Air-Fuel Ratio Control Using Downstream Sensor Heater Activation
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Solution Overview
Problem
Conventional air-fuel ratio control apparatuses face challenges in performing feedback control during low-temperature engine starts due to the risk of water adhesion on gas sensors, leading to delayed activation of heaters and incomplete control of the air-fuel ratio before the exhaust system reaches the moisture evaporation temperature.
Innovation Solution
An air-fuel ratio control apparatus with upstream and downstream gas sensors, each with a heating element, and a control system that determines the engine's start state to adjust the sensor heaters' temperatures, allowing early feedback control using the downstream sensor during low-temperature starts and the upstream sensor when not in a low-temperature state, without waiting for the exhaust system to reach the moisture evaporation temperature.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If the heater of the downstream gas sensor is activated early to enable feedback control, then the feedback control timing is improved, but the sensor element may break due to thermal shock from condensed water adhesion
Solution Approach 1:
The control device activates the heater of the downstream gas sensor before the exhaust system reaches the moisture evaporation temperature, enabling early feedback control. This preliminary action allows the sensor to be operational during low-temperature start states, reducing the time loss while the heater prevents condensed water adhesion that would cause thermal shock
Solution Approach 2:
The heater acts as an intermediary between the downstream gas sensor and condensed water in the exhaust passage. By heating the sensor element, the heater prevents condensed water from adhering to the sensor, thereby eliminating the thermal shock that would otherwise cause sensor breakage while allowing early activation
2Reliability
If the exhaust system temperature is waited to reach moisture evaporation temperature before activating the sensor, then sensor breakage is prevented, but feedback control is delayed
Solution Approach 1:
Instead of waiting for the exhaust system to reach moisture evaporation temperature, the control device performs preliminary activation of the downstream gas sensor heater. This allows feedback control to start earlier while the heater simultaneously prevents condensed water adhesion, resolving the time loss without compromising sensor reliability
3Reliability
If open control is used during the waiting period before moisture evaporation temperature is reached, then sensor breakage is prevented, but air-fuel ratio control accuracy is reduced
Solution Approach 1:
The control device performs preliminary activation of the downstream gas sensor heater before moisture evaporation temperature is reached. This enables feedback control to commence immediately rather than relying on open control, thereby maintaining air-fuel ratio control accuracy while the heater prevents sensor breakage from condensed water adhesion
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
Enables early and accurate feedback control of the air-fuel ratio, reducing the risk of sensor breakage and ensuring proper control even during low-temperature starts, while determining catalyst deterioration for optimal performance.
Implementation Method 1
a downstream gas sensor which is provided in the exhaust passage to be located on the downstream side of the catalyst and which includes a detection element and an element heating heater
Implementation Method 2
detects the concentration of a specific gas (e.g., oxygen) contained in exhaust gas using a gas sensor
Implementation Method 3
condensed water may adhere to a hot sensor element heated by the heater. In such a case, the sensor element may break due to thermal shock
Data Source
AI summary
When an internal combustion engine (1) is determined to be in a low-temperature start state (an affirmative determination is made in S120), an air-fuel ratio control apparatus (10) controls the temperature of a downstream detection element (17) of a downstream gas sensor (15) to a downstream target temperature by driving a downstream heater (16) of the downstream gas sensor (15) (S170), and feedback-controls the air-fuel ratio of exhaust gas based on the output of the downstream gas sensor (15) (S190). When the engine (1) is determined not to be in the low-temperature start state (a negative determination is made in S120), the air-fuel ratio control apparatus (10) drives an upstream heater (25) of an upstream gas sensor (22) and feedback-controls the air-fuel ratio of exhaust gas based on the output of the upstream gas sensor (22) (S270).