Car Maintenance Basics

Chapter 10 Project 2 Automobile maintenance measurement technology ([-])
②When the length of the inner diameter micrometer itself is less than 50mm, use a special wrench to loosen the measuring head of the fixed sleeve, and then check it with the outer diameter micrometer until it is accurate (some inner diameter micrometers can also adjust the measuring head of the movable sleeve) .

③When the inner diameter micrometer is installed with an extension rod, it can also be checked and corrected by a method similar to the above.

[-]. Percentage table
A dial gauge is an indicating gauge.The dial indicator is easy, accurate and fast to measure, so it is widely used in auto repair.Such as checking the bending of shaft parts, the meshing clearance of gears, the out-of-roundness of journals, and the flatness errors of parts, etc.

1.百分表的构造与刻度原理百分表的精度为0.01mm，量杆的移动距离有0-3mm，0-5mm，0-10mm等几种，其构造如图4-7所示。

When measuring, if the measuring rod moves 1mm inwards, the linked large pointer rotates for a full circle, and the small pointer rotates a small division at the same time, so that the small pointer can indicate the number of full circles of the large pointer's rotation and also indicate the millimeters moved by the measuring rod .The large dial is divided into 100 equal division lines. The large pointer rotates once and passes through the 100 scale lines on the large dial. Therefore, each scale line on the large dial represents the moving distance of the measuring rod by 0.01mm.The large dial can rotate with the housing and can be fixed at any position with a set screw.

2. Precautions for use and maintenance of the dial indicator

①Before use, check whether the measuring rod of the dial gauge moves flexibly, whether the pointer jumps or does not return, and find out the reason if there is any problem.

②When in use, install the dial indicator on the bracket, and use the contact at the end of the measuring rod to touch the surface to be measured, so that the tested machine part moves or rotates according to certain requirements, and observes the gap or gap of the tested machine part from the dial. Deviation size.

③When measuring, the measuring rod probe and the measured part should be wiped clean.Pre-compress the measuring rod 1-3mm on the surface to be measured (the small pointer rotates 1-3 divisions) to eliminate the clearance of the measuring rod and the margin required for measurement.In this way, both positive and negative numbers can be read out during measurement.Then fasten the watch, see where the small pointer stops, and then turn the movable dial so that the long pointer is aligned with the "0" line on the surface, and then the measurement can be performed.

④In order to ensure accurate measurement, the measuring rod should be perpendicular to the surface to be measured during measurement.When measuring a cylindrical workpiece, the measuring rod should be consistent with the diameter of the workpiece.

⑤ When using, handle with care, do not move the measuring head too much, so as not to accelerate the wear of the parts in the watch, especially do not make the measuring rod move too far, that is, do not exceed the measuring range of the watch, otherwise the watch will be broken inner parts.

⑥ For blanks or workpieces with significant concave-convex surfaces, the dial indicator should not be used for measurement to prevent damage to the dial indicator.

⑦ The complete set of dial indicators should also pay attention to the maintenance of the bracket to make it intact.After the magnetic watch stand is used up, the switch in the middle should be pushed to one end to make the iron block lose its magnetism, so as to ensure sufficient magnetism when used.

[-]. Measuring cylinder table
The cylinder gauge, also known as the inner diameter dial gauge, is used to measure the bore diameter.It is mainly used to measure the roundness, cylindricity and wear of the engine cylinder in automobile repair.

1. The structure of the gauge

The upper part of the measuring cylinder gauge is a dial indicator, and the lower part is a measuring rod device, as shown in Figure 4-8.In order to measure cylinders with different diameters, various measuring rods of different lengths are available, and the measuring range is marked on each measuring rod for easy selection.

2. How to use the gauge
① Generally speaking, according to the standard size of the cylinder, adjust the outer micrometer to the standard size value, and then lock the brake handle.

②Install the measuring cylinder meter.According to the standard size of the cylinder, choose the appropriate extension rod.

③ Correct the "0" bit.The length of the extension rod should be adjusted appropriately, and the lock nut should be tightened.When installing the dial indicator, there must be a certain pre-pressure.Place the extension rod and the movable measuring head correctly between the measuring rods of the adjusted outer micrometer, turn the movable dial at this time, the big pointer is aligned with the "0" mark line of the positive scale ih, and remember where the small pointer is s position.

④ Extend the watch stand into the cylinder and swing back and forth for measurement.If the pointer is exactly at the "0" position, it means that the inner diameter of the measured cylinder is the same as the standard size; if the pointer leaves the "0" position in a clockwise direction, it means that the active measuring rod is shortened. The scale value, the difference is the actual size of the cylinder; if the pointer leaves the "0" position in the counterclockwise direction, it means that the active measuring rod is elongated. and are the actual dimensions of the cylinder.

Rotate the measuring cylinder gauge in the same plane to measure the roundness of the cylinder; move the measuring cylinder gauge up and down to measure the cylindricity of the cylinder.

3. Precautions when using the measuring cylinder gauge

① When measuring, the measuring rod should be perpendicular to the axis of the cylinder.During specific measurement, the measuring cylinder gauge should be slightly swung left and right at each measuring point.When swinging, the reading indicating the minimum value of the watch hand is the correct reading at this point, as shown in Figure 4-9.

②When the measuring cylinder gauge is taken out or placed in the hole, and when the correct position of the measuring cylinder gauge is required to move the position and direction of the measuring rod during the measurement process, the gauge must be slightly tilted so that the measuring head returns to a free state , to reduce wear on the probe during movement.Especially when the cylinder gauge is pulled out from the cylinder with cylinder shoulder, it should not be too fast, otherwise the movable gauge head of the gauge holder will be easily damaged.

③ After use, remove the dial indicator and measuring rod respectively and wipe them clean, apply anti-rust oil, and put them in a box for storage after checking the accessories.

Seven, thickness gauge
Thickness gauges (also known as feeler gauges, micrometers, etc.) are used to measure the gap between two parallel surfaces, such as measuring valve clearance, piston ring opening clearance, etc.It consists of a group of thin steel sheets with different thicknesses, and each sheet is marked with numbers such as 0.03, 0.04, and 0.10 (unit: mm), as shown in Figure 4-10.

task implementation
According to the guidance of the work order, complete the measurement of the 410 thickness gauge on the auto parts using the auto measurement tool.In the process of task implementation, they will learn the operating procedures and maintenance methods of automobile maintenance equipment, and implement them in groups to complete the work within the specified time.

[-]. Tool preparation

Tip: Before implementing the homework, each group should prepare the materials and tools needed for this learning task according to the table below.

[-]. Technical standards and requirements
① All operations meet the requirements for safe operation.

②All operations conform to the operating specifications of automobile measuring instruments.

③ Safety accidents are not allowed during the operation.

[-]. The work to be done

1. Measurement of axis straightness error
The straightness of the axis refers to the shape error of the central element of the axis.A measurement method consistent with the definition of straightness of an axis is very difficult.In actual measurement, a simple radial circular runout is often used to replace the straightness error of the axis, so that the measured values ​​are approximate and can meet the accuracy required by the technical requirements in general production.

The measurement of straightness error is mostly used for straight shaft parts that are prone to bending deformation and can be straightened during work.As shown in Figure 4-11, it is the measurement of the straightness of the drive shaft axis.Use a V-shaped iron to set up the transmission shaft, and slowly rotate the transmission shaft by hand. The difference between the maximum and minimum readings of the dial gauge pointer is the radial circular runout error of the measurement plane.The same measurement is carried out at different positions in the axial direction, and half of the measured maximum radial circular runout value can be used as the axis straightness error.

2. Measurement of flatness error
The flatness of a part indicates how uneven a plane is.After the working plane of the part is deformed, unevenness or warping will inevitably occur on the plane, and the surface condition will affect the position accuracy and sealing effect of the parts.Therefore, there are restrictions on the flatness error for the matching plane and the working plane of the parts.

For the shape error of a plane, the flatness is related to the straightness in a given plane.The straightness error refers to the shape error in the direction of the measured straight line in a plane perpendicular to the plane; while the flatness error refers to the shape error of the measured plane in a given plane in any direction perpendicular to it.That is, the flatness error is the straightness error in all directions within the measured plane.Therefore, the measurement of the flatness error can be replaced by the measurement of the straightness error in each direction.

The following takes the measurement of the lower plane of the cylinder head as an example to introduce the method of measuring flatness with a knife-edge sample ruler commonly used in automobile maintenance.This method generally uses a feeler gauge to measure the gap formed between the deformation plane and the knife-edge-shaped sample ruler (or ruler) to measure the flatness error, and is mostly used to measure the flatness of the cylinder block and cylinder head.When measuring, use a knife-edge sample ruler with a length equal to or slightly greater than the full length of the measured plane, as shown in Figure 4-12, keep the sample ruler in close contact with the measured plane, and use a feeler gauge along each measurement line to measure the distance between the sample ruler and the measured plane. The maximum value of the gap between the measured planes can be used as the flatness error of the plane.It should be noted that the flatness requirements of the cylinder block or cylinder head are not the same in the full length and in the local area.For example, the flatness of the lower plane of the six-cylinder cast iron cylinder head shall not be greater than 0.3mm in the whole length range, and shall not be greater than 50mm in every 50mmX0.05mm range.

When using a knife-edge sample ruler to measure flatness, the contact position of the concave plane is at both ends, and a stable contact can be formed.As for the convex plane, the contact position is in the middle, and stable contact cannot be formed. At this time, the gap at both ends should be adjusted to be equal before measurement, otherwise the measurement error will be too large.The measurement by this method is an approximate value, but it is widely used in production because of the simple equipment and convenient measurement.

The above-mentioned use of straightness errors in all directions of the measured plane to replace the flatness error of its plane is only reasonable for the plane of the cylinder block and cylinder head where the measured surface is solid, while the plane of the cover facing the transmission case, For irregular annular narrow planes such as the bottom plane of the cylinder block, it is not suitable to use this method.At this time, usually the transmission housing buckle is placed on the inspection platform, and after making it in stable contact, it is measured with a feeler gauge. The maximum gap is the flatness error of the surface.If it is not in stable contact, the difference between the maximum gap and half of the gap variation value when the part swings is the flatness error.

3. Measurement of roundness and cylindricity error

The roundness error refers to the actual value of the deviation of the actual circle from the ideal circle on the cross section, and is generally measured by the two-point method.The roundness tolerance zone refers to the area between concentric circles whose radius difference is the tolerance value on the same cross section.

The cylindricity error is the actual value of the deviation of the actual cylindrical surface from the ideal cylindrical surface.In the measurement of cylindricity error, the two-point method used refers to taking half of the difference between the maximum value and the minimum value of the measured diameter at any position or direction on the surface of the measured cylinder.Its tolerance zone refers to the area between two coaxial cylindrical surfaces whose radius difference is the tolerance value.

下面以汽缸为例说明圆度、圆柱度的测量。如图4-13所示，在推力方向轴向截面上、中、下处分别测得直径值为犇在轴向方向轴向截面上、中、下处分别测得直径值为Dl，D，2，D3，m1=1-1)/为该汽缸在上横截面处的圆度，AR2=(D2-2>/为该汽缸在中横截面处的圆度，3=3一3)/为该汽缸在下横截面处的圆度，取1、2、3中最大值作为该汽缸的圆度。取DiDDsDlDkD中两者差值最大的一半作为该汽缸的圆柱度。

4. Measurement of coaxiality error
Concentricity refers to the error of the measured axis to the reference axis.It refers to the positional relationship between two axes, which is equal to twice the maximum distance of the measured axis from the reference axis in value.The measurement of coaxiality is mostly used for shaft and hole parts.For the same shaft, when the selected datum is different, the measured coaxiality error will also be different.

The following introduces two methods of measuring coaxiality commonly used in automobile maintenance.

(1) Measurement of coaxiality tester
Take the front and rear main bearing housing holes of the cylinder block as the measurement reference, and use the special tester as shown in Figure 4-14.

Measure 3 places in the axial direction of each seat hole, take the maximum value, calibrate the direction, make a record, and finally convert the coaxiality error.

(2) Coaxial measuring rod measurement

This measurement method is to insert a measuring stick with the same size as the measured seat hole into the seat hole. If each seat hole is in the coaxial line, the measuring rod can be inserted smoothly.For the coaxiality requirements of the main bearing housing holes of the crankshaft of the cylinder block, since the coaxiality difference of each adjacent two housing holes is not equal to the coaxiality error of all the housing holes, the measuring rods should be made of different lengths of two.

5. Measurement of circular runout
Circular runout includes radial circular runout and end face full runout.

(1) radial circular runout

The degree of change of the measured surface to the radial runout of the reference axis is the radial circular runout.Its measurement method has been introduced in Item [-], and will not be repeated here.

(2) full end runout

If the plane of the rotating part deviates from its rotation plane (the plane perpendicular to the axis of rotation), there will inevitably be a jump on the end face of the plane, and the degree of jump is the total runout of the end face.

Figure 4-15 shows the method of measuring the full runout of the end face.Turn part 1, and measure the full runout of the end face of the part from dial gauge 2.The larger the radius of the measuring point, the larger the resulting runout.Generally, in the inspection technology, it is stipulated that there should be a certain amount of runout within a certain radius.

[-]. Self-evaluation

1. Summarize what are the main testing equipment commonly used in automobile maintenance?
2. Please write down your experience of this learning task.

3. Self-evaluation of the learning environment (including dress, learning attitude, mastery of knowledge and skills, completion of work pages, etc.).

[-]. Group evaluation

Evaluation status of serial number evaluation items
Good to bad

1 team spirit
2 Whether learning is proactive
3 The situation of obeying the work arrangement

4 Use of tools and instruments
5. Tool finishing and site cleaning
[-]. Teacher Evaluation

Evaluation status of serial number evaluation items
Good to bad

1 Attendance
2 dressing situation

3 classroom order
4 Whether learning is proactive
5. Fill out the learning task book

6 Use of tools and instruments
7. Tool finishing and site cleaning
thinking and practice
1. Briefly describe the scale principle of the vernier caliper with an accuracy of 0.02mm.

2. What precautions should be taken when using vernier calipers?
3. Briefly describe the reading method of the outer micrometer.

4. What are the precautions for using the outer micrometer?

5. Briefly describe how to use the cylinder meter.

6. Briefly describe how to measure the axis straightness error?
7. Briefly describe the method of measuring flatness error with a knife-shaped sample ruler.

8. Briefly describe the measurement method of roundness and cylindricity error.

(End of this chapter)