Types of Ignition System | Battery and Magneto Ignition System

Battery or coil ignition system

         Most of the modern spark ignition engines use battery ignition system. The system consists of the following constituents:

· Battery

· Ignition switch.

· Induction coil.

· Circuit / contact breaker.

· Condenser.

· Distributor.

01 - BATTERY IGNITION SYSTEM - CIRCUIT OF COIL IGNITION SYSTEM

      One terminal of the battery is ground to the frame of the engine, and other is connected through the ignition switch to one primary terminal of the ignition coil. The other primary terminal is connected to one end of the contact points to ground. The primary circuit of the ignition breaker is together and switch is closed. The secondary terminal of the coil is connected to the central contact of the distributor and hence to distributor rotor. The secondary circuit consists of secondary winding of the coil, distributor and four spark plugs. The contact breaker is driven by a cam whose speed is half the engine speed and breaks the primary circuit one for each cylinder during one complete cycle of the engine

      The breaker points are held on contact by a spring except when forced apart by lobs of the cam.

     To start with, the ignition switch is made on and the engine is cranked and turned by hand when the contacts touch, the current flows from battery through the switch, primary winding of the induction coil to circuit breaker points and the circuit is completed through the ground. A condenser connected across the terminals of the contact breaker points prevent the sparking at these points. The rotating cam breaks open the contacts immediately and breaking of this primary circuit brings about a change of magnetic field; due to which a very high voltage to the tune of 8000 to 12000 V is produced across the secondary terminals. Because of high voltage the spark jumps through the gap in the spark plug and air-fuel mixture is ignited in the cylinder.

     On account of its combined cheapness, convenience of maintenance, attention and general suitability, it has been adopted universally on automobiles.

Magneto-ignition system

     The magneto-ignition system is similar in principle to battery system except that the magnetic field in the core of the primary and secondary windings is produced by a rotating permanent magnet. As the magnet turns, the field is produced from a positive maximum to a negative maximum and back again.

01 - MAGNETO IGNITION SYSTEM - TYPES OF IGNITION SYSTEM

      As this magnetic field falls from a positive maximum value, a voltage and current are induced in the primary winding. The primary current produces a magnetic field of its own which keeps the total magnetic field surrounding the primary and secondary winding approximately constant. When the permanent magnet has turned for enough so that its contribution to the total field is strongly negative, the breaker points are opened and the magnetic field about the secondary winding suddenly goes from high positive value to a high negative value. This induces a high voltage in the secondary winding which is led to the proper spark plug by the distributor.

     The magneto is an efficient, dependable, self-contained unit which is normally preferred for aircraft engines because storage batteries are heavy and troublesome. Special starting means are required, however, as the magneto will not furnish enough voltage for ignition at low speeds. Variation in ignition timing is more difficult with the magneto, since the breaker point must be opened when the rotating magnets are in the most favorable position. It is possible to change the engine crank angle at which the magneto points open without disturbing the relationship between point opening ad magnet position by designing the attachment pad so that the entire magneto body may be rotated a few degrees about its own shaft. Obviously this method is not as satisfactory as rotating a timer cam-plate.

Types of Quick Return Mechanism | Mechanism in Shaper Machine

TYPES OF QUICK RETURN MECHANISM

There are three types of quick return mechanism

1. Hydraulic drive

2. Crank and slotted link mechanism

3. Withworth mechanism

HYDRAULIC DRIVE

       Inside the hydraulic cylinder a piston reciprocates. Between the piston and the ram a piston rod is connected. So, the ram reciprocates along with the piston. Two entries are provided near the each end of the cylinders. A four-way control valve connects these two entries with the reservoir which contains the fluid. The reservoir is connected to the valve with the help of a drain pipes and a supply pipe.

01 - hydraulic mechanism - quick return mechanism

      The supply pipe is again connected to the reservoir by a pump and relief valve. The valve is actuated by the lever and trip dog fitted to the ram. Oil is sucked by the gear pump from the reservoir at a particular pressure. This high pressure oil goes to the cylinder through the four-way valve. The oil allowed from the pump to the left side of the piston which forces the piston to move the ram towards right (R). It is called as forward or cutting stroke. In this stroke, oil flows out on the right side entry to the reservoir through the four-way valve and drain pipe. The lever hits one trig dog at the end of this stroke. Now, the lever position is changed. Due to this, the supply pipe supplies the oil on the right side of the piston which moves the ram towards left called as return stroke or nan-cutting stroke.in this stroke the high pressure oil covers on lesser area on the cylinder. Due to this, the pressure force will increase. Hence, this return stroke is faster by supplying the same quantity of oil.

CRANK AND SLOTTED LEVER MECHANISM

          In this mechanism the ram is actuated by gear drives associated with electric motor. First, the electric motor drives the pinion gear. Next, the pinion gear drives the bull gear which rotates in opposite direction due to external gear meshing. A radial slide is provided on the bull gear. A sliding block is assembled on this slide. The block can be positioned in radial direction by rotating the stroke adjustment screw.

01  - crank and slotted lever mechanism - quick return mechanism

          The sliding block has a crank pin. A rocker arm is freely fitted to this crank pin. The rocker arm sliding block slides in the slot provided in the rocker arm called as slotted link. The upper end has fork which is connected to the ram block by a pin while the bottom end of the rocker arm is pivoted.

01 - crank and slotted lever mechanism - quick return mechanism

         When the pinion gear rotates along with the bull gear, the crank will also rotate. Due to this, the rocker arm sliding block also rotates in the same circle. Simultaneously, the sliding block slides up and down in the slot. This movement is transmitted to the ram which reciprocates. Hence, the rotary motion is converted in reciprocating motion.

WITHWORTH QUICK RETURN MECHANISM

         The shaft of an electric motor drives the pinion which rotates the bull gear. The bull gear has a crank pinion. A sliding block slides over this crank pin and slides inside the slot of a crank plate. A connecting rod connects the pin at one end and ram at the other end.

01 - withworth quick return mechanism - Quick return mechanism

        When the pinion rotates, the bull gear is also rotated along with the crank pin. At the same time, the sliding block slides on the slot provided on the crank plate. This makes the ram to move up and down by the connecting rod.

The two important cases in this mechanism are

1. At an angle of the bull gear rotates in anti-clockwise direction and the ram moves in forward direction.

2. When the bull gear rotates further in the same direction at an angle of the return stroke will take place. Here the angle is lesser than angle . So, the time taken for the return stroke is reduced.