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?