls the closing of the contact and the making and breaking of the primary current during the rotation process. The capacitor and the contact are connected in parallel. Its task is to form a loop for the primary induced back EMF, reduce the ablation of the contact and speed up the on-off rate of the primary current. The end use of centrifugal ignition advance device and vacuum ignition advance device is also reflected in the contact pair, so that the ignition advance angle changes with the change of engine speed and load, so as to obtain the best ignition advance angle. The working condition of ignition system is not only affected by the contact, but also closely related to the technical conditions of ignition advance device, capacitor and cam. Therefore, when people analyze the working conditions of ignition system, they should contact these relevant electrical appliances and parts. For example, when the edges and corners of the cam are seriously worn, it will affect the opening and closing time of the contact; When the capacitor leaks electricity, the contact will ablate rapidly.
Application analysis of battery contact technology
As far as the contact is concerned, its technical status is important, including: the size of the gap, the size of the contact surface, the ablation degree of the contact surface, and the tension of the spring.
(1) The direct factor affecting the spring tension is the thermal effect of the primary current. When the generator voltage is too high, the primary current is too large, and the low-speed working time of the engine is too long, when the additional resistance is short circuited or the secondary coil of the ignition coil is short circuited, the spring will be annealed and the tension will be weakened due to the enhancement of thermal effect.
(2) Although the sparks between contacts are protected by capacitors, they can not be completely eliminated. Therefore, the ablation of contacts by sparks is naturally inevitable. There are many factors involved in contact ablation; ① The regulating voltage of the generator is too high and the primary current is too large; ② Improper matching of ignition coil and capacitor capacity; ③ The contact surface is dirty or the contact surface is too small; ④ The capacitor has fault or poor contact; ⑤ Contact clearance is too large or too small; ⑥ Short circuit of primary coil or additional resistance; ⑦ The engine runs too long at low speed.
(3) The size of contact gap not only affects the closing angle, primary current and secondary voltage, but also affects the ignition timing. Therefore, when adjusting the ignition timing, the clearance of the contact must be adjusted first.
(4) The contact surface of the contact affects the contact resistance, primary current and secondary voltage, so ensuring that the two contact surfaces of the contact are parallel is an important content of contact maintenance.
In short, for the ignition system of the battery, the circuit breaker is not only the key component, but also the weakest link. Therefore, the daily maintenance of contacts is very important.