SAE HS-788-1980 SAE Manual on Design and Application of Leaf Springs.pdf

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1、 SAE Manual on Design and Application of Leaf Springs SAE HS-788 Published by: Society of Automotive Engineers, Inc. 400 Commonwealth Drive Warrendale, PA 15096-0001 U.S.A. Phone: (41 2) 776-4841 Fax: (412) 776-5760 All technical reports, including standards approved and practices recommended, are a

2、dvisory only. Their use by anyone engaged in industry or trade or their use by governmental agencies is entirely voluntary. There is no agreement to adhere to any SAE Standard or Recommended Practice, and no commitment to conform to or be guided by any technical report. In formulating and approving

3、technical reports, the Technical Board, its councils, and committees will not investigate or consider patents which may apply to the subject matter. Prospective users of the report are responsible for protecting themselves against liability for infringement of patents, trademarks, and copyrights. Co

4、pyright O 1982 Society of Automotive Engineers, Inc. All rights reserved. Printed in the United States of America. ISBN 0-89883-383-3 Permission to photocopy for internal use or personal use, or the internal or personal use of specific clients, is granted by SAE for libraries and other users registe

5、red with the Copyright Clearance Center (CCC), provided that the base fee of $50 per page is paid directly to CCC, 222 Rosewood Dr., Danvers, MA O1 923. Special requests should be addressed to the SAE Publications Group. O-89883-383-3/82 $50 SPRING COMMITTEE H. M. Reigner (Sponsor), Eaton Corp., Eng

6、ineering this was issued in 1970 as SAE J788a. Following the mandate of the SAE Board of Directors in 1969 that “SAE will include SI units in SAE Standards and other technical reports,” it was decided to update and revise the Manual for metric leaf spring designs. The previous editions of the Manual

7、 used U.S. Customary Units, typically inch (in), pound (lb), pound per square inch (psi). This edition of the Manual uses SI Metric Units in accordance with provisions of “Rules for SAE Use of SI (Metric) Units,” SAE 5916. The millimeter (mm) has been chosen as the unit of length. In the Internation

8、al System of Units (Systme International: SI) a clear distinction is made between the kilogram (kg) as the unit applicable to mass (in place of the pound-mass, or pound avdp, and the newton (N) as the unit applicable to (load or) force in place of the pound-force. The term mass is commonly taken as

9、a measure of the amount of material a body contains. More accurately, it is the property of a body that is a measure of its inertia (or a measure of its resistance to a change in motion). The term (load or) force refers to an influence that, if applied to a free body, results in an acceleration of t

10、he body. Thus, force equals mass times acceleration, with: 1 N = 1 kg * 1 m/s2. An increase in force is actually an increase in acceleration. The term weight can appear as a quantity to mean either mass or force. When it refers to the inertia property of the body, it should be designated as mass and

11、 measured in units of kg. But it may refer to a vertical downward force (also referred to as “force of gravity” and as “gravitational pull”) which requires an equal but opposite force to restrain the mass of the body against free fall. In accordance with the recommenda- tion of the SAE Metric Adviso

12、ry Committee, it should then be designated as force of gravity and measured in units of N. This equals the bodys mass times the acceleration of gravity (which, by Interna- tional Agreement, is generally accepted as 9.806 650 m/s2 on the surface of the earth). Thus, a body of 1 kg mass will “weigh” 1

13、 kg 9.806 650 m/s2 = 9.806 650 N on the surface of the earth. The Manual utilizes the series of mm widths and thicknesses of the standard SAE round edge “flat” spring steel bars introduced in SAE 51123. This is based on Preferred Numbers (see American National Standard ANSI 217.1) and specifies the

14、configuration of the cross section of the bars. Tables are provided to show the mass per meter length and the moment of inertia for each size of these bars. These actual moments of inertia are employed in the spring calculation formulae, thus insuring greater accuracy than the formerly used term wt3

15、/12 which applies only to an exactly rectangular cross section. The calculations for spring rate have been improved by refinements in the choice of the stiffening factor which are explained in greater detail. In presenting this work, the Spring Committee wishes to emphasize that the text should not

16、be regarded as a compilation of design or manufacturing specifications, but rather as a reference work which conveys information on solving problems encountered with leaf springs. However, much of the data developed for this Manual have formed the basis for the SAE Standards “Leaf Springs for Motor

17、Vehicle Suspension” (SAE 5510: “made to Customary U.S. Units” and SAE 51123: “made to Metric Units”), which are in the SAE Handbook. The Spring Committee recognizes that time and effort have been spent in generous measure by members and advisors of the Subcommittee who were selected to write and edi

18、t this third revision of the Manual. Thanks are herewith extended by the Committee . TABLE OF CONTENTS Chapter 1 Chapter 2 Chapter 3 Chapter 4 Chapter 5 Chapter 6 Chapter 7 Chapter 8 GENERAL DATA 1 2 . General Characteristics of Leaf Springs . 3 . Leaf Springs for Vehicle Suspension 1 . Introduction

19、 . 1 1 2 NOMENCLATURE AND SPECIFICATIONS 5 1 . Nomenclature . 5 2 . Specification Requirements . 12 3 . Spring Eye Tolerances . 12 DESIGN ELEMENTS . 15 1 . Leaf Sections . 15 2 . Leaf Ends . 16 3 . Spring Eyes and Spring Ends . 16 4 . Spring Eye Bearings . 17 6 . Center Bolt and Cup Center 20 5 . Sh

20、ackles . 19 7 . Center Clamp 20 8 . Alignment Clips 22 9 . Rebound Leaves 24 10 . Variable Rate Springs . 24 GEOMETRY . 27 1 . Deflection Theory . 27 2 . Cantilever Spring . 27 3 . Semi-Elliptic Spring . 28 4 . Center Link Extension Method 28 5 . Two-Point Deflection Method . 31 6 . Layouts and Nome

21、nclature . 34 DESIGN CALCULATIONS 37 1 . Rate. Load and Stress . 37 2 . Stiffening Factor 39 3 . Preliminary Calculations . 40 4 . Stress Distribution 44 5 . Sample Calculation 48 6 . Variable or Progressive Rate Springs . 53 7 . Strength of Spring Eyes 58 INSTALLATION EFFECTS . 61 1 . Characteristi

22、cs of Shackles . 61 2 . Windup of Springs 73 3 . Twist of Springs 77 INTERLEAF FRICTION 81 1 . Characteristics 81 2 . Measurement . 81 3 . Control . 81 OPERATING STRESS AND FATIGUE LIFE 83 1 . Operating Stress 83 2 . Fatigue Life 83 3 . Evaluation of Fatigue Test Results . 85 Chapter 9 MATERIAL AND

23、PROCESSING 97 1 . Steel 97 2 . Mechanical Properties . , . 97 3 . Surface Decarburization 97 98 99 4 . Mechanical Prestressing 5 . Surface Finishes and Protecting Coatings . Chapter 10 DESIGN DATA FOR SINGLE LEAF SPRINGS . 101 1 . Single Leaf Types . 101 2 . Rate Calculations 101 3 . Rate Factors 10

24、8 4 . Stress Calculations 108 5 . Practical Details 113 6 . Camber of Single Leaf Springs 114 7 . Sample Calculations . 114 . . Appendix A Conversion Table 121 Appendix B Derivation of Formulae for the Tabulated Values in Tables 5.2 and 5.3 . 121 . Chapter 1 Type F-1 F-2 F-4 P-2 T- 1 T-2 General Dat

25、a Energy Spring Design Jlkg Cingle leaf or all leaves full length Properly stepped multi-leaf with Be = O 20 Single leaf with H = O20 122 therefore J, = O 40 Single leaf with Je = O 36 1 O8 43 94 Cingle leaf with H = O 16 121 Single leaf wtth Je = O40 H = 016 therefore J, = O 496 105 1. Introduction

26、 This Manual is written as a guide for the designer of leaf spring installations. It contains information which will make it possible to calculate the space required for a leaf spring, to provide suitable attachments, and to determine the elastic and geometric properties of the assembly. The detail

27、design of the spring itself also is described, but it was not the intention of the Committee to lay down fixed rules for this. The choice of leaf lengths, leaf thick- nesses, and leaf curvatures depends upon the type of in- stallation and upon the kind of service. Only an ex- perienced spring engine

28、er can make the best choice of these factors. It is therefore recommended that the de- signer of a leaf spring installation consult a spring maker before the design is finalized. For standards and practices not covered in this Manual, see the current SAE Handbook. No attempt has been made to investi

29、gate or consider patents which may apply to subject matter presented in this Manual. Those who intend to use any of the construc- tions described herein should make their own investiga- tions and arrangements in order to avoid liability for in- fringements. The term multi-leaf has generally been app

30、lied to springs of constant width and with stepped leaves, each of constant thickness, except where leaf ends may be tapered in thickness. More recently, the term has been extended to include an assembly of stacked “single” leaves, each of which is characterized by tapering either in width or in thi

31、ckness or by a combination of both. Chapter 10 includes design data for single leaf springs which may be of variable width and constant thickness, constant width and variable thickness, or a combination of variable width and variable thickness. 2. General Characteristics of Leaf Springs The leaf spr

32、ing, like all other springs, serves to absorb and store energy and then to release it. During this cycle the stress in the spring must not exceed a certain maxi- mum in order to avoid settling or premature failure. This consideration limits the amount of energy which can be Stored in any spring. For

33、 leaf springs based on a maximum stress of 1100 MPa, the energy listed in Table 1.1 may be stored in the active part of the spring. If consideration of the inactive part of the spring required for axle anchorage, spring eyes, For description of Type see Chapter 10 etc., is included, the energy per k

34、g of the total spring mass will be less than shown. For comparison, the stored energy in the active material of a helical spring of round bar section is 510 J/kg at 1100 MPa, and for a torsion bar of round section is 390 J/kg at 965 MPa. This comparison shows that a leaf spring is heavier in mass th

35、an other types of springs. Balancing this disadvantage of mass, the leaf spring possesses the advantage that it can also be used as an attaching linkage or structural member. In order to be economically competitive, the leaf spring must therefore be so designed that this advantage is fully utilized.

36、 Also, a leaf spring made entirely of full length leaves of constant thickness (see type F-1) is very much heavier and less efficient than a leaf spring made of properly stepped leaves (see type F-2) or single leaf springs (see types F-4, P-2, T-1, and T-2). The maximum permissible leaf thickness fo

37、r a given deflection is proportional to the square of the spring length. By choosing too short a length, the designer often makes it impractical for the spring maker to build a satis- factory spring, although the requirements for normal load, deflection, and stress can be fulfilled. For example: A c

38、ube of steel, weighing 44 kg and mea- suring about 178 mm on each side, can be made into a spring carrying a load of 16 O00 N at 125 mm deflection with a stress of 480 MPa. If 1500 mm is allowed for the length, the spring will look like Fig. 1.1. It will consist of 10 leaves, each 75.0 mm wide and 1

39、0.00 mm thick. If only 750 mm is allowed for the length, the spring will look like Fig. 1.2. It will consist of 80 leaves, each 75.0 mm wide and only 2.50 mm thick. When springs are made with stepped leaf lengths of type F-2, it is desirable to choose a length so that the spring will have no less th

40、an three leaves. Springs with many leaves 1 .- I 75.0 mm - 1500mm 10 LEAVES I Fig. 1.1-Leaf spring of type F-2 Practical design with adequate length 1 75.0 mm 1 FL 750 mm -1 Fig. 1.2-Leaf spring of type F-2 Impractical design with inade- quate length are sometimes used for heavy loads, but they are

41、economi- cal only where the shortening of the spring leads to defi- nite savings in the supporting structure. In addition, al- lowance will have to be made for increased spring rate and greater eye stress, assuming the same load and width are used. In most installations the spring is also subject to

42、 windup loads. A typical example is that of the suspension spring (in a vehicle with Hotchkiss drive) which must withstand both driving and braking torque. The stresses under such loads are inversely proportional to the spring length; and the windup stiffness is proportional to the square of the len

43、gth for the spring of given load rate (see Chapter 6). This is another reason why it is important to make the spring long enough and to check the resulting stresses and deflections. When a leaf spring is used as an attaching linkage, it will tend to guide the supported members in a certain geomet- r

44、ical path (see Chapter 4). If no other guiding members are used, the desired geometry must be obtained by properly placing the supporting parts on the structure which car- ries the spring. If other guiding members are used, their geometry must fit that of the spring, or forces may be set up that wil

45、l cause failure. 3. Leaf Springs for Vehicle Suspension Leaf springs are most frequently used in suspensions. This Manual, therefore, contains information which is most useful in the design of suspension springs, but it is also applicable to leaf springs for other installations. The characteristics

46、of a spring suspension are affected chiefly by the spring rate and the static deflection of the spring. The rate f a spring is the change of load per unit of deflection (N/mm). This is not the same amount at all positions of the spring, and is different for the spring as installed. Static dejection

47、of a spring equals the static load divided by the rate at static load; it determines the stiffness of the suspension and the ride frequency of the vehicle. In most cases the static deflection differs from the actual deflection of the spring between zero load and static load, due to influences of spr

48、ing camber and shackle effect. A soft ride generally requires a large static deflection of the suspension. There are, however, other considerations and limits, among them the following: 1. A more flexible spring will have a larger total deflection and will be heavier. 2. In most applications a more

49、flexible spring will cause more severe striking through or will require a larger “ride clearance” (the spring travel on the vehicle from the design load position to the metal-to-metal contact posi- tion), disregarding rubber bumpers. 3. The change of standing height of the vehicle due to a variation of load is larger with a more flexible spring. The static deflection to be used also depends upon the available ride clearance. Further, the permissible static deflection depends upon the size of the vehicle because of considerations of stability in braking,