Hi josh here and you're watching 610BOB’s
taredowns. Where we take stuff apart to find out how they work. Today, power steering box. How does hydraulic
fluid assist you steering? This is a power steering box. This one is
out of an f250 pickup truck. If your vehicle has one, it is probably much smaller. But,
to my knowledge, they are all pretty much the same. Some cars do use a power steering
rack, but that is different from what we're talking about here. This is your input shaft. Your steering wheel
turns this shaft. After some internal magic, this output shaft
turns. A pitman arm is attached to this wich is then connected to some other links which
turns your wheels. But how exactly does that magic work? Well, let's take it apart to find out. Hmm, that doesn't clear it up much. Hang on. [sound effect] grinding on metal [sound effect] steel hitting floor Here we go, that's better. This ball lead screw turns with the steering
wheel. As it turns, it screws in or out of the piston. Since the ball lead screw can’t
move up or down, it pulls the piston up or pushes it down. Just like a nut on a bolt. This piston is also a rack and the output
shaft is a pinion. As the piston moves up and down, it pushes against the teeth on the
output shaft. This causes the output shaft to turn. If you're wondering why it's called a ball
lead screw, there are ball bearings inside the piston. So instead of the lead screw using threads
to turn against, it uses these ball bearings. This reduces the friction required to rotate
the lead screw, increasing the efficiency of the system. This is basicly a gear box. It reduces the the input speed while increasing
the input torque. But that's just a steering gear box. This
is a POWERED steering box. So where the power? Remember I kept on referring to that part
as the piston? Well, that's because it is a hydraulic piston. Turn one way, high pressure
fluid fills the top of the piston, pushing the piston down. Turn the other way, high
pressure fluid fills the bottom of the piston, pushing the piston upward. This positive feedback valve... wait. What? Positive feedback valve.
This valve monitors the amount of torque applied to the input shaft.
It's a positive feedback valve because as the amount of torque applied to the input
shaft goes up, the amount of fluid that is allowed to pass through the valve also goes
up. So the harder it is to turn the steering wheel,
the more fluid that is sent to assist you. But how does this work? Well, the valve works on the exact same principles
as this torque wench. The more torque that is applied to the torque wrench, the more
the handle deflects. There are 4 parts that we will be looking
at. The metering rod, which you can see poking out right here. That goes from here to the
top of the ball lead screw. We will also be looking at the input shaft, the valve sleeve,
and the ball lead screw. The valve sleeve is pinned to the ball lead
screw. So it can't turn in relation to the lead screw. The Input shaft however is only
tied to the ball lead screw via the metering shaft. Just like the torque wrench, the metering
rod has some give to it. As the torque applied to the input shaft goes up, the metering rod
deflects more and more. This causes the input shaft to rotate a little in relation to the
ball lead screw and the valve sleeve. And when I say that the input shaft rotates
a little, I do mean a little. If the input shaft rotates too much in relation
to the ball lead screw, the metering rod could deform or break. So there are built in stops to prevent this. This is the top of the ball lead screw. You
can see the metering rod broken off here. There are flat spots here and here. There are similar flat spots on the input
shaft. The input shaft goes into the ball lead screw. There is enough play to allow
the input shaft to spin a little. But not enough to permanently deform the metering
rod. These stops would be used if your power steering
system wasn’t working, or you maxed out the power steering system. So here's the valve pieces. Understand…
No? Well I don’t blame you. TO THE CHALK BOARD! Ok, so here's the lineup, when the other team
comes this way, oh wait, wrong chalk board. Hang on. So here is the valve looking down on it.
Disclaimer, nothing here is to scale, this is just a general simplified diagram. This is what the valve looks like when there
is no torque applied to the steering wheel. The fluid comes out of the high pressure port,
wallows around a bit, and exits through the return. When we need a little power, the metering
rod allows the input shaft rotate a little; in comparison to the outer sleeve. This starts
to direct some of the high pressure fluid to one side of the piston. It also directs
some of the fluid from the other side of the piston to the return line where it ends up
back into your power steering reservoir. This happens on all four side of the valve. When we need all power You yell down to the engine room, Scotty,
we need more power. Then you hear back, I’m giving it all she's
got captain, She cant take much more of this! [Sound Effect] Crickets Yea, that was a terrible, terrible accent. Yeaaa, no. When the torque on the steering
wheel is so great, that the input shaft’s limiters engage, you need as much power steering
as you car can muster. When happens, this part of the valve practically closes off.
Directing all high pressure fluid to one side of the piston. And it directs all fluid from
the other side of the piston to the return line. Oh, then you hear from the valve, I’m giving
it all she got captain! Moving on, the same is true when you turn
the other way. The fluid is just directed to the opposite side of the piston.
And when you don’t need the power steering any more, either because nothing is fighting
the wheels or your done your turn, the torque on the steering wheel is zero. The valve then
returns to center. This allows the fluid to wallow around without a care in the world. Basically, as torque on the input shaft goes
up, this gap closes, directing fluid to one side of the piston. Here are the fluid paths coming out of the
valve sleeve. You have top of the piston, High pressure, bottom of the piston, and return
comes out of the input shaft through these holes. The valve housing helps direct fluid to the
power steering box through these holes. There are slots in the housing to help direct fluid
and help keep fluid velocity low by giving the fluid more room. The high pressure and return port goes directly
to the ports on the outside of the housing. This is where you connect your power steering
hoses to the power steering box. Fluid goes to and from the valve body and
the piston through these ports. One goes directly into the top of power steering box. The other port goes into this passageway where
it goes down to the bottom of the power steering box. And exits here, at the bottom of the piston. And that is how a power steering box works.
Just a torque metering valve controlling a hydraulic piston slash nut slash rack moving
up and down to rotate a pinion. Simple! Yikes Yea, you may want to rewatch this video a
couple of times. I did read a couple websites explaining how
the valve worked. So I’ll include links in the description
and a couple of cards in the video to these websites. This was in prep of my next video; DIY Hydro
Assist. Even though you only needed to know like %10
of what I just said. Anyway, be be sure to check that video out
when it comes out. Also if you have any questions, let me know
down below. Also, if you want to yell at me about my really
bad Star Trek voices, go ahead. Before you go, I do have to admit, there is
one thing that I do not understand. What this thing is for. It is basically a spring pushing
two pins into the input shaft. For what, I have no idea. I would say it is a bearing
or a stabilizer, but there are only two pins. Got any ideas? Let me know in the comments.
