Valve auto-calibration command parameters (continued)
Command
Description
YactDiffThreshold
Set the ‘change threshold’ for ‘steering actuator position’/‘steered wheel position’ (Yact) that is the criterion for detecting a
flow. The position change, ∆Yact, is measured in the time-out period for each main spool position set-point increment.
A low threshold (< 20) will detect very small flows but is sensitive to e.g. noise from the wheel angle sensor. Too low
thresholds will often result in false flow detection which again results in too conservative software dead-bands.
A high threshold (> 60) requires a significant position changes. Further-more, the calibration time increases because the
main spool needs to be increment to a higher set-point before the necessary output flow is present.
Yact is the scaled ‘steering actuator position’/‘steered wheel position’.
TimeOutPeriod
The time between two consecutive steps of the automatic calibration process and thus sets the measurement time in which
∆Yact is measured.
A value <500 could reduce the calibration time, but requires careful selec-tion of the YactDiffThreshold setting. A value
>1000 significantly in-creases the calibration time requirement.
XspCalibrationOffset - Main spool displacement offset which is subtracted from the detected spool set-
point which satisfies the ‘output flow detected’ criterion. Subtracting the offset from the detected spool
set-points results in the open-loop software dead-bands values.
XspCalibrationOffset is a parameter value and is used for both left and right spool direction.
XspCalibrationOffset parameters
Symbol
Index
Default
Value range
XspCalibrationOffset
758
25
0 -300 (scaled main spool set-points, Xsp)
XspCalibrationOffset is a parameter value and not intended to be modified on each auto-calibration
invocation.
Valve auto-calibration procedure
The valve calibration procedure and how all involved parameters are used, works as follows.
The procedure is showed for the right dead-band only.
Spool displacement
[Xsp]
Steering actuator speed
Steered wheel angle speed
∆Yact/dt
0
Xspr_0
1
2
Xcal_r
YactDiffThreshold
3
4
XspStartSearch
5 Compensate Xspr_1000 value
1. The main spool set-point starts at XspStartSearch
•
∆Yact is calculated as the difference measured in TimeOutPeriod ms
•
Every TimeOutPeriod ms, the main spool set-point is incremented by XspIncrementSize
•
Step 1 is repeated until step 2 becomes valid
2. The measured ∆Yact exceeds YactDiffThreshold
3. The current Xsp is stored and denoted Xcal_r
4. The open-loop dead-band parameter is calculated as Xspr_0 = Xcal_r – XspCalibrationOffset
•
The Xspr_0 value is written to eeprom
5. The main spool set-point where the valve outputs it nominal maximum flow, Xspr_1000, (see Valve
transfer function) is adjusted equally to the Xspr_0 change. As an example; if the detected Xspr_0 has
Operation Manual
PVED-CL Controller for Electro-Hydraulic Steering, Version 1.38
Installation
28 |
©
Danfoss | May 2016
11025583 | AQ00000216en-US0302
