Altitude Engine Speed Limiting for Hybrid Vehicle NVH Control
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Solution Overview
Problem
Hybrid electric vehicles face challenges in maintaining desired engine performance at higher altitudes, where reduced torque and increased engine speed lead to objectionable noise, vibration, and harshness (NVH) issues, affecting customer comfort and vehicle acceleration.
Innovation Solution
A system and method that adjusts the target engine speed from sea level settings to an NVH engine speed limit at higher altitudes, reducing demanded engine power when torque is not attainable, and calculating engine power based on the difference between demanded and attainable power to minimize NVH, using a piecewise linear function of sea level engine speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the target engine speed is increased at higher altitudes to compensate for reduced torque, then the engine can deliver sufficient power, but the NVH (noise, vibration, and harshness) becomes objectionable
Solution Approach 1:
The patent applies parameter changes by modifying the target engine speed parameter based on altitude conditions. The controller adjusts the target engine speed to be lower than what would be required for full power compensation, thereby changing the operating parameters to achieve an acceptable balance between power delivery and NVH characteristics at higher altitudes.
2Power
If the target engine speed is increased to meet power demand at altitude, then sufficient torque is delivered, but small changes in accelerator pedal position result in large changes in engine speed
Solution Approach 1:
The patent modifies the engine speed parameter response characteristics by implementing an altitude-based speed limit. This parameter change ensures that engine speed changes remain proportional to accelerator pedal position changes even at higher altitudes, preventing excessive sensitivity while maintaining adequate torque delivery capability.
Data Source
AI summary
A system and method for controlling a hybrid vehicle having an engine, first and second electric machines coupled to a traction battery and configured to operate primarily as a motor and a generator, respectively, and a controller in communication with the engine and the first and second electric machines include increasing target engine speed from a sea level speed to deliver a demanded engine power at altitude up to an NVH engine speed limit. The system and method may reduce the demanded engine power based on an attainable engine power associated with the NVH engine speed limit. A demanded wheel power may be reduced in response to the reduced engine power.