| 摘要 |
Methods and systems for indicating brake booster degradation when braking is suspended may include comparing expected brake booster vacuum with measured brake booster vacuum, and indicating a fault when the difference between the two values exceeds a threshold. In one example, the expected brake booster vacuum is computed differently depending on whether intake manifold vacuum or vacuum from one or more vacuum-powered pumps dominates evacuation of the brake booster. Expected brake booster vacuum may be computed based on expected brake booster mass air flow and brake booster volume; when measured brake booster vacuum is less than intake manifold vacuum, expected brake booster mass air flow may be computed as a function of intake manifold vacuum and measured brake booster vacuum, whereas expected brake booster mass air flow may be computed based on flow characteristics of the pump(s) when measured brake booster vacuum is not less than intake manifold vacuum. |
