Variable Compression Ratio Engine Control for Hybrid Drivability
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Solution Overview
Problem
Conventional engine compression ratio adjustment technologies in hybrid vehicles face constraints such as reduced volumetric efficiency, torque, and power when lowering compression ratio, leading to frequent engine pull-ups and pull-downs that degrade fuel economy due to pumping and friction losses, and cause torque pulsations and noise issues.
Innovation Solution
Implementing a variable compression ratio (VCR) engine mechanism that mechanically alters piston position within the cylinder, combined with battery power to reduce compression ratio during engine pull-ups and pull-downs, and adjust compression ratio based on driver demand and battery state of charge to minimize frequent switching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If cam timing adjustments are used to reduce effective compression ratio, then compression ratio can be varied, but volumetric efficiency, torque, and power are reduced
Solution Approach 1:
The patent implements a variable compression ratio mechanism that dynamically adjusts the piston position relative to the cylinder head using an actuator. This allows the compression ratio to be changed during operation without affecting valve timing, thereby maintaining volumetric efficiency and engine power while achieving the desired compression ratio variation for different operating conditions.
Solution Approach 2:
The patent replaces the cam timing adjustment mechanism with a direct mechanical compression ratio adjustment mechanism. Instead of using cam phasers to indirectly affect compression through timing changes, the system directly alters the combustion chamber volume by moving the piston or cylinder head position, eliminating the trade-off between compression ratio adjustment and engine power output.
2Adaptability or versatility
If compression ratio is frequently switched to respond to operator pedal demand, then engine can adapt to load changes, but fuel economy degrades due to pumping and friction losses during transitions
Solution Approach 1:
The control system predicts upcoming load changes based on driver behavior patterns and proactively adjusts the compression ratio before the actual load change occurs. This preliminary adjustment reduces the frequency and magnitude of compression ratio transitions, thereby minimizing pumping and friction losses during transitions while still maintaining adaptability to load changes.
Solution Approach 2:
The patent introduces an electric actuator as an intermediary mechanism to enable smooth and rapid compression ratio adjustments without mechanical linkage losses. The actuator provides precise control over piston position and compression ratio, allowing the system to minimize unnecessary transitions while quickly responding to genuine load changes, thus improving fuel economy without sacrificing adaptability.
3Loss of energy
If compression ratio is reduced during engine pull-up and pull-down events, then pumping and friction losses are reduced, but torque pulsations and noise increase in the low speed range
Solution Approach 1:
The patent dynamically adjusts multiple parameters simultaneously during engine pull-up and pull-down events. When reducing compression ratio to minimize pumping losses, the system concurrently modifies spark timing, fuel injection timing, and air intake parameters to compensate for torque pulsations and noise. This coordinated parameter adjustment allows the system to achieve energy efficiency while maintaining smooth engine operation in the low speed range.
Data Source
AI summary
Methods and systems are provided for synergizing the benefits of a variable compression ratio engine in a hybrid vehicle system. A vehicle controller may hold the engine in a lower compression ratio during engine pull-ups and pull-downs, in particular when passing through a low speed region where compression bobbles can occur. During engine operation, in response to a change in driver demand, the controller may opt to switch the compression ratio or maintain a current compression ratio while smoothing a torque deficit using motor torque, the selection based on fuel economy.