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 entirelyvoluntary, and its applicability and suitability for any particular use, including any patent infringement arising therefr
2、om, is the sole responsibility of the user.”SAE reviews each technical report at least every five years at which time it may be revised, reaffirmed, stabilized, or cancelled. SAE invites your written comments andsuggestions.Copyright 2017 SAE InternationalAll rights reserved. No part of this publica
3、tion may 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 (outsid
4、e USA)Fax: 724-776-0790Email: CustomerServicesae.orgSAE WEB ADDRESS: http:/www.sae.orgSAE values your input. To provide feedback on thisTechnical Report, please visithttp:/standards.sae.org/AIR857AAEROSPACE INFORMATION REPORT AIR857 REV. AIssued 1964-12Revised 1996-08Reaffirmed 2017-10Superseding AI
5、R857Speed Variation of D-C MotorsRATIONALEAIR857A has been reaffirmed to comply with the SAE Five-Year Review policy.1. SCOPE:The scope of this SAE Aerospace Information Report (AIR) is a review of the factors contributing tospeed variation of d-c motors, a presentation of typical data showing speed
6、 variation as a functionof certain variables for representative motors, and a recommendation of a means of improvingcommunications between motor users and manufacturers.The following analysis is limited to variations in voltage, torque, temperature, and altitude of thesame magnitude as in MIL-M-8609
7、.FIGURE 12. APPLICABLE DOCUMENTS:The following publications form a part of this document to the extent specified herein. The latestissue of SAE publications shall apply. The applicable issue of other publications shall be the issuein effect on the date of the purchase order. In the event of conflict
8、 between the text of thisdocument and references cited herein, the text of this document takes precedence. Nothing in thisdocument, however, supersedes applicable laws and regulations unless a specific exemption hasbeen obtained.2.1 U.S. Government Publications:Available from DODSSP, Subscription Se
9、rvices Desk, Building 4D, 700 Robbins Avenue,Philadelphia, PA 19111-5094.MIL-M-8609MIL-M-8609A3. STATEMENT OF PROBLEM:3.1 Many applications of d-c motors require a quantitative knowledge of variations in motor speedand performance under various voltage inputs, ambient temperatures, altitudes, coolin
10、gconditions, and manufacturing tolerances. The basic specification, MIL-M-8609, is limited in thatit merely requires that speed should be within 10% of the rated value after a heat run at ratedvoltage and sea level ambient.3.2 The problem facing motor users in preliminary design work is to predeterm
11、ine what speeds will beencountered at other than rated torque, at other than rated voltage, at various ambienttemperatures and atmospheric pressures, for a group of production motors built over a longinterval of time.3.3 Additionally, it appears that many users are in need of recommendations as to w
12、hat parametersto specify, and how to specify them in order to obtain optimum designed motors meeting theirrequirements in size, weight, and cost.4. THEORY (GENERAL RELATIONSHIPS):Basic equations describing the performance of a d-c motor with negligible armature reaction.Vt= Ec+ eb+ IaRa+ IaRs(Eq.1)E
13、c= Ke S (Eq.2)=+aIbIffFroelichs equation for the machine saturation curve (Eq.3)_ SAE INTERNATIONAL AIR857A Page 2 of 164. (Continued):where:a & b = magnetic circuit constantsIf= field excitation current = magnetic flux per poleEc= counter voltage developed by armatureKe& Kt= winding constantsS = ar
14、mature speedVt= line voltage at motor terminalseb= brush contact voltage dropIa= armature currentRa= armature resistanceRs= series field resistanceCombining and solving for speed yields the expression( )SVeIRRKbIaItbaaseff= +(Eq.4)For a series motor (Ia= If)( )SVeIRRKbIaItbaaseaa= +(Eq.5)For a shunt
15、 motor (Rs= o)SVeIRKbIaItbaaeff=+(Eq.6)For a permanent magnet motor = KMa constantSVeIRKKtbaacM=1(Eq.7)_ SAE INTERNATIONAL AIR857A Page 3 of 165. SPEED VARIATION DUE TO TORQUE VARIATIONS:A d-c motor adjusts itself to an increase or decrease in load torque by drawing increased ordecreased armature cu
16、rrent in accordance with Equation 8:T = Kt Ia(Eq.8)Initially, then, changes in torque affect motor speed because of the corresponding change inarmature current in accordance with Equations 4, 5, 6, or 7. The series motor is more drasticallyaffected because Iagoverns speed inversely, whereas in a shu
17、nt or permanent magnet motor Iaappears only as a subtrahend, which in most cases is a small percentage of the net numerator ofEquation 6 or 7.6. SPEED VARIATION DUE TO TEMPERATURE VARIATIONS:Due to changes in heating occasioned by the change in motor losses accompanying loadvariations, a further eff
18、ect on speed will result as winding resistances change. Generally thedecrease in shunt field current due to shunt field resistance increase has more effect on speedthan a proportionate change in armature or series field resistance. The speed of a shunt motormay, in general, be expected to increase a
19、s internal temperatures increase. In a series motorwhere If= Iaand in a permanent magnet motor where the field is practically a constant, the speedwill decrease as Raand Rsincrease.When a shunt motor is operated well beyond the knee of the saturation curve, the expression:aIbIff+, Equation 3 becomes
20、 more nearly a constant with variations in Ifcaused by variations intemperature. The reciprocal of this expression in Equation 6 also becomes nearly a constant. Inthis case the shunt motor speed will decrease as temperature increases as in the permanentmagnet motor.Another factor contributing to spe
21、ed variation with temperature is the effect of increased bearinggrease viscosity at low temperatures. The added torque required to overcome such losses resultsin a reduction of motor speed at low temperatures. This factor is generally more noticeable onminiature and/or high speed motors than on larg
22、e, lower speed units. Also, it is more noticeable atthe beginning of a run than it is after grease viscosity has decreased due to normal heating of themotor.In the case of extreme temperature motors, another factor affecting speed is reduction of thepermeability of steel as the Curie temperature is
23、approached. This effects a reduction in Equation 3 as temperature is increased and appears as a speed increase in Equations 5 and 6. Over the temperature range of MIL-M-8609 this factor is generally negligible._ SAE INTERNATIONAL AIR857A Page 4 of 167. SPEED VARIATIONS DUE TO ALTITUDE VARIATIONS:Alt
24、itude variations may act in three ways to affect motor speed:a. Increase in motor temperature in the case of fan-cooled motors, due to reduction in air densitywhich also causes a small reduction in fan power requirements.b. Increase in temperature due to change in heat transfer parameters as altitud
25、e is increased.c. Change in brush contact drop and in brush friction.Effects of items a. and b. on speed have been discussed previously in Sections 5 and 6.A discussion of the effects of altitude, and the associated changes in humidity, on brushperformance are beyond the scope of this document and a
26、re generally negligible on 28 V motors.8. SPEED VARIATIONS DUE TO INPUT VOLTAGE VARIATIONS:Equation 7 shows that the speed of a permanent magnet motor is zero until the voltage Vtisgreater than the sum of eband IaRa, the brush voltage drop and the voltage drop due to armatureresistance. From this po
27、int on, the speed-voltage characteristic is practically a straight line up torated voltage. In some cases this characteristic may extend beyond 50% overvoltage. Thedeviation from a straight line characteristic is caused by the IaRaportion of Equation 7. Thearmature current will increase gradually as
28、 voltage and speed increase with a constant torque loadand more rapidly as overspeed conditions are reached. As IaRaincreases, the speed decreases.Equation 5 shows that the speed of a series motor is zero until Vtis greater than the sum of ebandIa(Ra+ Rs). The armature current Iaof a series motor wi
29、ll also increase as voltage and speedincrease with a constant torque load. Since Iaappears in two portions of Equation 5 the deviationfrom a straight line will generally be greater than for a permanent magnet motor. An increase in Ia(Ra+ Rs) causes a decrease in speed, and since bIaIaa+is equal to 1
30、(from Equation 3), anincrease in Iawill cause to increase 1to decrease, and the value of S, the motor speed todecrease. The change in due to the increase in Iawill vary depending on what portion of the fieldsaturation curve the motor is operating.Similar reasoning can be applied to Equation 6 for th
31、e shunt motor except If, the shunt field current,will increase in direct proportion to Vtrather than gradually as for Ia. Thus the factor bIaIff+willdecrease more rapidly and the speed voltage characteristic can be expected to deviate more froma straight line than for a series motor._ SAE INTERNATIO
32、NAL AIR857A Page 5 of 169. RECOMMENDATIONS:It is recommended that motor users accurately predetermine the percent variation which the drivendevice can tolerate, for each of the above governing factors, and include this information in theDetail Requirements Form, Figure 1 of MIL-M-8609A. Only those f
33、actors of importance to theparticular application should be included, in order to provide as much design latitude as possible.If speed variation data as a function of the other variables is desired for information, it should beobtained from test data taken on prototypes during qualification tests. T
34、est data other than thosenormally taken during qualification tests may not be readily available and may require separatenegotiation.It is noted that paragraph 4.5.2.2 of MIL-M-8609A allows a 10% variation in speed due tomanufacturing tolerances, and an additional 5% variation due to the effects of e
35、nvironmental testson a motor (which should approximate the effects of normal usage and wear encountered inservice). For a quantitative picture of the variation in speed due to the other factors previouslydiscussed, it is recommended that the typical data presented herewith be studied.In order to obt
36、ain reasonable agreement in results obtained from motors of various sizes anddesigns, a “reference rating” was established for each motor by noting the value of torque atmaximum power output, and then rating the unit at a torque load equal to half this value.PREPARED BY SAE SUBCOMMITTEE AE-7B, MOTOR
37、S & MAGNETIC DEVICESOF SAE COMMITTEE AE-7, AEROSPACE ELECTRICAL POWER & EQUIPMENT_ SAE INTERNATIONAL AIR857A Page 6 of 16FIGURE 2_ SAE INTERNATIONAL AIR857A Page 7 of 16FIGURE 3_ SAE INTERNATIONAL AIR857A Page 8 of 16FIGURE 4_ SAE INTERNATIONAL AIR857A Page 9 of 16- 10 -FIGURE 5_ SAE INTERNATIONAL A
38、IR857A Page 10 of 16FIGURE 6_ SAE INTERNATIONAL AIR857A Page 11 of 16FIGURE 7_ SAE INTERNATIONAL AIR857A Page 12 of 16FIGURE 8_ SAE INTERNATIONAL AIR857A Page 13 of 16FIGURE 9_ SAE INTERNATIONAL AIR857A Page 14 of 16FIGURE 10_ SAE INTERNATIONAL AIR857A Page 15 of 16FIGURE 11_ SAE INTERNATIONAL AIR857A Page 16 of 16
