JP2005100056A - Piston design support program, and method and device for supporting design - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piston design support program for making piston design more efficient. <P>SOLUTION: In the piston design support program, a specification value on a piston shape is inputted, a piston model which can be deformed in accordance with a prescribed rule is read from a database, and the piston model is deformed based on the inputted specification value. The database includes at least a main body model showing a shape of a combustion chamber face of the piston and a space model showing a space shape which is to be cut from the main body model as the piston models. The main body model and the space model are deformed in accordance with the specification value. The main body model is cut in a shape displayed by the space model, and 3D shape data of the whole piston is created. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a design support program, a design support method, and a design support apparatus for supporting a piston shape design by a computer.

  Conventionally, various pistons have been designed according to the destination and the displacement (see, for example, Patent Document 1). Since the shape of the piston is easy to change compared to a cylinder block or the like, the piston is subject to a fine design change for the purpose of realizing a target compression ratio, emission performance, and the like.

On the other hand, since there are many restrictions on the design of the piston and various dimensional values are related to each other in a complicated manner, the design of the piston is generally performed with the intuition of an expert. When designing a piston using 3D-CAD (Computer Aided Design) software, the entire piston is designed as one component, and there was no idea of further subdividing it.
Japanese Patent Publication No.7-86336

  However, conventionally, a plurality of pistons having a common shape must be designed completely separately, which is inefficient. In addition, the piston on the combustion chamber side and the other shapes were not clearly designed separately, so that an efficient piston design could not always be realized. That is, even when trying to design different pistons having the same shape on the combustion chamber side of the piston, the design of the piston has to be performed again from the beginning. Furthermore, it is necessary for the user to change the piston shape after grasping complicated rules for piston design.

  The present invention has been made to solve the above-described problems of the prior art, and an object of the present invention is to provide a technique for making the piston design more efficient.

In order to achieve the above object, a program according to the present invention provides:
On the computer,
An input process for inputting specification values related to the piston shape;
A reading step of reading a piston model that can be deformed according to a predetermined rule from a database;
A deformation step of deforming the piston model based on the specification values input in the input step;
Is a piston design support program that supports the design of the piston shape of the internal combustion engine,
The database includes, as the piston model, at least a main body model representing the shape of the combustion chamber surface of the piston, and a spatial model representing a spatial shape to be scraped from the main body model,
The deformation step is characterized in that both the main body model and the space model are deformed according to the specification values, and the main body model is cut into a shape represented by the space model.

  The space model includes a skirt internal space model representing a shape inside the skirt of the piston.

  The space model includes a skirt external space model representing the shape of the outer surface of the skirt of the piston.

  The space model includes a pin hole space model representing a shape of a pin hole into which a pin for holding a connecting rod is inserted.

In the input step, as the specification value, a dimension for the whole piston is input,
The deformation step is characterized in that the space model is scraped from the body model after deforming each of the body model and the space model according to the dimensions of the whole piston.

In the input step, the thickness of the piston is input as the specification value,
In the deforming step, the skirt internal space model is scraped from the main body model in a state where the skirt internal space model is arranged at a position separated from the main body model by a distance corresponding to the wall thickness input in the input step. It is characterized by that.

In the input step, as the specification value, a dimension for determining the shape of the skirt internal space model and a minimum wall thickness of the piston are input,
In the deformation step, the skirt internal space model is deformed according to the specification value input in the input step, and the thickness of the piston model generated by cutting the skirt internal space model from the main body model is determined. An error notification or re-deformation is performed when the thickness is less than the minimum thickness.

The main body model includes an intake side piston model including an intake side recess provided to prevent interference with the intake valve, and an exhaust side piston model including an exhaust side recess provided to prevent interference with the exhaust valve. Including
In the deformation step, both the intake side piston model and the exhaust side piston model are respectively deformed, and the deformed intake side piston model and the exhaust side piston model are combined.

The intake side model and the exhaust side model are subdivided according to symmetry, respectively.
The deformation step is characterized in that the intake side model and the exhaust side model are combined and mirrored according to the symmetry.

The input step inputs a target compression ratio as the specification value,
The skirt internal space model includes a portion representing the space shape of the crown back,
The deformation step is characterized in that the larger the target compression ratio input in the input step is, the larger the radius of the crown back of the skirt internal space model is.

The input step inputs a pin boss interval as the specification value,
The skirt internal space model includes a portion representing the space shape of the crown back,
The deformation step is characterized in that the radius of the crown back of the skirt internal space model is increased as the pin boss interval input in the input step is smaller.

The input step inputs a skirt inner diameter as the specification value,
The skirt internal space model includes a portion representing the space shape of the crown back,
The deformation step is characterized in that the smaller the inner diameter of the skirt input in the input step is, the larger the radius of the crown back of the skirt internal space model is.

In order to achieve the above object, the method according to the present invention comprises:
An input step in which the input means receives input of specification values related to the piston shape;
A reading step of reading a piston model that can be deformed according to a predetermined rule from a database;
A deformation step of deforming the piston model based on the specification values input in the input step;
A piston design support method for supporting the design of the piston shape of an internal combustion engine,
The database includes, as the piston model, at least a main body model representing the shape of the combustion chamber surface of the piston, and a spatial model representing a spatial shape to be scraped from the main body model,
The deformation step is characterized in that both the main body model and the space model are deformed according to the specification values, and the main body model is cut into a shape represented by the space model.

In order to achieve the above object, an apparatus according to the present invention provides:
Input means for accepting input of specification values relating to the piston shape;
Reading means for reading a piston model that can be deformed according to a predetermined rule from a database;
Deformation means for deforming the piston model based on the specification values input by the input means;
A piston design support device for supporting the design of the piston shape of the internal combustion engine,
The database includes, as the piston model, at least a main body model representing the shape of the combustion chamber surface of the piston, and a spatial model representing a spatial shape to be scraped from the main body model,
The deformation means deforms both the main body model and the space model in accordance with the specification values, and scrapes the main body model into a shape represented by the space model.

  According to the present invention, the piston design can be made more efficient by introducing a new idea of a piston model that automatically deforms while observing predetermined rules in accordance with specification values. In other words, because there is a kind of program for creating CAD data by deforming the piston shape by inputting the specification value of the piston model, even when designing a different piston, the specification value is input to the piston model. This makes it possible to design the piston shape very easily.

  Here, the piston model program must include a deformation rule according to the specification value, and requires a very advanced technique and a large number of man-hours to create. In the present invention, such a piston model is required. The model is prepared for the appropriate part that defines the piston shape, deformed appropriately according to the specification value for the whole piston, and then merged to make the piston model easy to design and calculate the piston shape when inputting the specification value. Processing efficiency can be achieved.

  That is, in the database, a body model representing the shape of the combustion chamber surface of the piston and a space model representing the space shape to be scraped from the body model are prepared in advance, and both the body model and the space model are prepared according to the specification values. Is deformed, and the deformed main body model is cut into the shape represented by the deformed space model, so that the shape related to the combustion performance can be designed independently of other shapes, and the entire design is efficiently performed. be able to.

  In addition, when the space model includes a skirt internal space model that represents the shape inside the piston skirt or a skirt external space model that represents the shape of the piston skirt outer surface, the shape related to combustion performance and the shape related to heat dissipation performance are independent. Therefore, the overall design of the piston becomes more efficient. Also, it is possible to design only the inside of the skirt independently of the crown shape in consideration of interference with the connecting rod.

  When the pin hole space model representing the shape of the pin hole for inserting the pin for holding the connecting rod is included as the space model, the design change of the pin hole shape accompanying the change of the pin is changed to the combustion chamber such as the crown shape. Piston design can be made more efficient because it can be performed independently of the surface design change.

  When the main body model and the space model are deformed according to the dimensions for the whole piston and then the space model is scraped off from the main body model, the piston designer only has to input the dimensional values for the whole piston, Since it is not necessary to input the dimensional value for each model in consideration, the piston can be designed very simply.

  Enter the thickness of the piston as a specification value, and scrape the skirt internal space model from the main body model in a state where the skirt internal space model is placed at a position separated from the main body model by a distance corresponding to the input thickness. Since the overall piston shape is determined in this way, the piston designer only has to input the piston wall thickness as before, and it is not necessary to input the location of each model. It can be done very simply.

  The main body model includes an intake side piston model including an intake side recess provided to prevent interference with the intake valve, and an exhaust side piston model including an exhaust side recess provided to prevent interference with the exhaust valve. Because the entire piston is designed by deforming both the intake side piston model and the exhaust side piston model, and combining the deformed intake side piston model and exhaust side piston model, the intake side and exhaust side are made independent. Can be designed and combined in various ways.

  The intake-side model and the exhaust-side model are subdivided according to the symmetry, respectively, and the piston model is generated as a whole by mirroring according to the symmetry, so it is possible to reduce the capacity and deformation process of the model Become.

  When a target compression ratio is input as a specification value and a skirt internal space model including a portion representing the space shape of the crown back is deformed, the larger the target compression ratio, the larger the radius of the crown back, the larger the target compression. If the ratio is large, it is possible to obtain a shape that enhances the heat dissipation performance, and a more appropriate piston shape.

  If the pin boss interval is input as a specification value, the skirt internal space model includes a portion representing the space shape of the crown back, and the smaller the input pin boss interval is, the larger the radius of the crown back of the skirt internal space model is. Thus, it is possible to compensate for the decrease in the heat dissipation area accompanying the decrease in the pin boss interval by improving the heat dissipation performance by increasing the radius on the back of the crown.

  If the inner diameter of the skirt is entered as a specification value and the radius of the crown back of the skirt internal space model is increased as the input skirt inner diameter is smaller, the reduction of the heat radiation area due to the decrease of the skirt inner diameter is reduced. It can be compensated by improving the heat dissipation performance due to the increase.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The embodiment described below is an example of means for realizing the present invention, and the present invention includes modifications or variations of the following embodiment without departing from the spirit of the present invention. In this specification, the piston model is an object expressed by coordinate data of a plurality of points representing the piston shape and the correlation between the points. The specification values refer to dimensions and reference values for determining the shape and position of the piston and its peripheral parts, and performance values of the piston.

(About piston and its design)
FIG. 10 is a diagram illustrating an example of a piston and peripheral components that can be designed by the support system according to the embodiment of the present invention.

  First, a piston and its peripheral parts to be designed by the piston design support program will be described with reference to FIG.

  In the figure, 1000 is a DOHC 4-valve 4-cycle gasoline engine (hereinafter simply referred to as an engine). The engine 1000 includes a cylinder block 1110 having a cylinder 1110a, a cylinder head 1120 assembled on the upper surface of the cylinder block 1110, a piston 1130 fitted in the cylinder 1110a so as to be able to reciprocate, and a piston 1130. Connecting rod 1140, pin 1135 for connecting piston 1130 and connecting rod 1140, crank 1150 for supporting connecting rod 1140, and counterweight attached to connecting rod 1140 on the opposite side of crank 1150 (hereinafter also referred to as C / W) 1160, and a gasket (hereinafter also referred to as GSKT) 1190 is sandwiched between the cylinder block 1110 and the cylinder head 1120. A combustion chamber 1200 surrounded by the piston 1130 and the cylinder head 1120 is formed in the cylinder 1110a, and the crank chamber 1300 in which the crank 1150 is accommodated is separated from the piston 1130.

  An intake port 1220 and an exhaust port 1230 are formed in the cylinder head 1120, and an intake valve 1171 that opens and closes an opening of the intake port 1220 on the combustion chamber 1200 side, and an exhaust that opens and closes an opening of the exhaust port 1230 on the combustion chamber 1200 side. A valve 1172 is provided. The intake valve 1171 reciprocates as the intake cam 1181 rotates, and the exhaust valve 1172 reciprocates as the exhaust cam 1182 rotates.

  Further, FIG. 10 shows one intake valve 1171 and one exhaust valve 1172, but since it is a four-valve engine, two are actually provided.

  FIG. 11 is a perspective view showing the external appearance of the piston 1130 alone. As shown in FIG. 11, the outer peripheral edge of the upper surface of the piston 1130 has a planar shape perpendicular to the central axis of the piston 1130, and the portion excluding the outer peripheral edge is a circle when viewed from the central axis direction of the piston 1130. A crown 1130a having a shape is formed.

  Two recesses (recesses) 1130 b are formed on the upper surface of the piston 1130 at positions facing the intake valve 1171 so that the piston 1130 does not interfere (collision) with the intake valve 1171. Similarly, two recesses 1130 c are formed at positions facing the exhaust valve 1172. The two recesses 1130b have exactly the same shape, and the two recesses 1130c have exactly the same shape. Therefore, the piston 1130 can be divided into two parts forming a mirror image by a plane 1500 passing through its central axis.

  Further, three piston ring grooves 1130d (referred to as a top ring, a second ring, and an oil ring from the top) for fitting the piston ring are formed in the vicinity of the top portion on the side peripheral surface of the piston 1130. Further, a portion sandwiched between the piston ring grooves 1130d is called a land, and from the top, they are called a top land 1130f, a second land 1130g, and a third land 1130h. Furthermore, the lower part of the piston is hollow, and its wall surface is called a skirt 1130j. A pin hole 1130k is formed in the skirt 1130j.

  The crown 1130a has a shape that protrudes in a convex shape, is flat (flat), or is recessed in a concave shape.

  The volume of the combustion chamber 1200 shown in FIG. 10 changes according to the shape of the recesses 1130b and 1130c and the shape of the crown 1130a, and the compression ratio changes accordingly. In other words, the diameter, protrusion height, and the like of the crown 1130a are determined according to the target compression ratio. That is, it is necessary to adjust the recess shape and the crown shape so that the volume of the combustion chamber 1200 (the volume when the piston 1130 is at the top dead center) becomes a value determined from the target compression ratio.

  When designing such a piston with a computer system such as CAD, roughly determine the piston shape from the dimensions that determine the shape of the piston and the relative position with the surrounding components, and then set the target performance values such as the target compression ratio and target strength. While verifying whether or not to achieve, determine the fine piston shape. Once the piston shape is determined to a certain degree of detail, precise calculation is performed by CAE (Computer Aided Engineering) using the three-dimensional shape data, the rigidity of the skirt 1130j, the static stress such as the pin hole 1130k, the crown Calculation of thermal stress of 1130a and behavior analysis when the piston 1130 reciprocates are performed.

  Since precise calculation in CAE takes time, it is important to perform sufficient verification before bringing it into CAE and to make the piston shape as appropriate as possible in order to increase the efficiency of the piston design. Therefore, in the present embodiment, the following piston design support system is used.

<First Embodiment>
(Overall system configuration)
First, the overall configuration of the piston design support system as the first embodiment of the present invention will be described.

  FIG. 1 is a diagram illustrating the configuration of a piston design support system 100 according to this embodiment. A piston design support system 100 in FIG. 1 includes a computer 101 and a database server 102 as a piston design support apparatus connected by a local area network 103.

  The computer 101 includes a CPU 111, a ROM (Read Only Memory) 113, a RAM (Random Access Memory) 114, an HD (Hard Disk) 115, an input / output interface (I / O) 116, an image processing unit 118, and a communication unit 119. And are connected to each other by a bus 112. An input device 120 and a display 117 are provided outside the main body, and are connected to the input / output interface 116 and the image processing unit 118, respectively.

  Among these, the CPU 111 is an arithmetic / control processor that controls the entire computer 101. The ROM 113 is a non-volatile memory that stores a boot program executed by the CPU 111, a fixed value, and the like. The RAM 114 is a volatile memory for temporarily storing data and programs. Furthermore, the HD 115 is a storage medium as a storage unit that stores an OS executed by the computer 101 and various program modules. The input / output interface 116 is an interface for inputting / outputting data between the computer main body and the input device 120.

  The input device 120 is a device such as a keyboard or a mouse that inputs commands and data. The display 117 is a liquid crystal display that outputs characters and image data that are arithmetically processed by the image processing unit 118 based on a control command from the CPU 111. A device such as a CRT. The image processing unit 118 is a unit that performs arithmetic processing on image data to be displayed on the display 117. The communication unit 119 is a unit for transmitting and receiving data to and from the database server 102 via a wireless or wired communication line.

  More specifically, the RAM 114 temporarily stores a program execution area 114a for temporarily storing a program to be executed by the CPU 111 during the piston design support process, and various specification value data of the piston input by the user. An original value storage area 114b, various model storage areas 114c for storing various models relating to the piston, and a display image storage area 114d for temporarily storing display images are provided.

  The HD 115 stores a program module for supporting piston design. Specifically, a specification value input module 115a for inputting piston related specification value data, a verification module 115b for verifying whether or not the specification value is appropriate, and a database reading module 115c for reading various models from a database. , A model deformation module 115d for deforming various models read from the database based on the specification values, an interval / thickness calculation module for calculating the piston-valve interval, the thickness of the crown back, etc. using the deformed piston model 115e, a volume calculation module 115f for performing various volume calculations using a deformed piston model and the like, and a compression ratio calculation module 115g for calculating a compression ratio using the combustion chamber volume calculated by the volume calculation module 115f Stored as a program.

  FIG. 2 is a diagram showing various data stored in the database server 102. As shown in FIG. 2, the database server 102 includes a piston generation model 121, specification value data 122, two-dimensional verification data 123, and a three-dimensional verification model 124. The piston generation model 121 includes an intake side model 211, an exhaust side model 212, a skirt internal space model 213, a skirt external space model 214, and a pin hole model 215. Here, the intake side model 211 is a model including an intake side recess 1130b provided to prevent interference with the intake valve 1171. On the other hand, the exhaust side model 212 is a model including an exhaust side recess 1130 c provided to prevent interference with the exhaust valve 1172. The intake side model 211 and the exhaust side model 212 are subdivided models according to symmetry. Further, the intake side model 211 and the exhaust side model 212 do not have information on the internal space to be cut out or the external space to be cut in the skirt 1130j. That is, here, each of the intake side model 211 and the exhaust side model 212 has a ¼ cylindrical shape including one recess, a crown, and a ring groove in the upper part. The database server 102 stores a plurality of intake side models 211 and exhaust side models 212 as piston generation models 121 according to the crown type. That is, the intake side model 211 and the exhaust side model 212 included in the piston generation model 121 can be classified into three types of a convex type, a flat type, and a concave type according to the crown type. Of course, such classification is not limited, and may be classified into two types, for example, a convex type and a concave type, or divided into four or more types according to the shape of the crown, and the intake side model 211 and An exhaust side model 212 may be prepared. Further, the intake side model 211 and the exhaust side model 212 can also be referred to as a main body model representing the shape of the combustion chamber surface of the piston.

On the other hand, the skirt inner space model 213 and the skirt outer space model 214 are space models that represent the space shapes to be scraped from the main body model. The skirt internal space model 213 represents the internal shape of the skirt 1130j of the piston 1130, and the skirt external space model 214 represents the external surface shape of the skirt 1130j of the piston 1130. The skirt inner space model 213 and the skirt outer space model 214 are also subdivided according to symmetry, and here, the actual skirt inner space and outer space are halved by a plane passing through the piston central axis. It has a cut shape. This cut surface is the same as the cut surfaces included in the intake side model 211 and the exhaust side model 212.
The top of the skirt internal space model 213 represents the shape of the crown back.

  The pin hole model 215 is a model representing the shape of the pin hole 1130k into which the pin 1135 for holding the connecting rod 1140 is inserted.

The specification value data 122 includes data on specification values input by the user. The two-dimensional verification data 123 is data used for verifying the specification values input by the user using mathematical formulas and two-dimensional data before generating the three-dimensional data. The two-dimensional verification data 123 includes a verification formula 231 using specification values as parameters, and two-dimensional shape data 232 representing the piston 1130, valves 1171 and 1172, connecting rod 1140, and counterweight 1160 in a plane. The three-dimensional verification model 124 includes a valve model 241 and a volume model 242. The volume model 242 includes a volume model representing a space between the outer peripheral surface of the piston and the inner peripheral surface of the cylinder around the piston ring fitting groove. This volume model is divided into a plurality of ring volume models indicating a space formed between the bottom surfaces of the plurality of piston ring fitting grooves and the inner peripheral surface of the cylinder, and a land volume model between the ring volume models. .

(Piston design support processing)
FIG. 3 is a diagram schematically showing processing by the piston design support program.

  When the user starts the piston design support program and designs the piston, first, in step S301, the piston design support program generates an input screen for the basic specification values related to the piston shape by the specification value input module 115a. This is displayed on the display 117. Therefore, if the file name of the specification value data 122 is designated, the specification value data 122 is read from the database server 102 and set as a basic specification value. If the file name is not specified, the user is prompted to input the specification values one by one on the input screen.

  FIG. 4A is a diagram illustrating an example of a basic specification value input screen. In the basic specification value input screen 400 shown in FIG. 4A, the following can be input as basic specification values.

  ・ Minimum wall thickness standard: The minimum wall thickness to be satisfied by the piston.

  Target ski standard: The minimum value that must be satisfied by the skid between the piston surface and peripheral parts such as connecting rods and valves.

  Cam lift data: This shows how each of the intake side cam 1181 and the exhaust side cam 1182 lifts each valve. Since the rotational angular velocities of these cams are equal to the rotational angular velocities of the crank 1150, here, the valve lift amounts of the respective cams corresponding to the crank angles are shown as text data. FIG. 5 is a graph showing the cam lift data with the crank angle on the horizontal axis and the valve lift amount on the vertical axis.

  Valve timing: This shows how much the opening timing of the intake side valve 1171 and the closing timing of the exhaust side valve 1172 deviate from the timing at which the piston 1130 is located at the top dead center in terms of the crank angle. This is shown in FIG. 5 by BTDC (Before Top Dead Center) and ATDC (After Top Dead Center). The ramp height is derived from the cam lift data.

  Layout conditions: bore diameter, crank diameter, connecting rod length (from the center of the shaft where the connecting rod and crank are connected to the center of the pin hole), C / W virtual disk radius, combustion chamber volume, valve center height, intake valve This is the layout condition of peripheral parts other than the piston dimensions such as the clamping angle and the exhaust valve clamping angle. Here, the bore diameter represents the inner diameter of the cylinder 1110a. Further, as the combustion chamber volume, the space volume on the cylinder head 1120 side and the space volume based on the gasket thickness, which do not consider the piston shape, are input. The valve center height means the distance from the upper surface of the gasket 1190 to the valve center. The valve center represents the intersection of the reciprocal axis of the intake valve 1171 and the reciprocal axis of the exhaust valve 1172. The intake valve sandwiching angle and the exhaust valve sandwiching angle represent angles formed by the reciprocating direction of the intake valve 1171 and the exhaust valve 1172 and the reciprocating direction of the piston 1130. Other layout requirements include gasket thickness, block height (distance from crankshaft to block top surface), valve offset (distance from valve center to cylinder center axis), pin offset (from pin center axis) The distance to the center axis of the piston), the vertical distance from the pin hole center to the bottom of the skirt, etc. can be entered.

  ・ Piston specifications: Piston diameter, intake and exhaust side recess centers (distance from the center of the piston to the recess center), intake and exhaust side recess depth, crown thickness, and skirt outer shape including skirt outer diameter , Various dimensions indicating the internal shape of the skirt including the skirt inner diameter, various dimensions indicating the pin hole shape, depth, width and position of each ring groove, distance from the valve center to the center of the piston pin, compression height ( Distance from the center of the pin hole to the top surface of the crown).

-Valve specification values: dimensions indicating valve shapes such as intake valve diameter, exhaust valve diameter, etc. Returning to FIG. 3, in step S302, 2D verification is performed using the basic specification values input as described above. To do. 2D verification is verification by numerical calculation performed before constructing a three-dimensional piston model. This is performed by substituting the basic specification value into the verification formula 231 stored in the database server 102. When the verification is completed, the verification result is displayed in step S303. FIG. 4B is a diagram showing a verification result display screen 410 showing the verification result. Here, whether the wall thickness of the skirt is greater than the minimum thickness standard, whether the distance between the intake valve and the exhaust valve and the piston is greater than the standard value, whether the connecting rod and the crown back surface The result of verification is shown whether or not the clearance between the counter weight and the piston is equal to or greater than the reference value, and whether or not the closest distance between the counterweight and the piston is equal to or greater than the reference value. That is, “OK” is displayed when the reference value is satisfied, and “NG” is displayed when the reference value is not satisfied.

  Here, taking an example of the verification formula 231, the thickness of the skirt portion is derived by subtracting the skirt inner diameter from the skirt outer diameter reference dimension and dividing the result by two. The gap between the connecting rod and the crown back surface is derived by subtracting the crown thickness from the compression height, and further subtracting the small end radius of the connecting rod (the radius of the end where the pin is inserted). In addition, the gap between the counterweight and the piston is obtained by subtracting the square of the pin offset from the square of the length of the connecting rod and taking the square root, and further, the distance from the center of the pin hole to the lower end of the skirt, the crank radius, It is derived by subtracting the C / W virtual disk radius.

  Other items that can be verified as 2D verification are whether the input value of the recess depth is smaller than the allowable maximum depth derived from the specification values for the valve and the piston, between the pin hole and the oil land groove. Whether the wall thickness of the pin satisfies the reference value, whether the surface pressure, various stresses, and the amount of deflection of the pin hole are equal to or less than the reference value. Note that the maximum allowable depth of the recess is derived from the target ski criteria, cam lift data, valve timing, crank radius, connecting rod length, pin offset, valve height, block height, gasket thickness, etc. . The maximum allowable depth of the recess varies depending on the cam angle (crank angle). Here, calculation is performed when the piston is located at the top dead center (cam angle 0 °), and further, calculation is performed for all cam angles of the cam lift data, and the minimum value is selected.

  The display of the verification result is not limited to the display by characters as shown in FIG. The two-dimensional shape data 232 may be read from the database server 102 and deformed according to the basic specification values, and the piston, valve, connecting rod, and counterweight may be displayed two-dimensionally to represent interference and wall thickness errors.

  If the verification result is OK as a result of these displays, the process proceeds from step S304 to step S305. If the verification result is not OK and there is a problem with some specification value, the procedure returns to step S301 to change the specification value. .

  In step S305, detailed specification values are input. That is, the piston design support program generates a detailed specification value input screen related to the piston shape by the specification value input module 115 a and displays it on the display 117. Therefore, if the file name of the specification value data 122 is also designated, the specification value data 122 is read from the database server 102 and set as a detailed specification value. If the file name is not specified, the user is prompted to input detailed specification values one by one on the input screen.

  As the detailed specification values input here, the following values can be input.

  -Target compression ratio: The target compression ratio. The compression ratio is the ratio between the maximum combustion chamber volume and the minimum combustion chamber volume.

・ Search range for automatic optimization: Lower limit and upper limit of crown depth / height ・ Details around ring and land: Top land outer diameter, top ring, second ring, oil ring, bottom of each groove Including the outer diameter, and the width of each of the top land, top ring, second land, second ring, third land, and oil ring. Also includes chamfers and rounds around rings and lands.

  Next, the process proceeds to step S306, and a crown type representing whether the surface of the piston on the combustion chamber side is flat, convex, or concave is selected as a part of the specification value.

  In the verification result display screen shown in FIG. 4B, three selections of a “3D verification (flat)” button 411, a “3D verification (convex)” button 412, and a “3D verification (concave)” button 413 are selected. The button is displayed. If the detailed specification values have already been input in step S301, these 3D verification buttons 411 to 413 can be selected. When any one of these buttons is selected, the crown type is selected.

  For example, when an appropriate crown type for achieving the target compression ratio is unknown, a flat type 3D piston model is first constructed, and the compression ratio is measured using the piston model. When the measured compression ratio is smaller than the target compression ratio, it can be determined that the combustion chamber volume is insufficient. Therefore, if the compression ratio is measured again by selecting the concave mold again to increase the combustion chamber volume. Good. Also, if the measured compression ratio is larger than the target compression ratio, it can be determined that the combustion chamber volume is excessive, so if the compression ratio is measured again by selecting the convex shape again to reduce the combustion chamber volume. Good. Furthermore, when the measured compression ratio is equal to the target compression ratio or the difference is sufficiently small, it is not necessary to select the crown type again, and the analysis process in CAE may be performed as it is.

  Next, in step S307, a piston base model that can be deformed according to a predetermined rule is read from the database. Specifically, the intake side piston model and the exhaust side piston model corresponding to the crown type inputted as the specification value, the skirt internal space model 213, the skirt external space model 214, and the pin hole model 215 are retrieved from the database. Read.

  In step S308, based on the specification values input in steps S301 and S305, the piston generation model read in step S307 is deformed, and in step S309, the piston model is constructed by combining them.

  FIG. 6 is a diagram for explaining a piston model construction method.

  First, the 1/2 main body model 601 is generated by combining the intake side model 211 and the exhaust side model 212 modified according to the specification values. As described above, the intake-side model 211 and the exhaust-side model 212 stored in the database server 102 have a shape obtained by cutting the piston into 1/4 in the reciprocating axis direction. A half body model 601 having a shape obtained by cutting a cylindrical piston in half is generated.

  Next, the inner space model 213 deformed according to the specification value is cut off from the 1/2 body model. Since the internal space model 213 has a ½ shape as described above, the shape obtained by scraping the inner space model 213 from the ½ body model is as shown in 602. Next, the external space model 214 is further removed from the shape indicated by 602. As a result, a ½ piston model (no pin hole) indicated by 603 is generated. Then, a 1/2 piston model is generated by further scraping the pin hole model 215 from this 1/2 piston model (without the pin hole), and further mirroring the 1/2 piston model around the cut surface, The entire piston model 604 is built.

  The internal space model 213 and the external space model 214 may be arranged at positions separated from the main body model by a distance corresponding to the thickness inputted as the specification value, and the skirt internal space model may be scraped from the main body model. The inner space model 213 may be modified so that the inner diameter of the skirt input as a value becomes equal to the outer diameter of the inner space model 213. The internal space model 213 and the external space model 214 are deformed in synchronization so that the positions of the pin holes do not shift.

Returning to FIG. 3, 3D verification is performed in step S310 using the piston model constructed in step S309. 3D verification is verification of piston dimensions and piston performance in a three-dimensional space, and calculates wall thicknesses and gaps and volume calculations that are impossible with 2D verification. For example, if a 3D piston model is constructed and the compression ratio calculation module 115g is used, an accurate combustion chamber volume can be calculated and the compression ratio can be obtained therefrom. Specifically, the volumes of V4 and V5 shown in FIG. 7A are measured using a 3D piston model. FIG. 7A is a partial cross-sectional view showing a space surrounded by the piston 1130, the cylinder block 1110, the gasket 1190, and the cylinder head 1120 when the piston is located at the top dead center. The volumes of V2 and V3 are input in advance as detailed specification values. If V1 is the displacement of one cylinder,
V1 = (bore diameter / 2) ² × π × (crank diameter × 2)
Represented by
Furthermore, the values of V1 to V5 are
Compression ratio = V1 / (V2 + V3 + V4 + V5) +1
By substituting into, the compression ratio is obtained. Then, by comparing this compression ratio with the target compression ratio input as the detailed specification value, it is determined whether or not the engine using this piston achieves the desired performance.

Further, by reading out the three-dimensional valve model 241 from the database server 102, deforming and arranging the three-dimensional valve model 241 according to various specification values, and using a CAD distance command, as shown in FIG. The shortest distance 701 between the accurate valve and the piston can be obtained, and it can be verified whether or not the interval is equal to or larger than a predetermined reference value. Similarly, the shortest distance between the crown / recess surface and the inner surface of the top ring groove and the shortest distance between the crown / recess surface and the crown back surface are calculated by the interval / thickness calculation module 115e. Whether the value is satisfied can be verified. In addition, since the height or depth of the crown from the top surface of the piston is determined when the 3D piston model is constructed, the gap between the crown back surface and the connecting rod is obtained more accurately using the following formula according to the crown type. It becomes possible.
Flat: Gap = Compression height-Crown thickness-Connecting rod small end diameter / 2
For convex type: Gap = compression height-crown thickness-connecting rod small end diameter / 2 + crown depth For concave type: Gap = compression height-crown thickness-connecting rod small end diameter / 2-crown depth

  Further, the volume model 242 is read from the database server 102, and based on the piston outer diameter, cylinder inner diameter, ring, and detailed dimensions around the land (piston ring fitting groove width and depth) input as detailed specification values. By deforming, the volume of the spaces 801 to 806 between the outer peripheral surface of the piston and the inner peripheral surface of the cylinder shown in FIG. 7C can be easily calculated using the volume calculation module 115f. The volume of the space combining the space 801 and the space 802 is called a topland volume, and the volume of the space combining the space 803 and the space 804 is called a second land volume, and the space 805 and the space 806 are combined. The volume of the space is called the third land volume.

  From these volumes oil consumption and emission performance can be derived. The pressure difference between the combustion chamber 1200 and the crank chamber 1300 depends on the arrangement of the top ring, the second ring, and the oil ring, and in order to improve the shut-off so that unburned gas does not enter the crank chamber The volume ratio of the six spaces divided in the volume model 242 is important.

  Returning to FIG. 3 again, the result of 3D verification in step S310 is displayed in step S311. FIG. 8 is an example of a 3D verification result display screen. As shown in the figure, the measurement values derived by the 3D verification are displayed for the compression ratio, gap, wall thickness, and land volume. The volumes indicated by 1 to 6 in the land volume correspond to the volumes of the spaces 801 to 806 in FIG.

  In FIG. 8, a piston 3D display button 811, an internal space 3D display button 812, an automatic optimization button 813, a specification value re-input button 814, and a save end button 815 are displayed, and are selected. The following processing is performed.

  When the piston 3D display button 811 or the internal space 3D display button 812 is selected, the process proceeds from step S312 to step S313, and the constructed piston model 604 or the deformed internal space model 213 is displayed on the display 117. Here, when the piston model 604 is displayed, it is displayed while hiding the connection surface between the piston generation models.

  When the automatic optimization button 813 is selected, the process proceeds from step S312 to step S315 through step S314, and the piston shape is automatically optimized to approximate the target compression ratio. Specifically, first, the target compression ratio input as the specification value is compared with the measured compression ratio, and the crown height or depth of the piston is changed according to the difference. Then, the piston model is deformed according to the changed crown height or depth, the compression ratio for the deformed piston model is calculated, and the difference between the calculated compression ratio and the target compression ratio is a predetermined value (for example, If not within ± 0.01), the crown height (or depth) of the piston model is changed and the compression ratio is calculated again. Then, the deformation and the compression ratio calculation are repeated a plurality of times until the difference between the calculated compression ratio and the target compression ratio is within a predetermined value. If the difference between the calculated compression ratio and the target compression ratio falls within a predetermined value, the piston shape closest to the target compression ratio is determined.

  When the specification value re-input button 814 is selected, the process advances from step S312 to step S301 or step S315 through step S314 and step S315, and returns to the specification value input screen.

  When the save end button 815 is selected, it is determined that the verification result is OK, and the process proceeds from step S314 to step S316, where all piston models and specification values are saved, and the piston design support program is ended.

(Model transformation rules)
Next, the model deformation rule in step S308 will be described in detail. In step S308, both the intake-side model 211 and the exhaust-side model 212 are deformed, but it is not always necessary to separately input the specification values for each, and the dimensions for the entire piston are input as the specification values. In addition, both the intake side model 211 and the exhaust side model 212 are deformed in association with each other. For example, the outer diameters of the arc portions of the intake side model 211 and the exhaust side model 212 read from the database server 102 are enlarged or reduced at the same scale with respect to the cylinder diameter inputted as the specification value.

  Further, when the intake side model 211 and the exhaust side model 212 are deformed, the sectional shapes of the intake side recess 1130b and the exhaust side recess 1130c are independently determined based on the specification values. For example, the recess shape determination rule is set so that the intake-side recess and the exhaust-side recess are deformed into different shapes even if the same value is input as the recess depth. This is because the intake recess is required to have an effect of improving the convection of the intake air, but the exhaust recess cannot be required to have such an effect.

  The recess shape determination rule will be described with reference to FIG. FIG. 9A is a longitudinal sectional view of the piston 1130 viewed from the pin axis direction. The depth of the intake side recess is D1, the radius of the bottom of the intake side recess (the radius of curvature of the corner formed by the bottom surface and the side surface) is R1, the inclination of the bottom surface of the intake side recess (the angle formed by the bottom surface and the horizontal surface) is S1, The angle between the intake side recesses is indicated by α. Similarly, the depth of the exhaust recess is D2, the radius of the bottom of the exhaust recess is R2, the slope of the bottom of the exhaust recess is S2, and the sandwich angle of the exhaust recess is β. Further, the inner diameter of the skirt is indicated by φ.

  According to the recess shape determination rule, even if the intake side recess depth D1 and the exhaust side recess depth D2 input as the specification values are the same value, the inclination S1 of the bottom surface of the intake side recess and the inclination S2 of the bottom surface of the exhaust side recess And the corner radius R1 formed by the bottom surface and the side surface of the intake side recess is different from the corner radius R2 formed by the bottom surface and the side surface of the exhaust side recess. The bottom surface of the intake-side recess 1130b is deformed so that the bottom surface is as horizontal as possible and the bottom radius R1 is increased in order to improve the convection characteristics of the intake air. On the other hand, the inclination angle S2 of the bottom surface of the exhaust-side recess 1130c only needs to be equal to the sandwiching angle β of the exhaust-side valve (thereby, the bottom surface of the exhaust-side recess 1130c becomes parallel to the valve head surface). It may be a predetermined value.

  The radius R2 on the bottom surface of the exhaust side recess is basically set in accordance with the shape of the valve on the exhaust side. The intake side has the advantage of increasing the radius to facilitate convection, but the exhaust side has no relation to convection, so the shape depends on the valve shape on the exhaust side.

  When the intake-side recess depth D1 and the exhaust-side recess depth D2 that are input as the specification values are changed, the intake-side recess 1130b has at least the bottom surface inclination S1 or the corner R R1 formed by the bottom surface and the side surface. However, for the exhaust-side recess 1130c, neither the slope S2 of the bottom surface nor the corner radius R2 formed by the bottom surface and the side surface changes.

  On the other hand, in step S308, the internal space model 213 is deformed in accordance with the specification value, and at that time, deformation is performed in accordance with the internal space shape determination rule. The internal space shape determination rule will be described with reference to FIG. FIG. 9B is a longitudinal sectional view of the piston 1130 viewed from a direction perpendicular to the pin axis. In FIG. 9 (b), R3 of the crown back in the internal space (the radius of curvature of the corner between the back surface of the crown and the inner surface of the skirt) is indicated by R3, and the pin boss interval is indicated by P.

  According to the internal space shape determination rule, the larger the target compression ratio input as the specification value is, the larger the radius R3 on the crown back of the skirt internal space model is. Further, the smaller the pin boss interval P inputted as the specification value, the larger the radius R3 on the crown back of the skirt internal space model. Further, the smaller the skirt inner diameter φ input as the specification value is, the larger the radius R3 on the crown back of the skirt internal space model is.

  This rule is due to the fact that the crown back R3 is an element that strongly influences the cooling performance (heat radiation performance). In other words, the inside of the piston 1130 is where the crown back is closest to the combustion chamber 1200, and the engine oil injected into the crank chamber 1300 efficiently draws heat from the back of the crown leads to improved heat dissipation. Here, in order for the engine oil to efficiently remove heat from the back of the crown, it is necessary to improve the circulation of the engine oil on the back of the crown. For this purpose, the radius R3 on the back of the crown may be increased. In addition, by increasing the radius R3 on the back of the crown, the heat generated on the back of the crown can be easily released to the skirt portion via the radius on the back of the crown, and heat propagation (heat escape) is improved. You can also. However, on the other hand, the amount of R3 on the back of the crown is increased by the increase in weight, so it is not preferable to increase R3 unnecessarily.

  Therefore, as described above, when the target compression ratio is large and the amount of generated heat is increased, or when the pin boss interval P or the skirt inner diameter φ is small and the entire heat radiation area is reduced, the heat radiation performance on the back of the crown. In order to improve the R, the R 3 is increased. By applying this rule, it is possible to determine the most suitable R R3 on the crown back with a balance between heat dissipation and weight.

(Effect of embodiment)
According to this embodiment, it is possible to easily design a piston that satisfies a predetermined constraint condition. Since the piston generation model having an efficient shape is stored in the database, the processing load and the data amount can be reduced. In addition, the piston design can be automatically optimized. Anyone can easily design a piston that satisfies the target compression ratio. Even if the target compression ratio is changed variously, it is possible to design a piston that realizes the target compression ratio in a short time.

  The present invention can be applied to the design of a piston provided not only in a vehicle engine but also in any internal combustion engine.

It is a block diagram which shows schematic structure of the piston design assistance system which concerns on embodiment of this invention. It is a figure which shows the structure of the database server contained in the piston design assistance system which concerns on embodiment of this invention. It is a flowchart which shows the flow of the piston design assistance process which concerns on embodiment of this invention. It is a figure which shows the screen displayed in the piston design assistance system which concerns on embodiment of this invention. It is a graph which shows the relationship between a piston displacement curve and a valve lift curve. It is a figure which shows the transition of the piston model constructed | assembled by the piston design assistance system which concerns on embodiment of this invention. (A) is a figure which shows the structure of a combustion chamber, (b) is a figure which shows the shortest distance of a valve and a piston, (c) is a figure which shows the structure of a land volume. It is a figure which shows the screen displayed in the piston design assistance system which concerns on embodiment of this invention. It is a figure explaining the deformation | transformation rule of the model for piston production | generation by the piston design assistance system which concerns on embodiment of this invention. It is the schematic which shows the structure of the engine provided with the piston which can be designed using the piston design assistance system concerning this invention. It is the schematic which shows the piston which can be designed using the piston design assistance system concerning this invention.

Claims (14)

On the computer,
An input process for inputting specification values related to the piston shape;
A reading step of reading a piston model that can be deformed according to a predetermined rule from a database;
A deformation step of deforming the piston model based on the specification values input in the input step;
Is a piston design support program that supports the design of the piston shape of the internal combustion engine,
The database includes, as the piston model, at least a main body model representing the shape of the combustion chamber surface of the piston, and a spatial model representing a spatial shape to be scraped from the main body model,
In the piston design support program, the deformation step deforms both the main body model and the space model according to the specification values, and scrapes the main body model into a shape represented by the space model.   2. The piston design support program according to claim 1, wherein the space model includes a skirt internal space model representing a shape inside a piston skirt. 3.   2. The piston design support program according to claim 1, wherein the space model includes a skirt external space model representing a shape of an outer surface of a skirt of the piston.   2. The piston design support program according to claim 1, wherein the space model includes a pin hole space model representing a shape of a pin hole into which a pin for holding a connecting rod is inserted. In the input step, as the specification value, a dimension for the whole piston is input,
The said deformation | transformation process cuts off the said space model from the said main body model, after changing each of the said main body model and the said space model according to the dimension with respect to the said whole piston. Piston design support program. In the input step, the thickness of the piston is input as the specification value,
In the deformation step, the skirt internal space model is scraped from the main body model in a state where the skirt internal space model is arranged at a position separated from the main body model by a distance corresponding to the wall thickness input in the input step. The piston design support program according to claim 2, wherein: In the input step, as the specification value, a dimension for determining the shape of the skirt internal space model and a minimum wall thickness of the piston are input,
In the deformation step, the skirt internal space model is deformed according to the specification value input in the input step, and the thickness of the piston model generated by cutting the skirt internal space model from the main body model is determined. 3. The piston design support program according to claim 2, wherein error notification or re-deformation is performed when the thickness is less than the minimum thickness. The main body model includes an intake side piston model including an intake side recess provided to prevent interference with the intake valve, and an exhaust side piston model including an exhaust side recess provided to prevent interference with the exhaust valve. Including
2. The deformation step includes deforming both the intake side piston model and the exhaust side piston model, and combining the deformed intake side piston model and the exhaust side piston model. Piston design support program. The intake side model and the exhaust side model are subdivided according to symmetry, respectively.
9. The piston design support program according to claim 8, wherein in the deformation step, the intake side model and the exhaust side model are combined and mirrored according to the symmetry. The input step inputs a target compression ratio as the specification value,
The skirt internal space model includes a portion representing the space shape of the crown back,
3. The piston design support program according to claim 2, wherein the deformation step increases the radius of the crown back of the skirt internal space model as the target compression ratio input in the input step increases. The input step inputs a pin boss interval as the specification value,
The skirt internal space model includes a portion representing the space shape of the crown back,
3. The piston design support program according to claim 2, wherein the deforming step increases the radius of the crown back of the skirt internal space model as the pin boss interval input in the input step is smaller. The input step inputs a skirt inner diameter as the specification value,
The skirt internal space model includes a portion representing the space shape of the crown back,
3. The piston design support program according to claim 2, wherein in the deformation step, the radius of the crown back of the skirt internal space model is increased as the inner diameter of the skirt input in the input step is smaller. An input step in which the input means receives input of specification values related to the piston shape;
A reading step of reading a piston model that can be deformed according to a predetermined rule from a database;
A deformation step of deforming the piston model based on the specification values input in the input step;
A piston design support method for supporting the design of the piston shape of an internal combustion engine,
The database includes, as the piston model, at least a main body model representing the shape of the combustion chamber surface of the piston, and a spatial model representing a spatial shape to be scraped from the main body model,
The deforming step deforms both the main body model and the space model according to the specification value, and scrapes the main body model into a shape represented by the space model. Input means for accepting input of specification values relating to the piston shape;
Reading means for reading a piston model that can be deformed according to a predetermined rule from a database;
Deformation means for deforming the piston model based on the specification values input by the input means;
A piston design support device for supporting the design of the piston shape of the internal combustion engine,
The database includes, as the piston model, a body model representing at least the shape of the combustion chamber surface of the piston, and a space model representing a space shape to be scraped from the body model,
The deformation means deforms both the main body model and the space model according to the specification values, and scrapes the main body model into a shape represented by the space model.

Images