To achieve this, the EHPS software provides linear or non-linear ramps which in effect creates an orifice
across the main spool to tank by holding the valve open near its closing position until all kinetic energy is
dispatched into heat for some time. Ramps work on the valve spool set-point.
Sr sets the method. The ramp times can be disabled, fixed or related to vehicle speed. Set Sr to:
•
0 to select no ramps (default),
•
1 to select fixed ramp times, or
•
2 for speed dependent ramp times.
The figure below shows the operation of ramps with fixed ramp times and illustrates different ramp
scenarios. Qr is the request port flow commanded with the steering wheel. Qramp the ramp limited port
flow and can be regarded as the result of the ramp function.
time
1000
-1000
750
500
250
0
-250
-500
-750
1 unit = 0.1% of max. por
t flo
w
Qr, Qramp
Tfo
YsetFr, fast ramp down range
Qr Requested port flow
Qramp ramp port flow
YsetFr
YAbortDownRamp
P005 205E
slow ramp down range
Up ramp
Slow down ramp
Slow down ramp
Fast down ramp
Tro
Tfr
-YsetFr
YAbortDownRamp
}
}
}
Abort down ramp
Symbol
Index
Default
Value range
Sr
4y17
0
0 (default)
Ramps with Fixed Ramp Times
Sr Selects the ramp type. The ramp function can be disabled, fixed or related to vehicle speed. Set Sr to 1
to select fixed ramps.
Lr Sets the linearity of the ramp-up curve. The default value is a linear ramp.
Lf Sets the linearity of the slow ramp-down curve. The default value is a linear ramp.
Tro Sets the ramp-up time to open the valve from zero to max port flow. The time applies for both ports.
To gain the best performance, the ramp-up time shall be set larger than the inherent ramp up time of the
main spool.
See
on page 22 for these ramp times.
Tfo Sets the ramp-down time to close the valve from max to zero port flow. The time applies for both
ports. It has most effect when the ramp-up time is set larger than the inherent ramp down time of the
main spool.
See
on page 22 for these ramp times.
YsetFr Experience shows that ramping down from maximum flow towards medium flows do not cause
as much jerk as ramping down from medium flows towards no flow (close to the valve dead-bands). In
order to “expedite” the ramping at large flows, a flow range can be set up where the spool can move
faster down to a flow range, where the slow down ramp is active. The overall goal with the parameter is
too optimize steering response time without degrading the anti-jerk performance. Set up fast ramp down
time Tfr before tuning this parameter. Setting YsetFr to 1000 eliminates the effect of the fast ramp down.
Typical settings are 500-800. Use trial and error.
Example:
A value of 800 can be interpreted as allowing the spool to ramp down with a fast ramp for flow requests
between maximum flow (1000) and 800/1000 of maximum flow.
Operation Manual
PVED-CL Controller for Electro-Hydraulic Steering, Version 1.38
Steering by Low Priority Steering Device – Open Loop
82 |
©
Danfoss | May 2016
11025583 | AQ00000216en-US0302