JPH09211051A - Disconnection-diagnosing apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable disconnection diagnosis without influencing resolution of an analog signal collected from outside. SOLUTION: A microcomputer 12 having an A/D-conversion input port 12i and a three-state buffer output port 12o connected via a diagnosis resistor Rs switches and selects an analog input collection mode and a disconnection diagnosis mode appropriately, wherein in the analog input collection mode, the three-state buffer output port 12o is switched to a high impedance output state for substantially voiding existence of the diagnosis resistor Rs, while in the disconnection diagnosis mode, the three-state buffer output port 12o is switched to a high/low output state for identifying an analog signal input to the A/D-conversion input port 12i with respect to a threshold for determining whether disconnection exists. Thus correct A/D-conversion of the analog signal and proper detection of disconnection may be possible.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a disconnection diagnostic device capable of diagnosing the presence or absence of disconnection of an analog input circuit connected to an arithmetic unit without degrading signal detection accuracy.

[0002]

2. Description of the Related Art With the computerization of on-vehicle control units, the computational load on the microcomputer, which is the center of the unit, is increasing, and engine control, anti-lock brake control, traction control, four-wheel steering control, etc. It can be said that the role of the microcomputer for complexly digesting programs for various control purposes such as airbag control is very important. A wheel speed sensor, a steering angle sensor, etc. are connected to such a microcomputer as a sensor for detecting a wheel speed pulse, a steering angle, etc. These sensors are controlled via a signal line bundled in a wire harness. Because it is connected to the unit,
If the wire harness is broken, there is a danger that it will immediately fall into an uncontrollable state.

For this reason, a disconnection diagnostic device for diagnosing the disconnection of the signal line communicating with the sensor is mounted on the vehicle to detect the disconnection and avoid the control system on the safe side and at the same time notify the occurrence of an abnormality without inserting hair. The number of built-in control units themselves is increasing. Even if it is called disconnection detection, it is necessary to take appropriate measures for disconnection diagnosis of analog signal lines after considering the effect of circuit addition to the signal line on the signal level. It has been recommended to use a high input impedance element, such as an operational amplifier, which has a small effect on.
However, such an operational amplifier is originally relatively expensive, and since the disconnection detection part is easily exposed to surge noise, a protective circuit and a protective element that protect the circuit from surge noise are indispensable, and such additional parts are manufactured. There was a problem that increased the cost.

On the other hand, in order to realize the disconnection diagnosis inexpensively and easily, for example, the disconnection diagnosis apparatus 1 shown in FIG. 5 has been proposed and already put into practical use. In the figure, a resistor formed by connecting a variable resistor Rv and a fixed resistor Rf in series constitutes an analog signal circuit 2 for detecting a physical quantity by changing it into a resistance value. For example, an angle value of a rotating shaft of a motor. Corresponds to a potentiometer or the like for converting the resistance value into a resistance value. Both ends of the analog signal circuit 2 are connected to a power supply output terminal 3v and a ground terminal 3g provided in the control unit 3, and a resistance output terminal for outputting a resistance value corresponding to the angle value of the motor rotation shaft,
It is connected to the analog input terminal 3i of the control unit 3. The analog input terminal 3i has an input resistor R for current limiting.
It is connected to the A / D conversion input port 4i of the microcomputer 4 via i. An A / D converter 5 is connected to the A / D conversion input port 4i, and the input voltage Vs is converted into a binary digital signal and taken in. As a result, the resistance value output indicating the angle value is output to the microcomputer 4
Is input to

By the way, the angle value of the motor rotation axis takes the minimum value when the resistance output terminal of the analog signal circuit 2 is shown in FIG.
The resistance output voltage Vt at this time is the minimum value Vmin = Rf · Vcc / (Rv
+ Rf). On the other hand, in the case where the wire harness is broken at the portion indicated by the mark X in FIG. 5, the A / D conversion input port 4i of the microcomputer 4 is opened when it is assumed that the diagnostic resistance Rs described later does not exist. Therefore, the input voltage Vs of the A / D converter 5 becomes indefinite. Moreover, since the A / D conversion input port 4i becomes high impedance, the microcomputer 8 falls into a latch-up state. Therefore, in order to avoid such latch-up, a method has been used in which a diagnostic resistor Rs is branched and connected in the middle of a signal line connecting the input resistor Ri and the A / D conversion input port 4i, and one end of the diagnostic resistor Rs is grounded. It was

In this case, since the diagnostic resistor Rs plays the role of a pull-down resistor, even if the disconnection occurs at the above-mentioned portion marked with "X", the input voltage Vs is almost equal to the ground level (0V) at the A / D conversion input port 4i. ) Voltage is applied.
As a result, the microcomputer 4, which has detected a voltage close to the ground level which is less than the minimum voltage Vmin in the normal state through the A / D converter 5, disconnects the signal input system reaching the A / D conversion input port 4i. Can be judged,
Moreover, even though it is in the disconnection state, since the A / D conversion input port 4i is pulled down to the ground level through the diagnostic resistor Rs, the microcomputer 8 does not fall into the latch-up state, and the disconnection is generated with an alarm signal. Can be notified.

[0007]

In the above-described conventional disconnection diagnosis apparatus 1, for example, the resistances Ri and Rs are set to have substantially the same resistance value (for example, Ri = Rs = 100 KΩ), and the resistance value of the variable resistance Rv is set to the resistance Ri. , Rs, the input voltage Vs is equal to the resistance output voltage Vt.
About half, that is, Vs = Vt / 2. The value of this input voltage Vs is Vs when the diagnostic resistor Rs is not provided.
This means that the resolution is reduced to 1/2 as compared with (= Vt). In order to avoid such a decrease in resolution, it is best to make the resistance value of the diagnostic resistor Rs larger than the input resistor Ri. For example, by setting Rs = 1 MΩ, the resolution is considerably improved. However, since the A / D converter 5 always has a leakage current of several μA, the leakage current flowing into the diagnostic resistor Rs when the wire harness is disconnected has an input voltage Vs that reaches a level confusing with a normal signal input. It happened. For this reason, in the conventional disconnection diagnosis apparatus 1, as the resistance value of the diagnostic resistor Rs is increased in order to avoid the deterioration of the resolution due to the A / D converter 5, the risk of the occurrence of disconnection increases, and vice versa. As the resistance value of the diagnostic resistor Rs is made smaller in order to improve the disconnection detection accuracy, a decrease in resolution due to the A / D converter 5 cannot be avoided,
Since a circuit design that meets these conflicting requirements is required, there is a problem that the degree of freedom in selection is extremely narrow.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned conventional problems and to provide a disconnection diagnosing device capable of diagnosing disconnection without affecting the resolution of an analog signal fetched from the outside. .

[0009]

In order to achieve the above object and solve the above problems, the present invention provides an analog signal circuit for converting a physical quantity into an analog signal and outputting the analog signal, and a predetermined output of the analog signal circuit. An input matching circuit for limiting the amplitude within the lower limit range, an A / D conversion input port for inputting the analog signal taken in by the input matching circuit, and a three-state output state of high / low output or high impedance output An arithmetic unit having a state buffer output port and a diagnostic resistor for connecting the A / D conversion input port and the three-state buffer output port are provided, and the arithmetic unit appropriately operates in an analog input capture mode and a disconnection diagnosis mode. Select to switch, and in analog input capture mode, set the three-state buffer output port to high To the impedance output state to substantially eliminate the presence of the diagnostic resistor, and in the disconnection diagnostic mode, switch the three-state buffer output port to the high / low output state and input to the A / D conversion input port. The present invention is characterized in that the presence or absence of disconnection is determined by performing threshold value determination on the generated analog signal.

In the present invention, the analog signal circuit is a potentiometer whose resistance value changes in accordance with a physical quantity, or the input matching circuit uses the power supply voltage as an upper limit voltage and the ground level as a lower limit voltage. It is characterized by including a pair of diodes for clamping signals.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. 1 is a block diagram showing a basic configuration of an embodiment of the disconnection diagnosis apparatus of the present invention, FIG. 2 is a circuit configuration diagram showing a specific circuit configuration of the disconnection diagnosis apparatus shown in FIG. 1, and FIG. 3 is a flowchart showing an operation program of the microcomputer shown in FIG. 2.

The disconnection diagnosis device 11 shown in FIGS. 1 and 2 has a microcomputer 12 as an arithmetic unit, and has three output states of high / low output or high impedance output in addition to the A / D conversion input port 12i. The three-state buffer output port 12o is provided, and the AD converter 13 and the three-state buffer 14 are connected to the respective ports 12i and 12o. Also, the diagnostic resistance Rs
Are connected by connecting both ports 12i and 12o.

The AD conversion input port 12i of the microcomputer 12 is connected to the analog signal circuit 2 via the input matching circuit 15. The input matching circuit 15 includes an input resistor Ri, a capacitor C, and a pair of clamping diodes D1 and D2. The capacitor C forms a low-pass filter together with the input resistor Ri, and has a function of removing high-frequency noise superimposed on the signal line of the resistance output voltage Vt. Also, a pair of diodes D
1 and D2 clamp high-voltage surge pulses superposed on the signal line of the resistance output voltage Vt to the power supply voltage Vcc and the ground level, respectively, and set the input voltage Vs of the A / D converter 5 to the upper and lower limit voltage range 0 <. It plays a role of protecting the microcomputer 12 by limiting the amplitude to Vs <Vcc.

In the case of this embodiment, the microcomputer 12 and the input matching circuit 15 are housed in the control unit 16, and both ends of the analog signal circuit 2 are connected to the power output terminal 16v and the ground terminal 16g of the control unit 16. A resistance output terminal for outputting a resistance value corresponding to the angle value of the motor rotation shaft is connected to the analog input terminal 16i of the control unit 16. Further, the control unit 16 is
Similar to the conventional control unit 3, it contributes to all control purposes required for vehicle-mounted electronic devices such as engine control, anti-lock brake control, traction control, four-wheel steering control, and airbag control.

The three-state buffer 14 incorporated in the microcomputer 12 is a non-inverting logic element with a control terminal, and when data "0" is set to its input terminal LV, the three-state buffer output port 12o has a low level (0V). ) Is output and data “1” is output.
Set to three-state buffer output port 12
A high level (Vcc) is output to o. Further, when the control data “0” is set to the control terminal OC, the three-state buffer output port 12o assumes the third state, that is, the high impedance output state, and the diagnostic resistance R is substantially set.
It is possible to eliminate s in the disconnected state. In addition, when the control data “1” is set to the control terminal OC, a voltage corresponding to the high / low of the data of the input terminal LV is output, and the series of data set to the input terminal LV and the control terminal OC is This is performed according to an operation program built in the microcomputer 12.

Here, the microcomputer 12 switches between the analog input taking-in mode and the disconnection diagnosis mode by time division according to the operation program shown in FIG.
This operation program is executed by the microcomputer 8
It is started in synchronization with the processing cycle of the control program built in.

First, in step (101) of FIG. 3, when it is determined that the analog input capture mode is selected, the microcomputer 12 proceeds to the following step (1).
02), control data “0” is set to the control terminal OC of the three-state buffer 14, and the three-state buffer output port 12o is switched to the high impedance output state. As a result, the presence of the diagnostic resistor Rs is substantially eliminated, and the state is the same as when the diagnostic resistor Rs is not connected to the analog signal line. As a result, the resistance output voltage Vt
Is not divided by the resistors Ri and Rs, and is input to the A / D conversion input port 12i as Vs = Vt. Therefore, even if the resistance value of the diagnostic resistor Rs is not set to a large value, there is no need to worry about the deterioration of the resolution, and the A / D conversion is performed on the A / D converter 13 in step (103). By doing so, highly accurate analog / digital conversion is possible.

On the other hand, in the disconnection diagnosis mode, in the step (104) following the judgment step (101),
Data "0" is set to the input terminal LV of the three-state buffer 14. Next, in step (105), the control data “1” is set to the control terminal OC of the three-state buffer 14, and the three-state buffer output port 12o is switched to the low output state. As a result, the analog signal input to the A / D conversion input port 12i is divided by the voltage division ratio Rs / (Ri + Rs) and supplied to the AD converter 13. Here, when the resistance value Ri = Rs = 100 KΩ is used as an example, the voltage division ratio k is 1/2, and the input voltage Vs Vt / 2 is A / D converted by the A / D converter 13 in step (106). D converted.

Since the minimum voltage Vmin of the resistance output voltage Vt relating to the analog signal circuit 2 is known, the input voltage Vs is set to kVmin (=
The presence or absence of disconnection is determined by the threshold value determination based on Vmin / 2). That is, if Vs ≧ kVmin, the wire harness is not broken, and conversely, if Vs <kVmin, the wire harness is broken. When the disconnection occurs, the analog signal line is pulled down via the diagnostic resistor Rs, so that the input voltage Vs becomes almost 0V. The voltage value obtained by multiplying the leakage current leaking from the A / D converter 13 by the resistance value of the diagnostic resistor Rs is also included in this approximately 0V, and the voltage value is sufficiently lower than kVmin. It goes without saying that it is designed to Thus, in step (108), the disconnection judgment is made,
Measures are taken such as returning the control system to the safe side (fail safe mode) or issuing an alarm. The analog input acquisition and the disconnection diagnosis are repeatedly performed every control cycle, and therefore the disconnection state is not overlooked for a long time.

As described above, according to the disconnection diagnosis device 11, the A / D conversion input port 12i and the three-state buffer output port 12o connected with the diagnosis resistor Rs are connected.
The microcomputer 12 having a timely switching selection between the analog input capturing mode and the disconnection diagnosis mode,
In the analog input capture mode, the three-state buffer output port 12o is switched to a high impedance output state, and the existence of the diagnostic resistor Rs is substantially eliminated.
In the disconnection diagnosis mode, the three-state buffer output port 12o is switched to the high / low output state and the A /
Since the analog signal input to the D conversion input port 12i is discriminated by the threshold value to determine the presence / absence of disconnection, even if the resistance value of the diagnostic resistor Rs is set to be approximately the same as the resistance value Ri of the input matching circuit 15. , A sufficient voltage value necessary for maintaining the signal detection accuracy can be secured, and therefore the resolution value is improved as in the conventional case, so that the resistance value of the diagnostic resistor Rs is set too large and A / D conversion is performed when a disconnection occurs. Input port 12
Since the leakage current leaking from i does not hinder the disconnection detection and the resistance value of the diagnostic resistor Rs does not need to be unreasonably increased, the input voltage Vs of the A / D conversion input port 12i in the disconnection diagnosis mode is also reduced. If the disconnection does not occur, the resistance detection voltage Vt in the analog input capture mode is set to the resistance value Ri of the input matching circuit 15 and the diagnostic resistance Rs.
The voltage can be clearly discriminated by the voltage division ratio k = Rs / (Ri + Rs) as a diagnostic voltage during non-breakage, and if a breakage occurs, it leaks from the A / D conversion input port 12i. It is possible to clearly determine the threshold value as the diagnostic voltage at the time of disconnection, which is the value obtained by multiplying the leakage current by the resistance value of the diagnostic resistor Rs, and unlike the conventional case, it is not necessary to make a contradictory choice between ensuring analog signal resolution and eliminating false diagnostics. Therefore, the degree of freedom in circuit design is high, and it can be applied to a wide range of disconnection diagnosis.

Further, the input matching circuit 15 clamps the analog signal with the power supply voltage Vcc as the upper limit voltage and the ground level as the lower limit voltage to clamp a pair of diodes D.
Since the output voltage of the analog signal circuit 2 is superposed on the output voltage of the analog signal circuit 2, the pair of diodes D
The amplitude is limited to the input voltage by 1 and D2.
A / D converter 13 connected to D conversion input port 12i
It is possible to prevent the microcomputer 12 from malfunctioning due to an excessive input or an excessive input via the above, and it is possible to surely eliminate an erroneous diagnosis due to the surge voltage even in the disconnection diagnosis mode.

Although the fixed resistance Rf is connected to the ground terminal 16g side with respect to the variable resistance Rv in the analog signal circuit 2 in the above embodiment, the disconnection diagnostic device 21 shown in FIG. As described above, when the fixed resistance Rf is connected to the power output terminal 16v side, the data “1” is set to the input terminal LV of the three-state buffer buffer 14 in the disconnection diagnosis mode, and the control data is further set to the control terminal OC. The high level output (Vcc) may be supplied from the three-state buffer 14 by setting "1". That is, since the analog signal circuit 2 is composed of a potentiometer whose resistance value changes in accordance with a physical quantity, for example, the power supply voltage Vcc and its fraction up to a fraction thereof, depending on the common range of the voltage output due to the resistance change of the potentiometer. If the voltage range of the three-state buffer is 0, the three-state buffer output port 12o may be switched to the low level in the disconnection diagnosis mode, and if the normal range is a fraction of the power supply voltage Vcc and the ground level, the three-state buffer. By taking measures such as switching the output port 12o to a high level in the disconnection diagnosis mode, appropriate measures can be taken according to the specifications of each potentiometer.

Further, in the above description, the wire harness disconnection detection has been described. However, an event equivalent to the condition determined as the wire disconnection in the flowchart of FIG. 3, for example, the wire disconnection inside the control unit 16 such as the input resistance Ri, etc. It is clear that can also be detected accurately as well.

[0024]

As described above, according to the present invention,
An arithmetic unit having an A / D conversion input port and a three-state buffer output port connected with a diagnostic resistor,
Switch between analog input capture mode and disconnection diagnosis mode at the appropriate time.In analog input capture mode, switch the three-state buffer output port to high-impedance output state, virtually eliminate the existence of diagnostic resistor, and switch to disconnection diagnosis mode. If so, the three-state buffer output port is switched to the high / low output state, and the A / D
Even if the resistance value of the diagnostic resistor is set to the same level as the resistance value of the input matching circuit, the signal detection accuracy is maintained because the analog signal input to the conversion input port is determined by the threshold value to determine the presence or absence of disconnection. Since a sufficient voltage value necessary for the above can be secured, and therefore the resolution is improved as in the conventional case, the resistance value of the diagnostic resistor is set too large and the leakage leaks from the A / D conversion input port when a disconnection occurs. The current does not hinder disconnection detection, and since the resistance value of the diagnostic resistor does not need to be unreasonably increased, if the input voltage of the A / D conversion input port in the disconnection diagnosis mode does not occur, As a diagnostic voltage at the time of non-interruption, the output voltage of the analog signal circuit in the analog input capture mode is compressed by a voltage division ratio that is almost determined by the resistance value of the input matching circuit and the diagnostic resistance. The threshold value can be accurately determined, and when a disconnection occurs, the threshold value can be clearly determined as the disconnection diagnostic voltage of a value obtained by multiplying the leakage current leaking from the A / D conversion input port by the resistance value of the diagnostic resistor. Since it is not necessary to make a trade-off between ensuring analog signal resolution and eliminating false diagnostics as in the past, the degree of freedom in circuit design is high and it is possible to apply it to a wide range of disconnection diagnostics. Play.

Further, according to the present invention, since the analog signal circuit is constituted by the potentiometer whose resistance value changes in accordance with the physical quantity, for example, the power supply voltage and the number thereof can be changed according to the common range of the voltage output due to the resistance change of the potentiometer. If the voltage range is up to one-tenth, the three-state buffer output port may be switched to the low level in the disconnection diagnosis mode, and if the common range is a fraction of the power supply voltage and the ground level. By taking measures such as switching the output port of the three-state buffer to the high level in the disconnection diagnosis mode, it is possible to take an appropriate action according to the specifications of each potentiometer.

Furthermore, according to the present invention, an input matching circuit is
Since it has a pair of diodes that clamp the analog signal with the power supply voltage as the upper limit voltage and the ground level as the lower limit voltage, even if a surge voltage or the like is superimposed on the output voltage of the analog signal circuit, the pair of diodes causes the input voltage with respect to the input voltage. Amplitude is restricted, and the arithmetic unit can be prevented from malfunctioning due to excessive input or excessive input via the A / D converter connected to the A / D conversion input port, and also due to surge voltage in the disconnection diagnosis mode. There is an effect that erroneous diagnosis can be reliably eliminated.

[Brief description of drawings]

FIG. 1 is a block diagram showing a basic configuration of an embodiment of a disconnection diagnosis apparatus of the present invention.

FIG. 2 is a circuit configuration diagram showing a specific circuit configuration of the disconnection diagnostic device shown in FIG.

FIG. 3 is a flowchart showing an operation program of the microcomputer shown in FIG.

FIG. 4 is a circuit configuration diagram showing another embodiment of the disconnection diagnostic device shown in FIG.

FIG. 5 is a circuit configuration diagram showing an example of a conventional disconnection diagnosis device.

[Explanation of symbols]

 2 analog signal circuit 3 control unit 11, 21 disconnection diagnostic device 12 microcomputer (arithmetic device) 12i A / D conversion input port 12o three-state buffer output port 13 A / D converter 14 three-state buffer 15 input matching circuit 16 control unit 16v power output terminal 16g ground terminal 16i analog input terminal

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Kensuke Otake, 1-4-4 Jomi, Chuomi-ku, Osaka-shi, Osaka, NEC Home Electronics Co., Ltd. (72) Hirotaka Kojima Jomi, Chuo-ku, Osaka-shi, Osaka 1-4-24, NEC Home Electronics Co., Ltd.

Claims (3)

[Claims] 1. An analog signal circuit for converting a physical quantity into an analog signal and outputting the analog signal, an input matching circuit for acquiring the output of the analog signal circuit while limiting the amplitude within a predetermined upper and lower limit range, and an input matching circuit for acquiring the output. An A / D conversion input port for inputting an analog signal and a three-state buffer output port for taking three output states of high / low output or high impedance output;
The arithmetic unit comprises a diagnostic resistor for connecting the / D conversion input port and the three-state buffer output port, and the arithmetic unit selects the analog input capturing mode and the disconnection diagnostic mode at appropriate times. Switching the three-state buffer output port to a high impedance output state, substantially eliminating the presence of the diagnostic resistor, and switching the three-state buffer output port to a high / low output state in the disconnection diagnosis mode, A disconnection diagnosis apparatus characterized in that an analog signal input to an A / D conversion input port is discriminated by a threshold value to determine the presence or absence of disconnection. 2. The disconnection diagnosis apparatus according to claim 1, wherein the analog signal circuit is a potentiometer whose resistance value changes according to a physical quantity. 3. The disconnection diagnosis apparatus according to claim 1, wherein the input matching circuit includes a pair of diodes that clamp the analog signal with a power supply voltage as an upper limit voltage and a ground level as a lower limit voltage.