Engine rail pressure-oxygen sensor combined control method and system

Abstract

The engine rail pressure-oxygen sensor combined control method and system of the present application obtains the actual oxygen concentration in the engine exhaust based on the excess air coefficient of gasoline or diesel fuel, and then obtains the excess air coefficient of the methanol-diesel dual fuel engine, thereby obtaining the EGR rate, and combining the pressure inside the high-pressure common rail pipe, realizes the combined control of the engine through the rail pressure and the oxygen sensor. The present application solves the problem of weak anti-interference ability of the traditional control circuit, and accurately calculates the excess air coefficient of the methanol-diesel dual fuel engine, and the calculated excess air coefficient of the methanol-diesel dual fuel engine is closer to the actual working condition, which is the key application direction of the combination of automobile power engineering and embedded control technology, and can improve the engine combustion efficiency and emission performance.

Description

Technical Field

[0001] This invention relates to the field of internal combustion engine power system control technology, and in particular to an engine rail pressure-oxygen sensor combined control method and system. Background Technology

[0002] In existing technologies, rail pressure control in high-pressure common rail systems mostly employs traditional PID algorithms. A microcontroller collects pressure signals and adjusts the fuel metering valve to achieve a closed loop. The excess air coefficient is calculated directly based on the characteristics of gasoline or diesel, and EGR rate acquisition relies on specific hardware (such as a carbon dioxide sensor). Existing technologies suffer from the following prominent problems: First, insufficient anti-interference capability. The common-ground design leads to ground level fluctuations and high-frequency electromagnetic interference in the engine compartment directly intruding into the signal link, causing rail pressure sampling deviations and oxygen sensor signal distortion, affecting control accuracy. Second, poor adaptability of the control strategy, failing to meet the operational requirements of methanol-diesel dual-fuel engines. Traditional control algorithms do not consider the characteristics of methanol-diesel dual-fuel engines, directly calculating the excess air coefficient based on traditional gasoline / diesel fuels, resulting in significant discrepancies with the actual value under specific operating conditions. Third, traditional solutions require specific hardware (such as a carbon dioxide sensor) to achieve EGR rate control, significantly increasing system costs. Summary of the Invention

[0003] This invention discloses a method and system for joint control of engine rail pressure and oxygen sensor to overcome the above-mentioned technical problems.

[0004] To achieve the above objectives, the technical solution of the present invention is as follows:

[0005] A method for joint control of engine rail pressure and oxygen sensor includes the following steps:

[0006] S1: Obtain the pressure inside the engine's high-pressure common rail;

[0007] S2: Obtain the excess air coefficient based on gasoline / diesel fuel to obtain the oxygen concentration in the engine exhaust gas, and then obtain the excess air coefficient of the methanol-diesel dual-fuel engine.

[0008] S3: Obtain the EGR rate based on the oxygen concentration in the engine exhaust gas and the excess air coefficient of the methanol-diesel dual-fuel engine;

[0009] S4: Based on the pressure inside the engine's high-pressure common rail, the EGR rate, and the excess air coefficient of the methanol-diesel dual-fuel engine, the engine rail pressure and oxygen sensor are jointly controlled.

[0010] Beneficial Effects: This invention provides an engine rail pressure-oxygen sensor joint control method and system. By obtaining the actual oxygen concentration in the engine exhaust gas based on the excess air coefficient of gasoline or diesel fuel, it further obtains the excess air coefficient of a methanol-diesel dual-fuel engine, thereby calculating the EGR rate. Combined with the pressure inside the engine's high-pressure common rail, this achieves joint control of the engine via rail pressure and oxygen sensors. This invention solves the problem of weak anti-interference capability in traditional control circuits. It accurately calculates the excess air coefficient for methanol-diesel dual-fuel engines, resulting in an excess air coefficient closer to actual operating conditions. This represents a key application direction combining automotive powertrain engineering and embedded control technology, improving engine combustion efficiency and emission performance. Attached Figure Description

[0011] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0012] Figure 1 This is a flowchart of the engine rail pressure-oxygen sensor joint control method of the present invention;

[0013] Figure 2 This is a schematic diagram of the heater MOSFET driving optocoupler circuit in an embodiment of the present invention;

[0014] Figure 3 This is a schematic diagram of the DIAHG signal optocoupler circuit in an embodiment of the present invention;

[0015] Figure 4 This is a schematic diagram of the DIAHD signal optocoupler circuit in an embodiment of the present invention;

[0016] Figure 5 This is a schematic diagram of the CJ125 chip circuit in an embodiment of the present invention;

[0017] Figure 6 This is a schematic diagram of the circuit connection of the oxygen sensor module in an embodiment of the present invention;

[0018] Figure 7 This is a schematic diagram of the heating module fault determination process in an embodiment of the present invention;

[0019] Figure 8 This is a schematic diagram of the communication protocol structure in an embodiment of the present invention;

[0020] Figure 9 This is a schematic diagram of the microcontroller module circuit in an embodiment of the present invention;

[0021] Figure 10 This is a schematic diagram of the operational amplifier module circuit in an embodiment of the present invention;

[0022] Figure 11 This is a schematic diagram of the isolation amplifier module circuit in an embodiment of the present invention;

[0023] Figure 12 This is a schematic diagram of the signal isolation output module circuit in an embodiment of the present invention;

[0024] Figure 13 This is a schematic diagram of the execution module circuit in an embodiment of the present invention;

[0025] Figure 14 This is a schematic diagram of the EGR rate calculation process in an embodiment of the present invention;

[0026] Figure 15 This is a schematic diagram illustrating the principle of the PID control algorithm in an embodiment of the present invention;

[0027] Figure 16 This is a schematic diagram illustrating the principle of the fuzzy PID control algorithm in an embodiment of the present invention. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] This embodiment introduces a combined control method for engine rail pressure and oxygen sensor, such as... Figure 1 As shown, it includes the following steps:

[0030] S1: Obtain the pressure inside the engine's high-pressure common rail;

[0031] S2: Obtain the excess air coefficient based on gasoline / diesel fuel through the oxygen sensor module to obtain the oxygen concentration in the engine exhaust gas, and then obtain the excess air coefficient of the methanol-diesel dual-fuel engine.

[0032] Preferably, the calculation method used to obtain the excess air coefficient corresponding to the methanol-diesel dual-fuel engine is as follows:

[0033] S21: Obtain the oxygen concentration in engine exhaust gas ;

[0034] Specifically, it is first based on the excess air coefficient of conventional fuels (including the excess air coefficient of gasoline or diesel fuel). With the oxygen concentration in engine exhaust The relation (1) is derived The calculation formula (2) is based on the measured values. The results calculated the exhaust gas ;

[0035] (1)

[0036] (2)

[0037] In the formula: Excess air coefficient based on gasoline / diesel fuel; The hydrogen-to-carbon ratio of the fuel; This refers to the oxygen concentration in the engine exhaust.

[0038] S22: Obtain the amount of each component in the engine exhaust gas after complete combustion of a unit mole of methanol-diesel mixture;

[0039] Specifically, this embodiment is based on the chemical reaction formula (3) obtained from the complete combustion of methanol and air, the chemical reaction formula (4) obtained from the complete combustion of diesel and air, and the molar percentage of methanol in the methanol-diesel blend. The amounts of carbon dioxide, oxygen, nitrogen, and water in the engine exhaust gas produced by the combustion of a unit mole of mixed fuel were obtained. Among these, the main components of diesel fuel are those with a carbon number range of C... 10 ~C 22 It is mainly composed of alkanes, cycloalkanes, and aromatics, with a carbon number of C60. 12 Hydrocarbons account for a dominant proportion of the total hydrocarbon content; among them, hydrocarbon C... 12 H 23 The carbon-hydrogen ratio of the sample is highly consistent with the weighted average carbon-hydrogen ratio of various hydrocarbon components in diesel fuel. Therefore, this embodiment uses C... 12 H 23 As a typical substance characterizing the overall elemental composition of diesel fuel, it can be calculated using the following chemical reaction formula (4).

[0040] (3)

[0041] (4)

[0042] Specifically, since the molar percentage of methanol in the blended fuel is Then the molar percentage of diesel in the blended fuel is Based on chemical reaction formulas (3) and (4), it is possible to deduce the composition of the engine exhaust gas. , , and The amount of substance. For example, its generation originates from the complete combustion of methanol and diesel: according to reaction formula (3), the molar percentage of methanol-diesel mixture per unit mole is... The complete combustion of methanol can produce mol Similarly, the molar percentage of a unit mole of methanol-diesel blend is 1- The complete combustion of diesel fuel can produce mol (i.e.) mol) Therefore, the total amount of fuel produced by the complete combustion of one mole of mixed fuel is... The amount of substance is:

[0043] mol;

[0044] in, The amount of methanol-diesel mixture produced in the engine exhaust after complete combustion of a unit mole of the mixture. Amount of substance; This represents the molar percentage of methanol in a methanol-diesel blend.

[0045] Using the method described above, it is possible to obtain the amount of methanol-diesel mixture produced in the engine exhaust gas after complete combustion of a unit mole of methanol-diesel mixture. The amount of substance is:

[0046] mol;

[0047] in, The amount of methanol-diesel mixture produced in the engine exhaust after complete combustion of a unit mole of the mixture. Amount of substance;

[0048] Specifically, the remaining gas in engine exhaust amount of substance It needs to be achieved through actual supply. With theoretical consumption Calculation of the difference:

[0049] mol;

[0050] in, After a unit mole of methanol-diesel blend is completely combusted, the amount of methanol-diesel blend in the engine exhaust gas is... Amount of substance; This refers to the excess air coefficient for a methanol-diesel dual-fuel engine.

[0051] Specifically, according to reaction formula (3), the molar percentage of methanol-diesel blend fuel per unit mole is: The complete combustion of methanol requires the consumption of mol Similarly, the molar percentage of a unit mole of methanol-diesel blend is 1- The complete combustion of diesel fuel requires 17.75 (1- ) mol Therefore, the total energy consumed by the complete combustion of one mole of mixed fuel is... Quantity (theoretical requirement) Quantity, denoted as )for: mol; therefore, based on the definition of excess air coefficient, it can be considered that the actual oxygen supplied per unit mole of methanol-diesel blend is... The amount of substance is: )mol; based on this, the remaining mol can be obtained Amount of substance .

[0052] Specifically, in a complete combustion reaction, It does not participate in chemical reactions. It is known to be present in air. The molar percentage is 0.21. Its molar percentage in air is 0.79, therefore in exhaust gas The amount of substance is equal to the actual amount supplied to the air. The amount of substance, that is:

[0053]

[0054] in, The amount of methanol-diesel mixture in the engine exhaust gas after complete combustion of a unit mole is... The amount of substance.

[0055] S23: Obtain the oxygen concentration in the engine exhaust gas based on the amount of each component in the engine exhaust gas after complete combustion of a unit mole of methanol-diesel mixture. The relationship between the excess air coefficient and the excess air coefficient of the methanol-diesel dual-fuel engine is used to obtain the excess air coefficient of the methanol-diesel dual-fuel engine.

[0056] Specifically, based on the amount of carbon dioxide, oxygen, nitrogen, and water in the exhaust gas. , , And the derivation formula (5) for oxygen concentration, yielding the oxygen concentration in engine exhaust gas. The relationship between the excess air coefficient and the methanol-diesel dual-fuel engine is shown in formula (6).

[0057] (5)

[0058] (6)

[0059] Furthermore, the excess air coefficient of the exhaust gas... Solving from equation (6), we obtain the excess air coefficient of the exhaust gas. With oxygen concentration in exhaust gas The relationship between the molar percentage of methanol (c1) and equation (7):

[0060] (7)

[0061] In the formula: This refers to the excess air coefficient for a methanol-diesel dual-fuel engine.

[0062] S3: Based on the oxygen concentration in the engine exhaust and the excess air coefficient of the methanol-diesel dual-fuel engine After iterative calculation, the EGR rate is obtained, such as... Figure 14 As shown;

[0063] The preferred method for obtaining the EGR rate is as follows:

[0064] S31: Set the initial EGR rate and obtain the oxygen concentration of the intake mixture. ;

[0065] Specifically, first, an initial value for the EGR rate is set, and the intake air-fuel mixture oxygen concentration is obtained based on this initial EGR rate setting. The expression (8);

[0066] (8)

[0067] In the formula: This refers to the oxygen concentration in the intake air mixture. This is the initial EGR rate; This refers to the oxygen concentration in the engine exhaust.

[0068] S32: Obtain the molar mass of engine exhaust gas ;

[0069] (9)

[0070] In the formula: This refers to the molar mass of the engine exhaust gas, specifically the molar mass of the EGR gas.

[0071] S33: Based on the oxygen concentration of the intake mixture and the molar mass in engine exhaust To obtain the ratio of the mass flow rate of engine exhaust gas to the mass flow rate of air. ;

[0072] Specifically, since the oxygen in the intake mixture is composed of a certain proportion of oxygen from the EGR and oxygen from the air (the exhaust pipe and the intake pipe are connected), expression (10) can be derived based on this composition relationship.

[0073] (10)

[0074] In the formula: This indicates the molar amount of oxygen in the intake air-fuel mixture; This indicates the molar amount of oxygen in the EGR in the intake air-fuel mixture; It represents the molar amount of oxygen in the air;

[0075] Since the mole fraction and the volume fraction are the same, a variant of equation (10) (11) can be obtained as follows:

[0076] (11)

[0077] In the formula, Indicates the oxygen concentration of the intake air mixture; This represents the molar flow rate of the intake air-fuel mixture, in kmol / h. This refers to the oxygen concentration in the engine exhaust. This represents the molar flow rate of the EGR, in kmol / h. This indicates the oxygen concentration in the air, which is 0.2095. This represents the molar flow rate of air, in kmol / h.

[0078] The following relationship exists between the molar flow rate, the mass flow rate, and the molar mass of a substance:

[0079] (12)

[0080] In the formula: The molar flow rate of the substance; Mass flow rate of the substance; denoted as . represents the molar mass of the substance.

[0081] Therefore, formula (11) can be transformed into:

[0082] (13)

[0083] in,

[0084] (14)

[0085] In the formula: , , These are the mass flow rates of the intake air-fuel mixture, engine exhaust gas, and air, respectively. , , These are the molar masses of the intake mixture, engine exhaust, and air, respectively. It is 28.9647 kg / kmol.

[0086] By combining equations (13) and (14) and simplifying, we obtain equation (15):

[0087] (15)

[0088] Specifically, during the first iteration, the formula contains an unknown quantity (the molar mass of the intake mixture). Therefore, it is assumed that it is equal to the molar mass of air (28.9647 kg / kmol), and the EGR rate is calculated accordingly.

[0089] S34: Obtain the EGR rate based on the ratio of the mass flow rate of the engine exhaust gas to the mass flow rate of the air; and update the molar mass of the intake mixture based on the EGR rate;

[0090] Specifically, according to the definition of EGR rate—the ratio of the mass of EGR gas to the total mass of the intake gas (expression (16), which can be obtained by algebraic transformation as expression (17)).

[0091] (16)

[0092] (17)

[0093] In the formula, For EGR gas mass, This refers to the quality of fresh air entering the engine's intake. EGR rate;

[0094] Preferably, the molar mass of the intake mixture is updated as follows:

[0095] Due to the total amount of substance in the intake mixture The amount of substance equal to the EGR gas The amount of matter with fresh air The sum, as in equation (18):

[0096] (18)

[0097] Substituting equation (12) into equation (18), we can obtain equation (19):

[0098] (19)

[0099] By combining equations (19) and (10), the molar mass of the intake air can be derived. See equation (20).

[0100] (20)

[0101] In this embodiment, the final EGR rate is obtained after 5 iterations of calculation, thus completing the solution for the EGR rate.

[0102] S35: Based on the EGR rate and the updated molar mass of the intake mixture, repeat the iterations set in S31-S34 to obtain the final EGR rate.

[0103] S4: Based on the pressure inside the engine's high-pressure common rail, the EGR rate, and the excess air coefficient of the methanol-diesel dual-fuel engine, the engine rail pressure and oxygen sensor are jointly controlled.

[0104] This embodiment also discloses a control system using an engine rail pressure-oxygen sensor joint control method, including: a rail pressure sensor, an oxygen sensor, an oxygen sensor module, a microcontroller module, an execution module, and an isolation sampling module;

[0105] The rail pressure sensor is used to obtain the internal pressure of the engine high-pressure common rail tube, and to obtain the voltage signal UB corresponding to the internal pressure of the engine high-pressure common rail tube.

[0106] The oxygen sensor is used to obtain the oxygen concentration difference inside and outside the oxygen sensor and the temperature when the oxygen sensor is working.

[0107] The oxygen sensor module is used to acquire the excess air coefficient voltage signal UA based on the oxygen concentration difference (gasoline / diesel fuel); and to acquire the voltage signal UR corresponding to the operating temperature of the oxygen sensor.

[0108] Specifically, the oxygen sensor is installed in the engine exhaust pipe. The LSU4.9 wide-range oxygen sensor used in this embodiment is a zirconium dioxide (ZrO2) type wide-range air-fuel ratio sensor, an improved design based on traditional oxygen sensors. It mainly consists of a heated narrow-range oxygen sensor, a pump battery, and a diffusion chamber. Compared to traditional narrow-range oxygen sensors, it adds two core components: the pump battery and the diffusion chamber. This wide-range oxygen sensor, with its special structural design, can not only achieve precise control of the air-fuel ratio in ordinary engines, but also demonstrates its application advantages in lean-burn engine air-fuel ratio control scenarios. The target operating temperature of the oxygen sensor is set at 795℃. Under this temperature condition, its built-in zirconium dioxide crystal, through the oxygen concentration difference between the inside and outside of the crystal, drives oxygen ions to migrate within the crystal, thereby generating a pumping oxygen current. This pumping oxygen current is transmitted to the matching oxygen sensor module. Simultaneously, the oxygen sensor outputs a signal representing its own temperature, which is also transmitted to the same oxygen sensor module.

[0109] Specifically, the oxygen sensor and oxygen sensor module are directly connected. To ensure the oxygen sensor operates at the target temperature of 795℃, the microcontroller needs to acquire a voltage signal UR reflecting the current temperature from the oxygen sensor module through an isolated sampling module. The control objective is to adjust UR to the reference voltage of 0.9V corresponding to 795℃. A fuzzy PID control algorithm is used to obtain the PWM signal, and a signal isolation output module is employed, such as... Figure 12 As shown, the MOSFET in the oxygen sensor module drives the oxygen sensor to heat it to the target temperature. The oxygen sensor module also amplifies and analyzes the pump current from the oxygen sensor, converting it into the corresponding excess air coefficient voltage signal UA. Simultaneously, it amplifies and analyzes the oxygen sensor's own temperature signal, converting it into the corresponding sensor temperature voltage signal UR. Furthermore, it diagnoses the oxygen sensor's operating status and outputs corresponding fault codes based on different sensor operating states. The principle of the fuzzy PID control algorithm in this embodiment is as follows: Figure 16 As shown;

[0110] Among them, the rail pressure sensor acquires the voltage signal UB corresponding to the internal pressure of the engine's high-pressure common rail, and the oxygen sensor module acquires the voltage signal UA based on the excess air coefficient of gasoline / diesel fuel and the voltage signal UR corresponding to the chip temperature when the oxygen sensor is working. All of these are implemented using the product's built-in functions, so they will not be described in detail here.

[0111] The oxygen sensor module in this embodiment uses the CJ125, an integrated control chip designed by Bosch GmbH, Germany, specifically for the LSU4.X series wide-range oxygen sensors, packaged in a 32-pin LQFP32 package. This chip, with its highly integrated modular design, not only simplifies the hardware circuit structure but also significantly improves the operational reliability of the wide-range oxygen sensor controller and air-fuel ratio control system. Its core functions include pump current control, oxygen concentration voltage regulation, sensor temperature monitoring, and fault diagnosis, and it is widely used in automotive exhaust treatment and engine air-fuel ratio closed-loop control. According to the technical specifications in the LSU4.9 wide-range oxygen sensor technical manual, the core heating parameters of this sensor are as follows: standard operating temperature is 795℃; rated supply voltage is 7.5V (corresponding to 7.5W heating power); heating element impedance is 3.2Ω at an ambient temperature of 20℃. It is particularly important to note that a short-term (≤30s) peak voltage of 13V is permissible during the cold start phase, but the steady-state operating voltage must be controlled within 12V.

[0112] Specifically, thermodynamic analysis shows that when the sensor reaches its optimal operating temperature of 790℃, a 7.5V supply voltage and a corresponding 1A operating current can achieve thermal equilibrium. During cold start-up, the initial 12V voltage generates a transient power of 45W (corresponding to a 3.75A inrush current), which places stringent requirements on the thermal management circuit: a closed-loop control strategy is needed to achieve a smooth transition of the temperature gradient, avoiding sensor failure due to thermal shock while ensuring that the current does not exceed the device's limits. Therefore, the oxygen sensor temperature needs to be monitored during operation.

[0113] The microcontroller module is used to acquire the voltage signal UB corresponding to the internal pressure of the engine's high-pressure common rail, the voltage signal UA based on the excess air coefficient of gasoline / diesel fuel, and the voltage signal UR corresponding to the temperature when the oxygen sensor is operating, through an isolated sampling module. Based on the target pressure value and the voltage signal UB corresponding to the internal pressure of the engine's high-pressure common rail, a PID control algorithm is used to obtain the rail pressure control PWM signal. Based on the voltage signal UA based on the excess air coefficient of gasoline / diesel fuel, the excess air coefficient is obtained to obtain the EGR rate, and then a PID control algorithm is used to obtain the EGR valve control PWM signal. Based on the voltage signal UR corresponding to the temperature when the oxygen sensor is operating, with the control target of adjusting UR to the reference voltage of 0.9V corresponding to 795℃, a fuzzy PID control algorithm is used to obtain the heating control PWM signal. The principle of the PID control algorithm in this embodiment is as follows: Figure 15 As shown;

[0114] Specifically, the rail pressure and excess air coefficient sampling module in this embodiment, i.e., the isolation sampling module, consists of an operational amplification module and an isolation amplification module, such as... Figure 10 and Figure 11 As shown, an isolation amplification + differential amplification scheme is adopted, which can isolate ground plane fluctuation interference, block high-frequency crosstalk, reduce signal distortion, significantly improve the long-term reliability and anti-interference capability of the rail pressure-oxygen sensor control system, reduce signal distortion, ensure control accuracy, and significantly reduce the risk of the system being affected by external interference. On-chip sampling is used for sampling, but the signal output range of the CJ125 and the rail pressure sensor is 0~5V, while the STM32's ADC reference voltage is 3.3V. Therefore, this embodiment achieves signal adaptation through isolation amplification + differential amplification: first, the 0~5V signal is converted to 0~2.5V, and then output as a ±4V differential signal; subsequently, the signal is amplified twice by a differential amplifier, ultimately achieving the conversion from the 0~5V signal to the 0~3.3V ADC signal. Evaluation shows that the maximum sampling frequency of this embodiment reaches 275kHz, far exceeding the sampling requirements of engine control.

[0115] In this embodiment, the microcontroller module uses STMicroelectronics' STM32F103C8T6 microprocessor as the core control unit, such as... Figure 9 As shown. This chip is a high-performance microcontroller from STMicroelectronics, suitable for real-time control and embedded applications. Its core functions and technical characteristics are as follows:

[0116] (1) It adopts a 32-bit ARM Cortex-M3 core with a maximum clock speed of 72MHz;

[0117] (2) Built-in 64KB on-chip flash memory;

[0118] (3) Equipped with 20KB of on-chip static RAM;

[0119] (4) Integrated 8MHz internal RC oscillator, supporting 4~16MHz external crystal oscillator;

[0120] (5) Equipped with a phase-locked loop (PLL) frequency multiplier, which can be configured to generate a 72MHz system clock;

[0121] (6) It integrates two 12-bit successive approximation A / D converters, supporting a total of 10 external input channels;

[0122] (7) Includes 7 timers (1 advanced control timer, 3 general-purpose timers, 2 basic timers, and 1 system timer), supporting input capture, output comparison, and PWM generation functions;

[0123] (8) Supports up to 16 channels of 16-bit pulse width modulation (PWM) output;

[0124] (9) Equipped with 3 Universal Synchronous / Asynchronous Serial Communication Interfaces (USART);

[0125] (10) Integrates two serial peripheral interfaces (SPI);

[0126] (11) Includes 2 I2C interfaces, supporting standard mode and 400kHz fast mode;

[0127] (12) It has one USB 2.0 full-speed device interface;

[0128] (13) Equipped with one Controller Area Network (CAN) module, supporting the CAN 2.0B protocol;

[0129] (14) Equipped with a 7-channel direct memory access (DMA) controller;

[0130] (15) Supports wide voltage supply (2.0V~3.6V) and integrates on-chip voltage regulator;

[0131] The execution module controls the fuel metering valve of the engine high-pressure fuel pump according to the rail pressure control PWM signal; controls the chip temperature of the oxygen sensor, i.e. the heating resistance of the oxygen sensor, through the heating module according to the heating control PWM signal; and controls the opening of the EGR valve connected to the engine intake and exhaust passages according to the EGR valve control PWM signal, ultimately realizing the joint control of the engine rail pressure and oxygen sensor.

[0132] Specifically, in this embodiment, the IRF540 N-channel MOSFET is selected as the core execution element, such as... Figure 13 This device employs a TrenchFET® trench structure, exhibiting excellent operational stability. Its extremely low on-resistance—only 0.032Ω at VGS=10V and 0.035Ω at VGS=4.5V—effectively reduces loop current loss. With a drain-source breakdown voltage of up to 100V, it boasts robust withstand voltage performance, capable of handling medium to high voltage applications. The continuous drain current is 45A at 25℃ (30A at 125℃), and the pulsed drain current can reach 135A, demonstrating significant high-current carrying capacity. Furthermore, in terms of reliability and adaptability, the device has a maximum power consumption of 61W at 25℃. Combined with a high junction temperature design of 175℃ and a low thermal resistance TO-220AB package, it offers excellent heat dissipation and high-temperature stability. It also complies with RoHS compliance requirements, making it perfectly suited for medium to high voltage and medium to high power design scenarios. At the control logic level, dynamic impedance matching is achieved by adjusting the PWM duty cycle.

[0133] Specifically, by controlling the fuel metering valve of the engine's high-pressure fuel pump, the pressure inside the engine's high-pressure common rail is controlled; and by controlling the opening of the EGR valves in the engine's intake and exhaust passages, the engine's EGR rate is controlled, including:

[0134] S41: When idling: When the pressure inside the engine's high-pressure common rail is less than the first pressure threshold (60MPa), the excess air coefficient of the methanol-diesel dual-fuel engine is set to... , EGR rate: 5% 10%;

[0135] In this embodiment, when the engine is in idling condition (at which time the engine has no external power output and the speed is maintained at the lowest stable speed), the pressure inside the high-pressure common rail of the engine is less than 60 MPa, ensuring that the rail pressure is controlled at a low level, usually 40-60 MPa, to avoid excessive fuel atomization and excessively rich air-fuel mixture caused by excessively high injection pressure. At the same time, the excess air coefficient of the methanol-diesel dual-fuel engine is set to 1.1-1.3, which is slightly higher than the theoretical air-fuel ratio, to ensure complete combustion to reduce idling vibration and HC emissions. The EGR rate is kept at a low level of 5%-10% to prevent excessive dilution of the air-fuel mixture by exhaust gas, which would lead to unstable combustion.

[0136] S42: When operating under partial load: the pressure inside the engine's high-pressure common rail is greater than or equal to the first pressure threshold (60 MPa) and less than the second pressure threshold (140 MPa), and the excess air coefficient of the methanol-diesel dual-fuel engine is set to... , EGR rate: 10% 30%;

[0137] In this embodiment, under partial load conditions (engine output power is 30%-70% of rated power, which is the main operating condition for daily driving), the rail pressure is adjusted to 60-140 MPa according to load requirements. By optimizing the injection pressure, the fuel atomization quality and mixture uniformity are improved. The excess air coefficient of the methanol-diesel dual-fuel engine is maintained in the range of 1.0-1.1, balancing combustion efficiency and emission control. The EGR rate can be moderately increased to 10%-30%. Exhaust gas recirculation is used to reduce the in-cylinder combustion temperature and suppress NO. X Emissions are reduced, while the clean combustion properties of methanol reduce particulate matter generation;

[0138] S43: Under full load conditions: When the pressure inside the engine's high-pressure common rail is greater than or equal to the second pressure threshold (140 MPa) and less than the third pressure threshold (200 MPa), the excess air coefficient of the methanol-diesel dual-fuel engine is set to... , EGR rate: 5%;

[0139] In this embodiment, when operating under full load (engine output rated power, such as high-speed overtaking or hill climbing), the rail pressure needs to be increased to the highest level (140-200 MPa) to ensure sufficient fuel supply and strong injection momentum. The excess air coefficient of the methanol-diesel dual-fuel engine is close to the theoretical value (0.95-1.05) to maximize fuel energy conversion efficiency. The EGR rate is reduced to below 5% or turned off to avoid the exhaust gas dilution mixture affecting power output. At the same time, the optimized ratio of methanol to diesel compensates for combustion stability under high load.

[0140] In this embodiment, when in transient transition conditions (such as acceleration and deceleration), the internal pressure of the engine's high-pressure common rail needs to respond quickly to load changes (rapidly increasing pressure during acceleration and timely decreasing pressure during deceleration) to avoid power interruption or excessively rich mixture caused by fuel supply lag. The excess air coefficient of the methanol-diesel dual-fuel engine is dynamically adjusted according to transient load fluctuations (the excess air coefficient of the methanol-diesel dual-fuel engine decreases during acceleration to meet power demand, and increases during deceleration to purify exhaust gas). The EGR rate is flexibly adapted by rapidly adjusting the valve opening. During acceleration, the EGR rate is temporarily reduced to ensure power response, and during deceleration, the EGR rate is increased to recover exhaust energy and reduce emissions, ensuring the smoothness and controllability of the transition process.

[0141] This embodiment requires targeted adjustments to the fuel injection strategy, combustion control parameters, and emission optimization targets of the methanol-diesel dual-fuel engine based on different engine operating conditions, fuel rail pressure, excess air coefficient, and EGR rate, in order to achieve synergistic optimization of power performance, economy, and emission indicators. The operating conditions cover typical engine operating scenarios, mainly including idling, partial load, full load, and transient transition conditions (such as acceleration and deceleration).

[0142] This embodiment establishes a rail pressure-oxygen sensor joint control system to achieve real-time adjustment of the thermal EGR rate in a methanol-diesel dual-fuel engine under low-load mode. This embodiment uses an STM32 microcontroller to build the dual-fuel engine rail pressure control system and a Bosch LSU4.9-based dual-channel wide-range oxygen sensor performance detection system. The system comprises three parts: hardware circuitry, software control, and a host computer display. The hardware circuitry includes modules for interface control, power supply, microcontroller, heating control, and communication. Based on the hardware circuitry, C language and LabVIEW are used as development tools to design the software control program and the host computer display program, respectively, to achieve rail pressure control of the dual-fuel engine and control of the pump current and temperature of the dual-channel oxygen sensors. The temperature of the oxygen sensor chip is controlled.

[0143] Specifically, this embodiment also includes a power supply module. The power supply module employs an isolated design, providing electrical isolation for the microcontroller module, oxygen sensor module, communication module, and heating module, effectively mitigating the risk of interference between modules. To adapt to the harsh operating environment of automotive engines, the system adopts a 12V battery power supply solution. The corresponding power architecture includes three independent voltage conversion modules, capable of achieving electrical isolation from 12V to 12V, a 12V to 5V step-down conversion, and a 5V to 3.3V secondary step-down conversion, meeting the voltage requirements of different modules.

[0144] Preferably, such as Figure 7 As shown, the method for determining whether the chip temperature of the oxygen sensor can be controlled via the heating module is as follows:

[0145] The system first completes the initialization configuration, including core parameters such as the judgment time interval and judgment variables. When the system waits for the preset judgment time interval, it reads the fault code output by the CJ125 chip.

[0146] When the heating module is not activated, acquire the heater gate control signal DIAHG and the heater drain current signal I_DIAHD from the oxygen sensor module; such as Figure 5 ;

[0147] If the heater gate control signal DIAHG is low and the heater drain current signal I_DIAHD ∈ -100µA~100µA, then the temperature of the oxygen sensor can be controlled by the heating module. Otherwise, the chip temperature of the oxygen sensor cannot be controlled by the heating module. In this case, the corresponding fault code is immediately fed back to the host computer.

[0148] When the heating module is started, the heater gate control signal and heater drain current signal I_DIAHD are acquired a set number of times at a set sampling time interval.

[0149] If the heater gate control signal DIAHG is high and the heater drain current signal I_DIAHD is in the range of -1000µA to -350µA, and the ratio of this number of times to the set number of times is greater than 0.95, then the heating module can control the chip temperature of the oxygen sensor. In this case, the heating module is considered to be normal. Otherwise, the heating module cannot control the chip temperature of the oxygen sensor. In this case, the heating module is considered to be abnormal, and the corresponding fault code is immediately fed back to the host computer.

[0150] Specifically, the independent oxygen sensor heater fault determination algorithm described above in this embodiment, combined with hardware signal feedback and software logic verification, enables accurate identification of faults such as heater open circuit, thereby improving system reliability and preventing system failures caused by oxygen sensor heater malfunctions.

[0151] Specifically, in a non-isolated design, the oxygen sensor module (using the CJ125 chip) shares a ground terminal with the oxygen sensor heating pin. During the initial heating phase, the oxygen sensor generates significant power, resulting in a large current injection into the ground plane. This severely interferes with the oxygen sensor module's ground plane, temporarily disabling its functionality. The module only returns to normal operation once the oxygen sensor temperature stabilizes and the heating power drops to a steady-state value. To address this issue, this embodiment employs optocoupler isolation to separate the oxygen sensor heating pin from the oxygen sensor module. While this fundamentally prevents a large current injection into the oxygen sensor module's ground plane, it introduces unique challenges to oxygen sensor fault diagnosis: due to the optocoupler isolation, the module's native fault diagnosis logic cannot obtain the heater's operating status. Therefore, this embodiment optimizes the optocoupler wiring topology and combines it with fault diagnosis code written in C language to construct a collaborative diagnostic scheme of "hardware signal feedback + software logic judgment." This effectively identifies faults such as open circuits and short circuits in the heater, preserving the core advantages of the isolation design while improving the completeness of the system's fault diagnosis.

[0152] like Figure 2 As shown, the PA8 pin of the microcontroller module outputs a heating control PWM signal. The logic level and voltage correspondence are as follows: logic 0 corresponds to 0V, and logic 1 corresponds to 3.3V. This PWM signal is isolated and converted by optocoupler U31 to generate a drive signal for MOSFET Q1. The logic level and voltage correspondence are as follows: logic 0 corresponds to 0V, and logic 1 corresponds to 12V. This drive signal is connected to the gate (G) of MOSFET Q1 through pin 6 of optocoupler U31. The drain (D) of MOSFET Q1 outputs signal H-1, which serves as the negative drive signal for the oxygen sensor heater (thermal resistance), used to control the on / off state of the oxygen sensor thermal resistance. The specific connection relationship is as follows... Figure 6 As shown; the positive terminal of the oxygen sensor heater (thermal resistance) is directly connected to a 12V power supply.

[0153] like Figure 2 , Figure 3As shown, the PWM drive signal DIAHG-12V (connected to the gate (G) of MOSFET Q1) is input to the signal input terminal of optocoupler U16. The signal level is defined as follows: logic 0 corresponds to 0V, logic 1 corresponds to 12V. After isolation and level conversion by optocoupler U16, the output signal level remains consistent (logic 0 corresponds to 0V, logic 1 corresponds to 5V). Figure 5 As shown, the converted 5V level PWM signal is connected to pin 4 (i.e., the DIAHG pin) of the oxygen sensor module.

[0154] like Figure 2 , Figure 4 As shown, the signal H-1 output from the drain (D) of MOSFET Q1 is input to the signal input terminal of optocoupler U17. After isolation and transmission by optocoupler U17, it is led out through its output pin (i.e., the DIAHD pin). As shown in Figure 4, this output pin (DIAHD pin) is connected to pin 6 (functional identifier: DIAHD) of the oxygen sensor module. Through the electrical isolation of optocoupler U17, physical isolation is achieved between the oxygen sensor heater circuit (the side where signal H-1 is located) and the oxygen sensor module side, avoiding mutual interference between the two circuits.

[0155] Specifically, the working principle of the oxygen sensor heater in this embodiment is explained as follows:

[0156] Power supply circuit configuration: The positive terminal of the built-in thermistor of the oxygen sensor heater is directly connected to the 12V vehicle power supply, and the negative terminal is connected to the source (S) of MOSFET Q1 through the drain (D) terminal, and finally grounded through the source, forming a complete power supply circuit to provide a stable power supply foundation for the heater. On / off control logic: When the optocoupler U31 outputs a 12V high-level drive signal (logic 1 state), MOSFET Q1 meets the conduction condition and turns on, the heater power supply circuit is closed, current flows through the built-in thermistor, heat is generated through the Joule effect, and the sensor heating process is started; when the optocoupler U31 outputs a 0V low-level signal (logic 0 state), MOSFET Q1 is turned off, the power supply circuit is disconnected, and the heating process is terminated.

[0157] To achieve precise control of the heater temperature, the control system outputs a pulse width modulation (PWM) signal and uses its periodic on / off characteristics to dynamically adjust the heating duty cycle, ultimately achieving dynamic and stable control of the heater temperature and ensuring that the oxygen sensor is in its optimal operating temperature range under all engine operating conditions.

[0158] Specifically, the core principle of the CJ125 chip in determining heater faults is to monitor the current (I_DIAHD) and voltage (V_DIAHD) of the DIAHD pin, and combine this with the high and low level states of DIAHG (heater gate control signal), to distinguish between the normal operating state and fault type of the heater. The specific logic is as follows: Under normal operating conditions: When the heater is on, the heater gate control signal DIAHG is at a high level (heater is on), then I_DIAHD is -1000µA to -350µA; when the heater is off, DIAHG is at a low level (heater is off), then I_DIAHD is 350µA to 10000µA. Under typical fault conditions: Ground short circuit (SC2G): When a ground short circuit fault occurs, DIAHG is at a low level, and the monitoring current I_DIAHD of the DIAHD pin exhibits a negative large current characteristic, with a range consistent with that when the heater is turned on (-1000 µA~-350 µA); Power supply short circuit (SC2VB): When a power supply short circuit fault occurs, DIAHG is at a high level, and the monitoring current I_DIAHD of the DIAHD pin ranges from -100 µA to 10000 µA, with the positive large current range (100 µA~10000 µA) serving as the fault characteristic criterion; Open circuit fault (OL): When an open circuit fault occurs, DIAHG is at a low level, and the monitoring current I_DIAHD of the DIAHD pin exhibits a small current characteristic, with a range of -100 µA~100 µA.

[0159] Specifically, the CJ125 chip monitors the current (I_DIAHD) and voltage (V_DIAHD) parameters of the DIAHD pin in real time, and combines this with the high and low level states of the heater gate control signal (DIAHG) to accurately determine the normal operating status and fault type of the heater. In this system design, the DIAHG pin and the DIAHD pin adopt an electrical isolation design: the system can directly identify the level state of the DIAHG pin through the on / off state of the optocoupler; however, the current signal of the DIAHD pin cannot be effectively transmitted to the control unit through the optocoupler. Therefore, this embodiment acquires the error codes output by the CJ125 chip through multiple pre-detections, and performs fault status analysis based on these error codes, ultimately achieving indirect and accurate determination of the heater's operating status and fault type.

[0160] Specifically, the DIAHD pin of the CJ125 chip is electrically isolated from the oxygen sensor heating circuit via an optocoupler. When the oxygen sensor heater is not turned on, the DIAHD pin is pulled down to ground via the pull-down resistor of the U17 optocoupler, and the current I_DIAHD flowing through the DIAHD pin approaches zero. According to the CJ125 chip's built-in open-circuit fault (OL) judgment rule: if an open-circuit fault occurs in the oxygen sensor heating circuit, the DIAHG signal is low, and the monitoring current I_DIAHD flowing through the DIAHD pin exhibits a small current characteristic, with a value range of -100 µA to 100 µA. The CJ125 chip will immediately determine that the heating circuit is in an open-circuit fault state.

[0161] When the oxygen sensor heating control function is activated, pin 3 of the optocoupler U17 corresponding to the DIAHD pin outputs a high level. At this time, the system meets the judgment conditions mentioned above: that is, when the heater is in the on state, the heater gate control signal (DIAHG) is high, and the current I_DIAHD flowing through the DIAHD pin is in the range of -1000 µA to -350 µA. The system will output a "normal" status code.

[0162] Specifically, to ensure stable system operation, this embodiment designs and optimizes the communication protocol scheme, covering frame header, frame trailer, data length, and data content. The specific definitions are as follows: the frame header uses hexadecimal (Hex) identifier "AA55", and the frame trailer uses hexadecimal (Hex) identifier "00 00 08 7F"; the data frame includes CJ125 diagnostic code signal, common rail pressure signal, oxygen sensor signal, temperature signal, and excess air coefficient signal, with the specific structure as follows... Figure 8 As shown.

[0163] Specifically, the PID control in this embodiment has advantages such as simple structure and good robustness. In the high-pressure common rail system, the dynamic characteristics of the rail pressure are mainly dominated by linear inertial elements such as fuel compressibility and injector flow characteristics, and the disturbance sources (such as the periodic fluctuations of the high-pressure pump) have modelable regularity. Since the system can be established with an accurate mathematical model through the mass-flow balance differential equation, traditional PID control is sufficient. The optimal control values ​​of Kp, Ki, and Kd were determined experimentally, achieving millisecond-level dynamic response while ensuring parameter stability. At the same time, the continuous correction effect of the integral term can effectively suppress the static pressure deviation caused by changes in fuel viscosity, and its low computational complexity makes it a perfect match for the high-frequency PWM control requirements of the fuel metering valve.

[0164] Specifically, the heating process of the wide-range oxygen sensor faces multiple complex operating conditions: the heating element exhibits a strong positive temperature coefficient (resistance increases non-linearly with temperature), exhaust flow disturbances cause drastic changes in the heat transfer coefficient, and the sensor's thermal inertia induces a significant hysteresis effect. Therefore, this embodiment combines the advantages of PID control and fuzzy control, employing a fuzzy PID controller for heating control of the wide-range oxygen sensor: based on real-time temperature deviation and rate of change, Kp, Ki, and Kd are dynamically adjusted to adapt to the non-linear characteristics of the oxygen sensor heating and dynamic disturbances in rail pressure, enhancing control adaptability and enabling rapid and accurate achievement of control objectives under different temperature, humidity, and other environmental conditions. For example, the proportional gain Kp is increased during the rapid heating phase to improve response speed, while the proportional gain is decreased and the integral action is strengthened during the isothermal phase to suppress overshoot.

[0165] Specifically, the rail pressure-oxygen sensor joint control system of this embodiment was deployed in the laboratory on a 135-cylinder single-cylinder methanol-diesel dual-fuel engine test platform. Its core service is to regulate the thermal EGR rate in real time under low engine load mode, and ultimately achieve the independent operation goal of "precise rail pressure control + engine closed-loop control", providing technical support for engine combustion optimization and stable operating conditions.

[0166] In the core rail pressure control stage, this embodiment's system constructs a three-channel PID control architecture based on an STM32F103C8T6 microcontroller for the methanol fuel common rail, diesel fuel common rail, and control rail required for engine operation. The methanol fuel common rail dynamically matches the in-cylinder direct injection pressure requirements according to engine load; the diesel common rail provides a stable pressure foundation for ignition diesel supply; and the control rail ensures the accuracy of the injector-driven fuel pressure. The STM32 acquires real-time rail pressure signals from the three rails through an isolation amplification module (converting 0~5V sensor signals to 0~3.3V signals adapted to a 3.3V ADC), and combines this with dynamic adjustment of the PWM duty cycle of the IRF540N channel MOSFET to achieve millisecond-level rail pressure response. The static rail pressure deviation is controlled within ±2%, laying the foundation for stable engine fuel supply. The entire system achieves communication between the upper and lower computers via RS-232 serial port (level conversion is completed by MAX232CSE). The upper computer can display the rail pressure, oxygen sensor temperature and key engine operating parameters in real time. The system can independently complete the dynamic adjustment of rail pressure, EGR rate regulation and closed-loop control of engine operating conditions without external intervention, providing a reliable experimental platform for emission control and combustion efficiency optimization of 135-bore single-cylinder engine under low load conditions.

[0167] This embodiment obtains the actual oxygen concentration in the engine exhaust gas based on the excess air coefficient of gasoline or diesel fuel, and then obtains the excess air coefficient of the methanol-diesel dual-fuel engine. Based on this, the EGR rate is calculated. Combined with the pressure inside the engine's high-pressure common rail, joint control of the engine is achieved through rail pressure and oxygen sensors. This invention solves the problem of weak anti-interference capability of traditional control circuits. It accurately calculates the excess air coefficient for methanol-diesel dual-fuel engines, and the calculated excess air coefficient is closer to actual operating conditions. This embodiment is particularly suitable for precise control of the thermal EGR rate under low-load conditions. It requires no specific hardware and can be achieved using only a conventional oxygen sensor, significantly reducing costs. It aims to improve engine combustion efficiency and emission performance, representing a key application direction combining automotive powertrain engineering and embedded control technology.

[0168] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An engine rail pressure-oxygen sensor combined control method characterized by, The method comprises the following steps: S1: obtaining the pressure inside the high-pressure common rail pipe of the engine; S2: obtaining the excess air coefficient based on gasoline / diesel fuel to obtain the oxygen concentration in the exhaust gas of the engine, and then obtaining the excess air coefficient of the methanol-diesel dual-fuel engine; The method for obtaining the excess air coefficient corresponding to the methanol-diesel dual-fuel engine is as follows: S21: obtaining the amount of substance of each component in the exhaust gas of the engine after complete combustion of unit mole of methanol-diesel mixed fuel, and the formula used is as follows: in, The amount of methanol-diesel mixture produced in the engine exhaust after complete combustion of a unit mole of the mixture. Amount of substance; This represents the molar percentage of methanol in a methanol-diesel blend. The amount of methanol-diesel mixture produced in the engine exhaust after complete combustion of a unit mole of the mixture. Amount of substance; The amount of methanol-diesel mixture in the engine exhaust gas after complete combustion of a unit mole is... Amount of substance; This refers to the excess air coefficient for a methanol-diesel dual-fuel engine. The amount of methanol-diesel mixture in the engine exhaust gas after complete combustion of a unit mole is... Amount of substance; S22: obtaining the oxygen concentration in the engine exhaust according to the amount of substance of each component in the engine exhaust after complete combustion of the unit mole of the methanol-diesel fuel mixed fuel and the relationship between the excess air coefficient corresponding to the methanol-diesel dual fuel engine to obtain the excess air coefficient corresponding to the methanol-diesel dual fuel engine; wherein the oxygen concentration in the exhaust gas of the engine The relationship between the excess air ratio corresponding to the methanol-diesel dual fuel engine is expressed as follows: The excess air coefficient corresponding to the methanol-diesel dual-fuel engine is expressed as follows: S3: obtaining the EGR rate according to the oxygen concentration in the exhaust gas of the engine and the excess air coefficient of the methanol-diesel dual-fuel engine; S4: realizing the joint control of the engine through the rail pressure and the oxygen sensor according to the pressure inside the high-pressure common rail pipe of the engine, the EGR rate and the excess air coefficient of the methanol-diesel dual-fuel engine.

2. The engine rail pressure-oxygen sensor combined control method according to claim 1, characterized by, The method for obtaining the EGR rate is as follows: S31: setting an initial EGR rate and obtaining the oxygen concentration of the intake mixture; S32: obtaining the molar mass in the exhaust gas of the engine; S33: obtaining the ratio of the mass flow of the exhaust gas of the engine to the mass flow of air according to the oxygen concentration of the intake mixture and the molar mass in the exhaust gas of the engine; S34: obtaining the EGR rate according to the ratio of the mass flow of the exhaust gas of the engine to the mass flow of air, and updating the molar mass of the intake mixture according to the EGR rate; S35: based on the EGR rate and the updated molar mass of the intake mixture, repeating the iteration set by S31-S34 for a certain number of times to obtain the final EGR rate.

3. The engine rail pressure-oxygen sensor combined control method according to claim 2, characterized by, In the S31, the oxygen concentration of the intake air mixture is acquired The formula used is as follows: In the formulae: is the oxygen concentration of the intake mixture; is the initial EGR rate; is the oxygen concentration in the exhaust gas of the engine.

4. The engine rail pressure-oxygen sensor combined control method according to claim 2, characterized by, In S32, the formula used to obtain the molar mass in the exhaust gas of the engine is as follows: wherein: The molar mass of the engine exhaust gas, i.e. the molar mass of the EGR gas, is calculated using the following formula.

5. The engine rail pressure-oxygen sensor combined control method according to claim 2, characterized by, In S33, the formula used to obtain the ratio of the mass flow of the exhaust gas of the engine to the mass flow of air is as follows: wherein represents the oxygen concentration of air; is the ratio of the mass flow of the engine exhaust gas to the mass flow of air; is the molar mass of the intake air mixture; is the molar mass of air.

6. The engine rail pressure-oxygen sensor combined control method according to claim 2, characterized by, In S34, the formula used to obtain the EGR rate is as follows: wherein is the mass of EGR gas, is the mass of fresh air in the engine intake air, is the EGR rate; The formula used to update the molar mass of the intake mixture is as follows: 。 7. The engine rail pressure-oxygen sensor combined control method according to claim 1, characterized by, S4 comprises: S41: When in idle operating condition: the pressure inside the high-pressure common rail pipe of the engine is less than the first pressure threshold; the excess air coefficient corresponding to the methanol-diesel dual-fuel engine: 10%; EGR rate: 5% 10%. S42: When in a partial load working condition: the pressure inside the high-pressure common rail pipe of the engine is greater than or equal to a first pressure threshold and less than a second pressure threshold; the excess air coefficient corresponding to the methanol-diesel dual-fuel engine: ; EGR rate: 10% 30%. S43: when in full load working condition: the pressure inside the high-pressure common rail pipe of the engine is greater than or equal to the second pressure threshold value and less than the third pressure threshold value; the excess air coefficient corresponding to the methanol-diesel dual-fuel engine: ; the EGR rate: 5%.

8. The control system of the engine rail pressure-oxygen sensor combined control method according to any one of claims 1 to 7, characterized by, a rail pressure sensor, an oxygen sensor, an oxygen sensor module, a microcontroller module, an execution module, and an isolated sampling module; The rail pressure sensor is used to obtain the pressure inside the high-pressure common rail pipe of the engine to obtain the voltage signal UB corresponding to the pressure inside the high-pressure common rail pipe of the engine; The oxygen sensor is used to obtain the difference in oxygen concentration inside and outside the oxygen sensor and the temperature of the oxygen sensor when it is working; The oxygen sensor module is used to obtain the excess air coefficient voltage signal UA based on gasoline / diesel fuel according to the difference in oxygen concentration, and obtain the voltage signal UR corresponding to the temperature of the oxygen sensor when it is working. The microcontroller module is used to acquire a voltage signal UB corresponding to an engine high-pressure common rail pipe internal pressure, an excess air coefficient voltage signal UA based on gasoline / diesel fuel, and a voltage signal UR corresponding to a temperature of the oxygen sensor in operation through an isolated sampling module; to acquire a rail pressure control PWM signal by using a PID control algorithm according to a target pressure value and the voltage signal UB corresponding to the engine high-pressure common rail pipe internal pressure; to acquire an excess air coefficient based on gasoline / diesel fuel according to the excess air coefficient voltage signal UA based on gasoline / diesel fuel, so as to acquire an EGR rate, and then acquire an EGR valve control PWM signal by using a PID control algorithm; and to acquire a heating control PWM signal by using a fuzzy PID control algorithm according to the voltage signal UR corresponding to the temperature of the oxygen sensor in operation. The execution module is used to control an engine high-pressure fuel pump fuel metering valve according to the rail pressure control PWM signal, control a chip temperature of the oxygen sensor through the heating module according to the heating control PWM signal, and control an EGR valve opening of an engine intake and exhaust passage according to the EGR valve control PWM signal, so as to finally realize joint control of the engine rail pressure and the oxygen sensor.

9. The control system of an engine rail pressure-oxygen sensor combined control method according to claim 8, characterized by, A method for determining whether the chip temperature of the oxygen sensor can be controlled by the heating module is as follows: When the heating module is not started, a heater gate control signal DIAHG and a heater drain current signal I_DIAHD of the oxygen sensor module are acquired; If the heater gate control signal DIAHG is at a low level and the heater drain current signal I_DIAHD ∈-100µA~100µA, the temperature of the oxygen sensor can be controlled by the heating module at this time, otherwise, the chip temperature of the oxygen sensor cannot be controlled by the heating module; After the heating module is started, the heater gate control signal and the heater drain current signal I_DIAHD are acquired for a set number of times every interval of a set sampling time interval; If the heater gate control signal DIAHG is at a high level and the heater drain current signal I_DIAHD ranges from-1000µA to-350µA for a number of times, if a ratio of the number of times to the set number of times is greater than 0.95, the chip temperature of the oxygen sensor can be controlled by the heating module, otherwise, the chip temperature of the oxygen sensor cannot be controlled by the heating module.

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