Hybrid Vehicle Torque Control for LSPI Prevention
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Solution Overview
Problem
Hybrid vehicles with internal-combustion engines and forced induction devices experience excessive low-speed pre-ignition (LSPI), leading to torque fluctuations and engine deterioration, particularly in low-rotation, high-load areas, and the use of octane boosters in fuel can exacerbate this issue by altering the fuel's distillation profile.
Innovation Solution
A hybrid vehicle control system that includes sensors to detect LSPI, a rotating electric machine, a power storage device, and a controller that restricts maximum torque to prevent the engine from entering the LSPI area and compensates with electric power when necessary, setting a higher electric power limit for the electric machine during LSPI occurrences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the engine operates in low-rotation, high-load area to increase output torque, then the power output is improved, but low speed pre-ignition (LSPI) is more likely to occur
Solution Approach 1:
The maximum torque limit is made dynamic rather than fixed. The control device adjusts the maximum torque based on detected LSPI occurrences, allowing the torque limit to vary according to engine conditions and LSPI risk levels, thus preventing entry into LSPI-prone operating regions while maintaining power output when safe
Solution Approach 2:
The system changes the torque parameter dynamically by adjusting the maximum torque limit based on LSPI detection results. When LSPI is detected, the maximum torque is reduced to prevent operation in low-rotation, high-load areas where LSPI is likely to occur
2Reliability
If an octane booster is added to fuel to increase octane rating, then knock resistance is improved, but the distillation profile changes and maximum distillation temperature increases, making LSPI more likely to occur
Solution Approach 1:
The control device implements a feedback mechanism by detecting LSPI occurrences and using this information to adjust the maximum torque limit. This closed-loop control allows the system to respond to actual LSPI conditions rather than relying solely on fuel composition assumptions
Solution Approach 2:
The system takes preliminary action by pre-defining a maximum torque limit that prevents operation in LSPI-prone regions. When LSPI is detected, the torque limit is further restricted before the engine can enter dangerous operating conditions
3Reliability
If the maximum torque is restricted to prevent LSPI, then LSPI occurrence is reduced, but the engine output becomes insufficient
Solution Approach 1:
The control device serves multiple functions: it prevents LSPI by restricting maximum torque, detects LSPI occurrences, and dynamically adjusts torque limits based on detected conditions. This multi-functional approach allows the system to maintain power output when LSPI is not present while preventing it when detected
Data Source
AI summary
A vehicle includes an engine including a forced induction device, a knock sensor and a crank angle sensor that detect an occurrence of LSPI, a battery that supplies electric power to a second motor generator, and an ECU. When an occurrence of the LSPI is detected, the ECU restricts a maximum torque, which can be output by the engine with the forced induction device, more than when an occurrence of the LSPI is not detected to prevent an engine operating point from being included in an LSPI area, and when an output of the engine becomes insufficient along with the restriction on the maximum torque, the engine compensates for an amount of the insufficient output with electric power supplied from the battery.