Hydraulic steering vs electric?
Discussion
Max_Torque said:
Mr2Mike said:
MagneticMeerkat said:
In conclusion, therefore, the method of providing power assistance isn't of much relevance.
That was a long post just to make a pointless and incorrect conclusion.The feel isn't so much about the amount of assistance provided as the internal friction within the steering system. With an EPAS system (at least the one on the Civic), when it's providing little or no assistance (i.e. higher speeds) you are effectively turning the assist motor via the worm and wheel, and via the torque sensor which is effectively a spring. This can give enough friction to destroy any feedback and make the steering feel imprecise.
Because your car only has a 12v battery, an electric machine powerful enough to move the steering road wheels when at zero speed (say 1kW) is a big, heavy and high inertia device that must be coupled to the steering rack bar via a large reduction ratio (in order to provide enough force). The rotational inertia of the motor is therefore referenced to the racks linear motion via the gear reduction ratio, and hence appears to be massive. So, high frequency vibrations, typically those that are a result of road surface, tyre tread / carcase shuffling etc, get damped and do not make it up to the handwheel. This results in a "lack of feel" to a skilled driver.
Because these are damped by the motors inertia, the system cannot even measure this high frequency component, no matter what torque sensor or control bandwidth is available.
Later systems in the last couple of years have moved to low inertia high torque brushless motors mounted directly on the rack, driving via a lower reduction ratio in an effort to increase the systems control bandwidth. These electric racks look like this:
In future, as the Tier1 suppliers like Valeo, Bosch, and Denso, revise and improve there steering system products i can't see any reason that we couldn't return to really excellent levels of feedback at all frequencies, especially when we move to a higher vehicle system voltage (42V etc)
However, the biggest "Killer" of steering feel over the last 15 years is NOT the steering system itself, but the vehicles tyres and chassis settings!
Tyres are now very wide, and very very stiff / low profile. Those lovely old skool changes in weighting as the tyre started to slip were more a result of the centre of pressure moving around the geometric steering centre point, as the tyre carcass deformed and the vehicle rolled. Modern cars have extreme lateral stiffness, and because they are heavy and powerful, must control the interaction between contact patch and steering geometery very closely (otherwise the large forces will just rip the wheel out of your grasp!
Cars which have classically good steering feel are the ones that are light, have relatively low lateral limits on taller, narrow tyres. As a result, these show the largest and most linear change in handwheel loadings verses tyre slip angle. And being light, have small lightweight suspension/steering components with low inertia, and hence do not damp out the higher frequency road surface vibrations etc
Edited by Max_Torque on Sunday 28th December 12:08
buggalugs said:
You've undersold the complexity of the hydraulic system a little bit there.
How do you work that out?EHPS systems still uses basically the same racks.
EPS or column mounted systems use a rack minus the hydraulic parts but there is still a rack and what that lacks in the few parts that make the difference between assisted and no assisted is more than made up for by the column assemblies added complexity.
so no I have not underestimated the system and besides the rack is an assembly,it counts as one unit.
If you want to be pedantic lets have an exploded view of a EHPS system including all its sub components,including all those components that make up the various electronic parts and all the parts that supply power or data to the system,or the same for the EPS/column system.
Edited by shoehorn on Sunday 28th December 12:58
shoehorn said:
buggalugs said:
You've undersold the complexity of the hydraulic system a little bit there.
How do you work that out?EHPS systems still uses basically the same racks.
EPS or column mounted systems use a rack minus the hydraulic parts but there is still a rack and what that lacks in the few parts that make the difference between assisted and no assisted is more than made up for by the column assemblies added complexity.
so no I have not underestimated the system and besides the rack is an assembly,it counts as one unit.
If you want to be pedantic lets have an exploded view of a EHPS system including all its sub components,including all those components that make up the various electronic parts and all the parts that supply power or data to the system,or the same for the EPS/column system.
Edited by shoehorn on Sunday 28th December 12:58
The issue with hydraulic PAS is as follows:
1) it has a mechanical "calibration" that cannot be modified between platforms without hardware changes (unlike EPAS, that simply can be flashed with a different calibration) hence, you have parts commonality across your fleet, with the corresponding cost savings
2) it is "dumb". To add technologies that are rapidly becoming std, like lane assist, park assist, dynamic steering control, steering mode / weighing selection etc is either not possible, or extremely complex.
3) It costs more to assemble, uses fluids that have a service life, and must be "bled and leak checked during manufacturing. It also needs fluid reservoirs and inspection / servicing
4) It has a high parasitic loss, as the hydraulic pump is "open spool" and hence pumping fluid around the system at all times, even when not steering. This is typically worth between 3 and 5 g/km CO2 and hence with modern cars dipping into the low 100's, becoming an un-acceptable loss (If you are buying a big V8, with say 300g/km, it is less important, but the majority of the market is LOW CO2.
5) The system cannot "self diagnose". Steering system faults cannot be spotted and reported by the steering system, something that the EPAS can obviously do.
6) It requires your engine to have a larger,more complex FEAD (Front End Accessory Drive) and the extra belt, mounts, and tensioner all cost money, add complexity, mass, and limit service life.
7) It is "cross system" dependent. With the rack being on the subframe, the pump on the engine, and the reservoir often on the chassis. This is a real PITA, as it requires flexibility of the interlinking services, and adds significant lead time and design complexity (your chassis design team must liase with your engine team, and your cooling team, and your crash team, and your "underbonnet" team, to ensure that the steering systems, which interacts with all those systems, fits, does not clash etc. Then you must carry out millions of miles of testing to ensure the pipes do no vibrate, chaffe or age, the system doesn't overheat, throw it's belt, fail it's tensioner etc etc etc.
EPAS is easier to manufacture/service and results in higher fuel efficiency, so when in early 2012 it also became cheaper than existing HPAS it became a no brainer to fit it. Even companies like Porsche, who had a "we won't be going EPAS" stand until then, could not ignore the benefits and hence included it on their latest models.
Edited by anonymous-user on Sunday 28th December 13:17
shoehorn said:
buggalugs said:
You've undersold the complexity of the hydraulic system a little bit there.
How do you work that out?EHPS systems still uses basically the same racks.
EPS or column mounted systems use a rack minus the hydraulic parts but there is still a rack and what that lacks in the few parts that make the difference between assisted and no assisted is more than made up for by the column assemblies added complexity.
so no I have not underestimated the system and besides the rack is an assembly,it counts as one unit.
If you want to be pedantic lets have an exploded view of a EHPS system including all its sub components,including all those components that make up the various electronic parts and all the parts that supply power or data to the system,or the same for the EPS/column system.
EPS is simpler than a hydraulic setup, it has fewer parts, if something's wrong it will tell you what and and there's no fluid to worry about. You can argue that black's white if you want but I remain unconvinced!
Electro Hydraulic Power Steering (EHPAS) was a Stopgap. It enabled the manufacturers to reduce parasitic loses and add functionality on existing platforms without having to do a compete chassis/BIW re-design. Because the steering rack is common with conventional engine driven Hydraulic assistance, the OEM's only had to package the new electro hydraulic power unit and they could get most of the end user benefits. At the time (mid 2000's) true EPAS was expensive as it was a low volume, unproven product, and was generally a "Low power" solution (brushed motors, separate control unit) that could not be used on the sort of (large/premium) platforms that could actually afford to add it!.
Between 2005 and 2010, the Tier1's spent millions developing and integrating there EPAS product portfolio's, and now the integrated electrically assisted rack is a high volume, low cost device.
Between 2005 and 2010, the Tier1's spent millions developing and integrating there EPAS product portfolio's, and now the integrated electrically assisted rack is a high volume, low cost device.
Max_Torque said:
Cars which have classically good steering feel are the ones that are light, have relatively low lateral limits on taller, narrow tyres. As a result, these show the largest and most linear change in handwheel loadings verses tyre slip angle. And being light, have small lightweight suspension/steering components with low inertia, and hence do not damp out the higher frequency road surface vibrations etc
Good info. Last point explains why my old 106 rally had such nice steering. Prob would have felt as good with pasEdited by Max_Torque on Sunday 28th December 12:08
Max_Torque said:
The crucial word you are all looking for, and failing to find is INERTIA, not friction!
No Max, the word I was looking for and found was friction, in the case of the CTR rack anyway 
The reason it's so bad is that the plastic wheel that engages with the worm on the motor appears to swell as it ages, which makes the worm and wheel bind up. The motor can still power it easily but, as I'm sure you know, when driving a worm and wheel backwards (i.e. steering at high vehicle speed with negligible assistance) you only need the slightest bit of friction for it to bind. The torque sensor comes before the worm and wheel, and when assistance is minimal or off, the torque sensor simply absorbs the first few degrees of angular motion until there is sufficient torque to overcome the static friction, after which too much angle is usually applied. It's very similar to driving a car with a manual rack that someone has wound way too much preload on, you end up making very 'digital' corrections and it's very tiring on a long trip.I agree that inertia will damp feedback and the EPAS system has the extra geared up mass of the motor armature to move which is a significant amount of inertia, but the fact it does this by driving a worm and wheel in reverse makes thing even worse (at least on the CTR).
In the system you show above, can the still rack drive the motor ok (i.e. can you steer with no motor assistance at all)? The thread looks like too fine a pitch to allow this?
Edited by Mr2Mike on Sunday 28th December 16:15
A good point is the mx5 the mk1 was original designed to have pas from the start but for some reason the uk wanted a car without it and imo the rack they chose for the non powered steered cars are crap, the pas system is a delight to drive with the non pas system is heavy, lacking in feel and the ratio on the rack isn't set up for the mx5.
Go to the mk3 and they are an electronic system which is way to light and lose a lot of feel in the steering, similar system in my sister mazda 2 and its way to light for me, my sister though loves it.
Go to the mk3 and they are an electronic system which is way to light and lose a lot of feel in the steering, similar system in my sister mazda 2 and its way to light for me, my sister though loves it.
buggalugs said:
Nobody cares about EHPS because that's not where things are going, it was mostly a way to get PAS on cars where the rack was a long way from the engine without running long pipes everywhere.
EPS is simpler than a hydraulic setup, it has fewer parts,if something's wrong it will tell you what and and there's no fluid to worry about. You can argue that black's white if you want but I remain unconvinced!
Yes but that was not the argument,EPS is simpler than a hydraulic setup, it has fewer parts,if something's wrong it will tell you what and and there's no fluid to worry about. You can argue that black's white if you want but I remain unconvinced!
which was that electric was simpler than conventional hydraulic,which it clearly is not.
Eps/column mounted stuff or rack mounted uses a complex (by comparison)steering column or a rack and both use complex electronics to control and power them.
It may be better at many things and may be even cheaper but there is no way on this earth it is simpler or less complex as a whole.
These systems may have less mechanical components the but the control and actual assistance side has been complicated by the use of electronics,that`s besides what it needs for a decent power supply and all that entails in its self.
Diagnosis of conventional systems faults is diabolically easy anyway,so trying to convince me that the eps benefits you by telling you what`s wrong with it(as long as you have the right expensive diagnostics tools anyway)is utter nonsense as if it fails you will almost certainly need to replace the whole expensive unit,or if you get lucky pay for an expensive repair that might last.
On the aspect of failure,which its self is laughable as is proven by the massive industry that has sprung up to rebuild and repair these,even some decent motor factors are stocking some of the more common units.
And as electronics are involved im sure even Max Torque will concede that the quality of components used in these things is usually less than desirable.
I have witnessed first hand and heard of at least twice elsewhere of a column system fault on a Vauxhall Agila/Corsa that input from the wheel would randomly send the steering spinning uncontrollably to full left lock at a scary and unstoppable rate,resulting in a horrible judder through the steering wheel when it reaches the end of its travel.
You literally could not stop it,myself and 17 stone of hairy biker could not,what chance for some old lady?
The only way thing you could do to return it was to unplug the thing,centre the wheel and plug it back in,it was nigh on impossible to steer with it unplugged as you are then left trying to drag the motor round at speed because it is massively geared against you.
No matter how one eyed you choose to look at it,that is dangerous.
Vauxhall tried miserably to assure us that it was impossible and that it was fail safe,that was until one of their own service guys took it for a drive and walked back twenty minutes later as white as a ghost,supporting his obviously damaged right hand by the wrist with his left.
If my conventional system fails I just have slightly heavy steering and maybe a puddle.
but thats not the point,a rack,some pipes,a pump and maybe a cooler(which is basically a long pipe anyway)will always be simpler than an electric system.
itcaptainslow said:
There are some decent EPAS systems, and some awful hydraulic systems. However, the way I see it; it's more difficult to get good feel out of EPAS than hydraulic, especially a "natural" feel.
It does seem to be a worrying trend that steering feel is slowly dying...comparing even a Mk1 Focus to a Mk3, the Mk1 steering is delightful.
The Mk1 Focus is very nice to drive. All the controls feel great: properly weighted steering with good feedback, a positive gearshift, good pedal weighting. The Mk2 Focus was worse in these respects and I'm not surprised to hear that the Mk3 is probably worse again.It does seem to be a worrying trend that steering feel is slowly dying...comparing even a Mk1 Focus to a Mk3, the Mk1 steering is delightful.
Max_Torque said:
The complexity or otherwise of the subsystems is not the issue as that is negated by mass production (have a look at how many pieces are in say laptop, and how little you can buy one for!).
The issue with hydraulic PAS is as follows:
1) it has a mechanical "calibration" that cannot be modified between platforms without hardware changes (unlike EPAS, that simply can be flashed with a different calibration) hence, you have parts commonality across your fleet, with the corresponding cost savings
2) it is "dumb". To add technologies that are rapidly becoming std, like lane assist, park assist, dynamic steering control, steering mode / weighing selection etc is either not possible, or extremely complex.
3) It costs more to assemble, uses fluids that have a service life, and must be "bled and leak checked during manufacturing. It also needs fluid reservoirs and inspection / servicing
4) It has a high parasitic loss, as the hydraulic pump is "open spool" and hence pumping fluid around the system at all times, even when not steering. This is typically worth between 3 and 5 g/km CO2 and hence with modern cars dipping into the low 100's, becoming an un-acceptable loss (If you are buying a big V8, with say 300g/km, it is less important, but the majority of the market is LOW CO2.
5) The system cannot "self diagnose". Steering system faults cannot be spotted and reported by the steering system, something that the EPAS can obviously do.
6) It requires your engine to have a larger,more complex FEAD (Front End Accessory Drive) and the extra belt, mounts, and tensioner all cost money, add complexity, mass, and limit service life.
7) It is "cross system" dependent. With the rack being on the subframe, the pump on the engine, and the reservoir often on the chassis. This is a real PITA, as it requires flexibility of the interlinking services, and adds significant lead time and design complexity (your chassis design team must liase with your engine team, and your cooling team, and your crash team, and your "underbonnet" team, to ensure that the steering systems, which interacts with all those systems, fits, does not clash etc. Then you must carry out millions of miles of testing to ensure the pipes do no vibrate, chaffe or age, the system doesn't overheat, throw it's belt, fail it's tensioner etc etc etc.
EPAS is easier to manufacture/service and results in higher fuel efficiency, so when in early 2012 it also became cheaper than existing HPAS it became a no brainer to fit it. Even companies like Porsche, who had a "we won't be going EPAS" stand until then, could not ignore the benefits and hence included it on their latest models.
I understand that,The issue with hydraulic PAS is as follows:
1) it has a mechanical "calibration" that cannot be modified between platforms without hardware changes (unlike EPAS, that simply can be flashed with a different calibration) hence, you have parts commonality across your fleet, with the corresponding cost savings
2) it is "dumb". To add technologies that are rapidly becoming std, like lane assist, park assist, dynamic steering control, steering mode / weighing selection etc is either not possible, or extremely complex.
3) It costs more to assemble, uses fluids that have a service life, and must be "bled and leak checked during manufacturing. It also needs fluid reservoirs and inspection / servicing
4) It has a high parasitic loss, as the hydraulic pump is "open spool" and hence pumping fluid around the system at all times, even when not steering. This is typically worth between 3 and 5 g/km CO2 and hence with modern cars dipping into the low 100's, becoming an un-acceptable loss (If you are buying a big V8, with say 300g/km, it is less important, but the majority of the market is LOW CO2.
5) The system cannot "self diagnose". Steering system faults cannot be spotted and reported by the steering system, something that the EPAS can obviously do.
6) It requires your engine to have a larger,more complex FEAD (Front End Accessory Drive) and the extra belt, mounts, and tensioner all cost money, add complexity, mass, and limit service life.
7) It is "cross system" dependent. With the rack being on the subframe, the pump on the engine, and the reservoir often on the chassis. This is a real PITA, as it requires flexibility of the interlinking services, and adds significant lead time and design complexity (your chassis design team must liase with your engine team, and your cooling team, and your crash team, and your "underbonnet" team, to ensure that the steering systems, which interacts with all those systems, fits, does not clash etc. Then you must carry out millions of miles of testing to ensure the pipes do no vibrate, chaffe or age, the system doesn't overheat, throw it's belt, fail it's tensioner etc etc etc.
EPAS is easier to manufacture/service and results in higher fuel efficiency, so when in early 2012 it also became cheaper than existing HPAS it became a no brainer to fit it. Even companies like Porsche, who had a "we won't be going EPAS" stand until then, could not ignore the benefits and hence included it on their latest models.
Edited by Max_Torque on Sunday 28th December 13:17
Although cars have a belt anyway so putting another pulley in the system is hardly the end of the world,also some pumps piggy back other rotating parts.
But the point is that in terms of complexity how can 3 parts,a pump,pipes and rack be more complex than any eps system,just by virtue of its electronics alone.
Take as an example any one part of that electronic system,
You and a maybe a handful of others on here will understand them and their effects on the rest of the system.
that is just one small part of a system That is alien and therefore complex to 99% of the population.
Many people on here probably understand how a hydraulic system works.
Just being easier to package and produce,cheaper or better which will always remain debatable,does not make it less complex.
Many parts which were mechanical or mechanically powered are now electric,I`m not arguing the benefits of either method other than that mechanical powered system is simpler in terms of what it need to operate and to be understood.
you would spend eons trying to teach some one a quarter of what you know about electronics and still be banging your head against the wall
My 8 Y/O would grasp enough working knowledge of a hydraulic power steering system in an hour.
shoehorn said:
I understand that,
Although cars have a belt anyway so putting another pulley in the system is hardly the end of the world,also some pumps piggy back other rotating parts.
But the point is that in terms of complexity how can 3 parts,a pump,pipes and rack be more complex than any eps system,just by virtue of its electronics alone.
Take as an example any one part of that electronic system,
You and a maybe a handful of others on here will understand them and their effects on the rest of the system.
that is just one small part of a system That is alien and therefore complex to 99% of the population.
Many people on here probably understand how a hydraulic system works.
Just being easier to package and produce,cheaper or better which will always remain debatable,does not make it less complex.
Many parts which were mechanical or mechanically powered are now electric,I`m not arguing the benefits of either method other than that mechanical powered system is simpler in terms of what it need to operate and to be understood.
you would spend eons trying to teach some one a quarter of what you know about electronics and still be banging your head against the wall
My 8 Y/O would grasp enough working knowledge of a hydraulic power steering system in an hour.
There's also the significant wastage involved with an engine driven setup. The greatest power assistance is needed when the car is stationary or manoeuvring at low speeds. This happens at low revs so the hydraulic pump needs to be designed in such a way that it can provide full pressure when the engine is idling. At higher speeds, the pump spins faster thus works more efficiently however there's less need for it. When the car is in motion steering effort is drastically reduced, as well as the fact you don't tend to need lock to lock spinning sessions at sixty miles an hour. Hollywood stunts notwithstanding. Although cars have a belt anyway so putting another pulley in the system is hardly the end of the world,also some pumps piggy back other rotating parts.
But the point is that in terms of complexity how can 3 parts,a pump,pipes and rack be more complex than any eps system,just by virtue of its electronics alone.
Take as an example any one part of that electronic system,
You and a maybe a handful of others on here will understand them and their effects on the rest of the system.
that is just one small part of a system That is alien and therefore complex to 99% of the population.
Many people on here probably understand how a hydraulic system works.
Just being easier to package and produce,cheaper or better which will always remain debatable,does not make it less complex.
Many parts which were mechanical or mechanically powered are now electric,I`m not arguing the benefits of either method other than that mechanical powered system is simpler in terms of what it need to operate and to be understood.
you would spend eons trying to teach some one a quarter of what you know about electronics and still be banging your head against the wall
My 8 Y/O would grasp enough working knowledge of a hydraulic power steering system in an hour.
To get round this the pump has a built in pressure release, in that it's got the potential to generate loads of hydraulic pressure at motorway speeds, but doesn't. The pressure isn't needed and has to remain constant, ideally it would get lower but not sure if that's possible. As such much of the pressurised fluid drains out of a release valve and is recirculated.
I know you probably don't care, but it's inefficient. Not only is there the mechanical drag of the pump, there's the fearsome effort of pumping a load of thick, oily fluid around for no reason whatsoever. It's akin to running the central heating in summer. Nothing to stop you but essentially pointless. As such electric systems are better, they get round this nonsense by providing assistance on demand. Which is the perfect model for something that isn't constantly needed.
nickfrog said:
Not all down to EPAS or hydraulic. My GT86 EPAS has better steering feel than many hydraulic set ups found in performance cars. Someone mentioned BMW's late hydraulic steering : that gave so little feedback, it hardly matters if the epas removed what little there was.
I agree with this. Drove the last of the hydraulic 330d's and was shocked at how little feel there was compared to my old E36. The GT86 I also drove was much better but surprisingly definitely still not as good as the EPAS on my Ibiza FR. Took them both down the same road and the Ibiza was definitely moving around more which is odd given most reviews identify the Ibiza as poor and the 86 as heroic "for EPAS".Edited by nickfrog on Saturday 27th December 22:38
just give it up
you claimed hydraulic power steering was less complicated than electric, you've had it clearly explained by someone who clearly knows a fair amount on the subject. You may understand hydraulics better than electrics so find hydraulics simpler to understand, but that doesn't make it actually simpler, just simpler to you.
I've replaced both a belt driven power steering pumps and an electric pump from an hydro electric power steering system, i still don't fully understand how the rack it's self works, and none were simple jobs, they involved draining the fluid, disconnecting the fluid tank, disconnecting high and low pressure pipes yet the electric power steering motor i replaced could not have been much simpler, it was a direct drive on the steering column, unbolted pulled, disconnected the single connector and replaced I honestly don't see what you think is so complex about it.
you claimed hydraulic power steering was less complicated than electric, you've had it clearly explained by someone who clearly knows a fair amount on the subject. You may understand hydraulics better than electrics so find hydraulics simpler to understand, but that doesn't make it actually simpler, just simpler to you.
I've replaced both a belt driven power steering pumps and an electric pump from an hydro electric power steering system, i still don't fully understand how the rack it's self works, and none were simple jobs, they involved draining the fluid, disconnecting the fluid tank, disconnecting high and low pressure pipes yet the electric power steering motor i replaced could not have been much simpler, it was a direct drive on the steering column, unbolted pulled, disconnected the single connector and replaced I honestly don't see what you think is so complex about it.
What is it with you lot?
You clearly do not seem to understand what the word complex means,or are missing the point!
I am not arguing whether electric or hydraulic is better,or discussing the perceived virtues or disadvantages of either system other than from the fact of complexity of design and operation
as I have clearly stated and yes I understand the advantages of using computers to control stuff better than conventional mechanical methods even at an initial cost.
But How the hell can an electronic system that needs various data sources from various sensors,a computer or 2 to decipher and use that data,a motor,gearing,complicated software,relays,modules and decent controlled electrical supply be any simpler than something that boils down to basic physics.
Some one explain how moving fluid or air through a pipe to move something at the other end is simpler using electricity and a lot of components.
As I said convenience for the manufacturer,benefit for the user,cost,efficiency or what ever benefit you see fit to use in any aspect does not at all validate the claim that its less complex.
Even breaking it down to components,the most complex part of a hydraulic system would be a valve,
a ball bearings trapped in a hole being pushed by a spring,hardly complex compared to even a simple microchip or an electric motor.
So how the hell is it less complex or less simple?
Hydraulics are simple to implicate and simple to repair with little knowledge,we have built the world using hydraulics,farming uses it,the building industry,manufacturing,the next time some one digs a road,lifts something heavy,or comes to recover your broken down car they will be using hydraulics because it is not complex.
You clearly do not seem to understand what the word complex means,or are missing the point!
I am not arguing whether electric or hydraulic is better,or discussing the perceived virtues or disadvantages of either system other than from the fact of complexity of design and operation
as I have clearly stated and yes I understand the advantages of using computers to control stuff better than conventional mechanical methods even at an initial cost.
But How the hell can an electronic system that needs various data sources from various sensors,a computer or 2 to decipher and use that data,a motor,gearing,complicated software,relays,modules and decent controlled electrical supply be any simpler than something that boils down to basic physics.
Some one explain how moving fluid or air through a pipe to move something at the other end is simpler using electricity and a lot of components.
As I said convenience for the manufacturer,benefit for the user,cost,efficiency or what ever benefit you see fit to use in any aspect does not at all validate the claim that its less complex.
Even breaking it down to components,the most complex part of a hydraulic system would be a valve,
a ball bearings trapped in a hole being pushed by a spring,hardly complex compared to even a simple microchip or an electric motor.
So how the hell is it less complex or less simple?
Hydraulics are simple to implicate and simple to repair with little knowledge,we have built the world using hydraulics,farming uses it,the building industry,manufacturing,the next time some one digs a road,lifts something heavy,or comes to recover your broken down car they will be using hydraulics because it is not complex.
shoehorn said:
a ball bearings trapped in a hole being pushed by a spring,hardly complex compared to even a simple microchip or an electric motor.
So how the hell is it less complex or less simple?
Depends on how you define complexSo how the hell is it less complex or less simple?
a microchips are some of the simplest things in the world, this is why they are produced in the billions per year, they rival the simplicity of a screw or a paper clip.
Just because you don't understand them does not make them complex, to me i can't see why anyone would consider a microchip, with no moving parts to be more complex with something with multiple moving parts.
If you want to insist a control unit which comes in a box, requires no maintenance ever, is complex because it's got dozens of components inside and some proprietary programming, then it's complex, but that is not how manufactures see it, they don't care what's in the box, just that it's easy to package, cheap to mass produce and reliable.
RE: complexity of HPAS.
I think you'll find that the EPAS systems rely on basic physics just the same as HPAS systems!
Saying "HPAS" is simple because it only uses moving mechanical parts and EPAS is complex because it uses non moving electronic parts is ridiculous.
Saying "ah, but anyone can understand how a hydraulic PAS systems works" is rubbish. I bet 99% of people on this site do NOT understand the fundamental control parameters and how you would tune them to optimise the servo response curve produce a stable yet responsive system for an open spool hydraulic PAS system!
Do a bit of googling on the racks spool valve, the compromises and extremely fine tolerances on the machined parts, the complexity of sealing oil at 100bar and 150degC,the effects of temperature on the pump and spool, the requirement to match the pump output volume to a wide range of engine speeds,the response required to avoid hydraulic lag or phase delay, the size, profile and wear characteristics of the control orifices, the spring constant and max limit stops for the spool torque bar, the necessary damping & system stiffness to avoid rack Pogo, etc etc. All those things are engineered in incredible detail, and have been perfected over 50years. And, every time you make a new model or platform, you need to do all that development/calibration & validation again, which is hugely expensive and time consuming.
Fundamentally, the conventional hydraulic power assistance system is an analogue system, and as such it has a huge level of uncertainty. An electronic system, whilst complex, is deterministic and operates primarily as a digital state machine.
The simple fact is that EPAS is now CHEAPER than HPAS, which tells you that it is overall a "simpler" system, as it costs less, so the total amount of "work done" must be smaller (in effect, in our capatalist economy money = effort expended) For example, in the time it takes to machine, check and setup the spool valve in a conventional rack, a pick 'n place machine and oven can have assembled, built and checked probably 10 complete EPAS racks. The perceived "complexity" of each solution is largely irrelevant when you get to volume production.
You also may not really be interested in having a diagnostic capability in your car, but generally speaking, and as we move towards more and more automated cars, the Authorities and OEMs are. For every example of say a basic/early Corsa EPAS system failing (and they did) i bet if you actually looked you could find 10 hydraulic system failures, from thrown/failed belts, to loss of fluid, to pumps overheating, rack seals failing. A guy i work with put his 306Gti6 in the barriers on a track day because the system overheated, and chucked it's fluid out all over his front tyres for example.
I think you'll find that the EPAS systems rely on basic physics just the same as HPAS systems!
Saying "HPAS" is simple because it only uses moving mechanical parts and EPAS is complex because it uses non moving electronic parts is ridiculous.
Saying "ah, but anyone can understand how a hydraulic PAS systems works" is rubbish. I bet 99% of people on this site do NOT understand the fundamental control parameters and how you would tune them to optimise the servo response curve produce a stable yet responsive system for an open spool hydraulic PAS system!
Do a bit of googling on the racks spool valve, the compromises and extremely fine tolerances on the machined parts, the complexity of sealing oil at 100bar and 150degC,the effects of temperature on the pump and spool, the requirement to match the pump output volume to a wide range of engine speeds,the response required to avoid hydraulic lag or phase delay, the size, profile and wear characteristics of the control orifices, the spring constant and max limit stops for the spool torque bar, the necessary damping & system stiffness to avoid rack Pogo, etc etc. All those things are engineered in incredible detail, and have been perfected over 50years. And, every time you make a new model or platform, you need to do all that development/calibration & validation again, which is hugely expensive and time consuming.
Fundamentally, the conventional hydraulic power assistance system is an analogue system, and as such it has a huge level of uncertainty. An electronic system, whilst complex, is deterministic and operates primarily as a digital state machine.
The simple fact is that EPAS is now CHEAPER than HPAS, which tells you that it is overall a "simpler" system, as it costs less, so the total amount of "work done" must be smaller (in effect, in our capatalist economy money = effort expended) For example, in the time it takes to machine, check and setup the spool valve in a conventional rack, a pick 'n place machine and oven can have assembled, built and checked probably 10 complete EPAS racks. The perceived "complexity" of each solution is largely irrelevant when you get to volume production.
You also may not really be interested in having a diagnostic capability in your car, but generally speaking, and as we move towards more and more automated cars, the Authorities and OEMs are. For every example of say a basic/early Corsa EPAS system failing (and they did) i bet if you actually looked you could find 10 hydraulic system failures, from thrown/failed belts, to loss of fluid, to pumps overheating, rack seals failing. A guy i work with put his 306Gti6 in the barriers on a track day because the system overheated, and chucked it's fluid out all over his front tyres for example.
I think the thing here is be wary of version 1.0 of anything.
ABS, cruise control, traction control, EPS : with all of these, the first version was arguably inferior to the best analogue systems, which as Max_Torque pointed out (indirectly), have had generations of refinement for both performance and reliability.
However, once you get to about the third generation, the digital / electronic solution is superior to the best of its analogue ancestors.
Of course, if the engine is in the right place, and the car weighs the right amount, you don't need power assist at all
ABS, cruise control, traction control, EPS : with all of these, the first version was arguably inferior to the best analogue systems, which as Max_Torque pointed out (indirectly), have had generations of refinement for both performance and reliability.
However, once you get to about the third generation, the digital / electronic solution is superior to the best of its analogue ancestors.
Of course, if the engine is in the right place, and the car weighs the right amount, you don't need power assist at all
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