JP2012169715A - Sensor fault detection apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inexpensive and compact sensor fault detection apparatus.SOLUTION: The sensor fault detection apparatus includes: an output selection circuit for receiving output voltages of a plurality of sensors divided via a voltage dividing circuit connected to a power line and respective non-grounded ends of the plurality of sensors, and outputting a selected one of the output voltages of the plurality of sensors thus input; an analog/digital conversion circuit for converting the sensor output voltage input via the output selection circuit to a digital value; and an on/off-switchable bypass circuit for bypassing the voltage dividing circuit, between the power line and the output side of the output selection circuit. A sensor output voltage input via the output selection circuit with the bypass circuit on is converted to a digital value, and a sensor fault is determined according to the digital value.

Description

  The present invention relates to a sensor failure detection apparatus.

  In the field of detecting a physical quantity as an electrical quantity, the physical quantity is detected by an analog sensor, the output of the analog sensor is converted to a digital value by an analog / digital (hereinafter referred to as A / D) conversion circuit, and this digital value is processed centrally. A method of performing arithmetic processing by an apparatus (hereinafter referred to as CPU) is generally used.

  In the A / D converter, in addition to detecting the failure of the analog signal side circuit, a device that detects disconnection of the analog signal line has been devised (see Patent Document 1).

JP-A-10-209863

  The configuration of Patent Document 1 can accurately detect a failure of the analog signal side circuit, but has a problem that the circuit configuration is complicated.

  FIG. 5 shows an example of the configuration of a conventional sensor failure detection apparatus 2. The sensor failure detection device 2 includes a plurality of sensor circuits U1 and U2 and a microcomputer 10 to which these sensor circuits are connected.

  The sensor circuit U1 includes a sensor S1 having one end grounded, a voltage dividing resistor R11 that is provided between the power supply line (Vcc) and the sensor S1 and divides the output voltage of the sensor S1, and a voltage dividing resistor R11. A capacitor C1 that removes noise superimposed on the output voltages of the plurality of sensors divided through the resistor R11 and an output voltage of the sensor S1 divided through the voltage dividing resistor R11 are input. A protective resistor R12 that protects the inflow of overcurrent to the microcomputer 10 and a bypass circuit K1 of the voltage dividing resistor R11 is formed between the power supply line (Vcc) and the sensor S1, and the bypass circuit is turned on / off. And a transistor T1 to be performed. The output voltage of the sensor S1 is input to the AD conversion input port AD1 of the microcomputer 10, and the transistor T1 is turned on / off (that is, the bypass circuit K1 is turned on / off) by the output port P1 of the microcomputer 10.

  Similarly to the sensor circuit U1, the sensor circuit U2 includes a sensor S2, a voltage dividing resistor R21, a capacitor C2, a protective resistor R22, a bypass circuit K2, and a transistor T2. The output voltage of the sensor S2 is input to the AD conversion input port AD2 of the microcomputer 10, and the transistor T2 is turned on / off (that is, the bypass circuit K2 is connected / disconnected) by the output port P2 of the microcomputer 10.

  In the microcomputer 10, a well-known CPU 11, ROM 12, RAM 13, AD conversion circuit 14, and signal input / output circuit I / O 15 are connected via a bus line 16 so that data transmission is possible. The CPU 11 executes the control program stored in the ROM 12 to detect the voltage output from the sensor, and executes various processes based on the detected voltage.

  In the case of detecting the failure of the sensor S1 in the configuration of FIG. 5 (the same applies to the sensor S2), the transistor T1 is turned on, the bypass circuit K1 is turned on, the influence of the voltage dividing resistor R11 is removed, and the output of the sensor S1 Detect voltage directly. When no failure of the sensor S1 is detected, the transistor T1 is turned off and the bypass circuit K1 is turned off. That is, one AD conversion input port and one transistor control output port are used for each sensor circuit.

  For this reason, a control device using a large number of sensors requires transistors as many as the number of sensors, which increases the number of parts and increases the size of the device, as well as an input port for AD conversion of a microcomputer and an output port for transistor control. However, since only the sensor is required, there is a problem that functions that can be realized by the control device are reduced.

  Against the background of the above problems, an object of the present invention is to provide a sensor failure detection device that can be reduced in cost and size.

Means for Solving the Problems and Effects of the Invention

  A sensor failure detection apparatus for solving the above problems is connected to a plurality of sensors whose one end is grounded and outputs an analog value, and to each other end of the power supply line and the plurality of sensors that are not grounded, A voltage dividing circuit that divides the output voltage of the sensor and an output voltage of the plurality of sensors divided through the voltage dividing circuit are input, and one of the input output voltages of the plurality of sensors is selected. An output selection circuit for outputting, an analog / digital conversion circuit for converting the output voltage of the sensor input through the output selection circuit into a digital value, and a power supply line and the output side of the output selection circuit. A bypass circuit that bypasses the pressure circuit, and a switching circuit that switches conduction / shut-off of the bypass circuit. The analog / digital conversion circuit operates the output selection circuit with the bypass circuit conducted. The output voltage of the sensor input and converted into a digital value, and further comprising a failure determination circuit for determining a failure of the sensor based on the converted digital value.

  With the above configuration, the number of bypass circuits and transistors are one each regardless of the number of sensors, so that the number of components (that is, elements constituting the transistor and its peripheral circuits) can be reduced. Further, only one output port of the CPU is required for conducting / blocking the bypass circuit. In addition, because the sensor output voltage is input via the output selection circuit, the number of CPU AD conversion input ports is one regardless of the number of sensors, and the unnecessary AD input ports are diverted to other applications. (For example, sensors can be added, or an AD input port is used as a general-purpose input port).

  The failure determination circuit in the sensor failure detection device of the present invention determines whether the sensor failure is a short-circuit failure or an open failure.

  Generally, sensor failure includes a short-circuit failure in which the sensor is short-circuited and outputs a voltage near 0 V, and an open failure in which the sensor is disconnected and outputs a voltage close to the applied voltage to the sensor. . With the above configuration, these two failures can be determined as in the conventional configuration.

  The sensor failure detection apparatus of the present invention includes an open failure factor detection circuit that is provided between the output side of the output selection circuit and the ground and outputs a voltage corresponding to the cause of the open failure to the analog / digital conversion circuit. The failure determination circuit determines the cause of the open failure based on the output voltage from the open failure factor detection circuit converted by the analog / digital conversion circuit with the bypass circuit shut off when an open failure occurs. To do.

  In addition to the state in which the sensor is disconnected, the open failure includes a state in which the output voltage of the sensor remains substantially equal to the voltage applied to the sensor but is not disconnected (also referred to as “power supply sticking”). . With the above configuration, the cause of the open failure can be determined as in the conventional configuration.

  In addition, the sensor failure detection apparatus of the present invention includes a failure determination timing determination circuit that determines whether or not a predetermined failure determination timing has arrived, and the failure determination circuit includes a failure determination timing determination circuit and a failure determination timing determination circuit. When it is determined that has arrived, a sensor failure is determined.

  With the above configuration, it is possible to determine the failure of the sensor without affecting the operation of the sensor or the system using the sensor.

  The failure determination timing determination circuit in the sensor failure detection apparatus of the present invention determines that the failure determination timing has arrived when the sensor failure detection apparatus is powered on.

  Even with the above-described configuration, it is possible to determine the arrival of the failure / failure determination timing without affecting the operation of the sensor or the system using the sensor and without performing the complicated failure determination timing determination process.

The block diagram which shows the structure of the sensor failure detection apparatus of this invention. The flowchart explaining a sensor failure detection process. The flowchart explaining a sensor failure determination process. The flowchart explaining another example of a sensor failure detection process. The block diagram which shows the structure of the sensor failure detection apparatus by a prior art.

  Hereinafter, a sensor failure detection apparatus of the present invention will be described with reference to the drawings. In FIG. 1, the structure of the sensor failure detection apparatus 1 of this invention is shown. The sensor failure detection apparatus 1 includes a plurality of sensor circuits U11 and U21 and a microcomputer 10 to which these sensor circuits are connected. The number of sensor circuits is not limited as long as it is two or more.

  The sensor failure detection device 1 is included in, for example, an ECU for controlling an air conditioner (hereinafter referred to as “air conditioner ECU”) or an ECU for controlling an engine (hereinafter referred to as “engine ECU”) mounted on a vehicle. The air conditioner ECU performs AD conversion on the vehicle interior temperature, the temperature outside the vehicle, the amount of solar radiation, the evaporator temperature (analog value), and the like measured by sensors, and performs air conditioning control based on the results. Further, the engine ECU performs AD conversion on the accelerator opening, engine speed, vehicle speed, cooling water temperature, intake air temperature, engine rotation angle (analog value), etc. measured by sensors, and based on the results. Engine rotation control is performed.

  The sensor circuit U11 is obtained by removing the transistor T1 and the bypass circuit K1 from the sensor circuit U1 of FIG. 5, and includes a sensor S1, a voltage dividing resistor R11, a capacitor C1, and a protective resistor R12. Since this is the same as FIG. 5, a detailed description thereof is omitted here. Similarly, since the sensor circuit U21 is obtained by removing the transistor T2 and the bypass circuit K2 from the sensor circuit U2 of FIG. 5, detailed description thereof is omitted here. The voltage dividing resistors R11 and R21 correspond to the voltage dividing circuit of the present invention.

  Since the configuration of the microcomputer 10 is also the same as that in FIG. 5, a detailed description thereof is omitted here. The CPU 11 corresponds to a failure determination circuit and a failure determination timing determination circuit of the present invention. The AD conversion circuit 14 corresponds to the analog / digital conversion circuit of the present invention.

  The output voltage output from each of the sensors S1 and S2 via the protective resistors R12 and R22 is input to an output selection circuit 20 that selects and outputs one of a plurality of analog inputs such as a known analog switch. Is done. That is, the detection voltage of the sensor S1 is input to the input terminal In1, and the detection voltage of the sensor S2 is input to the input terminal In2. Then, according to the selection instruction of the output port P2 of the microcomputer 10 (a plurality of output ports may be used for the selection instruction), one is selected from the plurality of sensor circuits. The detection voltage of the selected sensor is input from the output terminal out to the AD conversion input port AD1 of the microcomputer 10.

  A bypass circuit K3 of voltage dividing resistors R11 and R12 is formed between the output terminal out of the output selection circuit 20 and the power supply line (Vcc), and a transistor T3 for conducting / cutting off the bypass circuit K3 is connected. Yes. As a result, only one bypass circuit and one transistor are required for each sensor circuit, regardless of the number of sensor circuits. Therefore, the number of parts (ie, cost) can be reduced, and the wiring pattern can be simplified. . The transistor T3 corresponds to the switching circuit of the present invention.

  In addition, a resistor R3 for determining an open failure factor is connected between the output terminal out (that is, the input port AD1) of the output selection circuit 20 and the ground. The resistor R3 corresponds to the open failure factor detection circuit of the present invention.

  A sensor failure detection process in the microcomputer 10 will be described with reference to FIG. This process is included in the control program described above. First, the power is turned on (S11: Yes), and initialization processing for initializing the microcomputer and setting the above-described ECU state to the initial state is performed (S12). Subsequently, a failure of each sensor is detected. By executing it between the initialization process and the normal process, it is possible to reliably detect a sensor failure and to prevent the normal process from being affected. In addition, it is determined that the failure determination timing has arrived at the initialization processing execution timing when the power is turned on (power-on reset). In this case, since the sensor failure detection process is automatically executed when the power is turned on, a circuit and a program for determining the failure determination timing are not particularly required.

  Next, a command is sent from the CPU 11 to the output selection circuit 20, and the input is switched to a sensor (for example, sensor S1) that is a target of failure detection (S13). Subsequently, the CPU 11 controls the output port P1 to turn on the transistor T3, that is, to turn on the bypass circuit K3 (S14). As a result, the voltage dividing resistor R11 does not generate a voltage, and the voltage generated by the sensor S1 when the power supply voltage (Vcc) is directly applied is input to the input port AD1.

  Next, the voltage input in the above state is AD converted by the AD conversion circuit 14 (S15). After AD conversion, the CPU 11 controls the output port P1 to turn off the transistor T3, that is, to turn off the bypass circuit K3 (S16).

  Next, based on the voltage value (digital value) after AD conversion, for example, a failure determination process for determining the presence or absence of a failure is performed as follows (S17, see FIG. 3).

  And when it determines with the sensor having failed (S18: Yes), the process at the time of failure is performed (S19). In the process at the time of failure, for example, a failure flag assigned to each sensor on the RAM 13 is set. Subsequent processing is different from that of a sensor or a system using the sensor. For example, the digital value of the failed sensor is fixed to a value for fail-safe.

  On the other hand, when it is determined that the sensor is normal (S18: No), or after executing the process at the time of failure in step S19, it is determined whether or not failure determination has been performed for all the sensors connected to the output selection circuit 20. If the failure determination is not performed for all the sensors (S20: No), the process returns to step S13, a command is sent from the CPU 11 to the output selection circuit 20, and the input is switched to the next sensor (for example, the sensor S2). And the failure determination after step S14 is implemented.

  On the other hand, when failure determination is performed for all sensors (S20: Yes), normal processing in an ECU (air conditioner ECU, engine ECU, etc.) in which the microcomputer 10 is mounted is executed (S21).

  A failure determination process corresponding to step S17 in FIG. 2 will be described with reference to FIG. Here, it is determined that the sensor is normal when the output voltage of the sensor is within the range of the lower limit value 0.5V (referred to as V1) to the upper limit value 4.5V (referred to as V2). First, it is determined whether the output voltage of the sensor is below the upper limit value V2.

  When the output voltage of the sensor is lower than the upper limit value V2 (S31: No), it is determined whether or not it is lower than the lower limit value V1, and when it is lower than the lower limit value V1 (S32: Yes), it is determined that there is a short circuit failure (S34). On the other hand, when it exceeds the lower limit value V1, that is, when it is within the range of the lower limit value V1 to the upper limit value V2 (S32: No), it is determined as normal (S33).

  On the other hand, when the output voltage of the sensor exceeds the upper limit value V2 (S31: Yes), it is determined as an open failure (S35). At this stage, it can be determined whether or not there is an open failure, but as described above, there are a sensor in a “disconnected” state and a “power-on” state. Hereinafter, processing for determining which of these states will be described. Of course, a configuration may be adopted in which only short-circuit faults and open faults are detected, the subsequent steps are not executed, and open faults are not discriminated.

  First, the AD conversion circuit 14 again AD converts the output voltage from the sensor (S36). At this time, the transistor T3 is in an off state because step S16 is being executed, and the bypass circuit K3 is in a cut-off state. Next, it is determined whether or not the sensor voltage after AD conversion is lower than the lower limit value V1. When the sensor voltage is lower than the lower limit value V1 (S37: Yes), the input port AD1 is grounded via the resistor R3. Therefore, it is determined as an open failure due to disconnection (S39). On the other hand, when the voltage value exceeds the lower limit value V1, that is, when the voltage value corresponds to the voltage dividing ratio with the resistor R1 (S37: No), the power supply (Vcc) is applied to the sensor S1, so An open failure is determined (S38).

  With reference to FIG. 4, another example of the sensor failure detection process in FIG. 2 will be described using the sensor S <b> 1 as an example. This process is executed in the normal process (in step S21 in FIG. 2), whereas the process in FIG. 2 is executed between the initialization process and the normal process. is there. Moreover, since this process is a modification of the process of FIG. 2, the same code | symbol is attached | subjected about the process step same as FIG. 2, and detailed description here is omitted.

  Each sensor measures at a constant period (for example, several msec to several hundred msec) according to the measurement object. Therefore, in this process, failure determination is performed prior to measurement of the sensor output voltage. First, it is determined whether or not the measurement timing of the sensor S1 has arrived. When it is determined that the measurement timing has arrived (S10: Yes), the process of steps S13 to S17 in FIG. 2 is performed to determine whether the sensor S1 has failed. In this case, the measurement timing becomes the failure determination timing.

  When it is determined that the sensor S1 has failed (S18: Yes), it is determined that the failure determination timing has arrived, and processing at the time of failure is performed as in FIG. 2 (S19). On the other hand, when it is determined that the sensor S1 is normal (S18: No), normal processing is performed (S191). That is, the output voltage from the sensor S1 in this state (the bypass circuit K3 is in the cut-off state) is AD converted by the AD conversion circuit 14, and this is used as a sensor voltage to perform a predetermined process.

  For the other sensors (S2 and the like), the processing as described above is performed when each measurement timing arrives, and corresponding processing is performed depending on whether the sensor is normal or malfunctioning.

  Although the embodiments of the present invention have been described above, these are merely examples, and the present invention is not limited to these embodiments, and the knowledge of those skilled in the art can be used without departing from the spirit of the claims. Various modifications based on this are possible.

DESCRIPTION OF SYMBOLS 1 Sensor failure detection apparatus 10 Microcomputer 11 CPU (failure determination circuit, failure determination timing determination circuit)
14 AD conversion circuit (analog / digital conversion circuit)
20 Output selection circuit K3 Bypass circuit R11, R21 Voltage dividing resistor (voltage dividing circuit)
R3 resistance (open failure factor detection circuit)
S1, S2 sensor T3 transistor (switching circuit)
U11, U21 sensor circuit

Claims (5)

A plurality of sensors whose one end is grounded and outputs an analog value;
A voltage dividing circuit connected to the other end of each of the plurality of sensors that is not grounded to divide the output voltage of the sensor;
An output selection circuit that receives an output voltage of the plurality of sensors divided through the voltage dividing circuit, and selects and outputs one of the input output voltages of the plurality of sensors;
An analog / digital conversion circuit that converts the output voltage of the sensor input through the output selection circuit into a digital value;
A bypass circuit provided between the power supply line and the output side of the output selection circuit and bypassing the voltage dividing circuit;
A switching circuit for switching conduction / interruption of the bypass circuit;
With
The analog / digital conversion circuit converts the output voltage of the sensor input through the output selection circuit into a digital value in a state where the bypass circuit is conducted,
A sensor failure detection apparatus, further comprising a failure determination circuit that determines failure of the sensor based on the converted digital value.   The sensor failure detection device according to claim 1, wherein the failure determination circuit determines whether the failure of the sensor is a short-circuit failure or an open failure. An open failure factor detection circuit which is provided between the output side of the output selection circuit and the ground and outputs a voltage corresponding to the cause of the open failure to the analog / digital conversion circuit;
The failure determination circuit is configured to convert the open circuit based on an output voltage from the open failure factor detection circuit converted by the analog / digital conversion circuit in a state where the bypass circuit is cut off when the open failure occurs. The sensor failure detection apparatus according to claim 2, wherein a failure factor is determined. A failure determination timing determination circuit for determining whether or not a predetermined failure determination timing has arrived;
The sensor according to any one of claims 1 to 3, wherein the failure determination circuit determines a failure of the sensor when the failure determination timing determination circuit determines that the failure determination timing has arrived. Fault detection device.   The sensor failure detection device according to claim 4, wherein the failure determination timing determination circuit determines that the failure determination timing has arrived when power is supplied to the sensor failure detection device.

Images