Hybrid Vehicle Engine Speed Control for Emissions and Comfort
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In hybrid vehicles, the mismatch between engine rotation speed and vehicle speed can lead to discomfort for drivers and increased emissions, particularly when the engine rotation speed increases rapidly before vehicle speed, and during shifts where the power required does not change, causing a virtual speed level shift without actual speed change.
Innovation Solution
A hybrid vehicle configuration with an engine, first and second motors, a planetary gear mechanism, and an electronic control unit that sets a target engine rotation speed based on vehicle speed and shift position, controlling power output to match the required driving force while limiting power at low coolant temperatures to reduce emissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the engine rotation speed is increased rapidly to meet power requirements when the accelerator is stepped on, then the required power is satisfied, but the driver feels discomfort due to mismatch between engine rotation speed and vehicle speed
Solution Approach 1:
The patent applies dynamics by making the engine rotation speed target value variable based on vehicle speed and shift position. The ECU dynamically adjusts the target engine rotation speed to match the current driving conditions, ensuring that engine speed changes are synchronized with vehicle speed changes. This resolves the contradiction by making the power transmission system adaptive rather than fixed, allowing the engine to operate at appropriate speeds for each shift position while maintaining good driving feeling.
Solution Approach 2:
The patent changes the parameter of engine rotation speed target value based on shift position and vehicle speed. By establishing a relationship where target engine rotation speed varies with shift position (1st gear: higher speed, 2nd gear: medium speed, 3rd gear: lower speed), the system ensures that engine speed changes match driver expectations during acceleration. This parameter adjustment resolves the discomfort feeling while maintaining sufficient power output.
2Productivity
If the stepped transmission upshifts with increase in vehicle speed, then fuel efficiency is improved, but the driver feels discomfort when engine rotation speed does not decrease due to unchanged required power
Solution Approach 1:
The patent applies parameter changes by setting different target engine rotation speeds for each shift position. When upshifting occurs, the ECU automatically adjusts the target engine rotation speed downward according to the new shift position, even if the required power remains unchanged. This creates the expected speed change feeling for the driver while maintaining fuel efficiency benefits of upshifting. The key is that target engine speed is decoupled from required power and instead is determined by shift position and vehicle speed.
Solution Approach 2:
The system uses feedback by continuously monitoring vehicle speed and shift position to determine the appropriate target engine rotation speed. The ECU compares actual engine speed with the target speed and adjusts engine control accordingly. This feedback mechanism ensures that during upshifts, the engine rotation speed decreases to match driver expectations, while the system still operates in the most fuel-efficient mode for the current driving conditions.
3Speed
If the engine operates at high power to meet driving requirements, then acceleration performance is improved, but emissions degrade at low coolant temperature
Solution Approach 1:
The patent applies dynamics by making the target engine rotation speed adaptive to coolant temperature. When coolant temperature is low, the system dynamically adjusts the target engine rotation speed to be lower than the standard value, thereby reducing power output and emissions. As the engine warms up, the target speed increases to standard levels, restoring full acceleration performance. This dynamic adjustment resolves the contradiction by temporarily reducing performance requirements during cold start while maintaining emissions control.
Solution Approach 2:
The patent changes the parameter of target engine rotation speed based on coolant temperature conditions. The ECU modifies the target speed parameter according to temperature thresholds: at low temperature, use reduced target speed; at normal temperature, use standard target speed. This parameter change strategy allows the system to balance acceleration performance with emissions control during cold start, while restoring full performance once the engine is warmed up.
Data Source
AI summary
A hybrid vehicle includes an electronic control unit configured to: set a target rotation speed of an engine based on a vehicle speed and a shift position; set a driving force when an upper-limit power is output to a drive shaft as an upper-limit driving force; set a target engine power such that the smaller of the upper-limit driving force and the required driving force is output to the drive shaft; and control the engine, the first motor, and the second motor such that the engine to rotate at the target rotation speed and to output the target power. At this time, the upper-limit power is set to be lower when a coolant temperature of the engine is low than when the coolant temperature is high.