1. Pressure and Speed Limits

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

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

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

5. Load Vs Life Hi
PRESSURE
Low
Short
Long
LIFE

6. 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.

7. Max vs Rated Pressure
MAXIMUM
CONTINUOUS
PRESSURE
TIME

8. 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.

9. Speed Limits

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

11. 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

12. 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

13. 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

14. 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.

15. 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.

16. 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.

17. 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

18. 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.

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

20. Secondary Braking Insist that your customers provide a
secondary means of braking
on ALL vehicle propulsion systems!

21. Check Speed Limits
Check max angle limits of base units in catalog
Check charge pump limits
Check reduced displacement variable motor limits

22. 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!

23. 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

24. Reduced Angle Motor Example
What is Rated speed limit of 51V110 at 22 deg 22 deg = 32 deg * (sin 32) (sin 22) = * (sin 32) (sin 22) = 3960 rpm
catalog reduced angle displacement max = 4500 rpm
use lesser of calculated vs. catalog, i.e rpm

25. The Million Dollar QuestionY 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.

26. Duty Cycle Definition
What is a Duty Cycle?

27. 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.

28. Duty Cycle Calculations
Calculation procedures vary.
Procedure has dramatic effect on predictions.
Sauer-Danfoss uses conservative procedures.
Competition: Compare calculation procedures.

29. 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.

30. 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.

31. Weighted Speed
Every duty cycle also has a weighted speed:

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

33. 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

34. Typical Pressure Distribution
MAX LOAD
HILL CLIMB
NORMAL POWER
PRESSURE
These are work cylces, each of them is measured independently.
LEVEL GROUND
IDLE
% Time

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

36. Thank You
Questions?