Description And Operation-Vacuum Booster Systems
DESCRIPTION
The system consists of the following components:
| CALLOUT | DESCRIPTION |
|---|---|
| 1. | Brake Booster |
| 2. | Engine Connection |
| 3. | Check Valve |
| 4. | Check Valve/Vacuum Pressure Sensor |
| 5. | Check Valve |
| 6. | Vacuum Pump |
| 7. | Relay |
The vacuum boost system consists of a vacuum brake booster and supplemental Electric Vacuum Pump (EVP). The vacuum hose assembly connects in parallel from the brake booster to the EVP and the intake manifold. There is a check valve located in each path of the vacuum hose assembly. The vacuum pressure sensor is located on the brake booster and hard-wired to the Anti-Lock Brake (ABS)/Electronic Stability Program (ESP) Module. The vacuum hose assembly typically connects to the sensor for most vehicles. The sensor also has an integrated check valve.
GENERAL VACUUM BOOSTER SYSTEM OPERATION:
The Electric Vacuum Pump (EVP) system is designed to provide supplemental vacuum during low engine vacuum conditions. The engine is able to produce approximately 72% of BARO. The EVP is able to produce more vacuum than the engine. This allows the system vacuum to reach the programming turn off of 83% of BARO that is required. When the EVP is not running, the check valve in the EVP side of the hose assembly is closed by the engine vacuum. When the EVP is operating the check valve in the intake manifold path is closed due to the EVP producing more vacuum than the engine. On a normally operating system, the pump will operate in the following manner:
- With the engine running and vehicle speed below 7 mph the EVP is commanded on when the vacuum pressure sensor signal is at or below 55% of BARO. The pump will run until the vacuum pressure sensor signal reaches 65% of BARO.
- With the engine running and vehicle speed above 8 mph , the EVP is commanded on at or below 69% of BARO and turns off at 83% of BARO.
- When the engine is off , Vacuum pump should not run if the ignition is in acc/run with 0 rpms. The only exception to this is the DT program, which allows the pump to run at 0 rpms ONLY when in an ESS auto stop condition.
The EVP helps maintain the system vacuum between a normal range of 610-850 mbar (61-85 kPa) with the engine running. Anything under approximately 600 mbar (60 kPa) can create a hard pedal condition.
The EVP is especially important on vehicle applications where the engine is not running the entire time, such as for hybrid or Stop/Start equipped vehicles. This system maintains a consistent brake pedal feel under all driving conditions. The vacuum pressure sensor signal information is then sent to the Powertrain Control Module (PCM) over the CAN Bus. The PCM energizes the vacuum pump relay through a Low Side Driver (LSD) to provide battery voltage to the vacuum pump and control pump operation.