The BACS is a device that provides both the functions of the turbocharger boost compensator and the HAC. The HAC valve maintains the constant pressure in the constant pressure chamber located below the diaphragm and thus has the function of the HAC.
The basic construction is the same as that of the turbochargerboost compensator.
(1) Low-altitude drivingThe air is introduced into the constant pressure chamber from the filter. Then, a vacuum is applied by the vacuum pump to make the pressure lower than normal atmospheric pressure at all times.
(2) High-altitude drivingThe atmospheric pressure, of the air which is introduced into the constant pressure chamber, is lower at high altitude. When the atmospheric pressure is low, the bellows expand to make the vacuum passage from the vacuum pump narrow. As a result, the vacuum pressure, which is applied to the constant pressure chamber, decreases. Thus, the pressure inside the constant pressure chamber stays the same at both the low-altitude and high-altitude driving. The HAC functions to maintain the pressure in the constant pressure chamber by moving the push rod in accordance with the change in atmospheric pressure on the top part of the diaphragm.
Diesel Engine PCS (Power Control System)
The PCS is a device that reduces the maximum injection volume when the vehicle is driven under a certain conditions such as 1st or reverse gear. Normally, the VSV is off and a vacuum from the vacuum pump is applied to the power control valve. Accordingly, the power control lever rotates clockwise causing the governor tension lever to separate. When the VSV is on, the air is let into the power control valve causing the power control lever to rotate counterclockwise. Thus, the power control lever causes the tension lever to rotate clockwise and this reduces the maximum fuel injection volume.