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برنامج تدريبى مجانى داخل المنتدى فى هندسة السيارات / جزء (1) (2)

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  1. [21]
    mohamed abouzahra
    mohamed abouzahra غير متواجد حالياً
    عضو متميز
    الصورة الرمزية mohamed abouzahra


    تاريخ التسجيل: Nov 2006
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    MANUAL RESET TYPE
    When a circuit breaker is opened by an over-current condition, the circuit breaker requires reset. To do so, insert a small rod (paper clip) to reset the bimetal plate as shown below.




    AUTOMATIC RESETTING TYPE - MECHANICAL
    Circuit breakers that automatically reset are called "cycling" circuit breakers. This type of circuit breaker is used to protect high current circuits, such as power door locks, power windows, air conditioning, etc. The automatically resetting circuit breaker contains a bimetal strip. The bimetal strip will overheat and open from the excess current by an overcurrent condition and is automatically reset when the temperature of the bimetal strip cools.



    AUTO RESET CONSTRUCTION AND OPERATION
    A cycling circuit breaker contains a metal strip made of two different metals bonded together called a bimetal strip. When heat from the excessive current is higher than the circuit breaker current rating the two metals change shape unevenly. The strip bends upwards and a set of contacts open to stop current flow. With no current flowing the bimetal strip cools and returns to its normal shape, closing the contacts, and resuming the current flow. Automatically resetting circuit breakers are said to "cycle" because they cycle open and closed until the current returns to a normal level.




    AUTOMATIC RESETTING SOLID STATE TYPE - PTC
    A Polymer PTC (for Positive Temperature Coefficient) is a special type of circuit breaker called a thermistor (or thermal resistor). A PTC thermistor increases resistance as its temperature in increased. PTCs, which are made from a conductive polymer, are solid state devices, which means they have no moving parts. PTCs are commonly used to protect power window and power door lock circuits.



    POLYMER PTC CONSTRUCTION AND OPERATION
    In its normal state, the material in a polymer PTC is in the form of a dense crystal, with many carbon particles packed together. The carbon particles provide conductive pathways for current flow. This resistance is low. When the material is heated from excessive current, the polymer expands, pulling the carbon chains apart. In this expanded "tripped" state, there are few pathways for current. When current flow exceeds the trip threshold, the device remains in the "open circuit" state as long as voltage remains applied to the circuit. It resets only when voltage is removed and the polymer cools. PTCs are used to protect power window and power door lock circuits.




    فى نهاية الموضوع نرجو منكم الدعاء

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    ان الله فى عون العبد ما دام العبد فى عون اخيه
    كل ما هو جديد فقط

  2. [22]
    mohamed abouzahra
    mohamed abouzahra غير متواجد حالياً
    عضو متميز
    الصورة الرمزية mohamed abouzahra


    تاريخ التسجيل: Nov 2006
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    الموضوع الخامس عن المقاومة المتغيرة
    ولها استخدمات كتير اوى فى السيارات من ابسطهم مقياس كمية الوقود ايضا معرفة كمية الهواء فى الانظمة القديمة وغيرها نشوف الموضوع احسن .

    Variable Resistors
    ________________________________



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    ان الله فى عون العبد ما دام العبد فى عون اخيه
    كل ما هو جديد فقط

  3. [23]
    mohamed abouzahra
    mohamed abouzahra غير متواجد حالياً
    عضو متميز
    الصورة الرمزية mohamed abouzahra


    تاريخ التسجيل: Nov 2006
    المشاركات: 718
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    RESISTORS
    All electrical circuits require resistance to operate correctly. Resistors are sometimes added to an electrical circuit to limit current flow, create voltage drops, or provide different operating modes. All resistors are rated in both a fixed ohm value of resistance and a power rating in watts. (Watt = Volts X Amps)

    Three basic categories of resistors are used in automotive electrical systems:
    1. Fixed;
    2. Stepped or tapped;
    3. Variable.
    Each has different characteristics and usage ranging from a simple fan circuit to a completed computer circuit.


    FIXED RESISTORS
    Fixed-value resistors are divided into two category types of resistors: Carbon / Metal Oxide and Wire-Wound.

    Carbon and Metal Oxide Film



    Wire-Wound


    Fixed Resistor
    Electrical Symbol



    CARBON RESISTORS
    Carbon resistors are commonly used in electronic systems. Carbon is mixed with binder; the more carbon, the lower the resistance. Carbon resistors have a fixed resistance value and are used to limit current flow. They are rated in watts and most have color-code bands to show the resistance value. A typical resistor has a watt rating from 0.125W to 2.0 W.

    Note: Metal-Oxide Film is sometimes used instead of carbon. While carbon is commonly used for ratings up to 0.5 watt , Metal-Oxide Film provide, better high-temperature satiability and is often used for 1.0 - 2.0 watt resistors.

    Carbon


    Metal Oxide Film



    RESISTOR RATING COLOR BANDS
    The first two bands set the digit or number value of the resistor.
    The third band, also known as the multiplier band, is the number of zeros added to the number value.
    The last band is the Tolerance band. Example: +/- 10%



    RESISTOR COLOR BAND CHART
    The chart below is used to interpret the color bands on the carbon resistor. Another chart is used to show the value of tolerance band colors (not shown).




    Using the illustration below:
    The first color band is Green with a value of "5".
    The second color band is Red with a value of "2".
    The third band is Black with a value of "0" zero. (No zeros are added)

    So the resistor has a base value of 52 ohms.




    READING COLOR BANDS - TOLERANCE VALUE
    Resistors vary in tolerance (accuracy). Common tolerance values are 20%, 10%, 5%, 2%, or 1%, simply meaning the maximum percent allowable difference the resistor value actually is from the designed value rating. A 1% resistor is a higher quality resistor than one with a 20% rating.
    The tolerance band (last band) is silver with a value of 10%.
    So, the resistance value is "52 ohms plus or minus 5.2 ohms" (46.8 to 57.2 ohms).




    FIXED RESISTOR USAGE
    Fixed resistors are often used in voltage division circuits. One example is the computer sensor circuit shown below. Notice two resistors, R1 and R2, are placed in series. A fixed resistor R1, known as a pull-up resistor, is used to create a voltage drop point. As the resistance of water temp sensor (R2) changes, so does its voltage drop. This change also changes the voltage drop of R1. A monitor circuit inside the computer measures this voltage drop in between the two resistors.



    WIRE-WOUND RESISTORS
    Wire-wound resistors are made with coils of resistance wire. Often enclosed in ceramic to help dissipate heat and protect the resistor wire, they are accurate and heat stable. The resistance value is often marked. Wire-wound are used in higher watt circuits often 2W or higher. An ignition ballast resistor is an example of a wire wound resistor.




    STEPPED OR TAPPED RESISTORS
    A stepped or tapped resistor has two or more fixed taps that provide different resistance values. These taps allow current to flow through all or part of the resistor, which changes the amount of current flowing through the circuit. Stepped resistors can also be encased in ceramic and are nothing more than a series of fixed resistors placed end to end.





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    ان الله فى عون العبد ما دام العبد فى عون اخيه
    كل ما هو جديد فقط

  4. [24]
    mohamed abouzahra
    mohamed abouzahra غير متواجد حالياً
    عضو متميز
    الصورة الرمزية mohamed abouzahra


    تاريخ التسجيل: Nov 2006
    المشاركات: 718
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    STEPPED RESISTOR OPERATION
    An example of a stepped resistor in operation is the blower motor circuit shown below. Notice the blower resistor is in series with the blower motor. Higher resistance in series will lower the current flow; thus, higher blower resistor resistance will result in lower blower speeds.
    In low speed current flows through the entire resister from pin#3 though pin#1 to ground (shown in blue). The motor will be in low speed because less current is flowing. Moving the blower switch to medium 2 speed opens a path for current out pin #4 to ground. Current flows through pin#3 and out pin#4 to ground (shown in green). Current will flow through only part of the resistor. The motor will be in medium 2 speed causing the blower motor to spin faster compared to low speed because more current is flowing through the circuit.



    VARIABLE RESISTORS
    Variable resistors provide an infinite amount of resistance values. Variable resistors are used by electrical circuits to provide information on temperature, position, or light source.
    There are four types of variable resistors used:
    Rheostats
    Potentiometers
    Thermistors
    Photoresistor

    Generic Variable Resistor
    Electrical Symbol




    RHEOSTAT
    Rheostats at one time were used in the headlamp switch to dim or brighten dash panel lighting and pre-OBDII fuel gauge sending units. Rheostats have two connections, one to the fixed end of a resistor and the other to a sliding contact on the resistor. Turning the control moves the sliding contact away from or toward the fixed end, increasing or decreasing the resistance. Rheostats control resistance, thus controlling current flow.


    Rheostat Symbol




    Variable Resistor Symbol



    RHEOSTAT OPERATION
    As the wiper moves along the rheostat it exposes more or less of the resistor. Moving the wiper towards the high places a small portion of the resistor in series with the light, causing the light to glow bright. Moving the wiper toward the low, places a larger portion of the resistor in series with the lamp; this increased resistance causes less current to flow lowering the intensity of the light. Rheostats are not used on computer circuits because of temperature variations on the resistor when the wiper arm is moved.



    POTENTIOMETER
    Potentiometers are used to measure changes in position. Potentiometers have three connections or legs: the reference, signal, and ground. The reference is at one end of a resistor and the Ground is at the other end. Current flows from the Reference through the resistor to Ground creating a voltage drop across the resistor. The Signal is a sliding contact (movable wiper arm) that runs across the resistor. Unlike a rheostat, its main purpose is not to vary resistance but to vary the voltage in a circuit.


    Potentiometer Symbol



    Variable Resistor Symbol



    POTENTIOMETER OPERATION
    Remember a potentiometer has three legs, the reference (R), the signal (S) , and the ground (G) as shown below. 5 volts is supplied to the reference, current flows from the reference (R) through the entire resistor to ground (G). The Signal wiper slides across the resistor changing measure voltage as it moves. As the wiper moves towards the reference (R), the measured signal voltage at (S) will increase. As the wiper moves away from the Reference (R) towards ground (G), the measured signal voltage drops.



    POTENTIOMETER APPLICATIONS
    Since potentiometer are used to measure changes in position they naturally are used for throttle, EGR, AC blend door, and power seat position sensors. All potentiometers have three wires and are used to measure position changes.



    THERMISTOR
    Thermistors are resistors that change resistance as the temperature changes. These are ideal in electrical circuits where measuring temperature change is required. There are two types of thermistors:
    NTC (Negative Temperature Coefficient)
    NTC thermistors: as the temperature goes down, the resistance goes up, and as the temperature goes up, the resistance drops. This type is used today in automotive applications.

    PTC (Positive Temperature Coefficient)
    PTC thermistors: as the temperature go down, the resistance goes down also, and as the temperature goes up, the resistance increases.

    Thermistor
    Electrical Symbol



    THERMISTOR APPLICATIONS
    Thermistors are used as Air, Coolant, EGR, and Automatic Air Temperature sensors. All thermistors have two wires and are used to measure temperature changes. When placed in series with a fixed (pull-up) resistor, thermistors create a variable voltage drop circuit, which is ideal for use by computer circuits. Engine coolant temperature sensor (ECT) is shown below.



    THERMISTOR OPERATION
    In the example below, as the engine warms up, R2 (water temp sensor) increases in temperature; this lowers the resistance of R2. The drop in R2 resistance results in a decreased voltage drop across R2 (less voltage is used). This decreased voltage drop across R2 causes the voltage drop across R1 to increase. R1 now uses more voltage. This increased voltage drop of R1 results in a lowered measured voltage by the monitor circuit and is seen by the computer as an increase in engine temperature. The reverse is true as the water temp sensor cools.



    PHOTORESISTORS
    A photoresistor, or photoconductive cell, is basically a light sensitive resistor whose resistance changes as light is exposed to it. Basically photoresistors change resistance as light intensity changes. The photoresistor has high resistance with no light exposed and decreases in resistance as light intensity increases. A common automotive use for photoresistors is the automatic headlamp circuit.
    Photo Resistor
    Electrical Symbol



    PHOTORESISTOR OPERATION
    A photoresistor is placed in the automatic headlight circuit shown below. The photoresistor operates a normally closed headlight relay. During daylight driving light shines on the photoresistor, lowering its resistance, causing current to flow allowing the relay coil to energize, opening the relay contacts, thus preventing the headlights from operating. When the photoresistor is in darkness, its resistance increases preventing enough current flow through the relay coil to keep the relay contacts open. The closed relay contacts allow current to flow to the headlights causing them to turn on. Photoresistors respond slowly to changes in light intensity and may require several minutes to stabilize.


    ان شاء الله سوف ننتقل الى الموضوع السادس

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    ان الله فى عون العبد ما دام العبد فى عون اخيه
    كل ما هو جديد فقط

  5. [25]
    م/عماد
    م/عماد غير متواجد حالياً
    عضو
    الصورة الرمزية م/عماد


    تاريخ التسجيل: Jul 2007
    المشاركات: 25
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    انامعاك فى الموضوع الشديد بس عايزك تفصل تفصيل كامل فى ميكانيكاالسيارات

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  6. [26]
    mohamed abouzahra
    mohamed abouzahra غير متواجد حالياً
    عضو متميز
    الصورة الرمزية mohamed abouzahra


    تاريخ التسجيل: Nov 2006
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    اخى العزيز م / عماد
    حدد لى الموضوع الى انت عايزة وان شاء الله لو فى مقدرتى انى اجيبة ان شاء الله هجيبة

    بس لاحظ ان مهندس السيارات الى بقى مهندس كهرباء يعنى شغل السيارات الحديثة نسبة الميكانيكا بة بسيطة جدا
    حتى محركات الديزل الجديدة .

    وعلى العموم انا تحت امرك فى اى شى تحتاجة ان شاء الله ويوفقنى فى ذلك .

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    ان الله فى عون العبد ما دام العبد فى عون اخيه
    كل ما هو جديد فقط

  7. [27]
    elbary
    elbary غير متواجد حالياً
    عضو


    تاريخ التسجيل: Mar 2007
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    بارك الله فيك

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  8. [28]
    mohamed abouzahra
    mohamed abouzahra غير متواجد حالياً
    عضو متميز
    الصورة الرمزية mohamed abouzahra


    تاريخ التسجيل: Nov 2006
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    كل الموضوع دة ومفيش ردود
    يعنى بلاش احسن الواحد يكمل باقية الدورة ما دام الموضوع مفيش حد قد يستفيد منة

    ومشكور على الرد يا بشمهندس (elbary

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    ان الله فى عون العبد ما دام العبد فى عون اخيه
    كل ما هو جديد فقط

  9. [29]
    eng_mechanic
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    عضو فعال


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    موضوع جميل بس يا ريت اللى عنده فيديو على السيارات يراسلنى على ****** علىeng_mechanic2005واكون شاكر ليكم جميعا

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  10. [30]
    eng_mechanic
    eng_mechanic غير متواجد حالياً
    عضو فعال


    تاريخ التسجيل: Aug 2007
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    شكرا للرقابه

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