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Lexus had a problem with the electric-assist rack and pinion steering assy in some specific cars. There was a recall issued for the assy in late 2008, and dealer new stock of the affected parts were scrapped, as well as the parts pulled off cars due to recall. I picked some up for $cheap beginning in early 2009.
These looked like something to inspect further, since i could now get them for under $5 each, and if i got a working anything out of them, i figured i'd break even at $5. Here's what i found.
These units are extremely well built. Like, in a cleanroom. Almost every thread is also staked (this led me to cut the first motor in two to get it apart!). There is the traditional rack and pinion drive, with an electronic position sensor on the pinion input shaft. On the same shaft as the rack is a ball screw, about 8 inches of precision hot rolled thread. The motor has a hollow shaft, with the rack running thru the motor shaft. The shaft has a permanent magnet in it, under a stainless steel wrap. The motor is a 3 phase design, with position sensor. The copper motor wires are welded, not soldered, to the pins that exit the motor. The rack is internally threaded at each end, for a ball joint with the steering rods sticking out of that.
Once the steering rods are removed from each end, we have this. I also removed the pinion gear input. The motor housing is 7.5 inches long, not counting bearings. The housing is nearly exactly 3.5 inches diameter. In this picture, the motor is in the housing section with the barcode on it, and the thrust bearing is in the domed end bolted onto it on the left.
Here's the manual input pinion gear:
Here's the end of the motor shaft with the ball nut inside it:
After removing the rack and screw, here's a look into the end with the ball nut:
Here is the whole rack/screw, it's 25.5 inches long:
Here's the ball screw portion:
Here's the rack portion:
This is the ends of the rack:
Here's the bare motor shaft. It's actually a tube, the rack-screw runs left-right thru the tube as the tube spins. The lobes at length 6.75 are the position indicator. The flange at 8 is one inner race of back-to-back thrust bearings, the other end of the shaft is supported by a ball bearing. The permanent magnet resides under the stainless steel sleeve that's from 2.5 to 6.5. The ball nut is inside this shaft, at the right end.
The opposed thrust bearings. Single common outer race, two inner races. Shown with one inner race removed. Preload is set by the nut in the background being screwed onto one end of the motor shaft.
See the "teeth" above the motor poles? The rounded lobes on the motor shaft change the reluctance of that iron, providing rpm and position feedback.
The other end of the housing. All the copper-to-copper is welded, not soldered. The difference is melting temperature and durability.
Staking is used in several places to resist coming apart:
As i mentioned, i cut the motor at one end, because i saw no way to get it open without force, and i didn't want to force it and break something i could have used as a spare part later. The dull aluminum is what i cut with the bandsaw, rotating the housing against the blade. The shiney steel is the outer race of the doubled thrust bearing, which i decided to not cut thru, even before i knew what it was.
I liked them so much i got 21 more!