1. Field of the Invention
The invention relates to a vehicle brake system, and more specifically, to a method and system for actuating an electric vacuum pump associated with a brake booster.
2. Description of Related Art
In motor vehicles, brake boosters boost the force applied by a driver to assist driver operation of a brake pedal. Conventional designs include a negative-pressure brake booster that uses a pressure difference to generate a force. A piston arranged in a chamber is coupled to the main brake cylinder. When not in operation, negative pressure exists on both sides of the working piston. Upon brake pedal actuation, the side facing towards the brake pedal is placed at ambient pressure. The negative pressure on the opposite side generates a force that acts on the main brake cylinder.
In the case of motor vehicles having an internal combustion engine, a connection to the intake manifold of the engine provides the negative pressure. Some motor vehicles, in particular an electric or hybrid vehicle, use an electrically operated vacuum pump to provide the negative pressure. The electrically operated vacuum pump connects to the brake booster and generates the negative pressure necessary for operation thereof.
Monitoring the pressure or negative pressure prevailing in the brake booster determines availability of sufficient auxiliary braking force. Since any braking operation causes air to flow into the brake booster and bring about at least partial pressure compensation, the vacuum pump reestablishes the vacuum. However, operating the vacuum pump constantly, even when the pressure in the brake booster has a sufficiently low value, is uneconomical, reduces pump service life, and a power source unnecessarily loads the pump.
Using a negative pressure sensor on the brake booster and comparing a current negative pressure value with a threshold value provides a mechanism for switching on the pump only as required; specifically, restarting the vacuum pump when the negative pressure value drops below the threshold value. Using a sensor of this type increases the costs, weight, and complexity of the vehicle.
In some instances, brake boosters producing negative pressure by a connection to the intake manifold may do so without a pressure sensor on the brake booster.