Herringbone Planetary Gear Transmission Device With Constant Meshing Characteristics Constructed Tooth Pair

Abstract

Provided is a herringbone planetary gear transmission device with a constant meshing characteristics constructed tooth pair, which relates to the technical field of gear transmission. The transmission device includes a sun gear with a constructed tooth pair, a planetary gear with a constructed tooth pair and an internal gear with a constructed tooth pair based on conjugate curves. Normal tooth profiles of the gears with a constructed tooth pair in the present disclosure are all the same combined curve and can be machined by using the same cutter. A common normal at an inflection point or a tangent point of the curve passes through a pitch point of a meshing gear pair, and a sliding ratio of the meshing gear pair is adjusted according to an adjusted position of the inflection point or the tangent point. A contact ratio of the meshing gear pair is designed as an integer.

Description

CROSS REFERENCE TO RELATED APPLICATION

This patent application claims the benefit and priority of Chinese Patent Application No. 202310632426.8, filed with the China National Intellectual Property Administration on May 31, 2023, the disclosure of which is incorporated by reference herein in its entirety as part of the present application.

TECHNICAL FIELD

The present disclosure relates to the technical field of gear transmission, and in particular, to a herringbone planetary gear transmission device with a constant meshing characteristics constructed tooth pair.

BACKGROUND

For planetary gear transmission, external meshing between a sun gear and a plurality of planetary gears and internal meshing between an internal gear and the plurality of planetary gears are often used, and the plurality of planetary gears participate in meshing to share a load and achieve power splitting. Compared with an ordinary gear transmission system, planetary gear transmission has the advantages of compact structure, strong bearing capacity, high power density, large transmission ratio, steady transmission, and the like, and is widely used in fields of aerospace, vehicles and vessels, wind power generation, engineering machinery, and the like.

The patent No. CN 105114542 A discloses a planetary gear transmission device based on a herringbone gear with conjugate curves. A gear pair constructed in the above patent includes a convex-tooth gear and a concave-tooth gear, and a pair of gears with concave and convex tooth profiles in the gear pair needs machining by means of different cutters, which increases a manufacturing cost of the gear pair. The concave and convex tooth profiles lead to a limited curvature radius at a meshing point of the gear pair, thereby limiting further improvement of the bearing capacity of the gear pair. With regard to selection of a contact point, tooth surface interference occurs at a pitch point, making it difficult to achieve a zero sliding ratio. During meshing, the contact point moves in a tooth width direction, which leads to a time-varying meshing force. Therefore, there is an urgent need to innovate a tooth profile design based on an existing design theory of gears with spatial conjugate curves, so as to improve meshing performance of a meshing gear pair of a planetary gear transmission device with a constructed tooth pair and reduce a production and manufacturing cost of the planetary gear transmission device with a constructed tooth pair.

SUMMARY

In view of this, the present disclosure provides a herringbone planetary gear transmission device with a constant meshing characteristics constructed tooth pair. In the planetary gear transmission device, a sun gear with a constructed tooth pair, a planetary gear with a constructed tooth pair and an internal gear with a constructed tooth pair have the same normal tooth profile, with a constant curvature radius at a meshing point that tends to infinity, a constant sliding ratio and a constant direction of a meshing force action line, and the transmission device technically features low manufacturing cost, high bearing capacity, high transmission efficiency, low vibration and noise, and the like.

A herringbone planetary gear transmission device with a constant meshing characteristics constructed tooth pair disclosed in the present disclosure includes a sun gear with a constructed tooth pair, a planetary gear with a constructed tooth pair and an internal gear with a constructed tooth pair based on conjugate curves, where a normal tooth profile curve Γ_s1 of the sun gear with a constructed tooth pair, a normal tooth profile curve Γ_s2 of the planetary gear with a constructed tooth pair and a normal tooth profile curve Γ_s3 of the internal gear with a constructed tooth pair are continuous combined curves Γ_L with the same curve shape, and the continuous combined curves Γ_L include a combined curve Γ_L1 of an odd power function curve and a tangent at an inflection point thereof, a combined curve Γ_L2 of a sine function curve and a tangent at an inflection point thereof, a combined curve Γ_L3 of an epicycloid function curve and a tangent at an inflection point thereof, a combined curve Γ_L4 of an odd power function, a combined curve Γ_L5 of a sine function, or a combined curve Γ_L6 of an epicycloid function; the continuous combined curve is formed by two continuous curves, a connection point of the two continuous curves is an inflection point or a tangent point of the continuous combined curve, and the inflection point or the tangent point of the continuous combined curve is a designated point located on a meshing force action line of a gear pair; and normal tooth profiles are swept along given conjugate curves to obtain tooth surfaces of the sun gear with a constructed tooth pair, the planetary gear with a constructed tooth pair and the internal gear with a constructed tooth pair.

Further, in the herringbone planetary gear transmission device with a constant meshing characteristics constructed tooth pair, when the continuous combined curve Γ_L is the combined curve Γ_L1 of the odd power function curve and the tangent at the inflection point thereof, the continuous combined curve Γ_L is formed by an odd power function curve Γ_L12 and a tangent Γ_L11 at an inflection point of the odd power function curve; a rectangular coordinate system is established at the tangent point of the continuous combined curve, and an equation of the combined curve Γ_L1 of the odd power function curve and the tangent at the inflection point thereof is as follows:

$\{\begin{array}{c}{\Gamma }_{L11}:x_{10}=t,y_{10}=0\left(t_1\le t<0\right)\\ {\Gamma }_{L12}:x_{10}=t,y_{10}={\mathrm{At}}^{2n-1}\left(0\le t\le t_2\right)\end{array},$

• • where x₁₀ and y₁₀ are x-axis and y-axis coordinate values of the combined curve in the rectangular coordinate system, respectively; a parameter t is an independent variable of the equation; t₁ and t₂ are value ranges of the continuous curve; A is a coefficient of the equation; and n is a degree of the independent variable and is a positive integer.

Further, in the herringbone planetary gear transmission device with a constant meshing characteristics constructed tooth pair, when the continuous combined curve Γ_L is the combined curve Γ_L2 of the sine function curve and the tangent at the inflection point thereof, the continuous combined curve Γ_L is formed by a sine function curve Γ_L22 and a tangent Γ_L21 at an inflection point of the sine function curve; a rectangular coordinate system is established at the tangent point of the continuous combined curve, and an equation of the combined curve Γ_L2 of the sine function curve and the tangent at the inflection point thereof is as follows:

$\{\begin{array}{c}{\Gamma }_{L21}:x_{20}=t,y_{20}=\mathrm{kt}\left(t_1\le t<0\right)\\ {\Gamma }_{L22}:x_{20}=t,y_{20}=A\sin \left(\mathrm{Bt}\right)\left(0\le t\le t_2\right)\end{array},$

• • where x₂₀ and y₂₀ are x-axis and y-axis coordinate values of the combined curve in the rectangular coordinate system, respectively; a parameter t is an independent variable of the equation; t₁ and t₂ are value ranges of the continuous curve; k is a slope of the tangent at the inflection point of the sine function curve; and A and B are coefficients of the equation.

Further, in the herringbone planetary gear transmission device with a constant meshing characteristics constructed tooth pair, when the continuous combined curve Γ_L is the combined curve Γ_L3 of the epicycloid function curve and the tangent at the inflection point thereof, the continuous combined curve Γ_L is formed by an epicycloid function curve Γ_L32 and a tangent Γ_L31 at an inflection point of the epicycloid function curve; a rectangular coordinate system is established at the tangent point of the continuous combined curve, and an equation of the combined curve Γ_L3 of the epicycloid function curve and the tangent at the inflection point thereof is as follows:

$\{\begin{array}{c}{\Gamma }_{L31}:x_{30}=t,y_{30}=\mathrm{kt}\left(t_1\le t<0\right)\\ \begin{array}{c}{\Gamma }_{L32}:\\ x_{30}=\left(R+r\right)\sin t-e\sin \left(\left(R+r\right)t/r\right)\left(0\le t<t_2\right)\\ y_{30}=\left(R+r\right)\cos t-e\cos \left(\left(R+r\right)t/r\right)-\left(R+r-e\right)\end{array}\end{array},$

• • where x₃₀ and y₃₀ are x-axis and y-axis coordinate values of the combined curve in the rectangular coordinate system, respectively; a parameter t is an independent variable of the equation; t₁ and t₂ are value ranges of the continuous curve; k is a slope of the tangent at the inflection point of the epicycloid function curve; R and r are radii of a cycloidal moving circle and fixed circle, respectively; and e is an eccentric distance.

Further, in the herringbone planetary gear transmission device with a constant meshing characteristics constructed tooth pair, when the continuous combined curve Γ_L is the combined curve Γ_L4 of the odd power function, the continuous combined curve Γ_L is formed by a first odd power function curve Γ_L41 and a second odd power function curve Γ_L42; a rectangular coordinate system is established at the inflection point of the continuous combined curve, and an equation of the combined curve Γ_L4 of the odd power function is as follows:

$\{\begin{array}{c}{\Gamma }_{L41}:x_{40}=t,y_{40}={\mathrm{At}}^{2n1-1}\left(t_1\le t<0\right)\\ {\Gamma }_{L42}:x_{40}=t,y_{40}={\mathrm{Bt}}^{2n2-1}\left(0\le t<t_2\right)\end{array},$

where x₄₀ and y₄₀ are x-axis and y-axis coordinate values of the combined curve in the rectangular coordinate system, respectively; a parameter t is an independent variable of the equation; t₁ and t₂ are value ranges of the continuous curve; A and B are coefficients of the equation; and n1 and n2 are degrees of the independent variable and are positive integers.

Further, in the herringbone planetary gear transmission device with a constant meshing characteristics constructed tooth pair, when the continuous combined curve Γ_L is the combined curve Γ_L5 of the sine function, the continuous combined curve Γ_L is formed by a first sine function curve Γ_L51 and a second sine function curve Γ_L52; a rectangular coordinate system is established at the inflection point of the continuous combined curve, and an equation of the combined curve Γ_L5 of the sine function is as follows:

$\{\begin{array}{c}{\Gamma }_{L51}:x_{50}=t,y_{50}=A_1\sin \left(B_{1}t\right)\left(t_1\le t<0\right)\\ {\Gamma }_{L52}:x_{50}=t,y_{50}=A_2\sin \left(B_{2}t\right)\left(0\le t<t_2\right)\end{array},$

where x₅₀ and y₅₀ are x-axis and y-axis coordinate values of the combined curve in the rectangular coordinate system, respectively; a parameter t is an independent variable of the equation; t₁ and t₂ are value ranges of the continuous curve; and A₁, B₁, A₂ and B₂ are coefficients of the equation.

Further, in the herringbone planetary gear transmission device with a constant meshing characteristics constructed tooth pair, when the continuous combined curve Γ_L is the combined curve Γ_L6 of the epicycloid function, the continuous combined curve Γ_L is formed by a first epicycloid function curve Γ_L61 and a second epicycloid function curve Γ_L62; a rectangular coordinate system is established at the inflection point of the continuous combined curve, and an equation of the combined curve Γ_L6 of the epicycloid function is as follows:

$\{\begin{array}{c}\begin{array}{c}{\Gamma }_{L61}:\\ x_{60}=-\left(R_1+r_1\right)\sin t+e\sin \left(\left(R_1+r_1\right)t/r_1\right)\left(t_1\le t<0\right)\\ y_{60}=-\left(R_1+r_1\right)\cos t+e\cos \left(\left(R_1+r_1\right)t/r_1\right)-\left(R_1+r_1-e\right)\end{array}\\ \begin{array}{c}{\Gamma }_{L62}:\\ x_{60}=\left(R_2+r_2\right)\sin t-e\sin \left(\left(R_2+r_2\right)t/r_2\right)\left(0\le t<t_2\right)\\ y_{60}=\left(R_2+r_2\right)\cos t-e\cos \left(\left(R_2+r_2\right)t/r_2\right)-\left(R_2+r_2-e\right)\end{array}\end{array},$

• • where x₆₀ and y₆₀ are x-axis and y-axis coordinate values of the combined curve in the rectangular coordinate system, respectively; a parameter t is an independent variable of the equation; t₁ and t₂ are value ranges of the continuous curve; R₁ and r₁ are radii of a first epicycloid moving circle and fixed circle, respectively, and R₂ and r₂ are radii of a second epicycloid moving circle and fixed circle, respectively; and e is an eccentric distance.

Further, in the herringbone planetary gear transmission device with a constant meshing characteristics constructed tooth pair, a curve equation of the normal tooth profile curve Γ_s1 of the sun gear with a constructed tooth pair obtained by rotating the continuous combined curve Γ_L around an origin of the rectangular coordinate system by an angle α₁ is as follows:

$\{\begin{array}{c}{x}_{01}=x_{n0}\cos {\alpha }_1-y_{n0}\sin {\alpha }_1\\ y_{01}=x_{n0}\sin {\alpha }_1+y_{n0}\cos {\alpha }_1\end{array}\left(n=1,2,3,4,5,6\right),$

• • where x₀₁ and y₀₁ are x-axis and y-axis coordinate values of the normal tooth profile curve of the sun gear with a constructed tooth pair in the rectangular coordinate system, respectively.

Further, in the herringbone planetary gear transmission device with a constant meshing characteristics constructed tooth pair, a curve equation of the normal tooth profile curve Γ_s2 of the planetary gear with a constructed tooth pair obtained by rotating the normal tooth profile curve Γ_s1 of the sun gear with a constructed tooth pair around the origin of the rectangular coordinate system by an angle of 180° is as follows:

$\{\begin{array}{c}{x}_{02}=x_{01}\cos \left(180°\right)-y_{01}\sin \left(180°\right)\\ y_{02}=x_{01}\sin \left(180°\right)+y_{01}\cos \left(180°\right)\end{array},$

• • where x₀₂ and y₀₂ are x-axis and y-axis coordinate values of the normal tooth profile curve of the planetary gear with a constructed tooth pair in the rectangular coordinate system, respectively.

Further, in the herringbone planetary gear transmission device with a constant meshing characteristics constructed tooth pair, a curve equation of the normal tooth profile curve Γ_s3 of the internal gear with a constructed tooth pair obtained by rotating the normal tooth profile curve Γ_s2 of the planetary gear with a constructed tooth pair around the origin of the rectangular coordinate system by an angle of 180° is as follows:

$\{\begin{array}{c}{x}_{03}=x_{02}\cos \left(180°\right)-y_{02}\sin \left(180°\right)\\ y_{03}=x_{02}\sin \left(180°\right)+y_{02}\cos \left(180°\right)\end{array},$

• • where x₀₃ and y₀₃ are x-axis and y-axis coordinate values of the normal tooth profile curve of the internal gear with a constructed tooth pair in the rectangular coordinate system, respectively.

Further, in the herringbone planetary gear transmission device with a constant meshing characteristics constructed tooth pair, a tooth surface Σ₁ of the sun gear with a constructed tooth pair is obtained by sweeping the normal tooth profile curve Γ_s1 of the sun gear with a constructed tooth pair along a given helix, with a tooth surface equation as follows:

$\{\begin{array}{c}{x}_{\sum 1}=x_{01}\cos \theta -y_{01}\cos \beta \sin \theta +r_1\cos \theta \\ y_{\sum 1}=x_{01}\sin \theta +y_{01}\cos \beta \cos \theta +r_1\sin \theta \\ z_{\sum 1}=\pm \left(r_1\theta \cot \beta -y_{01}\sin \beta \right)\end{array},$

where in the sign “±”, the sign “+” indicates a left tooth surface, and the sign “−” indicates a right tooth surface; x_Σ1, y_Σ1 and z_Σ1 are coordinate values of the tooth surface of the sun gear with a constructed tooth pair, respectively; β is a helix angle of the gear pair, θ is an angle of a given contact line, and r₁ is a pitch radius of the sun gear with a constructed tooth pair.

Further, in the herringbone planetary gear transmission device with a constant meshing characteristics constructed tooth pair, a tooth surface Σ₂ of the planetary gear with a constructed tooth pair is obtained by sweeping the normal tooth profile curve Γ_s2 of the planetary gear with a constructed tooth pair along a given helix, with a tooth surface equation as follows:

$\{\begin{array}{c}{x}_{\sum 2}=x_{02}\cos \theta -y_{02}\cos \beta \sin \theta +r_2\cos \theta \\ y_{\sum 2}=x_{02}\sin \theta +y_{02}\cos \beta \cos \theta +r_2\sin \theta \\ z_{\sum 2}=\pm \left(r_2\theta \cot \beta -y_{02}\sin \beta \right)\end{array},$

where in the sign “±”, the sign “+” indicates a left tooth surface, and the sign “−” indicates a right tooth surface; x_Σ2, y_Σ2 and z_Σ2 are coordinate values of the tooth surface of the planetary gear with a constructed tooth pair, respectively; β is a helix angle of the gear pair, θ is an angle of a given contact line, and r₂ is a pitch radius of the planetary gear with a constructed tooth pair.

Further, in the herringbone planetary gear transmission device with a constant meshing characteristics constructed tooth pair, a tooth surface Σ₃ of the internal gear with a constructed tooth pair is obtained by sweeping the normal tooth profile curve Γ_s3 of the internal gear with a constructed tooth pair along a given helix, with a tooth surface equation as follows:

$\{\begin{array}{c}{x}_{\sum 3}=x_{03}\cos \theta -y_{03}\cos \beta \sin \theta +r_3\cos \theta \\ y_{\sum 3}=x_{03}\sin \theta +y_{03}\cos \beta \cos \theta +r_3\sin \theta \\ z_{\sum 3}=\pm \left(r_3\theta \cot \beta -y_{03}\sin \beta \right)\end{array},$

• • where in the sign “±”, the sign “+” indicates a left tooth surface, and the sign “−” indicates a right tooth surface; x_Σ3, y_Σ3 and z_Σ3 are coordinate values of the tooth surface of the internal gear with a constructed tooth pair, respectively; β is a helix angle of the gear pair, θ is an angle of a given contact line, and r₃ is a pitch radius of the internal gear with a constructed tooth pair.

Further, in the herringbone planetary gear transmission device with a constant meshing characteristics constructed tooth pair, a contact ratio of a meshing gear pair with a constructed tooth pair is designed as an integer, thereby achieving meshing transmission with a constant stiffness.

Further, in the herringbone planetary gear transmission device with a constant meshing characteristics constructed tooth pair, the sun gear with a constructed tooth pair, the planetary gear with a constructed tooth pair and the internal gear with a constructed tooth pair each are designed in the form of a herringbone gear, thereby achieving a constant meshing force action line.

Compared with the prior art, the present disclosure has the following beneficial effects: A sun gear with a constructed tooth pair, a planetary gear with a constructed tooth pair and an internal gear with a constructed tooth pair in the present disclosure have the same normal tooth profile, and can be machined by using the same cutter, thus reducing a manufacturing cost. A curvature radius at a meshing point is constant and tends to infinity, which improves the bearing capacity of a gear pair. A sliding ratio during meshing is constant and may be designed as a zero sliding ratio, which improves transmission efficiency of the gear pair and reduces wear during transmission. The sun gear with a constructed tooth pair, the planetary gear with a constructed tooth pair and the internal gear with a constructed tooth pair each are in the form of a herringbone gear, thereby achieving a constant meshing force action line. A contact ratio of the meshing gear pair is designed as an integer, which can achieve a constant meshing stiffness, thus greatly reducing vibration noise of the gear pair.

BRIEF DESCRIPTION OF THE DRAWINGS

To more clearly describe the technical solutions of the embodiments of the present disclosure, the accompanying drawings required in the embodiments are described briefly below. It should be understood that the following accompanying drawings illustrate only some embodiments of the present disclosure and therefore should not be construed as a limitation on the scope thereof. For those of ordinary skill in the art, other relevant accompanying drawings can also be obtained from these accompanying drawings without any creative effort.

FIG. 1 is a schematic diagram of a combined curve of an odd power function curve and a tangent at an inflection point thereof according to an embodiment of the present disclosure;

FIG. 2 is a schematic diagram illustrating formation of a normal tooth profile in a herringbone planetary gear transmission device with a constant meshing characteristics constructed tooth pair having a combined curve of an odd power function curve and a tangent at an inflection point thereof as a tooth profile curve according to an embodiment of the present disclosure;

FIG. 3 is a schematic diagram illustrating construction of a gear tooth surface in a herringbone planetary gear transmission device with a constant meshing characteristics constructed tooth pair having a combined curve of an odd power function curve and a tangent at an inflection point thereof as a tooth profile curve according to an embodiment of the present disclosure;

FIG. 4 is a schematic entity diagram of a herringbone planetary gear transmission device with a constant meshing characteristics constructed tooth pair having a combined curve of an odd power function curve and a tangent at an inflection point thereof as a tooth profile curve according to an embodiment of the present disclosure;

FIG. 5 is a schematic diagram illustrating a curvature radius at a meshing point of a gear pair of a herringbone planetary gear transmission device with a constant meshing characteristics constructed tooth pair having a combined curve of an odd power function curve and a tangent at an inflection point thereof as a tooth profile curve according to an embodiment of the present disclosure;

FIG. 6 is a schematic diagram of a designated point on a meshing force action line of a gear pair of a herringbone planetary gear transmission device with a constant meshing characteristics constructed tooth pair according to an embodiment of the present disclosure;

FIG. 7 is a schematic diagram illustrating a sliding ratio at a meshing point of a gear pair of a herringbone planetary gear transmission device with a constant meshing characteristics constructed tooth pair having a combined curve of an odd power function curve and a tangent at an inflection point thereof as a tooth profile curve according to an embodiment of the present disclosure; and

FIG. 8 is a schematic diagram illustrating a meshing force of a gear pair of a herringbone planetary gear transmission device with a constant meshing characteristics constructed tooth pair according to an embodiment of the present disclosure.

DESCRIPTION OF REFERENCE SIGNS

• • 1—Sun gear with a constructed tooth pair, 2—Planetary gear with a constructed tooth pair, 3—Internal gear with a constructed tooth pair.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The present disclosure will be further described in detail below with reference to FIGS. 1 to 8.

In a herringbone planetary gear transmission device with a constant meshing characteristics constructed tooth pair disclosed in the present disclosure, as shown in FIGS. 1 to 8, normal tooth profile curves of a sun gear 1 with a constructed tooth pair, a planetary gear 2 with a constructed tooth pair and an internal gear 3 with a constructed tooth pair are continuous combined curves with the same curve shape, and each meshing point of the sun gear 1 with a constructed tooth pair, the planetary gear 2 with a constructed tooth pair and the internal gear 3 with a constructed tooth pair is at an inflection point or a tangent point of the continuous combined curve.

In the embodiment of the present disclosure, basic parameters of the herringbone planetary gear transmission device with a constant meshing characteristics constructed tooth pair are as follows: Module m=8, number of teeth of the sun gear 1 with a constructed tooth pair: z₁=20, number of teeth of the planetary gear 2 with a constructed tooth pair: z₂=31, number of teeth of the internal gear 3 with a constructed tooth pair: z₃=82, addendum coefficient h_a*=0.5, tip clearance coefficient c*=0.2, addendum h_a=4 mm, dedendum h_f=5.6 mm, helix angle β=30°, and unilateral tooth width w=50 mm.

With a combined curve of an odd power function curve and a tangent at an inflection point thereof as an example, the combined curve of the odd power function curve and the tangent at the inflection point thereof was drawn in a rectangular coordinate system σ₁ (O₁-x₁,y₁), as shown in FIG. 1. With a coefficient A=1.2 and n=2, an equation of a combined curve Γ_L1 (formed by an odd power function curve Γ_L12 and a tangent Γ_L11 at an inflection point of the odd power function curve) of an odd power function curve and a tangent at an inflection point thereof is as follows:

$\{\begin{array}{c}{\Gamma }_{L11}:x_{10}=t,y_{10}=0\left(t_1\le t<0\right)\\ {\Gamma }_{L21}:x_{10}=t,y_{10}=1.2t^3\left(0\le t\le t_2\right)\end{array},$

where x₁₀ and y₁₀ are x-axis and y-axis coordinate values of the combined curve in the rectangular coordinate system σ₁, respectively; a parameter t is an independent variable of the equation; and t₁ and t₂ are value ranges of the continuous curves.

Provided is a schematic diagram illustrating formation of normal tooth profiles of gears with a constructed tooth pair having a combined curve of an odd power function curve and a tangent at an inflection point thereof as a tooth profile curve according to an embodiment of the present disclosure, with an inflection point P being a meshing point, as shown in FIG. 2. In the figure, a tooth root of the sun gear 1 with a constructed tooth pair, a tooth root of the planetary gear 2 with a constructed tooth pair and a tooth root of the internal gear 3 with a constructed tooth pair are tangent segments. The tooth root of the sun gear 1 with a constructed tooth pair, a tooth tip of the planetary gear 2 with a constructed tooth pair and a tooth tip of the internal gear 3 with a constructed tooth pair are cubic power function curve segments. When the continuous combined curve Γ_L rotates around an origin of the rectangular coordinate system by an angle α₁ to obtain a normal tooth profile curve Γs of the sun gear with a constructed tooth pair, the value of the rotation angle α₁ needs to be determined according to specific parameters of the gear, with a general value range as follows: 0°<α₁<180°. A specific formation process and a tooth profile curve equation of the normal tooth profile of the gear with a constructed tooth pair are as follows:

The combined curve Γ_L1 of the odd power function curve and the tangent at the inflection point thereof rotates around the rectangular coordinate system σ₁ by an angle of α₁=120° to obtain the normal tooth profile curve Γ_s1 of the sun gear 1 with a constructed tooth pair, with a curve equation as follows:

$\{\begin{array}{c}{x}_{01}=x_{10}\cos \left(120°\right)-y_{10}\sin \left(120°\right)\\ y_{01}=x_{10}\sin \left(120°\right)+y_{10}\cos \left(120°\right)\end{array},$

• • where x₀₁ and y₀₁ are x-axis and y-axis coordinate values of the normal tooth profile curve of the sun gear 1 with a constructed tooth pair in the rectangular coordinate system σ₁, respectively.

A normal tooth profile curve Γ_s2 of the planetary gear 2 with a constructed tooth pair is obtained by rotating the normal tooth profile curve Γ_s1 of the sun gear 1 with a constructed tooth pair around the origin of the rectangular coordinate system σ₁ by an angle of 180°, with a curve equation as follows:

$\{\begin{array}{c}{x}_{02}=x_{01}\cos \left(180°\right)-y_{01}\sin \left(180°\right)\\ y_{02}=x_{01}\sin \left(180°\right)+y_{01}\cos \left(180°\right)\end{array},$

• • where x₀₂ and y₀₂ are x-axis and y-axis coordinate values of the normal tooth profile curve of the planetary gear 2 with a constructed tooth pair in the rectangular coordinate system σ₁, respectively.

A normal tooth profile curve Γ_s3 of the internal gear 3 with a constructed tooth pair is obtained by rotating the normal tooth profile curve Γ_s2 of the planetary gear 2 with a constructed tooth pair around the origin of the rectangular coordinate system σ₁ by an angle of 180°, with a curve equation as follows:

$\{\begin{array}{c}{x}_{03}=x_{02}\cos \left(180°\right)-y_{02}\sin \left(180°\right)\\ y_{03}=x_{02}\sin \left(180°\right)+y_{02}\cos \left(180°\right)\end{array},$

where x₀₃ and y₀₃ are x-axis and y-axis coordinate values of the normal tooth profile curve of the internal gear 3 with a constructed tooth pair in the rectangular coordinate system σ₁, respectively.

FIG. 3 is a schematic diagram illustrating construction of tooth surfaces of gears with a constructed tooth pair having a combined curve of an odd power function curve and a tangent at an inflection point thereof as a tooth profile curve according to an embodiment of the present disclosure. A specific construction process and a tooth surface equation of the tooth surface of each gear with a constructed tooth pair are as follows:

A tooth surface Σ₁ of the sun gear 1 with a constructed tooth pair is obtained by sweeping the normal tooth profile curve Γ_s1 of the sun gear 1 with a constructed tooth pair along a given helix, with a tooth surface equation as follows:

$\{\begin{array}{c}{x}_{\sum 1}=x_{01}\cos \theta -y_{01}\cos \left(30°\right)\sin \theta +92.376\cos \theta \\ y_{\sum 1}=x_{01}\sin \theta +y_{01}\cos \left(30°\right)\cos \theta +92.376\sin \theta \\ z_{\sum 1}=\pm \left[92.376\theta \cot \left(30°\right)-y_{01}\sin \left(30°\right)\right]\end{array},$

• • where in the sign “±”, the sign “+” indicates a left tooth surface, and the sign “−” indicates a right tooth surface; and x_Σ1, y_Σ1 and z_Σ1 are coordinate values of the tooth surface of the sun gear 1 with a constructed tooth pair.

Similarly, a tooth surface Σ₂ of the planetary gear 2 with a constructed tooth pair is obtained by sweeping the normal tooth profile curve Γ_s2 of the planetary gear 2 with a constructed tooth pair along a given helix, with a tooth surface equation as follows:

$\{\begin{array}{c}{x}_{\sum 2}=x_{02}\cos \theta -y_{02}\cos \left(30°\right)\sin \theta +143.183\cos \theta \\ y_{\sum 2}=x_{02}\sin \theta +y_{02}\cos \left(30°\right)\cos \theta +143.183\sin \theta \\ z_{\sum 2}=\pm \left[143.183\theta \cot \left(30°\right)-y_{02}\sin \left(30°\right)\right]\end{array},$

• • where in the sign “±”, the sign “+” indicates a left tooth surface, and the sign “−” indicates a right tooth surface; x_Σ2, y_Σ2 and z_Σ2 are coordinate values of the tooth surface of the planetary gear 2 with a constructed tooth pair; and θ is an angle of a given contact line.

Similarly, a tooth surface Σ₃ of the internal gear 3 with a constructed tooth pair is obtained by sweeping the normal tooth profile curve Γ_s3 of the internal gear 3 with a constructed tooth pair along a given helix, with a tooth surface equation as follows:

$\{\begin{array}{c}{x}_{\sum 3}=x_{03}\cos \theta -y_{03}\cos \left(30°\right)\sin \theta +378.742\cos \theta \\ y_{\sum 3}=x_{03}\sin \theta +y_{03}\cos \left(30°\right)\cos \theta +378.742\sin \theta \\ z_{\sum 3}=\pm \left[378.742\theta \cot \left(30°\right)-y_{02}\sin \left(30°\right)\right]\end{array},$

where in the sign “±”, the sign “+” indicates a left tooth surface, and the sign “−” indicates a right tooth surface; x_Σ3, y_Σ3 and z_Σ3 are coordinate values of the tooth surface of the internal gear 3 with a constructed tooth pair; and θ is an angle of a given contact line.

FIG. 4 is a schematic entity diagram of a herringbone planetary gear transmission device with a constructed tooth pair having a combined curve of an odd power function curve and a tangent at an inflection point thereof as a tooth profile curve according to an embodiment of the present disclosure. An addendum circle and a dedendum circle are generated by stretching. Trimming, stitching, rounding, and other operations are performed on the tooth surfaces of the sun gear 1 with a constructed tooth pair, the planetary gear 2 with a constructed tooth pair and the internal gear 3 with a constructed tooth pair to obtain a schematic entity diagram of the herringbone planetary gear transmission device with a constructed tooth pair having the same tooth profile of continuous combined curves.

In the embodiment of the present disclosure, the normal tooth profile curves of the sun gear 1 with a constructed tooth pair, the planetary gear 2 with a constructed tooth pair and the internal gear 3 with a constructed tooth pair each may alternatively be a combined curve Γ_L2 of a sine function curve and a tangent at an inflection point thereof, a combined curve Γ_L3 of an epicycloid function curve and a tangent at an inflection point thereof, a combined curve Γ_L4 of an odd power function, a combined curve Γ_L5 of a sine function, or a combined curve Γ_L6 of an epicycloid function, with a curve equation as follows:

When the continuous combined curve Γ_L is the combined curve Γ_L2 of the sine function curve and the tangent at the inflection point thereof, the continuous combined curve Γ_L2 is formed by a sine function curve Γ_L22 and a tangent Γ_L21 at an inflection point of the sine function curve; a rectangular coordinate system is established at the tangent point of the continuous combined curve, and an equation of the combined curve Γ_L2 of the sine function curve and the tangent at the inflection point thereof is as follows:

$\{\begin{array}{c}{\Gamma }_{L21}:x_{20}=t,y_{20}=\mathrm{kt}\left(t_1\le t<0\right)\\ {\Gamma }_{L22}:x_{20}=t,y_{20}=A\sin \left(\mathrm{Bt}\right)\left(0\le t\le t_2\right)\end{array},$

• • where x₂₀ and y₂₀ are x-axis and y-axis coordinate values of the combined curve in the rectangular coordinate system, respectively; a parameter t is an independent variable of the equation; t₁ and t₂ are value ranges of the continuous curve; k is a slope of the tangent at the inflection point of the sine function curve; and A and B are coefficients of the equation.

When the continuous combined curve Γ_L is the combined curve Γ_L3 of the epicycloid function curve and the tangent at the inflection point thereof, the continuous combined curve Γ_L3 is formed by an epicycloid function curve Γ_L32 and a tangent Γ_L31 at an inflection point of the epicycloid function curve; a rectangular coordinate system is established at the tangent point of the continuous combined curve, and an equation of the combined curve Γ_L3 of the epicycloid function curve and the tangent at the inflection point thereof is as follows:

$\{\begin{array}{c}{\Gamma }_{L31}:x_{30}=t,y_{30}=\mathrm{kt}\left(t_1\le t<0\right)\\ \begin{array}{c}{\Gamma }_{L32}:\\ x_{30}=\left(R+r\right)\sin t-e\sin \left(\left(R+r\right)t/r\right)\left(0\le t<t_2\right)\\ y_{30}=\left(R+r\right)\cos t-e\cos \left(\left(R+r\right)t/r\right)-\left(R+r-e\right)\end{array}\end{array},$

• • where x₃₀ and y₃₀ are x-axis and y-axis coordinate values of the combined curve in the rectangular coordinate system, respectively; a parameter t is an independent variable of the equation; t₁ and t₂ are value ranges of the continuous curve; k is a slope of the tangent at the inflection point of the epicycloid function curve; R and r are radii of a cycloidal moving circle and fixed circle, respectively; and e is an eccentric distance.

When the continuous combined curve Γ_L is the combined curve Γ_L4 of the odd power function, the continuous combined curve Γ_L4 is formed by a first odd power function curve Γ_L41 and a second odd power function curve Γ_L42; a rectangular coordinate system is established at the inflection point of the continuous combined curve, and an equation of the combined curve Γ_L4 of the odd power function is as follows:

$\{\begin{array}{c}{\Gamma }_{L41}:x_{40}=t,y_{40}={\mathrm{At}}^{2n1-1}\left(t_1\le t<0\right)\\ {\Gamma }_{L42}:x_{40}=t,y_{40}={\mathrm{Bt}}^{2n2-1}\left(0\le t\le t_2\right)\end{array},$

where x₄₀ and y₄₀ are x-axis and y-axis coordinate values of the combined curve in the rectangular coordinate system, respectively; a parameter t is an independent variable of the equation; t₁ and t₂ are value ranges of the continuous curve; A and B are coefficients of the equation; and n1 and n2 are degrees of the independent variable and are positive integers.

When the continuous combined curve Γ_L is the combined curve Γ_L5 of the sine function, the continuous combined curve Γ_L5 is formed by a first sine function curve Γ_L51 and a second sine function curve Γ_L52; a rectangular coordinate system is established at the inflection point of the continuous combined curve, and an equation of the combined curve Γ_L5 of the sine function is as follows:

$\{\begin{array}{c}{\Gamma }_{L51}:x_{50}=t,y_{50}=A_1\sin \left(B_{1}t\right)\left(t_1\le t<0\right)\\ {\Gamma }_{L52}:x_{50}=t,y_{50}=A_2\sin \left(B_{2}t\right)\left(0\le t\le t_2\right)\end{array},$

• • where x₅₀ and y₅₀ are x-axis and y-axis coordinate values of the combined curve in the rectangular coordinate system, respectively; a parameter t is an independent variable of the equation; t₁ and t₂ are value ranges of the continuous curve; and A₁, B₁, A₂ and B₂ are coefficients of the equation.

When the continuous combined curve Γ_L is the combined curve Γ_L6 of the epicycloid function, the continuous combined curve Γ_L6 is formed by a first epicycloid function curve Γ_L61 and a second epicycloid function curve Γ_L62; a rectangular coordinate system is established at the inflection point of the continuous combined curve, and an equation of the combined curve Γ_L6 of the epicycloid function is as follows:

$\{\begin{array}{c}\begin{array}{c}{\Gamma }_{L61}:\\ x_{60}=\left(R_1+r_1\right)\sin t+e\sin \left(\left(R_1+r_1\right)t/r_1\right)\left(t_1\le t<0\right)\\ y_{60}=\left(R_1+r_1\right)\cos t+e\cos \left(\left(R_1+r_1\right)t/r_1\right)+\left(R_1+r_1-e\right)\end{array}\\ \begin{array}{c}{\Gamma }_{L62}:\\ x_{60}=\left(R_2+r_2\right)\sin t-e\sin \left(\left(R_2+r_2\right)t/r_2\right)\left(0\le t<t_2\right)\\ y_{60}=\left(R_2+r_2\right)\cos t-e\cos \left(\left(R_2+r_2\right)t/r_2\right)-\left(R_2+r_2-e\right)\end{array}\end{array},$

where x₆₀ and y₆₀ are x-axis and y-axis coordinate values of the combined curve in the rectangular coordinate system, respectively; a parameter t is an independent variable of the equation; t₁ and t₂ are value ranges of the continuous curve; R₁ and r₁ are radii of a first epicycloid moving circle and fixed circle, respectively, and R₂ and r₂ are radii of a second epicycloid moving circle and fixed circle, respectively; and e is an eccentric distance.

In the present disclosure, the inflection point or the tangent point of the continuous combined curve is as follows:

• • 1 When the continuous combined curve is a combined curve of an odd power function, a combined curve of a sine function or a combined curve of an epicycloid function, a connection point of the continuous combined curve is an inflection point, that is, a concave-convex boundary point of the curve, a second derivative of the curve is zero at this point, and second order derivative signs near two sides of this point are opposite;
  • 2 when the combined curve is a combined curve of an odd power function curve and a tangent at an inflection point thereof, a combined curve of a sine function curve and a tangent at an inflection point thereof, or a combined curve of an epicycloid and a tangent at an inflection point thereof, a connection point of the combined curve is an inflection point of the odd power function curve, the sine function curve or the epicycloid (meaning the same as 1), which is also a tangent point of the odd power function curve, the sine function curve or the epicycloid at the tangent.

At the inflection point or the tangent point of the continuous combined curve, the curvature of the curve is zero, that is, the curvature radius tends to infinity. When the continuous combined curve is the combined curve of the odd power function, the combined curve of the sine function, or the combined curve of the epicycloid function, the curvature radii on two sides of the inflection point tend to infinity; or when the continuous combined curve is the combined curve of the odd power function curve and the tangent at the inflection point thereof, the combined curve of the sine function curve and the tangent at the inflection point thereof, or the combined curve of the epicycloid function curve and the tangent at the inflection point thereof, the curvature radius at the inflection point on the side of the odd power function curve, the sine function curve or the epicycloid function curve tends to infinity, and the curvature radius on the side of the tangent is infinite. The curvature radius of the combined curve is calculated based on given parameters in the embodiment, as shown in FIG. 5. The curvature radius of a straight line segment in the combined curve in FIG. 5 is infinite, the curvature radius at the inflection point tends to infinity, and the curvature radius of the cubic power function curve segment gradually decreases and then increases, but is still far less than the curvature radius at the inflection point. This means that the curvature radius at a contact point of the gear pair with a constructed tooth pair tends to infinity, which improves the bearing capacity of the gear pair with a constructed tooth pair.

In the embodiment of the present disclosure, the inflection point or the tangent point of the continuous combined curve is a designated point located on a meshing force action line of the gear pair. The designated point is specifically defined as a given point at a pitch point or near the pitch point on the meshing force action line of the gear pair with a constructed tooth pair that is a straight line which forms a certain angle (pressure angle) with a horizontal axis by means of the pitch point. FIG. 6 is a schematic diagram of a designated point on a meshing force action line of a gear pair. In the figure, P is the designated point on the meshing force action line of the gear pair; P₁ and P₂ are limit points of the position range of the designated point; a straight line N₁N₂ is the meshing force action line of the gear pair; ax is a pressure angle; O₁ and O₂ are central points of the sun gear 1 with a constructed tooth pair and the planetary gear 2 with a constructed tooth pair, respectively; and r₁ and r₂, r_a1 and r_a2, and r_f1 and r_f2 are pitch radii, addendum circle radii, and dedendum circle radii of the sun gear 1 with a constructed tooth pair and the planetary gear 2 with a constructed tooth pair, respectively. The designated point P is a given point usually located at a pitch point or near either of two sides of the pitch point, and a variation area of the designated point does not exceed a half of a tooth height.

According to the principle of gear meshing, it can be known that there is no relative sliding between tooth surfaces when the gear pair with a constructed tooth pair meshes at the pitch point. FIG. 7 is a schematic diagram illustrating a sliding ratio at a meshing point of a gear pair of a herringbone planetary gear transmission device with a constant meshing characteristics constructed tooth pair having a combined curve of an odd power function curve and a tangent at an inflection point thereof as a tooth profile curve according to an embodiment of the present disclosure. Since the gear pair of the herringbone planetary gear transmission device with a constant meshing characteristics constructed tooth pair having the same tooth profile of continuous combined curves meshes at a pitch point at any time in the embodiment, the gear pair with a constructed tooth pair can achieve zero-sliding meshing. When the inflection point or the tangent point of the combined curve does not coincide with the pitch point, the sliding ratio of the gear pair with a constructed tooth pair is also constant but is not zero. A closer inflection point or tangent point of the continuous curve to the pitch point indicates a smaller sliding ratio of the gear pair with a constructed tooth pair, vice versa. When the inflection point or the tangent point coincides with the pitch point, the gear pair with a constructed tooth pair can achieve zero-sliding meshing transmission, which reduces the wear between tooth surfaces and improves the transmission efficiency of the gear pair with a constructed tooth pair.

Further, when the gear pair with a constructed tooth pair having the same tooth profile of the continuous combined curves has a contact ratio designed as an integer, the meshing stiffness of the gear pair with a constructed tooth pair is a constant, and at this time, a meshing force of the gear pair with a constructed tooth pair at any meshing position is determined. Therefore, when the contact ratio is designed as an integer, the gear pair with a constructed tooth pair having the same tooth profile of the continuous combined curves has a constant meshing state at any time, which effectively ensures stability of dynamic meshing performance of the gear pair with a constructed tooth pair and can effectively reduce vibration noise of the gear pair with a constructed tooth pair.

A schematic diagram illustrating a meshing force of a meshing gear pair is established with the herringbone planetary gear transmission device with a constant meshing characteristics constructed tooth pair as an example, as shown in FIG. 8. For a right side of the herringbone meshing gear pair with a constructed tooth pair, a meshing force F_n1 during meshing of the gear pair may be decomposed into an axial force F_a1, a radial force F_r1, and a circumferential force F_t1. For a left side of the herringbone gear pair with a constructed tooth pair, a meshing force F_n2 during gear meshing may be decomposed into an axial force F_a2, a radial force F_r2, and a circumferential force F_t2. When only the right side of the gear pair is considered, during meshing, with the movement of the meshing point in a tooth width direction, the meshing force F_n1 of the gear pair also translates in the tooth width direction, and a change in stress state leads to a periodic change in excitation factors of the gear pair, which seriously affects dynamic meshing performance of the gear pair. When the two sides of the herringbone gear pair with a constructed tooth pair are both considered, since left and right side teeth are completely symmetrical, the axial forces F_a1 and F_a2 on tooth surfaces of the two sides cancel out each other, the radial forces F_r1 and F_r2 on the two sides are simplified to a central position of the herringbone gear pair with a constructed tooth pair in the tooth width direction, and the circumferential forces F_t1 and F_t2 on the two sides are also simplified to the central position of the herringbone gear pair with a constructed tooth pair in the tooth width direction. Therefore, a position and a direction of an action line of a combined force F_n of the meshing forces F_n1 and F_n2 of the herringbone meshing gear pair with a constructed tooth pair are determined at any time, which improves stability of the herringbone meshing gear pair with a constructed tooth pair during meshing.

Finally, it should be noted that the above embodiments are only intended to explain, rather than to limit the technical solutions of the present disclosure. Although the present disclosure is described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that modifications or equivalent substitutions may be made to the technical solutions of the present disclosure without departing from the purpose and scope of the technical solutions of the present disclosure, and such modifications or equivalent substitutions should fall within the scope of the claims of the present disclosure.

Claims

1. A herringbone planetary gear transmission device with a constant meshing characteristics constructed tooth pair, comprising a sun gear (1) with a constructed tooth pair, a planetary gear (2) with a constructed tooth pair and an internal gear (3) with a constructed tooth pair based on conjugate curves, wherein a normal tooth profile curve Γs1 of the sun gear (1) with a constructed tooth pair, a normal tooth profile curve Γs2 of the planetary gear (2) with a constructed tooth pair and a normal tooth profile curve Γs3 of the internal gear (3) with a constructed tooth pair are continuous combined curves ΓL with the same curve shape, and the continuous combined curves ΓL comprise a combined curve ΓL1 of an odd power function curve and a tangent at an inflection point thereof, a combined curve ΓL2 of a sine function curve and a tangent at an inflection point thereof, a combined curve ΓL3 of an epicycloid function curve and a tangent at an inflection point thereof, a combined curve ΓL4 of an odd power function, a combined curve ΓL5 of a sine function, or a combined curve ΓL6 of an epicycloid function; the continuous combined curve is formed by two continuous curves, a connection point of the two continuous curves is an inflection point or a tangent point of the continuous combined curve, and the inflection point or the tangent point of the continuous combined curve is a designated point located on a meshing force action line of a gear pair; and normal tooth profiles are swept along given conjugate curves to obtain tooth surfaces of the sun gear (1) with a constructed tooth pair, the planetary gear (2) with a constructed tooth pair and the internal gear (3) with a constructed tooth pair.

2. The herringbone planetary gear transmission device with a constant meshing characteristics constructed tooth pair according to claim 1, wherein when the continuous combined curve ΓL is the combined curve ΓL1 of the odd power function curve and the tangent at the inflection point thereof, the continuous combined curve ΓL is formed by an odd power function curve ΓL12 and a tangent ΓL11 at an inflection point of the odd power function curve; a rectangular coordinate system is established at the tangent point of the continuous combined curve, and an equation of the combined curve ΓL1 of the odd power function curve and the tangent at the inflection point thereof is as follows:

3. The herringbone planetary gear transmission device with a constant meshing characteristics constructed tooth pair according to claim 1, wherein when the continuous combined curve ΓL is the combined curve ΓL2 of the sine function curve and the tangent at the inflection point thereof, the continuous combined curve ΓL is formed by a sine function curve ΓL22 and a tangent ΓL21 at an inflection point of the sine function curve; a rectangular coordinate system is established at the tangent point of the continuous combined curve, and an equation of the combined curve ΓL2 of the sine function curve and the tangent at the inflection point thereof is as follows:

4. The herringbone planetary gear transmission device with a constant meshing characteristics constructed tooth pair according to claim 1, wherein when the continuous combined curve ΓL is the combined curve ΓL3 of the epicycloid function curve and the tangent at the inflection point thereof, the continuous combined curve ΓL is formed by an epicycloid function curve ΓL32 and a tangent ΓL31 at an inflection point of the epicycloid function curve; a rectangular coordinate system is established at the tangent point of the continuous combined curve, and an equation of the combined curve ΓL3 of the epicycloid function curve and the tangent at the inflection point thereof is as follows:

5. The herringbone planetary gear transmission device with a constant meshing characteristics constructed tooth pair according to claim 1, wherein when the continuous combined curve ΓL is the combined curve ΓL4 of the odd power function, the continuous combined curve ΓL is formed by a first odd power function curve ΓL41 and a second odd power function curve ΓL42; a rectangular coordinate system is established at the inflection point of the continuous combined curve, and an equation of the combined curve ΓL4 of the odd power function is as follows:

6. The herringbone planetary gear transmission device with a constant meshing characteristics constructed tooth pair according to claim 1, wherein when the continuous combined curve ΓL is the combined curve ΓL5 of the sine function, the continuous combined curve ΓL is formed by a first sine function curve ΓL51 and a second sine function curve ΓL52; a rectangular coordinate system is established at the inflection point of the continuous combined curve, and an equation of the combined curve ΓL5 of the sine function is as follows:

7. The herringbone planetary gear transmission device with a constant meshing characteristics constructed tooth pair according to claim 1, wherein when the continuous combined curve ΓL is the combined curve ΓL6 of the epicycloid function, the continuous combined curve ΓL is formed by a first epicycloid function curve ΓL61 and a second epicycloid function curve ΓL62; a rectangular coordinate system is established at the inflection point of the continuous combined curve, and an equation of the combined curve ΓL6 of the epicycloid function is as follows:

8. The herringbone planetary gear transmission device with a constant meshing characteristics constructed tooth pair according to claim 2, wherein a curve equation of the normal tooth profile curve Γs1 of the sun gear (1) with a constructed tooth pair obtained by rotating the continuous combined curve ΓL around an origin of the rectangular coordinate system by an angle α1 is as follows:

9. The herringbone planetary gear transmission device with a constant meshing characteristics constructed tooth pair according to claim 8, wherein a curve equation of the normal tooth profile curve Γs2 of the planetary gear (2) with a constructed tooth pair obtained by rotating the normal tooth profile curve Γs1 of the sun gear (1) with a constructed tooth pair around the origin of the rectangular coordinate system by an angle of 180° is as follows:

10. The herringbone planetary gear transmission device with a constant meshing characteristics constructed tooth pair according to claim 9, wherein a curve equation of the normal tooth profile curve Γs3 of the internal gear (3) with a constructed tooth pair obtained by rotating the normal tooth profile curve Γs2 of the planetary gear (2) with a constructed tooth pair around the origin of the rectangular coordinate system by an angle of 180° is as follows:

11. The herringbone planetary gear transmission device with a constant meshing characteristics constructed tooth pair according to claim 8, wherein a tooth surface Σ1 of the sun gear (1) with a constructed tooth pair is obtained by sweeping the normal tooth profile curve Γs1 of the sun gear (1) with a constructed tooth pair along a given helix, with a tooth surface equation as follows:

12. The herringbone planetary gear transmission device with a constant meshing characteristics constructed tooth pair according to claim 9, wherein a tooth surface Σ2 of the planetary gear (2) with a constructed tooth pair is obtained by sweeping the normal tooth profile curve Γs2 of the planetary gear (2) with a constructed tooth pair along a given helix, with a tooth surface equation as follows:

13. The herringbone planetary gear transmission device with a constant meshing characteristics constructed tooth pair according to claim 10, wherein a tooth surface Σ3 of the internal gear with a constructed tooth pair is obtained by sweeping the normal tooth profile curve Γs3 of the internal gear (3) with a constructed tooth pair along a given helix, with a tooth surface equation as follows:

14. The herringbone planetary gear transmission device with a constant meshing characteristics constructed tooth pair according to claim 1, wherein a contact ratio of a meshing gear pair with a constructed tooth pair is designed as an integer, thereby achieving meshing transmission with a constant stiffness.

15. The herringbone planetary gear transmission device with a constant meshing characteristics constructed tooth pair according to claim 1, wherein the sun gear (1) with a constructed tooth pair, the planetary gear (2) with a constructed tooth pair and the internal gear (3) with a constructed tooth pair each are in the form of a herringbone gear, thereby achieving a constant meshing force action line.

16. The herringbone planetary gear transmission device with a constant meshing characteristics constructed tooth pair according to claim 3, wherein a curve equation of the normal tooth profile curve Γs1 of the sun gear (1) with a constructed tooth pair obtained by rotating the continuous combined curve ΓL around an origin of the rectangular coordinate system by an angle α1 is as follows:

17. The herringbone planetary gear transmission device with a constant meshing characteristics constructed tooth pair according to claim 4, wherein a curve equation of the normal tooth profile curve Γs1 of the sun gear (1) with a constructed tooth pair obtained by rotating the continuous combined curve ΓL around an origin of the rectangular coordinate system by an angle α1 is as follows:

18. The herringbone planetary gear transmission device with a constant meshing characteristics constructed tooth pair according to claim 5, wherein a curve equation of the normal tooth profile curve Γs1 of the sun gear (1) with a constructed tooth pair obtained by rotating the continuous combined curve ΓL around an origin of the rectangular coordinate system by an angle α1 is as follows:

19. The herringbone planetary gear transmission device with a constant meshing characteristics constructed tooth pair according to claim 6, wherein a curve equation of the normal tooth profile curve Γs1 of the sun gear (1) with a constructed tooth pair obtained by rotating the continuous combined curve ΓL around an origin of the rectangular coordinate system by an angle α1 is as follows:

20. The herringbone planetary gear transmission device with a constant meshing characteristics constructed tooth pair according to claim 7, wherein a curve equation of the normal tooth profile curve Γs1 of the sun gear (1) with a constructed tooth pair obtained by rotating the continuous combined curve ΓL around an origin of the rectangular coordinate system by an angle α1 is as follows: