Hybrid Vehicle Catalyst Light-Off via ISG Speed Control
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Solution Overview
Problem
Hybrid electric vehicles face challenges in reducing cold start emissions, particularly in achieving rapid catalyst light-off and maintaining low emissions during series mode operation with a large power output internal combustion engine.
Innovation Solution
The method involves detecting a cold start condition, operating the engine at high speed with a lean air-fuel ratio, utilizing an integrated starter generator for rapid catalyst heating, and adjusting valve timings and fuel injection to achieve rapid catalyst light-off and minimize NOx emissions, while transitioning to stoichiometric conditions to maintain catalyst efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the internal combustion engine operates at low speed and low load during cold start, then fuel consumption is reduced, but the catalyst heating rate is insufficient and light-off time is extended
Solution Approach 1:
The patent replaces the mechanical approach of directly running the engine at high speed with an electrical approach. The integrated starter generator (ISG) motor is used to drive the engine crankshaft to high speed (1500-4000 rpm) during cold start, achieving rapid catalyst heating without requiring the engine to produce high mechanical power output. This electrical assistance allows the engine to operate at low load while still achieving the high rotational speed needed for catalyst light-off.
2Temperature
If the internal combustion engine operates at high speed and high load during cold start, then the catalyst heats up rapidly, but the power output available for vehicle propulsion is reduced
Solution Approach 1:
The patent segments the functions of engine operation into two independent controls: rotational speed control and load control. The ISG motor separately controls the engine speed to achieve rapid catalyst heating, while the engine load is kept low to maintain power availability for propulsion. This segmentation allows independent optimization of catalyst heating rate and power output without the traditional trade-off.
Solution Approach 2:
The integrated starter generator serves as an intermediary device that decouples the relationship between engine speed and power output. By using the ISG motor to provide the torque needed for high-speed engine rotation during cold start, the system mediates between the conflicting requirements of rapid catalyst heating and power availability for vehicle propulsion.
3Temperature
If the air-fuel ratio is enriched (lambda < 1) during cold start, then the catalyst receives more fuel for heating, but NOx emissions increase
Solution Approach 1:
The patent changes the operational parameters of engine cold start by maintaining lean or stoichiometric air-fuel ratios (lambda ≥ 1) while achieving rapid catalyst heating through high engine speed enabled by the ISG motor. This parameter change eliminates the need to enrich the air-fuel ratio for catalyst heating, thereby preventing NOx formation while still achieving rapid light-off through the kinetic energy from high-speed operation.
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 approach results in significantly reduced NOx emissions by achieving rapid catalyst light-off and maintaining efficient operation, contrasting with traditional methods that use low speed and rich lambda values, and effectively reduces HC and CO emissions through optimized combustion and catalyst operation.
Implementation Method 1
utilizing the vehicle's electric motor/generator to transfer a negative torque to the internal combustion engine during cold-start conditions
Implementation Method 2
injecting fuel into the combustion engine such that combustion at a lambda value, λ, is achieved
Implementation Method 3
the moment when the catalyst reaches 50% of its efficiency
Implementation Method 4
rapid heating up of the catalyst
Data Source
AI summary
A method of reducing cold start emissions in a series mode hybrid electric vehicle, including an internal combustion engine with an exhaust duct having a catalyst and a downstream oxygen sensor, an output of the combustion engine being connected to an electric generator with a power output of at least 10 kW that is connected to an electric motor which is coupled to a drive shaft of two or more wheels. The method includes detecting a cold start condition, injecting fuel into the engine such that combustion at a lambda value, λ, is achieved for which λ>1, running the engine at a speed of 1000 rpm or higher, determining if the efficiency of the catalyst reaches a first level, setting λ to about 1 after the predetermined efficiency level of the catalyst has been reached, and reducing the speed to working conditions when the catalyst efficiency reaches a second level.