Oxygen sensors

03-04-2019 - Reports

 

PART I | Evolution and types.


 

1. Introduction 
2. Oxygen sensor components
3. Oxygen sensor evolution
4. Oxygen sensor types
     4.1 Zirconia oxygen sensor
     4.2 Titania oxygen sensor 
     4.3 Wideban oxygen sensor



1. INTRODUCTION 

Crude oil is running out and we're moving, in leaps and bounds, towards the electric vehicle. But this transition to a 100% clean vehicle must be done by improving the efficiency and ecology of the current combustion vehicles, which still have many years of life in the market. And, although it seems ironic to speak of ecology when we're referring to vehicles that pollute the environment, we can assure you that the technological advances of recent years are contributing to the drastic reduction of harmful gas emissions into the atmosphere, which are responsible for the greenhouse effect. According to a recent study of the AMB (Metropolitan Area of Barcelona) with regard to PM (particle matter), 1 20-year-old car pollutes as much as 36 modern-day cars and, in the case of NOx (Nitrogen Oxide), pollutes as much as 5 modern-day cars. Looking at the motorcycle statistics, the ratio is 1:17. For this reason, the European authorities who regulate exhaust emissions have set out increasingly restrictive policies. From the 90s until now, EU standards have got increasingly stronger with the enactment of consecutive directives from Euro2, Euro3, up to the current Euro6c. Some manufacturers have had problems and have not passed the tests, which has posed a great challenge to engineers of engines, afterburner systems and the design of oxygen sensors. The control of gas emissions is handled by the software which manages the ECU, the brain of the vehicle. But, in the same way that our brain makes the decision to move our hand if we notice it's burning, any decision made by the ECU depends directly on what the "sensors" distributed throughout the vehicle "tell" it. One of these sensors is the well-known oxygen sensor  (also known as the Oxygen Sensor), which is placed in the exhaust pipe and is specifically responsible for reducing the emission of harmful gases into the atmosphere. It continuously detects the proportion of oxygen in the remaining exhaust gas, so that the ECU can adjust the amount of fuel required to the optimum value. All vehicles with a catalytic converter have at least one Lambda Probe (regulating) which is located before the catalytic converter. However, vehicles that apply the OBD (On-Board Diagnostic) systems, are equipped with a second oxygen sensor (diagnostic) which is located on the back of the catalytic converter and reports on the correct operation of the regulating Lambda Probe while also correcting any deviation. These oxygen sensor also control the life cycle of the catalytic converter, letting us know when it's exhausted and needs to be replaced. But why is it called a Lambda Probe? Well, the Lambda factor (ƛ) indicates the air-fuel ratio compared to the ideal stoichiometric ratio of 14.7 parts air to 1 part fuel (in weight). If this comparison gives a lambda factor greater than 1, then we have a fuel-lean mixture. If the lambda factor is less than 1, we have a fuel-rich mixture .


 
2. OXYGEN SENSOR COMPONENTS

 





CABLES

Cable coating made of fluoropolymer with high performance at extreme temperatures.


CERAMIC CLAMP
Complete assembly in our facilities.


CERAMIC INSULATORS 

Technical ceramics designed to ensure watertightness and avoid contamination. Degree of protection water resistance IP68, able to operate in continuous immersions of water.


SENSOR
Sensor technology of multilayer ceramic planar technology. Manufactured in controlled environments such as a clean room.
 

 




 
3. OXYGEN SENSOR EVOLUTION


It's important to understand that the first Lambda Probes date back to the 1970s, where the EGO-type probes of the time were not heatable and had a useful response time of more than 120 seconds. This means that the ECU did not receive a clear reading until 2 minutes after the vehicle was started, when the engine was cold and emitting more pollutants. Generally speaking, throughout these years, people have attempted to improve the speed, stability and accuracy of the probe response, regardless of the engine speed, and to achieve a shorter start-up time, that is, the time it takes the sensor to reach its working temperature, as well as to improve its resistance and durability. The oxigen sensor  have evolved considerably; worth noting are the introduction of heatable probes, the emergence of probes with a response proportional to the lambda parameter, also known as wideband or AFR "air fuel ratio" probes, and the development of planar technology. The Spanish company FAE, Francisco Albero, S.A.U, has bet strongly on the latter, having been developing its own planar technology for years and putting into operation a White Room of over 700 m2 for the development and manufacturing of thousands of high-tech, high-quality sensors and probes for clients around the world. 



4. OXYGEN SENSOR TYPES

 

4.1 ZIRCONIA OXYGEN SENSORS

Binary Oxygen sensotrs are made of ceramics composed of Zirconium Dioxide or Zirconia. They contain a solid electrolyte that provides an electrical voltage, which is obtained by comparing two atmospheres (exhaust gases on one side and outside air on the other), and is sensitive to the concentration of oxygen in the exhaust gases. Fuel-rich mixtures produce a high voltage and fuel-lean mixtures produce a low voltage, thus giving an on-off binary response with only two values: 0 or 1, which is easily interpretable electronically.


 

4.2 TITANIA OXYGEN SENSORS

This oxygen sensor  is made of a Titanium Dioxide ceramic element. Unlike the Oxygen sensor based on Zirconium Dioxide, these do not generate any voltage, and the sensor material is submerged in the exhaust gases without the need for outside air. These probes always include a heater, and, at high temperatures, the resistance of this material is sensitive to the difference in oxygen concentration of the exhaust gases. For a fuel-rich mixture, the resistance drops to minimum values and for a fuel-lean mixture, it rises to maximum values. The ECU powers the Lambda Probe with a fixed voltage and reads the response of the Lambda Probe through a voltage divider circuit

 

4.3 WIDEBAND OXYGEN SENSORS

Unlike the binary Zirconia Lambda Probes, the Wideband Lambda Probes provide a continuous, non-binary response to the detected lambda value. Therefore, they measure the composition of the exhaust gases with great accuracy, which also makes them suitable for diesel and gasoline engines. These contain two electrochemical cells that work concurrently. One of them measures the rich or lean character of the gas mixture, similar to the binary Lambda Probes. The reaction of the other electrochemical cell is influenced by the signal of the first cell and by the amount of oxygen in the combustion gas. The joint functioning of the two cells provides a positive electric current for lean mixtures, negative for rich mixtures and zero in the case of a perfect or stoichiometric mix. The current generated by the Wideband Lambda Probes is calibrated and must also be transformed into voltage so that it can be read by the vehicle's ECU. For this reason, the Probe has in-built calibration resistance in the connector. This resistance is different for each probe, so you should not, under any circumstances, replace one Lambda Probe with another by cutting the wires.

 

There are two types of wideband oxigen sensor: 

 

The first generation Wideband Probes contain an external air reference channel similar to that of the binary Zirconia oxygen sensor.


 

The second generation Wideband Probes don't need this reference channel to work. Compared to the first generation probes, the absence of the channel helps to save the amount of power consumed by the probes, the initial heating time is shorter and there is greater signal stability throughout their useful life.

Depending on the application of each vehicle, a first or second generation Wideband Probe is necessary, but they are not interchangeable with each other


 

Difference in the response between a binary Zirconia Lambda Probe and an Air Fuel Ratio Probe; the first is a binary response (1 or 0) but in the Air Fuel Ratio probe the response is progressive, so the ECU can accurately measure the composition of the exhaust gases at all times and therefore act with greater precision; the response of the binary Zirconia Probe only reports whether the mixture is rich or lean, but not the exact level of the gas mixture.