Driveshaft Speed Sensor

[jayb]

Jay, always the innovator! 

Just watch, his next step will be a algorithm linked to the driveshaft sensor and the EFI controller that, by sensing tire slip, instantly kills some timing or like a stutter box, drops some cylinders to kill power!.

Those are already out there Bob.  Some guys are using microprocessors to watch the driveshaft speed sensor for any sudden, non-linear changes to the acceleration, and using that as an electronic trigger to change the tune on the fly during a pass.  In fact that is the way an anti-lock brake system works.  The microprocessor watches the output of the wheel speed sensors and when there is a sudden deviation from a linear speed or acceleration, it kicks in the ABS brakes to modulate brake line pressure.

[Drew Pojedinec]

Yeah, a fella on the FE forums had one some time back in an AC Cobra.  Seems that car would be the most appropriate usage for that system, as I can't imagine ever being able to get good traction with some of the monster engines people stuff into those.

[Falcon67]

Those are already out there Bob.  Some guys are using microprocessors to watch the driveshaft speed sensor for any sudden, non-linear changes to the acceleration, and using that as an electronic trigger to change the tune on the fly during a pass.  In fact that is the way an anti-lock brake system works.  The microprocessor watches the output of the wheel speed sensors and when there is a sudden deviation from a linear speed or acceleration, it kicks in the ABS brakes to modulate brake line pressure.

LOL - from a friend that is a senior Ford tech at a Lincoln dealer:  Lady brought in a car that would start crapping out somewhere close to 60 MPH.  Run fine up to a point, then act like someone threw out the anchor.  After several days of testing sensors and head scratching, they figured out that she had a blowout on a recent trip and the replacement tire on the right rear was a bit smaller than the others.  Once the wheel speed deviated enough from the others, computer thought the car was going into a skid and applied the brakes.

[Heo]

Same with my wifes 500 sl . Over 90 km/h
you could not lock the cruicecontrol and some other
strange things.The shop manager on Mercedes laughed
and said I bet you put on bigger rear tires right?
Yeaaa but..   Change back to smaller and its like new
 

[rcodecj]

My cars have working speedometers but I use my gps for a speedometer.
It is mounted up just above the dash where I don't have to look down at the speedometer.
Kind of like having a heads up display.
One of my cars has the tach in the way of the speedometer anyway. 
Also they sell gps speedometers that look just like any other gauge.

[cammerfe]

I am once again reminded of my recurring thought that JayB is neater than spats on a duck.

KS

[fryedaddy]

i know its different but my son needed a speedo,he mounted a sensor on his brake caliper and a pick-up on his wheel to get his mph

[Nightmist66]

Jay, do you think there is enough clearance that the reluctor will not bottom out against the back of the tailhousing? Also, do you think the reluctor will cause any imbalance to the driveshaft?

Overall a very neat and ambitious project.

[jayb]

I ran through the suspension travel and had plenty of clearance.  However, in order to take the driveshaft out, I will have to remove the target; the driveshaft will not slide far enough forward with the target bolted on to allow it to get past the rear end yoke and come out. 

I can't imagine there's enough weight there to cause a balance issue, but I guess we'll see...

[shady]

put the bolt heads opposite each other, if it's not too late.

[WConley]

I would echo Shady's advice.  Hopefully you made the same part in two halves so the bolts are indeed opposite each other.

Driveshafts are very sensitive to imbalance.  All you need typically is one or two worm-screw hose clamps to balance a buzzy one.  With your gearing that shaft has to be spinning up pretty fast.

Have you also determined the critical speed of that shaft?  There should be a max rpm spec for any aftermarket driveshaft and you can run up against that pretty easily in a drag car.  Now that the GV unit is gone your shaft is much longer, reducing critical speed.

- Bill

[machoneman]

Good point on balance Bill.

My uncle Bill had a near new shop van that one day seemingly picked up a bad vibration at 65 or faster. The dealership had looked it over a number of times, wheels, driveshaft, etc. with no luck. Then, after more carping, Dodge sent out a factory rep to look it over. Next day, Bill got the call to come and pick it up. He and the tech hit the highway and all was fine. Back at the dealership, the rep. showed Bill out back in the parts department what it was.

A tiny dent on one side of the very long aluminum driveshaft! Apparently, the local quick oil change shop used a side lift hoist and the lift arms pinched the shaft just a tad. Btw, Bill was amazed such a tiny dent could throw off the balance so much.   

[WConley]

Balance is a funny thing on high-speed rotary machinery.  In grad school I built a laboratory for studying composite helicopter tail rotor shafts.  The drive unit was a 1-ton variable-speed motor with a step-up transmission attached.  It could zing the output up to 10,000 rpm if we wanted.  The whole unit was mounted to a huge cast iron table grouted into the floor

There was a bit of detectable vibration in the base plate when we ran the thing up.  The professor rigged up a pair of Hall-effect sensors to look  at 12:00 and 3:00 on the output coupling flange and we studied the signal with an oscilloscope.  We calculated the correction mass and angular location on the output flange and I machined one up.

My machined part ended up being a 5-gram brass washer!  I mounted that little guy to the correct spot on the flange.  The 1-ton machine then ran as smoothly as could be at all speeds.

[jayb]

You guys are scaring me about the balance.  I did not machine the parts so that they had screws coming from the opposite sides, so there is going to be some imbalance there.  Saving grace (hopefully) is that it is fairly close to the center of rotation, so hopefully it won't make any noticeable vibration.  I guess if worst comes to worst I can have the driveshaft rebalanced with the target bolted on, and then mark it somehow so that it is always installed in the same spot.  Or maybe just balance the target...

Critical speed for this driveshaft is over 8500 RPM, so I'm not too worried about that.  It is a 4" diameter aluminum driveshaft, and even though its a foot longer than the old one, according to the Mark Williams critical speed tables I won't come close.

[westcoastgalaxie]

Jay even though it is close to center I would still reconsider.  I would be concerned with premature wear on the output shaft bearing and seal. I don't have driveshaft experience but I do work for a centrifuge company. Forces in a g-field are easy calculation, you may want to run some numbers.

While I don't design the equipment I do balance and service them. As mentioned balancing is a matter of grams only degrees of difference or separation. Also symmetry is always key with design as well as locking fasteners or designing fasteners that are not perpendicular to I guess what you might call the center. Think of how you use the natural forces to keep the fastener in place.

As for locking fasteners we use either loctite, locking patches or locking washers. Typically not split lock but instead nordloc washers.

Keep in mind these centrifuges while balanced are subject to vibrations and the size and speed typically generate g's in the neighborhood of 1400.