A dual unloading groove bearing for an aeroengine fuel control device

Abstract

The present invention relates to a bearing with an asymmetric double unloading groove. The bearing adopts an asymmetric double unloading groove structure. There is no specific method in the existing manuals that can be followed for this kind of double unloading groove design. The technical solution of the present invention refers to the specific process of the gear meshing movement of a gear pump, innovatively proposes a way to solve the trapped oil pressure, and verifies through experiments that the design of this double unloading groove is feasible and has a better actual effect compared with the conventional unloading groove. The design of this kind of double unloading groove is proposed based on an in-depth analysis of the influence of the unloading groove on the internal flow field of the gear pump, taking into account dynamic loads, controlling pressure pulsation and noise.

Description

Technical Field

[0001] The present invention relates to a double unloading groove bearing for an aeroengine fuel control device, belonging to the technical field of mechanical design. Background Art

[0002] In the gear pump of the fuel supply system of an aero-turbine engine, in order to ensure continuous gear transmission and eliminate oil leakage, the overlap coefficient ε of the gear pump in the bearing design is greater than 1. Thus, within a certain angular range, there are two pairs of teeth meshing simultaneously, and a closed volume appears between the teeth. When the two meshing points are symmetrically located with respect to the pitch point, the closed volume reaches the minimum. The trapped oil is forcibly compressed by the gear, and the pressure increases sharply. Although partial pressure relief can be achieved through the clearance, a very high pressure still generates between the teeth, causing the bearing to bear a large excess load. As the gear continues to rotate, the closed volume continuously increases until the first pair of teeth disengages from the meshing. At this time, if the liquid replenishment is insufficient, a certain degree of vacuum will be formed in the trapped oil volume, resulting in air gaps and reducing the volumetric efficiency. Therefore, an unloading groove is opened in the trapped oil area to prevent the above-mentioned trapped oil phenomenon. The existing typical unloading grooves are as follows Figure 1 As shown in the figure:

[0003] a The circular unloading groove is better at alleviating cavitation, but worse at alleviating trapped oil pressure;

[0004] b The rectangular unloading groove is better at alleviating trapped oil pressure, but the worst at alleviating cavitation;

[0005] c The full-structure unloading groove is the best at alleviating cavitation, but the worst at alleviating trapped oil pressure;

[0006] At the same time, due to the large opening of the typical product, the end face load on the bearing is large.

[0007] For increasingly precise machining means and gears with a meshing coefficient much greater than 1, the reduction of the tooth side clearance will cause poor oil flow between adjacent volume chambers that should be connected, and it is easy to form an equivalent closed volume. Summary of the Invention

[0008] The present invention is precisely designed to solve the problems existing in the above-mentioned prior art, and provides a double unloading groove bearing for an aeroengine fuel control device. Its purpose is to better avoid the trapped oil and cavitation phenomena, improve the design of the unloading groove. The new structural design can not only alleviate the cavitation situation, but also have better ability to relieve trapped oil. At the same time, the opening area of the unloading groove is reduced, and the load is decreased.

[0009] The purpose of the present invention is achieved through the following technical solutions:

[0010] This kind of bearing with an asymmetric double unloading groove is installed in a gear pump. Symmetric unloading grooves are machined on both sides of the inner wall 1 of the bearing opposite to the gear. It is characterized in that the unloading grooves machined on the inner wall 1 of the bearing are distributed on both sides of the central vertical plane 3 of the center connection line 2 of the gear. Two unloading grooves are distributed on each side, and the unloading grooves on both sides are arranged facing each other and are asymmetric. The following takes one side of the inner wall 1 of the bearing as an example to illustrate the shape, structure and position of the asymmetric double unloading groove:

[0011] Among the above-mentioned gears, the right gear is the driving gear, which rotates counterclockwise and drives the left driven gear to rotate clockwise. The unloading grooves are all arc-shaped grooves, arranged along the same circumferential radius of the gear center. The radius from the inner edge of the unloading groove to the gear center is R1, the radius from the outer edge of the unloading groove to the gear center is R2, the arc angle of the unloading groove to the gear center is a, and the arc angle from the side of the adjacent unloading groove to the gear center is b;

[0012] Among the unloading grooves, the unloading grooves on the inner wall 1 of the bearing on the driving gear side are unloading groove II and unloading groove IV in turn along the counterclockwise direction, and the unloading grooves on the inner wall 1 of the bearing on the driven gear side are unloading groove I and unloading groove III in turn along the clockwise direction. Among them, the right side edge of the unloading groove I seen from the gear center coincides with the center connection line 2 of the gear, and the included angle between the left side edge of the unloading groove II seen from the gear center and the center connection line 2 of the gear is c, and c > b. Among the above parameters:

[0013] The angle a is calculated according to the following formula 1:

[0014] a = 1.25×θ0 Formula 1

[0015] In the formula: θ0 = 360 / z, z is the number of teeth of the gear;

[0016] The angle b is equal to the tooth space width angle γ of the gear, that is: b = γ. The tooth space width angle γ is the included angle of the gear center of the connection line of the two intersection points of the involute on both sides of the tooth space and the base circle of the gear;

[0017] The angle c is calculated according to the following formula 2:

[0018]

[0019] In the formula: p n = πmcosα, m is the module of the gear, and α is the pressure angle of the pitch circle of the gear;

[0020] The radius R1 from the inner edge of the unloading groove to the gear center is calculated according to the following formula 3:

[0021] R1 = (1.01~1.03)r f Formula 3

[0022] In the formula: r f is the root circle radius of the gear;

[0023] The radius R2 from the outer edge of the unloading groove to the gear center is calculated according to the following formula 4:

[0024] R2 = (0.98 - 0.99)D / 4 Formula 4

[0025] In the formula: D is defined as the initial diameter of the oil unloading engagement. The determination method is to rotate the driving gear on the right clockwise, push the driven gear on the left to rotate counterclockwise, define the engagement line between the two as the virtual engagement line, the virtual engagement line intersects with the involute of the gear when the closed volume appears between the teeth of the driving gear and the driven gear, and the diameter with the center of the driven gear as the symmetry point of the intersection point is the initial diameter D of the oil unloading engagement mentioned above;

[0026] The depth h of the unloading groove is calculated according to the following formula 5:

[0027] h = (0.5 - 1)m Formula 5.

[0028] The characteristics of the technical solution of the present invention are:

[0029] At present, the form of the unloading groove calculated according to the manual is simple. For the opening of the double unloading groove, its position not only needs to meet the unloading requirements, and the most crucial thing is that it can completely eliminate the influence of the tooth side clearance on the operation of the whole pump under different conditions. Since the actual situations of each closed cavity are considered separately, theoretically, the trapped oil pressure impact can be eliminated to the greatest extent. Therefore, theoretically, it has great superiority compared with the conventional unloading groove.

[0030] The technical solution of the present invention adopts an asymmetric double unloading groove structure. There is no specific method to follow for this kind of double unloading groove design in the existing manual. The technical solution of the present invention refers to the specific process of the gear meshing movement of the gear pump, and innovatively proposes a way to solve the trapped oil pressure, and verifies through experiments that the design of this double unloading groove is feasible and has a better actual effect compared with the conventional unloading groove. The design of this double unloading groove is proposed on the basis of deeply analyzing the influence of the unloading groove on the internal flow field of the gear pump, considering dynamic loads, controlling pressure pulsation and noise. Brief Description of the Drawings

[0031] Figure 1 It is a schematic diagram of the structure of a typical existing unloading groove

[0032] Figure 2 It is a schematic diagram of the design structure of the asymmetric double unloading groove described in the present invention

[0033] Figure 3 It is a schematic diagram of the dimensions of the asymmetric double unloading groove described in the present invention

[0034] Figure 4 It is a schematic diagram of the tooth groove width angle γ of the gear described in the present invention

[0035] Figure 5 Schematic diagram of the initial engagement diameter D for oil unloading described in the present invention

[0036] Figure 6 Schematic diagram of the gear in the embodiment of the present invention

[0037] Figure 7 Schematic diagram of the initial engagement position of the gear closed volume in the embodiment of the present invention

[0038] Figure 8 Schematic diagram of the intermediate engagement position of the gear closed volume in the embodiment of the present invention

[0039] Figure 9 Schematic diagram of the termination engagement position of the gear closed volume in the embodiment of the present invention Detailed implementation mode

[0040] The technical solution of the present invention will be further described in detail below in conjunction with the drawings and embodiments:

[0041] See the appendix Figure 6 As shown, the driving gear and the driven gear in the gear pump in this embodiment are external meshing non-modified involute spur cylindrical gears, and their geometric parameters are as follows:

[0042] Module m: m = 2

[0043] Number of teeth z: z = 11

[0044] Helix angle β of the pitch cylinder: β = 0

[0045] Pressure angle α of the pitch circle: α = 25°

[0046] Addendum coefficient

[0047] Radial clearance coefficient c * : c * = 0.25

[0048] See the appendix Figures 2-5 As shown, the structure of the asymmetric double unloading groove designed according to the above gear is as follows: Symmetric unloading grooves are processed on both sides of the bearing inner wall 1 opposite to the gear. It is characterized in that the unloading grooves processed on the bearing inner wall 1 are distributed on both sides of the central vertical plane 3 of the center connection line 2 of the gear, and two unloading grooves are distributed on each side. The unloading grooves on both sides are arranged facing each other and are asymmetric. The shape, structure and position of the asymmetric double unloading groove will be described below by taking one side of the bearing inner wall 1 as an example:

[0049] Among the above gears, the right gear is the driving gear, which rotates counterclockwise and drives the driven gear on the left to rotate clockwise. The unloading grooves are all arc-shaped grooves, arranged along the same circumferential radius of the gear center. The radius from the inner edge of the unloading groove to the gear center is R1, the radius from the outer edge of the unloading groove to the gear center is R2, the arc angle of the unloading groove to the gear center is a, and the arc angle from the side of the adjacent unloading groove to the gear center is b;

[0050] Among the unloading grooves, the unloading grooves on the inner wall 1 of the bearing on the driving gear side are unloading groove II and unloading groove IV in counterclockwise order, and the unloading grooves on the inner wall 1 of the bearing on the driven gear side are unloading groove I and unloading groove III in clockwise order. Among them, the right side edge of unloading groove I as seen from the gear center coincides with the gear center connection line 2, and the included angle between the left side edge of unloading groove II as seen from the gear center and the gear center connection line 2 is c, and c > b. Among the above parameters:

[0051] The angle a is calculated according to the following formula 1:

[0052] a = 1.25×θ0 Formula 1

[0053] In the formula: θ0 = 360 / z = 360÷11 = 32.73°, z is the number of teeth of the gear;

[0054] The angle b is equal to the tooth space width angle γ of the gear, that is: b = γ, and the tooth space width angle γ is the included angle of the connection line between the two intersection points of the involute on both sides of the tooth space and the gear base circle with the gear center;

[0055] The angle c is calculated according to the following formula 2:

[0056]

[0057] In the formula: p n = πmcosα, m is the modulus of the gear, and α is the pressure angle of the pitch circle of the gear;

[0058] The radius R1 from the inner edge of the unloading groove to the gear center is calculated according to the following formula 3:

[0059] R1 = (1.01~1.03)r f Formula 3

[0060] In the formula: r f is the root circle radius of the gear;

[0061] The radius R2 from the outer edge of the unloading groove to the gear center is calculated according to the following formula 4:

[0062] R2 = (0.98~0.99)D / 4 Formula 4

[0063] In the formula: D is defined as the initial diameter of unloading engagement. The determination method is to rotate the driving gear on the right clockwise to push the driven gear on the left counterclockwise, and define the meshing line between the two as the virtual meshing line. The virtual meshing line intersects with the involute of the gear when a closed volume appears between the teeth of the driving gear and the driven gear. The diameter with the center of the driven gear as the symmetry point of the intersection point is the initial diameter of unloading engagement D mentioned above;

[0064] The depth h of the unloading groove is calculated according to the following formula 5:

[0065] h = (0.5 - 1)m Formula 5.

[0066] See the appendix Figures 7-9 As shown, in the above structural design, in the initial position state, both the cavity V1 and the cavity V2 are connected to the unloading groove II and the unloading groove I. Due to the symmetrical characteristics of the gear structure, one side of the angle a is horizontal, and the other end is considered that the outermost limit position of the unloading groove should avoid the tooth profile shielding on the left side respectively to be away from the center line of the meshing gear, so the limit position should be greater than the angle of each tooth;

[0067] In the above structural design, the groove width of the unloading groove is determined by R1 and R2. In order to avoid the mutual leakage of the oil in the cavity V1 and the cavity V2, the intermediate gap between the volumes of the cavity V1 and the cavity V2 is very small. Therefore, it is designed that R1 = (1.01 - 1.03)r f and R2 = (0.98 - 0.99)D / 4.

[0068] In the above structural design, when the gears are meshed to the middle position, at this time, the lower side of the tooth 2 on the driven gear completely closes the unloading groove I. At this moment, the tooth 1 on the driving gear closes the unloading groove II, and the unloading groove III and the unloading groove IV start to leak out. It is designed that the normal direction p of the two meshing points at this time n = πmcosα, at this time c is obtained. At the same time, to avoid absolute oil entrapment and allow for slight leakage, the angle at this place is rounded down;

[0069] In the above structural design, to ensure that the cavity V1 and the cavity V2 are respectively connected to the unloading groove III and the unloading groove IV immediately after being disengaged from the unloading groove I and the unloading groove II, it is designed that the angle b is equal to the tooth groove width angle γ of the gear.

[0070] The movement process of the asymmetric double unloading groove in cooperation with the gear is as follows:

[0071] The tooth profiles of the driving gear and the driven gear start to mesh from a point at the root of the tooth profile of the driving gear and the vertex of the driven gear, and then the position of the meshing point moves downward along the meshing line. The tooth 1 on the driving gear and the tooth 2 on the driven gear start to mesh. At this time, the tooth 4 on the driving gear and the tooth 3 on the driven gear have not disengaged yet. Therefore, two closed spaces, cavity V1 and cavity V2, are formed. At this time, the side clearance of the gear allows cavity V1 and cavity V2 to remain in communication.

[0072] In this embodiment, the overlap coefficient ε is 1.29, which is much greater than 1 and the machining accuracy is relatively high. Since the side clearance of the gear is small, cavity V1 and cavity V2 are two equivalent closed spaces. When designing the unloading groove, the oil leakage and cavitation problems of both spaces need to be considered simultaneously.

[0073] During the oil pressure process, the closed space V1+V2 becomes smaller from larger. Cavity V1 communicates with the oil discharge cavity through unloading groove II, and cavity V2 communicates with the oil discharge cavity through unloading groove I. When the gear continues to rotate, due to the relatively low position of unloading groove I, the closed cavity V1+V2 can always communicate with the oil discharge cavity through unloading groove I;

[0074] When the gear pump continues to rotate and the closed cavity V1+V2 becomes larger from smaller, cavity V1 communicates with the oil suction cavity through unloading groove IV, and cavity V2 communicates with the oil suction cavity through unloading groove III. When the gear continues to rotate, due to the relatively low position of unloading groove III, the closed cavity V1+V2 can always communicate with the oil suction cavity through unloading groove III. It can be seen that the unloading process of the double unloading groove eliminates the influence of the side clearance and can better relieve and eliminate the trapped oil pressure while ensuring the design principle.

[0075] Compared with the prior art, the solution of the present invention well satisfies the volume change law of the two closed cavities V1+V2, while the conventional unloading groove cannot meet its unloading requirements. Through experimental verification, the gear pump designed and manufactured with the technical solution of the present invention has strong anti-trapped oil and anti-cavitation capabilities and less load during the working process. At the same time, the groove opened on the high-pressure side is relatively small, which increases the structural strength of the bearing and improves the life reliability. The unloading groove gear bearing has passed the 1500h life verification.

Claims

1. A bearing with an asymmetric double unloading groove, which is installed in a gear pump. Symmetric unloading grooves are machined on both sides of the inner wall (1) of the bearing opposite to the gear. It is characterized in that: The unloading grooves machined on the inner wall (1) of the bearing are distributed on both sides of the central vertical plane (3) of the center connection line (2) of the gears. There are two unloading grooves distributed on each side. The unloading grooves on both sides are arranged facing each other and are asymmetric. The following takes one side of the inner wall (1) of the bearing as an example to illustrate the shape, structure and position of the asymmetric double unloading grooves: Among the above-mentioned gears, the right gear is the driving gear, which rotates counterclockwise and drives the left driven gear to rotate clockwise. The unloading grooves are all arc grooves and are arranged along the same circumferential radius of the gear center. The radius from the inner edge of the unloading groove to the gear center is R1, the radius from the outer edge of the unloading groove to the gear center is R2, the arc angle of the unloading groove to the gear center is a, and the arc angle of the side of the adjacent unloading groove to the gear center is b; Among the unloading grooves, the unloading grooves on the inner wall (1) of the bearing on the driving gear side are unloading groove II and unloading groove IV in counterclockwise order, and the unloading grooves on the inner wall (1) of the bearing on the driven gear side are unloading groove I and unloading groove III in clockwise order. Among them, the right side edge of unloading groove I seen from the gear center coincides with the center connection line (2) of the gears, and the included angle between the left side edge of unloading groove II seen from the gear center and the center connection line (2) of the gears is c, and c>b. Among the above parameters: The angle a is calculated according to the following formula 1: a = 1.25×θ0 Formula 1 In the formula: θ0 = 360 / z, z is the number of teeth of the gear; The angle b is equal to the tooth groove width angle γ of the gear, that is: b = γ. The tooth groove width angle γ is the included angle of the gear center of the connecting line of the two intersection points of the involute on both sides of the tooth groove and the base circle of the gear; The angle c is calculated according to the following formula 2: where: p n = πmcosα, where m is the module of the gear and α is the pressure angle of the pitch circle of the gear; The radius R1 from the inner edge of the unloading groove to the gear center is calculated according to the following formula 3: R1 = (1.01 to 1.03)r f Formula 3 where: r f is the root circle radius of the gear; The radius R2 from the outer edge of the unloading groove to the gear center is calculated according to the following formula 4: R2 = (0.98~0.99)D / 4 Formula 4 In the formula: D is defined as the initial diameter of oil unloading meshing. The determination method is to rotate the right driving gear clockwise to drive the left driven gear to rotate counterclockwise, and define the meshing line of the two as the virtual meshing line. The virtual meshing line intersects with the involute of the gear when the closed volume appears between the teeth of the driving gear and the driven gear. The diameter of the intersection point symmetric about the center of the driven gear is the initial diameter D of the oil unloading meshing mentioned above; The depth h of the unloading groove is calculated according to the following formula 5: h = (0.5~1)m Formula 5.

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