- Detail

Abstract: through the design of jt6770 passenger car windshield, this paper introduces the design and calculation process of hyperboloid windshield lip curve, and gives the calculation program of calculating the left windshield lip curve

key words: design and calculation of bus windshield stop curve

according to the plan of "jt6770 advanced bus technology development" of the key scientific and technological project of the Ninth Five Year Plan of the Ministry of communications, the Ministry of communications organized the Chongqing Institute of highway science of the Ministry of communications and some manufacturers to jointly develop jt6770 passenger cars. In order to make this model suitable for roads and some tourist routes with better conditions, higher requirements are put forward for the shape and main performance indicators of the whole vehicle. In order to make the windshield not only reflect the elegant and lively style, but also meet the requirements of reducing wind resistance when driving at high speed, hyperboloid panoramic laminated safety glass is selected and assembled by bonding process. In order to obtain accurate wind stop curve, we use computer to carry out CAD calculation in the design, and achieved satisfactory results

1 determination of coordinate system

the coordinate system used in this paper is the same as the coordinate system specified in the body drawing

the straight line drawn along the long section of the upper surface of the upper edge of the frame longitudinal beam is the zero line of Z coordinate, which is positive above the zero line of Z coordinate and negative below

the straight line drawn through the center of the front axle and perpendicular to the zero line of the coordinate in the height direction is the zero line of the X coordinate. When viewed along the forward direction of the vehicle, it is positive behind the zero line of the X coordinate and negative in front

the longitudinal center line of the vehicle is the zero line of Y coordinate. When viewed along the forward direction of the vehicle, it is positive on the left and negative on the right of the zero line of Y coordinate

2 the shape curve of the windshield

the shape of the windshield and even the whole front wall is closely related to the shape of the whole vehicle, and has a decisive influence on the shape of the whole vehicle. Therefore, the success of the modeling design of a vehicle model largely depends on the determination of the shape curve of the windshield. Through computer-aided design, we optimized the exterior design and formulated several shape design schemes. After fully listening to the opinions of experts, we finally determined the shape curve of the windshield shown in Figure 1

it can be seen from Figure 1 that each section curve parallel to the xoy plane of the windshield is composed of three arcs R10000, R308 and R41, and the R41 arc is exactly tangent to the side surface, and the X coordinate of the tangent point is the same as that of the front end face of the first column. The tangent connecting lines between the three arcs are all spatial curves. It can be seen from the side view that the side view arcs of the contour curve and the first column curve are different, and the center of the two arcs do not coincide. For brittle materials such as gray cast iron, cast aluminum alloy, concrete, masonry and resin, the center of the front end face arc r7690 of the first column is (x=6246.14, z=10.95), the center of the contour curve r8168 is (x=6504.65, z=-428.08), and the center of the upper frame arc r9810 of the windshield is (y=0, z=-7700), The center of the circular arc r12000 on both sides is (y= ± 10850, z=600)

Figure 1 Sketch map of the windshield of jt6770 passenger car

3 installation form of windshield glass

installation form of windshield glass, there are three commonly used types: riding glue, hanging glue and bonding. Jt6770 bus adopts bonding form. Figure 2 shows the installation form of the lower edge of the windshield, figure 3 shows the installation form of the upper edge of the windshield, and Figure 4 shows the installation form of both sides of the windshield. It can be seen from the figure that the inner and outer ends of the upper and lower edges of the windshield are directly welded with the upper and lower frame beams of the windshield. After the front frame beam is positioned, it is easy to find a suitable material supplier and calculate the space curve of the upper and lower ends according to its installation relationship. The installation seams on both sides are formed by butt welding the spatial surfaces of the inner and outer seams. In order to make the butt welding of the seams on both sides meet the requirements of the shape and the installation of the windshield glass, an accurate seam curve must be given through calculation. Next, we will focus on the calculation process of the lip curve on both sides

Figure 2 Figure 3 figure 4

4 calculation of the two lip curves of the windshield (taking the left lip as an example)

take any horizontal section of the windshield, and the Z coordinate of the section is Z, and the section shown in Figure 5 is obtained. According to the previously determined shape curve and the installation form of the windshield, the coordinates of the characteristic points of the lip curve are gradually derived. For the convenience of calculation, the following definitions are made first:

(a, b) - the center of R308 arc

(A1, B1) - tangent point of R308 arc and R41 arc

(A2, B2) - tangent point of R10 000 arc and R308 arc

(A3, B3) - the intersection of the inner edge line of the inner and outer lip (as the lip positioning point)

(A4, B4) - tangent point between R41 arc and side wall

(A5, B5) - characteristic point 1 of outer lip

(A6, B6) - characteristic point 2 of outer lip

(A7, B7) - characteristic point 3 of outer lip

4.1 (A4, B4) calculation of point coordinates

known: the Z coordinate of the section is Z; The side view arc of the front end face of the first column is r7690, and its center coordinate is: (x=6 246.14, σ z=10.95); The arc on both sides of the front face is r12000, and its center coordinate is: (y = ± 10850, z=600) (see Figure 1); R41 circle is tangent to the side surface, and the X coordinate of the tangent point is the same as that of the front end face of the first column (see Figure 5). Find the coordinates of (A4, B4) points

solution: the side view arc equation of the front end face of the first column is:

(6 246.14-a4) 2+ (z-10.95) 2=76902 (1)

the left arc equation of the front wall front view is:

(b4+10 8502+ (z-600) 2=120002 (2)

obtained from formula (1):

obtained from formula (2):

4.2 (a, b) calculation of point coordinates

4.2.1 calculation of the center of R10000 large circular arc

it is known that the Z coordinate of the section is Z; The side view arc of the outer contour of the front wall is r8168, and its center coordinate is: (x=6504.65, z=-428.08); R10000 the Y coordinate of the center of the large circular arc is O, and its X coordinate is OD

find the X coordinate od of the center of R10000 large circular arc

solution: the equation of r8168 arc is:

(6504.65-x) 2+ (z+428.08) 2=8 1682 (3)

obtained from formula (3): while the Y coordinate of the center of R10000 large arc is O, so the x value obtained from formula (4) is the X coordinate when the Y coordinate of R10000 large arc is O (see Figure 1). From this we can get:

4.2.2 Calculation of the center of R41 arc

it is known that the R41 arc and the side surface are tangent to the front end face of the first column, that is, the X coordinate of the tangent point is the same as that of the front end face of the first column (see Figure 5)

find the center of R41 arc

solution: according to the known conditions, the center coordinate of R41 arc is (A4, b)

4.2.3 (a, b) calculation of point coordinates

known: R308 arc and R41 arc are tangent to (A1, B1) points; R10000 arc is tangent to R308 arc at point (A2, B2) (see Figure 5)

find the coordinates of (a, b) points

solution: the following equations can be obtained from the known conditions:

(od-a) 2+b2= (10) 2 (5)

(a-a4) 2+ [(b) -b] 2= () 2 (6)

the above (5) and (6) simultaneous equations can be solved by computer programming, so as to obtain the coordinates of (a, b) points

4.3 (A1, B1) calculation of point coordinates

known: (a, b) and (A4, B4) coordinates of points; R308 arc and R41 arc are tangent to points (A1, B1) (see Figure 5)

find the coordinates of (A1, B1) points

solution: the following equation can be obtained from the known conditions:

the coordinates of (A1, B1) points can be solved from the above formula:

4.4 (A2, B2) calculation of point coordinates

known: (a, b) coordinates of points; R10000 coordinates of arc center are (OD, O); R10000 arc and R research on the experimental machine 1 there is no short 308 arc tangent to (A2, B2) point (see Figure 5)

find the coordinates of (A1, B1) points

solution: the following equation can be obtained from the known conditions:

the coordinates of (A2, B2) points can be solved from the above formula:

Figure 5 cross section of the lip on both sides of the windshield (left)

calculation of the coordinates of 4.5 (A3, B3) points

known: the extension line of the connecting line between point (a, b) and point (A3, B3) coincides with the inner edge line of the outer lip. Let this extension line intersect with the outer arc R308 at point P (see Figure 5), and the distance from point (A3, B3) to point P is T1

find the coordinates of (A3, B3) points

solution: see Figure 4: t1=8+6.75+7=21.75

the following equation can be obtained from the known conditions:

b3=b (7)

(a-a3) 2+ (b3-b)) 2= (.75) 2 (8)

substitute (7) into (8) to obtain:

4.6 (A5, B5) calculation of point coordinates (see Figure 6)

known: (a, b), (A3, B3) coordinates of points.The seam is made of 1mm steel plate (i.e. h=1)

find the coordinate

solution of: (A5, B5) point: the straight line equation passing through points (a, b) and (A3, B3) is: (9)

the straight line equation parallel to the straight line (9) and the vertical distance is h is: (10)

r308 the equation of arc is:

(a-a5) 2 (y-b) 2=3082 (11)

from equation (9):

and the point (A5, B5) is a straight line (10) and R308 intersection of arcs, h α And A5, B5 are substituted into equations (10) and (11), and the following equations are obtained: (13)

(a5-a) 2+ (b5-b) 2=3082 (14)

the above simultaneous equations (12), (13) and (14) can be solved by computer programming, so as to obtain the coordinates of (A5, B5) points

4.7 (A6, B6) calculation of point coordinates (see Figure 6)

known: (A5, B5) coordinates of points; (A6, B6) is a point on the straight line (10). Let the distance between (A5, B5) and (A6, B6) points be t2

calculate the coordinates of (A6, B6) points

solution: since h=1, we can make: T2 ≈ t1=8+6.75+7=21.75

from the known conditions, we can get the following equation:

from the solution of the above adjustable report situation equation:

a6=a5+21.75sin α

b6=b.75cos α

where α Given by (12)

4.8 (A7, B7) calculation of point coordinates (see Figure 6)

known: (A6, B6) coordinates of points; If the connecting points (A3, B3), (A7, B7) form a straight line, the straight line is perpendicular to the straight line (9) and intersects with the straight line (10) at the point (A6, B6), and set the distance between the points (A6, B6) and (A7, B7) as H1

find the coordinates of (A7, B7) points

solution: see Figure 4: h1=17+8=25

from the known conditions, the following equation can be obtained:

from the solution of the above equation:

a7=acos α

b7=bsin α

where α Given by (12)

5 calculation program

through the previous calculation, we have obtained the shape curve of the outer lip on both sides of the windshield. The shape curve of the inner lip on both sides of the windshield can be obtained by using a calculation method similar to that of the outer lip according to the constraints given in Figure 5, which will not be described in detail here

according to the solution equation of each point derived above, the calculation program is compiled with QBASIC language, which can calculate the coordinates of each characteristic point of the inner stop on both sides of the windshield on any Z section, so as to obtain the characteristic curve of the inner stop on both sides of the windshield. The calculation program is omitted

6 conclusion

hyperboloid modeling is increasingly used for passenger car windshield, and the geometric characteristics of the double curved surface determine that the calculation of the positioning parameters of the windshield lip curve is cumbersome and complicated, and the calculation workload is large. Therefore, it is necessary to use computer in the design of CAD calculation, which can not only improve the work efficiency, reduce the labor intensity of designers, but also reduce the calculation error, improve the accuracy of calculation results, and further improve the design quality of passenger cars. (end)

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