Engine Throttle Control for Brake Booster Vacuum Variability
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Solution Overview
Problem
Existing vehicle control systems face variability in air charge and air-to-fuel ratio during engine starts due to interactions between vacuum levels in the brake booster and intake manifold pressure, leading to increased exhaust emissions, especially at different altitudes.
Innovation Solution
Adjusting engine parameter settings such as throttle position, cam timing, and spark timing based on the vacuum reservoir pressure during engine starts to maintain consistent manifold pressure and improve air-fuel control, using an engine controller to perform control routines that account for the brake booster vacuum level.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a valve is placed between the brake booster and the intake manifold to equalize pressure, then the variability in air charge is reduced, but the intake manifold pressure cannot be consistently set from one engine start to another and consistent MAP level cannot be attained at high altitudes
Solution Approach 1:
The system dynamically adjusts the throttle position parameter based on detected brake booster vacuum levels and operating conditions (including altitude). By changing the throttle position parameter in response to vacuum variations, the system maintains consistent intake manifold pressure across different altitudes and brake booster states, resolving the contradiction between air charge consistency and altitude adaptability.
2Reliability
If the throttle position is adjusted based on brake booster vacuum level, then the intake manifold pressure consistency is improved, but the system complexity increases
Solution Approach 1:
The system employs feedback control by continuously monitoring the brake booster vacuum level and using this information to adjust the throttle position. This feedback mechanism enables the system to maintain consistent intake manifold pressure without requiring complex additional hardware, as it leverages existing sensors and actuators in a closed-loop control configuration.
Solution Approach 2:
The existing throttle actuator, originally designed for basic throttle control, is repurposed to also control intake manifold pressure during engine starting by responding to brake booster vacuum levels. This multi-functional use of the throttle mechanism avoids adding separate dedicated pressure control hardware, thereby maintaining system simplicity while achieving pressure consistency.
Data Source
AI summary
Methods and systems are provided for reducing variability in air-fuel control due to variations in brake booster vacuum levels at an engine start. A throttle position is adjusted during an engine start based on the vacuum availability in the brake booster to control a rate of intake aircharge flow. By allowing aircharge to enter the intake manifold at a more consistent rate, air-fuel control is improved and exhaust emissions are reduced.