Brake liquid level signal identification circuit structure with fault diagnosis and diagnosis method

Abstract

The invention discloses a brake liquid level signal identification circuit with a fault diagnosis function and a diagnosis method. The liquid level sensor comprises a liquid level signal identification module M1 and a liquid level sensor circuit module M2. In the liquid level signal identification module M1, a whole formed by connecting a power supply V3, a diode D1 and a resistor R14 in series is connected with a whole formed by connecting a capacitor C5 and a resistor R15 in series in parallel, a resistor R13 is connected with the capacitor C5 in parallel, the capacitor C5 and the resistor R15 are led out to serve as an output end and are connected to external power supply voltage through the diode D1, and the resistor R14 and the resistor R15 are led out to be connected to a liquid level sensor circuit module M2 with a liquid level switch SW1. The liquid level signal recognition module detects the potential change in the liquid level sensor circuit module in real time to know whether the oil can liquid leakage fault exists or not, fault diagnosis including connection disconnection, signal ground short circuit and power supply short circuit on the internal modules is integrated, and the safety and reliability of vehicle braking are improved through the diagnosis.

Description

Technical Field

[0001] The present invention belongs to the field of passenger car sensor circuit design, and in particular relates to a brake fluid level signal recognition circuit structure with fault diagnosis and a diagnosis method. Background Art

[0002] Brake fluid level sensors are commonly used in vehicles to monitor brake fluid levels and sound an alarm when the fluid level is too low, which is crucial for driving safety. Brake fluid level sensors operate as normally closed electronic alarms. When the fluid level is normal, a magnet pulls the reed inside a reed switch, closing the circuit and turning off the alarm light. When the fluid level drops, a float pulls the magnet downward, opening the reed inside the reed switch, breaking the circuit and illuminating the alarm light. As vehicle braking safety requirements increase, existing brake fluid level sensors and detection circuits lack self-diagnostic capabilities, such as short-circuit and open-circuit fault diagnosis, making them unable to meet vehicle functional safety requirements. Summary of the Invention

[0003] In order to solve the problems existing in the background technology, the present invention proposes a brake fluid level signal recognition circuit structure and a diagnosis method with fault diagnosis.

[0004] The technical solutions of the present invention are as follows:

[0005] 1. A brake fluid level signal recognition circuit with fault diagnosis:

[0006] The circuit includes two parts: a liquid level signal recognition module M1 and a liquid level sensor circuit module M2; the liquid level signal recognition module M1 includes a power supply V3, a diode D1, resistors R13 to R15, a capacitor C5 and a diode D2. The power supply V3, diode D1 and resistor R14 are connected in series in sequence, and the capacitor C5 and resistor R15 are connected in series in sequence. The entire series connection of the power supply V3, diode D1 and resistor R14 and the entire series connection of the capacitor C5 and resistor R15 are connected in parallel. The resistor R13 is connected in parallel to the capacitor C5. The output end of the brake liquid level signal recognition circuit is drawn between the capacitor C5 and the resistor R15, and is simultaneously connected to the external power supply voltage through the diode D1. The output end of the liquid level sensor circuit module M2 with the liquid level switch SW1 is drawn between the resistor R14 and the resistor R15.

[0007] The positive electrode of the power supply V3 is connected to the anode of the diode D1, the cathode of the diode D1 is connected to the resistor R14, and the negative electrode of the power supply V3 is grounded.

[0008] The liquid level sensor circuit module M2 includes a liquid level switch SW1, a resistor R17 and a resistor R16. The liquid level switch SW1 and the resistor R16 are connected in parallel and then in series between the resistor R17 and the ground. The other end of the resistor R17 is connected between the resistor R14 and the resistor R15 of the liquid level signal recognition module M1.

[0009] It also includes a micro control unit MCU, and the output end of the brake fluid level signal recognition circuit is connected to the ADC analog-to-digital conversion port MCU_AD_BFLI of the micro control unit MCU.

[0010] The liquid level switch SW1 changes synchronously with the liquid level. When the liquid level is normal, the liquid level switch SW1 is closed; when the liquid level drops below the alarm line, the SW1 switch is opened.

[0011] 2. A method for diagnosing and identifying brake fluid level signal faults:

[0012] The method detects the potential change in the liquid level sensor circuit module M2 in real time through the liquid level signal recognition module M1, and distinguishes and judges the following working conditions: 1 - normal liquid level, 2 - abnormal liquid level, 3 - liquid level signal short circuit to ground, 4 - liquid level signal short circuit to power supply, and 5 - liquid level signal is not connected.

[0013] The method specifically receives the voltage value U(MCU_AD_BFLI) in real time through the ADC analog-to-digital conversion port MCU_AD_BFLI of the microcontroller unit MCU and then performs the following judgment:

[0014] When the liquid level switch SW1 in the liquid level sensor is closed, the voltage value U(MCU_AD_BFLI) is U(R17_2)*(R13) / (R13+R15), and U(R17_2)=(V3-VD)*((R17) / / (R15+R13)) / ((R17) / / (R15+R13)+R14), which is the following formula, then the liquid level is normal at this time;

[0015]

[0016] When the liquid level switch SW1 in the liquid level sensor is disconnected, the voltage value U(MCU_AD_BFLI) is 0V, and U(R17_2)=(V3-VD)*((R17+R16) / / (R15+R13)) / (((R17+R16) / / (R15+R13))+R14)), the following formula is expanded, then the liquid level is abnormal at this time;

[0017]

[0018] When the voltage value U(MCU_AD_BFLI) is 0V, the liquid level signal is short-circuited to the ground;

[0019] When the voltage value U(MCU_AD_BFLI) is the voltage value of the controller's internal constant voltage output source 3.3V plus 0.7V, the liquid level signal is short-circuited to the power supply;

[0020] When the voltage value U(MCU_AD_BFLI) is (V3-VD)*(R13 / (R14+R15+R13)), the liquid level signal is not connected.

[0021] In all three cases, fault injection is performed on terminal 2 of resistor R17 in the circuit diagram, and the liquid level switch SW1 can be closed or closed.

[0022] Wherein, V3 represents the constant voltage output source inside the controller, whose output voltage is 3.3V, VD represents the forward voltage drop of diode D1, which is 0.7V, U(R17_2) represents the voltage at pin 2 of resistor R17, and R13 to R17 represent the resistance values ​​of the corresponding resistors R13 to R15.

[0023] The circuit of the present invention is designed in the controller, and there is an external vehicle-mounted 12V to 3.3V power supply module inside the controller. The constant voltage output source inside the controller can actually also be used to supply 3.3V to the external power supply.

[0024] The beneficial effects of the present invention are:

[0025] In the present invention, the liquid level signal recognition module M1 detects the potential changes in the liquid level sensor circuit module M2 in real time to determine whether there is an oil tank leakage fault. The M1 module also integrates internal fault diagnosis of the M2 circuit module: including disconnection, signal short circuit to ground, and short circuit to power supply. The above diagnosis improves the safety and reliability of vehicle braking. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a schematic diagram of a brake fluid level signal recognition circuit with fault diagnosis. DETAILED DESCRIPTION

[0027] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0028] like Figure 1 As shown, the circuit includes two parts: a liquid level signal recognition module M1 and a liquid level sensor circuit module M2, and a microcontroller unit MCU; the liquid level signal recognition module M1 includes a power supply V3, a diode D1, resistors R13 to R15, a capacitor C5 and a diode D2. The power supply V3, the diode D1 and the resistor R14 are connected in series in sequence, and the capacitor C5 and the resistor R15 are connected in series in sequence. The whole of the power supply V3, the diode D1 and the resistor R14 is connected in series and the whole of the capacitor C5 and the resistor R15 is connected in parallel. The resistor R13 is connected in parallel to the capacitor C5. The output end of the brake liquid level signal recognition circuit is drawn between the capacitor C5 and the resistor R15 and is connected to the external power supply voltage 3.3V through the diode D1. The output end of the liquid level sensor circuit module M2 with the liquid level switch SW1 is drawn between the resistor R14 and the resistor R15.

[0029] The positive electrode of the power supply V3 is connected to the anode of the diode D1, the cathode of the diode D1 is connected to the resistor R14, and the negative electrode of the power supply V3 is grounded.

[0030] The liquid level sensor circuit module M2 includes a liquid level switch SW1, a resistor R17 and a resistor R16. The liquid level switch SW1 and the resistor R16 are connected in parallel and then in series between the resistor R17 and the ground. The other end of the resistor R17 that is not connected to the liquid level switch SW1 and the resistor R16 is connected between the resistor R14 and the resistor R15 of the liquid level signal recognition module M1.

[0031] The output end of the brake fluid level signal recognition circuit is connected to the ADC analog-to-digital conversion port MCU_AD_BFLI of the micro control unit MCU, that is, the voltage is detected in real time through the ADC analog-to-digital conversion port MCU_AD_BFLI to determine the brake fluid level signal state.

[0032] like Figure 1 As shown, in a specific implementation, in the liquid level signal recognition module M1, the positive electrode of pin 1 of the power supply V3 is connected to the anode of pin 1 of the diode D1, the cathode of pin 2 of the diode D1 is connected to pin 2 of the resistor R14, pin 1 of the resistor R14 is connected to pin 1 of the resistor R15 and pin 2 of the resistor R17, pin 2 of the resistor R15 is connected to pin 1 of the resistor R13, pin 1 of the diode D2, pin 1 of the capacitor C5, and the ADC analog-to-digital conversion port MCU_AD_BFLI of the microcontroller unit MCU; pin 2 of the capacitor C5 is grounded, pin 2 of the resistor R13 is grounded, and pin 1 of the diode D2 is connected to the power supply voltage 3V3.

[0033] like Figure 1 As shown, in the liquid level sensor circuit module M2, pin 1 of the resistor R17 is connected to pin 2 of the resistor R16 and pin 1 of the liquid level switch SW1, pin 1 of the resistor R16 is grounded, and pin 2 of the liquid level switch SW1 is grounded.

[0034] In this implementation, diodes D1 and D2 are BAS21. Resistor R14 has a resistance of 3K, resistor R15 has a resistance of 30K, resistor R13 has a resistance of 100K, resistor R17 has a resistance of 1K, resistor R16 has a resistance of 3.57K, and capacitor C5 has a capacitance of 100nF. Power supply V3 has a voltage of 3.3V. The forward voltage drop of diodes D1 and D2 is 0.7V.

[0035] The liquid level switch SW1 changes synchronously with the liquid level. In the liquid level sensor circuit module M2, when the liquid level is normal, the liquid level switch SW1 is closed; when the liquid level drops below the alarm line, the SW1 switch is opened.

[0036] Under the circuit design scheme of the present invention, the method further detects the potential changes in the liquid level sensor circuit module M2 in real time through the liquid level signal recognition module M1, and can distinguish and judge the following working conditions of the liquid level sensor through different voltage values: 1-normal liquid level, 2-abnormal liquid level, 3-liquid level signal short-circuited to ground, 4-liquid level signal short-circuited to power supply, 5-liquid level signal is not connected.

[0037] In the specific implementation, the voltage value U(MCU_AD_BFLI) is received in real time through the ADC analog-to-digital conversion port MCU_AD_BFLI of the microcontroller unit MCU, and the following judgment is made:

[0038] 1) Liquid level is normal:

[0039] The SW1 switch in the liquid level sensor is closed:

[0040] In the liquid level sensor circuit module M2, the liquid level sensor resistor R16 is short-circuited to ground. At this time, the voltage of pin 2 of resistor R17 is:

[0041] U(R17_2)=(V3-VD)*((R17) / / (R15+R13)) / ((R17) / / (R15+R13)+R14)

[0042] U(R17_2)=(3.3V-0.7V)*((1K) / / (30K+100K)) / ((1K) / / (30K+100K)+3K))=0.65V

[0043] Here, / / represents parallel connection, and / represents division. When the switch is closed, resistor R16 is short-circuited, so terminal 1 of resistor R17 is grounded. The overall circuit structure is V3 passing through diode D1 and then through resistor R14 in series. R15 and R13 are connected in series and then in parallel with R17.

[0044] At this time, the voltage U(MCU_AD_BFLI) at MCU_AD_BFLI is:

[0045] U(MCU_AD_BFLI)=U(R17_2)*(R13) / (R13+R15)=0.65V*(100K) / (100K+30K)=0.5V

[0046] Therefore, when the voltage value received in real time by the ADC analog-to-digital conversion port MCU_AD_BFLI is 0.5V, the brake fluid level signal is normal and the fluid level is normal.

[0047] 2) Abnormal liquid level:

[0048] The SW1 switch in the liquid level sensor is disconnected:

[0049] The liquid level sensor resistor R17 in M2 is connected in series with the resistor R16. At this time, the voltage of pin 2 of the resistor R17 is:

[0050] U(R17_2)=(V3-VD)*((R17+R16) / / (R15+R13)) / (((R17+R16) / / (R15+R13))+R14))

[0051] U(R17_2)=(3.3V-0.7V)*((1K+3.75K) / / (30K+100K)) / (((1K+3.57K) / / (30K+100K))+3K)=1.56V

[0052] At this time, the voltage U2 at MCU_AD_BFLI is:

[0053] U(MCU_AD_BFLI)=U(R17_2)*(R13) / (R13+R15)=1.56V*(100K) / (100K+30K)=1.2V

[0054] Therefore, when the voltage value received in real time by the ADC analog-to-digital conversion port MCU_AD_BFLI is 1.2V, the brake fluid level signal is abnormal and the fluid level is abnormal.

[0055] 3) Liquid level signal is short-circuited to ground:

[0056] When the pin 2 of the R17 resistor in the liquid level sensor is short-circuited to the ground, U(R17_2)=0V.

[0057] At this time, the voltage U2 at MCU_AD_BFLI is:

[0058] U(MCU_AD_BFLI)=U(R17_2)*R13 / (R15+R13)=0V*(100K) / (30K+100K)=0V

[0059] Therefore, when the voltage value received in real time by the ADC analog-to-digital conversion port MCU_AD_BFLI is 0V, the brake fluid level signal is abnormal and the fluid level signal is short-circuited to the ground.

[0060] 4) Liquid level signal is short-circuited to the power supply:

[0061] When the pin 2 of the R17 resistor in the liquid level sensor is short-circuited to the ground, U(R17_2)=16V.

[0062] At this time, theoretically, the voltage U3 at MCU_AD_BFLI is:

[0063] U(MCU_AD_BFLI)=U(R17_2)*R13 / (R15+R13)=16V*(100K) / (30K+100K)=12.3V

[0064] However, because diode D2 is clamped to the 3.3V power supply, the actual voltage at MCU_AD_BFLI is:

[0065] U(MCU_AD_BFLI)=3.3V+0.7V=4V

[0066] Therefore, when the voltage value received in real time by the ADC analog-to-digital conversion port MCU_AD_BFLI is 4V, the brake fluid level signal is abnormal and the fluid level signal is short-circuited to the power supply.

[0067] 5) Liquid level signal is not connected:

[0068] Pin 2 of resistor R17 in the liquid level sensor is disconnected.

[0069] The resistor R16 of the liquid level sensor in M2 is short-circuited to ground. At this time, the voltage U2 at MCU_AD_BFLI is:

[0070] U(MCU_AD_BFLI)=(V3-VD)*(R13 / (R14+R15+R13))=(3.3V-0.7V)*(100K / (3K+30K+100K))=1.95V.

[0071] Therefore, when the voltage value received in real time by the ADC analog-to-digital conversion port MCU_AD_BFLI is 1.95V, the brake fluid level signal is abnormal and the fluid level signal is not connected.

[0072] The judgment logic under the final recognition circuit is as follows:

[0073] Table 1

[0074] state U(MCU_AD_BFLI) 1-Liquid level normal 0.4V <U(MCU_AD_BFLI)<0.6V 2- Abnormal liquid level 1.1V<U(MCU_AD_BFLI)<1.3V 3-Liquid level signal short circuit to ground U(MCU_AD_BFLI)<0.1V 4-Liquid level signal short circuit to power supply 3.9V <U(MCU_AD_BFLI)<4.1V 5-Liquid level signal is not connected 1.85V<U(MCU_AD_BFLI)<2.05V

[0075] By using the above table to make a real-time judgment on the interface U (MCU_AD_BFLI), it is possible to immediately obtain whether the liquid level signal is in an abnormal state and the type of abnormal state.

[0076] Therefore, the present invention detects the potential changes in the liquid level sensor circuit module M2 in real time through the liquid level signal recognition module M1, and quickly and accurately knows whether there is an oil tank leakage fault in real time. The M1 module integrates fault diagnosis of the M2 circuit module, thereby improving the safety and reliability of vehicle braking.

[0077] The above specific embodiments are used to illustrate the present invention rather than to limit the present invention. Any modifications and changes made to the present invention within the spirit of the present invention and the protection scope of the claims shall fall within the protection scope of the present invention.

[0078] The above description is only a preferred embodiment of the present invention. Therefore, any equivalent changes or modifications made according to the structure, characteristics and principles described in the scope of the patent application of the present invention are included in the scope of the patent application of the present invention.

Claims

1. A brake fluid level signal recognition circuit with fault diagnosis, characterized by: It consists of two parts: a liquid level signal recognition module M1 and a liquid level sensor circuit module M2; the liquid level signal recognition module M1 includes a power supply V3, a diode D1, resistors R13 to R15, a capacitor C5 and a diode D2. The power supply V3, the diode D1 and the resistor R14 are connected in series in sequence, and the capacitor C5 and the resistor R15 are connected in series in sequence. The whole of the power supply V3, the diode D1 and the resistor R14 is connected in series and the whole of the capacitor C5 and the resistor R15 is connected in parallel. The resistor R13 is connected in parallel to the capacitor C5. The output end of the brake liquid level signal recognition circuit is drawn between the capacitor C5 and the resistor R15, and is connected to the external power supply voltage through the diode D1 at the same time. The output end of the liquid level sensor circuit module M2 with the liquid level switch SW1 is drawn between the resistor R14 and the resistor R15.

2. The brake fluid level signal recognition circuit with fault diagnosis according to claim 1, characterized in that: The positive electrode of the power supply V3 is connected to the anode of the diode D1, the cathode of the diode D1 is connected to the resistor R14, and the negative electrode of the power supply V3 is grounded.

3. The brake fluid level signal recognition circuit with fault diagnosis according to claim 1, characterized in that: The liquid level sensor circuit module M2 includes a liquid level switch SW1, a resistor R17 and a resistor R16. The liquid level switch SW1 and the resistor R16 are connected in parallel and then in series between the resistor R17 and the ground. The other end of the resistor R17 is connected between the resistor R14 and the resistor R15 of the liquid level signal recognition module M1.

4. The brake fluid level signal recognition circuit with fault diagnosis according to claim 1, characterized in that: It also includes a micro control unit MCU, and the output end of the brake fluid level signal recognition circuit is connected to the ADC analog-to-digital conversion port MCU_AD_BFLI of the micro control unit MCU.

5. The brake fluid level signal recognition circuit with fault diagnosis according to claim 1, characterized in that: The liquid level switch SW1 changes synchronously with the liquid level. When the liquid level is normal, the liquid level switch SW1 is closed; when the liquid level drops below the alarm line, the SW1 switch is opened.

6. A brake fluid level signal fault diagnosis and identification method applied to the brake fluid level signal identification circuit according to any one of claims 1 to 5, characterized in that: The method detects the potential change in the liquid level sensor circuit module M2 in real time through the liquid level signal recognition module M1, and distinguishes and judges the following working conditions: 1 - normal liquid level, 2 - abnormal liquid level, 3 - liquid level signal short circuit to ground, 4 - liquid level signal short circuit to power supply, and 5 - liquid level signal is not connected.

7. A brake fluid level signal fault diagnosis and identification method applied to the brake fluid level signal identification circuit of claim 6, characterized in that: The method specifically receives the voltage value U(MCU_AD_BFLI) in real time through the ADC analog-to-digital conversion port MCU_AD_BFLI of the microcontroller unit MCU and then performs the following judgment: When the voltage value U(MCU_AD_BFLI) is U(R17_2)*(R13) / (R13+R15), and U(R17_2)=(V3-VD)*((R17) / / (R15+R13)) / ((R17) / / (R15+R13)+R14), the liquid level is normal. When U(R17_2)=(V3-VD)*((R17+R16) / / (R15+R13)) / (((R17+R16) / / (R15+R13))+R14)), the liquid level is abnormal at this time; When the voltage value U(MCU_AD_BFLI) is 0V, the liquid level signal is short-circuited to the ground; When the voltage value U(MCU_AD_BFLI) is the voltage value of the constant voltage output source inside the controller plus 0.7V, the liquid level signal is short-circuited to the power supply; When the voltage value U(MCU_AD_BFLI) is (V3-VD)*(R13 / (R14+R15+R13)), the liquid level signal is not connected. Wherein, / / represents parallel calculation, / represents division, V3 represents the constant voltage output source inside the controller, whose output voltage is 3.3V, VD represents the forward voltage drop of diode D1, which is 0.7V, U(R17_2) represents the voltage at pin 2 of resistor R17, and R13 to R17 represent the resistance values ​​of the corresponding resistors.

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