Virtual simulation method of diesel engine movement mechanism considering rotating speed fluctuation

Abstract

The invention aims to provide a virtual simulation method of a diesel engine movement mechanism considering rotation speed fluctuation. The method comprises the following steps: acquiring structure and material parameters of a valve mechanism, acquiring contact parameters of the valve mechanism, acquiring cam lift data, acquiring rigidity damping parameters and structure parameters of a gear transmission system, and acquiring cylinder pressure data. The output torque of a gas distribution unit, the angular acceleration of a cam shaft and the angular acceleration and torque of each gear are predicted respectively, the load torque state is judged, the crankshaft rotation angular acceleration is predicted, and the crankshaft dynamic angular velocity and the angular velocity fluctuation quantity are calculated. All motion mechanisms of the diesel engine are included, all kinetic parameters of the motion mechanisms of the diesel engine can be predicted, and the prediction result is complete. The influence of crankshaft rotating speed fluctuation caused by the load on the kinetic parameters of the diesel engine movement mechanism is considered, and the prediction result better conforms to engineering practice. Complex mathematical theories are not needed, a common numerical method can be adopted for solving, the calculation scale is small, and the calculation speed is high.

Description

Technical Field

[0001] The present invention relates to a diesel engine simulation method, specifically a kinematic mechanism simulation method. Background Art

[0002] As an efficient power device, diesel engines are widely used in fields such as automobiles, ships, and power generation equipment. Its core kinematic mechanism consists of a crank - connecting rod mechanism, which converts the reciprocating motion of the piston into the rotational motion of the crankshaft, thereby realizing the conversion and output of energy. During the actual operation of a diesel engine, due to the periodic changes in the combustion process in the cylinder, load fluctuations, and the dynamic characteristics of the mechanical system, the rotational speed of the crankshaft often fluctuates. This rotational speed fluctuation not only affects the working efficiency of the engine but may also lead to increased mechanical vibration, noise, and even affect the reliability and service life of the engine.

[0003] Currently, the dynamic analysis of the kinematic mechanism of diesel engines is mainly based on the steady - state assumption, that is, assuming that the crankshaft rotates at a constant speed. However, in actual operation, rotational speed fluctuations are inevitable, especially under transient conditions (such as starting, accelerating, sudden load changes, etc.), where rotational speed fluctuations are more significant. Traditional steady - state analysis methods cannot accurately reflect the influence of rotational speed fluctuations on the dynamic behavior of the kinematic mechanism. Especially in the case of high rotational speeds or frequent load changes, this neglect may lead to misjudgment of the system's dynamic characteristics. Therefore, establishing a virtual simulation system for diesel kinematic mechanisms that can consider rotational speed fluctuations is of great significance for deeply understanding the dynamic characteristics of diesel engines, optimizing their designs, and improving operating stability.

[0004] Existing dynamic simulation methods usually simplify the crank - connecting rod mechanism into a particle system and calculate the resultant force of the inertial force and cylinder pressure through Newton's second law. However, this method does not fully consider the influence of rotational speed fluctuations on the system's dynamic response. Especially at high speeds or under variable operating conditions, rotational speed fluctuations will significantly change the force states and motion characteristics of components such as the crank and connecting rod. In addition, rotational speed fluctuations may also trigger resonance phenomena in the mechanical system, further exacerbating vibration and noise problems. Summary of the Invention

[0005] The purpose of the present invention is to provide a virtual simulation method for a diesel engine kinematic mechanism considering rotational speed fluctuations, which can improve the prediction accuracy of the dynamic parameters of the diesel engine kinematic mechanism.

[0006] The purpose of the present invention is achieved as follows:

[0007] A virtual simulation method for a diesel engine kinematic mechanism considering rotational speed fluctuations according to the present invention is characterized by including the following steps:

[0008] (1) Obtain the equivalent mass of the short arm of the valve train rocker arm, the equivalent mass of the long arm, the bending stiffness coefficient and damping coefficient of the rocker arm; obtain the lumped mass parameters of the push rod, the lumped mass parameters of the valve, the lumped mass parameters and stiffness parameters of the valve spring, and the contact parameters of the valve train; input the cam lift data at the current moment; obtain the force exerted by the valve spring on the upper spring seat and the force exerted by the cam and the tappet in the normal direction at the contact point; establish the dynamic equation of the multi-mass valve train; obtain the output torque of a single valve unit; establish the dynamic equation of the rigid body rotation of the camshaft and predict the angular acceleration of the rigid body rotation of the camshaft;

[0009] (2) Obtain the comprehensive meshing stiffness coefficient and meshing damping coefficient of the gear transmission system; the moment of inertia and base circle radius of the crankshaft gear, the camshaft gear, and the idle gear; obtain the dynamic meshing force between the crankshaft gear and the idle gear and the dynamic meshing force between the camshaft gear and the idle gear; predict the angular acceleration of the crankshaft gear, the angular acceleration of the idle gear, and the angular acceleration of the camshaft gear;

[0010] (3) Input the data of the driving power source at the current moment; obtain the crank angle and calculate the acceleration of the piston; calculate the connecting rod swing angle and the total force on the center of the piston pin; predict the output torque of a single crank-connecting rod unit; calculate the friction and pumping loss torque of the diesel engine; judge the load state according to the magnitude of the instantaneous angular velocity of the crankshaft and the rated speed of the diesel engine, and then judge the positive and negative of the load torque;

[0011] (4) Predict the angular acceleration of the rigid body rotation of the crankshaft according to the driving torque, the load torque, and the moment of inertia of the crankshaft; integrate the angular acceleration of the rigid body rotation of the crankshaft with respect to time once to obtain the dynamic angular velocity of the crankshaft rotation and obtain the fluctuation amount of the crankshaft angular velocity;

[0012] (5) Return to step (1) to perform the prediction process for the next moment.

[0013] The present invention may further include:

[0014] 1. The dynamic equation of the multi-mass valve train in step (1) is:

[0015]

[0016] In the formula, M T , M P1 , M P2 , M A1 , M A2 , M R , M V are respectively the mass of the tappet, the first lumped mass of the simplified push rod, the second lumped mass of the simplified push rod, the equivalent mass of the short arm of the rocker arm, the equivalent mass of the long arm of the rocker arm, the lumped mass at the valve stem end, and the lumped mass at the valve seat end; x P1 , x P2For the first concentrated mass of the push rod and the mass displacement in the second concentration of the push rod; x A1 and x A2 are the displacements of the short arm end and the long arm end of the rocker arm; x V is the displacement of the valve head; i arm is the rocker ratio; l st is the initial deformation of the spring element in the simplified model of the valve stem, l se is the initial contact deformation between the valve head and the valve seat. K E and C E are the stiffness coefficient and damping coefficient of the valve stem model.

[0017] 2. The angular acceleration of the rigid body rotation of the camshaft in step (1) is:

[0018]

[0019] where J TS is the moment of inertia of the camshaft.

[0020] 3. In step (2), the angular acceleration of the crankshaft gear is the angular acceleration of the idler gear is the angular acceleration of the camshaft gear is and their predictions are respectively:

[0021]

[0022] where J Q is the moment of inertia of the crankshaft gear, J I is the moment of inertia of the idler gear, J T is the moment of inertia of the camshaft gear; F QI (t) is the dynamic meshing force between the crankshaft gear and the idler gear, F TI (t) is the dynamic meshing force between the camshaft gear and the idler gear, T GQ (t) is the torque of the crankshaft on the crankshaft gear, T GT (t) is the torque of the camshaft on the camshaft gear;

[0023]

[0024] where G Q and I Q are the shear modulus and polar moment of inertia of the connecting section between the crankshaft main journal and the crankshaft gear, Δl Q is the unit length of the connecting section between the crankshaft main journal and the crankshaft gear, is the torsional angular displacement difference between the crankshaft main journal and the crankshaft gear;

[0025]

[0026] In the formula, G T and I T are the shear modulus and polar moment of inertia of the connecting section between the camshaft journal and the camshaft gear, Δl T is the unit length of the connecting section between the camshaft journal and the camshaft gear, is the torsional angular displacement difference between the camshaft journal and the camshaft gear.

[0027] 4. The process of calculating the piston acceleration in step (3) is as follows:

[0028]

[0029] In the formula, θ C is the crank angle, r C is the crank radius, ω C is the rated speed of the diesel engine, λ is the crank connecting rod ratio, i.e., λ = r C / l R0 , where l R0 is the connecting rod length.

[0030] 5. The total force on the piston pin center in step (3) is F, and its calculation process is as follows:

[0031]

[0032] In the formula, d P is the piston crown diameter; M P is the mass in reciprocating motion, including the concentrated mass of the piston group and the equivalent mass of the small end of the connecting rod, i.e., M P = M G + M S , M G is the mass of the piston group, M S is the equivalent mass of the small end of the connecting rod; a P is the acceleration of the mass in reciprocating motion.

[0033] 6. The prediction of the output torque of a single crank connecting rod unit in step (3) is:

[0034]

[0035] In the formula, r C is the crank radius, θ C is the instantaneous angular displacement of the crank, θ R is the instantaneous swing angle of the connecting rod.

[0036] 7. The friction and pumping loss torque of the diesel engine in step (3) is T f , and its calculation process is as follows:

[0037]

[0038] Wherein, V i is the displacement of a single cylinder, ω C is the rated speed of the diesel engine, and is the number of cylinders of the diesel engine.

[0039] 8. The instantaneous angular velocity of the crankshaft in step (3) is The rated speed of the diesel engine is ω C , the load torque is T Load , if then the sign before T Load is negative; if then the sign before T Load is positive.

[0040] 9. The angular acceleration of the rigid body rotation of the crankshaft in step (4) is Its prediction is:

[0041]

[0042] Wherein, T RC (t) is the driving torque, T Load is the load torque, J QS is the moment of inertia of the crankshaft, including the moment of inertia of the crankshaft body, the moment of inertia of the concentrated mass at the big end of the connecting rod, and the flywheel.

[0043] The advantages of the present invention are as follows:

[0044] (1) The present invention encompasses all the motion mechanisms of the diesel engine, can predict all the dynamic parameters of the motion mechanisms of the diesel engine, and the prediction results are complete.

[0045] (2) The present invention takes into account the influence of the load-induced crankshaft speed fluctuation on the dynamic parameters of the motion mechanisms of the diesel engine, and the prediction results are more in line with the engineering practice.

[0046] (3) The present invention does not require complex mathematical theories and can be solved by using common numerical methods, such as the finite difference method and the fourth-order Runge-Kutta method, and has the advantages of small calculation scale and fast calculation speed. Description of the Drawings

[0047] Figure 1 is the flow chart of the present invention;

[0048] Figure 2 is the prediction model of the virtual simulation system of the present invention. Wherein, y P is the vertical displacement of the piston; θ C is the crank angle displacement; θ TS is the camshaft angle displacement; θ Q is the crankshaft gear angle displacement; θ I is the idler gear angle displacement; θ Tis the angular displacement of the camshaft gear: ω C is the rated speed of the diesel engine; T Load is the load torque. Specific implementation manner

[0049] The present invention will be described in more detail with reference to the accompanying drawings as follows:

[0050] Combined with Figure 1-2 , the present invention is implemented according to the following steps:

[0051] Step 1: Obtain the equivalent mass M of the short arm of the valve rocker of the valve train A1 , the equivalent mass M of the long arm A2 , the bending stiffness coefficient K of the rocker A , the damping coefficient C of the rocker A .

[0052] Step 2: Obtain the concentrated mass parameters of the push rod. The push rod is simplified into a two-mass model, and the two concentrated masses are obtained as M P1 and M P2 , both with a size of M P / 2; obtain the tensile and compressive stiffness coefficient K of the push rod P , the structural damping coefficient C P .

[0053] Step 3: Obtain the concentrated mass parameters of the valve. The valve is simplified into a two-mass model, obtain the concentrated mass M at the valve stem end R , the concentrated mass M at the valve seat end V , the tensile and compressive stiffness coefficient K of the valve stem E , the damping coefficient C E .

[0054] M R = M RL + M E / 2 (1)

[0055] M V = M VH + M E / 2 (2)

[0056] In the formula, M RL is the sum of the masses of the upper spring seat and the spring lock piece, M E is the mass of the valve stem, M VH is the mass of the valve head.

[0057] Step 4: Obtain the concentrated mass parameters and stiffness parameters of the valve spring. The valve spring is simplified into a multi-mass model, the degree of freedom is n, obtain the concentrated mass M of the inner spring model I , the concentrated mass M of the outer spring model O and the stiffness parameter K of the inner spring modelI The stiffness parameter K of the outer spring model O is as follows:

[0058] M I = M SI / n (3)

[0059] K I = (n + 1)K SI (4)

[0060] M O = M SO / n (5)

[0061] K O = (n + 1)K SO (6)

[0062] In the formula, M SI and K SI are the mass and stiffness of the inner spring respectively, and M SO and K SO are the mass and stiffness of the outer spring respectively.

[0063] Step 5: Obtain the contact parameters of the valve train. Determine the contact stiffness K CT , contact damping C CT and initial clearance δ CT between the cam and the tappet; the contact stiffness K TP , contact damping C TP and initial clearance δ TP between the tappet and the push rod; the contact stiffness K PA , contact damping C PA and initial clearance δ PA between the push rod and the rocker arm; the contact stiffness K AV , contact damping C AV and initial clearance δ AV between the rocker arm and the valve; the contact stiffness K VS , contact damping C VS and initial clearance δ VS between the valve and the valve seat; the friction coefficient between the tappet and the guide hole the friction coefficient between the rocker arm and the rocker shaft the friction coefficient between the valve stem and the valve guide

[0064] Step 6: Input the cam lift data at the current moment, i.e., h C .

[0065] Step 7: Obtain the force N exerted by the valve spring on the upper spring seat S , the force N in the normal direction of the contact point between the cam and the tappet CT。

[0066]

[0067] In the formula, C I is the damping coefficient of the inner ring spring model, and C O is the damping coefficient of the outer ring spring model; l I and l O are the initial deformations of the spring elements in the simplified models of the inner ring spring and the outer ring spring respectively; x R , x I1 , x O1 , x T are the displacements of the upper spring seat, the first concentrated mass of the simplified inner ring spring, the first concentrated mass of the simplified outer ring spring, and the tappet respectively.

[0068] Step 8: Establish the dynamic equation of the multi-mass valve train.

[0069]

[0070] In the formula, M T , M P1 , M P2 , M A1 , M A2 , M R , M V are the tappet mass, the first concentrated mass of the simplified push rod, the second concentrated mass of the simplified push rod, the equivalent mass of the short arm of the rocker arm, the equivalent mass of the long arm of the rocker arm, the concentrated mass at the valve stem end, and the concentrated mass at the valve seat end respectively; x P1 , x P2 are the displacements of the first concentrated mass and the second concentrated mass of the simplified push rod; x A1 , x A2 are the displacements of the short arm end and the long arm end of the rocker arm; x V is the displacement of the valve head; i arm is the rocker arm ratio; l st is the initial deformation of the spring element in the simplified model of the valve stem, and l se is the initial deformation of the contact between the valve head and the valve seat. K E and C E are the stiffness coefficient and damping coefficient of the valve stem model.

[0071] Step 9: Obtain the output torque T CT (t) of a single valve train unit.

[0072]

[0073] In the formula, μ is the friction coefficient, and R O is the base circle radius of the cam. In the case of multiple valve train units, the output torque of the valve train is the sum of the output torques of all valve train units.

[0074] Step 10: Establish the rigid body rotational dynamics equation of the camshaft to predict the angular acceleration of the rigid body rotation of the camshaft

[0075]

[0076] In the formula, J TS is the moment of inertia of the camshaft. T GT (t) is the torque of the camshaft on the camshaft gear.

[0077] Step 11: Obtain the comprehensive meshing stiffness coefficient K M and the meshing damping coefficient C M of the gear transmission system; the moments of inertia J i (i = Q, T, I) and the base circle radii R i (i = Q, T, I) of the crankshaft gear, camshaft gear, and idle gear. Among them, the subscripts Q, T, and I represent the crankshaft gear, camshaft gear, and idle gear respectively.

[0078] Step 12: Obtain the dynamic meshing forces F QI (t) between the crankshaft gear and the idle gear, and F TI (t) between the camshaft gear and the idle gear:

[0079]

[0080] In the formula, θ i (i = Q, T, I) is the angular displacement.

[0081] Step 13: Predict the angular acceleration of the crankshaft gear the angular acceleration of the idle gear the angular acceleration of the camshaft gear

[0082]

[0083] In the formula, J Q is the moment of inertia of the crankshaft gear, J I is the moment of inertia of the idle gear, J T is the moment of inertia of the camshaft gear; F QI (t) is the dynamic meshing force between the crankshaft gear and the idle gear, F TI (t) is the dynamic meshing force between the camshaft gear and the idle gear, T GQ (t) is the torque of the crankshaft on the crankshaft gear, T GT (t) is the torque of the camshaft on the camshaft gear.

[0084]

[0085] where G Q and I Q are the shear modulus and polar moment of inertia of the connecting section between the crankshaft main journal and the crankshaft gear, and Δl Q is the unit length of the connecting section between the crankshaft main journal and the crankshaft gear, and the torsional angular displacement difference between the crankshaft main journal and the crankshaft gear;

[0086]

[0087] where G T and I T are the shear modulus and polar moment of inertia of the connecting section between the camshaft journal and the camshaft gear, and Δl T is the unit length of the connecting section between the camshaft journal and the camshaft gear, and the torsional angular displacement difference between the camshaft journal and the camshaft gear.

[0088] Step 14: Input the driving force source data at the current moment, i.e., the cylinder pressure f G .

[0089] Step 15: Obtain the crank angle θ C , and calculate the acceleration a P of the piston:

[0090]

[0091] where r C is the crank radius, ω C is the rated speed of the diesel engine, λ is the crank connecting rod ratio, i.e., λ = r C / l R0 . Among them, l R0 is the connecting rod length.

[0092] Step 16: Calculate the instantaneous swing angle θ R of the connecting rod:

[0093] θ R = arcsin(λsinθ C ) (20)

[0094] Step 17: Calculate the total force F on the piston pin center as:

[0095]

[0096] where d P is the piston top diameter; M P is the mass in reciprocating motion, including the concentrated mass of the piston group and the replaced mass of the small end of the connecting rod, i.e., M P = M G + M S , MG is the mass of the piston group, M S is the substituted mass of the small end of the connecting rod; a P is the acceleration of the reciprocating mass.

[0097] Step 18: Predict the output torque T RC (t) of a single crank - connecting rod unit:

[0098]

[0099] where r C is the crank radius, θ C is the instantaneous angular displacement of the crank, θ R is the instantaneous swing angle of the connecting rod. In the case of multiple crank - connecting rod units, the output torque of the crank - connecting rod mechanism is the sum of the output torques of all crank - connecting rod units.

[0100] Step 19: Calculate the friction and pumping loss torque T f of the diesel engine:

[0101]

[0102] where V i is the displacement of a single cylinder, ω C is the rated speed of the diesel engine, is the number of cylinders of the diesel engine

[0103] Step 20: Determine the load state according to the magnitude of the instantaneous angular velocity of the crankshaft and the rated speed ω C of the diesel engine, and then judge the sign of the load torque T Load If then the sign in front of T Load is negative; if then the sign in front of T Load is positive.

[0104] Step 21: Predict the angular acceleration RC (t) of the rigid body rotation of the crankshaft according to the driving torque T Load , the load torque T QS and the moment of inertia J

[0105]

[0106] where J QS is the moment of inertia of the crankshaft, including the moment of inertia of the crankshaft body, the moment of inertia of the concentrated mass at the big end of the connecting rod and the flywheel.

[0107] Step 22: The angular acceleration of the rigid body rotation of the crankshaft Integrate with respect to time once to obtain the dynamic angular velocity of the crankshaft rotation Obtain the fluctuation amount Δω of the crankshaft angular velocity through the following formula:

[0108]

[0109] Step 23: Return to Step 1 to perform the prediction process at the next moment.

Claims

1. A virtual simulation method for a diesel engine kinematic mechanism taking into account speed fluctuations, characterized by: The steps include: (1) Obtain the equivalent mass of the short arm of the valve mechanism rocker arm, the equivalent mass of the long arm, the bending stiffness coefficient and the damping coefficient of the rocker arm; obtain the concentrated mass parameters of the push rod, the concentrated mass parameters of the valve, the concentrated mass parameters and stiffness parameters of the valve spring, and the contact parameters of the valve mechanism; input the cam lift data at the current moment; obtain the force of the valve spring on the spring seat, and the force of the cam and the tappet in the normal direction of the contact point; establish the dynamic equation of the multi-mass valve mechanism; obtain the output torque of a single valve unit; establish the rigid body rotation dynamic equation of the camshaft, and predict the angular acceleration of the rigid body rotation of the camshaft; (2) Obtain the comprehensive meshing stiffness coefficient and meshing damping coefficient of the gear transmission system; the rotational inertia and base circle radius of the crankshaft gear, camshaft gear, and idler gear; obtain the dynamic meshing force between the crankshaft gear and the idler gear, and the dynamic meshing force between the camshaft gear and the idler gear; predict the angular acceleration of the crankshaft gear, the angular acceleration of the idler gear, and the angular acceleration of the camshaft gear; (3) Input the current driving force source data; obtain the crank angle and calculate the acceleration of the piston; Calculate the total force of the connecting rod swing angle and the piston pin center; predict the output torque of a single crank-connecting rod unit; calculate the friction and pumping loss torque of the diesel engine; determine the load state based on the instantaneous angular velocity of the crankshaft and the rated speed of the diesel engine, and then determine whether the load torque is positive or negative; (4) predicting the angular acceleration of the crankshaft rigid body rotation according to the driving torque, the load torque, and the crankshaft rotational inertia; integrating the angular acceleration of the crankshaft rigid body rotation with respect to time once to obtain the dynamic angular velocity of the crankshaft rotation and the fluctuation amount of the crankshaft angular velocity; (5) Return to step (1) and proceed with the prediction process for the next moment.

2. The virtual simulation method of a diesel engine kinematic mechanism taking into account speed fluctuation according to claim 1 is characterized in that: The dynamic equation of the multi-mass valve train in step (1) is: Where M T 、M P1 、M P2 、M A1 、M A2 、M R 、M V They are respectively the mass of the tappet, the first concentrated mass of the simplified push rod, the second concentrated mass of the simplified push rod, the equivalent mass of the short rocker arm, the equivalent mass of the long rocker arm, the concentrated mass at the valve stem end, and the concentrated mass at the valve seat end; x P1 、x P2 The displacement of the first concentrated mass and the second concentrated mass of the push rod; x A1 、x A2 is the displacement of the short arm end and the long arm end of the rocker arm; x V is the displacement of the valve head; i arm is the rocker arm ratio; l st is the initial deformation of the spring unit in the simplified valve stem model, l se K is the initial contact deformation between the valve head and the valve seat. E With C E are the stiffness coefficient and damping coefficient of the valve stem model.

3. The virtual simulation method of a diesel engine kinematic mechanism taking into account speed fluctuation according to claim 1 is characterized by: Angular acceleration of the camshaft rigid body rotation in step (1) for: In the formula, J TS is the moment of inertia of the camshaft, T CT (t) is the output torque of the valve unit.

4. The virtual simulation method of a diesel engine kinematic mechanism taking into account speed fluctuation according to claim 1 is characterized by: In step (2), the angular acceleration of the crankshaft gear is The angular acceleration of the idler gear is The angular acceleration of the camshaft gear is The predictions are: In the formula, J Q is the moment of inertia of the crankshaft gear, J I is the moment of inertia of the idler gear, J T is the moment of inertia of the camshaft gear; F QI (t) is the dynamic meshing force between the crankshaft gear and the idler gear, F TI (t) is the dynamic meshing force between the camshaft gear and the idler gear, T GQ (t) is the torque of the crankshaft on the crankshaft gear, T GT (t) is the torque of the camshaft on the camshaft gear; In the formula, G Q and I Q is the shear modulus and polar moment of inertia of the crankshaft main journal and crankshaft gear connection section, Δl Q is the unit length of the connecting section between the crankshaft main journal and the crankshaft gear, is the torsional angular displacement difference between the crankshaft main journal and the crankshaft gear; In the formula, G T and I T is the shear modulus and polar moment of inertia of the connection section between the camshaft journal and the camshaft gear, Δl T is the unit length of the connection section between the camshaft journal and the camshaft gear, It is the torsional angular displacement difference between the camshaft journal and the camshaft gear.

5. The virtual simulation method of a diesel engine kinematic mechanism taking into account speed fluctuation according to claim 1 is characterized by: The process of calculating the piston acceleration in step (3) is: In the formula, θ C is the crank angle, r C is the crank radius, ω C is the rated speed of the diesel engine, λ is the crank-connecting rod ratio, that is, λ=r C / l R0 , where l R0 is the connecting rod length.

6. The virtual simulation method of a diesel engine kinematic mechanism taking into account speed fluctuation according to claim 1 is characterized by: The total force at the center of the piston pin in step (3) is F, and its calculation process is: Where, d P is the piston top diameter; M P is the mass for reciprocating motion, including the concentrated mass of the piston group and the replacement mass of the small end of the connecting rod, that is, M P =M G +M S , M G is the mass of the piston group, M S is the mass of the connecting rod small end; a P is the acceleration of the reciprocating mass.

7. The virtual simulation method of a diesel engine kinematic mechanism taking into account speed fluctuation according to claim 1 is characterized by: Step (3) The prediction of the output torque of a single crank-connecting rod unit is: In the formula, r C is the crank radius, θ C is the instantaneous angular displacement of the crank, θ R is the instantaneous swing angle of the connecting rod.

8. The virtual simulation method of a diesel engine kinematic mechanism taking into account speed fluctuation according to claim 1 is characterized by: The friction and pump loss torque of the diesel engine in step (3) is T f , the calculation process is: Where V i is the displacement of a single cylinder, ω C is the rated speed of the diesel engine, is the number of cylinders in a diesel engine.

9. The virtual simulation method of a diesel engine kinematic mechanism taking into account speed fluctuation according to claim 1 is characterized by: The instantaneous angular velocity of the crankshaft in step (3) is The rated speed of the diesel engine is C , load torque is T Load ,if Then T Load The leading sign is negative; if Then T Load The preceding sign is positive.

10. The virtual simulation method of a diesel engine kinematic mechanism taking into account speed fluctuation according to claim 1, characterized in that: Step (4) The angular acceleration of the crankshaft rigid body rotation is Its prediction is: Where, T RC (t) is the driving torque, T Load is the load torque, J QS It is the rotational inertia of the crankshaft, including the rotational inertia of the crankshaft body, the rotational inertia of the concentrated mass at the big end of the connecting rod, and the flywheel.

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