Liquid level sensor and vehicle

Abstract

The application provides a liquid level sensor. In the liquid level sensor, a signal input end is connected with a first connection end of a first capacitor and a first connection end of a liquid level detection equivalent circuit, one end of a diagnosis pull-up resistor is connected with the first connection end of the liquid level detection equivalent circuit, the other end of the diagnosis pull-up resistor is connected with a power supply; a second connection end of the liquid level detection equivalent circuit and a second connection end of the first capacitor are both connected with one end of a diagnosis pull-down resistor, the other end of the diagnosis pull-down resistor is grounded; wherein the state of a detection contact of the liquid level sensor is judged by detecting the voltage of the first connection end and the second connection end of the liquid level detection equivalent circuit, so as to diagnose the abnormality of the detection contact. The application also provides an automobile comprising the above liquid level sensor.

Description

Technical Field

[0001] This invention relates to the field of electronic circuit technology, and in particular to a liquid level sensor and an automobile. 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, determining whether it is full or empty, and prompting the user to take appropriate action. The circuit design and implementation of the coolant level sensor are of great significance to the safe operation of the car engine and related equipment.

[0003] Currently, existing liquid level sensors can only determine whether the liquid level is empty or full. However, if the detection contacts of the liquid level sensor are faulty, such as short circuit to the power supply, short circuit to ground, or open circuit, they cannot be identified. This can easily lead to inaccurate liquid level detection, false alarms, and potential hazards to safe driving. Summary of the Invention

[0004] One objective of this invention is to provide a liquid level sensor that can diagnose faults in the sensor's detection contacts, thereby improving the sensor's detection accuracy, reducing the risk of false alarms, and enhancing driving safety. This invention also provides an automobile.

[0005] To achieve the above objectives, one aspect of the present invention provides a liquid level sensor. The liquid level sensor includes a liquid level detection equivalent circuit, a diagnostic pull-up resistor, a first capacitor, and a diagnostic pull-down resistor; a signal input terminal is connected to a first connection terminal of the first capacitor and a first connection terminal of the liquid level detection equivalent circuit; one end of the diagnostic pull-up resistor is connected to the first connection terminal of the liquid level detection equivalent circuit, and the other end of the diagnostic pull-up resistor is connected to a power supply; a second connection terminal of the liquid level detection equivalent circuit and a second connection terminal of the first capacitor are both connected to one end of the diagnostic pull-down resistor, and the other end of the diagnostic pull-down resistor is grounded; wherein, the state of the detection contact of the liquid level sensor is determined by detecting the voltage between the first and second connection terminals of the liquid level detection equivalent circuit, thereby diagnosing any abnormalities in the detection contact.

[0006] Optionally, the states of the detection contacts of the liquid level sensor include a normal state, a short circuit to power supply state, a short circuit to ground state, and an open circuit state. The normal state, the short circuit to power supply state, the short circuit to ground state, and the open circuit state of the detection contacts correspond to different voltage ranges. The voltages of the first and second connection terminals of the liquid level detection equivalent circuit are compared with the voltage ranges corresponding to the normal state, the short circuit to power supply state, the short circuit to ground state, and the open circuit state to diagnose any abnormalities in the detection contacts of the liquid level sensor.

[0007] Optionally, the liquid level sensor further includes a first signal acquisition terminal and a second signal acquisition terminal; the first signal acquisition terminal is connected to a first connection terminal of the liquid level detection equivalent circuit, and the second signal acquisition terminal is connected to a second connection terminal of the liquid level detection equivalent circuit; the state of the detection contact of the liquid level sensor is determined by detecting the voltage of the output signals of the first signal acquisition terminal and the second signal acquisition terminal.

[0008] Optionally, the liquid level sensor further includes a fourth resistor, and the first capacitor is connected to the signal input terminal through the fourth resistor; the first connection terminal of the fourth resistor is connected to the signal input terminal, and the second connection terminal of the fourth resistor is connected to the first connection terminal of the first capacitor.

[0009] 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 fourth resistor and the first connection terminal of the liquid level detection equivalent circuit; the signal input circuit is used to convert the PWM signal input to the signal input terminal and output it to improve the stability of the signal input.

[0010] Optionally, the signal input circuit includes a first resistor, a second resistor, a third resistor, 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 one end of the first resistor, the other end of the first resistor is connected to a power supply, and the second connection terminal of the first switch is grounded; one end of the second resistor is connected to the signal input terminal and the other end 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 a power supply, the second connection terminal of the second switch is connected to one end of the third resistor, and the other end of the third resistor is grounded; the first connection terminal of the liquid level detection equivalent circuit and the first connection terminal of the fourth resistor are both connected to the second connection terminal of the second switch.

[0011] Optionally, the liquid level sensor further includes a signal comparison circuit; one input port of the signal comparison circuit is connected to the first connection terminal of the first capacitor, and the output port of the signal comparison circuit is connected to the third signal acquisition terminal. The signal comparison circuit compares the reference signal and the signal output from the first connection terminal of the first capacitor and then outputs the corresponding signal to the third signal acquisition terminal. The resistance and capacitance values ​​of the liquid level detection equivalent circuit are different when the detected object is in an empty liquid level state and a full liquid level state. The level of the output signal from the third signal acquisition terminal is used to determine whether the detected object is in an empty liquid level state or a full liquid level state.

[0012] Optionally, the input signal at the signal input terminal is a PWM signal; when the third signal acquisition terminal outputs a PWM signal within one PWM cycle, it is determined that the detected object is in an empty liquid level state; when the third signal acquisition terminal continuously outputs a low-level signal within one PWM cycle, it is determined that the detected object is in a full liquid level state.

[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 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 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 liquid level sensor further includes a ninth resistor and a second capacitor; one end of the ninth resistor is connected to the output port of the signal comparison circuit, the other end of the ninth resistor is connected to one end of the second capacitor and the third signal acquisition terminal, and the other end of the second capacitor is grounded.

[0015] Optionally, the liquid level sensor further includes a twelfth resistor and a third capacitor; one end of the twelfth resistor is connected to the first connection terminal of the liquid level detection equivalent circuit, the other end of the twelfth resistor is connected to the first signal acquisition terminal and one end of the third capacitor, and the other end of the third capacitor is grounded.

[0016] Optionally, the liquid level sensor further includes a thirteenth resistor and a fourth capacitor; one end of the thirteenth resistor is connected to the second connection terminal of the liquid level detection equivalent circuit, the other end of the thirteenth resistor is connected to the second signal acquisition terminal and one end of the fourth capacitor, and the other end of the fourth capacitor is grounded.

[0017] Another aspect of the present invention provides an automobile. The automobile includes the aforementioned liquid level sensor.

[0018] The liquid level sensor provided by this invention, and its application in automobiles, involves connecting a diagnostic pull-up resistor and a diagnostic pull-down resistor to the two ends of the liquid level detection equivalent circuit of the liquid level sensor, respectively. By detecting the voltage at the first and second connection terminals of the liquid level detection equivalent circuit, the state of the detection contact of the liquid level sensor is determined, thereby diagnosing any abnormalities in the detection contact. This improves the detection range and accuracy of the liquid level sensor, reduces the risk of false alarms, and enhances driving safety. Furthermore, the liquid level sensor offers flexible detection methods, low cost, and stable and reliable performance. Attached Figure Description

[0019] Figure 1 This is a circuit diagram of a liquid level sensor provided in an embodiment of the present invention. Detailed Implementation

[0020] The liquid level sensor and automobile 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.

[0021] In order to diagnose faults in the detection contacts, improve the detection accuracy of the liquid level sensor, and reduce the risk of false alarms, this embodiment provides a liquid level sensor.

[0022] Figure 1 This is a circuit diagram of a liquid level sensor provided according to an embodiment of the present invention. Figure 1 As shown, the liquid level sensor provided in this embodiment includes a liquid level detection equivalent circuit, a diagnostic pull-up resistor R10, a first capacitor C, and a diagnostic pull-down resistor R11.

[0023] The signal input terminal is connected to the first connection terminal of the first capacitor C1 and the first connection terminal of the liquid level detection equivalent circuit; one end of the diagnostic pull-up resistor R10 is connected to the first connection terminal of the liquid level detection equivalent circuit, and the other end of the diagnostic pull-up resistor R10 is connected to the power supply VCC; the second connection terminal of the liquid level detection equivalent circuit and the second connection terminal of the first capacitor C1 are both connected to one end of the diagnostic pull-down resistor R11, and the other end of the diagnostic pull-down resistor R11 is grounded; wherein, the state of the detection contact of the liquid level sensor is determined by detecting the voltage of the first connection terminal and the second connection terminal of the liquid level detection equivalent circuit, so as to diagnose the abnormality of the detection contact.

[0024] For example, the object detected by the level sensor can be an engine, and the level sensor can be used to detect the level of engine coolant and diagnose the status of the detection contacts of the level sensor.

[0025] To facilitate the detection of the voltage at the first and second connection terminals of the liquid level detection equivalent circuit, refer to Figure 1 As shown, the liquid level sensor may further include a first signal acquisition terminal and a second signal acquisition terminal; the first signal acquisition terminal may be connected to the first connection terminal of the liquid level detection equivalent circuit at node P, and the second signal acquisition terminal may be connected to the second connection terminal of the liquid level detection equivalent circuit at node N; the state of the detection contact of the liquid level sensor is determined by detecting the voltage of the output signals of the first signal acquisition terminal and the second signal acquisition terminal.

[0026] It should be noted that the state of the detection contact of the liquid level sensor can include a normal state, a short circuit to power supply state, a short circuit to ground state, and an open circuit state. The voltage ranges of the first and second connection terminals in the equivalent short circuit of the liquid level detection can be divided according to these states. This results in different voltage ranges corresponding to the normal, short circuit to power supply, short circuit to ground, and open circuit states. By comparing the voltages of the first and second connection terminals in the equivalent short circuit (i.e., the voltages of the output signals from the first and second signal acquisition terminals) with the voltage ranges corresponding to the normal, short circuit to power supply, short circuit to ground, and open circuit states, abnormalities in the liquid level sensor's detection contacts can be diagnosed.

[0027] In this embodiment, the resistance values ​​of the diagnostic pull-up resistor R10 and the diagnostic pull-down resistor R11 can be selected according to the liquid level detection equivalent circuit.

[0028] refer to Figure 1 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, the first connection terminal of the fourth resistor R4 is connected to the signal input terminal, and the second connection terminal of the fourth resistor R4 is connected to the first connection terminal of the first capacitor C1.

[0029] In this embodiment, the input signal at the signal input terminal is a pulse width modulation (PWM) signal, but it is not limited to this. (See reference...) Figure 1 As shown, the liquid level sensor may also include a signal input circuit, which converts the PWM signal input from the signal input terminal and outputs it to the first connection terminal of the liquid level detection equivalent circuit and the first connection terminal of the first capacitor C1 (specifically, the first connection terminal of the fourth resistor R4) to improve the stability of the signal input.

[0030] 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 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 power supply VCC, and the second connection terminal of the second switch M2 is grounded. The first connection terminal of the liquid level detection equivalent circuit and the first connection terminal of the fourth resistor R4 can both be connected to the second connection terminal of the second switch M2 at node B to connect to the signal input terminal.

[0031] In this embodiment, when the control terminal of the first switch M1 is at a high level, the first switch M1 is closed, and the first and second connection terminals of the first switch M1 are connected. When the control terminal of the second switch M2 is at a low level, the second switch M2 is closed, and the first and second connection terminals of the second switch M2 are connected. For example, the first switch M1 can be an NMOS and the second switch M2 can be a PMOS.

[0032] Furthermore, the signal input circuit may also include a first resistor R1, a second resistor R2, and a third resistor R3.

[0033] 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.

[0034] The first terminal of the first switch M1 is connected to the power supply VCC via a first resistor R1. One end of the first resistor R1 is connected to the first terminal of the first switch M1, and the other end of the first resistor R1 is connected to the power supply VCC. In this embodiment, the first resistor R1 is a current-limiting resistor used to protect the first switch M1.

[0035] 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.

[0036] refer to Figure 1As shown, the liquid level sensor may further include a signal comparison circuit; one input port of the signal comparison circuit can be connected to the first connection terminal of the first capacitor C1 at node A, and the output port of the signal comparison circuit is connected to the third signal acquisition terminal. The signal comparison circuit compares the reference signal with the signal output from the first connection terminal of the first capacitor C1 and outputs the corresponding signal to the third signal acquisition terminal. The resistance and capacitance values ​​of the liquid level detection equivalent circuit are different when the detected object is in an empty liquid level state and a full liquid level state; the level of the output signal from the third signal acquisition terminal is used to determine whether the detected object is in an empty liquid level state or a full liquid level state.

[0037] For details, please refer to Figure 1 As shown, the signal comparison circuit includes comparator U1A. Comparator U1A compares the reference signal with the signal output from the first connection terminal of the first capacitor C1 and outputs the corresponding signal to the third signal sampling terminal. The output terminal of comparator U1A is the output port of the signal comparison circuit.

[0038] Furthermore, the signal comparison circuit may include a fifth resistor R5, a sixth resistor R6, a seventh resistor R7, and an eighth resistor R8.

[0039] refer to Figure 1 As shown, one end of the fifth resistor R5 is connected to the first connection terminal of the first capacitor C1, 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, and the other end of the sixth resistor R6 is connected to the output port of the signal comparison circuit.

[0040] One end of the seventh resistor R7 is connected to the 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 the comparator U1A. The other end of the eighth resistor R8 is grounded.

[0041] It should be noted that in this embodiment, the threshold switching level of comparator U1A is set by 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 comparator U1A to transition from low to high is V. H V H =V ref ×(R5+R6)÷R6; where V ref The voltage of the reference signal, V ref =V cc ×R8÷(R7+R8), V cc The power supply voltage is V. 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,Vref 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.

[0042] Continue to refer to Figure 1 As shown, the liquid level sensor may also include a ninth resistor R9 and a second capacitor C2. The output port of the signal comparison circuit is connected to the third signal acquisition terminal through the ninth resistor R9. 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.

[0043] 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 connection terminal 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 connection terminal 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 connection terminal 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 connection terminal 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.

[0044] 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.

[0045] For example, the input signal at the signal input terminal is a PWM signal. The duty cycle of the PWM signal is, for example, 1%, so that the charging time of the capacitor in the liquid level sensor is short, but it is not limited to this.

[0046] refer to Figure 1 As shown, during the high-level phase of the PWM signal, the control terminal of the first switch M1 is a high-level signal, and the first switch M1 is closed. The control terminal of the second switch M2 is grounded and is a low-level signal, and the second switch M2 is closed. The second connection terminal of the second switch M2 is connected to the power supply VCC and outputs a high-level signal.

[0047] The liquid level detection equivalent circuit is an externally provided load circuit. It has different resistance and capacitance values ​​depending on whether the liquid level is empty or full. The resistance and capacitance values ​​of the liquid level detection equivalent circuit can be adjusted according to the actual liquid level condition. Specifically, the capacitance value of the liquid level detection equivalent circuit in the empty liquid level state is much smaller than the capacitance value in the full liquid level state.

[0048] During the high-level phase of the PWM signal, capacitors C1, C2, C3, and C4 are charged simultaneously. Since the capacitance values ​​of C2, C3, and C4 are much smaller than that of C1, they charge very quickly. Therefore, during the high-level phase of the PWM signal, the voltage at the first connection terminal of capacitor C1 is primarily determined by C1 itself and the capacitance of the equivalent liquid level detection circuit.

[0049] During the high-level phase of the PWM signal, since the capacitance value of the equivalent circuit for level detection in the empty liquid level state is much smaller than that in the full liquid level state, the voltage at the first connection terminal of the first capacitor C1 can reach the low-to-high transition threshold voltage V of the comparator U1A within a unit charging time, i.e., within one PWM cycle, when the detection object is in the empty liquid level state. H When comparator U1A outputs a high-level signal, meaning the signal comparison circuit outputs a high-level signal, the output signal at the third signal acquisition terminal is also a high-level signal. When the object being detected is at full liquid level, the voltage at the first connection terminal of the first capacitor C1 cannot reach the threshold voltage V for the low-to-high transition of comparator U1A. H When the comparator U1A outputs a low-level signal, the output signal of the third signal acquisition terminal is also a low-level signal.

[0050] During the low-level phase of the PWM signal, the first capacitor C1, the second capacitor C2, the third capacitor C3, and the fourth capacitor C4 are not charged. Therefore, the voltage at the first connection terminal of the first capacitor C1 cannot reach the low-to-high transition threshold voltage V of the comparator U1A in both the empty and full liquid level states of the detected object. H When the signal comparison circuit outputs a low-level signal, the output signal of the third signal acquisition terminal is also a low-level signal.

[0051] Therefore, within one PWM cycle, when the third signal acquisition terminal outputs a PWM signal, it is determined that the detected object is in an empty liquid level state; within one PWM cycle, when the third signal acquisition terminal continuously outputs a low-level signal, it is determined that the detected object is in a full liquid level state.

[0052] In the liquid level sensor provided in this embodiment, the level of the output signal at the third signal acquisition terminal can be used to determine whether the detected object is in an empty or full liquid level state. By detecting the voltage at the first and second connection terminals of the liquid level detection equivalent circuit, specifically by detecting the voltage of the output signals at the first and second signal acquisition terminals, it can be determined whether the detection contact of the liquid level sensor is in a normal state, a short circuit to the power supply state, a short circuit to ground state, or an open circuit state. This improves the detection range and accuracy of the liquid level sensor, reduces the risk of false alarms, and improves driving safety. Moreover, the liquid level sensor has a flexible detection method, low cost, and stable and reliable performance.

[0053] This embodiment also provides a vehicle that includes the above-described liquid level sensor.

[0054] For example, this level sensor can be used to detect the state of engine coolant and also has the function of diagnosing the state of the sensor's detection contacts. Specifically, the level sensor can detect whether the engine coolant is full or empty, and it can also diagnose whether the detection contacts are in a normal state, short-circuited to power, short-circuited to ground, or open-circuit state.

[0055] 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 liquid level sensor, characterized in that, It includes a liquid level detection equivalent circuit, a diagnostic pull-up resistor, a first capacitor, a diagnostic pull-down resistor, and a signal comparison circuit; The signal input terminal is connected to the first connection terminal of the first capacitor and the first connection terminal of the liquid level detection equivalent circuit. One end of the diagnostic pull-up resistor is connected to the first connection terminal of the liquid level detection equivalent circuit, and the other end of the diagnostic pull-up resistor is connected to the power supply. The second connection terminal of the liquid level detection equivalent circuit and the second connection terminal of the first capacitor are both connected to one end of the diagnostic pull-down resistor, and the other end of the diagnostic pull-down resistor is grounded. The liquid level sensor further includes a first signal acquisition terminal and a second signal acquisition terminal. The first signal acquisition terminal is connected to a first connection terminal of the liquid level detection equivalent circuit, and the second signal acquisition terminal is connected to a second connection terminal of the liquid level detection equivalent circuit. The state of the detection contact of the liquid level sensor is determined by detecting the voltage of the output signals of the first and second signal acquisition terminals. The state of the detection contact of the liquid level sensor includes a normal state, a short circuit to power supply state, a short circuit to ground state, and an open circuit state. The normal state, the short circuit to power supply state, the short circuit to ground state, and the open circuit state of the detection contact correspond to different voltage ranges. The voltage of the output signals of the first and second signal acquisition terminals is compared with the voltage ranges corresponding to the normal state, the short circuit to power supply state, the short circuit to ground state, and the open circuit state to diagnose the abnormality of the detection contact of the liquid level sensor.

2. The liquid level sensor as described in claim 1, characterized in that, It also includes a fourth resistor, through which the first capacitor is connected to the signal input terminal; the first connection terminal of the fourth resistor is connected to the signal input terminal, and the second connection terminal of the fourth resistor is connected to the first connection terminal of the first capacitor.

3. The liquid level sensor as described in claim 2, characterized in that, It 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 fourth resistor and the first connection terminal of the liquid level detection equivalent circuit; the signal input circuit is used to convert the PWM signal input from the signal input terminal and output it to improve the stability of the signal input.

4. The liquid level sensor as described in claim 3, characterized in that, The signal input circuit includes a first resistor, a second resistor, a third resistor, 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 one end of the first resistor, and the other end of the first resistor is connected to a power supply. The second connection terminal of the first switch is grounded. One end of the second resistor is connected to the signal input terminal, and the other end is grounded. The control terminal of the second switch is connected to the first connection terminal of the first switch, and the first connection terminal of the second switch is connected to a power supply. The second connection terminal of the second switch is connected to one end of the third resistor, and the other end of the third resistor is grounded. The first connection terminal of the liquid level detection equivalent circuit and the first connection terminal of the fourth resistor are both connected to the second connection terminal of the second switch.

5. The liquid level sensor as described in claim 1, characterized in that, An input port of the signal comparison circuit is connected to the first connection terminal of the first capacitor, and the output port of the signal comparison circuit is connected to the third signal recovery terminal. The signal comparison circuit compares the reference signal and the signal output from the first connection terminal of the first capacitor and then outputs the corresponding signal to the third signal recovery terminal. The resistance and capacitance values ​​of the liquid level detection equivalent circuit are different when the detection object is in an empty liquid level state and a full liquid level state; the detection object is determined to be in an empty liquid level state or a full liquid level state by detecting the level of the output signal of the third signal acquisition terminal.

6. The liquid level sensor as described in claim 5, characterized in that, The input signal at the signal input terminal is a PWM signal; when the third signal acquisition terminal outputs a PWM signal within one PWM cycle, it is determined that the detected object is in an empty liquid level state; when the third signal acquisition terminal continuously outputs a low-level signal within one PWM cycle, it is determined that the detected object is in a full liquid level state.

7. The liquid level sensor as described in claim 5, 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 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 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.

8. The liquid level sensor as described in claim 5, characterized in that, The liquid level sensor also includes a ninth resistor and a second capacitor; one end of the ninth resistor is connected to the output port of the signal comparison circuit, the other end of the ninth resistor is connected to one end of the second capacitor and the third signal acquisition terminal, and the other end of the second capacitor is grounded.

9. The liquid level sensor as described in claim 1, characterized in that, It also includes a twelfth resistor and a third capacitor; one end of the twelfth resistor is connected to the first connection terminal of the liquid level detection equivalent circuit, the other end of the twelfth resistor is connected to the first signal acquisition terminal and one end of the third capacitor, and the other end of the third capacitor is grounded.

10. The liquid level sensor as described in claim 1, characterized in that, It also includes a thirteenth resistor and a fourth capacitor; one end of the thirteenth resistor is connected to the second connection terminal of the liquid level detection equivalent circuit, the other end of the thirteenth resistor is connected to the second signal acquisition terminal and one end of the fourth capacitor, and the other end of the fourth capacitor is grounded.

11. A car, characterized in that, Including the liquid level sensor as described in any one of claims 1 to 10.

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