Method for diagnosing a liquid level sensor

Abstract

The application provides a liquid level sensor diagnosis method. The liquid level sensor diagnosis method comprises the following steps: detecting the signal of the output end of a signal comparison circuit; if the output end of the signal comparison circuit outputs a PWM signal; detecting the voltage of a first detection contact and a second detection contact of a liquid level detection equivalent circuit; if the voltage of the first detection contact is greater than a ninth threshold value and the voltage of the second detection contact is less than a seventh threshold value, diagnosing that at least one detection contact of the liquid level detection equivalent circuit is in an open circuit state under a full liquid level condition; wherein the ninth threshold value is related to the voltage of an internal power supply, the seventh threshold value is greater than zero and the difference between the seventh threshold value and zero is within a set range. In this way, the abnormal state of the detection contact of the liquid level sensor in an open circuit state under a full liquid level condition can be accurately diagnosed, which helps to improve the detection accuracy of the liquid level sensor and improve driving safety.

Description

Technical Field

[0001] This invention relates to the field of electronic circuit technology, and in particular to a diagnostic method for a liquid level sensor. Background Technology

[0002] Monitoring the coolant level in a car's engine is crucial. In high-temperature conditions, unknowingly low coolant levels can lead to engine overheating, potentially causing cylinder scoring. In low-temperature conditions, a low coolant level can cause the engine or radiator to freeze and become damaged, severely impacting driving safety. Therefore, a coolant level sensor is installed in the vehicle's system to detect the coolant level, diagnose whether it is full or empty, and prompt the user to take appropriate action. The circuit design and diagnostic scheme of the coolant level sensor are of great significance for the safe operation of the car engine and related equipment.

[0003] Existing diagnostic methods for liquid level sensors cannot clearly diagnose faults in the sensor's detection contacts, thus failing to promptly identify and locate problems with these contacts, posing a threat to safe driving. Summary of the Invention

[0004] This invention provides a diagnostic method for a liquid level sensor, which can accurately diagnose the abnormal state of the sensor's detection contact being open-circuited when the liquid level is full. This helps to improve the detection accuracy of the liquid level sensor and enhance driving safety.

[0005] To achieve the above objectives, the present invention provides a diagnostic method for a liquid level sensor. The liquid level sensor includes a liquid level detection equivalent circuit, a diagnostic pull-down resistor, a first capacitor, and a signal comparison circuit. The signal input terminal is connected to the first input terminal of the signal comparison circuit and the first connection terminal of the first capacitor. The first detection contact of the liquid level detection equivalent circuit is connected to an internal power supply, the first input terminal of the signal comparison circuit, and the first connection terminal of the first capacitor. The second detection contact of the liquid level detection equivalent circuit is grounded after passing through the diagnostic pull-down resistor. The second connection terminal of the first capacitor is connected to the second detection contact of the liquid level detection equivalent circuit. The diagnostic method for the liquid level sensor includes: detecting the signal at the output terminal of the signal comparison circuit; if the output terminal of the signal comparison circuit outputs a PWM signal; detecting the voltage of the first and second detection contacts of the liquid level detection equivalent circuit; if the voltage of the first detection contact is greater than a ninth threshold and the voltage of the second detection contact is less than a seventh threshold, diagnosing that at least one detection contact of the liquid level detection equivalent circuit is in an open-circuit state under full liquid level conditions; wherein, the ninth threshold is related to the voltage of the internal power supply, and the seventh threshold is greater than zero and the difference from zero is within a set range.

[0006] Optionally, the diagnostic method for the liquid level sensor further includes: detecting the signal at the output terminal of the signal comparison circuit; if the output terminal of the signal comparison circuit outputs a PWM signal, detecting the voltage of the first detection contact and the second detection contact of the liquid level detection equivalent circuit; if the voltage of the first detection contact of the liquid level detection equivalent circuit is greater than a third threshold and the voltage of the second detection contact of the liquid level detection equivalent circuit is less than or equal to a fourth threshold, diagnosing that the first detection contact is short-circuited to the external power supply when the liquid level is empty; if the voltage of the first detection contact of the liquid level detection equivalent circuit is greater than a fifth threshold and the voltage of the second detection contact of the liquid level detection equivalent circuit is greater than a sixth threshold, diagnosing that the second detection contact is short-circuited to the external power supply when the liquid level is empty; wherein the third threshold and the sixth threshold are both related to the voltage of the external power supply, the fourth threshold is related to the capacitance value of the first capacitor, and the fifth threshold is related to the voltage of the internal power supply.

[0007] Optionally, the diagnostic method for the liquid level sensor further includes: detecting the signal at the output terminal of the signal comparison circuit; if the output terminal of the signal comparison circuit continuously outputs a low-level signal, detecting the voltage of the first detection contact and the second detection contact of the liquid level detection equivalent circuit; if the voltage of the first detection contact of the liquid level detection equivalent circuit is less than a seventh threshold and the voltage of the second detection contact is less than or equal to a fourth threshold, diagnosing the first detection contact as being short-circuited to ground in the case of an empty liquid level; if the output terminal of the signal comparison circuit outputs a PWM signal, detecting the voltage of the first detection contact and the second detection contact of the liquid level detection equivalent circuit; if the voltage of the first detection contact of the liquid level detection equivalent circuit is greater than an eighth threshold and the voltage of the second detection contact of the liquid level detection equivalent circuit is less than a fourth threshold, diagnosing the second detection contact as being short-circuited to ground in the case of an empty liquid level; wherein, the fourth threshold is related to the capacitance value of the first capacitor, the seventh threshold is greater than zero and the difference from zero is within a set range, and the eighth threshold is related to the voltage of the internal power supply.

[0008] Optionally, during the process of detecting the signal at the output terminal of the signal comparison circuit, detecting the voltage of the first detection contact of the liquid level detection equivalent circuit, and detecting the voltage of the second detection contact of the liquid level detection equivalent circuit, the signal input terminal continuously inputs a PWM signal.

[0009] Optionally, the liquid level sensor includes a first signal acquisition terminal, a second signal acquisition terminal, and a third signal acquisition terminal; the first signal acquisition terminal is connected to a first detection contact of the liquid level detection equivalent circuit, the second signal acquisition terminal is connected to a second detection contact of the liquid level detection equivalent circuit, and the third signal acquisition terminal is connected to the output terminal of the signal comparison circuit; the voltages of the first and second detection contacts of the liquid level detection equivalent circuit are detected at the first and second signal acquisition terminals, respectively, and the signal at the output terminal of the signal comparison circuit is detected at the third signal acquisition terminal.

[0010] Optionally, the liquid level sensor further includes a signal input circuit, one end of which is connected to the signal input terminal, and the other end of which is connected to the first connection terminal of the first capacitor and the first detection contact of the liquid level detection equivalent circuit.

[0011] Optionally, the signal input circuit includes a first switch and a second switch. The control terminal of the first switch is connected to the signal input terminal. The first connection terminal of the first switch is connected to an internal power supply. The second connection terminal of the first switch is grounded. The control terminal of the second switch is connected to the first connection terminal of the first switch. The first connection terminal of the second switch is connected to an internal power supply. The second connection terminal of the second switch is connected to the first detection contact of the liquid level detection equivalent circuit and the first connection terminal of the first capacitor.

[0012] Optionally, the signal comparison circuit compares the reference signal with the signal at the first input terminal of the signal comparison circuit and then outputs the corresponding signal.

[0013] Optionally, the signal comparison circuit includes a comparator, a fifth resistor, a sixth resistor, a seventh resistor, and an eighth resistor; one end of the fifth resistor is connected to the signal input terminal and the first connection terminal of the first capacitor, the other end of the fifth resistor is connected to the first signal input terminal of the comparator and one end of the sixth resistor, the other end of the sixth resistor is connected to the output port of the signal comparison circuit, one end of the seventh resistor is connected to the internal power supply, the other end of the seventh resistor is connected to one end of the eighth resistor and the reference signal input terminal of the comparator, and the other end of the eighth resistor is grounded.

[0014] Optionally, the capacitance of the liquid level detection equivalent circuit is greater when the liquid level is full than when the liquid level is empty, and the resistance is less when the liquid level is full than when the liquid level is empty.

[0015] In the diagnostic method for a liquid level sensor provided by this invention, the signal at the output terminal of the signal comparison circuit is first detected. If the output terminal of the signal comparison circuit outputs a PWM signal, the voltage of the first and second detection contacts of the liquid level detection equivalent circuit is then detected. If the voltage of the first detection contact is greater than a ninth threshold and the voltage of the second detection contact is less than a seventh threshold, it is diagnosed that at least one detection contact of the liquid level detection equivalent circuit is in an open-circuit state under full liquid level conditions. The ninth threshold is related to the voltage of the internal power supply, and the seventh threshold is greater than zero and the difference from zero is within a set range. Using this diagnostic method for a liquid level sensor, the abnormal state of an open-circuit detection contact under full liquid level conditions can be accurately diagnosed, which helps improve the detection accuracy of the liquid level sensor and enhance driving safety. Attached Figure Description

[0016] Figure 1 A flowchart of a diagnostic method for a liquid level sensor provided in an embodiment of the present invention.

[0017] Figure 2 The circuit diagram of a liquid level sensor provided in an embodiment of the present invention is shown. Detailed Implementation

[0018] In order to accurately diagnose the abnormal state of the detection contacts of the liquid level sensor, improve the detection accuracy of the liquid level sensor, and improve driving safety, this invention provides a diagnostic method for the liquid level sensor.

[0019] The diagnostic method for the liquid level sensor proposed in this invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The advantages and features of this invention will become clearer from the following description. It should be noted that the drawings are all in a very simplified form and use non-precise proportions, and are only used to facilitate and clarify the illustration of the embodiments of this invention.

[0020] Figure 1 A flowchart of a diagnostic method for a liquid level sensor provided in an embodiment of the present invention. Figure 2 The circuit diagram of a liquid level sensor provided in an embodiment of the present invention is shown.

[0021] like Figure 2 As shown, the liquid level sensor includes a liquid level detection equivalent circuit, a diagnostic pull-down resistor R11, a first capacitor C1, and a signal comparison circuit. The signal input terminal is connected to the first input terminal of the signal comparison circuit and the first connection terminal of the first capacitor C1. The first detection contact P of the liquid level detection equivalent circuit is connected to the internal power supply VCC, the first input terminal of the signal comparison circuit, and the first connection terminal of the first capacitor C1, respectively. The second detection contact N of the liquid level detection equivalent circuit is grounded after passing through the diagnostic pull-down resistor R11. The second connection terminal of the first capacitor C1 is connected to the second detection contact N of the liquid level detection equivalent circuit.

[0022] refer to Figure 1 As shown, the diagnostic method for the liquid level sensor includes: detecting the signal at the output terminal of the signal comparison circuit; if the output terminal of the signal comparison circuit outputs a PWM signal; detecting the voltage of the first detection contact P and the second detection contact N of the liquid level detection equivalent circuit; if the voltage of the first detection contact P of the liquid level detection equivalent circuit is greater than a ninth threshold and the voltage of the second detection contact N of the liquid level detection equivalent circuit is less than a seventh threshold, diagnosing that at least one detection contact of the liquid level detection equivalent circuit is in an open-circuit state under full liquid level conditions; wherein, the ninth threshold is related to the voltage of the internal power supply, and the seventh threshold is greater than zero and the difference between it and zero is within a set range.

[0023] Specifically, the ninth threshold is close to the voltage of the internal power supply VCC, and the ninth threshold is related to the voltage of the internal power supply VCC and the circuit status of the liquid level sensor. The seventh threshold is close to zero, and the difference between the seventh threshold and zero is within a small set range. For example, the ninth threshold is 3.2V and the seventh threshold is 0.5V, but it is not limited to these. In this embodiment, the circuit status of the liquid level sensor includes the resistance of the components in the circuit, etc.

[0024] In this embodiment, the signal comparison circuit compares the reference signal with the signal at its first input terminal and then outputs a corresponding signal. Figure 2 As shown, the first input terminal of the signal comparison circuit is connected to the first connection terminal of the first capacitor C1 at node A.

[0025] The liquid level detection equivalent circuit is a load circuit, and it has different resistance and capacitance values ​​when the detected liquid level is empty and full. The resistance and capacitance values ​​of the liquid level detection equivalent circuit can be adjusted according to the actual liquid level state. Specifically, the capacitance of the liquid level detection equivalent circuit is much larger when the liquid level is full than when it is empty, and the resistance is smaller when the liquid level is full than when it is empty.

[0026] In this embodiment, during the detection of the signal at the output terminal of the signal comparison circuit, the voltage of the first detection contact of the liquid level detection equivalent circuit, and the voltage of the second detection contact of the liquid level detection equivalent circuit, a PWM signal is continuously input to the signal input terminal. For example, the duty cycle of the PWM signal is 1%, thus shortening the charging duration of the capacitor in the liquid level sensor, but this is not a limitation.

[0027] It should be noted that when one detection contact (i.e., the first or second detection contact) of the liquid level detection equivalent circuit is in an open-circuit state at full liquid level, and a PWM signal is input to the signal input terminal, during the high-level phase of the PWM signal, the voltage at the first input terminal of the signal comparison circuit can reach the low-to-high transition threshold voltage V of the signal comparison circuit. H The signal comparator circuit outputs a high-level signal; during the low-level phase of the PWM signal, the first capacitor C1 is not charged, and the voltage at the first input terminal of the signal comparator circuit cannot reach the low-to-high transition threshold voltage V of the signal comparator circuit. H The signal comparison circuit outputs a low-level signal. Therefore, in the open-circuit state where the first detection contact and / or the second detection contact is at full liquid level, the output of the signal comparison circuit outputs a PWM signal.

[0028] refer to Figure 2 As shown, the liquid level sensor may include a first signal acquisition terminal, a second signal acquisition terminal, and a third signal acquisition terminal. The first signal acquisition terminal is connected to a first detection contact of the liquid level detection equivalent circuit, the second signal acquisition terminal is connected to a second detection contact of the liquid level detection equivalent circuit, and the third signal acquisition terminal is connected to the output terminal of the signal comparison circuit. In the diagnostic method for the liquid level sensor of this application, the voltages of the first and second detection contacts of the liquid level detection equivalent circuit can be detected at the first and second signal acquisition terminals, respectively, and the signal at the output terminal of the signal comparison circuit can be detected at the third signal acquisition terminal. The first, second, and third signal acquisition terminals are configured to facilitate the detection of the voltages of the first and second detection contacts P and N of the liquid level detection equivalent circuit, as well as the detection of the signal at the output terminal of the signal comparison circuit.

[0029] In this embodiment, the voltage of the first signal acquisition terminal can be used to characterize the voltage of the first detection contact of the liquid level detection equivalent circuit, the voltage of the second signal acquisition terminal can be used to characterize the voltage of the second detection contact of the liquid level detection equivalent circuit, and the signal of the third signal acquisition terminal can be used to characterize the output signal of the signal comparison circuit.

[0030] In this embodiment, the diagnostic method for the liquid level sensor may further include: detecting the signal at the output terminal of the signal comparison circuit; if the output terminal of the signal comparison circuit outputs a PWM signal, detecting the voltage of the first detection contact P and the second detection contact N of the liquid level detection equivalent circuit; if the voltage of the first detection contact of the liquid level detection equivalent circuit is greater than a third threshold and the voltage of the second detection contact N of the liquid level detection equivalent circuit is less than or equal to a fourth threshold, diagnosing that the first detection contact P is in a state of short circuit to external power supply under empty liquid level conditions; if the output terminal of the signal comparison circuit outputs a PWM signal, the voltage of the first detection contact of the liquid level detection equivalent circuit is greater than a fifth threshold and the voltage of the second detection contact of the liquid level detection equivalent circuit is greater than a sixth threshold, diagnosing that the second detection contact N is in a state of short circuit to external power supply under empty liquid level conditions; wherein, the third threshold and the sixth threshold are both related to the voltage of the external power supply, the fourth threshold is related to the capacitance value of the first capacitor, and the fifth threshold is related to the voltage of the internal power supply.

[0031] In detail, both the third and sixth thresholds are close to the voltage of the external power supply, and both are related to the voltage of the external power supply and the circuit status of the liquid level sensor. In this embodiment, the third threshold can be greater than the sixth threshold. The fifth threshold is close to the voltage of the internal power supply VCC of the liquid level sensor. For example, the third threshold is 4.5V, the fourth threshold is 2.5V, the fifth threshold is 4.5V, and the sixth threshold is 2.5V, but it is not limited to these.

[0032] It should be noted that when the first or second detection contact is short-circuited to the external power supply with an empty liquid level, and a PWM signal is input to the signal input terminal, during the high-level phase of the PWM signal, the voltage at the first input terminal of the signal comparison circuit can reach the low-to-high transition threshold voltage V of the signal comparison circuit. H The signal comparator circuit outputs a high-level signal; during the low-level phase of the PWM signal, the first capacitor C1 is not charged, and the voltage at the first input of the signal comparator circuit cannot reach the low-to-high transition threshold voltage V of the signal comparator circuit. H The signal comparison circuit outputs a low-level signal. Therefore, when the first or second detection contact is in an empty liquid level state and short-circuited to the external power supply, the signal comparison circuit outputs a PWM signal.

[0033] For example, the external power source is the car's battery, but it is not limited to this.

[0034] The diagnostic method for the liquid level sensor may further include: detecting the signal at the output terminal of the signal comparison circuit; if the output terminal of the signal comparison circuit continuously outputs a low-level signal, detecting the voltage of the first detection contact P and the second detection contact N of the liquid level detection equivalent circuit; if the voltage of the first detection contact of the liquid level detection equivalent circuit is less than a seventh threshold and the voltage of the second detection contact is less than or equal to a fourth threshold, diagnosing the first detection contact P as being short-circuited to ground under empty liquid level conditions; if the output terminal of the signal comparison circuit outputs a PWM signal, detecting the voltage of the first detection contact P and the second detection contact N of the liquid level detection equivalent circuit; if the voltage of the first detection contact of the liquid level detection equivalent circuit is greater than an eighth threshold and the voltage of the second detection contact of the liquid level detection equivalent circuit is less than a fourth threshold, diagnosing the second detection contact N as being short-circuited to ground under empty liquid level conditions; wherein, the fourth threshold is related to the capacitance value of the first capacitor C1, the seventh threshold is close to zero, the seventh threshold is greater than zero and the difference from zero is within a set range, the eighth threshold is related to the voltage of the internal power supply VCC, and the eighth threshold is close to the voltage of the internal power supply VCC. For example, the seventh threshold is 0.5V and the fourth threshold is 2.5V, but it is not limited to these.

[0035] It should be noted that when the first detection contact P is short-circuited to ground with an empty liquid level and a PWM signal is input to the signal input terminal, the voltage at the first input terminal of the signal comparison circuit cannot reach the low-to-high transition threshold voltage V of the signal comparison circuit. H The output of the signal comparison circuit is a low-level signal.

[0036] When the second detection contact is short-circuited to ground with an empty liquid level, during the high-level phase of the PWM signal, the voltage at the first input terminal of the signal comparison circuit can reach the low-to-high transition threshold voltage V of the signal comparison circuit. H The signal comparator circuit outputs a high-level signal; during the low-level phase of the PWM signal, the first capacitor C1 is not charged, and the voltage at the first input terminal of the signal comparator circuit cannot reach the low-to-high transition threshold voltage V of the signal comparator circuit. H The signal comparison circuit continuously outputs a low-level signal. Therefore, when the second detection contact is short-circuited to ground in the case of an empty liquid level, the signal comparison circuit outputs a PWM signal.

[0037] The diagnostic method for the liquid level sensor may further include: detecting the signal at the output of the signal comparison circuit; if the output of the signal comparison circuit outputs a PWM signal, detecting the voltage of the first and second detection contacts of the liquid level detection equivalent circuit; if the voltage of the first detection contact of the liquid level detection equivalent circuit is less than the voltage of the internal power supply VCC and the voltage of the second detection contact of the liquid level detection equivalent circuit is less than or equal to a fourth threshold, diagnosing the first and second detection contacts as being in a normal state under empty liquid level conditions. Wherein, the actual voltage of the first detection contact P is related to the voltage of the internal power supply VCC and the circuit condition of the liquid level sensor; the fourth threshold is close to zero and is related to the capacitance value of the first capacitor C1, for example, the fourth threshold is equal to 2.5V.

[0038] It should be noted that in the normal state where the first and second detection contacts are at an empty liquid level, and a PWM signal is input to the signal input terminal, during the high-level phase of the PWM signal, the voltage at the first input terminal of the signal comparison circuit can reach the low-to-high transition threshold voltage V of the signal comparison circuit. H The signal comparator circuit outputs a high-level signal; during the low-level phase of the PWM signal, the first capacitor C1 is not charged, and the voltage at the first input terminal of the signal comparator circuit cannot reach the low-to-high transition threshold voltage V of the signal comparator circuit. H The signal comparison circuit outputs a low-level signal. Therefore, in the normal state where the first and second detection contacts are at an empty liquid level, the signal comparison circuit outputs a PWM signal.

[0039] The diagnostic method for the liquid level sensor may further include: detecting the signal at the output terminal of the signal comparison circuit; if the output terminal of the signal comparison circuit continuously outputs a low-level signal, detecting the voltage of the first detection contact P and the second detection contact N of the liquid level detection equivalent circuit; if the voltage of the first detection contact P of the liquid level detection equivalent circuit is greater than a first threshold and the voltage of the second detection contact N of the liquid level detection equivalent circuit is greater than a second threshold, diagnosing that at least one detection contact of the liquid level detection equivalent circuit is in a state of short circuit to external power supply under full liquid level conditions; wherein, both the first threshold and the second threshold are related to the voltage of the external power supply.

[0040] In this embodiment, the first threshold is related to the voltage of the external power supply and the circuit status of the liquid level sensor. The first threshold is close to but less than the voltage of the external power supply. For example, the first threshold can be 3.2V, but it is not limited to this. The second threshold is also related to the voltage of the external power supply and the circuit status of the liquid level sensor. The second threshold is close to but less than the voltage of the external power supply. In this embodiment, the first threshold is less than the second threshold. For example, the second threshold can be 3.5V.

[0041] In one embodiment of this application, when a low-level signal is continuously output at the output terminal of the signal comparison circuit, the voltage of the first detection contact P of the liquid level detection equivalent circuit is greater than a first threshold, and the voltage of the second detection contact N of the liquid level detection equivalent circuit is greater than a second threshold; if the voltage of the first detection contact P of the liquid level detection equivalent circuit is greater than the voltage of the second detection contact N, it is diagnosed that the first detection contact P of the liquid level detection equivalent circuit is short-circuited to an external power supply when the liquid level is full; if the voltage of the second detection contact N of the liquid level detection equivalent circuit is greater than the voltage of the first detection contact P, it is diagnosed that the second detection contact N of the liquid level detection equivalent circuit is short-circuited to an external power supply when the liquid level is full. For example, if the voltage of the first detection contact P is 4.5V and the voltage of the second detection contact N is 3.5V, it is diagnosed that the first detection contact P of the liquid level detection equivalent circuit is short-circuited to an external power supply when the liquid level is full, but this is not limited to this. For example, if the voltage of the first detection contact P is 3.3V and the voltage of the second detection contact N is 4.2V, the second detection contact N of the liquid level detection equivalent circuit is diagnosed as being short-circuited to the external power supply when the liquid level is full, but this is not the only possibility.

[0042] In another embodiment of this application, when a low-level signal is continuously output at the output terminal of the signal comparison circuit, the voltage of the first detection contact P of the liquid level detection equivalent circuit is greater than a first threshold, and the voltage of the second detection contact N of the liquid level detection equivalent circuit is greater than a second threshold; if the first threshold is greater than the second threshold, it is diagnosed that the first detection contact P of the liquid level detection equivalent circuit is short-circuited to the external power supply when the liquid level is full; if the second threshold is greater than the first threshold, it is diagnosed that the second detection contact N of the liquid level detection equivalent circuit is short-circuited to the external power supply when the liquid level is full.

[0043] It should be noted that when the detected object is at full liquid level, the resistance of the liquid level detection equivalent circuit is very small, equivalent to a short circuit. The voltage of the first detection contact P is pulled low by the second detection contact N, and the voltage of the first output terminal of the signal comparison circuit is pulled low. Therefore, when the first detection contact and / or the second detection contact is at full liquid level, it is short-circuited to the external power supply. When a PWM signal is input to the signal input terminal, the voltage of the first input terminal of the signal comparison circuit cannot reach the low-to-high transition threshold voltage V of the signal comparison circuit (specifically, the comparator U1A of the signal comparison circuit). H The signal output by the signal comparison circuit is a low-level signal.

[0044] The diagnostic method for the liquid level sensor may further include: detecting the signal at the output of a signal comparison circuit; if the output of the signal comparison circuit continuously outputs a low-level signal, detecting the voltage of the first detection contact P and the second detection contact N of the liquid level detection equivalent circuit; if the voltage of the second detection contact of the liquid level detection equivalent circuit is less than a seventh threshold, diagnosing that at least one detection contact of the liquid level detection equivalent circuit is short-circuited to ground under full liquid level conditions. The seventh threshold is close to zero, or in other words, the seventh threshold is greater than zero and the difference from zero is within a small set range. The actual value of the seventh threshold is related to the circuit condition of the liquid level sensor. For example, the seventh threshold is 0.5V, but it is not limited to this.

[0045] Specifically, if the output of the signal comparison circuit continuously outputs a low-level signal, the voltage of the second detection contact of the liquid level detection equivalent circuit is less than the seventh threshold, and the voltage of the first detection contact of the liquid level detection equivalent circuit is less than or equal to the seventh threshold, the first detection contact P is diagnosed as being short-circuited to ground under full liquid level conditions. If the output of the signal comparison circuit continuously outputs a low-level signal, the voltage of the second detection contact of the liquid level detection equivalent circuit is less than the seventh threshold, and the voltage of the first detection contact of the liquid level detection equivalent circuit is greater than zero and less than the voltage of the internal power supply VCC, the second detection contact N is diagnosed as being short-circuited to ground under full liquid level conditions.

[0046] It should be noted that when the first or second detection contact is short-circuited to ground at full liquid level and a PWM signal is input to the signal input terminal, the voltage at the first input terminal of the signal comparison circuit cannot reach the low-to-high transition threshold voltage V of the signal comparison circuit. H The signal comparison circuit outputs a low-level signal.

[0047] The diagnostic method for the liquid level sensor may further include: detecting the signal at the output terminal of the signal comparison circuit; if the output terminal of the signal comparison circuit continuously outputs a low-level signal, detecting the voltage of the first and second detection contacts of the liquid level detection equivalent circuit; if the voltages of both the first and second detection contacts of the liquid level detection equivalent circuit are greater than zero and less than the voltage of the internal power supply VCC, diagnosing the first and second detection contacts as being in a normal state under full liquid level conditions. The actual voltage values ​​of the first and second detection contacts of the liquid level detection equivalent circuit are related to the circuit condition of the liquid level sensor.

[0048] It should be noted that in the normal state where the first and second detection contacts are at full liquid level, and a PWM signal is input to the signal input terminal, the voltage at the first input terminal of the signal comparison circuit cannot reach the low-to-high transition threshold voltage V of the signal comparison circuit. H The signal comparison circuit outputs a low-level signal.

[0049] refer to Figure 2 As shown, the liquid level sensor also includes a diagnostic pull-up resistor R10, and the first detection contact P of the liquid level detection equivalent circuit is connected to the internal power supply VCC through the diagnostic pull-up resistor R10.

[0050] In this embodiment, the liquid level sensor may further include a signal input circuit, one end of which is connected to the signal input terminal, and the other end of which is connected to the first connection terminal of the first capacitor C1 and the first detection contact P of the liquid level detection equivalent circuit.

[0051] For example, the signal input circuit includes a first switch M1 and a second switch M2. The control terminal of the first switch M1 is connected to the signal input terminal, the first connection terminal of the first switch M1 is connected to the internal power supply VCC, and the second connection terminal of the first switch M1 is grounded. The control terminal of the second switch M2 is connected to the first connection terminal of the first switch M1, the first connection terminal of the second switch M2 is connected to the internal power supply VCC, and the second connection terminal of the second switch M2 is grounded. The first detection contact P and the first connection terminal of the first capacitor C1 in the liquid level detection equivalent circuit can both be connected to the second connection terminal of the second switch M2 at node B to connect to the signal input terminal.

[0052] In this embodiment, when the control terminal of the first switch M1 is high, the first switch M1 is closed, and its first and second connection terminals are connected. When the control terminal of the second switch M2 is low, the second switch M2 is closed, and its first and second connection terminals are connected. For example, the first switch M1 can be an NMOS, and the second switch M2 can be a PMOS. During the high-level phase of the PWM signal, when the control terminal of the first switch M1 is high, the first switch M1 is closed; when the control terminal of the second switch M2 is grounded (low level), the second switch M2 is closed; and the second connection terminal of the second switch M2 is connected to the internal power supply VCC and outputs a high-level signal.

[0053] Furthermore, the signal input circuit may also include a first resistor R1, a second resistor R2, and a third resistor R3.

[0054] One end of the second resistor R2 is connected to the signal input terminal, and the other end is grounded. Setting the second resistor R2 can provide a stable low-level signal when no PWM signal is input, thereby improving the detection accuracy and stability of the liquid level sensor.

[0055] The first connection terminal of the first switch M1 is connected to the internal power supply VCC via a first resistor R1. One end of the first resistor R1 is connected to the first connection terminal of the first switch M1, and the other end of the first resistor R1 is connected to the internal power supply VCC. In this embodiment, the first resistor R1 is a current-limiting resistor used to protect the first switch M1.

[0056] One end of the third resistor R3 is connected to the second connection terminal of the second switch M2, and the other end is grounded. In this embodiment, the third resistor R3 is a current-limiting resistor, which can protect the second switch M2 and also provide a fast discharge path for the first capacitor C1.

[0057] refer to Figure 2 As shown, the liquid level sensor may further include a fourth resistor R4, and the first capacitor C1 is connected to the signal input terminal through the fourth resistor R4. Specifically, one end of the fourth resistor R4 is connected to the signal input circuit at node B, and the other end of the fourth resistor R4 is connected to the first connection terminal of the first capacitor C1 and the first input terminal of the signal comparison circuit at node A.

[0058] refer to Figure 2 As shown, the signal comparison circuit of the liquid level sensor includes comparator U1A. Comparator U1A compares the reference signal with the signal at the first input terminal of the signal comparison circuit and outputs the corresponding signal to the third signal acquisition terminal. The output terminal of comparator U1A is the output port of the signal comparison circuit.

[0059] Continue to refer to Figure 2 As shown, the signal comparison circuit may also include a fifth resistor R5, a sixth resistor R6, a seventh resistor R7, and an eighth resistor R8.

[0060] refer to Figure 2 As shown, one end of the fifth resistor R5 is connected to the first connection terminal of the first capacitor C1 at node A. The other end of the fifth resistor R5 is connected to the first signal input terminal of comparator U1A and one end of the sixth resistor R6. The other end of the sixth resistor R6 is connected to the output port of the signal comparison circuit. The end of the fifth resistor R5 connected to the first connection terminal of the first capacitor C1 is the first input terminal of the signal comparison circuit. The fifth resistor R5 is connected to the signal input terminal through the fourth resistor R4.

[0061] One end of the seventh resistor R7 is connected to the internal power supply VCC, and the other end of the seventh resistor R7 is connected to one end of the eighth resistor R8 and the reference signal input terminal of comparator U1A. The other end of the eighth resistor R8 is grounded.

[0062] It should be noted that in this embodiment, the threshold switching level of the signal comparison circuit (specifically comparator U1A) can be set using the fifth resistor R5, the sixth resistor R6, the seventh resistor R7, and the eighth resistor R8. Specifically, the threshold voltage for the output of the signal comparison circuit, i.e., comparator U1A, to transition from a low level to a high level is V. H V H =V ref ×(R5+R6)÷R6; where V ref The voltage of the reference signal, Vref =V cc ×R8÷(R7+R8), V cc This is the voltage of the internal power supply VCC. The threshold voltage for the comparator U1A's output to transition from high to low is V. L V L =[V ref ×(R5+R6)-V pu [×R5]÷R6,V ref The voltage of the reference signal, V ref =V cc ×R8÷(R7+R8), V pu This is the high-level voltage output by comparator U1A.

[0063] Continue to refer to Figure 2 As shown, the liquid level sensor may also include a ninth resistor R9 and a second capacitor C2. One end of the ninth resistor R9 is connected to the output port of the signal comparison circuit, and the other end of the ninth resistor R9 is connected to one end of the second capacitor C2 and the third signal acquisition terminal. The other end of the second capacitor C2 is grounded.

[0064] The liquid level sensor may also include a twelfth resistor R12, a thirteenth resistor R13, a third capacitor C3, and a fourth capacitor C4. The first detection contact of the liquid level detection equivalent circuit is connected to the first signal acquisition terminal via the twelfth resistor R12. Specifically, one end of the twelfth resistor R12 is connected to the first detection contact P of the liquid level detection equivalent circuit, and the other end of the twelfth resistor R12 is connected to the first signal acquisition terminal and one end of the third capacitor C3, with the other end of the third capacitor C3 grounded. The second detection contact N of the liquid level detection equivalent circuit is connected to the second signal acquisition terminal via the thirteenth resistor R13. Specifically, one end of the thirteenth resistor R13 is connected to the second detection contact of the liquid level detection equivalent circuit, and the other end of the thirteenth resistor R13 is connected to the second signal acquisition terminal and one end of the fourth capacitor C4, with the other end of the fourth capacitor C4 grounded.

[0065] It should be noted that resistors R9 (ninth), R12 (twelfth), and R13 (thirteenth) are current-limiting filter resistors, and capacitors C2 (second), C3 (third), and C4 (fourth) are filter capacitors. Using these resistors filters the output signal at the signal acquisition end, improving the quality of the output signal. The capacitance values ​​of capacitors C2, C3, and C4 are significantly smaller than that of capacitor C1.

[0066] When a PWM signal is input to the signal input terminal, during the high-level phase of the PWM signal, the first capacitor C1, the second capacitor C2, the third capacitor C3, and the fourth capacitor C4 are charged simultaneously. Since the capacitance values ​​of the second capacitor C2, the third capacitor C3, and the fourth capacitor C4 are much smaller than the capacitance value of the first capacitor C1, their charging speed is very fast. Therefore, during the high-level phase of the PWM signal, the voltage at the first input terminal of the signal comparison circuit is mainly determined by the capacitance of the first capacitor C1 and the capacitance of the liquid level detection equivalent circuit.

[0067] In the diagnostic method for a liquid level sensor provided by this invention, the signal at the output terminal of the signal comparison circuit is first detected. If the output terminal of the signal comparison circuit outputs a PWM signal, the voltages of the first detection contact P and the second detection contact N of the liquid level detection equivalent circuit are then detected. If the voltage of the first detection contact P is greater than a ninth threshold and the voltage of the second detection contact N is less than a seventh threshold, it is diagnosed that at least one detection contact of the liquid level detection equivalent circuit is in an open-circuit state under full liquid level conditions. The ninth threshold is related to the voltage of the internal power supply, and the seventh threshold is greater than zero and the difference from zero is within a set range. Using this diagnostic method for a liquid level sensor, the abnormal state of an open-circuit detection contact under full liquid level conditions can be accurately diagnosed, which helps to improve the detection accuracy of the liquid level sensor and improve driving safety.

[0068] It should be noted that the terms "first," "second," and "third" used in this application are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined as "first," "second," or "third" may explicitly or implicitly include one or at least two of that feature. The terms "one end" and "the other end" generally refer to two corresponding parts, and include not only endpoints.

[0069] The above description is merely a description of preferred embodiments of the present invention and is not intended to limit the scope of the present invention. Any person skilled in the art can make possible changes and modifications to the technical solutions of the present invention by utilizing the methods and techniques disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solutions of the present invention shall fall within the protection scope of the technical solutions of the present invention.

Claims

1. A diagnostic method for a liquid level sensor, characterized in that, The liquid level sensor includes a liquid level detection equivalent circuit, a diagnostic pull-down resistor, a first capacitor, and a signal comparison circuit. The signal input terminal is connected to the first input terminal of the signal comparison circuit and the first connection terminal of the first capacitor. The first detection contact of the liquid level detection equivalent circuit is connected to an internal power supply, the first input terminal of the signal comparison circuit, and the first connection terminal of the first capacitor, respectively. The second detection contact of the liquid level detection equivalent circuit is grounded after passing through the diagnostic pull-down resistor. The second connection terminal of the first capacitor is connected to the second detection contact of the liquid level detection equivalent circuit. The diagnostic method for the liquid level sensor includes: Detect the signal at the output of the signal comparison circuit; If the output terminal of the signal comparison circuit outputs a PWM signal; The voltage of the first and second detection contacts of the liquid level detection equivalent circuit is detected. If the voltage of the first detection contact is greater than the ninth threshold and the voltage of the second detection contact is less than the seventh threshold, it is diagnosed that at least one detection contact of the liquid level detection equivalent circuit is in an open circuit state under full liquid level conditions. The ninth threshold is related to the voltage of the internal power supply, and the seventh threshold is greater than zero and the difference from zero is within a set range.

2. The diagnostic method for a liquid level sensor as described in claim 1, characterized in that, Also includes: Detect the signal at the output of the signal comparison circuit; If the output terminal of the signal comparison circuit outputs a PWM signal, the voltage of the first and second detection contacts of the liquid level detection equivalent circuit is detected. If the voltage of the first detection contact of the liquid level detection equivalent circuit is greater than the third threshold and the voltage of the second detection contact of the liquid level detection equivalent circuit is less than or equal to the fourth threshold, the state of short circuit to external power supply when the first detection contact is in the case of empty liquid level is diagnosed. If the voltage of the first detection contact of the liquid level detection equivalent circuit is greater than the fifth threshold and the voltage of the second detection contact of the liquid level detection equivalent circuit is greater than the sixth threshold, the state of short circuit to external power supply when the second detection contact is empty liquid level is diagnosed. The third threshold and the sixth threshold are both related to the voltage of the external power supply, the fourth threshold is related to the capacitance value of the first capacitor, and the fifth threshold is related to the voltage of the internal power supply.

3. The diagnostic method for a liquid level sensor as described in claim 1, characterized in that, Also includes: Detect the signal at the output of the signal comparison circuit; If the output of the signal comparison circuit continuously outputs a low-level signal, the voltage of the first detection contact and the second detection contact of the liquid level detection equivalent circuit is detected. If the voltage of the first detection contact of the liquid level detection equivalent circuit is less than the seventh threshold and the voltage of the second detection contact is less than or equal to the fourth threshold, the first detection contact is diagnosed as being short-circuited to ground in the case of empty liquid level. If the output terminal of the signal comparison circuit outputs a PWM signal, the voltage of the first detection contact and the second detection contact of the liquid level detection equivalent circuit is detected. If the voltage of the first detection contact of the liquid level detection equivalent circuit is greater than the eighth threshold and the voltage of the second detection contact of the liquid level detection equivalent circuit is less than the fourth threshold, the second detection contact is diagnosed as being short-circuited to ground in the case of empty liquid level. The fourth threshold is related to the capacitance value of the first capacitor, the seventh threshold is greater than zero and the difference from zero is within a set range, and the eighth threshold is related to the voltage of the internal power supply.

4. The diagnostic method for a liquid level sensor as described in any one of claims 1 to 3, characterized in that, During the process of detecting the signal at the output terminal of the signal comparison circuit, detecting the voltage of the first detection contact of the liquid level detection equivalent circuit, and detecting the voltage of the second detection contact of the liquid level detection equivalent circuit, the signal input terminal continuously inputs a PWM signal.

5. The diagnostic method for a liquid level sensor as described in any one of claims 1 to 3, characterized in that, The liquid level sensor includes a first signal acquisition terminal, a second signal acquisition terminal, and a third signal acquisition terminal; the first signal acquisition terminal is connected to a first detection contact of the liquid level detection equivalent circuit, the second signal acquisition terminal is connected to a second detection contact of the liquid level detection equivalent circuit, and the third signal acquisition terminal is connected to the output terminal of the signal comparison circuit; the voltages of the first and second detection contacts of the liquid level detection equivalent circuit are detected at the first and second signal acquisition terminals, respectively, and the signal at the output terminal of the signal comparison circuit is detected at the third signal acquisition terminal.

6. The diagnostic method for a liquid level sensor as described in any one of claims 1 to 3, characterized in that, The liquid level sensor also includes a signal input circuit, one end of which is connected to the signal input terminal, and the other end of which is connected to the first connection terminal of the first capacitor and the first detection contact of the liquid level detection equivalent circuit.

7. The diagnostic method for a liquid level sensor as described in claim 6, characterized in that, The signal input circuit includes a first switch and a second switch. The control terminal of the first switch is connected to the signal input terminal. The first connection terminal of the first switch is connected to an internal power supply. The second connection terminal of the first switch is grounded. The control terminal of the second switch is connected to the first connection terminal of the first switch. The first connection terminal of the second switch is connected to an internal power supply. The second connection terminal of the second switch is connected to the first detection contact of the liquid level detection equivalent circuit and the first connection terminal of the first capacitor.

8. The diagnostic method for a liquid level sensor as described in any one of claims 1 to 3, characterized in that, The signal comparison circuit compares the reference signal with the signal at the first input terminal of the signal comparison circuit and then outputs the corresponding signal.

9. The diagnostic method for a liquid level sensor as described in claim 8, characterized in that, The signal comparison circuit includes a comparator, a fifth resistor, a sixth resistor, a seventh resistor, and an eighth resistor; one end of the fifth resistor is connected to the signal input terminal and the first connection terminal of the first capacitor, the other end of the fifth resistor is connected to the first signal input terminal of the comparator and one end of the sixth resistor, the other end of the sixth resistor is connected to the output port of the signal comparison circuit, one end of the seventh resistor is connected to the internal power supply, the other end of the seventh resistor is connected to one end of the eighth resistor and the reference signal input terminal of the comparator, and the other end of the eighth resistor is grounded.

10. The diagnostic method for a liquid level sensor as described in any one of claims 1 to 3, characterized in that, The capacitance of the liquid level detection equivalent circuit is greater when the liquid level is full than when the liquid level is empty, and the resistance is less when the liquid level is full than when the liquid level is empty.

Images