Starter Motor

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  • Starter Motor

    Precio : Gratis

    Publicado por : dnfsdd816

    Publicado en : 29-10-21

    Ubicación : Alicante

    Visitas : 2



    Starter Motor

    Starter Motor
        Motor starters are usually fitted with a trip device which deals with overcurrents from

    just above normal running current of the motor to the stall current. The aim should be for

    the device to match the characteristics of the motor so that full advantage may be taken of

    any overload capacity. Equally, the trip device must open the starter contactor before

    there is any danger of permanent damage to the motor.
        Contactors are not normally designed to cope with the clearance of short-circuit

    conditions, and it is therefore usual for the contactor to be backed up by HRC fuses or by

    circuit-breaker.
        The arrival on the scene of very compact motor starters and the need to provide proper

    back-up protection to them has posed a problem. BS EN 60947-4-1 (1992) (previously BS 4941)

    ‘Motor starters’, describes three types of co-ordination, the most onerous condition

    (type C) requiring that under fault conditions there shall be no damage to the starter or

    to the overload relay. The usual back-up device will be the HRC fuse. It is important that

    the user check with the manufacturer's catalogue to ensure that the correct fuse is

    used to secure this co-ordination.
        The starter motor in your

    automobile is a DC motor. If you were to accidentally reverse the battery polarity, the DC

    motor would still rotate in the same direction. Reversing polarity of the battery will not

    cause the motor to rotate in the opposite direction.
        To reverse the direction of rotation of this type of motor, either the current through

    the stator winding or the current through the armature must be reversed. Reversing both of

    them will result in the same magnetic polarities between the armature and the stator poles.

    This results in the same direction of rotation.
        The industry's standard for reversing the direction of rotation of a DC motor is to

    reverse the direction of the current through the armature. When a DC motor has more than

    one set of windings, shunt and series, as well as interpoles, the currents through all the

    stator windings would need to be reversed in order to change direction of rotation. This is

    far more complicated than merely reversing armature current.
        All engines require a toyota starter motor to turn them over before firing. In conventional

    vehicles, this is a straightforward, but powerful, direct-current electric motor. When the

    starter switch is activated by the driver, current flows to a solenoid attached to the

    starter motor. This current moves a lever into the solenoid that then causes a cogwheel of

    the motor to mesh with the teeth on the circumference of the flywheel. At the same time, an

    electrical contact is closed to allow a large current to flow and rotate the starter motor

    as well as the engaged flywheel. Typically, currents of hundreds of amperes are required to

    start the engine and are provided by the battery, which is generally a 12-V lead–acid

    module. The battery is recharged by the alternator–rectifier combination when the engine

    is running. Automotive batteries have improved enormously over the years and have far

    longer lives than formerly, even though they may be called upon to power many more

    functions. Although guarantees may be for two or three years, in practice batteries often

    operate for eight years or longer before failing. Moreover, modern car batteries no longer

    require periodic ‘topping-up’ with de-ionized water. Further information on the evolution

    of the lead–acid battery is given in Section 7.4, Chapter 7.
        A starter motor is required to run the internal combustion engine up to a speed

    sufficient to produce satisfactory carburation.
        The starter motor is mounted on the engine casing and a pinion on the end of the

    BMW starter motor

    shaft engages with the flywheel teeth. The gear ratio between pinion and flywheel is about

    10:1. A machine capable of developing its maximum torque at zero speed is required. The

    series wound motor has speed and torque characteristics ideal for this purpose.
        The engagement of the pinion with the flywheel is effected in different ways. Perhaps

    the two most commonly used are the inertia engaged pinion and the pre-engaged pinion

    methods.
        In inertia engagement the drive pinion is mounted freely on a helically threaded sleeve

    on the armature motor shaft. When the starter switch is operated, the armature shaft

    revolves, causing the pinion, owing to its inertia, to revolve more slowly than the shaft.

    Consequently, the pinion is propelled along the shaft by the thread into mesh with the

    flywheel ring gear. Torque is then transmitted from the shaft to the sleeve and pinion

    through a heavy torsion spring, which takes up the initial shock of engagement. As soon as

    the engine fires, the load on the pinion teeth is reversed and the pinion tends to be

    thrown out of engagement. Inertia drives are usually inboard, i.e. the pinion moves inward

    towards the starter motor to engage with the ring gear; an inboard is lighter and cheaper

    than an outboard starter.
        To obtain maximum lock torque (i.e. turning effort at zero speed), the flux and

    armature current must be at a maximum, so resistance in the starter circuit (windings,

    cables, switch and all connections) must be a minimum; any additional resistance will

    reduce the starting torque. Generally, the inertia engaged

    mercedes starter

    motor
    is energised via a solenoid switch, permitting the use of a shorter starter

    cable and assuring firm closing of the main starter-switch contacts, with consequent

    reduction in voltage drop. The use of graphite brushes with a high metallic content also

    assists in minimising loss of voltage.
        While inertia drive has been the most popular method of pinion engagement for British

    petrol-engined vehicles, the use of outboard pre-engaged drive is increasing. The pre-

    engaged starter is essential on all vehicles exported to cold climates and for compression

    ignition engines which need a prolonged starting period.
        The simplest pre-engaged type of drive is the overrunning clutch type. In this drive,

    the pinion is pushed into mesh by a forked lever when the starter switch is operated, the

    lever often being operated by the plunger of a solenoid switch mounted on the motor casing.

    Motor current is automatically switched on after a set distance of lever movement. The

    pinion is retained in mesh until the starter switch is released, when a spring returns it.

    To overcome edge-to-edge tooth contact and ensure meshing, spring pressure or a rotating

    motion is applied to the pinion. An overrunning clutch carried by the pinion prevents the

    motor armature from being driven by the flywheel after the engine has fired. Various

    refinements may be incorporated, especially in heavy-duty starters. Among these are: a slip

    device in the overrunning clutch to protect the motor against overload; a solenoid switch

    carrying a series closing coil and a shunt hold-on coil; an armature braking or other

    device to reduce the possibility of re-engagement while the armature and drive are still

    rotating; a two-stage solenoid switch to ensure full engagement of the starter pinion into

    the flywheel teeth before maximum torque is developed (Figure 44.15).
        The engine may be started either by an electric

    honda starter motor

    or by compressed air. 
        An increasing used form of motor starter is known as “soft start”. Soft starters

    utilise sold state technology, typically thyristors, to supply the motor.
        In a “soft starter” voltage and frequency of supply to the motor is varied in a

    controlled way in order to provide the required torque as the speed increases up to full

    load.
        Soft starts can be arranged to provide up to 200% full load torque at starting, whilst

    limiting the current drawn from the supply to perhaps 350% rather than the 600% typically

    experienced from direct on line. Other parameters and facilities including kick start

    ability, ramp time to full speed and low load energy saving are available depending upon

    supplier.
        Soft starters are available for the largest 400/600 volt motors. By specifying soft

    starters the specification of the associated supply system can be relaxed since large

    starting currents and resultant voltage drops will not occur.
        Some users are specifying speed control inverters for motor starting even when full

    speed control facilities are not needed. So used inverters provide a soft starter

    capability, have good motor control, protection and diagnostic facilities as well as

    providing an energy saving function, if needed.
        The engine starting quality is strongly influenced by the

    Jeep starter motor

    and the injection strategy. Indeed, an insufficient amount of kinetic energy initially

    provided to the system will not compensate for the energy loss caused by the DMF resonance.

    An adequate starter motor must be carefully chosen to fulfil this requirement, even under

    critical conditions with low battery voltage or corroded components of the starter system.

    Moreover, the engine should not be fired too soon during the starting phase before the

    starter motor reaches a stationary speed.

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