Glow plug for internal combustion engine

Abstract

A glow plug has a heating coil made of an alloy of iron, chromium and aluminum, a control coil made of nickel and serially connected with the heating coil, a heater case made of an inconel material and accommodating the coils therein, and a current line through which an electric current adjusted at a duty ratio changeable based on a voltage of the current according to a pulse width modulation control is supplied to the coils. The alloy of the heating coil and nickel of the control coil are superior in durability at high temperature. The inconel material of the case is superior in heat resisting property. In response to the current, resistance of the control coil is heightened, and the heating coil is heated to a maximum temperature to heat an air-fuel mixture of a combustion chamber of a diesel engine.

1 . A glow plug comprising:
 a heating coil made of an alloy of iron, chromium and aluminum;   a control coil made of nickel and serially connected with the heating coil;   a current supply line through which an electric current adjusted according to a pulse width modulation control is supplied to the control coil and the heating coil to heat the heating coil to a maximum temperature while heightening a resistance of the control coil; and   a heater case, made of an inconel material, that accommodates the heating coil and the control coil so as to dispose the control coil on a rear side of the heating coil and insulates the heating coil and the control coil from a heated medium disposed outside the heater case, the heated medium being heated by the heating coil through the heater case.   
   
   
       2 . The glow plug according to  claim 1 , wherein a length of the control coil along an axial direction of the heater case is set in a range from 5 to 12 mm. 
   
   
       3 . The glow plug according to  claim 1 , further comprising a housing that holds a rear end of the heater case, wherein a sum of the length of the control coil and a length of the heating coil along the axial direction is smaller than a length of the heater case such that the control coil is placed out of a rear portion of the heater case facing the housing. 
   
   
       4 . The glow plug according to  claim 1 , wherein the heater case has three or more cylindrical portions having different diameters such that the diameter of the heater case is made small toward a front side opposite to the rear side. 
   
   
       5 . The glow plug according to  claim 4 , wherein the control coil is disposed only in the cylindrical portion which has the smallest diameter among those of the cylindrical portions and is disposed on the front side. 
   
   
       6 . The glow plug according to  claim 4 , wherein the heater case further has a taper portion disposed between one cylindrical portion, having the smallest diameter among those of the cylindrical portions and disposed on the front side, and another one of the cylindrical portions adjacent to the one cylindrical portion having the smallest diameter, and the control coil is disposed only in both the cylindrical portion having the smallest diameter and the taper portion. 
   
   
       7 . The glow plug according to  claim 1 , wherein each of the heating and control coils is made of a wire of which a diameter is set within a range from 0.31 to 0.35 mm.