Car Maintenance Basics

Chapter 9 Project 1 Automobile maintenance measurement technology ([-])
Various parts on the car will have different degrees of wear and deformation during use, such as bending, twisting, warping and other deformations.In particular, the deformation of some basic parts or some main parts of the assembly will lead to the destruction of the mutual assembly relationship between the parts, which will deteriorate the technical performance of the assembly and the car, reduce the power of the car, and increase the fuel consumption of the car. shorten the life of the car.

The degree of deformation of a part is measured by the shape error and position error of the part.Shape errors mainly include errors such as straightness, flatness, roundness, and cylindricity.Position errors mainly include errors such as parallelism, perpendicularity, coaxiality, symmetry, and circular runout.

In the technical standard of automobile repair, shape and position errors account for a large proportion.Under the premise of being technically feasible and economically reasonable, according to the functional requirements of the automobile assembly and basic parts, the corresponding shape and position tolerance requirements are put forward, which has an important impact on the quality of automobile repair.

For the measurement of shape and position error, the measurement datum should be selected as design datum and machining datum as much as possible.It is best to unify the three benchmarks of measurement, design, and processing, which can improve measurement accuracy.The measurement of shape and position error of parts is affected by many factors.In order to make the measurement result close enough to the true error of the measured part, the measurement work must follow some common conditions and requirements.When measuring, the surface state of the part must be guaranteed, and surface defects such as scratches and roughness must be eliminated. The measurement method shall be selected according to the measurement accuracy requirements, and the measurement position, measurement section and measurement point shall be selected according to the structural characteristics, functional requirements, processing technology and other factors of the part. number.

Commonly used measuring tools for car maintenance

learning purpose

Knowledge goal:

Learn about the types of auto repair measuring tools.

Master the basics of auto repair measurement tools.

Master the use of vehicle maintenance measurement tools.

Skill Goal:
Will use various maintenance measurement tools correctly.{-Able to use the measuring tools commonly used in automobile maintenance to measure the shape and position errors of commonly used automobile parts.

task description
Under the guidance of relevant knowledge, understand the commonly used measuring tools for car maintenance.Under the guidance of the work order task, the auto repair measurement tool can be used to measure the auto parts.By learning and mastering the skills of using automobile maintenance measurement tools, record and archive the completed work, and consciously maintain safe operation and 5S work requirements.

related information
The correct use of common measuring tools for automobile maintenance is the knowledge that the majority of automobile maintenance personnel must master, and it is the premise to ensure the accuracy of measurement data and the quality of maintenance.

The material of the measuring ruler is generally a thin stainless steel plate, so it is also called a steel ruler or a steel ruler.It is mainly used to measure the length and width of the plane of spare parts, and can also be used to determine the dimensions measured by internal and external calipers.Metric lines are engraved on the face of the scale and a metric to imperial conversion table is engraved on the back.In addition to engraved with metric lines, some measuring rulers can also have corresponding imperial lines, as shown in Figure 4-1.

游标卡尺是工业上常用的测量仪器，是一种测量长度、内外径、深度的量具。其精度可分为0.10mm、0.05mm和0.02mm等数种。游标卡尺的规格有125mm、200mm、300mm、500mm和1000mm等。

1. The structure of the vernier caliper

The vernier caliper is composed of two parts, the main ruler and the sliding vernier attached to the main ruler.The main ruler is generally in mm, and the vernier has 10, 0 or 50 divisions. According to the division, the vernier calipers can be divided into ten-degree vernier calipers, twenty-degree vernier calipers, and fifty-degree vernier calipers.The main scale and vernier of the vernier caliper have two sets of movable claws, which are the inner measuring claw and the outer measuring claw. The inner measuring claw is usually used to measure the inner diameter, and the outer measuring claw is usually used to measure the length and outer diameter.The structure of the vernier caliper is shown in Figure 4-2.

2. Scale principle and reading method of vernier caliper
(1) Scale principle of vernier caliper

If you use A to represent the minimum division value of the main scale, use Na to represent the number of divisions of the vernier.Usually the length of the divisions of the vernier is designed to be equal to the total length of the divisions on the main ruler (xa-1), and the difference between the minimum scale value (xa) of the main scale (xa) and the minimum scale value on the vernier is used to improve the measurement accuracy.If the minimum scale value on the cursor is 6, then there is.

[-]. Vernier caliper

Inner fastening butterfly wire

Nb=(N-1)
The difference is
The multiple is called the vernier coefficient, usually 1 or 2.It can be seen that, a-timing, the larger the N, the smaller the difference (rn-6), and the higher the accuracy of the reading during measurement.The difference is usually called the graduation value or precision of the vernier, which is the principle of the vernier graduation.Vernier calipers of different models and specifications may have different lengths and divisions, but the basic principles of the verniers are the same.A 1-degree vernier caliper with a vernier coefficient of 50, N=50, a=1mm, and a division value of 1=0.02mm, this value is the minimum reading that can be read during measurement (also the display error of the instrument), as shown in the figure 4-3 shown.

(2) Reading method
When reading, the length L of the object to be measured can be divided into two parts and read out and then added.First read the integer part L0 above mm at the position aligned with the vernier "1" line on the main scale, and then read the part less than 1mm on the vernier.

k is the ordinal number of the engraved line on the vernier that is most aligned with a certain engraved line on the main ruler.

多游标卡尺的游标上常标有数值，犔2可以直接由游标上读出。如图4-4所示，可以从游标上直接读出犔2为0.24mm。

3. Usage and Precautions

① Before measuring, the measuring surface of the workpiece and the main scale, clamping feet and tip of the depth gauge of the vernier caliper should be cleaned.

②Before use, close the clamping feet and check whether the main and auxiliary scale parts are aligned.

③When reading, the vernier caliper should be kept in a horizontal state, and the line of sight should be facing the engraved line, so as to avoid reading due to incorrect line of sight.

④ Do not use a vernier caliper to measure a workpiece that is too hot.

⑤ During use, care should be taken to protect the measuring surface of the caliper feet, and the vernier caliper cannot be used to measure the surface and operation error of forgings and castings.

surface of the moving workpiece.

⑥ After the caliper is used up, it should be oiled and stored properly. The vernier caliper that has not been used for a long time should be wiped clean and oiled, and placed in a box. Be careful not to rust or make it dirty.

[-]. Outer diameter micrometer
Micrometer, also called spiral micrometer or separation card, is a precision measuring tool with a measurement accuracy of up to 0.01mm.According to the purpose, there are two kinds of inner diameter micrometer and outer diameter micrometer. The outer diameter micrometer is used to measure the outer diameter of parts.

1. Structure

外径千分尺的规格按测量范围划分，有0-25mm、25-50mm、50-75mm、75-100mm、100-125mm等多种。它由尺架、固定测杆、微分筒、带螺母的固定套筒、紧定手柄、棘轮等组成，如图4-5所示。

2. Scale principle
The outer micrometer is based on the principle of the screw pair, which converts the angular displacement into a linear displacement, and uses the scale relationship between the fixed sleeve and the differential sleeve to achieve an accuracy of 0.01mm.A baseline is engraved on the axial surface of the fixed sleeve with a nut, and many millimeters of engraved lines are evenly engraved on the base line, and the upper and lower similar engraved lines are staggered by 0.5mm.As far as the upper and lower sides of the baseline are concerned, there is 1mm between every two scale lines, one side of the baseline is the integer part of the fixed sleeve, and the other side is the position of the half scale line (0.5mm).There are 50 engraved lines on the conical surface of the micrometer tube. Since there is a precision thread behind the movable measuring rod, the pitch is 0.5mm. Therefore, when the micrometer cylinder rotates once, the movable measuring rod will move 0.5mm, and the micrometer cylinder will cover it at the same time. Or expose a half scale line (ie 0.5mm scale line) of the fixed sleeve.Therefore, when the micrometer tube rotates one grid (that is, 1/50 cycle), the moving amount of the movable measuring rod is: 0.5X1/50=0.01mm, so the measurement accuracy of the micrometer can reach 0.01mm.

3. Reading method
① Read the integer first.Look at the exposed part of the numbered engraved line on the fixed sleeve on the left side of the differential, which is the integer part of the measured part size.

② Read decimals.See which scribe line on the microtube aligns with the axial scribe line on the fixed sleeve.First read the reading, and then see if the half scale line (0.5mm scale line) is exposed. If the half scale line is not exposed, then the reading of the scale line just read is a decimal; if the half scale line is exposed, then Add 0.5mm as mm decimal (fractional part).When reading, pay attention to whether the 0.5mm engraved line is exposed, otherwise you will read less or more 0.5mm.

③Add the two readings together (add the integer part and the decimal part), which is the reading of the micrometer.

4. How to use
① Before use, check whether the zero position of the micrometer is correct.When checking, clean the measuring end face of the calibration rod and the micrometer, put the calibration rod between the fixed measuring rod and the movable measuring rod, turn the ratchet to make the measuring surface contact until it makes a "cracking" sound, and check the micrometer on the conical surface. Whether the zero line coincides with the zero line of the fixed sleeve baseline, if not, it should be corrected.

②Before use, you should also pay attention to its sensitivity.When turning the ratchet, the ratchet should be able to drive the differential cylinder to rotate flexibly, and there must be no stagnation or mutual friction between the differential cylinder and the fixed sleeve during the whole process.After the microtube is fixed by hand, or the movable measuring rod is fastened with the brake ring, the ratchet should be able to make a crisp "cracking" sound.

③ When measuring, the workpiece to be measured should be wiped clean. When the measuring rods on both sides are close to the workpiece, do not turn the micrometer tube again, so as not to damage the micrometer or affect the accuracy.Generally, you only turn the ratchet, and after the ratchet makes a "quack" sound, you can gently shake the micrometer to make the measuring surface and the surface of the workpiece in good contact. Avoid contacting only the edge of the measuring surface, and turn the ratchet again if necessary, and finally read count.If you want to take the micrometer down for reading, you should first fix the movable measuring rod with a brake ring or a tightening handle, and then take it down for reading.

④ When measuring, hold the bow frame with your left hand and rotate the micrometer cylinder with your right hand. The axis of the micrometer rod should be perpendicular or parallel to the center line of the workpiece.In order to eliminate measurement errors, it is best to measure several times at the same position and take the average value.

⑤ When adjusting the micrometer in a relatively large range, the micrometer cylinder should be rotated at first instead of the ratchet, which saves time and prevents premature wear of the ratchet.But do not rotate the micrometer tube quickly, in case the movable measuring rod slams into the workpiece to be measured and damages the micrometer.When backing off the scale, the microtube should be rotated instead of the back cover or ratchet to prevent the back cover from loosening and affecting the zero position or causing premature wear of the ratchet.

5. Zero adjustment method

Before using the outer micrometer, a zero check must be carried out to see if the zero line on the cone surface of the differential cylinder coincides with the zero line on the baseline of the fixed sleeve.If it is not coincident, it must be adjusted, and the adjustment method is as follows:
①Adjustment method of 0-25mm micrometer. The 0-25mm micrometer can be directly calibrated when adjusting the micrometer. First, turn the micrometer tube so that the movable measuring rod and the fixed measuring rod are in light contact. cap), and then turn the microtube so that the zero line on the conical surface coincides with the zero line on the base of the fixed sleeve.Hold the microtube with your left hand to keep it from turning, tighten the back cover with your right hand, and finally loosen the brake ring.Then turn the microtube, and when the ratchet makes a sound, check whether the zero position is correct. If it is correct, the adjustment is complete, otherwise the above steps must be repeated for adjustment.

②Adjustment method of micrometer above 25mm. The adjustment of the micrometer above 25mm should be calibrated with a calibration rod (or gauge block). The method is to use the calibration rod as a measuring workpiece to measure. calibration.If the reading is inconsistent with the standard size of the calibration rod, it means that the zero position is not accurate, and the adjustment method is the same as that of the 0-25mm micrometer.

6. Matters needing attention
① The micrometer is only used to measure precision parts, and must not be used to measure rough surfaces such as blanks.

② It is forbidden to use a micrometer to measure the running or high temperature parts.

③ It is strictly forbidden to use the micrometer as a caliper, or as a hammer to hit other objects.

④The calibration rod should be kept intact.When it must be disassembled for maintenance, special attention should be paid to the anti-collision of its thread, and the microtube should not be tightened forcefully during use.

⑤ When the brake ring is braked or the fastening handle is locked, do not turn the microtube to avoid thread damage and inaccurate readings.

⑥ When using an outer micrometer, it should be noted that its range is compatible with the size range of the workpiece.

⑦ Pay attention to cleaning, wipe it carefully after use, and put it in the box properly to avoid damage.

[-]. Inner diameter micrometer
The inner diameter micrometer is used to measure the inner diameter of the inner hole of the part or the inner dimension of the groove.Its specifications are 50-300mm, 50-550mm and so on.

1. The structure and use of the inner diameter micrometer (1) Structure The inner diameter micrometer is composed of a measuring rod, a movable sleeve, a fixed sleeve with a thread inside and a baseline engraved on the outside, a stop screw and a measuring head. The basic structure is shown in Figure 4- 6.

(2) Scale principle
The scale principle of the inner diameter micrometer is the same as that of the outer diameter micrometer.Its basic measuring head has a maximum measuring range of 50-75mm.In order to increase the measuring range, it is equipped with an extension rod.A complete set of inner micrometers is attached with a set of extension rods, which are selected according to the measurement range, and the numbers of the measurement range are engraved on the extension rods.The two ends of the inner diameter micrometer are generally arc-shaped where they are in contact with the machine part.

(3) How to use
Before use, first use calipers or calipers or a ruler to measure the approximate size of the part to be measured, and then select a suitable inner diameter micrometer.When in use, the fixed sleeve with the left hand is in contact with the hole wall of the measured part, and the movable sleeve is rotated with the right hand so that the measuring head is in contact with the hole wall, and then the stop screw is tightened to read out the measurement size.When using, pay attention to holding the micrometer flat, and then turn the movable sleeve, and swing slightly from side to side in the horizontal position while turning, so as to measure the maximum diameter.

2. Calibration of inner diameter micrometer
Like outside micrometers, inside micrometers generally require inspection before use.If there is an error, it must be corrected. The method steps are as follows:

①转动活动套筒，使其圆锥面上的“0”线与刻有基线的固定套筒“50”刻线对齐，然后用25-50mm(或50-75mm)的外径千分尺测量其长度，检查此时内径千分尺本身最小长度是否等于50mm。

(End of this chapter)