Description:TECHNICAL FIELD
[001] The embodiments herein generally relate to engine pistons and more particularly, to a method and a system for manufacturing the engine piston skirt with reduced asperities thereby achieving better surface finish.
BACKGROUND
[002] Generally, an engine piston is used to transfer combustion power to an engine crankshaft via a connecting rod. Typically, the manufacturing of engine piston involves machining a piston skirt area is machined on the engine piston by using machining tools, coating the machined piston skirt area with a composite coating agent, and the coated piston is subjected to manual quality inspection and dispatching the piston after quality inspection. The piston skirt of the engine piston which is produced by using the conventional manufacturing process is subjected to uneven surface finish which increases the possibility of friction between the engine piston and engine cylinder liner due to tighter clearance allowed between the engine piston and the engine cylinder. This in turn may result in wear and tear of the engine piston and/or the engine cylinder liner during lubricant starved condition. The wear and tear between pistons and cylinder bores is problematic as it may lead to decreased engine performance and may increase the chances of causing engine failure.
[003] Therefore, there exists a need for a method and a system for manufacturing the engine piston skirt with reduced asperities, which obviates the aforementioned drawbacks.
OBJECTS
[004] The principal object of embodiments herein is to provide a method and a system for manufacturing the engine piston skirt with reduced asperities thereby achieving better surface finish.
[005] Another object of embodiments herein is to flatten peaks of the engine piston skirt.
[006] Another object of embodiments herein is to reduce friction between the engine piston skirt and engine cylinder thereby reducing wear and tear on the engine piston thereby ensuring better lifetime of the engine piston.
[007] These and other objects of embodiments herein will be better appreciated and understood when considered in conjunction with following description and accompanying drawings. It should be understood, however, that the following descriptions, while indicating embodiments and numerous specific details thereof, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the embodiments herein without departing from the spirit thereof, and the embodiments herein include all such modifications.
BRIEF DESCRIPTION OF DRAWINGS
[008] The embodiments are illustrated in the accompanying drawings, throughout which like reference letters indicate corresponding parts in various figures. The embodiments herein will be better understood from the following description with reference to the drawings, in which:
[009] Fig. 1 depicts a perspective view of an engine piston, according to embodiments as disclosed herein;
[0010] Fig. 2 to Fig. 4 illustrate the engine piston inserted into a surface finishing device for flattening peaks of piston skirt, according to embodiments as disclosed herein;
[0011] Fig. 5 an exploded view showing locating members used for aligning a first fixture member with a second fixture member of the fixture, according to embodiments as disclosed herein;
[0012] Fig. 6 illustrates a waveform created exterior surface of piston skirt while performing conventional machining on a convention piston;
[0013] Fig. 7 illustrates a waveform created exterior surface of piston skirt while performing optimized machining on the engine piston, according to embodiments as disclosed herein;
[0014] Fig. 8 illustrates a tool which is used for machining piston skirt of the engine piston, according to embodiments as disclosed herein;
[0015] Fig. 9 illustrates surface texture of surface finished piston skirt of the engine piston after flattening peaks of the piston skirt by using the surface finishing device, according to embodiments as disclosed herein;
[0016] Fig. 10 illustrates the engine piston inserted into a surface finishing device and an actuator is coupled to the engine piston for flattening peaks of piston skirt, according to another embodiments as disclosed herein;
[0017] Fig. 11 illustrates the engine piston inserted into a surface finishing device and an actuator is coupled to the fixture of the surface finishing device for flattening peaks of piston skirt, according to another embodiments as disclosed herein; and
[0018] Fig. 12 depicts a flowchart indicating steps of a method of manufacturing the engine piston skirt with reduced asperities, according to embodiments as disclosed herein.
DETAILED DESCRIPTION
[0019] The embodiments herein and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.
[0020] The embodiments herein achieve a method and a system for manufacturing an engine piston skirt with reduced asperities thereby achieving better surface finish. Referring now to the drawings Figs 1 through 12, where similar reference characters denote corresponding features consistently throughout the figures, there are shown embodiments.
[0021] Fig. 1 depicts a perspective view of an engine piston (10), according to embodiments as disclosed herein. The engine piston (10) includes a piston top land (11L), a piston ring section (11R) and a piston skirt (12). The piston ring section (11R) extends from the piston top land (11L). The piston skirt (12) extends from the piston ring section (11R). The piston skirt (12) includes an exterior surface (12S). A plurality of ring grooves (11G) are formed in the piston ring section (11R) to receive rings such as compression rings (not shown) and an oil ring (not shown). The piston skirt (12) of the engine piston (10) is machined by traversing the length of the piston skirt (12) with a turning machine that is operated by computer numeric control (CNC). For purposes of example, the machine may utilize a tool (300) (as shown in fig. 8) such as a polycrystalline diamond tool or a single diamond tipped insert to perform the machining process. A tool nose radius of the tool (300) is at least 0.7+0.05 mm. The machining process creates a surface finish with a wave form (12W) (as shown in fig. 7) having peaks (12P) and valleys (12V) (as shown in fig. 7) on the exterior surface (12S) of the piston skirt (12). The dimension (Y) represents the peak-to-peak distance of the wave form (12W) and is defined by the transverse feed rate (in mm/revolution) of the turning operation by which the piston skirt (12) surface is machined. The peak-to-peak distance of the wave form (12W) is also referred to as roughness profile pitch. One revolution of the machine leads to the formation of one complete wave. Fig. 6 illustrates a waveform created exterior surface of piston skirt while performing conventional machining on a convention piston. For example, conventional pistons are machined with a transverse feed rate in a range between 0.17 and 0.23 mm per revolution results in a peak-to-peak distance (P) between 170 and 230 µm. Further, the dimension (Q) represents the difference between the highest peak and lowest valley within an assessment length. The assessment length is defined as the evaluation length and is typically equal to five times the cut-off length. It is the amount of material used for measuring the surface characteristics of a machine component. The dimension (Q) is also referred to as roughness total or roughness depth (Rz). Roughness total (Rz) is typically measured in micrometer (μm). The roughness total (Rz) of surface finish achieved by the conventional piston is in the range between 9 and 15 μm. A similar measured property is the surface roughness average (Ra). Roughness average (Ra) is defined as the arithmetic average distance of a roughness profile (points on the wave form) from its mean line (the mean “height” of the wave form). The roughness average (Ra) of surface finish achieved by the conventional piston is 3.290 μm. Further, another measured property is the valley radius which is also referred to as roughness profile radius. The valley radius of surface finish achieved by the conventional piston is 0.5 mm.
[0022] Fig. 7 illustrates a waveform (12W) created exterior surface (12S) of piston skirt (12) while performing optimized machining on the engine piston (10), according to embodiments as disclosed herein. In an embodiment, the engine piston (10) is machined with a transverse feed rate in a range between 0.14 and 0.22 mm per revolution (mm/ rev) results in the peak-to-peak distance (Y) between 140 to 220 µm. The dimension (Z) is also referred to as roughness total (Rt) or roughness depth. The roughness total (Z/ Rt) of surfaced finish achieved by the engine piston (10) is in the range between 3 and 9 μm. Furthermore, the roughness average (Ra) of surfaced finish achieved by the engine piston (10) is 1.453 μm. The valley radius of surfaced finish achieved by engine piston (10) is 0.7 mm. It can be observed from the aforementioned description and corresponding figures (fig. 6 and fig. 7), that the measured surface properties (peak to peak distance, roughness total & roughness average) of the machined piston skirt (12) surface of the engine piston (12) is lesser than the measured surface properties of the conventional machined piston skirt surface of conventional pistons. The exterior surface (12S) of the piston skirt (12) is coated with composite coating after machining the piston skirt (12).
[0023] Fig. 2 to Fig. 4 illustrate the engine piston (10) inserted into a surface finishing device (100) for flattening peaks (12P) of piston skirt (12), according to embodiments as disclosed herein. In an embodiment, the surface finishing device (100) includes a fixture (102A, 102B), a plurality of locating members (103A) (as shown in fig. 5), a plurality of locking members (103B), and a plurality of peak flattening members (104) (as shown in fig. 2, fig. 3 and fig. 5) affixed to the fixture (102A, 102B) at its inner side. The fixture (102A, 102B) includes a first fixture member (102A) and a second fixture member (102B) (as shown in fig. 3) which is joined with the first fixture member (102A) by using the locating members (103A) and the locking members (103B) to form the fixture (102A, 102B). For the purpose of this description, the first fixture member (102A) is considered as a first half of the fixture (102A, 102B), and the second fixture member (102B) is considered as a second half of the fixture (102A, 102B). Each of the first and second fixture member (102A, 102B) includes a base (102AB, 102BB), a curvature wall (102AW, 102BW) and a pair of flanges (102AF). The base (102AB, 102BB) of the first and second fixture members (102A, 102B) are adapted to support legs (12L) (as shown in fig. 2) of the piston skirt (12). The curvature wall (102AW, 102BW) extends from the base (102AB, 102BB). The profile of the curvature wall (102AW, 102BW) of each of the fixture member (102A, 102B) matches with the profile of the piston skirt (12). Each flange (102AF) extends from corresponding end of the curvature wall (102AW, 12BW). Each peak flattening member (104) is provided on the curvature wall (102AW, 102BW) of corresponding fixture member (102A, 102B) at its inner side. The locating members (103A) are adapted to align/ locate the first fixture member (102A) with the second fixture member (102B). For example, each locating member (103A) is adapted to be received by a locating member receiving portion (hole, not shown) defined on the flange (102AF, 102BF) of each of the first and second fixture member (102A, 102B) for aligning the first fixture member (102A) with the second fixture member (102B). For the purpose of this description and ease of understanding, each locating member (103A) is considered to be a dowel pin. The locking members (103B) are adapted to lock/fasten the first fixture member (102A) with the second fixture member (102B). For the purpose of this description and ease of understanding, each locking member (103B) is adapted to be received by a locking member receiving portion (thread hole, not shown) defined on the flange (102AF, 102BF) of each of the first and second fixture member (102A, 102B) for locking/fastening the first fixture member (102A) with the second fixture member (102B). For the purpose of this description and ease of understanding, each locking member (103B) is considered to be a fastener such as but not limited to hexagonal head bolts. The peak flattening members (104) are configured to flatten peaks (12P) (asperities) of the piston skirt (12). Each peak flattening member (104) is at least one of an emery paper or emery cloth and abrasive based medium. It is also within the scope of the invention to use any surface finishing means for flattening peaks (asperities) of the piston skirt (12). An operator (user) holds at least one of the piston top land (11L) and the piston ring section (11R), and linearly moves or rotationally moves or a combination of both linearly and rotationally moves the piston skirt (12) against the peak flattening members (104) of the surface finishing device (100) for flattening the peaks (12P) of the piston skirt (12). Further, in another embodiment, an actuator (500) can be coupled to the engine piston (10) to linearly move or rotate the piston skirt (12) against the peak flattening members (104) for flattening the peaks (12P) of the piston skirt (12). For example, an output member (502) (as shown in 10) of the actuator (500) can be directly connected to the legs (12L) (as shown in fig. 10) of the piston skirt (12) at its inner side. In another example, the output member (502) of the actuator (500) can be indirectly coupled to the piston skirt (12) at its inner side by using clamps or spacers. Further, in another embodiment, the output member (502) of the actuator (500) can be coupled to the fixture (102A, 102B) (as shown in fig. 11) to linearly move or rotate the fixture (102A, 102B) with respect to the piston skirt (12) for rubbing the peak flattening members (104) against the piston skirt (12) for flattening the peaks (12P) of the piston skirt (12). The actuator (500) is one of a linear actuator and a rotary actuator. In an embodiment, the actuator (500) is operated by a manual ON/OFF switch which switches ON or switches OFF electric current supply from a power source to the actuator (500). It is also within the scope of the invention to operate the actuator (500) through an electronic control unit. The surface finishing device (100), the tool (300), the actuator (500) and the ON/OFF switch/ electronic control unit forms a system (400) (as shown in fig. 10 and fig. 11) for manufacturing the engine piston skirt (12) with reduced asperities.
[0024] Fig. 9 illustrates surface texture of surface finished piston skirt (12) of the engine piston (10) after flattening peaks of the piston skirt (12) by using the surface finishing device (100), according to embodiments as disclosed herein. After flattening the peaks (12P) by using the surface finishing device (100), the exterior surface (12S) of the piston skirt (12) now exhibit a peak-to-peak distance (Y) in the range of 100 to 130 µm, and the roughness total or roughness depth (Z/ Rt) of less than 4.2 μm and a roughness average (Ra) of less than 1.2 μm which is lower than the measured surface properties (peak to peak distance, roughness total & roughness average) of conventional piston. It is clearly evident from the aforementioned description and corresponding figures (fig. 7 and fig. 9), that the image clearly indicates that the peaks (12P) of surface finished piston skirt (12) surface of the engine piston (12) is significantly flattened compared to unflatten peaks of the conventional machined piston. Therefore, the piston skirt (12) of the engine piston (10) has better surface finish (smooth surface finish) than the conventional machined piston skirt surface of conventional pistons.
[0025] Fig. 12 depicts a flowchart (200) indicating steps of a method (200) for manufacturing the engine piston skirt (12) with reduced asperities, according to embodiments as disclosed herein. At step (202), the method (200) includes, machining, by a tool (300), an engine piston skirt (12) defined on the engine piston (10) by maintaining a speed of the tool (300) in a range between 2000 rpm and 3000 rpm and maintaining a feed rate of the tool (300) in a range between 0.14 mm/revolution to 0.22 mm/revolution.
[0026] At step (204), the method (200) includes performing coating operation on the machined piston skirt (12). Further, at step (206), the method (200) includes flattening, by a surface finishing device (100), peaks (12P) of the coated piston skirt (12).
[0027] Further, the method step (206) includes rubbing the coated piston skirt (12) of the engine piston (10) against a peak flattening member (104) of the surface finishing device (100) thereby flattening peaks of the coated piston skirt (12). Further, the method step (206) includes introducing/inserting the engine piston (10) into a fixture (102A, 102B) of the surface finishing device (100) such that the coated piston skirt (12) of the engine piston (10) is facing against the peak flattening member (104) which is affixed to an inner side of the fixture (102A, 102B) prior to rubbing the coated piston skirt (12) of the engine piston (10) against the peak flattening member (104) of the surface finishing device (100).
[0028] Further, the method step of rubbing the coated piston skirt (12) of the engine piston (10) against the peak flattening member (104) of the surface finishing device (100) includes linearly moving, by manually or automatically by using a linear actuator (500), the coated piston skirt (12) of the engine piston (10) against the peak flattening member (104) of the surface finishing device (100) for flattening the peaks (12P) of the coated piston skirt (12).
[0029] Further, the method step of rubbing the coated piston skirt (12) of the engine piston (10) against the peak flattening member (104) of the surface finishing device (100) includes linearly moving, by manually or automatically by using a linear actuator (500), the fixture (102A, 102) of the surface finishing device (100) with respect to the piston skirt (12) for rubbing the peak flattening members (104) against the coated piston skirt (12) of the engine piston (10) thereby flattening the peaks (12P) of the coated piston skirt (12).
[0030] Furthermore, the method step of rubbing the coated piston skirt (12) of the engine piston (10) against the peak flattening member (104) of the surface finishing device (100) includes rotating, by manually or automatically by using a rotary actuator (500), the coated piston skirt (12) of the engine piston (10) against the peak flattening member (104) of the surface finishing device (100) for flattening the peaks (12P) of the coated piston skirt (12).
[0031] Furthermore, the method step of rubbing the coated piston skirt (12) of the engine piston (10) against the peak flattening member (104) of the surface finishing device (100) includes rotating, by manually or automatically by using a rotary actuator, the fixture (102A, 102B) of the surface finishing device (100) with respect to the piston skirt (12) for rubbing the peak flattening members (104) against the coated piston skirt (12) thereby flattening the peaks (12P) of the coated piston skirt (12).
[0032] Furthermore, the method step of rubbing the coated piston skirt (12) of the engine piston (10) against the peak flattening member (104) of the surface finishing device (100) includes rotationally and linearly moving, by manually or automatically by using actuators, the coated piston skirt (12) of the engine piston (10) against the peak flattening member (104) of the surface finishing device (100) for flattening the peaks (12P) of the coated piston skirt (12).
[0033] The technical advantages of the surface finishing device (100) used in conjunction with the method (200) for manufacturing the engine piston skirt (12) with reduced asperities are as follows. The engine piston (10) has the piston skirt (12) with better surface finish. The engine piston (10) has reduced friction with engine cylinder thereby reducing wear and tear on the engine piston resulting in better lifetime of the engine piston. The piston skirt (12) of the engine piston is provided with reduced flattened peaks compared to unflatten peaks of conventional pistons.
[0034] The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modifications within the spirit and scope of the embodiments as described herein.
, Claims:We claim,
1. A method (200) of manufacturing an engine piston (10), said method (200) comprising:
machining, by a tool (300), a piston skirt (12) on said engine piston (10) by maintaining a speed of said tool (300) in a range between 2000 rpm to 3000 rpm, and maintaining a feed rate of said tool (300) in a range between 0.14 mm/revolution to 0.22 mm/revolution;
performing coating operation on said machined piston skirt (12); and
flattening, by a surface finishing device (100), peaks (12P) of said coated piston skirt (12).
2. The method (200) as claimed in claim 1, wherein said flattening, by said surface finishing device (100), peaks (12P) of said piston skirt (12) includes,
rubbing said coated piston skirt (12) of said engine piston (10) against a plurality of peak flattening members (104) of said surface finishing device (100) thereby flattening the peaks (12P) of said coated piston skirt (12).
3. The method (200) as claimed in claim 2, wherein said flattening, by said surface finishing device (100), peaks (12P) of said piston skirt (12) includes,
introducing or inserting said engine piston (10) into a fixture (102A, 102B) of said surface finishing device (100) such that the coated piston skirt (12) of said engine piston (10) is facing against said peak flattening members (104) which is affixed to an inner side of said fixture (102A, 102B) prior to said rubbing the coated piston skirt (12) of said engine piston (10) against said peak flattening members (104) of said surface finishing device (100).
4. The method (200) as claimed in claim 2, wherein said rubbing the coated piston skirt (12) of said engine piston (10) against said peak flattening members (104) of said surface finishing device (100) includes,
rotating, by manually or automatically by using a rotary actuator (500), the coated piston skirt (12) of said engine piston (10) against said peak flattening member (104) of said surface finishing device (100) for flattening the peaks (12P) of said coated piston skirt (12).
5. The method (200) as claimed in claim 2, wherein said rubbing the coated piston skirt (12) of said engine piston (10) against said peak flattening members (104) of said surface finishing device (100) includes,
linearly moving, by manually or automatically by using linear actuator (500), the coated piston skirt (12) of said engine piston (10) against said peak flattening member (104) of said surface finishing device (100) for flattening the peaks (12P) of said coated piston skirt (12).
6. The method (200) as claimed in claim 2, wherein said rubbing the coated piston skirt (12) of said engine piston (10) against said peak flattening members (104) of the surface finishing device (100) includes rotationally and linearly moving, by manually or automatically by using actuators, said coated piston skirt (12) of said engine piston (10) against said peak flattening member (104) of said surface finishing device (100) for flattening said peaks (12P) of said coated piston skirt (12),
wherein
each of said peak flattening member (104) is at least one of an emery paper, emery cloth and abrasive based medium;
said tool (300) is at least a polycrystalline diamond tool; and
a tool nose radius of said tool (300) is at least 0.7+0.05 mm.
7. The method (200) as claimed in claim 1, wherein said flattening, by said surface finishing device (100), peaks (12P) of said coated piston skirt (12) includes,
linearly moving, by manually or automatically by using a linear actuator (500), said fixture (102A, 102) of said surface finishing device (100) with respect to said piston skirt (12) for rubbing said peak flattening members (104) against the coated piston skirt (12) of the engine piston (10) thereby flattening the peaks (12P) of the coated piston skirt (12).
8. The method (200) as claimed in claim 1, wherein said flattening, by said surface finishing device (100), peaks (12P) of said coated piston skirt (12) includes,
rotating, by manually or automatically by using a rotary actuator (500), the fixture (102A, 102B) of the surface finishing device (100) with respect to said piston skirt (12) for rubbing the peak flattening members (104) against the coated piston skirt (12) thereby flattening the peaks (12P) of the coated piston skirt (12).
9. A system (400) for manufacturing an engine piston (10) having a piston skirt (12P), said system (400) comprising:
a surface finishing device (100), wherein said device (100) includes,
a fixture (102A, 102B); and
a plurality of peak flattening members (104) affixed to said fixture (102A, 102B) at its inner side, wherein said peak flattening members (104) are configured to flatten peaks (12P) of said piston skirt (12).
10. The system (400) as claimed in claim 9, wherein said fixture (102A, 102B) includes a first fixture member (102A) and a second fixture member (102B),
wherein
said surface finishing device (100) includes,
a plurality of locating members (103A) are adapted to align said first fixture member (102A) with said second fixture member (102B); and
a plurality of locking members (103B) are adapted to lock said first fixture member (102A) with said second fixture member (102B) to form said fixture (102A, 102B).
11. The system (400) as claimed in claim 10, wherein each of said fixture member (102A, 102B) includes,
a base (102AB, 102BB);
a curvature wall (102AW, 102BW) extending from said base (102AB, 102BB); and
a pair of flanges (102AF), wherein each of said flange (102AF, 102BF) extends from end of said curvature wall (102AW, 12BW),
wherein
each of said peak flattening member (104) is provided on said curvature wall (102AW, 102BW) of corresponding said fixture member (102A, 102B) at its inner side,
each of said locating member (103A) is adapted to be received by a locating member receiving portion defined on said flange (102AF, 102BF) of each of said first and second fixture members (102A, 102B) for aligning said first fixture member (102A) with said second fixture member (102B);
each of said locking member (103B) is adapted to be received by a locking member receiving portion defined on said flange (102AF, 102BF) of each of said first and second fixture member (102A, 102B) for locking said first fixture member (102A) with said second fixture member (102B).
12. The system (400) as claimed in claim 9, wherein said peak flattening members (104) are configured to flatten peaks (12P) of said piston skirt (12) upon one of manually moving said piston skirt (12) against said peaks flattening member (104) or manually moving said fixture (102A, 102B) with respect to said piston skirt (12),
wherein manual movement includes one of linear movement, rotary movement or a combination of both linear and rotational movement.
13. The system (400) as claimed in claim 9, wherein said system (100) includes an actuator (502) having an output member (502) adapted to be coupled to one of said fixture (102A, 102B) or legs (12L) of said piston skirt (10) at its inner side , wherein said actuator (500) is piston skirt (12) configured to linearly move or rotate said piston skirt (12) against said peak flattening members (104) for flattening the peaks (12P) of said piston skirt (12) wherein said actuator (500) is one of a linear actuator and a rotary actuator.
14. The system (400) as claimed in claim 9, wherein said actuator (500) is configured to linearly move or rotate said fixture (102A, 102B) for rubbing said peak flattening members (104) against said for flattening the peaks (12P) of said piston skirt (12).
15. The system (100) as claimed in claim 9, wherein each of said peak flattening member (104) is at least one of an emery paper or emery cloth and abrasive based medium.
16. An engine piston (10) comprising:
a piston top land (11L);
a piston ring section (11R) extending from said piston top land (11L);
a piston skirt (12) extending from said piston ring section (11R), wherein said piston skirt (12) defines an exterior surface (12S) adapted to a coated with a composite coating, wherein said exterior surface (12S) includes a surface finish in a wave form (12W) with peaks (12P) and valleys (12W),
wherein
a roughness total (Z) of said surface finish is less than 4.2 μm;
a roughness average (Ra) of said surface finish is less than 1. 2 μm; and
a peak to peak distance (Y) of said surface finish is in the range of 100 to 130 µm.