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Here's the simple answer
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Posted by James Uhl (more from James Uhl) on Fri, 24 May 2002 21:02:19 Share Post by Email
In Reply to: Saab Sensonic Clutch - Question, Martin B, Sun, 19 May 2002 02:36:15
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Sensonic uses a control module to monitor:

A gearshift motion sensor

A gear selector sensor

A clutch temperature sensor

A final drive speed sensor

Engine speed from Trionic

Throttle position from Trionic

Brake on/off signal from the brake pedal switch

And wheel speed from ABS



It uses this information to determine when to disengage and engage the clutch. It's quite a sophisticated system with a high level of self-learning ability - that is, the more you drive after a major repair (or during break-in), the smoother it gets, automatically. The gearshift motion sensor is the foundation..... the ACS (automatic clutch system) ECU monitors that sensor for movement. It compares that movement against the gear selector sensor (inside the gearbox). If both sensors show movement (a change in hundredths of a volt) then the clutch is disengaged. If only the gearshift motion sensor voltage is changing, then this is interpreted as powertrain flex or a rough road and the clutch remains engaged.



Pulling away from a stop the ACS ECM most closely monitors the torque request (throttle opening), engine RPM, and the gear selector sensor. All of these are placed together to determine how actively to engage the clutch. For example - heavy throttle, first gear - SPIN THOSE WHEELS! It engages the clutch just like side-stepping it would. As long as it doesn't sense that engine RPM is dropping, it'll act in that manner. I've chosen to install significantly wider, stickier tires that don't slip. As a result, I no longer get Sensonic harshly engaging the clutch. Instead, what I see is the ACS system slipping the clutch on a hard accel.



The computer operates an electrical motor coupled to a worm gear. The worm gear drives a fairly large circular gear, which is spring-dampened to operate a standard hydraulic clutch master cylinder. From there on, the clutch system is standard - no special slave cylinder, or hoses, or clutch components.



Downshifting is handled in the same logical manner as acceleration. The ACS ECU will re-engage the clutch as you’re decelerating (just as you would) to help slow the vehicle.



If you're at a stop in third gear, the SID (Saab Information Display) above the radio will advise you to "Shift Down." The same message will be displayed if you're driving in too high of a gear and lugging the engine. However, motion can be started in second gear to allow a lower level of torque to the front wheels to aid in better/more controlled winter driving.



If you leave the car in gear with the engine running while you run into a convenience store (or check the mail, etc) the engine will shut off after ten seconds of not seeing the brake pedal depressed. But if the engine is left running and NOT in gear, it will work just like a normal car.


posted by 24.98.122...
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