Joined: 26 Oct 2007 Posts: 11 Location: Helsinki, Finland
Posted: Sun Nov 11, 2007 5:15 pm Post subject:
ricola wrote:
(I am one of the mechanical design engineers that worked on it).
Ok, I thought the ones who have these in heavy cars used for racing just don't drive hard enough to break them.
It's such a nice solution that I guess we have to check it later on, maybe next year.
Henrik
PS. Love your homepage, it has been a big source for inspiration. Thanks for making it, it must have taken much of your time. _________________ T3 Race Taxi
All our EPS system are designed around de-rating when they get to their thermal limits, these are normally based around learner driver parking cycles, so you shouldn't ever get a situation of it shutting down unexpetedly.
Rich
PS website is easy to keep updated now, once the structure is there it isn't such a big deal to maintain.. _________________ http://www.ricola.co.uk
Joined: 30 Jan 2006 Posts: 652 Location: North Staffordshire
Posted: Fri Dec 07, 2007 11:32 am Post subject:
I've been researching the Corsa EPS system this week after a customer showed me picture of his install last weekend. I had no idea the system was so compact and self contained before.
I think I've learned a lesson to look further in VWKD than the Subaru pages! I had no idea this thread was here.
I found a very interesting technical paper on EPS by a guy at the company who makes the chips which control it, Freescale Semiconductor. See:
ignore all the boring stuff about motor theory - there's some interesting stuff in there too!
Power assistance limit:
The interesting bits to me were that EPS has so far only been fitted to small cars because 12V automotive electronics limits the motor power to around 1kW (I admit that I don't really understand why. Surely for a given voltage, more ams = more power?). Maybe around 80A is the limit for any one system because of the alternators available? It infers that 1kW of assistance is not considered enough for larger vehicles. When I'm parking my Syncro with manual steering and 255 tyres, 1kW of assistance sounds fantastic to me!
I know there are plans to make automotive electronics a higher voltage in the future (possibly 42V), and this power limit for EPS is one of the reasons why, apparently. Also, a number of the sites I read predisted they hydraulic power steering will be obsolete within five years.
Corsa vs Fiat Punto:
The corsa and Fiat Punto apparently share the same platform (news to me), and both have EPS. Probably the same system, I guess, but with different control strtatgies as the Punto has the 'City' button which gives ou even lighter steering. How heavy can the steering really be in a Corsa or a Punto anyway? They're not exactly big cars. It's beyond me wht such cars suddenly need power steering really, but it they're going to include nice technologt which is suitable for us modifiers, then it sounds good to me.
EPS Inputs:
The EPS ECU has inputs of vehicle speed and engine speed. My guess is that the engine speed signal is used to prevent the motor drawing full current at idle. The VSS signal is used to give a variable amount of assistance with speed accordint to an assistance map stored in the ECU. This gives a clue as to how the Fiat 'City' button may work - it probably alters the VSS input.
Control units for Corsa EPS:
I also had a look at the control modules for the Corsa EPS available on eBay. These basically create a fake VSS and tacho signal to keep the EPS ECU happy, and the adjustable ones vary the VSS frequency to adjust the amount of assistance. Interssting that these cost up to £100 on eBay, yet I can imagine how they work (two astable multivibrator circuits), and the circuitry would cost no more than £5.
I notice that non of them mention that by fitting the control unit rather than driving the steering ECU with a real VSS signal, you lose the automatic speed sensitive power assistance feature - one of the big advantages of the electronic systems. However, in a Subaru conversion you already have engine and vehicle speed signals. I have bolt on VSS sensors available for all VW's from the 1950's to 1992. If these are compatible with the Corsa signals, then no interface should be needed, and you'd retain the speed sensitivity. If the signals are not compatible, then I already know of a device which will let you recalibrate them (I have one on my camper to give correct speedo readings on my Subaru instrumentation despite having different tyre sizes). Combining one of these with the vehicle speed sensors I already have available would give you both user adjustability of the amount of assistance available, and automatic speed sensitivity, which sounds ideal. Certainly worth investigating, anyway.
Economy:
Also a few sites said independently that removing the hydraulic power steering pump should give about a 1 - 3mpg improvement. Definitely wothr having with petrol at over £1 / litre
Motor failure problem:
Ricola Rich - very interesting to see that you worked on the system. I guess that was the MGF install? Is it basucally the same unit as the Corsa?Can you confirm something I read on a couple of sites - that the motor failures also mentioned here were limited to the Corsa B, and the Corsa C had a new motor fited to solve the problem? They certainly do seem to have had a motor reliability problem at some point, as if you Google 'Corsa power steering' most of the results you get are about a failure mode where you only get assistance in one direction, and non in the other. If this problem is fixed in the Corsa C, then this will be the unit of choice to base our conversions on.
I thougt that the MGF was the frst car to be fitted with EPS, but it turns out it wasn't. Honda did it first, on the NSX. Their system was built into the rack rather then the column though.
I'm very interested in seeing whether it is possible and practical to engineer a bolt on system for T25's based on the Corsa unit, done properly (with no cut and shut steering shafts, etc). I know of a company which specilaises in making steering shaft U/J assemblies in small quantities, so it may be possible.......
I'm about to join a T25 and Subaru Forester column together for my Forester 2.5 XT / Suncro project. It looks like that may have just got more comples - the column now needs to go from T25 - Corsa - Forester! Anybody want to buy the LHD T25 power steer rack I was planning to use? _________________ Regards,
Richard,
R J Engineered Solutions
Quality Subaru Powered VW Components
www.rjes.com
excellent addition to the archive Rich (RJES). Im particularly interested in what you say about the regulation modules - if you think you could make one for that sort of money or anything under £40 which is the cheapest ive come accross (ricola rich found it) then I would be very interested!!! or indeed if theres anyway to get it working from a VSS and Subaru ECU that would be even better. Unfortunatly im only maybe a month away from purchasing a module but would still be interested to change it later for a better solution.
Can you post up or PM me the details of the UJ company as i will shortly need to shorten my corsa UJ link to link it to the rascal rack.
EPS systems mostly work on the basis of a torque sensor in the steering column, the more torque that you apply at the wheel the more torque it will generate at the other end via the motor. Column drive systems only work on demand (ie directly geared to the motor via a gearbox) so they don't waste energy unless you are steering.
They are tuned to give assistance dependant on your input torque, however this varies with speed, so the maximum assistance a system will give will drop as you speed up (note this torque is not automatically applied as soon as you turn the wheel, still depends on your input torque).
Systems are indeed limited by the voltage and current available, I am working on some higher power systems (up to 120A) but these are a result of better control hardware. This is why you see them on the smaller cars, what you have to take into consideration is the amount of assistance for different suspension geometry (mostly caster) can be huge, this gives better stability also. Remember even in tiny hot hatches that they have heavy engines sitting over the steering rack so even the smallest supermini will need more power than we would ever need in our rear engined cars!
The reason the Corsa system is so popular is that it is the most recent that isn't heavily integrated into the CAN circuit, the inputs are relatively simple. The speed signal it requires is about 30 pulses per wheel rev, the problem with using a multiplier on a 4 pulse (subaru) system is instability at low speeds...
I work for TRW and we didn't design the Corsa/MGF system (although all the ebay ads seem to think we did!), we did do the Fiat/Renault one and several others but they are too reliant on CAN for easy aftermarket use. I also work on rack mounted belt drive systems and EPHS systems which is a remote motor/pump unit, this gives improved emmisions as it is on demand, not continuously sucking power from the engine, it also helps in packaging as you can imagine most engine bays these days are particularly crowded!
Engine speed is used as it only operates when the engine is running to save emptying your battery. City buttons merely increase the available limit of assistance at lower speeds. Each system is tuned according to a customer's required parameters.
Making up one of these control boxes is indeed only a few pounds worth of contents, looking inside mine I'd say about £4?
I was very keen to have vehicle speed as an input but due to instabilities as mentioned above we never got there (my phantom only has 1 pulse/rev on the VSS!). In practice, the adjustable VSS signal works very well on its own.
Joined: 30 Jan 2006 Posts: 652 Location: North Staffordshire
Posted: Fri Dec 07, 2007 11:25 pm Post subject:
Hello Rich,
Thanks for the very informative relpy. You can't beat getting the info from someone who knows first hand. It's intersting thet they Corsa system uses so many pulses per turn on the VSS. I guess that's either because they need to have many pulses to get a useful signal at low speed, or maybe because the signal is coming from an ABS sensor? I can get an 8 pulse per turn VSS for beetles, bays and splitties, but my design for T25's is limited to 4 pulses per turn. I could go back to my older design of CV joint mounted VSS, and use 30 pulses per turn, then devide that down for the Subaru ECU / speedo input (the pulse multiplier I use to calibrate the signal apparently divides too).
I hadn't thought that the engine speed input could just turn the EPS system on. I suppose you don't really want to have 100A relays to power it up externally when the control system can just be switched off instead. Makes a lot of sense.
I guess that even the CAN bus EPS systems must be fairly autonomous, so they are as fail safe as possible? If it's just the VSS input which is 'hidden' in the CAN bus, then my VSS supplier also makes black boxes which extract a square wave VSS signal from the CAN bus of many modern cars. I suppose what you'd need here is the opposite - a box which you feed with a real VSS signal which turns it into CAN bus signals. I know a couple of CAN bus designers from my old job who could come up with something to do that if there was a requirement, but there probably isn't as the Corsa units are so simple to connect. _________________ Regards,
Richard,
R J Engineered Solutions
Quality Subaru Powered VW Components
www.rjes.com
It isn't the engine speed itself that turns it on, it is still controlled by relays and the ECU is powered up with ignition, it just doesn't give assistance unless the engine is running.
I'm very mechanical at heart so don't get into the detailed electronics, I guess you could simulate some of the CAN signals but as you say, not much point when there is an alternative... There's also the small matter of finding out exactly what the particular EPS system wants so unless you have a contact of somebody involved in the design there would be a lot of reverse engineering. _________________ http://www.ricola.co.uk
As I maybe have to replace my steering anyway, I think it's a great idea to fit an EPS. Thanks RJES and Ricola for all the info!
I could live with the EPS working in some kind of "fixed" mode, is that what the dummy boxes do? On the other hand, if the input signal controls the sensitivity of the EPS it can't be too hard to feed it with the signal it wants.
Gotta finish all my other projects first though, but I'm for sure interested in a setup!
Joined: 30 Jan 2006 Posts: 652 Location: North Staffordshire
Posted: Mon Dec 10, 2007 9:01 pm Post subject: Demon Tweeks / DC Electronics EPS System
The one on Demon Tweaks' site appears to be the Corsa unit with very short shafts, with their own ECU. It's made by DC Electronics - see http://www.wiringlooms.com/EPAS.aspx for more details. As it states that it can be configured with no laptop, it can't do anything clever like swap the assistance maps which ricola Rich mentioned above. The ECU seems to have the simulation of the VSS and tacho signals built in.
From what I read on them the other day, it sounds like there is some pretty clever stuff going on in the Corsa EPS ECU, with bespoke chips produced for EPS control by Freescale Semiconductors. Personally I'd rather have a production car ECU, as I think far more money will have been spent on making it work properly (limiting the torque at full lock so the motor does not burn out, etc). Maybe this DC Electronics system just putd the rosad car ECU in a new bos, and adds another board to simulate the tacho and VSS?
The one from Demon Tweeks costs nearly £2000 + VAT, and a quick read of their site reveals that you also then need to buy the harness and ECU for £225 + VAT. That makes it over £2500 in total. Slightly outside of anyone on here's budget I suspect! _________________ Regards,
Richard,
R J Engineered Solutions
Quality Subaru Powered VW Components
www.rjes.com
Joined: 06 Sep 2007 Posts: 76 Location: West Aussie
Posted: Mon Jan 07, 2008 5:29 am Post subject:
Hey, any more progress on this eps conversion? I am thinking of doing the same on our v6 lowlight. The Opel Corsa B & C were rebadged and sold in Australia as the Holden Barina, so finding a steering column at a local wreckers wont be a problem. The v6 also runs a vss, so I think I could modify the signals to suit the eps ecu.
hello guys, i have spoken to DC Electronics before in the past (nice guys), i knew they were developing an eps system years ago before i had a camper and eps became eps. they were designing it for rally cars and rjes they played a big part for subaru _________________
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