JP4192803B2 - Engine performance prediction analysis method, prediction analysis system and control program thereof - Google Patents

Description

  The present invention relates to a predictive analysis method, a predictive analysis system, and a control program for predicting engine performance by analyzing the motion of a working fluid using CFD (Computational Fluid Dynamics).

  Conventionally, in order to evaluate the performance of an engine, a transmission, etc., various measurement / test methods as disclosed in Patent Document 1, for example, have been proposed. Patent Document 2 discloses a simulation system that can evaluate powertrain performance without waiting for completion of engine development.

  As such a simulation technique, it is generally performed to analyze engine intake / exhaust flow and combustion gas motion by applying CFD and to predict engine performance based on the analysis result. That is, for example, a virtual experiment (simulation) for simulating a complicated flow of intake air sucked from the intake port into the combustion chamber by numerical calculation using a computer is performed, and for example, the shape of the intake port is determined based on the result of the simulation. As a result, it is possible to reduce the development man-hours spent on repeating trial productions and experiments, and to perform efficient design and development.

  Especially in recent years, the remarkable progress in computer computing power has made it possible to simulate the complex shape of intake ports and the flow of intake air in three dimensions without actually prototyping the engine. It is possible to predict changes in intake flow resistance and cylinder volumetric efficiency when the intake port shape is changed.

  Nonetheless, there is no simulation system that can simulate the flow of intake air and exhaust gas associated with engine operation in three dimensions. Even though the computer's computing power has improved, the shape of the intake / exhaust passage that differs for each cylinder of a multi-cylinder engine, the situation of gas exchange in the combustion chamber, and the burned gas that blows out from the combustion chamber to the exhaust system. This is because it is unrealistic to describe all gas flows and the like as three-dimensional flows.

  Therefore, in order to predict the overall performance of an engine (output, drivability, emissions, etc.), for example, first, experimental data obtained by investigating various performance characteristics of the engine are accumulated, and the performance Build a database that statistically correlates characteristics. At the same time, simulation is performed using a simple physical model (analysis model, numerical calculation model) that simulates the flow of intake and exhaust as a one-dimensional flow. The engine performance is predicted by combining knowledge obtained from the performance characteristic database and one-dimensional simulation results.

  In addition to the one-dimensional simulation using the simple model as described above, for example, a simulation that simulates only the intake air flow in the intake port in three dimensions is also performed, and analysis is performed by considering both results in combination. Improvement of the accuracy is also carried out. However, such a three-dimensional CFD analysis program is generally difficult to handle and has a lot of know-how required for setting to improve accuracy, and the load is concentrated on a dedicated analysis engineer. There was a tendency to delay development due to lack.

  In this regard, the inventors of the present application are based on a simple physical model that simulates the intake / exhaust flow of the engine as a one-dimensional flow as described above, and a part of this model is automatically three-dimensionally as necessary. We have developed a system that can be operated by replacing the model. In this system, the overall intake / exhaust flow of the engine is calculated using a simple one-dimensional model, and a three-dimensional model is used for parts that require particularly high analysis accuracy. A boundary condition is given from the obtained flow field data, and a three-dimensional CFD calculation is automatically performed.

In addition, this system employs a user-friendly interface and automates troublesome settings unique to the three-dimensional CFD analysis program so that even a dedicated analysis engineer can easily handle it.
Japanese translation of PCT publication No. 2002-526762 JP 2002-148147 A

  However, in general, the flow of intake and exhaust of the engine is partially unsteady flow with very large fluctuations. For example, in the independent exhaust passage for each cylinder in the exhaust manifold, the exhaust valve of the corresponding cylinder is closed, From the state where the exhaust from the cylinder of the engine is flowing back relatively slowly from the downstream side to the upstream side, the exhaust valve of the corresponding cylinder opens and the burned gas of high temperature and high pressure blows out at a high speed. The flow condition changes in the range.

  Therefore, as in the system described above, only the flow of intake and exhaust at a predetermined part of the engine is simulated as a three-dimensional flow, and calculation is performed in parallel while transferring the flow field data by the one-dimensional and three-dimensional CFD calculations. When the process is advanced, numerical vibrations (vibrations in calculation of flow variable values) due to changes in boundary conditions occur in the three-dimensional CFD calculation, and there is a possibility that the calculation may diverge. The amplitude of such numerical vibration tends to be large when the calculation is performed in relatively coarse time increments in order to shorten the calculation time.

  In particular, when the simulation is started, the flow field that is spatially discretized in the three-dimensional analysis model is almost stationary, and the flow velocity at each calculation point is zero (0). When the flow field calculation is started under conditions, large numerical vibrations are likely to occur because the calculation is from the initial value 0, and the calculation often diverges and the system goes down.

  In general, to solve the problem of calculation divergence in the CFD, the time step of calculation is shortened, the discretization method (scheme) is set to a low-order with high stability, or a physical model. Although there is a known method of making the calculation grid (mesh) of the same shape as uniform as possible, if the time increment is shortened, the calculation time directly increases, and a low-order scheme In the case of adopting, a numerical error accompanying discretization acts as a so-called numerical viscosity, so that a reduction in analysis accuracy is inevitable.

  In addition, it is impossible to automatically generate a mesh so that all of them have a substantially uniform shape, such as an intake / exhaust passage of an engine. It takes a lot of work and time to do.

  The present invention has been made in view of such a point, and an object of the present invention is to analyze the flow of intake and exhaust of the engine by at least one-dimensional and three-dimensional CFD calculations, thereby predicting the performance of the engine. In this case, the method of giving the boundary condition in the CFD calculation is devised to make the analysis accuracy sufficiently high, while suppressing the divergence of the calculation due to the numerical vibration and preventing the system from going down.

  In order to achieve the above object, in the present invention, when the CFD calculation is started for the first time at the start of the analysis, the run-up period in which the CFD calculation is performed preliminary while gradually changing the boundary condition in a preset manner. The original CFD calculation is started with the flow field data obtained by the calculation of the running period as an initial value.

  More specifically, the present invention relates to a one-dimensional and three-dimensional CFD program for simulating the flow of engine intake and exhaust using at least one-dimensional and three-dimensional CFD analysis models, respectively, and one of the programs. Based on the calculated flow field data, a data exchange program for providing a boundary condition for CFD calculation by the other program is prepared, and each of the programs is executed by a computer device to exhaust at least from a part of the intake system It is intended for a predictive analysis method that analyzes the flow of intake and exhaust air over a part of the system and thereby predicts engine performance.

  When at least one of the CFD programs is executed for the first time at the start of analysis, the CFD calculation is executed while gradually changing the boundary conditions in a preset manner, and the flow field thus obtained is set to the initial state. A new CFD calculation is started.

  By analyzing the flow of intake and exhaust using at least one-dimensional and three-dimensional CFD analysis models in a simulation for simulating the operating state of the engine by the above method, the physical characteristics of the engine, such as volume efficiency and loss factor, for example. Thus, performance characteristics such as engine output and fuel consumption can be predicted. At that time, if the entire flow of intake and exhaust is simulated as a one-dimensional flow, and only the part where the flow of intake and exhaust is particularly important in performance prediction is simulated as a three-dimensional flow, sufficient prediction accuracy is ensured. However, the calculation time can be shortened.

  In such a case, when CFD calculation is performed by combining analysis models having different dimensions, the calculation result data is transferred so that the flow state matches at the boundary of each model. When the flow field in the analysis model is in a substantially stationary state as shown in FIG. 5, the CFD calculation is not started using the value of the flow variable given to the boundary surface of the model as the boundary condition, but the given value The CFD calculation is performed in a preliminary manner while gradually changing in a predetermined manner until it becomes (the period during which this calculation is performed is hereinafter also referred to as a run-up period).

  By doing so, since the change in the boundary condition for each calculation time step is reduced during the run-up period, it is possible to suppress the occurrence of large numerical vibrations and to prevent the divergence of the calculation. Then, if the flow field in the analysis model obtained by the calculation in the run-up period is set as an initial state and CFD calculation using this model is newly started, a highly accurate unsteady state using a higher-order scheme is obtained. Even if the flow calculation is performed, it is possible to suppress the numerical vibration caused by the sudden change of the boundary condition and prevent the system from going down.

  Here, as the degree of change of the boundary condition in the run-up period is more gradual, it is easier to suppress numerical vibrations and the divergence of the calculation can be prevented more reliably. On the other hand, the run-up period becomes longer and the calculation is delayed. In addition, whether the numerical vibration increases or not is greatly affected by the shape of the analysis model including the mesh.For example, when the shape of the passage through which intake and exhaust flows is complicated and the number of deformed meshes is large, The deviation of flow variables between the mesh and the mesh tends to increase, and the numerical vibration tends to increase.

  Focusing on this point, in the first aspect of the invention, the method of changing the boundary condition in the run-up period is set in advance in association with at least the analysis model. In other words, the boundary condition is changed relatively gently for a model that is likely to cause divergence of calculation, while it is changed relatively quickly for a model that is less likely to diverge. By doing so, it is possible to suppress the numerical vibration caused by the sudden change in the boundary condition and prevent the system from being down while shortening the run-up period for that purpose.

  On the other hand, in the invention of claim 2, in particular, the method of changing the boundary condition in the run-up period is not devised to change the condition uniformly over the entire period. In the latter half of the period, it is maintained at a substantially constant condition for a predetermined period.

  In this way, the CFD calculation is performed in the second half of the run-up period with the boundary condition maintained substantially constant, so that relatively small numerical vibrations generated in the first half of the period are quickly attenuated, and the entire analysis model The flow field becomes a steady state with little fluctuation. Then, by starting the original CFD calculation in such a state, the operational effect of suppressing the numerical vibration as described above and preventing the system from going down becomes more reliable.

  In the predictive analysis method according to the first and second aspects of the present invention, the flow field variation obtained from the previous calculation results during the execution of the CFD calculation while changing the boundary conditions during the run-up period as described above. It is preferable to modify the change of the boundary condition based on the state (invention of claim 3).

  That is, even when the CFD calculation is actually being performed during the run-up period, if it is considered that there is a risk that the flow field variation obtained by this will cause the calculation to diverge, the method for changing the boundary condition should be relaxed. Modify to be. On the other hand, when the flow field fluctuation is small, the boundary condition is changed a little earlier so as to shorten the run-up period. Thereby, the method of changing the boundary conditions during the run-up period can be optimized, and the operational effects of the invention can be enhanced as much as possible. Note that only the CFD calculation in the run-up period may be repeated first, and the change condition of the boundary condition may be optimized in advance based on the calculation result.

  Next, the invention of claim 4 comprises a one-dimensional and three-dimensional CFD program for simulating the flow of engine intake and exhaust using at least one-dimensional and three-dimensional CFD analysis models, respectively. An object of the present invention is a predictive analysis system that executes and analyzes the flow of intake and exhaust air from at least a part of the intake system to a part of the exhaust system, thereby predicting the performance of the engine.

  Then, one of the two CFD programs is executed to calculate the flow field of intake / exhaust, and the flow field data calculated by the first CFD calculation means is used to calculate the CFD of the other CFD program. Boundary condition giving means for giving a calculation boundary condition, and when the other CFD program is executed for the first time at the start of the analysis, the boundary condition is set in advance in the condition given by the boundary condition giving means. And a second CFD calculation unit that executes the other CFD program using the flow field data calculated by the first calculation unit as an initial value. Furthermore, the approach mode setting means for setting the way of changing the boundary condition by the approach calculation means in association with at least the analysis model A configuration that includes a.

  According to the predictive analysis system described above, in the simulation for simulating the operating state of the engine, basically, the first CFD calculation unit executes either one-dimensional or three-dimensional CFD program, and the intake / exhaust gas calculated thereby is calculated. Based on the flow field data, a boundary condition for the CFD calculation by the other CFD program is given by the boundary condition giving means, and the other CFD program is executed by the second CFD calculation means using this boundary condition.

  At that time, when a boundary condition is first given to the other CFD calculation at the start of analysis, the other CFD program is executed while the boundary condition is gradually changed in a preset manner by the run-up calculation means. (Running period) The CFD calculation is started by the second CFD calculation means with the flow field data thus calculated as an initial value. Further, the way of changing the boundary condition by the approach calculation means is set in association with at least the analysis model by the approach mode setting means.

  Therefore, according to the prediction analysis system according to the invention of claim 4, the prediction analysis method according to the invention of claim 1 described above can be automatically executed, and the effects thereof can be easily obtained.

  In the above system, the first and second CFD calculation means execute one-dimensional and three-dimensional CFD programs, respectively, and the run-up calculation means is initially set by the second CFD calculation means at the start of analysis. It is preferable that the three-dimensional CFD program is executed before (3).

  That is, when the simulation is started, the flow field in the three-dimensional analysis model is substantially stationary. Therefore, when the CFD calculation is started by giving a boundary condition to this model, the initial value is obtained at each calculation point in the model. Since the value of the flow variable having a zero (0) changes greatly after the first time step, large numerical vibrations are likely to occur. Therefore, the effect of the invention of preventing the system from being down by providing a run-up period before starting the three-dimensional CFD calculation in such a situation is particularly effective. In this case, it is preferable that the way of changing the boundary condition by the running calculation means is set as the running mode setting means in association with the simulated operating condition of the engine (invention of claim 6).

  Further, as a method of changing the boundary condition in the run-up calculating means, it is preferable that the boundary condition is first changed at a predetermined degree of change and maintained substantially constant for a predetermined period thereafter. invention). In this way, as in the invention of claim 2 described above, the CFD calculation is performed with the boundary condition maintained substantially constant in the latter half of the run-up period, and the flow field in the entire analysis model is in a steady state. After that, the original CFD calculation is started, so that the operational effect of suppressing the numerical vibration and preventing the system from being down is further ensured.

  Further, for the prediction analysis system having the same premise configuration as that of the invention of claim 4, the first and second CFD calculation means, boundary condition imparting means, and run-up calculation means, which are the same as those of the present invention, are provided. The approach condition setting means for setting the method of changing the boundary condition in the computing means is not provided, but the boundary condition is first changed at a predetermined degree of change in the approach computing means, and is maintained substantially constant for the subsequent predetermined period. (Invention of claim 8).

  According to the prediction analysis system having this configuration, the above-described prediction analysis method according to the invention of claim 2 can be automatically executed, and the operation effect can be easily obtained.

  In the predictive analysis system according to the invention of claim 8 as well, the approach of changing the boundary condition by the approach calculation means is set in association with at least one of the simulation operation condition defining the engine simulation operation state and the analysis model. Preferably, the mode setting means is provided (invention of claim 9), and the running mode setting means is arranged so that the fluctuation of the calculated flow field becomes relatively small during the CFD calculation by the running calculation unit. It is more preferable to modify the way of changing the boundary condition based on the calculation results up to this point (invention of claim 10). By doing so, it is possible to automatically execute the predictive analysis method according to the above-described invention of claim 3 and easily obtain the effects thereof.

  Next, the invention of claim 11 of the present application includes a one-dimensional and three-dimensional CFD program for simulating the flow of engine intake and exhaust using at least one-dimensional and three-dimensional CFD analysis models, respectively. The control program of the predictive analysis system that executes the program and analyzes the flow of intake and exhaust air from at least a part of the intake system to a part of the exhaust system and thereby predicts the engine performance is targeted.

  Then, one of the two CFD programs is executed to calculate the flow field of intake and exhaust, and based on the flow field data calculated by the first CFD calculation step, the CFD by the other CFD program is calculated. A boundary condition giving step for giving a boundary condition for the operation, and the condition given in the boundary condition giving step in a mode in which the boundary condition is set in advance when the other CFD program is first executed at the start of the analysis. A run-up calculation step for performing the CFD calculation while gradually changing to a second step, and a second CFD calculation step for executing the other CFD program using the flow field data calculated in the run-up calculation step as an initial value. In addition, at least the analysis module shows how to change the boundary condition in the run-up calculation step. It shall have a run-up mode setting step of setting in association with Le.

  By controlling the computer system with the control program, the computer system becomes an engine performance prediction analysis system according to the invention of claim 4, and thereby, the same effect as that of the invention of claim 4 can be obtained.

  In the first and second CFD calculation steps of the control program, one-dimensional and three-dimensional CFD programs are executed, respectively, and the run-up calculation step is first performed in the second CFD calculation step at the start of analysis. When the dimension CFD program is executed, it is preferably executed before the second CFD calculation step. Thus, the same effect as that attained by the 5th aspect can be attained.

  In that case, in the approach mode setting step, it is preferable to set the way of changing the boundary condition in the approach calculation step in association with the simulated operation condition of the engine (invention of claim 13).

  In the approach calculation step, it is preferable that the boundary condition is first changed at a predetermined degree of change, and is maintained substantially constant for a predetermined period thereafter (invention of claim 14). Thus, the same effect as that attained by the 7th aspect can be attained.

  Further, the control program having the same premise configuration as that of the invention of claim 11 is provided, and has the same first and second CFD calculation steps as those of the present invention, a boundary condition assigning step, and a run-up calculation step, and the run-up calculation There is no run-up mode setting step for setting how to change the boundary condition in the step. In the run-up calculation step, the boundary condition is first changed at a predetermined change degree, and is maintained substantially constant for a predetermined period thereafter. (Invention of claim 15).

  By controlling the computer system with this control program, the computer system becomes an engine performance prediction analysis system according to the invention of claim 8, and the same operation effect as that of the invention of claim 8 is thereby obtained.

  In the control program according to the fifteenth aspect of the present invention, the method of changing the boundary condition in the approach calculation step is set in association with at least one of the simulated operation condition and the analysis model that defines the simulated operation state of the engine It is preferable to have an aspect setting step (invention of claim 16), and in the approach mode setting step, the flow field to be calculated is relatively reduced during the CFD calculation in the approach calculation step. It is more preferable to modify the way of changing the boundary condition based on the calculation results up to (invention of claim 17). If it does so, the same effect as each invention of Claims 9 and 10 will be obtained by the above-mentioned control program.

As described above, according to the engine performance prediction analysis method, the prediction analysis system, and the control program thereof according to the present invention, the engine intake / exhaust flow is analyzed by at least one-dimensional and three-dimensional CFD computations. When predicting the engine performance based on this, especially when starting the CFD calculation at the start of the analysis, considering that the numerical vibration caused by the change of the boundary condition occurs and the calculation is likely to diverge, While the conditions were gradually changed, a preliminary run period for performing the CFD calculation was provided in advance, and the original CFD calculation was started using the flow field data obtained by the calculation during the run period as an initial value. Adopting a higher-order discretization scheme for calculation to sufficiently improve the prediction accuracy of engine performance, It can be prevented, and this makes it possible to improve the practicality of the design and development support tools.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. It should be noted that the following description of the preferred embodiment is merely illustrative in nature, and is not intended to limit the present invention, its application, or its use.

(Overall system configuration)
FIG. 1 is a conceptual diagram showing an overall configuration of an engine performance prediction analysis system A according to an embodiment of the present invention. This system simulates the flow of intake and exhaust, which are working fluids of the engine, by one-dimensional and three-dimensional CFD computations, and simulates combustion in a cylinder by a chemical reaction equation, and combines them, Driving simulation is performed. This system is characterized by automating data exchange between one-dimensional and three-dimensional CFD computations and data exchange between CFD computations and chemical reaction simulation (chemical reaction SIM), for example, a throttle valve The flow of intake and exhaust from the cylinder to the catalytic converter can be dynamically simulated, so that extremely high-precision analysis can be easily performed.

  Reference numerals 1, 1,... Shown are computer apparatuses that mainly execute CFD operations. In this embodiment, in particular, a plurality of high-speed server computers are arranged in parallel in order to cope with an enormous amount of operations of three-dimensional CFD. Connected and used (hereinafter referred to as “calculation server”). Each of these arithmetic servers 1 incorporates a storage device such as a hard disk drive and is connected to an image display device 10 such as a display. Further, although not shown, an output device such as a printer and a keyboard for accepting an input operation by an operator. An input device such as a mouse is also connected. The storage device includes at least one-dimensional and three-dimensional CFD programs for simulating the flow of intake and exhaust, a dedicated preprocessor for constructing a physical model (analysis model, numerical calculation model) therefor, and a combustion state Are stored, and a chemical reaction simulation program for simulating the image and an image processing program for displaying an image of a simulation result by each of the programs.

  The arithmetic servers 1, 1,... Can access the model database DB11 by a general method as needed during the operation. The model DB 11 stores a physical model of an engine used for one-dimensional and three-dimensional CFD calculations, and stores the model in a state classified for each part of the engine. A model newly constructed by the preprocessor is also stored. The model of the physical model is a basic part of a portion where intake or exhaust flows, such as an intake system surge tank, independent intake passage, intake port, exhaust system exhaust port, exhaust manifold, EGR passage, etc. A part model that simulates a shape and whose physical property values such as dimensions, shape and material, surface state, and thermal conductivity can be changed, and is hereinafter referred to as a template part in this embodiment.

  By providing the model DB 11 in which the data of the template part that can change the dimension, shape, and physical property value is stored, the dimension, shape, and the like of the template part read from the model DB 11 are corrected and combined. If a calculation grid (mesh) is generated inside, a physical model of the engine for CFD calculation can be constructed. In addition, since the model once constructed in this way is also stored in the model DB 11, the model can be corrected as necessary, and engine design changes can be easily handled.

  In the model DB 11, as will be described in detail later, when a three-dimensional CFD calculation is started under a predetermined situation where the boundary condition changes greatly, a run-up calculation performed to alleviate the change in the boundary condition is performed. A running mode map in which modes (how to change boundary conditions) are preset for each physical model of the engine is also stored.

  Further, the arithmetic servers 1, 1,... Can access the chemical reaction database DB12 by a general method as needed during the operation. This chemical reaction DB 12 is a representative of various gas components (chemical species) in the intake air that are filled in the in-cylinder combustion chamber of the engine and contribute to combustion. They are stored in a state of being grouped in advance in association with the set. Therefore, as will be described in detail later, according to the state in the cylinder obtained as a result of the CFD calculation, a corresponding group of gas components is read from the chemical reaction DB 12, and the chemical reactions of these gas components are respectively simulated. By this, the combustion state can be simulated.

  Reference numeral 2 shown in the figure is a computer device that is connected to an experimental data database DB 13 (experiment DB) that mainly stores engine specification values, physical characteristics and performance characteristics in association with each other and manages the data ( Hereinafter, it is referred to as an experimental DB server. In other words, the data accumulated in the past experiments and developments related to engines and transmissions are organized by well-known statistical analysis methods, and the engine specifications and their physical characteristics (for example, volumetric efficiency, combustion characteristics, loss factor, etc.) Etc.) and performance characteristics thereof (for example, output, fuel consumption, emission, etc.) are stored in the experiment DB 13 as empirical formulas associated with each other. Based on this empirical formula, for example, performance characteristics can be predicted from engine specification values and physical characteristics.

  Reference numeral 3 shown in the figure is a computer device of a three-dimensional CAD system for supporting engine design (hereinafter referred to as a design CAD server). The design CAD server 3 executes a general-purpose CAD program for machine design and structural analysis, and accesses the design database DB 14 (design DB) by a general method as necessary during the operation. The engine design CAD data can be called up or changed and stored in the design DB 14 anew. That is, the design DB 14 stores three-dimensional design CAD data of various engines in a state where they can be extracted and used individually for each part of the engine.

  Reference numerals 5, 5,... Are terminals (PC terminals) each formed of a personal computer, which are arranged in plural in the powertrain design department, development department, experimental department, etc. Are connected to the calculation servers 1, 1,..., The experiment DB server 2 and the design CAD server 3 so as to be capable of bidirectional communication. When the system control program is executed in accordance with the operation of the operator in each PC terminal 5, each PC terminal 5 is connected to the calculation servers 1, 1,... Via the network 6 (login). A so-called server / client environment is configured, and commands and files are exchanged mainly with the computing servers 1, 1,..., Thereby executing an engine operation simulation.

  The experiment DB server 2, the design CAD server 3, and the PC terminal 5 each have a built-in storage device such as a hard disk drive, as in the calculation server 1, and are connected to a display 10, an output device, an input device, and the like. Yes.

(CFD calculation)
Next, the operation simulation of a 4-cycle 4-cylinder gasoline engine will be described as a specific example of the one-dimensional and three-dimensional CFD.

  In this example, in order to shorten the time required for the CFD calculation as much as possible, a part of the engine is replaced with a three-dimensional CFD as necessary while basically using a one-dimensional CFD. That is, for example, as shown in FIG. 2A, a one-dimensional CFD physical model M1 from the throttle valve thv upstream of the intake passage of the engine to the catalytic converter cat through the combustion chambers of the first to fourth cylinders c1 to c4 is obtained. Basically, for example, when the main purpose of the analysis is to examine the deviation of the exhaust flow flowing into the catalytic converter cat, the exhaust manifold exm is replaced with a three-dimensional model M3 as shown in FIG. is there.

  More specifically, in the illustrated one-dimensional model M1, an independent intake passage from the surge tank st to each of the cylinders c1 to c4 and a common intake passage from the throttle valve thv to the surge tank st are basically provided. Are respectively represented as a collection of pipes, and similarly, an independent exhaust passage from each cylinder c1 to c4 to a collection portion of the exhaust manifold exm, and a common exhaust passage from the exhaust collection portion to the inlet of the catalytic converter cat, respectively. Expressed as a collection of tubes. The surge tank st and the first to fourth cylinders c1 to c4 are represented as containers. Although not shown in the figure, the EGR passage for returning a part of the exhaust from the collection portion of the exhaust manifold exm to the upstream of the surge tank st may be represented as a collection of pipes.

  In such a one-dimensional model M1, the flow of intake and exhaust flowing in the pipe is regarded as a one-dimensional flow of a compressible viscous fluid, and pressure p, density ρ, velocity u, and temperature T representing the state of the flow. Each equation of well-known mass conservation, momentum conservation, and energy conservation is solved by numerical calculation. That is, the value of the flow variable is calculated using a characteristic equation obtained by, for example, the characteristic curve method based on each of the conservation equations, and the intake / exhaust flow from the throttle downstream to the catalyst upstream is calculated in predetermined time increments (for example, crank Describe each angle. At this time, it is assumed that the internal state of the container is uniform and the fluid flowing in from the pipe is instantaneously and uniformly distributed. Further, an appropriate boundary condition is given at the joint portion between the tubes or between the tube and the container. Further, it is preferable to consider the influence of the bending condition of the pipe, friction on the wall surface, heat loss, and the like.

  On the other hand, the three-dimensional model M3 of the exhaust manifold exm simulates the shapes of the independent exhaust passages s1 to s4 and the downstream common exhaust passages s5 for each cylinder, for example, on the inner wall surface of these passages. A layer mesh of a predetermined size is pasted, and the mesh is cut into a space in the passage and divided into calculation grids. In the three-dimensional CFD, the exhaust flow in the passage is regarded as a three-dimensional flow of a compressible viscous fluid, and the respective conservation equations are solved as in the case of the one-dimensional case. That is, the flow field in the passage is calculated under the boundary condition given by the one-dimensional CFD calculation or the chemical reaction SIM described later, using, for example, a difference equation that is discretely expressed in time and space. By repeating this calculation at predetermined time intervals, the state of the flow in the exhaust manifold that changes from time to time can be described in three dimensions.

  When combining 1-dimensional and 3-dimensional CFD in this way, the part where the flow of intake and exhaust gas is switched between 1-dimensional and 3-dimensional, that is, the boundary surface of the 3-dimensional model, is based on the calculation result of the 1-dimensional CFD. A boundary condition (a value of a flow variable on the boundary surface) of a three-dimensional CFD is given. Generally, in a one-dimensional flow, the flow variables p, ρ, u, T are equal in the cross section of the flow. The boundary surface is set at a part where the flow is substantially uniform over the entire cross section so that accurate simulation can be performed even if it is passed to the three-dimensional boundary surface as it is. preferable.

  Then, while passing the calculation data in this way, the overall intake / exhaust flow is calculated using the simple one-dimensional model M1, and the part requiring particularly high accuracy (in this case, the exhaust manifold) is automatically selected. Since the calculation is performed by replacing the model with the three-dimensional model M3, the 1 + 3-dimensional CFD simulation can be realized very easily, and the calculation amount for the analysis is reduced while ensuring the accuracy of the analysis. The time required can be shortened.

  Further, the exhaust manifold three-dimensional model M3 can be divided into, for example, the independent intake passages s1 to s4 and the common exhaust passage s5, so that the entire exhaust manifold is not replaced with the three-dimensional model M3, but each cylinder. If only the independent exhaust passages s1 to s4 corresponding to each of c1, c2,... in the exhaust stroke are replaced with a three-dimensional model, the amount of calculation can be further reduced.

(Chemical reaction simulation)
As described above, the flow of the intake and exhaust of the engine is simulated by CFD. In this embodiment, the combustion state of the air-fuel mixture and combustion gas in the cylinder in the compression and expansion strokes is ignored while ignoring the motion. The chemical reaction simulation is done. Specifically, first, the state of intake air charged in the combustion chamber in the cylinder, that is, the pressure p, the density ρ, the speed u, and the temperature T is obtained by the one-dimensional or three-dimensional CFD calculation as described above. At that time, considering that the bottom dead center of the cylinder is different from the closing timing of the intake valve, the cylinder is filled by simulating the return of the intake air after flowing into the cylinder once. The state of inspiration can be obtained accurately.

  In this way, the pressure p and temperature T of the combustion chamber at the initial stage of the compression stroke are obtained, and the strength of the in-cylinder flow is obtained from the intake flow velocity u. On the other hand, the air-fuel ratio of the air-fuel mixture (or the amount of fuel supplied to the cylinder), the amount of burnt gas (internal EGR gas) remaining in the combustion chamber, the cylinder wall temperature, etc. The rotation speed, etc.). That is, in this embodiment, a map in which physical values such as the air-fuel ratio, the internal EGR gas amount, and the cylinder wall temperature are set in advance in association with the operating state of the engine is provided, and based on the operating state of the engine being simulated. A plurality of physical quantity values are read from the map.

  Then, as described above, if a plurality of physical quantity values representing the state of the combustion chamber in the initial stage of the compression stroke are obtained based on the result of the CFD calculation and the engine operating conditions, as schematically shown in FIG. By reading the group of gas components corresponding to the set of physical quantities from the chemical reaction DB 12, the components of the working gas used for the chemical reaction simulation are made to reflect the flow simulation by CFD and the engine operating conditions. be able to.

  As shown in FIG. 3, the data of the gas component group in the chemical reaction DB 12 includes various hydrocarbons mainly supplied as fuel, nitrogen and oxygen in the air, and hydrocarbons contained in the EGR gas. A representative one corresponding to a set of physical quantities representing the state of the cylinder is stored together with its reaction formula among carbon dioxide, water vapor, and the like. That is, in general, if all the chemical species related to engine combustion and their reaction formulas are listed, this is more than about 3000 types, and if all of them are to be calculated, the amount of calculation will increase significantly. This will prolong the simulation time.

  In this regard, if we focus on not only all the chemical reactions but also those that are particularly important in simulating the state of combustion, that is, typical ones that simulate combustion, it is at most tens to hundreds. Therefore, in this embodiment, only representative chemical reactions that change depending on the operating state of the engine are extracted so as to be a predetermined number (for example, 100) or less, and only representative gas components corresponding thereto are extracted. It is made to store in chemical reaction DB12. As a result, the number of gas components used in the chemical reaction simulation becomes appropriate, and the amount of calculation can be greatly reduced while ensuring the required accuracy. Further, the size of the chemical reaction DB 12 can be made moderate.

  Then, based on the gas components (chemical species) of the group extracted as described above, first, in the compression stroke of the cylinder, the pressure p of the combustion chamber rises as the piston rises, and the temperature T rises accordingly. And the reaction of each gas component under such conditions will be sequentially described in consideration of heat being taken away by heat exchange with the cylinder wall surface. By the chemical reaction simulation in the compression stroke, it is possible to reproduce the pre-flame reaction before the spark ignition is performed in the cylinder, the occurrence of preignition, and the like.

  Also, in the vicinity of the compression top dead center of the cylinder, the ignition of the air-fuel mixture by spark ignition is simulated, and the progress of the chemical reaction (combustion) is taken into account when the expansion stroke ends while taking into account the increase in the combustion chamber volume in the cylinder expansion stroke Describe sequentially. And the composition of burned gas in the cylinder obtained as a result of the chemical reaction simulation in the expansion stroke, the total calorific value and heat exchange with the cylinder wall surface, the work applied to the piston, the lowering of the piston The state of burned gas (exhaust gas) discharged from the combustion chamber when the cylinder moves to the exhaust stroke is obtained based on the expansion of the combustion chamber volume accompanying the above. This data is the initial value of the exhaust flow in the CFD program described above.

(Simulation overview)
Next, a simulation procedure by the engine performance prediction analysis system A according to this embodiment will be described. As shown schematically in FIG. 4, first, an operator performs a predetermined input operation according to a screen display or the like on any of the PC terminals 5, 5,. ) Is input (S1). This is an identification code for specifying the engine model stored in the model DB 11, an operating condition (simulated operating condition) of the engine to be simulated, and the like when the engine model has already been constructed. If is not constructed, information necessary for constructing the model is further included.

  For example, the model of the four-cylinder engine shown in FIG. 2 will be described. Geometric data representing dimensions and shapes of the engine intake and exhaust systems, combustion chambers, etc., physical data representing physical characteristics such as heat transfer coefficient thereof, or Instead of the detailed data, a code for designating engine data stored in the experiment DB 13 or the design DB 14 is input to the PC terminal 5.

  Further, for which part of the engine the three-dimensional model is used is selected, and further, in which stroke of the cylinder the three-dimensional calculation is selected for that part. That is, for example, if the purpose of analysis is to support engine exhaust system design and development, the operator selects and sets the exhaust manifold to use a three-dimensional model M3 as shown in FIG. Furthermore, it is preferable to set so that the three-dimensional CFD calculation is performed only when the corresponding cylinders in the independent exhaust passages s1 to s4 are in the exhaust stroke.

  Subsequently, in step S2, an engine model is constructed based on the simulation data input in step S1, or is read from the model DB 11 and stored in the internal storage device (memory) of the arithmetic servers 1, 1,. Store. For example, as shown in FIG. 2 (a), it is divided into a one-dimensional CFD model M1 extending from a part of the intake system to a part of the exhaust system, and independent exhaust passages s1 to s4 for each cylinder c1 to c4. Possible exhaust manifold 3D models M3 are stored in memory.

  In the case of newly constructing a three-dimensional model M3, for example, based on the simulation data, three-dimensional design CAD data representing the shape of the exhaust manifold is read from the design DB 14 into the PC terminal 5. A model creation command attached with data designating boundary surface and mesh information is created and transmitted to the calculation servers 1, 1,. Upon receiving this command, the preprocessor is activated in the arithmetic servers 1, 1,..., And a layer mesh is pasted on the inner wall surface of the exhaust manifold passage, and the mesh is cut into the internal space.

  Alternatively, when another model creation command is transmitted from the PC terminal 5 to the calculation servers 1, 1,... Based on the initial setting data, the calculation servers 1, 1,. By reading template part data representing the basic shape of the tank and changing the dimensions and shape of the part, a three-dimensional model having a mesh for CFD calculation is constructed.

  In addition, regarding the chemical reaction simulation, a container model that defines a change in the cylinder volume with respect to a change in the crank angle, a change in heat transfer coefficient according to the cylinder wall temperature, and the like is used. This container model is a zero-dimensional physical model in the sense that there is no motion of the gas mixture or combustion gas inside.

  As described above, using the models stored in the memory of the calculation servers 1, 1,..., In step S3, a simulation calculation is performed to simulate the flow of intake and exhaust during engine operation and the state of combustion in the combustion chamber. To give an example of details of the arithmetic processing, in this embodiment, while the PC terminal 5 and the arithmetic servers 1, 1,... 1, 1,..., One-dimensional and three-dimensional CFD operations and chemical reaction simulation are executed simultaneously.

  For example, as a processing procedure of the CFD calculation, first, boundary conditions (flow variables p, ρ, u, T, etc.) at the beginning of the simulation and simulated engine operating conditions are input to the one-dimensional CFD calculation model M1 (S31). : Condition input), based on this, a one-dimensional flow characteristic equation is calculated (S32: CFD calculation). That is, in the model M1 shown in FIG. 2A, the boundary values of the flow variables at the throttle valve thv that is the boundary on the inlet side of the flow and the catalytic converter cat that is the boundary on the outlet side are given based on the simulation data. As a result, the flow fields of the intake and exhaust air from the downstream of the throttle valve thv to the catalytic converter cat through the combustion chambers of the cylinders c1 to c4 are obtained.

  In the subsequent step S33, the flow field data is stored, and boundary conditions of the three-dimensional CFD are given based on the data. That is, the data of the one-dimensional flow field is transferred as a data file from the calculation servers 1, 1,... To the PC terminal 5, and the PC terminal 5 that has received the data file receives a predetermined value from the data of the one-dimensional flow field. The values (boundary values) of the flow variables p, ρ, u, and T (boundary values) at the boundary surfaces of the three-dimensional model (in this embodiment, the inlets and outlets of any of the independent exhaust passages s1 to s4) are determined by the method. Is created and returned to the calculation servers 1, 1,...

  Subsequently, the calculation servers 1, 1,... That have received the execution file start a three-dimensional CFD program, and input predetermined calculation conditions including the boundary conditions to the three-dimensional model M3 of the exhaust manifold (S34: Based on this, a difference equation for a three-dimensional flow is calculated (S35: CFD calculation). That is, among the exhaust manifold model M3 shown in FIG. 2B, a three-dimensional model of the independent exhaust passages s1 to s4 in which the corresponding cylinder is in the exhaust stroke is used, and the flow variables at the inlet and outlet (boundary surface) thereof. Of the exhaust gas flowing in the passage (flow variables p, ρ, u, T), that is, the flow field of the exhaust gas is obtained in three dimensions. Then, the three-dimensional flow field data thus obtained is stored in the memory of the arithmetic servers 1, 1,... (S36: data storage).

  Of the flow field data at the beginning of the simulation thus obtained in 1 + 3 dimensions, for example, the data related to combustion in the cylinder and the state of burned gas discharged from the cylinder will be described later. The data is rewritten based on the result of the chemical reaction simulation (data conversion, provision and rewriting: S37). Thereafter, the crank angle of the engine is advanced by a minute crank angle (time increment) set in advance (increment: S38), and it is determined whether or not the crank angle position set as the end of the simulation is reached (S39). If so, the process returns to step S31, and the one-dimensional and three-dimensional CFD calculations (S31 to S36) are repeatedly executed for each minute crank angle.

  In this way, 1 + 3 dimensional CFD calculation is repeatedly performed for each minute crank angle from the beginning to the end of the simulation, so that the flow of the intake / exhaust flow field of the engine changes from moment to moment in time series. Are stored in the internal storage of the calculation servers 1, 1,. Although not shown, the intake flow boundary conditions (variables p, ρ, u, T, etc.) adjusted by the engine throttle valve are considered to be substantially constant when the engine is in a steady operation state. Further, in a transient state in which the operating state changes, a change amount (transient change amount) of the throttle opening for each set crank angle is separately provided by a control program that simulates the engine control logic so as to correspond to the change.

  In parallel with the above-described 1 + 3-dimensional CFD calculation, the calculation of the chemical reaction simulation (chemical reaction SIM) is performed for each cylinder in the compression stroke and the expansion stroke. That is, when one of the cylinders (hereinafter, for example, described as the first cylinder c1) shifts from the intake stroke to the compression stroke as the simulation progresses, the CFD calculation described above is performed as schematically shown in FIG. Calculation result data is transmitted from the calculation servers 1, 1,... To the PC terminal 5. The PC terminal 5 that has received this data obtains the pressure p, temperature T, etc. of the intake air charged in the first cylinder c1 and the ratio of EGR gas in the intake air based on the data, and determines the current operating conditions of the engine. Based on this, the values of physical quantities such as air-fuel ratio and cylinder wall temperature are read from the map, a set of physical quantities representing the state in the cylinder is specified, and a chemical reaction simulation program including an identification code corresponding to the set of physical quantities is executed The file is transmitted to the arithmetic servers 1, 1,... (Data exchange between the programs is shown as result processing * 1 in the figure).

  Upon receiving the execution file, a chemical reaction simulation program is started in the arithmetic servers 1, 1,..., And as shown in the flow of FIG. 4, group data of gas components corresponding to the set of physical quantities of the identification code is stored in the chemical reaction DB 12. (S41: reading of chemical species), and describes the chemical reaction of the gas component at a preset small crank angle (time increment) while simulating the expansion of the combustion chamber volume by the container model of the first cylinder c1. (S42: Chemical reaction calculation), and the result is stored (S43: Data storage). Such calculation of the chemical reaction formula is repeatedly performed for each minute crank angle from the initial stage of the compression stroke to the end of the expansion stroke of the cylinder c1, and thereby the compression and expansion strokes in the combustion chamber in the cylinder c1. Data describing the state of the working gas in chronological order is stored in the storage device as a result of the chemical reaction calculation.

  When the first cylinder c1 finishes the expansion stroke and shifts to the exhaust stroke, the chemical reaction simulation for the cylinder c1 is finished, and as shown in FIG. Data such as the composition of burned gas (exhaust gas) discharged from the combustion chamber, the heat generated by combustion, and the work amount are transmitted from the calculation servers 1, 1,. In the PC terminal 5 receiving this data, the initial state of the exhaust flow blown out from the cylinder based on the composition of the burned gas (exhaust gas) discharged from the combustion chamber of the first cylinder c1, the heat generated by the combustion, the work amount, etc. , P, ρ, u, and T are obtained, and a data file of this variable and a predetermined command for rewriting the operation result data of the CFD operation based on the data file are created, and the operation servers 1, 1,. Return to

  Then, the calculation servers 1, 1,... That have received the command and the file are portions of the compression stroke and expansion stroke of the first cylinder c1 in the calculation result data of the one-dimensional CFD calculation in step S37 of the flow of FIG. Will be rewritten. Further, the gas component data in the chemical reaction DB 12 is corrected based on the composition of the exhaust gas in consideration of EGR.

  As described above, in step S3 of the main program, the CFD calculation and the chemical reaction simulation calculation are performed in parallel in synchronization with the change of the crank angle of the engine from the start to the end of the simulation. When the crank angle position set as the end of the simulation is reached (determination is YES in S39), the process proceeds to step S4, the simulation result is output, and then the control ends (end).

  As the output of the simulation result in the step S4, the necessary data is read out from the data of the time series calculation results stored in the storage device of the calculation servers 1, 1,... And transferred to the PC terminal 5, Based on this data, a predetermined evaluation value relating to engine performance may be output. For example, the output characteristics of the engine, the fuel consumption characteristics, the change in volumetric efficiency of each cylinder accompanying the change in the engine operating state, etc. may be graphed and displayed on the display of the server 1, 1,. In addition, for example, the result of the three-dimensional CFD calculation regarding the flow of exhaust gas in the exhaust manifold may be visualized and displayed as an image.

  Step S32 of the flow shown in FIG. 4 corresponds to a first CFD calculation step of calculating the flow field of intake and exhaust of the engine by executing a one-dimensional CFD program, and similarly, step S35 is a three-dimensional CFD program. To correspond to the second CFD calculation step of calculating the flow field of intake and exhaust. Steps S33 and S34 correspond to a boundary condition applying step for providing a boundary condition for the three-dimensional CFD calculation in the second calculation step based on the flow field data calculated in the first CFD calculation step. .

  In the prediction analysis system A of this embodiment, the calculation servers 1, 1,... Are executed in the calculation servers 1, 1,. A first CFD computing unit 1a that executes a program and a second CFD computing unit 1c that executes a three-dimensional CFD program are configured. .. And the PC terminals 5, 5,... Execute the steps S33, S34 of the flow, so that the calculation servers 1, 1,. The boundary condition providing means 1b for providing boundary conditions for the three-dimensional CFD calculation is configured based on the flow field data calculated by the one-dimensional CFD program.

(Running period in CFD calculation)
By the way, as described above, when the engine intake / exhaust flow is only partially simulated as a three-dimensional flow, flow field data obtained by one-dimensional CFD calculation is automatically given as a boundary condition of the three-dimensional CFD. Due to the significant change in the boundary condition, numerical vibration (vibration in the calculation of the flow variable value) may occur in the three-dimensional CFD calculation, and the calculation may diverge.

  For example, in each independent exhaust passage of the exhaust manifold, when the corresponding cylinder shifts from the expansion stroke to the exhaust stroke and the exhaust valve opens, from which high-temperature and high-pressure burned gas blows out at a high speed, the exhaust flow rate suddenly increases. To rise. More specifically, FIG. 6 shows the change in the exhaust flow velocity at a predetermined portion of the exhaust manifold observed over one combustion cycle of the first cylinder. According to FIG. 6, as shown as * 1, * 2. In addition, it can be seen that the flow velocity increases every time the exhaust flow from each cylinder reaches the observation point.

  Therefore, as described above, when only one of the independent exhaust passages of the exhaust manifold is simulated by a three-dimensional model, the pressure p, density ρ, velocity u of the exhaust flow at the exhaust inlet side boundary surface of this model, The temperature, etc. T, that is, the boundary condition given as a result of the one-dimensional CFD calculation changes very greatly, which causes a large numerical vibration.

  In particular, at the start of the simulation shown as * 1 in the figure, the spatially discrete flow field in the three-dimensional physical model is in a substantially stationary state, and the flow velocity u at each calculation point is zero (0 Therefore, when the boundary condition is suddenly given to the model and the calculation of the unsteady flow field as shown in Fig. 7 (a) is started, after one time step at each calculation point in the model The exhaust flow velocity rapidly increases from the initial value 0, and as a result, a large numerical vibration is generated as schematically shown in FIG. 5B, and the calculation is diverged and the system is often down.

  On the other hand, if, for example, a highly stable low-order scheme is adopted so that the numerical error due to discretization acts as a so-called numerical viscosity, the numerical vibration is suppressed and the stability is increased. In some cases, the accuracy is inevitably lowered.

  In view of such a point, in the prediction analysis system A of this embodiment, when the three-dimensional CFD calculation is first started at the start of the simulation as described in * 1, the boundary condition given from the calculation result of the one-dimensional CFD Is used as it is, for example, as schematically shown in FIG. 7 (c), the boundary condition is given from the condition before the change (exhaust flow velocity value 0 in the example in the figure) to the condition after the change (in the example in the figure). In addition, a run-up period during which CFD calculation (hereinafter also referred to as run-up calculation) is performed in advance is provided while gradually changing the exhaust flow rate value).

  That is, as shown by the solid line in the figure, first, in the first half of the run-up period, the boundary condition is changed with a preset gradient so that the boundary condition has a predetermined degree of change with respect to the change in time (or crank angle). A three-dimensional CFD operation is executed based on the conditions. If the boundary condition is gradually changed in this way, the change at each time step is reduced, and the numerical vibration at each calculation point in the model is small as schematically shown by the broken line in FIG. Further, in the second half of the period, the three-dimensional CFD calculation is executed while maintaining the boundary condition substantially constant for a predetermined period. By doing so, small numerical vibrations generated in the first half of the period are also quickly damped, and the flow field becomes almost steady throughout the model.

  Then, if the flow field in the model in such a steady state is set as an initial state and a new CFD calculation is started, a highly accurate unsteady flow using a high-order differential scheme is used. Even if the calculation is performed, the calculation does not diverge and the system can be prevented from being down.

  Below, the said approach calculation is demonstrated concretely based on the flow of FIG. This flow is executed before the three-dimensional CFD calculation is performed in steps S34 to S36 of the main program (FIG. 4) at the beginning of the simulation. First, in step S340 after the start, the start of the simulation is performed. If it is not the start time, the control is terminated and the process proceeds to step S34 of the main program. On the other hand, if the determination is YES and the simulation is the start time, the process proceeds to step S341.

  In this step S341, referring to the running condition map read from the model DB 11, the running conditions corresponding to the models s1 to s4 of the independent exhaust passages used for the three-dimensional CFD calculation are selected. The reason why the running condition is set in association with the model is as follows. In other words, the milder the degree of change in the boundary condition during the run-up period, the easier it is to suppress numerical vibrations and more reliably prevent the divergence of calculations, but on the other hand, the longer the run-up period, the more calculation This is not preferable because it causes a delay. In addition, whether or not the numerical vibration actually increases is greatly affected by the shape of the model including the mesh.For example, when the shape of the passage through which intake and exhaust flows is complex and the number of deformed meshes is large, The deviation of flow variables between the mesh and the mesh tends to increase, and the numerical vibration tends to increase.

  Therefore, for models that tend to diverge with such large numerical oscillations, it is necessary to change the boundary conditions sufficiently gently.For example, in the first half of the run-up period, the boundary condition change gradient is moderated. Or make the second half of the time longer. On the other hand, for models in which divergence is unlikely to occur, it is preferable to change the boundary conditions relatively quickly by making the gradient relatively steep or by shortening the latter half of the period. For this reason, in this embodiment, appropriate run-up conditions corresponding to each model are obtained in advance by experiments or the like, and stored in the model DB as a boundary condition map. The approach condition corresponding to is read from the map and set.

  Furthermore, in the step S341, the approach condition read out as described above is changed in accordance with the simulated operation condition of the engine (for example, the simulated load state, rotation speed, temperature, etc.). That is, for example, when the simulated operating condition of the engine is in a high load state, the exhaust gas temperature is high and the flow rate is high, it is preferable to change the boundary condition more gently than in the case of simulating a low load state. For example, when simulating engine cold, high-temperature and high-pressure exhaust flows in a state where the temperature in the wall and passage of the exhaust manifold is relatively low, so that the temperature difference between the two is relatively small. It is preferable to change the boundary conditions more slowly than the above.

  Then, in accordance with the approach condition set by correction as described above, in step S342, the boundary condition is slightly changed and input to the three-dimensional model, and in step S343, the CFD calculation is performed in the same manner as in step S35 of the main program. . Subsequently, in step S344, the flow field data is stored in the memory in the same manner as in step S36, and in the subsequent step S345, the crank angle is incremented in the same manner as in step S38. Then, in the following step S346, it is determined whether or not the crank angle range corresponding to the run-up period has passed (run-up period has passed?). If this determination is NO, the process returns to step S342, and the run-up calculation (S342-S342). On the other hand, if the determination is YES, the run-up calculation is terminated, the process proceeds to step S35 of the main program, and the original CFD calculation is started.

  In other words, while the boundary conditions of the three-dimensional model are gradually changed during the run-up period, a preliminary three-dimensional CFD calculation is performed, so that the flow field becomes almost steady throughout the model. By starting a new three-dimensional CFD calculation as an initial state, even if the CFD calculation is a high-precision three-dimensional unsteady flow calculation using a higher-order scheme, it is possible to prevent the calculation from diverging.

  In the run-up calculation flow shown in FIG. 8, step S341 is a run-up mode setting step in which the run-up conditions, that is, how to change the boundary conditions during the run-up period are set in association with the simulated operating conditions of the engine and the three-dimensional model. It corresponds to.

  In addition, considering that steps S342 to 346 execute the three-dimensional CFD calculation for the first time at the start of the simulation, the boundary condition given based on the result of the one-dimensional CFD calculation changes more than a predetermined value. Thus, the boundary condition is gradually changed in a preset manner, and this corresponds to a run-up calculation step for executing a three-dimensional CFD program.

  Moreover, in this embodiment, the calculation server 1, 1, ... comprises the run-up mode setting means 1d and the run-up calculation means 1e by performing the said run-up mode setting step and the said run-up calculation step, respectively.

  In the middle of the approach calculation, the approach condition may be corrected based on the flow field fluctuation state obtained from the previous calculation results. That is, when NO is determined in step S346 of the flow of FIG. 8 and the process returns to step S342, whether or not the fluctuation state of the flow field increases with time based on the flow field data stored in the memory. If it is determined that the fluctuation of the flow field is large, for example, the change gradient of the boundary condition in the first half of the run-up period is reduced by a predetermined value, and the change is corrected so as to be relatively gentle. On the other hand, if the fluctuation is not large, for example, the change gradient is increased by the predetermined value, and the boundary condition is corrected so as to be changed earlier (step S347 indicated by a virtual line in the figure).

  If the steps S342 to 345 are repeated according to the corrected approach condition after correcting the approach condition as described above, the method of changing the boundary condition in the approach period can be optimized. Therefore, the step S347 includes a running mode correction step for correcting the change of the boundary condition based on the calculation result so far, so that the fluctuation of the calculated flow field becomes relatively small during the CFD calculation. Corresponding to

(Function and effect)
Therefore, according to the engine performance prediction analysis system A according to this embodiment, when analyzing the flow of the intake and exhaust of the engine by the application of CFD, a one-dimensional engine model M1 is basically used. Since the CFD calculation is performed and the three-dimensional model M3 is used for the preselected part under the boundary condition given by the one-dimensional CFD calculation, the engine output Performance characteristics such as fuel efficiency and fuel efficiency can be predicted with sufficiently high accuracy, and the amount of calculation for that can be greatly reduced, thereby shortening the time required for analysis.

  In addition, when starting the three-dimensional CFD calculation for the first time at the start of the simulation, the boundary condition obtained by the one-dimensional CFD is not used as it is, but the CFD calculation (running calculation) is preliminarily changed while gradually changing the boundary condition. Since the original CFD calculation is started with the initial run time of the flow field with less fluctuation required by this run-up calculation as the run-up period to be performed, high-precision three-dimensional unsteady flow using a higher-order scheme By executing the calculation and sufficiently increasing the prediction accuracy of the engine performance, it is possible to suppress the numerical vibration caused by the sudden change of the boundary condition in the calculation and to prevent the system from being down due to the divergence of the calculation.

  In addition, in the run-up period, the boundary conditions are not uniformly changed over the whole period, but the conditions are gradually changed in the first half of the period, and then maintained at a substantially constant condition for a predetermined period. Therefore, after the relatively small numerical vibration generated in the first half of the period is also attenuated and the flow field becomes a substantially steady state as a whole in the model, the original CFD calculation can be started. As described above, the effect that the system down can be prevented is more certain.

  Furthermore, the method of changing the boundary condition during the run-up period (run-up condition) is appropriately set in association with the state of the three-dimensional model. Since the model that is difficult to diverge can be changed relatively quickly and even the run-up period can be shortened, the utility as a design / development support tool is extremely high.

(Other embodiments)
In addition, this invention is not limited to the said embodiment, Other various embodiment is included. In other words, in the above-described embodiment, the run-up calculation for reducing the change in the boundary condition is performed in the three-dimensional CFD calculation. However, this run-up calculation can also be applied to the one-dimensional CFD calculation.

  In the above embodiment, the approach condition is set in association with the CFD model and the simulated engine operation condition. However, the present invention is not limited to this, and it may be set in association with only one of them. Good.

  In the above embodiment, the boundary condition is gradually changed in the first half of the run-up period and kept constant in the second half. However, the present invention is not limited to this, and the boundary condition may be gradually changed over the entire period. Good.

  Furthermore, in the above-described embodiment, the case where the three-dimensional CFD calculation is performed on the exhaust manifold of the engine has been described. However, the present invention is not limited to this. For example, the shape of the intake system surge tank, the entire intake port, and the combustion chamber Even when the shape near the intake port opening is simulated in three dimensions, a run-up period can be provided before the three-dimensional CFD calculation.

  In the above embodiment, the chemical reaction simulation is performed for the compression and expansion strokes of each cylinder. However, this is not performed, and the flow of the intake and exhaust of the engine is simulated only by one-dimensional and three-dimensional CFD. You may make it do.

  Moreover, although the said embodiment demonstrated the case where the simulation about a 4-cycle engine was performed, it cannot be overemphasized that a 2-cycle engine and a rotary engine can also be simulated.

  As described above, the engine performance prediction analysis system or the like according to the present invention has a sufficiently high engine performance prediction accuracy by high-precision CFD calculation, while preventing the system down caused by that, and the automation rate. Therefore, it has sufficient practicality as a design / development support tool, and is particularly useful for the design / development of automobile engines.

1 is an overall configuration diagram of an engine performance prediction analysis system A according to an embodiment of the present invention. It is a schematic diagram which shows an example of the physical model for CFD calculation. It is explanatory drawing which shows a response | compatibility with the group of the physical quantity showing the state in a cylinder, and the group data of the gas component in chemical reaction DB. It is a main flowchart which shows the outline of the procedure of simulation. It is explanatory drawing which shows typically switching of CFD and chemical reaction simulation, and transmission / reception of the data accompanying this. It is a graph which shows the change of the exhaust gas flow velocity in the predetermined part of an exhaust manifold. (A) At the start of the simulation, (a) how to give conventional boundary conditions, (b) the state of numerical vibrations generated by this, and (c) the case of the present invention for performing a run-up calculation, respectively, are schematically shown. It is explanatory drawing. It is a flowchart which shows the procedure of run-up calculation.

Explanation of symbols

A Engine performance prediction analysis system M1 One-dimensional CFD analysis model M3, s1 to s5 Three-dimensional CFD analysis model 1, 1,... Operation server 1a First CFD calculation means 1b Boundary condition giving means 1c Second CFD calculation means 1d Running mode setting means 1e Run-up calculation means

Claims (17)

A one-dimensional and three-dimensional CFD program for simulating the flow of engine intake and exhaust using a one-dimensional and three-dimensional CFD analysis model, respectively;
A data exchange program for providing boundary conditions for CFD computations by the other program based on the flow field data computed by the one program,
A predictive analysis method for causing the computer program to execute the programs and analyzing the flow of intake and exhaust gas from at least a part of the intake system to a part of the exhaust system, thereby predicting engine performance,
When executing at least one of the CFD programs for the first time at the start of analysis, the CFD calculation is executed while gradually changing the boundary conditions in a manner preset in advance for each analysis model,
A method for predicting and analyzing engine performance, wherein a CFD calculation is newly started with the flow field thus obtained as an initial state. A one-dimensional and three-dimensional CFD program for simulating the flow of engine intake and exhaust using a one-dimensional and three-dimensional CFD analysis model, respectively;
A data exchange program for providing boundary conditions for CFD computations by the other program based on the flow field data computed by the one program,
A predictive analysis method for causing the computer program to execute the programs and analyzing the flow of intake and exhaust gas from at least a part of the intake system to a part of the exhaust system, thereby predicting engine performance,
When executing at least one of the CFD programs for the first time at the start of analysis, the boundary conditions are set in advance in a manner that is set in advance, and then the CFD calculation is performed while maintaining a substantially constant period for a predetermined period. Run,
A method for predicting and analyzing engine performance, wherein a CFD calculation is newly started with the flow field thus obtained as an initial state.   In the middle of executing the CFD calculation while changing the boundary condition in a preset manner, the change condition of the boundary condition is corrected based on the flow field fluctuation state obtained from the previous calculation result. 3. The engine performance prediction analysis method according to claim 1, wherein the engine performance is predicted and analyzed. 1D and 3D CFD programs that simulate the intake and exhaust flow of the engine using 1D and 3D CFD analysis models, respectively. A predictive analysis system that analyzes the flow of intake and exhaust air over a part of the exhaust system and thereby predicts engine performance,
First CFD calculation means for executing one of the CFD programs to calculate the flow field of intake and exhaust;
Boundary condition giving means for giving a boundary condition for CFD calculation by the other CFD program based on flow field data calculated by the first CFD calculation means;
When the other CFD program is executed for the first time at the start of analysis, CFD computation is performed in a manner in which boundary conditions are set in advance, gradually changing until the conditions given by the boundary condition applying means are satisfied. An approach calculation means,
Second flow CFD calculation means for executing the other CFD program using the flow field data calculated by the run-up calculation means as an initial value,
The engine performance prediction analysis system further comprises a running mode setting unit that sets at least how the boundary condition is changed by the running calculation unit in association with the analysis model. The first and second CFD computing means execute one-dimensional and three-dimensional CFD programs, respectively;
5. The run-up calculation means executes the three-dimensional CFD program before the first execution of the three-dimensional CFD program by the second CFD calculation means at the start of analysis. Engine performance prediction analysis system.   6. The engine performance prediction / analysis system according to claim 5, wherein the approach mode setting means sets the way of changing the boundary condition by the approach calculation means in association with the simulated operation condition of the engine.   The engine according to any one of claims 4 to 6, wherein the run-up calculating means changes the boundary condition at a predetermined degree of change first, and maintains it for a predetermined period thereafter. Performance prediction analysis system. 1D and 3D CFD programs that simulate the intake and exhaust flow of the engine using 1D and 3D CFD analysis models, respectively. A predictive analysis system that analyzes the flow of intake and exhaust air over a part of the exhaust system and thereby predicts engine performance,
First CFD calculation means for executing one of the CFD programs to calculate the flow field of intake and exhaust;
Boundary condition giving means for giving a boundary condition for CFD calculation by the program of the other CFD based on flow field data calculated by the first CFD calculation means;
When the other CFD program is executed for the first time at the start of analysis, CFD computation is performed in a manner in which boundary conditions are set in advance, gradually changing until the conditions given by the boundary condition applying means are satisfied. An approach calculation means,
Second flow CFD calculation means for executing the other CFD program using the flow field data calculated by the run-up calculation means as an initial value,
The engine performance predicting and analyzing system according to claim 1, wherein the run-up calculating means changes the boundary condition at a predetermined degree of change, and maintains the boundary condition for a predetermined period thereafter.   9. The method according to claim 8, further comprising: a running mode setting unit that sets a method of changing the boundary condition by the running calculation unit in association with at least one of a simulated driving condition that defines a simulated driving state of the engine and an analysis model. The engine performance prediction analysis system described in 1.   The approach mode setting means corrects the method of changing the boundary condition based on the previous calculation results so that the fluctuation of the calculated flow field becomes relatively small during the CFD calculation by the approach calculation means. The engine performance prediction analysis system according to any one of claims 4 to 7, wherein the engine performance prediction analysis system. 1D and 3D CFD programs that simulate the intake and exhaust flow of the engine using 1D and 3D CFD analysis models, respectively. A control program for a predictive analysis system that analyzes the flow of intake and exhaust air over a part of the exhaust system and thereby predicts engine performance,
A first CFD calculation step of executing one of the two CFD programs to calculate a flow field of intake and exhaust;
A boundary condition giving step for giving a boundary condition for CFD calculation by the other CFD program based on the flow field data calculated by the first CFD calculation step;
When the other CFD program is executed for the first time at the start of analysis, the boundary conditions are set in advance, and the CFD calculation is performed while gradually changing until the conditions given in the boundary condition applying step are satisfied. A run-up calculation step;
A second CFD calculation step of executing the other CFD program using the flow field data calculated in the run-up calculation step as an initial value,
The engine performance prediction analysis system control program further includes a running mode setting step for setting a method of changing the boundary condition in the running calculation step in association with at least the analysis model. In the first and second CFD calculation steps, one-dimensional and three-dimensional CFD programs are executed, respectively.
12. The control according to claim 11, wherein the run-up calculation step is executed before the second CFD calculation step when the three-dimensional CFD program is first executed in the second CFD calculation step at the start of analysis. program.   The control program according to claim 11, wherein in the approach mode setting step, the method of changing the boundary condition in the approach calculation step is set in association with the simulated operation condition of the engine.   The control program according to any one of claims 11 to 13, wherein in the approach calculation step, the boundary condition is first changed at a predetermined change degree, and is maintained substantially constant thereafter. 1D and 3D CFD programs that simulate the intake and exhaust flow of the engine using 1D and 3D CFD analysis models, respectively. A control program for a predictive analysis system that analyzes the flow of intake and exhaust air over a part of the exhaust system and thereby predicts engine performance,
A first CFD calculation step of executing one of the two CFD programs to calculate a flow field of intake and exhaust;
A boundary condition giving step for giving a boundary condition for CFD calculation by the other CFD program based on the flow field data calculated by the first CFD calculation step;
When the other CFD program is executed for the first time at the start of analysis, the boundary conditions are set in advance, and the CFD calculation is performed while gradually changing until the conditions given in the boundary condition applying step are satisfied. A run-up calculation step;
A second CFD calculation step of executing the other CFD program using the flow field data calculated in the run-up calculation step as an initial value,
In the approach calculation step, the boundary condition is first changed at a predetermined degree of change, and is maintained substantially constant for a predetermined period thereafter.   16. The approach mode setting step of setting the way of changing the boundary condition in the approach calculation step in association with at least one of the simulated operation condition and the analysis model that defines the simulated operation state of the engine. The control program described in 1.   In the course of the CFD computation in the run-up computation step, the vehicle further includes a run-up mode modification step that modifies the method of changing the boundary condition based on the computation results so far, so that the fluctuation of the computed flow field becomes relatively small. The control program according to any one of claims 11 to 14, and 16.

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