Oxygen Sensor Compensator Circuitry for PWM Heater Noise Masking
Find Innovative SolutionsGenerate Solutions
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 with a feedback control loop is introduced, which detects PWM signal edges and suspends the determination and output of compensation current for a programmable set time, reducing noise interference and maintaining the reference cell voltage, thereby minimizing disruptions to the control loop.
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 extracts the harmful effect of PWM edges by detecting them and separating the compensation current determination from the PWM switching events. The digital compensator suspends compensation current updates during PWM transitions, effectively removing the source of measurement errors while maintaining temperature control functionality.
Solution Approach 2:
The patent applies preliminary action by detecting PWM edges in advance and proactively suspending compensation current determination before the harmful effects can occur. This anticipatory approach prevents pump cell current errors before they are generated, rather than attempting to correct them afterward.
2Temperature
If PWM control is used to control the ceramic heater, then the sensor temperature can be maintained, but large DV/DT and DI/DT in the heater wires cause noise coupling onto other wires in the cable
Solution Approach 1:
The patent introduces an intermediary mechanism - the digital compensator with PWM edge detection capability - that mediates between the PWM heater control and the pump cell current measurement. This intermediary detects PWM edges and prevents noise coupling by suspending compensation current determination during PWM transitions, protecting the measurement system from electrical interference.
3Reliability
If the compensator continuously determines compensation current, then the reference cell voltage can be maintained, but the PWM switching edges cause extended period pump cell current errors
Solution Approach 1:
The patent applies periodic action by implementing periodic suspension of compensation current determination synchronized with PWM switching cycles. The digital compensator periodically halts compensation current updates at specific phases (during PWM edges) while continuing to maintain reference cell voltage stability during non-suspension periods, creating a rhythmic pattern that prevents measurement errors.
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 feedback control loop configured to maintain the reference cell at a reference voltage
Implementation Method 2
This temperature is achieved by use of a resistive ceramic heating element within the sensor
Implementation Method 3
the automotive 12V battery voltage is applied across the element in a pulse width modulated fashion
Data Source
Figure 1
Figure 2
Figure 3
AI summary
Compensator circuitry (200) is provided for an oxygen sensor (1) which includes a pump cell (5) and a reference cell (4). The compensator circuitry (200) includes a feedback control loop which maintains the reference cell (4) at a reference voltage. The feedback control loop includes a digital compensator (43) which determines and outputs a compensation current to the pump cell (5) dependent on a reference voltage measured from the reference cell (4). The digital compensator (43) 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.