Application of ground bolts in automobiles
The automotive electrical system uses direct current. All circuits have positive and negative poles. Generally, the automotive circuit uses a single-wire system, that is, the battery positive line is directly connected to each electrical equipment. The negative battery line is directly placed on the metal parts of the vehicle body, and the electrical equipment is used. The negative line is placed close to the chassis and body metal parts. The engine and the car chassis (frame or sub-frame) and the body sheet are used as a common passage. The way the negative line is connected to the body is called grounding. Also known as grounding.
Grounding plays an important role in the automotive circuit, so the quality of the grounding is the key to the safety of the automotive electrical equipment. Poor car grounding will cause many failures, such as the loosening of the engine ground wire fastening bolts, or the corrosion of the ground wire joints causing the resistance to increase, which will cause poor contact, causing voltage F drop or work failure.
The grounding on the car is a hole type terminal, and the hole type terminal is bolted to the chassis or the body metal part by a nut. There are two types of bolts used: one for ordinary bolts and one for special ground bolts.
Ordinary bolt-fixed grounding terminal In order to ensure the reliability of the grounding, the paint on the chassis or body metal parts that are in contact with the iron-plated terminals should be scraped off before assembling the bolts, then the grounding terminal is assembled and Vaseline is applied to prevent Rusty.
The special grounding bolts are used to assemble the grounding iron terminals. Due to the special structure of the grounding bolts, the iron bolts can be directly assembled in the projection welding nuts on the frame or the body metal, and the assembly is convenient and quick.
Ground bolt structure
The structure of the ground bolt is shown in Fig. 1. Fig. 2 is a cross section of the bolt A of Fig. 1, and Fig. 3 is a section of the bolt B of Fig. 1.
Working principle of ground bolt
When the ground bolt passes through the grounding terminal on the wire harness and enters the projection nut on the frame or the body sheet metal, the three oblique groove at the lower end of the stud acts as a reamer, and the inside of the convex weld nut hole on the frame Most of the paint is scraped off, and the flattened plane on both sides of the studs squeezes the remaining paint in the hole of the projection nut to ensure good electrical contact between the stud and the projection nut.
The spring washers and flat washers on the bolts secure the grounding terminals on the vehicle wiring harness. After the assembly is completed, the grounding bolt has good electrical conductivity. Therefore, after the electric appliance is energized, the current flows from the negative pole of the appliance to the wiring harness grounding terminal through the ground bolt and then through the projection nut back to the frame or body. The gold and the whole vehicle form a complete circuit, and the electrical appliances work normally.
Figure 1 Ground bolt structure
1-stud 2 - nut 3 - spring washer 4 - flat washer 5 - stud groove on the lower end of the stud
Figure 2 A section
1-Medal bolt stud 2 is a flat plane in which the two sides of the stud are axially symmetrical
Figure 3 Three oblique grooves on the inverted truncated cone at the lower end of the stud
Figure 4 How to assemble the bolts on the car
1-stud 2 - nut 3 - spring washer 4 - flat washer 5 - stud groove on the lower end of the inverted truncated cone 6 - frame or body sheet metal 7 - frame or the cast nut on the body 8 - the grounding terminal 9-harness on the harness
Ground bolt selection
3.1 traditional grounding method
In the traditional way of grounding, to ensure good contact and continuity between the grounding terminal of the wire harness and the frame, special tools must be used to scrape off the frame of the frame at the ground or the paint of the body sheet metal, and then assemble it. Tie Duan, after installing the iron terminal, it is also necessary to apply Vaseline protection to prevent rust. This process is time-consuming and laborious, and the quality cannot be guaranteed and affects production efficiency.
3.2 ground bolt bolting method
It is convenient to assemble the iron bolts by tapping the bolts through the grounding terminal of the wire harness and tightening them. Although the bolts have the advantage of being convenient and quick to assemble, if the bolts are improperly selected, the phenomenon that the appliances are not working properly may occur.
3.3 Selection of ground bolts
The bolts should be selected according to the hole position in the assembly position and the thickness of the frame or body sheet metal.
Size choice:
Since the ground bolt is electrically conductive by scraping off the paint in the frame or the gold-plated upper projection nut of the body body, the diameter of the bolt bolt stud is to be matched with the projection nut to perform the paint scraping effect.
Length selection:
The length of the bolts directly determines the paint-scraping effect and the contact performance with the frame or body sheet metal.
Figure 5 The state of starting the paint after the bolts and nuts are assembled
Figure 6 State of the bolt assembly after tightening
Define the maximum distance from the front end of the nut to the bolt stud of the bolt (shown in Figure 5), the thickness of the spring washer is D1, the thickness of the washer is D2, and the thickness of the grounding terminal on the harness is D3, frame or body The thickness of the sheet metal is D4, the thickness of the projection nut is DS, and the length of the bolt assembly is Ls (shown in Figure 6), then Ls=D1+D2+D3+D4, the length L must be greater than Ls, the bolt It has the effect of scraping paint after assembly.
Since the ground bolt is the first step of the slanting groove on the inverted truncated cone at the lower end of the stud, the paint in the projection nut should be completely scraped off, and the lower end of the stud is inverted after the bolt is assembled. It is best to expose at least two threaded teeth (as shown in Fig. 6), and the flat surface of the studs which are axially symmetrical on both sides can be used as a scraping paint to scrape all the paint in the projection nut. Reduce the contact resistance at the grounding point.
to sum up
The quality of the grounding is the key to the safety of the automotive electrical appliances. Therefore, when using the grounding bolts, it is necessary to select the appropriate length of the bolts according to the different positions used, different frame or sheet metal thickness. The reliability of iron.
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