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Design Guidelines
Hydraulic Fan Drive Systems
www.danfoss.com
Design Guidelines
Hydraulic Fan Drive Systems
Revision history |
Table of revisions |
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January 2020 |
Updated Appendix H with new graphs for all frame sizes |
0401 |
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July 2018 |
Appendix H - new graphs for some frame sizes |
0303 |
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May 2018 |
add notes: H1 pumps with fan drive control |
0302 |
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April 2017 |
Updated Appendix H chapter |
0301 |
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July 2015 |
Danfoss layout - Add Appendix I - RDM Fan Drives |
0201 |
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2006 - 2013 |
Various changes. |
AA up to BC |
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2 | © Danfoss | January 2020 |
AB00000019en-000401 |
Design Guidelines |
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Hydraulic Fan Drive Systems |
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Contents |
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Introduction |
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Abstract................................................................................................................................................................................................ |
5 |
Overview.............................................................................................................................................................................................. |
5 |
Principles of Operation................................................................................................................................................................... |
5 |
Power Savings ................................................................................................................................................................................... |
6 |
Modulation Preferred Over on/off Fan Speed Control....................................................................................................... |
6 |
Fan Drive Design |
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Design Considerations.................................................................................................................................................................... |
7 |
Fan Drive Components |
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Fan Drive Element Selection........................................................................................................................................................ |
8 |
Estimate of Maximum Input Torque to the Pump................................................................................................................ |
8 |
System Design Parameters |
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Sizing.................................................................................................................................................................................................. |
10 |
Sizing Equations............................................................................................................................................................................. |
12 |
Equations..................................................................................................................................................................................... |
12 |
Variables....................................................................................................................................................................................... |
12 |
Axial Flow Fan Power Formula.................................................................................................................................................. |
13 |
System Design Data Form........................................................................................................................................................... |
14 |
Engine details............................................................................................................................................................................. |
14 |
Power steering........................................................................................................................................................................... |
14 |
Fan information......................................................................................................................................................................... |
15 |
Control preference................................................................................................................................................................... |
15 |
Reservoir...................................................................................................................................................................................... |
15 |
Fluid............................................................................................................................................................................................... |
16 |
Filtration....................................................................................................................................................................................... |
16 |
Technical Features......................................................................................................................................................................... |
17 |
Shaft Loads and Bearing Life...................................................................................................................................................... |
17 |
Maximum Pump Speed............................................................................................................................................................... |
17 |
Minimum Pump and Motor Speed.......................................................................................................................................... |
17 |
Motor Starting Pressure (open circuit motors).................................................................................................................... |
17 |
Motor Free Run Pressure............................................................................................................................................................. |
17 |
Input Torque Ratings.................................................................................................................................................................... |
18 |
Pump Drive Conditions................................................................................................................................................................ |
18 |
Tapered Shaft and Hub Connections...................................................................................................................................... |
18 |
Pump Suction.................................................................................................................................................................................. |
18 |
Case Drain Pressure....................................................................................................................................................................... |
19 |
Filtration............................................................................................................................................................................................ |
19 |
Operating Temperatures............................................................................................................................................................. |
19 |
Fluids.................................................................................................................................................................................................. |
19 |
Mounting.......................................................................................................................................................................................... |
20 |
Axial Thrust Motors....................................................................................................................................................................... |
20 |
Piping................................................................................................................................................................................................. |
21 |
Reservoir............................................................................................................................................................................................ |
21 |
Cavitation and Aeration Damage............................................................................................................................................. |
21 |
Cooling............................................................................................................................................................................................... |
22 |
Pressure Protection and Ratings............................................................................................................................................... |
22 |
Bearing Life Expectancy............................................................................................................................................................... |
22 |
Glossary |
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Terminology..................................................................................................................................................................................... |
23 |
Appendix A-Fan Performance |
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Fans..................................................................................................................................................................................................... |
24 |
Fan Performance............................................................................................................................................................................ |
24 |
Axial Thrust....................................................................................................................................................................................... |
25 |
Fan Laws............................................................................................................................................................................................ |
26 |
Example 1.................................................................................................................................................................................... |
28 |
Example 2.................................................................................................................................................................................... |
28 |
© Danfoss | January 2020 |
AB00000019en-000401 | 3 |
Design Guidelines |
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Hydraulic Fan Drive Systems |
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Contents |
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Example 3.................................................................................................................................................................................... |
28 |
Example 4.................................................................................................................................................................................... |
29 |
Appendix B-Fan Drive Sizing Equations |
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Fan Drive Sizing Equations and Derivations........................................................................................................................ |
30 |
Hydraulic System Comparisons................................................................................................................................................ |
32 |
Appendix C-Fan Drive Sizing Equations, using Variable Displacement Motors |
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Hydraulic Systems with 2 Position, Variable Displacement Motors, Equations and Derivations..................... |
34 |
Spreadsheet to Calculate the Optimum Minimum Displacement for 2 Position Variable Motor.................... |
35 |
Appendix D-Pressure change due to transient flow in a passage |
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Pressure Change due to Transient Flow in a Passage, Equations and Derivations................................................ |
37 |
Appendix E-Influence of Bypass Valve Pressure Drop in Open Circuit Systems |
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Appendix F1-Influence of temperature, pressure and relative humidity on specific weight of air |
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Influence of Temperature, Pressure and Relative Humidity on Specific Weight of Air........................................ |
43 |
Appendix F2-Influence of Altitude on Atmospheric Pressure |
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Influence of Altitude on Atmospheric Pressure.................................................................................................................. |
45 |
Appendix F3-Influence of generic altitude on atmospheric pressure |
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Influence of Generic Altitude on Atmospheric Pressure................................................................................................. |
46 |
Appendix G-Influence of reversed fan rotation on system performance |
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Appendix H-System considerations for H1 fan drives with reversed fan rotation |
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System Considerations for H1 Fan Drives with Reversed Fan Rotation..................................................................... |
54 |
Pressure Limiter Adjusting Procedure.................................................................................................................................... |
54 |
Additional Information concerning the H1 Fan Drive Controller Option.................................................................. |
55 |
FDC Start and End Current.......................................................................................................................................................... |
55 |
Operating Envelope for H1 Pumps with Fan Drive Control............................................................................................ |
56 |
Sensitivity to Prime Mover Speed Changes (Load Sensitivity) - (J Frame as example)......................................... |
63 |
H1 FDC Response Time (with Typical Fan Drive System Loading)............................................................................... |
66 |
Application startup method (to account for PL offset).................................................................................................... |
66 |
Appendix I-System Considerations for RDM Fan Drives |
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System Considerations for RDM Fan Drives......................................................................................................................... |
68 |
Reversing Sequence................................................................................................................................................................ |
68 |
Shift Rate Control...................................................................................................................................................................... |
69 |
System Considerations........................................................................................................................................................... |
71 |
Zero RPM Motor Output......................................................................................................................................................... |
75 |
Reference Literature |
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Open Circuit Axial Piston Pumps.............................................................................................................................................. |
76 |
Open/Closed Circuit Axial Piston Motors.............................................................................................................................. |
76 |
Controllers........................................................................................................................................................................................ |
76 |
System Guidelines......................................................................................................................................................................... |
76 |
Closed Circuit Axial Piston Pumps........................................................................................................................................... |
76 |
4 | © Danfoss | January 2020 |
AB00000019en-000401 |
Design Guidelines
Hydraulic Fan Drive Systems
Introduction
Abstract
Fan drive system sizing relies heavily on the input received from the customer. All system sizing calculations are based on the required fan power @ trim speed data given to the hydraulic system design engineer. This data is a statement of the fan drive motor shaft power that is required to turn a fan at the required speed to push, or pull, a required volume of air across coolers/radiators. The usual sequence of events is:
•The engine manufacturer advises the customer, or cooling system designer, of the heat dissipation required from the cooling system, charge air cooler etc. This information is combined with the heat rejection data for any accessories and work functions on the machine (such as : transmission cooler, hydraulic cooler, and A/C condenser) to determine the maximum heat rejection profile for the system.
•The customer’s cooling pack manufacturer uses this data to size the cooling package and generally recommends a fan to suit this need, providing the rated fan power, rated fan speed, and the fan speed and static pressure required to satisfy the cooling needs of the system.
•With this information, knowing the minimum engine speed at which maximum fan speed needs to occur, the hydraulic system designer can size the hydraulic fan drive system.
Overview
One goal of this document is to provide the reader with the equations and formulae needed to size a hydraulic fan drive, given that they are provided with the following information:
•Rated fan power.
•Rated fan speed.
•Fan speed required to meet the maximum cooling needs of the cooling system.
•Engine speed at which maximum system cooling is required.
This document also provides an explanation of the terms and factors used in the derivation of the sizing equations. In addition, the reader is provided with recommendations of simple system design solutions that will help provide a viable system with satisfactory performance.
Principles of Operation
The vehicle’s cooling fan is driven by a hydraulic motor, which in turn, is driven by a hydraulic pump. The hydraulic pump can be driven directly off of the engine supplied PTO (Power Take Off), or with a belt drive. An electrically controlled proportional pressure control valve modulates the fan speed depending on a temperature reading. In a cold condition, the fan idles with very low power consumption. During the hot condition, the maximum fan speed is controlled by a pressure control valve, which adjusts the fan speed to meet the cooling needs of the total system. Every system has a temperature, which allows for the most efficient performance. The electronic control system, attempts to maintain the coolant at the optimum design temperature, which the “system integrator” selects during the design phase of the project.
Fan speed vs engine temperature
<![endif]>Fan speed (rpm)
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Engine temperatur e
To optimize the cooling system operation in various environmental conditions and to minimize parasitic losses, the Danfoss modulating fan drive system enables the fan cycle to be designed to specific heat
© Danfoss | January 2020 |
AB00000019en-000401 | 5 |
Design Guidelines
Hydraulic Fan Drive Systems
Introduction
rejection requirements for a wide range of environmental conditions. Vehicle manufacturers have complete control of the fan cycle by choosing the appropriate temperature limits.
The Danfoss modulating fan drive system remains at idle speed until conditions require increased fan speeds. By regulating the pressure drop across the hydraulic motor, modulation of fan speed occurs, and over-cooling is prevented.
Power Savings
In the fan off condition, the fan may idle at approximately 30% of rated speed, but it will only consume about 3% of rated power. The Danfoss modulating fan drive system allows the system designer to size the fan for the engine speed at which maximum heat rejection occurs. The fan speed will remain essentially constant at all higher engine speeds. Consequently, the fan will not require excessive parasitic losses as engine speed increases. In systems where the engine speed at maximum heat rejection is 80% of the governed speed, the power savings compared to over-speeding a mechanically driven fan can be as high as 95%.
Modulation Preferred Over on/off Fan Speed Control
Fan speed modulation occurs over a temperature range chosen by the system’s designer. This eliminates the sudden changes in speed that cause dramatic changes in noise levels. Similarly, large accelerations of components, which may limit the reliability for long-term operation, are eliminated. Modulation also allows intermediate levels of cooling without unnecessary cycling of the fan between minimum and maximum speed. The calibration temperature, operating range, and ramp times can be varied independently by the system designer to achieve the desired level of temperature control.
6 | © Danfoss | January 2020 |
AB00000019en-000401 |
Design Guidelines
Hydraulic Fan Drive Systems
Fan Drive Design
Design Considerations
•Parasitic losses from excessive fan speed are high. Power consumed by a fan is proportional to fan speed cubed (speed3).
•Heat rejection to the atmosphere does not increase linearly with engine speed.
•Overheating and/or over cooling the system will result in loss of efficiency and productivity.
•Overheating, and/or over cooling the engine can result in increased emissions to the environment.
•The proportion of operating time during which full fan speed (maximum fan power) is needed is typically about 20% and can be as low as 5%.
•Mounting the fan directly to the engine requires large fan blade tip clearances due to normal engine vibration and movement. This leads to loss of fan performance. Mounting the fan directly to a hydraulic motor can minimize tip clearance and boost fan performance significantly.
Hydraulic fan drive system designers select components for unique combinations of engine, fan, and application parameters. Do not exchange/change fan system components indiscriminately. Design factors which determine the selection of the fan drive system for a particular engine, or vehicle, include:
•Engine set point and maximum heat rejection
•Pump rotation
•Pump input torque limitations
•Maximum applied pressure and speed limits for the individual components
•Fit-up and available installation space
•Pump support structure requirements for individual engine mounting combinations
•Specific engine and accessory temperature control limits
Fan drive element selection
Fan drive Element |
Design parameter |
Design flexibility |
Design champion |
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Engine & accessories |
Power, speed, total heat rejection and duty cycle |
Yes |
OEM |
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PTO & Gearing |
Engine to pump gear ratio |
Sometimes |
OEM’s choice of engine |
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supplier |
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Pump(s) |
Displacement, pressure, speed, fixed pump or variable pump, mounting |
Yes |
Danfoss technical |
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& drive line |
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representative, & OEM |
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Fan drive control |
Sensor input(s), control output, number of control elements |
Yes |
Danfoss technical |
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representative, & OEM |
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Motor(s) |
Displacement, pressure, speed, fixed motor or variable motor, mounting |
Yes |
Danfoss technical |
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& coupling |
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representative, & OEM |
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Fan(s) |
Fan rated power @ rated speed, fan diameter, number of blades, blade |
Yes |
OEM & cooling specialists |
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pitch, proximity of blades to heat exchanger, direction of air flow |
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Shroud(s) |
Type of shroud (flat plate, short duct, venturi), blade axial position in |
Yes |
OEM & cooling specialists |
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shroud, tip clearance |
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Air flow stream(s) |
Air flow rate & static pressure across heat exchanger(s), maximum |
Sometimes |
OEM & cooling specialists |
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ambient air temperature, minimum atmospheric pressure, hot air |
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recirculation, baffles, louvres & obstructions |
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Heat exchangers |
Physical size, height & width, number of heat exchangers in air flow |
Yes |
OEM & cooling specialists |
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stream, side-by-side, axial stack, materials selected, construction, |
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number and types of tubes, tube configuration, fin density |
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© Danfoss | January 2020 |
AB00000019en-000401 | 7 |
Design Guidelines
Hydraulic Fan Drive Systems
Fan Drive Components
Fan Drive Element Selection
Optimizing the size of fan drive elements depends on selecting the correct components and gear ratios. By matching these components to the fan power requirements, the required unit sizes can be quickly determined. The pump and motor displacements, input gear ratios, engine set point, and pressure limits can be adjusted to provide some optimization of component size. Along with the sizing equations presented in this article, a Danfoss fan drive sizing computer tool is available to assist with sizing the hydraulic components.
Many modulating hydraulic fan drives rely on dedicated pumps to provide flow to the fan circuit for optimum sizing. Other circuits are available that provide additional flow for power assisted steering and other accessory systems. In these, and many other circuits, the sizing equations and fan drive sizing tool may still be used to select the required components. Note that the design limits for associated design elements are not identified in this article. They may be reviewed by referring to the Danfoss technical information for the components being considered. Machine designers should verify that all design parameters are met for all drive line components.
While the methods described in this article may be useful, they do not represent the only approach to sizing hydraulic components. Contact your Danfoss representative if questions of interpretation exist.
Collect the application sizing parameters as identified in the System Design Parameters chapter of this document. Pay particular attention to the minimum engine speed at which maximum heat rejection to the atmosphere is required. When sizing the pump for the application, the system designer should ensure that the engine set point under hot oil condition is less than the engine speed at which maximum heat rejection occurs. Failure to do this can result in a condition where the cooling system may not provide adequate cooling when maximum work loading and maximum ambient conditions occur simultaneously.
Engine set poin t
(Fan Trim Speed)
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Engine speed (rpm )
P106 107E
Sample graph, performance prediction will vary depending on choice of input parameters.
One of the first things that the systems designer should consider is whether the maximum pump torque needed will exceed the input torque limitation of the pump drive. One way to calculate this is to divide the fan power requirement by an estimate of the hydraulic system’s overall efficiency and then determine the input torque requirement at the pump speed that is equivalent to the maximum heat rejection speed of the engine.
Estimate of Maximum Input Torque to the Pump
Compare the estimated maximum input torque to the maximum available input torque at the pump drive; this will determine the design margin that is available to the designer. The hydraulic system designer should consult with the vehicle system’s designer, and/or the prime mover’s technical support staff for assistance, if required.
8 | © Danfoss | January 2020 |
AB00000019en-000401 |
Design Guidelines
Hydraulic Fan Drive Systems
Fan Drive Components
SI system
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[ |
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( PfkW ) • (9549.0) |
] |
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Pump torque,Tp(N•m) ≈ |
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Pump torque,Tp(lbf•in) ≈ |
[( |
(Ne) |
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• R) |
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Where: |
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PfkW |
= Max fan power, kW [hp] |
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(Ne • R) = Pump speed, rpm |
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R |
= Pump/Engine ratio |
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Ne |
= Engine speed, rpm |
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0.7 |
= ηt for hydraulic system (pump |
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(N•m)
(lbf • in)
and motor)
Converting terms
Pump torque,Tp(lbf•in) = |
Tp(N•m) • 8.8507 |
(lbf•in) |
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Pump torque,Tp(lbf•ft) = |
Tp(N•m) • 0.7376 |
(lbf•ft) |
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Pump torque,Tp(N•m) = |
( |
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Tp(lbf•in) |
) |
(N•m) |
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8.8507 |
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Pump torque,Tp(lbf•ft)= |
( |
Tp(lbf•in) |
) |
(lbf•ft) |
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12.0 |
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© Danfoss | January 2020 |
AB00000019en-000401 | 9 |
Design Guidelines
Hydraulic Fan Drive Systems
System Design Parameters
Sizing
Fan drive system sizing relies heavily on the input received from the customer. All system sizing calculations are based on the required fan power @ trim speed data given to the hydraulic system design engineer. This data is a statement of the fan drive motor shaft power that is required to turn a fan at the required speed to push, or pull, a required volume of air across coolers/radiators. The usual sequence of events is:
•The engine manufacturer advises the customer, or cooling system designer, of the heat dissipation required from the cooling system, charge air cooler etc. This information is combined with the heat rejection data for any accessories and work functions on the machine (such as : transmission cooler, hydraulic cooler, and A/C condenser) to determine the maximum heat rejection profile for the system.
•The customer’s cooling pack manufacturer will then use this data to size the cooling package and will generally recommend a fan to suit this need, providing the rated fan power, rated fan speed, and the fan speed required to satisfy the cooling needs of the system.
•With this information, knowing the minimum engine speed at which maximum fan speed needs to occur, the hydraulic system designer can size the hydraulic fan drive system.
To completely understand any fan drive system is to understand the fan load characteristics. Fans are unique in that the power to drive the fan changes with the cube of the fan speed, as follows:
Pf=k•(Nf)3
Pf1 / Pf2 = (Nf1 / Nf2)3 Where:
Pf = fan power (kW, hp) Nf = fan speed (rpm)
1,2 = subscripts for two different conditions k = Fan power coefficient
Fan power is defined as the power required to drive the shaft connected to the fan and is equal to the output power of the motor.
When a given fan speed is doubled; the required power to drive the fan increases by a factor of 8.
Fan power requirements (Example)
Fan rating = 22 kW @ 2000 rpm
<![endif]>Fan power (kW)
40
35
30
25
20
15
10
5
0 
0 500 1000 1500 2000 2500
Fan speed (RPM)
P106 108E
Since fan power is a function of both pressure and flow (fan speed), it follows that the relationship between fan speed and system pressure is
∆P1 / ∆P2 = (Nf1 / Nf2 )2
Where: ΔP = delta pressure across the hydraulic motor (bar, psid)
An accurate value of the fan rating is critical to the correct selection of components and their settings.
10 | © Danfoss | January 2020 |
AB00000019en-000401 |
Design Guidelines
Hydraulic Fan Drive Systems
System Design Parameters
Although the cubic relationship between fan power and fan speed has been consistently verified experimentally, it is still an approximation of the fan behavior. Therefore, to avoid significant errors in predicting power requirements, the fan power rating should be taken at a speed representative of typical fan operation.
For example, for a system in which the fan usually operates in a speed range of 1800-2200 rpm, a fan rating specified at 2000 rpm will yield more accurate results than a rating specified at, say, 1500 or 2500 rpm.
Fan curves provided by the fan manufacturer are often developed under ideal conditions. It is unlikely that a fan will exhibit exactly the same performance in an actual application (because of: shrouding, heat exchange airflow characteristics, and air density). Only through test data taken on the actual vehicle can a fan’s performance characteristics be accurately determined. The curve below illustrates the differences between predicted performance and actual performance of a fan installed in a vehicle. The system designer/integrator is encouraged to confirm their performance predictions via test over the entire operating speed range of the engine, and to refine their prediction model with a revised fan power coefficient when they rerun the sizing calculations.
Fan power requirements (example) Fan rating = 22 kW @ 2000 rpm
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Fan speed min -1(rpm) |
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P106 109E |
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||||||||||||||||||
© Danfoss | January 2020 |
AB00000019en-000401 | 11 |
Design Guidelines
Hydraulic Fan Drive Systems
System Design Parameters
Sizing Equations
Equations |
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Based on SI units |
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Based on English units |
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= |
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Vg • n • ηv |
(l/min) |
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Vg • n • ηv |
(US gal/min) |
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Input torque M= |
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Vg • ∆p |
(N•m) |
Input torque M= |
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Vg • ∆p |
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(lbf•in) |
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20 • π • ηm |
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Input power P = |
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Vg• n• ∆p |
(kW) |
Input power P = |
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Vg• n• ∆p |
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600 000 • ηm |
396 000 • ηm |
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Motors |
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Based on SI units |
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Output torque M |
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Vg • ∆p • ηm |
(N•m) |
Output torque M |
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Vg • ∆p • ηm |
(lbf•in) |
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Output power P |
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Q • ∆p • ηt |
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Output power P |
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Q • ∆p • ηt |
(hp) |
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1714 |
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Variables
SI units [English units]
Vg = Displacement per revolution cm3/rev [in3/rev] pO = Outlet pressure bar [psi]
pi = Inlet pressure bar [psi]
∆p = pO - pi (system pressure) bar [psi] n = Speed min-1 (rpm)
ηv = Volumetric efficiency ηm = Mechanical efficiency
ηt = Overall efficiency (ηv • ηm)
SI unit formulas are based on cm3, bar, N, N•m, W.
English formulas are based on in3, psi, lbf•in, hp.
12 | © Danfoss | January 2020 |
AB00000019en-000401 |
Design Guidelines
Hydraulic Fan Drive Systems
System Design Parameters
Axial Flow Fan Power Formula
Power to system parameter relationships
Pf2 |
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(N )3 |
• (D )5 • ν |
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∆P1 |
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D1 |
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Pf1 = Power of fan at known condition #1 Pf2 = Power of fan at condition #2
N1 = Fan speed at condition #1 N2 = Fan speed at condition #2 D1 = Fan diameter at condition #1 D2 = Fan diameter at condition #2
ν1 = Specific weight of air at condition #1 ν2 = Specific weight of air at condition #2 r 1 = Density of air at condition #1
r 2 = Density of air at condition #2
∆P1 = Hydraulic and/or Static Pressure at condition #1 ∆P2 = Hydraulic and/or Static Pressure at condition #2 V1 = Flow rate of air at condition #1
V2 = Flow rate of air at condition #2
© Danfoss | January 2020 |
AB00000019en-000401 | 13 |
Design Guidelines
Hydraulic Fan Drive Systems
System Design Parameters
System Design Data Form
Print this form. Fill in all the fields and check the appropriate check boxes. Fax the filled out form to your Danfoss Power Solutions Technical Sales Representative.
Engine details
Manufacturer |
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Model or Series |
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Pump Drive |
Engine PTO |
Ratio |
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:1 |
Input torque |
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Belt Drive |
(engine to pump) |
limit: |
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Pump Rotation |
Clockwise, Right hand |
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Speeds |
Counterclockwise, Anti-clockwise, Left hand |
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Low Idle |
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Governed |
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High Idle |
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Power steering
(if applicable)
Controlled Flow Requirement |
US gal/min |
l/min |
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Steering Pressure |
psi |
bar |
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(maximum) |
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O |
C KW |
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N |
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K |
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RCLO |
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P106110 |
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||
P104 376E
14 | © Danfoss | January 2020 |
AB00000019en-000401 |
Design Guidelines
Hydraulic Fan Drive Systems
System Design Parameters
|
Fan information |
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Manufacturer |
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Model or Series |
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Fan Diameter |
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in |
mm |
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Fan Input Power |
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HP |
kW |
At speed |
|
rpm |
Fan Rotation |
Clockwise |
(viewed on motor shaft, see illustration) |
Counterclockwise |
Clo
c
kwise
Fan Trim Speed |
|
rpm |
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C o unterclo
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e |
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is |
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w |
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ck |
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Set Point at Fan Trim Speed |
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rpm |
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(engine speed where max heat load occurs) |
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Coolant Temperature at Fan Trim Speed |
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°F |
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°C |
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(coolant temp where max fan speed is required) |
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||
Note: To properly size and specify a fan drive system, fan power requirements must be stated as accurately as possible. Fan power requirements can be determined from fan curves supplied by the manufacturer. Radiator and cooler manufacturers will supply air flow requirements based on heat loads. Air flow information must include accurate air flow and static pressure to determine correct fan power requirements.
Control preference
Electro-Hydraulic Modulating |
Electro-Hydraulic ON/OFF |
Single Input
Multiple Inputs
Reservoir
Reservoir Capacity |
US gal |
liter |
|
|
|
© Danfoss | January 2020
Design Guidelines
Hydraulic Fan Drive Systems
System Design Parameters
Fluid
Hydraulic Fluid Type
Viscosity |
|
at 40° C [104°F] |
cSt |
SUS |
|
at 100° C [212°F]
Maximum Fluid Temperature |
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°C |
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°F |
|||
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P104 379E |
|
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Filtration |
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Filter Position |
Inlet Line |
Filter Flow |
Full Flow |
|||||||
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Pressure Line |
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Partial Flow |
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Return Line |
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(recommended) |
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Filter Rating |
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micron |
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x ratio |
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Note: Do not locate the filter cartridge inside the reservoir. This reduces the reservoir capacity and reduces the dwell time (the time the oil |
|
spends in the resrevoir). It also increases the potential for damage to the hydraulic components due to aeration of the oil. |
P104 380E |
|
16 | © Danfoss | January 2020 |
AB00000019en-000401 |
Design Guidelines
Hydraulic Fan Drive Systems
System Design Parameters
Technical Features
In this document, we introduce the equations that are used to size the components of a modulating fan drive system. In addition to these principles, there are several other factors to consider to ensure that the hydraulic system performs to expectations. Following are some considerations you are encouraged to address during the design phase.
Shaft Loads and Bearing Life
For information on shaft loads and bearing life, refer to:
•Series 45 Technical Information 520L0519
•Series 40 Motors Technical Information 520L0636
•Series 42 Pumps Technical Information 11022637
•H1 Pumps Technical Information Manuals (see Reference Literature at the back of this manual)
Maximum Pump Speed
Pump displacement, and centrifugal filling of the pumping chambers, limit maximum pump speed. Unless otherwise specified, maximum rated pump speeds are based on operation at sea level with hydraulic fluids having a specific gravity of 0.9 and a viscosity of 58 SUS (9 cSt) at 180° F (80° C). Speed limits for a particular application depend on the absolute pressure and oil viscosity. Speed limits for individual products may be found in their respective technical information bulletins. Consult a Danfoss representative for operation outside of these published limits.
Minimum Pump and Motor Speed
Volumetric efficiency limits minimum pump speed. If lower than recommended starting or operating speeds are required, contact a Danfoss representative for assistance. Piston motors are designed for continuous operation at low speed, and at rated pressure. Motors may be started from zero speed on fan drives, and torque will increase with speed.
Motor Starting Pressure (open circuit motors)
No-load motor start-up pressures may range from 100 to 725 psid (7 to 50 dbar), depending on displacement. This property of the motor is dependent on motor design parameters, the CSF (Coefficient of Static Friction), and it is inversely proportional to motor displacement. For example: The starting torque for any given motor is largely dependent on the pitch diameter of the pistons and the CSF. Since torque is dependent on the product of pressure and displacement, and starting torque is essentially constant for any given frame size; starting pressure will be dependent on displacement, in an inverse relationship. To minimize starting pressure, select the smallest frame size for the required motor displacement.
Besides displacement, there are several factors which also effect motor starting pressure. They include: pressure rise rate (pressure gradient), temperature, fluid viscosity, motor return pressure (back pressure), fan inertia, pump flow rate, and piece-to-piece variation between motors.
Motor Free Run Pressure
Free run pressure is the minimum delta pressure across the motor that is required to keep the motor turning when there is no cooling demand. Free run pressure is dependent on motor displacement and shaft speed.
If the delta pressure across the motor is allowed to fall below the free run pressure; the motor will stop, and it will be necessary for the motor to go through the starting condition (start-up procedure) when cooling is needed again. In most applications, it is desirable to initiate fan rotation when the engine starts and prevent the motor from stopping, while the engine is running.
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Design Guidelines
Hydraulic Fan Drive Systems
System Design Parameters
Input Torque Ratings
When applying pumps in multiple configurations, ensure the input torque limitations are met for each section and for cumulative sections. Refer to individual product technical information bulletins for specific product torque limits. Always ensure that any individual pump in a multiple unit does not exceed its respective torque rating.
C Caution
Torques in excess of recommended values may cause premature input shaft, or unit, failure.
Pump Drive Conditions
Most Danfoss products are available with SAE and metric, standard spline, tapered key, or cylindrical keyed drive shafts for direct or indirect drive applications. An intermediate coupling is the preferred method for direct drives, thereby eliminating radial and axial loading. Direct Drive (or plug-in or rigid) spline drives can impose severe radial loads on the pump shaft when the mating spline is rigidly supported. Increased spline clearance does not alleviate this condition. Both concentricity and angular alignment of shafts are important to pump life. Misalignment can induce excessive side loads on bearings and seals, causing premature failure.
Overhung load drives (chain, belt, or gear) are permissible. Contact Danfoss for assistance. The allowable radial shaft loads are a function of the load magnitude, the load position, the load orientation, and the operating pressure of the hydraulic pump. All external shaft loads will have an effect on bearing life and may affect pump performance. In applications where external shaft loads cannot be avoided; optimizing the position, orientation, and magnitude of the radial load can minimize their influence on the pump. A tapered input shaft is recommended for applications where radial shaft loads are present. (Spline shafts are not recommended for belt or gear drive applications, the clearance between the mating splines will prevent accurate alignment of the drive elements and will contribute to excessive wear of the spline.) For belt drive applications, a spring loaded belt-tensioning device is recommended to avoid excessive radial loads on the input shaft.
Note for H1 pump with an FDC: Due to the failsafe functionality of the H1P FDC control the pump will stroke to max. displacement in case the input signal to the pump control and the Diesel engine will be switched off at the same time. In this situation a low loop event can occur which may damage the pump. Therefore, it’s strictly recommended to keep the input signal to the pump control alive while switching off the engine.
For further information please contact your Danfoss representative
Tapered Shaft and Hub Connections
Tapered shaft/hub connections provide excellent control of both axial and radial position of the drive coupling or fan assembly. When using the tapered connection, additional effort should be used to insure that there is adequate axial clamping load between the hub and the shaft. The designer is encouraged to establish that there is:
•Adequate clearance under the bolt/nut to insure full axial load may be applied to the taper without bottoming out.
•Adequate clearance between the top of the key and the bottom of the keyway in the hub. Interference between the top of the key and the bottom of the keyway will prevent the hub from seating onto the taper of the shaft. This will compromise the ability of the shaft to transmit its full torque capacity, and may result in failure of the shaft.
Pump Suction
For maximum pump life, the inlet pressure should not drop below 0.8 bar absolute [6 in. Hg vac.] at the pump inlet port.
For cold start conditions, inlet pressure down to 0.6 bar absolute [12 in. Hg vac.] is acceptable for short durations. The possibility of damage due to fluid cavitation and aeration is proportional to decreases in
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Design Guidelines
Hydraulic Fan Drive Systems
System Design Parameters
inlet pressure. In addition, oil film lubrication may be disrupted by low inlet pressure. These factors, either singularly or combined, may contribute to a decrease in pump life. Multiple changes in either diameter or direction can have a significant effect on the resistance to flow in inlet passages and can result in a substantial increase in the effective length of the inlet line. For this reason, Danfoss recommends that the inlet line contain a minimum number of adaptor fittings, tees, and elbows; as each are a source of additional restriction and, potentially, a source of leakage.
C Caution
Continuous operation with inlet pressures below 0.8 bar absolute [6 in. Hg vac.] can cause premature unit failure. Ensure adequate flow/pressure head at the pump inlet at all times.
Case Drain Pressure
Maximum pressure limitations for both case drain and inlet passages are available by consulting the appropriate technical information bulletin for the products being applied. Both line length and diameter influence the pressure drop of the fluid in these passages as it flows to/from the reservoir. In addition, both steady state flow velocity and transient conditions, which can accelerate the fluid in these passages, must be considered when determining their correct size. Of the two design parameters: line length and diameter, diameter has the most influence on the success of the design. Increasing line diameter can decrease both the steady state and the transient pressure drops exponentially. For additional information on steady state pressure drops in hydraulic passages, the reader is encouraged to consult any good text on basic hydraulic design. For additional information on transient pressure drops, refer to Appendix D.
Introducing additional flow from external sources into these return lines can also result in transient pressure pulses that may exceed the drain, or case pressure limits of these products. Danfoss recommends that the bearing drain and case drain lines return directly to the reservoir and remain dedicated to their intended function without connecting them to additional flow sources.
Filtration
To prevent premature wear, it is imperative that only clean fluid enters the pump and hydraulic circuit. A filter capable of controlling the fluid cleanliness to class 22/18/13 (per ISO 4406-1999) or better, under normal operating conditions, is recommended. At initial start up, the system can be at Class 25/22/17 but should not be run at high speed or pressure until the Class 22/18/13 is achieved through filtration. Since the filter must be changed at regular intervals, the filter housing should be located in an accessible area. Appropriate filter change intervals may be determined by test or by gauges indicating excessive pressure drop across the filter element.
For more information refer to Design Guideline for Hydraulic Fluid Cleanliness, Technical Information
520L0467.
Operating Temperatures
With Buna seals and normal operating conditions, the system temperature should not exceed 82 °C [180 °F] except for short periods to 93 °C [200 °F]. With optional Viton elastomer, the system may be operated at continuous temperatures up to 107°C [225°F] without damage to the hydraulic components.
C Caution
Operation in excess of 107 °C [225 °F] may cause external leakage or premature unit failure.
Fluids
A mineral based fluid is recommended that includes additives to resist corrosion, oxidation and foaming. The oil should have a maximum viscosity commensurate with system pressure drop and pump suction pressures. Since the fluid serves as a system lubricant, as well as transmitting power, careful selection of the fluid is important for proper operation and satisfactory life of the hydraulic components. Hydraulic
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Design Guidelines
Hydraulic Fan Drive Systems
System Design Parameters
fluids should be changed at appropriate intervals determined by test, supplier, or by change in color, or odor, of the fluid.
Every 10°C [18°F] rise in continuous reservoir temperature over 80°C [176 °F] decreases the life of the oil by ½.
For additional technical information on hydraulic fluids refer to Hydraulic Fluids and Lubricants 520L0463 Technical Information Bulletin and specific product technical bulletins.
For information relating to biodegradable fluids, see Danfoss publication Experience with Biodegradable Hydraulic Fluids 520L0465 or consult the Danfoss Technical Services Department.
Mounting
The pump mount/drive should be designed to minimize axial and radial loads on the shaft. When using an indirect (chain, belt, or gear) drive, contact Danfoss to determine permissible load limits and orientation of the installation.
The motor mount should be designed to position the motor/fan assembly within the shroud for optimum fan performance and to locate the leading edge of the fan blades relative to the adjacent surface of the heat exchanger. The support structure should be constructed so that it will be robust against forces and deflections due to shock and vibration as well as the loads applied to it by the fan and the hydraulic plumbing that will be connected to the motor.
Axial Thrust Motors
When a fan is directly mounted onto the drive shaft of a hydraulic motor, it imparts both a radial and an axial thrust load onto the shaft. In general, the weight of the fan is insignificant when compared to the radial load capacity of the bearings in the motor. But, the axial thrust load must be considered carefully. Under normal operating conditions, Danfoss motors have adequate axial thrust capacity for most fans that are applied in the industry, but they do have limitations. It is recommended that the system designer determine the axial thrust force that will be produced by the fan and compare it to the values listed below:
Series 40 motors external shaft load limits
|
Unit |
M25 |
M35/44 |
M46 |
|
|
|
|
|
Me |
N•m [lbf•in] |
29 [256] |
25 [221] |
24 [212] |
T |
N [lbf] |
848 [190] |
966 [217] |
1078 [242] |
|
|
|
|
|
L and K motors external shaft load limits
Frame |
|
L |
|
K |
|
|
|
|
|
|
|
Mounting configuration |
|
SAE |
Cartridge |
SAE |
Cartridge |
|
|
|
|
|
|
Maximum allowable external moment (Me) |
N•m |
7.7 |
21.7 |
13.3 |
37.5 |
|
|
|
|
|
|
|
[lbf•in] |
68 |
192 |
118 |
332 |
|
|
|
|
|
|
Maximum allowable thrust load (T) |
N |
750 |
|
1100 |
|
|
|
|
|
|
|
|
lbf |
169 |
|
247 |
|
|
|
|
|
|
|
Refer to Appendix-A for equations that will assist in calculating the axial thrust loads from the fan.
Calculated loads should be confirmed by test.
For shaft load limit calculations on Series 90 motors and H1B motors, contact your Danfoss representative.
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Design Guidelines
Hydraulic Fan Drive Systems
System Design Parameters
Piping
The choice of piping size and installation should always be consistent with minimizing maximum fluid velocity. This will reduce system noise, pressure drops and overheating, thereby adding to cost savings for the operation of the system. Inlet piping should be designed to prevent continuous pump inlet pressures below 0.8 bar abs. [6 in. Hg vac.] or 0.6 bar abs. [12 in. Hg vac.] during start-up. When selecting pipe sizing, recognize pressure drops are related to flow velocity. Danfoss recommends limiting the maximum average mean flow velocity to 5 m/sec [15 ft/sec.] in pressure lines, and 2.5 m/sec [7 ft/sec.] in suction lines.
In addition to limiting maximum flow velocity, it is recommended that the designer select the hoses, fittings and integral valve elements to be compatible with the desired working pressure of the hydraulic system. The following documents may be used to determine the working pressure ratings for the respective system elements:
•SAE J514: for working pressure ratings and fitting installation torques for - O-ring boss fittings/ports and JIC 37º flared tubing connections
•SAE J518: for working pressure ratings and bolt installation torques for SAE code 61 4-Bolt flange fittings/ports,
•SAE J517: for working pressure ratings for SAE hydraulic hose
•SAE J1453: for working pressure ratings for flat face O-ring fittings.
Reservoir
The reservoir should be designed to accommodate expected maximum volume exchange during all system operating modes and to prevent aeration of the fluid as it passes through the reservoir. Return and inlet lines should be positioned below the reservoir low oil level and be located as far as possible from each other. A diffuser and a baffle plate located between the pump inlet and return line is desirable to reduce turbulence and to allow the oil to de-aerate before it re-enters the pump.
Reservoirs must be sized to ensure de-aeration of the oil before it re-enters the pump. For dwell times of less than 90 seconds, the system designer is encouraged to verify that entrained air (bubbles) are not included in the oil that is being transmitted from the reservoir to the pump. This may be accomplished by placing a sight gage into the inlet line between the reservoir and the pump. Placing a variable frequency strobe light source behind the sight gage will improve the observer’s ability to see air bubbles present in the fluid as it passes through the inlet line.
Danfoss encourages system designers to locate the reservoir so that the oil level in the reservoir will remain above the level of the inlet port of the pump under all conditions. By doing this, a positive head is produced that can offset the effects of line losses and altitude on the inlet pressure available at the pump.
Danfoss also encourages system designers to consider the potential for air to be introduced into the inlet line within the reservoir via the introduction of a vortex or whirlpool, between the surface of the oil and the inlet port. One way to discourage a vortex is to locate a baffle between the inlet passage, or suction strainer, and the surface of the oil. The system designer should consider the design parameters of size and position for the baffle to ensure that a vortex cannot form if the reservoir attitude is at its extremes, the oil level is at or below the minimum recommended capacity, or if sloshing occurs due to operation of the machine.
Cavitation and Aeration Damage
Hydraulic oil used in the majority of systems contains about 10% dissolved air by volume. This air, under certain conditions of vacuum within the system, is released from the oil causing air bubbles. These entrained air bubbles collapse if subjected to pressure, and this collapse creates erosion of the adjacent metal surfaces and degradation of the oil. Because of this, it becomes obvious that the greater the air content within the oil, or the greater the vacuum in the inlet line, the more severe will be the resultant damage. The main causes of over-aeration of the oil are air leaks, particularly on the inlet side of the pump, and flow line restrictions such as inadequate pipe sizes, elbow fittings and sudden changes in flow passage cross-sectional area. To avoid cavitation problems when using Danfoss pumps and motors, avoid defects in plumbing and construction, maintain pump inlet pressure and rated speed requirements, and ensure reservoir size and follow recommended guidelines.
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Design Guidelines
Hydraulic Fan Drive Systems
System Design Parameters
When entrained air entering the pump is pressurized at the pump outlet, it is forced into solution in the oil as the bubbles collapse. This super-saturated solution of dissolved air and oil will release its air when the pressure is released. Symptoms of this condition can be observed by oil / foam escaping from the fill port of the reservoir when the system is shut down.
Cooling
Depending on duty cycle and reservoir/line construction, an oil-cooler may be required. The oil-cooler size is based on typical power losses in the hydraulic circuit. The oil cooler is usually placed in the return line to the reservoir.
Pressure Protection and Ratings
The pump, as well as other system components, has pressure limitations. Thus a relief valve, or pressure limiting device, must be installed in the system, and its setting must be consistent with the product ratings. Refer to the relevant Danfoss technical bulletins for this information.
C Caution
Failure to install a relief valve or over-pressure protection may result in premature unit failure.
Bearing Life Expectancy
All Danfoss piston pumps and motors utilize anti-friction, rolling element bearings, and journal bearings, which have an oil film maintained at all times between the bearing surfaces. If this oil film is sufficiently sustained through proper system maintenance and the product’s operating limits are adhered to, a long bearing life can be expected.
A B10 type life expectancy number is generally associated with rolling element bearings. Bearing life is a function of speed, system pressure, and other system parameters such as oil viscosity and oil cleanliness.
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Design Guidelines
Hydraulic Fan Drive Systems
Glossary
Terminology
Trim speed is the maximum fan speed required at the full-on condition. This is equal to, or greater than, the fan speed required to meet the maximum cooling needs of the cooling system.
Engine set point is the engine speed at which trim speed should occur, and is provided by the cooling system designer. This is equal to, or less than, the engine speed at which maximum system cooling is required.
Fan power at trim is the power that needs to be generated at the motor shaft to drive the fan at trim speed.
Fan rating is the value by which different types of fans can be compared. Usually designated as X power @ Y rpm and equates back to an air volume (mass flow rate) that can be moved per minute at the Y rpm.
To assist with the sizing exercise, Danfoss has developed a sizing tool to perform the necessary calculations. Within the sizing tool, worksheets are provided for both fixed displacement pump/fixed displacement motor, and variable displacement pump/fixed displacement motor hydraulic systems. The sizing tool has been provided to your Danfoss representative.
Refer to the data sheets on pages in the System Design Parameters chapter. When the data on these sheets is complete, calculations can be made to determine the most suitable pump/motor/controller combination for the application based on:
•Pump drive available (torque, shaft, mounting flange, overall space envelope)
•System pressure required
•Additional flow/pressure required from the pump, (for example: steering flow)
•Control type requested by the customer
•Limiting operating parameters of the fan drive family products
•Fit (space envelope)
Contact your Danfoss representative for a report of the performance prediction generated by the fan drive sizing tool.
For systems using axial piston pumps, refer to AE Note 2010-02 for sizing calculations. Contact your Danfoss representative for access to AE Note 2010-02.
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Design Guidelines
Hydraulic Fan Drive Systems
Appendix A-Fan Performance
Fans
Fans are generally divided into two classifications:
•Centrifugal or radial flow - in which the air flows radially thru the impeller within a scroll type of housing
•Axial flow - in which the air flows axially thru the impeller within a cylinder or ring.
The typical axial flow fan is commonly referred to as a propeller fan, and is customarily used for free delivery, or against low resistance. They are usually mounted within a circular ring or shroud with a circular opening.
Fan Performance
Fan performance is a measure of volume, total pressure, static pressure, speed, power input, mechanical efficiency, and static efficiency, at a stated density. Some useful definitions are:
Volume delivered by a fan is the number of cubic feet of air per minute (or, cubic meters per second), expressed at fan inlet conditions.
Total pressure is the rise of pressure from fan inlet to fan outlet.
Velocity pressure is the pressure corresponding to the average velocity, determined from the volume of airflow at the fan outlet area.
Static pressure is the total pressure diminished by the fan’s velocity pressure. Static pressure is a measure of the fan’s performance and is reported by the fan manufacturer in their technical literature. Static pressure is also a measure of the resistance to the flow of air thru the heat exchanger.
Power output is expressed in horsepower (or, kilowatts) and is based on fan volume and fan total pressure.
Power input is expressed in horsepower (or, kilowatts) and is the measured power delivered to the fan shaft.
Mechanical efficiency of a fan is the ratio of power output to power input.
Static efficiency of a fan is the mechanical efficiency multiplied by the ratio of static pressure to the total pressure.
The theoretical power required to move a quantity of air may be determined by the following formula:
SI system |
3 |
|
|
|
N |
|
|
|||
|
|
|
|
|
|
|||||
Theoretical power = ( |
m |
|
)• |
(Total pressure, [Pa],[ |
|
]) |
|
|||
|
m2 |
|
||||||||
sec |
|
[watts] |
||||||||
|
|
|
|
|
|
|
(1.0) |
|
|
|
English system |
( |
|
ft3 |
|
)• (Total pressure, [in H20]) |
|
|
|||
Theoretical hp = |
min |
[hp] |
|
|||||||
|
|
|
|
|
|
(6356) |
|
|
||
|
|
|
|
|
|
|
|
|
|
|
Pressure and power both vary with air density.
Fan efficiencies may be determined by the following formulae:
24 | © Danfoss | January 2020 |
AB00000019en-000401 |
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