EP2489871A2

EP2489871A2 - Glow plug energization control unit

Info

Publication number: EP2489871A2
Application number: EP20120156200
Authority: EP
Inventors: Kazunari Kobuko; Takayuki Sakurai; Masayoshi Matsui
Original assignee: NGK Spark Plug Co Ltd
Current assignee: Niterra Co Ltd
Priority date: 2011-02-21
Filing date: 2012-02-20
Publication date: 2012-08-22
Also published as: KR20120095807A; JP5667468B2; KR101562425B1; JP2012172568A

Abstract

[Objective] To provide a glow plug energization control unit which can stably operate a function of de-energizing an energizing FET when an ON failure occurs in the energizing FET.

[Means for Solution] A GCU 31 includes an energizing FET 51 and a reverse connection protection FET 41, and a parasitic diode 411 which enables a glow plug 1 to be energized by a power supply VA is formed in the reverse connection protection FET 41 in a reverse direction with respect to a parasitic diode formed in the energizing FET. The GCU 31 includes a switch 71 which can switch the reverse connection protection FET 41 between ON and OFF, and a fuse 81 which disconnects an electrical connection between the power supply VA and the energizing FET 51 owing to heat generation of the reverse connection protection FET 41 through feeding an electrical current to the parasitic diode 411. When an ON failure of the energizing FET 51 is detected, the reverse connection protection FET 41 is caused to generate heat by the reverse connection protection FET 41 being turned off to cause current to flow through the parasitic diode 411.

Description

[Technical Field]

The present invention relates to an energization control unit of a glow plug used for preheating a diesel engine, or the like.

[Background Art]

In general, a glow plug having a heater is used for preheating a combustion engine such as a diesel engine, and the glow plug generates heat based on power supplied from a power supply (a battery).
Conventionally, as an energization control unit which controls heat generation of a glow plug, there has been known one including an energization signal output portion for outputting an energization signal (a PWM signal) which determines whether or not the glow plug can be energized by a power supply, and an energizing FET (field effect transistor) which is turned on when the energization signal from the energization signal output portion is input, enabling an output voltage from the battery to be applied to the glow plug.
Meanwhile, the energizing FET has a parasitic diode formed in parallel between the source and the drain of the energizing FET. As the parasitic diode is in a reverse direction with respect to a direction in which current flows between the power supply and glow plug, no current flows through the parasitic diode in the event that the power supply is connected in correct polarity. However, when the power supply is connected in reverse polarity, the parasitic diode is in a forward direction with respect to a direction in which reverse current flows between the power supply and glow plug. This may lead to a possibility that the glow plug is continuously energized. As a result of this, there is fear that the glow plug is overheated and fails.
Therefore, there is known a technology wherein, in order to prevent energization of the glow plug when the power supply is connected in reverse polarity, a reverse connection protection FET is provided in series between the power supply VA and energizing FET in such a way that the source and the drain of the reverse connection protection FET are in a reverse direction with respect to those of the energizing FET (for example, refer to Patent Document 1). According to the technology, a parasitic diode formed in the reverse connection protection FET is in a reverse direction with respect to the parasitic diode of the energizing FET. Because of this, even when the power supply is connected in reverse, the parasitic diode of the reverse connection protection FET is in a reverse direction. Thus, it is possible to avoid energization of the glow plug.
However, with the technology, when the energizing FET fails while remaining in an ON condition (an ON failure) due to a short circuit between the glow plug and power supply, or the like, a high current continues to flow through the energizing FET in the ON condition and the parasitic diode of the reverse connection protection FET, and furthermore, the energizing FET is overheated, posing a risk, in the worst case, of the energization control unit catching fire. Therefore, there has been proposed a technology wherein, when an ON failure occurs in the energizing FET, an electricity supply path is disconnected by heat generation of the energizing FET so that no electricity is supplied to the energizing FET (for example, refer to Patent Document 2). To describe the technology in detail, a conducting member configuring one portion of the electricity supply path, after being fixed by solder, is biased by a spring member, and the conducting member is flipped up by the biasing force of the spring member when the solder melts owing to the heat generation of the energizing FET, thereby disconnecting the electricity supply path.

[Related Art Documents]

[Patent Documents]

[Patent Document 1] W02008/108330
[Patent Document 2] DE102005040308B4

[Summary of the Invention]

[Problems to be solved by the Invention]

However, although an ON failure occurs in the energizing FET, the failure condition differs widely. Specifically, when the energizing FET becomes internally conductive due to the ON failure, the internal resistance value thereof varies according to the failed FET, and the energizing FET becomes conductive by having a high resistance component (an "ON failure"), or conversely, becomes conductive by having a low resistance component. Consequently, there is fear that variation (an ON failure due to differing internal resistance) occurs in the heat generation behavior of the energizing FET, and furthermore, that variation occurs in a time from an ON failure occurring in the energizing FET until the energizing FET is de-energized (the conducting member is flipped up). That is, with the technology described in Patent Document 2, there is fear that it is not possible to stably operate a de-energization function (it is not possible to predict the operation of the de-energization function).
The invention has been contrived bearing in mind the heretofore described circumstances, and an object thereof lies in providing a glow plug energization control unit which can stably operate a function of de-energizing an energizing FET when an ON failure occurs in the energizing FET.

[Means for Solving the Problems]

Hereafter, each configuration suitable for solving the above object will be described and divided into sections. Working effects peculiar to each corresponding configuration are added as necessary.
Configuration 1. A glow plug energization control unit of this configuration is a glow plug energization control unit including:

an energizing FET disposed between a power supply for supplying power to a glow plug and the glow plug; and
a reverse connection protection FET connected in series between the power supply and the energizing FET,
the unit switching between an energizing state and a de-energizing state based on energization signals input into a gate of the energizing FET, wherein
the reverse connection protection FET has a parasitic diode which supplies electricity from the power supply to the glow plug in a reverse direction with respect to a parasitic diode formed in the energizing FET,
a failure detection portion detects that the energizing FET has failed in an ON condition,
a switch switches between ON and OFF of the reverse connection protection FET,
a protection portion is disposed in an electricity supply path between the power supply and the energizing FET and disconnects an electrical connection therebetween in response to heat generation of the reverse connection protection FET through feeding an electrical current to the parasitic diode of the reverse connection protection FET, and
when the failure detection portion detects a failure of the energizing FET, the switch switches the reverse connection protection FET from ON to OFF so that current flows through the parasitic diode of the reverse connection protection FET, whereby the reverse connection protection FET generates heat.

According to the configuration 1, as the reverse connection protection FET is provided, it is possible to prevent continuous energization of the glow plug when the power supply is connected in reverse.
Also, according to the configuration 1, when an ON failure of the energizing FET is detected by the failure detection portion, the reverse connection protection FET is caused to generate heat by the reverse connection protection FET being turned off to cause current to flow through the parasitic diode of the reverse connection protection FET. Then, owing to the heat generation of the reverse connection protection FET, an electrical connection of the power supply and energizing FET is disconnected in the protection portion, which results in de-energizing the energizing FET. That is, according to the configuration 1, the energizing FET is de-energized based on the heat generation of the reverse connection protection FET, whose heat generation condition varies little, caused by causing current to flow through the parasitic diode, rather than the heat generation of the energizing FET whose heat generation condition may vary according to a failure condition. Herein, a voltage drop in the parasitic diode is stable at a typical value of, for example, on the order of 0.8V, because of which it is also possible to predict a heat generation temperature at which the reverse connection protection FET generates heat. Consequently, it is possible to operate a function of de-energizing the energizing FET stably (as assumed on a designer and manufacturer side). As a result of this, it is possible to carry out a detailed setting relating to de-energization function, such as an adjustment of a time from the ON failure occurring until the de-energization. Thus, a worst situation, such as firing of the energization control unit, may be avoided.
As the protection portion which de-energizes the energizing FET, it is possible to employ, for example, configurations 2 and 3 to be described hereafter.
Configuration 2. A glow plug energization control unit of this configuration is such that, in the configuration 1, the protection portion is a fuse, connected in series between the power supply and energizing FET, which melts down owing to the heat generation of the reverse connection protection FET through feeding an electrical current to the parasitic diode of the reverse connection protection FET.
According to the configuration 2, it is possible to easily realize the function of de-energizing the energizing FET, and also, it is possible to reduce the size and manufacturing cost of the unit.
In order that the heat of the reverse connection protection FET can be efficiently transferred to the fuse, the fuse may be brought into direct contact with the reverse connection protection FET, or may be brought into indirect contact with the reverse connection protection FET via a high thermal conductive member. The high thermal conductive member preferably has a certain degree of thermal resistance, considering the heat generation of the reverse connection protection FET.
Configuration 3. A glow plug energization control unit of this configuration is such that, in the configuration 1, the protection portion includes:

a conductive conducting portion connected in series between the power supply and energizing FET by solders which can melt owing to the heat generation of the reverse connection protection FET through feeding an electrical current to the parasitic diode of the reverse connection protection FET; and
a biasing portion which biases the conducting portion toward a side away from the electricity supply path between the power supply and energizing FET.

According to the configuration 3, working effects the same as those of the configuration 1 are achieved. Also, it is possible to easily realize the function of de-energizing the energizing FET.

[Brief Description of the Drawings]

[Fig. 1] Fig. 1 (a) is a partially broken front view showing a configuration of a glow plug, and Fig. 1 (b) is a partially enlarged sectional view showing a configuration of a leading end portion of the glow plug.
[Fig. 2] Fig. 2 is a block diagram showing an outline configuration of a GCU and the like.
[Fig. 3] Fig. 3(a) and Fig. 3(b) are a diagram for illustrating a disposal position of a fuse, wherein Fig. 3 (a) is a plan schematic diagram of a substrate configuring the GCU, and Fig. 3 (b) is a sectional schematic diagram of the substrate and the like.
[Fig. 4] Fig. 4 is a block diagram showing an outline configuration of a GCU and the like in a second embodiment.
[Fig. 5] Fig. 5(a) to Fig. 5(b) are a diagram for illustrating a protection portion, wherein Fig. 5 (a) is a plan schematic diagram of a substrate configuring the GCU, Fig. 5 (b) is a bottom schematic diagram of the substrate, and Fig. 5 (c) is a sectional schematic diagram of the substrate and the like.
[Fig. 6] Fig. 6 is a sectional schematic diagram of the substrate and the like for illustrating a disposal position of a fuse in another embodiment.
[Fig. 7] Fig. 7 is a block diagram showing an outline configuration of a GCU and the like in another embodiment.

[Modes for Carrying Out the Invention]

Hereafter, a description will be given of embodiments, while referring to the drawings.

[First Embodiment]

A glow control unit (GCU) 31 acting as an energization control unit controls energization of a glow plug 1, and is used for a starting aid, an improvement in drive stability, and the like, of a diesel engine (hereafter called an "engine") EN of an automobile.
Firstly, a description will be given of an outline configuration of the glow plug 1 controlled by the GCU 31, prior to a description of the GCU 31. Fig. 1 (a) is a partially broken front view of the glow plug 1, and of Fig. 1 (b) is a partially enlarged sectional view of a leading end portion of the glow plug 1. In Figs. 1 (a) and 1 (b), a description will be given with the lower side of the drawings as the leading end side of the glow plug 1 and the upper side as the rear end side.
As shown in of Fig. 1 (a), the glow plug 1 includes a housing 2, a center pole 3, a ceramic heater 4, a metal pipe 5, a terminal pin 6, and the like.
The housing 2, as well as being formed from a predetermined metallic material (for example, an iron-based material such as S45C), has an axial hole 7 extending in a direction of an axis CL1. Furthermore, a threaded portion 8 for use in mounting the glow plug 1 in the engine EN and a tool engagement portion 9 of hexagonal cross section for bringing a tool such as a torque wrench into engagement therewith are formed on the outer periphery of the housing 2.
Also, the metallic center pole 3 of a round bar form is housed in the axial hole 7 of the housing 2. Furthermore, the leading end portion of the center pole 3 is press fitted into the rear end portion of a cylindrical connecting member 10 formed from a metallic material (for example, an iron-based material such as SUS), and the rear end portion of the ceramic heater 4 is press fitted into the leading end portion of the connecting member 10. Because of this, the center pole 3 and ceramic heater 4 are mechanically and electrically connected via the connecting member 10.
Furthermore, the metallic terminal pin 6 for connecting an energizing cable is fixed by caulking onto the rear end portion of the center pole 3.
Moreover, the metal pipe 5 is formed into a cylindrical shape from a predetermined metallic material, and joined to the leading end portion of the housing 2. The metal pipe 5 holds an intermediate portion of the ceramic heater 4 in the direction of the axis CL1, and the leading end portion of the ceramic heater 4 is in a condition in which it is exposed from the leading end of the metal pipe 5.
In addition, as shown in Fig. 1 (b), the ceramic heater 4 includes a base substance 21 of a round bar form extending in the direction of the axis CL1 and an elongated U-shaped heater element 22 embedded inside the base substance 21. The base substance 21 is configured of an insulating ceramic (for example, silicone nitride or alumina), while the heater element 22 is configured of a conductive ceramic, based on a ceramic material, which contains a conductive material (for example, molybdenum or tungsten silicide, nitride, or carbide).
Also, the heater element 22 includes a heat generating portion 23 disposed at the leading end portion of the ceramic heater 4 and a pair of bar- like lead portions 24 and 25 extending from the heat generating portion 23 to the rear end side. Then, an electrode lead-out portion 26 is provided in a position closer to the rear end of one lead portion 24, protruding in a direction of the outer periphery in such a way as to be exposed on an outer peripheral surface of the ceramic heater 4, and the electrode lead-out portion 26 is in contact with an inner peripheral surface of the connecting member 10. Also, an electrode lead-out portion 27 is also provided in a position closer to the rear end of the other lead portion 25, protruding in a direction of the outer periphery in such a way as to be exposed on an outer peripheral surface of the ceramic heater 4, and the electrode lead-out portion 27 is in contact with an inner peripheral surface of the metal pipe 5.
Next, a description will be given of the GCU 31 which is a feature of the invention.
Fig. 2 is a block diagram showing an outline configuration of the GCU 31 which carries out a control of energization of the glow plug 1, and the like. Although one glow plug 1 is shown in Fig. 2, actually, the glow plug 1 is provided in each cylinder of the engine EN, and power is supplied to each glow plug 1 via a diverging point DP from a power supply VA which outputs a predetermined voltage (for example, 12V). Also, an energizing FET 51, to be described hereafter, is provided corresponding to each glow plug 1.
The GCU 31 operates in accordance with power supplied from the power supply VA, and is connected via a predetermined communication unit (for example, a CAN) to an electronic control unit (ECU) 91 of the automobile. Also, the GCU 31 includes a reverse connection protection FET (field effect transistor) 41, the energizing FET 51, a controller (in the embodiment, an ASIC) 61, a switch 71, and a fuse 81 acting as a protection portion.
The reverse connection protection FET 41 is for preventing an overheat failure of the energizing FET 51 when the power supply VA is connected in reverse polarity. The reverse connection protection FET 41 is interposed in an electricity supply path electrically connecting the power supply VA and glow plug 1, and specifically, the drain thereof is connected to the energizing FET 51, while the source thereof is connected to the power supply VA. That is, the reverse connection protection FET 41 is disposed in such a way that the source and drain thereof are in a reverse direction with respect to the source and drain of the energizing FET 51. Also, in the embodiment, the reverse connection protection FET 41 is configured of an N-channel MOSFET, and only one is provided between the diverging point DP of power supplied from the power supply VA to each glow plug 1 and the power supply VA. The reverse connection protection FET 41 in the embodiment is of very low on resistance (for example, several milliohms).
In addition, the reverse connection protection FET 41 has a parasitic diode 411 formed in parallel between the source and drain of the same reverse connection protection FET 41, and the parasitic diode 411 is in a forward direction with respect to the direction in which current flows from the power supply VA to the glow plug 1. However, a voltage drop when current flows through the parasitic diode 411 is much larger than a voltage drop when current flows through the on resistance of the reverse connection protection FET 41. Consequently, in a condition in which current is flowing from the power supply VA to the glow plug 1, little or no current flows through the parasitic diode 411 unless the reverse connection protection FET 41 is turned off.
The energizing FET 51 is provided in each glow plug 1, and the drain is connected to the drain of the reverse connection protection FET 41, while the source is connected to the glow plug 1. In the embodiment, an N-channel MOSFET is used as the energizing FET 51, and the energizing FET 51 is such that the on resistance thereof is very low (for example, several milliohms).
Also, the energizing FET 51 has a parasitic diode 511 formed in parallel between the source and drain of the same energizing FET 51, and the parasitic diode 511 is in a reverse direction with respect to the direction in which current flows from the power supply VA to the glow plug 1.
The controller 61 controls energization of the glow plug 1 by the power supply VA, and is an ASIC including an energization signal output portion 62 which outputs signals for switching between energization and de-energization of the glow plug 1 to the gate of the energizing FET 51, a charge pump circuit (CP circuit) 63 with a voltage rise function, and a failure detection portion 64. Power for the controller 61 to operate inside the GCU 31 is supplied to the controller 61 from the power supply VA.
The energization signal output portion 62 is controlled by the ECU 91, and inputs a rectangular energization signal (a PWM signal) indicating a timing of energization of the glow plug 1 by the power supply VA into the gate of the energizing FET 51. Specifically, when the glow plug 1 is energized by the power supply VA, a high signal is output to the energizing FET 51. Meanwhile, when stopping the energization of the glow plug 1 by the power supply VA, a low signal is output to the energizing FET 51. The energization signal output portion 62 is connected to the charge pump circuit 63, and an energization signal output from the energization signal output portion 62 is raised in voltage by the charge pump circuit 63.
The charge pump circuit 63 is connected to the gate of the reverse connection protection FET 41 via a drive circuit 65 having predetermined transistor 651, diodes 652 and 653, and the like, and outputs a predetermined high voltage [for example, (a voltage output from the power supply VA)+10V] to the gate of the reverse connection protection FET 41. The charge pump circuit 63 operates when an engine key (not shown) is turned on, and when the engine key is on, the reverse connection protection FET 41 is turned on by the charge pump circuit 63 and drive circuit 65 except when a failure of the energizing FET 51 is detected by the failure detection portion 64. Meanwhile, when the engine key is in an off condition, the output from the charge pump circuit 63 is turned off, as a result of which the reverse connection protection FET 41 is turned off. As the charge pump circuit 63 (controller 61) is activated in conjunction with the turning on of the engine key in this way, when the power supply VA is connected in reverse polarity, the reverse connection protection FET 41 is turned off in the same way as when the engine key is in the off condition. Consequently, when the power supply VA is connected in reverse polarity, the parasitic diode 511 of the energizing FET 51 is in a forward direction with respect to a direction in which reverse current flows, but the reverse connection protection FET 41 is off, and the parasitic diode 411 thereof is in a reverse direction with respect to the direction in which the reverse current flows. As a result of this, current is prevented from flowing through the parasitic diode 511 of the energizing FET 51, thus preventing an overheat failure of the energizing FET 51.
The failure detection portion 64, based on voltage across each energizing FET 51 input into the controller 61, determines whether or not the energizing FET 51 is failed in an "ON condition", and outputs a result of the determination to the ECU 91. Specifically, when voltage across the energizing FET 51 is comparatively high at a timing at which the energizing FET 51 is turned off (that is, when the energizing FET 51 is energized despite being at an off timing), the failure detection portion 64 determines that the energizing FET 51 is failed while remaining in the ON condition (an "ON failure"), and sends a failure signal to the ECU 91. The ECU 91 outputs an energization enable signal to the controller 61 at a normal time, but stops outputting the energization enable signal when receiving a failure signal.
The switch 71 includes a switching portion 72 and a signal detection portion 73.
The switching portion 72 includes a transistor or the like, and is interposed between the reverse connection protection FET 41 and charge pump circuit 63. The switching portion 72 enables the gate voltage output from the charge pump circuit 63 to the reverse connection protection FET 41 to switch between on and off.
The signal detection portion 73 detects whether or not an energization enable signal is output from the ECU 91, and outputs a detection result signal to the switching portion 72. Specifically, when an energization enable signal is output from the ECU 91 (at the normal time), the signal detection portion 73 outputs a signal which turns on the switching portion 72 as a detection result signal. That is, when the energizing FET 51 is normal, the reverse connection protection FET 41 and charge pump circuit 63 are electrically connected, and the reverse connection protection FET 41 is turned on.
Meanwhile, when no energization enable signal is output from the ECU 91 (at a failure time), the signal detection portion 73 outputs a signal which turns off the switching portion 72 as a detection result signal. That is, when an ON failure occurs in the energizing FET 51, the electrical connection of the reverse connection protection FET 41 and charge pump circuit 63 is disconnected, and the reverse connection protection FET 41 is turned off. As a result of this, current flows to the parasitic diode 411 of the reverse connection protection FET 41. When the engine key is on and the glow plug 1 is not energized too, an energization enable signal from the ECU 91 is stopped, but in this case, the energizing FET 51 is off in the event that the energizing FET 51 is normal. Because of this, no current flows between the power supply VA and glow plug 1, and it does not happen that the reverse connection protection FET 41 generates heat.
The fuse 81 is connected in series between the power supply VA and reverse connection protection FET 41, and as shown in Figs. 3(a) and 3(b), is fixed to a substrate CB on which the reverse connection protection FET 41 and energizing FET 51 are disposed [the controller 61, the switch 71, a harness, and the like, are provided on the substrate CB, but in Figs. 3 (a) and 3 (b), an illustration thereof is omitted for the sake of simplicity]. Also, in the embodiment, the fuse 81 is disposed on the reverse connection protection FET 41, and is in contact with the reverse connection protection FET 41 across an adhesive AD superior in both thermal resistance and thermal conductivity. Because of this, the heat of the reverse connection protection FET 41 is efficiently transferred to the fuse 81. The fuse 81 does not melt down owing to heat generation (for example, up to the order of 175°C) of the reverse connection protection FET 41 or energizing FET 51 at a time of normal use, while when the reverse connection protection FET 41 is caused to generate heat by causing current to flow through the parasitic diode 411, the preset meltdown temperature of the fuse 81 is set to a predetermined temperature (for example, 200°C to 250°C) in such a way that the fuse 81 melts down owing to the heat generation (for example, up to the order of 300°C) of the reverse connection protection FET 41.
Next, a description will be given of an operation of the heretofore described GCU 31.
Firstly, when the energizing FET 51 is normal, the switching portion 72 is turned on, and the reverse connection protection FET 41 is also turned on.
On an ON failure occurring in the energizing FET 51 in this condition, the ON failure of the energizing FET 51 is detected by the failure detection portion 64, and a failure signal is output to the ECU 91. The ECU 91 which has received the failure signal stops the output of the energization enable signal, as a result of which the switching portion 72 and thus the reverse connection protection FET 41 are turned off. By the reverse connection protection FET 41 being turned off, current flows through the parasitic diode 411 of the reverse connection protection FET 41, and the reverse connection protection FET 41 generates heat. Then, on the reverse connection protection FET 41 being heated to a high temperature exceeding the preset meltdown temperature of the fuse 81, the fuse 81 disposed on the reverse connection protection FET 41 melts down. As a result of this, the electrical connection of the power supply VA and energizing FET 51 is disconnected, and the energization of the energizing FET 51 is stopped.
As heretofore described in detail, according to the embodiment, as the reverse connection protection FET 41 is provided, it is possible to prevent continuous energization of the glow plug 1 when the power supply VA is connected in reverse.
Also, when an ON failure of the energizing FET 51 is detected by the failure detection portion 64, current is caused to flow through the parasitic diode 411 to cause the reverse connection protection FET 41 to generate heat by turning off the reverse connection protection FET 41, and the fuse 81 is caused to melt down by the heat generation of the reverse connection protection FET 41, thus de-energizing the energizing FET 51. That is, the energizing FET 51 is de-energized based on the heat generation of the reverse connection protection FET 41, whose heat generation condition varies little, caused by causing current to flow through the parasitic diode 411, rather than the heat generation of the energizing FET 51 whose heat generation condition may vary according to a failure condition. Consequently, it is possible to operate a function of de-energizing the energizing FET 51 stably (as assumed on a designer and manufacturer side) . As a result of this, it is possible to carry out a fine setting relating to a de-energization function such as an adjustment of a time from the ON failure occurring until the de-energization, and it is possible to avoid a worst situation such as the GCU 31 catching fire.
In addition, in the embodiment, as the fuse 81 is in contact with the reverse connection protection FET 41 across the adhesive AD superior in thermal conductivity, it is possible to efficiently transfer the heat of the reverse connection protection FET 41 to the fuse 81. Consequently, when an ON failure occurs in the energizing FET 51, it is possible to cause the fuse 81 to melt down swiftly, and furthermore, it is possible to promptly de-energize the energizing FET 51.
Meanwhile, in a metal glow plug having a heating coil, it may happen that the heating coil is disconnected comparatively early by continuous energization accompanying an ON failure of an energizing FET, and the energizing FET is de-energized at a comparatively early point from the ON failure occurring. In response to this, in a ceramic glow plug having the ceramic heater 4 as in the embodiment, a disconnection or the like of the glow plug 1 is unlikely to occur, and it is easy for current to flow through the energizing FET 51 over a long period (that is, it is easy for the energizing FET 51 to overheat). Consequently, the GCU 31 which can rapidly de-energize the energizing FET 51 when an ON failure occurs is particularly effective when used for a control of energization of the ceramic glow plug for which energization of the energizing FET 51 for a long period is a concern.

[Second Embodiment]

Next, a second embodiment will be described centered on differences from the first embodiment. In the first embodiment, the fuse 81 is used as the protection portion, but in the second embodiment, as shown in Fig. 4 and Figs. 5(a) to 5 (c) [in Figs. 5(a) to 5(c), in the same way as in Figs. 3 (a) and 3 (b), the controller 61 and the like are omitted from the illustration for the sake of simplicity of illustration], a mechanism including a conducting portion 102 and a biasing portion 103 is used as a protection portion 101.
The conducting portion 102 is formed from a conductive metallic plate (for example, a copper plate) superior in thermal resistance. Also, the conducting portion 102, by being fixed to the back surface of the substrate CB by predetermined solders 104 disposed on the substrate CB, is interposed in an electricity supply path between the power supply VA and reverse connection protection FET 41. The solders 104 are such that the constituent material, disposal position, volume, and the like, are set in such a way that the solders 104 do not melt owing to the heat generation of the reverse connection protection FET 41 or energizing FET 51 at the time of normal use, while the solders 104, when the reverse connection protection FET 41 is caused to generate heat by causing current to flow through the parasitic diode 411, melt owing to the heat generation.
The biasing portion 103 is configured of a predetermined spring member, and one end thereof is in contact with the conducting portion 102 through a hole portion HO formed in the substrate CB, while the other end is fixed to a casing CA to which the substrate CB is attached. Also, the biasing portion 103 is provided between the conducting portion 102 and casing CA in a condition in which it is compressed in a longitudinal direction, and biases the conducting portion 102 toward a side away from the electricity supply path between the power supply VA and reverse connection protection FET 41.
In the GCU 31 having this kind of protection portion 101, when an ON failure occurs in the energizing FET 51, the reverse connection protection FET 41 is turned off, and current is caused to flow through the parasitic diode 411, in the same way as in the first embodiment. Because of this, the reverse connection protection FET 41 reaches a high temperature, meaning that the solders 104 melt, the conducting portion 102 becomes detached from the substrate CB, and the conducting portion 102 is separated from the substrate CB by a biasing force from the biasing portion 103. As a result of this, the electrical connection of the power supply VA and energizing FET 51 is disconnected, and the energization of the energizing FET 51 is stopped.
As above, according to the second embodiment, working effects the same as those of the first embodiment are achieved. That is, as the energizing FET 51 is de-energized based on the heat generation of the reverse connection protection FET 41 caused by causing current to flow through the parasitic diode 411, it is possible to stably operate the function of de-energizing the energizing FET 51.
The invention, not being limited to the description details of the heretofore described embodiments, may be implemented in, for example, the following ways. Of course, other application examples and modification examples not illustrated hereafter are also naturally possible.

(a) In the first embodiment, the fuse 81 is disposed on the reverse connection protection FET 41, but the disposal position of the fuse 81 is not particularly limited as long as it is a position in which the fuse 81 can melt down owing to the heat generation of the reverse connection protection FET 41 caused by causing current to flow through the parasitic diode 411. Also, the fuse 81 may be fixed to the casing CA, for example, as shown in Fig. 6, rather than the fuse 81 being fixed to the substrate CB. In this case, in order to efficiently transfer the heat of the reverse connection protection FET 41 to the fuse 81, a configuration may be such that the fuse 81 is disposed on the reverse connection protection FET 41 in a condition in which the substrate CB is attached to the casing CA. Also, a thermal conductive sheet or the like with good thermal conductivity may be interposed between the fuse 81 and reverse connection protection FET 41.

(b) In the second embodiment, the conducting portion 102 is disposed on the substrate CB, but the disposal position of the conducting portion 102 is not particularly limited, provided that the solders 104 fixing the conducting portion 102 can melt owing to the heat generation of the reverse connection protection FET 41 caused by causing current to flow through the parasitic diode 411. Consequently, for example, the conducting portion 102 may be disposed, across the solders 104, in a region of the casing CA positioned above the reverse connection protection FET 41. Also, in the second embodiment, the biasing portion 103 is configured in such a way as to bias the conducting portion 102 through the hole portion HO formed in the substrate CB but, the configuration of the biasing portion 103 not being limited to this, it is sufficient to bias the conducting portion 102 toward a side away from the electricity supply path between the power supply VA and energizing FET 51. Furthermore, a metallic plate is used as the conducting portion 102 but, for example, a shunt resistor may be used as the conducting portion 102.

(c) In the heretofore described embodiments, the fuse 81 or protection portion 101 is provided between the power supply VA and reverse connection protection FET 41, but the fuse 81 or protection portion 101 may be provided between the reverse connection protection FET 41 and diverging point DP.

(d) In the heretofore described embodiments, only one reverse connection protection FET 41 is provided, but plural reverse connection protection FETs 41 may be provided in parallel in order to increase current capacity in response to an increase in the number of glow plugs 1. In this case, all the reverse connection protection FETs 41 are turned off when an ON failure occurs in the energizing FET 51.

(e) In the heretofore described embodiments, the reverse connection protection FET 41 is configured of an N-channel MOSFET, but the reverse connection protection FET 41 may be configured of a P-channel MOSFET. Also, in this case, it is not necessary to provide the drive circuit and, as shown in Fig. 7, it is sufficient to operate the switching portion 72 in such a way that the gate of the reverse connection protection FET 41 is grounded at the normal time, and the gate of the reverse connection protection FET 41 is connected to the power supply VA when an ON failure occurs in the energizing FET 51.

(f) In the heretofore described embodiments, the GCU 31 is configured in such a way as to control energization of the ceramic glow plug having the ceramic heater 4, but the object controlled by the GCU 31 is not limited to this. For example, the dimensions of each member, the composition of the ceramic heater, and the like, can be appropriately changed to ones which it is easy for the GCU 31 to control. Also, the glow plug is not limited to the ceramic glow plug. Consequently, the GCU 31 may be configured in such a way as to control energization of a metal glow plug having a heating coil.

(g) In the heretofore described embodiments, the GCU 31 and ECU 91 are provided separately, but the ECU 91 may be configured in such a way as to have the function of the GCU 31, and the energization of the glow plug 1 controlled by the GCU function which the ECU 91 has.

(h) In the heretofore described embodiments, the controller 61 is configured of an ASIC, but the controller 61 may be configured of a microcomputer. Also, in this case, when an ON failure of the energizing FET 51 is detected, the reverse connection protection FET 41 may be switched between on and off by the switching portion 72 being directly switched between on and off by the controller 61, rather than via the ECU 91 or signal detection portion 73. In general, no charge pump circuit is incorporated in the microcomputer. Consequently, a P-channel FET for which no driving charge pump circuit is necessary may be used as the reverse connection protection FET 41 or energizing FET 51. A charge pump circuit may be provided separately, and an N-channel FET used as the reverse connection protection FET 41 or energizing FET 51.

[Description of Reference Numerals and Signs]

1 ...: Glow plug
31 ...: GCU (energization control unit)
41 ...: Reverse connection protection FET
411 ...: Parasitic diode
51 ...: Energizing FET
64 ...: Failure detection portion
71 ...: Switch
81 ...: Fuse (protection portion)
101 ...: Protection portion
102 ...: Conducting portion
103 ...: Biasing portion
104 ...: Solder
VA ...: Power supply

Claims

1.
A glow plug energization control unit comprising:

an energizing FET disposed between a power supply for supplying power to a glow plug and the glow plug; and

a reverse connection protection FET connected in series between the power supply and the energizing FET,

the unit switching between an energizing state and a de-energizing state based on energization signals input into a gate of the energizing FET, wherein

the reverse connection protection FET has a parasitic diode which supplies electricity from the power supply to the glow plug in a reverse direction with respect to a parasitic diode formed in the energizing FET,

a failure detection portion detects that the energizing FET has failed in an ON condition,

a switch switches between ON and OFF of the reverse connection protection FET,

a protection portion is disposed in an electricity supply path between the power supply and the energizing FET and disconnects an electrical connection therebetween in response to heat generation of the reverse connection protection FET through feeding an electrical current to the parasitic diode of the reverse connection protection FET, and

when the failure detection portion detects a failure of the energizing FET, the switch switches the reverse connection protection FET from ON to OFF so that current flows through the parasitic diode of the reverse connection protection FET, whereby the reverse connection protection FET generates heat.

2.
The glow plug energization control unit according to claim 1, wherein
the protection portion is a fuse, connected in series between the power supply and the energizing FET, which melts down owing to the heat generation of the reverse connection protection FET through feeding an electrical current to the parasitic diode of the reverse connection protection FET.

3.
The glow plug energization control unit according to claim 1, wherein
the protection portion includes:

a conducting portion connected in series between the power supply and the energizing FET by solders which melt owing to the heat generation of the reverse connection protection FET through feeding an electrical current to the parasitic diode of the reverse connection protection FET; and

a biasing portion which biases the conducting portion toward a side away from an electricity supply path between the power supply and the energizing FET.