Uses Of Starter Motors And Their History Engineering Essay

Motor Starters are switches specially designed for starting motors. These switches are designed to control the flow of current. There are basically two types of motor starters, Manual Starters and Magnetic Starters.

Uses of STARTER In a Motor :

1: To give starting resistance to motor.

2:Starter is used to safe the motor winding from the high starting

current.

3: Starter is used in a motor to control the limit of high starting current.As the motor starts(in case of DC motor) high current occurs which is controlled by use of high resistance slowly cut out of the circuit.

History

Both Otto cycle and Diesel cycle internal-combustion engines require the pistons which is used to convert pressure into motion.

Originally, a hand crank(handle) was used to start engines, but it was difficult, and dangerous to start an engine. Even though cranks had an overrun mechanism, when the engine started, the crank could begin to spin along with the crankshaft and it might strike the person starting the engine. Care has to be taken to prevent the spark from backfiring. In short we can say that there is a lot of risk while starting the engine with a a crank.Moreover, increasingly larger engines with higher compression ratios made hand cranking a more physically demanding endeavour.

While there was a need of starter, as in 1899, Clyde J. Coleman applied for U.S. Patent 745,157 for an electric automobile self-starter – inventing one that worked successfully in most conditions did not occur until 1911 when Charles F. Kettering of Dayton Engineering Laboratories Company (DELCO) invented and filed for U.S. Patent 1,150,523 for the first useful electric starter. (Kettering had replaced the hand crank on NCR’s cash registers with an electric motor five years earlier.) One aspect of the invention lay in the realization that a relatively small motor, driven with higher voltage and current than would be feasible for continuous operation, could deliver enough power to crank the engine for starting. At the voltage and current levels required, such a motor would burn out in a few minutes of continuous operation, but not during the few seconds needed to start the engine. The starters were first installed by Cadillac on production models in 1912. The Model T relied on hand cranks until 1919; by 1920 most manufacturers included self-starters.The electric starter ensured that anyone could easily start and run an internal combustion engine car, and this made it the design of choice for car buyers from that day forward.

Details about the Starters used->

Following starters used to operate motor starter

Electric starter

Gear reduction starter

Pneumatic starter

The Principal at which motor starter is worked

Electric starter used in motor starter

Electric starter

Main Housing

Overrunning clutch

Armature

Field coils

Brushes

Solenoid

What is motor starter?

“A starter motor is a high-torque electric motor for turning the gear on the engine flywheel.”

The modern starter motor is either a permanent-magnet or a series-parallel wound direct current electric motor with a solenoid switch (similar to a relay) mounted on it. When current from the starting battery is applied to the solenoid, usually through a key-operated switch, it pushes out the drive pinion on the starter driveshaft and meshes the pinion with the ring gear on the flywheel of the engine. Before the advent of key-driven starters, most electric starters were actuated by foot-pressing a pedestal located on the floor, generally above the accelerator pedal.

Solenoid

The solenoid also closes high-current contacts for the starter motor, which begins to turn. Once the engine starts, the key-operated switch is opened, a spring in the solenoid assembly pulls the pinion gear away from the ring gear, and the starter motor stops. The starter’s pinion is clutched to its driveshaft through an overrunning sprag clutch which permits the pinion to transmit drive in only one direction. In this manner, drive is transmitted through the pinion to the flywheel ring gear, but if the pinion remains engaged (as for example because the operator fails to release the key as soon as the engine starts), the pinion will spin independently of its driveshaft. This prevents the engine driving the starter, for such backdrive would cause the starter to spin so fast as to fly apart. However, this sprag clutch arrangement would preclude the use of the starter as a generator if employed in hybrid scheme mentioned above; unless modifications are made. Also, a standard starter motor is only designed for intermittent use which would preclude its use as a generator.

Overrunning clutch

This overrunning-clutch pinion arrangement was phased into use beginning in the early 1960s; before that time, a Bendix drive was used. The Bendix system places the starter drive pinion on a helically-cut driveshaft. When the starter motor begins turning, the inertia of the drive pinion assembly causes it to ride forward on the helix and thus engage with the ring gear. When the engine starts, backdrive from the ring gear causes the drive pinion to exceed the rotative speed of the starter, at which point the drive pinion is forced back down the helical shaft and thus out of mesh with the ring gear.

An intermediate development between the Bendix drive developed in the 1930s and the overrunning-clutch designs introduced in the 1960s was the Bendix Folo-Thru drive. The standard Bendix drive would disengage from the ring gear as soon as the engine fired, even if it did not continue to run. The Folo-Thru drive contains a latching mechanism and a set of flyweights in the body of the drive unit. When the starter motor begins turning and the drive unit is forced forward on the helical shaft by inertia, it is latched into the engaged position. Only once the drive unit is spun at a speed higher than that attained by the starter motor itself (i.e., it is backdriven by the running engine) will the flyweights pull radially outward, releasing the latch and permitting the overdriven drive unit to be spun out of engagement. In this manner, unwanted starter disengagement is avoided before a successful engine start.

Starter used in motor starter :

Gear-reduction starters

Chrysler Corporation contributed materially to the modern development of the starter motor. In 1962, Chrysler introduced a starter incorporating a geartrain between the motor and the driveshaft. Rolls Royce had introduced a conceptually similar starter in 1946, but Chrysler’s was the first volume-production unit. The motor shaft has integrally-cut gear teeth forming a drive gear which mesh with a larger adjacent driven gear to provide a gear reduction ratio of 3.75:1. This permits the use of a higher-speed, lower-current, lighter and more compact motor assembly while increasing cranking torque. Variants of this starter design were used on most vehicles produced by Chrysler Corporation from 1962 through 1987. The Chrysler starter made a unique, readily identifiable sound when cranking the engine.

This starter formed the design basis for the offset gear reduction starters now employed by about half the vehicles on the road, and the conceptual basis for virtually all of them. Many Japanese automakers phased in gear reduction starters in the 1970s and 1980s. Light aircraft engines also made extensive use of this kind of starter, because its light weight offered an advantage.

Those starters not employing offset geartrains like the Chrysler unit generally employ planetary epicyclic geartrains instead. Direct-drive starters are almost entirely obsolete owing to their larger size, heavier weight and higher current requirements. Ford also issued a nonstandard starter, a direct-drive “movable pole shoe” design that provided cost reduction rather than electrical or mechanical benefits. This type of starter eliminated the solenoid, replacing it with a movable pole shoe and a separate starter relay.

The Ford starter operated as follows:

The operator closed the key-operated starting switch.

A small electric current flowed through the starter relay coil, closing the contacts and sending a large current to the starter motor assembly.

One of the pole shoes, hinged at the front, linked to the starter drive, and spring-loaded away from its normal operating position, swung into position. This moved a pinion gear to engage the flywheel ring gear, and simultaneously closed a pair of heavy-duty contacts supplying current to the starter motor winding.

The starter motor cranked the engine until it started. An overrunning clutch in the pinion gear uncoupled the gear from the ring gear.

The operator released the key-operated starting switch, cutting power to the starter motor assembly.

A spring retracted the pole shoe, and with it, the pinion gear.

FEATURES / BENEFITS

â€¢ It is Compact .

â€¢ It has high torque.

â€¢ It has high durability.

â€¢ It has self-contained clutch shaft.

Electric starter

The modern starter motor is a series-wound direct current electric motor with a solenoid switch (similar to a relay) mounted on it. When low-current power from the starting battery is applied to the solenoid (the thin, grey wire in the image above), usually through a key-operated switch, it pushes out a small pinion gear on the starter motor’s shaft and meshes it with the ring gear on the flywheel of the engine. The solenoid also closes high-current contacts (powered through the thick red cable in the image) for the starter motor and it starts to run. Once the engine starts, the key-operated switch is opened, a spring in the solenoid assembly pulls the pinion gear away from the ring gear, and the starter motor stops. Modern starter motors have a “bendix” a gear and integral freewheel, or overrunning clutch, that enables the flywheel to automatically disengage the pinion gear from the flywheel when the engine starts.

Chrysler and Ford both contributed to the starter market, with two types that were very different to those used on vehicles today.

Chrysler manufactured a gear reduction starter employing a small gear to drive a larger gear attached to the starter’s pinion gear shaft. This allowed lower current to be drawn from the battery to run the starter, and still had the initial torque needed to turn the flywheel approximately at 200 rpm. This starter is also smaller and integrates the starter solenoid in the starter case, instead of having it mounted externally. Since this design weighs less, it has also been adapted to some light aircraft engines, where minimizing weight is very important.

Ford’s version was slightly more complicated. The engineers at Ford Motor Company used a “positive engagement” style starter. This type of starter eliminated the solenoid, replacing it with a moveable armature and a separate starter relay. An armature is a part made of ferromagnetic metal that is magnetized by a coil of copper ribbon wound around it, creating an electromagnet. The Ford starter operated as follows:

The operator closed the key-operated starting switch.

A small electric current flowed through the starter relay coil, closing the contacts and sending a large current to the starter motor assembly.

The armature moved a pinion gear to engage the flywheel ring gear, and simultaneously closed a pair of heavy-duty contacts supplying current to the starter motor winding.

The starter motor cranked the engine until it started. An overrunning clutch in the pinion gear uncoupled the gear from the ring gear.

The operator released the key-operated starting switch, cutting power to the starter motor assembly.

A spring retracted the armature, and with it, the pinion gear.

Current Ford starter designs incorporate the starter solenoid into the starter motor assembly, instead of mounting it on the firewall or on a fender.

Starter motor

A starter is an electric motor needed to turn over the engine to start it.

A starter consists of the very powerful DC electric motor and starter solenoid that is attached to the motor (see the picture).

A starter motor requires very high current to crank the engine, that’s why it’s connected to the battery with large cables (see lower diagram).

The negative (ground) cable connects “-“battery terminal to the engine block close to the starter.

The positive cable connects “+”battery terminal to the starter solenoid.

The starter solenoid works as an electric switch – when actuated, it closes the circuit and connects the starter motor to the battery. At the same time, it pushes the starter gear forward to mesh with the engine’s flywheel.

How the starting system works:

When you turn the ignition key to the “Start”position, the battery voltage goes through the starter control circuit and activates the starter solenoid, which in turn energizes the starter motor. The starter motor cranks the engine.

A starter can only be operated when the automatic transmission shifter is in “Park”or “Neutral”position or if the car has a manual transmission, when the clutch pedal is depressed.

To accomplish this, there is a Neutral safety switchinstalled at the automatic transmission, (or at the clutch pedal).

When the automatic transmission is not in “Park”or “Neutral”(or when the clutch pedal is not depressed), the neutral safety switch is open and the starter relay disconnects the starter control circuit.

Simplified diagram of typical starting system

Pneumatic Starter

A Pneaumatic motor is a machine which converts in the form of compressed air into mechanical work. It converts it either in linear or rotary motion. Linear motion can come from piston actuator,while rotary motion is supplied by a piston air motor. These motors are very successful in hand-held tool industry.

Classification

Linear

In order to achieve linear motion from compressed air, a system of pistons is most commonly used. The compressed air is pumped into an air tight chamber that houses the shaft of the piston. Also inside this chamber a spring is coiled around the shaft of the piston in order to hold the chamber completely open when air is not being pumped into the chamber. As air is pumped into the chamber the force on the piston shaft begins to overcome the force being exerted on the spring. As more air is pumped into the chamber, the pressure increases and the piston begins to move down the chamber. When it reaches its maximum length the air pressure is released from the chamber and the spring completes the cycle by closing off the chamber to return to its original position.

Piston motors are the most commonly used in hydraulic systems. Essentially, piston motors are the same as hydraulic pumps except they are used to convert hydraulic energy into mechanical energy. Piston motors are often used in series of two, three, four, five, or six cylinders that are enclosed in a housing. This allows for more power to be delivered by the pistons because several motors are in sync with each other at certain times of their cycle

Rotary

Another type of pneumatic motor, known as a rotary vane motor, uses air to produce rotational motion to a shaft. The rotating element is a slotted rotor which is mounted on a drive shaft. Each slot of the rotor is fitted with a freely sliding rectangular vane.[3] The vanes are extended to the housing walls using springs, cam action, or air pressure, depending on the motor design. Air is pumped through the motor input which pushes on the vanes creating the rotational motion of the central shaft. Rotation speeds can vary between 100 and 25,000 rpm depending on several factors which including the amount of air pressure at the motor inlet and the diameter of the housing.[1]

Rotary motion vane type air motors are used to start large industrial diesel or natural gas engines. Stored energy in the form of compressed air, nitrogen or natural gas enters the sealed motor chamber and exerts pressure against the vanes of a rotor. Much like a windmill, this causes the rotor to turn at high speed. Because the engine flywheel requires a great deal of torque to start the engine, reduction gears are used. Reduction gears to create high torque levels with the lower amounts of energy input. These reduction gears allow for sufficient torque to be generated by the engine flywheel while it is engaged by the pinion gear of the air motor or air starter.

Application

A widespread application of small pneumatic motors is in hand-held tools, power ratchet wrenches, drills, sanders, grinders, cutters, and so on. Though overall energy efficiency of pneumatics tools is low and they require access to a compressed-air source, there are several advantages over electric tools. They offer greater power density (a smaller pneumatic motor can provide the same amount of power as a larger electric motor), do not require an axillary speed controller (adding to its compactness), generate less heat, and can be used in more volatile atmospheres as they do not require electric power.Some gas turbine engines and Diesel engines, particularly on trucks, use a pneumatic self-starter. The system consists of a geared turbine, an air compressor and a pressure tank. Compressed air released from the tank is used to spin the turbine, and through a set of reduction gears, engages the ring gear on the flywheel, much like an electric starter. The engine, once running, powers the compressor to recharge the tank.

On larger diesel generators found in large shore installations and especially on ships, a pneumatic starting gear is used. The air motor is normally powered by compressed air at pressures of 10-30 bar. The air motor is made up of a center drum about the size of a soup can with four or more slots cut into it to allow for the vanes to be placed radially on the drum to form chambers around the drum. The drum is offset inside a round casing so that the inlet air for starting is admitted at the area where the drum and vanes form a small chamber compared to the others. The compressed air can only expand by rotating the drum which allows the small chamber to become larger and puts another one of the cambers in the air inlet. The air motor spins much too fast to be used directly on the flywheel of the engine, instead a large gearing reduction such as a planetary gear is used to lower the output speed. A Bendix gear is used to engage the flywheel.

Some smaller diesel engines such as ones found on tugboats and lifeboats use hydraulic start motors in which the air motor is replaced with a hydraulic motor. While running, the engine shouldn’t be shut down unless the hydraulic accumulators for the starting motor are recharged. Otherwise there is a manual hand pump to slowly pump up the accumulators.

Since large trucks typically use air brakes, the system does double duty, supplying compressed air to the brake system. Pneumatic starters have the advantages of delivering high torque, mechanical simplicity and reliability. They eliminate the need for oversized, heavy storage batteries in prime mover electrical systems.

BIBLOGRAPHY

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