Pressure and Speed Limits

Transmission Design Elements Sauer-Danfoss Hydraulic Unit Design Pressure and Speed Ratings Component Sizing Customer Machine Design Fluid Quality Circuit Transmission

Pressure & Speed Limits BULLETIN PURPOSE Provide understanding of ratings and their relationship to expected life. BLN-9884

Key Concepts Maximum and Rated pressure Expected life Maximum and Rated speed Duty cycle

Load Vs Life Hi PRESSURE Low Short Long LIFE

Unit Life Upper life limit Rotating group Bearings Actual life Heat Contamination Viscosity and lubricity of fluid Calculated max life assumes perfect conditions, actual life depends on actual conditions. Contamination is a very common factor in transmission failures.

Max vs Rated Pressure MAXIMUM CONTINUOUS PRESSURE TIME

Pressure Maximum Pressure Continuous 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 Exceeding maximum pressure reduces life by factor of exponent used in calculation Exceeding continuous pressure reduces life.

Speed Limits

Consider Operating Conditions Normal driving High idle/no load Overrunning load Must know something about the frictional characteristics of engine

If Above Continuous, Contact Sauer-Danfoss Speed Ratings If Above Continuous, Contact Sauer-Danfoss Swashplate Units Bent Axis (Series 51) 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 S90 charge pump The gerotor charge pump was operated at excessive inlet vacuum condition or highly aerated oil. The intrained air implodes causing the "pitting / errosion" on the gerotor surface.

Over speed S51 piston The centrifugal forces on the piston along with a loss of pressure balance on the piston ring and a degradation of the fluid viscosity result in wear on the piston skirt and piston bore. The piston ring fracture is the result of the wear on the lower skirt, reducing the support for the ring.

Over speed S20 piston The force to keep the piston in its bore was greater than the force pulling it out of the block bore.

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.

Drive Design Finalization Operating parameter check Pressures < recommended limit Speeds < recommended limit Expected life achieved

Secondary Braking Insist that your customers provide a secondary means of braking 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: æ Speed at ö æ Speed at ç ç ö Tan Max Angle = ´ è reduced angle ø è maximum angle ø Tan Reduced Angle æ Speed at æ Speed at æ Sin Max Angle ö ç ö ç ö = ´ ç ÷ è reduced angle ø è maximum angle ø è Sin Reduced Angle ø 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 rpm Maximum Speed Frame Size (Full Displ.) (Min. Displ.) 080 110 160 250 3100 2800 2500 2200 4000 3400 5000 4500 3600 3200 2700 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 Y C C E Y L What does “Duty cycle” mean? Duty cycle is the most important concept when it comes to calculating expected life. Without a good duty cycle it is impossible to get a good prediction of product life.

Duty Cycle Definition What is a Duty Cycle?

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.

Weighted Speed Every duty cycle also has a weighted speed:

Weighted Speed Equation for weighted speed is Weighted Speed is not calculated using the traditional “weighted average” formula:

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 PRESSURE These are work cylces, each of them is measured independently. LEVEL GROUND IDLE % Time

Combining duty cycles Max load 2% Hill climbing 20% 40% Normal power Life estimate 25% Level ground 13% Idle

Thank You Questions?