This can happen (and does) with the electric pump failing as well as the alternator failing. Not just gm either.
At least with the belt system you would normally get some warning about belt failure before it happened; and a check on it at every service.
Progress ! Advancing backwards !
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NC. The problem with this set up is that there are just too many potential failure points in the chain to give acceptable reliability. Involving an extra stage of energy conversion (mechanical to electrical, then back again) is just a lunatic scheme compared with the well established and reliable hydraulic pump and rams used on older and larger vehicles. Even an alternator diode or brush failure will affect the steering on these newer vehicles. Cost, of course, has been the driving factor here, as usual.
I accept that either system relies on a belt drive, but putting the whole load through the alternator (which has the smallest radius pulley and hence the maximum stress) is not my idea of a well engineered system - I'll stick with a separate hydraulic pump.
659.
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I tend to disagree with your view about cost.
I would say that electric power steering is just the next step in gaining energy efficiency - the electric system will only draw engine power when it is needed, rather than taking power all the time the engine is running. Of course, it was more reliable when engines drove cooling fans directly from the water pump pulley, but I don't think that many would go back to that system. (I accept the FWD drivetrain layout makes that almost impossible anyway)
I can't believe that the electrical PAS system is cheaper in terms of component costs - although it is probably a lot simpler to install on the production line.
I take it you are talking of drive belt stress - I don't think that many are being shredded, so, probably not a problem.
However, I think that it might be better if the system could run from the battery for a short period if the alternator were to fail at speed.
Number_Cruncher
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I would say that electric power steering is just the next step in gaining energy efficiency - the electric system will only draw engine power when it is needed, rather than taking power all the time the engine is running.
It's only a matter of time before coolant pumps go the same way. I believe there are engines being designed now with electronically controlled, motor driven coolant pumps.
All this stuff is great in theory on a new-ish car that is covered by a warranty, but after 5-10 years of vibration, damp, temperature extremes and all the other things that electronics are notorious for not coping well with, will it be such a good idea? Not only will an electric pump be susceptible to the same bearing / seal / impeller failure of a mechanical pump, but you now have electronic sensors, a control unit, wiring and connectors that have to be working properly too. Over time, this has to have an impact on reliability.
Cheers
DP
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Yes, I think that's fair comment.
But, you could embedd the alternator windings into the flywheel, and make it into a combined starter/alternator/driveline damper. If the PAS and coolant are electrically driven, you could do away with the drive belt, and build an engine without a crankshaft penetration in the front cover, thus doing away with the crank oil seal, and the pulleys, belts and tensioners of the old drive. This would probably need a different form of torsional damper for the crankshaft nose, as the oil would attack the rubber if you simply housed a typical current design inside the crankcase, but this is surely not difficult to design.
If such systems became commonplace, the drive motors and sensors would soon be available cheaply (I remember having the same discussions/debates when electronic fuel injection became the norm in the early 90's, and contrary to the expectations of the cynics then, ECUs arent breaking expensively every few years). In general, most ECUs are extraordinarily reliable, you are many times more likely to have a simple wiring fault.
While I agree that if you make a system more complex, you do tend to decrease the reliability, I would say that most cars today are amazingly reliable compared with the cars we all found acceptable 15 - 20 years ago. There is, of course, a trade off - how much cost and reliability are you prepared to trade to give better performance and economy and emissions. Today's cultural outlook is pushing design towards the performance and economy side of the equation.
Number_Cruncher
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And the car is. ???????? Then the alternator fails the battery voltage can drop below the threshold and the power steering pump shutsdown but I would only expect the voltage to drop thet far if you were driving at night with all the lights and blower on. Regards Peter
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I reckon its a mk 4 Astra, designed before Vauxhall started fitting EPS warning lights on the instrument cluster for the electrohydraulic power steering system.
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Yes, an Astra. Nothing to do with the belts, just a sudden complete alternator shut-down. Indeed at 70 the pas was not really needed, but what if it happened on a roundabout. Fortunately I've recently had heavy cars without power assist, and still have the muscles to match, A concern is that nowhere in the handbook does it say anything about the loss of pas if the alternator warning comes on. I think this should be highlighted, rather than the general instruction to refer to dealer.
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And ~£300 and 2 hours at dealers
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Indeed at 70 the pas was not really needed, but what if it happened on a roundabout.
Again, not much., PAS is really a parking aid. Once you're moving and the wheels rotating, the steering is a lot lighter anyway.
{ps, I've added the car details to the subject header}
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Ok I said roundabout, I was thinking urban driving/mini roundabout. At below 15 the steering really loads up, and below 5 virtually impossible to get full lock in time to complete any manoeuver in 1 go
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Yes, an Astra. Nothing to do with the belts, just a sudden complete alternator shut-down. Indeed at 70 the pas was not really needed, but what if it happened on a roundabout. Fortunately I've recently had heavy cars without power assist, and still have the muscles to match, A concern is that nowhere in the handbook does it say anything about the loss of pas if the alternator warning comes on. I think this should be highlighted, rather than the general instruction to refer to dealer.
Astra mk 4 is old technology now, Thats why the newer designs of Vauxhalls with this same electrohydraulic steering setup have the EPS warning light fitted on the instrument cluster to warn of power steering problems / failure.
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So GM's answer to the problems with this convoluted technology is to fit a warning lamp to tell you that your steering assistance is faulty - a good time to take your eyes off the road. What a laughable "solution".
NC. The company I worked for looked long and hard at flywheel alternators and the like and a real advantage was never found. The cost of repairs to such an integrated unit could be frightening - at least our friend here can "just" unbolt his alternator and fit a new one.
I think other than cost (reduces the number of driven items), the main reason for the adoption of this type of power steering on smaller vehicles is space. Now that aircon is a universal fitment, it's getting hard to fit all these driven devices around the free end of a small engine - particularly when installed transversely.
I'll stick with my hydraulic system. The "idle" losses when little fluid is being displaced are very low with the best pumps.
659.
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You already have warning lights for low brake fluid, low oil pressure & over temperature, whats wrong with one more warning light for the power steering?
At least Vauxhall now fit a warning light for the power steering, some other manufactures dont.
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The obvious advantage to electrical drives is flexibility. To take a simplified example, an electric fan can do a great job of cooling while the engine is only ticking over in traffic, where if you designed a hard driven mechanical fan, you would have to over-size it to enable good cooling ticking over in traffic, and then pay the penalty in having to drive it all the time when motoring at speed.
I agree that maintenance of an integrated flywheel unit could be problematic - however, if it were designed with maintenance in mind (like Vauxhall FWD clutches of the 80' and early 90's), then, I'm sure that problem could be mitigated.
I suspect we will all see the pros and cons such features in a different light, and I can understand your view of wanting to stick to belt driven PAS. In our case, we have one electric PAS, and one mechanical.
I'm not so sure I agree with you about the losses - the hydraulic pump is a fixed displacement, and working against a pressure relief valve when idle will still absorb power. Now, an electronically controlled variable displacement PAS pump might be a good compromise between our extremes of view! Again, PAS pumps have to be oversized, because they have to provide sufficient assistance at tickover, as soon as you raise the revs beyond tickover, you are just wasting power pumping fluid past the pressure relief valve.
Number_Cruncher
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This is getting like a good natured design discussion - I'll have another go:
An electric fan drive certainly gives versatility and is essential with a transverse engine (although Peugeot, bless them, did once try a "round the corner" belt drive). Where mechanical arrangements permit, as in a NS engine installation, a viscous coupling serves very well, providing a large air flow if required at high temperatures with virtually no idling losses - on my car you can hold the fan whilst the engine is ticking over cold (if you're brave). Again, as long as the layout is favourable, you can avoid two energy conversions and utilise high energy absorption in the fan when and only when you need to.
Papers have been written on flywheel alternators (I wrote one), but although access is a major issue, there are potential problems with siting semiconductors in poorly ventilated areas prone to heat soak and any sliding contacts will have unacceptable linear speeds and will be prone to contamination. Brushless machines give a less good performance per unit copper weight due to there being an extra air gap. I'd better stop there.
Modern PAS pumps are indeed variable displacement (swash plate drive) and relatively little energy is expended pushing high volumes of fluid through relief valves. The better pumps tend to be fitted to the more upmarket vehicles though - too expensive for Ford and GM.
659.
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>>This is getting like a good natured design discussion
Indeed, most enjoyable!
Yes, the viscous drives are quite good when they work properly. I can remember replacing quite a few on Carltons and Senators though - are they reliable now? My father used to have some trucks with a good system - Leylands with the Rolls-Royce Eagle engines were fitted with a pneumatic fan clutch, which decoupled the fan from the belt drive until the engine reached a given temperature. Didn't Chrysler 180s have a similar set up, but using a magnetic clutch?
Are the sliding speeds for a flywheel alternator too high? I can imagine that clutch contamination would be an issue, but surely that's something that could be overcome by fitting the brush spec to the application. Is brush life dependant upon obtaining almost hydrodynamic conditions with charged gas instead of oil? (This is true for the brushes used in some rail traction motors, and if you want to tow the train, you have to lift the brushes because they don't create the cushioning layer of charged gas unless there is some current passing) Would you necessarily mount the semi-conductors in the heat soaked area - could they not be remotely sited?
I suppose that the energy you use in pushing fluid past the relief valve depends upon how high the system pressure is set to be - but the pump only sees a delta p across its ports wherever the fluid goes, and given given this, the pump's displacement, and the angular velocity, you have the power consumption.
I didn't know about the modern pumps being variable displacement - although it's quite an obvious thing to do to reduce energy consumption.
Where I think the electric PAS systems are lacking is in their need to convert back to hydraulic power. The newer systems that can use an electric motor to directly add assistance will be potentially even more flexible.
Number_Cruncher
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