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

Abstract

The invention discloses 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. The method comprises the steps that firstly, the size of a driving gear is selected; step 2, selecting a gear tooth number z and an end face modulus mt; 3, determining the tooth width b of the gear; step 4, selecting a gear helical angle beta m; 5, selecting the spiral direction of the gear; step 6, determining a gear pressure angle alpha n; step 7, determining a tooth addendum coefficient # imgabs0 # and a top clearance coefficient c *; 8, determining a displacement coefficient x; step 9, selecting a tangential displacement coefficient xt; step 10, determining a gear backlash of the gear pair; and 11, calculating gear tooth parameters of the gear pair. The tooth addendum coefficient # imgabs 1 # and the tip clearance coefficient c * are selected, and gear tooth structure parameters and gear pair meshing clearances of the tapered tooth unequal tip clearance spiral bevel gear pair are designed, so that the overlap ratio during meshing of the gear pair is increased, the bearing capacity of the gear pair is improved, and the structural size and weight of the gear pair are reduced.

Description

Technical Field

[0001] The invention relates to a design method for a spiral bevel gear with tapered teeth and unequal top clearance for an aero-engine, belongs to the technical field of aero-engine transmission systems, and is suitable for aero-engine transmission systems with high performance and high precision requirements. Background Art

[0002] In spiral bevel gear transmission, according to whether the tooth top clearances of the large end and the small end of the bevel gear pair are consistent when the gear pair is working, the spiral bevel gears can be divided into equal tooth top clearance spiral bevel gears and unequal tooth top clearance spiral bevel gears.

[0003] like Figure 1 As shown in the figure, the equal tooth tip clearance spiral bevel gear has the same tooth 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 one point, and the vertex of the face cone intersects the inner side of the vertex of the pitch cone. When the gear pair is working, the face cone generatrix of the bevel gear is parallel to the root cone generatrix of the matching gear, and the face cone angle δ of the driven bevel gear is a2 Root cone angle δ with the driving gear f1 The sum is equal to the axial intersection angle ∑ of the gear pair, and the tooth top clearance of the gear pair is completely equal from the large end to the small end.

[0004] like Figure 2 As shown in the figure, the tooth tip clearance of spiral bevel gears with unequal tooth tip clearance gradually decreases from the large end to the small end of the gear pair, and the face cone generatrix, root cone generatrix and pitch cone generatrix of the gear intersect at one point. When the gear pair is working, the face cone generatrix of the bevel gear and the root cone generatrix of the matching gear are no longer parallel to each other, and the face cone angle δ of the driven bevel gear is a2 Root cone angle δ with the driving gear f1 The sum is no longer equal to the shaft angle ∑ of the gear pair, and the tooth top clearance of the gear pair gradually decreases from the large end to the small end.

[0005] Although the spiral bevel gear with tapered teeth and unequal top clearance is mentioned in my country's bevel gear design manual and related standards, its parameter selection and gear tooth parameter calculation methods are not introduced in detail, and there is no introduction to its practical application in the field of aircraft engine transmission.

[0006] To this end, the present invention proposes a design method for a spiral bevel gear with tapered teeth and unequal top clearance for an aircraft engine, which provides a new design method for the intersecting shaft transmission of an aircraft engine. Summary of the invention

[0007] In order to solve the above technical problems, the present invention provides a design method for spiral bevel gears with tapered teeth and unequal top clearance for aircraft engines.

[0008] The present invention is achieved through the following technical solutions:

[0009] A design method for a spiral bevel gear with tapered teeth and unequal top clearance for an aircraft engine comprises the following steps:

[0010] Step 1: Select the size of the driving gear according to the torque;

[0011] Step 2: Select the number of gear teeth z and the end module m t ;

[0012] Step 3: Determine the tooth width b of the gear;

[0013] Step 4: Select the gear helix angle β m , so that the end face overlap ε F More than 1.25;

[0014] Step 5: Select the spiral direction of the gears so that the driving gear and the driven gear have a tendency to change from the meshing state to the separation state under the action of the axial thrust;

[0015] Step 6: Determine the gear pressure angle α n ;

[0016] Step 7: Determine the tooth addendum coefficient and the head clearance coefficient c * ;

[0017] Step 8: Determine the displacement coefficient x;

[0018] Step 9. Select the tangential displacement coefficient x t ;

[0019] Step 10: Determine the tooth side clearance of the gear pair;

[0020] Step 11: Calculate the gear tooth parameters of the gear pair.

[0021] In step 1, the torque Mz is first calculated.

[0022]

[0023] In the formula, P is the rated power, n1 is the 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 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 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 2, when the two gears of the gear pair are of different sizes, the number of teeth of the small gear is an odd number, the number of teeth of the small gear and the number of teeth of the large gear avoid having a common divisor, and the sum of the number of teeth of the small gear and the large gear is not less than 40.

[0026] The tooth width b in step three is ≤ 30% of the outer cone distance, or does not exceed 10 times the end face module.

[0027] The end face overlap ε in step 4 F Calculate as follows:

[0028]

[0029] In step 4, the helix angle β m Designed for 25°;

[0030] In step 6, the gear pressure angle α n Designed for 20°.

[0031] In step 7, the tooth addendum coefficient and the head clearance coefficient c * The corresponding designs are 0.9 and 0.25.

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

[0033] x1=-x2 (3),

[0034] The displacement coefficient x1 of the pinion is calculated as follows:

[0035]

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

[0037] Then, according to the transmission ratio of the gear pair, select the displacement coefficient x1 of the pinion.

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

[0039] In the step 10, the circumferential backlash j of the gear pair is first calculated. t ,

[0040]

[0041] In the formula, j n is the normal backlash of the gear pair;

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

[0043] The beneficial effect of the present invention is that by selecting a non-standard tooth addendum coefficient and the head clearance coefficient c* The gear structure parameters and meshing clearance of the spiral bevel gear pair with tapered teeth and unequal top clearance are designed to increase the overlap of the spiral bevel gear pair during meshing, improve the gear pair load-bearing capacity, and reduce the gear pair structure size and weight. The spiral bevel gear designed by this design method has the advantages of high load-bearing capacity, good operating stability, small structure size and high reliability, and is especially suitable for the transmission field of intersecting shafts of aircraft engines. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 It is a schematic diagram of the structure of a spiral bevel gear with tapered teeth and equal top clearance;

[0045] Figure 2 It is a schematic diagram of the structure of a spiral bevel gear with tapered teeth and unequal top clearance;

[0046] Figure 3 Schematic diagram of parameters of spiral bevel gears with tapered teeth and unequal top clearance. DETAILED DESCRIPTION

[0047] The technical solution of the present invention is further described below, but the scope of protection claimed is not limited to the description.

[0048] The purpose of the present invention is to require that parts in the aircraft engine transmission system have high load-bearing capacity and low weight under high speed and high load conditions. The present invention proposes a design method for a spiral bevel gear with tapered teeth and unequal top clearance for aircraft engines, which increases the height of the gear teeth, increases the tooth top clearance and meshing clearance, and improves the load-bearing capacity of the spiral bevel gear under high speed and high load conditions, while reducing the gear structure size and weight under the condition of transmitting the same power.

[0049] like Figure 2 and Figure 3 As shown, the design method of a spiral bevel gear with tapered teeth and unequal top clearance for an aircraft engine according to the present invention comprises the following steps:

[0050] 1) Select the size of the driving gear according to the torque: When determining the size of the driving gear for driving, use the torque formula for calculation, the formula is as follows:

[0051]

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

[0054]

[0055] 2) Select the number of gear teeth z and the large end face module m t :The number of teeth of spiral bevel gear can be selected arbitrarily. Generally, the number of teeth of small gear should be an odd number. The number of teeth of small gear and large gear should avoid having a common divisor. The sum of the number of teeth of small gear and large gear should not be less than 40. The module of the large end face of the selected gear is m t The value should conform to the recommended value in GB 12368-90 as much as possible, or any value can be selected based on usage experience. t When determining the size of the modulus, it can initially be selected based on the working torque transmitted when the gear pair is working or based on design experience, and finally the strength calculation can be used to determine whether the modulus value meets the requirements.

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

[0057] 4) Select the gear helix angle β m :The helix angle should be large enough to make the end face overlap ε F More than 1.25, ε F The larger the value, the smoother the transmission will work and the lower the noise will be. F When ε is 1.5 to 2.0, the effect is best. F Calculated using the following formula:

[0058]

[0059] The larger the selected helix angle, the greater the axial thrust of the gear when it is working. In the present invention, for the tapered tooth unequal top clearance spiral bevel gear pair, the midpoint helix angle β of the tooth width is m Designed for 25°.

[0060] 5) Select the gear spiral direction: The gear spiral direction and rotation direction determine the direction of the gear axial thrust. When selecting the spiral direction, the direction of the axial thrust when the gear is working should be selected so that the master and slave gears tend to push each other away from the meshing, so as to increase the gear meshing clearance when the gear is running, and avoid interference between the gear pairs due to no clearance, causing gear damage. If conditions do not allow, an axial force tending to separate should also be generated on the driving gear or the driven gear. Generally, the spiral direction of the driving bevel gear should be left-handed when rotating clockwise, 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:A large pressure angle can increase the strength of spiral bevel gears and reduce the minimum number of teeth without undercutting. However, for small-sized gears, a large pressure angle is prone to cause the tooth tip to become sharp and the blade tip width to be too small, and the gear pair overlap is reduced. In the present invention, the standard pressure angle α of the unequal top clearance spiral bevel gear is n Designed for 20°.

[0062] 7) Determine the tooth top height coefficient and the head clearance coefficient c * :These two parameters determine the gear tooth height h a , tooth root height h f , full tooth height h, working tooth height h' and tooth top clearance c. and the head clearance coefficient c * The corresponding designs are 0.9 and 0.25; by selecting a large tooth addendum coefficient ha*, the tooth addendum and tooth root height of the unequal top clearance spiral bevel gear are increased, thereby increasing the working tooth height of the gear; by selecting the top clearance coefficient c*, the full tooth height of the unequal top clearance spiral bevel gear is increased, thereby increasing the tooth addendum clearance during the meshing process of the gear pair, and avoiding interference between the top cone generatrix of the active spiral bevel gear and the tooth bottom or tooth bottom transition arc radius of the driven spiral bevel gear when the gear pair is working.

[0063] 8) Determine the modification coefficient x: In order to increase the gear strength of the pinion and eliminate the root cutting of the pinion, the tooth top height of the pinion should be increased, and the tooth top height of the large gear should be reduced accordingly. The modification coefficients of the large and small gears are equal in size and opposite in sign, that is:

[0064] x1=-x2 (3),

[0065] The displacement coefficient x1 of the pinion is determined according to the formula:

[0066]

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

[0068] Then, according to the transmission ratio of the gear pair, select the displacement coefficient x1 of the pinion from Table 2. If there are two numbers to choose from, use the smaller value.

[0069] Table 2 Arc bevel gear tooth height modification coefficient table

[0070]

[0071]

[0072] 9) Select the tangential displacement coefficient x tIn the design of spiral bevel gears, in addition to using high displacement to increase the strength of the pinion, a tangential displacement correction is also used to increase the tooth thickness of the pinion by x. t ×m t , and the tooth thickness of the large gear is reduced accordingly, and the reduction in the tooth thickness of the large gear is also x t ×m t ; By reducing the thickness of the gear teeth, the meshing clearance of the gear pair is increased to avoid meshing interference caused by excessive overlap of the gear pair. After such correction, the strength of a pair of meshing gear teeth can be nearly equal. According to the number of teeth of the pinion and the transmission ratio, the tangential displacement coefficient x is selected according to Table 3. t .

[0073] Table 3 Tangential modification coefficient x of circular arc bevel gear t Choice

[0074]

[0075] 10) Determine the tooth side clearance of the gear pair: The tooth side clearance refers to the shortest normal distance between the non-working tooth surfaces when the gear teeth are meshing. If the tooth side clearance is too small, there will be loud noise during operation, the tooth surface will wear quickly, and it is easy to get stuck; if the tooth side clearance is too large, it is easy to cause impact. The normal meshing clearance of the spiral bevel gear pair can be determined according to the provisions of HB-0-92, based on the selected minimum normal side clearance type and the gear pair normal side clearance tolerance type. In the actual processing and assembly of the gear pair, due to the difficulty in detecting the normal side clearance, the circumferential side clearance is usually specified in the design drawings and inspection instructions. t , circumferential clearance j t and normal backlash j n The relationship between them is calculated according to the following formula:

[0076]

[0077] For the spiral bevel gear with tapered teeth and unequal top clearance, the selected modification coefficient is larger than that of the bevel gear with equal top clearance, which leads to an increase in the actual working tooth height and overlap of the gear teeth, and the tooth root interference phenomenon is more likely to occur during operation. Therefore, the tooth side clearance value of the gear pair is designed to be in the formula (5) as follows: t Add 50% to the calculated value.

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

[0079] Table 4 Calculation method of gear tooth parameters of spiral bevel gear with tapered teeth and unequal top clearance

[0080]

[0081] Specifically, the present invention proposes a design method for a spiral bevel gear with tapered teeth and unequal top clearance for an aircraft engine, which adds a new design mode for power transmission between intersecting shafts of an aircraft engine. Compared with the commonly used spiral bevel gear with equal top clearance, the spiral bevel gear with tapered teeth designed by this method has the advantages of high overlap, high load-bearing capacity under high load and high speed conditions, small structural size and light weight.

Claims

1. A design method for a spiral bevel gear with tapered teeth and unequal top clearance for an aircraft engine, characterized in that: The following steps are involved: Step 1: Select the size of the driving gear according to the torque; Step 2: Select the number of gear teeth z and the end module m t ; Step 3: Determine the tooth width b of the gear; Step 4: Select the gear helix angle β m , so that the end face overlap ε F More than 1.25; Step 5: Select the spiral direction of the gears so that the driving gear and the driven gear have a tendency to change from the meshing state to the separation state under the action of the axial thrust; Step 6: Determine the gear pressure angle α n ; Step 7: Determine the tooth addendum coefficient and the head clearance coefficient c * ; Step 8: Determine the displacement coefficient x; Step 9. Select the tangential displacement coefficient x t ; Step 10: Determine the tooth side clearance of the gear pair; Step 11: Calculate the gear tooth parameters of the gear pair.

2. The design method of spiral bevel gear with tapered teeth and unequal top clearance for aircraft engines according to claim 1, characterized in that: In step 1, the torque Mz is first calculated. In the formula, P is the rated power, n1 is the speed of the driving gear, and K0 is the overload coefficient; Then, the torque Mz is compared with the starting torque of the starter. If 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 1 / 2 of the starting torque of the starter. Otherwise, the size of the driving gear is selected according to the torque Mz.

3. The design method of spiral bevel gear with tapered teeth and unequal top clearance for aircraft engines according to claim 1, characterized in that: In the step 2, when the two gears of the gear pair are of different sizes, the number of teeth of the small gear is an odd number, the number of teeth of the small gear and the number of teeth of the large gear avoid having a common divisor, and the sum of the number of teeth of the small gear and the large gear is not less than 40.

4. The design method of spiral bevel gears with tapered teeth and unequal top clearance for aircraft engines according to claim 1, characterized in that: The tooth width b in step three is ≤ 30% of the outer cone distance, or does not exceed 10 times the end face module.

5. The design method of spiral bevel gear with tapered teeth and unequal top clearance for aircraft engines according to claim 1, characterized in that: The end face overlap ε in step 4 F Calculate as follows:

6. The design method of spiral bevel gears with tapered teeth and unequal top clearance for aircraft engines according to claim 1, characterized in that: In step 4, the helix angle β m Designed for 25°; In step 6, the gear pressure angle α n Designed for 20°.

7. The design method of spiral bevel gears with tapered teeth and unequal top clearance for aircraft engines according to claim 1, characterized in that: In step 7, the tooth addendum coefficient and the head clearance coefficient c * The corresponding designs are 0.9 and 0.

25.

8. The design method of spiral bevel gears with tapered teeth and unequal top clearance for aircraft engines according to claim 1, characterized in that: In step eight, when the two gears of the gear pair are of different sizes, the modification coefficient x2 of the large gear is equal to the modification coefficient x1 of the small gear, and the signs are opposite, that is: x1=-x2 (3), The displacement coefficient x1 of the pinion is calculated as follows: In the formula, Z1 is the number of teeth on the small gear, and Z2 is the number of teeth on the large gear; Then, according to the transmission ratio of the gear pair, select the displacement coefficient x1 of the pinion.

9. The design method of spiral bevel gears with tapered teeth and unequal top clearance for aircraft engines according to claim 1, characterized in that: In step nine, when the two gears of the gear pair are of different sizes, the tangential displacement coefficient x is selected according to the number of teeth of the pinion and the transmission ratio of the gear pair. t .

10. The design method of spiral bevel gear with tapered teeth and unequal top clearance for aircraft engines according to claim 1, characterized in that: In the step 10, the circumferential backlash j of the gear pair is first calculated. t , In the formula, j n is the normal backlash of the gear pair; Then, the tooth side clearance of the gear pair is determined as the circumferential side clearance j t 1.5 times of.

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