Demystifying the O2 Sensor | How Oxygen Sensors Work
23 هزار بار بازدید -
4 سال پیش
-
Oxygen sensors are devices used
Oxygen sensors are devices used by vehicles to monitor emissions when paired with a catalytic converter. They’re also used to measure how rich or lean combustion is within a narrow band of the air-fuel ratio. This measurement is based on the oxygen present in the exhaust stream. In most modern vehicles equipped with 4 cylinder engines, there are two oxygen sensors, typically one before the catalytic converter and one after. Some vehicles outfitted with a V6 and V8 engine have even more oxygen sensors, to help monitor their systems.
The oxygen sensor was first developed in the late 1970s for Volvo by the Robert Bosch Company. These early sensors relied on the heat produced from the exhaust stream in order to heat up to their operating temperature. The issue with this was the latency in which sensors began to respond since it took nearly a minute for the probes to warm up.
Entering the 1980s, oxygen sensors became mandatory equipment on vehicles when the state of California realized the potential for these sensors to have a significant impact on the reduction of emissions. By the mid-1990s, every state in the United States had laws mandating the necessity of the oxygen sensor.
When it was first introduced, the oxygen sensor did not offer the fine adjustments that would come later in advancements in fuel delivery. Fuel injection eventually replaced the carburetor and assisted with these adjustments needed to be made with the input provided from the sensor to the vehicle's ECU. The mixture of air and fuel can now be delivered to the engine much more efficiently. Which improved fuel consumption and allowed modern electronic fuel injection and emissions control possible.
For more on this fascinating subject matter, check out my two-part series on engine efficiency which goes into further detail into advancements in automotive fuel delivery.
How oxygen sensors work
Typically, oxygen sensors are located on an engine’s exhaust system and they help determine, in real-time, whether the air-fuel ratio of a combustion engine is rich or lean.
But despite being located in the exhaust stream, oxygen sensors do not directly measure the air or the fuel entering the engine. But rather when data from oxygen sensors are used in conjunction with information from other sensors, it can be applied to indirectly determine the optimal air-fuel ratio.
This closed-loop method of control allows fuel injection to refine injector output according to real-time sensor data rather than operating with a predetermined or open-loop fuel map.
Though, their placement varies depending on the engine configuration and the number of exhaust banks. For our purposes, we will use an inline engine with a single exhaust bank. One sensor is placed before the catalytic converter. This sensor, also known as the upstream or pre-cat sensor is responsible for regulating the optimal fuel supply. And the second sensor which is referred to as the downstream or post-cat sensor is located just after the catalytic converter and monitors the efficiency of the cat.
The process starts as high pressure and temperature exhaust gases exit the exhaust cylinder during the exhaust phase. Subsequently, the gases then travel through the exhaust manifold where it eventually comes in contact with the upstream or pre-cat sensor.
At this point, let’s take a deep dive into the composition of the oxygen sensor and how it works exactly; to further our understanding of this complex system.
Creating a seal between the probe end of the sensor and the ambient air is the gasket of the oxygen sensor; typically made of a crush sealing washer.
Looking closely, the core of the sensor is composed of a heating element and connected to a heater connection.
The sensing probe at the front of the sensor consists of a zirconium dioxide sensing element which is enclosed in a steel shell.
The steel shell is then encased in a protective tube which makes contact with passing exhaust gases.
The sensing element is further connected to platinum electrodes and wire leads down the line of the sensor.
Holding the entire assembly within the steel body is a ceramic holder which aids in bringing the probe up to temperature.
As the exhaust gas travels through the drilled holes on the protection tube, oxygen molecules found in the fumes come in contact with the sensing element. While this happens, ambient air is allowed to flow through the gaps located between the wire leads via the heat connection where it becomes heated to enable the ions to produce voltage.
As previously mentioned, the sensor does not actually measure oxygen concentration, but rather the difference between the amount of oxygen in the exhaust stream and the amount of oxygen outside of the exhaust.
The variance in the concentration of oxygen molecules in the exhaust gases versus the ambient air drives the oxygen ions from higher to lower concentration.
The oxygen sensor was first developed in the late 1970s for Volvo by the Robert Bosch Company. These early sensors relied on the heat produced from the exhaust stream in order to heat up to their operating temperature. The issue with this was the latency in which sensors began to respond since it took nearly a minute for the probes to warm up.
Entering the 1980s, oxygen sensors became mandatory equipment on vehicles when the state of California realized the potential for these sensors to have a significant impact on the reduction of emissions. By the mid-1990s, every state in the United States had laws mandating the necessity of the oxygen sensor.
When it was first introduced, the oxygen sensor did not offer the fine adjustments that would come later in advancements in fuel delivery. Fuel injection eventually replaced the carburetor and assisted with these adjustments needed to be made with the input provided from the sensor to the vehicle's ECU. The mixture of air and fuel can now be delivered to the engine much more efficiently. Which improved fuel consumption and allowed modern electronic fuel injection and emissions control possible.
For more on this fascinating subject matter, check out my two-part series on engine efficiency which goes into further detail into advancements in automotive fuel delivery.
How oxygen sensors work
Typically, oxygen sensors are located on an engine’s exhaust system and they help determine, in real-time, whether the air-fuel ratio of a combustion engine is rich or lean.
But despite being located in the exhaust stream, oxygen sensors do not directly measure the air or the fuel entering the engine. But rather when data from oxygen sensors are used in conjunction with information from other sensors, it can be applied to indirectly determine the optimal air-fuel ratio.
This closed-loop method of control allows fuel injection to refine injector output according to real-time sensor data rather than operating with a predetermined or open-loop fuel map.
Though, their placement varies depending on the engine configuration and the number of exhaust banks. For our purposes, we will use an inline engine with a single exhaust bank. One sensor is placed before the catalytic converter. This sensor, also known as the upstream or pre-cat sensor is responsible for regulating the optimal fuel supply. And the second sensor which is referred to as the downstream or post-cat sensor is located just after the catalytic converter and monitors the efficiency of the cat.
The process starts as high pressure and temperature exhaust gases exit the exhaust cylinder during the exhaust phase. Subsequently, the gases then travel through the exhaust manifold where it eventually comes in contact with the upstream or pre-cat sensor.
At this point, let’s take a deep dive into the composition of the oxygen sensor and how it works exactly; to further our understanding of this complex system.
Creating a seal between the probe end of the sensor and the ambient air is the gasket of the oxygen sensor; typically made of a crush sealing washer.
Looking closely, the core of the sensor is composed of a heating element and connected to a heater connection.
The sensing probe at the front of the sensor consists of a zirconium dioxide sensing element which is enclosed in a steel shell.
The steel shell is then encased in a protective tube which makes contact with passing exhaust gases.
The sensing element is further connected to platinum electrodes and wire leads down the line of the sensor.
Holding the entire assembly within the steel body is a ceramic holder which aids in bringing the probe up to temperature.
As the exhaust gas travels through the drilled holes on the protection tube, oxygen molecules found in the fumes come in contact with the sensing element. While this happens, ambient air is allowed to flow through the gaps located between the wire leads via the heat connection where it becomes heated to enable the ions to produce voltage.
As previously mentioned, the sensor does not actually measure oxygen concentration, but rather the difference between the amount of oxygen in the exhaust stream and the amount of oxygen outside of the exhaust.
The variance in the concentration of oxygen molecules in the exhaust gases versus the ambient air drives the oxygen ions from higher to lower concentration.
4 سال پیش
در تاریخ 1399/03/01 منتشر شده
است.
23,034
بـار بازدید شده