CN104485194A - Variable-magnetic-force-line-distribution ratio electromagnet - Google Patents

Abstract

The invention discloses an electromagnet with variable magnetic field line distribution ratio, which comprises a guide sleeve (2), a yoke (3), a control coil (4), a magnetic isolation ring (5), a basin-shaped pole shoe (6), and a valve interface block (7), the push rod (8) and the moving iron core (10), the working surfaces of the valve interface block (7) and the moving iron core (10) are respectively an inner concave curved turning surface and an outer convex curved turning surface , the rotary shafts of the two curved rotary surfaces are all along the axis of the moving iron core, and their generatrices are both quadratic curves with similar shapes. is a narrow torus. The present invention can significantly improve the dynamic linear performance of the proportional electromagnet without changing the basic structure, shape and interface size of the existing proportional electromagnet. The contact area is very small, so the magnetic isolation pad used in the current proportional electromagnet can be eliminated to simplify the structure.

Description

An electromagnet with variable magnetic field line distribution ratio

technical field

The invention relates to a proportional electromagnet, in particular to an electromagnet with variable magnetic field line distribution ratio.

Background technique

As one of the key components in the electro-hydraulic proportional control device, the function of the proportional electromagnet is to convert the current signal input by the proportional control amplifier into force or displacement. Therefore, the electro-hydraulic proportional control technology puts forward strict requirements on the displacement-force characteristics of the proportional electromagnet, that is, the proportional electromagnet must have a horizontal displacement-force characteristic curve. Within its effective working stroke, when the coil current is constant, its The output force remains constant regardless of the displacement of the moving iron core (armature).

The structure of the existing proportional electromagnet is shown in Figure 1, which consists of a plastic end cover 1, a guide sleeve 2, a yoke 3, a control coil 4, a magnetic isolation ring 5, a basin-shaped pole piece 6, a valve interface block 7, and a push rod 8 , magnetic isolation pad 9, moving iron core 10 and end cover interface block 11, in which except plastic end cover 1, magnetic isolation ring 5, coil 4, push rod 8, magnetic isolation pad 9, other parts are made of magnetically conductive material production. The working principle of this proportional electromagnet diagram is shown in Figure 2 (for the sake of clarity, the section lines of some parts are deleted in the figure): the magnetic field lines generated by the coil 4 pass through the working air gap between the moving iron core 10 and the valve interface block 7 Divided into two branches, Φ1 and Φ2, of which the Φ1 branch passes through the working air gap at the bottom of the pot-shaped pole shoe axially through the moving iron core 10, and then passes through the valve interface block 7, the magnetic yoke 3, and the guide sleeve 2, and returns to the moving part. The iron core 10 forms a closed loop; the Φ2 branch passes through the moving iron core 10 obliquely through the tapered periphery of the basin-shaped pole shoe, reaches the front end of the guide sleeve, and then passes through the valve interface block 7, the magnetic yoke 3, and the guide sleeve 2, and returns to the moving The iron core 10 forms a closed loop. The axial components of the electromagnetic force generated by the branches Φ1 and Φ2 on the moving iron core 10 are F1 and F2 respectively, and their resultant force is the driving force F received by the moving iron core, as shown in FIG. 3 .

It can be seen from Figure 3 that the current proportional electromagnet mainly relies on the special-shaped basin-shaped pole piece to divide the magnetic force line into two branches, and adjusts the relative axial electromagnetic component force generated by the two magnetic force line branches through the relative size of the basin-shaped pole piece. Size, so that a section of approximately horizontal linear region (that is, the working stroke of the proportional electromagnet) is produced on the displacement-force curve of the moving iron core. Due to the relatively fixed shape of the pole piece, it is difficult to accurately adjust the relative magnitude of the electromagnetic force of the two branches during design, resulting in problems such as poor linearity of the displacement-force characteristic of the current proportional electromagnet and relatively short working stroke.

Contents of the invention

The object of the present invention is to provide an electromagnet with variable magnetic field line distribution ratio and good linearity of displacement-force characteristic and long working stroke.

In order to achieve the above object, the solution adopted in the present invention is: a variable magnetic force distribution ratio electromagnet, including a guide sleeve, a yoke, a control coil, a magnetic isolation ring, a valve interface block, a push rod and a moving iron core, and the moving iron core , The valve interface block and the control coil are installed in the magnetic yoke, wherein the moving iron core and the valve interface block are distributed forward and backward along the axial direction, the control coil is located outside the moving iron core and the valve interface block, the guide sleeve and the magnetic isolation ring are arranged on the moving iron Between the core, the valve interface block and the control coil, the push rod is connected to the moving iron core and passes through the valve interface block. The guide sleeve includes the front guide sleeve and the rear guide sleeve, and the magnetic isolation ring is located between the front and rear guide sleeves , the working end surfaces of the valve interface block and the moving iron core are respectively a concave curved turning surface and an outwardly convex curved turning surface. And the shapes are similar, when the moving iron core is at the maximum position of the stroke, the contact surface with the valve interface block is a narrow ring surface.

The generatrices of the above two curved surfaces of revolution are hyperbolas, parabolas or elliptical arcs.

The generatrices of the above two curved surfaces of revolution are formed by smooth connections of multiple conic curves.

The technical scheme of the invention can be used for both one-way proportional electromagnet and two-way proportional electromagnet.

In the present invention, due to the special shape of the working air gap (revolving body basin-shaped pole shoe) formed between the moving iron core and the valve interface block, when the moving iron core is at different positions of its displacement stroke, the control valve is controlled according to the principle of minimum magnetic resistance. The magnetic field lines emitted by the coil will form different distributions when passing through the working air gap. When the displacement of the moving iron core is small, the reluctance of the working air gap is large, but because the angle between the direction of most of the magnetic force lines in the working air gap and the axial direction is very small, the axial component of the electromagnetic force is relatively large; when the moving iron core is displaced When it is larger, the reluctance of the working air gap is small, but because the angle between the direction of most of the magnetic force lines in the working air gap and the axial direction is very large, the axial component of the electromagnetic force is small, so the moving iron core is displaced in most of the The axial electromagnetic force received during the stroke can remain relatively stable, that is, the horizontal displacement-force characteristic curve is realized, the linearity of the displacement-force characteristic of the electromagnet is better, and the working stroke of the moving iron core is also longer.

On the premise of not changing the basic structure, shape and interface size of the existing proportional electromagnet, the invention determines the shape and size parameters of the moving iron core and the working end face busbar of the valve interface block through accurate calculation, and can accurately control the working time of the moving iron core. The distribution of the magnetic force lines of the magnetic field in the working air gap can significantly improve the dynamic linearity performance (displacement-force characteristic linearity and working stroke width) of the proportional electromagnet. In addition, since the moving iron core is at the maximum position of the stroke and the valve interface block The contact area of the working surface is very small, and magnetic saturation occurs there, so the axial electromagnetic force is not large, so the magnetic isolation pad used in the current proportional electromagnet can be canceled to simplify the structure.

Description of drawings

Figure 1 is a structural schematic diagram of a traditional proportional electromagnet.

Fig. 2 is a working principle diagram of the traditional proportional electromagnet shown in Fig. 1 .

Fig. 3 is a schematic diagram of the displacement-force characteristic curve of the traditional proportional electromagnet shown in Fig. 1 .

Fig. 4 is a structural schematic diagram of the unidirectional proportional electromagnet of the present invention (when the moving iron core is in a small displacement).

Fig. 5 is a structural schematic diagram of the unidirectional proportional electromagnet shown in Fig. 4 when the moving iron core is in a large displacement.

Fig. 6 is a schematic diagram of force calculation of the moving iron core in the present invention.

Fig. 7 is a schematic diagram of the displacement-force characteristic curve of the proportional electromagnet of the present invention.

Fig. 8 is a structural schematic diagram of the bidirectional proportional electromagnet of the present invention.

In Figure 1-3: 1—Plastic end cap 2—Guide sleeve 3—Magnetic yoke 4—Control coil 5—Magnetic isolation ring 6—Pot-shaped pole shoe 7—Valve interface block 8—Push rod 9—Magnetic isolation pad 10— Moving iron core 11—end cover interface block

In Figure 4-7: 1—Plastic end cap 2—Guide sleeve 3—Magnetic yoke 4—Control coil 5—Magnetic isolation ring 6—Pot-shaped pole shoe 7—Valve interface block 8—Push rod 9—Working air gap 10— Moving iron core 11—end cover interface block

In Figure 8: 1—Magnetic Yoke 2—Control Coil 3—Moving Iron Core 4—Magnetic Isolation Ring 5—Guide Sleeve 6—Push Rod 7—Valve Interface Block 8—Magnetic Isolation Ring

Detailed ways

The present invention will be described in further detail below in conjunction with the accompanying drawings and embodiments.

Example 1 One-way proportional electromagnet

As shown in Figure 4 and Figure 5, the one-way proportional electromagnet of the present invention includes a guide sleeve 2 made of magnetically permeable material, a magnetic yoke 3, a valve interface block 7, a moving iron core 10, an end cover interface block 11 and a non-magnetic material. Plastic end cover 1, control coil 4, magnetic isolation ring 5 and push rod 8 made of magnetically permeable material, wherein the moving iron core 10, valve interface block 7 and control coil 4 are installed in the yoke 3, and the control coil 4 is located in the moving Outside the iron core 10 and the valve interface block 7, the guide sleeve 2 and the magnetic isolation ring 5 are arranged between the moving iron core 10, the valve interface block 7 and the control coil 4, and the push rod 8 is connected to the moving iron core 10 and passes through the The valve interface block 7, the guide sleeve 2 includes a front guide sleeve and a rear guide sleeve, and the magnetic isolation ring 5 is located between the front and rear guide sleeves. The working end face of the valve interface block 7 is a concave hyperbolic revolving surface, the working end face of the moving iron core 10 is a convex hyperbolic revolving surface, and the axes of rotation of the two hyperbolic revolving surfaces are all along the axis of the moving iron core 10 , the shape and size of the busbars are similar, but the curvature is slightly different, so the working air gap 9 between the two forms a special shape of the rotor basin-shaped pole piece 6, and the slight difference in curvature makes the moving iron core 10 reach During the maximum displacement, the contact surface of the two working end surfaces is a narrow ring surface.

In order to calculate the axial electromagnetic force F _x on the moving iron core 10, any point can be selected on the moving iron core 10, and a micro-annular surface (as shown in Figure 6) with an axial width approaching to 0 is taken after this point, the The area of the micro-annulus is dS, the magnitude of the generated electromagnetic force is dF _x , and the angle between its direction and the axis of the electromagnet is θ (as shown in Figure 6). According to the electromagnetic field theory, there are:

${\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; =</span>\frac{{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; d\&phi;</span>}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; \&mu;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; wxya</span>}}\mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; EdG</span>}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; \&mu;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; wxya</span>}}\mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; )</span>$

In the above formula:

dF _x : the axial component force of the electromagnetic force on the 10 micro-annulus of the moving iron core;

dφ: Magnetic flux on the 10 micro-ring surface of the moving iron core (wb);

μ ₀ : vacuum permeability (constant)

dS: moving iron core 10 micro-annulus area

θ: The angle between the electromagnetic force on the 10 micro-annulus of the moving iron core and the axis of the electromagnet;

E: magnetomotive force;

dG: The micro-permeance corresponding to the magnetic force lines emitted by the 10 micro-rings of the moving iron core

Integrating dF _x along the busbar of the working face of the moving iron core 10, the axial electromagnetic force suffered by the moving iron core 10 at any position in the stroke can be obtained, namely:

F _x = ∫dF _x

Set the busbar equation of the moving iron core 10 working face as: a ₁ x ² +b ₁ y ² +c ₁ =0;

The busbar equation of the working face of the valve interface block 7 is: a ₂ x ² +b ₂ y ² +c ₂ =0;

Then the above formula can be written as:

$\begin{array}{c}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; =</span>\frac{{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; d\&phi;</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; b</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; c</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; b</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; c</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; \&mu;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; wxya</span>}}\mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; b</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; c</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; b</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; c</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; )</span>\\ <span\; class="notranslate">\; =</span>\frac{{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; EdG</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; b</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; c</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; b</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; c</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; \&mu;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; wxya</span>}}\mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; b</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; c</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; b</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; c</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; )</span>\end{array}$

It can be seen from the above formula that the micro-permeability dG, the angle θ between the electromagnetic force and the electromagnet axis are all functions of the quadratic curve parameters (a ₁ , b ₁ , c ₁ , a ₂ , b ₂ , c ₂ ), and as As the working displacement of the moving iron core 10 increases (to the right), the micro-permeability dG gradually increases, the included angle θ also gradually increases, and the value of cos(θ) decreases. Therefore, as long as the appropriate quadratic curve parameters (a ₁ , b ₁ , c ₁ , a ₂ , b ₂ , c ₂ ) are designed according to the performance requirements of the electromagnet, the increase of the micro-permeability dG can be guaranteed to be the same as the cos(θ ) values decrease in a similar magnitude, so that the displacement-force characteristic curve of the moving iron core 10 over the entire motion stroke is shown in Figure 7, which has good linearity and a wide linear region.

The shape and size parameters of the moving iron core 10 and the busbar of the valve interface block 7 are determined through precise design and calculation, so that the distribution of the magnetic field lines of the magnetic field in the working air gap 9 of the moving iron core 10 during the stroke can be precisely controlled. When the axial dimension of the working air gap 9 is large (that is, when the displacement of the moving iron core 10 is small), the angle between the magnetic line of force and the axis is small, and the axial component of the electromagnetic force on the moving iron core 10 is relatively large; when the working air gap 9 When the axial dimension is small (that is, when the displacement of the moving iron core 10 is large), the angle between the magnetic field line and the axis is relatively large, and the axial component force of the electromagnetic force on the moving iron core 10 is small; therefore, the moving iron core 10 is The displacement-force characteristic curve on the motion stroke is as shown in Figure 7, compared with the displacement-force characteristic curve (as shown in Figure 3) of the existing proportional electromagnet, the linearity of the displacement-force characteristic curve of the proportional electromagnet of the present invention is better , the working stroke width is also significantly increased, which can effectively improve the working performance of the proportional electromagnet. At the same time, because the moving iron core 10 and the busbar of the valve interface block 7 are similar in shape, when the moving iron core 10 reaches the maximum displacement, the two work The contact surface of the two surfaces is a narrow torus, and since the contact area is very small, magnetic saturation will occur on the torus, and the electromagnetic force on the moving iron core 10 is relatively small, so there is no need to use the existing magnetic isolation pad.

The working end surfaces of the moving iron core 10 and the valve interface block 7 of the present invention can also adopt a turning surface whose busbar is a parabola or an elliptical arc, or a curved turning surface whose busbar is composed of multiple quadratic curves smoothly connected.

Example 2 Bi-directional proportional electromagnet

As shown in Figure 8, the two-way proportional electromagnet of the present invention includes a yoke 1 made of a magnetically conductive material, a guide sleeve 5, a moving iron core 3, a valve interface block 7 and a control coil 2 made of a nonmagnetically conductive material, The magnetic isolation rings 4, 8 and the push rod 6, the yoke 1, the control coil 2, the valve interface block 7 and the push rod 6 are two, symmetrically distributed on the left and right, and the two magnetic yokes 3 are connected by the magnetic isolation ring 8 , the control coil 2 and the valve interface block 7 are installed in the yoke 1 on the same side, the moving iron core 3 is located between the left and right valve interface blocks 7, and the push rods 6 are respectively fixed at both ends of the moving iron core 3. The guide sleeve 5 and the magnetic isolation ring 8 are arranged between the moving iron core 3, the valve interface block 7 and the control coil 2. The guide sleeve 5 is composed of the front guide sleeve, the middle guide sleeve and the rear guide sleeve. A magnetic isolation ring 4 is provided between the guide sleeves, and between the middle guide sleeve and the rear guide sleeve.

In this embodiment, the working end surfaces of the left and right valve interface blocks 7 are concave elliptical arc rotary surfaces, the two working end surfaces of the moving iron core 3 are convex elliptical arc rotary surfaces, and the rotation axes of all elliptical arc rotary surfaces All along the axis of the moving iron core 3, the shape and size of the generatrices are similar, only the curvature is slightly different, and the slight difference in curvature makes the contact surface of the two working surfaces a narrow torus when the moving iron core 10 reaches the maximum displacement.

The above are only specific embodiments of the present invention. It should be pointed out that those skilled in the art can make some modifications and improvements without departing from the principles of the present invention, which should also be regarded as the protection scope of the invention.

Claims (3)

1. a variable magnetic force line distribution proportion electromagnet, comprise guide pin bushing (2), yoke (3), control coil (4), magnetism-isolating loop (5), valve interface block (7), push rod (8) and dynamic iron core (10), dynamic iron core (10), valve interface block (7) and control coil (4) are installed in yoke (3), wherein dynamic iron core (10) and valve interface block (7) distribute vertically, control coil (4) is positioned at the outside of dynamic iron core (10) and valve interface block (7), guide pin bushing and magnetism-isolating loop (5) are located at dynamic iron core (10), between valve interface block (7) and control coil (4), push rod (8) is connected to dynamic iron core (10) and goes up and pass valve interface block (7), guide pin bushing (2) comprises leading portion guide pin bushing and back segment guide pin bushing, before magnetism-isolating loop (5) is positioned at, between back segment guide pin bushing (2), it is characterized in that: the operative end surface of described valve interface block (7) and dynamic iron core (10) is respectively the curved-line surface of revolution of indent and the curved-line surface of revolution of evagination, the gyroaxis of two curved-line surface of revolution is all along dynamic iron core axis, its bus is conic section and shape is similar, when dynamic iron core (10) is in the maximum position of stroke, the contact-making surface of itself and valve interface block (7) is a narrow anchor ring.

2. a kind of variable magnetic force line distribution proportion electromagnet according to claim 1, is characterized in that: the bus of two curved-line surface of revolution is hyperbola, parabola or elliptic arc.

3. a kind of variable magnetic force line distribution proportion electromagnet according to claim 1, is characterized in that: the bus of two curved-line surface of revolution is made up of the smooth connection of multistage conic section.