Sloped controller Turbocharger Aftercooler Air reference lines Scavange oil return Induction Y Figure 3-20.  An aftercooler installation.  applies a greater pressure to the aneroid. This increases the  amount of upper deck pressure necessary to compress the  aneroid and thereby open the oil restrictor valve. This means  that the scheduled absolute value of upper deck pressure that  is required to overcome the aneroid is variable by throttle  position. As the throttle is opened wide, the manifold pressure  and upper deck pressure requirements greatly increase. and increases the charge air density, which improves the  turbocharger performance for that engine design. On engine  start, the controller senses insufficient compressor discharge  pressure (deck pressure) and restricts the flow of oil from the  wastegate actuator to the engine. This causes the wastegate  butterfly valve to close. As the throttle is advanced, exhaust  gas flows across the turbine increases, thereby increasing  turbine/compressor shaft speed and compressor discharge  pressure. The controller senses the difference between upper  deck and manifold pressure. If either deck pressure or throttle  differential pressure rises, the controller poppet valve opens,  relieving oil pressure to the wastegate actuator. This decreases  turbocharger compressor discharge pressure (deck pressure).  The sloped controller is designed to maintain the rated  compressor discharge pressure at wide-open throttle and to  reduce this pressure at part throttle settings.  [Figure 3-22] A diaphragm, coupled with a spring-supported bellows for  absolute pressure reference, is exposed to deck pressure and  intake manifold pressure through ports located before and  after the throttle, respectively. This arrangement constantly  monitors deck pressure and the pressure differential between  the deck and manifold pressure due to a partially closed  throttle. If either deck pressure or throttle differential pressure  rises, the controller poppet opens and decreases turbocharger  discharge (deck) pressure. The sloped controller is more  The VAPC contains an oil control valve similar to the  other controllers that were discussed.  [Figure 3-21]  The oil  restrictor is actuated by an aneroid bellows that is referenced  to upper deck pressure. A cam connected to the throttle  mechanism applies pressure to the restrictor valve and  aneroid. As the throttle is opened to greater values, the cam  Sloped Controller Variable Absolute Pressure Controller (VAPC)  3-16