pressure and speed limits. transmission design elements sauer-danfoss hydraulic unit design pressure...
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Pressure and Speed Limits
Transmission Design Elements
Sauer-DanfossHydraulic
Unit DesignPressure
and Speed Ratings
ComponentSizing
CustomerMachineDesign
FluidQuality
CircuitDesign
TransmissionDesign
Pressure & Speed Limits
BULLETIN PURPOSE
BLN-9884
• Provide understanding of ratings and their relationship to expected life.
Key Concepts
• Maximum and Rated pressure
• Expected life
• Maximum and Rated speed
• Duty cycle
Load Vs Life
LIFEShort Long
Low
Hi
PR
ES
SU
RE
Unit Life
• Upper life limit– Rotating group– Bearings
• Actual life– Heat– Contamination– Viscosity and lubricity of fluid
Max vs Rated Pressure
TIME
PR
ES
SU
RE
MAXIMUM
CONTINUOUS
Pressure
• Maximum Pressure– Highest intermittent pressure allowed– Determined by max. machine load demand– Less than 2% of total operating time
• Continuous Pressure– Pressure expected when performing normal function– Normal input power, max. pump displacement – Weighted average
Speed Limits
Consider Operating Conditions
• Normal driving
• High idle/no load
• Overrunning load– Must know something about the frictional
characteristics of engine
Speed Ratings
Swashplate Units Bent Axis (Series 51)
If Above Continuous,
Contact Sauer-Danfoss
Not always block lift first
Rated Speed
• Life inversely proportional to speed
• Highest speed recommended at full power
• Highest speed for normal life
• Varies with angle
• Must always check Maximum speed limit
Maximum Speed
• Highest operating speed permitted• Risk immediate failure if exceeded• May loose driveline power if exceeded• Highest negative power (downhill braking)• Catalog ratings…:
– pumps: always reflect maximum swashplate angle– fixed motors: always reflect maximum swashplate
angle– variable motors: both maximum and minimum angle
are published
Cavitation damage
Over speed
Over speed
Design Speed Considerations
• Full power• Full braking• Prime mover speed change• Pump drive ratios• Tolerance and drift of engine governors• Hydraulic unit volumetric losses• Tolerance in hydraulic unit displacement
Maximum Speed Considerations
• Maximum motor operating speeds must be determined and compared to Maximum speed limits.
• For vehicle propel drives this usually occurs during down-hill braking conditions.
• Another severe condition is zero delta pressure at high engine idle speed.
•Operating parameter check
•Pressures < recommended limit
•Speeds < recommended limit
•Expected life achieved
Drive Design Finalization
Secondary Braking
Insist thatInsist that youryour customers provide a customers provide a secondary means of braking secondary means of braking
on ALL vehicle propulsion systems!on ALL vehicle propulsion systems!
Insist thatInsist that youryour customers provide a customers provide a secondary means of braking secondary means of braking
on ALL vehicle propulsion systems!on ALL vehicle propulsion systems!
Check Speed Limits
•Check max angle limits of base units in catalog
•Check charge pump limits
•Check reduced displacement variable motor limits
Reduced Angle Speed Calculation
• Swashplate Units:
• Bent Axis Units:
Speed at
reduced angle
Speed at
maximum angle
Tan Max Angle
Tan Reduced Angle
Speed at
reduced angle
Speed at
maximum angle
Sin Max Angle
Sin Reduced Angle
Do not use speeds greater than the "Reduced
Angle" speeds shown in the tables!
Series 51 Speed Limits
• Maximum Speed is the highest speed permitted.Rated Speed
rpmMaximum Speed
rpmFrameSize (Full Displ.) (Min. Displ.) (Full Displ.) (Min. Displ.)
080
110
160
250
3100
2800
2500
22004000
3400
5000
4500
4000
3600
3200
2700
5000
4250
6250
5600
Reduced Angle Motor Example
• What is Rated speed limit of 51V110 at 22 deg
speed @ 22 deg = speed @ 32 deg * (sin 32)(sin 22)
= 2800 * (sin 32) (sin 22)
= 3960 rpm• catalog reduced angle displacement max = 4500 rpm• use lesser of calculated vs. catalog, i.e. 3960 rpm
The Million Dollar Question
DU
TY
CY
CL
E
Duty Cycle Definition
• What is a Duty Cycle?
DUTY CYCLE 1
Condition % Time Delta SpeedPressure
(bar) (rpm)
1 1.0% 450 17002 2.0% 350 17503 5.0% 250 18404 16.0% 200 19005 30.0% 180 19506 34.0% 150 20007 9.0% 100 21008 3.0% 50 2200
SUM: 100.0%
Cumulative Damage
• Cumulative damage, or more precisely, cumulative fatigue damage, is the total damage to a component as a result of repeated cyclic loading.
– Stress levels are not great enough to cause the component to fail under static loading.
– Related to crack initiation within the material.
Duty Cycle Calculations
• Calculation procedures vary.
• Procedure has dramatic effect on predictions.
• Sauer-Danfoss uses conservative procedures.
• Competition: Compare calculation procedures.
What is Weighted Pressure?
• Weighted pressure serves as a general indication of a duty cycle’s severity
– The greater the weighted pressure, the lower the predicted life.
– Of the three criteria for weighted pressure, this one is the least demanding.
Calculating Weighted Pressure
• Weighted pressure equation:
• Equation does not include any information concerning the shaft speed at each condition.
• For duty cycles with equal weighted pressures, the life will be the same only if the speed at every condition is the same for both duty cycles.
P = %Time P + %Time P + ... %Time w 1 1
exp
2 2
exp
j
Pj
exp exp1
Weighted Speed
• Every duty cycle also has a weighted speed:
Weighted Pressure = Root Mean Octic Pressure = (SUM(Column G))^(1/ EXP) 263 barWeighted Speed = SUM(Column H)/ (Weighted Pressure)^EXP 2206 rpmPredicted L20 Kit Life Using Load-Life Equation & Weighted Values 4875 hours
Predicted L20 Kit Life Using %Time/Life Method 4875 hours
Weighted Speed
• Equation for weighted speed is
• Weighted Speed is not calculated using the traditional “weighted average” formula:
RPMP P
Pw
j
w
= %Time RPM P + %Time RPM ...%Time RPM1 1 1 2 2 j j
exp exp exp
exp
2
RPMw %Time RPM + %Time RPM + ...%Time RPM1 1 2 2 j j
Duty Cycle Reduction
• Knowing how to calculate the predicted life or the weighted pressure for a customer’s duty cycle is good thing to know, but…
• How do I measure a duty cycle? – Usually too many conditions– Can’t test everything at once
Typical Pressure Distribution
MAX LOAD
HILL CLIMB
NORMAL POWER
LEVEL GROUND
% Time
PR
ES
SU
RE
Hi
Lo
IDLE
Combining duty cycles
Hill climbing
Normal power
Level ground
Idle
Max load
Life estimate
2%
20%
40%
25%
13%
Thank You
• Questions?
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