How They Work


How they work          diagnosing problems          porting and polishing          rebuilding nosedrives          Swaps and upgrades          Adding a boost gauge         

replacing needle bearings     adding a nosedrive drain          supercharger oil change          pulley size suggestions          links, references, and sources


Eaton Superchargers are positive displacement blowers.  What this means is that they have a pair of overlapping/interlocking rotors that spin opposite each other (one clockwise, the other counter-clockwise) and are driven by the pulley from one of the engine belts.  On the Series 1 L67 engine, the belt that drives the Supercharger also drives the water pump and AC compressor.  On the Series 2 L67, the belt that drives the Supercharger only drives the AC compressor in addition.  For this reason, a Series 2 L67 can 'limp' without the SC belt, but the Series 1 L67 will overheat quickly without the belt driving the water pump.  The rotors spin inside the case compressing the air coming in from the inlet (throttle body) and deliver the compressed air in the form of boost (indicated on the gauge) to the lower intake manifold where it waits until an intake valve opens.

The DRIVE sequence of a setup like this is described rather simply:  Belt drives pulley.  Pulley spins input (nosedrive) shaft.  Behind the pulley is a seal to prevent Supercharger oil from escaping.  Nosedrive shaft spins in two bearings lubricated by this oil.  At the end of this shaft are 3 pins that lock into a flexible coupler (this coupler prevents gear damage by absorbing the shock load of a quick jump on the throttle, so the force flexes the coupler rather than break gear teeth).  This coupler joins the input shaft to one of the rotor shafts via 3 identical pins.  So when the input shaft spins, one rotor spins.  Each rotor has an identical gear on it with a 1:1 ratio.  So the two rotors spin in a counter-rotating fashion.  One clockwise, the other counter-clockwise.  The rotors shafts are sealed between the gear housing and compressor chamber for two reasons.  One reason is to prevent manifold pressure (boost) from pressurizing the oil chamber (causing leaks) and the other is to prevent the oil from leaking into the compressor housing.  Each rotor shaft is retained by a bearing on each end of the shaft. 

 

The CONTROL sequence is described rather simply as well:  When boost is not needed (idle or light-load driving conditions), the air is actually bypassed inside the supercharger before the rotors.  The air comes out the bottom of the supercharger into the lower intake manifold through a bypass valve designed much like a throttle plate.  Spring force from the actuator (Boost Control Actuator, BCA) and vacuum coming from the Boost Control Solenoid hold the valve closed to create boost in it's default state.  In order to BYPASS boost when not needed (idle or light-load driving conditions), vacuum from the BCS must be turned off by the PCM to allow the vacuum at the top of the BCA to overcome it's own internal spring force.  In simpler terms, with the car off, spring force inside the BCA holds the bypass closed.  When the car is idling, the BCS turns off, allowing the vacuum ported to the top of the BCA to overcome the spring force and open the bypass.  So the vacuum port at the top of the BCS always has vacuum on it if the car is running, but the vacuum going to the bottom of the BCA only has vacuum when boost is desired (helping the spring in the BCA to hold the bypass closed).  The control vacuum is switched on or off by the Boost Control Solenoid (BCS) via the PCM.  Various other inputs are required.  For instance, after a spirited wide-open-throttle (WOT) run, when you let off the throttle, the PCM sees the throttle position sensor (TPS) change state, and realizes that you let off the accelerator.  In this situation, the PCM commands the BCS to dump boost, and allows vacuum to overcome the spring force in the BCA in order to OPEN the bypass valve and dump the incoming air from the throttle body directly into the lower intake manifold (LIM) before the rotors in the supercharger have a chance to compress it. 

Boost Control Actuator (BCA) circled in yellow, and Boost Control Solenoid (circled in light blue).  These are shown in their state of 'rest' (engine not running, no vacuum to control/actuate), which is also their state of full boost or bypass CLOSED.  At the bottom left end of the BCA (end of the actuator rod), you can see the bypass valve shaft.  The BCA pulls this upward, opening the bypass when it is commanded to (in park or neutral, or other conditions dictated by the PCM).

 

 

M62 Bypass Valve on the under side of the supercharger.  M90 is similar.  This is the closed position, allowing full boost.  It rotates when pulled by the BCA, and turns 90 degrees to the open position, just like the throttle plate in your throttle body.


How they work          diagnosing problems          porting and polishing          rebuilding nosedrives          Swaps and upgrades          Adding a boost gauge         

replacing needle bearings     adding a nosedrive drain          supercharger oil change          pulley size suggestions          links, references, and sources


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