Engine starting control method and system under static working condition

Abstract

The invention discloses an engine starting control method and system under a static working condition, and relates to the technical field of hybrid electric vehicles, and the method comprises the following steps: calculating an engine resistance moment based on an engine starting kinematics model; based on the engine starting kinetic model, the motor rotating speed, the engine rotating speed and the transmission shaft torque serve as state variables, the motor torque serves as a control variable, the engine resistance torque serves as an interference variable, and the motor rotating speed and the engine rotating speed serve as output variables, and a state equation is constructed; a Luenberger type system state observer is constructed; and based on the Luenberger type system state observer, a preset engine rotating speed curve and a preset motor rotating speed curve, rotating speed curve trajectory tracking is carried out, so that an optimal control law is obtained, and the optimal torque of the motor in the process of reversely dragging and starting the engine through the transmission shaft is represented. While starting rapidity is guaranteed, the torque peak value of the transmission shaft is reduced, and the use reliability of the transmission shaft is effectively guaranteed.

Description

Technical Field

[0001] The present application relates to the technical field of hybrid electric vehicles, and in particular to an engine start control method and system under stationary conditions. Background Art

[0002] Hybrid vehicles mainly achieve the goal of energy conservation and emission reduction through functions such as automatic engine start and stop, brake energy recovery, motor assistance, optimization of engine working efficiency and pure electric driving. Hybrid vehicles are generally equipped with two or more power sources, including traditional internal combustion engines, electric drive devices and energy storage devices, and achieve optimal energy distribution through good matching, optimization and coordinated control. In order to improve transmission efficiency and reduce fuel consumption, the use of torque converters is eliminated in the hybrid system, so that the engine and the transmission system are directly coupled, which not only improves the efficiency of the transmission system, but also greatly reduces the damping of the transmission system. Therefore, the power transmission system of hybrid vehicles is more prone to torque fluctuations. For the hybrid system, when starting the engine under static conditions, one motor is in braking mode, and the other motor outputs a driving torque to drag the engine to a specified speed for ignition and start. In this process, the drive shaft needs to bear the driving torque from the motor and the resistance torque of the engine rotation at the same time, which is prone to large torque fluctuations. Excessive torque peaks may even cause the drive shaft to break. Summary of the invention

[0003] The purpose of the present application is to provide an engine start control method and system under stationary conditions, which can effectively suppress torque fluctuations on the drive shaft, reduce torque peaks, and ensure the safety of the drive shaft while quickly starting the engine.

[0004] To achieve the above objectives, this application provides the following solutions:

[0005] In a first aspect, the present application provides an engine start control method under stationary conditions, comprising:

[0006] Constructing a hybrid power system simulation model of a vehicle under stationary conditions; the hybrid power system simulation model includes a motor, a transmission shaft and an engine;

[0007] Based on the hybrid power system simulation model, an engine starting kinematic model and an engine starting dynamic model are constructed;

[0008] Calculating the engine drag torque based on the engine starting kinematic model;

[0009] Based on the engine starting dynamics model, the motor speed, the engine speed and the transmission shaft torque are used as state variables, the motor torque is used as a control variable, the engine resistance torque is used as an interference variable, and the motor speed and the engine speed are also used as output variables to construct a state equation;

[0010] Based on the state equation, a Luenberger type system state observer is constructed; the Luenberger type system state observer is used to reconstruct the transmission shaft torque based on the motor speed and the engine speed;

[0011] Based on the Luenberger type system state observer, the preset engine speed curve and the preset motor speed curve, speed curve trajectory tracking is performed to obtain an optimal control law; the optimal control law represents the optimal torque of the motor during the process of reverse-drag starting the engine through the transmission shaft.

[0012] In a second aspect, the present application provides an engine start control system under stationary conditions, comprising:

[0013] A system simulation model building module, used to build a hybrid power system simulation model of a vehicle under static conditions; the hybrid power system simulation model includes a motor, a transmission shaft and an engine;

[0014] A kinematic model and a dynamic model building module, used to build an engine starting kinematic model and an engine starting dynamic model based on the hybrid power system simulation model;

[0015] An engine drag torque determination module, used for calculating the engine drag torque based on the engine starting kinematic model;

[0016] a state equation determination module, for constructing a state equation based on the engine starting dynamics model, taking the motor speed, the engine speed and the transmission shaft torque as state variables, taking the motor torque as a control variable, taking the engine resistance torque as an interference variable, and taking the motor speed and the engine speed as output variables;

[0017] An observer determination module, configured to construct a Luenberger type system state observer based on the state equation; the Luenberger type system state observer is configured to reconstruct the transmission shaft torque based on the motor speed and the engine speed;

[0018] The optimal control law determination module is used to track the speed curve trajectory based on the Luenberger system state observer, the preset engine speed curve and the preset motor speed curve to obtain the optimal control law; the optimal control law represents the optimal torque of the motor in the process of reversely starting the engine through the transmission shaft.

[0019] According to the specific embodiments provided in this application, this application discloses the following technical effects:

[0020] The present application discloses an engine starting control method and system under static working conditions, which calculates the engine resistance torque based on the engine starting kinematic model; constructs a state equation based on the engine starting dynamics model, taking the motor speed, engine speed and transmission shaft torque as state variables, taking the motor torque as the control variable, taking the engine resistance torque as the interference variable, and taking the motor speed and the engine speed as output variables; constructs a Luenberger type system state observer based on the state equation; and performs speed curve trajectory tracking based on the Luenberger type system state observer, a preset engine speed curve and a preset motor speed curve to obtain an optimal control law, and the optimal control law characterizes the optimal torque of the motor in the process of starting the engine through reverse dragging of the transmission shaft. The present application can effectively suppress the torque fluctuation on the transmission shaft, reduce the torque peak, and ensure the safety of the transmission shaft while starting the engine quickly. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0022] Figure 1 This is a flow chart of the engine start control method under stationary conditions of this application;

[0023] Figure 2 This is a schematic diagram of the crank-connecting rod mechanism of this application;

[0024] Figure 3 This is the force diagram of the crank-connecting rod mechanism for this application;

[0025] Figure 4 This is a schematic diagram of the engine starting dynamics model under static conditions in this application;

[0026] Figure 5 This is a schematic diagram of the G(s) frequency response curve of this application;

[0027] Figure 6This is a schematic diagram of the H(s) frequency response curve of this application;

[0028] Figure 7 This is a schematic diagram of the Z(s) frequency response curve of this application;

[0029] Figure 8 This is the structure diagram of the Luenberger state observer for this application;

[0030] Fig. 9 This is a comparison chart of the simulation results of the Luenberger torque observer for this application;

[0031] Fig.10 This is the block diagram of the optimal control system for this application;

[0032] FIG11 is a simulation result of PID control in the present application; wherein FIG11(a) is a time-power element torque diagram obtained by PID control simulation, FIG11(b) is a time-power element speed diagram obtained by PID control simulation, and FIG11(c) is a time-drive shaft torque diagram obtained by PID control simulation;

[0033] Figure 12 is the simulation result of LQT control adopted in this application; wherein, Figure 12(a) is the time-power element torque diagram obtained by LQT control simulation, Figure 12(b) is the time-power element speed diagram obtained by LQT control simulation, and Figure 12(c) is the time-drive shaft torque diagram obtained by LQT control simulation. DETAILED DESCRIPTION

[0034] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0035] The present application provides an engine start control method and system under stationary conditions. In order to suppress the torque fluctuation on the transmission shaft and reduce the torque peak during the engine start process of a hybrid vehicle, a hybrid system dynamics model is established and a quadratic optimal control algorithm is applied to control the engine to track the target optimal speed curve, and the motor torque trajectory with the best performance index is calculated. Simulation results show that the designed quadratic optimal speed tracking control strategy can effectively suppress the torque fluctuation on the transmission shaft, reduce the torque peak, and ensure the safety of the transmission shaft while quickly starting the engine.

[0036] In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, the present application is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0037] In an exemplary embodiment, Figure 1 As shown, the present application provides an engine start control method under stationary conditions, comprising:

[0038] Step 100, constructing a hybrid power system simulation model of a vehicle under static conditions; the hybrid power system simulation model includes a motor, a transmission shaft and an engine. The engine is a crank-connecting rod structure, including a cylinder, a piston, a crank, a crankcase and a connecting rod.

[0039] Specifically, when the motor is driving the engine, it must overcome certain resistance torques, including cylinder compression resistance torque, piston friction resistance torque, valve mechanism friction resistance torque, piston group reciprocating motion inertia torque and accessory operation resistance torque. This application uses a research method that combines theory and experiment to analyze the resistance torque in the engine process.

[0040] Step 200: construct an engine starting kinematic model and an engine starting dynamic model based on the hybrid power system simulation model.

[0041] (I) The construction of the engine starting kinematic model is shown in the following steps:

[0042] In order to facilitate the kinematic analysis of the crank-connecting rod mechanism, a schematic diagram of the crank-connecting rod mechanism is established, as shown in Figure 2 As shown in the figure, O represents the center of the crankshaft; OB represents the crank; A represents the center of the piston pin; B represents the center of the crank pin; AB represents the connecting rod; A1 and A2 represent the upper and lower dead centers of the piston respectively; α represents the rotation angle of the crank; β represents the swing angle of the connecting rod relative to the center line of the cylinder, and the first cylinder of the engine is taken as an example here. The kinematic parameters of the crank-connecting rod mechanism are shown in Table 1.

[0043] Table 1 Kinematics parameters of crank-connecting rod mechanism

[0044] parameter Numeric Crank radius R(mm) 72.62 Connecting rod length L(mm) 262 Connecting rod ratio 0.277

[0045] Assuming that the crank rotates clockwise, when the crank rotates through an angle α, the displacement of the piston is:

[0046]

[0047] because:

[0048]

[0049] so:

[0050] sinβ=λsinα(3)

[0051]

[0052] Substituting formula (4) into formula (1), we can obtain:

[0053]

[0054] Using Taylor's formula to expand equation (4), we can get:

[0055]

[0056] Substituting equation (6) into equation (1), and simplifying using the trigonometric function relationship, we can obtain:

[0057] x=R(a 0 +a 1 cosα+a 2 cos2α+a 4 cos4α+a 6 cos6α+……) (7)

[0058] The coefficients are expressed as follows:

[0059]

[0060] a 1 =-1

[0061]

[0062]

[0063]

[0064] Considering that λ is a small value less than 1, the values ​​of λ in equation (7) are very small and can be ignored. Therefore, equation (7) can be approximately written as a composite component that only retains the two main harmonic components of the displacement, as shown below:

[0065]

[0066] Differentiating equation (8) gives an approximate solution for the piston velocity:

[0067]

[0068] Similarly, by differentiating equation (9), we can obtain the approximate solution of the piston acceleration:

[0069]

[0070] The forces acting on the crank-connecting rod mechanism mainly include gas force and inertia force, such as Figure 3 As shown, the force acting on the piston is decomposed into several components for calculation.

[0071] The forces acting on the crank-connecting rod mechanism have the following transmission relationship:

[0072]

[0073] The single cylinder torque is:

[0074]

[0075] And because:

[0076] F=F j +F g (14)

[0077] And combined with formula (10), the reciprocating inertia force can be obtained as:

[0078] F j =-m j a=-m j Rω 2 (cosα+λcos2α)(15)

[0079] Based on the above formula, the resistance torque M of the first cylinder of the engine can be obtained: L1 The calculation formula is:

[0080]

[0081] Because, only the gas pressure is required to calculate the cylinder output torque. g -α curve, converted to F g .

[0082] F g =(pp 0 )S p (17)

[0083] Where p is the air pressure in the cylinder; p 0 is the air pressure in the crankcase; S p is the effective area of ​​the piston top.

[0084] The sum of the cylinder compression resistance torque and the piston reciprocating inertia torque, that is, the resistance torque of a single cylinder during engine starting, is calculated by equation (16) and equation (17). The resistance torques of other cylinders are then calculated by equation (18). Finally, the total engine resistance torque during starting can be calculated.

[0085]

[0086] Among them, M Li represents the resistance torque of the i-th cylinder of the engine, ω represents the engine crank speed, F g Indicates the cylinder compression resistance, m j represents the mass of the crank-connecting rod mechanism, R represents the radius of the crank, α i represents the rotation angle of the crank of the first cylinder of the engine, β i represents the swing angle of the connecting rod in the first cylinder of the engine relative to the cylinder centerline, i = 1,...,6, T e Indicates the engine resistance torque.

[0087] (II) The construction of the engine starting dynamics model is shown in the following steps:

[0088] Considering the elasticity and damping of the elastic coupling, and considering the remaining components as completely rigid and undamped rotating inertial components, and expressing them in the form of concentrated mass, the dynamic model of the series-parallel hybrid power system can be obtained. Figure 4 As shown, J E , J A , J B are the equivalent moments of inertia of the engine, motor A, and motor B respectively; J 01 , J 02 , J 11 , J 12 are the equivalent moments of inertia of clutch CL0 active disc, clutch CL0 driven disc, clutch CL1 active disc, and clutch CL1 driven disc respectively; J f1 , J f2 are the equivalent moments of inertia of the two front transmission gears; J s1 , J s2 , J s3 are the equivalent moments of inertia of the sun gears of the three planetary gear mechanisms; J r1 , J r2 , J r3 are the equivalent moments of inertia of the ring gears of the three planetary gear mechanisms; J c1 , J c2 , J c3 are the equivalent rotational inertia of the planet carriers of the three planetary gear mechanisms respectively.

[0089] When the vehicle starts from a standstill, the clutch CL0 is engaged, the clutch CL1 is disengaged, the brake BK is engaged, the motor B is in braking mode, and the engine is started by reverse dragging by the motor A. According to the speed relationship of the planetary gear mechanism, it can be obtained:

[0090]

[0091] In the formula, k 1 , k 2are the characteristic parameters of the planetary gear mechanisms PG1 and PG2 (ratio of the number of teeth on the ring gear to the number of teeth on the sun gear); n r1 、n c1 are the rotation speeds of the ring gear and the planet carrier of the planetary gear mechanism PG1; n c2 is the rotation speed of the planetary carrier of the planetary gear mechanism PG2.

[0092] make:

[0093]

[0094] but:

[0095] n c2 =s 1 n A , n c1 =s 2 n A , n f1 =i q s 1 n A (twenty one)

[0096] In order to facilitate calculation and avoid analyzing the internal forces of the planetary gear, the present application uses the Lagrange equation to establish the dynamic equation of the engine starting process.

[0097] The system kinetic energy includes the rotational kinetic energy of the engine, motor, external meshing gear of the front transmission, the ring gear of the planetary gear set, and the planetary carrier. At the same time, in order to facilitate subsequent analysis, the kinetic energy of the front transmission and the planetary gear set is equivalent to the motor output shaft, as shown in formula (22).

[0098]

[0099] The system potential energy is reflected as the elastic potential energy of the elastic link on the transmission shaft, and the calculation formula is shown in formula (23).

[0100]

[0101] The system dissipated energy is concentrated in the damping link on the transmission shaft, and the calculation formula is shown in formula (24).

[0102]

[0103] The driving torque of motor A and the resistance torque of the engine are selected as generalized forces, as shown in formula (25).

[0104] Q 1 =T A , Q 2 =-T E (25)

[0105] Substituting the system kinetic energy, potential energy and dissipated energy into the generalized Lagrangian equation, as shown in equation (26), the dynamic equation of the engine starting process of the parallel-parallel hybrid power system under static conditions can be obtained, as shown in equation (27).

[0106]

[0107] Among them, J A represents the equivalent moment of inertia of motor A, represents the angular acceleration of motor A, T A represents the driving torque of motor A, i q Indicates the front transmission ratio, s 1 Represents the proportionality coefficient, T S Represents the transmission shaft torque, J E represents the equivalent moment of inertia of the engine, is the engine angular acceleration, T E represents the engine resistance torque, k represents the stiffness of the transmission shaft, θ A Represents the motor rotation angle, θ E represents the engine rotation angle, c represents the damping of the transmission shaft, Indicates the speed of motor A, Indicates engine speed.

[0108] Step 300, based on the engine starting kinematic model, calculate the engine resistance torque; the specific calculation formula is shown in formula (16), formula (17) and formula (18) above.

[0109] Step 400, based on the engine starting dynamics model, the motor speed, the engine speed and the transmission shaft torque are used as state variables, the motor torque is used as a control variable, the engine resistance torque is used as an interference variable, and the motor speed and the engine speed are also used as output variables to construct a state equation. That is:

[0110]

[0111] The state equation is:

[0112]

[0113]

[0114]

[0115] in, represents the derivative of the state variable, y represents the output variable, x represents the state variable, u represents the control variable, d represents the disturbance variable, [] T represents the transpose of the matrix, and k represents the stiffness of the transmission shaft.

[0116] The torque fluctuation of the transmission shaft during the engine start-up process under static conditions will directly manifest as the fluctuation of vehicle acceleration, which will cause vehicle vibration and reduce ride comfort. According to the state space expression, that is, the state equation (29), the transfer function between the motor A torque and the transmission shaft torque can be derived. Substituting the actual parameters into the following equation:

[0117]

[0118] Take k S Different values ​​of G(s) are plotted as follows: Figure 5 As shown, k S1 <k S2 <k S3 <k S4 .analyze Figure 5 It can be seen that in the low-frequency band, the frequency response curves under different stiffnesses overlap, and the amplitude and phase are constant; near the resonant frequency, the amplitude-frequency characteristic and phase-frequency characteristic curves fluctuate violently, and the greater the stiffness, the more violent the fluctuation; in the high-frequency band after crossing the resonant frequency, the frequency response curves under different stiffnesses tend to overlap again.

[0119] Next, we continue to analyze the system characteristics. According to the system state equation of formula (29), after substituting the actual parameters, we can obtain the transfer function between the torque of motor A and the engine speed:

[0120]

[0121] Draw the frequency response characteristic curve of H(s) under different stiffness, such as Figure 6 As shown, it can be seen that under different stiffness, the amplitude-frequency characteristic and phase-frequency characteristic curves of the system overlap in the low frequency band, fluctuate near the resonant frequency, and the greater the stiffness, the more violent the fluctuation, and tend to overlap in the high-frequency stage after crossing the resonant frequency. According to the above analysis, during the engine start-up process, motor A reverses the engine start-up, causing the transmission shaft torque to suddenly change, and the system frequency band is so wide that it covers the resonant frequency, which in turn causes the transmission system to resonate, and ultimately causes the engine speed to fluctuate.

[0122] According to the system state equation of formula (29), after substituting the actual parameters, the transfer function between the torque of motor A and the speed of motor A can be obtained as follows:

[0123]

[0124] Draw the frequency response characteristic curve of Z(s) under different stiffness, such as Figure 7As shown, the trough and peak of the amplitude-frequency characteristic curve correspond to the anti-resonance frequency and resonant frequency of the system respectively. In the low frequency band, the amplitude-frequency characteristic curve and the phase-frequency characteristic curve under different stiffness coincide with each other; near the anti-resonance and resonant frequencies of the system, both the amplitude-frequency characteristic and the phase-frequency characteristic curve fluctuate, and the greater the stiffness, the more violent the fluctuation. Through the analysis of the frequency response characteristics of the system, it can be seen that when the torque of the transmission shaft changes suddenly, that is, when the system frequency band covers the anti-resonance frequency and the resonant frequency, the speed of motor A will fluctuate.

[0125] Step 500: construct a Luenberger type system state observer based on the state equation; the Luenberger type system state observer is used to reconstruct the transmission shaft torque based on the motor speed and the engine speed.

[0126] In engineering practice, torque measurement devices are not widely used on vehicles due to factors such as high cost and limited use conditions. In order to obtain the torque value on the transmission shaft and facilitate the analysis and evaluation of the effect of the control strategy, this application establishes a Luenberger type system state observer to observe the torque on the transmission shaft. The Luenberger observer uses the feedback principle to gradually make the estimated state value approach the actual state value. The state space expression of the engine starting process under static conditions is shown in formula (29), and the observability matrix of the system is:

[0127] N = [CCACA 2 ] T (33)

[0128] According to the above observability matrix, it is easy to obtain that the rank of the observability matrix is ​​rank(N)=3, the system is completely observable, and the existence condition of the Luenberger observer is satisfied, and the system state observer can be designed.

[0129] According to the state equation (29) of the engine starting process under static conditions, the system state is reconstructed using the Luenberger observer. Since the speed data of motor A and the engine can be directly obtained through sensor measurement, only a one-dimensional reduced dimension observer is needed to reconstruct the torque on the transmission shaft.

[0130] First, the state variables are decomposed into two parts according to detectability. Among them, the two state variables of motor A speed and engine speed can be directly measured, so let:

[0131]

[0132] It is necessary to observe the torque on the transmission shaft, so:

[0133] x 2 =[TS ](35)

[0134] The torque of motor A and the engine is selected as the system input, that is:

[0135] u=[T A T E ] T (36)

[0136] The state-space representation of the system will be of the form:

[0137]

[0138] A 21 =[ki q s 1 -k],

[0139]

[0140] Based on the above division, the original system is divided into two subsystems.

[0141] The state space expression of the first subsystem is:

[0142]

[0143] The state space expression of the second subsystem is:

[0144]

[0145] make:

[0146] z=A 12 x 2 (40)

[0147] but:

[0148]

[0149] M, z are respectively the input and output of the subsystem to be observed.

[0150] In summary, the observer equation is:

[0151]

[0152] The equation appears Increased the difficulty of implementation, in order to eliminate Introducing variables:

[0153]

[0154] Then, the observer equation becomes:

[0155]

[0156] in, represents the intermediate variable, represents the observed value of the torque on the transmission shaft, and G represents the configuration matrix.

[0157] Since the motor A speed and the engine speed are directly measurable, there is no estimation error in these two state components. In order to verify that the estimation error of the torque on the transmission shaft has the desired decay rate, equation (42) can be subtracted from equation (39) to obtain the state estimation error equation.

[0158]

[0159] After eliminating items, we can get:

[0160]

[0161] Since the system is observable, it must be possible to make (A 22 -GA 12 ) to obtain any configuration of the poles, thereby ensuring that the error can decay to zero as quickly as the designer expects. So far, the design of the Luenberger state observer for the torque on the transmission shaft has been completed. The structure of the entire observer is as follows: Figure 8 shown.

[0162] Based on the hybrid power system simulation model, the designed Luenberger observer is simulated and verified. The observation results of the torque on the transmission shaft are as follows: Fig. 9 As shown, compared with the simulated measurement value, the observed transmission shaft torque has an initial observation error, and the observed value can change with the change of the measured value during the rest of the time; the peak value of the torque on the transmission shaft measured during the simulation process is 1731Nm, and the observed peak value is 1798Nm, with only a 3.9% deviation between the two.

[0163] Step 600, based on the Luenberger type system state observer, the preset engine speed curve and the preset motor speed curve, the speed curve trajectory is tracked to obtain an optimal control law; the optimal control law represents the optimal torque of the motor in the process of reverse starting the engine through the transmission shaft.

[0164] During the process of reverse-tow starting the engine by motor A, the torque fluctuation on the transmission shaft corresponds to the speed fluctuation of the engine and motor A. From equation (27), it can be seen that if the speed of the engine and motor A keeps changing linearly (angular acceleration is a constant), the torque on the transmission shaft will change evenly, which can suppress the torque fluctuation on the shaft. Therefore, the speed trajectory of the engine and motor A is set and control is applied to track the trajectory, and the control problem of suppressing the torque fluctuation on the transmission shaft during the engine start-up process is transformed into a speed tracking control problem. The tracker problem is a type of quadratic optimal control problem, and its control purpose is to make the output closely follow a desired output without consuming too much control energy.

[0165] Step 600 specifically includes:

[0166] 1) Based on the state equation, the system controllability matrix is ​​determined; according to the state space expression (29) of the engine starting process under static conditions, the system controllability matrix is ​​obtained as follows:

[0167] M=[BABA 2 B](47)

[0168] It is easy to obtain that the rank of the controllability matrix is ​​rank(M)=3, and the system is fully controllable.

[0169] 2) Based on the system controllability matrix, the Luenberger type system state observer, the preset engine speed curve and the preset motor speed curve, a performance functional is determined; and the tracking trajectories of the engine and motor A are set as:

[0170]

[0171] In the formula, α A is the angular acceleration of motor A; α E is the engine angular acceleration. In the tracking trajectory, the angular acceleration of the engine and motor A is set to a constant value, that is, the speed of the engine and motor A changes according to a linear law.

[0172] Based on the above system controllability matrix, the set tracking trajectory, and the data observed by the Luenberger type system state observer, the error vector is defined as:

[0173] e(t)=z(t)-y(t)(49)

[0174] Find the optimal control that minimizes the following performance functional:

[0175]

[0176] The letters in formula (50) are explained as follows:

[0177]

[0178] Where J represents the performance index value, [t 0 ,t f ] represents the time series, e represents the error vector, q 11 and q 12 Respectively represent the importance attached to the motor A and engine speed tracking error; q 2 Represents the importance attached to the control cost of motor A; q 01 and q 02 They respectively represent the importance attached to the tracking error of motor A and engine speed terminal moment.

[0179] 3) According to the state equation and the performance functional, determine the Hamiltonian function; specifically, according to the minimum principle, the Hamiltonian function can be written as:

[0180]

[0181] The following equation is derived from the extreme value conditions:

[0182]

[0183]

[0184] The canonical equation of the system is:

[0185]

[0186] make:

[0187] λ(t)=P(t)x(t)-g(t) (56)

[0188] Substituting formula (56) into formula (53), we get:

[0189]

[0190] Taking the derivatives of both sides of equation (56) we get:

[0191]

[0192] Combining equations (54), (56) and (57), we can obtain:

[0193]

[0194] Combining equation (55) and equation (56), we can get:

[0195]

[0196] As long as there is an optimal solution, equations (59) and (60) hold for all x(t) and z(t), and the following conclusions can be drawn:

[0197] (1) The following matrix differential equation must be satisfied:

[0198]

[0199] (2) The following vector differential equation must be satisfied:

[0200]

[0201] Their boundary conditions are:

[0202]

[0203] 4) Solve the Hamiltonian function to obtain the optimal control law. Solve P(t) and g(t) from equations (61) and (62), and substitute them into equation (57) to obtain the optimal control law u*(t), that is, the optimal torque output of motor A during the reverse start of the engine. It can be obtained from equations (61) and (63) that the solution of P(t) is independent of the selection of z(t), so it can be obtained in the time series [t 0 ,t f ] directly solve P(t). This application uses the fourth-order Runge-Kutta method to solve P(t) in reverse order, and the solution expression is:

[0204]

[0205] Where h is the selected simulation step size. The initial conditions required for the solution are obtained by equation (63), and the initial conditions are related to the weight matrix Q 0 It is related to the value of .

[0206] Similarly, according to the selected z(t) and the solved P(t), the fourth-order Runge-Kutta method is used to calculate the time series [t 0 ,t f ] and solve g(t) in reverse order. The solution expression is:

[0207]

[0208] The initial condition is determined according to equation (63) and the weight matrix Q 0 and z(t f ) are all relevant.

[0209] In summary, this is the problem of the designed tracker. The system structure is as follows Fig.10 shown.

[0210] Finally, based on the hybrid power system simulation model, the optimal control law derived above is applied to verify the effect of engine start optimal control (LQT). At the same time, proportional-integral-derivative control (PID) is used as a control to compare the proposed control strategy.

[0211] Figure 11 shows the simulation results when PID control is used. As shown in Figure 11(a), after receiving the engine start command, motor A outputs a driving torque to reverse the engine to reach the ignition speed. Due to the combined effect of the torque surge of motor A and the engine resistance torque, the torque on the transmission shaft changes suddenly. As shown in Figure 11(c), the torque peak reaches 1731Nm, which affects the safety of the transmission shaft and may even cause the transmission shaft to break in severe cases. As shown in Figure 11(b), the engine speed gradually increases under the action of the torque of motor A, reaching 800r / min for the first time at 0.40s. After that, the engine maintains operation at idle speed, and motor A stops outputting driving torque and starts to operate under the drive of the engine.

[0212] Figure 12 is the simulation result when LQT control is used. For the process of engine starting under vehicle static conditions, when solving the LQT controller, its boundary conditions are the same, that is, the engine and the motor are both in a static state. At the same time, considering the complexity of real-time calculation in actual vehicle application, this application chooses to calculate the controller offline, save the calculated optimal control law, and perform interpolation calculation in actual vehicle application. Unlike PID control, the torque of motor A rises to the maximum torque and then remains constant. Under LQT control, the torque of motor A changes dynamically to ensure that the speed of the engine and motor A increases evenly, thereby reducing the torque fluctuation on the drive shaft. The peak torque during the startup process is 1463Nm, which is 15.5% lower than that of PID control. The entire startup process takes 0.34s, which is 15.0% shorter than that of PID control.

[0213] The detailed data of the comparison of the simulation results of PID and LQT control are shown in Table 2. It can be seen that compared with PID control, LQT control can reduce the peak torque of the transmission shaft while ensuring the rapidity of startup, thereby effectively ensuring the reliability of the transmission shaft, and therefore has a better control effect.

[0214] Table 2 Comparison of simulation results using PID and LQT control

[0215] parameter PID LQT reduce Peak torque of transmission shaft (Nm) 1731 1463 15.5％ Start time(s) 0.40 0.34 15.0％

[0216] Based on the same inventive concept, the embodiment of the present application also provides an engine start control system under stationary conditions. The implementation scheme for solving the problem provided by the system is similar to the implementation scheme recorded in the above method. Therefore, the specific limitations of one or more system embodiments provided below can refer to the limitations of the method above, and will not be repeated here. The engine start control system under stationary conditions of the present application includes:

[0217] The system simulation model building module is used to build a hybrid power system simulation model of a car under static conditions; the hybrid power system simulation model includes a motor, a transmission shaft and an engine.

[0218] The kinematic model and dynamic model construction module is used to construct an engine starting kinematic model and an engine starting dynamic model based on the hybrid power system simulation model.

[0219] The engine drag torque determination module is used to calculate the engine drag torque based on the engine starting kinematic model.

[0220] The state equation determination module is used to construct a state equation based on the engine starting dynamics model, with the motor speed, engine speed and transmission shaft torque as state variables, the motor torque as a control variable, the engine resistance torque as an interference variable, and the motor speed and the engine speed as output variables.

[0221] The observer determination module is used to construct a Luenberger type system state observer based on the state equation; the Luenberger type system state observer is used to reconstruct the transmission shaft torque based on the motor speed and the engine speed.

[0222] The optimal control law determination module is used to track the speed curve trajectory based on the Luenberger system state observer, the preset engine speed curve and the preset motor speed curve to obtain the optimal control law; the optimal control law represents the optimal torque of the motor in the process of reversely starting the engine through the transmission shaft.

[0223] In an exemplary embodiment, the present application provides an electronic device, including a memory and a processor, wherein the memory is used to store a computer program, and the processor runs the computer program to enable the electronic device to perform an engine start control method under stationary conditions. Optionally, the electronic device may be a server.

[0224] In an exemplary embodiment, the present application also provides a computer-readable storage medium storing a computer program, which implements an engine start control method under stationary conditions when executed by a processor.

[0225] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the system disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part.

[0226] This article uses specific examples to illustrate the principles and implementation methods of this application. The description of the above embodiments is only used to help understand the method and core ideas of this application. At the same time, for those skilled in the art, according to the ideas of this application, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting this application.

Claims

1. A method for controlling engine start-up under stationary conditions, characterized in that: Methods include: Constructing a hybrid power system simulation model of a vehicle under stationary conditions; the hybrid power system simulation model includes a motor, a transmission shaft and an engine; Based on the hybrid power system simulation model, an engine starting kinematic model and an engine starting dynamic model are constructed; Calculating the engine drag torque based on the engine starting kinematic model; Based on the engine starting dynamics model, the motor speed, the engine speed and the transmission shaft torque are used as state variables, the motor torque is used as a control variable, the engine resistance torque is used as an interference variable, and the motor speed and the engine speed are also used as output variables to construct a state equation; Based on the state equation, a Luenberger type system state observer is constructed; the Luenberger type system state observer is used to reconstruct the transmission shaft torque based on the motor speed and the engine speed; Based on the Luenberger type system state observer, the preset engine speed curve and the preset motor speed curve, the speed curve trajectory tracking is performed to obtain the optimal control law; the optimal control law represents the optimal torque of the motor in the process of reversely starting the engine through the transmission shaft.

2. The engine start control method under stationary conditions according to claim 1, characterized in that: The engine is a crank-connecting rod structure, including a cylinder, a piston, a crank, a crankcase and a connecting rod; The calculation formula of the engine resistance torque is as follows: The resistance torque of the first cylinder of the engine is M L1 The calculation formula is: F g =(p-p0)S p ; The resistance torque of the i-th cylinder of the engine is M Li The calculation formula is: The calculation formula of engine drag torque is: Among them, α represents the rotation angle of the crank of the first cylinder of the engine, α i represents the rotation angle of the crank of the first cylinder of the engine; ω represents the engine crank speed, F g Indicates the cylinder compression resistance, m j represents the mass of the crank-connecting rod mechanism, R represents the radius of the crank, β represents the swing angle of the connecting rod in the first cylinder of the engine relative to the center line of the cylinder, and β i represents the swing angle of the connecting rod in the first cylinder of the engine relative to the cylinder centerline, i=1,...,6; λ represents the connecting rod ratio, p represents the air pressure in the cylinder; p0 represents the air pressure in the crankcase; S p represents the effective area of ​​the piston top, T e represents the engine resistance torque, and L represents the connecting rod length.

3. The engine start control method under stationary condition according to claim 1, characterized in that: The engine starting dynamics model is: Among them, J A represents the equivalent moment of inertia of motor A, represents the angular acceleration of motor A, T A represents the driving torque of motor A, i q represents the front transmission ratio, s1 represents the proportional coefficient, T S Represents the transmission shaft torque, J E represents the equivalent moment of inertia of the engine, is the engine angular acceleration, T E represents the engine resistance torque, k represents the stiffness of the transmission shaft, θ A Represents the motor rotation angle, θ E represents the engine rotation angle, c represents the damping of the transmission shaft, Indicates the speed of motor A, Indicates engine speed.

4. The engine start control method under stationary condition according to claim 3, characterized in that: The state equation is: u=T A ,d=T E , in, represents the derivative of the state variable, y represents the output variable, x represents the state variable, u represents the control variable, d represents the disturbance variable, [] T represents the transpose of the matrix, and k represents the stiffness of the transmission shaft.

5. The engine start control method under stationary condition according to claim 4, characterized in that: The Luenberger type system state observer is: THE 21 =[out q s1-k], in, represents the intermediate variable, represents the observed value of the torque on the transmission shaft, and G represents the configuration matrix.

6. The engine start control method under stationary condition according to claim 4, characterized in that: Based on the Luenberger system state observer, the preset engine speed curve and the preset motor speed curve, the speed trajectory is tracked to obtain the optimal control law, which specifically includes: Based on the state equation, determining the system controllability matrix; Determining a performance functional based on the system controllability matrix, the Luenberger type system state observer, a preset engine speed curve, and a preset motor speed curve; Determining a Hamiltonian function according to the state equation and the performance functional; The Hamiltonian function is solved to obtain an optimal control law.

7. The engine start control method under stationary condition according to claim 6, characterized in that: The performance functional is: <h2 style=";text-align:left;direction:ltr"> <h2 style=";text-align:left;direction:ltr"> Q2=q2,<h2 style=";text-align:left;direction:ltr"> Among them, J represents the performance index value, [t0,t f ] represents the time series, e represents the error vector, q 11 and q 12 They represent the importance attached to the motor A and engine speed tracking error respectively; q2 represents the importance attached to the control cost of motor A; q 01 and q 02 They respectively represent the importance attached to the tracking error of motor A and engine speed terminal moment.

8. The engine start control method under stationary condition according to claim 7, characterized in that: The calculation formula of the optimal control law is: Among them, the solution of P(t) and g(t) satisfies the following equations: The matrix differential equation is: The vector differential equation is: The boundary conditions are: Among them, u * (t) represents the optimal control law.

9. An engine start control system under stationary conditions, characterized in that: The system includes: A system simulation model building module, used to build a hybrid power system simulation model of a vehicle under static conditions; the hybrid power system simulation model includes a motor, a transmission shaft and an engine; A kinematic model and a dynamic model building module, used to build an engine starting kinematic model and an engine starting dynamic model based on the hybrid power system simulation model; An engine drag torque determination module, used for calculating the engine drag torque based on the engine starting kinematic model; a state equation determination module, for constructing a state equation based on the engine starting dynamics model, taking the motor speed, the engine speed and the transmission shaft torque as state variables, taking the motor torque as a control variable, taking the engine resistance torque as an interference variable, and taking the motor speed and the engine speed as output variables; An observer determination module, configured to construct a Luenberger type system state observer based on the state equation; the Luenberger type system state observer is configured to reconstruct the transmission shaft torque based on the motor speed and the engine speed; The optimal control law determination module is used to track the speed curve trajectory based on the Luenberger system state observer, the preset engine speed curve and the preset motor speed curve to obtain the optimal control law; the optimal control law represents the optimal torque of the motor in the process of reversely starting the engine through the transmission shaft.

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