Glow plug duty cycle modulating apparatus

• US 4,312,307 A
• Filed: 02/04/1980
• Issued: 01/26/1982
• Est. Priority Date: 02/04/1980
• Status: Expired due to Term

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Cooper, Lawrence E.
• Primary Examiner(s): Nelli, Raymond A.
• Application Number:
  US06/118,286
• Time in Patent Office: 722 Days
• Field of Search: 123/145 A, 123/179 BG, 337/102, 219/492, 219/493, 219/494, 219/486, 219/333
• US Class Current: 123/145.00A
• CPC Class Codes: F02B 3/06 with compression ignition compression ignition engines using air or gas for blowing fuel into compressed air in cylinder F02B13/02
• CPC Class Codes: F02N 19/04 by heating of fluids used in engines
• CPC Class Codes: F02P 19/022 using intermittent current supply

Abstract

A control for modulating the duty cycle of diesel engine glow plugs has two heat sensitive, normally closed switches each thermally coupled to a respective positive temperature coefficient (PTC) of resistivity heater in turn thermally coupled to a common heat sink. The heat sensitive switches are serially connected to each other, to an ignition switch and to a glow plug relay. The PTC heaters are connected to a point between the heat sensitive switches and the relay and to ground. A third PTC heater is disposed on the heat sink intermediate the first and second heaters and thermally coupled to the heat sink. The third heater is connected to an alternator and serves to cut off power to the glow plugs after a selected after glow stage. The two heat sensitive switches can be selected to open at approximately the same temperature for a random operating mode or at slightly different temperatures for a sequential operating mode. The common operating mode is a redundant high reliability operating mode whereas the sequential operating mode, using slightly different temperatures allows one switch to control the cycling and the second to be a back up safety control. In one preferred embodiment a "wait" lamp is connected between the ignition switch a double pole relay used to latch the lamp in the deenergized state when the first "off" time of the heat sensitive switches occurs. In a second embodiment the "wait" lamp is connected between the alternator and the coil of the glow plug relay with a diode serially connected to the lamp to preclude alternator current from energizing the lamp.

Claims

1. Apparatus for providing a thermal analog of diesel engine glow plugs and to modulate the duty cycle of power supplied to such glow plugs comprising

a housing, first and second ceramic like heater elements disposed in the housing, a heat sensitive, normally closed switch mounted on top of each of the first and second heater elements in thermally coupled relation with each respective heater element, heat sink means thermally coupled to both the first and second heater elements, means to connect the switches in series circuit relation and connectable to means controlling the energization of the glow plugs and to an ignition switch, one of the two switches modulating the current flow to the glow plugs, the other of the two switches as a back up protector, means to electrically energize the first and second heater elements only when current is passing through both heat sensitive switches, and means to interrupt current flow to the glow plugs upon the occurrence of a preselected condition.

2. Apparatus according to claim 1 in which the means to interrupt current flow to the glow plugs includes a third ceramic-like heater element and heat sink means thermally coupled thereto and to the first and second switches, the third heater element connectable to an alternator of the diesel engine so that upon starting of the engine heat is generated by the third heater element.

3. Apparatus according to claim 2 in which the heater elements are composed of material having a positive temperature coefficient (PTC) of resistance.

4. Apparatus according to claim 2 in which the heater elements are composed of barium lead titanate doped with a rare earth.

5. Apparatus according to claim 1 in which the normally closed heat sensitive switches are selected to switch to an open contacts position at approximately the same temperature.

6. Apparatus according to claim 1 in which the normally closed heat sensitive switches are selected to switch to an open contacts position at slightly different temperatures.