JP2010085058A - Glow plug short circuit detecting device and heat generation system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a glow plug short circuit detection device accurately and immediately detecting shortcircuit of a glow plug by changing a current threshold or the like in correspondence to a temperature rising state of the glow plug, and a heat generation system equipped with the short circuit detection device for a glow plug. <P>SOLUTION: In the short circuit detection device, a controller 20 includes a short circuit detection device 30 for detecting the short circuit of the glow plug 1. The short circuit detection device 30 includes a voltage detection part 32 measuring a voltage value (a detected voltage value) corresponding to a current value passing through the glow plug 1, and an operational amplifier 36 comparing the detected voltage value with a predetermined voltage threshold and determining short circuit or non-short circuit of the glow plug 1. The short-circuiting detection device 30 includes a threshold generating part 34 generating a voltage threshold, the threshold generating part 34 generates a first voltage threshold in an initial energization period to the glow plug 1, and it generates a second voltage threshold with a voltage value smaller than the first voltage threshold value after passage of the initial energization period. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a device for detecting a short circuit in a glow plug used for preheating a diesel engine and the like, and a heat generation system including the device.

  As a glow plug used for preheating a diesel engine, a sheath heater in which a heat generating coil containing chromium (Cr), aluminum (Al) or the like is enclosed in a metal tube having a closed tip is generally used. Are known.

  Conventionally, as a control device for controlling the heat generation of the glow plug, an energization signal output means for outputting a signal for determining whether the glow plug can be energized from a power supply (battery), and when the signal is input to the gate A device including an FET for opening an energization path from the battery to the glow plug is known (see, for example, Patent Document 1). The operation of the control device will be described in detail. When the key switch is turned to the on position, the energization determination unit is configured so that the temperature of the sheath heater rises toward the first target temperature sufficient to start the engine. However, by outputting a signal permitting energization, the energization path of the FET is opened, and power is supplied from the battery to the glow plug. Then, after the temperature of the sheath heater reaches the first target temperature, the glow plug (heat generating coil) is supplied to the sheath heater so that the temperature of the sheath heater maintains the second target temperature for a predetermined time (for example, 180 seconds). Control energization. More specifically, the energization signal output unit changes the open time of the energization path of the FET by changing and outputting the width (time) of the signal permitting energization in one cycle. As a result, the amount of power supplied to the glow plug is controlled (PWM control), and as a result, the temperature of the sheath heater is controlled to be the second target temperature.

  By the way, due to thermal expansion, mechanical shock, or the like, the base end portion of the heating coil may be in contact with the tube, that is, the glow plug may be short-circuited. Here, if the glow plug is short-circuited, the resistance value of the glow plug decreases, so that sufficient heat generation performance cannot be exhibited, or overcurrent is applied to electronic components such as FETs. There is a risk of damage to the flow and electronic components. Therefore, it is necessary to provide a device that can quickly detect a short-circuit of the glow plug in order to minimize the influence of the short-circuit.

Here, as a device for detecting a short-circuit of the glow plug, a predetermined current threshold value based on a current (rush current) flowing through the glow plug at the start of energization is set in advance, A device that determines that the glow plug is short-circuited when the current threshold is exceeded is conceivable.
Japanese Patent Laid-Open No. 2004-232907

  However, as the temperature of the heating coil rises with energization, the resistance value of the heating coil increases. Therefore, as shown in FIG. 7, the glow plug current gradually becomes small. Here, when the heat generating coil becomes hot and the base end side of the heat generating coil and the tube come into contact with each other due to thermal expansion or the like (that is, when the glow plug is short-circuited), as described above, On the other hand, a larger current flows than in a normal state (when not short-circuited). However, since the current threshold value based on the inrush current at the start of energization is relatively large, a short circuit occurs when the heating coil becomes hot, and the current flows through the glow plug as shown by the dotted line in FIG. Even if the current value increases, the current value does not exceed the current threshold value, and it may be determined that no short circuit has occurred in the glow plug. In addition, even if the heat generation time elapses and the contact portion between the heat generating coil and the tube increases and the current flowing through the glow plug exceeds the current threshold, it takes a relatively long time to detect a short circuit. As a result, the temperature rise of the sheath heater may be insufficient, or an overcurrent may flow to the electronic component for a relatively long period of time.

  The present invention has been made in view of the above circumstances, and its purpose is to detect a glow plug short-circuit accurately and promptly by changing a current threshold value or the like corresponding to the temperature rise state of the glow plug. Another object of the present invention is to provide a glow plug short-circuit detection device that can be used, and a heat generation system including the glow plug short-circuit detection device.

  Hereinafter, each configuration suitable for solving the above-described object will be described in terms of items. In addition, the effect specific to the corresponding structure is added as needed.

Configuration 1. The glow plug short-circuit detection device of this configuration includes a measuring means for measuring a current value flowing through the glow plug,
A short-circuit determination unit that compares the current value measured by the measurement unit with the current threshold generated by the threshold generation unit that generates a predetermined current threshold, and determines whether the glow plug is short-circuited or non-short-circuited. A glow plug short-circuit detection device,
The threshold generation means includes
A first current threshold is generated as the current threshold in the initial energization period to the glow plug, and a second current that is smaller than the first current threshold as the current threshold after the initial energization period to the glow plug has elapsed. A threshold value is generated.

  The “initial energization period” means a period from the start of energization to the glow plug until a predetermined time elapses. As the predetermined time, for example, the temperature of the sheath heater is the first target temperature. The time to reach can be listed.

  According to the configuration 1, in the initial energization period in which the resistance value of the heat generating coil is relatively small, a short-circuit of the glow plug is determined using a relatively large first current threshold, and the resistance value of the heat generating coil is relatively small. After the passage of a large initial energization period, a short-circuit of the glow plug is determined using a relatively small second current threshold. That is, by generating a current threshold value that matches the temperature rise state (resistance value) of the glow plug, the current difference between the current threshold value and the glow plug current when not short-circuited can be made relatively small. As a result, even when the heating coil is at a high temperature, an increase in the glow plug current due to a short circuit can be detected more reliably, and as a result, the glow plug short circuit can be accurately performed regardless of the temperature state of the heating coil. And can be detected promptly.

  Configuration 2. In the glow plug short-circuit detection device according to this configuration, in the above configuration 1, the threshold value generation unit sets the current threshold value to be generated when the energization time to the glow plug reaches a preset time. The current threshold value is changed to the second current threshold value.

  The “preset time” may be, for example, a time acquired empirically as a time required for the glow plug to reach the first target temperature.

  According to the said structure 2, the effect similar to the said structure 1 is show | played fundamentally. In addition, in the present configuration 2, when the energization time to the glow plug reaches a preset time, the current threshold value generated by the threshold value generation unit is changed. For this reason, for example, without requiring a complicated process (for example, measurement of the integrated power amount supplied to the glow plug, etc.) required when the current threshold is changed in accordance with the actual temperature of the heating coil. It is possible to change the current threshold value, thereby suppressing problems such as complexity of the apparatus and increase in cost.

Configuration 3. The glow plug short-circuit detection device of the present configuration includes, in the configuration 1, the energization signal output means for outputting a PWM signal for determining whether or not the glow plug is energized,
The threshold generation means changes the current threshold to be generated from the first current threshold to the second current threshold based on the PWM signal.

  According to the said structure 3, the effect similar to the said structure 1 is show | played fundamentally. In general, the glow plug is temperature-controlled based on a signal (PWM signal) in which the width (time) of the energization signal that permits energization in one cycle is variously changed. The current threshold is changed based on the PWM signal [for example, when the width of the energization signal is relatively large (rapid temperature rise period), the first current threshold is generated, and when the width of the energization signal is relatively small (temperature The second current threshold value is generated). Thereby, the current threshold corresponding to the temperature change of the glow plug can be generated without measuring the actual temperature of the glow plug. In addition, since the current threshold value is changed based on a commonly used PWM signal, there is no need to provide a separate device for determining the timing for changing the current threshold value, thereby preventing device complexity and cost increase. can do.

  Configuration 4. The glow plug short-circuit detection device of this configuration is characterized in that, in the above configurations 1 to 3, the threshold value generating means generates three or more types of the current threshold value.

  According to the configuration 4, the threshold value generation unit can generate a plurality of current threshold values such as the third and fourth current threshold values in addition to the first current threshold value and the second current threshold value. As a result, the current threshold value can be changed in multiple stages, so that the current difference between the glow plug current and the current threshold value can be made relatively small in a longer time within the energization time. As a result, a short-circuit of the glow plug can be detected more quickly and with higher accuracy.

Configuration 5. The glow plug short-circuit detection device of this configuration includes a measuring means for measuring a voltage value based on a current flowing through the glow plug,
A short-circuit determination unit that compares the voltage value measured by the measurement unit with the voltage threshold generated by the threshold generation unit that generates a predetermined voltage threshold, and determines whether the glow plug is short-circuited or non-short-circuited. A glow plug short-circuit detection device,
The threshold generation means includes
A first voltage threshold is generated as the voltage threshold in the initial energization period to the glow plug, and a second voltage smaller than the first voltage threshold as the voltage threshold after the initial energization period to the glow plug has elapsed. A threshold value is generated.

  As in the configuration 5, the short-circuit of the glow plug may be detected by comparing the voltage value based on the current flowing through the glow plug and the voltage threshold value. Even in this case, similarly to the above-described configuration 1 and the like, it is possible to detect a short-circuit of the glow plug with high accuracy and promptly.

  Configuration 6. In the glow plug short-circuit detection device according to this configuration, in the above configuration 5, the threshold value generation unit generates the voltage threshold value to be generated when the energization time of the glow plug reaches a preset time. The voltage threshold value is changed to the second voltage threshold value.

  According to the said structure 6, the effect similar to the said structure 2 will be show | played.

Configuration 7. The glow plug short-circuit detecting device of this configuration includes the energization signal output means for outputting a PWM signal for determining whether the glow plug is energized or not in the above configuration 5.
The threshold generation means changes the voltage threshold to be generated from the first voltage threshold to the second voltage threshold based on the PWM signal.

  According to the said structure 7, the effect similar to the said structure 3 is show | played.

  Configuration 8. The glow plug short-circuit detection device according to this configuration is characterized in that, in any one of the configurations 5 to 7, the threshold value generation means generates three or more types of the voltage threshold values.

  According to the said structure 8, the effect similar to the said structure 4 will be show | played.

Configuration 9 The glow plug short-circuit detection device of this configuration is any one of the above configurations 5 to 8, wherein the measurement unit includes a shunt resistor connected in series to the glow plug,
A voltage value based on a current flowing through the glow plug is measured based on a potential difference between both ends of the shunt resistor.

  According to the configuration 9, the voltage value based on the current flowing through the glow plug can be measured relatively easily.

  From the viewpoint of suppressing the loss of power supplied to the glow plug as much as possible, it is preferable to make the resistance value of the shunt resistor as small as possible. However, when the resistance value of the shunt resistor is reduced, the potential difference between both ends of the shunt resistor is also reduced. For this reason, a differential amplifier may be provided so as to amplify the potential difference between both ends of the shunt resistor.

Configuration 10 The glow plug short-circuit detection device of this configuration is any one of the above configurations 5 to 9, wherein the threshold value generating means is
A first resistor having one end connected to a predetermined first threshold generation power supply;
A second resistor having one end connected to the other end of the first resistor and the other end grounded;
A third resistor having one end connected between the first resistor and the second resistor;
A transistor having a collector connected to the other end of the third resistor and an emitter connected to a predetermined second threshold generation power supply;
A threshold change signal output means connected to the base of the transistor and outputting a threshold change signal for opening and closing a current-carrying path between the collector and emitter of the transistor;
The threshold generation means generates the first voltage threshold by closing the energization path between the collector and emitter of the transistor, and opens the energization path between the collector and emitter of the transistor. The second voltage threshold is generated.

  According to the configuration 10, the threshold generation means includes a transistor, a threshold change signal output means, three resistors, and two threshold change power supplies. In this case, the two voltage thresholds can be switched relatively easily only by changing the threshold change signal. Further, the voltage threshold value can be increased or decreased by variously changing the resistance values of the first to third resistors. That is, it is possible to set an appropriate voltage threshold according to the use environment and use conditions relatively easily without any particular difficulty.

Configuration 11 The glow plug short-circuit detection device according to any one of the above configurations 1 to 10,
A heat generation system including a glow plug which is a target of short circuit detection by the glow plug short circuit detection device.

  As in the configuration 11, the technical idea may be embodied in a heat generation system including a glow plug. In this case, basically the same effects as those of the above-described configuration 1 and the like are exhibited.

  Hereinafter, an embodiment will be described with reference to the drawings. First, the structure of the glow plug 1 that is energized and controlled by the glow plug control device 20 will be described. Fig.1 (a) is a partially broken front view which shows an example of the glow plug which comprises a sheath heater, FIG.1 (b) is sectional drawing of a glow plug front-end | tip part.

  As shown in FIGS. 1A and 1B, the glow plug 1 includes a cylindrical metal shell 2 and a sheath heater 3 attached to the metal shell 2.

  The metal shell 2 has a shaft hole 4 penetrating in the direction of the axis C1, and the outer peripheral surface thereof has a hexagonal cross section for engaging a screw portion 5 for attachment to a diesel engine and a tool such as a torque wrench. The tool engaging portion 6 is formed.

  The sheath heater 3 is configured by integrating the tube 7 and the middle shaft 8 in the direction of the axis C1.

  The tube 7 is a cylindrical tube whose front end portion is mainly composed of iron (Fe) or nickel (Ni), and the rear end of the tube 7 is sealed with an annular rubber 17 between the center shaft 8. ing.

  In addition, inside the tube 7, a heating coil 9 joined to the tip of the tube 7 and a control coil 10 connected in series to the rear end of the heating coil 9 are insulated powder such as magnesium oxide (MgO) powder. 11 is enclosed. However, although the heat generating coil 9 is electrically connected to the tube 7 at its tip, the outer peripheral surface of the heat generating coil 9 and the control coil 10 and the inner peripheral surface of the tube 7 are insulated from each other by the intervening insulating powder 11. It has become.

  The heating coil 9 is constituted by a resistance heating wire made of, for example, an Fe-chromium (Cr) -aluminum (Al) alloy. On the other hand, the control coil 10 is a resistor whose main component is a material having a temperature coefficient of electrical resistivity greater than that of the material of the heat generating coil 9, for example, Co or Ni represented by a cobalt (Co) -Ni-Fe alloy. It is composed of heating lines. Thereby, the control coil 10 increases the electric resistance value by receiving its own heat generation and heat generation from the heat generation coil 9, and controls the power supply amount to the heat generation coil 9. Therefore, relatively large electric power is supplied to the heating coil 9 in the initial stage of energization, and the temperature of the heating coil 9 rises rapidly. Then, the control coil 10 is heated by the heat generation, the electric resistance value increases, and the power supply to the heat generating coil 9 decreases. As a result, the temperature rise characteristic of the sheath heater 3 becomes a form in which the temperature is saturated after the temperature is rapidly raised in the initial stage of energization, and thereafter the power supply is suppressed by the action of the control coil 10. That is, the presence of the control coil 10 makes it possible to prevent the temperature of the heat generating coil 9 from excessively rising (overshoot) while improving the rapid temperature rise.

  In addition, the tube 7 is formed with a small-diameter portion 7a that accommodates the heat generating coil 9 and the like at the distal end thereof by swaging or the like, and a large-diameter portion 7b that is larger in diameter than the small-diameter portion 7a on the rear end side. Is formed. The large diameter portion 7 b is press-fitted and joined to the small diameter portion 4 a formed in the shaft hole 4 of the metal shell 2, so that the tube 7 is held in a state of protruding from the tip of the metal shell 2.

  The middle shaft 8 is inserted at its tip into the tube 7, is electrically connected to the rear end of the control coil 10, and is inserted through the shaft hole 4 of the metal shell 2. The rear end of the middle shaft 8 protrudes from the rear end of the metal shell 2. At the rear end of the metal shell 2, the rubber-made O-ring 12, the resin-made insulating bush 13, and the insulating bush 13 are removed. A pressing ring 14 for preventing and a nut 15 for connecting a current-carrying cable are fitted into the middle shaft 8 in this order from the tip side.

  Next, the control device 20 of the glow plug 1 having the short-circuit detection device 30 of the glow plug 1 which is a feature of the present invention will be described.

  As shown in FIG. 2, the control device 20 includes a supply switching device 40 for switching power supply / non-supply to the glow plug 1, a short-circuit detection device 30 for detecting a short-circuit of the glow plug 1, and a CPU. ECU (electronic control unit) 50 provided.

  The supply switching device 40 includes an energization signal output unit 42 as an energization signal output unit and an FET (field effect capacitor) 44.

  The energization signal output unit 42 is connected to the gate of the FET 44. Further, the energization signal output unit 42 is controlled by the ECU 50, and a PWM signal representing a timing of energizing the glow plug 1 from a power supply (battery) VB having a predetermined output voltage (for example, 12V), Output to the gate of the FET 44. The operation of the energization signal output unit 42 will be described in detail. The energization signal output unit 42 outputs a High signal as a PWM signal to the gate of the FET 44 when power is supplied from the power supply device VB to the glow plug 1. On the other hand, when power supply from the power supply device VB to the glow plug 1 is stopped, the energization signal output unit 42 outputs a Low signal as a PWM signal to the gate of the FET 44. In the temperature control of the sheath heater 3, so-called PWM (Pulse-Width-Modulation) control for controlling the energization amount to the glow plug 1 by changing the width of the High signal in one cycle is performed. It has become.

  The FET 44 has a source connected to the power supply device VB and a drain connected to the glow plug 1 via a shunt resistor 322 described later. In addition, when a High signal is input to the gate of the FET 44 as a PWM signal, the energization path between the source and the drain is opened, and power is supplied from the power supply device VB to the glow plug 1. On the other hand, when a Low signal is input as a PWM signal to the gate of the FET 44, the energization path between the source and the drain is closed, and the supply of power from the power supply device VB to the glow plug 1 is stopped.

  Next, the short-circuit detection device 30 for the glow plug 1 which is a feature of the present invention will be described in detail.

  The short-circuit detection device 30 includes a voltage detection unit 32 as a measurement unit, a threshold generation unit 34 as a threshold generation unit, and an operational amplifier 36 as a short-circuit determination unit.

  The voltage detection unit 32 includes a shunt resistor 322 having a predetermined low resistance value and a differential amplifier 324. The shunt resistor 322 has one end connected to the drain of the FET 44 and the other end connected to the glow plug 1. Further, the potential difference between both ends of the shunt resistor 322 is amplified by the differential amplifier 324 and output to one end of the operational amplifier 36. That is, the voltage detection unit 32 detects (measures) a voltage value (detection voltage value) based on the current flowing through the glow plug 1 and outputs the detection voltage value to the operational amplifier 36.

The threshold generation unit 34 includes a signal output unit 342 as a threshold change signal output unit, a transistor 344, a first resistor T1, a second resistor T2, a third resistor T3, and a predetermined output voltage ( For example, a threshold generation power supply VDD having V _A ) is provided.

  The signal output unit 342 is connected to the base of the transistor 344. The signal output unit 342 is controlled by the ECU 50 and outputs a threshold value changing signal to the transistor 344. More specifically, the signal output unit 342 is a time set in advance as a time required to set the temperature of the sheath heater 3 to a first target temperature sufficient for starting the engine (hereinafter referred to as a “rapid temperature rising period”). During this time, a Low signal is output to the transistor 344 as a threshold changing signal. On the other hand, for a predetermined time after the elapse of the preset time (that is, the time for maintaining the temperature of the sheath heater 3 at a predetermined second target temperature; hereinafter referred to as “temperature stabilization period”), the signal The output unit 342 outputs a High signal to the transistor 344 as a threshold value changing signal.

  The transistor 344 has an emitter connected to the threshold generation power supply VDD and a collector connected to one end of the third resistor T3. Further, the transistor 344 opens or closes the energization path between the collector and the emitter based on a threshold value changing signal from the signal output unit 342 input to its base. More specifically, when the threshold change signal is a Low signal, the energization path between the collector and the emitter is closed, while when the threshold change signal is a High signal, the energization between the collector and the emitter is performed. The route is released.

In addition, each of the first resistor T1 and the second resistor T2 has a predetermined resistance value (for example, R _T1 , R _T2 ), and both ends thereof are connected to each other. The other end of the first resistor T1 is connected to the threshold generation power supply VDD, and the other end of the second resistor T2 is grounded. In addition, the other end of the third resistor T3 having a predetermined resistance value (for example, R _T3 ) is connected between the first resistor T1 and the second resistor T2. Further, the other end of the operational amplifier 36 is connected between the first resistor T1 and the second resistor T2.

Here, the operation of the threshold generation unit 34 will be described in detail. When a Low signal is output from the signal output unit 342 as a threshold change signal, the energization path between the collector and emitter of the transistor 342 is opened, and the operational amplifier 36 A predetermined first voltage threshold is output to the other end [in this embodiment, the first voltage threshold is R _T2 / [R _T1 · R _T3 / (R _T1 + R _T3 ) + R _T2 ] × V It becomes the value represented by the formula of _A ]. The first voltage threshold is a current equal to the maximum current (inrush current) that can flow to the glow plug 1 when power is supplied from the power supply device VB to the normal (non-short-circuited) glow plug 1. The voltage is set to be larger than the voltage value output from the differential amplifier 324 by a predetermined value when flowing through the shunt resistor 322.

Returning to the description of the operation of the threshold generator 34, when a High signal is output from the signal output unit 342 as a threshold change signal, the energization path between the collector and emitter of the transistor 344 is closed. As a result, a predetermined second voltage threshold value is output to the other end of the operational amplifier 36. [In this embodiment, the second voltage threshold value is an expression of R _T2 / (R _T1 + R _T2 ) × V _A. It will be the value represented]. The second voltage threshold value is that power is supplied from the power supply device VB to the normal (non-short-circuited) glow plug 1 in the stage where the sheath heater 3 is maintained at the second target temperature (temperature stabilization period). In this case, when a current equal to the maximum current that can flow through the glow plug 1 is passed through the shunt resistor 322, the voltage value is set to be larger by a predetermined value than the voltage value output from the differential amplifier 324. . Further, since the resistance value of the glow plug 1 during the rapid temperature rise period is relatively small, the inrush current is relatively large. On the other hand, the resistance value of the glow plug 1 during the temperature stabilization period is relatively large, and thus normal. The maximum current that can flow to the glow plug 1 is relatively small. Therefore, the second voltage threshold is set to a value smaller than the first voltage threshold.

  The operational amplifier 36 compares the detection voltage value detected by the voltage detection unit 32 with the first voltage threshold value or the second voltage threshold value output from the threshold value generation unit 34, and outputs a determination result signal indicating the determination result to the ECU 50. Output for. More specifically, when the detected voltage value is equal to or less than the voltage threshold value generated by the threshold value generator 34, it is determined that the glow plug 1 is not short-circuited, and a Low signal is sent to the ECU 50 as a determination result signal. Is output. On the other hand, when the detected voltage value exceeds the voltage threshold value, it is determined that the glow plug 1 is short-circuited, and a High signal is output to the ECU 50 as a determination result signal.

  In addition, when it is determined that a short circuit has occurred in the glow plug 1 (when a High signal is input as a determination result signal from the operational amplifier 36), the ECU 50 controls the energization signal output unit 42, The High signal of the PWM signal is switched to the Low signal. Thereby, when a short circuit occurs in the glow plug 1, the power supply to the glow plug 1 is stopped.

  Next, the short-circuit determination device 30 described above will be described separately for the case where the glow plug 1 is normal (non-short-circuit state) and the case where the glow plug 1 is short-circuited. Note that when the Low signal is output as the PWM signal from the energization signal output unit 42, no power is supplied to the glow plug 1. Therefore, the detected voltage value detected by the voltage detection unit 32 is inevitably smaller than the voltage threshold value, and the operational amplifier 36 outputs a Low signal as a determination result signal. Therefore, hereinafter, it will be described that the High signal is output as the PWM signal from the energization signal output unit 42.

  First, the case where the glow plug 1 is normal (non-shorted state) will be described.

  During the rapid temperature increase period of the glow plug 1, the signal output unit 342 outputs a Low signal as a threshold value changing signal. Therefore, the energization path between the collector and emitter of the transistor 344 is opened, and a relatively large first voltage threshold is input to the operational amplifier 36 as shown in FIG. On the other hand, the detected voltage value based on the current flowing through the glow plug 1 is detected by the voltage detector 32 and the detected voltage value is input to the operational amplifier 36 [Note that the temperature of the sheath heater 3 (heat generating coil 9) As the resistance value of the heating coil 9 increases due to the increase, the detected voltage value gradually decreases.] The operational amplifier 36 compares the input detection voltage value with the first voltage threshold value. Here, since the detected voltage value is equal to or lower than the first voltage threshold value, it is determined that the glow plug 1 is normal, and a Low signal is output as a determination result signal to the ECU 50.

  Next, during the temperature stabilization period after the rapid temperature increase period, a high signal as a threshold value changing signal is output from the signal output unit 342. Therefore, the energization path between the collector and emitter of the transistor 344 is closed, and the second voltage threshold is input to the operational amplifier 36. On the other hand, a detection voltage value based on the current flowing through the glow plug 1 is detected by the voltage detection unit 32, and the detection voltage value is input to the operational amplifier 36 (in the temperature stabilization period, the sheath heater 3 Therefore, the resistance value of the heating coil 9 hardly changes, and as a result, a substantially constant detection voltage value is input to the operational amplifier 36). The operational amplifier 36 compares the input detection voltage value with the second voltage threshold value. Here, since the detected voltage value is less than or equal to the second voltage threshold, it is determined that the glow plug 1 is normal, and a Low signal is output as a determination result signal to the ECU 50.

  Next, the case where the glow plug 1 is short-circuited will be described. As for the case where the glow plug 1 is short-circuited, the glow plug 1 is short-circuited when the engine is started and when the temperature is stabilized (when the engine temperature is relatively high). A case can be mentioned. Therefore, hereinafter, the case where the glow plug 1 is in a short-circuited state from the start of the engine and the case where the glow plug 1 is in a short-circuited state during the temperature stabilization period will be described separately.

  First, the case where the glow plug 1 is in a short-circuited state from the start of the engine will be described. During the rapid temperature increase period, the signal output unit 342 outputs a Low signal as a threshold value changing signal, and the first voltage threshold value is input to the operational amplifier 36. On the other hand, a detection voltage value based on the current flowing through the glow plug 1 is detected by the voltage detection unit 342, and the detection voltage value is input to the operational amplifier 36. Since the glow plug 1 is in a short-circuited state from the beginning, an inrush current larger than the maximum value of the current that can flow through the glow plug 1 in a normal state flows through the glow plug 1, and as shown in FIG. A detection voltage value exceeding one voltage threshold is detected. The operational amplifier 36 compares the input detection voltage value and the first voltage threshold value, and determines that the glow plug 1 is in a short-circuited state because the detection voltage value exceeds the first voltage threshold value. Is output to the ECU 50. The ECU 50 to which the High signal is input controls the energization signal output unit 342 to change the energization signal from the High signal to the Low signal. As a result, the supply of power to the glow plug 1 is stopped.

  Next, a case where the glow plug 1 is short-circuited during the temperature stabilization period will be described. In the rapid temperature increase period, as shown in FIG. 5, the detected voltage value is equal to or lower than the first voltage threshold as in the case where the glow plug 1 is normal. Therefore, the glow plug 1 is normal by the operational amplifier 36. It is determined. On the other hand, in the temperature stabilization period, the contact portion between the heat generating coil 9 and the tube 7 increases due to the thermal expansion of the heat generating coil 9, and the resistance value of the glow plug 1 is lower than normal. For this reason, the value of the current flowing through the glow plug 1 increases, and consequently the detection voltage value increases. When the detected voltage value exceeds the second voltage threshold value, it is determined by the operational amplifier 36 that the glow plug 1 is in a short-circuited state, and a High signal is output to the ECU 50 as a determination result signal. The ECU 50 to which the High signal is input changes the energization signal output from the energization signal output unit 42 from the High signal to the Low signal, and the supply of power to the glow plug 1 is stopped.

  As described above in detail, according to the short-circuit detection device 30 in the present embodiment, the glow plug 1 is short-circuited using a relatively large first voltage threshold during an initial energization period in which the resistance value of the heating coil 9 is relatively small. After the initial energization period when the resistance value of the heating coil 9 is relatively large, the short-circuit of the glow plug 1 is determined using a relatively small second voltage threshold. That is, by generating a voltage threshold value that matches the temperature rise state (resistance value) of the glow plug 1, the voltage difference between the voltage threshold value and the detected voltage value when not short-circuited can be made relatively small. Thereby, even when the heating coil 9 is at a high temperature, it is possible to more reliably detect an increase in the detected voltage value due to the short circuit. As a result, the glow plug 1 is short-circuited regardless of the temperature state of the heating coil 9. Can be detected accurately and promptly.

  Further, in the present embodiment, the voltage threshold value generated by the threshold value generation unit is changed when the energization time to the glow plug 1 reaches a preset time. For this reason, for example, complicated processing (for example, measurement of the integrated electric energy supplied to the glow plug, etc.) required when changing the voltage threshold corresponding to the actual temperature of the heating coil 1 is not required. Thus, the voltage threshold value can be changed, and as a result, problems such as complexity of the apparatus and increase in cost can be suppressed.

  In addition, the threshold generation unit 34 includes a transistor 344, a signal output unit 342, three resistors T1, T2, and T3, and a threshold generation power supply VDD. In this case, the two voltage threshold values can be switched relatively easily only by changing the threshold value changing signal output from the signal output unit. Further, the voltage threshold value can be increased or decreased by variously changing the resistance values of the first to third resistors T1, T2, and T3. That is, it is possible to set an appropriate voltage threshold according to the use environment and use conditions relatively easily without any particular difficulty.

  In addition, it is not limited to the description content of the said embodiment, For example, you may implement as follows. Of course, other application examples and modification examples not illustrated below are also possible.

  (A) In the above embodiment, the short circuit detection device 30 is configured to detect a short circuit of the glow plug 1 (metal glow plug) having the heating coil 9. It is not limited to metal glow plugs. Therefore, it is good also as comprising so that the short circuit detection apparatus 30 may detect the short circuit of the ceramic glow plug which has a ceramic heater. However, with regard to the ceramic glow plug, it is difficult for a situation such as a short circuit due to thermal expansion or the like like a heating coil to occur. Therefore, the short circuit detection device 30 is particularly significant when the metal glow plug is a target for short circuit detection.

  (B) In the above embodiment, the threshold voltage generator 34 generates the first voltage threshold during a preset time (rapid temperature rise period), and the predetermined time (temperature stabilization) after the rapid temperature rise period elapses. Period), the second voltage threshold is generated. That is, the voltage threshold is changed when the energization time to the glow plug 1 becomes a preset time, but the change timing of the voltage threshold is not limited to this. Therefore, for example, the voltage threshold value may be changed when the width of the High signal in one cycle of the energization signal is equal to or less than a predetermined width. Alternatively, the voltage threshold value may be changed when the integrated amount of power supplied to the glow plug 1 reaches a predetermined value set in advance.

  (C) In the above embodiment, two types of voltage thresholds, ie, the first voltage threshold and the second voltage threshold are used. For example, as shown in FIG. For example, three or more voltage thresholds may be used. In this case, since the voltage threshold value can be changed in multiple stages, the voltage difference between the glow plug current and the voltage threshold value can be made relatively small in more time within the energization time. As a result, the short circuit of the glow plug 1 can be detected more quickly and with higher accuracy.

  (D) In the above embodiment, the glow plug 1 is determined to be short-circuited by using the detected voltage value detected based on the current flowing through the glow plug 1. That is, the comparison target in the short circuit determination is a voltage value. On the other hand, it is good also as detecting the short circuit of the glow plug 1 by detecting the electric current which flows into the glow plug 1, and comparing the said electric current and two or more types of electric current threshold values. That is, the comparison reference for the short circuit determination may be the current value.

  (E) In the above embodiment, the threshold value generation unit 34 is provided, and the short circuit determination is performed by the operational amplifier 36 comparing the voltage threshold value generated by the threshold value generation unit 34 with the detected voltage value. In contrast, the detected voltage value is input to the ECU 50 as it is, and the ECU 50 (virtually) generates a voltage threshold value, and the generated voltage threshold value is compared with the detected voltage value. Short circuit determination may be performed. That is, the ECU 50 may be configured to include the functions of the threshold value generator 34 and the operational amplifier 36.

  (F) The shape or the like of the glow plug 1 is not limited to the above-described embodiment. For example, the tube 7 may have a straight shape in which the large-diameter portion 7b is omitted and the outer diameter is substantially constant. Good. Further, the small diameter portion 4a of the shaft hole 4 of the metal shell 2 may be omitted, and the tube 7 may be press-fitted into the shaft hole 4 having a straight shape in the axial direction.

  (G) The control coil 10 may be omitted, and the rear end of the heating coil 9 may be directly joined to the middle shaft 8.

(A) is the partially broken front view of the glow plug of this embodiment, (b) is the elements on larger scale of the glow plug front-end | tip part. It is a block diagram which shows the structure of the control apparatus of a glow plug. It is a graph which shows the relationship between a voltage threshold value and a detection voltage value about the glow plug in a non-short-circuit state. It is a graph which shows the relationship between a voltage threshold value and a detection voltage value about the glow plug in a short circuit state from the time of engine starting. It is a graph which shows the relationship between a voltage threshold value and a detection voltage value about the glow plug which reached the short circuit state after engine starting. It is a graph which shows the several voltage threshold value etc. in other embodiment. It is a graph which shows the relationship between the electric current threshold value in a prior art, and a spark plug electric current.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Glow plug, 30 ... Short circuit detection apparatus, 32 ... Voltage detection part as a measurement means, 34 ... Threshold generation part as a threshold value generation means, 36 ... Operational amplifier as a short circuit determination means, 42 ... Energization as an energization signal output means Signal output unit, 322... Shunt resistor, 342... Signal output unit as threshold value changing signal output means, 344... Transistor, T1... First resistor, T2 ... second resistor, T3. Power supply for threshold generation.

Claims (11)

Measuring means for measuring the current value flowing through the glow plug;
A short-circuit determination unit that compares the current value measured by the measurement unit with the current threshold generated by the threshold generation unit that generates a predetermined current threshold, and determines whether the glow plug is short-circuited or non-short-circuited. A glow plug short-circuit detection device,
The threshold generation means includes
A first current threshold is generated as the current threshold in the initial energization period to the glow plug, and a second current that is smaller than the first current threshold as the current threshold after the initial energization period to the glow plug has elapsed. A short-circuit detecting device for a glow plug, characterized by generating a threshold value.   The threshold generation means changes the current threshold to be generated from the first current threshold to the second current threshold when the energization time to the glow plug reaches a preset time. The glow plug short-circuit detection device according to claim 1. Comprising energization signal output means for outputting a PWM signal for determining whether or not energization is possible for the glow plug;
2. The glow plug short-circuit detection according to claim 1, wherein the threshold generation unit changes the generated current threshold from the first current threshold to the second current threshold based on the PWM signal. apparatus.   4. The glow plug short-circuit detection device according to claim 1, wherein the threshold generation unit generates three or more types of the current thresholds. 5. A measuring means for measuring a voltage value based on a current flowing through the glow plug;
A short circuit determination unit that compares the voltage value measured by the measurement unit with the voltage threshold generated by the threshold generation unit that generates a predetermined voltage threshold, and determines whether the glow plug is short-circuited or non-short-circuited. A glow plug short-circuit detection device,
The threshold generation means includes
A first voltage threshold is generated as the voltage threshold in the initial energization period to the glow plug, and a second voltage smaller than the first voltage threshold as the voltage threshold after the initial energization period to the glow plug has elapsed. A short-circuit detecting device for a glow plug, characterized by generating a threshold value.   The threshold generation means changes the voltage threshold to be generated from the first voltage threshold to the second voltage threshold when the energization time to the glow plug reaches a preset time. The glow plug short-circuit detection device according to claim 5. Comprising energization signal output means for outputting a PWM signal for determining whether or not energization is possible for the glow plug;
6. The glow plug short-circuit detection according to claim 5, wherein the threshold value generation unit changes the voltage threshold value to be generated from the first voltage threshold value to the second voltage threshold value based on the PWM signal. apparatus.   The glow plug short-circuit detection device according to claim 5, wherein the threshold generation unit generates three or more types of the voltage thresholds. The measuring means includes a shunt resistor connected in series to the glow plug,
9. The glow plug short-circuit detection device according to claim 5, wherein a voltage value based on a current flowing through the glow plug is measured based on a potential difference between both ends of the shunt resistor. 10. The threshold generation means includes
A first resistor having one end connected to a predetermined first threshold generation power supply;
A second resistor having one end connected to the other end of the first resistor and the other end grounded;
A third resistor having one end connected between the first resistor and the second resistor;
A transistor having a collector connected to the other end of the third resistor and an emitter connected to a predetermined second threshold generation power supply;
A threshold change signal output means connected to the base of the transistor and outputting a threshold change signal for opening and closing a current-carrying path between the collector and emitter of the transistor;
The threshold generation means generates the first voltage threshold by closing the energization path between the collector and emitter of the transistor, and opens the energization path between the collector and emitter of the transistor. The glow plug short-circuit detection device according to claim 5, wherein the second voltage threshold is generated. The glow plug short-circuit detection device according to any one of claims 1 to 10,
A heat generation system including a glow plug which is a target of short circuit detection by the glow plug short circuit detection device.

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