A piston and a method for preparing the same

Abstract

The present invention relates to a piston and a preparation method thereof, wherein a piston comprises a piston head and a piston skirt located below the piston head, characterized in that: a first convex portion and a first groove for limiting the upward and downward movement of the piston head and the piston skirt are matched between the butt surfaces of the piston head and the piston skirt, the end of the first convex portion has a laterally extending tooth portion, the first groove has a tooth groove matching the tooth portion at the position corresponding to the tooth portion, and the piston head is installed on the piston skirt by the limiting cooperation of the first convex portion and the first groove. In this way, the connection between the piston head and the piston skirt is more firm, avoiding the problem of piston failure caused by bolt connection in the prior art; the preparation method of the piston is simple, and the manufacturing cost is reduced.

Description

Technical Field

[0001] The invention relates to a piston, in particular to a piston used for a high-power diesel engine and a preparation method thereof. Background Art

[0002] As one of the most critical parts of a high-power diesel engine, the piston works under very harsh conditions. High temperature, high pressure and high-speed reciprocating motion require the piston to have comprehensive performance requirements such as high strength, high wear resistance, high heat resistance, high fatigue performance, low thermal expansion, high heat conduction and light weight.

[0003] At present, the steel top and aluminum skirt combined piston of high-power diesel engine are formed by forging process, the piston skirt is formed by casting or forging process, and the steel top and aluminum skirt are connected by bolts. For example, the Chinese utility model patent "A kind of automobile piston with long service life", whose patent number is CN201920206555.X (authorization announcement number is CN209838550U) discloses a kind of automobile piston with long service life, including a piston head and a piston skirt, a threaded hole is provided in the middle of the upper surface of the piston head, a piston gasket is circumferentially mounted on the threaded hole, a first annular groove is provided on the front of the piston head, and a second annular groove is provided on the lower surface of the first annular groove. Another example is the Chinese invention patent application "An Engine Piston", whose patent application number is CN201410620892.5 (application publication number is CN105332813A), which discloses an engine piston including a piston head and a piston skirt, and the piston head and the piston skirt are split structures; the piston head is processed with an annular groove, a combustion chamber and an internal cooling oil channel, and a separate central pin seat is arranged in the middle of the inner cavity of the piston head, and the end of the central pin seat away from the piston head is processed with a pin hole perpendicular to the axis of the piston head; the piston skirt is cylindrical; the central pin seat of the piston head penetrates into its cylindrical inner cavity from one end of the piston skirt; relative to the central pin seat that penetrates into its inner cavity, the piston skirt is provided with a pin seat hole coaxial with the pin hole of the central pin seat on the side wall, and the piston head and the piston skirt are pin-connected with a three-pin seat structure through the above structure.

[0004] The steel tops of the pistons in the above structures are relatively thick (accounting for about 1 / 5 to 1 / 3 of the height of the piston), and the bolt connection method has poor reliability. During use, due to the different thermal expansion coefficients of steel and aluminum, the bolt connection is likely to fail, causing the steel top to fall off; in addition, the relatively large weight of the piston will increase the inertia of the piston during movement, which will also cause the piston to fail prematurely; in addition, this type of piston has low thermal conductivity and relatively high manufacturing costs.

[0005] Therefore, it is necessary to further improve the existing piston. Summary of the invention

[0006] The first technical problem to be solved by the present invention is to provide a piston with a firm connection and a piston head that is not easy to fall off, in view of the current status of the above-mentioned prior art.

[0007] The second technical problem to be solved by the present invention is to provide a method for preparing the above-mentioned piston.

[0008] The technical solution adopted by the present invention to solve the above-mentioned first technical problem is: a piston, including a piston head and a piston skirt located below the piston head, characterized in that a first convex portion and a first groove are matched between the mating surfaces of the piston head and the piston skirt to limit the up and down movement of the two, the end of the first convex portion has a laterally extending tooth portion, and the first groove has a tooth groove matching the tooth portion at the position corresponding to the tooth portion, and the piston head is installed on the piston skirt through the limiting cooperation of the first convex portion and the first groove.

[0009] The first convex part can be formed on the lower surface of the piston head, and the first concave part can be formed on the upper surface of the piston skirt. Alternatively, the first convex part can be formed on the upper surface of the piston skirt, and the first concave part can be formed on the lower surface of the piston skirt. However, preferably, the first convex part is arranged at a position near the middle of the lower surface of the piston head and extends downward. There are a plurality of teeth, which are arranged at intervals along the circumferential direction on the outer peripheral wall of the lower end of the first convex part, and the first concave part is formed on the upper surface of the piston skirt and is concave downward. In this way, the connection between the piston head and the piston skirt is more firmly established.

[0010] In order to further increase the firmness of the connection between the piston head and the piston skirt, a second convex part and a second groove are matched between the butt joint surfaces of the piston head and the piston skirt to limit the up and down movement of the two. The second convex part is arranged at intervals with the first convex part, or the second convex part is arranged at intervals with the first groove. The end of the second convex part has an extension part extending laterally outward, and the second groove has a receiving groove matching the extension part at the position corresponding to the extension part. In this way, the piston head is limited to the piston skirt by the matching connection of the first convex part and the first groove and the second convex part and the second groove, without the need to set bolts, which reduces the cost while ensuring the firmness of the connection.

[0011] The longitudinal section of the second protrusion may be L-shaped or T-shaped, but from the perspective of secure connection, preferably, the extension portion is formed by extending outward from the peripheral wall of the second protrusion, and the longitudinal section of the second protrusion is an inverted T-shape as a whole.

[0012] The second protrusion can be formed on the upper surface of the piston skirt or on the lower surface of the piston head, but preferably, the second protrusion is formed on the upper surface of the piston skirt adjacent to the edge and extends upward, and the second groove is formed on the lower surface of the piston head and is recessed upward, and the longitudinal section of the second groove is T-shaped.

[0013] In order to increase the circumferential connection between the piston head and the piston skirt, the second protrusions and second grooves are arranged in groups, and there are at least two groups, and are arranged at intervals along the circumference around the first protrusions or first grooves.

[0014] Preferably, an annular cooling oil channel is formed between the piston head and the piston skirt, the top surface of the cooling oil channel is bent downward, and the cooling oil channel is located between the first convex portion and the second convex portion. In this way, the contact area between the cooling oil channel and the piston head is increased, so that the cooling effect on the piston head is enhanced, and the heat resistance of the piston is improved.

[0015] The technical solution adopted by the present invention to solve the second technical problem is: a method for preparing the piston as described above, characterized in that it comprises the following steps in sequence:

[0016] S1: Forging the alloy steel into the shape of the piston head;

[0017] S2: Install the piston squeeze casting mold on the squeeze casting equipment to make it work properly;

[0018] S3: placing the aluminum alloy into a melting electric furnace for melting, refining, and modification, and stabilizing the temperature of the aluminum alloy melt at 750° C. to 760° C.;

[0019] S4: preheating the piston extrusion casting mold, the preheating temperature of which is T0;

[0020] S5: preheating the ceramic soluble salt core and the piston head of the formed cooling oil channel, wherein the preheating temperature is T1, T1>T0;

[0021] S6: placing a ceramic soluble salt core at a position of the piston head corresponding to the cooling oil passage, then placing the piston head into a piston extrusion casting mold with the first convex portion of the piston head facing upward, then pouring the aluminum alloy melt of step S3 into the piston extrusion casting mold, closing the mold and applying pressure, and opening the mold after maintaining the pressure to take out the casting;

[0022] S7: Dissolve the ceramic soluble salt core with water to prepare a piston with a cooling oil channel.

[0023] Specifically, the preheating temperature T0 in step S4 is 200℃~280℃; the preheating temperature T1 in step S5 is 500℃~550℃, and the preheating time is 1h~2h; the pressurization pressure in step S6 is 100MPa~120MPa, and the pressure is maintained for 120s~180s. If the mold temperature is too low, the aluminum alloy melt will not be well combined with the piston head, and the skirt will also be prone to cold shut, insufficient pouring and other defects. If the temperature is too high, the aluminum alloy melt will splash out during the mold closing and pressurization during the extrusion casting process, and the mold life will be significantly reduced. Therefore, T0 is 200℃~280℃; if the preheating temperature T1 is too low, the ceramic salt core will be heated rapidly and cracks will be generated during the extrusion casting process, and the aluminum liquid will squeeze into the ceramic salt core, blocking the smooth flow of the internal cooling oil cavity, and the piston will be scrapped; if the preheating temperature T1 is too high, the ceramic salt core and the piston will expand too much, resulting in deformation. If the pressure is too high for too long, the ceramic salt core will break too low. If the pressure is too low for too short, the aluminum alloy structure of the skirt will not be dense and the bonding rate with the head will be reduced.

[0024] Specifically, the piston head is made of 38MnVS6 steel or 42CrMo steel, which has good heat resistance and volume stability.

[0025] Compared with the prior art, the advantages of the present invention are that the piston head and the piston skirt of the piston are fixedly connected by matching first protrusions and first grooves, wherein the peripheral wall of the first protrusion has teeth, and the first groove has tooth grooves matching the teeth, and the matching connection of the first protrusion and the first groove limits the upward and downward relative movement of the piston head and the piston skirt, thereby making the connection between the piston head and the piston skirt more secure, avoiding the problem of piston failure caused by bolt connection in the prior art; the preparation method of the piston is simple, and the manufacturing cost is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is a cross-sectional view of Embodiment 1 of the present invention;

[0027] Figure 2 for Figure 1 A cross-sectional view of the piston skirt in FIG.

[0028] Figure 3 is a top view of the piston skirt in the first embodiment;

[0029] Figure 4 A bottom view of the piston head in the first embodiment;

[0030] Figure 5 is a partial cross-sectional view at the location of the second convex portion in the first embodiment;

[0031] Figure 6 for Figure 5 A partial cross-sectional view of the piston head in FIG.

[0032] Figure 7 for Figure 5 Partial cross-sectional view of the piston skirt. DETAILED DESCRIPTION

[0033] The present invention is further described in detail below with reference to the accompanying drawings. Example

[0034] like Figures 1 to 7 As shown, the piston of the embodiment of the present invention comprises a piston head 1 and a piston skirt 2 located below the piston head 1, wherein the piston head 1 is made of 38MnVS6 steel.

[0035] like Figure 1 As shown, the top surface of the piston head 1 is recessed downward to form a combustion chamber 13, and the bottom wall of the combustion chamber 13 has a protrusion 131 extending upward near the middle, so that the longitudinal section of the combustion chamber 13 is ω-shaped.

[0036] like Figure 1 and Figure 4 As shown, the lower surface of the piston head 1 has a first convex portion 11, which is arranged near the middle of the lower surface of the piston head 1 and extends downward. The lower end of the first convex portion 11 has a tooth portion 111 extending laterally outward. Figure 4 As shown, there are multiple teeth 111, and they are arranged circumferentially on the outer peripheral wall of the first protrusion 11; Figure 2 As shown, a first groove 22 is formed on the upper surface of the piston skirt 2 at a position corresponding to the first convex portion 11, and the first groove 22 matches the first convex portion 11, and the first groove 22 has a tooth groove 221 matching the tooth portion 111 at a position corresponding to the tooth portion 111, so the opening of the first groove 22 is small at the top and large at the bottom, that is, the longitudinal section of the first groove 22 is in an inverted T shape as a whole; the middle position of the above-mentioned piston head 1 is installed at the corresponding position of the piston skirt 2 through the limiting cooperation of the first convex portion 11 and the first groove 22, so that the limiting cooperation of the first convex portion 11 and the first groove 22 limits the relative movement of the piston head 1 and the piston skirt 2 up and down. The connection between the upper end of the first convex portion 11 and the piston head is rounded, the radius of the rounded corner is 2mm, and the angle formed between the outer edge of the tooth portion 111 and the lower end surface of the first convex portion 11 is a, and a is 60°.

[0037] like Figure 1 , Figures 3 to 7As shown, the lower surface of the piston head 1 has a plurality of second grooves 12 that are recessed upwards at positions adjacent to the circumference. In this embodiment, there are four second grooves 12, which are arranged at intervals along the circumferential direction on the periphery of the first convex portion 11. The upper surface of the piston skirt 2 has second convex portions 21 that extend upwards at positions corresponding to the second grooves 12. There are four second convex portions 21, and the upper end portion of each second convex portion 21 has an extension portion 211 that extends laterally outwards. The longitudinal section of the second convex portion 21 as a whole can be It is L-shaped or inverted T-shaped. In this embodiment, the extension portion 211 is formed by extending the peripheral wall of the second convex portion 21 outward. The cross section of the extension portion 211 is circular. The outer diameter of the extension portion 211 is 40 mm, and the longitudinal section of the second convex portion 21 is T-shaped; the second groove 12 is provided with a receiving groove 121 matching the extension portion 211 at a position corresponding to the extension portion 211, and the second groove 12 matches the second convex portion 21, and the longitudinal section of the second groove 12 is also T-shaped. In this way, Figure 5 As shown, the surrounding of the piston head 1 is installed on the corresponding position of the piston skirt 2 through the limiting cooperation of the second convex part 21 and the second groove 12. In this way, the limiting cooperation of the second convex part 21 and the second groove 12 limits the relative movement of the piston head 1 and the piston skirt 2 up and down. The width B1 of the bottom opening of the second groove 12 is 12mm, the maximum width B2 in the second groove 12 is 20mm, the height L of the second convex part 21 is 10mm, the thickness h2 of the lower end of the second convex part 21 is 30mm, and the connection between the extension part 211 and the second convex part 21 is a smooth transition. In this embodiment, the connection between the extension part 211 and the second convex part 21 is rounded, and the radius of the rounded corner is 2mm.

[0038] like Figure 1 and Figure 3 As shown, an annular cooling oil channel 3 is formed between the piston head 1 and the piston skirt 2. The cooling oil channel 3 is located between the first groove 22 and the second protrusion 21. The top surface of the cooling oil channel 3 is bent downward, so that the contact area between the cooling oil channel 3 and the piston head 1 is increased, so that the cooling effect on the piston head 1 is enhanced, and the heat resistance of the piston is improved.

[0039] The preparation method of the piston comprises the following steps in sequence:

[0040] S1: Forging the alloy steel into the shape of the piston head 1;

[0041] S2: Install the piston squeeze casting mold on the squeeze casting equipment to make it work properly;

[0042] S3: placing the aluminum alloy into a melting electric furnace for melting, refining, and modification, and stabilizing the temperature of the aluminum alloy melt at 750°C;

[0043] S4: preheating the piston extrusion casting mold, wherein the preheating temperature T0 is 250° C.;

[0044] S5: preheating the ceramic soluble salt core of the formed cooling oil channel 3 and the piston head 1, wherein the preheating temperature T1>T0, the preheating temperature T1 is 550°C, and the preheating time is 1h;

[0045] S6: placing a ceramic soluble salt core at a position of the piston head 1 corresponding to the cooling oil passage 3, then placing the piston head 1 into a piston extrusion casting mold with the first convex portion 11 of the piston head 1 facing upward, then pouring the aluminum alloy melt of step S3 into the piston extrusion casting mold, closing the mold and applying pressure at a pressure of 110 MPa, and opening the mold to take out the casting after maintaining the pressure for 160 seconds;

[0046] S7: The ceramic soluble salt core is dissolved with water to prepare a piston having a cooling oil channel 3 . Example

[0047] The piston structure and the piston preparation method of this embodiment are the same as those of the above-mentioned embodiment 1, and the only difference is that: 1) the piston head 1 is made of 42CrMo steel; 2) the specific parameters in the piston preparation method are different. Specifically, in step S3, the temperature of the aluminum alloy melt is stabilized at 755°C; the preheating temperature T0 in step S4 is 280°C, the preheating temperature T1 in step S5 is 500°C, and the preheating time is 2h. In step S6, the pressurization pressure is 100MPa and the pressure is maintained for 180s. Example

[0048] The piston structure and the piston preparation method of this embodiment are the same as those of the above-mentioned embodiment 1, and the only difference is that the specific parameters in the piston preparation method are different. Specifically, in step S3, the temperature of the aluminum alloy melt is stabilized at 760°C; the preheating temperature T0 in step S4 is 200°C, the preheating temperature T1 in step S5 is 520°C, and the preheating time is 1.5h. In step S6, the pressurization pressure is 120MPa and the pressure is maintained for 120s.

Claims

1. A piston, comprising a piston head (1) and a piston skirt (2) located below the piston head (1), characterized in that: A first convex portion (11) and a first concave groove (22) are matched between the butt joint surfaces of the piston head (1) and the piston skirt (2) for limiting the relative upward and downward movement of the two. The end of the first convex portion (11) has a tooth portion (111) extending laterally outward, and the first concave groove (22) has a tooth groove (221) matching the tooth portion (111) at a position corresponding to the tooth portion (111). The piston head (1) is mounted on the piston skirt (2) by limiting the first convex portion (11) and the first concave groove (22). A second convex portion (21) and a second concave portion (12) are matched between the butt joint surfaces of the piston head (1) and the piston skirt (2) for limiting the relative upward and downward movement of the two. The second convex portion (21) and the first convex portion (11) are arranged at intervals, or the second convex portion (21) and the first concave portion (22) are arranged at intervals. The end of the second convex portion (21) has an extension portion (211) extending laterally outward, and the second concave portion (12) is provided with a receiving groove (121) matching the extension portion (211) at a position corresponding to the extension portion (211); The extension portion (211) is formed by extending outward from the peripheral wall of the second convex portion (21), and the longitudinal section of the second convex portion (21) is in an inverted T shape as a whole.

2. The piston according to claim 1, characterized in that: The first protrusion (11) is arranged at a position near the middle of the lower surface of the piston head (1) and extends downward. There are multiple teeth (111) and they are arranged at intervals along the circumferential direction on the outer peripheral wall of the lower end of the first protrusion (11). The first groove (22) is formed on the upper surface of the piston skirt (2) and is recessed downward.

3. The piston according to claim 1, characterized in that: The second protrusion (21) is formed on the upper surface of the piston skirt (2) at a position adjacent to the edge and extends upward, the second groove (12) is formed on the lower surface of the piston head (1) and is recessed upward, and the longitudinal section of the second groove (12) is T-shaped.

4. The piston according to claim 1, characterized in that: The second convex portions (21) and the second concave portions (12) are arranged in groups, and there are at least two groups, and are arranged at intervals along the circumferential direction on the periphery of the first convex portions (11) or the first concave portions (22).

5. The piston according to claim 1, characterized in that: An annular cooling oil passage (3) is formed between the piston head (1) and the piston skirt (2); the inner top surface of the cooling oil passage (3) is bent downward, and the cooling oil passage (3) is located between the first convex portion (11) and the second convex portion (21).

6. A method for preparing a piston as claimed in claim 5, characterized in that: The following steps are included in sequence: S1: Forging the alloy steel into the shape of the piston head (1); S2: Install the piston squeeze casting mold on the squeeze casting equipment to make it work properly; S3: placing the aluminum alloy into a melting electric furnace for melting, refining, and modification, and stabilizing the temperature of the aluminum alloy melt at 750° C. to 760° C.; S4: preheating the piston extrusion casting mold, the preheating temperature of which is T0; S5: preheating the ceramic soluble salt core of the formed cooling oil channel (3) and the piston head (1), wherein the preheating temperature is T1, T1>T0; S6: placing the ceramic soluble salt core at a position of the piston head (1) corresponding to the cooling oil passage (3), then placing the piston head (1) into a piston extrusion casting mold, with the first convex portion (11) of the piston head (1) facing upward, then pouring the aluminum alloy melt of step S3 into the piston extrusion casting mold, closing the mold and applying pressure, and after maintaining the pressure, opening the mold and taking out the casting; S7: Dissolve the ceramic soluble salt core with water to prepare a piston with a cooling oil channel (3).

7. The preparation method according to claim 6, characterized in that: The preheating temperature T0 in step S4 is 200°C to 280°C; the preheating temperature T1 in step S5 is 500°C to 550°C, and the preheating time is 1h to 2h; the pressurizing pressure in step S6 is 100MPa to 120MPa, and the pressure is maintained for 120s to 180s.

8. The preparation method according to claim 6, characterized in that: The piston head (1) is made of 38MnVS6 steel or 42CrMo steel.

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