Oxygen Sensor Compensator Circuit for Accurate Pump Current Sensing
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Solution Overview
Problem
The PWM control of the ceramic heater in wide-range oxygen sensors disrupts the closed-loop control of the reference and pump cells, causing noise coupling and errors in pump current readings, which limits the ability to obtain accurate engine synchronous measurements.
Innovation Solution
A digital compensator circuitry is introduced that suspends the determination and output of compensation current for a programmable set time after detecting PWM signal edges, using a programmable digital compensator and PWM edge detection to minimize noise interference and maintain the reference cell voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If PWM control is used to control the ceramic heater, then the sensor temperature can be tightly controlled, but the PWM switching edges cause pump cell current errors and disrupt the closed loop control of the reference and pump cells
Solution Approach 1:
The patent applies preliminary action by detecting PWM edges in advance and proactively suspending the compensator circuitry before the PWM switching edges can disrupt the pump cell current measurements. The suspending operation is triggered by edge detection circuitry that identifies PWM transitions, allowing the system to prevent measurement errors before they occur rather than correcting them afterward.
2Temperature
If PWM control is used to control the ceramic heater, then the sensor temperature can be tightly controlled, but large DV/DT's and large DI/DT's in the heater wires cause noise coupling onto other wires in the cable
Solution Approach 1:
The patent uses the suspending operation as an intermediary mechanism that isolates the sensitive pump cell current measurements from the harmful electromagnetic interference generated by PWM switching. By temporarily disabling the compensator circuitry during PWM transitions, the system creates a protective barrier that prevents noise coupling from the heater wires to the signal wires in the same cable harness.
3Stability of the object's composition
If the compensator circuitry operates continuously to maintain reference cell voltage, then the control loop stability is maintained, but pump current readings are corrupted by PWM switching edges
Solution Approach 1:
The patent implements periodic action by rhythmically suspending and resuming the compensator circuitry in synchronization with the PWM control signal. The compensator operates normally during stable periods, maintains control loop stability, and is periodically suspended during PWM transitions to prevent measurement corruption. This periodic suspension-resumption cycle aligns with the PWM frequency, allowing the system to maintain overall stability while achieving accurate periodic measurements.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution significantly reduces pump current disturbances, allowing for more accurate and reliable engine synchronous pump current measurements by masking noise from the PWM edges, thereby improving the stability of the control loop.
Implementation Method 1
a resistive ceramic heating element within the sensor... The impedance of the sensor reference cell is measured and used to indicate the temperature of the sensor. A control loop is utilized to modify the PWM duty cycle to adjust the amount of heating
Implementation Method 2
A digital compensator, configured to determine and output a compensation current to said pump cell dependent on a reference voltage measured from said reference cell, and further configured to suspend the determination and output of said compensation current for a set time dependent on detection of edges in an oxygen sensor heater Pulse Width Modulation (PWM) signal
Data Source
AI summary
Compensator circuitry is provided for an oxygen sensor which includes a pump cell and a reference cell. The compensator circuitry includes a feedback control loop which maintains the reference cell at a reference voltage. The feedback control loop includes a digital compensator which determines and outputs a compensation current to the pump cell dependent on a reference voltage measured from the reference cell. The digital compensator also suspends the determination and output of the compensation current for a set time which is dependent on detection of edges in an oxygen sensor heater Pulse Width Modulation signal.