Supercharger Assembly
Supercharger assembly is a positive displacement pump designed to supply an excess volume of intake air to engine by increasing air pressure and density in the intake manifold. Supercharger assembly incorporates a by-pass system to reduce air handling losses when boost is not required, resulting in better fuel economy. (Scheme 12) Supercharger can increase torque across entire engine operating range from 25-50 percent without compromising driveability or emissions.
Supercharger is matched to engine by its displacement and belt ratio, and can provide excess airflow at any engine speed. Drive gears for supercharger are pressed into place and are not serviceable. Supercharger must be replaced as a unit. Supercharger contains 2 belt driven 3-lobed helical cut rotors which are supported by ball bearings in front and needle bearings at the rear. The rotors helical shape and internal specialized porting provide a smooth discharge flow and low noise levels during operation.
Scheme 12
Idle Air Control Valve Assembly
Idle Air Control (IAC) valve assembly is used to control idle speed and provide a dashpot function. IAC valve assembly meters inlet air around the throttle plate through a by-pass within the IAC valve assembly and throttle body. (Scheme 13)- (Scheme 15).
The Powertrain Control Module (PCM) determines desired idle speed or air by-pass and signals the IAC valve assembly through specified duty cycle. The IAC solenoid is built into IAC valve assembly. IAC solenoid responds by positioning the IAC valve to control amount of air by-passed. PCM monitors engine speed and adjusts IAC duty cycle to achieve desired RPM. IAC valve assembly is not adjustable and cannot be cleaned.
On applications with air assisted injectors, IAC valve supplies a small jet of air into path of fuel injectors, creating an increase in fuel atomization at low speed and light load conditions. (Scheme 14)
Scheme 13
Scheme 14
Scheme 15
Variable Cam Timing Unit Assembly
Variable Cam Timing (VCT) unit assembly is coupled to camshaft through a helical spline in the VCT unit chamber. (Scheme 16) When flow of oil is shifted from one side of the chamber to the other, differential change in oil pressure forces piston to move linearly along the axis of the camshaft. This linear motion is translated into rotational camshaft motion through the helical spline coupling. A spring installed in the chamber is designed to hold camshaft in minimum overlap position (5 degrees) when oil pressure is too low to maintain adequate position control. Camshaft is allowed to rotate up to 30 degrees.
Scheme 16
Orifice Tube Assembly
Orifice tube assembly is the section of tubing connecting exhaust system to intake manifold. Orifice tube provides a flow path for exhaust gas to intake manifold. The orifice tube contains a metering orifice and 2 pressure pick-up tubes. (Scheme 17) The metering orifice creates a measurable pressure drop across it as EGR valve opens and closes. The pressure differential across the orifice is picked up by DPFE EGR sensor which provides feedback to PCM.
