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Old 21st March 2012, 17:03   #16
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Default Re: How does Electric power steering work?

Quote:
Originally Posted by Rehaan View Post

EPSs are capable of providing just as much (or more) feel and feedback than a hydraulic unit - it just depends on how the system has been implemented and tuned.
Live examples are Renault Fluence and Ford Fiesta. It is just that it has to be calibrated in the right manner in order to give a proper feel and feedback. It should be light (not super light) and giving maximum assistance at parking speeds, moderate assistance in medium speeds and minimal/no assistance at high speeds. My question is there any mechanical component that works to the command of ECU codes to provide this varying levels of assistance? Or is it that the motor rotates faster at low speeds and slower at high speeds and then totally disconnects when no assistance is required?

Quote:
Originally Posted by im_srini View Post
In the Swift the EPS motor is on the steering rack rather than on the column & as far as I can see, it does not have a clutch.
The EPS is column/rack mounted based on packaging? What specific advantages/disadvantages do each of these have?
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Old 22nd March 2012, 00:32   #17
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Default Re: How does Electric power steering work?

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Originally Posted by im_srini View Post
Here are some pics...

General description of parts in the Alto's EPS...
Hi,
Wish I could thank you more than once!

If the block diagram is to be believed, then
a) the motor is a simple DC motor, with wound armature and field.
b) Armature is controlled by a full (H, with four switches) bridge. So can be made to turn both ways.
c) Field is also controlled. Possibly used to control torque.

Torque is a differential signal, possibly from a full bridge, though only two arms are shown in the diagram.

Shamed by you, decided to crack open my dust laden books. From which I got the answer to
Quote:
Originally Posted by smartcat View Post
Any idea what is the average percentage fuel saved by shifting to EPS from hydraulic steering unit in a normal sized car?
which is 0.3l to 0.7l per 100 Km. Which is quite significant.

Quote:
Originally Posted by vvijay View Post
It is just that it has to be calibrated in the right manner in order to give a proper feel and feedback. It should be light (not super light) and giving maximum assistance at parking speeds, moderate assistance in medium speeds and minimal/no assistance at high speeds.
Should be. A parameterizable system. Unfortunately designing/ implementing such a electrical system (with accurate appropiate feel at all times) is not easy (read cheap).

Regards
Sutripta
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Old 22nd March 2012, 02:47   #18
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Default Re: How does Electric power steering work?

Quote:
Originally Posted by vvijay View Post
My question is there any mechanical component that works to the command of ECU codes to provide this varying levels of assistance? Or is it that the motor rotates faster at low speeds and slower at high speeds and then totally disconnects when no assistance is required?



The EPS is column/rack mounted based on packaging? What specific advantages/disadvantages do each of these have?
We are not at all talking about the steering assistance system motor's speed, the steering assistance system will help only by providing torque assistance, the speed will always be equal to the drivers steering input (turning speed of the steering wheel )
There is a torque sensor in the form of a torsion bar, measures the effort the driver puts on the steering wheel, of course the system is designed to lessen this effort, we, humans work more as a sophisticated PID controller where in we know when to stop steering when we are moving at a speed and at the same time in the parking lot, when we are stand still we keep turning the wheel (say full lock). The control unit has a set of maps (lookup tables) which is calibrated (sometimes according to each vehicle type within a platform) This maps has each set point, based on the inputs to the controller, it signals the motor which helps by providing us with the torque. Based on the sensor values which goes up to as precise as decimal degrees (angle) the set point is chosen.

The system is purely classified based on the position of the motor. Of course for higher torque assistance systems eg. Vans or trucks the packaging is definitely an issue, there is a bigger motor size requirement.
The torque required to steer the vehicle can be broadly said to be dependent on the weight of the vehicle (Of course let us leave off the additional points such as caster angle change etc..,) Mounting it on steering column is much simpler solution and also compact. Toyota IQ is such a wonder.

Of course the fuel economy advantage has always been an arguable point. I have hereby enclosed picture (a photo from my own work, sorry for the poor quality as I dont have a scanner)which compares the energy requirement(w) of the different steering systems (Electro hydraulic system uses an electric motor to run the power steering pump, which traditionally was run continuously by an engine via belts)

It is clear the EPS uses only 7.6% of energy.
Source: Miyazeki. H, Technical trends in steering systems, 7th JFPS international symposium, Sept 08. The comparative study was done on a Japanese cycle called 10-15 mode which is also used to measure fuel consumption values.
How does Electric power steering work?-photo.jpg

For more information you can look into the website of ZF lenksysteme (a reputed steering systems supplier, I guess its also available in English)

Last edited by rranjith_kum : 22nd March 2012 at 03:13. Reason: additional info
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Old 22nd March 2012, 10:29   #19
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Quote:
Originally Posted by Sutripta View Post
Hi,
which is 0.3l to 0.7l per 100 Km. Which is quite significant.
I read somewhere that a power steering hydralic pump takes about 5-10% of engine power, so the fuel consumption by PS should be more..im not sure..

Brilliant Srini, I got the information i was looking for...Thanks !!!!

Quote:
Originally Posted by im_srini View Post
Are the 2 thin wires black ? I tried looking up the EPS section in the Alto's service manual, it says that the motor has a 4-pin connector with 1 red & 1 black wire for the motor & 2 black wires for a clutch (I think something similar to the A/C clutch). Here are some pics...
So its not a servo motor or a stepper motor.its a electric motor with a clutch..

the thin wires are in grey. I guess Alto's system and zen systems should be the same. Number of wires from each socket seems to the same.

Thanks for the posting the pics, I appreciate the efforts you have taken the scan the pics .
Do you have a soft copy of altos manual? Im not able to get the service manual for zen.
I want the voltage and current values at each terminals.

Quote:
Originally Posted by im_srini View Post
T1000, of course, the assumption is that the EPS in the Zen would be very close or even identical to the one in the Zen. Looking at the Swift's EPS, it appears to be a more sophisticated unit. In the Swift the EPS motor is on the steering rack rather than on the column & as far as I can see, it does not have a clutch. The EPS control module in the Swift also has many more diagnostic codes. Will put up the pics if its of interest to anybody...
I downloaded Swift's service manual. it is more sophisticated system.
Some of the differences i can make out are
1. No clutch in the motor.
2. PS gets input about front wheels rpm(both left and right separately.
3. It has a self check of torque sensors, self check is run at the time of cranking the engine.
4. Torque sensor amplifier , to increase the resolution to get better feedback
5. PS is connected to ABS and Airbag systems.

Last edited by Rehaan : 22nd March 2012 at 14:20.
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Old 22nd March 2012, 12:15   #20
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Default Re: How does Electric power steering work?

while looking for information on PS, I came across another interesting thing,

There is a sensor called CMP sensor connected to camshaft.
CMP sensor sends information about engine rpm to ECU.
This sensor sends 6 pulses per rotation to ECU.

I got another DIY idea for a "Low cost digital RPM meter".

A parallel wire can be pulled out fom CMP sensor and pulse information fed to a microcontroller like PIC18f4550 or a low end microcontroller.
MIC can count the pulses and display RPM in a LCD module.
the total cost of the project wont exceed 300-400 rs!

Let me do it and post the results in DIY section.
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Old 22nd March 2012, 14:23   #21
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Default Re: How does Electric power steering work?

Quote:
Originally Posted by T1000 View Post
A parallel wire can be pulled out fom CMP sensor and pulse information fed to a microcontroller like PIC18f4550 or a low end microcontroller.
MIC can count the pulses and display RPM in a LCD module.
the total cost of the project wont exceed 300-400 rs!

Let me do it and post the results in DIY section.
Rather than trying to count 6 pulses per rotation on an engine thats spinning at high RPM, why don't you use something like a spark plug lead as the trigger (fires 1/3, 1/4, 1/6 as often - more managable). I think you can wrap a wire/coil around the spark-plug lead, and everytime it fires, you can pick up the signal.

cya
R
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Old 22nd March 2012, 18:17   #22
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Default Re: How does Electric power steering work?

Quote:
Originally Posted by Rehaan View Post
Rather than trying to count 6 pulses per rotation on an engine thats spinning at high RPM, why don't you use something like a spark plug lead as the trigger (fires 1/3, 1/4, 1/6 as often - more managable). I think you can wrap a wire/coil around the spark-plug lead, and everytime it fires, you can pick up the signal.
cya
R
Well sounds like a better idea.
There are some advantages too
1. Its non-intrusive method, no need to tamper with ECU wires.
2. Will work both in carb and MPFI vehicles.

Timing probe tester works the same way, a magnetic ring is wrapped around one of the spark plug wires. The probe flashes light whenever a spark plug is fired.


Will a permanent coil around the spark plugs wires affect the strength of the spark?

Other things like MIC will remain the same.
Anyways i havent started work
ill have to connect a oscilloscope and test both the options...

Will post the results soon.

Thanks Rehaan.
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Old 22nd March 2012, 21:01   #23
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Default Re: How does Electric power steering work?

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Originally Posted by rranjith_kum View Post
This maps has each set point, based on the inputs to the controller, it signals the motor which helps by providing us with the torque.
Not getting the concept of a set-point in this case. Could you pls. explain. (The power assist, If I'm not mistaken, is essentially a servo system. )


Quote:
Originally Posted by T1000 View Post
I read somewhere that a power steering hydralic pump takes about 5-10% of engine power,
5 - 10% of peak engine power! I'm sure that is not the case.

Regards
Sutripta
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Old 22nd March 2012, 21:13   #24
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Default Re: How does Electric power steering work?

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Originally Posted by T1000 View Post
Timing probe tester works the same way, a magnetic ring is wrapped around one of the spark plug wires. The probe flashes light whenever a spark plug is fired.
Hi,
With 1 pulse / 2 revolutions (or 1 for 1 in a wasted spark system), the tricky part is to balance the damping (so that the needle does not jitter at idle) with the need for for fast accurate readings when you are gunning the engine.

A F-V (or F-I) converter is simple enough, but check out the application notes/ white papers for say LM2907/ 2917.

Regards
Sutripta

PS - Tachs OT for this thread!

Last edited by Sutripta : 22nd March 2012 at 21:22.
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Old 23rd March 2012, 01:15   #25
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Default Re: How does Electric power steering work?

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Originally Posted by Sutripta View Post
Not getting the concept of a set-point in this case. Could you pls. explain. (The power assist, If I'm not mistaken, is essentially a servo system. )
Well I guess I really didnt make it clear enough.

By map I mean something like a normal table, with x and y axis, based on the sensor values (lets say X parameter and Y parameter) the controller looks and picks out a result value from the table (say the value corresponding to the x and y coordinates) Usually these values are the ones which are calibrated, these values maybe the parameters which influence the resistance or the current flow to the motor. Of course all these based on how sophisticated the system is. With a z axis it obviously gets more detailed.

I meant these values as set points (perhaps it has better name) but then what I acutally wanted to mean is that there are some standardised situation or cases, say, based on engine rpm - idle condition, 2000 rpm; based on vehicle speed 0km/h or standstill and 20km/h and 130km/h etc., these values are results from testing or calculated using mathematical models, the rest of the table is interpolated and smoothened or it would be too much work, the standardised cases are chosen in such a way that a trend could always be noticed or at least be arrived upon.

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Old 23rd March 2012, 20:44   #26
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Default Re: How does Electric power steering work?

^^^
Hi,
To us, a set point is a goal/ target value which the controlled variable should attain. Job of the controller to see to it. In this case it should be the torque generated by the assist system. Which should be (lets assume for simplicity's sake) proportional to the human input. The value of the coefficient will vary depending on a number of external factors, chief of these being speed.

If this is context, don't see how a table can store a setpoint in this case.

Regards
Sutripta

Last edited by Sutripta : 23rd March 2012 at 20:51. Reason: sp
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Old 13th August 2017, 07:45   #27
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Default Re: How does Electric power steering work?

This seems informative: http://www.caranddriver.com/features...n-test-feature
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