What does rack and pinion do?

Answer 1

To my understanding, in a Power Steering system, the pinion is like a cog attached to the steering column. The rack is connected to the piston, supplying fluid ports which provide high pressure to one side or the other resulting in your wheels moving.

Hopefully my crappy answer will inspire a better one.

My answer...

If you have ever used a log splitter, its the exact same thing... kinda...

You have to hoses going to the rack. One is the pressure, and one is the return. The pump is always moving fluid when the engine is running.

When your warming your car up the fluid goes right through the rack valve and back to the pump tank. When you turn the steering wheel, a tiny torsion bar directs some of that fluid to one side of the rack piston, depending on which way you want to turn.

If your car is sitting still the torsion bar will have alot of tension when you turn the wheel, and give lots of oil to the rack piston. If your blasting down the highway and turn the wheel there is very little torque on the torsion bar, so it diverts a tiny amount of fluid to the rack piston. On the rack you will notice two steel tubes going to the rack housing. These tubes carry the fluid from the valve to one side of the piston or the other, and also carry the fluid from the unused side of the piston back to the tank.

Back to the log splitter, the more you move the valve handle the faster the splitting wedge moves, same with your rack, except it moves the valve more or less for you.

Ever notice when you rev the motor on your log splitter the wedge moves faster?

Well your lucky that your car does not do the same. Imagine at an idle you need two people to steer, and at high RPMs the wheel would be way top easy. Power steering pumps have two valves built into them. One is a pressure relief valve so when you steer to the end of travel, it does not brake the pump shaft. The other valve is basically a flow divider.

The "flow divider" has two paths for the outlet fluid, one is the controlled flow, the other is the excess flow. The controlled flow is always the same (pretty much) no matter how fast you are turning the pump, and goes to the rack valve. The excess flow changes with engine speed, and is sent right back to the tank.

For you race car builders... if your driver is whining about the steering, you can buy different torsion bars, which will deflect at different rates. This gives you the opportunity to make the steering softer or harder, which ever the driver prefers. These are typically the recirculating ball type gear boxes and not racks.

For you snow plowers, you can use a second power steering pump to provide your plow valve fluid... get rid of that pesky electric motor! You just need to tweek the "flow divider" and plug the relief valve, but make sure your control valve has a built in adjustable relief valve.

Want a hydraulic winch on the front of your truck? Use a second power steering pump.

Want a slow log splitter, hook up a second pump.... Anything is possible now that you have a hydraulic pump!!!

Have fun, and try not to spray oil all over your shop!