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MG MGB Technical - epas power steering
|Having now got well past my sell by date I've decided to try fitting an mgf epas power steering column. I've just about sorted the mechanical aspects of fitting. The wiring has me a little puzzled (I am an old fart after all ) has anyone got any experience of this conversion and any helpful feed back.|
I presume you've got the controller/ECU to go with the steering column. I had the same idea and picked up a column and controller at a reasonable price. Other than the connections between the ECU, motor and torque sensor, you'll need a speed related input or something to generate an input, see link below for a Corsa unit, the F one would be similar. You'll also need an input that simulates the input from the engine ECU, the F system won't work if it thinks the engine isn't running. Finally, I think, there's an output for the dash warning light. See link to diagram below
There was an article 5 or 6 months ago in one of the magazines about someone using a Renault unit, he was selling kits to do the job.
I haven't got around to fitting this yet as there's quite a lot of mechanical work to get it to fit and it's only really a problem at parking speeds since I fitted a castor reduction kit. I do however still run a standard steering wheel, I find this works better than the smaller wheel the car came fitted with and I can also see the gauges that were obscured by the smaller wheel.
I'd be interested to hear how you get on as I may re-consider doing this, especially as I've been given a very nice wooden rimmed wheel that fit the F's splines perfectly.
thanks for the advice. The corsa kit wont work on the MGF column. I've got the ECU and I cut some of the wiring from a scrapper. The problem is using an engine output. The mgf uses a transducer on the speedo drive I think. There is a white and black wire to engine output. do you think it would work if this was connect to the rev counter? The steering wheel connection is the same as an mini cooper or a MGA. the other end connects directly to the top end of the mgb steering rack. This by getting a second UJ and swapping the connection from the steering column end of the mgf (the spare one) to the end which connects to the mgb end. That doesn't make much sense when I reread it. If you look at yours you'll see what I mean. I removed all the mgf brackets except the big one near the motor. I've also rotated the whole box 90 degrees clockwise. Tomorrow I'm going to try and assemble everything, wish me luck.
I only included the link to the Corsa unit as an example. I do have an F that I'm working myself up to replacing the head gasket, if need be I could stick a scope on the ECU and speed inputs. Once I know what waveforms/inputs are needed it shouldn't be hard to make something.
The Corsa unit (link in previous email) although not compatible will almost certainly work on the same principle. It will provide a square wave with a frequency inversely proportional to the amount of assistance required, higher frequency less assistance, lower frequency more assistance. In the Corsa unit you have to set this manually, in the F the frequency is proportional to speed. What were you thinking of doing? I believe it's possible to get a unit that goes in line with the speedo cable or you could attach a magnet/magnets to the front UJ on the prop and use a reed switch.
I've been trying to visualise the setup with the UJ's you describe, do you end up with 1 or 2 UJ's? If it's 2 I think the shaft to the rack would need additional support near to the UJ.
The link below gives a bit more info and it also includes a link to setting the torque sensor if you're not already familiar with this.
Found the below info on mg-rover.org BBS, see link below
"The EPAS ECU needs two square wave signals, it can be tricked by supplying a 1000 to 3000 Hz signal for the RPM and a 100 to 250Hz signal for the roadspeed.
The early MGF had a mechanical speedo with no sensor on the gearbox, it's speedo had a spinning magnet which operated a reed switch that provided the EPAS signal.
You could use a signal from the points for RPM but you would need to clamp it's level to a safe amplitude so that it doesn't damage the EPAS ECU."
|BOB THANKS AGAIN FOR THE INFORMATION. The UJ set up is the same as the TF but the UJ that connects to the TF rack is different to the MGB rack end. SO to use the collapsible section of theTF steering the end that connects to the TF steering rack is different to the end that connects to the TF seeing column. Theuj that connects to the TF rach must be dismantled and replaced with a one the same as that which connects to the TF steering column. THat makes sense I think. I'm still thinking about the electric side of things, but your superior knowledge will prove most helpful. The trouble is My A level lectures were in the afternoon and I usually slept thu them. (and it was over 50 years ago. On a brighter note I now have the column in stalled. I was mistaken when I said the mga boss fitted the TF column. It is about 1mm too big. I've ordered a new TF boss so I can ose the Momo steering wheel that I've had haning on the wall for years. will keep you up to speed on progress. regards Ian|
|I have now installed the TF column in the B There were no insurmountable problems fitting it. The only one that caused any concern was sealing the bulkhead round the column shaft. I'm a retired podiatrist and remembered I had some old silicone putty. I greased the column with petroleum jelly. Then moulded the putty round it and it works a treat. I have wired everything up with the exception of the engine speed and road speed wires. This is still the stumbling block. Is it possible to use the impulses from a RVC smiths tacho? I've got an old rubber bumper tacho, taken it to bits. There is a black and a red wire going to the meter part of the instrument. Do you (or anyone else) know if the red wire will produce the correct pulse to activate the TF steering ECU?|
|Those wires do gives pulses to the movement, increasing in frequency as the engine speed increases. And as each pulse has the same voltage and duration the effect is to cause the needle to move further round the dial as the frequency of the pulses increases. |
But what engine signal into the ECU does the TF use, i.e. what form of pulse? If it's just a pulse wheel on the crank like for ignition and fuel you could probably use the points/coil pulses.
|I'd be cautious about connecting it directly to the coil without something to clamp the voltage at a safe level. The voltage present at the coil will have spikes on it that would have the potential (note the pun) to damage the ECU. I haven't measured the output of the engine ECU on an F/TF but I would expect it to a be square wave of either 5V or 12V that increases frequency proportional to the engine RPM.|
|I think the sensor for engine speed is a square wave pulse of amplitude 5 volts max. I've measured the pulse from the coil this is spiked up to a max of about 12 volts. If I strip the pcb out of the old tachometer and connect the red wire to the TF sensor wire it should give the result I want. The other problem is the road speed sensor which progressively reduces the power assistance to the steering This is connected somehow to the speed sensor on the gearbox. The other power steering conversion (Vauxhall corsa)has an aftermarket loom which connects to the ECU via a potentiometer to vary the piwer assist. Does anyone know how this works> Thanks for the help. Bob I've enclosed a picture of the TF column with my bracket ready to install in the "B" regards Ian
|"damage the ECU."|
That's the point. One starts with what the ECU requires, then decides what could be used to generate that and any interfacing required. The coil -ve spikes at 250v so that needs to be taken into account in any isolation circuitry. There is a difference in the type of waveform between the coil and the tach movement, I'd expect the coil to be closer to what generates the pulses on a TF. I'd also expect the road speed indicator to be much the same as the rpm indicator, except on the output of the gearbox instead of effectively the input.
I obviously misunderstood what you were advocating when you said “use the points/coil pulses” I interpreted this as connecting directly to the points/coil and I wanted to caution against this. I would agree with you in that I'd expect the waveform required would probably more resemble that seen at the coil.
The offer still stands to put a scope on the inputs but I can't do it just at the moment as I'm halfway through an HG change on the F.
| Bob Thanks for the offer. I'd be interested to see the results. I've dismantled the R/B tacho .There is a pulsed output Which according to what I have gleaned from various sources is a square wave output. However without an oscilloscope I can't tell what it is. The reading from my multimeter seems to show an output of 0.15 to perhaps 3 volts. What I can't understand is red wire which outputs to the meter part of the tachometer, is also connected to the green wire which goes to the voltage stabiliser and thence to the main MGB fuse box. I'm getting deeper and deeper out of my depth. It's frustrating as I've fitted a 14" steering wheel in anticipation of having power steering. I'm exhausted just getting it out of the garage. incidentally, M B is a 1974 The headlight and indicator switch fits on the TF column fine. These lf canceller Of the TF is too small to work with the MGB switch. I've uploaded a picture of my solution I fabricated an annulus in Perspex and cut segments from it to glue over the TF self canceller. regards Ian
|The mechanical movement in a tachometer requires either a steady voltage or a series of pulses in order for it to register anything. The tachometer electronics generate a square-wave pulsed output as you say, with a fixed length 'on' pulse. As the rate of input pulses goes up, these pulses get closer together, and because of the fixed 'on' pulse the effect of the increasing rate is to shorten the off pulses, which increases the ratio of the on periods to the off periods, or to put it another way the average voltage over time goes up. A mechanical movement cannot move instantaneously, and so smooths out the pulses to give a steady reading. Effectively it is displaying the ratio of the on pulses to the off pulses, so as the on pulses come in quicker and the off pulses get shorter, the movement reads higher.|
Where the voltage is derived from to send to the meter is up to the designer, and the designer of the tach electronics basically decided to connect one side of the meter to a 6v reference derived from a zener diode and a resistor, and use the electronics to connect 12v pulses to the other side. So the meter is getting 6v pulses across its two terminals, but the wire carrying the pulses to it is switching between 6v and 12v.
I think you are barking up the wrong tree and starting at the wrong end in trying to understand the tach. You need to be examining and understanding the signals that are generated by the crank and gearbox sensors on the TF, which go into the ECU, and replicate those.
FWIW this describes the functioning of the tach http://www.classictiger.com/techtips/motach.html
|Paul , Thanks for your explanation. I'll have to find the specific outputs from the sensors as you say. regards Ian|
I'd be interested in see how you get on. I've ben toying with the idea of fitting a Vauxhaul Corsa EPAS as I have 195's and they make the low speed steering very heavy.
I've been struggling to find a decent pulse generator to indicate speed (wheels, not engine) and have been looking at frigging an ABS sensor onto the car, but haven't got that far yet.
all the best,
|hi Grant. I hav'nt look on the site for a while. I got a bit disheartened. My epas is fitted but still not working. I bought a corsa controller to try to modify itbut this didn't work. Its cold in the garage so Im concentrating on planning the TTbranch of the MGCC's price bishops run 2014 instead. The Vauxhall solution seems to be more popular. regards Ian|
This thread was discussed between 14/10/2013 and 02/12/2013
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