Design method of tapered tooth unequal addendum spiral bevel gear for aero-engine

Abstract

This invention discloses a design method for a tapered, unequal-clearance helical bevel gear for aero-engines, belonging to the technical field of aero-engine transmission systems. The method includes: Step 1, selecting the dimensions of the driving gear; Step 2, selecting the number of teeth z and the transverse module m. t Step 3: Determine the gear tooth width b; Step 4: Select the gear helix angle β. m Step 5: Select the gear helix direction; Step 6: Determine the gear pressure angle α. n Step 7: Determine the addendum coefficient and clearance coefficient c. * Step 8: Determine the displacement coefficient x; Step 9: Select the tangential displacement coefficient x t Step 10: Determine the tooth backlash of the gear pair; Step 11: Calculate the gear tooth parameters. This is done by selecting the addendum coefficient and clearance coefficient c. * The tooth structure parameters and meshing clearance of the tapered tooth unequal clearance spiral bevel gear pair are designed to increase the overlap ratio during gear meshing, improve the load-bearing capacity of the gear pair, and reduce the structural size and weight of the gear pair.

Description

TECHNICAL FIELD

[0001] The application relates to a design method of a tapered tooth unequal tip clearance spiral bevel gear for an aero-engine, and belongs to the technical field of aero-engine transmission systems. BACKGROUND

[0002] In spiral bevel gear transmission, according to whether the tip clearance of a large end and a small end of a bevel gear pair is consistent when the gear pair works, the spiral bevel gear can be divided into an equal tip clearance spiral bevel gear and an unequal tip clearance spiral bevel gear.

[0003] As shown in Fig. Figure 1 , the equal tip clearance spiral bevel gear is the same in tip clearance from the large end to the small end of the gear pair, the root cone generatrix of the gear intersects with the pitch cone generatrix at a point, and the vertex of the face cone intersects with the inside of the pitch cone vertex. When the gear pair works, the face cone generatrix of the bevel gear is parallel to the root cone generatrix of the matched gear, the sum of the face cone angle δ a2 of the driven bevel gear and the root cone angle δ f1 of the driving gear is equal to the shaft intersection angle Σ of the gear pair, and the tip clearance of the gear pair is completely equal from the large end to the small end.

[0004] As shown in Fig. Figure 2 , the unequal tip clearance spiral bevel gear is gradually reduced in tip clearance from the large end to the small end of the gear pair, the face cone generatrix, the root cone generatrix and the pitch cone generatrix of the gear intersect at a point. When the gear pair works, the face cone generatrix of the bevel gear is not parallel to the root cone generatrix of the matched gear, the sum of the face cone angle δ a2 of the driven bevel gear and the root cone angle δ f1 of the driving gear is not equal to the shaft intersection angle Σ of the gear pair, and the tip clearance of the gear pair is gradually reduced from the large end to the small end.

[0005] Although the tapered tooth unequal tip clearance spiral bevel gear is mentioned in the design manual of bevel gears and related standards in China, the method for selecting parameters and calculating gear parameters is not introduced in detail, and the actual application in the field of aero-engine transmission is not introduced.

[0006] Therefore, the application provides a design method of a tapered tooth unequal tip clearance spiral bevel gear for an aero-engine, and provides a new design method for intersecting shaft transmission of an aero-engine. SUMMARY

[0007] To solve the above technical problems, the application provides a design method of a tapered tooth unequal tip clearance spiral bevel gear for an aero-engine.

[0008] The application is realized by the following technical scheme:

[0009] A design method of tapered tooth unequal tip clearance spiral bevel gear for aero-engine, comprising the following steps:

[0010] Step one, selecting the size of driving gear according to torque;

[0011] Step two, selecting gear tooth number z and end face modulus m t ;

[0012] Step three, determining the gear tooth width b;

[0013] Step four, selecting gear spiral angle β m , so that the end face coincidence degree ε F exceeds 1.25;

[0014] Step five, selecting the gear spiral direction, so that the driving gear and the driven gear have the tendency to change from the meshing state to the separated state under the action of axial thrust;

[0015] Step six, determining the gear pressure angle α n ;

[0016] Step seven, determining the addendum coefficient and tip clearance coefficient c * ;

[0017] Step eight, determining the displacement coefficient x;

[0018] Step nine, selecting the tangential displacement coefficient x t ;

[0019] Step ten, determining the gear side clearance of the gear pair;

[0020] Step eleven, calculating the gear tooth parameters of the gear pair.

[0021] The torque Mz is calculated first in the step one,

[0022]

[0023] In the formula, P is the rated power, n1 is the rotation speed of the driving gear, and K0 is the overload coefficient;

[0024] Then, the torque Mz is compared with the starting torque of the starter, if the 1 / 2 of the starting torque of the starter is greater than the torque Mz, the size of the driving gear is selected according to the 1 / 2 of the starting torque of the starter, otherwise, the size of the driving gear is selected according to the torque Mz.

[0025] In the step two, when the sizes of the two gears of the gear pair are different, the pinion tooth number is selected as an odd number, the pinion tooth number and the gear tooth number avoid common divisor, and the sum of the pinion tooth number and the gear tooth number is not less than 40.

[0026] The tooth width b in the step three is less than 30% of the outer taper distance, or no more than 10 times of the face module.

[0027] The face coincidence degree epsilon in the step four F The calculation is made according to the following formula:

[0028]

[0029] The helix angle beta in the step four m is designed as 25°.

[0030] The gear pressure angle alpha in the step six n is designed as 20°.

[0031] The addendum coefficient in the step seven and the addendum clearance coefficient c * are designed as 0.9 and 0.25 respectively.

[0032] In the step eight, when the two gears of the gear pair are different in size, the modification coefficient x2 of the large gear is equal to the modification coefficient x1 of the small gear, and the signs are opposite, i.e.:

[0033] x1=-x2 (3),

[0034] The modification coefficient x1 of the small gear is calculated according to the following formula:

[0035]

[0036] In the formula, Z1 is the number of teeth of the small gear, and Z2 is the number of teeth of the large gear.

[0037] Then, according to the transmission ratio of the gear pair, the modification coefficient x1 of the small gear is selected.

[0038] In the step nine, when the two gears of the gear pair are different in size, the tangential modification coefficient x t is selected according to the number of teeth of the small gear and the transmission ratio of the gear pair.

[0039] In the step ten, the circumferential side clearance j t of the gear pair is calculated first,

[0040]

[0041] In the formula, j n is the normal side clearance of the gear pair.

[0042] Then, the tooth side clearance of the gear pair is determined as 1.5 times of the circumferential side clearance j t .

[0043] The beneficial effects of the present application are that: by selecting the non-standard addendum coefficient and the addendum clearance coefficient c* The application discloses a design method of a tapered tooth unequal-addendum spiral bevel gear for an aero-engine, which is characterized by the following steps: determining the tooth structure parameters and the meshing gap of the spiral bevel gear pair by the tooth height, the addendum difference and the dedendum difference of the gear pair, so as to increase the coincidence degree of the spiral bevel gear pair during meshing, improve the load capacity of the gear pair, and reduce the structure size and weight of the gear pair. The spiral bevel gear designed by the method has the advantages of high load capacity, good running stability, small structure size and high reliability, and is especially suitable for the transmission field of intersecting shafts of aero-engines. BRIEF DESCRIPTION OF DRAWINGS

[0044] Figure 1 Fig. 1 is a structural schematic diagram of a tapered tooth equal-addendum spiral bevel gear;

[0045] Figure 2 Fig. 2 is a structural schematic diagram of a tapered tooth unequal-addendum spiral bevel gear;

[0046] Figure 3 Fig. 3 is a parameter schematic diagram of the tapered tooth unequal-addendum spiral bevel gear. DETAILED DESCRIPTION

[0047] The technical solutions of the application are further described below, but the scope of protection is not limited to the description.

[0048] The application aims to require that the parts in the transmission system of an aero-engine have high load capacity and low weight under high speed and high load conditions. The application provides a design method of a tapered tooth unequal-addendum spiral bevel gear for an aero-engine, which increases the tooth height, the addendum difference and the dedendum difference, improves the load capacity of the spiral bevel gear under high speed and high load conditions, and reduces the structure size and weight of the gear under the condition of the same transmission power.

[0049] As shown in Figs. 1 to 3, the design method of the tapered tooth unequal-addendum spiral bevel gear for an aero-engine comprises the following steps: Figure 2 and Figure 3

[0050] 1) Selecting the size of the driving gear according to the torque: when the size of the driving gear is determined, the torque formula is used for calculation, and the formula is as follows:

[0051]

[0052] wherein Mz is the torque, P is the rated power, n1 is the rotating speed of the driving gear, and K0 is the overload coefficient. The torque Mz obtained according to the formula (1) is compared with the starting torque of the starter. If the 1 / 2 of the starting torque of the starter is greater than the torque Mz calculated according to the formula (1), the size of the driving gear should be selected according to the 1 / 2 of the starting torque of the starter, otherwise, the size of the driving gear should be selected according to the torque Mz. The overload coefficient K0 is selected according to Table 1. ​

[0053] Table 1 Overload coefficient K0

[0054]

[0055] 2) Select the gear tooth number z and the big end face modulus m t : The tooth number of the spiral bevel gear can be selected arbitrarily, the tooth number of the pinion should be selected as an odd number, the tooth numbers of the pinion and the gear should avoid having a common divisor, and the tooth numbers of the pinion and the gear should not be less than 40. When selecting the big end face modulus m t of the gear, the value should be as close as possible to the recommended value in GB 12368-90, or an arbitrary value can be selected according to the use experience. When selecting the big end face modulus m t , the value can be selected initially according to the working torque of the gear pair during operation or by referring to the design experience, and finally the modulus value is determined whether it meets the requirements through strength calculation.

[0056] 3) Determine the gear tooth width b: When selecting the tooth width b of the spiral bevel gear pair, the tooth width b should be ≤ 30% of the outer pitch distance or not more than 10 times the end face modulus.

[0057] 4) Select the gear spiral angle β m : A large enough spiral angle should be selected so that the end face coincidence degree ε F is more than 1.25, and the greater the ε F , the more stable the transmission operation and the lower the noise. When the ε F is 1.5-2.0, the effect is the best, and the ε F is calculated according to the following formula:

[0058]

[0059] The greater the selected spiral angle, the greater the axial thrust of the gear during operation. In the present application, for the tapered tooth unequal tip clearance spiral bevel gear pair, the spiral angle β m at the tooth width midpoint is designed as 25°.

[0060] 5) Select the gear spiral direction: The gear spiral direction and the rotation direction determine the direction of the axial thrust of the gear. When selecting the spiral direction, the direction of the axial thrust of the gear during operation should be selected so that the driving gear and the driven gear both tend to push away from each other during meshing, so as to increase the gear meshing clearance during the operation of the gear, avoid the mutual interference of the gear pair due to no clearance, and cause the damage of the gear. If the condition does not allow, an axial force tending to separate should be generated on the driving gear or the driven gear. Generally, when the driving bevel gear rotates clockwise, the spiral direction should be left-handed, and the driven bevel gear should be right-handed; when rotating counterclockwise, the situation is just the opposite.

[0061] 6) Determine the gear pressure angle α n: Large pressure angle can increase the strength of spiral bevel gear, reduce the minimum number of teeth without generating undercut, but for small size gear, large pressure angle is easy to produce tooth tip sharp and tool tip width too small, and make the gear pair coincidence degree decline. In the present application, the unequal tip gap spiral bevel gear standard pressure angle a n is designed as 20°.

[0062] 7) Determine the addendum coefficient and the tip clearance coefficient c * : The two parameters determine the values of the gear tooth height h a , dedendum height h f , full tooth height h, working tooth height h' and tooth tip clearance c. In the present application, the addendum coefficient ha and the tip clearance coefficient c * are designed as 0.9 and 0.25; by selecting a large addendum coefficient ha * to increase the addendum height and dedendum height of the unequal tip gap spiral bevel gear, thereby increasing the working tooth height of the gear; by selecting the tip clearance coefficient c * to increase the full tooth height of the unequal tip gap spiral bevel gear, thereby increasing the tooth tip clearance during the meshing process of the gear pair, avoiding the interference between the driving spiral bevel gear tip cone generatrix and the driven spiral bevel gear tooth bottom or tooth bottom transition circular arc radius during the operation of the gear pair.

[0063] 8) Determine the displacement coefficient x: in order to increase the strength of the pinion gear and eliminate the undercut of the pinion gear, the addendum height of the pinion gear should be increased, and the addendum height of the gear should be correspondingly reduced, the displacement coefficients of the pinion gear and the gear are equal in size and opposite in sign, that is:

[0064] x1=-x2 (3),

[0065] The displacement coefficient x1 of the pinion gear is determined by the formula:

[0066]

[0067] In the formula, Z1 is the number of teeth of the pinion gear, and Z2 is the number of teeth of the gear;

[0068] Then, according to the transmission ratio of the gear pair, select the displacement coefficient x1 of the pinion gear from Table 2, if there are two numbers can be selected, use the small value.

[0069] Table 2 Tooth height displacement coefficient table of circular arc tooth bevel gear

[0070]

[0071]

[0072] 9) Select the tangential displacement coefficient x tIn the design of spiral bevel gear, besides using high modification to increase the strength of pinion, tangential modification is also used to increase the thickness of pinion gear teeth by x t ×m t , and correspondingly reduce the thickness of gear gear teeth by x t ×m t ; by reducing the thickness of gear teeth, the meshing gap of gear pair is increased to avoid the meshing interference phenomenon caused by too large gear pair coincidence degree. After such modification, the strength of a pair of meshing gear teeth can be close to each other, and the tangential modification coefficient x t is selected according to the number of pinion gear teeth and the transmission ratio in Table 3.

[0073] Table 3 Selection of tangential modification coefficient x t of circular-arc tooth bevel gear

[0074]

[0075] 10) Determine the gear side gap of gear pair: the gear side gap refers to the shortest normal distance between non-working tooth surfaces when the gear teeth are engaged. If the gear side gap is too small, the noise is large during work, the tooth surface wears fast, and it is easy to be locked. If the gear side gap is too large, it is easy to cause impact. The normal meshing gap of spiral bevel gear pair can be determined according to the selected minimum normal side gap type and gear pair normal side gap tolerance type according to the provisions of HB-0-92. In the actual processing and assembly of gear pair, since the normal side gap detection is difficult, the circumferential side gap j t is usually specified in the design drawing and inspection instruction, and the relationship between the circumferential side gap j t and the normal side gap j n is converted according to the following formula:

[0076]

[0077] For tapered tooth unequal top gap spiral bevel gear, since the selected modification coefficient is larger than that of equal top gap bevel gear, the actual working tooth height and coincidence degree of gear teeth are increased, and tooth root interference phenomenon is more likely to occur during work. Therefore, the gear side gap value of the gear pair is designed to increase by 50% based on the calculated value of the circumferential side gap j t .

[0078] 11) After the basic parameters of spiral bevel gear pair are preliminarily determined, the specific tooth parameters of gear pair are calculated according to the calculation method in the following table.

[0079] Table 4 Calculation method of tooth parameters of tapered tooth unequal top gap spiral bevel gear

[0080]

[0081] Specifically, the application provides a design method of a tapered tooth unequal-addendum spiral bevel gear for an aero-engine, which provides a new design method for power transmission between intersecting shafts of the aero-engine, and the tapered tooth unequal-addendum spiral bevel gear designed by the method has the advantages of high coincidence, high bearing capacity under high load and high speed, small structure size and light weight compared with the commonly used equal tooth-addendum spiral bevel gear.

Claims

1. A method of designing a tapered tooth unequal-addendum spiral bevel gear for an aeroengine, characterized in that: It comprises the following steps: Step one, according to the torque, the size of the driving gear is selected; Step two, select gear teeth and face module ; Step three, determining the gear width ; Step four, select helix angle of gear so that the end face coincidence degree exceeds 1.25; Step five, the helical direction of the gear is selected, so that the driving gear and the driven gear have the tendency to change from the meshing state to the separated state under the action of the axial thrust force; Step six, determining the gear pressure angle ; Step seven, determining the addendum coefficient and the tip clearance coefficient ; Step eight, determining the shift coefficient ; Step nine, selecting a tangential displacement coefficient ; Step ten, the tooth gap of the gear pair is determined; Step eleven, the tooth parameters of the gear pair are calculated; The step four will be designed with helix angle Design is 25°; The step six will gear pressure angle is designed to 20°; The addendum coefficient in step seven and the tip clearance coefficient corresponding to 0.9 and 0.25; In step ten, the circumferential side play of the gear pair is calculated first , （5）， In the formula, is the normal side clearance of the gear pair; The tooth side clearance of the gear pair is then determined as 1.5 times the circular side clearance. of 1.

5.

2. The method of designing a tapered tooth unequal addendum spiral bevel gear for an aircraft engine as set forth in claim 1, wherein: The step one calculates the torque first , （1）， wherein P is the rated power, ω is the rotational speed of the drive pinion, K is the overload factor; Then, the torque is compared with the starting torque of the starter motor, and if the starting torque of the starter motor is greater than the torque by 1 / 2, the size of the driving pinion is selected by 1 / 2 of the starting torque of the starter motor, and otherwise, the size of the driving pinion is selected by the torque .

3. The method of designing a tapered tooth unequal addendum spiral bevel gear for an aircraft engine as claimed in claim 1, wherein: In the step two, when the sizes of the two gears of the gear pair are different, the number of teeth of the pinion is selected as an odd number, the number of teeth of the pinion and the number of teeth of the gear avoid having a common divisor, and the sum of the number of teeth of the pinion and the number of teeth of the gear is not less than 40.

4. The method of designing a tapered tooth unequal addendum spiral bevel gear for an aircraft engine as set forth in claim 1, wherein: The tooth width in step three ≤ 30% of the outer taper, or no more than 10 times the face module.

5. The method of designing a tapered tooth unequal addendum spiral bevel gear for an aircraft engine as claimed in claim 1, wherein: The end face coincidence degree in the step four The calculation is performed by the following formula: （2）。 6. The method of designing a tapered tooth unequal addendum spiral bevel gear for an aircraft engine as claimed in claim 1, wherein: In the step eight, when the two gears of the gear pair are of different sizes, the modification coefficient x2 of the large gear and the modification coefficient of the small gear are equal and the signs are opposite, that is: （3）， The modification coefficient of the pinion The calculation is made according to the following formula: （4）， In the formula, Z1 is the number of teeth of the pinion, and Z2 is the number of teeth of the gear; Then, according to the transmission ratio of the gear pair, the modification coefficient of the pinion is selected .

7. The method of designing a tapered tooth unequal addendum spiral bevel gear for an aircraft engine as described in claim 1, wherein: When the two gears of the gear pair are of different sizes, the tangential modification coefficient is selected according to the number of gear teeth and the transmission ratio of the gear pair in step nine .

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