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Steering Displacement and Speed Calculator

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Alright I put this together just to simplify a lot of the numbers that were coming out of the CBR steering pump thread, but figured it could be handy for anyone tinkering with their steering system. It's a basic calculator that determines pump RPM for different engine speeds based on pulley sizes, then calculates how much the pump is theoretically flowing based on pump displacement. Between P pumps, TC pumps, CB/CBR pumps and trophy truck pumps there are various displacements, so adjust that cu/in per revolution to your pump size (I may add some reference data at a later date). Then it has an integrated feature for when the factory flow control opens, and has an assumed efficiency of that valve (90% seems pretty close to some reference data I've seen).

Then if you calculate the volume of your steering system (piston surface area * stroke of steering box + ram piston surface area minus shaft surface area * stroke of ram) and enter those numbers, you can get theoretical lock to lock speed.

CBR Pump Thread for future reference: https://irate4x4.com/general-4x4/246...m-applications

*EDIT*
Update V1.3......1-15-21
-Added Pump Pressure Output
-Added Steering Force (At Knucke) Note: Steering Ram stroke is needed for math to dictate knuckle travel, even if not using assist)

Download link:
https://alpinepeakprecision.com/tech/steeringpump/PS Pump Displacement Chart - V1.3.xlsx

Power%20Steering%20Displacement%20-%20V1.3.jpg


Power%20Steering%20Displacement%20-%20V1.2.jpg
 
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Good to see people that get it, nice work. Since there is so much talk about pump displacements, here is what I have measured and know to be true to help you guys keep your numbers accurate:

- TC pumps: 0.64 in3 (10.5cc)
- SPX-1/CBR XR race pump: 0.67 in3 (11.3cc)
- Cast iron CB pumps including my CB-X series: 0.80 in3 (13.1cc)
- P pumps: 0.95 in3 (15.6cc)
- CBR pumps: Varies... I have found everything from 0.67in3 to 0.95in3 in the ones I have opened up including new and rebuilt PSC models
- "Trophy Truck" pumps (based on a Saginaw big bearing model referred to as P235 although they go by a few names): 1.22 in3 (20.0cc)



for when this thread gets moved over to the "tech" section by Austin
 
Then if you calculate the volume of your steering system (bore * stroke of steering box + bore * stroke of ram) and enter those numbers, you can get theoretical lock to lock speed.

Remember to subtract the volume that the rod itself takes up within the cylinder...it's not insignificant.

(and also technically ([pi*bore^2]/4*stroke) ... might be an easy update to just input ram & rod dimensions and have a formula for the displacement box)
 
Remember to subtract the volume that the rod itself takes up within the cylinder...it's not insignificant.

(and also technically ([pi*bore^2]/4*stroke) ... might be an easy update to just input ram & rod dimensions and have a formula for the displacement box)

Thanks, I forgot to clarify that here but did include notes for shaft diameter in some FB posts I put up. Agreed though I may just want to add formulas for ram and box working dimensions, I think that will be added to the next update.
 
Thanks, I forgot to clarify that here but did include notes for shaft diameter in some FB posts I put up. Agreed though I may just want to add formulas for ram and box working dimensions, I think that will be added to the next update.

Figured you knew it but want to clarify for those reading along. Thanks for putting it together, cool utility :beer:
 
I figure this is a good place to bring this up, but I've noticed in a few different vehicles (haven't tried in a solid axle U4 rig yet) but there always seems to be massive resistance when "over correcting" and I don't want to believe it's a characteristic of full hydro steering. I believe it's the 3/8" fittings on the ram, but I also don't 100% believe that either because that should restrict movement at all times, not just steering one way then trying to quickly steer the other way. So is it an orbital issue? I don't wanna say it's the pump, because it has pressure and flow to support it (PSC p-pump)

I post here to try to bring this to light for everyone who deals with the same thing or never really noticed til now.
 
I figure this is a good place to bring this up, but I've noticed in a few different vehicles (haven't tried in a solid axle U4 rig yet) but there always seems to be massive resistance when "over correcting" [...]

I post here to try to bring this to light for everyone who deals with the same thing or never really noticed til now.

I noticed the same thing and I'm thinking about upgrading my steering system to avoid this. I am hopping a CB-X pump from radial dynamics would solve my issue.
 
I figure this is a good place to bring this up, but I've noticed in a few different vehicles (haven't tried in a solid axle U4 rig yet) but there always seems to be massive resistance when "over correcting" and I don't want to believe it's a characteristic of full hydro steering. I believe it's the 3/8" fittings on the ram, but I also don't 100% believe that either because that should restrict movement at all times, not just steering one way then trying to quickly steer the other way. So is it an orbital issue? I don't wanna say it's the pump, because it has pressure and flow to support it (PSC p-pump)

I post here to try to bring this to light for everyone who deals with the same thing or never really noticed til now.

This actually has everything to do with how much flow rate your pump is putting out. When you turn the steering wheel, the orbital valve takes a precise volume of fluid out of the main hydraulic circuit and forces it to the ram. Since the valve is fixed displacement, that means that the flow rate of fluid it is moving is dependent on the displacement volume and the rate that you turn the steering wheel.

If this flow rate exceeds what the pump is supplying to the valve (during quick corrections), then you reach a situation where the orbital is essentially trying to pull fluid out of the pump rather than letting the pump push fluid to the valve and in this case, there is no chance to build pressure so therefore, steering feels stiff and locked up.

If you guys both want to talk more, I'd be happy to go through your setups in detail and put some numbers on where you are falling short so that you know exactly what changes you need to make without guessing.
 
sounds like a good case for a load sensing valve/steering unit and a pump that can meet the demands :flipoff2:

I would agree except there are no good variable displacement pumps suitable for what we are doing and you still need something with enough displacement to at least get close to flow demand at idle engine speed which is the biggest challenge.
 
I would agree except there are no good variable displacement pumps suitable for what we are doing and you still need something with enough displacement to at least get close to flow demand at idle engine speed which is the biggest challenge.

variable displacement pump isn't a requirement, though it would be nice to have one available that could tolerate the RPM range and not be as expensive as they are. it would make for some fun packaging. edit: for the eaton load sense valve, i should have added a T line for the pressure relief to tank drain, which can be tied into the EF line ONLY IF you are running NO circuits off the EF

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eatons much more detailed version

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This sounds crazy, but has anyone ran some sort of CVT to turn their PS pump?
Certainly adds complexity but there may be some benefits. This would effectively give you a varying pulley size.

I am speaking without doing much research on this part, but has anyone ran hydraulic PS but the PS pump was driven by an electric motor? Essentially an electric hydraulic pump running off the dual batteries and alternator.
 
This sounds crazy, but has anyone ran some sort of CVT to turn their PS pump?
Certainly adds complexity but there may be some benefits. This would effectively give you a varying pulley size.

I am speaking without doing much research on this part, but has anyone ran hydraulic PS but the PS pump was driven by an electric motor? Essentially an electric hydraulic pump running off the dual batteries and alternator.

lot's of rear steer rigs run electric over hydraulic and lot's of liftgates use a similar system. to get decent volume they put up a pretty taxing electrical load so outside of packaging in remote from the engine locations, it is a tough sell.
 
variable displacement pump isn't a requirement, though it would be nice to have one available that could tolerate the RPM range and not be as expensive as they are. it would make for some fun packaging. edit: for the eaton load sense valve, i should have added a T line for the pressure relief to tank drain, which can be tied into the EF line ONLY IF you are running NO circuits off the EF

eatons much more detailed version


The way these circuits are drawn doesn't help the situation of pump output being lower than steering demand particularly at low RPM. Whether using an open center orbital or closed center with load sensing valve won't change the maximum rate that fluid can be pushed into the ram.
 
This sounds crazy, but has anyone ran some sort of CVT to turn their PS pump?
Certainly adds complexity but there may be some benefits. This would effectively give you a varying pulley size.

I am speaking without doing much research on this part, but has anyone ran hydraulic PS but the PS pump was driven by an electric motor? Essentially an electric hydraulic pump running off the dual batteries and alternator.

This thought has crossed my mind or better yet, using a CVT accessory drive which keeps everything in a happier range including alternator and AC compressor (if you have one). Of course, packaging, cost, and reliability are the biggest challenges there that make it somewhat impractical with the equipment that is currently available.

And like Philip said, rear steer setups commonly use electric hydraulic pumps but the problem with trying to run one full time is the power. Even a small steering pump like a TC can consume up to 5 or 10 HP. The bigger pumps like TT pumps consume easily 20+ HP. With a 12VDC motor, it becomes impractical to try and keep something like that going full time.
 
The way these circuits are drawn doesn't help the situation of pump output being lower than steering demand particularly at low RPM. Whether using an open center orbital or closed center with load sensing valve won't change the maximum rate that fluid can be pushed into the ram.

what it does do though is allow you to run a much larger pump that will flow enough GPM at a low RPM while safely bypassing the substantial extra volume through lower restriction lines and without subjecting the steering valve to the great flow discrepancies that you get with a typical open center steer valve and high volume pump.

because the load sense valve is handling most of the dividing work, the steering valve is free to work with what it considers ideal, and thus react more quickly and more consistently.
 
I hear you although that still means having an enormous flow rate to handle through the reservoir and into the pump. My strong preference is still to use a larger displacement pump with internal flow regulation which makes the whole setup much more simplified and compact. The closed center load sensing setup is really most useful when you have a hydraulic circuit serving many different functions as you are building on your rig but for a dedicated steering system, the load sensing setup will work but is unnecessary.
 
I hear you although that still means having an enormous flow rate to handle through the reservoir and into the pump. My strong preference is still to use a larger displacement pump with internal flow regulation which makes the whole setup much more simplified and compact. The closed center load sensing setup is really most useful when you have a hydraulic circuit serving many different functions as you are building on your rig but for a dedicated steering system, the load sensing setup will work but is unnecessary.

in general i fully agree. I also think a lot of people are running steering valves/orbitals designed for significantly more fluid than they are making. for running a single circuit, load sense valve, which can be made affixed to the steering valve to make it more compact, takes care of the regulation and pressure relief and flow control better than the cheap diverter and cheap steering valve options. "only" adds about $600 to the system cost for people running unregulated pumps, so you can save a couple hundred on the pump side :laughing:

again, the large lines to handle the volume do become a serious issue and the internal pump certainly wins in that regard :beer:
 
rear steer setups commonly use electric hydraulic pumps but the problem with trying to run one full time is the power. Even a small steering pump like a TC can consume up to 5 or 10 HP. The bigger pumps like TT pumps consume easily 20+ HP. With a 12VDC motor, it becomes impractical to try and keep something like that going full time.

However, the Electric pumps are constant flow. When combined with open Center steering valve, would draw 1.2hp at 400psi/6gpm, and 5hp at 1000psi/6gpm (no losses)
Wouldn’t need an awefully huge displacement pump for most situations, and how often are we making over 1500 psi ? 5%?
 
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However, the Electric pumps are constant flow. When combined with open Center steering valve, would draw 1.2hp at 400psi/6gpm, and 5hp at 1000psi/6gpm (no losses)
Wouldn’t need an awefully huge displacement pump for most situations, and how often are we making over 1500 psi ? 5%?

5 horsepower at 12 VDC is over 380 amps, that is the biggest issue for constant duty. going from alternator to battery to electric motor to hydraulic pump with 380 amps, versus belt to hydraulic pump.

1.2 hp is ~90 amps.
 
5 horsepower at 12 VDC is over 380 amps, that is the biggest issue for constant duty. going from alternator to battery to electric motor to hydraulic pump with 380 amps, versus belt to hydraulic pump.

1.2 hp is ~90 amps.
Then I guess I will have to run it off 400vdc then
 
5hp at 400V gets you down to 10 amps or so. Can't forget the added hazards of running at 400V. Rub the wire on anything and it could be a bad day quick.
 
Then I guess I will have to run it off 400vdc then

i think there is a whole bunch of validity to running a hybid ice/electric drivetrain, but now we are pretty far outside the scope of normal and the value of "compact" starts to get lost :laughing:


nobody blinks an eye at a winch drawing 400 amps potentially, but like rear steer, it isn't high use.
 
we ran e pump system in formula offroad rig couple years 2007-2015.
dual batts and 120amp alternator.
it was drivable but didnt have enough volume/pressure to run really good.
here some in car footage it in action, you can see the pump in the passenger floor

formula offroad 2013 bålsta sun - YouTube

do you happen to remember what volume/pressure you were running?
 
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