Disconnection detection method and disconnection detection circuit

Abstract

To provide a disconnection detection method capable of detecting a sign of disconnection in an input acquisition circuit.SOLUTION: A supply voltage Vs in which supply and non-supply are switched by ON / OFF of an input switch SW1 is inputted to a control unit 301 via a connector 2. An end in a side of the control unit 301 of the connector 2 is grounded via an internal pull-down resistor R1, and is connected to a comparison determination part 401 via an input route resistor Rs. A state in which a resistance value is larger than normal although an input acquisition circuit is not disconnected yet is defined as a state having a sign of disconnection of the input acquisition circuit. The comparison determination part 401 determines presence or absence of disconnection or a sign of disconnection of the input acquisition circuit on the basis of an input voltage determination result obtained by comparing an input voltage Vin as a voltage in a side of the comparison determination part 401 of the input route resistor Rs with threshold voltages of the three levels of a first high threshold voltage Vth1a, a second high threshold voltage Vth1b, and a low threshold voltage Vth2.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for detecting a broken wire. and disconnection detection circuit Regarding. [Background technology]

[0002] 2. Description of the Related Art Conventionally, a disconnection detection method for detecting a disconnection abnormality in an electric circuit has been known.

[0003] For example, in the anti-skid device disclosed in Patent Document 1, a brake lamp switch and a brake lamp are connected in series between the vehicle battery and ground. A controller detects whether the brake lamp switch is in the ON or OFF state based on the voltage supplied between the brake lamp switch and the brake lamp via a connector. If the brake lamp is disconnected or the connector is loosened, an abnormality is detected based on the voltage levels of two input ports of the anti-skid control device.

[0004] In addition, in the disconnection detection circuit disclosed in Patent Document 2, a data line is connected to a connection point of voltage dividing resistors (i.e., pull-up resistor and pull-down resistor) of a power supply voltage. When the data line is disconnected, a window comparator detects that the potential of the data line has become an intermediate level potential of the power supply voltage. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 1-186454 [Patent Document 2] Japanese Patent Application Publication No. 9-270802 Summary of the Invention [Problem to be solved by the invention]

[0006] The conventional technologies described in Patent Documents 1 and 2 are capable of detecting disconnections, but are unable to detect abnormalities caused by resistance increasing due to aging. When the resistance increase progresses and exceeds a disconnection detection threshold, a disconnection is unexpectedly detected. If the input signal to the circuit is a start / stop signal for a vehicle system function, the system operation or function may unexpectedly stop due to a fail-safe. It is also conceivable that the system or function cannot be restarted.

[0007] The present invention has been made in view of the above points, and its object is to provide a method for detecting a disconnection in an input acquisition circuit, which is capable of detecting a symptom of a disconnection in which the resistance value is higher than normal, even though the disconnection has not occurred. , and a disconnection detection circuit used in the disconnection detection method The aim is to provide 。 [Means for solving the problem]

[0008] The present invention provides a supply voltage (Vs) that can be switched between supply and non-supply by turning on / off an input switch (SW1), or Indicates voltage level In the control unit (301-304) to which the Hi / Lo level signal is input via the connector (2), the comparison / determination unit (401-404) at least Connector breakage Line The Hi / Lo level signal is, for example, an external communication signal or a sensor signal. Supply voltage or level signal voltage input from outside the control unit via a connector is compared with a predetermined threshold voltage. Compare do.

[0009] The control unit side end of the connector is grounded via an internal pull-down resistor (R1) and is also connected to the comparison / determination unit via an input path resistor (Rs).

[0010] In one aspect of the present invention, the end of the connector opposite the control unit is grounded via an external pull-down resistor (Rd), and the end of the connector on the control unit side is further connected to a high potential line via an internal pull-up resistor (R3). 。

[0011] The comparison / determination unit determines whether or not there is a break in the connector and also whether or not there is a sign of a break in the external pull-down resistor.

[0012] The comparison and determination unit compares an input voltage (Vin), which is a voltage on the comparison and determination unit side of the input path resistance, with three or more threshold voltage levels including a first high threshold voltage (Vth1a), a second high threshold voltage (Vth1b), and a low threshold voltage (Vth2) set in order from highest to lowest, based on the input voltage determination result: connector Specifically, the comparison and determination unit makes the following determination based on the results of multiple consecutive input voltage determinations.

[0013] [1] When the number of times that the first condition, that is, the input voltage is higher than the first high threshold voltage, is met is equal to or greater than the first determination number, it is determined that the input switch is ON or the level signal is Hi. [2] When the number of times that the second condition, that is, the input voltage is higher than the second high threshold voltage and lower than the first high threshold voltage, is satisfied is equal to or greater than the second determination number, connector It is determined that there are signs of a broken wire.

[0014] [3] When the number of times that a third condition, that is, the input voltage is higher than the low threshold voltage and lower than the second high threshold voltage, is satisfied is equal to or greater than a third determination number, connector is determined to be disconnected. [4] When the number of times that the fourth condition, that is, the input voltage is lower than the lower threshold voltage, is met is equal to or greater than the fourth determination number, it is determined that the input switch is OFF or the level signal is Lo.

[0015] In the present invention, connector In addition to the obvious disconnect between connector For example, when applied to a control unit of a vehicle system, it can prevent unexpected system or function shutdowns that may occur when a disconnection is detected. [Brief explanation of the drawings]

[0016] [Figure 1] 1A is a circuit diagram of a disconnection detection circuit according to a first embodiment, and FIG. 1B is a determination condition table. [Figure 2]FIG. 4 is a schematic diagram showing an input voltage determination state in the first embodiment. [Figure 3] 1 is a judgment flowchart (1) of a disconnection detection method [embodiment 1]. [Figure 4] 10 is a judgment flowchart (2) of the disconnection detection method [embodiments 1 and 2]. [Figure 5] 10 is a judgment flowchart (3) of the disconnection detection method [embodiment 1]. [Figure 6] 10 is a judgment flowchart (1) of a disconnection detection method [embodiment 2]. [Figure 7] 10 is a judgment flowchart (3) of the disconnection detection method [embodiment 2]. [Figure 8] 10 is a judgment flowchart (4) of the disconnection detection method [embodiment 2]. [Figure 9] FIG. 3 is a circuit diagram of a disconnection detection circuit according to a first comparative example. [Figure 10] FIG. 5 is a schematic diagram showing an input voltage determination state in a first comparative example. [Figure 11] FIG. 10 is a circuit diagram of a disconnection detection circuit according to a second embodiment. [Figure 12] FIG. 10 is a schematic diagram showing an input voltage determination state in the second embodiment. [Figure 13] FIG. 10 is a circuit diagram of a disconnection detection circuit according to a second comparative example. [Figure 14] FIG. 10 is a schematic diagram showing an input voltage determination state in a second comparative example. [Figure 15] 10A is a circuit diagram of a disconnection detection circuit according to a third embodiment, and FIG. 10B is a determination condition table. [Figure 16] FIG. 11 is a schematic diagram showing an input voltage determination state in the third embodiment. [Figure 17] FIG. 11 is a schematic diagram showing an input voltage determination state in a modified example of the third embodiment. [Figure 18] FIG. 10 is a circuit diagram of a disconnection detection circuit according to a fourth embodiment. [Figure 19] 5A and 5B are schematic diagrams illustrating other examples of abnormalities that can be detected by the disconnection detection circuit of the first embodiment. [Figure 20] 10A and 10B are schematic diagrams illustrating other examples of abnormalities that can be detected by the disconnection detection circuit of the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0017] An embodiment of a wire break detection method according to the present invention will be described with reference to the drawings. First to fourth embodiments, which are examples of multiple circuit configurations for implementing this wire break detection method, are collectively referred to as "the present embodiment." The circuit diagrams of each embodiment and comparative example show only the portion of an arbitrary system to which a supply voltage is input in the first, second, and fourth embodiments, and only the portion to which a Hi / Lo level signal is input in the third embodiment. The system may perform any operation, such as driving an actuator, using the input supply voltage, etc.

[0018] In the first, second, and fourth embodiments, a supply voltage is input to the system's control unit via a connector. The supply or non-supply of the supply voltage is switched by turning an input switch provided in the supply path on or off. In the third embodiment, Hi / Lo level signals such as external communication and sensor signals are input to the system's control unit via a connector. The circuit from the input path of the supply voltage or level signal to the connector is called the "input acquisition circuit." The control unit has an internal "comparison and judgment unit" that compares the input voltage with a predetermined threshold voltage to judge the connection state of the circuit, and the comparison and judgment unit detects a break in the input acquisition circuit. The internal and external circuits of the control unit involved in break detection are collectively called the "break detection circuit."

[0019] The reference numerals for the "control unit" and the "comparison / determination unit" in the first to fourth embodiments are "30" and "40," respectively, followed by the embodiment number "1," "2," "3," or "4" in the third digit. Similarly, the first comparative example for the first embodiment and the second comparative example for the second embodiment are followed by the number "9" or "8" in the third digit. Substantially identical components in the embodiments and comparative examples are given the same reference numerals, and descriptions thereof will be omitted.

[0020] (First embodiment) The configuration of the open circuit detection circuit of the first embodiment will be described with reference to FIGS. 1(a), 1(b), and 2. As shown in FIG. 1(a), a supply voltage Vs is input to a control unit 301 from a supply path provided with an input switch SW1 via a connector 2. The input switch SW1 in the first embodiment corresponds to a system startup switch. Hereinafter, the end of the connector 2 on the control unit 301 side will be referred to as the "inner end," and the end opposite the control unit 301 will be referred to as the "outer end." The outer end of the connector 2 is grounded via an external pull-down resistor Rd. The "outside" in the "external pull-down resistor" refers to the outside of the control unit 301.

[0021] For example, as disclosed in Patent Document 1 (JP Patent Publication No. 1-186454A), in a vehicle brake system, the input switch SW1 functions as a brake lamp switch, and the external pull-down resistor Rd functions as a brake lamp. When the input switch SW1 is ON, current flows through the external pull-down resistor Rd, turning on the brake lamp. Currently, LED-type brake lamps are the mainstream, but in conventional filament-type lamps, there have been cases where the filament broke. This type of break is called a "break in the external pull-down resistor Rd."

[0022] The connector 2 is regarded as a connector resistor Rc, which is a type of resistive element. The connector 2 has an end on the input switch SW1 side and an end on the control unit 301 side electrically connected to wiring in the harness and the board. An interruption of the power supply to the control unit 301 due to a disconnection in the connector 2 itself or poor contact in the terminals is referred to as a "disconnection in the connector 2."

[0023] A break in the connector 2 or the external pull-down resistor Rd is defined as a “break in the input acquisition circuit.” In other words, the break detection method according to the first embodiment detects a break in the connector 2 or the external pull-down resistor Rd as one failure mode called a “break in the input acquisition circuit,” and does not distinguish between them.

[0024] Furthermore, a state in which the connector 2 or the external pull-down resistor Rd has a resistance value higher than normal, but has not yet reached a break, is defined as a state in which there is a sign of a break in the input acquisition circuit. For example, a state in which the resistance value has increased due to aging deterioration of the switch contacts, connectors, wiring, etc. corresponds to a state in which there is a sign of a break. In the comparative example described below, it is not possible to detect the occurrence of a sign of a break. In contrast, the break detection method according to the first embodiment is characterized by determining the presence or absence of a sign of a break in the input acquisition circuit in addition to detecting a break in the input acquisition circuit.

[0025] The control unit 301 is provided with an internal pull-up resistor R3, an internal pull-down resistor R1, an input path resistor Rs, a comparison / determination unit 401, and a notification output circuit 7. The inner end of the connector 2 is grounded via the internal pull-down resistor R1, and is connected to the input IC50 of the comparison / determination unit 401 via the input path resistor Rs. The inner end of the connector 2 is also connected to a high-potential line via the internal pull-up resistor R3. In this example, a supply voltage Vs is applied to the high-potential line. Here, the voltage at the inner end of the connector 2 is referred to as the "control unit input voltage Vin0."

[0026] The comparison / determination unit 401 of the first embodiment includes an input IC 50 including three comparators 51a, 51b, and 52 and a signal processing circuit 55, a microcomputer 60, and a non-volatile memory 65. Hereinafter, the end of the input path resistance Rs on the comparison / determination unit 401 side will be referred to as the "determination terminal." Inside the input IC 50, the determination terminal of the input path resistance Rs is grounded via an insulating resistor R2 whose resistance value is significantly larger than the input path resistance Rs. Hereinafter, the symbols for each resistor represent the symbol of the resistive element and also represent its physical property, that is, its resistance value. The + input terminal of each comparator 51a, 51b, and 52 is connected to the other end of the input path resistance Rs, and the - input terminal is connected to a supply source of the respective threshold voltage.

[0027] The "voltage at the judgment end of the input path resistor Rs" input to the positive input terminal of each of the comparators 51a, 51b, and 52 is referred to as the "input voltage Vin." Vin={R2 / (Rs+R2)}×Vin0 However, since "Rs << R2", it is considered that "Vin ≒ Vin0".

[0028] As the three-level threshold voltages of the comparators 51a, 51b, and 52, in order from the higher one, the first high-order threshold voltage Vth1a, the second high-order threshold voltage Vth1b, and the low-order threshold voltage Vth2 are set. That is, the relationship of "Vth2 < Vth1b < Vth1a" holds. Also, for example, the second high-order threshold voltage Vth1b is set to the same value as the high-order threshold voltage Vth1 of the first comparative example described later.

[0029] The first high-order comparator 51a outputs an A signal when the input voltage Vin is higher than the first high-order threshold voltage Vth1a. The second high-order comparator 51b outputs a B signal when the input voltage Vin is higher than the second high-order threshold voltage Vth1b. The low-order comparator 52 outputs a C signal when the input voltage Vin is higher than the low-order threshold voltage Vth2.

[0030] The signal processing circuit 55 processes the output signals (A signal, B signal, C signal) of the comparators 51a, 51b, and 52 and outputs them to the microcomputer 60. The first to fourth conditions used in the determination flowcharts shown in FIGS. 3 to 5 are defined as shown in FIG. 1(b). In FIG. 1(b), H for each signal means that the input voltage Vin is higher than the threshold voltage, and L means that the input voltage Vin is lower than the threshold voltage.

[0031] [[ID=I6]] The microcomputer 60 includes an arithmetic unit 61 that executes arithmetic logic and a memory 62 that stores information such as the number of times the condition is satisfied. The microcomputer 60 determines the ON / OFF of the input switch SW1, the disconnection of the input acquisition circuit, and the presence or absence of disconnection signs based on the input voltage determination result obtained by comparing the input voltage Vin with the three-level threshold voltages Vth1a, Vth1b, and Vth2 by the input IC50.

[0032] 2, when the input voltage Vin is higher than the first high threshold voltage Vth1a, the first condition is met, and it is determined that the input switch SW1 is ON (SW1_ON determination 1). When the input voltage Vin is higher than the second high threshold voltage Vth1b and lower than the first high threshold voltage Vth1a, the second condition is met, and it is determined that the input switch SW1 is ON and there is a sign of a disconnection (SW1_ON determination 2, disconnection sign determination). In the following description and drawings, "determination that there is a sign of a disconnection" will be referred to as "disconnection sign determination" for convenience.

[0033] When the input voltage Vin is higher than the low-level threshold voltage Vth2 and lower than the second high-level threshold voltage Vth1b, the third condition is met and it is determined that the input acquisition circuit is open (open-circuit determination).When the input voltage Vin is lower than the low-level threshold voltage Vth2, the fourth condition is met and it is determined that the input switch SW1 is OFF (SW1_OFF determination).

[0034] When the microcomputer 60 detects that the input acquisition circuit is disconnected or that there is a sign of a disconnection, it issues a command to the notification output circuit 7 inside the control unit 301. The notification output circuit 7 notifies the abnormality to a notification display device 8 outside the control unit 301 or a vehicle ECU, etc., via CAN communication or the like. The notification display device 8 displays a warning to the user using a lamp or the like. The non-volatile memory 65 continues to store the count value of the number of determinations written while the microcomputer 60 is operating, even when the microcomputer 60 is stopped operating. Specifically, in the determination flowchart [Embodiment 2] (FIGS. 4, 6 to 8), the non-volatile memory 65 stores the long-term disconnection sign count in a deterioration degree counter.

[0035] A further explanation of the settings of the second upper threshold voltage Vth1b and the lower threshold voltage Vth2 is provided below. As mentioned above, we approximate "Vin ≈ Vin0" and define the input voltage ratio K of the input voltage Vin to the supply voltage Vs as "K = Vin / Vs." The input voltage ratio K when the input switch SW1 is ON, when the connector 2 or the external pull-down resistor Rd is disconnected, and when the input switch SW1 is OFF is defined as Kon, Kbr, and Koff, respectively.

[0036] The parallel resistance of the internal pull-up resistor R3 and the connector resistor Rc is expressed as "R3 / / Rc". The parallel resistance of the internal pull-down resistor R1 and the "series resistance of the connector resistor Rc and the external pull-down resistor Rd" is expressed as "R1 / / (Rc+Rd)". The input voltage ratios Kon, Kbr, and Koff are represented by Expressions (1), (2), and (3), respectively.

[0037] Kon =R1 / (R3 / / Rc+R1) ···(1) Kbr =R1 / (R3+R1) ···(2) Koff={R1 / / (Rc+Rd)} / [R3+{R1 / / (Rc+Rd)}] ···(3)

[0038] Regarding the magnitude relationship between the parallel resistance and one of the resistances, Expressions (4) and (5) hold. R3 / / Rc<R3 ···(4) R1 / / (Rc+Rd)<R1 ···(5)

[0039] From Expressions (1), (2), and (4), "Kbr<Kon". The second high threshold voltage Vth1b is set so as to satisfy Expression (6). Kbr×Vs<Vth1b<Kon×Vs ···(6)

[0040] From Expressions (2), (3), and (5), "Koff<Kbr". The low threshold voltage Vth2 is set so as to satisfy Expression (7). Koff×Vs<Vth2<Kbr×Vs ···(7)

[0041] (Determination flowchart [Example 1]) Next, referring to FIGS. 3 to 5, [Example 1] regarding the specific determination method of the disconnection detection method by the comparison determination unit 401 will be described. The determination flowcharts of FIGS. 3 to 5 are connected via the connection marks ST, Y1, Y2, YR, and NR. In the description of the flowchart, the symbol "S" means a step. In the figure, the input acquisition circuit is denoted as the "SW1 circuit". The determination count numbers such as "2" and "5" of the condition satisfaction count are examples and may be changed as appropriate.

[0042] At the start of the determination in [Embodiment 1], if it is determined in S00 that the input switch SW1 is OFF, the process immediately proceeds to S05.

[0043] In S05, the first, second, third, and fourth condition fulfillment counts are reset to 0. In S11, it is determined whether the first condition is fulfilled, and if YES, the process proceeds to S12. If NO in S11, it is determined in S21 whether the second condition is fulfilled, and if YES, the process proceeds to S22. If NO in S21, it is determined in S31 whether the third condition is fulfilled, and if YES, the process proceeds to S32. If NO in S31, it is determined in S41 whether the fourth condition is fulfilled, and if YES, the process proceeds to S42.

[0044] In S12, the first condition fulfillment count is incremented, and in S13, the third and fourth condition fulfillment counts are reset to 0. In S14, it is determined whether the first condition fulfillment count is equal to or greater than the first determination count (e.g., 2 times). If the answer is NO in S14, it is determined in S16 whether the sum of the first condition fulfillment count and the second condition fulfillment count is equal to or greater than the total determination count (e.g., 2 times). If the answer is YES in S14 or YES in S16, the second condition fulfillment count is reset to 0 in S17. If the answer is NO in S16, the process returns to before S11, and the determination of the input voltage Vin is repeated. For example, if the first condition fulfillment count is 1, the second condition fulfillment count is 0, and the total determination count is 1, the process proceeds to the second loop while carrying forward "first condition fulfillment count=1."

[0045] In S18 following S17, it is determined that "the input switch SW1 is ON," assuming that the connector 2 is not broken. In other words, it is determined that the supply voltage Vs is being supplied to the control unit 301. Furthermore, in S19, assuming that the process will proceed to S18 via YES in S27, it is determined, as in S14, whether the first condition satisfaction count is equal to or greater than the first determination number (for example, 2 times).

[0046] If the answer is YES in S19, the process returns to before S05, the first, second, third, and fourth condition fulfillment counts are reset to 0, and the judgment of the input voltage Vin is repeated. If the answer is NO in S19, the process returns to before S11, and the judgment of the input voltage Vin is repeated. For example, if the first condition fulfillment count is 1, the second condition fulfillment count is 1, and the total number of judgments is 2, the process proceeds to the second loop while carrying forward "first condition fulfillment count = 1, second condition fulfillment count = 1".

[0047] In S22, the second condition fulfillment count is incremented, and in S23, the third and fourth condition fulfillment counts are reset to 0. In S26, it is determined whether the second condition fulfillment count is equal to or greater than the second determination count (for example, 5 times). Here, in the case of poor contact at the contacts, it is expected that the contact resistance will become unstable, so the second determination count is set to a value greater than the first determination count to make a more reliable determination. If the result in S26 is YES, in S28, it is determined that "there is a sign of a disconnection in the input acquisition circuit" (disconnection sign determination). Next, in S29, it is notified that there is a sign of a disconnection.

[0048] If the answer is NO in S26, then in S27 it is determined whether the sum of the first condition fulfillment count and the second condition fulfillment count is equal to or greater than the total number of determinations (for example, 2). If the answer is YES in S27, then in S18 it is determined that "the input switch SW1 is ON." If the answer is NO in S27, then the process returns to before S11, and the determination of the input voltage Vin is repeated. For example, if the first condition fulfillment count is 0, the second condition fulfillment count is 1, and the total number of determinations is 1, then the "second condition fulfillment count=1" is carried forward and the process proceeds to the second loop.

[0049] If S21 returns YES on the second cycle after S27 returns NO, S26 returns NO and S27 returns YES, and the process proceeds to S18. In other words, when the second condition is met twice in a row, it is not possible to determine for certain that there is a sign of a disconnection, but it is determined that "input switch SW1 is ON," i.e., that supply voltage Vs is being supplied to control unit 301. Therefore, it is possible to ensure system startup and functionality.

[0050] Furthermore, if the second condition continues to be satisfied, after four loops of "S21: YES → S26: NO → S27: YES → S18 → S19: NO", on the fifth loop, it is determined as YES in S26, and it is determined as "there are signs of a break in the input acquisition circuit" in S28.

[0051] In S32, the third condition fulfillment count is incremented, and in S33, the first, second, and fourth condition fulfillment counts are reset to 0. In S34, it is determined whether the third condition fulfillment count is equal to or greater than the third determination count (for example, 2 times). If the answer is YES in S34, it is determined in S38 that "the input acquisition circuit is broken." Then, in S39, a notification that there is a break is issued.

[0052] In S42, the fourth condition fulfillment count is incremented, and in S43, the first, second, and third condition fulfillment counts are reset to 0. In S44, it is determined whether the fourth condition fulfillment count is equal to or greater than the fourth determination count (for example, 2 times). If the result in S44 is YES, then, assuming that the connector 2 and the external pull-down resistor Rd are not disconnected, it is determined in S48 that "the input switch SW1 is OFF."

[0053] As in the case of NO in S16, S19, and S27, if the answer is NO in S34, S41, or S44, the process returns to before S11 and the determination of the input voltage Vin is repeated. For example, if the third or fourth condition is met twice in a row, the determination in S34 or S44 is YES.

[0054] After the determinations in S29, S39, and S48, the process returns to before S05, the first, second, third, and fourth condition satisfaction counts are reset to 0, and then the determination of the input voltage Vin is repeated.

[0055] (Determination Flowchart [Example 2]) Next, with reference to Figures 6 to 8, a description will be given of [Example 2] relating to a specific determination method of the disconnection detection method by the comparison and determination unit 401. In [Example 2], Figure 4 of [Example 1] is used in common, and Figures 6 and 7 are used instead of Figures 3 and 5 of [Example 1]. Furthermore, processing unique to [Example 2] is shown in Figure 8. Here, the differences from [Example 1] will be mainly described.

[0056] In [Example 2], the number of times that the second condition is met, for example, three times in a row, during operation of the microcomputer 60 is stored in the memory 62 as a long-term disconnection indication count, and is also written to a deterioration counter in the non-volatile memory 65. The value written to the deterioration counter continues to be stored even when the input switch SW1 is turned off and the microcomputer 60 stops operating. If the long-term disconnection indication count increases over a long period of time, the value of the deterioration counter in the non-volatile memory 65 is updated. If the long-term disconnection indication count exceeds the long-term determination count (for example, 10,000 times), the comparison and determination unit 401 determines that "there is a disconnection indication in the input acquisition circuit."

[0057] 6 shows a flow for initializing the deterioration counter in the nonvolatile memory 65. After it is determined in S00 that the input switch SW1 is OFF, it is determined in S01 whether the deterioration counter in the nonvolatile memory 65 has been initialized. If the deterioration counter has not been initialized and the answer is NO in S01, "0" is written to the deterioration counter in S02, and the deterioration counter is marked as initialized in S03.

[0058] After S03, if the answer is YES in S01, the process proceeds to S04. In S04, the comparison and determination unit 401 reads the value of the deterioration counter in the nonvolatile memory 65 and sets it as the long-term disconnection indication count. After S04, in S05, the first, second, third, and fourth condition satisfaction counts are reset to 0, but the long-term disconnection indication count is maintained.

[0059] In Figure 7, steps S24, S251, and S252 are added to Figure 5. In S24, it is determined whether the second condition satisfaction count is equal to or greater than a quasi-second determination count (e.g., 3 times) that is set less than the second determination count (e.g., 5 times) in S27. If the result in S24 is YES, a "long-term disconnection indication determination" is output in S251, meaning "there is a long-term disconnection indication." In S252, the long-term disconnection indication count is incremented, and the process proceeds to S26.

[0060] The comparison / determination unit 401 compares the long-term disconnection symptom count with the value of the deterioration counter in the nonvolatile memory 65 at a predetermined timing, and if the count has increased since the previous comparison, stores the count in the deterioration counter. In S51 of FIG. 8, it is determined whether it is time to read the deterioration counter value, and if YES, the process proceeds to S52.

[0061] In S52, it is determined whether the long-term disconnection indication count is greater than the degradation counter value in the nonvolatile memory 65. If the answer is YES in S52, the long-term disconnection indication count is written to the degradation counter in the nonvolatile memory 65 in S53.

[0062] In S54, it is determined whether the long-term disconnection symptom count has exceeded the long-term determination count (for example, 10,000 times). If the result in S54 is YES, a disconnection symptom determination is made for the input acquisition circuit, as in S28 and S29 in Figure 7, and a notification is issued that "a disconnection symptom is present." If the result in any of S51, S52, or S54 is NO, the process returns to before S51 and the determination is repeated.

[0063] (Comparison with the first comparative example) As described above, the comparison and determination unit 401 of the first embodiment can determine whether the input switch SW1 is on / off, whether the input acquisition circuit is disconnected, and whether there are any signs of disconnection, based on the input voltage determination result by the input IC 50, which compares the input voltage Vin with the three-level threshold voltages Vth1a, Vth1b, and Vth2.

[0064] 9 and 10, the configuration of a wire break detection circuit according to a first comparative example relative to the first embodiment will be described. In the wire break detection circuit according to the first comparative example shown in FIG. 9, the external configuration of the control unit 309 is the same as that of the first embodiment, and the outer end of the connector 2 is grounded via an external pull-down resistor Rd. The arrangement of resistors inside the control unit 309 is also the same as that of the first embodiment. An internal pull-up resistor R3 and an internal pull-down resistor R1 are connected to the inner end of the connector 2, which divide the supply voltage Vs to generate an intermediate potential.

[0065] The comparison / determination unit 409 of the first comparative example includes an input IC 509 including two comparators 51 and 52 and a signal processing circuit 55, and a microcomputer 60. The high-level comparator 51 compares the input voltage Vin with a high-level threshold voltage Vth1. The low-level comparator 52 compares the input voltage Vin with a low-level threshold voltage Vth2. The presence or absence of a non-volatile memory is not an issue.

[0066] 10, when the connector 2 is not disconnected and the input switch SW1 is ON, the input voltage Vin to the comparison / determination unit 408 is higher than the high threshold voltage Vth1. When the connector 2 is not disconnected and the input switch SW1 is OFF, the input voltage Vin is lower than the low threshold voltage Vth2, which corresponds to the lower limit of the intermediate potential generated by the internal pull-up resistor R3 and the internal pull-down resistor R1. When the connector 2 or the external pull-down resistor Rd is disconnected, the input voltage Vin becomes an intermediate level higher than the low threshold voltage Vth2 and lower than the high threshold voltage Vth1.

[0067] The open circuit detection circuit of the first comparative example can detect an open circuit in the connector 2 or the external pull-down resistor Rd. However, it cannot detect an abnormality caused by an increase in resistance due to aging. When the resistance increase progresses and exceeds the open circuit detection threshold, an open circuit is unexpectedly detected. As a result, for example, in a vehicle system control unit, the system or function may be unexpectedly stopped due to a fail-safe. It may also be impossible to restart the system or function.

[0068] In the first embodiment, an additional comparator is added to the input IC 50 in the open circuit detection circuit of the first comparative example, and the connection state of the input acquisition circuit is determined using a total of three levels of threshold voltages: two levels of high threshold voltages Vth1a and Vth1b and one level of low threshold voltage Vth2. As a result, in the first embodiment, in addition to obvious open circuits in the input acquisition circuit, it is possible to detect the occurrence of signs of open circuit, such as an increase in the resistance value of the input acquisition circuit above normal. For example, when applied to a control unit of a vehicle system, it is possible to prevent unexpected system or function shutdowns that may occur when an open circuit is detected.

[0069] (Second embodiment) Next, the configurations of the second embodiment and the second comparative example will be described with reference to Figures 11 to 14. In the open circuit detection circuit of the second embodiment shown in Figure 11, an external pull-up resistor Ru is provided in parallel with the input switch SW1. No external pull-down resistor Rd is provided at the outer end of the connector 2. Furthermore, inside the control unit 302, an internal pull-down resistor R1 is provided at the inner end of the connector 2, but no internal pull-up resistor R3 is provided. "Open circuit in the input acquisition circuit" mainly means "open circuit in the connector 2."

[0070] Similar to the comparison / determination unit 401 of the first embodiment, the comparison / determination unit 402 of the second embodiment includes an input IC 50 including three comparators 51a, 51b, and 52 and a signal processing circuit 55, a microcomputer 60, and a non-volatile memory 65. The three threshold voltage levels of the comparators 51a, 51b, and 52 are set, in descending order, as a first high threshold voltage Vth1a, a second high threshold voltage Vth1b, and a low threshold voltage Vth2. For example, the second high threshold voltage Vth1b is set to a value equivalent to the high threshold voltage Vth1 of the second comparative example.

[0071] As shown in FIG. 12, when the input voltage Vin is higher than the first high threshold voltage Vth1a, it is determined that the input switch SW1 is ON (SW1_ON determination). When the input voltage Vin is higher than the second high threshold voltage Vth1b and lower than the first high threshold voltage Vth1a, it is determined that the input switch SW1 is ON and there is a sign of disconnection (disconnection sign determination).

[0072] When the input voltage Vin is higher than the low threshold voltage Vth2 and lower than the second high threshold voltage Vth1b, it is determined that the input switch SW1 is OFF (SW1_OFF determination). When the input voltage Vin is at the ground level, that is, lower than the low threshold voltage Vth2, it is determined that the input acquisition circuit is disconnected (disconnection determination). Thus, in the second embodiment, the order of the SW1_OFF determination and the disconnection determination is reversed compared to the first embodiment.

[0073] Supplement regarding the setting of the second high threshold voltage Vth1b and the low threshold voltage Vth2. The premise and symbol settings follow those of the first embodiment. Let the input voltage ratio K at the time of disconnection of the connector 2 be Kbr. The input voltage ratios Kon, Koff, and Kbr are represented by equations (8), (9), and (10), respectively. Note that the resistance when the input switch SW1 is ON is assumed to be sufficiently smaller than the external pull-up resistor Ru.

[0074] Kon =R1 / (Rc+R1) ···(8) Koff=R1 / (Ru+Rc+R1) ···(9) Kbr =0···(10)

[0075] From equations (8) and (9), "Koff < Kon" holds. The second high threshold voltage Vth1b is set to satisfy equation (11). Koff×Vs<Vth1b<Kon×Vs ···(11)

[0076] From equations (9) and (10), "Kbr < Koff" holds. The low threshold voltage Vth2 is set to satisfy equation (12). Kbr×Vs<Vth2<Koff×Vs ···(12)

[0077] The determination flowchart of the second embodiment can be easily inferred by modifying the relationship between the SW1_OFF determination and the disconnection determination in the determination flowchart of the first embodiment. In particular, the determination flow relating to the disconnection indication determination is the same as that of the first embodiment, including the long-term disconnection indication determination using the nonvolatile memory 65, and therefore a duplicated description will be omitted.

[0078] (Comparison with the second comparative example) 13, the comparison / determination unit 408 is composed of an input IC 508 including two comparators 51 and 52 and a signal processing circuit 55, and a microcomputer 60. The high-level comparator 51 compares the input voltage Vin with a high-level threshold voltage Vth1. The low-level comparator 52 compares the input voltage Vin with a low-level threshold voltage Vth2. The presence or absence of a non-volatile memory is not an issue.

[0079] 14, when the input switch SW1 is ON, the input voltage Vin to the comparison / determination unit 408 is higher than the high threshold voltage Vth1. When the input switch SW1 is OFF, the input voltage Vin is at an intermediate level higher than the low threshold voltage Vth2 and lower than the high threshold voltage Vth1. When the connector 2 is disconnected, the input voltage Vin becomes the ground level, which is lower than the low threshold voltage Vth1.

[0080] The disconnection detection circuit of the second comparative example can detect disconnection of the connector 2, but cannot detect the occurrence of abnormal symptoms caused by an increase in resistance due to aging. In the second embodiment, one comparator of the input IC 50 is added to the disconnection detection circuit of the second comparative example, and the connection state of the input acquisition circuit is determined using a total of three levels of threshold voltage, making it possible to detect the occurrence of disconnection symptoms.

[0081] (Third embodiment) Referring to FIGS. 15(a), (b) and FIG. 16, the configuration of the disconnection detection circuit according to the third embodiment will be described. As shown in FIG. 15, in the third embodiment, Hi / Lo level signals such as external communication and sensor signals are input to the control unit 303 via the connector 2. For example, the Hi signal is a voltage signal of 5V and the Lo signal is a voltage signal of 0V.

[0082] The configuration other than the comparison determination unit 403 inside the control unit 303 is the same as that of the first embodiment. The input IC503 of the comparison determination unit 403 includes four comparators 51a, 51b, 52b, 52a and a signal processing circuit 55. The + input terminals of each of the comparators 51a, 51b, 52b, 52a are connected to the other end of the input path resistor Rs, and the - input terminals are connected to the supply source of each threshold voltage.

[0083] As the four-level threshold voltages of each of the comparators 51a, 51b, 52b, 52a, in order from the higher one, the first high-order threshold voltage Vth1a, the second high-order threshold voltage Vth1b, the second low-order threshold voltage Vth2b, and the first low-order threshold voltage Vth2a are set. That is, the relationship is "Vth2a < Vth2b < Vth1b < Vth1a". The comparison determination unit 403 of the third embodiment compares the input voltage Vin with the four-level (i.e., three levels or more) threshold voltages Vth1a, Vth1b, Vth2b, Vth2a.

[0084] The first high-order comparator 51a outputs an A signal when the input voltage Vin is higher than the first high-order threshold voltage Vth1a. The second high-order comparator 51b outputs a B signal when the input voltage Vin is higher than the second high-order threshold voltage Vth1b. The second low-order comparator 52b outputs a C signal when the input voltage Vin is higher than the second low-order threshold voltage Vth2b. The first low-order comparator 52a outputs a D signal when the input voltage Vin is higher than the first low-order threshold voltage Vth2a.

[0085] The signal processing circuit 55 processes the output signals (signal A, signal B, signal C, and signal D) of the comparators 51a, 51b, 52b, and 52a and outputs them to the microcomputer 60. In Fig. 15(b), H of each signal means that the input voltage Vin is higher than the threshold voltage, and L means that the input voltage Vin is lower than the threshold voltage.

[0086] 15(b) and 16, when the input voltage Vin is higher than the first high threshold voltage Vth1a, it is determined by the A signal that a Hi-level signal has been input (Hi-level determination 1). When the input voltage Vin is higher than the second high threshold voltage Vth1b and lower than the first high threshold voltage Vth1a, it is determined by the B signal that "a Hi-level signal has been input and there is a sign of a disconnection in the input acquisition circuit" (Hi-level determination 2, disconnection sign determination).

[0087] When the input voltage Vin is higher than the second low threshold voltage Vth2b and lower than the second high threshold voltage Vth1b, the C signal determines that the input acquisition circuit is open (open circuit determination). When the input voltage Vin is higher than the first low threshold voltage Vth2a and lower than the second low threshold voltage Vth2b, the D signal determines that "a Low level signal is being input and there is a sign of an open circuit in the input acquisition circuit" (Lo level determination 2, open circuit sign determination). When the input voltage Vin is lower than the first low threshold voltage Vth2a, the A to D signals are not output and it is determined that a Low level signal has been input (Lo level determination 1).

[0088] As described above, in the third embodiment, the comparison / determination unit 403 compares the input voltage Vin with four levels of threshold voltages Vth1a, Vth1b, Vth2b, and Vth2a, making it possible to determine whether there is a sign of a disconnection in either the Hi-level signal or the Lo-level signal state.

[0089] (Modification of the third embodiment) In a configuration in which the supply voltage Vs is input to the control unit according to the first embodiment, the comparison / determination unit may be configured to compare the input voltage Vin with four or more levels of threshold voltages Vth1a, Vth1b, Vth2b, and Vth2a. In this case, the schematic diagram showing the input voltage determination state in FIG. 16 is rewritten as shown in FIG. 17. In FIG. 17, two levels of lower threshold voltages Vth2a and Vth2b are set on the low potential side of the disconnection determination region, as compared to FIG. 2 of the first embodiment.

[0090] When the input voltage Vin is higher than the first low threshold voltage Vth2a and lower than the second low threshold voltage Vth2b, it is determined that a sign of disconnection (stuck at OFF) of the input switch SW1 has occurred (SW1_OFF determination 2, disconnection sign determination).When the input voltage Vin is lower than the first low threshold voltage Vth2a, it is determined that the input switch SW1 is OFF (SW1_OFF1 determination).

[0091] (Fourth embodiment) FIG. 18 shows a circuit diagram of a disconnection detection circuit according to the fourth embodiment. In the fourth embodiment, the control unit 304 does not have an input IC, and the comparison / determination unit 404 is composed only of a microcomputer. The input voltage Vin is converted into an analog-to-digital converter and acquired by the calculation unit 61 of the microcomputer. The calculation unit 61 compares the AD-converted value of the input voltage Vin with the threshold voltages Vth1a, Vth1b, and Vth2 stored in the memory 62 to determine whether or not there is a disconnection or a symptom of a disconnection in the input acquisition circuit. The determination logic is the same as in the first embodiment, which uses a comparator. Furthermore, the notification output when it is determined that there is a disconnection or a symptom of a disconnection is also the same as in the first embodiment.

[0092] (Other embodiments) 1(a), i.e., the configuration of the open circuit detection circuit in which the input switch SW1 and the external pull-down resistor Rd are connected in series, is shown again in Fig. 19. In this open circuit detection circuit, when the input voltage Vin is higher than the second high threshold voltage Vth1b and lower than the first high threshold voltage Vth1a (see Fig. 2), in addition to the abnormality of "increased resistance of connector resistor Rc" indicated by the dashed x mark, the following abnormalities can be detected as indicated by the solid x marks. [1] When the input switch SW1 is OFF, the resistance of the external pull-down resistor Rd increases. [2] Increase in resistance of the ON contact of input switch SW1 when it is ON.

[0093] 20 shows the configuration of the second embodiment of the open circuit detection circuit shown in Fig. 11, i.e., the open circuit detection circuit in which the external pull-up resistor Ru is connected in parallel with the input switch SW1. When the input voltage Vin is higher than the second high threshold voltage Vth1b and lower than the first high threshold voltage Vth1a (see Fig. 12), this open circuit detection circuit can detect the abnormality of "increased resistance of connector resistor Rc" indicated by the dashed x mark, as well as the following abnormalities indicated by the solid x marks. [1] When the input switch SW1 is OFF, the resistance of the external pull-up resistor Ru decreases. [2] Increase in resistance of the ON contact of input switch SW1 when it is ON.

[0094] The present invention is not limited to the above-described embodiment, and can be embodied in various forms without departing from the spirit of the invention. [Explanation of symbols]

[0095] 2 connectors, 301-304···Control unit, 401-404... Comparison and Judgment Department, 50, 503 ··· Input IC, 51a, 51b, 52, 52a, 52b... Comparators, 55 Signal processing circuit, 60 ···Microcomputer, Rd: External pull-down resistor, Rs: Input path resistance, R1: Internal pull-down resistor, R3: Internal pull-up resistor, SW1: Input switch.

Claims

1. In a control unit (301-304) to which a supply voltage (Vs) that is switched between supply and non-supply by turning an input switch (SW1) ON / OFF or a Hi / Lo level signal indicating a voltage level is input via a connector (2), a comparison / determination unit (401-404) that compares the supply voltage or the voltage of the level signal input via the connector from outside the control unit with a predetermined threshold voltage, said method comprising: The end of the connector on the control unit side is grounded via an internal pull-down resistor (R1) and is connected to the comparison / determination unit via an input path resistor (Rs), The comparison and determination unit The input voltage (Vin) is a voltage on the comparison / determination unit side of the input path resistor, and the input voltage determination result is obtained by comparing the input voltage (Vin) with three or more threshold voltage levels including a first high threshold voltage (Vth1a), a second high threshold voltage (Vth1b), and a low threshold voltage (Vth2) set in descending order, based on the input voltage determination results obtained multiple times in succession. When the number of times that a first condition, in which the input voltage is higher than the first high threshold voltage, is satisfied is equal to or greater than a first determination number, it is determined that the input switch is ON or that the level signal is Hi; determining that there is a sign of disconnection of the connector when the number of times a second condition, that is, the input voltage is higher than the second high threshold voltage and lower than the first high threshold voltage, is met is equal to or greater than a second determination number; determining that the connector is disconnected when the number of times that a third condition, that is, the input voltage is higher than the low threshold voltage and lower than the second high threshold voltage, is met is equal to or greater than a third determination number; When the number of times that a fourth condition that the input voltage is lower than the lower threshold voltage is met is equal to or greater than a fourth determination number, the method determines that the input switch is OFF or that the level signal is Lo.

2. 2. The disconnection detection method according to claim 1, wherein the second determination count is set to a value greater than the first determination count.

3. The end of the connector opposite the control unit (301, 303, 304) is grounded via an external pull-down resistor (Rd); The control unit side end of the connector is further connected to a high potential line via an internal pull-up resistor (R3), 3. The disconnection detection method according to claim 1, wherein the comparison / determination unit determines whether or not the external pull-down resistor is disconnected and whether or not there is a sign of a disconnection, in addition to the connector.

4. A disconnection detection circuit used in the disconnection detection method according to claim 1 or 2, The comparison and determination unit (401-403) an input IC (50, 503) including three or more comparators (51a, 51b, 52, 52a, 52b) that compare the input voltage with each of the threshold voltages, and a signal processing circuit (55) that processes an output signal of each of the comparators; a microcomputer (60) that determines whether or not there is at least a disconnection or a sign of a disconnection in the connector based on the input voltage determination result by the input IC; An open-wire detection circuit including:

5. 5. The disconnection detection circuit according to claim 4, wherein the comparison / determination unit further includes a non-volatile memory (65) for continuously storing the count value of the number of determinations written during operation of the microcomputer when the operation of the microcomputer is stopped.

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