Method and apparatus for detecting an open circuit in a glow plug group for combination with a glow plug heating control circuit

• US 4,500,775 A
• Filed: 03/31/1983
• Issued: 02/19/1985
• Est. Priority Date: 04/02/1982
• Status: Expired due to Fees

• Current Assignee: Nippondenso Co., Ltd. (DENSO Corporation)
• Original Assignee: Nippondenso Co., Ltd. (DENSO Corporation)
• Inventors: Hotta, Seiko, Sangu, Osamu
• Primary Examiner(s): Paschall, M. H.
• Application Number:
  US06/480,923
• Time in Patent Office: 691 Days
• Field of Search: 219/202, 219/203, 219/497, 219/492, 219/493, 219/508, 219/501, 219/483, 219/486, 307/39-41, 324/51, 324/52, 340/652, 340/660, 340/662, 340/664, 123/179 B, 123/179 H
• US Class Current: 219/497
• CPC Class Codes: F02P 19/027 Safety devices, e.g. for diagnosing the glow plugs or the related circuits

Abstract

In a method and apparatus for detecting an open circuit in a glow plug group for combination with a heating control circuit of the glow plug group mounted on an internal combustion engine, an output signal generated from a detecting element connected in series with the glow-plug group while electric power is supplied to the glow plug group is applied to a first comparator to detect a change of the composite resistance of the glow plug group due to a temperature rise caused by its heating. At this time, if an open circuit failure has occurred in the glow plug group, the state of the resistance change of the glow plug group varies greatly. The first comparator produces a time measurement signal indicating a time when the composite resistance of the glow plug group has reached a predetermined value and supplies the time measurement signal to a glow plug open circuit detecting circuit. In a glow plug open circuit detecting circuit, a second comparator produces a time limit signal which continues for a preset time-length from the time of application of a power supply voltage, and a gate circuit gates the time measurement signal with the time limit signal and generates a glow plug open circuit detection signal for actuating an open circuit indicator only when the time indicated by the time measurement signal is shorter than the preset time-length.

Claims

1. A method for detecting an open circuit occurring in a glow plug group including a plurality of glow plugs connected in parallel, for combination with a glow plug heating control circuit for controlling the supply of electric powe to said glow plug group on the basis of an output signal indicative of a change of the composite resistance of said glow plug group produced from a detecting element connected in series with said glow plug group while detecting a heating condition of said glow plug group, after a power supply switch is turned on, comprising the steps of:

generating a heating time signal indicative of a time length in which the heating condition of said glow plug group detected by said detecting element reaches a predetermined heating condition after the start of the supply of electric power to said glow plug group initiated by the turning-on of said power supply switch;

generating a time limit signal indicative of a preset time-length starting in response to the turning-on of said power supply switch;

comparing the heating time signal with the time limit signal; and

producing an open circuit detection signal for indicating the occurrence of an open circuit in said glow plug group only when the time length indicated by the heating time signal is shorter than the preset time-length.

2. A method according to claim 1, wherein the preset time-length is corrected in accordance with one of a power supply voltage and a voltage related thereto at the time of the turning-on of said power supply switch.

3. A method according to claim 1, wherein the preset time-length is corrected in accordance with a temperature of said glow plug group at the start of the supply of electric power to said glow plug group.

4. An apparatus for detecting an open circuit occurring in a glow plug group including a plurality of glow plugs connected in parallel, for combination with a glow plug heating control circuit for controlling an electric power supply to said glow plug group through a power supply switch on the basis of an output signal indicative of a change of the composite resistance of said glow plug group produced from a detecting element connected in series with said glow plug group while detecting a heating condition of said glow plug group, after said power supply switch is turned on, comprising:

first comparator means for receiving output signals from said detecting element and producing a heating condition detection signal indicative of a heating condition of said glow plug group;

a glow plug open circuit detecting circuit including;

time signal generating means for starting its operation in response to the turning-on of said power supply switch and producing a time lapse signal indicative of a time elapsed from the start of its operation;

second comparator means for receiving the time lapse signal from said time signal generating means and a preset time-length signal indicative of a preset time-length and producing a time limit signal which continues during the preset time-length; and

gate means for receiving the heating condition detection signal from said first comparator means and the time limit signal from said second comparator means, said gate means gating the time limit signal with the heating condition detection signal and thereby producing a glow plug open circuit detection signal indicative of the detection of the occurrence of an open circuit in said glow plug group only when said gate means has received the heating condition detection signal while said gate means is receiving the time limit signal; and

open circuit indicating means for indicating the occurrence of an open circuit in said glow plug group in response to the glow plug open circuit detection signal from said glow plug open circuit detecting circuit.

5. An apparatus according to claim 4, wherein said second comparator means of said glow plug open circuit detecting circuit comprises hold circuit means constructed to be driven by the glow plug open circuit detection signal from said gate means of said glow plug open circuit detecting circuit to hold a state of having detected the occurrence of an open circuit of said glow plug open circuit detecting circuit.

6. An apparatus according to claim 4, a power supply input to said time signal generating means of said glow plug open circuit detecting circuit is connected to a power supply side end of said detecting element connected in series with said glow plug group.

7. An apparatus according to claim 5, a power supply input to said time signal generating means of said glow plug open circuit detecting circuit is connected to a power supply side end of said detecting element connected in series with said glow plug group.