Institut Kemahiran MARAJasin, Melaka

INFORMATION SHEET

PROGRAMME : A14 - SIJIL TEKNOLOGI BAIKPULIH BADAN KENDERAAN

SESSION : SEMESTER : 2

CODE/COURSE :TAB 2042 / BASIC AUTOMOTIVE ELECTRICAL AND ELECTRONIC

SHEET NO : A14/M03/IS06

LECTURER : MD HAFIZI BIN MOHAMAD WEEK : 2

TOPIC : M03 CIRCUIT AND TERMINALS

SUB-TOPIC :

03.01 WIRE HARNESS03.02 COLOR CODING03.03 TERMINALS AND SOCKET03.04 RELAYS, SWITCHERS AND SOLENOIDS03.05 EARTH03.06 POWER WINDOW

LEARNING OUTCOME :

Pelajar-pelajar mesti boleh:1. Terangkan mengenai medan magnet.2. Terangkan mengenai elektromagnet.3. Terangkan mengenai solenoid.4. Terangkan operasi solenoid.5. Nyatakan kegunaan solenoid.

TAJUK : KEMAGNETAN

TUJUAN

Litar elektrik amat penting dalam sistem elektrikal kenderaan. Ia membolehkan komponen-komponen elektrik kenderaan berfungsi dengan sempurna. Pelbagai kaedah digunakan untuk menyampaikan sesuatau tindakan bagi menggerakkan komponen elektrik kenderaan. Penghasilan elektromagnet amat penting dalam menggerakkan satu unit kerja. Kertas penerangan ini akan menerangkan maksud tersebut.

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PENERANGAN

MEDAN MAGNET

Medan magnet ialah kawasan disekitar satu magnet atau satu pengalir yang membawa arus di mana satu daya magnet akan bertindak pada satu bahan magnet. Magnet mempunyai dua kutub iaitu kutub selatan dan kutub utara. Arus yang mengalir melalui satu pengalir akan menghasilkan satu medan magnet disekitar pengalir tersebut. Arus yang mengalir akan menghasilkan medan magnet apabila melalui suatu pengalir. Medan magnet yang mengalir adalah sepusat mengelilingi pengalir. Medan magnet terdiri daripada garisan magnet atau fluks magnet.

Gambarajah 6.1 Medan Magnet

Gambarajah 6.2 Medan oleh dawai yang membawa arus

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Gambarajah 6.3 Medan Magnet pada pengalir

ELEKTROMAGNET

Medan magnet yang dihasilkan oleh aliran arus melalui dawai boleh dikuatkan lagi dengan menebat dawai dan melilitkannya pada teras besi. Medan magnet akan tertumpu di teras besi dan ia akan menjadi magnet selagi arus mengalir melalui dawai itu. Elektromagnet merupakan satu medan magnet yang terjadi hasil daripada pergerakkan arus yang melalui pengalir yang dililitkan pada satu teras besi. Ia merupakan satu medan magnet sementara. Apabila arus elektrik diputuskan maka medan magnet tersebut akan hilang.

Gamabarajah 6.4 Medan magnet yang terhasil disekeliling dawai pengalir

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SOLENOID

Solenoid merupakan satu gegelung pengalir yang panjang berbentuk seperti selinder yang bertindak sebagai alat elektromagnet di mana akan menghasilkan medan magnet apabila arus mengalir melaluinya. Solenoid selalunya digunakan untuk menukarkan tenaga elektrik kepada tenaga mekanikal yang bertindak seperti suis. Solenoid adalah penting kerana ianya boleh menghasilkan medan magnet terkawal dan juga sebagai elektromagnet.

Solenoid merupakan komponen elektromagnet yang boleh menggerakkan logam plunger besar atau teras. Pergerakkan teras ini boleh digunakan untuk menutup sesentuh elektrik yang besar atau menggerakkan sesuatu bahagian untuk tujuan penyambungan. Selain itu juga pergerakkan ini mungkin digunakan untuk mengunci pintu kereta atau menutup beberapa penyambungan elektrik. Dalam automotif, starter solenoid digunakan untuk melengkapkan penyambungan bateri ke litar motor penghidup. Ia bertindak sebagai relay yang besar untuk menyambungkan arus yang tinggi dalam litar. Ada juga starter solenoids yang menggerakkan starter gear bersambung dengan flywheel ring gear untuk mengengkol enjin.Solenoid yang kecil boleh digunakan untuk mengawal engine throttle position dan kelajuan enjin.

Gambarajah 6.5 Contoh solenoid

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Gambarajah 6.5 Salah satu contoh penggunaan solenoid

Lihat gambarajah 6.5, menunjukkan contoh salah satu kegunaan solenoid. Arus elektrik akan mengalir melalui belitan solenoid dan menghasilkan medan magnet. Medan magnet ini akan menolak teras ke dalam belitan menyebabkan teras akan bersentuh dengan titik sesentuh solenoid menjadikan litar tertutup dan arus boleh mengalir. Apabila arus diputuskan daripada belitan solenoid, tindakakn spring akan membolehkan teras kembali pada kedudukan asalnya.

OPERASI SOLENOID

Solenoid bagi penggunaan automotif terdiri daripada gegelung wayar pengalir (coil), field dan plunger. Gegelung wayar pengalir mengandungi lilitan wayar tembaga yang mempunyai lilitan yang padat serta tersusun. Apabila arus mengalir melalui gegelung wayar, satu medan magnet yang kuat akan terhasil disekeliling gegelung wayar. Medan magnet ini akan bergerak memasuki bahagian tengah gegelung wayar sehingga membentuk lingkaran.

Gambarajah 6.6. Medan magnet disekeliling gegelung pengalir

Gegelung pengalir ini akan ditempatkan di dalam perumah yang berbentuk selinder berlubang yang diperbuat daripada bahan pengalir. Memandangkan medan magnet boleh bergerak dengan mudah melepasi besi, perumah ini menambahkan kekuatan medan magnet. Plunger yang berbentuk bulat mempunyai muncung bercas positif di satu bahagian. Apabila dimasukkan ke

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bahagian tengah gegelung wayar tersebut akan menyebabkan medan magnet semakin bertambah. Bahagian bawah plunger yang leper dan bercas negatif akan menghasilkan kawasan yang besar membolehkan medan magnet bertambah kuat.

Gambarajah 6.7 Medan magnet bertambah kuat apabila gegelung wayar dimasukkan kedalam perumah besi

Gambarajah 6.8 Medah magnet semakin bertambah kuat apabila dimasukkan teras besi ditengah-tengah gegelung besi.

Apabila diletakkan bebanan dihadapan plunger ini akan menyebabkan solenoid itu menolak dan apabila diletakkan bebanan dibelakang solenoid ianya akan menarik.

Gambarajah 6.9 Pengerakan plunger yang menarik dan menolak bebanan hasil daripada terjadinya medan magnet.

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PENGGUNAAN SOLENOID

a. Electromechanical solenoids

Electromechanical solenoids consist of an electromagnetically inductive coil, wound around a movable steel or iron slug (termed the armature). The coil is shaped such that the armature can be moved in and out of the center, altering the coil's inductance and thereby becoming an electromagnet. The armature is used to provide a mechanical force to some mechanism (such as controlling a pneumatic valve). Although typically weak over anything but very short distances, solenoids may be controlled directly by a controller circuit, and thus have very low reaction times.

The force applied to the armature is proportional to the change in inductance of the coil with respect to the change in position of the armature, and the current flowing through the coil (see Faraday's law of induction). The force applied to the armature will always move the armature in a direction that increases the coil's inductance.

Electromechanical solenoids are commonly seen in electronic paintball markers, pinball machines, dot matrix printers and fuel injectors.

The rotary solenoid is an electromechanical device used to rotate a ratcheting mechanism when power is applied. These were used in the 1950s for rotary snap-switch automation in electromechanical controls. Repeated actuation of the rotary solenoid advances the snap-switch forward one position. Two rotary actuators on opposite ends of the rotary snap-switch shaft, can advance or reverse the switch position.

The rotary solenoid has a similar appearance to a linear solenoid, except that the core is mounted in the center of a large flat disk, with two or three inclined grooves cut into the underside of the disk. These grooves align with slots on the solenoid body, with ball bearings in the grooves.

When the solenoid is activated, the core is drawn into the coil, and the disk rotates on the ball bearings in the grooves as it moves towards the coil body. When power is removed, a spring on the disk rotates it back to its starting position, also pulling the core out of the coil.

The rotary solenoid was invented in 1944 by George H. Leland, of Dayton, Ohio, to provide a more reliable and shock/vibration tolerant release mechanism for air-dropped bombs. Previously used linear (axial) solenoids were prone to inadvertent releases. U.S. Patent number 2,496,880 describes the electromagnet and inclined raceways that are the basis of the invention. Leland's engineer, Earl W. Kerman, was instrumental in developing a compatible bomb release shackle that incorporated the rotary solenoid. Bomb shackles of this type are found in a B-29 aircraft fuselage on display at the National Museum of the USAF in Dayton, Ohio. Solenoids of this variety continue to be used in countless modern applications, and are still manufactured under Leland's original brand "Ledex", now owned by Johnson Electric.

b. Rotary voice coil

This is a rotational version of a solenoid. Typically the fixed magnet is on the outside, and the coil part moves in an arc controlled by the current flow through the coils. Rotary voice coils are widely

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employed in devices such as disk drives.

c. Pneumatic solenoid valves

A pneumatic solenoid valve is a switch for routing air to any pneumatic device, usually an actuator, allowing a relatively small signal to control a large device. It is also the interface between electronic controllers and pneumatic systems.

d. Hydraulic solenoid valves

Hydraulic solenoid valves are in general similar to pneumatic solenoid valves except that they control the flow of hydraulic fluid (oil), often at around 3000 psi (210 bar, 21 MPa, 21 MN/m²). Hydraulic machinery uses solenoids to control the flow of oil to rams or actuators to (for instance) bend sheets of titanium in aerospace manufacturing. Solenoid-controlled valves are often used in irrigation systems, where a relatively weak solenoid opens and closes a small pilot valve, which in turn activates the main valve by applying fluid pressure to a piston or diaphragm that is mechanically coupled to the main valve. Solenoids are also in everyday household items such as washing machines to control the flow and amount of water into the drum.

Transmission solenoids control fluid flow through an automatic transmission and are typically installed in the transmission valve body.

e. Automobile starter solenoid

In a car or truck, the starter solenoid is part of an automobile starting system. The starter solenoid receives a large electric current from the car battery and a small electric current from the ignition switch. When the ignition switch is turned on (i.e. when the key is turned to start the car), the small electric current forces the starter solenoid to close a pair of heavy contacts, thus relaying the large electric current to the starter motor.

Starter solenoids can also be built into the starter itself, often visible on the outside of the starter. If a starter solenoid receives insufficient power from the battery, it will fail to start the motor, and may produce a rapid 'clicking' or 'clacking' sound. This can be caused by a low or dead battery, by corroded or loose connections in the cable, or by a broken or damaged positive (red) cable from the battery. Any of these will result in some power to the solenoid, but not enough to hold the heavy contacts closed, so the starter motor itself never spins, and the engine does not start.

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Gambarajah 6.10 Solenoid bagi motor penghidup kenderaan.

KESIMPULAN

EXERCISE

1. Terangkan secara ringkas mengenai elektromagnet.

2. Terangkan secara ringkas mengenai solenoid.

3. Nyatakan aplikasi solenoid pada kejuruteraan.

REFERENCE

1. Akademi Saga, Basic Electrical & electronic System Information Sheet, Shah Alam, Selangor: Edaran Otomobil Nasional Berhad.

2. Akademi Saga, Basic Electrical & electronic System Work Sheet, Shah Alam, Selangor: Edaran Otomobil Nasional Berhad.

3. Tom Denton, Automobile Electrical & Electronic Systems4. DTAF IKM Jasin, Information Sheet Auto-Electric5. Toyota Service Training 1989, Fundamentals of Electricity, Vol 14(Step 2), Toyota Motor

Corporation.6. V.A.W. Hillier1986, Fundamentals of Automotive Electronics, Croydon College: Stanley Thornes

Ltd. System7. Automotif Electrical/electronic System8. James E.Duffy 1998, Auto Electricity and Electronics Technology : The Goodheart-Willcox

Company, Inc.

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