electric power steering pump?

[BlackVert]

anyone ever heard of an electric power steering pump?

how much pressure does the power steering system need to work?

would a fuel pump provide enough pressure?

 

[BlackVert]

ttt

 

[Michael Yount]

Power steering operates at very high pressures - MUCH higher than the fuel pump. Many new car systems are using electric powered steering racks - these are the steer by wire systems on high end cars -- there is no physical connection between the steering wheel and the wheels. Think a big-ass solenoid. Similar in function to the new drive by wire throttle on the 05 Stang - no cable between throttle pedal and throttle body; and drive by wire brakes on some of the big German sedans. Some of the hybrids are running either electric racks or electric pumps so you have power steering when the engine is turned off.

Retrofitting a Stang to either of those systems would cost a fortune and wouldn't offer any improvement over the systems that are on the car.

 

[BlackVert]

Thanks. I was just musing about the possibility of removing the parasitic drag on the engine from the power steering pump, but still having power steering.

It sounds like it not really feasible though.

Any guesses on what the PSI would be?

 

[Michael Yount]

You're not thinking it through. The parasitic drag wouldn't be eliminated. It would simply be transferred from the power steering pump to the alternator. The more current you ask the alternator to put out, the harder it is to turn.

But you're not the only one that thinks electric power is free....

 

[Michael Yount]

I believe the high pressure custom hose they made to mate the Ford pump to my Volvo rack is rated at something like 2250 psi. The power steering system deals with pressures that are an order of magnitude higher than the pressure put out by the fuel pump.

 

[crazypete]

Everyone is so pumped about drive by wire but I think it is a massive catastrophe waiting to happen 10 years down the road when connectors start to fray, wires strip, solenoids fail and electric motors become weak. There is no direct backup. If our PS fails, we can still turn the wheel. We can still brake and our throttle is still mechanical. Driving without these backups is a big gamble.

Get a 18:1 manual rack. It's not as bad as you think and it's lighter than either of the aforementioned setups and probably cheaper than electric.

 

[BlackVert]

You're not thinking it through. The parasitic drag wouldn't be eliminated. It would simply be transferred from the power steering pump to the alternator. The more current you ask the alternator to put out, the harder it is to turn.

But you're not the only one that thinks electric power is free....

I understand that it is not free, but isn't it almost certain to to be much less total drag than the cumulative drag from both the ALT and the PS?

But it sounds like the amperage required for a pump to supply enough pressure to the system makes it not very feasible. Otherwise, I would think people would have done it by now.

 

[Michael Yount]

BlackVert - why would you think it would take less overall power from the motor for an electric pump or rack? You're still doing the same amount of work with the steering - so a similar amount of energy has to come from somewhere - and that somewhere is the engine. The question is the efficiency of the mechanical pump/rack, vs. the efficiency of the alternator and the electric pump/rack. The only way there's a significant gain is (just like with electric fans) is if you can do away with the load entirely when you're driving straight - which is what the electric racks can do. But if you're simply driving an electric pump to power up the hydraulic rack - you're not gonna save much if any by converting to electric.

Pete - I wouldn't say a lot folks are hyped up by the drive by wire systems. The fact is that most folks don't know anything at all about how the mechanical systems in their cars work in the first place. So whether there is a direct connect or not between the steering wheel, brake pedal and/or gas pedal and the devices being controlled is completely lost on most consumers. It's only the enthusiasts for the most part that know what's up with all that - and we're a VERY small % of the driving public. And the systems all have fail-safe modes. The automotive engineering folks talk frequently with their lawyers - they're not gonna put a system out there that's any worse in failure mode than what you have in our cars if you, for example, have a hydraulic failure in a brake line, or break a tie rod end.

As to what happens when all that power stuff starts to fail - well - we're already pregnant with that one. Today's expensive luxury cars will be doomed to economic-driven junk yard status. The 2002 BMW 745 had no less than 125 electric motors in the car. Imagine when that stuff and it's control systems start to fail. Many cars with lots of miles left in them will be doomed to the junk yard because the 3rd or 4th owner simply can't afford to fix a power seat, or a power braking/steering system.

 

[Michael Yount]

Having experienced a broken throttle cable - you're pretty well stuck at least until you can pull over and turn the idle speed up a bit to allow you to drive it home. And the power steering is so hard to turn that many drivers - especially women and men that aren't very strong - would have a hard time turning the car at low speed anyway is the pump failed.

 

[crazypete]

The only reasonable backup to drive by wire steering is an old fasion steering shaft. I cant see any other solution other than redundant solenoids, redundant steering wheel sensors and redundant actuators. By the time all that redundancy is built in, is the system better than the original and cost effective at the same time? No. How can it be? PS pumped steering has been pleasing customers for decades on existing high end cars...it's simple (reliable) and has an inherent backup in it's mechanical design, its smooth and quiet. I guess I'm getting old if I dont see the revolutionary breakthrough in drive by wire.

Fly by wire is different. At 10000 feet, if you suddenly cant turn, you still have a good shot at pulling the double o's and taking the silk elevator. Senders and actuators in that environment are much more efficient than their hydraulic and cable driven predecessors. This is what got people excited about it I guess....if it works in the stealth fighter/f-16, why not put it in my shiny new car?

On the ground...if you suddenly cant steer your car, you're probably testing out your airbags or hugging the inside of your windshield in a second or two.

BTW....the PS pump gives absolute negligable (1 hp or so) drag when going straight. Additionally, PS drag when turning is irrelevant since you never drag race in circles anyways and full throttle turning produces interesting results best left to other people. Keep the pump or go to a manual rack is weight is a concern.

 

[crazypete]

I dotn think low speed is the problem. At low speed , you still have your brakes and can salvage the situation somewhat by screeching to a stop and taking a little fenderbender. I'm talking about highway driving....hitting a pothole and having a sender come loose.

I've actually lost a motor on the highway. Going 89 south through vermont....the engine just died. I let off the clutch to neutral it and lost the PS. It wasnt super easy wax-on wax-off but it wasnt super hard to turn either. It was steerable and that was enough to safely coast to a stop.

I always wondered..... why didnt "gearbox" steering do better? Some gear multiplication would do the same thing as all this high pressure tubing and pumps and leaky racks.

 

[Michael Yount]

You're preaching to the choir Pete - I don't favor the drive by wires because 'feel' is artificial. And feel - steering and brakes especially - is critical to us old road racers/autocrossers.

And speaking of road racers/autocrossers - there are actually people who have been known to race their cars in ways that require the wheel to be turned while the throttle is applied. Your biases are showing there Pete. Pull your pants up.

 

[Michael Yount]

The same issues are possible in cars with conventional steering and brakes - it's just that different pieces have to break. If you've ever lost a ball joint or end link at speed, or had a wheel/tire come off - it's pretty hairy. I suspect properly engineered electric systems have equal or lower chances of failure.

Worm/roller boxes 1) take up space, 2) don't provide the same feel, 3) add weight and 4) don't offer the packaging flexibility that rack/pinion does. Better mouse trap. For a drag car where you'd just as soon not turn - go for the old steering boxes. For those of us that actually like lateral and braking g's better than acceleration g's - we'll take our racks thanks very much.

 

[Stang8URMPRT]

I also believe running the p/s off an electric motor would give you more power then having the alt make more power. I highly doubt the alternator would take "that much more power" to turn another 5-10 amp. With that reasoning, no one would run an electric water pump. I'm sure you can rig up something like the small electric motors used to run mechanical water pumps. Please Mr. Yount... gimme something saying the alternator having to pull 5-10 more amps takes a drastic amount more power to turn vs. the power steering pump.

 

[crazypete]

Actually, I dont drag race. For some inexplicable reason...I just like to build fast cars then baby them. Maybe the competition bug will bite me someday (soon, methinks ).

Those throttle turns are not at full throttle though, right? You brake right before a turn to plant the front, hold speed in the middle and rocket out at the turn exit...but the rocketing is not WOT, is it?

My WOT turning usually results in interesting spinning experiences and lots of screaming and leaving loopdey loop rubber marks on the road. Mustangs just like to spin. I dont.

By the way..in defense of power steering.....when I got my FR 18:1 rack...I never envisioned how punishing it can be just to keep the wheels straight with a rack. You can feel each "hit" as potholes and wavy roads try to jerk the car around. You should see my street! It's a slolom. My friends from south mass who live on unpaved roads visit me and say my street is worse than theirs!

 

[crazypete]

To turn a pair of tires while the car is stopped takes more than 5-10 amps of 12 volt current. I think 30-50 amps minimum..

 

[Boss 351]

No the electric water pump is turned off during the 1/4 mile run, and turned back on at the other end of the track and so would the electric steering, if such a product existed IMO...

 

[BlackVert]

BTW....the PS pump gives absolute negligable (1 hp or so) drag when going straight.

who would've thought?

 

[Michael Yount]

Pete - go to driving school my friend - yes you are full throttle AS SOON AS YOU CAN BE exiting the turn. Sometimes traction limits you, sometimes not. In fact a 'straight -a-way is defined as the area between any 2 places on the track where you can have the throttle flat on the floor. To road racers/auto-xers, 'straights' have nothing to do with whether the steering wheel is turned or not; they have everything to do with where the throttle is.

8urimport - What makes you think you can generate enough power to run a powersteering pump with only 5 to 10A? We don't have to 'hope', 'think', or just guess at the numbers here guys. People actually DESIGN this stuff. As others said, the biggest benefits of electric fans and water pumps is that they don't run all the time - and you can turn them off for 8-12 seconds during the run.

10 amps at 14 volts is 140 watts. Let's get really conservative and say the alternator generates at 60% efficiency - so it takes 233 watts of power from the engine to generate that 140 watts of power for the pump. That's a whopping .3HP -- so you're right, that's not much. It's probably less than that as the alternator is probably more efficient than 60%. Think about it - do you think you'll be able to generate a couple thousand psi of hydraulic pressure with enough volume to drive the rack with a .3HP electric motor? That doesn't pass the common sense test for me. It's gonna take more than that - how much more? About the same amount it takes to drive the mechanical pump -- remember, the motor still has to drive basically the same hydraulic pump. You're just driving it off of an electric motor instead of off a pulley from the engine. So what you're really doing is comparing the losses in the mechanical pulley system with the losses in the alternator/wiring/electric motor. Not enough to gain there to justify the swap - and it may even take more.

The reason water pump and fan swaps work is because 1) you don't have to run them full out all the time, and 2) they're sized for the max needed at low speeds. The mechanical units have to be sized to flow enough at idle -- and then they consume even more power as revs increase. In the case of the mechanical fan - it's bass-ackwards. It moves the least it's capable of when you need it most; and it consumes the most power (at revs) when you don't need it at all. Now there's a potential power saver - and the reason why you rarely see vehicles with mechanical fans any longer.