Manufacturing method of parking gear of AT gearbox

Abstract

The invention relates to a manufacturing method of a parking gear of an AT gearbox. The manufacturing method comprises the following steps of S1, burdening; s2, pressing; s3, sintering is carried out; s4, finishing is conducted; s5, heat treatment; according to the manufacturing method of the parking gear of the AT gearbox, the pre-alloy powder which is based on Fe-Cr-Mo and is easier to compress is adopted, low-temperature pressing and high-temperature sintering are combined, the yield strength of the powder is reduced firstly, diffusion and densification are promoted through high temperature, more gaps of a green body are closed, and therefore the overall strength of the green body is improved, and the yield of the parking gear of the AT gearbox is improved. After the surface hardness and the fatigue resistance are improved through finishing, quenching and tempering are carried out, the bearing capacity and the impact resistance of the gear are improved, overall deformation is controlled, and the whole manufacturing method simplifies the operation procedures and reduces the manufacturing cost while ensuring the performance of the parking gear of the AT gearbox.

Description

Technical Field

[0001] This invention relates to the field of AT transmission manufacturing technology, and in particular to a method for manufacturing a parking gear of an AT transmission. Background Technology

[0002] The parking gear is a key component in an automatic transmission, used in conjunction with the parking pawl. When the parking pawl engages with the teeth of the parking gear, the transmission components stop operating, bringing the vehicle to a standstill. Conversely, when the parking pawl disengages from the teeth, the vehicle can then move. Because the parking gear primarily bears torque in the automatic transmission, it must possess sufficient strength to meet the required specifications.

[0003] Chinese invention patent CN106868419A discloses a powder metallurgy parking gear for an automatic transmission and its preparation method. The parking gear uses Fe as a matrix and contains, by weight percentage, 0.25–0.38% C, 1.48–1.85% Cu, 1.55–1.85% Ni, and 2.50–2.85% Cr. The forming process involves the following steps: first, uniformly mixing the measured raw materials; then, sequentially performing compression molding, pre-sintering, secondary compression molding, secondary sintering, deburring, and tooth surface heat treatment. This preparation method improves the material's strength properties by adding a high Cr content. Furthermore, by appropriately increasing the pressing pressure based on conventional powder metallurgy processes, the density of the material is further strengthened, resulting in a significant increase in the tooth surface hardness after heat treatment.

[0004] However, the above-mentioned method for preparing parking gears for automatic transmissions still has some drawbacks. Although increasing the pressing pressure can enhance the material density, it will exacerbate mold wear and increase manufacturing costs.

[0005] Therefore, the present invention proposes a method for manufacturing the parking gear of an AT transmission to solve the above problems. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a method for manufacturing parking gears of AT transmissions, which improves the strength of parking gears of AT transmissions, has high manufacturing efficiency, and low cost.

[0007] To solve the above-mentioned technical problems, the technical solution of the present invention is: a method for manufacturing a parking gear of an AT transmission, the innovation of which lies in: including the following steps: S1. Ingredients: Prepare raw materials according to the following percentage composition: C 0.23-0.33%, Cu 1.6-1.8%, Ni 1.7-2.2%, Cr 1.7-2.1%, Mo 0.3-0.5%, Fe as balance; mix the raw materials evenly to obtain pre-alloyed powder; S2. Pressing: The prepared raw materials are added to the press mold and pressed into shape to obtain a density ≥7.3g / cm³. 3 Gear blanks; S3. Sintering: The gear green blank is fed into a sintering furnace and sintered at high temperature under vacuum or high-purity hydrogen atmosphere to obtain a density ≥7.5g / cm³. 3 Fully densified gear semi-finished products; S4. Finishing: Finishing the teeth of the fully densified gear semi-finished product, and then rolling the tooth surface of the fully densified gear semi-finished product to obtain the finished gear semi-finished product. S5. Heat treatment: The finished gear semi-finished product is hot oil quenched, tempered and then cooled in oil at room temperature to obtain the finished parking gear of the AT transmission.

[0008] Furthermore, in step S2, a lubricant is added to the pre-alloyed powder before pressing and mixed evenly, with the amount of lubricant added being 0.7~0.8% of the pre-alloyed powder.

[0009] Furthermore, in step S2, the pressing temperature is controlled at 135~155℃ and the pressing pressure is 730~760MPa.

[0010] Furthermore, in step S3, the temperatures of the pre-sintering section, high-temperature section, and heat preservation section of the sintering furnace are controlled at 800~1000℃, 1200~1300℃, and 900~1100℃, respectively. The gear blanks are kept in the high-temperature section for 6~8 hours and in the heat preservation section for 5~7 hours.

[0011] Furthermore, in step S5, the quenching temperature is 830~860℃ and the tempering temperature is 500~550℃.

[0012] The advantages of this invention are: The manufacturing method of the parking gear of the AT transmission of the present invention uses Fe-Cr-Mo based pre-alloyed powder that is easier to compress. It combines low-temperature pressing and high-temperature sintering to first reduce the yield strength of the powder, and then uses high temperature to promote diffusion and densification, closing more voids in the green blank, thereby improving the overall strength of the green blank. After finishing to improve the surface hardness and fatigue strength, it is quenched and tempered to improve the gear's load-bearing capacity and impact resistance, and control the overall deformation. The entire manufacturing method simplifies the operation process and reduces the manufacturing cost while ensuring the performance of the parking gear of the AT transmission. Detailed Implementation

[0013] To further illustrate the technical means and effects of the present invention in achieving the intended purpose, the following detailed description of the specific implementation methods, structures, features and effects of the present invention, in conjunction with preferred embodiments, is provided below.

[0014] Example This embodiment provides a method for manufacturing a parking gear in an automatic transmission, including the following steps: S1. Ingredients: Prepare raw materials according to the following percentage composition: C 0.23-0.33%, Cu 1.6-1.8%, Ni 1.7-2.2%, Cr 1.7-2.1%, Mo 0.3-0.5%, Fe as balance; mix the raw materials evenly to obtain pre-alloyed powder; S2. Pressing: Add lubricant to the pre-alloyed powder and mix evenly. The amount of lubricant added is 0.75% of the pre-alloyed powder. Add the prepared raw material with lubricant to the press mold and press it into shape. Control the temperature at 145℃ and the pressing pressure at 750MPa to obtain a density of 7.35g / cm³. 3 Gear blanks; S3. Sintering: The gear green blank is fed into a sintering furnace and sintered at high temperature under a vacuum or high-purity hydrogen atmosphere. The temperatures of the pre-sintering section, high-temperature section, and holding section of the sintering furnace are controlled at 900℃, 1250℃, and 1000℃, respectively. The gear green blank is held in the high-temperature section for 7 hours and in the holding section for 6 hours, obtaining a density of 7.52 g / cm³. 3 Fully densified gear semi-finished products; S4. Finishing: Finishing the teeth of the fully densified gear semi-finished product, and then rolling the tooth surface of the fully densified gear semi-finished product to obtain the finished gear semi-finished product. S5. Heat treatment: The finished gear semi-finished product is hot oil quenched, tempered, and then cooled in oil at room temperature. The quenching temperature is 850℃ and the tempering temperature is 520℃ to obtain the finished parking gear of the AT gearbox.

[0015] The manufacturing method of the parking gear of the AT transmission of the present invention uses Fe-Cr-Mo based pre-alloyed powder that is easier to compress. It combines low-temperature pressing and high-temperature sintering to first reduce the yield strength of the powder, and then uses high temperature to promote diffusion and densification, closing more voids in the green blank, thereby improving the overall strength of the green blank. After finishing to improve the surface hardness and fatigue strength, it is quenched and tempered to improve the gear's load-bearing capacity and impact resistance, and control the overall deformation. The entire manufacturing method simplifies the operation process and reduces the manufacturing cost while ensuring the performance of the parking gear of the AT transmission.

[0016] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for manufacturing a parking gear in an automatic transmission, characterized in that: Includes the following steps: S1. Ingredients: Prepare raw materials according to the following percentage composition: C 0.23-0.33%, Cu 1.6-1.8%, Ni 1.7-2.2%, Cr 1.7-2.1%, Mo 0.3-0.5%, Fe as balance; mix the raw materials evenly to obtain pre-alloyed powder; S2. Pressing: The prepared raw materials are added to the press mold and pressed into shape to obtain a density ≥7.3g / cm³. 3 Gear blanks; S3. Sintering: The gear green blank is fed into a sintering furnace and sintered at high temperature under vacuum or high-purity hydrogen atmosphere to obtain a density ≥7.5g / cm³. 3 Fully densified gear semi-finished products; S4. Finishing: Finishing the teeth of the fully densified gear semi-finished product, and then rolling the tooth surface of the fully densified gear semi-finished product to obtain the finished gear semi-finished product. S5. Heat treatment: The finished gear semi-finished product is hot oil quenched, tempered and then cooled in oil at room temperature to obtain the finished parking gear of the AT transmission.

2. The method for manufacturing the parking gear of an AT transmission according to claim 1, characterized in that: In step S2, a lubricant is added to the pre-alloyed powder before pressing and mixed evenly. The amount of lubricant added is 0.7~0.8% of the pre-alloyed powder.

3. The method for manufacturing the parking gear of an AT transmission according to claim 1, characterized in that: In step S2, the pressing temperature is controlled at 135~155℃ and the pressing pressure is 730~760MPa.

4. The method for manufacturing the parking gear of an AT transmission according to claim 1, characterized in that: In step S3, the temperatures of the pre-sintering section, high-temperature section, and heat preservation section of the sintering furnace are controlled at 800~1000℃, 1200~1300℃, and 900~1100℃, respectively. The gear green blank stays in the high-temperature section for 6~8 hours and in the heat preservation section for 5~7 hours.

5. The method for manufacturing the parking gear of an AT transmission according to claim 1, characterized in that: In step S5, the quenching temperature is 830~860℃ and the tempering temperature is 500~550℃.