Exhaust temperature acquisition system for vehicle
阅读说明：本技术 一种车用排气温度采集系统 (Exhaust temperature acquisition system for vehicle ) 是由 李曦 林伟勋 周宇浩 李怡 于 2020-11-20 设计创作，主要内容包括：本发明公开了一种车用排气温度采集系统,属于汽车排气温度采集技术领域,包括置于待测排气环境的热电偶传感器和置于汽车冷端环境的电压采集电路、外部励磁电流源电路和微控制器；电压采集电路采集热电偶传感器产生的差动电压信号；外部励磁电流源电路测量冷端环境的冷端电压；微控制器将冷端电压信号换算后得到的冷端温度信号,进而转换为冷端补偿电压信号以对差动电压信号进行冷端补偿得到热电偶传感器的绝对电压信号,通过微控制器计算得到待测排气的实际温度。本发明通过对热电偶传感器的电压信号进行增益,经采集后得到热端与冷端的温度差,并通过测量冷端电阻进行温度补偿,得到实际的温度值,有效地提高了温度测量的精度。(The invention discloses an exhaust temperature acquisition system for a vehicle, which belongs to the technical field of automobile exhaust temperature acquisition and comprises a thermocouple sensor arranged in an exhaust environment to be detected, a voltage acquisition circuit arranged in an automobile cold end environment, an external excitation current source circuit and a microcontroller; the voltage acquisition circuit acquires a differential voltage signal generated by the thermocouple sensor; an external excitation current source circuit measures the cold end voltage of a cold end environment; the microcontroller converts the cold end temperature signal obtained after the cold end voltage signal conversion into a cold end compensation voltage signal so as to perform cold end compensation on the differential voltage signal to obtain an absolute voltage signal of the thermocouple sensor, and the actual temperature of the exhaust to be measured is obtained through calculation of the microcontroller. The invention gains the voltage signal of the thermocouple sensor, obtains the temperature difference between the hot end and the cold end after acquisition, and obtains the actual temperature value by measuring the cold end resistance for temperature compensation, thereby effectively improving the temperature measurement precision.)
1. The system for collecting the exhaust temperature for the vehicle is characterized by comprising a thermocouple sensor arranged in an exhaust environment to be detected and a collecting device arranged in an environment at the cold end of the vehicle, wherein the thermocouple sensor is connected with the collecting device through a lead;
the acquisition device comprises a voltage acquisition circuit, an external excitation current source circuit and a microcontroller;
the voltage acquisition circuit is respectively connected with the thermocouple sensor and the microcontroller; the external excitation current source circuit is connected to the microcontroller;
the voltage acquisition circuit is used for acquiring a differential voltage signal generated by the thermocouple sensor and inputting a voltage signal obtained by gain amplification of the differential voltage signal to the microcontroller;
the external excitation current source circuit is used for providing constant current, measuring cold end voltage of a cold end environment and transmitting a measured cold end voltage signal to the microcontroller;
the microcontroller is used for converting the cold end voltage signal to obtain a cold end temperature signal, linearly converting the cold end temperature signal to a cold end compensation voltage signal to perform cold end compensation on a differential voltage signal generated by the thermocouple sensor to obtain an absolute voltage signal of the thermocouple sensor, and calculating the actual temperature of the exhaust to be measured through the microcontroller.
2. The exhaust temperature acquisition system for the vehicle as claimed in claim 1, wherein the microcontroller comprises an a/D conversion module, an SPI communication module, a data processing module and a CAN communication module;
the input end of the A/D conversion module is connected with the external excitation current source circuit, and the output end of the A/D conversion module is connected with the first input end of the data processing module; the input end of the SPI communication module is connected with the voltage acquisition circuit, and the output end of the SPI communication module is connected with the second input end of the data processing module; the output end of the data processing module is connected with the input end of the CAN communication module; the output end of the CAN communication module is connected with an external communication receiving device;
the SPI communication module is used for setting the gain of the voltage variable gain circuit; the A/D conversion module is used for receiving the cold end voltage signal and transmitting the cold end voltage signal to the data processing module; the data processing module is used for calculating the real-time temperature of exhaust and sending the real-time temperature information to the upper computer through the CAN communication module.
3. The exhaust temperature acquisition system for the vehicle as claimed in claim 1 or 2, wherein the voltage acquisition circuit comprises a voltage bias circuit, a linear reference power circuit, a voltage variable gain circuit and an A/D acquisition circuit;
the voltage bias circuit is connected to the thermocouple sensor, the voltage bias circuit is also connected to the A/D acquisition circuit through the voltage variable gain circuit, the voltage variable gain circuit is connected to the microcontroller, and the linear reference power supply circuit is connected to the A/D acquisition circuit;
the voltage bias circuit is used for providing stable reference potential for the differential voltage signal generated by the thermocouple sensor; the voltage of the linear reference power supply circuit is used for providing stable reference voltage for the differential voltage signal acquisition; the voltage variable gain circuit is used for amplifying the differential voltage signal and transmitting the amplified differential voltage signal to the A/D acquisition circuit; the A/D acquisition circuit is used for acquiring the amplified differential voltage signal and transmitting the differential voltage signal to the microcontroller.
4. The exhaust temperature collection system for the vehicle of claim 3, wherein the voltage bias circuit comprises a capacitor C1, a capacitor C2, a capacitor C3, a resistor R1 and a resistor R2;
the capacitor C2 is connected in series with the capacitor C3 and then connected in parallel with the capacitor C1, and the resistor R1 is connected in series with the resistor R2;
a voltage signal V1 and a voltage signal V2 at two ends of the thermocouple sensor are input into the voltage bias circuit, and a voltage signal V2 is connected with a voltage bias provided by the voltage division of the output voltage of the linear reference power circuit through a resistor R1 and a resistor R2; the capacitor C1, the capacitor C2 and the capacitor C3 are used for filtering the voltage signal V1 and the voltage signal V2 and then leading the filtered voltage signals to the voltage variable gain circuit.
5. The exhaust temperature collecting system according to claim 4, wherein the microcontroller is further configured to set a gain of the voltage variable gain circuit according to a range of differential voltage, and the voltage signal obtained by amplifying a voltage difference between the voltage signal V1 and the voltage signal V2 by the voltage variable gain circuit is collected by the A/D converter circuit.
6. The exhaust temperature collecting system for vehicle as claimed in claim 5, wherein the A/D converting circuit collects a voltage value of
Wherein GAIN is a GAIN multiple, VREFP is an output voltage of the linear reference power circuit, and VREFN is a ground voltage.
7. The exhaust gas temperature acquisition system for the vehicle as claimed in claim 6, wherein the output voltage of the linear reference power supply circuit is 4V.
8. The exhaust temperature collecting system for the vehicle as claimed in any one of claims 1 to 7, wherein said external excitation current source circuit comprises a constant current source, a thermistor R4, a resistor R3, a capacitor C4, a capacitor C5 and an inductance L1;
the thermistor R4 is connected in parallel with the capacitor C4, and the capacitor C4 is connected in parallel with the capacitor C5; the resistor R3 and the inductor L1 are connected in series;
the constant current source is used for providing constant current to the thermistor R4 and generating a cold end voltage signal which enters the microcontroller after being filtered by the resistor R3, the capacitor C4, the capacitor C5 and the inductor L1 to calculate a cold end temperature.
9. The system of claim 8, wherein the cold end temperature is calculated by the formula:
wherein R istIs the resistance value of the thermistor R4 at the current temperature, R is the nominal resistance value of the thermistor at the normal temperature, B is the parameter of the thermistor, T1The temperature is Kelvin at room temperature.
Technical Field
The invention belongs to the technical field of automobile exhaust temperature acquisition, and particularly relates to an automobile exhaust temperature acquisition system.
Background
As Chinese economy develops and enters the transformation and upgrading stage, environmental protection treatment is increasingly paid attention by people. The exhaust emission of motor vehicles is one of the main causes of air pollution, the state upgrades the relevant emission standards of the motor vehicles, and the detection strength of the emission standards of the motor vehicles is increased, so that the exhaust treatment is an important test which must be faced by the motor vehicle industry at present. An important part of an exhaust gas treatment system is used for measuring and controlling the exhaust temperature of a motor vehicle, and a high-temperature-resistant temperature sensor for measuring the exhaust temperature is particularly important as a core component of the exhaust gas treatment system.
Influenced by environmental factors, the exhaust temperature sensor needs to work in a high-temperature environment for a long time and simultaneously needs to bear the vibration of an engine and the integral vibration of a vehicle, so that the exhaust temperature sensor needs to have the characteristics of high temperature resistance, excellent shock resistance and sensitive response at the same time. The temperature element of prior art's exhaust temperature sensor all adopts PT200 resistance, and temperature element PT200 resistance is placed at the high temperature measurement end, and the lead wire machinery or welded connection that high temperature resistant and mutual insulation are passed through to measurement end and cold junction, and the cold junction is connected the standard plug-in components that link to each other with motor vehicle control, and machinery or welded connection have the shortcoming of structural stability difference, and it is very easily to take place to destroy under high temperature and the vibration environment for a long time to be located for temperature sensor's life reduces. Although the prior art tries to improve the secondary structure, the improved structure is complex, the manufacturing difficulty is high, the cost is high, and the popularization and the use are difficult.
Disclosure of Invention
Aiming at the defects or the improvement requirements of the prior art, the invention provides a vehicle exhaust temperature acquisition system, so that the technical problems of poor high-temperature resistance stability and low acquisition precision of an exhaust temperature acquisition device in the prior art are solved.
In order to achieve the above object, according to one aspect of the present invention, there is provided an exhaust temperature collecting system for a vehicle, including a thermocouple sensor disposed in an exhaust environment to be measured and a collecting device disposed in an environment at a cold end of the vehicle, the thermocouple sensor being connected to the collecting device through a wire;
the acquisition device comprises a voltage acquisition circuit, an external excitation current source circuit and a microcontroller;
the voltage acquisition circuit is respectively connected with the thermocouple sensor and the microcontroller; the external excitation current source circuit is connected to the microcontroller;
the voltage acquisition circuit is used for acquiring a differential voltage signal generated by the thermocouple sensor and inputting a voltage signal obtained by gain amplification of the differential voltage signal to the microcontroller;
the external excitation current source circuit is used for providing constant current, measuring cold end voltage of a cold end environment and transmitting a measured cold end voltage signal to the microcontroller;
the microcontroller is used for converting the cold end voltage signal to obtain a cold end temperature signal, linearly converting the cold end temperature signal to a cold end compensation voltage signal to perform cold end compensation on a differential voltage signal generated by the thermocouple sensor to obtain an absolute voltage signal of the thermocouple sensor, and calculating the actual temperature of the exhaust to be measured through the microcontroller.
Preferably, the microcontroller comprises an A/D conversion module, an SPI communication module, a data processing module and a CAN communication module;
the input end of the A/D conversion module is connected with the external excitation current source circuit, and the output end of the A/D conversion module is connected with the first input end of the data processing module; the input end of the SPI communication module is connected with the voltage acquisition circuit, and the output end of the SPI communication module is connected with the second input end of the data processing module; the output end of the data processing module is connected with the input end of the CAN communication module; the output end of the CAN communication module is connected with an external communication receiving device;
the SPI communication module is used for setting the gain of the voltage variable gain circuit; the A/D conversion module is used for receiving the cold end voltage signal and transmitting the cold end voltage signal to the data processing module; the data processing module is used for calculating the real-time temperature of exhaust and sending the real-time temperature information to the upper computer through the CAN communication module.
Preferably, the voltage acquisition circuit comprises a voltage bias circuit, a linear reference power circuit, a voltage variable gain circuit and an A/D acquisition circuit;
the voltage bias circuit is connected to the thermocouple sensor, the voltage bias circuit is also connected to the A/D acquisition circuit through the voltage variable gain circuit, the voltage variable gain circuit is connected to the microcontroller, and the linear reference power supply circuit is connected to the A/D acquisition circuit;
the voltage bias circuit is used for providing stable reference potential for the differential voltage signal generated by the thermocouple sensor; the voltage of the linear reference power supply circuit is used for providing stable reference voltage for the differential voltage signal acquisition; the voltage variable gain circuit is used for amplifying the differential voltage signal and transmitting the amplified differential voltage signal to the A/D acquisition circuit; the A/D acquisition circuit is used for acquiring the amplified differential voltage signal and transmitting the differential voltage signal to the microcontroller.
Preferably, the voltage bias circuit includes a capacitor C1, a capacitor C2, a capacitor C3, a resistor R1, and a resistor R2;
the capacitor C2 is connected in series with the capacitor C3 and then connected in parallel with the capacitor C1, and the resistor R1 is connected in series with the resistor R2;
a voltage signal V1 and a voltage signal V2 at two ends of the thermocouple sensor are input into the voltage bias circuit, and a voltage signal V2 is connected with a voltage bias provided by the voltage division of the output voltage of the linear reference power circuit through a resistor R1 and a resistor R2; the capacitor C1, the capacitor C2 and the capacitor C3 are used for filtering the voltage signal V1 and the voltage signal V2 and then leading the filtered voltage signals to the voltage variable gain circuit.
Preferably, the microcontroller is further configured to set a gain of the voltage variable gain circuit according to a range of differential voltage, and the voltage signal obtained by amplifying a voltage difference between the voltage signal V1 and the voltage signal V2 by the voltage variable gain circuit is collected by the a/D conversion circuit.
Preferably, the voltage value collected by the A/D conversion circuit is
Wherein GAIN is a GAIN multiple, VREFP is an output voltage of the linear reference power circuit, and VREFN is a ground voltage.
Preferably, the output voltage of the linear reference power supply circuit is 4V.
Preferably, the external excitation current source circuit includes a constant current source, a thermistor R4, a resistor R3, a capacitor C4, a capacitor C5, and an inductance L1;
the thermistor R4 is connected in parallel with the capacitor C4, and the capacitor C4 is connected in parallel with the capacitor C5; the resistor R3 and the inductor L1 are connected in series;
the constant current source is used for providing constant current to the thermistor R4 and generating a cold end voltage signal which enters the microcontroller after being filtered by the resistor R3, the capacitor C4, the capacitor C5 and the inductor L1 to calculate a cold end temperature.
Preferably, the calculation formula of the cold end temperature is as follows:
wherein R istIs the resistance value of the thermistor R4 at the current temperature, R is the nominal resistance value of the thermistor at the normal temperature, B is the parameter of the thermistor, T1The temperature is Kelvin at room temperature.
Preferably, the output current of the constant current source is 11 μ a.
In general, compared with the prior art, the above technical solution contemplated by the present invention can achieve the following beneficial effects:
1. according to the invention, the voltage signal of the thermocouple sensor is gained, the temperature difference between the hot end and the cold end is obtained after the voltage signal is collected, and the temperature compensation is carried out by measuring the cold end resistance, so that the actual temperature value is obtained, and the temperature measurement precision is effectively improved;
2. the microcontroller adopted by the invention CAN provide SPI communication, CAN communication and high-precision A/D conversion, and CAN effectively ensure the accuracy of temperature signal acquisition, the stability of communication with an upper computer and the precision of cold end temperature measurement.
Drawings
FIG. 1 is a schematic structural diagram of an exhaust temperature collection system for a vehicle according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of a voltage acquisition circuit provided by an embodiment of the present invention;
fig. 3 is a schematic diagram of an external excitation current source circuit according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
Fig. 1 is a schematic structural diagram of an exhaust gas temperature acquisition system for a vehicle according to an embodiment of the present invention. As shown in fig. 1, the present invention provides an exhaust temperature collecting system for a vehicle, which includes a thermocouple sensor and a collecting device. The thermocouple sensor is arranged in the temperature environment of exhaust to be detected, the acquisition device is arranged in the temperature environment of the cold end of the automobile, and the thermocouple sensor is connected with the acquisition device through a lead.
The acquisition device consists of a voltage acquisition circuit, an external excitation current source circuit and a microcontroller.
Specifically, the microcontroller consists of an A/D conversion module, an SPI communication module, a data processing module and a CAN communication module. The input end of the A/D conversion module is connected with the external excitation current source circuit, and the output end of the A/D conversion module is connected with the first input end of the data processing module; the input end of the SPI communication module is connected with the voltage acquisition circuit, and the output end of the SPI communication module is connected with the second input end of the data processing module; the output end of the data processing module is connected with the input end of the CAN communication module; and the output end of the CAN communication module is connected with an external communication receiving device.
The working principle of the acquisition device is as follows: after the microcontroller is started, firstly, system initialization is carried out, a gain multiple is set according to the specific range of voltage fluctuation of the thermocouple sensor, then, a voltage signal of the thermocouple sensor is read through the SPI communication module, a voltage signal of a sampling resistor passing through an external excitation current source circuit is read through the A/D conversion module, operation is carried out on the voltage signal to obtain cold junction temperature compensation voltage, then, corresponding operation is carried out on the voltage signal data of the thermocouple sensor to obtain a temperature value which needs to be actually measured, finally, the temperature data are sent to an upper computer through the CAN communication module, and the temperature data are repeatedly operated in the microcontroller through a timer in one period.
To explain further, as shown in fig. 1, the voltage acquisition circuit is composed of a voltage bias circuit, a linear reference power supply circuit, a voltage variable gain circuit and an a/D acquisition circuit.
Specifically, the voltage bias circuit comprises a capacitor C1, a capacitor C2, a capacitor C3, a resistor R1 and a resistor R2, wherein the capacitor C2 is connected in series with the capacitor C3 and then connected in parallel with the capacitor C1, and the resistor R1 is connected in series with the resistor R2.
Fig. 2 is a schematic diagram of a voltage acquisition circuit according to an embodiment of the present invention. Voltage signals V1 and V2 of the thermocouple sensor are input into the voltage bias circuit, wherein V2 is connected with voltage bias provided by the output voltage of the existing reference power supply circuit after being divided by R1 and R2, voltage signals V1 and V2 are filtered by capacitors C1, C2 and C3 and then are led into the voltage variable gain circuit, and the microcontroller sets the gain of the voltage variable gain circuit through an SPI bus according to the range of the actual signal. In this embodiment, the output voltage of the linear reference power supply circuit is 4V, and since a 4V reference power supply is adopted, a signal is required to be as large as possible during gain, and the maximum signal cannot exceed the reference power supply voltage.
Preferably, the variable gain stages of the voltage variable gain circuit are 2, 4, 6, 8, 16, 32, 64, 128. For example, if the thermocouple sensor operates at 0-30mV, the gain factor is set to 128, and if the thermocouple sensor operates at 0-60mV, the gain factor is set to 64.
The voltage variable gain circuit amplifies the voltage difference between the voltage signals V1 and V2 to form a voltage signal V3, transmits the voltage signal V3 to the 16-bit A/D conversion circuit for collection, and sends the voltage signal V3 to the microcontroller through the SPI bus.
The voltage value collected by the A/D conversion circuit is as follows:
wherein GAIN is a GAIN multiple, VREFP is an output voltage of the linear reference power circuit, and VREFN is a ground voltage.
Fig. 3 is a schematic diagram of an external excitation current source circuit according to an embodiment of the present invention. The external excitation current source circuit consists of a constant current source, a thermistor R4, a resistor R3, a capacitor C4, a capacitor C5, an inductor L1 and a plurality of leads. The thermistor R4 is connected in parallel with the capacitor C4, and the capacitor C4 is connected in parallel with the capacitor C5; the resistor R3 and the inductor L1 are connected in series.
Specifically, the constant current source is configured to provide a constant current to the thermistor R4 and generate a cold-end voltage signal, and the cold-end voltage signal enters the microcontroller after being filtered by the resistor R3, the capacitor C4, the capacitor C5, and the inductor L1 to calculate a cold-end temperature, where the calculation formula is as follows:
wherein R istIs the resistance value of the thermistor R4 at the current temperature, R is the nominal resistance value of the thermistor at the normal temperature, B is the parameter of the thermistor, T1The temperature is Kelvin at room temperature.
Further, the present inventionThe calculation process of the data processing module is as follows: the differential voltage of the thermocouple sensor is V1-V2, which is relative to the temperature difference Thot-Tcold。ThotTo measure the tip temperature, it is located in the exhaust environment being measured. T iscoldReferred to as the cold end temperature, which is located in the measurement system environment. Since the thermocouple sensor can only measure one temperature difference, it cannot measure an absolute temperature. In order to determine the absolute temperature of the measured environment, cold end compensation is therefore required. To obtain TcoldThen, a standard thermocouple lookup table is used to find its equivalent cold junction voltage. Next, differential thermocouple voltages V1-V2 were measured and the equivalent cold end voltage was added. Finally, the resulting voltage is converted to temperature using a standard thermocouple lookup table. All the above processes are performed within the data processing module.
In one embodiment of the invention, TcoldAnd 20 ℃, wherein the thermocouple sensor is a K-type thermocouple sensor. The cold end equivalent voltage was 0.798mV according to a type K thermocouple table. Next, the measured differential thermocouple voltages V1-V2 are added to the cold end equivalent voltage. The thermocouple voltage was measured to be 4.096mV, and the total voltage was 0.798mV +4.096mV versus 4.894 mV. The resulting voltage is then converted to temperature according to a type K thermocouple table, and the process is completed within the microcontroller.
Further, based on the design of the present invention, when the voltage acquisition circuit measures the voltage of the thermocouple sensor, the gain amplification factor of the signal can be manually set according to the magnitude of the acquired signal, so that the signal approaches the maximum measurement range, and the reading precision is improved. The temperature compensation is carried out on the voltage signal of the cold end resistor, so that the temperature measurement precision is effectively improved, and in addition, the DC-DC power supply module adopted by the invention is compatible with a 24V/12V power supply simultaneously, so that the vehicle exhaust temperature acquisition system based on the invention can be applied to more occasions and feels good detection precision.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.