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Car Forum / Driving, Maintenance, Tuning / Maintenance and Repair / September 2005do power steering pumps with clutches exist?
Has any manufacturer tried fitting a clutch to a power steering pump in order to prevent the pump from running when the driver is not steering much? I would envision the clutch being engaged when there was any movement in the rack input shaft, and then when there was enough twist, the valves would direct fluid (now under pressure since the pump was engaged) to the appropriate side as usual. Just curious if anyone has seen a system like this or knows why it is impractical (perhaps the gas savings are neglectable). > Has any manufacturer tried fitting a clutch to a power steering pump > in order to prevent the pump from running when the driver is not [quoted text clipped - 4 lines] > if anyone has seen a system like this or knows why it is impractical > (perhaps the gas savings are neglectable). My Integra has variably assisted steering (more car speed, less boost). Assist control is effected through pressure modulation, the modulated pressure being measured against a constant reference pressure that is present in the system. The primary input seems to be a small fluid pump that is incorporated into the speedometer drive gear housing. Do any air-conditioning systems work this way? > My Integra has variably assisted steering (more car speed, less boost). > > Assist control is effected through pressure modulation, the modulated > pressure being measured against a constant reference pressure that is > present in the system. The primary input seems to be a small fluid pump > that is incorporated into the speedometer drive gear housing. That device is more like a governor than a pump. > Do any air-conditioning systems work this way? Most A/C systems cycle their compressor off either when the evaporator temp sensor reaches a preset temp or when the pressure cycling switch reaches a preset pressure in the low side of the system. A few systems remain engaged constantly but they control the flow of refrigerant through the low side at a set pressure. Even these types have the capability to shut off the compressor in the event of loss of refrigerant or excessively high pressure. Toyota MDT in MO >> My Integra has variably assisted steering (more car speed, less boost). >> [quoted text clipped - 15 lines] > have the capability to shut off the compressor in the event of loss of > refrigerant or excessively high pressure. Don't forget the variable displacement A/C compressors. These are constantly engaged, but vary the displacement of the compressor to match the demand. From http://pss.delphi.com/na_eng/products_cat.asp?articleid=6008 : "V-5 Compressors "The first volume-produced variable displacement compressor, the five-piston V-5 automatically adjusts displacement to match the vehicle's air conditioning demand. A control valve in the V-5's rear head senses evaporator load and automatically changes displacement to match that load. Unlike cycling clutch air conditioning systems, Delphi's V-5's continuous displacement feature results in smooth, continuous compressor operation without any clutch cycling, improving air conditioning performance and fuel economy." Toyota (and most other manufacturers) is also planning on deploying variable displacement compressors. Ed > Don't forget the variable displacement A/C compressors. Don't worry, I didn't ;) The V5 has been around for a while, and, though implimented differently than typical EVR EPR STV POA etc. systems, it still accomplishes a similar outcome. It is a good idea, but seems to yield little real world benefit IMHO. Toyota MDT in MO >>Don't forget the variable displacement A/C compressors. > > Don't worry, I didn't ;) but don't you wish you could? > The V5 has been around for a while, and, though implimented differently > than typical EVR EPR STV POA etc. systems, it still accomplishes a > similar outcome. It is a good idea, but seems to yield little real > world benefit IMHO. Except to generate aggravation among people who a) own cars equipped with a V5 compressor and b) the mechanics who get yelled at by car owners because the damn things don't last to the end of the driveway. When they are working, variable-displacement compressors achieve the same result as the Evaporator Pressure Regulator type systems you mentioned first- they take much of the load off the compressor input shaft, but leave the shaft spinning. EPR systems do it by allowing the compressor to pull against a partial vacuum (caused by the EPR valve closing and limiting refrigerant return flow from the evaporator). Much simpler than mechanically altering the displacement of a compressor. The drawback to EPR systems is that they begin throttling down the cooling capacity at relatively high evaporator temperatures (45-50 degrees F) which slows down the rate at which the system can cool down a hot car. Cycling clutch systems hold the evap temp right at 35-40 degrees F by cycling the compressor on when the evap temp hits ~40, and off when it hits ~38 as needed. More mechanical wear, and you can feel the compressor cycling- but better overall cooling. > When they are working, variable-displacement compressors achieve the > same result as the Evaporator Pressure Regulator type systems you [quoted text clipped - 10 lines] > hits ~38 as needed. More mechanical wear, and you can feel the > compressor cycling- but better overall cooling. Good observations. I guess a big reason the variable displacement units were used was to eliminate the "feel" of clutch cycling. But God forbid you don't take every precaution in the book and use the exact oil in a V5 while servicing a GM. And good luck with the R134a conversion on one of those... Toyota MDT in MO > Good observations. I guess a big reason the variable displacement > units were used was to eliminate the "feel" of clutch cycling. But God > forbid you don't take every precaution in the book and use the exact > oil in a V5 while servicing a GM. And good luck with the R134a > conversion on one of those... Well the idea must not be all bad. Toyota is developing (with Denso) similar compressors. Ed > Well the idea must not be all bad. Toyota is developing (with Denso) similar > compressors. The variable displacement idea is fine. Luckily, Nippon Denso has a history of engineering vastly more durable automotive components than Delco(phi). Of course, this observation has been formed from years of wrenching, reading, and talking to peers, so it is only opinion. If Denso (Nippon or USA) supplies a VDC, I'm sure it will be a quality product. Toyota MDT in MO >>Well the idea must not be all bad. Toyota is developing (with Denso) similar >>compressors. > > The variable displacement idea is fine. Luckily, Nippon Denso has a > history of engineering vastly more durable automotive components than > Delco(phi). Yeah, if you ignore the early versions of the NipponDenso C-171 ;-) To be fair, the later versions are as good as a Sanden. > Well the idea must not be all bad. Toyota is developing (with Denso) similar > compressors. > > Ed Denso's track record is a *little* better than GMs when it comes to being able to produce a reliable compressor. I'd have more confidence if it were Sanden, but Denso's not a bad bet. Now if York were still a leader in automotive compressor industry, I'll bet they could do it with their eyes closed. > Denso's track record is a *little* better than GMs when it comes to > being able to produce a reliable compressor. I'd have more confidence if > it were Sanden, but Denso's not a bad bet. Now if York were still a > leader in automotive compressor industry, I'll bet they could do it with > their eyes closed. Yeah, but few auto manufacturers are specing out one foot cube sized compressors these days :) BTW, see my response to the dickweed known simply as * further down this thread. Toyota MDT in MO > > My Integra has variably assisted steering (more car speed, less > > boost). [quoted text clipped - 6 lines] > > That device is more like a governor than a pump. Yes, that's what I meant by "primary input". I guess I should have said "primary SIGNAL input". The hoses leading to that pump are tiny and carry low pressure. The pump is there solely to drive a spring-loaded pressure regulation system within the main pump. > > Do any air-conditioning systems work this way? > [quoted text clipped - 6 lines] > have the capability to shut off the compressor in the event of loss of > refrigerant or excessively high pressure. Would a power steering system with a clutch need a pressure regulation system anyway? Impractical because too slow to respond, I imagine. > Has any manufacturer tried fitting a clutch to a power steering pump in > order [quoted text clipped - 8 lines] > Just curious if anyone has seen a system like this or knows why it is > impractical (perhaps the gas savings are neglectable). When you aren't steering, there is little load on the power steering pump. It is mostly just circulating the oil. If you actually tried to implement a clutching system, it would be constantly switching in and out, and probably would result in steering hesitation because of the delay between sensing steering effort, clutch engagement, and pressure delivery. My Vue has electrically operated power steering. I think this is probably the wave of the future. Whenever the manufacturers make the jump to higher voltage systems (48 volts?), a lot of accessories will change over from belt drive to electric drive. Ed C. E. White <cewhite3@mindspring.com> wrote in article <_HpVe.10967$_84.8012@newsread1.news.atl.earthlink.net>... > When you aren't steering, there is little load on the power steering pump. > It is mostly just circulating the oil. A power steering pump is a positive displacement pump. When idling, the pump is providing its highest, full system pressure - up to the limits of the pressure relief valve. When you steer, it simply directs some of that available pressure to the correct valving inside the steering box/rack. Since it is tripping the pressure relief valve - and providing FULL system pressure - power steering pressure is at its highest at idle - using a corresponding percentage of engine power. Revving the engine does not produce more system pressure since the pressure relief valve maintains the maximum system pressure - simply spilling a higher volume of fluid back to the reservoir to maintain the maximum design pressure. If you want to lower the load on the engine, replace the pressure relief valve with one that has a lower pressure relief value. Since you will be lowering the system pressure, you will also, of course, end up with less power assist. No free lunch!!! > C. E. White <cewhite3@mindspring.com> wrote in article > <_HpVe.10967$_84.8012@newsread1.news.atl.earthlink.net>... [quoted text clipped - 12 lines] > When you steer, it simply directs some of that available pressure to the > correct valving inside the steering box/rack. Nnnnnooo..... at least not the PS systems I'm familiar with. Yes, its a positive displacement pump, and yes when its idling it is pumping its full VOLUME. But until the steering gear redirects the flow to the cylinder to do work in moving the rack, the pressure at the output of the steering pump is essentially zero because the steering gear (at idle, wheels dead-ahead) just directs the fluid right back to the pump return line. You can stick a pressure gauge on the PS supply hose and see the pressure shoot up (and thus increase the load on the pump) when you turn the wheels. > When idling, the pump is providing its highest, full system pressure - up > to the limits of the pressure relief valve. Not hardly. Excess volume is diverted back to the reservoir. > When you steer, it simply directs some of that available pressure to the > correct valving inside the steering box/rack. True. > Since it is tripping the pressure relief valve - and providing FULL system > pressure - power steering pressure is at its highest at idle - using a > corresponding percentage of engine power. False. > If you want to lower the load on the engine, replace the pressure relief > valve with one that has a lower pressure relief value. Sounds like the latest Rice Tuner trick. > No free lunch!!! Certainly not, though the simple concept of pressure regulation is employed in P/S systems so that max pressure is not built up when it isn't needed. Toyota MDT in MO > C. E. White <cewhite3@mindspring.com> wrote in article > <_HpVe.10967$_84.8012@newsread1.news.atl.earthlink.net>... [quoted text clipped - 30 lines] > > No free lunch!!! You actually have it backwards. When you are not steering, the oil circulates freely. When you steer, you essentially put a blockage in the return line, which creates pressure in the system and applies it to the appropriate side of the hydralic cylinder. Normally the only time oil passes throught the relif valve is when you crank the steering over against the stop and hold it there. This essentially blocks the return line while the stops prevents the steering gear from moving and reopening the return line. This is when you get the squealing noise (caused by oil passing through the relief valve). Ed C. E. White <cewhite3@mindspring.com> wrote in article <vHIVe.11266$9i4.6847@newsread2.news.atl.earthlink.net>... > > C. E. White <cewhite3@mindspring.com> wrote in article > > <_HpVe.10967$_84.8012@newsread1.news.atl.earthlink.net>... [quoted text clipped - 37 lines] > throught the relif valve is when you crank the steering over against the > stop and hold it there. This essentially blocks the return line while the > stops prevents the steering gear from moving and reopening the return line. > This is when you get the squealing noise (caused by oil passing through the > relief valve). > > Ed Put a pressure guage on the output side of a P.S. pump at idle, then get back to me.......... > Put a pressure guage on the output side of a P.S. pump at idle, then get > back to me.......... Been there, done that. Pressure is zero until you turn the wheel. Next? Steve <no@spam.thanks> wrote in article <ju2dnQfQG8HvorXeRVn-tg@texas.net>... > > Put a pressure guage on the output side of a P.S. pump at idle, then get > > back to me.......... > > Been there, done that. Pressure is zero until you turn the wheel. Next? I DID say on the output side of the PUMP.....not the steering box. If you got zero pressure on the output side of the PUMP, it is apparent that you haven't been doing it correctly......that, or you have been allowing bad pumps to slip past you. From a GM (not Chilton, Haynes, Motor, etc.) Service Manual..... 1. Disconnect pressure hose at union of pump, use a small container to catch any fluid which might leak. 2. Connect tool J-5176-21 to pump union. 3. Using pressure guage J-5176-02, adaptrerfitting J-5176-22 connect gage to other hose (Fig. 3-2) The power steering system may be tested using either J-5176-02 as described here or with available tool J-25323 Power Steering Analyzer which will measure flow rate in adition to pressure. 4. Open valve on gage. 5. Start engine, allow system to reach full operating temperature and check fluid level adding fluid if required. When engine is at normal operating temperature, the pressure reading on the guage (valve open) should be in the 552-862 kpa (80-125 psi) range. If this pressure is above 1380 kpa (200 psi) check the hoses for restrictions and poppet valve for proper assembly. ******************************************* If you got ZERO pressure at the pump output at idle speed....as YOU claim.....it would appear that you have a pressure problem.... ......or would YOU like to explain why the General Motors factory service manual is wrong in stating that there should be 80-125 p.s.i. there - NOT zero????? Next? > When engine is at normal operating temperature, the pressure reading on > the gage (valve open) should be in the 552-862 kpa (80-125 psi) range. > If this pressure is above 1380 kpa (200 psi) check the hoses for > restrictions and poppet valve for proper assembly. > ......or would YOU like to explain why the General Motors factory service > manual is wrong in stating that there should be 80-125 p.s.i. there - NOT > zero????? Well, this is really a distraction, but GM f.cks up so much other stuff (such as their use of the nonword "gage" in place of "gauge", and, um, the design and engineering of virtually everything they sell) that errors in their FSMs would not surprise me. Daniel J. Stern <dastern@127.0.0.1> wrote in article <Pine.GSO.4.58.0509141512390.21006@alumni.engin.umich.edu>... > Well, this is really a distraction, but GM f.cks up so much other stuff > (such as their use of the nonword "gage" in place of "gauge", and, um, the > design and engineering of virtually everything they sell) that errors in > their FSMs would not surprise me. So, based on your statement, would you be willing to hold your thumb over the end of the pressure-side hose while the engine is running?????? .....or would you rather assume that GM just MIGHT be close with their estimate of pressure????? There's just something about a printed specification in a factory service manual produced by an international corporation that places it somewhat above the statements of a total stranger - the credentials of whom have not been established - on the internet.... I used to try and give sound advice, but with so many whackos out there giving such unsubstantiated, off-the-wall, obviously inexperienced advice, I figure it's a lot more fun screwing with the people who THINK they know something. .....and, yes, the varied spelling of guage/gage is verbatim from the manual.. > Daniel J. Stern <dastern@127.0.0.1> wrote in article > <Pine.GSO.4.58.0509141512390.21006@alumni.engin.umich.edu>... [quoted text clipped - 7 lines] > So, based on your statement, would you be willing to hold your thumb over > the end of the pressure-side hose while the engine is running?????? No, because then there *would* be pressure. > .....or would you rather assume that GM just MIGHT be close with their > estimate of pressure????? Depends on the test procedure. If it involves having the pressure gauge simply teed into the hose, I would suspect that they're wrong. If it involves actually removing the hose and putting a pressure gauge at the end of it, then maybe they're right. > There's just something about a printed specification in a factory service > manual produced by an international corporation that places it somewhat > above the statements of a total stranger - the credentials of whom have not > been established - on the internet.... have you thought at all about how a power steering system actually operates? > I used to try and give sound advice, but with so many whackos out there > giving such unsubstantiated, off-the-wall, obviously inexperienced advice, > I figure it's a lot more fun screwing with the people who THINK they know > something. It's less fun reading posts from people who think they know something simply because they read it in a book therefore it must be true. (although I must admit that's a little better than someone who read something on tha intraweb therefore it must be true...) > .....and, yes, the varied spelling of guage/gage is verbatim from the > manual.. well, there's only one correct spelling of the word "GAUGE..." nate > ... with so many whackos out there > giving such unsubstantiated, off-the-wall, > obviously inexperienced advice, ... Like yourself. > obviously inexperienced advice, Sorry, I just wanted to see that one more time. Hee hee! Toyota MDT in MO >So, based on your statement, would you be willing to hold your thumb over >the end of the pressure-side hose while the engine is running?????? Restricting the hose with the end of your thumb will increase the flow RATE at that point, but the flow VOLUME is the same. The pressure on your thumb corresponds to the amount of increase in the flow rate that is necessary to get past the restriction. > Steve <no@spam.thanks> wrote in article > <ju2dnQfQG8HvorXeRVn-tg@texas.net>... [quoted text clipped - 45 lines] > > Next? Your "understanding" of GM's service procedure is flawed, as is your contradiction from first post to current one. I don't expect you to grasp this, but maybe someone else reading this, who is equipped with logical comprehensive skills, will benefit from an explanation. Measure at the pump, or measure at the gear, it's all the same (save for minor real world losses such as hose swelling, tubular friction losses, fluid turbulence over distance, etc.) So even if Steve *were* a fool (which he isn't) and wanted to waste time, he would measure at the steering box high pressure fitting. Of course it's typically easier to measure at the pump fitting, so that's where a sharp guy like Steve would actually measure it. You, OTOH, would probably do all of this *theoretically* in a service manual that hasn't a smudge or grease stain on it. So Steve would see a very small pressure reading at idle with no steering input, or any engine speed, really -- even if he measured at the gear!!! The pressure would be much lower than the max allowable quoted in the GM test. The fluid, as stated by others and myself, is being recirculated through the system, IOW there is minimal restriction to flow. The system is operating at minimum restriction WHEN not under steering demand as dictated by referential rotation of the torsion valve in the input shaft of the steering gear. I'll admit that Steve did use the word "zero" to describe pressure at unloaded idle. I know what he means, because, as I stated above, there is VERY LITTLE pressure in the high side, just a ton of fluid volume trying to make it's way through the two hoses and the reductions present throughout the steering gear valving. Actual truth: Lower pressure exists in a relaxed steering state than when steering input creates high side system restriction. You previously stated: "When idling, the pump is providing its highest, full system pressure - up to the limits of the pressure relief valve." Now you cite GM to prove your point that at idle there is NOT max pressure. Hmmmmm........ contradiction, anyone? Actual truth: At max system load, say, steering to the lock, max pressure is realized at the point just before the overpressure relief valve opens. This *could* occur at idle. Hey, if the valve spring is particularly stiff, it could be at higher RPMs. You see, a PDP *can* create higher pressure at higher RPMs if the pump tolerances are such that fluid bypass doesn't occur and the same or higher restriction is still available to the high side. (And the necessary HP is available, and the belt doesn't slip, and the housing doesn't explode, etc. etc.) You can respond and blather about what you REALLY meant to say in your posts, but then you would have to allow Steve his one grievous error in using the word ZERO, when he meant VERY LITTLE. Or you could try to learn something instead of insisting that your book learnin' beats out our book comprihenshun' and real world practice. Toyota MDT in MO > Steve <no@spam.thanks> wrote in article > <ju2dnQfQG8HvorXeRVn-tg@texas.net>... [quoted text clipped - 8 lines] > > I DID say on the output side of the PUMP.....not the steering box. Correct. Which is the same as the input side to the steering box. Which is at zero (essentially- sub 10 PSI with good hoses) pressure when the wheel is in neutral dead-ahead condition. > If you got zero pressure on the output side of the PUMP, it is apparent > that you haven't been doing it correctly......that, or you have been > allowing bad pumps to slip past you. Not at all, since there is not SUPPOSED to be pressure there until you turn the wheel! > From a GM (not Chilton, Haynes, Motor, etc.) Service Manual..... <snip> > ......or would YOU like to explain why the General Motors factory service > manual is wrong in stating that there should be 80-125 p.s.i. there - NOT > zero????? > > Next? Maybe because GM designs stupid PS systems and I'm looking at Chryslers? Not likely, even if GM WERE that stupid, running the pump against 80-125 PSI under neutral-steer condtions would generate so much heat that the fluid would roast in no time. Maybe the "special tool J-5176" places a test restriction in the line in order to test the steering pump. What I know is that if you simply "tee" a gauge into the pump OUTPUT hose with the rest of the system normally connected, you see virtually zero pressure until you start to turn the steering wheel. Then, pressure rises against effort and will max out when the relief valve trips as you turn the steering wheel against the lock at the limit of its travel. I replied to this before, but th ereply seems to have vanished. The 80-125 psi is not the pressure necessary to operate the steering gear, it is just a reflection of the resistance in the circuit when you are not steering - .i.e. the pressure needed to overcome the interent restriction in the circuit when you are not actually steering. If you actually measured the pressure in this manner when you were steering, the pressure would be over 1200 psi. Regards, Ed White I replied to this before, but the reply seems to have vanished. The 80-125 psi value is not the pressure necessary to operate the steering gear, it is just a reflection of the resistance in the hydraulic circuit when you are not steering - i.e. the pressure needed to overcome the interent restriction in the circuit when you are not actually steering and the oil is basically circulating through the system. If you actually measured the pressure in this manner when you were steering, the pressure would be over 1200 psi. Regards, Ed White >If you actually measured the pressure in this manner when you > were steering, the pressure would be over 1200 psi. Ed, would you just stop and think about the implications of that statement for a second or two? 1200 PSI- in a rubber hose? More pressure than the main boilers of the USS Wisconsin produce? On a par with the combustion pressure in a diesel? > >If you actually measured the pressure in this manner when you > > were steering, the pressure would be over 1200 psi. [quoted text clipped - 5 lines] > More pressure than the main boilers of the USS Wisconsin produce? > On a par with the combustion pressure in a diesel? Those ain't no ordinary rubber hoses. If you cut one up they look like something that you'd use to drive the hydraulic cylinders for a backhoe or something. 1200 PSI is on the high side for a PS system but I suppose it is possible for certain systems held hard against the stops. 800-1000 PSI probably isn't unusual. nate >>>If you actually measured the pressure in this manner when you >>>were steering, the pressure would be over 1200 psi. [quoted text clipped - 9 lines] > something that you'd use to drive the hydraulic cylinders for a backhoe > or something. ' Except that the still don't have an internal steel braid like *real* high-pressure hoses do.... because they never see anything close to 1200 PSI. I forget exactly what the relief valve pressure setting on my Mopars is (the valve is inside the pump, so it limits what the rubber hose would ever see) but I think its order of 200-300 PSI, which is only achieved when you turn the wheel hard against the stops. > >>>If you actually measured the pressure in this manner when you > >>>were steering, the pressure would be over 1200 psi. [quoted text clipped - 16 lines] > hose would ever see) but I think its order of 200-300 PSI, which is only > achieved when you turn the wheel hard against the stops. Au contraire mon frere, just so happens I was just looking under the hood of a power-steering-equipped Studebaker the other day with the Bendix "ram" type power steering (think 60's Corvette style) and the hoses were badly weathered and the outer rubber layer was disintegrating. There is definitely a steel braid underneath there. IIRC the Bendix style actually runs at a lower pressure than some more modern systems, but that may be my mind playing tricks on me. nate > Au contraire mon frere, just so happens I was just looking under the > hood of a power-steering-equipped Studebaker the other day with the > Bendix "ram" type power steering (think 60's Corvette style) and the > hoses were badly weathered and the outer rubber layer was > disintegrating. There is definitely a steel braid underneath there. Well, Studebaker did merge with Packard, and Packard often took overkill in engineering to new extremes, too :-) I doubt you'll find steel braided PS hoses under any modern car hood... but I could be wrong. Multi-layer nylon braided hoses work fine (and last 20+ years) on all the cars I've owned. Sigh. The high pressure hose on the delivery side of the pump are not just "rubber hoses." See http://www.delphi.com/pdf/ppd/chsteer/pwr_strg_hoses.pdf Do you think hydraulic hoses are "rubber" hoses? Why do you think power steering pumps use O-Ring fittings? I just looked at the power steering pump relief valve specs for my Expedition. The minimum pressure that the relief valve opens at is 1300 psi. I think you need to do some research on the sort of pressures needed to actually operate steering gear. Ed > Sigh. The high pressure hose on the delivery side of the pump are not > just "rubber hoses." [quoted text clipped - 13 lines] > > Ed Just to clarify, 11.4 MPa is about 1650 PSI (for the metric-impaired.) nate > Sigh. The high pressure hose on the delivery side of the pump are not > just "rubber hoses." > > See http://www.delphi.com/pdf/ppd/chsteer/pwr_strg_hoses.pdf > > Do you think hydraulic hoses are "rubber" hoses? Yeah. Multi-layer einforced with nylon braiding, which puts puts them in the medium pressure capacity range. Real high-pressure rubber hoses have a steel braid layer also. > Why do you think power steering pumps use O-Ring fittings? You act as if O-ring fittings are particularly high-pressure fittings. They aren't, and some PS hoses actually use a metal-to-metal flare joint (which IS a high-pressure fitting). > I just looked at the power steering pump relief valve specs for my > Expedition. The minimum pressure that the relief valve opens at is 1300 > psi. OK, fine. But that's when you crank the wheel against the locks. Its still practically ZERO pressure in the high-pressure hose when the wheels are dead-ahead with no steering input. > > Sigh. The high pressure hose on the delivery side of the pump are not > > just "rubber hoses." [quoted text clipped - 12 lines] > They aren't, and some PS hoses actually use a metal-to-metal flare joint > (which IS a high-pressure fitting). OK. I agree flare fittings are often used for high pressure hydraulic connections, but why do you think O-rings aren't for high pressure connections? My farm equipment hydraulics use quick connects that use O-rings to provide the seals. Other permanent connections use flare fittings, but swivel fittings include O-rings. My farm equipment hydraulics work at much higher pressures than typical power steering systems. > > I just looked at the power steering pump relief valve specs for my > > Expedition. The minimum pressure that the relief valve opens at is 1300 [quoted text clipped - 3 lines] > still practically ZERO pressure in the high-pressure hose when the > wheels are dead-ahead with no steering input. I am in agreement with you, except the open flow pressure (depending on where you measure it) is significantly above zero, but certainly nowhere near the relief valve pressure. Flow resistance in the circuit (pressure drop through hoses, control valves etc) require that the open flow pressure at the pump outlet is above zero - otherwise there would be no flow. And I think they actually include an orifice in the control gear to guarantee a minimum open flow pressure. Ed >>>Sigh. The high pressure hose on the delivery side of the pump are not >>>just "rubber hoses." [quoted text clipped - 17 lines] > connections? My farm equipment hydraulics use quick connects that use > O-rings to provide the seals. O They're actually good to pretty high pressures, depending on the O-ring material and the type of O-ring groove. But there's a point somewhere around 5-8 kpsi (don't you love mixing metric prefixes with SAE units? ;-) ) where reusable O-rings will flow right out of their grooves. You can use one-use brass or copper O-rings up past that point, but even then there comes a point where you have to go to something that doesn't have a free-floating sealing element (the O-ring) to get pushed out of position. I'm an EE, but I work with MEs who build deep-submergence oceanographic pressure vessels. >>>I just looked at the power steering pump relief valve specs for my >>>Expedition. The minimum pressure that the relief valve opens at is 1300 [quoted text clipped - 11 lines] > think they actually include an orifice in the control gear to guarantee a > minimum open flow pressure. You're right. I've always tried to say "essentially zero" in previous posts. Depending on engine speed, it might actually be a few psi to a few tens of psi. The whole train of argument, though, was to point out that the pump DOES NOT continuously provide 100% of its working pressure to the steering rack or gear, as was claimed waaaay back up the thread. > Has any manufacturer tried fitting a clutch to a power steering pump in order > to prevent the pump from running when the driver is not steering much? I would [quoted text clipped - 3 lines] > Just curious if anyone has seen a system like this or knows why it is > impractical (perhaps the gas savings are neglectable). Seems like a lot of complexity for a little benefit. However, before I actually read your post (but had read the subject line) I was immediately reminded of the Studebaker mechanical power steering introduced in the early 50's. AFAIK all of the vehicles so fitted were recalled and retrofitted with Saginaw hydraulic setups however, and info. on this system is difficult to find. I haven't tried Googling for it, but if you have any mechanical curiosity, it might be a good read if you can find a description of it. Now I am trying to remember where *I* read an article on it... I think it was probably an old back issue of Turning Wheels (Studebaker club magazine) I do know I've seen at least one photograph of such a system - where you'd expect to see a PS pump, there's a belt-driven pulley with a U-jointed shaft going straight into the steering box. I believe that a system of clutches inside the steering box applied or released depending on what was required to provide the assist. I have absolutely no idea how well it worked, but apparently not well enough. nate (with a '55 coupe, with the early Saginaw hydraulic box. Did you know there's seperate sections of the steering box, one lubricated by the power section's fluid, and one lubricated by conventional gear oil? Neither did my car's previous owner!) >> Has any manufacturer tried fitting a clutch to a power steering pump in >> order [quoted text clipped - 33 lines] > power section's fluid, and one lubricated by conventional gear oil? > Neither did my car's previous owner!) Also, '55-'57 (and earlier) Chevy's had a *part-time* power steering; I believe you had to exert a certain amount of force on the steering wheel for the ps to give any assist. Felt much like conventional steering on the road, but like p-steering when turning corners/parallel parking. Did a nice job, other than leaking fluid, IIRC. s |
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