1、_SAE Technical Standards Board Rules provide that: “This report is published by SAE to advance the state of technical and engineering sciences. The use of this report is entirely voluntary, and its applicability and suitability for any particular use, including any patent infringement arising theref
2、rom, is the sole responsibility of the user.” SAE reviews each technical report at least every five years at which time it may be reaffirmed, revised, or cancelled. SAE invites your written comments and suggestions. Copyright 2009 SAE International All rights reserved. No part of this publication ma
3、y be reproduced, stored in a retrieval system or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of SAE. TO PLACE A DOCUMENT ORDER: Tel: 877-606-7323 (inside USA and Canada) Tel: +1 724-776-4970 (outside US
4、A) Fax: 724-776-0790 Email: CustomerServicesae.org SAE WEB ADDRESS: http:/www.sae.orgSAE values your input. To provide feedback on this Technical Report, please visit http:/www.sae.org/technical/standards/ARP1280BAEROSPACERECOMMENDEDPRACTICEARP1280 REV. B Issued 1976-03 Reaffirmed 2002-07 Revised 20
5、09-12 Superseding ARP1280A (R) Aerospace - Application Guide for Hydraulic Power Transfer Units RATIONALEARP1280 has been updated to Revision B for the following reasons: (a) new technical information has been introduced, (b) the references called up in the document have been updated, (c) some of th
6、e figures have been redrawn, and (d) editorial changes have been made to improve the readability of the document 1. SCOPE This SAE Aerospace Recommended Practice (ARP) is an application guide for hydraulic power transfer units and describes: The various types Typical design approaches Their operatio
7、nal characteristics and limitations Circuit recommendations Typical applications The scope of this ARP is limited to devices that transfer power between hydraulic systems and do so by means of rotary subassemblies such as hydraulic motors and pumps. 1.1 Purpose The purpose of this document is to app
8、rise the system designer of the available options in power transfer units, configuration tradeoffs, and system design precautions in their application. 2. REFERENCES 2.1 Applicable Documents The following publications form a part of this document to the extent specified herein. The latest issue of S
9、AE publications shall apply. The applicable issue of other publications shall be the issue in effect on the date of the purchase order. In the event of conflict between the text of this document and references cited herein, the text of this document takes precedence. Nothing in this document, howeve
10、r, supersedes applicable laws and regulations unless a specific exemption has been obtained.Copyright SAE International Provided by IHS under license with SAENot for ResaleNo reproduction or networking permitted without license from IHS-,-,-SAE ARP1280B Page 2 of 212.1.1 SAE Publications Available f
11、rom SAE International, 400 Commonwealth Drive, Warrendale, PA 15096-0001, Tel: 877-606-7323 (inside USA and Canada) or 724-776-4970 (outside USA), www.sae.org. ARP24 Determination of Hydraulic Pressure Drop AIR737 Aerospace Hydraulic and Pneumatic Specifications, Standards, Recommended Practices, an
12、d Information Reports ARP819 Fluid System Characteristics Affecting Hydraulic Pump Operation ARP994 Recommended Practice for the Design of Tubing Installations for Aerospace Fluid Power Systems AIR1899 Aerospace Military Aircraft Hydraulic System Characteristics AIR1922 System Integration Factors Th
13、at Affect Hydraulic Pump Life AS1241 Fire Resistant Phosphate Ester Hydraulic Fluid for Aircraft 2.1.2 U.S. Government Documents Available from the Document Automation and Production Service (DAPS), Building 4/D, 700 Robbins Avenue, Philadelphia, PA 19111-5094, Tel: 215-697-6257, http:/assist.daps.d
14、la.mil/quicksearch/.MIL-PRF-5606 Hydraulic Fluid, Petroleum Base; Aircraft, Missile and Ordnance MIL-PRF-83282 Hydraulic Fluid, Fire Resistant Synthetic Hydrocarbon Base, Aircraft 2.1.3 ISO Publications Available from American National Standards Institute, 25 West 43rdStreet, New York, NY 10036-8002
15、, Tel: 212-642-4900, www.ansi.org. ISO22089 Aerospace Hydraulic Power Transfer Units General Specifications 2.2 Definitions The power transfer unit (PTU) is a device which uses some of the hydraulic power in one hydraulic system to supplement the hydraulic power in a second system without the interc
16、hange of fluid between the systems. PTUs can be designed to transfer power from one system to a second system in one direction only (unidirectional), or they can be designed to transfer power in either direction between two systems (bidirectional). 3. PTU CONCEPT The basic concept of a PTU is a hydr
17、aulic motor driving a pump, mounted back-to-back. The displacement of each of these may be the same or different. Accordingly, PTUs can be used as pressure reducers, as pressure intensifiers, or to maintain the same pressure in both systems. Occasionally they are used as flow dividers. If bidirectio
18、nal operation is required, both the pump and the motor reverse their functions; that is, that which previously operated as a pump now functions as a motor and vice versa. The fact that the shaft between the two subassemblies reverses direction of rotation is, conceptually, incidental. If the pressur
19、e relationship between the two systems must remain the same in both directions of operation (rather than reverse also), one or both of the subassemblies that make up the PTU must be of a variable displacement design. Copyright SAE International Provided by IHS under license with SAENot for ResaleNo
20、reproduction or networking permitted without license from IHS-,-,-SAE ARP1280B Page 3 of 21The PTU is a torque balanced device. A change in the pressure ratio between the motor side (primary system) and the pump side (secondary system) will result in a torque imbalance between the motor and pump sid
21、es of the PTU. This will then cause the PTU to start turning (driven by the motor side) and thereby supply power to the pump side and increase the secondary system pressure until a torque balance is re-established. At this point the PTU will maintain a speed proportional to the flow demand of the se
22、condary system, and will stop again if there is no flow demand. During steady state operation, the torque output of the motor side will always equal the torque input to the pump side. Any torque unbalance between the motor and the pump will cause a change in speed and thus flow. 4. GENERAL DESIGN AN
23、D QUALIFICATION REQUIREMENTS ISO22089 provides design, production acceptance testing and qualification requirements for PTUs. 5. OPERATIONAL CHARACTERISTICS Friction, pump and motor efficiencies, and the inherently very high torque-to-inertia ratio result in several characteristics that are unique t
24、o the PTU. These must be thoroughly understood to prevent damaging operation such as overspeed, excessive acceleration, instability, cogging, etc. 5.1 PTU Efficiency From a system performance standpoint, the torque efficiency of a PTU is much more important than its overall efficiency. Torque effici
25、ency is a measure of the differential pressure across the motor in relation to that across the pump. Since a PTU is very seldom used in continuous duty applications, the overall efficiency, which is a measure of heat rejection, is of secondary importance. Equations that quantify these relationships
26、are shown below in Equations 1 to 7. =2pumpofD x pumpacrossPTorqueInputPumplTheoretica(Eq. 1) =2motorofD x motoracrossPTorqueOutputMotorlTheoretica(Eq. 2) torqueinletpumpActual100 x torqueoutputpumpUseful(%)EfficiencyTorquePump =(Eq. 3) torquemotorInput100 x outputtorquemotorActual(%)EfficiencyTorqu
27、eMotor =(Eq. 4) NOTE: The actual pump input torque is assumed to be equal to the actual motor torque output. This is because the motor directly drives the pump by a shaft.efficiencytorqueMotor x efficiencytorquePumpEfficiencyTorquePTU =motormotorpumppumpDxP100 x D x P(%)EfficiencyTorquePTU=(Eq. 5)Co
28、pyright SAE International Provided by IHS under license with SAENot for ResaleNo reproduction or networking permitted without license from IHS-,-,-SAE ARP1280B Page 4 of 21motor(in)pump(in)motor(out)pump(out)Q x Q100 x Q x Q(%)Efficiencyc VolumetriPTU =pumpmotor(in)motorpump(out)D x Q100 x D x Q= (E
29、q.6) motor(in)motorpump(out)pumpQ x P100 x Q x P(%)EfficiencyOverallPTU= (Eq. 7) where:P = Differential pressure, psi (kPa) D = Displacement, in3/rev (ml/rev) Q = Flow, gpm (l/min) The torque efficiency should be considered at the following two points: Stall torque efficiency, as it affects the diff
30、erential pressure at which the unit will come on line. It is strongly influencedby static friction which is very unpredictable and varies from unit to unit and start to start. Stall torque efficiencies are generally slightly higher for relatively larger displacement units than for the smaller ones.
31、Full flow torque efficiency, as it affects the operating differential pressure between the two systems. It is driven primarily by mechanical and viscous losses. 5.2 Frictional Effects During startup, the change from static friction to running friction has a significant effect on operation. At breaka
32、way, thereis a significant torque unbalance between the motor side and pump side which diminishes substantially as soon as the PTU rotates. Depending on the magnitudes of the friction and flow demand, this can cause continuous start-stop action (instability) or low speed cogging. 5.3 PTU Acceleratio
33、n Acceleration of the PTU is primarily a function of the magnitude of the torque unbalance at breakaway and the hydraulic power available to the motor side. PTU inertia and dynamic friction are negligible factors. Zero to rated flow acceleration times of 15 to 20 ms are common if the flow rate to th
34、e motor is not controlled. Such acceleration times are substantially faster than those for typical pump installations and will usually create damaging inlet cavitation problems because the system cannot accelerate the column of inlet fluid fast enough to keep up with the demand of the pump side of t
35、he PTU. 5.4 Overspeed Overspeeding of the PTU, which would cause significant damage to the unit, can occur if the flow to the motor side is not properly limited. The speeds reached during transients are an important consideration and warrant careful analysis. 5.5 Acoustic Noise For a number of reaso
36、ns, hydraulic pumps and motors tend to produce relatively high acoustic noise levels. The compromises required in the design of the PTU impacts not only the efficiency but also effects pressure pulsations and acoustic noise. In addition, a PTU is often installed in closer proximity to crew or passen
37、ger locations than is typically thecase for pumps or motors. Depending on size and speeds, noise levels can easily reach 110 to 115 dB levels and may in such cases warrant some environmental design and installation precautions. With proper isolation and if speeds are kept low, noise levels as low as
38、 80 to 90 dB may be obtained. Copyright SAE International Provided by IHS under license with SAENot for ResaleNo reproduction or networking permitted without license from IHS-,-,-SAE ARP1280B Page 5 of 215.6 PTU Control Valves The various PTU control valve options discussed throughout this ARP can b
39、e part of the system, potentially integrated with other functions, or they can be integrated into the PTU. The choice is generally influenced by weight, space, and cost tradeoffs. 5.7 PTU System Failure Cases The PTU should be designed such that there is no possibility of intermixing the fluids of t
40、he two independent systems.Not only must the PTU and the hydraulic system it is installed in itself be so designed such that no single failure will disable both systems, but also each system must be so designed that a component failure in one system will not cause a loss of power in the other system
41、.Similarly, the systems that interface with the PTU should be designed so as to minimize the possibility of a failure in either one having an effect on the other. 5.8 Control and Indication 5.8.1 Control and Operation Strategy Typically a PTU can be used at specific periods such as: During a flight
42、that are considered to be high-risk times, for example during take-off, initial climb and approach/landing Aircraft pre-flight checks During ground maintenance The decision on whether to control a PTU manually or automatically is generally dictated by their application, as a PTU can be operated with
43、 or without any pilot intervention. For example: a) If the PTU is used as a back up pump for an entire hydraulic system, then the control could be both automatic and manual. During a flight, the control of the PTU could be automatic, such that it is selected to run under specific flight conditions a
44、nd/or the detection of a failure of the secondary system. Alternatively, the PTU control could be a manual operation with the pilot either selecting it on at specific periods during the flight, or selecting it on following the loss ofthe main system power source(s).NOTE: It is not recommended to lea
45、ve a PTU running continuously throughout each flight. This is because there will be a reduction in the potential reliability primarily due prolonged running at low speed which results in excessive bearing wear. Additionally, there should be a means of manually selecting the PTU on for ground checks,
46、 either for pre-flight or for ground maintenance purposes. b) If the PTU is for a specific sub-system or sub-systems then it should be linked into the operation of the sub-system(s) so that it is automatically available to supply hydraulic power only when that sub-system is operated, without any pil
47、ot intervention. For example, if a PTU is used to provide additional hydraulic power for the landing gear extension/retraction system (LGERS), then the selection of the PTU could be linked into the LGERS control system such that it operates only during the extension/retraction sequences.If the PTU i
48、s automatically controlled, there should be a means provided to enable the PTU to be selected off, without any pilot intervention, following: A failure or loss of fluid in the secondary system, or The loss of pressure or prime in the primary system Copyright SAE International Provided by IHS under license with SAENot for ResaleNo reproduction or networking permitted without license from IHS-,-,-SAE ARP1280B Page 6 of 21This not only minimizes the potential of losing the primary system in a case of a failure in the secondary system, but also prevents unneces
