PURPOSE: To ensure the negative pressure of a booster while an engine is automatically stopping by driving an electric motor type vacuum pump when the negative pressure goes below the lower bound value and stopping the above- mentioned pump when the negative pressure exceeds the upper bound value that is higher than the lower bound.
CONSTITUTION: The negative pressure chamber of a brake booster 46 is connected to the negative pressure port 54 of an air intake pipe 52 through a check valve 50 by a pipe 48. In addition, the above-mentioned negative pressure chamber is also connected to an electric motor type vacuum pump 60 through a check valve 58 by a separate pipe 56. The above-mentioned pipe 48 is provided with two negative pressure detection switch 64 and 66. Besides, while an engine is automatically stopping, an electronic control unit 12 determines the signals from the switch 64. When the negative pressure is below the lower bound value, a relay 62 is operated and a vacuum pump is driven. When the negative pressure is increased and the electronic control unit 12 assumes the negative pressure to be higher than the upper bound value using the signals from the switch 66, the relay 62 is set to OFF and the vacuum pump 60 is stopped.
KOIDE TOSHIKAZU
KAWAMURA TAKAHIDE
