Hybrid vehicle engine start-stop control method and system, medium and product

Abstract

The invention discloses a hybrid electric vehicle engine start-stop control method and system, and relates to the technical field of hybrid electric vehicles, and the method comprises the steps: building a power coupling mechanism dynamic model in the hybrid electric vehicle engine start-stop process under a driving condition; determining a state space expression of a stage of reversely dragging the engine by the motor based on the power coupling mechanism dynamic model; based on the state space expression, determining a prediction model of the engine reverse dragging stage of the motor; constructing an objective function based on the prediction model, and solving the objective function to obtain an optimal control quantity; controlling the hybrid power vehicle in the clutch speed regulation stage and the engine working point regulation stage based on a PID controller; and based on the optimal control quantity, the hybrid power vehicle in the stage that the motor reversely drags the engine is controlled. According to the invention, the output torque fluctuation can be effectively inhibited, the impact degree of the whole vehicle is reduced, and the running smoothness of the whole vehicle in the start-stop process of the engine is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of hybrid vehicle, and in particular to a hybrid vehicle engine start-stop control method, system, medium and product. Background Art

[0002] As the number of cars in the world increases year by year, oil resources become increasingly scarce, and environmental awareness in various countries gradually increases, modern society has higher and higher requirements for energy conservation and environmental protection of cars. Research on key hybrid technologies will help improve my country's independent research and development capabilities for hybrid vehicles, develop independent brands of hybrid vehicles, and catch up with the world's advanced level in the field of new energy technology.

[0003] Hybrid vehicles mainly achieve energy conservation and emission reduction through functions such as automatic engine start-stop, brake energy recovery, motor assistance, optimization of engine efficiency and pure electric driving. Among them, the automatic engine start-stop technology will reasonably control the engine start-stop according to the operating status of the vehicle to reduce the inefficient working time of the engine, thereby improving the system efficiency of hybrid vehicles. Although the automatic engine start-stop can improve fuel economy and reduce exhaust emissions, it will also bring a series of problems to the vehicle's drivability, comfort and vibration characteristics.

[0004] 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 improves the efficiency of the transmission system while greatly reducing the damping of the transmission system. Therefore, the power transmission system of hybrid vehicles is more prone to torque fluctuations. Summary of the invention

[0005] Based on this, the purpose of the present invention is to provide a hybrid vehicle engine start-stop control method, system, medium and product to effectively suppress output torque fluctuations, reduce the impact of the entire vehicle, and improve the smoothness of the vehicle's driving during engine start-stop.

[0006] To achieve the above object, the present invention provides the following solutions:

[0007] A hybrid vehicle engine start-stop control method, comprising:

[0008] The dynamic model of the power coupling mechanism in the engine start-stop process of a hybrid vehicle under driving conditions is established; the engine start process includes the clutch speed regulation stage, the motor reverse engine drag stage and the engine operating point adjustment stage, and the engine stop process includes: the motor reverse engine drag stage and the engine operating point adjustment stage;

[0009] Determine the state space expression of the motor reverse-drag engine stage based on the power coupling mechanism dynamics model;

[0010] Determine a prediction model for the motor reverse-drag engine phase based on the state space expression;

[0011] Controlling the hybrid vehicle in the clutch speed regulation phase and the engine operating point adjustment phase based on the PID controller;

[0012] Constructing an objective function based on the prediction model, and solving the objective function to obtain an optimal control amount;

[0013] Controlling the hybrid vehicle in the clutch speed regulation phase and the engine operating point adjustment phase based on the PID controller;

[0014] The hybrid vehicle in the motor-engine reverse-drag phase is controlled based on the optimal control amount.

[0015] To achieve the above object, the present invention also provides the following solution:

[0016] A hybrid vehicle engine start-stop control system, comprising:

[0017] The power coupling mechanism dynamic model establishment module is used to establish the power coupling mechanism dynamic model in the engine start-stop process of the hybrid vehicle under driving conditions; the engine start process includes the clutch speed regulation stage, the motor reverse engine drag stage and the engine working point adjustment stage, and the engine stop process includes: the motor reverse engine drag stage and the engine working point adjustment stage;

[0018] A state space expression determination module, used to determine the state space expression of the motor reverse drag engine stage based on the power coupling mechanism dynamics model;

[0019] A prediction model determination module, used to determine the prediction model of the motor reverse drag engine stage based on the state space expression;

[0020] An objective function construction and solution module, used to construct an objective function based on the prediction model, and solve the objective function to obtain an optimal control amount;

[0021] A first control module, for controlling the hybrid vehicle in a clutch speed regulation phase and an engine operating point adjustment phase based on a PID controller;

[0022] The second control module is used to control the hybrid vehicle in the motor-reverse-engine phase based on the optimal control amount.

[0023] To achieve the above object, the present invention also provides the following solution:

[0024] A computer-readable storage medium stores a computer program, which, when executed by a processor, implements the above-mentioned hybrid vehicle engine start-stop control method.

[0025] To achieve the above object, the present invention also provides the following solution:

[0026] A computer program product includes a computer program, and when the computer program is executed by a processor, the hybrid vehicle engine start-stop control method is implemented.

[0027] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0028] Aiming at the engine start-stop process under the driving condition of the power system of a parallel-parallel hybrid vehicle, in order to suppress the output torque fluctuation and reduce the impact degree of the whole vehicle, the present invention specifically analyzes the engine start-up process and the engine stop process respectively, divides the engine start-up process into three stages: clutch speed regulation, motor reverse engine drag and engine working point adjustment, and divides the engine stop process into two stages: engine working point adjustment and motor reverse engine drag, designs different engine start-stop control strategies for each stage, effectively suppresses the output torque fluctuation, reduces the impact degree of the whole vehicle, and improves the driving smoothness of the whole vehicle during the engine start-stop process. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the embodiments of the present invention 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 invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0030] Figure 1 A flow chart of a hybrid vehicle engine start-stop control method provided by the present invention;

[0031] Figure 2 It is a structural schematic diagram of a series-parallel hybrid power system;

[0032] Figure 3 The flow chart of the engine starting process is as follows;

[0033] Figure 4 The engine shutdown process flow chart is as follows;

[0034] Figure 5 Schematic diagram of the power coupling mechanism model;

[0035] Figure 6 It is a schematic diagram of the staged engine start control process;

[0036] Figure 7 This is the control block diagram of the clutch speed regulation stage during the engine starting process;

[0037] Figure 8 This is the control block diagram of the motor reverse-drag engine stage during the engine starting process;

[0038] Fig. 9 This is the control block diagram of the engine operating point adjustment phase during the engine starting process;

[0039] Fig.10 It is a schematic diagram of the simulation results of the engine start without adopting the segmented coordinated control;

[0040] Fig.11 This is a schematic diagram of the simulation results of the engine startup segmented PID control;

[0041] Fig.12 The schematic diagram of the simulation results of the engine startup segmented MPC control;

[0042] Fig.13 This is a schematic diagram comparing the simulation results of engine startup segmented PID and MPC control;

[0043] Fig.14 It is a schematic diagram of the staged engine shutdown control process;

[0044] Fig.15 It is a schematic diagram of simulation results of engine shutdown segmented PID control;

[0045] Fig.16 It is a schematic diagram of the simulation results of the engine shutdown segmented MPC control;

[0046] Fig.17 This is a schematic diagram comparing the simulation results of engine shutdown segmented PID and MPC control. DETAILED DESCRIPTION

[0047] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0048] The purpose of the present invention is to provide a hybrid vehicle engine start-stop control method and system, which can effectively suppress output torque fluctuations, reduce the impact of the whole vehicle, and improve the smoothness of the whole vehicle during engine start-stop.

[0049] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0050] Embodiment 1

[0051] like Figure 1 As shown, the hybrid vehicle engine start-stop control method provided in this embodiment includes the following steps:

[0052] S1: Establish a dynamic model of the power coupling mechanism during the engine start-stop process of a hybrid vehicle under driving conditions; the engine start process includes the clutch speed regulation stage, the motor reverse engine drag stage and the engine operating point adjustment stage, and the engine stop process includes: the motor reverse engine drag stage and the engine operating point adjustment stage.

[0053] S2: Determine the state space expression of the motor reverse-drag engine stage based on the power coupling mechanism dynamics model.

[0054] S3: Determine a prediction model for the motor reverse-drag engine phase based on the state space expression.

[0055] S4: constructing an objective function based on the prediction model, and solving the objective function to obtain an optimal control quantity.

[0056] S5: Controlling the hybrid vehicle in the clutch speed regulation phase and the engine operating point adjustment phase based on the PID controller.

[0057] S6: Controlling the hybrid vehicle in the motor-engine reverse-drag phase based on the optimal control amount.

[0058] Furthermore, step S1 specifically includes:

[0059] (1) Analysis of characteristics of series-parallel hybrid power system

[0060] The research object of this invention is a series-parallel hybrid power system, whose configuration is as follows Figure 2 As shown, it is mainly composed of an engine, a front drive, a motor A, a motor B, three planetary gear rows (PG), a clutch CL0, a clutch CL1 and a brake BK.

[0061] During actual vehicle operation, depending on the different power requirements of the vehicle, the vehicle can be driven in different operating modes by controlling the engagement and disengagement of the clutch and brake, such as pure electric drive, mechanical drive, hybrid drive, regenerative braking and other modes.

[0062] During driving, when the hybrid power system switches from pure electric mode to hybrid drive EVT1 mode, motor A and motor B need to jointly drag the engine to the ignition speed for starting. In this process, the intervention of the engine torque (drag torque before ignition and driving torque after ignition) will cause fluctuations in the output torque, which will cause longitudinal impact of the vehicle and affect the smoothness of the vehicle's driving. Similarly, when the hybrid power system switches from hybrid drive EVT1 mode to pure electric mode, motor A and motor B need to jointly drag the engine crankshaft to a stationary state for shutdown. In this process, the change of engine torque (driving torque before shutdown and drag torque after shutdown) will also cause fluctuations in output torque and reduce the smoothness of vehicle driving. Therefore, it is necessary to control the engine start-stop process under driving conditions to ensure the smooth change of output torque and improve the smoothness of vehicle driving.

[0063] (2) Analysis of the engine starting process under driving conditions

[0064] For the series-parallel hybrid power system under study, when starting and accelerating in pure electric mode, the vehicle controller determines whether to switch modes based on the vehicle speed, battery pack SOC status and driver pedal signal. When entering the mode switching process, the first step is to adjust the speed of the driven end of the clutch CL0. When the speed difference between the active and driven ends of the clutch CL0 is less than the set threshold, the clutch CL0 is controlled to engage. When the active and driven ends of the clutch CL0 are fully engaged, motor A and motor B are controlled to reversely drag the engine to the ignition speed. After the engine is ignited and started, the speed is actively adjusted to adjust the speed to the fuel economy zone. At this point, the engine starting process is completed. Based on the above analysis, the entire engine starting process is divided into three stages, namely the clutch speed regulation stage, the motor reverse drag engine stage, and the engine operating point adjustment stage. Figure 3 As shown in Figure 2, corresponding control strategies are designed for different stages to achieve the optimal comprehensive control effect.

[0065] (3) Analysis of engine shutdown process under driving conditions

[0066] For the hybrid power system under study, the vehicle controller determines whether to perform the engine shutdown operation to switch from the EVT1 hybrid drive mode to the pure electric mode based on the vehicle speed, the battery pack SOC status and the driver's pedal signal. When entering the engine shutdown process, first, in the EVT1 hybrid drive mode, the motor is used to adjust the engine operating point to reduce the engine speed; when the engine speed is reduced to meet the shutdown conditions, the engine is cut off from fuel and shut down. At this time, the engine torque changes from a driving torque to a drag torque, and the motor is used to drag the engine so that its speed drops quickly and steadily to zero. At the same time, the clutch CL0 is controlled to disengage, and finally the system enters the pure electric mode, and the engine shutdown process is completed. According to the above analysis, the entire engine shutdown process is divided into two stages: engine operating point adjustment and motor reverse dragging of the engine. Figure 4 shown.

[0067] (4) Engine start-stop process control evaluation indicators

[0068] The performance indicators of the engine start-stop process under driving conditions can be expressed by impact degree and start-stop time.

[0069] The impact degree, which is the derivative of the longitudinal acceleration of the vehicle, can characterize the smoothness of the start-stop process of the hybrid system engine. The calculation formula is:

[0070]

[0071] The unit of impact strength j is m / s 3 For the impact strength standard, the German standard requires |j|≤10m / s 3 , Chinese standard requires |j|≤17.64m / s 3 . a represents acceleration, V represents velocity, and t represents time.

[0072] Start-stop time is the total time required to complete the engine start or stop process. From the perspective of vehicle dynamics, the shorter the time required for the engine start-stop process, the better. However, too short a time will lead to excessive impact, thus affecting the smoothness of the vehicle's driving. Therefore, it is necessary to strike a balance between the impact and the start-stop time.

[0073] (4) Dynamic equations of engine start-stop process under driving conditions

[0074] During the engine start-stop process under driving conditions, motor A and motor B jointly drive the engine to the ignition speed for ignition start or to the flameout speed for flameout shutdown. For this start-stop process, a power coupling mechanism model of the hybrid system is established, such as Figure 5 shown.

[0075] Taking into account the rotational inertia of each component, the dynamic model of the power coupling mechanism during the engine start-stop process under driving conditions is established:

[0076]

[0077] In the formula, J c2 is the moment of inertia of the planet carrier c2; is the angular acceleration of the coupling mechanism input end; T i is the torque at the input end of the coupling mechanism; T c2 is the planet carrier c2 torque; J c1 is the moment of inertia of the planet carrier c1; J r2 is the moment of inertia of the ring gear r2; is the angular acceleration of the planet carrier c1; T c1 is the planet carrier c1 torque; T r2 is the ring gear r2 torque; J A is the equivalent moment of inertia of motor A; J r1 is the moment of inertia of the ring gear r1; is the angular acceleration of motor A; T A is the torque of motor A; T r1 is the ring gear r1 torque; J B is the equivalent moment of inertia of motor B; J s1 , J s2 , J s3 are the moments of inertia of sun gear s1, sun gear s2, and sun gear s3 respectively; is the angular acceleration of motor B; T B is the torque of motor B; T s1 is the sun gear s1 torque; T s2 is the sun gear s2 torque; T s3 is the torque of the sun gear s3; J o J is the moment of inertia of the vehicle body equivalent to the output shaft; c3 is the moment of inertia of the planet carrier c3; is the angular acceleration of the coupling mechanism output end; T o is the torque at the output end of the coupling mechanism; T f is the vehicle load torque.

[0078] According to the speed characteristics of the planetary gear of the power coupling mechanism, its angular velocity relationship is:

[0079] ω B +k1ω A -(1+k1)ω c1 =0 (7)

[0080] ω B +k2ω r2 -(1+k2)ω i =0 (8)

[0081] ω B -(1+k3)ω o =0 (9)

[0082] ω c1 -ω r2 =0 (10)

[0083] In the formula, ω r2 is the angular velocity of the ring gear r2, and k1, k2, and k3 are the characteristic parameters of the planetary gears 1, 2, and 3, respectively.

[0084] According to the torque characteristics of the planetary gear of the power coupling mechanism, the torque relationship is:

[0085] T s1 :T r1 :T c1 =1:k1:(-1-k1) (11)

[0086] T s2 :T r2 :T c2 =1:k2:(-1-k2) (12)

[0087] T s1 :T c3 =1:(-1-k3) (13)

[0088] Where, T c3 is the torque of planet carrier c3.

[0089] Combining the above formulas, the relationship between the angular velocity change rates of the input and output ends of the coupling mechanism can be derived as follows:

[0090]

[0091] In the formula, m 11 、m 12 、m 21 、m 22 is the equivalent inertia.

[0092]

[0093] Furthermore, step S2 specifically includes:

[0094] Formula (1) can be further deduced, namely:

[0095]

[0096] Where, j is the impact strength of the vehicle; R c is the wheel radius; i r is the main reducer transmission ratio;o is the angular velocity of the coupling mechanism output end.

[0097] From formula (15), it can be seen that if the speed of the output end of the coupling mechanism can keep the angular acceleration constant, the longitudinal impact degree is theoretically zero, which can eliminate the impact of the whole vehicle. Therefore, the speed trajectory of the output shaft of the coupling mechanism is given and control is applied to track the trajectory, so as to transform the smoothness control problem during the engine start-stop process into a speed tracking control problem.

[0098] The speed trajectory of the coupling mechanism input and output is set as:

[0099]

[0100] In the formula, α i is the angular acceleration of the coupling mechanism input end; ω o (t0) is the initial angular velocity of the output end of the coupling mechanism at this stage; α o is the angular acceleration at the output end of the coupling mechanism.

[0101] Select the state variable of the system as x = [x1 x2] T =[ω i ω o ] T ; The control variable is u=[u1u2] T =[T A T B ] T ; The disturbance is d = [d1 d2] T =[T i T f ] T ; Output variable is y = [y1 y2] T =[x1x2] T .

[0102] According to formula (14), the state space expression of the motor reverse drag engine process can be obtained as:

[0103]

[0104] in, is the first-order derivative of the state variable, A is the system matrix of the state-space expression, B is the control matrix of the state-space expression, W is the interference matrix of the state-space expression, and C is the output matrix of the state-space expression.

[0105]

[0106] The control quantity constraint is the maximum forward and reverse torque that motor A and motor B can output, that is:

[0107]

[0108] Where, T Amin (t), T Amax (t) is the lower and upper torque limits of motor A; T Bmin (t), T Bmax (t) is the lower and upper torque limits of motor B.

[0109] In order to calculate in real time, the model is discretized and the sampling time is set to τ s , then the state space expression is:

[0110] x d (k+1)=A d x d (k)+B d u d (k)+W ξ d(k) (23)

[0111] Among them, x d (k) is the state variable at time k; x d (k+1) is the state variable at time k+1; u d (k) is the control quantity at time k; d(k) is the disturbance quantity at time k; A d is the system matrix of the discrete state space expression; B d is the control matrix of the discrete state space expression; W ξ is the interference matrix of the discrete state space expression.

[0112] x d (k) = [x1(k)x2(k)] T (twenty four)

[0113] u d (k) = [u1(k)u2(k)] T (25)

[0114] d(k)=[d1(k)d2(k)] T (26)

[0115]

[0116] set up:

[0117] Δx d (k) = x d (k)-x d (k-1), Δu d (k) = u d (k)-u d (k-1)(29)

[0118] but:

[0119] Δx d (k) = A d Δx d (k)+B d Δu d (k)(30)

[0120] Define new state variables:

[0121]

[0122] Then the new augmented model is:

[0123]

[0124] Where Δx d (k) is the increment of the state variable at time k; Δu d (k) is the increment of the control quantity at time k; x(k+1) is the state variable at time k+1; x(k) is the state variable at time k; A aug is the state matrix of the new augmented model; B aug is the control matrix of the new augmented model; u d (k) is the control vector at time k; y(k) is the output variable at time k; C aug is the output matrix of the new augmented model.

[0125]

[0126] Furthermore, step S3 specifically includes:

[0127] In order to reduce the amount of online calculation and facilitate real-time control, the prediction time domain is defined as 3 and the control time domain is defined as 1, then the output prediction model can be obtained as follows:

[0128] Y p =S x x(k)+S u ΔU(k) ​​(34)

[0129]

[0130] Where y(k+1|k) is the predicted value of the system output vector y(k+1) at time k for time k+1; y(k+2|k) is the predicted value of the system output vector y(k+2) at time k for time k+2; y(k+3|k) is the predicted value of the system output vector y(k+3) at time k for time k+3; Y p is a matrix composed of y(k+1|k), y(k+2|k), y(k+3|k); S x and S uis the coefficient matrix in the prediction model equation; ΔU(k) ​​is the optimal control increment at time k.

[0131] Furthermore, step S4 specifically includes:

[0132] In the process of motor A and motor B pulling the engine, the reference signal of the output y1(k) and y2(k) is set to r(k)=[y 1ref (k)y 2ref (k)] T , so that the speed at the input and output of the coupling mechanism can track the reference signal r(k) in real time. Therefore, the goal is to minimize the error between the speed at the input and output of the coupling mechanism and the reference speed. The objective function expression is:

[0133]

[0134] The optimal control increment ΔU obtained by solving is:

[0135]

[0136] Therefore, the optimal control quantity at time k is:

[0137] u(k) * =u(k-1)+ΔU(k) ​​(38)

[0138] Where, J is the objective function; R is the vector matrix of the reference signal; is the weight matrix of the control vector; ΔU is the optimal control increment; T is the transpose; y1(k+i|k) is the predicted value of the output y1(k+i) at time k for the output at time k+i; y2(k+i|k) is the predicted value of the output y2(k+i) at time k for the output at time k+i; 1ref (k) is the reference value of the output variable y1(k); 2ref (k) is the reference value of the output variable y2(k); r w1 is the weight value; Δu1(k) is the control increment of u1; Δu2(k) is the control increment of u2; u1 and u2 are the control quantities; S x and S u is the coefficient matrix in the prediction model; x(k) is the state vector at time k; u(k-1) is the control quantity at time k-1.

[0139] Thus, the optimal torque output of motor A and motor B during the process of the motor reverse-driving the engine can be obtained.

[0140] Furthermore, step S5-step S6 specifically include:

[0141] (1) Engine start process control strategy

[0142] Through the above analysis of the engine starting process under driving conditions, the three stages obtained by division, namely the clutch speed regulation stage, the motor reverse engine stage and the engine operating point adjustment stage, are controlled separately. According to the process characteristics of each stage, the corresponding control strategy is designed to achieve the optimal comprehensive control effect. The segmented engine starting control process is as follows: Figure 6 shown.

[0143] 1) Clutch speed regulation stage

[0144] Use motor A to reduce the speed difference between the active and driven ends of the clutch, that is, reduce the idling speed of the input end of the coupling mechanism to ensure that the clutch is engaged at a low speed difference. According to the angular velocity coupling relationship, the angular velocity of the input end of the coupling mechanism is made zero, and the target angular velocity of motor A at this stage can be obtained:

[0145]

[0146] In this stage, the torque of motor A is controlled by PID. Due to the existence of torque coupling equation (40), the change of the torque of motor A will affect the output torque.

[0147]

[0148] Therefore, the output torque is stabilized by coordinating the torque of motor A and motor B. The torque coordination control algorithm in the clutch speed regulation stage is as follows: Figure 7 As shown in the figure, at this stage, the PID controller calculates the target torque of the output motor A according to the difference between the actual speed of motor A and the target speed; in the driver model, the required torque of the whole vehicle, that is, the output target torque, is analyzed according to the pedal opening signal; the target torque of motor B is calculated by using the torque coupling relationship between the torque of motor A, the torque of motor B and the output torque.

[0149] It is defined as α is the opening of the accelerator pedal, α>0 is the opening of the accelerator pedal, and α<0 is the opening of the brake pedal. The pedal opening is expressed as:

[0150] e(t)=v A_tar -v A_act

[0151]

[0152] e(t) is the error value; v A_tar is the target vehicle speed; v A_act is the actual vehicle speed; Δα is the change in throttle opening; K p is the scale parameter.

[0153] The functional relationship between the pedal opening and the required torque is:

[0154] T need =α 2 T max (42)

[0155] T need is the required torque, T max is the maximum driving torque.

[0156] 2) The motor reverses the engine stage

[0157] Under the premise of ensuring the stable output torque, the engine is reversed from static to ignition speed by motor A and motor B. In this stage, the torque of motor A and motor B is controlled by the model predictive controller designed in the previous article. The control block diagram is shown in the figure. Figure 8 The input of the model predictive controller is the actual speed and reference speed of the coupling mechanism input end and the actual speed and reference speed of the coupling mechanism output end, and the output is the optimal torque output of motor A and motor B calculated in real time.

[0158] 3) Engine operating point adjustment stage

[0159] When motor A and motor B drag the engine to the ignition speed, the engine will ignite and start, enter the active speed regulation stage, output torque to the outside, and finally adjust the speed to the fuel economy zone.

[0160] According to the proportional relationship between the torque of motor A and the engine torque (43), the torque of motor A can be calculated as:

[0161]

[0162] The torque of motor B can be calculated according to the torque coupling relationship (40) between the output torque, the engine torque and the torque of motor B.

[0163] In the engine operating point adjustment stage, the PID controller calculates the target torque of the output engine according to the difference between the actual engine speed and the target speed; the target torque of motor A is calculated according to the proportional relationship between the torque of motor A and the engine torque; in the driver model, the required torque of the whole vehicle, that is, the output target torque, is analyzed according to the pedal opening signal; the target torque of motor B is calculated by using the torque coupling relationship between the engine torque, the torque of motor B and the output torque. The torque coordination control algorithm at this stage is as follows: Fig. 9 shown.

[0164] (2) Engine shutdown process control strategy

[0165] According to the analysis of the engine shutdown process, the corresponding control strategy is designed for the divided engine operating point adjustment stage and the motor reverse engine drag stage. The staged engine shutdown control process is as follows: Fig.14 shown.

[0166] 1) Engine operating point adjustment stage

[0167] Motor A is used to assist the engine in quickly adjusting the working point, reducing the speed to the fuel cut-off speed (ne<800r / min). In this stage, the torque of motor A is controlled by PID. The input of the PID controller is the difference between the actual engine speed and the target speed, and the output is the torque control command of motor A.

[0168]

[0169] ω e_act is the actual engine speed; e_tar is the target engine speed; k Ap , k Ai , k Ad is the PID parameter; T A_cmd is the torque command of motor A.

[0170] Because of the torque coupling relationship, changes in the torque of motor A will affect the output torque. Therefore, during the engine shutdown process, it is necessary to coordinate the torque of motor A and motor B to maintain the vehicle's demand for output torque.

[0171] 2) The motor reverses the engine stage

[0172] In this stage, the engine crankshaft is reversed to a stationary state by motor A and motor B. The impact degree of the whole vehicle is defined as the rate of change of the longitudinal acceleration of the vehicle over time. The impact degree index is used to measure the stability of the output torque and the smoothness of the whole vehicle's driving. From the definition of the impact degree, it can be seen that if the acceleration of the whole vehicle is a constant value, that is, the output end of the coupling mechanism can keep the angular acceleration constant, the impact degree of the whole vehicle is theoretically zero.

[0173] In this stage, the model predictive control method is used to control the torque of motor A and motor B. The reference model of the system is set as:

[0174]

[0175] Where: i (t0) is the initial speed of the coupling mechanism input end at this stage; α i is the angular acceleration of the coupling mechanism input end; ω o (t0) is the initial speed of the output end of the coupling mechanism at this stage; α o is the angular acceleration at the output end of the coupling mechanism.

[0176] Simulation Results and Analysis

[0177] (1) Engine starting process

[0178] In order to verify the effectiveness of the MPC-based control strategy during engine startup, a simulation verification was conducted based on a parallel-parallel hybrid power system simulation platform. The simulation process used models without segmented coordinated control and with segmented PID control as references to compare the performance of segmented MPC control and verify the control effect.

[0179] Fig.10 The simulation results of engine starting under driving conditions without adopting segmented coordinated control are shown in Figure 2. Fig.10 (a) to (f) in the figure represent the curves of vehicle speed, torque, speed, acceleration, impact and working mode. The system initially works in pure electric mode. Fig.10 As shown in (f), working mode 2 is pure electric mode, working mode 3 is engine start mode, and working mode 4 is hybrid drive EVT1 mode. At 7.7s, the engine start command is received, the clutch CL0 is engaged, and the engine reaches the ignition speed under the joint drag of motor A and motor B for ignition start, and the system enters EVT1 mode. During this process, when the clutch CL0 is engaged, the engine speed is zero, and the speed of the coupling mechanism input end is 625r / min, as shown in Fig.10 As shown in (c) in the figure, there is a large speed difference between the clutch active plate and the driven plate, which leads to a large impact when the clutch is engaged, and the torque of motor A and motor B both produce a step-type sudden increase, such as Fig.10 As shown in (b) in the figure, and because the engine needs to be dragged to rotate, the increase in the torque of motor A is greater than that of motor B, which causes a sudden drop in the output torque of the coupling mechanism. At 7.9s, the engine is ignited and started, and the engine torque changes from the drag torque before ignition to the driving torque after ignition. This step change causes a sudden increase in the output torque of the coupling mechanism. The two sudden changes in the output torque of the coupling mechanism seriously affect the smoothness of the vehicle's driving, which is reflected in the acceleration and impact degree, which correspond to the minimum and maximum values ​​respectively, as shown in Fig.10 (d) and Fig.10 From (e) in the figure, we can see that when the torque suddenly drops, the acceleration is the minimum value of 0.02m / s 2 The impact strength is the minimum value -6.58m / s 3 When the torque suddenly increases, the acceleration is the maximum value of 1.73m / s 2 The maximum impact strength is 33.70m / s 3 During the engine start-up process under the driving conditions without segmented coordinated control, the maximum impact degree far exceeds the specified standard value, so it is necessary to optimize the control to reduce the impact degree and improve the smoothness of the vehicle's driving.

[0180] The simulation results of engine starting under driving conditions using segmented PID control are as follows: Fig.11 At 7.7s, the system enters the clutch speed regulation stage of the engine start working mode from the pure electric drive mode, as shown in Fig.11 As shown in (f), starting stage 1 represents the clutch speed regulation stage, starting stage 2 represents the clutch engagement stage, starting stage 3 represents the motor reverse engine drag stage, and starting stage 4 represents the engine operating point adjustment stage. During the period of 7.7s to 8.7s, the engine starting process is in the clutch speed regulation stage. In this stage, the speed of the coupling mechanism input end is reduced by regulating the speed of motor A, as shown in FIG. Fig.11 As shown in (c), when the speed difference between the clutch active plate and the driven plate is less than the threshold value (the present invention sets the speed difference threshold value for clutch engagement to 50r / min), the clutch is controlled to engage, and then the engine start process enters the motor reverse-drag engine stage. Within the time period of 8.8s-9.3s, according to the difference between the actual engine speed and the ignition speed, the output torque of motor A is controlled by the PID algorithm, and motor B determines its own output torque according to the vehicle drive power requirement and the output torque of motor A. At 9.3s, the engine start process enters the engine operating point adjustment stage, and the engine speed is adjusted to about 1600r / min to ensure that the engine operates in the fuel economy zone. At 10.4s, the engine start process is completed, and the vehicle enters the hybrid drive EVT1 mode. Fig.11 (b) shows that during the entire engine startup process, the output torque fluctuation using segmented PID control is 1356 Nm, which is 68.8% lower than 4341 Nm without segmented coordinated control. Fig.11 As shown in (d) in the figure, the acceleration fluctuation range of the segmented PID control is 0.71m / s2~1.28m / s2, which is 0.02m / s2 when the segmented coordinated control is not adopted. 2 ~1.73m / s 2 Compared with the previous period, it has decreased by 66.7%; Fig.11 (e) It can be seen that the use of segmented PID control can ensure that the vehicle impact is limited within the specified standard range. The maximum absolute value of the impact is 33.70m / s when the segmented coordinated control is not used. 3 becomes 7.48m / s 3 , reduced by 77.8%, thus ensuring the smoothness of vehicle driving.

[0181] Fig.12 is the simulation result of piecewise MPC control, such as Fig.12As shown in (c), at 7.7s, motor A is used to adjust the speed of the clutch driven end to ensure that the clutch engages at a low speed difference, so that the impact of the engagement process can be controlled within a smaller range; at 8.8s, the engine start process enters the motor reverse-drag engine stage, and the MPC controller calculates the optimal torque output of motor A and motor B online, so that the speed of the coupling mechanism input and output ends tracks the reference speed to ensure that the output torque changes smoothly. At 10.1s, the engine operating point adjustment stage is entered, and the engine adjusts the speed to the fuel economy zone; at 11.2s, the engine start process is completed, and the vehicle enters the hybrid drive EVT1 mode. The engine officially participates in the vehicle drive, motor A works in the power generation state, and motor B works in the electric state. By Fig.12 (b) shows that during the entire engine starting process, the output torque has a small variation range, with a fluctuation of 831 Nm, which is 80.9% lower than the output torque fluctuation of 4341 Nm without segmented coordinated control. After adopting segmented MPC control, the acceleration and impact of the vehicle during the engine starting process under driving conditions can be controlled within a small variation range, with an acceleration fluctuation range of 0.74 m / s 2 ~0.99m / s 2 The maximum absolute value of the impact is 2.92m / s 3 , compared with 0.02m / s without coordinated control 2 ~1.73m / s 2 、33.70m / s 3 Compared with the previous control, the difference was 85.4% and 91.3% respectively. It can be proved that the use of segmented MPC control can effectively reduce the fluctuation of output torque, narrow the range of acceleration change, greatly reduce the impact of the whole vehicle, and improve the smoothness of the whole vehicle during engine starting.

[0182] In order to further compare the effects of segmented PID control and segmented MPC control, the vehicle speed, output torque, acceleration and impact degree in the simulation results of the two are compared, as shown in Figure 2. Fig.13 shown. Fig.13 (a) in the figure shows that there is no significant difference between the two control methods in terms of their impact on vehicle speed, and both methods can ensure the normal driving of the vehicle. Fig.13 It can be seen from (b), (c) and (d) in Figure 1 that compared with the segmented PID control, the segmented MPC control can further reduce the fluctuation of the output torque, making the fluctuation range of the acceleration smaller and the maximum value of the impact smaller. Table 1 gives the detailed data of the simulation results comparison between the segmented PID control and the segmented MPC control under driving conditions.

[0183] The detailed data of the simulation results before and after the MPC control are shown in Table 1. It can be seen that MPC can significantly reduce the output torque peak value and the maximum absolute value of the impact degree, and reduce the fluctuation range of the output torque, thereby ensuring the safety of the output shaft and the smoothness of the vehicle's driving, and therefore has a good control effect.

[0184] Table 1

[0185]

[0186] (2) Engine shutdown process

[0187] In order to verify the effectiveness of the engine shutdown segmented MPC control strategy, the present invention uses a basic model using a segmented PID control strategy as a reference to compare the performance of the segmented MPC control.

[0188] Fig.15 The simulation results of the engine shutdown process under driving conditions using segmented PID control are given. Fig.15 (a) in the figure shows that the actual vehicle speed can basically keep up with the required vehicle speed after adopting the segmented PID control. Fig.15 From (b), (c) and (f), we can see that the vehicle enters the engine shutdown mode at 12.5s, and at the same time enters the first stage of the shutdown process, namely the engine operating point adjustment stage. Motor A is converted from the power generation state to the electric state, and the output negative torque has a sudden drop, thereby assisting the engine to quickly reduce the speed; at 13.8s, the engine is adjusted to the flameout speed, thus entering the second stage of the shutdown process, namely the motor reverse drag engine stage. At this time, the engine is turned off and the drag resistance torque is output to the outside. The output torque command of motor A is determined by the PID control algorithm based on the difference between the actual engine speed and the zero speed, and the output torque of motor B is determined based on the required power of the whole vehicle and the output torque of motor A; at 15.0s, the engine shutdown process is completed, the vehicle works in the pure electric drive mode, motor A stops working, and the whole vehicle is driven by motor B. During the entire engine shutdown process, the fluctuation of the output torque is 2275Nm. Fig.15 From (d) and (e), we can see that the changes in acceleration and impact are consistent, and the fluctuation range of acceleration is 0.13m / s 2 ~1.21m / s 2 The maximum absolute value of the impact is 10.35m / s 3 .

[0189] Fig.16 is the simulation result of using segmented MPC control. Fig.16From (b), (c) and (f) in the figure, it can be seen that at 12.5s, the system enters the engine shutdown mode, and uses motor A to assist the engine in adjusting the working point, so that its speed is reduced to the flameout speed; at 13.8s, the engine is shut down, and the engine is shut down. In view of the sudden change from the output driving torque to the drag torque and the change of the drag torque, the optimal torque output of motor A and motor B is calculated online through the designed MPC controller, and the engine crankshaft is quickly dragged to zero speed while ensuring the smooth change of the output torque of the coupling mechanism; at 15.3s, the engine speed drops to zero, the shutdown process is completed, and the vehicle enters the pure electric drive mode. During the entire engine shutdown process, the fluctuation of the output torque is 836Nm, which is 63.3% lower than the 2275Nm of the segmented PID control. Fig.16 (d) and (e) show that the acceleration fluctuation range is 0.38m / s 2 ~0.76m / s 2 , and 0.13m / s of segmented PID control 2 ~1.21m / s 2 Compared with the previous test, it was reduced by 64.8%, and the maximum absolute value of the impact was 4.35m / s 3 , and 10.35m / s of segmented PID control 3 Compared with the segmented PID control, the segmented MPC control can more effectively suppress the fluctuation of the output torque, reduce the fluctuation range of acceleration, reduce the impact degree, and improve the smoothness of the vehicle's driving.

[0190] Fig.17 The simulation results of vehicle speed, output torque, acceleration and impact of segmented PID control and segmented MPC control are compared more intuitively.

[0191] The detailed data of the simulation results of the engine shutdown process using segmented PID control and segmented MPC control are shown in Table 2. It can be seen that the segmented MPC control can significantly reduce the output torque peak and the maximum absolute value of the impact degree, reduce the fluctuation of the output torque and the fluctuation range of the acceleration, thereby ensuring the safety of the output shaft and the smoothness of the vehicle's driving, and therefore has a good control effect.

[0192] Table 2

[0193] parameter PID MPC reduce Output torque peak Nm 3234 2251 30.4％ Output torque fluctuation Nm 2275 836 63.3％ <![CDATA[Acceleration fluctuation range m / s 2 > [0.13,1.21] [0.38,0.76] 64.8％ <![CDATA[Maximum absolute value of jolt m / s 3 > 10.35 4.35 58.0％

[0194] The present invention is directed to a parallel-parallel hybrid vehicle power system and an engine start-stop process under driving conditions. In order to suppress output torque fluctuation and reduce the impact of the entire vehicle, a specific analysis is performed on the engine start-up process and the engine stop-down process, the engine start-up process is divided into three stages: clutch speed regulation, motor reverse engine drag and engine operating point adjustment, the engine stop-down process is divided into two stages: engine operating point adjustment and motor reverse engine drag, different engine start-stop control strategies are designed for each stage, the output torque fluctuation is effectively suppressed, the impact of the entire vehicle is reduced, and the driving smoothness of the entire vehicle during the engine start-stop process is improved.

[0195] Embodiment 2

[0196] In order to execute the method corresponding to the above-mentioned embodiment 1 to achieve the corresponding functions and technical effects, a hybrid vehicle engine start-stop control system is provided below.

[0197] The system includes:

[0198] The power coupling mechanism dynamic model establishment module is used to establish the power coupling mechanism dynamic model during the engine start-stop process of a hybrid vehicle under driving conditions; the engine start process includes the clutch speed regulation stage, the motor reverse engine drag stage and the engine operating point adjustment stage, and the engine shutdown process includes: the motor reverse engine drag stage and the engine operating point adjustment stage.

[0199] The state space expression determination module is used to determine the state space expression of the motor reverse drag engine stage based on the power coupling mechanism dynamics model.

[0200] The prediction model determination module is used to determine the prediction model of the motor reverse drag engine stage based on the state space expression.

[0201] The first control module is used to control the hybrid vehicle in the clutch speed regulation stage and the engine operating point adjustment stage based on the PID controller.

[0202] The second control module is used to control the hybrid vehicle in the motor reverse drag engine stage based on the prediction model of the motor reverse drag engine stage.

[0203] 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.

[0204] This article uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only used to help understand the method and core ideas of the present invention. At the same time, for those skilled in the art, according to the ideas of the present invention, 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 the present invention.

Claims

1. A hybrid vehicle engine start-stop control method, characterized in that: include: Establish a dynamic model of the power coupling mechanism during the engine start-stop process of a hybrid vehicle under driving conditions; The engine start process includes the clutch speed regulation stage, the motor reverse engine drag stage and the engine operating point adjustment stage, and the engine shutdown process includes: the motor reverse engine drag stage and the engine operating point adjustment stage; Determine the state space expression of the motor reverse-drag engine stage based on the power coupling mechanism dynamics model; Determine a prediction model for the motor reverse-drag engine phase based on the state space expression; Constructing an objective function based on the prediction model, and solving the objective function to obtain an optimal control amount; Controlling the hybrid vehicle in the clutch speed regulation phase and the engine operating point adjustment phase based on the PID controller; The hybrid vehicle in the motor-engine reverse-drag phase is controlled based on the optimal control amount.

2. The hybrid vehicle engine start-stop control method according to claim 1, characterized in that: The expression of the power coupling mechanism dynamic model is: Among them, J c2 is the moment of inertia of the planet carrier c2; is the angular acceleration of the coupling mechanism input end; T i is the torque at the input end of the coupling mechanism; T c2 is the planet carrier c2 torque; J c1 is the moment of inertia of the planet carrier c1; J r2 is the moment of inertia of the ring gear r2; is the angular acceleration of the planet carrier c1; T c1 is the planet carrier c1 torque; T r2 is the ring gear r2 torque; J A is the equivalent moment of inertia of motor A; J r1 is the moment of inertia of the ring gear r1; is the angular acceleration of motor A; T A is the torque of motor A; T r1 is the ring gear r1 torque; J B is the equivalent moment of inertia of motor B; J s1 , J s2 , J s3 are the moments of inertia of sun gear s1, sun gear s2, and sun gear s3 respectively; is the angular acceleration of motor B; T B is the torque of motor B; T s1 is the sun gear s1 torque; T s2 is the sun gear s2 torque; T s3 is the torque of the sun gear s3; J o J is the moment of inertia of the vehicle body equivalent to the output shaft; c3 is the moment of inertia of the planet carrier c3; is the angular acceleration of the coupling mechanism output end; T o is the torque at the output end of the coupling mechanism; T f is the vehicle load torque.

3. The hybrid vehicle engine start-stop control method according to claim 1, characterized in that: The state space expression of the motor reverse drag engine stage is: Among them, x(k+1) is the state vector at time k+1; x(k) is the state vector at time k; A aug is the state matrix; B aug is the control matrix; u d (k) is the control vector at time k; y(k) is the output variable at time k; C aug is the output matrix; The expression of the prediction model is: Y p =S x x(k)+S u ΔU(k) Among them, y(k+1|k) is the predicted value of the output vector y(k+1) at time k+1; y(k+2|k) is the predicted value of the output vector y(k+2) at time k+2; y(k+3|k) is the predicted value of the output vector y(k+3) at time k+3; Yp is the matrix composed of y(k+1|k), y(k+2|k) and y(k+3|k); Sx and Su are coefficient matrices; ΔU(k) ​​is the optimal control increment at time k.

4. The hybrid vehicle engine start-stop control method according to claim 1, characterized in that: The expression of the objective function is: u(k) * =u(k-1)+ΔU(k) Where, J is the objective function; R is the vector matrix of the reference signal; is the weight matrix of the control vector; ΔU is the optimal control increment; T is the transpose; y1(k+i|k) is the predicted value of the output vector y1(k+i) at time k for time k+i; y2(k+i|k) is the predicted value of the output vector y2(k+i) at time k for time k+i; y 1ref (k) is the reference value of the output variable y1(k); 2ref (k) is the reference value of the output variable y2(k); r w1 is the weight value; Δu1(k) is the control increment of u1; Δu2(k) is the control increment of u2; u1 and u2 are the control quantities; S x and S u is the coefficient matrix in the prediction model; x(k) is the state vector at time k; u(k-1) is the control quantity at time k-1.

5. The hybrid vehicle engine start-stop control method according to claim 1, characterized in that: The hybrid vehicle is controlled based on the PID controller in the clutch speed regulation stage and the engine operating point adjustment stage, specifically including: During the clutch speed regulation phase of the engine starting process: According to the actual speed and target speed of motor A, the target torque of motor A is calculated by using PID controller; Determine the required torque of the whole vehicle according to the actual vehicle speed and the target vehicle speed of the hybrid vehicle; According to the target torque of the motor A and the required torque of the whole vehicle, the target torque of the motor B is calculated by using a torque coupling relationship calculation formula; Controlling the hybrid vehicle according to the target torque of the motor A and the target torque of the motor B; During the engine operating point adjustment phase of the engine start-stop process: According to the actual engine speed and target speed, the PID controller is used to calculate the target torque of the engine; According to the target torque of the engine, the target torque of the motor A is calculated using a proportional relationship; Determine the required torque of the whole vehicle according to the actual vehicle speed and the target vehicle speed of the hybrid vehicle; According to the target torque of the motor A and the required torque of the whole vehicle, the target torque of the motor B is calculated by using a torque coupling relationship calculation formula; The hybrid vehicle is controlled according to the target torque of motor A and the target torque of motor B.

6. The hybrid vehicle engine start-stop control method according to claim 5, characterized in that: The torque coupling relationship calculation formula is: Among them, T o is the torque at the output end of the coupling mechanism; T A is the torque of motor A; T B is the torque of motor B; k1, k2, k3 are the planetary gear characteristic parameters of planetary gear 1, 2, 3 respectively.

7. The hybrid vehicle engine start-stop control method according to claim 6, characterized in that: The proportional relationship is: Among them, T e is the engine torque.

8. A hybrid vehicle engine start-stop control system, characterized in that: include: A power coupling mechanism dynamics model building module is used to build a power coupling mechanism dynamics model during the engine start-stop process of a hybrid vehicle under driving conditions; The engine start process includes the clutch speed regulation stage, the motor reverse engine drag stage and the engine operating point adjustment stage, and the engine shutdown process includes: the motor reverse engine drag stage and the engine operating point adjustment stage; A state space expression determination module, used to determine the state space expression of the motor reverse drag engine stage based on the power coupling mechanism dynamics model; A prediction model determination module, used to determine the prediction model of the motor reverse drag engine stage based on the state space expression; An objective function construction and solution module, used to construct an objective function based on the prediction model, and solve the objective function to obtain an optimal control amount; A first control module, for controlling the hybrid vehicle in a clutch speed regulation phase and an engine operating point adjustment phase based on a PID controller; The second control module is used to control the hybrid vehicle in the motor-reverse-engine phase based on the optimal control amount.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the hybrid vehicle engine start-stop control method according to any one of claims 1 to 7 is implemented.

10. A computer program product, comprising a computer program, characterized in that When the computer program is executed by a processor, the hybrid vehicle engine start-stop control method according to any one of claims 1 to 7 is implemented.

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