With the steady growth in recent years of vehicle electronic systems, the number of sensors used in automobiles has also risen dramatically. Current vehicles can contain forty to fifty of such sensors. Among the types of sensors commonly provided are pressure sensors in the vehicle fuel systems, air bag sensors, over-current and over temperature-protection sensors, oxygen sensors for exhaust gas systems, catalyst temperature sensor, etc. With most if not all of such sensors, signal conditioning will be necessary for most sensor elements. Raw sensors exhibit some level of offset voltage in output signal level when no stimulus is applied to the sensor. Typically, a potentiometer or a trim resistor branch circuit that is laser trimmed for calibration is employed to calibrate the output signal from the sensor.
For example, in the case of exhaust sensors the trim resistor is used in the automotive oxygen sensor output to ECU circuitry connection system. Hitherto, this trim resistor has been provided as an integral part of the sensor wiring output connector assembly. In one commercially provided connector assembly six male blade terminals are provided and four of the terminals are crimped to wires coming from the sensor. The remaining two terminals are insert molded into the connector assembly and one end of each terminal is soldered to a contact pad on the trim resistor substrate. An opening is provided on the side of the connector assembly to install the trim resister and allow access for the laser trimming operation. The opening is then closed and sealed with a cover and gasket.
In this prior art construction currently in use the ceramic substrate and terminals are pre-molded parts that are inserted as a pre-molded part into the connector assembly mold and then secured therein as a mold-over part. Hence the connector assembly construction must be designed to match the connector assembly family currently used in the given wiring system of the vehicle design. This current practice is thus limited in flexibility and adaptability when it is desired to provide resistance trim capability as an add-on to exhaust system sensors in automotive vehicle electronic systems. Mold tooling costs are also a problem when system design changes are mandated.
There is thus a need to provide a trim resistor connector assembly construction that can be economically manufactured, assembled and installed to be operably coupled as an add-on to new as well as existing sensor wiring assemblies. In addition, there is the continuing need to improve exhaust sensor performance by enhancing calibration circuit construction. There is also the ongoing need to reduce the expense of the calibrating means for the sensor, and one that can be employed to calibrate the sensor prior to installing in the vehicle.