JP3980336B2 - Method for manufacturing a closed cavity piston - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to the field of hydrodynamic units, such as transmissions, pumps, or motors, and more particularly, the invention relates to closed cavities that slidably reciprocate within a cylinder bore of a hydrodynamic unit, or oil volume reduction. Regarding the piston.
[0002]
[Prior art]
Known closed cavity pistons are used in hydrodynamic units for various agricultural machines, lawn mowers and construction machines.
[0003]
One conventional type of closed cavity, or oil volume reducing piston, has an elongated cylindrical main body and a truncated cylindrical cap. One end of the main body is closed and the other end has a deep target-like or annular cavity formed therein by a relatively costly “target drill” operation. The stem remains in the center by the target drilling operation. This stem is integral with the closed end of the main body and projects towards the open end.
[0004]
The cap is cold formed and has opposed closed and open ends. At the open end, the open end of the cap has an annular groove and a truncated stem portion so that the cap is aligned and mated with the stem and outer wall of the main body.
[0005]
This conventional piston is assembled by adding a washer between the stem and the inner wall of the main body near the open end. This washer is intended to help center and stabilize the stem during welding. Next, the cap and the main body are inertial friction welded along a single lateral plane where the respective open ends coincide.
[0006]
[Problems to be solved by the invention]
This results in a lightweight hollow closed cavity piston, but due to the cost and complexity of the target drilling operation, the piston is relatively expensive.
[0007]
Considering that a hydrodynamic unit typically requires several pistons for each unit, the cost of the piston has a significant impact on the overall cost of the unit and the hydrodynamic transmission in which these units are installed. give.
[0008]
Accordingly, there is a need for a closed cavity piston that does not require a target drill operation and that reduces costs, and a method for manufacturing the same.
[0009]
[Means for Solving the Problems]
The present invention relates to a closed cavity piston for a hydrodynamic unit and a method of manufacturing the same.
[0010]
The closed cavity piston of the present invention includes an elongate piston body and a separately formed piston cap having an elongate stem and a head disposed thereon. The piston body has a closed end and an open end with a cavity. The cavity has a bottom wall adjacent to the closed end and an outer wall that terminates as a rim at the open end.
[0011]
The stem of the piston cap is inertial friction welded to the bottom wall of the piston body, and the head of the piston cap is welded to the rim of the piston body, covering the inlet opening and closing the inner cavity in a sealed state.
[0012]
Both piston parts can be formed by known relatively inexpensive cold forming techniques. The stem of the cap is inserted into the cavity of the body until it engages the bottom wall, and then after the preheating of the cap, at the boundary between the stem and the bottom wall and at the boundary between the head and the rim, the piston body Inertial friction welding.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
1 and 2 show a piston rim formed by conventional inertia friction welding. As briefly described so far, the piston 10 has a steel piston body 12 , a cold formed steel piston cap 14, and a metal washer 16. The piston body 12 has a closed end, an open end, and an annular inner cavity 18. A stem 20 projects from the closed end of the piston body, and the free end 22 of the stem 20 is in the same plane as the rim 24 of the piston body 12. The piston cap 14 is cylindrical like the piston body 12 and is formed cold.
[0014]
However, due to the elongated stem 20, the piston body 12 cannot be cold formed. Instead, costly target drill operations are required to form the cavity 18 and stem 20. The cap 14 is inertia welded to the piston body 12 in a single lateral plane that includes the rim 24 and the end 22 of the stem 20.
[0015]
With reference to FIGS. 3 and 4, the piston 30 of the present invention includes a steel piston body 32 and a steel piston cap 34. The piston body 32 is elongated further and a open end 32A and a closed end 32 B facing (Fig. 4). The piston body 32 is cylindrical and has a generally cylindrical inner cavity 38 located in the center, around which a cylindrical wall extends.
[0016]
The open end 32 </ b> A of the piston body 32 has an inlet opening 39 inside, from which an inner cavity 38 extends inward, a bottom wall 40 adjacent to the closed end, and adjacent to the inlet opening 39. In the open end portion 32A of the piston main body 32, a rim 44, that is, an outer wall 42 that terminates as a contact portion is formed.
[0017]
The bottom wall 40 has a socket or contact surface 46 therein that has a recessed central portion 48 and a countersink 50 that extends within the portion.
[0018]
In the embodiment shown in FIGS. 3 and 4, the recessed central portion 48 is conical and is between 90 degrees and 165 degrees, more preferably 118 if the part is not cold formed into a full bottom wall shape. The inclination angle is up to about 120 degrees, which can be formed by a standard drill having a drill point of degree.
[0019]
The counter sink 50 forms an angle B of approximately 15 degrees with respect to a plane perpendicular to the central axis in the longitudinal direction of the piston body 32.
[0020]
The cap 34 has an elongated cylindrical stem 52 with a central longitudinal axis, opposing first and second ends, and a head 54 provided at the first end. A head 54 protrudes outward from the stem 52 in the lateral direction with respect to the longitudinal axis of the stem. The head 54 is sufficiently large to cover the inlet opening 49 of the piston body 32.
[0021]
Head 54 of the cap 34, as the piston 30 further lighter may include an optional annular recess or groove 4 8 surrounding the stem 52. The cap 34 has a rim or contact surface 55 (FIG. 4) that coincides with the contact surface 44 on the piston body 32.
[0022]
In the embodiment shown in FIGS. 3 and 4, the second end of the stem 52, i.e. the contact surface 56, is approximately the same as the recess-shaped central portion 48 in the bottom wall of the piston body 32, i.e. the surface of the socket 46. It is conical to match and engage.
[0023]
The countersink 50 of the socket 46 helps guide the second stem end 56 into the recess 48. The conical second end 56 of the stem has a tilt angle of about 90 to 165 degrees, more preferably up to about 120 degrees.
[0024]
In the embodiment shown in FIG. 5, the piston cap 34A to the piston body 32 is attached, the piston body 32, inside the central bore, i.e. an inner cavity 38A, rim, namely an outer wall 42A having the contact surface 44A 3 and 4 in that it has a bottom wall 40A.
[0025]
However, the second end of the stem 52A, i.e. the contact surface 56A has a planar surface extending at right angles to the longitudinal axis of the stem. Similarly, the recessed central portion 48A of the socket 46A has a round region defined by a planar contact surface extending perpendicular to the longitudinal axis of the piston body 32A. Round have regions of the recess 48 A has approximately the same diameter as the diameter of the second end 56A of the stem 52A.
[0026]
A counter sink 50A is provided for guiding the stem into the recess 48A.
[0027]
The method for producing the piston 30 or 30 ' of the present invention is basically the same. It is preferable that both the piston bodies 32 and 32 ′ and the piston caps 34 and 34A are provided in such a state that the stem and the bottom wall already formed by the cold forming method can be easily welded.
[0028]
Alternatively, the part can be machined from the beginning. Therefore, in any case, a relatively expensive target drill operation is not necessary.
[0029]
The stems 52, 52A are inserted into the inner cavities 38, 38A until they engage the bottom walls 40, 40A. Next, parts 32 and 34 or 32 'and 34A are rotated together and joined together by friction inertia welding.
[0030]
The length of the stems 52, 52A is slightly longer than the depth of the cavities 38, 38A, taking into account the normal loss of length associated with inertial welding. Therefore, the stem length LS is longer than the cavity depth CD by a length sufficient to account for material loss at both the stem-bottom wall interface and the plane-rim interface. .
[0031]
However, care must be taken that the LS is not too long than the CD. In such a case, the welded portion of the rim is adversely affected and the stem is bent. Problems arise with bent stems when trying to drill a conventional small longitudinal orifice hole later through the stem and through the piston.
[0032]
Friction inertia welds are formed at two different boundaries (55 and 44; 56 and 48A) in at least two different planes. By cold forming such piston bodies (32 and 32 ') and caps (34 and 34A), it is possible to obtain the true shape of these parts without machining, so You can save a lot of money.
[0033]
However, to cold form these parts, the two boundary surfaces (in FIGS. 4 and 5, between the cap 55 and the rim surface 44 of the piston body, as well as 56 and 56A in FIGS. 4 and 5). And between 48 and 48A). These surfaces are spaced apart in the longitudinal direction and are located inside and outside. Inner boundaries (eg 56 and 48) are particularly difficult to weld due to inertia because their mutual areas are narrow and the amount of heat generated during rotation is small.
[0034]
Accordingly, the piston structure according to the present invention is welded by an inertial method in which a longitudinal force is applied to the main body 32 and the cap 34 in the opposite direction and one member must be rotated with respect to the other fixed member. In order to be able to do so, it has been found that parts must be preheated in critical areas in order to achieve acceptable welding. Acceptable welding means welding with no defects in the thickness of the smallest cross section to be joined (ie the thickness of the stem for the internal weld).
[0035]
An analysis of acceptable welds is performed by metallurgical methods to exclude welds that have voids, cracks, or other conventional elements, or other strength and durability imperfections.
[0036]
Furthermore, it has been found that heat, pressure and rotational speed conditions must be balanced with predetermined parameters in order to be able to tolerate an effective weld, particularly an inner weld, in the apparatus of the present invention. Experiments show that in order to achieve acceptable inertia welding, the following high (H), medium (M) and low (L) values from temperature, pressure, and speed must be met. It was.
[0037]
Table I-Acceptable welds in hydrodynamic pistons for inner welds
Speed, pressure, and heat parameters for the part
Low (L) Medium (M) High (H)
Speed (rpm) 4700 4800 4900
Pressure (psi) 1400 1500 1600
Amount of heat applied (Kw) 8.1 8.8 9.5
[0038]
Table 2-Acceptable welds for internal welds in hydrodynamic pistons
It has been found acceptable to produce parts. (1) Speed, (2) Pressure, and (3) Combination from heat quantity parameters
HHH LHH LLH
HHL MMM HLH
LHL LLL HLL
[0039]
From the drawings and the above description, it can be seen that the geometric attributes of the cap, stem end, and piston body are parameters that can be adjusted to optimize the integrity of the friction inertia weld.
[0040]
Based on the foregoing, it will be appreciated that the present invention can satisfy at least the objectives described above.
[0041]
CROSS REFERENCE WITH RELATED APPLICATIONS This application is based on a continuation-in-part of pending application 09 / 722,617 filed with the US Patent Office on November 27, 2000.
[Brief description of the drawings]
FIG. 1 is a transverse cross-sectional view in the longitudinal direction of a conventional piston.
2 is an exploded view of the piston of FIG. 1 in a longitudinal cross section.
FIG. 3 is a longitudinal central cross-sectional view of a piston manufactured in accordance with the present invention.
4 is an exploded view of the piston of FIG. 3 in a longitudinal section.
FIG. 5 is an exploded view similar to FIG. 4 showing another stem and bottom wall structure.
[Explanation of symbols]
10 piston 12 piston body 14 piston cap 16 washer 18 cavity 20 stem 22 free end 24 rim 30 piston
30A Piston 32 Piston body
32 'piston body
32A Open end
32B Closed end 34 Piston cap
34A Piston cap 38 Cavity
38A Cavity 39 Inlet opening 40 Bottom wall
40A Bottom wall 42 Outer wall
42A outer wall 44 rim
44A Rim 46 Contact surface
46A Contact surface 48 Recessed central portion
48A Recessed center part 50 Countersink
50A counter sink 52 stem
52A stem 54 head
54A Head 55 Contact surface
55A contact surface
56 Second end
56A Second end 58 groove
58A Groove

Claims (11)

A method of manufacturing a closed cavity piston comprising :
Removing an elongated piston body having an inner cavity, a closed end, an open end, and an outer wall extending around the cavity and terminating at a first contact surface at the open end of the piston body;
Providing in the cavity a second contact surface spaced longitudinally from the first contact surface;
Third and fourth contact surfaces having an elongated stem having a conical or planar surface at the tip and a head disposed on the stem and aligned with the first and second contact surfaces of the piston body, respectively Take out the cap element with
Inertial friction welding simultaneously welds the first surface to the third surface and the second surface to the fourth surface, thus applying longitudinal pressure to the piston body and cap element so that the respective contact surfaces are longitudinal. Maintaining in close engagement, then rotating one of the piston body and cap element relative to the other to generate sufficient heat between the engaged contact surfaces to weld the surfaces together; A method of manufacturing a closed cavity piston comprising:   The method of claim 1, wherein the engaged contact surface is preheated prior to performing the inertia friction welding.   The method of claim 1, wherein the parameter for the applied longitudinal pressure is 1400-1600 psi and the parameter for the rotational speed of the rotating member is 4700-4900 rpm.   The method of claim 3 wherein the engaged contact surface is preheated prior to performing the inertia friction welding.   The method according to claim 4, wherein the parameter of the preheat amount in Kw is 8.1 to 9.5.   Low (L), medium (M) and high (H) values for speed (L): 4700 rpm; (M): 4800 rpm; and (H): 4900 rpm for pressure (L): 1400 psi; (M ): 1500 psi; and (H): 1600 psi, with respect to the amount of heat applied (L): 8.1 Kw; (M): 8.8 Kw; 6. The method of claim 5, wherein HHL; HHL; LHL; LHH; MMM; LLL; LLH; and approximately within the combined range of one of HLH and HLL. It has a internal weld boundary, between the end cap element and the piston body with a head provided on the elongate stem and said stem having a conical shape or flat surface, internal welding by inertia friction welding In the method of forming the part,
Preheating the internal welding interface;
Applying a longitudinal pressure opposite the cap element and the piston body to frictionally engage the cap element and the piston body at a boundary;
Rotating the cap element or the piston body, generating sufficient heat between the engaged contact surfaces and welding the surfaces together to form an internal connection.   8. The method of claim 7, wherein the parameter for the applied longitudinal pressure is 1400-1600 psi and the parameter for the rotational speed of the rotating member is 4700-4900 rpm.   The method of claim 8 wherein the engaged contact surface is preheated prior to performing the inertia friction welding.   The method according to claim 9, wherein the parameter of the preheat amount in Kw is 8.1 to 9.5.   Low (L), medium (M) and high (H) values for speed (L): 4700 rpm; (M): 4800 rpm; and (H): 4900 rpm for pressure (L): 1400 psi; (M ): 1500 psi; and (H): 1600 psi, with respect to the amount of heat applied (L): 8.1 Kw; (M): 8.8 Kw; and (H): 9.5 Kw, and the speed, pressure and heat parameter levels are 11. The method of claim 10, wherein the method is approximately within the combined range of one of HHH; HHL; LHL; LHH; MMM; LLL;

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