JP4958924B2 - Glow plug fault diagnosis device - Google Patents

Description

  The present invention relates to a glow plug failure diagnosis apparatus for diagnosing a failure in a glow plug used in a diesel engine and a glow controller that controls energization to the glow plug.

  In a diesel engine (hereinafter, simply referred to as “engine”. Therefore, when simply described as “engine” in the present specification, it means a diesel engine.) If the temperature is low, the ignitability of the fuel will deteriorate and the engine will be difficult to start. Therefore, the engine is started in a state where the combustion chamber or the like is preheated using a glow plug and the ignitability of the fuel is improved.

  Such a glow plug has a built-in heater that generates heat when energized. The heater is a resistor whose resistance value basically does not substantially change. Therefore, in order to facilitate temperature control, in many cases, a glow plug having a built-in control coil whose resistance value greatly changes according to temperature is used in addition to the heater. Generally, the glow plug is attached to the engine block of the engine so that the front end of the heater is located in the combustion chamber.

  A glow controller that controls energization of a glow plug generally performs the following control. That is, when the ignition switch, which changes state according to the operation of the ignition key, is switched to the ON position, the temperature of the glow plug heater rises toward a target temperature (for example, 1000 ° C.) sufficient for starting the engine. In other words, the energization of the heater is controlled so that large electric power is supplied. Such control is called pre-glow or the like. In the case of a glow plug capable of rapid heating, the heater can be raised to the target temperature in about several seconds.

  After the glow plug heater reaches the target temperature, energization of the heater is controlled so that the heater temperature is maintained at the target temperature (eg, 900 ° C.) for a predetermined period (eg, 180 seconds). Such control is called afterglow or the like. In the afterglow control, electric power smaller than that of the pre-glow is supplied to the heater.

  Before starting the engine, the startability of the engine can be improved by maintaining the heater of the glow plug at a sufficiently high temperature. In addition, after starting the engine, the glow plug heater is maintained at a sufficiently high temperature to prevent engine knocking, noise, white smoke, and hydrocarbon (HC) emissions. Can be suppressed.

  Glow controllers that control energization of the glow plug are disclosed in, for example, Patent Document 1 and Patent Document 2.

  In the technique described in Patent Literature 1, energization to the heater of the glow plug is switched on / off using a relay having a mechanical contact. In the technique described in Patent Document 2, a switching transistor (ie, FET) is used to switch on / off of energization to the heater of the glow plug. Further, the signal input to the transistor is subjected to pulse width modulation control (that is, PWM control), thereby enabling precise control of the power supplied to the heater.

  By the way, in the glow controller as described above, it is necessary to diagnose a failure or the like. For example, if a failure such as disconnection of the heater (ie, open) occurs in the glow plug, the engine combustion chamber cannot be heated, and the engine is difficult to start. Therefore, it is necessary to inform the driver of the occurrence of the failure. In addition to the disconnection of the heater, there may be a failure of a relay or a transistor inside the glow controller or a short circuit.

  With regard to Patent Document 1, a switch element for failure diagnosis is connected to a path provided in parallel with a contact of a relay for turning on / off energization of a heater of a glow plug. When the relay is off, the switch element is turned on for a short time to energize the heater, and the failure is diagnosed by the voltage detected at this time.

  Further, although not related to the glow controller, Patent Document 3 discloses a technique for diagnosing a failure in a circuit that controls energization of a heater. Patent Document 3 discloses that diagnosis is performed based on a combination of an on / off state of a switching element that controls energization and a detected signal level.

  By the way, when energization control is performed on the heater of the glow plug, for example, when an excessive current flows due to a short circuit or the like, there is a possibility that a more serious failure than the above may occur. In addition, when the temperature of the switching element that switches energization on / off abnormally rises, the switching element or the like may be destroyed, thereby causing further failure.

  Conventionally, in order to protect the glow controller circuit from such overcurrent and abnormal heat generation, it has been necessary to provide a special element such as a temperature sensor or a protection circuit having a relatively complicated configuration. However, in recent years, switching elements (for example, FET: field effect transistor) incorporating a self-protection function are commercially available. By using this switching element for turning on / off the energization of the heater, it is not necessary to add a special protection circuit or sensor, and the cost can be reduced.

  A switching element with a built-in self-protection function automatically shuts off the current when excessive current continues to flow and the temperature of the switching element rises above a predetermined value, protecting the switching element itself and other circuits. In addition, when the temperature falls, the original state is automatically restored and the interruption of the current is released, so that it is not necessary to provide any other special control circuit.

JP 2002-13461 A JP 2007-292063 A JP-A-5-73157

  However, even when a switching element incorporating such a self-protection function is employed, a problem may occur when diagnosing a fault in the glow controller. That is, it is impossible to distinguish between a state in which the switching element fails and no current flows, and a state in which no current flows due to the protection function inside the switching element.

  If the switching element fails and no current flows, the diagnosis that the failed switching element needs to be replaced is sufficient. However, if the protection function inside the switching element is activated and no current flows, the normal state is restored due to a decrease in temperature, so that it is not enough to diagnose that there is no need to replace the switching element.

  In other words, there should be some cause that the protection function inside the switching element works and no current flows. Therefore, when the glow controller diagnoses the failure, it is necessary to distinguish between the failure of the switching element and the operating state of the protection function.

  However, since the switching element with a built-in self-protection function does not output a signal indicating whether the protection function is working, the glow controller cannot recognize whether the protection function is working. In particular, when pulse width modulation control (that is, PWM control) is performed on the current flowing through the heater, when a control signal (that is, a PWM signal) indicating an ON state is input to the switching element, the current flows through the switching element. After a while, the self-protection function may be activated to interrupt the current.

  Therefore, depending on the timing of monitoring whether or not current is flowing through the switching element, it may be recognized that current is flowing, or it may be recognized that current is not flowing. The glow controller cannot determine when the self-protection function works. Therefore, it is difficult to correctly diagnose whether or not the switching element has failed and whether the self-protection function is working.

  The present invention has been made in view of the above-described circumstances, and its purpose is to control on / off of energization by pulse width modulation control using a switching element incorporating a self-protection function. It is an object of the present invention to provide a glow plug failure diagnosis apparatus capable of correct diagnosis.

(1) A glow plug failure diagnosis apparatus according to the present invention includes:
A switching element that turns on / off energization of a glow plug from a predetermined power supply line; and a pulse signal generation unit that generates a periodically changing pulse signal for controlling the switching element. Is used for a glow controller with a built-in self-protection function that cuts off current against excessive current flowing through itself or excessive heat generation of the switching element itself,
Glow plug fault diagnosis device,
A current detection circuit for detecting a current flowing through the glow plug;
A signal latch circuit that temporarily holds a state of a current signal output from the current detection circuit;
A voltage detection circuit for detecting a voltage applied to the glow plug for energization;
When energization to the glow plug is in an on state, the voltage signal output from the voltage detection circuit and the current signal output from the signal latch circuit are monitored, and based on the state of the voltage signal and the current signal A diagnostic processing circuit for performing diagnostic processing on at least the presence or absence of a failure;
Is provided.
(2) In the glow plug fault diagnosis device of (1) above,
After the signal latch circuit has a reset control input terminal for resetting the state of the current signal being held, and the diagnostic processing circuit has switched the switching element from on to off after the pulse signal It is preferable that a predetermined reset signal is given to the reset control input terminal of the signal latch circuit.
(3) In the glow plug fault diagnosis apparatus of (1) above,
It is preferable that the diagnostic processing circuit is configured to output a diagnostic result relating to disconnection of the glow plug when the voltage detected by the voltage detection circuit is equal to or higher than a predetermined value.
(4) In the glow plug fault diagnosis apparatus of (1) above,
When the diagnostic processing circuit detects that the voltage detected by the voltage detection circuit is less than a predetermined value and that a predetermined current is flowing by a current signal output from the signal latch circuit, It is preferable that the diagnosis result regarding the operation of the self-protection function of the switching element is output.
(5) In the glow plug failure diagnosis apparatus of (1) above,
When the diagnostic processing circuit detects that the voltage detected by the voltage detection circuit is less than a predetermined value and the current signal output from the signal latch circuit does not flow, It is preferable that the diagnosis result regarding the failure of the switching element is output.

According to the glow plug failure diagnosis apparatus having the configuration of (1), the diagnosis processing circuit determines whether or not there is a failure based on the voltage detected by the voltage detection circuit and the current detected by the current detection circuit. Diagnosis can be made. In addition, since the signal latch circuit is provided, the current signal output from the current detection circuit can be held for a while. In other words, after the current flows to the glow plug, when the current is interrupted by the self-protection function of the switching element, a signal indicating that the current is detected is held in the signal latch circuit, so that the diagnosis process Even if the circuit refers to the current signal at an arbitrary timing, it can be correctly diagnosed whether or not the current flows. When the switching element has failed and is maintained in the OFF state, current does not always flow even when the control signal applied to the switching element is switched to the ON state, so that it is distinguished from the state in which the self-protection function has worked. Can do.
According to the glow plug failure diagnosis apparatus having the configuration (2), since the diagnosis processing circuit performs reset control of the signal latch circuit, the holding state of the signal latch circuit until the diagnosis processing circuit refers to the current signal. Can be maintained. Therefore, the degree of freedom regarding the timing at which the diagnostic processing circuit refers to the current signal is increased.
According to the glow plug failure diagnosis apparatus having the configuration (3), it is possible to make a diagnosis regarding disconnection of the glow plug. That is, when a disconnection occurs in the glow plug that is a load of the glow controller, a load current does not flow, so that a voltage applied to the glow plug becomes higher than that in a normal state. Therefore, it is possible to identify the presence or absence of disconnection.
According to the glow plug failure diagnosis apparatus having the configuration (4), it is possible to make a diagnosis regarding the operation of the self-protection function of the switching element. That is, when it is detected that a predetermined current is flowing by the current signal output from the signal latch circuit, no failure has occurred in the switching element, and the self-protection function of the switching element is working. It is determined. On the other hand, if the voltage detected by the voltage detection circuit is less than a predetermined value, it is determined that there is no glow plug disconnection.
According to the glow plug failure diagnosis apparatus having the configuration (5), it is possible to make a diagnosis regarding the failure of the switching element. If the switching element is not broken, even if the self-protection function is activated, a signal indicating that the current has flowed since the current is interrupted by the heat generated after a predetermined current flows for a short time. Is held in the signal latch circuit. Therefore, when it is detected that a predetermined current is not flowing by the current signal output from the signal latch circuit, the switching element is broken because the current does not flow before the self-protection function is activated. Can be diagnosed.

  According to the present invention, a correct diagnosis can be made even when energization on / off is controlled by pulse width modulation control using a switching element incorporating a self-protection function. That is, after the current flows to the glow plug, when the current is interrupted by the self-protection function of the switching element, a signal indicating that the current is detected is held in the signal latch circuit. Even if the current signal is referred to at an arbitrary timing, it can be correctly diagnosed whether or not the current flows. When the switching element has failed and is maintained in the OFF state, current does not always flow even when the control signal applied to the switching element is switched to the ON state, so that it is distinguished from the state in which the self-protection function has worked. Can do.

  The present invention has been briefly described above. Further, details of the present invention will be further clarified by reading through the modes for carrying out the invention described below with reference to the accompanying drawings.

It is a system block diagram which shows the structure of the principal part regarding the glow controller carrying the glow plug failure diagnostic apparatus of this invention. It is a time chart which shows the waveform of the signal of each part in the glow controller shown in FIG. 1, and the timing of control. It is a flowchart which shows the content of the process regarding the failure diagnosis in the glow controller shown in FIG.

  A preferred embodiment of a glow plug failure diagnosis apparatus according to the present invention will be described below with reference to FIGS.

  A glow plug 50 shown in FIG. 1 is attached to an engine block of an engine and used to heat a combustion chamber or the like in a cylinder. The glow plug 50 incorporates a heater in the same manner as a general glow plug that is commercially available. Specifically, the glow plug 50 includes a heat generating coil that generates heat when energized and a control coil for performing temperature control. The resistance value of the heating coil hardly changes with temperature change. The resistance value of the control coil changes greatly with respect to temperature changes. The heating coil and the control coil are electrically connected in series, and both ends of the series connection are electrically connected to the two terminals 50a and 50b.

  That is, when a voltage is applied between the terminals 50a and 50b, a current flows through the heat generating coil and the glow plug 50 generates heat. Also, due to the action of the control coil, a relatively large current flows when the temperature is low and the temperature rises rapidly, and when the temperature rises, the current decreases and the temperature rise is suppressed.

  Although only a single glow plug 50 is shown in FIG. 1, when controlling a four-cylinder engine, for example, it is necessary to install four glow plugs for each cylinder. When a plurality of glow plugs 50 are used, there are cases where a plurality of glow plugs 50 are connected in parallel and the energization of these is simultaneously turned on / off, or the energization of the plurality of glow plugs 50 is individually turned on / off. In some cases. There may be a case where a plurality of glow plugs 50 are connected in series and these energizations are simultaneously turned on / off.

  Energization of the glow plug 50 is controlled by the glow controller 100 shown in FIG. The glow controller 100 is also called GCU (that is, Glow Control Unit). The battery voltage VB supplied from the battery 55 mounted on the vehicle is applied between the terminals 50a and 50b of the glow plug 50 via the glow controller 100, whereby current flows through the glow plug 50 and the internal heating coil generates heat. To do.

  As shown in FIG. 1, the glow controller 100 includes a microcomputer 110, a current detection circuit 120, a voltage detection circuit 130, a signal latch circuit 140, and an energization control switching transistor Q1. A DC power supply voltage Vcc is applied as a power source to circuits such as the microcomputer 110. The DC power supply voltage Vcc is a stabilized voltage {for example, 5 V (volt)} and is generated based on the battery voltage VB.

  The energization control switching transistor Q1 performs switching for switching on / off of voltage application from the battery 55 to the glow plug 50. The energization control switching transistor Q1 is a MOS FET with a built-in self-protection function. In other words, the energization control switching transistor Q1 automatically cuts off the current for protection when an excessive current flows in itself or when an abnormal temperature rise is detected. When the temperature returns to normal or excessive current is not detected, the protection function is released and the original state is restored. However, it cannot be monitored from the outside whether or not the protective function is working inside the energization control switching transistor Q1. A specific example of the energization control switching transistor Q1 is PROFET (registered trademark) manufactured by Infineon Technologies AG. However, since the output voltage value of the output port P1 of the microcomputer 110 is actually smaller than the voltage value of the battery voltage VB, for example, between the output port P1 of the microcomputer 110 and the conduction control switching transistor Q1 and the battery 55, for example. It is preferable to provide an NPN bipolar transistor and an open collector circuit composed of a plurality of resistors so as to be electrically connected.

  The microcomputer 110 mainly controls on / off of the energization control switching transistor Q1 according to a program prepared in advance. The pulse signal SGpwm output from the output port P1 of the microcomputer 110 for controlling on / off of the switching transistor Q1 is a signal having a constant cycle and a variable pulse width (that is, a PWM signal). The period of the pulse signal SGpwm (see also Tpwm in FIG. 2) is set to, for example, about 1/40 second in order to avoid the fluctuation of the temperature of the glow plug 50.

  Normally, when the pulse signal SGpwm is turned on (ie, high level: HI), the conduction control switching transistor Q1 is turned on. When the pulse signal SGpwm is turned off (ie, low level: LO), the conduction control switching transistor is turned on. Q1 becomes non-conductive.

  The voltage applied to the glow plug 50 is changed by changing the pulse width of the pulse signal SGpwm and changing the ratio between the conduction period and the non-conduction period of the conduction control switching transistor Q1 (in other words, changing the duty ratio). The effective value can be changed. For example, if the pulse signal SGpwm having a duty ratio of 50% is applied to the conduction control switching transistor Q1 when the battery voltage VB is 12V, an effective value voltage of about 6V is applied to the glow plug 50. That is, the microcomputer 110 can adjust the energization state of the glow plug 50 by changing the pulse width of the pulse signal SGpwm.

  The current detection circuit 120 is a circuit for detecting whether a current of a predetermined value or more (that is, a normal range) flows from the battery 55 to the glow plug 50. As shown in FIG. 1, the current detection circuit 120 includes a resistor R1, a differential amplifier 121, a transistor Q2, and a resistor R4.

  As the resistor R1, a resistor having a very small resistance value is used so that the current flowing through the glow plug 50 is not greatly affected. When the current Igp flows through the glow plug 50, the differential amplifier 121 amplifies and outputs a voltage drop signal generated between the terminals of the resistor R1 due to this current. The transistor Q2 is an NPN-type bipolar transistor that is turned on / off according to the level of the signal output from the differential amplifier 121. That is, when a current Igp greater than a predetermined value is flowing, the output of the differential amplifier 121 is at a high level, the transistor Q2 is turned on, and the current signal SGi is at a low level (ie, LO). When the current Igp is not flowing or when the current is small, the output of the differential amplifier 121 becomes low level, the transistor Q2 is turned off, and the current signal SGi becomes high level (ie, HI). That is, the current signal SGi output from the current detection circuit 120 is a binary signal indicating whether or not a current Igp of a predetermined value or more is flowing through the glow plug 50.

  The signal latch circuit 140 is a circuit for temporarily holding the state of the current signal SGi output from the current detection circuit 120. As shown in FIG. 1, the signal latch circuit 140 includes an AND gate G1, a resistor R5, and a transistor Q3.

  The current signal SGi output from the current detection circuit 120 is applied to one input terminal of the AND gate G1. A resistor R5 and a transistor (specifically, a PNP bipolar transistor) Q3 are connected to the other input terminal of the AND gate G1. The current signal SGi2 output from the AND gate G1 is applied to the input port P3 of the microcomputer 110 and simultaneously fed back to the other input terminal of the AND gate G1. Further, the reset signal RST output from the output port P2 of the microcomputer 110 is applied to the base terminal which is the control input of the transistor Q3.

  That is, in the initial state, the transistor Q3 is temporarily turned on by the reset signal RST, and a high level is applied to the other input terminal of the AND gate G1. In this state, when the current signal SGi applied to one input terminal of the AND gate G1 is switched from the high level to the low level, the current signal SGi2 that is the output of the AND gate G1 is switched from the high level to the low level. At the same time, since the current signal SGi2 is fed back to the other input terminal of the AND gate G1 through the resistor R5, even if the current signal SGi is subsequently switched from the low level to the high level, the reset signal RST is next Until it is applied, the state of the current signal SGi2 remains unchanged.

  For this reason, the microcomputer 110 can identify whether or not the current Igp of a predetermined value or more has flowed through the glow plug 50 without being affected by the timing at which the state of the current signal SGi switches by referring to the current signal SGi2. it can. Specific timing will be described later.

  The voltage detection circuit 130 is a circuit for detecting the voltage Vgp applied between the terminals 50a and 50b of the glow plug 50. Although the actual voltage detection is performed by the microcomputer 110, the voltage Vgp is larger than the allowable voltage range (specifically, within 5V) that can be handled by the microcomputer 110. Therefore, the voltage detection circuit 130 divides the voltage Vgp. Convert to a voltage within the allowable range. That is, the voltage detection circuit 130 is a voltage dividing circuit configured by connecting resistors R2 and R3 in series.

  The microcomputer 110 has an analog input port A / D for detecting an analog level. That is, the microcomputer 110 can read the level of the voltage signal SGv applied to the analog input port A / D by converting it into a digital signal. The level of the voltage signal SGv is proportional to the voltage Vgp and is determined by the voltage division ratio of the voltage detection circuit 130.

  As shown in FIG. 1, the microcomputer 110 of the glow controller 100 is connected to the main controller 200. The main control device 200 is also called an ECU (ie, Electronic Control Unit) and performs various controls on the vehicle such as engine control.

  Main controller 200 provides glow controller 100 with an instruction value of the effective voltage applied to glow plug 50. According to this instruction value, the microcomputer 110 determines the pulse width (in other words, the duty ratio) of the pulse signal SGpwm. However, main controller 200 generates an instruction value for the effective voltage assuming that battery voltage VB is a specified value (for example, 12 V), whereas actual battery voltage VB varies. Accordingly, the microcomputer 110 detects an error of the battery voltage VB and reflects the result on the pulse width (in other words, the duty ratio) of the pulse signal SGpwm in order to eliminate the influence of the fluctuation of the battery voltage VB. The glow controller 100 notifies the main controller 200 of information representing the result of diagnosis.

  Note that the energization control of the glow plug 50 according to the operation state of the engine key and the state of the engine may be performed in the same manner as the technique disclosed in Patent Document 2.

  A specific example of the signal of each part in the glow controller 100 shown in FIG. 1 is shown in FIG. As shown in FIG. 2, the pulse signal SGpwm output from the microcomputer 110 alternately repeats a high level (ie, HI) on state and a low level (ie, LO) off state at a constant period Tpwm. PWM signal. The effective value of the voltage Vgp applied to the glow plug 50 can be adjusted by changing the pulse width (that is, Ton).

  As shown in FIG. 2, the waveform of the voltage Vgp applied to the glow plug 50 is normally equivalent to the pulse signal SGpwm. That is, when the pulse signal SGpwm becomes high level (ie, HI), the energization control switching transistor Q1 is turned on, and the battery voltage VB is applied to the terminal 50a of the glow plug 50 via the energization control switching transistor Q1 and the resistor R1. Since the voltage is applied, the voltage Vgp is also at a high level (ie, HI: 12V, for example). When the pulse signal SGpwm is at a low level (ie, LO), the energization control switching transistor Q1 is turned off, so that the voltage Vgp is also at a low level (ie, LO: 0V). The waveform of the voltage signal SGv is similar to the voltage Vgp.

  As shown in FIG. 2, the waveform of the current Igp flowing through the glow plug 50 is also usually equivalent to the pulse signal SGpwm. That is, when the voltage Vgp applied to the glow plug 50 becomes a high level (ie, HI), a current flows through the glow plug 50, and when the voltage Vgp becomes a low level (ie, LO), no current flows through the glow plug 50. The current signal SGi output from the current detection circuit 120 is at a low level (ie, LO) when the current Igp flows, and is at a high level (ie, HI) when the current Igp does not flow.

  On the other hand, for example, when the terminals 50a and 50b of the glow plug 50 are short-circuited (that is, short-circuited), an excessive current Igp flows when the voltage Vgp becomes a high level. In that case, the energization control switching transistor Q1 detects an overcurrent, and the energization control switching transistor Q1 itself cuts off the current Igp by the self-protection function. That is, even when the pulse signal SGpwm is maintained at a high level (that is, HI) as at time t12 shown in FIG. 2, the current Igp is controlled to be at a low level (that is, under the control of the conduction control switching transistor Q1). , LO).

  In this case, for example, if the current signal SGi is referenced at time t24, it can be confirmed that the current Igp has flowed, but if the current signal SGi is referenced at time t34, it cannot be confirmed that the current Igp has flowed. That is, when referring to the current signal SGi, a different detection result is obtained according to the difference in the reference timing, and correct diagnosis cannot be performed. Therefore, a signal latch circuit 140 is provided.

  As shown in FIG. 2, when the current signal SGi is at a low level (ie, LO), the current signal SGi2 is also switched to a low level (ie, LO). However, since the state of the current signal SGi2 is held by the signal latch circuit 140, even if the current signal SGi is switched to a high level (ie, HI), the current signal SGi2 is kept at a low level (ie, LO) until the reset signal RST appears. ). When the reset signal RST appears, the current signal SGi2 is switched to a high level (that is, HI).

  Therefore, for example, when the current signal SGi2 is referred to at time t34, it can be confirmed that the current Igp has flowed since the current signal SGi2 is at a low level (ie, LO) as in the case of time t24. That is, it is possible to prevent an erroneous diagnosis result due to a difference in timing.

  The microcomputer 110 detects the level of the voltage Vgp by periodically referring to the voltage signal SGv at each time t21, t22, t23, t24,... After the pulse signal SGpwm is switched from the low level to the high level. . Further, the microcomputer 110 periodically refers to the current signal SGi2 at each time t31, t32, t33, t34,... When the pulse signal SGpwm is at a high level, and detects whether or not a predetermined current Igp has flowed. To do. Also, at each time t41, t42, t43, t44,... After the end of the reference to the current signal SGi2, the reset signal RST is switched to a low level (that is, LO) for a short time, and the signal latch circuit 140 Apply a reset.

  The contents of control of the microcomputer 110 for diagnostic processing are shown in FIG. The contents of the control in FIG. 3 will be described below. In addition, the process of step S11-S20 shown in FIG. 3 is repeatedly performed periodically. That is, when step S20 ends, the process returns to step S11 and is repeated.

  In step S11, the microcomputer 110 switches the pulse signal SGpwm output to the output port P1 to a high level (ie, HI). This timing corresponds to each of the times t01, t03, and t05 shown in FIG. 2, for example. Thereby, if normal, the energization control switching transistor Q1 is turned on, and energization of the glow plug 50 is started. That is, the voltage Vgp becomes a high level and the current Igp flows.

  In step S12, the microcomputer 110 samples the voltage of the voltage signal SGv input to the analog input port A / D, converts it to a digital signal, and reads it. That is, a level corresponding to the voltage Vgp applied between the terminals 50a and 50b of the glow plug 50 is detected. This timing corresponds to each time t21, t22, t23,... Shown in FIG. That is, before the pulse signal SGpwm is switched to a low level, it is necessary to execute step S12 to detect the voltage Vgp.

  In step S13, the microcomputer 110 compares the level corresponding to the voltage Vgp read in step S12 with a predetermined threshold thv for diagnosis, and the voltage Vgp is high (ie, HI) / low (ie, based on the comparison result). , LO) is discriminated. {Here, it is determined that the value is equal to or higher than the threshold thv is high (ie, HI), and the value that is less than the threshold thv is low (ie, LO)}. The threshold thv is set to an intermediate level between the normal voltage Vgp level and the battery voltage VB. If the voltage Vgp is high (ie, HI) in the comparison result of step S13, the process proceeds to step S14, and if the voltage Vgp is low (ie, LO), the process proceeds to step S15.

  In step S14, the microcomputer 110 determines a diagnosis relating to the glow plug 50 being disconnected (in other words, the terminals 50a and 50b are open), and reflects the result in the output. That is, since the voltage Vgp is high (ie, HI) in the comparison result of step S13, this voltage is closer to the battery voltage VB than in the normal state. That is, since the glow plug 50 is disconnected, it can be diagnosed that the voltage Vgp is higher than usual. The diagnosis result is notified from the microcomputer 110 to, for example, the main control device 200 and used for displaying the diagnosis result.

  In step S15, the microcomputer 110 reads the current signal SGi2 output from the signal latch circuit 140 at the input port P3. This timing corresponds to each time t31, t32, t33,... Shown in FIG. That is, after the pulse signal SGpwm becomes high level, it is necessary to read the current signal SGi2 by executing step S15 before outputting the reset signal RST.

  In step S16, the microcomputer 110 identifies whether the current signal SGi2 read in step S15 is high (ie, HI) / low (ie, LO). If high, the microcomputer 110 proceeds to step S18. If low, the microcomputer 110 proceeds to step S17. move on.

  In step S17, the microcomputer 110 diagnoses the possibility that the self-protection function of the energization control switching transistor Q1 is activated and interrupts the energization of the glow plug 50, and reflects the result in the output. That is, when executing step S17, it can be confirmed that the voltage Vgp is normal and the current Igp has flowed from the state of the current signal SGi2, so that some problem has occurred (that is, the temperature of the glow plug 50 is If not, it can be diagnosed as a result of the self-protection function of the energization control switching transistor Q1.

  For example, if the terminals 50a and 50b of the glow plug 50 are short-circuited, the current Igp flows temporarily after the pulse signal SGpwm becomes high level, and the current Igp is excessive. When this is detected, the current Igp is immediately cut off (this corresponds to the state at time t12 in FIG. 2). As a result, the time during which the current Igp flows is very short and the glow plug 50 does not generate heat, but as a result of the current Igp flowing, the current signal SGi2 becomes low level.

  Accordingly, in step S17, a diagnosis result indicating a state where there is a possibility of overcurrent or abnormal heating and the self-protection function of the energization control switching transistor Q1 is operating is output.

  In step S18, the microcomputer 110 performs a diagnosis regarding whether the energization control switching transistor Q1 itself has failed and is fixed in the off state, and reflects the result in the output. That is, when step S18 is executed, the current Igp does not flow at all even after the pulse signal SGpwm becomes a high level (that is, the ON state), and the glow plug 50 is not disconnected. It can be diagnosed that the switching transistor Q1 has failed regardless of the self-protection function.

  In step S19, the microcomputer 110 switches the pulse signal SGpwm from a high level to a low level. This timing corresponds to each time t02, t04,... Shown in FIG. That is, since the predetermined ON time Ton has elapsed since the pulse signal SGpwm was switched to a high level, the pulse signal SGpwm is switched to the OFF state. The on-time Ton is determined based on the duty ratio corresponding to the effective voltage required for the voltage Vgp, the period Tpwm, and the battery voltage VB. When the pulse signal SGpwm is switched to a low level, the energization control switching transistor Q1 is switched off and ends energization of the current Igp.

  In step S20, the microcomputer 110 outputs the reset signal RST (ie, low level) from the output port P2 only for a short time. This timing corresponds to each time t41, t42, t43,... Shown in FIG. That is, after the reading of the current signal SGi2 in step S15 is completed and the pulse signal SGpwm is further switched to a low level, the reset signal RST is output before the pulse signal SGpwm is switched to a high level, and the signal latch circuit 140 Reset the state to the initial state.

  As described above, the glow plug failure diagnosis apparatus of the present invention can be used for diagnosing a failure in a glow plug used in an engine and a glow controller that controls energization thereof. In particular, even when the on / off of energization of the glow plug is controlled by a pulse signal such as a PWM signal using a switching element having a self-protection function, it can be used to output a more accurate diagnosis result.

  As described above, the present invention has been described in detail by exemplifying embodiments that are considered to be the most practical and preferable at the present time, but the present invention is limited to the embodiments disclosed in the present specification. However, various modifications such as improvements can be made as appropriate without departing from the spirit or concept of the invention that can be read from the claims and the entire specification of the present application, and a glow plug failure diagnosis apparatus with such changes is possible. Should also be understood as being included within the scope of the present invention.

  Note that the configuration of the components in the above-described embodiment is arbitrary and is not limited as long as the present invention can be achieved. For example, for the above-described transistor, an FET may be used instead of the bipolar transistor, and similarly, a bipolar transistor may be used instead of the FET. Further, the PNP transistor may be changed to an NPN transistor by an appropriate circuit change. Similarly, the NPN transistor may be changed to a PNP transistor by an appropriate circuit change. Further, the P-channel FET may be changed to an N-channel FET by an appropriate circuit change. Similarly, the N-channel FET may be changed to a P-channel FET by an appropriate circuit change. .

  Needless to say, the glow plug may be used for purposes other than the diesel engine.

50: Glow plugs 50a, 50b: Terminal 55: Battery 100: Glow controller 110: Microcomputer 120: Current detection circuit 121: Differential amplifier 130: Voltage detection circuit 140: Signal latch circuit 200: Main controller G1: AND gate Q1 : Switching transistors Q2, Q3 for energization control: transistors R1 to R5: resistors SGpwm: pulse signals SGi, SGi2: current signal SGv: voltage signal RST: reset signal VB: battery voltage Vcc: DC power supply voltage

Claims (5)

A switching element that turns on / off energization of a glow plug from a predetermined power supply line; and a pulse signal generation unit that generates a periodically changing pulse signal for controlling the switching element. Is used for a glow controller with a built-in self-protection function that cuts off current against excessive current flowing through itself or excessive heat generation of the switching element itself,
Glow plug fault diagnosis device,
A current detection circuit for detecting a current flowing through the glow plug;
A signal latch circuit that temporarily holds a state of a current signal output from the current detection circuit;
A voltage detection circuit for detecting a voltage applied to the glow plug for energization;
When energization to the glow plug is in an on state, the voltage signal output from the voltage detection circuit and the current signal output from the signal latch circuit are monitored, and based on the state of the voltage signal and the current signal A diagnostic processing circuit for performing diagnostic processing on at least the presence or absence of a failure;
A glow plug fault diagnosis device comprising: After the signal latch circuit has a reset control input terminal for resetting the state of the current signal being held, and the diagnostic processing circuit has switched the switching element from on to off after the pulse signal 2. The glow plug failure diagnosis apparatus according to claim 1, wherein a predetermined reset signal is given to a reset control input terminal of the signal latch circuit.   2. The glow plug failure diagnosis apparatus according to claim 1, wherein the diagnosis processing circuit outputs a diagnosis result relating to disconnection of the glow plug when the voltage detected by the voltage detection circuit is equal to or higher than a predetermined value.   When the diagnostic processing circuit detects that the voltage detected by the voltage detection circuit is less than a predetermined value and that a predetermined current is flowing by a current signal output from the signal latch circuit, 2. The glow plug failure diagnosis apparatus according to claim 1, wherein a diagnosis result regarding the operation of the self-protection function of the switching element is output.   When the diagnostic processing circuit detects that the voltage detected by the voltage detection circuit is less than a predetermined value and the current signal output from the signal latch circuit does not flow, 2. The glow plug failure diagnosis apparatus according to claim 1, wherein a diagnosis result relating to a failure of the switching element is output.

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