Select Ramps With Fixed Ramp Times; Example - Danfoss pved-cl Operation Manual

Operation Manual
PVED-CL Controller for Electro-Hydraulic Steering, Version 1.38
Steering by High Priority Steering Device – Open Loop
Symbol
Sr

Select Ramps with Fixed Ramp Times

© Danfoss | May 2016
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.
Index
3y17
The below figure shows the operation of ramps with fixed ramp times and illustrates different ramp
scenarios. Qr is the request port flow commanded with the high priority steering device. Qramp the ramp
limited port flow and can be regarded as the result of the ramp function.
Qr, Qramp
1000
YsetFr, fast ramp down range
750
500
250
0
Tfr
Tro
-250
Tfo
-500
-YsetFr
-750
-1000
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 Technical Data
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 Technical Data
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 to 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.
Tfr This time defines the applied ramp time in the fast ramp-down range. It is defined as the ramp time
from maximum flow to no flow. This means that in practice, the actual fast ramp-down time is
proportional to the fast ramp-down range divided by 1000.
Default
0
Qr Requested port flow
Qramp ramp port flow
YsetFr
YAbortDownRamp
Up ramp
slow ramp down range
Slow down ramp
}
YAbortDownRamp
Abort down ramp
}
Slow down ramp
}
Fast down ramp
on page 22.
on page 22.
Value range
Must be set at 0
time
P005 205E
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