Closed Loop Test - Data Analysis
Closed Loop Test - Data Analysis
(OP)
When testing the dynamic behaviour of a vehicle, you have two options:
- Open loop test:
The whole test procedure is precisely determined (speed,steering wheel angle build up,..)
The driver is not part of the information loop and so there is no feedback.
- Closed loop test:
The test driver has to follow a road or trajectory, taking corners at different speeds, with unspecified steering wheel angles.
The driver introduces feedback in the information loop.
If you acquire data from such a closed loop test, you get a whole cloud of data,
which has to be filtered and curve fitted to achieve results similar to those from an open loop test.
If there is anyone who has experience analysing and processing this kind of closed loop data,
I would like to discuss the different, possible approaches and the quality of the results that can be achieved.
Thank you!
Greetings
Xplode
- Open loop test:
The whole test procedure is precisely determined (speed,steering wheel angle build up,..)
The driver is not part of the information loop and so there is no feedback.
- Closed loop test:
The test driver has to follow a road or trajectory, taking corners at different speeds, with unspecified steering wheel angles.
The driver introduces feedback in the information loop.
If you acquire data from such a closed loop test, you get a whole cloud of data,
which has to be filtered and curve fitted to achieve results similar to those from an open loop test.
If there is anyone who has experience analysing and processing this kind of closed loop data,
I would like to discuss the different, possible approaches and the quality of the results that can be achieved.
Thank you!
Greetings
Xplode





RE: Closed Loop Test - Data Analysis
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Closed Loop Test - Data Analysis
the focus is on steering and the appropriate manoeuvres:
constant radius turn, constant velocity sweeping steer manoeuvre for different lateral acceleration levels,..
The closed loop data is acquired from test runs on a handling track, performed at different paces.
The aim is to filter the closed loop data in such a way (limited speed range or lateral acceleration, only using the start of a steering manoeuvre,..) that similar results can be achieved as with the open loop tests.
Greetings
Xplode
RE: Closed Loop Test - Data Analysis
There are a few test we run open loop in the real world, you need a lot of real world.
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Closed Loop Test - Data Analysis
The data acquisition system measures:
- vx
- ax
- ay
- steering wheel angle and torque
- body motions: pitch, yaw and roll
- slip angle
- ...
Currently I was examining the results of steering wheel angle vs. lateral acceleration, as an example.
Greetings
Xplode
RE: Closed Loop Test - Data Analysis
but I was still thinking about the necessary complexity of the model.
Do you use a full multi-body-model or a simpler, mathematical model?
Have you compared your simulation results of the open loop tests with real world open loop data?
Are these results satisfying or is there still a significant difference?
How do you measure the driver actions? Steering wheel angle, brake pressure, wheel torque,..?
For the closed loop tests, do you use a simple, easy-to-install data acquisition system (Microsat, VBox,..) or a higher quality measurement system?
Cheers
Xplode
RE: Closed Loop Test - Data Analysis
I rarely correlate to open loop data, but yes, I have done so. We really don't run many open loop tests. We have a steering robot to run them.
Mostly the results are as good as the tire data. Sometimes the agreement is very good straight out of the box, other times it never works.
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Closed Loop Test - Data Analysis
RE: Closed Loop Test - Data Analysis
Remember that the vehicle has no idea where it is, so steer angle inputs are easy to do in simulation and track testing, but the vehicle operates in moment control: It searches around for tire and suspension/chassis forces and moments to balance the moment in the steering shaft. Where it goes to get the job done is controlled caos. Yeah, really good cars go where they are pointed, but there's only a few of them...
And, Captain Peacock, I am unanimous in my opinion on this.
RE: Closed Loop Test - Data Analysis
I suppose working back from that you could use GPS to provide your yaw velocity data. Hmm.
I need to use a non linear model because my linear range work is largely calibration of the model, so that for the non linear range (ultimate handling, rollover, etc) I know the model itself is good, and all the problems are in the tire models.
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Closed Loop Test - Data Analysis
I can conclude the simulation process is very helpful, as long as you have an appropriate and good model of the data.
Are there any system identification tools or techniques that are particularly useful or which result in high correlation? I have a basic knowledge on the identification process, but I'm not really into the more complex theories..
Is there anyone who has performed a 'simple' dataprocessing (filtering, statistical analysis,..) and curve fitting on such closed loop data? With any satisfying results?
I have performed a small test, with medium quality closed loop data from the handling track. I made a selection of data points, based on the range for speed and lateral acceleration, according to the procedure describing the open loop test.
As an example, I examined the cross-plot steering wheel angle vs. lateral acceleration.
A polynomial fit through the selection resulted in a similar curve as the open loop results.
As there was only data available from a limited number of runs, this explains the differences between open/closed loop results.
Has anyone performed similar dataprocessing?
Would a larger number of dataruns increase the accuracy of the closed loop results? Or is it hard to expect any decent correlation using this method?
Xplode
RE: Closed Loop Test - Data Analysis
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.